JP3204070B2 - Pre-coated steel sheet with excellent formability, which is used after applying the final coating after forming - Google Patents

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 which is required for excellent formability and appearance of a coating film, particularly for automobiles. The present invention relates to a precoated steel sheet exhibiting excellent moldability and coating film appearance.

[0002]

2. Description of the Related Art Conventionally, in order to obtain a product in which a coated steel sheet is coated, a method of applying a coating after forming a surface-treated steel sheet such as a plated steel sheet has been adopted. This method is called a post-coat method because it is painted after the forming process. However, this post-coating method requires a large-scale facility including environmental measures, because chemical treatment and painting are applied to the large-capacity housing after molding, which is a major problem especially in the home appliance field. Had become. Also, in the application of automobile parts, after forming a surface-treated steel sheet, an electrodeposition coating, an intermediate coating and a top coating are applied, so that the coating process is extremely complicated and complicated. was there. On the other hand, a so-called pre-coated steel sheet obtained by applying a coating to a coil-shaped or sheet-shaped steel sheet or a plated steel sheet can be made into a product simply by forming it, and a complicated coating process such as a post-coating method is required. Since they are not required, they are now widely used for home appliances and interior materials.

[0003]

However, the pre-coated steel sheet currently used has the high quality and high sharpness required for applications such as refrigerator doors and the formability capable of withstanding severe processing at the same time. It was not satisfying. Further, even in the use of automobile members, they did not satisfy the high degree of coating appearance and durability required for the members. In addition, conventionally used pre-coated steel sheets are not designed on the premise that they are painted after forming, and therefore, even if they are painted after forming, the required performance as described above is not sufficiently satisfied. Could not be satisfied.

[0004] As described above, the conventional pre-coated steel sheet cannot provide high formability and high quality coating film performance, and cannot provide a high quality coating film required for home appliances (for example, refrigerator doors) and automobiles. To obtain it, a complicated and complicated coating process by the post-coating method was required. In view of this situation, the present invention provides a new pre-coated steel sheet that has the same coating performance as that of the post-coat method and is excellent in formability by being used after being subjected to final coating after forming. Invented. This steel sheet can be called a so-called semi-precoated steel sheet, and the coating process on the user side can be largely omitted. Further, after the final coating, the steel sheet is required for applications such as home electric appliances (for example, refrigerator doors) and automobiles. There is a great advantage over the conventional method that a high coating film performance can be obtained.

[0005]

The precoated steel sheet of the present invention is used after being subjected to a final coating after forming, and has the following constitution. (1) The center line average roughness (Ra) of the plated surface is 0.1 to
A chemical conversion coating is formed on the plating surface of a zinc-based plated steel sheet having a plating weight of 0.8 g / m ² or more per surface and a glass transition point of 50 to 120 ° C. on the upper surface thereof, and the surface of the coating film A precoated steel sheet having excellent formability, wherein a precoated film having a dynamic friction coefficient of 0.05 to 0.14 is formed, and a final coating is applied after forming.

(2) In the precoated steel sheet of (1),
The pre-coating film is a coating containing a polyester resin composed of a polyester polyol and an amino resin and / or an isocyanate compound as a main component, and containing 0.02 to 2.0 parts by weight of a lubricant based on 100 parts by weight of a resin solid content. A pre-coated steel sheet which is excellent in formability and is used after applying a final coating film after forming.

[0007]

The zinc-coated steel sheet used as the base sheet of the precoated steel sheet of the present invention includes a zinc-based alloy-coated steel sheet and a zinc-based composite-coated steel sheet in addition to the galvanized steel sheet. , Alloyed hot-dip galvanized steel sheet (including, for example, zinc-5% aluminum alloy-coated steel sheet, zinc-55% aluminum alloy-coated steel sheet, etc.), electrogalvanized steel sheet, composite galvanized steel sheet, electric alloy galvanized steel sheet, etc. A plated steel sheet can be used.

[0008] galvanized steel sheet, plating basis weight per one side is insufficient in corrosion resistance is less than 10 g / m ^2, the order to the plating unit weight per one side and 10 g / m ² or more. Further, from the viewpoints of corrosion resistance, workability, and economy, it is preferable that the basis weight of plating be in the range of 20 to 100 g / m ² . In the present invention, the center line average roughness (Ra) of the plating layer surface is defined as 0.1 to 0.8. If the center line average roughness (Ra) is less than 0.1, the coating film adhesion is insufficient, while if it exceeds 0.8, the sharpness after final coating becomes insufficient.

A chemical conversion coating is formed on the plating surface of the zinc-based plated steel sheet by a chemical conversion treatment such as a phosphate treatment or a chromate treatment. The chemical conversion coating is applied for the purpose of improving the adhesion between the plated steel sheet and the upper coating film and improving the corrosion resistance. Examples of the phosphate treatment include zinc phosphate treatment, iron phosphate treatment, and lead phosphate treatment. Examples of the chromate treatment include a reactive chromate treatment, an electrolytic chromate treatment, and a coating chromate treatment. Further, silica, phosphoric acid, a resin component and the like may be added to the chromate treatment liquid for the purpose of improving corrosion resistance and adhesion.

The upper layer of the chemical conversion coating has a glass transition point of 50 to 120 ° C. and a dynamic friction coefficient of 0.0100 on the coating surface.
A pre-coated film of 5 to 0.14 is formed. If the glass transition point of the pre-coated coating film is less than 50 ° C, the coating film hardness is insufficient. On the other hand, if the glass transition point exceeds 120 ° C, elongation of the coating film that can withstand molding processing cannot be obtained. The coating film surface is liable to be damaged. Also, from the above viewpoint,
A more preferred range of the glass transition point is 60 to 110 ° C. On the other hand, if the coefficient of kinetic friction of the coating surface of the pre-coated coating film is less than 0.05, the interlayer adhesion with a top coating film (a coating film formed by a final coating applied after molding processing; the same applies hereinafter) is insufficient. If it exceeds 0.14, the moldability will decrease. In addition, adjustment of the dynamic friction coefficient of the pre-coated film surface
Usually, it can be carried out by adjusting the type and the amount of the lubricant added to the coating film.

The main components of the resin forming the precoat film are polyester polyol, amino resin and / or
Alternatively, it is preferable to use a polyester resin composed of an isocyanate compound, and for example, a so-called modified polyester resin in which a part of a polyester polyol is modified with epoxy or the like is also included. As a resin for forming a coating film, in addition to the above-mentioned polyester resin, an epoxy resin,
Acrylic resin, vinylidene fluoride resin, silicone polyester resin, vinyl chloride resin, etc. are conceivable, but among these, epoxy resin, acrylic resin and silicone polyester resin are poor in flexibility, so they are coated during molding. The film is easily cracked or peeled. Further, since the vinylidene fluoride resin is non-adhesive, the interlayer adhesion with the overcoat film is poor. Further, since the coating film of the vinyl chloride resin is soft, workability at the time of molding is poor, and it is not preferable from the viewpoint of environmental pollution and the like.

The polyester polyol used in the present invention preferably has at least two hydroxyl groups in one molecule and has a number average molecular weight in the range of 1,000 to 30,000, preferably in the range of 2,000 to 20,000. Further, the hydroxyl group in the molecule of the polyester polyol may be at any of the terminal or the side chain in the molecule. Number average molecular weight of polyester polyol is 1000
When the number average molecular weight exceeds 30,000, the coating film hardness becomes insufficient and the viscosity becomes high, so that a large amount of a diluting solvent is required. The number average molecular weight of the polyester polyol is a molecular weight in terms of polystyrene measured by gel permeation chromatography.

The polyester polyol is a copolymer obtained by heating and reacting a polybasic acid component and a polyhydric alcohol component by a known method. As the polybasic acid component, for example, phthalic anhydride, isophthalic acid, terephthalic acid, trimellitic anhydride, maleic acid, adipic acid, fumaric acid and the like can be used. Further, as the polyhydric alcohol component, for example, ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol,
Dipropylene glycol, polypropylene glycol,
1,4-butanediol, 1,6-hexanediol,
Neopentyl glycol, triethylene glycol, glycerin, pentaerythritol, trimethylolpropane, trimethylolethane, and the like can be used.
Commercially available polyester polyols include, for example, Almatex manufactured by Mitsui Toatsu Chemicals, Inc., alkynol and desmophen manufactured by Sumitomo Bayer Urethane Co., Ltd., and Byron manufactured by Toyobo Co., Ltd.

The polyester polyol forms a cured coating film by reaction with a curing agent. An amino resin and / or an isocyanate compound can be used for the curing reaction of the polyester polyol. The amino resin used in the present invention is a resin obtained by the reaction of urea, benzoguanamine, melamine and the like with formaldehyde, and may be one which has been alkyl etherified with an alcohol such as methanol or butanol. Specifically, methylated urea resin, n-butylated benzoguanamine resin, methylated melamine resin, n-butylated melamine resin, iso-
Butylated melamine resin and the like can be mentioned. Examples of commercially available amino resins include Cymel manufactured by Mitsui Cyanamid Co., Ltd., U-Ban manufactured by Mitsui Toatsu Chemicals, Sumimar manufactured by Sumitomo Chemical Co., Ltd., and Melan manufactured by Hitachi Chemical Co., Ltd. Can be The mixing ratio of the polyester polyol and the amino resin is preferably from 95/5 to 65/35 in terms of the weight ratio of the solid content of the polyester polyol / amino resin.

The isocyanate compound is a compound having an isocyanate group in the molecule. When the isocyanate compound is used as a curing agent for a coating film of a precoated steel sheet as in the present invention, the isocyanate group is phenol, cresol, an aromatic secondary amine, It is desirable to use an isocyanate compound blocked with a blocking agent such as a tertiary alcohol, lactam, or oxime. These blocking agents are released from the isocyanate compound by heating at a predetermined temperature during baking. Examples of such blocked isocyanate compounds include hexamethylene diisocyanate and its derivatives, tolylene diisocyanate and its derivatives, 4,4'-diphenylmethane diisocyanate and its derivatives, xylylene diisocyanate and its derivatives, isophorone diisocyanate and its derivatives, and trimethylhexane. Examples include methylene diisocyanate and derivatives thereof.

Commercially available isocyanate compounds include:
Examples thereof include Sumidur and Desmodur manufactured by Sumitomo Bayer Urethane Co., Ltd., and Coronate manufactured by Nippon Polyurethane Co., Ltd. The isocyanate compound and the polyester polyol are preferably blended so that the molar ratio (NCO / OH) between the isocyanate group of the isocyanate compound and the hydroxyl group of the polyester polyol is 0.7 to 1.4. The molar ratio (NCO / OH) is 0.
If it is less than 7, the curing of the coating film is insufficient, and the expected hardness and strength of the coating film may not be obtained. On the other hand, if the molar ratio (NOC / OH) exceeds 1.4, a side reaction between excess isocyanate groups may occur, and the workability of the coating film may be reduced. In addition, as a curing agent, an amino resin and an isocyanate compound can be used in combination within the range of the mixing ratio described above.

It is preferable to add a lubricant to the pre-coated film for the purpose of reducing the frictional resistance of the film at the time of molding. Examples of the lubricant include hydrocarbon waxes such as paraffin and low molecular weight polyethylene, silicone waxes, amide waxes, and polyester waxes. Further, the amount of the lubricant to be added depends on the resin component 10
The content is preferably in the range of 0.02 to 2.0 parts by weight with respect to 0 parts by weight. If the amount of the lubricant is less than 0.02 parts by weight, the lubricity of the coating film surface is insufficient, and the moldability is poor. On the other hand, if the addition amount exceeds 2.0 parts by weight, the lubricating property becomes excessive, and the press at the time of molding becomes insufficient, so that an unnecessary slip phenomenon or the like occurs. In addition, from the above viewpoint, a more preferable range of the amount of the added lubricant is 0.03 to 0.5 part by weight.

The corrosion resistance required of the precoated steel sheet varies depending on the application and the use environment, but in order to obtain particularly excellent corrosion resistance, strontium chromate, zinc chromate, barium chromate or the like is used as a rust preventive pigment in the precoated film. A so-called hardly soluble chromate fine powder can be added. Among them, strontium chromate is most preferable because it can maintain long-term corrosion resistance. The amount of addition is not particularly limited.
It is preferable that the amount be in the range of 1 to 80 parts by weight based on parts by weight.

In the pre-coated film, curing catalysts (tin octoate, dibutyl tin dilaurate, lead 2-ethylhexoate, etc.) and inorganic pigments (calcium carbonate, kaolin, clay, alumina, Silica, titanium oxide, talc, barium sulfate, mica, etc.), organic pigments (Vengala, manganese blue, carbon black, chrome yellow, chrome green, quinacridone red, etc.) and other various additives can be added as required. it can. In preparing the coating composition, the above components can be blended using a usual disperser or kneader such as a sand grind mill, a ball mill or a blender.

The thickness of the precoat film is not particularly limited, but is preferably in the range of 5 to 30 μm. When the film thickness is less than 5 μm, the sharpness after the top coat is insufficient,
On the other hand, when the thickness exceeds 30 μm, cracks and the like are easily generated on the surface of the coating film during baking and curing of the coating film, and peeling of the coating film called enamel hair is likely to occur during cutting or punching.
The pre-coated steel sheet of the present invention is subjected to a final coating on part or all of the pre-coated steel sheet after being subjected to the forming process. A pretreatment step such as polishing may be added to the above.

The method of coating the pre-coated coating film is not particularly limited, but is preferably applied by a method such as roll coater coating or curtain flow coating. After the coating, hot air drying, infrared heating, induction heating, etc. And a resin is crosslinked to obtain a cured coating film. The baking temperature (attained plate temperature) during heat curing is preferably 200 to 250 ° C., and the baking time is preferably about 40 seconds to 3 minutes.
Needless to say, the coating structure of the precoated steel sheet of the present invention can be applied only to one side of the steel sheet, and in that case, the other one side may be a base steel sheet surface, a plated surface, or any other coating surface. it can.

[0022]

[Examples] Various zinc-coated steel sheets (all with a thickness of 0.6
mm) was subjected to a coating type chromate treatment or a phosphate treatment, and then a precoated film was applied and baked to produce precoated steel sheets, and each of the produced precoated steel sheets was subjected to various tests described below. Table 1 shows the composition and properties of the polyester polyol used in the paint for the pre-coated film, Tables 2 and 3 show the composition of the paint for the pre-coated film, and Tables 4 and 5 show the production of the pre-coated steel sheet of each example. The conditions and the results of various tests are shown.

[Production of Polyester Polyol Used for Precoat Coating Film] In a reaction vessel equipped with a heating device, a stirrer, a rectification column, a decompression device and a thermometer, dimethyl terephthalate was added in the proportions shown in Table 1; Dimethyl isophthalate,
Ethylene glycol, neopentyl glycol and manganese acetate catalyst are charged, and 180 to 210 ° C in a nitrogen atmosphere
To carry out a transesterification reaction, and methanol was distilled off.
Further, trimethylolpropane was added, and the polymerization reaction was carried out by gradually reducing the pressure to 10 mmHg while heating to 250 ° C., and the polyester polyols P-1 to P shown in Table 1 were reacted.
-3 was obtained. The obtained polyester polyol was adjusted to a nonvolatile content of 60 to 70% with a cyclohexanone solvent. Further, the molecular weight of the polyester polyol was adjusted by the polymerization reaction time. As for the molecular weight, the number average molecular weight was measured using gel permeation chromatography using a standard polystyrene calibration curve.

[Production of paint for pre-coated film] According to the compounding ratios shown in Tables 2 and 3, P-1 to P-
After mixing the polyester polyol 3, an amino resin or isocyanate compound as a curing agent, a pigment, a curing catalyst, and an additive (lubricant), the mixture was dispersed for 1 hour using a sand mill containing glass beads having a diameter of about 1 mm. Further, cyclohexane is added as a solvent to reduce the nonvolatile content to 4%.
Adjusted to be 0 to 60%, and 8 shown in Tables 2 and 3
Various types of precoat paints T-1 to T-8 were obtained.

[Test / Evaluation Method] (1) Pencil Hardness A pencil hardness test was performed according to the method of JIS-K5400 8.4.1, and the pencil hardness was evaluated. (2) T-bend workability A close-contact bending (0T bending) test was performed in a room at 20 ° C., and the coating film of the processed portion was observed using a 30-fold loupe to check for cracks in the coating film. Thereafter, a tape peeling test was performed on the coating film of the processed portion. According to the tape peeling test, those in which the coating film did not peel were passed (合格), and those in which the coating film was peeled were failed (x). In addition, among those which passed the test, those in which no crack was observed in the coating film and the tape did not peel off were evaluated as excellent (）). (3) Cylindrical drawing test A flat bottom cylindrical deep drawing test was performed in a room at 20 ° C under the conditions of a blank diameter of 125 mm, a punch diameter of 50 mm, and a drawing ratio of 2.5. Excellent if no damage such as scratches are observed on the coating film surface after deep drawing (◎), pass if no surface flaw is observed by visual observation 30 cm away (○), pass if there is a surface flaw Rejected (x).

(4) Adhesion test for topcoat coating (cross-cut tape method) Topcoat paint on precoated steel sheet (Kansai Paint Co., Ltd.)
Magiclon no. 300 white) to give an average dry film thickness of 30 μm.
After baking and drying for 20 minutes, it was left in a room at 20 ° C. for 24 hours. After standing, 8.5.2 of JIS-K5400 (199)
According to the method of 3), in a room at 20 ° C., first, a 10 × 10 square grid of 1 mm square is formed on the overcoated film with a cutter knife, and an adhesive tape is stuck on the grid and immediately applied. The adhesive tape was instantaneously peeled off from the film surface, and the number of grids remaining without peeling was 100%, which is excellent (◎), and 98% or more and less than 100% passed (合格).
Those with less than 98% were rejected (x).

(5) Topcoat Coating Film Sharpness After precoating the precoated steel sheet by the above method (4), the sharpness of the topcoat coating film was measured using a PGD type sharpness gloss meter manufactured by Japan Color Research Institute. evaluated. Those with a PGD value of 1.0 or more were rated as excellent (◎), those with 0.8 or more and less than 1.0 were rated as good (○), and those with a PGD value of less than 0.8 were rated as unacceptable (x). (6) Impact Deformation Test (DuPont Type) After a pre-coated steel sheet was overcoated by the method of (4), an impact deformation test of the overcoated coating film was performed. JIS-K5
400. Apply the method of 8.3.2 (1993), test 1kg weight, 50cm height, test the case where the coating surface of the test piece is upward and downward, and test tape peeling both upward and downward When the coating film was not peeled off, it was judged as acceptable (O), and when it was peeled off, it was unacceptable (X). Further, those in which no crack was observed in the coating film and the coating film did not peel off the tape were evaluated as excellent (（).

(7) Corrosion resistance test (salt spray test) The above-mentioned (4) was applied to a precoated steel sheet which had been subjected to 0T processing at 20 ° C.
The samples coated with a top coat were prepared according to the above method, and the corrosion resistance of each sample was evaluated by a salt spray test (SST). In this test, the back surface of the test surface was completely hidden with a tar epoxy paint. After 1000 hours of SST, each coating film on the flat portion, the processed portion, and the cut end of the sample was observed, and there was no abnormality such as coating film swelling, rust, discoloration, and the like on the flat portion. Those in which the swelling of the coating film occurred only within 3 mm from the processed part or the cut end were evaluated as pass (O), and the others were evaluated as unacceptable (X). In addition, among those that passed, particularly those in which the swelling of the coating film occurred only within 1 mm from the processed portion and within 2 mm from the cut end were rated as excellent (◎).

In Tables 4 and 5, in Comparative Examples 1 and 2, the basis weight of galvanized steel sheet was 10 g / m 2.
^Since it is less than ² , the corrosion resistance is poor. In Comparative Example 3, since the center line average roughness (Ra) of the surface of the galvanized steel sheet exceeded 0.8, the clarity after the top coat was insufficient. Comparative Example 4 had a glass transition point of 50 ° C.
Drawability is poor because it is less than. In Comparative Examples 5 and 6, the amount of the added lubricant was not appropriate, and the kinetic friction coefficient of the surface of the pre-coated film was out of the range of the present invention, so that the molding processability was poor. Also has insufficient adhesion. As described above, the precoated steel sheets of Comparative Examples 1 to 6 deviating from the conditions of the present invention have satisfactory performance in any of corrosion resistance, moldability, top coat adhesion, impact resistance, and top coat sharpness. Not been. On the other hand, the precoated steel sheets of Examples 1 to 11 of the present invention have excellent performance in all of the formability, the adhesion of the overcoat, the sharpness of the overcoat, the impact resistance and the corrosion resistance. Is evident.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

Note that * 1 to * 6 in Tables 2 and 3 indicate the following contents. * 1: Polyester polyol symbol described in Table 1 * 2: M: Melamine compound (Cymel 303, manufactured by Mitsui Cyanamid Co., Ltd., nonvolatile content 100% by weight), N: Blocked isocyanate compound (Sumitomo Bayer Urethane)
* 3: Rutile type titanium dioxide pigment (Taipaek CR93, manufactured by Ishihara Sangyo Co., Ltd.) * 4: Rust preventive pigment; strontium chromate (manufactured by Kikuchi Color Co., Ltd.) * 5: A; 20% by weight solution of p-toluenesulfonic acid in cyclohexanone, D: 20% by weight of dibutyltin dilaurate in cyclohexanone * 6: Cyclohexanone * 7: PE; polyethylene wax, ES; polyester wax

[0034]

[Table 4]

[0035]

[Table 5]

Note that * 1 to * 7 in Tables 4 and 5 indicate the following contents. * 1: GI: hot-dip galvanized steel sheet, GA: galvannealed steel sheet, EG: electro-galvanized steel sheet, EN: zinc-nickel alloy electro-plated steel sheet, GL: zinc-55%
Aluminum alloy plated steel sheet * 2: Coating weight per side * 3: Center line average roughness (Ra) * 4: Cr; coating type chromate treatment, P: zinc phosphate treatment * 5: described in Tables 2 and 3 Paint No. * 6: Measured value by electromagnetic film thickness meter * 7: AS using HEIDON-14 manufactured by Haydon
Dynamic friction coefficient obtained from the load caused by sliding at a load of 500 g according to TM1894

[0037]

The precoated steel sheet of the present invention described above is
It can be made into a product just by applying the final coating after molding, and it has excellent moldability such as press moldability, and excellent coating adhesion, sharpness and corrosion resistance when the final coating is applied ing. For this reason, especially in applications where high moldability and coating film performance are required, a coated member having excellent coating film performance can be easily manufactured without going through a complicated coating process as in the past. .

Continued on the front page (51) Int.Cl. ⁷ Identification code FI B32B 15/18 B32B 15/18 27/18 27/18 Z 27/36 27/36 C23C 2/06 C23C 2/06 2/26 2/26 2/28 2/28 22/00 22/00 Z C25D 5/26 C25D 5/26 C 5/48 5/48 (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 28/00 B05D 7 / 00 B32B 15/00 C23C 2 / 00,22 / 00

Claims (2)

(57) [Claims] 1. A center line average roughness (Ra) of a plating surface is 0.1 to 0.8, and a plating weight per one surface is 10 g.
/ M ² or more, a chemical conversion coating is formed on the plated surface of a zinc-based plated steel sheet, and a glass transition point of 50 to 120 ° C. is formed thereon.
A pre-coated steel sheet having excellent pre-processability, which is used after forming a pre-coated film having a dynamic friction coefficient of 0.05 to 0.14 on the surface of the coating film and applying a final coating after the forming process. 2. A pre-coated coating film comprising a polyester-based resin comprising a polyester polyol and an amino resin and / or an isocyanate compound as a main component, and lubricating 0.02 to 2.0 parts by weight based on 100 parts by weight of resin solids. 2. A precoated steel sheet having excellent formability, which is used by applying a final coating after the forming process according to claim 1, which is a coating film containing an agent.