JP2000015741A - Galvanized steel plate excellent in thermal discoloring resistance, fuming properties on heating, corrosion resistance after heating, and scratch resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To contrive to improve the thermal discoloring resistance, fuming properties on heating, corrosion resistance after heating, scratch resistance and adhesion of a steel plate by a method wherein a straight silicone resin film, the deposition amount of which is specified, is formed on the surface of a galvanized steel plate. SOLUTION: On the surface of a galvanized steel plate, a processing solution mainly made of a specified straight silicone resin is coated and then fired for forming a film. An organic group included in this straight silicone resin is a methyl group. The deposition amount of the straight silicone resin is set to be 0.1-3 g/m2 in terms of SiO2. The SiO2 component included in the straight silicone resin is 60% or more of the total weight of the film. Further, a straight silicone resin film includes 20 pts.wt. or less of a crystalline lubricant to 100 pts.wt. of the straight silicone resin film. This crystalline lubricant is an organic lubricant, the softening point of which is 70 deg.C or higher. Thus, even under an elevated temperature environment, characteristics excellent in a thermal discoloring resistance and fuming resistance can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a galvanized steel sheet which can be used for various parts of automobiles, home appliances and building materials, and has excellent heat discoloration resistance, smoke generation upon heating, corrosion resistance after heating and scratch resistance. Things.

[0002]

2. Description of the Related Art Galvanized steel sheets are used in a wide range of fields such as automobiles, home electric appliances, and building materials from the viewpoint of durability and economy. Conventionally, for the purpose of imparting functions such as corrosion resistance and paintability, a thin-film resin coating process of performing a chromate treatment on the surface of a galvanized steel sheet and further forming a thin resin film of several microns on the surface has been performed. .

[0003] However, such galvanized steel sheet does not have heat resistance, and when exposed to a high-temperature environment such as around an engine room of an automobile, a shrink band of a stove, a microwave oven, a cathode ray tube of a television, or a welded portion, there is no heat. There are problems such as discoloration, smoke, odor, and deterioration of corrosion resistance due to heat. If only chromate treatment is used,
Although there is no organic component, discoloration during heating is suppressed, but there is a problem that the film is extremely thin, so that the film is damaged during processing, the appearance is deteriorated, and the corrosion resistance of the damaged part is deteriorated.

As a method for solving such a problem, for example, (1) JP-A-4-33844,
(2) Japanese Patent Application Laid-Open No. H6-117981 has been proposed. As a technique using a silicone resin, (3) JP-A-63-102929 has been proposed.

[0005]

The above prior art (1)
(2) is obtained by subjecting a plated steel sheet to a chromate treatment, and further applying a treatment liquid (water glass) based on silicic acid and made water-soluble with an alkali metal oxide to the upper layer, followed by drying. There is a problem that the alkali metal component remains in the film, resulting in poor water resistance, and consequently poor corrosion resistance. Further, the prior art of (2) has a drawback that it is inferior in lubricity and consequently inferior in scratch resistance at the time of processing, because it is composed only of an inorganic component.

In the prior art (3), a ladder-type silicone resin is formed on a galvanized steel sheet on which a chemical conversion coating is formed. For this reason, there is a problem that the cured film becomes too hard, has poor scratch resistance during processing, and has poor adhesion to the film when processed.

As described above, in the prior art, there was no galvanized steel sheet excellent in discoloration upon heating, corrosion resistance, scratch resistance and adhesion. Accordingly, an object of the present invention is to solve such problems of the prior art, and to provide galvanized steel sheets excellent in both heat discoloration resistance, smoke generation upon heating, corrosion resistance after heating, scratch resistance and adhesion. Is to provide.

[0008]

Means for Solving the Problems The inventors of the present invention have made intensive studies on means for solving the above-mentioned problems, and as a result, have found that a zinc-based plating solution using a processing solution containing a specific straight silicone resin as a main component is used. By treating the steel sheet surface, a galvanized steel sheet having excellent heat discoloration resistance, smoke emission during heating, corrosion resistance after heating, and scratch resistance has been newly found.

The present invention has been made based on such findings, and the features thereof are as follows. [1] resistance to thermal discoloration of the straight silicone resin film on the surface of the galvanized steel sheet characterized by being 0.1 to 3 g / m ² formed in terms of SiO _2, heated during the fuming, after heating corrosion resistance and Galvanized steel sheet with excellent scratch resistance.

[2] Metallic C
A chromate-treated layer of 100 mg / m ² or less in terms of r is formed, and a straight silicone resin film is formed on the surface of the chromate-treated layer in an amount of 0.1 to 3 g / m ^{2 in} terms of SiO _2. Discoloration upon heating, smoke emission upon heating,
Galvanized steel sheet with excellent corrosion resistance and scratch resistance after heating.

[3] The galvanized steel sheet according to claim 1 or 2, wherein the organic group contained in the straight silicone resin film is a methyl group. [4] SiO ₂ in the straight silicone resin film
The galvanized steel sheet according to any one of claims 1 to 3, wherein a component is 60% or more of the total coating weight.

[5] The galvanized steel sheet according to any one of claims 1 to 4, wherein the straight silicone resin film contains not more than 20 parts by weight of a crystalline lubricant based on 100 parts by weight of the straight silicone resin.

[6] The straight silicone resin 10
0 parts by weight of an organic lubricant having a softening point of 70 ° C. or more
The galvanized steel sheet according to claim 5, wherein the content is 0 part by weight or less.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below together with the reasons for limiting the invention. The plated steel sheet of the present invention has a coating formed by applying a treatment liquid containing a specific straight silicone resin as a main component to the surface of a zinc-based plated steel sheet and baking it.

Silicone generally means siloxane (-
It is a general term for a material having a (Si-O-Si-) portion, and a resin, oil, rubber, or the like is used. Therefore, the straight silicone resin used in the present invention will be described. A siloxane (—Si—O—Si—) is used as a skeleton, and a hydroxyl group (—OH) and an alkoxyl group (—OR:
R is an organic group) or a material having an organic group bonded thereto and having both organic and inorganic properties, and is characterized by being not modified with other organic resins. Further, the film is flexible because it does not have a crosslinked structure, and is characterized by having excellent scratch resistance. The organic group bonded to a silicon atom, a methyl group (-CH _3), ethyl group (-C ₂ H _5), phenyl _{group, (- C 6 H 5)} , a vinyl group (-CH = CH ₂₎ , a butyl group (-C ₃ H ₇₎ can be mentioned. In addition, the straight silicone resin used may contain these organic groups alone, or may contain two or more different organic groups. When a modified silicone resin other than a straight silicone resin is used, the modified organic resin component is thermally decomposed when heated, causing discoloration and smoking, which is not preferable.

Further, among the organic groups, those having a methyl group having a small number of carbon atoms are more preferable from the viewpoint of fuming caused by decomposition of the organic components by heating. The amount of the straight silicone resin attached is preferably 0.1 to 3 g / m ^{2 in} terms of SiO ₂ . An amount of less than 0.1 g / m ² is not preferable because it has poor scratch resistance during roll forming and press molding, and an amount exceeding 3 g / m ² is inferior in smoke emission during heating and adhesion during bending.

S contained in straight silicone resin
Preferably, the iO ₂ component accounts for at least 60% of the total coating weight. This is SiO _{2 in} straight silicone resin
This is because the components other than the components are hydroxyl groups or organic groups, and when the number of organic groups increases, the smoke-generating properties deteriorate.

The straight silicone resin film of the present invention preferably contains not more than 20 parts by weight of a crystalline lubricant based on 100 parts by weight of the straight silicone resin film. The reason for adding a crystalline lubricant such as an organic lubricant to the silicone resin film is that the organic lubricant and the like are more effective in preventing roll forming, scratching and galling of the resin film and plating surface caused by press molding and the like. This is because it has an action of preventing the occurrence of a blemishes. The reason for using a substance having a softening point of 70 ° C. or higher as an organic lubricant is not preferable if the temperature is lower than 70 ° C. because organic components are easily decomposed and smoking properties are poor. Softening point 70
As an organic lubricant having a softening point of 9 ° C. or more, micro stalin wax (softening point 70 to 90 ° C.), polyethylene (softening point 9
0 to 140 ° C), polypropylene (softening point 140 to 17)
0 ° C.) and ethylene tetrafluoride (softening point: 320 ° C.). The above-mentioned lubricants may be added alone, or two or more different lubricants may be used in combination. The acid value of microstalin wax, polyethylene, or polypropylene may be 0 or more than 0, or a combination thereof. Since the silicone resin is of a solvent type, it is preferably added in the form of powder or a state in which the silicone resin is dispersed in a solvent in advance.

Examples of the crystalline lubricant include inorganic lubricants other than the above-mentioned organic lubricants, such as graphite, boron nitride and molybdenum disulfide. Such a lubricant can be preferably used when fuming properties are important, but may be slightly inferior in scratch resistance compared to organic ones, and may be appropriately selected and used depending on the purpose of use. be able to.

The amount of the organic lubricant is preferably 20 parts by weight or less based on 100 parts by weight of the straight silicone resin. If the amount is more than 20 parts by weight, the amount of organic components increases, and the smoke emission during heating is inferior. A more preferable addition amount is 10 parts by weight or less from the viewpoint of fuming properties. On the other hand, when the amount of the inorganic crystalline lubricant is more than 20 parts by weight, the scratch resistance is deteriorated, which is not preferable.

The resin film formed as described above is
For the purpose of improving corrosion resistance, a chromate film may be formed on the zinc-based plating layer of the zinc-based plated steel sheet. The method for forming the chromate film may be performed by any known means such as coating treatment, electrolytic treatment, and reaction treatment. Further, the chromate film may contain silica, resin or the like.

The amount of the chromate film attached is preferably 100 mg / m ² or less per one side of the steel sheet in terms of metallic Cr. If the amount of the chromate film is more than 100 mg / m ² , not only the effect of improving the corrosion resistance after heating corresponding to the amount of the chromate film is not obtained, but also the cohesive failure of the chromate film itself occurs during the processing, and the adhesiveness is not obtained. Therefore, it is not preferable.

The coated steel sheet which forms the above-mentioned film is at least one of nickel, iron, aluminum, cobalt, molybdenum and the like in addition to zinc, galvanized steel sheet manufactured by electroplating, hot-dip plating, and adhesion plating. Zinc alloy-plated steel sheet containing one component, and dispersion-plated steel sheet containing silica, alumina, etc. in a plating film. More preferably, from the viewpoint of heat resistance, the melting point of the plated metal is high zinc-nickel alloy plated steel sheet,
It is a zinc-55% aluminum alloy plated steel sheet. In addition, a hot-rolled steel sheet, a hot-rolled steel sheet having no plating film, a hot-dip aluminum-plated steel sheet which is not a zinc-based coating, and a hot-rolled steel sheet having no plating film can be used.

[0024] The base steel sheet of the galvanized steel sheet is also
It is not particularly limited, various compositions, surface roughness,
A rolling method can be used. The formation of the resin film on the surface of the galvanized steel sheet is performed as follows. In other words, a roll coater,
A predetermined amount of a coating film is formed by applying the above-described paint mainly composed of the straight silicone resin by a known method such as a curtain flow coater or spray coating. Next, the zinc-coated steel sheet coated with the paint is heated to a temperature of 80 to 250 ° C. or lower by a hot air stove or an induction heating device and baked to volatilize the solvent in the paint and form a resin film.

The baking temperature of the above resin film is 80 to 2
The range is 50 ° C. or lower. If the baking temperature is less than 80 ° C,
It is not preferable because the curing of the resin film is insufficient and the scratch resistance during processing is poor. On the other hand, if the temperature exceeds 250 ° C., the curing of the resin film proceeds excessively, and the organic groups in the straight silicone resin are decomposed and volatilized, which is not preferable because of poor scratch resistance.

[0026]

EXAMPLE After both sides of the following galvanized steel sheet were alkali-degreased, a paint mainly composed of a straight silicone resin was applied to the plated surface by a roll coating method (adhesion amount was adjusted by a wet application amount), and then induced. The specimen was baked in a heating furnace in a range of a maximum reached plate temperature of 60 to 270 ° C. to prepare a test material. In addition, some of the test materials were formed by applying a coating type chromate treatment to form 30 to 150 mg / m ^{2 in} terms of metal Cr before forming the resin film.

(1) Electrogalvanized steel sheet (0.8 m thick)
m, coating weight 20 g / m ² ) (2) zinc-nickel alloy plated steel sheet (sheet thickness 0.8 m
m, coating weight 20 g / m ² ) (3) hot-dip galvanized steel sheet (sheet thickness 0.8 mm, coating weight 90 g / m ² ) (4) alloyed hot-dip galvanized steel sheet (sheet thickness 0.8 mm, plating adhesion) 45g / m ² ) (5) Hot-dip zinc-5% aluminum alloy-coated steel sheet (sheet thickness 0.8 mm, plating adhesion amount 90 g / m ² ) (6) Hot-dip zinc-55% aluminum alloy-plated steel sheet (sheet thickness 0. 8 mm, coating weight 70 g / m ² ) The composition of the coating material used for each test material is shown in Tables 1 and 2, together with the chromium coating weight and the resin coating weight.

The test materials prepared from the paints used were evaluated for heat discoloration resistance, smoke resistance, corrosion resistance after heating, scratch resistance, and bending adhesion. The results are shown in Tables 3 and 4. The performance evaluation method is described below.

[Evaluation of Performance] (1) Heat-resistant discoloration After each test material reached 600 ° C., it was heat-treated for 1 hour, and the discoloration of the surface of the test material was visually determined. The evaluation criteria are as follows.

○: No discoloration: Discoloration to light gray △: Discoloration to blue ×: Discoloration to brown (2) Smoke emission Visualization of the emission of smoke from each test material until the plate temperature reaches 600 ° C. Was determined. The evaluation criteria are as follows.

○: no smoke generated ○: smoke was slightly observed △: smoke was clearly observed ×: marked smoke was generated (3) Corrosion resistance after heating After the test material reached a plate temperature of 600 ° C., 1 A plurality of test pieces of 70 mm x 150 mm were cut out from the heat-soaked specimen, and a salt spray test specified in JIS Z 2371 was performed on these test pieces, and the area of red rust occurrence after 500 hours was visually determined. The evaluation criteria are as follows.

○: No red rust generation ○: Red rust generation area 5% or less △: Red rust generation area 5% or more 30% or less ×: Red rust generation area 30% or more (4) Scratch resistance FIG. 1 is a schematic front view. The testing machine shown was used. As shown in FIG. 1, the tester includes a female die 1 having a flat surface fixed to one side 2a of a box-shaped frame 2, and a substantially horizontal ridge having a predetermined height facing the female die 1. A male die 4 having a male die 3 and the other side 2b of the frame 2 for supporting the male die 4 and moving the male die 4 horizontally toward the female die 1
And a hydraulic cylinder 5 fixed to the hydraulic cylinder. The male die 4 is fixed to a rod 5 a of a hydraulic cylinder 5 via a load cell 6. In addition, the width | variety of the protrusion 3 of the male die 4 is 10 m, and the length of the front-end | tip is 1 mm.

The test material is inserted vertically into the gap between the female die 1 and the male die 4 and the hydraulic cylinder 5 is operated to
50 kgf of test material 7 by female die 1 and male die 4
(500 kgf / cm ² ). Next, the test material 7 was pulled upward at a speed of 500 mm / min, as indicated by an arrow, and damage to the coating and plating of the portion slid at that time was visually evaluated. The evaluation criteria are as follows.

○: no scratches: slight damage to the coating, but no plating damage △: coating damage, small plating damage ×: coating damage, large plating damage (5) Bending adhesion The test material was subjected to 0T close-contact bending, a cellophane tape was stuck to the bent portion, rubbed well and sufficiently adhered, and then peeled, and the degree of the peeled film was visually evaluated. The evaluation criteria are as follows.

○: no peeling: slight peeling △: partial peeling ×: almost peeling

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

[0039]

[Table 4]

As is clear from Tables 1, 2 and 3 and 4, the zinc-coated steel sheet on which the coating according to the present invention is formed has resistance to discoloration due to heating, smoke generation, corrosion resistance after heating, and scratch resistance. Excellent in both properties and bending adhesion. On the other hand, the comparative examples are inferior in any of heat discoloration resistance, smoke generation, corrosion resistance after heating, scratch resistance and bending adhesion.

[0041]

As described above, the galvanized steel sheet of the present invention has excellent properties of heat discoloration and smoke generation, and excellent corrosion resistance after heating in an environment exposed to high temperatures. Further, it has excellent properties such as flaws on the film and plating surface when processed as a part and adhesion of the film.

[Brief description of the drawings]

FIG. 1 is a schematic front view of a testing machine for evaluating the scratch resistance of a test material.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Bead 2 Frame 3 Ridge 4 Bead 5 Hydraulic cylinder 6 Load cell 7 Test material

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masaru Sagiyama 1-2-1 Marunouchi, Chiyoda-ku, Tokyo F-term in Nihon Kokan Co., Ltd. 4D075 BB74X BB92X BB92Y CA02 CA18 CA33 CB08 DB05 DC02 DC12 DC18 EA37 EB42 EB43 EB56 EC07 EC51 EC54 EC60 4F100 AB03A AB18A AK01B AK04H AK52B BA02 CA30B EH71A EJ69A GB07 GB32 GB48 JA04B JA13B JB02 JJ03 JJ07 JK14 YY00B 4K026 AA02 AA07 AA12 AA12 BB08 DA06 BA06 DA06 BA08

Claims (6)

[Claims] 1. A discoloration resistance upon heating, smoke generation upon heating, and after heating, wherein a straight silicone resin film is formed on the surface of a zinc-based plated steel sheet at 0.1 to 3 g / m ^{2 in} terms of SiO _2. Galvanized steel sheet with excellent corrosion and scratch resistance. To 2. A surface of the galvanized steel sheet to form a 100 mg / m ² or less of the chromate treatment layer with a metal Cr terms, 0.1 the straight silicone resin film on the surface of the chromate treatment layer in terms of SiO ₂ 3 g / m ² , characterized by resistance to discoloration upon heating, smoke generation upon heating,
Galvanized steel sheet with excellent corrosion resistance and scratch resistance after heating. 3. The galvanized steel sheet according to claim 1, wherein an organic group contained in the straight silicone resin film is a methyl group. 4. The galvanized steel sheet according to claim 1, wherein the SiO ₂ component in the straight silicone resin film accounts for 60% or more of the total film weight. 5. The straight silicone resin film,
The galvanized steel sheet according to any one of claims 1 to 4, further comprising 20 parts by weight or less of a crystalline lubricant based on 100 parts by weight of the straight silicone resin. 6. The galvanized steel sheet according to claim 5, wherein the crystalline lubricant is an organic lubricant having a softening point of 70 ° C. or higher.