US3450465A - Mirror with a partially reflecting thin metal alloy coating on a plastic base - Google Patents

Description

June 17, 1969 s. R. FRANCE ET AL 3,450,465

MIRROR WITH A PARTIALLY REFLECTING THIN METAL ALLOY COATING ON A PLASTIC BASE Original Filed July 26, 1962 APRETREATING OF PLASTIC MATERIAL SUCH AS METHYL METHACRYLATE, POLYCARBONATE,RIGID VINYL BY STEPS OF I. CLEANING FIRST SURFACE WITH SOLUTION OF 25% PHOSPI-IOR'IC ACID 25% ALCOHOL, 50% WATER. 2.RINSING IN TAP AND/OR DEMINERALIZED WATER. 3.8LOWING DRY.

8. FIRST SURFACE METAL COATING BY VAPOR DEPOSITING UNDER VACUUM FROM ASOURCE FOR TIME INTERVAL AT PREDETERMINED VOLTAGE AND TEMPERATURE USING SUBSTANTIALLY 60 Z NICKEL,I6% CHROMIUM, 22.5% IRON,I.5% SILICON.

6. POST TREATING TO INCLUDE STEPS OF I. SUSPENDING METALIZED PLASTIC MATERIAL FOR PREDETERMINED TIME AT PREDETERMINED TEMPERATURE IN WETTED SOLUTION OF CHROMIC AND SULFURIC ACIDS.

2.RINSING IN TAP AND/OR DEMINERALIZED WATER.

3. BLOWING DRY.

Q. ADDING OPAQUE BACKING MEANS. A I

INVENTORS Stanley A. France BY Frank/m E. Mar/ca Their Afro/nay United States Patent 3,450 465 MIRROR WITH A PARTIALLY REFLECTING THIN METAL ALLOY COATING ON A PLASTIC BASE Stanley R. France, Dayton, and Franklin E. Merica, Fairbom, Ohio, assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Continuation of application Ser. No. 212,662, July 26, 1962. This application Aug. 2, 1968, Ser. No. 756,710 Int. Cl. G02b 17/00 US. Cl. 350-278 1 Claim ABSTRACT OF THE DISCLOSURE A mirror comprising a main body portion of plastic material having an opaque backing on one side'thereof and a partially reflecting thin metal alloy coating vapor deposited upon the other side thereof.

This application is a continuation of parent application Ser. No. 212,662, filed July 26, 1962, now abandoned.

This invention relates to an article of manufacture such as a rear view mirror and a procedure for improved first surface metallic coating on plastic material during the manufacture thereof.

An object of this invention is to provide a new and improved procedure and resulting mirror-like article of manufacture having a plastic body with a first surface metallic mirror-like coating to provide a wear-resistant surface.

Another object of this invention is to provide procedure resulting in a wear-resistant surface having good optical mirror-like coatings on thermoplastic and thermosetting plastic materials subjected to steps of pretreating to include cleaning with a solution of phosphoric acid and alcohol, rinsing with water as well as blowing dry,

vaporizing to include electrodeposition of metal alloy' having nickel, chromium and iron in predetermined ratio under substantial vacuum at a predetermined distance from the plastic surface for a time interval at a predetermined voltage and post treating to include suspending a mirror-like metalized plastic material for a time interval at a predetermined temperature in a solution of chromic and sulphur acids followed by rinsing in water and blowing dry.

A further object of this invention is to provide procedure resulting in a wear-resistant first surface metallic coating on plastic material from a group consisting of methyl methacrylate, polycarbonates, rigid vinyl and the like subjected to steps of pretreating to include cleaning the plastic material to remove oil, greases, dirt and the like with a mixture of substantially 25% ethyl alcohol, 25% phosphoric acid and 50% water at temperatures in a range at least that of the room and below that destructive to the plastic material, rinsing thoroughly in tap water, rinsing in flowing demineralized water and blowing dry; vaporizing to include a preheating and subsequent metal coating by vapor deposition under substantial vacuum such as less than one micron at a voltage of substantially one hundred volts for approximately fortyfive seconds applied to a filament as a vapor source of a chemical composition of generally 60% nickel, 16% chromium, 22.5% iron and 1.5% silicon spaced at a predetermined distance from the plastic material and post treating to include suspending the metalized mirror-like plastic material for a predetermined time interval and at a predetermined temperature in a solution of by weight of chromic acid, 10% by volume of sulphuric acid and approximately 5 cc. of suitable wetting agent, rinsing in tap water, rinsing in demineralized water and finally blowing dry.

Another object of this invention is to provide a mirrorlike article to manufacture to include a flexible plastic main body portion of material such as methyl methacry late, polycarbonate, rigid vinyl and the like initially cleaned and dried, a primary vapor-coated layering of thin metalized alloy material such as a composition of substantially 60% nickel, 16% chromium, 22.5% iron and 1.5% silicon applied under vacuum and post treated with an acidic solution rinsed away prior to drying and an opaque backing means to adhere to a side of the plastic body portion opposite to that of the metalized layering. Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings where- 111 preferred embodiments of the present invention are clearly shown.

In the drawings:

FIGURE 1 provides a block diagram representing procedure in accordance with the present invention.

FIGURE 2 is an enlarged and sectioned perspective view of a mirror-like article of manufacture produced in accordance with the present invention.

The present invention provides a new and improved procedure and resulting mirror-like article of manufacture which needs to be provided with only a first-surface metallic mirror-like coating. FIGURE 1 illustrates in a block diagram steps performed in accordance with the present invention to obtain mirror-like metal-to-plastic adhesion on a smooth glass-like surface. An article of manufacture or mirror means generally indicated by numeral 10 is shown in FIGURE 2 and includes a laminated structure having a main plastic body portion 11. This body portion can be made of a piece of plastic material such as methyl methacrylate, polycarbonates, vinyl and the like. The plastic body portion 11 has a surface 12 on one side thereof that is subjected to a procedure of pretreating in a sequence of steps capable of removing oil, greases, dirt and the like. In accordance with the present invention, this pretreat cleaning step includes using a solution of phosphoric acid and an alcohol mixed in water at room temperature. A cleaning solution or agent found'to be particularly successful is a mixture of 25 ethyl alcohol, 25 phosphoric acid and 50% water. Maintaining substantially this ratio of ingredients for the step of cleaning at room temperature or at least at temperatures lower than destruction temperatures of particular plastic materials used is advantageous for treating the surface 12 of the main plastic body portion 11 which is then subjected to first rinsing thoroughly in tap water and then secondarily rinsing in running demineralized water followed by a step of drying such as by blowing heated air from a suitable source over the surface 12.

The step of cleaning during this pretreating of surface 12 can be accomplished by a swabbing with a cottonwool pad and the like using the solution of one part phosphoric acid, one part alcohol and two parts water at a temperature between that of the room and below that which would be destructive to the particular plastic material used for the body portion 11. After the rinsing and blowing dry, the plastic body portion 11 with the clean surface 12 is placed into an apparatus having a vacuum chamber equipped with a suitable heating unit capable of heating and vaporizing a metal such as an alloy and/or metallic salt to the vaporizing temperature thereof. The heating unit per se can have a tungsten or molybdenum filament and the metal, alloy, and/or metallic salt to be evaporated may be placed in direct contact with the filament or placed in a container adjacent to the filament. Thus, either direct or indirect heating from the filament can be used to eifect vapor deposition of metallized material onto the clean surface 12 during positioning thereof in the vacuum chamber.

As indicated in FIGURE 1, a metal alloy composition of substantially 60% nickel, 16% chromium, 22.5% iron and 1.5% silicon was found to be particularly satisfactory during the vaporizing or first surface metal coating by vapor depositing under vacuum from a source for a time interval at predetermined voltage and temperature values. The filament can be provided to include a coil with six loops made from approximately eight inches of threestrand 3X 30 tungsten wire to be located a distance from the surface 12 of the plastic body portion 11. This distance, for example, can be eight inches. Vacuum pressure at a value of one micron or less and substantially one hundred volts power for approximately forty-five seconds time interval will provide metal coating and vapor depositing while distance from the plastic material to the filament is maintained so that excessive heating during metalizing does not produce out-gasing of the plastic material. It is to be understood that for material vaporization a tungsten filament is used though other filaments may be found suitable. Thickness of the metalized coating is relatively thin thereby tending to improve abrasion resistance and adherence.

In FIGURE 2 there is shown a primary surface metallic mirror-like coating or thin metalized alloy layering 14 which adheres to the surface 12 of the plastic main body portion 11 subjected to the cleaning in accordance with the present invention. Along a surface or side of the plastic body portion 11 a location opposite to or remote from the surface 12 subjected to cleaning and vaporized coating, there is provided a suitable dark or opaque backing means 15 to block passage of light therethrough and thereby completing the mirror-like structure 10 to include only the plastic body portion 11, the backing means 15 as well as the metalized coating or layer 14 without need for any outer covering of organic material, lacquer, paint and the like which was previously needed. A suitable C- shaped clip means 16 attached to a bracket 17 can be provided for mounting of the mirror-like structure 10 relative to a frame 18 for a vehicle windshield 19. It is to be understood that other mounting structure can be provided and the clip 16 with bracket 17 is shown for purposes of illustration only.

Further in accordance with the procedure of the present invention, there is a post treating to include steps of suspending metalized plastic material such as the body portion 11 having the coating 14 on one side thereof in a solution of chromic and sulphuric acids suitably wetted. It is to be understood that this post treating is effected relative to the side of the mirror provided with the coating 14 prior to addition of the backing means 15 to an opposite side thereof. The step of suspending in this solution for substantially five minutes at approximately 100 F. occurs advantageously in a solution having a composition of chromic acid and sulphuric acid. Good results were obtained with a solution having 10% chromic acid by weight, 10% sulphuric acid by volume, and cc. of a suitable wetting agent such as a salt of homologous series of substituted aromatic sulfonic acids. The wetting agent can be tied with ethyl methyl, sulphate as well as any one of several ketones.

After suspending the metalized mirror means in the foregoing solution, there is provided an initial rinsing in tap water followed by further rinsing in demineralized Water and finally a blowing and drying of the mirror means. Finally the opaque backing means is added to complete the mirror. Drying temperatures in all cases must be lower than distortion temperature of the plastic substrate or body portion 11. The post treating results in removal of any absorbed gases which may have been formed during metal deposition. The resulting metalized layering provides approximately only 50% reflection of white light rays. There is no need for any second surface metal layering or for any front painting to protect material such as aluminum from oxidation. Since there is no second surfacing on the metalized layering 14, all second surface problems are avoided. It has been found that a mirror structure manufactured in accordance with the procedural steps of the present invention provides good adhesion of the metallic coating to the plastic first surface. The coating 14 is quite thin and the resistance to surface abrasion resulting from use of nickel and chromium alloy material is such that no secondary surfacing is required. The drying can be caused to occur in a heated oven under vacuum. Particular apparatus used does not form part of the present invention and can be varied to perform the procedural steps outlined in the foregoing description and in the drawings. The backing means can be black in color and the main plastic body portion 11 can be made of thermosetting as well as thermoplastic material.

While the embodiments of the present invention as herein disclosed constitute preferred forms, it is to be understood that other forms might be adopted.

We claim:

7 1. A mirror comprising a main body portion of plastic material selected from the group consisting of methyl methacrylate, polycarbonates and vinyl, and opaque backing means on one side thereof, and a partially reflecting wear-resistant thin metal coating only on an opposite side of the body portion, said wear-resistant thin metal coating being an alloy composition consisting of substantially 60% nickel, 16% chromium, 22.5% iron and 1.5% silicon vapor deposited under vacuum said thin metal coating having approximately only 50% reflection of white light rays.

References Cited UNITED STATES PATENTS 2,390,424 12/ 1945 Colbert. 2,464,256 3/ 1949 Packer. 2,567,713 9/ 1951 Kaplan. 2,884,337 4/1959 Homer et al. 2,907,672 10/ 1959 Irland et a1. 3,094,430 6/ 1963 Skwierinski.

DAVID H. RUBIN, Primary Examiner.

US. Cl. X.R.

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