Molding method and molding system for liquid crystal polymer sheet

Abstract

To provide a molding method and a molding system capable of molding a liquid crystal polymer sheet with a stable shape when a liquid crystal polymer is used as a raw material and an extrusion molding die is used for molding sheets.SOLUTION: A molding system for a liquid crystal polymer sheet according to an embodiment has: an extrusion device 1 for heating and melting a liquid crystal polymer, provided with a screw therein; an extrusion molding die 2 for extruding the liquid crystal polymer heated and melted by the extrusion device 1 into a sheet shape; and a lip heater embedded in a lip portion of the extrusion molding die 2. In this case, when the liquid crystal polymer sheet 100 is molded, a temperature difference at the lip portion of the extrusion molding die 2 is kept at 5°C or less.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method and system for forming a liquid crystal polymer sheet. [Background technology]

[0002] A known method for molding a resin sheet involves melting raw material pellets using an extruder and extruding the resulting molten resin into a sheet from an extrusion die (T-die) (see, for example, Patent Document 1 (JP 2018-36535 A)).

[0003] In this case, when selecting a liquid crystal polymer as the material for the resin sheet and attempting to mold a resin sheet made of liquid crystal polymer, due to the special properties of the polymer, it is necessary to determine the molding conditions for the resin sheet taking into consideration temperature control, fluidity within the piping, etc.

[0004] That is, liquid crystal polymers have a characteristic that their viscosity changes greatly depending on the temperature change at the molding temperature. In addition, the extrusion molding die (T-die) for molding the resin into a sheet has a resin discharge port formed in a long horizontal slit shape, so the temperature difference around the lip of the extrusion molding die tends to be relatively large. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-36535 A Summary of the Invention [Problem to be solved by the invention]

[0006] Here, if the temperature difference around the lip portion becomes large, the neck-in amount of the liquid crystal polymer extruded from the extrusion molding die may become uneven on the left and right sides, or the sheet thickness may not be uniform, and a liquid crystal polymer sheet with a stable shape may not be obtained.

[0007] SUMMARY OF THE PRESENTLY PREFERRED EMBODIMENTS OF THE PRESENT EMBODIMENT An object of the present invention is to provide a molding method and molding system capable of molding a liquid crystal polymer sheet having a stable shape when a liquid crystal polymer is used as a raw material and the sheet is molded using an extrusion molding die.

[0008] Other objects and novel features will become apparent from the description of this specification and the accompanying drawings. [Means for solving the problem]

[0009] According to one embodiment, a method for forming a resin sheet made of a liquid crystal polymer includes a step of conveying a heated and molten liquid crystal polymer by an extrusion device having an internal screw, and a step of extruding the heated and molten liquid crystal polymer into a sheet shape from an extrusion die, in which the temperature difference at the lip of the extrusion die is within 5°C. Effect of the Invention

[0010] According to one embodiment, a method and system for molding a liquid crystal polymer sheet can be provided that can obtain a liquid crystal polymer sheet with a stable shape even when molding a liquid crystal polymer into a sheet shape. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram showing a schematic configuration of a molding system for a liquid crystal polymer sheet according to a first embodiment. [Diagram 2] FIG. 2 is a schematic diagram illustrating the schematic configuration of an extrusion device used in the molding system for the liquid crystal polymer sheet according to the first embodiment. [Diagram 3] FIG. 2 is a schematic diagram illustrating the configuration of an extrusion molding die used in the molding system for the liquid crystal polymer sheet according to the first embodiment. [Figure 4] 1A and 1B are schematic diagrams (front view and bottom view) illustrating the configuration of an extrusion molding die used in a molding system for a liquid crystal polymer sheet according to embodiment 1. FIG. [Diagram 5]FIG. 2 is a schematic diagram illustrating a schematic configuration of an extrusion molding die used in a molding system for a liquid crystal polymer sheet according to Modification 1. [Figure 6] FIG. 11 is a schematic diagram illustrating the schematic configuration of an extrusion device used in a molding system for a liquid crystal polymer sheet according to Modification 2. [Figure 7] 13 is a schematic diagram (front view and bottom view) illustrating a schematic configuration of an extrusion molding die used in a molding system for a liquid crystal polymer sheet according to Modification 3. FIG. [Figure 8] 1 is a graph showing (a) the temperature dependence and (b) the shear rate dependence of a liquid crystal polymer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment will be described in detail with reference to the drawings. In all drawings referred to in describing the embodiment, the same reference numerals are used for components having the same or substantially the same functions. In addition, as a rule, components that have been described once will not be described repeatedly.

[0013] <Preliminary considerations> Before describing the present embodiment, the characteristics of the liquid crystal polymer in extrusion molding will be described. In extrusion molding, an extrusion device equipped with a screw is used to heat and melt the raw material resin, knead it using the shearing force of the screw, extrude the resulting melt from an extrusion die of a predetermined shape, and solidify the resin to obtain a molded product of a desired shape.

[0014] Here, in this embodiment, a liquid crystal polymer is the object to be molded. A liquid crystal polymer is a thermoplastic resin that exhibits liquid crystal-like properties in which linear chains of molecules are regularly arranged in a molten state, and is an aromatic polyester resin that has a basic structure of parahydroxybenzoic acid and various components ester-bonded in a linear manner. This embodiment relates to a technology for obtaining a sheet made of a liquid crystal polymer, and a thermotropic liquid crystal polymer is used.

[0015] Known examples of such liquid crystal polymers include a polycondensate of ethylene terephthalate and parahydroxybenzoic acid (heat-resistant temperature: 60 to 180°C), a polycondensate of 2,6-hydroxynaphthoic acid and parahydroxybenzoic acid (heat-resistant temperature: 180 to 250°C), and a polycondensate of phenol, phthalic acid and parahydroxybenzoic acid (heat-resistant temperature: 250 to 350°C).

[0016] Liquid crystal polymers generally have a smaller melting enthalpy ΔH than resins widely used in extrusion molding (such as polypropylene and high-density polyethylene). This means that they melt and solidify easily, and because liquid crystal polymers tend to be oriented in the flow direction and solidify, the range of conditions for forming molded products such as sheets and films is narrow.

[0017] The following describes an example in which a polycondensate of phenol, phthalic acid, and parahydroxybenzoic acid (heat-resistant temperature: 250-350°C) is used as a liquid crystal polymer molding material. Such liquid crystal polymers have high temperature and shear rate dependence compared to resins widely used in extrusion molding. Figure 8(a) shows the temperature dependence of the viscosity of liquid crystal polymer (LCP), polypropylene (PP), and high-density polyethylene (HDPE), while Figure 8(b) shows the shear rate dependence of the viscosity of liquid crystal polymer (LCP), polypropylene (PP), and high-density polyethylene (HDPE). Examples of molding temperature ranges for each resin are also shown.

[0018] As shown in Figure 8(a), liquid crystal polymers have a narrower range of molding temperatures than other resins, but their viscosity changes are large, indicating that they are highly temperature-dependent. Therefore, because the resin properties change greatly with changes in molding temperature, molding conditions are severe and molding operations are difficult.

[0019] As shown in Figure 8(b), liquid crystal polymers have a larger change in viscosity due to changes in shear rate than other resins. Although not plotted in the figure, when the shear rate becomes 10 / sec or less, the viscosity increases rapidly, and this characteristic also means that the molding conditions are severe and molding operations are difficult.

[0020] Therefore, as described above, if the temperature difference around the lip of the extrusion die becomes large, the neck-in amount of the liquid crystal polymer extruded from the extrusion die may become uneven on the left and right sides, or the sheet thickness may not be uniform, making it difficult to obtain a liquid crystal polymer sheet with a stable shape.

[0021] Therefore, the inventors have investigated a method and system for molding liquid crystal polymer sheets that can eliminate the above-mentioned problems, have a smooth surface, can be molded into a stable sheet shape, and can be molded efficiently.

[0022] [Embodiment 1] <Molding system> The liquid crystal polymer sheet molding system according to the present embodiment (hereinafter, sometimes simply referred to as "molding system") is a molding system having an extrusion device and an extrusion die. Below, the schematic configuration of the molding system capable of a series of operations from extrusion molding to stretching the resin sheet will be described with reference to the drawings. Figure 1 is a schematic diagram showing an example of the configuration of the molding system according to the present embodiment, which is equipped with an extrusion device and an extrusion die.

[0023] Here, S1 is a twin-screw kneading extruder, S2 is a T-die, S3 is a raw fabric cooling device (CAST device), S4 is a transverse stretching device (TD device), and S5 is a winding device.

[0024] For example, liquid crystal polymer material (pellets) is added to the raw material supply section of the twin-screw kneading extruder S1 in Figure 1, and transported (conveyed) while being mixed. The kneaded product (molten resin) is extruded through the slit of the T-die S2, and the roll rotation speed of the raw material cooling device S3 is made faster than the speed of the resin extruded from the T-die S2, so that the thickness is adjusted while stretching in the MD, thereby forming a liquid crystal polymer sheet.

[0025] The thin film is then stretched in the transverse direction by a transverse stretching device (TD device) S4 in a separate process. After stretching, the thin film is heat-set to relieve the internal stress during stretching, and the thin film transported from the transverse stretching device (TD device) S4 is wound up by a winding device S5.

[0026] As described above, the resin sheet is stretched in the TD direction, where MD (Machine Direction) is the direction in which the resin sheet is transported, and TD (Transverse Direction) is the direction intersecting with the transport direction of the resin sheet.

[0027] Therefore, in the following description, MD may be referred to as the “machine direction” or the “longitudinal direction”, and TD may be referred to as the “transverse direction”. MD and TD are directions that intersect with each other, more specifically, are directions that are perpendicular to each other.

[0028] By using such a molding system, a resin film can be produced. That is, the twin-screw kneading extruder S1 and the T-die S2 mold a resin sheet made of a liquid crystal polymer material, and then stretch the resin sheet to produce a resin film.

[0029] <<Extrusion equipment configuration>> The extrusion device used in this embodiment can be used as the twin-screw kneading extruder S1 described above. As an example of the extrusion device in this embodiment, as shown in Fig. 2, an extrusion device 1 having a resin supply port 11 connected to a raw material supply part Ta, a cylinder 12 having a screw 12a therein, an extrusion part 13, a connection pipe 14 connecting the extrusion part 13 and the extrusion molding die 2 and through which the molten resin flows, and a rotation drive mechanism 15 driving the screw of the cylinder 12 can be exemplified.

[0030] The raw material supplying part Ta supplies the liquid crystal polymer material to the cylinder 12. The liquid crystal polymer material to be supplied may be in various forms such as pellets, powder, flakes, etc., and may be, for example, fed from above into the raw material supplying part Ta having a hopper by a feeder or the like, and supplied into the cylinder 12 via the resin supplying port 11. The following describes an example in which the liquid crystal polymer to be supplied is in the form of pellets.

[0031] The cylinder 12 has a screw 12a therein. Fig. 2 shows a side view of the cylinder 12 in cross section so that the internal structure of the cylinder 12 of the extrusion device 1 (the twin-screw kneading extruder S1 in Fig. 1) can be seen.

[0032] By rotating this screw 12a, the supplied liquid crystal polymer material is gradually transported inside the cylinder 12 to the extrusion section 13 side (downstream side). This screw 12a may be a twin screw having two screws or a single screw having one screw. A twin screw extrusion device having two screws has the flexibility to freely change operating conditions such as the screw rotation speed and barrel set temperature, and also has various advantages such as high transportability and continuous processability.

[0033] The cylinder 12 is formed, for example, by connecting a plurality of cylinder blocks, and each cylinder block has a space inside which the liquid crystal polymer can be transported. A screw 12a is provided in this space, and the screw 12a is connected to a rotation drive mechanism 15. The rotation drive mechanism 15 rotates the screw 12a, so that the liquid crystal polymer can be transported in the cylinder 12.

[0034] In addition, the cylinder 12 is provided with a heater so that its temperature can be adjusted. The liquid crystal polymer is transported from the raw material supply section Ta toward the extrusion section 13, during which the liquid crystal polymer is gradually heated by the heater, and a melt-plasticized liquid crystal polymer is easily obtained. The melt-plasticized liquid crystal polymer thus obtained can be easily transported within the cylinder 12, and is transported further downstream.

[0035] The extrusion unit 13 is a member that extrudes the molten liquid crystal polymer transported inside the cylinder 12 into a connection pipe 14 that is connected to the extrusion die 2. The extrusion unit 13 preferably transfers the liquid crystal polymer while shearing it, while maintaining the pressure inside the cylinder 12.

[0036] The connection pipe 14 is a pipe that connects the extrusion section 13 and the extrusion die 2, and serves to circulate the molten and sufficiently kneaded liquid crystal polymer to the extrusion die 2 while maintaining that state.

[0037] In this connection pipe 14, a heater or the like is provided so that the molten liquid crystal polymer can flow in a molten state to the extrusion molding die 2, and the temperature inside this connection pipe 14 is maintained at the melting temperature of the liquid crystal polymer.

[0038] The rotation drive mechanism 15 is a device for rotating the screw 12a provided in the cylinder 12. The screw rotated by the rotation drive mechanism 15 transports the liquid crystal polymer inside the cylinder 12.

[0039] When the extrusion device 1 is a twin-screw extrusion device, the two screws are arranged parallel to each other and rotated. The two shafts may be arranged to mesh with each other, or may not be arranged to mesh with each other. When the number of screws is two, the twin-screw with two screws is preferable to the single-screw with one screw because of high raw material conveying efficiency and high kneading performance, and therefore, when the screw diameter is the same, the twin-screw with two screws can increase the extrusion amount. In addition, the extension direction of the cylinder 12 and the extension direction of the screw in the cylinder 12 are the same.

[0040] <<Extrusion die configuration>> The extrusion die used in this embodiment can be used as the T-die S2 described above. As an example of the extrusion die in this embodiment, as shown in Figures 3 and 4, an extrusion die 2 having a die body 21 connected to a connection pipe 14, a slit 22 for discharging a molten liquid crystal polymer in a sheet form, and a lip heater 23 provided on the lip portion of the die body 21 (the area adjacent to the slit 22) can be exemplified.

[0041] Here, Fig. 2 is a side view showing the extrusion die 2 corresponding to the T-die S2 shown in Fig. 1, and the cast roll 31 and the cooling roll 32 corresponding to the raw fabric cooling device S3. Fig. 3 is a front view (Fig. 3(a)) of the extrusion die 2 as seen from the downstream side (transverse stretching device side) in the conveying direction of the liquid crystal polymer sheet 100, and a bottom view (Fig. 3(b)) of the extrusion die 2 as seen from below (the side where the slit 22 is provided).

[0042] Molten liquid crystal polymer is supplied to this extrusion molding die 2 from the extrusion device 1 through a connecting pipe 14, and the molten liquid crystal polymer is discharged in sheet form from a discharge port, slit 22. Fig. 3 shows that the liquid crystal polymer is discharged in sheet form onto a casting roll 31, and a liquid crystal polymer sheet 100 is sent via a cooling roll 32 to a downstream longitudinal stretching device S4.

[0043] The die body 21 can have the same structure as a conventionally known die used as an extrusion molding die (T-die). The die body 21 has a flow path through which the molten liquid crystal polymer is supplied from the extrusion device 1 through the connection pipe 14 and guides the molten liquid crystal polymer to the slit 22.

[0044] The slit 22 can have the same structure as a conventionally known die used as an extrusion molding die (T-die). The slit 22 allows the molten liquid crystal polymer to be discharged from the die body 21 to the outside in the form of a sheet, and the liquid crystal polymer is cooled by a cast roll 31 or the like to obtain a liquid crystal polymer sheet.

[0045] The lip heater 23 is a heater embedded in the lip portion of the die body 21 of the extrusion die 2. That is, the lip heater 23 is a member that is provided in the vicinity of the slit 22 and heats the molten liquid crystal polymer discharged from the slit 22 so as to maintain the temperature at a desired temperature.

[0046] As shown in Figure 4, this lip heater 23 is provided at the lip portion of the die body 21 of the extrusion molding die 2, and is positioned and controlled so as to enable stable extrusion of the liquid crystal polymer from the slit 22 while maintaining the molten state of the liquid crystal polymer flowing through the flow path provided inside the die body 21.

[0047] The lip heater 23 may be provided on one side of the slit 22 (or the flow path immediately preceding it), but is preferably provided on both sides. Also, the lip heater 23 is preferably provided along the longitudinal direction of the slit 22. This lip heater 23 reduces the temperature difference depending on the discharge position of the liquid crystal polymer discharged from the slit 22, making it possible to obtain a stable sheet-like liquid crystal polymer sheet 100.

[0048] Also, the length (width) L of the lip heater 23 H is the length (width) of the slit L S Ratio to (L H / L S) is preferably set to be in the range of 0.8 to 1.0, and more preferably in the range of 0.9 to 1.0. By setting it in such a range, the temperature difference depending on the discharge position of the liquid crystal polymer discharged from the slit can be reduced, and a stable sheet-like liquid crystal polymer sheet 100 can be obtained.

[0049] At this time, it is preferable to arrange the slit 22 and the lip heater 23 so that their centers are aligned. That is, the temperature adjustment by the lip heater 23 is preferably performed in a central region of 80% to 100% of the width of the slit 22, and more preferably in a central region of 90% to 100%.

[0050] The temperature control may be performed by controlling the heating state of the lip heater 23 with a control unit to adjust the temperature to a desired level. In this case, it is preferable to provide a temperature sensor at the lip of the die body 21 so that the lip heater 23 can be turned on and off or its output can be adjusted while checking the temperature of the lip.

[0051] <Forming method> Next, a method for forming a liquid crystal polymer sheet will be described using an example in which a forming system having the above-described apparatus shown in FIGS. 2 and 3 is used.

[0052] First, a liquid crystal polymer material is supplied to the raw material supply unit Ta. The liquid crystal polymer material supplied here may be in various forms such as pellets, powder, flakes, etc. The liquid crystal polymer used in this embodiment may be any known liquid crystal polymer without any particular limitations.

[0053] Examples of the polycondensate include the above-mentioned polycondensate of ethylene terephthalate and parahydroxybenzoic acid (heat-resistant temperature: 60 to 180° C.), the polycondensate of 2,6-hydroxynaphthoic acid and parahydroxybenzoic acid (heat-resistant temperature: 180 to 250° C.), the polycondensate of phenol, phthalic acid and parahydroxybenzoic acid (heat-resistant temperature: 250 to 350° C.), and modified polymers thereof. Among these, the polycondensate of phenol, phthalic acid and parahydroxybenzoic acid (heat-resistant temperature: 250 to 350° C.) is preferred.

[0054] The liquid crystal polymer supplied to the raw material supply section Ta is supplied into the cylinder 12 via the resin supply port 11 provided in the cylinder 12. The liquid crystal polymer supplied into the cylinder 12 is transported inside the cylinder 12 to the extrusion section 13 side (downstream side) by the rotation of the screw 12a. At the same time, the liquid crystal polymer is heated by a heater provided in the cylinder 12 so that the temperature gradually increases. The liquid crystal polymer softens and melts due to this heating and shear energy caused by the rotation of the screw 12a, and in the molten state, it is further transported inside the cylinder 12 (transportation process).

[0055] When the molten liquid crystal polymer reaches the extrusion section 13 from the tip of the screw 12 a , it is extruded directly from the extrusion section 13 into the connection pipe 14 , and then flows through the connection pipe 14 to be extruded into the extrusion die 2 .

[0056] When the liquid crystal polymer that has flowed through the connection pipe 14 reaches the extrusion die 2, it flows through the flow path of the extrusion die 2 and is extruded into a sheet form from the slit 22 (conveying process). At this time, the extrusion die 2 is controlled by a lip heater 23 provided on its lip portion (the area adjacent to the slit 22) so as to reduce the temperature difference depending on the location of the sheet-like liquid crystal polymer extruded from the slit 22.

[0057] This control is preferably performed by keeping the temperature difference at the lip within 5°C, and more specifically, the temperature of the surface of the die body 21 on which the slit 22 is formed within 5°C. To control the temperature in this manner, for example, a plurality of pairs of temperature sensors are provided inside the extrusion die 2, each pair being disposed at an equal distance from the slit 22, in the width direction of the slit, and feedback control is performed based on the temperatures measured by the temperature sensors. The temperature sensors are preferably provided at both ends of the slit 22 or in the vicinity thereof, and are preferably provided at positions that are point-symmetric with respect to the center point of the slit and line-symmetric with respect to the center line (axis) of the slit.

[0058] By controlling the temperature of the lip portion to within 5° C. in this manner, the thickness of the liquid crystal polymer sheet 100 can be made more uniform, and the sheet shape can be stabilized with less bias between the left and right sides of the sheet.

[0059] [Variation 1] In the molding system according to the embodiment described above, the extrusion device 1 and the extrusion molding die 2 can be connected by a connection pipe 14 provided with a pipe elbow, for example, as shown in FIG.

[0060] With this configuration, the molten resin is supplied from the top and discharged from the bottom of the extrusion die 2. Therefore, the liquid crystal polymer supplied to the extrusion die 2 flows smoothly from top to bottom, and the liquid crystal polymer can be prevented from accumulating inside the die.

[0061] On the other hand, when a piping elbow is provided as described above, the flow path is bent, so that the liquid crystal polymer is likely to stagnate at the bent portion, and the temperature of the liquid crystal polymer at the stagnation portion may drop and solidify. When such solidification occurs, the solidified liquid crystal polymer adheres to the inner wall of the piping, narrowing the flow path, and it becomes impossible to smoothly circulate a predetermined amount of liquid crystal polymer. If the solidification of the liquid crystal polymer progresses further, the connecting piping 14 may become clogged, and the molding operation itself may become impossible.

[0062] Therefore, in this modified example, it is preferable to provide a breaker plate and a gear pump in addition to a piping elbow in the connecting piping 14, thereby thoroughly mixing the liquid crystal polymer while smoothing the flow of the liquid crystal polymer in the connecting piping 14 and suppressing solidification of the liquid crystal polymer within the piping.

[0063] The breaker plate is a perforated plate provided at the tip of the cylinder 12 in the extrusion device 1, which regulates the flow of the molten liquid crystal polymer in the extrusion section 13 and increases the back pressure within the cylinder 12 to improve the kneading state.

[0064] The gear pump is a component that has multiple gears and can transport a constant amount of molten liquid crystal polymer between the gears, and can stably transport the liquid crystal polymer in the connecting pipe 14, facilitating the smooth flow of the liquid crystal polymer in the connecting pipe 14. In addition, the gear pump can suppress the generation of pulsation in the liquid crystal polymer flowing into the extrusion die 2, making it easier to achieve a uniform thickness for the liquid crystal polymer sheet.

[0065] The piping elbow is a pipe having a bent flow path, and as described above, it favors the flow of the liquid crystal polymer in the extrusion die 2. Here, in the piping elbow, the shape of the flow path makes it easy for stagnation to occur, but here, when the inner diameter of this pipe is D, it is preferable that the outer diameter is 1.5D or more. By satisfying such a relationship, it is possible to suppress a decrease in the temperature of the liquid crystal polymer in the piping elbow and to flow the liquid crystal polymer in a molten state to the extrusion die 2. Therefore, it is possible to suppress solidification of the liquid crystal polymer in the pipe, and it is possible to efficiently flow the liquid phase polymer.

[0066] In this variant example 1, a liquid crystal polymer sheet is molded using the extrusion device 1, connecting pipe 14, and extrusion die 2 configured as described above, but the connecting pipe 14 connecting the extrusion device 1 and the extrusion die 2 is particularly distinctive.

[0067] The molding operation is the same as in the above embodiment. Also, as in the above embodiment, the shear rate of the liquid crystal polymer flowing through the connection pipe 14 is preferably 10 / sec or more. By flowing the liquid crystal polymer through the connection pipe 14 while satisfying the above shear rate in this manner, clogging in the connection pipe 14 due to solidification of the liquid crystal polymer can be suppressed.

[0068] In this first modification, by providing the breaker plate, gear pump, and piping elbow in the connection pipe 14 as described above, it becomes easier to ensure the above shear rate.

[0069] [Variation 2] In addition, in the molding system according to the embodiment described above, for example, as shown in Fig. 6, a vent portion 16 can be provided in the cylinder 12 of the extrusion device 1. Fig. 6 is a schematic diagram illustrating the general configuration of the extrusion device 1. Fig. 6 is a side view showing the cylinder 12 in cross section.

[0070] The liquid crystal polymer used in the present embodiment is heated, melted and transported in the cylinder 12 as described above, but the heating may cause a part of the polymer to decompose and generate decomposition gases. For example, when a polycondensate of phenol, phthalic acid and parahydroxybenzoic acid (heat-resistant temperature: 250 to 350°C) is used, heating to 290°C or higher generates decomposition gases such as methylparaben, 4-hydroxybenzoic acid, and phenyl-4-hydroxybenzoate.

[0071] At this time, the decomposition gas accumulates in the cylinder 12. If a large amount of the decomposition gas is generated, the pressure inside the cylinder will exceed the set pressure, and there is a risk that the decomposition gas will remain in the molten liquid crystal polymer and be transported to the next process.

[0072] If decomposition gas remains in the molten liquid crystal polymer, it will also be contained in the liquid crystal polymer sheet 100 extruded from the extrusion molding die 2, and if this gas is reheated during the subsequent stretching operation, it may cause defects such as holes being formed in the liquid crystal polymer sheet.

[0073] Here, in this modified example, a vent portion 16 is provided as shown in Fig. 6. The vent portion 16 is formed with an opening above the cylinder 12, and is capable of discharging gas within the cylinder 12 to the outside of the cylinder 12. Therefore, by providing the vent portion 16, the decomposition gas generated within the cylinder 12 is discharged to the outside through the vent portion 16, so that the decomposition gas does not accumulate excessively within the cylinder 12, and the occurrence of the above-mentioned problems can be suppressed.

[0074] 6 shows an example in which two vent portions 16 are provided, but the number of vent portions 16 may be one or three or more. In addition, the position of the vent portion 16 is preferably a position where a large amount of decomposition gas is generated, so that the increase in pressure due to the decomposition gas and the amount of the decomposition gas remaining in the liquid crystal polymer can be reduced.

[0075] [Variation 3] In addition, in the molding system according to the embodiment described above, for example, as shown in Fig. 7, in the extrusion molding die 2, the lip heater 23 embedded in the lip portion can be divided along the slit 22. Fig. 7 is a diagram showing a front view (Fig. 6(a)) of the extrusion molding die 2 as seen from the downstream side in the conveying direction (stretching device side) and a bottom view (Fig. 6(b)) as seen from below the extrusion molding die 2 (the side where the discharge port is provided).

[0076] By providing separate lip heaters 23 in this manner and controlling the temperature of each lip heater 23 independently, more precise temperature control is possible, making it easier to adjust the temperature difference at the lip portion to within 5° C. In this case, by providing a temperature sensor at the lip portion of the die body 21 corresponding to each lip heater 23, the control can be made more preferable.

[0077] 7, the number of divisions of the lip heater 23 is three, but it may be two, four or more. Also, the number of divisions of the lip heater may be different on either side of the slit 22.

[0078] The invention made by the inventor has been specifically described above based on an embodiment, but it goes without saying that the present invention is not limited to the above embodiment and can be modified in various ways without departing from the gist of the invention. [Explanation of symbols]

[0079] 1... extrusion device, 2... extrusion die, 11... resin supply port, 12... cylinder, 13... extrusion section, 14... connection pipe, 15... rotation drive mechanism, 21... die body, 22... slit, 23... lip heater, 31... casting roll, 32... cooling roll, 100... liquid crystal polymer sheet

Claims

1. A method for forming a liquid crystal polymer sheet, comprising: (a) conveying a heated and melted liquid crystal polymer by an extrusion device having a screw therein; (b) extruding the heated and melted liquid crystal polymer obtained in the step (a) from an extrusion die into a sheet shape; However, the temperature difference at the lip of the extrusion die is kept within 5°C.

2. The method for forming a liquid crystal polymer sheet according to claim 1, The method for molding a liquid crystal polymer sheet further comprises the steps of: providing a lip heater embedded in the lip portion of the extrusion die; and adjusting the temperature of the lip portion by means of the lip heater.

3. The method for forming a liquid crystal polymer sheet according to claim 1, The method for molding a liquid crystal polymer sheet, wherein the lip heaters are provided on both sides of a slit, which is an outlet of the extrusion die, along the longitudinal direction of the slit.

4. The method for forming a liquid crystal polymer sheet according to claim 1, The method for forming a liquid crystal polymer sheet, wherein the temperature difference is satisfied within a range of 90% or more of a central region with respect to a width of a slit of the extrusion die.

5. The method for forming a liquid crystal polymer sheet according to claim 1, The method for forming a liquid crystal polymer sheet comprises setting a shear rate of the liquid crystal polymer to 10 / sec or more in a connecting pipe that connects the extrusion device to the extrusion die.

6. The method for forming a liquid crystal polymer sheet according to claim 1, The method for molding a liquid crystal polymer sheet, wherein the connecting piping includes a breaker plate, a gear pump, and a piping elbow.

7. The method for forming a liquid crystal polymer sheet according to claim 1, The method for forming a liquid crystal polymer sheet comprises carrying out the step (a) while discharging gas generated inside the extrusion device to the outside.

8. A method for forming a liquid crystal polymer sheet, comprising: (a) conveying a heated and melted liquid crystal polymer by an extrusion device having a screw therein; (b) extruding the heated and melted liquid crystal polymer obtained in the step (a) from an extrusion die into a sheet shape; The method for forming a liquid crystal polymer sheet comprises setting a shear rate of the liquid crystal polymer to 10 / sec or more in a pipe connecting the extrusion device to the extrusion die.

9. The method for forming a liquid crystal polymer sheet according to claim 8, The method for molding a liquid crystal polymer sheet, wherein the piping includes a breaker plate, a gear pump, and a piping elbow.

10. A liquid crystal polymer sheet forming system, including: an extrusion device having an internal screw for heating and melting the liquid crystal polymer; and an extrusion molding die for extruding the liquid crystal polymer heated and melted in the extrusion device into a sheet shape; A liquid crystal polymer sheet molding system having a lip heater embedded in the lip of the extrusion die.

11. The liquid crystal polymer sheet molding system according to claim 10, A liquid crystal polymer sheet molding system, wherein the lip heaters are provided on both sides of a slit, which is an outlet of the extrusion molding die, along the longitudinal direction of the slit.

12. The liquid crystal polymer sheet molding system according to claim 10, A liquid crystal polymer sheet molding system having a control unit that adjusts the temperature difference of the lip portion of the extrusion molding die to within 5°C using the lip heater.

13. The liquid crystal polymer sheet molding system according to claim 12, The control unit of the liquid crystal polymer sheet molding system is configured to satisfy the temperature difference within a range of 90% or more of a central region relative to the width of the slit of the extrusion molding die.

14. The liquid crystal polymer sheet molding system according to claim 10, A molding system for a liquid crystal polymer sheet, wherein the lip heater is divided into multiple pieces and provided in the longitudinal direction of the slit in the lip portion.

15. The liquid crystal polymer sheet molding system according to claim 10, The liquid crystal polymer sheet molding system, wherein the piping includes a breaker plate, a gear pump, and a piping elbow.

16. The liquid crystal polymer sheet molding system according to claim 10, The extrusion device is a molding system for a liquid crystal polymer sheet, and has a vent portion that can discharge to the outside decomposition gas generated by decomposition of the liquid crystal polymer.

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