JPS63107781A - Rust preventing coating method of galvanized steel plate - Google Patents

Abstract

PURPOSE:To enable BH steel plate to be processed at low temperatures for maintenance of its properties by preparing a coating agent with a mixture of epoxy resin and fine powder silica silane coupling agent using an aqueous chromate processing solution containing an alcohol compound as a reduction agent. CONSTITUTION:A chromate processing solution which is applied to galvanized steel plate and zinc alloy plated steel plate when a rust-preventive coat is formed on automobile steel plate, consists of 0.3-1.0mol/l of chromic acid, 0.1-1.0mol/l of phosphoric acid and 0.1-1.0mol/l of alcohol compound. This chromate processing solution is subjected to reduction baking at as low a temperature as 80-150 deg.C, then a next coating agent is applied. That is, fine powder silica and silane coupling agent are added to aqueous dispersive epoxy resin obtained by subjecting 40-90pts.wt. of diglycedil ether, 5-35pts.wt. of diphenol and 2-15pts.wt. of coreactive surfactant to reaction. This mixture allows baking at 80-150 deg.C.

Description

[Detailed description of the invention] Technical fields> The present invention relates to an anticorrosion coating method.

<Background of the invention> In recent years, both in Japan and abroad, snow-melting salt has been sprayed on roads during snowfall, and as a result, there has been an increasing demand for rust prevention for automotive steel sheets, and galvanized steel sheets and zinc alloy-plated In the so-called synchrometal treatment, which applies chromate treatment to steel plates and is seen in Japanese Patent Publication No. 47-8882, the reduction treatment temperature reaches 240℃ to 280℃)
Then, apply a zinc-rich paint over it, or apply a mixture of an epoxy resin emulsion, silica fine powder, and a flukoxysilane compound, such as that found in an inorganic-organic composite resin paint (Special Publication Show Go-50179).
The use of anti-rust coated steel sheets baked at 0 to 300°C is increasing.

On the other hand, as a measure to save fuel consumption in automobiles, there is a tendency to reduce weight by making plates thinner, and the use of high-strength steel plates is being considered in order to supplement the safety against impact caused by thinner plates. has been done. However, high-strength steel plates are difficult to press.

Therefore, when pressed, it has the softness of ordinary steel sheet.

It would be extremely desirable if it could be made into a high-strength steel sheet in the subsequent process.In fact, it would maintain the softness of an ordinary steel sheet during the forming process, and bake under the electrodeposition coating baking conditions (180 to 180℃ for 20 minutes, which must be passed in the automobile body manufacturing process). BH rust steel sheets (hake-hardened steels), which harden under 30 minutes to become high-strength steel sheets, have already been developed for this purpose.

However, in the rust-preventing coatings using chromate treatment and inorganic-organic composite resin paints known to date, baking is carried out at temperatures of 200°C or higher as described above, so BH rust-resistant steel sheets cannot be used without post-treatment such as a skin bath. Characteristics cannot be extracted.

Under these circumstances, the inventors of the present invention have conducted extensive research and have developed a chromate treatment that can be reduced at low temperatures and an inorganic-organic composite paint that can be baked at temperatures below 160°C, without impairing the properties of BH rusted steel sheets. We developed a coating method using

<Structure of the invention> That is, according to the present invention.

Chromic acid applied to galvanized (including zinc alloy plated) steel sheets
0.3-1. O%/lz/fL phosphoric acid
An aqueous chromate treatment solution consisting of 0, 1 Nl, O mol/1 alcohol compound 0.1 to 1.0 mol/9° is applied, and the burn-in is treated at 80 to 150°C, and on top of that, a) Diglycidyl ether of dihydric phenol 40-90 parts by weight Mouth) Dihydric phenol 5-35 parts by weight c) i)
Co-reactive surfactant 2 consisting of a reaction product reacted in a molar ratio of diisocyanate X mole ii) dihydric phenol X mole iii) long chain aliphatic polyether glycol 1 mole (where X is 2 to 6) ~15 parts by weight of reaction product, average molecular weight of about 80o~20.0
An inorganic-organic composite paint consisting of 10 to 200 parts by weight of finely divided silica and 0.1 to 30 parts by weight of a silane coupling agent was applied to 100 parts by weight of the solid content of the emulsion of water-based dispersible epoxy resin No. 00. A method of anti-rust coating of metal is provided which comprises baking.

Lafromic acid here refers to CrO2. Alcohol compounds are compounds having hydroxyl groups such as alcohols, glycols, and sugars in a narrow sense.

The aqueous chromate treatment solution of the present invention may contain a mineral acid and/or an organic acid at a concentration of up to 0.001 molar, mineral acid meaning an inorganic acid such as sulfuric acid, nitric acid, hydrochloric acid, hydrofluoric acid, etc.
The organic acid means a reducing organic acid such as formic acid, lactate acid, tartaric acid, and amber acid.

These are not essential ingredients in the composition of the present invention.

Conventional aqueous chromate treatment solutions use organic acids and their derivatives as reducing agents, so the reduction treatment temperature is 240~240℃.
However, in the present invention, an alcohol compound is used as a reducing agent, and phosphoric acid acts as a promoter of the reduction reaction, so the organic acid can be reduced at 80 to 150°C.In the composition of the present invention, an organic acid is essential. Although it is not a component, it is preferable to use it because it acts as a reduction catalyst.
Valent chromium is efficiently reduced to trivalent chromium, and at 80°C
It shows a reduction rate of 95% or more at 0% and 100°C.

In the present invention, 'C' refers to 'a) Diglycidyl ether of dihydric phenol 40-9
0 parts by weight mouth) Dihydric phenol 5-35 parts by weight c) i)
Co-reactive surfactant 2 consisting of a reaction product reacted in a molar ratio of diisocyanate X mole ii) dihydric phenol X mole iii) long chain aliphatic polyether glycol 1 mole (where X is 2 to 6) ~15 parts by weight of reaction product, average molecular weight of about 800-20.0
00 water-based dispersible epoxy resin emulsion" is a composition containing an epoxy resin described in detail in JP-A No. 59-88125, and commercially available products such as "Aquat" from Tobu Kasei Co., Ltd. - Available under the trademark 35201J.

The "fine powder silica" referred to herein is represented by "Aerosil" (trade name). So-called colloidal silica obtained by gas-phase hydrolysis of silicon chloride, or so-called colloidal silica obtained by dispersing ultrafine particles of silicic anhydride in water with a particle size of 1 to 100, using water as a dispersion medium. Or it is fine powdered silica called silica sol.

The "silane coupling agent" herein refers to what is generally called a silane coupling agent, such as aminoalkoxysilane, epoxysilane, and glycidoxysilane.

While conventional inorganic-organic composite resin coating agents using epoxy resin emulsions required baking temperatures of 200℃ or higher, the coating agent used in the method of the present invention requires baking temperatures of 150℃ or higher.
You can bake it below.

<Specific disclosure of the invention> The present invention will be explained in detail below using examples.

EXAMPLE A fixed amount of ion exchange water and chromic acid anhydride are added to a container equipped with a stirrer and completely dissolved under stirring. Next, a fixed amount of a mixture of phosphoric acid and ethylene glycol is added to uniformly dissolve the mixture to obtain a chromate treatment solution.

To prepare the epoxy resin-fine silica-alkoxysilane mixture, measure and inject the epoxy resin emulsion into a container equipped with a stirrer, add a constant 7H alkoxysilane while stirring,
After making it uniform, gradually add fine powdered silica and make it uniform.

The chromate treatment solution is Cr 03 H3PO4 alcohol compound A O
,8sol O,3mol EG'
0.5 molB 0.8 mol
1.0 mat EG' 0
．． 5 anoICO, 8 mol O, 3 mol
EG' 0.1 agolD
O, 8 mol O, 3 mol EtOH20,5
molE O, 8 mol 1. Five types were prepared: Omol sucrose 0.5 mall ethylene glycol 2 ethanol.

As a mixed coating of epoxy resin, finely divided silica, and flukoxysilane.

a Aqua tote 35201 40% 'i>
Part Aerosil 200 7.2 tons h; Part γ-propylaminotriethoxysilane 2 tons ψ Part b Aquat) 35201 40 parts by weight Snowtex N 36 parts by weight γ-glycidoxypropyltrimethoxysilane
Three types were prepared: 2 parts by weight C Aquatote 35201 40 parts by weight Snowtex C36 parts by weight β-(3,4 epoxycyclohexyl)ethyltrimethoxysilane 2 parts by weight.

Apply the above-prepared chromate treatment solution to a pre-degreased steel plate with a coating weight of 20 g/m2 and coated with a zinc-nickel alloy on one side, using a known bar coater, roll coater, etc. so that the amount of chromium deposited is 10 to 500 mg/m2. It was painted using the above method and baked at a maximum temperature of 120°C. This chromate treated layer is referred to as the first layer.

Furthermore, the epoxy resin emulsion-fine powder silica-alkoxysilane mixture prepared above was coated onto the previously chromate-treated steel plate using a known method such as a bar coater or roll coater so that the dry film pressure was 1.5. It was painted and baked at a maximum temperature of 120°C. This coating layer is called the second layer.

The results are summarized in the table below.

In the table.

The Cr reduction rate is determined by the amount of initial Cr deposited on the steel plate after passing through the treatment liquid, as unreduced Cr is eluted into the treatment liquid when a chromate-treated coated steel sheet is passed through a commercially available alkaline degreasing liquid. It was expressed as a ratio of the amount of Cr deposited.

2# Edibility shows the results after 100 cycles of a composite corrosion test (salt spray → dry → wet 3 cycles, 7 days).

O: Red rust occurrence θ%, o: 20%, Δ: 50% X:
80% or more 3 processing parts are cylindrical drawing (50mm diameter x 25mm depth)
means part.

4 Evaluation was made based on the amount of coating peeled off at the cylindrical constriction section.

@: 3 mg/piece or less, ×: 5■g/piece or more.

As seen in this table, known products cannot achieve good Cr reduction rate, corrosion resistance, and workability unless heated to 250°C.

Claims (1)

[Claims] 1. Chromic acid 0.3-1.0 mol/l Phosphoric acid 0.1-1.0 mol/l Alcohol compound 0.1-1. Apply an aqueous chromate treatment solution consisting of 0 mol/l, and
℃ reduction baking treatment, and then a) dihydric phenol diglycidyl ether 40-90
Parts by weight b) 5 to 35 parts by weight of dihydric phenol c) i) X moles of diisocyanate ii) X moles of dihydric phenol iii) Molar ratio of 1 mole of long-chain aliphatic polyether glycol (X is 2 to 6) A co-reactive surfactant consisting of the reaction product reacted with 2 to 15 parts by weight of the reaction product having an average molecular weight of about 800 to 20,0
00 water-dispersible epoxy resin emulsion solid content 1
A rust-preventing coating method for metals, which comprises applying an inorganic-organic composite paint consisting of 10 to 200 parts by weight of fine powder silica and 0.1 to 30 parts by weight of a silane coupling agent to 0.00 parts by weight, and baking at 80 to 150°C.