Energy beam curable composition

There is provided an energy beam curable resin composition which comprises as an essential component a cationically polymerizable substance and an effective amount of an onium salt of a Lewis acid represented the following formula (I). ##STR1## [where X is a sulfonio group represented by the following formula (II)]. ##STR2## (where at least one of R.sub.1 -R.sub.10 is (A) a C.sub.1 -C.sub.18 aliphatic group having at least one hydroxyl group or (B) a C.sub.3 -C.sub.19 aliphatic group having a group of --OCH.sub.2 CH.sub.2 O--).

FIELD OF INDUSTRIAL APPLICATION 
The present invention relates to a composition capable of curing upon 
irradiation with an energy beam. More particularly, it relates to a resin 
composition which, when used as a coating material, readily cures and 
affords a cured coating film which gives off very little odor and bleeds 
very little decomposition products induced by irradiation. 
PRIOR ART AND PROBLEMS THEREOF 
Photopolymerizable polymeric materials have been under active study, 
particularly in the area of coating, from the standpoint of energy saving, 
space saving, and environmental pollution. However, the polymerization of 
such materials is based mainly on the radical polymerization of double 
bonds. For example, an epoxy resin, despite its good physical properties, 
does not readily undergo photopolymerization without the introduction of 
double bonds, which is accomplished in actual by the modification with an 
acrylic compound. 
There is disclosed in U.S. Pat. No. 3,794,576 (Feb. 26, 1974) issued to 
Watt a new photopolymerizable epoxy resin composition having both good 
rheological properties and capability of rapid curing. This resin 
composition contains a photosensitive aromatic diazonium salt as a 
photopolymerization initiator. Upon exposure to light, the diazonium salt 
decomposes to liberate a Lewis acid which takes part in the polymerization 
of epoxy resin monomers. The aromatic diazonium salt, however, has a 
disadvantage of liberating nitrogen gas together with a Lewis acid upon 
photodecomposition. The nitrogen gas thus liberated causes foaming when 
the coating film of epoxy resin is thicker than 15 .mu.m. Therefore, it is 
not suitable for thick coating. Another disadvantage is that an epoxy 
resin composition containing the diazonium salt gradually cures even in 
the absence of light. Because of this poor storage stability, the 
diazonium salt is not suitable for one-pack compositions. 
Extensive studies have been made to overcome the above-mentioned 
disadvantages of the diazonium salt initiator, and improvements were made 
in thick coating and storage stability. As the result, there were 
disclosed an aromatic sulfonium salt initiator and an aromatic iodonium 
salt initiator and a curable resin composition containing it in Japanese 
Patent Publication Nos. 14278/1977, 14277/1977, and 19581/1984 and 
Japanese Patent Laid-open No.53181/1979. 
The composition containing an aromatic onium salt mentioned above is 
inferior in curability to the one containing a diazonium salt. Where the 
aromatic onium salt is an aromatic sulfonium salt, the composition 
containing it gives off an ill-smelling low-molecular weight compound when 
irradiated with an energy beam, with the result that the coating film has 
a foul smell. In order to eliminate this disadvantage, there was proposed 
a high-molecular weight aromatic sulfonium salt having a specific group in 
Japanese Patent Laid-open No. 55420/1981. However, it still is not 
satisfactory although it eliminates the disadvantage to some extent. Upon 
irradiation, it forms a low-molecular weight compound such as bisphenyl 
sulfide, which remains in the coating film, causing the film to smell. 
It is an object of the present invention to provide an energy beam curable 
resin composition which is superior in curability and storage stability 
and, upon irradiation with an energy beam, liberates a very little amount 
of low-molecular weight compound such as diphenyl sulfide which is not 
desirable from the standpoint of odor, safety, and film properties. 
MEANS TO SOLVE THE PROBLEMS 
The object of the invention is achieved by an energy beam curable resin 
composition which comprises as essential constituents a 
cation-polymerizable substance and an effective amount of an onium salt of 
a Lewis acid represented by the following formula (I). 
##STR3## 
[where X is a sulfonio group represented by the following formula (II). 
##STR4## 
(where R.sub.1 -R.sub.10 are each a hydrogen atom, halogen atom, nitro 
group, alkoxy group, C.sub.1 -C.sub.18 aliphatic group, or C.sub.6 
-C.sub.18 substituted or unsubstituted phenyl, phenoxy, or thiophenoxy 
group, with at least one of R.sub.1 -R.sub.10 being (A) a C.sub.1 
-C.sub.18 aliphatic group having at least one hydroxyl group or (B) a 
C.sub.3 -C.sub.19 aliphatic group having a group of --OCH.sub.2 CH.sub.2 
O--.); 
Y is a group represented by the above formula (II), hydrogen atom, halogen 
atom, nitro group, alkoxy group, C.sub.1 -C.sub.18 aliphatic group, 
C.sub.6 -C.sub.18 substituted or unsubstituted phenyl, phenoxy, or 
thiophenoxy group, and n=1-3 and m=1-2; and 
Z is a group represented by the formula MQ.sub.l (III) or the formula 
MQ.sub.l-1 OH (IV). (where M denotes B, P, As, or Sb; Q denotes a halogen 
atom; and l is an integer of 4 to 6.)] 
A cationically polymerizable substance to use in the invention includes 
epoxy resins, vinyl ethers, cyclic ethers and ketones, lactones, oxetanes, 
styrenes, acroleins, vinyl arenes (e.g., 4-vinylbiphenyl), alicyclic vinyl 
compounds (e.g., vinylcyclohexane), spiro-orthoesters, 
spiro-orthocarbonates, bicyclo-orthoesters, isobutylene, dienes (e.g., 
butadiene and isoprene), and phenol-formaldehyde resins. They are in the 
form of monomer or prepolymer. Preferable among them is epoxy resins. 
The epoxy resins used in this invention are known aromatic epoxy resins, 
alicyclic epoxy resins, and aliphatic epoxy resins. Preferred aromatic 
epoxy resins are a polyglycidyl ether derived from polyhydric phenol 
having at least one aromatic nucleus or alkylene oxide adduct thereof. 
Their examples include glycidyl ether resins produced by the reaction 
between bisphenol A or alkylene oxide adduct thereof and epichlorohydrin, 
and they also include epoxy-novolac resins. Preferred alicyclic epoxy 
resins include polyglycidyl ethers derived from a polyhydric alcohol 
having at least one aliphatic ring, and they also include cyclohexene 
oxide-containing compounds or cyclopentene oxide-containing compounds 
produced by epoxidizing a cyclohexene ring-containing compound or 
cyclopentene ring-containing compound with a proper oxidizing agent such 
as hydrogen peroxide and peracid. Typical examples of polyglycidyl ether 
include one which is produced by the reaction between hydrogenated 
bisphenol A or alkylene oxide adduct thereof and epichlorohydrin. In 
addition, preferred aliphatic epoxy resins include polyglycidyl ethers of 
an aliphatic polyhydric alcohol or alkylene oxide adduct thereof. Their 
typical examples include diglycidyl ether of 1,6-hexanediol, triglycidyl 
ether of glycerin, diglycidyl ether of polyethylene glycol, diglycidyl 
ether of polypropylene glycol, and polyglycidyl ether of polyether polyol 
obtained by adding one or more kinds of alkylene oxide (e.g., ethylene 
oxide and propylene oxide) to an aliphatic polyhydric alcohol (e.g., 
ethylene glycol, propylene glycol, and glycerin). The above-mentioned 
epoxy resins may be incorporated with a diluent such as monoglycidyl ether 
of an higher aliphatic alcohol and a monoglycidyl ether of phenol or 
cresol or polyether alcohol obtained by adding alkylene oxide thereto. 
The above-mentioned aromatic epoxy resins, alicyclic epoxy resins, and 
aliphatic epoxy resins may be used individually as the cationically 
polymerizable substance in the the curable composition of this invention. 
However, they may be properly combined with one another according to the 
desired performance. 
The onium salt of a Lewis acid, which is the other essential constituent in 
this invention, is represented by the following formula. 
##STR5## 
[where X is a sulfonio group represented by the following formula (II)]. 
##STR6## 
R.sub.1 -R.sub.10 are independently selected from various kinds of groups 
excluding basic groups such as amino groups. Preferably, they are a 
hydrogen atom, halogen atom (e.g., F, Cl, Br, and I), nitro group, alkoxy 
group (e.g., CH.sub.3 O-- and C.sub.2 H.sub.5 O--), C.sub.1 -C.sub.18 
aliphatic group (e.g., hydrocarbon group such as CH.sub.3 --, C.sub.2 
H.sub.5 --, and (CH.sub.3).sub.2 CH--; cyclic hydrocarbon group such as 
cyclohexyl group; and those which contain a hetero atom in the main chain 
or substituent group (e.g., 
##STR7## 
--S--CH.sub.3, --O--CH.sub.2 --CH.sub.2 --OH, --O--CH.sub.2 Ph, and or 
substituted or unsubstituted phenyl group, phenoxy group, or thiophenoxy 
group. 
To achieve the object of the invention, at least one of R.sub.1 -R.sub.10 
is (A) a C.sub.1 -C.sub.18 aliphatic group having at least one hydroxyl 
group or (B) a C.sub.3 -C.sub.19 aliphatic group having a group of 
--OCH.sub.2 CH.sub.2 O--. 
The substituent group belonging to (A) includes monoalcohol and polyalcohol 
represented by, for example, --CH.sub.2 OH, --CH.sub.2 CH.sub.2 OH, 
--O--CH.sub.2 --CH.sub.2 --CH.sub.2 --CH.sub.2 --OH, --SCH.sub.2 CH.sub.2 
OH, 
##STR8## 
Examples of the substituent groups belonging to (B) include --CH.sub.2 
O--CH.sub.2 --CH.sub.2 --O--CH.sub.3, 
##STR9## 
--O--CH.sub.2 CH.sub.2 --.sub.2 OH, --O--CH.sub.2 CH.sub.2 --.sub.2 
OCH.sub.3, and --OCH.sub.2 CH.sub.2 --.sub.3 OH. 
R.sub.1 to R.sub.10 may be any of the substituent groups defined by (A) and 
(B). Where eight or nine of R.sub.1 to R.sub.10 are hydrogen atoms, 
R.sub.3 and/or R.sub.8 should be the substituent groups defined by (A) and 
(B), for the ease of synthesis. 
Y in the above formula (I) is a group represented by the formula (II), or a 
hydrogen atom, halogen atom, nitro group, alkoxy group, C.sub.1 -C.sub.18 
aliphatic group, C.sub.6 -C.sub.18 substituted or unsubstituted phenyl 
group, phenoxy group, or thiophenoxy group (which are all defined as 
above). 
n is an integer of 1 to 3, and m is an integer of 1 to 2. Where Y is a 
sulfonio group represented by the formula (II), m is 2. 
Z is a group represented by the formula MQ.sub.l (III) or the formula 
MQ.sub.l-1 OH (IV). (where M denotes B, P, As, or Sb; Q denotes a halogen 
atom (preferably Cl or F); and l is an integer of 4 to 6. Examples of Z 
include BF.sub.4, PF.sub.6, AsF.sub.6, SbF.sub.6, and SbF.sub.5 OH. 
The onium salt of a Lewis acid used in this invention may be synthesized by 
(i) the reaction to form a sulfonium salt from a starting material having 
the desired substituent group, or by (ii) synthesizing an adequate 
substituted or unsubstituted group sulfonium salt and subsequently 
converting or introducing the substituent group. 
Examples of the onium salt of Lewis acid represented by the formula (I) are 
given below. 
##STR10## 
The curable composition of this invention is composed essentially of 100 
wt. parts of a cationically polymerizable substance and 0.1 to 15 parts by 
weight, preferably 0.4 to 8 parts by weight, of the onium salt of Lewis 
acid represented by the formula (I). The adequate ratio is determined 
according to the type and dosage of energy beam and other many factors 
such as desired cure time, temperature, humidity, and coating thickness. 
The curable composition of this invention is a liquid having a viscosity of 
1 to 100,000 centipoise at 25.degree. C. or a solid soluble in a solvent. 
Upon irradiation of energy beam such as ultraviolet light, it becomes dry 
to touch or solvent-insoluble within a tenth of minute to several minutes. 
The energy beam is not specifically limited so long as it has sufficient 
energy to induce the decomposition of an initiator. The preferred energy 
beam is an electromagnetic wave energy beam having a wavelength of 2000 
.ANG. to 7000 .ANG. produced by a high- or low-pressure mercury-vapor 
lamp, xenon lamp, bacteriocidal lamp, and laser; electron beam and X rays. 
The exposure to an energy beam is usually 0.5 seconds to 10 seconds, 
depending on the intensity of the energy beam used. Exposure longer than 
this may be desirable for thick coatings. A tenth of second to several 
minutes after irradiation, the composition becomes dry to touch through 
the cationic polymerization. Irradiation may be preferably accompanied by 
heating to promote the cationic polymerization. 
The composition of this invention may be incorporated with a solvent for 
dilution and an inert resin or prepolymer for modification, so long as 
they do not adversely affect the cationic polymerization. In addition, the 
composition may be incorporated with an organic carboxylic acid or acid 
anhydride for the improvement of electrical properties, or blended with a 
polyol or flexible prepolymer to impart rubbery resilience. 
The composition of this invention is usually a transparent liquid; and it 
may be incorporated with an inert pigment, dye, filler, antistatic agent, 
flame retardant, gelation inhibitor, flow regulator, surface active agent, 
adhesion improver, processing aid, viscosity adjustor, sensitizer, 
ultraviolet light absorber, and the like, according to the intended use. 
The amount of these additives depends on the performance required and the 
curing characteristics. 
The composition of this invention can be applied to metal, wood, rubber, 
plastics, glass, and ceramics. 
The composition of this invention will find use as paint, ink, adhesive, 
molding material, casting material, glass fiber impregnant, putty, and 
sealer. It can also be applied to electrical materials because of the 
superior electrical properties of epoxy resins. The major applications 
include capacitor, resistance, light emitting diode, semiconductor, 
printed board, transformer, motor, wire, solar battery, relay, switch, and 
other electrical and electronic parts. In addition, the composition will 
find use in the optical application because of its good clarity. 
The composition of this invention cures in a short time upon irradiation 
with an energy beam, and it passes into a cured product having good 
physical properties, forming very little amount of low molecular weight 
compound that causes an offensive odor and adversely affects the 
properties of the coating film.

EXAMPLES 
The invention is now described in more detail with reference to the 
following examples, which are not intended to limit the scope of the 
invention. 
Example 1 
4,4'-bis-[bis(p-fluorophenyl)sulfonio]phenylsulfide-bishexafluorophosphate 
was stirred in a large excess of ethylene glycol in the presence of sodium 
hydroxide at room temperature for 1 day. The reaction mixture was poured 
into water to give a light-yellow oily substance. This substance was 
washed with water several times and then purified by silica gel column 
chromatography. Thus there was obtained white solid in a yield of 70%. 
This substance was identified by .sup.13 C--NMR, .sup.3 H--NMR, and IR as 
4,4'-bis[bis(p-2-hydroxyethoxyphenyl)sulfonio]phenylsulfide-bishexafluorop 
hosphate (Compound 1). (The results of .sup.13 C--NMR were: 163.3, 140.3, 
133.3, 132.4, 131.3, 126.0, 117.3, 114.6, 70.5 and 59.2 ppm, TMS as the 
internal reference and DMSO-d.sub.6 as the solvent.) 
The above-mentioned procedure was repeated, except that ethylene glycol was 
replaced by carbitol, to give 
4,4'-bis[bis(p-1,4,7-trioxanonylphenyl)sulfonio]phenylsulfide-bishexafluor 
ophosphate (compound 2). 
For comparison, the following compounds were synthesized by the known 
process. Triphenylsulofonium-hexafluorophosphate (compound 3); 
diphenyl-4-thiophenoxyphenylsulfonium-hexafluorophosphate (compound 4): 
and bis[4-(diphenylsulfonio)phenyl]sulfide-bishexafluorophosphate 
(compound 5). [Journal of Polymer Science, Polymer Chemistry Edition, Vol. 
18, p. 2677, 1980; Vol. 22, p. 1789, 1984]. 
The above-mentioned five compounds were examined for photodegradation in 
the following manner. Each compound was dissolved in a methanol-water 
mixture (1:9) to give a 2000 ppm solution. The solution was exposed to 
ultraviolet light emitted by four fluorescent lamps FL6E (6 W) (made by 
Sankyo Denki Co., Ltd.) placed 10 cm away, for 30 minutes. The 
low-molecular weight compounds formed by exposure were identified by gas 
chromatography. The column was Tenax GC (1 m), and the temperature was 
raised from 150.degree. C. to 270.degree. C. at a rate of 15.degree. 
C./min. The results are shown in Table 1. 
TABLE 1 
______________________________________ 
Identification of Decomposition Product 
Compd 1 Compd 2 Compd 3 Compd 4 
Compd 5 
______________________________________ 
Diphenyl 
&lt;0.5% &lt;0.5% 30% 25% 31% 
sulfide 
Diphenyl 
&lt;0.5% &lt;0.5% 6% 8% 5% 
sulfoxide 
Others* &lt;2% -- -- -- -- 
______________________________________ 
*Low-molecular weight compounds having a molecular weight lower than 200. 
The decomposition products of Compound 1 were identified as 
bis(p-2-hydroxyethoxyphenyl)sulfide (about 20%) and 
bis(p-2-hydroxyethoxyphenyl)sulfoxide (about 5%). These compounds are all 
odorless solids. 
Example 2 
Compound 1 and compound 5 were individually dissolved in propylene 
carbonate to give 33% solutions. Each of the solution (5.77 parts by 
weight and 4.5 parts by weight) was added to an epoxy resin formulation 
composed of 80 parts by weight of Celloxide 2021 (alicyclic epoxy resin 
made by Daicel Chemical Ind. Ltd.) and 20 wt. parts of DY-022 
(butanediol-diglycidyl ether being available from Nagase Sangyo Co., 
Ltd.). 
The resulting mixture was applied to an aluminum test panel (in coating 
thickness of 10 .mu.m), and the coating was irradiated with a 
high-pressure mercury-vapor lamp, whereby a cured coating was obtained. 
The coating film was examined for elusion according to the method 
stipulated in the Food Sanitation Law (Notification No. 20 of the Ministry 
of Public Welfare, February 1982). The amount of residues on evaporation 
was measured. The results are shown in Table 2. 
TABLE 2 
______________________________________ 
Amount of Residues on Evaporation 
Conditions of extraction 
Compound 1 Compound 5 
______________________________________ 
20% alcohol, 60.degree. C., 30 min. 
&lt;10 ppm 15 ppm 
Water, 95.degree. C., 30 min. 
&lt;10 ppm 20 ppm 
n-heptane, 25.degree. C., 60 min. 
&lt;10 ppm &lt;10 ppm 
4% acetic acid, 60.degree. C., 30 min. 
&lt;10 ppm 17 ppm 
______________________________________ 
In the case of compound 5, 0.1 to 0.4 ppm of diphenyl sulfide was detected 
in the evaporation residues; but in the case of compound 1, it was not 
detected at all, nor bis(p-2-hydroxyethoxyphenyl)sulfide. 
Example 3 
In 100 g of ERL-4221 (alicyclic epoxy resin, made by Union Carbide Corp.) 
was dissolved 3.4 mmol of the compound of Example 1 (1.7 mmol in the case 
of bis-sulfonium salt). The resulting solution was applied to an aluminum 
test panel (in coating thickness of 5 .mu.m), and the coating film was 
irradiated with a high-pressure mercury-vapor lamp (80 W/cm) placed 10 cm 
away. The tack-free time (time for the coating film to dry to touch) was 
measured. The results are shown in Table 3. The compositions were good in 
storage stability, with no increase in viscosity after storage at 
40.degree. C. for 3 months. 
TABLE 3 
______________________________________ 
Tack-free Time 
Compound 
Compound Compound Compound 
Compound 
1 2 3 4 5 
______________________________________ 
2 sec. 2 sec. 5 sec. 2 sec. 2 sec. 
______________________________________ 
Example 4 
The following epoxy resin formulations 1 and 2 were prepared. Formulation 
1: 80 parts of ERL-4221 and 20 parts of DY-022 Formulation 2: 20 parts of 
ERL-4221, 60 parts of Ep-4100 (bisphenol A epoxy resin, made by Asahi 
Denka Co., Ltd.), and 20 parts of DY-022. 
To 100 g of each formulation was added 1.7 mmol of compound 1. In 
comparative examples, to 100 g of each formulation was added 3.4 mmol of 
tris(p-hydroxyphenyl)sulfonium-hexafluorophosphate having the phenolic 
hydroxyl group (compound 6). The resulting composition was examined for 
curing characteristics in the same manner as in Example 3. The cured 
coating film was exposed to a bacteriocidal lamp for 100 hours to examine 
the yellowing of the coating film. The results are shown in Table 4. 
TABLE 4 
______________________________________ 
Compound 1 
Compound 2 
______________________________________ 
Tack-free time 
Formulation 1 2 sec. 5 sec. 
Formulation 2 10 sec. &gt;60 sec. 
Color of coating film 
Formulation 1 Good Greatly yellowed 
Formulation 2 Good Greatly yellowed 
______________________________________