JPH0491909A - Polytetrafluoroethylene tubular body and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a tubular body having a smooth surface and little heat shrinking property by coating the inwall surface of a mold with a polytetrafluoroethylene dispersion, heating the inwall surface at a temperature higher than the melting point of polytetrafluoroethylene and forming the tubular body on the inwall surface of the mold. CONSTITUTION:The wall surface of the cylindrical section of a mold is coated with a polytetrafluoroethylene(PTFE) dispersion, and the wall surface is heated at a temperature higher than the melting point of PTFE. A dispersion medium in the dispersion applied on the mold is evaporated and removed by the heating, and a PTFE tubular body is formed on a coated surface. Consequently, the PTFE tubular body obtained has the excellent smoothness of a surface while heat shrinkage factors in the longitudinal direction and the circumferential direction at the temperature higher than the melting point of PTFE are brought to 5% or less. The coating of the PTFE dispersion to the mold and heating at a temperature less than the melting point of PTFE are repeated, thus adjusting the wall thickness of the tubular body.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to polytetrafluoroethylene (hereinafter referred to as PTFE).
This invention relates to a thin-walled tubular body made of a thin-walled tubular body made of

(Prior Art) PTFE is excellent in heat resistance, chemical resistance, low friction, non-adhesiveness, etc., and taking advantage of these properties, it is used in various industrial applications.

For example, one specific example is coating the surfaces of rolls used for conveying products, intermediates, etc. in production lines for various articles with PTl''E thin-walled tubular C.

This PTFE coated roll is made by fixing a thin PTFE tubular body prepared in advance inside a mold, setting a core bar in the center of the tubular body, and then filling the gap between the tubular body and the core bar with liquid plastic or rubber. It can be obtained by injection hardening and then taking out from the mold.

The method for manufacturing the PTFE tubular body used here includes, for example, forming a mixture of PTFE powder, naphtha, liquid paraffin, and other liquid lubricants into a tube shape by extrusion and/or rolling, and then removing the liquid lubricant. Then P
It is heated to a temperature higher than the melting point of TFH and fired, and then the PT
A method (Japanese Patent Publication No. 33-263') is known in which the diameter is expanded and thinned by stretching in the radial direction under high temperature conditions higher than the melting point of FE.

(Problems to be Solved by the Invention) However, the thin-walled tubular body obtained by such conventional method Q is oriented by stretching, and therefore residual heat shrinkage stress is inevitable. Therefore, due to heating when coating the roll surface with this material, heat shrinkage (vs. depending on the stretching ratio when producing the bone and bone tubular body, but normally, even at a temperature below the melting point of PTFE, about 5 to 30% of the heat is generated) The shrinkage rate (at temperatures above the melting point, the heat shrinkage rate is about 50-85%) may appear and wrinkles may occur, and furthermore, if the residual heat shrinkage stress is large, cracks or cracks in the tubular body may occur. It may also cause tearing.

In addition, when stretching a PTFE tubular body, if the tubular body is placed in a size regulating tube and the tubular body is pressurized and stretched in the radial direction to make it thinner, some stretching is also performed in the length direction. However, when stretched in the longitudinal direction, friction is generated between the tubular body and the regulating tube, which causes the surface of the thin-walled tubular body to be roughened and the smoothness of the thin tubular body to be obtained to be deteriorated.

(Means for solving the problem) The present inventor has solved the problem 1-1 of the prior art.
- As a result of various studies, the mold and P T F E
The inventors discovered that the intended purpose could be achieved by using disversion, and took two steps to complete the present invention.

That is, the PTFE tubular body according to the present invention is characterized in that the heat shrinkage rate in the longitudinal direction and the circumferential direction is 5% or more when the temperature is higher than the melting point of PTFE.

In addition, 1. The method for producing a PTFE tubular body, which is another aspect of the present invention, involves coating the inner wall surface of the mold with PTFE dispersion and heating it to a temperature higher than the melting point of PTFE. This method is characterized by forming a tubular body and then removing the tubular body from the mold.

The mold used in the present invention has a cylindrical part, and in the method of the present invention, the wall surface of this cylindrical part is
:7-'Isbar, /"! 7 '!'-Spray method,
Apply by any means such as brushing. This dispersion contains additives such as pigments and fillers, and is easy to apply, and commercially available products can also be used. P T
Preferably, the FE concentration is about 20-50%.

After applying PTFE dispersion to the mold, it is heated to a temperature higher than the melting point of PTFE. By this heating, the dispersion medium in the dispersion coated on the mold is evaporated and removed, and a PTFE tubular body is formed on the coated surface. The heating is performed at a temperature of about 350 to 380, for example.
°C1 heating time can be set to about 1 to 3 minutes.

In addition, apply PTFE dispersion to the mold.
If heated to a high temperature above the melting point of TFE, rapid evaporation of the dispersion medium will occur, which may cause the resulting tubular body to contain air bubbles, so to prevent this, first heat it at a relatively low temperature. removing some or most of the dispersion medium;
Then, the temperature is increased to -1 = - above the melting point of P'r1.''E, and the remaining -V-dissolving medium is removed. Laws may also be adopted.

In addition, 1. During heating work, the work can be done while rotating the mold in order to prevent the PTFE dispenser applied to the wall of the mold from sagging. .

In the method of the present invention, a green tubular body is formed by repeatedly applying a PTFE dispersion to a mold and l) heating below the melting point of TFE;
Thereafter, the tubular body can be fired by heating at a temperature higher than the melting point of PTFE, thereby making it possible to adjust the wall thickness of the tubular body.

In the method of the present invention, P is thus applied to the inner surface of the mold.
After the TFE tubular body is formed, it is peeled from the mold. In order to facilitate this peeling, a mold release treatment such as applying a silicone resin to the cylindrical portion of the mold may be performed prior to application of 1'') TFE dispersion.

The P T F E tubular body of the present invention thus obtained has excellent surface smoothness and low heat shrinkage in the longitudinal and circumferential directions at temperatures above the melting point of T F E. It has less than 5% F, which is smaller than conventional products.

(Effects of the Invention) According to the horn method of the present invention, a tubular body with no residual heat shrinkage stress can be obtained by a round wheel operation, and this tubular body has a smooth surface and shows almost no heat shrinkability. There are advantages.

(Example) Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example PTFE dispersion was spray applied to the core part of a mold having a 50 mm diameter cylindrical part (the cylindrical part was plated with chrome) and heated at 7.80°C for 5 minutes and 32 hours.
The dispersion medium was sequentially heated at 0''C for 5 minutes to remove the dispersion medium in the dispersion to form a PTFE tubular body.The dispersion used had a PTFE concentration of 30%.

After repeating this coating and heating 6 times, the tubular body was fired by heating at 380°C for 5 minutes, cooled to room temperature, and taken out from the mold to obtain a 1) 1゛FE fired tubular body with a wall thickness of 50 μm. Ta.

Comparative Example I PTF E Fine Powder] 00 parts by weight and 22 parts by weight of naphtha were uniformly mixed, and this mixture was formed into a tube using a mold with a diameter of 7.2 mrn and a core bottle diameter of 6.1 mm. The naphtha is extruded and heated at 370°C for 3 minutes to remove the naphtha and sinter it.

Next, while applying an internal pressure of 0.7 kg/afl to this tubular body, it was stretched in the radial direction in a metal regulating tube with an inner diameter of 50 mrn (temperature at the time of stretching was 400''C), and taken out from the regulating tube. PTF with outer diameter 49°4mm
An E-fired tubular body was obtained.

Comparative Example 2 The length direction of the PTFE tubular body obtained in Comparative Example 1 was fixed and heated at a temperature of 300″C for 10 minutes to obtain a tubular body.

The properties of the tubular bodies obtained in Examples and Comparative Examples were tested in the manner described below, and the results are shown in Table 1. In Table 1, (length 1 indicates the length direction of the tubular body, and [circle] indicates the circumferential horn direction of the tubular body.

, tensile strength and elongation] at a temperature of 25° [at a human tensile speed of 50 mm/rnin,
Measurement is performed using a tensile tester.

[Heat shrinkage rate]

The tubular body is heated at a temperature of 350° C. for 10 minutes, and the temperature is calculated according to formula (1). Note that A in formula (1) indicates the method before heating, and B indicates the method after heating.

- B Heat shrinkage rate (%) -
Average roughness (Ra) and maximum roughness (Rr
nax).

〔exterior] Visually observe the appearance of the tubular body.

Table 1

Claims (2)

[Claims] (1) A polytetrafluoroethylene tubular body having a heat shrinkage rate of 5% or less in the longitudinal direction and the circumferential direction at a temperature equal to or higher than the melting point of polytetrafluoroethylene. (2) Apply polytetrafluoroethylene dispersion to the inner wall of the mold, then heat to a temperature higher than the melting point of polytetrafluoroethylene to form a tubular body on the inner wall of the mold, and then mold this tubular body into a mold. A method for producing a polytetrafluoroethylene tubular body, characterized by removing it from a mold.