TWI408188B - One liquid coating material and manufacture of a high glossy coating layer utilizing the same - Google Patents

Abstract

Disclosed is a manufacture of a high glossy coating layer, including dissolving polyurethane in a mixed solvent to form a polyurethane solution, dispersing a nano-pigment in propylene glycol methyl ether acetate to form a pigment solution, adding the polyurethane solution to the pigment solution for forming an one liquid coating material, spraying the coating material on an object and low temperature baking the coating material to form a film, and curing the film in a humid environment to provide a high glossy coating layer.

Description

Single liquid type coating and method for forming high gloss coating

This invention relates to a high gloss coating, more particularly to a single liquid coating for its application.

When a visible light having an incident angle of 60 degrees was applied to the coating, the light intensity of the reflected light was measured at a position of 60 degrees of reflection angle using a general gloss meter. If the light intensity exceeds 90% and even reaches 100% total reflection, the coating is a so-called high gloss coating. At present, the main coating for high gloss coating applications is a two-liquid coating. So-called two-liquid coatings generally contain resins, hardeners, pigments, and other processing aids. The type of the curing agent depends on the type of the resin, and if the resin is an epoxy resin, the curing agent is a cationic curing agent. If the resin is an acrylic resin (commonly known as acrylic), the hardener is a radical initiator such as a thermal initiator or a photoinitiator. If the resin is a polyurethane, the hardener may be an amine or an alcohol such as a diol, a triol, or a polyol. In general, the two-liquid type curing time takes more than three days, which increases the time cost and is disadvantageous in mass production. However, if a single-liquid type coating which does not require a hardener is used, although the aging time can be shortened, the high gloss requirement cannot be achieved. In summary, there is a need for a coating that can simultaneously take into account both short curing time and high gloss.

The invention provides a single liquid type coating comprising a pigment solution and a polyurethane solution; wherein the polyurethane solution is a polyurethane resin dissolved in a mixed solvent; and the pigment solution is a nano pigment dispersed in monomethyl ether propylene glycol acetate.

The invention also provides a method for forming a high gloss coating comprising dissolving a polyurethane resin in a mixed solvent to form a polyurethane solution; dispersing the nano pigment in monomethyl ether propylene glycol acetate to form a pigment solution; The solution is added to the pigment solution to form a single liquid type coating; the single liquid type coating is sprayed on the object; the low temperature baking single liquid type coating is formed into a film; and the object is placed in a humid environment to harden the single liquid type coating to form a high Glossy coating.

In the method of forming a high gloss coating of the present invention, a polyurethane solution is first prepared. A polyurethane solution is formed by dissolving a polyurethane resin (PU) in a mixed solvent. As described above, the hardened polyurethane can be added by adding a hardener such as an amine or an alcohol. However, this method, the so-called two-liquid type coating, will greatly extend the curing time. Another hardening method is high heat hardening. However, some materials such as the common materials of the display frame will be distorted after exceeding 65 ° C, so the coating is not suitable for high heat hardening after spraying or coating on the above objects. Therefore, the hardening method employed in the polyurethane of the present invention is a moisture hardening method, and mainly uses moisture in the air as a hardener for the polyurethane. This method eliminates the need for additional hardeners, simplifies the complexity of the work, and shortens the curing time to 3-6 hours, which can greatly reduce the cycle time of the operation. In one embodiment of the invention, the isocyanate groups of the polyurethane comprise from about 5 to about 7 weight percent, and the molecular weight of the polyurethane groups is between about 2,000 and 20,000. The weight ratio of the mixed solvent to dissolve the polyurethane resin to the polyurethane resin is between about 2:1 and 1:1. The solvent mixture should be considered for compatibility with the polyurethane resin as well as moderate volatility and boiling point. In an embodiment of the invention, the boiling point of the mixed solvent is between about 70 ° C and 150 ° C, such as 7 parts by weight of propylene glycol methyl ether acetate, 3 parts by weight of C _2-8 A mixture of alcohols and 5 parts by weight of C _2-5 esters. It must be noted that in the case where the baking temperature needs to be lower than 65 ° C to avoid deformation of the article, if the boiling point of the mixed solvent is too high, a relatively long low-temperature baking time is required to remove the mixed solvent. However, if the boiling point of the mixed solvent is too low, the rapidly volatilized organic solvent will cause unevenness on the surface of the coating.

The pigment solution can be formed by dispersing the nano-sized pigment in monomethyl ether propylene glycol acetate. The dispersion method can be a common mechanical stirring dispersion, and the beads can be added to be bead mill dispersion. Nano-sized pigments have a particle size between about 50 nm and 500 nm, such as 90s, 52s, or 32s sold by Nanotechnology Institute. The weight ratio of monomethyl ether propylene glycol acetate to nano-sized pigment used to disperse the nano-scale pigment is between about 2:1 and 8:1.

It must be noted here that the order of preparation of the above pigment solution and the polyurethane solution is not in order, and may be simultaneously prepared. A single liquid coating is formed by adding a polyurethane solution to the pigment solution. In an embodiment of the invention, the weight ratio of the polyurethane solution to the pigment solution is between about 1:2 and 3:1. It must be noted that if the above mixing is a small amount of preparation such as less than 2 kg, there is little difference in adding the polyurethane solution to the pigment solution or adding the pigment solution to the polyurethane solution. However, if the above mixing step is a large amount of preparation, such as 10 kg larger than the industrial grade, the mixing step must add a polyurethane solution to the pigment solution, and the formed single liquid type coating has high gloss after forming the coating. This is because when the pigment solution is added to the polyurethane solution, a relatively small amount of the nano-sized pigment is covered by the polyurethane, so that the desired gloss cannot be exhibited.

Then, the above single-liquid type coating is sprayed on a high-priced 3C product such as a computer case, a display frame, a mobile phone case, and the like. Although there are many ways to form a coating on an article, the manner of spraying is more in accordance with the needs of the present invention. Then, the low-temperature baking single-liquid type coating is formed into a film, and the mixed solvent is removed by evaporation. The temperature of low temperature baking is between 30 ° C and 60 ° C to avoid excessive temperature damage to objects. Finally, the object is placed in a humid environment to harden the single liquid coating to form a high gloss coating. The humidity of the wet environment is preferably between 20% and 100%, and the higher the humidity, the shorter the hardening time. In an embodiment of the invention, the hardening time is between about 3 and 6 hours. Through the above steps, a high gloss coating having a film thickness of about 16 to 45 microns can be formed, and the reflectance at a viewing angle of 60 degrees is between about 90% and 100%. The color of the above high gloss coating may be CINO.P.Bk No. 7 (black), PY 139', 150' (yellow), PR 122', 177', 254' (red), PB 15:1', Colors such as 15:3' (blue), PG 7', 36' (green), and PV 23 (purple).

In order to make those skilled in the art more aware of the features of the present invention, the following examples are further illustrated.

5 g of the nano-grade pigment (90 s sold by Nanotechnology Institute of the World) was stirred and dispersed in 25 g of monomethyl ether propylene glycol acetate to form a pigment solution. 25 g of ethyl acetate, 15 g of isopropyl alcohol, and 10 g of monomethyl ether propylene glycol acetate were uniformly mixed to form a mixed solution. After dissolving 25 g of the polyurethane resin in the above mixed solution to form a polyurethane solution, the polyurethane solution was poured into a pigment solvent to form a one-liquid type coating. After spraying the paint on the display frame, it was baked at a low temperature in an oven at 60 ° C for 30 minutes, and then taken out in an environment of 50% relative humidity for 4 hours to obtain a high gloss coating of 20 μm thick. The reflectance at a 60 degree viewing angle was about 93% as measured by a gloss meter sold by BYK Chemicals.

While the invention has been described above in terms of several preferred embodiments, it is not intended to limit the scope of the present invention, and any one of ordinary skill in the art can make any changes without departing from the spirit and scope of the invention. And the scope of the present invention is defined by the scope of the appended claims.

Claims (13)

A single liquid type coating comprising: a pigment solution and a polyurethane solution; wherein the polyurethane solution is a polyurethane resin dissolved in a mixed solvent; the pigment solution is a nanometer pigment dispersed in a monomethyl ether propylene glycol acetate In the ester; wherein the weight ratio of the polyurethane solution to the pigment solution is between about 1:2 and 3:1; wherein the polyurethane solution has a weight ratio of the polyurethane resin to the mixed solvent of about 1:1 to Between 1:2; wherein the pigment solution has a weight ratio of the nano-sized pigment to the monomethyl ether propylene glycol acetate of between about 1:2 and 1:8; wherein the polyurethane resin comprises 5 to 7 weight percent isocyanate groups and have a molecular weight of between about 2,000 and 20,000. The one-liquid type coating according to claim 1, wherein the mixed solvent has a boiling point of between about 70 ° C and 150 ° C. The one-liquid type coating according to claim 1, wherein the mixed solvent is a mixture of monomethyl ether propylene glycol acetate, an alcohol of C _2-8 , and an ester of C _2-5 . The one-liquid type coating according to claim 1, wherein the nano-sized pigment has an average particle diameter of about 50 to 500 nm. A method for forming a high gloss coating comprising: dissolving a polyurethane resin in a mixed solvent to form a polyurethane solution Dissolving a nano-sized pigment in a monomethyl ether propylene glycol acetate to form a pigment solution; adding the polyurethane solution to the pigment solution to form a single liquid type coating; spraying the single liquid type coating Forming a single liquid coating onto the film; and baking the article in a humid environment to harden the single liquid coating to form a high gloss coating; wherein the polyurethane solution and the pigment solution The weight ratio is between about 1:2 and 3:1; wherein the polyurethane solution has a weight ratio of the polyurethane resin to the mixed solvent of between about 1:1 and 1:2; wherein the pigment solution is The weight ratio of the nano-sized pigment to the monomethyl ether propylene glycol acetate is between about 1:2 and 1:8; wherein the polyurethane resin comprises from 5 to 7 weight percent of isocyanate groups, and the molecular weight thereof is about Between 2000 and 20000. The method for forming a high gloss coating according to claim 5, wherein the mixed solvent has a boiling point of between about 70 ° C and 150 ° C. The method for forming a high gloss coating according to claim 5, wherein the mixed solvent is a mixture of monomethyl ether propylene glycol acetate, C _2-8 alcohol, and C _2-5 ester. The method for forming a high gloss coating according to claim 5, wherein the nano-sized pigment has an average particle diameter of about 50 to 500 nm. The method for forming a high gloss coating according to claim 5, wherein the low temperature baking temperature is between about 30 ° C and 60 ° C. The method for forming a high gloss coating according to claim 5, wherein the moisture environment has a humidity of about 20% to 100%. The method for forming a high gloss coating according to claim 5, wherein the one-liquid type coating has a hardening time of about 3 to 6 hours in the moisture environment. The method for forming a high gloss coating according to claim 5, wherein the high gloss coating has a reflectance of about 60% to 100% with a viewing angle of 60 degrees. A method of forming a high gloss coating according to claim 5, wherein the high gloss coating has a thickness of between about 16 microns and 45 microns.