JP2005521774A - Rubber-acrylic adhesive formulation - Google Patents

Abstract

The present invention relates to pressure sensitive adhesive formulations of acrylic polymers grafted with hydrogenated rubber. In one embodiment, the polymer comprises a hydroxyalkyl (meth) acrylate ester that is crosslinked with a titanium-containing chelating metal alkoxide. The adhesive formulation provides a unique combination of adhesion to low energy surfaces and high temperature cohesive strength.

Description

  The present invention relates to pressure sensitive adhesive formulations. Specifically, the present invention relates to a pressure sensitive adhesive formulation comprising an acrylic polymer grafted with an ethylene-butylene rubber macromer.

  A typical acrylic pressure sensitive adhesive formulation is a copolymer of alkyl ester monomers and a functional monomer such as acrylic acid, which may be crosslinked using, for example, an aluminum chelate compound. These adhesives generally have poor adhesion to low energy surfaces. Although the adhesive may be tackified with rosin esters to improve low surface energy adhesion, tacking eliminates heat resistance and results in poor aging characteristics. Even if good aging properties are compromised, tackified acrylic dispersions are sufficient for some applications, such as most paper label applications, and are indeed a powerful paper label technology. However, these tackified acrylic adhesives do not have sufficient resistance to degradation for many graphics and industrial tape applications where acrylic solutions are conventionally used.

  Rubber-resin blends are often used for adhesion to polyolefins and other low energy substrates. Typical formulations are natural rubber or styrene block copolymers tackified with rosin esters. These formulations provide excellent tack and cohesive strength, but lead to discoloration and loss of tack due to aging due to oxidative decay and UV-induced decay. In addition to being more expensive, fully hydrogenated rubber or resin formulations usually do not have the required adhesion performance.

  US Pat. No. 5,625,005 describes a hybrid rubber-acrylic pressure sensitive adhesive as having good UV resistance and aging characteristics with high adhesion to non-polar surfaces Has been. Despite this advancement in the field, pressure sensitive adhesives with sufficient adhesion and chemical resistance for industrial tape and transfer film applications and external graphics applications on low energy surfaces where surface adhesion is difficult There remains a need for improved polymer compositions that can be used to produce The present invention addresses this need.

  The present invention provides adhesive formulations with outstanding coating properties that adhere to a wide variety of substrates, including low energy surfaces, while maintaining their performance properties at higher temperatures in the dry state.

  One aspect of the present invention is directed to a pressure sensitive adhesive comprising an acrylic polymer grafted with a rubber macromer. Ethylene-butylene macromers are preferred for use. In one embodiment, the acrylic polymer has at least one low glass transition (Tg) alkyl acrylate monomer containing from about 4 to about 18 carbon atoms in the alkyl group, and a high glass transition (i.e., about At least one monomer having a Tg) higher than 0 ° C. In a preferred embodiment of the invention, the acrylic polymer may further comprise at least one hydroxy functional monomer and / or may also comprise at least one carboxy functional monomer. In a particularly preferred embodiment, a crosslinking agent such as an aluminum crosslinking agent or a titanium crosslinking agent is used.

  Another aspect of the present invention is a pressure sensitive adhesive comprising an acrylic polymer containing at least one low Tg alkyl acrylate monomer containing from about 4 to about 18 carbon atoms in the alkyl group grafted with the rubber macromer. Is directed. Preferably, the macromer is an ethylene-butylene macromer and the polymer is crosslinked using a titanium crosslinker. In a preferred embodiment, the acrylic polymer also comprises at least one high Tg monomer, at least one hydroxy functional monomer and / or at least one carboxy functional monomer in addition to the alkyl acrylate monomer. In order to provide excellent and unexpected high temperature performance, the use of titanium-containing metal alkoxide crosslinkers has been found.

  Yet another aspect of the present invention is directed to a method of making a pressure sensitive adhesive comprising an acrylic polymer grafted with a rubber macromer, preferably an ethylene-butylene macromer. There, the macromer is substantially free of metals or strong acids. Preferably, the molecular weight of the macromer used to make the adhesive is in the range of about 2,000 to about 10,000. The process includes reacting an acrylic polymer component with a rubber macromer component, the macromer component being substantially free of the catalyst used to prepare the macromer component.

  Yet another aspect of the present invention is directed to adhesive articles including pressure sensitive adhesive hybrid polymers, such as industrial tapes, transfer films, and the like. In one particularly preferred embodiment, the hybrid polymer includes ethylene-butylene macromer, 2-ethylhexyl acrylate or similar low Tg acrylic monomer, methyl acrylate or similar high Tg monomer, and preferably such as hydroxyethyl acrylate Hydroxy functional monomers are included.

Detailed Description of the Invention As used herein, the term "pressure-sensitive adhesive" refers to the immediate adhesion to most substrates with the application of a small amount of pressure, and the persistence of stickiness. A viscoelastic material that maintains a Pressure sensitive in the sense of the term as used herein if it has the properties of a pressure sensitive adhesive itself or if it functions as a pressure sensitive adhesive by mixing with pressure sensitive adhesives, plasticizers or other additives. The adhesive is a polymer.

  The adhesive polymers of the present invention include, but are not limited to, ethylene-butylene macromers, ethylene-propylene macromers, and ethylene-butylene-propylene macromers, of acrylic polymers grafted with rubber macromers. It is a rubber-acrylic hybrid polymer containing a main chain. In general, hybrid polymers are obtained by copolymerizing alkyl acrylate ester monomers in the presence of macromers containing reactive acrylic or methacrylic end groups. This leads to a comb copolymer having an acrylic backbone and a macromer branch.

  More particularly, the acrylic polymer backbone intended to be used in the practice of the present invention is formed with acrylate monomers of one or more low Tg alkyl acrylates. Low transition point monomers are those having a Tg of less than about 0 ° C. Preferred alkyl acrylates that may be used in the practice of the present invention have up to about 18 carbon atoms in the alkyl group, preferably from about 4 to about 10 carbon atoms in the alkyl group. The alkyl acrylates used in the present invention include butyl acrylate, amyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, decyl acrylate, dodecyl acrylates, isomers thereof, and combinations thereof. The preferred alkyl acrylate used in the practice of the present invention is 2-ethylhexyl acrylate.

  The monomer system used to produce the acrylic backbone polymer can be based solely on low Tg alkyl acrylate ester monomers, but high Tg monomers and / or functional comonomers, particularly carboxy-containing functionalities It is preferred to modify the monomers and / or more preferably including hydroxy-containing functional monomers.

  High Tg monomer components that may be present, and preferably present in certain embodiments, include methyl acrylate, ethyl acrylate, isobutyl methacrylate, and / or vinyl acetate. The high Tg monomers may be present in total, up to about 50%, preferably from about 5 to about 50%, more preferably from about 10 to about 40% by weight, based on the total weight of the hybrid polymer. .

  The acrylic backbone polymer may include one or more functional monomers. Carboxy functional monomers and / or hydroxy functional monomers are preferred.

  Carboxy functional monomers will usually be present in the hybrid polymer in an amount up to about 7% by weight, more typically from about 1 to about 5% by weight, based on the total weight of the monomers. Useful carboxylic acids preferably contain from about 3 to about 5 carbon atoms and include, among others, acrylic acid, methacrylic acid, itaconic acid and the like. Acrylic acid, methacrylic acid and mixtures thereof are preferred.

  In a particularly preferred embodiment, the acrylic backbone includes hydroxy functional monomers such as hydroxyalkyl (meth) acrylate esters, and acrylic polymers used to form the backbone of the present invention include acrylic Ester / hydroxy (meth) alkyl ester copolymers are preferred. Specific examples of hydroxy functional monomers include hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate and hydroxypropyl methacrylate. Hydroxy functional monomers are generally used in amounts of about 1 to about 10%, preferably about 3 to about 7%.

  Other comonomers can be used to change the Tg of the acrylic polymer, to further enhance adhesion to various surfaces, and / or to enhance shear properties at high temperatures. Such comonomers include N-vinylpyrrolidone, N-vinylcaprolactam, N-alkyl (meth) acrylamides such as t-octylacrylamide, cyanoethyl acrylates, diacetone acrylamide, N-vinylacetamide, N-vinyl. Formamide, glycidyl methacrylate and allyl glycidyl ether are included.

  The monomer ratio of the acrylic polymer is adjusted so that the main chain polymer has a glass transition point of less than about -10 ° C, preferably from about -20 ° C to about -60 ° C.

  Macromers that may be used to obtain graft copolymers are glass transition temperatures of about −30 ° C. or less, preferably about −50 ° C. to about −70 ° C., as determined by differential scanning calorimetry (DSC). Have And they are present in an amount of about 5 to about 50% by weight of the hybrid polymer. Such macromers are commercially available from Kraton Polymers. The molecular weight of the macromer can be in the range of about 2,000 to about 30,000, as determined by gel permeation chromatography (GPC), but the macromers for use in the practice of the invention are preferably about It has a molecular weight in the range of 2,000 to about 10,000.

  In general, saturated rubber macromers can be produced by a number of well-known methods. As described in US Pat. No. 5,625,005, the disclosure of which is hereby incorporated by reference, one method includes, for example, hydroxyl termination formed from 1,3-butadiene and / or isoprene monomers. Anionic polymerization to produce a conjugated diene polymer. As taught in U.S. Reissue Pat. No. 27,145 and U.S. Pat. No. 4,970,254, the disclosures of which are incorporated herein by reference, at least 90% of unsaturation in low molecular weight monools. %, Preferably at least 95% reduction can be achieved by catalytic hydrogenation. Reasonably saturated rubber monools are available from Kraton Polymers. Kraton® L 1203 is the preferred grade. In the final step, the hydroxyl ends are reacted to form acrylate or methacrylate groups by any of a number of known methods. These include, as described in US Pat. No. 5,625,005, by reaction with acid chlorides by using strong acids or metal containing catalysts (eg compounds such as Ti, Sn, etc.) Alternatively, esterification or transesterification by a urethane reaction using a metal catalyst is included.

  Metals or acids remaining in the macromers used to produce adhesives based on rubber acrylic hybrid polymers, especially those containing hydroxyl-functional containing polymers, can adversely affect adhesive properties. Was found here. For some applications, somewhat lower levels of metals or acids may be used, but it is preferred that the macromers are substantially free of the catalyst used in their polymerization. As defined herein, “substantially free” means that the presence of residual catalyst in the polymerized macromer does not cause problems in the production of hybrid polymers. Removal of residual catalyst has already been achieved by using methods well known in the art.

  The hybrid polymer of the present invention may be prepared by conventional polymerization methods well known to those skilled in the art. These methods include, but are not limited to, solution polymerization, suspension polymerization and bulk polymerization. In solution polymerization, graft polymers are synthesized by conventional free radical techniques using a solution mixture. Preferably, a solvent mixture of ethyl acetate, hexane and / or heptane, and toluene provides the solubility required for good coating behavior at low and high coverage. In the practice of the present invention, it may be advantageous to reduce the monomer content remaining after polymerization using conventional methods known in the art.

  Preferred adhesive compositions are preferably cross-linked using a chemical cross-linking agent. Although the use of aluminum and titanium crosslinkers may be employed for the practice of the present invention, the use of titanium-containing metal alkoxide crosslinkers is necessary for high temperature performance and hydroxyalkyl (meth) acrylates. It has been found to be a preferred crosslinking agent for esters. Although the use of a titanium crosslinker imparts a yellow color to the final product, it is hardly a problem in many applications. The crosslinker is usually added in an amount of about 0.3 to about 2% by weight of the hybrid polymer.

The adhesive composition of the present invention is preferably imparted with tackiness. The acrylic and rubber components of the hybrid polymer are believed to form a Miroku phase separation structure in the solid state. The basis for this comes from the fact that two different Tg's are found in the temperature spectrum of the viscoelastic properties corresponding to each component. Tackifying resins useful in these compositions are compatible with the rubber macromer phase. A tackifier that is compatible with the acrylic phase can of course be used with any acrylic polymer, and the hybrid polymer of the present invention is no exception. However, such tackifiers are usually derived from natural rosin and have unsatisfactory aging characteristics. It is an object of the present invention to eliminate these problems. Accordingly, preferred tackifiers are synthetic hydrocarbon resins derived from petroleum. Non-limiting examples of rubber phase association resins include aliphatics such as those available from Goodyear under the trade name "Wingtack" (registered trademark) and from Exxon as "Escorez" (registered trademark) 1300 series Olefin derivative resins are included. Tackifying resin typical C ₅ in this class, diene piperylene and 2-methyl-2-butene - an olefin copolymer has a softening point of about 95 ° C.. This resin is commercially available under the trade name “Wingtack”. The resin usually has a ring and ball softening point of about 20 ° C. to 150 ° C. as determined by ASTM method E28. From Exxon Corporation "Escorez" ® aromatic C ₉ available in 2000 Series / aliphatic olefin-derived resins are also useful. Hydrogenated hydrocarbon resins are particularly useful when long term resistance to oxidation and UV exposure is required. These hydrogenated resins include resins such as “Escorez” 5000 series of hydrogenated alicyclic resins from Exxon, and “Arcon” (registered trademark) series resins by Arakawa Chemical Industries. resins of C ₉ and / or C ₅ hydrogenated, such as, such as "Regairez" (registered trademark) 1018,1085 and "Regalite" (registered trademark) R series resins from Hercules Specialty Chemicals Inc. Hydrogenated aromatic hydrocarbon resins are included. Other useful resins include hydrogenated polyterpenes such as “Clearon” ® P-105, P-115, and P-125 from Japan's Anne Crude Oil Industry.

  The tackifying resin is usually present at a level of 5-50% by weight of the adhesive composition, preferably at a level of 10-40% by weight of the adhesive composition.

  Formulated adhesives include excipients, diluents, emollients, plasticizers, antioxidants, anti-irritants, opacifiers, fillers such as clay and silica, pigments And mixtures thereof, preservatives, as well as other ingredients or additives.

  The pressure sensitive adhesives of the present invention can be advantageously used in the manufacture of adhesive articles, including but not limited to industrial tapes and transfer films. The adhesive articles are useful over a wide temperature range, have improved UV resistance, polyolefins such as polyethylene and polypropylene, polyvinyl fluoride, ethylene vinyl acetate, acetal, polystyrene, powder coating Adheres to a wide variety of substrates, including low energy surfaces such as paints. Single-sided tapes and double-sided tapes, as well as backing films and single films are included in the scope of the present invention. Labels, decals, nameplates, decorative and reflective materials, reclosable fasteners, anti-theft and anti-imitations are included, but are not limited thereto.

  In one embodiment, an adhesive article includes an adhesive applied to at least one major surface of a backing having first and second major surfaces. Useful backing substrates include, but are not limited to, foams, metals, fibers, and various polymer films such as polypropylene, polyamide and polyester. The adhesive may be present on one or both surfaces of the backing. If the adhesive is applied to both surfaces of the backing, the adhesive on each surface can be the same or different.

  In the following examples, the following test methods were used.

Coating Preparations Adhesive solutions were cast on a silicone coated release liner, air dried for 15 minutes and then dried at 250 ° C. for 3 minutes in a forced air oven. The films were then laminated to the back film and conditioned overnight at 22 ° C. and 50% relative humidity. Unless otherwise indicated, the dried adhesive film thickness was 1 mil (25 microns) and the back film was a 2 mil polyester film.

Peel Adhesion The peel adhesion at 180 degrees between the backing and the adhesion test panel was measured according to Test Method No. 1 of Pressure Sensitive Tape Council (PSTC) in Northbrook, Illinois as follows. The peel strength was measured after the stainless steel (SS) panel was wetted for 20 minutes or as otherwise indicated. The test was also performed on high density polyethylene (HDPE) panels. Unless otherwise indicated, all tests were conducted at 22 ° C. and 50% relative humidity.

Shear fixing force Shear fixing force was measured according to PSTC test method number 7 as follows. After the test panel was wetted for 15 minutes, the fixing force was measured in a state where a shear load of 1 kg was applied to an area of 0.5 inch (1.3 cm) × 1 inch (2.5 cm). The test was also performed on high density polyethylene (HDPE) panels. Unless otherwise indicated, all tests were conducted at 22 ° C. and 50% relative humidity.

Shear fracture temperature (SAFT)
SAFT measurements were made by placing a 1 inch × 1 inch bonded specimen in a 140 ° F. (60 ° C.) oven under a 1 kg shear load (wet at room temperature for 15 minutes before applying the load). ) The oven temperature was then increased by 10 ° F. every 10 minutes and the temperature was recorded until the bond broke.

Example 1
This example illustrates the preparation of a hybrid polymer solution using a methacrylate-terminated macromer substantially free of strong acid or metal catalyst. The average molecular weight of the macromer was measured by GPC in relation to polystyrene standards and was found to be 6600 daltons for Mn and 7200 daltons for Mw.

  59.73 g of 2-ethylhexyl acrylate (2-EHA), 22.72 g of ethylene-butylene macromer, 17.05 g of methyl acrylate (MA), 5.67 g of 2-hydroxyethyl acrylate (2-HEA), An initial charge mixture containing 55.0 g of ethyl acetate (EtOAc), 64.19 g of hexanes (standard mixed with isomer grade), and 0.28 g of azobis (isobutyronitrile (AIBN)) was prepared. Charged to a 4-necked 3 liter round bottom flask equipped with a stainless steel stirrer, thermometer, condenser, water bath, and funnel slowly added.The initial charge was heated to reflux with stirring. After 10 minutes, 229.0 g of 2-EHA, 128.59 g of ethylene-butylene macromer, 65.45 g of MA, 21.84 g of 2-HEA, hex A monomer mixture containing 27.5 g of Suns and an initiator mixture containing 236.5 g of EtOAc, 55.0 g of hexanes and 1.38 g of AIBN, separately at the same time and over a period of 2 and 3 hours. The contents of the flask were maintained at reflux for an additional 2 hours from the end of the addition, and then the residual monomers were added by a short half-life initiator added over 1 hour. The solution was refluxed for an additional hour and then a diluent consisting of 183.3 g toluene was slowly added to the contents while the reactor contents were cooled to room temperature. The polymer solution maintained fluid viscosity throughout the reaction and showed no tendency to climb the stirring mandrel of the reactor.

  The polymer solution had a solids content of 42.7% and a Brookfield viscosity of 2500 mPa · s. The average molecular weight determined by gel permeation chromatography was Mw 560,000 and Mn 34,000.

Examples 2 and 3
Since it has been found that the use of a strong acid catalyst or a metal catalyst used to adjust the macromer has an adverse effect, an experiment to examine the action of the strong acid catalyst on the polymerization process (Example 2), and polymerization An experiment (Example 3) was conducted to examine the effect of the metal catalyst on the process.

Example 2
A series of polymers were prepared according to the procedure described in Example 1. The macromers used to prepare this series of polymers contained p-toluenesulfonic acid (p-TSA) at various concentrations. The adverse effects of high levels of p-TSA are shown in Table 1. At high levels of acid, network formation in the polymer dramatically increased the solution viscosity during the process. This ultimately leads to gel formation and unusable products. This problem is first revealed as the tendency of the solution to climb the stirring mandrel. This phenomenon is known as the Weissenberg effect. It causes poor agitation and increases torque, thus requiring additional power to maintain agitation. In extreme cases, it can damage the bearing and seal of the mandrel. Even if it is not gelled, the resulting polymer will have poor flowability and leveling during the adhesive coating process.

Example 3
A polymer solution was prepared according to Example 1. The macromers used to prepare these polymers contained tin at various concentrations. The adverse effects of high levels of tin are shown in Table 2.

Example 4
A polymer solution was prepared according to Example 1 using an equimolar concentration of hydroxypropyl methacrylate in place of the HEA monomer. The macromers used to prepare these polymers contained tin at various concentrations as provided in Table 3. There are no problems in the polymerization process and high levels of tin can be tolerated with this monomer.

Example 5
This example illustrates polymer preparation with and without high Tg acrylic comonomer. Two series of hybrid polymers were prepared according to the procedure of Example 1 except that the diluted solution was ethyl acetate. In its second series, HEA monomer was used instead of acrylic acid (AA). The experimental design investigated the effect of hydroxyl functionality on the use of high Tg monomers, the level of macromers, and the effect of carboxyl functionality. The results are shown in Table 4.

  In the case of polymer solution D, the viscosity was very high, but this procedure allowed all the compositions in the design to be prepared. To help control the viscosity, as used in Example 1, dilution with hydrocarbon or aromatic hydrocarbon solvent instead of ethyl acetate is preferred. The molecular weights determined by GPC are all high.

Example 6
This example illustrates the adhesion performance test for the polymers prepared in Example 5. Samples were tested according to the procedure described above. The results are shown in Table 5.

  The results show that very poor shear strength is obtained in the absence of methyl acrylate, which is a high Tg monomer.

Example 7
This example shows the effect of adding a titanium crosslinking agent to the polymer solution in Example 5. Sample D and Sample I were removed because they already exhibited good cohesive strength. A solution consisting of 12.3 g isopropyl alcohol, 15.3 g 2,4-pentanediol and 2.4 g Tyzor® GBA (available from Du Pont, Wilmington, Del.) Was prepared. Tyzor GBA is a 75% alcohol solution of bis (2,4-pentandionate-O, O ′) bis (2-propanolate) -titanium. The crosslinker solution was stirred into the polymer solution at the indicated concentration (weight to polymer weight) and the adhesion performance was measured. The results are shown in Tables 6 and 7.

  This indicates that although the titanium crosslinker effectively increases the cohesive strength, for high cohesive strength it is necessary to have a high Tg monomer in the polymer composition (Sample C, Compare E with samples A and B, and compare samples H and J with samples F and G). Although a trade-off between adhesive strength and cohesive strength is expected with the addition of a cross-linking agent, it appears that the peel strength of the hydroxy-functional polymers F and G drops dramatically even on stainless steel. It is done.

Example 8
This example shows the compatibility of the hydrocarbon tackifying resin with the polymers in Example 5. These tackifying resins were dissolved in the polymer solution in high addition amounts (60 parts tackifier for 100 parts polymer on dry weight basis). The solutions were cast on glass plates, dried and visually inspected for transparency. The transparent one was judged to be compatible. The tackifiers used in this experiment were Wingtack® 95, a C ₅ resin available from Goodyear, and Escorez 2596, an aromatic / aliphatic resin available from ExxonMobile. there were. The results are shown in Table 8 with C indicating compatibility and I indicating incompatibility.

  These results indicate that the less polar hydroxy functional polymers have a wider compatibility than the carboxy functional materials. They also show that hydroxy-functional polymers containing methyl acrylate, which is a high Tg monomer, i.e. samples H, I and J are compatible and not containing them, i.e. samples F and G are not compatible. Also shows unexpectedly.

Example 9
This example illustrates the effect on the adhesive performance of the formulated with C ₅ aliphatic hydrocarbon tackifying resin. A series of mixtures were prepared with increasing levels of tackifier. On a dry weight basis, 10 parts, 20 parts and 40 parts Wingtack 95, 0.8 parts Tyzor GBA, and 0.5 parts Irganox® 1010 (Ciba Specialty Chemicals) for 100 parts polymer J Antioxidants sold by the company) were mixed into the solution. The adhesion performance was measured according to the method in Example 6. For comparison, using two acrylic polymers sold by the National Starch and Chemical Company, DURO-TAK® 72-8746 (referred to as A) and DURO-TAK 80-1105 (referred to as B) Formulations were made at 15 parts and 40 parts, respectively, with respect to rosin ester tackifier 100. The results are shown in Table 9.

  The results show that the hybrid polymer has excellent responsiveness to tackifiers and provides a substantial increase in peel strength on stainless steel and especially on HDPE, which is a low surface energy substrate It is shown that. The hybrid pressure sensitive adhesive of the present invention has a cohesive strength much higher than that of acrylic at a high addition amount of a tackifier, and therefore exhibits an excellent balance in properties. Unexpectedly, the heat resistance measured by SAFT is significantly higher for hybrid pressure sensitive adhesives, and the higher cohesive strength is superior to acrylic with very little addition of tackifier.

Example 10
This example demonstrates the effect on adhesion performance of blending with a hydrogenated alicyclic hydrocarbon tackifying resin. The mixture was prepared as described in Example 8 using 40 parts Escorez 5415 and 40 parts Escorez 5600 for 100 parts polymer J. The crosslinker was 1.2 parts Tyzor GBA per 100 parts polymer. Escorez 5415 is a hydrogenated alicyclic resin having a ring and ball softening point of 118 ° C. Escorez 5600 is a hydrogenated aromatic modified alicyclic resin having a ring and ball softening point of 103 ° C. Both adhesives gave transparent films that were compatible with the polymer. The adhesive coating thickness was 2 mils, and the adhesion performance was measured according to the method in Example 6. The results are shown in Table 10. For comparison, the results for Wingtack 95 are shown under similar formulation parameters and test conditions.

  The results show that the hybrid polymers are compatible with hydrogenated cycloaliphatic resins and that these resins provide additional heat resistance at a slight cost in peel strength on HDPE, which is a low energy substrate. It is shown that.

Example 11
In this example, the titanium crosslinker is compared to the aluminum crosslinker. Expressed based on the weight of the dry polymer, a polymer solution was prepared and formulated according to Example 1 using 40% Wingtack 95 and 0.8% Tyzor GBA (75% active). A second solution was prepared in the same manner except that Tyzor was replaced with an equivalent concentration (0.7%) of aluminum tris (acetylacetonate). Then, according to the above procedure, these adhesives were applied and tested. The results are shown in Table 11.

  Tests have shown that aluminum crosslinkers are not effective in developing cohesive strength compared to titanium. In order to confirm the superiority of the titanium cross-linking agent in the present invention, two samples were further prepared and tested at a high aluminum concentration. The results shown in the table above show that increasing aluminum has a slightly positive effect on shear strength but reduces peel adhesion.

Example 12
This example shows the effect of having both hydroxyl and carboxyl functionality in the polymer. A polymer solution was prepared by the method of Example 1 using 4 wt% HEA and 1 wt% AA in place of 5 wt% HEA in the example polymer. This is referred to as polymer K. A second polymer solution, designated L, was prepared using 0.15 wt% glycidyl methacrylate as an additional component. The adhesion performance of these polymers, tested at a dry coat thickness of 2 mils without any additional formulation, is shown in Table 12.

  Both polymers K and L showed excellent performance as unblended base polymers. In particular, high cohesion and heat resistance provide compatibility for a wide range of formulations, accept additional tackifiers, and / or reduce the level of crosslinker. See Example 13.

Example 13
This example shows that polymers with a combination of hydroxyl and carboxyl functionality can be formulated to provide substantially improved heat resistance while maintaining a high level of peel adhesion. ing. This example further shows that aluminum crosslinkers can also be used in this case. As shown in Table 13, a polymer solution was blended with Wingtack 95 tackifying resin and a crosslinking agent. Their weight is expressed based on the weight of the solid polymer. The coating thickness of the adhesive was 2 mil.

  These results indicate that a very large improvement in heat resistance has been achieved. They further show that an aluminum crosslinker can be used with polymer L with some sacrifice in heat resistance but a good balance in properties. This should be compared to the poor results obtained when trying to crosslink the hydroxy functional polymer of Example 1 with aluminum (see Example 11). The use of aluminum may be desirable in applications where it is important to be colorless.

  It will be apparent to those skilled in the art that many modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. The specific embodiments described herein are provided by way of example only, and the present invention should be limited only by the language of the claims, with sufficient scope to which the claims are given Is.

Claims (43)

  A pressure sensitive adhesive comprising an acrylic polymer grafted with a rubber macromer, the polymer comprising at least one alkyl acrylate monomer containing from about 4 to about 18 carbon atoms in the alkyl group, and about 0 ° C A pressure sensitive adhesive comprising at least one monomer having a higher glass transition point.   The adhesive of claim 1, wherein the macromer comprises poly (ethylene-butylene), poly (ethylene-propylene) or poly (ethylene-butylene-propylene).   The adhesive of claim 1, wherein the macromer has a molecular weight of about 2,000 to about 10,000.   The adhesive of claim 1, wherein the macromer has a glass transition point of from about -50C to about -70C.   The adhesive according to claim 1, wherein the polymer further comprises at least one hydroxy-functional monomer and / or at least one carboxy-functional monomer.   The adhesive of claim 5, wherein the polymer comprises at least one hydroxy functional monomer.   The adhesive of claim 5, wherein the polymer comprises at least one carboxy functional monomer.   The adhesive of claim 5, wherein the polymer further comprises a glycidyl methacrylate monomer.   The adhesive according to claim 7, wherein the polymer is crosslinked using an aluminum crosslinking agent.   The adhesive of claim 7, wherein the polymer also comprises a hydroxy functional monomer.   The adhesive of claim 9, wherein the polymer also comprises a hydroxy functional monomer.   The adhesive of claim 6, wherein the polymer comprises 2-ethylhexyl acrylate, methyl acrylate and hydroxyethyl acrylate or hydroxypropyl methacrylate.   The adhesive of claim 12, wherein the polymer comprises 2-ethylhexyl acrylate, methyl acrylate and hydroxypropyl methacrylate, and further comprises acrylic acid.   The adhesive of claim 12, wherein the polymer comprises 2-ethylhexyl acrylate, methyl acrylate and hydroxyethyl acrylate, and further comprises acrylic acid.   The adhesive of claim 1 further comprising a tackifier.   The adhesive of claim 15, wherein the tackifier is a hydrocarbon tackifier.   The adhesive of claim 16, wherein the tackifier is a hydrogenated hydrocarbon tackifier.   A pressure sensitive adhesive comprising an acrylic polymer grafted with a rubber macromer, the polymer comprising at least one alkyl acrylate monomer containing from about 4 to about 18 carbon atoms in the alkyl group. And wherein the polymer is crosslinked using a titanium crosslinking agent.   The adhesive of claim 18, wherein the macromer comprises poly (ethylene-butylene), poly (ethylene-propylene) or poly (ethylene-butylene-propylene).   The adhesive of claim 18, wherein the macromer has a molecular weight of about 2,000 to about 10,000.   The adhesive of claim 18, wherein the macromer has a glass transition point of from about -50C to about -70C.   The adhesive of claim 18, wherein the polymer further comprises at least one monomer having a glass transition point greater than about 0 ° C.   The adhesive of claim 18, wherein the polymer further comprises at least one hydroxy functional monomer and / or at least one carboxy functional monomer.   24. The adhesive of claim 23, wherein the polymer comprises a hydroxy functional monomer.   24. The adhesive of claim 23, wherein the polymer comprises a carboxy functional monomer.   24. The adhesive of claim 23, wherein the polymer further comprises a glycidyl methacrylate monomer.   The adhesive of claim 24, wherein the polymer comprises 2-ethylhexyl acrylate.   28. The adhesive of claim 27, wherein the polymer further comprises methyl acrylate and hydroxyethyl acrylate or hydroxypropyl methacrylate.   29. The adhesive of claim 28, wherein the polymer comprises 2-ethylhexyl acrylate, methyl acrylate and hydroxypropyl methacrylate, and further comprises acrylic acid.   29. The adhesive of claim 28, wherein the polymer comprises 2-ethylhexyl acrylate, methyl acrylate and hydroxyethyl acrylate, and further comprises acrylic acid.   The adhesive of claim 18 further comprising a tackifier.   32. The adhesive of claim 31, wherein the tackifier is a hydrocarbon tackifier.   The adhesive of claim 32, wherein the tackifier is a hydrogenated hydrocarbon tackifier.   A method for producing a pressure sensitive adhesive by reacting an acrylic polymer component with a rubber macromer component, wherein the macromer component is substantially free of the catalyst used to prepare the macromer component Method.   35. The method of claim 34, wherein the macromer comprises poly (ethylene-butylene), poly (ethylene-propylene) or poly (ethylene-butylene-propylene).   35. The method of claim 34, wherein the macromer is substantially free of metal-containing catalyst.   35. The method of claim 34, wherein the macromer is substantially free of strong acid catalyst.   35. The method of claim 34, wherein the macromer has a molecular weight of about 2,000 to about 10,000.   35. The method of claim 34, wherein the macromer has a glass transition point of about -50C to about -70C.   A product comprising the adhesive of claim 1.   41. The product of claim 40, which is a pressure sensitive adhesive tape.   A product comprising the adhesive of claim 18.   43. The product of claim 42, wherein the product is a pressure sensitive adhesive tape.