JPH07156245A - Extrusion molding die for polymer - Google Patents

Abstract

PURPOSE:To control uniformly the thickness in the width direction of a sheet to be extruded and provide an excellent extrusion molding die by controlling thermal energy applied to auxiliary heaters and also controlling the thermal energy applied to the whole of the auxiliary heaters within the given range even when differences are made in the applied energy. CONSTITUTION:A plurality of auxiliary heaters 3 for controlling independently the temperature of a molten polymer in the vicinity of a main heater 2 and a die 1 for heat the molten polymer in the die 1 are disposed. The temperature of the molten polymer is raised or lowered by respective auxiliary heaters 11, ... 20 for uniformize the thickness in the width direction of a sheet to be extruded in an extrusion molding die. Thermal energy applied to respective auxiliary heaters 11, ... 20 is controlled, and a control means 6 for controlling the thermal energy amount applied to the whole of auxiliary heaters in a certain range, even when differences are made in the amount of thermal energy applied to respective auxiliary heaters by the increase and decrease of the thermal energy, is disposed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a die for extruding a polymer in the form of a sheet, and more particularly to a die for extruding a sheet to control the thickness of the extruded sheet uniformly in the width direction and to obtain a polymer having excellent controllability. It relates to an extrusion die.

[0002]

2. Description of the Related Art Heretofore, many devices and methods have been proposed for correcting a thickness in a sheet width direction to obtain a sheet having a uniform thickness in a step of extruding a molten polymer into a sheet form from a die.

One of the main methods is to partially correct the opening of the die lip of a die for extruding a molten polymer into a sheet in accordance with the thickness unevenness in the width direction of the sheet.
However, with this method, it is difficult to control the thickness in the narrow portion of the lip, and if excessive deformation is locally applied to the lip, permanent deformation occurs, and the "unevenness" of thickness unevenness that is not adjusted during subsequent extrusion molding. And the device becomes more complicated.

The other main method is to locally change the temperature of the molten polymer in the width direction of the die, and the amount of discharge of the polymer extruded from the die due to the corresponding change in the viscosity of the molten polymer. Is uniform over the entire width of the die.
For example, JP-A-48-16975 and JP-A-49-
The method described in Japanese Patent No. 45964 is a typical example.

[0005]

The above-mentioned method of adjusting the thickness by temperature has greatly improved the technique for making the discharge amount of the molten polymer extruded from the die lip opening uniform over the entire width of the die. In actual production,
Further, it has been revealed that the following problems exist.

That is, in this method, all the auxiliary heating devices are heated in advance with a predetermined amount of heat before the start of sheet extrusion, and after the start of extrusion, the amount of heat is reduced in the thick part of the sheet and reduced in the thin part of the sheet. Then, increase the heating amount and adjust so that the thickness of the sheet in the width direction becomes uniform. In such an operation, the reduction of the heating amount has the effect of locally increasing the apparent viscosity of the molten polymer and reducing the discharge amount of the molten polymer, while the increase of the heating amount lowers the apparent viscosity of the molten polymer. This brings about the effect of locally increasing the discharge amount of the molten polymer.

Here, the auxiliary heating device is, for example, a rod-shaped cartridge heater embedded perpendicularly to the die lip land surface, or the rod-shaped cartridge heater is arranged parallel to the flow of the polymer on the die lip land surface. A sheet heater or a sheet heater arranged parallel to the die lip land surface.

It is possible to make the sheet uniform without increasing or decreasing the thermal energy input to the local auxiliary heating device. For example, it is possible to make the thickness of the discharged sheet uniform by unidirectional control only by increasing the input energy to the auxiliary heating device without previously inputting thermal energy to the auxiliary heating device. Since only the operation of reducing the apparent viscosity of the molten polymer is given in the operation, the time until uniformization is significantly delayed depending on the thickness unevenness at the start of sheet ejection, and the accuracy is not sufficient. It's hard to say.

Therefore, it can be said that the two-way control is preferable in which the heat energy is further applied to the thin portion and the heat energy is reduced to the thick portion on the basis of the preset heat energy. However, even with this method, if the initial setting value is too low, there will be a limit to the operation for correcting the thick portion, and if the setting value is too high, it will be impossible to correct the thin portion. There is a problem that an excessive or insufficient heating portion occurs between the setting position of the heating device and the intermediate position between the auxiliary heating device and the adjacent auxiliary heating device, and a new sheet thickness unevenness corresponding to the arrangement position of the auxiliary heating device occurs. . Further, the heat output level of the auxiliary heating device has an optimum value with good controllability in which the change in thickness is neither sensitive nor insensitive. Therefore, in the actual thickness unevenness adjustment, the heat capacity of the auxiliary heating device is selected in consideration of the size of the thickness unevenness generated, the thickness increasing / decreasing ability of the auxiliary heating device, and the optimum controllability of the auxiliary heating device. It is necessary to determine the default value of. Further, after the thermoplastic polymer is discharged, in order to correct the thickness unevenness of the sheet in the die width direction, if the energy input to each auxiliary heating device in the die width direction is individually adjusted, it is input to the entire auxiliary heating device. It is unavoidable that the generated heat energy changes over time, and in some cases the amount of energy input to the entire auxiliary heating device will increase significantly compared to the initial set value, and in other cases it will increase significantly. The phenomenon of decrease occurs.

As a result, even if the energy input to each auxiliary heating device over the entire die width is initially set to an optimum value in consideration of the optimum controllability of the auxiliary heating device before the start of discharge, the auxiliary heating device is not heated. Since the average heating amount of the apparatus changes with time over the entire width of the die, the controllability of the auxiliary heating apparatus changes with time, and it becomes impossible to stably obtain a sheet having a desired uniform thickness. Further, as described above, if the total input energy is too small or too large, the thickness adjusting operation reaches the limit, and it is no longer possible to manufacture a uniform sheet in the die width direction.

Therefore, an object of the present invention is to adjust the thickness unevenness of a thermoplastic polymer sheet by controlling the temperature as described above.
The controllability of the auxiliary heating device can always be kept in a good state, and thus the change in the viscosity of the molten polymer in the die opening over time can be reduced, and a sheet having a uniform thickness in the running direction can be produced. An object of the present invention is to provide a polymer extrusion molding die for producing a sheet having a uniform thickness, which does not actually cause inconveniences such as deterioration of a discharge sheet and inhibition of homogeneity of physical properties.

[0012]

According to the present invention, an object of the present invention is a die for extruding and molding a molten polymer into a sheet, wherein the molten polymer in the die is heated and maintained at a predetermined temperature in advance. Main heating device and a plurality of auxiliary heating devices for locally and almost independently controlling the temperature of the molten polymer in the vicinity of the opening of the die, and the temperature of the molten polymer is controlled by each auxiliary heating device. In a polymer extrusion molding die, which locally raises or lowers the temperature to make the thickness of the extruded sheet uniform, the heat energy to be fed to each auxiliary heating device is controlled, and the heat energy of the heat energy is controlled. An extrusion die for polymer, characterized in that a control means is provided for controlling the amount of heat energy input to the entire auxiliary heating device within a certain range even if there is a difference in thermal energy input to each auxiliary heating device due to increase or decrease. By It is achieved Te.

In the present invention, the polymer is a thermoplastic polymer such as polyester such as polyethylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate and polybutylene terephthalate, polyolefin such as polyethylene, polypropylene and polystyrene, nylon 6 The thermoplastic polymers such as polyamide and polycarbonate as described above or the above copolymers, and among them, polyester is preferable.

In the present invention, the die for extruding and molding the polymer in a sheet form in a molten state is a main heating device for heating and maintaining the molten polymer in the die at a predetermined temperature in advance.
A plurality of auxiliary heating devices that locally and almost independently control the temperature of the molten polymer in the vicinity of the opening of the die, and locally increase the temperature of the molten polymer by each auxiliary heating device or This is a die that lowers the temperature and extrudes the sheet to have a uniform thickness in the width direction. The main heating device and the auxiliary heating device may be conventionally known or used. Examples of the main heating device include an electric heating system (heater heating system) and a heating medium heating system. As the auxiliary heating device, for example, a rod-shaped cartridge heater embedded perpendicularly to the die lip land surface, or a rod-shaped cartridge heater arranged parallel to the flow of the molten polymer on the die lip land surface, or An example is a sheet heater arranged parallel to the die lip land surface.

In this extrusion molding die, according to the present invention,
The heat energy input to each auxiliary heating device is controlled according to the unevenness of the sheet thickness, and the control means is provided so that the total of the heat energy input to the auxiliary heating device is always within a certain range. Therefore, in order to always obtain good controllability in adjusting the viscosity of the molten polymer in the lip opening, it is necessary to keep the average heating amount of the auxiliary heating device in a constant range regardless of time over the entire width of the die. It will be realized.

Further, in the present invention, the total range of the heat energy input to the auxiliary heating device is within a range of 20% above and below the initial set value in consideration of optimum controllability, and preferably within a range of 15% above and below.

The present invention will be further described with reference to the drawings.
FIG. 1 is a schematic side sectional view of an extrusion molding die of a sheet material showing one embodiment of the present invention. In FIG. 1, 1 is a main body of an extrusion molding die, 2 is a main heating device, 3 is a die opening 4
It is an auxiliary heating device that changes the temperature of the molten polymer extruded from the.

FIG. 2 is a schematic front view of the die shown in FIG. In FIG. 2, reference numerals 11, 12, ...
It is the auxiliary heating device 3 shown in FIG. 3, and shows an example in which ten auxiliary heating devices are provided. 6 is an auxiliary heating device 1
It is a control device that controls the thermal energy such that the total of the thermal energy of 1, 12, ..., 20 is kept within a certain range, and the molten polymer to be discharged has a uniform thickness in the die width direction.

In such an embodiment, the main body 1 of the extrusion molding die and the thermoplastic polymer 5 inside the die are heated and maintained at a predetermined temperature by the main heating device 2. And die opening 4
The auxiliary heating device 3 is operated to locally change the viscosity of the molten polymer in the die opening 4 according to the thickness unevenness of the thermoplastic polymer sheet discharged from It is intended.

The operation of the controller 6 will now be described. Before extruding the thermoplastic polymer, the initial setting heat energy of each auxiliary heating device is set to q ₁ , and the initial setting heat energy of Q ₁ is set to the entire auxiliary heating device. It is assumed that energy is input and the heating is performed substantially uniformly in the die width direction. Here, if the heat energy input to some of the auxiliary heating devices is increased by Δq ₁ in order to make the thickness of the discharge sheet uniform, the heat energy input by the other auxiliary heating devices will be reduced to Δq ₁ . The total amount of input heat energy to the auxiliary heating devices 11 to 20 is reduced by (1 ±
0.2) is controlled to fit Q _1. The adjustment of the thermal energy is usually performed by adjusting the voltage and / or the current.

An example of the output distribution of the auxiliary heating device at this time is shown in FIG. FIG. 3 shows the output distribution when the thermal energy Δq ₁ is additionally input to the auxiliary heating devices 14, 15, 16. And FIG. 4 is an output distribution in which the control device 6 is actuated in the output distribution shown in FIG. That is, FIG.
Thermal energy [Delta] q _1, which is additionally introduced to the auxiliary heating device 14, 15, 16, is reduced thereby output distributed almost Setsuto thermal energy by means of the auxiliary heating device 11～13,17～20 commensurate with the [Delta] q ₁ . By controlling in this way, optimal control can be performed without significantly changing the total amount of heat energy input to the entire auxiliary heating device, and a uniform sheet can be obtained. In this control, depending on the case, the reduction rates in the auxiliary heating devices 11 to 13 and 17 to 20 may be slightly different.

In practice, such a control method can be arbitrarily set depending on the physical properties of the molten thermoplastic polymer, the die shape, and the extrusion conditions.

Further, in the above operation, when it is desired to reduce the input heat energy by Δq ₁ contrary to the above, the operation reverse to the above may be performed.

Unless control is performed so that the total amount of heat energy input to each auxiliary heating device falls within a certain range as in the present invention, the total amount of heat energy input to the auxiliary heating device is as shown in FIG. There is a case where a sheet having a uniform thickness cannot be obtained because the controllability is not obtained because the operation is performed in a region where the heat output of the auxiliary heating device is significantly changed over time, which is a limit. is there.

However, if the control device 6 is provided so that the total amount of thermal energy to be input falls within a certain range, when sheet thickness is corrected by increasing / decreasing thermal energy input to the auxiliary heating device after sheet discharge is started, sheet discharge is started. If the initial setting value of the thermal energy input to the auxiliary heating device is appropriately determined before, the total thermal energy input to the auxiliary heating device does not change over a limited range over time and is uniform. A sheet of various thickness can be obtained.

[0026]

As described above, in the conventional technique, the total heat energy input to the auxiliary heating device changes with time, so that the heat output of each auxiliary heating device is too high,
If the temperature is too low, an excessively or insufficiently heated portion may occur in the die lip width direction, and optimal controllability may not be obtained. On the other hand, according to the present invention, it is possible to provide an extrusion molding die capable of forming a sheet having a uniform thickness by appropriately controlling the die lip auxiliary heating device.

[Brief description of drawings]

FIG. 1 is a schematic side cross-sectional view of an extrusion die for a molten polymer showing an embodiment of the present invention.

2 is a schematic front view of the extrusion molding die of FIG. 1. FIG.

FIG. 3 is a diagram showing an output distribution of an auxiliary heating device.

FIG. 4 is a diagram showing an output distribution of an auxiliary heating device.

[Explanation of symbols]

 1 Main Body of Extrusion Molding Die 2 Main Heating Device 3 Auxiliary Heating Device 4 Die Lip 5 Polymer Extruded in Sheet Form 6 Heating Energy Control Unit 11, ......, 20 Individual Auxiliary Heating Device

Claims (1)

[Claims] 1. A die for extruding and molding a molten polymer into a sheet, a main heating device for preliminarily heating and maintaining the molten polymer in the die at a predetermined temperature, and a melt weight near the opening of the die. A plurality of auxiliary heating devices for controlling the temperature of the coalescence locally almost independently are provided, and the temperature of the molten polymer is locally raised or lowered by each auxiliary heating device in the width direction of the sheet to be extruded. In a polymer extrusion die having a uniform thickness, the thermal energy input to each auxiliary heating device is controlled, and the increase or decrease of the thermal energy causes a difference in the thermal energy input to each auxiliary heating device. Even so, the polymer extrusion molding die is provided with a control means for controlling the amount of heat energy input to the entire auxiliary heating device within a certain range.