CA1297617C - Coating deposition mask material - Google Patents

Abstract

Abstract A novel material for masking ceramic or glass surfaces which is suitable in either vacuum sputter coating or pyrolytic deposition operations has been developed consisting of a high boiling, water miscible solvent, a dissolved water soluble film former, and a mineral powder.

Description

12976i7 COATING DEpOSITION MASK NAT~RIAL

This application is directed to a coating deposition mask material which finds particular use in coating a ceramic substrate, such as glass, so that only certain parts or areas of that substrate will have a coating applied thereto in a coating deposition process.
Particular coating deposition processes o~ interest are vacuum sputter deposition and pyrolytic deposition of coating materials.
There are many applications where it would be desirable to decorate a ceramic panel with patterns or designs of a metallic or metallic oxide coating. These panels can be fabricated into products for architectural and automotive applications. Some of the potential applications for such products include vision units and spandrals for building exteriors, interior glazings (for example, room dividers, gla~s doors, etc.), sloped glazings and automotive sunroofs, opera windows and vi~ion glas~.
The most desirable procedure for applying such patterns of films is by means of a vacuum sputtering deposition process or by a pyrolytic deposition process.
In order to carry out such processes, it is necessary to mask or cover the portion of the ceramic substrate which is not to be decorated by the metallic or metallic oxide coating. Unfortunately, these particular processes do not lend themselves to standard mechanical masking practices for many different reasons. Previously known proceæses do not adhere a masking material sufficiently tightly to the substrate surface and in a sufficiently uniform manner to give a good line definition between a coated area and an uncoated area.

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"` 1297617 , Previously known mask materials also tend to warp, buckle, or otherwise deform when heated to a coating temperature in the pyrolytic deposition process.
In the pyrolytic deposition process, normally the substrate to be coated has its surface heated to a temperature in a range of 500-65~C. Other disadvantages of previously known mask materials are that they cannot be made thin enough to prevent nonuniform coating thicknesses at the edge of the mask. SUch coatings are also difficult to make in intricate patterns Such previously used masking materials include materials such as a masking resist material mixed with water or a masking resist material mixed with an oil.
our invention is directed to a coating deposition mask material which enables the decoration of a ceramic substrate with a metallic or metallic oxide compound by vacuum sputter deposition or by pyrolytic deposition processes. The mask material of our invention is easily applled as a liquid by a silk screen printing process and other techniques sUch as rolling or spraying. Our inventive mask material becomes a cohesive solid after drying and provides good adhesion to the substrate upon which it is placed so that the mask material will not be dislodged prior to or during the coating process. Our mask material also provides good adhesion to the substrate surface to produce a uniformly crisp image pattern of the coating material. Addi-tionally, the mask material can be removed with water washing before or after drying.
For a vacuum sputtering coating operation, our mask material has the following additional advantages. A
nonvolatile portion of the mask material has a very low vapor pressure after drying so that there will be no noticeable out-gassing of the coating material when exposed to the very low pressure required for vacuum sputtering deposition. Additionally, the mask material :

-`-`` 1297~17 is easily removed in a water washiny operation without the use of harsh detergents or abrasive materials which could damage the coating applied by a vapor deposition operation.
With respect to a pyrolytic deposition coating process, the mask material of our invention remains effective and sufficiently refractory and can withstand temperatures in excess of 600C (1100F) without reacting with the glass. This is not to say, however, that part of the mask material does not change or decompose during the course of the pyrolytic deposition coating process or vacuum sputtering coating processes.
A search conducted on the subject matter of this specification in the [l.S. Patent and Trademark office resulted in the citation of the following U.S. patents:
3,900,641; 3,978,249; 4,093,754; 4,1~3,919; 4,242,401;
and 4,324,815. We believe that none of these patents either suggest or disclose the mask material of our invention for the reasons set forth individually below.
V.S. Patent 3,900,641 issued on August 19, 1975 for ~Method of Forming Decorative Panels.~ This patent discloses simulated stained glass panels produced from a clear plastic sheet upon which are printed transparent colors in a desired pattern and simulated lead strips separating the various colored areas. A silk screen printing method is taught to achieve this result involving special inks and silk screen materials. The patent, however, does not disclose a coating deposition mask material which may be su~jected either to high heating temperatures in a pyrolytic coating process or to vacuum in a vacuum deposition process.
U.S. Patent 3,978,249 issued on August 31, 1976 for ~Method for Producing Intricate Metal Designs on Glass.~ The method taught in this patent includes the application to a sheet of glass of the negative of the desired design by a silk screen printing operation or ,~ .....
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lZ97617 other screening techniques utilizing a screenable pasting agent which screens through the negative pattern and adheres te~porarily to the glass. The entire glass sheet is then coated with the ~esired metal, usually aluminum, according to known metallizing techniques in which flame atomized metal is applied to the heated glass sheet and thus bonds thereto. The metallized surface is then brushed with wire rotary brushes which remove the metal from those areas where the screenable pasting agent has been applied. The screening material or deposition mask material of this invention is not what we have invented because our masking material may be removed in a water washing operation and does not require the contact therewith of wire rotary brushes in order to remove the same. If wire rotary brushes were used on coatings applied by the vacuum sputtering process, the applied materials would also be removed.
U.S. Patent 4,093,754 issued June 6, 1978 and U.S. Patent 4 133 919 issued January 9, 1979 are both directed to a ~Method of Making Decorative Panels.~ Both patents issued to the same inventor and generally disclose a method of making a decorative panel in which a liquid masking material is applied to a surface of the panel and is cured to form a substantially solid masking layer on the surface. The mixture applied is basically a rubber masking material. A pattern comprising at least one unmasked area and at least one masked area is formed in the masking layer either simultaneously with the applciation of the liquid masking material or subsequent to the curing step. The surface of the panel is then treated to render the unmasked area of the surface of the panel visually distinguishable from the masked areas. In one em~odiment of the invention, the masking layer is elastomeric and the surface of the panel is treated by sand blasting, after which the masking layer is removed.
The entire process may be repeated to provide a dual , ,.

lZg7617 density effect. Neither of these patents disclose a masking material in accordance with our invention, that masking material being one which finds utilization in providing a water removable coating deposition mask for vacuum sputtering coating operations and for pyrolytic decomposition coating operations.
U.S. Patent 4,242,401 issued on December 30, 1980 for "Screen-Printing Mask" and U.S. Patent 4,324,815 issued April 13, 1982 for "Screen-Printing Mask and Method~ are both assigned to the same company and are generally directed to the same subject matter.
In these patents, a method is disclosed of forming a film or fine line which is very thick in comparison with its width by repeated printing with heterogeneous or homogeneous printing pastes by using a screen-printing masX. A screen-printing mask has spacing means formed thereon for spacing the screen apart from the work surface. Again, these patents do not disclose the coating dQposition mask material of the invention.
This invention relates to a material for forming a coating deposition mask and, in particular, to a material for forming a coating deposition mask for a ceramic substrat2, such as glass, which is to be sub-jected to a coating deposition in a coating deposition process selected from the group of coating deposition processes consisting essentially of vacuum sputtering deposition and pyrolytic deposition.
In accordance with the teachings of the invention, the coating deposition mask material, hereinafter CDM material, consists of three components:
~a) a volatile portion, (b~ a water soluble film forming portion, and (c) a finely divided mineral portion. These components are herein described and characterized.

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The volatile portion is a liquid which does not evaporate rapidly during the routine and customary process of practicing the arts of silk screen printing or other forms of printing or other methods of coating. It would evaporate at the same rate as water or slower, depending upon the exact open time required. It is, however, easily driven off from useful wet coatings in a forced air drying operation which is capable of raising the glass temperature to 75-150C. This includes liquids which distill completely between 70-300C or have a room temperature vapor pressure between 40mm Hg and O.OOlmm Hg.
It would also be soluble in water, that is, miscible in excess water or miscible in all ratios with water. It leaves no residue after drying which will out-gas and interfere with the vacuum sputtering coating operation.
The volatile portion of the material forms from 40-95~ by weight of the CDM material.
The CDM material also includes a water soluble film forming portion which is soluble in the volatile portion of the material. The film forming portion forms from 1-40~ by weight of the CDM material. The ilm forming portion becomes adhesively bonded to a surface of the ceramic substrate when the volatile portion of the CDM material is driven off.
The film forming portion also binds together or acts as a binder for the particles of the finely divided mineral portion after the volatile portion of the CDM
material is driven off. This film forming portion is an organic polymer which forms a film when cast from cold water solution or from the volatile portion of our inventive material when dried. The film forming portion remains cold water soluble after drying and after vacuum sputtering so as to be easily removed from the surface of the glass or ceramic with a room temperature water wash.
The finely divided mineral portion forms from 10-70% by weight of the CDM material and is 2-60 times ., 1 .,.

~297617 more abundant than the film forming portion by weight.
Good coverage by this mineral is essential when pyrolytic deposition decorative coatings are to be applied. It i5 often used with vacuum sputtered decorative coatings, as the mineral portion is a convenient means of increasing the screening viscosity of the CDM material. Furthermore, its use provides a convenient means of visibly verifying the overall quality of the mask prior to drying.
The mineral portion is nonreactive with the ceramic substrate. The mineral also has no gas generation components contained therein after the volatile portion of the CDM material has been driven off. The film forming portion of the CDM material has bound the mineral portion of the CDM material together and to the surface of the ceramic substrate. The mineral portion of the CDM material does not react with the substrate at tQmperatures in a range of 300-650C.
The novel features that are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with advantages thereof, will best be understood from the following description of specific embodiments as set forth in the various examples.
The following description is what is considered to be a disclosure of the preferred embodiments of the CDM material of the invention. The following description also sets forth what is now contemplated to be the best mode of making the CDM
material. This description, however, i8 not intended to be a limitation upon the broader principles of the teachings of the invention, and while preferred components are taught for the CDM

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lZ97~17 material in accordance with the requirements of the laws, it does not mean that other components cannot be used to make this CDM material, particularly if the results are the same.

Example l This example shows a coating deposition mask (CDM) material in accordance with the teachings of our invention. In this case a liquid phase was made up of a volatile portion 97% by weight dipropylene glycol with the balance being a water soluble film forming portion formed of hydroxypropylcellulose (HPC) having a Brookfield viscosity of about lOOOcp at 24C. In accordance with the teachings of our invention, the volatile portion and the water soluble film forming portion which formed the liquid phase of the CDM material of our invention formed a mutual solvent-solute mixture having a low vapor pressure, was completely miscible in cold water, and formed a film upon drying from this particular volatile portion. HPC is insoluble in water above 45C, but is still effective in the practice of this invention. The mixture should have a viscosity in the range of 700-1500cp prior to being mixed with the finely divided mineral portion to form the CDM material.
In this case the finely divided mineral portion was formed from aluminum hydroxide in the form of gibbsite (aluminum hydroxide) having a particle size less than 325 mesh. Sufficient of the aluminum hydroxide (about 45~ by weight) was added to the liquid portion of the CDM material to form a final material which had a viscosity of 15,000cp at room temperature 24C. In accordance with the broad teachings of the CDM material of our invention, the final mixture was dryable at 125C
in lO minutes, adhered to the glass it was silk screen printed upon, and bound together the aluminum hydroxide !~ d ` ~Zg7617 particles. The mineral portion was about 30 times as abundant as the film forming portion.
The particular CDM material formed as discussed above was silk screen printed on a number of glass samples. The material on the glass samples was force dried for three minutes at 150C in a circulating oven.
The dipropylene glycol was thus driven off with the film forming material remaining behind to bind the finely divided mineral portion together and to the glass surfac~
to form the coating deposition mask.
Various samples were coated with a variety of metallic compounds by both vacuum sputtering and pyrolytic deposition. In all cases the mask gave a pattern with sharp detail. The samples were washed after coating operation with wash water and the deposition mask material was easily removed there~rom.
Samples which were subjected to vacuum sputter coating process were checked to see how much out-gassing there was. Dried sample-~ were weighed and placed in a coater at a pre8sure of 2.6 x 10-6 torr for 15 minute~. Samples were weighed again and showed no measurable weight loss which indicated no measurable out-gassing when subjected to vacuum.
The CDM material suitable for use in our invention may be applied as discussed above by a silk screen printing operation. The material may also be applied by spraying, rolling or other suitable methods required to develop the required pattern.
With respect to drying time, force drying required for the medium, usually at temperatures of 200F
(93C) or higher, have dried the medium in five minutes or less.
Vacuum sputtering coating done under high vacuum (10 3 torr) requires a very low vapor pressure of dried material to minimize out-gassing, which our materials have. In a similar manner, pyrolytic deposition of metal , . ..

~297617 coatings done at temperatures of 500-650C needs a material which will function at these severe temperatures. our CDM material set forth herein does that.
The material is water removable after either process. washing times can be reduced with the use of high pressure jets of water or very light sceubbing action in conjunction with the application of water.

Example 2 This example sets forth another specific embodiment of a material which is suitable for forming a coating deposition mask. In this case the liquid portion was dipropylene glycol mixed with poly~ethyloxazoline), molecular weight of 500,000 which is the cold water soluble film forming portion. This material is unsoluble in water above 52C. In this specific example, 95~ by weight of dipropylene glycol was used to 5~ by weight of the other material to form the liquid portion of the CDM
material. When mixed, these materials had a Brookfield viscosity of 826cp. The liquid mixture was mixed with magnesium silicate (talc) less than 325 mesh particle size. Sufficient talc was mixed with the liquid portion of the vehicle to form a screenable medium which has a viscosity of lO,OOOcp at room temperature of 75F (24C).
once again this material was applied to various samples of glass as a CDM material and dried. The samples were either treated by a pyrolytic deposition process or by a vacuum sputtering ope.ation. In either case, the deposition mask gave clear, sharp lines and was 3a not affected by the processing conditions laying down the deposition coating. Also, the mask materials were easily removed in a cold water wash operation.

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Example 3 This example sets forth still another embodiment of a CDM material which is included within the teachings of our invention. In this situation, the volatile portion of the liquid part of the coating CDM material included 36% by weight dipropylene glycol and 55% by weight water. The volatile portion had added thereto 9~
by weight of a water soluble film forming portion formed of polyvinylpyrrolidone having an average molecular 10 weight of 700,000.
This liquid portion o~ the CDM material had a final viscosity of about 1250cp at room temperature 75F
(25C). This liquid portion was mixed with alumina silicate (clay) finer than 325 mesh to form a final screenable material which had a viscosity of about 12,000cp, Samples of khis CDM material were applied to many glass substrates and dried. The glass substrates were sub~ected to a vacuum deposition operation or a pyrolytic deposition operation. Once again, the material set forth above withstood the rigors o~ either the vacuum or high temperature environments and remained on the sample to form clear, sharp lines of delineation and was easily removed in a hot or cold water washing operation.

Example 4 The volatile portion was 71.4% of the total by weight and is dipropylene glycol mono methyl ether (BP, 188C, vapor pressure at 25C, 0.36mm Hg). The film forming portion was 4.0~ of the total by weight and was HPC, molecular weight of 150,000. The viscosity of this liquid portion was 1176cp (Brookfield). The mineral portion was talc (hydrated magnesium silicate) sp. gr, of 2.75, particle size of less than one micron. The mineral portion was 24.9% by weight of the total. The mineral ``~ 1297~;~7 portion was 6.2 times the film forming portion by weight. The final viscosity was 753ncp.
This material silk screened well, using a 235 mesh polyester commercial grade screen of a test pattern. It left a smooth surface and crisp edges. It dried easily and accepted the pyrolytic treatment well.
Nothing out-gassed in the sputtering operations. The final products were easily cleaned in cold running water.

Example 5 The volatile portion of this example was 6.15~
of the total weight and was diethylene glycol (~P, 245C:
vapor pressure at 25C is less than O.Olmm Hg). The film forming part was 5.0% by weight of the total and was poly(ethyloxazoline) mol weight 200,000. The viscosity Of this liquid portion was 500cp. This mineral portion was gibbsite (aluminum hydroxide) with a sp. gr. of 2.42. Gibbsite was 33.5% by weight of the total and 6.7 times the film former by weight. The final viscosity was 6590cp.
A commercial grade silk screen (polyester at 235 mesh) was used with good result. The material dried easily in an oven. Patterns retained their definition through both the pyrolytic process and the sputtered film process. The residue or film washed off easily in cold running water.

While particular embodiments of our invention have been illustrated and described, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the invention, and it is intended to cover in the appended claims all such modifications and equivalents as fall within the true spirit and scope of the method of our invention.

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Claims (4)

1. A material for forming a coating deposition mask for a ceramic substrate which is to be subjected to a coating deposition in a coating deposition process selected from the group of coating deposition processes consisting essentially of vacuum sputtering deposition and pyrolytic deposition, said material comprising:
a liquid portion, including (a) a volatile portion which is driven off when said material is heated to a temperature in a range of 75-150°C, said volatile portion forming at least 65% by weight of said liquid portion of said material and having a boiling point at or between 70-300°C or distilling between 70-300°C, said volatile portion also having a room temperature vapor pressure between 40 mm Hg and 0.001 mm Hg and being miscible in water; said volatile material being present in an amount of 40 to 95 wt.% of the weight of the coating deposition mask;(b) a water-soluble film forming portion which is soluble in said volatile portion of said material, said film forming portion forming the remainder of said liquid portion of said material and being an organic film-forming polymer, said film forming portion becoming adhesively bonded to a surface of the substrate when said volatile portion of said material is driven off, said film forming portion of said material being removable from said surface of the substrate in a cold water washing operation, said liquid portion forming a water soluble film when dried, said film-forming portion being present in an amount of 1 to 40 wt.% of the weight of the coating deposition mark; and (c) a solid portion formed of a finely divided mineral portion, said mineral portion having a particle size smaller than the mesh opening in the silk screening process or openings in other process or decorating equipment and being nonreactive with the substrate, said mineral portion also have no gas generation components contained therein after said volatile portion of said material has been driven off and said film forming portion of said material has bound said mineral portion of said material together and to said surface of the substrate, said mineral portion also being 2 to 60 times the weight of the said film forming portion, said mineral portion of said material also being non heat decomposable at temperatures in a range of 300 to 650°C.

2. The material of claim 1, wherein said film forming portion is hydroxypropylcellulose which can be removed subsequently by washing in water having a temperature below 45°C.

3. The material of claim 1, wherein said film forming portion is poly(ethyloxazoline) which can be removed subsequently by washing in water having a temperature below 52°C.

4. The material of claim 1, wherein said film forming portion is polyvinylpyrrolidone which can be removed subsequently by washing in water at any temperature.