阅读说明：本技术 一种高强度低伸长聚四氟乙烯超细长丝的制造工艺 (Manufacturing process of high-strength low-elongation polytetrafluoroethylene ultra-fine filaments ) 是由 阙福明 于 2019-09-20 设计创作，主要内容包括：本发明属于聚四氟乙烯功能性材料制备领域,特别涉及一种高强度低伸长聚四氟乙烯超细长丝的制造工艺。本发明通过将聚四氟乙烯分散颗粒料低温给油处理,熟化,真空模压成型,推压挤出料条,压出薄膜,进行三次纵向加热拉伸,并分别限定三次纵向加热拉伸的拉伸温度、拉伸倍率和拉伸速率,得到PTFE扁丝,并将扁丝加捻制备成圆丝,加热拉伸定型,制备成500～550dtex PTFE长丝。通过本发明工艺制备出的长丝,线密度小,且实现了强度高、伸长率低的理想指标,有利于聚四氟乙烯长丝的广泛应用。(The invention belongs to the field of preparation of polytetrafluoroethylene functional materials, and particularly relates to a manufacturing process of a high-strength low-elongation polytetrafluoroethylene ultra-thin filament. The PTFE flat filament is prepared by low-temperature oiling treatment of polytetrafluoroethylene dispersed particles, curing, vacuum compression molding, pushing and extruding an extruded material strip, extruding a film, carrying out three times of longitudinal heating and stretching, respectively limiting the stretching temperature, stretching ratio and stretching speed of the three times of longitudinal heating and stretching to obtain the PTFE flat filament, twisting the flat filament to prepare a round filament, and carrying out heating, stretching and shaping to prepare the 500-550 dtex PTFE filament. The filament prepared by the process has small linear density, realizes ideal indexes of high strength and low elongation, and is beneficial to wide application of the polytetrafluoroethylene filament.)

1. A manufacturing process of a high-strength low-elongation polytetrafluoroethylene ultra-thin filament is characterized by comprising the following steps: the preparation process comprises the following steps: carrying out three times of sintering and stretching treatment on the calendered and degreased polytetrafluoroethylene film, wherein the three times of sintering and stretching treatment are respectively as follows:

(1) first sintering and stretching: putting the polytetrafluoroethylene film into a drafting and shaping oven for stretching, wherein a plurality of drafting rollers are arranged in the oven, and the rollers are arranged in a vertically staggered manner;

the first heating temperature is 380-430 ℃, and the total stretching ratio is 18-20 times;

(2) winding: winding the thin film stretched out for the first time into a rolled film, placing the rolled film for natural cooling, and placing the film for cooling for more than 6 hours;

(3) and (3) second sintering and stretching: longitudinally cutting the film cooled in the step (2), and feeding the cut film into an oven for second heating and stretching; heating at 425-435 ℃, stretching at a stretching ratio of 6-8 times and a stretching speed of 12m/min, and naturally cooling to room temperature;

(4) and (3) third sintering and stretching: longitudinally cutting the PTFE film obtained in the step (3), and performing third heating stretching on the cut PTFE film through an arc-shaped plate to obtain a PTFE flat wire;

(5) and (3) twisting the PTFE flat filaments obtained in the step (4) by a twisting machine to prepare round filaments, winding the twisted filaments, and stretching and shaping to obtain 500-550 dtex PTFE filaments.

2. The process of manufacturing a high strength low elongation polytetrafluoroethylene ultra-fine filament according to claim 1, wherein: and (2) 5 drafting rollers are arranged in the drafting and shaping oven in the step (1), the stretching multiple of each drafting roller is different, and the stretching multiple of the rollers from film feeding to film discharging is 17%, 11%, 17%, 11% and 44% of the total stretching multiple in sequence.

3. The process of manufacturing a high strength low elongation polytetrafluoroethylene ultra-fine filament according to claim 1, wherein: and (2) the film in the step (1) enters the oven at a stretching speed of 2-3 m/min, and the film out of the oven at a stretching speed of 25-30 m/min.

4. The process of manufacturing a high strength low elongation polytetrafluoroethylene ultra-fine filament according to claim 1, wherein: and (3) placing and cooling for 12-24 hours in the step (2).

5. The process of manufacturing a high strength low elongation polytetrafluoroethylene ultra-fine filament according to claim 1, wherein: the surface temperature of the arc-shaped plate in the step (3) is 350-380 ℃, the drawing linear speed is 25-30 m/min, and the drawing multiplying power is 1 time.

6. The process of manufacturing a high strength low elongation polytetrafluoroethylene ultra-fine filament according to claim 1, wherein: the twisting number of the twisting in the step (5) is 360-380 twists/m, and the heating, stretching and shaping temperature is 300-350 ℃.

7. The process for manufacturing a high strength low elongation polytetrafluoroethylene ultra-fine filament according to any one of claims 1 to 6, wherein: before sintering and stretching treatment, the method also comprises the following treatment steps:

(1) mixing materials: adding lubricating oil into the polytetrafluoroethylene dispersed granules, stirring uniformly, and storing for more than 8 hours at a low temperature lower than 15 ℃;

(2) curing: putting the polytetrafluoroethylene mixture stored in the step (1) into a curing box, and curing for 10-12 hours at a constant temperature of 45-50 ℃;

(3) pre-pressing: putting the cured polytetrafluoroethylene mixture obtained in the step (2) into a prepressing material cylinder for double-sided prepressing to obtain a blank, wherein the oil cylinder pressure is 8-12 MPa, and prepressing for 35-50 min for forming;

(4) extrusion by pushing: putting the blank in the step (3) into a pushing and pressing die cavity for pushing and pressing, continuously extruding to obtain a strip material, and putting the strip material into water at 50 ℃ for heat preservation for 6 hours;

(5) rolling and film forming: feeding the strip material subjected to heat preservation in the step (4) into a calender through a guide plate to be pressed into a film;

(6) degreasing: degreasing the film rolled in the step (5) by using degreasing oil recycling equipment to obtain a degreasing film;

(7) and sintering, stretching and twisting the degreasing film for multiple times.

8. The process of manufacturing a high strength low elongation polytetrafluoroethylene ultra-fine filament according to claim 7, wherein: the lubricating oil is paraffin oil, and the adding amount of the lubricating oil is 25-32% of the mass of the polytetrafluoroethylene dispersed granules.

Technical Field

The invention belongs to the field of preparation of polytetrafluoroethylene functional materials, and particularly relates to a preparation method of polytetrafluoroethylene filaments with high strength and low elongation.

Background

The Polytetrafluoroethylene (PTFE) has the excellent characteristics of temperature resistance, corrosion resistance, aging resistance, non-adhesion, non-hydrolysis and the like, and the PTFE filament yarn produced by the PTFE can be used as sewing thread for sewing PTFE high-temperature resistant dust removal bags, can also be woven into cloth and nets by warp and weft after being doubled and twisted, and is suitable for reinforcing materials such as ionic membranes, rubber pads and the like.

Wherein the polytetrafluoroethylene filter material meets the requirements of gas dust particle discharge in the current various chemical industriesConcentration of radioactive substance<20mg/Nm³The preferred filter material. The filter material is made into various filter bags, filter plates, filter elements and dust removing equipment, so that the aim of environmental protection and standard reaching of discharge is fulfilled. The filter material can be subjected to frequent vibration and tension in a dust filter or dust removing equipment, and if the filter material is low in strength and easy to damage, the filter material is stretched to be large and loosened after being stressed, so that the working performance is affected. Strength and elongation are therefore one of the most important quality requirements for filter materials. The strength and elongation of the filter material are determined by the filter material base cloth, and the base cloth is woven by the filaments, so the strength and elongation of the filaments determine the strength and elongation of the filter material.

At present, PTFE filaments produced by domestic manufacturers generally have the problems of low strength and overlarge elongation, so that the weaving process and the quality of the filter material base fabric are not influenced a little, and the quality of the filter material is difficult to improve. Some manufacturers produce filaments with high strength but large elongation, and other filaments with low elongation, which meet the requirements, but the strength is not enough, and the polytetrafluoroethylene filaments produced by the manufacturers at present have the main quality indexes: the strength is generally 26cN/tex (centiNewton/tex), the maximum strength is 36cN/tex, and the elongation at break is generally between 11 and 28 percent. All have the problems of low strength and large elongation. The quality requirements of high strength and low elongation of the polytetrafluoroethylene filter material silk cannot be completely met, which causes great confusion to customers.

In the CN201610134558.8 polytetrafluoroethylene filament and the preparation method and application thereof, the sintered and drafted flat filament is twisted by a twisting machine to prepare a round filament, the round filament is shaped at the temperature of 375-400 ℃, and the shaped round filament is quenched at the temperature of 0-5 ℃ so as to ensure the strength of the polytetrafluoroethylene filament, wherein a special quenching device is needed, the process is complex, the cost is high, and the improvement of the crystallinity of the polytetrafluoroethylene is not facilitated. In the manufacturing process of the CN201410468609.1 high-strength low-elongation polytetrafluoroethylene filament, the high-temperature, high-stretching speed, stretching ratio and high-density process are adopted, the strength and the elongation at break of the prepared filament have excellent effects, but the filament can only reach the linear density of more than 1000D and has larger thickness, and the filament can not meet the requirements of the polytetrafluoroethylene filament with higher stretching ratio and smaller linear density under the high process. The conventional superfine polytetrafluoroethylene filament with the linear density of about 500dtex has the monofilament strength of only 13-14N, the breaking strength of 30cN/tex and the elongation at break of about 10 percent, and is difficult to obtain higher effect on the mechanical property. With the increasing demand, the development of ultrafine polytetrafluoroethylene filament products with smaller line density and higher strength is also needed.

The crystallinity of the PTFE polymer is one of important factors influencing the mechanical property of the PTFE polymer, and the higher the crystallinity is, the higher the breaking strength is, and the improvement of the breaking elongation is limited. However, in the conventional process, the crystallinity of the PTFE base tape is improved by heat treatment, which is only about 70%. Further, the process for producing PTFE filaments disclosed in the prior art is difficult to achieve. Therefore, it is necessary to further explore, continuously develop and develop the production technology, break through the technical bottleneck, and find out a new technology and a new method of the polytetrafluoroethylene ultrafine filament manufacturing technology which can improve the strength and reduce the elongation at break.

Disclosure of Invention

In order to solve the technical problems, the invention provides a manufacturing process of a high-strength low-elongation polytetrafluoroethylene ultra-thin filament. By researching the heat treatment stretching process, the molecular chain structure of the polytetrafluoroethylene is rearranged regularly to a larger extent, and the orientation degree and the crystallinity of the PTFE are improved, so that the strength of the PTFE filament is improved, and the elongation is reduced.

The technical scheme adopted by the invention is as follows:

a manufacturing process of a high-strength low-elongation polytetrafluoroethylene ultra-thin filament comprises the following specific operation steps:

(1) mixing materials: adding lubricating oil into the 550-560 um polytetrafluoroethylene dispersed granules, uniformly stirring in a stirrer, discharging after stirring, and storing for more than 8 hours in a low-temperature environment lower than 15 ℃; preferably 0 to 5 ℃.

Further, the lubricating oil is paraffin oil, and the adding amount of the lubricating oil is 25-32% of the mass of the polytetrafluoroethylene dispersed granules;

(2) curing: putting the polytetrafluoroethylene mixture stored in the step (1) into a curing box, and curing for 10-12 hours at a constant temperature of 45-50 ℃;

(3) pre-pressing: putting the cured polytetrafluoroethylene mixture obtained in the step (2) into a prepressing material cylinder for double-sided prepressing, wherein the pressure of an oil cylinder is 8-12 MPa, and prepressing for 35-50 min for forming to obtain a blank;

(4) extrusion by pushing: putting the blank in the step (3) into a pushing and pressing die cavity for pushing and pressing, continuously extruding a strip material, and putting the strip material into water at 50 ℃ for heat preservation for 6 hours;

wherein, in the pushing extrusion operation, the compression ratio is 240-300, and the speed of extruding the material strip is 230-240 mm/min; the cross section of the control bar is oblate.

(5) Rolling and film forming: feeding the strip material subjected to heat preservation in the step (4) into a calender through a guide plate to be pressed into a film;

wherein, during rolling, the temperature of a press roll is 67-72 ℃, and the linear speed of the rolling is 12-16 m/min;

(6) degreasing: degreasing the film rolled in the step (5) by using degreasing oil recycling equipment to obtain a degreasing film;

(7) first sintering and stretching: and (2) putting the degreased film into a drafting and shaping oven for first heating and stretching, wherein 5 drafting rollers are arranged in the oven, the rollers are vertically staggered to form an S shape (as shown in figure 1), and the film is put into the oven and is heated and stretched to obtain the film.

The heating temperature is 380-430 ℃, the total stretching ratio is 18-20 times, the stretching speed of the film entering the oven is 2-3 m/min, and the stretching speed of the film exiting the oven is 25-30 m/min.

Wherein, the stretching ratio of each drafting roller is different and is 17 percent, 11 percent, 17 percent, 11 percent and 44 percent of the total stretching ratio in sequence.

And during the first drafting, the heating temperature and the stretching mode are adjusted to increase the stretching multiplying power of the PTFE film to 18-20 multiplying powers, so that the stretching orientation degree of the PTFE film is improved to the maximum extent. If the multiplying power is less than 18 times, the molecular orientation is not beneficial, and if the multiplying power is more than 20 times, the filament breakage phenomenon is easy to occur, the production efficiency is influenced, and the fracture strength of the fiber is reduced due to the excessively high plasticizing tension. Therefore, a draw ratio of 18 to 20 is a preferable condition, and the strength of the fiber can be remarkably improved at the draw ratio.

And the stretching multiples of the rollers are different, so that the improvement of the stretching multiple is facilitated, and the longitudinal molecular orientation degree is gradually improved, so that the strength and the uniformity of the filaments are improved.

(8) Winding: and (3) pulling out the film stretched out for the first time, winding the film into a roll film at the speed of 30-35 m/min, placing the film for natural cooling after winding, and placing the film for cooling for more than 6 hours.

Further, preferably, the standing and cooling time is 12-24 h, and after the standing is finished, the subsequent operation is carried out;

through detection, after the PTFE film is stretched, cooled and placed for the first time, the crystallinity of the PTFE film reaches 50-55%.

The winding and cooling aims to reduce the cooling rate and prolong the cooling time, the thermal motion of molecular chains is weakened and regularly arranged after the PTFE is cooled to a temperature below the melting temperature from a melt, the cooling time is relatively long, the internal structure can be adjusted in a sufficient time, and the molecular chains can be rearranged and enter regular lattices. Therefore, the longer the slow cooling time, the longer the crystallization time, and the more sufficient the internal crystallization.

(9) And (3) second sintering and stretching: and (4) longitudinally slitting the film placed in the step (8), cutting, and then heating and stretching in an oven for the second time.

Heating at 425-435 ℃, stretching at 6-8 times and at a stretching rate of 12m/min to obtain the PTFE film, and naturally cooling to room temperature. The room temperature of the preferred operating chamber is below 20 ℃.

And after naturally cooling to room temperature, detecting that the crystallinity of the PTFE film reaches 75-80% for the second time.

(10) And (3) third sintering and stretching: and (4) longitudinally slitting the PTFE film obtained in the step (9), and performing third heating stretching on the cut PTFE film through an arc-shaped plate to obtain the flat PTFE filament.

Wherein the surface temperature of the arc-shaped plate is 350-380 ℃, the stretching linear speed is 25-30 m/min, the stretching magnification is 1 time, the PTFE filament is cooled to room temperature at a cooling rate of 0.5-2.0 ℃/min, and the crystallinity of the PTFE filament after the third stretching reaches 85-88%.

(11) Twisting the stretched flat filaments obtained in the step (10) by a twisting machine to prepare round filaments, winding the twisted filaments, and stretching and shaping to obtain PTFE round filaments with a certain specification;

wherein the twisting number is 360-380 twists/m, and the heating, stretching and shaping temperature is 300-350 DEG C

The linear density of the obtained PTFE round wire is 500-550 dtex.

The invention has the beneficial effects that:

(1) the invention adopts vacuum compression molding, greatly reduces the air in the molded plastic, improves the density and the uniformity of the semi-finished product, and plays a key role in improving the quality of the product in the subsequent pushing and pressing and calendering processes; the cross section of the extruded strip is oblate, and the extruded strip is soaked in warm water after being pushed, so that the method plays a key role in improving the width of a calendered film and the longitudinal arrangement orientation degree of fibers;

(2) according to the invention, through 3 times of stretching operations, the temperature and the cooling mode for each stretching are respectively set, the mobility of PTFE molecular chains is large under high-temperature stretching, and the macromolecules in amorphous regions have enough fluidity, so that the chips among the molecular chains can be fully unwound, the process can be smoothly carried out under high-magnification hot stretching, the alignment orientation degree can be improved, and the molecular chains are ensured to be regularly aligned through the cooling mode, the structure is adjusted, and the crystallization is more sufficient. Compared with the prior art, the strength of the PTFE filament is increased, and the elongation at break is reduced.

Drawings

FIG. 1 is a schematic diagram of the drawing machine in the draw-setting oven of the present invention.

Detailed Description