JPH0369351A - Precoated steel plate - Google Patents

Abstract

PURPOSE:To obtain a delustered precoated steel plate having excellent workability, flawing resistance and corrosion resistance by successively forming an undercoating layer and the top coating layer of delustering paints onto the surface of a zinc group plated steel plate through a chemical treatment layer composed of a phosphate or a chromate and shaping the undercoating layer with a paint containing a specific quantity or more of a specific resin containing bisphenol A and specific quantities of blocked isocyanate and an amino resin. CONSTITUTION:An undercoating layer and a top coating layer consisting of delustering paints are formed onto the surface of a zinc group plate steel plate through a chemical treatment layer composed of a phosphate or a chromate in a precoated steel plate. The under coating layer is formed of paint containing a resin containing bisphenol A in the resin structure and having weight average molecular weight of 1000 or 60000 at the rate of 10 wt.% or more per paint-resin solid matter and blocked isocyanate and/(or) an amino resin at the rate of 10 or 40 wt.% per the paint-resin solid matter. A film is liable to be cracked and peeled on fabrication when the molecular weight of the resin containing bisphenol A is less than 1000, and working coatability is deteriorated when it exceeds 60000.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a prepainted steel sheet that can be suitably used for interior and exterior building materials, home appliances, utensils, automobile interior materials, etc. This invention relates to a matte pre-coated steel sheet with excellent scratch resistance and corrosion resistance.

[Prior Art] In recent years, there has been a strong demand for matte precoated steel sheets with a more luxurious appearance in the industry that manufactures products such as interior and exterior materials for buildings, home appliances, utensils, and automobile interior materials.

In response to such demands, several matte precoated steel sheets have been developed. One of them is particle size 5 to 2.
One is a paint containing inorganic powder such as silica or alumina with a particle size of 0 μm applied to a steel plate, and the other is a paint containing a thermoplastic resin powder such as nylon or polypropylene with a particle size of 20 to 50 μm applied to a steel plate. It is something. Among these, pre-coated steel sheets coated with paint containing inorganic powder have a merely matte appearance. In terms of texture, it is similar to ordinary painted steel sheets, and has the cool feeling that steel sheets have, and is not sufficient in terms of decorativeness.

On the other hand, pre-coated steel sheets coated with paints containing thermoplastic resin powder have a semi-matte appearance with a matte texture and are slightly superior to pre-coated steel sheets coated with paints containing inorganic powders. Show your feelings. However, this pre-coated steel sheet also has the cool feeling that steel sheets have and is insufficient in terms of matte properties.

By the way, paints containing colored elastic polymer beads (spherical powder) and elastic resin binders are known as decorative paints for concrete walls and plastic substrates. This paint gives the substrate a multicolored super matte appearance and a cloth-like soft feel.

[Problems to be Solved by the Invention] Therefore, the present inventors thought that if a paint containing the above-mentioned colored elastic polymer beads and a resin binder was applied to a steel plate, a high-grade pre-coated steel plate with excellent decorative properties could be obtained. .

However, even if this paint is applied directly to the steel plate,
It was discovered that the adhesion to the steel plate was poor, which caused problems in workability and scratch resistance, and that a satisfactory pre-coated steel plate could not be obtained. That is, when this pre-coated steel sheet is molded into various products, the paint film peels off, and scratches occur on the paint film during molding or when the product is used. In addition, it was found that the coating film itself had insufficient barrier properties against corrosive substances, and that consideration should therefore be given to the rust prevention properties of the steel plate.

Therefore, an object of the present invention is to provide a matte precoated steel sheet with excellent workability, scratch resistance, and corrosion resistance.

[Means for Solving the Problems] The pre-coated steel sheet of the present invention has an undercoat layer and a topcoat layer made of a matte paint, which are sequentially formed on the surface of a zinc-based plated steel sheet via a chemical conversion treatment layer using phosphate or chromate. The undercoat layer contains at least 10% by weight of a resin containing bisphenol A in its resin structure and having a weight average molecular weight of 1,000 to 60,000 based on the solid content of the paint resin, and a blocked isocyanate and/or amino resin as a solid content of the paint resin. It is characterized in that it is formed from a paint containing 10 to 40% by weight per minute.

The undercoat layer is preferably a coating film having a glass transition point of 30°C or higher.

Preferably, the top coat layer is made of one or more resins selected from polyurethane resins, polyester resins, acrylic resins, acrylic urethane resins, epoxy resins, and/or modified resins thereof, and has an average particle diameter of 20 to 150.
Colored spherical resin powder with a diameter of 30 to 8 μm is added to the solid content of the coating film.
It is formed by a paint containing 0% by volume, and this paint contains polyurethane resin, epoxy resin, acrylic resin,
It contains one or more of acrylic urethane resin, polyester resin, vinyl acetate resin, chloroprene resin, and/or modified resin thereof as a binder.

This invention will be explained in more detail below.

The present inventors applied a decorative paint containing colored elastic resin beads and an elastic resin binder to a steel plate to obtain a pre-coated steel plate with excellent practical performance such as paint film adhesion, workability, scratch resistance, and corrosion resistance. I researched as much as possible. As a result, the intended purpose was achieved by using a zinc-plated steel sheet as the steel sheet, and sequentially forming an undercoat layer on the surface of the sheet through a chemical conversion treatment layer using phosphate or chromate, and a topcoat layer using a matte paint. I found out what I can do.

First, the steel plate that becomes the substrate of the prepainted steel plate of this invention is
As mentioned above, it is a galvanized steel plate.

Such galvanized steel sheets include hot-dip galvanized steel sheets, alloyed hot-dip galvanized steel sheets, hot-dip Zn-A1 alloy-plated steel sheets, electrogalvanized steel sheets, electrolytic Zn-Ni plated steel sheets, and electric Zn-Mn plated steel sheets. , electric Zn-
Examples include Fe-plated steel plates. Prepainted steel sheets are usually cut and assembled into various products, so there are cut surfaces where the steel is exposed. Zinc plating is
Effectively prevents corrosion of the steel on its exposed surface.

The chemical conversion treatment applied to the zinc-based plated steel sheet is performed using phosphate or chromate. This phosphate and/or
Alternatively, the chemical conversion treatment with chromate can be carried out by a method known per se.

For example, examples of the phosphate treatment include zinc phosphate treatment, zinc calcium phosphate treatment, and manganese phosphate treatment. For chromate treatment, chromate, silica sol, phosphoric acid, acrylic resin, vinyl ester resin, vinyl acetate acrylic emulsion, carboxylated styrene butadiene latex, diisopropanolamine-modified epoxy resin, and other resins, hard silica, etc. Examples include coating type chromate treatment consisting of seeds or more, and electrolytic chromate treatment.

This chemical conversion treatment can impart strong adhesion to the zinc-based plating surface, which otherwise has poor adhesion to the undercoat. The chemical conversion treatment layer is usually 0.3g in the case of phosphate treatment.
/m2 to 3g/m2, and in the case of chromate treatment, it is 10mg/m2 to 150m in terms of metallic chromium.
It is formed with a coating weight of g/m2.

In this way, an undercoat layer is formed on the surface of the galvanized steel sheet on which the chemical conversion treatment layer has been formed. This undercoat layer is formed of a paint (undercoat) containing a resin having a weight average molecular weight of 1,000 to 60,000 and containing bisphenol A in its resin structure in an amount of 10% by weight or more based on the solid content of the paint resin. If the molecular weight of the bisphenol A-containing resin is less than 1000, the formed coating film will be hard and brittle, and the coating film will be likely to crack or peel during molding of a pre-coated steel sheet.

On the other hand, if the molecular weight exceeds 60,000, although it is preferable in terms of processability, coating properties deteriorate and coating becomes difficult. Moreover, if the blending amount is less than 10%, a coating film with good adhesion to both the top coating film and the base steel plate cannot be obtained.

Examples of bisphenol A-containing resins include bisphenol A epoxy resin, alkanolamine modified bisphenol A epoxy resin, polyethylene glycol modified bisphenol A epoxy resin, polyester modified bisphenol epoxy resin, bisphenol A modified polyester resin, and urethane modified bisphenol. It is an A type epoxy resin. These resins are bisphenol A1
In addition, the resin structure also contains a hydroxyl group.

The undercoat containing the above-mentioned bisphenol A-containing resin contains blocked inocyanate and/or amino resin as a curing resin in an amount of 10 to 40% by weight of the total resin solid content. If the amount of curing resin is less than 10%, the coating film will not be cured sufficiently, while if it exceeds 40%, the coating will be hard and brittle, which may cause cracking or peeling of the coating during the molding process of pre-coated steel sheets. arise.

Examples of blocked isocyanate resins include hexamethylene diisocyanate, metaxylene diisocyanate, dimeryl diisocyanate, isophorone diisocyanate, trile:/diisocyanate, diphenylmethane diisocyanate, or derivatives thereof.
It is a resin blocked with ε-caprolactam, methyl ethyl ketoxime, benzophenone oxime, etc.

Examples of the amino resin include benzoguanamine resin, dicyandiamide, urea resin, melamine resin, acetoguanamine resin, isomelamine resin, and derivatives thereof.

The undercoat layer after curing preferably has a glass transition temperature of 30°C or higher, usually from 30°C to 100°C.

Note that the undercoat may contain other resins as resin components in addition to the bisphenol A-containing resin and the curing resin. Furthermore, extender pigments such as talc, precipitated barium sulfate, silica, clay, calcium carbonate, titanium oxide, iron oxide, cyanine blue, quinacrid red,
One or more of color pigments such as carbon black, strontium chromate, barium potassium chromate, zinc chromate, lead chromate, orthophosphate, polyphosphate, calcium molybdate, zinc molybdate, etc. Can be blended.

This undercoat layer can be formed to a dry film thickness of 1 to 30 μm using a roll coater, a flow coater, an electrostatic airless coating machine, an air spray coating machine, or the like.

Now, on the undercoat layer thus formed, a normal decorative paint (top coat) containing colored elastic resin beads (spherical powder) and an elastic resin binder can be applied.
It is possible to provide a prepainted steel sheet having desired excellent performance. However, it has been found that when the top coat satisfies the following conditions, a more excellent pre-coated steel sheet can be obtained.

First, the average particle size of the colored spherical resin powder is set to 20 to 150.
μm, and the blending ratio is 30 to 8 μm based on the solid content of the coating film.
The content should be 0% by volume. If the average particle diameter is less than 20 μm, a coating film with a cloth-like soft feel cannot be obtained, and if it exceeds 150 μm, the coating film will be rough and non-uniform, resulting in poor decorative properties. Furthermore, if the amount is less than 30%, a coating film with a matte appearance cannot be obtained, and the coating film tends to become glossy and lose its cloth-like soft feel.

The colored spherical resin powder is composed of known polyester resins, polyurethane resins, acrylic resins, acrylic urethane resins, epoxy resins, and/or modified resins thereof, and is colored into a desired color with pigments or dyes. Note that it is preferable to mix 2F1 or more of the colored spherical resin powders, each colored in a different color.

Next, as the binder resin, polyurethane resin, epoxy resin, acrylic resin, acrylic urethane resin, polyester resin, vinyl acetate resin, chloroprene resin, and modified resins thereof are used. These binder resins adhere more firmly to the colored spherical resin powder and the undercoat layer.

The top coat layer is coated with a dry film thickness of 20 mm using a roll coater, flow coater electrostatic airless or air spray coating machine, etc.
It can be formed to a thickness of from 90μ to 90μ.

[Examples] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples of the present invention. In the following examples, the amounts of each component are parts by weight unless otherwise indicated.

Examples 1 to 10, Comparative Examples 1 to 4 Hot-dip galvanized steel sheets with a coating weight of 60 g/m (thickness 0
．． 5mm) with zinc phosphate (Nihon Bariki Rising Co., Ltd.)
Chemical conversion treatment using RBTIOI (manufactured by RBTIOI) was applied, resulting in a coating weight of 1.0.
A chemical conversion treatment layer of g/m2 was formed. On top of this chemical conversion treatment layer, an undercoat paint mainly composed of the blended resin shown in Table 1 below was applied using a bar coater to a dry film thickness of 1 to 30 μm, and Dry baked for seconds. Table 1 shows the glass transition temperature (Tg) of each undercoat film after dry baking.

For the top coat, an acrylic urethane resin clear paint (V Top Clear, manufactured by Dainippon Toyo Co., Ltd.) is used as the binder resin, and this paint contains colored spherical polyurethane resin powder (blue powder/white powder/ Red powder-315/2 (volume ratio)) was blended and dispersed in a proportion of 60% by volume of the solid content of the top coat. This top coat paint was applied onto the undercoat film using an electrostatic air spray coating machine so that the dry film thickness was 20 to 90 μm, and was dried and baked in an atmosphere at 120° C. for 20 minutes.

Table 2 shows the performance of the prepainted steel sheet thus obtained.

[Effects of the Invention] As described above, the precoated steel sheet of the present invention exhibits a matte color appearance with a cloth feel due to the colored spherical resin powder appropriately contained in the top coat layer, and moreover, The coating layer is tightly adhered to and integrated with the steel plate by appropriately selected base and undercoat coatings. Therefore,
The pre-coated steel sheet of this invention is less likely to cause peeling or damage to the coating film during bending, handling, transportation, etc., and is less likely to cause blistering of the coating film or rusting of the base steel even when used in a humid environment. This is an excellent pre-painted steel sheet with high practicality. Therefore, the prepainted steel sheet of the present invention can be advantageously used as a material for high-grade products that require decorativeness and decorative durability, such as interior and exterior materials for buildings, home appliances, vessels, and automobile interior materials.

Claims (4)

[Claims] (1) An undercoat layer and a topcoat layer made of a matte paint are sequentially formed on the surface of a zinc-plated steel sheet through a chemical conversion treatment layer using phosphate or chromate, and the undercoat layer is formed within the resin structure. By a coating material containing bisphenol A-containing resin having a weight average molecular weight of 1,000 to 60,000 in a proportion of 10% by weight or more based on the solid content of the coating resin, and a blocked isocyanate and/or amino resin in a proportion of 10 to 40% by weight based on the solid content of the coating resin. A prepainted steel plate characterized by being formed. (2) The precoated steel sheet according to claim 1, wherein the undercoat layer is a coating film having a glass transition point of 30°C or higher. (3) The topcoat layer is a colored spherical resin with an average particle diameter of 20 to 150 μm and is made of one or more of polyurethane resin, polyester resin, acrylic resin, acrylic urethane resin, epoxy resin, and/or modified resin thereof. 3. The precoated steel sheet according to claim 1, wherein the precoated steel sheet is formed from a coating material containing powder in a solid content of the coating film in an amount of 30 to 80% by volume. (4) The top coat layer is polyurethane resin, epoxy resin,
Any one of claims 1 to 3, which is formed from a paint containing as a binder one or more of acrylic resin, acrylic urethane resin, polyester resin, vinyl acetate resin, chloroprene resin, and/or modified resin thereof. Prepainted steel sheet according to item 1.