JP2005153337A - Precoated metal sheet with excellent resistance to contamination and solvent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a precoated metal sheet excellent in the antistaining properties and solvent resistance of a coating film. <P>SOLUTION: This precoated metal sheet excellent in the antistaining properties and solvent resistance has at least a coating film which is formed by applying a coating composition to one side or both sides of a metal sheet to which chemical forming treatment is applied and baking and drying the coated metal sheet. Herein, the coating composition contains a polyester resin (A) with a number average molecular weight of 10,000-50,000 having a glass transition temperature of 25°C or above, an amino resin (B), an acidic catalyst (C) and a volatile basic substance (D) as essential components and is characterized in that the solid component of the amino resin (B) is 10-32 pts.mass with respect to 100 pts.mass of the solid component of the total polyester resin of (A). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a pre-coated metal plate having excellent corrosion resistance after press molding, and is used for home appliances, building materials, civil engineering, machinery, automobiles, furniture, containers, etc. It is characterized by exhibiting stain resistance and solvent resistance.

  For home appliances, building materials, automobiles, and the like, precoated metal sheets coated with a colored coating film have been used in place of conventional post-painted products that have been painted after processing. This metal plate is obtained by coating a metal plate that has been subjected to a pretreatment for metal, and is generally used after being molded and then processed. For this reason, the coating film to be coated on the metal plate is required to have a high degree of workability while satisfying the performance required for conventional post-coating such as contamination resistance.

  In order to solve this problem, Patent Documents 1 to 3 and the like disclose a method for improving the resin composition and a technique for variously modifying the paint composition. Patent Document 3 discloses a polyester-melamine in which a polyester resin having a glass transition point of 5 to 40 ° C. and a number average molecular weight of 15,000 to 30,000 and a hexamethoxymethylolated melamine resin are blended in a mass ratio of 75/25 to 55/45. Disclosed is a coating composition for a coated metal plate that is excellent in red magic contamination and processability by a coating comprising 1 to 2 parts by mass of an amine block of dodecylbenzenesulfonic acid per 100 parts by mass of resin. Has been.

JP-A-61-32351 Japanese Patent Laid-Open No. 62-21830 JP-A-2-269168

  However, the technique of Patent Document 3 has a problem that it is inferior in organic solvent resistance although it is excellent in workability and contamination. If the organic solvent resistance of the pre-coated metal sheet coating is inferior, when wiping the contaminants attached to the coating surface with the organic solvent, leaving the organic solvent attached to the coating surface, There arises a problem that the coating film swells or discolors.

  Then, this invention makes it the subject to solve the said problem in a prior art and to provide the precoat metal plate which is excellent in the stain resistance of a coating film, and solvent resistance.

  As a result of intensive studies on a coating film excellent in solvent resistance, the present inventors greatly influenced the glass transition temperature (Tg) of the coating film on the solvent resistance, and includes a polyester resin having a high Tg in the coating film. And found that the solvent resistance is improved. Although the coating film using high Tg resin was said to be inferior in workability, it was also found that processability can be secured by adjusting the molecular weight of the resin, the addition amount of the curing agent, and the pigment concentration to be added. By baking and curing paints that contain polyester resin, amino resin, acid catalyst, and volatile basic substances as essential components, the hard amino resin is concentrated on the surface layer during the bake-hardening process, improving stain resistance. In addition, the present inventors have found that a precoated metal sheet having excellent stain resistance and solvent resistance and excellent workability can be obtained.

The present invention has been completed based on such knowledge, and the gist of the present invention is as follows.
(1) On one or both sides of a metal sheet subjected to chemical conversion treatment, (A) a polyester resin having a glass transition temperature of 25 ° C. or higher and a number average molecular weight of 10,000 to 50,000, (B) an amino resin, (C) acidic A catalyst, and (D) a volatile basic substance as an essential component, and the solid content of (B) amino resin is from 10 to 32 parts by mass relative to 100 parts by mass of the solid content of all polyester resins of (A) A pre-coated metal sheet having at least a stain resistance and a solvent resistance, characterized by having at least a coating film formed by applying a coating composition and baking and drying the coating composition.
(2) The coating composition further contains a pigment, and the content thereof is 80 parts by mass or less with respect to 100 parts by mass of the total resin solid content. Excellent pre-coated metal plate.

  According to the present invention, it is possible to provide a pre-coated metal plate which is excellent in stain resistance and excellent in solvent resistance. Therefore, even if an organic solvent adheres to a product using a pre-coated metal plate, the coating film does not swell, and contaminants attached to the product can be wiped off with various types of organic solvents. It was. Therefore, it has become possible to maintain the beautiful appearance of the product for a long time. Therefore, the present invention can be said to be an industrially highly valuable invention.

  The present invention, on one or both sides of the metal plate subjected to chemical conversion treatment, (A) a polyester resin having a glass transition temperature of more than 40 ° C. and a number average molecular weight of 10,000 to 50,000, (B) an amino resin, The acid-based catalyst and (D) a volatile basic substance are included as essential components, and the solid content of (B) amino resin is 10 to 32 mass with respect to 100 mass parts of solid content of all polyester resins of (A). It is achieved by having at least a coating film formed by applying a coating composition comprising parts and baking and drying.

  For the metal plate used in the present invention, generally known metal materials can be used. The metal material may be an alloy material. For example, a steel plate, a stainless steel plate, an aluminum plate, an aluminum alloy plate, a titanium plate, a copper plate, etc. are mentioned. The surface of these materials may be plated. Examples of the type of plating include zinc plating, aluminum plating, copper plating, nickel plating and the like. These alloy platings may be used. In the case of steel plates, generally known steel plates and plated steel plates such as hot dip galvanized steel plates, electrogalvanized steel plates, zinc-nickel alloy plated steel plates, hot galvannealed steel plates, aluminum plated steel plates, aluminum-zinc alloyed steel plates, etc. Applicable.

As the chemical conversion treatment for the metal plate used in the present invention, zinc phosphate chemical conversion treatment, coating chromate treatment, electrolytic chromic acid treatment, reaction chromate treatment, chromate-free chemical conversion treatment, or the like can be used. As the non-chromate chemical conversion treatment, those treated with an aqueous solution containing a silane coupling agent, a zirconium compound, a titanium compound, tannin or tannic acid, a resin, silica, etc. are known. JP-A-9-241576, JP-A-2001-89868, JP-A-2001-316845, JP-A-2002-60959, JP-A-2002-38280, JP-A-2002-266081, A known technique described in Kaikai 2003-253464 or the like may be used. These chemical conversion treatments are commercially available, for example, chromate treatment “ZM-1300AN” manufactured by Nihon Parkerizing Co., Ltd., chromate-free chemical conversion treatment “CT-E300N” produced by Nihon Parkerizing Co., Ltd. The treatment “Surfcoat ^™ NRC1000” or the like can be used.

(A) The polyester resin having a number average molecular weight of 10,000 to 50,000 and having a Tg of 25 ° C. or higher is a resin having a generally known ester group, which constitutes the coating composition to be applied to the precoated metal sheet of the present invention. Oil-free polyester resins, alkyd resins, linear polymer polyesters, and branched polyesters can be used. Commercially available, for example, manufactured by Toyobo Co., Ltd. of "Byron ^TM" (oriental Bosabisha registered trademark of) or, to use the Sumika Bayer Urethane Co., Ltd. "Desmophen ^TM" (Sumika Bayer Urethane Co., Ltd. registered trademark), etc. be able to. A plurality of these may be mixed. However, in order to ensure processability, the Tg must be 25 ° C. or higher and the number average molecular weight must be 10,000 to 50,000. A polyester resin having a Tg of less than 25 ° C. is unsuitable because of poor solvent resistance. When a plurality of polyester resins are mixed, the Tg of the entire mixed polyester resin may be 25 ° C. or higher. The number average molecular weight of the polyester resin used in the present invention must be 10,000 to 50,000. If the number average molecular weight is less than 10,000, the processability is inferior, and if it exceeds 50,000, it is difficult to dissolve in a solvent and form a paint. In addition, when mixing several polyester resin, the number average molecular weights of the whole mixed polyester resin should just be 10000-50000.

The (B) amino resin constituting the coating composition to be coated on the precoated metal plate of the present invention is generally a methylated melamine resin, butylated melamine resin, imino group melamine resin, benzoguanamine resin, glycoluril resin, urea resin, etc. A known amino resin can be used. Those that are commercially available, for example, Mitsui Cytec "Cymel ^TM", "My coat ^TM" (both Mitsui Cytec registered trademark), manufactured by Dainippon Ink and Chemicals, Inc. "BECKAMINE ^TM", "Super BECKAMIN ^TM (Both are registered trademarks of Dainippon Ink & Chemicals, Inc.) and the like. A plurality of types of amino resins may be mixed and used. Among these, in particular, when hexamethoxymethylated melamine is used, the balance between stain resistance and workability is good and more preferable. Moreover, content of these amino resins must be 10-32 mass parts by solid content of amino resin with respect to 100 mass parts of solid content of polyester resin. If the content of the amino resin is less than 10 parts by mass, the stain resistance of the coating film decreases, and if it exceeds 32 parts by mass, the processability decreases, which is not suitable.

The acid catalyst (C) constituting the coating composition to be applied to the precoated metal sheet of the present invention is necessary for promoting the curing of the amino resin. The acidic catalyst may be any acidic catalyst having an amino resin curing acceleration function, and generally known catalysts such as dodecylbenzenesulfonic acid can be used. Commercially available products such as an acidic catalyst “Catalyst ^™ ” manufactured by Mitsui Cytec can be used. The addition amount of the acidic catalyst is not particularly defined, and can be appropriately selected and used as necessary. Increasing the amount of acid catalyst added further accelerates the curing of the amino resin, which increases the cross-linking density of the coating film and improves the stain resistance, but tends to decrease the processability. It is necessary to select the quantity as needed. The addition amount of the acidic catalyst is more preferably 0.3 to 5.0% by mass based on the total resin solid content in the paint because the balance between stain resistance and workability is excellent.

The (D) volatile basic substance constituting the coating composition to be applied to the precoated metal plate of the present invention stops the catalytic function of the acidic catalyst in the coating by neutralizing the acidic catalyst or blocking the acidic catalyst. In the process of baking and drying paints containing these, the catalytic function of the acidic catalyst is improved by volatilizing and dissociating only the volatile basic substance that was neutralizing or blocking the acidic catalyst near the surface of the coating film. It is added for the purpose of exerting and promoting the curing of the amino resin in the vicinity of the surface layer of the coating film to form an amino resin concentrated layer. Therefore, as long as it is a volatile basic substance that exhibits such a function, a generally known substance such as 2-dimethylamino-ethanol can be used. The amount of volatile basic substance to be added is not particularly specified, and can be added as required, such as the type of drug to be added, but only the number of equivalents necessary to neutralize the acid of the acidic catalyst. Addition is preferred. A commercially available acid catalyst in which the acid catalyst is already amine-blocked, for example, “Catalyst ^™ 602” manufactured by Mitsui Cytec Co., Ltd. may be used.

  The coating composition to be applied to the pre-coated metal sheet of the present invention is more preferable when the above-mentioned additive substance is dissolved in an organic solvent such as thinner to make a coating and the application work becomes simple.

  Various pigments may be added to the prepared coating composition. That is, a coloring pigment can be added for coloring, a rust preventive pigment can be added to give a rust preventing function, or an extender pigment can be added. As the color pigment, generally known pigments such as titanium oxide, carbon black, titanium yellow, cobalt blue and the like can be used. As the rust preventive pigment, generally known ones such as strontium chromate, zinc phosphate, aluminum dihydrogen tripolyphosphate, silica, Ca ion exchange silica, zinc molybdate and the like can be used. As the extender pigment, generally known pigments such as calcium carbonate and talc can be used. A mixture of these pigments may be used. The addition amount of these pigments is not particularly specified, but if it is 80 parts by mass or less with respect to 100 parts by mass of the total resin solid content in the paint, it is more preferable because the processability is not deteriorated. In particular, when the amino resin addition amount in the coating film of the present invention is more than 10 parts by mass and less than 32 parts by mass with respect to 100 parts by mass of the polyester resin, the processability may be reduced by the addition of the pigment. When the pigment addition amount is 80 parts by mass or less with respect to 100 parts by mass of the total resin solid content, the processability is better and more preferable. The pigment may not be added.

  Moreover, generally well-known additives, for example, a matting agent, a leveling agent, a wax, an antifoaming agent, etc. can be added to these coating materials as needed.

  The precoated metal sheet of the present invention has at least a coating film obtained by applying the above-described coating composition and baking and drying it. The film thickness is not particularly defined and can be appropriately selected as necessary, but a dry film thickness of 1 to 100 μm is preferable. If it is less than 1 μm, the effect of painting is small in terms of design and anticorrosion, and if it exceeds 100 μm, there may be uneven coating during painting. More preferably, it is 5-50 micrometers. In addition, as for the precoat metal plate of this invention, in order to exhibit the performance of stain resistance and solvent resistance, it is desirable that this coating film is formed in the outermost surface.

  Moreover, generally well-known primer coating and intermediate coating can also be applied to the lower layer (upper layer of chemical conversion treatment) of the coating film of the present invention. Commercially available primer paints and intermediate paints may be used. In particular, when a plumer coating is applied, corrosion resistance and adhesion are improved, which is more preferable. As the primer paint, generally known antirust pigments such as strontium chromate, zinc phosphate, aluminum dihydrogen triphosphate, silica, Ca ion exchange silica, zinc molybdate and the like can be used. Moreover, the same resin as the coating film of the present invention can be used as the primer coating resin, and in particular, a resin containing an epoxy group is more suitable because adhesion is improved. A material containing a silane coupling agent is also preferable because adhesion is improved. The film thickness of the primer coating or the intermediate coating is not particularly specified and can be appropriately selected as necessary, but a dry film thickness of 1 to 100 μm is preferable. If it is less than 1 μm, the effect of painting is small in terms of design and anticorrosion, and if it exceeds 100 μm, there is a risk of uneven coating during coating.

  The pre-coated metal plate of the present invention is a generally known method such as brush coating, spray coating, roll coater coating, curtain flow coater coating, roller curtain coater coating, die coater coating, etc. It is obtained by painting with. Among these coating methods, roll coater coating, curtain flow coater coating, roller curtain coater coating, and die coater coating can be applied continuously on the coil coating line, sheet coating line, etc. More preferred.

  Moreover, generally well-known dry baking methods, such as a hot air oven, a direct-fire type oven, a far-infrared oven, an induction heating type oven, can be used for the drying baking method in coating.

  Hereinafter, the details of the test materials used in the examples will be described.

  Details of the paint used will be described below.

Byron ^TM 103, an amorphous polyester resin manufactured by Toyobo Co., Ltd. (Tg: 47 ° C., number average molecular weight: 23000 [denoted as B-103 in Table 1)), amorphous polyester resin manufactured by Toyobo Co., Ltd. in a "Byron ^TM 63CS" (Tg: 7 ° C., a number average molecular weight: 20000 [described in Table 1 and B-63CS]), an amorphous polyester resin Toyobo "Vylon ^TM GK220" (Tg : 53 ° C., number average molecular weight: 3000 (shown as B-GK220 in Table 1)), and “Byron ^™ GK130”, an amorphous polyester resin manufactured by Toyobo Co., Ltd. (Tg: 19 ° C., number average molecular weight : 7000 [described as B-GK130 in Table 1]) was prepared. "Byron ^TM 103", "Byron ^TM GK220", "Byron ^TM GK130" are the pellet or sheet form, these organic solvent (cyclohexanone in weight ratio: Solvesso 150 = 1: Using a mixture 1) Used by dissolving in In addition, “Byron ^™ 63CS” was used as it was because the polyester resin was already dissolved in an organic solvent (mixed in a mass ratio of cyclohexanone: solvesso 150 = 1: 1). In addition, a resin in which "Byron ^TM 103" and "Byron ^TM 63CS" were mixed at a solid content ratio of 1: 1 was also prepared and used in the experiment (in Table 1, B-130 and B-63CS Described as mixing). The Tg of this mixed resin was measured by thermomechanical analysis (TMA).

Next, “Cymel ^™ 303”, which is a hexamethoxymethylated melamine resin manufactured by Mitsui Cytec Co., Ltd., was prepared as an amino resin. Further, dodecylbenzenesulfonic acid was used as an acidic catalyst, and this was neutralized with 2-dimethylamino-ethanol, which is a volatile basic substance. Incidentally, 2-dimethylamino-ethanol was neutralized by adding an equivalent number necessary for neutralizing dodecylbenzenesulfonic acid. Furthermore, as an additive pigment, titanium oxide “Taipeku ^™ CR95” manufactured by Ishihara Sangyo Co., Ltd. was prepared.

  And these compositions were mixed as needed, and the coating composition was produced by stirring. Table 1 shows the details of the prepared paint. The acidic catalyst neutralized with the volatile basic catalyst was added in an amount of 0.5% by mass with respect to the resin solid content in the coating composition for all coating compositions.

  Hereinafter, the details of the precoated metal plate used in the experiment will be described.

Zinc-nickel alloy-plated steel sheet “Zinclite” (hereinafter referred to as ZL) manufactured by Nippon Steel Co., Ltd., electro-galvanized steel sheet “Zincoat” (hereinafter referred to as EG) manufactured by Nippon Steel Co., Ltd., and Nippon Steel Corporation A hot-dip galvanized steel sheet “Silver Zinc” (hereinafter referred to as GI) manufactured by the company was prepared as an original plate. A plate thickness of 0.6 mm was used. The plating adhesion amount of ZL used in this experiment was 20 g / m ^{2 on} one side, and the nickel amount in the plating layer was 12%. The EG plating adhesion amount was 20 g / m ² on one side, and the GI plating adhesion amount was 60 g / m ² on one side.

Next, spray degrease the prepared original plate with 2% by weight 50% aqueous solution of alkaline degreasing solution “FC-4336” manufactured by Nihon Parkerizing Co., Ltd., washed with water, and dried, then chromate-free chemical produced by Nihon Parkerizing Co., Ltd. Treatment “CT-E300N” was applied with a roll coater and dried in a hot air oven. The drying conditions in the hot air oven were 60 ° C. at the ultimate temperature of the steel plate. The coating amount of chromate-free treatment was applied so that the total solid content was 200 g / m ² .

  Next, one side of the metal plate that has been subjected to chemical conversion treatment is made of Nippon Paint's FL641 primer containing Ca ion-exchanged silica as a rust preventive pigment, and the other side is a back paint made by Nippon Paint. Each “FL100HQ” was coated with a roll coater and dried and cured in an induction heating furnace blown with hot air under the condition that the ultimate temperature of the metal plate was 210 ° C. After drying and baking, water was sprayed onto the painted metal plate and cooled with water. In addition, the primer coating material produced what was painted and what was not painted as needed.

  Further, the prepared coating composition was applied on the primer primer thus coated with a roll coater, and dried and cured under the condition that the ultimate plate temperature of the metal plate was 210 ° C. in an induction heating furnace in which hot air was blown. And after dry baking, the pre-coated metal plate was obtained by wiping water on the coated metal plate with a spray and cooling it with water.

  Table 2 describes the details of the prepared precoated metal sheet.

Hereinafter, the details of the evaluation method of the prepared precoated metal sheet will be described.
1. Coating film processability test The prepared pre-coated metal plate was bent 180 ° (adhesion bending), and the coating film in the processed part was visually observed to check for cracks in the coating film. When bending 180 °, bend so that the surface of the pre-coated metal plate faces the outside of the bend, and then tightly bend with two spacers of the same thickness as the pre-coated metal plate sandwiched inside the bend (Generally known as 2T bending). Moreover, the adhesive tape was affixed on the process part, and the residual state of the coating film was observed visually when this was peeled off vigorously.

Evaluation of coating film cracking and peeling is ○ when there is no coating film cracking or peeling, △ when a slight crack or peeling is observed in the coating film, × when there is a clear large crack or peeling in the coating film × As evaluated.
2. Magic Contamination Test A red magic ink was applied to the surface of a precoated metal plate and allowed to stand at room temperature for 24 hours, and the trace after wiping off the magic ink applied with xylene was evaluated. The case where the magic mark disappeared and was not visible was evaluated as ◯, the case where the magic mark remained slightly was evaluated as △, and the case where the magic mark did not disappear was evaluated as ×.
3. Solvent resistance test The sample was immersed in toluene for 24 hours, and the film swelling state after immersion was visually observed and evaluated. ○ when the surface of the paint film is unchanged compared to before immersion, △ when the paint film surface has slight traces of worm-swelling and slight swelling of the paint film is observed, and worms appear on the paint film surface. The case where there was a violent swelling such as swelling, and the swelling of the coating film was observed to be marked as x.
4. Corrosion resistance test Cut scratches were made on the coating surface of the prepared precoated metal sheet, and a salt spray test was performed by the method described in JIS K 5400.9.1. The salt water was sprayed on the surface of the test piece with the cross cut. The test time was 120 hours. Then, measure the swollen width of the coating film from the cut part on the surface side, ○ if the cut part swollen width is 3 mm or less on one side, △ if the cut part swollen width is more than 3 mm on one side and 5 mm or less, and the cut part swollen width is The case of more than 5 mm on one side was evaluated as x.

  Details of the evaluation results will be described below.

  Table 3 shows the evaluation results of the pre-coated metal plate produced. The precoated metal sheets of the present invention (Invention Examples No. 1 to 10) are excellent in stain resistance and solvent resistance, and are excellent in workability. In particular, when the amount of pigment added in the coating film is 80 parts by mass or less with respect to 100 parts by mass of the total resin solid content (Invention Examples No. 1, 2, 4 to 10), the processability may be deteriorated. It is more suitable because it can provide designability and the like. In addition, those that are not coated with a primer coating containing a rust preventive pigment (Invention Example No. 10) are excellent in processability, stain resistance, and solvent resistance, but are also required to have corrosion resistance because they have reduced corrosion resistance. For application, it is more preferable to apply a primer coating.

  On the other hand, polyester resins having a Tg of 25 ° C. or lower (Comparative Examples No. 11 and 13) are unsuitable because of poor solvent resistance. Further, polyester resins having a number average molecular weight of less than 10,000 (Comparative Examples Nos. 12 and 13) are unsuitable because of poor processability. Furthermore, the amount of amino resin added is less than 10 parts by weight with respect to 100 parts by weight of the polyester resin (Comparative Example No. 14), and the film does not contain an acidic catalyst (Comparative Example No. 15), Those in which the volatile basic substance is not contained in the coating film (Comparative Example No. 16) are inadequate because of poor stain resistance.

Claims (2)

  On one side or both sides of the metal plate subjected to chemical conversion treatment, (A) a polyester resin having a glass transition temperature of 25 ° C. or higher and a number average molecular weight of 10,000 to 50,000, (B) an amino resin, (C) an acidic catalyst, and (D) A coating composition comprising a volatile basic substance as an essential component, and (A) solid content of (B) amino resin is 10 to 32 parts by mass with respect to 100 mass parts of solid content of all polyester resins A precoated metal sheet having at least a coating film formed by applying an object and baking and drying, and having excellent stain resistance and solvent resistance.   2. The precoat metal having excellent stain resistance and solvent resistance according to claim 1, wherein the coating composition further contains a pigment, and the content thereof is 80 parts by mass or less with respect to 100 parts by mass of the total resin solid content. Board.