JP2009133033A - Synthetic fiber paper, electrical insulating paper and method for producing synthetic fiber paper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a synthetic fiber paper and an electrical insulating paper, having a strong adhesive strength and a strong dielectric breakdown strength. <P>SOLUTION: The synthetic fiber paper comprising a polyphenylene sulfide fiber contains the polyphenylene sulfide fiber which has a shape of a single fiber cross section regulated so that the ratio (major axis/minor axis) of the major axis to the minor axis of the single fiber cross section is ≥1.5, and at least a part of which is thermally fused. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to synthetic fiber paper and electrical insulating paper.

  Electrical insulation paper used for motors, capacitors, transformers, cables, etc. is required to have heat resistance, chemical resistance, hydrolysis resistance, etc. in order to withstand the harsh usage conditions of motors, etc. It is required to be high. In addition, when performing a bending process or the like, a strong in-layer adhesive strength is required so as not to peel in the layer.

  As a means of obtaining a dense wet nonwoven fabric using polyphenylene sulfide fibers (hereinafter referred to as PPS fibers) excellent in heat resistance, chemical resistance, and hydrolysis resistance, ultra-fine PPS fibers are proposed (patent) Reference 1).

  However, it has been difficult to uniformly disperse very fine fibers such as nanofibers in water, and it has been very difficult to obtain a wet nonwoven fabric that is dense and has no pinholes.

In addition, although the example of the wet nonwoven fabric using a flat fiber exists in patent document 2, 3, it did not contribute to the improvement of the in-layer adhesive strength of a wet nonwoven fabric.
JP 2006-257618 A JP 2003-49388 A JP 2006-200066 A

  An object of the present invention is to provide a synthetic fiber paper and an electrical insulating paper having a high in-layer adhesive strength and a high dielectric breakdown strength.

  That is, the present invention includes a synthetic fiber paper made of polyphenylene sulfide fiber, wherein the polyphenylene sulfide fiber has a ratio of a major axis to a minor axis of a single fiber cross section (major axis / minor axis) of 1.5 or more, The synthetic fiber paper is characterized in that at least a part thereof is heat-sealed.

  The present invention is also an electrically insulating paper comprising the synthetic fiber paper of the present invention.

  Moreover, this invention includes the process of heat-sealing the wet nonwoven fabric containing the polyphenylene sulfide fiber whose ratio (major axis / minor axis) of the major axis and the minor axis of the single fiber section is 1.5 or more by heat and pressure treatment. Is a method for producing synthetic fiber paper.

  According to the present invention, it is possible to provide a synthetic fiber paper and an electrical insulating paper having a high in-layer adhesive strength and a high dielectric breakdown strength.

  The synthetic fiber paper of the present invention consists of PPS fibers. PPS is a polymer containing phenylene sulfide units such as p-phenylene sulfide units and m-phenylene sulfide units as repeating units. PPS may be a homopolymer of any of these units, or a copolymer having both units. Moreover, the copolymer with another aromatic sulfide may be sufficient.

  Moreover, as a weight average molecular weight of PPS, 40000-60000 are preferable. By setting it to 40,000 or more, good mechanical properties as PPS fibers can be obtained. Further, by setting the viscosity to 60000 or less, the viscosity of the melt spinning solution is suppressed, and a special high pressure resistant spinning equipment is not required.

  It is important that the PPS fibers include those whose ratio of the major axis to the minor axis (major axis / minor axis) of the single fiber cross section is 1.5 or more (hereinafter referred to as “flat PPS fiber”). By including the flat PPS fiber, the void portion becomes smaller than when only a perfect circular fiber is used, a dense synthetic fiber paper can be obtained, and a high dielectric breakdown strength can be expressed. . If the ratio of the major axis to the minor axis (major axis / minor axis) is less than 1.5, the gap cannot be reduced and a dense synthetic fiber paper cannot be obtained. The ratio of the major axis to the minor axis (major axis / minor axis) of the flat PPS fiber is preferably 2.0 or more. On the other hand, the upper limit is preferably 25.0 or less. When it becomes larger than 25.0, the fiber is easily twisted, and the twisted portion becomes a fist and a void is formed, which easily causes a defect.

  The single fiber fineness of the flat PPS fiber is preferably 0.1 to 7.0 dtex. If it is thinner than 0.1 dtex, the fiber strength becomes weak and the paper strength becomes weak. Moreover, when it becomes thicker than 7.0 dtex, the space | gap size of the node part when a fiber twists in a papermaking process will become large, and it will become difficult to crush a space | gap by a subsequent process.

  The cut length of the flat PPS fiber is preferably 0.1 to 10 mm, more preferably 0.4 to 6 mm. When it is shorter than 0.1 mm, it becomes like a powder, and it becomes difficult to form a wet nonwoven fabric without falling off. Moreover, when it becomes longer than 10 mm, a fiber will become easy to twist. When twisted, the twisted portion becomes a node, and a gap is easily formed in the portion.

  As for the presence or absence of crimp in the flat PPS fiber, there are advantages to those having and not having crimps. A flat PPS fiber having crimps is suitable for obtaining a wet nonwoven fabric having excellent strength by making the flat fiber difficult to twist, suppressing the generation of void defects, and improving the entanglement of the fibers. ing. On the other hand, flat PPS fibers that do not have crimps are suitable for obtaining a uniform wet nonwoven fabric with little unevenness.

  Flat PPS fiber may be either drawn fiber or undrawn fiber, but when wet non-woven fabric is heat-pressed to densify, adjacent single fibers are deformed and heat-sealed. And it is preferable that it is an unstretched fiber at the point which becomes easy to crush a space | gap.

  As a method for obtaining flat PPS fibers, for example, it can be obtained by using a known method using a flat or rectangular base.

    For example, after PPS polymer pellets are dried at 140 to 180 ° C. for about 3 to 24 hours, melted with an extruder type spinning machine, the polymer temperature (spinning temperature) is 295 to 320 ° C., and the pore size is 0.1 to It can be obtained by spinning from a rectangular or elliptical base such as a slit outlet having a major axis / minor axis ratio (major axis / minor axis) of 1.5 mm or more at 1.0 mm.

  The flat fiber obtained by the above means may be stretched by about 2.0 to 5.0 times as necessary, or may be used in an unstretched state.

  Moreover, a flat PPS fiber can also be obtained by slitting a PPS film.

  The mixing ratio of flat PPS fibers in the synthetic fiber paper of the present invention is preferably 10% or more, and more preferably 50% or more. When the mixing ratio is less than 10%, a sufficient densification effect cannot be obtained.

As basic weight of the synthetic fiber paper of this invention, 30-300 g / m < ² > is preferable. By setting it to 300 g / m ² or less, the wet non-woven fabric can be thinned, space saving can be achieved, and a flexible synthetic fiber paper that does not generate cracks during bending can be obtained. On the other hand, if it is thinner than 30 g / m ² , sufficient dielectric breakdown strength cannot be obtained.

  An example of the method for producing the synthetic fiber paper of the present invention is shown.

  First, PPS fibers including flat PPS fibers are dispersed in water to form a papermaking dispersion.

The total amount of fibers with respect to the papermaking dispersion is preferably 0.005 to 5% by mass. By setting it as 0.005 mass% or more, a wet nonwoven fabric with a large basis weight of 30 g / m ² or more can be efficiently obtained. Moreover, by making it 5 mass% or less, the dispersion state of a fiber becomes good and a uniform wet nonwoven fabric can be obtained.

  In order to improve water dispersibility, dispersants for papermaking, such as dispersants and oils composed of cationic, anionic, and nonionic surfactants, and antifoaming agents that suppress foaming are added. May be.

  The papermaking dispersion can be made into paper by using a round net type, long net type, slanted net type paper machine or hand-made paper machine, and dried with a Yankee dryer or rotary dryer to make a wet nonwoven fabric. .

  It is important that the method for producing a synthetic fiber paper of the present invention includes a step of heat-pressing a wet nonwoven fabric containing flat fibers. In the heat and pressure treatment, the inclusion of flat PPS fibers is very beneficial for obtaining a dense synthetic fiber paper. The flat fibers have contact between adjacent fibers, and there are already few gaps before the heat and pressure treatment, and the gaps can be easily crushed to obtain a dense synthetic fiber paper. Further, when the heat and pressure treatment is performed and the heat bonding is performed, the bonding area is increased, so that the adhesive strength is increased and the adhesive strength within the paper layer can be improved. At this time, the flat fiber is preferably an undrawn yarn in which the fiber is easily deformed by heat in order to crush the gap.

  As a means for heat and pressure treatment, a hot press using a flat plate, a calendar, or the like can be employed. Among these, a calendar that can be processed continuously is preferable. As the calendar roll, a metal-metal roll, a metal-paper roll, a metal-rubber roll, or the like can be used.

  The pressure for the heat and pressure treatment is preferably 98 to 7000 N / cm. The space | interval between fibers can be crushed by setting it as 98 N / cm or more. On the other hand, by setting it to 7000 N / cm or less, it is possible to prevent the synthetic fiber paper from being torn in the heating and pressurizing treatment step and stably perform the treatment.

  As temperature of a heat press treatment, 150-250 degreeC is preferable, More preferably, it is 170-230 degreeC. When the temperature is lower than 150 ° C., the fibers are not heat-sealed and a dense synthetic fiber paper cannot be obtained. On the other hand, when the temperature exceeds 250 ° C., the PPS fiber becomes too soft and sticks to a heating / pressurizing device such as a calendar roll or a hot press plate, resulting in a rough or stuck surface. The synthetic fiber paper cannot be obtained without peeling.

  The process passing speed when calendering is employed as the heat and pressure treatment is preferably 2 to 30 m / min, more preferably 3 to 20 m / min. Good working efficiency can be obtained by setting it as 2 m / min or more. On the other hand, by setting it to 30 m / min or less, heat can be conducted also to the fiber inside the synthetic fiber paper, and the effect of heat fusion of the fiber can be obtained.

  The synthetic fiber paper obtained as described above is dense and has high dielectric breakdown strength, and can be suitably used for electrical insulating paper.

[Measurement and evaluation method]
(1) Ratio of major axis to minor axis of single yarn cross section (major axis / minor axis)
Using an optical electron microscope, the longest diameter and the shortest diameter were measured at the single yarn cross section, and the long diameter was divided by the short diameter.

(2) Basis weight According to JIS L 1906: 2000, three 10 cm × 10 cm test pieces were sampled, each mass (g) in a standard state was measured, and the average value was calculated as the mass per 1 m ² (g / g m ² ).

(3) Electrical breakdown strength Measured according to JIS K 6911: 1995. Test specimens of about 10 cm × 10 cm are collected from five different specimens, and the specimens are sandwiched between disc-shaped electrodes with a diameter of 25 mm and a mass of 250 g, air is used as the test medium, and a voltage is applied at 0.25 kV / second. While increasing, an AC voltage having a frequency of 60 Hz was applied, and the voltage when dielectric breakdown was measured. The obtained dielectric breakdown voltage was divided by the thickness of the central portion measured in advance, and the dielectric breakdown strength was calculated.

(4) In-layer adhesive strength Measured according to JIS K 2111: 2002 (12.2: measurement of adhesive strength). Five test pieces of 50 mm × 200 mm were taken, and the center of the layer was torn 20 mm in the length direction as much as possible over the entire width of the test piece, and the unstripped part was held by hand so that the tearing point was at a right angle, 300 m The average value of 5 test pieces of adhesive strength was calculated and converted to a width of 10 mm.

(5) Presence / absence of thermal fusion The surface of the test piece was observed with an electron microscope at a magnification of 300 times to confirm the presence / absence of thermal fusion.

[Example 1]
(Round cross section PPS fiber)
As PPS fibers having a round single fiber cross section, stretched PPS fibers having a single fiber fineness of 1.0 dtex and a cut length of 6 mm (Torcon, manufactured by Toray Industries, Inc., product number S101) were used.

(Flat PPS fiber)
PPS polymer pellets are dried at 160 ° C. for 10 hours and then melted with an extruder-type spinning machine. The polymer temperature (spinning temperature) is 315 ° C., and the slit type discharge has a long side of 0.7 mm and a short side of 0.3 mm. It was extruded from the hole and wound at a speed of 600 m / min to obtain a 3.1 dtex flat fiber. This was cut to 6 mm with a guillotine type cutter to obtain cut fibers of flat PPS fibers. The ratio of major axis / minor axis of the obtained flat fiber was 2.3.

(Dispersion)
The blending amount of the round cross-section PPS fiber was 8.0 g / L, and the mixture was stirred together with 1 L of water into a household juicer mixer to obtain a dispersion of the round cross-section PPS fiber. The stirring time was 10 seconds in order to prevent the fibers from getting tangled.
Further, a flat PPS fiber dispersion was prepared in the same manner with the amount of the flat PPS fiber being 8.0 g / L.

(Paper)
A handmade paper machine of size 25 cm × 25 cm and height 40 cm with a 140-mesh handmade paper net installed on the bottom of each of the round cross-section PPS fiber dispersion and the flat PPS fiber dispersion 1 L (Kumaya Riki Kogyo Co., Ltd.) The water was added to make the total amount of the papermaking dispersion 20 L, and the mixture was sufficiently stirred with a stir bar.
Then, the water from the handsheet machine was drained, and the wet paper remaining on the papermaking net was transferred to the filter paper.

(Dry)
The wet paper was put together with the filter paper into a rotary dryer, and the process of drying at a temperature of 125 ° C., a process passing speed of 0.5 m / min, and a process length of 1.25 m (processing time of 2.5 min) was repeated 5 times. .

(Heat and pressure treatment)
The wet-processed non-woven fabric was peeled from the filter paper and passed through a calendering machine composed of an iron roll and a paper roll to obtain a synthetic fiber paper. The calendar conditions were a temperature of 230 ° C., a pressure of 100 kN / 25 cm (4 kN / cm), and a roll rotation speed of 3 m / min.

[Example 2]
(Round cross section PPS fiber)
The same one as used in Example 1 was used.

(Flat PPS fiber)
The same one as used in Example 1 was used.

(Dispersion)
A dispersion of a round cross-section PPS fiber was prepared in the same manner as in Example 1 except that the blending amount of the round cross-section PPS fiber was 2.4 g / L.
Further, a flat PPS fiber dispersion was prepared in the same manner as in Example 1 except that the amount of the flat PPS fiber was 2.4 g / L.

(Paper)
A wet paper was obtained in the same manner as in Example 1 except that the dispersion liquid of the round cross-sectional PPS fiber and the dispersion liquid of the flat PPS fiber were used.

(Dry)
A wet nonwoven fabric subjected to a drying process was obtained in the same manner as in Example 1 except that the above wet paper was used and the number of repetitions of the drying process was two.

(Heat and pressure treatment)
A synthetic fiber paper was obtained in the same manner as in Example 1 except that the wet-processed non-woven fabric was used.

[Example 3]
(Round cross section PPS fiber)
The same one as used in Example 1 was used.

(Flat PPS fiber)
A PPS film having a thickness of 4.6 μm (“Torelina” manufactured by Toray Industries Inc., type 1 × 00) was slit to a width of 0.1 mm to obtain a slit yarn. This was cut into a cut length of 6 mm with a guillotine type cutter to obtain a cut fiber of flat PPS fiber. The obtained flat PPS fiber had a major axis / minor axis ratio of 21.7 and a fineness of 6.0 dtex.

(Dispersion)
Using the round cross-section PPS fiber, a dispersion of a round cross-section PPS fiber having a blending amount of 8.0 g / L was prepared in the same manner as in Example 1.
Moreover, the dispersion liquid of the flat PPS fiber of the compounding quantity 8.0g / L was prepared like Example 1 except having used the said flat PPS fiber.

(Paper)
A wet paper was obtained in the same manner as in Example 1 except that the dispersion liquid of the round cross-sectional PPS fiber and the dispersion liquid of the flat PPS fiber were used.

(Dry)
A wet nonwoven fabric subjected to a drying treatment was obtained in the same manner as in Example 1 except that the wet paper was used.

(Heat and pressure treatment)
A synthetic fiber paper was obtained in the same manner as in Example 1 except that the wet-processed non-woven fabric was used.

[Comparative Example 1]
(Round cross-section PPS fiber (1.0 dtex))
The same round cross-section PPS fiber as used in Example 1 was used as the round cross-section PPS fiber (1.0 dtex).

(Round cross section PPS fiber (3.0 dtex))
An unstretched PPS fiber having a single fiber fineness of 3.0 dtex and a cut length of 6 mm (“Torcon” manufactured by Toray Industries, Inc., product number S111) was used as a round cross-section PPS fiber (3.0 dtex).

(Dispersion)
Using the round cross-section PPS fiber (1.0 dtex), a dispersion of a round cross-section PPS fiber (1.0 dtex) having a blending amount of 8.0 g / L was prepared in the same manner as in Example 1.
Moreover, the dispersion liquid of the round cross-section PPS fiber (3.0 dtex) of compounding quantity 8.0g / L was prepared like Example 1 except having used the said round cross-section PPS fiber (3.0 dtex).

(Paper)
A wet paper was obtained in the same manner as in Example 1 except that the dispersion liquid of the round cross-section PPS fiber (1.0 dtex) and the dispersion liquid of the round cross-section PPS fiber (3.0 dtex) were used.

(Dry)
A wet nonwoven fabric subjected to a drying treatment was obtained in the same manner as in Example 1 except that the wet paper was used.

(Heat and pressure treatment)
A synthetic fiber paper was obtained in the same manner as in Example 1 except that the wet nonwoven fabric was used and the temperature under the calendar conditions was 80 ° C.

[Comparative Example 2]
(Round cross section PPS fiber)
The same one as used in Example 1 was used.

(Flat PPS fiber)
The same one as used in Example 1 was used.

(Dispersion)
A dispersion of a round cross-section PPS fiber was prepared in the same manner as in Example 1 except that the blending amount of the round cross-section PPS fiber was 0.3 g / L.
Also, a flat PPS fiber dispersion was prepared in the same manner as in Example 1 except that the amount of the flat PPS fiber was 0.3 g / L.

(Paper)
An attempt was made to obtain a wet paper in the same manner as in Example 1 except that the round cross-section PPS fiber dispersion and the flat PPS fiber dispersion were used.
However, the wet paper was thin and could not be peeled off while maintaining its shape from the papermaking net, and a sample could not be obtained.

[Comparative Example 3]
(Round cross section PPS fiber)
The same one as used in Example 1 was used.

(Flat PPS fiber)
The same one as used in Example 1 was used.

(Dispersion)
A dispersion of a round cross-section PPS fiber was prepared in the same manner as in Example 1 except that the blending amount of the round cross-section PPS fiber was 13.0 g / L.
Also, a flat PPS fiber dispersion was prepared in the same manner as in Example 1 except that the amount of the flat PPS fiber was 13.0 g / L.

(Paper)
A wet paper was obtained in the same manner as in Example 1 except that the dispersion liquid of the round cross-sectional PPS fiber and the dispersion liquid of the flat PPS fiber were used.

(Dry)
A wet nonwoven fabric subjected to a drying treatment was obtained in the same manner as in Example 1 except that the wet paper was used.

(Heat and pressure treatment)
A synthetic fiber paper was obtained in the same manner as in Example 1 except that the wet nonwoven fabric was used and the temperature under the calendar conditions was 80 ° C.

  Synthetic fiber paper obtained by mixing flat fibers and heat-pressurizing was able to obtain a wet nonwoven fabric having high dielectric breakdown strength and strong inter-layer adhesive strength.

  The synthetic fiber paper of the present invention can be used as an insulating paper used for motors, capacitors, transformers, cables and the like.

Claims (6)

Synthetic fiber paper comprising polyphenylene sulfide fiber, wherein the polyphenylene sulfide fiber has a ratio of major axis to minor axis (major axis / minor axis) of a single fiber cross section of 1.5 or more, and at least a part Synthetic fiber paper characterized in that is heat-sealed. The synthetic fiber paper according to claim 1, wherein at least a part of the polyphenylene sulfide fiber is an undrawn yarn. The synthetic fiber paper of Claim 1 or 2 whose single fiber fineness of the said polyphenylene sulfide fiber is 0.1-7.0 dtex. The synthetic fiber paper in any one of Claims 1-3 whose basic weight is 30-300 g / cm < ² >. An electrically insulating paper comprising the synthetic fiber paper according to any one of claims 1 to 4. A synthesis characterized by including a step of heat-sealing a wet nonwoven fabric containing polyphenylene sulfide fibers having a major axis / minor axis ratio (major axis / minor axis) of 1.5 or more in a single fiber section by heat-pressing treatment. Manufacturing method of fiber paper.