JPS6244030B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to structural adhesives, particularly electrocoat-fixing structural adhesives. Structural member joints, such as door hemmings in automobiles, are joined by spot welding or structural adhesives (hereinafter simply referred to as adhesives), but in the case of spot welding, the strength is concentrated only in the welded parts. Adhesives are commonly used. Such adhesives are required not only to have adhesive strength but also to have long-term rust prevention ability.Especially in production lines for automobiles, etc., electrocoating paints are used in the electrocoating process of structural members bonded with adhesives. Due to insufficient adhesion to adhesives, paint film peeling and pinholes occur over time, leading to rusting, which has become a problem. In order to solve these problems, conventional methods have been used to add conductive carbon black to adhesives, but this method has various drawbacks because it requires adding an extremely large volume of conductive carbon black. . For example, if a large amount of conductive carbon black is added to a relatively low-viscosity bisphenol-type epoxy resin adhesive, there will be no problem in terms of viscosity adjustment;
Sufficient peel strength could not be obtained (usually less than 3 kg/25 mm, which is 10 ml, which is required as an adhesive for automobile door hemming).
), and if a large volume of conductive carbon black is added to a relatively high-viscosity modified epoxy resin adhesive, the adhesive becomes extremely viscous, which only worsens the dispensing and coating properties. However, air bubbles are likely to be mixed in during the manufacturing or dispensing of the adhesive, resulting in pinholes. Furthermore, in the case of conventional epoxy resin adhesives containing conductive carbon black, the non-hydrophilic liquid epoxy resin that partially oozes out onto the applied adhesive surface is not compatible with the water-based electrodeposition paint. This causes areas around the adhesive where the electrodeposition paint does not adhere, causing rust. As a result of extensive studies in view of the current situation, the inventors of the present invention have found that by using a liquid polyhydroxy compound and conductive carbon black in combination, an electrically conductive adhesive can be developed without impairing the peel strength, which is important for adhesives. It was discovered that excellent fixing properties of the deposited film could be obtained, and the present invention was completed. That is, the present invention relates to an adhesive mainly composed of an epoxy resin and a latent curing agent, which is characterized by containing a liquid polyhydroxy compound compatible with the epoxy resin and conductive carbon black. The epoxy resin and latent curing agent which are the main components of the adhesive according to the present invention are not particularly limited, and those conventionally commonly used in adhesives may be used as appropriate. Epoxy resins include bisphenol type epoxy resin, urethane-modified epoxy resin, rubber (NBR etc.) improved matrix type epoxy resin,
Examples include polybutadiene type epoxy resins, but particularly preferred is a combination of bisphenol type epoxy resins and urethane-modified epoxy resins. Typically, such urethane-modified epoxy resins have an average molecular weight of about 450-650 and an epoxy equivalent of about 215-650.
250, with a viscosity (25℃) of about 25000~65000cps. In addition, examples of latent curing agents include dicyandiamide, BF ₃ -amine complexes, quaternary ammonium salts, metal salts of carboxylic acids, triethanolamine borate, triethanolamine titanate, and imidazole. A combination of these is preferred. The liquid polyhydroxy compound used in the present invention is compatible with the above-mentioned epoxy resin, and examples thereof include polyether polyols, polyester polyols, acrylic polyols, and hydrous acid group compounds such as castor oil derivatives and tall oil derivatives. Particularly preferred are polyether polyols. Typically, such polyhydroxy compounds have a hydroxyl value of about 20 to 500 mgKOH/g and a viscosity (at 25°C) of about
With 500-5000cps. The blending amount of the liquid polyhydroxy compound depends on the type of structural member and is not particularly limited, but for example, the optimum blending amount in adhesives for various structural members for automobiles is about 5 to 15% by weight of the epoxy resin. be. Generally, if the amount of the liquid polyhydroxy compound is too small, it is difficult to obtain the effects of the present invention, and conversely, if it is too large, part of the adhesive applied to the structural member will be dispersed during the degreasing, chemical conversion, and electrodeposition coating processes. There is a risk of detachment. Since the liquid polyhydroxy compound is hydrophilic, it has a good affinity with water-soluble electrocoating paints, and the primary fixation of the electrocoated film before curing to the adhesive is extremely good, allowing the electrocoating paint to adhere to the area around the adhesive. There will be no parts that are not done. In addition, the hydroxyl groups of the liquid polyhydroxy compound react with active groups such as isocyanato groups in the electrodeposited coating film during heat curing to form a tough film on the adhesive surface. The secondary fixability of the electrodeposited coating film is also extremely good. Furthermore, the hydroxyl group of the liquid polyhydroxy compound does not react with the epoxy resin in the adhesive at room temperature.
It reacts when heated and significantly improves the adhesive properties of the adhesive, especially its peel strength and adhesion to oil-covered iron panels. The viscosity of the liquid polyhydroxy compound can be selected relatively freely over a wide range, so even if a large amount of conductive carbon black is added, the viscosity of the adhesive can be adjusted without causing pinholes due to bubble inclusion. Can be done. The conductive carbon black used in the present invention is not particularly limited, and conventional ones may be appropriately blended, and examples thereof include acetylene black, ketchen black, and the like. The amount of conductive carbon black is usually about 4 to 6% by weight of the compound; if it is too small, it will be difficult to obtain a uniform electrodeposition coating, and if it is too large, the above-mentioned problems will likely occur. In addition to the above-mentioned components, the adhesive according to the present invention may appropriately contain conventional additives such as titanium oxide, iron oxide (red iron oxide), graphite, calcium carbonate, and talc. By using the adhesive according to the present invention, it is possible to impart excellent fixing properties to electrodeposited coatings without impairing the peel strength and shear strength, which are important for adhesives. Hereinafter, the present invention will be explained with reference to Examples. Examples 1 to 4 and Comparative Examples 1 to 3 Seven types of adhesive compositions were prepared according to the formulations shown in Table 1.

[Table] Each of the obtained adhesive compositions 1 to 4 and 1' to 3' was applied to an oil-surfaced steel plate (90% x 150 x 0.8 mm) in the shape of 10 mm (width) x 100 mm (length) x 0.5 mm (thickness) to prepare a test panel for electrodeposition. Remove the panel with degreasing solution (Ridrine SD)
-200℃, 60~65℃) for 3 minutes, rinsed with water for 30 seconds, and then soaked in the chemical conversion treatment solution (Granogin DP3000N-
1, 48-50℃) for 2 minutes, and after washing with water for 30 seconds,
After draining and drying at 120°C for 5 minutes, it was subjected to cationic electrodeposition using an amine-modified epoxy resin using a conventional method (applied voltage: 190V, application time: 3 minutes, electrodeposition bath temperature: 30°C). After washing the painted panels with water for 30 seconds, baking them at 180℃ for 30 minutes to create coated panels 1~
4 and 1' to 3' were prepared and the coating film properties etc. were measured. The results are shown in Table-2. The test panel for adhesion was 25 x 160 x for peeling.
0.5mm steel plate (JIS G3141 SPCC-SD), 25×100×1.6mm steel plate for shearing (JIS G3141 SPCC-SD)
, apply the above adhesive composition to an oil-surfaced steel plate that has been previously degreased with toluene and coated with the above anti-rust oil,
180 while crimped with clips (adhesion thickness approx. 0.1mm)
It was cured at ℃ x 30 minutes.

[Table] As is clear from Table 2, by using the adhesive composition of the present invention, not only extremely excellent electrodeposited film fixing properties and adhesive peel strength can be obtained, but also pinhole prevention. There were almost no occurrences.

Claims (1)

[Scope of Claims] 1. An adhesive mainly composed of an epoxy resin and a latent curing agent, characterized in that it contains a liquid polyhydroxy compound compatible with the epoxy resin and conductive carbon black. glue. 2. The adhesive according to item 1, wherein the conductive carbon black is acetylene black. 3. The adhesive according to item 1, wherein the liquid polyhydroxy compound is a polyether polyol.