JPH04226579A - Adhesive for low-temperature use - Google Patents

Abstract

PURPOSE: To provide an adhesive for structure having a combination of high adhesive bond impact strength and high bulk tensile elongation even at a low temp. of about -23°C (-10° F) or lower and having reversibility even at a low temp.

CONSTITUTION: The adhesive compsn. is constituted of a methacrylic ester monomer, an elastomer monomer soluble in a monomer having Tg of -25°C or lower and a free radical forming catalyst. The constitutional components of this adhesive can develop high adhesive bond impact strength and high bulk tensile elongation when they are used in the adhesion of an assembly.

COPYRIGHT: (C)1992,JPO

Description

[Detailed description of the invention]

0001

TECHNICAL FIELD This application is a continuation-in-part of US patent application Ser. No. 07/238,302, filed August 29, 1988.

This application relates to structural acrylic adhesives.

BACKGROUND OF THE INVENTION Structural acrylic adhesives are rubber toughened adhesive systems that cure rapidly at room temperature and provide excellent adhesive properties. Such adhesives are characterized by high peel strength, shear strength, and chemical resistance. They are also resistant to various substrate surface contaminants such as oil.

[0003] A fast-curing adhesive is disclosed in US Pat. No. 3,832,274.
It is stated in the issue. This adhesive is approximately -9.4°C (15°C)
Made from an elastomer, an acrylic monomer, and a redox catalyst with a Tg of less than or equal to

Structural adhesives containing chlorosulfonated polyethylene or sulfonyl chloride and chlorinated polymers have been described in US Pat.
No. 72 and No. 4,287,106.

[0005] US Pat. No. 4,126,504, US Pat. No. 434
No. 8,503 and No. 4,451,615 disclose various combinations of elastomers, acrylic monomers, catalysts and other additives.

Adhesives based on diene polymers such as polybutadiene, polyisoprene, butadiene-styrene copolymers and ABS grafted polymers with the addition of vinyl monomers, adhesion promoters and the like are described in US Pat. No. 4,287,106. ing.

A methacrylic acid-based adhesive comprising chlorinated or chlorosulfonated polyethylene and a core-shell type graft copolymer is disclosed in US Pat. No. 4,536,548.
It is disclosed in No. 6.

[0008]

The use of plastics in structures, such as automobiles, is increasing, and plastics, like metals, can be used to form bonds that can last under a wide variety of conditions. The demand for adhesives continues and increases.

[0009] A particular requirement for structural adhesives is not only to have high adhesive bond impact strength when measured at low temperatures, but also to have high bulk tensile elongation.

The present invention is directed to structural adhesives. In one aspect, the present invention relates to structural adhesives having high adhesive bond impact strength. In another aspect, the present invention relates to structural adhesives having high bulk tensile elongation at low temperatures of about -23°C (-10°F) or lower. In yet another aspect, the present invention relates to structural adhesives having bulk tensile elongation that is largely reversible even at low temperatures.

[0011]

[Means for Solving the Problems] The adhesive composition of the present invention comprises: A) a methacrylic acid ester monomer;
C) a core-shell graft copolymer that swells in, but does not dissolve in, the monomer; and D) a free radical generating catalyst.

0012

Advantageous Effects The adhesive compositions of the present invention, when used in bond assembly, exhibit high adhesive bond impact strength (at least about 0.32kg-m/cm2 (15ft-lb
/sq. in. )) and high bulk tensile elongation (10%
(above) will produce a combined effect.

[0013]

EXAMPLES Monomers useful in this invention are methacrylic acid ester monomers in which the alcohol portion of the ester group contains from 1 to 8 carbon atoms. Examples of such ester monomers include methyl acrylate, 2-ethylhexyl methacrylate (2-ethyhexy
methacrylate), cyclohexyl methacrylate and mixtures thereof. A preferred ester monomer is methyl methacrylate.

Other monomers that can be used in combination with methacrylic acid monomers are acrylic esters, where the alcohol portion of the ester contains from 1 to 8 carbon atoms, examples being methyl acrylate, ethyl acrylate, Butyl acrylate and 2-ethylhexyl acrylate
ate). Other useful monomers are acrylonitrile, methacrylonitrile, styrene, vinyltoluene, and the like.

Useful monomer compositions include at least about 50
methacrylic acid monomer and preferably at least about 50 weight percent methyl methacrylate monomer.

Another monomer used in combination with the methacrylate monomer is free radical polymerizable ethylenic unsaturation.
erizable ethylenically un
saturated) mono- or polycarboxylic acids. Acrylic acid, methacrylic acid, crotonic acid, maleic acid and fumaric acid are examples of such acids. A preferred acid is methacrylic acid.

Elastomers useful in the present invention have secondary glass transition temperatures (Tg) of about -25°C or less and are soluble in the monomers described above. Useful elastomers are synthetic high polymers that exhibit plastic flow. Suitable elastomers are those commercially available for use in adhesives or pressure-sensitive adhesives.

A class of elastomers suitable for use in the present invention are polychloroprene and copolymers of butadiene or isoprene with styrene, acrylonitrile, acrylic esters, methacrylic esters and the like. Other useful elastomers are copolymers of ethylene and acrylic esters, monopolymers of epichlorohydrin, and copolymers of epichlorohydrin and ethylene oxide.

Examples of useful polymers as directed by ASTM D1418 include their commercial or common names and chemical descriptions. CR-neoprene-polychloroprene; NBR-nitrile rubber-approximately 2
Butadiene-acrylonitrile copolymer containing from 5 to about 45 weight percent acrylonitrile; COX
- Hycar 1072 - butadiene-acrylonitrile copolymer modified with carboxylic acid groups; SGR-GR-S - styrene-butadiene copolymer containing from about 10 to about 30 acceptance percent styrene; ABR - acrylic rubber-acrylic acid butadiene copolymer; and CO,ECO-hydrin (Hydri
n) 100 and 200-homopolymers or copolymers of epichlorohydrin and ethylene oxide. Another useful elastomer is a copolymer of ethylene and an acrylic ester, such as methyl acrylate and ethyl acrylate, where the copolymer contains at least 30 weight percent of the acrylic ester and such The elastomer is sold by DuPont under the Vamac trademark.

Elastomers useful in the present invention are described in the "Handbook of Plastics and Elastomers" published by McGraw-Hill.
(1975 edition)
, pages 1-106-119, which are herein incorporated by reference.

Particularly useful elastomers are polychloroprene and block copolymers of styrene and butadiene or isoprene; such block copolymers are available from Shell Oil Company under the trademark Krato.
n). Copolymers of styrene and diene monomers are described in detail in US Pat. No. 4,041,103 and US Pat. No. 4,242,470, which are incorporated herein by reference.

[0022] Apart from the low Tg and solubility properties, the unique requirements of a particular adhesive are adjusted to match the suitable molecular weight, viscosity properties and other constituents of the adhesive. Since there are no other limitations on the identity of the elastomer, other elastomeric polymers having a Tg of -25°C or less and soluble in the methyl methacrylate monomer may also be employed.

Useful elastomers are those that are soluble in the monomers used in the adhesives of this invention. These elastomers have a molecular weight of about 10 to about 35 methyl methacrylate.
A solution of weight percent elastomer can be formed. As used herein, the term "solution" refers not only to true solutions, but also includes colloidal systems exhibiting normal or substantially Newtonian rheological properties.

The core-shell graft copolymers useful in this invention have a "resilient" core, a "hard" shell, and swell in the monomer composition but do not dissolve therein. The "core" or spine polymer of the graft copolymer has a glass transition temperature substantially below ambient temperature. The "shell" polymer grafted onto the spinal column polymer has a glass transition temperature substantially above ambient temperature. Ambient temperature is defined as the temperature range in which the adhesive is used.

Examples of useful core-shell graft copolymers include polymers of "hard" monomers such as styrene, acrylonitrile or methyl methacrylate from "soft" or "elastomeric" monomers such as butadiene or ethyl acrylate. It is grafted to the prepared elastic core.

US Pat. No. 3,985,703, incorporated herein by reference, describes useful core-shell polymers in which the core is suitably made from butyl acrylate, but also from ethyl, isobutyl, 2-ethylhexyl , or other alkyl acrylates or mixtures thereof. The core polymer can optionally contain up to 20 percent copolymerizable monomers such as styrene, vinyl acetate, methyl methacrylate, butadiene, isoprene, and the like. The core polymer can optionally contain up to 5 percent crosslinking monomers having two or more nonconjugated double bonds of approximately equal reactivity, such as ethylene glycol diacrylate, butylene glycol dimethacrylate, or the like. Alternatively, two unequal reactivities, such as diallyl maleate and allyl methacrylate, can be used.
It can contain up to 5 percent grafted monomers having one or more nonconjugated double bonds.

The shell stage is suitably polymerized from methyl methacrylate and optionally other lower alkyl methacrylates such as ethyl, butyl, or mixtures thereof. Up to about 40 weight percent of the shell monomer can be styrene, vinyl acetate, vinyl chloride, and the like.

Other useful core-shell graft copolymers are U.S. Pat. No. 3,984,497;
and No. 4,034,013, which are incorporated by reference in this description.

Yet another useful core-shell polymer is the "MBS" polymer, as described in US Pat. No. 4,304,709, which is incorporated by reference. M
BS polymers are made by polymerizing methyl methacrylate in the presence of polybutadiene or polybutadiene copolymer rubber.

Other patents describing various useful core-shell graft copolymers include US Pat. No. 3,944,631;
No. 4,306,040 and No. 4,495,324, each of which is incorporated by reference.

The core-shell graft copolymers used in the present invention swell dimensionally during bond formation but do not dissolve. Adhesives so formed exhibit improved spreading and flow properties, which are highly desirable in many uses of adhesives. For example, when adhesives are applied to articles by syringe application, many adhesives string between the location where the applicator is used and the next location of the applicator. The present invention allows small drops of adhesive to be applied to the articles to be bonded without stringing the adhesive.

Another component of the compositions of this invention is a polymerization catalyst with or without other components that enhance the reaction of the catalyst. Catalysts are free radical generators that cause the polymerization of acrylate and methacrylate compounds. Such catalysts include peroxides, hydroperoxides,
Peresters, peracids, radiant energy such as ultraviolet light, and heat. Examples of this catalyst are benzoyl peroxide,
Cumene hydroperoxide, t-butyl peroxide,
dicumyl peroxide
de), t-butyl peroxide acetate, t-butyl perbenzoate, di-t-butyl azodiisobutyronitrile and the like. These free radical generating catalysts are present in an amount of from about 0.01 to about 1 based on the weight of the adhesive composition.
Used in an amount of 0 weight percent. Preferably, the catalyst is used in an amount of about 0.05 to about 3 weight percent.

Other components that enhance the reaction of the catalyst are initiators or activators and promoters. Initiators and activators, which are used interchangeably, include t-amines and aldehyde-amine reaction products. Useful t-amines include N,N-dimethylaniline, N,N-dimethyltoluidine, N,N-diethylaniline, N,N-
Contains diethyltoluidine and its analogs. Aldehyde-amine reaction products include butyraldehyde-aniline and butyraldehyde-butylamine compositions.

[0034] The accelerator is cobalt naphthenate, nickel,
Organic salts of transition metals such as manganese or iron, copper octoate, copper acetylacetonate, iron hexoate, or iron propionate.

Initiators or activators, if used, are added in amounts up to about 15 weight percent based on the weight of the adhesive. A preferred amount is 0.01 to about 5 percent. Accelerators are used in amounts up to about 0.5 weight percent, preferably from about 1 ppm to about 0.5 weight percent.

The compositions of the invention are usually prepared in two parts, one containing the free radical catalyst and the other containing the initiator or activator and promoter, if used. include. Immediately before use, both are mixed with each other and the mixture is applied to at least one of the surfaces to be bonded. As an interchangeable example, the one containing the catalyst can be applied to one side and the one containing the activator can be applied to the other side. When pressed together, they intermix and polymerize, resulting in an adhesive bond.

[0037] The adhesive composition of the present invention has an adhesive composition of about 55 to about 75
0 to about 15 weight percent methacrylic acid ester monomer, about 5 to about 20 weight percent acid monomer.
weight percent elastomer and from about 10 to about 30
weight percent core-shell graft copolymer. This weight percentage is based on the total weight of the components. Preferably, the composition comprises about 60 to about 70 weight percent methacrylate monomer, about 2 to about 10 weight percent acid monomer, about 8 to about 15 weight percent elastomer, and about 15 to about 20 weight percent core. Contains shell graft copolymer.

[0038] The adhesive composition of the present invention has a temperature of -23°C (-10°C).
High adhesive bond impact strength (approximately 0.32 kg-m/cm2 (15 ft.
-lb/sq. in. ) or higher) and high bulk tensile elongation (10% or higher). The bulk tensile elongation of this composition is large and reversible even in low temperature tests. This highly reversible elongation rate contributes to the adhesive's excellent performance in impact-resistant constructions at low temperatures.

The composition of the present invention can be heated from -23°C to -29°C (
It is particularly useful for bonding thermoplastic automotive bumpers that must pass simulated crash impact tests at temperatures between -10°F and -20°F. In this test, which measures energy management ability, the bumper is mounted horizontally and moved in various positions and positions using a pendulum or hydraulic ram at a rate corresponding to a crash of about 4 km/h or about 8 km/h (2.5 or 5 mph). The impact is received at an angle. In this test, the bumper and adhesive bond lines experience high impact forces and deflections as much as 3 or 4 inches on center. After the test, the bumper returns to its original shape. The high impact strength and high elongation, especially reversible elongation, of the compositions of the invention at low temperatures are clearly advantageous for this bumper application.

High temperature coefficient up to 82°C (180°F) and high impact strength and elongation at -23°C (-10°F) or below make bumpers and bumpers resistant to impact and other high stresses and highly robust. It is very useful for structural integrity and other structural applications where structural integrity is required.

In the experimental examples described below, the elastomer was dissolved in the monomer by mixing until a single solution was obtained and no visible rubber particles were visible. Other components, such as core-shell polymers, were then added to the elastomer solution and stirred until a coarse paste was formed. Mixing with a high shear disperser was continued until a smooth paste was obtained.

Adhesive strength tests are performed by mixing formulations using peroxide catalyst pastes or by combining two adhesive polymer-in-monomer solutions, one containing peroxide and the other containing catalyst activator. I was disappointed.

The adhesive was tested as follows.

Lap shear strength (
ASTM D-1002)

The adhesive shear strength of a bond formed between a substrate, such as a polycarbonate/polyester thermoplastic (Xenoy, obtained from General Electric Co.), is 25 mm x 76 m of the substrate.
Measurements were made by applying enough adhesive to one end of a 25 mm x 12.5 mm x 0.25 mm adhesive gap to one end of a 25 mm x 12.5 mm x 0.25 mm sample. A 0.25 mm wire shim or washer was used to adjust the bond thickness. A second sample was placed over the adhesive coated sample to provide the appropriate lap shear profile in a mold designed to properly match the specimen.

After a curing time of 24 to 28 hours at room temperature, the adhesion was tested at a separation rate of 1.27 mm/min.

IMPACT STRENGTH (ASTM D-950) The impact strength of the adhesive was measured on a 12.7 mm diameter and 76 mm length instead of a test specimen having the dimensions specified in the ASTM test method.
Tested according to ASTM D-950 procedures, except using steel bars or rods with 2 mm and 9.5 mm, respectively. The surfaces to be glued together were first cleaned with a solvent and then roughened with fine sand. After bonding, the specimens were conditioned at room temperature for 2 days before testing.

Bulk Adhesive Stress-Strain (ASTM B-6
38) Sufficient adhesive composition is mixed to form a cured adhesive approximately 2.5 mm thick and the tensile test "dumbbell" is removed from the metal die as specified in ASTM test methods. It was cut using Although specified, rather stress-strain tests were performed at the indicated temperatures using a separation rate of 5 mm/min.

Cold Shock Test for Plastic Substrates This test was designed to simulate the impact and deflection forces that a bonded structural assembly, such as a bumper, would experience under test conditions. This test is useful for evaluating the effect of "squeezing" at the bonded edges during impact operations on the entire bonded assembly. If the cured adhesive is not sufficiently elastic to cushion under impact and stretch conditions, the adhesive bead will begin to crack and spread throughout the bonded assembly, resulting in a defective product.

[0050] When conducting the test, a length of 15.2 cm was used.
, 15.2cm bead of 5g mixed adhesive
x 2.5 cm was applied to the entire centerline length of the plastic sample. A 2.5 cm long, 1.3 mm diameter stainless steel wire was placed approximately 6 mm from each end parallel to the plastic and perpendicular to the bead of adhesive. 15.2cm x 1.
A 3 cm plastic strip was pressed onto the adhesive until it made contact with the wire. The bonded assembly was allowed to cure at room temperature for at least 24 hours.

Before testing, the assembly was heated to -23°C (-1
0°F) for at least 15 minutes. The cooled specimen was placed in a modified National Forge fitted with a 6.7 m/kg (10 ft/lb) hammer.
Tested by placing in a Model TM 52004 Izod-Charby impact tester. A fixture was used to hold the specimen with a 2.5 cm plastic strip at each end opposite the impact hammer and allow the hammer to strike the plastic. The surface of the hammer in contact with the plastic is approximately 1 cm2. At the lowest point of the pendulum motion striking the assembly, the hammer will be approximately 3.
It moves at 4 m/s (11 ft/s). After the hammer strikes the cooled plastic, if the hammer rebounds and leaves the test specimen intact, the result is recorded as passing. If the plastic breaks at the point of impact, the result is recorded as a failure. Often, the hammer hits the plastic and it bounces off, causing the edges of the plastic to crack the fixture. This is recorded as an "end crack". It is considered a pass because the action of the attachment assembly on the plastic places excessive stress on the bonded assembly at these fulcrums.

The components used in the experimental examples are as follows. MMA - Methyl methacrylate monomer with 22-28 ppm hydroquinone inhibitor MAA - BMA methacrylate with 250 ppm hydroquinone inhibitor - Butyl methacrylate 2
- EHMA - 2-ethylhexyl methacrylate neoprene - approximately 20 as measured on a model LVT visometer with UL adapter
Polychloroprene homopolymer nitrile rubber with a Brookfield solution viscosity of 35 mPa from - specific gravity of 0.98 and from 30 to
Mooney viscosity of 45 ML-4, 100°C (212°F)
medium acrylonitrile content (medium ac
Carboxy modified butadiene-acrylonitrile elastomer Hypalon with rylonitrile content) Chlorosulfonated polyethylene with 30-43 percent chlorine and 1.1 percent sulfur - DuPont Polaroid KM 753 - Methacrylate with high butadiene content - Butadiene-styrene core-shell polymer - Rohm & Haas Polaroid KM 330 - All acrylic core-shell polymer - Rohm & Haas Gelloy 1020 - Acrylic rubber core and styrene-acrylonitrile shell Core-shell polymer hydrin 10×1
- Brookfeed viscosity of 2.5 x 105 cps (
27 °C), liquid epichlorohydrin homopolymer with Tg of -25 °C and number average molecular weight of 4000 DMT - N,N-dimethyl-p-tolidine ZMTI - 2-mercaptotoluimidazole zinc bamac - ethylene-methyl acrylate copolymer Gum - Kraton D 1320x from DuPont - Styrene-isoprene branched copolymer - Tylin from Shell Oil - Chloropolyethylene containing 42% chlorine - DPESC from Dow Chemical - Diphenyl ether
Disulfonyl chloride BHT-2,6-di-t-
Butyl p-cresol CHP - 80 weight percent cumene hydroperoxide BPO paste in cumene - 55 percent benzoyl peroxide paste in benzyl butyl phthalate plasticizer Vanax 808 - Butyraldehyde-aniline condensation product - Earl Vanderbilt Company Made

[0053] The peroxide paste used in the experimental examples was prepared as follows. Hydrin 10 x 1, 2
5 parts by weight and trioctyl trimellitate plasticizer, 25
parts by weight in a plastic container and heated to 43°C (10°C).
0°F). 10 parts of KM753 were added gradually as the mixture was sheared using a Hockmeyer Institute high shear mixer. Shearing was continued for 5 minutes after all KM753 was added. The mixture was then heated to 43°C (
Placed in oven at 100° F. for 1 hour and sheared again until a smooth paste was obtained. After cooling, BPO
40 parts of paste were added and the mixture was sheared again until a homogeneous and smooth paste was obtained.

The following table lists the components used to form the adhesive composition and shows the test results of the cured adhesive. Neoprene, nitrile rubber and Hypalon elastomer were dissolved in MMA to create 20, 25 and 40 weight percent solutions, respectively. All other components were combined by direct addition and mixed as described above.

The experimental examples having columns A and B are two-part adhesives that are combined in a 1:1 weight ratio immediately before use. In other experimental examples (one-component adhesive),
Peroxide paste was added at a 1:10 paste to adhesive mix ratio before use.

Table 1 shows Experimental Example 3, which is an experimental example of the prior art.
Figure 1 shows a greatly improved cold elongation of the inventive compositions of Experimental Examples 1 and 2 as compared to Example 1 and Example 2.

[0057]

[Table 1]

Table 2 shows the impact resistance at low temperatures of the plastic assemblies bonded using the components of the present invention in Examples 4 and 5 compared to Example 6 using prior art components. Showing improvement. Steel impact test results show that Examples 4, 5 and 6 have comparable impact strength when measured by conventional methods.

[0059]

[Table 2]

Table 3 presents another example of an adhesive composition that provides high elongation and resists low temperature impact deficiencies when used to bond plastics. Examples 7 and 8 were conducted using an elastomer with a Tg of -25°C or less, and Example 9 used an elastomer with a Tg of -25°C or higher.

[0061]

[Table 3]

The experimental examples listed in Table 4 show other adhesives tested at low temperatures. The adhesive of Example 10 contains a core-shell polymer but is not a low Tg elastomer. In Experimental Example 11, a core-shell polymer and a Tg of -25°C or higher
and an elastomer having. In Experimental Example 12, low T
g elastomer but no core-shell polymer. Example 13 contains a low Tg elastomer and a non-core-shell polymer. In Experimental Example 14, low T
g Contains both an elastomer and a core-shell polymer.

[0063]

[Table 4]

The experimental examples listed in Table 5 demonstrate the reduction of adhesive to Xenoy plastic by increasing the level of nitrile rubber. Maximum amount of nitrile rubber and non-core
Example 15, which contains a shell polymer, has the lowest lap shear strength on the xenoid plastic. Examples 16 and 17 containing elastomers within the scope of the present invention and core-shell polymers have good tensile strength and elongation upon separation and adhesion to xenoid plastics. Experimental Example 18, which contained less elastomer than the claimed range of the present invention, had good tensile strength and adhesion, but the elongation upon separation was insufficient.

[0065]

[Table 5]

The basic principles, preferred embodiments and operating means of the invention have been described. However, the invention to be protected herein is not to be limited to the particular embodiments disclosed, as these should be considered as illustrative rather than limiting. Variations and changes may occur to those skilled in the art without departing from the spirit of the invention.

Claims (7)

[Claims] Claims: a) methacrylic acid ester monomers and b) nitrile rubber, polychloroprene, copolymers of butadiene or isoprene with styrene, copolymers of butadiene or styrene with acrylic esters, with butadiene or styrene methacrylic esters. copolymers selected from the group consisting of copolymers of ethylene and acrylic acid ethers, homopolymers of epichlorohydrin, and copolymers of epichlorohydrin and ethylene oxide, and which are soluble in the ester monomer and have a Tg of about -25°C or less. c) a core-shell graft copolymer that swells in, but does not dissolve in, said monomer; and d) a free radical generating catalyst. 2. The adhesive composition according to claim 1, wherein the copolymer of butadiene or isoprene and styrene is a block copolymer. 3. Adhesive composition according to claim 1, characterized in that it contains an ethylenically unsaturated mono- or polycarboxylic acid capable of free radical polymerization. 4. The adhesive composition according to claim 3, wherein the acid is methacrylic acid. 5. The adhesive composition of claim 1, wherein the methacrylate monomer is at least 50 weight percent methyl methacrylate. 6. The adhesive composition of claim 1, wherein the elastomeric polymer is soluble in the monomer in an amount of about 10 to about 35 weight percent based on the weight of the solution. [Claim 7] T of the core-shell graft copolymer
Claim 1 characterized in that g is substantially below ambient temperature and the Tg of the shell is substantially above ambient temperature.
Adhesive composition as described.