Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
1998-06-01
2001-06-12
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S138000, C428S402240
Reexamination Certificate
active
06245483
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a photosensitive resin composition which can be developed with an aqueous developer and is useful for flexographic printing. In particular, the present invention relates to a photosensitive resin composition for flexographic printing which have a wide proper range of light exposure time (light exposure latitude) and improved printing reproducibility.
BACKGROUND OF THE INVENTION
As photosensitive resin original sheets for flexographic printing, those to be developed by organic solvents had been known. However, in such conventional photosensitive resin original sheets had safety problems for a human body and the environment such as toxicity, flammability and the like.
Then, photosensitive resin compositions for photosensitive resin original sheets which can be developed with an aqueous developer have been proposed as a substitute for such conventional photosensitive resin original sheets. For example, JP-A 63-8648 discloses a photosensitive resin composition in which hard and finely divided organic particles are included to improve properties of the resultant printing matrix such as mechanical strength, impact resilience and the like. JP-A 2-175702, JP-A 3-228060, JP-A 4-293907, JP-A 4-293909, JP-A 4-294353, JP-A 4-340968, JP-A 5-32743, JP-A 5-150451 and JP-A 5-204139 disclose photosensitive resin compositions in which finely divided crosslinkable resin particles are included to provide developability with an aqueous developer and aqueous ink resistance and to improve printability. JP-A 59-36731 discloses a photosensitive resin composition in which ink receptivity of the resultant printing matrix is improved by providing two-phase structure to the composition, whose continuous phase contains a diazo compound and a bichromate and whose dispersed phase contains particles having a particle size of 10 &mgr;m or less.
However, since such a photosensitive resin composition has multiple phase structure, irradiated actuating light does not go straight through the composition, but it is refracted at the interfaces between phases and scattered in the resin. When such a photosensitive resin composition is used as an original printing sheet, the imaged part of a relief obtained by developing is thicker than its original image on a negative film, or the depth of a non-imaged part is smaller due to light scattering upon light exposure for imaging. Then, when printing is carried out by using such a relief, it is likely that the image of the resultant printed matter is thicker than that of the original image, dot parts darken (dot gain), and printing quality is deteriorated because too much ink is adhered to a non-imaged part. Since these tend to be accelerated by excess light exposure, attention should be given to avoid excess light exposure. However, for reproducing a minute or fine image as a relief after developing, sufficient light exposure is required. That is, the range of proper light exposure time (light exposure latitude) of a photosensitive resin printing original sheet having multiple phase structure is apt to be narrower.
OBJECT OF THE INVENTION
The present invention is directed to solution of the above-described problems of photosensitive resin compositions and the main object of the present invention is to inhibit light scattering in a photosensitive resin composition.
Thus, one object of the present invention is to provide a photosensitive resin composition for flexographic printing having wide light exposure latitude and improved printing reproducibility, as well as having developability with an aqueous developer and improved aqueous ink resistance.
This object as well as other objects and advantages of the present invention will become apparent to those skilled in the art from the following description.
SUMMARY OF THE INVENTION
In JP-A 3-72353, JP-A 3-171139 and JP-A 7-168358, the resent inventors have proposed a photosensitive resin printing original sheet having improved printability obtained by controlling phase structure of hydrophobic and hydrophilic phases of the photosensitive resin layer in the photosensitive resin printing original sheet and adjusting an average particle diameter of the dispersed phase in the photosensitive resin layer to 0.001 to 10 &mgr;m. According to the present invention, a photosensitive resin composition having improved printing reproducibility can be obtained by adjusting the difference in refractive indexes of the core phase and the matrix phase of the photosensitive resin composition to 0.010 or less to inhibit light scattering in the composition.
That is, according to the present invention, there is provided a photosensitive resin composition which comprises:
(1) a core phase mainly composed of a non-crosslinkable hydrophobic polymer (A) having a glass transition temperature at 5° C. or lower;
(2) a shell phase mainly composed of a hydrophilic polymer;
(3) a matrix phase mainly composed of a mixture of a hydrophobic polymer (B) which is immiscible with the hydrophobic polymer (A) and a non-gaseous ethylenic unsaturated compound; and
(4) a photopolymerization initiator, and the difference between refractive index of said hydrophobic polymer (A) of said core phase (1) and that of said mixture of said hydrophobic polymer (B) and said non-gaseous ethylenic unsaturated compound of said matrix phase (3) being 0.010 or less.
In addition, in the present invention, it is of importance to control miscibility between the compounding components one another to maintain the above-described phase- separated structure.
Although it has been known to improve transparency of a material having multiple phase structure by reducing the difference in refractive indexes of phases to inhibit light scattering in optical materials such as lenses, such technique has not been known heretofore in the art of photosensitive resin compositions.
DETAILED DESCRIPTION OF THE INVENTION
The photosensitive resin composition of the present invention has phase-separated structure comprising dispersed particles composed of a core phase, i.e., the nuclei of the particles, and a shell phase which covers about the core phase, and a matrix phase which surrounds the dispersed particles.
The core phase of the composition of the present invention is mainly composed of a non-crosslinkable hydrophobic polymer (A) having a glass transition temperature of 5° C. or lower. The term “hydrophobic” used herein means such properties that the polymer is not soluble in and is not swollen with water or a developer mainly composed of water. The difference between the refractive index of the hydrophobic polymer (A) and that of a mixture of the hydrophobic polymer (B) and the non-gaseous ethylenic unsaturated compound which is the main component of the matrix phase as described hereinafter is 0.010 or less.
The hydrophobic polymer (A) has a glass transition temperature of 5° C. or lower and includes a polymer to be used as a general-purpose elastomer. When a glass transition temperature of the hydrophobic polymer (A) is higher than 5° C., rubber resilience of the resultant photosensitive resin printing matrix is remarkably lowered to adversely influence on its printability. This is undesired.
Examples of the hydrophobic polymer (A) include isoprene rubber, butadiene rubber, 1,2-polybutadiene, styrene-butadiene rubber, chloroprene rubber, nitrile-butadiene rubber, styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, butyl rubber, ethylene-propylene rubber, chlorosulfonated polyethylene, butadiene-(meth)acrylate copolymer, acrylonitrile-(meth)acrylate copolymer, epichlorohydrin rubber, chlorinated polyethylene, silicone rubber and urethane rubber, among others. In particular, nitrile-butadiene rubber and chlorinated polyethylene are preferred.
The term “(meth)acrylate” used herein includes both acrylate and methacrylate. Likewise, term “(meth)acrylic acid” used herein includes both acrylic acid and methacrylic acid.
The hydrophobic polymer (A) is compounded in an amount of 10 to 60%, preferably 20 to 50% by weight base
Nakamori Masahiko
Oshimo Chihiro
Wada Tohru
Ashton Rosemary
Baxter Janet
Morrison & Foerster / LLP
Toyo Boseki Kabushiki Kaisha
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