JPWO2004072157A1 - Polytetrafluoroethylene fibrous powder, polytetrafluoroethylene paper product, polytetrafluoroethylene molded article, and method for producing polytetrafluoroethylene fibrous powder - Google Patents

Abstract

In a differential scanning calorimeter analysis performed at a rate of temperature increase of 5 ° C. per minute, a polytetrafluoroethylene fibrous material in which the peak area ratio on the low temperature side in the obtained melt endothermic curve is 88.5% or more of the total peak area It is a powder. Further, it is a paper product made of the polytetrafluoroethylene fibrous powder and excellent in pressure uniformity, air permeability, and dust collection.

Description

  The present invention is a polytetrafluoroethylene paper product excellent in pressure uniformity, air permeability, and dust collection property, polytetrafluoroethylene fibrous powder as a raw material thereof, a molded product made of the paper product, and excellent in production efficiency. The present invention relates to a method for producing polytetrafluoroethylene fibrous powder. Specifically, the present invention relates to a method for producing a polytetrafluoroethylene fibrous powder that can provide a paper made of polytetrafluoroethylene having a smooth surface and excellent air permeability when made.

Polytetrafluoroethylene (hereinafter abbreviated as PTFE) has excellent chemical resistance, heat resistance, mechanical properties, and electrical properties, and its uses are diverse, mainly in industrial applications. Accordingly, the usage forms are various, and the paper-like products are used for filter paper, heat insulating materials, insulating materials and the like.
Various methods are known as methods for producing paper products. For example, in Japanese Examined Patent Publication No. 45-8165, PTFE fibrous powder having an average fiber length of 100 to 5000 μm and an average form factor of 5 or more or a composition obtained by uniformly mixing this with a filler is dispersed in a liquid. A method is disclosed in which a paper stock is made, paper-made, dried, and then peeled off from the base material and fired. The PTFE fibrous powder used here is obtained by pulverizing raw material PTFE by applying a strong shearing force at a high temperature. It is described that, during the pulverization, the pulverizer itself may be heated or the powder may be heated, and further, a method of pulverizing while blowing hot air is described as being most preferable.
However, there is only such a description, there is no disclosure about specific implementation contents and examples, and there is no description about the temperature conditions during the pulverization treatment. Conventionally, it has been pulverized under a temperature condition of about 20 to 50 ° C., but when treated under this temperature condition, a relatively fine PTFE powder having a particle size of 5 μm or less is produced, and it becomes a hard PTFE paper with low air permeability. There is a problem.
In contrast, the inventors have found a method for producing a PTFE paper product as described in Japanese Patent Publication No. 40-11642, Japanese Patent Publication No. 45-14127, and the like, and this is excellent in cushioning properties and pressure uniformity. I found. However, there has been no knowledge as to what kind of properties the PTFE fibrous powder satisfying can provide a uniform paper product suitable for a cushioning material, a filter material and the like.
In addition, in order to improve the mechanical strength, it is necessary to manually attach reinforcing yarns or back with a wire mesh, resulting in problems such as non-uniform distortion and shortening the service life, as well as the excellent electrical properties of PTFE. When using as a substrate material taking advantage of the characteristics, it was difficult to reduce the thickness due to the problem of self-holding.

The present invention clarifies the above problems and overcomes this problem, and has a uniform physical property distribution and is a PTFE paper product having excellent cohesiveness, pressure equalization, air permeability, and dust collection properties, and a raw material thereof. An object of the present invention is to provide a PTFE fibrous powder, a molded article made of the PTFE paper product, and a method for producing the PTFE fibrous powder excellent in production efficiency.
That is, according to the present invention, in the 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 melt endothermic curve is 88.5% or more of the total peak area. It relates to PTFE fibrous powder.
The PTFE fibrous powder preferably has an average fiber length of 100 to 5000 μm and an average form factor of 5 or more.
The specific surface area measured by the nitrogen adsorption method is preferably 4.0 m ² / g or more.
The present invention also relates to a polytetrafluoroethylene paper product obtained by using the PTFE fibrous powder as a raw material and through a paper making process.
Furthermore, in the differential scanning calorimeter analysis performed at a rate of temperature increase of 5 ° C. per minute, the peak area ratio on the low temperature side in the obtained melt endothermic curve is 88.5% or more of the total peak area, A process for producing a polytetrafluoroethylene fibrous powder having an average fiber length of 100 to 5000 μm and an average form factor of 5 or more, the raw material polytetrafluoroethylene powder being fed into a hopper by a supply means, the raw material The present invention relates to a method for producing a polytetrafluoroethylene fibrous powder comprising a step of supplying polytetrafluoroethylene powder from the hopper to a stretching treatment tank, a step of stretching treatment by a stretching means, and a step of classifying after the stretching treatment.
In the manufacturing method, it is preferable to supply the raw material polytetrafluoroethylene powder from the hopper to the stretching tank using the flow of the medium.
It is preferable to remove polytetrafluoroethylene powder having a particle size of 5.0 μm 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 treatment is preferably 10 to 200 kcal / kg.
The present invention also relates to a molded article obtained from the PTFE paper product.

  FIG. 1 shows an example of a melting endotherm curve obtained by analyzing a PTFE powder with a differential scanning calorimeter, and two peak curves obtained by peak separation of the melting endotherm curve.

FIG. 1 shows an example (solid line) of a melting endotherm curve (hereinafter also referred to as a DSC curve) obtained by analyzing PTFE powder with a differential scanning calorimeter, and two peak curves obtained by separating the DSC curve into peaks. (Broken line) is shown.
When a differential scanning calorimeter is measured on a PTFE fine powder having a normal molecular weight, a double peak or a single peak clearly having a shoulder is observed from around 337 ° C. to around 340 ° C. as shown in FIG. It can be seen. This is because the release of the microbrown motion of the molecule that has been unraveled in the polymerization process of PTFE, and the release of the micro brown motion of the molecule that has not progressed in the polymerization process. The molecule that consists of the second (high temperature side) peak (or shoulder) due to and has not been unraveled during the PTFE polymerization process is first unraveled by the temperature rise, and then the microbrown motion of the molecule Since release occurs, a time lag occurs from the occurrence of the first peak, and a melting peak (or shoulder) appears on the high temperature side. For this reason, if the measurement is performed at a too slow rate of temperature increase, the time lag becomes very small, and it is difficult to distinguish from the appearance.
Since the molecular weight of PTFE molecules is much larger than that of general-purpose molten resins, there are cases in which it is more energetically stabilized to be organized with a single molecular chain than to be organized as a group. In particular, in the polymerization process, since molecules exist with relatively little binding force from the surroundings, it can be said that conformational stabilization with a single molecular chain is likely to occur. However, unlike polymerization / growth reactions in an ideal space, there are not a few molecules that form an organization under the influence of external forces such as shear force and intermolecular forces.
In the process of molding and sintering the PTFE powder, as the molecular unraveling progresses more and the fusion between the structures increases, not only a molded product with excellent cohesive force but also without deformation is obtained. In the case of an object, the stress is transmitted uniformly and the pressure uniformity is excellent.
As described above, the molecular chain unraveling may have occurred during the temperature rise. However, when it depends only on the thermal unraveling operation, it is difficult to uniformly control it and partly excessive heat is applied. In such a case, there is a problem that the site is firmly organized and the fusion with other tissues is lost. In order to avoid this, it is preferable to use both unraveling by external force and unraveling by heat.
When the molecular unraveling has been completed, it is often not possible to form the paper product in a favorable state. This is because in the process of papermaking, the external force and heat applied to the PTFE fibrous powder have progressed its organization and have passed through the optimum state for organization as a papermaking product. It is thought that there is. For this reason, it is easily understood that it is necessary to control the properties of the papermaking product that the PTFE fibrous powder is in an optimal unraveling state before papermaking. The melting peak on the DSC curve of the PTFE powder that has been completely unraveled becomes a single peak, which shifts to around 325 to 328 ° C. and is not included in the PTFE fibrous powder of the present invention.
It can be said that the peak area in the melting endothermic curve obtained in the differential scanning calorimeter is directly proportional to the amount of heat, and is generally proportional to the number of molecules in an allowable range. Therefore, as shown in FIG. 1, when a DSC curve having two peaks or one shoulder-clear peak is separated into two normal distributions or other distribution curves as shown by a broken line, a peak (P _L ) Is proportional to the number of molecules unraveled, and the peak on the high temperature side (P _H ) Area is proportional to the number of molecules that have not been unraveled, so the ratio of the PTFE molecules that have been unraveled is the lower end of the melting endotherm curve obtained in the differential scanning calorimeter. Peak (P _L ) And the ratio of the total peak area.
A double peak or a single peak with a clear shoulder can be mathematically understood as a composite curve of three or more normal distributions, but since it has two vertices, two normal distributions or It is considered that separation as a similar distribution curve is sufficiently valid, and reasonable results have been obtained in the study of the present invention. It is sufficient to understand that the partially undissolved molecules are included in the normal distribution of the molecules that have not been unconstrained as having a small amount of heat necessary for unraveling in the evaluation.
The composite absorption peak can be separated by approximation using a Gaussian-Lorentian type curve. Compared to the case where only a Gaussian type curve or a Lorentian type curve is used, there is a feature that the degree of deviation is small, and this technique is also used in many commercially available analytical instruments. In the present invention, the two apparent vertices found in the PTFE powder as a raw material are given as initial values, and the approximation is performed without any limitation, thereby determining the basic peak position. The basic peak positions obtained by this are 339.14 ° C and 343.01 ° C. Based on this, the linear and half-value widths are not limited, and only the peak temperature is limited to 0.6 to 0.7 ° C or less from the initial value. Thus, the composite curve was separated into two by approximation and the peak area was obtained. In this study, information on the raw material powder was used to shorten the time required to converge the value, 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 endotherm curve was 88.5% or more of the total peak area. It is preferable that it is 92.0% or more and 99.5% or less. When 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 product tends to be deformed, and the cushioning property of the obtained paper product tends to be poor. is there. As described above, when the peak area on the low temperature side is too large, that is, when two peaks (or shoulders) are not observed, the paper product cannot often be formed into a preferable state.
In general, in molding methods such as papermaking and compression molding, unlike molding methods that involve uniform melting at the molecular level, the specific surface area of the raw material is largely involved in the cohesive strength, that is, the mechanical properties of the molded product, and within a certain range. The greater the specific surface area, the better the mechanical properties of the molding. This is because the contact area of each raw material increases, and the stress transmission point as a structure increases, and as a result, the mechanical properties of the entire structure improve. The same applies to PTFE. The larger the specific surface area of the PTFE fibrous powder, the greater the cohesive force, and the resulting structure is excellent in mechanical properties without being deformed. On the other hand, the more the fusion of PTFE fibrous powders occurs, the smaller the specific surface area of the paper product, and it is important for estimating the physical properties of the paper product to show a reduction rate of the specific surface area above a certain level. It can be said that it becomes a parameter.
The same applies to the PTFE fibrous powder and its molded product. The larger the specific surface area of the PTFE fibrous powder, the greater the cohesive force, and the molded product with excellent mechanical properties without deformation. It is done. Therefore, in the present invention, the specific surface area of the PTFE fibrous powder is 4.0 m. ² / G or more, preferably 5.0 m ² / G or more, 8.5m ² / G or less is more preferable. Here, the specific surface area is a value measured by a nitrogen adsorption method. Specific surface area is 4.0m ² If it is less than / g, the cohesive force is insufficient, and the mold is likely to collapse during molding. Further, the molded product lacks uniformity, and desired physical properties cannot be obtained. Specific surface area is 8.5m ² When it is larger than / g, the weight per unit area of the paper product that is easily packed with fibrous powder tends to be large, and the air permeability tends to be low and the cushioning property tends to be difficult to be exhibited.
In order to exhibit the characteristics as paper, it is preferable that the shape of the raw material powder is fibrous, and generally it can be shown that it is fibrous by a form factor, but a shape in which many whiskers are elongated. In the case of amorphous powders having a shape, the cohesive strength as paper may be exhibited, but the shape factor may not be fibrous. In such a case, by specifying the specific surface area together with the form factor, it is possible to determine whether the raw material can exhibit the properties as paper. In view of these, it may be considered that the fiber is all or part of which is stretched by an external force and exhibits 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, and each is a hydrogen atom or a fluorine atom, n is an integer of 1 to 5), and formula (II):
CF ₂ = CF-OR ^f (II)
(Wherein R ^f Is modified with 0 to 5 mol% of at least one monomer selected from the group consisting of fluorine-containing (alkyl vinyl ether) (hereinafter abbreviated as PAVE) represented by C1-C3 fluorine-containing alkyl group) Examples thereof include TFE copolymers (modified PTFE).
Examples of the fluoroolefin represented by the formula (I) include perfluoroolefins such as hexafluoropropylene (hereinafter abbreviated as HFP); fluoroolefins such as perfluorobutylethylene.
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), perfluoro ( Propyl vinyl ether) (hereinafter abbreviated as PPVE).
The raw material PTFE powder used in the present invention is obtained by polymerization using a polymerization initiator in the presence of a water-soluble fluorine-containing dispersant. In order to lower the molecular weight of the resulting polymer, methods such as increasing the amount of the polymerization initiator, adding a chain transfer agent, or adding a modifying monomer are employed. Examples of the polymerization initiator include persulfates and organic peroxides. Examples of the chain transfer agent include hydrocarbons such as hydrogen and propane, and water-soluble compounds such as ethanol.
The average particle diameter of the raw material PTFE powder thus obtained is preferably 5 to 2000 μm. If the average particle size is smaller than 5 μm, there are a lot of fine powders after the treatment, so that the paper is hard and has low air permeability. On the other hand, when the average particle size exceeds 2000 μm, coarse powder remains after the treatment, and the paper has a rough surface.
The PTFE fibrous powder of the present invention can be produced by, for example, the following production method using an apparatus having a raw material hopper, a stretching treatment tank, and a classification device.
First, the raw material PTFE powder is charged into the raw material hopper from a supply machine, and the raw material PTFE powder is supplied from the raw material hopper to the stretching treatment tank. Supply of the raw material PTFE powder to the stretching tank may be performed by dropping due to its own weight, or may be performed mechanically depending on the form of the raw material 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 with high fluidity such as liquid or gas.
The stretching tank is provided with stretching means (details will be described later), and the raw material PTFE powder is stretched to obtain a PTFE fibrous powder. Here, when processing the raw material PTFE powder, it is preferable to control the progress of unraveling the PTFE fibrous powder by controlling the amount of energy applied to the PTFE powder during the process.
Subsequently, only the sufficiently stretched powder is selected by the classifier and sent to the next classifier. The other powders are returned to the stretching tank and further processed. Finally, the PTFE powder having a particle size of 5 μm or less is removed by a classifier (measurement method will be described later) to obtain the PTFE fibrous powder of the present invention.
Hereinafter, each process is explained in full detail.
In the step of supplying the raw material PTFE powder from the raw material hopper to the stretching treatment tank, when a material having a small particle size is used, it is hardened in the hopper and it becomes difficult to drop and supply by its own weight. In that case, liquid such as water can be forcibly supplied to the stretching treatment tank as a medium. When storing the obtained PTFE fibrous powder without immediately sending it to the papermaking process, it is not preferable to use a liquid medium. Therefore, it is possible to supply the raw material PTFE powder using a gas such as dry air as a medium. it can. However, the movement of the rotating body in the stretching treatment tank or the discharge of the stretched raw material PTFE powder may be affected, which is not preferable. By such an operation, PTFE fibrous powder having an average fiber length of 100 to 5000 μm and an average form factor of 5 or more can be produced very efficiently.
Moreover, it is preferable to utilize the frictional heat at the time of extending | stretching process temperature. Thereby, it becomes easy to fibrillate and there exists a tendency for the powder of the comparatively stable fiber length to be obtained. Accordingly, the stretching means is preferably one that performs a stretching process using frictional force. Examples of such stretching means include a hammer mill and a screen mill, but it is preferable that the apparatus is capable of stretching a raw material powder by applying a shearing force only in one direction by a rotating body.
By controlling the amount of energy applied to the PTFE powder from the stretching means during the stretching process to 10 to 200 kcal / kg, it is possible to prevent the occurrence of PTFE aggregates. In particular, it is preferable to control the energy amount to 10 to 60 kcal / kg. The PTFE paper made with the PTFE fibrous powder thus obtained has many entanglements between the fibrous powders, and locally obtains a PTFE paper product having excellent cushioning properties with heat fusion between the powders. be able to. Here, if the amount of energy applied from the stretching means to the PTFE powder is less than 10 kcal / kg, short fibrous powder increases and sufficient physical entanglement cannot be obtained. Moreover, when the amount of energy exceeds 200 kcal / kg, thermal fusion between the fibrous powders tends not to 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 applied to the stretching means. The amount of energy applied to the stretching means is the amount of energy per kg of the PTFE powder required to maintain the stretching rotational speed when the PTFE powder is stretched by the stretching means. The current of the stretching means during stretching and idling. It can be determined from the difference in values. When the raw material is supplied to the stretching tank using a medium, the amount of heat to be applied must be calculated including the amount of heat given from the temperature difference from the medium, based on a room temperature of 40 ° C. or less.
In the step of classifying after processing the PTFE powder, after the raw material PTFE powder is processed, a classification operation is performed by a classifier. By this classification operation, PTFE fibrous powder that is insufficiently stretched can be prevented from flowing out of the stretching treatment tank. Therefore, a PTFE fibrous powder having an average fiber length of 100 to 5000 μm can be obtained efficiently. In particular, the average fiber length is preferably 100 to 4000 μm. When the average fiber length is less than 100 μm, a part of the net-like base material falls off during paper making, causing pinholes. On the other hand, when the average fiber length exceeds 5000 μm, it is difficult to produce paper having a uniform thickness because the fiber length is long. Examples of the classifying device include a classifying screen and the like, and those capable of separating powder with a predetermined size as a boundary are preferable.
Further, by removing PTFE fibrous powder having a particle size of 5 μm or less, the air permeability of the PTFE paper product made using the powder is improved, which is preferable in terms of flexibility and excellent cushioning properties. Furthermore, it is preferable to remove PTFE fibrous powder having a particle size of 10 μm or less.
Here, the particle size is measured using a laser diffraction particle size distribution measuring device HELOS & RODOS system (manufactured by SYMPATEC) while dispersing PTFE fibrous powder with 3 bar compressed air. The particle size means 50% particle size.
Further, the average form factor of the PTFE fibrous powder is preferably 5 or more, and more preferably 10 or more. The upper limit value of the average form 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 smaller than 5, it is difficult to peel off from the net-like base material after firing, and it becomes a poorly finished paper having poor surface smoothness and appearance (fluffing, distortion).
The PTFE fibrous powder thus obtained can be made by the following method.
First, the PTFE fibrous powder is uniformly dispersed in water or the like with a dispersant to form a paper material. At this time, an organic polymer reinforcing fiber, an inorganic filler or the like may be added to the stock. This stock is made on a substrate such as a net. After that, it is dried and fired to obtain a PTFE paper. In particular, when an organic polymer reinforced fiber is contained, a filter having a larger area can be installed without lining, thereby reducing the size of the filter unit.
The thickness of the PTFE paper obtained by papermaking is preferably 0.02 mm or more and 8.00 mm or less, more preferably 0.05 mm or more and 6.00 mm or less, although it depends on the application. More preferably, it is 0.10 mm or more and 4.00 mm or less. When the thickness is less than 0.02 mm, the collection ability tends to be insufficient when used as a filter. When the thickness is larger than 8.00 mm, the paper product is creep-deformed by its own weight, so that the uniformity of the basis weight tends to be impaired.
The surface smoothness of the PTFE paper obtained by papermaking is preferably 10.5 μm or less, and more preferably 10.0 μm or less. When the surface smoothness is larger than 10.5 μm, there is a tendency to become fuzzy and dust during handling. In addition, surface smoothness here is arithmetic mean roughness by a stylus type surface roughness meter as mentioned later.
The air permeability of the PTFE paper obtained by papermaking is preferably 5.5 sec / cmφ · 300 mL or more and 14.0 sec / cmφ · 300 mL or less, although it depends on the use of the PTFE paper. More preferably, it is 0.0 sec / cmφ · 300 mL or more and 13.0 sec / cmφ · 300 mL or less. When the air permeability value is less than 5.5 sec / cmφ · 300 mL, the collection efficiency tends to be inferior, and when the air permeability value is greater than 14.0 sec / cmφ · 300 mL, the processing capacity Tend to be inferior. Here, the air permeability is a value obtained by measuring the time required for 300 mL of air to pass through a 1 cmφ orifice using a Gurley tester, as will be described later.
The paper product of the present invention is not only used as a so-called paper, but also processed into a three-dimensional shape and used as a molded product. For example, when a paper-made product is formed by sheet stamping, a plate-like product having unevenness such as an exterior plate is obtained. Further, for example, when fixed in a cylindrical shape, it can be used as a belt-like cushion material or a filter. In this way, by processing a paper product into a three-dimensional shape, it is possible to impart a three-dimensional shape regardless of sticking to a base material or the like, and to develop a function based on the shape.
The PTFE molded product of the present invention can be applied to various uses by imparting physical properties that cannot be exhibited by PTFE by combining with other materials. For example, in order to impart hot dimensional stability such as high strength and reflow resistance that cannot be exhibited by a molded product of a single PTFE, it may be mixed with powder, fiber, fibrid, etc. made of aramid and molded. If mixed with fibers or fibrids made of polybenzthiazole, improvement in wear resistance can be expected. Even if the molded product obtained from the mixture with other materials is in the shape of a cylinder or a rectangular parallelepiped, if the fibrous powder of the present invention is used, the composite has a relatively good dispersibility by an easy dry mixing method. Is obtained. Although dry mixing is easy, wet mixing may be used if necessary. It is also possible to obtain mixed paper products based on these findings. Thus, in order not to impair the high heat resistance of PTFE, it is preferable that the melting | fusing point is 200 degreeC or more, More preferably, it is 220 degreeC or more. The component does not necessarily need to be an organic substance, and one or two or more kinds of counterpart materials should be appropriately selected according to the purpose. Examples of these include fibers such as polyparaphenylene benzoxazole, liquid crystalline polyester, aramid pulp, glass, and carbon, but the present invention is not limited to these examples. Moreover, melting | fusing point is a numerical value calculated | required by DSC method.
As mentioned above, in order to maintain heat resistance, it is preferable that the mating material has high heat resistance when composited, but it is necessary to provide high heat resistance depending on the application that does not particularly require heat resistance. There is no. For example, if you want to improve the strength of the paper product while maintaining the charging characteristics of PTFE, you can also select acrylic fiber cuts, fibrids, etc. as the mating material. In order to expand the product, polyamide, polyester, polyolefin or the like can also be selected as a counterpart material.
The paper product of the present invention can be applied to various uses because of its excellent heat resistance, but in some cases, it can be used as a more suitable material by forming the above-mentioned composite paper product. For example, if it is used as a core material for compression molding, it is possible to prevent generation of scratches at the sheet stamping molded product and the edge portion of the mold, and to ensure excellent releasability continuously. In addition to being able to collect electrostatically when used as a filter medium, it is possible to exhibit durability against strong acids and strong alkalis and filterability at high temperatures. If it is used as a wire-wrapping covering material, since it has pores inside, it exhibits superior insulating properties and can also be expected to have properties as a heat insulating layer. To make a cylindrical belt material, it is possible to easily obtain a seamless belt with excellent releasability by making paper using a cylindrical seamless mesh. do it. If it is used as a positioning paper for solder reflow processing, it is expected that the workability is remarkably improved with less solder adhesion. When used as insulating paper, it is possible to prevent adhesion of a liquid agent from the surroundings and to safely protect a control unit such as a pump unit for a long time. With the increase in information processing speed and communication speed, circuit board materials are also required to have a low dielectric constant corresponding to high frequencies. However, if PTFE paper or mixed paper products are applied to this, only excellent electrical characteristics are exhibited. In addition, if combined with a reinforcing material, sufficient dimensional stability and heat resistance can be expected. As disclosed in JP-A-2002-23131, it is known to use PTFE paper as a cushioning material in a liquid crystal production line, but there are various cushioning properties required in other applications, and dimensional stability and A mixed paper product 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 therefore, it is suitable as a raw material for a composite molded product.
When composited with other materials in these applications, the PTFE properties are not sufficiently exhibited if the weight fraction of PTFE is less than 2%, and if it exceeds 98%, the effect of adding components other than PTFE is sufficient. I can't get it. Therefore, the weight fraction of components other than PTFE contained in the mixed molded product is preferably 2 to 98%, more preferably 4 to 96%, and still more preferably 5 to 95%.
Next, the present invention will be described more specifically based on examples, but the present invention is not limited to these examples.
In addition, each physical property value measured in the Example of this invention is measured with the following method.
(Average fiber length)
The powder is measured with an electron microscope, and the obtained fiber direction length of 200 points or more is obtained by arithmetic mean, and in the measurement, the length of 80 μm or less is not measured.
(Average form factor)
The powder is measured with an electron microscope, and is obtained by an arithmetic average of 200 or more form factors obtained by dividing the length in the obtained fiber direction by the width of the fiber. In the measurement, the length is 80 μm or less. Things shall not be measured.
(Air permeability)
The time required for 300 mL of air to pass through a 1 cmφ orifice is measured for the PTFE paper using a Gurley tester.
(Surface smoothness)
The arithmetic average roughness of the PTFE paper is measured with a stylus type surface roughness meter.
(Cushioning)
Using a compression tester, the compression work of PTFE paper and the compression recovery work when repeated 10 times are measured and expressed as relative values when the standard sample is 100. The greater the cushion, the greater the value. The standard sample means a PTFE paper having a value of 60% compression recovery work / compression work x 100 (%).
(Differential scanning calorimetry)
Using RPC-220 manufactured by Seiko Instruments Inc., measurement was performed at a heating rate of 5 ° C./min and a sample amount of 3 mg. JIS-K7123 was used as a reference.
(Peak area ratio)
Differential scanning calorimetry analysis is performed at a rate of temperature increase of 5 ° C. per minute, and the obtained DSC curve is separated into two peak curves using a Gaussian-Lorentian type curve, and the area of the low-temperature side peak is all peaks Divide by area to calculate peak area ratio.
(Paper thickness)
The PTFE paper is measured using a dial gauge H type (a pressure of 200 g or less).
(Specific surface area)
The specific surface area of the powder was evaluated by a nitrogen adsorption method in a standard accessory cell using a Biosorb manufactured by Yuasa Ionics Co., Ltd.
(tensile strength)
Using a Tensilon STA-1150 manufactured by Orientec Co., Ltd., a 15 mm wide sample was measured at a chuck distance of 100 mm and a tensile speed of 200 mm / min, and the tensile strength was calculated by the following conversion formula.
Tensile strength (MPa) = (Measured value (N) / 15 mm) / Sample thickness (mm)

Examples 1-3

比較例１〜３
表２に記載の温度の熱風で原料ＰＴＦＥ粉末を延伸処理槽に供給し、延伸処理した以外は、実施例１と同様にしてＰＴＦＥ繊維状粉末を得た。得られたＰＴＦＥ繊維状粉末は、それぞれ表２に記載の平均繊維長、平均形態係数、ピーク面積比率および比表面積を有していた。
ついで、実施例１と同様にして抄造し、それぞれ厚み０．４７〜０．５１ｍｍのＰＴＦＥ製ペーパーを得た。得られたＰＴＦＥ製ペーパーの表面平滑性、透気度、クッション性、および抗張力は、表２に示すとおりであった。比較例１で得られたＰＴＦＥ製ペーパーは透気性が著しく悪くフィルター用途に全く適さない。また何れのＰＴＦＥ製ペーパーにおいても裁断時にほつれが生じてしまい、カット部の寸法保持性に劣ることが確認された。

A polymer obtained by emulsion polymerization of 100 mol% of tetrafluoroethylene was used as a raw material PTFE powder (average particle size 570 μm). The obtained raw material PTFE powder was fed into a hopper by a feeder. Next, the PTFE powder was supplied to a stretching treatment tank (tank inner diameter 160 mmφ) equipped with a rotating blade while being appropriately supplemented with dry air, and subjected to a stretching treatment. The grinding capacity was 10-15 kg / hour. The results of calculating the amount of energy given to the raw material powder at this time are as shown in Table 1.
The lower surface of the stretching tank is partially meshed, and only those smaller than a certain size were allowed to exit the stretching tank. This was treated with a standard classification sieve to remove powder of 5 μm or less.
To 10 parts by weight of the obtained PTFE fibrous powder, 0.25 parts by weight of a dispersant (manufactured by Toho Chemical Industry Co., Ltd., Nonal 206) and 1000 parts by weight of water were mixed to obtain a paper stock. The stock was made with a round net type paper machine. The paper making speed was 1 m / min. Subsequently, drying (150 degreeC, 10 minutes) and baking (380 degreeC, 10 minutes) were carried out, and the paper made from PTFE of thickness 0.49-0.52 mm was obtained, respectively.
The surface smoothness, air permeability, cushioning properties and tensile strength of the obtained PTFE paper were as shown in Table 1. Any paper has moderate air permeability and a smooth surface. In addition, none of the papers frayed at the edges during cutting, and exhibits a good cohesive force.

Comparative Examples 1-3
A PTFE fibrous powder was obtained in the same manner as in Example 1 except that the raw material PTFE powder was supplied to the stretching treatment tank with hot air at the temperature shown in Table 2 and subjected to the stretching treatment. The obtained PTFE fibrous powder had the average fiber length, the average form factor, the peak area ratio, and the specific surface area described in Table 2, respectively.
Subsequently, paper was made in the same manner as in Example 1 to obtain PTFE paper having a thickness of 0.47 to 0.51 mm. Table 2 shows the surface smoothness, air permeability, cushioning properties, and tensile strength of the obtained PTFE paper. The PTFE paper obtained in Comparative Example 1 has extremely poor gas permeability and is not suitable for filter applications. Moreover, in any PTFE paper, fraying occurred at the time of cutting, and it was confirmed that the dimension retention of the cut part was inferior.

  A mixed paper product was obtained in the same manner as in Example 1, except that 2 parts by weight of aramid pulp (manufactured by Toray Industries, Inc., Kevlar pulp) was added to 8 parts by weight of PTFE fibrous powder during wet papermaking. When the linear thermal expansion coefficient from room temperature to 250 ° C. was measured, it was 0.5 ppm, and it was confirmed that excellent hot dimensional stability was exhibited.

  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 collection, electrical properties, and mechanical properties. Further, according to the present invention, PTFE fibrous powder having an average fiber length of 100 to 5000 μm and an average form factor of 5 or more can be obtained efficiently.

Claims (9)

In a differential scanning calorimeter analysis performed at a rate of temperature increase of 5 ° C. per minute, a polytetrafluoroethylene fibrous material in which the peak area ratio on the low temperature side in the obtained melt endothermic curve is 88.5% or more of the total peak area powder. The polytetrafluoroethylene fibrous powder according to claim 1, which has an average fiber length of 100 to 5000 µm and an average form factor of 5 or more. The polytetrafluoroethylene fibrous powder according to claim 1, wherein the specific surface area measured by the nitrogen adsorption method is 4.0 m ² / g or more. A polytetrafluoroethylene paper product obtained by using the polytetrafluoroethylene fibrous powder according to claim 1 as a raw material and through a paper-making process. In the differential scanning calorimeter analysis performed at a rate of temperature increase of 5 ° C. per minute, the peak area ratio on the low temperature side in the obtained melt endothermic curve is 88.5% or more of the total peak area, and the average fiber length is 100 A method for producing a polytetrafluoroethylene fibrous powder having an average form factor of 5 or more, which is ˜5000 μm, the raw polytetrafluoroethylene powder being fed into a hopper by a supply means, the raw polytetrafluoroethylene powder A method for producing a polytetrafluoroethylene fibrous powder comprising a step of supplying the hopper from the hopper to a stretching tank, a step of stretching by a stretching means, and a step of classifying after stretching. 6. The method for producing a polytetrafluoroethylene fibrous powder according to claim 5, wherein the raw material polytetrafluoroethylene powder is supplied from the hopper to the drawing treatment tank by using the flow of the medium. The method for producing a polytetrafluoroethylene fibrous powder according to claim 5, wherein the polytetrafluoroethylene powder having a particle size of 5.0 µm or less is removed by a classification step performed after the stretching treatment. The method for producing a 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. A molded article obtained from the polytetrafluoroethylene paper product according to claim 4.

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