KR100985274B1 - Aqueous coating composition for painting plastic substrate, and method of fabricating plastic case using the same - Google Patents

Abstract

An aqueous coating composition for plastic coating and a plastic case coated therewith is provided. The composition contains 30 wt% to 70 wt% of water-dispersed polyurethane resin, 0.01 wt% to 3 wt% of hardener, 0.1 wt% to 20 wt% of pigment, and 0.01 wt% to 30 wt% of additive. By using the coating composition containing the above water-dispersed polyurethane as a base resin, a coating film is produced that does not generate volatile organic compounds (VOC) without any deterioration in physical properties as compared with the case of using a coating composition containing an oil-based resin. Can be.

Description

Aqueous coating composition for painting plastic substrate, and method of fabricating plastic case using the same}

The present invention relates to coating compositions, and more particularly to aqueous coating compositions.

Plastics have been used in a variety of applications in the field of electronic products, such as telephones, to reduce the thickness of products. Since the plastic is less scratch resistance or hardness than glass or metal, to compensate for this, a plurality of coating layers, for example, an undercoating layer and a top coating layer are formed on the plastic.

Meanwhile, in recent years, as the use of volatile organic compounds (VOCs) is regulated worldwide, researches for converting existing oily coatings into aqueous coatings have been conducted in various industrial fields.

Therefore, there is a need to form coating layers applied on such plastics also using an aqueous coating agent.

However, plastics have a very large difference in properties, such as glass transition temperature and solubility in organic solvents, depending on the base material, so that the aqueous coating agent applicable to each material may vary.

The problem to be solved by the present invention is to provide an aqueous coating composition for plastic coating and a plastic case manufacturing method using the same.

Technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

One aspect of the present invention to achieve the above object provides an aqueous coating composition for plastic coating. The composition contains 30 wt% to 70 wt% of water-dispersed polyurethane resin, 0.01 wt% to 3 wt% of hardener, 0.1 wt% to 20 wt% of pigment, and 0.01 wt% to 30 wt% of additive.

Another aspect of the present invention to achieve the above object provides a plastic case manufacturing method. First, an aqueous coating composition containing 30 wt% to 70 wt% of water-dispersed polyurethane resin, 0.01 wt% to 3 wt% of a curing agent, 0.1 wt% to 20 wt% of pigment, and 0.01 wt% to 30 wt% of additives on a plastic substrate To form an undercoat layer. A top coating layer is formed on the under coating layer.

According to the present invention, in the case of using a coating composition containing an oil-based resin by using a coating composition containing the water-dispersed polyurethane as a base resin to form a coating film on a plastic substrate, specifically a polycarbonate-based substrate. Compared to the above, a coating film which does not generate volatile organic compounds (VOCs) without any deterioration in physical properties can be obtained.

Technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

Hereinafter, preferred embodiments of the present invention will be described in more detail in order to describe the present invention in more detail. However, the present invention is not limited to the embodiments described herein but may be embodied in other forms.

The aqueous coating composition for plastic coating according to an embodiment of the present invention contains a water-dispersible polyurethane dispersion, a curing agent, a pigment, and an additive. The composition may contain 30 wt% to 70 wt% of the water-dispersible polyurethane resin, 0.01 wt% to 3 wt% of the curing agent, 0.1 wt% to 20 wt% of the pigment, and 0.01 wt% to 30 wt% of the additive. have.

The water-dispersible polyurethane resin is a new material capable of forming a coating film using water as a solvent, and is not very excellent in adhesion to a plastic substrate, in particular, a polycarbonate-based substrate, and has excellent wear resistance and chemical resistance. Therefore, by using the coating composition containing the water-dispersed polyurethane as a base resin to form a coating film on the polycarbonate substrate, if the physical properties are not lowered at all compared to the case of using a coating composition containing an oil resin It is possible to obtain a coating film which does not generate a volatile organic compound (VOC).

Such a water dispersion type polyurethane resin may be anionic. In addition, the water-dispersed polyurethane resin may be an aliphatic poly (carbonate-diol) type or an aliphatic polyester (aliphatic polyester) type. The water-dispersible polyurethane resin of the aliphatic poly (carbonate-diol) type has a backbone similar to that of the polycarbonate, which is a substrate material, and thus may exhibit more excellent adhesion on the polycarbonate substrate.

The curing agent may be a polyaziridine as a material capable of reacting with the terminal carboxyl group of the water-dispersible polyurethane resin. As the polyaziridine and the terminal carboxyl groups of the water-dispersed polyurethane react to form an amino ester, the polyurethane is crosslinked. The polyaziridine may be pentaerythritol-tris- (β- (N-aziridinylpropionate) (Pentaerythritol-tris- (β- (N-aziridinyl) Propionate).

The pigment may be a paste form, that is, a material in which the pigment is dispersed in a stable state on a solution. Specifically, the pigment may be an inorganic pigment such as titanium oxide, carbon black or iron oxide, or an organic pigment such as phthalocyanine blue, phthalocyanine green, or perylene red.

The additive may be at least one selected from the group consisting of a leveling agent, a slip agent, a defoamer, and a thickener.

The smoothing agent is used to improve the spreadability and appearance during painting work by reducing the surface tension of the paint, it may be a silicon-based material. In the case of the aqueous coating solution, since the surface tension of water is higher than that of the organic solvent, the wettability of the substrate to be coated may be poor. By adding the leveling agent, the wettability may be improved. Preferably, the leveling agent may be silicone glycol. The smoothing agent may be contained in 0.01wt% ~ 1wt%. If the content of the leveling agent is 0.01wt% or less, there is a problem that the coating film is poorly adhered to the material due to the lack of a wetting effect of the coating solution.

The slip agent is an additive for improving slip property of the coating film, and may be polyethylene wax. The slip agent may be contained in an amount of 0.01 wt% to 5 wt%.

The antifoaming agent is to improve workability by removing air bubbles during coating composition preparation or coating, and may be a polysiloxane-based material. The antifoaming agent may be contained in 0.01wt% ~ 1wt%.

The thickener is a material for adjusting the viscosity of the coating composition, it may be a glycol-based material. The thickener may be contained in 0.01wt% ~ 20wt%.

1 is a cross-sectional view showing a plastic case including a coating film formed using an aqueous coating composition according to an embodiment of the present invention.

Referring to FIG. 1, an undercoat layer 13 is formed by applying an aqueous coating composition on a plastic substrate 10. The plastic substrate 10 may be a polycarbonate substrate. The polycarbonate substrate is a substrate having excellent impact resistance and heat resistance, and may be a substrate suitable for an electronic case, in particular, a mobile phone case.

The aqueous coating composition may be a composition as described above. The undercoat 13 may be formed using a bar coating technique. The undercoat 13 may be hot air dried. This drying process is preferably 5 to 10 minutes in consideration of the throughput (throughput). To this end, the undercoat 13 may be dried at 70 ℃ or more. In addition, the undercoat 13 may be dried at 70 ~ 80 ℃. When the drying temperature exceeds 80 ° C., deformation of the substrate, in particular, the polycarbonate substrate may occur.

The undercoat 13 may have a thickness of 5 μm or more in consideration of reliability. In addition, the undercoat 13 may have a thickness of 5 ~ 10㎛. When the undercoat 13 has a thickness exceeding 10 μm, the drying time may be increased, thereby reducing the throughput.

The top coating layer 15 is formed on the under coating layer 13. The top coating layer 15 may be formed using an oily coating solution. The oil coating solution is a solution using an oil solvent such as xylene and / or toluene, and may be a two-component coating solution in which an oil resin solution and an oil curing agent solution are separately applied. Specifically, the oil-based resin solution is 40 to 50 wt% acrylic urethane resin, 20 to 30 wt% toluene, 15 to 25 wt% PMA (1- (4-methoxyphenyl) propan-2-amine), 5 to 10 wt% xylene, 10-20 wt% butyl acetate. The oil curing agent solution may contain 55 to 65 wt% of polyisocyanate and 35 to 45 wt% of xylene. The top coating layer 15 may also be formed using a bar coating method, the thickness after drying may be 20 to 20 ~ 25 ㎛.

Hereinafter, preferred examples are provided to aid the understanding of the present invention. However, the following experimental examples are only for helping understanding of the present invention, and the present invention is not limited to the following experimental examples.

Experimental Examples; examples>

Evaluation of adhesion of undercoat

<Manufacture example 1>

5 g of water-dispersible polyurethane resin of aliphatic poly (carbonate-diol) type, 0.5 g of silver paste as pigment, and 0.05 g of polyaziridine were added to 10 ml of distilled water and sonicated for several minutes to prepare an undercoat solution. It was. The undercoating solution was coated on a carbonated substrate injection molding using a mayer bar coating method to form an undercoating film. The undercoating film was hot air dried at 80 ° C. for 5 minutes. The thickness of the coating film after drying was about 5 μm.

<Manufacture example 2>

A coating film was formed under the same conditions as Preparation Example 1, except that an aliphatic polyester type water dispersible polyurethane resin was used as the base resin.

Comparative Example 1

A coating film was formed under the same conditions as Preparation Example 1, except that an acrylic copolymer emulsion was used as the base resin.

Comparative Example 2

A coating film was formed under the same conditions as in Preparation Example 1, except that an aqueous dispersion-based acrylic-urethane copolymer (acrylic-urethane copolymer dispersion) was used as the base resin.

After forming 100 checkered cells by cross-cutting at intervals of 1 mm on the coating films formed through Preparation Examples 1 and 2 and Comparative Examples 1 and 2, the adhesive films were separated from the substrate. The number of cells to be investigated.

The results according to the adhesion evaluation examples are shown in Table 1 below.

TABLE 1

Preparation Example 1 Production Example 2 Comparative Example 1 Comparative Example 2 Base resin Water Dispersible Polyurethane Resin Water Dispersible Polyurethane Resin Acrylic Copolymer Emulsion Water Dispersible Acrylic-Urethane Copolymer type Aliphatic poly (carbonate-diol) Aliphatic polyester - - Particle charge state Negative ion Negative ion - Negative ion Particle size - - - Colloid Solid content (%) 35 35 45 40 PH (25 ℃) 8.0 8.0 6.5 8.0 Viscosity (25 ° C, mPa.s) 100 125 200 150 MFFT (℃) - - 67 - The tensile strength 4500 5450 - 4,000 kidney(%) 160 220 - 120 Acid value (mg, @ KOH, 1g) - - - 12 Adhesion
(100 exits) 0/100 0/100 20/100 15/100 Minimum Film Forming Temperature (MFFT) = Minimum Temperature

Referring to Table 1, the coating film using the water-dispersible polyurethane resin according to Preparation Examples 1 and 2 did not deviate even one cell in the adhesion evaluation, while using the acrylic copolymer emulsion according to Comparative Example 1 20 cells were separated from the coating film, and 15 cells were separated from the coating film using the water-dispersible acrylic-urethane copolymer according to Comparative Example 2. From these results, it can be seen that the coating film using the water dispersible polyurethane resin can be adhered well on the polycarbonate substrate.

Solvent resistance evaluation of undercoat

<Manufacture example 3>

The two-part type oily top coating solution was coated on the undercoat according to Preparation Example 1 by using a mayer bar coating method to form a top coating. The thickness of the top coating film was about 20 μm. The two-component oil-based top coating solution is 40 to 50 wt% acrylic urethane resin, 20 to 30 wt% toluene, 15 to 25 wt% PMA (1- (4-methoxyphenyl) propan-2-amine), 5 to An oily resin solution having 10 wt% xylene, 10-20 wt% butyl acetate, and a crosslinker solution having 55-65 wt% polyisocyanate and 35-45 wt% xylene were prepared.

&Lt; Preparation Example 4 &

A top coating film was formed under the same conditions as in Preparation Example 3 except that the top coating film was formed on the undercoating film according to Preparation Example 2 using a two-part oily top coating solution.

Comparative Example 3

A top coating film was formed under the same conditions as in Preparation Example 3 except that the top coating film was formed on the undercoating film according to Comparative Example 1 by using a two-part oily top coating solution.

<Comparative Example 4>

A top coating film was formed under the same conditions as in Preparation Example 3 except that the top coating film was formed on the under coating film according to Comparative Example 2 using a two-part type oily top coating solution.

The color and state of the coating films formed through Preparation Examples 3 and 4, and Comparative Examples 3 and 4 are shown in Table 2 below.

TABLE 2

Production Example 3 Preparation Example 4 Comparative Example 3 Comparative Example 4 Base resin Water Dispersible Polyurethane Resin Water Dispersible Polyurethane Resin Acrylic Copolymer Emulsion Water Dispersible Acrylic-Urethane Copolymer type Aliphatic poly (carbonate-diol) Aliphatic polyester - - color silver silver discoloration discoloration condition No swelling No swelling With swelling With swelling

Referring to Table 2, the undercoating film using the water-dispersible polyurethane resin according to Preparation Examples 3 and 4 is the color of the undercoat film is maintained as it is after the top coating film is formed, there is no swelling phenomenon, Comparative Example 3 and 4 of the coating film after the top coating film was formed, the color of the undercoat film discolored and at the same time a swelling phenomenon appeared. From these results, it can be seen that the aqueous undercoating film using the water dispersible polyurethane resin is excellent in solvent resistance to the oily top coating solution.

Under with or without hardener Coating film  Property evaluation

Production Example 5

A coating film was formed under the same conditions as Preparation Example 1, except that 0.1 g of polyaziridine as a curing agent was used.

Comparative Example 5

A coating film was formed under the same conditions as Preparation Example 1 except that no curing agent was used.

<Hot resistance test>

Substrates having the coating films formed through Preparation Examples 1 and 5, and Comparative Example 5 were immersed in hot water at 80 ° C. for 60 minutes and then taken out, and then tested to see if the coating film was released from the substrate using an adhesive tape.

<RCA Abrasion Test>

After rubbing 500 times of 275 g of paper on the coating films formed through Preparation Examples 1 and 5, and Comparative Example 5 using an RCA wear tester, the condition of the coating films was examined.

Resistant Cosmetic Test

After applying UV cream on the coating films formed through Preparation Examples 1 and 5, and Comparative Example 5, and left for 24 hours in a chamber maintained at 60 ℃, 90% humidity, and then taken out, using an adhesive tape It was tested whether the coating film deviated from the substrate.

It is shown in Table 3 below whether the coating film peeling according to the hot water resistance test, RCA wear test, cosmetics test for the coating film according to Preparation Examples 1 and 5, and Comparative Example 5.

TABLE 3

Preparation Example 1 Preparation Example 5 Comparative Example 5 Curing agent condition Polyaziridine 0.1wt% 0.2 wt% polyaziridine none Hot water resistance test X X ○ RCA Abrasion Test X X X Resistant Cosmetic Test X X ○ ○: coating film peeling occurs, X: coating film peeling does not occur

Referring to Table 3, the coating films (manufacture examples 1 and 5) formed by using a coating solution containing a poly aziridine as a curing agent has no coating film by hot water resistance test, RCA wear test and cosmetic test. It did not peel off. However, the coating film (Comparative Example 5) formed using the coating solution containing no polyaziridine as a curing agent was peeled off in the hot water resistance test and the cosmetic test. From these results, it can be seen that when the polyaziridine is used as the curing agent, the hot water resistance, the RCA wear resistance and the cosmetic properties of the undercoating film formed on the polycarbonate substrate are satisfactory.

Under Coating film  According to the thickness after drying Coating film  Property evaluation

<Manufacture example 6>

A coating film was formed under the same conditions as in Preparation Example 1, except that the thickness of the coating film after drying was 3 μm.

<Manufacture example 7>

A coating film was formed under the same conditions as in Preparation Example 1, except that the thickness of the coating film after drying was 9 μm.

Table 4 shows the peeling of the coating film according to the hot water resistance test, the RCA abrasion test, the cosmetic test according to Preparation Examples 1, 6 and 7.

TABLE 4

Preparation Example 6 Preparation Example 1 Preparation Example 7 Thickness after drying of undercoat 3 μm 5 μm 9 μm Hot water resistance test ○ X X RCA Abrasion Test ○ X X Resistant Cosmetic Test ○ X X ○: coating film peeling occurs, X: coating film peeling does not occur

Referring to Table 4 above, when the undercoating film had a thickness of 3 μm after drying (Production Example 6), the coating film was peeled off by a hot water resistance test, an RCA wear test, and a cosmetic test. However, in the case where the thickness of the undercoating film after drying was 5 µm or more (Manufacturing Example 1, Preparation Example 7), the coating film was not peeled off by the hot water resistance test, the RCA wear test and the cosmetic test. From these results, it can be seen that when the thickness of the coating film after drying is 5 µm or more, the hot water resistance, the RCA wear resistance, and the cosmetic properties of the undercoat film formed on the polycarbonate substrate are satisfactory.

Under drying temperature Coating film  Property evaluation

<Manufacture example 8>

Undercoat film was formed under the same conditions as Preparation Example 1 except that the coating film was hot-air dried at 60 ° C. for 5 minutes.

<Manufacture example 9>

An undercoat was formed under the same conditions as in Preparation Example 1, except that the coating film was hot-air dried at 60 ° C. for 10 minutes.

Production Example 10

An undercoating film was formed under the same conditions as in Preparation Example 1 except that the coating film was hot-air dried at 70 ° C. for 5 minutes.

Production Example 11

An undercoating film was formed under the same conditions as in Preparation Example 1 except that the coating film was dried in hot air at 70 ° C. for 10 minutes.

Production Example 12

An undercoat was formed under the same conditions as in Preparation Example 1, except that the coating layer was dried at 80 ° C. for 10 minutes.

Preparation Example 1, and the coating film peeling according to the hot water resistance test, RCA abrasion test, cosmetics test for the under coating films according to Preparation Examples 8 to 12 are shown in Table 5.

TABLE 5

Preparation Example 8 Preparation Example 9 Preparation Example 10 Preparation Example 11 Preparation Example 1 Production Example 12 Dry condition 60 ℃, 5 minutes 60 ℃, 10 minutes 70 ℃, 5 minutes 70 ℃, 10 minutes 80 ℃, 5 minutes 80 ℃, 10 minutes Hot water resistance test ○ ○ X X X X RCA Abrasion Test ○ X X X X X Resistant Cosmetic Test ○ X X X X X ○: coating film peeling occurs, X: coating film peeling does not occur

Referring to Table 5, when the coating film drying conditions are 60 ℃, 5 minutes (Manufacturing Example 8), the coating film was peeled off by the hot water resistance test, RCA wear test and cosmetics test, the coating film drying conditions are 60 ℃, 10 In the case of powder (production example 9), the coating film was peeled off by the RCA wear test and the cosmetic test except for the hot water resistance test. However, when the coating film drying conditions are 70 ° C and 5 minutes (Manufacturing Example 10), 70 ° C and 10 minutes (Manufacturing Example 11), 80 ° C and 5 minutes (Manufacturing Example 1) and 80 ° C and 10 minutes (Manufacturing In Example 12), the coating film was not peeled at all by the hot water resistance test, the RCA abrasion test, and the cosmetic test. From these results, it can be seen that the coating film drying conditions are preferably 70 ° C or higher.

In the above, the present invention has been described in detail with reference to preferred embodiments, but the present invention is not limited to the above embodiments, and various modifications and changes by those skilled in the art within the spirit and scope of the present invention. This is possible.

1 is a cross-sectional view showing a plastic case including a coating film formed using an aqueous coating composition according to an embodiment of the present invention.

Claims (14)

delete delete delete delete delete delete delete 30 wt% to 70 wt% of water dispersible polyurethane resin, 0.01 wt% to 3 wt% of pentaerythritol-tris- (β- (N-aziridinylpropionate), 0.1 wt% to 20 wt% Forming an undercoating layer using an aqueous coating composition containing a pigment, 0.01 wt% to 30 wt% additive, and the balance of water; and 40 to 50 wt% of acrylic urethane resin, 20 to 30 wt% of toluene, 15 to 25 wt% of PMA (1- (4-methoxyphenyl) propan-2-amine), 5 to 10 wt% on the undercoat layer The top coating layer using an oily resin solution containing xylene, and an oily resin solution containing 10 to 20 wt% butyl acetate, and an oily curing agent solution containing 55 to 65 wt% polyisocyanate and 35 to 45 wt% xylene. Plastic case manufacturing method comprising the step of forming. The method of claim 8, The plastic substrate is a plastic case manufacturing method of a polycarbonate substrate. delete delete The method of claim 8, The under coating film is a plastic case manufacturing method formed by hot air drying at 70 ~ 80 ℃. The method of claim 8, The undercoating film is a plastic case manufacturing method having a thickness of 5 ~ 10㎛ after drying. The method of claim 8, The water-dispersed polyurethane resin is an aliphatic poly (carbonate-diol) type, or aliphatic polyester type plastic case manufacturing method.

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