1 This invention relates to a novel phatosensi-tive resin composition containing pullulan as a compo-nentO More particularly, the invention is concerned with a novel photosensitive resin composition compris-ing pullulan~ which is a polymer having repetition units of maltotriose~ and/or a derivative of said pullulan, a photopolymerizable monomer, a photosen-sitizer and a thermal polymerization inhibitor, or comprising the said pullulan~ which has been incor-porated with a photoactive reaction group to providephotosensitivity,-and a photosensitizer.
Recently, photosensitive resins for letter-presses or photoresists have been developed in the field of printing~ and nylon-~ PVA- and cellulose acetate-type resins have already been proposed as photosensitive resins ~or letterpresses. Plates made of the nylon- and cellulose acetate-type photo-sensitive resins are developed with aqueous alkali solutions or organic solvents such as alcohols~ whlle those of the- PVA type resins can be developed with watsr. That a photosensitive resin plate can be developed with water is markedly advantageous from the standpoint of waste water treatment and the like.
However, an aquous solution of PVA is high in viscosity~
for example a 20 % aqueous solution of PVA having a polymerization degree of 2,400 and a saponification degree of 88 % has a viscosity of more than 100,000 cps at 25C.~ so that the aqueous PVA solution can be handled with difficulty. The highness in viscosity of the aqueous PVA solution results in such disadvan-tage .. ... . ~ . .. , . :
that at the time of production of resin plate, a long period of time is required for mixing the solution with other monomer and additives such as photopolymerization initiator and -the like.
Moreover, PVA is not always high in rate of dissolution in water, so that a long time is required for the development of PVA plate with water and, during the period OL development, more or less amount of the resin at cured portion is also dissolved out, with the result that the image obtained tends to become indistinct.
If the molecular weight of PVA is made lower in order to decrease the viscosity of the PVA solution, a resin plate obtained :from the PVA solution is correspondingly deteriorated in mechanical strength. Further, to aecrease the viscosity by bringing PVA
into a dilute aqueous solution at the time of preparation of its solution is entirely uneconomical in view of the tirne required for evaporation of water at the time of production of resin plate.
On the other hand, photoresists made of PVA of the cinnamoyl ester type have extensively been used in the field of semi-conductor industries. However, PVA of said type has been deprived of its characteristic water solubility, so that organic solvents should be used for preparation of solutions of said PVA and for development of plates made of said resin. In any case, regulations conce~ning the toxicity of photosensitive resins have come to be more and more strict, so that non-toxicity o~ said resins is the most important condition.
Under such circumstances as mentioned above, -~ iS57~
the present inventors made extensive studies with an aim to obtain substitutes for the above-mentioned resins to ~ind that when pullulan is used as a starting material, it is possible to obtain a photosensitive resin composition low in viscosity and substantially free from toxicity which can be prepared by use of water and can be formed into a photosensitive plate capable of beinq developed with water to give a clear image.
Based on this finding, the inventors have accomplished the present invention.
! 10 The present invention provides a novel photosensitive resin composition which comprises pullulan and/or its deriva-tive, a photo-polymerizable monomer, a sensitizer and a thermal polymerization inhibitor.
The present invention also provides a novel photo-sensitive resin composition which comprises pullulan incorpor-ated with a photoactive reaction group to provide pho-tosensit-ivity and a photosensitizer.
According to one aspect of the present invention therefore there is provided a photosensitive resin composition which comprises 30 to 90 parts ~y weight of one member or a mixture of two or more selected from pullulan having a molecular weight of 10,000 to ~,000,000 and its es-terified derivatives, 70 to 10 parts by weight of a photopolymerizable monomer, a sensitizer and a thermal polymerization inhibitor.
According to another aspect of the present invention there is provided a photosensitive resin composition which com-prises a cinnamoylated ester of pullulan and a sensitizer.
The pullulan used in the present invention is a polymer [refer to Applied Microbiology, Vol. 11, 211 - 215 (1963)~ having repetition units of maltotriose which is - represente~ by the formula, -:
; - 3 -~ `~ .
0 ~ ~ 0 ~ ~ ~ H CH20 ~
~-o ~ ~ ~ ~ H C~l2H
1 wherein n is an integer of 20 to 8~000. An aqueous - solution of the pullulan is completely colorless and transparent5 and a film obtained by casting said aqueous solution is also colorless and transparent. In the present invention, pullulan having a molecular weight of 10~000 to 4~000~000~ preferably 20~000 to 200~000 is used. The pullulan may be used as it is, or, for improvement in compatibility or crosslinkability, ma~ be modified by acetylation or the like esterifica-tion reaction, utilizing the hydroxyl groups containea-in the molecule of pullulan. The degree of reaction`
with the hydroxyl group at the time of modification~
is represented by a substitutlon degree, which varies from ~ to 3 depending on the number of reacted hydroxyl groups. A substltution degree of 1 shows that 1~3 of the hydroxyl groups have been substituted, and a sub-stitution degree of 3 shows that all the hydroxyl groups ha~e been substituted. - ~
The photopolymerizable monomer, which is used in the case where pullulan is used as it is~ is a monomer high in compatibility with pullulan such as, -for example, acrylamide~ acrylic acid, methacrylic .
acid~ 2-hydroxyethyl methacrylate or N-vinylpyrrolldone. ~ ;
_ 1~ _ :~
1 Alternatively, a crosslinkable monomer such as nona-ethylene glycol dimethacrylate or the like may also be used. In this case, the curing of resin at the - exposed portion is further promoted to give a more - 5 clear image. The mixing proportions of pullulan and the above-mentioned monomer are 30 to 90 and 70 to 10 parts by weight, preferably 50 to 80 and 50 to 20 parts by weight, respectively. In case pullulan has been enhanced in compatibility by acetylation, a photosensitive resin composition may be prepared by mixing the pullulan with a monomer incompatible there-- with, e.g. a monomer high in crosslinking efficiency such as ethylene glycol dimethacrylate or triethylene glycol dimethacrylate, or a water-insoluble monomer such as vinyl acetate, methyl methacrylate, glycidyl methacrylate, ethyl acrylate~ cyclohexyl acrylate~
and the like. In this case~ the proportion of the ~onomer is 10 to 200 parts by weight per 100 parts by weight of the acetylated pullulan. In case the acetylation is effected to a substitution degree of less than 1.2, the pullulan is not only improved in compatibility with the-said monom~r but also can give a resin capable of forming a water-developable relief. The acetylation of pullulan may be conducted, for example, by dropping acetic anhydride into a solu-tion of pullulan in dimethylformamide while heating the solution in the presence of pyridine as a catalyst~
In order to enhance the crosslinkability of pullulan according to esterification reaction by introducing an acryloyl or the like photoactive group into the ~5~t'~
1 pullulan, there may be adopted, for example, such procedure that the pullulan in the form of a solution in dimethyl~ormamide or the like solvent is reacted with a halide o~ an unsatura~ed acid in the presence of pyridine as a catalyst. That is, when an ester of pullulan with an unsaturated organic acid such as acrylic acid, methacrylic acid, fumalic acid, maleic acid, crotonic acid, itaconic acid, citraconic acid or the like is used as a matrix resin, it is possible to obtain a photosensitive resin composition parti-cularly suitable for production of letterpresses improved not only in resolving power but also in photosensitive speed. The higher the substitution degree of the hydroxyl groups of pullulan, the more enhanced the letterpresses in resolving power and photosensitive speed.
The sensitizer used in the present invention is a water-soluble sensitizer such as~ ~or example, uranyl nitrate, sodium anthraquinone-~-sulfonate, an a-carbonyl alcohol such as ber. oin or a-methylbenzoin, or an -carbonyl ether such as benzoin methyl ether.
The prcportion of-the sensitizer is-0.5 to 5 parts by weight per 100 parts by weight of the monomer.
The thermal polymerization inhibitor used in the present ivvention is a quinone such as hydro-quinone or methylhydroquinone, or a phenol such as p-methoxyphenol. The proportion of the inhibitor is 0.1 to 1 part by weight per 100 parts by weigh~ of the monomer.
While the above-mentioned composition ïs .
5~ ~ ~
1 suitable chiefly lor production o~ a letterpress, the use of a crosslinkable polymer is preferable for production of a resist material required to be high in resolving powder. For example, a cinnamoyl ester of pullulan crosslinks when subjected to photo-dimeriza-- tion reaction, and hence can give a resist material excellent in image reproductivity and thermal stability~
The cinnamoyl ester of pullulan can be obtained by reacting pullulan with cinnamoyl chloride in the presence of pyridine as a catalyst. In this case, if the cinnamoyl group substitution degree is suppressed to less than 0.8, the pullulan is not deprived of its inherent water solubility and hence forms a photosensitive resin capable of giving a plate which is developable with water and can form a clear image derived from the use of cinnamoyl group, and in the development of said plate, the handling of developer is also simple. In case higher`resolving power and photosensitive speed are required, the cinnamoyl group substitution degree of pullulan may be made more than 1. In this case~`the pullulan is deprived of its water solubilïty, so that the photo-sensitive resin compcsition, or plate, should be prepared, or develope`d, by use of an organic solvent or a mixture of water and an organic solvent, such as dimethylformamide, acetone, chloroform or an acetone-water mixture.
The sensitizer to be used in the case of pullulan brought to the form of cinnamoyl ester is 5-nitroacenaphthene, 3-methyl-1~3-diaza-1,9-benzanthrone .. , . . _ _ _. .. . .. . .. . .. . .. . . . . . . . .
1 or a Michler's ketone. The propor-tion of the sensitizer is 1 to 20 parts by weight per 100 parts by weight of the cinnamoyl pullulan.
A solution of a mixture comprising the above-mentioned pullulan or derivati~e thereof, monomer, sensitizer and thermal polymerization inhibitor, or a solution of a mixture comprising the above-mentioned pullulan derivative and sensitizer, is cast and dried, whereby a transparent, solid, photosensitive resin can be obtained. In each case, the viscosity of the solution is low, for example the viscosity of a 30 %
aqueous solution of pullulan having a molecular weight of 150,000 is 1,000 cps. at 25C., and thus is far lower than that of the previously mentioned PVA
sQlution. Furthermore~ pullulan or its derivative is high in rate of dissolution, so that a photosensi- `
tive resin solution containing pullulan or its deriva-tive, or a photosensitive resin plate obtained by - casting the said solution, can be prepared, or~developed, easily and quickl~
Another important feature of the present invention is-that pullulan is similar in-structure-to natural high polymers, and is non-toxic and edible~
so that the wash liquid thereof can be discarded ~ -without causing any trouble of environmental pollutlon.
Further, pullulan is easily decomposed by micro- -organisms, so that discarded pullulan can advantageously be destroyed spontaneously. Accordingly~ when a composition is prepared by mixing pullulan with other non-toxic materials~ the resulting photosensitive resin - ~ ... .
.. .: -- . :.. . . . . - . :
l has no toxicity and hence brings about no problem con-cerning the waste water formed by treatment of the resin.
The photosensitive resin composition of the present invention, which is prepared by using pullulan as a starting material~ can be used not only as a photo-sensitive film for letterpress or resist but also as an original plate for duplicate-making. Furthermore, the composition may be used also as a matrix for photo-curable inks or paints.
The present invention is illustrated in detail below with reference to Examples, but the inven-tion is not limited to the Examples. ;
Example 1 10 Grams of pullulan having a molecular weight of 150,000 was dissolved in ~0 g. of water.
To the resulting aqueous solution was added 21 ~ g of an aqueous solution formed by dissolving 5 g. of acryl~
- amide in 20 g. of water. This solution was incorpora-ted with 0.0432 g. of sodium anthraquinone-a-sulfonate and 0.00~32 g. of hydroquinone to prepare a photo-sensitive resin composition. The composition was cast on an iron plate coated with a paint and the~
air-dried overnight to obtain a photosensitive resin plate having a thickness of 0.6 mm. The resin plate was completely transparent. This resin plate was broll~ht into close contact with a negative film, exposed for lO minutes to a 3 K~ high préssure mercury l~mp at a distance of 75 cm. and then washed for l rninute in _ 9 _ .
1 running water to obtain a reLief image having a thick-ness of o.6 mm.
Example 2 Example 1 was repeated9 except that the acrylamide was replaced by acrylic acid~ whe~eby a relief image corresponding to the negative was obtained.
Example 3 A mixture comprising 50 g. of pullulan anhydride having a molecular weight of 320,000 and 100 g. of pyridine was dissolved in 500 g. of dimeth~l-formamide. Into the resulting solution, 30 g. of acetic anhydride was dropped over a period of 1 hour with stirring at 65C. The resulting mixture was reacted at said temperature for additionàl 1 hour and - 15 then cooled. Subsequently, ethanol was added to the reactlon mixture to deposit a preclpitate. The pre-cipitate was recovered by filtration, dissolvèd in -- water, deposited again~by addition of ethanol~ and then washed and dried to obtain 65 g. of a pol~mer having a hydroxyl group substitution degree of 0.6.
A solution of 70 g. of the above-mentioned polymer in 350 g. of dimethylformamide was incorporated with 30 g. of triethylene glycol dimethacrylate~
0.3 g. of sodium anthraquinone-a-sulfonate and 0.03 g.
of hydroquinone to prepare a photosensltive resin - composition. This composition was treated in the same manner as in Example 1 to obt~in a clear relief image.
. - ' ~5576~
l Example ~
5 Grams of pullulan was dissolved at an elevated temperature in l~o ml. of dimethylformamide.
To the resulting solution, 3~1 g. of acryloyl chloride was added, and then 20 ml. of pyridine was gradually added with stirring. With addition of pyridineg vigorous generation of heat was observed. After the generation of heat had become less, the solution was heated to 60 to 70C. and reacted at said temperature for about 20 minutes with continuous stirring. The reaction solution was poured into a large amout of ethanol to deposit a polymer precipitate, which was then recovered by filtration, washed 2 times with ethanol and thereafter vacuum-dried to obtain a polymer~
which was an acryloylation product having a substitu~
tion degree of lØ
A solution of 70 g. of the above-mentioned polymer in 350 g. of water was incorporated with 30 gO
of 2-hydroxyethyl methacrylate, 0.3 g. of sodium anthraquinone-a-sulfonate and 0.03 g. of hydroquinone.
Subsequently, the solution was cast on a coated iron plate and then air-dried overnight to evaporate the water,-whereby a photosensitive resin plate having a thickness of 0.6 mm. was obtained. This resin plate was exposed in the same manner as in Example l and then washed with water to obtain a clear relief image.
The resin plate was excellent in water washability .
1 Example 5 Cinnamoylation of pullulan:
5 Grams of pullulan was dissolved at an elevated temperature (75 C) in 40 ml. of dimethyl-formamide. To the resulting solution, 5 g. ofcinnamoyl chlor1de was addecL~ and then 25 ml. of pyridine was gradually added with stirring. With addition of pyridine, vigorous generation of heat was observed. After the generation of heat had become less, the solution was heated to 60 to 70C.
and reacted at said temperature for aboùt 1.5 hours with continous stirring. The reaction solution was poured into a large amolmt of ethanol to deposit a polymer precipitate, which was then recovered b~
filtration, washed 2 times with ethanol and thereafter vacuum-dried to obtain a polymer, which was a cinna~moylated - pullulan having a substi~tution degree of 1.
Preparation of photosensitive composition by use of cinnamoylated pullulan~
~A solution of 1 g. of the above-mentioned cinnamoylated pullulan in 5 g. of dimethylformamide was incorporated with 0.1 g. of 5-nitroacenaphthene .
- as a sensitizer. Subsequently~ the solution was cast on a glass plate and then dried to obtain a photo-25 ~ sensitive resin plate. This plate was brought into close contact with a negative, exposed for 3 minutes to a 3 KW high pressure mercury lamp at a distance of 75 cm. and then washed for about 30 seconds with dimethylformamide~ whereby only the unexposed portion was completely washed off to glve a clear posltive ~355761~
1 image Example 6 Cinnamoylated pullulan having a substitution degree of 0.75 was synthesized in the same manner as in Example 5. A solution of 1 g. of this cinnamoylated pullulan in 5 g. of water was incorporated with 0.1 g.
of sodium anthraquinone-a-sulfonate as a sensiti~er.
Subsequently, the solution was cast on a glass plate and then dried at room temperature to obtain a photo-sensitive resin plate. This plate was brought intoclose contact with a negative, exposed for 3 minutes to a 3 KW high pressure mercury lamp at a distance of 75 cm. and then washed for 30 seconds with water, whereby only the unexposed portion was completely !
washed off to give a clear positive image. The resin plate was excellent in water washability.
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