JP7392318B2 - Paper made from fluorine fibers - Google Patents

Description

The present invention relates to paper making made of fluorine fibers.

Paper making is in demand in a wide range of fields, and is used for a variety of products such as filters, separators, and even electrical insulation materials. The required thickness, heat resistance, and density vary depending on the application. For this reason, it is important not only to optimize paper manufacturing conditions, but also to optimize the characteristics and physical properties of the fibers used as raw materials.

In recent years, notebook PCs, smartphones, tablets, etc. have become more popular, and these have made a major contribution to the development of an IT society. For this reason, there is a desire to improve the sophistication of lithium-ion batteries used in electronic devices such as notebook PCs, smartphones, and tablets, and to develop all-solid-state secondary batteries that are expected to be safer and have higher performance. Under these circumstances, the performance of insulating paper such as paper or insulating sheets used in electronic devices is required to be improved. The heat resistance and thickness required for insulating materials differ depending on the environment in which they are used, but for high-performance secondary batteries such as all-solid-state secondary batteries, the operating environment temperature can exceed 200°C, so Such heat resistance is required. Furthermore, regarding the thickness, it is required to be thinner than 50 μm. In order to solve these problems, it is desired to make paper using fluorine fibers whose operating temperature exceeds 200° C., but paper having a thickness of less than 50 μm has not been produced using fluorine fibers.

A known technique for making paper using fluorine fibers is to obtain fluorine fiber-containing paper by mixing fluorine fibers with a substance that has a self-adhesive function, such as polyvinylpyrrolidone, and then remove the self-adhesive function material. (See Patent Document 1). In Example 2 of Patent Document 1, fluorine fiber mixed paper obtained by dispersing and mixing 90 wt% of fluorine fibers made of a copolymer of tetrafluoroethylene and ethylene and having a fiber diameter of 10 μm and 10 wt% of polyvinylpyrrolidone is heated at 90°C or higher. Fluorine fiber paper is obtained by passing it through hot water. However, the thickness is described as 110 μm, making it unsuitable as an insulating member for electronic devices. Further, although fluorine fibers with a fiber diameter of 10 μm are used, it is thought that it is difficult to reduce the thickness further because a substance having a self-adhesive function is used.

Another known technique is to disperse an aqueous dispersion of polytetrafluoroethylene in a matrix component, and then heat and sinter the undrawn polytetrafluoroethylene polymer fiber obtained by spinning it from a spinneret ( (See Patent Document 2). In Example 1 of Patent Document 2, a paper sheet obtained by wet papermaking of a papermaking raw material obtained by dispersing undrawn polytetrafluoroethylene polymer fibers in water was heat-treated at 400 ° C. for 4 minutes and sintered. It is described that a fluorine fiber sheet is obtained by subjecting the sintered sheet to a heat treatment at 325° C. for 24 hours, and stretching the sintered sheet in the longitudinal and transverse directions at a stretching ratio of 1:3. However, the thickness is described as 87 μm, making it unsuitable for use as an insulating member for electronic devices. Furthermore, since undrawn polytetrafluoroethylene polymer fibers are used, it is difficult to reduce the fiber diameter, and it is considered difficult to further reduce the thickness.

In order to obtain thin and thick paper, we believe that it is important to reduce the fiber diameter of the fibers that are the raw material for paper making, and to make paper using raw materials with small fiber diameters.

Japanese Patent Application Publication No. 165598/1983 Japanese Patent Application Publication No. 3-130496

The object of the present invention is to maintain the properties of fluorine-based fibers as a material, such as excellent heat resistance, chemical resistance, electrical insulation, friction properties, and weather resistance, while reducing the thickness of the fluorine fibers, making them suitable for insulating members for electronic devices. The objective is to obtain paper made of fluorine-based fibers.

The paper made of fluorine fibers of the present invention which solves the above problems is characterized in that the fibers constituting the paper are composed only of two or more types of fluorine fibers having different melting points, and at least some of them are fused. It is something to do.

The paper made from fluorine-based fibers of the present invention is made only of two or more types of fluorine-based fibers with different melting points, and at least some of them are fused together, so that while maintaining the characteristics of the fluorine-based fiber as a material, It is possible to provide paper made of fluorine-based fibers that can be made thin and suitable for insulating members for electronic devices.

<Fluorine fiber>
As the fluorine-based fiber in the present invention, any fiber can be used as long as 90% or more of the repeating structural units of the polymer are composed of a monomer containing one or more fluorine atoms in the main chain or side chain. However, the fibers composed of monomers with a larger number of fluorine atoms are more preferable. ), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA, melting point 310°C), polyvinylidene fluoride (PVDF, melting point 156-178°C), ethylene-tetrafluoroethylene copolymer (ETFE, melting point 270°C) ), and fibers of ethylene/chlorotrifluoroethylene copolymer (ECTFE, melting point 220-245°C). Among these fluorine fibers, at least two types of fluorine fibers with different melting points (hereinafter, the fluorine fiber with a high melting point may be referred to as fluorine fiber A, and the fluorine fiber with a low melting point may be referred to as fluorine fiber B) The paper making of the present invention is configured. Among these, PTFE is preferable for the fluorine-based fiber A, and PFA, which has a melting point close to that of PTFE, is preferable for the fluorine-based fiber B. In addition, the fluorine-based fibers used in the present invention can also be used in combination of three or more types. Furthermore, the fluorine-based fibers may contain 1 to 25% of cellulose and their carbides.

The fiber diameter of the fluorine-based fiber in the present invention is preferably 1.5 μm or more and 20 μm or less for both the fluorine-based fiber A and the fluorine-based fiber B. As long as it is within this range, the fiber diameters of the fluorine-based fiber A and the fluorine-based fiber B may be different. When the diameter is 1.5 μm or more, the fibers do not become too easily entangled with each other and are easily dispersed uniformly. When the thickness is 20 μm or less, the fibers do not become too hard, and the entanglement force between the fibers can be maintained within an excellent range. As a result, sufficient paper strength can be obtained and paper can be made that is difficult to tear.

Furthermore, the fiber length of the fluorine-based fibers for both fluorine-based fibers A and B is preferably 0.5 mm or more and 15 mm or less, more preferably 1 mm or more and 8 mm or less. As long as it is within this range, the fiber lengths of fluorine-based fiber A and fluorine-based fiber B may be different. By setting the thickness to 0.5 mm or more, the strength of the paper can be increased due to the entanglement of the fibers. Furthermore, by setting the thickness to 15 mm or less, it is possible to prevent unevenness from occurring due to entanglement of fibers becoming lumpy.

The cross-sectional shape of the fluorine-based fibers A and B in the present invention is not particularly limited, and the cross-section may be any shape such as round, β-shape, C-shape, triangular, flat, dogbone shape, multilobal shape, etc. There may be. Further, it may have a hollow shape. The cross-sectional shapes of the fluorine-based fiber A and the fluorine-based fiber B may be different.

Furthermore, both the fluorine fiber A and the fluorine fiber B may be fibrillated fluorine fibers. Here, fibrillation refers to a state in which a fiber is split into two or more fibers in the warp direction, each of which is thinner than the original fiber, or has a fluffy portion on the fiber surface. Fibrillation improves the entanglement between fibers and improves paper strength, making it possible to obtain paper with excellent process passability during papermaking. Examples of means for fibrillating fluorine-based fibers include a Niagara beater, a homogenizer, a disc refiner, a laika machine, a pestle and a mortar.

<Paper made from fluorine fibers>
The mixing ratio of fluorine fiber B in paper making is preferably 10% or more and 90% or less, more preferably 15% or more and 80% or less, and even more preferably 20% or more and 70% or less. By setting the blending ratio of the fluorine-based fiber B within the above range, paper having excellent tensile strength and tear strength can be obtained. When the blending rate of fluorine-based fiber B is less than 10%, the proportion of the thermally bonded portion is insufficient, and the tensile strength and tear strength of the paper become weak. On the other hand, if the mixing ratio of fluorine-based fiber B exceeds 90%, the paper becomes film-like and the tear strength is extremely reduced.

Here, the proportion of fluorine-based fiber B is determined by taking a 5 cm square sample length x width of the sample before heating and pressure treatment, separating it into each fiber, drying each fiber in an oven at 100 ° C, and then weighing is measured and calculated as mass % from the ratio.

In the papermaking process described below, processing tension is applied, so in order to prevent paper from deforming and breaking due to processing tension, fluorine fibers containing a fibrillated matrix component are used in combination, and the intertwining of the fibers can withstand the processing tension. It is desirable to provide the minimum paper strength. The fluorine fiber containing a matrix component is an intermediate of a drawn fluorine fiber yarn obtained by the matrix spinning method described below, and is a fluorine fiber that has not undergone a firing process. Since the fibers have not undergone a firing process, the matrix components remain in the fibers. As mentioned above, means for fibrillating the fluorine-based fibers include, but are not limited to, a Niagara beater, a homogenizer, a disc refiner, a light machine, a mortar and a mortar.

The degree of fibrillation can be confirmed by the freeness of a Canadian freeness tester according to JIS P 8121-2 (2012), and it is preferable that the freeness is between 10 and 900 ^cm3 , and between 10 and 600 ^cm3 . It is more preferable that it is, and more preferably that it is 10 to 300 cm ³ . When the degree of fibrillation is low, that is, when the freeness is too high, entanglement by fibrils decreases, and the paper strength of the dry web decreases. On the other hand, if the degree of fibrillation is large, that is, if the freeness is too low, the efficiency of the fibrillation process will decrease and the load of the dewatering process during papermaking will increase.

The mixing ratio of fluorine-based fibers containing fibrillated matrix components is preferably 0 to 50%, more preferably 5 to 40%, and even more preferably 10 to 30%. By setting the mixing ratio of the fluorine-based fibers containing the fibrillated matrix component within the above range, it is possible to impart appropriate paper strength to the dry web. If the blending ratio of fluorine-based fibers containing fibrillated matrix components is greater than the above range, although the paper strength of the dry web is sufficient, it is not preferable because the mechanical properties of the paper after heating and pressure treatment described below will deteriorate. .

Here, the proportion of fluorine-based fibers containing fibrillated matrix components is determined by taking a 5 cm square sample length x width, separating it into each fiber, and heating and pressurizing each fiber at 100℃. After drying in an oven, the weight is measured and the ratio is calculated as mass %.

Next, an example of the method for manufacturing paper made of fluorine fibers of the present invention will be explained.

<Method for producing fluorine fiber>
Known methods for producing fluorine-based fibers include a split exfoliation method, a paste extrusion method, a melt spinning method, and a matrix spinning method (also referred to as an emulsion method).

The split exfoliation method is a manufacturing method in which fluororesin powder is compressed in a cylinder, sintered, split exfoliated, and then stretched.

The paste extrusion method is a manufacturing method in which a fluororesin is kneaded with a powdered wax-like lubricant, formed into a rod or film, the lubricant is removed, and the product is stretched and fired (in some cases, it is not fired). However, with these two manufacturing methods, the cross section of the final fibrous material obtained by cutting into thin pieces is inevitably flat, random and less uniform, and the disadvantage is that there is variation in tearing strength after paper processing. there were.

Furthermore, the melt spinning method is a manufacturing method in which fluororesin powder is heated at a temperature higher than its melting point, and the molten resin is spun from a spinneret to form fibers. This manufacturing method produces highly uniform fluorine-based fibers by spinning from a spinneret, but it cannot be applied to materials such as PTFE, which has a high melting point and exhibits almost no fluidity even above the melting point.

For these reasons, it is preferable to use the matrix spinning method to produce the fluorine-based fibers of the present invention. In the matrix spinning method, a mixture of viscose or the like as a matrix and an aqueous dispersion of a fluororesin is discharged from a spinneret into a coagulation bath to form fibers, which are then refined and then fired. By firing at a temperature equal to or higher than the melting point of the fluororesin, most of the matrix polymer is fired and scattered, the fluororesin is melted, and the particles are fused together, thereby providing subsequent stretchability for the first time. After firing, the undrawn yarn is directly drawn in 1 or 2 steps to obtain a drawn fluorine-based fiber yarn. Strength is developed during this stretching process. Thereafter, the fluorine-based fiber used in the present invention can be obtained by cutting the obtained fluorine-based fiber drawn yarn to a predetermined fiber length. This manufacturing method yields highly uniform fluorine-based fibers by spinning from a spinneret. Furthermore, by changing the die design and spinning/drawing conditions, the fiber diameter can be reduced, making this manufacturing method suitable for making paper thinner.

In the spinning dope, the proportion of the fluororesin is preferably 75 to 93% by mass, and in this case, the proportion of the matrix component is preferably 7 to 25% by mass. When the proportion of the fluororesin in the spinning dope is 75% by mass or more, fusion between the fluororesin particles progresses during the firing process, making it difficult for thread breakage to occur, resulting in a fluororesin fiber with high process stability. It will be done. On the other hand, when the proportion of the fluororesin is 93% by mass or less, yarn breakage is less likely to occur during the spinning process. Viscose, polyvinyl alcohol, sodium alginate, and hydroxypropyl cellulose are used as the matrix component, and in the present invention, it is preferable to use viscose. As the coagulation bath, an aqueous solution of an inorganic mineral acid and/or an inorganic salt is used, and in the present invention, it is preferable to use a mixed aqueous solution of sulfuric acid and sodium sulfate.

Fibrillated pulp-containing fluorine-based fibers are made into fibers using the matrix spinning method, and before firing, are processed using mechanical equipment such as a Niagara beater, homogenizer, disc refiner, Raikai machine, mortar and mortar, or water jet punch. It is fibrillated with. The matrix resin used in the matrix spinning method is preferably one that is easily fibrillated, such as a cellulose resin such as viscose.

<Paper made from fluorine fibers>
Fluorine fiber A and fluorine fiber B (fluorine fiber containing a fibrillated matrix component if necessary) are each dispersed in water. In addition, when fluorine-based fibers containing fibrillated matrix components are included at the same time, the fluorine-based fiber raw material to be fibrillated is dispersed in water and subjected to mechanical treatment using a Niagara beater, homogenizer, disc refiner, Raikai machine, etc. Furthermore, these dispersions are mixed at a predetermined ratio to form a papermaking dispersion.

The total amount of fluorine fibers A, B, and fluorine fibers including the fibrillated matrix component based on the total weight of the papermaking dispersion is preferably 0.05 to 5% by mass. If the total amount is less than 0.05% by mass, production efficiency will decrease and the load on the dehydration process will increase. On the other hand, if it exceeds 5% by mass, the dispersion state of the fibers deteriorates and it becomes difficult to obtain uniform papermaking.

The dispersion may be prepared separately in advance by separately preparing a dispersion of fluorine fiber A, a dispersion of fluorine fiber B, and a dispersion of fluorine fiber containing a fibrillated matrix component, and then mixing them. The fluorine-based fiber A and the fluorine-based fiber B may be directly mixed and dispersed in the same tank and then mixed with a dispersion containing fluorine-based fibers containing a matrix component that has been separately fibrillated. The method of separately preparing and mixing a dispersion liquid of each fiber is preferable in that the stirring time can be controlled separately according to the shape and characteristics of each fiber, and the method of preparing a dispersion liquid of each fiber separately is preferable in that the stirring time can be controlled separately according to the shape and characteristics of each fiber. A method of mixing a dispersion containing fluorine-based fibers containing a fibrillated matrix component after adjusting the above is preferable from the viewpoint of simplifying the process.

In order to improve water dispersibility, dispersants and oil agents such as cationic, anionic, and nonionic surfactants are used in papermaking dispersions. A viscous agent to prevent foaming, and an antifoaming agent to suppress foaming may be added.

The dispersion for paper making prepared as described above is made into paper using a paper machine such as a circular net type, fourdrinier type, or inclined net type, or a hand-made paper machine, and then dried with a Yankee dryer, a rotary dryer, etc., and then dried. Web. Thereafter, this is subjected to heat and pressure treatment to obtain wet papermaking. In the present invention, simultaneous heating and pressurization is referred to as heating/pressure treatment, and is distinguished from a treatment such as drying that only involves heating but does not apply pressure. Furthermore, the term "dry web" refers to paper that has not been subjected to this heating and pressure treatment among wet-processed paper.

As the means for heating and pressurizing, any means may be used as long as heating and pressurizing can be performed at the same time, and for example, a hot press using a flat plate, a calender, etc. can be employed. Among these, calenders that can be processed continuously are preferred. As the rolls of the calendar, a combination of metal-metal rolls, metal-paper rolls, metal-rubber rolls, etc. can be used.

The temperature condition for the heating/pressure treatment is preferably a temperature that is higher than the melting point of the fluorine fiber B and lower than the melting point of the fluorine fiber A. If the treatment temperature is lower than the melting point of fluorine-based fiber B, fluorine-based fiber A and fluorine-based fiber B will not be thermally fused, making it impossible to obtain paper with excellent mechanical properties. On the other hand, if the melting point of the fluorine-based fiber A is exceeded, the dry web becomes too soft and sticks to heating and pressing equipment such as a calendar roll or a hot press plate, making it impossible to stably mass-produce it. Moreover, when paper is made, the surface becomes rough. Furthermore, rapid temperature changes cause paper to shrink significantly, making stable mass production impossible. A gradual temperature increase process is preferred. Further, when calendering is employed as the heating/pressure treatment, the pressure is preferably 98 to 7000 N/cm. By setting it to 98 N/cm or more, the voids between fibers can be crushed. On the other hand, by setting it to 7000 N/cm or less, tearing of the wet nonwoven fabric during the heating/pressure treatment process can be prevented, and the treatment can be stably performed. The process speed is preferably 1 to 30 m/min, more preferably 2 to 20 m/min. Good working efficiency can be obtained by setting the speed to 1 m/min or more. On the other hand, by setting the speed to 30 m/min or less, heat can be conducted to the fibers inside the paper making, and the fibers can be effectively thermally fused.

In this way, it is possible to obtain the paper of the present invention in which at least a portion of two or more types of fluorine fibers having different melting points are fused together.

Next, the present invention will be specifically explained based on Examples. However, the present invention is not limited only to these examples. Various modifications and modifications can be made without departing from the technical scope of the present invention. Note that the methods for measuring various characteristics used in this example are as follows.

[Measurement/evaluation method]
(1) Fiber diameter A sample is randomly extracted from the drawn fluorine fiber yarn before cutting, and a cross-sectional photograph is taken using the embedding method as described below. Thirty fibers were randomly selected from the photographed images, and the distance between the parallel lines was measured, regarding the contour lines of the fibers as parallel lines. Note that the observed fibers are circular. If it is not circular, assume the smallest rectangle or square that circumscribes the fiber outline, and double the average length of the long side and short side (corresponding to the length of one side in the case of a square). The particle size is as follows.

<Embedding method>
Apply some tension to the sample thread on the molding frame and fix it with adhesive tape. Heat at 200°C to melt the paraffin and stearic acid mixture. When the temperature reaches 130°C, add ethyl cellulose little by little and keep warm for 1 hour while stirring to remove bubbles. After cooling the temperature to 100°C, pour it into a molding frame. After cooling and solidifying, cut into blocks of appropriate size. A section (approximately 7 μm thick) is cut from the block using a microtome and placed on a glass slide. At this time, spread a thin layer of Albumen on the slide glass (Albumen is a mixture of egg white and glycerin in equal parts and 1 wt % of sodium salicylate added as a preservative). After being left in a dryer kept at 70°C for 20 minutes for heat treatment and drying, it is immersed in an isoamyl acetate bath for about 1 hour for deembedding, and then air-dried. Place a drop of liquid paraffin on the slide glass, gently place a cover glass on it to prevent air from entering, and take a photo using a microscope.

(2) Melting point This is a value measured by a method based on JIS K7121 (2012) 4.2 (2). The melting point is defined as the value of the melting peak temperature when heated at 10° C./min under a nitrogen stream. Note that both the glass transition temperature and the melting point are the measured values of the first run measured under the above conditions.

(3) Based on JIS P8124 (2011), take three 20cm x 20cm test pieces per 1m of sample width, weigh the mass (g) of each in standard condition, and calculate the average value per ^1m2 . It was expressed in mass (g/m ² ).

(4) Thickness In accordance with JIS P8118 (2014), a test piece of 20 cm x 20 cm was taken, and 10 different locations on the sample were measured using a thickness measuring machine under a pressure of 100 kPa using a presser with a diameter of 16 mm. After waiting 10 seconds for the thickness to settle, the thickness was measured and the average value was calculated.

(5) Tear strength Measured under conditions based on JIS P8116 (2000). Since the obtained sample was a handmade sample and had low fiber orientation, only the tear strength in the longitudinal direction was measured.

(6) Fusion of fibers Using a scanning electron microscope VE-9800 manufactured by KEYENCE, a 20 cm x 20 cm test piece was taken from the sample after heating and pressurizing, and cross-sectional observation was performed at 10 different locations on the sample. The presence or absence of fusion was measured by performing the test at a magnification of 100 times.

(7) Air permeability Measured under conditions based on JIS-P8117 (2009). A 5 cm x 5 cm test piece was taken, measurements were taken at three different locations on the sample, and the average value was calculated. However, samples with extremely poor air permeability that were difficult to measure were marked as unmeasurable, and were determined to be films without voids, rather than paper.

(8) Freeness Measured using a Canadian freeness tester in accordance with JIS P 8121-2 (2012).

[Manufacturing method/manufacturing equipment]
《Hand-made paper machine》
A handmade paper machine (manufactured by Kumagai Riki Kogyo) with a size of 30 cm x 30 cm and a height of 40 cm was used, with a 140 mesh handmade paper screen installed at the bottom.

《Rotary dryer》
A rotary dryer (ROTARY DRYER DR-200 manufactured by Kumagai Riki Kogyo) was used for drying after hand-making the paper.

《Heating/pressurizing》
Heating and pressure were applied using a hydraulic three-roll calendering machine (manufactured by Yuri Roll, model IH type H3RCM) consisting of an iron roll and a paper roll.

[Example 1]
After mixing 50% by mass of viscose and 50% of an aqueous PTFE dispersion having a concentration of 60%, defoaming was performed under a reduced pressure of 10 Torr to obtain a stock solution with a PTFE resin content of 87.0% relative to the viscose. This stock solution was discharged into a coagulation bath through a nozzle having a plurality of discharge holes.
The coagulation bath was a mixed aqueous solution with a sulfuric acid concentration of 10.0% and a sodium sulfate concentration of 11.0%, and the temperature was 10°C. Next, the coagulated unfired yarn was washed with hot water at a temperature of 80° C., and then introduced into an alkaline bath containing an aqueous solution of caustic soda having a concentration of 0.12% for refining to completely remove acid components. After that, the unfired yarn led from the alkaline bath is squeezed with a nip roller, and then fired using a firing roller whose temperature is gradually raised from 280°C to 350°C while giving 4% relaxation. The yarn was taken off at a high speed to obtain an undrawn yarn. The undrawn yarn was then hot-stretched at a temperature of 350° C. to obtain a drawn PTFE yarn with a round cross-section. The obtained PTFE drawn yarn was cut into 6 mm pieces to obtain fluorine-based fiber A. Fluorine-based fiber B was obtained in the same manner as fluorine-based fiber A, except that an FEP aqueous dispersion was used and the firing temperature was changed from 230°C to 300°C.

Fluorine-based fiber A: 70 parts by mass of PTFE fibers were dispersed in water to prepare a dispersion having a fiber concentration of 0.10% by mass. Next, fluorine-based fiber B: 30 parts by mass of FEP fibers were dispersed in water to prepare a dispersion having a fiber concentration of 0.15% by mass. A mixed solution was prepared by beating with a Niagara beater for 20 minutes. The fibers after the Niagara beater had web strength for hand-sheeting operations. These were mixed and further water was added to form a dispersion of 70 parts by mass of PTFE fibers and 30 parts by mass of FEP fibers at a concentration of 0.07% by mass. Wet paper was produced using this dispersion using a hand paper machine. The web obtained by dewatering with a roller was dried for 70 seconds at 110°C using a rotary dryer to obtain a dry web, and then the iron roll surface temperature was 220°C, the linear pressure was 490 N/cm, and the roll was rotated. After heating and pressurizing one side at a speed of 3 m/min, the other side was heated and pressurized at an iron roll surface temperature of 250°C, a linear pressure of 490 N/cm, and a roll rotation speed of 3 m/min to obtain paper. Ta. Moreover, when the cross section of the sample after heating and pressurizing was observed, a part of the fluorine-based fiber B:FEP fiber was fused.

The obtained paper had a basis weight of 40 g/m ² and a thickness of 21.2 μm. It also had excellent air permeability and functioned as a paper-making material.

[Example 2]
Fluorine-based fiber B was obtained in the same manner as fluorine-based fiber A in Example 1, except that a PFA aqueous dispersion was used and the firing temperature was changed from 230°C to 300°C.

In Example 1, the same procedure was followed except that the fluorine-based fiber B: FEP fiber was changed to PFA fiber, the ratio of PTFE fiber: PFA fiber was changed to 70:30, and the iron roll surface temperature was changed from 250 to 270 ° C. A paper was made. The fibers after the Niagara beater were slightly fibrillated on the fiber surface and had web strength for manual papermaking. Moreover, when the cross section of the sample after heating and pressurizing was observed, a part of the fluorine-based fiber B:PFA fiber was fused.

The obtained paper had a basis weight of 40 g/m ² and a thickness of 20.2 μm. It also had excellent air permeability and functioned as a paper-making material.

[Example 3]
In Example 1, fluorine-based fiber A: PTFE fiber was changed to PFA fiber, fluorine-based fiber B: PFA fiber was changed to FEP fiber, the ratio of PFA fiber: FEP fiber was 70:30, and the iron roll surface temperature was 220. → Paper was made using the same procedure except that the temperature was changed to 250°C. The fibers after the Niagara beater were slightly fibrillated on the fiber surface and had web strength for manual papermaking. Moreover, when the cross section of the sample after heating and pressurizing was observed, a part of the fluorine-based fiber B:FEP fiber was fused.

The obtained paper had a basis weight of 41 g/m ² and a thickness of 27.3 μm. It also had excellent air permeability and functioned as paper making.

[Example 4]
In Example 2, in addition to fluorine-based fiber A and fluorine-based fiber B, in the manufacturing process of fluorine-based fiber A, fluorine-based fibers that were made into fibers by a matrix spinning method and before firing were used, and fibrillated fibers treated with a Niagara beater were used. Fluorine-based fibers containing matrix components were also used. Paper was made using the same procedure except that the ratio of PTFE fiber: PFA fiber: fluorine fiber containing a fibrillated matrix component was 40:30:30. Note that the freeness of the fibrillated fluorine-based fibers was 657 cm ³ , and the strength of the dry web was significantly improved and was at a level that was easy to handle. Moreover, when the cross section of the sample after heating and pressurizing was observed, a part of the fluorine-based fiber B:PFA fiber was fused.

The obtained paper had a basis weight of 40 g/m ² and a thickness of 21.0 μm. It also had excellent air permeability and functioned as paper making.

[Example 5]
Paper was produced in the same manner as in Example 4, except that the fiber diameters of fluorine fiber A and fluorine fiber B were changed to 3 μm and 19 μm. Moreover, when the cross section of the sample after heating and pressurizing was observed, a part of the fluorine-based fiber B:PFA fiber was fused.

The obtained paper had a basis weight of 41 g/m ² and a thickness of 11.4 μm. It also had excellent air permeability and functioned as paper making.

[Comparative example 1]
Paper was produced in the same manner as in Example 1, except that the proportion of PTFE fibers was changed to 100 and the surface temperature of the iron roll was changed to 300°C. Moreover, when the cross section of the sample after heating and pressurizing was observed, the PTFE fibers were formed into a film and fused together.

The obtained paper had a basis weight of 45 g/m ² and a thickness of 14.1 μm. However, it was difficult to measure the air permeability, and it did not have a paper-making function.

[Comparative example 2]
Paper was produced in the same manner as in Example 1, except that the fiber diameter of the PTFE fibers was changed to 20 μm. Moreover, when the cross section of the sample after heating and pressurizing was observed, the PTFE fibers were formed into a film and fused together.

The obtained paper had a basis weight of 41 g/m ² and a thickness of 58.2 μm. However, it was difficult to measure the air permeability, and it did not have a paper-making function.

[Comparative example 3]
In Example 3, paper was made in the same manner as in Example 3, except that the proportion of PFA fibers was changed to 100 and the iron roll surface temperature was changed to 270°C. Furthermore, when the cross section of the sample after heating and pressurization was observed, the PFA fibers were formed into a film and fused together.

The obtained paper had a basis weight of 41 g/m ² and a thickness of 18.9 μm. However, it was difficult to measure the air permeability, and it did not have a paper-making function.

Regarding the paper made of fluorine-based fibers produced in Examples 1 to 5 and Comparative Examples 1 to 3, the above-mentioned (3) basis weight, (4) thickness, (5) tear strength, and (6) air permeability were determined. An evaluation was conducted and the results are shown in Table 1. As a result, the paper made from fluorine-based fibers in the present invention maintains the properties of fluorine-based fibers as a material, such as excellent heat resistance, chemical resistance, electrical insulation, friction properties, and weather resistance, while being thinner. It was clear that the paper was made from fluorine-based fibers and was suitable for insulating materials for electronic devices.

Claims (2)

A paper machine characterized in that the fibers constituting the paper machine are composed only of two or more types of fluorine-based fibers having different melting points, and at least a portion of the fibers are fused together. The papermaking according to claim 1, comprising fluorine-based fibers containing a fibrillated matrix component.