阅读说明：本技术 可uv固化的环氧/丙烯酸酯粘合剂组合物 (UV curable epoxy/acrylate adhesive compositions ) 是由 K·S·谢弗 T·Q·查斯特克 C·A·安德森 于 2016-05-13 设计创作，主要内容包括：本发明描述了包含(甲基)丙烯酸四氢糠酯共聚物；环氧树脂；聚醚多元醇；和羟基官能成膜性聚合物的粘合剂组合物。所述粘合剂可用于结构和半结构粘结应用。(The present invention describes a polymer composition comprising a tetrahydrofurfuryl (meth) acrylate copolymer; an epoxy resin; a polyether polyol; and a hydroxy-functional film-forming polymer. The adhesives are useful in structural and semi-structural bonding applications.)

1. A curable composition comprising

Tetrahydrofurfuryl (meth) acrylate copolymers;

b. an epoxy resin component;

c. a polyether polyol;

d. a hydroxy-functional film-forming polymer; and

e. a cationic photoinitiator.

2. The curable composition of claim 1, wherein the tetrahydrofurfuryl (meth) acrylate copolymer comprises

a) Tetrahydrofurfuryl (meth) acrylate monomer;

b) C1-C8 alkyl (meth) acrylate monomers;

a cationic reactive functional (meth) acrylate monomer.

3. The curable composition of claim 1, wherein the weight ratio of the epoxy resin to the acrylate polymer is from 1.1:1 to 5: 1.

4. The curable composition of claim 1, wherein the tetrahydrofurfuryl (meth) acrylate copolymer comprises a cationically reactive (meth) acrylate functional monomer.

5. The curable composition of claim 1 wherein the film-forming polymer is selected from the group consisting of phenoxy resins, Ethylene Vinyl Acetate (EVA) copolymers, polycaprolactone polyols, polyester polyols, and polyvinyl acetal resins.

6. The curable composition of any one of claims 1-5, comprising:

15 to 50 parts of tetrahydrofurfuryl (meth) acrylate copolymer;

b.25 to 50 parts of an epoxy resin component;

c.5 to 15 parts of polyether polyol;

d. a hydroxy-functional film-forming polymer;

wherein the sum of a) to d) is 100 parts by weight; and

e. a cationic photoinitiator.

7. The curable composition of any one of claims 1-5, further comprising a sensitizer.

8. A method of preparing the curable composition of any one of claims 1-7, the method comprising the steps of:

a) at least partially polymerizing the monomer mixture to produce a tetrahydrofurfuryl (meth) acrylate copolymer;

b) combining the copolymer with an epoxy resin, a polyether polyol, the hydroxyl-functional film-forming polymer, a cationic photoinitiator, and optionally an additional free radical photoinitiator;

c) optionally coating the mixture;

d) and (4) photopolymerization.

9. The method of claim 8, wherein the monomer mixture of step a) is partially polymerized into a syrup copolymer composition comprising a tetrahydrofurfuryl (meth) acrylate copolymer solute in a solvent monomer.

10. An adhesive article comprising a substrate and a layer of the curable composition of any one of claims 1 to 7 on a surface of the substrate.

Technical Field

The present invention relates to structural and semi-structural bonding adhesives, adhesive articles, and methods for making adhesives and articles. The invention also relates to articles comprising one or more components bonded together with a structural bonding adhesive.

Background

Structural adhesive tapes can be used to bond one or more substrates to one another. Many structural adhesive tapes fall into one of two groups: (1) a thermally curable structural adhesive tape, and (2) an Ultraviolet (UV) activatable structural adhesive tape. As the class name indicates, heat curable structural adhesive tapes require heat to cure the adhesive composition of the tape. UVi structural adhesive tape contains an adhesive composition that will begin to cure when exposed to ultraviolet light, but does not require heat for curing. Heat may be used to accelerate UVi the cure rate of the structural adhesive tape.

Typically, a length of structural adhesive tape or die cut tape sheet is removed from the roll and attached to the first substrate using finger pressure. In the case of UVi structural adhesive tape, the structural adhesive tape may be exposed to actinic radiation such as UV. A second substrate is then brought into contact with the exposed surface of the structural adhesive tape and pressure is applied to the substrate for a period of time. The heat curable structural adhesive tape and optional UVi structural adhesive tape are then exposed to heat and the assembly is allowed to cool. The result is a bonded article.

In addition, the conventional Uvi structural adhesive tape formulation has high cold flow characteristics. Cold flow is a measure of the creep behavior of a material at non-elevated temperatures. Many conventional UVi belt materials have undesirably high cold flow characteristics that result in significant material flow under winding tension and stack weight. Thus, these materials may require refrigeration and/or special packaging to maintain dimensionally stable rolls and die cut portions.

In addition, many current structural adhesive compositions require heat to cure the adhesive composition. In the process of making the bonded article, the bonded article must be subjected to a heating step to cure the adhesive composition and a cooling step to allow further processing and/or packaging of the bonded article. A method of manufacturing bonded articles that does not require a heating step would be highly desirable from a processing standpoint.

What is needed in the art is a structural adhesive or bonding tape formed from an adhesive composition formulation that has low temperature bonding properties and/or can be used to bond different substrates having different coefficients of thermal expansion. Further, what is needed in the art is an UVi construction adhesive tape having a tape construction that allows the tape to be photoactivatable from one side of the tape. Typical substrates associated with UVi structural adhesive tapes are opaque to UV light and thus prevent UV initiation after full assembly bonding.

Disclosure of Invention

The present disclosure addresses some of the difficulties and problems discussed above by the discovery of new structural or semi-structural adhesives with improved cold flow properties as well as excellent adhesion properties. The structural bonding adhesive has the desired strength and bonding properties. The adhesive is photo-activated (i.e., initiates curing upon exposure to a light source) and does not require heat for curing. Structural bonding adhesives may be used in many applications, particularly as adhesives for bonding one or more substrates together.

"semi-structural adhesives" are those cured adhesives having a lap shear strength of at least about 0.75MPa, more preferably at least about 1.0MPa, and most preferably at least about 1.5 MPa. However, those cured adhesives having particularly high lap shear strength are known as structural adhesives. "structural adhesives" are those cured adhesives having a lap shear strength of at least about 3.5MPa, more preferably at least about 5MPa, and most preferably at least about 7 MPa.

In many embodiments, these binders provide at least one of the following: 1) lap shear value >5MPa, 2) >40N plastic to glass cracking value, and 3) < 500% strain creep using the test methods described herein.

The present invention describes a curable pressure sensitive adhesive which, when cured, provides a semi-structural or structural adhesive, wherein the pressure sensitive adhesive comprises:

a) tetrahydrofurfuryl (meth) acrylate copolymers;

b) an epoxy resin;

c) a polyether polyol;

d) a hydroxy-functional film-forming polymer; and

e) a photocatalyst.

The invention also includes the following items:

1. a curable composition comprising

15 to 50 parts of tetrahydrofurfuryl (meth) acrylate copolymer;

b.25 to 50 parts of an epoxy resin component;

c.5 to 15 parts of liquid polyether polyol;

10 to 25 parts of a hydroxy-functional film-forming polymer;

wherein the sum of a) to d) is 100 parts by weight; and

e. 0.1 to 1 part of cationic photoinitiator per 100 parts of a) to d).

2. The curable composition of clause 1, wherein the tetrahydrofurfuryl (meth) acrylate copolymer comprises

a)40-60 wt%, preferably more than 50 to 60 wt% tetrahydrofurfuryl (meth) acrylate monomer;

b)40-60 wt%, preferably 40 to less than 50 wt% of a C1-C8 alkyl (meth) acrylate monomer;

c)0-10 wt% of a cationically reactive functional (meth) acrylate monomer;

wherein the sum of a) to c) is 100% by weight.

3. The curable composition of any one of the preceding items, wherein the weight ratio of the epoxy resin to acrylate polymer is from 1.1:1 to 5: 1.

4. The curable composition of any one of the preceding items, wherein the epoxy resin comprises a cationically reactive (meth) acrylate functional monomer in an amount of 0.1 to 5 weight percent.

5. The curable composition of any one of the preceding items, wherein the film-forming polymer is selected from phenoxy resins, ethylene-vinyl acetate (EVA) copolymers, polycaprolactone polyols, polyester polyols, and polyvinyl acetal resins.

6. The curable composition according to any one of the preceding items, wherein the cationic photoinitiator is a sulfonium salt or an iodonium salt.

7. The curable composition of any one of the preceding items, wherein the epoxy resin comprises two or more epoxy resins, wherein at least one epoxy resin has an epoxy equivalent weight of about 300 to about 500 and at least one epoxy resin has an epoxy equivalent weight of about 1000 to about 1200.

8. The curable composition according to any one of the preceding items, wherein the tetrahydrofurfuryl (meth) acrylate copolymer does not have acid-functional monomer units.

9. The curable composition of any one of the preceding items, wherein the molar average carbon number of the C1-C8 alkyl (meth) acrylate is 3-6.

10. The curable composition according to any one of the preceding items, wherein the tetrahydrofurfuryl (meth) acrylate copolymer is a tetrahydrofurfuryl/butyl acrylate copolymer.

11. The curable composition of any one of the preceding items comprising:

25 to 35 parts of tetrahydrofurfuryl (meth) acrylate copolymer;

b.35 to 45 parts of an epoxy resin component;

c.5 to 15 parts of polyether polyol;

10 to 25 parts of a hydroxy-functional film-forming polymer;

wherein the sum of a) to d) is 100 parts by weight; and

e. 0.1 to 1 part of cationic photoinitiator per 100 parts of a) to d).

12. The curable composition according to any one of the preceding items, wherein the hydroxy-functional film-forming polymer is selected from phenoxy resins, ethylene-vinyl acetate (EVA) copolymers (solid at 25 ℃), polycaprolactone polyols, polyester polyols and polyvinyl acetal resins that are solid at 25 ℃.

13. The curable composition of clause 12, wherein the hydroxy-functional film-forming polymer has a hydroxyl number of at least 0.01.

14. A method of making the adhesive according to any one of the preceding items, comprising the steps of:

a) at least partially polymerizing the monomer mixture of (monomers) to produce a tetrahydrofurfuryl (meth) acrylate copolymer;

b) combining the copolymer with an epoxy resin, a polyether polyol, the hydroxyl-functional film-forming polymer, a cationic photoinitiator, and optionally an additional free radical photoinitiator;

c) optionally coating the mixture;

d) and (4) photopolymerization.

15. The method of clause 14, wherein the monomer mixture of step a) is partially polymerized into a syrup copolymer composition comprising a tetrahydrofurfuryl (meth) acrylate copolymer solute in a solvent monomer.

16. The method of clause 14, wherein the monomer mixture of step a) is fully polymerized to the THA copolymer.

17. The method of any of the preceding items 14-15, wherein the combining step b) is melt blending.

18. The method of clause 17, wherein the melt blending step is in an extruder.

19. An adhesive article comprising a substrate and a layer of the curable composition of any one of items 1 to 13 on a surface of the substrate.

20. The adhesive article of clause 19, wherein the composition has been partially cured.

21. The adhesive article of item 19, further comprising a release liner.

22. A method of bonding comprising the steps of: providing a substrate having on a surface thereof a layer of the curable composition according to any of items 1-13, exposing the curable adhesive layer to actinic radiation to initiate curing, affixing the first substrate to a second substrate, and optionally heating the bonded substrates.

23. The curable composition of any one of clauses 1-13, further comprising a sensitizer.

24. The curable composition of clause 23, wherein the sensitizer is selected from: ketones, coumarin dyes, xanthene dyes, acridine dyes, thiazole dyes, thiazine dyes, oxazine dyes, azine dyes, aminoketone dyes, porphyrins, aromatic polycyclic hydrocarbons, para-substituted aminostyryl ketone compounds, aminotriaryl methanes, merocyanines, squarylium dyes, and pyridinium dyes.

Detailed Description

The adhesive composition comprises, in part, a tetrahydrofurfuryl (meth) acrylate copolymer component. Unless otherwise indicated, THF acrylate and methacrylate will be abbreviated THFA. More specifically, the adhesive composition comprises tetrahydrofurfuryl (meth) acrylate, C₁-C₈A copolymer of a (meth) acrylate and optionally a cationically reactive functional (meth) acrylate.

The copolymer comprises, in addition to tetrahydrofurfuryl (meth) acrylate, C (meth) acrylate₁-C₈An alkyl ester monomer. Useful monomers include the acrylate and methacrylate esters of methanol, ethanol, propanol, isopropanol, butanol, pentanol, hexanol, heptanol, and octanol, including all isomers and mixtures thereof. Preferably the alcohol is selected from C₃-C₆Alkanols, and in certain embodiments, alkanols have a carbon number molar average of C₃-C₆. It has been found that in this range the copolymer has sufficient miscibility with the epoxy resin component and it allows formulation of a UViSBT with a useful overall balance of adhesive properties including lap shear.

The carbon number molar average may be calculated as follows: each alkanol (C)_1-8Alkanol) multiplied by the carbon number of each alkanol, and dividing the result by the total moles of alkanol:

∑_α-ω[ (number of moles of alkanol) × (# number of carbon atoms of alkanol)]Method for producing alkanolα to ω.

In addition, the copolymer may further contain a cationic reactive monomer, i.e., a (meth) acrylate monomer having a cationic reactive functional group. Examples of such monomers include, for example, glycidyl acrylate, glycidyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, and alkoxysilylalkyl (meth) acrylates, such as trimethoxysilylpropyl acrylate.

For the stability of the polymerizable composition, the copolymer is substantially free of acid functional monomers, the presence of which will initiate polymerization of the epoxy resin prior to UV curing. For the same reason, it is preferred that the copolymer does not contain any amine functional monomer. Further, it is preferred that the copolymer does not contain any acrylic monomers having moieties that are sufficiently basic to inhibit cationic cure of the adhesive composition.

THFA copolymers typically comprise polymerized monomer units of:

a)40-60 wt.%, preferably >50 to 60 wt.% tetrahydrofurfuryl (meth) acrylate

b)40 to 60 wt.%, preferably 40 to 50 wt.% (meth) acrylic acid C₁-C₈Preferably C₃-C₆An alkyl ester monomer;

c)0 to 10 wt%, preferably 1 to 5 wt%, of a cationic reactive functional monomer;

wherein the sum of a) to c) is 100% by weight.

The adhesive composition comprises one or more THFA acrylate copolymers in an amount that varies depending on the desired properties of the adhesive. Desirably, the adhesive composition comprises one or more THFA acrylate copolymers in an amount of 15 to 50 parts by weight, preferably 25 to 35 parts by weight, based on100 parts total weight of monomers/copolymers in the adhesive composition.

The adhesive comprises one or more epoxy resins. The epoxy resins or epoxides useful in the compositions of the present disclosure can be any organic compound having at least one oxirane ring that is polymerizable by ring opening, i.e., an average epoxy functionality greater than one, and preferably at least two. The epoxides may be monomeric or polymeric, as well as aliphatic, cycloaliphatic, heterocyclic, aromatic, hydrogenated, or mixtures thereof. Preferred epoxides contain more than 1.5 epoxy groups per molecule and preferably contain at least 2 epoxy groups per molecule. Useful materials typically have a weight average molecular weight of from about 150 to about 10,000, and more typically from about 180 to about 1,000. The molecular weight of the epoxy resin is typically selected to provide the desired properties of the cured adhesive. Suitable epoxy resins include linear polymeric epoxides having terminal epoxy groups (e.g., polyalkylene oxide glycol diglycidyl ether), polymeric epoxides having backbone epoxy groups (e.g., polybutadiene polyepoxide), and polymeric epoxides having pendant epoxy groups (e.g., glycidyl methacrylate polymers or copolymers), and mixtures thereof. Epoxide-containing materials include compounds having the general formula:

wherein R1 is alkyl, alkyl ether or aryl, and n is 1 to 6.

These epoxy resins include aromatic glycidyl ethers (such as those prepared by reacting a polyhydric phenol with an excess of epichlorohydrin), cycloaliphatic glycidyl ethers, hydrogenated glycidyl ethers, and mixtures thereof. Such polyhydric phenols may include resorcinol, catechol, hydroquinone and polynuclear phenols such as p, p ' -dihydroxydibenzyl, p ' -dihydroxydiphenyl, p ' -dihydroxyphenylsulfone, p ' -dihydroxybenzophenone, 2' -dihydroxy-1, 1-dinaphthylmethane, and 2,2', 2,3' -di-hydroxyphenylmethyl-, di-hydroxydiphenyldimethylmethane, dihydroxydiphenylethylmethyl-methane, dihydroxydiphenylmethylpropyl-methane, dihydroxydiphenylethylphenyl-methane, dihydroxydiphenylpropylphenyl-methane, dihydroxydiphenylbutylphenyl-methane, dihydroxydiphenylcresyl-ethane, dihydroxydiphenylcresylmethyl-methane, dihydroxydiphenyldicyclohexylmethane and dihydroxydiphenylcyclohexane, The 2,4', 3', 3,4 'and 4,4' isomers.

Useful curable Epoxy Resins are also described in various publications, including, for example, the Handbook of Epoxy Resins (Handbook of Epoxy Resins) (1967) published by McGraw-Hill Book Co., N.Y.) at L ee and Neville, and the Encyclopedia of Polymer Science and Technology (Encyclopedia of Polymer Science and Technology), 6, page 322 (1986).

The choice of epoxy resin used depends on its intended end use. If a greater amount of ductility is required in the tie layer, an epoxy with a softened backbone may be desirable. Materials such as bisphenol a diglycidyl ether and bisphenol F diglycidyl ether can provide the desired structural adhesive properties achieved by these materials when cured, while the hydrogenated versions of these epoxy resins can be used to be compatible with substrates having oily surfaces.

Examples of commercially available epoxies that may be used in the present disclosure include bisphenol A diglycidyl ethers (e.g., those available under the trade names EPON 828, EPON1001, EPON1004, EPON2004, EPON1510, and EPON1310 from Momentive Specialty Chemicals, Inc.), and those available under the trade names D.E.R.331, D.E.R.332, D.E.R.334, and D.E.N.439 from Dow Chemical Co.), bisphenol F diglycidyl ethers (e.g., those available under the trade name ARA L DITE GY 281 from Huntsman Chemical Corporation), diglycidyl epoxy functional group-containing silicone resins, flame retardant epoxy resins (e.g., a flame retardant epoxy resin available under the trade name DER560, a bisphenol brominated epoxy resin available from Dow Chemical Co., and 1, 4-butanediol.

An epoxy-containing compound having at least one glycidyl ether terminal moiety and preferably having a saturated or unsaturated cyclic backbone may optionally be added to the composition as a reactive diluent. Reactive diluents can be added for various purposes, such as to aid in the processing process, e.g., to control viscosity in the composition and during curing, to soften the cured composition, and to compatibilize various materials in the composition.

Examples of such diluents include cyclohexanedimethanol diglycidyl ether, resorcinol diglycidyl ether, p-tert-butylphenyl glycidyl ether, cresyl glycidyl ether, neopentyl glycol diglycidyl ether, trimethylolethane triglycidyl ether, trimethylolpropane triglycidyl ether, triglycidyl-p-aminophenol, N, N ' -diglycidylaniline, N, N, N ', N ', -tetraglycidyl-m-xylylenediamine, and vegetable oil polyglycidyl ethers reactive diluents are commercially available under the trade names HE L OXY 107 and DURA N10 from Charentive specialty Chemicals, Inc. the compositions may contain toughening agents to help provide the desired lap shear, peel resistance, and impact strength.

The adhesive composition desirably contains one or more epoxy resins having an epoxy equivalent weight of from about 100 to about 1500. More desirably, the adhesive contains one or more epoxy resins having an epoxy equivalent weight of from about 300 to about 1200. Even more desirably, the adhesive contains two or more epoxy resins, wherein at least one epoxy resin has an epoxy equivalent weight of from about 300 to about 500 and at least one epoxy resin has an epoxy equivalent weight of from about 1000 to about 1200.

The adhesive composition may comprise one or more epoxy resins in amounts that vary depending on the desired characteristics of the structural adhesive layer. Desirably, the adhesive composition includes one or more epoxy resins in an amount of 25 to 50 parts by weight, preferably 35 to 45 parts by weight, based on100 parts total weight of monomers/copolymers in the adhesive composition.

The adhesive composition also contains a lower M_wIn an amount of 5-15 parts relative to 100 parts total weight of monomer/copolymer in the adhesive composition.

Examples of such hydroxy-functional polyether compounds include, but are not limited to, polyoxyethylene and polyoxypropylene glycols; polyoxyethylene and polyoxypropylene triols and polyoxytetramethylene glycols. Polyoxyalkylene polyols are particularly suitable for delaying the curing reaction so that the "open time" of the adhesive composition can be increased. As used herein, the term "open time" is used to refer to the period of time after the adhesive composition is irradiated during which the adhesive composition remains sufficiently uncured to bond a second substrate thereto.

The open time of the adhesive composition is desirably about 1.6J/cm of exposure²At least 2 minutes after the energy dose of actinic radiation. However, if one or both substrates bonded together are translucent to the radiation to which the structural adhesive layer is to be exposed, the open time is immaterial, since in this case exposure to this radiation can be effected through the translucent substrates after the two substrates have been attached to one another by the adhesive. When both substrates of the assembly are opaque, the adhesive will be exposed to actinic radiation prior to attaching the second substrate thereto. In this case, an open time of at least 2 minutes is desired to allow suitable processability of the structural adhesive layer.

Commercially available hydroxy-functional poly (alkyleneoxy) compounds suitable for use in the present invention include, but are not limited to, PO L YMEG^TMA series of polyoxytetramethylene glycols (available from Riandedsel corporation of Jackson, Tenn., Inc., L yondelball, Inc.), TERATHANE^TMA series of polyoxytetramethylene glycols (Invista, Newark, Del.) from Invista, Newark, Del.) PO L YTHF from BASF Corp., Charlotte, N.C, Charlotte, N.C.)^TMSeries of polyoxytetramethylene glycols, ARCO L^TMSeries of polyoxypropylene polyols (from Bayer materials science, Inc. (Bayer MaterialScience, &lTtTtransfer = L "&gTtT L &lTtT/T &gTtT osAngeles, Calif.) and VORANO L^TMA series of polyether polyols (Dow Automotive Systems, Auburn Hills, MI) from olben mountain, michigan).

The adhesive layer also contains at least one hydroxyl-functional film-forming polymer having at least one and desirably at least two hydroxyl groups. Furthermore, the term hydroxyl-functional film-forming polymer does not include the above polyether polyols which also contain hydroxyl groups. Desirably, the film-forming polymer is substantially free of other "active hydrogen" containing groups, such as amino moieties and mercapto moieties. In addition, the film-forming polymer is also desirably substantially free of groups that may be thermally and/or photolytically labile such that the compound does not decompose when exposed to actinic radiation and/or heat during curing.

The hydroxyl-containing film-forming polymer contains two or more primary or secondary aliphatic hydroxyl groups (i.e., the hydroxyl groups are bonded directly to a non-aromatic carbon atom). In some embodiments, the hydroxy-functional film-forming polymer has a hydroxyl number of at least 0.01. It is believed that the hydroxyl groups participate in the cationic polymerization with the epoxy resin.

The hydroxy-functional film-forming polymer may be selected from phenoxy resins, Ethylene Vinyl Acetate (EVA) copolymers (solid at 25 ℃), polycaprolactone polyols, polyester polyols and polyvinyl acetal resins which are solid at 25 ℃. The hydroxyl group may be a terminal position or may be a side chain of a polymer or copolymer.

It has been found that the addition of a film-forming polymer to a structural adhesive composition improves the dynamic lap shear strength of the adhesive layer and/or reduces cold flow.

One useful class of hydroxyl-containing film-forming polymers are hydroxyl-containing phenoxy resins. Particularly desirable phenoxy resins are those derived from the polymerization of diglycidyl bisphenol compounds. Generally, the number average molecular weight of the phenoxy resin is less than 60,000, desirably in the range of about 20,000 to about 30,000. Commercially available phenoxy resins suitable for use in the present invention include, but are not limited to, PAPHEN available from International Consumer corporation (Inchem Corp., Rock Hill, SC) of Rokkel, south Carolina^TMPKHP-200 and SYNFAC^TMA series of polyoxyalkylated bisphenol A (Milliken Chemical, Spartanburg, S.C.) from Milliken Chemical, Spartanburg, south Carolina, for example, SYN FAC^TM8009. 773240, 8024, 8027, 8026, 8071, and 8031;

a second useful class of hydroxyl-containing film-forming polymers are Ethylene Vinyl Acetate (EVA) copolymer resins. The EVA resin contains a small amount of free hydroxyl groups and it is believed that the EVA copolymer is further deacetylated during cationic polymerization.

Suitable ethylene-vinyl acetate copolymer resins include, but are not limited to, thermoplastic ethylene-vinyl acetate copolymer resins containing at least about 28 weight percent vinyl acetate. In one embodiment of the invention, the ethylene vinyl acetate copolymer comprises a thermoplastic copolymer containing at least about 28 weight percent vinyl acetate, desirably at least about 40 weight percent vinyl acetate, more desirably at least about 50 weight percent vinyl acetate, and even more desirably at least about 60 weight percent vinyl acetate, based on the weight of the copolymer. In another embodiment of the invention, the ethylene vinyl acetate copolymer contains an amount of vinyl acetate in the copolymer in the range of from about 28% to about 99% by weight vinyl acetate, desirably from about 40% to about 90% by weight vinyl acetate, more desirably from about 50% to about 90% by weight vinyl acetate, and even more desirably from about 60% to about 80% by weight vinyl acetate.

Examples of commercially available ethylene-vinyl acetate copolymers useful in the present invention include, but are not limited to, the Elvax series, including E L VAX^TM150. 210, 250, 260, and 265 (from dupont de Nemours and co., Wilmington, Del., te.) from wilminton, dela corporation, westward, texas, atava from Celanese, inc., Irving, TX)^TMSeries L EVAPREN from Bayer corporation of Pittsburgh, Pa., Bayer Corp^TM400, comprising L EVAPREN^TM450. 452 and 456 (45% by weight vinyl acetate), L EVAPREN^TM500HV (50% by weight vinyl acetate); L EVAPREN^TM600HV (60% by weight vinyl acetate); L EVAPREN^TM700HV (70% by weight vinyl acetate), and L EVAPREN^TMKA 8479(80 wt% vinyl acetate), each from langerhans (L anxess Corp.).

Additional useful film-forming polymers include TONE from Dow chemical, Midland, MI, Midland, Mich^TMPolycaprolactone polyol series from bostonCAPA of Inc. (Perstorp Inc.)^TMSeries of polycaprolactone polyols, DESMOPHEN^TMA series of saturated polyester polyols (available from Bayer Corporation, Pittsburg, Pa.) such as DESMOPHEN^TM631A75。

The adhesive layer comprises one or more hydroxyl-containing film-forming polymer resins in an amount that varies depending on the desired characteristics of the structural adhesive layer. Desirably, the binder composition comprises one or more hydroxyl-containing film-forming polymer resins in an amount up to about 25 parts by weight based on100 parts total weight of monomers/copolymers in the binder composition. More desirably, the adhesive composition comprises one or more film-forming polymeric resins in an amount of from about 10 to about 25 parts by weight based on100 parts total weight of monomers/copolymers in the adhesive composition. Even more desirably, the structural adhesive layer of the structural adhesive tape of the present invention comprises one or more film-forming polymeric resins in an amount of from 15 to about 20 parts by weight based on100 parts total weight of the monomers/copolymers in the adhesive composition.

Broadly, a curable adhesive composition comprises:

15 to 50 parts of a THFA (meth) acrylate copolymer;

b.25 to 50 parts of an epoxy resin component;

c.5 to 15 parts of polyether polyol;

10 to 25 parts of a hydroxy-functional film-forming polymer;

wherein the sum of a) to d) is 100 parts by weight; and

e. 0.01 to 1 part of cationic photoinitiator per 100 parts of a) to d).

In many embodiments, the amount of epoxy resin is greater than the THFA copolymer; the weight ratio of the epoxy resin to the acrylate polymer is 1.1:1 to 5: 1.

The adhesive composition may also contain up to about 50 parts by weight (relative to 100 parts by weight of a) to d)), desirably up to about 10% of various additives such as fillers, stabilizers, plasticizers, tackifiers, flow control agents, cure rate retarders, adhesion promoters (e.g., silanes and titanates), adjuvants, impact modifiers, expandable microspheres, thermally conductive particles, electrically conductive particles, and the like, such as silica, glass, clay, talc, pigments, colorants, glass beads or bubbles, and antioxidants, in order to reduce the weight and/or cost of the structural adhesive layer composition, adjust the viscosity, and/or provide additional reinforcement or modify the thermal conductivity of the adhesive compositions and articles of the invention such that a more rapid or uniform cure can be achieved. The nature of the additives and their amounts should not interfere with the light transmittance of the curable adhesive.

The adhesive composition may be prepared by combining a tetrahydrofurfuryl (meth) acrylate copolymer with an epoxy resin, a polyether polyol, a hydroxy-functional film-forming polymer and a cationic photoinitiator, and by photopolymerizing the mixture with actinic radiation, preferably UV radiation.

In some embodiments, the (meth) acrylate copolymer is prepared separately by free radical polymerization of the monomer mixture with a photoinitiator or a thermal initiator. The copolymers can be prepared by any conventional free radical polymerization method, including solution, radiation, bulk, dispersion, emulsion, solventless, and suspension methods. The resulting adhesive copolymer may be a random (co) polymer or a block (co) polymer.

Thermal initiators useful for preparing THFA copolymers are initiators that generate free radicals upon exposure to heat that initiate (co) polymerization of the monomer mixture. Suitable water-soluble initiators include those selected from the group consisting of: potassium persulfate, ammonium persulfate, sodium persulfate, and mixtures thereof; a redox initiator (such as a reaction product of the above-mentioned persulfate with a reducing agent (such as those selected from sodium metabisulfite and sodium bisulfite)); and 4,4' -azobis (4-cyanovaleric acid) and its soluble salts (e.g., sodium, potassium). Suitable initiators also include those selected from the group consisting of: azo compounds, such as VAZO^TM64(2,2' -azobis (isobutyronitrile)) and VAZO^TM52(2,2' -azobis (2, 4-dimethylvaleronitrile)), both available from dupont (e.i. dupont de Nemours Co.), peroxides such as benzoyl peroxide and lauroyl peroxide; and mixtures thereof. A preferred oil-soluble thermal initiator is (2,2' -azobis (isobutyronitrile)).

When used, the thermal initiator may comprise from about 0.05 to about 1 part by weight, preferably from about 0.1 to about 0.5 parts by weight, based on100 parts by weight of the monomer component in the pressure sensitive adhesive.

Useful photoinitiators include: benzoin ethers such as benzoin methyl ether and benzoin isopropyl ether; substituted acetophenones, such as Irgacure^TM651 photoinitiator 2, 2-dimethoxyacetophenone, available from Pasf corporation (BASF, &lTtT transfer = L "&gTt L &lTt/T &gTt udwigshafen, Germany) from Lodvishhong, Germany, under the trade name Esacure^TMKB-1 photoinitiators are available from Saedoma, West Chester, Pa., 2-dimethoxy-2-phenyl-l-acetophenone, and dimethoxy hydroxyacetophenone, from Sartomer Co., U.S.A., substituted α ketones, such as 2-methyl-2-hydroxypropiophenone, aromatic sulfonyl chlorides, such as 2-naphthalene-sulfonyl chloride, and photosensitive oximes, such as 1-phenyl-1, 2-propanedione-2- (O-ethoxy-carbonyl) oxime, with substituted acetophenones being particularly preferred among these initiators.

Preferred photoinitiators are photoactive compounds which undergo Norrish I cleavage to generate free radicals, such cleavage being initiated by addition of double bonds to acrylic. Such photoinitiators are preferably present in an amount of 0.1 to 1.0 part by weight per 100 parts of the monomer mixture. The monomer mixture and photoinitiator may be irradiated with activating UV radiation to polymerize the monomer component. The UV light source can be of two types: 1) relatively low intensity light sources, such as backlights, provide typically 10mW/cm in the wavelength range of 280 to 400 nanometers²Or lower (according to a method approved by the National Institute of Standards and Technology, the United states National Institute of Standards and Technology), such as Electronic Instrumentation and Technology Inc. of Stirling, Virginia&Uvimap manufactured by Technology, Inc (Sterling, VA))^TMUM 365L-S radiometer), and 2) a relatively high intensity light source such as a medium pressure mercury lamp, which provides typically more than 10mW/cm²Preferably at 15mW/cm²And 450mW/cm²The strength of (d) in between. For example, 600mW/cm can be used successfully²Strength ofAnd an exposure time of about 1 second. The intensity can be from about 0.1 to about 150mW/cm²Preferably from about 0.5 to about 100mW/cm²And more preferably from about 0.5 to about 50mW/cm²Within the range of (1).

A typical solution polymerization process is carried out by: the monomer, a suitable solvent and optionally a chain transfer agent are added to the reaction vessel, the free radical initiator is added, purged with nitrogen, and the reaction vessel is maintained at an elevated temperature (typically in the range of about 40 to 100 ℃) until the reaction is complete, typically about 1 to 24 hours, depending on batch size and temperature. Examples of the solvent are methanol, tetrahydrofuran, ethanol, isopropanol, acetone, methyl ethyl ketone, methyl acetate, ethyl acetate, toluene, xylene, and ethylene glycol alkyl ether. These solvents may be used alone or as a mixture thereof.

The polymerization may be carried out in the presence of a suitable solvent, such as ethyl acetate, toluene and tetrahydrofuran that are unreactive with the functional groups of the components of the syrup polymer, or preferably in the absence of a solvent.

The syrup polymer technique includes partially polymerizing monomers to produce a syrup polymer comprising a THFA (meth) acrylate copolymer and unpolymerized monomers. The syrup polymer composition is polymerized to a useful coating viscosity so that it can be combined with other components of the adhesive composition, optionally coated onto a substrate (such as a tape backing) and further polymerized. The partial polymerization provides a coatable solution of the THFA (meth) acrylate solute copolymer in one or more solvent monomers. It will be appreciated that if a slurry polymerization process is used, additional free radical initiator is required to fully polymerize the solvent monomers after compounding.

Polymers may also be prepared using solventless polymerization methods, such as the continuous free radical polymerization methods described in U.S.4,619,979 and 4,843,134(Kotnour et al); a substantially adiabatic polymerization process using a batch reactor as described in U.S.5,637,646 (Ellis); and the methods described for polymerizing the encapsulated pre-adhesive compositions described in U.S.5,804,610(Hamer et al). Preferably, the first copolymer is prepared by an adiabatic batch polymerization process, wherein the total of the absolute value of any energy exchanged to and from the batch during the reaction process will be less than about 15% of the total energy released by the corresponding amount of polymerization reaction that occurred during the time that polymerization had occurred, as described in U.S. 56327646 (Ellis), which is incorporated herein by reference.

Preferably, the components are mixed and photopolymerized using the methods described in WO9607522(Hamer et al) and u.s.5,804,610(Hamer et al), both incorporated herein by reference, for the methods described for polymerizing encapsulated pre-adhesive compositions.

In the method of Hamer, the packaging material used to form the reaction vessel or container is preferably made of a material that does not substantially adversely affect the desired adhesive properties when mixed with the adhesive composition. Hot melt coated adhesives prepared from a mixture of the adhesive composition and the encapsulating material may have improved adhesive properties compared to hot melt coated adhesives prepared from the adhesive composition alone.

In some embodiments, the reaction mixture is coated onto a carrier web, then covered with a sheet material, and polymerized, wherein the carrier web, the sheet material, or both, can be hot melt coated with an adhesive. If both the carrier web and the sheet material are hot melt coatable, the resulting composite can be fed directly into a hot melt coater, or cut into smaller strips or sheets and then fed into a hot melt coater. If only one of the carrier web and the sheet material is hot melt coatable with the adhesive, the non-coatable entities are removed prior to hot melt coating the adhesive. To facilitate handling after removal of the non-coatable entity, the polymerized adhesive can be folded over on itself such that the coatable entity substantially wraps the major surface of the coated adhesive. The adhesive web may then be fed into a hot melt coater, or it may be cut into smaller strips or pieces and hot melt coated.

If either the carrier web or the sheet material cannot be hot melt coated with the adhesive, it should be processed so that the adhesive can be easily removed therefrom, if desired. Such asTreatments include silicone release coatings, polyfluoropolyether coatings, and polyvinyl fluoride coatings (such as Teflon @)^TM)。

If desired, a chain transfer agent may be added to the monomer mixture to produce a THFA copolymer having the desired molecular weight. Examples of useful chain transfer agents include, but are not limited to, those selected from carbon tetrabromide, alcohols, mercaptans, and mixtures thereof. When present, preferred chain transfer agents are isooctyl thioglycolate and carbon tetrabromide.

The chain transfer agent is used in an amount such that the THFA copolymer has a tan of 0.75 to 3.0 at the processing temperature of the adhesive (e.g. 120 ℃). The monomer mixture may also contain up to about 5 parts by weight of a chain transfer agent, typically from about 0.01 to about 5 parts by weight (if used), preferably from about 0.05 to about 0.5 parts by weight, based on100 parts by weight of the total monomer mixture.

The components of the adhesive composition may be combined and mixed in a suitable mixing vessel and at an elevated temperature sufficiently low to avoid decomposition of any photoinitiator present in the adhesive composition. While the mixing time may vary, the components of the adhesive composition are desirably mixed for a sufficient period of time to form a homogeneous mixture of the components.

After mixing, the adhesive composition can be formed into its final shape by a variety of different methods. For example, the adhesive composition may be coated onto a release liner using a heated knife coater to form a layer. Alternatively, the components of the adhesive composition may be compounded in an extruder and then extruded through a die having the desired profile to produce a shaped adhesive strip; i.e. a strip having a desired cross-sectional shape. In another method, the adhesive composition may be extruded as a block and delivered between a pair of motor-driven chill rolls spaced apart a predetermined distance to form a flat sheet of structural adhesive layer adhesive composition, which may then be calendered to a desired thickness.

In a batch process, the adhesive composition is prepared by mixing the various ingredients in one or more suitable containers, desirably containers that are opaque to actinic radiation. Liquid components, such as liquid epoxide and hydroxyl-containing material, can be pre-mixed in a first vessel at a temperature sufficient to liquefy the components. The components may be added simultaneously or sequentially in any order; however, it is desirable to add the cationic photoinitiator after all other components have been thoroughly mixed.

In a continuous process, the adhesive composition is mixed in an extruder, such as a twin screw extruder equipped with downstream ports, static mixers, and appropriate output orifices (i.e., film die, sheet die, profile die, etc.) and wind-up rolls as needed. The winding line speed can be adjusted according to the output form as required.

The compounded adhesive composition may be cured with a cationic photoinitiator. Suitable photoinitiators include, but are not limited to, onium salts and cationic organometallic salts, both described in U.S. Pat. No. 5,709,948 and photoactivatable organometallic complex salts such as those described in U.S. Pat. Nos. 5,059,701, 5,191,101 and 5,252,694.

Useful onium salts include diazonium salts, such as aryl diazonium salts; halonium salts such as diaryliodonium salts; sulfonium salts, such as triarylsulfonium salts; selenonium salts, such as triarylselenonium salts; sulfonium salts such as triarylsulfonium salts; and other classes of onium salts such as triarylphosphonium and arsonium salts, and pyrylium and thiopyrylium salts.

Suitable aromatic iodonium complex salts are described in more detail in U.S. Pat. No. 4,256,828. In one embodiment of the present invention, the desired aromatic iodonium complex salt is [ (Ar)₂I]⁺[PF6]^-Or [ (Ar)₂I]⁺[SbF₆]^-Wherein Ar is the same or different and each comprises an aromatic group having 4 to 20 carbon atoms.

The aromatic iodonium complex salts useful in the present invention are photosensitive in the ultraviolet region of the spectrum. However, it can be sensitive to the near ultraviolet and visible range of the spectrum by known sensitizers of photolyzable organohalogen compounds. Exemplary sensitizers include colored aromatic polycyclic hydrocarbons, as described in U.S. Pat. No. 4,250,053. Suitable sensitizers should be selected so as not to significantly interfere with the cationic cure of the epoxy resin in the adhesive composition.

Suitable sulfonium salts include triaryl-substituted salts, such as triphenylsulfonium hexafluoroantimonate and p- (phenyl (phenylthio) diphenylsulfonium hexafluoroantimonate are desired sulfonium salts other sulfonium salts useful in the present invention are described in more detail in U.S.5,256,828 and 4,173,476 aromatic sulfonium complex salts useful in the present invention are generally photosensitive in the ultraviolet region of the spectrum, however, they can be sensitive to the near ultraviolet and visible ranges of the spectrum by selective sensitizer groups, such as those described in U.S.4,256,828 and 4,250,053.

If a sensitizer is used in combination with the onium salt as described above, it should be selected so as not to significantly interfere with the cationic curing of the epoxy resin in the adhesive composition.

In some embodiments, a sensitizer may be used as a dye or indicator that 1) identifies the location of the adhesive in the connector; 2) participating in a curing reaction; and 3) undergo a color change reflecting the onset of cure. When used as a color change indicator in a curable composition, the composition may be cured at an irradiation wavelength corresponding to λ max of the photoinitiator rather than the sensitizer. The initial acid released from the initiator reacts with the sensitizer to effect a color change.

Suitable sensitizers are believed to include compounds of the class of ketones, coumarin dyes (e.g., coumarins), xanthene dyes, acridine dyes, thiazole dyes, thiazine dyes, oxazine dyes, azine dyes, aminoketone dyes, porphyrins, aromatic polycyclic hydrocarbons, para-substituted aminostyryl ketone compounds, aminotriaryl methanes, merocyanines, squarylium dyes, and pyridinium dyes.

By way of example, a preferred class of ketone sensitizers has the formula:

A-CO-(Y)_b-B

wherein Y is CO or CR¹¹R¹²Wherein R is¹¹And R¹²May be the same or different and may be hydrogen, alkyl, alkaryl or aralkyl, B is 1 or 0, and A and B may be the same or different and may be substituted (with one or more non-interfering substituents) or unsubstituted aryl, alkyl, alkaryl or aralkyl groups, or A and B may together form a cyclic structure which may be a substituted or unsubstituted alicyclic, aromatic, heteroaromatic or fused aromatic ring.

Suitable ketones in the above formula include monoketones (b ═ 0), such as 2,2-, 4-or 2, 4-dihydroxybenzophenone, di-2-pyridone, di-2-furanone, di-2-phenylthioketone, benzoin, fluorenone, quinones (e.g., chloranil, 2-aza-3-carboxy-9-fluorenone, and the like), chalcones, Michler's ketone, 2-fluoro-9-fluorenone, 2-chlorothiaxanthone, acetophenone, benzophenone, 1-or 2-naphthone, 9-acetylanthracene, 2-, 3-or 9-acetylphenanthrene, 4-acetylbiphenyl, phenylpropanone, n-butylbenzene, pentanone, 2-, 3-or 4-acetylpyridine, 3-acetylcoumarin, and the like suitable diketones include aralkyl diketones such as anthraquinone, phenanthrenequinone, o-, m-and p-diacetylbenzene, 1,3-, 1,4-, 1,5-, 1,6-, 1, 7-and 1, 7-diacetyl-1, 3' -and 2-acetyl-diketones, 3' -and the like, and include anthraquinone, phenanthrenequinone, o-, m-, and p-diacetyl-diacetylbenzene, 1,3-, 3' -diacetyl, 2,3' -and the like, 2,3' -diacetyl, 3, 2,3' -and the like, 3' -diacetyl-and the like, 2,3' -diacetyl-and 2, 3-diketones include the like, 2, 3-and 2-diacetyl compounds include the like, 2-diacetyl, 2, 3-and 2-diacetyl, 3-diketones, 2-and 2-diacetyl, 3-and the like, 2-diacetyl, and the like, 3-diacetyl, 3-and 2-diacetyl compounds including the like, 2-diacetyl-and 3.

Other preferred sensitizers include rose bengal, methylene violet, fluorescein, eosin yellow, eosin Y, ethyl eosin, eosin Bluish, edible acerola flavin blends, 4',5' -dibromofluorescein.

Among the onium cationic photoinitiators, sulfonium compounds are preferred for thermal stability.

Another class of photoinitiators suitable for use in the present invention include photoactivatable organometallic complex salts such as those described in U.S. patents 5,059,701, 5,191,101 and 5,252,694. Such organometallic cation salts can have the general formula:

[(L¹)(L²)M^m]^+eX^-

wherein

M^mRepresents a metal atom selected from groups IVB, VB, VIB, VIIB and VIII of the periodic Table of the elements, ideally Cr, Mo, W, Mn, Re, Fe and Co;

L¹denotes 0, 1 or 2 ligands donating pi electrons, wherein the ligands may be the same or different, and each ligand may be selected from substituted and unsubstituted alicyclic and cyclic unsaturated compounds and substituted and unsubstituted carbocyclic aromatic and heterocyclic aromatic compounds, each compound being capable of donating 2 to 12 pi electrons to the valence shell of the metal atom M.

Ideally, L¹Selected from substituted and unsubstituted η³Allyl, η 5-cyclopentadienyl, η 7-cycloheptatrienyl and η 6-aromatic compounds selected from η 6-benzene and substituted η 6-benzene compounds (e.g., xylene), and compounds having 2 to 4 fused rings, each compound capable of reacting to M^mThe valence shell of (a) contributes 3 to 8 pi electrons;

L²denotes 0 or 1 to 3 ligands which contribute an even number of sigma electrons, wherein the ligands may be the same or different and each ligand may be selected from the group consisting of carbon monoxide, nitrosonium, triphenylphosphine, triphenylantimony and derivatives of phosphorus, arsenic and antimony, with the proviso that L¹And L²To M^mThe total electron charge contributed results in a net residual positive charge of e of the complex;

e is an integer having a value of 1 or 2, representing the residual charge of the complex cation; and is

X is a halogen-containing complex anion as described above.

Suitable commercially available cationic initiators include, but are not limited to, aromatic sulfonium complex salt FX-512^TM(Minnesota Mining and manufacturing company, St. Paul, Minn.) CD-1012, St.Paul, St.^TMAnd CD-1010^TM(Sartomer, Exton, Pa.) of exxoton, pennsylvania; UVOX^TMUVI-6976, aromatic sulfonium complex salt (Dow Chemical, Midland, Mi.); and IRGACURE^TM261, cationic organometallic complex salts (BASF Corporation, Florham Park, NJ), of Florham Park.

Wherein the cationic photoinitiator for curing the adhesive composition is a metallocene salt catalyst, optionally accompanied by a promoter such as an oxalate ester of a tertiary alcohol, as described in U.S. Pat. No. 5,436,063, but this is optional. Oxalate promoters which may be used include those described in U.S. patent 5,252,694. The accelerator may comprise from about 0.01 to about 5 weight percent, desirably from about 0.1 to about 4 weight percent of the structural adhesive layer composition, based on the total weight of resins (THFA copolymer, epoxy resin, polyether polyol, and film-forming polymer) present in the composition.

The adhesive composition contains one or more cationic photoinitiators in amounts that vary depending on the light source and the degree of exposure. Desirably, the adhesive composition comprises one or more cationic photoinitiators in an amount of from 0.1 to 1 part by weight, based on100 parts total weight of the adhesive composition. More desirably, the structural adhesive layer of the structural adhesive tape of the present invention comprises one or more photoinitiators in an amount of from about 0.2 to about 0.5 parts by weight, based on100 parts total weight in the adhesive composition.

The cured, partially cured, or uncured adhesive composition may be coated on a substrate to form an adhesive article. For example, the substrate may be flexible or inflexible and may be formed of a polymeric material, a glass or ceramic material, a metal, or a combination thereof. Some substrates are polymeric films such as those made from polyolefins (e.g., polyethylene, polypropylene, or copolymers thereof), polyurethanes, polyvinyl acetate, polyvinyl chloride, polyesters (polyethylene terephthalate or polyethylene naphthalate), polycarbonate, poly (methyl (meth) acrylate (PMMA), ethylene-vinyl acetate copolymers, and cellulosic materials (e.g., cellulose acetate, cellulose triacetate, and ethyl cellulose).

Other substrates are metal foils, nonwovens (e.g., paper, cloth, nonwoven), foams (e.g., polyacrylic, polyethylene, polyurethane, neoprene), and the like. For some substrates, it may be desirable to treat the surface to improve adhesion to the crosslinking composition, or both. Such treatments include, for example, the application of primer layers, surface modification layers (e.g., corona treatment or surface abrasion), or both.

In some embodiments, the adhesive article includes a nonwoven scrim embedded in the adhesive layer.

In some embodiments, the substrate is a release liner to form an adhesive article that configures the substrate/adhesive layer/release liner. The adhesive layer may be cured, uncured or partially cured. The release liner typically has a low affinity for the curable composition. Exemplary release liners can be made from paper (e.g., kraft paper) or other types of polymeric materials. Some release liners are coated with an outer layer of a release agent, such as a silicone-containing material or a fluorocarbon-containing material.

The present disclosure further provides a method of bonding comprising the steps of: providing a substrate (or workpiece) having a layer of a curable composition on a surface of the substrate (or workpiece), exposing the adhesive layer to actinic radiation (e.g., UV) to initiate curing, and attaching the first substrate to a second substrate (or workpiece), and optionally heating the bonded workpieces.