Water-developable plate package

Details Water-developable plate package Water-developable plate package

2000-02-25

2001-09-18

Copenheaver, Blaine (Department: 1771)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Composite having voids in a component

C428S319300, C428S319700, C430S155000, C430S162000, C430S167000, C430S271100, C430S273100, C430S285100, C430S909000, C430S281100

Reexamination Certificate

active

06291060

ABSTRACT:

TECHNICAL FIELD
The present invention concerns a package in which water-developable plates are packaged in a laminated state for transportation or storage. The plate constituting the package is a sheet-like plate comprising a photosensitive layer made of a photosensitive resin composition having water-developability and protective films covering both surfaces of the photosensitive layer.
BACKGROUND ART
A water-developable plate is a plate in which a photosensitive layer is hydrophilic before exposure and a relief image is formed by crosslinking an image-forming area by the exposure. Accordingly, the plate is subjected to a developing treatment after the exposure (removal of unexposed area of the photosensitive layer) with water or an aqueous alkali solution. On the other hand, a solvent-developable plate requires a developing treatment after exposure using an organic solvent, which is troublesome in handling. Therefore, the water-developable plate which is more simple in the developing treatment has become predominant as a plate for use in letterpress.
On the other hand, the plate is in the form of a sheet and usually has a structure of covering both surfaces of photosensitive layer of a predetermined thickness comprising a photosensitive resin composition with protective films. In transportation and storage, a plurality of sheet-like plates are laminated and a laminate is packaged with a light screening film and placed, for example, in a corrugated board box. The water-developable plate involves a problem of causing deformation in the plate during transportation or storage at a high temperature and a high humidity in summer.
It is considered that the problem is attributable to easy moisture absorption since the photosensitive layer of the water-developable plate is hydrophilic. Therefore, for preventing moisture absorption of the water-developable plate at a high temperature and a high humidity in summer, the following countermeasures have been adopted in the prior art. That is, in a case of a solvent-developable plate, when a laminate of plates are packaged with a light screening film
4
into a package
6
, only the packaging ends are secured at several positions by tapes
5
, for example, as shown in FIG.
3
(
a
), but in a case of a water-developable plate, all of the portions through which moisture can intrude are secured with a tape
5
, for example, as shown in FIG.
3
(
b
). Alternatively, the humidity is lowered in a transportation environment or a storage site for the package.
However, the package of the plates are usually packaged on every about ten sheets with a light screening film and they are used in most cases such that about two or three sheets of them are taken out per one day while other remaining plates are stored. Accordingly, in the countermeasures described above, a method of securing all the portions of the light screening film through which moisture can intrude complicates the tape securing operation after taking out the plates.
As a method of avoiding this complication, it may be considered to package plates sheet by sheet. However, since this requires the stringent packaging described above on each sheet for all plates, the operation upon packaging is troublesome. Further, the countermeasure for lowering the humidity in the transportation circumstance or the storage site of the package involves a problem in view of the cost and reliable moisture proofness.
The present invention has been accomplished taking notice on such problems in the prior art and it is a subject thereof to prevent occurrence of deformation of the plates in a package in which water-developable plates are packaged in a laminated state during transportation or storage at a high temperature and a high humidity in summer, without complicating the operations at the time of use or packaging of plates and without increasing the cost remarkably.
DISCLOSURE OF THE INVENTION
For solving the foregoing subject, the present invention provides a water-developable plate package in which sheet-like plates each comprising a photosensitive layer made of a photosensitive resin composition having water-developability and protective films covering both surfaces of the photosensitive layer are packaged in a laminated state for transportation or storage, wherein an open cell foamed sheet is sandwiched between a plate and another plate.
In this case, since the photosensitive layer of the water-developable plate is hydrophilic, it tends to absorb moisture, but the moisture is absorbed mainly from the end faces of the photosensitive layer in a package in which only the water-developable plates are laminated. Thus, only the portion near the end faces (edges) of the photosensitive layer formed at a uniform thickness is swollen greatly, while portions near the central area remain substantially unchanged for the thickness with respect to the initial state. That is, it is considered that deformation of the plate as described above occurs in the package in which only the water-developable plates are laminated because of uneven hygroscopicity in a plane of the photosensitive layer.
Based on the finding described above, the present inventors found that deformation of the water-developable plate can be suppressed by allowing moisture to be absorbed uniformly within a plane of the photosensitive layer, instead of preventing moisture absorption in the photosensitive layer and have accomplished the present invention.
According to the water-developable package of the present invention, since an open cell foamed sheet is sandwiched between the plates, moisture is absorbed by the plate not only from the end faces but also from the vicinity of the central area of the plate. That is, since moisture is absorbed in the package also through the foamed sheet, and moisture entering from the end faces to the cells inside of the foamed sheet transfers through the open cells in the direction of the thickness and in the direction of the plate plane of the foamed sheet, moisture reaches through the foamed sheet also to the central area of the plate.
Since this moderates ununiform absorption of moisture in the plane of the plate during transportation or storage, deformation of the plate is suppressed.
Further, even when the plates are laminated in a state where dusts are deposited on the outer surface of the protective film, since the foamed sheet functions as a buffer in the water-developable package of the present invention, unevenness caused by dusts is less formed in the photosensitive layer.
In the water-developable plate package according to the present invention, higher air permeability of the foamed sheet to be used is preferred since moisture tends to reach through the foamed sheet as far as the central area of the plate more easily. Specifically, it is preferred to use a foamed sheet having an air permeability of 0.1 cc/(cm
2
·sec) or more based on air permeability measurement according to “JIS L-1096 A method”, and it is more preferred to use a foamed sheet of 1.0 cc/(cm
2
·sec) or more.
Further, since a foamed sheet having a particularly high air permeability has a low compression strength and makes it difficult to stably hold plates, the air permeability of the foamed sheet used in the water-developable plate package according to the present invention is preferably 500 cc/(cm
2
·sec) or less based on in the air permeability measurement described above. Further, while there is no particular restriction on the thickness of the foamed sheet used in the water-developable plate package according to the present invention, it is preferred that the thickness is, for example, approximately equal with the thickness of the photosensitive layer of the plate (generally, 0.5 mm or more and 10.0 mm or less).
Further, the open cell foamed sheet is generally prepared by a method of blowing a polymer such as urethane rubber, ethylene propylene rubber or polyethylene to at first form a block or sheet having closed cells entirely, and then communicating the closed cells with each other under compression with a roll, for example. When the

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