Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting – Controlling heat transfer with molding material
Patent
1988-03-10
1989-10-03
Lowe, James
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
Controlling heat transfer with molding material
264 401, 2641761, 425141, 425144, 425170, 4253791, B29C 4792, B29C 4786, B29D 701
Patent
active
048714933
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. TECHNICAL FIELD
The present invention relates to a process and apparatus for the preparation of thermoplastic resin films by extruding a molten thermoplastic resin onto a surface of a cooling roll from a die, in which a homogeneous film with a reduced thickness unevenness is stably formed (in the instant specification, the term "film" is used in a broad sense to include not only an ordinary film but also a sheet, a foil and the like).
2. BACKGROUND ART
As the conventional process for the preparation of a thermoplastic resin film, a process is known in which a molten thermoplastic resin is extruded in the form of a film from a T-die and the extrudate is cooled and solidified by a cooling roll.
This process, however, is defective in that the flow quantity of the molten resin per unit length in the width direction of the die varies and, therefore, thickness unevenness often occurs in the width direction of the film.
As the means for reducing the thickness unevenness in the width direction of the film, a process is known in which the gap of a resin flow route is mechanically changed by utilizing the thermal expansion of a metal (see Catalogue of Measurex Japan Ltd., Feb. 27, 1986). However, in this process, since the expansion and contraction of the metal and distortions of the lip portion are utilized for controlling the thickness unevenness, the precision of control of the thickness unevenness is unsatisfactory.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to solve the above-mentioned problems and provide a process and apparatus in which a homogenous film having a reduced thickness unevenness can be stably prepared with high precision of control of the thickness unevenness.
In accordance with one aspect of the present invention, there is provided a process for preparing a film of a thermoplastic resin by extruding a molten thermoplastic resin onto the surface of a cooling roll from a die, characterized in that a heater in which a temperature profile varying in the width direction can be set is arranged in the width direction in the vicinity of a die lip, a temperature sensor for detecting a resin temperature profile in the vicinity of the outlet of the die lip and a thickness sensor capable of detecting a thickness profile in the width direction of a film are disposed, and the output of said heater is controlled according to signals from the temperature sensor and thickness sensor, whereby the thickness of the film in the width direction is automatically adjusted.
In accordance with another aspect of the present invention, there is provided an apparatus for the preparation of thermoplastic resin films, which comprises a die for extruding a molten thermoplastic resin and at least one cooling roll for cooling a resin film extruded in the molten state from said die, said apparatus further comprising (a) a heater which is arranged in the vicinity of a die lip of said die and in which a temperature profile varying in the width direction of the film can be set, (b) a temperature sensor for detecting a resin temperature profile in the vicinity of the outlet of said die lip, (c) a thickness sensor capable of detecting a thickness profile in the width direction of the film and (d) a controller for controlling the output of said heater while receiving signals from said thickness sensor and temperature sensor, wherein the thickness in the width direction of the film can be automatically adjusted.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram showing the structure of an apparatus for the preparation of thermoplastic resin films, which is used in carrying out one embodiment of the present invention; and FIG. 2 is a diagram illustrating the structure of a die portion of said apparatus.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will now be described in detail with reference to the accompanying drawings. Referring to FIG. 1, a thermoplastic resin molten and kneaded in an extruder (not shown) flows into a die 2 through a joint 1 and is extruded out
REFERENCES:
patent: 3341388 (1967-09-01), Bunyea
patent: 3761553 (1973-09-01), Richardson
patent: 3883279 (1975-05-01), Heyer
patent: 4409160 (1983-10-01), Kogo et al.
patent: 4426239 (1984-01-01), Upmeier
patent: 4454084 (1984-06-01), Smith et al.
Lowe James
Showa Denko Kabushiki Kaisha
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