KR20090093850A - Resin-coated steel sheet having excellent anti-scratch properties - Google Patents

Abstract

In the resin-coated steel sheet of the present invention, a resin film having a thickness of 12 µm or less is formed on a surface of a cold rolled steel sheet or an alloyed hot dip galvanized steel sheet, and the Tg of the film is -10 ° C to 32 ° C. It is an excellent resin coated steel sheet. By such a structure, a scratch hardly arises in any process, such as a resin coating steel plate manufacturing process, a press working process, the assembling process after a process, and the conveyance process after becoming a product, and can be suitable for strict level scratch resistance.

Description

Resin-coated steel sheet excellent in scratch resistance {RESIN-COATED STEEL SHEET HAVING EXCELLENT ANTI-SCRATCH PROPERTIES}

TECHNICAL FIELD The present invention relates to a resin coated steel sheet used for automobiles, home appliances, building materials, and the like. Specifically, the present invention relates to a resin coated steel sheet manufacturing process, a press working process, an assembling process after processing, and a conveying process after becoming a product. It is related with the resin coating steel plate which a scratch does not produce easily.

DESCRIPTION OF RELATED ART Conventionally, the method of forming a resin film on the metal plate surface in order to improve designability and corrosion resistance is known. The resin coating is required to have good workability, corrosion resistance, scratch resistance and the like, and various studies have been conducted to improve these characteristics.

For example, Japanese Patent Application Laid-Open No. 2007-168273 has excellent workability in which a coating film containing a resin particle having a Tg of 70 to 120 ° C is contained in a resin having a glass transition temperature (hereinafter referred to as Tg) of 10 to 50 ° C. Steel plate is described. In addition, Japanese Laid-Open Patent Publication No. 2001-9366 discloses a precoated steel sheet that can withstand strict molding processes such as drawing by a coating film containing a polyester resin having a Tg of 20 to 80 ° C as a main component. In addition, Japanese Patent Application Laid-open No. Hei 9-111183 discloses a technique of improving workability by a resin coating film containing a polyester resin having a Tg of -25 to 35 ° C as a main component.

However, in these prior arts, no efforts have been made to meet the recent strict levels of scratch resistance. For example, although a pencil hardness test is known as a method for evaluating whether or not scratches easily occur on the resin film at the edge of a metal plate or the like, the pencil hardness itself is not evaluated in Japanese Patent Laid-Open No. 2007-168273. In addition, although evaluation of pencil hardness is performed in Japanese Patent Laid-Open No. 2001-9366 and Japanese Patent Laid-Open No. Hei 9-111183, it is only H and does not have a resin film structure which can endure the pencil of hardness. That is, when the soft resin which can be followed at the time of processing, such as drawing and bending, is selected, scratch resistance tends to worsen.

When the scratches of the metal plate come into contact with the edges of the metal plate, the quality appearance is remarkably degraded, resulting in defective products, which is directly linked to the cost. For this reason, improvement of scratch resistance is calculated | required and the level becomes strict every year.

As a technique focused on scratch resistance, for example, Japanese Patent Application Laid-Open No. 2007-230099 recognizes that workability and scratch resistance are opposite properties (lightweight coating) in order to achieve both characteristics. A technique for forming a hard island-like overcoat is described above. However, the scratch resistance of the portion where the hard coat film is not formed remains inferior, and the process is complicated to form the coat of the structure, leading to high cost.

Therefore, in the present invention, in view of the various circumstances described above, scratches are less likely to occur in any of processes such as a resin coated steel sheet manufacturing process, a press working process, an assembling process after processing, and a conveying process after becoming a product. The object of the present invention was to provide a resin coated steel sheet which can be suitable for the castle.

In the present invention, a resin coated steel sheet is formed with a resin film having a thickness of 12 µm or less on the surface of a cold rolled steel sheet or an alloyed hot dip galvanized steel sheet, and has a glass transition temperature (Tg) of -10 ° C to 32 ° C.

The resin film obtained from the raw material composition containing the organic solvent soluble polyester resin and the melamine type crosslinking agent contained in the raw material composition are both preferred embodiments of the present invention.

Since the resin-coated steel sheet of this invention provided the thin resin film which has a specific Tg on the surface of the cold-rolled steel plate or alloyed hot-dip galvanized steel plate with a big hardness, the resin coated steel plate excellent in the scratch resistance which has a pencil hardness of 3H or more is provided. Could. Moreover, since the resin-coated steel sheet of this invention hardly produces a scratch in various processes, generation | occurrence | production of a defective product is reduced and it contributes also to cost reduction. Therefore, the resin coated steel sheet of this invention is useful for automobiles, home appliances, building materials, etc.

In the resin-coated steel sheet according to the present invention, the original plate (the plate before the resin film is formed) must be a cold rolled steel sheet or an alloyed hot dip galvanized steel sheet (hereinafter, may be referred to as the original plate). These are because the Vickers hardness is large, and it has been found by the present inventors that the hardness of this disc affects the scratch resistance. In the hot-dip galvanized steel sheet which is used abundantly conventionally, since a galvanized layer is soft, even if it forms the same resin film as the steel plate of this invention, sufficient scratch resistance is not obtained. Thus, after considering the scratch resistance and the hardness of the disc, the technical idea of making the Tg and the film thickness of the resin film suitable for the hardness of the disc is unique to the present invention. The castle could be achieved. On the other hand, the alloyed hot dip galvanized steel sheet of the present invention is a steel sheet (GA steel sheet) having a plating layer alloyed with zinc and iron.

The hardness of the cold rolled steel sheet or the alloyed hot dip galvanized steel sheet is preferably Vickers hardness of 100 Hv or more. Since the hardness of a cold rolled sheet steel is considered to be larger than at least the Vickers hardness of Fe, it becomes 100 Hv or more. The hardness of the alloyed hot-dip galvanized steel sheet is considered to be almost the same as the Vickers hardness of the δ1 phase because the plating layer is mainly composed of the δ1 phase, and is 284 to 300 Hv. Although the adhesion amount of an alloying hot dip galvanizing layer is not specifically limited, In order to prevent peeling of the plating layer at the time of bending, it is preferable to set it as 50 g / m <2> or less, and 40g / m <2> or less is more preferable. What is necessary is just to determine the thickness of a disc suitably according to a use. On the other hand, when the irregularities are provided on the surface of the disc, scratches become less noticeable, which is a preferred embodiment of the present invention.

The film thickness of the resin film is 12 micrometers or less. It is because when hardness exceeds 12 micrometers, the hardness of a disc will not be reflected in a film characteristic, and pencil hardness will fall. More preferably, it is 10 micrometers or less, More preferably, it is 8 micrometers or less. The lower limit of the film thickness is not particularly limited, but considering the corrosion resistance and the lubricity, the film thickness is preferably 0.3 µm or more.

On the other hand, the resin film (other resin film) which does not satisfy the prescribed range of Tg of this invention may be formed in the resin film side and / or film surface side as long as it is 2 micrometers or less in thickness. For example, if it is a 12 micrometers resin film, 10 micrometers of them may be a resin film which satisfy | fills the prescribed range of this invention. It is because the effect of this invention is expressed and exhibits favorable scratch resistance, even if another 2 micrometers or less resin film is formed in the lower side and / or upper side of the resin film which satisfy | fills the prescribed range of this invention.

In this invention, Tg of the said resin film is set to -10 degreeC-+32 degreeC. In the present invention, the disc has a hardness that does not plastically deform even when a stress is applied, and the resin film has a softness enough to disperse and relax the stress, which is effective for reflecting the hardness of the disc in scratch resistance. Tg was set in this range. Conventionally, in order to improve scratch resistance, it is thought that it is effective to harden a resin film, and resin with high Tg has been used, but when Tg of resin is raised, workability required as a coated steel plate will deteriorate, and Tg Raising the scratch resistance did not improve that much. In the present invention, it is presumed that the Tg of the resin film is set relatively low, thereby preventing the concentration of local stresses leading to scratches, leading to a significant improvement in scratch resistance.

However, when Tg of a resin film is lower than -10 degreeC, in a normal use environment, since a resin film becomes soft too much and a scratch easily arises, it is unpreferable. As for Tg of a resin film, 0 degreeC or more is more preferable, and 5 degreeC or more is more preferable. Since pencil hardness tends to fall when Tg exceeds 32 degreeC, Tg shall be 32 degrees C or less. 25 degrees C or less is more preferable, and 19 degrees C or less of Tg is more preferable.

In order to measure the Tg of the resin film, for example, the resin film may be scraped off from the steel sheet and subjected to a differential scanning calorimeter (DSC) at a temperature range of -100 ° C to 180 ° C and a temperature increase rate of 20 ° C / min under a nitrogen atmosphere. The resin film may include known additives such as rust inhibitors, gloss removers, fillers, and pigments, in addition to the resin component (which may be the case of resin + crosslinking agent), but Tg is not affected by the dispersed solid additive. Tg of a resin film can be measured by the method.

As resin which can be used for forming a resin film, if Tg of a resin film satisfy | fills the said range, it will not specifically limit, General purpose resin can be used. Examples thereof include polyester resins, acrylic resins, urethane resins, polyolefin resins, fluorine resins, silicone resins, mixtures of these resins or modified resins. When thermosetting resins, such as an epoxy resin and an unsaturated polyester resin, are used as a raw material of a matrix resin, the cured coating film obtained will become too hard and a deformation | transformation ability will become small, and it is not preferable in this invention. Considering that the resin coated steel sheet requires properties such as bending workability, film adhesion, and corrosion resistance, a polyester resin of an organic solvent-soluble type (non-crystalline) is preferable.

As a polyester resin of the organic solvent soluble type, the "Byron (trademark)" series made by Toyo Spinning Co., Ltd. is suitable at the point which can obtain abundant kind. The polyester resin may be crosslinked with melamine resin or the like. As melamine resin, there exists "Sumimal (registered trademark)" series made by Sumitomo Chemical Co., Ltd., and "Cymel (registered trademark)" series made by Mitsui Cytec. On the other hand, it is preferable to mix | blend the ratio of resin and a crosslinking agent so that a crosslinking agent (after reaction) may be 5-30 mass% in the resin film after drying from a viewpoint of the balance of workability and durability.

The Tg of the Byron (trademark) series of said toy spinning company is as follows. Byron 103 (47 ℃), Byron 200 (67 ℃), Byron 220 (53 ℃), Byron 226 (65 ℃), Byron 240 (60 ℃), Byron 245 (60 ℃), Byron 270 (67 ℃), Byron 280 (68 ℃), Byron 290 (72 ℃), Byron 296 (71 ℃), Byron 300 (7 ℃), Byron 500 (4 ℃), Byron 516 (-17 ℃), Byron 550 (-15 ℃), Byron 560 (7 ° C), Byron 600 (47 ° C), Byron 630 (7 ° C), Byron 650 (10 ° C), Byron GK110 (50 ° C), Byron GK130 (15 ° C), Byron GK140 (20 ° C), Byron GK150 (20 ℃), Byron GK180 (0 ℃), Byron GK190 (11 ℃), Byron GK250 (60 ℃), Byron GK330 (16 ℃), Byron GK360 (56 ℃), Byron GK590 (15 ℃), Byron GK640 (79 ° C), Byron GK680 (10 ° C), Byron GK780 (36 ° C), Byron GK810 (46 ° C), Byron GK880 (84 ° C), Byron GK890 (17 ° C), Byron BX1001 (-18 ° C), etc. Can be. These Tg are the temperatures described on the home page. In addition, those having a molecular weight (Mn) is in the range of ^{3 × 10 3 ~ 30 × 10} 3.

The resin film of this invention may contain electroconductive particle for giving electroconductivity. As electroconductive particle, what provided the electroconductive layer, such as a metal, on the surface of a metal particle or an inorganic or organic polymer particle, etc. are mentioned. As the metal particles, magnetic powder, nickel, iron phosphide and the like can be suitably used from the viewpoints of conductivity and corrosion resistance. In the case where it is necessary to further impart electromagnetic shielding performance to the resin coated steel sheet, magnetic metal powder having good conductivity and also having electromagnetic wave absorbability may be used as the conductive particles. As such a magnetic metal powder, Pharmaroy (Ni-Fe type alloy whose Ni content is 35 mass% or more), sendust (Si-Al-Fe type alloy), carbonyl iron, etc. are suitable. As for the average particle diameter of electroconductive particle, about 3-30 micrometers are preferable generally. In addition, this average particle diameter r is 50% volume average particle diameter by a laser diffraction method (scattering formula).

In order to manufacture the resin-coated steel sheet of this invention, it is preferable to employ | adopt the method of preparing the raw material composition of a resin film, and apply | coating and drying this to the said original board. As the raw material composition, a resin, a crosslinking agent to be added as necessary, etc. are diluted with an organic solvent or the like to use a viscosity suitable for coating. Although it does not specifically limit as an organic solvent, Aromatic hydrocarbons, such as toluene and xylene; Aliphatic esters such as ethyl acetate and butyl acetate; Alicyclic hydrocarbons such as cyclohexane; Aliphatic hydrocarbons such as hexane and pentane; Ketones, such as methyl ethyl ketone and cyclohexanone, etc. are mentioned. As for solid content concentration of a raw material composition, about 5-60 mass% is preferable.

You may add various well-known additives used in the field of resin coating steel plate, such as a gloss remover, a sieving pigment, a rust preventive agent, an antisettling agent, a wax, to the said raw material composition in the range which does not impair the objective of this invention. Moreover, you may add the additive for providing heat dissipation, such as carbon black.

The method of apply | coating the said raw material composition to a raw material is not specifically limited, The bar coating method, the roll coating method, the spray method, the curtain flow coating method, etc. are employable. Although drying is carried out after application | coating, in a crosslinking agent addition system, it is preferable to heat-dry at the temperature which a crosslinking agent can react. Specifically, heat drying may be performed at 100 to 250 ° C. for about 1 to 5 minutes. On the other hand, cold rolled steel sheets and alloyed hot-dip galvanized steel sheets are subjected to well-known surface treatments (base treatments) such as chromate treatment, non-chromate treatment, and phosphate treatment in advance for the purpose of improving corrosion resistance, adhesion to resin coating, and the like. It may be implemented.

EXAMPLE

The present invention is further described by the following examples, but the following examples do not limit the present invention, and modifications within the scope not departing from the spirit of the present invention are included in the present invention. In addition, when not specifically mentioned below, "%" shall represent "mass%", and "part" shall represent "mass part", respectively.

〔negative〕

The used disc and its abbreviation are shown below. In addition, plating was performed on both surfaces of a metal plate. In addition, these original plates were "CTE-213" by Nippon Park Carizing Co., Ltd., and performed base-processing. The drying temperature was 100 degreeC by the reached plate temperature, and it dried for 1 minute. The adhesion amount was 100 mg / m <2>.

GA: alloyed hot dip galvanized steel sheet ... plate thickness; 0.5 mm, plating adhesion amount; 40g / m <2> per side, Fe amount during plating; 8.6%

CR: cold rolled steel sheet

EG: galvanized steel sheet ... plate thickness; 0.5 mm, plating adhesion amount; 20g / ㎡ each side

GI: Hot-dip galvanized steel plate ... plate thickness; 0.5 mm, plating adhesion amount; 40g / m2 each

〔Suzy〕

Toyo Spinning Co., Ltd. organic solvent-soluble polyester resin Byron (registered trademark) series was used. The kind used and Tg are shown.

Byron BX1001 (Tg: -18 ° C), Byron GK180 (Tg: 0 ° C), Byron 500 (Tg: 4 ° C), Byron GK680 (Tg: 10 ° C), Byron GK590 (Tg: 15 ° C), Byron GK140 (Tg Byron GK780 (Tg: 36 ° C), Byron GK840 (Tg: 46 ° C), Byron GK360 (Tg: 56 ° C), Byron GK250 (Tg: 60 ° C), Byron 200 (Tg: 67 ° C), Byron 296 (Tg: 71 ° C)

Two or more kinds of polyesters were blended and used to obtain a predetermined Tg. In addition, in order to make it predetermined Tg, you may blend in the following ways. The Tg of the blend of two kinds of raw materials is determined as follows.

Tg (b) = Tg (c1) × w1 / 100 + Tg (c2) × (100-w1) / 100

Here, Tg (b): Tg of the blend, Tg (c1): Tg of the first raw material, w1: weight fraction (%) of the first raw material, Tg (c2): Tg of the second raw material.

Therefore, what is necessary is just to adjust w1 so that the predetermined Tg (b) may be obtained. Even when there are three or more types of raw materials, the weight fraction of each raw material may be adjusted similarly. For example, Experiment No. The blend which obtained Tg = 5 degreeC of 7-12 was taken the same weight of Tg = 0 degreeC Viron GK180 and Tg = 10 degreeC Viron GK680, dissolved in the cyclohexane of a solvent, and mixed with the crosslinking agent, and the composition was prepared.

[Cross-linking system]

A melamine resin ("Sumimal (registered trademark) M-40ST": manufactured by Sumitomo Chemical Co., Ltd.) was used.

[Conductive Particles]

Nickel powder ("CNS-10" by Nikko Corporation; average particle diameter 6.3 micrometers; abbreviated to Ni in the table), Fe-Ni alloy magnetic powder (Mitsubishi steel perma: 78Ni-1Mo-FP; average particle diameter 7.6 micrometers) Table In the above, Fe-Ni is omitted. In addition, these average particle diameters are 50% volume average particle diameter measured by the laser diffraction method (scattering formula) using the microtrack FRA9220 by Leeds & Northrup.

[Heat radiating agent]

Carbon black ("Mitsubishi Carbon Black MA100" by Mitsubishi Chemical Corporation; average particle diameter 24nm) was used. In the table, abbreviated as CB.

[Preparation of Raw Material Composition for Resin Coating]

Both of polyester resin and the said crosslinking agent (80% of solid content) were mixed so that polyester resin might be 80% and crosslinking agent (dry) 20% in 100% of coating film solid content. Dilute with xylene / cyclohexanone mixed solvent (xylene: cyclohexanone = 1: 1) so that the solid content concentration of the raw material composition is 10 to 30%, and stir 10 minutes at 10000 rpm with a hand homogenizer to prepare the raw material composition. Prepared. In Experiment 4, the raw material composition to which electroconductive particle and / or carbon black were added was used. The addition amount (%) in a table | surface is a percentage with respect to the total 100 mass% of the said polyester resin, a crosslinking agent (dry), and an additive.

[Production of resin coating steel plate]

The raw material composition for resin coating was coated with various originals by bar coating so as to have the film thickness shown in the table, and baked for 2 minutes at a plate temperature of 230 ° C. in a hot air drying furnace to produce a resin coated steel sheet. The adhesion amount was adjusted by changing the number of times of bar coating. The thickness of the resin film of the table | surface is the value computed from the adhesion amount and the specific gravity of resin.

[Measurement of Tg]

Based on JIS K 7121, it measured using the differential scanning calorimeter (brand name: Thermo Plus DSC8230: Rigaku Corporation make). Specifically, the resin film was scraped off with the cutter knife from the resin coated steel sheet produced as mentioned above, and the sample was taken. This sample was set to a differential scanning calorimeter, cooled to -100 ° C, heated up to 180 ° C at a rate of 20 ° C / min at a stable time point, and the glass transition temperature (Tg) was obtained from the obtained DSC curve.

[Scratch resistance (pencil hardness)]

The pencil hardness test in accordance with JIS K 5600-5-4 was done. The judgment criteria were as follows.

◎: no scratch on the pencil of 4H or more

○: Scratch at 4H, no scratch at 3H

(Triangle | delta): Scratch in 3H and no scratch in 2H

X: It becomes less than H that there is no scratch

Experiment 1

The Tg and the scratch resistance of the resin film were examined. The original plate is an alloyed hot dip galvanized steel sheet in Table 1, and a cold rolled steel sheet in Table 2. The results are shown in Tables 1 and 2. When Tg of a resin film exists in the range of -10 degreeC-+32 degreeC, it turns out that it is excellent in scratch resistance.

Experiment 2

The example in which the film thickness of the resin film exceeds the prescribed range of this invention was examined (Table 3). Even if Tg is within the prescribed range of the present invention, it can be seen that the scratch resistance is lowered when the film thickness is 13 µm.

Experiment 3

The scratch resistance at the time of adding electroconductive particle and / or carbon black was examined. Table 4 shows the result. When the Tg of the resin film was outside the range of the present invention, scratch resistance was lowered.

Experiment 4

The scratch resistance in the case where the original plate is an electrogalvanized steel sheet (EG) and a hot dip galvanized steel sheet (GI) outside of the provisions of the present invention was examined. The results are shown in Table 5. The scratch resistance was inferior due to the lack of hardness of the original.

The resin-coated steel sheet of the present invention can be used in automobiles, home appliances, furniture, building materials, and the like, and is suitable for applications requiring a high level of scratch resistance in addition to these fields.

Claims (3)

A resin coated steel sheet having a resin film having a thickness of 12 µm or less formed on a surface of a cold rolled steel sheet or an alloyed hot dip galvanized steel sheet, and having a glass transition temperature of -10 ° C to 32 ° C. The method of claim 1, The resin-coated steel sheet obtained by the said resin film obtained from the raw material composition containing an organic solvent soluble polyester resin. The method according to claim 1 or 2, A resin coated steel sheet containing a melamine-based crosslinking agent in the raw material composition.