Packaged pressure sensitive adhesives

Abstract

Packaged adhesive compositions include a thermoplastic packaging material and a pressure sensitive adhesive composition contained within the packaging material. The pressure sensitive adhesive composition is an adiabatically polymerized composition prepared from a reaction mixture of an alkyl(meth)acrylate monomer, a reinforcing monomer, a photocrosslinkable monomer, and at least one initiator. The packaged adhesive composition is hot melt processable to form a pressure sensitive adhesive layer. The hot melt processed packaged adhesive composition has a higher 180° Peel Force and a higher Shear Holding Power than the same hot melt processed adhesive that has not been packaged.

Description

[0001] PACKAGED PRESSURE SENSITIVE ADHESIVES

[0002] Summary

[0003] Disclosed herein are packaged pressure sensitive adhesives, articles prepared with the packaged pressure sensitive adhesives, and methods of forming adhesive articles.

[0004] In some embodiments, the packaged adhesive compositions comprise a packaging material comprising a thermoplastic polymer, and a pressure sensitive adhesive composition contained within the packaging material. The pressure sensitive adhesive composition comprises an adiabatically polymerized composition prepared from a reaction mixture comprising at least one alkyl(meth)acrylate monomer with alkyl groups comprising 4-20 carbon atoms, at least one reinforcing monomer selected from an acid-functional monomer, a base-functional monomer, or a macromonomer, at least one photocrosslinkable monomer; and at least one initiator. The packaged adhesive composition is hot melt processable to form a pressure sensitive adhesive layer. The hot melt processed packaged adhesive composition has a higher 180° Peel Force and a higher Shear Holding Power than the same hot melt processed adhesive that has not been packaged.

[0005] Also disclosed are adhesive articles. In some embodiments, the adhesive articles comprise a substrate with a first major surface and a second major surface; and a pressure sensitive adhesive layer disposed on at least a portion of the first major surface of the substrate. The pressure sensitive adhesive layer comprises the hot melt coated packaged pressure sensitive adhesive described above. The pressure sensitive adhesive layer includes thermoplastic particles that are the residue of the packaging material.

[0006] Methods of preparing adhesive articles comprise providing a substrate with a first major surface and a second major, and hot melt coating a packaged pressure sensitive adhesive composition onto at least a portion of the first major surface of the substrate to form a pressure sensitive adhesive layer. The packaged pressure sensitive adhesive composition is described above. The method further comprises exposing the adhesive layer to actinic radiation to crosslink the adhesive layer.

[0007] Detailed Description

[0008] Adhesives have been used for a variety of marking, holding, protecting, sealing and masking purposes. One type of adhesive, a pressure sensitive adhesive, is particularly useful for many applications. The use of adhesives, especially pressure sensitive adhesives, in areas such as the medical, electronic and optical industries is increasing. Often the pressure sensitive adhesives are used to form adhesive articles. A wide range of adhesive articles are possible. Adhesive articles include simple articles such as tapes and film articles as well as more complex articles including devices. The articles comprise a substrate with a first major surface and a second major surface, and a pressure sensitive adhesive layer disposed on at least a portion of the first major surface of the substrate. The substrate can be a polymeric film, a tape backing, or the surface of a device.

[0009] Many classes of pressure sensitive adhesive have been prepared to address the needs of a wide range of articles. Often these pressure sensitive adhesives are provided as solutions or solvent-borne mixtures, often solutions or solvent-borne mixtures containing large amounts of solvents. Upon coating or dispensing, the solvent needs to be removed to produce an adhesive layer. Often the solvent is removed through the use of elevated temperature processing such as heating with an oven. Such solvent removal steps can add cost to the formed articles because solvent removal requires additional steps. Not only are additional steps involved, often these steps require specialized care, precautions and equipment because the solvents are volatile and generally flammable. In addition, shipment of adhesive solutions adds additional expense because of the added weight of solvent and may require special shipment precautions due to the presence of solvent. Environmental concerns are also an issue with solvent borne adhesive systems, since, even with the use of solvent reclamation equipment, solvent release to the environment is likely.

[0010] Therefore, 100% solids adhesive systems have been developed. Among these 100% solids systems are hot melt processable adhesives, including hot melt processable pressure sensitive adhesives. Difficulties have arisen when solvent processing has been replaced by hot melt processing. Often it is difficult to replicate the properties of solvent delivered adhesive layers with hot melt delivered systems.

[0011] Additionally, because 100% solids pressure sensitive adhesives are tacky polymeric compositions, handling of these compositions, especially on a large scale can be problematic. A wide variety of techniques have been developed to deal with these handling issues. One such technique is the preparation of (meth)acrylate-based pressure sensitive adhesive polymers or compositions within a thermoplastic polymeric package as described by for example, PCT Publication No. WO 97 / 23945. These packages can then be handled without contacting the tacky polymeric composition. The entire package can then be hot melt processed, for example in an extruder or similar mixing device, and coated to form a pressure sensitive adhesive layer. This layer contains not only the pressure sensitive adhesive polymer or composition, but also the remnants of the pouch material. In some uses, such as optical applications, these particle remnants can be problematic. Additionally, there are limitations on the polymers that can be prepared within a package.

[0012] Other solventless processes have been developed such as the bulk adiabatic polymerization process for ethylenically unsaturated monomers described in US Patent No. 5,986,011. These bulk polymerization (meth)acrylate-based polymers because they are not made in solvent are different from polymers prepared by solvent polymerization methods. In general, these bulk polymers have a lower molecular weight than solvent polymerized adhesive polymers. These polymers have desirable properties, but because they are relatively low molecular weight tacky polymers, they can be very difficult and costly to handle and process to form adhesive articles.

[0013] Disclosed herein are adhesive compositions that are pressure sensitive adhesives contained within a thermoplastic package. The pressure sensitive adhesive polymers are not prepared within the package, rather they are prepared by bulk polymerization techniques and placed within the package. Because the polymer is pre-made, packages of virtually any size with at least one dimension ranging from 2 centimeters (less than 1 inch) to 25 centimeters (10 inches) can be used. Additionally, the packages can be in a wide range of shapes.

[0014] The packaged adhesives are conveniently shipped, handled, and dispensed into, for example, hot melt processing equipment. The pressure sensitive adhesives, when hot melt coated, form adhesive layers that contain thermoplastic polymer particles dispersed within them. The thermoplastic polymer particles are the residue of the packaging material after hot melt processing. Surprisingly it has been found that the pressure sensitive adhesive layers with the thermoplastic polymer particles have increased 180° Peel Adhesion and Shear Holding Power when compared with the same pressure sensitive adhesive layer without the thermoplastic polymer particles. Thus, the adhesive compositions of this disclosure not only are conveniently shipped, handled and dispensed, but also have improved adhesive properties.

[0015] Previous adhesive disclosures, PCT Publication No. WO 97 / 23577 and PCT Publication WO 97 / 18166, have taught blends of a wide range of pressure sensitive adhesives with thermoplastic polymers and that these blends have improved adhesive properties over the pressure sensitive adhesives without the thermoplastic polymers. Typically, the thermoplastic polymer in these blends is at least 5% by weight of the adhesive layer often considerably higher, so it is surprising that the low level of thermoplastic material in the current adhesive layers, in many instances less than 3% by weight, can improve the adhesive properties. Without wishing to be bound by theory, it is believed that the polymers formed by the bulk adiabatic polymerization technique are sufficiently different from the conventional pressure sensitive adhesives disclosed in PCT Publication No. WO 97 / 23577 and PCT Publication WO 97 / 18166 that the effect of thermoplastic particles is therefore also different. Additionally, typically the current pressure sensitive adhesive layers are crosslinked after hot melt coating, and this may also affect the behavior of the final pressure sensitive adhesive layer. The term “adhesive” as used herein refers to polymeric compositions useful to adhere together two adherends. Examples of adhesives are pressure sensitive adhesives.

[0016] Pressure sensitive adhesive compositions are well known to those of ordinary skill in the art to possess properties including the following: (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 to be cleanly removable from the adherend. 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 holding power. Obtaining the proper balance of properties is not a simple process.

[0017] The term “(meth)acrylate” refers to monomeric acrylic or methacrylic esters of alcohols. Acrylate and methacrylate monomers or oligomers are referred to collectively herein as "(meth)acrylates”. Materials referred to as “(meth)acrylate -based” are materials that contain one or more (meth)acrylates as the primary components of the material.

[0018] The term “siloxane -containing” as used herein refer to polymers that contain siloxane units. The terms silicone or siloxane are used interchangeably and refer to units with dialkyl or diaryl siloxane i-SiFTO-J repeating units.

[0019] The terms "room temperature" and "ambient temperature" are used interchangeably to mean temperatures in the range of 20°C to 25 °C.

[0020] The terms “Tg” and “glass transition temperature” are used interchangeably. If measured, Tg values are determined by Differential Scanning Calorimetry (DSC) at a scan rate of 10°C / minnte, unless otherwise indicated. Typically, Tg values for copolymers are not measured but are calculated using the well-known Fox Equation, using the homopolymer Tg values provided by the monomer supplier, as is understood by one of skill in the art.

[0021] The term “adjacent” as used herein when referring to two layers means that the two layers are in proximity with one another with no intervening open space between them. They may be in direct contact with one another (e.g. laminated together) or there may be intervening layers.

[0022] The terms “polymer” and “macromolecule” are used herein consistent with their common usage in chemistry. Polymers and macromolecules are composed of many repeated subunits. As used herein, the term “macromolecule” is used to describe a group attached to a monomer that has multiple repeating units. The term “polymer” is used to describe the resultant material formed from a polymerization reaction.

[0023] The term “alkyl” refers to a monovalent group that is a radical of an alkane, which is a saturated hydrocarbon. The alkyl can be linear, branched, cyclic, or combinations thereof and typically has 1 to 20 carbon atoms. In some embodiments, the alkyl group contains 1 to 18, 1 to 12, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, cyclohexyl, n-heptyl, n-octyl, and ethylhexyl.

[0024] The term “aryl” refers to a monovalent group that is aromatic and carbocyclic. The aryl can have one to five rings that are connected to or fused to the aromatic ring. The other ring structures can be aromatic, non-aromatic, or combinations thereof. Examples of aryl groups include, but are not limited to, phenyl, biphenyl, terphenyl, anthryl, naphthyl, acenaphthyl, anthraquinonyl, phenanthryl, anthracenyl, pyrenyl, perylenyl, and fluorenyl.

[0025] The terms “free radically polymerizable” and “ethylenically unsaturated” are used interchangeably and refer to a reactive group which contains a carbon -carbon double bond which is able to be polymerized via a free radical polymerization mechanism.

[0026] As defined herein, by "essentially adiabatic" it is meant that the total of the absolute value of any energy exchanged to or from the batch during the course of reaction will be less than about 15% of the total energy liberated due to reaction for the corresponding amount of polymerization that has occurred during the time that polymerization has occurred. Essentially adiabatic reactions are exemplified in, for example, US Patent No. 5,986,011 (Ellis).

[0027] Disclosed herein are packaged adhesive compositions comprising a packaging material comprising a thermoplastic polymer, and a pressure sensitive adhesive composition contained within the packaging material. The pressure sensitive adhesive composition comprises an adiabatically polymerized composition prepared from a reaction mixture comprising at least one alkyl(meth)acrylate monomer with alkyl groups having 4-20 carbon atoms, at least one reinforcing monomer selected from an acid-functional monomer, a base-functional monomer, or a macromonomer, at least one photocrosslinkable monomer; and at least one thermal initiator.

[0028] The packaged adhesive composition is hot melt processable to form a pressure sensitive adhesive layer, where the hot melt processed packaged adhesive composition has a higher 180° Peel Force and a higher Shear Holding Power than the same hot melt processed adhesive that has not been packaged. 180° Peel Force and Shear Holding Power are fundamental properties of pressure sensitive adhesives, and the techniques for measuring these values are described in detail in the Examples section.

[0029] The packaged adhesive compositions include a packaging material that forms a package that contains the pressure sensitive adhesive. The methods of preparing packaged adhesive compositions are similar to those described in US Patent No. 6,294,249 (Hamer et al.). However, whereas Hamer et al. packaged a pre-adhesive composition, that is to say a composition that was later polymerized to form a pressure sensitive adhesive, in the current disclosure, a pre -made pressure sensitive adhesive composition is packaged. Since the pre-made pressure sensitive adhesives have a relatively low viscosity, the same techniques that are used with the polymerizable pre-adhesive compositions can be used to form the packages.

[0030] In some embodiments, two lengths of thermoplastic film are heat sealed together across the bottom and on each of the lateral edges on a liquid form-fill-seal machine to form an open- ended package. The pressure sensitive adhesive composition is pumped through a hose to fill the package, and the package is then heat sealed across the top to completely surround the pressure sensitive adhesive composition.

[0031] Generally, the form-fill-seal machine is equipped with an impulse sealer to form the top and bottom seal across the packages. Such a sealer has one or two sets of jaws that clamp the package shut before scaling. A sealing wire is then heated to effect the seal, and the seal is cooled before the jaws are released. The sealing temperature is generally above the softening point and below the melting point of the film used to form the package.

[0032] Alternatively, a single length of film can be folded lengthwise and sealed on one edge, filled with the pressure sensitive adhesive composition, and sealed. In another embodiment, a single length of film can be pulled through a forming collar, sealed to form a tube, filled with the pressure sensitive adhesive composition, and sealed. Another embodiment can be carried out on commercial liquid form- fill-seal machines. A source of such machines is the Packaging Machinery Division of Eagle Corp. It is contemplated that the seals can be effected in any of a number of different configurations to form multiple pouches across and down the lengths of film. For example, in addition to the seals on the lateral edges, a seal can also be formed down the center of the lengths of film so that a cross seal will form two filled packages. The packages can either be left attached to each other by the cross-seals and / or vertical seals, or they can be cut into individual packages or strands of packages.

[0033] The packaging material is a thermoplastic material that generally melts at or below the processing temperature of the pressure sensitive adhesive composition (in other words, the temperature at which the pressure sensitive adhesive composition flows). The packaging material generally has a melting point of 200°C or less, or 170°C or less. In some embodiments, the melting point ranges from 90°C to 150°C. The packaging material may be a flexible thermoplastic polymeric film. The flexible thermoplastic polymeric films are prepared from thermoplastic materials. Suitable thermoplastic materials include polyethylene, and ethylene copolymers such as ethylene / polyolefin copolymers and ethylene / vinyl copolymers such as ethylene vinyl acetate (EVA), ethylene methyl acrylate (EMA), ethylene acrylic acid (EAA), EAA ionomers, and polypropylene, and other thermoplastic materials such as acrylics, polyphenylene ether, polyphenylene sulfide, acrylonitrile-butadiene-styrene copolymer (ABS), polyurethanes, and others know to those skilled in the art. Blends of thermoplastic materials may also be used. Particularly suitable thermoplastic materials are polyethylene and EVA.

[0034] The flexible thermoplastic films range in thickness from 0.01 mm to 0.25 mm. The thicknesses typically range from 0.025 mm to 0.127 mm to obtain films that have good strength during processing while being thin enough to heat seal quickly and minimize the amount of film material used.

[0035] The amount of packaging material depends upon the type of material and the desired end properties. The amount of packaging material present in the adhesive layer typically ranges from 2 and 15 weight %, and more typically between 3 and 5 weight %. In some particularly suitable embodiments, the packaging material is present in the adhesive layer in an amount of less than 3% by weight.

[0036] The packaged adhesive composition also comprises an adiabatically polymerized pressure sensitive adhesive composition. The adiabatically polymerized pressure sensitive adhesive is a (meth)acrylate-based polymer that is polymerized by a method similar to that described in US Patent No. 5,986,011.

[0037] In some embodiments, the polymerization method comprises providing a first reaction mixture, deoxygenating the first reaction mixture, heating the first reaction mixture to a temperature above the activation temperature of the thermal initiator of the first reaction mixture; allowing the first reaction mixture to polymerize under essentially adiabatic conditions to yield an at least partially polymerized mixture, cooling the at least partially polymerized mixture, adding an additional thermal initiator, and a chain transfer agent to the partially polymerized mixture to form a second reaction mixture, deoxygenating the second reaction mixture, heating the second reaction mixture to a temperature above the activation temperature of the additional thermal initiator, and allowing the second reaction mixture to polymerize under essentially adiabatic conditions to form a polymer.

[0038] The first reaction mixture comprises at least one alkyl(meth)acrylate monomer with alkyl groups comprising 4-20 carbon atoms, at least one reinforcing monomer, at least one photocrosslinkable monomer, and at least one thermal initiator.

[0039] A wide range of alky l(meth) acrylate monomers are suitable. The alkyl(meth)acrylate monomers are described by Formula I:

[0040] CH2=CR1-(CO)-O-R2

[0041] Formula I where R1is an H atom or a methyl group;

[0042] -(CO)- is a carbonyl group C=O; and

[0043] R2is an alkyl group with 4-20 carbon atoms. Examples of suitable alkyl (meth)acrylate comprises n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, isoamyl (meth)acrylate, 2-methylbutyl (meth)acrylate, n- hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 4-methyl-2-pentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-methylhexyl (meth)acrylate, n-octyl (meth) acrylate, isooctyl (meth)acrylate, 2- octyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, isobornyl (meth)acrylate), adamantyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, 2 -propylheptyl (meth)acrylate, isotridecyl (meth)acrylate, isostearyl (meth)acrylate, octadecyl (meth)acrylate, 2- octyldecyl (meth)acrylate, dodecyl (meth)acrylate, lauryl (meth)acrylate, heptadecanyl (meth)acrylate, branched alkyl (meth)acrylates that are (meth)acrylic acid esters of Guerbet alcohols having 12 or more carbon atoms as described in PCT Patent Application Publication WO 2011 / 119363 (Clapper et al.), and combinations thereof.

[0044] In some embodiments, the alkyl (meth)acrylate comprises an alkyl (meth)acrylate of Formula I, where R2is an alkyl group with 8-16 carbon atoms. Examples include 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isobornyl (meth) acrylate), n-decyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, branched alkyl (meth)acrylates that are (meth)acrylic acid esters of Guerbet alcohols having 12 or more carbon atoms as described in PCT Patent Application Publication WO 2011 / 119363 (Clapper et al.), and combinations thereof.

[0045] The first reaction mixture also comprises at least one reinforcing monomer. A wide variety of reinforcing monomers are suitable, typically acid-functional monomers, base-functional monomers, or macromonomers.

[0046] Examples of acid-functional monomers include ethylenically unsaturated carboxylic acids, ethylenically unsaturated sulfonic acids, and ethylenically unsaturated phosphoric acids, and mixtures thereof. Examples of such compounds include, but are not limited to, those selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, fumaric acid, crotonic acid, citraconic acid, maleic acid, B-carboxyethyl acrylate, sulfoethyl methacrylate, and the like, and mixtures thereof.

[0047] Examples of base-functional monomers include acrylamides, N,N-dialkyl substituted acrylamides, N-vinyl lactams, and N,N-dialkylaminoalkyl acrylates, and mixtures thereof. Illustrative examples include, but are not limited to, those selected from the group consisting of N,N-dimethyl acrylamide, N,N-dimethyl methacrylamide, N,N-diethyl acrylamide, N,N-diethyl methacrylamide, N,N-dimethylaminoethyl methacrylate, N,N-dimethylaminopropyl methacrylate, N,N-dimethylaminoethyl acrylate, N,N-dimethylaminopropyl acrylate, NVP (N-vinyl pyrrolidone), and the like, and mixtures thereof.

[0048] Macromers are macromolecular monomers. Examples of macromonomers are macromeric (meth)acrylates. Examples of macromeric (meth)acrylates such as (meth)acrylate- terminated styrene oligomers and (meth)acrylate-terminated polyethers, such as are described in PCT Patent Application WO 84 / 03837 and European Patent Application EP 140941. Methacrylate-terminated polydimethylsiloxane macromer are described in US Patent No. 4,693,935 (Mazurek).

[0049] Particularly suitable reinforcing monomers include acrylic acid, NVP (N-vinyl pyrrolidone), a siloxane-containing macromer, or a styrene-containing macromer.

[0050] The first reaction mixture further comprises at least one photocrosslinker. Photocrosslinkers have a free radically polymerizable group to co-polymerize with the monomers described above, and also contain a photosensitive group. Upon exposure to the right wavelength of light, typically high intensity ultra-violet (UV) radiation, the photosensitive group forms free radicals which can form crosslinks in the polymer.

[0051] Suitable photocrosslinkers in the mono-ethylenically unsaturated aromatic ketone comonomers that are free of ortho-aromatic hydroxyl groups such as those described in US Patent No. 4,737,559 (Kellen et al.). Specific examples include para-acryloxybenzophenone (ABP), para-acrylyoxyethoxybenzophenone, para-N-(methylacryloxyethyl)- carbamoylethoxybenzophenone, para-acryloxyacetophenone, ortho-acrylamidoacetophenone, acrylated anthraquinones, and the like. Particularly suitable are ABP para-acryloxybenzophenone and AeBP Acryloxy Ethyl Benzophenone.

[0052] The first reaction mixture also includes at least one thermal initiator. Suitable thermal initiators include various azo compound such as those commercially available under the trade designation VAZO from E. I. DuPont de Nemours Co. (Wilmington, DE, USA) including VAZO 67, which is 2,2’-azobis(2-methylbutane nitrile), VAZO 64, which is 2,2’-azobis(isobutyronitrile), VAZO 52, which is (2,2’-azobis(2,4-dimethylpentanenitrile), and VAZO 88, which is 1,1’- azobis(cyclohexanecarbonitrile); various peroxides such as benzoyl peroxide, cyclohexane peroxide, lauroyl peroxide, di-tert-amyl peroxide, tert-butyl peroxy benzoate, di-cumyl peroxide, and peroxides commercially available from Atofina Chemical, Inc. (Philadelphia, PA) under the trade designation LUPEROX (e.g., LUPEROX 101, which is 2,5-bis(tert-butylperoxy)-2,5- dimethylhexane, and LUPEROX 130, which is 2,5-dimethyl-2,5-di-(tert-butylperoxy)-3-hexyne); various hydroperoxides such as tert-amyl hydroperoxide and tert-butyl hydroperoxide; and mixtures thereof.

[0053] The first and second reaction mixture may also include additional optional components as long as the optional components do not interfere with the reaction or subsequent curing of the polymer. In particularly, the second reaction mixture may further contain a chain transfer agent to control the molecular weight of the resultant (meth)acrylate copolymer. Examples of useful chain transfer agents include, but are not limited to, carbon tetrabromide, alcohols (e.g., ethanol and isopropanol), mercaptans or thiols (e.g., lauryl mercaptan, butyl mercaptan, tert-dodecyl mercaptan, ethanethiol, isooctylthioglycolate, 2-ethylhexyl thioglycolate, 2-ethylhexyl mercaptopropionate, ethyleneglycol bisthioglycolate), and mixtures thereof.

[0054] As mentioned above, the packaged adhesive composition comprises the adiabatic polymerized reaction mixture contained within the package. The packages can have a wide variety of shapes and sizes. In some embodiments it may be more convenient to have larger packages than are typically suitable when the packages are also the reaction vessels for the polymerization of the reaction mixtures. In some embodiments, the packages are relatively small in other embodiments the packages may be relatively large. Because the packages can have a variety of shapes the size of the three-dimensional packages can be described by at least one dimension. This dimension can be length, width or depth. In some embodiments at least one dimension of the package is from 2 centimeters (less than 1 inch) to 25 centimeters (about 10 inches).

[0055] Also disclosed herein are adhesive articles. In some embodiments, the adhesive article comprises a substrate with a first major surface and a second major surface and a pressure sensitive adhesive layer disposed on at least a portion of the first major surface of the substrate. The pressure sensitive adhesive layer comprises a hot melt coated pressure sensitive adhesive and thermoplastic particles dispersed in the pressure sensitive adhesive. The pressure sensitive adhesive comprises an adiabatically polymerized composition prepared from a reaction mixture comprising at least one alkyl(meth)acrylate monomer with alkyl groups comprising 4-20 carbon atoms, at least one reinforcing monomer selected from an acid-functional monomer, a basefunctional monomer, or a macromonomer, at least one photocrosslinkable monomer, and at least one thermal initiator. The adhesive article has a higher 180° Peel Force and a higher Shear Holding Power than the same adhesive article with the same pressure sensitive adhesive composition without the thermoplastic particles.

[0056] Typically, the pressure sensitive adhesive layer comprises a low concentration of thermoplastic particles. In some embodiments, the thermoplastic particles comprise than 3-5% by weight of the pressure sensitive adhesive layer. In some embodiments, the thermoplastic particles comprise less than 3% by weight of the pressure sensitive adhesive layer.

[0057] The thermoplastic particles comprise polyethylene, ethylene vinyl acetate, ethylene methyl acrylate, ethylene acrylic acid, ethylene acrylic acid ionomers, polypropylene, acrylic polymers, polyphenylene ether, polyphenylene sulfide, acrylonitrile-butadiene-styrene copolymers, polyurethanes, and mixtures and blends thereof.

[0058] The adiabatically polymerized reaction mixtures that form the pressure sensitive adhesive layer are the pressure sensitive adhesive compositions in a package described above. The thermoplastic particles are residual particles resulting from the hot melt processing of a packaged adhesive composition, wherein the packaged adhesive composition comprises a packaging material comprising a thermoplastic polymer, and the adiabatically polymerized pressure sensitive adhesive composition contained within the packaging material.

[0059] Besides the pressure sensitive adhesive and thermoplastic polymer particles, the pressure sensitive adhesive layer may also comprise additional materials. In some embodiments, the pressure sensitive adhesive layer further comprises at least one additional adhesive composition, wherein the at least one additional adhesive composition comprises a packaged adhesive composition or a non-packaged adhesive composition. Other additional materials can also be included in the pressure sensitive layer. In some embodiments, the adhesive layer further comprises at least one additive selected from plasticizers, tackifiers, antimicrobials, fillers, fibers.

[0060] The adhesive article also comprises a substrate. A wide range of substrates are suitable. The substrate may be a release liner, a rigid surface, a tape backing, a film, or a sheet. The adhesive composition can be coated onto a release liner, coated directly onto a substrate, a film or a backing, or formed as a separate layer (e.g., coated onto a release liner) and then laminated to a substrate or film. In some embodiments the adhesive is a transfer tape, i.e. it is disposed between two release liners.

[0061] In some embodiments it may be desirable to impart a microstructured surface to one or both major surfaces of the adhesive. It may be desirable to have a microstructured surface on at least one surface of the adhesive to aid air egress during lamination. If it is desired to have a microstructured surface on one or both surfaces of the adhesive film, the adhesive coating or film may be placed on a tool or a liner containing microstructuring. The liner or tool can then be removed to expose an adhesive film having a microstructured surface. Generally, with optical applications it is desirable that the microstructure disappear over time to prevent interference with optical properties. In medical applications it may be desirable for the microstructure to remain to provide a path for fluid egress.

[0062] The substrate included in the adhesive article can contain polymeric materials, glass materials, ceramic materials, metal-containing materials (e.g., metals or metal oxides), or a combination thereof. The substrate can include multiple layers of material such as a support layer, a primer layer, a hard coat layer, a decorative design, and the like. The substrate can be permanently or temporarily attached to an adhesive film. For example, a release liner can be temporarily attached and then removed for attachment of the adhesive film to another substrate.

[0063] The substrate can have a variety of functions such as, for example, providing flexibility, rigidity, strength, support, MVTR (moisture vapor transmission rate) properties, or optical properties such as, for example, reflectivity, antireflectivity, polarization, or transmissivity (e.g., selective with respect to different wavelengths). That is, the substrate can be flexible or rigid; reflective or non -reflective; visibly clear, colored but transmissive, or opaque (e.g., not transmissive); and polarizing or non-polarizing.

[0064] Representative examples of polymeric substrates include those that contain polycarbonates, polyesters (e.g., polyethylene terephthalates and polyethylene naphthalates), polyurethanes, poly(me th) acrylates (e.g., polymethyl methacrylates), polyvinyl alcohols, polyolefins such as polyethylenes and polypropylenes, polyvinyl chlorides, polyimides, cellulose triacetates, acrylonitrile-butadiene-styrene copolymers, and the like.

[0065] In other embodiments, the substrate is a release liner. Any suitable release liner can be used. Examples of suitable liners include paper, e.g., kraft paper, or polymeric films, e.g., polyethylene, polypropylene or polyester. At least one surface of the liner can be treated with a release agent such as silicone, a fluorochemical, or other low surface energy based release material to provide a release liner. Suitable release liners and methods for treating liners are described in, e.g., U.S. Patent Nos. 4,472,480, 4,980,443 and 4,736,048. The liner can have a microstructure on its surface that is imparted to the adhesive to form a microstructure on the surface of the adhesive film. The liner can then be removed to expose an adhesive film having a microstructured surface.

[0066] The adhesive articles can have a wide range of uses. In some embodiments, the adhesive articles are medical articles. Some of the medical articles are intended to be attached to mammalian skin. In these embodiments, the adhesive layer adheres to mammalian skin.

[0067] Also disclosed herein are methods for preparing adhesive articles. In some embodiments, the method of preparing an adhesive article comprises providing a substrate with a first major surface and a second major, and hot melt coating a packaged pressure sensitive adhesive composition onto at least a portion of the first major surface of the substrate to form a pressure sensitive adhesive layer. The packaged pressure sensitive adhesive composition comprises a packaging material comprising a thermoplastic polymer and a pressure sensitive adhesive composition contained within the packaging material. The pressure sensitive adhesive composition comprises an adiabatically polymerized composition, where the hot melt coated pressure sensitive adhesive composition comprises thermoplastic particles dispersed within the pressure sensitive adhesive layer has a higher 180° Peel Force and a higher Shear Holding Power than the same pressure sensitive adhesive layer without the thermoplastic particles.

[0068] Methods of preparing hot melt processable packaged adhesive compositions are described in detail above. The adiabatically polymerized pressure sensitive adhesive composition is placed into a thermoplastic package to form the packaged pressure sensitive adhesive composition. The packages have at least one dimension of the packages is from 2 centimeters to 25 centimeters.

[0069] The method of forming the adiabatically polymerized composition has been described in detail above. In some embodiments, the method of forming the adiabatically polymerized composition comprises providing a first reaction mixture comprising, an ethylenically unsaturated silicone-containing monomer, at least one additional ethylenically unsaturated monomer, a chain transfer agent, and a thermal initiator, deoxygenating the first reaction mixture, heating the first reaction mixture to a temperature above the activation temperature of the thermal initiator, allowing the first reaction mixture to polymerize under essentially adiabatic conditions to yield an at least partially polymerized mixture, cooling the at least partially polymerized mixture, adding an additional thermal initiator, and a chain transfer agent to the partially polymerized mixture to form a second reaction mixture, deoxygenating the second reaction mixture, heating the second reaction mixture to a temperature above the activation temperature of the additional thermal initiator, allowing the second reaction mixture to polymerize under essentially adiabatic conditions to form a polymer.

[0070] The packaged adhesive compositions are hot melt processed through the use of a hot melt mixing apparatus to form a pressure sensitive adhesive layer. A variety of hot melt mixing techniques using a variety of hot melt mixing equipment are suitable for processing the packaged adhesive compositions. Both batch and continuous mixing equipment may be used. Examples of batch methods include those using a BRABENDER (e. g. a BRABENDER PREP CENTER, commercially available from C.W. Brabender Instruments, Inc.; South Hackensack, NJ) or BANBURY internal mixing and roll milling equipment (e.g. equipment available from Farrel Co.; Ansonia, CN). Examples of continuous methods include single screw extruding, twin screw extruding, disk extruding, reciprocating single screw extruding, and pin barrel single screw extruding. Continuous methods can utilize distributive elements, pin mixing elements, static mixing elements, and dispersive elements such as MADDOCK mixing elements and SAXTON mixing elements. A single hot melt mixing apparatus may be used, or a combination of hot melt mixing equipment may be used to process the packaged adhesive compositions of this disclosure.

[0071] The output of the hot melt mixing is coated onto a substrate to form an adhesive layer. If a batch apparatus is used, the resulting hot melt blend can be removed from the apparatus and placed in a hot melt coater or extruder and coated onto a substrate. If an extruder is used to prepare a hot melt blend, the packaged adhesive composition can be directly extruded onto a substrate to form an adhesive layer. After forming, the adhesive layer or film can be solidified by quenching using both direct methods (e.g. chill rolls or water batch) and indirect methods (e.g. air or gas impingement).

[0072] The pressure sensitive adhesive layer comprises thermoplastic particles that are the residue of the packaging material of the packaged adhesive composition that was hot melt coated. In some embodiments, the thermoplastic particles comprise than 3-5% by weight of the pressure sensitive adhesive layer. In other embodiments, the thermoplastic particles comprise less than 3% by weight of the pressure sensitive adhesive layer.

[0073] In some embodiments it may be desirable to crosslink the pressure sensitive adhesive layer after the pressure sensitive adhesive layer is formed. Crosslinking can be carried out by exposing the pressure sensitive adhesive layer to actinic radiation to activate the photocrosslinkers copolymerized with the other monomers to form the pressure sensitive adhesive composition. Typically the actinic radiation is UV light, often high intensity UV light.

[0074] Examples These examples are merely for illustrative purposes only and are not meant to be limiting on the scope of the appended claims. All parts, percentages, ratios, etc. in the examples and the rest of the specification are by weight, unless noted otherwise. The following abbreviations are used: cm - centimeters; mm - millimeters; m - meters; oz - ounces; g - grams; kg - kilograms; ml - milliliters; min - minutes; hr - hours; rad - radians; Pa - Pascals; mJ - milliJoules; OD - outer diameter; CW = cross web direction; DW = down web direction. The terms “weight %”, “% by weight”, and “wt%” are used interchangeably.

[0075] Table of Abbreviations

[0076] Test Methods

[0077] 180° Peel Adhesion

[0078] This peel adhesion test is similar to the test method described in ASTM D 3330-90, with a stainless steel or Fruehauf substrate described in the test.

[0079] Adhesive coated films were cut into 1.27 centimeter by 15 centimeter strips. Each strip was then adhered to a 10 centimeter by 20 centimeter clean, substrate surface using a 2 -kilogram roller passed once over the strip. The bonded assembly dwelled at room temperature for about one minute and was tested for 180° peel adhesion using an IMASS slip / peel tester (Model 3M90, commercially available from Instrumentors Inc., Strongsville, OH) at a rate of 2.3 meters / minute (90 inches / minute) over a five second data collection time. Two samples were tested; the reported peel adhesion value is an average of the peel adhesion value from each of the two samples.

[0080] DMA-Dynamic Mechanical Analysis

[0081] Rheology data such as G’ (storage elastic modulus) and G” (loss modulus), tan5 (= G’7G’) were measured by Dynamic Mechanical Analysis.

[0082] The rheometer used for these measurements is a TA Instruments AR1500ex with a Peltier plate on the bottom for temperature control and a 20 mm parallel plate fixture above the sample which is oscillated by an electromagnetic drive system.

[0083] Sample preparation: Samples prepared by stacking 12 layers of PSA thickness was 2.0 mm, and then a test piece was punched out to 8mm diameter.

[0084] Sample Run: Dynamic time sweep at 1 rad / s with an applied stress of 1000 Pa and a Peltier plate temperature of 100°C, with a duration of 2 minutes

[0085] Shear Strength

[0086] This shear strength test is similar to the test method described in ASTM D 3654-88.

[0087] Adhesive coatings on film were cut into 2.5 centimeter (1 inch) by 15 centimeter (6 inch) strips. Each strip was then adhered to a stainless steel panel such that a 2.5 centimeter by 2.5 centimeter portion of each strip was in firm contact with the panel and one end portion of the tape being free. The panel with coated strip attached was held in a rack such that the panel formed an angle of 178° with the extended tape free end which was tensioned by application of a force of 250 grams applied as a hanging weight from the free end of the coated strip. The 2° less than 180° was used to negate any peel forces, thus ensuring that only shear strength forces were measured, in an attempt to more accurately determine the holding power of the tape being tested. The time elapsed for each tape example to separate from the test panel was recorded as the shear strength. All shear strength failures (if the adhesive failed at less than 10,000 minutes) reported herein were cohesive failures of the adhesive. Each test was terminated at 10,000 minutes, unless the adhesive failed at an earlier time (as noted).

[0088] MYTR-Moisture Vapor Transmission Rate

[0089] Test materials were evaluated for moisture vapor transmission using water contact (inverted cup) and vapor contact (Upright Cup) methods which were a modified version of the test methods described in ASTM E96.

[0090] Inverted Cup

[0091] After placing 25 ml of distilled water in a Paddington cup having a 3.5 cm opening (commercially available from Bio-Med Engineering, LTD, Liversedge, West Yorkshire, England), a 2.54 cm diameter sample of the test material was clamped to the flange using sealing rings and screw clamps. The sample was then placed in a circulating oven in an inverted position and was maintained at 37°C. and a relative humidity of 20%. After preconditioning for about 4 hours, an initial sample weight was recorded and the sample returned to the inverted position in the oven. The cup was removed from the oven between 16 and 24 hours later and re -weighed to determine moisture loss. The moisture vapor transmission of each sample was reported in grams per square meter per 24 hours.

[0092] Upright Cup

[0093] 50 mis distilled water was placed in a jar having a 2.54 cm opening. A 3.8 cm diameter sample of the test material was clamped to the flange using sealing rings and screw clamps. The sample was then placed in a circulating oven in an upright position and was maintained at 37°C. and a relative humidity of 20%. After preconditioning for about 4 hours, an initial sample weight was recorded and the sample returned to the upright position in the oven. The cup was removed from the oven between 16 and 24 hours later and re-weighed to determine moisture loss. The moisture vapor transmission of each sample was reported in grams per square meter per 24 hours.

[0094] Shrinkage Test The 24 hr applied shrinkage test is carried out on a Fruehauf panel. The X gash test: a 2 inch x 2 inch (5 cm x 5 cm) sample was applied to the Fruehauf panel, and an X gash was cut into the sample, the sample was allowed to dwell for 24 hr, and the gap size was measured in mils and converted to micrometers.

[0095] Examples E1-E2 and Comparative Examples CE1-CE2

[0096] Samples of PSA-1 were used as is in Comparative Examples CE1 and CE2, and samples of PSA-1 were packaged in EVA film in Examples El and E2.

[0097] Metering the Adhesive:

[0098] A pail unloader provided by Graco, was used to meter PSA-1 adhesive from a 20 liter epoxy-coated metal pail. The platen, hoses, pumps, and metering elements are all heated to 120°C. The pail unloader used the platen to generate pressure in the adhesive pail. The pressure helps draw material into a piston pump fixed on top of the heated platen. The adhesive is pumped from the piston pump into a 1.5 meter hose which leads to a turbine volumetric flow meter. The adhesive was then metered out at 150 cm3 / min using a automated pin valve into a 3 meter hose. For samples that were packaged, the hose fed into a 9mm OD hose that is parallel with a heat sealer, model number F900 and was loosely wrapped by an EVA package. At the end of the 9 mm hose, the adhesive filled the EVA package. The adhesive in the EVA package was placed into an aluminum tray to cool.

[0099] Creating the Package:

[0100] A 10 cm wide EVA film was pulled off a roll with no resistance. It was pulled through a V-slot that created a fold in the film. The folded EVA film was manually steered into the heater on the F900 Sealer. The edges on the film were convectively heated to 115°C while being pulled into a nip. The edges of the film were pressed together by a spring-tensioned nip roller. The edges were then cooled to 25 °C using pressurized air and conduction from the nip idlers.

[0101] Creating Adhesive Coatings

[0102] The adhesives were coated on either Backing- 1 or Liner- 1. For Comparative Examples CE1 and CE2 PSA-1 was extruded from a twin screw extruder, for Examples El and E2, the packaged PSA-1 samples were extruded from a Bonnot extruder into a twin screw extruder. All extruded samples were coated through a rod die to a thickness of 2 mils (51 micrometers). The adhesive samples were photocrosslinked with 50 mJ using a UV lamp. The samples were tested for 180° Peel Adhesion and MVT according to the test methods described above. The data are presented in Table 1. Table 1

[0103] Examples E3-E4 and Comparative Examples CE3-CE6

[0104] The adhesive samples coated on Liner- 1 (CE1 and E2) were laminated to different backings (Backing-2 or Backing-3). For samples CE5 and CE6 the coated adhesive was exposed to an extra dose of UV radiation (80 mJ). The samples were tested for 180° Peel Adhesion, tan delta (DMA) and Shrinkage according to the test methods described above. The sample descriptions are presented in Table 2, 180° Peel Adhesion data are presented in Table 3, the Tan delta data are shown in Table 4, and the Shrinkage data are presented in Table 5. Table 2

[0105] Table 3

[0106] Table 4

[0107] Table 5

[0108] Examples E5-E7 and Comparative Example CE7

[0109] To test if the same effect is achieved with hot melt blends of adiabatically polymerized pressure sensitive adhesive and pellets of packaging material, samples of PSA-1 was hot melt coated (Comparative Example CE7) and PSA-1 with different levels of Packaging Pellets (Examples E5-E7) were prepared.

[0110] Metering the Adhesive:

[0111] A pail unloader provided by Graco, was used to meter PSA-1 adhesive from a 20-liter epoxy-coated metal pail. The platen, hoses, pumps, and metering elements are all heated to 120°C. The pail unloader used the platen to generate pressure in the adhesive pail. The pressure helps draw material into a piston pump fixed on top of the heated platen. The adhesive is pumped from the piston pump into a 1.5 meter hose which leads to a turbine volumetric flow meter. The adhesive was then metered out at 150 cm3 / min using an automated pin valve into a 3 meter hose into a Bonnot extruder. For those examples that include blended Packaging Pellets, the desired amount of Packaging Pellets were fed in a weight feeder into the same feed of the Bonnot extruder. Creating Adhesive Coatings The adhesives were coated onto Liner- 1. The samples were extruded from a Bonnot extruder into a twin screw extruder. All extruded samples were coated through a rod die. to a thickness of 1 mil (25 micrometers). The adhesive samples were photocrosslinked with 50 mJ using a UV lamp. The samples were laminated to Backing- 1 and tested for 180° Peel Adhesion, Shear, and upright MVT according to the test methods described above. The data are presented in Table 6.

[0112] Table 6

Claims

What is claimed is:

1. A packaged adhesive composition comprising: a packaging material comprising a thermoplastic polymer; and a pressure sensitive adhesive composition contained within the packaging material, the pressure sensitive adhesive composition comprising: an adiabatically polymerized composition prepared from a reaction mixture comprising: at least one alkyl(meth)acrylate monomer with alkyl groups comprising 4-20 carbon atoms; at least one reinforcing monomer selected from an acid-functional monomer, a base-functional monomer, or a macromonomer; at least one photocrosslinkable monomer; and at least one initiator; wherein the packaged adhesive composition is hot melt processable to form a pressure sensitive adhesive layer, wherein the hot melt processed packaged adhesive composition has a higher 180° Peel Force and a higher Shear Holding Power than the same hot melt processed adhesive that has not been packaged.

2. The packaged adhesive composition of claim 1, wherein the packaging material comprises polyethylene, ethylene vinyl acetate, ethylene methyl acrylate, ethylene acrylic acid, ethylene acrylic acid ionomers, polypropylene, acrylic polymers, polyphenylene ether, polyphenylene sulfide, acrylonitrile-butadiene-styrene copolymers, polyurethanes, and mixtures and blends thereof.

3. The packaged adhesive composition of claim 1, wherein the adiabatically polymerized composition is polymerized by a method comprising: providing a first reaction mixture comprising: at least one alkyl(meth) acrylate monomer with alkyl groups comprising 4-20 carbon atoms; at least one reinforcing monomer selected from an acid-functional monomer, a base-functional monomer, or a macromonomer; at least one photocrosslinkable monomer; and at least one thermal initiator; deoxygenating the first reaction mixture;heating the first reaction mixture to a temperature above the activation temperature of the thermal initiator; allowing the first reaction mixture to polymerize under essentially adiabatic conditions to yield an at least partially polymerized mixture; cooling the at least partially polymerized mixture; adding an additional thermal initiator, and a chain transfer agent to the partially polymerized mixture to form a second reaction mixture; deoxygenating the second reaction mixture; heating the second reaction mixture to a temperature above the activation temperature of the additional thermal initiator; allowing the second reaction mixture to polymerize under essentially adiabatic conditions to form a polymer.

4. The packaged adhesive composition of claim 1, wherein the at least one alkyl(meth)acrylate monomer with alkyl groups comprising 8-16 carbon atoms or mixtures of alkyl (meth)acrylates with alkyl groups comprising 8-16 carbon atoms.

5. The packaged adhesive composition of claim 1, wherein the at least one reinforcing monomer is selected from AA, NVP, a siloxane-containing macromer, or a styrene-containing macromer.

6. The packaged adhesive composition of claim 1 wherein at least one dimension of the package is from 2 centimeters to 25 centimeters.

7. An adhesive article comprising: a substrate with a first major surface and a second major surface; and a pressure sensitive adhesive layer disposed on at least a portion of the first major surface of the substrate, wherein the pressure sensitive adhesive layer comprises a hot melt coated pressure sensitive adhesive and thermoplastic particles dispersed in the pressure sensitive adhesive, wherein the pressure sensitive adhesive comprises: an adiabatically polymerized composition prepared from a reaction mixture comprising: at least one alkyl(meth)acrylate monomer with alkyl groups comprising 4-20 carbon atoms; at least one reinforcing monomer selected from an acid-functional monomer, a base-functional monomer, or a macromonomer;at least one photocrosslinkable monomer; and at least one thermal initiator; wherein the adhesive article has a higher 180° Peel Force and a higher Shear Holding Power than the same adhesive article with the same pressure sensitive adhesive composition without the thermoplastic particles.

8. The adhesive article of claim 7, wherein the thermoplastic particles comprise 3-5% by weight of the pressure sensitive adhesive layer.

9. The adhesive article of claim 7, wherein the thermoplastic particles comprise less than 3% by weight of the pressure sensitive adhesive layer.

10. the adhesive article of claim 7, wherein the thermoplastic particles comprise polyethylene, ethylene vinyl acetate, ethylene methyl acrylate, ethylene acrylic acid, ethylene acrylic acid ionomers, polypropylene, acrylic polymers, polyphenylene ether, polyphenylene sulfide, acrylonitrile-butadiene-styrene copolymers, polyurethanes, and mixtures and blends thereof.

11. The adhesive article of claim 7, wherein the thermoplastic particles are residual particles resulting from the hot melt processing of a packaged adhesive composition, wherein the packaged adhesive composition comprises: a packaging material comprising a thermoplastic polymer; and the adiabatically polymerized pressure sensitive adhesive composition contained within the packaging material.

12. The adhesive article of claim 7, wherein the pressure sensitive adhesive layer further comprises at least one additional adhesive composition, wherein the at least one additional adhesive composition comprises a packaged adhesive composition or a non-packaged adhesive composition.

13. The adhesive article of claim 7, wherein the adhesive layer adheres to mammalian skin.

14. The adhesive article of claim 7, wherein the adhesive layer further comprises at least one additive selected from plasticizers, tackifiers, antimicrobials, fillers, fibers.

15. A method of preparing an adhesive article comprising: providing a substrate with a first major surface and a second major; andhot melt coating a packaged pressure sensitive adhesive composition onto at least a portion of the first major surface of the substrate to form a pressure sensitive adhesive layer, wherein the packaged pressure sensitive adhesive composition comprises: a packaging material comprising a thermoplastic polymer; and a pressure sensitive adhesive composition contained within the packaging material, the pressure sensitive adhesive composition comprising: an adiabatically polymerized composition, wherein the hot melt coated pressure sensitive adhesive composition comprises thermoplastic particles dispersed within the pressure sensitive adhesive layer has a higher 180° Peel Force and a higher Shear Holding Power than the same pressure sensitive adhesive layer without the thermoplastic particles.

16. The method of claim 15, wherein the method of forming the adiabatically polymerized composition comprises: providing a first reaction mixture comprising: an ethylenically unsaturated silicone-containing monomer; at least one additional ethylenically unsaturated monomer; a chain transfer agent; and a thermal initiator; deoxygenating the first reaction mixture; heating the first reaction mixture to a temperature above the activation temperature of the thermal initiator; allowing the first reaction mixture to polymerize under essentially adiabatic conditions to yield an at least partially polymerized mixture; cooling the at least partially polymerized mixture; adding an additional thermal initiator, and a chain transfer agent to the partially polymerized mixture to form a second reaction mixture; deoxygenating the second reaction mixture; heating the second reaction mixture to a temperature above the activation temperature of the additional thermal initiator; allowing the second reaction mixture to polymerize under essentially adiabatic conditions to form a polymer.

17. The method of claim 15, wherein the thermoplastic particles comprise than 3-5% by weight of the pressure sensitive adhesive layer.

18. The method of claim 15, wherein the thermoplastic particles comprise less than 3% by weight of the pressure sensitive adhesive layer.

19. The method of claim 15, further comprising exposing the adhesive layer to actinic radiation to crosslink the adhesive layer.

20. The method of claim 15, wherein the packaged pressure sensitive adhesive composition comprises packages wherein at least one dimension of the packages is from 2 centimeters to 25 centimeters.

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