Methods for coating polycarbonate surfaces

Abstract

A method for coating a surface made of transparent or translucent polycarbonate with a clear lacquer, comprising the steps a. providing and, if necessary, cleaning the surface, and b. applying the clear lacquer directly to the surface, as well as the additional feature c. treating the surface with UV radiation before the application of the clear lacquer, wherein an energy input in the range of 1000 to 25000 mJ / cm² is applied to the surface during the UV treatment.

Description

[0001] The invention described below relates to a method for coating a surface made of a transparent or translucent material. Polycarbonate.

[0002] Coating transparent or translucent polycarbonate substrates is problematic in many cases. When coating with Paints containing organic solvents allow these solvents to penetrate the surface of the polyurethane substrate and cause visible microcracks. This has a very negative impact on the transparency / translucency of the polycarbonate substrate.

[0003] To avoid this effect, the applicant attempted to apply an exclusively water-based clear varnish to the surface of ... to apply the coating to the surface. However, the resulting coating showed poor adhesion properties.

[0004] The invention described herein was based on the objective of providing an improved technical solution for coating To provide polycarbonate substrates with a clear coat.

[0005] This problem is solved by the method with the features of claim 1. Further developments of the invention can be found in the dependent claims.

[0006] The method according to claim 1 always comprises the following two steps: a) providing and, if necessary, cleaning the surface and b) application of the clear coat directly onto the surface.

[0007] The method is characterized in particular by the fact that c) before the application of the clear coat, the surface is treated by means of UV radiation. is being treated.

[0008] Surprisingly, it has been found that the problem of microcracks can be solved by a comparatively simple UV treatment. The issue could not be fully resolved. It is not yet definitively clear how UV radiation affects the surface. However, it is a fact that... a surface treated in this way can also be coated with paints containing a high proportion of an organic solvent, without that the aforementioned microcracks occur.

[0009] In a preferred embodiment, the method according to the invention comprises at least one of the immediately following additional Features a. to c.: a. During the UV treatment of the surface, an energy input in the range of 1000 to 25000 mJ / cm² occurs. b. In During the UV treatment of the surface, an energy input in the range of 1500 to 15000 mJ / cm² occurs. c. During the UV treatment of the The surface receives an energy input in the range of 2000 to 12000 mJ / cm2.

[0010] In particular, the immediately preceding feature c. is preferred.

[0011] In a preferred embodiment of the method, it is characterized by one of the following features a. and b.: a. The UV radiation is generated using a mercury vapor lamp, a quartz lamp, a black light lamp, or a UV LED. b. The UV- Radiation is generated by means of a corona discharge.

[0012] The UV radiation is particularly preferably generated by means of one of the aforementioned lamps, in particular the mercury lamp. With this The energy input during UV treatment can be particularly well controlled.

[0013] In a preferred embodiment of the method according to the invention, this method is characterized by at least one of the directly the following additional features: a. The surface defines one side of a film or sheet made of transparent or translucent polycarbonate. b. The film has a thickness in the range of 50 µm to 900 µm. c. The plate has a thickness in the range of 1 mm to 10 mm.

[0014] The above features a. and b. as well as a. and c. in combination are particularly preferred.

[0015] In a possible further development of the invention, the method includes the following additional feature: a. The cleaning that corresponds to the task The application of the clear coat preferably includes cleaning with water or with an alcohol, in particular isopropanol.

[0016] In a further embodiment, the method according to the invention comprises at least one of the following features a. and b.: a. The clear coat comprises a hydroxy-functional resin and an isocyanate-functional hardener. b. The clear coat comprises at least one organic Solvents, in particular xylene and / or butyl acetate.

[0017] Features a. and b. are implemented in combination with each other in particularly preferred embodiments.

[0018] Particularly preferred is the inclusion of at least one organic solvent in the clear varnish in a proportion of 3 to 40 wt.%, preferably 5 wt.%. up to 20 wt.%, particularly preferably 5 to 10 wt.%.

[0019] A major advantage of the method according to the invention is that the surface treatment does not have to be included in the painting process, in which the The clear coat must be integrated into the existing UV treatment. Alternatively, the UV treatment can be carried out long before the clear coat is applied, for example... immediately after the production of a polycarbonate substrate with the surface to be coated by extrusion or injection molding.

[0020] Accordingly, the method according to the invention preferably has at least one of the following features: a. The treatment of the The surface is treated with UV radiation at least 2 hours before the application of the clear coat. b. The treatment of the The surface is treated with UV radiation at least 2 days before the application of the clear coat. c. The treatment of the The surface is exposed to UV radiation at least 2 weeks before the application of the clear coat.

[0021] Further features of the invention and advantages resulting from the invention will become apparent from the following exemplary embodiments, which will be used to explain the invention. The embodiments described below serve only for illustration and better understanding. Understanding of the invention and are in no way to be understood as limiting. (1) 3 mm thick transparent polycarbonate sheets were produced using a mercury lamp treated with UV radiation according to the following parameters: Test No. Distance of UV lamp to surface [cm] Energy input [mJ / cm3] Shielding gas Crack formation 1 10 10197 No No 2 10 5577 No No 3 20 2730 No No 4 22 8039 Yes No 5 22 4403 Yes No 6 22 2083 Yes No

[0022] The energy input was measured during each irradiation using a measuring cell of type UMD 1 from IST Metz GmbH, located in Nürtingen, Germany, determined. Two hours after treatment, a polyurethane resin and a hardener were applied to the plate to a thickness of 30 µm. applied. The polyurethane resin contained approximately 10 wt% of a mixture of organic solvents, including xylene, Butyl acetate and solvent naphtha, and was free of colored pigments or other dyes. In experiments 4 to 6, the UV- Treatment was carried out under protective gas (nitrogen).

[0023] After drying the lacquer coating formed from the polyurethane resin, the coated polycarbonate sheets were optically inspected. No microcracks were observed in any case. (2) 3 mm thick transparent polycarbonate sheets were inspected using a mercury lamp. treated with UV radiation according to the following parameters: Test No. Distance of UV lamp to surface [cm] Energy input [mJ / cm3] Shielding gas Crack formation 1 10 10240 No No 2 10 5550 No No 3 10 2792 No No 4 22 8209 Yes No 5 22 4252 Yes No 6 22 2132 Yes No

[0024] The energy input was measured during each irradiation using a measuring cell of type UMD 1 from IST Metz GmbH, located in Nürtingen, Germany, definitely.

[0025] One day after the treatment, a polyurethane resin and a hardener were applied to the plate to a thickness of 30 µm. Polyurethane resin contained approximately 10 wt% of a mixture of organic solvents, including xylene, butyl acetate and Solvent naphtha, and was free of colored pigments or other dyes. In experiments 4 to 6, the UV treatment was carried out under The procedure involved the use of a protective gas (nitrogen).

[0026] After drying the lacquer coating formed from the polyurethane resin, the coated polycarbonate sheets were optically inspected. No microcracks were observed in any case. (3) 3 mm thick transparent polycarbonate sheets were inspected using a mercury lamp. treated with UV radiation according to the following parameters: Test No. Distance of UV ray to surface [cm] Energy input [mJ / cm2] Shielding gas Crack formation 1 10 10403 No No 2 10 5725 No No 3 10 2808 No No 4 22 8179 Yes No 5 22 4548 Yes No 6 22 2181 Yes No

[0027] The energy input was measured during each irradiation using a measuring cell of type UMD 1 from IST Metz GmbH, located in Nürtingen, Germany, definitely.

[0028] Four days after the treatment, a polyurethane resin and a hardener were applied to the plate to a thickness of 30 µm. Polyurethane resin contained approximately 10 wt% of a mixture of organic solvents, including xylene, butyl acetate and Solvent naphtha, and was free of colored pigments or other dyes. In experiments 4 to 6, the UV treatment was carried out under The procedure involved the use of a protective gas (nitrogen).

[0029] After drying the lacquer coating formed from the polyurethane resin, the coated polycarbonate sheets were optically inspected. No microcracks were observed in any case. (4) 3 mm thick transparent polycarbonate sheets were inspected using a mercury lamp. treated with UV radiation according to the following parameters: Test No. Distance of UV lamp to surface [cm] Energy input [mJ / cm3] Shielding gas Crack formation 1 10 10513 No No 2 10 5079 No No 3 10 2868 No No 4 22 7930 Yes No 5 22 4415 Yes No 6 22 2145 Yes No

[0030] The energy input was measured during each irradiation using a measuring cell of type UMD 1 from IST Metz GmbH, located in Nürtingen, Germany, definitely.

[0031] Seven days after the treatment, a polyurethane resin and a hardener were applied to the plate to a thickness of 30 µm. Polyurethane resin contained approximately 10 wt% of a mixture of organic solvents, including xylene, butyl acetate and Solvent naphtha, and was free of colored pigments or other dyes. In experiments 4 to 6, the UV treatment was carried out under The procedure involved the use of a protective gas (nitrogen).

[0032] After drying the lacquer coating formed from the polyurethane resin, the coated polycarbonate sheets were optically inspected. No microcracks were observed in any case. comparative experiment

[0033] A polyurethane resin and a hardener were applied to a 3 mm thick transparent polycarbonate sheet without prior UV treatment. Applied in a thickness of 30 µm. The polyurethane resin contained approximately 10 wt% of a mixture of organic solvents. including xylene, butyl acetate and solvent naphtha, and was free of colored pigments or other dyes.

[0034] After drying the lacquer coating formed from the polyurethane resin, the coated polycarbonate sheet was visually inspected. Significant cracking was observed and was already visible to the naked eye.

Claims

[1] Method for coating a surface made of a transparent or translucent polycarbonate with a clear varnish comprising the steps a. Preparation and, if necessary, cleaning of the surface, and b. Application of the clear coat directly onto the surface, as well as the additional feature c. Treatment of the surface using UV radiation before the application of the clear coat. [2] The method of claim 1 with at least one of the following additional features: a. During the UV treatment of the surface, an energy input in the range of 1000 to 25000 mJ / cm2 occurs. b. During the UV treatment of the surface, an energy input in the range of 1500 to 15000 mJ / cm2 occurs. c. During the UV treatment of the surface, an energy input in the range of 2000 to 12000 mJ / cm2 occurs. [3] Method according to claim 1 or according to claim 2 with one of the following additional features: a. The UV radiation is generated using a mercury vapor lamp, a quartz lamp, a black light lamp or a UV LED. b. The UV radiation is generated by means of a corona discharge. [4] Method according to any of the preceding claims with at least one of the following additional features: a. The surface defines one side of a film or sheet made of transparent or translucent polycarbonate. b. The film has a thickness ranging from 50 µm to 900 µm. c. The plate has a thickness ranging from 1 mm to 10 mm. [5] Method according to any of the preceding claims with the following additional feature: a. The cleaning includes cleaning with water or with alcohol. [6] Method according to any of the preceding claims with the following additional feature: a. The clear varnish comprises a hydroxy-functional resin and an isocyanate-functional hardener. b. The clear varnish comprises at least one organic solvent, in particular xylene and / or butyl acetate. [7] Method according to any of the preceding claims with any of the following additional features: a. The surface is treated with UV radiation at least 2 hours before the application of the clear coat. b. The surface is treated with UV radiation at least 2 days before the application of the clear coat. c. The surface is treated with UV radiation at least 2 weeks before the application of the clear coat.