US2238472A - Light-diffusing body and method of producing same - Google Patents

Description

I06. COMPOSiTIONS,

COATING 0R PLAST'C .45 Patented Apr. 15, 1941 UNITED STATES PATENT Cross Reference OFFICE LIGHT-DIFFUSING BODY AND METHOD OF PRODUCING SAME Jersey No Drawing. Application August 9, 1938,

Serial 223,854 7 SCIaims M This invention relates to the coating of hollow glass bodies or hollow vitreous articles such as incandescent electric lamp bulbs or the like.

In the manufacture of electric incandescent lamps it has been recognized for some years.

that there are important advantages in providing a translucent or frosted bulb. Included among these advantages are the reduction of glare of the incandescent filament and the diffusion of the light emanating therefrom. Various methods have been employed to render the bulb light-diffusing; for instance, a common method of accomplishing this result is to frost the glass either inside or outside by means of an etching fluid, or the bulb may be made either partially or wholly of an opal glass, or a coating of light-diffusing nature may be applied either to the inside or to the outside of the bulb.

The production of good light-diffusing bulbs has become increasingly important with the increased efficiency rating of lamps at present manufactured. For instance, a 60 watt lamp at first had an efliciency of 11.6 lumens per watt, whereas a lamp of this same wattage now has an efficiency of 13.97 lumens per watt, the increased efficiency being in the main due to the use of filaments, notably tungsten, which concentrate the light source to a relatively small space. Because of the increased intensity and concentration of the light source, bulbs hitherto designed or treated to produce translucent lightdifiusing surfaces are now inadequate properly to diffuse the light. The result is that such lamps manifest a very considerable amount of the very localized brightness and glare which present methods of frosting or coating, or making of opalescent glass, were originally designed to eliminate.

Opal glass is very expensive and has not been found to be practicable in the quantity production of electric incandescent lamp bulbs. Frosting by etching requires great care in controlling the action of the etching fluid, and invariably results in a bulb considerably weaker than a clear, unfrosted bulb.

Moreover, no satisfactory method has hitherto been devised to coat the inside of lamp bulbs of all types and wattages. It has not hitherto been practical to coat gas-filled lamps of the kind known in the industry as type C or gasfilled incandescent lamps, and even in the case of vacuum lamps it has been found unsatisfactory to coat lamps larger than 40 watt size. It is true that gas-filled lamps are on the market which have an inside coatin on the round of g s-a...

the bulb only, but such lamps must be burned I in a position with the base upward in order to avoid rapid blackening and unduly short life.

It is an object of the present invention to provide a lamp with an efiicient and lasting inside coating of light-diffusing characten'and a process for applying this coating. The lamps of the invention may range from the smallest sizes to the largest of 300 watts or larger, and these lamps may be either the vacuum type or gas-filled, and may be burned in any position required by ordinary fixtures, without undue blackening within the normal commercial life of the lamp.

In applying the invention, a white light-diffusing coating is first prepared having approximately the following formula:

Li iopo grams 575 20 SoWof sodium silicate in distilled water-(specific grav1ty of sol'fitio'lf' Another satisfactory formula is as follows:

Bar hate grams.. 800

Solution of sodium silicate in distilled water, speci c gravi y o .014, the ratio of si'l'i'ca to soda being 3.22 to 1 cc.. 2400 It is very important that the aqueous component of the sodium silicate solution should be free from foreign mineral content, and for this reason it is highly advantageous not to use ordinary tap water but to distil tHFWEtEFWhich entersififithe composition of the coating material. The presence of even small quantities of minerals or acids seriously affects the color of the coating and may produce other undesirable effects.

The solid component of the coating, which may be some other non-volatile, refractory, substantially insoluble, water-free, finely divided solid pigment, such as titanium oxide, barium sulphate, or combinations of titanium oxide and 5ar1umsulpfiate, or of titanium oxide and lithopone myst b c; very pure. Materials of this type s ould be chemical! ure or rea ent ure. They should E free from any appreciable amounts of water, substances containing water, substances, as soluble salts, which will unite or combine with water, or substances which will combine with other materials to give off water or other undesirable volatile compounds that might subsequently be freed in a lamp during the time the filament is incandescing.

Further, the ratio of silica to soda of the Examiner 8 QOAHNG R PLAsHu m U HUIUI UIICB sodium silicate should be relatively high so that the working and drying qualities of the liquid coating material are enhanced. Such ratio may vary between 3.22 and 3.86 of silica to gne of soda-that is, or eadh par 0 so um o e mo) there will be 3.2 parts of silicon oxide (SiOz).

The concentration of the sodium silicate is also highly important. Sodium silicate of a gravity of 1.01, for instance, results in a lamp which has undesirable swirling markings in the coating due to the action taking place within the bulb during exhaust. On the other hand. if sodium silicate of a specific gravity of 1.02 is used, the glass bulb is rendered so brittle that it breaks under very slight shocks. At the concentration mentioned in the formula, namely, specific gravity of 1.014, and the silica soda ratio of 3.22 to 1, neither of these undesirable results are efiected.

. The foregoing briefly outlines the various requirements for coating materials best suited for use in the process of the invention. Such coating materials are particularly described and claimed in an application of Walter E. Koemer, filed concurrently herewith.

An illustrative method of coating bulbs by utilizing the foregoin type of coating composition proceeds as follows: The clear bulbs are first heated in an oven at an oven temperature of approximately 200 C. The bulbs remain in this oven from one to two minutes. The bulbs are then sprayed by means of a spray gun of well known type, the air used in this gun being pre-filtered and pre-dried. The filtering of the air is carried out with great care to separate and remove all traces of moisture, oil, and other foreign substance. Due to this filtering and heating, and to the fact that the coating is applied while the bulbs are still hot from the pre-heating, the coating material is partially dehydrated when it settled on the inner surface of the pro-heated bulbs. It is also important that the atomizin gun be brushed each time the spraying operation is interrupted, with a solution of C. P. sodium hydroxide in distilled water, in order to remove from the nozzle of the gun any coating material which may have hardened thereon.

An important step in the process follows. When the bulbs are coated as above described, they are aged for a period of at least 48 hours at room temperature. It is believed that a natural drying of the coating takes effect in this manner with practically total elimination of moisture or water vapor. If this drying effect were -sought by artificial heating at this stage of the process, a shell of coating material would form that would imprison a great deal of the moisture which later, during the operation of the lamp, would be released into the bulb with deleterious efiects upon the filament and coating.

While we have stated that the above-mentioned aging treatment is carried out for a period of at least 48 hours, at room temperature, it should be understood that conditions of humidity have an important bearing on the time of drying. During humid days the drying time may have to be extended, whereas on dry days it may be shortened.

We may, however, desire to effect more constancy in drying time by conditioning the air so that proper drying conditions are obtained.

The next step is accomplished at the time the mounts are sealed into the bulbs. Just previous to sealing in, the sprayed bulbs are baked at an oven temperature of 350 C. and the bulbs are kept in this oven at this oven temperature from one to two minutes depending upon the size of the bulbs. During this heating, dry filtered air is blown into the bulbs to facilitate better circulation of the hot air within the bulbs and also to eliminate water vapor as fast as it is released. The bulbs are then sealed in and exhausted and during this step the temperature on the sealing-in machines and exhaust ovens should be increased to about 400 to 450 C. in order to remove the last traces of moisture. The temperature employed in this step should be greater than that employed on the sealing-in and exhausting of the clear glass bulb or bulbs inside-frosted by etching, as the coating on the inside of the bulbs of this invention acts as a heat insulator and requires a greater heat to penetrate to the glass to drive out the water vapor.

Instead of sealing the lamp directly after drying and exhausting as above outlined, we may fill the same with nitrogen or other suitable gas in order to produce a gas-filled, instead of a vacuum yp mp;

What we claim is:

1. The method of producing a light-diffusing coating on the interior surface of a hollow, vitreous body which comprises preheating and drying said surface at an oven temperature of 200 C., depositing thereon a coating material consisting of a pigment incorporated in a solution of sodium silicate in distilled water, said solution having a specific gravity of 1.014, drying said applied coating at room temperature for a period of at least 48 hours, baking and further drying said coated body at an oven temperature of approximately 350 C., and finally hermetically sealing and exhausting said body at a temperature of 400 to 450 C.

2. The method of producing a light-diffusing coating on the interior surface of a hollow vitreous body which comprises preheating and drying said surface, depositing thereon a coating material consisting of a pigment incorporated in a solution of sodium silicate in distilled water, said solution having a specific gravity of 1.014, drying said applied coating at room temperature for a period of approximately 48 hours, and finally heating, air-drying, hermetically sealing and exhausting said body at elevated temperatures.

3. The method of making light-diffusing incandescent electric lamps which comprises preheating and drying the interior of vitreous bulbs, coating the said interior surface with a coating material consisting of a pigment incorporated in a solution of sodium silicate in distilled water, said solution having a specific gravity of 1.014, drying said applied coatin at room temperature for a period of approximately 48 hours, heating and further drying said coated bulb at elevated temperature, sealing a mount in said bulb, and finally exhausting said bulb and sealing the exhaust tube thereof at a temperature of 400 to 450 C.

4. The method of making light-diffusing incandescent electric lamps which comprises preheating and drying the interior of vitreous bulbs,

coating the said interior surface with a coating material consisting of a pigment incorporated in a solution of sodium silicate in distilled water, said solution having a specific gravity of 1.014, drying said applied coating at room temperature for a period of approximately 48 hours, heating and further drying said coated bulb, and finally forming the same into a lamp at a temperature of 400 to 450 C.

5. The method of making light-diffusing incandescent electric lamps which comprises preand then quickly at elevated temperature, and heating and drying the interior of vitreous bulbs, finally forming the same into a lamp at elevated coating the said interior surface with a coating temperature.

material consisting of lithopone incorporated in WALTER E. KOERNER.

a solution of sodium silicate in distilled water, said 5 ALFRED F. BAHLKE. solution having a specific gravity of 1.014, drying STUART F. MARVIN.

said coated bulb first slowly at room temperature