Pressure sensitive adhesives

Abstract

Pressure sensitive adhesive (PSA) compositions that include at least one urethane (meth)acrylate oligomer having a molecular weight between about 2,000 g/mol and about 50,000 g/mol and an OH number of from 0.01 mg KOH/g to 100 mg KOH/g, at least one mono (meth)acrylate functional monomer and at least one tackifying resin. The PSA systems may also optionally include other additives, such as at least one initiator system that includes at least one photo-initiator or free radical initiator. The PSA systems are liquid at a temperature of 25° C.±2° C. with a viscosity of 15,000 cPs or less and are adapted to form smooth, uniform coatings or films upon curing without the application of heat, whereby the resulting films have advantageous properties with respect to peel strength, tack and shear resistance. In embodiments, the PSA systems include less than 1 wt % of solvent and less than 1 wt % of water or are free of solvent and are free of water.

Claims

1. A curable composition comprising: a) about 30 wt % to 75 wt % of at least two urethane (meth)acrylate oligomers, each of said oligomers having an average in number molecular weight Mn of from 2,000 g/mol to 50,000 g/mol; b) about 10 wt % to 60 wt % of at least one mono (meth)acrylate functional monomer; c) about 1 wt % to 50 wt % of at least one tackifying resin; and d) up to 5 wt % of at least one initiator system; e) up to 5 wt % of at least one multifunctional monomer; f) up to 3 wt % of at least one wetting agent; and g) optionally, other additives, wherein the sum of percentages of a) + b) + c) + d) + e) + f) + g) is 100%; and wherein the at least two urethane (meth)acrylate oligomers have a mean OH value from 2 mg KOH/g to 50 mg KOH/g and an average in number-functionality of 1.2 to 1.8 (meth)acrylates.

2. The curable composition of claim 1, wherein the d) at least one initiator system comprises at least one photo-initiator selected from the group consisting of α-hydroxyketones, phenylglyoxylates, benzyldimethylketals, α-aminoketones, mono-acyl phosphines, bis-acyl phosphines, phosphine oxides and metallocenes and combinations thereof.

3. The curable composition of claim 1, wherein component a) has an average in number-functionality of from 1.3 to 1.7 (meth)acrylates.

4. The curable composition claim 1, wherein said composition has a glass transition temperature Tg of 20° C. or less when cured or wherein the composition is liquid at a temperature of 25° C. ±2° C.

5. The curable composition of claim 4, wherein the c) at least one tackifying resin c) is hydrogenated.

6. The curable composition of claim 1, wherein the composition comprises less than 1 wt % of non-reactive solvent and less than 1 wt % of water.

7. The curable composition of claim 1, wherein the c) at least one tackifying resin has a softening temperature of 80° C. or less.

8. The curable composition of claim 1, wherein the b) at least one mono (meth)acrylate functional monomer is selected from the group consisting of alkoxylated tetrahydrofurfuryl acrylate, isobornyl acrylate, tetrahydrofurfuryl acrylate, caprolactone acrylate, 2(2-ethoxyethoxy) ethyl acrylate, 2-phenoxyethyl acrylate, tetrahydrofurfuryl methacrylate, isooctyl acrylate, 2-octyl acrylate, 2-ethylhexyl acrylate and combinations thereof.

9. The curable composition of claim 1, wherein the c) at least one tackifying resin is selected from the group consisting of piperylene-based hydrocarbon resins which may be hydrogenated and hydrogenated or non-hydrogenated rosin esters, modified by maleic anhydride rosin esters.

10. The curable composition of claim 1, wherein said composition is an adhesive curable composition which is a pressure sensitive adhesive curable composition.

11. The curable composition of claim 1, wherein the b) at least one mono (meth)acrylate functional monomer is selected from the group consisting of alkoxylated tetrahydrofurfuryl acrylate and isobornyl acrylate.

12. The curable composition of claim 1, wherein each of said urethane (meth)acrylate oligomers a) has an average in number molecular weight Mn of from 5,000 g/mol to 25,000 g/mol.

13. The curable composition of claim 1, wherein the d) at least one initiator system comprises 1-hydroxy-cyclohexyl-phenyl ketone.

14. A film, wherein it is formed by curing a curable composition as defined in claim 1.

15. A method of coating a substrate comprising: applying the curable composition as defined in claim 1 to a substrate and then curing said curable composition, wherein the curing comprises curing by exposure to one of the group consisting of visible radiation, UV radiation, LED radiation, laser radiation, electron-beam radiation, peroxide, peroxide and an accelerator, heat and combinations thereof.

16. The method of claim 15, wherein the said applying comprises applying by spraying, knife coating, roller coating, casting, drum coating, dipping and combinations thereof.

17. A cured composition, wherein it is obtained by the curing of a curable composition as defined in claim 1.

18. The cured composition of claim 17, wherein it is a cured adhesive composition.

19. The cured composition of claim 17, wherein it is a cured coating composition.

20. The cured composition of claim 17, wherein said cured composition is a pressure sensitive adhesive in the form of an adhesive tape, an adhesive sheet, an adhesive spray, a product package, a product label, a construction article or a medical product.

21. The cured composition of claim 20, wherein it is for packaging, labelling, construction, model making, medicine and construction applications.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The PSA systems described herein may comprise at least one urethane (meth)acrylate oligomer, at least one mono (meth)acrylate functional monomer and at least one tackifying resin. In embodiments, the a) at least one urethane (meth)acrylate oligomer, the b) at least one mono (meth)acrylate functional monomer and the c) at least one tackifying resin make up 100% by weight of the PSA systems described herein. The PSA systems may also optionally comprise other additives, such as an additive selected from the group consisting of photo-initiators, multifunctional monomers, wetting agents, adhesion promoters, fillers, rheology modifiers, thixotropic agents, plasticizers, UV absorbers, UV stabilizing agents, dispersants, antioxidants, antistatic agents, lubricants, opacifying agents, anti-foam agents, rheology agents and the like and combinations thereof.

(2) I—Urethane (Meth)Acrylate Oligomer a)

(3) In embodiments, The PSA systems described herein may comprise at least one urethane (meth)acrylate oligomer. In embodiments, the at least one urethane (meth)acrylate oligomer comprises a mixture of at least two urethane (meth)acrylate oligomers with select chains terminated by two (meth)acryloyl groups and/or select chains terminated by one (meth)acryloyl group and one free OH group. In embodiments, the at least one urethane (meth)acrylate oligomer comprises a urethane (meth)acrylate according to formula (I):

(4) ##STR00002##

(5) In embodiments, the at least one urethane (meth)acrylate oligomer may be a bio-based urethane oligomer. In embodiments, the at least one urethane (meth)acrylate oligomer may be derived from polyethers, polyesters, polycarbonates, polybutadienes, diols or from their mixtures. In embodiments, the at least one urethane (meth)acrylate oligomer may be derived from polyesters including poly-condensation polyesters resulting from reaction of: 1) polyols and carboxylic polyacids and 2) anhydrides and polyesters resulting from ring opening polymerization of lactones, such as caprolactone.

(6) In embodiments, the at least one urethane (meth)acrylate oligomer has an n value (e.g., the number of urethane repeating units) from 2 to 20 or from 3 to 10 or from 3 to 5. Preferably, m (e.g., the number of methylene repeating units) may have a value from 2 to 4. The at least one urethane (meth)acrylate oligomer may have a backbone comprising free OH groups, wherein a mean OH value may be from about 0.01 mg KOH/g and about 100 mg KOH/g or from about 0.5 mg KOH/g to about 100 mg KOH/g or from about 1 mg KOH/g to about 50 mg KOH/g or from about 2 mg KOH/g to about 50 mg KOH/g or from about 3 mg KOH/g to about 10 mg KOH/g.

(7) In embodiments, the at least one urethane (meth)acrylate oligomer has an average in number-functionality, in (meth)acrylates, of from about 1 to about 2 (meth)acrylates or from about 1.1 to about 1.9 (meth)acrylates or from about 1.2 to about 1.8 (meth)acrylates or from about 1.3 to about 1.7 (meth)acrylates or less than 2 (meth)acrylates. In some cases, the average in number functionality with respect to terminal (meth)acryloyl groups means that the complement to 2 of the global functionality does correspond to the OH group mean functionality.

(8) In embodiments, R.sub.1 may be a diisocyanate radical selected from the group consisting of alkylene, cycloalkylene, arylene, arylalkylene and combinations thereof; R.sub.2 may be a diol radical selected from the group consisting of alkylenes, cycloalkylenes, arylalkylenes and combinations thereof; R.sub.3 comprises a moiety of R.sub.4—OH that has a mean OH value of about 0.01 mg KOH/g to about 100 mg KOH/g and R.sub.3 comprises a moiety of —R.sub.5-(meth)acryloyl; R.sub.4 and R.sub.5 being a bivalent radical selected from the group consisting of alkylenes, cycloalkylenes, arylalkylenes and combinations thereof.

(9) In embodiments, the at least one urethane (meth)acrylate oligomer may have a molecular weight of from about 1,000 g/mol to about 200,000 g/mol or from about 2,000 g/mol to about 50,000 g/mol and preferably between about 5,000 g/mol and about 25,000 g/mol. In embodiments, the at least one urethane (meth)acrylate oligomer may be present in the adhesive composition at from about 5% to about 90% by weight or from about 10% to about 85% by weight or from about 20% to about 80% by weight or from about 30% to about 75% by weight or from about 40% to about 60% by weight.

(10) II—Mono (Meth)Acrylate Functional Monomer b)

(11) In embodiments, the at least one mono (meth)acrylate functional monomer may be present in the composition at from about 1% to about 80% by weight or from about 2% to about 75% by weight or from about 3% to about 70% by weight or from about 5% to about 65% by weight or from about 10% to about 60% by weight or from about 20% to about 40% by weight.

(12) In embodiments, the at least one mono (meth)acrylate functional monomer may be selected from the group consisting of alkoxylated tetrahydrofurfuryl acrylate (SR611), isobornyl acrylate (SR506), tetrahydrofurfuryl acrylate (SR285), caprolactone acrylate (SR495B), 2-(2-ethoxyethoxy) ethyl acrylate (SR256), 2-phenoxyethyl acrylate (SR339), tetrahydrofurfuryl methacrylate (SR203), isooctyl acrylate (SR440), 2-octyl acrylate, 2-ethylhexyl acrylate and combinations thereof.

(13) III—Tackifying Resin c)

(14) In embodiments, the at least one tackifying resin may comprise a hydrogenated C.sub.4 hydrocarbon resin (such as piperylene-based) or hydrogenated or non-hydrogenated rosin esters, including those modified by maleic anhydride rosin esters. In embodiments, the at least one tackifying resin is hydrogenated. In embodiments, the at least one tackifying resin has a softening temperature of 80° C. or less. In embodiments, the at least one tackifying resin may be present in the adhesive composition at from about 1% to about 50% by weight or from about 2% to about 35% by weight or from about 3% to about 25% by weight or from about 4% to about 15% by weight or from about 5% to about 10% by weight.

(15) In embodiments, the at least one tackifying resin may be selected from the group consisting of Sylvatac® RE 25, Sylvatac® RE 40, Sylvalite® RE 10L, Sylvalite® 80HP (Arizona Chemical), Teckros® HRL and Teckros® RL5 (Teckrez).

(16) IV—Other Additives

(17) In embodiments, the PSA systems may also optionally comprise other additives, such as one or more of photo-initiators, multifunctional monomers, wetting agents, adhesion promoters, fillers, rheology modifiers, thixotropic agents, plasticizers, UV absorbers, UV stabilizing agents, dispersants, antioxidants, antistatic agents, lubricants, opacifying agents, anti-foam agents, rheology agents and the like and combinations thereof may be included.

(18) In embodiments, sufficient amounts of an initiator system comprising at least one photo-initiator may be optionally included in the compositions so as to render the compositions curable with radiant energy, such as UV light. Preferably, the compositions may include from about 0.1% by weight to about 20% by weight of the initiator system, preferably about 2% to about 15% by weight. Suitable photo-initiators for use in the compositions described herein may include compounds selected from the group consisting of α-hydroxyketones, phenylglyoxylates, benzyldimethylketals, α-aminoketones, mono-acyl phosphines, bis-acyl phosphines, phosphine oxides, metallocenes and combinations thereof. In embodiments, the at least one photo-initiator may be 1-hydroxy-cyclohexyl-phenyl-ketone.

(19) In embodiments, the compositions described herein do not comprise any initiator and are rendered curable with electron beam energy.

(20) In embodiments, sufficient amounts of an initiator system comprising at least one free radical initiator and/or accelerator may be optionally included in the compositions so as to render the compositions as chemically curable. Preferably, the compositions may include from about 0.1% by weight to about 20% by weight of the initiator system, preferably about 2% to about 15% by weight. Suitable free radical initiators for use in the compositions described herein may include peroxides and hydro-peroxides and suitable accelerators may include tertiary amines or other reducing agents based on metal salts. Such chemical curing may also take place at lower temperatures when using accelerators.

(21) In embodiments, sufficient amounts of at least one multifunctional monomer and/or wetting agent may be optionally included in the composition. Such additives may be present in the compositions described herein from about 0.1% by weight to about 20% by weight or from about 1% to about 10% by weight.

(22) In embodiments, the PSA systems do not contain adhesion promoters and are free of adhesion promoters, as the systems themselves possess sufficient adhesion properties.

(23) In embodiments, the compositions comprise less than 5% by weight of solvent and less than 5% by weight of water or less than 3% by weight of solvent and less than 3% by weight of water or less than 1% by weight of solvent and less than 1% by weight of water or less than 0.5% by weight of solvent and less than 0.5% by weight of water. Preferably, the compositions do not comprise any solvent and do not comprise any water. The solvents may be non-reactive solvents including ketones such as acetone or methyl ethyl ketone, alkyl acetates such as ethyl acetate or butyl acetate, alcohols such as isopropyl alcohol and ethanol, alkanes such as hexane, alkenes such as toluene and combinations thereof. By non-reactive solvents, it is meant solvents that are saturated and not available for participation in polymerization.

(24) In embodiments, the PSA systems have a glass transition temperature, Tg, of about 20° C. or less when cured or about 10° C. or less when cured or about 0° C. or less when cured and may range from about 20° C. to about −30° C. when cured. The glass transition temperatures may be determined by the DMA method with a sweep rate of 3° C. per minute.

(25) One subject of the present invention relates to a curable composition comprising: a) 30 wt % to 75 wt %, preferably 40 wt % to 60 wt % of at least one urethane (meth)acrylate oligomer having an average in number molecular weight Mn (measured by GPC) of from 2,000 g/mol to 50,000 g/mol, preferably 5,000 g/mol to 25,000 g/mol; b) about 10 wt % to 60 wt %, preferably 20 wt % to about 40 wt % of at least one mono (meth)acrylate functional monomer; c) about 1 wt % to 50 wt %, preferably 2 wt % to 35 wt % of at least one tackifying resin; and optionally d) up to 5 wt % of at least one initiator system; e) up to 5 wt % of at least one multifunctional monomer; f) up to 3 wt % of at least one wetting agent; and g) other additives. with the sum of % of a)+b)+c)+d)+e)+f)+g) being 100%.

(26) The d) component is more particularly present and said d) at least one initiator system comprises at least one photo-initiator, preferably selected from the group consisting of α-hydroxyketones, phenylglyoxylates, benzyldimethylketals, α-aminoketones, mono-acyl phosphines, bis-acyl phosphines, phosphine oxides and metallocenes and combinations thereof and is preferably 1-hydroxy-cyclohexyl-phenyl ketone.

(27) More particularly, components a)+b)+c) is equal to 100% by weight of the said curable composition which composition comprises only components a), b) and c).

(28) The said curable composition can have a glass transition temperature Tg of 20° C. or less when cured, preferably of 0° C. or less when cured (Tg measured by Dynamic mechanical analysis experiments at a frequency of 1 Hz and heating rate of 3° C./min) or the said composition may be liquid at a temperature of 25° C.±2° C. and more particularly said composition comprises less than 1 wt % of non-reactive solvent and less than 1 wt % of water, preferably the composition being free of non-reactive solvent and being free of water.

(29) The said other additives h) may be selected from the group consisting of matting agents, colorants, dyes, pigments, adhesion promoters, fillers, rheology modifiers, thixotropic agents, plasticizers, UV absorbers, UV stabilizing agents, dispersants, antioxidants, antistatic agents, lubricants, opacifying agents, anti-foam agents, rheology agents and combinations thereof.

(30) The said tackifying resin c) preferably has a softening temperature of 80° C. or less measured by Ring and Ball method (like ASTM D6493). More particularly, said resin c) is selected from the group consisting of piperylene-based hydrocarbon resins which may be hydrogenated and hydrogenated or non-hydrogenated rosin esters, modified by maleic anhydride rosin esters, preferably the c) at least one tackifying resin is hydrogenated.

(31) Preferably, said component b) at least one mono (meth)acrylate functional monomer is selected from the group consisting of alkoxylated tetrahydrofurfuryl acrylate, isobornyl acrylate, tetrahydrofurfuryl acrylate, caprolactone acrylate, 2(2-ethoxyethoxy) ethyl acrylate, 2-phenoxyethyl acrylate, tetrahydrofurfuryl methacrylate, isooctyl acrylate, 2-octyl acrylate, 2-ethylhexyl acrylate and combinations thereof and more preferably is alkoxylated tetrahydrofurfuryl acrylate and/or isobornyl acrylate.

(32) More preferably, the said component a) at least one urethane (meth)acrylate comprises a urethane (meth)acrylate oligomer according to formula (I):

(33) ##STR00003##
wherein 2≤n≤20, preferably 3≤n≤10 and 2≤m≤4;
R.sub.1 being a diisocyanate radical selected from the group consisting of alkylene, cycloalkylene, arylene, arylalkylene and combinations thereof;
R.sub.2 being a diol radical selected from the group consisting of alkylenes, cycloalkylenes and arylalkylenes;
R.sub.3 comprises a moiety of R.sub.4—OH such that component a) has a mean OH value of 2 mg KOH/g to 50 mg KOH/g, preferably 3 mg KOH/g to 10 mg KOH/g and R.sub.3 comprises a moiety of —R.sub.5-(meth)acryloyl such that component a) has an average in number functionality of from 1.2 to 1.8 (meth)acrylates, preferably from 1.3 to 1.7 (meth)acrylates; and
R.sub.4 and R.sub.5 being a bivalent radical selected from the group consisting of alkylenes, cycloalkylenes and arylalkylenes.

(34) Preferably, the said curable composition according to the invention is an adhesive curable composition and more particularly a pressure sensitive adhesive curable composition.

(35) The invention covers also a film which is formed by curing a curable composition as defined above according to the present invention.

(36) Another subject of the invention relates to a method of coating a substrate comprising: applying the curable composition as defined above according to the invention to a substrate and then curing the said curable composition.

(37) The said curing preferably comprises curing by exposure to one of the group consisting of visible radiation, UV radiation, LED radiation, laser radiation, electron-beam radiation, peroxide, peroxide and an accelerator, heat and combinations thereof, more preferably by exposure to UV and/or visible radiation.

(38) The said applying comprises applying by spraying, knife coating, roller coating, casting, drum coating, dipping and combinations thereof.

(39) Another subject of the invention relates to a cured composition, which is obtained by the curing of a curable composition as defined above according to the present invention.

(40) Preferably, said cured composition is a cured adhesive composition. Said cured composition may be also a cured coating composition.

(41) A more specific subject of the present invention is a cured adhesive composition which is obtained by curing a curable composition as defined above according to the present invention which cured adhesive is preferably a pressure sensitive adhesive in the form of an adhesive tape, an adhesive sheet, an adhesive spray, a product package, a product label, a construction article or a medical product and more particularly said pressure sensitive adhesive is for packaging, labelling, construction, model making, medicine and construction applications.

(42) The invention also covers the use of the curable composition of the present invention in adhesives and preferably in pressure sensitive adhesives.

(43) Another subject of the invention relates to a final product which is a pressure sensitive adhesive, produced by using a curable composition as defined above according to the present invention.

(44) In embodiments, the said curable compositions are liquid at a temperature of 25° C.±2° C. with a viscosity of less than 15,000 cPs or less than 12,500 cPs or less than 10,000 cPs. Such viscosity features facilitates spreading of the composition on a substrate for film formation. The compositions may be applied to a substrate in any known conventional manner, for example, by spraying, knife coating, roller coating, casting, drum coating, dipping and the like and combinations thereof. Indirect application to a substrate using a transfer process may also be used. The substrate may be any commercially relevant substrate, such as a high surface energy substrate or a low surface energy substrate, such as a metal substrate or plastic substrate, respectively. The substrates may comprise stainless steel, paper, cardboard, glass, polyolefins, PET, PVC, PMMA, PC, composites and wood.

(45) In embodiments, methods for preparing a pressure sensitive adhesive film from the compositions described herein may comprise coating the composition on a substrate and curing the composition. The coating may take place at ambient temperature or near ambient temperature (such as in the range of 10-35° C.). In embodiments and once a layer of the pressure sensitive adhesive compositions described herein have been applied to a substrate, the layer may be cured. Curing may be carried out by at least three routes: 1) curing with a photo-initiator using radiant energy (such as UV light, visible light and/or LED light); 2) curing without any initiator using electron beam energy and 3) curing with chemicals (such as peroxides, hydro-peroxides) at low temperature with an accelerator (such as tertiary amines or another reducer based on metal salts).

(46) The layer of the pressure sensitive adhesive compositions described herein may be exposed to energy for a time effective to cause cross-linking of the at least one urethane (meth)acrylate oligomer and the at least one mono (meth)acrylate functional monomer to cure the applied compositions. The intensity and/or wavelength may be adjusted as desired to achieve the desired extent of curing. The time period of exposure is not particularly limited, so long as the time period is effective to cure the compositions into a solid PSA film. Time frames for exposure to energy to cause sufficient cross-linking is not particularly limited and may be from at least about 5 seconds or at least about 30 seconds or at least about 1 minute or at least about 5 minutes or at least about 10 minutes.

(47) The following parameters defined in the present invention are determined as follows: Tgs: by Dynamic mechanical analysis at a frequency of 1 Hz and heating rate of 3° C./min Mn values: by conventional GPC as disclosed below in more details.

(48) The molecular weight Mn and polydispersity Mw/Mn are determined by conventional gel permeation chromatography (GPC). A small sample was dissolved in tetrahydrofuran (THF) and injected into a liquid chromatograph (Agilent 1100 Series) equipped with HP PLGel® GPC columns (5 um, 100 A, 250×4.6 mm; 3 um MiniMix-E, 250×4.6 mm and 5 um MiniMix-D, 250×4.6 mm). The components of the sample were separated by the GPC columns based on their molecular sizes in solution. The components were detected by a Hewlett-Packard 1047A® refractive index detector and recorded by Agilent HPLC Chemstation® and Polymer Laboratories GPC software. Polystyrene standards of known molecular weight and narrow dispersity were used to generate a calibration curve. The OH value is determined by Radiometer TitraLab® TM865 Autotitrator. A 4-5 gram sample is dissolved in 25 ml tetrahydrofuran (THF), then 25 ml p-toluenesulfonyl isocyanate (TSI) reagent was added volumetrically and stirred for 10 minutes. The sample was then titrated with 0.25 M concentration tetrabutylammonium hydroxide. The results are reported in mg KOH/g by the autotitrator. (Meth)acrylate average in number functionality of a) is the calculated theoretical functionality. Softening point of tackifying resin c): by Ring and ball standard method, like ASTM D6493 currently used for hydrocarbon and rosin ester tackifying resins.

EXAMPLES

(49) Table 1 provides structural characteristics for the oligomer according to a) (e.g., aliphatic polyester urethane acrylate 1, “Oligomer 1”) of Examples 1-4 of the compositions described herein. The oligomer has a theoretical average in number-functionality of 1.6; an experimental mg KOH/g of 5.18; a molecular weight (GPC Mw) of 22,339 g/mol; a number average molecular weight (GPC Mn) of 9,189 g/mol and an equivalent molecular weight per acrylate of 5,743. In the compositions, n in formula (I) above is 4.

(50) TABLE-US-00001 TABLE 1 Structural Characteristics of the Oligomer Used for Examples 1-4 Experimental Equivalent Theoretical OH# (mg GPC GPC Mn Per Example Functionality KOH/g) Mn Mw n Acrylate Oligomer 1.6 5.18 9,189 22,339 4 5743 1

(51) The ingredients and their proportions (in wt %) for Examples 1-4 are provided below in Tables 2-5, respectively, along with the corresponding peel, tack and shear properties for each of Examples 1-4. In embodiments, the oligomers (e.g., urethane acrylates) may be contained in the compositions in a wt % range from about 40%-60%. In embodiments, the at least one mono (meth)acrylate functional monomer may be contained in the compositions in a wt % range from about 15%-40%. In embodiments, the tackifying resin may be contained in the compositions in a wt % range of about 5%-35%. In embodiments, the photo-initiator may be contained in the compositions in a wt % range of about 2%-3%.

Example 1

(52) TABLE-US-00002 TABLE 2 Ingredients and Properties of Example 1 Adhesive Composition Ingredient Amount (%) a) Oligomer 1 (a) 58.20 b) Alkoxylated tetrahydrofurfuryl acrylate (b) 35.90 d) Irgacure ® 2022 (d) 2.90 c) Teckros ® HRL (tackifying resin c) 3.00 Adhesive Properties Test Performance 180 Peel on stainless steel 6.14 lb/in 180 Peel on polypropylene 6.05 lb/in Probe tack 1.35 lb Shear (1″ × 1″, 1 kg) 33 hrs

Example 2

(53) TABLE-US-00003 TABLE 3 Ingredients and Properties of Example 2 Adhesive Composition Ingredient Amount (%) a) Oligomer 1 (a) 58.20 b) Alkoxylated tetrahydrofurfuryl acrylate (b) 21.34 b) SR506A 14.55 d) Irgacure ® 2022 (d) 2.91 e) Sylvatac ®RE25 (c) 3.00 Adhesive Properties Test Performance 180 Peel on stainless steel 4.12 lb/in 180 Peel on polypropylene 4.76 lb/in Probe tack 1.86 lb Shear (1″ × 1″, 1 kg) 82 hrs

Example 3

(54) TABLE-US-00004 TABLE 4 Ingredients and Properties of Example 3 Adhesive Composition Ingredient Amount (%) a) Oligomer 1 (a) 42.00 b) Alkoxylated tetrahydrofurfuryl acrylate (b) 15.40 b) SR506A 10.50 d) Irgacure ® 2022 (d) 2.10 e) Sylvatac ®RE40 (c) 30.00 Adhesive Properties Test Performance 180 Peel on stainless steel 6.41 lb/in 180 Peel on polypropylene 6.29 lb/in Probe tack 1.74 lb Shear (1″ × 1″, 1 kg) 29 hrs

Example 4

(55) TABLE-US-00005 TABLE 5 Ingredients and Properties of Example 4 Adhesive Composition Ingredient Amount (%) a) Oligomer 1 (a) 45.00 b) Alkoxylated tetrahydrofurfuryl acrylate (b) 16.50 b) SR506A 11.25 d) Irgacure ® 2022 (d) 2.25 e) Sylvatac ®RE40 (c) 25.00 Adhesive Properties Test Performance 180 Peel on stainless steel 5.5 lb/in 180 Peel on polypropylene 7.41 lb/in Probe tack 1.82 lb Shear (1″ × 1″, 1 kg) 30 hrs

(56) The following sample preparation and testing procedures were used in evaluating the performance of films prepared from the compositions according to Examples 1-4. Number average molecular weights were determined by GPC using polystyrene as a standard. The pressure sensitive adhesive compositions of Examples 1-4 were casted using a square drawdown directly onto the surface of 2 mil polyethylene terephthalate (PET) film. The pressure sensitive adhesive compositions of Examples 1-4 were cured under UV light using a 400-watts/inch mercury vapor lamp at curing energy about 1 mJ/cm.sup.2. The pressure sensitive adhesive compositions of Examples 1-4 were then laminated onto a release liner. One-inch strips were cut for testing. Samples for 180° peel adhesion testing were prepared by applying a 1 inch strip of the samples to a standard stainless steel or polypropylene panel using a 4.5 pound automatic roller. The laminated samples were then allowed to dwell for 3 days at 72° F. (22.2° C.) and 50% humidity before testing. The peel strength was measured according to ASTM-D903-98 at an angle of 180° and a speed of 12 in/min. The tack was measured according to ASTM-D2979-95 using a probe tack tester PT-500 from ChemInstruments. One square inch of samples was used for probe tack test. The shear adhesion was measured according to ASTM 4498-95. Adhesive sample with 1 inch width and 3 inch length was used for shear testing. One square inch of adhesive was applied to the stainless steel panel and was then allowed to dwell for 1 hour before testing. 1 kg weight was then applied. The time when the sample failed and the weight dropped was recorded.

(57) As can been seen, the pressure sensitive adhesive compositions of Examples 1-4 produced films that demonstrate good peel properties on both stainless steel and polypropylene substrates. For stainless steel substrates, the peel strength of the films of the pressure sensitive adhesive compositions of Examples 1-4 ranged from about 4.0 lb/in to about 6.5 lb/in. For polypropylene substrates, the peel strength of the films of the pressure sensitive adhesive compositions of Examples 1-4 ranged from about 4.75 lb/in to about 7.50 lb/in. As can also been seen, the pressure sensitive adhesive compositions of Examples 1-4 produced films that demonstrate good tack properties. The tack of the films of the pressure sensitive adhesive compositions of Examples 1-4 ranged from about 44 lb/in.sup.2 to about 61 lb/in.sup.2. As can further been seen, the pressure sensitive adhesive compositions of Examples 1-4 produced films that demonstrate good shear properties. The time it took for the 1 kg weight to drop was about 30 hours to about 82 hours for the films of the pressure sensitive adhesive compositions of Examples 1-4.

COMPARATIVE EXAMPLE

(58) Table 6 provides structural characteristics for the oligomer (e.g., polyester urethane acrylate 2, “Oligomer 2”) of Comparative Example 1. The oligomer is a di-functional urethane acrylate without free OH groups in the backbone.

(59) TABLE-US-00006 TABLE 6 Structural Characteristics of the Oligomer Used for Comparative Example 1 Experimental Comparative Theoretical OH# GPC GPC Example 1 Functionality (mg KOH/g) Mn Mw Oligomer 2 2.0 0.0 5,803 11,837

(60) The oligomer has a theoretical average in number-functionality of 2; a molecular weight (GPC Mw) of 11,837 g/mol and a number average molecular weight (GPC Mn) of 5,803 g/mol.

(61) Comparative Example 1 includes similar amounts (e.g., wt % values) of oligomers, (meth)acrylate functional monomers and tackifying resins as in Examples 1-4. Table 7 lists the ingredients and their weight % (wt %) values, along with properties, for Comparative Example 1. The oligomer (e.g., urethane acrylate oligomer 2) is contained in the composition in a wt % of 45%. The at least one (meth)acrylate functional monomer is contained in the composition in a wt % of about 28 wt %. The tackifying resin is contained in the composition in a wt % of 25%. The photo-initiator is contained in the composition in a wt % of 2.25%.

(62) TABLE-US-00007 TABLE 7 Ingredients and Properties of Comparative Example 1 Adhesive Composition Ingredient Amount (%) Urethane acrylate Oligomer 2 45.00 SR611 16.50 SR506A 11.25 Irgacure ® 2022 2.25 Sylvatac ® RE40 25.00 Adhesive Properties Test Performance 180 Peel on stainless steel 3.28 lb/in 180 Peel on polypropylene 2.73 lb/in Probe tack 2.35 lb Shear (1″ × 1″, 1 kg) 30 hrs

(63) The sample preparation and testing procedures that were used in evaluating the performance of films prepared from the composition according to Comparative Example 1 were the same as those described above for Examples 1-4. The pressure sensitive adhesive composition of Comparative Example 1 produced a film that did not perform as well as the films produced from the compositions of Examples 1-4, particularly with respect to peel strength and tack. For stainless steel substrates, the peel strength of the film of the pressure sensitive adhesive composition of Comparative Example 1 was about 3.3 lb/in, whereas for Examples 1-4 the peel strength ranged from about 4.0 lb/in to about 6.5 lb/in. For polypropylene substrates, the peel strength of the film of the pressure sensitive adhesive composition of Comparative Example 1 was about 2.7 lb/in, whereas for the Examples 1-4 the peel strength ranged from about 4.75 lb/in to about 7.50 lb/in. With respect to tack, the probe tack of the film of the pressure sensitive adhesive composition of Comparative Example 1 was 1.35 lb, whereas for Examples 1-4 the probe tack ranged from about 1.35 to about 1.88 lb.

(64) When the word “about” is used in this specification in connection with a numerical value, it is intended that the associated numerical value include a tolerance of ±10% around the stated numerical value. Moreover, when reference is made to percentages in this specification, it is intended that those percentages are based on weight, i.e., weight percentages.

(65) It will now be apparent that a new, improved and nonobvious PSA systems has been described in this specification with sufficient particularity as to be understood by one of ordinary skill in the art. Moreover, it will be apparent to those skilled in the art that modifications, variations, substitutions, and equivalents exist for features of the PSA systems which do not materially depart from the spirit and scope of the embodiments disclosed herein. Accordingly, it is expressly intended that all such modifications, variations, substitutions, and equivalents which fall within the spirit and scope of the invention as defined by the appended claims shall be embraced by the appended claims.