Resin sheet stretching method and stretching device

Abstract

To provide a resin sheet stretching method and stretching device capable of obtaining a resin filmhaving a uniform thickness more efficiently.SOLUTION: A resin sheet stretching device 1 according to an embodiment comprises: rolls R1 to R10 disposed in a stretching region SA for stretching a resin sheet 100 made of polyethylene in a conveyance direction; rolls R11 to R12 disposed in a relaxation region RA for relaxing the resin sheet 100 stretched in the stretching region SA in a direction opposite to the conveyance direction; and a control unit 2 for controlling a speed difference between a circumferential speed of the roll R10 and a circumferential speed of the roll R11 adjacent to each other so as to relax the resin sheet 100.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method and apparatus for stretching a polyethylene resin sheet. [Background technology]

[0002] A known method for producing a resin film involves melting pellets, which are a raw material, in an extruder and extruding the resulting molten resin from an extrusion die (T-die) into a sheet shape.

[0003] If necessary, the sheet-shaped resin sheet is further stretched by sequential biaxial stretching, in which the resin sheet is stretched in the vertical direction (traveling direction) through multiple rolls and then stretched in the horizontal direction (direction perpendicular to the traveling direction) after the vertical stretching, to obtain the desired thickness, shape, etc. (see, for example, Patent Document 1 (JP 2021-54030 A)).

[0004] The longitudinal stretching device used for the longitudinal stretching uses a plurality of heated rolls to stretch the resin sheet in the longitudinal direction (travel direction) by the difference in peripheral speed between the rolls. After this longitudinal stretching, the next step of transverse stretching is carried out while maintaining the stretched state. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-54030 Summary of the Invention [Problem to be solved by the invention]

[0006] Here, when a crystalline resin such as polyethylene is used as the raw material, the shrinkage rate during molding tends to be large, and when the resin is stretched (drawn), the molecules may become oriented in a specific direction, resulting in distortion.

[0007] If this distortion is cooled and fixed as it is, the distortion will remain inside the resin sheet as stress (residual stress), and during the subsequent lateral stretching, the initial load will be large, resulting in problems such as a decrease in uniformity in the thickness of the resin film and deterioration of physical properties, and there is a risk that the resin sheet cannot be produced efficiently.

[0008] Therefore, there is a demand for a method and apparatus for stretching a resin sheet that can more efficiently obtain a resin film having a uniform thickness.

[0009] Other objects and novel features will become apparent from the description of this specification and the accompanying drawings. [Means for solving the problem]

[0010] According to one embodiment, a method for stretching a resin sheet includes a step of stretching a polyethylene resin sheet in a conveying direction by a roll arranged in a stretching region, and a step of relaxing the stretched resin sheet in a direction opposite to the conveying direction by a roll arranged in a relaxation region.

[0011] Here, the relaxation is preferably achieved by making the peripheral speed of the roll in the relaxation region slower than the peripheral speed of the roll in the stretching region, between the roll in the adjacent stretching region and the roll in the relaxation region. Effect of the Invention

[0012] According to one embodiment, it is possible to provide a resin sheet stretching method and a stretching device that can more efficiently obtain a resin film having a uniform thickness. [Brief description of the drawings]

[0013] [Figure 1] 1 is a schematic diagram showing a configuration of an extrusion molding system having a stretching device according to an embodiment. [Diagram 2] FIG. 1 is a schematic diagram showing a configuration of a stretching device according to an embodiment. [Diagram 3]FIG. 2 is a diagram showing processing conditions (roll temperatures) during stretching in Examples and Comparative Examples according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] 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.

[0015] <Extrusion molding system> Before describing the stretching method and the stretching device according to the present embodiment, a schematic configuration of an extrusion molding system equipped with a stretching device will be described first. Fig. 1 shows a schematic diagram of a configuration example of a resin film manufacturing system equipped with a stretching device.

[0016] 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 longitudinal stretching device (MD device), S5 is a transverse stretching device (TD device), and S6 is a winding device.

[0017] For example, a resin material (pellets) is added to the raw material supply section Ta of the twin-screw kneading extruder S1 in Figure 1, and transported (conveyed) while being mixed. The kneaded product (molten resin) is extruded from the slit of the T-die S2 and cooled in the raw material cooling device S3 to form a resin sheet.

[0018] Next, the resin sheet is stretched in the longitudinal direction by a longitudinal stretching device (MD device) S4, and further stretched in the transverse direction by a transverse stretching device (TD device) S5. After stretching, heat setting is performed to relieve internal stress during stretching, and the resin film transported from the transverse stretching device (TD device) S5 is wound up by a winding device S6.

[0019] As described above, the resin sheet is stretched in the MD and TD directions, where MD (Machine Direction) is the direction in which the resin sheet is conveyed, and TD (Transverse Direction) is the direction intersecting with the conveyance direction of the resin sheet.

[0020] Therefore, in the following description, MD may be referred to as the “transport direction” or the “longitudinal direction,” and TD may be referred to as the “lateral direction.” MD and TD are directions that intersect with each other, more specifically, are directions that are perpendicular to each other.

[0021] A resin film can be produced by such a production system. That is, the longitudinal stretching apparatus (MD apparatus) S4 is used as one of the apparatuses constituting the system for producing a resin film from a resin material.

[0022] <Resin materials> In addition, in this embodiment, a method and an apparatus for producing a resin film by stretching a polyethylene resin sheet as the resin sheet are used. That is, the resin material used in this embodiment is polyethylene.

[0023] Polyethylene is a crystalline resin, and as described above, there is a risk of the production efficiency decreasing due to the influence of molecular orientation during stretching. In contrast, in the present embodiment, a method and apparatus for stretching a resin sheet can be provided that can more efficiently obtain a polyethylene resin film having a uniform thickness.

[0024] The polyethylene used here is not particularly limited, but linear low density polyethylene (LLDPE), high density polyethylene (HDPE), etc., which are suitable for producing resin films, are preferred.

[0025] <Stretching device configuration> The stretching device according to the present embodiment can be used as the above-described longitudinal stretching device (MD device) S4. That is, the device stretches the resin sheet obtained by molding the resin sheet in the longitudinal direction (MD) of the twin-screw kneading extruder S1. Hereinafter, a configuration example of the stretching device according to the present embodiment will be described in detail with reference to the drawings.

[0026] FIG. 2 is a schematic diagram showing the configuration of a stretching device 1 according to this embodiment. The stretching device 1 has a plurality of rolls R1-R12 and a control unit 2 that controls the temperature and circumferential speed of the plurality of rolls R1-R12. The plurality of rolls R1-R12 are provided in either a stretching region SA where the resin sheet 100 is stretched or a relaxation region RA where the resin sheet 100 is relaxed after stretching, depending on the action of the rolls. However, the number of rolls can be changed depending on the line speed and the thickness of the film. This embodiment is characterized in that the device configuration has a relaxation region RA immediately after the stretching region SA. The circumferential speed can also be called the feed speed or conveyance speed when viewed from the resin sheet side.

[0027] In addition, this stretching device 1 may have a pressure roll PR that presses the resin sheet 100 when performing the stretching and relaxation processes, and a feed roll FR that sends the resin sheet 100 to a downstream device after the stretching and relaxation processes are completed.

[0028] [Stretch area] Next, the stretching region SA will be described in detail. The stretching region SA is a region where the resin sheet 100 sent from the upstream raw fabric cooling device S3 is stretched in the longitudinal direction (conveyance direction). Rolls R1 to R10 are arranged in the stretching region SA. Conversely, it can be said that the stretching region SA is formed by the rolls R1 to R10.

[0029] The rolls R1 to R10 are provided to stretch the resin sheet 100, and first heat the resin sheet 100 to near its melting temperature (Tm), and after the resin sheet 100 is sufficiently heated, they operate to stretch the resin sheet 100 in the longitudinal direction. The rolls R1 to R10 are heating rolls that are each heated to a predetermined temperature so as to achieve the above-mentioned effect.

[0030] The rolls R1 to R10 heat the resin sheet 100 as described above, and the circumferential speeds of the rolls are adjusted and controlled so that the resin sheet 100 is stretched. The circumferential speeds are determined according to the stretching conditions. Depending on the difference in the circumferential speeds, the resin sheet 100 can be stretched to a desired stretch ratio. More detailed stretching conditions will be described in the explanation of the control unit and the method for stretching the resin sheet.

[0031] [Relaxation area] The relaxation region RA in this embodiment is a region where a process is performed to relax or remove distortion (residual stress) caused by stretching the resin sheet 100 in the stretching region SA. This relaxation region RA may be provided immediately following the stretching region SA. Rolls R11 and R12 are disposed in this relaxation region RA. Conversely, it can be said that the relaxation region RA is formed by the rolls R11 and R12.

[0032] The rolls R11-R12 operate to relax the resin sheet 100 stretched in the longitudinal direction in the direction opposite to the stretching direction. Specifically, in the relaxation region RA, the rolls R11-R12 are adjusted and controlled so that their peripheral speeds are slower than the peripheral speed of the last roll R10 in the stretching region SA (the roll closest to the relaxation region RA in the stretching region SA). This peripheral speed is determined according to the relaxation conditions. More detailed relaxation conditions will be described in the explanation of the control unit and the stretching method for the resin sheet.

[0033] The treatment in the relaxed region is preferably carried out while the resin sheet 100 is kept heated to the relaxation temperature, and is preferably carried out while the resin sheet 100 is kept at a higher temperature within the relaxation temperature range.

[0034] [Control Unit] The control unit 2 is a member that controls the operation of the rolls R1 to 12. As described above, the rolls R1 to 12 are rotated to a predetermined temperature and a predetermined peripheral speed, respectively, and are operated so that the stretching process can be performed and then the relaxation process can be performed. The temperature and rotational operation of these rolls R1 to R12 are controlled by the control unit 2.

[0035] Therefore, the control unit 2 and each of the rolls R1-12 are connected by a path (such as a signal wiring 21) for transmitting a signal commanding the operation. The control unit 2 is capable of independently controlling the temperature and rotation speed of each of the rolls R1-12.

[0036] In the stretching region SA, the temperature of the resin sheet 100 is preheated and then gradually increased to near the melting temperature (Tm). For example, the rolls R1 to R9 are heating rolls that increase the temperature of the resin sheet 100 to a temperature at which the resin sheet 100 can be sufficiently stretched. The heating temperature at this time is preferably in the range of, for example, 50 to 105°C. At this time, the temperature is increased stepwise from the roll R1 to R9.

[0037] Then, with the resin sheet 100 being sufficiently heated, the control unit 2 makes the peripheral speed of the roll R10 faster than the peripheral speeds of the rolls R1 to R9, whereby the resin sheet 100 is stretched in the longitudinal direction (conveying direction) to perform the stretching process.

[0038] In the relaxation region RA, the temperature of the rolls R11 to R12 is maintained at a temperature at which relaxation can be efficiently performed on the stretched resin sheet 100. Here, the temperature of the rolls R11 to R12 is preferably maintained at a temperature at which α-relaxation can be achieved, and is more preferably maintained in the range of 45 to 100° C., further preferably in the range of 50 to 100° C., and particularly preferably in the range of 60 to 100° C. Within this temperature range, by increasing the roll temperature for relaxation, residual stress can be efficiently removed.

[0039] Then, the control unit 2 controls the peripheral speed of the roll R11 adjacent to the roll R10 to be slower than that of the roll R10, thereby performing a relaxation process in which the resin sheet 100 is relaxed in the opposite direction to the longitudinal direction (transport direction) in which the resin sheet 100 is stretched in the stretching process. Here, in the relaxation region RA, the heated state of the resin sheet 100 is preferably maintained at the temperature described above.

[0040] [others] The resin sheet 100 stretched through the relaxation region RA is further sent to a downstream device such as a transverse stretching device S5 by a feed roll FR. This feed roll FR may be any roll capable of directly transporting the resin sheet 100 that has been subjected to the relaxation treatment, and is preferably cooled to a temperature at which the resin is solidified (fixed). When such cooling is performed, the temperature of this feed roll FR is preferably in the range of 20 to 40°C, more preferably in the range of 25 to 35°C.

[0041] When cooling is performed by the feed roll FR, a flow path through which cooling water can flow may be provided inside the feed roll FR, and the cooling water may be circulated and circulated inside the flow path. The peripheral speed of the feed roll FR is set to be the same as that of the rolls R11 to R12, and the sheet is transported to the transverse stretching device S5 in the next process.

[0042] A cooling area may be provided between the relaxation area RA and the feed roll FR to cool and solidify (fix) the resin sheet. When a cooling area is provided, the rolls arranged in the cooling area may be set to the same temperature conditions as those for cooling by the feed roll, and are configured so that cooling water can flow through the inside of the rolls. When a cooling area is provided, the feed roll FR does not need to have a flow path for cooling water inside, and it is sufficient if it can simply transport the stretched resin sheet 100.

[0043] The temperature and rotation speed of the feed roll FR and the rolls in the cooling region can also be controlled by the above-mentioned control unit 2. The control unit 2 can also control other members constituting the stretching device 1 to meet predetermined conditions. Furthermore, the control unit 2 can also control the operation of some or all of the devices in the extrusion molding system.

[0044] <Method of stretching resin sheet> Next, a longitudinal stretching method according to the present embodiment will be described below. Taking the case where the above-mentioned longitudinal stretching device 1 is used as an example, the longitudinal stretching method according to the present embodiment will be described with reference to Figs.

[0045] The resin sheet stretching method according to the present embodiment first performs a step of stretching a polyethylene resin sheet 100 in the machine direction (transport direction) by rolls R1 to R10 arranged in a stretching region SA (step (a)).

[0046] The resin sheet 100 is, for example, a resin sheet obtained from a raw sheet cooling device S3 of an extrusion molding system. The resin sheet 100 is supplied to the stretching device 1 and transferred in order to the stretching region SA and the relaxation region RA described above, where the resin sheet 100 is stretched.

[0047] The resin sheet 100 is sufficiently heated while being transported under the temperature conditions described in the control unit of the stretching device above, and then while maintaining the heated state, the resin sheet 100 can be stretched in the longitudinal direction (transport direction), for example, by making the circumferential speed of roll R10 faster than the circumferential speeds of rolls R1 to R9.

[0048] Here, the ratio of the peripheral speed of the roll R10 to the peripheral speed of the rolls R1 to R9 is the stretching ratio during longitudinal stretching. This stretching ratio can be set to any desired value, and is preferably, for example, 2 to 6 times, and more preferably 3 to 5 times.

[0049] More specifically, for example, the temperature of each roll is controlled so that rolls R1-R2 are 65° C., roll R3 is 95° C., rolls R4-R5 are 105° C., rolls R6-R8 are 100° C., and rolls R9-R10 are 95° C., while the peripheral speed of rolls R1-R9 is 10 m / min and roll R10 is 45-50 m / min, and the temperature of each roll is controlled so that rolls R1-R9 are 10 m / min and roll R10 is 45-50 m / min, respectively. This peripheral speed can be appropriately changed depending on the draw ratio.

[0050] Next, after step (a), the stretched resin sheet 100 is relaxed in the direction opposite to the machine direction (transport direction) by rolls R11 to R12 (step (b)).

[0051] This step (b) is preferably carried out immediately after the stretching step. Here, the relaxation treatment is carried out by rolls R11 and R12 provided immediately after the stretching region SA.

[0052] Here, the relaxation can be performed by making the peripheral speed of the roll R11 arranged in the rear stage slower than the peripheral speed of the roll R10 arranged in the front stage between the roll in the adjacent stretching region and the roll in the relaxation region (i.e., between the rolls R10 and R11 adjacent to each other across the stretching region SA and the relaxation region RA), thereby performing the relaxation treatment of the resin sheet 100. In this case, the rate of relaxation is preferably 3 to 12%, and more preferably 5 to 10%.

[0053] This rate of relaxation can be expressed as a rate taking into consideration the stretching ratio in the stretching region SA. For example, when the stretching ratio is 5 times, when the length of the resin sheet 100 in the longitudinal direction (transport direction) before stretching is 100, the length after stretching is 500. Here, the rate of relaxation can be calculated with respect to the length after stretching when the length before stretching of 100 is used as the standard. Therefore, the rate of relaxation at this time can be calculated as a percentage (%) of 500, such as 15 to 60 (3 to 12%) or 25 to 50 (5 to 10%).

[0054] Furthermore, for example, when the stretching ratio is 3 times, if the length of the resin sheet 100 in the longitudinal direction (transport direction) before stretching is 100, the length after stretching is 300. When calculated in the same manner as above, the relaxation rate at this time can be calculated as a percentage (%) of 300 to be 9 to 36 (3 to 12%) or 15 to 30 (5 to 10%).

[0055] To obtain the relaxation rate in the above example, the peripheral speed of the rolls may be set to a speed corresponding to the relaxation rate. For example, when the peripheral speed of the roll R9 in the stretching region SA is 10 m / min, the peripheral speed of the roll R10 is 50 m / min, and the stretch ratio is 5 times, the peripheral speed of the rolls R11 and R12 is slowed down by the relaxation rate, as calculated above, to preferably 48.5 to 44.0 m / min (relaxation rate: 3 to 12%), and more preferably 47.5 to 45.0 m / min (relaxation rate: 5 to 10%).

[0056] To perform the relaxation, it is preferable to maintain the temperature of the rolls R11 to R12 in the relaxation region RA at a temperature that facilitates relaxation. This temperature can be determined according to the α-relaxation temperature of the polyethylene that constitutes the resin sheet 100. Here, the α-relaxation temperature is the temperature that causes α-relaxation (α-dispersion) of the polyethylene, and can also be said to be the temperature at which the crystals of the polyethylene are relaxed. The α-relaxation temperature of polyethylene is about 0 to 100°C, and among these, the relaxation temperature in this embodiment is preferably in the range of, for example, 45 to 100°C, more preferably in the range of 50 to 100°C, and even more preferably in the range of 60 to 100°C.

[0057] After the stretching and relaxation processes, the resin sheet 100 can be fixed by lowering the temperature of the stretched resin sheet 100 using a cooling roll through which cooling water flows, and then transported to a downstream device by the cooling roll. In this embodiment, the feed roll FR may be a cooling roll, or, as described above, a cooling roll for fixing the resin may be additionally provided after the relaxation region RA. EXAMPLES

[0058] The resin sheet stretching apparatus and method according to the present embodiment will be described in detail below using examples and comparative examples.

[0059] (Comparative Example 1, Examples 1-2) The extrusion molding system shown in Figure 1 was prepared. First, a raw material consisting of LLDPE-BX202 (product name, manufactured by Sabic Corporation) mixed with 3.75 mass% of migratory slip agent M24201 was fed into the cylinder from the raw material feeder Ta, and the raw material was melted and transported while being heated to about 230°C inside the cylinder, and the molten resin was extruded into a sheet shape from the T-die S2 provided at the tip of the twin-screw kneading extruder S1.

[0060] The extruded molten resin was fixed into a sheet shape by a raw sheet cooling device (CAST device) S3 with a roll temperature of 25° C. and a water temperature of 30° C., to obtain a resin sheet 100 with a thickness of about 1350 μm.

[0061] Next, the obtained resin sheet 100 was stretched by a longitudinal stretching device (MD device) S4 and a transverse stretching device (TD device) S5, and a resin film having a thickness of about 30 μm was taken up by a winding device S6.

[0062] At this time, as the longitudinal stretching device (MD device) S4, stretching was performed in the longitudinal direction (transport direction) using the stretching device 1 having the configuration shown in Fig. 2. Here, the stretching process was performed under the temperature conditions shown in Fig. 3, by controlling each roll at the peripheral speed shown below.

[0063] First, in Comparative Example 1, the device configuration (roll configuration) was the same as in Fig. 2, but treatment was performed under conditions in which the relaxed region RA did not exist. That is, the peripheral speed of the rolls R1 to R9 was 10 m / min, and the peripheral speed of the rolls R10 to R12 was 45 m / min. That is, the magnification in the machine direction (MD) was 4.5 times.

[0064] In addition, in Examples 1 and 2, the peripheral speeds of rolls R1 to R9 were set to 10 m / min, the peripheral speed of roll R10 was set to 45 m / min, and the peripheral speeds of rolls R11 to R12 were set to 40.5 m / min to provide a relaxation region RA.

[0065] In the above-mentioned Comparative Example 1 and Examples 1 and 2, after the longitudinal stretching, transverse stretching at a ratio of 9 times was subsequently carried out by a transverse stretching device (TD device) S5 to obtain a resin film.

[0066] (Examples 3 to 4) In Examples 3 and 4, the longitudinal stretching ratio was set to 5 times that of Examples 1 and 2. That is, in Examples 3 and 4, the peripheral speeds of rolls R1 to R9 were set to 10 m / min, the peripheral speed of roll R10 was set to 50 m / min, and the peripheral speed of rolls R11 and R12 was set to 45 m / min, and the stretching ratio in the longitudinal direction (MD) was set to 5.0 times, and other than these, resin films were produced in the same manner as in Examples 1 and 2.

[0067] [Test example] The effective width of the resin film obtained above was examined.

[0068] This effective width can be calculated by measuring the width where the thickness of the obtained resin film is within ±3% of the target thickness, and calculating the ratio of the measured value to the total width of the obtained resin film. Here, the calculated value in Comparative Example 1 is set to 1.0 (reference value), and the effective width ratios in the following Examples are calculated and shown in Table 1 below.

[0069] [Table 1]

[0070] From the above results, it was found that the effective width of the resin film can be increased by performing a relaxation treatment after stretching. It was also found that the effective width can be further increased by setting the treatment temperature of the relaxation treatment after stretching to a high temperature within the range of the relaxation temperature.

[0071] That is, it was found that by applying the resin sheet stretching method and stretching device of the present embodiment, a resin film having a more stable thickness and a wider effective width can be obtained more efficiently than ever before.

[0072] 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]

[0073] 1...stretching device, 2...control section, 21...signal wiring, 100...resin sheet, R1 to R12...rolls, RA...relaxation region, SA...stretching region

Claims

1. A method for stretching a resin sheet, comprising: (a) stretching the polyethylene resin sheet in a first direction by a first roll disposed in a stretching region; and (b) after the step (a), relaxing the stretched resin sheet in a direction opposite to the first direction by a second roll disposed in a relaxation region.

2. The method for stretching a resin sheet according to claim 1, A method for stretching a resin sheet, wherein in the step (b), the relaxation is performed by making the peripheral speed of the second roll, of the first roll and the second roll adjacent to each other, slower than the peripheral speed of the first roll.

3. The method for stretching a resin sheet according to claim 2, The method for stretching a resin sheet, wherein the resin sheet after the stretching is relaxed at a rate of 3 to 12%.

4. The method for stretching a resin sheet according to claim 1, The method for stretching a resin sheet, wherein the relaxation is performed by maintaining a temperature of the second roll at a temperature at which α relaxation can occur for the polyethylene.

5. The method for stretching a resin sheet according to claim 4, The method for stretching a resin sheet is carried out while maintaining the temperature of the second roll at 45 to 100°C.

6. A resin sheet stretching device, comprising: a first roll disposed in a stretching region for stretching the polyethylene resin sheet in a first direction; A second roll disposed in a relaxation region for relaxing the resin sheet stretched in the stretching region in a direction opposite to the first direction; and A control unit controls a peripheral speed of the first roll and a peripheral speed of the second roll so as to relax the resin sheet.

7. The resin sheet stretching apparatus according to claim 6, The control unit controls the peripheral speed of the second roll, which is adjacent to the first roll and the second roll, to be slower than the peripheral speed of the first roll.

8. The resin sheet stretching apparatus according to claim 7, The control unit controls the peripheral speeds of the first roll and the second roll so as to relax the resin sheet after the stretching by 3 to 12%.

9. The resin sheet stretching apparatus according to claim 6, The control unit controls the temperature of the second roll so as to maintain the temperature at a temperature at which α relaxation can occur for the polyethylene.

10. The resin sheet stretching apparatus according to claim 9, The control unit controls the temperature of the second roll to be maintained at 45 to 100° C.

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