METHODS AND APPARATUS FOR PRODUCING COATED ARTICLES

Abstract

A method of producing a coated opaque article including a) applying from one or more inkjet heads a coating composition comprising at least 30 wt % of solvent to a surface of a transparent or opaque article to be coated; b) drying the coating composition for at least 30 seconds; and c) curing the coating composition to form a cured coating. The coating composition has a viscosity of from 5 to 50 cp at 25 C. and when the article to be coated is a transparent article, an opaque coating is applied to another surface of the article after step c), thereby rendering the coated article opaque.

Claims

1-13. (canceled)

14. A method of producing a coated opaque article, the method comprising: a) applying from one or more inkjet heads a coating composition comprising at least 30 wt % of solvent to a surface of a transparent or opaque article to be coated; b) drying the coating composition for at least 30 seconds; and c) curing the coating composition to form a cured coating; wherein: the coating composition has a viscosity of from 5 to 50 cp at 25 C., and wherein: when the article to be coated is a transparent article, an opaque coating is applied to another surface of the article after step c).

15. The method according to claim 14, wherein the cured coating has a thickness in the range of from 3 to 50 microns.

16. The method according to claim 14, wherein the coating composition has a viscosity in the range of from 7 to 12 cp at 25 C.

17. The method according to claim 14, wherein the distance between the one or more inkjet heads and the surface of the article to be coated is in the range of from 2 to 20 mm.

18. The method according to claim 14, wherein the solvent is 1-methoxy-2-propanol.

19. The method according to claim 14, wherein the coating composition is a transparent, colorless, hardcoat composition.

20. The method according to claim 14, wherein step c) comprises curing the coating composition by UV.

21. The method according to claim 14, wherein the article to be coated is formed from injection moulded acrylic or polycarbonate.

22. The method according to claim 14, wherein the article to be coated comprises a transparent body having an obverse surface and a reverse surface, and the reverse surface comprises an opaque coating, and step a) further comprises applying the coating composition to the obverse surface of the article.

23. An apparatus for producing a coated opaque article, comprising: a conveyor for supporting a transparent or opaque article to be coated; one or more inkjet heads containing a coating composition comprising at least 30 wt % solvent and having a viscosity of from 5 to 50 cp at 25 C.; and a curing station for curing the coating composition to form a cured coating; wherein: the one or more inkjet heads and the curing station are arranged such that, in use, it takes at least 30 seconds for the article to travel from the one or more inkjet heads to the curing station.

24. An apparatus according to claim 23, wherein the apparatus further comprises a heat source between the one or more inkjet heads and the curing station.

25. An apparatus according to claim 23, wherein the coating composition is a transparent, colorless, hardcoat composition.

Description

DESCRIPTION OF THE DRAWINGS

[0028] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

[0029] FIG. 1 shows an article suitable for coating by the method of the invention;

[0030] FIG. 2 shows a flowchart according to an embodiment of the invention; and

[0031] FIG. 3 shows an apparatus according to an embodiment of the invention

DETAILED DESCRIPTION

[0032] While the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention. lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[0033] Referring now to FIG. 1, an article to be coated 100 has an obverse surface 101 and a reverse surface 102. The article 100 may be of any shape suitable for the intended application. Generally the article 100 may have a thickness of at least 500 microns, preferably at least 1 mm, more preferably at least 2 mm. Generally the thickness of the article will be at most 20 mm, preferably at most 15 mm, more preferably at most 12 mm and most preferably at most 10 mm. For example, the thickness of the article 100 may be in the range of 750 microns to 3 mm.

[0034] The size of the article 100 may be relatively small. For example, the article 100 may have a longitudinal dimension of up to 20 cm and a transverse dimension of up to 15 cm. The article 100 of the present invention may also be a larger article, for example an article suitable for use as a car window pillar.

[0035] The article 100 may be transparent or opaque. Optionally, the article 100 comprises a transparent body 104 and the reverse surface 102 of the article 100 comprises an opaque coating. Optionally, the article 100 may comprise a transparent area 103, for example, a display screen, which optionally is not coated with the coating composition.

[0036] Optionally, the obverse surface 101 of the article 100 is flat. Alternatively, the obverse surface 101 of the article is uneven such that it comprises one or more structures projecting from or recession into the obverse surface 101. Optionally, the distance between the highest point and the lowest point on the obverse surface 101 is from 0 to 20 mm.

[0037] In one embodiment of present invention, the coating composition is applied to the entire obverse surface 101 of the article 100. In another embodiment of the present invention, the coating composition is selectively applied to a portion of the obverse surface 101 of the article 100.

[0038] Now referring to FIG. 2, one embodiment of the present invention comprises step a) applying from one or more inkjet heads a coating composition to a surface 101 of the article 100; followed by step b) drying the coating composition for at least 30 seconds and followed by step c) curing the coating composition to form a cured coating. The coating composition comprises at least 30 wt % of solvent and has a viscosity of from 5 to 50 cp at 25 C. When the article to be coated is a transparent article, an opaque coating is applied to another surface of the article after step c), thereby rendering the coated article opaque.

[0039] Optionally, step b) further comprises heating the article with a heat source, for example by heated air. During step b), the temperature of the article may be increased from room temperature to about 50 C., optionally about 60 C., alternatively about 70 C.

[0040] Preferably, a pre-treatment is performed on the article to be coated prior to step a) of the present invention. The obverse surface 101 of the article 100 may, for example, be cleaned with a cleaning agent or a soft brush. The cleaning agent may be, for example, propanol or a water/propanol mixture.

[0041] Preferably the method of the present invention is performed in a clean environment substantially free from dust and other atmospheric contaminants which may detrimentally affect the coating process by causing defects in the coating or by affecting the bonding of the coating composition to the article and/or its subsequent curing. Preferably the method of the present invention is carried out in an environment separated from the ambient atmosphere. This may be achieved by operating the method of the present invention in a clean room or an enclosure, particularly a tent which has its own integral air/gas supply. In this way the tent atmosphere may be modified, e.g. to provide an inert atmosphere for the curing process and/or a positive tent pressure to exclude contaminants.

[0042] Now referring to FIG. 3, an apparatus 300 according to one embodiment of the present invention comprises a conveyor 301 for supporting an article to be coated 100, one inkjet head 302 and a curing station 303. The inkjet head 302 contains a coating composition (not shown) comprising at least 30 wt % solvent and. having a viscosity of from 5 to 50 cp at 25 C. The inkjet head 302 comprises one or more rows of inkjet nozzles (for clarity, only four rows of inkjet nozzles 304a to 304d are shown in the figure) for applying the coating composition to a surface 101 of the article 100. The distance between the inkjet head 302 and the curing station 303, and the speed of the conveyor are selected such that, in use, it takes at least 30 seconds for the article 100 to travel from the inkjet head 302 to the curing station.

[0043] The speed of the conveyer may be adjustable according to, for example, the required thickness of the cured coating and/or the required time for the article to travel through the drying zone. Optionally, the speed of the conveyer is from 1 m/min to 3 m/min, for example 2 m/min. The apparatus 300 may further comprise an air tunnel (not shown in FIG. 3) between the inkjet head 302 and the curing station 303, the air tunnel being arranged to heat the article 100 before it reaches the curing station 303.

[0044] The location and the height of the inkjet head 302 may also be adjustable according to, for example, the nature of the surface of the article to be coated. For example, if the surface is uneven, and has projecting or raised parts, the inkjet head can be arranged at a greater distance from the conveyor to allow the article to be coated to pass underneath. The inkjet head 302 may be connected to a control unit (not shown in FIG. 3). The thickness of the cured coating may be controlled by software and the thickness of the cured coating may be influenced by the choice of heads and the speed of the conveyer. The skilled person is familiar with inkjet heads suitable for inkjet printing which may be used in the present invention. The inkjet head may be, for example, a Konika Minolta KM 1024MH head or a Konika Minolta KM 1024LH head. The maximum coating width of the jet head may be from 50 to 100 mm, for example 75 mm. The size of the drops emitted from the jet head may be between 5 to 100 picolitres, optionally from 10 to 50 picolitres, for example 14 picolitres, alternatively 42 picolitres.

[0045] The distance between the obverse surface 101 of the article 100 and the jet head 302 may be from 1 mm to 20 mm, optionally from 1 mm to 5 mm, for example 2 mm. The small distance between the head and the surface to be coated reduces the risk of atmospheric disturbance and the vertical application of the coating composition reduces or eliminates the occurrence of orange peel.

[0046] The present invention is further described by way of Examples below.

Example

1. Preparation of the Article to be Coated

[0047] The article to be coated was a plaque of opaque polycarbonate with a size of 70 mm70 mm and a thickness of 3 mm. The article to be coated was pre-cleaned by wiping carefully with isopropanol using a lint free, soft cloth and allowed to dry. After the pre-cleaning, the article to be coated was placed on a conveyor in a position below the inkjet head.

2. Preparation of the Coating Composition

[0048] The coating composition was prepared by diluting a proprietary hardcoat formulation (purchased from Nano-X, Germany, reference number 3611, nominal solids: 50%) with 1-methoxy-2-propanol until the viscosity of the coating composition was approximately 9 cp as measured on a Brookfield RVT Viscometer, spindle No. RV2, 20 rpm at 25 C.

3. Setting Up of the Apparatus

[0049] The inkjet head used was a Konika Minolta KM 1024LH, 42 picolitre ink jet head. The nozzle plate of the inkjet head is fixed at a height of 2 mm above the surface of the article to be coated. The coating resolution of the head across the plaque was 360 dpi and the resolution in the machine direction was set by the shaft encoder and the associated software. The curing station was a UV unit (Fusion 300) based on a medium pressure mercury vapour lamp with reflector and air cooling. The energy rating of the UV unit was 300 watts per inch and was set up around 100 mm above the conveyor. A drying tunnel was arranged between the inkjet heads and the curing station. The length of the drying tunnel was 2 meters. A temperature gradient was established along the drying tunnel by using three individually controlled heating units to ensure a gradient along the zone from 25 C. at the coating station to approximately 70 C. just before the UV unit to control rate of evaporation.

4. Coating of the Article

[0050] The linear speed of the conveyor was set at 2 m/min, so that each plaque took 60 seconds to travel through the drying tunnel. During the drying step, all the solvent was removed from the coating composition prior to reaching the UV curing unit. The coated plaque was then passed under the UV unit while travelling at the same general process speed of 2 m/min.

[0051] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein.