JPH06220355A - Primer coating and method for producing coated steel plate using the same - Google Patents

Abstract

PURPOSE:To prepare the subject new coating capable of being thickly coated and forming flexible coating films excellent in moldability, etc., and giving coated steel plates having excellent moldability, corrosion resistance and adhesivity by adding a pigment to a vehicle having a specific composition. CONSTITUTION:This new coating comprises 100 pts.wt. (as solid content) of a vehicle comprising (A) 50-90wt.% (as solid content) of a linear polyester resin having a hydroxyl group value of 8-25mgKOH/g and (B) 50-10wt.% (as solid content) of the 50:50 to 80:20 weight ratio mixture of an epoxy resin and a melamine resin as a main component, and (C) 40-100 pts.wt. of a pigment. The component A has preferably a number-average mol.wt. of 5000-25000 and a glass transition point of 10-50 deg.C. The epoxy resin in the component B has preferably a number-average mol.wt. of 400-27000 and an epoxy equivalent of 200-2000, and the melamine resin is preferably a methylated melamine resin, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel undercoat paint and a method for producing a coated steel sheet using the same. More specifically, the present invention relates to a thick coating type undercoating paint having excellent forming processability and corrosion resistance, and a method for producing a coated steel sheet using the undercoating paint.

[0002]

2. Description of the Related Art A coated steel sheet having a thickness of 0.3 to 0.8 mm, which is generally called a pre-coated steel sheet, is cut and formed into a desired use for a roof or a building. It is currently widely used in parts such as exteriors that require long-term durability, electrical equipment, indoor equipment, vehicle interiors, building interiors, and the like. When the coated steel sheet is formed and processed, the cut end surface is always exposed. Even in a construction property, the cut end face is the site where blisters and rust are most likely to occur. Generally, as a coated plate used for a coated steel plate, a cold rolled steel plate, a galvanized steel plate, an aluminum / zinc alloy plated steel plate, a stainless steel plate, an aluminum plate, a metal plate such as an aluminum alloy plate, or the like is used. As a general coating method of a coated steel sheet, a method of applying an undercoat paint having adhesiveness and anticorrosive property once or twice and then applying a finish paint once or twice is adopted. As the finish paint, there are cases where only the topcoat paint is used and cases where the intermediate paint and the topcoat paint are combined. In this case, as the undercoat paint to be used, a paint mainly containing an epoxy resin is predominant. As such a conventionally known technique, Japanese Patent Publication No. 63-
11950, JP-A-59-179340,
Japanese Examined Patent Publication No. 3-11266, Japanese Unexamined Patent Publication No. 2-174977.
It is disclosed in Japanese Patent Publication No. In addition, JP-A-2-233
Japanese Patent No. 183 discloses an undercoat paint of an acrylic modified polyester resin. However, the undercoat paint mainly composed of the above-mentioned epoxy resin has a hard coating film, and when an attempt is made to make it thicker, a side effect occurs during baking of the coating film,
There are problems such as cracks during molding. Therefore, in order to maintain good moldability and adhesiveness, it is possible to apply a coating film thickness of at most about 10 μm. Further, in the undercoat paint of the above acrylic modified polyester resin, the main vehicle is obtained by chemically bonding an acrylic component to the polyester resin, and when the undercoat paint is applied, the dry coating film thickness is 5 to 15 μm. However, it is described that if the coating is made thicker, there is a tendency for armpits to occur, which is not preferable. 15 undercoat paint
If it is as thin as less than μm, even if the intermediate coating and top coating are applied over it, moisture will easily penetrate into the coating, and the cut end surface and the processed part will easily swell, exhibiting the original corrosion resistance. Can not do it.

[0003]

Under the above circumstances, the present invention provides a coating film thickness of about 30 μm with one coating, is excellent in moldability, and has a cut end face and a scratched portion. The undercoating paint that can also exhibit the corrosion resistance of the forming part, and by using this undercoating paint, the purpose was to provide a coated steel sheet having excellent forming workability, adhesion, and corrosion resistance. is there.

[0004]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that a specific linear polyester resin and a predetermined proportion of an epoxy resin and a melamine resin are used as a color-developing agent. Found that the object can be achieved by the undercoat paint containing a predetermined amount of a pigment containing a mixture of a predetermined proportion,
The present invention has been completed based on this finding. That is, in the present invention, the solid content is (A) hydroxyl value of 8
~ 25mgKOH / g linear polyester resin 50 ~ 90
%, And (B) 50 to 50% by weight of a mixture of (B) an epoxy resin and a melamine resin in a weight ratio of 50:50 to 80:20, as a main component, and a solid content of the colorant of 100% by weight. The present invention provides an undercoat paint containing 40 to 100 parts by weight of a pigment for each part, and a method for producing a coated steel sheet using the undercoat paint.

The present invention will be described in detail below. In the undercoat paint of the present invention, (A) a linear polyester resin (polymer polyester resin mainly having a linear structure) and (B) a mixture of an epoxy resin and a melamine resin are used as the main components of the color developing agent. . The linear polyester resin as the component (A) has a hydroxyl value of 8 to 25 mg KOH.
It is necessary to use those having a number average molecular weight of 5,000 to 25,000 and a glass transition point of 1
Those in the range of 0 to 50 ° C. are preferable. Examples of such a linear polyester resin include commercially available products such as Byron 59CS, GK13CS [manufactured by Toyobo Co., Ltd., trade name], Beckolite M-6801-30 [manufactured by Dainippon Ink and Chemicals Co., Ltd., trade name] ]and so on. In the linear polyester resin, if the number average molecular weight is less than 5,000, the coating film is excessively hardened to lower the processability.
If it exceeds 5,000, a large amount of solvent is required to dissolve the resin, and the solid content of the coating becomes low, making it difficult to thicken the coating film. Also, the glass transition point is 1
If the temperature is lower than 0 ° C, the hardness of the coating film decreases, and if it exceeds 50 ° C, the moldability decreases. Further, if the hydroxyl value is less than 8 mgKOH / g, the coating film crosslink density will be insufficient, and the coating material applied on it will be easy to open during baking and drying. If it exceeds 25 mgKOH / g, the coating film crosslink density will be high, and molding processing Sex decreases. On the other hand, the epoxy resin used as one component of the component (B) has a number average molecular weight of 400 to 2,700 and an epoxy equivalent of 200.
Those in the range of to 2,000 are preferred. Such an epoxy resin is commercially available as Epicoat # 8.
28, # 834, # 1001, # 1004, # 1007
[Yukaka Shell Epoxy Co., Ltd., trade name] etc. Further, as the melamine resin used as the other component of the component (B), a methylated melamine resin or a butylated melamine resin compatible with the above linear polyester resin is preferable.

In the color developing agent in the undercoat paint of the present invention, the component (A) linear polyester resin and the component (B) are used.
The mixing ratio of the mixture of the component epoxy resin and the melamine resin is such that the solid content of the component (A) is 50 to 90.
It is necessary that the weight% and the component (B) are in the range of 50 to 10 weight%. The mixing ratio of the epoxy resin as the component (B) and the melamine resin is 50: 5 by weight.
It must be in the range 0 to 80:20. If the content of the component (A) is less than 50% by weight, it will be 1 of the undercoat paint.
It is difficult to obtain a dry coating film with a thickness of about 30 μm by repeated coating,
In addition, the moldability is poor, and when it exceeds 90% by weight (B)
Since the resin amount of the component is insufficient and the adhesiveness to the substrate is lowered, neither of the objects of the present invention can be achieved. Pigments such as rust preventive pigments, coloring pigments and extender pigments are used in the undercoat paint, and solvents and various additives generally used in paints can be added. As the rust preventive pigment, a chromic acid-based rust preventive pigment, that is, strontium chromate, calcium chromate, barium chromate, zinc chromate and the like can be used, but strontium chromate is most suitable. Examples of extender pigments include calcium carbonate, clay, talc, synthetic silica, natural silica,
Antimony trioxide, barium sulfate, precipitated barium sulfate, kaolin and the like can be used. The addition amount of all pigments is selected in the range of 40 to 100 parts by weight with respect to 100 parts by weight of the solid content of the color spreader. If the amount is less than 40 parts by weight, the side wall is liable to be generated and sufficient anticorrosive force cannot be obtained, and if the amount exceeds 100 parts by weight, the bending workability is deteriorated and the corrosion resistance of the processed part is deteriorated. As the solvent, an aromatic hydrocarbon solvent such as toluene or xylene, ethyl acetate, butyl acetate, cellosolve solvent, methyl isobutyl ketone, isophorone, cyclohexanone or the like can be used. As described above, the undercoat paint of the present invention uses the linear polyester resin that forms a more flexible coating film as the main component of the color-developing agent, thereby suppressing the occurrence of armpits and applying a single coating solution of about 30 μm. Thick coating is possible, and even in a thick film having a thickness of about 60 μm for double coating, excellent moldability is provided, and the original corrosion resistance can be sufficiently exhibited.

Next, a method for manufacturing a coated steel sheet according to the present invention will be described. First, examples of the coated plate to be used include metal plates such as cold rolled steel plate, galvanized steel plate, aluminum / zinc alloy plated steel plate, stainless steel plate, aluminum plate, and aluminum alloy plate. A hot dip galvanized steel sheet, a 5% aluminum / zinc alloy plated steel sheet, and a 55% aluminum / zinc alloy plated steel sheet are preferable in terms of excellent corrosion resistance. The surface of the coated plate can be subjected to a chemical conversion treatment prior to coating in consideration of adhesion to the coating film and the like. As the chemical conversion treatment,
Generally used as a coating base treatment,
Zinc phosphate treatment or coating type or reactive type chromate treatment can be preferably applied to hot dip galvanized steel sheet, 5% aluminum / zinc alloy plated steel sheet, and coating type to 55% aluminum / zinc alloy plated steel sheet. Alternatively, reactive chromate treatment can be preferably applied. As a method for coating a coated steel sheet, first, the undercoat paint described above is applied by roller coating so that the dry coating film thickness becomes about 20 to 30 μm, and the plate temperature is reached at 250 ± 10 ° C. to heat and dry. When the undercoat paint is applied twice, the above steps can be repeated to obtain a total film thickness of about 40 to 60 μm. Then, apply the topcoat paint by roller coating 1
It is applied so that the dry coating film thickness is about 10 to 30 μm per re-coating, and it is heated and dried at the reached plate temperature ± 10 ° C. of each type of top-coat paint. When the top coating composition is applied twice, the above steps can be repeated to obtain a total coating thickness of about 20 to 40 μm. As described above, by applying 2c2b (2 coat 2 bake) to 4c4b of the undercoat paint and the topcoat paint, a coated steel sheet having a total coating film thickness of about 40 to 100 μm can be obtained. As the top-coat paint used in the above method, polyester resin-based paints, acrylic resin-based paints, polyvinylidene fluoride resin-based paints, silicone polyester resin-based paints, alkyd resin-based paints, and the like can be used. However, as the topcoat paint to be used in combination with the thick coat type undercoat paint of the present invention which is particularly excellent in moldability, a polyvinylidene fluoride resin-based topcoat paint excellent in durability and flexibility is most preferable. The performance of the base coating film is maximized.

[0008]

The present invention will be described in more detail by way of examples, which should not be construed as limiting the invention thereto. The performance of the coated steel sheet was evaluated as follows. (1) Workability test The workability of each test piece cut into a width of 5 cm was tested in a room at 20 ° C. 2T in the table means that two sheets of the same coated plate as the test piece to be processed are sandwiched inside (OT is the test piece as it is) and the coating film is placed outside and bent 180 degrees. Observe the bent tip with a magnifying glass 10 times,
The following criteria were evaluated. ⊚: No cracks ◯: Cracks 10% or less (pass) Δ: Cracks more than 10% and less than 50% (fail) ×: Cracks 50% or more (2) Impact deformation test JIS K-5400 (1979) ) The method of 6.13.3B was applied, the weight was 1 kg, the height was 50 cm, and the coated surface of the test piece was tested upward and downward, and evaluated according to the following criteria. ◎: No peeling of cellophane tape ○: 10% or less of cellophane tape peeling area (pass) △: More than 10% and less than 50% of cellophane tape peeling area (fail) ×: 50% or more of cellophane tape peeling area

(3) Boiling water resistance test After the test piece was immersed in boiling water for 5 hours, the presence or absence of abnormality in the coating film was visually observed and evaluated according to the following criteria. ○: No abnormalities on the coated surface (pass) △: Slight blistering is recognized (fail) x: Clear blistering is recognized (4) Corrosion resistance test Specimens processed at each level depending on the type of topcoat paint , JIS Z-2371 (salt spray test)
In accordance with the above, a test was conducted for 2,500 hours, (a) the blister generation state of the flat surface portion, (b) the blister generation state of the processed portion, and (c) the blister generation state of the cross-cut portion were observed, and evaluated according to the following criteria. ○: No abnormalities on the coated surface (pass) △: Slight blisters are recognized (fail) x: Blisters and white rust are recognized Further, (d) The blister generation width from the end face of the cut is measured and is 6 mm or less. Was accepted.

(5) Presence or absence of armpits When a test piece was prepared, the presence or absence of armpits was observed on the coated surface at the time of drying each of the undercoat and topcoat, and the evaluation was made according to the following criteria. ◯: No abnormalities on the coated surface (pass) Δ: Slight blistering is recognized (fail) X: Clear side is recognized Note that other test is no longer performed on the test piece that has a side arm and fails. It was (6) Adhesion test First, JIS K-54 was applied to the test piece coating film in a room at 20 ° C.
According to the method of 6.15 (cross-cut test) of No. 00, a cross-cut is made with a cutter knife, and the test piece is extruded by an Erichsen tester by 6.0 mm from the back surface of the part. After that, sufficiently adhere the cellophane adhesive tape on the grid and immediately immediately peel off the cellophane tape in the direction perpendicular to the coating surface, pass the grid with 100 grids remaining without peeling, 9
9 or less was rejected.

Preparation Example 1 Preparation of Undercoat Paint According to the formulation shown in Table 1, first, a linear polyester resin and a part of a mixed solvent were mixed, and then a pigment was added and uniformly mixed, and then an attritor was used. Particle size 30μm
Dispersed below. Furthermore, after adding epoxy resin, melamine resin and acid catalyst, appropriately add the remaining mixed solvent,
Viscosity for Ford Cup # 4 120 ± 10 seconds (25 ℃)
And 13 types of undercoat paints U1 to U13 were prepared. Note that U1 to U5 are undercoat paints according to the present invention, and U6 to U13 are undercoat paints for comparative samples.

[0012]

[Table 1]

[0013]

[Table 2]

Note 1) Byron 59CS [trade name of Toyobo Co., Ltd. Number average molecular weight; 5000-80
00, non-volatile content; 50 wt%, hydroxyl value; 12-22 mgKOH
/ G, glass transition point 15 ° C.] 2) Byron GK13CS [trade name of Toyobo Co., Ltd.] Number average molecular weight; 5000-80
00, nonvolatile content; 50 wt%, hydroxyl value; 16-25 mg KO
H / g, glass transition point 24 ° C.] 3) Beckolite M-6801-30 [trade name of Dainippon Ink and Chemicals, Inc.]. Number average molecular weight; 1
5000, non-volatile content; 30 wt%, hydroxyl value; 8-15 mg
KOH / g, glass transition point 30 ° C.) 4) Byron 29XS [trade name of Toyobo Co., Ltd.] Number average molecular weight; 20000-2
5000, nonvolatile content; 35 wt%, hydroxyl value; 5-8 mg KO
H / g, glass transition point 70 ° C.] 5) Byron 51CS [trade name of Toyobo Co., Ltd.] Number average molecular weight; 20000-2
5000, non volatile matter; 40wt%, hydroxyl value; 5-8mgKOH
/ G, glass transition point 4 ° C.] 6) DYNAPOL LH812 [trade name of Dynamit Nobel Co., Ltd. Number average molecular weight; 300
0, non-volatile content: 60 wt%, hydroxyl value: 35 mg KOH / g, glass transition point 30 ° C. 7) Epicoat 1001 [trade name of Yuka Shell Epoxy Co., Ltd. Nonvolatile matter: 60wt
%, Epoxy equivalent; 450 to 500] 8) Epicoat 834 [trade name of Yuka Shell Epoxy Co., Ltd. Nonvolatile matter: 50wt
%, Epoxy equivalent; 225 to 280] 9) Epicoat 1007 [trade name of Yuka Shell Epoxy Co., Ltd. Nonvolatile matter; 50wt
%, Epoxy equivalent; 1750 to 2700] 10) Sumimar M55 [trade name of Sumitomo Chemical Co., Ltd.] Nonvolatile matter; 70 wt% butanol solution] 11) Solvesso # 150 / cyclohexanone = 50/5
0 (wt%) 12) p-toluenesulfonic acid, 20 wt% solution

Examples 1 to 17 and Comparative Examples 1 to 22 Coating plates shown in Tables 2 to 5 (all have a thickness of 0.4 mm)
In accordance with the type of paint, the number of times of coating, the coating thickness and the baking temperature shown in Tables 2 to 5, the undercoat paint and the topcoat paint were successively applied to the respective plates subjected to the chemical conversion treatment, and the examples, A total of 39 types of test pieces were obtained including the comparative examples. The types of the top-coat paint used and the ultimate plate temperature (baking temperature) during drying are as follows. (1) Polyester resin top coating, pre-color No. Three
800 White [trade name of NOF CORPORATION] Hereinafter, referred to as E] Reached plate temperature: 220 ° C. (2) Acrylic resin-based top coating material, pre-color No. 251
0 White [trade name of NOF CORPORATION] Hereinafter referred to as AC]
Reachable plate temperature: 220 ° C. (3) Polyvinylidene fluoride resin-based top coating, pre-color No. 8000 white [trade name of NOF CORPORATION]. Less than,
Denoted as DVF] Plate temperature reached: 250 ° C. (4) Silicone polyester resin-based top coating, pre-color No. 4600 White [trade name of NOF CORPORATION] Hereinafter, referred to as SE] Ultimate plate temperature: 220 ° C. The performance of each of the coated steel plates thus obtained was evaluated. The results are shown in Tables 2-5.

[0016]

[Table 3]

[0017]

[Table 4]

[0018]

[Table 5]

[0019]

[Table 6]

[0020]

[Table 7]

[0021]

[Table 8]

Note 1) Type of coated plate GF: 5% Al-Zn hot dip plated steel sheet, coating weight;
Y-25 GI: Hot-dip galvanized steel sheet, coating weight; Z-25 GL: 55% Al-Zn hot-dip steel sheet, coating weight; Y-25 2) Kind of chemical conversion treatment Cr: Coating type chromate treatment P: Phosphorus Zinc Acid Treatment As is apparent from the test results of Table 2, in Comparative Examples 1 to 12 which deviate from the undercoat paint and the manufacturing method of the present invention, there is a remarkable occurrence of armpits at the time of baking and drying the coating, and other comparisons. The test piece also failed in any of the other test items and was not satisfactory. On the other hand, in Examples 1 to 12 according to the method of the present invention, the occurrence of an armpit was not seen even in the undercoating paint of 30 μm, and it passed all the test items such as moldability and corrosion resistance. It is clear that the method for producing a coated steel sheet using a paint and a fluorine-based topcoat paint using the same is an excellent paint and method. Further, as can be seen from the test results of Tables 3 to 5, in the examples using the undercoat paint of the present invention, the polyester resin-based, silicone polyester resin-based, and acrylic resin-based topcoat paints used were flexible. Since it is inferior to the polyvinylidene fluoride resin-based top coating composition in terms of performance, the formability of the coated steel sheet is somewhat unsatisfactory, but the impact resistance is higher than that of the conventional and coated steel sheet with the undercoating material deviating from the present invention (each comparative example). , Adhesion,
It is clear that it has excellent corrosion resistance.

[0023]

EFFECTS OF THE INVENTION The undercoat paint of the present invention enables the use of a linear polyester resin which forms a more flexible coating film, and enables a thick coating of about 30 μm in one coating, and a thickness of about 60 μm in two coatings. It is an epoch-making undercoat paint that can have excellent moldability even in the film. Further, according to the method for producing a coated steel sheet of the present invention, the total coating film thickness is increased to about 40 to 100 μm by using the above-mentioned undercoating paint and further applying the overcoating paint, and at the same time, excellent moldability is obtained. A coated steel sheet having corrosion resistance and adhesiveness can be obtained.

Front Page Continuation (72) Inventor Kajiyama To: 138-6-103 Setogaya-cho, Hodogaya-ku, Yokohama-shi, Kanagawa (72) Inventor Yusuke Maeda 1-7 Amigaido, Matsubara-shi, Osaka C-810 (72) ) Inventor Anhei Sakamoto 202-3 Kitanoyukiya, Togane, Chiba Prefecture (72) Inventor Koji Kobayashi 3-20-2-4-104 Shirahata, Chuo-ku, Chiba City, Chiba Prefecture (72) Kenji Shirakami Tamashima, Kurashiki City, Okayama Prefecture Otoshima 1795-2-B-201 (72) Inventor Hajime Kimura 254-2 Kitanoyukiya, Togane City, Chiba Prefecture

Claims (2)

[Claims] 1. A solid content of (A) hydroxyl value of 8 to 25 mg
KOH / g linear polyester resin 50-90% by weight,
And (B) the weight ratio of the epoxy resin and the melamine resin is 5
A color-developing agent as a main component containing 50 to 10% by weight of a mixture of 0:50 to 80:20, and the color-developing agent solid content of 10
An undercoat paint containing 40 to 100 parts by weight of a pigment based on 0 part by weight. 2. A method for producing a coated steel sheet, which comprises using the undercoat paint according to claim 1.