Acrylate-based pressure-sensitive adhesives including hydrophobic oil

Abstract

Radiation-crosslinkable, pressure-sensitive adhesive precursors including 50 wt.% to 90 wt.% of an acrylic ester copolymer, the acrylic ester copolymer comprising a C4 to C16 acrylic monomer, and 10 wt.% to 50 wt.% of a hydrophobic oil. The pressure-sensitive adhesive precursor mixture may be cross-linked using electron beam radiation to provide an adhesive composition having a corrected gel content greater than 50%, clean removal from stainless steel, and instant wet-out to both smooth and structured surfaces with controlled adhesion and with low adhesion build. Methods for preparing such radiation-crosslinkable, pressure-sensitive adhesive precursors as well as adhesives comprising a crosslinked form of the radiation-crosslinkable pressure sensitive adhesive precursor are provided and articles including these adhesives.

Description

[0001] ACRYLATE-BASED PRESSURE-SENSITIVE ADHESIVES INCLUDING HYDROPHOBIC OIL

[0002] TECHNICAL FIELD

[0003] The present disclosure relates generally to the field of adhesives, more specifically to the field of radiation crosslinked pressure sensitive adhesives which contain an acrylic ester copolymer and a hydrophobic oil.

[0004] BACKGROUND

[0005] Adhesives are used in a variety of marking, holding, protecting, sealing, and masking applications. Adhesive tapes generally comprise a backing, or substrate, and an adhesive. One type of adhesive, a pressure sensitive adhesive, is particularly preferred for many applications. Pressure sensitive adhesives (“PSAs”) are well known persons having ordinary skill in the relevant arts to possess certain properties at room temperature, including: (1) aggressive and permanent tack, (2) adherence with no more than finger pressure, (3) sufficient ability to hold onto an adherend, and (4) sufficient cohesive strength.

[0006] Materials that have been found to function well as pressure sensitive adhesives are polymers designed and formulated to exhibit the requisite viscoelastic properties resulting in a desired balance of tack, peel adhesion, and shear strength.

[0007] SUMMARY

[0008] In one aspect, the present disclosure provides radiation-crosslinkable, pressure-sensitive adhesive precursor including 50 wt.% to 90 wt.% of an acrylic ester copolymer, the acrylic ester copolymer comprising a C4 to C16 acrylic monomer, and 10 wt.% to 50 wt.% of a hydrophobic oil. The pressuresensitive adhesive precursor mixture may be cross-linked using electron beam radiation to provide an adhesive composition having a corrected gel content greater than 50%, clean removal from stainless steel, and instant wet-out to both smooth and structured surfaces with controlled adhesion and with low adhesion build.

[0009] In another aspect, methods for preparing such radiation-crosslinkable, pressure-sensitive adhesive precursors as well as adhesives comprising a crosslinked form of the radiation-crosslinkable pressure sensitive adhesive precursor are provided.

[0010] In another aspect, articles including these adhesives are provided herein.

[0011] DETAILED DESCRIPTION

[0012] In the present disclosure, singular forms such as “a,” “an,” and “the” are often used for convenience. However, it should be understood that the singular is meant to include the plural unless the singular alone is called for either explicitly or by context.

[0013] The most commonly used polymers for preparation of pressure-sensitive adhesives (“PSAs”) include natural rubber, synthetic rubbers (e.g., styrene / butadiene copolymers (“SBR”) and styrene / isoprene / styrene (“SIS”) block copolymers), various (meth)acrylate (e.g., acrylate and methacrylate) copolymers, and silicones.

[0014] There is need for a clean, easily removable (e.g., gentle-to-skin) acrylate-based PSA with at least the benefits of a silicone gel-based PSA. Silicone gels are softer than silicone PSAs and have characteristics such as, for example, low lift, low residue, “gentle” to “aggressive” skin bonding adjustable through formulation changes, low-temperature bonding performance, masking and roughsurface tape applications, and bonding to oily surfaces. Similarly, acrylic PSAs tend to form strong aggressive bonds to skin and smooth surfaces such as stainless steel. Acrylic PSAs are used in medical stick-to-skin tapes but require a balance of cohesive strength, removal without stripping skin, and enough compliance to stay bonded to skin over 24 hours without edge lifting. Acrylic PSAs are not typically modified with high levels of hydrophobic oil due to inherent immiscibility and lack of cohesive strength. The addition of the hydrophobic oil in combination with electron beam cross-linking provides a gel which is softer compared to traditional acrylates, reduces the long-term adhesion build, and facilitates the need for less aggressive removal force.

[0015] Adhesive composition and performance are also dependent upon the intended use of the adhesive. Some uses require a gentle tape, whereas other uses require an aggressive tape. If an adhesive is adhered to a sensitive area of the body, commonly a “gentle” tape is used. However, if it is critical that the adhesive remain adhered for an extended period of time or if the adhesive is adhered to an area which is very mobile, a more aggressive tape is used. The term "gentle" adhesive generally refers to an adhesive for which the adhesion does not substantially build over time. The term "aggressive" adhesive refers to an adhesive which has a substantial resistance to lifting or peeling.

[0016] Medical adhesives are generally used in wound dressings, surgical drapes, bandages, and tapes. These items are commonly constmcted of a backing coated with an adhesive. A liner may or may not be used to protect the adhesive. The performance of the adhesive is in part dependent upon the occlusivity of the backing. Backings are generally categorized by their porosity into either nonocclusive or occlusive backings. When nonocclusive backings are used to prepare bandages or the like for medical applications the resulting bandage typically does not adhere well to skin over extended time periods. Though not wishing to be bound to a particular theory, this probably occurs because the bandages cannot release water vapor which leads to retention of moisture and in turn causes the adhesive to lift from the skin.

[0017] Conformability and cohesiveness are two inversely related properties which are each important to consider when preparing or selecting adhesives for medical applications. It is typically desirable for a medical adhesive to conform to the terrain of the skin to which it is adhered as this may enhance comfort to the wearer and may also ensure a higher initial adhesion to the skin because the adhesive is able to flow into the skin's topography. However, if an adhesive is too conformable it may lack the cohesiveness necessary to remove the dressing from skin with the adhesive intact. If an adhesive lacks cohesive strength the adhesive on a bandage may split upon an attempt to remove the bandage leaving some adhesive residue adhered to the skin and some adhesive removed along with the bandage backing; this characteristic is unacceptable to most medical professionals and patients.

[0018] To address at least the issues discussed above, the present disclosure provides tacky, hydrophobic oil-gel acrylic ester pressure- sensitive adhesives (“PSAs”) that are softer than typical acrylic PSAs through the addition of hydrophobic oil. The addition of hydrophobic oil results in adhesives that may be useful for bonding to smooth surfaces, rough surfaces, and skin surfaces. These PSAs may have characteristics, such as, for example, high oil loading ( / .e.,10 to 50 wt.%), high corrected gel content (i.e., greater than 50 wt.%), no oily residue, and instant wet-out as a consequence of having a low glass transition temperature (“Tg”) at 1Hz frequency e.g., where -60°C < Tg< -20°C.

[0019] In some embodiments, provided are radiation-crosslinkable pressure-sensitive adhesive precursors comprising 40 wt.% to 90 wt.%, optionally 40 wt.% to 80 wt.%, optionally 50 wt.% to 90 wt.%, optionally 50 wt.% to 80 wt.% of an acrylic ester copolymer and 10 wt.% to 50 wt.%, optionally 20 wt.% to 40 wt.% of a hydrophobic oil.

[0020] Acrylic Ester Copolymer

[0021] Acrylic ester copolymer useful in embodiments of the present disclosure are known in the art and are described, for example, in U.S. Pat. No. 9,102,774 (Clapper et al.), U.S. RE 24,906 (Ulrich) and U.S. Pat. No. 5,804,610 (Hamer et. al.). Such acrylic acid ester copolymers may be prepared by methods known to those of ordinary skill in the relevant arts from C4 to C16 acrylic monomers.

[0022] In some preferred embodiments, the C4 to C16 acrylic monomer comprises 10 wt.% to 100 wt.%, optionally 20 wt.% to 80 wt.%, optionally 30 wt.% to 70 wt.% of a CIO to C16 acrylic monomer. CIO to C16 acrylic monomers useful in embodiments of the present disclosure include those selected from the group consisting of primary (“1°”) acrylic monomers, secondary (“2°”) acrylic monomers, and combinations thereof. Examples of such CIO to C 16 acrylic monomers may include, but are not limited to decyl acrylate, isononyl acrylate, dododecyl acrylate, 2-propylheptyl acrylate, isodecyl acrylate, tridecyl acrylate, 2-decylacrylate, 2-dodecylacrylate, 2-tetradecylacrylate, and combinations thereof.

[0023] In some preferred embodiments, the C4 to C16 acrylic monomer comprises 10 wt.% to 100 wt.%, optionally 20 wt.% to 80 wt.%, optionally 30 wt.% to 50 wt.% of a C4 to C8 acrylic monomer. Examples of such C4 to C8 acrylic monomers may include, but are not limited to, butyl acrylate, hexyl acrylate, octyl acrylate, 2-ethylhexylacrylate, 2-octyl acrylate, iso-octylacrylate, and combinations thereof. In some preferred embodiments, the radiation-crosslinkable pressure sensitive adhesive precursor of the present disclosure includes an acrylic ester copolymer free of insoluble gel as determined by the Corrected Gel Test. In some preferred embodiments, the radiation-crosslinkable pressure sensitive adhesive precursor of the present disclosure includes an acrylic ester copolymer free of multifunctional acrylates, such as, for example, hexanediol diacrylate, trimethylolpropane triacrylate. In some preferred embodiments, the radiation-crosslinkable pressure sensitive adhesive precursor may have a weight average molecular weight (“Mw”) of 500,000 g / mol to 1,500,000 g / mol, optionally 750,000 g / mol to 1,000,000 g / mol as determined by gel permeation chromatography (“GPC”).

[0024] Hydrophobic Oil

[0025] Hydrophobic oils useful in embodiments of the present disclosure are typically oils having low solubility in water (i.e., < 1% wt.%). Examples of such hydrophobic oils commercially available include paraffinic oils such as KAYDOL USP grade oil available from Sonnebom, Inc. and the CALSOL 9 series available from Calumet Specialty Products Partners, L.P., Indianapolis, Indiana.; naphthenic oils such as the CALSOL 5 series having a molecular weight range from 350 to 1000 gr / mol available from Calumet Specialty Products Partners, L.P., Indianapolis, Indiana; and polypropylene glycols having a molecular weight range from 400 to 2000 gr / mol such as Poly glycol P-1000E and P-2000E from Dow Chemical Company, Midland, Michigan.

[0026] Another potentially useful class of hydrophobic oils are the polybutenes having terminal unsaturation such as, for example, the INDOPOL L and H series from Ineos Oligomers, League City, Texas, and hydrogenated polybutenes such as, for example, PANALANE L and H series available from Vantage Specialty Chemicals, Deerfield, Illinois. Useful polybutenes generally have molecular weight range from 350-1500 gr / mol.

[0027] It has been observed that the presence of aromatic content may reduce electron beam curing efficiency. The hydrophobic oils compatible with embodiments of the present disclosure produce minimal interference with the electron beam curing step.

[0028] Additional Additives

[0029] Radiation-crosslinkable pressure-sensitive adhesive precursors of the present disclosure may include additional additives depending on the envisaged properties for the resulting crosslinked pressuresensitive adhesive.

[0030] In some embodiments, the radiation-crosslinkable pressure-sensitive adhesive precursor may further include up to 5 wt.%, optionally up to 4 wt.%, or optionally up to 2 wt.% of a polar acrylic monomer. Examples of polar acrylic monomers useful in embodiments of the present disclosure include, without limitation, acrylic acid, N,N-dimethylacrylamide, and combinations thereof.

[0031] In some embodiments, the radiation-crosslinkable pressure-sensitive adhesive precursor may further including up to 10 wt.%, up to 5 wt.%, up to 4 wt.%, or up to 2 wt.% of a high Tgacrylate monomer. Examples of high Tgacrylate monomers useful in embodiments of the present disclosure include, without limitation, isobomyl acrylate, polystyrene macromonomer, and combinations thereof. In some embodiments, the radiation-crosslinkable pressure sensitive adhesive precursor may include an additive selected from the group consisting of a photoinitiator, a chain transfer agent, an antioxidant, a tackifying resin, and combinations thereof.

[0032] In some embodiments, the radiation-crosslinkable pressure-sensitive adhesive precursor may include an amount of a photo initiator in parts per hundred of the acrylic monomers (“pphm”). In some preferred embodiments the radiation-crosslinkable pressure-sensitive adhesive precursor may include up to 0.1 pphm, up to 0.5 pphm, or up to 1 pphm of the photo initiator. Examples of photo initiator useful in embodiments of the present disclosure include, without limitation, 2,2-dimethoxy-l,2-diphenylethan-l- one (commercially available as OMNIRAD 651 (formerly IRGACURE 651)) from IGM Resins USA Inc., Charlotte, North Carolina, 2-hydroxy-2-methyl-l-phenyl-propan-l-one (commercially available as OMNIRAD 1173) from IGM Resins USA Inc., 1 -hydro xy-cyclohexyl-phenyl-ketone (OMNIRAD 184) from IGM Resins USA Inc., and combinations thereof.

[0033] In some embodiments, the radiation-crosslinkable pressure-sensitive adhesive precursor may include an amount of a chain transfer agent in parts per hundred of the acrylic monomers (“pphm”). In some preferred embodiments the radiation-crosslinkable pressure-sensitive adhesive precursor may include up to 0.001 pphm, up to 0.005 pphm, or up to 0.01 pphm of the chain transfer agent. Examples of chain transfer agents useful in embodiments of the present disclosure include, without limitation, iso-octyl thioglycolate (“IOTG”), carbon tetrabromide (“CBr4”), and combinations thereof.

[0034] In some embodiments, the radiation-crosslinkable pressure-sensitive adhesive precursor may include an amount of an antioxidant in parts per hundred of the acrylic monomers (“pphm”). In some preferred embodiments the radiation-crosslinkable pressure-sensitive adhesive precursor may include up to 0.1 pphm, up to 0.2 pphm, up to 0.5 pphm, or up to 1 pphm of the antioxidant. Examples of chain antioxidant useful in embodiments of the present disclosure include, without limitation, primary antioxidants such as the sterically hindered phenols including IRGANOX 1076 (octadecyl-[3-(3,5-di-tert- butyl-4-hydroxyphenyl)propionate) and IRGANOX 1010 (pentaerythritol tetrakis [3- [3,5-di-tert-butyl-4- hydroxyphenyl]propionate) antioxidants, both available from BASF Corporation, and combinations thereof.

[0035] In some embodiments, the radiation-crosslinkable pressure-sensitive adhesive precursor may further including up to 20 wt.%, up to 10 wt.%, up to 5 wt.%, or up to 1 wt.% of a tackifying resin. Solid tackifying resins that may be useful in embodiments of the present disclosure typically develop tack in the adhesives including the radiation-crosslinkable pressure-sensitive adhesive precursor and have softening points (“SP”) less than 120°C. Examples of useful commercially available solid resins include C5 aliphatic hydrocarbon-derived resins such as the ESCOREZ 1000 series from ExxonMobil Chemical Co., Irving, Texas, the WINGTACK series available from Cray Valley, Exton, Pennsylvania, the PICCOTAC series available from Eastman Chemical Co., Kingsport, Pennsylvania, and the QUINTONE series available from Zeon Corp., Tokyo, Japan. Other potentially useful resins include cycloaliphatic C9 hydrocarbon resins such as the ARKON P series (fully hydrogenated) and ARKON M series (partially hydrogenated) from Arakawa Chemical Inc., Chicago, Illinois; cycloaliphatic CIO hydrocarbons such as the ESCOREZ 5000 series from ExxonMobil Chemical Co.; hydrogenated pure monomer resins such as the REGALREZ series from Eastman Chemical Co.; gum rosin esters such as the FORAL series and the STAYBELITE A and E series from Pinova, Inc., Brunswick, GeoOrgia; tall oil rosin esters such as the SYLVATAC and SYLVALITE series from Kraton Polymers LLC, Houston, Texas, the WESTREZ 5000 series from MeadWestvaco Corp., Richmond, Virginia, and the PERMALYN series from Eastman Chemical Co.; polyterpenes such as the PICCOLYTE A, F, C and S series from Pinova, Inc.; turpentines such as SYLVARES TP 2019 from Kraton Polymers LLC. Examples of useful commercially available liquid resins include, but are not limited to: alpha-pinene-derived polyterpenes such as that available under the trade name PICCOLYTE A25 Pinova, Inc.; beta-pinene-derived polyterpenes such as that available under the trade name PICCOLYTE S25 from Pinova, Inc.; hydrogenated C9-derived aliphatic resins such as that available under the trade name REGALREZ 1018 from Eastman Chemical Co., and that available under the trade name WINGTACK 10 from Cray Valley; and tall oil-based liquid rosin esters such as that available under the trade name SYLVALITE RE10L from Kraton Polymers. The compatible tackifying resins can be a mixture of solid and liquid and should have minimal interference with the electron beam curing step. The presence of aromatic content may reduce electron beam curing efficiency.

[0036] Radiation-Crosslinkable Pressure-Sensitive Adhesive Precursor and Adhesive Preparation and Articles Including the Same

[0037] Radiation-crosslinkable pressure-sensitive adhesive precursors of the present disclosure are readily prepared and processible via both hot melt and solvent mixing and coating processes known to those of ordinary skill in the relevant arts and are described in International Publication WO 2016 / 106003 (D’Haese et al.) The radiation-crosslinkable pressure-sensitive adhesive precursor mixtures may be exposed to electron beam (“EB”) radiation to induce cross-linking of the radiation-crosslinkable pressuresensitive adhesive precursor and provide an adhesive composition. EB doses suitable for embodiments of the present disclosure are typically 4 Megarads (“MR”) to 10 MR. Adequate gel content and crosslinking have been achieved, for example, at 6 MR and 175 kilovolts (“kV”) accelerating energy for coating thicknesses ranging from 0.001” to 0.004” (0.00254 cm to 0.01016 cm). The final composition preferably has a corrected gel content greater than 50%. This generally corresponds to enough crosslinking to provide clean removal (i.e., no oily residue) and no onset of flow (i.e., no G7G” cross-over temperature) from ambient temperature (e.g., 22°C) temperatures to temperatures greater than 150°C at 1 Hz frequency. G’ is the storage modulus and G” is the loss modulus. The corresponding tangent delta (8) ranges at 1Hz frequency from 0.4 - 0.6 at temperatures greater than 22°C to provide a pressure-sensitive adhesive that is useful for clean removal from stainless steel. The coating compositions can be blended with compatible polymer components and / or foamed prior to EB cross-linking.

[0038] The radiation crosslinked pressure sensitive adhesives and radiation crosslinked pressure sensitive adhesive precursors of the present disclosure, in particular the hot melt and solution processable adhesives and precursors, may advantageously be used to prepare a wide range of adhesive tapes and articles. Many of these tapes and articles contain backings or other substrates to support the layer of adhesive. Other adhesive tapes and articles do not contain a backing or substrate layer and therefore are free standing adhesive layers. Double-sided tapes are an example of such an adhesive article. Double-sided tapes, also called “transfer tapes”, are adhesive tapes that have adhesive on both exposed surfaces. In some transfer tapes, the exposed surfaces are simply the two surfaces of a single adhesive layer. Other transfer tapes are multi-layer transfer tapes with at least two adhesive layers that may be the same or different, and in some instances intervening layers that may not be adhesive layers. For example, a multi-layer transfer tape may be a 3 layer construction with an adhesive layer, a film layer and another adhesive layer. The film layer can provide handling and / or tear strength or other desirable properties. In this disclosure, double-sided adhesives are prepared that comprise one free standing layer of pressure sensitive adhesive. Since the double-sided adhesives are free standing, they must have sufficient handling strength to be handled without the presence of a supporting layer.

[0039] Adhesives of the present disclosure may be useful in the preparation of medical articles including adhesives such as, for example, surgical tapes and drapes, bandages, athletic tapes, and wound dressings. The adhesives disclosed herein may be coated using solvent or hot melt methods well known in the art onto any backing suitable for medical uses including, for example, occlusive (substantially nonbreathable) and non-occlusive (breathable) backings. Occlusive backings are also known as low porosity backings. Nonlimiting examples of occlusive backings include films, foams, and laminates thereof. Nonlimiting examples of nonocclusive backings include woven substrates, nonwoven substrates such as hydroentangled materials or melt blown webs, foams, and thermally embossed nonwoven substrates. The adhesives of the present invention are amenable to continuous (knife or contact rod), discontinuous (e.g., stripe coating) or pattern coating which can provide either spatially distinct (e.g., dots, triangles or squares) or spatially thick and thin regions of the adhesive on the substrate.

[0040] Objects and advantages of this disclosure are further illustrated by the following non-limiting examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this disclosure.

[0041] EXAMPLES

[0042] Unless otherwise noted or readily apparent from the context, all parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight. Unless otherwise indicated, materials used in the examples were obtained from commercial suppliers (e.g., Aldrich Chemical Co., Milwaukee, Wisconsin) and / or made by known methods. The following abbreviations are used in the Examples section: pphm=part per hundred of the acrylic monomers, EB=electron beam, rpm= revolutions per minute, in=inches, mil=thousandths of an inch, °F=degrees Fahrenheit, °C=degrees Celsius, min=minutes, mW=milliWatts, cm2=square centimeters, oz=ounces, Hz=Hertz.

[0043] Materials Used in the Examples

[0044] Test Methods

[0045] Gel Content Test Method

[0046] Samples were scraped from polyethylene terephthalate (PET) film following EB crosslinking. For each sample, approximately 0.5 grams of the adhesive components from each sample was weighed. The weight is referred to in the formula below as the sampled weight. The weighed amount of sample was added to 50 grams of 50 / 50 toluene / ethyl acetate in a glass jar that was placed on a mechanical roller at room temperature for 1-2 days. The mixture was filtered through a 200-mesh screen. The screen and insoluble material were dried at 220 °F (104°C) for 1-2 hours. The weight of insoluble component was measured and referred to in the formula below as insoluble weight. The corrected gel content was calculated according to the formula:

[0047] ~

[0048] Corrected gel content where / ARC is the (sampled weight*preparatory example formulation weight fraction), where the preparatory formulation weight fraction = Preparatory Example wt% / 100. Adhesion to Stainless Steel Test Method Samples coated on PET film and EB crosslinked were tested for adhesion to stainless steel (ATSS) at controlled temperature and humidity (CTH) conditions. The ATSS was measured using 12 inches per minute (ipm) (4.7 cm / min) rate in 180° peel geometry. 6 inches (3 cm) long 1 inches (0.4 cm) wide tapes were tested within 5 minutes of bonding the tapes to a cleaned steel panel using a 3M90 slip / peel tester available under the trade designation T65871 from Instrumentors, inc.; Strongsville, OH. The tapes were bonded using 4 passes of a 4.5-pound roller. The averaging time was 2 seconds for 12 ipm. The resulting peel force was recorded as ATSS and cleanliness of the steel surface was evaluated and recorded as Failure Mode in Table 4.

[0049] Dynamic Mechanical Analysis (DMA) Test Method

[0050] Testing was performed using an ARES-G2 rheometer available from TA Instruments, New Castle, DE, having 8 mm Aluminum disposable parallel plates attached to both upper and lower fixtures. The “Low and High Temperature Ramp” test method was used to measure the temperature dependence of Tangent Delta (Tan 8) and the loss / storage moduli (G’ and G”, respectively) at 1 Hz frequency. After EB crosslinking, samples were scraped from PET films using a dental pick and pressed to 1-2 mm thickness and allowed to thermally relax. After a 180 second hold at 30 °C, the first ramp of the DMA test was started at 30 °C and the temperature was ramped down at 3 °C / min until a defined Tan Delta peak (glass transition temperature / Tg) was reached. The second ramp of the DMA test involved ramping the temperature from 30 °C to 150 °C at a rate of 3 °C / min. Results from both ramps were combined to determine the Tan Delta value. The auto strain adjustment was enabled to ensure the material was in the Linear Viscoelastic Region (LVR) during all temperature ramps.

[0051] Preparatory Examples (PE-1 and PE-2)

[0052] For each Preparatory Example, an acrylic ester copolymer was prepared as follows: a monomer mixture was prepared by blending acrylic monomers, IOTG, PHOTOINITIATOR, and ANTIOXIDANT A in ajar in the amounts indicated in Table 2. To this mixture was added a magnetic stir bar, and the mixture was placed on a stir plate, forming a curable composition. EVA FILM was heat sealed to form open ended receptacles each measuring 18 cm by 5 cm. Each receptacle was filled with approximately 24 grams of the curable composition. Air was forced out of the open end which was then sealed using a heat sealer (obtained under the trade designation “MIDWEST PACIFIC IMPULSE SEALER” from J. J. Elemer Corp., St. Louis, MO). A sealed EVA film receptacle having the curable composition enclosed within the was immersed in a constant temperature water bath at 16 °C and irradiated with ultraviolet light (365 nm, 4.5 mW / cm2) for nine minutes on each side to polymerize the curable composition. The curable composition in its receptacle was placed in the melt mixer for use in Examples and Comparative Examples, as described below. Table 2. Compositions

[0053] Examples (EX-1 through EX-6) and Comparative Examples (CE-1 and CE-2)

[0054] Each sample, PE-1 or PE-2, as indicated in Table 3, was mixed with ANTIOXIDANT B and KAYDOL, in amounts indicated in Table 3, using a melt mixer (a 30mm diameter twin-screw extruder). For each sample, 140 grams of the mixture was charged into the mixer and mixed at 150 rpm screw speed for 3 minutes. The mixture was discharged via a heated gear pump operating at 200 rpm. The samples were coated at approximately 4 inches wide and 18 grains / 24 in2coating weight (0.003 in thick - 75 grams / meter2(GSM)) onto 1.2 mil thick PET film or Crepe Paper, as indicated in Table 3, using a contact die. A release coated PET liner was laminated to surface of the sample opposite the PET film or Crepe Paper. Samples were exposed to radiation from an electron beam source using a Model CB-300 electron beam generating apparatus (available from Energy Sciences, Inc. (Wilmington, Mass.). The uncured material was exposed to EB irradiation through the release liner. Sample compositions, EB doses after the release liner, and coating weights are presented in Table 3. Characterization of the samples following EB irradiation is presented in Table 4.

[0055] Table 3. Example and Comparative Example Compositions Table 4. Characterization of Examples and Comparative Examples nm = not measured cln = clean removal, no residue observed on stainless steel panel after 180° peel

[0056] All cited references, patents, and patent applications in the above application for letters patent are herein incorporated by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control. The preceding description, given in order to enable one of ordinary skill in the art to practice the claimed disclosure, is not to be construed as limiting the scope of

Claims

What is claimed is:

1. A radiation-crosslinkable pressure sensitive adhesive precursor comprising:40 wt.% to 90 wt.% of an acrylic ester copolymer, wherein the acrylic ester copolymer comprises a C4 to C16 acrylic monomer; and10 wt.% to 50 wt.% of a hydrophobic oil.

2. The radiation-crosslinkable pressure sensitive adhesive precursor of claim 1 comprising 40 wt.% to 80 wt.%, optionally 50 wt.% to 90 wt.%, or optionally 50 wt.% to 80 wt.% of the acrylic ester copolymer.

3. The radiation-crosslinkable pressure sensitive adhesive precursor of claim 1, wherein the C4 to C16 acrylic monomer comprises 10 wt.% to 100 wt.%, optionally 20 wt.% to 80 wt.%, optionally 30 wt.% to 70 wt.% of a CIO to C16 acrylic monomer.

4. The radiation-crosslinkable pressure sensitive adhesive precursor of claim 3, wherein the CIO to Cl 6 acrylic monomer is selected from the group consisting of primary acrylic monomers, secondary acrylic monomers, and combinations thereof.

5. The radiation-crosslinkable pressure sensitive adhesive precursor of claim 4, wherein the CIO to C16 acrylic monomer is selected from the group consisting of decyl acrylate, isononyl acrylate, 2- dododecyl acrylate, 2-propylheptyl acrylate, isodecyl acrylate, tridecyl acrylate, 2-decylacrylate, 2- tetradecylacrylate, and combinations thereof.

6. The radiation-crosslinkable pressure sensitive adhesive precursor of claim 1, wherein the C4 to C16 acrylic monomer comprises 10 wt.% to 100 wt.%, optionally 20 wt.% to 80 wt.%, optionally 30 wt.% to 50 wt.% of a C4 to C8 acrylic monomer.

7. The radiation-crosslinkable pressure sensitive adhesive precursor of claim 6, wherein the C4 to C8 acrylic monomer is selected from the group consisting of butyl acrylate, hexyl acrylate, octyl acrylate, 2 -ethylhexylacrylate, 2-octyl acrylate, iso-octylacrylate,-and combinations thereof.

8. The radiation-crosslinkable pressure sensitive adhesive precursor of claim 1 comprising 10 wt.% to 50 wt.%, optionally 20 wt.% to 40 wt.% of the hydrophobic oil.

9. The radiation-crosslinkable pressure sensitive adhesive precursor of claim 1, wherein the hydrophobic oil is selected from the group consisting of a paraffinic oil, a naphthenic oil, a polypropyleneglycol having a molecular weight range from 400 to 2000 g / mol, a polybutene having a molecular weight range from 350 to 1500 g / mol, and combinations thereof.

10. The radiation-crosslinkable pressure sensitive adhesive precursor of claim 1, further comprising 0.01 wt.% to 5 wt.%, optionally 0.01 wt.% to 4 wt.%, optionally 0.01 wt.% to 2 wt.% of a polar acrylic monomer.

11. The radiation-crosslinkable pressure sensitive adhesive precursor of claim 10, wherein the polar acrylic monomer is selected from the group consisting of acrylic acid, N,N-dimethylacrylamide, and combinations thereof.

12. The radiation-crosslinkable pressure sensitive adhesive precursor of claim 1, further comprising 0.1 wt.% to 10 wt.%, optionally 0.1 wt.% to 5 wt.%, optionally 2 wt.% to 5 wt.% of a high Tg acrylate monomer.

13. The radiation-crosslinkable pressure sensitive adhesive precursor of claim 1, wherein the high Tgacrylate monomer is selected from the group consisting of isobomyl acrylate, polystyrene macromonomer, and combinations thereof.

14. The radiation-crosslinkable pressure sensitive adhesive precursor of claim 1, further comprising an additive selected from the group consisting of a photoinitiator.l, a chain transfer agent, an antioxidant, a tackifying resin, and combinations thereof.

15. The radiation-crosslinkable pressure sensitive adhesive precursor of claim 1 having a weight average molecular weight Mw of 500,000 g / mol to 1,500,000 g / mol, optionally 750,000 g / mol to 1,000,000 g / mol as determined by gel permeation chromatography.

16. The radiation-crosslinkable pressure sensitive adhesive precursor of claim 1, wherein the acrylic ester copolymer is free of insoluble gel as determined by the Corrected Gel Test.

17. The radiation-crosslinkable pressure sensitive adhesive precursor of claim 1, wherein the acrylic ester copolymer is free of multifunctional acrylates.

18. An adhesive comprising a crosslinked form of the radiation-crosslinkable pressure sensitive adhesive precursor of claim 1.

19. The adhesive of claim 18, wherein the crosslinked form of the radiation-crosslinkable pressure sensitive adhesive precursor is formed by exposure of the radiation-crosslinkable pressure sensitive adhesive precursor to electron beam radiation.

20. The adhesive of claim 18, wherein the adhesive has a corrected gel content of 50 wt.% to 90 wt.%, optionally 50 wt.% to 80 wt.%, optionally 50 wt.% to 70 wt.%.

21. An article comprising the precursor of claim 1.

22. An article comprising the adhesive of claim 18.

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