JPH0240273B2 - KANETSUKOKASEIKOZOYOSETSUCHAKUZAI - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-curable structural adhesive, and more particularly to a structural adhesive that has a rust-preventing function and is good in electrocoatability. Recently, structural adhesives used in the assembly and bonding of automobile bodies have been given anti-corrosive properties in addition to improving the durability of the car body, and/or have been applied with electrodeposition coating after application of such adhesives. Improvements in the rust prevention properties of car body steel plates are being considered. Therefore, products containing anti-rust pigments made of heavy metals (lead, chromium, etc.), which have excellent anti-corrosion properties, have been adopted. There were problems such as insufficient rust prevention properties because the peripheral edge of the cured product could not be electrodeposited. On the other hand, a method has also been adopted in which carbon or metal powder is blended to impart some conductivity and electrodeposition coating is performed. This method does not cause rust if the paint film is not damaged, but the storage stability of the adhesive may be poor and pinholes may occur in the adhesive layer during electrodeposition coating. Alternatively, when a rust prevention test was carried out by cross-cutting the coating film, rust was found to develop from the cross-cut portions, and eventually the rust could even reach the adhesive interface, impeding the adhesive function, which was unsatisfactory. Therefore, the present inventors believe that if a structural adhesive consisting of an epoxy resin and a latent hardening agent is combined with a special rust preventive agent and ferrite that is harmless to humans and animals, it will have an active rust preventive function and will be able to be used for electrodeposition coating. The present inventors have discovered that this enables them to obtain a structural adhesive that can unexpectedly dramatically improve rust prevention properties, leading to the completion of the present invention. That is, the present invention uses ferrite represented by MO・F ₂ O ₃ (M is a divalent metal) and a water content of 0.5% in an adhesive consisting of an epoxy resin and a latent curing agent.
The present invention provides a heat-curable structural adhesive characterized in that it contains the following phosphate (% by weight, the same applies hereinafter). As the epoxy resin used in the present invention, ordinary ones known in the art may be used, such as glycidyl ether type, glycidyl ester type,
Examples include glycidylamine type, linear aliphatic epoxide type, alicyclic epoxide type, etc., and depending on coating workability and desired physical properties of the cured product,
The seeds or mixtures of two or more are provided for use. The latent curing agent used in the present invention is a normal curing agent that exhibits a curing effect when heated, and is generally
Those activated in the temperature range of 80 to 250°C may be used. Specific examples of such curing agents include dicyandiamide, 4,4'-diaminodiphenylsulfone, imidazole derivatives (2-n-heptadecyl imidazole, etc.), isophthalic acid dihydrazide, N,N-dialkyl urea derivatives, N,N- Examples include dialkylthiourea derivatives and melamine derivatives, and one or a mixture of two or more of these may be used. The amount used may be determined depending on the desired cured state, and is usually selected in the range of 1 to 30 parts per 100 parts (parts by weight, hereinafter the same) of the epoxy resin. The ferrite used in the present invention is MO・Fe ₂ O ₃ (M
is a sintered composite powder of metal oxide-iron oxide represented by divalent metal). As the above divalent metal,
Magnesium, manganese, barium, nickel,
Examples include strontium and zinc. Barium or zinc is particularly preferred. Such ferrites may typically be used in amounts ranging from 20 to 150 parts per 100 parts of epoxy resin. If the amount is less than 20 parts, the adhesion of the electrodeposited paint tends to deteriorate and the rust prevention effect tends to be poor, and if it exceeds 150 parts, the viscosity of the adhesive becomes high, resulting in insufficient fluidity and coating problems. This poses a problem in workability, and the physical properties of the cured product tend to be fragile, making it unsuitable for improving the peel strength required for structural adhesives. In addition, the content of ferrite in the adhesive is usually 10 to 70%, preferably 30 to 70%, depending on electrodeposition coating properties, adhesion properties, coating workability, etc.
It may be selected within the range of 50%. The phosphate used in the present invention is a white powder having crystal water that is harmless to humans and animals, such as aluminum dihydrogen tripolyphosphate (AlH ₂ P ₃ O ₁₀ ·nH ₂ O,
n=2 to 4) or zinc phosphate (Zn ₃ (PO ₄ ) ₂ ), and aluminum dihydrogen tripolyphosphate is particularly preferred from the viewpoint of rust prevention. When using such a phosphate, it is heated and dehydrated in advance (usually at a temperature of 100° C. or higher for 30 minutes or more) to set the moisture content to 0.5% or less. If the water content exceeds 0.5%, foaming occurs due to moisture volatilization during heating and curing of the adhesive, making it difficult to obtain the desired physical properties of the cured product, and furthermore, the rust prevention effect decreases. This phosphate is usually made of epoxy resin 100
may be used in a range of 15 to 60 parts. In addition, the content of phosphate in the adhesive is usually 5 to 5.
It may be selected in the range of 30%, preferably 10-20%. If it is less than 5%, the desired rust prevention effect cannot be obtained;
Moreover, if it exceeds 30%, the cured physical properties tend to become brittle. The thermosetting structural adhesive according to the present invention is composed of the above-mentioned epoxy resin, latent curing agent, ferrite, and phosphate in a predetermined ratio, and has excellent rust prevention properties and electrocoatability. However, in order to further increase peel strength and improve flexibility, polysulfide rubber, urethane rubber, nitrile-butadiene rubber, etc. are added or reacted, or flexible epoxy resin (Yuka Ciel Epoxy Co., Ltd.) (Epicoat 871, manufactured by Dow Chemical Company, DER732, etc.) and plasticizers (DOP, DBP, etc.) may be added, and fine particles of vulcanized rubber may be dispersed to absorb stress and create a sea-island structure. A so-called matrix structure can also be provided. In this way, flexibility agents and plasticizers can be added without impairing the excellent mechanical and electrical properties of epoxy resins, and if necessary, ordinary pigments, fillers (talc, carbonate, etc.) can be added to the epoxy resin. calcium, silicic acid, clay, etc.)
Appropriate amounts of the following can also be blended. The composition of the adhesive of the present invention may be adjusted according to a conventional method. For example, after uniformly kneading the entire amount of the above-mentioned essential components and optionally additional components in a vertical mixer, Z-type kneader, or disper, Pass it through a roll, and if necessary, return it to the mixer or kneader and subject it to defoaming treatment while stirring for 30 minutes or more under reduced pressure of 5 to 30 mmHg. If you defoam like this,
When the adhesive of the present invention is heated and cured at a temperature of 130 to 200°C, foaming can be completely prevented. According to the adhesive of the present invention having the above-mentioned structure, it is possible to suppress rusting on the iron plate base material, and also to apply ordinary electrodeposition coating to the surface of the adhesive layer. Anti-corrosion effect can be obtained. The adhesive of the present invention can be used, for example, in assembling and joining automobile bodies, such as side doors, bonnets,
It is used to form hemmings around the edges of inner panel steel plates and outer panel steel plates obtained by press forming trunks, roof panels, etc., and fixes the two steel plates by adhering them and creating a watertight/airtight seal. In this case, spot welding may or may not be used together. If electrodeposition coating is performed after such adhesive fixation,
The adhesive can be used under the baking curing conditions of the electrodeposition paint (e.g.
It cures in a non-foaming state simultaneously with the curing of the electrodeposition paint (heating at a temperature of 130 to 200°C for 20 to 60 minutes), thereby exhibiting adhesive and watertight performance. Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples. Examples 1 to 3 The components shown in Table 1 below are kneaded in a kneader, passed twice through three rolls, and then defoamed and stirred in the kneader again to prepare a thermosetting structural adhesive. Comparative Examples 1 to 3 Heat-curable structural adhesives are prepared in the same manner as Examples 1 to 3 using the components shown in Table 1 below. The adhesives of the above Examples and Comparative Examples were tested for electrocoating paint adhesion and rusting properties as described below, and the results are shown in Table 1. Adhesiveness of electrodeposition paint Dry steel plate after degreasing with toluene (70×100×0.8
After applying adhesive in a constant width of 30 mm and gradually thinning from 2 mm to a thickness of 2 mm, the adhesive was immersed in a cationic electrodeposition paint solution manufactured by Kansai Paint Co., Ltd., and applied at 200 volts and 0.5 ampere for 60 seconds. Electrodeposition coating is applied, followed by washing with running water and drying and curing at 180°C for 30 minutes. Thereafter, the state of application of the electrodeposition paint is visually observed. Rustability After evaluating the adhesion of the above electrodeposition paint, the test panel was left in a salt spray test device according to JIS K5400 for 1000 hours, and the presence or absence of rusting was evaluated visually. 【table】

Claims (1)

[Claims] 1. A ferrite represented by MO.Fe ₂ O ₃ (M is a divalent metal) and a phosphate with a water content of 0.5% by weight or less are blended into an adhesive consisting of an epoxy resin and a latent curing agent. A thermosetting structural adhesive characterized by: 2. The adhesive according to item 1 above, wherein M of the ferrite is barium or zinc. 3. The adhesive according to item 1 or 2 above, wherein the content of the ferrite is 10 to 70% by weight. 4. The adhesive according to item 1 above, wherein the phosphate is aluminum dihydrogen tripolyphosphate or zinc phosphate. 5. The adhesive according to any one of items 1 to 4 above, wherein the content of the phosphate is 5 to 30% by weight.