KR20120008498A - Precoated metal sheet having excellent scratch resistance and method for producing the same - Google Patents

Abstract

A precoat metal plate having at least one layer of coating film on the metal plate. The precoated metal sheet was subjected to a 5 mN load on the coating film at a temperature of 25 ° C. using a microhardness tester, press-fitted the indenter, and then removed the load, and measured the load and indentation depth applied to the indenter at this time. Recovery rate: α (α = (D _M -D _E ) × 100 / (D _M -D _O ), except that D _O : indentation depth immediately after loading on indenter, D _M The indentation depth when the load participating in the indenter reaches 5 mN, D _E : the indentation depth immediately before the indenter load is completely removed) is 70% or more, and has a high elastic coating film on the outermost layer. A precoat metal sheet having excellent scratch resistance is provided.

Description

Precoated metal sheet excellent in scratch resistance and manufacturing method thereof {PRECOATED METAL SHEET HAVING EXCELLENT SCRATCH RESISTANCE AND METHOD FOR PRODUCING THE SAME}

The present invention relates to a surface-treated metal sheet excellent in scratch resistance. The precoat metal plate of this invention is the precoat metal plate which prepainted the coating material which can be used especially suitably for the use on the premise of carrying out the shaping | molding process after coating.

The precoated metal sheet of the present invention can be suitably used in, for example, household appliances, building materials, civil engineering, machinery, automobiles, furniture, containers and the like.

In place of the post-coating products that have been conventionally coated after processing for home appliances, building materials, automobiles, and the like, precoated metal sheets coated with colored coating films are used. This metal plate is generally coated with a coating material after carrying out chemical conversion treatment on the metal plate. The metal plate is generally used after being cut and press-molded after coating the coating material.

Since the coating film of a precoat metal plate is shape | molded after coating film formation, workability is calculated | required. In order to improve the processability of the coating film, in general, a technique of making the coating film flexible by using a resin having a low glass transition temperature and having a high molecular weight is common. However, such a coating film has excellent workability but is low in hardness and susceptible to scratching. It was a problem. Moreover, in recent years, although the coated steel plate which has high gloss is calculated | required from a design viewpoint, a scratch is easy to be outstanding in a high gloss coating film, and the scratch resistance in high gloss became a big subject.

As a method of solving such a problem, Patent Document 1 blends an amine block body of dodecylbenzenesulfonic acid into a polyester melamine coating film containing a polyester resin having a glass transition point of 5 to 40 ° C. and a hexamethoxymethylol melamine resin. By coating and drying a coated plastic material formed on a metal plate, and a technique of achieving both workability and high hardness is disclosed, and Patent Document 2 also discloses a coating material for a precoated steel sheet containing a compound having a specific composition, a polyol and a curing agent as a main component. By coating, a technique of achieving both workability and high hardness is disclosed. In addition, Patent Literatures 3 to 5 disclose techniques for improving scratch resistance by adding fine particles in a coating film.

Patent Document 1 Japanese Unexamined Patent Publication No. 2-269168 Japanese Unexamined Patent Publication No. Hei 7-316498 Japanese Unexamined Patent Publication No. Hei 9-111183 Japanese Laid-Open Patent Publication No. 10-219188 Patent document 5 Unexamined-Japanese-Patent No. 11-90322

As described above, in recent years, precoated steel sheets have been developed with excellent workability and high hardness. However, all of them are hard and hard to scratch. However, the precoated steel sheet is rubbed with a harder object than the coating film and scratches the coating film. Did not prevent the occurrence of scratches, the problem was that the scratches remain permanently. For this reason, it has been desired to further improve the scratch resistance of the coating film for precoat metal sheet having high workability. However, as an approach approaching with the hardness of the coating film increases the hardness, the workability is deteriorated. It was considered difficult to achieve both scratch resistance and workability at high dimensions. On the other hand, the technique which improves scratch resistance by adding microparticles | fine-particles in a coating film has the subject that while scratch resistance improves by addition of microparticles | fine-particles, gloss falls and color tone is inhibited.

The present invention does not merely harden the coating film as a means to solve the above problems in the prior art, but even if scratches occur in the coating film, the coating film deformation of the scratch portion is recovered with time, so that the scratches disappear or are visible to the naked eye. An object of the present invention is to provide a precoated metal sheet and a method of manufacturing the same, which pay attention to the recovery of the coating film deformation of the scratch portion so as not to be noticeable, thereby achieving both scratch resistance and high workability.

This invention further makes it a subject to provide a scratch resistance in the state which maintained the outstanding gloss and color tone, without adding microparticles at all by this function.

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining in order to solve the said subject, it not only expresses rubber elasticity to a coating film, but also gives a specific recovery characteristic to this rubber elasticity, and even if a depression and a scratch generate | occur | produce in this coating film (it does not become plastic deformation) Over time, it has been found that very suitable elastic recovery is possible.

As a result of further studies based on the above findings, the present inventors further found that the coating film having the above specific recovery characteristics has flexibility and excellent processability.

The coating film having the specific recovery characteristics as described above is, for example, a polyester resin or a polyester elastomer resin having a glass transition point of cryogenic temperature in a coating film resin, and is used as a thermosetting coating film resin in which a curing agent is added thereto. It can achieve suitably.

This invention is completed based on the said knowledge. What this invention makes the summary is as follows, for example.

(1) A precoat metal sheet having a coating film of at least one layer on the metal sheet, wherein a load of 5 mN is applied to the coating film at a temperature of 25 ° C. using a microhardness tester, the indenter is press-fitted, and the load is removed. Indentation depth recovery rate determined by measuring the load applied and the indentation depth: α (α = (D _M -D _E ) × 100 / (D _M -D _O ), where D _O : immediately after the loading of the indenter Indentation depth, D _M The indentation depth when the load applied to the indenter reaches 5 mN, D _E : the indentation depth before the complete removal of the indenter load) is 70% or more. The pre-coated metal sheet having excellent scratch resistance, characterized in that the scratches disappear or become inconspicuous.

(2) Said scratch recovery rate: The precoat metal plate excellent in scratch resistance characterized by having the high elastic coating film layer whose (alpha) is 85% or more in outermost layer.

(3) The pre-coated metal sheet excellent in scratch resistance according to (1) and (2) above, wherein the mirror glossiness described in JIS-K5600-4-7 of the high elastic coating film is 90% or more at 60 degrees of geometric conditions. .

(4) The scratch resistance according to any one of (1) to (3) above, wherein the highly elastic coating film contains 4 parts by mass or less of fine particles with respect to 100 parts by mass of the total resin of the main resin and the curing agent of the coating film. This excellent precoat metal plate.

(5) The above-mentioned (1), wherein the main resin of the high elastic coating film is a thermosetting resin in which a curing agent is blended with either polyester resin or polyester elastomer resin, and the glass transition point of the main resin is -10 ° C or lower. The precoat metal plate excellent in the scratch resistance in any one of (4)-(4).

(6) The glass-coating point of the main resin of the said highly elastic coating film is -30 degrees C or less, The precoat metal plate excellent in the scratch resistance as described in said (5) characterized by the above-mentioned.

(7) The precoat metal plate excellent in the scratch resistance as described in said (5)-(6) whose hardening | curing agent mix | blended with the main resin of the said high elastic coating film is melamine resin.

(8) The precoat metal sheet having excellent scratch resistance according to any one of the above (1) to (7), wherein the precoat metal sheet has a coating layer structure of two or more layers having a coating film under the high elastic coating film.

(9) In the precoat metal plate, the high elastic coating film of the outermost layer is a clear coating film containing no pigment, and further has a colored coating film under the high elastic coating film, (1) to (8) above. The precoat metal plate excellent in the scratch resistance of any one of Claims.

(10) The above-mentioned (9), wherein the main resin of the colored film is a thermosetting resin in which a curing agent is added to either the polyester resin or the polyester elastomer resin, and the glass transition point of the main resin is -10 deg. The precoat metal plate excellent in the scratch resistance of description.

(11) The scratch resistance according to any one of (8) to (10) above, wherein Ra (center line average roughness) at the interface between the high elastic coating layer and the coating layer located below this layer is 0.3 to 0.8. Excellent precoat metal plate.

(12) In the manufacturing method of the precoat metal plate as described in any one of said (8)-(11), the coating material for forming the uppermost highly elastic coating layer on a metal plate, and the coating material for forming the coating layer below it are undried state. A precoat metal sheet excellent in scratch resistance, wherein the multilayered coating film in an undried state is dried and cured at the same time.

According to the present invention, it is possible to provide a precoated metal sheet having better scratch resistance than the conventional one, and for home appliances, building materials, civil engineering, machinery, automobiles, furniture, and containers manufactured using the precoated metal sheet. When manufacturing and assembling parts, scratches due to handling are less likely to occur, and the production yield is improved, and even when handled more easily than conventional materials, scratches due to handling become less likely to occur, thereby improving work efficiency. It became. Moreover, since the scratch resistance of each product using this was greatly improved compared with the conventional one by using the precoat metal plate of this invention, the product quality was improved. Therefore, the present invention can be said to be an invention of extremely high industrial value.

1 is a relationship between the indentation load and the time until the indenter is press-fitted with a load of up to 5 mN, measured using a microhardness meter, and then the load is removed to completely remove the load.
2 is a relationship between indenter indentation depth and load obtained when measured with a microhardness tester.
FIG. 3 is a relationship between indenter indentation depth and load after zero point correction of data in FIG. 2; FIG.
4 is unevenness of the coating film interface.

The present invention uses a micro hardness tester to apply a load of 5 mN to a coating film at room temperature of 25 ° C., press-fit the indenter, remove the load, and measure the indentation depth recovery rate obtained by measuring the load and the indentation depth applied to the indenter at this time. α (α = (D _M -D _E ) × 100 / (D _M -D _O ), where D _O is the indentation depth immediately after starting to apply the load to the indenter, and D _M is the predetermined load that participates in the indenter. When the indentation depth when the load is reached, D _E : the indentation depth immediately before the indenter is completely removed from the indenter) is coated on the metal plate with a rubber elastic coating film of 70% or more, so that the coating film elastically recovers even if a scratch occurs in the coating film. It is characterized by disappearing or inconspicuous. If the indentation depth recovery rate is less than 70%, this scratch is not suitable after the scratch has actually occurred so as not to become inconspicuous. It is more suitable if the indentation depth recovery rate is 85% or more.

The precoated metal sheet of the present invention is characterized in that the indentation depth recovery rate: α is 70% or more when the coating film properties are measured by a microhardness meter at (25 ± 1) ° C.

The microhardness tester for obtaining the indentation depth recovery rate of α of the present invention can generally use a microhardness meter capable of measuring the hardness of a resin such as a known coating film. Commercially available measuring devices, for example, Fischer Scope H100V manufactured by Fischer Instruments, Inc. may be used. The method described in German DIN-50359-1 can be used. Although the shape of the indenter is not particularly limited, generally known indenters such as Vickers square pyramid diamond indenters, Belkovic triangular pyramid diamond indenters, knuckle diamond indenters, and tungsten carbide ball indenters can be used. The method of applying or removing the load to the indenter may be performed continuously or may be applied or removed from the step load.

In the present invention, the indentation depth recovery ratio: D _O and the indentation depth immediately after the indenter was completely removed were defined as D _E as a parameter for obtaining? D _O indicates the position of the indenter on the outermost surface of the coating film, that is, the zero point, before the load is applied to the indenter. Since it is difficult to detect the zero point skillfully in an actual measuring device, the position of the indenter in which the load and the indentation depth were first detected when the measurement device is loaded with the indenter and the measurement is started is defined as D _O as the zero point. . In addition, D _E indicates the position of the indenter (end point of the test) when the load is completely removed in the process of removing the indenter load. Depending on the measuring device, it may be difficult to detect the position where the load of the indenter is completely removed. Therefore, the position where the measuring device immediately before the load is completely removed can be detected may be D _E. Although D _O and D _E may differ in terms of mechanical precision by the measuring device, the zero point indicated by each measuring device or the point corresponding thereto and the end point of the test and the point corresponding thereto can be applied.

In fact, the relationship between the time and the indentation load was shown by pressing the indenter with a load of up to 5 mN, measured using a microhardness tester, and then removing the load to completely remove the load. 2 and 3 show the relationship between the indenter indentation depth and the load, and the points D ₀ , D _E and D _M. Fig. 2 is an example of the relationship between the indenter indentation depth and the load according to the data obtained when measured with a Fisher scope H100V manufactured by Fisher-Instrument Co., a commercially available measuring device, and points of D _O , D _E , and D _M. FIG. 3 shows the relationship between the indenter indentation depth and the load and the points of D _O , D _E , and D _M after zero point correction of the data of FIG. 2.

The precoat metal plate of this invention is a thermosetting resin which mix | blended the hardening | curing agent with either the polyester resin or the polyester elastomer resin, and the main resin of the said high elastic coating film, and the glass transition point of a main resin shall be -10 degrees C or less, More suitable. This is because the indentation depth recovery rate α of the high elastic coating film is 70% or more, and the workability of the coating film is also suitably secured. If the glass transition point is more than -10 ° C, the indentation depth recovery rate of the coating film may be less than 70%, which is not preferable. More preferably, it is -30 degrees C or less. The lower limit of the glass transition point of the main resin is not particularly specified. However, if the glass transition point is too low, the coating film becomes too soft and easily broken, so that the elastic recovery may not be completed completely, and scratches are likely to occur. This is very suitable. Moreover, when main resin other than polyester resin or polyester elastomer is used, since the workability of a coating film may fall, it is unpreferable. Moreover, when a hardening | curing agent is not mix | blended with main resin, since film-forming will become inadequate and it may have adhesiveness, it is not preferable.

The polyester resin which can be used suitably for the main resin of the high elastic coating film of this invention can use a well-known thing generally. A commercially available thing, for example, the polyester resin "Byron ^® " series by Toyobo Corporation, the polyester resin "Desmophen" series by Sumica Bayer Urethane Co., etc. can be used. Polyester elastomers may also be generally known, for example, polybutylene terephthalate and the like.

Generally the hardening | curing agent mix | blended with the main resin of the high elastic coating film of this invention can add a well-known hardening | curing agent for paints, for example, hardening | curing agents, such as a melamine resin and an isocyanate. What is marketed, for example, the melamine resin "Cymel ^® " series made by Mitsui Cytec, "My Coat ^® " series, the melamine resin "Super Beck Carmine ^® " series made by DIC Corporation, the isocyanate "sumizule" made by Sumika Bayer Urethane Co., Ltd. ^® "series," Desmodule ^® "series, etc. can be used.

When the said hardening | curing agent is melamine resin, since the indentation depth recovery rate of a coating film becomes larger than using another hardening | curing agent, it is more suitable. The addition amount of a hardening | curing agent can be suitably selected as needed. In the case of melamine resin, 10-100 mass parts is suitable for 100 mass parts of main resins. If it is less than 10 parts by mass, the coating film may be uncured. If it is more than 100 parts by mass, the coating may be brittle and the workability may be reduced. When isocyanate is added to a hardening | curing agent, it is good to add so that the equivalence ratio of the OH group of the polyester resin to mix | blend with the NCO group of isocyanate may be OH / NCO = 0.8-1.2. If OH / NCO is less than 0.8 or more than 1.2, unreacted functional groups remain in the main resin or the curing agent in the coating film, and there is a risk of uncuring. When it is added so that OH / NCO = 1.0, unreacted functional groups of the main resin or the curing agent in the coating film are hard to remain, and the hardness and workability of the coating are very suitable for the hardness.

When the precoat metal plate of this invention is a precoat metal plate which laminated | stacked 2 or more layers of coating films, when the uppermost coating film is the said high elastic coating film, since it is possible to provide the outstanding scratch resistance in addition to the function which the underlayer coating film has, it is suitable. For example, in the case of a two-layer precoat metal plate coated with a primer coating film containing an rust-preventive pigment on a metal plate and coated with a high elastic coating film colored thereon, excellent scratch resistance can be provided in addition to excellent corrosion resistance.

The high elastic coating film of this invention may be colored. Among the colored pigments, the addition of carbon black is particularly preferable since the scratch recovery is improved. This is presumably because the addition of carbon black to the resin and the carbon black have a high affinity with the resin, and thus the elastic modulus of the coating film increases and the scratch recovery rate also increases. In addition, if the high elastic coating film of the present invention does not contain any fine particles or is 4 parts by mass or less with respect to 100 parts by mass of the total resin in which the main resin and the curing agent are combined, the gloss can be enhanced while maintaining excellent scratch resistance. More suitable.

In addition, in the case of the two-layer precoat metal plate coated with a colored undercoat coating film coated on the metal plate and coated with a high elastic coating film of clear thereon, not only scratch resistance but also various colors can be provided, and high gloss is imparted. can do. Furthermore, by coating a primer coating film containing an rust-preventing pigment on a metal plate, coating a medium coating film colored thereon, and coating a high elastic coating film thereon, corrosion resistance and high gloss and scratch resistance can be imparted. If the high elastic coating film of the outermost layer is a clear coating film, it is more suitable because it can provide scratch resistance in addition to the coating film performance of the conventional precoat metal plate by coating it on the conventional precoat metal plate.

As a coating film other than an uppermost layer, a well-known coating film for precoat metal plates, for example, a polyester coating film, an acrylic coating film, a urethane coating film, an epoxy coating film, etc. can be used. Commercially available coating films for precoat metal sheets can also be used. In addition, you may use the high elastic coating film of this invention for coating films other than outermost layer.

Pigments, such as a coloring pigment and an antirust pigment, may be added to the high elastic coating film of the uppermost layer of the precoat metal plate of this invention, and the coating film of another layer as needed. As a coloring pigment, generally well-known inorganic type pigments and organic type pigments, such as titanium oxide, carbon black, and chrome yellow, can be used.

As the rust preventive pigment, generally known rust preventive pigments such as strontium chromium, potassium chromate, calcium chromate, aluminum tripolyphosphate, calcium adsorbed silica, zinc phosphate and zinc phosphite can be used. However, in recent years, since rust preventive pigments containing hexavalent chromium, such as strontium chromium, potassium chromate, and calcium chromate, are environmentally loaded substances, those which do not contain these are more suitable.

Moreover, you may add various additives, such as a gloss remover, a leveling agent, an antifoamer, a slip agent, and a wax, to the coating film of this invention as needed.

When the precoat metal plate of this invention is a precoat metal plate which laminated | stacked 2 or more layers of coating films, when this is processed, since elastic deformation energy tends to remain in the high elastic coating film after processing, work adhesiveness may fall. However, when manufacturing the precoat metal plate of this invention which laminated | stacked 2 or more layers of coating films, the coating material for forming the uppermost highly elastic coating film layer, and the coating material for forming the coating film layer below it are laminated | stacked in the undried state, When it manufactures by the so-called wet-on-wet method which dry-hardens simultaneously the unpainted multilayered coating film, the coating film adhesiveness in a process part improves and it is more suitable.

When multilayer simultaneous coating or wet-on-wet coating is applied, Ra (center line average roughness) of an interface can be controlled to 0.3-0.8 micrometer more suitably. If Ra of an interface is less than 0.3 micrometer, the adhesiveness after a process will fall, and when it is more than 0.8 micrometer, there exists a possibility that an appearance defect may arise. Ra of an interface can be achieved by controlling the surface tension of each coating laminated | stacked at the time of multilayer simultaneous coating or wet-on-wet coating. When 0.3 mN / m ≤ [surface tension of paint on lower layer]-[surface tension of paint on upper layer] <5 mN / m, Ra at the interface is easily set to 0.3 to 0.8 µm, which is very suitable. If [surface tension of the paint on the lower layer side]-[surface tension of the paint on the upper layer side] is less than 0.3 mN / m, Ra at the interface may be more than 0.8 µm, and at 5 mN / m, the Ra of the interface is exceeded. May be less than 0.3 µm. In addition, in this invention, Ra of this interface can be measured by the following method (namely, the method according to JIS-B-0601-1982). That is, after photographing the vertical cross section of the interface on which surface roughness Ra is to be measured with a micrograph, the unevenness (roughness curve) of the interface is traced, and the center line average of this interface is obtained in accordance with JIS-B-0601-1982. The roughness Ra can be obtained.

As a coating method of this wet-on-wet, the lower layer coating film is layered by a roll coater or a curtain coater, and the top layer highly elastic coating film is coated with a curtain coater, or a high elastic coating film and the lower layer coating film below are slide hopper type multilayer simultaneous coating type curtains. The coating method using a coater etc. can be employ | adopted. In addition, these coated films can be dry-cured by a hot air oven, an infrared oven, a near infrared oven, an induction heating oven, or the like.

The film thickness of the high elastic coating film layer of this invention is not specifically defined, It can select suitably as needed, and it is very suitable in it being 3-25 micrometers. It is because there exists a possibility that the scratch resistance effect may not fully be exhibited when it is less than 3 micrometers, and when it exceeds 25 micrometers, the coating defect called boiling may generate | occur | produce when baking a coating film. When the precoat metal plate of this invention has a coating layer of two or more layers, 3-25 micrometers is suitable also for the film thickness of coating layers other than a high elastic coating layer. It is because there exists a possibility that the effect which coat | covered the coating film layer may not be exhibited when it is less than 3 micrometers, and there exists a possibility that the coating defect called boiling may generate | occur | produce when baking a coating film more than 25 micrometers.

The precoat metal plate of this invention is more suitable because coating film adhesiveness improves when a coating film is coat | covered after carrying out chemical conversion treatment on a metal plate. The chemical conversion treatment is generally known chromate treatment, electrolytic chromic acid treatment, trivalent chromium treatment, zinc phosphate treatment, zirconia-based treatment, commercial chromate free conversion treatment, treatment with a silane coupling agent, containing a silane coupling agent and a water-soluble resin. A chemical conversion treatment can be used. Since chromate treatment contains hexavalent chromium which is an environmental load substance, the chromate free conversion treatment which does not contain this is more suitable. Although the treatment method of these chemical conversion treatments can be generally apply | coated by a well-known application | coating method, it apply | coats using a roll coater, and drying with a dryer or oven is more suitable for a high working efficiency.

The precoat metal plate of this invention may be coated on the back surface of the surface which coats a high elastic coating film layer. In general, the back coating can coat a known back coating for a precoat metal sheet, for example, a polyester paint, an epoxy paint, a urethane paint, an acrylic paint, and the like. Only one layer may be coated and two or more layers may be applied. Moreover, you may coat the high elastic coating film layer of this invention.

As a metal plate used for the precoat metal plate of this invention, a well-known metal plate, for example, an aluminum plate, a copper plate, a steel plate, a plated steel plate, a stainless steel plate, etc. can be used. For galvanized steel sheet, hot dip galvanized steel sheet, electro galvanized steel sheet, zinc-iron alloy plated steel sheet, zinc-nickel alloy plated steel sheet, zinc-55% aluminum alloy plated steel sheet, zinc-13% aluminum-3% magnesium alloy plated steel sheet In general, known steel sheets such as aluminum plated steel sheets can be used. This metal plate can be suitably selected and used as needed.

[Example]

The detail of an Example is described below.

1. Metal plate

A hot dip galvanized steel sheet having a plate thickness of 0.5 mm was used. As for the zinc adhesion amount, the one surface of 45 g / m <2> was used.

2. Chemical treatment liquid

An aqueous solution containing 5 g / l of a silane coupling agent, 1.0 g / l of water-dispersed silica and 25 g / l of an aqueous acrylic resin was prepared to obtain a chemical conversion treatment liquid. As the silane coupling agent, γ-glycidoxypropyltrimethoxysilane, “Snowtec-N” manufactured by Nissan Kagaku Co., Ltd. was used for fine silica, and polyacrylic acid was used for an aqueous acrylic resin.

3. Primer Paint

Melamine resin "Cyme ^® 303" made by Mitsui Cytec Co., Ltd. is made by Mitsui Cytec Co., Ltd. by mass ratio of resin solid content to 10 mass parts of 100 mass parts of polyester resin solid content by "Bylon ^® 290" (glass transition point 72 degreeC) which is polyester resin made by Toyobo Corporation Add to add. Furthermore, 0.5 mass% of acidic catalyst "catalyst ^TM 600" by Mitsui Cytec Co., Ltd. was added to the mixed solution of this polyester resin and melamine resin, and the clear coating material was created. Furthermore, primer coating was created by adding 30 mass parts of tripolyaluminum dihydrogen phosphate "K-WHITE ^® # 105" made from Teika Corporation with respect to 100 mass parts of resin solids of the sum total of polyester resin and melamine resin in this clear paint. .

4. Medium coating

Melamine resin "Cyme ^® 303" made by Mitsui Cytec Co., Ltd. is made by Mitsui Cytec Co., Ltd. by the mass ratio of resin solid content to "Bylon ^® 200" which is a polyester resin made by Toyobo Corporation (glass transition point 67 degreeC), and it is 10 mass parts of polyester resin solids 10 Add to mass parts. Furthermore, 0.5 mass% of acidic catalyst "catalyst ^TM 600" by Mitsui Cytec Co., Ltd. was added to the mixed solution of this polyester resin and melamine resin, and the clear coating material was created. In addition, the middle coating film was created by adding 5 mass parts of carbon black "Toka Black # 7300" by Tokai Carbon Co., Ltd. to 100 mass parts of resin solids of a total of polyester resin and melamine resin in this clear paint (hereinafter, Commonly called middle coat). In addition, Tg containing polybutylene terephthalate as the main component is a melamine resin "Cymel ^® 303" manufactured by Mitsui Cytec Co., Ltd. in a cyclohexanone melted product of a polyester elastomer at -36 ° C, in a mass ratio of resin solids, 20 mass parts is added with respect to 100 mass parts of solid content, and acidic catalyst "catalyst ^TM " made by Mitsui Cytec Co., Ltd. is added to the mixed solution of this polyester resin and melamine resin. A high-elastic medium coating material was prepared by adding 5 parts by mass of 0.5 mass% of Toka Carbon Co., Ltd. and carbon black "Toka Black # 7300" manufactured by Tokai Carbon Co., Ltd. with respect to 100 parts by mass of the total resin solids of the polyester resin and melamine resin Hereinafter referred to as high elastic middle coating).

5. Top Paint (High Elasticity Paint)

Polyester resin "Byron ^® 290" (glass transition point 5 degrees Celsius) and "Byron ^® 550" (glass transition point -15 degrees Celsius) made by Toyobo are mix | blended in ratio of 1: 1 by solid mass ratio, and cyclohexanone: Solbe The solvent melt | dissolved product of the polyester resin of glass transition point (henceforth Tg) -10 degreeC was created by melt | dissolving and stirring in the solvent (mass ratio) mixed in the small 150 = 1: 1. In addition, this resin irradiated the glass transition point by the thermal analysis method after volatilizing the solvent powder of the created solvent melt | dissolution product, and confirmed that it was 10 degreeC.

In addition, Tg which melt | dissolved in the solvent (mass ratio) which mixed only polyester resin "Byron ^® 550" (glass transition point-15 degreeC) made from Toyobo Corporation in cyclohexanone: Solvesso 150 = 1: 1 is polyester of -15 degreeC Solvent melt | dissolution products of resin were also created.

Moreover, the cyclohexanone melt | dissolved product of the polyester elastomer whose Tg which has polybutylene telephthalate as a main component of -36 degreeC was also created.

As a comparison, the Tg dissolved in the solvent (mass ratio) which mixed only polyester resin "Byron ^® 290" (to glass transition point 5) by Toyobo Corporation in cyclohexanone: Solvesso 150 = 1: 1 of the polyester resin of 5 degreeC Solvent melts were also prepared.

By adding 5 to 120 parts by mass of melamine resin "Cymel ^® 303" manufactured by Mitsui Cytec Co., Ltd., at a mass ratio of the resin solids, to the melted product of each polyester or polyester elastomer prepared next. And the mixed solution of polyester resin / melamine resin in which melamine resin addition amount differs were created. In addition, the acid catalyst "Catalyst ^TM " made by Mitsui Cytec Co., Ltd. was added to the mixed solution of this polyester resin and melamine resin. 600 "was added and the melamine hardening type clear coating material was created. In addition, OH / NCO = 1.0 is an equivalent ratio of isocyanate resin "Sumizule ^® BL3175" made by Sumika Bayer Urethane Co. It was blended as much as possible. In addition, depending on the need of clear silica coatings during Tokai Carbon Co., Ltd. Carbon Black "Toka Black # 7300", to be manufactured in Japan ah "AEROSIL ^TM 200 ", nylon fine particles" Olgasol 2002 EX-D "by Ato Shimi Co., Ltd., and phenol resin fine particles" Bellpearl R-800 "by Kanebo Corporation were added.

6. backside paint

The back surface paint and Olga 100 beige made by Japan Fine Coatings Co., Ltd. were prepared.

7. Preparation of Precoat Steel Sheet

The metal plate was degreased by immersing in a 2 mass% concentration of FC-4336 (made by Nippon Parkarizing Co., Ltd.) and an aqueous solution at a temperature of 60 ° C for 10 seconds, and dried after washing with water. Moreover, the chemical conversion treatment liquid was apply | coated to both surfaces of the metal plate with the roll coater, and it dried in the hot air drying furnace, and obtained the chemical conversion treatment film layer. The adhesion amount of the chemical conversion treatment liquid was coated so that the adhesion amount of the entire dry film was 100 mg / m 2. The achieved plate temperature at the time of chemical conversion treatment drying was 60 degreeC.

Next, a primer coating was applied to the surface of the metal plate subjected to chemical conversion treatment so as to have a dry film thickness of 5 μm with a roll coater, and the other surface was coated with a roll coater so as to have a coating film thickness of 5 μm, followed by blowing hot air. The coating film layer was obtained by dry-curing on the conditions which the reaching plate temperature of a metal plate will be 210 degreeC with an induction heating furnace. After dry baking, the coated metal plate was sprayed with water to cool the water. In addition, the middle coat and the top coat are laminated on the primer coating layer by a slide-hopper type catheter coater at the same time, and the induction heating furnace in which hot air is blown through the laminated coat is simultaneously used under the condition that the reaching plate temperature of the metal plate is 230 ° C. Dry-baking and water-cooling obtained the precoat metal plate which is a test material (The precoat steel plate produced by this method is hereafter called "3 coat 2 bake" or "3C2B."). In addition, when coated with a slide hopper type curtain coater, an appropriate amount of BYK-additive "BYK-333" made by BYK is added to the top coating material, and the surface tension of the top coating film is 3 mN / m than the surface tension of the middle coating material to be laminated together. The degree was adjusted to increase.

In addition, if necessary, the intermediate coating material is coated on the undercoat with a roll coater, and simultaneously dried and baked under conditions that reach the plate temperature of the metal plate at 230 ° C. in an induction heating furnace in which hot air is blown, and after cooling with water, The coating material was coated with a roll coater, dried and baked at the same time under the condition that the plate reached the temperature of the steel plate was 230 ° C. in an induction heating furnace in which hot air was blown, and water cooled to obtain a precoated steel sheet as a test material. The metal plate is hereinafter referred to as "3 coat 3 bake" or "3C3B").

In addition, since the line which manufactures the precoat metal plate sample of this invention was a 2-baking line which has only two ovens, when producing the sample of 3C3B, the line was plated twice and the sample was produced. Moreover, as needed, the sample of 1 coat 1 bake (1C1B) and 2 coat 2 bake (2C2B) which does not have a primer coat layer and a intermediate coat layer was also produced. In addition, the intermediate coating film was made into 15 micrometers of dry film thickness, and the film thickness of the top coating film was created. The detail of the produced precoat steel plate is put together in Table 1.

The following evaluation test was done about the precoat steel plate thus created. In addition, also about any test, the test on which the surface which coated the top coating film was performed was evaluated.

1. Observation of painting appearance

The appearance of the coating of the prepared precoat metal sheet was visually observed and the occurrence of boiling defects was observed.

2. Mechanical properties of saw coating

The relationship between the indentation load and the indentation depth was measured using the microhardness meter "Fisscope Scope H100V" made by Fischer Instruments, Inc., on the surface of the produced precoated steel sheet. This measurement was performed at the temperature of 25 degreeC. The indenter was gradually subjected to a step load such that the maximum load was 5 mN at 60 step loads using a Vickers square pyramid diamond indenter, and the indenter was pressed into the coating film. The step interval was set to 1 s, and each step load was applied under the condition of increasing proportionally. In addition, after the load reached 5 mN, the load was reduced under the same conditions as when the load was increased, and the indentation depth of the indenter until the indentation load became zero was measured. The relationship between the time of this condition and a load is shown in FIG.

In addition, D ₀ , D _M , and D _E shown in the indentation depth-indentation load diagram shown in FIG. 2 were obtained, and the indentation depth recovery ratio α = (D _M -D _E ) × 100 / (D _M -D _O ) was calculated. .

3. Machinability Test

The precoated steel sheet thus prepared was subjected to 180 ° bending (a process commonly referred to as 1T bending) with spacers having the same thickness between them, and the coating film of the processed portion was visually observed 20 times with a loupe to visually crack the coating film. The presence or absence was examined. Bending processing was processed in 20 degreeC atmosphere.

The evaluation of the coating film crack was observed at 20 times loupe, and there was no coating film crack at all. When observed at 20 times loupe, there was a small crack on the coating film. Even if this was recognized by (triangle | delta) and visual observation, the case where the big crack which was clear was located in the whole process part was evaluated as x.

4. Process adhesion test

A tape was affixed on the coating film of the processed part of the sample which performed the processability test of said 3., and the peeling state of the coating film at the time of peeling this tape was observed by 20 times loupe and visual observation, and the peeling degree of the coating film was investigated.

The evaluation of coating peeling is ◎ the case where no film peeling is observed even when observed at 20 times loupe, and when the 20 times loupe is observed, there are minute cracks in the coating film. (Triangle | delta) and the case where large peeling which was clear also with the naked eye on the whole process part were evaluated as x as a case where peeling is recognized.

5. Scratch Recovery Test

In accordance with JIS.K.5600.5.4 scratch hardness (pencil method), scratches were put on the coating film surface with a pencil having hardness of H, 2H, and 3H. And the recovery condition of the scratch after this was immersed in boiling water for 1 minute was visually observed and evaluated.

The evaluation is ◎ when no scratch is recognized on the part scratched with a pencil of 3H, and ○ when a scratch is recognized on the part scratched with a pencil of 3H, but the scratch is not recognized on the part of 2H. When the scratch was recognized but the scratch was not recognized in the part of H, when the scratch was recognized also in the part which was scraped with (triangle | delta) and the pencil of H, it was set as x.

6. Ra measurement of the interface between the high elastic coating film and the coating film located below

The precoat metal plate was cut vertically so that the coating film cross section could be observed, and the cut | disconnected precoat metal plate was embedded in resin, the cross section was ground, and the cross-sectional photograph of the coating film by 3500-times scanning electron microscope was taken. Next, the transparent resin sheet (using a commercially available OHP sheet) was covered on the photograph, and the unevenness | corrugation of a coating film interface was traced correctly. And as shown in FIG. 4, the area of the vertical line part was measured with the image processing apparatus, and Ra was computed from Formula (I) as the average value.

In addition, the thing which computed Ra falls in the range of 0.3-0.8 micrometer was (circle) and the thing outside the range of 0.3-0.8 micrometer was evaluated as (triangle | delta).

7. Gloss measurement

The mirror glossiness of the prepared precoat metal plate was measured. The measuring method was measured on condition of 60 degree of geometric conditions based on JIS-K5600-4-7. Moreover, the following references | standards evaluated.

When mirror glossiness is 95 or more: ○

When mirror glossiness is 90 or more and less than 95: △

If mirror glossiness is less than 90: ×

Hereinafter, the detail of an evaluation result is described. The evaluation result of the precoat metal steel plate produced in Table 2 is shown. All the indentation recovery rates shown in Table 2 are measured at "25 degreeC."

The precoated metal sheets (Inventive Examples 1 to 21) having an indentation depth recovery rate of 70% or more of the present invention are excellent in scratch recovery properties because they recover even if scratches occur and the scratches become inconspicuous. On the other hand, the indentation depth recovery rate of less than 70% (Comparative Examples-22 to 25) is unsuitable because the scratch recovery property is inferior and scratches are left permanently when scratches occur.

The resin having a glass transition point of more than -10 ° C in the top coating film of the outermost layer (Comparative Examples-22, 23) has a tendency to be less than 70% indentation depth recovery and tends to be excellent in scratch recovery properties. Preference is given to using polyester resins or polyester elastomer resins having a glass transition point of −10 ° C. or lower (Invention Examples 11 to 21). The glass transition point having a glass transition point of -30 ° C or lower (Inventive Example 1 3, 6, 9 to 21, etc.) is more suitable because the indentation depth recovery rate is more than 85%, and the scratch recovery is also excellent.

When the curing agent used in the high elastic coating film is that of isocyanate (original invention example-15) and melamine resin (inventive examples-17 to 14), the melamine resin used has a high indentation depth recovery rate and excellent scratch recovery properties. More suitable.

The addition amount of the melamine resin is suitably 10 to 100 parts by mass with respect to 100 parts by mass of the polyester resin or the polyester elastomer resin. The thing of less than 10 mass parts (comparative example-24) has a low indentation depth recovery rate, and there exists a tendency for scratch recovery to fall, and the thing of more than 100 mass parts (invention example 14) tends to be inferior to workability.

The film thickness of the high elastic coating film is very suitably 3 to 25 µm, and less than 3 µm (Comparative Example-25) has a low indentation depth recovery rate and a low scratch recovery property, and more than 25 µm (Invention Example) -18) The occurrence of defects due to boiling in part was recognized in the baking process.

In addition, the coating material for forming the high elastic coating film layer of the uppermost layer and the coating material for forming the coating film layer below it are laminated | stacked in the undried state, and were manufactured by the method of simultaneously drying this undried multilayer film. Invention Examples-4 to 18) are more suitable because the processing adhesiveness is improved than those in which these coating films are repeatedly produced by coating baking for each single layer (Invention Examples-1 to 3, 19).

In addition, coating the primer under the high elastic coating film (Inventive Examples 1 to 19) is preferable to coating one layer of only the high elastic coating film on the metal plate (Invention Examples 20 to 20), because it is excellent in work adhesiveness.

In the precoated metal sheet of the present invention, the amount of fine particles added in the high elastic coating film layer is more than 4 parts by mass based on 100 parts by mass of the total amount of the main resin and the curing agent (Examples of the present invention-1 to 6, 28 to 35). Since the tendency to do so is suitable, the amount of fine particles added is preferably less than 4 parts by mass. However, the addition of carbon black in the high elastic coating film (for example, Example 6 of the present invention) has a higher indentation depth recovery rate and excellent scratch recovery performance compared to the one without addition (for example, Example 9 of the present invention). Since there exists this, adding carbon black is more suitable.

Claims (12)

A precoat metal sheet having at least one layer of coating film on the sheet metal, using a microhardness tester, a load of 5 mN is applied to the coating film at a temperature of 25 ° C., press-fitted the indenter, and the load is removed. Indentation depth recovery rate determined by measuring the load and indentation depth: α (α = (D _M -D _E ) × 100 / (D _M -D _O ), where D _O : indentation depth immediately after starting to apply load to the indenter, D _M The indentation depth when the load applied to the indenter reaches the 5 mN, D _E: indentation depth immediately preceding complete removal of the load of the indenter) is excellent in scratch resistance, characterized in that having a high modulus film on the outermost surface layer of 70% or more free Coat metal plate. Said scratch recovery rate: The precoat metal plate excellent in scratch resistance characterized by having the high elastic coating film layer whose (alpha) is 85% or more in outermost layer. The pre-coated metal sheet having excellent scratch resistance according to claim 1 or 2, wherein the mirror glossiness described in JIS-K5600-4-7 of the high elastic coating film is 90% or more at 60 degrees of geometric conditions. The scratch-resistance according to any one of claims 1 to 3, wherein the highly elastic coating film contains 4 parts by mass or less of fine particles with respect to 100 parts by mass of the total resin of the main resin and the curing agent of the coating film. Excellent precoat metal plate. The main resin of the said high elastic coating film is a thermosetting resin which mix | blended the hardening | curing agent with either polyester resin or polyester elastomer resin, and also the glass transition point of main resin of any one of Claims 1-4. A pre-coated metal sheet excellent in scratch resistance, characterized by being -10 deg. The glass coating point of the main resin of the said highly elastic coating film is -30 degrees C or less, The precoat metal plate excellent in the scratch resistance of Claim 5 characterized by the above-mentioned. The precoat metal plate excellent in scratch resistance of Claims 5 and 6 whose hardening | curing agent mix | blended with the main resin of the said highly elastic coating film is melamine resin. 8. The precoat metal sheet having excellent scratch resistance according to any one of claims 1 to 7, wherein the precoat metal sheet is a two or more layered coating structure having a coating film under the high elastic coating film. The said precoat metal plate is a clear type coating film which does not contain a pigment, and has a colored coating film in the lower layer of this high elastic coating film in any one of Claims 1-8. A precoat metal sheet excellent in scratch resistance. The main resin of the said colored film is a thermosetting resin which mix | blended a hardening | curing agent with either polyester resin or polyester elastomer resin, and the glass transition point of this main resin is -10 degrees C or less, Precoated metal sheet with excellent scratch resistance. The scratch resistance according to any one of claims 8 to 10, wherein the Ra (center line average roughness) of the interface between the high elastic coating layer and the coating layer disposed below is 0.3 to 0.8. Precoat metal plate. The manufacturing method of the precoat metal plate as described in any one of Claims 8-10 WHEREIN: Laminating | stacking the paint for forming the uppermost highly elastic coating layer on the metal plate, and the paint for forming the coating layer below it in an undry state. And a dry coating of this undried multilayered coating film at the same time. The precoat metal sheet excellent in scratch resistance.

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