JPS6154341B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF THE INVENTION This invention relates to paint coating compositions. For more details, please refer to our chromate-treated galvanized coating, which is made of (a) an oil-free alkyd resin containing tannic acid as one component and (b) an amino resin, and provides a coating film with particularly excellent secondary adhesion after boiling water tests and corrosion resistance tests. This invention relates to a paint coating composition for steel plates. In recent years, oil-free alkyd resins have high coating film hardness and flexibility, which are difficult to achieve with oil-modified alkyd resins, and have excellent gloss, weather resistance, stain resistance, and chemical resistance. It has come to be widely used as a coating resin for automobiles, household appliances, machinery, steel furniture, cans, cans, colored galvanized iron, etc. However, in these fields, a high degree of water resistance and corrosion resistance are required in addition to the above-mentioned coating film performance, so there has been a problem that oil-free alkyd resin alone cannot sufficiently satisfy the required performance. Furthermore, since coating films in such fields are required to have flexibility and corrosion resistance at the same time, the use of epoxy esters and the like has been considered, but the corrosion resistance has not always been sufficient. On the other hand, the use of galvanized steel sheets as a material for the objects to be coated is increasing due to the cost, ease of processing, and durability of the material, and therefore the adhesion of the coating film to such materials is increasing. In addition, corrosion resistance is also required to a large extent. In addition, although coatings made from galvanized steel sheets have significantly better corrosion resistance than those made from regular steel,
For applications requiring high coating film performance, blister resistance and secondary adhesion were poor. Therefore, when a high level of coating performance is required, from the material perspective, in order to improve the adhesion with the paint,
After chromate treatment, phosphate treatment is further performed. However, in the case of galvanized steel sheets that have undergone chromate treatment, a sufficient phosphate film may not be obtained, and chromium ions may be leached into the treatment bath, so waste liquid treatment is not necessary to prevent pollution. There was a problem that it had to be done. On the other hand, from the perspective of paints, several examples have long been known in which phenolcarboxylic acids and the like are blended into various paints in order to improve the corrosion resistance of paint films.
For example, as described by RNFaulkner et al., a solvent in which catechol, pyrogallol, gallic acid, or its ester is introduced into vegetable oil, fatty acid ester, alkyd resin, vegetable oil-modified epoxy ester resin, or vegetable oil-modified polyamide resin using a catalyst such as a metal alkoxide. -based liquid paints have been developed. (For example, UK Patent No. 1045118, US Patent No.
No. 3304276, No. 3321320, Oil and Color
Journal of the oil published by Chemist's Association
and Color Chemist′s Association Volume 50, 524
(1967), etc.) However, these resins could not be applied to the above-mentioned industrial paint field, which requires a high degree of appearance and film performance. The present inventors had previously applied for a coating composition for paint consisting of an oil-free alkyd resin and an amino resin reacted with polyhydric phenol carboxylic acid (Japanese Patent Application Laid-open No. 50968/1983), but as a result of subsequent studies. In particular, by using an oil-free alkyd resin reacted with a specific amount of tannic acid, it is possible to obtain a composition that exhibits a specific effect on secondary adhesion after boiling water and corrosion resistance tests on galvanized steel sheets during chromate treatment. This led to the completion of the present invention. In other words, the present invention is made of an oil-free alkyd resin containing tannic acid as one component and an amino resin, and has high hardness and flexibility. The object of the present invention is to provide a paint coating composition that provides a coating film having particularly excellent adhesion. That is, the present invention provides (a) tannic acid reacted with an acid value of 1 to 20% by weight.
50KOHmg/g or less, hydroxyl value 50-250KOH
mg/g oil-free alkyd resin
The present invention relates to a paint coating composition for chromate-treated galvanized steel sheets, comprising: ...50 to 95% by weight, and (b) amino resin...50 to 5% by weight. The oil-free alkyd resin used in the present invention is obtained by esterifying tannic acid and polycarboxylic acid, and if necessary, monovalent carboxylic acid and polyhydric alcohol. be. Therefore, the coating film formed from the composition of the present invention containing the resin as one component has high hardness and flexibility, and also has excellent secondary adhesion after boiling water and corrosion resistance tests. In order to exhibit the above characteristics, it is essential to use tannic acid as the carboxylic acid component of the oil-free alkyd resin of the present invention. The component is 1 of the oil-free alkyd resin components.
The reaction is carried out in a proportion of ~20% by weight, preferably 2-10% by weight. In the above range, the component is 1% by weight
If this is not the case, after synthesizing the oil-free alkyd resin, the effect of improving the secondary adhesion of the coating film formed using the amino resin on the chromate treatment of the galvanized steel sheet will not be so great. On the other hand, if the above component is used in an amount exceeding 20% by weight, the resulting cured coating film becomes brittle and a decrease in weather resistance is observed. In addition, since a substantially sufficient effect can be obtained within 20% by weight, it is economically undesirable to use significantly more than 20% by weight. The acid value of the oil-free alkyd resin used in the composition of the present invention is 50 KOHmg/g or less (resin solid content: hereinafter, all acid values in the present invention are the same), and the hydroxyl value is 50 to 250 KOHmg/g (resin solid content). Solid content: (hereinafter, all hydroxyl values in the present invention are the same). Further, the molecular weight is preferably about 3,000 to 150,000 in terms of weight average molecular weight. The weight average molecular weight is determined by gel permeation chromatography [Toyo Soda Co., Ltd.]
A801 model manufactured by Manufacturer). (Hereinafter, the weight average molecular weight in the present invention is measured in the same manner.) The acid value of the oil-free alkyd resin is
If it exceeds 50 KOHmg/g, the alkali resistance etc. of the resulting coating film will be significantly reduced. On the other hand, if the hydroxyl value is less than 50KOHmg/g, there will be less remaining hydroxyl groups available for reaction with the amino resin.
This is not preferred because the crosslinking reaction becomes insufficient and the coating performance deteriorates. Conversely, the hydroxyl value is 250KOH
If it exceeds mg/g, it is not preferable because the water resistance of the resulting coating film tends to decrease due to the increase in polar groups. If the weight average molecular weight of the oil-free alkyd resin is lower than 3000, the properties of the oil-free alkyd resin cannot be fully exhibited. Also
If it exceeds 150,000, the viscosity of the oil-free alkyd resin solution becomes high, which impairs coating workability, so both are not very preferable. The polycarboxylic acids and monocarboxylic acids used in the synthesis of the oil-free alkyd resin used in the present invention include, for example, phthalic acid (anhydride), isophthalic acid, trimellitic acid (anhydride), pyromellitic acid (anhydride), and tetrahydrocarboxylic acid. Phthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, hemicic anhydride, succinic anhydride, adipic acid, benzoic acid, paratertiary butyl Examples include benzoic acid. These may be used alone or in a mixture of two or more. Furthermore, monovalent fatty acids and the like can also be used if necessary. Furthermore, polyhydric alcohol components used in oil-free alkyd resin synthesis include ethylene glycol, diethylene glycol, propylene glycol, neopentyl glycol, dipropylene glycol, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, and dipentaerythritol. , butylene glycol, pentanediol, trimethylpentanediol, hexanediol, 1,4-cyclohexanedimethanol, (hydrogenated) bisphenol A, etc., and these are used singly or as a mixture of two or more. Further, if necessary, Cardular E (manufactured by Ciel Chemical Co., Ltd., trade name) may be used in combination. The oil-free alkyd resin in the present invention is
It can be obtained by esterifying the tannic acid, polycarboxylic acid, and if necessary monovalent carboxylic acid and polyhydric alcohol by a known method. That is, there is no particular restriction on the reaction method. Generally, the reaction may be continued at a temperature of about 200 to 250°C until a predetermined acid value is reached. The oil-free alkyd resin thus obtained is mixed with an amino resin to obtain the composition of the present invention. As the amino resin used in combination with the oil-free alkyd resin, all general amino resins for paints can be used. The amount used is 5-50% for 95-50% by weight of oil-free alkyd resin.
% by weight. If the amino resin is used in an amount less than 5% by weight, the performance of the coating film will deteriorate, while if it is used in an amount exceeding 50% by weight, the characteristics of the oil-free alkyd resin of the present invention will not be utilized, which is not preferable. The composition comprising the oil-free alkyd resin and amino resin of the present invention may further contain curing accelerators, for example, mineral acids such as phosphoric acid and hydrochloric acid, and aromatic acids such as p-toluenesulfonic acid and benzenesulfonic acid. One or more organic acids such as sulfonic acid, phthalic acid monoester, and maleic acid monoester can be used. In addition, phenol resins, polybutadiene resins, alkyd resins, epoxy resins, epoxy ester resins, silicone resins, cellulose resins, isocyanate compounds, etc. can be added to the composition of the present invention depending on its use and purpose. Furthermore, as necessary, various additives such as rust preventive pigments, coloring pigments, extender pigments, other coating film-forming resins, flow aids, anti-sag agents, color separation preventive agents, and surface conditioners are added. A coating composition can be obtained by adding a desired amount and mixing and kneading using a known kneading method such as a sand mill, ball mill, roll mill, paint mixer, etc. Various well-known coating methods such as brush coating, dip coating, spray coating, electrostatic coating, and roll coating can be applied to the composition of the present invention thus obtained. Moreover, a normal top coat may be applied on the coating film for aesthetic purposes or other purposes. The heat curing conditions after coating of the paint coating composition of the present invention include the content of crosslinkable functional groups in the composition, the film thickness,
It varies depending on the presence or absence of a curing accelerator. Usually 100~
A cured coating film can be obtained by heating and drying for 5 to 40 minutes at an appropriate temperature in the temperature range of 200°C. The thus obtained cured coating film has extremely excellent corrosion resistance on chromate treatment of galvanized steel sheets, that is, secondary adhesion after boiling water resistance and salt spray resistance tests. The present invention will be explained below with reference to Examples. still,
"Parts" or "%" represent "parts by weight" or "% by weight." [Method for producing oil-free alkyd resin solution] (1) Oil-free alkyd resin No. 1 (hereinafter abbreviated as PE-1) In a reaction vessel equipped with a stirrer, a thermometer, a reflux dehydrator, and a nitrogen gas inlet pipe, Neopentyl glycol 27.5 parts, trimethylolpropane 16.5 parts
parts, isophthalic acid 14.5 parts, phthalic anhydride 13.0 parts
After the reaction temperature reached 235°C, the reaction was continued for 3 hours, the reaction temperature was lowered to 190°C, and then 10 parts of tannic acid was added. Furthermore
The reaction was carried out at 190°C for 1.5 hours to obtain an oil-free alkyd resin having an acid value of 8.3, a hydroxyl value of 168, and a weight average molecular weight of 7,100. This was diluted to a non-volatile content of 60% with a mixed solvent of xylene/methyl isobutyl ketone = 90/10 (parts) to give PE-1. (2) Oil-free alkyd resin No. 2 (hereinafter abbreviated as PE-2) In the same reaction vessel as in (1) above, 28.0 parts of neopentyl glycol and 17.2 parts of trimethylolpropane were added.
1 part, 29.8 parts of isophthalic acid, and 20.0 parts of adipic acid were heated in a nitrogen gas atmosphere, and the reaction was continued for 4.5 hours after the reaction temperature reached 235°C.
The reaction temperature was lowered to 190℃, and then tannic acid 5
of the mixture was added, and the reaction was further carried out at 190°C for 1.5 hours.
An oil-free alkyd resin having an acid value of 9.3, a hydroxyl value of 148, and a weight average molecular weight of 8,500 was obtained. This is xylene/methyl isobutyl ketone =
It was diluted to 60% non-volatile content with a 90/10 (parts) mixed solvent to obtain PE-2. (3) Oil-free alkyd resin No. 3 (hereinafter abbreviated as PE-3) In the same reaction vessel as in (1) above, 28.5 parts of neopentyl glycol and 13.5 parts of trimethylolethane were added.
parts, isophthalic acid 17.0 parts, phthalic anhydride 15.0 parts
1 part and 23.0 parts of adipic acid, heated in a nitrogen gas atmosphere, and after the reaction temperature reached 230°C,
After continuing the reaction for an hour, the reaction temperature was lowered to 195°C, then 3 parts of tannic acid was added, and then 195°C
Reaction was carried out at ℃ for 1.5 hours, acid value 8.1, hydroxyl value
105, and an oil-free alkyd resin having a weight average molecular weight of 38,500 was obtained. This was diluted to a nonvolatile content of 60% with a mixed solvent of xylene/methyl isobutyl ketone = 90/10 (parts) to obtain PE-3. (4) Oil-free alkyd resin No. 4 (hereinafter abbreviated as PE-4) In the same reaction vessel as in (1) above, 28.3 parts of neopentyl glycol and 17.2 parts of trimethylolpropane were added.
1 part, adipic acid 20.5 parts, and isophthalic acid 31.0 parts, and heated in a nitrogen gas atmosphere until the reaction temperature reached
After continuing the reaction for 5 hours after reaching 230℃, the reaction temperature was lowered to 195℃, then 3 parts of gallic acid was added, and the reaction was further carried out at 195℃ for 1 hour, resulting in an acid value of 8.8, a hydroxyl value of 154, and a weight Average molecular weight 9500
An oil-free alkyd resin was obtained. This is xylene/methyl isobutyl ketone =
It was diluted to 60% non-volatile content with a 90/10 (parts) mixed solvent to obtain PE-4. (5) Oil-free alkyd resin No. 5 (hereinafter abbreviated as PE-5) 27.6 parts of neopentyl glycol and 17.8 parts of trimethylolpropane in the same reaction vessel as in (1) above.
1 part, 32.8 parts of isophthalic acid, and 21.8 parts of adipic acid, and heated in a nitrogen gas atmosphere until the reaction temperature reached
After reaching 230℃, the reaction was carried out for 5.5 hours, and the acid value was
6.8, an oil-free alkyd resin having a hydroxyl value of 145 and a weight average molecular weight of 8,500 was obtained. This is xylene/methyl isobutyl ketone = 90/10 (parts)
Dilute PE-5 to 60% non-volatile content with a mixed solvent of
And so. [Melamine resin kneading base production method] Melamine resin [Super Betsukamine L-117-
70B; Trade name manufactured by Dainippon Ink and Chemicals Co., Ltd. To 10.7 parts, add 30 parts of titanium dioxide, 6.3 parts of xylol, 2.5 parts of butyl cellosolve, and 1.5 parts of acetone, and knead in a pot mill to a thickness of 10μ or less (measured with a grind gauge). This was used as a kneading base for melamine resin. [Examples 1 to 3 and Comparative Examples 1 and 2] 37.5 parts of each oil-free alkyd resin solution of PE-1 to PE-5 and 51 parts of the kneaded base of the melamine resin were mixed, and chromate of galvanized steel sheet was prepared. Paint with an applicator on a treated plate [Pentite chromate treated steel plate: manufactured by Nisshin Steel Co., Ltd.] to a dry film thickness of 25 ± 3 microns, heat cure at 150°C for 20 minutes, and then remove the coating. It was subjected to a performance test. The test results are shown in Table 1.

[Table] It is clear from the comparative test results table that the coating film obtained from the composition of the present invention exhibits excellent performance in adhesion, hardness, Erichsen, and impact resistance on chromate treatment of galvanized steel sheets. In addition, it exhibited particularly excellent performance in boiling water resistance and secondary adhesion after salt spray tests.

Claims (1)

[Scope of Claims] 1 (a) 1 to 20% by weight of tannic acid is reacted,
Acid value 50KOHmg/g or less, hydroxyl value 50~
250KOHmg/g oil-free alkyd resin
...50 to 95% by weight; (b) an amino resin ...50 to 5% by weight; a paint coating composition for a chromate-treated galvanized steel sheet.