JPH0431037A - Low-gloss precoated steel plate - Google Patents

Abstract

PURPOSE:To obtain a low-gloss precoated steel plate having favorable scratch resistance and plate-out resistance, by applying and baking sequentially an under coating material containing a specified rust-preventive pigment, an intermediate coating material prepared to have a specified gloss, and a finish coating material having a low pigment content and a low gloss. CONSTITUTION:An undercost containing 5-60 phr of a rust-preventive pigment is overcoated sequentially with an intermediate coating material having a 60-degree specular reflectivity of 1-60% and a finish coating material having a 60-degree specular reflectivity of 1-15%. Where the surface of a plate to be coated is free of contaminants such as oil, the surface may be directly coated. It is preferable, however, to carry out a known pre-treatment for enhancing practical adhesion to a coat film and corrosion resistance. Examples of such known pre-treatment include phosphate conversion treatments, chromate conversion treatment, and coating with a chromic acid based coating agent. Where it is necessary to enhance coat film quality to provide excellent scratch resistance, an under coating material is applied to a pre-treated surface, and then the intermediate coating material and the finish coating material are applied.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a pre-coated steel sheet used for building materials such as roofs, storm shutters, exterior wall siding, shutters, etc., and metal products such as household appliances and fixtures. The present invention relates to a pre-coated steel sheet having a low gloss appearance that is resistant to scratches, particularly during handling or processing and forming.

[Conventional technology 1] Pre-painted steel sheets are coated on flat plate materials such as galvanized steel sheets, alloyed galvanized steel sheets, stainless steel sheets, aluminum steel sheets, etc. using a roll coater, curtain flow coater, etc., and then painted and baked, and then applied to roofs, storm doors, exterior wall siding, and shutters. In addition to being widely used in processing and molding, it is also used in metal products such as home appliances and fixtures. Compared to the so-called post-coating method, in which a steel plate is first formed into a complex shape and then painted, this type of pre-coated copper sheet has the advantage of streamlining the painting process, ensuring uniform quality, and reducing the use of paint. It has advantages such as increased efficiency.

Since such pre-painted steel sheets are molded after painting is baked, the paint for pre-painted E sheets is required to have good bendability, roll formability, embossing pressability, and drawing workability, and good adhesion to the metal base. is necessary.

On the other hand, in order to improve productivity, the coating speed has been increased to 100~
High-speed workability is required as the coating is carried out at a speed of 150 m/min. A uniform finished appearance is also required.

The prepainted steel sheet manufactured in this way cannot avoid warping, distortion, etc. of the sheet that occurs during processing and forming, or during construction, and the gloss may appear to change depending on the viewing angle after construction. One way to alleviate this problem is to use a pre-coated steel sheet with a low gloss appearance, which is coated with a low gloss appearance paint and baked.

On the other hand, when pre-painted steel sheets are processed and formed by roll forming, press forming, etc. after painting is baked onto a flat plate material, there is a problem in that the surface of the pre-painted steel sheets tends to be scratched by the metal of the forming machine. requires scratch resistance.

Conventional top coats are required to have hiding properties and weather resistance properties, and are generally used with a pigment content of 3 to 140 phr (% by weight per solid resin content: hereinafter referred to as phr). For example, 20 to 140 phr is used for inorganic pigments, and 3 to 20 phr for organic pigments.

Furthermore, the lower the gloss appearance, the rougher the unevenness on the surface of the steel sheet coating, the more likely it is that scratches from the metal of the molding machine will form, and the lighter the color, the more noticeable they will be.

In addition, when handling a pre-coated steel sheet with a low gloss appearance, in the case of a dark color, pigments may migrate from the coating surface to the worker's gloves, or coloration may occur on snow during construction. There is a problem in that an out phenomenon is observed.

In this way, low gloss steel sheets include general pre-painted steel sheets +
In addition to the required performance of the plate, scratch resistance and plate-out resistance are further issues that need to be solved.

Currently commercially available low-gloss precoated A plates still have some problems.

For example, it is disclosed in Japanese Patent Publication No. 50-25485 that low gloss can be obtained by incorporating glass fiber into a paint.

However, the scratch resistance was not sufficient in light colors that made scratches more noticeable.

In addition, pre-coated steel sheets using paint containing inorganic substances such as mica, alumina, and silica sand (Japanese Unexamined Patent Publication No. 60-40172) have sufficient scratch resistance and plate-out resistance. I can't say that it is.

[Problem to be solved by the invention]

The purpose of this invention is to produce a pre-coated A-board which has a low-gloss appearance, is resistant to scratches during processing and molding or construction, and does not cause plate-out among the pre-coated M-boards that require the above-mentioned performance.

[Means for Solving the Problems] According to the present invention, (a) an undercoat paint containing 5 to 5 Qphr of anticorrosive pigment (b) an intermediate paint with a 60° specular reflectance of 1 to 60% (c)
A low-gloss precoated steel sheet is provided, characterized in that it is formed by overcoating a top coat with a 60° specular reflectance of 1 to 15%.

The steel plates to be coated that can be applied to the present invention include cold rolled steel plates,
These include hot-dip (alloy) galvanized steel sheets, electrolytic (alloy) galvanized steel sheets, aluminum sheets, and stainless steel sheets.The coating method is curtain flow coater or roll coater.If painting is possible, long coils are used. It does not matter if it is a short sheet-shaped cutting board.

Furthermore, if the surface of the plate to be coated is not contaminated with oil or other contaminants, it may be painted as is, but for practical purposes, known pre-treatment is required to improve adhesion and corrosion resistance with the paint film. It is preferable to perform These known pretreatments include phosphate-based chemical conversion treatment, chromate-based chemical conversion treatment, and coating treatment with a chromic acid-based coating agent.

When it is necessary to improve the quality of a coating film that is less prone to scratching, which is the objective of the present application, an undercoat is applied after the pretreatment, and then an intermediate coat and a topcoat are applied. As the undercoat paint that can be used, any known undercoat paint currently used for colored steel plates can be used, and is appropriately selected depending on the type of steel material to be coated. In addition, an undercoat is necessary to provide anti-corrosion properties. For that purpose, add 5 to 60ph of anti-rust pigment.
It is essential to contain r. As the rust-preventing pigment, one or two types of chromate pigments such as strontium chromate, zinc chromate, and calcium chromate, and non-chromate pigments such as aluminum tripolyphosphate and calcium molybdate are used.

If the content is less than 5 phr, the rust prevention ability is insufficient;
If it exceeds 0 phr, performance such as boiling water resistance and water resistance will deteriorate. Epoxy and/or polyester resins and modified resins thereof are particularly suitable as the resin, and the film thickness is 1-1 O/Im. Furthermore, when processability is particularly required, polyester resins are suitable. If the primer coating has a film thickness of 1 μm or less, corrosion resistance and adhesion to the substrate will be poor, and if it has a film thickness of 10 μm or more, workability will deteriorate.

As an intermediate coating, a coating film with a 60 degree specular reflectance adjusted to 1 to 60% is required. As the resin system, well-known top coating resins currently used for colored steel plates, such as oil-free polyester resins, linear polymeric polyester resins, acrylic resins, and alkyd resins, can be used.

In order to improve the adhesion with the top coat, these intermediate coatings are coated with an inorganic gloss modifier with a particle size of 1 to 100 μl, such as silicon oxide, alumina, diatom, etc., to achieve a 60 degree specular reflectance of 1 to 60.
It is necessary to adjust to %.

If the particle size of the gloss adjusting agent is 1 μm or less, the gloss adjusting effect will be insufficient, and if it exceeds 100 μm, the coating workability will be poor, so it is inappropriate. If the 60 degree specular reflectance exceeds 60%, the surface roughness will be insufficient and adhesion with the top coat will not be obtained sufficiently, and if there are processing scratches, the difference in gloss with the top coat will be large, resulting in scars. It is noticeable and inconvenient. On the other hand, if it is less than 1%, the coating film will become weak and processability will deteriorate.

Further, the pre-coated steel sheet is colored with an intermediate coating, and the intermediate coating contains a known coloring pigment. for example,
These include rutile titanium oxide, carbon black, iron oxide pigments, phthalocyanine, and quinacridone. The pigment content in the intermediate coating is preferably 4 to 150 phr.

The film thickness of the intermediate coating is preferably 8 to 25 μm; if it is less than 8 μm, it is difficult to obtain a desired hue, and long-term durability such as corrosion resistance is poor. If it exceeds 25 μm, it is not preferable because it tends to cause a decrease in workability.

If necessary, known antifoaming agents, leveling agents, etc. can be used in combination with the intermediate coating material.

The function of the top coat is to provide scratch resistance and plate-out resistance. For this purpose, the pigment content in the top coat is 3 to 40 phr. If the pigment content exceeds 40 phr, the scratch resistance and plate-out resistance will be poor and the purpose cannot be achieved. If it is less than 3 phr, a gloss window will appear and the initial purpose will not be met. The types of pigments used include rutile titanium oxide, ultrafine titanium oxide with low hiding power, carbon blank, iron oxide pigments, phthalocyanine, and quinacridone. Resin-based paints include oil-free polyester resin paints, linear polymer polyester resin paints,
Acrylic resin paint, alkyd resin paint, silicone polyester resin paint, and silicone acrylic resin paint can be applied.

If necessary, known antifoaming agents, leveling agents, ultraviolet absorbers, etc. can be used in combination with the top coating.

The top coat is applied with the 60 degree specular reflectance adjusted to 1 to 15%. If the 60 degree specular reflectance is 15% or more, the light/
R9 came out and the initial objective could not be satisfied. If it is less than 1%, the coating film becomes brittle, has poor workability, and has poor scratch resistance. Further, the gloss is adjusted by using an inorganic gloss adjusting agent having a particle size of 1 to 100 μm, such as silicon oxide, alumina, diatom, etc. If the particle size of the gloss adjusting agent is less than 1 μm, the gloss adjusting effect tends to be insufficient, and if the particle size exceeds 100 μm, the coating workability will be poor and therefore it is inappropriate. The film thickness of the top coat is 2~
The film thickness is preferably 25 μm; if it exceeds 25 μm, workability tends to deteriorate, and if the film thickness is less than 2 μm, weather resistance tends to be poor.

Ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, neopentyl glycol, 1.2-1.8-2.
3-1.4 butanediol, ■, 5-bentanediol, 16-hexanediol, hydrogenated bisphenol A,
Hydroxyalkylated bisphenol A, 1.4 cyclohexane dimetatool, 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl 3-hydroxypropionate (BASHPN), NN-bis-(2-hydroxyethyl) Dimethylhydantoin, polytetramethylene ether glycol, polycaprolactone polyol, glycerin, sorbitol, annitol, trimethylolethane, trimethylolpropane, trimethylolbutane, hexanetriol, pentaerythritol, dipentaerythritol, tris-(hydroxyethyl)isocyanate, etc. One or more of these may be used.

Examples of polybasic acids include phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, methyltetrahydrophthalic acid, methyltetrahydrophthalic anhydride, hymic anhydride, and trihydrophthalic anhydride. Mellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, isophthalic acid, terephthalic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, adipic acid, mazelaic acid, sebacic acid, succinic acid, succinic anhydride Acid, lactic acid, dodecenyl succinic acid, dodecenyl succinic anhydride, cyclohexane-1
, 4-dicarboxylic acid, endoacid anhydride, and the like can be used. As a polyester resin, the molecular weight is 3
,000 to io, ooo, acid value of 1 to 30 and hydroxyl value of 10 to 250 (per solid content).The resin may contain oil or fatty acid of 30 to 30% if necessary.
It is possible to impart flexibility by adding up to about %.

In addition, organic silicone 5 is added to the above polyester resin.
It is also possible to use silicone polyester resins obtained by reacting up to 50% by weight.

The acrylic resin used in the present invention can be obtained, for example, by polymerizing the following monomers by a conventional method.

(1) Ethylene monomers having a hydroxyl group such as hydroxylmethyl (meth)acrylate, hydroxyl ethyl (meth)acrylate, hydroxylpropyl (meth)acrylate, hydroxylbutyl (meth)acrylate, and N-methylolacrylamine ( 2) (meth)acrylic acid, crotonic acid, itaconic acid,
Ethylenic monomers having carboxyl groups such as fumaric acid and maleic acid (3) Methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl acrylate, n-propyl acrylate, acrylic n-butyl acid,
Ethylene that can be copolymerized with monomers (1) and (2) such as (meth)acrylic acid alkyl esters such as isobutyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, and n-dodecyl acrylate. and (4) (meth)acrylonitrile, styrene, etc. are used.

The molecular weight of the acrylic resin preferably used in the present invention is 5000 to 30.000 in terms of number average molecular weight.

In addition, organic silicone has a content of 5 to 50% compared to the above acrylic resin.
A silicone acrylic resin obtained by reacting % by weight can be used.

The hardening side that can be used in the present invention includes:
Examples include melamine resins such as n-butylated melamine resin and isobutylated melamine resin, and melamine resins such as Hend's guanamine resin. These resins are usually obtained by addition reaction or addition condensation reaction of an aldehyde such as formaldehyde or paraformaldehyde to an amino compound such as melamine or Henzuguanamine, and a carbon number 1.
It is obtained by etherification with a monohydric alcohol of ~4.

Specific examples of melamine resins include alkinomethylmelamine resins in which the alkoxy group is a methoxy group, ethoxy group, n-butquine group, -butoxy group, or the like.

When using these melamine resins as crosslinking agents for polyester resins, polyester resin/amino resin-6/
A ratio (weight ratio) of 4 to 8/2 is suitable.

As the crosslinking agent component of the acrylic resin, amino resins, particularly melamine resins, urethane resins, etc. can be used. The ratio (weight ratio) of acrylic resin/melamine resin is 9/1 to 6/4, preferably 8/2 to 7/3.

Urethane resins include HMDI, IPDI, and TDI.
Block type isocyanate compounds such as , naphthalene diisocyanate and the like can be used, and MEK oxime and the like are commonly used as blocking agents. When these urethane resins are used as crosslinking agents, the -NCO/-0)1 equivalent ratio is preferably from 6/4 to 2/8.

The present invention is not just a three-coat matte coating, but a primer that provides anticorrosion properties, and an intermediate coating that colors the coating, and a topcoat that has a relatively low pigment content and does not have sufficient hiding power. The coating satisfies the scratch resistance and plate-out resistance.In other words, the scratch resistance and plate-out resistance are determined by the amount of pigment normally used in the paint film to provide hiding power. We discovered that if there were any problems, we were not satisfied with the results, and developed a 3-coat system to achieve the original objectives of a paint film: corrosion resistance, aesthetics, and weather resistance under low-gloss coatings.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but it goes without saying that the scope of the present invention is not limited to these Examples.

1 to 6 and 1 to 3 As shown in Table 1, material GI (galvanized steel plate/fabric weight Z25. plate thickness 0.35 mm), aluminum plate (plate thickness 0.4 mm) and stainless steel plate (S (1s304. plate thickness) 0.3501111) was pretreated as shown in Table 1, and the undercoat, intermediate coat, and topcoat were applied.The baking conditions were the highest board temperature reached for each, undercoat at 200°C, intermediate coat at 210"C.
1 Top coat was applied at 220°C.

Further, various evaluations shown in Table 2 were performed on the obtained coating film. The results are also shown in Table 2.

The above test pieces were prepared by carrying out predetermined treatment and drying to obtain coated steel plates.

In the present invention, a copper plate is subjected to a known pre-painting treatment, an undercoat containing an anti-rust pigment is baked, and the gloss is increased to 1 to 60.
A low gloss Pre2 1-E with good scratch resistance and plate-out resistance that can be obtained by baking an intermediate coat adjusted to % and then baking a low gloss top coat with a low pigment content. It is an industrially useful invention that can be expected to provide better performance than conventional prepainted steel sheets without degrading the performance of conventional prepainted steel sheets.

Claims (1)

[Scope of Claims] 1. (a) Undercoat paint containing 5 to 60% by weight of anti-rust pigment based on solid resin content (b) Intermediate paint with 60° specular reflectance of 1 to 60% (c)
A low-gloss precoated steel sheet characterized by being formed by overcoating a top coat with a 60° specular reflectance of 1 to 15%.