WO2025181577A1 - Curable adhesive composition comprising epoxy, initiator and metal compound, articles and methods - Google Patents

Abstract

An adhesive article is described comprising a support and a layer of a curable adhesive composition disposed on the support. The curable adhesive composition comprises a pressure sensitive adhesive comprising an organic polymer and an epoxy component; a cationic initiator; and a metal compound. The metal compound can neutralize excess acid generated by the initiator while allowing high epoxy conversion rates. In some embodiments, the metal compound comprises an anion having at least one hydroxyl group and at least one group selected from oxide, PO^- or SO^-. Representative examples include AIO(OH), Ca₅(PO₄)₃(OH), and Ca(PO₃)OCH₂(CHOH)(CH₂OH) Also described are curable epoxy compositions and methods of making an adhesively bonded article.

Description

CURABLE ADHESIVE COMPOSITION COMPRISING EPOXY, INITIATOR AND METAL COMPOUND, ARTICLES AND METHODS

SUMMARY

In one embodiment, an adhesive article is described comprising a support and a layer of a curable adhesive composition disposed on the support. The curable adhesive composition comprises a pressure sensitive adhesive comprising an organic polymer and an epoxy component; a cationic initiator; and a metal compound. The inclusion of the metal compound can provide beneficial properties such as neutralizing excess acid that is generated by the initiator while allowing high epoxy conversion rates. In some emboidments, a solution of the initiator, water and metal compound at a weight ratio of 2:2:0.05 has a pH of 6-8 after heating. In another embodiment, the adhesive composition together with the initiator and metal compound has a surface pH greater than 1, 2, 3, or 4. In some embodiments, the metal compound comprises an anion having at least one hydroxyl group and at least one group selected from oxide, PO’, or SO". Representative examples include AIO(OH), ChTPChHOH). and Ca(PO₃)OCH₂(CHOH)(CH₂OH)

In another embodiment, a composition is described comprising an epoxy component; a cationic initiator; and a metal compound comprising an anion having at least one hydroxyl group and at least one group selected from oxide, PO", or SO".

In another embodiment, a method of making a bonded article is described comprising providing an adhesive article or composition as described herein; contacting the adhesive layer or adhesive composition to a substrate; and curing the composition by exposure to actinic radiation, heat, or a combination thereof.

Organic Polymer

In some emboidments, the adhesive composition (e.g. of the curable tape) comprises an organic polymer. The organic polymer may also be characterized as a film forming component.

In some embodiments, the organic polymer may be an elastomer. Common elastomers include (meth)acrylic elastomers (i.e. elastomers prepared by the polymerization of (meth)acrylic monomers), polyurethanes, natural rubber, synthetic rubber such as butyl rubber, isobutyl, nitrile or butadiene rubbers, polyolefins, fluoropolymers, silicones, and styrenic block copolymers. Styrenic block copolymers comprise one or more styrenic end blocks and an unsaturated, partly hydrogenated or fully hydrogenated polydiene block, most commonly polybutadiene, polyisoprene, orpoly(iso)butylene.

In some embodiments, the organic polymer is thermoplastic. Common thermoplastic organic polymers include polyolefins such as poly(ethylene), poly(propylene), poly(vinyl chloride), poly(styrene), poly(oxymethylene), polyethylene oxide), polyethylene terephthalate ), poly(carbonate), poly (phenylene oxides), poly(urethanes), poly(ureas), acrylonitrile-butadiene-styrene (ABS), poly (amides), poly (lactate) (PLA), poly (etheretherketone) (PEEK), poly (sulfone) (PSU), poly(ethersulfone)(PES), and poly(meth)acrylates. In some emboidments, the curable adhesive composition comprises at least 30, 35, 40, 45, or 50 wt.% of organic polymer, based on the total organic components of the adhesive composition. In some emboidments, the curable adhesive composition comprises no greater than 60, 55, or 50 wt.% organic polymer. In some embodiments, the adhesive composition may comprise a continuous phase of organic polymer and an epoxy component dispersed within the continuous phase of organic polymer.

The curable adhesive composition is typically a pressure sensitive adhesive prior to curing due to the selection of organic polymer. In some embodiments, the adhesive composition is pressure sensitive after curing. When the uncured adhesive and organic polymer is a pressure sensitive adhesive, the uncured adhesive and organic polymer thereof typically has a glass transition temperature less than 25, 20, 15, 10, or 0°C. In some embodiments, the Tg may be calculated based on the Fox equation. The uncured adhesive and organic polymer thereof typically has a shear storage modulus (G’) of less than 3 x 10⁶ dyne/cm² (0.3 MPa) at approximately room temperature (25°C) and a frequency of 1 Hz.

In other embodiments, the adhesive composition is a semi-structural or structural adhesive after curing. As used herein, the term “semi-structural adhesive" refers to those cured compositions that have an overlap shear strength of at least 1.5 megaPascals (MPa). More preferably, the overlap shear strength is at least 2.0 or at least 3.0 MPa. Those cured compositions having a particularly high overlap shear strength, however, are referred to herein as “structural adhesives”. Structural adhesives are those cured compositions that have an overlap shear strength of at least 4, at least 5, at least 6, or at least 7 MPa.

In some embodiments, the organic polymer is a thermoplastic polymer having a thermal transition at a temperature of at least 90, 100, 110, 120, 130, 140, 150, or 160°C. In the case of thermoplastic organic polymers the thermal transition temperature is typically a melt temperature. In other embodiments, the thermal transition temperature may be a glass transition temperature (Tg). In some embodiments, the organic polymer is a thermoplastic or thermosetting polymer having a thermal transition at a temperature of no greater than 300, 250, or 200°C.

The organic polymer may be exposed to a temperature greater than the thermal transition temperature when making the adhesive composition or when applying the adhesive composition to a substrate. In some emboidment, curable (e.g. adhesive) composition is exposed to a temperature in a range of 90-160°C during manufacturing or use of the article. As demonstrated by the forthcoming examples, although acid scavenging additives such as aluminum trihydroxide in combination with acidgenerating initiators and water can exhibit a neutral pH at ambient temperature, this same combination of components can be highly acidic (e.g. pH of 0.5) after exposure to elevated temperatures.

(Meth)acrylic -based multiblock copolymer

In some embodiments, the organic polymer comprises an acrylic block copolymer. The acrylic block copolymer is typically a triblock copolymer having an A-B-A structure with the A and B blocks selected to have solubility parameters that are sufficiently different to cause phase separation between the A blocks and the B block. To create the phase separation, the two A blocks and the B block of the (meth)acry lie-based triblock copolymer A-B-A are typically selected to have different glass transition temperatures. The A blocks, which typically have a higher glass transition temperature than the B, can be referred to as “hard” blocks while the B block can be referred to as a “soft” block. The A blocks are usually selected to be more rigid than the B block. The A blocks can be thermoplastic and can provide semi-structural or structural strength and/or shear strength to the adhesive composition. The B block can be a viscous material and can provide tack and adhesive strength to the adhesive composition.

The A blocks of the (meth)acrylic -based triblock copolymer A-B-A are typically selected to have a glass transition temperature (T_g) equal to at least 50°C as measured using Dynamic Mechanical Analysis. In some embodiments, the glass transition temperature is at least 60°C, at least 70°C, at least 75°C, at least 80°C, at least 90°C, or at least 100°C. The glass transition temperature can be up to 200°C, up to 190°C, up to 180°C, up to 175°C, up to 170°C, up to 160°C, up to 150°C, up to 140°C, up to 130°C, up to 125°C, up to 120°C, up to 110°C, or up to 100°C. Exemplary ranges of glass transition temperatures of the A blocks include 50 to 200°C, 75 to 200°C, 70 to 175°C, 75 to 150°C, or 80 to 140°C.

The B block of the (meth)acry lie-based triblock copolymer A-B-A is a viscous segment and is typically selected to have a glass transition temperature no greater than 20°C as measured using Dynamic Mechanical Analysis. In some embodiments, the glass transition temperature is no greater than 10°C, no greater than 5°C, no greater than 0°C, no greater than -10°C, no greater than -20°C, or no greater than -30°C. The glass transition temperature is often at least -70°C, at least -60°C, at least -50°C, at least -40°C, or at least -30°C depending on the composition of monomers used to form the B block. Exemplary ranges for the glass transition temperature of the B block include -70 to 20°C, -70 to 10°C, -70°C to 0°C, -50 to 0°C, -70 to -10°C, -50 to -10°C, -70 to -20°C, -50 to -20°C, -70 to -30°C, or -50 to -30°C.

The (meth)acrylic-based triblock copolymer A-B-A has two polymeric A blocks and one polymeric B block. Each of these blocks can be a homopolymer or a copolymer (e.g., a random copolymer). The (meth)acrylic -based triblock copolymer A-B-A usually contains 10 to 55 weight percent A blocks and 45 to 90 weight percent B blocks based on a total weight of the (meth)acry lie -based triblock copolymer. The (meth)acrylic -based triblock copolymer contains at least 10, at least 20, at least 25, at least 30, or at least 35 weight percent and up to 55, up to 50, up to 45, up to 40, or up to 35 weight percent A block based on the total weight of the (meth)acry lie-based triblock copolymer. The (meth)acry lie-based triblock copolymer contains at least 45, at least 50, at least 55, or at least 60 weight percent and up to 90, up to 80, up to 75, up to 70, up to 65, or up to 60 weight percent of the B block based on the total weight of the (meth)acrylic-based triblock copolymer. Together, the weight percent of the A blocks and the weight percent of the B block is nearly 100 weight percent based on the total weight of the (meth)acrylic -based triblock copolymer (i.e., there can be a small amount of initiator residue present as well). In some examples, the (meth)acrylic -based block copolymer contains 15 to 55 weight percent A blocks and 45 to 85 weight percent B block, 15 to 40 weight percent A block and 60 to 85 weight percent B block, 20 to 55 weight percent A blocks and 45 to 80 weight percent B block, 20 to 40 weight percent A block and 60 to 80 weight percent B block, or 20 to 35 weight percent A block and 65 to 80 weight percent B block. Each of the two A blocks of the (meth)acrylic -based triblock copolymer A-B-A can be about the same weight. That is, the weight ratio of the two A blocks of the (meth)acrylic-based triblock copolymer is often 1:1 or close to 1:1 such as greater than 0.9:1. However, other weight ratios can also be used such as in a range of 0.65: 1 to 0.99: 1. In many cases, the weight ratio of the two A blocks of the (methacrylicbased triblock copolymer is no lower than 0.65:1, 0.7:1, 0.75:1, 0.8:1, 0.85:1, 0.9:1, 0.95:1, 0.98:1, or 0.99:1.

Each A block of the (meth)acry lie-based triblock copolymer A-B-A is usually prepared from a monomer composition that includes an alkyl methacrylate. Suitable alkyl methacrylates for preparing the A blocks often have an alkyl group with 1 to 10 carbon atoms, 1 to 8 carbon atoms, 1 to 6 carbon atoms, 1 to 5 carbon atoms, or 1 to 4 carbon atoms. If the alkyl group has 3 to 5 carbon atoms, it is typically branched. If the alkyl group has 6 to 10 carbon atoms, it is typically cyclic or bicyclic.

Example alkyl methacrylates include methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, cyclohexyl methacrylate, methylcyclohexyl methacrylate, 3,3,5-trimethylcyclohexyl methacrylate, and isobomyl methacrylate. These monomers, when polymerized as a homopolymer, have a glass transition temperature equal to at least 50°C.

In some instances, the A blocks are homopolymers and each homopolymer is a poly(alkyl methacrylate). Example poly(alkyl methacrylates) include poly(methyl methacrylate), poly(ethyl methacrylate), poly(isopropyl methacrylate), poly(isobutyl methacrylate), poly(sec -butyl methacrylate), poly(tert-butyl methacrylate), poly(cyclohexyl methacrylate), poly(methylcyclohexyl methacrylate), poly(3,3,5-trimethylcyclohexyl methacrylate), and poly(isobomyl methacrylate).

In addition to the alkyl methacrylate monomers, the first monomer composition used to form the first A block can include other optional monomers provided the resulting polymeric blocks have a glass transition temperature that is equal to at least 50°C when measured using Dynamic Mechanical Analysis. In some embodiments, the first monomer composition can include other (meth)acrylic -based monomers such as alkoxy substituted alkyl methacrylates, aryl methacrylates, aralkyl methacrylates, aryloxy substituted alkyl methacrylate, cyclic alkyl acrylates having a cyclic group with 6 to 10 carbon atoms, bicyclic alkyl acrylates having a bicyclic alkyl group with at least 8 carbon atoms, or a mixture thereof. Suitable alkoxy substituted alkyl methacrylates often have an alkyl group with 1 to 4 carbon atoms and an alkoxy group with 1 to 4 carbon atoms. An example is 2-methoxyethyl methacrylate. Suitable aryl methacrylates typically have an aryl group with 6 to 10 carbon atoms. An example aryl methacrylate is phenyl methacrylate. Suitable aralkyl methacrylates typically have aralkyl groups with 7 to 10 carbon atoms. An example aralkyl methacrylate is benzyl methacrylate. Suitable aryloxy -substituted alkyl methacrylates often have an aryloxy-substituted alkyl group with 7 to 10 carbon atoms. An example aryloxy-substituted alkyl methacrylate is 2-phenoxyethyl methacrylate. An example cyclic alkyl acrylate is cyclohexyl acrylate and an example bicyclic acrylate is isobomyl acrylate.

In still other embodiments, the first monomer composition used to form the A blocks can include various optional (meth)acrylic-based polar monomers provided the glass transition temperature of each resulting block is equal to at least 50°C. If present, these polar monomers are usually present in an amount no greater than 10, no greater than 5, no greater than 2, or no greater than 1 weight percent based on a total weight of the monomers in the respective monomer composition. Suitable polar monomers include, for example, a hydroxy group or a glycidyl group. Typically, acidic monomers and nitrogen-containing monomers are not selected (e.g., the first monomer composition is often free of such monomers). Specific monomers include, but are not limited to, hydroxy alkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate as 2-hydroxypropyl (meth)acrylate, as well as glycidyl (meth)acrylate. In many embodiments, however, there are no polar monomers in the A blocks.

In other embodiments, the first monomer composition used to form the A blocks can include other optional monomers that are not (meth)acry lie -based monomers provided that greater than 80 weight percent of the monomers in the block are (meth)acrylic-based monomers and provided that the resulting polymeric blocks have a glass transition temperature that is equal to at least 50°C when measured using Dynamic Mechanical Analysis. Examples of these other monomers are vinyl monomers such as styrene, styrene-type monomers (e.g., alpha-methyl styrene, 3-methyl styrene, 4-methyl styrene, ethyl styrene, isopropyl styrene, tert-butyl styrene, dimethyl styrene, 2,4,6-trimethyl styrene, and 4-methoxy styrene), and vinyl acetate.

The A blocks of the (meth)acrylic -based triblock copolymer are often a homopolymer formed from an alkyl methacrylate and the resulting polymeric block has a glass transition temperature equal to at least 50°C as measured using Dynamic Mechanical Analysis. In some specific embodiments, both A blocks are the same homopolymer, which is a poly(alkyl methacrylate). In some more specific embodiments, the A blocks are poly(methyl methacrylate).

The B block of the (meth)acry lie-based triblock copolymer A-B-A is typically formed from monomers that will provide polymeric blocks having a glass transition temperature no greater than 20°C as measured using Dynamic Mechanical Analysis. The B block is often prepared from a monomer composition that includes an alkyl acrylate. Stated differently, the B block is a polymeric material formed from a second monomer composition that includes an alkyl acrylate. Suitable alkyl acrylates for forming the B block often have an alkyl group with 2 to 20, 2 to 18, 2 to 12, or 2 to 10 carbon atoms. The alkyl group can be linear, branched, cyclic, or a combination thereof (e.g., the alkyl can have a cyclic group plus a branched or linear group).

Specific examples of alkyl acrylate monomers that can be used to form the B block include, but are not limited to, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate, scc-butyl acrylate, n-pentyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-methylbutyl acrylate, 4-methyl-2-pentyl acrylate, cyclohexyl acrylate, 2-methylhexyl acrylate, n-octyl acrylate, 2-octyl acrylate, isooctyl acrylate, 2- ethylhexyl acrylate, isononyl acrylate, n-decyl acrylate, isodecyl acrylate, lauryl acrylate, isotridecyl acrylate, isostearyl acrylate, and octadecyl acrylate. Many of these monomers, when polymerized to form a homopolymer, have a glass transition temperature no greater than 20°C when measured using Dynamic Mechanical Analysis. In some instances, the B block is a homopolymer. Examples of homopolymers include, but are not limited to, poly(ethyl acrylate), poly(n-propyl acrylate), poly(n-butyl acrylate), poly(isobutyl acrylate), polytscc-butyl acrylate), poly(isoamyl acrylate), poly(n-hexyl acrylate), poly(2 -methylbutyl acrylate), poly(4-methyl-2 -pentyl acrylate), poly(cyclohexyl acrylate), poly(2 -methylhexyl acrylate), poly(n-octyl acrylate), poly(2 -octyl acrylate), poly(isooctyl acrylate), poly(2 -ethylhexyl acrylate), poly(isononyl acrylate), poly(n-decyl acrylate), poly(isodecyl acrylate), poly(lauryl acrylate), poly(isotridecyl acrylate), poly(isostearyl acrylate), and poly(octadecyl acrylate). In some more specific instances, the B block is poly(n-butyl acrylate), poly(n-octyl acrylate), poly(2 -octyl acrylate), poly(isooctyl acrylate), poly (2 -ethylhexyl acrylate), or poly(isononyl acrylate). In some even more specific instances, the B block is poly(n-butyl acrylate).

In addition to the alkyl acrylate monomers, the second monomer composition used to form the B block can further include optional monomers provided the resulting polymeric blocks has a glass transition temperature that is no greater than 20°C when measured using Dynamic Mechanical Analysis.

In some embodiments, the second monomer composition used to form the B block can optionally include a heteroalkyl (meth)acrylate, an aralkyl acrylate, an aryloxy substituted alkyl acrylate, or an alkyl methacrylate having an alkyl group that is linear or branched with at least 6 carbon atoms. Suitable heteroalkyl acrylates include, but are not limited to 2-ethoxy ethyl (meth)acrylate, 2-methoxy ethyl acrylate, and 2-(2-ethoxyethoxy)ethyl acrylate. Suitable aralkyl acrylates include, but are not limited to, 2 -biphenylhexyl acrylate and benzyl acrylate. An example aryloxy substituted alkyl acrylate is 2-phenoxy ethyl acrylate. Suitable alkyl methacrylates are n-decyl methacrylate, lauryl methacrylate, n-octyl methacrylate, isooctyl methacrylate, 2-ethylhexyl methacrylate, and n-hexyl methacrylate.

In still other embodiments, the second monomer composition used to form the B block can include various (meth)acrylic-based polar monomers provided the glass transition temperature of these blocks is no greater than 20°C when measured using Dynamic Mechanical Analysis. If present, these polar monomers are usually present in an amount no greater than 10, no greater than 5, no greater than 2, or no greater than 1 weight percent based on a total weight of the monomers in the respective monomer composition. Suitable polar monomers include, for example, a hydroxy-substituted alkyl (meth)acrylate. The polar monomer is typically not an acidic monomer or a nitrogen containing monomer (e.g., the second monomer composition is often free of such monomers). Specific polar monomers include, but are not limited to, (meth)acrylic acid, 2-hydroxyethyl (meth)acrylate, and 2-hydroxypropyl (meth)acrylate. In many embodiments, however, there are no polar monomers in the B block.

The B block of the (meth)acrylic -based triblock copolymer is often a homopolymer formed from an alkyl acrylate and the resulting polymeric block has a glass transition temperature no greater than 20°C as measured using Dynamic Mechanical Analysis. In some specific embodiments, the B block is a poly(alkyl acrylate). In some more specific embodiments, the B block is poly(n-butyl acrylate), poly(n- octyl acrylate), poly(2 -octyl acrylate), poly(isooctyl acrylate), poly(2 -ethylhexyl acrylate), or poly (isononyl acrylate). In some (meth)acrylic-based triblock copolymers, each A block comprises monomeric units derived from methyl methacrylate and the B block comprises monomeric units derived from n-butyl (meth)acrylate such as n-butyl acrylate.

The (meth)acrylic-based triblock copolymer A-B-A often has a weight average molecular weight (M_w) that is at least 25, at least 30, at least 35, at least 40, at least 45, or at least 50 kiloDaltons (kDa) and up to 200, up to 190, up to 180, up to 175, up to 170, up to 160, up to 150, up to 140, up to 130, up to 125, up to 120, up to 115, up to 110, up to 100, up to 90, up to 80, or up to 75 kDa. The weight average molecular weight is often in a range of 50 to 200, 50 to 175, or 50 to 150 kDa. The weight average molecular weight is typically determined using gel permeation chromatography with polystyrene standards.

The (meth)acry lie-based triblock copolymer can be synthesized using any suitable technique. Suitable techniques can include, for example, anionic polymerization, radical polymerization, group transfer polymerization, and ring-opening polymerization reactions. The polymerization can be a “living” or “controlled/living” polymerization, which can advantageously produce block copolymer stmetures that are well defined. Specific synthesis methods include atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer polymerization (RAFT) processes. Such processes are disclosed, for example, in U.S. Pat. Nos. 7,255,920 (Everaerts et al.), 6,734,256 (Everaerts et al.), and 6,806,320 (Everaerts et al.). Other synthesis methods include the use of controlled radical initiators that are bis-dithiocarbamate or bis-dithiocarbonate compounds such as those disclosed in U. S. Pat. Nos. 10,400,055 (Griesgraber et al.), 10,640,686 (Roscoe et al.), and 10,913,807 (Yurt et al.) as well as U.S. Patent Application Publication 2021/0095097 (Lewandowski et al.).

Living polymerizations can also provide block copolymers with sharp transitions between the blocks. Block copolymers having A blocks and a B block can have regions near the block borders that contain a mixture of monomeric units of A and monomeric units of B. When a living polymerization technique is used, the size of such regions can be minimized, or even eliminated, leading to a sharper transition from an A block to a B block. This can be beneficial when phase separation is desired because a region of mixed monomeric units can be compatible with both blocks, thereby reducing the phase separation. On the other hand, a sharp transition with minimal regions of mixed monomeric units can promote phase separation.

Suitable commercially available (meth)acrylic -based triblock copolymers can be obtained from under the trade designation “KURARITY” from Kuraray Co., Ltd. (Tokyo, Japan). These include, for example, KURARITY LA2330, L3320, and LA2250. Other suitable commercially available (meth)acrylic-based triblock copolymers can be obtained from under the trade designation “NANOSTRENGTH” from Arkema (Colombes, France). These include, for example, NANOSTRENGTH M51, M52, M53, M55, M65, and M75.

In some embodiments, the curable adhesive composition comprises at least 10, 20, 30, 40 or 50 wt.% of (meth)acrylic -based multiblock copolymer based on a total organic components of the adhesive composition. In some embodiments, the curable adhesive composition comprises no greater than 70, 65, or 60 wt.% of (meth)acry lie-based multiblock copolymer.

In addition to the triblock copolymer, the curable composition can optionally include a (meth)acrylic -based diblock copolymer. The diblock copolymer, which can be referred to as a C-D diblock copolymer, typically includes a C block that can prepared from the same monomers that are described above as being suitable for forming the A blocks in the triblock copolymer. Further, the D block of the diblock copolymer can be prepared from the same monomers described above as being suitable for forming the B blocks in the triblock copolymer. If a diblock is used in combination with a triblock copolymer, the A and C blocks are often formed from the same monomer(s) while the B and D blocks are often formed from the same monomer(s).

The (meth)acrylic -based diblock copolymer often contains 5 to 30 weight percent C block and 70 to 95 weight percent D block. The amount of the C block and be at least 5, at least 10, at least 15, or at least 20 weight percent and up to 30, up to 25, up to 20, or up to 15 weight percent based on a total weight of the diblock copolymer. The amount of the D block can be at least 70, at least 75, at least 80, at least 85 weight percent and up to 95, up to 90, up to 85, or up to 80 weight percent. The sum of the amount of the C block and D block equals (or approaches due to a small amount of initiator residue) 100 weight percent.

The weight average molecular weight of the (m eth)acry lie -based diblock is often in a range of 30 to 150 kDa. The weight average molecular weight is often at least 30, at least 40, at least 50, at least 60, at least 70, at least 80, at least 90, or at least 100 kDa and up to 150, up to 140, up to 130, up to 120, up to 110, up to 100, up to 90, or up to 80 kDa. The weight average molecular weight can be determined by gel permeation chromatography using polystyrene standards.

The curable composition typically contains 0 to 30 weight percent of the optional (meth)acry lie- based diblock copolymer based on the total weight of organic components in the curable composition. If present, the amount can be at least 5, at least 10, at least 15, or at least 20 weight percent and up to 30, up to 25, up to 20, up to 15, or up to 10 weight percent. In many embodiments, the curable composition does not contain the optional (meth)acrylic -based diblock copolymer.

Optional (Meth)acrylic-monomer(s) and copolymer thereof

In some emboidment, the curable adhesive composition comprises a (meth)acrylic monomer and/or copolymer thereof. In some emboidments, the (meth)acrylate component is a monofunctional (meth)acrylate monomer having a single (meth)acrylate group or a multifunctional (meth)acrylate monomer comprising two or more (meth)acrylate groups.

Suitable monomers include for example C1-C10 alkyl acrylate, C3-C8 cycloalkyl acrylate, C6- C12 aryl acrylate, C1-C10 alkyl methacrylate, C3-C8 cycloalkyl methacrylate and C6-C12 aryl methacrylate, wherein C1-C10 alkyl, C3-C8 cycloalkyl and C6-C12 aryl may be substituted by one or a plurality of substituents. The substituent may be independently selected from hydroxy, carboxy, and epoxy; and the substituent may also be C3-C8 cycloalkyl, C6-C12 aryl or C6-C12 aryloxy optionally substituted by hydroxy, carboxy or epoxy. Examples of C1-C10 alkyl acrylate include, but are not limited to one or a plurality of methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, and hexyl acrylate. Examples of C1-C10 alkyl methacrylate include, but are not limited to methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, or hexyl methacrylate and the like. Examples of C3-C8 cycloalkyl acrylate include, but are not limited to cyclopropyl acrylate, cyclobutyl acrylate, cyclopentyl acrylate, or cyclohexyl acrylate, and the like. Examples of C3-C8 cycloalkyl methacrylate include, but are not limited to cyclopropyl methacrylate, cyclobutyl methacrylate, cyclopentyl methacrylate, or cyclohexyl methacrylate, and the like. Examples of C6-C12 aryl acrylate include, but are not limited to phenyl acrylate, or naphthyl acrylate, and the like. Examples of C6-C12 aryl methacrylate include, but are not limited to phenyl methacrylate, or naphthyl methacrylate, and the like.

When the (meth)acrylate monomer comprises a substituent selected from hydroxy, carboxy, and epoxy; the (meth)acrylate monomer may be characterized as a reactive (meth)acrylate monomer. Some examples of reactive monomers carrying epoxy include, but are not limited to glycidyl methacrylate (GMA), or (3,4-epoxy-cyclohexylmethyl)acrylate (ECA) and the like. Due to the use of a cationic photoinitiation system, the reactive functional group of the reactive (meth)acrylate monomer suitable for the present disclosure is preferably a reactive functional group containing no nitrogen, and preferably a reactive functional group containing no sulfur.

In some embodiments, the organic component comprises a poly(meth)acrylate prepared by polymerizing various (meth)acrylate monomers as described above. In some embodiments, the poly(meth)acrylate is a random copolymer.

In some embodiments, the poly(meth)acrylate comprises reactive functional groups selected from hydroxy, carboxy, and epoxy. In some embodiments, the polyacrylate comprises at least 1.5 or 2 wt.% and no greater than 30, 25, or 20 wt.% of polymerized units of monomer(s) containing a reactive functional group. In some emboidments, the amount of polymerized units of monomer(s) containing a reactive functional group is at least 3, 4, 5, or 6 wt.%. Due to the use of a cationic photoinitiation system, the reactive functional group preferably lacks nitrogen and lacks sulfur.

In some embodiments, the (meth)acrylate monomer or poly(meth)acrylate has a glass transition temperature of at least -35°C, -30°C, -25°C or -20 °C. In some embodiments, the (meth)acrylate component has a glass transition temperature of no greater than 10 °C, 5°C, 0°C, -5°C or -10 °C.

Epoxy Resin

The curable adhesive composition comprises at least one epoxy resin. Epoxy resins can be either a single material or a mixture of different materials selected to provide the desired viscosity characteristics before curing and to provide the desired mechanical properties after curing. If the epoxy resin is a mixture of materials, at least one of the epoxy resins in the mixture is typically selected to have at least two oxirane groups per molecule.

The portion of the epoxy resin molecule that is not an oxirane group (i.e., the epoxy resin molecule minus the oxirane groups) can be aromatic, aliphatic or a combination thereof and can be linear, branched, cyclic, or a combination thereof. The aromatic and aliphatic portions of the epoxy resin can include heteroatoms or other groups that are not reactive with the oxirane groups. That is, the epoxy resin can include halo groups, oxy groups such as in an ether linkage group, carbonyl groups, carbonyloxy groups, and the like. The epoxy resin can also be a silicone-based material such as a polydiorganosiloxane-based material. Due to the use of a cationic photoinitiator, the epoxy resin preferably lacks a nitrogen-containing functional group.

In most embodiments, the epoxy resin includes a glycidyl ether. Exemplary glycidyl ethers can be of Formula (V).

In Formula (V), group R¹ is a p-valent group that is aromatic, aliphatic, or a combination thereof. Group R¹ can be linear, branched, cyclic, or a combination thereof. Group R¹ can optionally include halo groups, oxy groups, carbonyl groups, carbonyloxy groups, and the like. Although the variable p can be any suitable integer greater than or equal to 1, p is often an integer in the range of 2 to 6 or 2 to 4. In many embodiments, p is equal to 2.

In some exemplary epoxy resins of Formula (V), the variable p is equal to 2 (i.e., the epoxy resin is a diglycidyl ether) and R¹ includes an alkylene (i.e., an alkylene is a divalent radical of an alkane and can be referred to as an alkane-diyl), heteroalkylene (i.e., a heteroalkylene is a divalent radical of a heteroalkane and can be referred to as a heteroalkane-diyl), arylene (i.e., a divalent radical of an arene compound), or mixture thereof. Suitable alkylene groups often have 1 to 20 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms. Suitable heteroalkylene groups often have 2 to 50 carbon atoms, 2 to 40 carbon atoms, 2 to 30 carbon atoms, 2 to 20 carbon atoms, 2 to 10 carbon atoms, or 2 to 6 carbon atoms. The heteroatoms in the heteroalkylene are often oxy groups. Suitable arylene groups often have 6 to 18 carbon atoms, 6 to 12 carbon atoms, or 6 to 10 carbon atoms. For example, the arylene can be phenylene. Group R¹ can further optionally include halo groups, oxy groups, carbonyl groups, carbonyloxy groups, and the like.

Some epoxy resins of Formula (V) are diglycidyl ethers where R¹ includes (a) an arylene group or (b) an arylene group in combination with an alkylene, heteroalkylene, or both. Group R¹ can further include optional groups such as halo groups, oxy groups, carbonyl groups, carbonyloxy groups, and the like. These epoxy resins can be prepared, for example, by reacting an aromatic compound having at least two hydroxyl groups with an excess of epichlorohydrin. Examples of useful aromatic compounds having at least two hydroxyl groups include, but are not limited to, resorcinol, catechol, hydroquinone, p,p'- dihydroxydibenzyl, p,p'-dihydroxyphenylsulfone, p,p'-dihydroxybenzophenone, 2,2'-dihydroxyphenyl sulfone, and p,p'-dihydroxybenzophenone. Still other examples include the 2,2', 2,3', 2,4', 3,3', 3,4', and 4,4' isomers of dihydroxydiphenylmethane, dihydroxydiphenyldimethylmethane, dihydroxydiphenylethylmethylmethane, dihydroxydiphenylmethylpropylmethane, dihydroxydiphenylethylphenylmethane, dihydroxydiphenylpropylenphenylmethane, dihydroxydiphenylbutylphenylmethane, dihydroxydiphenyltolylethane, dihydroxydiphenyltolylmethylmethane, dihydroxydiphenyldicyclohexylmethane, and dihydroxy diphenylcyclohexane.

Some commercially available diglycidyl ether epoxy resins of Formula (V) are derived from bisphenol A (i.e., bisphenol A is 4, 4’-dihydroxy diphenylmethane). Examples include, but are not limited to, those available under the trade designation EPON (e.g., EPON 828, EPON 872, EPON 1001F, EPON 1004, and EPON 2004) from Hexion Specialty Chemicals, Inc. in Houston, TX, those available under the trade designation DER (e.g., DER 331, DER 332, and DER 336) from Olin Epoxy (Clayton, MO, USA), and those available under the trade designation EPICLON (e.g., EPICLON 850) from Dainippon Ink and Chemicals, Inc. in Chiba, Japan. Other commercially available diglycidyl ether epoxy resins are derived from bisphenol F (i.e., bisphenol F is 2,2’-dihydroxydiphenylmethane).

Other epoxy resins of Formula (V) are diglycidyl ethers of a poly(alkylene oxide) diol. These epoxy resins can be referred to as diglycidyl ethers of a poly(alkylene glycol) diol. The variable p is equal to 2 and R⁴ is a heteroalkylene having oxygen heteroatoms. The poly(alkylene glycol) can be a copolymer or homopolymer. Examples include, but are not limited to, diglycidyl esters of polyethylene oxide) diol, diglycidyl esters of polypropylene oxide) diol, and diglycidyl esters of poly(tetramethylene oxide) diol. Epoxy resins of this type are commercially available from Polysciences, Inc. (Warrington, PA, USA) such as those derived from a polyethylene oxide) diol or from a polypropylene oxide) diol having a weight average molecular weight of about 400 Daltons, about 600 Daltons, or about 1000 Daltons. Other aliphatic epoxy resins of this type are commercially available from Nagase & Co., LTD (Osaka, Japan) under the trade designation DENACOL (e.g., DENACOL Ex-830).

Still other epoxy resins of Formula (V) are diglycidyl ethers of an alkane diol (R¹ is an alkylene and the variable p is equal to 2). Examples include a diglycidyl ether of 1,4-dimethanol cylco hexyl, diglycidyl ether of 1,4 -butanediol, and diglycidyl ethers of the cycloaliphatic diol formed from a hydrogenated bisphenol A such as those commercially available under the trade designation EPONEX 1510 from Hexion Specialty Chemicals, Inc. (Houston, TX, USA).

Yet other epoxy resins include silicone resins with at least two glycidyl groups and flame retardant epoxy resins with at least two glycidyl groups (e.g., a brominated bisphenol-type epoxy resin having with at least two glycidyl groups such as that commercially available from Dow Chemical Company (Midland, MI, USA) under the trade designation DER 580).

The epoxy resin is often a mixture of materials. For example, the epoxy resins can be selected to be a mixture that provides the desired viscosity or flow characteristics prior to curing. The mixture can include at least one first epoxy resin that is referred to as a reactive diluent that has a lower viscosity and at least one second epoxy resin that has a higher viscosity. The reactive diluent tends to lower the viscosity of the epoxy resin mixture and often has either a branched backbone that is saturated or a cyclic backbone that is saturated or unsaturated. Examples include, but are not limited to, the diglycidyl ether of resorcinol, the diglycidyl ether of cyclohexane dimethanol, the diglycidyl ether of neopentyl glycol, and the triglycidyl ether of trimethylolpropane. Diglycidyl ethers of cyclohexane dimethanol are commercially available under the trade designation HELOXY MODIFIER 107 from Hexion Specialty Chemicals (Columbus, OH, USA) and under the trade designation EPODIL 757 from Evonik Corporation (Essen, North Rhine-Westphalia, Germany). Other reactive diluents have only one functional group (i.e., oxirane group) such as various monoglycidyl ethers. Some exemplary monoglycidyl ethers include, but are not limited to, alkyl glycidyl ethers with an alkyl group having 1 to 20 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms. Some exemplary monoglycidyl ethers are commercially available under the trade designation EPODIL from Evonik Corporation such as EPODIL 746 (2 -ethylhexyl glycidyl ether) and EPODIL 748 (aliphatic glycidyl ether).

The epoxy resins often have an equivalent weight in a range of 50 to 750 grams/equivalent. The equivalent weight of the epoxy resin refers to the weight of resin in grams that contains one equivalent of epoxy. The equivalent weight is often no greater than 750 grams/equivalent, no greater than 700 grams/equivalent, no greater than 650 grams/equivalent, no greater than 600 grams/equivalent, no greater than 550 grams/equivalent, no greater than 500 grams/equivalent, no greater than 450 grams/equivalent, no greater than 400 grams/equivalent, no greater than 350 grams/equivalent, no greater than 300 grams/equivalent, or no great than 250 grams/equivalent and is often at least 50 grams/equivalent, at least 75 grams/equivalent, at least 100 grams/equivalent, at least 125 grams/equivalent, or at least 150 grams/equivalent. In some embodiments, the equivalent weight is often in a range of 50 to 750 grams/equivalent, 50 to 500 grams/equivalent, 100 to 500 grams/equivalent, 100 to 300 grams/equivalent, or 150 to 250 grams/equivalent.

In many embodiments, 100 weight percent of the epoxy resin is of Formula (V). In other embodiments, at least 95 weight percent, at least 90 weight percent, at least 85 weight percent, at least 80 weight percent, at least 75 weight percent, or at least 70 weight percent of the epoxy resin is of Formula (V).

In many embodiments, 100 weight percent of the epoxy resin is a diglycidyl ether (i.e., a compound of Formula (I) with p equal to 2). In other embodiments, the epoxy resin is a mixture of compounds of Formula (I) with p equal to 2 and compounds of Formula (I) with p not equal to 2. In such mixtures, the amount of the diglycidyl ether is often at least 50 weight percent, at least 60 weight percent, at least 70 weight percent, at least 75 weight percent, at least 80 weight percent, at least 85 weight percent, at least 90 weight percent, or at least 95 weight percent based on the total weight of the epoxy resin.

In some embodiments, the epoxy resin is free of compounds that have an oxirane group that is not a glycidyl group. If such compounds are included, however, they typically make up less than 30 weight percent, less than 20 weight percent, less than 10 weight percent, less than 5 weight percent, less than 2 weight percent, less than 1 weight percent, or less than 0.5 weight percent based on the total weight of the epoxy resin.

The curable adhesive composition of the adhesive (e.g. tape) article typically comprises at least 10, 15, 20, 25, or 30 wt.% epoxy resin based on a total weight of organic components of the curable adhesive composition. In some embodiments, the curable adhesive composition of the adhesive (e.g. tape) article comprises not greater than 40, 35, 30, or 25 wt.% of epoxy resin.

In another embodiment, the composition comprises an epoxy resin, an acid-generating cationic initiator, and the metal compound described herein. In this embodiment, the organic polymer is optional and thus the amount of epoxy resin is greater. In this embodiment, the amount of epoxy resin may be at least 40, 50, 60, 70, 80, 90 or 95 wt.% of the curable composition. Such composition may comprise little or no film forming organic polymer.

Cationic Photoinitiator

A cationic photoinitiator, which can also be referred to as a photoacid generator, is activated to initiate polymerization of the epoxy resin within the curable composition. It is typically selected to be sensitive to (activated by) radiation in the ultraviolet region of the electromagnetic spectrum. For example, the photoacid generator is often selected to be activated at wavelengths less than or equal to 380 nanometers in the ultraviolet region of the electromagnetic spectrum.

Some suitable photoacid generators are aryl-containing (e.g., bis(aryl-containing)) iodonium salts. Example aryl-containing iodonium salts such as those with two aryl groups such as bis(4-tert- butylphenyl) iodonium hexafluoroantimonate (available under the trade designation FP5034 from Hampford Research Inc. (Stratford, CT, USA)), bis(4-tert-butylphenyl) iodonium camphorsulfonate, bis(4-tert-butylphenyl) iodonium hexafluorophosphate, bis(4-tert-butylphenyl) iodonium tetraphenylborate, bis(4-tert-butylphenyl) iodonium tosylate, bis(4-tert-butylphenyl) iodonium Inflate, (4- methoxyphenyl)phenyl iodonium Inflate, bis(4-methylphenyl) iodonium hexafluorophosphate (available under the trade designation OMNICAT 440 from IGM Resins (Bartlett, IL, USA)), ([4- (octyloxy)phenyl]phenyl iodonium hexafluorophosphate), ([4-(octyloxy)phenyl]phenyl iodonium hexafluoroantimonate), (4-isopropylphenyl)(4-methylphenyl) iodonium tetrakis(pentafluorophenyl) borate (available under the trade designation RHODORSIL 2074 from Bluestar Silicones (East Brunswick, NJ, USA)), and 4-(2-hydroxy-l-tetradecycloxy)phenyl]phenyl iodonium hexafluoroantimonate.

Other suitable photoacid generators are triaryl sulfonium salts. Example triaryl sulfonium salts include, but are not limited to, triphenyl sulfonium hexafluoroantimonate (available under the trade designation CT-548 from Chitec Technology Corp. (Taipei, Taiwan)), diphenyl(4-phenylthio)phenyl sulfonium hexafluorophosphate, diphenyl(4-phenylthio)phenyl sufonium hexafluoroantimonate, bis(4- (diphenylsulfonio)phenyl)sulfide bis(hexafluorophosphate), and bis(4-(diphenylsulfonio)phenyl)sulfide hexafluoroantimonate. Blends of triaryl sulfonium salts are available from Synasia (Metuchen, NJ, USA) under the trade designation SYNA PI-6992 for hexafluorophosphate salts and under the trade designation SYNA PI-6976 for hexafluoroantimonate salts. Mixtures of triaryl sulfonium salts are commercially available from Aceto Pharma Corporation (Port Washington, NY, USA) under the trade designations UVI-6992 and UVI-6976.

Although the metal compounds are particularly advantageous for use in compositions comprising a photoacid generator, it is surmised that the metal compounds described herein may also be beneficial for thermal acid generators.

Upon exposure to thermal energy, TAGs undergo a fragmentation reaction and release one or more molecules of Lewis or Bronsted acid. Useful TAGs are thermally stable up to the activation temperature. Preferred TAGs are those in which the incipient acid has a pK_a value of less than or equal to 0. Useful thermal acid generators have an activation temperature of 150°C or less, preferably 140°C or less. As used herein, "activation temperature" is that temperature at which the thermal release of the incipient acid by the TAG in the adhesive formulation occurs. Typically the TAG will have an activation temperature in a range from about 50°C to about 150°C.

Useful classes of TAGs can include, for example, alkylammonium salts of sulfonic acids, such as triethylammonium p-toluenesulfonate (TEAPTS). Another suitable class of TAGs is that disclosed in U.S. Pat. No. 6,627,384 (Kim, et al.), the disclosure of which is incorporated herein by reference, which describes cyclic alcohols with adjacent sulfonate leaving groups, such as any of the compounds of the Formulas 1 to 4: Formula 3 Formula 4

The sulfonate leaving groups in compounds of Formulas 1 to 4 form acids upon the application of heat as is demonstrated in the mechanism shown below.

Suitable classes of thermal acid generators also include those described in U.S. Patent Nos. 7,514,202 (Ohsawa et al.) and 5,976,690 (Williams et al.), the disclosures of which are incorporated herein by reference.

The acid generator initiator is typically used in an of at least 0.5, 0.6, 0.7, 0.8 or 1 wt.% based on the total weight of of the curable composition. In some embodiments, the amount of acid generator initiator is no greater than 5, 4, 3, 2, or 1 wt.%.

In some embodiments, the curable composition is free of heat-activated curatives, such as dicyandiamide. In some embodiments, the curable composition is free of thermal acid generator.

Metal Compound

The curable composition further comprises a metal compound. In typical embodiments, the amount of metal compound is at least 0.5, 1, 1.5 or 2 wt.% wt.% of the composition. In typical embodiments, the amount of metal compound is no greater than 5, 4, 3, 2 or 1 wt.%.

With reference to Table 3 of the forthcoming examples, the metal compound is selected such than a solution of the acid generator initiator, water and metal compound at a weight ratio of 2:2:0.05 has a pH of 6-8 (e.g. 7) after heating.

The acid generator is activated by exposure to actinic radiation, such as UV light, and/or by exposure to heat. In the absence of the metal compound, the adhesive composition has a surface pH of 1 or less than 1 after activation of the initiator. With reference to Tables 4-5, the cured adhesive composition has a surface pH greater than 1, 2, 3, or 4 after activation of the initiator due to the presence of the metal compound. The metal compound is selected such that it does not interfere with the curing of the epoxy resin. With reference to Table 4, the adhesive composition has an epoxy conversion rate of at least 75, 80, 85, 90, 95 or 99%, 24 hours after (e.g. light and/or heat) activation of the initiator. In other words, the amount of unreacted epoxy of less than 25, 20, 15, 10, 5, or 1%

As evident by Table 4, use of zinc oxide and magnesium hydroxide resulted in low epoxy conversion rates.

In favored embodiments, the metal compound comprises an anion having at least one hydroxyl group and at least one group selected from oxide, PO’, or SO". The PO and SO group each have a negative charge. Anions with PO" or SO" include for example phosphate, phosphorate, phosphinate, sulfate, and sulfonate. Suitable metal compounds include, for example, AIO(OH), ChTPO-OTOH). and Ca(PO₃)OCH₂(CHOH)(CH₂OH)

Without intending to be bound by theory, it is surmised that the hydroxyl group(s) increases the solubility of the metal compound in the adhesive composition. Hydroxyl groups can also increase water solubility. In some embodiments, the metal compound may have a water solubility of at least 10, 20, 30, 40, or 50 g/L at 25°C. For example, calcium glycerol phosphate, depicted has a water solubility of 54.3 g/L.

Without intending to be bound by theory, it is surmised that the presence of the oxide group improves the neutralization of excess acid while allowing for high epoxy conversion rates.

In some embodiments, the metal compound may further comprise an organic substituent, such as a alkyl group. For example, one of the oxygen atoms of the PO" or SO group may be covalently bonded to an alkyl group. The presence of the alkyl group may improve the dispersibility of the metal compound in the curable composition. However, the presence of the alkyl group may impact the acid-neutralizing capacity of the metal compound.

The metal compound is typically solid particles that are combined with the curable composition. The metal compound typically has a median particle size ranging from 1 to 100 microns. The solid metal compound particles are typically not surface treated with a basic (e.g. amino) silane surface treatment.

Optional Core-Shell Rubber (CSR) Particles

The core-shell rubber particle refers to a particulate material having a rubber core. A core refers to the internal portion of the core-shell rubber. The core may be a central part forming the core-shell particle or an inner shell area of the core-shell rubber. A shell is a portion of the core-shell rubber located outside the rubber core, and may be one or a plurality of shell portions that usually form the outermost portion of the core-shell rubber particle. The shell material is preferably grafted or crosslinked onto the core, or both. The rubber core may account for 50% to 95% based on the weight of the core-shell rubber particle.

The core of the core-shell mbber suitable for the present invention may be formed by conjugated dienes, e.g., butadiene; low-grade alkyl esters of acrylic acid, e.g., n-butyl acrylate, ethyl ester, isobutyl ester; 2-ethylhexyl ester; or polymers or copolymers of polysiloxane. Specifically, the cores of CSR particles may be one or a plurality of substances selected from the following group consisting of methyl methacrylate butadiene styrene (MBS) monomers, methacrylate-acrylonitrile-butadiene-styrene (MABS) monomers, or combinations thereof. Examples of other compounds that can be used to form the core include ABS (acrylonitrile-butadiene-styrene), ASA (acrylate-styrene-acrylonitrile), acrylic substances, SAEPDM (styrene-acrylonitrile grafted onto the elastomer backbone of an ethylene-acrylic diene monomer), MAS (methacrylic-acrylic rubber styrene) and the like, and mixtures thereof. The size of CSR particles is generally at least 50 pr 100 nm and typically no greater than 300 nm, and the CSR particles are prepared through emulsion polymerization reaction. Kaneka Kane Ace MX series products commercially available from Japan are preferred.

The shell suitable for the core-shell rubber may comprise one or a plurality of acrylic polymers or acrylic copolymers. Specifically, the shell of a CSR particle may be formed of acrylic polymers, acrylic copolymers, or combinations thereof. In multiple embodiments, the (polymer) composition forming the shell of the core-shell mbber has sufficient affinity for the epoxy resin and (meth)acrylate component used as a matrix, to allow the core-shell rubber particles to exist as primary particles in the adhesive tape in solid form, and to stably disperse. Preferred CSR particles have polybutadiene rubber cores or styrene butadiene rubber cores (e.g., formed of MBS monomers) and shells formed of acrylic polymers or acrylic copolymers, wherein the core-shell rubber is optionally dispersed in the matrix, and the matrix is preferably selected from the group consisting of aromatic epoxy resins, particularly bisphenol A, F-based diglycidyl ether, and hydroxy compounds.

In some embodiments, curable adhesive composition comprises core-shell rubber is an amount of at least 0.5, 1, 2, 3, 4, 5, 5, 7, 8, 9, or 10 wt.% of the total organic component of the adhesive composition. In some embodiments, the curable adhesive composition comprises core-shell rubber is an amount no greater than 20, 15 or 10 wt.% of the total organic component of the adhesive composition.

In some embodiments, the core-shell rubber is dispersed in an epoxy or polyol medium, and especially in a polyol, the core-shell rubber particles are dispersed more uniformly and have better compatibility with (meth)acrylate component and epoxy resin used as the matrix.

Hydroxy-Containing Compounds

The curable adhesive composition optionally comprises hydroxy-containing compounds. The hydroxy -containing compounds include ether or ester derivatives thereof. In some embodiments, the hydroxy -containing compounds are polyols. When the epoxy group reacts through the cationic mechanism, the hydroxy -containing compound acts as a chain transfer agent, and the hydroxycontaining compound has a good dispersing effect on the core-shell rubber particles, making the core-shell rubber particles more compatible with the epoxy resin and (meth)acrylate component used as the matrix. Suitable polyols include for example polyether polyols and polyester polyols. The polyether polyol includes, but is not limited to, one or a plurality from the group consisting of polyether triols and polyether diols. The polyester polyol includes, but is not limited to, one or a plurality from the group consisting of polyester triols, polyester diols, and bisphenol A polyols. In some embodiments, the polyol may be selected from TONE 0230 Polyol, VORANOL 230-238 and VORANOL 2070, all commercially available from Dow Chemical Company, U.S.; and Dianol 285 commercially available from Seppic Corporation, France, etc. In one embodiment, the polyol is VORANOL 2070 commercially available from Dow Chemical Company, U.S., which is a polyether triol having a molecular weight of 700.

In some embodiments, the curable adhesive composition typically comprise a hydroxyl-functional component, such as a polyol, in an amount of at least 1, 1.5, 2, 1.5 or 3 wt.% of the total organic component of the adhesive composition. In some embodiments, the amount of hydroxyl-functional component, such as a polyol is no greater than 20, 15, 1, or 5 wt.% of the total organic components of the adhesive composition.

Other Additive

The curable adhesive composition may comprise additives such as adhesion promoters, crosslinkers, tackifying resins, and inorganic fillers.

The adhesive composition may comprise an adhesion promoter. A suitable adhesion promoter can be selected according to the surface to be bonded. The inventor has found that silane is an additive that improves the adhesion of the curable adhesive tape to metal (e.g. aluminum, stainless steel) and glass without influencing the curing reaction. Epoxy -containing reactive silanes are preferred, such as commercially available Silquest A187 (Momentive Performance Materials).

The curable adhesive composition may comprise a crosslinker. Preferred crosslinkers can be reacted and crosslinked with reactive polypropionate and include difunctional or polyfunctional isocyanates, and difunctional or polyfunctional amines. The crosslinker preferably does not substantially reduce the epoxy conversion rate.

The curable adhesive composition may comprise a tackifying resin. Such as rosin acid, rosin ester, terpene phenolic resin, hydrocarbon resin and Benzofuran indene resin. The type and amount of the tackifiers may have effect on tack, wetting, adhesion strength, and heat resistance performance.

The curable adhesive composition may comprise an inorganic filler. For example, fumed silica, aluminium oxide, conductive fillers, et.al. For example, Waker HDK H15, HDK H20, CAB-O-SIL TS- 610.

The curable adhesive composition may optionally comprise an organic solvent. Examples of solvent include ethyl acetate, n-butanol, isopropanol, acetone, acetic acid, benzene, toluene, ethylbenzene, isopropylbenzene, t-butylbenzene, heptane, cyclohexane, 1-chlorobutane, 1 -bromobutane, and 1- iodobutane. Combinations of solvents may be utilized. Since the organic solvent is no longer present in the cured adhesive composition, the total organic components of the adhesive composition does not include organic solvent.

In another embodiment, a curable adhesive tape is described comprising a layer of the curable adhesive composition layer disposed on a substrate. In some embodiments, the thickness of the adhesive layer (thickness of the dried adhesive) may be between 10 and 100, 150, or 200 pm.

The curable adhesive tape can be prepared by coating the curable adhesive composition onto a support (e.g. removable release liner, mesh, or a film) by a conventional coating method, and then removing the solvent by heating, to thereby form an adhesive film of a certain thickness, so as to obtain the (e.g. UV) curable adhesive tape. The curable adhesive composition can also be applied in the absence of solvent at an elevated temperature provided the organic (e.g. film forming) polymer is thermoplastic.

Useful coating methods include roll knife coating, comma roll coating, dragging blade coating, reverse roll coating, winding bar (Mayer) coating, gravure roll coating, slit-type die extrusion (Die) coating, and the like. Preferable coating methods are comma roll coating and slit-type die extrusion (Die) coating.

In some embodiments, the substrate of the tape is single-sided release (e.g. paper or film) liner provided on one side of the adhesive layer. The release liner can protect the adhesive layer. When in use, the release layer can be peeled off to expose the adhesive layer for use.

The adhesive article (e.g. tape) or composition can be used to make an article. The method generally comprising providing an adhesive or the curable composition; contacting the adhesive layer or curable composition to a substrate; and curing the composition by exposure to actinic radiation, heat, or a combination thereof. In some embodiments, the method comprise heating the adhesive composition to a temperature in the range of 90-160°C before or after applying the composition to the substrate(s). The adhesive layer or curable composition may be disposed between a first and second substate. The substrate may comprise an organic polymer, inorganic material, or a combination thereof. The adhesive article and composition is particularly advantageous for bonding metal substrates due to exhibiting reduced corrosion.

Unless stated otherwise, the following terms are defined as follows:

Herein the glass transition temperature (Tg) of a polymer (e.g. polyacrylate) can be determined by a method commonly used in the art such as DSC, or can be calculated through the FOX equation. The FOX equation is used to describe the relationship between Tg of a copolymer and Tg of a homopolymer constituting the component of the copolymer. For example, for a copolymer constituted by monomer units A, B, C and the like, Tg thereof can be represented by following formula:

1 W_A W —_B w

— = — + - + —_c - + ••• Tg Tg_z Tg_e Tg_c wherein

Tg is Tg of the copolymer;

WA, WB, WC, and the like are mass fractions of monomer units A, B, C and the like, respectively; and

TgA, TgB, TgC, and the like are Tg of the A homopolymer, B homopolymer, C homopolymer and the like, respectively.

The curable adhesive composition, article, and method as illustrated by the following examples.

EXAMPLES

Unless otherwise noted, all parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight. Unless otherwise indicated, all other reagents were obtained, or are available from fine chemical vendors such as Sigma-Aldrich Company, St. Louis, Missouri, or may be synthesized by known methods. Table 1 (below) lists materials used in the examples and their sources.

Table 1 - Additives pH Evaluation of Comparative ATH

In a glass vial the cationic photoinitiator (0432 described below), additive and water were combined in a weight ratio of 2:0.6:0.05. The mixture was homogenized and then heated in an oven at 160°C for 20 min to mimic the extrusion conditions. The mixture after heating was measured using pH strips. Drop in pH post heat treatment was indicative of pre-mature acid generation from the cationic photoinitiator, which could potentially trigger the cure of the adhesive, thus was a negative result, whereas no change was deemed as positive.

Table 2 - pH The comparative example demonstrates that significant amount of acid is generated when ATH and water are combined and heated at high temperature (160°C/20min). pH Evaluation of Other Metal Compounds

In a glass vial the cationic photoinitiator, additive, and water were combined in a weight ratio of 2:2:0.05. The mixture was homogenized and then heated in an oven at 160°C for 20min to mimic the extrusion conditions. The mixtures after heating were measured using pH strips. Drop in pH post heat treatment was indicative of generation of acid from the cationic photoinitiator which could potentially trigger the cure of the adhesive and was a negative result.

Table 3 - pH

Evaluation of Additives in Adhesive Composition

The following adhesive composition was prepared by thermally mixing the components.

The adhesive composition was dissolved in THF to prepare a 25 wt.% solution. The inorganic additives were incorporated at 2 wt.% loading by speed mixing into an adhesive solution. The resulting mixture was coated using a knife coater on a release liner with an intended dry thickness of ~4mil. The coating was dried in a hot air oven for 10 min at 70°C. The adhesives with additives were first laminated to a PET clear substrate and were UV-activated from the top using a 365nm LED (Omnicure AC8150 from Excelitas, Waltham, MA) with a total exposure of 8 J/cm² as measured by the 365nm band of a LEDCURE Four Band Profiler (EIT2.0 LLC, Leesburg, VA). Epoxy conversion was assessed by FTIR spectroscopy, 24 hours after UV exposure. The adhesive compositions with metal compound additives that showed high epoxy conversion were again laminated on a fresh clear PET liner with a dry pH paper (facing the adhesive) placed between the PET and adhesive for measuring the change in pH with and without any additives to assess the effectiveness of the additive as an anti-corrosive agent post UV cure as a function of time.

Adhesive compositions without organic polymer were also prepared:

828, 2200, and 0432 were massed into a polypropylene Max40 cup (FlackTek, Inc., Landrum, SC). The cup was closed with a polypropylene lid and mixed on a DAC150.1 FVZ-K SPEEDMIXER (FlackTek, Inc) for 140 seconds @ 2280 rpm, until homogeneous. CGP was added and the jar was mixed for 60 seconds at 2280 rpm and 60 seconds at 3500 rpm. Directly after mixing, aliquots were removed for epoxy conversion measurements and coated sample preparation.

Coated Liquid Adhesive Samples (without organic polymer) and pH Measurement

Each composition was coated between siliconized polyester liners on a knife coater set to a 4 mil gap. The coatings were UV-activated from top using a 365nm LED (Omnicure AC8150 from Excelitas, Waltham, MA) with total exposure of 8 J/cm² as measured by the 365nm band of an LEDCURE Four Band Profiler (EIT2.0 LLC, Leesburg, VA), and then heated in a forced air oven (Despatch Model LFD 1- 42-3 from ITW EAE, Minneapolis, MN) at 50 °C for 30 minutes. After dwelling for 72 hours at 21 °C, the bottom liner was peeled back from the resulting film sample and a 0-14 pH test strip (Product 8880-1 from Ricca Chemical, Arlington, TX) was inserted between them, with test surface facing the sample. After dwelling the test strip in contact with the sample for six hours, the resulting pH value was recorded.

Epoxy Conversion Spectra

Apiece of 10 mil (0.254 mm) silicone rubber (Diversified Silicone Products, Santa Fe Springs, CA), with a 0.46” (1.17 cm) hole in the center, was placed on top of a 2" x 3" x 0.04” (5.08 cm x 7.62 cm x 1mm) glass slide (VWR, Radnor, Pennsylvania). Several drops of the liquid mixture were deposited into the hole, then a 1" x 3" x 0.04” (2.54 cm x 7.62 cm x 1mm) glass slide (Model 2950 from Thermo Fisher Scientific, Waltham, MA) was applied, sandwiching the liquid between the glass slides. The construction was secured by clamping along the narrow slide edges using a small metal binder clip (Model 10667CT from Staples Inc., Framingham, Massachusetts) at the top and one mini metal binder clip (Model 10666CC from Staples Inc.) at the bottom. Initial "uncured" Fourier transform infrared (FTIR) spectra were taken in transmission mode using a Thermo Fisher Scientific NICOLET iS50 infrared spectrophotometer with DTGS KBr detector. Spectra consisted of 8 scans with a resolution of 8 (data spacing = 0.964 cm'¹) over the range of 6000-4000 cm'¹. The sample was removed from the IR, UV- activated from top using a 365nm LED (Omnicure AC8150 from Excelitas Inc, Waltham, MA) with total exposure of 8 J/cm² as measured by the 365nm band of an LEDCURE Four Band Profiler (EIT2.0 LLC, Leesburg, VA), and then heated in a forced air oven (Despatch Model LFD 1-42-3 from ITW EAE, Minneapolis, MN) at 50 °C for 30min. Afterward, “UV+X hour” FTIR spectra were taken in the same manner as before.

Epoxy Conversion Calculation

A peak associated with epoxy functionality (4548-4513 cm-1) was quantified using the Peak Area Tool in OMNIC 9.8.372 software (Thermo Fisher Scientific, Waltham, MA). This epoxy peak area was normalized by dividing by a reference peak area (4652-4590 cm-1), and this normalized peak area was used to calculate % epoxy conversion according to the following equation: 100

Table 4 - Epoxy Conversion and pH

Copper panel discoloration test

Adhesive tape samples of the same composition with ATH, Hydroxylapatite (HAp) and Calcium glycerophosphate (CGP) were then UV-activated and laminated to a copper panel for surface pH and anticorrosion testing. The tapes were visually inspected for discoloration indicative of corrosion after 1, 4, 5, and 7 days. All the tapes with HAp and CGP were found to be effective in preventing corrosion at 2 wt.% loading. At lower 1% loadings however, HAp and CGP were less effective at preventing corrosion after 5-7 days.

ATH at 0.6 wt.% was not effective in preventing corrosion after f day.

Claims

What is claimed is:

1. An adhesive article comprising: a support and a layer of curable adhesive composition disposed on the support, wherein the curable adhesive composition comprises: a pressure sensitive adhesive comprising an organic polymer and an epoxy component; a cationic initiator; and a metal compound.

2. The adhesive article of claim 1 wherein a solution of the cationic initiator, water and metal compound at a weight ratio of 2:2:0.05 has a pH of 6-8 after heating at 160 °C for 20 minutes.

3. The adhesive article of claims 1-2 wherein the adhesive composition has a surface pH greater than 1,

2, 3, or 4 after activation of the cationic initiator.

4. The adhesive article of claims 1-3 wherein adhesive composition has an amount of unreacted epoxy of less than 25, 20, 15, 10, 5, or 1%, 24 hours after activation of the initiator.

5. The adhesive article of claims 1-4 wherein the metal compound comprises an anion having at least one hydroxyl group and at least one group selected from oxide, PO’, or SO".

6. The adhesive article of claims 1-5 wherein the additive is selected from AIO(OH), CrntPO-iHOH). and Ca(PO₃)OCH₂(CHOH)(CH₂OH)₂

7. The adhesive article of claims 1-6 wherein the organic polymer is present in an amount ranging from 40 to 60 wt.%. of the total organic components of the adhesive composition.

8. The adhesive article of claims 1-7 wherein the organic polymer is a thermoplastic polymer.

9. The adhesive article of claims 1-8 wherein the adhesive composition is exposed to a temperature in a range of 90-160°C during manufacturing or use of the article.

10. The adhesive article of claims 1-9 wherein the epoxy component is present in an amount ranging from 20 to 60 wt.% of the total organic components of the adhesive composition.

11. The adhesive article of claims 1-10 wherein the composition further comprises a hydroxy-functional organic component present in an amount ranging from 5-30 wt.% of the total organic components of the adhesive composition.

12. The adhesive article of claims 1-11 wherein the initiator and metal compound comprise a phosphorous-based anion.

13. The adhesive article of claims 1-12 wherein the support is a removable release liner, a mesh, or a film.

14. A curable composition comprising: an epoxy component; a cationic initiator; and a metal compound comprising an anion having at least one hydroxyl group and at least one group selected from oxide, PO’, or SO".

15. The composition of claim 14 further comprising an organic polymer.

16. The composition of claims 14-15 wherein the composition is further characterized by claims 2-13.

17. A method of making an article comprising: providing an adhesive article of claims 1-14 or the curable composition of claims 14-16; contacting the adhesive layer or curable composition to a substrate; and curing the composition by exposure to actinic radiation, heat, or a combination thereof.

18. The method of claim 17 wherein the adhesive layer or curable composition is disposed between a first and second substate.

19. The method of claims 17-18 further comprising: heating the adhesive composition to a temperature in the range of 90-160°C before or after applying the composition to the substrate(s).