JPS61255975A - Sealing material for hemming portion - Google Patents

Abstract

PURPOSE:To provide the titled sealing material which is excellent in wiping-off properties after pre-curing and causes neither blister nor squeeze-out even when completely cured after electrodeposition and cam completely fill the inside of hemming portions, which comprises an epoxy resin and a specific curing agent. CONSTITUTION:An epoxy resin (A) is incorporated with a curing agent compris ing an org. acid hydrazide compd. of the formula (wherein R is an org. acid residue) in such an amount as well provide a ratio of the component (A) to the component (B) in terms of the amount of active hydrogen of 1:0.5-2.0 to obtain a sealing material for hemming portions. The sealing material is applied in a bead form around the peripheral portions of a shell plate of an automobile body, and an inner plate is mounted on the automobile body, and an inner plate is mounted on the automobile body, followed by hemming. The automobile body is heated at 120-150 deg.C for 5-20min to bring the sealing mate rial to a semisolid state. The squeezed-out semisolid sealing material is removed and the remainder is completely cured in the step of electrodeposition coating.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention is a sealing material used for rust prevention of hemming parts such as the joints between the outer and inner panels of automobile 7-doors, doors, and F-rank lids. (Prior Art) Conventionally, as a sealing material for the hemming part, epoxy resin has been used as described in Automotive Engineering Complete Book 18, Passenger Car Body, page 96. As the epoxy resin, a one-component heat-curing paste epoxy sealing material is used that uses latent curing agents such as dicyandiamide and imidazole as a curing agent.

Such a sealing material is usually applied continuously in a heavy manner to the peripheral edge of the outer panel, for example, when rust-preventing the hemming part of an automobile.
After the inner plates are assembled and passed through the hemming process and temporarily fixed with spot welding, the next step is to apply an electrodeposition coating, which is an undercoat, and harden the sealant by baking the electrodeposition coating open. (Problems to be Solved by the Invention) The conventional epoxy sealants have excellent adhesion and rust prevention properties, but they have the following problems in production lines. If the sealant is applied to the peripheral edge of the outer panel and hemmed to assemble the inner panel, and then baked in the electrodeposition coating process, thermal expansion of the sealant will cause blistering and protrusion, which will cause hemming to be performed in the next process. It becomes difficult to apply sealant (hereinafter referred to as body sealant) to the edges (where the outer and inner panels meet).Also, the latent hardeners used, such as dicyandiamide and imidazole, are sensitive. Due to its high temperature properties, it is difficult to maintain a semi-cured state to the extent that it is easy to remove the protruding epoxy sealant, and the electrodeposited paint is completely cured when baked open, so before applying the body sealant. Difficult to remove.

In addition, if the amount of epoxy sealant applied is reduced to an extent that does not cause blistering or extrusion during baking, it is difficult to say that the epoxy sealant will be completely filled inside the hemming part, which poses a problem in terms of rust prevention. Means for Solving the Problems) In order to solve the above problems, the inventors created epoxy sealants using various curing agents and tested them as sealants for hemming parts. The present invention was achieved by discovering that an epoxy sealing material using dihydrazide as a hardening agent can be preheated to give a semi-cured state that is excellent for removal by wiping means or the like.

Here, ``semi-cured state J with excellent removal workability'' refers to a state in which the semi-cured sealant can be easily peeled off with a cloth or spatula, and after removal, the sealant components are attached to the steel plate as the adherend material. It is necessary that there is no adhesion ◎After removing it,
If a sealant component adheres to a steel plate, it is undesirable from the viewpoint of quality and productivity because it has an adverse effect on electrodeposition coating properties and takes time to completely remove.

The hemming part sealing material of the present invention is a one-component thermosetting paste-like hemming part sealing material mainly composed of an epoxy resin and a hardening agent, and an organic acid dihydrazide compound is used as the hardening agent. It is characterized by , isophthalic acid dihydrazide, sebacic acid dihydrazide, p-oxybenzoic acid dihydrazide, and the like.

The amount of the organic acid hydrazide compound used is such that the ratio of the poly/boxy equivalent to the active hydrogen amount of the organic acid dihydrazide is 1:
0.5~1! If it is blended in a range of 2.0, preferably close to 1, sufficient adhesion and rust prevention properties can be provided as a sealant when completely cured.

Furthermore, the epoxy resin used in the sealing material of this invention is
Any material that has been conventionally used for adhesives or sealants may be used, and there are no particular restrictions.

Other fillers, plasticizers, additives, etc. that are conventionally used in sealants may be used as appropriate.

(Function) By containing the organic acid dihydrazide compound, the sealing agent of the present invention can be brought into a semi-cured state by an appropriate heating method. Therefore, in order to seal the hemming part, paste sealant is applied in a bead shape to the peripheral edge of the outer panel of the car body, the inner panel is assembled and hemmed, and then an appropriate heating method is applied. The sealant is preheated to a semi-cured state, and the semi-cured sealing material that protrudes at this time is removed by wiping means or the like, and can be fully cured in the electrodeposition coating process. When fully cured in this way, it will be 7 cr when fully filled.
There is no protrusion, and the subsequent application of body sealant can be performed without any problems.

As mentioned above, after applying the sealant to the application area and performing hemming, a method of preheating to a semi-cured state is preferably a method of heating at a temperature of 120 to 150"C for 5 to 20 minutes. However, if the temperature is 150° C. or higher and the time is extremely short, for example, within 1 minute, there is no practical problem.

(Example) This invention will be explained by the following examples and comparative examples.

Example 1 As shown in Table 1, epoxy resin Ebicoatna 828
(manufactured by Yuka Shell Epoxy, trade name) 80 parts by weight, rubber-modified epoxy resin R1451-1 (manufactured by NCR, trade name) 20 parts by weight, Ptadiene-Acrylonitrile Copolymer Hiker CtTBN180QX8 (manufactured by Gutdrich Chemical, Product name) 10 parts by weight, 10 parts by weight of isophthalic acid dihydrazide (manufactured by Nippon Hydrazine Kogyo) and 10 parts by weight.
Mix 80 parts by weight of K powder in a kneader to form a paste.
7) Seam +) Seam material was produced. This sealing material is coated with a curved steel plate (150X100X0.8
M) in a bead shape, then apply the front steel plate (15
0x25x0.8) and press it with a clip.12
It was heated at 0°C for 20 minutes to pre-cure it into a semi-cured state. When the protruding sealant was wiped off with a cloth, it was easily peeled off, and no sealant components were attached to the steel plate. Thereafter, electrodeposition coating was applied and cured at 165° C. for 30 minutes, and the sealant was completely cured without any protrusion. In addition, when adhesive strength was measured using the same procedure, interfacial peeling with a tensile shear strength of 3.51%/c4 was observed in a semi-cured state at 120°C for 20 minutes, and electrodeposition coating 1
Also listed in the table.

Examples 8 to 8 Examples were prepared in the same manner as in Example 1 using adipic acid dihydrazide (Example 1) and sebacic acid dihydrazide (Example 8) as curing agents at the compounding ratios shown in Table 1. Sealing materials Nos. 3 and 8 were produced.

Similar tests were conducted on these sealants, and the results are also listed in Table 1. It was found that both sealants have excellent removal workability in a semi-cured state.

Comparative Examples 1 to 8 Typical latent curing agents for epoxy resins such as alks, namely dicyandiamide (
Comparative Example 1), imidazole compound (Jt Comparative Example s),
Using boron monoethylamine (Comparative Example 8) -1
Sealing materials of Comparative Examples 1 to 3 were produced in the same manner as in Example 1. A similar test was conducted on these sealants, and the results are also listed in Table 1. It was difficult to pre-cure any of these, and even after pre-curing, the removal workability was poor.

(Effects of the Invention) As explained above, the hemming part sealing material of the present invention is a one-component thermosetting paste sealing material containing an epoxy resin and a curing agent as the main components, in which an organic acid dihydrazide compound is used as the curing agent. By using this product, it is easy to wipe off the sealant that protrudes after pre-curing, and there is no blistering or protrusion even after complete curing after electrodeposition coating, making it possible to completely fill the hemming area with sealant. This has the effect of not interfering with the body sealing application work performed in the next process.

Claims (1)

[Scope of Claims] 1. A hemming part sealing material in the form of a one-component thermosetting paste containing an epoxy resin and a curing agent as main components, characterized in that an organic acid dihydrazide-based compound is used as the curing agent. Sealing material for parts.