US2709766A

US2709766A - Fluorescent lamp

Info

Publication number: US2709766A
Application number: US229869A
Authority: US
Inventors: Nagy Rudolph; Eugene P Etzel
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1951-06-04
Filing date: 1951-06-04
Publication date: 1955-05-31
Anticipated expiration: 1972-05-31

Description

United States Patent FLUORESCENT LAMP Rudolph Nagy and Eugene P. Etzel, Upper Montclair, N. 5., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa a corporation of Pennsylvania No Drawing. Application June 4, 1951, Serial No. 229,869

'7 Claims. (Cl. 313-409) Our invention relates to fluorescent lamps and more particularly to binders for the fluorescent powder therein.

The inside surface of the envelope of a fluorescent lamp is coated with a luminescent powder, known as a phosphor, which emits visible light when excited by a source of radiation which is usually within the ultraviolet range. In order to effect adherence of the phosphor to the fluorescent lamp, a binder is commonly used with the phosphor coating. Various binders have been developed, but the one most used commercially consists of an organic substance, such as nitro-cellulose dissolved in a solvent, such as butyl acetate. After coating the lamp the organic binder is burned out by a process known as lehring.

While such organic binders have proved satisfactory in many respects, the fluorescent coatings still chip if the lamp is subjected to rough handling and mercury tracking may result if the lamp has mercury therein. Mercury tracking is caused by mercury globules striking the fluorescent coating and knocking it from the lamp envelope. This tracking problem is experienced chiefly in circular fluorescent lamps.

Therefore, the principal object of our invention is to provide an improved binder for finely divided particles such as phosphors.

Another object of our invention is to provide a binder for fluorescent lamp phosphors which will offer the maximum resistance to chipping and mercury tracking.

A further object of our invention is to improve the binding qualities of phosphor mixes by adding thereto a small proportion of powdered glass or glass forming materials.

Yet another object of our invention is to provide a glass which when added to the binder will not appreciably affect the light output of the lamp, either initially or at some other time during the life of the lamp.

Another object of our invention is to provide a method of applying a coating of luminescent particles to a surface, which coating has incorporated therein finely divided glass particles to aid in effecting adherence of the particles.

The novel features that we consider characteristic of my invention are set forth with particularity in the appended claims. The invention, itself, however, together with additional objects and advantages thereof may be best understood from the following description of specific embodiments.

In manufacturing fluorescent lamps, the phosphor is applied to the inside of the lamp by suspending it in a liquid vehicle, coating the inside surface with the suspension, and then evaporating the vehicle. In order to increase the adherence of the phosphor to the inside glass surface, a lacquer containing a binder is added to the vehicle. This lacquer commonly consists of an organic binder such as nitrocellulose and a solvent for the binder such as butyl acetate, amyl acetate, or ethylacetate. The solvent may also be used as the suspending vehicle for the phosphor. The final suspension and mixture which is used to coat the lamp is known to thetrade as the phosphor paint. This paint may also include other agents, as desired, such as one to increase its Wetting properties or a plasticizer.

We have found that the resistance of phosphor coatings in fluorescent lamps to chipping and mercury tracking may be decidedly improved by the addition of powdered glass to the binder used in the coating mixture. The glass is preferably a low melting point glass or chemical compound which will melt at lehring temperatures which are usually between 800 and 1300 F. In the practice of our invention, the glass may be mixed with the phosphor before it is suspended in the paint which is used to coat the inside surface of the fluorescent lamp envelope. The proportion of glass powder is not critical, but the optimum ratio appears to be approximately one part glass to 99 parts phosphor by weight? Preferably the glass powder is fine enough to pass a 400 mesh screen. be used.

If preferred, the glass binder may be added to the paint rather than mixing it with the phosphor prior to its suspension as was done above. This may be done by ballmilling the glass until a fine powder is produced. The powder is then suspended in an equal volume of binder lacquer and ballmilled once more. The resulting lacquer is mixed with the phosphor paint in such amounts so as to produce a ratio of approximately one part glass to 99 parts phosphor. The percentage of glass may be varied from .05 to 3 if so desired; however, one per cent appears to be optimum.

The following procedure was used in preparing sample lam s for test purposes. The glass powder was mixed with 150 Kg. of phosphor. The mixture of the phosphor and the glass was then added to 41 liters of butyl acetate. To this mixture was added 40 liters of nitrocellulose lacquer, which consisted of nitrocellulose dissolved in butyl acetate; the resultant mix was ballmilled for approximately 5 to 6 hours. After the ballmilling, another 84 liters of the nitrocellulose lacquer were added to the mixture; and the resultant product was ballmilled for approximately a half hour. Finally, an additional 168 liters of nitrocellulose lacquer were added; and the final product was mixed, as by means of an agitator. Lamps were then coated with the paint and lehred at ordinary lehring temperatures to remove the organic binder by burning in the presence of air.

The composition of the glass is important. In order to make a lamp coated with a phosphor containing an additive of glass commercially successful, the glass must not adversely affect the output or maintenance of the lamp. The following are raw mixes of glasses which have proved satisfactory.

Example I.A zinc aluminum phosphate glass Raw material ingredients: Parts by weight ZnO 81 Al(OH) 78 H3PO4 (85%) 98 The ingredients are preferably mixed in a Pyrex beaker and dried at 120-150 C; in an oven overnight. The dried mixture is then desirably ballmilled for 3 hours and fired at 1200 C. to produce a very fluid melt. The molten glass is poured onto a cold surface and ground to a fine powder by the usual mechanical means. The resulting glass has the following composition:

Component: Parts by weight ZnO 81 However, material passing 100 mesh can Example II.A zinc sodium bore-phosphate glass Raw material ingredients: Parts by weight Z110 44.7 Na2C03 1l./ H3303 6.2 H3P04 (85%) 40.2

The glass is prepared as in Example I. The resulting glass has the following composition:

Component: Parts by weight Na20 6.85 B203 3.45 P265 26.4

A complex boric oxide and phosphorus oxide glass having a low melting point and comprising:

Component: Per cent P205 2.87O

R2O3 10 or less R or less R0 15 or less has also proved satisfactory.

Example III Component: Per cent by weight P295 4.95

Lao 5.8

Example IV Component: Per cent by weight P205 9.4

(1210 7.0 LizO 10.5

Example V Component: Per cent by weight P205 50.0

SiOz 1.6

BaO 1.7

ZnO 6.7

Example VI Component: Per cent by weight P205 70.0 B203 5.0 ZnO 4.0 Si02 M 5-0 K20 15.0

Example VII Component: Per cent by weight P205 66.8

BaO 1.0

K20 16.6 ZnO 4.5

If more specific formulations are desired, the two following, which are derived from the above general formulation, may be used.

A. A low melting point glass consisting of the following components by weight: approximately 50% to about boric oxide, about 1% to about 15% phosphorous oxide as an additional network former, about 15% to about 25% total R0 and R20 content, and 0 to about 10% R203.

B. A low melting point glass consisting of the fol lowing ingredients in the given proportions by weight; phosphorous oxide, about 50% to about 75 SiOz and B203 as an additional network former, about 1% to about 18%; and R0 and R20, about 10% to 24%.

Examples It and 1V fall within the A formulation, and Examples Vi and VII fall with formulation B.

0f the above glasses, the zinc aluminum phosphate is preferable for use in production because it does not fuse as completely as the others thus facilitating the end cleaning after lehring, and the re-claiming of faulty lamps. The binding action of the z nc aluminum phosphate glass appears to be furnished by a sintering of the glass rather than an actual melting. The ability to re-claim lamps is important in reducing the shrinkage factor during manufacture. Where re-claiming and end cleaning are not important factors, the other glasses above are satisfactory since they do not appreciably reduce the lumens per watt output of the lamp at either the Zero hour reading or after hours of use. Other glasses may possibly be used but they are not preferred due to low maintenance and initial reduction of the output of the lamp.

The bulbs coated with one of the above glasses added to their coating mixture, showed increased resistance to mercury tracking and chipped coating. The bulbs were tested for chipping by placing them on a machine which vibrated them at a rapid rate. In lamps not embodying our invention, the phosphors rapidly flaked off while this was not true with lamps which had our glass binder therein.

It will be seen from the foregoing that we have provided an improved binder for effecting adherence of finely divided particles to supporting surfaces, as well as a method for applying the binders. When the glass binder is used with phosphors, they will offer maximum resistance to chipping and mercury tracking without adversely affecting the light output or the maintenance of the lamp.

While we have shown and described a specific embodiment of our invention, we are fully aware that many modifications thereof are possible. We do not intend to be restricted, therefore, except as is necessitated by the spirit and scope of the appended claims.

We claim:

1. A phosphor coating composition for coating 2. surface comprising finely divided particles and a binder to elfect adherence to said surface, said binder having therein approximately one part powdered glass for 99 parts of phosphor in said coating, said glass being a zinc aluminum phosphate glass.

2. A phosphor coating composition for coating 21 fluorescent lamp surface containing a binder to effect adherence of said phosphor to said surface, said binder comprising an organic substance and approximately one part glass for 99 parts of phosphor in said coating, said glass being a zinc aluminum phosphate glass.

3. A method of producing a phosphor coating on a surface comprising intimately mixing 1 part of zinc aluminum phosphate glass particles by Weight with 99 parts phosphor particles, suspending the mixture in a liquid vehicle containing an organic binder, applying a coating of the suspension to a surface, and heating the coating to burn out the organic binder and sinter the glass particles.

4. A coating composition for applying a phosphor coating to the inside surface of a fluorescent lamp envelope comprising, a binder, a solvent, and a finely divided phosphor capable of emitting visible light when exposed to ultraviolet radiation, said solvent being selected from the group consisting of butyl acetate, amyl acetate and ethyl acetate, said binder consisting of nitrocellulose and finely divided glass, said glass being comprised of about 81 parts by weight of zinc oxide, 51 parts by weight of aluminum oxide, and 64 parts by weight of phosphorus pentoxide, and the ratio by weight of said glass to said phosphor in said coating being from ODS/99.95 to 3/97.

5. A coating composition for applying a phosphor coating to the inside surface of a fluorescent lamp envelope comprising, a binder, a solvent, and a finely divided phosphor capable of emitting visible light when exposed to ultraviolet radiation, said solvent being selected from the group consisting of butyl acetate, amyl acetate and ethyl acetate, said binder consisting of nitrocellulose and finely divided glass, said glass being comprised of about 81 parts by weight of zinc oxide, 51 parts by weight of aluminum oxide, and 64 parts by weight of phosphorus pentoxide, and the ratio by weight of said glass to said phosphor in said coating being about 1 to 99.

6. In a fluorescent lamp, an envelope surface having a coating thereon, said coating consisting of a phosphor and a glass, said phosphor being capable of emitting visible light when exposed to ultraviolet radiation, said glass being sintered to said fluorescent lamp envelope surface and being comprised of about 81 parts by weight of zinc oxide, 51 parts by weight of aluminum oxide, and 64 parts by weight of phosphorus pentoxide, and the ratio of said glass to said phosphor in said coating being from ODS/99.95 to 3/97.

7. In a fluorescent lamp, an envelope surface having a coating thereon, said coating consisting of a phosphor and a glass, said phosphor being capable of emitting visible light when exposed to ultraviolet radiation, said glass being sintered to said fluorescent lamp envelope surface and being comprised of about 81 parts by weight of zinc oxide, 51 parts by weight of aluminum oxide, and 64 parts by weight of phosphorus pentoxide, and the ratio by weight of said glass to said phosphor in said coating being about 1 to 99.

References Cited in the file of this patent UNITED STATES PATENTS 2,203,898 Devries June 11, 1940 2,393,469 Hooley Jan. 22, 1946 2,400,147 Hooley May 14, 1946

Claims

6. IN A FLUORESCENT LAMP, AN ENVELOPE SURFACE HAVING A COATING THEREON, SAID COATING CONSISTING OF A PHOSPHOR AND A GLASS, SAID PHOSPHOR BEING CAPABLE OF EMITTING VISIBLE LIGHT WHEN EXPOSED TO ULTRAVIOLET RADIATION, SAID GLASS BEING SINTERED TO SAID FLUORESCENT LAMP ENVELOPE SURFACE AND BEING COMPRISED OF ABOUT 81 PARTS BY WEIGHT OF ZINC OXIDE, 51 PARTS BY WEIGHT OF ALUMINUM OXIDE, AND 64 PARTS BY WEIGHT OF PHOSPHORUS PENTOXIDE, AND THE RATIO OF SAID GLASS TO SAID PHOSPHOR IN SAID COATING BEING FROM 0.05/99.95 TO 3/97.