JP7658208B2 - Manufacturing method and manufacturing device for microporous polyolefin resin sheet - Google Patents

Description

The present invention relates to a method and an apparatus for producing a microporous polyolefin resin sheet.

First, a typical method for manufacturing a microporous polyolefin resin sheet will be described with reference to FIG. 7. FIG. 7 is a schematic diagram of a typical manufacturing apparatus for a microporous polyolefin resin sheet. As shown in FIG. 7, a sheet material 3, which is a mixture of polyolefin resin and a diluent, is discharged from a discharge port 5 of a die 1 toward a casting device 2, a reduced pressure space 9 between the sheet material 3 and the casting device 2 is covered with a reduced pressure chamber 4 provided upstream of the discharge port 5 in the sheet conveying direction, air is sucked from the reduced pressure chamber 4 through an opening 8 of the reduced pressure chamber 4 formed outside both ends of the sheet material 3 in the sheet width direction to bring the sheet material 3 into close contact with the casting device 2, and the sheet material 3 is cooled and solidified while being conveyed by the casting device 2 in a sheet manufacturing method.

Incidentally, a resin sheet manufacturing device disclosed in Patent Document 1 is a technology that appears to be similar at first glance to a preferred embodiment of the present invention. Patent Document 1 discloses a resin sheet manufacturing device that is provided with a straightening plate near the end of the sheet material in order to suppress thickness unevenness caused by membrane vibration of the sheet material. See Figure 8. Figure 8 is an arrow view observed from above in the height direction of the resin sheet manufacturing device of Patent Document 1. As shown in Figure 8, the straightening effect of the straightening plate 6 suppresses the formation of vortexes at the end of the sheet material 3, suppressing membrane vibration of the sheet material and reducing thickness unevenness of the resin sheet.

Japanese Patent Application Publication No. 10-180847

In recent years, there has been a strong demand for thinner resin sheets as products in which they are used become smaller and lighter. However, when a resin sheet is made thinner, the position at which the sheet discharged from the nozzle lands on the casting device is more likely to change when the pressure inside the decompression chamber fluctuates due to external factors such as pulsation of the blower air volume or temperature fluctuations between day and night. When the sheet position changes, the sheet material comes into contact with the side walls of the decompression chamber, causing the sheet to tear.

However, the above-mentioned Patent Document 1 does not disclose seat tearing caused by changes in seat position or a method for preventing this.

Therefore, the present invention provides a method and apparatus for producing a microporous polyolefin resin sheet that can stably produce sheets by suppressing changes in sheet position caused by pressure fluctuations in a decompression chamber.

The method for producing a microporous polyolefin resin sheet of the present invention, which solves the above problems, comprises discharging a sheet material, which is a mixture of a polyolefin resin and a diluent, from an outlet of a die toward a casting device, covering a reduced pressure space between the sheet material and the casting device with a reduced pressure chamber provided upstream of the outlet in the sheet transport direction, sucking air from within the reduced pressure chamber to bring the sheet material into close contact with the casting device, and cooling and solidifying the sheet material while transporting it with the casting device,
The air in the decompression chamber is sucked through an opening of the decompression chamber formed on the outer side of both ends of the sheet material in the sheet width direction,
Let H be the shortest distance from the discharge outlet to the outer peripheral surface of the casting device, and S1 be the area of the opening downstream of the sheet material in the sheet conveying direction when observing the opening from the outside in the sheet width direction, and 0<S1/ ^H2 ≦0.33.

In the method for producing a microporous polyolefin resin sheet of the present invention, when the cross-sectional area of the decompression space when the decompression chamber is observed from the outside in the sheet width direction is taken as M1, it is preferable that M1/H ² ≦2.0.

In the method for producing a microporous polyolefin resin sheet of the present invention, it is preferable that the decompression chamber is provided with a shielding plate that partially covers the opening, and S1 is adjusted by changing the area that the shielding plate covers the opening.

In the method for producing the microporous polyolefin resin sheet of the present invention, it is preferable to control the area that the shielding plate covers the opening based on the position of the sheet material.

The present invention provides a microporous polyolefin resin sheet manufacturing apparatus that solves the above problems, the apparatus comprising: a die for discharging a sheet material, which is a mixture of a polyolefin resin and a diluent, from an outlet; a casting device for cooling and solidifying the sheet material discharged from the outlet while conveying the sheet material; and a decompression chamber that is provided upstream of the outlet in the sheet conveying direction and covers a decompressed space between the sheet material and the casting device,
A hypothetical sheet material flow from the discharge port to the casting device during sheet production is defined as a virtual sheet material.
The decompression chamber is
An opening for sucking air from within the decompression chamber is formed at a position on the outer side of both ends of the virtual sheet material in the sheet width direction,
The shortest distance from the discharge outlet to the outer peripheral surface of the casting device is H, and when the opening is observed from the outside in the sheet width direction, the area of the opening downstream of the virtual sheet material in the sheet conveying direction is S1. The arrangement is such that 0<S1/ ^H2 ≦0.33.

In the manufacturing apparatus for the microporous polyolefin resin sheet of the present invention, the decompression chamber is preferably arranged so that, when the cross-sectional area of the decompression space observed from the outside in the sheet width direction is M1, M1/H2 ^≦ 2.0 is satisfied based on the virtual sheet material.

In the microporous polyolefin resin sheet manufacturing apparatus of the present invention, it is preferable that the decompression chamber is provided with a shielding plate that partially covers the opening, and the S1 can be adjusted by changing the area that the shielding plate covers the opening.

The microporous polyolefin resin sheet manufacturing apparatus of the present invention is preferably equipped with a displacement meter that measures the position of the sheet material.

[Terminology]
Next, the meaning of each term in the present invention will be explained.
The "sheet material" is a material that constitutes a sheet. As the sheet material, for example, a polyolefin solution resin prepared by mixing a polyolefin resin such as polyethylene, polypropylene, polystyrene, or polymethylpentene with a diluent and heating and melting it can be used. The diluent is not particularly limited as long as it is a substance that can be mixed or dissolved in the polyolefin resin. A solvent that is miscible with the polyolefin in a melt-kneaded state but is solid at room temperature may be mixed with the diluent. Examples of such solid diluents include stearyl alcohol, ceryl alcohol, and paraffin wax. In order to prevent spots during stretching, and in consideration of subsequent application, it is preferable that the diluent is liquid at room temperature. Examples of liquid diluents include aliphatic, cycloaliphatic, or aromatic hydrocarbons such as nonane, decane, decalin, paraxylene, undecane, dodecane, and liquid paraffin, and mineral oil fractions whose boiling points correspond to these, as well as phthalic acid esters that are liquid at room temperature, such as dibutyl phthalate and dioctyl phthalate. In order to obtain a gel-like sheet with a stable content of the liquid diluent, it is more preferable to use liquid paraffin. For example, the viscosity of the liquid diluent is preferably 20 to 200 cSt at 40° C. The blending ratio of the polyolefin resin and the diluent is preferably 10 to 50 mass% of the polyolefin resin, with the total of the polyolefin resin and the diluent being 100 mass%, from the viewpoint of improving the moldability of the extrudate. The homogeneous melt-kneading process of the polyolefin solution is not particularly limited, but examples thereof include a calendar, various mixers, and an extruder with a screw.

The term "casting device" refers to a device that conveys a sheet material discharged from a nozzle of a die downstream while cooling and solidifying it by tightly contacting the material. The form of the casting device is not particularly limited, but examples thereof include rolls and belts.
The term "width direction" refers to the direction that coincides with the width direction of the sheet material when it is formed into a sheet by a die.
The term "sheet conveying direction" refers to the direction in which the casting device conveys the sheet. The conveying destination is the downstream side, and the opposite side is the upstream side.
"Reduced pressure space" refers to a space formed between the sheet material and the casting device, which is covered with a reduced pressure chamber and is under negative pressure.
The term "vacuum chamber" refers to a device that covers a vacuum space and reduces the pressure to bring the sheet material into close contact with the casting device. In general, the pressure in the vacuum chamber is -1500 Pa or more and -50 Pa or less with respect to atmospheric pressure. The pressure in the vacuum chamber may be controlled according to the film forming conditions.

The "opening" refers to a part of the vacuum chamber that is connected to a suction device and sucks air from inside the vacuum chamber. The shape of the opening is not particularly limited, but examples thereof include a square, a rectangle, a trapezoid, a circle, and an ellipse. The opening may be subjected to a surface treatment such as nickel plating, chrome plating, or zinc plating. The suction device is not particularly limited, but examples thereof include a blower and a vacuum pump.
The term "shielding plate" refers to a member that partially covers an opening. The shape of the shielding plate is not particularly limited, but examples include a plate material and a punched material with holes.
The "virtual sheet material" is a projection of the flow of sheet material from the discharge outlet to the casting device during sheet production, and the sheet width of the virtual sheet material, the position where it lands on the casting device, and the trajectory from the discharge outlet to the casting device change depending on the production conditions.
The "side wall" refers to a portion of the decompression chamber that covers the surface of the decompression space perpendicular to the sheet width direction.

By using the polyolefin resin sheet manufacturing method and manufacturing device of the present invention, sheet position changes due to pressure fluctuations in the decompression chamber can be suppressed, sheet rupture can be suppressed, and sheets can be manufactured stably.

1 is a view of the apparatus for producing a microporous polyolefin resin sheet of the present invention, as viewed from the sheet width direction. FIG. 2 is a cross-sectional view perpendicular to the height direction along the line XX in FIG. 1. FIG. 1 is a view of a typical apparatus for producing a microporous polyolefin resin sheet, as viewed from the sheet width direction. 4 is a cross-sectional view perpendicular to the height direction along the line ZZ in FIG. 3. FIG. 2 is an arrow view of the production apparatus for a microporous polyolefin resin sheet of the present invention, observed from the sheet width direction, showing a reduced pressure space. 1 is a view of a polyolefin resin sheet production apparatus of the present invention equipped with a shielding plate, as viewed from the sheet width direction. FIG. 1 is a schematic diagram of a typical production apparatus for a microporous polyolefin resin sheet. 1 is a view of the resin sheet manufacturing apparatus of Patent Document 1 as seen from above in the height direction. 11 is a graph showing S1/ ^H2 and seat position change in each example and each comparative example.

The manufacturing method and production method of the polyolefin resin sheet of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to the embodiments described here. Note that components having the same uses and functions as those in the conventional technology may have the same reference numerals. Each dimension will be described with reference to Figures 1 and 2. Figure 1 is an arrow view of the manufacturing device of the polyolefin resin sheet of the present invention observed from the sheet width direction, and Figure 2 is a cross-sectional view perpendicular to the height direction along line X-X in Figure 1. When observing the opening 8 from the outside in the sheet width direction, the area of the part that is open downstream of the sheet material 3 in the sheet conveying direction is designated by symbol S1, and the shortest distance from the discharge port of the die 1 to the outer circumferential surface of the casting device 2 is designated by symbol H.

First, referring to Figures 3 and 4, we will explain the change in sheet position due to pressure fluctuations in the decompression chamber 4. Figure 3 is an arrow view of a typical polyolefin resin sheet manufacturing device observed from the sheet width direction, and Figure 4 is a cross-sectional view perpendicular to the height direction along line Z-Z in Figure 3. When the negative pressure in the decompression chamber 4 becomes stronger due to an external factor, the sheet material 3 is pulled upstream in the sheet conveying direction and moves from position A to position B. Then, the edge of the sheet material 3 comes into contact with the upstream edge 8a of the opening 8 in the sheet conveying direction or the side wall 4a of the decompression chamber 4, causing the sheet to tear.

As a result of repeated experiments and theoretical calculations, the inventors have found that by reducing S1, the sheet position change due to pressure fluctuations in the decompression chamber 4 can be suppressed. With reference to FIG. 2, the sheet position change due to pressure fluctuations in the decompression chamber 4 in the polyolefin resin sheet manufacturing apparatus of the present invention in which S1 is small will be described. S1 increases when the sheet material 3 moves upstream in the sheet conveying direction. Then, the flow resistance of the opening 8 decreases according to the increase rate of S1, and the suction pressure of the suction device (not shown) that sucks air also becomes weaker. As a result, the negative pressure in the decompression chamber 4 also becomes weaker. When S1 is large as in a general polyolefin resin sheet manufacturing apparatus, the increase rate of S1 due to the movement of the sheet material 3 is small, and the effect on the negative pressure in the decompression chamber 4 is also small. On the other hand, when S1 is small as in the polyolefin resin sheet manufacturing apparatus of the present invention, the increase rate of S1 is large, and the negative pressure in the decompression chamber 4 is also significantly weakened. As a result, the sheet material 3 tries to return to position A before moving to position B, so that the sheet position change due to pressure fluctuations in the decompression chamber 4 can be suppressed.

Here, the inventors further conducted experiments and theoretical calculations and found that by setting 0<S1/H ² ≦0.33, the sheet position change due to the pressure fluctuation in the decompression chamber 4 can be suppressed and sheet breakage can be prevented. When S1=0, that is, when there is no opening in the opening 8 downstream of the sheet material in the sheet conveying direction, the flow resistance of the opening 8 does not change much even if the sheet material 3 moves, so the influence on the suction pressure of the suction device and the negative pressure in the decompression chamber 4 is also small. In addition, since the amount of position change of the sheet material 3 due to the negative pressure in the decompression chamber 4 depends on H, the range in which the effect of the present invention can be obtained is defined by S1 normalized by H. More preferably, 0<S1/H ² ≦0.20. The range of H is not particularly limited, but if the opening 8 is too small, foreign matter and the like are easily clogged, so in reality, H is preferably 10 mm or more.

FIG. 5 is an arrow view of the polyolefin resin sheet manufacturing apparatus of the present invention observed from the sheet width direction, showing the reduced pressure space. In reality, the reduced pressure space is blocked by the side wall of the reduced pressure chamber 4, but the figure is of the reduced pressure space without the side wall. As shown in FIG. 5, when the cross-sectional area of the reduced pressure space is M1 when observed from the outside in the sheet width direction, it is preferable that M1/H ² ≦2.0 in the polyolefin resin sheet manufacturing method of the present invention. Even if M1/H ² is larger than 2.0, the effect of the present invention can be obtained, but by making M1/H ² ≦2.0, the effect of the reduction in the suction pressure of the suction device is transmitted to the entire inside of the reduced pressure chamber 4 in a short time, and the sheet position change can be further suppressed. More preferably, M1/H ² ≦1.7. The lower limit of M1/H ² is not particularly limited, but if M1 is too small, the negative pressure in the reduced pressure chamber 4 becomes non-uniform in the width direction, so that M1/H ² is preferably 1.3 or more in reality.

In the polyolefin resin sheet manufacturing method of the present invention, it is preferable to adjust S1 by changing the area that the shielding plate covers the opening. See Figure 6. Figure 6 is an arrow view of the polyolefin resin sheet manufacturing apparatus of the present invention equipped with a shielding plate 7, observed from the sheet width direction. S1 can be adjusted by moving the shielding plate 7 in the sheet conveying direction to change the area that covers the opening 8. Even if the position of the sheet material 3 changes due to a change in conditions, etc., S1 can be adjusted to an appropriate range without modifying the apparatus.

In the method for producing a polyolefin resin sheet of the present invention, it is preferable to control the area that the shielding plate 7 covers the opening based on the position of the sheet material 3. Even if the position of the sheet material 3 changes during film formation due to the environmental temperature, resin state, etc., S1 can be maintained within an appropriate range by controlling the area that the shielding plate 7 covers the opening 8 based on the position of the sheet material 3.

The polyolefin resin sheet manufacturing apparatus of the present invention is preferably equipped with a displacement meter (not shown) for measuring the position of the sheet material. The displacement meter and the shielding plate 7 may be connected to a control device (not shown), and automatic control may be performed so that the position of the shielding plate 7 is controlled by the control device in response to a signal indicating the position of the sheet material from the displacement meter.

An example of polyolefin resin sheet production using the polyolefin resin sheet production method of the present invention is shown below. Here, the area of the opening downstream of the sheet material in the sheet conveying direction when observed from the outside in the sheet width direction is S1 [ ^mm2 ], the shortest distance from the nozzle outlet to the outer peripheral surface of the casting device is H [mm], and the cross-sectional area of the reduced pressure space when observed from the outside in the sheet width direction is M1 [ ^mm2 ].

[Example 1]
A polyolefin resin sheet was actually produced using the polyolefin resin sheet production method of the present invention shown in Fig. 1, and the results of evaluating the amount of sheet position change due to pressure fluctuation will be described. The specific sheet production conditions in this embodiment are as follows.

(1) Sheet material:
High density polyethylene (HDPE): Viscosity 1000 Pa·s. Here, the viscosity was measured at a shear rate of 100/s and a temperature of 200° C. according to the method of JIS K7117-2.
Liquid paraffin (LP): kinetic viscosity of 50 cSt (at 40° C. mm ² /s).
The mixing ratio of HDPE and LP was HDPE:LP = 30:70 by mass.

(2) Extrusion:
The sheet material was extruded at a flow rate of 250 kg/hr using an extruder, passed through a gear pump and a filter, and then fed to a die. The temperature of the device up to the die was 220° C.

(3) Base:
The sheet material was discharged from a discharge port having a width of 500 mm and a gap of 2 mm, and formed into a sheet.

(4) Casting device:
The sheet was brought into close contact with a sheet forming roll rotating at a speed of 10 m/min at a temperature of 35° C., and then cooled and solidified. The discharge port of the die was located directly above the center of the sheet forming roll at a position where H was 40 mm.

(5) Decompression chamber:
The decompression chamber was installed upstream of the nozzle outlet in the conveying direction, and had a shape that covered the space between the sheet material discharged from the outlet and the cast device, with M1 being 3,400 ^mm2 and M1/ ^H2 = 2.1. The opening was a rectangle with the long side in the horizontal direction, with the long side being 70 mm and the short side being 32 mm, the distance from the nozzle outlet to the upper edge of the opening being 3 mm, and the distance from the lower edge of the opening to the sheet forming roll being 5 mm. The inside of the decompression chamber was suctioned to -400 Pa by a blower connected to the opening, with S1 being 320 ^mm2 and S1/ ^H2 = 0.20.

(6) Sheet Position Change The pressure in the decompression chamber was forcibly changed to -600 Pa, and the distance by which the position where the sheet material landed on the casting device moved upstream in the sheet conveying direction (hereinafter referred to as the sheet position change) was measured, and the result was 7.5 mm.

[Examples 2 to 5, Comparative Examples 1 to 4]
A sheet was produced by the same polyolefin resin sheet production method as in Example 1, except that the dimensions of the decompression chamber were changed as shown in Tables 1 and 2.
Tables 1 and 2 show the dimensions of the decompression chamber and the amount of change in seat position in each of the examples and comparative examples.

[Evaluation Results]
The relationship between S1/ ^H2 and the amount of seat position change in each example and comparative example will be described with reference to Fig. 9. Fig. 9 is a graph showing the amount of seat position change in each example and comparative example. The horizontal axis is S1/ ^H2 , the vertical axis is the amount of seat position change, ◯ is Examples 1 to 5, × is Comparative Examples 1 to 4, and the area within the dotted line is the range 0<S1/ ^H2 ≦0.33.

In the polyolefin resin sheet manufacturing methods of Examples 1 to 4, since 0<S1/H ² ≦0.33, the negative pressure in the decompression chamber was significantly weakened by the movement of the sheet material, and the amount of sheet position change was suppressed to 3.3 to 9.2 mm.

In the polyolefin resin sheet manufacturing method of Example 5, S1/ ^H2 was the same as in Example 1, but since M1/H2 was ^≦ 2.0, the effect of the decrease in suction pressure of the suction device was transmitted to the entire inside of the decompression chamber 4 in a short time, and the amount of change in the sheet position was suppressed to 5.1 mm from 7.5 mm in Example 1.

In the polyolefin resin sheet manufacturing method of Comparative Example 1, the sheet position change amount was large at 38.6 mm because S1/ ^H2 = 0. Note that, until the sheet position moved 38.6 mm, no sheet material was observed from the opening, and S1/ ^H2 = 0 remained.

In the polyolefin resin sheet manufacturing methods of Comparative Examples 2 to 4, S1/H ² >0.33, and therefore the sheet position change amount was large, ranging from 33.3 to 38.2 mm.

The present invention is not limited to polyolefin resin sheet manufacturing apparatus and manufacturing method, but can also be applied to solution resin sheet manufacturing apparatus and manufacturing method, die coating, etc., but the scope of application is not limited to these.

REFERENCE SIGNS LIST 1 die 2 casting device 3 sheet material 4 reduced pressure chamber 4a side wall 5 discharge port 6 straightening plate 7 shielding plate 8 opening 8a upstream end of opening in sheet conveying direction 9 reduced pressure space

Claims (8)

A sheet material containing a mixture of polyolefin resin and a diluent is discharged from a discharge port of a die toward a casting device,
a decompression chamber provided upstream of the discharge port in a sheet conveying direction covers a decompression space between the sheet material and the casting device;
A method for manufacturing a sheet, comprising the steps of: sucking air from within the decompression chamber to bring the sheet material into close contact with the casting device; and cooling and solidifying the sheet material while transporting it with the casting device,
The air in the decompression chamber is sucked through an opening of the decompression chamber formed on the outer side of both ends of the sheet material in the sheet width direction,
When the shortest distance from the discharge port to the outer peripheral surface of the casting device is H, and the area of the opening at the downstream side of the sheet material in the sheet conveying direction when the opening is observed from the outside in the sheet width direction is S1, 0<S1/ ^H2 ≦0.33 is satisfied.
A method for producing a microporous polyolefin resin sheet. The method for producing a microporous polyolefin resin sheet according to claim 1 , wherein M1/H ² ≦2.0 is satisfied, where M1 is a cross-sectional area of the decompression space when the decompression chamber is observed from the outside in the sheet width direction. the decompression chamber includes a shielding plate that partially covers the opening;
The method for producing a microporous polyolefin resin sheet according to claim 1 or 2, wherein the S1 is adjusted by changing an area of the shielding plate covering the opening. The method for producing a microporous polyolefin resin sheet according to claim 3, wherein the area that the shielding plate covers the opening is controlled based on the position of the sheet material. a die for discharging the sheet material, in which the polyolefin resin and the diluent are mixed, from a discharge port;
a casting device for cooling and solidifying the sheet material discharged from the discharge port while conveying the sheet material;
a decompression chamber provided upstream of the discharge port in a sheet conveying direction and covering a decompression space between the sheet material and the casting device,
A virtual sheet material is defined as an expected flow of the sheet material from the discharge outlet to the casting device during the production of the sheet.
The vacuum chamber comprises:
An opening for sucking air from within the decompression chamber is formed at a position on the outer side of both ends of the virtual sheet material in the sheet width direction,
The shortest distance from the discharge port to the outer peripheral surface of the casting device is H, and the area of the opening at the downstream side of the virtual sheet material in the sheet conveying direction when the opening is observed from the outside in the sheet width direction is S1. The casting device is arranged so that 0<S1/ ^H2 ≦0.33.
Manufacturing equipment for microporous polyolefin resin sheets. The microporous polyolefin resin sheet manufacturing apparatus according to claim 5, wherein the decompression chamber is disposed so that M1/ ^H2 ≦2.0 based on the virtual sheet material, where M1 is a cross-sectional area of the decompression space observed from the outside in the sheet width direction. the decompression chamber includes a shielding plate that partially covers the opening;
The apparatus for producing a microporous polyolefin resin sheet according to claim 5 or 6, wherein the S1 can be adjusted by changing the area of the shielding plate covering the opening. The microporous polyolefin resin sheet manufacturing device according to any one of claims 5 to 7, which is equipped with a displacement meter for measuring the position of the sheet material.

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