Adhesive composition

Abstract

A novel low odor two component acrylic-epoxy adhesive composition and a method of making the same.

Description

Background Technology

[0001] In the automotive industry, adhesives are used to assemble various components that bond to each other or to other parts of the vehicle. During the assembly of closures (doors, hoods, and trunk lids), some manufacturers require the adhesive to gain treatment strength through a 15-minute room-temperature curing process before the parts enter the high temperatures of the electrocoating oven (which can cause partial deformation of loosely bonded panels). During vehicle assembly, the bonded joints must also withstand the high temperatures of the painting and electrocoating ovens. Automakers increasingly view crimped flange joints as critical components in vehicle crashes. This is due to crash tests and real-world collision events where closures with adhesively bonded crimped flange joints can detach or separate in high-speed collisions. Therefore, room-temperature curing adhesives with heat resistance and impact peel strength are required for closure applications. Typically, adhesive compositions are two-component epoxy-acrylic blends designed to achieve rapid curing and heat resistance. However, these compositions are often quite brittle and do not provide the required impact peel strength.

[0002] Historically, several classes of reactive and non-reactive toughening agents have been used in two-component epoxy-acrylic hybrid adhesives. One of the most effective and popular reactive toughening agents is methacrylate-terminated butadiene rubber or methacrylate-terminated butadiene-acrylonitrile rubber. While these reactive toughening agents are highly effective in imparting impact resistance, their supply chain position is very poor, as there is only one source of their manufacture globally. Furthermore, the manufacture of these materials is hazardous and has a negative environmental impact.

[0003] The inventors of this invention have previously discovered that a product containing at least one methacrylate monomer and at least one T having a temperature of 0°C or lower... g A two-component hybrid adhesive composition with a methacrylate-terminated toughening agent exhibited good impact peel strength after exposure to an electrophoretic coating oven. This invention is disclosed in PCT / US23 / 024257, which is incorporated herein by reference in its entirety. However, one drawback of this composition is the perceived unpleasant odor of the acrylic monomers. While others in the art have attempted to use low-odor and low-vapor-pressure monomers in similar compositions, the results have not been desirable, primarily due to compatibility issues between the low-odor and low-vapor-pressure monomers used in the composition and the toughening agent. Therefore, there is a need to obtain a low-odor composition while maintaining all the desirable qualities of a two-component hybrid composition, such as a high level of impact peel strength. Summary of the Invention

[0004] This invention provides a novel two-component epoxy-acrylic hybrid adhesive composition having a portion of component A and a portion of component B. Component A comprises a) at least one methacrylate monomer having a vapor pressure of less than 10 Pa at 20°C; and b) at least one Tg having a vapor pressure of 0°C or lower. g The toughening agent is methacrylate-terminated; and a portion of component B contains at least one epoxy resin; and an oxidizing agent. Detailed Implementation

[0005] The inventors of this invention have discovered that it is possible to obtain epoxy-acrylic adhesives that exhibit rapid curing at room temperature, excellent impact peel strength even after exposure to high temperatures, and low odor. The two-component epoxy-acrylic adhesive composition of this invention comprises two parts: a portion of component A and a portion of component B.

[0006] Partial component A:

[0007] Part A of the adhesive composition comprises at least one methacrylate monomer. The methacrylate monomer is preferably a monomer with low odor and very low vapor pressure, typically less than 10 Pa at 20°C, preferably less than 8 Pa at 20°C, more preferably less than 6 Pa at 20°C, and most preferably less than 5 Pa at 20°C. In some preferred embodiments of the invention, the methacrylate monomer used in Part A will have the common chemical structure of Formula I and / or Formula II:

[0008]

[0009] In a preferred embodiment, the methacrylate monomer contains less than 0.5 wt.%, preferably less than 0.1 wt.%, and most preferably less than 0.01 wt.% of methacrylic acid based on the total weight of the methacrylate monomer.

[0010] In another preferred embodiment, portion A comprises two or more methacrylate monomers.

[0011] In even more preferred embodiments, the methacrylate monomers used in this invention are selected from isopropyl methacrylate, glyceryl methacrylate, or any mixture thereof. If a mixture is used, in this embodiment, the mass ratio between isopropyl methacrylate and glyceryl methacrylate can be between 3:1 and 1:3, and preferably between 2:1 and 1:2, and more preferably 1:1.

[0012] One or more methacrylate monomers preferably comprise 28-45 wt.%, more preferably 30-38 wt.%, and even more preferably 33-35 wt.%, of portion A, all based on the total weight of portion A.

[0013] Part A further comprises at least one toughening agent, preferably a methacrylate-terminated toughening agent as disclosed in PCT / US23 / 024257. In a preferred embodiment, the toughening agent comprises at least one polyether as part of its main chain.

[0014] In a preferred embodiment, the toughening agent has a T0 of 0°C or lower. g -20°C or lower, more preferably -40°C or lower T g .

[0015] In a preferred embodiment, at least one toughening agent is prepared by reacting a polyether polyol with a polyisocyanate in a ratio such that the resulting polymer is an NCO-terminated polymer, followed by end-capping with a hydroxyalkyl ester of methacrylate. The polyether polyol may be a diol or a triol, wherein a diol is preferred. In another preferred embodiment, the polyol is a poly(C2-C6-epoxy)diol, wherein C2, C3, and C4 are preferred, and C4 is particularly preferred [i.e., poly(tetrahydrofuran)diol or PTMEG].

[0016] In yet another preferred embodiment, the polyether polyol is selected from PTMEG having a molecular weight of 1,000 to 3,000 Da, preferably 1,500 to 2,500 Da, and more preferably about 2,000 Da. The equivalents and molecular weights were measured using the methods and instruments listed in the Examples of Use section on gel permeation chromatography (GPC).

[0017] The toughening agent may also contain a low molecular weight (< 250 Da) polyol having a functionality of 3 or 4, such as trimethylolpropane. If present, the low molecular weight polyol is preferably used at 0.1-3 wt.%, more preferably 0.25-1 wt.%, and particularly preferably 0.5 wt.%, based on the total weight of the toughening agent. In a preferred embodiment, the toughening agent comprises 0.1-3 wt.%, more preferably 0.25-1 wt.%, and most preferably 0.5 wt.%, of trimethylolpropane based on the total weight of the toughening agent.

[0018] Polyisocyanates can be aliphatic or aromatic, with aliphatic being preferred. In one embodiment, the polyisocyanate is a diisocyanate. In another embodiment, the polyisocyanate is an aliphatic diisocyanate. Examples include hexamethylene diisocyanate (HDI), isophorone diisocyanate, and methylene dicyclohexyl diisocyanate.

[0019] The hydroxyalkyl ester of methacrylate used for end capping is preferably a C2-C6-hydroxyalkyl ester, more preferably a C2-C4-hydroxyalkyl ester, and even more preferably a C2-C3-hydroxyalkyl ester, with C2-hydroxyalkyl ester being the most preferred, especially hydroxyethyl methacrylate (HEMA).

[0020] Toughening agents can also be manufactured by reacting a polyether polyol with a polyisocyanate in the presence of a polyurethane catalyst to produce an NCO-terminated prepolymer. The prepolymer is then reacted with a hydroxyalkyl ester of methacrylic acid, resulting in end-capping.

[0021] In a preferred embodiment, the toughening agent is manufactured by reacting PTMEG with HDI in the presence of a polyurethane catalyst to produce an NCO-terminated prepolymer. The prepolymer is then reacted with HEMA, resulting in end-capping.

[0022] In a preferred embodiment, the toughening agent has a number-average molecular weight (Mn) of 6,119 Da. n In another preferred embodiment, PTMEG has a molecular weight of 2,000 Da, and the toughening agent has a number-average molecular weight (Mn) of 6,119 Da. n In yet another preferred embodiment, the toughening agent has a weight-average molecular weight (Mn) of 15,084 Da. w ).

[0023] Part A typically comprises 10-30 wt.%, more preferably 15-25 wt.%, and particularly preferably 17-24 wt.%, of toughening agent based on the total weight of Part A. In a preferred embodiment, the toughening agent is prepared by reacting an aliphatic polyether diol with an aliphatic diisocyanate.

[0024] Part A may also include phosphorus-containing compounds as disclosed in PCT / US23 / 024257, selected from monoesters, diesters and esters of phosphonic acids having a unit having a vinyl or allyl unsaturation, as well as monoesters, diesters and triesters of phosphoric acids.

[0025] Examples of phosphorus-containing compounds include phosphoric acid; 2-methacryloyloxyethyl phosphate; bis-(2-methacryloyloxyethyl) phosphate; 2-acryloyloxyethyl phosphate; bis-(2-acryloyloxyethyl) phosphate; methyl-(2-methacryloyloxyethyl) phosphate; ethyl acryloyloxyethyl phosphate; methyl acryloyloxyethyl phosphate; ethyl acryloyloxyethyl phosphate; propyl acryloyloxyethyl phosphate, isobutyl acryloyloxyethyl phosphate, ethylhexyl acryloyloxyethyl phosphate, propyl acryloyloxyethyl phosphate halo, isobutyl acryloyloxyethyl phosphate halo, or ethylhexyl acryloyloxyethyl phosphate halo; vinylphosphine. Acids; cyclohexene-3-phosphonic acid; (α-hydroxybutylidene-2-phosphonic acid; 1-hydroxy-1-phenylmethane-1,1-diphosphonic acid; 1-hydroxy-1-methyl-1-diphosphonic acid; 1-amino-1-phenyl-1,1-diphosphonic acid; 3-amino-3-hydroxypropane-1,1-diphosphonic acid; amino-tris(methylenephosphonic acid); γ-amino-propylphosphonic acid; γ-glycidoxypropylphosphonic acid; phosphate-mono-2-aminoethyl ester; allylphosphonic acid; allylphosphonic acid; β-methacryloyloxyethylphosphonic acid; diallylphosphonic acid; β-methacryloyloxyethyl)phosphonic acid and allylmethacryloyloxyethylphosphonic acid. Preferred phosphorus compounds are 2-hydroxyethyl methacrylate phosphate and phosphono-oxidized (meth)acrylic acid monomers.

[0026] Part A may also contain a tertiary amine radical initiator as disclosed in PCT / US23 / 024257. Preferred examples include N,N-dimethylaniline, N,N-dimethylaminomethylphenol, and N,N-dimethyl-p-toluidine, wherein N,N-dimethyl-p-toluidine is a preferred initiator.

[0027] Partial B component

[0028] Part B contains at least one epoxy resin. Suitable epoxy resins include diglycidyl ethers of polyphenolic compounds (such as resorcinol, catechol, hydroquinone, bisphenol, bisphenol A, bisphenol AP (1,1-bis(4-hydroxyphenyl)-1-phenylethane), bisphenol F, bisphenol K, bisphenol M, tetramethylbiphenol), aliphatic glycols, and diglycidyl ethers of polyether glycols (such as C...). 2-24 Diglycidyl ethers of alkylene glycols and poly(ethylene oxide) glycols or poly(propylene oxide) glycols; phenol-formaldehyde phenolic varnish resins, alkyl-substituted phenol-formaldehyde resins (epoxy phenolic varnish resins), phenol-hydroxybenzaldehyde resins, cresol-hydroxybenzaldehyde resins, dicyclopentadiene-phenol resins and dicyclopentadiene-substituted phenol resins, and any combination thereof. Suitable diglycidyl ethers include diglycidyl ethers of bisphenol A resins, such as those marketed by Olin Corporation under the name DER. ® 330, DER® 331, DER ® 332, DER ® 383, DER ® 661 and DER ® 662 resin is for sale.

[0029] In a preferred embodiment, the at least one epoxy resin comprises the reaction product of epichlorohydrin and bisphenol A. In another preferred embodiment, the at least one epoxy resin comprises the liquid reaction product of epichlorohydrin and bisphenol A.

[0030] In a preferred embodiment, at least one epoxy resin comprises an epoxy resin as a liquid reaction product of epichlorohydrin and bisphenol A, the liquid reaction product having an epoxy equivalent weight of 182-192 g / equivalent (as measured according to ASTM D-1652), an epoxy percentage of 22.4%-23.6% (as measured according to ASTM D-1652), an epoxy group content of 5,200-5,500 mmol / kg (as measured according to ASTM D-1652), and a viscosity of 11,000-14,000 mPas at 25°C (as measured according to ASTM D-445).

[0031] In another preferred embodiment, the at least one epoxy resin comprises a bisphenol A-based epoxy resin with an epoxy equivalent weight of approximately 352.5 g / equivalent.

[0032] Part B comprises at least one epoxy resin at a weight of 20 to 80 wt.%, preferably 20 to 60 wt.%, and more particularly preferably 25 to 40 wt.%, based on the total weight of Part B.

[0033] Part B may also contain oxidants as disclosed in PCT / US23 / 024257. Examples of such oxidants include organic peroxides such as benzoyl peroxide and other diacyl peroxides, hydroperoxides such as cumene hydroperoxide, peresters such as β-butyl peroxybenzoate; hydroperoxide ketones such as methyl ethyl ketone hydroperoxide, organic salts of transition metals such as cobalt naphthenate, and compounds containing unstable chlorine such as sulfonyl chlorides. The most preferred oxidant is benzoyl peroxide.

[0034] The oxidizing agent, preferably an organic peroxide (such as benzoyl peroxide), is preferably present in part B at 3-10 wt.% based on the total weight of part B, more preferably 5-9 wt.%.

[0035] Optional ingredients

[0036] The adhesive composition of the present invention may contain additional optional ingredients, such as stabilizers / free radical scavengers added to both portion A and portion B, to extend the shelf life of the unmixed portion. Examples of stabilizers / free radical scavengers include 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, diethylhydroxylamine (DEHA), butylated hydroxytoluene (BHT), hydroquinone methyl ether, hydroquinone, benzoquinone, naphthoquinone, hydroxylamine, and nitrile oxides. Optional ingredients may also include fillers such as wollastonite, talc, fumed silica, calcium carbonate, and glass.

[0037] Part A may optionally contain a crosslinking agent, such as a divalent metal salt of methacrylate, such as zinc dimethacrylate, calcium dimethacrylate, magnesium dimethacrylate, or mixtures thereof. Part A may also optionally contain additional toughening agents. Suitable additional toughening agents are rubber-based, such as acrylate-based toughening agents, butadiene-based toughening agents, acrylonitrile-butadiene-based toughening agents, chlorinated or chlorosulfonated polyethylene, block copolymers of styrene and conjugated dienes (SBS, SIS), ethylene-acrylate elastomers, and core-shell graft copolymers. Specific examples may be copolymers of methyl 2-methyl-2-acrylate and 1,3-butadiene.

[0038] If used, the additional rubber-based toughening agent is preferably used in part A at 2-24 wt.%, more preferably 7.5-18.5 wt.%, and even more particularly preferably 10-15.75 wt.%, based on the total weight of part A.

[0039] Additional optional ingredients may include, for example, adhesion promoters, pigments, thixotropic agents, wetting agents, reactive diluents, antioxidants, inhibitors, and stabilizers. These ingredients may be used in amounts generally known to those skilled in the art to achieve their intended purpose.

[0040] Manufacturing method

[0041] At least one toughening agent is manufactured by the method disclosed in PCT / US23 / 024257, which includes the steps of: (1) mixing a polyether polyol and a polyisocyanate; (2) adding a catalyst capable of catalyzing the reaction of hydroxyl groups with isocyanate groups to form an isocyanate-terminated prepolymer; and (3) then reacting the isocyanate prepolymer with a hydroxyalkyl methacrylate such that the isocyanate groups are terminated with the hydroxyalkyl methacrylate. The reactions in steps (2) and (3) are typically carried out under vacuum or in a neutral atmosphere such as nitrogen or argon.

[0042] The catalyst is preferably selected from Lewis bases and Lewis acids. Suitable catalysts include tertiary amines, including diazabicyclo[2.2.2]octane, 2,4,6-tris((dimethylamino)methyl)phenol, DMDEE (2,2'-dimorpholinodiethyl ether), imidazoles such as 4-methylimidazole, triethanolamine, and organometallic catalysts, especially organotin compounds such as dibutyltin dilaurate and dioctyltin dineodecanate, and other metal catalysts such as tetrabutyl titanate, zirconium acetylacetonate, and bismuth neodecanoate.

[0043] How to use

[0044] In use, adhesive component A and component B are mixed until homogeneous and applied immediately. The mixing ratio of component A to component B is preferably from 2:1 to 10:1, with 4:1 being particularly preferred.

[0045] Suitable substrates include, for example, electro-galvanized steel, hot-dip galvanized steel, cold-rolled steel, and aluminum. Example

[0046] The following non-limiting examples are provided to further describe the invention. The components are listed in Table 1 below:

[0047] Table I. Components of the Comparative Examples and Examples of the Invention

[0048]

[0049] The following provides details about these ingredients and their sources:

[0050]

[0051] Table 2 lists the vapor pressures of the various methacrylates used in the examples:

[0052] Table 2. Vapor pressures of the methacrylates used in the examples.

[0053]

[0054] Examples of the preparation of the compositions and all details of their testing are disclosed in PCT / US23 / 024257, which is again incorporated herein by reference in its entirety. All physical characteristics (such as impact peel, lap shear, and T-peel tests) show comparable results between the comparative examples and the examples of the invention.

[0055] In addition, odor rating tests were performed on all instances using ASTM D4339, with the control instance serving as a reference sample. In this test, a panel of three people rated the odor of each instance compared to the reference. Each instance was characterized by each panel member as having an odor intensity less than, equal to, or greater than the reference instance.

[0056] The results of the odor rating test are summarized in Table 3.

[0057] Table 3. Odor rating test results of ASTM D4339 compared with comparative examples

[0058]

[0059] As shown in Table 3, when using low vapor pressure methacrylates, Examples 1 and 2 of the present invention exhibit less odor than the comparative examples, which used relatively high vapor pressure methacrylates. It should be noted that Example 3 of the present invention has substantially the same odor level as the comparative examples. This is due to the odor present in the toughening agent itself used in Part A. This toughening agent carries an odor that is identifiable in the presence of low-odor monomers. The urethane toughening agents used in Examples 1-2 of the present invention do not carry this odor.

Claims

1. A two-part epoxy-acrylic hybrid adhesive composition comprising a Part A component and a Part B component, wherein, The Part A component comprises a) at least one methacrylate monomer, wherein the vapor pressure of the methacrylate monomer is less than 10 Pa at 20 °C; and b) at least one methacrylate-terminated flexibilizer having a T g of 0 °C or less; and b) at least one methacrylate-terminated flexibilizer having a T g of 0 °C or less; and the Part B component comprises at least one epoxy resin; and an oxidizing agent.

2. The adhesive composition of claim 1, wherein, the Part A component further comprises a phosphorus-containing compound selected from the group consisting of monoesters of phosphonic acids, monoesters and diesters of phosphonic acids, and phosphoric acids.

3. The adhesive composition of claim 2, wherein, the Part A component further comprises a tertiary amine radical initiator.

4. The adhesive composition of any one of the preceding claims, wherein, the methyl methacrylate monomer has a vapor pressure of less than 6 Pa at 20 °C.

5. The adhesive composition of any one of the preceding claims, wherein, the Part A component comprises 28-45 wt.% of the methyl methacrylate monomer based on the total weight of the Part A component.

6. The adhesive composition of any one of the preceding claims, wherein, the methyl methacrylate monomer has a chemical structure of one of Formula I or II 。 7. The adhesive composition of any one of the preceding claims, wherein, the methyl methacrylate monomer is isopropylidene glyceryl methacrylate, glyceryl formal methacrylate, or a mixture thereof.

8. The adhesive composition of any one of the preceding claims, wherein, the toughener comprises at least one polyether as part of its backbone.

9. The adhesive composition of any one of the preceding claims, wherein, the at least one epoxy resin comprises a reaction product of epichlorohydrin and bisphenol A.

10. The adhesive composition of any one of the preceding claims, wherein, the Part B component comprises 20 to 80 wt.% of the at least one epoxy resin based on the total weight of the Part B component.

11. The adhesive composition of any one of the preceding claims, wherein, the oxidizing agent is benzoyl peroxide.

12. The adhesive composition of any one of the preceding claims, wherein, the Part B component comprises 3-10 wt.% of the oxidizing agent based on the total weight of the Part B component.

13. The adhesive composition of any one of the preceding claims, wherein, the one methacrylate-terminated toughener is an elastomeric urethane toughener terminated with a hydroxyl-functional methacrylate.

14. The adhesive composition of any one of claims 1 to 12, wherein, the one methacrylate-terminated toughener is a butadiene-acrylonitrile liquid rubber-based toughener.

15. A two-part epoxy-acrylic hybrid adhesive composition comprising a Part A component and a Part B component, wherein, The Part A component comprises a) 33 wt.% to 35 wt.% of glycerol formal methacrylate based on the total weight of the Part A component; and b) about 23 wt.% of an elastomeric urethane flexibilizer terminated with a hydroxyl functional methacrylate based on the total weight of the Part A component, having a Tg of 0°C or less g ; and the Part B component comprises at least one epoxy resin; and an oxidizing agent.

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