CA1080249A - Photopolymerizable recording material - Google Patents

Abstract

ABSTRACT
Photopolymerizable elements which comprise a base support bearing a photopolymerizable alyer comprising an ethylenically unsaturated monomer, an aqueous-alkali soluble polymeric binder, a photoinitiator and/or initiator system wherein the monomer is of the formula:

n is 2 to 6.
The monomers are novel. The elements are useful in preparing photoresists which have improved stripping properties in aqueous-alkali solutions.

Description

-~08Vz~g BACKGROU~D OF T~E INVENTION
~ield of the Invention This invention relates to photopolymerizable elements, and more particularly to such photopolymerizable elements containing new ethylenically unsaturated monomeric compounds. This invention also relates to new ethylenically unsaturated monomeric compounds which are mixed esters of glycols with acrylic and/or methacrylic acid and carbonic acid.
DescriDtion of the Prior Art Photopolymerizable elements are known to be useful in making relief images for use in the printing industry. Another important area of use is in the preparation of printed circuits. For this latter use, the light-sensitive photopolymerizable layer of a photopolymerizable element is brought into contact with a printed circuit board, e.g., copper substrate, and, after imagewise exposure, the unexposed areas are completely removed by means of a suitable solvent leaving the corresponding areas of the circuit board exposed to the air. The areas of the circuit board corresponding to the areas of the photopolymerizable element that have been removed can then either be etched or plated with metals by known methods. The areas of photopolymerized element remaining on the citcuit board, which served as a protective layer or resist during etching or plating, must now be removed ~- (stripped). Originally, the removal of the unexposed areas, as well as the stripping of the exposed photo-polymerized areas, was accomplished by means of organic

-2-108~)249 solvents which predominantly contained chlorinated hydrocarbons.
Organic solvents, however, are toxic and must be safely disposed of for ecological reasons. Aqueous-alkali soluble photopolymerizable compositions are now available for preparing printed circuits which overcome the aforementioned problems. In fact, compositions are known whereby both development after imagewise exposure and stripping of exposed residual areas of the photo-polymerized layer after the etching or plating stepscan be accomplished solely by means of an aqueous-alkali solution.
It is disadvantageous, however, that although the stripping of the exposed residual areas of the photo-polymerized layer is accomplished by an aqueous-alkali solution, such a solution does not dissolve the exposed residual areas. The exposed areas during stripping remain in the form of a thin film residue in the solution. The stripping step generally occurs in continuously running machines, and, as a result, the thin film residue obstructs nozzles, tubing, pumps of these machines making automatic stripping of the residual areas extremely difficult, if not impossible.
In addition, the undissolved film residues remaining in the stripping solution can be deposited onto the circuit board surface and thereby impair the subsequent etching process.
It is the object of this invention to provide a photopolymerizable element having a photopolymerizable layer which is developable in aqueous-alkali solution and the exposed areas of the photopolymerizable layer are dissolvable in an aqueous-alkali solution. Another

-3-l~VZ49 object is to provide new ethylenically unsaturated monomeric compounds for use in photopolymerizable elements.
SUMMARY OF THE I~VENTIO~l In accordance with this invention improved photopolymerizable elements are provided which comprise a base support bearing a layer of a photopolymerizable composition comprising (a) an ethylenically unsaturated monomeric compound, (b) an aqueous-alkali soluble polymeric binder, and (c) a photoinitiator and/or an initiator system;
the improvement wherein the monomeric compound has the general formula:
R

O - CO - O - C2H4 - O - CO - C = CH2 (C~2)n O CO O C2H4 - O - CO - C = CH2 R
wherein R is H or CH3 and n is a number from 2 to 6.
There is also provided novel ethylenically unsaturated monomeric compounds which are mixed esters of glycols and acrylic and/or methacrylic acid and : carbonic acid of the formula: R

2 n O CO O C2H4 0 CO C, CH2 R

wherein R is H or CH3 and n is a number from 2 to 6.

~: `

4~

DETAILED DESCRIPTION OF THE INVENTION
Photopolymerizable elements comprise a base support bearing a layer of a photopolymerizable composition containing an ethylenically unsaturated monomeric compound, a polymeric binder and a photo-initiator and/or initiator system. In the elements of this invention the polymeric binder is aqueous-;. alkali soluble and the ethylenically unsaturated monomeric : compound has the formula:

R
, 2 4 CO C CH2 . (CH2)n O - CO ~ ~ C2H4 ~ - CO - C = CH
R

wherein R is H or CH3 and n is from 2 to 6.
The monomeric compounds are mixed esters of glycols and acrylic and/or methacrylic acid and carbonic acid. The compounds are prepared by means of the esterification of bis-chloroformic acid ester of the corresponding glycol with 2-hydroxyethyl acrylate and/or 2-hydroxyethyl methacrylate according to known esterifica-tion methods. These monomeric compounds have a boiling point above 220C. at normal atmospheric pressure and a molecular weight of at least 346.
The preparation of a mixed ester of the : invention is described as follows:

Preparation of ethylene glycol-bis-[(2-methacryloyl-oxyethyl)carbonate]
: First Stage Ethylene glycol-bis-chloroformic acid ester ~80~49 is prepared by the reaction of ethylene glycol with phosgenes according to the data in Houben-Weyl, Methods of Organic Chemistry [Methoden der organ. Chemie], 4th ed., vol. VIII, pp. 102 and 103.
Second Stage Esterification using 2-hydroxyethyl methacrylate.
A solution of 80 ml dry pyridine in 90 ml benzene together with a spatual tip of hydroquinone is cooled while stirring with an ice/common salt mixture in a 50 ml 3-necked flask. To this solution is added dropwise a solution of 46.75 g ethylene glycol-bis-chloroformic acid in 50 ml benzene. The solution is subsequently further cooled down, wherein there is added a solution of 65 g methacrylic acid-2-hydroxy-ethyl ester in 60 ml benzene in a manner that the temperature does not rise above 0C. The reaction mixture is stirred at room temperature for 2 hours and is then poured into ice water, is acidified with HCl, and is then rinsed three times each with 5% by weight HCl and water. The organic phase is then dried over MgS~4 and is evaporated. There remains 51 g of the desired compound in the form of an oil. For purification, the oil is dissolved in chloroform, is filtered over neutral A12O3 and the chloroform is subsequently evaporated.
For stabilization, the oil is treated with hydroquinone - up to a concentration of 0.25 g/l.
Other representatives of the mixed esters can be prepared usihg other glycols in place of ethylene glycol and/or the corresponding acrylate in place of the methacrylate.
. , lV8~249 The new monomeric compounds can be used by themselves or in mixture with one another. Monomeric compounds can be present in an amount of about 10 to 50%
by weight based on the total weight of the photo-polymerizable composition.
The photopolymerizable elements are prepared by applying onto a base support the aforementioned ethylenically unsaturated monomeric compounds together with at least one alkali-aqueous soluble polymeric binder and photoinitiator and/or initiator system in their proper ratios using conventional coating methods and drying. The layers formed are generally in a thickness of 2 to 125 microns.
There are many known alkali-aqueous soluble polymeric binders which are suitable for use in the photopolymerizable element. The binders frequently contain alkali-aqueous soluble groups, e.g., acid anhydride, carboxyl, sulfoacid groups, etc. Examples of such binders include: Acrylic acid and/or methacrylic acid polymers and/or their copolymers together with other suitable monomers, such as, acrylic acid ester or other acryl derivatives, vinyl compounds, such as, vinyl ether, vinyl acetate or their saponification products, styrene, vinyl pyrrolidone, butadiene and related monomers; polyacrylic acid anhydride; copolymers of maleic acid anhydrides, maleic acid, maleic acid semiesters, -semiamides and/or anhydrides and derivatives of related compounds such as itaconic acid, with suitable comonomers such as styrene, ethylene, vinyl ethers, vinyl acetates, etc.; polystyrene 1~}8V249 sulfonic acid and/or copolymers thereof; cellulose derivatives, such as, carboxy methyl cellulose, cellulose phthalate or -succinate, alginic acid and derivatives thereof.
The polymeric binders can be present in an amount of about 30 to 80~ by weight based on the total weight of the photopolymerizable composition.
Practically any known photoinitiator and/or initiator system can be used in the photopolymerizable compositions. The initiator system initiating the addition polymerization reaction can contain one or more compounds which when activated by actinic radiation directly yield free radicals, or yield such free radicals when stimulated by a sensitizer compound which has been activated by actinic radiation.
Suitable photoinitiators and initiator systems include: aromatic ketones, e.g., benzophenone, Michler's ketone (4,4'-bis(dimethylamino)benzophenone), ; 4,4'-bis(diethylamino) benzophenone, 4-methoxy-4'-dimethylaminobenzophenone, 2-ethylanthraquinone, phen-anthraquinone and other aromatic ketones; benzoin, benzoin ethers, e.g., benzoin methyl ether, benzoin ethyl ether and benzoin phenyl ether, methyl benzoin, ; ethyl benzoin and other benzoins; and 2,4,5-triaryl-imidazole dimers, e.g., 2-(o-chlorophenyl)4,5-diphenyl imid&zole dimers, 2-(o-chlorophenyl)4,5-di(m-methoxyphenyl) imidazole dimers, 2-(_-fluorophenyl)4,5-diphenyl imidazole dimers, 2-(o-methoxyphenyl)4,5-diphenyl imidazole dimers, - 2-~-methoxyphenyl)4,5-diphenyl imidazole dimers, ~ 30 2-(_-methoxyphenyl)4,5-diphenyl imidazole dimers, 4~
2-4-di(_-methoxyphenyl)-5-phenyl~imidazole dimers, 2-(2,4-dimethoxyphenyl)-4,5-diphenyl imidazole dimers, 2-(~-methyl mercaptophenyl)4,S-diphenyl imidazole dimers, etc.
The 2,4,5-triaryl imidazole dimers, also known as hexaaryl biimidazoles are preferably used with an electron donator forming free radicals, such as, 2-mercaptobenzoxazole, leuco crystal voilet or tris-(4-diethylamino-2-methylphenyl)-methane. Sensitizers such as Michler's ketone can be added. Different energy transfer dyes, such as bengalrose and eosin Y can likewise be used.
The photoinitiator or initiator system can be present in an amount of about 0.1 to 10~ by weight, preferably 0.2 to 5.0% by weight, based on the total weight of the photopolymerizable composition.
Additionally, the photopolymerizable composi-tion can contain dyes, pigments and other additives, e.g., plasticizers, adhesion promoters, inhibitors, activators, surface-active agents, etc. These additives should be compatible with the compounds of the photopolymerizable compositions. They can be - present in known amounts.
The base support of the photopolymerizable element is a temporary support which is generally transparent, preferably a thin plastic film. Suitable supports include: cellulose ester films, polyethylene, polypropylene, polystyrene, polyethylene terephthalate and other polyesters. Preferably the photopolymerizable composition is coated on a film of polyethylene _g_ 1~80;~49 terephthalate which has been treated in a manner similar to that described in U. S. Patent 2,779,684.
The surface of the photopolymerizable layer can be protected by a removable cover sheet or layer as described in U. S. Patent 3,469,9~2. In the preparation of printed circuits or photoresist images, the cover sheet or layer, if present, is removed and the photopolymerizable layer is laminated onto a surface as described in U. S. Patent 3,469,982.
Preferably, the surfaces for such treatment are inorganic and, particularly, metal. Copper clad epoxy fiberglass circuit boards are used to make a printed circuit. The laminated photopolymerizable layer is then exposed ` imagewise to a known actinic radiation source, e.g., carbon arcs, mercury-vapor arcs, xenon arcs, etc., preferably through the transparent base support and the base support is removed. The exposed layer is then developed.
Development occurs by removing the non-polymerized areas of the photopolymerizable layer withan aqueous-alkali developer solution according to known methods, e.g., spraying, brushing, etc. The pH
of the developer solutions is preferably between g and 11. Suitable alkalies for the developer include:
alkali carbonates, borates, and hydroxide, etc., as well as known carbonate, borate and phosphate : buffer systems. Surface-active agents can be present in the developers.
After devRlopment, the resist-covered surface is further treated using known procedures for etching ::.
.

s ~VZ49 or plating.
The exposed portion of the photopolymerized layer remaining on the support is subsequently easily removed by treatment with an aqueous-alkali solution such as those described above which have been used for development but having a pH of at least 13. These solutions are strong alkali solutions containing 1 to 10% by weight alkali hydroxide. Generally the removal occurs at elevated temperatures between 30 and 90C., preferably between 40 and 80C., in continuously running machines.
In contrast to presently known aqueous-alkali workable resist materials, such as are described in U. S. Patents 3,833,384 and 3,887,450, wherein the aqueous-alkali solution removes the exposed resist layer from the etched or plated surface in the form of a thin film, the exposed resist layer of the present invention is removed by dissolving completely in the aqueous-alkali solution. This is a great advantage since the machines used for the removal of the layer are not polluted by the removed photopolymerizable composition. It is surprising that ethylenically unsaturated monomeric compounds could provide phot-polymerizable compositions with the above-mentioned affect. It was believed that during development, which also takes place in an aqueous-alkali solution, that there would not be sufficient differentiation between the exposed and unexposed areas of the photopolymerizable layer since even the exposed areas of the photo-polymerizable composition are dissolved in aqueous-alkali 1~8UZ49 medium.
EXAMPLES OF THE INVENI ION
The following examples illustrate the invention wherein the percentages are in weight percent.

A light-sensitive mixture having the following composition is applied onto a polyethylene terephthalate base support, is dried t and is provided with a transparent removable cover film:

5.0 g copolymer of methyl methacrylate and methacrylic acid, a product of E. I. du Pont de Nemours and Company, Inc., 4.5 g butane diol-bis[(2-methacryloyl-oxyethyl) carbonate], 0.5 g of a mixture of benzone phenone and Michler's ketone (ratio 20:1), and 20.0 g methylene chloride.
The coating thickness of the light-sensitive layer is 25 ~. After the removal of the cover film, the light-sensitive layer is laminated onto a copper clad epoxy fiberglass printed circuit board, as it is used for the preparation of printed circuits, and is exposed using a negative image for 40 seconds using a mercury vapor lamp (3,000 W) at a distance of 50 cm.
Development is accomplished by means of spraying the exposed laminated element with a 1%
sodium carbonate solution. The time for development is approximately 50 seconds at 28C.
The copper surface is subsequently etched in the usual manner using a ferric chloride solution, is rinsed, and then is dried. The removal of the exposed ~V~V;~4~

resist layer remaining on the etched copper surface is accomplished by treatment with a 3~ NaOH solution, which is appropriately stirred in the known manner, at 55C.
The exposed resist layer dissolved completely in the aqueous-alkali solution.

A light-sensitive mixture having the following composition is applied onto a base support as described in Example 1, is dried, and is provided with a transparent removable cover film:

5.0 g copolymer of methyl methacrylate-ethyl acrylate and acrylic acid, Carboset~ 525 (Goodrich-Chemical Corporation), 3.0 g of a copolymer of styrene and maleic acid semiester, SMA~ 17 352 (Arco Chemical Company), 1.5 g ethylene glycol-bis-[(2-methacryloyloxyethyl) carbonate], 0.5 g of a mixture of benzophenone and Michler's ketone (ratio 20:1), and 20.0 g methylene chloride.
The coating thickness of the light sensitive layer is 25 ~. The lamination, exposure, development, and etching are accomplished according to the data given in Example 1.
The removal of the exposed resist layer remaining on the etched copper surface is accomplished by treatment with a 3% NaOH solution, appropriately stirred, at 55C. The exposed resist layer completely ~issolves in the aqueous-alkali solution.

108~Z49 .
EXA~PLE 3 A light-sensitive mixture having the following ~ :
composition is applied onto a base support as described in Example 1:
Sample A

5.0 g of a copolymer of methyl methacrylate, ethyl acrylate and acrylic acid, Carboset~ 525 (Goodrich Chemical Corporation), 5.0 g ethylene glycol-bis-[(2-methacryloyloxyethyl) carbonate], 1.0 g of a mixture of benzophenone and Michler's ketone (ratio 20:1), and 20.0 g methylene chloride.
A light-sensitive mixture having the following composition is applied onto a second similar base support:
.. Sample B
.
:.~ 5.0 g of a copolymer of methyl methacrylate, ethyl acrylate and acrylic acid, Carboset~ 525 (Goodrich Chemical Corporation) 5.0 g compound of 2-hydroxy-3-methacryloyloxypropyl-p-(2-hydroxy-. 3-methacryloyloxypropoxy) benzoate.
(The compound is manufactured according to Example 3 of U. S. Patent 3,833,384), 1.0 g of a mixture of benzophenone and Michler's ketone (ratio 20:1), and ~.~ 30 20.0 g methylene chloride.
: The coating thickness of the light-sensitive layer with sample A and B is 25 ~. Both layers are exposed according to the data in Example 1 and are ~: ~eveloped by spraying with a 4% sodium carbonate solution for 4 minutes at 22C.
A~ter plating both samples, the exposed resist .~' .
, ~ . , .

1~)8~)ZD~9 layer remaining on the plated copper surface is removed ,' by treatment with a stirred 3% NaOH solution at 55C.
The exposed resist layer of sample A dissolves completely in this s~lution, while the resist layer of sample B
separates as a whole thin film from the copper surface and remains as a film in the removal solution.

A light-sensitive mixture having the following composition is applied onto a base support as described in Example 1, is dried, and is provided with a transparent . removable cover film:
5.0 g copolymer of methyl methacrylate-ethyl acrylate and acrylic acid, Carboset~ 525 (Goodrich Chemical Corporation), , 5.0 g ethylene glycol-bis-[(2-acryloyloxyethyl) carbonate], 0.5 g of a mixture of benzophenone and Michler's ketone (ratio 20:1), : 20 and . : 25.0 g tetrahydrofuran.
The coating thickness of the light-sensitive layer is 2S ~. Lamination exposure, development and etching are accomplished according to the data given in Example 1.
;~ . Removal of the exposed resist layer remaining ~ on the etched copper surface is accomplished by treatment ; with a stirred 8~ NaOH solution at 45~C. The exposed ,: ~ resist layer dissolves completely in this solution.

A light-sensitive mixture having the following composition is applied onto a base support as described in Example 1, is dried, and is provided with a transparent 1~8V~49 removable cover film:
5.0 g copolymer of styrene, maleic acid anhydride, maleic acid monomethyl-ester, Lytron~ (Monsanto Corporation), 2.5 g hexane diol-bis-[(2-methacryloyl-: oxyethyl) carbonate], 0.5 g of a mixture of benzophenone andMichler's ketone (ratio 20:1), and 20.0 g methylene chloride.
The coating thickness of the light-sensitive layer is 25 ~. Lamination, exposure, development and etching are accomplished according to the data given in Example 1.
Removal of the exposed resist layer remaining on the etched copper surface is accomplished by treatment with a stirred 5% NaOH solution at 50C. The exposed resist layer completely dissolves in this solution.

.

Claims (9)

1. In a photopolymerizable element which comprises a base support bearing a layer of a photo-polymerizable composition comprising (a) an ethylenically unsaturated monomeric compound, (b) an aqueous-alkali soluble polymeric binder, and (c) a photoinitiator and/or an initiator system;
the improvement wherein the monomeric compound has the general formula:

wherein R is H or CH3 and n is a number from 2 to 6.

2. A photopolymerizable element according to Claim 1 wherein the monomeric compound is ethylene glycol-bis-[(2-methacryloyloxyethyl) carbonate].

3. A photopolymerizable element according to Claim 1 wherein the monomeric compound is butane diol-bis-1(2-methacryloyloxyethyl) carbonate].

4. A photopolymerizable element according to Claim 1 wherein the monomeric compound is hexane diol-bis-1(2-methacryloyloxyethyl) carbonatel].

5. A photopolymerizable element according to Claim 2 wherein the polymeric binder is a mixture of a copolymer of methyl methacrylate/ethyl acrylate and acrylic acid and a copolymer of styrene and maleic acid semiester.

6. An ethylenically unsaturated monomeric compound of the formula wherein R is H or CH3 and n is a number from 2 to 6.

7. An ethylenically unsaturated monomer according to Claim 6 where n is 2.

8. An ethylenically unsaturated monomer according to Claim 6 where n is 4.

9. An ethylenically unsaturated monomer according to Claim 6 where n is 6.