KR20180022751A - Aromatic polyamide paper for electrical insulation and manufacturing method thereof - Google Patents

Abstract

The present invention relates to aramid paper for electric insulation and a method for manufacturing the same, and more particularly, to aramid paper for electric insulation used by mixing an aramid flock with an aramid pulp having a fiber length of not larger than a certain length, a development of fibrils not less than a certain level and a content of fine particles not less than a certain ratio in a predetermined ratio, and a method for manufacturing the same. The aramid paper for electric insulation comprises 20-40 wt% of the aramid flock and 60-80 wt% of the aramid pulp having the fine particle content of 20 wt% or more. The method for manufacturing the aramid paper for electric insulation according to the present invention has excellent formation index. Based on the formation index, the uniformity of electric insulation characteristics and mechanical properties are enhanced; a weight of the paper becomes lighter by enhancing a structure of the paper; the convenience of conveying the paper and the uniformity of the strength are enhanced; and the cohesion among the flocks can be eased.

Description

TECHNICAL FIELD The present invention relates to a wholly aromatic aramid paper for electrical insulation,

The present invention relates to a wholly aromatic aramid paper for electric insulation and a method for producing the same. More particularly, the present invention relates to an aramid pulp having an aramid flake, a fiber length of a certain length or less, a development of fibrils of a certain length or more, And a method for producing the same. [0002] The present invention relates to a wholly aromatic aramid paper for electric insulation having uniform electrical insulation,

Typical applications of industrial paper include electric insulating paper, honeycomb, separator, filter and the like. Among them, electric insulating paper, which is a sheet-like article having insulation property, is widely used for various electric appliances and parts. For example, it has been known that an insulating paper is disposed between them in order to electrically isolate a printed circuit board from a power source device in a cellular phone, or a field in which a surface of a high-voltage cable is covered with a sheet having insulation property.

In addition, electric insulating paper used for cellular phones, high-voltage cables, and the like is required to have an additional predetermined heat resistance according to each application, and has an excellent electrical insulating property and an insulating sheet having heat resistance, which is an aromatic polyamide (aramid) BACKGROUND ART [0002] Numerous researches and developments have been conducted in recent years on the production and application of sheets composed of pulp or fibers.

However, a sheet made of aramid pulp or fiber alone has generally been lacking in flexibility and strength, and research and development have been made to complement such strength and flexibility by using aramid fiber and other fibers as a binder. The aramid insulation paper disclosed in Japanese Patent JP 2535418 B has the disadvantage of lowering the bending rigidity and ensuring the flexibility by mixing the aramid and the polyester fiber, but has a disadvantage that electrical insulation and heat resistance are lowered again. Japanese Patent JP 5591046 B, But it has not been possible to obtain uniform electrical insulation as compared with insulating paper using only aramid in terms of electrical insulation.

Recently, in order to compensate for these drawbacks, Korean Patent Publication No. 2014-0040096 A discloses that 40 to 100% by weight of para-aramid film type fibrids prepared through a specific jet spin process other than aramid pulp and inorganic filler Discloses a technique for producing an electric insulating paper by using aramid microfilaments and aramid fibrids or pulps as non-resin type binders. .

However, the electrical insulating paper according to the conventional manufacturing technique has a constitution for binder such as thermoplastic fiber or inorganic filler which is essentially lower in strength than aramid pulp or fibrid than aramid. Particularly, in electric insulating paper, It has not been possible to provide concrete techniques for eliminating defective conveyance of paper, non-uniformity of strength, and agglomeration between flocs by improving geometry for uniform electrical insulation, which is an important property.

JP 2535418 B JP 5591046 B KR 2014-0040096 A KR 2014-0038935 A

SUMMARY OF THE INVENTION It is an object of the present invention to provide a wholly aromatic aramid paper for electric insulation having uniform electrical insulation properties through improvement in the coarseness of an aramid paper base and a method of manufacturing the same. will be.

Another aspect of the present invention is to provide a wholly aromatic aramid paper for electric insulation which comprises a certain proportion of aramid pulp, a fiber length of a certain length, a fibril development of a certain degree or more and a fineness content of a certain ratio or more, .

Another aspect of the present invention is to provide a wholly aromatic aramid paper for an electric insulating paper which solves problems of conveyance failure of paper, unevenness of strength, and cohesion between flocs, and a method for producing the same.

The physical properties of the electrical insulating paper should be excellent for uniform electrical insulation than the strength of the paper. However, conventional electrically insulating paper using aramid short fibers has a constitution for a binder such as thermoplastic fiber or inorganic filler which is essentially lower than aramid pulp or fibrid and is stronger than aramid. Particularly, in electric insulating paper, It has not been possible to provide a concrete technique for solving the defective conveyance of the paper, unevenness of the strength, and agglomeration between the flocs by improving the paper-making for uniform electrical insulation of physical properties.

Accordingly, in order to uniformly insulate electrical insulation of the electric insulating paper, a certain amount of aramid pulp having a fiber length of not more than a certain length, a fibril development of a certain degree and a fineness content of a certain ratio or more is used together with a para- aramid flock, There is provided a wholly aromatic aramid paper for electric insulation which is capable of imparting uniform electrical insulating properties of a paper without having the above-mentioned composition, and a process for producing the same.

The wholly aromatic aramid paper for electric insulation according to the present invention may comprise a mixture of aramid flakes and aramid pulp having a fine particle content of 20 wt% or more.

The blend may comprise 20 to 40% by weight of aramid flock and 60 to 80% by weight of aramid pulp.

In addition, the length of the aramid flake is 4 mm to 8 mm, the length of the aramid pulp is 0.5 mm to 0.8 mm, and the aramid pulp has a fineness of 150 to 250 ml.

A method for preparing a wholly aromatic aramid paper for an electric insulator according to the present invention comprises: preparing an aramid flock; Preparing an aramid pulp having a fine particle content of 20 wt% or more; Mixing the aramid flour and the aramid pulp at a ratio of 20:80 to 40:60 to prepare a feedstock; And a raw paper forming step of forming the paper stock as raw paper.

In addition, the length of the aramid flake is 4 mm to 8 mm, the length of the aramid pulp is 0.5 mm to 0.8 mm, and the aramid pulp has a fineness of 150 to 250 ml.

The wholly aromatic aramid paper for electric insulation according to the present invention has superior paper synthesis and improves uniformity of electric insulation property, mechanical property improvement and light weight by improvement of paper structure, easiness of conveying of paper and uniformity of strength And the problem of flocculation between the flocs can be solved.

The present invention relates to a method for improving the uniformity of electrical insulation properties by improving the electrical insulation paper by using aramid flock, a method of forming aramid pulp having a fiber length of not more than a certain length, a fibril development of a certain length, Aromatic aramid paper for electrical insulations, which imparts uniform electrical insulation of the paper without the use of additional binders, and a method of making the same.

The terms or words used in the present specification and claims are defined as follows but should not be construed to be limited to ordinary or dictionary meanings and the inventor shall not be construed to limit the scope of the term It should be construed as meaning and concept consistent with the technical idea of the present invention based on the principle that the concept can be properly defined.

"Fiber" means a unit of relatively flexible material having a high length to width ratio across a cross-sectional area perpendicular to the length, and is used interchangeably with the term "filament ". The cross-section of the filaments described herein can be of any shape, but is typically circular or bean-shaped. A fiber spun in a package on a bobbin is called a continuous fiber. Fibers can be cut into short lengths called staple fibers. The fibers can be cut to a shorter length called floc. The yarns, multifilament yarns or tows comprise a plurality of fibers. Yarn can be entangled / entangled or twisted.

"Staple fibers" means filaments of 15 cm or less, preferably 3 to 15 cm; And most preferably 3 to 8 cm in length. The staple fiber is straight (i.e., non-crimped) or crimped to have a serrated crimp along its length at any crimp (or repeat bend) frequency. The fibers may be in an uncoated or coated, or pretreated (e.g., pre-stretched or heat-treated) form.

 "Aramid" means a wholly aromatic polyamide, and is defined as a linearly-synthesized polymer characterized in that at least 60 mole% of the bonds connecting benzene rings are amide groups. The aramid is classified into para-aramid, meta-aramid and copolymers thereof at the substitution position of the amide group in the benzene ring. The para-aramid may be exemplified by polyparaphenylene terephthalamide and its copolymer, poly (paraphenylene) -copoly (3,4 diphenyl ether) terephthalamide and the like, and the meta-aramid may be poly (metaphenylene isophthalate) Amides and copolymers thereof. In the present invention, para-aramid can be more preferably selected.

The term "aramid pulp" refers to a fibrillated microfiber made of aramid. The aramid pulp can be formed into a sheet form in a paper machine after being dispersed in water in order to have superfine properties like ordinary wood pulp. In order to improve the mechanical properties, To induce the fibrillation of individual short fibers in a dispersed state.

More specifically, in the method for producing and fibrillating aramid pulp, first, the wound aramid filament is cut using a rotary cutter to produce aramid staple fibers having a predetermined length. Next, washing is carried out to remove foreign substances in the aramid staple fibers, that is, fine powders or emulsions, and it is preferable to carry out the washing at a temperature of room temperature or higher in order to easily remove the foreign materials.

Then, the washed aramid staple fiber is dispersed in water to carry out a dissociation process for producing a homogeneous slurry. It is preferable that the dissociation process is performed at a temperature of room temperature or higher to further remove the remaining tanning agent and improve the dispersibility of the aramid staple fibers. Through the dissociation process, each of the aramid staple fibers is separated into a plurality of monofilaments. The concentration of the aramid staple fibers in the slurry is preferably 1.0 to 2.0% by weight.

Then, the slurry uniformly dispersed in water is subjected to a beating process through the dissociation process. In the beating process, the aramid staple fibers are separated and cut as well as fibrillated using a refiner to produce fibrillated aramid staple fibers having an average length of the aramid staple fibers of 0.5 to 5 mm.

Optionally, if the fibrillation of the aramid staple fibers does not proceed smoothly, the dissociation process and the beating process may be repeated.

The slurry containing the fibrillated aramid staple fibers through the beating process is made into a sheet, followed by a squeezing process to remove water from the grass first, and the firstly moisture-removed grass is dried Whereby the water is removed in the second order. The dried grass is then crushed to produce the final aramid pulp.

Meanwhile, the beating process is one of the important processes for determining the freeness of the aramid pulp (Canadian Standard Freeness). This is because the degree of fibrillation of aramid pulp varies greatly depending on the degree of fibrillation of the aramid staple fibers through the beating process. That is, when the degree of fibrillation is good, the degree of freeness of the pulp becomes low, which means that the dispersibility of the aramid pulp is excellent. On the other hand, if the degree of fibrillation is poor, the degree of freeness of the pulp becomes high, which means that the dispersibility of the aramid pulp is poor. It is also important that the aramid pulp has uniform physical properties. If the fibrillation is uneven, the deviation of the degree of freeness becomes large. As the deviation of Yeosu becomes larger, the final product to which it is applied also increases the defective rate because the difference of physical properties between products increases.

"Floc" refers to fibers of shorter length than staple fibers. The flocs have a length of about 0.5 to about 15 mm and a diameter of 4 to 50 micrometers, preferably of 1 to 12 mm and a diameter of 8 to 40 micrometers. Flocs less than about 1 mm do not significantly affect the strength of the material to be used. Flocs or fibers of greater than about 15 mm are generally not functioning because the individual fibers can entangle and can not be properly and homogeneously dispersed throughout the material or slurry. Aramid flocs can be produced by cutting aramid fibers to short lengths without significant or optional fibrillization, such as those produced by the methods described in, for example, U.S. Patent Nos. 3,063,966, 3,133,138, 3,767,756, and 3,869,430 .

By "fibrids" is meant non-granular, fibrous, or film-like particles. They have a melting point or decomposition temperature of at least 320 in the wind. Fibrids are fibers rather than fibers in that they have a fiber-like region connected by a web. The fibrids have an aspect ratio of 5: 1 to 10: 1 and an average length of 0.2 to 1.0 mm. The thickness of the fibrid web is less than 1 or 2 micrometers and is typically a prime number of less than 1 micrometer. Prior to drying, the fibrids may be used in a wet state and deposited as a physically twisted binder around other components of the article. The fibrids may be prepared by any method, including using a fibridation apparatus of the type disclosed in U.S. Patent No. 3,018,091 in which the polymer solution is precipitated and sheared in a single step.

"Fibrils" means small fibers having a small diameter of from a few microns to a few microns of less than one micrometer and a length of about 10 to 100 micrometers. The fibrils typically extend from the main trunk of a larger fiber having a diameter of 4 to 50 micrometers. The fibrils act as hooks or fasteners to trap adjacent materials. Some fibers are fibrillated, while other fibers are not fibrillated or effectively fibrillated, in which case the fibers are not fibrillated. Poly (meta-phenylene terephthalamide) fibers are readily fibrillated to produce fibrils during polishing. The poly (meta-phenylene isophthalamide) fiber is not fibrillated.

 "Aramid flock" is a staple fiber made by cutting a continuous filament with a short length of unfibrilized aramid. The length of the aramid flock is usually 1 to 50 mm, and if the length is less than 1 mm, And when the length is 50 mm or more, it is known that it is not preferable because the possibility of occurrence of tangling is large when the sheet is formed, which tends to cause bonding.

However, in the present invention, when the flock having a diameter of 3 mm or less is used, the transfer of the paper is difficult and the irregularity of the strength is caused. When the diameter is 9 mm or more, cohesion between the flocks occurs and the length of the aramid flock is 4 mm to 8 mm Is preferred for the production of aramid paper for electric insulation.

 Further, in the production of aramid paper for electric insulation, it is more preferable to use 60 to 80% by weight of aramid pulp and 20 to 40% by weight of aramid flakes.

Hereinafter, the aramid paper for electric insulating paper of the present invention and its manufacturing method will be described in detail with reference to examples.

Preparation Example 1: Preparation of an aramid flock

1000 kg of N-methyl-2-pyrrolidone was maintained at 80 ^° C, and 80 kg of calcium chloride and 48.67 kg of para-phelenediamine were dissolved to prepare an aromatic diamine solution. The aromatic diamine solution is introduced into a reactor for polymerization and a molar amount of terephthaloyl chloride such as para-phenylenediamine is introduced into a reactor for polymerization and then stirred to obtain a poly (para-phenylene terephthalate) having an intrinsic viscosity of 6.8 Amide) polymer.

The polymer thus prepared was then dissolved in 99% concentrated sulfuric acid to prepare an optically anisotropic radiation dopant having a polymer content of 18% by weight. The prepared spinning dope was spinned using a spinneret and then solidified in a coagulation bath through an air layer to produce a filament. The filament was washed with water and dried, and then wound by a winder to obtain a poly (para-phenylene terephthalamide) filament. The poly (para-phenylene terephthalamide) filament was cut using a rotary cutter and cut into a length (3, 6, 9 mm) and used as an aramid flock.

Production Example 2: Preparation of aramid pulp

A homogeneous slurry was prepared by dispersing 20 kg of the aramid flake having a length of 6 mm or longer prepared in Preparation Example 1 in 1,000 L of water. The slurry thus prepared was poured into a refiner equipped with a refiner and then stirred for a predetermined time. After sampling, the specific surface area (SSA) of the aramid pulp, the Canadian Standard Freeness (CSF) and the fiber length Length: FL), which was used to control the basic properties of aramid pulp. The slurry after the beating process was dehydrated using a filter, dried and stored. The dried grass was crushed into small pieces using a pulverizer to prepare a final aramid pulp.

Production Example 3: Production of aramid pulp having a fine particle content of 20% or more

20 kg of aramid flock mixed with 10 to 20% by weight of 3-mm length flakes and 80 to 90% by weight of 6-mm or longer lengths of aramid flakes having different lengths prepared in Preparation Example 1 was mixed with 1,000 L of water to prepare a homogeneous slurry. The slurry thus prepared was poured into a refiner equipped with a refiner and then stirred for a predetermined time. After sampling, the specific surface area (SSA) of the aramid pulp, the Canadian Standard Freeness (CSF) and the fiber length Length: FL), which was used to control the basic properties of aramid pulp. The slurry after the beating process was dehydrated using a filter, dried and stored. The dried grass was crushed into small pieces using a pulverizer to produce final aramid pulp. The content of fine powder in the aramid pulp was 20% or more.

Example 1: Preparation of aramid paper for electric insulation

3 kg of the aramid flock of 6 mm length prepared in Preparation Example 1 and 7 kg of the aramid pulp having the fineness of 20% or more prepared in Preparation Example 3 were dispersed in 1,000 L of water to prepare a homogeneous slurry. The slurry thus obtained was made into a papermaking form, the water was removed from the squeezing roll, and the water-removed grass was dried at a temperature of 105 ^° C at a speed of 5 m / min using Yankee dry. Then, aramid paper for electrical insulation of 250g / m ² was produced at a speed of 3m / min using a hot roller at 250 ^° C.

Comparative Example 1

3 kg of the 6 mm length of the aramid flake prepared in Preparation Example 1 and 7 kg of the aramid pulp which had not been subjected to the process of increasing the amount of the fine powder prepared in Preparation Example 2 were dispersed in 1,000 L of water to obtain a homogeneous slurry . The slurry thus obtained was made into a papermaking form, the water was removed from the squeezing roll, and the water-removed grass was dried at a temperature of 105 ^° C at a speed of 5 m / min using Yankee dry. Then, aramid paper for electrical insulation of 250g / m ² was produced at a speed of 3m / min using a hot roller at 250 ^° C.

Comparative Example 2

An aramid paper for electrical insulation was prepared in the same manner except that the aramid flock of Example 1 and 3 mm and 9 mm length was used.

Comparative Example 3

An aramid paper for electric insulation was prepared in the same manner as in Example 1, except that 5 kg of aramid flock and aramid pulp were used, respectively.

Property evaluation

1) Measurement of Specific Surface Area (SSA)

The specific surface area (g) was measured using the nitrogen adsorption method by the BET measurement method.

2) Fiber Length (FL) measurement

The weight average length was measured using a "FiberExpert" table top analyzer (also known as "PulpExpert FS" available from Metoso Automation, Helsinki, Finland). The analyzer took photographic images of the pulp with a digital CCD camera as the pulp slurry passed through the analyzer and the integrated computer then analyzed the fibers in the image and calculated the weighted average length thereof.

3) Degree of Fibrillization (DF) measurement

The degree of fibrillation (DF) was measured using a "FiberExpert" table top analyzer (also known as "PulpExpert FS" available from Metoso Automation, Helsinki, Finland) Respectively.

4) Measure Canadian Standard Freeness (CSF)

The Canadian Standard Freeness (CSF) is a well-known measure of water drainage from slurry or dispersion of particles. The degree of freeness was measured by TAPPI Test 227. The data obtained from the performance of the test is expressed in Canadian Standard Freeness, which represents the millimeter of water drained from the aqueous slurry under certain conditions. The higher the number, the higher the drainage of water and water. Small values indicate a tendency for the dispersion to drain slowly. The greater the number of fibrils, the lower the rate at which water is drained through the forming paper matte, so the freeness of the fleece is inversely proportional to the freeness of the pulp.

The properties of aramid paper prepared by the method of Example 1 and Comparative Examples 1 to 3 were measured and reported in Table 1 below.

Basis weight
(g / m ² ) thickness
(mm) density
(g / cm ³⁾ strong
(N / mm ² ) Dielectric strength
(kV / min) MD CD Example 1 253 0.238 1.15 15.6 16.5 6.4 Comparative Example 1 251 0.252 1.02 6.9 11.6 5.6 Comparative Example 2 248 0.258 0.98 4.2 10.4 5.3 Comparative Example 3 254 0.232 1.2 3.9 8.5 5.9

As shown in Table 1, by using the refining process, 70% by weight of aramid pulp having a fiber length of less than a certain length, a large amount of fibril formation and a fine powder content of 20% or more and 30% by weight of aramid flock having a length of 6 mm The aramid paper for electric insulation has excellent dielectric strength.

On the other hand, in the present invention, when the flock having a diameter of 3 mm or less is used, the transfer of the paper is difficult and the irregularity of strength is generated. When the diameter is 9 mm or more, coagulation occurs between the flocks. Therefore, the length of the aramid flock is 4 mm to 8 mm Is preferable for the production of aramid paper for electrical insulation.

When the content of the aramid pulp is 50% or less in the production of the aramid paper for electric insulation, the strength is lowered. Therefore, the content of the aramid pulp is preferably 60 to 80% by weight, and the amount of the aramid flock is 20 to 40% It is more preferable to use them.

Claims (2)

20 to 40% by weight of a para-aramid flake having a length of 4 mm to 8 mm; and
And 60 to 80% by weight of para-aramid pulp,
The para-aramid pulp contains 20% by weight or more of fine particles prepared by using a refiner equipped with a refiner using an aramid flour mixed with 80 to 90% by weight of flakes having a length of 6 mm or more, Lt; RTI ID = 0.0 > 250ml. ≪ / RTI > Preparing a para-aramid flake having a length of 4 mm to 8 mm;
Containing at least 20% by weight of fine particles prepared by using a refiner fitted with a refiner using an aramid flour mixed with a mixture of 80 to 90% by weight of flakes having a length of 6 mm or more, and having a freeness of 150 to 250 ml Preparing an aramid pulp;
20 to 40% by weight of the para-aramid flour and 60 to 80% by weight of the para-aramid pulp are mixed to produce a feedstock; And
And a raw paper forming step of forming the above-mentioned paper stock as a raw paper. The method for producing a wholly aromatic aramid paper for electric insulated paper according to claim 1,