JP2010022911A - Method of manufacturing precoated steel plate and precoated steel plate manufactured by the method - Google Patents

Abstract

The present invention provides a method for producing a precoated steel sheet having excellent design and adhesion even when an upper film is made of a water-based paint.
SOLUTION: A water-soluble treatment liquid containing a water-soluble phenol resin (a) and a titanium compound (b) and not containing chromium is applied to the surface of a zinc-based plated steel sheet, and then at a temperature of 50 to 200 ° C. Applying a water-based paint containing a urethane-based water-based resin (A) and a color pigment (B) on the first film-forming step of forming a first film by drying, and the first film, A second film forming step of forming a second film by drying at a temperature within a range of 120 to 220 ° C. and higher than a drying temperature in the first film forming step, The content of the urethane-based aqueous resin (A) with respect to all the film-forming components of the film is 40 to 90% by mass, the adhesion amount of the first film is in the range of 0.01 to 1 g / m ² , The adhesion amount of the second film is in the range of 5 to 25 g / m ² [Selection] Fig. 1

Description

  The present invention relates to a method for producing a pre-coated steel sheet having excellent design and adhesion, and a pre-coated steel sheet produced by the manufacturing method, and particularly relates to a pre-coated steel sheet manufactured by the manufacturing method, particularly used in the fields of housings for home appliances, equipment for electronic devices, and the like. .

  Pre-coated steel sheets are widely used as outer panels for home appliances, furniture, building materials, etc., and are a technology that replaces the conventional post-coating that is applied after forming. Unlike the post-coating, the pre-coated steel sheet is formed after the coating, so that it is required that the coating film cracking and peeling of the portion where the coating film elongation occurs do not occur.

  The basic configuration of the precoated steel sheet is as follows. A base treatment having a rust prevention function is performed on a steel sheet such as a galvanized steel sheet, a lower layer film is formed thereon, and an upper layer film is further formed thereon. Of these, the lower layer film often contains additives that have corrosion resistance and wear resistance, and in order to improve the coating state of the upper layer film, a predetermined thickness is required to absorb the roughness of the steel sheet. Many have. On the other hand, the upper layer film is required to have various functions as the outermost layer, and specifically includes corrosion resistance, fingerprint resistance, lubricity, weldability, wear resistance, and the like. In order to realize these functions, it is necessary to contain rust preventives, lubricants, curing agents, pigments, and the like in an appropriate balance in addition to the base resin.

  In the precoated steel sheet having the above-described configuration, in order to realize a rust prevention function and corrosion resistance, a chromate treatment is mainly used for the base treatment, and a chromium-based rust preventive pigment has also been used for the lower layer film. However, in recent years, hexavalent chromium and a trivalent chromium film obtained by reducing hexavalent chromium due to an increase in environmental problems such as regulations such as WEEE (Waste Electrical and Electronic Equipment) and RoHS (Restriction of the use Hazardous Substances). Products formed with chromate treatment and products using chrome-based anticorrosive pigments as antirust agents tend to be avoided from users.

Thus, chromium-free pre-coated steel sheets have been developed. For example, Patent Document 1 includes a coating layer containing 100 parts by weight of an aqueous resin and 0.1 to 3000 parts by weight of a silane coupling agent as a base treatment layer, and a colored coating layer thereon as an upper layer. A pre-coated metal plate is disclosed.
JP 2000-265282 A

  Although it can be said that the ground treatment layer disclosed in Patent Document 1 is environmentally friendly in that it has an aqueous resin, according to the investigation of the present inventors, in the ground treatment layer according to Patent Literature 1, the upper film is made of an aqueous resin. In this case, it became clear that it is difficult to obtain a pre-coated steel sheet having excellent design properties and adhesion, particularly secondary adhesion (details such as evaluation methods will be described later).

  In fact, pre-coated steel sheets made of paint containing water-based resin (hereinafter referred to as “water-based paint”) are mainly used for internal parts, and home appliances and furniture that require design (beautiful appearance). It is rarely applied to places such as outer panels of building materials. In addition, in steel sheets for automobiles, in addition to extremely high designability, it is necessary to have high adhesion that can withstand an atmospheric exposure environment of 10 years or more. For this reason, coating with a film thickness of several tens of μm using a water-based paint is required. Has been. However, most of them are based on the post-coating method, and pre-coated steel sheets are not substantially employed.

  Therefore, the present invention ensures the basic properties (such as corrosion resistance and bending workability) required for pre-coated steel sheets even when the upper layer film is made of a water-based paint, and the design properties such as the exterior of the housing of home appliances. It is an object of the present invention to provide a pre-coated steel sheet and a method for producing a pre-coated steel sheet that can be used for applications requiring high-adhesiveness.

In order to solve the above-mentioned problems, the present inventor first examined the reason why a precoated steel sheet whose upper layer film is made of a water-based paint is mainly used for internal parts.
The water-based resin contained in the water-based paint as one of the main components includes a water-soluble resin in which the resin itself is water-soluble, and a state in which the resin is dispersed in water, such as an emulsion or suspension, although it is insoluble in water. Water-dispersible resin that can be maintained for a period of

  Water-based paints have been actively developed as an alternative to conventional solvent-based paints from the viewpoint of environmental friendliness. The advantages of water-based paints include reducing the effects of solvent-based paints on poisoning and damage to the human body, reducing the load on the insulator from the facility side, and reducing the amount of carbon dioxide that causes global warming. One example is reducing environmental impact.

  In order to use the water-based paint as the upper layer film, it is necessary to meet various performances such as corrosion resistance, fingerprint resistance, lubricity, and weldability. For this reason, in addition to the water-based resin described above, a large amount of silica, a rust inhibitor, a lubricant and the like are often contained. Since many of these are insoluble in water, it is necessary to disperse them in the paint as in the case of water-dispersible resins. In particular, in order to realize designability so that it can be applied to an exterior casing or the like, it is necessary to improve the uniformity of dispersion in the paint.

  Moreover, it is important that even if water-based resin or the like is uniformly dispersed in the paint, if the uniformity cannot be maintained even in the process where the solvent evaporates to form a paint film, the paint film may become uneven. It becomes. This unevenness not only deteriorates the design property but also causes a decrease in adhesion.

  Thus, in order to be able to use water-based paints for applications that require design and high adhesion, the uniformity in the state of the paint and the coating film after it is applied on the lower layer film And uniformity between them.

  As a result of repeated experiments focusing on the latter uniformity, it is important for the inventor to appropriately set the characteristics of the lower layer film in accordance with the upper layer film in order to realize this uniformity. It was found that it is necessary to set up a manufacturing method that fully considers the chemical interaction between the coating and the underlying coating.

The present invention completed based on the above findings is as follows.
(1) Apply a water-soluble treatment liquid containing a water-soluble phenol resin (a) and a titanium compound (b) and not containing chromium on the surface of a zinc-based plated steel sheet, and then drying at a temperature of 50 to 200 ° C. Applying a water-based paint containing the urethane-based water-based resin (A) and the color pigment (B) on the first film, and forming a first film by performing A second film forming step of forming a second film by drying at a temperature higher than the drying temperature in the first film forming step within a range of ˜220 ° C. The content of the urethane-based aqueous resin (A) with respect to all the film-forming components is 40 to 90% by mass, the adhesion amount of the first film is in the range of 0.01 to 1 g / m ² , and The adhesion amount of the second film is in the range of 5 to 25 g / m ^2. A method for producing a precoated steel sheet, wherein

  (2) The treatment liquid in the first film formation step further contains the silane coupling agent (c) in an amount of 10 to 90% by mass with respect to the total amount with the water-soluble phenol resin (a). The manufacturing method of the precoat steel plate as described in said (1).

  (3) The method for producing a precoated steel sheet according to the above (1) or (2), wherein the content of the titanium compound (b) in the treatment liquid in the first film formation step is 0.0010 mol or more per 1 kg of the treatment liquid. .

  (4) The manufacturing method of the precoat steel plate in any one of said (1) to (3) whose content of the coloring pigment (B) of said 2nd film | membrane is 1-40 mass%.

  (5) The manufacturing method of the precoat steel plate in any one of said (1) to (4) whose pH of the process liquid in said 1st film formation process is 2-6.5.

  (6) Any of (1) to (5) above, wherein the mass ratio of the total film forming component and the solvent in the treatment liquid in the first film forming step is 5 to 40 as the solvent / total film forming component. A method for producing a precoated steel sheet according to claim 1.

  (7) A precoated steel sheet having a composite coating composed of a first coating and a second coating manufactured by the manufacturing method described in any one of (1) to (6) above.

(8) Using a zinc-based plated steel sheet as a base material, containing a water-soluble phenolic resin (a) and a titanium compound (b) formed on the plating film on the front surface of the base material, and containing chromium 40% to 90% by mass of urethane-based aqueous resin (based on the first film having an adhesion amount of 0.01 to 1 g / m ² and the total film forming component formed on the first film). A) and 1 to 40% by weight of the color pigment (B), no chromium, and a second film having an adhesion amount of 5 to 25 g / m ² and a plating film on the back surface of the substrate. A precoated steel sheet, comprising: a formed conductive film not containing chromium and having a surface resistance of 10Ω or less.

(9) The precoated steel sheet according to (8), wherein the conductive film contains a water-soluble phenol resin (a) and a titanium compound (b), and the adhesion amount is 0.1 to 1 g / m ² .

  The pre-coated steel sheet according to the present invention comprises a composite film formed on the front surface, wherein the water-soluble phenolic resin and / or titanium compound constituting the first film (lower film) is the second film (upper film). It is easy to chemically interact with the urethane-based water-based resin that constitutes). For this reason, this precoat steel plate is excellent in the designability and adhesiveness, ensuring the basic characteristics which a precoat steel plate should have, such as a bending characteristic. Further, since the back surface satisfies both conductivity and corrosion resistance, the precoated steel sheet according to the present invention is particularly suitable as a housing of a display device such as a thin TV.

  In addition, since the production method according to the present invention includes a step of reliably generating the above-described chemical interaction, a precoated steel sheet excellent in design and adhesion is secured while ensuring basic characteristics such as corrosion resistance and bending characteristics. Can be provided.

Hereinafter, the best mode of the manufacturing method of the precoat steel plate concerning the present invention is explained.
1. First film forming step (1) Treatment liquid In the first film formation step according to the present invention, the following water-soluble treatment liquid is used.

  The treatment liquid according to the first film formation step is water-soluble and contains a water-soluble phenol resin (a). “Water-soluble phenolic resin” refers to an oligomer formed by condensation polymerization of phenols (a general term for chemical substances having a structure in which at least one hydrogen bonded to the carbon constituting the skeleton of the benzene ring is substituted with a hydroxyl group) and formaldehyde. A polymer that is soluble in an aqueous solvent (including those having water as a main component and having an organic solvent having high solubility in water such as alcohol).

  The water-soluble phenolic resin is a first water-soluble phenolic resin that contains this water-soluble phenolic resin by chemically interacting with the urethane-based aqueous resin contained in the water-based paint relating to the second film (upper film) described later. This contributes to maintaining the uniformity of the process in which the water-based paint relating to the second film (upper film) applied on the film (lower film) becomes a film.

  The average degree of polymerization of the water-soluble phenol resin is preferably 2 to 50, and preferably has at least one hydroxyl group in an oligomer or polymer state. A more preferred structure is a polymer molecule having a bisphenol-type repeating unit, in which hydrogen bonded to the skeleton constituting carbon of the benzene ring that has not undergone condensation polymerization with formaldehyde is a polar group other than a hydroxyl group, such as an amino group (ammonium salt). ), Substituted with a carbonyl acid, a sulfonyl acid group, or the like, or a hydroxyl group, an amino group (including an ammonium salt) at the terminal, a carbonyl acid, a sulfonyl acid group, or the like. What is substituted with a bonded alkyl group, for example, an aminomethyl group, for example, increases the solubility in a solvent and increases the possibility of chemical interaction with the second film (upper film) described later. Particularly preferable from the viewpoint.

  Moreover, the process liquid which concerns on a 1st film formation process contains a titanium compound (b). In addition to improving the corrosion resistance of the first film (underlayer film), the titanium compound (b) performs a chemical interaction with the urethane-based aqueous resin in the same manner as the water-soluble phenol resin, and the second film ( This contributes to the uniform formation of the upper layer coating. Examples of usable titanium compounds include water-soluble inorganic titanium compounds such as titanium sulfate, titanium oxysulfate, titanium hydrofluoric acid, and titanium ammonium fluoride, organic acid titanium salts such as titanium potassium oxalate and titanium citrate, and titanium alkoxides. Etc. A titanate coupling agent can also be used as the titanium compound.

  The content of the titanium compound (b) is preferably 0.0010 mol or more per 1 kg of the treatment liquid. If content of a titanium compound (b) is less than 0.0010 mol, the addition effect will not express but the corrosion resistance of the processed galvanized steel sheet will become inadequate. In addition, the conformability of the water-based paint used in the second film formation step, which will be described later, is deteriorated, and the adhesion of the second film (upper film) tends to be reduced. The upper limit of the content of the titanium compound (b) is not particularly limited, but if the amount is too much, the effect is saturated. A more preferable content of the titanium compound (b) is 0.0050 to 0.050 mol per kg of the treatment liquid.

The treatment liquid according to the first film formation step may further contain a known silane coupling agent (c) for further improvement of corrosion resistance.
Specifically, the following compositions (i) to (v) are exemplified.

(I) Those having an amino group: N- (2-aminoethyl) -3-aminopropylmethyldimethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane ;
(Ii) Those having an epoxy group: 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane;
(Iii) Those having a vinyl group: vinyltriethoxysilane;
(Iv) having a mercapto group: 3-mercaptopropyltrimethoxysilane;
(V) Those having a methacryloxy group: 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane.

The silane coupling agent (c) may be one kind or a plurality of kinds may be mixed.
When the silane coupling agent (c) is contained, the content of the silane coupling agent (c) with respect to the total amount with the water-soluble phenol resin (a) is preferably 10% to 90%. Preferably, it is 20% to 50%. When the content of the silane coupling agent (c) is less than 10%, the adhesive strength of the film with the surface of the base material (galvanized steel sheet) is lowered, so that the corrosion resistance and paintability may be insufficient. . On the contrary, when the content of the silane coupling agent (c) is more than 90%, the film forming property of the treatment liquid is lowered, and the corrosion resistance and top coatability of the treated galvanized steel sheet may be insufficient. .

  The solvent of the treatment liquid according to the first film formation step is mainly water, but may contain an organic material such as alcohol as long as the solubility of the solute can be maintained. Moreover, the mass ratio of the solvent and the film-forming component (water-soluble phenol resin (a) and titanium compound (b), and further, if necessary, the silane coupling agent (c)) is easy to apply. From the viewpoints of suppressing the occurrence of large-scale cracks in heat treatment and relaxing the treatment conditions, the solvent / film-forming component is preferably 5 to 40, more preferably 10 to 20.

  It is preferable that pH of the process liquid which concerns on a 1st film formation process is 2.0-6.5. Treatment liquids with a pH of less than 2.0 have excessively high reactivity with the substrate surface, resulting in poor coating, resulting in insufficient corrosion resistance, paintability, workability, etc. of the treated galvanized steel sheet. It is feared to show a tendency to become. If the pH of the treatment liquid exceeds 6.5, the water-soluble phenol resin (a) itself is likely to precipitate out of the treatment liquid, so that the life of the treatment liquid may be shortened. The treatment liquid pH is more preferably 3.0 to 6.0, and particularly preferably within the range of 3.5 to 5.5. If necessary, the pH of the treatment liquid can be adjusted by adding an appropriate acid or base. As the acid, phosphoric acid, acetic acid, nitric acid or the like is preferably used, and as the base, aqueous ammonia is preferably used.

  Moreover, the process liquid which concerns on a 1st film formation process does not contain chromium. Here, “chromium” means not only hexavalent chromium ions regulated by WEEE etc., but also other valence chromium ions such as trivalent chromium ions, metal chromium and chromium alloys.

(2) Zinc-based plated steel sheet The zinc-based plated steel sheet surface-treated in the first film forming step may be any galvanized steel sheet or zinc alloy-plated steel sheet. Examples of the plating include hot dip galvanizing, hot dip Zn-5% Al and Zn-55% Al zinc alloy plating, alloying hot dip galvanizing, electro galvanizing and electro Zn-Ni alloy plating. The plating adhesion amount is not particularly limited, and may be within a normal range (eg, 10 to 100 g / m ² ). If the upper layer is zinc-based plating, a multi-layer plated steel sheet can also be used. When the zinc-based plated steel sheet is double-sided plating, the plated surfaces on both sides may be treated with the treatment liquid of the present invention, or only one side may be treated.

(3) Manufacturing method of galvanized steel sheet having first film (underlayer film) Zinc-based galvanized steel sheet, which is a processing target member (base material) of the precoated steel sheet according to the present invention, is surface-treated with the treatment liquid of the present invention. Prior to this, it is preferable to clean the surface by applying an appropriate pretreatment well known to those skilled in the art. For example, as a pretreatment, the surface of the galvanized steel sheet can be degreased and washed with water.

  The treatment liquid can be applied by any appropriate method such as a roll coater method, a spray method, a dipping method, a spin coating method, or a curtain flow coating method. Application is preferably performed at a temperature of about 0 to 50 ° C.

  If it apply | coats by said method, it will continue to dry as it is, without performing water washing. The drying temperature is preferably in the range of 50 to 200 ° C. in terms of PMT (reaching plate temperature), and particularly preferably 70 to 95 ° C. If the drying temperature is too low, the adhesion between the first film (lower film) that has not been completely dried and the second film (upper film) described later may be reduced. On the other hand, if the drying temperature is too high, the lower layer film is excessively cross-linked, and the conformability of the water-based paint used in the second film forming step, which will be described later, deteriorates, and the adhesion of the second film (upper layer film). There is a concern about the decline. The drying time is not particularly limited as long as the film is sufficiently dried and the crosslinking does not proceed excessively, and may be appropriately set in consideration of the adhesion amount of the first film (lower layer film). Generally, it is 15 seconds to 120 seconds, preferably 30 seconds to 60 seconds.

  By the above treatment, on the plated film of the galvanized steel sheet, the water-soluble phenol resin (a) and the titanium compound (b), and optionally the silane coupling agent (c) are contained, and the first containing no chromium. A film (lower layer film) is formed so as to cover the surface of the plating film. As described above, the titanium compound (b) contributes to the improvement of the corrosion resistance of the first film (lower film) and the first film (lower film) of the aqueous resin for the second film (upper film). It contributes to the improvement of the familiarity above. When the silane coupling agent (c) is further present, the corrosion resistance and conformability are further improved.

(4) deposition of a first coating formed from the treatment liquid deposition volume present invention (lower layer film) is in the range of 0.01 to 1 g / m ^2. 0.1 to 0.5 g / m ² is particularly preferable. When the adhesion amount of the first film (lower film) exceeds 1 g / m ² , the adhesion and corrosion resistance effects of the first film (lower film) are saturated. Further, from the viewpoint of productivity, the smaller the amount of adhesion, the better. In addition, when it is calculated | required that a bending workability is improved, it is preferable to set the adhesion amount of a 1st membrane | film | coat (lower layer membrane | film | coat) small, specifically, less than 0.3 g / m < ² >. However, when the adhesion amount is less than 0.01 g / m ² , the corrosion resistance of the film is lowered.

2. Second film forming step In the second film forming step according to the present invention, an aqueous paint containing a urethane-based aqueous resin (A) and a color pigment (B) is used.

(1) Urethane-based aqueous resin Generally, as an aqueous resin, an epoxy resin, a phenol resin, an acrylic resin, a urethane resin, an olefin-carboxylic acid resin, a nylon resin, a resin having a polyoxyalkylene chain, polyvinyl Alcohol, polyglycerin, carboxymethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, and the like can be mentioned. Among these, a urethane-based aqueous resin is used in the second film forming step according to the present invention.

  The urethane-based aqueous resin is a low molecular weight compound having two or more active hydrogens such as a diol and a diamine, if necessary, a polyurethane composed of a polyol represented by polyester polyol and polyether polyol and a diisocyanate. What is necessary is just to use a chain that is elongated in the presence of a chain extender and is stably dispersed or dissolved in water.

  The method for stably dispersing or dissolving the polyurethane resin in water is not particularly limited, but the following method is exemplified. First, hydrophilicity is imparted by introducing a cationic group such as a hydroxyl group and a carboxyl group and / or an anionic group such as an amino group into the side chain or terminal of the polyurethane polymer, and it is dispersed or dissolved in water by self-emulsification. A method is mentioned. In this case, it becomes a water-soluble resin or a water-dispersible resin depending on the degree of dissociation and the amount of ionic groups introduced. It should be noted that the polyurethane polymer into which the ionic group is introduced is a prepolymer having a relatively low molecular weight, so that the solubility or high dispersibility is expressed, and the polymer is polymerized in the presence of a chain extender. There is also a method.

  In addition, the polyurethane polymer that has completed the reaction or the polyurethane group in which the terminal isocyanate group is blocked with a blocking agent such as oxime, alcohol, phenol, mercaptan, amine, or sodium bisulfite is forcibly applied to the water using an emulsifier and mechanical shearing force. And water-dispersible resin. Further, there is a method in which a urethane polymer having a terminal isocyanate group is mixed with water, an emulsifier and the above chain extender, and dispersion and high molecular weight are simultaneously performed using mechanical shearing force.

  Alternatively, there is also a method in which a water-soluble polyol such as polyethylene glycol is used as a polyol as a main polyurethane material and is dispersed or dissolved in water as a water-soluble polyurethane. Also in this case, it becomes a water-soluble resin or a water-dispersible resin depending on the content of the water-soluble polyol.

  Examples of the diisocyanate used in the urethane resin include aromatic, alicyclic and aliphatic diisocyanates. Specifically, hexamethylene diisocyanate, tetramethylene diisocyanate, 3,3′-dimethoxy-4,4. '-Biphenylene diisocyanate, p-xylylene diisocyanate, m-xylylene diisocyanate, 1,3- (diisocyanatomethyl) cyclohexanone, 1,4- (diisocyanatomethyl) cyclohexanone, 4,4'-diisocyanatocyclohexanone 4,4'-methylenebis (cyclohexyl isocyanate), isophorone diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-phenylene diisocyanate, diphenylmethane diisocyanate DOO, m- phenylene diisocyanate, 2,4-naphthalene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 4,4'-biphenylene diisocyanate and the like. Of these, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, hexamethylene diisocyanate and isophorone diisocyanate are particularly preferred.

The polyester skeleton can be obtained from a polyester polyol compound, and the polyether skeleton can be obtained from a polyether polyol compound.
The polyester polyol compound is obtained by an ester reaction between an organic acid and a polyol. As the polyol, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, neopentyl glycol, 1,2-butylene glycol, 1,3-butylene glycol, 1,4-butylene Low molecular weight polyols such as glycol, 3-methylpentanediol, hexamethylene glycol, hydrogenated bisphenol A, trimethylolpropane, and glycerin are exemplified. On the other hand, examples of organic acids include succinic acid, glutaric acid, adipic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, tetrahydrophthalic acid, endomethylenetetrahydrophthalic acid, and hexahydrophthalic acid. Examples thereof include those obtained by reaction with a basic acid and having a hydroxyl group at the terminal.

  The polyether polyol compound is obtained by dehydration condensation of the same or different polyols. Examples of the polyol include the polyols described above, and a bisphenol skeleton-containing glycol is preferable. Specific examples thereof include those obtained by adding alkylene oxides having 2 to 4 carbon atoms (for example, ethylene oxide, propylene oxide, butylene oxide) to bisphenols such as methylene bisphenol, ethylidene bisphenol, butylidene bisphenol, and isopropylidene bisphenol. Can be mentioned.

  The urethane-based aqueous resin (A) contained in the water-based paint used in the second film forming step according to the present invention may be a water-soluble resin or a water-dispersible resin. The water-soluble phenolic resin (a) and the titanium compound (b) in the first film (underlayer film), and the silane coupling agent (c) contained as necessary, chemically interact with the urethane-based aqueous resin (A). Therefore, even if the urethane-based aqueous resin (A) contained in the water-based paint is a water-dispersed resin, the water-based paint applied on the first film (lower film) has excellent uniform dispersibility.

  The content of the urethane-based aqueous resin (A) in the water-based paint used in the second film-forming step according to the present invention is the total film-forming component of the second film (upper-layer film) (urethane-based aqueous resin (A)). And the color pigment (B) and the following other components added as necessary.) The range in which the content of the resin component derived from the urethane-based aqueous resin (A) is 40 to 90% by mass. And By setting this range, the balance of various performances required for the composite film consisting of the first film (lower film) and the second film (upper film), such as adhesion, workability, and design, is realized in a high order. Is realized. If it is less than 40% by mass, the amount of the resin is too small relative to the amount of the pigment or additive, so that it becomes difficult to achieve the adhesion and workability, which are the basic characteristics of the film, at a predetermined level. On the other hand, if the amount exceeds 90% by mass, the amount of the resin is excessive with respect to the amount of the pigment or additive, and depending on the type of the color pigment (B), sufficient concealability cannot be obtained to obtain a desired design. May not be possible, or the performance desired to be secured by the additive may not be exhibited. The preferable range of the content of the urethane-based aqueous resin (A) is such that the content of the resin component derived from the urethane-based aqueous resin (A) is 50 to 90 mass as a ratio to the total film-forming component of the second film (upper film). %, Particularly preferably 55-90% by mass.

(2) Color pigment The color pigment (B) contained in the aqueous resin used in the second film forming step according to the present invention is not particularly limited, and any material may be used. Specifically, the color pigment (B) in the upper film is carbon black, titanium oxide, graphite, iron oxide, cobalt black, dial, titanium yellow, aluminum pigment, pearl, mica, calcium carbonate, barium sulfate, carbonic acid. Examples include barium, zinc white, alumina white, magnesium carbonate, phthalocyanine blue, phthalocyanine green, and cobalt blue. Of these, carbon black, titania, aluminum and pearl are desirable.

  The content of the color pigment (B) in the aqueous resin may be determined depending on the necessary color and hiding power. If a specific numerical range is illustrated, it is preferable to set it as 1-40 mass% as a ratio with respect to all the film formation components of a 2nd film | membrane (upper film), and it is especially preferable if it is 2-30 mass%. When it exceeds 40 mass%, bending workability will fall and the tendency in which a peeling in a bending process part will arise easily is shown. Further, if it is less than 1% by mass, sufficient concealability cannot be obtained, and there may be a problem in design properties depending on the application.

(3) Other components The aqueous resin used in the second film forming step according to the present invention includes, as other components, wax, extender pigment, rust preventive pigment, surfactant, antifoaming agent, thickener. In addition, a curing agent for diversifying the performance of the coating, beads, a crosslinking agent such as a block isocyanate-based crosslinking agent, a matting agent, and the like can be appropriately contained. The content of these other components as a whole is 40% by mass or less, preferably 1 to 20% by mass with respect to the total film-forming component of the second film (upper film).

  Examples of the wax include hydrocarbon compounds such as polyethylene wax, synthetic paraffin, natural paraffin, fatty acid amide compounds such as stearamide, palmitic acid amide, and methylenebisstearamide, polyfluoroethylene resin (polytetrafluoroethylene). Resin), polyvinyl fluoride resin, and polyvinylidene fluoride resin. About content of wax, 1-15 mass% is appropriate as a ratio with respect to all the film formation components in a 2nd membrane | film | coat (upper layer membrane | film | coat). If it is less than 1% by mass, the effect is hardly exhibited, and if it is contained more than the necessary amount, the stability of the paint tends to be impaired.

Examples of extender pigments include silica, barium sulfate, talc, mica, calcium carbonate, potassium titanate, and aluminum borate.
Examples of the rust preventive pigment include phosphoric acid-based, silica-based, molybdenum-based, and tungsten-based pigments.
In addition, it is preferable that any of these components contained in the above-mentioned water-based paint does not contain a chromium-based material, because the influence on the environment can be minimized.

(4) Solvent The main component of the solvent of the water-based paint used in the second film forming step according to the present invention is water, but from the viewpoint of improving dispersibility, alcohol, ether, ketone, amine, etc. A polar organic solvent may be used. The upper limit of the content is appropriately determined in accordance with the paint component as long as it does not adversely affect the properties of the obtained second film. A typical content in the case where an organic solvent is contained in the solvent is 10 to 20% by mass as a ratio to the total solvent.

(5) Manufacturing method of galvanized steel sheet (pre-coated steel sheet) having composite film In the second film forming step according to the present invention, a water-based resin is formed by a roll coater method, a spray method, a dipping (dipping) method, a spin coating method, It can be carried out by applying by any appropriate method such as curtain flow coating. Application is preferably performed at a temperature of about 0 to 50 ° C.

  After applying the water-based paint by the above method, heat treatment is subsequently performed. The heating temperature in the heat treatment is higher than the drying temperature in the first film formation step by PMT (maximum temperature reached) and is preferably in the range of 120 to 220 ° C, and particularly preferably 150 to 200 ° C. By appropriately performing this heat treatment, the first film (lower layer film) is also heated and cross-linked and fully cured, while at the same time improving adhesion to the plating film and the second film (upper layer film). Is done.

  If the heat treatment temperature is lower than 120 ° C., the second film (upper film) may not be sufficiently formed, and the adhesion to the first film (lower film) may be insufficient. When the temperature is lower than the drying temperature, the chemical interaction between the first film (lower film) and the second film (upper film) is reduced, and the adhesion to the first film (lower film) is also reduced. May decrease. When the heat treatment temperature is higher than 220 ° C., the composite film may be cracked when processed.

  As for the drying time, it is necessary to complete the drying of the second film (upper film) and to have chemical interaction with the first film (lower film). This may reduce workability. Accordingly, the drying time depends on the amount of the first coating (lower coating) and the second coating (upper coating), but should generally be 15 seconds to 120 seconds, preferably 30. Second to 60 seconds.

(6) coating weight of the second coating according to the adhesion amount present invention (upper layer coating) is desirably at 5 g / m ² or more, particularly preferably as long as 8 g / m ² or more. If the amount is less than 5 g / m ^{2, the} change in appearance when the amount of adhesion slightly changes, especially the color difference increases, so that strict management of the amount of adhesion is required in production, which may lead to a decrease in productivity. is there. Moreover, it is preferable that the upper limit of the adhesion amount of a 2nd membrane | film | coat (upper layer membrane | film | coat) shall be 25 g / m < ² >. This is because if the adhesion amount exceeds 25 g / m ² , the secondary adhesion tends to decrease and the coating cost increases.

  Here, the secondary adhesion refers to adhesion after the precoated steel sheet provided with the composite film is immersed in boiling water for a predetermined time, for example, 2 hours. This adhesion strength can be evaluated by, for example, performing a tape peeling test after a steel plate that has been cross-cut after dipping is stretched by 7 mm with an Erichsen stretch tester.

3. Surface treatment on the back surface of the pre-coated steel plate The pre-coated steel plate of the present invention is subjected to a surface treatment on the surface opposite to the surface on which the composite film is formed (the front surface), that is, on the plating film on the back surface. It may be. At this time, the treatment liquid is the treatment liquid in the first film formation step, and may be provided with the same film as the first film (lower layer film) by the same production method as that of the process. . Since the treatment liquid, the manufacturing method, and the adhesion amount are basically as described above, the description thereof is omitted.

However, when this pre-coated steel sheet is used for an electronic device typified by a thin TV including a display element such as a liquid crystal, PDP, or organic EL, the back surface is electrically conductive because it imparts an electromagnetic wave shielding function to the steel sheet. It is necessary to have. In order for the back surface to have conductivity, it is preferable that the adhesion amount is 0.5 g / m ² or less and the surface resistance is 10 Ω or less, more preferably 5 Ω or less, and the corrosion resistance required for the back surface is stably secured. From the viewpoint, it is preferably 0.1 to 0.5 g / m ² .

That is, it contains a water-soluble phenolic resin (a) and a titanium compound (b) formed on a plating film on the front surface of the base material, which is a zinc-based plated steel sheet, and does not contain chromium. , Based on the first film having an adhesion amount of 0.01 to 1 g / m ² and 40% to 90% by mass of the urethane-based aqueous resin (A) based on the total film forming component formed on the first film. ) And 1 to 40% by mass of the color pigment (B), and does not contain chromium, and is formed on the second film having an adhesion amount of 5 to 25 g / m ² and the plating film on the back surface of the substrate. In addition, the electromagnetic wave shielding member comprising a pre-coated steel plate that does not contain chromium and has a conductive film having a surface resistance of 10 Ω or less, while ensuring basic characteristics required as a pre-coated steel plate such as corrosion resistance, bending characteristics, and adhesion, Excellent design and conductivity , It is suitable as an electromagnetic wave shielding member for electronic equipment.

  In order to provide conductivity, a conductive member, specifically, graphite powder or metal powder may be dispersed in the coating on the back surface, but in order to ensure in-plane uniformity of conductivity. It is necessary to uniformly disperse the conductive member in the film, which increases production control items. Therefore, it is preferable not to have such a conductive member from the viewpoint of productivity. When the conductive member is dispersed in the treatment liquid, the content in the treatment liquid is set so that the ratio of the conductive member to the total film forming component of the first film (lower layer film) is 15% by mass or less. It is preferable that the amount is 10% by mass or less. When the amount exceeds 15% by mass, there is a concern that the adhesion and workability may be affected.

The following effects of the present invention are specifically illustrated by the following examples of the present invention and comparative examples. The examples of the present invention are merely examples, and do not limit the present invention.
1. Preparation of test plate (1) Test material The commercially available double-sided galvanized steel sheet shown below was used as a test material. In addition, the size of a test material is 200 mm x 300 mm.

・ Electrogalvanized steel sheet (EG)
Plate thickness 0.6mm, basis weight = 20/20 (g / m ² )
・ Hot galvanized steel sheet (GI)
Plate thickness 0.6mm, basis weight = 60/60 (g / m ² )
・ Alloyed hot-dip galvanized steel sheet (GA)
Plate thickness 0.6mm, basis weight = 60/60 (g / m ² )

(2) Degreasing treatment Each of the above test materials was degreased with an alkaline degreasing agent (Fine Cleaner 4480 manufactured by Nihon Parkerizing Co., Ltd.) and then washed with tap water.

(3) Formation of a front surface lower layer film (first film) and a back surface film A phenol resin-based treatment having the following composition on the front surface and the back surface of the specimen subjected to the above degreasing treatment The liquid was applied at room temperature using a bar coater, and PMT (maximum temperature of the test plate at the time of manufacture, hereinafter referred to as “final plate temperature”) was 100 ° C. (for some of the test materials, the ultimate plate temperature was It was dried for 40 seconds while changing the composition to form a front surface lower layer film (first film) and a back surface film containing a phenol resin.

Treatment liquid (solvent: water, pH: 4-5)
・ Water-soluble resin: phenolic resin (having bisphenol-type repeating unit structure)
Titanium compound: Titanium hydrofluoric acid (content: 10 mmol per 1 kg of treatment liquid)
Silane coupling agent: 3-mercaptopropyltrimethoxysilane Phosphoric acid: pH adjustment

  The mass ratio of the film forming component (aqueous resin, titanium compound and silane coupling agent) of the treatment liquid to water as the solvent was in the range of about 5 to 40 as the solvent / film forming component. The weight ratio of the water-soluble resin to the silane coupling agent was 1: 1.

  The amount of adhesion was adjusted by appropriately changing the ratio (solvent / film-forming component) and the type of bar coater. Moreover, the adhesion amount of the front surface lower layer film and the back surface film was calculated using a calibration curve prepared in advance by the fluorescent X-ray method for Ti in the film.

  In addition, about some test materials, the process liquid (Chuo Rika Kogyo Co., Ltd. ET-8) containing acrylic olefin resin is apply | coated similarly, and it is made to dry for 40 seconds, setting it as PMT75-100 degreeC, and acrylic olefin resin. A front surface lower layer film was formed.

(4) Formation of front surface upper layer film (second film) Aqueous urethane dispersion resin described in Table 1 (U6100 manufactured by Albertingk Boley GmbH) on the steel sheet on which both surfaces were formed by the above-described steps. In addition, an aqueous paint prepared by dispersing aluminum paste, carbon black, and / or titania in water was applied using a bar coater.

  In addition, the mass ratio in Table 1 is a ratio with respect to the film forming component (urethane resin, colored pigment). Further, the mass ratio of the film forming component to water as the dispersion medium was determined in consideration of the liquid viscosity and the like, and was in the range of about 0.8 to 1.7 as the water / film forming component.

Subsequently, a pre-coated steel plate was obtained by heat treatment for 40 seconds while setting the ultimate plate temperature at 160 ° C. The amount of adhesion here was adjusted by appropriately changing the type of bar coater.
In addition, about some test materials, heat processing was performed by changing PMT. In addition, the amount of adhesion of the upper surface coating (second coating) is calculated based on the weight change before and after film removal by removing the upper coating on the specified area of the paint sample with a remover (special remover manufactured by Shinto Paint Co., Ltd.). did.

2. Evaluation Method (1) Paint Appearance L, a, b values are measured using a Hunter color difference meter (Minolta Co., Ltd .: CR-300), and the L, a, b values of the reference sample are set to L _0. , A ₀ , b ₀ , and L, a, and b of the measurement sample are L _x , a _x , and b _x , the color difference ΔE of the measurement sample was obtained by the following equation.

ΔE = ((L _x −L ₀ ) ² + (a _X −a ₀ ) ² + (b _X −b ₀ ) ² ) ^1/2
This ΔE was measured by preparing precoated steel sheets with different adhesion amounts of 1 g / m ^{2 and using} the larger adhesion amount as a reference sample. In order to distinguish these steel plates, the measurement sample is No. 1. Reference sample is No. It was defined as 1R.

In general, since it is judged that there is no difference in color since ΔE is within 1 if ΔE is within 1, it was evaluated based on the following criteria.
○: Color difference ΔE is 1.00 or less (good)
×: Color difference ΔE exceeds 1.00 (poor)

(2) Secondary adhesion The prepared pre-coated steel sheet is immersed in boiling water, taken out after 2 hours, and 100 square grids (10 vertical × 10 horizontal) are prepared with a cutter knife, and an Erichsen overhang tester Then, a tape peeling test (tape: CT-24 manufactured by Nichiban Co., Ltd.) was conducted to examine the number of remaining masses and evaluated as follows.
○: 10 or less cells with peeling (good)
X: The number of cells with peeling exceeds 10 (bad)

(3) Workability An adhesion bending test (hereinafter referred to as “room temperature 0T test”) defined in JIS K5400 was performed on each pre-coated steel sheet, and the number of cracks at 0T at room temperature was evaluated. Observation was performed with a magnifying glass (magnification: 10 times) and evaluated as follows.
○: The number of cracks is 5 or less (good)
X: The number of cracks exceeds 5 (bad)

Furthermore, after tightly bending with a steel plate having the same thickness as the pre-coated steel plate to be evaluated at room temperature, a polyester tape (CT-24 manufactured by Nichiban Co., Ltd.) is applied to the bent part, and the tape is vigorously applied. A peeling test (hereinafter referred to as “room temperature 1TT test”) was performed. Observation was performed with a magnifying glass (magnification: 10 times) and evaluated as follows.
○: No adhesion of the film to the tape surface (no peeling, especially good)
Δ: Partial adhesion of the film to the tape surface (partial peeling: good)
×: The film is almost entirely attached to the tape surface.
Note that the peeled area ratio serving as the threshold of Δ and × was about 30%.

(4) Corrosion resistance of front surface After sealing the end surface of the prepared precoated steel sheet, a 5% salt spray test was conducted at 35 ° C for 120 hours. Observation was evaluated visually as follows.
○: No white rust generated (particularly good)
Δ: White rust generated Less than 10% (good)
X: White rust generation 10% or more (unsatisfactory)

(5) Surface resistance value of sample back surface In order to evaluate electroconductivity, the surface resistance value was measured using the apparatus shown in FIG. As shown in FIG. 1, two parallel grooves separated by a predetermined interval (60 mm in this embodiment) are formed in a substantially rectangular parallelepiped block made of PTFE (polytetrafluoroethylene). A substantially rectangular parallelepiped copper block is installed and fixed so as to be embedded in the PTFE block. These two copper blocks are each provided with a groove parallel to the groove of the PTFE block, and a gasket (EGUN1-0707 manufactured by Foam Kasei Co., Ltd.) in which a metal mesh is wound around the copper block is provided in the groove. It is installed and fixed so as to be partially embedded in In addition, for each of the copper blocks, one end of the lead wire is soldered, and the other end of each lead wire is connected to a multimeter (DIGITAL MULTITIMER 734 01 manufactured by Yokogawa Electric Corporation). .

Then, the pre-coated steel plate was placed on the gasket of this device so that the back surface was in contact with it, and the resistance value obtained by the multimeter in this state was set as the surface resistance value of the sample. evaluated. In addition, since the external load was not applied and contact was made only with the self-weight of the precoated steel sheet, the contact pressure of the precoated steel sheet to the gasket was 5 gf / cm ² .
In this contact state: ○: Surface resistance is 5Ω or less (particularly good)
Δ: Surface resistance value is 10Ω or less (good)
×: Surface resistance value exceeds 10Ω (unsatisfactory)

(6) Corrosion resistance of back side Corrosion resistance was also evaluated on the back side. After sealing the end face of the prepared precoated steel sheet, a 5% salt spray test was conducted at 35 ° C. for 120 hours. Observation was evaluated visually as follows.
○: No occurrence of red rust (good)
×: Red rust generated (unsatisfactory)

3. Evaluation results Tables 2 to 6 show the results of the above evaluations.

(1) Table 2
No. The steel plates to be treated in 1 to 11 were electrogalvanized steel plates (EG). When these were measured for color difference, No. 1 has a ΔE of 1.37. In all of Nos. 2 to 6, ΔE was 1.00 or less.

When the adhesion amount of the upper layer film on the front surface exceeded 25 g / m ² (No. 6, 6R), a problem occurred in secondary adhesion.
The bending workability was good when the lower layer adhesion amount on the front surface was 1.0 g / m ² or less, but a problem occurred when it exceeded 1.0 g / m ² (No. 9, 9R).

  No. 10, 10R, 11, and 11R, galvanized steel sheets (GI) and galvannealed steel sheets (GA) were used as galvanized steel sheets, respectively. A composite film was formed using A. As a result, there was no problem in any evaluation.

  No. In 12-17 and 12R-17R, the paint was changed to change the composition of the upper film. As a result, the samples 14, 14R, 17, and 17R were transparent samples with less coloring feeling. On the other hand, in 15, 15R, 16, and 16R, defects in bending workability were observed.

  Note that the underline in Table 2 indicates that the conditions are outside the scope of the present invention.

(2) Table 3
Table 3 shows the results of the tape peeling test (room temperature 1TT test) of the bent portion when the ultimate plate temperature of the upper surface layer is fixed at 160 ° C. Both are good in the normal temperature 0T test, but considering the lower surface adhesion amount and the lower plate temperature, the lower surface adhesion amount is less than 0.3 g / m ^2. In the test, it was confirmed that a good sample with no peeling of the film, that is, a particularly excellent bending workability was obtained. In addition, if the temperature of the lower surface of the front surface is in the range of 70 to 95 ° C., it is confirmed that a good sample with no peeling of the film in a normal temperature 1TT test, that is, a material excellent in bending workability can be obtained relatively stably. It was done.

(3) Table 4
Table 4 shows the results of the secondary adhesion test and the room temperature 1TT test when the ultimate temperature of the front lower layer and the lower layer are fixed at 100 ° C. It was confirmed that secondary adhesion was unsatisfactory when the upper layer reached plate temperature was less than 120 ° C., and when it exceeded 220 ° C., peeling of the film was observed in the room temperature 1TT test.

(4) Table 5
Table 5 shows the results of the tape peeling test (room temperature 1TT test) of the bent portion when the front surface lower layer film is made of acrylic olefin resin and the ultimate surface temperature of the front surface layer is fixed at 160 ° C. Shown in In this case, the secondary adhesion is unsatisfactory in any case regardless of the ultimate temperature of the lower layer, and the chemical interaction between the front lower layer film and the upper layer film is phenol. It was presumed that the occurrence was less than in the case of using a resin.

(5) Table 6
A coating was formed on the back surface by the same production method as that for forming the front surface lower layer film using the same treatment solution containing the phenol resin as that used for the front surface lower layer film. The back surface on which the film was thus formed was subjected to corrosion resistance evaluation and surface resistance measurement. The result is shown in FIG. In order to obtain excellent characteristics in terms of both the corrosion resistance and the surface resistance value of the back surface, it was confirmed that there was a suitable range for the adhesion amount of the back surface.

It is the schematic of the apparatus used for the measurement of surface resistance.

Claims (9)

Apply a water-soluble treatment liquid containing water-soluble phenolic resin (a) and titanium compound (b) and not containing chromium on the surface of the zinc-plated steel sheet, and then drying at a temperature of 50 to 200 ° C. A first film forming step of forming a first film;
On the first film, a water-based paint containing the urethane-based aqueous resin (A) and the color pigment (B) is applied, and is dried in the first film forming step within a range of 120 to 220 ° C. A second film forming step of forming a second film by drying at a temperature higher than the temperature,
The content of the urethane-based aqueous resin (A) with respect to all film forming components of the second film is 40 to 90% by mass,
The pre-coating characterized in that the adhesion amount of the first film is in the range of 0.01 to 1 g / m ² and the adhesion amount of the second film is in the range of 5 to 25 g / m ^2. A method of manufacturing a steel sheet.   The treatment liquid in the first film formation step further contains the silane coupling agent (c) in an amount of 10 to 90% by mass with respect to the total amount with the water-soluble phenol resin (a). The manufacturing method of the precoat steel plate of description.   The manufacturing method of the precoat steel plate of Claim 1 or 2 whose content of the titanium compound (b) in a process liquid in said 1st film formation process is 0.0010 mol or more per kg of process liquid.   The manufacturing method of the precoat steel plate in any one of Claim 1 to 3 whose content of the coloring pigment (B) of said 2nd film | membrane is 1-40 mass%.   The manufacturing method of the precoat steel plate in any one of Claim 1 to 4 whose pH of the process liquid in said 1st membrane | film | coat formation process is 2-6.5.   The precoated steel sheet according to any one of claims 1 to 5, wherein a mass ratio of the total film forming component and the solvent in the treatment liquid in the first film forming step is 5 to 40 as a solvent / total film forming component. Manufacturing method.   A precoated steel sheet comprising a composite film composed of a first film and a second film manufactured by the manufacturing method according to claim 1. Based on zinc-plated steel sheet,
A water-soluble phenol resin (a) and a titanium compound (b) formed on the plating film on the front surface of the base material, containing no chromium, and having an adhesion amount of 0.01 to 1 g / m ² The first film of
Containing 40 to 90% by mass of urethane-based aqueous resin (A) and 1 to 40% by mass of color pigment (B) based on the total film-forming component formed on the first film, chromium A second film having an adhesion amount of 5 to 25 g / m ² ,
A precoated steel sheet, comprising: a conductive film which is formed on a plating film on the back surface of the substrate and which does not contain chromium and has a surface resistance of 10Ω or less. The precoated steel sheet according to claim 8, wherein the conductive film contains a water-soluble phenol resin (a) and a titanium compound (b), and an adhesion amount thereof is 0.1 to 1 g / m ² .