WO2004072157A1

WO2004072157A1 - Polytetrafluoroethylene fibrous powder, polytetrafluoroethylene paper-like material, polytetrafluoroethylene molding and process for producing the polytetrafluoroethylene fibrous powder

Info

Publication number: WO2004072157A1
Application number: PCT/JP2004/001187
Authority: WO
Inventors: Norihiko Miki; Tadao Hayashi; Tetsuya Higuchi
Original assignee: Daikin Industries, Ltd.
Priority date: 2003-02-12
Filing date: 2004-02-05
Publication date: 2004-08-26
Also published as: CN1717436A; CN100374485C; TW200426161A; JPWO2004072157A1; TWI299044B; JP4277854B2

Abstract

A polytetrafluoroethylene fibrous powder which when subjected to differential scanning calorimetry performed at a rate of temperature rise of 5°C/min, exhibits a ratio of low temperature side peak area of 88.5% or more based on the whole peak area in an obtained fusion endothermic curve. There is also provided a paper-like material constituted of the polytetrafluoroethylene fibrous powder, which excels in uniform pressure capability, air permeability and dust collection performance.

Description

Akira Itoda Polytetrafluoroethylene fibrous powder, polytetrafluoroethylene papermaking, polytetrafluoroethylene molded product, and method for producing polytetrafluoroethylene fibrous powder

The present invention relates to a polytetrafluoroethylene papermaking material excellent in pressure equalizing property, air permeability, and dust collecting property, a polytetrafluoroethylene fiber fibrous powder as a raw material thereof, a molded article made of the papermaking material, and production. The present invention relates to a method for producing a highly efficient polytetrafluoroethylene fibrous powder. More specifically, the present invention relates to a method for producing a polytetrafluoroethylene fibrous powder capable of obtaining a polytetrafluoroethylene paper having a smooth surface and excellent air permeability when formed. Background art

Polytetrafluoroethylene (hereinafter abbreviated as PTFE) has excellent chemical resistance, heat resistance, mechanical properties, and electrical properties, and its use is wide-ranging, mainly for industrial use. Therefore, it can be used in a variety of forms, and paper-like products are used for filter paper, thermal insulation, and insulation.

Various methods are known as a method for producing a paper-like article. For example, Japanese Patent Publication No. 45-8165 discloses a PTFE fibrous powder having an average fiber length of 100 to 500 m and an average shape factor of 5 or more, or a filler mixed uniformly with this. A method is disclosed in which a paper composition is dispersed in a liquid to form a paper stock, which is made and dried, and then the paper is peeled off from the substrate and fired. The PTFE fibrous powder used here is a material that strongly shears raw PTFE at high temperatures. It is obtained by crushing by applying force. At the time of this pulverization, it is described that the pulverizer itself may be heated or the powder may be heated, and it is further described that a method of pulverizing while blowing hot air is most preferable. However, only such a description is given, but no specific contents and examples are disclosed, and no description is given of the temperature conditions at the time of the pulverization treatment. Conventionally, pulverization is performed at a temperature of about 20 to 50 ° C, but when processed at this temperature, relatively fine PTFE powder with a particle size of 5 im or less is generated, and is made of hard PTFE with low air permeability. There is a problem of becoming paper. On the other hand, the present inventors have found a method for producing a PTFE paper product as described in Japanese Patent Publication No. 40-11642 or Japanese Patent Publication No. 45-14127, which has excellent cushioning and pressure equalizing properties. Was found. However, there was no knowledge on what kind of properties PTFE fibrous powder could be used to obtain a uniform paper product suitable for cushioning materials and filter materials.

In order to improve mechanical strength, it is necessary to manually attach reinforcing threads and back up with wire mesh, resulting in problems such as non-uniformity of strain, shortening of service life, and the excellent electrical properties of PTFE. When used as a substrate material taking advantage of its characteristics, it was difficult to make it thinner due to the problem of self-holding. Disclosure of the invention

The present invention has been made to overcome the above problems by clarifying the above problems, and has a uniform distribution of physical properties, and is excellent in cohesiveness, pressure equalization, air permeability, and dust collecting properties. It is an object of the present invention to provide a PTFE fibrous powder, a molded article made of the PTFE paper product, and a method for producing the PTFE fibrous powder having excellent production efficiency.

That is, the present invention relates to a differential scanning calorimeter performed at a heating rate of 5 ° C. per minute. The analysis relates to a PTFE fibrous powder having a peak area ratio on the low temperature side of the obtained endothermic curve of 88.5% or more of the total peak area.

The PTFE fibrous powder preferably has an average fiber length of 100 to 5000 mm and an average shape factor of 5 or more.

The specific surface area measured by the nitrogen adsorption method is preferably 4.0 m ² Zg or more.

The present invention also relates to a polytetrafluoroethylene papermaking product obtained by using the PTFE fibrous powder as a raw material and going through a papermaking process.

Furthermore, in the present invention, in a differential scanning calorimeter analysis performed at a heating rate of 5 ° C per minute, the peak area ratio on the low-temperature side in the obtained melting endothermic curve is 88.5% or more of the total peak area. A method for producing a polytetrafluoroethylene fibrous powder having an average fiber length of 100 to 5,000 m and an average shape factor of 5 or more, comprising supplying a raw material polytetrafluoroethylene powder. Feeding the raw material polytetrafluoroethylene powder from the hopper to a stretching treatment tank, stretching by a stretching means, and classifying after stretching. The present invention relates to a method for producing a fluoroethylene fibrous powder.

In the above production method, it is preferable that the supply of the raw material polytetrafluoroethylene powder from the hopper to the stretching treatment tank is performed by using the flow of a medium. It is preferable to remove the polytetrafluoroethylene powder having a particle size of 5.0 m or less by a classification step performed after the stretching treatment.

The amount of energy applied to the polytetrafluoroethylene powder from the stretching means during the stretching process is preferably 10 to 200 kcalZkg. In addition, the present invention relates to a molded article obtained from the PTFE paper product. BRIEF DESCRIPTION OF THE FIGURES Figure 1 shows an example of a melting endothermic curve obtained by analyzing PTF powder with a differential scanning calorimeter, and two peak curves obtained by separating the peaks of the melting endothermic curve. BEST MODE FOR CARRYING OUT THE INVENTION

Fig. 1 shows an example of a melting endothermic curve (hereinafter also referred to as a DSC curve) obtained by analyzing PTFE powder with a differential scanning calorimeter (solid line), and two peak curves obtained by separating the peaks of the DSC curve. (Broken line).

Differential scanning calorimeter measurement of PTFE fine powder with normal molecular weight shows that there is a double peak or a clear shoulder from around 337 to around 340 ° C as shown in Fig. 1. A single peak is observed. This is due to the release of the first (lower temperature) peak (or shoulder) due to the release of the micro-Brownian motion of molecules that have been unraveled during the polymerization process of PTFE, and the micro-Brownian motion of the molecules that have not progressed during the polymerization process. Molecules that consist of a second (high-temperature side) peak (or shoulder) due to release, and that have not progressed during the polymerization of PTFE Since the release of the micro-Brownian motion occurs, a time lag occurs from the occurrence of the first peak, and a melting peak (or shoulder) appears on the apparently higher temperature side. Therefore, if the measurement is performed at a too slow heating rate, the time lag will be very small, and it will be difficult to distinguish from the apparent appearance.

Since the molecular weight of PTFE molecules is much larger than that of general-purpose molten resins, it may be more energy stable to organize them with a single molecular chain than to organize them as a group. In particular, it can be said that in the polymerization process, the molecules are present in a state where the binding force from the surroundings is relatively small, so that the conformational stabilization of one molecular chain is likely to occur. But Unlike the polymerization and growth reaction in the ideal space, some molecules are organized by interference from external forces such as shear force and intermolecular force.

In the process of molding and sintering the PTFE powder, the disintegration of molecules progresses further, and the more fusion between tissues occurs, the more the molded product with excellent cohesion and shape can be obtained. In the case of an object, the stress is transmitted uniformly, and the pressure is excellent.

As mentioned above, the disentanglement of the molecular chains may have occurred during the temperature rise.However, if only the thermal disentanglement operation was used, it would be difficult to achieve uniform control of the disassembly, and some excess heat would be applied. In such a case, there is a problem that the site is firmly organized and loses the adhesion to other tissues. To avoid this, it is preferable to use unraveling by external force and unraveling by heat at the same time.

When the disentanglement of molecules has been completed, it is often not possible to make papermaking into a favorable state. This is because, during the operation of papermaking, the external force and heat applied to the PTFE fibrous powder have advanced their organization, and have passed the optimal state for organization as paper. It seems that there is a cause. For this reason, it is easily understood that it is necessary to control the properties of the paper-making material so that the PTFE fibrous powder is in an optimum loosened state before paper-making. The melting peak on the DSC curve of the PTFE powder that has been completely unraveled is a single peak and shifts to around 325 to 328 ° C, and the PTFE fibrous powder of the present invention Is not included.

It can be said that the peak area in the melting endothermic curve obtained by the differential scanning calorimeter is directly proportional to the calorific value, and is proportional to the number of molecules in a generally accepted range. Therefore, as shown in Figure 1, two pins When a DSC curve with a single peak or peak is separated into two normal or other distribution curves, as shown by the dashed lines, the molecule whose peak area on the cold side is unraveled And the area of the peak (P _H ) on the high temperature side can be considered to be proportional to the number of undissociated molecules, so that the ratio of the dissociated PTFE molecules is It can be evaluated by the ratio of the area of the low-temperature side peak (P _L ) to the total peak area in the melting endothermic curve obtained by the differential scanning calorimeter.

A double peak or a single peak with a distinct shoulder can be mathematically understood as a composite curve with three or more multiple normal distributions, but since it has two vertices, it has two normal distributions or Separation as a distribution curve similar to this is considered sufficiently valid, and reasonable results have been obtained in the study of the present invention. This means that even partially unmoltened molecules are considered to have a small calorific value for unmolling, and are included in the normal distribution of unmolten molecules. The composite absorption peak can usually be separated by approximation using a Gaussian-Lorentian type curve. Compared to using either Gaussian-type or Lorentian-type curves alone, the degree of divergence is smaller, and this method is also used in the computational software attached to many commercially available analytical instruments. In the present invention, the basic peak position is determined by giving the two apparent vertices found in the PTFE powder as a raw material as initial values and performing approximation without any restriction. The basic peak positions obtained in this way are 339.14 ° «0 and 33.43.01, and based on this, the linear and half-value widths are not limited, and only the peak temperature is the initial value. From this, the composite curve was separated into two by approximation with the range limited to 0.6 to 0.7 or less, and the peak area was determined. In this study, we tried to reduce the time required for convergence of values. For this purpose, information on the raw material powder was used, but it can also be obtained directly from the melting curve of the fibrous powder.

The PTFE fibrous powder of the present invention was subjected to differential scanning calorimetry analysis at a heating rate of 5 ° C per minute, and the peak area on the low temperature side of the obtained melting endothermic curve was 88.5% of the total peak area. It is preferably 92.0% or more and 99.5% or less. If the low-temperature side peak area is less than 88.5% of the total peak area, the cohesive force tends to be insufficient and the molded article tends to lose its shape, and the obtained paper tends to have poor cushioning properties. is there. As already mentioned, when the peak area on the low temperature side is too large, that is, when two peaks (or shoulders) are not observed, it is often impossible to obtain a desirable state of molding the paper.

In general, in molding methods such as papermaking and compression molding, unlike the molding method that involves uniform melting at the molecular level, the specific surface area of the raw material greatly affects its cohesion, that is, the mechanical properties of the molded product. The larger the specific surface area, the better the mechanical properties of the molded product. This is due to an increase in the contact area of the individual raw materials, thereby increasing the stress transmission point as a structure, and as a result, improving the mechanical properties of the whole structure. This is the same in the case of PTFE. As the specific surface area of the PTFE fibrous powder increases, the cohesive force increases, and a structure that does not lose its shape and has more excellent mechanical properties can be obtained. On the other hand, the more the PTFE fibrous powders are fused together, the smaller the specific surface area of the paper product, and the specific surface area reduction rate exceeding a certain level is a prerequisite for estimating the physical properties of the paper product. It can be said that it will be an important night.

The same applies to the case of the PTFE fibrous powder and its molded product.The greater the specific surface area of the PTFE fibrous powder, the greater the cohesive force of the PTFE fibrous powder. Can be Therefore, in the present invention, the specific surface area of the PTFE fibrous powder may be 4.0 m ² / g or more. More preferably, it is not less than 5.0 m ² Zg and not more than 8.5 m ² Zg. Here, the specific surface area is a value measured by a nitrogen adsorption method. When the specific surface area is less than 4.0 m ² / g, the cohesive force is insufficient, and the mold easily collapses during molding. In addition, the molded product lacks uniformity, and the desired physical properties cannot be obtained. If the specific surface area is larger than 8.5 m ² Zg, the fibrous powder is likely to be densely packed, resulting in a large weight per unit area of the paper, resulting in low air permeability and a tendency to hardly exhibit cushioning properties. . In order to exhibit the properties of paper, it is preferable that the raw material powder has a fibrous shape.In general, the shape factor can indicate that the raw material is fibrous. In some cases, amorphous powders exhibiting cohesive strength as paper show cohesive strength but may not be fibrous in view factor. In such a case, by defining the specific surface area together with the view factor, it can be determined whether or not the raw material can exhibit the properties as paper. In view of these, it may be considered that the fibrous state means that all or a part thereof is stretched by an external force and can exhibit anisotropy in physical properties.

The raw material PTFE used in the present invention may be a homopolymer of tetrafluoroethylene (hereinafter abbreviated as TFE), or 95 to 100 mol% of TFE, and the formula (I):

CX ₂ = CY (CF ₂ ) _n Z (I)

(Wherein, X, Y and Z are the same or different, each is a hydrogen atom or a fluorine atom, and n is an integer of 1 to 5), and a formula (II):

CF ₂ = CF-OR ^f (II)

(Wherein, R ^f is a fluorine-containing alkyl group having 1 to 3 carbon atoms) At least one monomer selected from the group consisting of fluorine-containing (alkyl bier ether) (hereinafter abbreviated as PAVE) Modified TFE weight with 5 mol% Coalescence (modified PTFE).

Examples of the fluoroolefin represented by the formula (I) include perfluoroolefins such as hexafluoropropylene (hereinafter abbreviated as HFP).

Examples of the fluorine-containing (alkyl vinyl ether) represented by the formula (II) include perfluoro (methyl vinyl ether) (hereinafter abbreviated as PMVE), perfluoro (ethyl vinyl ether) (hereinafter abbreviated as PEVE), and perfluoro. (Propyl vinyl ether) (hereinafter abbreviated as PPVE).

The raw material PTFE powder used in the present invention can be obtained by polymerization using a polymerization initiator in the presence of a water-soluble fluorinated dispersant. In order to reduce the molecular weight of the obtained polymer, methods such as increasing the amount of a polymerization initiator, adding a chain transfer agent, or adding a modifying monomer are employed. Examples of the polymerization initiator include persulfates and organic peroxides, and examples of the chain transfer agent include hydrogen and hydrocarbons such as propane, and water-soluble compounds such as ethanol.

The raw material PTFE powder thus obtained preferably has an average particle size of 5 to 2000 m. If the average particle size is less than 5 zzm, the paper will be hard and have low air permeability due to the large amount of fine powder after treatment. If the average particle size exceeds 2 OO Om, coarse powder will remain after the treatment, resulting in a paper with a rough surface.

The PTFE fibrous powder of the present invention can be produced by the following production method using, for example, an apparatus having a raw material hopper, a stretching tank, and a classification device.

First, the raw material PTFE powder is charged from a supply machine into a raw material hopper, The raw material PTFE powder is supplied from the hopper to the stretching tank. The supply of the raw PTFE powder to the drawing tank may be performed by dropping under its own weight, or may be performed mechanically depending on the form of the raw PTFE powder, but the shape of the obtained PTFE fibrous powder is completely controlled. In order to achieve this, it is preferable to use a medium having a high fluidity such as a liquid or a gas.

The stretching treatment tank is provided with stretching means (details will be described later). Use fibrous powder. Here, when processing the raw material PTFE powder, it is preferable to control the amount of energy applied to the PTFE powder during the process to control the degree of unraveling of the PTFE fibrous powder.

Then, only the fully drawn powder is sorted out by the classifier and sent to the next classifier. Other powders are returned to the stretching tank for further processing. Finally, the PTF powder having a particle size of 5 m or less is removed by a classifier (the measuring method will be described later), and the PTF E fibrous powder of the present invention is obtained. Hereinafter, each step will be described in detail.

In the step of supplying the raw material PTFE powder from the raw material hopper to the stretching tank, if a material having a small particle size is used, it hardens in the hopper, and it becomes difficult to drop and supply the PTFE powder by its own weight. In that case, a liquid such as water can be forcibly supplied to the stretching tank as a medium. When the obtained PTFE fiber powder is stored without immediately sending it to the papermaking process, it is not preferable to use a liquid medium, so supply the raw PTFE powder using a gas such as dry air as the medium. be able to. However, it is not preferable because it may affect the movement of the rotating body in the stretching tank or the discharge of the stretched raw PTFE powder. By such an operation, a PTFE fibrous powder having an average fiber length of 100 to 500; m and an average shape factor of 5 or more can be produced very efficiently. The stretching treatment temperature preferably utilizes the frictional heat during stretching. This tends to make it easier to fibrillate and to obtain powder having a relatively stable fiber length. Therefore, it is preferable that the stretching means performs a stretching process using a frictional force. Such a stretching means includes, for example, a hammer mill and a screen mill, and is preferably an apparatus capable of applying a shearing force in one direction only by a rotating body to stretch the raw material powder. By controlling the amount of energy applied to the PTFE powder from the stretching means during the stretching process to 10 to 200 kcal Zkg, it is possible to prevent the generation of PTFE aggregates. In particular, it is preferable to control the energy amount to 10 to 60 kca 1Z kg. The PTFE paper made from the PTFE fibrous powder obtained in this way has much entanglement between the fibrous powders, and is locally excellent in cushioning properties accompanied by heat fusion between the powders. Papermaking can be obtained. Here, if the amount of energy added to the PTFE powder from the stretching means is less than 10 kca 1 Zkg, short fibrous powders increase and sufficient physical entanglement cannot be obtained. On the other hand, when the energy amount exceeds 200 kca 1 / kg, heat fusion between the fibrous powders tends to hardly occur. Here, the amount of energy applied to the PTFE powder from the stretching means during the stretching process can be defined by the amount of energy given to the stretching means. The amount of energy given to the stretching means is the amount of energy per 1 kg of the PTFE powder required to maintain the number of revolutions of the stretching when the PTFE powder is stretched by the stretching means. It can be obtained from the difference between the current values of When using a medium to supply the raw material to the stretching tank, the amount of heat to be applied must be calculated based on the room temperature of 40 ° C or less, including the amount of heat given from the temperature difference with the medium.

In the process of classifying PTFE powder after processing, the raw material PTFE powder is processed, and then classified using a classifier. By this classification operation, It is possible to prevent PTFE fibrous powder with insufficient elongation from flowing out of the stretching treatment tank. Therefore, a PTFE fibrous powder having an average fiber length of 100 to 5000 m can be efficiently obtained. In particular, the average fiber length is preferably from 100 to 4000. If the average fiber length is less than 100 zm, a part of the average fiber length will fall off from the net-like base material during papermaking, causing pinholes. On the other hand, if the average fiber length exceeds 5000 m, it will be difficult to produce paper with a uniform thickness because the fiber length is long. Examples of the classification device include a classification screen and the like, and a device capable of separating powder at a predetermined size as a boundary is preferable.

Furthermore, removing the PTFE fibrous powder having a particle size of 5 m or less is preferable in that the air permeability of the PTFE paper made using the powder is improved, and the PTFE is excellent in flexibility and cushioning property. Further, it is preferable to remove the PTFE fibrous powder having a particle size of lOzm or less.

Here, the particle size is measured using a laser diffraction type particle size distribution analyzer HELO S & RODOS system (manufactured by SYMPATEC) while dispersing the PTFE fiber powder with 3 bar compressed air. Particle size refers to 50% particle size.

Further, the average view factor of the PTFE fibrous powder is preferably 5 or more, more preferably 10 or more. The upper limit of the average view factor is not particularly limited, but is preferably 1000 or less. The average form factor is obtained by dividing the fiber length by the fiber width. When the average form factor is less than 5, the paper is difficult to peel off from the net-like base material after firing, resulting in a poorly finished paper having poor surface smoothness and appearance (fluffing, distortion).

The PTFE fibrous powder thus obtained can be paper-made by the following method.

First, the PTFE fibrous powder is uniformly dispersed in water or the like with a dispersant. And is considered as stock. At this time, an organic polymer reinforced fiber, an inorganic filler and the like may be added to the stock. The stock is formed on a substrate such as a net. After that, it is dried and fired to obtain PTFE paper. In particular, when organic polymer-reinforced fibers are contained, a filter having a larger area can be installed without backing, thereby reducing the size of the filter unit.

The thickness of the PTFE paper obtained by papermaking depends on the intended use, but is preferably 0.02 mm or more and 8.00 mm or less, more preferably 0.05 mmL¾ and 6.0 mm or less. More preferably, it is more than 0.10 mm and less than 4.00 mm. When the thickness is less than 0.02 mm, the trapping capacity tends to be insufficient when used as a filler. If the thickness is greater than 8.0 mm, the paper material will creep under its own weight, and the uniformity of the basis weight tends to be impaired.

Further, the surface smoothness of the PTFE paper obtained by papermaking is preferably 10.5 m or less, more preferably 10.0 m or less. If the surface smoothness is larger than 10.5 m, it tends to fluff and dust during handling. Here, the surface smoothness is an arithmetic average roughness measured by a stylus type surface roughness meter, as described later.

The air permeability of the PTFE paper obtained by making the paper depends on the use of the PTFE paper, but 5.5 sec / cm <) · 30 OmL or more, 14.0 sec cZcm <i ) · 30 OmL or less, more preferably 6.0 sec / cm (i) * 300 mL or more, and 13.0 sec / cπιφ · 300 mL or less. If the value of the air permeability is less than 5.5 se ο / οπιφ-300 ml, the collection efficiency of the fill tends to be inferior, and the value of the air permeability is 14.0 se ο / οτηφ- If it is larger than 30 OmL, the processing capacity tends to be poor. As described later, the air permeability is required for 30 OmL of air to pass through a 1 cm (f) orifice using a Gurley tester. Measured time.

The paper product of the present invention is not only used in a so-called paper form, but also processed into a cubic shape and used as a molded product. For example, when a paper product is subjected to sheet stamping, a plate-like material having irregularities such as an exterior plate is obtained. Further, for example, when it is fixed in a cylindrical shape, it can be used as a belt-shaped cushion material or a filter. By adding a paper product to a three-dimensional shape in this way, it is possible to impart a three-dimensional shape without relying on affixing to a base material, and to exert a function based on the shape.

By imparting physical properties that cannot be exhibited by PTFE by combining with other materials, the PTFE molded article of the present invention can be applied to more various uses. For example, to provide high dimensional stability such as high strength that cannot be exhibited by a molded product of PTFE alone, such as resistance to riff, it is possible to mix and mold with powders of aramide, fiber, fibrid, etc. Good. Abrasion resistance can be expected to be improved by mixing with fibers and fibers made of polyvinyl thiazole. Even if the molded product obtained from the mixture with other materials has a shape such as a columnar or rectangular parallelepiped, if the fibrous powder of the present invention is used, a relatively dry dispersing method can be used to obtain a relatively dispersible material. Good complexes are obtained. Dry mixing is easy, but wet mixing may be used if necessary. It is also possible to obtain mixed paper products based on these findings. As described above, the melting point of the mating partner material is preferably 200 or more, more preferably 220 ° C. or more, so as not to impair the high heat resistance of PTFE. The component does not necessarily need to be organic, and one or more mating materials should be appropriately selected according to the purpose. Examples of these include fibers such as polyparaphenylenebenzoxazole, liquid crystalline polyester, aramide pulp, glass, and carbon, but the present invention is not limited to these examples. The melting point is a value determined by the DSC method. As described above, in order to maintain heat resistance, it is preferable that the mating material used in the composite has high heat resistance, but it always has high heat resistance depending on applications that do not particularly require heat resistance. No need. For example, if it is desired to improve the strength of the paper while maintaining the charging characteristics of PTFE, it is possible to select a cut material of acrylic fiber, fibrid, etc. as the mating material. Polyamide, polyester, polyolefin, etc. can also be selected as mating materials for bulky paper materials to expand.

The paper product of the present invention can be applied to various uses owing to its excellent heat resistance, but in some cases, it can be used as a more suitable one by forming the above-mentioned composite paper product. For example, when used as a core material for compression molding, it is possible to prevent the occurrence of abrasion at the edge of the sheet stamping molded product and the die, and it is possible to ensure excellent releasability continuously. In addition, when used as a filter medium, it can not only electrostatically collect dust, but also exhibit durability against strong acids and strong alkalis and filterability at high temperatures. If it is used as a wire wrapping covering material, it has pores inside, so it can exhibit more excellent insulation properties and can also be expected to have properties as a heat insulating layer. To make a cylindrical belt material, it is easy to obtain a seamless belt with excellent releasability by making paper using a cylindrical seamless mesh, and strengthen it if further strength is required. It is only necessary to mix paper with fiber. If it is used as a positioning pattern paper for processing the solder riff opening, it is expected that there will be little solder adhesion and a marked improvement in workability. When used as insulating paper, it prevents liquids and the like from adhering to the surroundings and protects control units such as the pump unit safely for a long time. With the increase in information processing speed and communication speed, circuit boards are also required to have low dielectric constants that can handle high frequencies.However, if PTFE paper or mixed paper is used, only excellent electrical properties will be exhibited. Instead, if combined with a reinforcing material, sufficient dimensional stability and heat resistance can be expected You. Although it is known to use PTFE paper as a cushioning material in a liquid crystal production line as disclosed in JP-A-2002-23131, the cushioning properties required for other uses are various, and dimensional stability is required. Properties 混合 Mixed paper products can be applied as long as abrasion resistance is also required.

Since the PTFE fibrous powder is in a very bulky state, it is very easy to mix with other materials in a dry state, and thus it is suitable as a raw material for a composite molded product. When compounding with other materials in these applications, if the weight fraction of PTFE is less than 2%, the properties of PTFE will not be sufficiently exhibited, and if it exceeds 98%, the effect of adding components other than PTFE will be sufficient. Can not be obtained. Therefore, the weight fraction of components other than PTFE contained in the mixed molded product is preferably from 2 to 98%, more preferably from 4 to 96%, and still more preferably from 5 to 95%.

Next, the present invention will be described more specifically based on examples, but the present invention is not limited thereto.

The physical properties measured in the examples of the present invention were measured by the following methods.

(Average fiber length)

The powder is measured with an electron microscope, and the obtained length in the fiber direction of 200 points or more is the value obtained by arithmetic averaging. In the measurement, those with a length of 80 tim or less shall not be measured.

(Average view factor)

The powder is measured with an electron microscope, and the length in the fiber direction obtained is divided by the width of the fiber. The following shall not be measured.

(Air permeability)

Using a Gurley tester, 300mL of air Measure the time required to pass through the cm Φ orifice.

(Surface smoothness)

Measure the arithmetic average roughness of PTFTF paper with a stylus type surface roughness meter.

(Cushioning)

Using a compression tester, the compression work of PTFE paper and the compression recovery work after 10 repetitions were measured, and expressed as a relative value when the standard sample was taken as 100. The higher the cushioning, the higher the value. The standard sample is a specially-made paper whose compression work X 100 (%) is 60%.

(Differential scanning calorimetry)

The measurement was performed using RPC-220 manufactured by Seiko Instruments Inc. at a heating rate of 5 ° CZ for a sample amount of 3 mg. JIS—K7123 was referenced.

(Peak area ratio)

A differential scanning calorimeter analysis was performed at a heating rate of 5 ° C / min, and the obtained DSC curve was separated into two peak curves using a Gaussian-Lorentian type curve, and the area of the low-temperature side peak was calculated. Divide by peak area to calculate peak area ratio.

(Papermaking thickness)

The PTFE paper is measured using a dial gauge H type (pressurized 200 g or less).

(Specific surface area)

The specific surface area of the powder was evaluated by the nitrogen adsorption method using Biosorb manufactured by Yuasa Ionics Co., Ltd. in a standard accessory cell.

(tensile strength) Using a Tensilon STA-1 150 manufactured by Orientec Co., Ltd., a sample having a width of 15 mm was measured at a distance between chucks of 100 mm and a tensile speed of 20 OmmZ, and tensile strength was calculated by the following conversion formula.

Tensile strength (MPa) = (Measured value (N) / \ 5mm) Z sample thickness (mm) Examples 1-3

A polymer obtained by emulsion polymerization of 100 mol% of tetrafluoroethylene was used as a raw material PTFE powder (average particle size: 570 ^ m). The obtained raw material PTFE powder was fed into a hopper by a feeder. Next, the PTFE powder was supplied to a stretching tank equipped with a rotary blade (tank inner diameter: 16 Omπι) and stretched while appropriately assisting with dry air. The grinding capacity was 10-15 kgZ hours. The results of calculating the amount of energy applied to the raw material powder at this time are as shown in Table 1.

The lower surface of the stretching tank is partially meshed, so that only small pieces of a certain size are allowed to exit the stretching tank. This was treated with a standard classification sieve to remove powder of 5 m or less.

Dispersant (Toho Chemical Industry)

0.25 parts by weight of water and 1000 parts by weight of water were mixed to obtain a stock. The stock was made with a round mesh paper machine. The papermaking speed was lmZ minutes. Then, it was dried (150, 10 minutes) and fired (380 ° C, 10 minutes) to obtain 0.49 to 0.52 mm thick PTFE paper.

The surface smoothness, air permeability, cushioning property, and tensile strength of the obtained PTFE paper were as shown in Table 1. All papers have moderate air permeability and smooth surfaces. In addition, none of the papers exhibited fraying at the edges during cutting, and exhibited good cohesive strength. table 1

Comparative Examples 1-3

A PTFE fibrous powder was obtained in the same manner as in Example 1 except that the raw PTFE powder was supplied to the stretching tank with hot air at the temperature shown in Table 2 and stretched. The obtained PTFE fibrous powder had the average fiber length, average shape coefficient, peak area ratio, and specific surface area shown in Table 2, respectively.

Then, papermaking was performed in the same manner as in Example 1 to obtain PTFE paper having a thickness of 0.47 to 0.51 mm. The surface smoothness, air permeability, cushioning property, and tensile strength of the obtained PTFE paper were as shown in Table 2. The PTFE paper obtained in Comparative Example 1 has remarkably poor air permeability, and is not at all suitable for filter use. In addition, it was confirmed that any of the PTFE papers was frayed at the time of cutting and was inferior in dimensional retention of the cut portion. Table 2

^ 1 The peak position has shifted completely to the lower temperature side, and the unraveling has been completely completed.

2 Unmeasurable due to melting during measurement

Example 4

A mixed paper product was obtained in the same manner as in Example 1, except that 2 parts by weight of aramide pulp (manufactured by Toray Industries, Inc., Kepler pulp) was added to 8 parts by weight of the PTF E fibrous powder during wet papermaking. The coefficient of linear thermal expansion from room temperature to 250 ° C. was measured and found to be 0.5 ppm, indicating that it exhibited excellent hot dimensional stability. Industrial applicability

According to the present invention, it is possible to obtain a PTFE paper product having a uniform physical property distribution and excellent in cohesiveness, surface smoothness, pressure equalization, air permeability, dust collecting property, electrical properties, and mechanical properties. . Further, according to the present invention, it is possible to efficiently obtain a PTFE fibrous powder having an average fiber length of 100 to 500 Atm and an average shape factor of 5 or more.

Claims

The scope of the claims

1. In a differential scanning calorimeter analysis performed at a heating rate of 5 ° C / min, polytetrafluoyl whose peak area ratio on the low-temperature side in the obtained melting endothermic curve is 88.5% or more of the total peak area Polyethylene fibrous powder.

2. The polytetrafluoroethylene fibrous powder according to claim 1, having an average fiber length of 100 to 5000 m and an average view factor of 5 or more.

3. The polytetrafluoroethylene fibrous powder according to claim 1, wherein the specific surface area measured by a nitrogen adsorption method is 4.0 m ² Zg or more.

4. A polytetrafluoroethylene papermaking product obtained by using the polytetrafluoroethylene fibrous powder according to claim 1 as a raw material and passing through a papermaking process.

5. In the differential scanning calorimeter analysis performed at a heating rate of 5 ° C / min, the peak area ratio on the low-temperature side in the obtained melting endothermic curve is 88.5% or more of the total peak area, and the average fiber A method for producing a polytetrafluoroethylene fibrous powder having a length of 100 to 5000 m and an average view factor of 5 or more, wherein a raw material polytetrafluoroethylene powder is supplied by a supply means. A step of feeding the raw material polytetrafluoroethylene powder from the hopper to a stretching tank, a step of stretching by stretching means, and a step of classifying after stretching. A method for producing a styrene fibrous powder.

6. The method for producing a polytetrafluoroethylene fibrous powder according to claim 5, wherein the supply of the raw material polytetrafluoroethylene powder from the hopper to the stretching tank is carried out by using the flow of a medium.

7. The polytetrat according to claim 5, wherein a polytetrafluoroethylene powder having a particle size of 5 or less is removed by a classification step performed after the stretching treatment. A method for producing lafluoroethylene fibrous powder.

8. The polytetrafluoroethylene fibrous powder according to claim 5, wherein the amount of energy applied to the polytetrafluoroethylene powder from the stretching means during the stretching treatment is 10 to 200 kcal / kg. How to make the body.

9. A molded article obtained from the polytetrafluoroethylene paper-making product according to claim 4.