JP2006257228A - Adhesive composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adhesive composition having good adhesiveness and capable of attaining highly balanced high modulus, high heat resistance and low shrinkage when used as a structural adhesive, etc., in automobile assembly line, particularly for automobile steel plates. <P>SOLUTION: The present invention relates to the adhesive composition containing 3-10 wt% monofunctional epoxy resin, 40-60 wt% bi- or higher functional epoxy resin, 2-5 wt% latent curing agent and 10-30 wt% inorganic filler having ≥5 aspect ratio (L/D) and having ≥2,500 MPa tensile modulus at 20°C after curing and ≤5.0×10<SP>-5</SP>(1/°C) coefficient of linear expansion at 20°C. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is an adhesive composition, more specifically, a one-component thermosetting epoxy resin-based adhesive composition, particularly when used as an adhesive for automobile steel plates, and having excellent elastic modulus and heat resistance. The present invention relates to an adhesive composition having low shrinkage.

  Conventionally, as a structural adhesive in an automobile assembly line, a one-component heat-curable epoxy resin adhesive in which a latent curing agent is blended with an epoxy resin has been used. However, when such an adhesive is used as a structural adhesive in an automobile assembly line, there is a problem in that an outer plate is distorted on a joint surface after the adhesive is hardened due to the protrusion of the adhesive at a corresponding portion. . Such a problem is conspicuous in joining at a thin outer plate surface or a part where application management is difficult, for example, at a rear wheel arch portion of an automobile, and improvement thereof has been demanded.

  In order to deal with the above problems, it is important to suppress the curing / cooling shrinkage of the adhesive, but in the prior art, it is attempted to suppress the outer plate distortion by reducing the elastic modulus of the adhesive. (See Patent Document 1). However, this method has a problem that the glass transition point of the adhesive also decreases as the elastic modulus decreases, and as a result, the heat resistance and durability of the adhesive decrease.

Moreover, the adhesive composition to which calcium metasilicate was added using the polyfunctional epoxy resin is also known (refer patent document 2, 3). However, according to the techniques disclosed in these publications, only the polyfunctional epoxy resin is used, and calcium metasilicate is added for the purpose of imparting rust prevention or durability. For example, the linear expansion of the adhesive composition Since the coefficient is high, the performance is not sufficient when high balance between high elastic modulus, high heat resistance and low shrinkage is required.
Furthermore, a sheet metal containing a liquid epoxy resin, a latent curing agent, and an inorganic filler having an aspect ratio (L / D) of 5 or more for the purpose of improving the bending strength and rigidity of the sheet metal and preventing the sheet metal from being distorted. A reinforcing agent composition is known (see Patent Document 4).

JP-A-63-202680 JP-A-2-135273 JP-A-6-306345 JP 2002-22695 A

  The present invention has been obtained without the results of intensive studies in view of the above, such as for structural use in automobile assembly lines, especially when used as an adhesive for automobile steel sheets, good adhesion, It is an object of the present invention to provide an adhesive composition that can achieve highly balanced high elastic modulus, high heat resistance, and low shrinkage.

That is, the present invention is an inorganic material having a monofunctional epoxy resin of 3 to 10% by weight, a bifunctional or higher epoxy resin of 40 to 60% by weight, a latent curing agent of 2 to 5% by weight, and an aspect ratio (L / D) of 5 or more. Adhesive containing 10 to 30% by weight of filler, having a tensile elastic modulus at 20 ° C. after curing of 2500 MPa or more and a linear expansion coefficient at 20 ° C. of 5.0 × 10 ⁻⁵ (1 / ° C.) or less. Relates to the composition.

  In the present invention, a monofunctional epoxy resin and a bifunctional or higher functional epoxy resin are used in combination as the epoxy resin, and the adhesive composition of the present invention is based on the total weight of the composition, and the monofunctional epoxy resin is 3 to 10 weights. % And bifunctional or higher functional epoxy resin 40 to 60% by weight. In the present invention, by using a monofunctional epoxy resin and a bi- or higher functional epoxy resin in this way, a highly balanced high elastic modulus, high heat resistance and low shrinkage can be obtained, and handling of the adhesive composition Property is improved. The preferable content of the monofunctional epoxy resin is 4 to 8% by weight based on the total weight of the composition, and the preferable content of the bifunctional or higher functional epoxy resin is 45 to 55% by weight based on the total weight of the composition. .

  As the monofunctional epoxy resin in the present invention, those known in the art can be used. For example, poly (1-5) oxyalkylene (carbon number 2-4) phenyl or methylphenyl ether glycidyl ether, alkyl (C8-C18) Glycidyl ether, butylphenyl glycidyl ether, and tolyl glycidyl ether are mentioned. Among these, the use of alkyl (C12-14) glycidyl ether is preferable in order to achieve both adhesiveness, elastic modulus, heat resistance and low shrinkage. Such a monofunctional epoxy resin has a viscosity of 2 to 40 mPa · s (25 ° C.), which is preferable from the viewpoint of improving dischargeability, and a more preferable viscosity is 5 to 20 mPa · s (25 ° C.).

  As the bifunctional or higher functional epoxy resin in the present invention, those known in the art can be used, for example, glycidyl ether type, glycidyl ester type, glycidyl amine type, linear aliphatic epoxide type, alicyclic epoxide type. In addition, these modified products such as rubber-modified epoxy resins (bisphenol type epoxy resins (bisglycine A, bisphenol F, diglycidyl ether of bisphenol AD, diglycidyl ether of bisphenol A alkylene oxide adduct, etc.) and butadiene) -Reaction product with acrylonitrile- (meth) acrylic acid copolymer], urethane-modified epoxy resin [polytetramethylene ether glycol (weight average molecular weight: 500 to 5000), an excessive amount of diisocyanate (tolylene diene) A reaction product of a terminal NCO-containing urethane prepolymer obtained by reacting cyanate, diphenylmethane diisocyanate, etc.) and an OH-containing epoxy resin (such as diglycidyl ether of bisphenol A, diglycidyl ether of aliphatic polyhydric alcohol)], Examples thereof include thiocol-modified epoxy resins, and one or a mixture of two or more of these is used.

  As the resin component in the present invention, other thermoplastic resins known in the art may be used in addition to the above epoxy resin.

As the latent curing agent in the present invention, a normal curing agent that exhibits a curing action by heating and generally activated in a temperature range of 80 to 250 ° C. may be used. Specific examples of such a curing agent include dicyandiamide, 4,4′-diaminodiphenylsulfone, imidazole derivatives (such as 2-n-heptadecylimidazole), isophthalic acid dihydrazide, N, N-dialkylurea derivatives, N, N -A dialkylthiourea derivative, a melamine derivative, etc. are mentioned, Depending on hardening conditions and physical properties, these 1 type, or 2 or more types of mixtures are used for use. The content of the latent curing agent in the adhesive composition of the present invention is 2 to 5% by weight based on the total weight of the composition, preferably 3 to 5% by weight based on the total weight of the composition.
Moreover, the adhesive composition of the present invention may contain an appropriate amount of a curing aid known in the art in addition to the above-described latent curing agent, if necessary.

Examples of the inorganic filler that can be used in the present invention include calcium carbonate, barium sulfate, magnesium hydroxide, mica, talc, clay, silicic acid or various silicates, carbon black, and various metal powders. Among these, by using an aspect ratio (L / D) of 5 or more, preferably 10 to 35, more preferably 10 to 20, highly balanced high elastic modulus, high heat resistance and low shrinkage can be obtained. can get. In particular, calcium metasilicate having an aspect ratio of 10 to 20 is preferable. When the aspect ratio of the inorganic filler is not within the above range, a good balance of elastic modulus, heat resistance and shrinkage cannot be obtained, and outer plate distortion is likely to occur.
The content of the inorganic filler having an aspect ratio (L / D) of 5 or more in the adhesive composition of the present invention is 10 to 30% by weight based on the total weight of the composition, preferably 15 to 15 based on the total weight of the composition. 30% by weight.

If necessary, the adhesive composition of the present invention may further contain other inorganic fillers or organic fillers having an aspect ratio of less than 5 or rubber components (acrylonitrile-isoprene copolymer rubber, acrylonitrile-butadiene copolymer rubber, styrene- Butadiene copolymer rubber, butadiene rubber, isoprene rubber, etc.), conductive material [general formula: MeO · Fe ₂ O ₃ (Me is a divalent metal such as Mn, Ba, Co, Sr, Pb, Zn, Mg, Cd) ) Metal oxide-iron oxide sintered complex ferrite or α-Fe ₂ O ₃ particle powder, silver, copper, palladium, aluminum, nickel, zinc and other metal powders, ruthenium oxide, bismuth oxide, iridium oxide, etc. Metal oxide powder, carbon black powder, graphite powder, silver-coated glass powder, etc.] may be added in appropriate amounts.
The adhesive composition of the present invention may contain an appropriate amount of a plasticizer, a thixotropic agent, a hygroscopic agent, and the like as necessary in addition to the above-described components.

  The adhesive composition of the present invention is obtained by sequentially adding a predetermined epoxy resin, a latent curing agent, an inorganic filler having an aspect ratio (L / D) of 5 or more, and other additives according to a conventional method and mixing them. Can be manufactured.

  The adhesive composition of the present invention is usually applied to a predetermined location on a target structure according to a conventional method, and is heated and cured under baking conditions in an electrodeposition furnace in an electrodeposition coating process. Applicable structures include SPC steel sheet, electrogalvanized steel sheet, hot dip galvanized steel sheet, organic surface-treated steel sheet, alloyed galvanized steel sheet, zinc-nickel alloy plated steel sheet, tin-lead plated steel sheet, cationic electrodeposition A coated steel plate, an aluminum plate, a magnesium plate, etc. are included, and there is no restriction on the type.

The adhesive composition of the present invention has a tensile elastic modulus at 20 ° C. after curing of 2500 MPa or more, preferably 4000 to 6000 MPa. The adhesive composition of the present invention has a linear expansion coefficient at 20 ° C. after curing of 5.0 × 10 ⁻⁵ (1 / ° C.) or less, preferably 3.0 × 10 ^{−5 to} 5.0 × 10. ^-5 (1 / ° C).
The adhesive composition of the present invention is particularly useful as an automotive steel sheet adhesive, particularly an automotive rear foil arch adhesive, and can exhibit a highly balanced high modulus, high heat resistance and low shrinkage, It has the effect that outer plate distortion is less likely to occur.

  Hereinafter, the effectiveness of the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited thereto. In addition, the evaluation method of the physical property and performance in the following Example and a comparative example is as follows. Each component was blended based on parts by weight.

i) Viscosity and Viscosity Stability After the temperature of the test material was adjusted to 20 ° C., the viscosity (Pa · s) was measured with a Brookfield rotational viscometer (rotor No. 7, 10 rpm).
The test material was allowed to stand for 7 days in a 40 ° C. thermostatic chamber, then the temperature was adjusted to 20 ° C., and the viscosity (Pa · s) was measured with a Brookfield rotational viscometer (rotor No. 7, 10 rpm). Viscosity stability was calculated.
Viscosity stability (%) = {(viscosity after standing at 40 ° C. for 7 days−initial viscosity) / initial viscosity} × 100
ii) Linear expansion coefficient The test material was cured in a forced circulation oven under conditions of 180 ° C x 20 minutes, and then a sample with a predetermined size (cylinder with a diameter of 5 mm x height of 30 mm) was used. The coefficient (1 / ° C.) was measured.
iii) Elastic modulus The test material was cured in a forced circulation oven under the conditions of 180 ° C. × 20 minutes, and then measured with a dynamic viscoelastic device to obtain a tensile elastic modulus (MPa) at 20 ° C.
iv) Shear strength The test material was applied to an SPCC steel plate (25 × 100 × 1.6 mm) with a wrap length of 10 mm and cured in a forced circulation oven under the conditions of 180 ° C. × 20 minutes to obtain a test specimen. The shear bond strength (MPa) of this test specimen at 20 ° C. and 80 ° C. was measured with an autograph.
In addition, the determination criteria are as follows.
20 ° C. shear bond strength ○: 20 MPa or more, ×: less than 20 MPa
80 ° C shear adhesive strength ○: 12MPa or more, ×: less than 12Mpa v) Warpage amount The test material was applied to an aluminum plate (25 × 200 × 0.5mm) with a thickness of 1.5mm, and 180 ° C in a forced circulation oven. The specimen was cured by curing for 20 minutes. After cooling this test body to room temperature, as shown in FIG. 1, one side in the longitudinal direction was pressed and the warp height (mm) of the opposite side was determined.
In addition, the determination criteria are as follows.
○: 20 mm or less, ×: over 20 mm

[Example 1]
(A) Preparation of adhesive composition Each component was used in the ratio (% by weight) shown in Table 1 below and prepared according to the following procedure. First, the epoxy resin component was uniformly mixed and stirred with a planetary stirring mixer, and then a thermoplastic resin, a latent curing agent and a filler were blended and vacuum defoaming was performed.
(B) Evaluation Physical properties and performance were evaluated by the methods described above. The results are shown in Table 2.

[Comparative Examples 1-3]
An adhesive composition was prepared in the same manner as in Example 1 except that the composition of the adhesive composition was changed to the composition shown in Table 1, and physical properties and performance were evaluated. The results are shown in Table 2.

Note 1) Epicoat 828, manufactured by JER Corporation
Note 2) EPU-73, manufactured by Asahi Denka Co., Ltd.
Note 3) EPR1415-1 manufactured by Asahi Denka Co., Ltd.
Note 4) Epicoat 871, manufactured by JER Corporation
Note 5) ED-503, manufactured by Asahi Denka Co., Ltd.
Note 6) ED-502, manufactured by Asahi Denka Co., Ltd.
Note 7) F-351, manufactured by Nippon Zeon Co., Ltd.

As is clear from the above results, the adhesive composition of the present invention can achieve good adhesion, highly balanced high modulus, high heat resistance and low shrinkage. As shown in FIG. 2, the adhesive composition of the present invention is small in the temperature range where the linear expansion coefficient is wide, and does not generate strain on the outer plate. On the other hand, the thermosetting composition not according to the present invention has an insufficient balance of adhesiveness, high elastic modulus, high heat resistance and low shrinkage.
In Comparative Examples 1 and 2, instead of calcium metasilicate having L / D of 13 in Example 1, heavy calcium carbonate having L / D of 1 and calcium metasilicate having L / D of 3 were used. As the linear expansion coefficient increased, the result of the amount of aluminum warpage became insufficient.
In Comparative Example 3, an attempt was made to achieve low shrinkage by changing the type of the epoxy resin in Example 1, but the linear expansion coefficient increased and the shear strength became insufficient.
In Comparative Example 4, a bifunctional epoxy resin was used in place of the monofunctional epoxy resin in Example 1, but the viscosity stability deteriorated and the handleability of the adhesive composition became poor.

It is a figure which shows the measuring method of the curvature amount of the test material of an Example and a comparative example. It is a graph which shows the measurement result of the linear expansion coefficient of the test material in each Example and a comparative example.

Explanation of symbols

1: Aluminum plate 2: Adhesive

Claims (5)

Monofunctional epoxy resin 3 to 10 wt%, bifunctional or higher epoxy resin 40 to 60 wt%, latent curing agent 2 to 5 wt%, and aspect ratio (L / D) 5 or more inorganic filler 10 to 30 An adhesive composition containing a wt%, having a tensile modulus at 20 ° C. after curing of 2500 MPa or more and a linear expansion coefficient at 20 ° C. of 5.0 × 10 ⁻⁵ (1 / ° C.) or less.   The adhesive composition according to claim 1, wherein the inorganic filler has an aspect ratio of 10 to 20.   The adhesive composition according to claim 1 or 2, wherein the inorganic filler is calcium metasilicate.   The adhesive composition according to any one of claims 1 to 3, wherein the adhesive composition is for automobile steel sheets.   The adhesive composition according to claim 4, which is used for a rear wheel arch portion of an automobile.

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