Patent Publication Number: US-3878075-A

Title: Photopolymerization of pigmented binders using combinations of organic carbonyls and halogenated naphthalenes

Description:
United States Patent McGinniss Apr. 15, 1975 1 PHOTOPOLYMERIZATION 0F 3,661,588 5/1972 Chang 96/86 F PIGMENTED I D S G 3,673,140 6/1972 Ackerman et al. 204/159.19 3,759,807 9/1973 Osborn et a1. 204/l59.23  
 COMBINATIONS OF ORGANIC CARBONYLS AND HALOGENATED NAPHTHALENES Vincent Daniel McGinniss, Middleburgh Heights, Ohio Assignee: SCM Corporation, Cleveland, Ohio Filed: July 3, 1974 Appl. N0.: 485,594  
  Related US. Application Data Division of Ser. No. 346,350, March 30, 1973.  
 Inventor:  
 References Cited UNITED STATES PATENTS 6/1967 Brodie 204/l59.23  
 Primary ExaminerMurray Tillman Assistant Examiner-Thurman Kennis Page Attorney, Agent, or FirmThomas M. Schmitz [57] ABSTRACT An improved process for laser or UV curing of pigmented-binder systems comprising ethylenically unsaturated polymers containing at least about 0.05 weight parts of opacifying pigment per weight part of binder wherein the pigmented-binder system includes from about 0.5% up to about 3% of a halogenated derivative of naphthalene in combination with about 0.1 to 2% aromatic amino carbonyl photosensitizers and from about 0.5% to 2% aromatic ketone or aldehyde photosensitizers. The sensitized binder system is a substantially improved system suitable for curing by ultraviolet or laser energy sources.  
 4 Claims, No Drawings PHOTOPOLYMERIZATION OF PIGMENTED BINDERS USING COMBINATIONS OF ORGANIC QARBONYLS AND HALOGENATED NAPHTHALENES This is a division, of application Ser. No. 346,350, filed Mar. 30, 1973.  
 BACKGROUND OF THE INVENTION This invention pertains to an improvement in a process for curing ethylenically unsaturated vehicles used as binders for pigments and fillers in surface coatings, and particularly to curing such coatings with ultraviolet or laser radiation until the paint coating is hard and tack free.  
  It is well known that conventional convection ovens or infrared ovens or other heat sources may be used to heat cure or polymerize various polymeric binders used in surface paint coatings and usually the curing is promoted by a catalyst provided in the coating system. More recently, however, a broad spectrum of ultraviolet wave energy curing has been suggested for polymerizing binders wherein suitable ultraviolet sensitizers are incorporated in the coating system for initiating polymerization of the binder. The UV sources ordinarily produce wavelengths in the UV spectrum that are transmittable through a quartz and generally provide useful wavelengths between about 1600 Angstroms and about 4000 Angstroms. Typical UV emittors include various electric arc lamps, the plasma arc torch described in US. Pat. No. 3,364,387, and lasers having a lasing output in the UV spectrum range such as disclosed in US. Ser. No. 189,254. The subject matter of the foregoing references are incorporated herein by reference.  
  Although many prior art processes disclose desirable UV and laser curing of various polymers, the UV and laser curing processes are hindered by the pigments and fillers incorporated into opacifying paint systems.  
 Pigments, fillers and other inorganics very often absorb the wavelengths of the UV or laser source whereby the curing process is hindered. Accordingly, various promoters have been suggested for promoting UV and laser curing of ethylenically unsaturated polymers to promote crosslinking thereof. In US. Pat. No. 3,673,140, issued to Ackerman et 21]., light sensitizers are disclosed for printing ink polymers wherein the preferred sensitizers are stated to be acetophenone, benzophenone, Michlers Ketone, and mixtures thereof, and said patent is incorporated herein by reference. Although such light sensitizers are satisfactory, the speed of cure is inhibited considerably by measurable amounts of pigments, fillers, tincture pigments and like inorganics which are very often incorporated into opacified paint films.  
  It now has been found that UV and laser curing of ethylenically unsaturated binders is substantially improved by the inclusion of halogenated derivatives of naphthalene such as a-chloromethyl naphthalene, naphthalene sulfonyl chloride and the like into an opacified paint system.  
  Accordingly, the primary advantages and objectives of this invention include the economical and efficient utilization of UV and laser energy to cure the thermosetting ethylenically unsaturated binders containing fillers and pigments. A further advantage is that substantially improved room temperature curing with UV and laser sources result. Other advantages include suppressing volatization of solvents; improving the color and avoiding degradation of the paint film; avoiding shrinking and distortion of the paint film; and avoiding degradation of substrates such as plastic, paper, or fabric. Room temperature UV and laser curing is rapidly promoted and highly efficient even though the film is fairly thick, highly pigmented and/or heavily filled witn inerts. These and other advantages of this invention will become more apparent from the detailed description of the invention.  
 SUMMARY OF THE INVENTION Briefly, a photopolymerization process is provided for curing ethylenically unsaturated binders containing from about 5 to 200 weight parts of opacifying pigment per weight parts of binder, wherein the pigmentedbinder system includes at least about 0.5% by weight of a halogenated derivative of naphthalene in combination with 0.1 to 2% by weight of aromatic amino carbonyl photosensitizer and about 0.5% to 2% aromatic ketone or aldehyde sensitizer, based on the pigmentedbinder system, to efficiently promote a UV or laser cure of the binder.  
 DETAILED DESCRIPTION OF THE INVENTION The process of this invention is directed to UV or laser curing of ethylenically unsaturated binders filled with pigments, fillers, and other inorganics to provide a hard and tack-free opacified paint film. The pigmented-binder systems include a synergistic promoter of a halogen derivative of naphthalene in combination with aromatic carbonyl photosensitizer and aromatic ketones or aldehyde photosensitizer. The synergistic sensitizer of this invention substantially improves a complete room temperature cure of an ethylenically unsaturated polymer containing inorganics.  
  The snyergistic sensitizer is a halogenated derivative of naphthalene having at least one halogen attached to the a-atom attached to the naphthalene ring and generally represented by the following structural formula:  
 wherein A is either an alkyl radical having 1 to 8 carbon atoms, or a methylene phenyl group or a sulfonyl radical (-SO and X is a halogen being chlorine or bromine.  
  Preferred halogenated derivatives of naphthalene include for example: l-(chloromethyl)-naphthalene represented by the formula CH Cl or 1,5 di-(chloromethyl)-naphthalene represented by the formula CHzCl f CH2Cl or Z-naphthalene sulfonyl chloride represented by the or naphthalene-l,5disulfonyl chloride represented by the formula SO Cl or l-(chloroethyl)-naphthalene represented by the formula 1 /CHCH3 or l-(chlorohexyl)-naphthalene represented by the formula c1 c&#39;H- (CH2 4-CH3 or I-( bromohexyl)-naphthalene represented by the formula B r CH- (CH2 4-CH3 or l-(bromomethylene-phenyl)-naphthalene sented by the formula repreor 1-(bromomethyl)-naphthalene represented by the formula CH Br or like halogenated derivatives of naphthalene. The halogenated derivatives of naphthalene are utilized in this invention preferably in quantities of at least from about 0.5% to about 3% by weight based on the pigmentedbinder system comprising ethylenically unsaturated binder, pigments, fillers and like inert materials.  
  Halogenated derivatives of naphthalene may be produced by reacting l-naphthaldehyde or 2- naphthaldehyde with an alkyl or phenyl Grignard reagent in a standard Grignard reaction to produce an alcohol group on the a-carbon to the naphthalene which is then reacted with l-&#34;Cl at room temperature to produce a chlorinated derivative of naphthalene. Chloromethylated derivatives of naphthalene may be produced by known synthesis methods such as described in Chapter 3 of Organic Reactions, Vol. 1, John Wiley &amp; Sons (8th printing, 1960). Sulfonyl chloride derivatives of naphthalene may be produced by known synthesis methods such as described on page 693 et seq. of Organic Synthesis, Collective Vol. 4, John Wiley &amp; Sons (2nd printing, 1967).  
  The halogenated derivatives of naphthalene become synergized when used in combination with aromatic carbonyl photosensitizers such as phenyl carbonyl compounds and aromatic amine carbonyl compounds and sometimes referred to in the art as Michlers Ketones. Examples of aromatic amino photosensitizers include: Michlers Ketone [4,4 bis-(dimethylamino)- benzophenone]; 4,4 bis-(dimethylamino)- benzophenone; p-dimethylaminobenzaldehyde; 4,4 bis- (dimethylamino )-benzil; pdimethylaminobenzophenone; pdimethylaminobenzoin; p-dimethylaminobenzil; N-  
 substituted 9-acridanones; and those amino-aromatic (or phenyl) carbonyl compounds described in U.S. Pat. No. 3,661,588; and p-aminophenyl carbonyl compounds described in U.S. Pat. No. 3,552,973 and said patents are incorporated herein by reference. Aromatic amine carbonyl photosensitizers are preferably added to the pigmented binders in amounts of 0.1 to 2% by weight based on the pigmented-binder system.  
  The synergistic sensitizer of halogenated derivative of naphthalene is further utilized in combination with aromatic ketone or aldehyde sensitizers. Typical aromatic ketones and aldehydes include, for example: acetophenone; propiophenone; xanthone; benzaldehyde;  
 benzophenone; p-chlorobenzophenone; biacetyl; benzil; fluorenone; 3-nitro-4-chlorobenzophenone 2- carbonic acid; phenanthrenequinone; benzoin and alkyl ethers of benzoin; 2-chlorothioxanthone; IO-thioxanthenone; l-phenyl 1,2 propanedione oxime and the esters or ethers thereof; isatin; anthrone; hydroxypropylbenzoate; benzoylbenzoate acrylate; 2,4 dimethylbenzophenone; benzoylbiphenyl; acenaphthenequinone; dibenzosuberenone-S; and polymers and resins containing phenyl ketone or phenyl aldehydes. Aromatic ketone sensitizers are added to the pigmented-binder system in amounts of about 0.5% to 2% based on the pigmented-binder systems.  
  Aromatic amino carbonyl photosensitizers may be further derived from aminophenyl ketones or aldehydes contained in polymers or resins. Aromatic amino carbonyl groups may be incorporated into the polymer backbone by including at least about 5% by weight aromatic amino carbonyl group in the polymer. In synthesizing an aromatic amino carbonyl group into a polyester resin, for example, a diol of paramino benzophenone is esterified together with standard glycols and diacids. Similarly, an isocyanate reacted with diol paramino benzaldehyde or paramino benzophenone or the like may be incorporated into the urethane polymer backbone. Useful synergist producing diols may be produced, for example, by reacting active hydrogens on the amine of the amino carbonyl compounds with excess ethylene or propylene oxide to form N-substituted diethanol or dipropanol compounds. Other polymer such as acrylics, epoxies, silicones may be similarly synthesized. The aromatic or aldehyde sensitizers can be similarly incorporated into the polymer backbone. The sensitizer, for example, should contain a hydroxy or carboxy functional group for reacting with conventional reactants to produce polymers containing aromatic ketone or aldehyde sensitizer group in the polymer backbone. About 2 to of polymer having aromatic carbonyl compounds incorporated into the polymeric backbone is ordinarily added to the paint or binder systems whereby about 0.1 to 2.0% aromatic amine sensitizer and/or about 0.5 to 2% aromatic ketone or aldehyde sensitizer is combined with the synergistic halogen derivative of naphthalene.  
  The polymerizable binders used for this invention are those generally known as ethylenically unsaturated binders which are curable by free-radical induced addition polymerization using peroxy or azo-catalysts for a redox system, to produce a hard, tack-free surface by addition polymerization of ethylenically unsaturated polymers of monomers. Alternatively, the binders can be fluid material wherein the ultraviolet laser causes photochemical generation of a catalytic material or effects a rearrangement which initiates polymerization and that continues until a usefully cured hard surface coating film results. Examples of useful polymerizable binders are polymeric or monomeric materials, or a mixture thereof, especially those exhibiting polymerizable vinyl, acrylic, allylic, mercaptan, fumaric, maleic, or like binders having ethylenically unsaturated functionality. Reactive polymers include unsaturated polyesters, acrylics, epoxies, urethanes, silicones, amine, polyamide resins, and particularly acrylated resins such as acrylated silicone oil, acrylated polyester, acrylated urethanes, acrylated polyamides, acrylated soy bean oil, acrylated epoxy resin and acrylated acrylic resin. Examples of reactive ethylenically unsaturated monomers include a variety of acrylates such as hydroxyethyl acrylate, cyclohexyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, benzyl acrylate, 2- ethylhexyl acrylate, benzeol, phenyloxyethyl acrylate, lower alkoxy ethoxy acrylate, tetrahydro furfuryl acrylate, n-vinyl pyroladone vinyl acetate, styrene and substituted styrenes. Examples of ethylenically unsaturated binders include oligomers such as trimethylopropane diacrylate and triacrylate, ethylene glycol diacrylate and dimethacrylate, propoxylated bisphenol A diacrylate and dimethacrylate, and 1,6 hexane diol diacrylate pentaerythitol triacrylate.  
  The ethylenically unsaturated binder is combined with pigments, fillers and inerts to produce an opacified pigmented-binder system. Many useful pigments tend to absorb only minor amounts of energy in the UV range and hence pigments such as zinc oxide may be used quite favorably. Titania, such as anatase and particularly rutile, are particularly desirable in opacified paint coatings but provide opposition to a thorough cure by UV radiation. By utilizing the synergistic sensitizer of this invention, titania opacifying pigmentation may be advantageously used if desired. Other filler materials and coloring pigments include basic lead sulfate, magnesium silicate, silica, clays, wollastinite, talcs, mica, chromates, iron pigments, wood flower, microballoons, hard polymer particles and glass fiber or flake. Generally, it is desirable to use pigments which do not absorb considerable ultraviolet light in the same region of the UV spectrum as is absorbed by the synergistic sensitizer of halogenated derivative of naphthalene.  
  The pigmented-binder systems may be used for paint films having film thickness of less than 1 mil and preferably about 0.l to 0.5 mils thick.  
  The following examples further illustrate this invention but are not to be construed as limiting the scope of this invention. Unless otherwise stated herein all parts indicated are parts by weight and all percentages indicated are weight percentages.  
 EXAMPLE 1 A diacrylate (DER 332) was produced by reacting two moles of acrylic acid with 1 mole of diglycidyl ether of Bisphenol A with 0.2% benzyl dimethyl amine at C. until the acid number of reactant mixture was essentially zero.  
  An ethylenically unsaturated binder was produced by mixing at room temperature about 30 parts 2- ethylhexyl acrylate, about 30 parts pentaerythitol triacrylate, and about 30 parts diacrylate.  
  The foregoing binder was ground with rutile TiO to produce a pigmented polymerizable binder having a pigment-binder ration (P/B) of 0.9.  
 EXAMPLE 2 About 1.5% of Michlers Ketone and about 1.5% a-chloromethyl naphthalene were added to the pigmented binder of Example 1 based on the pigmented binder weight. The sample was drawn down on a steel panel to provide a 0.5 mil paint film and cured under nitrogen blanket on a plasma arc radiation system (PARS) for 0.1 seconds which provided a complete cure. A similar paint film cured by 10 seconds exposure to a conventional UV source with an inert atmosphere. The UV source was two 4000 watt mercury lamps placed 8 inches from the film. The inert atmosphere was created by placing a polyethylene film over the paint before curing to assimilate a nitrogen atmosphere.  
 EXAMPLE 3 EXAMPLE 5 The following were added to the pigmented binder composition of Example 1:  
 a. 1% acetophenone plus 0.1% Michlers Ketone b. 2% acetophenone plus 0.1% Michlers Ketone c. 1% acetophenone plus 0.2% Michlers Ketone d. 2% acetophenone plus 0.2% Michlers Ketone. I Each of the foregoing compositions (a)(d) were drawn down on a steel panel with a No. 10 WW rod and 5 In a manner similar to Example 2, the pigmented binder of Example 1 and containing sensitizers as indicated in the table below were drawn down on a steel panel with a No. 8 WW rod and exposed to a PARS of UV and produces the results indicated. 10  
 TABLE I Sample Curing Exposure No. Sensitizers Under lnert Atmosphere Results l 1.0% a-chloromethyl naphthalene 0.15 seconds with PARS Fully cured film 0.5% Michler&#39;s Ketone 8.00 seconds with UV Fully cured film 0.5% acetophenone 2 1.0% Michlers Ketone 0.20 seconds with PARS Uncured, wet film 8.00 seconds with UV Uncured, wet film 3 .5% a-chloromethyl naphthalene 0.08 seconds with PARS Fully cured film 2% dimethylaminobenzaldehyde 9.00 seconds with UV Fully cured film .8% benzil 4 .071 a-chloromethyl naphthalene 0.1 seconds with PARS Wet film, uncured 3% Michler&#39;s Ketone 5 .071 a-chloromethyl naphthalene 0.1 seconds with PARS Full cure .07: Michlers Ketone 6 .0% a-chloromethyl naphthalene 0.07 seconds with PARS Fully cured film .0% acetophenone 1% Michler&#39;s Ketone .0% a-chloromethyl naphthalene acetophenone 0% a-chloromethyl naphthalene 0% acetophenone 0% a-chloromethyl naphthalene 0% acetophenone &#34;7c Michlers Ketone 0% a-chloromethyl naphthalene 71 acetophenone 71 Michlers Ketone &#39;7: Michlers Ketone 7: phenanthrenequinone 7: u-chloromethyl naphthalene 71 Michlers Ketone 7r phenanthrenequinone EXAMPLE 4 An ethylenically unsaturated binder comprising 3 parts pentaerythitol triacrylate, 30 parts hydroxyethyl acrylate, and 30 parts diacrylate DER 332 was ground with TiO to make a pigmented binder having a pigment to binder ratio (P/B) of 0.8 to 1. The pigmented binder was combined with sensitizer combinations noted in the table below, drawn down on a steel panel with a No. WW rod and cured as indicated on a PARS unit.  
 TABLE II Exposure Time to PARS Sample lnert Atmosphere 0.05 seconds 0.05 seconds 0.05 seconds 0.07 seconds 0.07 seconds 0.10 seconds Michlers Ketone naphthalene sulfonyl chloride benzil 7n Michler&#39;s Ketone 0.05 seconds 2 02 20 O2 20%benzil 20 2O 20 02 0.10 seconds with PARS 0.10 seconds with PARS 0.07 seconds with PARS 0.07 seconds with PARS 0.15 seconds with PARS 0.07 seconds with PARS 0.07 seconds with PARS Wet film uncured Wet film uncured Fully cured film Fully cured film Fully cured film Tacky surface on film Fully cured film the film was cured for 0.1 seconds with a PARS unit which produced an undercured film having a tacky surface. Similarly, film samples were cured for 0.07 seconds with a PARS unit which did not cure the film.  
 EXAMPLE 6 An ethylenically unsaturated binder comprising parts pentaerythitol triacrylate, 30 parts hydroxyethyl acrylate, and 30 parts diacrylate DER 332 was ground with TiO to make pigmented binder having a pigment Result Surface cure Full cure Surface cure Full cure Surface cure Full cure Surface cure Full cure to binder ration (P/B) or 1 to l. About 0.3% by weight Michlers Ketone and 2% l-chloromethyl naphthalene were added to the paint mixture based on the pigmentbinder composition. The sensitizer indicated in Table sized by reacting glycidyl acrylate or glycidyl methacrylate reacted with the COOl-l group of an acid terminated aliphatic polyamide in a manner described in British Pat. No. 1,241,622. Acrylated-polyester resins II was roduced from the indi d reactants to were synthesized from a standard polyester such as du a en iti r ol m 0]&#39; prepolymer hi h was propylene glycol reacted with excess molar phthalic anadded to the pigmented binder in amounts indicated. hydnde to P 301d terminated polyester hich The sensitizer p y or p p y was produced was thereafter reacted with glycidyl acrylate or glycidyl methacrylate. In like manner, acrylated-acrylic resins by reacting the specified reactant together at about O were produced by reacting a standard acrylic resin conl20 C. to completion. A 0.8 mil paint film was drawn taming pendant oxtrane functionality with acrylic acid down on a steel panel with a No. 12 WW rod. The film to produce an ethylemcally unsaturated resin wherein was cured under inert atmosphere for 0.07 seconds on PARS nit A&#34; f th t t l S r f u r d glycidyl methacrylate. methylmethacrylate and butyl arovidin t L f e i y acrylate copolymerized in solution and thereafter rep m i i 3 l l g zgi g zi acted with acrylic acid. Similarly, acrylated-urethane 3 we e y g t t resins were synthesized by reacting a diol with a diisoi g O cure w en expose o m an met cyanate (e.g. TDI) with propyleneglycol to produce an a mosp isocyanate terminated urethane resin. The -NCO ter- Ethylenically unsaturated binders were synthesized i t d resin was thereafter r a t d with a hydroxy] in a conventional manner as follows. S1loxane-esterntaining acrylate such as hydroxyethyl acrylate to acrylate resins were produced by reacting a 2 to 8 carproduce an acrylated urethane resin. Binder composibon diol with acrylic or methacrylic acid to give a hytions synthesized in the foregoing explanatory manner droxylalkyl acrylate which was then reacted with a 4 to were ground with TiO pigment, sensitized with the 10 carbon dicarboxylic anhydride and a 2 to 21 carbon sensitizer combinations, as indicated in Table IV, atom diol. The resulting polyester was then reacted drawn down on a steel panel in a 0.7 mil film, exposed with a siloxane having 2 or more OH and/0r alkoxy to a PARS unit. The results for the identified composigroups. Similarly, acrylated-amide resins were synthetions are set forth in the following Table IV.  
 TABLE III Sample No. Reactant Sensitizer l 1 mole of 2-benzoylbenzoic acid 1 mole of propyleneoxide 2% hydroxypropyl Z-benzoylbenzoate prepolymer 2 Sample No. l toluenediisoczanote hydroxyethylacrylate 5% hydroxypropyl 2-benz0ylbenadduct zoate contained in a urethane resin 3 1 mole of Z-benzoylbenzoic acid glycidyl acrylate 27: Z-benzoylbenzoate contained in an acrylate monomer-prepolymer 4 1 mole of 2-benzoylhenzoic acid l mole DER 332 5% Z-benzoylbenzoate contained in an epoxy resin 5 1 mole Sample No. 4 excess molar acrylic acid 67: Z-henzoylbenzoate contained in an acrylate unsaturated epoxy resin 6 1 mole of phenolic resin excess molar benzoyl chloride 571 benzoyl substituted phenolic resin 7 1 mole of 3,3, 4.4 benzophenonetetracarhoxylic dianhy- 571 henzophenonetetracarboxylic dride 2 moles hydroxyethyl acrylate 2 moles of propydianhydride (BTDA) hydroxyethyllene oxide acrylate propylene oxide adduct (dihydroxypropyl ester of dihydroxyethylacrylate ester of BTDA) 8 2 moles of S-chloro-Z hydroxy benzophenone 1 mole of Phenolic benzophenone compound DER 332 in epoxy resin 9 2 moles of l-Cl-2a bromomethyl benzophenone 2&#39; carboxylic a-haloalkylbenzophenones in acid 1 mole of DER 332 epoxy resin 10 l mole of 4-chlorobenzophenone 2-carboxylic acid 1 mole Benzophenone carboxylic acid DER 332 derivatives in epoxy resin 1 l l mole of 2-hydroxy-4 chlorobenzophenone 1 mole of 3% phenolic benzophenone ethyleneimine ethyleneimine prepolymer l2 1 mole of 2,4 dihydroxybenzophenone 2 moles ethyleneimine 3% phenolic benzophenone ethyleneimine 13 1 mole of 2,4 dihydroxybenzophenone 1 mole of butanediol 5% phenolic benzophenone diglycidyl ether l mole acrylic acid epoxy resins 14 l mole of 2,4 dihydroxybenzophenone 2 moles of propylene 5% phenolic benzophenone oxide epoxy resin prepolymer 15 l mole of l-hydroxy xanthine 1 mole of DER 332 57: thioxanthone in epoxy resin 16 l mole aminobenzophenone excess molar propyleneoxide 3% dissoprepanolaminebenzophenone 17 1 mole methylaminobenzophenone 1 mole DER 332 Aminobenzophenone in epoxy resin TABLE IV Exposure Time Sample Photosensitizer to PARS No. Binder Composition Combination lnert Atmosphere Result 1 1 wt. part hydroxyethyl acrylate, 3.0% 4.4 bis (dimethyl- 0.10 seconds Undercured film 1 wt. part ethylene glycol diacrylate, amino) benzil; 1 wt. part hydroxyethyl acrylate, 2.0% benzil having a toluene diisocyanate adduct. The pigment-binder ratio (P/B) with TiO ground therein was 0.8  
 Sample No.  
  The foregoing examples are for illustration only and are not intended to be limiting. Variations and modifications are contemplated within the scope of this in vention, as defined in the appended claims.  
 Binder Composition 1 wt. part hydroxyethyl acrylate,  
 1 wt. part ethylene glycol diacrylate,  
  1 wt. part hydroxyethyl acrylate, having a toluene diisocyanate adduct. The P/B ratio with TiO was 0.8  
 1 wt. part 2-ethy1hexyl acrylate,  
  1 wt. part propylene glycol diacrylate, 1 wt. part polyester capped with glycidyl acrylate (molecular weight 3,000) ground with T10 to make a P/B of 1.0 1 wt. part 2-ethylhexyl acrylate,  
  1 wt. part propylene glycol diacrylate, 1 wt. part polyester capped with glycidyl acrylate (molecular weight 3,000) ground with TiO to make a P/B or 1.0 1 wt. part Z-phenoxyethyl acrylate,  
 1 wt. part pentaerythitol triacrylate,  
  1 wt. part acrylated silicone resin, ground with TiO to make a P/B ratio of 1.0  
 1 wt. part Z-phenoxyethyl acrylate,  
 1 wt. part pentaerythitol triacrylate,  
  I wt. part acrylated silicone resin, ground with TiO to make a P/B ratio of 1.0  
 1 wt. part cyclohexyl acrylate,  
 1 wt. part 1.6 hexandiol diacrylate,  
  1 wt. part acrylated soy bean oil, ground with TiO to make a P/B ratio of 0.9  
 1 wt. pan cyclohexyl acrylate,  
 1 wt. part 1.6 hexanediol diacrylate.  
 1 wt. part soy bean oil,  
 ground with TiO to make a P/B ratio of 0.9  
  1 wt. part hydroxypropyl methacrylate. 1 wt. part ethylene glycol dimethacrylate 1 wt. part methacrylated polyamide resin, ground with TiO to make a P/B ratio of 0.8  
 1 wt. part hydroxypropyl methacrylate,  
  1 wt. part ethylene glycol dimethacrylate.  
  1 wt. part methacrylated polyamide resin, ground with TiO to make a P/B ratio of 0.8  
 1 part benzil acrylate, 1 part acrylated resin composition, 1 part trimethylol propane triacrylate,  
 ground with TiO to make 21 W8 ratio I claim:  
  1. In a photopolymerization process for ultraviolet curing of a film comprising a pigmented binder system of 1 weight part of an ethylenically unsaturated binder 55 combined with about 0.05 to 2 weight parts of opacifying pigment, and exposing said film to an energy source containing UV energy having wavelengths between about 1600 A and 4000 A until said film is cured, the  
 improvement which comprises:  
 TABLE IV Continued Photoscnsitizer Combination 3.0% 4.4 bis (dimethylamino) benzil;  
 2.0% benzil;  
 1.5% 1-(chloromethyl)- naphthalene 0.3% Michlers Ketone; 1.0% Z-naphthyl phenyl ketone 0.3% Michler&#39;s Ketone; 1.0% Z-naphthyl phenyl ketone;  
 2.0% 1,5 di-(chloromethyl)- naphthalene 0.3% Michlers Ketone; 1.0% propiophenone or benzaldehyde 0.3% Michler&#39;s Ketone; 1.0% propiophenone or benzaldehyde;  
 1.0% 1-(chloromethy1)- naphthalene 0.3% Michlers Ketone; 1.0% benzil, biacetyl, or acenaphthenequinine 0.3% Michler&#39;s Ketone; 1.0% benzil biacetyl, or acenaphthenequinine;  
 1.0% Z-naphthalene sulfonyl chloride 0.5% dimethylaminobenzaldehyde. p-dimethylaminohenzil;  
 2.0% benzil 0.3% Michlers Ketone; 1.0% isatin or xanthone, or fluorenone, or thioxanthone;  
 1.0% l-(bromomethyl)-. naphthalene Exposure Time to PARS lnert Atmosphere 0. l 0 seconds 0.07 seconds 0.07 seconds 0.10 seconds Result Fully cured film Slightly undercured film Fully cured film slightly undercured 0.07 seconds 0. 10 seconds 0.07 seconds 0. 10 seconds 0. 10 seconds 0.10 seconds 0.07 seconds 1-( chloromethyl )-naphthalene;  
 60 group of l-6 carbon atoms.  
 binder;  
 Fully cured film Slightly undercured Fully cured film Slightly undercured film Fully cured film Slightly undercured film Fully cured film than said atomatic phenyl ketone. 2. The process of claim 1 wherein the halogenated 50 derivative of naphthalene is selected from the group consisting of: I  
 l ,5-di-( chloromethyl )-naphthalene;  
 2-naphthalene sulfonyl chloride;  
 naphthalene-1 ,S-disulphonyl chloride;  
 l-( bromomethyl )-naphthalene;  
 an a1pha-chloroalkyl-naphthalene having an alkyl group of 1-6 carbon atoms; and  
 an alpha-bromoalkyl-naphthalene having an alkyl 3. An ultraviolet, photopolymerizable pigmented binder system for use as an opacified film, comprising: a pigmented binder system comprising opacifying pigment and ethylenically unsaturated binder wherein said pigmented binder system contains about 0.05 to 2 weight parts of opacifying pigment per 1 weight part of said ethylenically unsaturated said binder system containing by weight about 0.5%  
 to 3% of a halogenated derivative of naphthalene having at least one halogen attached to the alphaatom attached to the naphthalene ring, 0.1% to 2% of an aromatic phenyl ketone, and at least 0.5% of 5 an aromatic photosensitizer selected from the group consisting of aromatic aldehydes and aromatic ketones different from said aromatic phenyl ketone. 4. The pigmented binder system of claim 3 wherein said halogenated derivative is selected from: