1. Field of the Invention
The present invention relates to a resin guiding device for an inflation molding apparatus, and for guiding an inflated molten resin which is extruded in a tubular shape from an inflation molding die, to a pair of take-up rolls, and also to a method of producing a film by using such an inflation molding apparatus.
2. Description of the Related Art
Usually, a production of a film by inflation molding technique is performed in the following manner. A molten resin is extruded in a tubular shape from an annular slit of an inflation molding die, and a gas such as the air is blown into the tubular resin to inflate the resin. The inflated tubular resin is folded into a flat shape by a pair of flat stabilizing plates placed to form a shape which is tapered as moving in the extrusion direction of the resin. The flattened resin is taken up by a pair of take-up rolls, and then wound up by a winding machine.
In such inflation molding, as the stabilizing plates for stabilizing the inflated tubular resin and folding the resin into a flat shape, used are plates which are not easily deformed, such as plates made of aluminum, stainless steel, or the like, or those into which an appropriate number of guiding rolls are incorporated in a direction perpendicular to the resin flow direction.
The above-described conventional techniques are very effective in the case where a general-purpose plastic which exhibits a relatively low modulus of elasticity and a relatively large tensile elongation during a process of cooling and solidifying, such as polyethylene (PE) or polypropylene (PP) is used as the resin. When a tubular resin is folded into a flat shape by a pair of stabilizing plates, wrinkles and the like may be sometimes caused in a film by inflation unevenness of the resin, or by the resistance difference between the resin and the stabilizing plates, etc. However, it is often that wrinkles and the like are not seen in a film of such a general-purpose plastic, which is obtained by flatly folding, taking up, and winding, because such a general-purpose plastic has plasticity even at a room temperature.
On the other hand, recently, expectations for an engineering plastic film which is excellent in heat resistance and has high modulus of elasticity, and hardly elongated are growing. A request for an inflation molding technique which can produce such a film at a relatively economical manner is expanding. As compared with such a general-purpose plastic, however, an engineering plastic exhibits a high modulus of elasticity and a small tensile elongation, that is, properties of hard, during a process of cooling and solidifying. When a resin is folded by flat stabilizing plate as in the conventional art, therefore, wrinkles, uneven thickness, and the like easily occur, whereby the appearance of a resulting film is often largely impaired.
It is an object of the invention to provide a resin guiding device for an inflation molding apparatus, and a film producing method which enable a film that has less wrinkles and thickness unevenness and that is excellent in appearance.
The object of the invention is to provide a resin guiding device for an inflation molding apparatus, which guides a molten resin extruded and blown into a tubular shaped resin from an inflation molding die, to a pair of take-up rolls, and characterized in that the resin guiding device comprises a pair of guiding members which are placed between the inflation molding die and the pair of take-up rolls. The guiding members respectively have curved contact faces which are in contact with the tubular resin. Said curved contact faces are mutually outward curved, and each of the curved contact faces has a shape corresponding to a rein shape so as to fold the tubular resin into a flat shape.