JPH0791505B2 - Undercoat paint composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to a coating composition for undercoating which is excellent in corrosion resistance, processability, adhesion to a base, and adhesion to a top coating film.

<Prior art> A large amount of steel sheets are used as materials for automobiles, building materials, and home appliances.For automobiles, there is a demand for improved corrosion resistance due to the spread of road deicing agents, and for building materials, maintenance-free for a long period of time. There is a demand for unprecedented high levels of corrosion resistance. As measures for improving it, there are a method of plating the base steel material, a chemical conversion treatment, and a method of applying an undercoat paint. Conventionally, as the paint used in the latter method,
Organic binders such as comb-based, phenolic resin, polyester resin, and epoxy resin mixed with anticorrosive pigments such as zinc chromate and strontium chromate,
Organic-inorganic composite coating composed of colloidal silica and water-based organic polymer proposed in JP-B-54-34406, JP-A-60-19907
The above-mentioned composite paint proposed in No. 4 in which the bond between the organic resin and the silica component is strengthened, JP-B-53-37096, JP-A-61-1
For example, zinc rich paint in which metal powder such as zinc powder is added to an organic binder as disclosed in No. 52444 is used.

<Problems to be solved by the invention> The combination of an organic binder, which is often used as an undercoating paint for home appliances and building materials, with an anticorrosion pigment has a high level of toxicity due to chromium pigments and insufficient corrosion resistance. In the situation where corrosion resistance is required, thick coating is indispensable, and there is a drawback that problems such as cracking and peeling of the coating film during processing are likely to occur. Further, although the organic polymer-silica composite coating has improved corrosion resistance, it is not sufficient, and also has poor alkali resistance and adhesion to the top coating film. Furthermore, although zinc-rich paint has remarkably improved corrosion resistance, it has insufficient press moldability due to the inclusion of zinc powder, pigments of relatively large particles such as metal powder, and corrosion resistance, workability,
There was no undercoat paint that could satisfy all the adhesion to the base and the adhesion to the top coating film, and its use was restricted.

The object of the present invention is to solve the above-mentioned drawbacks of the conventional undercoating coating composition, corrosion resistance, processability, adhesion to the base, and excellent adhesion to the top coating film, automobiles, building materials, metals for home appliances, etc. It is an object of the present invention to provide a highly corrosion-resistant coating composition used for undercoating a plate surface.

<Means for Solving Problems> The present invention for achieving the above-mentioned object includes (1) a non-volatile component of a coating material having a number average molecular weight of 900 to 15,000.
Epoxy resin 60 to 90% by weight, average diameter of primary particles 1
~ 10 mμ, surface area 270 m ² / g or more, and the silanol group concentration on the particle surface is 0.25 mmol per 100 m ² silica particles 10-40% by weight, characterized by containing a solvent-type metal plate surface undercoating high Corrosion resistant coating composition, (2) Number average molecular weight 900 to 15000 as the coating nonvolatile component
A total of 60 of the epoxy resin and the curing agent of the epoxy resin
~ 90% by weight, average primary particle size 1-10 mμ, surface area 270 m ²
/ g or more and the silanol group concentration of the particle surface is 10 to 40% by weight of silica particles having a concentration of 0.25 mmol or more per 100 m ^{2 of} solvent type metal plate surface undercoating high corrosion-resistant coating composition, is there.

<Function> The inventors have found that the silanol groups on the surface of silica particles are effective in improving the corrosion resistance of the coating material, and when the silica particles are blended with an appropriate resin selected, the average diameter of the primary particles of the blended silica particles becomes fine. , And found that the corrosion resistance improved dramatically as the specific surface area by the BET method increased (about the BET method, published by Kyoritsu Publishing Co., Ltd., Vol.
See "Surface Area"). Based on this knowledge, regarding the structure and molecular weight of the binder resin for paints, corrosion resistance, interaction with the surface of silica particles, dispersibility of silica particles, fluidity that flows along the irregularities of the substrate surface during thin film formation, base and topcoat As a result of diligent research from the viewpoint of interaction with the film, processability, etc., it was found that a remarkable effect of improving corrosion resistance can be obtained by blending the epoxy resin with the silica particles, and completed the present invention. .

That is, the epoxy resin used in the present invention is an organic solvent-soluble type epoxy resin having a number average molecular weight of 900 to 15000, corrosion resistance, silica particle dispersibility, adhesion with a base or topcoat coating, processability, during film formation. Has excellent liquidity.

Here, the epoxy resin means a resin having one or more epoxy groups in the molecule or an epoxy polyol resin obtained by reacting an epoxy resin with a compound having a group reactive with an epoxy group, for example, a glycidyl ether type. Examples thereof include epoxy resins, glycidyl ester type epoxy resins, alkanolamine-modified epoxy resins and the like. Examples of the glycidyl ether type epoxy resin include a bisphenol A type epoxy resin, a bisphenol F type epoxy resin, a resorcin type epoxy resin, or a mixed resin thereof. Expression (In the formula, R is H or CH ₃ ; -A- is> C (CH ₃ ) ₂ , -C
H ₂ -, - O-, Alternatively, a resin represented by -S-; n is 0 or an integer of 1 to 14) may be used.
Commercially available products such as "0", "EP-5700", "EP-5900", "Epiclon 4050", "9050" manufactured by Dainippon Ink and Chemicals, Inc. may be mentioned.

Next, an epoxy polyol resin obtained by reacting an epoxy resin with a compound having a group having reactivity with an epoxy group will be described. Examples of the compound having a group reactive with an epoxy group include a compound containing a phenol group, a compound containing an amino group, a compound containing a carboxyl group and the like.

Examples of the compound containing a phenol group used at this time include monohydric phenols, dihydric phenols and polyhydric phenols, and particularly preferred are monohydric or dihydric phenols. Examples of such monohydric phenols include phenol, Examples include cresol, xylenol, t-butylphenol, and the like, and examples of the divalent phenol include bisphenol A, bisphenol F, resorcin, and the like.

Examples of the compound containing an amino group include primary amines and secondary amines, with hydroxylamine containing a hydroxyl group being particularly preferred. The primary amine is, for example, methylamine, ethylamine, propylamine, etc., the secondary amine is, for example, dibutylamine, etc., and the hydroxylamine is, for example, ethanolamine, propanolamine, N-methylethanolamine, diethanolamine, diisopropanolamine. Etc.

Further, as the compound having a carboxyl group, for example, a monocarboxylic acid or a dicarboxylic acid or a polyvalent carboxylic acid may be mentioned, but a preferable one is a monocarboxylic acid or a dicarboxylic acid, and examples of the monocarboxylic acid include acetic acid, propionic acid, lactic acid, etc. Examples of the dicarboxylic acid include maleic acid, adipic acid, succinic acid, phthalic acid, isophthalic acid,
Tetrahydrophthalic acid and the like can be mentioned.

The reaction ratio between the epoxy resin and the compound having a group reactive with the epoxy group is in the latter with respect to the epoxy group in the former. The ratio of the group having reactivity with the epoxy group is 1.2 to 0.7, and preferably 1.1 to 0.9.

In addition, the reaction between the epoxy resin and the compound having a group reactive with the epoxy group can be carried out as described above when a compound having a group reactive with the epoxy group is used, for example, a compound having a phenol group or a carboxyl group. It may be carried out at a temperature of, for example, 80 to 250 ° C in the presence of such a catalyst, and when a compound having an amino group is used as a compound having reactivity with an epoxy group, it is carried out at a temperature of, for example, 60 to 150 ° C without a catalyst. be able to.

Two or more compounds having a group having reactivity with these epoxy groups may be used in combination. In this case, the reaction between the epoxy resin and the two or more compounds may be carried out simultaneously, or the first compound may be reacted first and the next compound may be further reacted.

Next, the number average molecular weight of the above-mentioned epoxy resin must be 900 or more because the workability is deteriorated when it falls below 900. When used as a thin film with a thickness of around 1μ, it is necessary for the paint to flow sufficiently along the irregularities of the base material during the baking process after coating, and to form a uniform film. Those with a number average molecular weight of over 15,000 will flow. Properties are insufficient, and it becomes difficult to form a uniform film. Also, good dispersibility of silica particles in the resin is important for improving corrosion resistance, and it is desirable that the silica particles be uniformly dispersed in the resin without agglomeration, but if the number average molecular weight exceeds 15,000, the dispersibility is improved. Deteriorates and corrosion resistance decreases. For the above two reasons, the molecular weight must be 15,000 or less.

The epoxy resin constitutes 60 to 90% by weight of the nonvolatile content of the paint. If the resin is less than 60% by weight, the adhesion of the top coating film,
A decrease in workability is observed, and when it is 90% by weight or more, the effect of compounding silica particles decreases, and the corrosion resistance deteriorates.

In the coating composition of the present invention, a curing agent such as an amino resin, a resol-type phenol resin, or a polyisocyanate resin is used as the nonvolatile content in the coating, and the total of the epoxy resin and the curing agent is
It can be contained in an amount of 60 to 90% by weight and heat-cured.

Examples of the amino resin include alkyl etherified formaldehyde resins such as formaldehyde or paraformaldehyde alkylated with an alkyl alcohol having 1 to 4 carbon atoms such as methanol, ethanol, n-propanol, isopropanol, and n-butanol, and urea, N. Condensation products of N'-ethylene urea, dicyandiamide, aminotriazine, etc.,
Specifically, methoxylated methylol urea, methoxylated methylol-N.N'-ethylene urea, methoxylated methylol dicyandiamide, methoxylated methylol melamine,
Methoxylated methylol benzoguanamine, butoxylated methylol melamine, butoxylated methylol benzoguanamine and the like can be mentioned.

General formula for resol type phenolic resin (In the formula, n is 0 to 5, Z is —CH ₂ or —CH ₂ —O—CH ₂ —, and R is C.
_{H 3, H, -C (CH} 3) 3, Or The thing represented by is mentioned.

As the polyisocyanate resin, the isocyanate group of a compound having more than one isocyanate group obtained by reacting an isocyanate-containing monomer such as tolylene diisocyanate, xylylene diisocyanate, and isophorone diisocyanate with a hydroxyl group-containing compound is phenol, methyl ethyl ketone, or oxime. , Those blocked with methanol or the like, those not blocked, and the like.

In addition, a compound having at least one group capable of reacting with a hydroxyl group, an epoxy group or the like contained in the epoxy resin or / and a compound which can serve as a catalyst for ring-opening polymerization of an epoxy group can be used as a curing agent. The mixing ratio of the curing agent to the epoxy resin can be arbitrarily selected.

Next, in the present invention, for the purpose of improving the corrosion resistance, the silica particles having an average particle diameter of 1 to 10 mμ and a specific surface area by the BET method of 270 m ² / g or more and a silanol group concentration on the particle surface of 0.25 mmol or more per 100 m ² are coated. It is used within the range of 10 to 40% by weight based on the nonvolatile content. If the average particle diameter of the primary particles of the silica particles is less than 1 mμ, the alkali resistance is lowered, which is not desirable, and if it exceeds 10 mμ, the effect of improving the corrosion resistance is reduced. Therefore, the average diameter of the primary particles of silica particles is 1-10 mμ
Must be in the range.

The silanol groups on the surface of silica particles make a significant contribution to the improvement of corrosion resistance. Surface treatment with a silane coupling agent, etc. improves the corrosion resistance even if the silanol groups on the surface have been reduced in the epoxy polyol resin. Has little effect. The surface silanol group density of untreated fumed silica particles with an average diameter of commercially available primary particles of 7 mμ is 100 m ²
However, when the silanol group density is less than 0.25 mmol per 100 m ² , the corrosion resistance decreases. Corrosion resistance similarly decreases even with silica particles having a specific surface area of less than 270 m ² / g by the BET method. A specific surface area of 800 m ² / g is desirable in terms of workability. As described above, the silica particles must have an average primary particle size of 1 to 10 mμ, a specific surface area by the BET method of 270 m ² / g or more, and a surface silanol group concentration of 0.25 mmol or more per 100 m ² . From the viewpoint of workability, it is preferably 1.0 mmol or less.

Examples of such silica particles include fumed silica and colloidal silica, but it is preferable to use fumed silica. The colloidal silica is difficult to mix with the organic solvent-soluble epoxy resin in the water dispersion type, and cannot be added in large amounts in the methanol dispersion type because the epoxy resin has poor methanol solubility. Further, colloidal silica contains ammonium ions and alkali metal ions for stabilizing the colloid, and these ions tend to reduce the anticorrosive ability of the coating film. Examples of fumed silica include “Aerosil 300” and “380” from Degussa. In addition, the amount of silica particles blended is 10 with respect to the nonvolatile content of the paint.
-40% by weight, preferably 15-25% by weight, less than 10% by weight has no effect of improving anticorrosion property, and more than 40% by weight causes deterioration of workability, alkali resistance and adhesion to the top coating film. Is recognized.

In the composition of the present invention, if necessary, various additives such as synthetic resins other than the above, organic or inorganic pigments, extender pigments, dispersants usually added to paints, anti-settling agents, leveling agents, etc., solvents Etc. can be added. The solvent is appropriately selected from various solvents such as various hydrocarbons, esters, ketones, alcohols and amides which are usually used in paints. The conversion to paint is carried out according to the usual preparation of solvent-based paint.

The undercoating coating composition of the present invention is extremely useful as an undercoating coating composition for automobiles, building materials, and steel sheets for home appliances, and as a base material for the steel sheets, hot-dip galvanized steel sheet, hot-dip galvanized steel sheet, electrogalvanized steel sheet, Used for electrolytic zinc / nickel or electrolytic zinc / iron alloy plated steel sheet, electrolytic zinc / iron double-layer plated steel sheet, cold rolled steel sheet, etc. The coating composition of the present invention is applied after cleaning the surface of these substrates as necessary with alkali degreasing or the like, and then directly or after performing a usual pretreatment. As the pretreatment for coating, chromate chemical conversion treatment or phosphate chemical conversion treatment is used. The former includes electrolytic chromate, coating chromate, and reactive chromate treatment, and the latter includes zinc phosphate treatment.

The coating composition of the present invention is applied by a suitable coating method such as spraying, roll coating, or shower coating, and dried to form a coating film. Baking and drying are preferably carried out at 100 to 250 ° C. It can be used as it is after the baking coating is formed, and acrylic resin, urethane resin,
Polyester resin, fluorine resin paint, electrodeposition paint, etc. may be used. The coating composition according to the present invention is 1 μm
The desired performance can be achieved with the front and rear thin films, but it does not prevent application of a thicker film.

<Examples> Hereinafter, the present invention will be described in more detail with reference to Examples. All parts in the examples represent parts by weight.

The resins and silica particles used in the examples of the present invention and the comparative examples are as follows.

Epoxy resin (a) Those within the scope of the present invention ○ Epoxy resin A: Epoxy polyol resin, number average molecular weight 3800, hydroxyl equivalent (solid equivalent) 290. The manufacturing method is as follows.

Asahi Denka Kogyo ADEKA Resin EP-5700 (epoxy equivalent 2000) obtained from bisphenol A and epichlorohydrin 1
Epoxy resin A was obtained by dissolving 50 parts in 100 parts of xylene and 50 parts of cyclohexanone, adding 8 parts of diethanolamine and heating and stirring at 120 ° C. for 4 hours.

○ Epoxy resin B: Epoxy polyol resin, number average molecular weight 1900, hydroxyl group equivalent (solid content value) 360. The manufacturing method is as follows.

Epoxy resin B was obtained by adding 18 parts of benzoic acid to 150 parts of epoxy resin having an epoxy equivalent of 1000 obtained from bisphenol F and epichlorohydrin and heating and stirring at 170 ° C. for 7 hours.

○ Epoxy resin C: "Adeka Resin EP-5" manufactured by Asahi Denka Co., Ltd.
900 ", Bifphenol A type epoxy resin, number average molecular weight 5500, epoxy equivalent 3000.

(A) What is outside the scope of the present invention ○ Epoxy resin X: "Epicoat 1255-HX-30" manufactured by Yuka Shell Epoxy Co., bisphenol A type epoxy resin,
Number average molecular weight of 30,000.

○ Epoxy resin Y: Asahi Denka Kogyo KK, "Adeka Resin EP
-4340 ", a bifphenol A type epoxy resin, and a number average molecular weight of 500 curing agent are all within the scope of the present invention.

Butylated melamine resin: "Melan manufactured by Hitachi Chemical Co., Ltd."
2000 ”○ Blocked polyisocyanate resin:“ Takenate B-846N ”manufactured by Takeda Pharmaceutical Company Limited, effective NCO 0% 8.5%.

Silica particles The silica particles used in the present invention examples and comparative examples are as follows,
Both are fumed silica manufactured by Degussa.

Next, a method of carrying out the present invention and comparative examples will be described.

Preparation of paint Add a curing agent to the epoxy resin if necessary, and further add fumed silica and a mixture of xylene and cyclohexanone at a weight ratio of 1/1 as a solvent, and stir and mix them to obtain a uniform mixture. A coating composition having a nonvolatile concentration of 20% by weight was obtained. Table 1 shows the composition of the non-volatile components of each paint in the examples of the present invention and the comparative examples.
Parts in Table 1 represent the weight of the solid content.

Preparation of test coated plate Cold-rolled steel plate (SPKD, thickness 0.8 mm) is pre-plated with Zn-Ni alloy (Ni content 11%, basis weight 20 g / m ² ).
Using a base material that has been subjected to electrolytic chromate treatment (basis weight: 40 mg Cr / m ² ), each coating composition obtained in the above Examples and Comparative Examples is roll-coated, baked at 200 ° C. for 30 seconds, and dried at 1 μm. A coated steel plate with a film thickness was made.

Test items and methods <Corrosion resistance> A salt spray test was conducted in accordance with JIS K 5400 7.8, and after 96 hours of continuous treatment, white rust generation area% at the cross cut part
I asked. The (red) display indicates the occurrence of red rust.

<Adhesion> Cellophane tape was peeled off according to JIS-K-5400 6.15, and the adhesion was examined.

<Bending processability> A 1T bending test was performed to evaluate cracks and peeling of the coating film in the bending process part.

○: No abnormality △: Cracks but no peeling ×: Peeling <Alkali resistance> 60% of the coated plate in NaOH aqueous solution (pH 13)
The dissolution of the coating film was examined by immersing it at 2 ° C. for 2 minutes and checking the weight before and after the immersion.

◯: Weight loss of 5% or less Δ: Weight loss of more than 5% and 30% or less ×: Weight loss of more than 30% <Adhesion of topcoat film> Cation after undercoating film is formed by baking Electro-deposition paint (Nippon Paint Power Top U-
100) electrodeposition coating (voltage DC210V 3 minutes electricity, bath temperature 28-30
℃, baking 170 ℃ 30 minutes) (film thickness 20μ) make a coated plate, 40
After soaking in warm water for 240 hours, leave at room temperature for 24 hours,
The adhesion was examined according to the method of (Note 2).

Table 1 shows the composition and test results of the non-volatile components of the coating compositions of Examples 1 to 6 of the present invention and Comparative Examples 1 to 6.

An example of the present invention and a comparative example will be described.

Inventive Examples 1 to 4 are those in which a butylated melamine resin is added as a curing agent, Inventive Example 5 is in which a blocked isocyanate resin is added, and Inventive Example 6 is in which no curing agent is added. In any of the formulations, the corrosion resistance, adhesiveness, bending workability, alkali resistance, and adhesion of the top coating film are good.

On the other hand, in Comparative Examples 1 and 2, the types of silica particles are out of the range of the present invention, and the corrosion resistance is extremely poor as compared with Inventive Example 1 in which the other formulations are exactly the same. In addition, Comparative Examples 3 and 4
Shows that the number average molecular weight of the epoxy resin exceeds the upper limit and the lower limit of the present invention range, respectively, but exceeds the upper limit (Comparative Example 3), the corrosion resistance exceeds the lower limit (Comparative Example 4), and the bending workability is poor. Become. Further, in Comparative Example 5, although the amount of the silica particles blended exceeds the upper limit of the range of the present invention, it is understood that the performance deteriorates in all the items. Comparative Example 6 does not contain silica particles and has extremely poor corrosion resistance as compared with the examples of the present invention, and it can be seen that the improvement of corrosion resistance by combining the epoxy resin of the present invention and silica particles is dramatic.

<Effects of the Invention> As described above, the composition for an undercoating material used in the undercoating of a metal plate surface for automobiles, building materials, home appliances, etc. of the present invention is a synergistic combination of an appropriate silica particle and a resin. As a result, it has a high corrosion resistance that cannot be usually predicted, and is excellent in adhesiveness, workability, and adhesiveness with a top coating film.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Nagaharu Ueno 1 Kimitsu, Kimitsu-shi, Chiba Inside Nippon Steel Corporation (72) Inventor Taiichi Kimura 5-13-16 Ginza, Chuo-ku, Tokyo Shin Nippon Steel Chemical Co., Ltd. (56) Reference JP-A-60-76568 (JP, A) JP-A-53-7737 (JP, A) JP-A-56-109812 (JP, A) JP-A-62-161865 (JP, A)

Claims (2)

[Claims] 1. A number average molecular weight of 900 to 1 as a non-volatile component of a paint.
Epoxy resin which is 5000 60-90% by weight, average particle diameter of primary particles 1-10 mμ, surface area 270 m ² / g or more, and silanol group concentration on the particle surface is 10-40 wt% silica particles 0.25 mmol or more per 100 m ^2. %, A solvent-type high corrosion-resistant coating composition for undercoating a metal plate surface. 2. A number average molecular weight of 900 to 1 as the nonvolatile content of the paint.
A total of 60 to 90% by weight of an epoxy resin of 5000 and a curing agent for the epoxy resin, an average diameter of primary particles of 1 to 10 mμ, and a surface area of 2
70m ² / g or more and the silanol group concentration on the particle surface is 100m ²
10-40% by weight of silica particles of 0.25 mmol or more
A high-corrosion-resistant coating composition for surface-coating a solvent-type metal plate, which comprises: