SU1752566A1 - Method for production blanks of polytetrafluoroethylene - Google Patents

Abstract

Uses: polytetrafluoroethylene recycling technologies; The essence of the invention: the primary polytetrafluoroethylene powder is loaded into the mold, pressed at a typical temperature at a pressure of 15-35 MPa. The pressure is released, the billet is heated together with the mold d6340-400 ° C. The second pressure is pressed with a specific pressure of 5-500 MPa for the time T {5.51-1010 1-0:, 015 (T-340}: P, where T is the heating temperature, &C; P is the pressing pressure, MPa; t - compaction time, pp. The pressure drops to zero and the billet is cooled.

Description

This invention relates to technologies for the processing of polymeric materials, in particular polytetrafluoroethylene, used for the manufacture of products for work in the radio, electronic, mechanical engineering and other industries.

At present, the industry is based on two-stage process for the production of primary polytetrafluoroethylene blanks: 1) production of blanks by cold pressing under pressure of 15-35 MPa; 2) subsequent long-term thermal treatment (sintering) in furnaces at 360-380 ° C.

The disadvantage of this method is the long process of making blanks due to the long time of free sintering,

A known method for producing blanks by sintering and cooling in a mold under pressure, in which the starting material is pressed at room temperature, then sintered in the mold itself. Until the sintering temperature is reached, the heating is carried out without pressure, upon reaching it, a pressure of 50-80 kg / cm 1 is created in the form, and this pressure is maintained for the entire holding period at the sintering and cooling temperatures.

The disadvantages of this method are the long duration of the process of making blanks, the strength of the products obtained.

4 The purpose of the invention is to reduce the time of manufacture of blanks while maintaining their physico-mechanical properties.

The goal is achieved by the fact that in the known method, which involves pressing the starting polytetrafluoroethylene at room temperature, heating, pressing and cooling, according to the invention, heating is carried out to 340-400 ° C, pressing is carried out at pressures of 5-500 MPa during time t XI

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5.51 1 (G

1-0.015 (7-340), where G is the time

pressing, s, P - pressing pressure, MPa; T is the pressing temperature, ° C; and before cooling, the pressure drops to zero. ,

The established dependence of the holding time on pressure and hot pressing temperature allows choosing the optimal mode for producing blanks with preserving their physicomechanical properties. The limitation on hot pressing temperatures is due to the fact that, at temperatures above 400 ° C, an intensive thermal decomposition of fluoroplast begins. 4, and 340 ° C is the melting point of crystallites.

The effect of pressure and temperature during hot pressing on the optimal sintering time of the workpiece is illustrated in Table 1.

Data on the physicomechanical properties of the obtained blanks at various temperatures and pressures, depending on the exposure time during hot pressing, are given in Table. 2

PRI me R 1. Getting the workpiece at a temperature of 370 ° C and a pressure of 5 MPa. The estimated pressing time of the proposed formula is 6060 s (Table 1). The essence of the technology for producing a preform is as follows. The primary powder of polytetrafluoroethylene (fluoroplast-4) is loaded into a mold with a diameter of 60 mm and pressed at a pressure of 15-35 MPa, then the pressure is released and the workpiece is heated together with the mold. Upon reaching the temperature corresponding to the temperature of the pseudo-melt (370 ° С ), the workpiece is again pressed with a specific pressure of 5 MPa, maintained for a calculated time of 6060 s, after which the dubbing is dropped and the bale is cooled (together with the mold) to 110-100 ° C. The obtained preparations have the following characteristics: 0р 2 6 М П а, ep 360%, 2 2.19 m 2 / m 3.

EXAMPLE 2 The same process sequence is used as in example 1, and the same parameters, but hot pressing is carried out for

8000 s (i.e., more calculated) The resulting blanks have the following characteristics: Op 26 MPa, ep 360%, and 2.19 MVM3.

Example Use the same process sequence and

the same parameters as in example 1, but the hot pressing is carried out for a time of 5000 s (i.e., less than the calculated one). The resulting blanks have the following parameters: cgr 20 MPa, ep 280%, and

2.14 m2 / m3.

As can be seen from the above examples, using the proposed modes (in particular, the estimated time of hot pressing), billets with optimal physicomechanical properties are obtained. The sintering time is shortened several times in comparison with the conventional method.

 deviation from the calculated burden

hot pressing1 physicomechanical properties either do not change (with an increase in time — see Example 2) or deteriorate (by reducing the time — see Example 3).

Claims (1)

Invention Formula A method for producing polytetrafluoroethylene preforms, including pressing a polytetrafluoroethylene powder at room temperature, heating, pressing and cooling, characterized in that, in order to reduce the time of production of preforms while maintaining their physical and mechanical properties, heating is carried out to 340-400 ° C, pressing is carried out at pressure 5-500 MPa over time t 5.51 j 10 0,015 (1-340). where-time R pressing, s; P is the pressing pressure, MPa; T is the pressing temperature, ° C, and before cooling, the pressure drops to zero. Table 1 five five five five 50 50 50 50 100 100 100 100 500 500 500 500 600 600 600 600 five five five five 50 50 50 50 100 100 100 100 500 500 500 500 table 2 temperature C 1802.05 2802, H 3602.19 3602.19 1902.00 2902.13 3602.19 3602.19 1702.0 2802, 3602.19 3602.19 1602.05 2802.13 3602.19 3602.19 1502.05 2502.11 2602.12 2602.11 350 ° C 1902.0 2802.12 3602.19 3602.19 1802.05 2902.14 3602.19 3602.19 1752,10 2802.13 3602.19 3602.19 1902,10 3002,13 3602.19 360,2,19 g175256610 , Continued table. 2 g-1g-cG GGI..It;