This Invention relates to acrylic copolymer latex compositions, useful as pressure-sensitive adhesives, which contain an Internal tackifying hydrocarbon resin having improved peel strength and shear properties obtained by including a small amount of a polyfunctional or crosslinkable comonomer in the polymerization reaction mixture. The tackifying hydrocarbon resin is dissolved in acrylic monomers to form a homogeneous solution and 1s present, along with the polyfunctional or crosslinkable comonomer, during the polymerization of the monomers to form the acrylic copolymer latex. Background of the Invention Tackified acrylic copolymers have long been used as pressure-sensitive. Such tackified copolymers have been prepared by adding a tackifying petroleum-based hydrocarbon resin or natural resin with an acrylic copolymer. While the resulting adhesive is often satisfactory to certain properties, such as tackiness and peel strength on substrates such as polyester or stainless steel, certain properties are found to be deficient, particularly the holding power on these substrates. Previously, increasing the peel strength of tackified acrylic copolymers to a value greater than 2.0 pounds per Inch often caused diminishing shear adhesion fail temperatures (SAFT) and holding power. It is desirable to maintain high holding power and SAFT, particularly when the pressure-sensitive adhesive is 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 an alkyl (meth ⁾ acrylate, a functional monomer such as acrylic acid, and a radical initiator

over a period of hours, with stirring, to form a pale yellow, transparent, solid hot-melt adhesive. Japanese Patent 0-59227967 discloses a hot-melt polymerization of an alkyl (meth)acrylate main monomer and a copolymerlzable functional monomer Including ( eth)acrylic acid, maleic anhydride, malelc acid, 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

⁹ dissolving a binder resin such as a vinyl resin, acetal resin, epoxy ⁰ resin or the like 1n a polymerizable liquid monomer such as styrene,

¹¹ vinyl toluene, ( eth)acrylic acid or its ester, and the like, and

¹² polymerizing the monomers in bulk.

¹³ In Japanese Patent 0-51125472, a petroleum resin emulsion is

¹⁴ obtained by polymerizing vinyl monomers in the presence of petroleum

15 resins having softening points of from 40 to 160 ^# C, an average 16 molecular weight of 300 to 3000, and an acid value and saponification 17 value of less than 1. The monomers include for example, alkyl 18 (meth)acrylates, vinyl acetates andvinyl chlorides, styrene, 1. acrylonltrile, and acrylic acid. The emulsified mixture is then 20 reacted in an emulsion polymerization reaction to form a shelf-stable emulsion adhesive. The resin emulsion produced is described as

22 having fine particle sizes and ample stability, and when cured, the

23 films produced have excellent water resistance and gloss.

Numerous approaches have been used to produce resin emulsions.

25 One approach is to dissolve the resin in a hydrocarbon solvent, 26 combine the resin solution and water to form an emulsion, and strip

27 off the solvent. Invariably some residual hydrocarbon solvent

28 remains 1n the finished emulsion, which is undesirable in certain 29 applications. This has led to the development of solvent-free 30 dispersions (see U.S. Patent No. 2,809,948) and emulsions (see U.S.

³¹ Patent No. 3,377,298) of petroleum resins. In both of these

³² formulations, ionic emulsifiers have been utilized; in the former a

³³ mixture of catlonic and non-ionic surface active agents is used to

³⁴ achieve a resin emulsion; and, in the latter an ionic surfactant is

³⁵ used in combination with an aqueous gel of a swelling earth to

³⁶ produce an emulsion paste of a petroleum resin.

³⁷ As mentioned above, there has generally been a decrease in shear

properties associated with an increase of peel strength and tackiness. There is a need to improve peel strength of pressure-sensitive adhesives while still maintaining a high SAFT. My copendlng application Serial No. 360507, filed Oune 2, 1989, for "Internal Resln-Tac fied 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-tacklfied acrylic copolymer which has an improved peel strength and SAFT for application as pressure-sensitive adhesives. It is a further object to provide a resin-tackified acrylic copolymer, wherein the tackifying resin is dissolved in the acrylic monomer solution with a crosslinkable monomer prior to the polymerization reaction to Improve the peel strength and adhesion properties. It 1s a still further objective of this Invention to cause add ⁱ tional Improvement In the SAFT by incorporating Into the monomer polymerization mixture a crosslinkable comonomer. It 1s a still further object of this Invention to provide pressure-sensitive adhesives useful to prepare tapes and useful laminating adhesives. 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. 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. 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 crosslinkable monomer. 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

polyolefin films where it 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 fail temperature (SAFT) provided by the presence of an effective amount of

5 the crosslinking comonomer.

6 Detailed Description of the Invention Resins useful in the instant invention are generally well known and are defined as hydrogenated natural resins and thermoplastic

9. resins obtained by polymerization, in the presence of a catalyst of

10 the Friedel-Crafts type, of steam-cracked petroleum distillates,

11 boiling in the range between about 30*C and 280*C, or any fraction of

12 these distillates boiling within the said range, or of polymerized

13 mixtures of olefins and diolefins.

14 The hydrocarbon resins useful according to this invention are

15 preferably petroleum resins prepared by homo and copolymerization of

16 olefins, diolefins, andvinyl aromatic components, predominantly the

17 C-5 to C-9 species, from distillates of cracked petroleum stocks.

18 The feed stncks for the resin must, however, have at least about 10X is by weight vinyl aromatic constituents, such as, for example,

20 styrenes, alpha-methyl styrene, indene and vinyl toluene and other

21 well known vinyl aromatic compounds. A Friedel-Crafts catalyst is

22 typically employed and this resin-forming polymerization is performed ³ at temperatures which range generally from 0 ^* to 70 ^* C. and preferably ⁴ from 30*C to 55*C. The resulting resin is then hydrogenated in 5 accordance with the methods described in U.S. Patent Nos. 4,650,829;

²⁶ 4,328,090 and 4,629,766 for example, the disclosures of which are

² incorporated herein by reference in their entirety for all purposes.

²⁸ The resulting hydrogenated resin retains a ring and ball softening

29 point in the range of -20*C to about 150 ^* C, preferably from about

³ 0 10*C to about lOO'C. In the practice of this invention the

³ 1 pressure-sensitive adhesive formed from resins having a softening

³ 2 point from 15'C to about 40*C typically find their best use as

³³ laminating adhesives or as adhesives for labels. Those having

³⁴ softening points from about 70*C to lOO'C for tapes.

35 Broadly, hydrocarbon resins are polymerized from petroleum

56 cracked distillates boiling in the range of about 30'C to 280 ^* C or

³⁷ 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 tr1fluoride, and the like or solutions, slurries, or complexes thereof. The reactions are conducted at temperatures in 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 1s prepared by the hydrogenation of polymerized olefinically unsaturated monomers derived from petroleum cracking, preferably cyclic diolefins, (such as, for example, dicyclopentadiene) styrene alpha-methylstyrene and the like. Such resins, their preparation and hydrogenation are well known 1n the art and are commercially available under the trade designation, for exar.f-le, ESCOREZ, Arcon, and the like. Naturally occurring resins suitable for use in the present invention may be resin esters or terpenes such as alpha-pinene, beta-pinene, carene, limonene or other readily available terpinous materials, alpha-pinene and limonene being preferred. The material may be pure or the commercially available concentrates such as gum terpentine or alpha-pinene concentrates, which tend to be mixtures of various terpinous materials. A suitable natural resin contains from about 70 to 95 wt.X alpha-pinene, the remainder being other terpenes. Limonene streams are available and are known to those skilled in the art. These are typical streams useful 1n the present invention. The hydrogenation of these naturally occurring resins is 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 aromaticity in the resin can be tolerated and the resin will still dissolve in the monomers to form a solution.

It has further been discovered that aliphatic resins, such as those formed from amylenes, piperylene, cydopentadiene 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, in order to form a suitable polymerization reaction mixture, it 1s 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 moruners used in Ihe practice of this invention are vinyl monomers which are polymerizable by free radical reaction, preferably those materials described as acrylics; i.e., alkyl(meth)acrylates and (meth)acrylic acid. 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(meth)acrylates having 1 to 3 carbon atoms in 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. The other monomer component is the ( eth) acrylic acid. Some preferred examples of monomers are as follows: acrylic acid, methacryHc acid, crotonic add, maleic acid, Itaconic acid, methyl (meth) acrylate, ethyl( eth)acrylate, propyl acrylate, 2-ethylhexyl acrylate, or n-butyl acrylate. Other monomer1c material which can be employed can include acrylonitrUe, vinyl acetate, vinyledene chloride, styrene, methyl styrene, and the like. The monomer mixture would contain from IX to about 15X, preferably about 2X to about 6X of the (meth) acrylic acid; 0 to about 50X, preferably about 10X to 35X, lower

alkyl (meth)acrylate; and from about 25X to 99X, preferably from 60X

² to about 88X upper alkyl( eth)acryl te. All percents are by weight

³ of the monomer mixture. It should be noted that some "acrylic"

⁴ monomer mixtures available include minor amounts of acrylonltrlle,

5 styrene, or vinyl acetate, and the like. 6 In the practice of the instant invention 1t has been discovered 7 that the peel strength, shear strength, and SAFT of Internally 8 tackified acrylic copolymers can be dramatically improved and 9 balanced by the incorporation in such reaction solution as described 10 above of a small amount usually up to about 3 wt.X, preferably from

0.1 to 2 wt.X of the reaction components; I.e., the monomer with the 1 ¹ 2 dissolved petroleum hydrocarbon resi n, a polyfunctional crossl i nkabl e

13 monomer. For instance, the crosslinkable comonomer helps to maintain

14 the holding properties, particularly the shear and SAFT unlike other 15 changes made to improve the peel strength. The effectiveness of the 16 added amount can be easily determined by the following the examples 17 set forth herein. Only a few simple experiments are necessary to 18 determine the small effective amcjnt necessary. 19.

This crosslin -ile comonomer can be (1) a linear dlene, (ϋ) an 20 olefin with a terminal functional group which acts as a starting

²¹ material, or (Hi) produced from a polyfunctional compound with a

²² functionality of from 2 to about 4, depending upon the starting

²³ material used to prepare the monomer including olefinlc, preferably

²⁴ terminal unsaturation. For example, a polyethylene or polypropylene

²⁵ glycol, the preferred species, would have a functionality of 2 and

²⁶ can be reacted with acrylic add to provide an acrylatediester with

27 the required double bonds to act as a crosslinking monomer. The 28 glycol would have an average molecular weight of from 200 to about 29 1000, preferably from 400 to 800. Other Initiators such as

³⁰ triethanola ine or trimethylolpropane could be reacted directly, or

³¹ reacted with an epoxide such as ethylene oxide or propylene oxide to adjust the molecular weight and then reacted, with a (meth)acrylic

³³ add to form a trimethacrylate, which is the preferred terminating

34 polymerizable species providing the terminal double bond. The 35 functional radical could be hydroxyl , amine, carboxyl , or cyano. The 36 preferred initiator is the ester of a polyhydroxy initiator. It was unknown and, of course, somewhat surprising that the incorporation of

a small amount of such crosslinkable monomer into the internally tackified copolymer would produce dramatic Improvement in the holding properties of pressure-sensitive adhesive. Some useful crosslinkable comonomers are the dimethacrylate of a 600 molecular weight polyethylene glycol and trlmethylolpropane trlmethacr l te. Of course, many other crosslinkable comonomers can be used and are readily determined by those in the art.

The above-mentioned crosslinkable monomers are dissolved in the polymerizable monomer solution in the presence of the hydrocarbon resin as mentioned above. Generally, the reaction of acrylic monomers to form acrylic copolymers is well-known to those of ordinary skill in the art to include the water to adjust the solids content, a surfactant to aid in the formation of monomer-in-water 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 after the polymerization. The surfactants useful In the practice of this invention are well-known and are present in quantities sufficient to place the reactants in th_ emulsion prior to reaction and maintain the product <_ι suspension after reaction. Of particular applicability are blends of anionic and nlonic surfactants having a HLB of from about 15 to 42, especially around 40. Especially preferred are the widely used disodlum sulfosucdnate as an anionic surfactant and ethylene oxide adducts of nonyl phenol as nonionic 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 1n the reaction mixture is an initiator, such as for example, sodium persulfate or an ammonium persulfate present in catalytic amounts well-known to those 9 skilled 1n the art, such as for example, about 0.1 part per 100 parts of reaction mixture. In some instances it may be advantageous to buffer the pH of the solution by including a well-known buffering agent such as, for example, sodium bicarbonate. ³ Notwithstanding the foregoing, the selected petroleum resin is ⁴ mixed with the selected monomers to form a monomer solution -> containing from about 10 to about 100 parts resin per 100 parts (PHR) ^t > of the liquid mixture of monomer reactants and more preferably from ⁷ about 20 to about 60 parts per 100 parts of monomer reactants. Most

preferably, from 25 to 55 parts resin per 100 parts monomer reactants are present. As stated herein before, the petroleum resin is selected so that it will be soluble 1n the monomer mixture at ambient temperatures, but notwithstanding such, the temperature could be raised to the point where it 1s easily solubHlzed; I.e., from about 25'C to about 40 ^* C.

Included also in the solution 1s polyfunctional crosslinkable monomers as mentioned above. The crosslinkable monomer may be incorporated in the entire polymerizable mixture or fed into 1t after the reaction has begun, thus being present in the later stages of the reaction. When the crosslinkable comonomer is not mixed with the entire mixture. It is preferably added with about the last 25X of the polymerizable reaction mixtures.

The molecular weight of such copolymers Is normally controlled by commonly known nonolefin chain transfer agent 1n the polymerization mixture. In the practice of the present invention, the copolymer 1s to be formed with no chain transfer agent being used which restricts the molecular weight of the copolymer. Simila.ly we have discovered that the presence of an antioxideu.t in the resin is to be avoided because it causes the same problem, low molecular weight of the polymer. It 1s preferred that the solution of monomers and resin be dispersed Into a water medium to form an emulsion at ambient temperatures in 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 1s normally carried out intermittently and over a period of time. For example, about 15 wt.X of the monomer solution would be charged would be initially etered Into the reaction mixture Initially and polymerized for a short period of time, to begin the reaction system. Preferably, no crosslinking monomer is present at this point. Normally when this is accomplished, the solids content of the reaction would be about 18 wt.X, which is preferably a benchmark content. Once the selected solids level is attained, the balance of the monomer solution 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 crossUnker 1s 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 80*C. The polymerization continues until the total solids content of the material in the reactor reaches its theoretical level based upon the amount of reactants charge to the reaction mixture, usually. In practice, about 45 to about 55 wt.X, but the overall solids content may be as high as 70X with there being no real lower Hrait. While there Is 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 solids in the form of a dispersed polymer latex is allowed to cool to room temperature, and the dispersed polymer latex 1s separated from coagulur- formed during polymerization, usually by filtration. In the practice of the Invention 200-mesh "sock" filter has been found satisfactory. Such latex can be coated on a substrate film for use as a tape, for example. 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 1n the art would readily recognize other processing parameters for such coated substrate. The latex coating usually results in a dried adhesive film of from about 0.5 to about 1.5 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 is in condition for use as a pressure-sensitive adhesive tape. In certain embodiments of the practice of this invention, the ³ adhesives formed find applications as non-pressure-sensitive ⁴ adhesives such as, for example, labels, laminating adhesives, binders ^ for woven and nonwoven fabrics, and binders for pressed wood ⁶ production. For example, the certain species useful as laminating ⁷ 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 1n the practice of the scope of such invention herein provided. Example 1 — Comparative This example Illustrates the synthesis of acrylic copolymer emulsions. The actual Ingredients charged into the reactor are summarized in Table 1 below. Various amounts of the chain transfer agent, t-dodecanethlol are used in the preparation of Samples 1-4, in order to obtain the copolymers with various molecular weight.

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 Witco Chemical 0.05 parts sodium persulfate 37.5 parts 2-ethylhexyl acrylate

10.5 parts ethyl acrylate

2.0 parts acrylic add 0-0.1 part t-dodecanethiol A 2-liter, 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 solution according to the composition (B) was prepared. When the reaction flask temperature was equilibrated at 65*C, 15 wt.X of the monomer solution (B) was added to the flask and allowed to polymerize for 30 minutes. The total solids at the end of the 30 minutes was about 18X. When the total solids reached this range, the remaining monomer solution (B) was evenly metered into the flask over a period of 3 hours. After the monomer addition, the reaction was allowed to continue at 65 ^* C

⁹ for 2 additional hours and then cooled to room temperature. Stirring ° was continued throughout the procedure.

11 The final total solids was 50X by weight, particle size 150-250

1 ² n , and Brookfield viscosity 500-1,000 cp. The coagulum content of

1 ³ about 2X of the total reactants charged was removed by filtration.

1 ⁴ Pressure-Sensitive Adhesive (PSA) Performance Test ⁵ The dispensed polymer latex prepared as described above was ⁱ⁶ knife-coated on a Mylar ^® film and dried in an air circulating ⁷ oven for 3 minutes at llO'C. The dried adhesive coating was

¹⁸ approximately 1.5 mils thick. The adhesive was bonded to a stainles? steel surface for PSA performance tests. Peel (180*) adhesion was

²⁰ obtained using Test No. PSTC-1 of the Pressure Sensitive Tape

² 1 Council. Shear test was performed using PSTC-7. SAFT (Shear

²² Adhesion Fall Temperature) test was similar to shear test except that

²³ the test temperature 1s increased at the rate of 10*F. per 15

²⁴ minutes. The temperature at which shear failed is reported as SAFT.

²⁵ Both SAFT and shear were tested at 1 square inch and 1,000-gram hang

²⁶ weight.

²⁷ PSA performance is sensitive to the molecular weight of the

²⁸ polymer. A chain transfer agent such as t-dodecanethiol 1s commonly used to control the molecular weight and demonstrate this 0 Samples 1-4 which were synthesized according to the above

³ procedures, but with various amounts of chain transfer agent.

TABLE 2

Dodecanethiol 180' Peel SAFT Shear

Samples (parts) (lb$/lπ) CF) (hrs)

1 0.0 1.1 290+ 100+ 2 0.025 1.1 290+ 100+ 3 0.05 1.6 290+ 18+

4 0.075 1.7 112 3

Samples with t-dodecanethiol 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. Example 2

The synthesis procedure described in Example 1 was followed using the initial charge and monomer emulsion compositions of Table 1, except that the monomer composition for the Samples 5-8 were changed to include different amounts of petroleum resins (ESCO EZ ECR-149—Exxon Chemical Company, Houston, TX, is a hydrogenat'.u hydrocarbon resin containing 50X aromatidty with a softening point of about 95*C) dissolved in the monomer solution as illustrated in Table 3 below (all ingredient units are in parts by weight). No chain transfer agent was used. ECR-149 has an average molecular weight of about 1000, 50 wt.X aromatidty and similar structure and softening point to the starting resin of resin emulsion ECR-109A. It is obtained by the hydrogenation of such starting resin (ECR-109A ⁾ .

TABLE 3

2-Ethylhexyl

Sampl ? ECR-149 Acryl ic Add Ethyl Acrylate Acrylate

5 10.0 1.6 8.4 30.0 6 11.6 2.3 7.7 28.4 7 11.6 1.5 8.1 28.8 8 15.0 1.4 7.4 26.2

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

TABLE 4

180' Peel SAFT Shear Samples (lbs/1n) CF) (hrs) 5 1.6 290+ 100+ 6 2.4 290+ 100+ 7 2.5 290+ 26 8 3.1 188 22

Comparing the results 1n 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 tacklfier. 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 (B) are the same as Example 1, except that the composition of the monomer solution which also contain the dissolved crosslinkable comonomer according to Table 5 below (all ingredient units are in parts by weight):

TABLE 5

Acryl1c Ethyl 2-Ethylhexyl S-

Samples ECR-149 A d Acrylate Acrylate 2-Z1

9 0 2.0 10.5 37.5 0.00

10 0 2.0 10.5 37.4 0.24

11 0 2.0 10.5 37.4 0.62

12 15 1.4 7.4 26.2 0.00

13 15 1.4 7.4 26.2 0.11

*S-252 is Polyethylene glycol (600 mol.wt.) dimethacirylate manufactured by Sartomer Compan: /

For Samples 10 and 11, the crosslinkable comonomer was mixed with the whole monomer emulsion. For Sample 13, the crosslinkable comonomer was only mixed with the last 25X monomer emulsion added to the reaction vessel. Table 6 below summarized the PSA performances of these samples:

TABLE 6

180* Peel SAFT Shear Sa les (lbs/in) CF.) (hrs) 9 1.1 290+ 100+ 10 1.0 290+ 100+ π 0.53 290+ 100+ 12 3.1 188 22 13 3.1 223. 87

Samples 1 to 3 demonstrate the effect of a crosslinkable comonomer on peel strength with no resin present. The peel strength normally suffers if the degree of the crosslinking is too high. By incorporating hydrocarbon resin in the acrylic copolymer particles, s in Sample 12, significant increase of peel strength is obtained. Sample 13 contains minor amounts of a crosslinkable 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 crosslinkable comonomers was added to the polymerizable solutions incorporating the resin ESCOREZ ECR-149-ID (EXXON), having a softening point of 90.5*C. The crosslinkable comonomer was changed as set forth in Table 7 below to illustrate the properties of the pressure-sensitive adhesives prepared and tested as described above.

TABLE 7

INTERNAL RESIN TACKIFYING ACRYLICS

CONTAINING IX (MOD CROSSLINKABLE COMONOMER

(RESIN USED: ECR-149-1D. SOFTENING POINT - 9P.5 ^« C

Resin

Sample Level Crosslinkable Peel SAFT Shear

Number (PHR) Comonomer (lbs/in) a (hrs)

14 40 Control, No Comonomer 2.6 253 100+

15 40 Glyddyl Acrylate 2.2 300+ 100+

16 40 2-Hydroxyethyl acrylate 2.2 300+ 39

17 40 N-Methylol Acrylamide 2.4 300+ 14

18 40 TMPTMA** 2.4 300+ 54

19 40 PEG-600-DMA***, 0.2X 2.3 280 100+

20 40 PEG-δOO-DMA***, 0.4X 2.4 287 100+

21 50 PEG-600-DMA***, 0.2X 2.7 219 100+

22 50 PEG-600-DMA***, 0.4X 2.6 241 100+

23 50 Control , No Comonomer 2.8 244 100+

**Trimethylolpropane Trimethacrylate (Sartomer-350). ***Polyethylene Glycol (600) Dimethacrylate (Sartomer-252),

Exampl e 5 Following the procedure set forth above 1n Examples 1 and 2, additional internally tackified acrylic copolymers containing crosslinkable comonomers were compared using resins having different softening points, to wit: ESCOREZ ECR-1 9 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 crosslinkable polyfunctional comonomer. As Is apparent from the foregoing description, the materials prepared and the procedures followed describe specific embodiments of the invention. It is 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, it is not intended that the invention be limited except by the appended claims.

TABLE 8

INTERNAL RESIN TACKIFYING ACRYLICS CONTAINING CROSSLINKABLE COMONOMER

1. ECR-149, SOFTENING POINT ■ 95 ^β C; 2. ECR-149-BPC, SOFTENING POINT » 87 ^β C

PSA PERFORMANCE

Level ( )

Sample Crosslinkable of X-l Peel SAFT Shear NυjTtbejc Regin (PHR) Comonomer Cθinonon.eι (lbs/in) (7.) (HOVfS)

24 ECR-1 9 40 PEG-600-DMA 0.2 2. 6 300+ 19 1

25 ECR-149 50 PEG- 600 -DMA 0.2 2.2 300+ 20 o 1

26 ECR-149-BPC 40 PEG-600-DMA 0.2 3 .1 223 87

27 ECR-149-BPC 50 PEG-600-DMA 0.2 3 . 1 131 57

28 ECR-149 40 — 0 3 . 1 188 22

29 ECR-149-BPC 40 — 0 2.7 136 71

30 ECR-149-BPC 50 — 0 3 .3 128 40