DESC:FIELD
The present disclosure relates to a waterborne heat seal coating composition and a process for its preparation.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicates otherwise.
Heat seal refers to a strong and rigid seal and is the most commonly used form for sealing. Heat sealing requires no special material such as pressure-sensitive acrylic emulsions. It requires heat to melt.
Substrate refers to any surface of an object to which ink or coating can be applied. The substrate includes a cellulose-based substrate, paper, paperboard, fabric, leather, textiles, stone, plastic, metalized foil, plastic or polymer film, glass, ceramic, metal, wood, composites, and inorganic materials and the like.
Glass transition temperature (abbreviated as Tg) is defined as a second order phase transition temperature where an amorphous material becomes glassy and brittle upon cooling and becomes soft and ductile upon heating.
Melting temperature refers to a temperature at which a substance changes from a solid to a liquid phase.
Softening point refers to a temperature at which a material softens beyond some arbitrary softness.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Heat seal coating products have been generally used in food, pharmaceutical, medical and industrial packaging applications. Examples of heat seal coating products include ethylene-vinyl acetate heat seal coatings and polymeric films such as biaxially oriented polypropylene that are often used in packaging by the application of heat and pressure, which seals the film to itself or to another substrate. However, such films generally exhibit poor heat-sealing characteristics, require high sealing temperature, have low seal strength, and have poor hot tack properties to the film. In addition, many of the coatings products currently do not adhere well to the packaging film surface and require the use of a primer to aid in enhancing the adhesion of the heat-sealable coating to the film surface.
The polymer typically used for heat-seal applications is polyethylene (PE). Most of the heat seal product (lacquer) currently used for press through packaging (PTP) is solvent type, generally containing vinyl chloride and vinyl acetate resin dissolved in organic solvents. PTP is generally used in the field of medical packaging. Different type of acrylate resins is then added according to the desired heat-sealing properties. They are blended with various additives in solutions. When the heat seal lacquer is being applied on aluminium foil, volatile organic compounds has emitted during the drying process. Most industries are not well equipped with solvent recycling facilities to reduce the volatile organic compounds emission hence the volatile organic compounds are directly going into the environment, thereby making the environment polluted and hazardous.
LIN, AGNIHOTRI and BEETZ, 2017 reported an aqueous dispersion as heat seal coatings comprise a blend of 10 to 90% by weight of one or more polyurethane dispersions; 90 to 10% by weight of one or more compatible ethylenic copolymer dispersions/emulsions; an anti-blocking additive at 0.1 to 12 weight % of the total solids; and optional additives including wetting, defoaming, thickener, antifungal additives for blister packaging applications.
CN111225959 discloses methods for preparing waterborne heat seal coating compositions that are prepared by melt blending of ethylene vinyl acetate copolymer with a tackifier, and wax in a first mixing apparatus to form a melt blend then contacting the melt blend with an initial aqueous stream comprising a neutralizing agent, water, and a surfactant in an emulsification zone of the second mixing apparatus to form a dispersion, and (C) diluting the dispersion with water in a dilution zone of the second mixing apparatus to form the waterborne heat seal coating composition.
Therefore, there is felt a need to provide a waterborne heat seal coating composition that mitigates the drawbacks mentioned hereinabove or at least provides a useful alternative.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to provide a waterborne heat seal coating composition.
Another object of the present disclosure is to provide a waterborne heat seal coating composition that has good heat seal characteristics, high seal strength, and excellent adhesion on the substrate and better hot tack properties to the film.
Still another object of the present disclosure is to provide a process for preparing a waterborne heat seal coating composition that is simple, efficient, environmental friendly and economical.
Yet another object of the present disclosure is to provide a waterborne heat seal coating composition, which is used for the coating of a substrate.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure relates to a waterborne heat seal coating composition comprising a polyurethane dispersion in an amount in the range of 35 wt.% to 50 wt.% with respect to the total weight of the composition, a wax in an amount in the range of 1 wt.% to 3 wt.% with respect to the total weight of the composition, a styrene-acrylic copolymer-based resin solution in an amount in the range of 25 wt.% to 35 wt.% with respect to the total weight of the composition, a mixture of acrylic emulsion and wax-modified acrylic emulsion in an amount in the range of 3.0 wt.% to 20 wt.% with respect to the total weight of the composition, a defoamer in an amount in the range of 0.01 wt.% to 0.1 wt.% with respect to the total weight of the composition, a preservative in an amount in the range of 0.05 wt.% to 0.15 wt.% with respect to the total weight of the composition; and a fluid medium in an amount in the range of 5 wt.% to 25 wt.% with respect to the total weight of the composition.
The present disclosure further relates to a process for preparing the waterborne heat seal coating composition comprising mixing a predetermined amount of a polyurethane dispersion, a predetermined amount of styrene-acrylic copolymer-based resin solution, a predetermined amount of a mixture of acrylic emulsion and wax-modified acrylic emulsion, a predetermined amount of a micronized wax dispersion of straight-chained hydrocarbon synthetic wax, a predetermined amount of fluid medium, a predetermined amount of a defoamer and a predetermined amount of a preservative under stirring to obtain the waterborne heat seal coating composition.
DETAILED DESCRIPTION
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, known processes or well-known apparatus or structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open-ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.
The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.
Conventionally, polymer-based heat seal coating products exhibit poor heat-sealing characteristics, require high sealing temperature, have low seal strength, and have poor hot tack properties to the film. In addition, many of the coating products currently do not adhere well to the packaging film surface and require the use of a primer to aid in enhancing the adhesion of the heat-sealable coating to the film surface. The polymer generally used for heat-seal applications is polyethylene. Most of the heat seal lacquer currently used for PTP is solvent type, generally containing vinyl chloride and vinyl acetate resin dissolved in organic solvents. Different type of acrylate resins is then added according to the desired heat-sealing properties. They are blended with various additives in solutions. When the heat seal lacquer is being applied on aluminium foil, volatile organic compounds has emitted during the drying process. Most industries are not well equipped with solvent to recycle/incineration facilities to reduce the volatile organic compounds emission hence the volatile organic compounds are directly going into the environment.
In an aspect, the present disclosure provides a waterborne heat seal coating composition.
In accordance with the present disclosure, the heat seal coating composition comprises a polyurethane dispersion in an amount in the range of 35 wt.% to 50 wt.% with respect to the total weight of the composition, a wax in an amount in the range of 1 wt.% to 3 wt.% with respect to the total weight of the composition, a styrene-acrylic copolymer-based resin solution in an amount in the range of 25 wt.% to 35 wt.% with respect to the total weight of the composition, a mixture of acrylic emulsion and wax-modified acrylic emulsion in an amount in the range of 3.0 wt.% to 20 wt.% with respect to the total weight of the composition, a defoamer in an amount in the range of 0.01 wt.% to 0.1 wt.% with respect to the total weight of the composition, a preservative in an amount in the range of 0.05 wt.% to 0.15 wt.% with respect to the total weight of the composition; and a fluid medium in an amount in the range of 5 wt.% to 25 wt.% with respect to the total weight of the composition.
In accordance with the embodiment of the present disclosure, the polyurethane dispersion is present in an amount in the range of 36 wt.% to 45 wt.% with respect to the total weight of the composition, preferably, in the range of 38 wt.% to 42 wt.% with respect to the total weight of the composition. In an exemplary embodiment of the present disclosure, the amount of the polyurethane dispersion is 39.00 wt.% with respect to the total weight of the composition.
In accordance with the embodiment of the present disclosure, the softening point of the polyurethane dispersion is in the range of 50 to 100°C. In an exemplary embodiment of the present disclosure, the softening point of the polyurethane dispersion is 60°C.
In accordance with the embodiment of the present disclosure, the glass transition temperature (Tg) of the polyurethane dispersion is in the range of -20°C to 50°C. In another embodiment of the present disclosure, the glass transition temperature (Tg) of the polyurethane dispersion is in the range of 0°C to 30°C. In still another embodiment of the present disclosure, the glass transition temperature (Tg) of the polyurethane dispersion is 20°C. In yet another embodiment of the present disclosure, the glass transition temperature (Tg) of the polyurethane dispersion is less than 10°C.
In accordance with the embodiment of the present disclosure, the heat seal initiation temperature of the polyurethane dispersion is in the range of 0°C to 200°C. In accordance with the embodiment of the present disclosure, the heat seal initiation temperature of the polyurethane dispersion is less than 150°C, preferably less than 110°C and more preferably less than 70°C. In an exemplary embodiment of the present disclosure, the heat seal initiation temperature of the polyurethane dispersion is 65°C. Higher seal initiation temperature will degrade the polymeric structure and reduces the production speed, which affects the final cost of the packaging pouch structure.
Polyurethane dispersions (PUDs) are urethane polymers, which are finely dispersed in water that is used both in waterborne one-component formulations and increasingly also in two-component systems. Unlike the organic solution, the molecular weight of PUDs dispersed in water does not observably affect the viscosity, which means that very high molecular weights can be applied at low viscosities.
The waterborne heat seal coating composition of the present disclosure is technologically advanced, as it does not emit volatile organic compounds during the drying process.
In accordance with the embodiment of the present disclosure, the wax is at least one selected from the group consisting of polyolefin wax (non-ionic wax dispersion), paraffin wax, microcrystalline wax, high density low molecular weight polyethylene wax and polypropylene wax. In an exemplary embodiment of the present disclosure, the wax is polyolefin wax (non-ionic wax dispersion).
In accordance with the embodiment of the present disclosure, the amount of the wax is in the range of 1 wt.% to 3 wt.% with respect to the total weight of the composition. In accordance with the embodiment of the present disclosure, the wax is present in an amount in the range of 1.5 wt.% to 2.5 wt.% with respect to the total weight of the composition. In an exemplary embodiment of the present disclosure, the amount of the wax is 1.6 wt.% with respect to the total weight of the composition.
In accordance with the embodiment of the present disclosure, the melting temperature (Tm) of the wax is in the range of 50°C to 150°C. In an exemplary embodiment of the present disclosure, the melting temperature (Tm) of the wax is 60°C. The wax used with a melting point of greater than 60°C works as a slip additive here to reduce the coefficient as well as an anti-blocking additive.
In another embodiment of the present disclosure, the average particle size of the wax is in the range of 1 to 10 µm. In an exemplary embodiment of the present disclosure, the average particle size of the wax is 5 µm.
In accordance with the embodiment of the present disclosure, the amount of the styrene-acrylic copolymer-based resin solution is in the range of 25 wt.% to 35 wt.% with respect to the total weight of the composition. In accordance with the embodiment of the present disclosure, the styrene-acrylic copolymer-based resin solution is present in an amount in the range of 26 wt.% to 34 wt.% with respect to the total weight of the composition, preferably, in an amount in the range of 28 wt.% to 33 wt.% with respect to the total weight of the composition. In an exemplary embodiment of the present disclosure, the amount of the styrene-acrylic copolymer-based resin solution is 31.5 wt.% with respect to the total weight of the composition.
In accordance with the embodiment of the present disclosure, the amount of the mixture of acrylic emulsion and wax-modified acrylic emulsion is in the range of 3.0 wt.% to 20 wt.% with respect to the total weight of the composition. In accordance with the embodiment of the present disclosure, the mixture of acrylic emulsion and wax-modified acrylic emulsion is present in an amount in the range of 12 wt.% to 16 wt.% with respect to the total weight of the composition. In an exemplary embodiment of the present disclosure, the amount of the mixture of acrylic emulsion and wax-modified acrylic emulsion is 13.1 wt.% with respect to the total weight of the composition.
In accordance with the embodiment of the present disclosure, the defoamer is polyether siloxane. In accordance with the embodiment of the present disclosure, the amount of the defoamer is in the range of 0.01 wt.% to 0.1 wt.% with respect to the total weight of the composition. In an exemplary embodiment of the present disclosure, the amount of the defoamer is 0.03 wt.% with respect to the total weight of the composition.
In accordance with the embodiment of the present disclosure, the preservative is Isothiazolinone. In accordance with the embodiment of the present disclosure, the amount of the preservative is in the range of 0.05 wt.% to 0.15 wt.% with respect to the total weight of the composition. In an exemplary embodiment of the present disclosure, the amount of the preservative is 0.1 wt.% with respect to the total weight of the composition.
In accordance with the embodiment of the present disclosure, the fluid medium is at least one selected from isopropyl alcohol and de-mineralised water. In an exemplary embodiment of the present disclosure, the fluid medium is a combination of isopropyl alcohol and de-mineralised water. In accordance with the embodiment of the present disclosure, the amount of the fluid medium is in the range of 5 wt.% to 25 wt.% with respect to the total weight of the composition.
In accordance with the embodiment of the present disclosure, the fluid medium is present in an amount in the range of 10 wt.% to 20 wt.% with respect to the total weight of the composition, preferably, in the range of 12 wt.% to 18 wt.% with respect to the total weight of the composition. In an exemplary embodiment of the present disclosure, the amount of the fluid medium is 14.67 wt.% with respect to the total weight of the composition.
In accordance with the embodiment of the present disclosure, a solid content of the waterborne heat seal coating composition is in the range of 25 wt.% to 45 wt.%, preferably in the range of 30 wt.% to 40 wt.% with respect to the total weight of the composition. In an exemplary embodiment of the present disclosure, the solid content of waterborne heat seal coating composition is 32.68 wt.% with respect to the total weight of the composition.
In accordance with the embodiment of the present disclosure, a viscosity of the waterborne heat seal coating composition at 30 oC is in the range of 18 to 25 secs.
In accordance with the embodiment of the present disclosure, a pH of the waterborne heat seal coating composition is in the range of 6 to 8. In an exemplary embodiment of the present disclosure, the pH of the waterborne heat seal coating composition is below 8. In an exemplary embodiment of the present disclosure, the pH of the polyurethane dispersion is 7.8.
In accordance with the embodiment of the present disclosure, a coefficient of friction of coating to the coating of the waterborne heat seal coating composition is in the range of 0.1 to 0.3. In an exemplary embodiment of the present disclosure, the coefficient of friction of coating to the coating of the waterborne heat seal coating composition is 0.21.
In accordance with the embodiment of the present disclosure, a coefficient of friction of coating to the metal of the waterborne heat seal coating composition is in the range of 0.2 to 0.3. In an exemplary embodiment of the present disclosure, the coefficient of friction of coating to the metal of the waterborne heat seal coating composition is 0.24.
In accordance with the embodiment of the present disclosure, the total surface energy of the waterborne heat seal coating composition is less than 40 to 55 dyne/cm. In an exemplary embodiment of the present disclosure, the total surface energy of the waterborne heat seal coating composition is 50 dyne/cm.
In accordance with the embodiment of the present disclosure, the heat seal initiation temperature of the waterborne heat seal coating composition is in the range of 70oC to 80oC. In an exemplary embodiment of the present disclosure, the heat seal initiation temperature of the waterborne heat seal coating composition is 65oC.
In accordance with the embodiment of the present disclosure, the heat seal strength at 140 oC at 30 PSI with a dwell time of 1 Sec of the waterborne heat seal coating composition is 950 g/25 mm on a coated substrate.
In accordance with the embodiment of the present disclosure, the hot tack properties of the waterborne heat seal coating composition on foil substrate are in the range of 450 to 600 g/25 mm.
In accordance with the embodiment of the present disclosure, the waterborne heat seal coating composition is a milky white colour in appearance.
In accordance with the embodiment of the present disclosure, the waterborne heat seal coating composition is used for coating paper, foil, and kraft paper.
In accordance with the embodiment of the present disclosure, the waterborne heat seal coating composition is used as inline coating/offline coating on metallized/laminate structure substrate for a wide range of applications for surface coating.
In accordance with the embodiment of the present disclosure, the waterborne heat seal coating composition has applications in the surface aesthetic coating, heat sealable coating, water, oil and grease resistant coating.
In accordance with the embodiment of the present disclosure, the waterborne heat seal coating composition has various technical advantages that include a high heat seal strength at low seal temperature, excellent hot tack properties, solvent-free material to avoid solvent retention, water-friendly heat seal coating, high production speed and excellent adhesion on aluminium foil and paper substrates.
The present disclosure includes water as a solvent for water-based heat seal coating. This means that volatile organic compounds will not be emitted during the drying process. At the same time, the working environment is significantly improved, giving additional protection to work health.
In another aspect, the present disclosure provided a process for preparing the waterborne heat seal coating composition.
The process is described in detail:
In accordance with the embodiment of the present disclosure, the waterborne heat seal coating composition is prepared by mixing a predetermined amount of the polyurethane dispersion, a predetermined amount of styrene-acrylic copolymer-based resin solution, a predetermined amount of mixture of acrylic emulsion and wax-modified acrylic emulsion, a predetermined amount of a micronized wax dispersion of straight-chained hydrocarbon synthetic wax, a predetermined amount of a fluid medium, a predetermined amount of a defoamer and a predetermined amount of a preservative under stirring to obtain the waterborne heat seal coating composition.
In a step, the predetermined amount of the polyurethane dispersion is mixed with the predetermined amount of styrene-acrylic copolymer-based resin solution, the predetermined amount of the mixture of acrylic emulsion and wax-modified acrylic emulsion, the predetermined amount of a micronized wax dispersion of straight-chained hydrocarbon synthetic wax, the predetermined amount of fluid medium, the predetermined amount of the defoamer and the predetermined amount of a preservative to obtain the waterborne heat seal coating composition.
In accordance with the embodiment of the present disclosure, the amount of the polyurethane dispersion is in the range of 35 wt.% to 50 wt.% with respect to the total weight of the composition. In an exemplary embodiment of the present disclosure, the amount of the polyurethane dispersion is 39.00 wt. % with respect to the total weight of the composition.
In accordance with the embodiment of the present disclosure, the amount of the styrene-acrylic copolymer-based resin solution is in the range of 25 wt.% to 35 wt.% with respect to the total weight of the composition. In accordance with the embodiment of the present disclosure, the styrene-acrylic copolymer-based resin solution is present in an amount in the range of 26 wt.% to 34 wt.% with respect to the total weight of the composition, preferably, in an amount in the range of 28 wt.% to 33 wt.% with respect to the total weight of the composition. In an exemplary embodiment of the present disclosure, the amount of the styrene-acrylic copolymer-based resin solution is 31.5 wt. % with respect to the total weight of the composition.
In accordance with the embodiment of the present disclosure, the amount of resin present in styrene-acrylic copolymer-based resin solution ranging from 30 wt.% to 40 wt.% with respect to the total weight of the resin solution.
In accordance with the embodiment of the present disclosure, the amount of the mixture of acrylic emulsion and wax-modified acrylic emulsion is in the range of 3.0 wt.% to 20 wt.% with respect to the total weight of the composition. In an exemplary embodiment of the present disclosure, the amount of the acrylic emulsion is 4.5 wt.% with respect to the total weight of the composition and the amount of the paraffin wax modified acrylic emulsion is 8.6 wt.% with respect to the total weight of the composition. In an exemplary embodiment of the present disclosure, the amount of the mixture of acrylic emulsion and wax-modified acrylic emulsion is 13.1 wt.% with respect to the total weight of the composition.
In accordance with the embodiment of the present disclosure, the amount of the micronized wax dispersion of straight-chained hydrocarbon synthetic wax is in the range of 1 wt.% to 3 wt.% with respect to the total weight of the composition. In an exemplary embodiment of the present disclosure, the amount of the micronized wax dispersion of straight-chained hydrocarbon synthetic wax is 1.6 wt.% with respect to the total weight of the composition.
In accordance with the embodiment of the present disclosure, the fluid medium is at least one selected from isopropyl alcohol and de-mineralised water. In an exemplary embodiment of the present disclosure, the fluid medium is a combination of isopropyl alcohol and de-mineralised water. In accordance with the embodiment of the present disclosure, the amount of the fluid medium is in the range of 5 wt.% to 25 wt.% with respect to the total weight of the composition. In an exemplary embodiment of the present disclosure, the amount of the fluid medium is 14.67 wt.% with respect to the total weight of the composition.
In accordance with the embodiment of the present disclosure, the defoamer is polyether siloxane. In accordance with the embodiment of the present disclosure, the amount of the defoamer is in the range of 0.01 wt.% to 0.1 wt.% with respect to the total weight of the composition. In an exemplary embodiment of the present disclosure, the amount of the defoamer is 0.03 wt.% with respect to the total weight of the composition.
In accordance with the embodiment of the present disclosure, the preservative is Isothiazolinone. In accordance with the embodiment of the present disclosure, the amount of the preservative is in the range of 0.05 wt.% to 0.15 wt.% with respect to the total weight of the composition. In an exemplary embodiment of the present disclosure, the amount of the preservative is 0.1 wt.% with respect to the total weight of the composition.
In accordance with the embodiment of the present disclosure, the polyurethane dispersion is prepared. The process comprises the following steps:
In a first step, a predetermined amount of a catalyst, and a predetermined amount of a dimethylol propionic acid is reacted with a predetermined amount of a diisocyanate at a first predetermined temperature under stirring to obtain a reaction mixture.
In accordance with the embodiment of the present disclosure, the catalyst is at least one selected from the group consisting of dibutyl tin dilaurate and Dibutyl (dodecanoyloxy) stannyl] dodecanoate. In an exemplary embodiment of the present disclosure, the catalyst is dibutyl tin dilaurate. In accordance with the embodiment of the present disclosure, the diisocyanate is at least one selected from the group consisting of hexamethylene diisocyanate, butane diisocyanate, Isophorone diisocyanate, 1-methyl-2,4- diisocyanatocyclo-hexane, 1-methyl-2,6-diisocyanatocyclo-hexane, norbornane diisocyanate, xylene diisocyanate, tetramethyl xylene diisocyanate, and hexahydro xylene diisocyanate. In an exemplary embodiment of the present disclosure, the diisocyanate is Isophorone diisocyanate.
In accordance with the embodiment of the present disclosure, the first predetermined temperature is in the range of 65 to 85oC. In an exemplary embodiment of the present disclosure, the first predetermined temperature is 70 oC.
In a second step, a predetermined amount of a polyester polyol is added under a nitrogen atmosphere into the reaction mixture at a second predetermined temperature for a predetermined time period to obtain a prepolymer.
In accordance with the embodiment of the present disclosure, the polyester polyol is at least one selected from the group consisting of adipic acid, succinic acid, phthalic acid anhydride, isophthalic acid, terephthalic acid, suberic acid, azelaic acid, sebacic acid, tetrahydrophthalic acid, maleic anhydride, ethylene glycol, propylene glycol, 1,3-propanediol, diethylene glycol, triethylene glycol, 1,4-butanediol, 1,6-hexanediol, trimethylpentanediol, 1,4-cyclo-hexanediol, 1,4-cyclohexane-dimethanol, neopentylglycol and 1,8-octanediol. In an exemplary embodiment of the present disclosure, the polyester polyol is a combination of neopentyl glycol, 1, 4-butanediol, and1, 6-hexanediol.
In accordance with the embodiment of the present disclosure, the second predetermined temperature is in the range of 55 to 75°C. In an exemplary embodiment of the present disclosure, the second predetermined temperature is 65 oC.
In accordance with the embodiment of the present disclosure, the predetermined time period is in the range of 0.5 hour to 4 hours. In an exemplary embodiment of the present disclosure, the predetermined time period is 3 hours.
In accordance with the embodiment of the present disclosure, the polyester polyols (a mixture of neopentyl glycol, 1, 4-butanediol, and 1, 6-hexanediol) are preliminarily mixed and placed in an oven at 80oC for 1 hr. Both the (isocyanate/hydroxide) [NCO]/[OH] molar ratio (r¼ 1.8) and the amount of DMPA (Dimethylol propionic acid) (4.55% w/w, based on the prepolymer) is kept constant and only the nature of the polyester polyol and its relative proportion with respect to diisocyanate is varied.

In a third step, a predetermined amount of an aqueous primary amine solution is added into the prepolymer mixture at a third predetermined temperature for a first predetermined speed followed by adding slowly demineralised water at a second predetermined speed and a predetermined amount of a chain extender to obtain the polyurethane dispersion.
In accordance with the embodiment of the present disclosure, a 20% molar excess of primary amine solution is added to ensure neutralization of the carboxylic group of DMPA.
In accordance with the embodiment of the present disclosure, the ethylenediamine is slowly added and thereafter the mixture is stirred for 90 min. The amount of EDA (ethylenediamine) added is calculated in order based on excess NCO equivalence to obtain a 1:1 [NCO] / [NH2] stoichiometry, 1:0.5 [NCO] / [NH2] stoichiometry, more preferably 1:0.5 [NCO] / [NH2] stoichiometry.
In accordance with the embodiment of the present disclosure, the third predetermined temperature is in the range of 15 to 35oC. In an exemplary embodiment of the present disclosure, the third predetermined temperature is 25 oC.
In accordance with the embodiment of the present disclosure, the first predetermined speed is in the range of 300 rpm to 400 rpm. In an exemplary embodiment of the present disclosure, the first predetermined speed is 350 rpm.
In accordance with the embodiment of the present disclosure, the second predetermined speed is in the range of 2000 rpm to 3000 rpm. In an exemplary embodiment of the present disclosure, the second predetermined speed is 2200 rpm.
In accordance with the embodiment of the present disclosure, the different components are used to prepare the polyurethane dispersion.
In accordance with the embodiment of the present disclosure, the component (A) used to prepare the polyurethane dispersion includes at least di-functional polyesters, polyethers, polyether polyamines, poly carbonates and polyester amides having a number average molecular weight of 500 to 6000. Examples include polyesters prepared from dicarboxylic acids or their anhydrides, e.g. adipic acid, succinic acid, phthalic acid anhydride, isophthalic acid, terephthalic acid, suberic acid, azelaic acid, Sebacic acid, tetrahydro phthalic acid, maleic anhydride, dimeric fatty acids and diols, e.g., ethylene glycol, propylene glycol, 1,3-propanediol, diethylene glycol, triethylene glycol, 1,4-butanediol, 1,6 hexanediol, trimethyl pentanediol, 1,4-cyclo-hexanediol, 1,4-cyclohexane-dimethanol, neopentyl glycol and 1,8-octanediol. The polyesters are also prepared from mono-, tri- or tetra functional raw materials, such as 2-ethyl hexanoic acid, benzoic acid, soya bean oil fatty acid, oleic acid, stearic fatty acid, sunflower oil fatty acid, trimellitic anhydride, trimethylol propane, glycerine and pentaerythritol.
In accordance with the embodiment of the present disclosure, the component (B) used to prepare the polyurethane dispersion to include low molecular weight compounds having a number average molecular weight of less than 500, preferably 1000 to 2000, that includes ethylene glycol, 1, 4-butanediol, 1, 6-hexanediol, neopentyl glycol, trimethylol propane, glycerine, pentaerythritol, trimethyl-pentanediol, propylene glycol, 1,3-propanediol, 1,4-cyclohexadimethanol, or their reaction products with ethylene and/or propylene oxide.
In accordance with the embodiment of the present disclosure, the component (C) used to prepare the polyurethane dispersion include di- and/or trifunctional aliphatic isocyanates e.g. hexamethylene diisocyanate, butane diisocyanate, isophorone diisocyanate, 1-methyl-2,4- and/or 2,6-diisocyanatocyclo-hexane, norbornane diisocyanate, xylene diisocyanate, tetramethyl xylene diisocyanate, hexahydro xylene diisocyanate, nonane triisocyanate and 4,4' diisocyanato dicyclo hexylmethane. Also, the joint use of aromatic isocyanates such as 2,4-and/or 2,6-diisocyanatotoluene or 4,4'-diisocyanato-diphenylmethane, as well as higher molecular weight or oligomeric poly isocyanates having a number average molecular weight of 336 to 1500. Preferably 4, 4’-diisocyanatodicyclohexylmethane, isophorone diisocyanate, hexa-methylene diisocyanate and/or 1-methyl-2, 4- and/or 2, 6-diisocyanat0-cyclohexane are used. More preferred are isophorone diisocyanate and/or hexamethylene diisocyanate or mixtures of 4, 4'-diisocyanato-dicyclohexylmethane with isophorone diisocyanate or hexamethylene diisocyanate. Preferably 4, 4'-diisocyanatodicyclohexylmethane, isophorone diisocyanate, hexa-methylene diisocyanate and/or 1-methyl-2, 4- and/or 2, 6-diisocyanato-cyclohexane are used. Especially preferred are isophorone diisocyanate and/or hexamethylene diisocyanate or mixtures of 4, 4’-diisocyanato-dicyclohexylmethane with isophorone diisocyanate or hexamethylene diisocyanate.
In accordance with the embodiment of the present disclosure, in addition to components (A), (B), and (C) the polyurethane dispersions are also prepared from less than 4 wt.% of component (D). Component (D) is selected from nonionic-hydrophilic polyethers containing one or two iso-cyanate-reactive groups, preferably hydroxyl groups, and preferably having a number-average molecular weight of 350 to 2500.
The process for the waterborne heat seal coating composition in accordance with the present disclosure has various advantages such as simple and convenient operation conditions, low operation costs, and good efficiency hence the process is industrially feasible. As a result of using non-toxic, inexpensive and easily available reagents, the process of the present disclosure is cost-efficient, economic and environmental friendly.
The foregoing description of the embodiments has been provided for purposes of illustration and is not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
The present disclosure is further illustrated herein below with the help of the following experiments. The experiments used herein are intended merely to facilitate an understanding of the ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the experiments should not be construed as limiting the scope of embodiments herein. These laboratory-scale experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial/commercial scale.
EXPERIMENTAL DETAILS
Process for the preparation of the waterborne heat seal coating composition in accordance with the present disclosure:
EXAMPLE: 1
Step A
Preparation of the polyurethane dispersions (PUDs) in accordance with the present disclosure:
0.090 g of dibutyl tin dilaurate and 16.29 g of Dimethylol Propionic acid were reacted with 67.86 g of diisocyanate at 70 oC under stirring to obtain a reaction mixture. 179.10 g of polyester polyols was incorporated under a nitrogen atmosphere into the reaction mixture at 65oC for 3 hours to obtain a prepolymer. 12.24 g of an aqueous primary amine solution was added into the prepolymer at 25oC at 350 rpm followed by adding slowly prepolymer into 413.46 g of DM water at 2200 rpm. Further, ethylene diamine was added at the same rpm to extend the chain length to obtain the polyurethane dispersion. The ketonic solvents are preferable solvents used to prepare prepolymer in mentioned prepolymer process. The solvent is removed via vacuum distillation. The polyurethane dispersion obtained in step (A) is characterized by having:
• the softening point of 60°C;
• the glass transition temperature (Tg) less than 10 °C; and
• the heat-seal initiation temperature of 65°C.
Step B
39.00 g of polyurethane dispersion (PUD), 31.50 g of styrene-acrylic copolymer-based resin solution, 4.50 g of acrylic emulsion, 1.60 g polyolefin wax (micronized wax dispersion of straight chained hydrocarbon) having a melting temperature of 60 °C and a particle size of 5 µm, 14.67 g of mixture of isopropyl alcohol and demineralised water (fluid medium), 8.60 g of paraffin wax modified acrylic emulsion, 0.03 g of polyether siloxane (defoamer solution) and a 0.1 g of Isothiazolinone (preservative) were mixed under stirring to obtain the waterborne heat seal coating composition. The characteristics of the waterborne heat seal coating composition are provided in Table 1;
Table 1: Characteristics of the waterborne heat-seal coating composition
Sr. No. Parameter Unit less Method Example 1
(waterborne heat seal coating composition)
1. Appearance Unit less Visual Milky White
2. Solid content % ASTM D-4713 32.68
3. pH Unit less 7.8
4. Viscosity at 30°C Seconds Ford Cup; B-4 16.68
5. Coating Wt. (dry GSM) g/m2 ASTM D-4321 2.5
6. Seal Initiation Temp. (S.I.T.) at Pressure = 30 PSI, Dwell time = 1 Sec. °C ASTM F-88 65

Inference:
The coating solution was applied to 70 to 80 GSM paper foil laminate structure on foil side to obtain a HSL coated paper foil laminate. The HSL coated paper foil laminate was dried by hair dryer first then after in oven to at 50°C for 1 minute. The dry coating weight was measured as 2.5 to 3.5 dry GSM after application of ready to use HSL coating solution.
The application properties of the HSL coated paper foil laminate structure is summarized in Table 2 shown below:
Table 2- Properties of the coated paper foil laminate structure
Tape test (Instant) Unit less Visual Pass
1. Heat-seal Strength at Temp. 140°C, Pressure = 30 PSI, Dwell time = 1 Sec. gf/25mm ASTM F-88 950 g/25 mm
2. CoF - Kinetic (Coating to Coating) Unit less ASTM D-1894 0.217
3. CoF - Kinetic (Coating to Metal) Unit less ASTM D-1894
0.241
4. Blocking Test at Pressure = 750 PSI, Temp. = 40°C, Time = 16 hrs)
(paper to foil laminate) Unit less With paper foil laminate structure Absent
5. Surface energy Dyne/cm ___ 50 Dyne/cm

TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a waterborne heat seal coating composition, which:
• is used for coating paper, foil, and Kraft paper;
• is used as inline surface coating/offline surface coating on metallized laminate structure substrate for a wide range of applications;
• is used in the surface aesthetic coating, heat sealable coating, water, oil and grease resistant coating;
• has a high heat seal strength at low seal temperature;
• have excellent hot tack properties; and
• has high production speed and excellent adhesion on aluminium foil and paper substrates.
A process for preparing the waterborne heat seal coating composition, which:
• is simple and convenient in operation;
• has a low operation costs, and good efficiency hence the process is industrially feasible;
• utilizes non-toxic, inexpensive and easily available reagents, hence economic; and
• no volatile organic compounds are emitted during the drying process, hence, environmental friendly.
The embodiments herein, the various features, and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein. The foregoing description of the specific embodiments so fully reveals the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein. The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure, as it existed anywhere before the priority date of this application. The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary. While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment, as well as other embodiments of the disclosure, will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.
,CLAIMS:WE CLAIM:
1. A waterborne heat seal coating composition comprising:
a) a polyurethane dispersion in an amount in the range of 35 wt.% to 50 wt.% with respect to the total weight of the composition;
b) a wax in an amount in the range of 1 wt.% to 3 wt.% with respect to the total weight of the composition;
c) a styrene-acrylic copolymer-based resin solution in an amount in the range of 25 wt.% to 35 wt.% with respect to the total weight of the composition;
d) a mixture of acrylic emulsion and wax-modified acrylic emulsion in an amount in the range of 3.0 wt.% to 20 wt.% with respect to the total weight of the composition;
e) a defoamer in an amount in the range of 0.01 wt.% to 0.1 wt.% with respect to the total weight of the composition;
f) a preservative in an amount in the range of 0.05 wt.% to 0.15 wt.% with respect to the total weight of the composition; and
g) a fluid medium in an amount in the range of 5 wt.% to 25 wt.% with respect to the total weight of the composition.
2. The waterborne heat seal coating composition as claimed in claim 1, wherein said wax is at least one selected from the group consisting of polyolefin wax, paraffin wax, microcrystalline wax, high density low molecular weight polyethylene wax and polypropylene wax, wherein said defoamer is polyether siloxane, said preservative is Isothiazolinone and said fluid medium is at least one selected from isopropyl alcohol and de-mineralized water.
3. The waterborne heat seal coating composition as claimed in claim 2, wherein said wax is polyolefin wax and said fluid medium is a mixture of isopropyl alcohol and de-mineralized water.
4. The waterborne heat seal coating composition as claimed in claim 1, wherein said polyurethane dispersion is present in an amount in the range of 36 wt.% to 45 wt.% with respect to the total weight of the composition, preferably, in the range of 38 wt.% to 42 wt.% with respect to the total weight of the composition, wherein said wax is present in an amount in the range of 1.5 wt.% to 2.5 wt.% with respect to the total weight of the composition, wherein said styrene-acrylic copolymer-based resin solution is present in an amount in the range of 26 wt.% to 34 wt.% with respect to the total weight of the composition, preferably, in the range of 28 wt.% to 33 wt.% with respect to the total weight of the composition, and wherein said fluid medium is present in an amount in the range of 10 wt.% to 20 wt.% with respect to the total weight of the composition, preferably, in the range of 12 wt.% to 18 wt.% with respect to the total weight of the composition.
5. The waterborne heat seal coating composition as claimed in claim 1, wherein said polyurethane dispersion has a softening point in the range of 50 °C to 100 °C, wherein said polyurethane dispersion has a glass transition temperature (Tg) in the range of -20°C to 50°C, wherein said polyurethane dispersion has a glass transition temperature (Tg) in the range of 0°C to 30°C, and wherein said polyurethane dispersion has a glass transition temperature (Tg) of less than 10°C.
6. The waterborne heat seal coating composition as claimed in claim 1, wherein said polyurethane dispersion has a heat seal initiation temperature of less than 150°C, preferably less than 110°C and more preferably less than 70°C.
7. The waterborne heat seal coating composition as claimed in claim 1, wherein said wax has a melting temperature (Tm) in the range of 50 to 150 °C.
8. The waterborne heat seal coating composition as claimed in claim 1 wherein, said solid content is in the range of 25 to 45 wt.% with respect to the total weight of the composition, preferably, in the range of 30 to 40 wt.% with respect to the total weight of the composition.

9. A process for preparing the waterborne heat seal coating composition, the process comprising a step of mixing a predetermined amount of a polyurethane dispersion with a predetermined amount of a styrene-acrylic copolymer-based resin solution, a predetermined amount of a mixture of acrylic emulsion and wax-modified acrylic emulsion, a predetermined amount of a micronized wax dispersion of straight chained hydrocarbon synthetic wax, a predetermined amount of fluid medium, a predetermined amount of a defoamer and a predetermined amount of a preservative under stirring to obtain the waterborne heat seal coating composition.
10. The process as claimed in claim 9, wherein a said:

• predetermined amount of said polyurethane dispersion is in the range of 35 wt.% to 50 wt.%;
• predetermined amount of said styrene-acrylic copolymer-based resin solution is in the range of 25 wt.% to 35 wt.%;
• predetermined amount of said mixture of acrylic emulsion and wax-modified acrylic emulsion is in the range of 3 wt% to 20 wt%;
• predetermined amount of said micronized wax dispersion of straight chain hydrocarbon synthetic wax is in the range of 1 wt% to 3 wt%;
• predetermined amount of said fluid medium is in the range of 5 wt.% to 25 wt.%;
• predetermined amount of said defoamer is in the range of 0.01 wt.% to 0.1 wt.%; and
• predetermined amount of said preservative is in the range of 0.05 wt.% to 0.15 wt.%,
wherein said wt% of each ingredient is with respect to the total wt% of said composition.
11. The process as claimed in claim 9, wherein said defoamer is polyether siloxane, wherein said fluid medium is at least one selected from the isopropyl alcohol and de-mineralized water and wherein said preservative is Isothiazolinone.
12. The process as claimed in claim 11, wherein said fluid medium is a mixture of isopropyl alcohol and de-mineralized water.
13. The process as claimed in claim 9, wherein said polyurethane dispersion is prepared by:

a) reacting a predetermined amount of a catalyst, a predetermined amount of a dimethylol propionic acid with a predetermined amount of diisocyanate at a first predetermined temperature under stirring to obtain a reaction mixture;
b) adding a predetermined amount of a polyester polyol under a nitrogen atmosphere into the reaction mixture at a second predetermined temperature for a predetermined time period to obtain a prepolymer; and
c) adding a predetermined amount of an aqueous primary amine solution into said prepolymer at a third predetermined temperature for a first predetermined speed followed by adding slowly demineralized water at a second predetermined speed followed by adding and a predetermined amount of a chain extender at the second predetermined speed to obtain the polyurethane dispersion.
14. The process as claimed in claim 13, wherein
• said catalyst is at least one selected from the group consisting of dibutyl tin dilaurate and Dibutyl (dodecanoyloxy)stannyl] dodecanoate, wherein said polyester polyol is at least one selected from the group consisting of adipic acid, succinic acid, phthalic acid anhydride, isophthalic acid, terephthalic acid, suberic acid, azelaic acid, sebacic acid, tetrahydrophthalic acid, maleic anhydride, ethylene glycol, propylene glycol, 1,3-propanediol, diethylene glycol, triethylene glycol, 1,4-butanediol, 1,6-hexanediol, trimethylpentanediol, 1,4-cyclo-hexanediol, 1,4-cyclohexane-dimethanol, neopentylglycol and 1,8-octanediol, wherein said diisocyanate is at least one selected from the group consisting of hexamethylene diisocyanate, butane diisocyanate, Isophorone diisocyanate, 1-methyl-2,4- diisocyanatocyclo-hexane, 1-methyl-2,6-diisocyanatocyclo-hexane, norbornane diisocyanate, xylene diisocyanate, tetramethyl xylene diisocyanate, and hexahydro xylene diisocyanate, and wherein said chain extender is at least one selected from the group consisting of ethylene diamine, diaminocyclohexane, diethylenetriamine, isophorone diamine, and aliphatic diol.
15. The process as claimed in claim 13, wherein
• said first predetermined temperature is in the range of 65 to 85°C, wherein said second predetermined temperature is in the range of 55 to 75°C wherein said third predetermined temperature is in the range of 15 to 35°C, wherein said predetermined time period is in the range of 0.5 hour to 4 hours and wherein said first predetermined speed is in the range of 300 to 400 rpm and said second predetermined speed is in the range of 2000 rpm to 3000 rpm.

Dated this 29th day of May, 2023

_______________________________
MOHAN RAJKUMAR DEWAN, IN/PA – 25
of R.K.DEWAN & CO.
Authorized Agent of Applicant

TO,
THE CONTROLLER OF PATENTS
THE PATENT OFFICE, AT NEW DELHI