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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a novel initiator for photopolymerization
of cationically polymerizable organic material. More paticularly, the
present invention relates to an initiator for photopolymerization which
can be added to cationically polymerizable organic material in a suitable
amount and can polymerize the cationically polymerizable material with
irradiation of active photo-energy, thereby converting the organic
material into high molecular weight state.
2. Disclosure of the Prior Art
Various onium salts such as diazonium salts, iodonium salts, sulfonium
salts, etc., and salts of metallocene complexes are known as initiator for
photopolymerization of cationically polymerizable material [for example,
Annual Reviews Materials Science, 13, 173-190 (1983); Journal of Radiation
Curing, 13 (10), 26-32 (1986); Japanese Patent Laid-open No. 151,996/75;
Japanese Patent Laid-open No. 15,261/81; and Japanese Patent Laid-open No.
210,904/83].
The working mechanism of these known initiators in photopolymerization are
as follows:
In case of using various diazonium salts, iodonium salts and sulfonium
salts, a Bronsted acid is generated at first by irradiation of U.V. light
in accordance with the Scheme I, II and III.
##STR1##
The generated Bronsted acid can react with the cationically polymerizable
organic material and the polymerization proceeds in accordance with Scheme
IV, whereby molecular chain of polymer grows.
##STR2##
On the other hand, in case of using a salt of metallocene complex, a Lewis
acid is generated with irradiation, and an insertion of monomer occurs at
the Lewis acid, whereby molecular chain of polymer grows.
##STR3##
A process of initiation of polymerization with conventional photoinitiators
comprises a generation of Bronsted acid or Lewis acid by irradiation of
U.V. light. The diffusion of these acids in monomer system and the
insertion of monomer into coordinate bond of these acids are
rate-determining step of polymerization. The diffusion of these acids or
the insertion of monomer is slower than diffusion of radical in
photoradical polymerization and accordingly the polymerization with the
conven-tional photoinitiators is slower than photoradical polymerization.
The maximum absorption wavelength of the conventional photoinitiators is
within ultraviolet shorter wavelength zone of not higher than 300 nm. when
a ray having the wavelength exceeding the zone mentioned above is used
-(for example, i ray 365 nm; g ray, 436 nm; photolithography with a
positive film), the acids which are essential for initiation of
polymerization are not generated, or even if the acids are generated,
their quantum efficiency is very low.
Therefore, when they are used for polymerization of colored cationical
photocuring compositions such as epoxy resin paint, etc.; photocuring
compositions usable for sealing, closing adhesion; industrial materials
such as photoresist material which is used for preparation of wiring
pattern on semiconductor or printed circuit board, they must be used in
much amount, or they must be used together with a sensitizer such as
aromatic condensed polynucleus compounds (for example, anthracene),
thioxanthone, benzoin alkyl ether, alkoxy acetophenone, etc. in order to
vest the resulting mixture with photosensitivity in longer wavelength zone
or improve reaction rate.
Even if the recipe mentioned above is adopted, insufficient thick film
curability is often observed and the cured material which does not have
desired physical properties is often obtained. In view of these factors, a
composition comprising an initiator which has both of photocuring and
thermo-curing has been developed. Such photoinitiators are disclosed in
for example, Japanese Patent Laid-open No. 210,904/83 and No. 223,020/86.
However, as the addition amount of photoinitiator increases, the amount of
photo-decomposition product increases, and as a result, unpolymerized low
molecular-weight compounds may be included in the obtained cured material
and remain therein. The use of sensitizer leads also the similar results.
When the cured materials including the unpolymerized low molecular weight
compounds are used in industrial field, there exist some defects such as
rapid deterioration of cured material, corrosion of mother material to be
coaded, etc.
An adoption of post-heat curing step is not preferable, because the period
of heat curing step is dependent to temperature of mother material to be
coated and temperature of atmosphere at which the heat curing is carried
out and accordingly the control of period of heat curing is difficult,
especially in automatic operation system. In addition, the adoption of
post-heat curing step leads an increasment in number of step and time and
accordingly injures the merits obtainable from use of photoinitiator
and/or sensitizer such as rapid curing, improvement of productivity, etc.
SUMMARY OF THE INVENTION
Since the phenomenon that an electric conductivity is generated by transfer
of electron between two materials was found, many charge-transfer
complexes comprising various combination of electron acceptor with
electron donor have been prepared. The use of such charge-transfer complex
as organic photoelectronic material which constitutes electroconductive
parts (such as electrode, etc), semi-conductor parts (such as polymer
battery, transistor, diode, etc.) have been studied. However, the
development of use based on other properties of charge-transfer complex
have not been attempted.
The inventor payed his attention to photochemical reaction which is induced
by an excitation of charge-transfer absorption band of the charge-transfer
complex, and he has attempted many researches to utilize such
photochemical reaction in photoinitiating cationic polymerization. As a
result, he found a novel initiator for photopolymerization which can solve
the problems of conventional cationic photopolymerization mentioned above,
in other words, it is possible to produce a cured products which have
sufficient hardness, good physical and electrical properties.
Therefore, an object of the present invention is an initiator for
photopolymerization of cationically polymerizable material, characterized
in that said initiator comprises a composite obtainable from a reaction
between (a) a charge-transfer complex consisting of biscyclopentadienyl
iron derivative and quinoid and (b) at least one salt selected from a
group consisting of tetrafluoroborates, hexafluorophosphates and
hexafluoroantimonates.
Another object of the present invention is a method for photopolymerization
of cationically polymerizable organic material, characterized in that said
cationically polymerizable organic material is exposed to light having the
wavelength of 200-500 nm in the presence of the initiator comprising a
composite obtainable from a reaction between (a) a charge-transfer complex
consisting of biscyclopentadienyl iron derivative and quinoid and (b) at
least one salt selected from a group consisting of tetrafluoroborates,
hexafluorophosphates and hexafluoroantimonates.
BRIEF DESCRIPTION OF THE INVENTION
The first ingredient (a) of initiator for photopolymerization of the
present invention is a charge-transfer complex which consists of a
biscyclopentadienyl iron derivative and a quinoid.
The charge-transfer complex can be prepared by rejecting
biscyclopentadienyl iron derivative with quinoid in the amount of 0.1-2
equivalents per stoichiometric amount of the former.
The usable biscyclopentadienyl iron derivative is a compound having a
general formula:
[(C.sub.5 H.sub.m R.sub.5-n ]Fe[C.sub.5 H.sub.m R'.sub.5-m]
wherein R and R' are straight or branched, saturated or unsaturated alkyl
group, substituted or non-substituted aryl group, carboxyl group, nitril
group, nitro group, or amino group; n and m are integer ranging from 0 to
5. The example of biscyclopentadienyl iron derivative includes ferrocene,
monoethyl ferrocene, monoacetyl ferrocene, 1,1'-diacetyl ferrocene,
monophenyl ferrocene, 1,1'-diphenyl ferrocene, monovinyl ferrocene,
monoformyl ferrocene, monocarboxy ferrocene, monocyano ferrocene,
1-acetyl-l'-cyano ferrocene, mononitro ferrocene,
1-ferrocenyl-2-nitroethylene, 1,2-diphenyl ferrocene,
1-ferrocenyl-1-piperidyl-2-nitropropane, 1,3,1',3'-tetraphenyl ferrocene,
1,2,4,1',2',4'-hexaphenyl ferrocene, 1,2,3,4,1',2',3',4'-octaphenyl
ferrocene, 1,2,3,4,5,1',2',3',4',5'-decaethyl ferrocene,
1,1'-dimethyl-2-ethyl ferrocene, etc. The biscyclopentadienyl iron
derivative is used in single or mixture of at least two members.
Particularly, suitable biscyclopentadienyl iron derivative is ferrocene.
The "quinoid" which constitutes the charge-transfer complex means compounds
having such structure that one of endocyclic double bonds in aromatic
compound is decreased and two exocyclic double bonds are present at p- or
o-position. The quinoid includes quinone in which the atoms of exocyclic
double bonds are oxygen; quinonimine in which the atoms of exocyclic
double bonds are oxygen and nitrogen; quinodiimine in which the atoms of
exocyclic double bonds are nitrogen; quinomethane in which the atoms of
exocyclic double bonds are carbon and oxygen; and quinodimethane in which
the atoms of exocyclic double bonds are carbon. In particular, the
suitable quinoid is at least one compound selected from among quinones and
quinodimethanes. The example of quinoid includes p-benzoquinone,
2,5-dichloro-p-benzoquinone, 2,6-dichloro-p-benzoquinone,
2,3-dichloro-5,6-dicyano-p-benzoquinone, bromonyl, chloranyl,
1,4-naphthoquinone, 2,3-dichloro-1,4-naphtoquinone, anthraquinone,
2-methyl-anthraquinone, 2-ethyl-anthraquinone, 2-chloro-anthraquinone,
anthraquinone-.beta.-carboxylic acid, 9,10-phenanthraquinone,
7,7,8,8-tetracyanoquinodimethane,
2,5-dimethyl-7,7,8,8-tetracyanoquinodimethane,
11,11,12,12,-tetracycnonaphtho-2,6-quinodimethane,
tetrafluoro-tetracyanoquinodimethane, etc.
The second ingredient (b) of initiator for photopolymerization of the
present invention is at least one salt selected from a group consisting of
tetrafluoroborates, hexafluorophosphonates and hexafluoroantimonates. More
particularly, it is selected from a group consisting of sodium, potassium
and silver salts of tetrafluoroboric acid, hexafluorophosphoric acid and
hexafluoroantimonic acid.
The second ingredient (b) is mixed with the charge-transfer complex (a) in
the amount of 0.1-2 equivalent, preferably 0.1-1 equivalent per
stoichiometric amount of the charge-transfer complex (a). When the second
ingredient (b) is used in the amount exceeding the range of 0.1-2
equivalent, the obtained initiator cannot initiate a polymerization.
On preparing the initiator for photopolymerization of the present
invention, the charge-transfer complex of biscyclopentadienyl iron
derivative and quinoid is firstly prepared as mentioned above. More
particularly, the biscyclopentadienyl iron derivative and quinoid at
mutual ratio selected from the range mentioned above are dissolved into a
good affinity solvent and they are reacted with each other for 1-40 hours
with heating under reflux. After undissolved materials are filtrated away,
the second ingredient (b) is added to filtrate and the reaction is carried
out for 5 min. to 2 hours with heating.
The initiator for photopolymerization of the present invention is present
in the obtained reaction system solution, and after filtration, it can be
added to cationically polymerizable organic material in the form of
solution or solid mixture obtained by removing solvent from said reaction
system solution.
The addition amount of the initiator for photopolymerization is within a
range of 0.01-5 weight parts, preferably 0.1-3 weight parts per 100 weight
parts of cationically polymerizable organic material.
The good affinity solvent suitable for the preparation or, initiator for
photopolymerization is selected from a group consisting of alcohols,
ethers, ketones, liquid nitril compounds, cyclic esters and carbonates.
The example thereof includes methanol, tetrahydrofuran, acetone,
methylethyl ketone, dioxane, acetonitril, benzonitril, propiolactone,
.epsilon.-caprolactone, propylene carbonate, etc.
The cationically polymerizable organic materials to which the initiator for
photopolymerization of the present invention can be applied are ethylenic
unsaturated compounds, heterocylic compounds, methylol compounds, etc. An
important character of the initiator for photopolymerization of the
present invention is an ability to convert a monomer into high molecular
weight state in a very short time, and accordingly the initiators of the
present invention prove their worth in case that they are applied to epoxy
resin which is a main ingredient of paints, adhesives, etc.
The "epoxy resin" means a compound which has a various molecular weight and
at least two oxirane rings in its molecular chain or side chain or at its
molecular end. As the compound, products obtainable from a reaction
between various diol or polyol compound and epichlorohydrin in the amount
equivalent to OH groups can be used. The example of epoxy resin includes
bisphenol A, bisphenol F, hydrogenation products or bromination products
thereof, cresol-novolak, phenolnovolak, polycondensation products between
polyhydric alcohol or the like and epichlorohydrine. The epoxydated resin
can be also used which are prepared by treating a cyclohexen
ring-containing compound or a compound having unsaturated double bonds
(such as polybutadiene, polyisoprene, etc.) with an organic peroxide (such
as peracetic acid, etc.) in order to introduce oxygen of oxirane type into
a molecular chain, side chain or ring structure.
These epoxy resins can be used in single, or in blend thereof or mixture
with other resin or powdery additives in accordance with desired
properties, method for application, etc. They can be diluted with a
suitable diluent to lower its viscosity. The diluent suitable for this
purpose is monoepoxy compound, the examples of which are phenylglycidyl
ether, glycidyl (metha)acrylate, styrene oxide, cyclohexyl oxide, etc.
When the initiator for photopolymerization of the present invention is
added to epoxy resin or other cationically polymerizable organic material,
the initiator can vest the cationically polymerizable organic material
with photopolymerization activity. The cationically polymerizable organic
material vested with photopolymerization activity by the initiator absorbs
an energy of 2000-6000 mJ/cm.sup.2, in general with irradiation of
near-ultraviolet light of 200-500 nm, preferably at least 300-400 nm and
form an un-tacky film. The irradiation of near-ultraviolet light can be
carried out under vacuum, inert gas-pressurized atmosphere or atmospheric
pressure, and the photopolymerization progresses rapidly at ambient
temperature or with cooling or heating. The cationically polymerizable
compound vested with photopolymerization activity by the addition of the
initiator of the present invention can be easily polymerized with
irradiation of light. When the polymerization is not completed with only
the irradiation, it can be completed by converting at first the
cationically polymerizable organic material to non-fluidized state by
irradiating (in case of epoxy resin, B-stage curing state) and then by
maintaining the organic material of non-fluidized state at ambient
temperature or heating, if necessary. In other words, when the initiator
for photopolymerization of the present invention is used, the rate and
degree of polymerization can be controlled in accordance with a purpose
and desired physical properties by adjusting the photoenergy.
To further illustrate the present invention, and not by way of limitation,
the following examples are given. In these examples, as reagents,
solvents, etc., commercially available products are used as such without
any purification. The used apparatus, irradiator of ultraviolet ray, etc.
are articles which are easily available.
EXAMPLE 1
An eggplant type flask made of Pyrex glass (capacity of 100 ml) provided
with a stirrer and a reflux condenser was charged with ferrocene (1.86 g)
and p-benzoquinone (1.08 g) together with methanol (100 ml) and the
resulting mixture was heated under reflux on an oil bath for 16 hours.
Before the solution cools; undissolved materials were filtrated away.
Sodium hexafluoroantimonate (1.29 g) was added to the filtrate and the
resulting mixture was heated under reflux on an oil bath for further 1
hour. Thereafter, the solution was cooled down to ambient temperature and
then to -20.degree. C. After removing the precipitates by filtration, the
filtrate was evaporated under reduced pressure to dryness. Thus a mixture
of yellow and black crystals was obtained with the yield of 77.5% .
EXAMPLE 2
Using the apparatus similar to that of Example 1, ferrocene (0.93 g) was
dissolved into methanol (100 ml) with heating. After confirming the fact
that ferrocene was completely dissolved into methanol,
2,6-dichloro-p-benzoquinone (0.88 g) was added to the resulting solution
and the obtained mixture was heated under reflux for 15 hours. Thereafter,
before the solution cools, undissolved materials were removed by
filtration. Sodium hexafluoroanitimonate (1.29 g) was added to the
filtrate and the resulting solution was heated under reflux for 1 hour.
The solution was cooled down to ambient temperature and further to
-20.degree. C. After removing the precipitated crystals by filtration, the
filtrate was evaporated under reduced pressure to dryness. Deep green
crystal was obtained with yield of 80.7%.
EXAMPLE 3
Using the apparatus similar to that of Example 2, the operation was carried
out in accordance with the procedure similar to that of Example 2 and
greenish brown crystal was obtained with yield 71.9%, starting from
methanol (100 ml), ferrocene (0.9 g), chloranyl (1.23 g) and sodium
hexafluoroantimonate (1,29%).
EXAMPLE 4
Using the apparatus similar to that of Example 2, in accordance with the
procedure similar to that of Example 2, ferrocene (0.43 g) was dissolved
into methanol (100 ml) with heating. To the resulting solution,
2,3-dichloro-5,6-dicyano-p-benzoquinone (0.113 g) was added and the
solution was heated under reflux for 3 hours. After the filtration in hot
was carried out, sodium hexafluoroantimonate (1.29 g) was added to the
filtrate and the resulting solution was heated under reflux for 1 hour.
Then the solution was subjected to the similar post-treatment and brown
crystal was obtained with yield of 86.8%.
EXAMPLE 5
Using the apparatus similar to that of Example 1,
2,3-dichloro-5,6-dicyano-p-benzoquinone (2.27 g) was dissolved into
acetonitril (100 ml). After ferrocene (1.86 g) was added to the resulting
solution, the solution was heated under reflux for 16 hours, and it was
cooled down to ambient temperature and further to -20.degree. C. The
precipitated crystal was recovered by filtration. After drying the crystal
at 65.degree. C., the crystal was dissolved again into methanol (100 ml).
Sodium hexafluoroantimonate (1.29 g) was added thereto and the resulting
solution was heated under reflux for 1 hour. The solution was cooled down
to ambient temperature and further to -20.degree. C. The precipitated
crystal was recovered by filtration and dried. The obtained crystal has a
color of deep brown.
EXAMPLE 6
Using the apparatus similar to that of Example 1, the operation was carried
out in accordance with the procedure similar to that of Example 1, a
mixture of yellow-black crystals was obtained with the yield of 76.7%,
starting from methanol (100 ml), ferrocene (1.86 g), 1,4-naphthoquinone
(1.58 g) and sodium hexafluoroantimonate (1.29 g).
EXAMPLE 7
In the apparatus of Example 1, the operation was carried out in accordance
with the procedure similar to that of Example 1. Starting from
tetrahydrofuran (100 ml), ferrocene (0.93 g),
7,7,8,8,-tetracyanoquinodimethane (1.02 g) and sodium hexafluoroantimonate
(1.29 g), a mixture of yellow-black crystals was obtained with the yield
of 84.4%.
EXAMPLE 8
In the apparatus described in Example 1, the operation was carried out in
accordance with the procedure similar to that of Example 1. Starting from
tetrahydrofuran (100 ml), ferrocene (1.86 g),
7,7,8,8-tetracyanoquinodimethane (1.02 g), 9,10-phenanthraquinone (1.04 g)
and sodium hexafluoroantimonate (1.29 g), red-brown crystal was obtained
with the yield of 90.6%.
EXAMPLE 9
Using the same apparatus as Example 1, 7,7,8,8-tetracyanoquinodimethane
(1.02 g) was dissolved into acetnitril (100 ml) with heating. Ferrocene
(0.93 g) was added thereto and the resulting solution was heated under
reflux for 16 hours. Thereafter, the filtration in hot was carried out,
sodium tetrafluoroborate (0.55 g) was added to the filtrate, which was
treated similarly to preceding Examples. As a result, green crystal was
obtained with the yield of 61.8%.
EXAMPLES 10-16
The initiators for photopolymerization prepared in preceding Examples 1-9
were added to cycloaliphatic epoxy resin [Ciba-Geigy, ARALDITE (registered
trade mark) CY-179] in the amount of 2 weight parts per 100 weight parts
of the epoxy resin and the mixture was stirred sufficiently to prepare a
uniform solution. This solution was applied uniformly on a glass plate
with a thickness of about 50 .mu.m and was exposed to light. The exposure
amount necessary to cure the solution to make a film and the hardness of
the obtained film were reported in Table 1.
The irradiation was carried out with a high pressure mercury lamp. The
light emitted by the mercury lamp was treated with a cold mirror and a
visible light cutting filter to transform the light into near-ultraviolet
light having the wavelength of 200-400 nm in order to prevent effects of
heat ray. The exposure amount was determined as accumulated luminous
energy. The hardness of film was determined by a comparison with the
hardness of lead of pencil in accordance with JIS-K-5400.
TABLE 1
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Exam- Luminous energy
ple necessary to make
Hardness
Color of
(No.) Initiator a film (mJ/cm.sup.2)
of film
film
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10 Example 1 6,000 F light-green,
transparent
11 Example 2 3,600 F green,
transparent
12 Example 3 3,600 H brown,
transparent
13 Example 4 5,400 2H brown,
transparent
14 Example 5 4,500 2H red-brown,
transparent
15 Example 7 2,700 3H green,
transparent
16 Example 8 4,500 H green-brown,
transparent
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EXAMPLES 17-20
In a glass ampoule bottle (15 ml), 7,7,8,8-tetracyanoquinodimethane (0.102
g) was added to acetnitril (10 g) and the bottle was sealed. The contents
were heated to 65.degree. C. with stirring by a magnetic stirrer. After
confirming the fact that 7,7,8,8-tetracyanoquinodimethane was completely
dissolved, a plug was removed, a predetermined amount of ferrocene was
added thereto, the bottle was sealed again, and the contents were heated
further for 16 hours with stirring. Thereafter, the still hot solution was
filtered, a predetermined amount of sodium hexafluoroantimonate was added
to the filtrate, the bottle was sealed, and the contents were heated at
65.degree. C. for further 1. hour with stirring. After the period lapsed,
the solution was cooled down to --20.degree. C., and the precipitated
crystal was filtered away. Thus obtained filtrate contained initiator for
photopolymerization in the amount of 1.9-2.3% and had a color of deep
green. This initiator for photopolymerization was added to and mixed with
bisphenol A type epoxy resin having the molecular weight of about 380
(epoxy equivalent=about 190) in such amount that the initiator for
photopolymerization is present at the content of 2 wt %. In this way, a
uniform solution was obtained. The solution was applied on a glass plate
at the thickness (as dry film) of about 50 .mu.m. The film was dried in a
hot fluid-circulating furnace at 65.degree. C. for 20 min. and was exposed
to light.
The feeding amount of ingredients of initiator, luminous energy necessary
to make a film, and hardness of film were reported in Table 2. The
luminous energy necessary to make a film, hardness of film were determined
similarly to the preceding Examples 10-16.
TABLE 2
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Luminous energy
Ex.
Ingredient of Initiator (g)
necessary to make
Hardness
No.
ferrocene
TCNQ
NaSbF.sub.6
mole ratio
a film (mJ/cm.sup.2)
of film
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17 0.093
0.102
0.129
1:1:1 3,600 2H
18 0.093
0.102
0.065
1:1:0.5
5,400 H
19 0.186
0.102
0.129
1:0.5:0.5
4,500 H
20 0.093
0.204
0.258
0.5:1:1
5,400 H
__________________________________________________________________________
The initiator for photopolymerization of the present invention have the
following merits in comparison with the conventional initiators.
1. The polymerization can be completed by an
irradiation of light having the wavelength of 200-500 nm.
2. Even when the initiator is added to monomer in comparatively small
amount, it can vest the monomer with photopolymerization activity because
of its high photopolymerization capacity.
3. Because the sensitizing wavelength zone is within a long wavelength
zone, it has a sufficient ability to initiate a photopolymerization
without any sensitizer.
4. The preparation thereof is very easy.
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