JPH01178534A - Porous polytetrafluoroethylene sheet and its production - Google Patents

Abstract

PURPOSE:To obtain the title sheet having an anisotropic coefficient of friction, by molding a polytetrafluoroethylene powder kneaded with a liquid lubricant into a sheet, removing the liquid lubricant from the sheet, densifying it and performing its orientation, compression and heat treatment. CONSTITUTION:A sheet is obtained by molding a mixture obtained by adding 5-50pts.wt. liquid lubricant (e.g., liquid paraffin) to 100pts.wt. unfired polytetrafluoroethylene (PTFE). After the liquid lubricant is removed from the sheet, the sheet is densified by pressing it at 25-300 deg.C to an apparent density of 2.0-2.2, oriented uniaxially at a rate of 300-1,300%, and further compressed to a sheet thickness 80-50% of that before being oriented. This sheet is heat-treated for several sec to 1min at a temperature higher than the crystalline melting point of PTFE to obtain a porous PTFE sheet 1 having a microstructure comprising inclinded continuous knots 2 arranged in parallel and a large number of microfibers 3 which connect the knots together and having a coefficient of friction of 0.5-1.2 in the direction of E.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a polytetrafluoroethylene (hereinafter referred to as PTFE) porous sheet having a novel microstructure and a method for producing the same.

(Prior art) Porous technology by stretching PTFE is known as 1, for example,
It is described in Japanese Patent Publication No. 2-13560, Japanese Patent Publication No. 18991-1980, etc.

In the Doi drawing method, a mixture of unfired PTFE powder and a liquid lubricant such as naphtha is formed into a predetermined shape by extrusion, etc. (so-called paste molding), and the lubricant is evaporated, extracted, etc. from the molded product. (The removal of the lubricant may be carried out during the next step of stretching, or may be carried out after the stretching.) First, the molded product is stretched at a temperature lower than the PTFEO point to make it porous.

The microstructure of a porous body obtained by this stretching method is disclosed in the above-mentioned Japanese Patent Publication No. 18991/1983.

That is, as shown in FIG. 6, this porous body 7 has many small holes.
The fibrils 8 are oriented in one direction (in the case of uniaxial stretching, they are oriented along the stretching direction), and the nodules 9 have their long axes aligned with the fibrils 8. The nodules are arranged along a direction K perpendicular to the orientation direction (direction perpendicular to the stretching direction), and the nodules are connected by fibrils. Note that the microstructure of the porous body can be observed using an electron microscope.

Other known porous PTFE materials have a microstructure consisting of relatively large and continuous nodules and a large number of small fibers interconnecting the nodules (Japanese Patent Laid-Open No. 59-1
45124□, Japanese Patent Application Laid-Open No. 1982-192539) (Problems to be Solved by the Invention) There are various uses for PTFE porous materials, and an example of this is application to the medical field. Can be done.

For example, a porous PTFE sheet having the above-mentioned microstructure may be wrapped around an affected area as a bandage, but since this bandage is breathable, it is preferable because it does not cause stuffiness.

However, this PTFE porous bandage has a problem in that it is easy to unwind due to its low friction properties, and a solution to this problem has been desired, but to date.

No useful method has been proposed.

(Means for solving the problems) The present invention solves the above-mentioned problems of the prior art.
The present invention relates to a P, TFI porous sheet having a microstructure consisting of continuous nodules arranged in parallel with each other and inclined in the same direction, and a large number of fibrils interconnecting the nodules.

The present invention will now be described without reference to Figure 7.

FIGS. 1 and 2 show a PTFE porous material according to the present invention. Oh,. The PTFE porous sheet 1 shown in Fig. 6.c.2° has continuous nodules 2 arranged parallel to each other and slanted, and a large number of nodules interconnecting these nodules. 3 fibrils (thickness: 1, usually about 0.1 to 1μ)
It has a microstructure consisting of

This microstructure can be observed by electron microscopy.

The continuous state of the knots 2 in this porous sheet 1 means that the knots 2 are continuous in the thickness direction of the sheet (in the direction of arrow A in FIG. 1) and in the direction of one side of the sheet (in the direction of arrow B in FIG. In the actual example, the porous shift 1 is elongated in the width direction). The dimensions of these continuous nodules may vary depending on the manufacturing conditions of the porous sheet, but usually they are approximately 30 to 50 θμ in the sheet thickness direction, approximately 200 to 10,000 μ in the sheet thickness direction, and The direction of the pond surface (the direction of arrow C in Figure VS2, in this example, the length direction of the porous sheet 1) is about 10 to 70 μwm.

In addition, the inclination of the nodules 2 means that when the porous sheet 1 is placed on a plane, the angle D formed between the plane and the nodules 2 (hereinafter referred to as the inclination angle) is smaller than 90' (preferably 20~
60°).

Such parallel arrangement, inclination and continuous shape of the nodules are described in the above-mentioned Japanese Patent Publication No. 11842-13560 and Japanese Patent Publication No. 51-1989.
There is a difference compared to the PTFE porous body of Publication No. 18991, which has scattered nodules. I hated it. Japanese Patent Publication No. 59-1451
PTF of Publication No. 24 and JP-A-59-192539 Bulletin
In the E porous body, the inclination angle is 90' and is not inclined, whereas in the present invention it is inclined, and in this respect, the PTFE porous sheet according to the present invention has a novel microstructure. In addition.

The PTFE porous sheet according to the present invention has a novel microstructure in that the nodules are inclined at an inclination angle. It exhibits a unique property called "coefficient anisotropy."

This friction coefficient anisotropy refers to the coefficient of friction (in the direction of arrow E in Figure 1) and the opposite direction (direction of arrow F in Figure 1) on the surface of the PTFE porous sheet.
1111 standard law (described later) means that it is different.

1) The PTFE porous sheet according to the present invention has a high coefficient of friction in the d and E directions of about 0.5 to 1.2.

The coefficient of friction in the F direction shows a low value of 0.1 to 0.3.

The friction coefficient in the E direction mainly depends on the inclination angle,
The friction coefficient in the direction of the seed nucleus where the value of D is small is large. on the other hand,
The coefficient of friction in the F direction is not affected by the angle of inclination, etc., and is almost constant.

The degree of friction coefficient anisotropy in the PTFE porous sheet according to the present invention can be expressed by the value obtained by dividing the monodentate coefficient 'kF in the E direction by the same (hereinafter, this value is referred to as the degree of anisotropy). The larger this value is, the greater the degree of anisotropy is. Note that the degree of anisotropy of the PT1'E porous sheet of the present invention is about 2 or more.

The PTFg porous sheet according to the present invention has friction coefficient anisotropy as described above and can be used as a bandage.

As shown in FIG. 3, it has been found that there is an advantage that loosening is less likely to occur after one winding when the winding is wrapped over the affected area 4 (the direction of arrow G is the winding end direction).

As shown in Figure 3 above, the reason why it is difficult for the sheet to unwind after winding it with PTFE porous sheet is that if the sheet wants to loosen, it must slide in the opposite direction to the direction of arrow G. This seems to be an attempt to prevent further sliding by interlocking the nodes of the overlapping sheets.

Next, an example of a method for manufacturing a porous PTFE sheet according to the present invention will be described. In this production method, a mixture of PTFE powder and an appropriate amount of liquid lubricant is formed into a sheet shape, and after removing the liquid lubricant from this 7-tate material, it is densified and then uniaxially stretched.

It is characterized in that it is further compressed and then heat treated at a temperature higher than the crystal melting point of PTFE.

In the above manufacturing method, first, a mixture of unfired PTFE powder and a liquid lubricant is formed into a sheet, and the liquid lubricant is removed from this sheet. This step may be the same as the method for producing the conventional porous PTFE body. That is, as a liquid lubricant.

A material that can wet the surface of PTFE and that can be removed by evaporation, extraction, etc. after obtaining a sheet is used,
A specific example is liquid paraffin.

Hydrocarbon oils such as naphtha and white oil, aromatic hydrocarbons such as toluene and xylene, alcohols, ketones, esters, and silicone oils.

Examples include fluorochlorocarbon oil, a solution prepared by adding a polymer VFE such as polyimbutylene or polyimprene to these solvents, and a mixture of two or more of these solvents, water or an aqueous solution containing a surfactant, and the like. Use of liquid lubricant is PT
It is usually about 5 to 50 parts by weight per 100 parts by weight of F'E powder. We also produce sheets of mixtures made by adding liquid lubricants to PTFE powder.

Extrusion, rolling, compression, a combination of these methods, etc. can be used. Furthermore, the liquid lubricant can be removed from the sheet material by evaporation, extraction, or the like.

In this method, the sheet-like material from which the liquid lubricant has been removed is densified and further oriented along the l-axis.

To densify a sheet-like material, for example, (a) press the sheet-like material with a press Ilf calendar roll at a temperature of about 2 seconds to 300°C, and reduce its apparent density to about 2.0 to 2.2 (apparent density before densification). The hanging density is usually about 1.5 to 1.6), or (b) heated for about 5 to 30 minutes at a temperature higher than about 300°C and lower than the melting point of PTFE, and This can be carried out by a method in which the coating density is set to about 1.7 to 1.9.

The sheet material thus densified is subjected to uniaxial stretching, at a stretching ratio of about 300 to 1300%. The temperature during stretching is set lower than the crystal melting point of PTFE when densification is performed using method (a), and when densification is performed using method (b).
) method, it is preferable to set the temperature lower than the temperature during the step.

By this uniaxial stretching, the sheet material becomes porous and has a microstructure consisting of continuous nodules arranged in parallel with each other and a large number of small fibers interconnecting the nodules.

However, this porous material has an angle of approximately 90° at the intersection of the nodules and fibrils, and does not have an inclined structure of the nodules.

Therefore, in method 2 of the present invention, after the above-mentioned 1s1 treatment, compression for inclining the nodule and heat treatment for fixing the nodule inclination and thinning are sequentially performed.

This compression can be applied, for example, to PT made porous by uniaxial stretching.
The FE sheet is passed through a rolling roll (at a temperature of .

Normally, a method of heating the temperature (approximately 25 to 50°C) can be adopted.

It is also possible to change the angle of inclination depending on the degree of compression. The degree of compression is adjusted so that the thickness of the sheet after rolling is about 80 to 50% of that before rolling.

In addition, the heat treatment was performed by maintaining the 7-t that had undergone the above compression process so that no dimensional change occurred, and heating it to a temperature equal to or higher than the crystalline melting point of PTFE (at time t!1, 6 currents were applied for about a few seconds to 1 minute). Let's do it. By this heat treatment, the inclined structure of the nodules is fixed and the sheet is fired. (Example) The present invention will be explained in detail below with reference to Examples.

Example 1 A mixture obtained by uniformly mixing 70 parts of unfired PTli'E fine powder (manufactured by Daikin Industries, Ltd., #H product name F103) and 30 parts by weight of liquid lubricant ethanol was heated at a temperature of 2.
Pass through a pair of metal rolling rolls maintained at 5°C. When this rolling is repeated, the degree of agglomeration of the paste-like material gradually increases and it becomes a sheet shape.

This sheet-like material is dried at room temperature to remove ethanol, and a long sheet-like material with a thickness of 100 μS and an apparent density of 1.50 is obtained.

Next, this sheet-like material was heated at a temperature of 325° C. for 30 minutes to densify it (apparent density: 1.8 L).

- Stretched 700% in the longitudinal direction at a temperature of ZOO°C to obtain a PTFE porous sheet with a thickness of 100μ and a porosity of 90%.

Next, this porous sheet was rolled at a roll spacing of 80 μm.
The nodules were passed through a metal rolling roll (temperature 25°C) with an inclination angle (the sheet thickness was 80 μm), and after rolling, the sheet was heated at a temperature of 360°C for 10 seconds without causing any dimensional change. A porous sheet with inclined nodules was obtained.

The inclination angle of this porous sheet was approximately 60°.

In order to determine the degree of anisotropy of this porous sheet, the coefficient of friction was measured by the following method.

As shown in FIG. 5, a porous sheet 1 is fixed to a base 5 using an adhesive 6 using a double-sided adhesive tape or other suitable means. Another porous sheet 1 is placed on top of this sheet 1 so that the inclination directions of the nodules on each sheet are the same, and an iron load 61 with a diameter of 150 Ii is placed. Note that the size of the surface of the load 6 in contact with the porous sheet 1 is approximately 1-. Next, move the upper sheet in the directions of arrows G and H in the figure.

The tension (Fl) when starting movement in the G direction and the tension (F2) when starting movement in the H direction are known. Then, calculate the coefficient of friction (μm) in the G direction and the **coefficient (μm) in the H direction using Inuyama and (m).

The results obtained are shown in Table 1. Note that N in the 1-car formula is the weight of the load (maximum).

μ! =2...(1) F Example 2 The interval between the metal rolling rolls for making the knots incline is 5
A PTFE porous sheet having an inclination angle of 30° was obtained by carrying out the same operations as in Example 1 except that the deviation was set to 0 μ.

The microstructure of this porous sheet was as shown in FIG. Note that the directions of arrows A and C in FIG.
It corresponds to that in the figure.

Comparative Example 1 All operations were carried out in the same manner as in Example 1, except that no compression was performed using metal rolling rolls to incline the nodules.
A porous sheet with a thickness of 100 μm was obtained.

This porous sheet has a microstructure consisting of continuous nodules arranged in parallel with each other and a large number of fibrils connecting the nodules, but the nodules are oblique (inclination angle 90°). ).

Comparative Example 2 The work was carried out in the same manner as in Example 1, except that the two steps of heating for densification and compression using metal rolling rolls for forming WB1-tilt were not performed, and the thickness was 90 μm, the porosity was An 87% porous sheet was obtained.

The microstructure of this porous sheet was the same as that shown in FIG.

Table 1 (Effects of the Invention) According to the present invention, a porous PTFE body having an anisotropic coefficient of friction can be obtained. □

[Brief explanation of the drawing]

FIGS. 1 and 2 are a perspective view and a front view schematically showing the microstructure of the PTFE porous sheet according to the present invention,
Figure 3 is a front view showing an example of the use of the porous sheet, Figure 4 is a scanning electron micrograph (200x magnification) showing an example of the microstructure of the porous sheet, and Figure 5 is the porous sheet. FIG. 6 is a front view showing a method for measuring the coefficient of friction of the conventional product, and FIG. 6 is a schematic diagram showing the microstructure of a conventional product. 1...PTFE porous sheet 2...Continuous nodules 3...Small fibers

Claims (2)

[Claims] (1) A polytetrafluoroethylene porous sheet having a microstructure consisting of continuous nodules arranged parallel to each other and inclined in the same direction, and a large number of fibrils interconnecting the nodules. (2) A mixture of polytetrafluoroethylene powder and an appropriate amount of liquid lubricant is formed into a sheet, and after removing the liquid lubricant from this sheet, it is densified, then uniaxially stretched, and further 1. A method for producing a polytetrafluoroethylene porous sheet, which comprises compressing and then heat-treating at a temperature equal to or higher than the crystalline melting point of polytetrafluoroethylene.