Note: Descriptions are shown in the official language in which they were submitted.
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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
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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
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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 4 C CH2
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.
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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
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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.
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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
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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
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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
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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
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medium.
EXAMPLES OF THE INVENI ION
The following examples illustrate the invention
wherein the percentages are in weight percent.
EXAMPLE 1
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
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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.
EXAMPLE 2
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.
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.
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
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, ~ . , .
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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.
EXAMPLE 4
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.
3 0 EXAMPLE 5
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
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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.
.
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