HK1069210B - Transparent article and method for producing the same - Google Patents

Description

Transparent object and method for producing same

Technical Field

The present invention relates to transparent objects, and in particular to a method for producing transparent objects with coatings, for example for improving their wear resistance and/or optical properties. The invention relates particularly, but not exclusively, to the production of transparent objects for use as windows in display devices.

Background

Display units such as calculators and mobile phones typically have a transparent (typically plastic) window having a thickness of at least 100 microns (e.g., 200 microns) that serves as a protective barrier for the display device and enables a user to see the displayed information.

For many applications, it may be desirable to improve the surface characteristics of the glazing to avoid factors such as abrasion, glare in intense or direct sunlight, and fogging under cold and/or humid conditions, for which a wide variety of coatings have been employed. These coatings are applied to the screen by techniques including spray coating, dip coating and curtain coating.

Although coatings have improved the physical and optical properties of display screens, the coating process itself has a number of disadvantages associated with it. In particular, the method is capital intensive, requires extensive facility and technical maintenance, and requires a high standard of technical support.

In addition, coating selected areas of the surface using the above-described method is very labor intensive, since the surface area that is to remain uncoated must be masked in order to perform the method.

Disclosure of Invention

It is an object of the present invention to avoid or mitigate the above mentioned problems.

According to one aspect of the present invention there is provided a method of producing a transparent object comprising a transparent substrate of plastics material having a thickness of at least 100 microns and an abrasion resistant surface coating of transparent resin, wherein the HAZE value measured according to ASTM D-1044 of the uncoated transparent substrate is in excess of 30% and the coated transparent substrate has a HAZE value of less than 10%, characterised in that the transparent resin is applied to the substrate by a jet printer.

Preferably, the transparent substrate has a thickness of at least 200 microns.

Preferably, the transparent substrate has a thickness of at least 300 microns.

Preferably, the transparent substrate has a thickness of at least 400 microns.

Preferably, the transparent substrate has a thickness of 750 micrometers to 3 millimeters.

Preferably, the jet printer comprises an inkjet type printer or a bubble jet printer.

Preferably, the jet printer is an ink jet type printer.

Preferably, selected areas of the transparent substrate remain uncovered.

Preferably, the transparent substrate has a longitudinal dimension of up to 20cm and a transverse dimension of up to 15 cm.

Preferably, the transparent substrate is continuously fed into a jet printer to perform the coating operation.

Preferably, the plastic material is polycarbonate, polyacrylate, polyester or allyl carbonate.

Preferably, the transparent resin applied by the jet printer is a curable resin, and the method further comprises the step of curing the transparent resin applied by the printer.

Preferably, after the coating is applied by the printer, the transparent substrate is then conveyed through a drying station and a curing station.

Preferably, the transparent resin coating layer has a thickness of 5 to 50 μm.

Thus, according to the present invention, a transparent resin coating is applied to a transparent substrate by a jet printer. Such printers provide a particularly convenient method of applying a coating (which may be continuous or discontinuous) as such printers may be operated under computer control to provide coating over a desired area of the substrate. Furthermore, in the mass production of transparent objects, such a printer is easy to prepare and provides a relatively inexpensive method for the precise application of the coating.

According to a further aspect of the present invention there is provided a display device comprising a transparent object produced according to the method of the preceding claims.

According to still another aspect of the present invention, there is provided a mobile phone including the aforementioned display device.

Generally, the substrate will have a thickness of at least 125 microns, preferably at least 150 microns, more preferably at least 175 microns, and most preferably at least 200 microns. Typical thicknesses will be at least 300 microns, more preferably at least 400 microns. In general, the thickness of the substrate will be at most 20 mm, preferably at most 15 mm, more preferably at most 12 mm, most preferably at most 10 mm. Typical substrate thicknesses will be at most 8 mm, more preferably at most 6 mm, even more preferably at most 5 mm, typically at most 4 mm.

Most often, the thickness will be in the range 750 microns to 3 millimeters.

The coating applied may for example be a coating that improves the abrasion resistance of the substrate (so-called "hard coating") and/or its optical properties (e.g. anti-fog coating). The coating may include a dye or pigment but still maintain transparency.

Preferably the jet printer is an ink jet type printer or a bubble (bubble) jet printer. More preferably the printer is an ink jet type printer. Particularly suitable printers are available from WEBER, model ML 500.

An ink-jet printer has a plurality of (e.g., 96) ink-ejecting ports (ink-ports). These ink ejection ports may be operated continuously or according to a specific program pattern to apply the coating. By operating the nozzle according to such a procedure, a coating on selected areas of the substrate can be obtained. For example, portions of the substrate that need to be attached to other components to form an assembly may be selectively left uncoated, such as edge portions.

The invention can be used to coat transparent substrates of relatively small dimensions, for example, having a longitudinal dimension of up to 20cm and a transverse dimension of up to 15 cm. Such substrates can be continuously fed into a jet printer for coating operations, so that smaller coated objects can be produced at high speed. However, the invention is also useful for coating larger substrates. Digital ink jet printers having a plurality of print heads are particularly suitable for coating larger substrates.

The invention is particularly suitable for applying coatings to substrates of plastics materials, which may be thermoplastic or thermosetting materials. Examples of suitable plastics include: polycarbonates, polyacrylates, polyesters and allyl carbonates (CR 39). Or the transparent substrate may be glass.

The resins applied by the jet printer are preferably formulated as a solution or suspension in a suitable carrier liquid. It is especially preferred that the solution or suspension has a viscosity of 50-500cP measured at 25 ℃ on a Brookfield RVT viscometer Spindle No. RV220rpm. Solutions or suspensions of this viscosity are particularly suitable for forming coatings by jet printing techniques.

Various types of resins can be coated using the techniques of the present invention, such as polyurethanes, acrylates siloxanes, acrylics and combinations thereof. It is particularly preferred that the resin is crosslinkable so as to be able to form a solidified coating on the substrate. Crosslinking can be achieved, for example, by air drying, uv curing or thermal curing.

"hardcoats" are generally based on acrylate or siloxane chemistry and cured using UV (ultraviolet) or thermal means. The antifog coating can be based, for example, on hydrophilic polyurethane.

A particularly preferred embodiment of the method of the present invention comprises continuously feeding the transparency into a jet printer, followed by a drying tunnel and a curing station. The coating is applied at the printer and the remaining solvent is removed on passage of the substrate through the drying tunnel. Finally, a curing station effects crosslinking of the resin (preferably by UV curing) to form an adherent coating on the transparent substrate.

The thickness of the resin coating will depend on the application of the substrate and/or the nature of the coating, but will generally be in the range of 5-100 microns. In the case of "hard coatings" for improved abrasion resistance, typical coating thicknesses are from 5 to 8 microns, since increasing the thickness does not have any beneficial effect on the coating properties, and indeed may have the opposite effect. Conversely, the antifogging properties of the coating may be improved by increasing the thickness of the coating, so thickness values in the range of 10-20 microns or higher may be most beneficial.

Preferably, the method of the present invention is carried out in a "clean" environment, i.e., substantially free of dust or other atmospheric components that could adversely affect the coating process by affecting the adhesion of the resin to the substrate and/or its subsequent curing.

Preferably the method of the invention is carried out in an environment independent of the ambient atmosphere. This can be achieved by operating the method of the invention in a "tent", preferably a tent having its own complete air/gas supply. In such a method, the tent atmosphere may be regulated, for example, to provide an internal atmosphere to perform the coating process and/or a positive tent pressure (i.e., a pressure above atmospheric pressure) to exclude contaminants.

As noted above, the resin may be one that is desirable to provide an abrasion resistant coating on a transparent substrate and/or to improve optical properties, for example by employing an anti-glare or anti-fog coating.

The invention is particularly useful for applying abrasion resistant coatings to plastic substrates. The wear resistance can be measured according to ASTM D-1044, where a CS10F standard wheel with a 500 gram load is rotated 1000 times on a sample. The HAZE value of the abraded substrate can then be measured. Uncoated acrylic and uncoated polycarbonate substrates gave HAZE values of about 30% and 33%, respectively (actual values depend on thickness and supply). The use of the present invention to apply a "hard coat" to these substrates makes it possible to reduce the HAZE value to a maximum value of less than 10% as allowed by the ASTM specification. For example, it is possible in certain cases to reduce the HAZE value and typically reach values of 2-4% and lower, for example 1-1.5%.

The advantages obtained by the above-described method according to the invention make it particularly suitable for producing transparent substrates for use in display devices in mobile phones or calculators, such as LCD devices.

Thus, according to a third aspect of the present invention, there is provided a display device having a display window which is a transparent object according to the second aspect of the present invention.

The method of the invention can be used, for example, to produce windows (for mobile phones or other articles with display devices) from a pre-molded transparent substrate which is then coated with a transparent coating according to the method of the invention. Alternatively, the transparent substrate may also be provided with an opaque border made of a suitably colored resin. The frame may be coated on the same side as the side coated with the clear coat or on the opposite side. In either case, the opaque border may be applied by gravure coating (padcoating) or jet printing. The use of a jet printer is particularly convenient when the opaque border is applied to the same side of the substrate that is coated with the clear coating.

Claims (16)

1. A method of producing a transparent object comprising a transparent substrate of a plastic material having a thickness of at least 100 micrometers and an abrasion-resistant surface coating consisting of a transparent resin, wherein the HAZE value measured according to ASTM D-1044 of the uncoated transparent substrate exceeds 30% and the coated transparent substrate has a HAZE value of less than 10%, characterized in that the transparent resin is applied to the substrate by means of a jet printer.

2. The method of claim 1, wherein the transparent substrate has a thickness of at least 200 microns.

3. The method of claim 2, wherein the transparent substrate has a thickness of at least 300 microns.

4. The method of claim 3, wherein the transparent substrate has a thickness of at least 400 microns.

5. The method of claim 4, wherein the transparent substrate has a thickness of 750 micrometers to 3 millimeters.

6. The method according to any one of claims 1 to 5, wherein the jet printer comprises an ink jet type printer or a bubble jet printer.

7. The method of claim 6, wherein the jet printer is an ink jet type printer.

8. The method of claim 1, wherein selected areas of the transparent substrate remain uncovered.

9. The method of claim 1, wherein the transparent substrate has a longitudinal dimension of up to 20cm and a transverse dimension of up to 15 cm.

10. The method of claim 1, wherein the transparent substrate is continuously fed into a jet printer for performing the coating operation.

11. The method of claim 1, wherein the plastic material is polycarbonate, polyacrylate, polyester, or allyl carbonate.

12. The method according to claim 1, wherein the transparent resin applied by the jet printer is a curable resin, the method further comprising the step of curing the transparent resin applied by the printer.

13. The method of claim 12, wherein the transparent substrate is subsequently conveyed through a drying station and a curing station after the coating is applied with the printer.

14. The method of claim 1, wherein the transparent resin coating has a thickness of between 5 and 50 microns.

15. A display device comprising a transparent object produced according to the method of any one of claims 1-14.

16. A mobile phone comprising the display device according to claim 15.