JP2005133260A - Composite paper-like material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a paper-like material composed of an engineering plastic fiber and having excellent strength, thermal dimensional stability, chemical resistance and abrasion resistance and unprecedentedly small water absorption and dielectric properties. <P>SOLUTION: The composite paper-like material is composed of a fibrous polytetrafluoroethylene (especially fibrous powder) and a fibrous polyimide. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a composite paper-like material composed of fibrous polyimide and fibrous polytetrafluoroethylene (PTFE).

  Various paper-like materials comprising fibers made of high-performance engineering plastics as a constituent component have been proposed, and are expected to be used as members of electronic devices such as substrate materials, heat-resistant structural materials, and the like. Among them, those using a fiber made of fluororesin as a constituent component are advantageous in terms of dielectric properties and friction properties, and various studies have been conducted.

  For example, Patent Document 1 proposes a paper-like material made of a fluororesin fiber and a heat-resistant engineering plastic fiber.

  Patent Document 2 proposes a sheet-like insulator obtained by impregnating a fiber base material composed of a mixture of insulating fibers and fluororesin fibers with an impregnating agent.

  Patent Document 3 proposes a low dielectric constant printed wiring board material in which a cyanate ester resin is combined with a mixed nonwoven fabric made of fluororesin fibers and heat-resistant engineering plastic fibers.

  Patent Document 4 proposes a fluorine-based resin composition in which polyimide fibers are blended with polytetrafluoroethylene resin as a sliding member.

  On the other hand, as for a paper-like material having a fiber made of polyimide as a constituent component, for example, Patent Document 5 proposes a base material nonwoven fabric for laminated plates in which polyimide fibers are bonded with a thermosetting binder.

  However, the fluororesin fibers employed in Patent Documents 1 to 3 are substantially in the form of chopped strands. When compared at the same weight, the fiber diameter is significantly larger than that of pulp-like materials, and the homogeneity when combined The problem remains. Further, from the viewpoint of the production method of the fluororesin fibers, the applied fluorofibers are sufficiently fired, and the function as a binder (binder) for binding the fibers to each other is insufficient. In order to obtain a sheet-like material by a wet papermaking method, some binder component must be blended. In many cases, the binder component is a factor that inhibits the properties of the obtained paper.

  In Patent Document 4, the form and the like of the polytetrafluoroethylene resin are not clearly shown and are unknown, but it is practically impossible to obtain a thin paper-like composite molded product as inferred from the production method. It is assumed.

Patent Document 5 employs a thermosetting resin as a binder for polyimide fibers. As described above, only the paper-like material in which the properties inherent to the polyimide fiber are hindered can be obtained by the thermosetting resin.
Japanese Patent Laid-Open No. 10-212686 Japanese Patent Laid-Open No. 11-144529 Japanese Patent No. 2762544 Japanese Patent No. 2983900 Japanese Patent Laid-Open No. 11-200210

  The present invention has been made in view of the background of the above-described prior art, and is excellent in strength, thermal dimensional stability, chemical resistance, wear resistance, and has a small value that has not been obtained in water absorption and dielectric properties. The object is to provide a paper-like material made of engineering plastic fibers.

  That is, the present invention relates to a composite paper-like material composed of both fibrous polyimide and polytetrafluoroethylene.

  The fibrous polyimide is not particularly limited, but a fiber obtained by fiberizing a thermoplastic polyimide resin by a melt spinning method or the like is cut into a certain length, preferably a short fiber, particularly a fiber having crystallinity. .

  The thermoplastic polyimide preferably has a glass transition temperature of 230 ° C. or higher and a melting point of 400 ° C. or lower. A glass transition point lower than 230 ° C. is not preferable because the heat resistance is poor. On the other hand, when the melting point exceeds 400 ° C., it is not preferable because processing by heat becomes difficult.

  As the fibrous polyimide, considering the uniformity of the resulting composite paper-like material, it is a short fiber, the average fiber length is 1 to 15 mm, preferably 2 to 8 mm, and the average fiber diameter is 3 to 30 μm, preferably Is preferably 4 to 20 μm.

  The raw yarn obtained from a thermoplastic polyimide resin having crystallinity by a melt spinning method or the like can enhance the orientation of the crystal part by heating and drawing under appropriate conditions. Fibrous polyimide with highly oriented crystal parts has small dimensional changes during heating and cooling, contributes to thermal dimensional stability when made into paper, and has low water absorption. Therefore, there is very little change in dimensions and electrical characteristics due to water absorption. “Fiber having crystallinity” is expressed by the crystallinity of the fibrous polyimide, and the crystallinity measured by the X-ray diffraction method is preferably 15% or more, more preferably 20% or more, and particularly preferably Means 25% or more. If the degree of crystallinity is less than 15%, the thermal dimensional change and water absorption tend to increase, which is not preferable.

（式中、Ｒは単環式芳香族、縮合多環式芳香族、芳香環が直接もしくは架橋員により結合された非縮合多環式芳香族から選ばれる４価の芳香族残基を示す。また、Ｘは直接結合、炭化水素基、カルボニル基、エーテル基、チオ基もしくはスルホニル基から選ばれる２価の残基を示し、Ｙ_１〜Ｙ_４は水素原子、アルキル基、アルコキシル基もしくはハロゲン基から選ばれる１価の残基を示す。）
これらポリイミドのうち上記一般式（1）においてＲは短環式芳香族であるものがより好ましく、Ｘは直接結合であるものがより好ましく、Ｙ_１〜Ｙ_４は水素原子であるものがより好ましい。 As the polyimide, a polyimide having a chemical structure represented by the following general formula (1) as a repeating unit is preferable because it can satisfy the above characteristics.

(In the formula, R represents a tetravalent aromatic residue selected from a monocyclic aromatic group, a condensed polycyclic aromatic group, and a non-condensed polycyclic aromatic group in which an aromatic ring is bonded directly or by a bridging member. X represents a divalent residue selected from a direct bond, a hydrocarbon group, a carbonyl group, an ether group, a thio group or a sulfonyl group, and Y _{1 to} Y ₄ represent a hydrogen atom, an alkyl group, an alkoxyl group or a halogen group. A monovalent residue selected from:
Among these polyimides, in the above general formula (1), R is more preferably a short-ring aromatic, X is more preferably a direct bond, and Y _{1 to} Y ₄ are more preferably hydrogen atoms. .

（式中、好ましくはｎは5〜200である）
このようなポリイミドは、例えば、商標名オーラム（三井化学社製）として入手可能である。 A particularly preferred specific example of such a polyimide is a polyimide having the following chemical structural formula (2) as a repeating unit.

(Wherein n is preferably 5 to 200)
Such a polyimide is available, for example, under the trade name Aurum (manufactured by Mitsui Chemicals).

  When fiberizing polyimide, polyimides having various chemical structures may be blended, and polyesters and polyolefins may be used as long as the properties required for the polyimide and paper-like material used in the present invention are not impaired. Other polymers such as polyamides, polyphenylene sulfide, polyether imide, polyether ether ketone, fluororesin may be blended, and further, titanium oxide, zinc oxide, magnesium oxide, alumina, silica, aluminum nitride, Inorganic fillers such as silicon nitride, boron nitride, silicon carbide, carbon black, graphite, mica may be blended.

The fibrous polytetrafluoroethylene used in the present invention is a fibrous powder. The fibrous powder made of polytetrafluoroethylene is preferably obtained by beating polytetrafluoroethylene powder, for example, and has a fiber shape as a whole while having non-uniform cocoon-shaped branches, and On the visual level, it shows the behavior as a powder. This fibrous powder preferably has an average fiber length of 5 to 2000 μm and an average form factor of 5 or more. Below this range, not only is the drainage poor in the papermaking process, the productivity is reduced, but only paper with a low air permeability can be obtained. If it exceeds this, the surface condition of the paper will deteriorate, making it difficult to obtain a thin and uniform paper. The specific surface area measured by the nitrogen adsorption method is preferably 4.0 m ² / g or more. Below this value, the binding function is inferior, and the strength of the resulting paper-like material is reduced. The average form factor is obtained by dividing the fiber length by the fiber width.

The polytetrafluoroethylene may be a tetrafluoroethylene homopolymer, or a copolymer of tetrafluoroethylene and a trace monomer other than tetrafluoroethylene, which is non-melt-processable (hereinafter referred to as “melt-processable”). Or modified polytetrafluoroethylene).
Examples of the trace monomer include perfluoroolefin, perfluoro (alkyl vinyl ether), cyclic fluorinated monomer, and perfluoroalkylethylene.
Examples of the perfluoroolefin include hexafluoropropylene, and examples of the perfluoro (alkyl vinyl ether) include perfluoro (methyl vinyl ether), perfluoro (propyl vinyl ether), and the like. Examples of the monomer include fluorodioxole, and examples of the perfluoroalkylethylene include perfluoromethylethylene.

  Fibrous polytetrafluoroethylene has a peak area ratio on the low temperature side of the melting endotherm curve obtained by differential scanning calorimetry (DSC) analysis performed at a heating rate of 5 ° C. per minute, which is 88.5% of the total peak area. It is preferable that it is a thing which has been partially baked as described above. A paper-like material having a smooth surface and excellent breathability can be obtained when papermaking. The upper limit is preferably 99.0%. If it is below these ranges, it is difficult to obtain smooth paper, and if it exceeds this range, the paper is lacking a unit and its operability is significantly impaired.

  It can be said that the peak area indicated by 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, the ratio of the polytetrafluoroethylene molecules unraveled can be evaluated by the peak ratio between the area of the low temperature side peak obtained from the differential scanning calorimeter and 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. This may be understood as 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 usually be separated by approximating using a Gaussian-Lorentian type curve. Compared to the case of using only Gaussian type or Lorentian type curves, there is a feature that the degree of deviation is small, and this method is used in most of the calculation software attached to commercially available analytical instruments. In this case, the basic peak position was determined by giving two apparent vertices found in the polytetrafluoroethylene powder as a raw material as initial values, and performing approximation without limiting this. For example, in the case of fibrous polytetrafluoroethylene used in Example 1 of the present invention, the basic peak positions obtained by this are 339.14 ° C and 343.01 ° C, and the linear and half-value widths are not limited based on this, and the peak temperature Only by limiting to 0.6 to 0.7 ° C. or less from the initial value, the composite curve was separated into two, and the peak area was obtained. In the above examination, information on the raw material powder is used to shorten the time required for convergence of the value, but it can also be obtained directly from the melting curve of the fibrous powder.

The composite paper-like material of the present invention is obtained by combining the above fibrous polyimide and polytetrafluoroethylene into paper. The compounding method is not particularly limited, but can be easily obtained with good productivity by applying paper making and mixing. From the viewpoint of obtaining a thin and uniform composite paper-like material, it is preferable to apply the wet papermaking method among the papermaking methods.

  The wet papermaking method comprises at least a dispersion step in which fibrous polytetrafluoroethylene is dispersed in water, a fibrous polyimide mixing step, a papermaking step, and a drying step.

In the dispersion step, fibrous polytetrafluoroethylene is added to water and fibrillated using a pulper or refiner equipped with a stirrer to obtain a fibrous polytetrafluoroethylene slurry. Usually, polytetrafluoroethylene has a large contact angle with water, and it is difficult to disperse it uniformly in water. Therefore, a dispersant is applied to the fiber or fibrous powder in advance or is added to the water to be dispersed. It is preferable to keep it. Although the dispersing agent to apply is not specifically limited, Nonionic polyoxyethylene alkyl ethers are preferable at the point which exhibits a dispersion effect by addition of a small amount.

  In the mixing step of mixing the fibrous polyimide, the fibrous polyimide is added to the fibrous polytetrafluoroethylene slurry obtained in the dispersing step, and the same treatment as in the dispersing step is performed to obtain a mixed slurry. Usually, the fibrous polyimide can be uniformly dispersed in the slurry without applying a dispersant.

  The blending ratio of fibrous polyimide and polytetrafluoroethylene may be appropriately adjusted according to the purpose of use, but the lower limit of the blending ratio of fibrous polyimide is 5% by mass, preferably 10% by mass. . The upper limit is preferably 90% by mass, more preferably 80% by mass. If the blending ratio of the fibrous polyimide is less than 5% by mass, the thermal dimensional stability and strength may be insufficient, and if it exceeds 90% by mass, the handling and strength of the composite paper-like material in the manufacturing process may be insufficient. The surface and dielectric properties may be insufficient.

  Next, the mixed slurry is made using a known wet papermaking apparatus exemplified by a circular net type wet paper machine, a short net type wet paper machine, a short net tilt type wet paper machine, or a long net tilt type wet paper machine. A composite paper-like material is formed by a drying process in which a paper-like material (paper-made material) is formed through a paper-making process, and the obtained paper-made material is dried by a hot-air type, contact type or radiation type dryer attached to the paper machine. obtain. In this papermaking method, when a pressurizing step for pressurizing the papermaking material in the thickness direction with a nip roll consisting of a pair of metal rolls is provided, fibrous polytetrafluoroethylene is pressure-bonded to the fibrous polyimide and has excellent shape retention. It can be a composite paper. The pressurization may be performed at room temperature, and the applied pressure is usually about 1 to 10 kgf / cm. Of course, if possible, the pressurization may be performed under heating. This pressurizing step may be performed between the paper making step and the drying step, or may be performed after the drying step.

Paper had a basis weight of the paper-like material after drying, 50 to 1500 g / m ^2, preferably carried out such that the 100~1200g / m ^2. When the basis weight is smaller than the value, the operability in the papermaking method is lowered and it tends to be difficult to produce stably. On the other hand, if the basis weight is too large, production problems such as reduction in drainage and insufficient drying in the paper making process tend to become prominent.

  Next, using a heating and pressurizing device exemplified by a roll press device such as a calender roll consisting of a pair of metal rolls or a double belt press device capable of performing a heat press between a pair of opposing metal belts, etc. By pressurizing the composite paper-like material obtained above under heating in the thickness direction, the fibrous powder made of polytetrafluoroethylene is fused to the fibrous polyimide, and the strength of the composite paper-like material is remarkably increased. That is, in addition to the step of obtaining a composite paper-like material by the wet papermaking method, a step of pressurizing the obtained paper-like material under heating causes the fibrous powder made of polytetrafluoroethylene to be melted into the fibrous polyimide. A composite paper material is obtained which has been applied, ie densified. In addition, it cannot be overemphasized that a heat pressurization process may be performed continuously following a papermaking process, and may be performed on another line.

  The heating temperature at the time of heating and pressing is preferably performed at a temperature equal to or higher than the melting point of polytetrafluoroethylene. When the final heating temperature is lower than the melting point, the effect of improving mechanical strength characteristics tends to be difficult to obtain. On the other hand, it shows that even if heat treatment below the melting point is performed until the final heating step, the binding force can be maintained within a certain range, and using such an intermediate, it is possible to obtain a processed product such as a laminate. Is possible. The heating temperature is preferably not higher than the temperature at which the polyimide forming the fibrous polyimide melts. When the polyimide is crystalline polyimide, the temperature is not higher than the melting point of the polyimide, and further 10 ° C. from the melting point. It is preferable that the temperature is lower. If the heating temperature exceeds the melting point of the polyimide, the fibrous polyimide is extremely melted, and the blending effect of the fibrous polyimide tends not to be exhibited. Usually, a heating temperature of about 340 to 380 ° C. may be adopted. In addition, melting | fusing point here means the value measured using a differential scanning calorimeter (the Perkin Elmer company make, Pyrisl DSC).

  Further, the pressurizing pressure at the time of heating and pressurizing is not particularly limited, but the higher the pressurizing pressure, the lower the porosity of the composite paper-like material obtained, and the tendency to be densified. For example, a pressurizing pressure of about 0.05 to 10 MPa can be employed.

  Furthermore, in the above-described steps, when the composite paper-like material of the present invention laminated in two or more layers is heated and pressurized, it becomes an integrated densified paper-like material with no layers. A densified paper material having a desired thickness can be obtained. At this time, by applying the composite paper material of the present invention having a different composition ratio to each layer, a composite paper material in which the composition of polyimide and polytetrafluoroethylene is changed in the thickness direction can also be obtained.

The thickness of the paper-like material obtained in this way is determined by the basis weight of the paper making process and the pressure applied under heating, depending on the number of laminated sheets and the degree of densification. From the surface, it is preferably 20 to 2000 μm, more preferably 25 to 800 μm. If the lower limit is not reached, the operability in the process tends to be low and the yield tends to decrease. If the upper limit is exceeded, only non-uniform dimensions tend to be obtained in the pressurizing step under heating. Further, the apparent density is preferably 0.3 to 2.1 g / cm ³ , and if it falls below this range, it tends not to be excellent in strength, and those exceeding this range tend to be substantially impossible to produce.

  Various additives can be blended in the composite paper-like material of the present invention within a range not impairing the object of the present invention. That is, short fibers and pulps made of other organic or inorganic substances, such as aramid, polyester, polyetherimide, polyetheretherketone, polysulfone, polyphenylene sulfide, polyketone, carbon, glass, alumina, etc. Or pulp-like materials, and various particles made of titanium oxide, zinc oxide, magnesium oxide, alumina, silica, aluminum nitride, silicon nitride, boron nitride, silicon carbide, carbon black, graphite, mica, molybdenum disulfide, etc. A thing (filler) may be mix | blended.

  For the purpose of imparting strength, a thermoplastic resin such as a polyimide resin or a precursor thereof, or a thermosetting resin such as an epoxy resin may be included depending on the purpose. In this case, the polyimide resin or a precursor thereof, an epoxy resin or the like is usually applied, sprayed or impregnated in the state of an emulsion or a solution.

  These additives may be used alone or in combination within a range that does not impair the object of the present invention, but the total mass during drying is 30% by mass or less based on the total mass of the composite paper of the present invention. It is preferable from the viewpoint of maintaining various characteristics.

  As described above, the composite paper-like material of the present invention can be made into a form in which the fibrous powder made of polytetrafluoroethylene is fused to the fibrous polyimide by the heating and pressing step, and is thus densified. The paper is excellent in strength. Further, even when the layers are laminated in the heating and pressurizing step, the phenomenon of destruction from the layers during use is not observed, and the strength level is substantially the same as that of the single layer. The strength is determined by the blending ratio and the degree of densification of the fibrous powder made of polytetrafluoroethylene and the fibrous polyimide, or the amount of the third component to be blended, etc., but is defined in, for example, JIS-P8113 In terms of the average breaking length obtained by the measurement method, it is usually in the range of 0.5 to 7 km.

  The composite paper-like material of the present invention has little dimensional change due to heat and is excellent in dimensional stability under high temperature use. As for dimensional stability, the average linear expansion coefficient at 20 to 230 ° C. is −20 to 30 μm / m · ° C. (value measured according to JIS-K7197) in both the production direction and the width direction of the composite paper-like material. It is preferable to be within the range. If the average linear expansion coefficient is out of the range of −20 to 30 μm / m · ° C., the dimensional change under high temperature use becomes large and tends to be unsuitable for use.

  In the present invention, by making a paper-like material constituted by randomly dispersing fibrous polyimide and polytetrafluoroethylene as described above, a paper-like material having an excellent balance between dimensional stability and directionality is obtained. Can be obtained.

  The composite paper-like material preferably has low water absorption, and the water absorption calculated by the following formula when left in an environment of 25 ° C. and 60% relative humidity for 24 hours is 0.5% or less. This is a preferred embodiment of the invention.

（式中、Ｗは吸湿後の不織布の質量を示し、Ｗ₀は絶乾時の不織布の質量を示す。）

(Wherein, W represents the mass of the nonwoven fabric after moisture absorption, and W ₀ represents the mass of the nonwoven fabric when absolutely dry.)

  In general, polyimide is known to have a relatively high water absorption due to its strong polarity in its imide group, and when used as a molded product, dimensional changes and changes in electrical characteristics tend to become a problem. there were. Similarly, in the paper-like material composed of conventional amorphous polyimide fibers, the size of water absorption has been a problem, but in the present invention, from crystalline polyimide fibers having low water absorption and polytetrafluoroethylene. By using the fibrous powder as a main constituent, it has become possible to obtain a high-performance composite paper-like material with low water absorption, which has never been achieved before. In particular, the polyimide represented by the chemical formula (1) or the chemical formula (2) has crystallinity and has a small proportion of imide groups in the chemical structure. From the viewpoint, it is preferable to use a fibrous polyimide composed of these.

The dielectric constant of both polyimide and polytetrafluoroethylene is low and excellent in insulation performance. Since the paper-like material of the present invention does not contain a third component serving as a binder, the composite paper-like material can be expected to have the same characteristics. The electrical characteristics were measured at 2.45 GHz at room temperature using a cylindrical dielectric constant evaluation device (consisting of a resonator manufactured by Kanto Electronics Co., Ltd. and a network analyzer manufactured by Agilent Technologies). Can be evaluated. In the composite paper-like material of the present invention, it varies depending on the content ratio of the fibrous powder composed of fibrous polyimide and polytetrafluoroethylene and the apparent density of the composite paper-like material. In this case, the dielectric constant obtained by the above measurement method is in the range of 2.0 to 3.1. Moreover, the dielectric loss obtained by the same measurement is in the range of 1 × 10 ^{−5 to} 3 × 10 ⁻³ .

  It is known that both chemical resistance and oxidation resistance are excellent in both polyimide and polytetrafluoroethylene, and the composite paper-like material of the present invention can be excellent in these characteristics. The chemical resistance can be evaluated by the change in weight, color, and shape after the composite paper-like material is immersed in the drug to be tested and left at room temperature for 1 week. There are large weight changes and dimensional changes, and in the case of swelling, there is a slight increase in weight, but generally used alcohol solvents, ether solvents, ketone solvents, ester solvents, amide solvents, etc. Have been found to have excellent properties with respect to many of the nonpolar solvents such as polar solvents, hydrocarbon solvents, and various oils and fuels. In addition, oxidation resistance is evaluated by immersing the composite paper-like material in a so-called Fenton reagent that contains a very small amount of an activator such as iron sulfate (III) in hydrogen peroxide water, and observing its deterioration due to oxidation. For example, even when immersed for 48 hours at 70 ° C., almost no deterioration was observed.

  Since the composite paper-like material of the present invention has a form in which polyimide having excellent wear resistance and polytetrafluoroethylene having excellent lubricity are uniformly blended, the frictional wear characteristics are excellent. For example, it can be evaluated with a thrust friction and wear tester (Toyo Baldwin; EMFIII-E) at room temperature and under non-lubricated conditions. Even if it slides at a moving speed for 48 hours, it shows good wear resistance and does not damage the mating material.

  Since the composite paper-like material of the present invention has the above-described characteristics, it is required to have a seamless belt, stamping mold, guard tube, flame retardant paper material, valve sheet, solder, which requires strength, heat resistance and thermal dimensional stability. It is the best material for pattern paper and cushioning materials. In addition, since it has excellent electrical characteristics, it can also be applied to circuit boards. Furthermore, since it is excellent also in chemical resistance and abrasion resistance, it is an excellent material as a filter, abrasive paper material, electrolyte membrane or sealing material.

  Hereinafter, the present invention will be described using examples.

(Production example of fibrous polyimide)
Aurum (trade name; manufactured by Mitsui Chemicals) was used as the polyimide resin. After the polyimide resin is melted at 415 ° C., a strand obtained by extruding from a 0.2 mm diameter die is taken up at a rate of 700 m / min, cooled and solidified, and then wound around a paper tube to obtain a fiber having a fiber diameter of approximately 23 μm. A polyimide was obtained. Next, this fibrous polyimide was stretched about 3 times in a heater at 350 ° C. to obtain a fibrous polyimide having a fiber diameter of approximately 12 μm. The obtained fibrous polyimide was advanced in crystal orientation by stretching. In this example, short fibers obtained by cutting this fibrous polyimide into 5 mm lengths were used. The short fiber had a crystallinity of 26% and a melting point of 389 ° C.

(Production example of polytetrafluoroethylene fibrous powder)
A polymer obtained by emulsion polymerization of 100 mol% of tetrafluoroethylene was used as a raw material polytetrafluoroethylene powder (average particle size: 570 μm). The obtained raw material polytetrafluoroethylene powder was fed into a hopper by a feeder. Next, the polytetrafluoroethylene powder was supplied to a stretching tank (rotor inner diameter: 160 mmφ) equipped with a rotating blade while being appropriately supported by dry air, and stretched. At this time, the lower surface of the stretching tank was partially meshed, and only those smaller than a certain size were allowed to exit the stretching tank. By treating this with a standard classification sieve, the powder of 5 μm or less was removed to obtain a raw material polytetrafluoroethylene fibrous powder.

The resulting polytetrafluoroethylene fibrous powder is
Average fiber length: 1.5μm
Average form factor: 40
Specific surface area: 6.38m ² / g
Low-temperature peak area ratio: 92.3%
Met.

(Example 1)
Add 3.2 parts by mass of polytetrafluoroethylene fibrous powder to water containing 0.1 parts by mass of polyoxyethylene alkyl ether per 1000 parts by mass of water, and stir using a stirrer (pulper) to disperse uniformly. It was.

  Next, 0.8 parts by mass of polyimide short fibers cut to a length of 5 mm were added to the system and stirred to obtain a slurry in which the raw materials were uniformly mixed and dispersed.

  This slurry was further diluted with water to a slurry concentration of 0.02% by mass and supplied to a short mesh inclined continuous paper machine to obtain a paper product continuously. The obtained paper product had a water content of about 30% by mass.

  Subsequently, pressure treatment with a linear pressure of 0.1 N / mm was continuously performed at room temperature with a nip roll composed of a pair of stainless steel rolls, and the polytetrafluoroethylene fibrous powder and the polyimide short fibers were pressure-bonded.

  Furthermore, it supplied to the conveyor type hot air dryer attached to the paper machine, and it dried, and it was set as the composite paper-like thing with a moisture content of 0 mass%.

  The resulting composite paper-like material is obtained by press-bonding polytetrafluoroethylene fibrous powder to fibrous polyimide to develop strength, and has good shape retention, and fibrous polyimide and polytetrafluoroethylene. The fibrous powder was uniformly dispersed and blended. A paper-like material obtained through this process is referred to as a composite paper-like material A.

  The composite paper-like material A obtained by the wet papermaking method was preheated at 240 ° C. for 2 minutes under no pressure using a continuous belt press (Sandvik), and then pressurized under a pressure of 25 N / mm. Heating was performed at 5 ° C. for 5 minutes, and then rapidly cooling to 50 ° C. while maintaining the pressurization, whereby a densified composite paper was continuously obtained. In the obtained composite paper-like material, the polytetrafluoroethylene fibrous powder was melted and fused to the polyimide short fiber surface, and the surface was smooth and had a dense structure. A dense paper-like material obtained through this step is referred to as a composite paper-like material B.

The obtained paper-like composite B had a basis weight of 256 g / m ² and a thickness of 154 μm. In addition, the average linear expansion coefficient, breaking length, water absorption, and dielectric constant were measured. The above results are summarized in Table 1.

The thickness was measured by a method of averaging 50 values obtained by measuring at a point interval of 100 cm ² (10 × 10 cm) with a digital thickness gauge.
The breaking length was measured according to JIS-P8113 using a universal testing machine (manufactured by Intesco).
The average linear expansion coefficient was measured according to JIS-K7197 using a TMA measuring apparatus (TA Instruments; TMA2940).
The water absorption was measured according to the above formula I.
The dielectric constant was measured by a method using the above-described cylindrical dielectric constant evaluation apparatus. The sample for measurement is obtained by laminating the composite paper-like material A into a dense body having a thickness of 1.4 mm in the same manner as the composite paper-like material B, and cutting this into a 1.4 mm width. A 1.4 mm square rod was used as a sample.

(Examples 2 to 5)
A composite paper B was obtained in the same manner as in Example 1 except that the blending ratio of the fibrous polyimide and the polytetrafluoroethylene fibrous powder was changed to Table 1. Various physical properties of the obtained composite paper-like material are summarized in Table 1.

(Comparative Example 1)
A paper-like material A composed of polyimide short fibers was made in the same manner as in Example 1 except that 4 parts by mass of polyimide short fibers were added without blending the polytetrafluoroethylene fibrous powder.

  Since the paper-like material of Comparative Example 1 does not contain polytetrafluoroethylene fibrous powder, the fibers are not pressure-bonded to each other, do not maintain the paper-like form, and obtain a satisfactory paper-like material A. I could not.

(Comparative Example 2)
A paper-like material B made of polytetrafluoroethylene fibrous powder was obtained in the same manner as in Example 1 except that 4 parts by mass of polytetrafluoroethylene fibrous powder was added without blending the polyimide short fibers. Various physical properties of the obtained paper B are summarized in Table 1.

(Comparative Example 3)
A composite paper-like material A was prepared in the same manner as in Example 1 except that polytetrafluoroethylene short fibers (trade name Toyoflon, manufactured by Toray Fine Chemical Co., Ltd.) having an average fiber length of 5 mm were used instead of the polytetrafluoroethylene fibrous powder. Made.
The polytetrafluoroethylene short fibers used in this comparative example are:
Average form factor: 250
Specific surface area: 0.1m ² / g
Peak area ratio on the low temperature side: 100%
Had.

  In this comparative example, because the polytetrafluoroethylene short fibers do not function sufficiently as binders, it is difficult to maintain a paper-like form because the fibers are not pressure-bonded, and a satisfactory paper-like product A could not be obtained. .

(Evaluation of oxidation resistance)
(Example 6)
The composite paper B obtained in Example 2 was cut into a length of 100 mm and a width of 10 mm as a sample. The sample was immersed in an oxidizing agent solution in which 20 ppm of iron (II) sulfate was dissolved in an aqueous solution of 30% by mass of hydrogen peroxide, kept at 70 ° C. and left for 80 hours. Thereafter, the sample was taken out, washed with water and dried, and then the fracture length was measured.

  Oxidation resistance with the relative value of the fracture length of the sample that has been immersed in pure water instead of the oxidizer solution and the sample that has been treated in the same way has a fracture length of 100% and is immersed in the oxidizer solution. It was used as an index. As a result, it showed high oxidation resistance of 95%. It is useful as a substrate for an electrolyte membrane that requires high oxidation resistance, such as a polymer fuel cell.

(Comparative Example 4)
A composite paper-like material B was obtained in the same manner as in Example 2 except that an aramid fiber (trade name: Twaron; manufactured by Nihon Aramid Co., Ltd.) having a fiber diameter of approximately 15 μm and an average fiber length of 6 mm was used instead of the polyimide short fiber. .

The obtained composite paper-like product had a basis weight of 296 g / m ² , a thickness of 295 μm, and a breaking length of 1.9 km. The obtained composite paper B was evaluated for oxidation resistance in the same manner as in Example 6. As a result, it was 63%, which was inferior in oxidation resistance.

(Slidability evaluation)
(Example 7)
The composite paper-like material A of Example 1 cut to 500 × 500 mm and laminated two times was heated to 350 ° C. under a pressure of 3 MPa using a press machine having a press plate with a heating device, and the temperature was increased to 350 ° C. And heated under pressure for 15 minutes to obtain a densified composite paper.

The resulting composite paper-like material had a density of 1.60 g / m ² and a thickness of 322 μm. Using a thrust frictional wear tester (manufactured by Toyo Baldwin; EMFIII-E) as a measurement sample, the resulting composite paper-like material cut into 30 x 30 mm was slid into a ring-shaped cross section with an outer diameter of 25 mm and an inner diameter of 20 mm. A sliding test was conducted using a jig made of carbon steel S45C as the moving surface. The surface roughness of the sliding surface of the counterpart material was Ra 0.5a, and the measurement was performed without lubrication. The wear amount and coefficient of friction of the sample were measured after sliding at room temperature for 20 hours at a peripheral speed of 100 m / min and a pressure of 0.49 MPa. The amount of wear was evaluated by the amount of change in the weight of the sample before and after the test. The coefficient of friction was calculated by reading the stress (torque) generated in the rotational direction with respect to the sample at the time of measurement using a load cell attached to the apparatus. The obtained results are shown in Table 2.

(Comparative Example 5)
A composite paper-like material A was obtained in the same manner as in Example 1 except that an aramid fiber (trade name: Twaron; manufactured by Nihon Aramid Co., Ltd.) having a fiber diameter of approximately 15 μm and an average fiber length of 6 mm was used instead of the polyimide short fiber. Furthermore, two sheets were laminated in the same manner as in Example 7 to obtain a composite paper. The density of the obtained composite paper-like material was 1.45 g / m ² and the thickness was 353 μm. The resulting composite paper-like material was subjected to a sliding test in the same manner as in Example 7. The obtained results are shown in Table 2.

As is clear from Table 2, the composite paper-like material of the present invention is excellent in slidability, has low wear even under high sliding conditions, and has a small friction coefficient.

Claims (14)

  A composite paper-like material made of both polytetrafluoroethylene and polyimide.   The composite paper-like product according to claim 1, wherein the fibrous polyimide is a fiber having crystallinity.   3. The composite paper-like material according to claim 1, wherein the polyimide is thermoplastic. The composite paper-like material according to any one of claims 1 to 3, wherein the polyimide is one represented by the following chemical formula (1):

(In the formula, R represents a tetravalent aromatic residue selected from a monocyclic aromatic group, a condensed polycyclic aromatic group, and a non-condensed polycyclic aromatic group in which an aromatic ring is bonded directly or by a bridging member. X represents a divalent residue selected from a direct bond, a hydrocarbon group, a carbonyl group, an ether group, a thio group or a sulfonyl group, and Y _{1 to} Y ₄ represent a hydrogen, alkyl group, alkoxyl group or halogen group. Indicates a monovalent residue selected.) The composite paper-like material according to any one of claims 1 to 4, wherein the polyimide is represented by the following chemical formula (2);

  6. The composite paper-like product according to claim 1, wherein the fibrous polyimide is a short fiber having an average fiber diameter of 3 to 30 μm and an average fiber length of 1 to 15 mm.   The composite paper according to any one of claims 1 to 6, wherein the fibrous polytetrafluoroethylene is a fibrous powder having an average fiber length of 100 to 5000 µm and an average form factor of 5 or more. State.   For polytetrafluoroethylene, the peak area ratio on the low temperature side of the melting endotherm curve obtained by measuring at a rate of temperature increase of 5 ° C. per minute in differential scanning calorimetry analysis is 88.5% or more of the total peak area. The composite paper-like material according to any one of claims 1 to 7, characterized in that   9. The composite paper-like material according to claim 1, wherein the fibrous polytetrafluoroethylene is thermally fused to the fibrous polyimide.   9. The method for producing a composite paper-like material according to any one of claims 1 to 8, wherein fibrous polytetrafluoroethylene and polyimide are produced by a papermaking method.   11. The method for producing a composite paper-like material according to claim 10, wherein the papermaking method is a wet papermaking method.   12. The composite paper-like material according to claim 11, wherein the paper-making method comprises a dispersion step of fibrous polytetrafluoroethylene, a mixing step of fibrous polyimide, a paper-making step, a pressing step, and a drying step. Production method.   13. The method for producing a composite paper-like material according to claim 12, further comprising a pressure treatment step under heating after the drying step. Used for any one selected from the group consisting of seamless belts, circuit boards, stamping molds, filters, guard tubes, flame retardant paper materials, solder paper, polishing paper materials, electrolyte membranes, sliding members, seal members, and cushioning materials. The composite paper-like material according to claim 1 to 9.