Method and Apparatus for Applying Material to Glass

Abstract

A method of applying a polymer to a glass surface includes applying atmospheric plasma to a glass surface, applying a film of polymerizable fluid to the surface and curing the film with high-energy radiation. Apparatus for applying atmospheric plasma includes positive and ground electrodes, and an emitter strip of porous material with a plasma gas diffusing between the electrodes and through the emitter strip onto the glass surface.

Description

Summary of Invention

[0024] According to the invention, a polymer coating is applied to a surface of a glass substrate. In a method of application, first under atmospheric conditions plasma is applied to the glass surface in order to clean and functionalize the surface. Second, a film of polymerizable liquid is applied to the plasma treated surface. Finally, the film is cured by exposing it to high-energy radiation.

[0025] In more detail, the plasma is applied by supplying a plasma gas through a plasma head that carries a positive electrode and a negative electrode. The plasma gas is supplied from a location between these electrodes. The porous metal emitter supplies the plasma gas by diffusion, or a porous ceramic emitter supplies the gas in the same way.

[0026] The plasma head may have a structure especially suited for treating a glass substrate such as a windshield. The structure includes a central electrode and an annular or outer electrode. Each electrode has an opposite polarity chosen between positive or ground. A dielectric emitter laterally surrounds the central electrode and emits the plasma gas. An annular outer electrode laterally surrounds the dielectric emitter. The central and outer electrodes create a plasma discharge between them, and the dielectric emitter delivers plasma gas into the plasma created between the electrodes.

[0027] An alternate structure for treating the periphery of a windshield with a plasma head employs an elongated porous metal emitter for plasma gas. A first elongated tubular electrode is disposed in a parallel position to the emitter. The first electrode is offset to a first lateral side of the emitter and connected for positive electrical polarity. A second elongated tubular electrode is disposed in a parallel position to the emitter. It is offset to a second lateral side of the emitter, opposite from the first elongated electrode. The second electrode is connected for ground electrical polarity. The two electrodes create a plasma discharge between themselves, and the porous emitter delivers plasma gas into the plasma created between the electrodes.

[0028] When treating a windshield to form a protective coating at the periphery, the polymerizable liquid should be chosen to produce a thermoset amorphous film when cured. The polymerizable liquid preferably contains acrylate, methacrylate, epoxy, polyurethane, vinyl components, and mixtures of these ingredients; a photo initiator; and an ultraviolet stabilizer. This liquid may contain polyurethane diacrylate, tripropyleneglycol diacrylate, trimethylolpropane triacrylate, an adhesion promoter, and a photo initiator. This method allows application of an unusually thick film, sufficient to establish a cured film having a thickness of at least 0.004 inches.

[0029] The surface of the glass substrate may be the convoluted peripheral surface of an automobile windshield. In this case, atmospheric plasma is applied to a peripheral portion of the windshield by mechanically guiding relative movement on three axes between the windshield and a plasma head delivering plasma. The plasma head follows the convoluted peripheral surface of the windshield. Also, the plasma head maintains a substantially uniform spacing from the windshield at the convoluted peripheral surface.

[0030] One embodiment of a plasma head for treating a preselected width of a glass windshield is formed of a base carrying a first dielectric tube and a second dielectric tube. Each tube is of a predetermined length and the tubes are mutually parallel. The predetermined length is the preselected width of glass windshield for treatment. A positive electrode extends longitudinally within the first tube, and a ground electrode extends longitudinally within the second tube.

[0031] The first and second tubes carry an elongated emitter between themselves. The base at least partially defines a diffusion chamber in gas communication with the emitter. The chamber contains a plasma gas. A supply of plasma gas feeds the diffusion chamber. The emitter is an elongated strip of porous metal. It is parallel to the first and second tubes and diffuses plasma gas from the diffusion chamber and into the plasma.

[0032] A second embodiment of a plasma head for treating a windshield employs a central electrode, preferably of positive electrical polarity. A dielectric emitter laterally surrounds the central electrode and emits a plasma gas. An annular outer electrode laterally surrounds the dielectric emitter and is of opposite polarity from the central electrode. The central and outer electrodes create a plasma discharge between themselves. The dielectric emitter delivers plasma gas into the plasma discharge created between the electrodes.

[0033] In the second embodiment of a plasma head, the emitter is a porous dielectric layer that permits plasma gas to diffuse through it while insulating the central electrode from the outer electrode. Further, a dielectric layer may laterally surround the outer electrode.

[0034] The accompanying drawings, which are incorporated in and form a part of the specification, illustrate preferred embodiments of the present invention, and together with the description, serve to explain the principles of the invention. In the drawings:

Brief Description of Drawings

[0035] Details of this invention are described in connection with the accompanying drawings that bear similar reference numerals in which:

[0036] Figure 1 is a perspective view of a plasma head that embodies features of the present invention.

[0037] Figure 2 is an end view of the plasma head of Figure 1.

[0038] Figure 3 is a perspective view of another plasma head embodying features of the present invention.

[0039] Figure 4 is a schematic view of the process embodied in the present invention.

Detailed Description

[0040] A method embodying features of the present invention includes the steps of applying atmospheric plasma to the surface in order to clean and functionalize the surface, applying a film of polymerizable fluid to the surface; and curing the film with high-energy radiation. The plasma treatment cleans the glass surface by removing contaminates. The plasma treatment functionalizes by creating reactive species on the surface, such as free radicals, cations, or anions that will bind to the top coating and by creating oxygenated groups such as hydroxyl, carboxyl or carbonyl.

[0041] Steady-state glow-discharge atmospheric plasma is applied with a plasma head such as described hereinafter. The plasma head is positioned at a selected distance from the glass surface and directed to emit plasma towards the glass surface. The nominal selected distance is about 0.25 inch with a maximum preferred distance of about 0.5 inch. The plasma head is maintained at the selected distance from the glass surface, and the glass surface and plasma head are moved relative to each other to apply plasma to the portions of the glass surface that will receive the polymerizable film. The plasma head could be moved by hand over the glass surface. However, mechanical control of the plasma head is better suited to maintain a uniform distance between the plasma head and the glass surface. Preferably an industrial robot or like mechanism moves the plasma head over the glass surface, or the glass surface is moved mechanically relative to the plasma head.

[0042] Known methods may apply a polymerizable fluid to the glass surface. United States Patent 6,276,741, incorporated herein by reference, discloses suitable methods. The fluid is applied to a thickness of about 0.004 inch to 0.009 inch. The characteristics of suitable polymerizable liquids include:

[0043] A liquid with the right reactivity towards radiation polymerization.

[0044] A liquid with the right viscosity for the spraying equipment.

[0045] A liquid that is stable under transportation and storing conditions.

[0046] A liquid that produces thermoset (heat stable) amorphous (clear/transparent) film.

[0047] A liquid that produces well-adhered film to glass.

[0048] A liquid that produces an impact resistant/absorbent film.

[0049] A liquid that produces a photo-resistant (UV stable) film.

[0050] A liquid that produces moisture resistant film.

[0051] By way of example, and not as a limitation, a suitable polymer would be a blend of acrylate/methacrylate, epoxy, polyurethane, or vinyl components mixed with photo initiators and UV stabilizers. More particularly a suitable coating formulation could include polyurethane diacrylate (oligomer), tripropyleneglycol diacrylate (monomer), trimethylolpropane triacrylate (monomer), acrylated silicone (adhesion promoter) and a photo initiator such as 1-hydroxy cyclohexyl phenyl ketone, which is sold under the trademark Irgacure 184 by Ciba Chemicals .

[0052] The step of curing may be accomplished with any high-energy radiation such as ultra violet (UV) light, electron beam (EB), or gamma radiation.

[0053] The method steps are illustrated in schematic Fig. 4. The invention is especially adapted for treating a work piece having the characteristics of a glass sheet or automobile windshield 100. This type of work piece has a substantial thickness and is rigid after forming. Prior known methods of applying plasma to a thin film or flexible web cannot be used. Instead, the work piece 100 may be moved, such as on a conveyor or by robotic means, signified by the arrow 106 below the work piece 100 in Fig. 4. Similarly, the treating equipment may be mounted on a robotic arm or other moveable mount 104 that is movable with respect to the work piece 100. Arrow 107 signifies that mount 104 may be relatively moveable with respect to the work piece 100. The plasma head may be one of the heads 10, 20 described below or another equivalently performing head.

[0054] In order to locate and maintain the head at a suitable or required spacing from the work piece, the head can be mounted on an automated, height adjustable arm mechanism 102. Such a mechanism can serve two functions. First, it moves the head over the surface of the work piece, which must include at least two axis movement in order to follow a convoluted surface. Second, the mechanism 102 can change the height position of the head dynamically as the head passes over a work piece 100 that is curved or irregular in surface profile, thus requiring a third axis of movement. The edge portions of a windshield are beneficially treated by this technology. Windshields come in many size and shape varieties. A plasma head must be guided in three axes to follow a convoluted edge path in order to treat such a variety of work pieces.

[0055] The plasma head 10, 20 of Fig. 4 is connected to a source of suitable plasma gas 108. The head also is connected to suitable voltage polarity and ground connections, indicated in the figures by conventional symbols. The plasma head can follow a three axis variable path to apply plasma 110 to preselected areas of a work piece 100, especially to the periphery. The source of plasma gas may be a pressurized tank of the gas.

[0056] A robotic carrier 104 also may guide an attached spray apparatus 112. After the gas fed plasma has functionalized the work piece, the spray apparatus 112 applies a film 116 of polymerizable fluid to the portions of the work piece previously treated by plasma 110. Similarly, the robotic carrier 104 may guide a source of curing radiation 114, especially high-energy radiation. This treatment ensures a good adherence of the film 116 to the work piece 100. The treatment provides a durable protective edge covering to a windshield.

[0057] Figures 1 and 2 show a first plasma head 10 embodying features of the present invention. The head 10 includes an elongated base 11, which may be of a plastic material. The base carries an elongated, rectangular, dielectric first tube 12 and an elongated, rectangular, dielectric second tube 13. A positive electrode 14 is imbedded in and extends through the first tube 12. Similarly, a ground electrode 15 is imbedded in and extends through the second tube 13. The base 11 or tubes 12, 13 carry a parallel emitter strip 16. The tubes 12, 13, the electrodes 14, 15, and the emitter strip 16 are of approximately the same lengths and are arranged in parallel alignment. The length the parallel components may define a working width of the head 10. A suitable width is the width of the peripheral edge of a windshield that is to be treated by applying a protective coating.

[0058] A supply of plasma gas, preferably substantially at atmospheric pressure, is available, as schematically illustrated by the particles labeled "GAS" in Fig. 1. Such gas may be supplied from a pressure tank. A conventional pressure regulator can regulate gas pressure. Suitable plasma gases are disclosed in the incorporated U.S. Patent 6,118,218. A few examples are helium, argon, mixtures of an inert gas with nitrogen, oxygen, carbon dioxide, methane, acetylene, propane, ammonia, or mixtures thereof. Plasma gases often contain a substantial quantity of helium, such as forty-five percent or more.

[0059] The base 11 includes a longitudinal channel 17 extending along one side juxtaposed to the first and second tubes 12, 13. The channel 17 serves as a diffusion chamber. Fig. 2 shows a gas port 18 that is defined in and extends through the body of base 11 from the channel 17 to the opposite side. The gas port supplies plasma gas into the diffusion chamber from a source 108, Figs. 2 and 4. The first and second tubes 12 and 13 are mounted in a parallel, spaced, side-by-side relationship on the body 11, at least partially over the channel 17. The emitter strip 16 is mounted between the first and second tubes 12 and 13, opposite channel 17. The emitter strip 16 is comprised of a porous material, such as a porous metal layer that allows passage of a plasma gas.

[0060] The positive electrode 14 is connected to a radio frequency (RF) voltage with an output frequency ranging between 10 to 30 kHz. The ground electrode 15 is connected to ground. The output nominal RF voltage is between 350 and 9000 volts. The power that may be applied across the positive and ground electrodes 14, 15 may be from 100 to 5,000 watts. The gas port 18 is connected to a plasma gas source 108. A plasma gas is injected into the gas port 18 at substantially atmospheric pressure and allowed to diffuse along channel 17, between the positive and ground electrodes 14 and 15, through the emitter strip 16, and onto the glass work piece to be functionalized.

[0061] Referring to Figure 3, a second plasma head 20 also embodies features of the present invention. Head 20 includes positive and ground electrodes with an emitter located between them. For example, a first or central electrode, which may be chosen as positive or ground, is the elongated cylindrical electrode 21 near the center of the head. This electrode preferably is connected for positive polarity. A cylindrical porous ceramic portion 22 laterally surrounds the positive electrode 21. The porous ceramic portion serves as an emitter of plasma gas and also insulates the central electrode 21.

[0062] A second or cylindrical electrode 23 surrounds the porous ceramic emitter 22. The second electrode is of the opposite polarity from the first and preferably is connected for ground polarity. Thus, the emitter is located between the two electrodes and delivers plasma gas into the plasma discharge created between the two electrodes. A cylindrical ceramic insulator 24 surrounds the second or ground electrode 23.

[0063] Ceramic insulator 22 is sufficiently porous to allow passage of a plasma gas. Gas is injected through the porous ceramic portion 22, between the positive electrode 21 and the ground electrode 23. The plasma head 20 provides a uniform gas delivery.

[0064] The method and apparatus of the present invention are capable of providing an unusually thick coating of 0.004 inch to 0.009 inch. The coating is established at high curing speed and with good uniformity, adhesion and optical properties.

[0065] The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly all suitable modifications and equivalents may be regarded as falling within the scope of the invention as defined by the claims that follow.

Claims

1. A method for applying a polymer coating to a surface of a glass substrate, comprising:

2. The method of Claim 1, wherein said first step further comprises:

3. The method of Claim 2, wherein said step of supplying a plasma gas further comprises:

4. The method of Claim 2, wherein said step of supplying plasma gas further comprises:

5. The method of Claim 2, wherein said step of supplying a plasma gas further comprises:

6. The method of Claim 2, wherein said step of supplying a plasma gas further comprises:

7. The method of Claim 1, wherein said second step further comprises:

8. The method of Claim 1, wherein said second step further comprises:

9. The method of Claim 1, wherein said second step further comprises:

10. The method of Claim 1, wherein said second step further comprises:

11. The method of Claim 1, wherein the surface of the glass substrate is the convoluted peripheral surface of an automobile windshield, and wherein said first step further comprises:

12. A plasma head for treating a preselected width of a glass windshield, comprising:

13. The plasma head of Claim 12, wherein said emitter comprises an elongated strip of porous metal, parallel to said first and second tubes, diffusing plasma gas from said diffusion chamber.

14. The plasma head of Claim 13, wherein:

15. A plasma head for treating a preselected width of a glass windshield with plasma, comprising:

16. The plasma head of Claim 15, wherein said emitter comprises a porous dielectric layer, diffusing plasma gas while insulating said central electrode from said outer electrode.

17. The plasma head of Claim 15, further comprising a dielectric layer laterally surrounding said outer electrode.