JPS6034591B2 - How to improve the corrosion resistance of electrodeposited coatings - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for improving the corrosion resistance of a mist coating.

Haze paints have been widely put into practical use, and their position as undercoats is being established.

By applying open coating, it adheres well to metal surfaces and has superior corrosion resistance compared to general solution-type or water-diluted paints, but by dispersing corrosion-resistant pigments,
Efforts are being made to provide long-term corrosion resistance. The electrodeposited metal is also surface treated with zinc phosphate to make it more corrosion resistant. However, safety and health issues regarding chromium-based pigments are currently being discussed, and it is not desirable to use large amounts of chromium-based pigments.

Further, although variations in the thickness of the surface treatment film affect its corrosion resistance, it seems to be quite difficult to uniformly treat the surface of a metal plate with a complex shape. The present inventor has focused on such points and has conducted research for many years on a method for improving the corrosion resistance of an exposed coating film from the viewpoint of the resin.

Inspired by the vulcanization of natural rubber, thioalcohol was added to the lightning coating, which uses an addition polymer, polycondensate, fatty acid, or a derivative thereof as a vehicle, and which has an olefinic double bond and a dissociable group. When we tried adding a compound having two or more functional groups of either thiophenol or thiophenol, we found that the corrosion resistance of exposed coatings was significantly improved, leading to the completion of the present invention. Investigation and investigation into the reasons for this improvement in corrosion resistance revealed that the SH groups of thioalcohols and thiophenols undergo an addition reaction with olefinic double bonds, increasing the crosslinking density of the coating film, and that the SH groups interact with metals at metal interfaces. It was found that this is due to physical or chemical adsorption, completely protecting the metal surface from the outside world.

In the present invention, the exposure paint having olefinic double bonds refers to natural or synthetic drying oil fatty acids, semi-drying oil fatty acids, derivatives thereof, 1,2-polyptadiene or 1,4-polyptadiene, or their derivatives. derivatives, compounds having two or more Q,8-olefins, which have carpoxyl, phosphoric acid groups, or amino groups in their skeletons, and introduce dissociable groups by neutralization, Refers to substances that can be made water-soluble.

Furthermore, in the present invention, a compound having two or more thioalcohol or thiophenol functional groups is a compound with the general formula HS-R, -COO (R,: phenyl group or reactive carbon-carbon group). Thioalcohols containing a carboxyl group represented by (C, 1C6 organic residues having no saturated bond) or esterification products of thiophenol and a compound having two or more hydroxyl groups, or esterification products with the general formula HS-R, SH (R,: same as the previous formula)
refers to dithioalcohol or dithiophenol represented by

Examples of carboxyl group-containing thioalcohols that can be used in the present invention include thioglycolic acid, Q-mercaptopropionic acid, 8-mercaptopropionic acid, and thiosalcylic acid; examples of compounds having two or more hydroxyl groups include, for example, ethylene glycol, propylene glycol,
Butanediol, bentanediol, hexanediol, diethylene glycol, polyethylene glycol (number average molecular weight of about 3000 or less), dipropylene glycol, polypropylene glycol (number average molecular weight of about 3000 or less)
(below), dimethylolpropionic acid, glycols such as hydrogenated bisphenol, triols such as trimethylolpropane, trimethylolethane, glycerin, tetraols such as bentaerystol, polyesters containing hydroxyl groups (2 or more), hydroxyl groups ( Examples include vinyl polymers containing 2 or more hydroxyl groups, hydroxyl group-containing epoxy resins, hydroxyl group-containing urethane resins, and esterification products of these thioalcohols or thiophenols with compounds containing hydroxyl groups.

The reaction ratio of carboxyl groups and hydroxyl groups in thioalcohol or thiophenol is equivalent or less, and one molecule contains two or more thioalcohol groups or thiophenol groups. This reaction is usually carried out by dehydration condensation at 150-200 pm. On the other hand, dithioalcohols include ethane dithiol, hexamethylene dithiol, decamethylene dithiol, and the like.

These compounds having two or more SH groups are added in an amount of 0.1 to 5% by weight in an electrodeposition coating material having an olefinic double bond.
The cured coating film after addition and hazing showed very good corrosion resistance.

At 0.1% by weight or less, any polythioalcohol,
Even with polythiophenol, its anticorrosion effect is small, and if it exceeds 5% by weight, flaking on the painted surface becomes severe, and the color and scratches of the paint film become severe.
It is preferable to use it in a range of % by weight.

Examples are shown below.

In the examples, all percentages are by weight. Example 1 1,4-volibutadiene with an average molecular weight of about 1000 was maleated and hydrocyclized to give an acid value of 100, and 1 mole of 1,6-hexanediol and 2 moles of thioglycolic acid were added at 160°C for 3 hours. Add 5% of the reacted and esterified compound to the resin solid content, and add 0.0% with triethyleneamine.
．． 7 equivalents were neutralized and diluted with water to a solid content of 10%.

This exposed paint was applied to a polished mild steel plate under conditions of 250V for 3 minutes, and then applied for 30 minutes at 170V. A coating film with a film thickness of 25 mm was obtained. When this coated plate was subjected to a salt spray test (salt concentration 5%) for 10 days, it was found that less than 3 ribs were peeled off at the cut portion. Example 2 A resin obtained by adding 4 moles of linseed petroleum fatty acid to Epiquat #828 (epoxy resin) manufactured by Shell was maleated by the usual method, ring-opened with water to give an acid value of 100, and 1 mole of bentaerythritol was added. 20 mol of thiosalcylic acid
A compound esterified by reaction at 0°C for 5 hours was added at 1% based on the solid content of the resin, and triethylamine was added to esterify the compound at 0.7%.
Equivalent neutralization and dilution with water to 10% solids content.

A zinc phosphate treated iron plate was immersed in this electrodeposition paint and the voltage was applied to 250V.
, for 3 minutes, and then at 190° C. for 20 minutes.
When the resulting coated plate with a film thickness of 28A was subjected to a salt spray test (same as in Example 1) for 15 days, the number of peelings at the cut portion was 3 skins or less. Example 3 An alkyd resin with an oil length of 40 and a terminal carboxyl group (number average molecular weight: 2500) was synthesized using trimethylolpropane, phthalic anhydride, neobentyl glycol, soybean oil and fat acid and trimellitic acid in a conventional manner.

The acid value was 50. Add 20% water-soluble melamine to this resin, neutralize it with 0.5 equivalents of triethylamine, and
It was diluted with water so that the solid content was 0%. This was esterified by reacting 1 mole of dimethylolpropionic acid with 2 moles of Q-mercaptopropionic acid at 160°C for 3 hours, and the equivalent amount was neutralized with triethylene amine to give a 10%
The resin was diluted with water so as to have a solid content, and was added in an amount of 40% based on the resin solid content. Apply this dew-deposited paint to a European steel plate at a polishing rate of 250.
V, electrodeposited for 3 minutes and baked at 150° C. for 30 minutes to obtain a coated plate with a film thickness of 20 mm.

When this was put on a salt spray for 10 days, the peeling of the cut part was less than 3 sides. Example 4 1,2- with terminal carboxyl group number average molecular weight 1000
Decamethylene dithiol was added in an amount of 8% based on the resin solid content to a product obtained by adding amide with 2 moles of hexamethylene diamine to 1 mole of polybutadiene, and the mixture was neutralized with 0.7 equivalents of acetic acid.
It was diluted with water to a solid content of 10%.

Apply this to 250V, polish for 3 minutes, and apply it to mild steel to remove 200q.
o, 2 degrees} Baking was performed to obtain a coated plate with a film thickness of 25 mm. When this coated plate was subjected to salt spray for 10 days, the peeling of the cut portion was less than 3 sides. Example 5 Acrylic acid, n
m-Butyl acrylate and styrene are copolymerized in a conventional manner to create an acrylic resin with an acid value of 10 and a number average molecular weight of about 5,000, and an unsaturated acrylic resin with glycidyl methacrylate added until the acid value reaches 50. Molecular weight approximately 9
A compound obtained by reacting 5 moles of thioglycolic acid with 00 polyester polyol* at 160 q○ for 3 hours to add esters was added at 10%, and the equivalent amount was neutralized with ammonia and diluted with water to make a 10% amount. Obtained paint.

This was electrodeposited on a steel plate treated with iron phosphate at 250V for 3 minutes.
After diluting water at 0° C. for 1 minute, it was cured by irradiation with a 10MR electron beam to obtain a coated plate with a film thickness of 30 mm. When this coated plate was subjected to salt spray for 7 days, it was found that less than 3 feet were peeled off at the cut portion. * Polyester polyol is made by condensing trimethylolpropane (3 moles), ethylene glycol (1 mole), adipic acid (1 mole), and phthalic anhydride (2 moles) according to a conventional method to give an acid value of 5.
It has a hydroxyl value of 180.

Comparative Examples The results of the salt spray properties of paints excluding polythiol and polythiophenol are shown below.

Claims (1)

[Claims] 1. Adding a compound having two or more thioalcohol or thiophenol groups to an electrodeposition coating whose vehicle is an addition polymer, polycondensate, fatty acid, or derivative thereof that has an olefinic double bond and a dissociable group. A method for improving the corrosion resistance of an electrodeposition coating film, characterized by adding 0.1 to 50% by weight.