METHOD FOR PRODUCING A REFLECTOR ON A REFLECTOR BASE MADE OF GLASS

Abstract

A method for producing a reflector on a reflector base made of glass is provided. According to the method, a metal-containing coating fluid is deposited on a coating surface and subjected to a burning-in treatment at a temperature below a softening temperature of the glass forming the reflector layer. Deposition of the coating fluid proceeds using a contactless method by inkjet technology. This makes it possible to deposit a reflector layer in a reproducible way and with tight tolerances having a specified layer thickness, as well as to create clean edges without a printing block or similar device. The coating fluid is moved by a print head equipped with a plurality of nozzles and is movable in a movement plane relative to the coating surface. The coating fluid is sprayed onto the coating surface by the print head under pressure and in the form of droplets emerging from the nozzles.

Claims

11. Method for producing a reflector on a reflector base (1) made of glass having a curved surface, which is provided in the area of a coating surface with a metal-containing mirror-reflective layer (3), the method comprising: depositing a metal-containing coating fluid (9) on the coating surface (6), and subjecting the deposited coating fluid to a burning-in treatment at a temperature below a softening temperature of the glass forming the reflector layer (3), wherein the coating fluid is deposited using a contactless method by inkjet technology, wherein the coating fluid (9) is moved by a print head (4) equipped with a plurality of nozzles (7) and movable at least in a movement plane (8) relative to the coating surface, and the coating fluid is sprayed onto the coating surface (6) by this print head under pressure and in the form of droplets (11) emerging from the nozzles (7).

12. Method according to claim 11, wherein the coating fluid (9) contains the metal in elemental form.

13. Method according to claim 11, wherein the coating fluid (9) has a viscosity in the range of 10 to 30 mPa.Math.s.

14. Method according to claim 11, wherein the relative movement between the coating surface (6) and print head (4) comprises a translational movement of the reflector base along the print head (4).

15. Method according to claim 11, wherein the reflector base (1) is provided as a cylinder and the coating surface (6) is provided as a longitudinal strip on an outer surface extending over a partial circumference of the cylinder, and wherein the print head (4) is designed to deposit the coating fluid (9) over a partial circumference of 60 angular degrees, preferably for a partial circumference of 90 angular degrees.

16. Method according to claim 15, wherein the longitudinal strip has a width in the range of 20 to 65 mm.

17. Method according to claim 15, wherein the reflector is formed on a lamp bulb of an infrared emitter.

18. Method according to claim 11, wherein the nozzles (7) have outlet openings running in a common outlet plane (5), and wherein between the outlet plane (5) and the coating surface (6) a distance in the range of 5 to 10 mm is set.

19. Method according to claim 11, wherein a reflector layer (3) is generated whose desired thickness is in the range of 50 nm to 200 nm, and wherein a thickness measured at five measurement positions distributed over the reflector layer (3) deviates by a maximum of 10% from the desired thickness.

20. Method according to claim 11, wherein the coating fluid (9) is deposited in a structure that generates transitions between transmission and reflection after the burning-in process.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0040] The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.

[0041] In the drawings:

[0042] FIG. 1 illustrates one embodiment of the reflector produced according to the present invention as a partial reflector layer on an infrared lamp tube together with a print head in a longitudinal section; and

[0043] FIG. 2 provides an enlarged view of the reflector layer with the print head of FIG. 1 in the axial cross section along line A.

DETAILED DESCRIPTION OF THE INVENTION

[0044] FIG. 1 shows schematically a horizontally oriented lamp tube 1 made of quartz glass having a lamp tube center axis 2 along which a partial circumference coating with a gold-containing reflector layer 3 is printed. FIG. 2 shows a view of the lamp tube 1 in a section A perpendicular to the longitudinal axis 2, in an enlarged representation. Both illustrations are not to scale. In particular, the thickness of the ink layer 3 is shown excessively thick for reasons of better visibility.

[0045] For each new printing process, a recipe is initially created that takes into account:

[0046] (i) the geometric shape of the glass profile to be printed and the coating contour, and

[0047] (ii) the jet characteristics of the print head.

[0048] Glass Profile and Coating Contour:

[0049] The outer jacket of the lamp tube 1 having an outer diameter of 19 mm should be printed over a length of 1000 mm and over a circumferential angle of 180 degrees with a reflective gold layer having a thickness of 200 nm.

[0050] Printing Device:

[0051] The printer used for this purpose has two structurally identical, heatable print heads 4, which can be moved along a semicircle 12 (in FIG. 2 indicated by a dashed line). These are distributed uniformly about the upper circumferential half of the lamp tube 1 and arranged relative to each other at an angle α of 90 degrees.

[0052] The maximum printing width of a print head is 65 mm. Both print heads 4 are equipped with a number of 1024 printing cells that are arranged in a regular 2×512 pattern. Each printing cell has an ink outlet nozzle 7, which is connected by a feed channel to a printing medium storage container that can likewise be heated. Each printing cell is equipped with a piezo element by which the ink outlet nozzle 7 can be opened and closed on demand. For the separate control of the printing cells and for the movement control of the print head in a specified movement plane 8, a microcomputer is provided.

[0053] Printing Ink:

[0054] A commercially available, metallo-organic, gold-containing ink is used, in which 15 weight percent elemental gold in an organic complex is dissolved in a solution made of n-heptane, turpentine oil, ethanol, and ethylene carbonate.

[0055] This ink is created to have properties so that it can be printed by inkjet technology, such that it produces good wetting with the glassy lamp surface and does not easily run off or form droplets. Its viscosity is set according to the temperature of the print head heating system and the storage reservoir heating system.

[0056] Printing Process:

[0057] First, the coverage of the surface to be coated with the ink is calculated, which is required to generate a specified minimum reflection with the lowest possible layer thickness of the final reflector layer (=minimum coverage). The minimum reflection is typically greater than 90%, determined using the IEC 62798 standard (“Test method for infrared emitters”). The ink is deposited using a program-controlled method, such that a surface coverage according to the minimum coverage is generated.

[0058] This layer thickness, depending on the requirement for the degree of reflection, lies in the range of 50 nm to 200 nm. The required thickness of the fluid coating medium layer and the consumption of coating medium are determined using the gold portion of the coating medium and by evaluating the flow rate of the individual outlet nozzles (by counting the droplets) and measuring the covered surface area.

[0059] The heating temperature is set to 35° C., and thus the viscosity of the printing medium is specified. Here, each droplet has a volume of 35 pl (picoliter). The droplet diameter of the ink droplets emerging from the outlet nozzles is therefore set to approximately 100 μm. The outlet openings of the nozzles 7 of a print head 4 lie in a common outlet plane 5. The distance between the outlet plane 5 and the coating surface 6 varies from nozzle to nozzle, but is held constant during the printing process. On average, it is approximately 1 mm, so that the average striking distance of a droplet is approximately 35 μm. The printing frequency is 5 kHz (5000 droplets/s).

[0060] The lamp tube 1 is guided by a transport conveyor 14 at a specified distance of approximately 1 mm under the stationary print heads 4 using a program-controlled method. Here, the gold-containing ink 9 emerges in the shape of fine droplets 11 (see FIG. 2) from the nozzles 7 and is printed within the specified circumferential angle of 180 degrees (see FIG. 2) on the surface of the lamp tube 1.

[0061] For generating the desired layer thickness, a single layer deposition is sufficient. The ink layer 3 forms a longitudinal strip that extends along the center axis over a circumferential angle of 180 degrees of the lamp tube outer surface. Each of the two print heads 4 is designed for depositing a partial coating over a partial circumference of 90 angular degrees, whereby it is ensured that the partial coatings abut each other or overlap. Here, several of the outer nozzles 10 on both sides of the 2×512 pattern, which have the greatest distance to the coating surface 6, can be switched off.

[0062] The layer 3 is heated during the printing process and in this way easily dried. After reaching the nominal thickness, the dried ink layer 3 is burned-in by heating to 700° C. in air, and thereby converted into a reflective layer. Here, the organic components are oxidized or volatilized, which results in a thorough cross linking and formation of a closed metal layer having good adhesion to the glass of the lamp tube 1.

[0063] The generated gold-containing reflector layer has a nominal thickness of 200 nm. The uniformity of the layer thickness is evidenced by a thickness measured at five uniformly distributed measurement positions that deviates by a maximum of 20 nm from the desired thickness.

[0064] This layer has a weight of 0.75 g (per tubular meter) of coating agent having a nominal content of pure gold of 0.12 g. The actual consumption is 0.13 g, and thus only approximately 8% over the theoretical value.

[0065] The adhesion is determined by a so-called “tape peel-off test.” Sufficient adhesion is shown if no metallic traces can be detected on the tape with the naked eye after an adhesive tape is applied to the surface and then immediately peeled off.

[0066] The printing method of the present invention is indeed optimized for the printing of cord-shaped glass profiles. In the same printing process and by the same printing device, however, in addition in the area of the one end of the lamp tube 1, lines for an electrical circuit are printed that form part of a temperature sensor by which the operating state of the lamp can be detected.

[0067] It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.