JPS636592B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a structural adhesive composition, more specifically a one-component heat-curable epoxy resin adhesive comprising an epoxy resin and a heat-activated curing agent.
This invention relates to a novel structural adhesive containing Fe ₂ O ₃ particle powder that can be electrocoated. Among adhesives, structural adhesives used in particular for metal-to-metal joints have adhesive strength that is equal to or greater than the material and can withstand specific external forces that are applied to the material, as if the joint site and structure It exhibits such strong adhesive properties that it becomes one with objects. These structural adhesives have recently been widely used in the aircraft industry, automobile industry, can manufacturing, and electrical and electronic engineering fields, instead of or in combination with traditional methods such as riveting, bolting, and welding. has been done. Among these, structural adhesives are widely used in the assembly and joining of automobile bodies, for example, when forming inner panel steel sheets and outer panel steel sheets obtained by press forming, such as side doors, bonnets, and trunks. There is. That is, when the outer edge of the outer panel is hemmed against the outer edge of the inner panel steel plate toward the inside of the vehicle body, and then bonded and sealed watertight, the structural adhesive is applied in a linear manner to the outer edge of the inner panel. An assembly method is used in which the inner panel and the outer panel are fixed by applying the adhesive and welding both outer edges by spot welding or the like. Traditionally, structural adhesives used for this type of purpose include:
A one-component heat-curing epoxy resin-based structural adhesive containing anti-rust pigments such as red lead and zinc chromate, and metal powders such as aluminum that provide a slight electrical conductivity for spot welding and electrodeposition coating. is proposed. However, in this case, in the post-electrodeposition coating process, the electrodeposition paint does not adhere well to the adhesive coated surface and the coating periphery, and hydrogen gas is generated due to the electrode reaction of metal powder such as aluminum, resulting in poor adhesion. Many holes occur in the agent. As a result, if a rusting test using a salt spray device is conducted, there are drawbacks such as rusting from the adhesive application peripheral interface within 24 hours. This has become an even more important issue, especially with the use of thinner steel sheets to reduce the weight of automobiles, and the development of improved structural adhesives that can be electroplated and have excellent rust prevention properties. Development has become an extremely important issue. From this point of view, much research has been carried out, including studies on imparting rust prevention properties to adhesives and studies on imparting electrical conductivity to enable electrodeposition coating, but a satisfactory adhesive for metal structures has yet to be put into practical use. do not have. Under these circumstances, the inventor of the present invention conducted extensive research in order to obtain a desired structural adhesive, and as a result, developed ferrite or α-Fe ₂ O ₃ particles, which are a sintered composite of a special metal oxide and iron oxide. By using the powder as a component of a one-component heat-curable epoxy resin adhesive composition, the electrodeposition described above can be applied to the adhesive-coated surface without adding electrically conductive metal powder as in conventional products. The present invention was completed by discovering that the process can be applied to the surface and peripheral areas, and surprisingly, there was no rusting after more than 1,000 hours in a salt spray test. That is, the present invention provides an epoxy resin, a heat-activated curing agent, and a general formula: MeO.Fe ₂ O ₃ (Me is Ba, Mg
The present invention provides a structural adhesive characterized in that it is made of a sintered composite ferrite of divalent metal oxide-iron oxide represented by Zn or Zn) or α-Fe ₂ O ₃ particle powder. Examples of the epoxy resin of the present invention include common epoxy resins selected from glycidyl ether type, glycidyl ester type, glycidyl amine type, linear aliphatic epoxide type, alicyclic epoxide type, etc. In particular, glycidyl ether type epoxy equivalent A range of 150 to 300 is preferred. These epoxy resins may be used singly or in combination of two or more depending on the desired physical properties. The heat-activated curing agent may be any ordinary curing agent that exhibits curing action when heated, generally at temperatures of 80 to 200°C.
It is sufficient if it is active in the temperature range of . Such curing agents include, for example, dicyandiamide,
4,4'-diaminodiphenylsulfone, 2-n-
Examples include imidazole derivatives such as heptadecyl imidazole, isophthalic acid dihydrazide, N·N-dialkyl urea derivatives, N·N-dialkylthiourea derivatives, and the like. These are appropriately blended into the composition depending on the desired cured state, but are usually preferably used in an amount of 1 to 15 parts per 100 parts (parts by weight, same hereinafter) of the epoxy resin. In the present invention, the sintered composite ferrite consisting of metal oxide and iron oxide represented by the formula: MeO・Fe ₂ O ₃ is usually produced by mixing powders of metal oxide and iron oxide and firing at 1000 to 1400°C. , which has been ground into powder particles of approximately 200 microns or less. Further, α-Fe ₂ O ₃ in the present invention is produced by heating iron hydroxide, iron nitrate, iron oxalate, etc., dehydrating them, firing and pulverizing them.
More specifically, the sintered composite ferrite is
Fe ₂ O ₃ and metal oxides or carbonates (BaCO ₃ ,
ZnO, MgO, etc.) at a molar ratio of 4.
Mix thoroughly in a ball mill or the like at a ratio of 6 to 6, calcinate at 1000 to 1400℃ using a conventional method, coarsely crush using a roll, crusher, etc., and then crush using an atomizer, pipe-lay thin mill, attritor, etc. The desired product can be obtained by pulverizing or finely pulverizing and then classifying. Note that it is preferable that the classified average particle size be 50 μm or less since this will not cause deterioration in the physical properties of the epoxy resin composition. The ferrite obtained in this way also has the effect of preventing sagging in pasty compositions, so there is no need to add asbestos powder, silicic acid, or silicate, which were conventionally used for this type of purpose. has. The composite sintered ferrite or α-Fe ₂ O ₃ ferrite or α-Fe ₂ O ₃ particle powder is made of epoxy resin.
It can be added in an amount of 20 to 150 parts per 100 parts.
If the amount is less than 20 parts, the electrocoating paint will have poor adhesion and will have a poor antirust effect. If the amount exceeds 150 parts, the fluidity of the composition will be insufficient, resulting in difficulties in workability, and it will also become physically fragile, which is undesirable from the standpoint of improving the peel strength required for structural adhesives. The amount of ferrite or α-Fe ₂ O ₃ added based on the total composition is in the range of 20 to 70% by weight, and the most desirable amount to be added is determined as appropriate based on electrodeposition coating properties, adhesive performance, workability, etc. . In addition, such ferrite or α-Fe ₂ O ₃ can be applied not only to one-component heat-curable epoxy resin compositions, but also to room-temperature-curable two-component compositions. It can also be used in adhesives such as resin and polyester, sealants, and paints. The composition of the present invention can be easily applied with electrodeposition paint and has excellent rust prevention properties and mechanical strength;
In order to further increase peel strength and flexibility, polysulfide rubber, urethane rubber, nitrile-butadiene rubber, etc. can be added as an internal plasticization method, or flexible epoxy resin [ Epicote 871 (Yuka Ciel Epoxy Co., Ltd.),
DER732 (Dow Chemical Co., Ltd.) and ordinary plasticizers (dioctyl phthalate, dibutyl phthalate, etc.) may be added as appropriate. Further, a method of forming a so-called matrix structure in which fine particles of vulcanized rubber are dispersed to form a sea-island structure for stress absorption may also be adopted. In this way, flexibilizing agents, plasticizers, solvents, fillers (talc, calcium carbonate, silicic acid, clay, carbon, etc.) can be used without impairing the excellent mechanical and electrical properties of epoxy resins. Furthermore, reaction catalysts, dyes and pigments, asbestos powder, etc. are added and blended as appropriate. As mentioned above, the composition of the present invention can be successfully applied with electrodeposition without the addition of a rust preventive agent, so there is almost no problem with rusting. Antirust pigments, such as red lead, zinc oxide, lead diamide, basic copper sulfate,
Basic pigments such as calcium leadate and zinc white, soluble pigments such as zinc chromate, strontium chromate, barium potassium chromate, and basic lead chromate, metal powder pigments such as zinc dust, etc. may be blended as appropriate. . Furthermore, electrodeposition coating becomes even more advantageous if appropriate amounts of carbon and metal powders such as silver powder, copper powder, or aluminum powder are used in combination to impart conductivity, but metal powders generate hydrogen gas due to electrode reactions during electrodeposition coating. However, since carbon powder has disadvantages such as impairing the storage stability of the composition, it should be avoided to add a large amount. The method for producing the structural adhesive composition of the present invention is to uniformly knead the entire amount of each of the above components in a vertical mixer, Z-type kneader or desper, pass through three rolls, return to the mixer or kneader again, ~
Defoaming is performed under reduced pressure of 10 mmHg with stirring for about 1 hour to obtain a one-component heat-curable epoxy resin composition. The structural adhesive of the present invention is particularly advantageously used when bonding combinations of metals to metals, metals to plastics, wood, or inorganic materials such as concrete. Adhesive, watertight and airtight sealing,
Can be used for anti-rust protection. In particular, the adhesive composition of the present invention is applied to an iron plate substrate, and after lamination and adhesion, it is electrodeposited as a base treatment for painting, and is cured under the baking curing conditions of the electrodeposition paint, for example, at a temperature of 130 to 200°C for 20 to 20 minutes. This is advantageous when curing can be performed simultaneously with curing of the electrodeposition paint within a range of 60 minutes. As described above, the structural adhesive of the present invention suppresses rust formation on the iron plate base material, and furthermore, since the composition can be electrodeposited on the surface, it has further excellent rust prevention properties. Hereinafter, the composition of the present invention will be explained in more detail with reference to Examples. Examples 1 to 3 The components shown in Table 1 were kneaded in the proportions shown in Table 1 using a kneader, passed through three rolls twice, and then defoamed and stirred using the kneader again to form an adhesive composition. Prepare. Comparative Examples 1-3 Adhesive compositions are prepared in the same manner as Examples 1-3 using the ingredients in Table 1. The compositions of Examples 1 to 3 and Comparative Examples 1 to 3 were tested for electrocoating paint adhesion and rusting properties as described below. Adhesiveness of electrodeposition paint: Dry steel plate after toluene degreasing (70×100×0.8
mm) with adhesives of Examples and Comparative Examples to a constant width of 30 mm.
After applying the paint gradually from 2 mm thick at an angle, it was immersed in Kansai Paint Co.'s cationic electrodeposition paint solution and applied with electricity at 200 volts and 0.5 amperes for 60 seconds. After washing with running water,
Dry curing was performed at 180°C for 30 minutes. Thereafter, the coating state of the electrodeposition paint was visually observed and evaluated. Rustability: After evaluating the adhesion of the electrodeposition paint, the test panel was left in a salt spray tester set to 5% saline for 100 hours, and the presence or absence of rust was visually evaluated. The results are shown in Table 1.

[Table] Comparative Example 4 An adhesive composition is prepared in the same manner as in Example 3, except that γ-Fe ₂ O ₃ powder is used instead of α-Fe ₂ O ₃ powder. This, Example 3 (α-Fe ₂ O ₃ ) and Example 1 (BaO・Fe ₂ O ₃ )
Comparison of adhesive strength with the composition was conducted in the following manner. Adhesive strength test Two degreased SPCC steel plates (25 x 150 x 0.8 mm)
After applying each adhesive at a certain thickness to the adhesive surface,
The two steel plates were stacked together, heat-cured at 180°C for 30 minutes, and the T-peel strength was measured using an autograph at 20°C. The results are shown below. γ-Fe ₂ O ₃ : 15Kg/in α-Fe ₂ O ₃ : 35〃 BaO・Fe ₂ O ₃ : 33〃

Claims (1)

[Claims] 1. An epoxy resin, a heat- _activated curing agent, and a sintered metal oxide- _iron oxide composite ferrite or α- A structural adhesive composition characterized in that it consists of Fe ₂ O ₃ particle powder. 2. The structural adhesive composition according to item 1 above, wherein Me of the ferrite is Ba. 3. The structural adhesive composition according to item 1 above, wherein the content of the ferrite is in the range of 20 to 70% by weight.