INTERNAL RESIN-TACKIFIED ACRYLIC POLYMERS CONTAINING CROSSLINKABLE COMONOMERS

1 This Invention relates to acrylic copolymer latex

₂ compos tions, useful as pressure-sensitive adhesives, which contain

3 an Internal tackifying hydrocarbon resin having Improved peel

4 strength and shear properties obtained by Including a smal l amount of

5 a cross l inkable comonomer In the polymerization reaction mi xture.

6 The tackifying hydrocarbon resin s dissolved In acrylic monomers to

7 form a homogeneous solution and Is present, along with the δ cross l nkable comonomer, during the polymerization of the monomers to 9 form the acrylic copolymer latex.

packground of the Invention 10 Tackified acryl ic copoly ers have long been used as n pressure-sensitive. Such tacki fied copolymers have been prepared by

¹² adding a tackifying petroleum-based hydrocarbon resin or natural

13 resin with an acrylic copolymer. Whi le the resulting adhesive Is 4 often satisfactory to certain properties, such as tackiness and peel

¹⁵ strength on substrates such as polyester or stainless steel , certain 6 properties are found to be deficient, particularly the holding power ⁷ on these substrates . Previously, Increasing the peel strength of ⁸ tackified acrylic copolymers to a value greater than 2.0 pounds per 9 Inch often caused diminishing shear adhesion fall temperatures (SAFT) ⁰ and holding power. It I s desirable to maintain high holding power

and SAFT, particularly when the pressure-sensitive adhesive 1s to be used to prepare an adhesive tape. The prior art describes attempts to prepare satisfactory tackified acrylic copolymers. For example, Japanese Patent 0-59213783 teaches the preparation of a hot-melt pressure-sensitive adhesive by first heating a tackifying resin having a softening point between 60 and 200*C to above Its melting point, and adding to the hot melt a polymerization mixture of a alkyl (meth)acrylate, a functional monomer such as acrylic add, and a radical Initiator over a period of hours, with stirring, to form a pale yellow, transparent, solid hot-melt adhesive. Japanese Patent J-59227967 discloses a hot-melt polymerization of an alkyl (meth)acrylate main monomer and a copolymerlzable functional monomer Including ( eth)acrylic add, malelc anhydride, malelc add, and the like, where a surfactant 1s present with the resin during the polymerization to form a solid mass, hot-melt adhesive. In Japanese Patent 53074041, a polymerized powdery toner product 1s obtained by dissolving a binder resin such as a vinyl resin, acetal resin, epoxy resin or the like In a polymerlzable liquid monomer such as styrene, vinyl toluene, (meth)acrylic add or Its ester, and the like, and polymerizing the monomers In bulk. In Japanese Patent J-51125472, a petroleum resin emulsion is obtained by polymerizing vinyl monomers 1n the presence of petroleum resins having softening points of from 40 to 160.C, an average molecular weight of 300 to 3000, and an add value and saponification value of less than 1. The monomers Include for example, alkyl (meth)acrylates, vinyl acetates and vinyl chlorides, styrene, acrylonltrlle, and acrylic add. The emulsified mixture is then reacted in an emulsion polymerization reaction to form a shelf-stable emulsion adhesive. The resin emulsion produced Is described as having fine particle sizes and ample stability, and when cured, the films produced have excellent water resistance and gloss. Numerous approaches have been used to produce resin emulsions. One approach 1s to dissolve the resin in a hydrocarbon

SUBSTITUTE SHEET

solvent, combine the resin solution and water to form an emulsion, and strip off the solvent. Invariably some residual hydrocarbon solvent remains In the finished emulsion, which Is undesirable In certain applications. This has led to the development of solvent-free dispersions (see U.S. Patent No. 2.B09.948) and emulsions (see U.S. Patent No. 3,377,298) of petroleum resins. In both of these formulations, Ionic emuls1f1ers have been utilized; In the former a mixture of cationic and non-1onlc surface active agents is used to achieve a resin emulsion; and, 1n the latter an Ionic surfactant 1s used 1n combination with an aqueous gel of a swelling earth to produce an emulsion paste of a petroleum resin. As mentioned above, there has generally been a decrease in shear properties associated with an Increase of peel strength and tackiness. There 1s a need to improve peel strength of pressure-sensitive adhesives while still maintaining a high SAFT. My copending application Serial No.360507, filed June 2, 19B9, for "Internal Resln-Tacklfied Acrylics Polymers" (P-1413) deals with the problem somewhat but further Improvement has been found to be desirable, particularly 1n improving the holding power at higher temperatures (SAFT). Accordingly, It is an object of this Invention to prepare a resin-tackified acrylic copolymer which has an improved peel strength and SAFT for application as pressure-sensitive adhesives. it 1s a further object to provide a resin-tackified acrylic copolymer, wherein the tackifying resin is dissolved In the acrylic monomer solution with a crossUnkable monomer prior to the polymerization reaction to improve the peel strength and adhesion properties. It is a still further objective of this invention to cause add#t1onal improvement in the SAFT by incorporating Into the monomer polymerization mixture a crossUnkable comonomer. It 1s a still further object of this invention to provide pressure-sensitive adhesives useful to prepare tapes and useful laminating adhesives.

- 4 -

Summary of the Invention A tackified acrylic copolymer Is prepared by dissolving a hydrogenated hydrocarbon resin In a liquid monomer mixture from which the copolymer Is to be prepared by free radical Initiated emulsion polymerization. In accordance with this Invention, Included In the reaction mixture is a small, but effective amount, usually from about 0.1 wt.X to about 3 wt.X, of a crossUnkable monomer. The resin, having an aromatic content of at least 10 wt.X, Is present In amounts of about 10 to about 100 parts by weight, preferably 20 to 60 parts, per 100 parts of the monomer solution. The resin Is dissolved In the monomers at ambient temperatures or higher, and the free-radical polymerization reaction is conducted, with stirring, at a temperature from about 25. C to about 90"C. A dispersion of polymer in the form of a latex is produced which may be easily applied to a substrate such as flexible polyester or polyolefln films where 1t Is dried to form a pressure sensitive adhesive having a balance of good peel strength and shear strength, with the additional advantage of a high shear adhesion fall temperature (SAFT) provided by the presence of an effective amount of the crosslinking comonomer.

Detailed Description of the Invention Resins useful in the Instant invention are generally well known and are defined as hydrogenated natural resins and thermoplastic resins obtained by polymerization, in the presence of a catalyst of the Friedel-Crafts type, of steam-cracked petroleum distillates, boiling in the range between about 30. C and 280'C, or any fraction of these distillates boiling within the said range, or of polymerized mixtures of oleflns and dioleflns. The hydrocarbon resins useful according to this Invention are preferably petroleum resins prepared by homo and copolymerization of olefins, dioleflns, and vinyl aromatic components, predominantly the C-5 to C-9 species, from distillates of cracked petroleum stocks. The feed stacks for the resin must, however, have at least about 101 by weight vinyl aromatic constituents, such as, for

SHEET

example, styrenes, alpha-methyl styrene, indene and vinyl toluene and other well known vinyl aromatic compounds. A Friedel-Crafts catalyst Is typically employed and this res1n-form1ng polymerization Is performed at temperatures which range generally from 0* to 70*C. and preferably from 30*C to 55 ^* C. The resulting resin Is then hydrogenated n accordance with the methods described In U.S. Patent Nos.4,650,829; 4,328,090 and 4,629,766 for example, the disclosures of which are ncorporated herein by reference In their entirety for all purposes. The resulting hydrogenated resin retains a ring and ball softening point in the range of -20 ^* C to about 150*C, preferably from about 10*C to about 100*C. In the practice of this Invention the pressure-sensitive adhesive formed from resins having a softening point from 15*C to about 40 ^* C typically find their best use as laminating adhesives or as adhesives for labels. Those having softening points from about 70.C to 100'C for tapes. Broadly, hydrocarbon resins are polymerized from petroleum cracked distillates boiling In the range of about 30*C to 280*C or any fraction boiling within this range having a vinyl aromatic content as set forth above. As Is well known, the resins are prepared by treating the distillate with from 0.25 to 2.5X by weight of a Frledel-Crafts-type catalyst such as aluminum chloride, aluminum bromide, boron trlfluoride, and the like or solutions, slurries, or complexes thereof. The reactions are conducted at temperatures 1n the range of 0* to 70 C, and preferably 30 ^* C to 55'C. Residual catalyst Is quenched by suitable methods such as addition of methyl alcohol and subsequent filtration, water, and/or caustic washing. The final solution 1s then stripped of unreacted hydrocarbons and low molecular weight oils by vacuum or steam distillation. Properties of the hydrocarbon resins can be varied by changing conditions and feedstock as is well known. The hydrocarbon resin Is prepared by the hydrogenation of polymerized oleflnlcally unsaturated monomers derived from petroleum cracking, preferably cyclic dioleflns, (such as, for example, dlcyclopentadlene) styrene alpha-methylstyrene and the like. Such resins, their preparation and hydrogenation are well known in the art

and are commercially available under the trade designation, for example, ESCOREZ, Arcon, and the like. Naturally occurring resins suitable for use In the present Invention may be resin esters or terpenes such as alpha-plnene, beta-plnene, carene, Hmonene or other readily available terplnous materials, alpha-plnene and ll onene being preferred. The material may be pure or the commercially available concentrates such as gum terpentine or alpha-plnene concentrates, which tend to be mixtures of various terplnous materials. A suitable natural resin contains from about 70 to 95 wt.X alpha-plnene, the remainder being other terpenes. Llmonene streams are available and are known to those skilled 1n the art. These are typical streams useful 1n the present Invention. The hydrogenation of these naturally occurring resins 1s well known and can be carried out using the procedures of the above-Identified U.S. Patents. In the practice of this Invention the most successful tackified acrylic copolymers are produced when the resin is soluble 1n the selected monomer mixture at ambient temperature. Such resin should have a molecular weight of from about 500 to about 5000, preferably from about 1000 to about 2500. Hhen the aromatic contents of the resin, usually a styrene or a vinyl toluene or vinyl xylene derivatives, decreases below about 30 wt.X, the mixture of acrylic monomers must be adjusted to reduce overall polarity of the monomer mixture in a manner well known to those skilled in such polymerizations. For example, a substitution of butyl acrylate for 2-ethylhexyl acrylate would reduce polarity. By lowering the polarity of the monomer mixture lower aromatidty 1n the resin can be tolerated and the resin will still dissolve 1n the monomers to form a solution. It has further been discovered that aliphatic resins, such as those formed from amylenes, piperylene, cyclopentadlene and Its derivatives are not necessarily soluble in the monomers selected, and thus are normally not used. In accordance with this invention, as previously mentioned, 1n order to form a suitable polymerization reaction mixture, It is necessary that the resins comprise from at

least about 10X to lOOX by weight vinyl aromatic content, preferably from about 20X to about 65X aromatic content; with 30X to 50X being the most preferred range. The monomers used In the practice of this Invention are vinyl monomers which are polymerlzable by free radical reaction, preferably those materials described as acrylics; I.e., alkyl(meth)acrylates and (meth)acryllc add. Mixtures of alkyl acrylates are usually Included, which affect the solubility of the petroleum resins prior to polymerization, as well as final properties of the composition. These acrylate monomer mixtures generally comprise lower alkyl ( eth)acrylates having 1 to 3 carbon atoms 1n the alkyl group of the ester and upper alkyl (meth)acrylates having 4 or more, usually up to about 14, preferably 4 to 8 carbon atoms. Other monomer components useful in accordance with the invention are the (meth) acrylic add(s). Some preferred examples of monomers are as follows: acrylic add, methacryϋc add, crotonlc add, malelc add, Itaconlc add, methyl (meth) acrylate, ethyl (meth)acrylate, propyl acrylate, 2-ethylhexyl acrylate, or n-butyl acrylate. Other monomeric material which can be employed can Include acrylonitrile, vinyl acetate, vlnylldene chloride, styrene, methyl styrene, and the Hke. The monomer mixture would contain from IX to about 15X, preferably about 2X to about 6X of the (meth) acrylic add; D to about 50X, preferably about 10X to 35X, lower alkyl (meth)acrylate; and from about 25X to 99X, preferably from 60X to about 88X upper alkyl (meth)acryl ate. All percents are by weight of the monomer mixture. It should be noted that some "acrylic" monomer mixtures available Include minor amounts of acrylonitrile, styrene, or vinyl acetate, and the like. in the practice of the Instant invention 1t has been discovered that the peel strength, shear strength, and SAFT of internally tackified acrylic copolymers can be dramatically Improved and balanced by the incorporation in such reaction solution of a small amount of up to about 3 wt.X, preferably from 0.1 to 2 wt.X of the reaction components. Usually the small amount can be a crossUnkable monomer. For instance, the crossUnkable monomer helps

- 8 -

to maintain the holding properties, particularly the shear and SAFT unlike other changes made to Improve the peel strength. The effectiveness of the added amount can be easily determined by following the examples set forth herein. This crossUnkable monomer can be any compound which contains at least 2 reactive non-conjugated double bonds. For example, an acrylated d1 ester with the required double bonds to act as a crosslinking monomer can be produced by reacting either a poly(oxyethylene) or poly(oxypropylene) glycol with acrylic add. The glycol would have an average molecular weight of from 200 to about 1000, preferably from 400 to 800. Other crossUnkable monomers can also be produced by reacting triethanolamine or tr1 methyl ol propane with a (meth)acryllc acid to form a trimethacrylate thus providing the terminal double bond. Functional end groups can be hydroxyl, amine, carboxyl, or cyano. Other useful preparation of such crosslinking agents is well known 1n the art. It was unknown and, of course, somewhat surprising that the incorporation of a small amount of such crossUnkable monomer Into the internally tackified copolymer would produce dramatic Improvement in the holding properties of pressure-sensitive adhesive. Some useful crossUnkable monomers are the dimethacrylate of a 600 molecular weight poly(oxyethylene) glycol and trimethylol propane trimethacrylate. Of course, many other crossUnkable comonomers can be used and are readily determined by those in the art. 5 The above-mentioned crossUnkable monomers are dissolved in 6the polymerizable monomer solution in the presence of the hydrocarbon 7 resin as mentioned above. Generally, the reaction of acrylate 8monomers to form acrylate copolymers is well known to those of ⁹ ordinary skill in the art to include the water to adjust the solids 0 content, a surfactant to aid 1n the formation of monomer-1n-water 1 emulsion and to act as a suspending agent for the solids in the final copolymer, which are dispersed in the aqueous medium both during and 3 after the polymerization. The surfactants useful in the practice of this Invention are well-known and are present 1n quantities 5 sufficient to place the reactants In the emulsion prior to reaction

- 9 -

and maintain the product 1n suspension after reaction. Of particular applicability are blends of anlonlc and non-1onlc surfactants having a HLB of from about 15 to 42, especially around 40. Especially preferred are the widely used dlsodium sulfosucdnate as an anlonlc surfactant and ethylene oxide adducts of nonyl phenol as nonlonlc surfactants. While the ranges of surfactants are well-known, the amount will preferably range from about 1 to about 5 parts, normally 2 to 4 parts, per 100 parts of the monomers. Also In the reaction mixture 1s an Initiator, such as for example, sodium persulfate or an 0 ammonium persulfate present in catalytic amounts well-known to those 1 skilled 1n the art, such as for example, about 0.1 part per 100 parts

12 of reaction mixture. In some instances it may be advantageous to

13 buffer the pH of the solution by Including a well-known buffering

14 agent such as, for example, sodium bicarbonate.

15 Notwithstanding the foregoing, the selected petroleum resin

16 is mixed with the selected monomers to form a monomer solution

1 ⁷ containing from about 10 to about 100 parts resin per 100 parts (PHR)

18 of the liquid mixture of monomer reactants and more preferably from

19 about 20 to about 60 parts per 100 parts of monomer reactants. Host

20preferably, from 25 to 55 parts resin per 100 parts monomer reactants

21 are present. As stated herein before, the petroleum resin is

22 selected so that It will be soluble In the monomer mixture at ambient

23temperatures, but notwithstanding such, the temperature could be

24raised to the point where It 1s easily solublUzed; I.e., from about

2525*C to about 40 ^* C.

26 Included also 1n the solution is polyfunctional

27crossUnkable monomers as mentioned above. The crossUnkable monomer

28may be incorporated in the entire poly erlzable mixture or fed into

291t after the reaction has begun, thus being present 1n the later

30stages of the reaction. When the crossUnkable monomer is not mixed

31with the entire mixture, 1t 1s preferably added with about the last

32.25X of the polymerlzable reaction mixtures.

33 In the practice of the present invention, the polymerization

34reaction Is to be carried out with no chain transfer agent being

35used. We have also discovered that the presence of an antloxidant in

the resin 1s to be avoided because It Inhibits crosslinking. It 1s preferred that the solution of monomers, crosslinking compound and resin be dispersed Into a water medium to form an emulsion at ambient temperatures 1n the presence of a satisfactory surfactant. The reaction mixture thus formed, including the Initiators, must be placed In a reaction vessel, evacuated of oxygen by nitrogen purge, and the polymerization reaction conducted with stirring 1n the sealed container preferably under a nitrogen blanket. The addition of the monomer solution containing the hydrocarbon resin and polyfunctional crosslinker Is normally carried out over a period of time. Typically, about 15 wt.X of the total reaction mixture would be charged Initially Into the reactor and polymerized for a short period of time to obtain solids content of about 17-20 wt.X. Optionally, no crosslinking monomer 1s present at this point. Once a selected solIds level 1s attained, the balance of the monomer solution containing crossUnkable compound would be evenly metered Into the reaction vessel over a period of time, normally several hours, usually 3 to 6 hours depending upon the size of the reaction and quantity to be added. Once the addition of the monomer solution Including the crosslinker is complete, the polymerization Is allowed to continue, usually for another hour while maintaining the reaction temperature, normally, with the range of from 45*C to about 90 ^* C, preferably between about 50'C and 85'C. The polymerization continues until the total solids content of the 5material in the reactor reaches its theoretical level based upon the 6amount of reactants charge to the reaction mixture, usually, in 7 practice, about 45 to about 55 wt.X, but the overall solids content 8may be as high as 70X with there being no real lower limit. While there 1s no real theoretical lower limit, a practical lower limit of about 30X solids content is recognized by those skilled in the art. In a commercial sense, the highest limits attainable are preferred. Once the reaction is complete the product 1n the form of a dispersed polymer latex Is allowed to cool to room temperature, and the dispersed polymer latex 1s separated from coagulum formed during ⁵ polymerization, usually by filtration. In the practice of the

Invention 200-mesh "sock" filter has been found satisfactory. Such latex can be coated, for example, on a substrates uch as film or paper for use as a tape. The coated substrate would be dried, usually by circulating hot air at from about 100*C to about 110'C for about a few, usually from about 2 to about 5, minutes. Those skilled In the art would readily recognize other processing parameters for such coated substrate. The latex coating usually results 1n a dried adhesive film of from about 0.3 to about 3.0 mils, preferably about 1.0 mil of thickness, even though thicker or thinner films may be desired In certain applications of the instant Invention. Thus dried and cured, the product 1s 1n condition for use as a pressure-sensitive adhesive tape. In certain embodiments of the practice of this Invention, the adhesives formed find applications as non-pressure-sens1t1ve adhesives such as, for example, laminating adhesives, binders for woven and nonwoven fabrics, and binders for pressed wood production. For example, the certain species useful as laminating adhesives; I.e., those with high peel strength but low shear properties, would be used to join two or more sheets of material together such as a layer of plastic sheeting to a layer of wood or a multiple layer of wood to form a plywood product. The foregoing invention having now been described, the following examples are provided to further teach the preferred embodiment and best modes for practicing the described Invention and to aid others In the practice of the scope of such Invention herein provided.

Example 1 - Comparative This example i l lustrates the synthesis of acryl ic copolymer emul sions . The actual Ingredi ents charged into the reactor are summarized in Table 1 below. Various amounts of the chain transfer agent, t-dodecaneth1ol are used in the preparation of Samples 1-4, 1n order to obtain the copolymers with various molecular weight.

- 12 -

TABLE 1

A. Initial Charge: 24.0 parts distilled water 0.1 parts Igepal CO-850, an ethylene oxide adduct of nonyl phenol (sold by GAF) 0.2 parts sodium bicarbonate 0.05 parts sodium persulfate B. Monomer Solution: 24.2 parts distilled water 3.16 parts Emcol K-8300, an anionic surfactant manufactured by Hitco Chemical 0.05 parts sodium persulfate 37.5 parts 2-ethylhexyl acrylate 10.5 parts ethyl acrylate 2.0 parts acrylic acid 0-0.1 part t-dodecaneth1ol

A 2-l1ter, four-neck reaction flask equipped with a stirrer, a condenser, a thermosensor, and a monomer addition tube was flushed with nitrogen for 15 minutes. The initial charge (A) was placed In the flask with stirring and continued nitrogen purging for additional 20 minutes. At the end of the 20 minutes, the temperature was raised to 65*C. In a separate vessel , a monomer emulsion according to the composition (B) was prepared. Hhen the reaction flask temperature was equilibrated at 65*C, 15 wt.X of the monomer solution (B) was added to the flask and al lowed to polymerize for 30 minutes. The total solids at the end of the 30 minutes was about 18X. When the total sol ids reached thi s range, the remai ni ng monomer emul sion (B) was evenly metered into the flask over a period of 3 hours . After the monomer addition, the reaction was al lowed to continue at 65 ^* C for 2 additional hours and then cooled to room temperature. Stirri ng was continued throughout the procedure. The final total sol ids was 50X by weight, particle size

150-250 nm, and Brookfleld viscosity 500-1,000 cp. The coagulum content of about 2X of the total reactants charged was removed by filtration.

Pressure-Sensitive Adhesive (PSA) Performance Test The polymer latex prepared as described above was knife-coated on a Mylar' ' film and dried In an air circulating oven for 3 minutes at llO'C. The dried adhesive coating was approximately 1.5 mils thick. The adhesive was bonded to a stainless steel surface for PSA performance tests. Peel (180*) adhesion was obtained using Test No. PSTC-1 of the Pressure Sensitive Tape Council. Shear test was performed using PSTC-7. SAFT (Shear Adhesion Fail Temperature) test was similar to shear test except that the test temperature Is Increased at the rate of 10'F. per 15 minutes. The temperature at which shear failed 1s reported as SAFT. Both SAFT and shear were tested at 1 square Inch and 1,000-gram hang weight. PSA performance is sensitive to the molecular weight of the polymer. A chain transfer agent such as t-dodecanethiol 1s commonly used to control the molecular weight. In order to demonstrate the MW effect on PSA properties, samples 1-4 were synthesized according to the above procedures, but with various amounts of chain transfer agent.

TABLE 2 Dodecanethiol 180 ^* Peel SAFT Shear parts (1bs/1n) i (hrs)

0.0 1.1 290+ 100+

0.025 1.1 290+ 100+

0.05 1.6 290+ 18 0.075 1.7 112 3

Samples with t-dodecaneth1ol level higher than 0.075 parts show cohesion failure In the peel test and have very poor shear, less than 1 hour. These samples are not useful for PSAs.

Exampl e 2 The synthesi s procedure described 1n Exampl e 1 was fol lowed using the Initial charge and monomer emulsion compositions of Table l , except that the monomer composi tion for the Samples 5-8 were changed to include different amounts of petroleum resins (ESCOREZ ECR-149— Exxon Chemical Company, Houston, TX, 1 s a hydrogenated hydrocarbon resin containing 50X aromaticlty with a softening point of about 95*C) di ssolved 1n the monomer solution as i llustrated in Tabl e 3 below (al l Ingredient units are In parts by weight) . No chain transfer agent was used. ECR-149 has an average molecul ar weight of about 1000 and 50 wt.X aromaticlty.

TABLE 3

The PSA performance results of above samples were obtained following same procedures and at same conditions are summarized on Table 4 below.

TABLE 4

UBSTITUTE SHEET

Comparing the results In Table 4 with Table 2, It Is clear that a significantly higher peel strength PSA product was obtained while maintaining high shear properties. The Improved balance of peel and shear properties cannot be obtained through conventional acrylic composition using externally Introduced tackifler.

Example 3 The same procedure as described In Example 1 above was followed per the tests below. All of the Initial charge (A) and the Monomer Solution (8) are the same as Example 1, except that the composition of the monomer solution which also contain the dissolved crossUnkable comonomer according to Table 5 below (all ingredient units are in parts by weight):

TABLE 5

For Samples 10 and 11 , the crossUnkabl e comonomer was mi xed wi th the whol e monomer emul sion. For Sampl e 13, the crossUnkabl e comonomer was only mi xed wi th the l ast 25# monomer emul sion added to the reaction vessel . Tabl e 6 below summarized the PSA performances of these sampl es :

- 16 -

TABLE 6

Samples 9 to 11 demonstrate the effect of a crossUnkable comonomer on peel strength with no resin present. The peel strength normally suffers 1f the degree of the crosslinking is too high. By incorporating hydrocarbon resin In the acrylic copolymer particles, as in Sample 12, significant Increase of peel strength Is obtained. Sample 13 contains minor amounts of a crossUnkable comonomer, S-252, together with the same amount of resin In the composition as that of Sample 12. The shear properties are much improved while the peel adhesion is maintained at the same level.

Example 4 Following the procedure and formulations of Examples 1 and 2, IX of several crossUnkable comonomers was added to the polymerlzable solutions incorporating the resin ESCOREZ ECR-149-ID (EXXON), having a softening point of 90.5 ^* C. The crossUnkable comonomer was change das set forth in Table 7 below to illustrate the properties of the pressure-sensitive adhesives prepared and tested as described above.

HEET

CT/US90/06805

- 17 -

TABLE 7

INTERNAL RESIN TACKIFYING ACRYLICS CONTAINING CROSSLINKABLE COMONOMER

(RESIN USED: ECR-149. SOFTENING POINT - 90.5«C)

* 1 wt.X unless otherwise noted ** Tri methyl ol propane Trimethacrylate (Sartomer-350) . *** Polyethylene Glycol (600) Dimethacrylate (Sartomer-252).

Example 5 Following the procedure set forth above In Examples 1 and 2, additional Internally tackified acrylic copolymers containing crossUnkable comonomers were compared using resins having different softening points, to wit: ESCOREZ ECR-149 having a softening point of 95*C. and ECR-149-BPC having a softening point of 87 ^* C. The results of these tests are given on Table 8 following. It Is seen by the foregoing that the internally tackified copolymers themselves have Improved holding properties by the

Inclusion of the effective amount of the crossUnkable polyfunctional comonomer. As Is apparent from the foregoing description, the materials prepared and the procedures followed describe specific embodiments of the invention. It 1s apparent from the foregoing description that, while predictive forms of the Invention have been illustrated and described, various modifications can be made without departing from the spirit and scope of this Invention. Accordingly, 1t 1s not Intended that the Invention be limited except by the appended claims.

ITUTE SHEET

TABLE β

INTERNAL RESIN TACKIFYING ACRYLICS CONTAINING CROSSLINKABLE COMONOMER

1. ECR-149, SOFTENING POINT - 95 ^Φ C; 2. ECR-149, SOFTENING POINT - 87*C