CA1122155A - Method of applying protective coating on lamp envelope - Google Patents
Method of applying protective coating on lamp envelopeInfo
- Publication number
- CA1122155A CA1122155A CA000325520A CA325520A CA1122155A CA 1122155 A CA1122155 A CA 1122155A CA 000325520 A CA000325520 A CA 000325520A CA 325520 A CA325520 A CA 325520A CA 1122155 A CA1122155 A CA 1122155A
- Authority
- CA
- Canada
- Prior art keywords
- lamp
- coating
- envelope
- dispensing means
- dispensing
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F21—LIGHTING
- F21K—NON-ELECTRIC LIGHT SOURCES USING LUMINESCENCE; LIGHT SOURCES USING ELECTROCHEMILUMINESCENCE; LIGHT SOURCES USING CHARGES OF COMBUSTIBLE MATERIAL; LIGHT SOURCES USING SEMICONDUCTOR DEVICES AS LIGHT-GENERATING ELEMENTS; LIGHT SOURCES NOT OTHERWISE PROVIDED FOR
- F21K5/00—Light sources using charges of combustible material, e.g. illuminating flash devices
- F21K5/02—Light sources using charges of combustible material, e.g. illuminating flash devices ignited in a non-disrupting container, e.g. photo-flash bulb
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C17/00—Surface treatment of glass, not in the form of fibres or filaments, by coating
- C03C17/28—Surface treatment of glass, not in the form of fibres or filaments, by coating with organic material
- C03C17/32—Surface treatment of glass, not in the form of fibres or filaments, by coating with organic material with synthetic or natural resins
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J61/00—Gas-discharge or vapour-discharge lamps
- H01J61/02—Details
- H01J61/30—Vessels; Containers
- H01J61/35—Vessels; Containers provided with coatings on the walls thereof; Selection of materials for the coatings
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J61/00—Gas-discharge or vapour-discharge lamps
- H01J61/02—Details
- H01J61/50—Auxiliary parts or solid material within the envelope for reducing risk of explosion upon breakage of the envelope, e.g. for use in mines
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
- H01J9/20—Manufacture of screens on or from which an image or pattern is formed, picked up, converted or stored; Applying coatings to the vessel
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01K—ELECTRIC INCANDESCENT LAMPS
- H01K1/00—Details
- H01K1/28—Envelopes; Vessels
- H01K1/32—Envelopes; Vessels provided with coatings on the walls; Vessels or coatings thereon characterised by the material thereof
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01K—ELECTRIC INCANDESCENT LAMPS
- H01K3/00—Apparatus or processes adapted to the manufacture, installing, removal, or maintenance of incandescent lamps or parts thereof
- H01K3/005—Methods for coating the surface of the envelope
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01K—ELECTRIC INCANDESCENT LAMPS
- H01K7/00—Lamps for purposes other than general lighting
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D1/00—Processes for applying liquids or other fluent materials
- B05D1/002—Processes for applying liquids or other fluent materials the substrate being rotated
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D1/00—Processes for applying liquids or other fluent materials
- B05D1/26—Processes for applying liquids or other fluent materials performed by applying the liquid or other fluent material from an outlet device in contact with, or almost in contact with, the surface
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D2203/00—Other substrates
- B05D2203/30—Other inorganic substrates, e.g. ceramics, silicon
- B05D2203/35—Glass
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
- B05D3/06—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by exposure to radiation
- B05D3/061—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by exposure to radiation using U.V.
- B05D3/065—After-treatment
- B05D3/067—Curing or cross-linking the coating
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Manufacturing & Machinery (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- General Engineering & Computer Science (AREA)
- Application Of Or Painting With Fluid Materials (AREA)
Abstract
METHOD OF APPLYING PROTECTIVE COATING
ON LAMP ENVELOPE
ABSTRACT OF THE DISCLOSURE
A method of applying a protective light transmitting coating on the exterior surface of the glass envelope of a lamp, the method comprising: holding the lamp with its longitudinal axis disposed horizontally and rotating the lamp about its longitudinal axis; dispensing a liquid coating material onto the rotating lamp envelope from a dispensing means located above the lamp; and allowing the envelope coating to be cure-hardened, such as by irradiation. The method is particularly useful for applying an optically clear photopolymer coating on the glass envelope bf a photoflash lamp and curing the coating by irradiation with a source of ultraviolet light.
ON LAMP ENVELOPE
ABSTRACT OF THE DISCLOSURE
A method of applying a protective light transmitting coating on the exterior surface of the glass envelope of a lamp, the method comprising: holding the lamp with its longitudinal axis disposed horizontally and rotating the lamp about its longitudinal axis; dispensing a liquid coating material onto the rotating lamp envelope from a dispensing means located above the lamp; and allowing the envelope coating to be cure-hardened, such as by irradiation. The method is particularly useful for applying an optically clear photopolymer coating on the glass envelope bf a photoflash lamp and curing the coating by irradiation with a source of ultraviolet light.
Description
BACKGROUND OF THE INVENTION
This invention relates to lamps wi-th a protective envelope I coating and, more particularly, to an improved method for applying 1 such a coating on the glass envelope of a lamp. The method of the invention is particularly useful for applying a UV curable photopolymer as a protective coating on the exterior surface of a photoflash lamp.
A typical photoflash lamp comprises an hermetically sealed glass envelope, a quantity of combustible material located in the envelope, such as shredded zirconium or hafnium foil, and a combustion supporting gas, such as oxygen, at a pressure well above one atmosphere. The lamp B ¦ ~
. .
~, ~ . .. . . . .
.
.,~ .
.
.
Il f, - ~2~5~ ~ I
I!
-23,3~9 1 also includes an electrically or percussively activated I primer for igniting the cornbustible m aterial to flash the lamp. Durinq lamp flashing, the glass envelope is subject I to sever-e thermal shock due to hot globules oF metal oxide I impinging on the walls oF the larnp. As a result cracks and crazes occur in the glass and, at higher internal pressures, containment hecomes impossible. In order to reinforce the glass envelope and improve its containment capability, it has been common pracLice to app1y a protective ' lacquer coating on tne lamp envelope by means of a dip process. To build up the desired coating thickness, the glass envelope is generally dipped a number of times into a lacquer solution containing a solvent ancl a selected resin, typically cellulose acetate. After each dip, the I lamp is dried to evâporate the solvent ancl leave the desire-i coating of cellulose acetate, or whatever other plastic , resin is employed. -¦! In the typical solvent dipping proces for applying ~I protective coatings, a large number of photoflash lamps ¦ are loaded on a rack and then successively dipped in a solver I solution and oven dried three or four times to build up the i desired coating thickness. Such a process is time consumingl ¦
¦ uses a large area o-F production floor space, and involves ¦
¦ considerable hand labor, all of which adds signi-Ficantly t I to manufac~uring costs. Further, as the lacquer solution I includes a highly flamable so1vent, such as acetone, ¦, an inadvertent flashing of one of the lamps in either the ¦' dip bath or drying oven can ignite the solvent fumes. Tp ¦~ substantially reduce or elirninate this hazard, costly ¦, automatic extinguishing equipment must be employed. in ¦ the event of a solvent tgnition, the resulting down time and consumption of fire extinguishing chemicals also adds to the manufacturing costs.
Another approach to providing a more economical and improved containing vessel is described in U.S. Patent ¦ 3,893,7g7, wherein a thermoplastic coating, such as poly-carbonate, is vacuum formed onto the exterTor surface of the glass envelope. The rnethod of applying the coating , comprises: placing the glass envelope within a preformed l~o I sleeve of the thermoplastic material; drawing a vacuum I in the space between the thermoplastic sieeve and the glass ¦, envelope; and, sirnultaneously heating the assembly ¦~ incrementally âlong its ler)gth7 whereby the temperature z _ _ ~ I
D-20,379 ~ and vacuum cause the thermoplastic to be incrementally formed onto the glass envelope with the interface substantially free of voids, inclusions and the like. Although this method provides an optically Il clear protective coating by means of a significantly faster and I safer manufacturing process which may be easily integrated on automated production machinery, it does present the disadvantage of requiring prefarmed plastic sleeves which must be individually desiyned for each Ij different lamp type, made or purchased, stocked, and fed into the ¦I production apparatus which applies the sleeves onto the envelopes.
lQ ll Further approaches toward providing improved protective coatings ¦ for lamps have related to the use of UV curable photopolymers. For ¦~ example, one prior method of coating a flashlamp with a photopolymer comprises the following steps. First, the lamp is held vertically with l the base up and dipped into a vat of the photopolymer at 60C and 1 extracted very slowly, the dip process taking about 45 seconds. The wet-coated lamp is then inverted with the base down and rotated at a speed of from one-half to four revolutions per second under a UV lamp, the cure period taking about 30 seconds. The resulting I -coating thickness is about 0.020". According to an alternative method, the flashlamp, while revolving, is sprayed with the liquid photopolymer and then transFerred directly into the ultraviolet lamp chamber. Another known method is somewhat similar except that either long or short stran~s of fiber glass are employed to reinforce the ¦ photopolymer coating. ;~
ll An immersion process for applying a UV cured coating on a photo-¦¦ flash lamp is also described in a published Japanese patent application ¦¦ identified as Public Disclosure Number 52-7720 and having a publication j date of January 21, 1977; a continuation of a continuation-in-part !l of a corresponding U.S. application issued as U.S. Patent 4,076,489 ~ on February 28~ 1978.
A somewhat critical aspect of the aforementioned UV cured coatings~
is that the shape and uniformity of thickness depends on the flow characteristics of the photopolymer "
-20,37 ¦~ r-esill ~s inrluencecl by the rorce oF gravity, orientation of tlle lamp a-rter coatin~, and viscosity o-F the resin.
! Cllanges in resin viscosity resnltirl~ ~rom chclrlges in il temperatul-e afrect both the repeatability of the shape of , the coating ancl the uniFormity of thickness. These ¦ irreg~larities are retained once the coating is hal-dened.
In the case of UV cured coatings used to protect flashlanlps I, from rup1:ure at the time of flashing, thin coating regions ¦I resulting from improper resin distribution can result in !I containment failures. The comparative integrity or ¦l containment for various types of vessel constructions can be evaluated by the use of special test lamp~, ~uch as I described in U.S. Patent 3,955,912 assigned to the present i assignee, which controllably induce bursting of the lamp i upon ignition. Accordingly, such test larnps were coated with UV cured photopolyrrlers by means of various mmersion techniques and compared in flash tests with similar test 1amps coated in accordance with the present invention.
The results showed that the repeatable uni-formity of the coating applied in accordance with the inven~ion provided sigllTFicantly superior containment characteristics over the lamps coated with the prior art immersion techniques.
SUMMARY OF THE INVENTION
Accotdingly, it is an object of this invention to provide an improved method for applying a protective coating on a lamp envelope.
A principa1 object of the invention is to provide an improved method for applying an ultraviolet curable coating ¦ on a photoflash lamp which minimizes coating irregularities pr~duced by gravity-indLIced flow or reflow of the coatiny.
These and other objects, advantages and fea~ures are attained in accordance with the invention by a method comprisirlg: holding the lamp with its longitudinal axis disposed horizontally and rotating the lamp about its longitudinal aX.is; dispensing a liguid coating material onto the envelope of the rotating lamp from dispensing means 70cated above the lamp; and allowing the coating on the lamp enyelope to be cure-hardened. To assure dispensing of the coating material frorn one end to the other of the rotating lamp envelope, relative linear motion may be provideld between the lamp and djspensing means, or the rotating lamp may be held in a fixed position be70w a fixed dispening means having a plurality of openings through which the __1~__ !i 5~
-20,379 ~ liquid coating material is dispensed. The method is particularly useful for applying photopolymer coatings on lamps which are substantially cure-hardened by irradiation with a source of ultraviolet light.
. . , ~ Rotation of the horizontally disposed lamp while coating material is dispensed from a location above the lamp exhibits surprising effectiveness in stabilizing the coating shape, once applied, for periods of up to thirty seconds prior to exposure for cure-hardening.
This method is particularly efFective for overcoming the viscosity Il characteristics encountered when using coating materials of UV curable 1l photopolymers. Uniform, repeatable coatings can be applied at il production line speeds, and when applied to photoflash lamps, the ,¦ resulting protectively coating vessel exhibits a superior containment i~ capability, along with excellent photometric characteristics. In 1~ addition to the above mentioned improvements in the resulting product, lS 1ll the method of applying lamp coatings according to the invention provides several advantages to the lamp manufacturing process. For example, the process can be solvent free; it requires a minimum of floor space; and it can be readily adapted to automated lamp production ~ apparatus. Further, cure time is reduced to periods oF less than a ,I minute. A hard cure is effected immediately, without the need for warehousing to assure a complete cure.
_RIEF DESCRIPTION OF THE DRAWINGS
¦ This invention will be more fully described hereinafter in conjunc-~ tion with the accompanying drawings, in which:
~1 FIG. 1 is an enlarged elevational view, partly in section, of an electrically ignitable photoflash lamp having a protective coating applied in accordance with the invention;
FIG. 2 illustrates a first method of applying a liquid coating ¦! material in accordance with the invention;
30 1l FIG. 3 is a cross-section schematically illustrating one method of cure-hardening the lamp coating by irradiation in accordance with the I invention; and ¦I FIG. 4 illustrates a second method of applying the liquid coating i' material in accordance with the invention.
I !
This invention relates to lamps wi-th a protective envelope I coating and, more particularly, to an improved method for applying 1 such a coating on the glass envelope of a lamp. The method of the invention is particularly useful for applying a UV curable photopolymer as a protective coating on the exterior surface of a photoflash lamp.
A typical photoflash lamp comprises an hermetically sealed glass envelope, a quantity of combustible material located in the envelope, such as shredded zirconium or hafnium foil, and a combustion supporting gas, such as oxygen, at a pressure well above one atmosphere. The lamp B ¦ ~
. .
~, ~ . .. . . . .
.
.,~ .
.
.
Il f, - ~2~5~ ~ I
I!
-23,3~9 1 also includes an electrically or percussively activated I primer for igniting the cornbustible m aterial to flash the lamp. Durinq lamp flashing, the glass envelope is subject I to sever-e thermal shock due to hot globules oF metal oxide I impinging on the walls oF the larnp. As a result cracks and crazes occur in the glass and, at higher internal pressures, containment hecomes impossible. In order to reinforce the glass envelope and improve its containment capability, it has been common pracLice to app1y a protective ' lacquer coating on tne lamp envelope by means of a dip process. To build up the desired coating thickness, the glass envelope is generally dipped a number of times into a lacquer solution containing a solvent ancl a selected resin, typically cellulose acetate. After each dip, the I lamp is dried to evâporate the solvent ancl leave the desire-i coating of cellulose acetate, or whatever other plastic , resin is employed. -¦! In the typical solvent dipping proces for applying ~I protective coatings, a large number of photoflash lamps ¦ are loaded on a rack and then successively dipped in a solver I solution and oven dried three or four times to build up the i desired coating thickness. Such a process is time consumingl ¦
¦ uses a large area o-F production floor space, and involves ¦
¦ considerable hand labor, all of which adds signi-Ficantly t I to manufac~uring costs. Further, as the lacquer solution I includes a highly flamable so1vent, such as acetone, ¦, an inadvertent flashing of one of the lamps in either the ¦' dip bath or drying oven can ignite the solvent fumes. Tp ¦~ substantially reduce or elirninate this hazard, costly ¦, automatic extinguishing equipment must be employed. in ¦ the event of a solvent tgnition, the resulting down time and consumption of fire extinguishing chemicals also adds to the manufacturing costs.
Another approach to providing a more economical and improved containing vessel is described in U.S. Patent ¦ 3,893,7g7, wherein a thermoplastic coating, such as poly-carbonate, is vacuum formed onto the exterTor surface of the glass envelope. The rnethod of applying the coating , comprises: placing the glass envelope within a preformed l~o I sleeve of the thermoplastic material; drawing a vacuum I in the space between the thermoplastic sieeve and the glass ¦, envelope; and, sirnultaneously heating the assembly ¦~ incrementally âlong its ler)gth7 whereby the temperature z _ _ ~ I
D-20,379 ~ and vacuum cause the thermoplastic to be incrementally formed onto the glass envelope with the interface substantially free of voids, inclusions and the like. Although this method provides an optically Il clear protective coating by means of a significantly faster and I safer manufacturing process which may be easily integrated on automated production machinery, it does present the disadvantage of requiring prefarmed plastic sleeves which must be individually desiyned for each Ij different lamp type, made or purchased, stocked, and fed into the ¦I production apparatus which applies the sleeves onto the envelopes.
lQ ll Further approaches toward providing improved protective coatings ¦ for lamps have related to the use of UV curable photopolymers. For ¦~ example, one prior method of coating a flashlamp with a photopolymer comprises the following steps. First, the lamp is held vertically with l the base up and dipped into a vat of the photopolymer at 60C and 1 extracted very slowly, the dip process taking about 45 seconds. The wet-coated lamp is then inverted with the base down and rotated at a speed of from one-half to four revolutions per second under a UV lamp, the cure period taking about 30 seconds. The resulting I -coating thickness is about 0.020". According to an alternative method, the flashlamp, while revolving, is sprayed with the liquid photopolymer and then transFerred directly into the ultraviolet lamp chamber. Another known method is somewhat similar except that either long or short stran~s of fiber glass are employed to reinforce the ¦ photopolymer coating. ;~
ll An immersion process for applying a UV cured coating on a photo-¦¦ flash lamp is also described in a published Japanese patent application ¦¦ identified as Public Disclosure Number 52-7720 and having a publication j date of January 21, 1977; a continuation of a continuation-in-part !l of a corresponding U.S. application issued as U.S. Patent 4,076,489 ~ on February 28~ 1978.
A somewhat critical aspect of the aforementioned UV cured coatings~
is that the shape and uniformity of thickness depends on the flow characteristics of the photopolymer "
-20,37 ¦~ r-esill ~s inrluencecl by the rorce oF gravity, orientation of tlle lamp a-rter coatin~, and viscosity o-F the resin.
! Cllanges in resin viscosity resnltirl~ ~rom chclrlges in il temperatul-e afrect both the repeatability of the shape of , the coating ancl the uniFormity of thickness. These ¦ irreg~larities are retained once the coating is hal-dened.
In the case of UV cured coatings used to protect flashlanlps I, from rup1:ure at the time of flashing, thin coating regions ¦I resulting from improper resin distribution can result in !I containment failures. The comparative integrity or ¦l containment for various types of vessel constructions can be evaluated by the use of special test lamp~, ~uch as I described in U.S. Patent 3,955,912 assigned to the present i assignee, which controllably induce bursting of the lamp i upon ignition. Accordingly, such test larnps were coated with UV cured photopolyrrlers by means of various mmersion techniques and compared in flash tests with similar test 1amps coated in accordance with the present invention.
The results showed that the repeatable uni-formity of the coating applied in accordance with the inven~ion provided sigllTFicantly superior containment characteristics over the lamps coated with the prior art immersion techniques.
SUMMARY OF THE INVENTION
Accotdingly, it is an object of this invention to provide an improved method for applying a protective coating on a lamp envelope.
A principa1 object of the invention is to provide an improved method for applying an ultraviolet curable coating ¦ on a photoflash lamp which minimizes coating irregularities pr~duced by gravity-indLIced flow or reflow of the coatiny.
These and other objects, advantages and fea~ures are attained in accordance with the invention by a method comprisirlg: holding the lamp with its longitudinal axis disposed horizontally and rotating the lamp about its longitudinal aX.is; dispensing a liguid coating material onto the envelope of the rotating lamp from dispensing means 70cated above the lamp; and allowing the coating on the lamp enyelope to be cure-hardened. To assure dispensing of the coating material frorn one end to the other of the rotating lamp envelope, relative linear motion may be provideld between the lamp and djspensing means, or the rotating lamp may be held in a fixed position be70w a fixed dispening means having a plurality of openings through which the __1~__ !i 5~
-20,379 ~ liquid coating material is dispensed. The method is particularly useful for applying photopolymer coatings on lamps which are substantially cure-hardened by irradiation with a source of ultraviolet light.
. . , ~ Rotation of the horizontally disposed lamp while coating material is dispensed from a location above the lamp exhibits surprising effectiveness in stabilizing the coating shape, once applied, for periods of up to thirty seconds prior to exposure for cure-hardening.
This method is particularly efFective for overcoming the viscosity Il characteristics encountered when using coating materials of UV curable 1l photopolymers. Uniform, repeatable coatings can be applied at il production line speeds, and when applied to photoflash lamps, the ,¦ resulting protectively coating vessel exhibits a superior containment i~ capability, along with excellent photometric characteristics. In 1~ addition to the above mentioned improvements in the resulting product, lS 1ll the method of applying lamp coatings according to the invention provides several advantages to the lamp manufacturing process. For example, the process can be solvent free; it requires a minimum of floor space; and it can be readily adapted to automated lamp production ~ apparatus. Further, cure time is reduced to periods oF less than a ,I minute. A hard cure is effected immediately, without the need for warehousing to assure a complete cure.
_RIEF DESCRIPTION OF THE DRAWINGS
¦ This invention will be more fully described hereinafter in conjunc-~ tion with the accompanying drawings, in which:
~1 FIG. 1 is an enlarged elevational view, partly in section, of an electrically ignitable photoflash lamp having a protective coating applied in accordance with the invention;
FIG. 2 illustrates a first method of applying a liquid coating ¦! material in accordance with the invention;
30 1l FIG. 3 is a cross-section schematically illustrating one method of cure-hardening the lamp coating by irradiation in accordance with the I invention; and ¦I FIG. 4 illustrates a second method of applying the liquid coating i' material in accordance with the invention.
I !
2~5si D-20,379 DESCRIPTION OF PREFERRED EMBODIMENT
The teachings of the present invention are suitable for the application of several different types of liquid protective coating 1 materials to the exterior envelope surface of a wide variety of lamps ll oF different sizes and shapes; however, the ihvention is particularly advantageous as a method for applying a UV-cured photopolymer coating on photo-flash lamps having tubular shaped envelopes with a volume of less than one cubic centimeter. This advantage rests in the signifi- !
Il cantly improved coating uniformity which is obtained, which in turn ~ results in the superior containment capability exhibited by a small ¦ photoflash lamps coated in accordance with the invention. For purposes i of example, the invention will be described as applied to the elec-¦ trically ignitable, filament-type photoflash lamp illustrated in FIG. l;¦
I¦ however, it will be understood that the same principals are applicable !¦ to high voltage or percussively ignited flashlamps.
¦ Referring to FIG. l, one embodiment of the coated lamp l is illustrated comprising an hermetically sealed lamp envelope 2 of glass tubing having a press 4 defining a base end thereof and an exhaust tip l 6 defining the other end thereof. Supported by the press 4 is an ignition means comprising a pair of lead-in wires 8 and lO extending through and sealed into the press base. A filament l2 spans the inner ends of the lead-in wires, and beads of primer l4 and 16 are typically located on the inner ends of the lead-in wires 8 and l3, respectively, at their junction with the filament. Typically, the lamp envelope 2 I has an internal diameter of less than one-half inch, and an internal ¦, volume of less than one cubic centimeter. A combustion-supporting ¦~ gas, such as oxygen, and a filamentary combustible material l8, such as shredded zirconium or hafnium foil, is disposed within the lamp Il envelope. Typically, the combustion-supporting gas fill is at a ~ pressure exceeding one atmosphere, with the more recent subminiature ¦ lamp types having oxygen fill pressures of up to several atmospheres.
~z~
D-20,379 As will be described in more detail hereinafter, the exterior surface of the glass envelope 2 is covered with a protective coating comprising a photopolymer 20.
A percussive type photoflash 1amp is described in several prior patents of the presert assignee; For example, fl - 6a - I
, I
~2 ~
D-20,379 U.S. Patent No. 3,674,411. As described there;n, the percussive lamp also includes a sea1ed glass envelope containing a filamentary combustible material and a combustion-supporting gas; however, the ignition means comprises a metal primer tube sealed in and extending from one end oF the glass envelope and containing a coaxially disposed wire anvil partially coated with a charge of fulminating material.
The high voltage type photoflash lamp is described in a number of Il patents of the present assignee; for example, U.S. Patent 4,059,388 and 4,059,389. As described therein, each of the lamps includes a 10 I sealed glass envelope containing a filamentary combustible material and a combustion-supporting gas; however, in the first-mentioned patent, the ignition means comprises a mass of primer material bridging a pair of lead in wires, one of which is enclosed in an insulating I sleeve. In the second-mentioned patent, the ignition means includes a 15 l' pair of spaced apart lead-in wires with spherically shaped terminations;a glass frit is coated over the lead-in wires, and primer material is coated over the frit-coated terminations. I
Il Although somewhat different in structure and operation, the fila-!~ ment, high-voltage, and percussive lamps are similar and that in each 20 ~¦ the ignition means is attached to one end of the lamp envelope and ~I disposed in operative relationship with respect to the filamentary ¦¦ combustible material. More specifically, the ignition filament 12 ofthe flashlamp of FIG. 1 is incandesced electrically by current passing l through the metal filament support leads 8 and 10, whereupon the 25 ¦ incandescent filament ignites the beads of primer 1~ and 16 which in turn ignite the combustible 18 disposed within the lamp envelope to ! provide the actinic light output. Operation of the percussive-type lamp is initiated by an impact onto the primer tube to cause deflagra-1~ tion of the fulminating material up through the tube to ignite the combustion material disposed within the lamp envelope. Operation of ' Il - 7 li ~ ~2~
D-20,379 the high-voltage pulse from, e.y., a piezoelectric crystal, is applied across the two lead-in wires, electrical breakdown of the primer causes its deflagration which~ in turn, ignites the shredded metallic combustible.
- 7a -"
r-~L~f~ .L~D~
D-20,379 ~ A number of advantages are obtained by using a photopolymer asprotective coating 20. The term "photopolymer" is underskood to mean a radiation curable polymer. Rapid curing of such a polymer results from any stimulus that generates free radicals. For example, free radical initiation can be effectively provided by a source of ultraviolet (UV) light or electron beams.
Ultraviolet light in the 185 to 400 nanometer wavelength range is required for UV cures. UV light from commercial mercury vapor, mercury-metal halide~ or pulsed xenon lamps is effective in the ,I required wavelength range.
Curing time with UV light can range from fractions of a second to a minute or two depending upon the film thickness, polymer structure¦
~1 UV light intensity, and initiator type concentration. Further, the Il curing can be effected in air, under the vacuum, or in an inert gas ll atmosphere, such as nitrogen.
¦~ The photopolymer basically comprises prepolymers used alone or ~¦ diluted with reactive monomers. To render the material UV curable, however, one must use a photosensitizer or photoinitiator (such as ~I benzoin ether) which will directly or indirectly give free radicals ~ when exposed to UV radiation, even at room temperature.
¦~ Examples of prepolymers include polyesters, epoxy acrylates, acrylics, polyurethanes, thiolenes, alkenes, or any of a number of ~¦ general groups. Examples of reactive monomers include styrenes, acrylic~, ¦ and methacrylic esters, and polyfunctional monomers, such as ethylene ll glycol diacrylate, trimethylol propane triacrylate, and pentaerythritol~
¦ tetraacrylate. The monomers also serve as viscosity reducing agents and, as such, they aresolvents which dissolve or are miscible with the prepolymer. Accordingly, the reactive monomers reduce the viscosity Il of the blend to workable levels and/or impart desirable properties il to the cured film.
Specific photopolymers we have found to be useful in coating , photoflash lamps are thiolene based materials available from W.~.
Grace ~ Company, Maryland and identified as ~CC Blend 15 ancl ~lend XRCP-7211. Approxirnately 99 percent by weight of these thiolene -20,379 ~ based photopolymers comprise a blend of prepolymers, such as di- or polyth;opolymers and di- or polyene-polymers; the balance - ~A -2~.~5~ `
D-20,~ of tIIe mixtllre compris~s a photoinitiatc)r, sucI~ as benzoin j cthel- or aroIllatic ket~ne, e.g., benzophene, an(l stabilizers, I~ which are small (luantities of free raclical scavengers.
fl Tl1e flow and viscosity ci1arac~eristics of the licluid li photopolymer can be acIjusted by addiIlg fume~ silica to I increase ti1e thixotropicity o~ the mixture. ~rhe increase~
viscosity enables application of a heavier coating and reduces gravity induced runback of the wet coating prior to ; cure. The viscosity can be decreased by hea;ing, or adding monomel-s as discussed above ¦ The photopolyrner compositions referred to above result ,i in an essentially solvent free process and solvent-free I coating. It is to be understood, however, that the method i ¦, to be described hereinafter is equally suitabl~ for use ¦¦ with solvent-containing photopolymers.
An exarnple of a liquid photopolymer that we have found ¦ to be particularly useful for coating photoflash lamps in I accordance with the present invention is an acrylo-urethane ¦ resin, available -Frorn the Hughson Chemical Company as Type No. 3Q75-20 or 3254-ll, with a viscosity near 7,gOO
centipose at 25~C.
In accordance with the present invention, we have discovered a significantly improved method for providing ; an optically clear protective coating on the exterior surface c?f the glass envelope of the lamp which minimizes the coating irregularities produced by grav;ty-induced flow or re-flow of the coating. As a result, the coating provide a superior containment vessel. The method pro~ides a significantly faster, saFer and more economical manuracturin~
process, and it may easily be integrated ireto automated production machinery.
According to the invention, the UV-curable photopolymer material is dispensed from above unto a horizontal, rotating lamp. Preferably, the liquid coating material is dispensed by means of a mechanically activated syringe which keeps the volume flow rate cons~ant, and thus, which is independent of the viscosity of the material. Horizoneal rotation of the specimen stabilizes the coating shape, once applied, for periods of up to thirty seconds prior to exposure to ultraviolet light for curing. We have founcl that in this rnanner uniform, repeatable coatings can be applied at production line speeds.
One method of applying the coating in accordance with the invention is illustrated in FIG. 2. ,he lamp l having a glass envelope 2 is held in a horizontal position. More I
I
D ?~/ ,79 sI-eci r ically, consj~cI- ihe longitlldinal aYis "a" passing thrc)~ h thc bas~ oF the l~mp, forrIie~ ~y press l~, an~ the end of th~ lam~ opp~site tlla~ base, intllis instance the exi~ust tip 6. The lamp 1 is held with its longitudiIlal ~ axis "a" dispos~cI hori~on~ally by means of a pincer-type holding h~acI 22 ~hich clamps th~ exterior portions of the metallic lead-in wires 8 and 10. The head ~2 may comprise a portion of a lathe-type mechanisrI-l which rotates the lamp about its longitudinal axis "a". While the horizontally disposed lamp envelope 2 is rotate(I in this manner,a needle-type dispensing means 24, located above the larnp, dispenses a liquicl c~ating material 20' unto the glass envelope 2 of the rotating lamp. In this embodiment there 1, is 2 relative linear motion provided between the lamp and ` the dispensing means to cause the coating material to cover ¦
¦ the ro~ating lamp envelope from one end to the other. More ¦
particularly, in ~IG. 2, the rotating lamp 1 is shown in a fix~d position while the dispensing means 2It above the lamp , is moved in a 1inear path from left to right, as illustrated ¦ by the arrow. Alternatively, the dispensing means may be ¦ held in a fixed position and the roating lamp may be moved li in a linear path with respect thereto. On the other hand, j both thelamp and the dispensing means may be moved in parallel but opposite directions, or in ~:he same direction I in parallel at different speqds~
1~ ¦ In a specific application of the method illustrated in ~I`G. 2, the above-mentioned photopolymer (Hughson Chemical ¦ Company Type 3075-20~ an acrylo--urathane resin with a i viscosity near 7,800 centipoise at 25C) was metered by ~ means of a mechanically ac~ivated syrirlge through a surgical j needle 24 having a ~6-gau~e size and a length of 1.25 ¦ inch. The dispensing end of the needle was spaced 0.2 inch from the surface of the lamp being coated. The volume ¦ flow rate was adjusted to provide approximately 0.05 cubic ¦ centimeters of resin per second. The motion Ot the needle ¦ 24 along the length of the lamp was 0.0448 inch per lamp ¦ rotation. The lamp rotation rate was 158 rpm, and flow was terminated near the tip of the lamp. After the conclusi n of the dispensing step, the lamp was allowed to remain rotating for a predetermined delay period, ranging from 7 seconds to 12 seconds, prior to the step of curing the coating by ultraviolet irradiation.
¦ Followin9 the above described coating and delay steps;
j the rotatingJ horizontal lamp 1 was exposed to UV radiation I --10-- 1, !
1'~ .
D-20,379 ~ having a peak wavelength near 313 nanometers generated by ten fluorescent lamps 26 (GTE Sylvania Incorporated Type F6T55 having an internal coating of No. 2021 Phospnor) arranged in a cylindrical fashion, as schematically illustrated in the cross-section of FIG. 3. Curing of the resin took place in nitrogen at a distance of 2 inches From the sources 26 in forty seconds. For example, in FIG. 3 the circular ll dashed-line 28 represents the position of the quartz tubing that may be i 'f used to provide the nitrogen purged container within which lamp 1 is Il held. The solid circular line 30 at the outer periphery represents 1O fl the cylindrical internal reflective housing containing the UV sources. f The cured coating products by this method measured 0.023 inch in thickness.
Il Subsequent to the curing step and post-cure cooling, a lubricant ¦I may be applied, such as by spraying, over the coating 20. This also ll functions as an antistàtic agent. Suitable lubricant materials include ; li Dow Corning type DC 230, which is a silicone in textile spirits, and f Dupont products such as the aqueous Duponol* (a sodium lauryl sulfate), Merpol* (a long chain alcohol-ethylene oxide condensate), and ~elec*
(an alcohol phosphate).
,~ Coatings produced according to the invention are more uniform in thickness than that provided by the previously described prior art ¦I techniques. This in turn provides reliable coating perFormance with ¦¦ regard to preventing rupture at the time of flashing. For example, ¦I this is particularly illustrated by Table I, below which illustrates ~ the comparative containment capabilities of lamp coatings applied by ~I different techniques, along with a comparative indication of the ¦¦ coa~ing irregularity. The lamps employed in obtaining the flash testing data of Table I were of the type described in U.S. Patent 3,955,912, I, which are particularly designed to controllably induce bursting of 1I the lamp upon ignition. In the first test (Test-l), the test lamp fl specimens, once dipped according to the indicated prior art technique, ,i .
Il * Trademark of E.I. Du Pont De Nemours & Co.
~, , ~,~ , _ 1 1 D-20,379 were immediately exposed to UV radiation while the tip remained down.
The cured coatings were irregular and thin in the press area 4. The thin area failed to provide adequate protection -Frorn rupture at the time of flashing. Test lamps similarly dippecl, bu-t remaining tip I down for periods exceeding 2 to 3 seconds before curing tip down, produced even more irregular coatings, resulting in higher coating failures.
llA -1' ~
D-20,3,J In a seconcl test (Tes~-2), test larnps were sirnilarly n coated but were inverted immcdiately ~fter dipping, pcrmilLi n9 t he resin to re~istrib-Ite (reflow) over the lclInp prior to curin9. The amo~nt of time allow~d for reFlow ¦
5,~ affected the uniForInity of tile coatin~ tickness as well.
. The longer tne reflow time the more non-uniforrn the coating. I
The third test (Test-3) illustrates the results i achieved with rest larnp.s coatecl in accordance with the I
present invention~ The significant improvement in 10. containment and the uniformity of coating thickness is evident.
I TABLE I
I Coating Difference in Failures Coating ~ ~lo. of Causi ng Thickness I
Test Description Lamps Rupt1Ire Lamp End-to-Enid I Test-l Immerslon coat, 10 80% 33%
tip~down cure I Test-2 Irnmersion coat, 52 23% 13%
I tip-up cure--! preceded by 2-sec. reflow .
j Test-3 horizontal 48 t5% ~3%
I rotating coat ¦ ~ollowed by ~ I
: ~ delay of up to : I 12 seconds prior to UV cure . I
The followingTable 2 relates to flash testing with
The teachings of the present invention are suitable for the application of several different types of liquid protective coating 1 materials to the exterior envelope surface of a wide variety of lamps ll oF different sizes and shapes; however, the ihvention is particularly advantageous as a method for applying a UV-cured photopolymer coating on photo-flash lamps having tubular shaped envelopes with a volume of less than one cubic centimeter. This advantage rests in the signifi- !
Il cantly improved coating uniformity which is obtained, which in turn ~ results in the superior containment capability exhibited by a small ¦ photoflash lamps coated in accordance with the invention. For purposes i of example, the invention will be described as applied to the elec-¦ trically ignitable, filament-type photoflash lamp illustrated in FIG. l;¦
I¦ however, it will be understood that the same principals are applicable !¦ to high voltage or percussively ignited flashlamps.
¦ Referring to FIG. l, one embodiment of the coated lamp l is illustrated comprising an hermetically sealed lamp envelope 2 of glass tubing having a press 4 defining a base end thereof and an exhaust tip l 6 defining the other end thereof. Supported by the press 4 is an ignition means comprising a pair of lead-in wires 8 and lO extending through and sealed into the press base. A filament l2 spans the inner ends of the lead-in wires, and beads of primer l4 and 16 are typically located on the inner ends of the lead-in wires 8 and l3, respectively, at their junction with the filament. Typically, the lamp envelope 2 I has an internal diameter of less than one-half inch, and an internal ¦, volume of less than one cubic centimeter. A combustion-supporting ¦~ gas, such as oxygen, and a filamentary combustible material l8, such as shredded zirconium or hafnium foil, is disposed within the lamp Il envelope. Typically, the combustion-supporting gas fill is at a ~ pressure exceeding one atmosphere, with the more recent subminiature ¦ lamp types having oxygen fill pressures of up to several atmospheres.
~z~
D-20,379 As will be described in more detail hereinafter, the exterior surface of the glass envelope 2 is covered with a protective coating comprising a photopolymer 20.
A percussive type photoflash 1amp is described in several prior patents of the presert assignee; For example, fl - 6a - I
, I
~2 ~
D-20,379 U.S. Patent No. 3,674,411. As described there;n, the percussive lamp also includes a sea1ed glass envelope containing a filamentary combustible material and a combustion-supporting gas; however, the ignition means comprises a metal primer tube sealed in and extending from one end oF the glass envelope and containing a coaxially disposed wire anvil partially coated with a charge of fulminating material.
The high voltage type photoflash lamp is described in a number of Il patents of the present assignee; for example, U.S. Patent 4,059,388 and 4,059,389. As described therein, each of the lamps includes a 10 I sealed glass envelope containing a filamentary combustible material and a combustion-supporting gas; however, in the first-mentioned patent, the ignition means comprises a mass of primer material bridging a pair of lead in wires, one of which is enclosed in an insulating I sleeve. In the second-mentioned patent, the ignition means includes a 15 l' pair of spaced apart lead-in wires with spherically shaped terminations;a glass frit is coated over the lead-in wires, and primer material is coated over the frit-coated terminations. I
Il Although somewhat different in structure and operation, the fila-!~ ment, high-voltage, and percussive lamps are similar and that in each 20 ~¦ the ignition means is attached to one end of the lamp envelope and ~I disposed in operative relationship with respect to the filamentary ¦¦ combustible material. More specifically, the ignition filament 12 ofthe flashlamp of FIG. 1 is incandesced electrically by current passing l through the metal filament support leads 8 and 10, whereupon the 25 ¦ incandescent filament ignites the beads of primer 1~ and 16 which in turn ignite the combustible 18 disposed within the lamp envelope to ! provide the actinic light output. Operation of the percussive-type lamp is initiated by an impact onto the primer tube to cause deflagra-1~ tion of the fulminating material up through the tube to ignite the combustion material disposed within the lamp envelope. Operation of ' Il - 7 li ~ ~2~
D-20,379 the high-voltage pulse from, e.y., a piezoelectric crystal, is applied across the two lead-in wires, electrical breakdown of the primer causes its deflagration which~ in turn, ignites the shredded metallic combustible.
- 7a -"
r-~L~f~ .L~D~
D-20,379 ~ A number of advantages are obtained by using a photopolymer asprotective coating 20. The term "photopolymer" is underskood to mean a radiation curable polymer. Rapid curing of such a polymer results from any stimulus that generates free radicals. For example, free radical initiation can be effectively provided by a source of ultraviolet (UV) light or electron beams.
Ultraviolet light in the 185 to 400 nanometer wavelength range is required for UV cures. UV light from commercial mercury vapor, mercury-metal halide~ or pulsed xenon lamps is effective in the ,I required wavelength range.
Curing time with UV light can range from fractions of a second to a minute or two depending upon the film thickness, polymer structure¦
~1 UV light intensity, and initiator type concentration. Further, the Il curing can be effected in air, under the vacuum, or in an inert gas ll atmosphere, such as nitrogen.
¦~ The photopolymer basically comprises prepolymers used alone or ~¦ diluted with reactive monomers. To render the material UV curable, however, one must use a photosensitizer or photoinitiator (such as ~I benzoin ether) which will directly or indirectly give free radicals ~ when exposed to UV radiation, even at room temperature.
¦~ Examples of prepolymers include polyesters, epoxy acrylates, acrylics, polyurethanes, thiolenes, alkenes, or any of a number of ~¦ general groups. Examples of reactive monomers include styrenes, acrylic~, ¦ and methacrylic esters, and polyfunctional monomers, such as ethylene ll glycol diacrylate, trimethylol propane triacrylate, and pentaerythritol~
¦ tetraacrylate. The monomers also serve as viscosity reducing agents and, as such, they aresolvents which dissolve or are miscible with the prepolymer. Accordingly, the reactive monomers reduce the viscosity Il of the blend to workable levels and/or impart desirable properties il to the cured film.
Specific photopolymers we have found to be useful in coating , photoflash lamps are thiolene based materials available from W.~.
Grace ~ Company, Maryland and identified as ~CC Blend 15 ancl ~lend XRCP-7211. Approxirnately 99 percent by weight of these thiolene -20,379 ~ based photopolymers comprise a blend of prepolymers, such as di- or polyth;opolymers and di- or polyene-polymers; the balance - ~A -2~.~5~ `
D-20,~ of tIIe mixtllre compris~s a photoinitiatc)r, sucI~ as benzoin j cthel- or aroIllatic ket~ne, e.g., benzophene, an(l stabilizers, I~ which are small (luantities of free raclical scavengers.
fl Tl1e flow and viscosity ci1arac~eristics of the licluid li photopolymer can be acIjusted by addiIlg fume~ silica to I increase ti1e thixotropicity o~ the mixture. ~rhe increase~
viscosity enables application of a heavier coating and reduces gravity induced runback of the wet coating prior to ; cure. The viscosity can be decreased by hea;ing, or adding monomel-s as discussed above ¦ The photopolyrner compositions referred to above result ,i in an essentially solvent free process and solvent-free I coating. It is to be understood, however, that the method i ¦, to be described hereinafter is equally suitabl~ for use ¦¦ with solvent-containing photopolymers.
An exarnple of a liquid photopolymer that we have found ¦ to be particularly useful for coating photoflash lamps in I accordance with the present invention is an acrylo-urethane ¦ resin, available -Frorn the Hughson Chemical Company as Type No. 3Q75-20 or 3254-ll, with a viscosity near 7,gOO
centipose at 25~C.
In accordance with the present invention, we have discovered a significantly improved method for providing ; an optically clear protective coating on the exterior surface c?f the glass envelope of the lamp which minimizes the coating irregularities produced by grav;ty-induced flow or re-flow of the coating. As a result, the coating provide a superior containment vessel. The method pro~ides a significantly faster, saFer and more economical manuracturin~
process, and it may easily be integrated ireto automated production machinery.
According to the invention, the UV-curable photopolymer material is dispensed from above unto a horizontal, rotating lamp. Preferably, the liquid coating material is dispensed by means of a mechanically activated syringe which keeps the volume flow rate cons~ant, and thus, which is independent of the viscosity of the material. Horizoneal rotation of the specimen stabilizes the coating shape, once applied, for periods of up to thirty seconds prior to exposure to ultraviolet light for curing. We have founcl that in this rnanner uniform, repeatable coatings can be applied at production line speeds.
One method of applying the coating in accordance with the invention is illustrated in FIG. 2. ,he lamp l having a glass envelope 2 is held in a horizontal position. More I
I
D ?~/ ,79 sI-eci r ically, consj~cI- ihe longitlldinal aYis "a" passing thrc)~ h thc bas~ oF the l~mp, forrIie~ ~y press l~, an~ the end of th~ lam~ opp~site tlla~ base, intllis instance the exi~ust tip 6. The lamp 1 is held with its longitudiIlal ~ axis "a" dispos~cI hori~on~ally by means of a pincer-type holding h~acI 22 ~hich clamps th~ exterior portions of the metallic lead-in wires 8 and 10. The head ~2 may comprise a portion of a lathe-type mechanisrI-l which rotates the lamp about its longitudinal axis "a". While the horizontally disposed lamp envelope 2 is rotate(I in this manner,a needle-type dispensing means 24, located above the larnp, dispenses a liquicl c~ating material 20' unto the glass envelope 2 of the rotating lamp. In this embodiment there 1, is 2 relative linear motion provided between the lamp and ` the dispensing means to cause the coating material to cover ¦
¦ the ro~ating lamp envelope from one end to the other. More ¦
particularly, in ~IG. 2, the rotating lamp 1 is shown in a fix~d position while the dispensing means 2It above the lamp , is moved in a 1inear path from left to right, as illustrated ¦ by the arrow. Alternatively, the dispensing means may be ¦ held in a fixed position and the roating lamp may be moved li in a linear path with respect thereto. On the other hand, j both thelamp and the dispensing means may be moved in parallel but opposite directions, or in ~:he same direction I in parallel at different speqds~
1~ ¦ In a specific application of the method illustrated in ~I`G. 2, the above-mentioned photopolymer (Hughson Chemical ¦ Company Type 3075-20~ an acrylo--urathane resin with a i viscosity near 7,800 centipoise at 25C) was metered by ~ means of a mechanically ac~ivated syrirlge through a surgical j needle 24 having a ~6-gau~e size and a length of 1.25 ¦ inch. The dispensing end of the needle was spaced 0.2 inch from the surface of the lamp being coated. The volume ¦ flow rate was adjusted to provide approximately 0.05 cubic ¦ centimeters of resin per second. The motion Ot the needle ¦ 24 along the length of the lamp was 0.0448 inch per lamp ¦ rotation. The lamp rotation rate was 158 rpm, and flow was terminated near the tip of the lamp. After the conclusi n of the dispensing step, the lamp was allowed to remain rotating for a predetermined delay period, ranging from 7 seconds to 12 seconds, prior to the step of curing the coating by ultraviolet irradiation.
¦ Followin9 the above described coating and delay steps;
j the rotatingJ horizontal lamp 1 was exposed to UV radiation I --10-- 1, !
1'~ .
D-20,379 ~ having a peak wavelength near 313 nanometers generated by ten fluorescent lamps 26 (GTE Sylvania Incorporated Type F6T55 having an internal coating of No. 2021 Phospnor) arranged in a cylindrical fashion, as schematically illustrated in the cross-section of FIG. 3. Curing of the resin took place in nitrogen at a distance of 2 inches From the sources 26 in forty seconds. For example, in FIG. 3 the circular ll dashed-line 28 represents the position of the quartz tubing that may be i 'f used to provide the nitrogen purged container within which lamp 1 is Il held. The solid circular line 30 at the outer periphery represents 1O fl the cylindrical internal reflective housing containing the UV sources. f The cured coating products by this method measured 0.023 inch in thickness.
Il Subsequent to the curing step and post-cure cooling, a lubricant ¦I may be applied, such as by spraying, over the coating 20. This also ll functions as an antistàtic agent. Suitable lubricant materials include ; li Dow Corning type DC 230, which is a silicone in textile spirits, and f Dupont products such as the aqueous Duponol* (a sodium lauryl sulfate), Merpol* (a long chain alcohol-ethylene oxide condensate), and ~elec*
(an alcohol phosphate).
,~ Coatings produced according to the invention are more uniform in thickness than that provided by the previously described prior art ¦I techniques. This in turn provides reliable coating perFormance with ¦¦ regard to preventing rupture at the time of flashing. For example, ¦I this is particularly illustrated by Table I, below which illustrates ~ the comparative containment capabilities of lamp coatings applied by ~I different techniques, along with a comparative indication of the ¦¦ coa~ing irregularity. The lamps employed in obtaining the flash testing data of Table I were of the type described in U.S. Patent 3,955,912, I, which are particularly designed to controllably induce bursting of 1I the lamp upon ignition. In the first test (Test-l), the test lamp fl specimens, once dipped according to the indicated prior art technique, ,i .
Il * Trademark of E.I. Du Pont De Nemours & Co.
~, , ~,~ , _ 1 1 D-20,379 were immediately exposed to UV radiation while the tip remained down.
The cured coatings were irregular and thin in the press area 4. The thin area failed to provide adequate protection -Frorn rupture at the time of flashing. Test lamps similarly dippecl, bu-t remaining tip I down for periods exceeding 2 to 3 seconds before curing tip down, produced even more irregular coatings, resulting in higher coating failures.
llA -1' ~
D-20,3,J In a seconcl test (Tes~-2), test larnps were sirnilarly n coated but were inverted immcdiately ~fter dipping, pcrmilLi n9 t he resin to re~istrib-Ite (reflow) over the lclInp prior to curin9. The amo~nt of time allow~d for reFlow ¦
5,~ affected the uniForInity of tile coatin~ tickness as well.
. The longer tne reflow time the more non-uniforrn the coating. I
The third test (Test-3) illustrates the results i achieved with rest larnp.s coatecl in accordance with the I
present invention~ The significant improvement in 10. containment and the uniformity of coating thickness is evident.
I TABLE I
I Coating Difference in Failures Coating ~ ~lo. of Causi ng Thickness I
Test Description Lamps Rupt1Ire Lamp End-to-Enid I Test-l Immerslon coat, 10 80% 33%
tip~down cure I Test-2 Irnmersion coat, 52 23% 13%
I tip-up cure--! preceded by 2-sec. reflow .
j Test-3 horizontal 48 t5% ~3%
I rotating coat ¦ ~ollowed by ~ I
: ~ delay of up to : I 12 seconds prior to UV cure . I
The followingTable 2 relates to flash testing with
3 ¦ regular production lamps. In Test-4, the regular lamps : . were coated according to the invention and exposed to UV
I radiation within a 12 second delay period after conclusion : ' of the step during which the coating was dispensed. Test-5 ¦~ provides a control group and relates to uncoated lamps oF
35 ¦ the same type.
: . .
TABLE 2_ . Coating DiFference in Failures Coati ng .
No.. of Causing Thickness Test Description Lamps Rupture Lamp End-to-En d _ . .... , . . _ I
Test-4 Less than 12 sec. 29 C~ - 2~
j stabilize.before .
~ exposure 1~5 I Test-5 Uncoated lamps lO 1U0% Not Applicable ¦ of same type I
The foregoing tables therefore clearly illustrate the effectiveness of the coating method of the invention in preventing rupture at the time of Flashing. Further, as ( D-20,3-j~ evideIlt from Table 2, the preferrecI clelay tirnes bet~een j the conclusion of resin cIispensirl~ and the begirlning of UV
¦ curing are less than 12 seconds.
~ An alternative emboclimellt for disperlsing the liquid I coating material 20' is illustrated in FIG. 4 In this instance, there is n~ relativ~ linear motion between the dispensing means and the rotating lamp. More specifically, as illustrated, the overheacl dispensing means 32 is fixed ~ and provided with a plurality of openings, or needle ori-fices 33, through which the liquid coating rnaterial 20' is dispensed onto the exterior surface of lamp 1, which is held in a fixed position while being rotated about its I longitudinal axis "a" under the dispensing means 32. A
j sufficient number of needle oriFices 33 are provided and I arranged so as to cause the dispensed coating material 20' ¦ to cover the rotating lamp envelope from one end to another, as illustrated I Variations of the above-described coating application ¦ technique have been tested and provecl to be effective.
I For example~ the opening size of each o~ the circular I~ ori~ice no~zles may range from l~ x 10 6 square inches ¦I to 5 x 10 3 square inches. Further, rectangular orifice li nozzles may be employed. The lamp rotation speed may be at a fjxed rate selected from a range oF 24 to 300 rpm. I
1 25 I In the case where there is relative linear motion between the lamp and the dispensing means, the traverse speeds may range from 0.010 inch to 0.125 inch per lamp revolu~iorl.
Anothe r preferred coating material is an epoxy-urethane ' type UV-cure resin. The traverse direction is not 1imited , to that shown in FIG. 2 but may travel from the tip of the ¦1 lamp toward the press 4.
Other modifications of the basic method include the use of elliptical or other orifice shapes. A plurality of I needles, or nozzles, all of the same slze and shape or ; 35 with combinations of various sizes and shapes may be used.
A vari~ble ro~ation speed or an oscillating motion may be employed during resin application.
Further, it may be quite desirable to provide a ¦ rotatton o~ the lamp during irradiation (the curing step) I which is at a substantially diFferent speed than the rotation or the lamp under the dispensing means. Variable I or intermittent rotation may be employed during exposure I' i'. ' .
~-20,37~ ¦, to UV radiat;on. The steps of tne rnethod rnay be repeated ¦l to build up a precl~ternlined Final coating thickness. Other II types of UV sources may be employed wherein the spectrum ! and power density are commensurate with the curing require ¦, mer-ts of given UV-cure resins, or a combinationoF UV sources II with differincJ UV emission may be used to provide a similar !~ effect. Another particularly desirable -feature for providing improved viscosity control is to employ heated or chilled 1 coating dispensers for preconclitioning the resin to facilitate 1 dispensing. Prior to the curing step, the delay period t step may include the use of racliant energy for facilitating ;
distribution of the coating applied by the dispensing means to thereby provide a smooth uniform coatin~ of the ¦ photopolymer on the surface of the glass envelope. Forced ¦ air or a mechanical blade may also be employed to assist in distribution of the applied coating. In certain instances it may ~e desirable during the curing phase to partially ¦
I cure the lamp while in a horizontal position followed ¦¦ by additional cure of the lamp coating in a non-hori~ontal position.
Regarding the various type resins that may be employed, the viscosities may range from 250 centipose to 106 ¦ centipose at 25C. Heating or chilling of the dispel,ser may then be employed to provide a viscosity at the ~5 application temperature of between 4000 and 7000 centipoise.
Although the invention has been described with respect to specific embodiments, it will be appreciated that modifications and changes may be made by those skilled in I the art without departing from the true spirit and scope ¦ o~ the invention. For example, the described coating method is also applicable to spherical or bulb shaped lamps, other l ~-than tubular, associated with other lightin~ applications, such as incandescent, fluorescent, and other types of arc l discharge lamps. Further, the method is not lim7ted to ¦ the application ofphotopolymer coatings but may be also employed with air-cure, moisture-cure, heat~cure, or hot m-lt type co tings.
.
I radiation within a 12 second delay period after conclusion : ' of the step during which the coating was dispensed. Test-5 ¦~ provides a control group and relates to uncoated lamps oF
35 ¦ the same type.
: . .
TABLE 2_ . Coating DiFference in Failures Coati ng .
No.. of Causing Thickness Test Description Lamps Rupture Lamp End-to-En d _ . .... , . . _ I
Test-4 Less than 12 sec. 29 C~ - 2~
j stabilize.before .
~ exposure 1~5 I Test-5 Uncoated lamps lO 1U0% Not Applicable ¦ of same type I
The foregoing tables therefore clearly illustrate the effectiveness of the coating method of the invention in preventing rupture at the time of Flashing. Further, as ( D-20,3-j~ evideIlt from Table 2, the preferrecI clelay tirnes bet~een j the conclusion of resin cIispensirl~ and the begirlning of UV
¦ curing are less than 12 seconds.
~ An alternative emboclimellt for disperlsing the liquid I coating material 20' is illustrated in FIG. 4 In this instance, there is n~ relativ~ linear motion between the dispensing means and the rotating lamp. More specifically, as illustrated, the overheacl dispensing means 32 is fixed ~ and provided with a plurality of openings, or needle ori-fices 33, through which the liquid coating rnaterial 20' is dispensed onto the exterior surface of lamp 1, which is held in a fixed position while being rotated about its I longitudinal axis "a" under the dispensing means 32. A
j sufficient number of needle oriFices 33 are provided and I arranged so as to cause the dispensed coating material 20' ¦ to cover the rotating lamp envelope from one end to another, as illustrated I Variations of the above-described coating application ¦ technique have been tested and provecl to be effective.
I For example~ the opening size of each o~ the circular I~ ori~ice no~zles may range from l~ x 10 6 square inches ¦I to 5 x 10 3 square inches. Further, rectangular orifice li nozzles may be employed. The lamp rotation speed may be at a fjxed rate selected from a range oF 24 to 300 rpm. I
1 25 I In the case where there is relative linear motion between the lamp and the dispensing means, the traverse speeds may range from 0.010 inch to 0.125 inch per lamp revolu~iorl.
Anothe r preferred coating material is an epoxy-urethane ' type UV-cure resin. The traverse direction is not 1imited , to that shown in FIG. 2 but may travel from the tip of the ¦1 lamp toward the press 4.
Other modifications of the basic method include the use of elliptical or other orifice shapes. A plurality of I needles, or nozzles, all of the same slze and shape or ; 35 with combinations of various sizes and shapes may be used.
A vari~ble ro~ation speed or an oscillating motion may be employed during resin application.
Further, it may be quite desirable to provide a ¦ rotatton o~ the lamp during irradiation (the curing step) I which is at a substantially diFferent speed than the rotation or the lamp under the dispensing means. Variable I or intermittent rotation may be employed during exposure I' i'. ' .
~-20,37~ ¦, to UV radiat;on. The steps of tne rnethod rnay be repeated ¦l to build up a precl~ternlined Final coating thickness. Other II types of UV sources may be employed wherein the spectrum ! and power density are commensurate with the curing require ¦, mer-ts of given UV-cure resins, or a combinationoF UV sources II with differincJ UV emission may be used to provide a similar !~ effect. Another particularly desirable -feature for providing improved viscosity control is to employ heated or chilled 1 coating dispensers for preconclitioning the resin to facilitate 1 dispensing. Prior to the curing step, the delay period t step may include the use of racliant energy for facilitating ;
distribution of the coating applied by the dispensing means to thereby provide a smooth uniform coatin~ of the ¦ photopolymer on the surface of the glass envelope. Forced ¦ air or a mechanical blade may also be employed to assist in distribution of the applied coating. In certain instances it may ~e desirable during the curing phase to partially ¦
I cure the lamp while in a horizontal position followed ¦¦ by additional cure of the lamp coating in a non-hori~ontal position.
Regarding the various type resins that may be employed, the viscosities may range from 250 centipose to 106 ¦ centipose at 25C. Heating or chilling of the dispel,ser may then be employed to provide a viscosity at the ~5 application temperature of between 4000 and 7000 centipoise.
Although the invention has been described with respect to specific embodiments, it will be appreciated that modifications and changes may be made by those skilled in I the art without departing from the true spirit and scope ¦ o~ the invention. For example, the described coating method is also applicable to spherical or bulb shaped lamps, other l ~-than tubular, associated with other lightin~ applications, such as incandescent, fluorescent, and other types of arc l discharge lamps. Further, the method is not lim7ted to ¦ the application ofphotopolymer coatings but may be also employed with air-cure, moisture-cure, heat~cure, or hot m-lt type co tings.
.
Claims (11)
1. A method of applying a protective light-transmitting coating on the exterior surface of a lamp envelope, said lamp having a longi-tudinal axis passing through a base. of the lamp and the end of the lamp opposite said base, said method comprising:
holding said lamp with said longitudinal axis thereof disposed horizontally and rotating said lamp about said longitudinal axis;
flow-dispensing a liquid photopolymer coating material onto the unheated envelope of said rotating lamp from dispensing means located above said lamp while maintaining a condition of no linear motion between said dispensing means and said rotating lamp, said dispensing means having a plurality of openings through which said liquid coating material is dispensed, said openings being arranged along the length of said lamp to cause said dispensed coating material to coyer said rotating lamp envelope from one end to the other; and allowing the coating of said lamp envelope to be cure-hardened.
holding said lamp with said longitudinal axis thereof disposed horizontally and rotating said lamp about said longitudinal axis;
flow-dispensing a liquid photopolymer coating material onto the unheated envelope of said rotating lamp from dispensing means located above said lamp while maintaining a condition of no linear motion between said dispensing means and said rotating lamp, said dispensing means having a plurality of openings through which said liquid coating material is dispensed, said openings being arranged along the length of said lamp to cause said dispensed coating material to coyer said rotating lamp envelope from one end to the other; and allowing the coating of said lamp envelope to be cure-hardened.
2. The method of Claim 1 wherein said lamp has an hermetically sealed tubular glass envelope and includes ignition means sealed through the base of said glass envelope and having an exterior metallic portion extending from said envelope, the end of said glass envelope Opposite said base defining an exhaust tip, and said lamp is held horizontally and rotated by means clamping said exterior metallic portion of the ignition means.
3. The method of Claim 1 wherein the coating on said lamp envelope is cured by irradiation.
4. The method of Claim 1 wherein said dispensing means is fixed, and said lamp is held in a fixed position while being rotated under said dispensing means.
5. The method of Claim 1 wherein said coating material is a liquid photopolymer comprising a UV curable synthetic polymer containing an organic photoinitiator or photosensitizer.
6. The method of Claim 5 wherein said dispensing means is temperature controlled to maintain said dispensed liquid photopolymer at a predetermined viscosity.
7. The method of Claim 5 wherein said liquid photopolymer is dispensed by means including a syringe for maintaining a constant flow rate.
8. The method of Claim 5 wherein said step of allowing the coating to be cure-hardened comprises rotation of said lamp while irradiating the coated envelope with a source of ultraviolet light for a predetermined period.
9. The method of Claim 8 wherein the rotation of said lamp during irradiation is at a substantially different speed than the rotation of said lamp under said dispensing means.
10. The method of Claim 8 including the further step of rotating said lamp For a predetermined delay period between the conclusion of said dispensing step and the start of said step OF curing by ultraviolet irradiation.
11. The method of Claim 10 wherein said delay period step includes the use of radiant energy for facilitating distribution of the coating applied by said dispensing means to thereby provide a smooth uniform coating of said photopolymer on the surface of said glass envelope.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US89627378A | 1978-04-14 | 1978-04-14 | |
| US896,273 | 1978-04-14 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1122155A true CA1122155A (en) | 1982-04-20 |
Family
ID=25405932
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000325520A Expired CA1122155A (en) | 1978-04-14 | 1979-04-12 | Method of applying protective coating on lamp envelope |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPS556785A (en) |
| BE (1) | BE875552A (en) |
| CA (1) | CA1122155A (en) |
| DE (1) | DE2915411A1 (en) |
| GB (1) | GB2018624B (en) |
| NL (1) | NL7902913A (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA1139711A (en) * | 1979-04-20 | 1983-01-18 | Burleigh H. Leach | Method of applying protective coating on lamp envelope |
| IT1141905B (en) | 1980-02-22 | 1986-10-08 | Siv Soc Italiana Vetro | PROCEDURE FOR OBTAINING A TRANSPARENT COATING ON NORMAL OR SAFETY GLASS SLABS |
| FR2598405A1 (en) * | 1986-05-07 | 1987-11-13 | Bouvet Vernis | BOTTLE REPAIR PROCESS |
| DE4335319A1 (en) * | 1993-10-15 | 1995-04-20 | Walter Holzer | Process and apparatus for the slurry-coating of coiled glass tubes |
| GB2283188B (en) * | 1993-10-26 | 1997-01-15 | Balmoral Group | Coated pipes and methods of making them |
| WO1995011761A1 (en) * | 1993-10-26 | 1995-05-04 | Balmoral Group Limited | Coated pipes and methods of making them |
| US7824595B2 (en) | 2004-08-13 | 2010-11-02 | Perma-Pipe, Inc. | Method and system for cast molding a fluid conduit |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS4841188U (en) * | 1971-09-16 | 1973-05-25 |
-
1979
- 1979-04-11 GB GB7912868A patent/GB2018624B/en not_active Expired
- 1979-04-12 CA CA000325520A patent/CA1122155A/en not_active Expired
- 1979-04-12 NL NL7902913A patent/NL7902913A/en not_active Application Discontinuation
- 1979-04-13 BE BE2/57731A patent/BE875552A/en not_active IP Right Cessation
- 1979-04-13 JP JP4442579A patent/JPS556785A/en active Granted
- 1979-04-17 DE DE19792915411 patent/DE2915411A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| GB2018624A (en) | 1979-10-24 |
| BE875552A (en) | 1979-07-31 |
| JPS5729801B2 (en) | 1982-06-24 |
| GB2018624B (en) | 1982-05-19 |
| JPS556785A (en) | 1980-01-18 |
| NL7902913A (en) | 1979-10-16 |
| DE2915411A1 (en) | 1979-10-25 |
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