KR102110215B1 - Process for producing raw material for papermaking, obtained raw material for papermaking, and heat-resistant electrical insulating sheet material obtained using said raw material - Google Patents

Abstract

The present invention is formed of a fibrid formed of aromatic polyamide, short fibers, or a mixture thereof, and aramid paper produced through calendering, high pressure spraying, and crushing the aramid paper as a constituent material of papermaking. It's about how. According to this manufacturing method, the raw material for papermaking which can be reused as a raw material for papermaking can be produced without using a calendered aramid paper, a chemical liquid, or the like.

Description

Manufacturing method of raw material for papermaking, obtained raw material for papermaking, and heat-resistant electric insulating sheet material using the raw material TECHNICAL }

The present invention relates to a method for recycling calendered aramid paper, and a heat-resistant electrically insulating sheet material. More specifically, the present invention relates to a method for recycling calendered aramid paper that enables reuse of calendered aramid paper that is incinerated or disposed of without using chemicals and the like, and a heat-resistant electrically insulating sheet material.

Papers made from high performance materials capable of imparting improved strength and / or thermal stability to papers have been developed. For example, aramid paper is a synthetic paper containing an aromatic polyamide, and has been used as a base for electrically insulating materials and aircraft honeycombs due to its excellent heat resistance, flame resistance, electrical insulation, toughness and flexibility. Of these materials, a paper comprising DuPont (USA) Nomex (registered trademark) fibers was mixed with poly (methphenyleneisophthalamide) floc and fibrid in water, and then It is manufactured by papermaking and then calendering the slurry. It is known that this paper has excellent electrical insulating properties while still having high strength and toughness at high temperatures.

Since the high-temperature and high-pressure treatment of aramid paper, such as a single material or a damaged material, is performed by calendering, it is not decomposed at all by water alone, so incineration or disposal is performed. In addition, after dissolving in an organic solvent, chemical recycling is also carried out to form flocs, fibrids, pulp, etc., which are papermaking raw materials, like virgin raw materials, and this method requires environmental considerations, and also costs Tends to increase

Further, regarding recycling of the dried aramid paper or aramid board, which has not been subjected to a high-temperature and high-pressure treatment by calendering, the processing method is described in Patent Documents 1 and 2. However, since the actual aramid paper is mostly calendered and used, it is difficult to say that these methods are practical.

In addition, Patent Document 3 discloses that a porous aramid molded article is prepared by using aramid paper pulverized aramid paper pulp and mixing paper with non-aramid fiber at a ratio of 90/10 to 10/90 to form a sheet. Since this molded product is porous, it is considered that electrical insulating properties are insufficient.

Japanese Patent Publication No. Hei 4-228696 Japanese Patent Publication No. 2003-290676 Japanese Patent Publication No. Hei 7-243189

An object of the present invention is to provide a method for producing a raw material for papermaking that disintegrates a calendered aramid paper into a raw material for papermaking that can be reused as a raw material for papermaking without using chemicals or the like.

Another object of the present invention is to provide a raw material for papermaking produced from calendered aramid paper.

Another object of the present invention is to provide a heat-resistant electrically insulating sheet material using the raw material for papermaking.

The present invention was made by the knowledge that when a specific aramid paper produced through calendering is subjected to high-pressure injection treatment and disintegration, a raw material for papermaking that can be recycled with excellent properties is obtained.

That is, the present invention is a method for producing a raw material for papermaking, characterized in that the aramid paper formed of a fibrid, a short fiber, or a mixture formed of an aromatic polyamide and manufactured through calendering is subjected to high pressure spray treatment and crushed. to provide.

The present invention also provides a raw material for papermaking produced by the above manufacturing method.

The present invention also provides a heat-resistant electrically insulating sheet material comprising the raw material for papermaking.

(Aramid)

In the present invention, aramid means a linear polymer compound (aromatic polyamide) in which 60% or more of the amide bond is directly bonded to the aromatic ring. Examples of such aramids include, for example, polymethphenylene isophthalamide and copolymers thereof, polyparaphenylene terephthalamide and copolymers thereof, poly (paraphenylene) -copoly (3,4 diphenyl ether) terephthalamide And the like. This aramid is industrially produced by, for example, a conventionally known interfacial polymerization method using isophthalate and metaphenylenediamine, a solution polymerization method, etc., and can be obtained as a commercial product, but is not limited to this. Among these aramids, polymethphenylene isophthalamide is preferably used because it has properties such as good moldability, heat adhesion, flame retardancy, and heat resistance.

(Aramid fibrid)

In the present invention, the aramid fibrid is a film-like aramid particle having super-lipidity and is also referred to as aramid pulp (see Japanese Patent Publication No. 35-11851, Japanese Patent Publication No. 37-5732, etc.).

The aramid fibrid is widely known to be used as a raw material for papermaking by performing an understanding and refining treatment similar to ordinary wood pulp, so-called refining treatment is performed for the purpose of maintaining quality suitable for the papermaking. Can be. This refining treatment can be performed by a disk refiner, beater, or other papermaking raw material processing equipment that has a mechanical cutting action. In this operation, the change in the shape of the fibrid can be monitored by the method of testing the freeness specified in Japanese Industrial Standard P8121 (Prinness). In the present invention, it is preferable that the degree of the aramid fibrid after the refining treatment is performed is within a range of 10 cm ³ to 300 cm ³ (Canadian Priness). In fibrids with a degree of freeness greater than this range, there is a possibility that the strength of the multi-thermal electrically insulating sheet material formed therefrom is lowered. On the other hand, when obtaining a degree of freeness smaller than 10 cm ³ , the utilization efficiency of the machine power to be input is reduced, and the throughput per unit time is often reduced, and the refinement of the fibrid is too advanced, so-called binder. It is easy to cause deterioration of function. Therefore, even if it is desired to obtain a degree of freeness smaller than 10 cm ³ , no significant advantage is seen.

(Short aramid fiber)

Short aramid fibers are cut fibers made of aramid, and such fibers include, for example, "Daijin Connect (registered trademark)" from Teijin, and "Nomex (registered trademark)" from DuPont. Although what can be obtained by a brand name, such as, is not limited to these.

The length of the aramid short fibers is generally 1 mm or more and less than 50 mm, preferably 2 to 10 mm. When the length of the short fibers is smaller than 1 mm, the mechanical properties of the sheet material are deteriorated, while those of 50 mm or more tend to cause entanglement, binding, and the like during the production of aramid paper by the wet method, causing defects. easy.

(Aramid paper)

In the present invention, aramid paper is a sheet-like article mainly composed of the above-mentioned aramid fibrid, aramid short fiber, or a mixture thereof, and generally has a thickness in the range of 20 μm to 1000 μm. In addition, the aramid paper generally has a basis weight in the range of 10 g / m ² to 1000 g / m ² .

Aramid paper is generally produced by a method of sheeting after mixing the aramid fibrid and aramid short fibers described above. Specifically, for example, after dry blending the aramid fibrids and aramid short fibers, a method of forming a sheet using an air flow, the aramid fibrids and aramid short fibers are dispersed and mixed in a liquid medium, and then liquid permeable A method of discharging and sheeting by discharging on a support, for example, a mesh or a belt, can be applied, and among them, a so-called wet brewing method using water as a medium is preferably selected. Here, the mixing ratio of the aramid fibrid and the aramid short fiber can be arbitrarily, but the ratio (mass ratio) of the aramid fibrid / aramid short fiber is preferably 1/9 to 9/1, more preferably 2 / 8 to 8/2 is preferred.

In the wet papermaking method, a method of winding a sheet into a sheet by dehydrating, watering and drying after dispersing an aqueous slurry of a single or a mixture containing at least aramid fibrid or short aramid fibers in a paper machine is dispersed. It is common. As a paper machine, a long paper machine, a net paper machine, an inclined paper machine, a combination paper machine, and the like are used. In the case of production in a combination paper machine, a composite sheet including a plurality of layers can be obtained by sheet forming and combining slurries having different mixing ratios. Additives such as dispersibility improvers, anti-foaming agents, and strength enhancers are used as needed at the time of annealing.

(Calendar processing)

It is known that the aramid paper obtained as described above improves mechanical strength in addition to density, crystallinity, heat resistance, and dimensional stability by thermal pressure between a pair of rolls at high temperature and high pressure. The conditions of the thermal pressure, for example, in the case of using a metal roll, the temperature of 100 to 350 ℃, linear pressure can be exemplified in the range of 50 to 400kg / cm, but is not limited to these. A plurality of aramid papers may be laminated at the time of thermal pressure. The above-described hot-pressing may be performed multiple times in any order.

(High pressure spray treatment)

In the present invention, the high-pressure injection treatment means that the calendered aramid paper is immersed in water, and is sprayed with water at a high pressure from a nozzle to collide with a hard body for collision or collide the calendered aramid paper with high pressure injection. By this, it refers to a process of crushing the calendered aramid paper to approach the shape of aramid fibrid and aramid short fibers.

A high-pressure homogenizer is preferably used as a device capable of such treatment, but is not limited to this.

Here, as a shape of the hard body for collision, a ball shape, a plate shape, etc. are mentioned, but it is not limited to these. Further, the diameter of the nozzle to be injected at high pressure is preferably 0.1 to 0.9 mm, but is not limited thereto.

In addition, the calendered aramid paper at the time of high pressure injection is preferably length-weighted average fiber length of 3 times or less of the nozzle diameter, more preferably 2 times or less, most preferably 1.5 times or less by a grinder or the like. It is good to crush up to the size of. If it is 1.5 times or less, clogging of the nozzle of the calendered aramid paper can be effectively suppressed.

As a method of pulverizing the calendered aramid paper, a method of pulverizing and pulverizing by a dry method, a wet method, or both means is preferable. The dry method is a method of using a shredder, a crusher, a kneader, or the like to decompose into fine particles by imparting an impact to aramid paper without substantially interposing moisture. In addition, the wet method is a method of imparting an impact to aramid paper in a water medium to reduce the particle size. A high-speed understanding machine, a refiner, a beater, etc. can be illustrated as a facility which performs such wet grinding efficiently, but is not limited to these.

As a condition of the high pressure injection treatment, the injection pressure is preferably in the range of 70 to 300 MPa. The injection speed is preferably in the range of 300 to 900 m / s.

Further, the concentration of the calendered aramid paper when immersed in water is preferably 0.1 to 10 wt%. When immersed in water, additives such as a dispersibility improving agent and an antifoaming agent can be used as necessary.

The high-pressure jetting treatment can be repeated as many times as necessary, but if the number of times is excessively high, it becomes expensive, and furthermore, cutting of a portion of the aramid short fibers proceeds, so that the shape of the short fibers as a papermaking raw material cannot be maintained. It is not desirable. In that sense, the retention ratio of the length-weighted average fiber length of the calendered aramid paper before and after the high-pressure jetting treatment is preferably 80% or more.

(Volume average particle size distribution, particle size peak)

In the present invention, the volume average particle size distribution is a distribution obtained by measuring the distribution of particles on a volume basis. In addition, a volume average particle diameter is a particle diameter which measured the particle diameter on a volume basis. In addition, a particle size peak is a peak of a volume average particle size distribution. In addition, since the raw material for papermaking of the present invention has a three-dimensional shape such as a fiber shape, a particle shape, or an irregular shape, the size and shape of the raw material for papermaking were specified using a particle size peak.

In addition, in the volume average particle size distribution, the particle size peaks in the range of 10 µm or more and less than 100 µm are considered to mainly represent the relative amount of the separated aramid short fibers, and it is believed that the aramid short fibers are generated after the high pressure spray treatment. I think it is happening.

Therefore, in the present invention, it is preferable to perform a high pressure jet treatment to generate a particle size peak in a range of 10 μm or more and less than 100 μm in the volume average particle size distribution of the aramid paper after the high pressure jet treatment, and entanglement as short fibers is likely to occur. , The strength of the heat-resistant electrical insulation sheet material is improved.

More preferably, the aramid paper is pulverized before the high pressure injection treatment, and in the volume average particle size distribution of the aramid paper before the high pressure injection treatment, there is a particle size peak in the range of 10 µm or more and less than 100 µm and the range of 100 µm or more and less than 1000 µm, respectively. It is preferable to perform a high-pressure injection treatment so that the frequency at each particle diameter peak after the injection treatment increases in the range of 10 µm or more and less than 100 µm, and decreases in the range of 100 µm or more and less than 1000 µm.

In the volume average particle size distribution of the calendered aramid paper, the particle size peak in the range of 10 µm or more and less than 100 µm mainly represents the relative amount of the separated aramid short fibers, and the particle size peak in the range of 100 µm or more and less than 1000 µm is mainly It is believed that the relative amount of the mixture of aramid short fibers and aramid fibrids that are not separated is thought to increase, and the frequency of the former particle size peak increases after the high-pressure injection treatment, and the frequency of the latter particle size peak decreases. It is believed that the amount is relatively increased, and the amount of the mixture of undivided aramid short fibers and aramid fibrids is relatively decreased.

Thereby, entanglement as a short fiber is liable to occur, and not only the strength of the heat-resistant electrically insulating sheet material is improved, but also the thickness unevenness of the heat-resistant electrically insulating sheet material is reduced.

(Heat-resistant electrical insulation sheet material)

The heat-resistant electrically insulating sheet material of the present invention is a sheet-like article containing the raw material for papermaking, and generally has a thickness in the range of 20 µm to 5 mm. Further, the heat-resistant electrically insulating sheet material generally has a basis weight in the range of 10 g / m ² to 5000 g / m ² , preferably 10 g / m ² to 200 g / m ² .

The content of the above-mentioned papermaking raw material in the heat-resistant electrically insulating sheet material is not particularly limited as long as it achieves the desired electrical insulation, but 5 to 80 mass% is maintained to maintain the process strength during the production of the heat-resistant electrically insulating sheet material. It is preferable, and 15 to 80 mass% is preferable to obtain sufficient electrical insulation, and 30 to 80 mass% is particularly preferable to express sufficient strength. The remaining amount is preferably a new aramid fibrid or a short aramid fiber in combination with this, but is not limited to these.

The heat-resistant electrically insulating sheet material is generally produced by a method of sheeting after mixing the above-mentioned raw material for papermaking with aramid fibrid or the like.

In sheet production, for example, after dry blending the aforementioned raw material for papermaking with aramid fibrid, a method of forming a sheet using an air flow, after dispersing and mixing the raw material for papermaking and aramid fibrid in a liquid medium, A liquid permeable support, for example, a method of sheeting by discharging on a net or a belt, drying by removing the liquid, etc. can be applied. Among these, a so-called wet irrigation method using water as a medium is preferably selected. do.

In the wet papermaking method, a method in which a single or a mixture of aqueous slurries containing at least the above-mentioned raw material for papermaking and aramid fibrid is fed to a paper machine for dispersion, followed by dewatering, watering and drying, and then wound up as a sheet. . As a paper machine, a long paper machine, a net paper machine, an inclined paper machine, a combination paper machine, and the like are used. In the case of production in a combination paper machine, a composite sheet including a plurality of layers can be obtained by sheet forming and combining slurries having different mixing ratios. Additives such as dispersibility improvers, anti-foaming agents, and strength enhancers are used as needed at the time of annealing.

In addition, other fibrous components (for example, aramid fiber, polyphenylene sulfide fiber, polyether ether ketone fiber, cellulose fiber, PVA fiber, polyester fiber, arylate fiber, liquid crystal polyester fiber, polyethylene naphthalate) Organic fibers such as fibers, glass fibers, rock wool, inorganic fibers such as asbestos and boron fibers) can be added.

In the heat-resistant electrically insulating sheet material of the present invention, since aramid fibrid has excellent properties as a binder, it can efficiently supplement fine particles and other additive components, and is a raw material in the production of the heat-resistant electrical insulating sheet material of the present invention. At the same time as the yield is good, it is possible to overlap the layers in a layer in the sheet, thereby reducing the through hole, thereby improving the electrical insulation properties.

The heat-resistant electrically insulating sheet material thus obtained can be improved in density and mechanical strength by heat-pressing at a high temperature and high pressure between a pair of flat plates or between metal rolls. The conditions of the thermal pressure, for example, in the case of using a metal roll, the temperature of 100 to 350 ℃, linear pressure can be exemplified 50 to 400kg / cm, but is not limited to these. It is also possible to simply press at room temperature without applying a heating operation. A plurality of heat-resistant electrically insulating sheet materials can also be laminated at the time of thermal pressure. The above-mentioned hot-pressing processing may be performed multiple times in any order.

Hereinafter, the present invention will be described with reference to examples. In addition, these Examples are provided to illustrate the content of the present invention by way of example, and do not limit the content of the present invention at all.

Example

(How to measure)

(1) Measurement of particle size distribution

The particle size distribution was measured by a light scattering type particle size distribution analyzer (Horiba Seisakusho, laser diffraction / scattering type particle size distribution device LA-910).

(2) Length weighted average fiber length

A length-weighted average fiber length for about 4000 fine particles was measured using a Fiber Quality Analyzer manufactured by Op Test Equipment.

(3) Measurement of basis weight and thickness

It was performed according to JIS C2300-2.

About the thickness nonuniformity, the thickness of 40 consecutive points was measured, and the standard deviation was made into the thickness nonuniformity.

(4) Calculation of density

It was calculated as basis weight ÷ thickness.

(5) Measurement of tensile strength

Tensilon tensile testing machine was conducted at a width of 15 mm, a chuck spacing of 50 mm, and a tensile speed of 50 mm / min.

(6) Speculation

Using the Gurley air permeability meter specified in JIS P8117, the time (in seconds) for 100 cc (0.1 dm ³ ) of air to pass through a sheet sample (area 642 mm ² ) pressed by a fastening plate having a hole with an outer diameter of 28.6 mm. It was measured.

(Raw material composition 1)

A fibrid of polymetaphenylene isophthalamide was prepared using a device for producing pulp particles (wet precipitation machine) composed of a combination of a stator and a rotor described in Japanese Patent Laid-Open No. 52-15621. This was treated with an understanding machine and a beater to adjust the length-weighted average fiber length to 0.9 mm (Yardness of aramid fibrid: 100 ml (Kanadian Priness)).

On the other hand, meta-aramid fibers (Nomex (registered trademark), monofilament fineness 2 denyl) manufactured by DuPont were cut to a length of 6 mm (hereinafter referred to as "aramid short fibers").

(Preparation of calendered aramid paper)

The prepared aramid fibrid and aramid short fibers were dispersed in water, respectively, to prepare a slurry. This slurry was mixed so that the fibrid and aramid short fibers were mixed in a ratio of 1/1 (mass ratio), and a sheet-like article was produced with a tapered hand-held paper machine (cross-section 625 cm ² ). Subsequently, this was heat-worked at a temperature of 330 ° C and a linear pressure of 300 kg / cm with a metal calender roll to obtain a calendered aramid paper.

(Raw material composition 2)

The calendered aramid paper was crushed with a shredder, and a sieve having a pore diameter of 1 mm (hereinafter referred to as Φ1 aramid paper) was prepared (length-weighted average fiber length of about 80% of the nozzle diameter).

8 parts by mass of the Φ 1 aramid paper was mixed at a rate of 92 parts by mass of water, and a high pressure homogenizer (Starburst 100 HJP-25080 manufactured by Sugino Machine Co., Ltd .: nozzle diameter 0.5 mm) was subjected to high pressure injection treatment under the conditions shown in Table 1. Then, it collided with a hard body (ceramic) for collision and crushed to obtain a raw material for papermaking.

(Examples 1 to 3, control example)

(Production of heat-resistant electrical insulation sheet material)

The prepared Φ1 aramid paper, the prepared raw material for paper, and the prepared aramid fibrid were each dispersed in water to prepare a slurry. This slurry was mixed to a mixing ratio (mass ratio) shown in Table 1, and a sheet-like article was produced with a tapered hand-held paper machine (cross-section 625 cm ² ). Subsequently, this was heat-pressed at a temperature of 330 ° C. and a linear pressure of 300 kg / cm with a metal calender roll to obtain a heat-resistant electrically insulating sheet material. Table 1 shows the main characteristic values of the heat-resistant electrically insulating sheet material thus obtained.

From the results of Table 1, the heat-resistant electrically insulating sheet material of the present invention (Examples 1 to 3) had a length-weighted average fiber length maintained in comparison with that before the high-pressure jet treatment (control), and cut the aramid short fiber component. From the fact that it did not progress too much, the strength was high, the thickness nonuniformity was small, and the change in appearance was not seen even at the treatment at 250 ° C for 10 minutes, so it was found that it was useful as a heat-resistant electrically insulating sheet material. In addition, by increasing the components corresponding to short aramid fibers having a length of 0.3 to 0.4 mm corresponding to each particle size peak 1, air permeability was lowered, and it was thought that micro-irregularity occurred on the surface, so as to face other sheets, resins, etc. The adhesive area at the time becomes large, and is particularly useful as a heat-resistant electrically insulating sheet material for laminates bonded with insulating films and insulating resins.

Claims (6)

Aramid paper formed of a fibrid, a short fiber, or a mixture thereof formed of an aromatic polyamide, and produced through calendering, is subjected to high pressure spray treatment and crushed into a constituent material of the aramid paper. The calendered aramid paper is immersed in water, and the calendered aramid paper which is jetted with water at a high pressure at a jetting pressure of 70 to 300 MPa, collides with a hard body for collision or jetted at a high pressure at a jetting pressure of 70 to 300 MPa. By colliding, the calendered aramid paper is crushed to process the approach of the aramid fibrid and the aramid short fibers to produce the raw material for papermaking. The production method according to claim 1, wherein a particle size peak is generated in a range of 10 µm or more and less than 100 µm in a volume average particle size distribution of the aramid paper pulverized by a high-pressure injection treatment. The method of claim 1, wherein the aramid paper is pulverized before the high-pressure spraying treatment, and in the volume average particle size distribution of the obtained pulverized aramid paper, there is a particle size peak in a range of 10 µm or more and less than 100 µm and a range of 100 µm or more and less than 1000 µm, respectively. The manufacturing method characterized in that the frequency at each particle size peak after the high pressure spray treatment on the pulverized aramid paper increases in the range of 10 µm or more and less than 100 µm, and decreases in the range of 100 µm or more and less than 1000 µm. The manufacturing method according to claim 3, wherein a retention ratio of the length average fiber length of the material constituting the crushed aramid paper after the high pressure jet treatment is 80% or more with respect to the material constituting the aramid paper before the high pressure jet treatment. The raw material for papermaking manufactured by the manufacturing method of any one of Claims 1-4. A heat-resistant electrically insulating sheet material comprising the raw material for papermaking according to claim 5.