JPS59179340A - Precoated steel plate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a triple-coated pre-coated steel sheet which is mainly used as a building material and has excellent weather resistance, workability and corrosion resistance.

Prepainted steel sheets are steel sheets that are coated with paint in advance. They are usually mass-produced continuously using a roll coater on cold-rolled steel sheets, galvanized steel sheets, or aluminized steel sheets. Because it is excellent, uniform, suitable for mass applications, and does not require painting after construction, its demand is increasing as a material for building materials, home appliances, office equipment, etc.

The main performance requirements for these pre-coated steel sheets include weather resistance, corrosion resistance, adhesion, workability, and scratch resistance, but it is impossible to satisfy all of these quality performances with one type of paint. , is technically very difficult. For this reason, conventionally, paints were divided into two types, with the undercoat responsible for adhesion and corrosion resistance, and the second coat responsible for weather resistance, workability, scratch resistance, etc., thereby further improving the quality and performance of each paint. "To" - shi,
The quality and performance of pre-coated steel sheets has been improved by applying these paints in a so-called 2-coat, 2-bake method, in which a base coat is applied and baked, and then a coated paint is applied and baked.

However, many conflicting performances are still required at the same time for a two-piece product. For example, generally speaking, if a coating film is hardened for the purpose of improving scratch resistance, processability deteriorates. Even with polyester paint, which is the most common top coat paint for pre-coated steel sheets, if the skeleton resin is selected with the aim of improving weather resistance and scratch resistance, the processability deteriorates and the paint becomes unable to withstand normal bending processes. On the other hand, if the skeleton resin is selected to improve processability, performance such as weather resistance and scratch resistance will deteriorate. For this reason, improvements have been made to conventional two-coat "-4" paints by mixing various resins to balance performance.

Aiming to further improve the quality of pre-coated steel sheets, the present inventor painted and baked a paint whose main component is epoxy resin with good adhesion as an undercoat, and used it as an intermediate coat with a relatively high A paint whose main component is acrylic-modified vinylidene fluoride resin, which has good properties, is applied and baked.Then, as a top coat, a paint whose main component is acrylic-modified vinylidene fluoride resin, which is relatively hard, has good processability, and weather resistance. It has been found that a precoated steel sheet with good weather resistance, workability, and corrosion resistance can be obtained by performing precoating using a three-coat method (painting and baking).

That is, the present invention provides the following features: 1. The undercoat film is formed from a paint whose main component is an epoxy resin, the intermediate coat film is formed from a paint whose main component is an acrylic-modified vinylidene fluoride resin, and the top coat film is formed from a paint whose main component is an acrylic-modified vinylidene fluoride resin. The present invention relates to a pre-coated steel sheet formed with a paint whose main component is polyvinylidene fluoride resin.

One aspect of the present invention will be described in detail below.

First, as the epoxy resin paint used for the undercoat, commercially available epoxy resin paints with good adhesion can be used. Examples of the epoxy resin include bisphenol type and various other modified products.

Acrylic-modified vinylidene fluoride resin, which is a mixture or reaction of vinylidene difluoride resin and acrylic resin, is used as the main component for the intermediate coat and top coat, and this coating has extremely excellent weather resistance and good processability. It is. Especially in the top coat, the vinylidene difluoride resin content is 70% by weight.
It is preferable to contain the above amount. In this case, when measuring ultraviolet transmittance in the 300 nm region, which is said to have a high energy level, a 7P topcoat film blocks approximately 95% of ultraviolet rays. Therefore, since the amount of transmitted ultraviolet rays is smaller in the intermediate coating than in the top coating, it is sufficient that the vinylidene difluoride resin content is less than 70% by weight.

Furthermore, it is preferable to use an intermediate coating film that has a higher coating elongation rate than the Kosa coating film. This is because a soft top coat has low hardness and inferior scratch resistance, so it is most preferable to use a relatively hard top coat and a soft intermediate coat that provides flexibility with a high elongation rate. be. As for the elongation rate of the intermediate coating, it is preferable to have an elongation rate that can withstand, for example, IT bending processing.

However, the elongation rate that can be applied to IT bending processing is JTS G
3312 (colored galvanized iron plate), when the thickness of the base steel plate is T and the inner diameter of one bend is IT, the surface of the coating film is observed with a magnifying glass of 10x magnification. This refers to the elongation rate of a coating film that is free from cracks.

Also, the hardness of the coating and the finish are determined by JTS G 33, for example.
It is preferable that the hardness of the coating film be F or higher in terms of pencil hardness by the method specified in Section 12.

All of the coating materials used in the present invention are prepared by adding necessary amounts of a solvent, a pigment, a curing agent, and additives commonly used in coating materials in addition to the resin main component which is the coating film forming element described in -I-.

In addition, anti-corrosion pigments have conventionally been commonly blended into undercoat paints. However, in the present invention, it has been found that corrosion resistance can be significantly improved by incorporating a rust preventive pigment such as a chromic acid compound into each of the intermediate coating and the undercoat. That is, the prepainted steel sheet of the present invention is
As the rust-preventive coating layer uses resin systems with different chromium elution rates for the undercoat and intermediate coat, it has better corrosion resistance than the same resin system but with just a thicker rust-preventive coating layer. This is because it is possible to elute hexavalent chromium, which is effective for corrosion, in a well-balanced manner, and the rust prevention effect can be greatly improved. The amount of anti-corrosion pigment is 5 to 5 parts per 100 parts by weight of resin for both undercoat and intermediate coat.
It is preferable to add it in an amount of 15 parts by weight. If the amount of the rust-preventive pigment added is less than 5 parts by weight, the rust-preventing effect of passivating the steel plate cannot be expected, and if it exceeds 15 parts by weight, the rust-preventing effect will not be improved much, but rather it will make the resin layer softer. This is undesirable because it tends to lack properties and has an adverse effect on processing performance, especially in intermediate coatings. The blending ratio of anti-rust pigments in the undercoat and intermediate coat varies depending on the film thickness ratio during coating film composition, so it is not limited, but the blending ratio of the undercoat/intermediate coat should be 8.
It is preferable to set it to about 71% to about 71%.

Next, regarding the film thickness, the conventional 2-coat undercoat film is 2~
8. - The coating film has a thickness of 10 to 35μ, and especially for acrylic modified vinylidene fluoride resin paints, it has a thickness of 25 to 35μ to cover processability and corrosion resistance. The reality is that this problem has been dealt with by using a thick film, but despite applying a thick layer of expensive top resin paint, no significant effects have been observed.

On the other hand, the 3-coat I-coat of the present invention has the advantage that the J-coat and intermediate coat can each be thinner than the conventional 2-coat coating. For example, the dry film thickness of the top coat is 5 to 30 microns, preferably 7 to 20 microns, and the intermediate coat is 3 to 207 liters, preferably 7 to 15 microns.

In both cases, the lower limit is a necessary value from the viewpoint of color effect and ultraviolet transmission, and the lower limit is a necessary value from the viewpoint of ease of painting.

7. The reason why each intermediate coating can be made into a thin film is that, as mentioned above, the ultraviolet transmittance is low.When measuring the ultraviolet transmittance in the region of 30Or+m, 7 pL of the Kosa coating film is sufficient for weather resistance, which is about 5 layers. Show your gender. Further, the annual decrease in film thickness of the acrylic modified vinylidene fluoride resin when exposed outdoors is 0.2 to 0.3 p. Therefore, there is no need to make the intermediate coating film thicker, and the resin used for the intermediate coating film has the advantage that the amount of expensive fluorine to be blended can be reduced compared to the case of a "-coat coating film."

Next, from the point of view of corrosion resistance, as mentioned above, the fender
By distributing -1 to both the intermediate and undercoat, corrosion resistance could be improved more than before.

In addition, by adjusting the color of the intermediate coating paint to a color similar to that of the "-coating paint", it is effective in making the color tone more stable from the viewpoint of concealment when the top coating film is a thin film.

Next, the manufacturing method of the pre-coated steel sheet of the present invention is not particularly limited. A coil coating method or the like is used. However, in the coil coating method, if the paint is rapidly dried and baked in a short period of time after being applied, a pinhole phenomenon called "waki" occurs due to the volatilization of the solvent.

If there is a coating defect such as a pinhole, water or oxygen will easily permeate through the defect, making it difficult to expect much protection from the underlying metal. This phenomenon is more likely to occur the thicker the film is coated, so in the case of a thicker film, the line speed is limited and there is a drawback that work efficiency and economic efficiency are lacking. In the 3-coat method of the present invention, the top coat, which was conventionally applied thickly, is divided into two layers and then baked.In other words, by coating and baking each layer in a thin layer, the line speed is not reduced. ,
It has economic advantages such as reducing fixed costs and variable costs in mass production by preventing the pinhole phenomenon.

For example, according to a trial example, in the case of two coats with a thickness of 30 μm, the line speed that could be applied without creating pinholes was 30 m/min. On the other hand, when this was coated with three coats each having a thickness of 15 g, the line speed was doubled to 80 m1 m1n without producing pinholes, and the production volume was doubled. When comparing at the same line speed, the cost increase for electricity, energy, etc. required for painting is approximately 1.2 times higher, but when line speed is taken into consideration, fixed costs and variable costs increase per medium production volume. is about 0
．． 8 times, and the total cost of 3 coats was greater than that of 2 coats.

As described above, the present invention has three layers of top coat, intermediate coat, and undercoat as 0-.
Demonstrates excellent corrosion resistance and processability.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples.

The mark in the table is an example for comparison.

Example 1 In order to confirm the influence of the appropriate coating film structure of the three coats and the elongation rate of the intermediate coating film on workability and corrosion resistance, tests were conducted using test pieces under the following conditions, and the results are shown in Table 1.

Base steel plate: 0.35 mm thick galvanized steel plate treated with zinc phosphate Paint, baking conditions, and film thickness: (1) Undercoat; epoxy resin paint, 210°C x 50 seconds, 5p; (2) Intermediate coat; 1st Paint shown in the table, 240°C x 65 seconds, 10p, (3)
-Coating: Acrylic modified vinylidene fluoride resin paint, 240
°CX 65 seconds, 10IL.

In the intermediate coat and undercoat, 6 and 8 parts by weight of strontium chromate were added as a rust preventive to 100 parts by weight of the resin, respectively. The higher the coating film elongation rate, the better the corrosion resistance and processability were obtained.

1 Example 2 In order to confirm the influence of the film thickness of the intermediate coating film on corrosion resistance and workability, a test was conducted using a test piece under the following conditions, and the results were reported in the second
Shown in the table. That is, the type and thickness of the undercoat and topcoat were kept constant, and the thickness of the intermediate coat was varied to compare the rust prevention effects.

Base steel plate: 3.35 mm thick galvanized steel plate treated with zinc phosphate Paint, baking conditions, and film thickness: (1) Undercoat; epoxy resin paint, 210°C x 50 seconds, 5k; (2) Intermediate coat; acrylic modified fluoride. Vinylidene chloride resin paint, 240°CX65
(3) J-coat; acrylic modified vinylidene fluoride resin paint, 240°C x 65 seconds, 100% for 100 parts by weight of resin. Strontium chromate was added as a rust preventive agent in an amount of 6 and 8 parts by weight, respectively.

Good corrosion resistance has been obtained when the intermediate coating film thickness is 3μ or more, preferably 7pL or more.

Example 3 2 In order to confirm the difference in performance between a 3-piece product and a 2-piece product, tests were conducted using test pieces under the following conditions, and the results are shown in Table 3.

Base steel plate: 0.35 mm thick galvanized steel plate treated with zinc phosphate Paint, baking conditions, and film thickness: (1) Undercoat; epoxy resin paint, 210°C x 50 seconds, 5p; (2) Intermediate coat; acrylic modified Vinylidene fluoride resin paint, 240°C for 65 seconds, film thickness shown in Table 3, (3) Top coat; acrylic modified vinylidene fluoride resin paint, 240°C for 65 seconds, film thickness shown in Table 3.

In addition, for the intermediate coat and undercoat, strontium chromate was added as a rust preventive pigment to 100 parts by weight of the resin, respectively, at 6 and 8 parts by weight.
Part by weight was added. In addition, in the case of a two-piece product, test pieces were prepared without using the above-mentioned intermediate coating. A three-piece product has better workability and corrosion resistance than a two-piece product.

Example 4 In order to confirm the influence of the appropriate coating film composition of the 3 coats and the presence or absence of rust inhibitors in the base coat and intermediate coat on corrosion resistance, a test was conducted using test pieces under the following conditions, and the results were reported in the 4th example. Shown in the table.

Base steel sheet: 0.35 mm thick galvanized steel sheet treated with zinc phosphate Paint, baking conditions, and film thickness: (1) Undercoat; epoxy resin paint, 210°C x 50 seconds, 5 pL, (2) Intermediate coat: 1st
Paint shown in the table, 240°C x 65 seconds, lOμ, (3)
-h coating; acrylic modified vinylidene fluoride resin paint, 24
0°C x 65 seconds, 10 pL.

Note that strontium chromate was used as the rust preventive agent (rust preventive pigment). Parts in the amount added represent parts by weight. Corrosion resistance is improved by appropriately blending anti-rust pigments into the bottom and intermediate coats.

Example 5 In order to confirm the short-time dry baking suitability of the top coat, a test was conducted under the following conditions, and the results are shown in Table 5.

Base steel plate: 0.35 mm thick galvanized steel plate treated with zinc phosphate Paint, baking conditions, and film thickness: (1) Undercoat; epoxy resin paint, 210°C x 50 seconds, 5 coats, (2) Top 4 coats; Acrylic modified vinylidene fluoride resin paint, baked as shown in Table 5 (=1 condition and film thickness.

The paint used in the experiment was a product of Dainichi Ink Chemical T-Gyo Co., Ltd. and had the following properties.

(1) Undercoat; epoxy resin (DIC-WY19) viscosity
100 seconds, coating film specific gravity 1.6, weight heating residue 42% (2) Intermediate coating; acrylic modified vinylidene fluoride resin (OI
C-BWY21) A Viscosity 130 seconds, specific gravity of the coating 1.7, weight heating residue 53% B Viscosity 130 seconds, coating specific gravity 1.6, weight heating residue 52% C Viscosity 150 seconds, coating specific gravity 1. 8. Weight heating residue
60% D viscosity 150 seconds, coating specific gravity 1.7, weight heating residue 50% (3) Top coat; acrylic modified vinylidene fluoride resin (DI
C-Fusso) Viscosity: 180 seconds, Coating film specific gravity: 1.8, Weight heating residue: 55% 5 6 Table 3 7 Table 5 19 The performance tests were conducted as follows.

(1) Corrosion resistance: Salt spray test (JIS Z 237+
) The occurrence of white rust on the 2T bent portion after 2000 hours was observed (Tables 1 to 4). Cross cut after 2000 hours
・We observed the occurrence of white rust on the Erichsen section (extruded 6 mm onto the coating surface using an Erichsen tester) and the Erichsen section (extrusion of 6 mm onto the coating surface using an Erichsen tester). (Tables 2 to 4).

White rust is judged using a 5-point system, where 5 means no white rust and 1 means significant white rust.

(2) Workability: Impact deformation test and 2T bending test (
JIS G 3312). Judgment is 5 on the 5 point system
：No cracks, ■：Significant peeling. The value of f is determined after peeling off the coating film with tape (Tables 1 and 3).

(3) Paint film hardness: Shown as the highest pencil hardness that does not cause scratches on the paint film using a method based on JIS G 3312 (No. 3
table).

(4) Scratch resistance: Visual judgment was made by scratching the coating film with a 10 yen coin. ■ marks are the best, and ○ marks are fair and 0 (Table 3).

(5) Weather resistance: Ducycle Weather Meter 10
The color difference ΔE of the coated film surface after 00 hours and the gloss retention rate (%) are shown (Table 3).

(6) Corrosion resistance (Table 3): Salt spray test (JISZ2
37+) The occurrence of white rust on the OT bent portion after 2000 hours was observed.

Patent applicant: Taiyo Steel Co., Ltd. Agent: Patent attorney Masao Inoue 1 -2shi

Claims (1)

[Scope of Claims] 1. The undercoat film is formed from a paint whose main component is an epoxy resin, the intermediate coat film is formed from a paint whose main component is an acrylic-modified bicolidene fluoride resin, and the top coat film is formed from a paint whose main component is an acrylic-modified bicolidene fluoride resin. A pre-coated steel sheet made of paint whose main component is acrylic modified vinylidene fluoride resin. 2. The precoated steel sheet according to claim 1, wherein the intermediate coating film is formed of a paint whose main component is an acrylic modified vinylidene fluoride resin having a higher elongation rate than the top coating film. 3. The precoated steel sheet according to claim 1 or 2, wherein the fluorine content in the intermediate coat is lower than the fluorine content in the top coat. 4. The precoated steel sheet according to claim 1.2 or 3, wherein the intermediate coat film and the undercoat film contain a rust preventive pigment.