Hard coating composition for metal substrate

Abstract

The object of the present invention is to provide a hard coating composition for a metal substrate, including a film-forming resin component which contains a urethane (meth)acrylate obtained by reacting a polyisocyanate compound, a polyol, and a (meth)acrylate monomer having a hydroxyl group, wherein the polyisocyanate compound is hydrogenated xylylene diisocyanate and/or dicyclohexylmethane diisocyanate.

Claims

1. A hard coating composition for a metal substrate consisting of: a film-forming resin component consisting of (i) a urethane (meth)acrylate obtained by reacting a polyisocyanate compound, a polyol, and a (meth)acrylate monomer having a hydroxyl group, and (ii) an active energy ray-curable component having an alicyclic structure, a photo-polymerization initiator, and a solvent, wherein the polyisocyanate compound is dicyclohexylmethane diisocyanate, the polyol is at least one selected from the group consisting of 1,4-cyclohexanediol and 2,2-bis(4-hydroxycyclohexyl)propane, the amount of the photo-polymerization initiator is within a range of 1 to 3 parts by mass with respect to 100 parts by mass of the urethane (meth)acrylate, the amount of the solvent is within a range of 0.001% to 40% by mass with respect to the total of the coating composition; the active energy ray-curable component is at least one selected from the group consisting of cyclohexyl(meth)acrylate, t-butylcyclohexyl(meth)acrylate, dicyclohexylpentanyl acrylate, tricyclodecane dimethanol (meth)acrylate, isobornyl (meth)acrylate, dimethyloltricyclodecane di(meth)acrylate, and dimethylol dicyclopentane diacrylate; and the amount of the active energy ray-curable component is within a range of 5% to 60% by mass with respect to the total of the film-forming resin component.

2. The hard coating composition for a metal substrate according to claim 1 which is used for an aluminum substrate.

3. A hard coating composition for a metal substrate consisting of: a film-forming resin component consisting of (i) a urethane (meth)acrylate obtained by reacting a polyisocyanate compound, a polyol, and a (meth)acrylate monomer having a hydroxyl group, and (ii) an active energy ray-curable component having an alicyclic structure, a photo-polymerization initiator, and a solvent, wherein the polyisocyanate compound is hydrogenated xylylene diisocyanate, the polyol is at least one selected from the group consisting of 1,4-cyclohexanediol and 2,2-bis(4-hydroxycyclohexyl)propane, the amount of the photo-polymerization initiator is within a range of 1 to 30 parts by mass with respect to 100 parts by mass of the urethane (meth)acrylate, the amount of the solvent is within a range of 0.001% to 40% by mass with respect to the total of the coating composition; the active energy ray-curable component is at least one selected from the group consisting of cyclohexyl(meth)acrylate, t-butylcyclohexyl(meth)acrylate, dicyclohexylpentanyl acrylate, tricyclodecane dimethanol (meth)acrylate, isobornyl (meth)acrylate, dimethyloltricyclodecane di(meth)acrylate, and dimethylol dicyclopentane diacrylate; and the amount of the active energy ray-curable component is within a range of 5% to 60% by mass with respect to the total of the film-forming resin component.

4. The hard coating composition for a metal substrate according to claim 1, wherein the polyol is 1,4-cyclohexanediol.

5. The hard coating composition for a metal substrate according to claim 1, wherein the polyol is 2,2-bis(4-hydroxycyclohexyl)propane.

6. The hard coating composition for a metal substrate according to claim 1, wherein the (meth)acrylate monomer having a hydroxyl group is 2-hydroxylethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, glycerol dimethacrylate, polyethylene glycol (meth)acrylate, or a combination thereof.

7. The hard coating composition for a metal substrate according to claim 6, wherein the (meth)acrylate monomer having a hydroxyl group is 2-hydroxylethyl(meth)acrylate.

8. The hard coating composition for a metal substrate according to claim 1, wherein 30% by mass or more of the urethane (meth)acrylate is contained in the film-forming resin component.

9. The hard coating composition for a metal substrate according to claim 3, wherein 30% by mass or more of the urethane (meth)acrylate is contained in the film-forming resin component.

Description

EXAMPLES

(1) Hereinafter, the present invention will be described in detail with reference to Examples.

Synthesis of Urethane Acrylates A to D

Synthesis Example 1

(2) 59 parts by mass of 1,6-hexanediol (manufactured by UBE INDUSTRIES, LTD.), and 194 parts by mass of hydrogenated xylylene diisocyanate (manufactured by MITSUI TAKEDA CHEMICALS, INC.) were charged to a 500 ml flask equipped with a stirrer and a thermometer. These were reacted in a nitrogen stream at 70 C. for four hours. Then, 116 parts by mass of 2-hydroxylethyl acrylate (manufacture by Kyoei Kagaku Kogyo), 0.6 parts by mass of hydroquinone, and 0.3 parts by mass of dibutyltin dilaurate were added to the flask. These were further reacted at 70 C. for five hours while air-bubbling the content inside the flask whereby urethane acrylate A was obtained.

Synthesis Example 2

(3) Urethane acrylate B was produced in the same manner as Synthesis Example 1 except that 262 parts by mass of dicyclohexylmethane diisocyanate (Sumitomo Bayer Urethane Co., Ltd.) were added instead of 194 parts by mass of hydrogenated xylylene diisocyanate.

Synthesis Example 3

(4) Urethane acrylate C was produced in the same manner as Synthesis Example 1 except that 222 parts by mass of isophorone diisocyanate (manufactured by Evonik Degussa Japan) were added instead of 194 parts by mass of hydrogenated xylylene diisocyanate.

Synthesis Example 4

(5) Urethane acrylate D was produced in the same manner as Synthesis Example 1 except that 168 parts by mass of hexamethylene diisocyanate (manufactured by Nippon Polyurethane Industry Co., Ltd.) were added instead of 194 parts by mass of hydrogenated xylylene diisocyanate.

Example 1

(6) A liquid coating composition was prepared by mixing each component at the solid content ratio (mass ratio) shown in Table 1.

(7) Then, the coating composition was spray-coated on the surface of an aluminum substrate with a spray gun such that the thickness of the cured coating film was 20 m. After the solvent was dried at 80 C. for three minutes, it was irradiated with a ultraviolet ray of 300 mJ (a value measured with UVR-N1 manufactured by Japan Storage Battery Co., Ltd.) using a high-pressure mercury-vapor lamp for two to three minutes to form a hard coat. This was used as a test piece.

(8) The test piece produced in this way was evaluated in terms of initial adherence properties, adherence properties after water-resistance test, rust resistance, and abrasion resistance (pencil hardness). The results are shown in Figure 1.

Examples 2 to 11 and Comparative Examples 1 to 8

(9) Each component was mixed at a solid content ratio (mass ratio) shown in Tables 1 and 2 to prepare a liquid coating composition. Except that each coating composition obtained in this way was use to prepare a test piece, initial adherence properties, adherence properties after water-resistance test, rust resistance, and abrasion resistance (pencil hardness) were evaluated in the same manner as Example 1 in the following way. The results are shown in Tables 1 and 2.

(10) [Preparation of Test Piece and Test Method]

(11) 1. Initial Adherence Properties

(12) The coating film of each test piece was cross-cut in a 1010 lattice pattern of 1 mm width, and tape was adhered to the cross-cut area and then removed. When the coating film was not adhered on the tape, it was evaluated as excellent. When the corner of the lattice was slightly cracked, it was evaluated as fair. When at least one lattice was separated from the substrate, adhering to the tape, it was evaluated as inferior. Based on this, test pieces were graded. The results are shown in Tables 1 and 2. In addition, the tape was a cellophane adhesive tape.

(13) 2. Adherence Properties after Water-Resistance Test

(14) With regard to Examples, test pieces were soaked in hot water at 40 C. for 240 hours and for 480 hours. Then, each test piece was cross-cut in a 1010 lattice pattern of 1 mm width, and a tape was adhered to the cross-cut area and then removed. On the other hand, with regard to Comparative Examples, test pieces were soaked in hot water at 40 C. for 240 hours. Then, each test piece was subjected to the same procedures.

(15) Each test piece was graded as excellent, fair or inferior, based on the above-mentioned standards. The results are shown in Tables 1 and 2.

(16) 3. Rust Resistance

(17) A CASS test (copper-accelerated acetic acid salt spray test) was conducted using a CASS test machine (SQ-800-CA produced by Itabashi Rikakogyo co Ltd.), based on JIS H 8681-2 for 120 hours and 240 hours in Examples and for 120 hours for Comparative Examples. When rust was not visually observed, it was evaluated as excellent. When rust was slightly observed, it was evaluated as fair. When rust was obviously observed, it was evaluated as inferior. The results are shown in Tables 1 and 2.

(18) 4. Abrasion Resistance (Pencil Hardness)

(19) The pencil hardness of each coating film was measured based on JIS K 5600. When the hardness thereof was 3H or higher, it was evaluated as excellent. When the hardness was less than 3H, it was evaluated as inferior. The results are shown in Tables 1 and 2.

(20) In addition, each components indicated in Tables are as follows.

(21) (1) Diethylene glycol diacrylate is manufactured by DAICEL-CYTEC COMPANY LTD.;

(22) (2) Dipropylene glycol diacrylate is manufactured by DAICEL-CYTEC COMPANY LTD.;

(23) (3) Trimethylolpropane triacrylate is manufactured by Nippon Kayaku Co., Ltd.;

(24) (4) Dipentaerythritol hexaacrylate is manufactured by Nippon Kayaku Co., Ltd.;

(25) (5) Cyclohexyl acrylate is BLEMMER CHA (product name) manufactured by NOF CORPORATION;

(26) (6) Dicyclopentanyl acrylate is FANCRYL FA-513A (product name) manufactured by Hitachi Chemical Co., Ltd.;

(27) (7) Dimethylol dicyclopentane diacrylate is IRR-214 (product name) manufactured by DAICEL-CYTEC COMPANY LTD.;

(28) (8) Tris(acryloxyethyl)isocyanurate is Aronix M-315 (product name) manufactured by TOAGOSEI CO., LTD.;

(29) (9) Methyl polymethacrylate is Acrybase LH101 (product name) manufactured by FUJIKURA KASEI CO., LTD. (solid content: 40% by mass);

(30) (10) Irgacure 184 (product name) is manufactured by Ciba Specialty Chemicals;

(31) (11) Irgacure 819 (product name) is manufactured by Ciba Specialty Chemicals;

(32) TABLE-US-00001 TABLE 1 Examples 1 2 3 4 5 6 7 8 9 10 11 Film- Urethane acrylate A 100 0 50 50 100 50 50 100 40 40 50 forming Urethane acrylate B 0 100 0 0 0 0 0 0 0 0 0 resin Active Diethylene 0 0 50 0 0 0 0 0 0 0 0 compo- energy glycol nent ray- diacryalte curable Dipropylene 0 0 0 50 0 0 0 0 0 0 0 component glycol diacrylate Trimethylol- 0 0 0 0 0 50 0 0 0 10 0 propane triacrylate Dipenta- 0 0 0 0 0 0 50 0 0 0 0 erythritol hexaacrylate Cyclohexyl 0 0 0 0 0 0 0 0 60 0 0 acrylate Dicyclo- 0 0 0 0 0 0 0 0 0 50 0 pentanyl acrylate Dimethylol 0 0 0 0 0 0 0 0 0 0 40 dicyclo- pentane diacrylate Thermo- Methyl 0 0 0 0 60 0 0 0 0 0 0 plastic polymeth- resin acrylate Photo- Irgacure 184 3 3 3 3 3 3 3 0 3 3 3 polymerization Irgacure 819 0 0 0 0 0 0 0 3 0 0 0 initiator Solvent Ethyl acetate 50 50 50 50 100 50 50 50 30 30 40 Evaluation Initial adherence Excel- Excel- Excel- Excel- Excel- Excel- Excel- Excel- Excel- Excel- Excel- properties lent lent lent lent lent lent lent lent lent lent lent Adherence After Excel- Excel- Excel- Excel- Excel- Excel- Excel- Excel- Excel- Excel- Excel- properties 240 lent lent lent lent lent lent lent lent lent lent lent after hours water- After Excel- Excel- Fair Fair Fair Fair Fair Excel- Excel- Excel- Excel- resistance 480 lent lent lent lent lent lent test hours Rust After Excel- Excel- Excel- Excel- Excel- Excel- Excel- Excel- Excel- Excel- Excel- resistance 120 lent lent lent lent lent lent lent lent lent lent lent hours After Excel- Excel- Fair Fair Fair Fair Fair Excel- Excel- Excel- Excel- 240 lent lent lent lent lent lent hours Abrasion Excel- Excel- Excel- Excel- Excel- Excel- Excel- Excel- Excel- Excel- Excel- resistance lent lent lent lent lent lent lent lent lent lent lent (Pencil hardness)

(33) TABLE-US-00002 TABLE 2 Comparative Examples 1 2 3 4 5 6 7 8 Film- Urethane acrylate C 100 0 0 0 0 0 0 0 forming Urethane acrylate D 0 100 0 0 0 0 0 0 resin Active energy Tris 0 0 100 0 0 0 0 0 component ray-curable (acryloxyethyl) component isocyanurate Diethylene 0 0 0 100 0 0 0 0 glycol diacryalte Dipropylene 0 0 0 0 100 0 0 0 glycol diacrylate Trimethylol 0 0 0 0 0 100 100 0 propane triacrylate Dipenta 0 0 0 0 0 0 0 100 erythritol hexaacrylate Thermoplastic Methyl 0 0 0 0 0 60 0 0 resin polymethacrylate Photo-polymerization Irgacure 184 3 3 3 3 3 3 3 0 initiator Irgacure 819 0 0 0 0 0 0 0 3 Solvent Ethyl acetate 50 50 50 50 50 100 50 50 Evaluation Initial Excel- Excel- Excel- Excel- Excel- Excel- Inferior Inferior adherence lent lent lent lent lent lent properties Adherence Inferior Inferior Inferior Inferior Inferior Excel- Inferior Inferior properties lent after water- resistance test Rust resistance Inferior Inferior Inferior Inferior Inferior Inferior Inferior Inferior Abrasion resistance Excel- Excel- Excel- Inferior Inferior Excel- Excel- Excel- (Pencil hardness) lent lent lent lent lent lent

(34) As shown in Tables 1 and 2, hard coats could be formed in the Examples, in which their adherence properties to the metal substrate were not lowered due to the water content therein, their rust resistance was excellent, and their abrasion resistance was also excellent having high pencil hardness. On the other hand, the adherence properties of hard coats were lowered due to the water content, and their rust resistance was also impaired in Comparative Examples 1 and 2 where polyisocyanate compounds other than hydrogenated xylylene diisocyanate and hydrogenated dicyclohexylmethane diisocyanate in synthesis of urethane (meth)acrylates. Moreover, a hard coat having sufficient adherence properties, rust resistance and abrasion resistance could not be formed in coating compositions not including a urethane(meth)acrylate (Comparative Examples 3 to 6).

(35) Additionally, with regard to Examples 1, 2 and 8 where their film-forming resin component was prepared with only urethane acrylate A or B, all the hard coats had excellent adherence properties, rust resistance and abrasion resistance. Furthermore, with regard to inclusion of the other components in the film-forming resin component in addition to urethane acrylate A, Examples 9 to 11 containing an active energy ray-curable component having an alicyclic structure showed very high adherence properties, rust resistance and abrasion resistance.

INDUSTRIAL APPLICABILITY

(36) According to the hard coating composition of the present invention, a hard coat that has excellent adherence properties to a metal substrate and that can impart high abrasion resistance or rust resistance to the metal substrate can be formed at a high productivity. Accordingly, the hard coating composition of the present invention can be applied to metal substrates used in various arts such as building materials or vehicle members, and therefore, has high industrial applicability.