WO2011017388A2

WO2011017388A2 - Emulsion copolymers for heat seal adhesive

Info

Publication number: WO2011017388A2
Application number: PCT/US2010/044333
Authority: WO
Inventors: Shui-Jen Raymond Hsu; Leander H. Bauer; Stephan A. Horvath
Original assignee: Lubrizol Advanced Materials, Inc.
Priority date: 2009-08-07
Filing date: 2010-08-04
Publication date: 2011-02-10
Also published as: WO2011017388A3

Abstract

This invention relates to a heat sealable adhesive composition for plastic and metal containers for moderate to high moisture food products. The adhesive comprises latex in water with a minimum film formation temperature near or below 25°C, blocking resistance up to 5O°C, heat seal-ability under reasonable conditions, good adhesive properties, and approval for food contact.

Description

EMULSION COPOLYMERS FOR HEAT SEAL ADHESIVE

Field of Invention

[0001] This application relates to waterborne copolymer dispersions having utility as heat seal coatings having good moisture resistance for food packaging and related uses. The copolymer dispersions are the result of a multi-stage (e.g., two- stage) polymerization that produces one rubbery copolymer with a low glass transition temperature and a second hard copolymer with a higher glass transition temperature.

Background of the Invention

[0002] Heat seal adhesives for high moisture food and condiments have traditionally been partially crystalline polymers applied from solvent based solutions to the lidding material. The lidding material with applied adhesive is stored until needed to package food or condiments. It is desirable that the adhesive applied to the lidding not adhere to any other portion of the lidding (adjacent lidding, etc.) while stored in warehouses awaiting use (this is referred to as having blocking). The food or condiments are added to a plastic container on a filling line, the lidding material is cut to shape and positioned over the container, the lidding and container are brought together in the presence of a heated platen (typically applied to the outside surface of the lidding) that melts and activates the adhesive (between the lidding and the container) to secure the lidding to the container and seal the package. The adhesive needs to have low moisture sensitivity so it does not swell, whiten or otherwise produce a weakened bond between the container and lidding during storage of the food or condiment. The adhesive has to be approved for food and condiment contact as the food or condiment can come into direct contact during shipping, sale, and post sale with the adhesive. When a consumer opens a heat sealed package of food or condiment, they generally prefer that the lidding with the adhesive attached thereto cleanly delaminate from the container and contained food or condiment.

[0003] U.S. 7,189,461 discloses aqueous based ethylene-vinyl acetate polymers emulsions containing crystalline segments resulting from ethylene linkages are useful in heat seal applications. Generally, solvent based partially crystalline polymers provide a distinct melting/softening temperature that can be selected to be a few degrees above the storage temperature of the adhesive prior to use and a few degrees below the heat seal temperature.

[0004] U.S. 6,368,707 discloses a polymer for a heat-sensitive adhesive sheet comprising a substrate having formed thereon an adhesive layer comprising a polymer "A" having a glass transition temperature of -1O⁰C or below obtained by emulsion-polymerizing alkyl(meth)acrylates and copolymer "B" having a glass transition temperature of 2O⁰C or more and being a water-soluble or water- dispersible copolymer from unsaturated carboxylic acid with other radically polymerizable monomers, wherein part of the entire amount of carboxyl groups in the copolymer are neutralized with a base having a boiling point of HO⁰C or below.

[0005] U.S. 6,258,887 discloses a multi-stage emulsion-polymer suitable for use in dirt pickup resistant coatings.

[0006] U.S. 5,385,967 discloses aqueous dispersions for heat-seal applications with a copolymer A having a glass transition of 50-150⁰C and copolymer B with a glass transition of -50 to 5O⁰C and at least one of the two copolymers containing from 3 to 70% by wt. of an ethylenically unsaturated C3-C5 mono- or dicarboxylic acid or the anhydride thereof. The examples of the patent generally showed the high glass transition temperature polymer with high amounts of ethylenically unsaturated C3-C5 mono- or dicarboxylic acid or the anhydride thereof. Such high glass transition temperature polymers with high amounts of carboxylic resins are generally known as support resins and while providing good colloidal stability tend to impart unacceptable moisture sensitivity in applications where exposure to moisture occurs.

[0007] U.S. 5,306,743 discloses an aqueous synthetic resin dispersion comprising latex particles having an average diameter below 145 or 100 nm consisting of a core material with a glass transition temperature above 6O⁰C and a shell material with a glass transition temperature below 8O⁰C, provided that the glass transition temperature of the shell is at least 20 K below that of the core (indicating a softer shell and harder core).

[0008] Heat seal adhesive is a broad category of materials. Some heat seal adhesives are applied as a hot fluid adhesive to one or more substrates to form an adhesive bond between two or more substrates. This adhesive type does not need blocking resistance as the adhesive typically is heated immediately before application to two or more substrates and is not stored in contact with several substrates where it may prematurely cause an adhesive bond. A subset of adhesives for seals is those products where an adhesive is applied to one substrate (typically cardboard, paper, or plastic packaging) and the adhesive and substrate is further processed or stored and later during final assembly a substrate near the adhesive is heated above an activation temperature at which temperature the heat seal adhesive then forms a bond between the original substrate and one or more additional substrates. In many cardboard, paper and plastic adhesive uses, the adhesive can have moisture sensitive components without having adhesion adversely affected (because they are used in relatively dry environments where the moisture effect on the adhesive is minimal).

Summary of the Invention

[0009] This invention discloses a copolymer film for a heat seal adhesive desirably having an estimated interfacial activation temperature between 100 and 200⁰C for forming an adhesive bond, said film comprising a principal copolymer being derived from drying an emulsion copolymer in latex form in water

characterized as having a) from 50 to 75 parts by weight of a soft acrylate copolymer having a Tg from about 0 to about -6O⁰C having from 0.2 to about 10 wt.% repeating units from a C3-C10 ethylenically unsaturated mono or dicarboxylic acid or its anhydride and from about 0.15 to about 3 wt.% based on weight of soft acrylate copolymer of repeating units from an active crosslinking monomer comprising two or more ethylenically unsaturated groups per molecule and b) from about 25 to about 50 parts by weight of a hard acrylate copolymer having a calculated Tg from about 50 to about 12O⁰C optionally including up to 10 wt.% repeating units from an ethylenically unsaturated C3-C10 mono or dicarboxylic acid or anhydride thereof and wherein said parts by weight are per 100 total parts by weight of said first acrylate copolymer and said second acrylate copolymer. In one embodiment for food contact, desirably the total combined amount of repeating units from styrene in said first and second acrylate copolymers is less than 50 parts by weight based upon 100 parts by weight of total copolymers. -A-

Detailed Description of the Invention

[0010] The two principal copolymers in the heat seal adhesive are a soft and a hard acrylate copolymer. The term acrylate copolymer is used understanding that the copolymer can have repeating units from various alkyl acrylates, alkyl methacrylates, and acrylic acid. The acrylic copolymers can include other ethylenically unsaturated monomers such as C3-C10 mono or dicarboxylic acids, allyl methacrylate, vinyl aromatic, vinyl ester, nitrile, vinyl halide, etc. Thus, in this specification, acrylic copolymer is a term used to describe a copolymer with at least 10 or 20 wt. % (more desirably at least 30 or 40 wt. %) repeating units derived from an acrylic or acrylate monomer.

[0011] In many cases, it is advantageous to utilize both an alkyl acrylate monomer and/or an alkyl methacrylate monomer is making the copolymers of this invention. These monomers can include alkyl acrylates, alkyl methacrylates, and alkyl ethacrylates. The alkyl group many contain from 1 to 15 carbon atoms and more desirably from 1 to 10 carbon atoms. Desirable acrylates include n-butyl acrylate, n-butyl methacrylate, ethylhexyl acrylate, ethyl acrylate, ethyl

methacrylate, methyl acrylate, and methyl methacrylate. In one embodiment where food contact is anticipated, it is desirable that at least 40, 45, 50, or 55 wt. % of the polymer from the multi-step polymerization comprises the various alkyl (meth or eth) acrylates. The use of (meth) or (eth) or (meth or eth) indicates (through out this specification) that the item in parentheses is optionally present.

[0012] Desirably the composition of the soft acrylate copolymer is adjusted so that the Tg (glass transition temperature) is from about -60 to about O⁰C, more desirably from about -50 to about -1O⁰C, and preferably from about -45 to about -30 or -15⁰C. Desirably the composition of the hard acrylate copolymer is adjusted so that the Tg is from about 50 to about 12O⁰C, more desirably from about 55 to about HO⁰C, and preferably from about 60 to about 100⁰C.

[0013] In preparing samples for heat sealing, it was determined that it is preferable that the soft acrylate copolymer be prepared in the first stage of the polymerization and the hard acrylate copolymer be prepared in the second stage of the polymerization, i.e., in the presence of the soft acrylate copolymer. Additional copolymers may be made during the multi-stage polymerization. If they have the appropriate Tg value, the amount of such copolymers can be included in the soft or hard copolymer. If their Tg value falls outside the appropriate Tg range, they will be considered to be neither the soft or hard copolymer.

[0014] Examples of ethylenically unsaturated monomers that can be used in the process of the invention include mono vinyl aromatic monomers, alpha-beta ethylenically-unsaturated carboxylic acid ester monomers, unsaturated monomers with carboxylic acid groups, vinyl ester monomers, and various combinations of these. The acrylate monomers are preferably selected from the group consisting of esters of acrylic and methacrylic acid (e.g., those with 4 to 30 carbon atoms) such as n-butyl (meth)acrylate, methyl(meth)acrylate, ethyl(meth)acrylate, 2-ethylhexyl- (meth)acrylate, cycloalkyl(meth)acrylates, such as isobornyl(meth)acrylate and cyclohexyl(meth)acrylate. Choices among the acrylate monomers are typically made to achieve the preferred glass transition temperatures (Tg) for the soft and hard copolymers. Methyl methacrylate is a known higher Tg acrylate. Acrylic and methacrylic acid have fairly high Tg values. The vinyl aromatic based monomers include styrene, i.e., styrene or substituted styrenes, for instance alpha-methyl styrene or t-butylstyrene; and vinyltoluene. The diene monomers include dienes such as 1,3-butadiene or isoprene, and mixtures thereof. The ethylenically unsaturated monomers can include vinyl esters with 4 to 25 carbon atoms, such as vinyl acetate, vinyl alkanoate or their derivatives or mixtures thereof can be used in the monomer composition. Nitriles, such as (meth)acrylonitrile, or olefmically unsaturated halides, such as vinyl chloride, vinylidene chloride, and vinyl fluoride can also be used. Preferred vinyl ester monomers include vinyl esters of versatic acids such as the monomers commercialized by Hexion Specialty Chemicals under the trade names VEOV A® 9, 10 and 11.

[0015] Unsaturated monomers with acid (e.g., carboxylic acid) functionality, which include monomers of which the acid groups are latent as, for example, in maleic anhydride, are suitably selected from, but not limited to: acrylic acid, methacrylic acid, oligomerized acrylic acids such as beta-carboxyethyl acrylate or its higher analogues (commercially available from Rhodia as Sipomer™ B-CEA), itaconic acid, fumaric acid, maleic acid, citraconic acid, or the anhydrides thereof. Other acid type monomers include styrene p-sulfonic acid, ethylmethacrylate-2- sulfonic acid and 2-acrylamido-2-methylpropane sulfonic acid. An acid bearing monomer could be polymerized as the free acid or as a salt, e.g., the NH₄ or alkali metal salts. Monomers with carboxylic acid functionality are preferred over other acid monomers, e.g., sulfonic acid.

[0016] Other monomers that may be present in amounts up to 5, 10, 15, or 20 weight percent based on the total monomers in the polymers of the multi-stage polymerization include acrylonitriles, vinyl chlorides, vinylidene chlorides, and amide functional monomers. Amide-functional comonomers include, but are not limited to, acrylamide and methacrylamide.

[0017] Another group of monomers which are useful in preparing the copolymers of the present invention are polar non-ionic monomers such as hydroxyalkyl (meth)acrylates, (meth)acrylamides and substituted (meth)acrylamides (e.g., N-methyl acrylamide), N-vinyl-2-pyrrolidone, N-vinyl caprolactam, 2- hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, (4-hydroxymethylcyclohexyl)-methyl (meth)acrylate, l-(2-((2- hydroxy-3-(2-propenyloxy)propyl)amino)ethyl)-2-imidazolidinone, N-methylol (meth)acrylamide, Sipomer® WAM, WAM II (from Rhodia) and other urido- containing monomers, dimethylaminoethyl (meth)acrylate, and

dimethylaminopropyl (meth)acrylamide. Mixtures of polar monomers also may be used. Those hydrophilic monomers should be used at appropriate levels, which do not impair the earlier water resistance.

[0018] Vinyl aromatic monomers can also be employed as the copolymerizable monomer. However, the total amount of vinyl aromatic monomers utilized in one embodiment for food contact for making the copolymer of this invention will typically not exceed about 50 weight percent and in another embodiment not to exceed 33 weight percent of the total weight of monomers employed in making the first and second copolymer (total polymers in multi-stage polymerization).

[0019] The polymerization techniques used to prepare such aqueous multi-stage emulsion-polymers are well known in the art such as, for example, as disclosed in U.S. Patent Nos. 4,325,856; 4,654,397; and 4,814,373. A multi-stage emulsion polymerization process usually results in the formation of at least two mutually incompatible polymer compositions, thereby resulting in the formation of at least two phases. The mutual incompatibility of two polymer compositions and the resultant multiphase structure of the polymer particles may be determined in various ways known in the art. The use of scanning electron microscopy using staining techniques to emphasize the difference between the phases. Such particles are composed of two or more phases of various geometries such as, for example, core/shell or core/sheath particles, core/shell particles with shell phases incompletely encapsulating the core, raspberry (three or more nodules per particle) morphology, core/shell particles with a multiplicity of cores, and interpenetrating network particles. It is believed that the morphology of the examples is raspberry rather than core shell.

[0020] Tg values used herein are those calculated by using the Fox equation; see T. G. Fox, Bull. Am. Physics Soc, Volume 1, Issue No. 3, page 123, (1956). The formula for calculating the Tg of a copolymer of monomers Ml and M2 is l/Tg(calc.)=w(Ml)/Tg(Ml)+w(M2)/Tg(M2), wherein Tg(calc) is the glass transition temperature calculated for the copolymer, w(Ml) is the weight fraction of monomer Ml in the copolymer, w(M2) is the weight fraction of monomer M2 in the copolymer, Tg(Ml) is the glass transition temperature of the homopolymer of Ml, and Tg(M2) is the glass transition temperature of the homopolymer of M2, with all temperatures being in ⁰K. Glass transition temperatures of homopolymers may be found, for example, in J. Brandrup and E. H. Immergut, ed., Polymer Handbook, Interscience Publishers.

[0021] It is desirable to include crosslinking monomers in at least the first soft acrylate copolymer. Crosslinking monomers are present in the structure of the soft acrylate copolymer in an amount from 0.1 or 0.15 to 3, preferably 0.3 or 0.5 to 2 percent by weight based on the weight of the soft acrylate copolymer. The crosslinking is chosen just high enough so that the extensibility of the copolymer film is only slightly decreased in comparison with that of a corresponding non- crosslinked soft acrylate copolymer, but the resistance to blocking is increased slightly due to the molecular weight increase. In a particular case, the degree of crosslinking is directed toward a particular use. For this purpose, a low content of crosslinking monomer is sufficient. It should be understood that to minimize blocking either crosslinking of the soft acrylate or raising the Tg of the hard acrylate copolymer can impart the desired result.

[0022] The crosslinking monomers have at least two ethylenically unsaturated, free radically polymerizable groups, suitable groups such as allyl, acryl, or methacryl groups, in the molecule. Compounds having at least three such groups, which may be the same or different, but preferably are the same, are preferred. Examples of crosslinking monomers are diol and polyolesters of acrylic acid and/or of methacrylic acid reacted with di- or poly-functional alcohols, such as ethylene glycol diacrylate and dimethacrylate, butylene glycol diacrylate and di methacrylate, dipropylene glycol dimethacrylate, propylene glycol dimethacrylate, pentaerythritol tri- or tetra- acrylate and methacrylate, trimethylolpropane triacrylate and trimethacrylate, and allyl acrylate and methacrylate, divinylbenzene and

trivinylbenzene, as well as triallyl cyanurate and triallyl isocyanurate. In many cases, graft crosslinking monomers which contain at least two ethylenically unsaturated, free radically polymerizable groups, among which is at least one allyl group, are particularly advantageous.

[0023] Conventional emulsifiers can be used to form the emulsion of monomers and to stabilize the growing latex particles. Typical anionic emulsifiers include alkali or ammonium alkyl sulfates, alkyl sulfonates, salts of fatty acids, esters of sulfosuccinic acid salts, alkyl diphenylether disulfonates, and the like, and mixtures thereof. Typical nonionic emulsifiers include polyethers, e.g., ethylene oxide and propylene oxide condensates, including straight and branched chain alkyl and alkylaryl polyethylene glycol and polypropylene glycol ethers and thioethers, alkyl phenoxypoly(ethyleneoxy) ethanols having alkyl groups containing from about 7 to about 18 carbon atoms and having from about 4 to about 100 ethyleneoxy units, and polyoxy-alkylene derivatives of hexitol, including sorbitans, sorbides, mannitans, and mannides; and the like, and mixtures thereof. Preferred surfactants include Dextrol™ OC-60, sodium lauryl sulfate, Dowfax™ 2Al, Aerosol™ OT, and dodecylbenzene sulfonate. Surfactants approved for food contact are listed in 21 CFR § 177.1010 Subpart B. Co-surfactants typically are employed in the

compositions of the present invention at levels of about 0 wt. % to about 3 wt. %. [0024] The emulsion polymerization employed in synthesizing the copolymer(s) of this invention is carried out in a conventional manner using well-known additives and ingredients, such as emulsifϊers, free radical polymerization initiators, and the like, and mixtures thereof. Either thermal or redox initiation processes may be used. The reaction temperature typically is maintained at a temperature lower than about 100⁰C throughout the course of the reaction. In one embodiment, a reaction temperature between about 25⁰C and 95⁰C is used.

[0025] For the purpose of adjusting pH at the outset of the polymerization pH control agents and buffers typically are added. The initial reactor pH will normally be within the range of about 3 to about 10. However, other pH values may be obtained in particular applications using pH control agents and buffers well known to those skilled in the art. Non-limiting examples of suitable pH control agents include but are not limited to ammonium and alkali metal hydroxides (such as sodium hydroxide and potassium hydroxide), and mixtures thereof, and the like. Non-limiting examples of suitable buffers include ammonium carbonate, sodium carbonate, sodium bicarbonate, and mixtures thereof, and the like. pH may be adjusted if desired at the end of the polymerization process according to the desired application.

[0026] In preparing the hard acrylate copolymer component, any chain-transfer agent, or mixtures thereof, may be used to control molecular weight. Suitable chain transfer agents include, for example, Ci to C12 alkyl or functional alkyl mercaptans, alkyl or functional alkyl mercaptoalkanoates, or halogenated hydrocarbons, and the like, and mixtures thereof. Chain transfer agents typically are employed at levels of about 0.1 weight percent to about 5 weight percent, based on total monomer weight of monomers used in the hard second acrylate copolymer.

[0027] The copolymers typically are prepared in the presence of water-soluble or organic solvent-soluble initiators (such as persulfates, peroxides, hydroperoxides, percarbonates, peracetates, perbenzoates, azo-functional compounds, and other free- radical generating species, and mixtures thereof, as is well known to those skilled in the art.

[0028] The latex formed by the multi-stage emulsion polymerization can optionally be diluted with additional water to any concentration (solids content) that is desired. Multi-stage polymerization is used to indicate that two or more stages can be present. The desirable feature from the multi-stage polymerization is that two or more different copolymer compositions are made such that a) a softer copolymer is present that provides wetting at the heat seal temperature and tack and b) a harder copolymer is present that helps prevent films the latex from adhering to adjacent materials during storage before use. This latex can then be used in the preparation of water based adhesive heat seal coatings employing techniques that are well-known to those skilled in the art.

[0029] Desired pigments, plasticizers, coalescing solvents, fillers, wetting agents, stabilizers, defoamers, dryers, antibacterial agents, fungicides, insecticides, antifouling agents, and anticorrosive agents can be mixed directly into the latex.

[0030] Pigments may be added to adhesive formulations to impart color.

Titanium dioxide is an example of a widely used pigment which imparts hiding and a white color. Mineral pigments (such as oxides of iron and chromium), organic pigments (such as phthalocyanine) and active anticorrosive pigments (such as zinc phosphate) are representative examples of other widely used pigments. Some representative examples of widely utilized fillers include chalks, clays, micas, barites, talcs, and silica.

[0031] A film forming, water based composition can be prepared utilizing a mixture of the copolymer with suitable additives, including but not limited to coalescing solvent and plasticizer. A wide variety of food contact approved plasticizers can be used in the practice of this invention.

[0032] The water based heat sealable adhesive composition, as an aqueous dispersion or solution, can then be applied as a coating onto a suitable substrate such as plastic, paper, foil, or combinations thereof. As has been explained, the water based heat sealable adhesive compositions of this invention are a particular value for application to lidding or other surfaces of high moisture food or condiment packaging. High moisture food and/or high moisture condiments are particularly taught as many of the heat sealable adhesives for conventional paper, plastic and cardboard packaging is useful for packaging low moisture items such as nuts, cereal, candy, sugar, flour, etc. [0033] The water based heat sealable adhesive is desirably applied to at least one surface of the packaging material (e.g. lidding) and allowed to dry to a film.

Desirable film thicknesses range from 2 to 50 g/m², more desirably from 3 to 30 g/m², and preferably from about 4 to 15 g/m² based on the dried weight of the adhesive per meter squared of surface.

[0034] It would be desirable to characterize the interfacial activation temperature that the adhesive experiences at the moment that the two surfaces are adhered together. We will call this the estimated interfacial activation temperature. It is believed to be between 100 and 200⁰C, more desirably between 120 and 175⁰C, and preferably between 135 and 15O⁰C. We know the platen temperature useful with the adhesives in the examples below was 163⁰C for 0.75 second of contact with an outer surface of the lidding material. Attempts to measure the adhesive temperature after contact with the heated platen resulted in the estimated temperatures.

[0035] This invention is illustrated by the following examples that are merely for the purpose of illustration and are not to be regarded as limiting the scope of the invention or the manner in which it can be practiced. Unless specifically indicated otherwise, parts and percentages are given by weight.

Abbreviations of the Chemicals Used in Examples:

DM water: de-mineralized water

DMC: dodecyl mercaptan

Dowfax™ 2Al : alkyldiphenyloxide disulfonate available from Dow

Amm. Carb.: Ammonium Carbonate

SLS: sodium lauryl sulphate

AA: Acrylic acid

MA: Methacrylic acid

MMA: Methyl methacrylate

A MA: Allyl Methacrylate

2-EHA: 2-ethylhexyl acrylate

APS: ammonium persulfate

n-BA: n-Butyl acrylate

BHP: tertiary butyl hydrogen peroxide

DDM: Dodecyl mercaptan ErA: Erythorbic acid

[0036] Example #1 (Comparative)

A monomer premix was made by mixing 230 grams of water, 16.67 grams of Dowfax 2Al, 3.33 grams of sodium lauryl sulfate, 1.0 grams of ammonium carbonate, 15 grams of methacrylic acid, 55 grams of methyl methacrylate, 250 grams of styrene, and 380 grams of 2-ethylhexyl acrylate. Initiator A was made by dissolving 2 grams of ammonium persulfate in 23 grams of water. Initiator B was made by dissolving 3 grams of ammonium persulfate in 100 grams of water. A 3- liter reaction vessel was charged as follows: 600 grams of water and 2.22 grams of Dowfax 2Al, and then was heated to 82⁰C under nitrogen. Initiator A was then added to the reaction vessel, followed by proportioning (metered in over a specified time) the monomer premix to the reaction vessel over a period of about 3 hours (a monomer premix feed rate of about 6.95 g/min). The reaction temperature was kept at 86 ⁰C during polymerization. At 30 minutes after premix proportioning started, initiator B was proportioned into the reaction vessel over a period of about 3 hours and 30 minutes. At 110 minutes after premix proportioning started, 300 grams of methyl methacrylate was added to the remaining monomer premix. After completion of initiator B feed, the temperature of the reaction vessel was maintained at 86⁰C for 60 minutes. The reaction vessel then was cooled to 57⁰C, and then 5.88 grams of 17% t-butyl hydroperoxide solution was added to the reaction vessel. After about 5 minutes, 35.3 grams of 3.68 % erythorbic acid solution was added to the reaction vessel. After 30 minutes, the addition of 40 wt.% more of t-butyl hydroperoxide solution and erythorbic acid solution was repeated based on the weight of the previous dose. After 30 minutes, the above the reaction vessel was cooled to room temperature and filtered through 100-micron cloth. Table 1 Recipe for Example 1

[0037] Example #2

The emulsion copolymer was made exactly same as Example #1, except monomer composition in the monomer premix was 15 grams of methacrylic acid, 55 grams of methyl methacrylate, 150 grams of styrene, and 480 grams of 2-ethylhexyl acrylate. At 110 minutes after premix proportioning started, 300 grams of styrene was added to the remaining monomer premix not methyl methacrylate as shown in Example #1.

[0038] Example #3 (Comparative)

The emulsion copolymer was made exactly same as Example #1, except monomer composition in the monomer premix was 15 grams of methacrylic acid, 150 grams of methyl methacrylate, 305 grams of styrene, and 180 grams of n-butyl acrylate. At 110 minutes after premix proportioning started, 350 grams of n-butyl acrylate was added to the remaining monomer premix not methyl methacrylate as shown in Example #1.

[0039] Example #4 (Comparative)

The emulsion copolymer was made exactly same as Example #1, except monomer composition in the monomer premix was 15 grams of methacrylic acid, 150 grams of styrene, and 430 grams of 2-ethylhexyl acrylate. At 90 minutes after premix proportioning started, 250 grams of styrene and 155 grams of methyl methacrylate were added to the remaining monomer premix not methyl methacrylate at 110 minutes as shown in Example #1.

Table 2, Comparison of Monomer Premixes for Examples 1-4

[0040] Example #5

A surfactant mixture was made by mixing 230 grams of water, 8.89 grams of Dowfax 2Al, 3.33 grams of sodium lauryl sulfate and 1.0 grams of ammonium carbonate. Then, it was split into two parts, surfactant Part A and B. Surfactant Part A was 173.22 grams, and surfactant Part B was 70 grams. Premix I was made by mixing surfactant Part A, 15 grams of methacrylic acid, 10 grams of allyl methacrylate, 75 grams of styrene, and 550 grams of 2-ethylhexyl acrylate. Premix II was made by mixing surfactant Part B, 5 grams of methacrylic acid, 255 grams of styrene, and 90 grams of 2-ethylhexyl acrylate. Initiator A was made by dissolving 2 grams of ammonium persulfate in 23 grams of water. Initiator B was made by dissolving 3 grams of ammonium persulfate in 100 grams of water. A 3 -liter reaction vessel was charged as follows: 620 grams of water and 1.33 grams of Dowfax 2Al, and then was heated to 82⁰C under nitrogen. Initiator A was then added to the reaction vessel, followed by proportioning the Premix I to the reaction vessel. The reaction temperature was kept at 86⁰C during polymerization. About 15 minutes after Premix I proportioning was finished, started the proportion of Premix II. Total proportion time for Premix I (66% of time) and Premix II (34% of time) was about 3 hours. At 30 minutes after Premix I proportioning started, initiator B was proportioned into the reaction vessel over a period of about 3 hours and 30 minutes. After completion of initiator B feed, the temperature of the reaction vessel was maintained at 86⁰C for 60 minutes. The reaction vessel then was cooled to 57⁰C, and then 5.88 grams of 17% t-butyl hydroperoxide solution was added to the reaction vessel. After about 5 minutes, 35.3 grams of 3.68% erythorbic acid solution was added to the reaction vessel. After 30 minutes, the addition of t-butyl hydroperoxide solution and erythorbic acid solution was repeated one more time at 40 wt.% levels based on the previous dose. After 30 minutes, the above the reaction vessel was cooled to room temperature and filtered through 100-micron cloth.

Table 3, Recipe for Example 5

[0041] Example #6 (Comparative)

The emulsion copolymer was made exactly same as Example #5, except that monomer composition in Premix I was 15 grams of methacrylic acid, 65 grams of styrene, and 470 grams of 2-ethylhexyl acrylate. Premix II was 5 grams of methacrylic acid, 330 grams of styrene, and 115 grams of 2-ethylhexyl acrylate.

[0042] Example #7 (Comparative)

The emulsion copolymer was made exactly same as Example #5, except that monomer composition in Premix I was 15 grams of methacrylic acid, 65 grams of styrene, and 470 grams of 2-ethylhexyl acrylate. Premix II was 5 grams of methacrylic acid, 330 grams of styrene, 115 grams of 2-ethylhexyl acrylate and 5 grams of n-dodecyl mercaptan.

[0043] Example #8

The emulsion copolymer was made exactly same as Example #5, except that monomer composition in Premix I was 15 grams of methacrylic acid, 10 grams of allyl methacrylate, 130 grams of styrene, and 495 grams of 2-ethylhexyl acrylate. Premix II was 5 grams of methacrylic acid, 255 grams of styrene, 90 grams of 2- ethylhexyl acrylate and 5 grams of n-dodecyl mercaptan.

Table 4, Recipes for Monomer Premix lor Examples 5-8

5 6 Comp. 7 Comp. 8

Monomer Premix 1

Methacrylic acid 15 15 15 15

Allyl Methacrylate 10 0 - 10

Styrene 75 65 65 130

2EHA 550 470 470 495

Monomer Premix 2

Methacrylic acid 5 5 5 5

Styrene 255 330 330 255

2-EHA 90 115 115 90

Dodecyl mercaptan - 5 5

[0044] Example #9

The emulsion copolymer was made exactly same as Example #5, except that monomer composition in Premix I was 15 grams of methacrylic acid, 10 grams of allyl methacrylate, 58 grams of styrene, and 467 grams of 2-ethylhexyl acrylate. Premix II was 5 grams of methacrylic acid, 330 grams of styrene, and 115 grams of 2-ethylhexyl acrylate.

[0045] Example #10

The emulsion copolymer was made exactly same as Example #5, except that monomer composition in Premix I was 15 grams of methacrylic acid, 10 grams of allyl methacrylate, 160 grams of styrene, and 465 grams of 2-ethylhexyl acrylate. [0046] Example #11

The emulsion copolymer was made exactly same as Example #5, except that monomer composition in Premix I was 25 grams of methacrylic acid, 10 grams of allyl methacrylate, 65 grams of styrene, and 550 grams of 2-ethylhexyl acrylate.

[0047] Example #12 (Comparative)

The emulsion copolymer was made exactly same as Example #5, except that Premix

II was proportioned first, then Premix I was proportioned after Premix II was done.

[0048] Example #13

The emulsion copolymer was made exactly same as Example #5, except that monomer composition in Premix I was 15 grams of methacrylic acid, 10 grams of allyl methacrylate, 38 grams of styrene, and 587 grams of 2-ethylhexyl acrylate.

Table 5, Recipes for Monomer Premix for Examples 9-13

[0049] Example #14

The emulsion copolymer was made exactly same as Example #5, except that monomer composition in Premix I was 15 grams of methacrylic acid, 10 grams of allyl methacrylate, 38 grams of styrene, and 587 grams of 2-ethylhexyl acrylate. Premix II was 5 grams of methacrylic acid, 275 grams of styrene, and 70 grams of 2- ethylhexyl acrylate. [0050] Example #15

The emulsion copolymer was made exactly same as Example #5, except that monomer composition in Premix I was 10 grams of methacrylic acid, 10 grams of allyl methacrylate, 80 grams of styrene, and 550 grams of 2-ethylhexyl acrylate. Premix II was 3 grams of methacrylic acid, 258 grams of styrene, and 90 grams of 2- ethylhexyl acrylate.

[0051] Example #16

The emulsion copolymer was made exactly same as Example #5, except that monomer composition in Premix I was 15 grams of acrylic acid, 10 grams of allyl methacrylate, 75 grams of styrene, and 550 grams of 2-ethylhexyl acrylate.

[0052] Example #17 (Comparative)

The emulsion copolymer was made exactly same as Example #5, except that

Premix I and Premix II were combined together first and then proportioned.

[0053] Example #18 (Comparative)

The emulsion copolymer was made exactly same as Example #5, except that monomer composition in Premix II was 5 grams of methacrylic acid, 238 grams of styrene, and 110 grams of 2-ethylhexyl acrylate.

[0054] Example #19

The emulsion copolymer was made exactly same as Example #5, except that monomer composition in Premix II was 5 grams of methacrylic acid, 174 grams of styrene, 81 grams of methyl methacrylate, and 90 grams of 2-ethylhexyl acrylate. Table 6, Recipes for Monomer Premix for Examples 14-19

[0055] The following tests were used to evaluate the heat seal adhesive. The water based copolymer dispersion was applied as a film with a dry coating weight of 4.5 to 5.5 g/m² and dried at 20-25⁰C (air temperature) on a foiled polyester film for 24 hours/days or in a forced air oven at 75⁰C for 5 minutes. For the blocking resistance testing, the specimen was mounted face to face or face to back and the specified pressure was applied for the specified time at the specified temperature. For the Heat Seal test, the specimen comprise the above heat seal adhesive dried onto a foiled polyester film in contact with sheets of high impact polystyrene (HIPS) that are meant to simulate the sealing surface of HIPS based containers.

Heat Seal

Sencorp Heat Sealer model 12AS/1 - heated upper bar

Conditions - 325F (163 C), 40 psi, 0.75 seconds

1 inch wide by 8 inches long specimens and comprised on film strip of adhesive coated aluminized polyester and one film strip of high impact polystyrene.

Seal Strength

ASTM F88 - unsupported sample specimen testing

MTS/Instron tensile tester/crosshead speed 12inches/min

Average of 4 test results

Report peel strength and if failure within adhesive was adhesive or cohesive

Koehler Blocking Test

Koehler Block Tester Model K530

Dried coated films tested

face-to-face - 2 specimens

face-to-back - 4 specimens 4 psi force on Koehler Spring

Report degree of blocking after 24 hrs at 120F and 140F, respectively

Blocking Results

No cling - falls apart very easily

Very slight cling - can hear a very slight ticking noise but can't feel any resistance.

Slight cling - can hear ticking and feel a slight resistance pulling them apart.

Cling - fairly tight pull usually will see slight transfer

Strong cling - Very tight hard to pull apart usually quite a bit of transfer

Blocked - Can't pull the sample apart usually without tearing the substrate.

Table 7, Adhesive Characteristics and Performance Examples 1-18

[0056] While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention.

Claims

WHAT IS CLAIMED IS:

1. A waterborne copolymer dispersion for heat sealable coatings comprising: a) from 50 to 75 parts by weight of a soft acrylate copolymer having a calculated Tg from -60 to O⁰C having 0.2 to about 10 wt.% repeating units from an ethylenically unsaturated C3-C10 mono or dicarboxylic acid(s) or its anhydride(s), from about 0.15 to about 3 weight % repeating units from an active crosslinking monomer(s) comprising two or more ethylenically unsaturated groups per molecule, and

b) from 25 to 50 parts by weight of a hard acrylate copolymer having a calculated Tg from 50 to 12O⁰C including from 0 to 10 wt.% repeating units from an ethylenically unsaturated C3-C10 mono or dicarboxylic acid(s) or anhydride(s) thereof, wherein said parts by weight are per 100 total parts by weight of said first acrylate copolymer and said second acrylate copolymer.

2. The waterborne copolymer dispersion of claim 1, further characterized by having particles with raspberry morphology of multiple domains with a single particle of said first and second acrylate copolymer.

3. The waterborne copolymer dispersion of claims 1 or 2, wherein said first and second acrylate copolymer are characterized by being derived from a multistage emulsion copolymerization where either said first acrylate copolymer is polymerized first and said second acrylate copolymer is polymerized in the presence of said first acrylate copolymer.

4. The waterborne copolymer dispersion of any of claims 1-3, wherein said copolymer dispersion has a minimum film formation temperature by ASTM 2354 test method of less than 2O⁰C in the absence of any coalescing solvent.

5. The waterborne copolymer dispersion of claim 4, wherein said first acrylate copolymer has a glass transition temperature of -10 to -5O⁰C.

6. The waterborne copolymer dispersion of claim 5 wherein said first acrylate copolymer is between 55 and 75 wt.% of the blend and said second acrylate copolymer is between 25 and 45 wt.% of said blend.

7. The waterborne copolymer dispersion of claim 5 or 6 formulated into a heat seal adhesive and applied to a lidding material for a food or condiment at a dried film weight of from about 3 to about 30 g/m².

8. The waterborne copolymer dispersion of claim 7 formulated and applied to a lidding material and then formed into packaged high moisture food or condiment.

9. The waterborne copolymer dispersion of claim 5, where the amount of C3- C5 mono- or dicarboxylic acid or the anhydride thereof in said second copolymer is at least 1 wt.% less than the amount of said C3-C5 mono- or dicarboxylic acid(s) or the anhydride(s) thereof in said first copolymer.

10. The waterborne copolymer dispersion of claim 5, wherein said first and second acrylate copolymers have an interfacial activation temperature of from about 120 to about 175⁰C.

11. The waterborne copolymer dispersion of claim 1 , wherein the total combined amount of repeating units from styrene in said first and second acrylate copolymers is less than 50 parts.

12. A heat seal adhesive for a high moisture food or condiment comprising the waterborne copolymer dispersion of claim 5.