Invention title: heat-shrinkable multilayer film and heat-shrinkable label
Technical field
[0001]
The present invention is a heat-shrinkable multilayer film capable of producing a labeled container having an excellent appearance by preventing layer displacement at the center seal portion when attached to a container as a heat-shrinkable label for dry heat shrinkage, and the heat thereof. The present invention relates to a heat-shrinkable label using a shrinkable multilayer film as a base film.
Background technology
[0002]
In recent years, many containers such as PET bottles and metal cans are equipped with a heat-shrinkable label obtained by printing or the like on a base film made of a heat-shrinkable resin.
Two types of methods, moist heat shrinkage and dry heat shrinkage, are widely used as a method of heating the heat shrinkable label and attaching it to the container.
[0003]
Moist heat shrinkage is a method of shrinking a heat shrinkable label by heating it with steam and attaching it to a container. Since water vapor has a high thermal conductivity, a sufficient amount of heat can be given to the thermosetting resin film in a short time, and the label mounting speed can be significantly increased. In addition, since heat unevenness in the atmosphere is unlikely to occur, there is little distortion or wrinkles of the printed pattern that are seen after mounting, and the shrinkage finish is excellent.
[0004]
On the other hand, dry heat shrinkage is a method in which a heat shrinkable label is shrunk by heating with hot air and attached to a container. The dry heat shrinkage is superior in terms of hygiene because it does not use water vapor as compared with the wet heat shrinkage. Further, it has an advantage that it can be contracted and mounted with simple equipment as compared with moist heat contraction. Therefore, when mounting on a container with a small number of lots or when mounting a heat-shrinkable label on a container before filling the contents, mounting by dry heat shrinkage is generally performed.
[0005]
As the heat-shrinkable label used when mounting by dry heat shrinkage, those made of polystyrene resin are the mainstream because of their excellent low-temperature shrinkage. However, since the polystyrene-based resin film has low rigidity, it is not suitable for machines and has a problem that problems such as label clogging are likely to occur. In addition, since polystyrene-based resin films have insufficient solvent resistance, there is also a problem that when they are used for packaging products containing oil, they may shrink or dissolve due to the adhesion of oil. It was.
[0006]
On the other hand, an attempt has been made to use a polyester-based film having excellent heat resistance and solvent resistance as a heat-shrinkable label instead of the polystyrene-based resin film. However, the polyester-based film has a problem that it has poor low-temperature shrinkage and shrinks rapidly, so that the printed pattern is likely to be distorted or wrinkled when it is attached to a container.
[0007]
On the other hand, Patent Document 1 discloses a hard multilayer shrinkable film in which an outer surface layer made of a polyester resin is laminated on an intermediate layer made of a polystyrene resin via an adhesive layer made of an olefin resin. ing. Further, in Patent Document 2, an outer surface layer made of a polyester resin made of a specific monomer is laminated on both sides of an intermediate layer made of a polystyrene resin, and the intermediate layer and the outer surface layer form an adhesive layer. A heat-shrinkable label with a base film laminated without interposing is disclosed. Further, Patent Document 3 discloses a laminated film having a surface layer made of a polyester resin, an intermediate layer made of a styrene resin, and an adhesive layer made of an adhesive resin.
[0008]
In such a heat-shrinkable label, as shown in FIG. 1, the front and back layers 5 and 6 are welded by a solvent seal, but when these heat-shrinkable labels are used for dry heat shrinkage, the labels are attached. In the dry heat shrinkage, the front and back layers 1, the adhesive layer 2, the intermediate layer 3 and the adhesive layer 4 on the outside of the label are attached to the front and back layers 5 on the container side in the center seal portion where the films are overlapped and welded by the solvent seal. There is a problem that layer shift occurs in the seal portion as shown in FIG. 2 due to the large shrinkage.
In particular, as a container for toiletries, a deformed container with a high design is used for sales promotion and differentiation from similar products, but such a deformed container has a high degree of difficulty in shrinking finish and has a general size cylinder. Exposed to hot air for longer than the container. For this reason, there is a problem that the layer shift between the intermediate layer and the front and back layers becomes large, and as a result, the appearance of the toiletry container is deteriorated. Further, when the layer shift becomes large, there is a problem that the film is torn from the portion where the shift occurs.
Prior art literature
Patent documents
[0009]
Patent Document 1: Japanese Patent Application
Laid-Open No. 61-41543 Patent Document 2: Japanese Patent Application Laid-Open No. 2002-351332
Patent Document 3: Japanese Patent Application Laid-Open No. 2006-15745
Outline of the invention
Problems to be solved by the invention
[0010]
In view of the above situation, the present invention is a heat-shrinkable multilayer film capable of producing a labeled container having an excellent appearance by preventing layer displacement at the center seal portion when attached to a container as a heat-shrinkable label for dry heat shrinkage. It is an object of the present invention to provide a heat shrinkable label using a film and the heat shrinkable multilayer film as a base film.
Means to solve problems
[0011]
The present invention is a heat-shrinkable multilayer film in which a front and back layer made of a polyester resin and an intermediate layer made of a polystyrene resin are laminated via an adhesive layer, and is immersed in warm water at 80 ° C. for 30 seconds. It is a heat-shrinkable multilayer film having a maximum shrinkage stress of 3.5 to 11 MPa.
The present invention will be described in detail below.
[0012]
As a result of diligent studies, the present inventors have determined in warm water at 80 ° C. in a heat-shrinkable multilayer film in which a front and back layers made of a polyester resin are laminated on an intermediate layer made of a polystyrene resin via an adhesive layer. By setting the maximum shrinkage stress when immersed for a long time within a predetermined range, it is possible to suppress layer displacement at the center seal portion of the label even when dry heat shrinkage is performed when exposed to hot air for a long time. , It has been found that a labeled container having an excellent appearance can be obtained, and the present invention has been completed.
In addition, "layer shift" means that when the heat-shrinkable label is attached to the container, the back layer and the intermediate layer are peeled off at the center seal portion of the heat-shrinkable label, and the surface layer, the adhesive layer and the intermediate layer are separated by the heat of the tunnel. Is a phenomenon in which the surface layer appears to be displaced due to contraction.
[0013]
The heat-shrinkable multilayer film of the present invention has a structure in which a front and back layer made of a polyester resin and an intermediate layer made of a polystyrene resin are laminated via an adhesive layer.
In the present specification, the front and back layers mean both the front layer and the back layer.
[0014]
(Front and back layers)
The front and back layers contain a polyester resin.
Examples of the polyester-based resin include those obtained by polycondensing a dicarboxylic acid component and a diol component. In particular, as the dicarboxylic acid component, an aromatic polyester-based resin in which terephthalic acid is 55 mol% or more out of 100 mol% of the dicarboxylic acid component is preferable. Further, as the dicarboxylic acid component, in addition to the terephthalic acid, o-phthalic acid, isophthalic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, octylsuccinic acid, cyclohexanedicarboxylic acid, naphthalenedicarboxylic acid, fumaric acid, maleic acid , Itaconic acid, decamethylenecarboxylic acid, anhydrides thereof, lower alkyl esters and the like can be contained.
[0015]
The diol component is not particularly limited, and for example, ethylene glycol, 1,3-propanediol, 1,4-butanediol, diethylene glycol, 1,5-pentanediol, 1,6-hexanediol, dipropylene glycol, and tri. Ethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-butanediol, 2,3-butanediol, 2,2-dimethylpropane-1,3-diol, 1,2-hexanediol, 2, Aliphatic diols such as 5-hexanediol, 2-methyl-2,4-pentanediol, 3-methyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, polytetramethylene ether glycol; Alicyclic type such as 2,2-bis (4-hydroxycyclohexyl) propane, alkylene oxide adduct of 2,2-bis (4-hydroxycyclohexyl) propane, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, etc. Examples include diols.
[0016]
Among the polyester-based resins, those containing a component derived from terephthalic acid as a dicarboxylic acid component and a component derived from ethylene glycol and / or 1,4-cyclohexanedimethanol as a diol component are used. preferable. By using such an aromatic polyester-based copolymer resin, excellent shrinkage can be imparted to the heat-shrinkable multilayer film.
When it is desired to further increase the shrinkage property, the content of the component derived from ethylene glycol is 60 to 80 mol% and the content of the component derived from 1,4-cyclohexanedimethanol is 10 out of 100 mol% of the diol component. It is preferable to use one having an amount of about 40 mol%.
[0017]
Such an aromatic polyester-based copolymer resin may further contain a component derived from diethylene glycol in an amount of 0 to 30 mol%, preferably 1 to 25 mol%, and more preferably 2 to 20 mol%. By using diethylene glycol, the tensile elongation at break in the main shrinkage direction of the heat-shrinkable multilayer film is increased, and when the label is peeled from the container, it is possible to prevent only the front and back layers on the inner surface side from remaining in the container due to delamination. Can be done. If the content derived from diethylene glycol exceeds 30 mol%, the low temperature shrinkage of the heat-shrinkable multilayer film becomes too high, and wrinkles are likely to occur when the film is mounted on a container.
[0018]
Further, as the polyester resin containing a component derived from terephthalic acid as the dicarboxylic acid component, one containing a component derived from 1,4-butanediol as a diol component can also be used. Such polyester-based resins are generally called polybutylene terephthalate-based resins.
The polybutylene terephthalate-based resin contains a component derived from terephthalic acid as the dicarboxylic acid component, and also contains a component derived from ethylene glycol and 1,4-cyclohexanedimethanol as a diol component. It is preferable to use it in combination with a copolymer resin. By using such a mixed resin, more excellent finishability can be imparted.
[0019]
The polybutylene terephthalate resin includes a polybutylene terephthalate resin consisting only of a component derived from terephthalic acid and a component derived from 1,4-butanediol, a dicarboxylic acid component other than the component derived from terephthalic acid, and /. Alternatively, it may be a polybutylene terephthalate resin containing a diol component other than the component derived from 1,4-butanediol.
The content of the dicarboxylic acid component other than the component derived from terephthalic acid is preferably 10 mol% or less of 100 mol% of the dicarboxylic acid component. By setting the content to 10 mol% or less, the heat resistance of the polybutylene terephthalate resin can be improved. The content of the diol component other than the component derived from 1,4-butanediol is preferably 10 mol% or less of 100 mol% of the diol component. By setting the content to 10 mol% or less, the heat resistance of the polybutylene terephthalate resin can be further improved.
[0020]
The amount of the polybutylene terephthalate resin added is not particularly limited, but is preferably 30% by weight or less. By setting the content to 30% by weight or less, natural shrinkage can be suppressed, and the rigidity of the film can be sufficiently improved.
[0021]
The preferable lower limit of the glass transition temperature of the polyester resin constituting the front and back layers is 55 ° C, and the preferable upper limit is 95 ° C. When the glass transition temperature is 55 ° C. or higher, the shrinkage start temperature of the heat-shrinkable multilayer film can be sufficiently raised, and natural shrinkage can be suppressed or blocking can be suppressed. When the glass transition temperature is 95 ° C. or lower, the low-temperature shrinkage and shrinkage finish of the heat-shrinkable multilayer film can be sufficiently improved, the decrease in low-temperature shrinkage over time can be suppressed, and the low-temperature shrinkage during stretching can be suppressed. Resin whitening can be suppressed. The more preferable lower limit of the glass transition temperature is 60 ° C., the more preferable lower limit is 65 ° C., the more preferable upper limit is 90 ° C., and the further preferable upper limit is 85 ° C.
The glass transition temperature of the polyester resin can be measured by a differential scanning calorimetry (DSC) by a method compliant with ISO 3146: 2000.
[0022]
The preferable lower limit of the tensile elastic modulus of the polyester resin constituting the front and back layers is 1000 MPa, and the preferable upper limit is 4000 MPa. When the tensile elastic modulus is 1000 MPa or more, the shrinkage start temperature of the heat-shrinkable film can be sufficiently raised, and natural shrinkage can be suppressed. When the tensile elastic modulus is 4000 MPa or less, the low-temperature shrinkage and shrinkage finish of the heat-shrinkable multilayer film can be sufficiently improved, and the decrease in low-temperature shrinkage over time can be suppressed. The more preferable lower limit of the tensile elastic modulus is 1500 MPa, and the more preferable upper limit is 3700 MPa.
The tensile elastic modulus can be measured by a method based on ASTM-D882 (TestA).
[0023]
The storage elastic modulus of the resin constituting the front and back layers at 70 ° C. is preferably 1.0 × 10 7 to 1.0 × 10 9 Pa.
By setting the storage elastic modulus at 70 ° C. to a relatively low range as described above, the shrinkage (softening) of the front and back layers can be started from a relatively low temperature of about 70 ° C. That is, the low temperature shrinkage of the front and back layers can be enhanced. As a result, the low-temperature shrinkage of the entire heat-shrinkable multilayer film can be enhanced, the difference in shrinkage behavior (softening behavior) between the front and back layers and the intermediate layer can be alleviated, and excellent shrinkage finish can be obtained. In addition, such excellent low temperature shrinkage is unlikely to decrease over time. The storage elastic modulus is determined by using a viscoelasticity measuring device such as Rheogel E-4000 (manufactured by UBM), a vibration frequency of 10 Hz, a strain of 0.1%, a heating rate of 3 ° C./min, and a measurement temperature of −120 ° C. It can be measured from to 150 ° C. under the condition of tension mode.
[0024]
Storage modulus at 70 ° C. is 1.0 × 10 7 is less than Pa, The natural shrinkage means that the heat-shrinkable multilayer film shrinks slightly when stored at room temperature (20 to 23 ° C.). If the natural shrinkage rate is large, the diameter of the heat-shrinkable multilayer film is smaller than the container diameter, and the heat-shrinkable multilayer film may not be attached to the container. The preferred lower limit of the storage elastic modulus at 70 ° C. is 2.5 × 10 7 Pa, and the more preferable lower limit is 5.0 × 10 7 Pa.
[0025]
Storage modulus at 70 ° C. is 1.0 × 10 9 When it is Pa or more, or or low temperature shrinkability and shrinkage finish property is lowered in heat shrinkable multilayer films, decrease in low temperature shrinkability with time becomes large To do. The preferred upper limit of the storage elastic modulus at 70 ° C. is 9.0 × 10 8 Pa, and the more preferable upper limit is 8.0 × 10 8 Pa.
[0026]
The storage elastic modulus of the front and back layers at a temperature other than 70 ° C. is not particularly limited, but at 75 ° C., it is preferably 1.0 × 10 6 to 5.0 × 10 8 Pa, more preferably 5.0 × 10 6 to. It is 2.5 × 10 8 Pa, preferably 1.0 × 10 6 to 1.0 × 10 8 Pa at 80 ° C. , more preferably 2.5 × 10 6 to 7.5 × 10 7 Pa. At 90 ° C., it is preferably 1.0 × 10 6 to 2.5 × 10 7 Pa, more preferably 2.0 × 10 6 to 1.0 × 10 7 Pa, and at 100 ° C., preferably 8.0 × 10 It is 5 to 1.0 × 10 7 Pa, more preferably 1.0 × 10 6 to 8.0 × 10 6 Pa.
[0027]
Commercially available polyester resins constituting the front and back layers include, for example, "Easter", "Engineering Lv" (manufactured by Eastman Chemical Company), "Bellpet" (manufactured by Bell Polyester Products), and "Novaduran" (Mitsubishi Engineering). (Made by Plastics) and the like.
[0028]
As the polyester-based resin contained in the front and back layers, the polyester-based resin having the above-mentioned composition may be used alone, or two or more kinds of polyester-based resins having the above-mentioned composition may be used in combination. Further, the polyester-based resin may be a polyester-based resin having different compositions in the front surface layer and the back surface layer, but is a polyester-based resin having the same composition in order to suppress troubles due to curling of the film or the like. Is preferable.
[0029]
The front and back layers are, if necessary, antioxidants, heat stabilizers, ultraviolet absorbers, light stabilizers, lubricants, antistatic agents, antiblocking agents, flame retardants, antibacterial agents, fluorescent whitening agents, colorants, etc. May contain the additive of.
[0030]
(Intermediate layer)
The heat-shrinkable multilayer film of the present invention contains the above-mentioned intermediate layer.
The intermediate layer contains a polystyrene resin.
Examples of the polystyrene-based resin include aromatic vinyl hydrocarbon-conjugated diene copolymers, aromatic vinyl hydrocarbon-conjugated diene copolymers, and aromatic vinyl hydrocarbons-aliphatic unsaturated carboxylic acid ester copolymers. Examples thereof include mixed resin, rubber-modified impact-resistant polystyrene, and the like. By using the above polystyrene-based resin, the heat-shrinkable multilayer film of the present invention can start shrinking from a low temperature and has high shrinkage.
[0031]
In the present specification, the aromatic vinyl hydrocarbon-conjugated diene copolymer refers to a copolymer containing a component derived from an aromatic vinyl hydrocarbon and a component derived from a conjugated diene.
The aromatic vinyl hydrocarbon is not particularly limited, and examples thereof include styrene, o-methylstyrene, and p-methylstyrene. These may be used alone or in combination of two or more. The conjugated diene is not particularly limited, and for example, 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and 1,3-hexadiene. And so on. These may be used alone or in combination of two or more.
[0032]
The aromatic vinyl hydrocarbon-conjugated diene copolymer is particularly excellent in heat shrinkage, and therefore preferably contains a styrene-butadiene copolymer (SBS resin). Further, in the aromatic vinyl hydrocarbon-conjugated diene copolymer, 2-methyl-1,3-butadiene (isoprene) is used as the conjugated diene in order to prepare a heat-shrinkable multilayer film having less fish eyes. It is preferable to contain the styrene-isoprene copolymer (SIS resin), styrene-isoprene-butadiene copolymer (SIBS) and the like used.
The aromatic vinyl hydrocarbon-conjugated diene copolymer may contain any one of the SBS resin, the SIS resin and the SIBS resin alone, or may contain a plurality of them in combination. When a plurality of SBS resin, SIS resin, and SIBS resin are used, each resin may be dry-blended, and a compound resin obtained by kneading and pelletizing each resin with a specific composition using an extruder is used. You may.
[0033]
When the aromatic vinyl hydrocarbon-conjugated diene copolymer contains SBS resin, SIS resin and SIBS resin alone or in combination, a heat-shrinkable multilayer film having particularly excellent heat-shrinkability can be obtained. The styrene content in 100% by weight of the aromatic vinyl hydrocarbon-conjugated diene copolymer is preferably 65 to 90% by weight, and the conjugated diene content is preferably 10 to 35% by weight. If the styrene content exceeds 90% by weight or the conjugated diene content is less than 10% by weight, the heat-shrinkable multilayer film is easily cut when tension is applied, or it may be unexpected during processing such as printing. It may break regardless. If the styrene content is less than 65% by weight, or if the conjugated diene content exceeds 35% by weight, foreign substances such as gels are likely to be generated during molding, and the heat-shrinkable multilayer film becomes weak. As a result, handleability may deteriorate.
[0034]
In the present specification, the aromatic vinyl hydrocarbon-aliphatic unsaturated carboxylic acid ester copolymer contains a component derived from an aromatic vinyl hydrocarbon and a component derived from an aliphatic unsaturated carboxylic acid ester. Refers to a copolymer.
The aromatic vinyl hydrocarbon is not particularly limited, and the same aromatic vinyl hydrocarbon as the aromatic vinyl hydrocarbon exemplified in the aromatic vinyl hydrocarbon-conjugated diene copolymer can be used. The above-mentioned aliphatic unsaturated carboxylic acid ester is not particularly limited, and examples thereof include methyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, and stearyl (meth) acrylate. Be done. Here, the (meth) acrylate refers to both acrylate and methacrylate.
[0035]
When a styrene-butyl acrylate copolymer is used as the aromatic vinyl hydrocarbon-aliphatic unsaturated carboxylic acid ester copolymer, the styrene content in 100% by weight of the styrene-butyl acrylate copolymer is 60. It is preferably ~ 90% by weight and the butyl acrylate content is preferably 10 to 40% by weight. By using an aromatic vinyl hydrocarbon-aliphatic unsaturated carboxylic acid ester copolymer having such a composition, a heat-shrinkable multilayer film having excellent heat-shrinkability can be obtained.
[0036]
The mixed resin of the aromatic vinyl hydrocarbon-conjugated diene copolymer and the aromatic vinyl hydrocarbon-aliphatic unsaturated carboxylic acid ester copolymer is not particularly limited, but the aromatic vinyl hydrocarbon-aliphatic non-polypolymer is not particularly limited. A mixed resin having a saturated carboxylic acid ester copolymer content of 80% by weight or less is preferable.
[0037]
The rubber-modified impact-resistant polystyrene is composed of a continuous phase composed of a ternary copolymer of styrene, alkyl methacrylate and alkyl acrylate, and a dispersed phase composed of a rubber component mainly composed of conjugated diene. It is the basis.
[0038]
Examples of the alkyl methacrylate forming the continuous phase include methyl methacrylate and ethyl methacrylate, and examples of the alkyl acrylate include methyl acrylate, ethyl acrylate, propyl acrylate and butyl acrylate.
The proportion of styrene in the copolymer forming the continuous phase is preferably 20 to 80% by weight, more preferably 30 to 70% by weight. The proportion of alkyl methacrylate is preferably 10 to 50% by weight, more preferably 15 to 40% by weight. The proportion of alkyl acrylate is preferably 1 to 30% by weight, more preferably 5 to 20% by weight.
[0039]
As the rubber component mainly composed of the conjugated diene forming the dispersed phase, polybutadiene or a styrene-butadiene copolymer having a styrene content of 5 to 30% by weight is preferable.
The particle size of the rubber component mainly composed of the conjugated diene forming the dispersed phase is preferably 0.1 to 1.2 μm, more preferably 0.3 to 0.8 μm. If the particle size is less than 0.1 μm, the impact resistance of the rubber-modified impact-resistant polystyrene may be insufficient, and if it exceeds 1.2 μm, the transparency of the intermediate layer may be lowered.
[0040]
In the rubber-modified impact-resistant polystyrene, the ratio of the continuous phase composed of a ternary copolymer of styrene, alkyl methacrylate and alkyl acrylate is 70 to 95% by weight, and the dispersed phase composed of a rubber component mainly composed of conjugated diene. The ratio is preferably 5 to 20% by weight. If the proportion of the dispersed phase is less than 5% by weight, the impact resistance of the rubber-modified impact-resistant polystyrene may be insufficient, and if it exceeds 20% by weight, the transparency of the intermediate layer is lowered. There is.
[0041]
The preferable lower limit of the Vicat softening temperature of the polystyrene resin is 60 ° C., and the preferable upper limit is 85 ° C. When the Vicat softening temperature is 60 ° C. or higher, the low-temperature shrinkage of the heat-shrinkable multilayer film is made good, and wrinkles can be prevented when the film is attached to the container. When the Vicat softening temperature is 85 ° C. or lower, the low-temperature shrinkage of the heat-shrinkable multilayer film can be sufficiently enhanced to prevent the generation of non-shrinkable portions when mounted on a container. The more preferable lower limit of the Vicat softening temperature is 65 ° C., and the more preferable upper limit is 80 ° C.
The Vicat softening temperature can be measured by a method conforming to ISO 306.
[0042]
The preferable lower limit of MFR (melt flow rate) of the polystyrene resin at 200 ° C. is 2 g / 10 minutes, and the preferable upper limit is 15 g / 10 minutes. If the MFR at 200 ° C. is less than 2 g / 10 minutes, it becomes difficult to form a film. If the MFR at 200 ° C. exceeds 15 g / 10 minutes, the mechanical strength of the film becomes low and it becomes unusable for practical use. The more preferable lower limit of MFR at 200 ° C. is 4 g / 10 minutes, and the more preferable upper limit is 12 g / 10 minutes. The MFR can be measured by a method compliant with ISO1133.
[0043]
Examples of commercially available polystyrene-based resins constituting the intermediate layer include "Clearene" (manufactured by Denki Kagaku Kogyo Co., Ltd.), "Asaflex" (manufactured by Asahi Kasei Chemicals Co., Ltd.), "Styrolux" (manufactured by BASF), and "PSJ". -Polystyrene "(manufactured by PS Japan Corporation) and the like.
[0044]
The intermediate layer preferably contains 1 to 60% by weight of the polystyrene resin (A) having a Vicat softening temperature of 80 ° C. or higher.
By containing the polystyrene-based resin (A) in a predetermined amount, the effect of suppressing layer shift in the center seal portion of the label when it is dry-heat-shrinked can be further improved.
Regarding the content of the polystyrene resin (A) in the intermediate layer, a more preferable lower limit is 5% by weight, a further preferable lower limit is 10% by weight, a more preferable upper limit is 50% by weight, and a further preferable upper limit is 35% by weight.
[0045]
The intermediate layer preferably contains 40 to 99% by weight of a polystyrene resin (B) having a Vicat softening temperature of less than 80 ° C.
By containing the polystyrene-based resin (B) in a predetermined amount, the effect of suppressing layer shift in the center seal portion of the label when it is dry-heat-shrinked can be further improved.
Regarding the content of the polystyrene resin (B) in the intermediate layer, a more preferable lower limit is 50% by weight, a further preferable lower limit is 65% by weight, a more preferable upper limit is 95% by weight, and a further preferable upper limit is 90% by weight.
[0046]
The ratio of the content of the polystyrene resin (A) to the content of the polystyrene resin (B) in the intermediate layer (content of polystyrene resin (A) / content of polystyrene resin (B)) is The preferred lower limit is 1/99, the more preferred lower limit is 10/90, the preferred upper limit is 60/40, and the more preferred upper limit is 50/50.
[0047]
The content of the styrene component in the intermediate layer is such that the preferable lower limit is 60% by weight, the more preferable lower limit is 70% by weight, the preferable upper limit is 90% by weight, and the more preferable upper limit is 80% by weight.
The content of the styrene component in the intermediate layer can be calculated based on the content of the polystyrene-based resin constituting the intermediate layer and the ratio of the styrene component in the polystyrene-based resin.
[0048]
The difference in the bicut softening temperature between the polystyrene-based resin (A) and the polystyrene-based resin (B) is preferably 5 ° C. or higher, more preferably 10 ° C. or higher, and more preferably 30 ° C. or lower. It is preferably 20 ° C. or lower, more preferably 20 ° C. or lower.
[0049]
The intermediate layer may be an antioxidant, a heat stabilizer, an ultraviolet absorber, a light stabilizer, a lubricant, an antistatic agent, an antiblocking agent, a flame retardant, an antibacterial agent, a fluorescent whitening agent, a colorant, etc., if necessary. May contain the additive of.
[0050]
(Adhesive Layer)
The heat-shrinkable multilayer film of the present invention is formed by laminating the front and back layers and the intermediate layer via an adhesive layer.
As the resin constituting the adhesive layer, a mixed resin containing a polystyrene-based resin and a polyester-based elastomer is preferable. Such an adhesive layer has a high affinity for both the polyester-based resin constituting the front and back layers and the polystyrene-based resin constituting the intermediate layer, and both can be bonded with high strength. Further, since the polyester resin constituting the front and back layers is dissolved or swollen in a solvent that dissolves the resin, the solvent can penetrate into the heat-shrinkable multilayer film during label production, and delamination occurs during subsequent heat shrinkage. It can be prevented from occurring.
[0051]
The polystyrene-based resin used for the adhesive layer preferably contains an aromatic vinyl hydrocarbon-conjugated diene copolymer because of its excellent adhesiveness, and in particular, a styrene-butadiene copolymer (SBS resin). Is preferably contained. When a styrene-butadiene copolymer is used, it is preferable that the content of butadiene is higher than that of the styrene-butadiene copolymer used in the intermediate layer from the viewpoint of excellent adhesiveness. Further, in order to produce a heat-shrinkable multilayer film having more excellent adhesiveness, 2-methyl-1,3-butadiene (isoprene) was used as the conjugated diene of the aromatic vinyl hydrocarbon-conjugated diene copolymer. It preferably contains a styrene-isoprene copolymer (SIS resin), a styrene-isoprene-butadiene copolymer (SIBS), and the like. Further, a hydrogenated styrene resin such as a styrene-butadiene-butylene copolymer (SBBS resin) or a styrene-ethylene-butylene copolymer (SEBS resin) obtained by hydrogenating an aromatic vinyl hydrocarbon-conjugated diene copolymer. May be contained in a range that does not become the main component of the polystyrene-based resin. When the hydrogenated styrene resin becomes the main component in the polystyrene resin, the transparency tends to decrease.
The polystyrene resin may contain any one of the SBS resin, the SIS resin and the SIBS resin alone, or may contain a plurality of the polystyrene resins in combination. When a plurality of SBS resin, SIS resin, SIBS resin, SBBS resin or SEBS resin are used, each resin may be dry-blended, and each resin is kneaded with a specific composition using an extruder. A pelletized compound resin may be used.
[0052]
When the polystyrene-based resin is an aromatic vinyl hydrocarbon-conjugated diene copolymer and contains SBS resin, SIS resin and SIBS resin alone or in combination, the heat shrinkage property is particularly excellent in the adhesive strength between the layers. Since a multilayer film can be obtained, the styrene content in 100% by weight of the aromatic vinyl hydrocarbon-conjugated diene copolymer is preferably 50 to 90% by weight, and the conjugated diene content is preferably 10 to 50% by weight. .. If the styrene content is less than 50% by weight, or if the conjugated diene content exceeds 50% by weight, foreign substances such as gel may easily be generated during molding. When the styrene content exceeds 90% by weight or the conjugated diene content is less than 10% by weight, the adhesive strength between the layers tends to decrease.
The styrene content in the aromatic vinyl hydrocarbon-conjugated diene copolymer is more preferably 60 to 80% by weight, further preferably 70 to 75% by weight. The conjugated diene content in the aromatic vinyl hydrocarbon-conjugated diene copolymer is more preferably 20 to 40% by weight, further preferably 25 to 30% by weight.
[0053]
When the hydrogenated styrene resin is mixed with the polystyrene resin, a heat-shrinkable multilayer film having excellent adhesive strength between the layers can be obtained. Therefore, the styrene content of the hydrogenated styrene resin is 20 to 80. The weight%, butadiene-butylene or ethylene-butylene content is preferably 20-80% by weight. If the styrene content is less than 20% by weight, the adhesive strength between the layers tends to decrease. If the styrene content exceeds 80% by weight, the heat resistance may decrease.
[0054]
The preferred lower limit of the vicut softening temperature of the polystyrene resin used for the adhesive layer is 50 ° C., and the preferred upper limit is 85 ° C. When the Vicat softening temperature is 50 ° C. or higher, the heat-shrinkable multilayer film can sufficiently suppress delamination between each layer by heating when it is attached to a container. When the Vicat softening temperature is 85 ° C. or lower, the adhesive strength of the heat-shrinkable multilayer film can be sufficiently improved. The more preferable lower limit of the Vicat softening temperature is 55 ° C., the more preferable lower limit is 60 ° C., the particularly preferable lower limit is 65 ° C., and the more preferable upper limit is 80 ° C.
The Vicat softening temperature can be measured by a method conforming to ISO 306.
[0055]
The preferable lower limit of MFR (melt flow rate) of the polystyrene resin used for the adhesive layer at 200 ° C. is 2 g / 10 minutes, and the preferable upper limit is 15 g / 10 minutes. If the MFR at 200 ° C. is less than 2 g / 10 minutes, the resin stays in the extruder in the continuous production process, and foreign substances such as gel are likely to be generated. If the MFR at 200 ° C. exceeds 15 g / 10 minutes, the pressure is not sufficiently applied in the film forming process, and the thickness variation tends to be large. The more preferable lower limit of MFR at 200 ° C. is 4 g / 10 minutes, and the more preferable upper limit is 12 g / 10 minutes. The MFR can be measured by a method compliant with ISO1133.
[0056]
The polyester-based elastomer used for the adhesive layer is composed of polyester, which is a hard segment, and polyether or polyester, which is a soft segment rich in rubber elasticity. Specifically, for example, a block copolymer composed of an aromatic polyester as a hard segment and an aliphatic polyether as a soft segment, an aromatic polyester as a hard segment, and an aliphatic polyester as a soft segment. Examples thereof include block copolymers composed of.
Further, the polyester-based elastomer is preferably a saturated polyester-based elastomer, and in particular, a saturated polyester-based elastomer containing a polyalkylene ether glycol segment as a soft segment is preferable. As the saturated polyester-based elastomer containing the polyalkylene ether glycol segment, for example, a block copolymer composed of an aromatic polyester as a hard segment and a polyalkylene ether glycol as a soft segment is preferable.
[0057]
When a block copolymer composed of aromatic polyester and polyalkylene ether glycol is used as the polyester-based elastomer, the ratio of the segment composed of polyalkylene ether glycol is preferably 5% by weight at the lower limit and 90% by weight at the upper limit. is there. If it is less than 5% by weight, the adhesiveness to the intermediate layer is lowered, and if it exceeds 90% by weight, the adhesiveness to the front and back layers is lowered. A more preferable lower limit is 30% by weight, a more preferable upper limit is 80% by weight, and a further preferable lower limit is 55% by weight.
[0058]
Examples of the polyalkylene ether glycol include polyethylene glycol, poly (propylene ether) glycol, poly (tetramethylene ether) glycol, poly (hexamethylene ether) glycol and the like.
[0059]
The preferable lower limit of the number average molecular weight of the polyalkylene ether glycol is 400, and the preferable upper limit is 6000. A more preferable lower limit is 600, a more preferable upper limit is 4000, a further preferable lower limit is 1000, and a further preferable upper limit is 3000. By using a polyalkylene ether glycol having a number average molecular weight within the above range, good interlayer strength can be obtained, which is preferable. In addition, in this specification, the number average molecular weight means what was measured by gel permeation chromatography (GPC).
[0060]
The method for producing the polyester-based elastomer is not particularly limited, and for example, (i) an aliphatic and / or alicyclic diol having 2 to 12 carbon atoms and (ii) an aromatic dicarboxylic acid and / or an alicyclic diol are produced. Using a dicarboxylic acid or an ester thereof and a (iii) polyalkylene ether glycol having a number average molecular weight of 400 to 6000 as a raw material, an oligomer is obtained by an esterification reaction or an ester exchange reaction, and then the oligomer is further polycondensed. Can be produced by
[0061]
As the aliphatic and / or alicyclic diol having 2 to 12 carbon atoms, for example, those commonly used as raw materials for polyesters, particularly polyester-based thermoplastic elastomers can be used. Specific examples thereof include ethylene glycol, propylene glycol, trimethylene glycol, 1,4-butanediol, 1,4-cyclohexanediol, and 1,4-cyclohexanedimethanol. Among these, ethylene glycol and 1,4-butanediol are preferable, and 1,4-butanediol is more preferable. These may be used alone or in combination of two or more.
[0062]
As the aromatic dicarboxylic acid and / or alicyclic dicarboxylic acid, for example, those commonly used as raw materials for polyesters, particularly polyester-based thermoplastic elastomers can be used. Specific examples thereof include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, cyclohexanedicarboxylic acid and the like. Among these, terephthalic acid and 2,6-naphthalenedicarboxylic acid are preferable, and terephthalic acid is more preferable. These may be used alone or in combination of two or more.
[0063]
Among the above polyester-based elastomers, for example, the product name "Primaloy" (manufactured by Mitsubishi Chemical Corporation), the product name "Perprene" (manufactured by Toyo Spinning Co., Ltd.), and the product name "Hitrel" (Toray DuPont) Made) and the like.
[0064]
The melting point of the polyester elastomer is preferably 120 to 200 ° C. If the temperature is lower than 120 ° C, the heat resistance is lowered, and when the container is coated as a heat-shrinkable label, peeling is likely to occur from the solvent center seal portion. If the temperature exceeds 200 ° C, sufficient adhesive strength may not be obtained. is there. A more preferable lower limit is 130 ° C., and a more preferable upper limit is 190 ° C.
The melting point can be measured using a differential scanning calorimeter (DSC-60, manufactured by Shimadzu Corporation).
[0065]
The melting point of the polyester-based elastomer is due to the copolymerization ratio and structure of the polyester which is a hard segment and the polyether or polyester which is a soft segment. Generally, the melting point of a polyester-based elastomer tends to depend on the copolymerization amount of a polyether or polyester which is a soft segment. When the copolymerization amount of the polyether or polyester is large, the melting point is low, and when the copolymerization amount is small, the melting point is high.
Further, the melting point of polyester, which is a hard segment constituting the polyester-based elastomer, can be adjusted by changing the copolymerization component, and the melting point of the entire polyester-based elastomer can be adjusted.
Further, when the molecular weight of the soft segment of the polyether or polyester is reduced, the blocking property of the obtained polyester-based elastomer is lowered, so that the melting point is likely to be lowered.
[0066]
The preferable lower limit of the durometer hardness of the polyester-based elastomer is 10, and the preferable upper limit is 80. By setting the durometer hardness to 10 or more, the mechanical strength of the adhesive layer is improved. By setting the durometer hardness to 80 or less, the flexibility and impact resistance of the adhesive layer are improved. The more preferred lower limit of durometer hardness is 15, the more preferred upper limit is 70, the more preferred lower limit is 20, and the more preferred upper limit is 60.
The durometer hardness can be measured by using the durometer type D by a method conforming to ISO18517.
[0067]
The preferable lower limit of the specific gravity of the polyester-based elastomer is 0.95, and the preferable upper limit is 1.20. By setting the specific gravity to 0.95 or more, heat resistance can be imparted, and peeling from the center seal portion can be suppressed when the container is coated as a heat-shrinkable label. Further, by setting the specific gravity to 1.20 or less, the adhesive strength between the front and back layers and the intermediate layer can be increased.
The more preferable lower limit of the specific gravity is 0.98, and the more preferable upper limit is 1.18.
The specific gravity can be measured by an underwater substitution method by a method based on ASTM D 792.
[0068]
The preferable lower limit of the tensile elastic modulus of the polyester-based elastomer constituting the adhesive layer is 1 MPa, and the preferable upper limit is 1000 MPa. If the tensile elastic modulus is less than 1 MPa, the mechanical strength of the adhesive layer tends to decrease. When the tensile elastic modulus exceeds 1000 MPa, the adhesive strength between the front and back layers and the intermediate layer tends to decrease. The more preferable lower limit of the tensile elastic modulus is 5 MPa, and the more preferable upper limit is 900 MPa. The tensile elastic modulus can be measured by a method based on ASTM-882 (TestA).
[0069]
The preferable lower limit of the glass transition temperature of the polyester-based elastomer constituting the adhesive layer is −70 ° C., and the preferable upper limit is 0 ° C. If the glass transition temperature is less than −70 ° C., resin blocking occurs and handling tends to be poor. When the glass transition temperature exceeds 0 ° C., the adhesive strength between the front and back layers and the intermediate layer tends to decrease. The more preferable lower limit of the glass transition temperature is −60 ° C., and the more preferable upper limit is −5 ° C. The glass transition temperature of the polyester-based elastomer can be measured using a differential scanning calorimeter.
[0070]
The polyester-based elastomer may be a modified product. Examples of the modified product include a polyester-based elastomer modified by grafting an α, β-ethylenically unsaturated carboxylic acid onto the polyester-based elastomer.
Examples of the α, β-ethylene unsaturated carboxylic acid include unsaturated carboxylic acids such as acrylic acid, maleic acid, fumaric acid, tetrahydrofumaric acid, itaconic acid, citraconic acid, crotonic acid, and isocrotonic acid; succinic acid 2 -Octen-1-yl anhydride, 2-dodecene-1-yl anhydride, 2-octadecene-1-yl anhydride, maleic anhydride, 2,3-dimethylmaleic anhydride, bromomalein Acid anhydride, dichloromaleic anhydride, citraconic acid anhydride, itaconic acid anhydride, 1-butene-3,4-dicarboxylic acid anhydride, 1-cyclopentene-1,2-dicarboxylic acid anhydride, 1,2, 3,6-Tetrahydrophthalic anhydride, 3,4,5,6-tetrahydrophthalic anhydride, exo-3,6-epoxy-1,2,3,6-tetrahydrophthalic anhydride, 5-norbornene- 2,3-Dicarboxylic acid anhydride, methyl-5-norbornen-2,3-dicarboxylic acid anhydride, endo-bicyclo [2.2.2] Oct-5-ene-2,3-dicarboxylic acid anhydride, bicyclo [2.2.2] Examples thereof include unsaturated carboxylic acid anhydrides such as Oct-7-ene-2,3,5,6-tetracarboxylic acid anhydride. Of these, acid anhydrides are preferred because of their high reactivity.
[0071]
In the adhesive layer, the preferable lower limit of the content of the polystyrene resin is 10% by weight, and the preferable upper limit is 95% by weight.
When the content of the polystyrene-based resin is 10% by weight or more, it is possible to suppress the formation of white streaks in the creases when the film is strongly folded in order to produce a heat-shrinkable label. Further, when the label is attached, the layer shift at the center seal portion can be sufficiently suppressed, and the appearance defect can be prevented. When the content of the polystyrene-based resin is 95% by weight or less, sufficient interlayer strength can be achieved at a low temperature and delamination can be suppressed. The more preferable lower limit of the content of the polystyrene resin is 30% by weight, the more preferable lower limit is 35% by weight, the more preferable upper limit is 80% by weight, and the further preferable upper limit is 70% by weight.
[0072]
In the adhesive layer, the preferable lower limit of the content of the polyester-based elastomer is 5% by weight, and the preferable upper limit is 90% by weight.
When the content of the polyester-based elastomer is 5% by weight or more, the interlayer strength at low temperature can be sufficiently improved, and delamination can be suppressed. When the content of the polyester-based elastomer is 90% by weight or less, it is possible to suppress the formation of white streaks in the creases when the film is strongly folded in order to produce a heat-shrinkable label. Further, when the label is attached, the layer shift at the center seal portion can be sufficiently suppressed, and the appearance defect can be prevented. A more preferable lower limit of the content of the polyester-based elastomer is 20% by weight, a further preferable lower limit is 30% by weight, a more preferable upper limit is 70% by weight, and a further preferable upper limit is 65% by weight.
[0073]
In the above-mentioned adhesive layer, as the polystyrene-based resin, a styrene-butadiene copolymer (SBS resin), a styrene-isoprene copolymer (SIS resin) using 2-methyl-1,3-butadiene (isoprene), and styrene- It preferably contains an isoprene-butadiene copolymer (SIBS) or the like. Further, the polyester-based elastomer preferably contains a block copolymer composed of polyester as a hard segment and polyalkylene ether glycol as a soft segment, and may be a modified product.
[0074]
The adhesive layer may be used as an antioxidant, a heat stabilizer, an ultraviolet absorber, a light stabilizer, a lubricant, an antistatic agent, an antiblocking agent, a flame retardant, an antibacterial agent, a fluorescent whitening agent, a colorant, etc. Additives may be included.
[0075]
The heat-shrinkable multilayer film of the present invention has a lower limit of 3.5 MPa and an upper limit of 11 MPa when immersed in warm water at 80 ° C. for 30 seconds. When the maximum shrinkage stress is 3.5 MPa or more, the shrinkage finish when mounted on a container can be sufficiently improved. When the maximum shrinkage stress is 11 MPa or less, the displacement between layers at the center seal portion of the label can be suppressed. In addition, deformation of the container when it is attached to the container can be suppressed. The preferable lower limit of the maximum contraction stress is 4.5 MPa, and the preferable upper limit is 10 MPa.
The maximum shrinkage stress refers to the maximum value of the shrinkage stress when the heat-shrinkable multilayer film is immersed in warm water at 80 ° C. for 30 seconds and the shrinkage stress is measured.
[0076]
The maximum shrinkage stress can be adjusted by, for example, the stretching conditions (stretching ratio, stretching temperature, etc.), the vicut softening temperature of the polystyrene resin used for the intermediate layer, and the like.
The contraction stress tends to decrease when the stretching temperature is increased, and the contraction stress tends to increase when the stretching temperature is decreased. The stretching temperature needs to be adjusted by the vicut softening temperature of the polystyrene resin used in the intermediate layer.
Further, when the stretching ratio in the lateral (TD) direction is lowered, the shrinkage stress is lowered, and when the stretching ratio is increased, the shrinkage stress is increased.
[0077]
In the heat-shrinkable multilayer film of the present invention, the preferable lower limit of the dry heat shrinkage rate at 70 ° C. for 10 seconds is 10%, and the preferable upper limit is 30%. When the dry heat shrinkage rate is 10% or more, wrinkles, printing distortion, and shrinkage unevenness of the heat shrinkable multilayer film can be suppressed when used as a heat shrinkable label for dry heat shrinkage. When the dry heat shrinkage rate is 30% or less, the handleability of the heat shrinkable multilayer film can be improved. The more preferable lower limit of the dry heat shrinkage rate is 12%, and the more preferable upper limit is 28%.
[0078]
Further, the heat-shrinkable multilayer film of the present invention has a preferable lower limit of 8% and a preferable upper limit of 25% for the dry heat shrinkage rate at 70 ° C. for 10 seconds after being allowed to stand in an atmosphere of 30 ° C. for 5 days. Since the dry heat shrinkage rate after standing in an atmosphere of 30 ° C. for 5 days is within the above range, the heat shrinkable multilayer film is used as a heat shrinkable label for dry heat shrinkage after long-term storage. Wrinkles, print distortion, and uneven shrinkage can be suppressed. The more preferable lower limit of the dry heat shrinkage rate after standing in an atmosphere of 30 ° C. for 5 days is 10%, and the more preferable upper limit is 23%.
[0079]
In the heat-shrinkable multilayer film of the present invention, the preferable lower limit of the dry heat shrinkage rate at 100 ° C. for 10 seconds is 65%, the more preferable lower limit is 70%, the preferable upper limit is 85%, and the more preferable upper limit is 80%.
[0080]
The dry heat shrinkage rate can be measured by the following method.
The heat-shrinkable multilayer film is cut to a length of 300 mm × 25 mm so that the TD direction (main shrinkage direction) is the long side, and a marked line is drawn so that the distance between the marked lines is 200 mm to use as a measurement sample ( (See FIG. 1). Next, both ends of the measurement sample were fixed to a pointer with a length of 520 mm, the heat-shrinkable multilayer film of the fixed part was bent outward (see FIG. 2), and a constant temperature and humidity chamber (Nagano Science) set to a predetermined temperature and humidity. Insert it into LH31-12M) manufactured by the company through a horizontal hole. Ten seconds after charging, the heat-shrinkable multilayer film is taken out, the distance between the marked lines is measured, and the shrinkage rate between the marked lines is calculated from the following formula.
Dry heat shrinkage rate (%) = {(200-distance between marked lines after shrinkage (mm)) / 200} x 100 As
the dry heat shrinkage rate, the average value of the measurement results for the three measurement samples is used. In addition, values ​​that are more than 2% away from the average value are not counted.
[0081]
The preferred lower limit of the total thickness of the heat-shrinkable multilayer film of the present invention is 20 μm, and the preferred upper limit is 80 μm. By setting the thickness of the entire heat-shrinkable multilayer film within the above range, it is excellent in economy and easy to handle.
In the heat-shrinkable multilayer film of the present invention, the preferable lower limit of the ratio of the thickness of the front and back layers to the intermediate layer (thickness of the front and back layers / thickness of the intermediate layer) is 1/12, and the more preferable lower limit is 1. / 10, the preferred upper limit is 1/3, and the more preferred upper limit is 1/4.
The thickness of the front and back layers means the thickness of each of the surface layer and the back layer.
[0082]
The ratio of the thickness of the front and back layers to the total thickness of the heat-shrinkable multilayer film of the present invention is such that the preferable lower limit is 7%, the more preferable lower limit is 8%, the preferable upper limit is 18%, and the more preferable upper limit is 16%. .. When the above ratio is 7% or more, the solvent resistance and heat resistance of the heat-shrinkable multilayer film can be sufficiently improved. When the above ratio is 18% or less, the label can be easily peeled off from the container.
For example, when the total thickness of the heat-shrinkable multilayer film of the present invention is 40 μm, the preferable lower limit of the thickness of the front and back layers is 2.8 μm, the more preferable lower limit is 3.2 μm, and the preferable upper limit is 7.2 μm. The preferred upper limit is 6.4 μm.
[0083]
The ratio of the thickness of the intermediate layer to the total thickness of the heat-shrinkable multilayer film of the present invention is such that the preferable lower limit is 60%, the more preferable lower limit is 65%, the preferable upper limit is 84%, and the more preferable upper limit is 82%. .. When the above ratio is 65% or more, the label can be easily peeled off from the container. When the above ratio is 84% ​​or less, the heat resistance of the heat-shrinkable multilayer film can be sufficiently improved.
For example, when the total thickness of the heat-shrinkable multilayer film of the present invention is 40 μm, the preferable lower limit of the thickness of the intermediate layer is 24 μm, the more preferable lower limit is 26 μm, the preferable upper limit is 33.6 μm, and the more preferable upper limit is 32. It is 0.8 μm.
[0084]
The ratio of the thickness of the adhesive layer to the total thickness of the heat-shrinkable multilayer film of the present invention is such that the preferable lower limit is 0.5%, the more preferable lower limit is 1%, the preferable upper limit is 5%, and the more preferable upper limit is 4%. Is.
For example, when the total thickness of the heat-shrinkable multilayer film of the present invention is 40 μm, the preferable lower limit of the thickness of the adhesive layer is 0.2 μm, the more preferable lower limit is 0.4 μm, the preferable upper limit is 2 μm, and the more preferable upper limit. Is 1.6 μm.
[0085]
The method for producing the heat-shrinkable multilayer film of the present invention is not particularly limited, but a method in which each layer is simultaneously molded by a coextrusion method is preferable. For example, in coextrusion with a T-die, the laminating method may be a feed block method, a multi-manifold method, or a method in which these are used in combination.
Specifically, for example, the polyester-based resin constituting the front and back layers, the polystyrene-based resin constituting the intermediate layer, and the resin constituting the adhesive layer are each put into an extruder adjusted to 160 to 250 ° C., and 220 to 220 to A method can be used in which the resin is extruded into a sheet by a multilayer die adjusted to 260 ° C., cooled and solidified by a take-up roll adjusted to 20 to 40 ° C., and then stretched in one or two axes. The stretching temperature needs to be changed depending on the softening temperature of the resin constituting the film or the shrinkage characteristics required for the heat-shrinkable multilayer film, but the preferred lower limit of the stretching temperature is 70 ° C., and the preferable upper limit is 120 ° C., more preferably. The lower limit is 75 ° C., and the more preferable upper limit is 115 ° C. The preferred lower limit of the fixed zone is 80 ° C., and the preferred upper limit is 120 ° C.
[0086]
By using the heat-shrinkable multilayer film of the present invention as a base film, a heat-shrinkable label can be obtained. Such a heat shrinkable label is also one of the present inventions.
The heat-shrinkable label of the present invention may use the heat-shrinkable multilayer film of the present invention as a base film and may have other layers such as an antistatic layer and a printing layer, if necessary.
[0087]
As a method of attaching the heat-shrinkable label of the present invention to a container, usually, the ends of the heat-shrinkable label of the present invention are adhered to each other using a solvent and processed into a tube shape (center seal processing), and then the container is processed. A method of heating and shrinking the heat-shrinkable label of the present invention while covering the label is adopted.
Effect of the invention
[0088]
According to the present invention, a heat-shrinkable multilayer film capable of producing a labeled container having an excellent appearance by preventing layer displacement at the center seal portion when attached to a container as a heat-shrinkable label for dry heat shrinkage. A heat shrinkable label using a heat shrinkable multilayer film as a base film can be provided.
A brief description of the drawing
[0089]
FIG. 1 is a schematic view showing a center seal portion of a heat-shrinkable label.
FIG. 2 is a schematic view showing a state of layer shift at the center seal portion of a heat-shrinkable label.
FIG. 3 is a schematic diagram showing a measurement sample in the dry heat shrinkage measurement.
FIG. 4 is a schematic diagram showing a measurement method for measuring the dry heat shrinkage rate.
Mode for carrying out the invention
[0090]
Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.
[0091]
In the examples and comparative examples, the following raw materials were used.
(Polyester resin)
-Polyester resin A: 100 mol% of terephthalic acid-derived component as dicarboxylic acid component, 65 mol% of ethylene glycol-derived component as diol component, 20 mol% of diethylene glycol-derived component, Polyester resin (glass transition temperature 69 ° C.)
(polystyrene resin) containing 15 mol% of 1,4-cyclohexanedimethanol-derived component ・ Polyester
resin A: styrene content 81.3% by weight, butadiene content Polyester-butadiene copolymer having an amount of 18.7% by weight, Vicat softening temperature 81 ° C.)
-Polyester resin B: Polyester having a styrene content of 77.7% by weight and a butadiene content of 22.3% by weight. -Butadiene copolymer, Vicat softening temperature 71 ° C.)
-
Polyester resin C: Styrene-butadiene copolymer Vicat softening temperature 76 ° C. with styrene content of 72% by weight and butadiene content of 28% by weight) (Polyester-based Elastomer)
・ Elastomer A: Made by Toray Dupont, Hytrel 2521, Durometer Hardness 55
[0092]
(Example 1)
Polyester resin A was used as the resin constituting the front and back layers.
As the resin constituting the adhesive layer, a mixed resin composed of 30% by weight of the elastomer A and 70% by weight of the polystyrene resin C was used.
As the resin constituting the intermediate layer, a mixed resin composed of 10% by weight of polystyrene resin A and 90% by weight of polystyrene resin B was used.
These resins were put into an extruder having a barrel temperature of 160 to 250 ° C., extruded from a multilayer die at 250 ° C. into a sheet having a three-layer structure, and cooled and solidified by a take-up roll at 30 ° C. Next, the roll was rolled in the MD direction at a stretching ratio of 1.5 times, followed by a preheating zone of 112 ° C. (passing time: 5.3 seconds), a stretching zone of 100 ° C. (passing time of 7.8 seconds), and a heat fixing zone of 102 ° C. (passing). After stretching in the TD direction at a stretching ratio of 6 times in a tenter stretching machine for a time of 5.3 seconds), the total thickness is 40 μm, and the surface layer (5.7 μm) / adhesive layer (adhesive layer). A heat-shrinkable multilayer film having a five-layer structure of 0.7 μm) / intermediate layer (27.2 μm) / adhesive layer (0.7 μm) / back layer (5.7 μm) was obtained.
[0093]
(Example 2)
Polyester-based resin A was used as the resin constituting the front and back layers.
As the resin constituting the adhesive layer, a mixed resin composed of 30% by weight of the elastomer A and 70% by weight of the polystyrene resin C was used.
As the resin constituting the intermediate layer, a mixed resin composed of 15% by weight of polystyrene resin A and 85% by weight of polystyrene resin B was used.
A heat-shrinkable multilayer film was obtained in the same manner as in Example 1 except that these resins were used.
The obtained heat-shrinkable multilayer film has a total thickness of 40 μm, and has a surface layer (5.7 μm) / adhesive layer (0.7 μm) / intermediate layer (27.2 μm) / adhesive layer (0.7 μm) / back layer. It had a five-layer structure of (5.7 μm).
[0094]
(Example 3)
Polyester-based resin A was used as the resin constituting the front and back layers.
As the resin constituting the adhesive layer, a mixed resin composed of 30% by weight of the elastomer A and 70% by weight of the polystyrene resin C was used.
As the resin constituting the intermediate layer, a mixed resin composed of 30% by weight of polystyrene resin A and 70% by weight of polystyrene resin B was used.
A heat-shrinkable multilayer film was obtained in the same manner as in Example 1 except that these resins were used.
The obtained heat-shrinkable multilayer film has a total thickness of 40 μm, and has a surface layer (5.7 μm) / adhesive layer (0.7 μm) / intermediate layer (27.2 μm) / adhesive layer (0.7 μm) / back layer. It had a five-layer structure of (5.7 μm).
[0095]
(Example 4)
Polyester-based resin A was used as the resin constituting the front and back layers.
As the resin constituting the adhesive layer, a mixed resin composed of 30% by weight of the elastomer A and 70% by weight of the polystyrene resin C was used.
As the resin constituting the intermediate layer, a mixed resin containing 45% by weight of the polystyrene-based resin A and 55% by weight of the polystyrene-based resin B was used.
A heat-shrinkable multilayer film was obtained in the same manner as in Example 1 except that these resins were used.
The obtained heat-shrinkable multilayer film has a total thickness of 40 μm, and has a surface layer (5.7 μm) / adhesive layer (0.7 μm) / intermediate layer (27.2 μm) / adhesive layer (0.7 μm) / back layer. It had a five-layer structure of (5.7 μm).
[0096]
(Example 5)
Polyester resin A was used as the resin constituting the front and back layers.
As the resin constituting the adhesive layer, a mixed resin composed of 30% by weight of the elastomer A and 70% by weight of the polystyrene resin C was used.
As the resin constituting the intermediate layer, a mixed resin composed of 50% by weight of polystyrene resin A and 50% by weight of polystyrene resin B was used.
A heat-shrinkable multilayer film was obtained in the same manner as in Example 1 except that these resins were used.
The obtained heat-shrinkable multilayer film has a total thickness of 40 μm, and has a surface layer (5.7 μm) / adhesive layer (0.7 μm) / intermediate layer (27.2 μm) / adhesive layer (0.7 μm) / back layer. It had a five-layer structure of (5.7 μm).
[0097]
(Example 6)
Polyester resin A was used as the resin constituting the front and back layers.
As the resin constituting the adhesive layer, a mixed resin composed of 65% by weight of the elastomer A and 35% by weight of the polystyrene resin C was used.
As the resin constituting the intermediate layer, a mixed resin containing 10% by weight of the polystyrene-based resin A and 90% by weight of the polystyrene-based resin B was used.
A heat-shrinkable multilayer film was obtained in the same manner as in Example 1 except that these resins were used.
The obtained heat-shrinkable multilayer film has a total thickness of 50 μm and has a five-layer structure of a surface layer (7 μm) / adhesive layer (1 μm) / intermediate layer (34 μm) / adhesive layer (1 μm) / back layer (7 μm). there were.
[0098]
(Example 7)
Polyester-based resin A was used as the resin constituting the front and back layers.
As the resin constituting the adhesive layer, a mixed resin composed of 65% by weight of the elastomer A and 35% by weight of the polystyrene resin C was used.
As the resin constituting the intermediate layer, a mixed resin composed of 15% by weight of polystyrene resin A and 85% by weight of polystyrene resin B was used.
A heat-shrinkable multilayer film was obtained in the same manner as in Example 1 except that these resins were used.
The obtained heat-shrinkable multilayer film has a total thickness of 50 μm and has a five-layer structure of a surface layer (7 μm) / adhesive layer (1 μm) / intermediate layer (34 μm) / adhesive layer (1 μm) / back layer (7 μm). there were.
[0099]
(Example 8)
Polyester resin A was used as the resin constituting the front and back layers.
As the resin constituting the adhesive layer, a mixed resin composed of 65% by weight of the elastomer A and 35% by weight of the polystyrene resin C was used.
As the resin constituting the intermediate layer, a mixed resin composed of 30% by weight of polystyrene resin A and 70% by weight of polystyrene resin B was used.
A heat-shrinkable multilayer film was obtained in the same manner as in Example 1 except that these resins were used.
The obtained heat-shrinkable multilayer film has a total thickness of 50 μm and has a five-layer structure of a surface layer (7 μm) / adhesive layer (1 μm) / intermediate layer (34 μm) / adhesive layer (1 μm) / back layer (7 μm). there were.
[0100]
(Example 9)
Polyester-based resin A was used as the resin constituting the front and back layers.
As the resin constituting the adhesive layer, a mixed resin composed of 65% by weight of the elastomer A and 35% by weight of the polystyrene resin C was used.
As the resin constituting the intermediate layer, a mixed resin composed of 45% by weight of polystyrene resin A and 55% by weight of polystyrene resin B was used.
A heat-shrinkable multilayer film was obtained in the same manner as in Example 1 except that these resins were used.
The obtained heat-shrinkable multilayer film has a total thickness of 50 μm and has a five-layer structure of a surface layer (7 μm) / adhesive layer (1 μm) / intermediate layer (34 μm) / adhesive layer (1 μm) / back layer (7 μm). there were.
[0101]
(Example 10)
Polyester-based resin A was used as the resin constituting the front and back layers.
As the resin constituting the adhesive layer, a mixed resin composed of 65% by weight of the elastomer A and 35% by weight of the polystyrene resin C was used.
As the resin constituting the intermediate layer, a mixed resin composed of 50% by weight of polystyrene resin A and 50% by weight of polystyrene resin B was used.
A heat-shrinkable multilayer film was obtained in the same manner as in Example 1 except that these resins were used.
The obtained heat-shrinkable multilayer film has a total thickness of 50 μm and has a five-layer structure of a surface layer (7 μm) / adhesive layer (1 μm) / intermediate layer (34 μm) / adhesive layer (1 μm) / back layer (7 μm). there were.
[0102]
(Comparative Example 1)
Polyester resin A was used as the resin constituting the front and back layers.
As the resin constituting the adhesive layer, a mixed resin composed of 30% by weight of the elastomer A and 70% by weight of the polystyrene resin C was used.
As the resin constituting the intermediate layer, a mixed resin composed of 70% by weight of polystyrene resin A and 30% by weight of polystyrene resin B was used.
A heat-shrinkable multilayer film was obtained in the same manner as in Example 1 except that these resins were used.
The obtained heat-shrinkable multilayer film has a total thickness of 40 μm, and has a surface layer (5.7 μm) / adhesive layer (0.7 μm) / intermediate layer (27.2 μm) / adhesive layer (0.7 μm) / back layer. It had a five-layer structure of (5.7 μm).
[0103]
(Comparative Example 2)
Polyester resin A was used as the resin constituting the front and back layers.
As the resin constituting the adhesive layer, a mixed resin composed of 30% by weight of the elastomer A and 70% by weight of the polystyrene resin C was used.
Polystyrene resin A was used as the resin constituting the intermediate layer.
A heat-shrinkable multilayer film was obtained in the same manner as in Example 1 except that these resins were used.
The obtained heat-shrinkable multilayer film has a total thickness of 40 μm, and has a surface layer (5.7 μm) / adhesive layer (0.7 μm) / intermediate layer (27.2 μm) / adhesive layer (0.7 μm) / back layer. It had a five-layer structure of (5.7 μm).
[0104]
(Comparative Example 3)
Polyester resin A was used as the resin constituting the front and back layers.
As the resin constituting the adhesive layer, a mixed resin composed of 30% by weight of the elastomer A and 70% by weight of the polystyrene resin C was used.
Polystyrene resin B was used as the resin constituting the intermediate layer.
A heat-shrinkable multilayer film was obtained in the same manner as in Example 1 except that these resins were used.
The obtained heat-shrinkable multilayer film has a total thickness of 30 μm, and has a surface layer (3.2 μm) / adhesive layer (0.7 μm) / intermediate layer (22.2 μm) / adhesive layer (0.7 μm) / back layer. It had a 5-layer structure of (3.2 μm).
[0105]
(Evaluation) The
heat-shrinkable multilayer films obtained in Examples and Comparative Examples were evaluated as follows. The results are shown in Table 1.
[0106]
(1) Shrinkage stress The
obtained heat-shrinkable multilayer film was cut into a size of 200 mm × 10 mm so that the TD direction (main shrinkage direction) was the long side, and used as a measurement sample. One of the measurement samples was fixed so that the distance between the chucks was 100 mm, and the other was connected to a load cell for load measurement and set (the output signal from the load cell is recorded by the recorder).
Then, the measurement sample was immersed in warm water adjusted to 80 ° C. together with the chuck for 30 seconds, and the contraction stress when the measurement sample contracted was measured. The maximum value in 30 seconds was taken as the measured value.
[0107]
(2) Dry heat shrinkage ratio The
obtained heat shrinkable multilayer film is cut into a size of 300 mm × 25 mm so that the TD direction (main shrinkage direction) is the long side, and the distance between the marked lines becomes 200 mm. A marked line was drawn as shown above to prepare a measurement sample (see FIG. 3). Next, both ends of the measurement sample were fixed to a pointer with a length of 520 mm, the heat-shrinkable multilayer film of the fixed portion was bent outward (see FIG. 4), and the temperature was set to 70 ° C. or 100 ° C. and the humidity was set to 25%. It was put into a constant temperature and humidity chamber (manufactured by Nagano Science Co., Ltd., LH31-12M) through a horizontal hole. Ten seconds after charging, the heat-shrinkable multilayer film was taken out, the marked line distance was measured, and the shrinkage rate between the marked lines was calculated from the following formula.
Dry heat shrinkage rate = {(200-distance between marked lines after shrinkage (mm)) / 200} × 100 As
the dry heat shrinkage rate, the average value of the measurement results for the three measurement samples was used. In addition, values ​​that are more than 2% away from the average value are not counted.
[0108]
(3) Layer shift The
obtained heat-shrinkable multilayer film is cut into 100 mm × 200 mm so that the TD direction (main shrinkage direction) is the long side, and cyclohexane 40 is 40 parts by weight of 1,4-dioxolane. Use a solvent mixed with the weight part to seal the solvent with a width of 5 mm so that it is parallel to the MD direction (direction orthogonal to the main contraction direction), fold it flat so that the center seal part is in the center, and heat the cylinder. A shrinkable label was obtained.
Then, the heat-shrinkable label was immersed in warm water at 100 ° C. for 30 seconds and shrunk by 5% in the TD direction using a jig capable of regulating the shrinkage rate in the TD direction.
At that time, the appearance of the center seal portion was observed to confirm the deviation between the intermediate layer and the front and back layers, and the evaluation was made according to the following criteria.
〇: The deviation between the intermediate layer and the front and back layers of the center seal portion was less than 0.1 mm.
X: The deviation between the intermediate layer and the front and back layers of the center seal portion was 0.1 mm or more.
[0109]
(4)
Wearability Using the heat-shrinkable multilayer films obtained in Examples 1 to 10 and Comparative Examples 1 to 3, labels having a folding diameter of 132 mm and a length of 110 mm were produced.
The Kabuse type shrink tunnel K-1000 (manufactured by Kyowa Denki Co., Ltd.) was set to a tunnel temperature of 95 ° C., an air volume of 20 Hz, and a belt speed of 25 Hz (passing time 25 seconds) to form tunnel 1.
Further, the Kabuse type shrink tunnel K-100 (manufactured by Kyowa Denki Co., Ltd.) was set to a tunnel temperature of 100 ° C., an air volume of 40 Hz, and a belt speed of 25 Hz (passing time 25 seconds) to form a tunnel 2.
Next, the obtained label was attached to a spray bottle (mold killer (registered trademark) spray bottle: capacity 400 ml, width 102 mm, depth 57 mm, height 164 mm), passed through tunnel 1, and passed under a normal temperature atmosphere for 7 seconds. After that, the label was contracted and attached by passing through the tunnel 2.
The wearability (wearing finish) of the label was evaluated as follows.
〇: There was no appearance defect due to insufficient shrinkage of the label.
X: Poor appearance was observed at the upper end of the label due to insufficient shrinkage.
[0110]
[table 1]

Industrial applicability
[0111]
According to the present invention, a heat-shrinkable multilayer film capable of producing a labeled container having an excellent appearance by preventing layer displacement at the center seal portion when attached to a container as a heat-shrinkable label for dry heat shrinkage. A heat shrinkable label using a heat shrinkable multilayer film as a base film can be provided.
Code description
[0112]
1 Front and back layer
2 Adhesive layer
3 Intermediate layer
4 Adhesive layer
5 Front and back layer
6 Front and back layer
7 Adhesive layer
8 Intermediate layer
9 Adhesive layer
10 Front and back layer
11 Container
The scope of the claims
[Claim 1]
A heat-shrinkable multilayer film in which a front and back layer made of a polyester resin and an intermediate layer made of a polystyrene resin are laminated via an adhesive layer, and is
immersed in warm water at 80 ° C. for 30 seconds. A heat-shrinkable multilayer film having a maximum shrinkage stress of 3.5 to 11 MPa.
[Claim 2]
The heat-shrinkable multilayer film according to claim 1, wherein the polyester-based resin constituting the front and back layers has a glass transition temperature of 55 to 95 ° C.
[Claim 3]
The polystyrene resin constituting the intermediate layer is a mixed resin containing a polystyrene resin (A) having a Vicat softening temperature of 80 ° C. or higher and a polystyrene resin (B) having a Vicat softening temperature of less than 80 ° C. The heat-shrinkable multilayer film according to claim 1 or 2.
[Claim 4]
The third aspect of the present invention, wherein the polystyrene-based resin constituting the intermediate layer is a mixed resin containing 1 to 60% by weight of the polystyrene-based resin (A) and 40 to 99% by weight of the polystyrene-based resin (B). Heat shrinkable multilayer film.
[Claim 5]
The heat-shrinkable multilayer film according to claim 1, 2, 3 or 4, wherein the adhesive layer contains 35 to 70% by weight of a polystyrene resin and 30 to 65% by weight of a polyester elastomer.
[Claim 6]
A heat-shrinkable label according to claim 1, 2, 3, 4 or 5, wherein the heat-shrinkable multilayer film is used.