A solid photopolymerizable composition, contains addition polymerizable ethylenically unsaturated monomer, initiating system, polymer binder and a microgel wherein preferably the binder and microgel form substantially a single phase and have a similar glass transition temperature above 25.degree. C. Although less preferred the solid composition can function without the binder. A preferred use is as a photoresist.

BACKGROUND OF THE INVENTION 
The present invention relates to photosensitive compositions which contain 
an additive component to influence one or more physical and/or chemical 
properties of the composition. Such properties can include, without 
limitation, storage stability, photospeed, ability to laminate and adhere 
to a substrate and ability to laminate over voids in a substrate. The 
additive can be added in a concentration to replace a portion or all of a 
component of the photosensitive composition, e.g., replacement of binder. 
Photosensitive compositions particularly useful as photoresists are well 
known in the prior art. Conventionally these compositions are stored in 
roll form. The composition is adhered to a support film to form a two ply 
material such as disclosed in U.S. Pat. No. 4,293,635 or more 
conventionally in a three ply material such as U.S. Pat. No. 3,469,982 
with the composition sandwiched between a support film and a cover sheet. 
The material is unwound from a roll and the cover sheet, if present, is 
removed from contact with the photosensitive composition prior to use in 
lamination to a substrate, e.g., in manufacture of printed circuit boards. 
In storage of the material a potential defect of cold flow exists. An 
excessive amount of cold flow results in the material becoming 
unacceptable, e.g., edge fusion occurs which prevents unwinding of a roll 
without damaging the continuity of the photopolymerizable composition. 
Generally storability with minimization of cold flow is imparted by proper 
selection and formulation of the components of the photopolymerizable 
material. An exception to a need to formulate storage stability in a 
composition is disclosed in U.S. Pat. No. 3,867,153. This publication 
teaches hardening of the edges of the roll such as by exposure to actinic 
radiation which prevents cold flow with the photopolymerizable composition 
effectively sealed within the roll. 
Use of an additive component to change physical properties in a composition 
is well known. One example is using beads as a filler in an organic 
polymer composition which may be optionally polymerizable as disclosed in 
U.S. Pat. No. 4,414,278. The polymeric beads are discrete, substantially 
nonswellable and crosslinked with an average diameter in the range of 0.7 
to 20 .mu.m. 
In contrast to the use of the highly crosslinked nonswellable beads in a 
composition are swellable microgels which are a separate and distinct 
component. Microgel is a term originated in the paint industry and it 
includes crosslinked spherical polymer molecules of high molecular weight 
such as of the order of 10.sup.9 to 10.sup.10 with a particle size of 0.05 
to 1 micron in diameter prepared by emulsion polymerization. Crosslinking 
renders these microgels insoluble but capable of swelling in strong 
solvent without destroying the crosslinked structure. The preparation and 
use of such microgels is described, e.g., in British Pat. No. 967,051 and 
U.S. Pat. No. 3,895,082. 
Use of a component described as a microgel in one type of photosensitive 
composition is disclosed in Japanese patent application No. 52,116301. The 
composition contains a major ingredient of a methacrylate ester and a 
microgel, a polymerizable monomer, a photoinitiator and a 
thermopolymerization inhibitor. The microgel is a rubber type substance 
obtained by a graft polymerization of a vinyl monomer with a so-called 
rubber type base material having particle diameter of 0.01 to 10 microns. 
This photosensitive composition is used for offset printing. 
A delustering coating composition which contains fine particles is 
disclosed in U.S. Pat. No. 4,518,472. The composition is applied to a 
molded article to provide high abrasion resistance or scratch resistance. 
Such composition for coating is a liquid which differs from the solid 
films of the present invention. 
SUMMARY OF THE INVENTION 
The present invention is directed to a photosensitive composition 
comprising 
(a) addition polymerizable ethylenically unsaturated monomer, 
(b) initiating system activated by actinic radiation, 
(c) preformed macromolecular polymer binder, and 
(d) microgel, 
wherein the photosensitive composition is a solid and wherein at least one 
of the following is present: 
(i) the polymer binder and microgel form substantially one phase as viewed 
by the naked eye, or 
(ii) the polymer binder and microgel have glass transition temperatures 
which do not differ by more than 50.degree. C. with the microgel having a 
glass transition temperature above 25.degree. C. 
Although less preferred it is possible to formulate the photosensitive 
composition without the polymeric binder. 
DETAILED DESCRIPTION OF THE INVENTION 
The starting materials for the solid photosensitive composition of the 
present invention ordinarily present as a film on a flexible backing 
material are well known in the prior art with the exception of the 
microgel of the type disclosed herein. The microgel allows a reformulation 
of the photosensitive composition which can be simply a different 
concentration of components to obtain comparable physical properties or 
comparable processing characteristics particularly in a preferred use as a 
photoresist in making of a printed circuit board. Alternatively the use of 
microgels in the photosensitive composition can aid to obtain superior 
photosensitive formulations, e.g., an increase in photospeed, better 
strippability of the composition from a substrate or improved ability to 
cover holes in a substrate during processing. 
The photosensitive composition will contain the microgel together with one 
or more addition polymerizable ethylenically unsaturated monomers, and an 
initiating system activated by actinic radiation and a performed 
monomolecular polymer binder. It has been found that a microgel can be 
used to replace all of the binder components for a composition useful as a 
photoresist. However in one mode a binder or combination of binders is 
present but in an amount insufficient to obtain all properties necessary 
in a commercially acceptable resist. Illustratively a suitable composition 
can be formulated which will not be storage stable without the added 
microgel component. A microgel can be utilized in a variety of ways to 
allow reformulation of the photosensitive composition. 
For the property of storage stability it can be measured in a short term 
test since true storage stability (such as the composition formed into a 
sheet and wound into a roll on a backing sheet) can take a considerable 
period of time, i.e., the order of months or even a year. The correlation 
of storage stability and particularly lack of substantial cold flow of the 
photosensitive composition causing edge fusion with a short term test can 
be measured herein by creep viscosity test. A storage stable composition 
will have a creep viscosity of at least 20 megapoise, preferably at least 
30 megapoise, and most preferably at least 40 megapoise. Another test for 
storage stability would be to store the composition in roll form for six 
(6) months at 25.degree. C. or for one (1) month at 40.degree. C. 
The introduction of the microgel can also influence photospeed and higher 
photospeeds have been obtained with the introduction of the microgel 
compared to a similar composition without the microgel. Therefore in one 
of the suitable modes of the present invention the microgel is added to 
facilitate an increase in photospeed. 
It has been discovered that the incorporation of microgels in a solid 
photosensitive composition as replacement for some or all of a binder 
provides thixotropic behavior, where under low shear conditions such as 
experienced in a roll during storage the film has high viscosity, but 
under high shear conditions such as lamination the photosensitive 
composition present as a dry film flows easily and conforms well to a 
substrate copper surface. This property aids in application of the 
photosensitive composition to a surface. Illustratively for a photoresist 
laminated to a surface such as a copper panel having predrilled holes, the 
ability of the composition to be laminated over the holes is essential. 
Microgels allow formulation of compositions with an enhanced ability to 
resist rupture. This ability is commonly referred to as tenting, where 
addition of the microgel can be advantageous. 
In compositions with a binder employed, the relationships between the 
binder and the microgel allows formulations to obtain the beneficial 
properties of the present invention, e.g., in a photoresist. One manner of 
defining this combination of components is that the polymer binder and 
microgel will form a single homogeneous phase. This homogeneous phase can 
be viewed with the naked eye. However, more preferably the presence of the 
single phase is present is viewed under a magnification of 10 times and 
more preferably a magnification of 100 times. 
An alternate manner of describing the combination of a preformed 
macromolecular binder and microgel is through glass transition 
temperature. Generally the glass transition temperature will not differ by 
more than 50.degree. C. and more preferably by more than 25.degree. C. 
Since one purpose of including the microgel in the composition is to 
increase viscosity, the glass transition temperature should also be above 
room temperature (25.degree. C.). Often the binder and microgel will be 
formulated from common monomers which aids compatibility of the two 
components although formulation in this manner is not necessary. 
It is understood that the definition of microgel herein is employed in its 
conventional definition. Such definition of a microgel excludes a highly 
crosslinked material such as in U.S. Pat. No. 4,414,278 which discloses 
beads which are substantially non-swellable. Illustratively a Swelling 
Test is set forth in this patent on column 4, lines 30 to 45 with a 
statement that any degree of swelling is undesirable. A representative 
sample of a microgel used in the present invention floated in a test 
solution of the patent rather than sank in accordance with polymeric beads 
of this patent. Accordingly this test is not considered relevant. Since 
the degree of crosslinking is controlled in manufacture of a microgel, a 
substantially nonswellable crosslinked polymeric bead (even of proper 
size) is not a microgel. Generally the microgels will be present in an 
average particle size range of from 0.1 to 1 microns and more preferably 
0.05 to 0.15 microns. 
Preferably the microgels of the present invention will swell in at least 
one of the following solvents: n-heptane, carbon tetrachloride, toluene, 
methylene chloride, ethyl acetate, acetone, acetonitrile, acetic acid, 
dimethylsulfoxide, dimethylformamide, formamide, water, aqueous ammonium 
hydroxide solution containing up to 10% by weight ammonia, aqueous 
potassium hydroxide solution containing up to 10% by weight potassium 
hydroxide, methylene chloride-methanol solution containing by weight 92% 
methylene chloride and 8% methanol, aqueous sodium carbonate solution 
containing by weight 1% sodium carbonate. 
The above list of solvent is not represented as being exhaustive of a 
solvent which will cause swelling of the microgel. However such list is 
believed to qualify microgels with a proper degree of crosslinking. 
As a test of swellability a 10 gram sample of the material, i.e., the 
microgel, is added to 100 grams of solvent. The microgel will swell at 
least 10%, i.e., at least a 10% increase in volume of the microgel will be 
obtained. The swelling conventionally will be greater, i.e., at least a 
50% increase. Swelling increases of at least 100% can also be realized 
with many of the microgels. 
Since microgels for addition to the photosensitive compositions will 
greatly increase the viscosity of a solvent by swelling through absorption 
of solvent, an alternate test is through measurement of an increase in 
viscosity of the solvent. Initially the solution viscosity of the solvent 
is measured such as using a Brookfield viscometer with a spindle 
appropriate for the viscosity of the solvent. Ten grams of a material for 
testing, i.e. the microgel candidate, is introduced into one hundred grams 
of the test solution. The material for testing and solvent are stirred at 
room temperature (i.e., approximately 25.degree. C.) for twenty-four 
hours. At the end of the time period additional test liquid is added to 
obtain a final weight of 110 grams, i.e., 100 grams solvent and 10 grams 
of the material for testing. The viscosity is again measured using the 
Brookfield viscometer and a spindle appropriate for the viscosity of the 
mixture. 
For qualification of a microgel in this procedure, the increase in 
viscosity of the solvent with the added material will be at least 100 
centipoise. Preferably the increase will be 1,000 centipoise and more 
preferably 3,000 centipoise. 
The microgels employed herein differ from introduction of additives in 
photosensitive compositions of the prior art. Illustratively the microgels 
differ over materials disclosed in Japanese patent application No. 
52,116301 which is believed to employ a principle of rubber toughening 
through the incorporation of microgels. The mechanism of rubber toughening 
of plastics is discussed by Seymour Newman and C. B. Bucknall in "Polymer 
Blends", D. R. Paul, ed., New York 1978, volume 2, pp. 63-127. The 
presence of small rubber particles dispersed in a matrix of a more brittle 
polymer promotes crazing in the matrix polymer on impact, delaying the 
onset of crack formation. The dispersed phase must be incompatible with 
the matrix polymer to remain as a discrete phase, and the temperature of 
use must be above the rubber's glass transition temperature in order for 
it to function as a toughening agent. Both of these requirements are met 
in the Japanese application No. 52-116301. The microgel materials cited 
(for example, polybutyl acrylate, polybutadiene, styrene/butadiene 
copolymer rubber, ethylene/propylene copolymer elastomer, polyisoprene) 
are referred to as elastomers which by definition have glass transition 
temperatures below room temperature. The discussion of the particle size 
of the rubber material indicates that the rubber exists as discrete 
particles in the finished article. 
As previously discussed the filler additives disclosed in U.S. Pat. No. 
4,414,278 differ from the microgel disclosed since the fillers are not 
microgels. The compositions of U.S. Pat. No. 4,518,472 differ from the 
composition herein since the compositions of the patent are coating 
liquids while the present formulations are solids with different utility. 
The microgels of the present invention are conventionally prepared by 
emulsion polymerization. The microgels are generally formed from 90 to 
99.5% by weight polymer component and 10 to 0.5% by weight crosslinking 
agent with these materials compatible in formation of a continuous phase 
system. The polymer components can be varied during polymerization to 
produce core and shell microgel with different interior and exterior 
composition. In the case where a polymeric binder is employed the weight 
ratio of the microgel to binder can vary widely, e.g., from 1:20 to 1:1. 
The microgels can be made from a wide variety of starting materials. 
Conventionally monoethylenically unsaturated monomers are used in 
preparing the bulk portion of the microgel, whereas the crosslinking 
agents contain at least two double bonds. 
Preferred monomers are methyl methacrylate, ethyl acrylate, methacrylic 
acid, butyl methacrylate, ethyl methacrylate, glycidyl methacrylate, 
styrene and allyl methacrylate; while other useful monomers include 
acrylonitrile, methacrylonitrile, acrylic acid, methacrylic acid and 
2-ethyl-hexyl acrylate. 
A preferred crosslinking agent is butanediol diacrylate; while others 
include ethylene glycol dimethacrylate, tetramethylene glycol diacrylate, 
trimethylol propane triacrylate, tetraethylene glycol dimethacrylate, 
methylene bisacrylamide, methylene bismethacrylamide, divinyl benzene, 
vinyl methacrylate, vinyl crotonate, vinyl acrylate, vinyl acetylene, 
trivinyl benzene, glycerine trimethacrylate, pentaerythritol 
tetramethacrylate, triallyl cyanurate, divinyl acetylene, divinyl ethane, 
divinyl sulfide, divinyl sulfone, hexatriene, triethylene glycol 
dimethacrylate, diallyl cyanamide, glycol diacrylate, ethylene glycol 
divinyl ether, diallylphthalate, divinyl dimethyl silane, glycerol 
trivinyl ether and the like. 
Conventionally one or more monomers and crosslinking agents are dispersed 
in water with suitable emulsifiers and initiators in manufacture of the 
microgel. Conventional anionic, cationic or nonionic emulsifiers and water 
soluble initiators can be employed. Examples of emulsifying agents are 
sodium lauryl sulfate, lauryl pyridine chloride, polyoxyethylene, 
polyoxypropylene, colloidal silica, anionic organic phosphates, magnesium 
montmorillonite, the reaction product of 12 to 13 moles of ethylene oxide 
with 1 mole of octyl phenol, secondary sodium alkyl sulfates and mixtures 
thereof. Usually from 0.25 to 4% of emulsifier based on the total weight 
of reactants is used. Examples of initiators are potassium persulfate, 
sodium persulfate, ammonium persulfate, tertiary butyl hydroperoxide, 
hydrogen peroxide, azo bis(isobutyronitrile), azo bis(isobutyroimidine 
hydro chloride), various redox (reduction-oxidation) systems such as 
hydrogen peroxide and ferrous sulfate and well-known persulfate-bisulfate 
combinations. Usually, from 0.05 to 5% by weight of initiator based on the 
weight of coploymerizable monomers is used. 
Microgels suitable for the practice of the present invention can be 
produced by the technique of emulsion polymerization as described in U.S. 
Pat. No. 3,895,082 (Also British Pat. No. 967,051 teaches a suitable 
method). This technique can also be modified be beginning the reaction 
with one set of monomers and then varying the ratios for the final part of 
the reaction in order to produce spherical microgels in which the first 
part of the polymer, i.e., the core is different monomer composition than 
the outer part of the polymer, i.e., the shell. A wide range of both 
homopolymer microgels and core shell microgels can be produced with 
varying polymer composition and crosslinking. For the present invention, 
it is desired that the glass transition temperature of the shell not 
differ from the polymer binder by more than 50.degree. C. and that the 
glass transition temperatures of both are and shall be above 25.degree. C. 
The art of emulsion polymerization is well known concerning reaction 
conditions to produce spherical microgels dispersed in a water phase. 
Unless the dispersion can be used as made and contain no objectional 
impurities or byproducts, it is usually necessary to convert the microgels 
to a dry powder prior to their use in a photosensitive composition. 
Well-known techniques of coagulation, filtration, washing and drying may 
be employed for this purpose. Spray drying is a particularly useful method 
for the present invention. Generally the amount of crosslinking agent in 
the microgel will be less than 20% by weight of the overall weight of the 
microgel and generally less than 10% by weight. It is understood that all 
of the crosslinking agent need not function in crosslinking. 
The solubility of the binder or insolubility of the microgels is determined 
by actual test. A sample of the solid material is weighed and placed in 
100 times by weight of solvent (see particularly the solvents previously 
listed). The sample is stirred for 15 minutes. Any solid remaining is then 
removed and dried and finally weighed to determine undissolved solid in 
comparison to the original sample weight. Because polymeric materials are 
not absolutely uniform and can contain certain impurities, the material 
can be considered soluble if up to 10% of the original sample remained 
undissolved after the test. Conversely the material can be considered to 
be insoluble if it weighs more than 90% of what it did originally. 
Generally the microgel will be present in an amount from 1 to 90 percent by 
weight of the components of monomer, initiating system, binder and 
microgel and preferably 5 to 40%. A more limited example of such range is 
from 8 to 15%. 
An example of the suitable concentrations by weight in a photosensitive 
composition based on these constituents is: 
(a) from 5% to 50% of an addition polymerizable ethylenically unsaturated 
monomer 
(b) from 0.01% to 15% of an initiating system activated by actinic 
radiation 
(c) from 0% to 90% of a preferred macromolecular polymer binder and 
(d) from 1 to 90% by weight of a microgel. 
A more limited example of component (a) is from 20% to 35% by weight, of 
component (b) is from 2% to 10% and of component (c) is 40 to 65%. 
Compositions of some of the microgels produced and tested and found useful 
for the practice of the present invention are detailed in Table I. All 
parts are by weight. 
TABLE I 
__________________________________________________________________________ 
MICROGEL COMPOSITION 
MICROGEL 
MMA EA MAA BMA EMA GMA STY 
AMA BDDA 
__________________________________________________________________________ 
A 51 29 20 -- -- -- -- 0.5 2 
B 51 29 20 -- -- -- -- -- 2 
C 51 29 20 -- -- -- -- -- 0.5 
D 51 29 20 -- -- -- -- -- 5 
E 51 29 20 -- -- -- -- -- 10 
F 45 26 29 -- -- -- -- -- 2 
G 51 29 20 -- -- -- -- -- 1.0 
H 51 29 20 -- -- -- -- -- 1.5 
I 51 29 20 -- -- -- -- -- 0.75 
J 51 29 -- -- -- 20 -- -- 0.75 
K 43.2 
-- -- 31 -- -- 20 2.9 2.9 
L 49.5 
-- -- -- 49.5 
-- -- 0.5 0.5 
M 51 29 20 -- -- -- -- 0.5 0.5 
N 39 35 26 -- -- -- -- -- 2 
O CORE 54 17 14 -- -- -- -- -- 2 
O SHELL 
48 26 26 -- -- -- -- -- 2 
P CORE 67 22 11 -- -- -- -- -- 2 
P SHELL 
21 41 38 -- -- -- -- -- 2 
Q 63.2 
-- -- 31 -- -- -- 2.9 2.9 
R 9.8 35.3 
23.5 
-- -- -- 29.4 
-- 1.9 
S 4.9 40.2 
23.5 
-- -- -- 29.4 
-- 1.9 
T 39 39 20 -- -- -- -- -- 2.0 
U 48.1 
-- -- -- 48.1 
-- -- 1.9 1.9 
__________________________________________________________________________ 
MMA = Methylmethacrylate 
EA = Ethyl Acrylate 
MMA = Methacrylic Acid 
BMA = Butyl Methacrylate 
EMA = Ethyl Methacrylate 
GMA = Glycidyl Methacrylate 
STY = Styrene 
AMA = Allyl Methacrylate 
BDDA = Butanediol Diacrylate 
As previously discussed the preferred photosensitive formulation with the 
microgel will contain a preformed polymeric binder ordinarily present in a 
concentration of not less than 40% by weight based on the combination of 
monomer, initiating system, microgel and binder. Suitable binders which 
can be used alone, if employed, or in combination with one another include 
the following: polyacrylate and alpha-alkyl polyacrylate esters, e.g., 
polymethyl methacrylate and polyethyl methacrylate; polyvinyl esters, 
e.g., polyvinyl acetate, polyvinyl acetate/acrylate, polyvinyl 
acetate/methacrylate and hydrolyzed polyvinyl acetate; ethylene/vinyl 
acetate copolymers; polystyrene polymers and copolymers, e.g., with maleic 
anhydride and esters; vinylidene chloride copolymers, e.g., vinylidene 
chloride/acrylonitrile; vinylidene chloride/methacrylate and vinylidene 
chloride/vinyl acetate copolymers; polyvinyl chloride and copolymers, 
e.g., polyvinyl chloride/acetate; saturated and unsaturated polyurethanes; 
synthetic rubbers, e.g., butadiene/acrylonitrile, 
acrylonitrile/butadiene/styrene, 
methacrylate/acrylonitrile/butadiene/styrene copolymers, 
2-chlorobutadiene-1,3 polymers, chlorinated rubber, and 
styrene/butadiene/styrene, styrene/isoprene/styrene block copolymers; high 
molecular weight polyethylene oxides of polyglycols having average 
molecular weights from about 4,000 to 1,000,000; epoxides, e.g., epoxides 
containing acrylate or methacrylate groups; copolyesters, e.g., those 
prepared from the reaction product of a polymethylene glycol of the 
formula HO(CH.sub.2).sub.n OH, where n is a whole number 2 to 10 
inclusive, and (1) hexahydroterephthalic, sebacic and terephthalic acids, 
(2) terephthalic, isophthalic and sebacic acids, (3) terephthalic and 
sebacic acids, (4) terephthalic and isophthalic acids, and (5) mixtures of 
copolyesters prepared from said glycols and (i) terephthalic, isophthalic 
and sebacic acids and (ii) terephthalic, isophthalic, sebacic and adipic 
acids; nylons or polyamides, e.g., N-methoxymethyl polyhexamethylene 
adipamide; cellulose esters, e.g., cellulose acetate, cellulose acetate 
succinate and cellulose acetate butyrate; cellulose ethers, e.g., methyl 
cellulose, ethyl cellulose and benzyl cellulose; polycarbonates; polyvinyl 
acetal, e.g., polyvinyl butyral, polyvinyl formal; polyformaldehydes. 
In the case where aqueous development of the photosensitive composition is 
desirable the binder should contain sufficient acidic or other groups to 
render the composition processible in aqueous developer. Useful 
aqueous-processible binders include those disclosed in U.S. Pat. No. 
3,458,311 and in U.S. Pat. No. 4,273,857. Useful amphoteric polymers 
include interpolymers derived from N-alkylacrylamides or methacrylamides, 
acidic film-forming comonomer and an alkyl or hydroxyalkyl acrylate such 
as those disclosed in U.S. Pat. No. 4,293,635. For aqueous development the 
photosensitive layer will be removed in portions which are not exposed to 
radiation but will be substantially unaffected during development by a 
liquid such as wholly aqueous solutions containing 2% sodium carbonate by 
weight. 
Suitable monomers which can be used as the sole monomer or in combination 
with others include the following: t-butyl acrylate, 1,5-pentanediol 
diacrylate, N,N-diethylaminoethyl acrylate, ethylene glycol diacrylate, 
1,4-butanediol diacrylate, diethylene glycol diacrylate, hexamethylene 
glycol diacrylate, 1,3-propanediol diacrylate, decamethylene glycol 
diacrylate, decamethylene glycol dimethacrylate, 1,4-cyclohexanediol 
diacrylate, 2,2-dimethylolpropane diacrylate, glycerol diacrylate, 
tripropylene glycol diacrylate, glycerol triacrylate, trimethylolpropane 
triacrylate, pentaerythritol triacrylate, polyoxyethylated 
trimethylolpropane triacrylate and trimethacrylate and similar compounds 
as disclosed in U.S. Pat. No. 3,380,831, 2,2-di(p-hydroxyphenyl)-propane 
diacrylate, pentaerythritol tetraacrylate, 2,2-di(p-hydroxyphenyl)-propane 
dimethacrylate, triethylene glycol diacrylate, 
polyoxyethyl-2,2-di-(p-hydroxyphenyl)-propane dimethacrylate, 
di-(3-methacryloxy-2-hydroxypropyl) ether of bisphenol-A, 
di-(2-methacryloxyethyl) ether of bisphenol-A, 
di-(3-acryloxy-2-hydroxypropyl) ether of bisphenol-A, di-(2-acryloxyethyl) 
ether of bisphenol-A, di-(3-methacryloxy-2-hydroxypropyl) ether of 
tetrachloro-bisphenol-A, di-(2-methacryloxyethyl) ether of 
tetrachloro-bisphenol-A, di-(3-methacryloxy-2-hydroxypropyl) ether of 
tetrabromo-bisphenol-A, di-(2-methacryloxyethyl) ether of 
tetrabromo-bisphenol-A, di-(3-methacryloxy-2-hydroxypropyl) ether of 
1,4-butanediol, di-(3-methacryloxy-2-hydroxypropyl) ether of diphenolic 
acid, triethylene glycol dimethacrylate, polyoxypropyltrimethylol propane 
triacrylate (462), ethylene glycol dimethacrylate, butylene glycol 
dimethacrylate, 1,3-propanediol dimethacrylate, 1,2,4-butanetriol 
trimethacrylate, 2,2,4-trimethyl-1,3-pentanediol dimethacrylate, 
pentaerythritol trimethacrylate, 1-phenyl ethylene-1,2-dimethacrylate, 
pentaerythritol tetramethacrylate, trimethylol propane trimethacrylate, 
1,5-pentanediol dimethacrylate, diallyl fumarate, styrene, 1,4-benzenediol 
dimethacrylate, 1,4-diisopropenyl benzene, and 1,3,5-triisopropenyl 
benzene. 
A class of monomers are an alkylene or a polyalkylene glycol diacrylate 
prepared from an alkylene glycol of 2 to 15 carbons or a polyalkylene 
ether glycol of 1 to 10 ether linkages, and those disclosed in U.S. Pat. 
No. 2,927,022, e.g., those having a plurality of addition polymerizable 
ethylenic linkages particularly when present as terminal linkages. 
Especially preferred are those wherein at least one and preferably most of 
such linkages are conjugated with a double bonded carbon, including carbon 
double bonded to carbon and to such heteroatoms as nitrogen, oxygen and 
sulfur. Outstanding are such materials wherein the ethylenically 
unsaturated groups, especially the vinylidene groups, are conjugated with 
ester or amide structures. 
Preferred free radical-generating addition polymerization initiators 
activatable by actinic light and thermally inactive at and below 
185.degree. C. include the substituted or unsubstituted polynuclear 
quinones which are compounds having two intracyclic carbon atoms in a 
conjugated carbocyclic ring system, e.g., 9,10-anthraquinone, 
1-chloroanthraquinone, 2-chloroanthraquinone, 2-methylanthraquinone, 
2-ethylanthraquinone, 2-tert-butylanthraquinone, octamethylanthraquinone, 
1,4-naphthoquinone, 9,10-phenanthrenequinone, 1,2-benzanthraquinone, 
2,3-benzanthraquinone, 2-methyl-1,4-naphthoquinone, 
2,3-dichloronaphthoquinone, 1,4-dimethylanthraquinone, 
2,3-dimethylanthraquinone, 2-phenylanthraquinone, 
2-3-diphenylanthraquinone, sodium salt of anthraquinone alpha-sulfonic 
acid, 3-chloro-2-methylanthraquinone, retenequinone, 
7,8,9,10-tetrahydronaphthacenequinone, and 
1,2,3,4-tetrahydrobenz(a)anthracene-7,12-dione. Other photoinitiators 
which are also useful, even though some may be thermally active at 
temperatures as low as 85.degree. C., are described in U.S. Pat. No. 
2,760,863 and include vicinal ketaldonyl alcohols, such as benzoin, 
pivaloin, acyloin ethers, e.g., benzoin methyl and ethyl ethers; 
.alpha.-hydrocarbon-substituted aromatic acyloins, including 
.alpha.-methylbenzoin, .alpha.-allylbenzoin and .alpha.-phenylbenzoin. 
Photoreducible dyes and reducing agents disclosed in U.S. Pat. Nos.: 
2,850,445; 2,875,047; 3,097,096; 3,074,974; 3,097,097; and 3,145,104 as 
well as dyes of the phenazine, oxazine, and quinone classes; Michler's 
ketone, benzophenone, 2,4,5-triphenyl-imidazolyl dimers with hydrogen 
donors, and mixtures thereof as described in U.S. Pat. Nos.: 3,427,161; 
3,479,185; and 3,549,367 can be used as initiators. Similarly the 
cyclohexadienone compounds of U.S. Pat. No. 4,341,860 are useful as 
initiators. Also useful with photoinitiators and photoinhibitors are 
sensitizers disclosed in U.S. Pat. No. 4,162,162. 
Thermal polymerization inhibitors that can be used in photopolymerizable 
compositions are: p-methoxyphenol, hydroquinone, and alkyl and 
aryl-substituted hydroquinones and quinones, tert-butyl catechol, 
pyrogallol, copper resinate, naphthylamines, beta-naphthol, cuprous 
chloride, 2,6-di-tert-butyl-p-cresol, phenothiazine, pyridine, 
nitrobenzene and dinitrobenzene, p-toluquinone and chloranil. Also useful 
for thermal polymerization inhibitors are the nitroso compositions 
disclosed in U.S. Pat. No. 4,168,982. 
Various dyes and pigments may be added to increase the visibility of the 
resist image. Any colorant used, however, should preferably be transparent 
to the actinic radiation used. 
In use the photosensitive composition for application to a substrate such 
as in making a printed circuit board, is conventionally supplied by a film 
which is well known in the art. 
A suitable support preferably having a high degree of dimensional stability 
to temperature changes may be chosen from a wide variety of films composed 
of high polymers, e.g., polyamides, polyolefins, polyesters, vinyl 
polymers, and cellulose esters. A preferred support for the present 
invention is polyethylene terephthalate. Also generally a cover sheet is 
present in the appropriate side of the photosensitive composition present 
in film form. The protective cover sheet is removed prior to lamination of 
the photosensitive composition to a substrate. The cover sheet may be 
chosen from the same group of polymer films listed as supports. 
Polyethylene and polyethylene terephthalate are particularly useful. 
Although in the above disclosure the photosensitive compositions have been 
disclosed as containing a polymeric binder, it is understood the suitable 
compositions which can function for example as photoresists need not 
contain a binder. In such case the photosensitive composition need only 
contain (1) an addition polymerizable ethylenically unsaturated monomer, 
(2) an initiating system activated by actinic radiation and (3) a 
microgel. Generally the percentage of these components on the basis of 
these three constituents will be by weight 10% to 60% and preferably 15% 
to 35% for component (1); 0.01% to 15% and preferably 2% to 10% for 
component (2) and 25% to 90% and preferably 30% to 65% for component (3). 
It is understood that in such compositions, a preformed polymer binder 
will not be present but conventional additives can be added such as those 
previously mentioned. 
A preferred use of compositions characterized herein is as a photoresist or 
a solder mask such as in making a printed circuit board. Such techniques 
are conventional in the art employing a solid material, e.g. U.S. Pat. No. 
3,469,982. The process is directed to laminating a photosensitive or a 
substrate comprising: 
(a) laminating to the substrate a supported solid photosensitive film, 
(b) imagewise exposing the layer to actinic radiation. 
(c) removing unexposed areas of the layer to form resist areas, 
(d) permanently modifying areas of the substrate which are unprotected by 
the resist areas by etching the substrate or by depositing a material onto 
the substrate. 
The support is conventionally removed before or after the exposure step. In 
the case of solder mask utility the step of depositing a material can be 
by application of solder. In a utility not involving direct use as a 
solder mask in initial application to a substrate (which is conductive 
with copper preferred circuitry therein) the resist areas are removed 
after step (d) which is conventional. 
The following examples serve to illustrate, the practice of the present 
invention. All percentages, ratios and parts are by weight unless 
otherwise indicated.

EXAMPLE 1 
Preparation of Microgel A Table I composition; 51 methylmethacrylate, 29 
ethyl acrylate, 20 methacrylic acid, 2 allylmethacrylate and 2 
butanedioldiacrylate crosslinker. 
The emulsion polymerization apparatus consisted of a 5 liter, 4 necked 
flask equipped with a mechanical stirrer, 1 liter addition funnel, 
thermometer, nitrogen inlet, water cooled condenser and a heating mantle. 
The flask was charged with 3360 g of deionized water and 20 g of a 30% 
aqueous solution of sodium lauryl sulfonate and this surfactant system was 
heated to 80.degree. C. under a nitrogen atmosphere. At that temperature, 
25% of a monomer mixture consisting of 420 g methylmethacrylate, 240 g 
ethyl acrylate, 165 g methacrylic acid, 16 g allyl methacrylate and 16 g 
1,4-butanediol diacrylate, was added in one shot. This was followed 
immediately by the addition of 10 ml of a 5% aqueous solution of potassium 
persulfate and 10 ml of a 7% aqueous solution of potassium phosphate. The 
reaction mixture turned milky and exothermed to 85.degree. C. The 
remainder of the monomer mixture was added over a period of 90 minutes 
while maintaining the temperature between 80.degree.-88.degree. C. When 
the addition was finished the reaction mixture was heated for an 
additional 2 hours at 80.degree.-85.degree. C. The bluish milky emulsion 
was cooled to room temperature and coagulated by adding methanol. The 
resulting slurry was filtered, washed twice with water, sucked dry and the 
resulting fine powder was dried in an oven at 100.degree. C. for four 
hours. The spherical shape of the powder particles was verified by 
microscopic examination. 
EXAMPLE 2 
Microgels B to N and Q to U in Table I 
Microgels were prepared as in Example 1 except that the monomer mixture was 
varied to give the the indicated composition. 
Core Shell Microgels O and P Table I 
Using the apparatus and basic procedure of Example 1, a variation was made 
in which a first monomer mixture reacts to form a core portion and a 
second monomer mixture completes the balance of the emulsion 
polymerization to produce a shell with a different composition. Microgel O 
was prepared with a first monomer mixture of 315 g methylmethacrylate, 180 
g ethyl acrylate, 55 g methacrylic acid and 10.7 g 1,4 butanediol 
diacrylate, which was added over 50 minutes. Then a second monomer mixture 
of 105 g methylmethacrylate, 60 g ethyl acrylate, 110 g methacrylic acid 
and 5.3 g 1,4 butanediol diacrylate was added over 40 minutes. 
Microgel P was similarly prepared by altering the monomer mixtures. 
EXAMPLE 3 
Comparative photoresist coating compositions were prepared as follows: 
______________________________________ 
Additive Control Invention 
______________________________________ 
Polymer binder methyl- 
62.5 52.5 
methacrylate/ethylacrylate/ 
methacrylic acid 51/29/20 
mol. wt. 50,000 acid no. 130 
Tg 87.degree. C. 
Microgel B -- 10.0 
Polyox .RTM. WSRN-3000 polyethylene 
0.5 0.5 
oxide mol. wt. 400,000 
Ethoxylated trimethylolpropane 
23.0 23.0 
triacrylate monomer 
Itaconic acid 1.0 1.0 
Maleic acid 1.0 1.0 
Urethane diacrylate monomer 
4.0 4.0 
Ethyl paradimethylaminobenzoate 
2.0 2.0 
Michler's ketone 0.15 0.15 
Benzophenone 5.2 5.2 
4-methyl-4-trichloromethyl- 
0.1 0.1 
cyclohexadienone 
Leuco crystal violet 0.3 0.3 
Diethyl hydroxylamine 
0.2 0.2 
Victoria green C.I. #42000 
0.04 0.04 
Victoria blue C.I. #42575 
0.04 0.04 
______________________________________ 
The composition was dissolved for coating in 67% by weight of solvent 
comprising 93% methylene chloride and 7% methanol. Films of approximately 
1.5 mil thickness were produced after coating on a support and drying to 
remove the solvent. 
Film samples were laminated to copper and tested for standard photoresist 
properties of photospeed, resolution, development in 1% aqueous sodium 
carbonate and stripping in 1.5% aqueous potassium hydroxide. In addition 
samples were tested for creep viscosity using the procedures originated by 
Diens and Klemm published in the Journal of Applied Physics, Vol. 17 pages 
458 to 471, 1946 on a Du Pont Thermal Mechanical Analyzer attached to a 
1090 console. Compared to the control the invention had slightly longer 
development and stripping stripping times at equivalent resolution but the 
photospeed was a full .sup.6 .sqroot.2 step higher. The control had a 
creep viscosity of 34 megapoise whereas the incorporation of microgels 
increased the value to 43 megapoise. 
The flexibility and adhesion of the photoresist compositions to copper was 
tested on both freshly laminated and aged laminated samples. Both the 
control and the invention were comparable when the copper was bent to 
varying angles or a crosshatched pattern scratched into the photoresist 
with a knife was covered with transparent adhesive tape and pulled off. 
Samples of both films were able to withstand the same amount of bending 
before showing surface fracture and with the same amount of crosshatching 
a similar amount of photoresist was removed by the tape. 
Both films were tested for tenting, i.e., the ability of a film to maintain 
its integrity when coated over a void. Cleaned copper-clad panels had 100 
holes each of the following diameters drilled: 6 mm, 4 mm and 3 mm. A 
photoresist film was then laminated over these holes using a Riston.RTM. 
model HRL-24 hot roll laminator at 105.degree. C.. The laminated panel was 
irradiated coventionally with a high pressure mercury vapor lamp to 
photopolymerize the layer over the holes. The coversheet was removed and 
the film was developed by lightly spraying with a 1% aqueous sodium 
carbonate solution and the number of broken tents was measured. The panels 
were then run through an acid etch and with approximately 1N HCl at 
pressures of 30/28 psi and broken tents were again measured. The results 
showed a general improvement in ability to tent as the concentration of 
microgel increased. 
A further photoresist coating composition was prepared with the same 
combination of components as the "Invention" except the ethoxylated 
trimethylolpropane triacrylate monomer was 24.5 (rather than 23.0), the 
itaconic acid was 0.5 (rather than 1.0), maleic acid was O (rather than 
1.0) and Victoria blue was 0.02 (rather than 0.04). Improved results were 
obtained over the control and the composition labelled "Invention". 
EXAMPLE 4 
Photoresist compositions were prepared as in Example 3 except that 
different levels of binder replacement were used up to and including total 
replacement of soluble binder by insoluble microgel. The relative 
properties of the control and microgel films are shown below. 
______________________________________ 
Variation of Microgel Content 
______________________________________ 
% Microgel 
0 10 12.4 15.6 19 31.2 62.5 
as film solids 
% Microgel 
0 16 20 25 30 50 100 
as binder 
replacement 
Dev. Rate 
875 805 788 735 709 551 116 
Photospeed 
22 23 24 24 24-25 23-24 23 
Resolution 
good good good good poor poor very 
poor 
Time to strip 
28 35 35 36 38 45 75 
Flex/ = = = = = = poorer 
adhesion 
Creep 34 43 58 53 63 163 542 
viscosity 
______________________________________ 
Development Rate is milligrams per minute removed on a sample which was 9 
square inches 
##STR1## 
Time to strip is in seconds 
Creep viscosity is megapoise 
= is similar 
While the film containing only microgel as a binder shows severe 
degradation in resolution and flexibility/adhesion, it still can function 
as a film suitable for making printed wiring boards and would be employed 
most advantageously where high creep viscosity was an important factor. 
It is also apparent from the data presented that when only 25% or less of 
the binder has been replaced by microgel there is a speed and creep 
viscosity advantage as a tradeoff for decreased development and stripping, 
but without any sacrifice in important properties such as resolution and 
flexibility/adhesion. 
EXAMPLE 5 
Photoresist compositions were prepared as in Example 3 except that the 
microgel particles used to replace 10% of the binder had varying levels of 
crosslinking. The results below compare the effects of 2%, 5% and 10% 
crosslinking of the microgels and a control film without microgel 
addition. Percent crosslinking denotes parts crosslinking monomer added 
during synthesis. The films prepared were 1.3 mil instead of 1.5 mil in 
Example 1 in order to provide a more severe test of tenting capability. 
______________________________________ 
Microgel Crosslinking 
Control 
2% 5% 10% 
______________________________________ 
Dev. Rate 814 781 790 838 
Photospeed 22 23-24 23-24 23 
Time to strip 
24 28 30 34 
Creep 52 61 63 112 
viscosity 
Tenting (6 mm 
2% 7% 9% 15% 
holes unbroken) 
______________________________________ 
Units are as previously specified 
These tests with 1.3 mil films show the consistent improvement in tenting, 
creep viscosity and photospeed for microgel incorporation. 
EXAMPLE 6 
A control and a coating containing 10% microgels were prepared as in 
Example 3 but no solvent was added. Instead the compositions were 
melt-extruded onto a support to examine relative properties in the absence 
of any organic solvent. When samples were laminated to copper and given 
chemical and physical tests it was determined that with the exception of 
longer strip times for both the control and the invention, the 
incorporation of microgels produced an advantage of photospeed and creep 
viscosity as a tradeoff lower higher development rate and longer time to 
strip. When samples were tested with 1.3 mil films as in Example 3 a 
significant advantage in tenting was observed for the invention versus the 
control. Thus it can be concluded that the microgel advantage is 
independent of coating method used for film preparation. 
EXAMPLE 7 
Photopolymer compositions were prepared similar to Example 3 except that 
different microgels were used. Table I contains a summary of the microgel 
compositions incorporated in these compositions to produce photoresist 
films. It was observed that microgels containing acid groups were easier 
to incorporate into these coating compositions, i.e., requiring shorter 
dispersion times. 
EXAMPLE 8 
Several photopolymer compositions were prepared as in Example 3 except that 
different primary binders and monomers were employed with the microgels. 
Binders used were: polymer of methylmethacrylate/ethylacrylate/acrylic 
acid/cyclohexylmethacrylate 15/40/25/20; amphoteric interpolymer from 40% 
n-tertoctyl acrylamide, 34% methylmethacrylate, 10% acrylic acid, 6% 
hydroxy propyl methacrylate and 4% t-butyl amino ethyl methacrylate; 
polymer of styrene butyl maleate; polymer of methyl 
methacrylate/2-ethyl-hexyl acrylate-methacrylic acid 65/31/2 and polymer 
of styrene methacrylic acid. Other monomers used were trimethylolpropane 
triacrylate and pentaerythritol triacrylate. Film samples were prepared 
similar to example in which the thicknesses varied from 1.29 to 1.79 mil 
due to viscosity differences. Improved creep viscosity and photospeed was 
observed when microgels were incorporated compared to a control with no 
microgels. 
EXAMPLE 9 
Microgels B and J from Table I were dispersed into the polymer binder of 
Example 3 using a 2-roll mill. Two 100 g portions of 50/50 
microgel/polymer were each mixed with 100 ml of methylene 
chloride/methanol 93/7 and allowed to stand for about 1 hour. The two roll 
mill was cleaned with 3:1 binder/triethylene-glycoldiacetate. The material 
was milled for 10 minutes at 175.degree. C. Mixing and melt looked good 
and the material was cut off and reintroduced several times during the 
run. At the end of 10 minutes the melted mixture was cut off the mill and 
allowed to cool. Prior to use in a photopolymer composition the material 
was hand ground. Films prepared with the milled materials showed the same 
creep viscosity advantage as compositions prepared by stirring. 
EXAMPLE 10 
Film samples with the composition of Example 3 containing microgels 
prepared as in Example 1 and melt extruded as in Example 6 were tested for 
printed circuit board manufacture. The films were laminated to a copper 
clad board and exposed on a PC24 Riston.RTM. exposure device through a 
circuit board test pattern. The film cover sheet was removed and the 
exposed boards were processed in a Riston.RTM. Aqueous Development System 
ADS-24 with 1% aqueous Na.sub.2 CO.sub.3 at 30.degree. C. at a conveyor 
setting of 150 using a top spray pressure of 30 psi and bottom of 29 psi. 
The samples were etched to remove copper in the nonresist areas and then 
the resist was removed by stripping with 1.5% aqueous potassium hydroxide. 
A detailed examination of the resulting printed circuit boards showed 
equivalent quality to boards similarly prepared with commercial 
photoresist films. 
EXAMPLE 11 
The comparative solubility of the binder and insolubility of the microgels 
was determined by actual test. A 1 gram sample in 100 ml of 2% aqueous 
sodium carbonate was stirred at 29.degree. C. for 10 minutes. The sample 
was centrifuged for 40-45 minutes and the supernatant decanted. The 
remaining solid was washed with a minimum amount of water, centrifuged, 
dried and weighed. The supernatant was also dried and weighed. The 
following is an experimental comparison of the polymer binder of Example 1 
and microgels C and G of Table I. 
______________________________________ 
Sample Solid Remaining Grams 
______________________________________ 
Polymer binder 
0.0150 
Microgel C 0.9736 
Microgel G 0.9674 
______________________________________ 
EXAMPLE 12 
The comparative swellability of the microgel B and the prior art 
polytrimethylolpropanetriacrylate beads of Example 1 of U.S. Pat. No. 
4,414,278 was determined by actual test. The viscosity of a test solution 
of 8% by weight methanol and 92% by weight methylene chloride was 
determined to be 2.5 centipoise using a Brookfield viscometer with a No. 2 
spindle. 10 g solid material of microgel B and polytrimethylolpropane 
triacrylate were introduced into separate 100 g test solutions and stirred 
for 24 hours. The weight was brought up to 110 g at the end of this time 
period to correct for any evaporation. Using the same Brookfield 
viscometer with a No. 2 spindle the viscosity of microgel B solution was 
3800 centipoise while the solution of polytrimethylolpropane triacrylate 
beads was 5.0 centipoise. In appearance at the end of the 24 hour period 
microgel B in the test solution was invisible, having assumed the same 
refractive index as the test solution (apparently by swelling) while the 
comparative test beads in the test solution had an identical milky 
appearance observed at the time of their initial introduction in the test 
solution.