JPH08109247A - One-pack type thermosetting epoxy resin composition - Google Patents

Abstract

PURPOSE: To improve the stability at room temp. and retention of strength of bonding to a metal by incorporating an epoxy resin having two or more epoxy groups and a hydroxyl group, a resol type phenolic resin, and a particular imidazole compd. CONSTITUTION: 100 pts.wt. epoxy resin having in one molecule a hydroxyl group and two or more epoxy groups and an epoxy equivalent of 180 to 4000, 3 to 30 pts.wt. resol type phenolic resin, and optionally 0.1 to 1 pt.wt. phosphoric acid, an org. solvent, a pigment, etc., are homogeneously added to and mixed with a soln. of 0.5 to 4 pts.wt. imidazole compd. of the formula I and/or the formula II dissolved in an org. solvent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a one-part thermosetting epoxy resin composition, which is used as a primer for a metal substrate, an adhesive for metals and the like.
Particularly, it is useful as a primer for polyolefin-coated metal.

[0002]

2. Description of the Related Art For corrosion protection of metals such as steel and steel pipes,
It has become common to coat the surface of a metal with a polyolefin resin such as polyethylene or polypropylene having excellent chemical stability. However, since the polyolefin resin is non-polar in terms of its chemical structure, the adhesive force is weak on a highly polar surface such as metal. Therefore, a method of coating a polyolefin resin by using or using a modified polyolefin resin modified with an unsaturated carboxylic acid or an acid anhydride thereof is used. However, the adhesive strength between the polyolefin resin and the metal decreases with an increase in temperature, humidity or salt concentration in the use environment. With respect to such a problem, Japanese Patent Application Laid-Open No. 56-1432 discloses a coating structure in which a metal base treatment and an epoxy primer treatment are used in combination, particularly an epoxy primer composition.
23, JP-A-59-222275, JP-A-60-2.
45544, JP-A-1-15054, JP-A-3-7
As disclosed in Japanese Patent No. 3340, there has been proposed a method of using an epoxy primer obtained by mixing an epoxy resin in which a specific epoxy resin is mixed with an inorganic pigment and an amine curing agent and curing the mixture by reaction.

By the treatment with these epoxy primers, the retention of high adhesive strength can be obtained. However, these epoxy primers generally do not have sufficient storage stability at room temperature and must be used within a short time after primer preparation. For this reason, the device surface and workability are constrained.

[0004]

DISCLOSURE OF THE INVENTION The present invention provides a one-component thermosetting epoxy primer which is stable at room temperature and is excellent in retaining adhesive strength with a metal.

[0005]

[Means for Solving the Problems] That is, the present invention is based on (a) 100 parts by weight of an epoxy resin having two or more epoxy groups in one molecule on the basis of solid content and having a hydroxyl group, (b) Resol type phenol resin 3 to 30 parts by weight,
(C) A one-part thermosetting epoxy resin composition, characterized by being 0.5 to 4 parts by weight of an imidazole compound represented by the formula (1) or / and the formula (2).

[0006]

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[0007]

[Chemical 4]

Hereinafter, the present invention will be described in detail. In the one-component thermosetting epoxy resin composition of the present invention, the ratio of the (b) resole type phenolic resin is 3 to 30 parts by weight, preferably 5 to 100 parts by weight of the epoxy resin (a) based on the solid content. 27 parts by weight. The ratio of the (c) imidazole compound is 0.5 to 4 parts by weight, preferably 0.
8 to 3.5 parts by weight.

When the amount of the component (b) is less than 3 parts by weight, the adhesive force with the metal is weak and thus the salt spray resistance is low, and when it exceeds 30 parts by weight, the storage stability of the epoxy resin composition is poor and the initial adhesive strength, Salt sprayability is also low. If the amount of the component (c) is less than 0.5% by weight, the adhesive strength with the polyolefin resin is weak, so that both the initial adhesive strength and the salt water resistance are low.
If it exceeds 5% by weight, the storage stability of the epoxy resin composition is poor and the salt spray resistance is also low.

The epoxy resin used in the present invention is 1
It has two or more epoxy groups in the molecule and also has a hydroxyl group. Examples include bisphenol type glycidyl ether. Examples of the bisphenol type glycidyl ether include bisphenol A diglycidyl ether, bisphenol F diglycidyl ether,
Examples thereof include bisphenol S diglycidyl ether, bisphenol AD diglycidyl ether, brominated bisphenol A diglycidyl ether, tetramethylbisphenol A diglycidyl ether, and glycidyl ether of bisphenol.

The epoxy resin used in the present invention preferably has an epoxy equivalent of 180 to 4000, more preferably 400 to 3500.
The resol type phenol resin used in the present invention is obtained by condensation reaction of phenols and formalin in the presence of alkali. Examples of the phenols used include those represented by formula (3).

[0012]

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The imidazole compound in the present invention is a latent curing agent and is soluble in organic solvents such as acetone, methyl ethyl ketone and 2-propanol. For example, 1-dodecyl-2-methyl-3-benzylimidazolium chloride, 1,3-dibenzyl-2
-Methylimidazolium chloride. If necessary, phosphoric acid can be added to the one-pack thermosetting epoxy resin composition of the present invention as a curing catalyst for the resol-type phenol resin. The ratio of phosphoric acid is 0.1 to 1 part by weight, preferably 0.3 to 0.8 part by weight, based on 100 parts by weight of the epoxy resin based on the solid content. If the ratio of phosphoric acid is less than 0.1 part by weight, the effect of improving the curability of the coating film by phosphoric acid is not obtained, and if it exceeds 1 part by weight, no further effect can be expected.

An organic solvent may be added to the one-part thermosetting epoxy resin composition of the present invention to adjust the viscosity.
Examples of the organic solvent include acetone, methyl ethyl ketone, methyl isobutyl ketone, toluene, xylene, and n.
-Propanol, 2-propanol, ethyl acetate, butyl acetate and the like can be mentioned. Further, a curing accelerator, a pigment and the like can be added if necessary.

The one-component thermosetting epoxy resin composition of the present invention is used as a solventless or solvent-type varnish depending on the method of use. As a method for preparing the one-component thermosetting epoxy resin composition of the present invention, for example, after stirring and dissolving an imidazole compound in an organic solvent, an epoxy resin, a resole-type phenol resin, phosphoric acid if necessary, an organic solvent, a pigment, etc. Add and mix evenly.

The one-part thermosetting epoxy resin composition of the present invention is applied to an adherend. Examples of the application method include a method of immersing an adherend in a one-component thermosetting epoxy resin composition, a spray coating method, a brush coating method, and a trowel coating method. Next, this coated material is heat-treated to obtain a cured coating film. As a heating method, an oven, far-infrared heating, high-frequency heating, or the like is used, and 330 ° C. in the oven for 1 to 6 minutes is a preferable method.

The use of the one-pack thermosetting epoxy resin composition of the present invention is as a primer for a polyolefin resin-coated metal, an adhesive between metals, and the like. When it is used as a primer for a polyolefin resin-coated metal, a cured coating film of a one-component thermosetting epoxy resin composition is formed, and a polyolefin resin is coated thereon by a method such as fluid immersion coating or electrostatic coating. When used as an adhesive for metals, the one-component thermosetting epoxy resin composition is applied to the bonded portion of one metal, and then the other metal is fixed with a bonding jig. And it heat-processes and makes it adhere.

The performance of the one-part thermosetting epoxy resin composition of the present invention is as follows. (A) Regarding storage stability, the viscosity after standing for 7 days in a 50 ° C. environment is 1.5 times or less the initial viscosity. (B) The coating film curability is 50 times or more in the acetone rub test after heat treatment at 330 ° C. for 3.5 minutes.

(C) The adhesion performance of the polyethylene-coated metal used as the primer in the salt spray test is such that peeling and swelling occur for 500 hours or more.

[0020]

【Example】

(1) The one-component thermosetting epoxy resin composition is prepared by dissolving an imidazole compound in an organic solvent with stirring, and then adding an epoxy resin and a resol-type phenol resin to this solution and mixing and dissolving them. Finally, the solid content was adjusted with an organic solvent. (2) The test coated plate is a metal plate (plate thickness 1.6 mm, material G3
141 (SPCC SD)) is degreased with acetone, then a one-component thermosetting epoxy resin composition is applied by immersing or spraying, then baked at 330 ° C. for 5 minutes, and immediately after that, fluidized dip coating of polyethylene powder (post-heating). 220 ° C, 3 minutes)
And created.

(3) The storage stability of the one-pack thermosetting epoxy resin composition was determined by measuring the initial viscosity, putting it in a closed container, and leaving it in an environment of 50 ° C. for 7 days to measure the viscosity. The viscosity multiple with respect to the initial viscosity was calculated from the formula. Viscosity multiple = (viscosity after standing for 7 days in a 50 ° C. environment) / (initial viscosity) (4) The test of the test coated plate was performed as follows.

(A) The initial adhesive strength was measured by cutting the coated plate to a substrate with a width of 10 mm and measuring the peel strength with an adhesive tape. (B) In the salt spray test, a test coated plate was cut up to the base material, tested with a salt spray tester according to JIS-Z-2371, and then the peeling occurrence time of the cut part was measured.

[0023]

Examples 1 to 8 One-component thermosetting epoxy resin compositions were prepared according to the compositions shown in Tables 1 and 2, and one-component thermosetting epoxy resin compositions and test coated plates were tested. The results are shown in Table 1.
~ 2. In each of Examples 1 to 8, good results were obtained.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

Comparative Examples 1 to 4 One-component thermosetting epoxy resin compositions were prepared according to the compositions shown in Table 3, and the one-component thermosetting epoxy resin composition and the test coated plate were tested. The results are shown in Table 3. Comparative Example 1 was based on Example 6 except that 1 part by weight of the resole-type phenol resin of Example 6 was used. As a result, salt spray resistance was low.

Comparative Example 2 was based on Example 6 except that the resole type phenolic resin of Example 6 was changed to 35 parts by weight based on the solid content. As a result, the storage stability of the epoxy resin composition was poor, and the initial adhesive strength and salt spray resistance were low. Comparative Example 3 was based on Example 5 except that the imidazole compound of Example 5 was changed to 0.2 part by weight. As a result, the initial adhesive strength and salt water spray resistance were low.

Comparative Example 4 was based on Example 5 except that the imidazole compound of Example 5 was changed to 4 parts by weight. As a result, the epoxy resin composition had poor storage stability and low salt spray resistance.

[0029]

[Table 3]

[0030]

The one-part thermosetting epoxy resin composition of the present invention is stable at room temperature, and the cured coating film of the composition has high adhesive strength and adhesive retention to both metal surface and polyolefin resin surface. Can develop sex.

Claims (2)

[Claims] 1. A solid content of (a) 3 to 30 parts by weight of a resole type phenolic resin, relative to 100 parts by weight of an epoxy resin having two or more epoxy groups in one molecule and having a hydroxyl group, (C) A one-part thermosetting epoxy resin composition, characterized by being 0.5 to 4 parts by weight of an imidazole compound represented by the formula (1) or / and the formula (2). Embedded image Embedded image 2. The one-part thermosetting epoxy resin composition according to claim 1, wherein phosphoric acid is added to 100 parts by weight of the epoxy resin.
A one-pack thermosetting epoxy resin composition, which is added in an amount of 0.1 to 1 part by weight.