JPH1034823A - Precoating steel sheet with excellent stain resistance and nonstickiness - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve stain resistance and nonstickiness in a precoating steel sheet having an overcoating film formed to contain polyester resin as a main component. SOLUTION: An overcoating film is formed by coating with polyester resin paint added with amino modified silicone oil containing 0.2 to 1.0wt.% of paint solid content and melamine hardener of 0.5 to 3.0wt.% excess to reaction equivalent with polyester resin, and drying it. Surface free energy of the film is set to 25 to 38erg/cm<2> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a precoated steel sheet having a polyester resin as a main component and having improved stain resistance and non-adhesion.

[0002]

2. Description of the Related Art Exterior members of home electric appliances, such as washing machine outer plates and range hood interior materials, have conventionally been manufactured by processing pre-coated steel plates for rationalization. Therefore, a precoated steel sheet whose top coat is mainly composed of a polyester resin having excellent workability is used as the precoated steel sheet. However, in recent years, the precoated steel sheet is required to be more and more excellent in workability in accordance with the sophistication of processing and the complexity of the shape of the exterior member.

In general, to improve the workability of a coating film, it is only necessary to lower the hardness of the coating film. However, when the hardness of the coating film is reduced, stain resistance and non-adhesiveness are reduced, and a clean feeling is always obtained. It becomes difficult to use the necessary home electric appliances as exterior members. In view of the above, various types of polyester-based resin coatings having improved stain resistance and non-adhesion have been proposed.

[0004] For example, the number average molecular weight of 15,000-30,
000 polyester resin and hexamethoxymethylol melamine resin in a weight ratio of 75/25 to 55/45, and 100 parts by weight of a polyester melamine resin, 1 to 2 parts by weight of an amino block of dodecylbenzenesulfonic acid. Part of a coating film (Japanese Patent Publication No. 6-8400) or 100 parts by weight of an amino resin,
5 to 100 parts by weight of a silicone-modified amino resin modified with 0.1 to 100 parts by weight and a number average molecular weight of 1
A coating film consisting of 100 to 100 parts by weight of a polyester resin or an acrylic resin of 000 to 100,000 (Japanese Patent Publication No. 4-76)
075).

[0005] However, these coatings have improved stain resistance, which allows the adhered substances to be washed away with a solvent or the like, but still have insufficient non-adhesiveness to remove the adhered substances by wiping.
For example, after drawing with a Q-mark felt pen on the coating film,
Can remove most of the ink,
Just wiping with an ink leaves ink.

[Problems to be solved by the invention]

[0006] The present invention provides a precoated steel sheet having improved anti-adhesion as well as stain resistance.

[0007]

According to the present invention, there is provided a precoated steel sheet having an overcoating film containing a polyester resin as a main component.
Applying a polyester resin paint to which 0.5% to 3.0% by weight of melamine hardener is added in excess of the reaction equivalent of 0% by weight of amino-modified silicone oil and polyester resin;
Formed by drying, surface free energy of coating film
Was to 25~38erg / cm ^2.

[0008]

Generally, the activity of a coating film is determined by the surface free energy.
It is said that the smaller the value is, the more inert the surface is, the less the dirt adheres, and the easier it is to wipe off even if it adheres. Therefore, it is said that reducing the surface free energy can improve both stain resistance and non-stickiness. However, in the case of a polyester resin coating film, even if the surface free energy is simply reduced, the stain resistance and the non-adhesiveness cannot be simultaneously improved. The present inventors have found that the physical properties are deteriorated and it is difficult to use them for exterior members of home electric appliances.

For example, in the case of a polyester resin coating film,
If the melamine curing agent is added to the paint in excess of the reaction equivalent to the resin, the surface free energy can be reduced, but when the coating is cured, the excess melamine curing agent self-condenses, and the coating hardness increases. And workability deteriorates. It is also known that the addition of silicone oil can reduce the surface free energy, but since silicone oil has poor compatibility with polyester resins, it may bleed to the surface of the coating film during curing of the coating film. Repelling occurs, and the appearance of the coating film becomes crumple.

Therefore, the present inventors have studied additives which can simultaneously improve stain resistance and non-stickiness without impairing the processability and appearance of the coating film. It has been found that a desired coating film can be formed if the latter is used in combination and the latter is used in excess of the equivalent of the polyester resin.

In the present invention, the stain resistance and non-adhesiveness are improved without impairing the processability and appearance of the coating film because the amino-modified silicone oil and the melamine curing agent are rich in reactivity, so It is presumed that the added melamine hardener reacts with the amino-modified silicone oil to prevent a reduction in coating processability, a bleed of the amino-modified silicone oil and a reduction in the appearance of the coating. For this reason, the addition amounts of the amino-modified silicone oil and the melamine curing agent need to be coordinated.

When the amount of the amino-modified silicone oil is less than 0.2 wt% of the solid content of the paint, that is, less than 0.2 wt% of the coating film, it shows almost the same stain resistance and non-adhesiveness as the non-added polyester resin. When the content exceeds 0.0 wt%, the non-adhesiveness is slightly improved, but the stain resistance is not improved, and bleeding to the surface of the coating film, deterioration in workability of the coating film and deterioration in appearance are caused. For this reason, the amount of addition is set to 0.2 to 1.0% by weight of the solid content of the paint.

The amino-modified silicone oil is obtained by introducing one or more amino groups into a polysiloxane, and the amino group may be introduced at a side chain, at a terminal, or at both of them. The amount of modification with an amino group may be appropriately selected,
If the modification amount is high, the compatibility with the polyester-based resin decreases, so that the modification amount is preferably low.

On the other hand, the melamine curing agent is added in an amount of 0.5 to 3.0 wt% in excess of the equivalent of the reaction with the polyester resin. When the content is less than 0.5 wt%, only stain resistance and non-adhesiveness which are almost the same as in the case of no addition are exhibited, and 3.
If the content exceeds 0 wt%, the stain resistance and the non-adhesiveness are improved, but the workability of the coating film is lower than in the case where no addition is made. As the melamine curing agent, methylated melamine,
Butylated melamine may be used.

The total amount of both additives is adjusted so that the surface free energy of the coating film is 25 to 38 erg / cm ² . The surface free energy of the polyester resin without addition is about 44 erg / cm ² , but 38 erg / cm ^2.
When it is less than cm ² , improvement in stain resistance and non-adhesion is clearly recognized. However, when it is less than 25 erg / cm ² , repelling or the like occurs at the time of coating, and the coating film is not uniform or the appearance is deteriorated.

[0016]

EXAMPLE A galvanized steel sheet (plate thickness 0.5 mm, zinc adhesion amount 45 g / m ² ) was subjected to a coating type chromate treatment.
Primer paint of polyester resin with dry film thickness of 5
μm, and baked and dried at 215 ° C. for 50 seconds, and then overcoated with a polyester-based resin to which an amino-modified silicone oil and a melamine resin curing agent were added in various ratios to a dry coating thickness. It was applied to a thickness of 16 μm and baked and dried at 230 ° C. for 60 seconds. The coated steel sheet thus obtained was examined for coating film workability, stain resistance and non-adhesion in the following manner. Table 1 shows the additives to the paint and the free energy of the coating surface.
Shows the coating film performance.

(1) Workability A steel plate having the same thickness was sandwiched inside and bent at 180 ° C. at room temperature of 20 ° C., and the minimum number of sandwiches (T) at which cracks did not occur in the coating film was evaluated. (2) Stain resistance Apply the ink with a Q-mark felt pen (red, black, blue) and leave it in a constant temperature and humidity room at 20 ° C and a relative humidity of 65% for 24 hours, then wipe off the ink with ethanol. The remaining state of the ink is visually observed, and the colorless residue is marked with ◎
Those with slight residual color were evaluated with the symbol 、, those with residual color were evaluated with the symbol 、, and those without color fading were evaluated with the symbol x.

(3) Non-adhesiveness Instead of wiping with ethanol for stain resistance, empty wiping with dry gauze was performed and evaluated according to the same standard. (4) Appearance of the coating The surface of the coating was visually observed, and a good one was evaluated with the symbol 、, a slightly defective skin with the symbol △, and one with a remarkably smooth skin was evaluated with the symbol ×. did.

[0019]

[Table 1] (1) The symbol A of the silicone oil is an amino-modified silicone oil with a small amount of modification, B is an alkyl-modified silicone oil, C is an amino-modified silicone oil with a large amount of modification,
The addition amount is a ratio to the solid content of the paint. (2) The melamine curing agent is a butylated melamine resin, and the amount of the melamine curing agent is an excess amount with respect to the reaction equivalent to the polyester resin.

[0020]

[Table 2]

[0021]

As described above, according to the present invention, it is difficult to simultaneously improve the stain resistance and the non-adhesiveness by adding the precoated steel sheet alone to the polyester resin top coat. The combination of silicone oil and melamine curing agent improved both disadvantages due to the synergistic effect.
The appearance and workability of the coating film do not deteriorate and there is no bleeding of silicone oil.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B32B 27/26 B32B 27/26 (72) Inventor Hiromitsu Fukumoto 7-1, Takatani-shinmachi, Ichikawa-shi, Chiba Nisshin Steel Co., Ltd.

Claims (1)

[Claims] 1. A precoated steel sheet on which an overcoating film containing a polyester resin as a main component is formed, wherein the overcoating film is made of an amino-modified silicone oil having a coating solid content of 0.2 to 1.0% by weight and a polyester resin. It is formed by applying and drying a polyester resin paint containing a melamine curing agent in an amount of 0.5 to 3.0 wt% excess from the reaction equivalent to the resin, and has a surface free energy of 25 to 38 erg /
Pre-coated steel sheet excellent in stain resistance and non-adhesiveness, characterized in that the steel sheet has a diameter of ² cm ² .