JPS60187536A - Method and apparatus for preparing porous body made of tetrafluoroethylene resin - Google Patents

Abstract

PURPOSE:To attain to shorten a processing time and to conserve energy in preparing a tetrafluoroethylene resin porous body high in mechanical strength, by simultaneously applying four processes of the evaporative removal of a liquid lubricant, orientation in an unbaked state, baking in an oriented state and orientation in a baked state to an unbaked tetrafluoroethylene resin molded article containing the liquid lubricant at an atmospheric temp. of 390 deg.C or more. CONSTITUTION:After an unbaked tetrafluoroethylene resin mixture containing a liquid lubricant is molded by an extrusion method, a rolling method or a method containing both of them, four processes of the evaporative removal of the liquid lubricant, orientation in an unbaked state, baking in an oriented state and orientation in a baked state are simultaneously performed at an atmospheric temp. of 390 deg.C or more. By this method, both Young modulus of 10,000kg/cm<2> or more and matrix strength of 1,100kg/cm<2> are satisfied and a firm tetrafluoroethylene resin porous body easy to handle even at room temp. is obtained.

Description

Detailed Description of the Invention (Technical Field) The present invention provides an energy-saving process in the liquid lubricant removal, stretching, and sintering steps in a method for producing a porous tetrafluoroethylene resin material with high mechanical strength, and also enables the energy-saving process. The present invention relates to manufacturing equipment.

(Prior art and its problems) Tetrafluoroethylene resin porous materials are used for various filters, diaphragms, and waterproof ventilation, taking advantage of the superior heat resistance, chemical resistance, electrical insulation, and water repellency of tetrafluoroethylene resin. It is used in electrical materials, electrical coating materials, sealing materials, etc. Several methods are already known for producing the material, but the most commercially attractive method is to make it porous through a stretching operation.

Basically, it is disclosed in Japanese Patent Publication No. 4/2-13560, and the first step is to mix tetrafluoroethylene resin powder and liquid lubricant, and then paste extrusion method, calender rolling method, or a combination of both. By doing so, a molded product in the shape of an unfired film, tube, or rod can be obtained. Steps after the second step are: 1) removing the liquid lubricant contained in the molded product by evaporation or extraction, 2) making it porous by stretching, and 2) firing at a temperature higher than the melting point of the tetrafluoroethylene resin. It consists of a step of fixing the porous structure. The reason why the steps after the second step have been divided in this way is as follows.

At conventional stretching temperatures (from room temperature to below the crystalline melting point of tetrafluoroethylene resin), stretching is not uniform due to the effect of the interfacial tension between the liquid lubricant and the resin, and the pore characteristics of the resulting porous material also deteriorate. This results in a non-uniform 4゛1η structure.

Furthermore, the firing process needs to be carried out at a temperature above the crystalline melting point of the tetrafluoroethylene resin, but since the stretching process has been carried out exclusively below the crystalline melting point, it has been separated from the stretching process.

In this way, the steps after the second step are performed separately in several different temperature atmospheres, and a large amount of stress is applied.
The production and production cost is seven, and there is a lot of savings.

The purpose of the present invention is to heat the second and subsequent steps at 4.30°C.
The purpose is to provide a manufacturing method that allows the above-mentioned atmosphere to be carried out simultaneously in one step, and by providing the manufacturing equipment, it is possible to reduce the processing time involved in manufacturing a porous polytetrafluoroethylene resin material. This is intended to shorten rlJ and save energy.

(Structure of the Invention) As a result of rigorous study of the temperature and operating conditions in the second and subsequent steps mentioned above, the inventor has discovered that under conditions where precise temperature distribution is controlled, an ambient temperature of 390°C or higher When an unfired tetrafluoroethylene resin molded product containing a liquid lubricant is stretched, the liquid lubricant is evaporated and the stretching progresses at the same time.Furthermore, firing occurs and at the same time, stretching after firing also occurs. I found it.

As a result of examining the conditions for realizing these steps more easily, we found that the hot air circulation furnace method is superior as a temperature distribution control method, and that the present invention is preferable by providing a catalyst in the furnace to promote combustion of the liquid lubricant. The present invention was completed by discovering that the present invention can be implemented easily.

When an unfired tetrafluoroethylene resin molded product containing an RFM body lubricant enters an atmosphere above the crystalline melting point of the tetrafluoroethylene resin, the resin temperature rises, but at the same time the liquid lubricant begins to evaporate. By absorbing this latent heat of vaporization (the temperature of the resin is maintained below the boiling point of the liquid lubricant), since tension is applied in this state, stretching in a limited range in the unfired state progresses, and the liquid lubricant is removed. The molded product becomes porous, with the molten parts as the core.The porosity that occurs in this way facilitates the evaporation of the liquid lubricant remaining inside the molded product.In other words, it becomes porous. Evaporation of the lubricant will proceed at the same time.Once the liquid lubricant has evaporated, the resin temperature will gradually rise, and when it exceeds the crystal melting point, sintering will begin.Tetrafluoroethylene resin has a low viscosity even above the crystal melting point. Due to the high tension applied from both ends, further stretching is performed and the fiber structure progresses.

The above process is schematically represented by FIGS. 1 to 5. Figure 1 shows the temperature profile during the heating process. When the molded product at room temperature reaches point A at the furnace inlet and is gradually heated up to the initial boiling point B of the liquid lubricant, the rate of temperature rise slows down due to the latent heat of vaporization, and when it reaches the carbonization point #, the temperature rises again. The temperature rise rate increases and reaches the crystalline melting point of the tetrafluoroethylene resin. Since the set furnace temperature is even higher, after absorbing a certain amount of latent heat, the temperature approaches the furnace temperature.

On the other hand, FIG. 2 shows the results of differential thermal analysis near the crystal melting point of an unfired tetrafluoroethylene resin molded product.

The endothermic peak shows a peak at 34.8°C and a shoulder at 338°C. Furthermore, a small peak appears near 380'C. These peaks are due to the crystal structure formed during polymerization of the tetrafluoroethylene resin.

On the other hand, after firing, these peaks are drastically reduced and at the same time a sharp peak appears at 327'C.

This means that the crystal structure changes before and after the firing process, and it was observed that the endothermic peak shifts to the higher temperature side when the temperature increase/decrease rate is rapid.

Figure 8 shows what kind of deformation tension is applied in the steady state where the liquid lubricant is evaporated and removed in the furnace, the unsintered state is stretched, fired, and then stretched after firing. A schematic diagram of the measurement is shown. A tension meter equipped with a strain gauge is connected to a pulley to continuously record the stress applied to both ends of the tetrafluoroethylene resin in the furnace.

Figure 4 shows the dynamic tension values when the stretching ratio is changed at a constant furnace temperature while being fed to the furnace at a feed rate of 31yi 7 minutes, and the furnace temperature is from 200℃ to 4.50℃. The measurement results are listed.

FIG. 5 shows the relationship between furnace temperature and stretching ratio at a constant dynamic tension, based on the graph in FIG. 4.

What can be seen from Matsu 15 is that under a dynamic tension of 1'0 (1), for example, a tetrafluoroethylene resin molded product containing liquid lubricant is placed in a furnace as shown in Figure 1. In Figure 1, there is almost no stretching between A and B, and between B and C, when the 0 point is about 250°C, stretching of less than about 1oo96 occurs, and between C and D. 3
Since the temperature is raised to about 50°C, it will be stretched to 800%, and at the same time as firing occurs from D to E, if the first limit of the furnace setting temperature is, for example, 4.00°C, then 14
．． It can be inferred that stretching of 00% or more has occurred.

Of course, since the stretching ratio is usually determined first in the upper and lower parts of the furnace, the dynamic tension changes depending on that value, and as a result, the ratio of the stretching ratio that occurs at each temperature also changes.

However, while repeating several experiments, we found that 38 in Figure 2
If the furnace temperature exceeds the endothermic peak of 0℃, for example, 4.00℃
I set it to . It was found that the mechanical strength of the obtained porous tetrafluoroethylene resin material, especially Young's modulus, matrix decay, and strength suddenly increased when measured at room temperature.

In other words, Young's modulus is 10.0 at a furnace temperature of 380°C or lower.
00 K97cm” or more, and matrix strength 1.1
However, by setting the furnace temperature to 890°C or higher, both of these requirements can be satisfied, and the porous tetrafluoride ethylene resin is easy to handle even at room temperature. Now I can get a body.

Furthermore, when a tetrafluoroethylene resin molding without liquid lubricant was supplied into the furnace, the Young's modulus was 10,000 K9.
/97cm for 2 or more chains and matrix strength 1,100
``I have confirmed that it is not possible to add both of the above to i+:+f.

Regarding the physical background of the production method of the present invention, j-1 is unknown, but it is expected to be related to the rate of temperature increase to a high temperature higher than the endothermic peak of 380°C and the cooling rate after temperature increase. Ru.

The manufacturing method of the present invention can be suitably carried out regardless of whether the molded product has a film, tube or rond shape.

In addition, liquid lubricants that are mixed with tetrafluoroethylene resin can be used as long as they can wet the resin surface and evaporate below the decomposition temperature of the resin, which is conventionally used in the paste extrusion method. A solvent having a boiling point range of 260° C. or less, which can be easily evaporated from the product, is more preferably used. Petroleum-based hydrocarbon solvent is easy to handle,
It is commonly used due to its price.

The ambient temperature in which the present invention is carried out needs to be 390°C or higher. The crystalline melting point of tetrafluoroethylene resin is 34.7°C
However, in order to satisfy both a high Young's modulus and matrix strength, it is necessary to have an even higher crystal melting point of 380' (:).

On the other hand, the ambient temperature affects the rate of temperature rise of the resin. That is, as the ambient temperature is raised, it becomes possible to simultaneously perform evaporation removal of the liquid lubricant, stretching, and firing at a faster rate. Even if the ambient temperature is above 450'C or even above 500°C, the present invention can be carried out by controlling the temperature distribution in the furnace to below 30°C, and the strength of both can be greatly increased. It was confirmed. The higher the ambient temperature, the more accurate the temperature distribution within the furnace is required. Highly accurate temperature control enables homogeneous and rapid heating and cooling of resin.

If the precision is low, there will be variations in the melting and recrystallization of the crystals, which will easily cause breakage due to resin decomposition during processing (and cause variations in the physical properties of porous materials.Such high-precision temperature control It has been found that a hot air circulation furnace is the most suitable heating means for achieving this in a high temperature atmosphere, as it can homogenize the temperature distribution within the furnace by circulating heated air at high speed.

Furthermore, incorporating a catalyst that promotes the oxidation of the evaporating lubricant into this furnace lowers the concentration of solvent in the furnace, keeping it below the explosion limit, and making effective use of the thermal energy from its combustion. Therefore, it is necessary to carry out the present invention.
We have found a way to reduce energy costs to a low level. At this time, the faster the circulating air speed, the more accurate the temperature distribution within the furnace will be. Therefore, it is desirable that the working temperature atmosphere should be 5"/sec or more, and should be 1 to 4. A wind speed of about Ottr/sec is suitable for Iα, but it needs to be changed depending on the shape of the molded product. Next, an apparatus that can suitably carry out the present invention will be described.

The basic structure is as shown in FIG. It consists of heating means and means for feeding and winding up the molded product to be treated. The heating means is of the hot air circulation type as already mentioned. Therefore, it has a double structure consisting of an inner cylinder part (4) through which the molded product passes and an outer cylinder part (5) in which the heater is installed. These two parts are in communication, and the heated air in the furnace is circulated at a constant flow rate by a fan (7).

The temperature inside the furnace is detected by a thermocouple (8) installed around the inner cylinder, and the temperature is controlled by feeding it back to the heater. The temperature inside the furnace is related not only to the flow rate and the amount of heat generated by combustion of the liquid lubricant, but also to the amount of outside air flowing in from the furnace inlet and outlet.

A pressure box (2) that can adjust the indoor pressure and a nozzle (u) that can adjust its length are installed at the furnace inlet and outlet to create a mechanism that can control the amount of outside air flowing in. In addition, as outside air flows in, a portion of the heated air inside the furnace is forcibly exhausted through the exhaust pipe to maintain the oxygen concentration necessary for combustion inside the furnace.

A catalyst is also provided at one or more locations where the heated air circulates.

A platinum group catalyst is one of the catalysts with the best oxidation ability and is preferably used for this purpose.

Next, the means for feeding and winding up the molded product will be described. Basically, since a stretching operation is involved, the winding section needs to be able to be driven at a higher speed than the feeding section. In addition, when the molded product is a film, for example, a roll is suitable, and in the case of a tube or a rond, a pair of capstans provided with a groove that matches the outer diameter of the molded product is useful. In addition, guide rolls, supply scunds, winders, various detectors, etc. will be arranged as appropriate.

(Example 1) Liquid lubricant Naphtha A5 (
(manufactured by Shell Oil Co., Ltd., boiling point range: 152-197'c) was blended and mixed at a ratio of 25 parts by weight, and after preforming, a tube with an outer diameter of about 3 and an inner diameter of 2 was extruded using a ram extruder. Next, using the apparatus shown in FIG. 6 with the liquid lubricant still contained in the molded product, the liquid lubricant was removed, stretched, and Simultaneous firing was performed.

As a result, homogeneous porous tubes were obtained in all cases. The liquid lubricant has been completely removed by evaporation, and the remaining amount of dupe extracted with acetone (extract dupe under reflux for 2 hours in an acetone and read the weight change before and after extraction) is determined to be 1llII. In both cases, the content was 1.1% by weight or less.

In addition, Table 2 summarizes the physical properties of the porous tube obtained, and the strength characteristics of the tube using the furnace temperature of 390'C or higher are that the matrix strength is 1100KF/α2, and at the same time, the Young's modulus is 10, 0OOK)/(1)2 or more. On the other hand, if an ambient temperature of 360° C. is used, at least one value of matrix strength or Young's modulus will be below the above-mentioned limit.

Characteristics of porous tube obtained from Table 2 4 pieces ↓ Calculated according to the following formula 2.2 FM == Fn
The actual tensile strength of the porous sample is 9/#1M”an;
The apparent specific gravity of the porous sample is Example 2゜Tetrafluoroethylene resin fine powder F104 100 parts by weight plus liquid lubricant naphtha! 5 in a ratio of 26 parts by weight, and after preforming, a bead-shaped molded product with an outer diameter of 25 gates was extruded using a ram extruder, and then passed through a roll mill to form I'
A film of 1 650 am and a thickness of 0.25 ruL was obtained. Next, while the film still contains the liquid lubricant, the liquid lubricant is removed under the conditions shown in Table 8 using a device equipped with the hot air circulation oven shown in the figure, a supply stand suitable for the film, and a guide roll winder. , stretching and firing at the same time. The properties of the obtained porous film are shown in Table 4. It can be seen that in all cases, films with high strength and sufficient air permeability were obtained.

Table 4゜ (Effects of the invention) When conventionally producing a porous tetrafluoroethylene resin body, liquid lubricant was removed in order to obtain a porous body from an unfired molded article containing liquid lubricant molded by the base method. However, with the present invention, these three steps can be performed simultaneously, making it possible to significantly reduce processing equipment, processing time, and energy costs. This greatly contributes to energy and labor savings.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the temperature rising process in the furnace, Figure 2 is a differential thermal spectrum near the crystal melting point, Figure 3 is a schematic diagram showing the measurement of stretching tension in the furnace, and Figure 4 is the measurement result of the tension. , FIG. 5 shows the relationship between temperature and stretching ratio of tetrafluoroethylene resin under constant tension, and FIG. 6 shows an apparatus used to carry out the method of the present invention. In FIG. 1, To is the furnace setting temperature, TI is the crystal melting point, and in FIG. In, FD is the dynamic tension, and in Fig. 6, (1
) feed capstan, (2) pressure box, (
3) Furnace body, (4) Inner cylinder part, (5) Outer cylinder part, (6) Catalyst, (7) Fan, (8) Thermocouple, (9) Heater, (
10 exhaust pipe, 0ω nozzle, μs winding capstan, αJ
Supply stand (tie winder) Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5

Claims (1)

[Scope of Claims] (1) After molding an unfired tetrafluoroethylene resin mixture containing a liquid lubricant by extrusion, rolling, or a method including both, a. ) Evaporation removal of the liquid lubricant b) Stretching in the unfired state C) Firing in the stretched state d) Stretching in the fired state By performing the 4 steps simultaneously, the Young's modulus is 10.0.
00 Ky/cm2 Matrix strength 1,100 K9
A method for producing a porous tetrafluoroethylene resin material having a mechanical strength of 7 cm2 or more. (2) The liquid lubricant was subjected to the four steps of evaporation removal of the liquid lubricant, stretching in the unfired state, firing in the stretched state, and stretching in the fired state at a controlled atmospheric temperature at a wind speed of 5 m/min. A method for producing a porous tetrafluoroethylene resin material according to claim (1), wherein the porous material is combusted using an oxidation catalyst. (3) The shape of the molded product formed by extrusion or rolling, or a method including both, of an unfired tetrafluoroethylene resin mixture containing a liquid lubricant is either film-like, tube-like, or rod-like. Claim No. 1 characterized in that (
1) A method for producing a porous tetrafluoroethylene resin body as described in item 1). (4) The method for producing a porous tetrafluoroethylene resin material according to claim (1), wherein the liquid lubricant has a boiling point range of 260°C or less. , 枦1 4 (5) /& Body temperature lubricant evaporation removal, stretching in unfired state, firing in stretched state, stretching in fired state 4
The tetrafluoroethylene resin porous body according to claim (1), wherein the atmospheric temperature in which the steps are simultaneously performed is 4.50°C or higher, and the temperature distribution in the furnace is 80°C or lower. manufacturing method. (6) The atmosphere temperature in which the evaporation removal of the liquid lubricant, the stretching in the unfired state, and the process are performed simultaneously is 500°C or higher, and the temperature distribution in the furnace is 30°C or lower. 1) A method for producing a porous tetrafluoroethylene resin body as described in item 1). (7) Evaporating and removing the liquid lubricant from an unfired tetrafluoroethylene resin molded product containing a liquid lubricant at an ambient temperature of 390°C or higher, stretching the unfired state, and firing the stretched state;
In an apparatus for manufacturing a porous polytetrafluoroethylene resin body by simultaneously performing four steps of stretching in a fired state, the heating furnace consists of an inner cylinder part through which the molded product passes and an outer cylinder part in which a heater is installed. The two parts are connected at both ends, and there is a means for circulating the atmosphere, a means for detecting the atmosphere temperature and adjusting the heat generation of the heater, and a means for controlling the outside air at the furnace inlet and outlet. A hot air circulation furnace consists of a means for adjusting the inflow of liquid, a means for forcibly exhausting part of the furnace atmosphere, and a catalyst for oxidizing liquid lubricant. 1. An apparatus for producing a porous tetrafluoroethylene resin body, comprising a winding means having a speed as high as 1000.degree.