CA1056386A - Photosensitizers - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Ethylenically unsaturated monomeric esters in the presence of keto-dioxolane compounds are polymerized upon exposure to a source of radiation.

Description

~0563~6 This invention relates to the use of keto-dioxolane compound as photoinitiators for ethylenically unsaturated mono-meric esters.
The use of photopolymerizable ethylenically unsaturated monomeric materials in coating compositions, printing inks, ad-hesives, and the like is known. It is also known that such mono-meric materials are converted into polymers by the action of radiation and that they will polymerize at an improved rate when exposed to radiation in the presence of a photoinitiator.
It has now been found that polymers of ethylenically unsaturated monomeric esters having improved curing speeds can be obtained with no sacrifice of quality of the product by carrying out the photopolymerization in the presence of a novel keto-dio-xolane compound.
The sensitizers of this invention have the following structure:

Il I ~

wherein R is alkyl of from one to about nine carbon -.: .. . , : ,: .

~0563~36 atoms, e.g., methyl, ethyl, propyl, pentyl, octy], or 2-ethyl-hexyl; alkyl of from one to about nine carbon atoms substituted with at least one halogen (chlorine, bromine, iodine, or fluorine), alkoxy, or the like; aryl of six ring carbon atoms; aryl of six ring carbon atoms substituted with at least one halogen, alkoxy, hydroxy, nitro, carboalkoxy, alkylamino, or the like; or cyclo-alkyl of five to eight ring carbon atoms.
Examples of such derivatives include, but are not limited to, 2-trichloromethyl-4-benzoyl-4-phenyl-1,3-dioxolane; 2-(p-dimethylaminophenyl)-4-benzoyl-4-phenyl-1,3-dioxolane; 2-methyl -4-benzoyl-4-phenyl-1, 3-dioxolane, and the like; and mixtures thereof.
The acyloin derivatives of this invention may be pre-pared by any known and convenient means, such as for example by the acid-catalyzed condensation of alpha-methylolbenzoin with an aliphatic or an aromatic aldehyde, e.g., p-dimethylaminobenzal-dehyde, acetaldehyde, chloral, furfural, and the like.
These keto-dioxolane derivatives are effective init-iators in the photopolymerization of a broad range of polymerizable ethylenically unsaturated monomeric compounds. Such a compound is generally a monomer or prepolymer, that is, a dimer, trimer, or other oligomer or mixture of copolymer.thereof, generally des-cribed as the acrylic acid, methacrylic acid, itaconic acid, and the like, ester of an aliphatic polyhydric alcohol such as for example the di- and polyacrylates, the di- and polymethacrylates, and the di~ and polyitaconates of ethylene glycol, .:, . . .

I 1~56386 ¦ triethylene glycol, tetraethylene glycol, tetramethylene glycol,

2 ¦ trimethylolethane, trimethylolpropane, butanediol, pentaerythri-

3 ¦ tol, dipentaerythritol, tripentaerythritol, other polypentaery-

4 ¦ thritols, sorbitol, d-mannitol, diols of unsaturated fatty acids, s ¦ and the like.
6 ¦ Typical compounds include, but are not limited to, tri-7 1 methylolpropane triacrylate, trimethylolethane triacrylate, tri-8 methy'lolpropane trimethacrylate, trimethylolethane trimethacry-9 late, tetramethylene glycol dimethacrylate, ethylene glycol o dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol diacrylate, pentaerythritol diacrylate, pentaerythritol 12 triacrylate, pentaerythritol tetraacrylate, dipentaerythritol 13 diacrylate, dipentaerythritol triacrylate, dipentaerythritol ~4 tetraacrylate, dipentaerythritol pentaacrylate, dipentaeryth-~s ritol hexacrylate, tripentaerythritol octoacrylate, pentaery-16 thritol dimethacryl'ate, pentaerythritol trimethacrylate, dipenta-17 erythritol dimethacrylate, dipentaerythritol tetramethacrylate, 18 tripentaerythritol octamethacrylate, pentaerythritol diitaconate, 19 dipentaerythritol trisitaconate, dipentaerythritol pentaita-20 conate, dipentaerythritol hexaitaconate, ethylene glycol dimetha-21 crylate, 1,3-butanediol diacrylate, 1,3-butanediol dimethacry-2~ late, 1,4-butanediol diitaconate, sorbitol triacrylate, sorbitol 23 tetraacrylate, sorbitol tetramethacry'late, sorbitol pentaacrylate, 24 sorbitol hexacrylate, and the like, and modifications, mixtures, 25 and prepolymers thereof.
26 Although the ratio of the amount of ester to the amount of 27 photoinitiator may be about 10-99:1-90, it is generally about 28 90-99:1~10- ! .
29 Commonly known modifiers may be incorporated into the for-mulations using these compositions, including plasticizers;
,1 . -4-10563~6 etting agents for the colorant, such as dichloromethylstearate 2 and other chlorinated fatty esters; leveling agents, such as 3 lanolin, paraffin waxes, and natural waxes; and the like. Such 4 modifiers are generally used in amounts ranging up to about 3 per cent by weight, preferably about 1 per cent, based on the 6 total ~eight of the formulation.
7 The formulations may be prepared in any kno~Jn and convenient 8 manner. Variables ~hich determine the rate at l~hicll a photo-g polymerizable composition ~ill dry include the nature of the o substrate, the specific ingredients in the composition, the concentration of the photoinitiator, the thickness of the material , ~2 tlle nature and intensity of the radiation source and its distance 13 from the material, the presence or absence of oxygen, and the 14 temperature of the surrounding atmosphere. Irradiation may be accomplished by any one or a combination of a variety of methods.
16 The composition may be exposed, for example, to actinic light 17 from any source and of any type as long as it furnishes an 18 effective amount of ultraviolet radiation, since the compositiQns 19 activatable by actinic light generally exhlbit their maximum sensitivity in the range of about 2000A. to 7000A., and pre-2~ ferably about 2000A. to 4000A.; gamma radiation emitters; and 22 the like; and combinations of these. Suitable sources include, 23 but are no.t limited to, carbon arcs, mercury vapor arcs, pulsed 24 xenon lamps, fluorescent lamps ~lith special ultraviolet light-emitting phosphors, argon glo~Y lamps, photographic flood lamps, 26 and so forth.
27 The time of irradiation must be sufficient to give the 28 effective threshold dosage. Irradiation may be carried out at 29 any convenient temperature, and most suitably is carried out at room temperature for practical reasons. Distances of the !
. _5_ ,. . ... , . ,- .

radiation source from the work may range from about l ;nch to 2 ¦ 6 feet, and preferably about 5 inches to 4 feet.
3 ~ Wherl cured by radiation, the compositions are dry, flexible, 4 ¦ abrasion resistant, and chemical resistant; also they have

5 ¦ excellent ink receptivity, hydrophilic-hydrophobic balance, dot

6 resolution, and initial roll-up, making them particularly suitable

7 in such applications as presensitized lithographic printing

8 plates and photoresists. The compositions are also useful as

9 binders for magnetic tape; printing inks; adhesives for foils, o films, papers, fabrics, and the like, coatings for metals, plastics, paper, ~ood, foils, textiles, glass, cardboard, box board, and the like; markers for roads, parking lots, airfields, 13 and sim;lar surfaces, and so forth. Stock which may be printed 14 includes paper, clay-coated paper, and box board. In addition, the compositions are suitable for the treatment of textiles, 16 both natural and synthetic, e.g., in vehicles for textile 17 printing inks or for specialized treatments of fabrics to produce 18 water repellency, o;l and stain resistance, crease res;stance, 19 etc.
When used as vehicles for inks, e.g., pr;nting inks, the 21 compositions may be pigmented with any of a variety of conven-22 tional organic or inorganic pigments, e.g., molybdate orange, 23 titanium dioxide, lithol rubine red,diarylide yellow, chrome 24 yellow, phthalocyan;ne blue, zinc ox;de, and carbon black, as well as colored w;th dyes in a conventional amount. The vehicle 26 may be used in an amount ran~ing from about 20 to 99.9 per cent 27 and the amount of colorant may range from about O.l to 80 per 28 cent of the weight of the total compositionO
29 Typical laminatior)s using the compositions of this invention as adhesives include polymer-coated cellop~ane to polypropylene, ~1 -6-~r~a~ ma~k) Mylar1to a metal such as aluminum or copper, polypropylene to 2 aluminum, and t~.e like.
3 The compositions may also be utilized for metal coatings 4 and particularly for metals which are to be subsequently printed.
s Glass and plastics may also be printed or coated ? and the coat-6 ings are conventionally applied by roller or spray. Pigmented 7 coating systems may be used for various polyester and vinyl 8 films; glassj polymer-coated cellophane; treated and untreated g polyethylene, for example in the form of disposable cups or o bottles; treated and untreated polypropylene; and the like.
1l Examples of metals which may be coated include sized and unsized 12 tin plate.
Photopolymerizable elements prepared from these compositions 4 comprise a support, e.g., a sheet or plate, having superimposed 5 thereon a layer of the above-described photopolymerizable material .
16 Suitable base or support materials include metals, e.g., steel, 17 aluminum, or copper, plates; sheets; and foils; and films or 18 plates connposed of various film-forming synthetic resins or high 19 polymers, e.g., vinyl chloride polymers; vinylidene chloride 20 polymers, vinylidene chloride copolymers ~lith vinyl chloride, 21 vinyl acetate, or acrylonitrile; and vinyl chloride copolymers 22 with vinyl acetate or acrylonitrile; linear condensation polymers 23 such as a polyester, e.g., polyethylene terephthalate; polya-2~ mides, etc. Fillers or reinforcing agents can be present in the 25 synthetic resin or polymer bases. In addition, highly reflec-26 tive bases may be treated to absorb ultraviolet light, or a 27 light absorbtive layer can be transposed between the base and 28 photopolymerizable layer.
29 Photopoiymerizable elements can be made by exposing to 30 radiation selected portions of the photopolymerizable layer .

., -10563~6 thereof until addition polymerization is completed to the desired depth in the exposed portions. The unexposed portions of the layer are then removed, e.g., by the use of solvents which dissolve the monomer or prepolymer but not the polymer.
When used as printing inks, coating compositions, and ad-hesives, the compositions described herein are used without vola-tile solvents and possess many advantages over conventional oleo-resinous and solvent-type inks and coatings. The substrate need not be pretreated or prepared in any way. The use of volatile solvents and the attendant health and fire hazards and odor are eliminated. The inks and coatings have excellent adhesion to the substrate after exposure to radiation. They have good gloss and rub-resistance and withstand temperatures as high as about 150C.
and as low as about -20C. The printed or coated sheets can be worked and further processed immediately after exposure to the energy source.
The invention and its advantages will be better under-stood with reference to the following illustrative examples, but it is not intended to be limited thereto. In the examples, the parts are given by weight unless otherwise specified. Unless other-wise indicated, when an ingredient is solid at room temperature, the mixture may be heated to melt the solid ingredient, but generally not above 100C., or it may be used in a mixture with other liquid ingredients. The atmospheric and temperature conditions were am-bient unless otherwise noted.
_ AMPLE 1 A mixture of 24.2 grams (0.1 mole) of ~-methylolbenzoin, 14.9 grams (0.1 mole) of p-dimethylaminobenzaldehyde, and 1.0 grams of p-toluenesulfonic acid was dissolved into 125 ml. of toluene and placed into a Dean-Stark apparatus. The reaction . .
.. , ........... . . : , - ~, .

' ' . ~ ''. ' ' ' ' ~ . ~ ,, , ' .. . .
: ' ' . ' , ' ' , ' ' ' ' I lOS6386 I
1 mixture l~as refluxed for 8 hours and the theoretical amount of t ¦ ~ater ~Jas collected.
3 ¦ The solution was cooled ~ashed ~ith 5% sodium carbonate 4 ¦ solution separated and dried. Concentration under reduced s pressure gave 32.3 grams of product melting at 118-1 20C.
6 Recrystallization from ethanol gave 29.6 grams (79.5% yjeld) 7 of 2-(p-dimethylaminophenyl )-4-benzoyl-4-phenyl-1 3-dioxolane 8 ~m.p. 128-129C.). The elemental analysis ~as as follows:
g C H N
o Calculated: 77.19 6.21 3.75 11 Found :77.31 6.15 3.73 13 The procedure of Example 1 was repeated except that the starting materials were ~-methylolbenzoin and chloral. The pro-~5 duct ~as a 63% yield of 2-trichloromethyl-4-benzoyl-4-phenyl-1 16 ¦ 3-dioxolane analyzed as follows:
17 1 C H Cl 18 1 Calculated: 54.91 3.50 28.67 19 1 . Found: 55.03 3.49 28.50 21 ¦ The procedure of Example 1 was repeated except that the 22 1 starting materials were o(-methylolbenzoin and cinnamaldehyde. The 6'~f13 23 ¦ dioxolane-tYpe product was obtained in a yield of 73% and 24 analyzed as follows:
C H
~6 Calculated: 80.88 5.66 27 Found: û0.97 5.62 28 EXA~PLE 4 29 The procedure of Example 1 was repeated except that the 30 starting materials were ~-methylolbenzoin and furfural. The _g_ dioxolane-tYPe product was obtained in a yield of 78% and analyzed as follows:
C H
Calculated: 74.99 5.03 Found: 74.56 5.07 _AMPLE 5 A composition comprising 95 parts of isocyanate-modified pentaerythritol triacrylate and 5 parts of 2-(p-dimethylamino-phenyl-4-benzoyl-4-phenyl-1,3-dioxolane was coated onto a glass slide at a wetfilm thickness of 0.3 mil and irradiated at a dis-tance of 1.5 inches from a 100-watt/inch ultraviolet lamp. The coating dried to a flexible abrasion-resistant film in 1.5 seconds.
E~AMPLE 6 (A) The procedure of Example 5 was repeated with each of the following sensitizers instead of 2-(p-dimethylaminophenyl-4-benzoyl-4-phenyl-1,3-dioxolane:
TABLE I

Sensitizer Cure speed, seconds none 10.0 2-trichloromethyl-4-benzoyl-4-phenyl -1,3-dioxolane 3,0 2-(p-dimethylaminophenyl)-4-benzoyl -4-phenyl-1,3-dioxolane 1.3 (B) For comparative purposes, sensitizers outside of the scope of this invention were tested in the same manner as above wi~h the following results:

1~ 1056386 ~ ¦ TABLE II
2 ¦ r~ Cure time, 3 I seconds ., ~
~ ¦ Benzoin 15 5 ¦~ -methylbenzoin 6.0 6 ¦O~-phenylbenzoin 5.5 7 ¦~-benzylbenzoin 7.5 8 ¦benzoin acetate 11.5 9 ¦ ~ -methylbenzoin ethylether 12 o ¦ benzil 11 II ¦ benzophenone 25 12 Thus it can be seen that compositions containing the specific 13 keto-d.ioxole compounds of this invention (part A) cure considera-14 bly faster than comparable compositions containing related sensi-I5 tizers that are not within the scope of this invention (part B).
. EXAMPLE 7 The procedure of Example 5 was repeated witll each of the 18 following esters instead of isocyanate-modified pentaerythritol v t~iacrylate. The resu7ts are tabulated below:
TABLE III
.. _ _ _ _ . . .
21 Ester Cure speed, 22 seconds ..
23 pentaerythritol tetraacrylate 2.1 24 triethanolpropane trimethacry1ate 3.6 ethylene glycol dimethacrylate 7.0 26 triethylene glycol diacrylate 3.8 27 1,3-butanediol diacrylate 5.0 28 1 ,4-butanediol diitaconate 7.1 29 sorbitol pentaacrylate4.3 .. . . .. ..

. .- . .

_AMPLE 8 A printing ink was prepared from the following:
Parts by Weight Product of Example 5 90 phthalocyanine green 10 A glass bottle printed with this green ink was exposed to a 100-watt/inch ultraviolet lamp at a distance of 2 inches. The ink dried in 3.0 seconds. It had excellent adhesion to the glass and ~ood grease- and rub-resistance.

The procedure of Example 8 was repeated with each of the following substrates instead of glass: clay-coated sulfite board, 32-pound coated paper, aluminum, and tin-free steel. The results were comparable.

.
A laminite was made of a film of polymer-coated Cellophane*
and a film of oriented polypropylene with a mixture of the fol-lowing ingredients between the two: 95 parts of trimethylolethane dimethacrylate and 5 parts of 2-trichloromethyl-4-benzoyl-4-phenyl-1,3-dioxolane.
The laminate was exposed at a distance of 2.0 inches from a 100-watt/inch ultra~iolet lamp. A tight bond was effected in 4.0 seconds.

_ The procedure of Example 10 was repeated with each of the following substrates: Saran*-coated Cellophane and Saran-coated Cellophane, corona-discharge surface-treated polyethylene and co-ated Cellophane, and polyvinylidene dichloride-coated polypropylene and Mylar*.
The laminations were successful as evidenced by tear seals * trade mark 12 _ having bond strengths of at least 300 grams per inch.
2 ¦ EXAMPLE 12 3 ¦ The procedures of Examples 5~ ere repeated except that 4 ¦ instead of being exposed to ultraviolet light the samples were 5 ¦ passed on a conveyor belt beneath the beam of a Dynacote 300,000-6 ¦ volt linear electron accelerator at a speed and beam current so 7 ¦ regulated as to produce a dose rate of 0.5 megarad.
8 ¦ These systems produced resinous materials of varying 9 ¦ degrees of hardness in films from 0.5 to 20 mils thick having o I tacky surfaces.
1l ¦ EXAMPLE 13 12 1 The procedures of Examples 5-11 were repeated except that 13 ¦ instead of being exposed to ultraviolet light the samples were 14 exposed to a combination of ultraviolet light and electron beam radiation in a variety of arrangements: ultraviolet light, then ~6 electron beam; electron beam, then ultraviolet light; ultraviolet ~7 light before and after electron beam; electron beam before and 18 after ultraviolet radiation; and simultaneous electron beam and ul,traviolet ight radiation. The results were co~parable.

26 .. ' .

28 .
29 .
.

Claims (16)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A photopolymerizable composition comprising (a) an ethylenically unsaturated monomeric ester and (b) a photosensitizer having the structure:

wherein R is selected from the group consisting of trichloromethyl, p-dimethylamino-phenyl, cinnamyl and furyl.

2. A photopolymerizable composition consisting essent-ially of about 10-99 parts of (a) an ethylenically unsaturated monomeric ester and about 1-90 parts of (b) a photosensitizer selected from the group consisting of of 2-trichloromethyl-4-ben-zoyl-4-phenyl-1, 3-dioxolane, 2-(p-dimethylaminophenyl)-4-benzoyl-4-pheny-1,3-dioxolane, 2-cinnamyl-4-benzoyl-4-phenyl-1,3-dioxolane, and 2-furyl-4-benzoyl-4-phenyl-1,3-dioxolane.

3. The composition of claim 1 wherein the ratio of the amount of ester (a) to sensitizer (b) is about 10-99:1-90.

4. The composition of claim 1 or claim 2 wherein the ratio of the amount of ester (a) to sensitizer (b) is about 90-99:

1-10 .

5. A photopolymerizable printing ink comprising the com-position of claim 1 or claim 2 and a colorant.

6. A photopolymerizable coating composition comprising the composition of claim 1 or claim 2.

7. A photopolymerizable adhesive comprising the compos-ition of claim 1 or claim 2.

8. A photopolymerizable element comprising a support and a coating thereon of the composition of claim 1 or claim 2.

9. A compound having the structure wherein R is selected from the group consisting of trichloromethyl, p-dimethylamino-phenyl, cinnamyl and furyl.

10. 2-Trichloromethyl-4-benzoyl-4-phenyl-1,3-dioxolane.

11. 2-(p-Dimethylaminophenyl)-4-benzoyl-4-phenyl-1,3-dioxolane.

12. 2-Cinnamyl-4-benzoyl4phenyl-1,3-dioxolane.

13. 2-Furyl-4-benzoyl-4-phenyl-1,3-dioxolane.

14. A method of producing polymeric material which com-prises exposing to a source of radiation an ethylenically unsatur-ated monomeric ester in the presence of the compound of claim 9 as the photosensitizer.

15. A method of producing polymeric material which com-prises exposing to a source of radiation about 10-99 parts of an ethylenically unsaturated monomeric ester in the presence of about 1-90 parts of the photosensitizer of claim 9.

16. The method of claim 14 or claim 15 wherein the photo-sensitizer is employed in an amount within the range of about 1-10 per cent, based on the total weight of the composition.