JP2002370279A - Polytetrafluoroethylene sheet and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polytetrafluoroethylene(PTFE) sheet having stable physical properties by suppressing occurrence of a strength unevenness of the PTFE sheet in a rolling step to a minimum limit. SOLUTION: A method for manufacturing the PTFE sheet comprises the steps of setting a value of (a thickness of a PTFE extrudate 1 before rolling)/(a thickness of PTFE sheet 2 after rolling) to 10 or less, in a rolling step of rolling the PTFT extrudate 1 obtained by extrusion molding a preform containing the PTFE and a lubricant in an extruding direction by using pressure rollers 3, and setting a value of (a width of the PTFE extrudate 1 after rolling)/(a width of the PTFE sheet 2 before rolling) to 1.1 or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polytetrafluoroethylene (hereinafter referred to as "PTFE") sheet and a method for producing the same. More specifically, the present invention relates to a PTFE sheet useful as a porous film, a sealing tape, etc. It relates to a manufacturing method.

[0002]

2. Description of the Related Art PTFE sheets are widely used as base materials for porous membranes, seal tapes, and adhesive tapes. In each of such applications, the stretchability of the PTFE sheet is used. The PTFE sheet is produced by the following procedure.

[0003] First, PTFE fine powder and a lubricant are mixed and molded at an appropriate pressure to obtain a preform.
Next, the preform is extruded while passing through an orifice to obtain a PTFE extruded product which is drawn into a rod shape or a ribbon shape. Next, the extruded PTFE is rolled using one or more rolling rolls in the extrusion direction to obtain a sheet-shaped molded product (PTFE sheet).

[0004] The PTFE sheet thus produced has high stretchability. Therefore, by stretching this PTFE sheet uniaxially or biaxially at an arbitrary magnification, it can be used for various applications such as a sealing tape and a porous film. At this time, to make the distribution of physical properties such as strength in all axial directions of the PTFE sheet uniform,
It is effective for stabilizing the physical properties of various products obtained from the TFE sheet.

Japanese Patent Publication No. 42-14178 discloses a PTFE having substantially equal elongation in all directions.
A method of making an extrudate is disclosed. In this manufacturing method, depending on the shape of a die for obtaining an extruded PTFE, P
It stabilizes the physical properties of the TFE extrudate. JP-A-11-216760 discloses a PTFE extruded product in which local unevenness in strength characteristics in a sheet surface is reduced, and a method for producing the same.

[0006] The extruded PTFE produced by these methods has uniform strength and elongation in each direction, but cannot be subjected to the stretching step because the strength in the extrusion direction is low as it is. So, this PTF
E It is necessary to roll the extrudate using one or more rolls so that the thickness becomes 1 mm or less. By this rolling step, the small fibers are appropriately oriented in the extrusion direction in the PTFE sheet, and the strength that can withstand the stretching is generated. If the stretching step is performed without passing through the rolling step, the PTFE sheet is not sufficiently stretched and breaks due to insufficient strength in the extrusion direction. As described above, the rolling step is an important step that greatly affects the physical properties of the PTFE sheet, like the extrusion step.

[0007]

The PTFE sheet manufactured by the method disclosed in the above publication is certainly PTFE.
In the extrudate stage, the strength and elongation are made uniform. However, there is a problem that the variation in strength is increased by the subsequent rolling process. A PTFE sheet having a variation in strength has non-uniform physical properties when stretched, and is not sufficiently stretched to be broken.

[0008] The present invention has been made in order to solve the above problems.
An object of the present invention is to obtain a PTFE sheet having stable physical properties while minimizing the occurrence of a variation in the strength of the PTFE sheet in the rolling step.

[0009]

In order to achieve the above object,
The present inventors have conducted intensive studies and found that the strength variation in the sheet width direction of the PTFE sheet is caused by the flow of the PTFE resin in the sheet width direction during rolling. That is, when the PTFE extruded product is rolled, the PTFE resin flows not only in the extrusion direction but also in the sheet width direction to spread the sheet width. However, the flow of the PTFE resin in the sheet width direction is not restricted at all. It is an unstable thing that cannot be done. As a result, the flow of the PTFE resin in the sheet width direction becomes non-uniform, and the strength varies in the sheet width direction.

[0010] In order to suppress the occurrence of strength variation due to the flow of the PTFE resin in the sheet width direction, the method of manufacturing a PTFE sheet of the present invention extrudes a preform containing PTFE and a lubricant. In the method for producing a PTFE sheet including a rolling step of rolling the obtained PTFE extrudate in the extrusion direction, (width of PTFE sheet after rolling) / (PTFE before rolling)
(Width of extruded product) is defined as 1.1 or less before and after rolling.

[0011] By setting the rate of width change before and after rolling to 1.1 or less as in the above method, the PTF during rolling is reduced.
The flow of the E resin in the sheet width direction can be minimized. As a result, variation in strength in the sheet width direction due to the flow of the PTFE resin in the sheet width direction can be minimized, so that a PTFE sheet having stable physical properties in the sheet width direction can be obtained. Also, PT
By stabilizing the physical properties of the FE sheet, the PT
The physical properties of the product obtained from the FE sheet are also stabilized.

Further, in order to suppress the occurrence of variation in strength due to the flow of the PTFE resin in the sheet width direction, a method of manufacturing a PTFE sheet according to the present invention comprises extruding a preform containing PTFE and a lubricant. In the method for producing a PTFE sheet including a rolling step of rolling the PTFE extruded product obtained in the above step in the extrusion direction, (thickness of PTFE extruded product before rolling) / (PT after rolling)
(Thickness of FEE sheet) may be used in which the rate of change in thickness before and after rolling is 10 or less.

By setting the rate of change in thickness before and after rolling to 10 or less as in the above method, the rate of change in width before and after rolling can be kept low, and the flow of PTFE resin in the sheet width direction can be reduced. . As a result, a PTFE sheet having stable physical properties in the sheet width direction can be obtained in the same manner as the method of setting the width change rate before and after rolling to 1.1 or less, and the physical properties of a product obtained from this PTFE sheet are also stabilized. The Rukoto.

Further, as an index indicating the intensity variation,
For example, an intensity variation rate is used. The intensity variation rate is obtained by taking samples at a plurality of points in the sheet width direction and using measured values of the intensity. Here, the rate of change in intensity at a plurality of points is defined as [(standard deviation of intensity) / (average value of intensity)] × 100.

[0015] The PTFE sheet of the present invention is a PTFE sheet produced by rolling an extruded PTFE extrudate, and has a strength variation rate in the sheet width direction of 10% or less. I do.

According to such a configuration, since the variation in strength in the sheet width direction is sufficiently reduced, the physical properties of the PTFE sheet are stabilized. Thereby, the physical properties of the product obtained from the PTFE sheet can be stabilized.

[0017]

An embodiment of the present invention will be described below with reference to the drawings.

In the method of manufacturing a PTFE sheet according to the present embodiment, first, a PTFE extruded product is prepared. Specifically, PTFE fine powder is mixed with a lubricant,
A preform is obtained by molding at an appropriate pressure, and the preform is extruded while passing through an orifice to produce a PTFE extrudate drawn in a rod shape or a ribbon shape. Although the shape of the PTFE extruded product is not particularly specified, the rate of width change before and after the rolling in the subsequent rolling process is 1.1.
In order to achieve the following, the cross section is preferably a rectangle rather than a circle, and more preferably a ribbon having a width that is at least 5 times larger than the thickness.

The PTFE extrudate produced as described above is rolled into a sheet using a one-stage or multi-stage rolling roll while containing a lubricant. FIGS. 1 and 2 are schematic diagrams showing the state of the rolling process.

FIG. 1 shows a PT roll using a one-stage rolling roll.
The state of single-step rolling of rolling the FE extrudate is shown. As shown in FIG. 1, the PT before rolling having a rectangular cross section
The FE extruded product 1 is rolled in the extrusion direction by a pair of rolling rolls 3 arranged so that the axial direction is orthogonal to the extrusion direction, and becomes a PTFE sheet 2. The illustrated rolling direction corresponds to the extrusion direction of the PTFE extrudate 1.

FIG. 2 shows a state of two-stage rolling in which a PTFE extruded product is rolled using two-stage rolling rolls. As shown in FIG. 2, the PTFE extruded material 11 having a rectangular cross section before rolling is first rolled in the extrusion direction by a first-stage rolling roll 14 arranged so that the axial direction is orthogonal to the extrusion direction. The PTFE extruded product 12 in the state where the first-stage rolling is completed is obtained. The illustrated rolling direction corresponds to the extrusion direction of the PTFE extrudate 11. Further, the PTFE extruded product 12 has a second-stage rolling roll 15 whose axial direction is orthogonal to the extruding direction and is located downstream of the first-stage rolling roll 14 in the rolling direction.
To form a PTFE sheet 13.

In the present embodiment, the width change rate before and after rolling is 1.1 or less. In addition, the width change rate before and after rolling is (width of PTFE sheet after rolling) / (PTFE before rolling).
Extrudate width). By controlling the width change rate before and after rolling in this way, the flow of the PTFE resin in the sheet width direction (direction perpendicular to the rolling direction) during rolling can be minimized. For this reason, it is possible to realize a PTFE sheet having a uniform strength while minimizing the occurrence of variation in strength.

In the present embodiment, in the rolling process,
The thickness change rate before and after rolling is controlled to 10 or less by controlling the gap and the like of the rolling rolls. The rate of change in thickness before and after rolling is (thickness of PTFE extruded product before rolling) / (PT after rolling)
FEE sheet thickness).

If the rate of change in thickness before and after rolling is greater than 10, the PTFE resin starts flowing in the sheet width direction, so that the rate of change in width before and after rolling is large. As a result, strength variations occur in the sheet width direction. Thus, as in the present embodiment, by suppressing the rate of change in thickness before and after rolling to 10 or less, the rate of change in width is suppressed, and the flow of PTFE resin in the sheet width direction is suppressed. Strength characteristics can be made uniform.

PTF obtained by the method described above
The E sheet is subjected to processes such as removal of lubricant, sintering, and porosity by stretching, if necessary. After these steps,
The strength characteristics of the PTFE sheet are made uniform.
Therefore, the physical properties of a product obtained from the PTFE sheet produced by the method of the present invention are also stabilized. In addition,
In the present embodiment, an intensity variation rate defined by [(standard deviation of intensity) / (average value of intensity)] × 100 is used as an index indicating intensity variation.

[0026]

The present invention will be described more specifically with reference to the following examples.

Example 1 100 parts by weight of PTFE fine powder (CD-123 manufactured by Asahi Glass) was mixed with 25 parts by weight of a liquid paraffin as a lubricant, and this mixture was preformed into a cylindrical shape. The preform was extruded with a fishtail die (FT die) to obtain a ribbon-shaped extruded PTFE. The extruded PTFE had a width of 80 mm and a thickness of 2.4 mm.

The PTFE extrudate as described above was rolled in the extrusion direction by a pair of metal rolling rolls (400 mm in diameter), ie, a single-stage rolling as shown in FIG. 1 to obtain a PTFE sheet.

In this embodiment, the rolling was performed at a roll rotation speed of 2 m / min with the gap between the rolling rolls being 0.35 mm. The thickness of the rolled PTFE sheet recovered slightly from the gap to 0.4 mm. Further, the sheet width after rolling was 82 mm. As shown in Table 1, in this example, the thickness change rate before and after rolling was 6, and the width change rate was 1.03.

Next, the PTFE sheet rolled as described above was fixed to a metal frame so as not to shrink, and left in a dryer at 120 ° C. for 15 minutes to remove the lubricant. The PTFE sheet obtained in this manner is
The samples were equally divided into 0 (lateral positions 1 to 10 from one side), and the strength in the extrusion direction and the width direction was measured for each of the samples at horizontal positions 1 to 10. The measured intensities, the average intensity, the standard deviation of the intensity, and the rate of change of the intensity are shown in Tables 2 and 3. The strength measurement sample had a width of 5 mm and a length of 30 mm. In addition, a tensile tester (Autograph AG manufactured by Shimadzu Corporation) was used for strength measurement.
Using -1), a tensile force is applied in the length direction of the sample,
The strength was measured by converting the maximum strength up to break per unit area.

(Example 2) In the rolling step of Example 2, an extruded PTFE was rolled in the same manner as in the rolling step of Example 1, except that the gap between the rolling rolls was 0.2 mm. The extruded PTFE used was also produced in the same manner as in Example 1. In the present embodiment, the PT
The thickness of the FE sheet was 0.24 mm. The sheet width after rolling was 85 mm. As shown in Table 1,
In this example, the rate of change in thickness before and after rolling was 10, and the rate of change in width was 1.06.

Further, in this embodiment, the strength was measured in the same manner as in the first embodiment. The measured intensities, mean intensities, standard deviations of intensities, and rate of change of intensities are shown in Table 2
And in Table 3.

Comparative Example In the rolling step of the comparative example, an extruded PTFE was rolled in the same manner as in Example 1 except that the gap between the rolling rolls was 0.15 mm. The extruded PTFE used was also produced in the same manner as in Example 1. The thickness of the PTFE sheet after rolling is 0.18 mm
It became. Further, the sheet width after rolling was 90 mm. As shown in Table 1, in the comparative example, the thickness change rate before and after rolling was 13.3, and the width change rate was 1.13.

Further, the strength of the comparative example was measured in the same manner as in Example 1. The measured intensities, the average intensity, the standard deviation of the intensity, and the rate of change of the intensity are shown in Tables 2 and 3.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

From the above results, when the rate of change in thickness before and after rolling is greater than 10 and the rate of change in width exceeds 1.1 as in the comparative example, the rate of change in both the extrusion direction strength and the width direction strength exceeds 10%. As a result, the variation in strength in the sheet width direction is large. On the other hand, when the rate of change in thickness is 10 or less and the rate of change in width is 1.1 or less as in Examples 1 and 2, the rate of change in both the extrusion direction strength and the width direction strength is 10% or less. The strength in the sheet width direction is made uniform.

As described above, it was confirmed that the strength of the PTFE sheet can be made uniform by appropriately controlling the rate of change in thickness and the rate of change in width before and after rolling. Therefore, the physical properties of a product obtained from the PTFE sheet manufactured by the method shown in Example 1 or Example 2 are also stabilized.

[0040]

As described above, according to the present invention, it is possible to provide a PTFE sheet having stable physical properties while minimizing the occurrence of a variation in the strength of the PTFE sheet in the rolling step. Further, by stabilizing the physical properties of the PTFE sheet, the physical properties of a product obtained from the PTFE sheet are also stabilized.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a state in which a PTFE extruded product is rolled using a single-stage rolling roll in one embodiment of the PTFE sheet manufacturing method of the present invention.

FIG. 2 is a schematic diagram showing a state in which a PTFE extruded product is rolled using a two-stage rolling roll in one embodiment of the PTFE sheet manufacturing method of the present invention.

[Explanation of symbols]

 1,11 PTFE extruded material before rolling 2,13 PTFE sheet after rolling 3,14,15 Roll roll 12 PTFE extruded material after single-step rolling

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Claims (3)

[Claims] 1. A polytetrafluoroethylene sheet produced by rolling an extruded polytetrafluoroethylene extrudate, wherein the strength variation rate in the sheet width direction is 10% or less. Polytetrafluoroethylene sheet. 2. A polytetrafluoroethylene sheet comprising a rolling step of rolling a polytetrafluoroethylene extrudate obtained by extruding a preformed body containing polytetrafluoroethylene and a lubricant in an extrusion direction. In the manufacturing method, (width of polytetrafluoroethylene sheet after rolling) /
(A width of a polytetrafluoroethylene extruded material before rolling) A method for producing a polytetrafluoroethylene sheet, wherein a width change rate before and after rolling is 1.1 or less. 3. A polytetrafluoroethylene sheet comprising a rolling step of rolling a polytetrafluoroethylene extrudate obtained by extruding a preformed body containing polytetrafluoroethylene and a lubricant in an extrusion direction. In the production method, the thickness change rate before and after rolling defined by (thickness of extruded polytetrafluoroethylene sheet before rolling) / (thickness of polytetrafluoroethylene sheet after rolling) is set to 10 or less. A method for producing a polytetrafluoroethylene sheet.