JPH09151299A - Epoxy resin composition for coating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an epoxy resin composition for coating materials, which is a one-package thermosetting resin composition, forms a coating film having very excellent adhesion and rust-preventive properties when it is applied to a stainless steel or aluminum sheet or plate coated with a press oil or a rust inhibiting oil and is therefore desirably used as a rust-inhibiting coating material for especially soft steel sheets for automobiles. SOLUTION: This epoxy resin composition mainly consists of 100 pts.wt. liquid epoxy resin derived from bisphenol A and/or bisphenol F, 5-50 pts.wt. mononuclear polyhydric phenol/urethane-modified epoxy resin and 1-20 pts.wt. latent curing agent for the epoxy resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an epoxy resin composition for coating, and more specifically, it is a one-pack type thermosetting resin composition, which is various steel plates and various aluminum alloys to which press oil or rust preventive oil is attached. The present invention relates to an epoxy resin composition for coating, which has excellent adhesiveness and rust preventive property by being coated on the base material and can be suitably used as a rust preventive coating material for automobile mild steel sheets.

[0002]

2. Description of the Related Art In recent years, improvement in corrosion resistance of automobile bodies has been demanded, and accordingly, steel sheets are subjected to various surface treatments such as galvanized steel sheets, zinc-nickel plated steel sheets, and further steel sheets obtained by coating an organic film on the plated steel sheet. Steel plate is used.
These steel plates are used to assemble a vehicle body by spot welding or MIG welding, and then chemical conversion treatment or electrodeposition coating is performed to ensure rust prevention.

This surface-treated steel sheet results in a portion such as the upper part of a vehicle body where rust prevention is not required so much, that is, a portion where even a mild steel sheet can sufficiently secure rust prevention performance. This steel plate is often used. Therefore, it is cost-effective to apply a rust preventive treatment by coating a rust preventive material only on a portion requiring rust preventive property after press forming using a mild steel plate instead of the surface treated steel plate. Conceivable. However, heretofore, there has been no optimum rust preventive material suitable for this application.

As a conventional material considered to be usable for this purpose, for example, a urethane-modified epoxy resin and a latent curing agent mixed with a rust preventive pigment or metal powder (Japanese Patent Laid-Open No. 60-206882). ), A specific rubber-modified epoxy resin or aromatic epoxy resin, and a latent curing agent mixed with conductive carbon black (JP-A-62-533).
No. 87), and a mixture of a urethane-modified epoxy resin and a rubber-modified epoxy resin and a latent curing agent with a specific rust-preventive pigment (JP-A-1-141971).

However, these materials were invented for use as an adhesive and do not necessarily meet the requirements as a rust preventive that can be coated. In other words, the most important thing as a rust preventive material is that it is necessary to be able to coat it to, for example, 300 μm or less like a paint, but these materials are used as an adhesive so that they can be automatically applied in a bead form on oil-faced steel plates. However, when it is thinly coated, there is a problem that repellency, voids, etc. are generated and the coating property is poor, and it is difficult to actually use it.

Even if these adhesives can be used for coating materials, the idea for improving the rust prevention of these materials is to impart high rust prevention to the epoxy resin itself. It is the idea to increase the rust preventive power when the composition is made by adding a filler called a rust preventive pigment to the composition, rather than to prevent it from being mixed. There are problems that it is difficult to obtain a stable rust preventive property depending on the distribution state of the rust pigment, and it is difficult to secure the rust preventive property for a long period of time due to the outflow from the composition depending on the pigment.

[0007]

SUMMARY OF THE INVENTION Therefore, the object of the present invention is to use as a coating material which gives a metal panel such as a mild steel plate which is not surface-treated, a high adhesion and an extremely excellent anticorrosion performance. It is to provide a novel epoxy resin composition that can be used.

[0008]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that a mononuclear polyhydric phenol / urethane modified epoxy resin and a latent curing agent obtained under predetermined conditions are By using the epoxy resin composition containing as the main component as a rust-preventive coating material,
The inventors have found that an epoxy resin composition for coating having excellent adhesion to metal panels and the like and anticorrosive properties can be obtained, and have reached the present invention.

[0009] The above object of the present invention is to provide bisphenol A
And / or based on 100 parts by weight of a liquid epoxy resin derived from bisphenol F, 5 to 50 parts by weight of mononuclear polyhydric phenol / urethane modified epoxy resin and 1 to 20 parts by weight of a latent curing agent of the epoxy resin are used as main components. It was achieved by the epoxy resin composition for coating characterized by containing. Hereinafter, the present invention will be described in more detail.

The mononuclear polyphenol / urethane-modified epoxy resin used in the present invention is a monoprecipitate obtained by reacting a urethane prepolymer obtained by reacting a polyhydroxy compound with an isocyanate compound with a mononuclear polyphenol. It is obtained by reacting a nuclear polyhydric phenol-modified urethane prepolymer with an epoxy resin.

In the present invention, the polyhydroxy compound is not particularly limited, but may be one usually used as a raw material of a urethane prepolymer generally called polyether polyol. The polyol component has a number average molecular weight of 60.
It is preferably in the range of 0 to 20,000. When the number average molecular weight is less than 600, the flexible component of the modified epoxy resin is insufficient and sufficient adhesion cannot be obtained. On the contrary, when the number average molecular weight exceeds 20,000, the viscosity of the modified epoxy resin becomes high and the coating becomes difficult. It becomes difficult to put it into practical use as a material.

In the present invention, in order to impart flexibility when reacting an isocyanate compound with a polyhydroxy compound derived from propylene oxide or ethylene oxide to give flexibility, an equivalent amount of isocyanate group and hydroxyl group is added. The ratio is 1.1 to 1.
It is necessary to prepare it in the range of 5.

By imparting flexibility in this way, a cured molecule of the composition tends to be hard and brittle because a rigid molecule is introduced by subsequent modification with a mononuclear polyhydric phenol, and the coating tends to be hard and brittle. It is possible to prevent the cause of deterioration of material performance.

By adjusting the equivalent ratio of the isocyanate group to the hydroxyl group in the range of 1.1 to 1.5, a urethane prepolymer having isocyanate groups at both ends which is excellent in flexibility is obtained, and an epoxy resin to be subsequently used. It is possible to modify the urethane. If the equivalent ratio of both is less than 1.1, it will be difficult to introduce isocyanate groups at both ends, while if it exceeds 1.5, a urethane prepolymer having a small molecular weight will be obtained and flexibility will be insufficient.

When synthesizing the above urethane prepolymer, the isocyanate compound used as the raw material is 2
Any one having at least one isocyanate group may be used, and specific examples thereof include toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate.

Examples of the mononuclear polyhydric phenol include catechol, 4-t-butylcatechol, and pyrogallol, but catechol is preferably used because of its easy reaction. The amount of the mononuclear polyhydric phenol used is not particularly limited, but it is preferably adjusted to 0.1 to 5% by weight in the mononuclear polyhydric phenol / urethane modified epoxy resin. The amount of mononuclear polyhydric phenol used is 0.
If it is less than 1% by weight, the rust prevention cannot be improved. On the other hand, if it exceeds 5% by weight, the amount of mononuclear polyhydric phenol added becomes too large, and on the contrary, the reactivity decreases and the unreacted amount increases, which is actually , It becomes difficult to obtain a modified epoxy resin, and even if it is obtained, when the modified epoxy resin is cured,
It becomes hard and causes a decrease in adhesion.

Next, the obtained mononuclear polyphenol-modified urethane prepolymer is reacted with an epoxy resin to obtain a mononuclear polyphenol / urethane-modified epoxy resin. The amount of the mononuclear polyphenol-modified urethane prepolymer used is not particularly limited, but generally, the content of the mononuclear polyphenol in the resin is 100 parts by weight of the epoxy resin.
It is preferable to adjust the amount to be in the range of 1 to 5% by weight.

When the amount of the mononuclear polyphenol-modified urethane prepolymer used is less than 0.1% by weight based on the mononuclear polyphenol content of the resin, the cured product of the coating material lacks flexibility and, conversely, 5%. If the content is more than wt%, the viscosity of the cured product will be high, and the workability when applying a coating material will be extremely reduced. From such a viewpoint, in the present invention, it is preferable to react the mononuclear polyhydric phenol-modified urethane prepolymer with 100 parts by weight of the epoxy resin in the range of 5 to 70 parts by weight.

As the epoxy resin used in the present invention, an epoxy resin derived from bisphenol A and / or bisphenol F and epichlorohydrin or a mixture thereof is used. At this time, the number of hydroxyl groups contained in the epoxy resin is preferably in the range of 0.1 to 2.0 on average in one molecule. When the number of hydroxyl groups contained in the epoxy resin is less than 0.1 on average in one molecule, it becomes difficult to modify with a urethane prepolymer and a predetermined modified epoxy resin cannot be obtained. On the contrary, when the number of hydroxyl groups is more than 2.0 on average, the epoxy resin becomes solid, and in practice,
Coating becomes difficult.

The mononuclear polyphenol / urethane modified epoxy resin thus obtained is an epoxy resin 1 derived from bisphenol A and / or bisphenol F.
It is mixed in the range of 5 to 50 parts by weight with respect to 00 parts by weight.
If the amount of mononuclear polyhydric phenol / urethane-modified epoxy resin is less than 5 parts by weight, the rust resistance is inferior, and if it is more than 50 parts by weight, the viscosity of the coating material increases, which makes it difficult to use and the cured product becomes hard, Adhesion to shocks will decrease.

The heat-activatable curing agent can be appropriately selected and used from known curing agents that exhibit a curing action by heating. For example, dicyandiamide, 4,
Imidazole derivatives such as 4'-diaminodiphenyl sulfone, 2-n-pentadecyl imidazole, dibasic acid dihydrazides such as adipic acid dihydrazide,
Examples thereof include N, N'-dialkylurea derivatives, alkylaminophenol derivatives, melamine and guanamine. These are appropriately blended in the composition depending on the equivalent weight of the epoxy resin used and the curing conditions, but it is usually preferred to blend in the range of 1 to 20 parts by weight with respect to 100 parts by weight of the epoxy resin.

The imidazole derivative, N, N'-dialkylurea derivative, alkylaminophenol derivative and the like can also be used as a curing accelerator. The amounts of the curing agent and the accelerator compounded are easily determined by conducting a test in advance.

[0023]

EXAMPLES The present invention will now be described in more detail by way of examples, which should not be construed as limiting the invention.

Example 1 As a polyhydroxy compound derived from propylene oxide, 100 g of polyether diol P2000 (manufactured by Asahi Denka Kogyo Co., Ltd., number average molecular weight of about 2000) was charged into a reactor, and 10 g of toluene diisocyanate was added dropwise to 80 A urethane prepolymer was obtained by reacting at 2 ° C. for 2 hours. The equivalent ratio of isocyanate groups to hydroxyl groups was 1.15.

To 100 g of the obtained urethane prepolymer, 4 g of catechol was added and reacted at 80 ° C. for about 1 hour,
20 g of this was taken out and reacted with 80 g of bisphenol A type epoxy resin Epicoat 828 (trade name of Yuka Shell Epoxy Co., Ltd.) for 2 hours. Then, the temperature was raised to 120 ° C. and the volatile matter was removed while reducing the pressure.

With respect to 100 parts by weight of the obtained mononuclear polyphenol / urethane-modified epoxy resin, 8 parts by weight of dicyandiamide as a latent curing agent and H3 as a curing accelerator.
4 parts by weight of 636S (product number manufactured by AC R Co., Ltd.) were added, mixed and defoamed to prepare an epoxy resin composition for coating. The obtained composition was applied to a mild steel plate with a bar coder to a thickness of 50 μm and baked at 170 ° C. for 20 minutes.

Using this test piece, salt water spray was carried out for 500 hours, and the appearance of rust was observed by appearance to check the rust preventive property. In addition, cross-cut was performed and cellophane tape was used to check the adhesion. The distance between the cross cuts was 1 mm, and the 100 eyes were evaluated. The result was expressed as X / 100 when x pieces of the 100th eyes were peeled off by peeling.

As a result, in this example, no rust was observed in the external appearance and 100/100 was obtained in the cross-cut test, which showed good rust prevention and adhesion, and was excellent as a rust prevention coating material for mild steel sheets. It turned out to show performance.

Examples 2 to 7 and Comparative Examples 1 to 5 Based on Table 1 as in Example 1, the mononuclear polyhydric phenol /
A urethane prepolymer was prepared, followed by a mononuclear polyphenol / urethane modified epoxy resin. Further, an epoxy resin and a curing agent were blended to obtain a coating material composition. These compositions were tested. The composition and performance of the adhesive composition are shown in Table 2.

[0030]

[Table 1]

[0031]

[Table 2]

Examples 1 to 7 all showed excellent rust prevention and adhesion to mild steel sheets. On the other hand, in the comparative examples, many of them are inferior in rust preventive property and adhesiveness, and none of them can be used as a rust preventive coating material for mild steel plates.

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Claims (7)

[Claims] 1. 1 to 50 parts by weight of a mononuclear polyhydric phenol / urethane modified epoxy resin and 100 parts by weight of a liquid epoxy resin derived from bisphenol A and / or bisphenol F and a latent curing agent 1 to 1 of an epoxy resin. Two
An epoxy resin composition for coating, which contains 0 part by weight as a main component. 2. A mononuclear polyhydric compound obtained by reacting a mononuclear polyhydric phenol / urethane modified epoxy resin with a urethane prepolymer obtained by reacting a polyhydroxy compound and an isocyanate compound with a mononuclear polyhydric phenol. The epoxy resin composition for coating according to claim 1, which is a resin obtained by reacting a phenol-modified urethane polymer and an epoxy resin. 3. The epoxy resin composition for coating according to claim 2, wherein the number average molecular weight of the polyhydroxy compound is in the range of 600 to 20,000. 4. The epoxy resin composition for coating according to claim 2 or 3, wherein the polyhydroxy compound is a polyether polyol compound derived from propylene oxide and / or ethylene oxide. 5. The urethane prepolymer comprises a polyhydroxy compound and an isocyanate compound as isocyanate groups /
It is obtained by reacting so that the equivalent ratio of hydroxyl groups is in the range of 1.1 to 1.5.
An epoxy resin composition for coating according to the above. 6. The epoxy resin has an average of 0.1 to 0.1 in the molecule.
The epoxy resin composition for coating according to claim 2, which has a hydroxyl group in the range of 2.0. 7. The mononuclear polyphenol is catechol, 4-
A mixture containing at least one selected from the group consisting of t-butyl catechol and pyrogallol, and 0.1% in a mononuclear polyhydric phenol / urethane modified epoxy resin.
The epoxy resin composition for coating according to claim 1, wherein the epoxy resin composition is contained in an amount of -5% by weight.