EP0181197A1

EP0181197A1 - Fluorescent lamp

Info

Publication number: EP0181197A1
Application number: EP85308047A
Authority: EP
Inventors: Akira c/o Patent Division of Taya; Hisami c/o Patent Division of Nira; Nobuyuki c/o Patent Division of Miyazaki; Takashi c/o Patent Division of Takayanagi
Original assignee: Asahi Glass Co Ltd; Toshiba Corp
Current assignee: Toshiba Corp; AGC Inc
Priority date: 1984-11-05
Filing date: 1985-11-05
Publication date: 1986-05-14
Also published as: KR900004821B1; JPS61110959A; KR860004452A

Abstract

A fluorescent lamp is disclosed which is provided on the outer surface of a glass tube thereof with a coating layer of a solvent-soluble fluorine-containing polymer containing an ultraviolet light absorbent. This fluorescent lamp suffers substantially no ultraviolet radiation, excels in such properties as tightness of adhesion of the coating layer to the glass tube, service life, transparency, heat-resisting property, and weather-resisting property, and is easy to manufacture.

Description

The present Application claims priority of Japanese patent application Serial No. 59-232926 filed November 5 1984.
This invention relates to a so-called ultravioletless fluorescent lamp which suffers ultraviolet radiation only minimally.
Heretofore, non-fading ultraviolet lamps (NU lamps) have come to be used in department stores, art galleries, museums, etc. as illuminating sources for places used in displaying articles which are vulnerable to light and, therefore, require special attention against the phenomenon of fading.
For the purpose of intercepting by absorption the ultraviolet light in the short wavelength region responsible for the phenomenon of fading, these NU lamps have the internal wall surfaces of their glass tubes coated with two layers, i.e. a lower layer of titanium dioxide (TiO ₂) and an upper layer of a fluorescent substance.
These NU lamps, however, have the following disadvantage as compared with lamps of the same class which incorporate no layer of titanium dioxide.

(1) The luminous flux is low (lower by about 5%).
(2) The color of the light is different.
(3) The color rendering property is low.
(4) The procedure of manufacture is complicated.

With a view to alleviating these drawbacks peculiar to the NU lamps as much as possible, an attempt has been made to decrease the thickness of layer of titanium dioxide.
This method, however, has entailed the disadvantage that the effect of titanium dioxide in absorbing ultraviolet light is no longer sufficient for the NU lamp to fulfil its function satisfactorily.
In the specification of Japanese Patent Application Laid-open Sho 58(1983)-47,058, there is proposed a method for covering the surface of the glass tube of an NU lamp with a thermally shrinkable tubular film made of such synthetic resin as polyvinyl chloride, polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, poly -&- caprolactam, polyhexamethylene adipamide, polycarbonate, or polymethyl methacrylate and containing an ultraviolet light absrobent.
In accordance with the known method described above, however, the thickness of the covering film is required to be increased because the amount of the ultraviolet light absorbent allowed to be incorporated in the synthetic resin is limited from the standpoint of compatibility, the amount of light passed through the wall of the glass tube is not sufficient because the occurance of an air layer between the glass and the film cannot be easily excluded completely, the properties of the fluorescent lamp such as tightness of adhesion of the covering film to the glass tube, service life, transparency, heat-resisting property, and weather-resisting property are not sufficient, and the fluorescent lamp itself is not easy to handle.
The inventors continued a diligent study devoted to overcoming the drawbacks suffered by the conventional method as described above. They have consequently found that a NU lamp free from the aforementioned drawbacks of the conventional method is obtained by forming on the outer surface of the glass tube of the NU lamp a coating layer of a solvent-soluble fluorine-containing polymer containing an ultraviolet light absorbent.
An object of this invention, therefore, is to provide a fluorescent lamp which suffers substantially no ultraviolet radiation, excels in such properties as tightness of adhesion of the coating film to the glass tube, service life, trans-parency, heat-resisting property, and weather-resisting property, and is easy to manufacture.
Fig. 1 and Fig. 2 are diagrams showing spectral energy distributions of typical fluorescent lamps embodying this invention. Fig. 3 is a diagram showing a spectral energy distribution of a fluorescent lamp involving no application of an ultraviolet light absorbent. Fig. 4 is a diagram showing a spectral energy distribution of a fluorescent lamp using titanium dioxide as an ultraviolet light absorbent.
The fluorescent lamp of this invention is characterized by being provided on the outer surface of a glass tube thereof with a coating layer of a solvent-soluble fluorine-containing polymer containing an ultraviolet light absorbent.
For the solvent-soluble fluorine-containing polymer to be used advantageously in the present invention, the intrinsic viscosity of this polymer is desired to fall in the range of 0.05 to 2.0 dl/g, preferably 0.07 to 0.8 dl/g, as measured in tetrahydrofuran at 30°C.
If the intrinsic viscosity is lower than the lower limit of the aforementioned range, the mechanical strength of the coating is not sufficient. If the intrinsic viscosity is higher the upper limit of the range, the composition of the polymer gains so much in viscosity that the concentration of the solution tends to be insufficient and the processibility of the polymer is impaired. A fluorine-containing polymer which is insoluble in a solvent proves unsuitable because it is incapable of forming a homogeneous film.
The aforementioned fluorine-containing polymer to be used in this invention can be an addition polymer type or a condensation polymer type.
The adiition polymer type fluorine-containing polymer is the addition polymer or addition copolymer of a fluorine-containing unsaturated compound containing a curing site such as hydroxyl group, epoxy group, carboxyl group, acid amide group, ester group, unsaturated bond, active hydrogen, or a halgen. The condensation polymer type fluorine-containing polymer is the epoxy resin possessing a fluorine-containing bifunctional group or the condesnate of a fluorine-containing diol, dibasic acid, dibasic anhydride, or diisocyanate and capable of forming an ester bond, an urethane bond, or an urea bond.
Further from the standpoint of the weather-resisting property and the mechanical property of the coating and the availability of the polymer, the fluorine-containing polymer is desired to be of an addition polymer type such as, for example, a copolymer of a fluoroolefin with a hydrocarbon vinyl ether.
For the aforementioned fluoroolefin-vinyl ether copolymer to be used advantageously in this invention, it is preferred to contain the units based on fluoroolefin and vinyl ether in respective proportions of 30 - 70 mol% and 70 - 30 mol%.
As the fluoroolefin moiety of the copolymer, tetrafluoroethylene or chlorotrifluoroethylene is proper selection. As the vinyl ether moiety of the copolymer, an alkylvinyl ether containing a straight, branched, or cyclic alkyl group of about two to eight carbon atoms is a proper selection.
The copolymer described above is desired to contain a comonomer moiety capable of providing a curing site in a concentration roughly in the range of 3 to 25 mol%.
As the comonomer capable of providing such a curing site, a funtional group-containing vinyl ether such as hydroxyalkyl-vinyl ether or glycidylvinyl ether is a proper selection.
The aforementioned copolymer is produced by causing a polymerization initiating agent or a polymerization initiating source such as an ionizing radiation to react upon a mixture of comonomers of prescribed proportions in the presence or absence of a polymerization medium thereby effecting a copolymerizing ·reaction.
When the fluorine-containing polymer to be used in the present invention possesses a curing site, it is allowed to incorporate therein a curing agent such as a polyfuntional compound capable of reacting with the curing site of the copolymer in a proportion in the range of 0.1 to 100 parts by weight, preferably 0.5 to 50 parts by weight, based on 100 parts by weight of the fluorine-containing polymer.
The fluorine-containing polymer can suitably incorporate therein a curing aid or a curing catalyst as occasion demands.
When a cold-curable film-forming composition is prepared by using a fluorine-containing polymer containing a curing site of hydroxyl group, a polyisocyanate or metal alkoxide can be used as the curing agent.
When this film-forming composition is prepared in a thermosetting type, a melamine resin curing agent, a urea resin curing agent, or a polybasic acid curing agent which is generally used for thermosetting acrylic coating materials can be used as the curing agent.
Typical examples of the aforementioned melamine resin curing agent are butylated methylol melamine resins, methylated methylol melamine resins, and e-oxy-m'odified methylol melamine resins. The degree of modification can be suitably selected in the range of 0 to 6 and the degree of self-condensation can also be suitably selected, depending on the kind of utility.
As the aforementioned urea resin curing agent, methylated urea resin or butylated urea resin, for example, can be used.
As the aforementioned polybasic acid curing agent, a longchain aliphatic dicarboxylic acid, an aromatic polycarboxylic acid or anhydride, or a block polyisocyanate can be used.
When the melamine resin curing agent or urea resin curing agent described above is used, the curing to be effected can be accelerated by addition thereto of an acidic catalyst.
When the film-forming composition is prepared by using a fluorine-containing polymer having a curing site of epoxy group, a polyamine, a polybasic carboxylic acid, a phenol, or a polyhydroxy compound, such as a phenol resin or a nonaromatic polyol can be used as a curing agent.
In the present invention, the ultraviolet light absorbent is incorporated in a proportion generally in the range of 0.5 to 30 parts by weight, preferably in the range of 1 to 25 parts by weight, based on 100 parts by weight of the fluorine containing polymer.
If the amount of the ultraviolet light absorbent is less than the lower limit of the aforementioned range, the thickness of the coating layer is required to be increased and consequently the amount of the fluorine-containing polymer to be increased for the purpose of fully attaining the effect in curbing the phenomenon of fading. If this amount exceeds the upper limit of the range, the coating layer tends to entail bleeding out the absorbent, degrade the transparency of the layer, and impair the tightness of adhesion of the layer on the outer surface of the glass tube of the fluorescent lamp.
As the ultraviolet light absorbent for the purpose of this invention, any of the various conventionally known ultraviolet light absorbents such as benzophenone type and benzotriazole type absorbents can be used. From the standpoint of characteristic of absorption, a benzotrioazole type ultraviolet light absorbent proves a desirable selection.
The film-forming composition containing the fluorine-containing polymer and the ultraviolet light absorbent is desired, from the standpoint of processibility, to be prepared in the form of a solution type coating material for the sake of this invention.
The solvent to be used in this coating material is desired to dissolve the fluorine-containing polymer and the ultraviolet light absorbent sufficiently and avoids corroding the outer surface of the glass tube of the fluorescent lamp. The volatility is also an important consideration for this solvent. Thus, it is desirable to use, in combination, two or more members selected suitably from the group consisting of aromatic hydrocarbons such as xylene and toluene, alcohols such as n-butanol, esters such as butyl acetate, ketones such as methyliscoutyl ketone, glycol ethers such as ethyl cellosolve, and saturated hydrocarbons such as n-hexane, ligroin, and mineral spirit.
The coating composition described above gives rise to a transparent coating of excellent gloss on volatilization of the solvent. The coating so formed may be used in its unmodified form as a lacquer type coating. It is, nevertheless, particularly desirable to obtain this coating as a curing coating by incorporating in the aforementioned fluorine-containing polymer a curing site and adding to the polymer, as a component of curing agent, a polyfunctional compound capable of reacting with the curing site.
To be used advantageously in the present invention, the coating layer formed on the outer surface of the glass tube is desired to have a thickness in the range of 5 to 200 µm, preferably 10 to 60 µm. If the thickness of the coating layer is greater than upper limit of the aforementioned range, the transparency of the produced coating is insufficient. Conversely if this thickness is smaller than the lower limit of the range, the effect of the coating layer in precluding the phenomenon of fading is impaired relatively and the coating tends to entail such defects as pinholes and, at the same time, the effect of the coating in preventing the glass tube, in case of accidental fracture, from being scattered in all directions. Thus, the thickness is desired to fall within the aforementioned range.
This coating composition is applied on the outer surface of the glass tube of the fluorescent lamp. The coating layer so formed may be given a curing treatment as occasion demand to form a clear coating.
Now, the present invention will be described more specifically below with reference to working examples.

Example 1

A terpolymer having an intrinsic viscosity of 0.42 dl/g as mesured in tetrahydrofuran at 30°C was prepared by polymerizing tetrafluoroethylene, cyclohexylvinyl ether, and hydroxybutylvinyl ether in a molar ratio of 50/40/10. A solution of 4.5 parts by weight of the flurine-containing polymer in 20 parts by weight of xylene and 0.5 part by weight of 2-hydroxy-4-n-octoxybenzophenone as an ultraviolet light absorbent and 0.83 part by weight of a polyisocyanate type curing agent (product of Japan Polyurethane Co., Ltd., marketed under trademark designation of "Coronate EH") were thoroughly mixed to form a homogeneous coating material.
Then, this coating composition was applied on the outer surface of a glass tube of a fluorescent lamp (product of Tokyo Shibaura Electric Co., Ltd. marketed under trade designation of FL20S.D) and heated at 150°C for five minutes to form a clear coating 30 µm in thickness.

Example 2

A four-component copolymer having an intrinsic viscosity of 0.23 dl/g as measured in tetrahydrofuran at 30 °C was prepared by polymerizing chlorotrifluoroethylene, cyclohexylvinyl ether, ethylvinyl ether, and hydroxybutyl vinyl ether in a molar ratio of 50/15/25/10. A solution of 4.5 parts by weight of the fluorine-containing polymer in 15 parts by weight of xylene and 0.5 part by weight of 2-(2'-hydroxy-3', 5'-ditertiary-butylphenyl)-5-chlorobenzotriazole as an ultraviolet light absorbent and 0.83 part by weight of a polyisocyanate type curing agent (the same curing agent as used in Example 1) were thoroughly mixed to form a homogeneous coating material. This coating material was applied on the outer surface of a glass tube of a fluorescent lamp (FL20S.D) and then heated at 150°C for five minutes to form a clear coating 30 µm in thickness.
The properties of the fluorescent lamps obtained in the foregoing working examples were as shown in the following table. In the table, the data given in the bracket "Comparative Experiment 1" represent the properties of a fluorescent lamp having no ultraviolet light absorbent applied on the outer surface of the glass tube thereof and those in the bracket "Comparative Experiment 2" represent the properties of a fluorescent lamp having a layer of titanium dioxide alone applied in a rate of 1.5 mg/cm² on the wall surface of the glass tube thereof.
Fig. 1, Fig. 2, and Fig. 3 represent spectral energy distribution curves of the fluorescent lamps obtained in Example 1, Example 2, and Comparative Experiments 1 and 2.
The coating layers obtained in the working examples described above were tested for ultraviolet light shielding property, transparency, and durability as follows.
A sample of the coating composition prepared in each of the working examples was applied in a dry thickness of 30p m with an applicator on a flat smooth glass sheet (2.5 mm in thickness) treated with a release agent in advance The applied layer was dried and cured, then immersed in hot water, and peeled off the glass sheet. The cured coating so separated was used as a test piece.
For comparison, a 90 : 10 (weight ratio) mixture of a varying synthetic resin and an ultraviolet light absorbent was tried to be extrusion molded into a film. Because of lack of compatibility, however, no homogeneous film could be obtained. Thus, a film obtained in a thickness of 50 µm by extrusion molding a mixture of 100 parts by weight of a synthetic resin and 0.5 part by weight of an ultraviolet absorbent, a proportion close to the limit of compatibility, was used as a comparative test piece. The synthetic resins used for comparision were polyethylene terephthalate (Comparative Experiment 3), polypropylene (Comparative Experiment 4), and poly-ε- caprolactam (Comparative Experiment 5). The ultraviolet light absorbent used therein was the same as that which was used in Example 1.
The ultraviolet light shielding property was determined by measuring an ultraviolet absorption spectrum of a given test piece and using the ratio of transmission found at a wavelength of 370 µm in the spectrum as the index thereof. The transparency and the durability were evaluated by measuring the change in the ratio of transmission at a wavelength of 500 µm before and after an accelerated test (carried out with a due cycle weathermether made by Suga Tester Co., Ltd., marketed under trade designation of "WEL- _SU_N-DC", for 400 hours). The results are shown in Table 2.
It is clear from the foregoing working examples, the fluorescent lamps according with the present invention have substantially equal total luminous fluxes and virtually equal light colors to the fluorescent lamps having no ultraviolet light absorbent applied thereon.
Moreover, these fluorescent lamps suffer notably lower transmittance of ultraviolet light than the fluorescent lamps having only a layer of titanium dioxide formed thereon. As noted from Fig. 1 and Fig. 3, they show extremely high absorption of light in the ultraviolet light region.
The coating layers obtained in acordance with the present invention far excel the coating layers based on synthetic resins not conforming with this invention, in terms of ultraviolet light shielding property, transparency, and durability.
In summary, the fluorescent lamps of the present invention have substantially equal total luminous fluxes and virtually equal change in light color to the fluorescent lamps having no ultraviolet light absorbent applied thereon. They are capable of intercepting ultraviolet light substantially completely.
Moreover, the fluorescent lamps of the present invention have the advantage of easier formability of the ultraviolet light absorbing layer than the conventional fluorescent lamps using titanium dioxide as an ultraviolet light absorbent.
Further, the fluorescent lamps of this invention far excel, in processability ultraviolet light shielding property, transparency, and durability, the fluorescent lamps provided with coatings based on other synthetic resins not conforming with this invention.

Claims

(1) A fluorescent lamp, characterized by being provided on the outer surface of a glass tube thereof with a coating layer of a solvent-soluble fluorine-containing polymer containing an ultravilet light absorbent.
(2) A fluorescent lamp according to Claim 1, wherein the intrinsic viscosity of said solvent-soluble fluorine-containing polymer as measured in tetrahydrofuran at 30°C falls in the range of 0.05 to 2.0 dl/g.
(3) A fluorescent lamp according to Claim 1 or Claim 2,wherein said solvent-soluble fluorine-containing polymer possessed at least one curing site selected from the class consisting of hydroxyl group, epoxy group, carboxyl group, acid a mide group, ester group, unsaturated bond, active hydrogen, and halogens.
(4) A fluorescent lamp according to any of Claims 1 through 3, wherein said solvent-soluble fluorine-containing polymer is a copolymer of a fluoroolefin with a hydrocarbon vinyl ether and contains the units based on fluoroolefin and vinyl ether in respective proportions of 30 - 70 mol% and 70 - 30 mol% and the unit based on hydroxyalkyl vinyl ether or glycidyl ether in a proportion of not more than 30 mol%.
(5) A fluorescent lamp according to any of Claims 1 through 4, wherein said ultraviolet light absorbent is contained in an amount in the range of 0.5 to 30 parts by weight, based on 100 parts by weight of said solvent-soluble fluorine-containing polymer.
(6) A fluorescent lamp according to any of Claim 1 through 5, wherein said coating layer has a thickness in the range of 5 to 200 µm.