GB1588368A - Flame retardant radiation sensitive element - Google Patents

Abstract

The radiation-sensitive element consists of a carrier which carries a layer of a composition which can be photo-polymerised. The composition consists of (1) at least one compound which can be addition polymerised and is ethylenically unsaturated, (2) an initiator which can be activated in the ultraviolet to visible range of the spectrum, and (3) at least 20% by weight of a binding agent which can be polymerised and itself contains at least 5% by weight of acrylonitrile, there being at least 5% by weight of halogen, related to the total weight of the composition, in said composition, the halogen being bonded in a covalent manner to at least one component of the composition. The element is flame-retarding and can be used as a photoresist or as a soldering mask.

Description

(54) FLAME RETARDANT RADIATION SENSITIVE ELEMENT (71) We, E. I. DU PONT DE NEMOURS AND COMPANY, a Corporation organised and existing under the laws of the State of Delaware, United States of America, of Wilmington, State of Delaware, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to radiation sensitive elements. More particularly, this invention relates to such elements which contain photopolymerizable compositions. Still more particularly, it relates to photopolymerizable elements which are flame retardant.

Radiation sensitive elements, i.e., dry layers of radiation sensitive compositions on a film support, are well known as being useful as photoresists for preparing printed circuits. The elements are also useful for other purposes. One important use is as dry, film solder masks wherein the radiation sensitive elements are applied to portions of a printed circuit board surface to confine solder to pad areas on the board and to prevent bridging between conductors during tinning operations and during soldering of components. A solder mask also functions to prevent or minimize corrosion of the bare copper conductors and as a dielectric to insulate certain components from adjacent circuitry. Since a solder mask remains on the finished circuit board, it usually is transparent to allow for ease of circuit inspection.

Known radiation sensitive compositions have many uses one important use being for solder masks. When used for this purpose, however, certain precautions must be followed.

A major problem with the known solder mask compositions is that they support combustion. Therefore extreme care must be followed when the solder mask compositions are exposed to elevated temperatures, e.g., during soldering. Because of the combustibility problems associated with solder mask compositions, dependent on their use, e.g., process and surface to which such compositions are applied, the United States government has set combustibility standards.

Useful solder mask compositions which are photopolymerizable can be prepared from at least one ethylenically unsaturated monomer, a polymeric compound and a photoinitiator or photoinitiator system. These compositions do not, however, meet the established combustibility standards. Several procedures are known to make such photopolymerizable compositions flame retardant. One procedure is to add commercially available flame retarding materials, e.g., Sb,OR, to the solder mask compositions. While achieving a high level of flame retardance, it was found that some of the properties of the compositions became inferior. It was therefore found desirable to either reduce substantially the amount of Sb,O3 present or to eliminate Sb2OR entirely. Accordingly, halogenated compounds have been added to polymerizable compositions to achieve the flame retardance standard and to avoid the problem with Sb2OX, for example. Surprisingly, in many instances the presence of halogenated compounds has achieved the desired results.

In Sony KK Japanese Application 17193 filed February 12, 1973 (Publication 49-1()7048/1974) photopolymerizable flame retardant resin compositions are described which are particularly suitable as surface coatings for printed circuit boards. The flame retardant compositions contain a halogenated bisphenol epoxy acrylic resin with ethylenic unsaturated-modified terminals. a polymer with ethylenically unsaturated-modified terminals, a viscosity modifier and a photoinitiator. The flame retardant compositions in the form of a printing ink are applied by means of silk screen printing. Screen printing poses several problems. The curable ink must flow; yet if too much flow occurs, there is "shadowing", or flow, of the ink into holes and into areas intended to be open. Misregistration can also result in a conductor adjacent to a pad being left open with subsequent bridging of solder in the tinning operation or in soldering components.

It is therefore desirable to avoid the above problems by using solder mask compositions as dry film. The dry films have further advantages over the silk screen technique, for example, the reduced time and ease of preparation of the masked circuit boards without the curing at elevated temperatures.

The present invention provides a radiation sensitive element comprising a support bearing a layer of a photopolymerisable composition which composition comprises at least one addition polymerisable ethylenically unsaturated compound having a boiling point greater than 100"C. at normal atmospheric pressure, an organic, free-radical generating addition polymerisation initiator activatable by actinic radiation in the ultraviolet to visible region of the spectrum, and at least 20% by weight of an organic polymeric binder containing at least 5% by weight of acrylonitrile, the composition containing at least 5% by weight covalently bonded halogen, based on the total weight of the composition, at least one of said addition polymerisable ethylenically unsaturated compound and said polymerisation initiator containing covalently bonded halogen.

The radiation sensitive elements of this invention are flame retardant and comprise the components described above. Such photopolymerizable compositions as described are limited only in that the components must be compatible with one another, and they must be capable of being formed into dry layers. A preferred photopolymerizable composition comprises: (1) up to four ethylenically unsaturated compounds, preferably two or three, 20 to 65% by weight; (2) up to three organic polymeric binders, preferably two, 20 to 35% by weight, at least one binder containing at least 5% by weight acrylonitrile; and (3) an organic, free-radical generating addition polymerization initiator or initiator system activatable by actinic radiation in the ultraviolet to visible region of the spectrum, 0.4 to 10.0% by weight, the composition containing at least 5% by weight halogen, e.g. bromine or chlorine, covalently bonded to at least one of the components of the composition. All the weight percentages are based on the total weight of the composition.

The halogen can be present in the composition covalently bonded to one, two or three of the components described above or any combination thereof, provided that at least one of components (1) and (3) contain halogen. Many different possibilities are illustrated in the examples. In a particularly preferred composition 10 to 50% by weight of the ethylenically unsaturated compounds are halogenated. At the lower level of halogen present in the composition up to 10% by weight of Sb2O3 can be present to further increase flame retardance. Above the 10% by weight amount the desirable properties of the photopolymerizable element, e.g. adhesion and surface smoothness, begin to degrade. As the amount of halogen in the composition increases the quantity of Sb203 can be reduced or eliminated entirely.

The preferred radiation sensitive element comprises a photo olymerizable layer with a thickness of about 0.0003 inch (0.0008 cm) to about 0.01 inch (0.025 cm) having adhered thereto with low to moderate adherence a thin, flexible, polymeric film support which transmits radiation actinic to the photopolymerizable layer. The other side of the photopolymerizable layer may have adhered thereto a protective coversheet with less adherence to the layer than adherence between the support and the layer.

A suitable strippable film support which preferably has a high degree of dimensional stability to temperature changes. may be chosen from a wide variety of films composed of high polymers. e.g.. polyamides, polyolefins, polyesters. vinyl polymers, and cellulose esters. and may have a thickness of from 0.00025 inch v (v0.0006 cm.) to 0.008 inch (ç0.02 cm.) or more. If exposure is to be made before removing the strippable support, it must, of course. transmit a substantial fraction of the actinic radiation incident upon it. If the strippable support is removed prior to exposure, no such restrictions apply. A particularly suitable support is a transparent polyethylene terephthalate film having a thickness of about 0.001 inch (n/0.0025 cm.) A suitable removable. protective. coversheet may be chosen from the same group of high polymer films described above and may have the same wide range of thicknesses. A cover sheet of 0.001 inch (v0.0025 cm.) thick polyethylene is especially suitable. Supports and coversheets as described above provide good protection to the photopolymerizable resist layer.

The flexible, photopolymerizable layer is prepared from monomeric components, polymeric binder components, photopolymerization initiators and other additives set forth below. It is understood that at least the minimum amount of halogen must be present and the binder must contain at least 5% by weight acrylonitrile. A desirable range of acrylonitrile is 5 to 15%.

Suitable monomers having a boiling point greater than 100"C. at normal pressure which can be used as the sole monomer or in combination with others include the following: 1,5-pentanediol diacrylate, ethylene glycol diacrylate, 1,4-butanediol diacrylate, diethylene glycol diacrylate, hexamethylene glycol diacrylate, 1,3-propanediol diacrylate, decamethylene glycol diacrylate, decamethylene glycol dimethacrylate, 1,4 cyclohexanediol diacrylate, 2,2-dimethylolpropane diacrylate, glycerol diacrylate, tripropylene glycol diacrylate, glycerol triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, 2,2-di(p-hydroxyphenyl)-propane diacrylate, pentaerythritol tetraacrylate, 2,2-di(phydroxyphenyl)-propane dimethacrylate, triethylene glycol diacrylate, polyoxyethyl-2,2di(p-hydroxyphenyl)-propane dimethacrylate, Di-(3-methyacryloxy-2-hydroxypropyl) ether of Bisphenol-A, Di-(2-methacryloxyethyl) ether of Bisphenol-A, Di-(3-acryloxy-:z- hydroxypropyl) ether of Bisphenol-A, Di-(2-acryloxyethyl)ether of Bisphenol-A, Di-(3methacryloxy-2-hydroxypropyl) ether of tetrachloro Bisphenol-A, Di(2methyacryloxyethyl) ether of tetrachloro Bisphenol-A, Di-(3-methyacryloxy-2hydroxpropyl)ether of tetrabromo Bisphenol-A, Di (2-methacryloxyethyl)ether of tetrabromo Bisphenol-A, Di-(3-methacryloxy-2-hydroxypropyl)ether of 1,4-butane diol, Di-(3methacryloxy-2-hydroxypropyl)ether of diphenolic acid, triethylene glycol dimethacrylate, pdlyoxypropyltrimethylol propane triacrylate (462), ethylene glycol dimethacrylate, butylene glycol dimethacrylate, 1,3-propanediol dimethacrylate, 1,2,4-butanetriol trimethacrylate, 2,2,4-trimethyl-1,3-pentanediol dimethacrylate, pentaerythritol trimethacrylate, 1-phenyl ethylene-l ,2-dimethacrylate, pentaerythritol tetramethacrylate, trimethylol propane trimethacrylate, 1,5-pentanediol dimethacrylate, diallyl fumarate, 1,4benzenediol dimethacrylate, 1,4-diisopropenyl benzene, and 1,3,5-triisopropenyl benzene.

Also useful in the photopolymerizable layer is at least one of the following ethylenically unsaturated compounds having a molecular weight of at least 300. Preferred monomers of this type are: an alkylene or a polyalkylene glycol diacrylate prepared from an alkylene glycol of 2 to 15 carbons or a polyalkylene ether glycol of 1 to 10 ether linkages, and those disclosed in U.S. Patent 2,927,022, e.g., those having a plurality of addition polymerizable ethylenic linkages particularly when present as terminal linkages and especially those wherein at least one and preferably most of such linkages are conjugated with a double bonded carbon, including carbon doubly bonded to carbon and to such heteroatoms as nitrogen, oxygen and sulfur. Outstanding are such materials wherein the ethylenically unsaturated groups, especially the vinylidene groups, are conjugated with ester or amide structures.

Suitable binders which can be used as the sole binder or in combination with others include the following: Polyacrylate and alpha-alkyl polyacrylate esters. e.g.. polymethyl methacrylate and polyethyl methacrylate; Polyvinyl esters, e.g., polyvinyl acetate, polyvinyl acetate/acrylate, polyvinyl acetate/methacrylate and hydrolyzed polyvinyl acetate; Ethylene/vinyl acetate copolymers; Polystyrene polymers and copolymers, e.g., with maleic anhydride and esters; Vinylidene chloride copolymers, e.g., vinylidene chloride/ acrylonitrile; vinylidene chloride/methyl methacrylate and vinylidene chloride/vinyl acetate copolymers; Polyvinyl chloride and copolymers, e.g., polyvinyl chloride/acetate; Saturated and unsaturated polyurethanes; Synthetic rubbers, e.g., butadiene/acrylonitrile, acrylonit rile/butadiene/styrene. methyl methacrylate/acrylonitrile/butadiene/styrene copolymers, 2-chlorobutadiene/1 ,3-polymers, chlorinated rubber, and styrene/butadiene/styrene, styrene/isoprene/styrene block copolymers; Polyethylene oxides of polyglycols having average molecular weights from about 4,000 to 1,000,000; Epoxides, e.g., epoxides containing acrylate or methacrylate groups; Copolyesters. e.g.. those prepared from the reaction product of a polymethylene glycol of the formula HO(CH2)nOH, where n is a whole number 2 to 10 inclusive. and (1) hexahydroterephthalic, sebacic and terephthalic acids, (2) terephthalic. isophthalic and sebacic acids. (3) terephthalic and sebacic acids, (4) terephthalic and isophthalic acids. and (5) mixtures of copolyesters prepared from said glycols and (i) terephthalic. isophthalic and sebacic acids and (ii) terephthalic, isophthalic, sebacic and adipic acids; Nylons or polyamides, e.g.. N-methoxymethyl polyhexamethylene adipamide; Cellulose esters, e.g.. cellulose acetate, cellulose acetate succinate and cellulose acetate butyrate: Cellulose ethers. e.g.. methyl cellulose, ethyl cellulose and benzyl cellulose; Polycarbonates; Polyvinyl acetal, e.g.. polyvinyl butyral. polyvinyl formal; Polyformaldehydes.

Preferred free-radical generating addition polymerization initiators activatable by actinic light and thermally inactive at and below 185 C. include the substituted or unsubstituted polynuclear quinones which are compounds having two intracyclic carbon atoms in a conjugated carbocyclic ring system. e.g.. 9,10-anthraquinone, 1-chloroanthraquinone, 2-chloroanthraquinone, 2-methylanthraquinone. 2-ethylanthraquinone, 2-tertbutylanthraquinone. octamethylanthraquinone, 1,4-naphthoquinone, 9,10- phenanthrenequinone. 1 ,2-benzanthraquinone. 2,3-benzanthraquinone, 2-methyl-1,4 napthoquinone, 2,3-dichloronaphthoquinone, 1,4-dimethylanthraquinone, 2,3dimethylanthraquinone, 2-phenylanthraquinone, 2-3-diphenylanthraquinone, sodium salt of anthraquinone alphasulfonic acid, 3-chloro-2-methylanthraquinone retenequinone, 7,8,9, 10-tetrahydronapththacenequinone, and 1,2,3 ,4-tetrahydrobenz(a)anthracene-7, 12- dione. Other photoinitiators which are also useful, even though some may be thermally active at temperatures as low as 85"C., are described in U. S. Patent 2,760,863 and include vicinal ketaldonyl alcohols, such as benzoin, pivaloin, acyloin ethers, e.g., benzoin methyl and ethyl ethers; a-hydrocarbon substituted aromatic acyloins, including a-methylbenzoin, a-allylbenzoin and a-phenylbenzoin. Photoreducible dyes and reducing agents disclosed in U. S. Patent 2,850,445; 2,875,047; 3,097,096; 3,074,974; 3,097,097; and 3,145,104 as well as dyes of the phenazine, oxazine, and quinone classes; Michler's Ketone, benzophenone, 2,4,5-triphenylimidazolyl dimers with hydrogen doners, and mixtures thereof as described in U. S. Patents 3,427,161; 3,479,185 and 3,549,367, can be used as initiators.

Other useful additives include thermal inhibitors, colorants, plasticizers, fillers, etc.

Some of the ingredients can act in a dual role. For example, in the monomer binder systems the ethylenically unsaturated photopolymerizable compound can also act as a plasticizer for the thermoplastic binder.

Thermal polymerization inhibitors that can be used in photopolymerizable compositions are: p-methoxyphenol, hydroquinone, and alkyl and aryl-substituted hydroquinones and quinones, tert-butyl catechol, pyrogallol, copper resinate, naphthylamines, beta-naphthol, cuprous chloride, 2.6-di-tert-butyl-p-cresol, phenothiazine, pyridine, nitroso dimers, nitrobenzene and dinitrobenzene, p-toluquinone and chloranil.

Various dyes and pigments may be added to increase the visibility of the resist image.

Any colorant used, however, should preferably be transparent to the actinic radiation used.

The radiation-sensitive photopolymerizable elements are useful as photoresists and solder masks. They are particularly advantageous because they possess flame retardance without the sacrifice of other properties, e.g., flexibility after exposure, adhesion, photospeed needed for resist and solder mask functionality. Utilizing the preferred elements it is possible to receive a favorable flammability rating, e.g., UL 94, with a printed circuit board of 0.030 inch (0.76 mm) and in some instances a circuit board as thin as 0.020 inch (0.51 mm).

Examples of the invention The following examples, wherein the percentages are by weight unless otherwise indicated, illustrate the invention.

In the examples the coating solutions were prepared by thoroughly mixing the indicated ingredients. After mixing, each solution was coated on a 0.001 inch (0.0025 cm) thick polyethylene terephthalate film so that the dried coating solution was 0.004 inch (0.01 cm.) thick. After solvent evaporation, the films were cut in 1/2 inch by 5 inch (1.27 x 12.7 cm.) strips and were laminated at a temperature of 90"C to both sides of a 1/32 inch (0.79 mm) thick Westinghouse epoxy glass laminate. The films were then exposed for two minutes to a 1000-watt mercury vapor arc (Colighte "DMVL"). The exposed samples were then tested for flammability using Underwriters' Laboratory's subject 94 Test (UL 94) and/or the Oxygen Index Method (ASTM D2863-70). The results of the flammability tests are indicated after the examples set forth below.

EXAMPLE 1 Components Solution (g) Trimethylolpropane triacrylate 25.0 Di-(3-acryloxy-2-hydroxypropyl) 40.0 ether of tetrabromo Bisphenol-A Benzophenone 6.0 Michler's Ketone 0.5 Methyl methacrylate resin 10.0 Methyl methacrylate (46)/acrylonitrile 33.0 (9)/butadiene (14)/styrene (31) resin Methylene chloride to make 150 The solution contained 13.32% by weight bromine. Utilizing the UL 94 test, five test strips prepared from the solution were tested and had an average combustion within 1.4 seconds after each of the first and second ignitions.

EXAMPLE 2 Components Solution l(g) Solution 2(g) Polyoxyethylated trimethylol- 23.0 25.0 propane triacrylate Di-(3-methacryloxy-2-ethyl) 33.0 22.0 ether of tetrabromo Bisphenol-A Benzophenone 5.0 6.0 Michler's Ketone 0.5 0.5 Methyl methacrylate/acrylo nitrile/butadiene/styrene resin as in Ex. 1 29.2 30.0 Methyl methacrylate resin as in Ex. 1 9.0 10.0 Antimony oxide - 6.0 Methylene chloride to make 275 275 Solution 1 contained 14.19% by weight bromine; Solution 2 contained 9.46% by weight bromine. Utilizing the UL 94 test five test strips prepared from each of the solutions were tested. Solution 1 had an average combustion within 1.8 seconds after each of the first and second ignitions. Solution 2 had an average combustion within 0.9 second. The maximum combustion time for all strips was within 10 seconds. The photopolymerizable elements of the example are useful in the process described in U. S. Patent 3,469,982.

EXAMPLE 3 Solutions(g) Components 1 2 3 4 5 6 7 Pentaerythritol triacrylate 41.5 30 18.5 7.0 30 24 30 Di-(3-acryloxy-2-ethyl)ether of tetrabromo bisphenol-A - 11.5 23 34.5 - 11.5 11.5 Dibromo neopentyl glycol diacrylate - - - - 11.5 - Michler's Ketone 0.4 0.4 0.4 0.4 0.4 0.4 0.4 Benzophenone 5.3 5.3 5.3 5.3 5.3 5.3 Chlorobenzophenone - - - - - - 5.3 Methyl methacrylate/acrylonitrile/butadiene) 42.5 42.5 42.5 42.5 42.5 42.5 42.5 styrene resin as in Ex. 1 Methyl methacrylate (95)/ethyl methacrylate (5) copolymer 10 10 10 10 10 10 10 Antimony oxide - - - - - 6 Monastral#Green (Pigment) 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Methylene Chloride 150 150 150 150 150 150 150 Sample 1 is a control. Each solution was tested by the Oxygen Index Method and the halogen content and the oxygen index numbers are set forth in the following table: Solutions 1 2 3 4 5 6 7 % Halogen by weight - 5.0 10 15 5 5 5 based on the total compositions Oxygen Index No. 18.1 19.2 20.1 20.7 19.2 21.1 19.2 An epoxy-fiberglass circuit board having a plurality of raised copper circuit lines was laminated at 850C with a photopolymerizable element prepared from solution above. The photopolymerizable composition was substantially free of components which would volatilize in the polymerized layer at temperatures reached in molten metal application.

The laminated board was cooled to room temperature, the supported side of the photopolymerizable element was exposed to ultraviolet radiation in an image pattern through the support, and the support was removed. Alternatively the support could be removed prior to exposure. The unexposed areas were then removed by washing them with 1,1,1-trichloroethane solvent which removed only the unexposed, unpolymerized areas and not the exposed, polymerized areas. Electrical components can then be added to the board with their wire leads bent over the appropriate circuit lines in the areas from which the areas of unexposed photopolymer had been removed.

The side of the circuit board having the circuit lines was then coated with flux and wave soldered at 3.5 feet (1.07m) per minute with a commercial wave soldering machine with a preheat station at 66" - 290"C. The solder was a eutectic mixture of 63% tin and 37% lead.

The solder pot also contained about 1-59 oil at 232-2600C. After application of the solder, the board was cooled and cleaned in 1,1,1-trichloroethane solvent. An excellent solder mask was achieved, one which was flame retardant as indicated above in this example.

EXAMPLE 4 Solutions (g) Components 1 2 3 4 Pentaerythritol Triacrylate 25.0 22.4 22.4 10.0 Di-(3-acryloxy-2-hydroxy- 25.0 9.4 9.4 10.0 propyl)ether of Bisphenol-A Di-(3-acryloxy-2-ethyl)ether - - - 15.0 of tetrabromo Bisphenol-A 2,2-Dibromo neopentyl glycol - - - 15.0 dimethacrylate 2,3-Dibromo propyl - 21.1 - methacrylate Tribromophenoxy ethyl - - 21.1 methacrylate Benzophenone - 5.3 5.3 5.3 Chlorobenzophenone 6.0 - - Michler's Ketone 0.5 0.4 0.4 0.4 Antimony Oxide - 6.7 6.7 Methyl methacrylate/acrylo- - 29.6 29.6 33.0 nitrile/butadiene/styrene co polymer as in Ex. 1 Methyl Methacrylate/Ethyl - 2.24 2.24 Methacrylate as in Ex. 3 Polymethyl methacrylate - 2.24 2.24 11.0 MonastraleGreen (pigment) 0.3 0.3 0.3 0.3 Poly(methyl methacrylate/ 2,3-dibromoethyl acrylate/ acrylonitrile/bis(beta chloroethyl)vinyl phosphonate) (63.6/18.2/9.1/9.1) 127.8 - - Methylene Chloride to make 275 275 275 250 The four solutions contained the following percentages of halogen: 13.3, 12.2. 13.0. 12.48, respectively. Utilizing the UL 94 test. the average combustion time for five test strips from each coating was within 5 seconds after each of the first and second ignitions. The maximum combustion time for all strips was within 10 seconds.

EXAMPLE 5 Components Solution (g) Pentaerythritol triacrylate 25.0 Polychloroprene 44.7 Di-(3-acryloxy-2-hydroxypropyl) ether 25.0 of Bisphenol-A 2-o-chlorophenyl-4,5-diphenylimidazolyl 3.0 dimer 2-mercaptobenzothiazole 0.5 Methyl methacrylate/acrylonitrile/buta- 3.6 diene/styrene copolymer as in Ex. 1 MonastralOreen (pigment) 0.3 Methylene Chloride 300 The solution contained 16.93% by weight chlorine. Utilizing the UL 94 test, the average combustion time for 5 test strips from the coating was within 25 seconds after each of the first and second ignitions. The maximum combustion time for all strips was within 30 seconds.

EXAMPLE 6 Components Solution (g) Dibromo neopentyl glycol diacrylate 41.5 Michler's ketone 0.4 Benzophenone 5.3 Methyl methacrylate/acrylonitrile/buta- 42.5 diene/styrene resin as in Ex. 1 Methyl methacrylate/ethyl methacrylate 10 copolymer as in Ex. 3 MonastralGreen (pigment) 0.3 Methylene Chloride to make 250 The solution contained 18% bromine. Utilizing the UL 94 test, the average combustion time for 5 test strips from the solution was within 5 seconds after each of the first and second ignitions. The maximum combustion time for all strips was within 10 seconds. The film was tested as a solder mask as described in Example 3 with excellent results being achieved.

EXAMPLE 7 Solutions (g) Components 2 Polychloroprene (2-chlorobutadiene 44.6 44.6 1,3) Pentaerythritol triacrylate 26.0 26.0 Di-(3-acryloxy-2-ethyl) 7.0 ether of tetrabromo Bisphenol-A Di-(3-acryloxy-2-hydroxy- 10.0 17.0 propyl)ether of Bisphenol-A 2-o-chlorophenyl-4,5-diphenyllimi- 4.0 4.0 dazolyl dimer 2-mercapto benzooxazole 1.0 1.0 2-mercapto benzothiazole 0.5 0.5 Methyl methacrylate/acrylonitrile/ 3.5 3.5 butadiene/styrene resin as in Ex. 1 MonastralGreen (pigment) 0.3 0.3 Antimony Oxide (Sb203) 3.5 3.5 Methylene Chloride to make 500 500 Solution 1 contained 20.0% halogen and solution 2 contained 17.0% halogen. Utilizing the UL 94 test, the average combustion time for 5 test strips prepared from solutions 1 and 2 was within 5 seconds after each of the first and second ignitions. The maximum combustion time for all strips was within 10 seconds. The films were tested as solder masks as described in Example 3 with excellent results being achieved.

Claims (11)

WHAT WE CLAIM IS:

1. A radiation sensitive element comprising a support bearing a layer of a photopolymerisable composition which composition comprises at least one addition polymerisable ethylenically unsaturated compound having a boiling point greater than 100"C at normal atmospheric pressure, an organic, free-radical generating addition polymerisation initiator activatable by actinic radiation in the ultraviolet to visible region of the spectrum, and at least 20% by weight of an organic polymeric binder containing at least 5% by weight of acrylonitrile, the composition containing at least 5% by weight covalently bonded halogen, based on the total weight of the composition, at least one of said addition polymerisable ethylenically unsaturated compound and said polymerisation initiator containing covalently bonded halogen.

2. An element according to claim 1 wherein only one ethylenically unsaturated compound is present and the compound is the sole halogenated compound in the photopolymerisable composition.

3. An element according to claim 1 wherein a halogenated ethylenically unsaturated compound is present together with at least one other ethylenically unsaturated compound.

4. An element according to claim 1 wherein a halogenated polymer binder is present together with at least one other binder.

5. An element according to claim 4 wherein at least one ethylenically unsaturated compound is nonhalogenated.

6. An element according to any one of the preceding claims wherein the composition contains up to 10% by weight antimony oxide.

7. An element according to any one of the preceding claims wherein the photopolymerisable composition comprises 20 to 65% by weight of up to four ethylenically unsaturated compounds; 20 to 350/e by weight of up to three organic polymeric binders; and 0.4 to 10.0% by weight of an organic, free-radical generating addition polymerisation initiator, all weight percentages being based on the total weight of the composition.

8. An element according to claim 7 wherein 10 to 50% by weight of the ethylenically unsaturated compounds are halogenated compounds.

9. An element according to any one of the preceding claims having a strippable coversheet on the photopolymerisable layer.

10. An element according to any one of the preceding claims wherein the addition polymerisable ethylenically unsaturated compound is at least difunctional.

11. An element according to claim 1 substantially as described in any one of the Examples.