| 摘要 |
834,733. Photosensitive element and process for preparing printing relief images. DU PONT DE NEMOURS & CO., E. I. Feb. 7, 1958 [Feb. 18, 1957], No. 4154/58. Class 98(2) A support carries a layer of an addition polymerizable ethylenically unsaturated component containing a photopolymerization initiator therefor, with the latter in higher concentration in a lower stratum next to the support than in an upper stratum which is not more than half of the total thickness of the layer; and this may be exposed as with divergent beams under a negative, which may have been made with use of a half-tone screen of 150 lines per inch, to polymerize the exposed areas to the insoluble state, after which removal of the unexposed unpolymerized portions produces reliefs broader at the base than the surface with, maybe, sides having a greater degree of taper at the lower parts than the upper. Materials for forming the layer are generally similar to those disclosed in Specifications 741,294, 741,441 and 741,470. Details are illustrated in seven examples which include considerable quality comparisons of procedure with various proportions and manners of introduction of the initiator and the effect of absence of this, thus in Example 1 an aluminium plate is provided with a specified antihalation layer and then a specified methacrylate type anchor layer which is polymerized to a hard resin by ultraviolet light, benzoin methyl ether in acetone solution as the initiator is then painted on to the anchor layer, dried and followed by a 30-mil viscous layer of 3/1 polypropylene glycol phthalate/maleate in styrene: a process negative is then laid down on to the still viscous polymer layer and exposed from a bank of twenty 30-watt fluorescent tubes for 10 or 12 minutes after which the unexposed areas are removed by brushing in acetone for two minutes to show printing characters with broad and firmly attached bases, while in absence of the benzoin methyl ether initiator the attachment is inadequate. Examples IIIV are similar, and Examples V-VII describe separate production of two superimposed layers on the support, which layers are mainly of cellulose esters with a proportion of triethylene glycol diacrylate and usually benzoin as initiator, the lower layer having 5 or 10 times the proportion of benzoin of the upper. Aqueous ammonia is used in some instances to remove unexposed material.
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