Technical Field
5 [0001] The present invention relates to a multilayer film, a packaging
material, and a package. Specifically, the present invention relates to a
polypropylene-based multilayer film which is excellent in heat resistance
and transparency and can be suitably used as a sealant film for a
packaging bag even in a harsh treatment such as boiling water treatment
10 or retort treatment, and a packaging material and a package obtained
using the polypropylene-based multilayer film.
Background Art
[0002] Since a polypropylene-based film is excellent in rigidity and heat
resistance, and is inexpensive, the polypropylene-based film may be used
15 as a sealant film in various packaging materials such as food packaging.
[0003] Patent Literature 1 proposes a polypropylene-based composite
film constituted by three layers including an intermediate layer formed of
a propylene/ethylene block copolymer, and both surface layers formed of
a propylene-based random copolymer.
20 [0004] Patent Literature 2 proposes a multilayer film constituted by both
surface layers containing an ethylene-α-olefin copolymer and a
propylene-based polymer, and an intermediate layer containing a
propylene polymer and an ethylene-propylene copolymer.
Citation List
25 Patent Literature
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[0005] [Patent Literature 1] Japanese Unexamined Patent Publication
No. 2017-132186
[Patent Literature 2] Japanese Unexamined Patent Publication
No. 2017-105174
5 Summary of Invention
Technical Problem
[0006] A polypropylene-based multilayer film is required to have, for
example, heat resistance that can withstand retort treatment, in which a
pressure treatment is performed at a high temperature of 120 to 135℃ for
10 disinfection and sterilization, or the like, and transparency for
maintaining visibility of contents. However, it is the current situation
that achieving excellent heat resistance and transparency at the same time
is difficult with a conventional polypropylene-based multilayer film.
[0007] The present invention has been made in view of the above15 described circumstances, and an objective of the present invention is to
provide a polypropylene-based multilayer film capable of achieving
excellent heat resistance and transparency at the same time. Another
objective of the present invention is to provide a packaging material and
a package that can be obtained by using the multilayer film.
20 Solution to Problem
[0008] As a result of intensive research to solve the above-described
problems, the inventors have found that it is important to incorporate a
mixture of predetermined amounts of different propylene-based polymers
in an outer layer in a polypropylene-based multilayer film, and thus
25 completed of the present invention.
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[0009] A multilayer film according to one aspect of the present invention
includes a first outer layer containing 70 to 30% by mass of a propylene
homopolymer (A) and 30 to 70% by mass of a propylene/ethylene
random copolymer (B) having an ethylene content of 5% by mass or less,
5 an inner layer containing a propylene/ethylene block copolymer (C) and
an ethylene/propylene copolymer elastomer (D), and a second outer layer
containing 70 to 30% by mass of the propylene homopolymer (A) and 30
to 70% by mass of the propylene/ethylene random copolymer (B) having
an ethylene content of 5% by mass or less, in that order.
10 [0010] In the above-described multilayer film, the outer layer contains
the propylene homopolymer (A) and the propylene/ethylene random
copolymer (B) having a predetermined ethylene content in a specific
amount ratio. Thereby, it is possible to suppress unevenness on a
surface, which is a factor that deteriorates transparency of the film, while
15 maintaining heat resistance. Such an effect cannot be obtained when a
propylene-based random copolymer is used in the outer layer (for
example, Patent Literature 1) or when an ethylene-α-olefin copolymer
and a propylene-based polymer are used in the outer layer (for example,
Patent Literature 2), and is a particularly suitable for applications with a
20 retort treatment.
[0011] In the one aspect, a ratio Mw (EPR)/Mw (PP) of a weight-average
molecular weight Mw (EPR) of an ethylene-propylene copolymer to a
weight-average molecular weight Mw (PP) of a propylene polymer in the
propylene/ethylene block copolymer (C) may be 1.5 or less. In this
25 case, the outer layer contains the propylene homopolymer (A) and the
propylene/ethylene random copolymer (B) in a specific amount ratio, and
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a ratio of weight-average molecular weights of the propylene polymer
and the ethylene-propylene copolymer in the propylene/ethylene block
copolymer (C) contained in the inner layer is a specific value or less.
Thereby, it is possible to further reduce a difference in refractive index in
5 the film, which is a factor that deteriorates transparency of the film, while
maintaining heat resistance. Such an effect cannot be obtained with
conventional multilayer films (for example, Patent Literature 1 and Patent
Literature 2), and is particularly suitable for applications with a retort
treatment.
10 [0012] In the one aspect, the inner layer may contain 90 to 50% by mass
of the propylene/ethylene block copolymer (C) and 10 to 50% by mass
of the ethylene/propylene copolymer elastomer (D). Thereby,
flexibility of the film is maintained, edge breakage of a heat seal portion
can be suppressed after retort treatment, and excellent heat sealing is
15 easily obtained.
[0013] In the one aspect, a total thickness of the first outer layer and the
second outer layer may be 16 to 42% based on a thickness of the
multilayer film. Thereby, both transparency and heat sealing are easily
achieved.
20 [0014] In the one aspect, a thickness of the inner layer may be 20 μm or
more. Thereby, flexibility of the film is easily maintained.
[0015] In the one aspect, a thickness in a lamination direction of the
ethylene-propylene copolymer present in the inner layer as a dispersing
element may be 1.5 μm or less. Thereby, transparency of the film is
25 easily maintained.
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[0016] A packaging material according to another aspect of the present
invention includes the multilayer film described above, and a base
material.
[0017] A package according to still another aspect of the present
5 invention is made from the packaging material described above.
Advantageous Effects of Invention
[0018] According to the present invention, it is possible to provide a
polypropylene-based multilayer film capable of achieving excellent heat
resistance and transparency at the same time. Also, according to the
10 present invention, it is possible to provide a packaging material and a
package that can be obtained by using the multilayer film.
Brief Description of Drawings
[0019] Fig. 1 is a cross-sectional view of a multilayer film according to
one embodiment of the present invention.
15 Fig. 2 is a diagram showing a total melting heat amount of a
propylene/ethylene random copolymer (B) used in example 1 and a result
in which a melting heat amount is divided at 135℃.
Fig. 3 is a diagram showing a total melting heat amount of a
propylene/ethylene random copolymer (E) used in comparative example
20 2 and a result in which a melting heat amount is divided at 135℃.
Fig. 4 is a cross-sectional image of an inner layer in example 1.
Fig. 5 is a cross-sectional image of an inner layer in example 10.
Description of Embodiments
[0020]
25 Fig. 1 is a cross-sectional view of a multilayer film according to
one embodiment of the present invention. A multilayer film 10 includes
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a first outer layer 1a, an inner layer 2, and a second outer layer 1b in that
order. The multilayer film can be used as a polypropylene-based
unstretched sealant film.
[0021] [First outer layer and second outer layer]
5 The first outer layer and the second outer layer contain a
propylene homopolymer (A) and a propylene/ethylene random
copolymer (B). The first outer layer and the second outer layer may be
collectively referred to as an outer layer simply. The first outer layer
and the second outer layer may have the same composition or may have
10 different compositions.
[0022] (Propylene homopolymer (A))
The propylene homopolymer (A) can be obtained by a method of
homopolymerizing propylene using, for example, a Ziegler-Natta type
catalyst or a metallocene catalyst. When the outer layer contains the
15 propylene homopolymer (A), excellent heat resistance can be imparted to
the outer layer.
[0023] As the propylene homopolymer (A), one having a melting start
temperature of 150℃ or higher and a melting peak temperature of 155℃
or higher when a differential scanning calorimetry (JIS K 7121) is
20 performed can be used. One having both the melting start temperature
and the melting point peak temperature within this range has excellent
heat resistance, and fusion does not easily occur on an inner surface of a
package after, for example, retort treatment at a high temperature is
performed.
25 [0024] As the propylene homopolymer (A), one having a melt flow rate
(MFR: ISO 1133) (temperature 230℃, load 2.16 kg) in a range of 2.0 to
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7.0 g/10 minutes can be used. When the melt flow rate is a lower limit
value or higher, a load on an extruder during forming processing is
reduced, a processing speed is unlikely to decrease, and excellent
productivity is easily maintained. Also, when the melt flow rate is an
5 upper limit value or lower, the outer layer tends to have excellent impact
resistance.
[0025] (Propylene/ethylene random copolymer (B))
The propylene/ethylene random copolymer (B) can be obtained
by copolymerizing ethylene as a comonomer with a main monomer
10 formed of propylene using, for example, a Ziegler-Natta type catalyst or
a metallocene catalyst. When the outer layer contains the
propylene/ethylene random copolymer (B), a multilayer film having
excellent transparency can be obtained.
[0026] As the propylene/ethylene random copolymer (B), one having a
15 melting start temperature of 140℃ or higher and a melting peak
temperature of 145℃ or higher when the differential scanning
calorimetry (JIS K 7121) is performed can be used. One having both
the melting start temperature and the melting point peak temperature
within this range has excellent heat resistance, and fusion does not easily
20 occur on an inner surface of the package after, for example, retort
treatment at a high temperature is performed.
[0027] As the propylene/ethylene random copolymer (B), one in which
a ratio ΔHh/ΔHl between a melting heat amount ΔHh at a higher
temperature than a measurement temperature 135℃ and a melting heat
25 amount ΔHl at a lower temperature than that when the differential
scanning calorimetry (JIS K 7121) is performed is in a range of 1.5 to 2.5
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can be used. When the above-described ratio is an upper limit value or
lower, flexibility of a film is maintained, edge breakage of a heat seal
portion can be suppressed after retort treatment, and a heat-seal strength
is unlikely to decrease. A lower limit of the above-described ratio can
5 be set to 1.5 from a viewpoint that fusion does not easily occur on an
inner surface of the package after the retort treatment.
[0028] An ethylene content of the propylene/ethylene random copolymer
(B) is 5% by mass or less. When the ethylene content is an upper limit
value or lower, heat resistance is not excessively deteriorated while
10 transparency is maintained, and fusion on an inner surface of the package
can be suppressed after retort treatment. From this point of view, the
ethylene content may be 4.5% by mass or less, and may be 4% by mass
or less. A lower limit of the ethylene content is not particularly limited,
but it can be set to 2% by mass from viewpoints that flexibility of the film
15 is maintained, edge breakage can be suppressed at the heat seal portion
after the retort treatment, and a heat-seal strength is unlikely to decrease.
[0029] The ethylene content of the propylene/ethylene random
copolymer (B) can be measured according to an ethylene content
quantification method (IR method) described on pages 412 to 413 of the
20 Polymer Analysis Handbook (May 10, 2013, 3rd printing) edited by the
Polymer Analysis Council of the Japan Society for Analytical Chemistry.
[0030] The outer layer contains 70 to 30% by mass of the propylene
homopolymer (A) and 30 to 70% by mass of the propylene/ethylene
random copolymer (B) having an ethylene content of 5% by mass or less.
25 When a contained amount of the propylene homopolymer (A) is 30% by
mass or more, excellent heat resistance can be maintained. From this
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point of view, the contained amount may be 35% by mass or more, and
may be 40% by mass or more. When the contained amount of the
propylene homopolymer (A) is 70% by mass or less, that is, a contained
amount of the propylene/ethylene random copolymer (B) having the
5 ethylene content of 5% by mass or less is at least 30% by mass or more,
excellent transparency and heat sealing can be exhibited. From this
viewpoint, the contained amount of the propylene homopolymer (A) may
be 65% by mass or less, and may be 60% by mass or less. From the
viewpoint described above, the contained amount of the
10 propylene/ethylene random copolymer (B) having the ethylene content of
5% by mass or less may be 35 to 65% by mass, and may be 40 to 60% by
mass.
[0031] [Inner layer]
The inner layer contains a propylene/ethylene block copolymer
15 (C) and an ethylene/propylene copolymer elastomer (D).
[0032] (Propylene/ethylene block copolymer (C))
The propylene/ethylene block copolymer (C) is a copolymer that
can be obtained by producing a propylene polymer (C1) in a first step and
then producing an ethylene-propylene copolymer (C2) by vapor phase
20 polymerization in a second step. The propylene/ethylene block
copolymer (C) is not a block copolymer in which a propylene polymer
terminal and an ethylene-propylene copolymer terminal are bonded, but
is a kind of blend-based copolymer. When the inner layer contains the
propylene/ethylene block copolymer (C), flexibility of the film is
25 maintained, edge breakage of the heat seal portion can be suppressed after
retort treatment, and excellent heat sealing is easily obtained.
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[0033] The propylene/ethylene block copolymer (C) contains a
propylene polymer component (C1) and an ethylene-propylene
copolymer component (C2) as constituent components as described
above. A ratio Mw (EPR)/Mw (PP) of a weight-average molecular
5 weight Mw (EPR) of an ethylene-propylene copolymer to a weightaverage molecular weight Mw (PP) of a propylene polymer in the
propylene/ethylene block copolymer (C) may be 1.5 or less. Thereby,
the inner layer can have more suitable transparency. From this point of
view, the ratio may be 1.3 or less, and may be 1.2 or less. A lower limit
10 of Mw (EPR)/Mw (PP) is not particularly limited, but can be set to 0.9
from a viewpoint of impact resistance.
[0034] The weight-average molecular weight ratio can be measured as
follows. First, 200 ml of n-decane is added to 5 g of the
propylene/ethylene block copolymer (C), and this is completely dissolved
15 at 145℃. Thereafter, it is allowed to be cooled to room temperature,
and then precipitates are filtered and separated. One obtained from the
filtration is used as the propylene polymer component (propylene resin
component), a solvent of the residual solution is completely removed in
a dryer, and thereby an ethylene-propylene copolymer component is
20 obtained. Each of the obtained components is added with 20 ml of a
mobile phase for GPC measurement, dissolved at 145℃, hot-filtered
through a sintered filter with a pore size of 1.0 μm, and thereby the filtrate
is prepared as a measurement solution. Using a HLC-8321GPC/HT
type high-temperature gel permeation chromatography manufactured by
25 Tosoh as a measuring device, a molecular weight is measured using a
simple PS conversion method under the conditions of a column size inner
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diameter of 7.5 mm, a length of 300 mm, a temperature of 140℃, odichlorobenzene (stabilizer; containing 0.025 wt% BHT) as a mobile
phase, and a flow rate 1.0 ml. For the obtained results, a ratio of the
weight-average molecular weight Mw (PP) of the propylene polymer
5 component and the weight-average molecular weight Mw (EPR) of the
ethylene-propylene copolymer component is defined as a weight-average
molecular weight ratio Mw (EPR)/Mw (PP).

CLAIMS
[Claim 1]
A multilayer film comprising:
a first outer layer containing 70 to 30% by mass of a propylene
5 homopolymer (A) and 30 to 70% by mass of a propylene/ethylene
random copolymer (B) having an ethylene content of 5% by mass or less;
an inner layer containing a propylene/ethylene block copolymer
(C) and an ethylene/propylene copolymer elastomer (D); and
a second outer layer containing 70 to 30% by mass of the
10 propylene homopolymer (A) and 30 to 70% by mass of the
propylene/ethylene random copolymer (B) having an ethylene content of
5% by mass or less, in that order.
[Claim 2]
The multilayer film according to claim 1, wherein a ratio Mw
15 (EPR)/Mw (PP) of a weight-average molecular weight Mw (EPR) of an
ethylene-propylene copolymer to a weight-average molecular weight Mw
(PP) of a propylene polymer in the propylene/ethylene block copolymer
(C) is 1.5 or less.
[Claim 3]
20 The multilayer film according to claim 1 or 2, wherein the inner
layer contains 90 to 50% by mass of the propylene/ethylene block
copolymer (C) and 10 to 50% by mass of the ethylene/propylene
copolymer elastomer (D).
[Claim 4]
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The multilayer film according to any one of claims 1 to 3, wherein
a total thickness of the first outer layer and the second outer layer is 16 to
42% based on a thickness of the multilayer film.
[Claim 5]
5 The multilayer film according to any one of claims 1 to 4, wherein
a thickness of the inner layer is 20 μm or more.
[Claim 6]
The multilayer film according to claim 2, wherein a thickness in
a lamination direction of the ethylene-propylene copolymer present in the
10 inner layer as a dispersing element is 1.5 μm or less.
[Claim 7]
A packaging material comprising the multilayer film according to
any one of claims 1 to 6, and a base material.
[Claim 8]
15 A package made from a packaging material according to claim 7.