GB1261868A - An apparatus for effecting the opacification treatment of a synthetic polymer film, and for rendering the film receptive to printing and writing - Google Patents

Abstract

1,261,868. Opacified and ink-receptive films. NIPPON KAKOH SEISHI K.K. 7 March, 1970, No. 11043/70. Heading B5B. An apparatus for imparting opacity and receptivity to printing ink and writability to a synthetic thermoplastic polymer film comprises in combination a feed roll for supplying a film web and a windup roll for receiving and collecting the treated film thereon. Positioned between the feed and wind up roll are arranged in series and in the following order: a swelling bath, at least one intermediate treating bath, a coagulating bath, an after-treatment bath, and a dryer unit. The intermediate treating bath and the coagulating bath comprise means to provide overflow of a part of the liquid within each bath into the immediately preceding bath, thereby providing an adjustment for the change caused by the carry-over of a part of liquid within each bath by the advancing film. The apparatus may further comprise means for feeding to the coagulating bath a coagulating agent selected to avoid the swelling or dissolving of the film and to be miscible with the swelling agent in the swelling bath. In addition it may comprise means for continuously withdrawing the liquid overflow from the first intermediate bath located adjacent to the swelling bath from the apparatus. The apparatus may be provided with a plurality of intermediate treating baths and means for controlling the concentration of the treating liquid; in the first intermediate treating bath between 1/3 and 2/3 of the swelling agent in the swelling bath; in the second intermediate bath, ¢ of the swelling agent in the first intermediate bath; in the third intermediate treating bath to (¢)<SP>2</SP> and so on to the nth intermediate treating bath, in which the concentration is reduced to ¢(n - 1). A liquid which is readily miscible with the swelling agent but does not exhibit any dissolving or swelling action on the film is referred to as a " coagulating agent", when the film web is passed through the bath consisting of this liquid only, the swollen surface layer of the film web is coagulated and the film web, after having been passed through a drying zone has on its surfaces a bright, opaque roughened layer. Any film consisting of synthetic thermoplastic polymeric material capable of being swollen by contacting it with a liquid " swelling agent " may be used, irrespective of whether it does or does not contain additives or is oriented or non-oriented. Polystyrene or polyvinyl chloride films are preferred. Swelling agents listed are acetone, alone or mixed with a small proportion of carbon tetrachloride, methyl ethyl ketone, methyl isobutyl ketone alone or mixed with a minor proportion of methanol, benzene mixed with a smaller proportion of methanol, tetrahydrofuran alone or mixed with a smaller proportion of methanol or water, and cyclohexanone alone or mixed with minor proportions of water and methanol or with a smaller proportion of isopropyl alcohol. Socalled "coagulating agents" whichmay be used are aliphatic saturated monohydric alcohols having from 1 to 4 carbon atoms in the molecule, these agents being used either alone or mixed with water. It is preferred that more than one intermediate treating bath between the swelling bath and the treating bath is used, and in the illustrated embodiment of the invention a series of four intermediate film treating baths are used. Each such intermediate bath consists of a mixture of the swelling agent used in the swelling bath and the coagulating agent used in the coagulating bath, the proportion of swelling agent in the intermediate baths diminishing in the direction of travel of the film. The proportion of the swelling agent in the first intermediate treating bath is so adjusted that the bath contains between one third and two thirds of swelling agent, the balance being coagulating agent, while the proportion of the swelling agent in the second, third and fourth intermediate treating baths is adjusted to be ¢, (¢)<SP>2</SP> and (¢)<SP>3</SP> respectively. Guide rollers and squeeze rollers are provided between each pair of adjacent baths to remove surplus liquid from the film web in its passage from each bath to the succeeding bath in the series and returning it to the preceding bath. The level of the liquid in the intermediate baths is higher in each successive bath and higher in the coagulating bath than in the last intermediate bath. Coagulating agent is continuously fed into the coagulating bath, from this bath overflows into the last intermediate bath and liquid then overflows successively into each of the intermediate baths countercurrent to the direction of travel of the film through the baths. After leaving the coagulating bath the film is passed through the nip of a pair of co-operating squeeze rolls and then through an after-treatment bath in which it is subjected to any desired treatment such as treating with an anti-static liquid or dyeing. The film web is then passed through the nip of a final pair of squeeze rolls followed by a drying zone and wound up on a collecting roll.