JP5086774B2 - Structural adhesive - Google Patents

Description

  The present invention relates to a structural adhesive for joining automobile structural panels, and more specifically, for example, a one-pack epoxy resin structure for use in joining automobile structural panels by a weld bond method in an automobile body assembly line. Relates to adhesives.

  In automobile assembly lines, structural panels are joined by a weld bond method that uses both adhesive bonding and spot welding to ensure vehicle body rigidity and strength. Adhesives are employed (Patent Documents 1 to 4).

On the other hand, steel plates are conventionally used as structural members of automobiles, but aluminum plates are being applied in accordance with needs for weight reduction. Considering the optimization of high strength and light weight, the combined use of steel plate and aluminum plate can be considered, and some cars manufactured by joining these are also on the market. However, a mechanical stopper is mainly used for the joining, and with the structural adhesive as described above, the application site is limited or a problem occurs in the durability and reliability. This is because conventional structural adhesives have poor extensibility after curing, and when used to join dissimilar materials with different linear expansion coefficients, the durability deteriorates due to the stress due to the difference in linear expansion coefficient. This is because there is a problem of peeling of the surface.
JP-A-4-145185 JP-A-5-148337 JP-A-5-156227 Japanese Patent Laid-Open No. 7-145225

  An object of the present invention is to provide a structural adhesive that can satisfactorily bond an automotive structural panel, particularly an automotive structural panel composed of different materials having different linear expansion coefficients.

The present inventors comprise (A) an epoxy resin and (B) a latent curing agent, have an elongation percentage of 15% or more after being cured at 170 ° C. for 20 minutes, a shear strength of 20 MPa or more, Further, the structural adhesive having an impact strength of 25 N / mm or more has been found to solve the above problems, and the present invention has been completed.
That is, the present invention includes the following.
[1] comprising (A) an epoxy resin and (B) a latent curing agent,
The elongation after curing at 170 ° C. for 20 minutes is 15% or more, the shear strength is 20 MPa or more, and the impact strength is 25 N / mm or more.
Structural adhesive for joining automotive structural panels.
[2] The structural adhesive according to [1], wherein the viscosity (measured at 40 ° C. under a shear rate of 20 sec ⁻¹ ) is 50 to 200 Pa · s.
[3] The structural adhesive according to the above [1] or [2], for joining automobile structural panels each made of different materials having different linear expansion coefficients.
[4] The structural adhesive according to [3], wherein one of the different materials is a steel plate and the other is an aluminum plate.

  The structural adhesive of the present invention has good workability and is excellent in adhesiveness after curing, extensibility, impact properties and durability, so that it is an automotive structural panel, particularly a dissimilar material having a different linear expansion coefficient (for example, , Steel plates and aluminum plates) can be suitably used for joining automobile structural panels.

  The structural adhesive of the present invention is an automotive structural panel, particularly an automotive structural panel composed of different materials having different linear expansion coefficients, for example, an automotive structural panel composed of a steel plate and an automotive structure composed of an aluminum plate. Used for joining panels.

  Examples of the automobile structural panel in the present invention include an outer panel and an inner panel that constitute a structural member having a closed cross-sectional structure such as an automobile pillar, a roof rail, and a sill.

Examples of the material constituting the automobile structural panel in the present invention include a steel plate, a plated steel plate (for example, a galvanized steel plate, a zinc-nickel steel plate), an aluminum plate, an aluminum alloy plate (for example, an aluminum-manganese alloy plate, aluminum-magnesium). Alloy plate), fiber reinforced plastic plate and the like. Among these materials, examples of the combination of materials having different linear expansion coefficients include a combination in which one is a steel plate (including a plated steel plate) and the other is an aluminum plate (including an aluminum alloy plate). .
The “linear expansion coefficient” here is a value determined by measurement with a TMA analyzer. In the present invention, “different linear expansion coefficients” means that the difference in linear expansion coefficients determined above is 2 × 10 ⁻⁶ cm / cm / ° C. or more, preferably 5 × 10 ⁻⁶ cm / cm / It means that it is over ℃.

  Examples of the epoxy resin of the component (A) in the structural adhesive of the present invention include a bisphenol type epoxy resin, a urethane-modified epoxy resin, a rubber-modified epoxy resin, a monofunctional aliphatic epoxy resin, a polypropylene glycol (PPG) -containing epoxy resin, and the like. Is mentioned.

Examples of the bisphenol type epoxy resin include bisphenol A, bisphenol F, brominated bisphenol A, diglycidyl ether of bisphenol AD, diglycidyl ether of an alkylene oxide adduct of bisphenol A, and the like.
Specific examples of the bisphenol-type epoxy resin include, for example, JERO Co., Ltd. Epicoat 828.

  As the urethane-modified epoxy resin, for example, an excess amount of a polyisocyanate compound is reacted with a polyether polyol to obtain a urethane prepolymer containing a free isocyanate group at the terminal (hereinafter referred to as a terminal NCO prepolymer). Examples thereof include those produced by reacting an epoxy resin having at least one hydroxyl group in one molecule (hereinafter referred to as OH epoxy resin).

  The polyether polyol (that is, polyoxyalkylene ether polyol) is a low molecular weight active hydrogen compound having two or more active hydrogens (for example, ethylene glycol, glycerin, trimethylolpropane, 1,2,6-hexanetriol, sucrose) Polyoxyethylene-propylene polyol of random or block copolymer obtained by ring-opening polymerization of propylene oxide and ethylene oxide in the presence of one or more of polyols such as pentaerythritol).

  Examples of the polyisocyanate compound include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, dodecamethylene diisocyanate, 1,3. -Cyclopentane diisocyanate, 1,6-hexane diisocyanate (HDI), 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 4,4'-methylenebis (cyclohexyl isocyanate), methyl 2,4-cyclohexane diisocyanate, methyl 2 , 6-cyclohexane diisocyanate, 1,4-bis (isocyanatomethyl) cyclohexane, 1,3-bis (isocyanate) Methyl) cyclohexane, m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4′-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 4,4′-diphenylmethane diisocyanate (MDI), 2,4- or 2,6-tri Diisocyanate (TDI), 4,4′-toluidine diisocyanate, dianidine diisocyanate, 4,4′-diphenyl ether diisocyanate, 1,3- or 1,4-xylylene diisocyanate, ω, ω′-diisocyanate-1,4- Examples include diethylbenzene.

  Examples of the OH epoxy resin include diglycidyl ether of 2,2-bis (4-hydroxyphenyl) propane [bisphenol A], diglycidyl ether of aliphatic polyhydric alcohol, and the like.

  In the reaction between the polyether polyol and the polyisocyanate compound, the ratio of the two is usually set so that the latter isocyanate group is 1.2 to 3 equivalents relative to the former hydroxyl group, and the temperature is 60 to 120 ° C. under a nitrogen atmosphere. The reaction may be carried out under a condition of ˜6 hours. In the reaction between the terminal NCO prepolymer and the OH epoxy resin, the ratio of the two is usually set so that the latter hydroxyl group is equivalent to or more (preferably 2 to 5 equivalents) of the former isocyanate group, and the temperature is 80 to The reaction is continued at 110 ° C. until the reaction between the isocyanate group and the hydroxyl group is completed.

Specific examples of the urethane-modified epoxy resin include, for example, a bisphenol A type epoxy resin modified with a urethane prepolymer having a terminal TDI trifunctional / number average molecular weight of 3000 PPG skeleton.
As used herein, “number average molecular weight” refers to that determined by GPC measurement.

  As the rubber-modified epoxy resin, for example, carboxyl-terminated acrylonitrile-butadiene rubber and bisphenol-type epoxy resin are blended at a weight ratio of 1: 5 to 4: 1, preferably 1: 3 to 3: 2, and 80 to What is manufactured by making it react at the temperature of 180 degreeC is mentioned. Examples of the acrylonitrile-butadiene rubber include, for example, CTBN (carboxyl-terminated butadiene-acrylonitrile rubber), and specifically, Hycar (registered trademark) CTBN1300 × 13 manufactured by Noveon.

  Examples of the monofunctional aliphatic epoxy resin include an aliphatic epoxy resin having a monofunctional / number average molecular weight of 250.

  Examples of the PPG-containing epoxy resin include an epoxy resin in which propylene glycol is added to the side chain of the bisphenol A skeleton having a number average molecular weight of 920 / viscosity of 800 mPa · s and the terminal is epoxidized.

  As the epoxy resin component (A) in the structural adhesive of the present invention, a mixture of two or more of the above-mentioned various epoxy resins is preferable. In particular, based on the entire epoxy resin component (A), a bisphenol type epoxy resin is used. 0 to 25% by weight, urethane-modified epoxy resin 40 to 60% by weight, rubber-modified epoxy resin 10 to 25% by weight, monofunctional aliphatic epoxy resin 1 to 7% by weight, and PPG-containing epoxy resin 5 to 5% A mixture containing 20% by weight is preferred.

  Examples of the latent curing agent of the component (B) in the structural adhesive of the present invention include those activated in a temperature range of 100 to 200 ° C., such as dicyandiamide, 4,4′-diaminodiphenylsulfone, and imidazole. Alternatively, derivatives thereof (such as 2-n-heptanedecylimidazole), isophthalic acid dihydrazide, N, N′-dialkylurea derivatives, N, N-dialkylthiourea derivatives, melamine derivatives and the like can be mentioned. These can be used alone or in a mixture of two or more. What is necessary is just to select the compounding quantity of the said latent hardener normally in the range of 5-20 parts with respect to 100 parts of said epoxy resin component (A) (a weight part, the following similarly), Preferably it is 5-15 parts. If it is less than 5 parts, curing is insufficient, and if it exceeds 20 parts, the cured product tends to be brittle and the adhesive strength tends to decrease.

In addition to the epoxy resin component (A) and the latent curing agent component (B), the structural adhesive of the present invention can be prepared by adding usual additives such as fillers (calcium carbonate, clay, silica, talc, as necessary). Etc.), rust preventives (aluminum trihydrogen phosphate dibasic tetrahydrate, zinc phosphate, etc.), conductive materials [general formula: MeO. Metal oxide-iron oxide sintered composite ferrite or α-Fe ₂ O ₃ particles represented by Fe ₂ O ₃ (Me is a divalent metal such as Mn, Ba, Co, Sr, Pb, Zn, Mg, Cd) Powder, metal powder such as silver, copper, palladium, aluminum, nickel, metal oxide powder such as ruthenium oxide, bismuth oxide, iridium oxide, carbon black, graphite powder, silver-coated glass powder], plasticizer, solvent, etc. Can be blended.

The structural adhesive of the present invention preferably has a viscosity (measured at 40 ° C. under a shear rate of 20 sec ⁻¹ ) of 50 to 200 Pa · s, preferably 100 to 150 Pa · s. When the viscosity exceeds 200 Pa · s, there is a possibility that the discharge property is deteriorated. On the other hand, in the case of less than 50 Pa · s, there is a possibility that the shape retainability (hanging property) is deteriorated.

The structural adhesive of the present invention has an elongation of 15% or more, preferably 18 to 25% after being cured at 170 ° C. for 20 minutes. When the elongation is less than 15%, there is a risk of peeling and rusting due to stress concentration in a durable cooling and cycling test at the time of dissimilar joining.
The “elongation rate” here is a value determined by a dumbbell test, as described in detail in Examples below.

The structural adhesive of the present invention has a shear strength of 20 MPa or more, preferably 23 MPa or more after being cured at 170 ° C. for 20 minutes. When the shear strength is less than 20 MPa, the vehicle is destroyed at the time of impact, and the collision safety performance of the automobile is lost.
The “shear strength” here is a value determined according to the JASO M353 shear strength test method, as will be described in detail in Examples below.

The structural adhesive of the present invention has an impact strength of 25 N / mm or more, preferably 30 N / mm or more after being cured at 170 ° C. for 20 minutes. When the impact strength is less than 25 N / mm, the collision safety performance of the automobile is lost.
The “impact strength” here is a value determined according to the wedge impact method of JIS K6865, as will be described in detail in Examples below.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.
[Examples 1 to 5 and Comparative Examples 1 and 2]
The components (parts by weight) shown in Table 1 below were kneaded with a kneader, then passed twice through three rolls, and again defoamed with a kneader to prepare an adhesive. The following tests were performed on each obtained adhesive. The results are shown in Table 1.

〔Test method〕
(1) Viscosity After the temperature of the material is adjusted to 40 ° C., the viscosity (Pa · s) under a shear rate of 20 sec ⁻¹ is measured using a pressure viscometer (JASO M323 viscosity test B method).
(2) Impact strength Using a steel sheet of JIS G3141, a test piece is prepared according to the wedge impact test of JIS K6865. Measurement is performed using a high-speed tensile testing machine. The average strength in the range of 25 to 90% of the total displacement during the test is divided by the test piece width to obtain the impact strength. The curing conditions are 170 ° C. and 20 minutes, and the test speed is 2 m / s.
(3) Shear strength The surface of a steel plate (1.6 × 25 × 100 mm) of JIS G3141 is degreased with toluene, an adhesive is applied to the surface, and then the same surface degreased steel plate is stacked and pressed, 170 A sample is cured by curing at 20 ° C. for 20 minutes. According to the shear strength test method of JASO M353, an autograph (Shimadzu Corporation, DSC-5000) is used and the tensile strength is measured at 50 mm / min.
(4) Peel strength (i) Bonding of similar materials The surface of a steel sheet (0.8 × 25 × 150 mm) of JIS G3141 is degreased with toluene, and an adhesive is applied to the surface. Press repeatedly, and cure under conditions of 170 ° C. for 20 minutes to obtain a sample. According to the JASO M353 peel strength test method, the 180 ° peel strength of the sample is measured at a tensile speed of 200 mm / min using an autograph (Shimadzu Corporation, DSC-5000).
(Ii) Bonding of different materials As materials having different linear expansion coefficients, steel plates (linear expansion coefficient: 11.7 × 10 ⁻⁶ cm / cm / ° C.) and aluminum alloy plates (linear expansion coefficient: 23.8 × 10 ⁻⁶ cm) / Cm / ° C.) and the peel strength is measured in the same manner as (i) above.
(5) Elongation rate After the material was cured at 170 ° C. for 20 minutes, it was molded into a JIS K6251 No. 6 dumbbell shape and pulled at 2 mm / min using an autograph (Shimadzu Corporation, DSC-5000). The length between the marked lines at the time of cutting is measured at a speed, and the elongation at cutting is calculated.
(6) Hat member crushing amount Adhesive is applied to the flange part (width 15 mm) of the hat member (cross-sectional shape 35 mm × 38 mm × length 200 mm, thickness 1.0 mmt), the flat plates are combined, and spot welding is performed at intervals of 50 mm. After performing, it bake-hardened to make a test piece. The amount of crushing when a 50 kg weight was dropped from a height of 2.8 m on the test piece was measured.
(7) Corrosion resistance Conforms to the method of JASO M353 corrosion environment test. After applying an adhesive to the surface of the steel sheet of JIS G3141, electrodeposition coating is performed, 40 ° C. 95% RH (relative humidity) × 2 hr (hours) → 35 ° C. 5% NaCl × 2 hr → 60 ° C. × 1 hr → 50 ° C. 95% RH × 6 hr → 60 ° C. × 2 hr → 50 ° C. 95% RH × 6 hr → 60 ° C. × 2 hr → −20 ° C. × 3 hr is taken as one cycle, and the state of the test piece at 80 cycles is observed. The case where the test piece was eroded by the rust at a depth of 0.1 mm or less was judged as ◯, and the case where it was 0.1 mm or more was judged as x.

1) Bisphenol A type epoxy resin: Epicoat 828 manufactured by JER Corporation
2) Urethane-modified epoxy resin: a bisphenol A type epoxy resin modified with a urethane prepolymer having a PPG skeleton having a trifunctional terminal TDI / average molecular weight of 3000.
3) CTBN-modified epoxy resin: obtained by mixing 1: 1 Epicoat 828 manufactured by JER Co., Ltd. and Hycar (registered trademark) CTBN 1300 × 13 manufactured by Noveon under a quaternary ammonium salt catalyst at 120 ° x 3 hr. Resin.
4) Monofunctional aliphatic epoxy resin: 1 functional / number average molecular weight 250 aliphatic epoxy resin, ie, EP-502 (Asahi Denka Co., Ltd.).
5) PPG-containing epoxy resin: Epoxy resin obtained by adding propylene glycol to the side chain of the bisphenol A skeleton having a number average molecular weight of 920 / viscosity of 800 mPa · s, that is, EP-4005 manufactured by Asahi Denka Co., Ltd.
6) Latent curing agent: Dicyandiamide

  As apparent from Table 1 above, the adhesives of Examples 1 to 5 exhibit predetermined values for elongation, shear strength, and impact strength, peel strength (same type and different types), impact characteristics (hat member crushing amount). And good durability. On the other hand, it is recognized that the adhesives of Comparative Examples 1 and 2 are inferior in terms of peel strength (different types), impact characteristics and durability.

Claims (4)

Comprising (A) an epoxy resin and (B) a latent curing agent,
170 ° C., elongation after curing for 20 minutes at conditions of 15% or more, the shear strength is more than 20 MPa, and impact strength Ri der least 25 N / mm,
The epoxy resin component (A) is 0 to 25% by weight of the bisphenol type epoxy resin, 40 to 60% by weight of the urethane-modified epoxy resin, and 10 to 25% of the rubber-modified epoxy resin based on the whole epoxy resin component (A). 1 to 7% by weight of monofunctional aliphatic epoxy resin and 5 to 20% by weight of PPG-containing epoxy resin,
The latent curing agent (B) comprises 5 to 20 parts with respect to 100 parts (parts by weight, the same applies hereinafter) of the epoxy resin component (A).
Structural adhesive for joining automotive structural panels. The structural adhesive according to claim 1, wherein the viscosity (measured at 40 ° C. under a shear rate of 20 sec ⁻¹ ) is 50 to 200 Pa · s.   The structural adhesive according to claim 1 or 2, for joining automobile structural panels each made of different materials having different linear expansion coefficients.   The structural adhesive according to claim 3, wherein one of the dissimilar materials is a steel plate and the other is an aluminum plate.