US2595867A

US2595867A - Organic backing

Info

Publication number: US2595867A
Authority: US
Inventors: Leslie D Mcgraw; Charles L Faust; Ernest R Mueller
Original assignee: Ohio Plate Glass Co
Current assignee: Ohio Plate Glass Co
Priority date: 1950-05-25
Filing date: 1950-05-25
Publication date: 1952-05-06
Anticipated expiration: 1969-05-06
Also published as: US2595800A

Description

May 6, 1952 (Preferable) Spray Primer Coat L. D. MQGRAW ETAL 2,595,867

ORGANIC BACKING Original Filed May 25, 1950 Deposition of Light Reflecting Layer on Light Transmitter FIGURE l Styrene Butadiene Base Composition Light Reflecting Layer Light Transmitter FIGURE 2 tyrene Butodiene Composition Coat Light Reflecting Layer Light Transmitter FIGURE 3 INVENTORS. Leslie D. McGraw BY Charles L..Faii'st Ernest R. Mueller W/ W MM AGENTS.

Patented May 6, 1952 oncnnrc BACKING V Leslie D. McGraw, Charles L. Faust, and Ernest R. Mueller, Columbus, Ohio, assignors, by mesne assignments, to Ohio Plate Glass Company, Toledo, Ohio, a corporation of Ohio Original application May 25, 1950, Serial No. 164,057. Divided and this application May 25, 1950, Serial No. 164,058

(Cl. 260--i1,5)

2 Claims.

This invention relates to protective backings or coatings for mirrors. More particularly, this invention relates to coating compositions for protecting the backs of mirrors, to a mirror coated with such compositions, to a mirror having a composite backing, and to a method of process for protectively coating mirrors.

While many compositions have been proposed in the prior art as backing materials for mirrors, they have been found to seriously lack the necessary protective ability to prevent deterioration or oxidation of the silver layer of the mirror over a long period of time. These materials sometimes contain residual corrosive agents or generate the same during exposure to the moisture-laden atmosphere resulting in attack or oxidation of the silver film, thus ruining the mirror. Likewise, these materials may crack or pit on aging to allow the silver to blacken, or white spots to appear, as well as permitting moisture to penetrate to the silver film and also deteriorate it. In industry it is desirable to produce mirrors in large sheets which are subsequently cut into commercial and retail sizes. It is essential that, during the cutting process, the protective backing material not adhere or stick to the cutting tool or abrasive wheel, and also that it not permit flaking or peeling of the silver film fromthe glass base. Likewise, when the edges of the mirror are finished or polished, the protective backing should wear awayreadily and should not cause the silver film to pull away from the edge. Another desirable featurein a commercial mirror backing is that it be sufficiently hard and tough to resist scratching or marring during assembling, handling and mounting. A still further property of a good mirror backing relates to its ability to prevent deterioration of the silver if there is an accidental scratch through the backing which exposes a small area of the silver. These properties have not heretofore been obtained adequately with organic backings that are available today, result ing in high cost of mirror manufacture and shortened life. Hence, it would be highly desirable to obtain a tough, readily-friable, moisture-impervious, noncorrosive and adherent mirror backing. A

It is, therefore, an object of this invention to provide a composition of matter which will protect the reflecting film of a mirror against deterioration, oxidation by the atmosphere, flaking or loosening of the film during cutting, and marring or scratching when handled and assembled in place.

It is another object of this invention to provide a method or process for coating a mirror 2 with a protective composition characterized by the 'fact that said composition protects the mirror againstfiaking, peeling, and scratching during manufacturing and finishing-operations and against oxidation and deterioration in use.

It is yet another object to provide a mirror having an adherent scratchand mar-resistant, nonflaking protective composition backing which materially increases the life of the mirror.

' It is a further object of this invention to provide a mirror having a composite backing which is characterized by having the aforementioned improved qualities.

It is a still further object of this invention to provide a method for producing a mirror having a composite backing which is characterized by having the aforementioned improved properties.

These and other objects and advantages of the present invention will become more apparent from the following detailed description, example, and drawing wherein,

Figure 1 is a flow sheet of the method or process disclosed herein, and i Figure 2 is a vertical cross-sectional view of the mirror of this invention having the protective coating composition thereon, and

Figure 3' is a vertical cross-sectional view of the mirror of this invention having the protective composition and a primer coat thereon and which represents one perferred embodiment of the present invention.

' the reflective layer or surface of the mirror and provides, on drying and hardening, a backing or outer {coating which prevents flaking 01. loosening of the reflective layer during manufacturing operations such as cutting, trimming or tapering, and resists mars and scratches during handling and deterioration by oxidation over relatively long periods of time. Moreover, the life of the mirror can be improved by disposing a primer coating between this outer backing and the reflective silver less film of the mirror.

In general, with reference to Figures 1 to 3 of the drawing, it will be seen that a mirror made by any well-known process, for example, such as the Rochelle salt'chemical reduction process, is simply sprayed with a mixture of the aforementioned ingredients and then allowed to airdry. The mirror can also contain an intermediate organic base primer coat disposed between the silver film and the outer protective composition by spraying, etc., when it is desirable to obtain a somewhat greater life and adherence of the other protective coating to the mirror.

The light-reflecting material has been described as a mirror although it is obvious that reflectors, semior selectively reflecting or even partially or semi-transparent, can be treated according to the invention disclosed herein in order to increase their life. as Well as to protect them against injury during manufacturing and assembly operations. The light-permeable or transmitting means of the mirror ispreferably glass, but plastic, cellophane and similar lighttransmitting or semior selectively light-transmitting materials may likewise be used which will not be adversely affected by a temperature up to: 120 C. The'light-refiecting. means on the mirror-can be of any metallic. orother'.sirnilar substance. For the purposes of this invention thin gold, copper, platinum, and silver films are preferable. It is only necessary to have a very thinfilm in order to obtain a good mirror. The silver or other metal may be deposited by processes of spraying, melting and puddling, vacuum evaporation, sputtering or sublimation, dipping, or by chemical reduction processes such as the Rochelle salt process. The Rochelle salt process is probably the best known process for producing good mirrors and is preferred in view of the fact that it deposits-a very thin, continuous, highlyreflectivefilm of metal which is very adherent to the glass.

It: is not precisely known why the combination of elements of the protective composition of this invention provides such a good coating material. However, it has been found that outside certain ranges or proportions of these materials, the resulting composition will not have the necessary protective properties or qualities as taught by the present invention. In the composition the critical ranges are as follows: the zinc oxide should be used in the amount of from 13 to 33 parts by weight, barytes in an amount of from 16 to 40.5 partsby weight, talcfrom 3.0 to 15.5 parts by weight, titanium dioxide from 6.0 to 11.5 parts by weight, styrene-butadiene co-polyrner in an amount of from 25 to 32 parts by weight, and sufiicient xylene to give good fiowability or viscosity for coating by painting, spraying, etc.

The amount of xylene used will vary depending on the fluidity or viscosity desired during mixing and spraying and is generally used in the ratio of from 60 to 120 parts by weight of xylene to about 30 to 60 parts by weight of the mixture of dry ingredients. Aryl hydrocarbons similar to xylene, such as toluene and benzene, can be substituted partially or wholly for the xylene.

A representative backing composition contains 16 parts by weight of zinc oxide, 25.7 parts by weight of barytes, 3.2 parts by weight talc, 6.1 parts by weight of titanium dioxide, 26.3 parts by weight of styrene-butadiene co-polymer and 136 parts by weight of Xylene. Xylene is usually added to the styrene followed by addition of the other ingredients. Additional xylene is added as needed to vary the viscosity and enable the composition to be readily sprayed. The composition after evaporation of the xylem procl'u'ced an excellent backing from 0.5 to 1.0 mil thick when applied to mirrors.

A primer coat is desirably added to the silver film prior to the deposition of the outer organicbase protective backing. Any primer coating Components A, Dose Grind:

Vinyl Butyrel Resin XYHL (polyvinyl butyral resin-as manufactured by the Bakelite Co.) 7. 2

Basic Zinc Chromate pigment or zinc tetroxy chroznate (M 1828-Mineral Pigment Corp. or 2259- Imperial Paper and Color 00.)

Talc (Asbestiuc 3X) Isopropanol (99%) olueue B. Acid Diluant:

Phosphoric Acid W" tor a Isopropanol (99%) The above ingredients are mixed prior to use. The mixture should, however, be reduced for application and used within eight to twelve hours after preparation to prevent excessive polymerization and evaporation of solvent and. diluent, e. g., water, isopropanol, and toluene. It is obvious that the proportions can be varied somewhat to still obtain desirable adherence and moisture-resistance properties which are necessary in helping to prevent deterioration of the silver film.

Any paint or rubber-mixing machinery can be used to mix the ingredients of the primer coating and also the outer coating. For example, a ball mill or three-r011 paint mill can readily be employed. The mixing process is discontinued at the time a homogeneous-appearing mixture is obtained which is in from about 20 to 40 minutes. The time will, of course, vary with the size of the equipment and amount of materials being used.

Customary paint-spraying equipment can be readily used to apply the primer and outer coatings. t is unnecessary to use special paintspraying' machinery or techniques in order to coat the mirror with the compositions disclosed herein. Moreover, it is not necessary that the coatings be only sprayed but they can be readily pplied by rollercoating, dipping, brushing, and so forth.

The air-drying and hardening step to enable the volatiles to evaporate and the polymersor resins to set may be done in the open atmosphere at room temperature. While the coatings are dry in about 45 minutes in air, they are not sufficiently hard for several hours. It is not critical that the coatings be dried in a stream of hot inert gas or heated, although such procedure can be utilized to materially reduce the time of drying. For example, it will take about 12 to 24 hours to dry and harden in air at room temperature while baking at '75-100 C. will take only from 30 to GO'minutes. It is, of course, apparent that when a primer coat is used, it must be allowed to dry and set before the outer organic base backing is applied.

The thicknesses of the primer and outer coatings can, of course, be varied by spraying, etc., for longer times or by repeating the procedures as often as desired.

While it is not essential, it is desirable that the materials used in the practice of the present invention be substantially pure in order to obtain consistent results. Unless otherwise specified, the Weights expressed in the specification and claims are parts by weight.

Thefollowing example will serve to illustrate the invention with more particularity to those skilled in the art.

14 parts by Weight of acicular zinc oxide meeting Maritime Commission specification 25-MC- 520, 16 parts by weight of medium oil-absorption barytes (approximately 99% BASO4-0.1 to 0.025 retained on 325 mesh screen), 8 parts by Weight of high oil-absorption talc (1.2 to 1.3% retained on 325 mesh screen), 6.5 parts by weight of rutile titanium dioxide (95% TiOz meeting Federal specification TT-T-425, Type III, class B), and 25 parts by weight of styrene-butadiene co-polymer (Pliolite S-5 as made by the Goodyear Tire and Rubber Co. 70 to 75% styrene). Xylene was added to the styrene prior to addition of other ingredients in the amount of 106 parts by weight. Next the components were mixed together on a three-roll mill until a homogeneous-appearing composition was obtained. This took about thirty-five minutes. The material was then put in a commercial paint sprayer and sprayed on the silvered back of a mirror to produce a, protective backing 0.9 mil thick. After 24 hours in air at room temperature, the backing was dry and hard.

Other examples were run in which the primer coat described supra was disposed between the silver film and the outer protective coating.

The tests below show the results of using the protective coating of this invention for mirror backings as compared to mirrors containing a shellac coating and containing no protective coating.

Test I A mirror containing only the protective outer organic coating described in this application on its back lost its brilliance within three days under an atmosphere of 100% humidity at 125 F.

Test II A shellac backing applied to a silvered mirror Without an intermediate coating offered protection for less than one day when exposed to an atmosphere of 100% relative humidity at 112 F.

Test III With no protective coating the silvered mirror lost its brilliance and adherence in one day at 112 F., 100% relative humidity.

Test IV the primer coat, was not readily scratched or marred, nor on cutting did the silver film flake or peel from the glass.

It is, thus, seen that the present invention discloses a new and novel protective-coating composition for minors containing zinc oxide, barytes, talc, titanium dioxide, butadiene-styrene co-polymer and xylene. This composition can be readily applied to the reflective back, layer or surface of the mirror and on drying resists atmospheric oxygen and moisture and thereby protects the reflective surface against deterioration. Moreover, during manufacturing and mounting operations, such as grinding, finishing or cutting, the reflective film does not flake or peel from mirrors containing the protective-backing composition of this invention. Additional improved results in adherence of the outer coating and resistance in deterioration of the silver film are obtained when a primer coating or layer is disposed bet on the metallic film and the outer organic base acking material.

It will be understood that while this invention has been described with particular reference to protective coatings for mirrors, and more specifically to silvered mirrors, it is to be understood that in its broad concept the process and the novel composition disclosed herein are applicable to any device containing reflecting or semi-reflecting surfaces which are subject to oxidation or deterioration, scratching, flaking during handling or manufacture, or after mounting or use, and, thus, the matter disclosed herein is to be construed as illustrative rather than limiting.

This application is co-pending with and related to McGraw, Faust, and Mueller application, Serial No. 164,057, filed May 25, 1950. The present case is a divisional application of application, Serial No. 164,057, which is directed to the production of a mirror or composite article having a laminated backing composed of a number of organic and inorganic coatings. The organic coating can be the organic-coating claimed in this case.

Having thus described theinvention, what is claimed as new and novel and is desired to be secured by Letters Patent is:

1. A composition of matter, comprising from 13 to 33 parts by weight of zinc oxide, from 16 to 40.5 parts by weight of barytes, from 3.0 to 15.5 parts by weight of talc, from 6.0 to 11.5 parts by weight of titanium dioxide, from 25 to 32 parts by weight of styrene-butadime co-polymer containing to styrene and xylene in an amount sufficient to give coating viscosity.

2. A composition of matter, consisting of 16 parts by weight zinc oxide, 25.7 parts by weight barytes, 3.2 parts by weight talc, 6.1 parts by weight titanium dioxide, 26.3 parts by weight styrene-butadiene co-polymer containing 70 to 75% styrene and xylene in an amount sufiicient to give coating viscosity.

LESLIE D. MoGRAW. CHARLES L. FAUST. ERNEST R. MUELLER.

REFERENCES CITED The following references are of record in the file of this patent:-

UNITED STATES PATENTS Number Name Date 2,294,940 Skolnik Sept. 8, 1942 2,394,930 McRae Feb. 12, 1946 2,410,733 Hewlett Nov. 5, 1946 2,419,512 Vesce Apr. 22, 1947 2,459,891 Nelson et al. Jan. 25, 1949 2,468,568 MoCusker Apr. 26, 1949 2,502,949 Howlett et al. Apr. 4, 1950