JPH0524814B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for manufacturing films (in the present invention, the meaning includes not only films but also sheets) by extruding a molten thermoplastic resin from a die onto the surface of a cooling roll. The present invention relates to a method for producing thermoplastic resin films that can stably form homogeneous films with less uneven thickness. [Prior Art] As a conventional method for producing a thermoplastic resin film, a method has been known in which a molten thermoplastic resin is extruded into a film through a T-die, and the extruded film is cooled and solidified using a cooling roll. However, this method has the disadvantage that uneven thickness tends to occur in the width direction of the film because there is a difference in the flow rate of the molten resin per unit length in the width direction of the die. Therefore, methods using a tie yoke bar, a movable lip, and a flexible lip (mechanically bending the lip part to change the opening degree of the lip) are known as methods for reducing the thickness unevenness in the width direction of the film. ing. That is, by changing the gap of the resin flow path near the die lip during film molding,
This is a method to adjust the uneven thickness of the film, but since this method changes the channel gap using a differential screw, etc., in other words, the accuracy of adjusting the uneven thickness is determined by the pitch and play of the screw, etc. was not completely satisfactory. Another known technique is to mechanically change the gap of the resin flow path by thermal expansion of the metal, but this method utilizes the expansion and contraction of the metal and the distortion of the lip, so it is not biased. A sufficient effect could not be obtained in terms of meat adjustment accuracy. [Problems to be Solved by the Invention] It is an object of the present invention to solve the above problems and to provide a heat treatment method that can stably produce homogeneous films with little thickness unevenness with high thickness unevenness adjustment accuracy. An object of the present invention is to provide a method for producing plastic resin films. [Means and effects for solving the problems] The present invention provides a method for manufacturing films by extruding a molten thermoplastic resin from a die onto a cooling roll surface, and provides a heater capable of setting different temperature profiles in the width direction. is installed near the lip of the die, at least a part of the heater is divided into a plurality of parts each having a width of 50 mm or less along the width direction of the die, and the heater is disposed at a distance of within 200 mm from the lip exit, and detecting a resin temperature profile near the lip outlet with an infrared temperature sensor, and eliminating the difference between a predetermined target temperature profile and the resin temperature profile by correcting the set temperature profile of the heater. The present invention relates to a method for producing thermoplastic resin films having highly uniform thickness, characterized in that the amount of resin extruded from the lip is made uniform in the width direction. Hereinafter, the present invention will be explained in detail with reference to the drawings. In FIG. 1, a thermoplastic resin melt-kneaded in an extruder (not shown) flows into a die 2 through a joint 1, is extruded from a die lip 3 to the outside of the die, passes through cooling rolls 4 and 5, and forms a film 6. It will be taken over as. A heater 8 is attached to the die 2 in order to keep the temperature of the entire die constant, and the heating temperature is detected by a thermocouple (not shown) or the like and adjusted by a temperature regulator (not shown). Reference numeral 7 is a die lip adjustment bolt, and by rotating this bolt, the amount of resin is adjusted, and uneven thickness of the film is roughly adjusted. Furthermore, as is clear from FIG. 2, near the die lip 3, a heater 9 is provided for adjusting the thickness unevenness in the width direction, and the heater 9 is electrically connected to a controller 11. An infrared temperature sensor 10 placed nearby is electrically connected. The heater 9 uses an electric heating system as a heat source, and is preferably divided into a plurality of blocks (for example, 18 blocks in the drawing) as shown, and the temperature can be set for each block. A target temperature profile is input to the controller 11 for each block of the heater 9. The controller 11 energizes the heater 9 in accordance with the target temperature to set the temperature. The energization method can be carried out by a tri-ac or the like, and a method of controlling the amount of heat generated by the heater 9 by changing the voltage value or current value, or a method of controlling the amount of heat generated by the heater 9.
Methods such as controlling the amount of heat generated by turning the power on and off are adopted. After the temperature of the heater 9 is set, the temperature of the molten resin extruded from the lip 3 changes according to the target temperature of each block of the heater 9. However, the molten resin temperature profile often differs from the target temperature profile due to the outside temperature and mutual interference between blocks, so after a certain period of time the controller 11 corrects the difference with the target profile. , and set the corrected temperature for the heater 9. By repeating the above operations, the temperature of the molten resin approaches the target profile, making it possible to control the temperature with high precision.
For example, if the thickness of the film is thin in some parts, the temperature setting of the corresponding heater 9 is increased to raise the temperature. Then, the flow rate of resin in the die lip 3 in the vicinity increases, the thickness of the film increases, the thickness deviation in the width direction of the film decreases, and a film with less difference in thickness can be obtained. In the present invention, the heater 9 for adjusting thickness unevenness is provided over the entire die width in the drawing, but since the edge of the film is not substantially used as a product,
It may be provided only in the middle part of the die width. It is necessary that the heater 9 has a block width of 50 mm or less, and it is particularly preferable that the heater 9 has a structure in which the temperature can be adjusted at 5 mm or more and 30 mm or less, and is divided into a plurality of blocks so that the temperature can be controlled independently. If the block width of the heater 9 exceeds 50 mm, the film thickness unevenness adjustment accuracy is not sufficient. The structure of the heater 9 uses electric heat as a heat source, and in order to maintain a uniform temperature within each block, the structural material is preferably a metal with good thermal conductivity, especially aluminum. A typical example of the heater 9 is a known aluminum cast heater in which the heater is surrounded by aluminum having good thermal conductivity. The distance at which the heater 9 is installed from the die lip 3 is also a factor that affects the accuracy of adjusting the thickness unevenness of the film, and if the distance is long, the accuracy of adjusting the thickness unevenness decreases. In the present invention, the distance from the die lip 3 to the heater 9 is 200 mm or less, preferably 150 mm or less.
mm or less, more preferably 5 mm or more and 100 mm.
It does not matter if even a portion of the heater 9 falls within the above range, so even if the other end of the heater 9 exceeds 200 mm, it is included in the present invention. Incidentally, there is a known technique in which a lip heater or a cartridge heater is provided in the die lip portion, but this is intended to keep the lip temperature constant, and is essentially completely different from the present invention. Furthermore, the thermoplastic resin used in the present invention can be any of those known for molding films, and typical examples include polyolefins such as polyethylene and polypropylene;
Polyester like polyethylene terephthalate, polyvinyl like polystyrene, nylon
Examples include polyamides such as 66 or nylon 6, and polycarbonates. Note that the die 2 used in the present invention is a die 2 used in the conventional uneven thickness adjustment method, such as a die yoke bar, a moving lip,
A flexible lip or the like may be used in combination, and when used in combination, it is desirable to perform coarse adjustment using the conventional method and fine adjustment using the method of the present invention. [Example] Hereinafter, the present invention will be explained in more detail with reference to Examples. Examples 1 to 4 and Comparative Examples 1 to 3 Polypropylene and low density polyethylene films were molded according to the steps shown in FIG. 1 under the conditions shown below. The base of the die 2 is a flexible type in both the example and the comparative example, with a lip width of 1500 mm and a lip gap of 0.5 mm, and the temperature sensor 10 used in the example is an infrared non-contact thermometer.
Further, as the heater 9, an electric type cast aluminum heater was used. Example 1 Molding conditions: extruder temperature 180°C to 240°C, joint temperature 240°C, die temperature 240°C, resin temperature profile 240 ⁺⁴ _-0 °C Example 2 The number of divisions of the heater 9 is different from Example 1. Comparative Example 1 under the same molding conditions Molding conditions: Extruder temperature 180°C to 240°C, joint temperature 240°C, die temperature 240°C Examples 3 and 4 Molding conditions: Extruder temperature 180°C to 200°C, joint temperature 200°C , die temperature 200℃, resin temperature profile 200℃ ⁺⁴ _-0 ℃ Comparative example 2 Molding conditions: Extruder temperature 180℃ to 200℃, joint temperature 200℃, die temperature 200℃ Comparative example 3 Molding conditions: Extruder temperature 180℃～200℃, joint temperature 200℃, die temperature 200℃, lip heater 204℃

【table】

〔Effect of the invention〕

As is clear from the above, when manufacturing films by extruding molten thermoplastic resin from a die onto a cooling surface, the present invention installs a heater that can set different temperature profiles in the width direction near the lip of the die. In addition, the amount of resin extruded from the lip is adjusted in the width direction using a temperature sensor that detects the resin temperature profile near the exit of the lip, resulting in less uneven thickness with high thickness adjustment accuracy. Films can be stably supplied. Films formed in this manner can exhibit high commercial value when applied to post-processing processes such as lamination and coating methods.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a thermoplastic resin film manufacturing apparatus using an embodiment of the present invention, and FIG. 2 is a block diagram of a die portion of the same apparatus. 2...Die, 3...Die lip, 4, 5...Cooling roll, 8...Heater, 9...Heater for adjusting uneven thickness,
10...Temperature sensor, 11...Controller.

Claims (1)

[Claims] 1. In a method for manufacturing films by extruding molten thermoplastic resin from a die onto the surface of a cooling roll, a heater capable of setting different temperature profiles in the width direction is installed near the lip of the die. , at least a portion of the heater is divided into a plurality of parts each having a width of 50 mm or less along the width direction of the die, the heater is disposed at a distance of within 200 mm from the lip exit, and the temperature of the resin near the lip exit is The profile is detected by an infrared temperature sensor, and the difference between a predetermined target temperature profile and the resin temperature profile is corrected by correcting the set temperature profile of the heater, thereby extruding from the lip. A method for producing thermoplastic resin films having highly uniform thickness, characterized by making the amount of resin applied uniform in the width direction. 2. The method for producing thermoplastic resin films having a highly uniform thickness according to claim 1, wherein aluminum is used as a heat conductor of the heater.