CA1056189A - Polymeric binders for aqueous processable photopolymer compositions - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Photopolymerizable compositions are described containing a polymerizable ethylenically unsaturated monomer, a photoinitiator or initiator system, and selected acidic polymeric binders. The organic binder mixture contains a compound chosen from each of two selected classes. These photopolymerizable compositions yield superior processability, i.e., on developing and stripping, in solely aqueous alkaline media devoid of organic solvents, decreased softness and/or tackiness, and improved adhesion when compared to the prior art. The compositions are particularly useful for preparing photo-resists.

Description

This lnvention pertains to improved photopolymer-izable compositions that are developable by aqueous alkaline solutions devoid of organic solvents.
It is desirable to have light-sensitive photo- :
polymerizable compositions which can be solvent developed with aqueous alkaline solutions without the need of an organic solvent because organic solvents are costly, may be hazardous with respect to toxicity and/or flammability, may become scarce due to petrochemical shortages, and may pollute the air and water. In general, it is the binder component of the photo-polymerizable composition that determines the solubility of the composition as well as other properties thereof as will be discussed hereinafter.
Representative of the references illustrating aqueous alkaline developable compositions is as follows: ~ ;
U.S. 2~853,368 (binder is a polymer containing salt-forming groups); 2,927,022 (binder is a cellulose polymer containing :: .
acid groups); OLS 2,123,702 (binder is a copolymer such as :
methylmethacrylate/~ethacrylic acid copolymer); OLS 2,205,14 (binder is an acid containing polymer such as styrene/mono-n~
butyl maleate copolymer or vinyl acetate/crotonic acid copolymer); and OLS 2,320,849 (binder is a vinyl addition :
polymer containing free carboxylic acid groups, such as of one or more alkyl acrylates copolymerized with an acrylic acid)~ :
However, the compositions described in these references, while not without merit in some applicationsj still exhibit certain deficiencies, especially when used as photoresists~
The usefulness of photopolymerizable compositions for dry ~;
film reslsts 3 which are laminated as a solid film to a sub~
strate, usually of copper, depends on the proper balance of

-2 - ~ :

~everal properties such as: solvent developability and strippability but res~stance to the etching or plating solutions in the polymerized state, low tackiness, high adhesion to substrate and flexibility.
The aqueous alkaline processable photopolymerizable compositions of the prior art suffer from one or more of the dlsadvantages that they are either too tacky or soft, or are too brittle, or have insufficient adhesion to the substrake to get high resolution images, or even if they are aqueous alkaline developable, the development time is excessive.
Tackiness, for example, leads to the photopolymerizable layer accepting dirt~ including air-borne dust~ etc.~ which may yield "pinholes" in the resist. Further, tacky layers make ~ `
lamination alignment difficult during photoresist element preparation. Also, some areas of the la~yer may adhere to the coversheet during its delamination from the layer. Excessive softness of the photopolymerizable layer on its storage in rolls can lead to cold flow causing edges of the layer to ;
- fuse togetherj lap to lap. If dirt or lint particles inad- -verkently get wound between the laps at manufacture, the localized pressure spots created cause the resist to flow leading to thin spots in the layer which will ultimately `
produce pinholes in printed circuit manufacture. During lamination under pressure and elevated temperature to the ;~
substrate~ soft layers flow excessively leading to distortions in the photopolymerizable layer in the form of ripples of alternating thick and thin areas.
The photopolymerizable compositions of the present invention overcome the disadvantages of the prior aqueous alkaline developable photopolymerizable compositions, i.e., _3_ ; . `` ` ` `

the present composit~ons are so-developable in a short amount of time~ and yet the composition is sufficiently flexible to be laminated as a dry film to a substrate and have high adhesion to the substrate and is neither tacky nor too soft, and develops suf~icient differential solubility during lmage-wise exposure that the polymerized areas resist the developer but can still be stripped upon treatmen-t with stronger aqueous alkaline solution which is devoid of organic solvent.
;. ~ -The photopolymerizable composition of the present invention comprises non-gaseous, ethylenically unsaturated compound capable of forming a high polymer by free~radical initiated chain addition polymerization; organic, radiation~
sensitive, free-radical generating photoinitiator system;and a mixture of binders comprising (A) 25-75% by weight of the ;-~
:.. ~.- , .
total amount of binder an acidic, organic, film-forming polymer having an acid number of at least 20 and which in the form of a fllm is adherent to copper and soluble in an alkaline, aqueous solution but insoluble in water,and preferably having ~ molecular weight of at least 30,000, and (B) a complementary 25-75~ by weight to total 100% of the total amount of binder of an ~cidic, organic pol~mer having a minimum acid number of at least 5 and which in the ~orm o~ a film is insoluble both in an alkaline, aqueous solution, and in water.
The adherence of the polymer film ~ayer)to copper is defined as zero delamination by the delamination test described in Examples 1-27 hereinafter.
Solubility in water or in an alkaline, aqueous solution is measured by spraying the water or solution on a 0.0003 to 0.0023 inch (0.0076 to 0.0584 mm) thick piece of the film which has been formed on a copper substrate. If the ~4~

, ~ ~

, fllm is completely removed fro~ the copper substrate by the spray in 300 seconds, it is considered soluble in the solution with which it is sprayed, otherwise the film is considered insoluble in such solution. The spray has a pressure of 20 psi (1.4 kg/cm2) and a temperature of 80-85F. t26-29C.). Alkaline, aqueous solution is 2 0.04 N NaOH solution.
Film-forming means that a uniform coherent film on copper is formed when the polymer is cast from a volatile solvent and dried at room temperature, which film has a thick-ness of o.oo76 to 0.0584 mm.
The present invention is based on the discovery that ; `
superior photopolymerizable compositions can be obtained using conventional initiators and polymerizable compounds, when combined with the mixture of selected acidic organic polymeric binders hereinbefore described. While it may be expected that acidic binders will dissolve in aqueous alkali, it is surprising that including the novel biDder combinations of this invention yield photopolymerizable compositions with appropriate adhesion and flexibility for photoresist applica-20 tions, particularly with improved solely aqueous alkali ~ ~
processability and decreased tackiness and/or softness. ~ ;
The superiority observed for the compositions of the present in~ention make them particularly useful for photoresist applications. In such applications 3 the exposed portion of the compositlons have satisfactory resistance to etching and plating solutions frequently encountered in the fabrication of printed circuits and chemically machined parts.
With respect to the components of the composition of the present invention, any free-radical generating photoinitlator system which initiates polymerizdtion of ~.' , ' " ' `

the polymerizable compound and does not subsequently terminate the polymeriza~ion can be used. The free-radical generating system preferably has at least one componen~ that has ~n ;
active radiation absorption band with a molar extinction coefficient of at least about 50 within the range o~ about O O
3400 to 7000A, and preferably 3400 to 5000A. "Active radiation -ab~sorption band" means a band of radiation which is active to produce the free radicals necessary to initiate polymerization of the polymerizable compound. The free-radical generating ~ . . . .
photoinitiator system can comprise one or more compounds which directly furnish free radicals when activated by radiation. It can also comprise a plurality of compounds, one of which yields free radicals after having been caused to do so by a sensitizer which is activated by the radiation.
Examples of photoinitiators include aromatic ketones such as benzophenone, Michler's ketone (4,4'-bis-(dimethyl- ;
amino)benzophenone)~ 4,4'-bis(diethylamino)benzophenone, 4-methoxy-4'-dimethylaminobenzophenone, 2-ethylanthra~uinone, phenanthraquinone, and other aromatic ketones; benzoin, benzoin ethers such as benzoin methyl ether, benzoin ethyl ether and benzoin phenyl ether, methylbenzoin, ethylbenzoin and other benzoins; and 2,4,5-triarylimidazole dimers such as 2-(o-chlorophenyl)-4,5-diphenylimidazole dimer, 2-(o-chloro-phenyl)-4,5~di(m-methoxyphenyl)imidazole dimer, 2-(o-fluoro-phenyl)-4,5-diphenylimidazole dimer, 2-(o-methoxyphenyl)-4,5-diphenylimidazole dimer, 2-(~-methoxyphenyl)-4,5-diphenylimid-azole dimer, 2,4-di(p-met~oxyphenyl)-5-phenylimidazole dimer, 2-(2,4-dimethoxyphenyl)-4,5-diphenylimidazole dimer, 2-(p-methylmercaptophenyl)-4,5-diphenylimidazole dimer, and the like dlsclosed in U.S. Patent 3,479gl85, in British Patent -~s~
,047,569, and U.S. Patent 3g7~4,557.
Additional photoinitiators include the 2~4,5-triaryl- ~ ~
imidazole dimers (also known as hexaarylbiimidazoles). These ~`
are used with a free-radical producin~ electron donor agent, ~ -such as 2-mercaptobenzoxa301e, leuco crystal violet or tris(4-di~thylamino-2-methylphenyl)-methane, which is preferred. Such sensitizers as Michler's ketone may be added. Various energy ~ ~;
transfer dyes, such as Rose Bengal and Eosin Y, can also be used. Additional examples of suitable initiators are disclosed ~ -in U.S. Patent 2,760,863. Other useful systems employ a tri~
arylimidazole dimer and a free-radical producing electron donor agent, with or without the use of a sensitizing compound as described in U.S. Patent 3,479,185. Another useful group of ~ `
- ~ .
initiators are those mixtures described in U.S. Patent 3,427~161.
. . .
The concentration of the ~ree-radical generating photolnitiator system is preferably about 0.1 to 10% by weight, and more preferably about 0.2 to 5.0% by weight based on the total weight of the photopolymerizable composition.
The instant-invention is not limited to the use of any particular polymerizable compound~ it being required ~ , only that the compound be non-gaseous, ethylenically unsaturated, and capable of addition polymerization. One or more of the ;
compounds can be present. A large number of useful compounds is available, generally characterized by a plurallty of terminal ethylenic groups. Among the suitable materials may ;~
be mentioned (a) various vinyl and vlnylidene monomers, e.g., vinyl carboxylates, a-alkylacrylates, a-substituted acrylic acids and esters thereof, vinyl esters, vinyl hydrocarbons~
acrylic and a-substituted acrylic acid esters of the poly~
methylene glycols and ether alcohols, all as disclosed in ; '' , -7~

;, . ~ , , ; . , , . ~ .
. .. . . .
. - . .... ..

U.S. Patent 2,760,363; (b) the various compounds disclosed (Col. 16-17) in U.S. Patent 2~927~022, and especially those havlng a plurality of addition-polymerizable ethyle~.ic link- ~
ages, particularly when present as terminal llnkages, and ~;
more especially those wherein at leas~ one and preferably most of such linkages are conjugated ~lith a doubly bonded carbon, including carbon doubly bonded to carbon or to such heteroatoms as nitrogen, oxygen and sulfur; (c) esters of pentaaerythritol compounds of the kind disclosed in U.S. ~
Patent 3,261,686; and (d) compounds of the kind described in ~ ~ ;
U.S. Patent 3,380,831, e.g., the reaction product of trimethylolpropane, ethylene oxide, and acrylic and methacrylic acids.
Many of the low molecular weight polymerizable components discussed previously, including both the mono- and poiyethylenically unsaturated compounds, will normally contain, as obtained commercially, minor amounts (about 50-100 parts per million by weight) of polymerization inhibitors to prevent spontaneous thermally induced polymerization before ~;
20 desired. The presence of these inhibitors, which are usually ~;~
, of the antioxidant type, in such amounts causes no undesirable ;
results in the practice of this invention, either as to speed or as to quality of polymerization. Among the suitable thermal polymerization inhibitors are p-methoxyphenol, hydro-quinone, alkyl- and aryl-substituted quinones and hydro-quinones, tert-butyl catechol, pyrogallol, copper resinate, naphthylamines, ~napththol, cuprous chloride, 2,6-di-tert butyl-p-cresol, phenothiazine, pyridine, nitrobenzene and dinitrobenzene, p-toluquinone, chloranil, and thiazine dyes, e.g~, Thionine Blue G (C.I. 52025)~ Methylene Blue B (C.I.

... . . . . .
: ~ ,: ' , ' ' ' ::

52015), and Toluidene Blue 0 (C.I. 52040).
The concentration of the polymerizable compound is preferably about 7.5 to 35~ by weight and more preferably about 15 to 25% by weight, based on the total weight of the photopolymerizable composition.
With respect to the binder mixture component cf the composition of the present invention, the polymer components thereof can generally be characterized as preformed, compatible macromolecular polymers.
Either of the polymer binder components (A) and (B) may be comprised of a plurality of polymers which are different but which comply with the respective criteria for these com-ponents. The polymers (A) and (B) are solid a~ room tem-perature. The (~) polymers are film-forming, i.ec, form a uniform, coherent film when coated from solution in an organic solvent and dried at room temperature as herebe~ore described.
The (B) polymers may~ but need not, be film-*orming. Hence, film~ of some (B) pol~mers may not be uniform and coherent, e.g,~ due to wrinkling and cracks in the film, which is never-theless adherent ~o a copper surface on which it is formed.
The photopolymerizable composition preferably contains about 15 to 60% by weight based on the total weight of the composition each of (A) polymer and (B) polymer and more preferably the concentration of the total binder mixture is about 55 to 92.4% by welght based on total weight of the composition. ~-Examples of (A) polymers and (B) polymers of the binder mixture are shown in Tables I and II, respectively.

~ .

_g_ .. . ..... ..... . .... .... ~, .. . .... ~ .,; . ... ... .. ...
- , :
' . .

.
o~
I~
~:
o o o .~ ~ ~ ~ , ., o ~ U~ ,~ ' o P~
U~
' ::
.~ g g o O o O
~ rl O o ~ :~ o o o o o o ~, ," ..
æ ~
,4 ~ ~ A /\ A ~U

~ ~
O U~ C~ ~ ~ (~I ~ ~ ~
t.1 ~ L ~ O , U~ .
t) ~ N
~q :~

O --' h Lf\ 9 ~: ~ ~o O
¢ ~ . '.

~. .
~ . . .
`;1- ' o ~

a) ~ u ~n ~ v .~ a ~ ~ a) ~1 5~ 0~ ~ ,D O
a~ ~ ~ ~a C5 ~S ¢ ~a ~ o t~
Ei O ~ a) u ~ o Ei ~ a ~ u o o ~:: o~ ii~ ~ o ~ a ¢
o Lr) U~ 0 O ~ 0 ,~ V h E~
e ` '~~ ¢ v~ P
¢

. ~

.. . . .

TABLE I
(Lç~end) 1. Measured ~ith an O~twald viscometer3 20CJ
on an 8.6~ ~olutlon ln denatured (2B) alcohol.
. Brook~ield V15CO9 itY (~pindle No. 2, 60 rpm, 25C) 10~ solution in methyl ethyl ketone (MEK).

3. As ln 2 above (but at 12 rpm), 17.5~ 6~1ution in MEK (60%~, methyl CEL~OSOLVE* (40%).

4. As ln 2 above, 1~% solution in C~2C12.

5~ As in 4 aboveJ 10~ solution ln CH2C12 (95~), i~opropanol (5%).

6. Accur~tely welgh ~pproxim~tely 1.0 gram o~
thoroughly dry product lnto a 250 cc. Erlen~
meyer rlask, add approxi~ately 50 cc. etha~ol a~d shake or heat to dissolve the poly~er. Add about 10 drops phenolphthalein ~olutio~ and tltrate with 0.1~ NaO~ i~ methanol. Run dupllcat~ s~ples. Acid nu~ber = (ml ~aOH) (NaO~ normality) (56.10)/Sample ~eight.

7. Ball and ring m~thod.

* - denotes trade mark - 11- ~ `

., . .. ,. . . , ,. , ., , . :
. . . .
- , - . :

bO ~) u~ .
~o o ~: ~
~J
~ o o ~ ~ ~

i ~
J~
o o ,~ ~r, I I I I I I I o ~O -c,q ~ .
~ y ~ ~:
~ o U~O ~) ~ ~ ~ ~ ~ ~ , N
H ~u~ r~ ~ ~ ~ `;t O O oo H E~p O '~
O ~o ' 1~ . ' _ C~ -a~ . ~
~,~ ~ Cl~ ~ ~ ~ I -- ~ o cc 1~ ~ o ~ a~

~ ~ ¢ oo ~ ~ ~ w ~ ~ r~ 'd h rl r~ ¢p ~n ~ u ~ a u ~ ~ a ~ o S~ O) ~ ~ O fi O ~ ~
o~) r~ ~ ~ ~ a) u ~ s ~~
o ~ U ~ ~ ~ U
p~ a) rd ~-~ i)~ ~ h Q) t~
, r~ ~ o co t) ~ U æ~ ~ O ~A
0, 0 O ~ ~ ~ ~ O ~I r I ~ H al 1 t:) .~ , .C S~,~ h ~ ~ ~ co oo 0 ~rl h ~A r 1 S:
o o a~ U V C~ r-l O E~ ~ X ~ ~ P ;~ P P ~1 E3 U~ h $ q~ m ¢ ~q ~ . ~ . , ..

bOC) ~: o ~ O O O
`~D 1 aJ ~ ~ j~ ,/ :
O O , Ir~ O O
O p~ ~ ~ ~) ~ r-~ I ' I ' I I ~ I
~1 ~J
O O O O O O O
~ O O O o o O o O.~rl 1~ r` o~ o o o o . ~ ~ 1 . o 0` 0 . o P . ':,:
_~ I . .
o .
l . . ~ ..
OO :1 ~ ~ ~ ~ C~Ir) ' Lt) O O
_~ O ~ o~ ~') ~ ~ ~ :
æ~ `~
., O O o ~ ~ C~ O ~ O o o~
~S ~ ~ ~ r l r~ ~

r l P~ .i r~

h ~ V

~ ~U~o ~ 8 r/~ ~ h r~~ r~ h hC~) ~

~ ~ ~ O ~ ¢ ~

:~ ~ a ~ P ~ ~

;: .

--i3~

: . `, : : - , .. , '. :
. A . . .

TABLE II
(Legend) 1. See note (6)~ Table 1.
2. See note ~2), Table I, but 10% in acetone.
3. As (2) aboveg 10,~ in CH2C12.
4. See note (2)~ Table I.
5. As (2) above, solvent 90~ CH2C12, 10% CH30H.
6. This value is the relative viscosity of the polymer; the relative viscosity of the polymers RR, SS, and TT is 11.4, 27, and 15.5, respectively.

. -It is surprising that polymer (B)g present in amounts varying from 15-60%, by weight, while insoluble as a film in a dilute caustic spray by the solubility test herein-before described, nevertheless permits the entire binder mixture to have the required solubility, whereby the un-polymerized film area of the entire photopolymerizable composition is readily soluble or dispersible under solely aqueous alkaline development to yield a clean, scum-free substrate surface.
Both polymers (A) and (B) are preferably vinyl addition polymers containing free carboxylic acid groups, which are preferably prepared from 30 to 94 mole percent of styrene or one or more alkyl acrylates and 70 to 6 mole percent of one or more a,~-ethylenically unsaturated carboxylic aclds. Suitable alkyl acrylates for use in preparing these polymeric binders include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, etc. Suitable a,~-ethylen-ically unsaturated carboxylic acids include acrylic acid, . . .,: - .:, , . ,, .. : .. , : .

~5~

methacrylic acid, crotonic acld, maleic acid or anhydrlde and the like.
These po]ymers can be prepared ~y ~ny of the polymerization techniques known to those skilled in the art.
Other components such as conventional addi~ives may be present in the photopolymerizable compositions of this invention. For example, small quantities of a dye may be present in the composition to aid the user to locate the position and presence of the residual polymerized portion, after the unpol~merized area of the layer has been dissolved away. The dye incorporated preferably should not absorb excessive amounts of radiation at the exposure wavelength or -~
inhibit the polymerization reaction. Examples of such dyes are disclosed in U.S. Patent 3~479,185.
When the compositions of the present invention are applied to metals such as for use as a photoresist, an adhesive aid is frequently added to the composition. Useful adhesive aids, which may be incorporated, include the mono-meric or polymeric organic silanes, and the nitrogen contain-ing heterocyclic compounds, e.g., benzotriazole, disclosed inU.S. 3,645,722, and U.S. 3,622,234.
In addition, other ingredients such as plasticizers, fillers, etc., also may be present as is well known in the art.
The components of the photopolymerizable compositions of the present invention will ordinarily be mi~ed together in .. .
a material that is a solvent for all of the components. The particular solvent used is not critical; it merely affords a practical method of obtaining coatings or self-supporting films of the compositions. Representative of solvents that may be .. , , . . , . .,, .. ~ . , , , ~ .. . , " . , . .~, ~ ~, . ~ . , , -5~

used, but in no way limiting are 2-propanone, 2-butanone, 2-pentanone, 1,2-dichloroethane, methyl acetate, dichloro-methane, trichloromethane, and ethyl acetate. Of course, when organic solvents are used, the polymers (A) and (B) must each be soluble therein.
In practlcing a preferred embodiment of the invention, an element containing an image-yielding photopolymerizable layer is made by coating a layer of the photopolymerizable composition on a suitable film supportOwhich has only a moderate adherence for the composition and is dimensionally stable to temperature changes. After drying the photopolymer-izable layer, a removable cover film is laminated to its surface. The photopolymeriæable composition is coated to give a dry coating thickness of about 0.0003 inch (0.0076 mm). A
sultable support film 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 (o.oo64 mm) to 0. oo8 inch (0.203 mm) or more. If exposure is to be made before removing the support film, it must, of course, transmit a substantial fraction of the actinic radiation incident upon it. If the ~ `
support film is removed prior to exposure, no such restrictions apply. A particularly suitable film is a transparent poly-ethylene terephthalate film having a thickness of about 0.001 inch (0~0254 mm). Suitable removable cover films may be chosen from the same group of high polymer films described above and may have the same wide range of thicknesses. A cover film of 0.001 inch thick (0.0254 mm) polyethylene is especially suitable. Support and cover films as described above provide good protection to the photopolymerizable layer. To apply ., ., . . .. ~ .. . , . ., .. . .. .. .. . . . , . .. _ - - ' -:
, . ., ~

~V~&~

the layer to, say, a copper-clad fiberglass rlgid support to be used as a printed circuit, the cover film is stripped from the element and the resist layer on its supporting film is then laminated with heated resillent pressure rolls to the copper surface of the rigid support. This provides a sensitized surface ready i~mediately for exposure but stlll protected ~ `
from dirt, lint and abrasion by virtue of the original support ~;
film. To produce a resist image, the element is exposed `
imagewise through the support film and said film is then peeled off and the exposed resist developed by washing away the un-exposed areas with dilute aqueous alkali which results in a rigid support bearing a relief resist image on its surface.
Because of the high chemical resistance of the binder ~ixture of polymers (A) and (B)~ the element may then be subJected to the conventional operations of plating, etching, etc. as is well known to those skilled in the arts using resist images.
The preferred process for forming photoresists on metal or other surfaces, including glass, ceramics, etc., with compositlons of this invention comprises: ~
(1) applying directly to such surface the photo- ~ -polymerizable composition as a dry solid layer having a thick-ness of at least 0.00005 inch (0.00127 mm) and low to moderate adherence to a thin, flexible~ polymeric film support;
preferably with heating or later heating at a temperature from 40C. to about 150C. to increase the degree of adherence be-tween said surface and said layer; then, in either order, (2) exposing the layer, imagewise, to actinic radiation to form a polymeric image on the surface; and ;
(3) stripping the film support from the resulting image-bearing layer;

...... ... . . . ... . .. .... ., . .... _ . , . .. ~ ~ ... . .

(4) washing away the unexposed areas of the layer to form a resist image of polymeric material which is developable with aqueous al~aline solutions devoid of organic solvents;
(5) permanently modifylng the areas on said surface which are left unprotected by the resist image by using a reagent capa~le of etching said areas or depositing a material on said areas.
The surface can then be treated with a suitable reagent to form an etched surface7 or plated or processed in other ways. The polymeric image can then be removed by means of a caustic aqueous solution devoid of organic solvent with or without the aid of mechanical action, e.g., by rubbing, brushing and/or abrading, etc., or by a combination of one or more such steps.
This process is useful for making decorative photo-engravings and chemically milled and electro-formed elements.
Examples of etchable metal surfaces are magnesium, zinc, copper, alloys of such metals, aluminum~ anodized and dyed anodized aluminum, steel, steel alloys, beryllium-copper alloys.
Development of imagewise-exposed compositions of the present invention is not limited to the development done in the solubility test described herein. The solubility test provides a way to compare development times. Conventional solely aqueous alkaline development solutions and equlpment can be used.
While the compositions of this invention are particu-larly applicable to photoresists, it will be obvious to one skilled in the art that the advantages discovered can be - - - - - , .. ...

, : ' , ' , '' .

~v~
beneficlal in alternate photopolymer applicatlons involving solvent washout. FGr example, the ~nventive compositions may be used to provide a photopolymerlzable coating on aluminum for a lithographic plate as described in U.S. 3,458,311.
The invention will be further illustrated by, but is not intended to be limited to the following examples, wherein parts and percentages are by weight unless otherwise noted.
Examples 1-27 These examples describe the delamination test, and solubility test used to classify the acidic organic polymers as (A) or (B) polymers. The polymers were each dissolved in an organic solvent, coated onto copper via a doctor blade, and air-dried. The dried coating thickness was measured; also, and the adhesion and film-~orming capability of the polymers were observed. Quantitative adhesion and solubility data were also obtained on the coated samples. Adhesivity (anchorage) was determined using a delamination test; solubility was measured using a wash-off test, both described in detail below.
For photopolymerizable compositions to be useful as photoresists, they need to adhere at least moderately well to a substrate, e.g., copper. Since the binder is normally the ma~or component of photopolymer compositions, it follows that the binder ltself should possess adequate adhesion (anchorage) to the substrate, e.g., copper. A convenient method for determining adhesivity of such a laminated structure (i.e., ~
binder layer coated on copper) is to measure the degree of de- ~;
lamination, i.e., the degree to which the organic binder layer or film is removable from the substrate. Tests of this type are well known in the art, e.g., U.S. 3,615,557, Ex. I; indeed, a similar procedure was used.
.: .

-19 ~ ' The delamination test was conducted as ~ollows:
Using a templatel tlle dried polymer/copper laminate described above was scored with a knife 7 through the polymer layer, to yield l/8 by 1/8 inch (3.175 x 3.175 mm) squares.
A piece o~ cellophane, pressure-sensitive, adhesive tape is then pressed down over the scored area and a loose end of the tape grasped at about a 90 angle to the film surface. The tape is pulled up briskly and the number of squares remaining on the copper counted. By comparing the number of squares on the adhesive tape after its brisk removal, versus the original number of squares scored (usually around 50), the percentage delamination can be readily calculated.
Solvent development of typical photopolymerizable layer requires removing unexposed, unpolymerized areas ~rom copper via a solvent. Again, since binder is usually the major component o~ the layer, the binder layer itself should be readily dissolved from substrate (e.g., copperj. Thus, the time required to completely wash-off the binder layer from the binder/copper laminate, using dilute aqueous NaOH (o.o4N, 0.16%) spray at 26-29 C., was determined. The laminates were mounted on an oscillating plate~ 15.24 cm. from spray nozzles; a pump was used to eject the spray at 1.4 kg/cm2. The holes in the nozzles used will pass a 5/64 in. t2 mm) drill, but will not pass a 3/32 in. (2.4 mm) drill. The nozzles used were obtained ;
from Spraying System Co., 3201 Randolph Street, Bellwoodg Illinois. The nozzles used were No. 1/8 GG 6 SQ.
The data obtained for the binders listed in Tables I
and II, per the above tests, are summarized in Table III.

` - ~"' `

.. .... . .

~5~

O ~. O o Ln o ~ Ln Ln o o o oo ~ ~ ~ o o o o o t, ~ o o ~ ~ ~ ~ ~
n a) ~ `J A A A ~ A
V) E ~ O O O O O O O o O O o O
o) I P

~ l .
. ', i ~ lU ~ ~
~ L~ ~
~ O .
U~

a _ ~ O ~ N ~ ~ Ln O ~ Ln C;~
Ch r-- I~ N ~ ~) OC) ~ 1~ 9 N ~
o 3 O O O N O O O O O O O O O
Ei ~
~ rl X
.~F~-- :' .
,_1 . '~
.
V ~_~
u ~ ~ x Z~ $ u~ u ~

, ' ' ~ ~ .
:

~ ,, , . ,. . . , , ., , ,, .. , .. . . . . . . . .. .. . , ` .... . ..

~S~

~a u) o ~:~ o o o ~ o o o o o o o o o l o o o o ~ o o o o o o o o o ~:
A A A ~ - A A A A A A A A ,.

.
.~
^,~ . ' :
. ~ ~
t.q O o o ~ O O O V
~3 ~ O E-' O '~ - O O
~_ ~ ~ ~ O
O E~
~Z; - -' ~ 0~
C~ ~ O ~ rl oa~ o ~ ~ F~ ~ ~ ~ ~ ~ ~ ~1 P~ ~
~ ~~r~ ~ ~rl Pq ~ rl h h S~
¢ ~ Q m U~
_~
o E~ ~, o o oo o o o o :.
,~ ~ ~ _ ~ ~ . ..
V ~ ~ . .

rlO ~ ~ -- oi . .

.
.

. ~ .

, . :

Controls I - XVII
_ A series of the same photopolymerizable composition in which only one polymer was present as a binder were prepared and subJected to the photoresist process. The polymer was either an (A) polymer or a (B) polyrner The photopolymerizable composition was as follows:
Components Grams Triethylene glycol dimethacrylate 20 Benzophenone 4 Michler's ketone 0.2 Victoria Pure Blue B0 0.1 ;
Binder 75.7 Copper cla~, epoxy-fiberglass boards were cleaned by scouring with an abrasive cleaner, swabbing and thoroughly rinsing in water, then dried with air ~ets.
The photopolymerizable compositions were coated, using a o.oo6 inch (0.1524 mm) doctor knife opening, onto 0.001 inch (0.0254 mm) thick polyethylene terephthalate transparent film, then dried in air. Each resist coating with ;~
its support was laminated to the clean copper with the surface of the photopolymerizable layer in contact with the copper surface, The lamination was carried out with the aid of .
rubber covered rollers operating at 100-115C. with a pressure of 3 pounds (1.362 kg) per lineal inch (2.54 cm) a~ the nip~
at a rate of 2 feet per minute (61 cm). The resulting ~
sensitized, copper clad board protected as it is by the ~ ~ -polyester film, could be held for later use if need be.
Actually it was exposed to light through a high-contrast ;
transparency image in which the conducting pattern appeared ~ ;
as transparent areas on an opaque background. The exposure - ... . : ' ,: : : .' : ' ~ , :. :
. . .

was carried out by placin~e~e~itized copper clad board (with its polyester ~ilm s~ill intact) and the transparency into a photographic printing frame. The radiation (exposure) source ~as a scanning mercury arc under 25 inches (635 cm) vacuum. After exposure, the polyethylene terephthalate poly-ester support film was peeled off and discarded leaving the exposed resist adherent to the copper surface. The board was then developed by placing it in a spray of 0.04 N NaOH, at 26-29C. at 1.4 kg~cm2 as described in the preceding Examples.
This step left the Pure Blue BO colored resist on the copper in the pattern of the clear areas of the exposing transparency and should leave no resist in the complementary opaque areas.
The boards were then etched with 45 Baume ferric chloride solution at 130F. (55C.). The boards were left in the etching apparatus until the copper was completely etched away in the areas not covered by the resist image. The etched board was rinsed in water and dried, leaving the resist covered copper conducting pattern on the fiberglass board. The resist was finally removed from the copper by 1-3 minute spraying .~
with 3% NaOH at 55C. The boards that looked unsatisfactory after the development step, i.e., the unpolymerized area was not removed, were generally not sub~ected to the etching step.
The polymers tested, organic coating solvents used, resist thickness, exposure time, development time, etching per~ormance, and other observations, are reported in Table IV.

D~
O ~ h ~`
~Q --I O
O p~ 1 0 h ~J~ h 1;~ rJ CU E3 S ,, o ~
..
~ ~ 1a) o ~ o I
p: l E~ 0 ~
~ h ~ O cB E3 ~ h q~ o cl h c) h El o o o ~ ~ ~ 5) o ~ o ~o ' o o o o o o o i I I o P~ .

o E3 0 o ~ N ~) A A
~'' ' a l o o Lr o o ~ u~ I o o o ~ ~
a ~ O O
h i~; ~ ~a~ ~ co co co co a:) co o ~ co o~
~ ~ ~,~ ~ O ~ 0~ ~1 0 0 ~O O O ~
1-l -i -i 0 ~ o ~

,1 ": :. ,.``
~ ~ ~ :'~'; .'' ~:
O O I ~ Q

O
C~ ~r) ~ ,I r~) V
$ ~
p¢ ~

O O C~ O N C\l V U2 g h ~ . ~~ .
~"0 ~ ` ' E~ ., ,1 h H H H p ~ j-l H H X ~q H
Ç H 1-1 H ;:~ p H 1-1 X
O

- ~5 -~ :
o ~.¦ 0 0 h ~i I I ~ o P; ^~1 ~4 0 14 al) ~ h O C~
,~,~: h~ ~ o ~ o o~ o o a~
bJ C~
~ h ~ ~ ~
~ I I I I P-~
S::
~, 8 g i . g pE~ ~

CO ~ ` ~
~ ~ .~ ~ ) CO ''~` '~''''"'' ~ ~ C)O ~ O ~ '' :~' E~; P~ < o ~1 ~: ',. ;~'"
I I _~ I _~ I . , I I P ~ ~ O I
tY') t~

~ ~ -, U~ .

O ~~ N
vu~ ~ "

H .
~3 a) H
p.
E~

H j~ ~ ~ H

. :, : ` `, : .
.. . ~ .. .
~` , .. : .........

Examples 28-4~) Photopolymerizable compositions, illustrative of the present inventiong were prepared and evaluated as re-sists exactly as described ~or the control experiments except as otherwise indicated in the summary of results shown in Table V~
In Table V~ the following abbreviations have been used~
TDMA = triethylene glycol dimethacrylate ~:
TMPTA a trimethylol propane triacrylate -PETA = pentaerythritol tri- and tetraacrylate, approx. 60:40 :
BP = benzophenone . :
MK = Michler~s ketone, 4,4'-bis(dimethylamino) ~:
.. . .
benzophenone HABI = 2-o-chlorophenyl-4,5-diphenylimidazolyl dimer (2,2'-bis(o-chlorophenyl)-4g4',5,5'- ;~
tetraphenylbiimidazole).
Leuco dye = tris-(4-N,N-diethylamino-o-tolyl)-methane 2-Aq = 2-tert-butylanthraquinone 2-EtAq = 2-ethylanthraquinone MEK = methy]. ethyl ketone ;~
' ' , , :

- ' .. . . . .
', ' ' ' :' , . , ~ . .

bO ~ 35~
.,1 ~
.c C, ~,.
o ~
~j GJ O O O O O. o o ~( ' . ..

r~ V O O O O O ~ O

U) ~ r QJ U r~ r~ O r-( C~ CS~ ~\. O O
~; ~ ` _~ ,--I O O I--1 . .

O - ~:, b5 _ ~ ~ o GJ U~
~1 ~_ ~ ,( U~ ~ U 0~ ô C, ô
~1 ~ ~ C~ O O' O
P~ .r r' r ~ r ~ ~ -~
t:~ I r V ~_) V ,~ ~ VJ

~::1 U~ : . . , GJ S I
~ ~C O O' p~ " : ,, ~ ~ . : . '' ..
-- H ~ ` t~
E3 ~0 H~) O ~ 0 r~
O E~ ~ ~ u~ ~ 'S C~ C.7 . ~ ' O
bD rt Ou~ O O ul O L~ O

h _ ~3 ~ ~O~ O rl N fr) ~ 15 c~ ~ c(-~ o - - - = = - - = - - = = =
F~

oooInooo ooo~ooo :~:

u~ o o oo u~ o u~ o o o ~ o o ~:
E~ ~q ~0 ~ ~ O ~ .~

c~ o o ~ ~ o~ o o~ o 0 ~ a~ o o ,~ o 1 -i O O O '~ O '~

N ~I COU CX~
~ ~ (Y~ ~o o a) --~d ~D C: N 0 1-- 0 5:~ ~ N CU
o ~ ~q o _ =~ - = ~1 r; C~ o o _V 'I ~ ~ V ~ trl ~ ~ ~ ~ c, O O C~J ~ V ~4 ID ~ CU N
O Cc ¢ c~
_ td. b .
~ _ O `-- o ~ ~ O
ct; ~ 3 ;~ h ~) ~3 o o `- ~
E~ ~ . ~ s ,_~ . = = = _ ~_, ~ ~3 _ = , , o ~ ~ ~_ o ~
~ ,~ ¢ p~, _ ..
1 ~ ~H
Q)--' a) o u~ oo o ~ ~ o o~ o~ o o L~
o V E-~ v ~:
V--H ~ ~ ..
h ~ Ir~ O L~ Lt~ O O 15~ O Ir~ O
,$ O ~ ~ ~ N '~D = r~
,~ v ~ ~ m q a~ ~ ~ ¢ m P~ .sc ¢ ~- ~

h ¢
¢ E-l ¢ ~ C~

~1 ~ ~ 0 cr~ o ~I C~l ~ ~ U~ ~ ~ 0~ O~
x ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
`

: ~ . . .
'~

~3S~

In additio~ to the data of Table V, the follow-ing remarks regarding resist performance further illustrate the advantages observed for the compositions of this lnvention~

Example Remarks (comparison with results from ~: Table IV) 28 Flexible, adherent, non-tacky film; no ripplemarks on lamination . .
29 Same as Ex. 28 ~ .

10 30 No softness, no ~ndentations, no scumming 31 Flexible, non-tacky film, good adhesion 32 Non-tacky film, good adhesion, no monomer - ~
exudation ~ -33 No ripple marks during lamination 34 Same as Ex. 33 ~
No scumming, no softness ~ :
36 Non-tacky film, no ripple or pressure marks 37 Non-tacky film, no softness or indentatîons 38 Same as Ex. 37 20 39 Same as Ex. 37 Flexible~ adherent filmg no so~tness or indentations 41 Same as Ex. 40 42 Non-tacky film, developed without scum 43 Flexible, adherent film, no tackiness3 softness, or indentations :
44 Non-tacky film with good adhesion to copper :
Same as Ex. 37 46 Same as Ex. 37 3o 47 No softness on ripple marks ... .. , . .. .. . , . .... .. ,~,~.. .
- ~ .

.
j Example Remarks (comparison wlth results from Table IV) ~-~
. . ~: .:
48 ~o ripple marks during lamlnation 49 Same as Ex. 48 '; ~ '..
A photopolymerizable composition was prepared `~ ~;
containing .
copolymer o~ methyl methacrylate 1.8 g and metha~rylic acid (binder BB) :~
10 polymethylme~hacrylate, mol. wt. 1.5 g 258,00 plasticizer of triethylene glycol .8 g dicaprate and dicaprylate mlxture trimethylolpropanetrlacrylate 3.4 g 10% solution in ethyl cellosolve of 18 g terpolymer o~ ethyl acrylate, methyl~
methacrylake, and acryllc acid (binder F) .. : :.
Michler's ~etone .1 g ~-~
trichloroethylene solvent 100 g ;
20 ethyl cello~olve 43 g c-chloro-hexaarylbiimidazole .4 g .: ~
- .
The above solution was coated on a polyester support an~ drled to giv~ a layer appro~imately 0.0005 ~ -inch thick. The dried layer was a uniform, coherent fllm whlch was non-tacky. The layer wa~ lmagewise exposed for -~:
30 ~econds with a xenon arc and developed i~ an alkalinef ;~
aqueous solution comprising a 10~ solution o~ sodium car~
bonate in water, the developer solu~ion being ~evold o~ any organic component. The unexposed areas were completely removed by the developer leav~ng the exposed, polymeri ed areas on the support.

Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follow:

1. In a photopolymerizable composition containing 0.1 to 10% by weight of an organic, radiation-sensitive, free radical generating photoinitiator system, 7.5 to 35% by weight of a nongaseous ethylenically unsaturated compound capable of forming a high polymer by free-radical initiated chain addition polymerization, and 55 to 92.4% by weight of polymeric binder, the improvement wherein the binder comprises a mixture of 15 to 60% by weight of (A) an acidic, organic, film forming polymer (1) being insoluble in water at 85°F, (2) having a molecular weight of at least 30,000, (3) having an acid number of at least 20, and (4) capable of forming a uniform coherent film on copper when cast from a volatile organic solvent and dried at normal room temperature, said film (a) ranging in thickness form 0.0003 to 0.0023 inch, (b) adhering to the copper such that zero delamination is found on a scribe cross-hatch test, and (c) dissolving completely within 5 minutes when sprayed with dilute aqueous alkali, 0.04N NaOH, at 20 lbs/in2 and 80 to 85°F; and 10 to 60% by weight of (B) an acidic, organic polymer (1) being insoluble in water at 85°F, (2) having an acid number of at least 5, and (3) in the form of a film ranging in thickness form 0.0003 to 0.0023 inch on copper being not completely soluble within 5 minutes when sprayed with dilute aqueous al-kali, 0.04N NaOH, at 20 lbs/in2 at 80 to 85°F, all weight percentages being based on the weight of the total composition.

2. A composition according to Claim 1, wherein binder component (A) is a copolymer of vinyl acetate and crotonic acid, a terpolymer of ethyl acrylate, methyl methacrylate, and acrylic acid, or cellulose acetate succinate.

3. A composition according to Claim 1 wherein binder component (B) is selected from the group consisting of a copolymer of toluene sulfonamide and formaldehyde, a copolymer of methyl methacrylate and methacrylic acid, a copolymer of methyl methacrylate, ethyl acrylate and meth-acryloxyethyl hydrogen maleate, a terpolymer of vinyl chloride, vinyl acetate and maleic acid, a copolymer of styrene and maleic anhydride, a terpolymer of methyl methacrylate, ethyl acrylate and methacrylic acid.

4. A photopolymerizable element comprising a film support bearing a layer of the composition of Claim 1.

5. A process for forming a photoresist on a surface comprising:
(1) applying to a surface the surface of a photopoly-merizable layer of an element of Claim 4; followed by (2) a step selected from the group consisting of (a) exposing the layer, imagewise, to actinic radiation to form a polymeric image and stripping the film support from the resulting image-bearing layer and (b) stripping the film support from the photopolymeriz-able layer and exposing the layer, imagewise, to actinic radiation to form a polymeric image;
(3) washing away the unexposed areas of the layer to form a resist image of polymeric material with an alkaline, aqueous solution, and (4) permanently modifying the adjacent areas on said sur-face which are unprotected by the resist image by using a re-agent capable of etching said areas or depositing a material on said areas.