JP3092231B2 - Coating composition for metal surface top coat - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating composition for a top coat on the outer surface of a metal workpiece, and more particularly to a coating composition for an outer top coat on a metal workpiece which has improved wet ink printability during halftone dot printing. It relates to a composition.

[0002]

2. Description of the Related Art Conventionally, metal-made products have been widely used for packaging containers for filling, storing, transporting beverages, foods, and the like, exteriors of dry batteries, and other uses.

[0003] As a material of these metal workpieces, tin (tin-plated steel plate), tin-free steel (chrome-plated steel plate), aluminum and the like are widely used. The outer surfaces of these metal workpieces are often painted in the state of coils and cut plates or in the middle of metal processing for the purpose of metal corrosion resistance, aesthetic appearance, product name display, and the like. Such a coating is generally applied to a metal directly or via a primer called size coating, for example, by applying an intermediate coat called white coating, and then printing characters, designs, and the like with ink. Further, a transparent top coat is applied thereon for the purpose of protecting the surface and improving the appearance. The above painting process,
Baking is performed for each process, but the baking time reduces productivity. Therefore, in recent years, in the above-mentioned coating process, after printing the ink without performing baking when printing with the ink, the top coat paint in the next process is often applied after being undried, and subsequently baked. Is being done.

However, when the topcoat paint is applied on the undried ink, the so-called "bleed phenomenon", in which the base ink flows together with the topcoat paint, is likely to occur. In addition, a so-called “emboss phenomenon” is likely to occur at the interface between the image portion and the non-image portion, where a step is formed. In addition, when the base ink is agglomerated and, in extreme cases, the color of the base ink appears to fade, a so-called “fading phenomenon” of the ink tends to occur. As described above, when a bleed phenomenon, an emboss phenomenon, a fading phenomenon, or the like occurs in the printed portion of the ink, the gloss often decreases. The property that these phenomena are unlikely to occur in a top coat paint and can be applied on undried ink is called wet ink printing suitability, and if the suitability is poor, the appearance of the printed matter is impaired.

[0005] In the printing method, so-called solid printing in which the ink is spread in a plane state, and in which the ink is spread in a dot form,
There is so-called halftone printing. Although halftone dot printing allows free and innovative designs, the interface between the image area and non-image area increases, so the required level of wet ink printability is higher than in solid printing. Become.

[0006] The main performance requirements for a topcoat paint are the suitability for coating and the formation of a coating film suitable for the metalworking step after painting. More specifically, regarding the former, the dent of the coating film layer, the occurrence of dents and the like, the suitability for wet ink printing, and the like described above are mentioned. For the latter, flexibility, toughness,
Excellent adhesion, no damage or peeling of coating film during metal processing (hereinafter simply referred to as metal workability), excellent abrasion resistance, resistance to trauma, etc. It does not occur. In addition, water resistance, chemical resistance, heat resistance, and the like are added depending on the use of the metal workpiece.

Heretofore, epoxy-based resins, alkyd-based resins, acrylic-based resins, polyester-based resins, and the like have been used as paints for top coats of metal workpieces. Some of these resins are excellent in metal workability and the like, and are also excellent in wet ink printability during solid printing. For example, there is known a paint obtained by esterifying an epoxy resin with a dehydrated castor oil fatty acid, in which a melamine resin is added as a curing agent to a so-called epoxy ester resin (Japanese Patent Publication No. 3-2311).
No. 0).

However, even in these systems, the wet ink printability at the time of halftone dot printing has not yet attained satisfactory performance, and there is a drawback that the design of printed matter is restricted.

[0009]

DISCLOSURE OF THE INVENTION The present inventors have studied a paint for a top coat on the outer surface of a metal workpiece which is excellent in wet ink printability in solid printing and satisfies wet ink printability in halftone printing. As a result,
The present invention has been reached.

[0010]

Next, the present invention will be described in detail. The present invention relates to a coating composition for a top coat on the outer surface of a metal workpiece, which comprises an acrylate or methacrylate polymer.

The acrylate ester polymer which is a wet ink printability improver used in the present invention can be synthesized by various methods. For example, acrylic acid can be synthesized from methanol, ethanol, n-propanol, 1-butanol,
2-methyl-1-propanol, 1-pentanol, 2
It is obtained by a method such as bulk polymerization, suspension polymerization, emulsion polymerization, and solution polymerization of an acrylate monomer esterified with an alcohol such as 1-ethyl-1-hexanol and 1-dodecanol. The molecular weight of the obtained polymer is 3000-13000, preferably 5000-900.
It can be used in the range of 0. If the molecular weight is less than 3,000, the effect of improving wet ink printability during halftone printing is inferior. If it exceeds 13,000, the effect of improving wet ink printability during halftone printing is not improved. Tends to cause deterioration of the coating film.

The methacrylic acid ester-based polymer, which is a wet ink printability improver used in the present invention, can be synthesized by various methods. For example, methacrylic acid can be synthesized from methanol, ethanol, n-propanol, 1-butanol, -Methyl-1-propanol, 1-pentanol, 2-ethyl-1-hexanol, methacrylic acid ester monomers esterified with alcohols such as dodecanol, etc., are subjected to bulk polymerization, suspension polymerization, emulsion polymerization,
It is obtained by a method such as solution polymerization. The molecular weight of the obtained homopolymer can be used in the range of 4,000 to 15,000, preferably 6,000 to 10,000.
When the molecular weight is less than 4000, the effect of improving wet ink printability during halftone printing is poor. When the molecular weight exceeds 15,000, the effect of improving wet ink printability during halftone printing is not improved. Tends to cause deterioration of the coating film.

The acrylic acid ester or methacrylic acid ester-based polymer which is a wet ink printability improver used in the present invention is particularly preferably a homopolymer of acrylic acid or 2-ethyl-1-hexyl methacrylate.

The wet ink printing suitability improver is preferably 0.03% by weight based on the solid content of the coating film forming main component.
It can be added in the range of 1 to 2.00, preferably 0.05 to 0.70. When the weight% is less than 0.01, the effect of improving wet ink printability during halftone dot printing is poor,
On the other hand, if it exceeds 2.00, not only the effect of improving wet ink printing suitability during halftone dot printing is not improved, but also dents and dents in the coating film layer are likely to occur.

The main components for forming a coating film used in the present invention are not particularly limited. For example, as the main resin, conventionally used epoxy resins, alkyd resins, acrylic resins, polyester resins, etc., are required for various applications such as metal workability, water resistance, chemical resistance, and heat resistance. It can be arbitrarily selected according to the like. Further, examples of the curing agent resin of these main resins include amino resins such as melamine resins, benzoguanamine resins, and urea resins, phenol resins, and epoxy resins, which have been conventionally used. Further, a catalyst such as phosphoric acid and p-toluenesulfonic acid, a metal chelate compound such as titanium chelate and aluminum chelate and the like may be used alone or in combination with a curing agent resin.

The coating composition for a top coat on the outer surface of a metal workpiece according to the present invention is generally used as a solution by dissolving it in an organic solvent, and the organic solvent used at that time is not particularly limited. Absent. For example, ethanol, n-propanol, n-butanol, diacetone alcohol, butyl carbitol, diethyl carbitol, toluene,
Xylene, Solvesso # 100, Solvesso # 150,
Ethyl acetate, butyl acetate, ethyl cellosolve, butyl cellosolve, cellosolve acetate, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, etc. may be used alone or in combination depending on the solubility, boiling point, evaporation rate and the like. From the viewpoint of wet ink printability, it is preferable to mix a cellosolve organic solvent.

The coating composition for an outer top surface of a metal workpiece according to the present invention may optionally contain a leveling agent, an anti-sagging agent, an antifoaming agent, an ultraviolet absorber, an antiaging agent, as long as the purpose is not adversely affected. It is also possible to use additives such as agents and plasticizers.

The coating composition for a top coat on the outer surface of a metal workpiece of the present invention can be applied to a metal material by any means. For example, it may be selected from roll coating, curtain flow coating, spray coating, electrostatic coating, and the like.

[0019]

Next, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited thereto. All parts and percentages in the examples are on a weight basis.

Example 1 60 parts of 2-ethyl-1-hexyl acrylate, 40 parts of xylene and 0.6 parts of benzoyl peroxide were charged into a 1 liter flask, and solution polymerization was carried out at 80 ° C.
%, Poly (2-ethyl-1-hexyl) acrylate having a molecular weight of 6,400.

An epoxy ester resin (DA-10 manufactured by Dainippon Ink and Chemicals, Inc.)
14) and benzoguanamine-based resin (Super Beckamine L-128-5 manufactured by Dainippon Ink and Chemicals, Inc.)
And 5) were mixed in a solid content of 80 parts and 20 parts, respectively. To this was added 0.1 part of the above-obtained product in terms of solid content to prepare a topcoat paint.

The baking conditions for this paint are 160 ° C., 10
Minute heating. Example 2 An alkyd-based resin (Beccolite 1307-60, manufactured by Dainippon Ink and Chemicals, Inc.) was used as a main component for forming a coating film.
EL) and a benzoguanamine-based resin (Super Beckamine 17-599, manufactured by Dainippon Ink and Chemicals, Incorporated) in the same manner as in Example 1 except that 50 parts and 50 parts of solid content were used, respectively. A paint for coating was prepared.

The baking conditions of this paint are 170 ° C., 1
Heat for 0 minutes. Example 3 Acrylic resin (Acrydic A-508, manufactured by Dainippon Ink and Chemicals, Inc.) and benzoguanamine-based resin (Super Beckamine 17-599, manufactured by Dainippon Ink and Chemicals, Inc.) Were mixed in the same manner as in Example 1 except that 60 parts and 40 parts of solid content were used, respectively, to prepare a top coat paint.

The baking conditions for this paint were 180 ° C., 1
Heat for 0 minutes. Example 4 A polyester-based resin (Beccolite CF-743, manufactured by Dainippon Ink and Chemicals, Inc.) was used as a coating film forming main element.
-50) and benzoguanamine-based resin (manufactured by Dainippon Ink and Chemicals, Super Beckamine L-128-5)
5) was mixed in the same manner as in Example 1 except that 70 parts and 30 parts of solid content were used, respectively, to prepare a top coat paint.

The baking conditions for this paint were 160 ° C., 1
Heat for 0 minutes. Example 5 60 parts of 2-ethyl-1-hexyl methacrylate, 40 parts of xylene, and 0.6 part of benzoyl peroxide were charged into a 1-liter flask, solution-polymerized at 80 ° C.
0% poly (2-ethyl-1-hexyl methacrylate) having a molecular weight of 7600 was obtained.

The same components as in Example 1 were used as the main components for forming a coating film, and 0.1 parts by weight of the above-obtained product was added as a solid component to prepare a coating for a top coat. The baking condition of this paint is heating at 160 ° C. for 10 minutes.

Example 6 A top coat paint was prepared in the same manner as in Example 5, except that the same components as those in Example 2 were used as the main components for forming the coating film.

The baking conditions for this paint were 170 ° C., 1
Heat for 0 minutes. Example 7 A coating for a top coat was prepared in the same manner as in Example 5, except that the same components as those in Example 3 were used as the main components for forming the coating film.

The baking conditions for this paint were 180 ° C., 1
Heat for 0 minutes. Example 8 A coating for a top coat was prepared in the same manner as in Example 5, except that the same components as those in Example 4 were used as the main components for forming the coating film.

The baking conditions for this paint were 160 ° C., 1
Heat for 0 minutes. Comparative Example 1 In Example 1, a paint for a top coat was prepared without adding a product.

The baking conditions for this paint were 160 ° C., 1
Heat for 0 minutes. Comparative Example 2 In Example 2, a paint for a top coat was prepared without adding a product.

The baking conditions for this paint were 170 ° C., 1
Heat for 0 minutes. Comparative Example 3 In Example 3, a top coat paint was prepared without adding the product.

The baking conditions for this paint were 180 ° C., 1
Heat for 0 minutes. Comparative Example 4 In Example 4, a coating material for a top coat was prepared without adding a product.

The baking conditions for this paint were 160 ° C., 1
Heat for 0 minutes. The following tests were performed on the obtained top coat paint. Tin plate with a thickness of 0.22 mm (manufactured by Nippon Steel Corporation, JIS G3303SPTEM)
RT-4CA B) was coated with white coating (1S-582, manufactured by Dainippon Ink and Chemicals, Incorporated) mainly composed of an acrylic resin and titanium oxide with a roll coater (dry coating amount 140 mg / 100 cm ² ), 1
Baking was performed by heating at 90 ° C. for 10 minutes. Then, an ink mainly composed of an alkyd resin and an organic pigment (manufactured by Dainippon Ink and Chemicals, MC
CCM Y-4 yellow) was simultaneously analyzed with a calibrator (KL-101, manufactured by Dainippon Screen Co., Ltd.) to have a dot area ratio of 20
% Dot color and solid color (both film thickness 1.5μ
m), and in a state where the ink is not dried without further baking, quickly apply a paint for the finished top coat with a roll coater (dry coating amount: 60 mg / 100 c)
m ² ), and quickly heated and baked under predetermined conditions to obtain test pieces.

A test of wet ink printing suitability was carried out on a halftone dot printed portion and a solid printed portion of the test piece obtained in this manner with a dot area ratio of 20%. Table 1 shows the results.

[0036]

[Table 1] The test method is as follows. (1) Visual Judgment The degree of ink bleeding, fading, embossing, etc. was visually judged.

The criteria for the visual judgment are as follows.・ ・ ・: Good △: Practically usable ×: Practically unusable (2) Specular glossiness The 60 ° specular glossiness of the printed portion was measured according to JIS Z8741.

For the measurement, a digital variable gloss meter (UGV-5K, manufactured by Suga Test Instruments Co., Ltd.) was used.

[0039]

The coating composition for a top coat on the outer surface of a metal workpiece according to the present invention is excellent in wet ink printability not only in solid printing but also in conditionally strict halftone printing. Therefore, a free and novel print design is possible, and various advantages such as elimination of the ink printing process, that is, improvement of productivity by simplifying the process and cost reduction can be expected.

Further, the acrylate or methacrylate-based polymer used in the coating composition for the metal outer surface top coat according to the present invention may be added to a conventionally used paint such as a silicone-based resin or oil or fat. Compared with the agent, dents and cissing of the coating layer are less likely to occur, and the adhesiveness to white coating or ink is less likely to be adversely affected. In addition, it is hard to bleed on the coating film surface, and it is hard to transfer to other materials in contact with the coating film surface. For example,
The outer surface is painted first in the state of the coil and the cutting board, and the additive is difficult to transfer even if the unpainted surface, that is, the painted outer surface contacts the inner surface, and the subsequent process such as painting the inner surface or the inner surface Hardly adversely affect the performance of

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C09D 7/12 C09D 201/00 CA (STN) CAOLD (STN) REGISTRY (STN)

Claims (1)

(57) [Claims] 1. 2-ethylhexyl acrylate or methacrylic acid is used for a total of 100 parts by weight of a film-forming main element composed of an amino resin and at least one selected from the group consisting of an epoxy ester resin, an alkyd resin and an acrylic resin. -An acrylic resin having a number average molecular weight of 4000 to 13000 obtained by polymerizing ethylhexyl
A coating composition for a top coat on the outer surface of a metal workpiece, which is contained in an amount of from 2.00 to 2.00 parts by weight.