Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Identified backing or protective layer containing
Patent
1993-08-17
1995-06-06
Neville, Thomas R.
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Identified backing or protective layer containing
430621, 430536, 430349, 430935, 162135, 162136, G03C 1775
Patent
active
054222354
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process for manufacturing photographic paper. It relates particularly to a process for conditioning photographic paper during and after the drying process.
Photographic papers are normally produced by coating a polyethylene resin coated paper support with various photographic layers such as silver halide emulsion layers, and with a colloid such as gelatin dispersed throughout the photographic layers. However, because swollen gelatin layers exhibit a low degree of abrasion resistance, it is normally necessary to improve the strength of the colloid layers by adding a hardener. This process is well known in the photographic industry, and numerous different varieties of hardeners are known. Vinyl sulfone-type hardeners are described for example in U.S. Pat. No. 3,481,872 and U.S. Pat. No. 3,642,486.
Photographic paper supports are conventionally produced in substantial lengths. In a normal manufacturing process, the paper is coated with photographic and other layers, and it is then dried before being wound up as a roll for storage.
In order to achieve a satisfactory hardness within the colloid dispersed throughout the photographic layers on the support, a sufficient period of time must be allowed for the cross-linking reaction brought about by the hardener to occur. Under normal manufacturing conditions it is therefore necessary to store a roll of paper for a period of time (typically a number of weeks) after the coating and drying process, to ensure that a sufficient hardness is achieved. However, storage constraints of this kind impose considerable costs on the manufacturing operation, and there is therefore a need for a method of accelerating the hardening reaction.
It has variously been suggested that significant increases in hardness can be obtained from short exposures to extreme temperatures. The reason for this is thought to be that more opportunities for cross-linking between gelatin and hardener molecules occur when the gelatin is in a mobile state, and mobility is increased with temperature. However, elevated temperatures may have adverse effects on the photographic coatings in the photographic paper. Moreover, when a roll of paper is cooled from an elevated temperature, the external portions of the roll cool more rapidly than the internal portions, and this can result in non-uniform hardness and sensitometric properties throughout the roll.
It has also been suggested that humidity levels in the photographic coatings may be relevant to the hardening process, but such suggestions have not achieved widespread acceptance.
According to the present invention there is provided a photographic paper production method comprising the steps of: silver halide emulsion layers and one or-more other hydrophilic colloid layers, at least one of said layers including a hardener; to 33.degree. C. and conditioning the photographic and other layers on the support to an equilibrium relative humidity (ERH) of from 55% to 70%; and until the photographic and other layers have achieved a MAST hardness (as hereinafter defined) of 25 grams or more.
When the method of the present invention is used in the production of a roll of photographic paper, the step of winding the support occurs directly after step (c), so that the temperature and ERH conditions are preserved. It is not necessary that the ERH conditions of the photographic and other layers be monitored or held constant after winding, but it is preferred that the coated support be stored within a moisture-proof casing or material.
Experimentation has confirmed that an increase in humidity leads to acceleration of the hardening reaction. More importantly and surprisingly, experimentation has revealed that considerable acceleration of the hardening reaction can be achieved with only a slight increase in temperature over representative prior art conditions, if humidity is increased. When humidification is provided in the photographic layers as described in step (c) above, the photographic layers are at favourable conditions for the hardening react
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Chapman John W.
Sierakowski Andrew F.
Whittle Robyn A.
Eastman Kodak Company
Neville Thomas R.
Snee, III Charles E.
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