JPH0274656A - Heat-resistant felt - Google Patents

Abstract

PURPOSE:To obtain a heat-resistant felt, having tightly formed entanglement between fibers and excellent in mechanical strength, shape retaining properties and dimensional stability and good in productivity and economical efficiency by laminating webs consisting of heat-resistant fibers having latent heat shrinkability, needle punching the laminated webs and heat-treating the needle punched webs. CONSTITUTION:Webs consisting of heat-resistant fibers (preferably aromatic polyimide fibers having preferably >=50% heat shrinkability) having latent heat shrinkability are laminated, subjected to previous entangling treatment by needle punching, then heat-treated (preferably at a temperature between the glass transition point and the maximum crystallization temperature of the above- mentioned fibers) and shrunk to tightly form entanglements between the fibers and afford a heat-resistant felt suitably used as substitutes for asbestos in buildings, etc.

Description

[Detailed description of the invention] [Industrial application field] The present invention is suitable for interior materials of buildings, aircraft, vehicles, etc.
Asbestos also has problems such as toxicity.
The present invention relates to a heat-resistant felt suitable as a substitute for products.

[Conventional technology]

Nonwoven fabrics are manufactured by three-dimensionally intertwining and strengthening multiple fiber layers using the needle punching method, and the apparent density and thickness can be changed by controlling the number of web layers and punching conditions. be. Therefore, using this nonwoven fabric, porous felt bodies having various mechanical properties and performances can be obtained.

In addition, felt made of heat-resistant fibers is used, for example, as (a) heat insulating and protective materials used in steel, ceramics, chemical plants, etc., and (b) to prevent scratches on high-temperature products in the steel and metal manufacturing process. (C) Cushion material in the molding process of various resin laminates; (d) Structural reinforcing material for fire-resistant structures, gasket material for various industries, and FJ friction material. It is widely used as a backing material, etc.

Therefore, the heat-resistant needle-punch felt body used for such applications has sufficient entanglement between fibers, has excellent dimensional stability, processability, shape retention, etc., and has low mechanical strength. It is desired that it be high.

[Problem to be solved by the invention]

However, many of the fibers commonly used as heat-resistant fibers have a relatively high modulus, and as a result, the resistance experienced by the needle during needle punching is high, resulting in needle breakage and product damage. There is a risk that various problems may occur due to wear and damage of the needle, such as needle pieces being mixed in with the needle.

Naturally, the higher the degree of entanglement between fibers, and the higher the density, the higher the incidence of this problem. For this reason, the needle punch conditions are restricted, which sometimes leads to a situation where sufficient mechanical strength cannot be obtained.

On the other hand, inorganic fibers such as carbon fibers, glass fibers, and ceramic fibers generally exhibit high heat resistance, are nonflammable, have excellent corrosion resistance, and exhibit extremely low creep even in high-temperature environments. In this respect, it is suitable as a material for heat-resistant felt, but on the other hand, since the fiber itself is extremely brittle, the needle punching method can easily crush the fiber, and the needles can be seriously damaged. was to be severely restricted. As a result, using these fibers, the apparent density is 0.
It was difficult to make a felt body of 2 g/cT1 or more. Therefore, in the past, it could only be used for felt bodies such as heat insulating mats, which had relatively low strength and density, and did not require much shape retention.

In addition, since stainless steel fibers are relatively tough, they will not be crushed during needle bunching, but they are still prone to needle breakage, and this can result in needle pieces getting mixed into the product. The risk of an accident remained.

For this reason, various measures have been taken to obtain felts that are heat resistant and stable in terms of strength. That is, (1) The first method is to insert a reinforcing base material such as a woven fabric made of heat-resistant fibers between the laminated webs to increase the strength of the felt body. However, in this method, the strength of the felt body completely depends on the strength of the reinforcing base material, so the above-mentioned problem caused by damage to the needle still remains.

■ The second method is to apply heat-resistant resin treatment to needle punch felt in order to reinforce the strength and shape retention of the felt body. This method involves resin impregnation, deliquescence, aging,
Since various processes such as drying are required, problems arise in terms of productivity and economy, that is, high costs, and heat-resistant resins that match the grade of heat-resistant fibers are themselves expensive. Moreover, since heat treatment at high temperature and for a long time is required, the above-mentioned productivity and economical problems are further amplified.

The third method is to create a web by blending heat-resistant fibers and low-melting-point thermoplastic fibers, and then thermocompressing the web at a temperature that exceeds the thermal bonding temperature of the thermoplastic polymer. At this time, in order to prevent shrinkage due to melting of the thermoplastic polymer, it has been known to fix the periphery of the nonwoven fabric or to apply tension to the nonwoven fabric. However, although this method is useful for improving the strength of nonwoven fabrics, it is necessary to apply relatively high pressure during the manufacturing process to improve affinity and adhesion with heat-resistant fibers of different components, and the elasticity , it has become difficult to obtain a felt body with a sterically entangled structure that has excellent shape retention, etc., and there have been problems in that heat resistance is reduced.

■ The fourth method is to heat-seal a web made by blending heat-resistant fibers and thermoplastic fibers with high heat-resistant grade by thermal processing. This method uses thermocompression bonding using polyamide fibers as adhesive elements. However, as far as the examples show, the material obtained by this method is an extremely low-density sheet-like nonwoven fabric with a basis weight of 30 g/n (, thickness of 1.3 M, and an apparent density of 0.023 g/c+iT). It is not a felt body with a composite structure.

■ The fifth method, as shown in JP-A No. 61-289162, is to create a web that is a blend of heat-resistant fibers and undrawn polyphenylene sulfide fibers, and
This is a method of obtaining a heat-resistant nonwoven fabric by applying thermocompression bonding to this under pressure at a temperature at which the undrawn fibers become plasticized and a fusion effect occurs. However, as seen in the examples, the material obtained by this method is a sheet-like nonwoven fabric with an apparent density of 0.1 g/cffl or less, and its tensile strength is also not sufficient.

■ The sixth method is to heat-shrink a web made by mixing polyester or acrylic shrink fibers with shrink-resistant fibers to create entanglement between the fibers, giving the nonwoven fabric mechanical strength and bending durability. This is a method to express such things. For example, as disclosed in JP-A-62-162059, composite acrylic short fibers with a heat shrinkage rate of 15 to 40% and specific synthetic fibers (e.g. polyester,
In this method, a synthetic fiber felt body is obtained by needle-punching a web made of a mixture of polyolefins (polyolefins, polyamides), and then heat-treating the web. However, this method is not originally intended to obtain a heat-resistant felt body. Furthermore, as far as can be seen from the examples, the apparent density of the felt body obtained was relatively low, such as 0.174 g/cm.

■ The seventh method, as disclosed in Japanese Patent Publication No. 61-58583, combines a woven fabric made of wholly aromatic polyamide fibers with a web, and then needle-punches the resulting fabric, which has an apparent density of 0.2 g. This is a method for obtaining a high-density felt body by heating and compressing a felt body having a density of /c+d or more. However, although the felt body obtained by this method starts from a relatively high-density needle-punch felt body and is compressed at high temperature, the rate of increase in density is limited to a range of only 10 to 25%. It becomes. This is because the increase in the density of the felt body is not achieved by strengthening the entanglement of the fiber webs, and strong compression of more than 25% will have an unfavorable effect on the elasticity retention of the resulting felt body.

As mentioned above, if you want to use the needle punch method using the above various methods and obtain a heat-resistant felt body with sufficient strength, durability, elasticity, shape retention, etc. It becomes necessary to subject the punch felt body to various treatments such as heat treatment, resin processing, binder processing, and press processing, which causes an increase in costs in terms of productivity and economy.

For this reason, the present inventors focused on the high shrinkage of aromatic polyimide fibers, which had been considered a drawback in the past, and as a result of research, found that the high shrinkage of these types of fibers is They found that it is extremely convenient for strengthening entanglement, and have completed the present invention.The purpose is to have excellent performance such as heat resistance, and to improve productivity and economy. The purpose of the present invention is to provide a heat-resistant felt with good properties.

[Means to solve the problem]

In order to achieve the above object, the present invention involves laminating webs made of heat-resistant fiber materials with latent shrinkage that shrink under a predetermined range of thermal atmosphere conditions, and pre-entangling them with a needle punch to form a primary felt body. The felt body is then heat-treated under the above-mentioned hot atmosphere conditions to tightly entangle the fibers to obtain a desired product.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to Examples.

Aromatic polyimide fibers are suitable as the fibers having latent heat shrinkability used in the present invention. This fiber is made of, for example, benzophenone tetracarboxylic anhydride (BTDA), toluylene diisocyanate (TDT) and methylene diphenyl diisocyanate (MDI), commercially available as Lenzing P-84J (trade name: Lenzing AG, Austria). The main component is a polycondensation product with a mixture of these three materials. The chemical composition of this fiber itself is known, for example, as shown in U.S. Pat. After this point, an irreversible curing reaction that generates heat occurs within a short period of time. (rl) During this curing reaction, extremely high stresses with a high degree of shrinkage act. (c) At this time, shrinkage hardening occurs without heat fusion, that is, while the fiber shape is maintained, and the mechanical properties such as the section modulus and modulus of the fiber are significantly strengthened. (d) Since the fibers have an irregular and asymmetric cross-sectional shape, they shrink while adding a crimped shape suitable for reinforcing the entanglement between the fibers during shrinkage and hardening. (The heat-resistant and flame-retardant properties of the ladle fibers, which are caused by their basic chemical structure, are maintained as they are even through this heat treatment. This is an extremely advantageous property in constructing the heat-resistant felt of the present invention. The present inventors' research has revealed that the present invention is based on such fibers having a high degree of latent heat shrinkage (also referred to as high shrinkage fibers).

The heat-resistant felt of the present application can be manufactured using a web made only of the above-mentioned high-shrinkage fibers, or ■a web made by blending high-shrinkage fibers with other heat-resistant fibers. There are two.

That is, the heat-resistant felt body of the present invention can be produced by laminating a plurality of webs consisting only of high-shrinkage fibers or webs in which heat-resistant fibers are blended, and pre-entangling them using a needle punching method. A primary felt body is created, and then heat treated to create a significantly high tension due to overall shrinkage, and this tension forces the entire felt body to become compact and harden. Manufactured.

The heat-resistant felt of the present invention produced in this manner exhibits high density and hardness with mechanical properties that are unexpectedly high from the strength of the single fibers before heat treatment.

In this case, the high-shrinkage fibers are blended with other heat-resistant fibers and subjected to pre-entanglement treatment. Accompanying stress is generated and acts, and the same effect as described above is produced when the nonwoven fabric is fixed or heat set under tension, under a free cent condition.

The effect of shrinkage and hardening of the entire felt is determined by the blending ratio of the side fibers, and this effect sufficiently strengthens the tightness at the fiber entanglement points, resulting in excellent mechanical strength, shape retention, and size. Forms felt with good stability.

Therefore, in both cases (1) and (2) above, the highly shrinkable fiber used has a high glass transition point of, for example, 300°C or higher, and the temperature between this glass transition point and the maximum crystallization temperature is 5 without heat melting and maintaining the initial weight.
A drawn yarn spun to exhibit a heat shrinkage of 0% or more and a non-quality aromatic polyimide fiber that has not been subjected to heat relaxation is used. The fibers preferably have an asymmetric cross-sectional shape in order to enhance the entanglement effect in the pre-entanglement treatment and heat treatment, and are crimped to a number of 5 to 25 crimps/25 mm. Further, from the viewpoint of preventing yarn breakage and increasing entanglement hardening, it is desirable that the single yarn denier is 1 to 10 deniers and satisfies the practical strength of 3 g/d during needle punching.

On the other hand, the heat-resistant fibers to be blended with the high-shrinkage fibers can be arbitrarily selected depending on the purpose, but at the temperature at which the heat treatment is performed, the heat-resistant fibers should be small (and do not melt or decompose), and should be It is preferable that the practical strength is 3 g/d.

Organic thermal fibers that meet these conditions include fully aromatic polyamide fibers such as polyparaphenylene terephthalamide, polyvalphenylene diphenyl ether terephthalamide, and polymetaphenylene isophthalamide, aromatic polyamide fibers, and aromatic polyamide fibers. Polyamide-imide fibers, aromatic polyimide fibers, such as copolyimide fibers and polybenzimidazole fibers formed by condensation polymerization of the BTDA and a mixture of para-phenylene diamine and meta-phenylene diamine, are selected, and are heat-shrinkable under the heat treatment conditions. Also included.

In addition, in the present invention, unlike the case of conventional heat-resistant fibers, it is also possible to use carbon fibers, glass fibers, ceramic fibers such as alumina-silica fibers, stainless steel fibers, rock wool, and the like. That is, as mentioned above, inorganic fibers alone are subject to extremely serious limitations in felt formation, such as crushing, scattering, and falling of the raw fibers and abrasion damage to clothing and needles during the web creation stage and needle punching stage. However, when mixed with the highly shrinkable polyimide fibers and other organic heat-resistant fibers, the problems of operability and workability in the pre-entanglement treatment described above can be reduced to a practical level. It is. Note that the use of a material that adds smoothness, such as a silicone oil agent, in the web preparation stage is effective in promoting these improvements without essentially impairing the present invention.

Therefore, when blending high-shrinkage fibers such as high-shrinkage polyimide fibers with heat-resistant fibers, or when blending these blends with other materials as necessary, the combination of high-shrinkage fibers It is preferable that the high shrinkage fibers account for at least 30% by weight. If this blending ratio is less than 30%, the fiber entanglement density during heat treatment will be insufficient, making it difficult to obtain a felt body with sufficient strength and shape retention.

In addition, when the heat-resistant fibers are inorganic fibers, the blending ratio of high-shrinkage fibers is determined by the need to maintain practical productivity at the web creation stage and pre-entanglement stage, as described above.
It is desirable that it is 0% or more.

On the other hand, to create the web, methods known per se such as the usual carding method and air-laying method can be applied, but in this case, it is necessary to uniformly mix the fibers, sufficiently spread the fibers, and perform cross-layer lamination. , which is important in obtaining a stable felt body. In addition, the -order felt body is made by laminating webs of, for example, 50 to 3000 g/rrr, and using a two-dollar punch method using a barbed needle to give an apparent density of 0.
．． It is created by pre-entanglement treatment so that it has a density of about 0.05 to 0-3 g/cA, but in the case of a case made by blending inorganic fibers, the apparent density is 0.05 to 0.15 g/cffl.
It is preferable to control the load during needle punching so that the It goes without saying that even with this level of apparent density, sufficient practical strength and shape retention can be obtained by applying the necessary heat treatment.

The heat treatment temperature is determined by the characteristics of the highly shrinkable fibers constituting the primary felt body. Further, the time required for heat treatment is practically controlled by the basis weight of the needle bunch felt. For example, if the material is relatively light (less than LOOOg/%), it is recommended to set it to 5 to 10 minutes, and if it is thicker than 1000 g/n (more than 1000 g/n), it is recommended to set the time to about 10 to 30 minutes. ,
A well-known heating furnace such as a hot air circulating gas dryer, an electric dryer, or an infrared heater may be used, and no special heat treatment equipment is required. Furthermore, in cases where it is necessary to impart smoothness to the surface of the secondary felt body, or when it is necessary to prevent the felt base material from falling off or to regulate the thickness,
A hot press treatment using a commonly used flat plate hot press may also be performed. In this case, the pressurizing conditions are basically sufficient to apply a light load. In addition, when heat treating a cylindrical primary felt body preliminarily formed using a tubular needle rocker, a support body having a diameter that takes into account changes in heat shrinkage of the felt body is required in advance.

The usefulness of the present invention will be demonstrated below with some specific examples.

In this specific example, high shrinkage polyimide fibers are used as high shrinkage fibers, and the characteristics and thermogravity of these fibers
The differential thermal analysis (TG-DSC) results are as shown in Table 1 and FIG.

Table 1 Thermogravimetric analysis and dry heat exposure test (
As shown in the measurement example of the limiting oxygen index (250°C, 110 hours), this high shrinkage polyimide fiber has excellent heat resistance and flame retardancy, and is also characterized by the aromatic nature of the polymer chain and the stability of the imide bond. It has the basic characteristics of fibers based on the unique molecular structure of the polymer, such as its properties.

As shown by curve A in Fig. 1, the glass transition point is about 315°C, the maximum crystallization temperature is around 400°C, and when it exceeds 500°C, it shows a tendency to carbonize. It has thermal properties such that it decomposes at around 600°C. For this reason, the production of gaseous combustible decomposition organisms is suppressed, and it does not burn with flames, making it a highly safe flame-retardant fiber with excellent flame retardant, non-spreading, and non-melting properties. Become.

In this case, no weight loss was observed in the temperature range between the glass transition point and the maximum crystallization temperature, as shown in curve 8.

Considering these characteristics or properties, the heat treatment temperature for this fiber can be specified in the range of approximately 315"C to 400°C, but in reality it is approximately 315"C to 360°C.
Entanglement can be completed even within the C range, so if this range is utilized, it will be advantageous in selecting other heat-resistant fibers to be mixed. For example, if this fiber is 330
When exposed for 10 minutes in a hot atmosphere condition of °C, the fibers contracted into curls with hardening, and the average shrinkage rate was 62%.

In addition, even at temperatures below the glass transition point, shrinkage of the fibers is observed from around 270°C, but in this case, either a long heat treatment is required or the shrinkage effect of the fibers is incomplete. This causes problems such as a decrease in thermal dimensional stability.

[Specific Example 1] Using high shrinkage polyimide fiber with a single yarn denier of 3 deniers and a fiber length of 60 kaku, having the characteristics shown in the examples in Table 1,
A web was formed using a roller card and laminated using a crosslayer to create a laminated web having a basis of 1150 g/rrr. This was punched using a needle rocker using a barbed needle while sequentially stacking the laminated webs, and Table 2
Basis weight 800g/bo, thickness 10mm as shown in sample A of
Six primary felt bodies with an apparent density of 0.08 g/CTII were prepared.

Next, 5 of these were put into a hot air dryer with no load, and heated to 270°C and 300°C1320'C13 respectively.
Set the ambient temperature to 40°C and 1360°C and set the temperature to 10 each.
The five samples obtained in this manner were designated as sample B, sample C1, sample D, sample E, and sample F, respectively. Table 2 shows the changes in mechanical properties of these samples A-F.

Table 2 As is clear from Table 2, the primary felt body formed by pre-entanglement becomes highly tight near the glass transition point of the fibers, and is highly mechanically resistant while maintaining high heat resistance (weight retention). The material changes into a high-density hard felt body (Sample D, Sample E, Sample F) with high physical strength.

The high-density hard felt bodies created in this way (Sample D, Sample E, and Sample F) are created only by entangling fibers, so even though they are hard felt bodies with good shape retention. It has moderate flexibility. That is, in the conventional resin-impregnated felt body, the resin peeled off and cracked when subjected to repeated bending tests, but the heat-resistant felt of the present invention did not cause such phenomena.

Figure 2 shows the surface and cross section of sample A before heat treatment (electron microscope x
Figure 3 is a photograph showing the surface and cross section of the sample after heat treatment (electron microscope X, 200 times).

These photos show the structural changes in the primary felt body before and after heat treatment, and as is clear in each photo, the felt body increases its fineness through heat treatment and becomes extremely tightly intertwined as it shrinks into a curl shape. I understand.

Also, felt bodies before and after heat treatment (Samples A and D)
The results of the combustion test are shown in Table 3.

Table 3 In this case, sample A has sample A to sample C groups in a representative sense, but none of the samples continues to burn, and furthermore,
It shows a high degree of flame retardancy even after heat treatment, proving its suitability as a fire-resistant structural material with excellent mechanical properties.

[Specific Example 2] A web prepared by mixing polyparaphenylene terephthalamide fibers at a weight ratio of 2 oz was laminated on highly shrinkable polyimide fibers, and after pre-entanglement, the web was exposed to a hot atmosphere condition of 330°C for 30 minutes. The heat-resistant felt of the present invention was used as a spacer in an annealing process of an aluminum plate at an annealing temperature of 350°C. On the other hand, a woven fabric or a needle felt made of polyparaphenylene terephthalamide fibers was used as a similar spacer. Among the latter, spacers made of fabric cannot be used because texture marks are left on the surface of the aluminum plate during annealing. In addition, a spacer made of needle felt is too soft and has poor workability. That is, polyparaphenylene terephthalamide fibers do not shrink due to heat and have no choice but to increase the density of felt by needle pricking, so even when made the hardest, the density is in the range of 0.2 to 0.35 g/cffl. This is because it only becomes .

Therefore, although it is thought that felts using polyparaphenylene terephthalamide fibers can be treated with resin to give them hardness and improve durability, this is not possible. In other words, as mentioned above, the operating temperature is as high as 350°C, and the one-time annealing temperature is as long as 7 hours, so there is no resin that can withstand this, and gas from the decomposition of the resin adheres to the aluminum plate. This is because it may cause clouding on the surface.

On the other hand, the spacer made of the heat-resistant felt of the present application has a density that shrinks to 0.6 g/cffl due to heat, and is not only stiff and easy to work with, but also can be annealed 26 times at a temperature of 350°C. It was able to withstand the durability of repeated use.

[Specific Example 3] This is a case where the present invention is applied to a top roll of a plating line of a steel plate. A plated plate having a temperature of 350° C. to 450° C. passes through this top roll, but since the plate has just been plated, it is easily damaged. Conventionally, this roll was coated with asbestos fabric, but there was a problem in that the fabric was cut by the edges of the steel plate, and its useful life was only 14 days.

Therefore, this roll was coated with a tube-shaped web laminate by mixing high-shrinkage polyimide fibers and polybenzimidazole fibers at a weight ratio of 70:30, and the rolls were covered with steel bands on both sides. Shrinkage molding was performed using a hot air oven at 330°C to obtain the heat-resistant felt of the present invention. By the way, the basis weight is 2500g/rrf,
The diameter of the roll is 1200 mm, the length is 1500 mm,
The felt body has a diameter of 1210 mrB and a length of 1750 mm.
It was designed to.

When a plated board having a temperature of 350°C to 450°C was passed under the above conditions, no damage was caused to the board. In addition, unlike asbestos fabrics, it was not cut by the edges of the steel plate, and could be used for 32 days without any problems.

[Specific Example 4] This is an example of application to a brick manufacturing process in the ceramic industry. Cushion material is used in this process to prevent scratches on the bricks. When inorganic fibers such as ceramic fibers, asbestos, and glass fibers are used as cushioning materials, they do not have crimps and are brittle, making it difficult to form them into felt. .1g/
The density was only about CD, making it unsuitable as a cushioning material, and kraft paper was used for -a, but since bricks are fired at 250'C, at most 1 to 2
I could only use it a few times.

Therefore, this cushioning material was blended with high shrinkage polyimide fiber and glass fiber at a weight ratio of 50:50, a web was formed using a card machine, and this laminate was punctured with needles at a rate of 3000 times/in. 800g to go
/rt(, a felt body with a density of 0.20g/cnl was created and heat treated at 330°C to create a heat-resistant felt of 1600g/rr(with a shrinkage of 50% in area.This felt The polyimide fibers were well intertwined with the glass fibers, and the density was 0.50 g/c+d.

When used in a brick firing process under the above conditions, the durability was 6 months.

[Specific Example 5] This is an example of application to a tension butt in the cold rolling process of steel manufacturing. In this process, a tension bat is used to prevent the steel plate from meandering, but this bat is usually made of 65% wool and nylon blended at a ratio of 70:30.
A triple-woven product with a density of 0.00 g/m'' and a density of 0.59 g/cm' is used.

In this case, since the felt body is only pierced by needles, there is less intertwining of the fibers, which causes fluffing and hair loss during use.
In addition, fraying occurs with wear, and the service life is only 1 day.
There were only five days.

In contrast, the heat-resistant felt of the present invention, namely 1. Polyimide fibers were made into a web with card, needle pricked 3000 times/in2, and heat treated at 330°C for 30 minutes to produce a web with the same basis weight as the woven fabric, 6500g/m'', and density 0.80g/am'. A felt body was prepared and heat treated. When this was used as a tension bat in a cold rolling process, no fuzzing, hair loss or fraying occurred and a service life of 28 days could be obtained.

That is, while woven fabrics are mainly made of wool, the heat-resistant felt of the present invention is made of synthetic fibers, and the strength and high density of these fibers contribute to the increase in service life.

As explained above, the heat-resistant felt of the present application, which is formed only by high degree of fiber entanglement between fibers without using any reinforcing members, has the following characteristics: (1) Because the fibers are sufficiently entangled, the dimensions as a product are Excellent stability and shape retention, and high mechanical strength.

(2) Since processes such as resin processing, binder processing, and press working are not required, manufacturing is efficient, which is economically advantageous.

(3) Since it does not require heat fusion or chemical adhesion, it does not cause accidents such as deterioration or peeling due to inappropriate chemical affinity with the fibers to be bonded, and is therefore heat resistant. It becomes possible to select a wide variety of fibers.

(4) In addition, when low modulus high shrinkage polyimide fibers are applied, it is possible to realize a felt body with practical mechanical strength even when blended with high modulus fibers or brittle inorganic fibers, and further, This has the excellent effect of reducing the load in the web forming process and needle punching process.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and various modifications can be made without changing the gist thereof.

[Effects of the Invention] As described above, the present invention produces a primary felt body by laminating webs made of heat-resistant fiber materials with latent shrinkability that shrink under a predetermined range of thermal atmosphere conditions, and pre-entangling them with a needle bunch. The felt body is heat-treated under the above-mentioned hot atmosphere conditions to tighten the entanglement between the fibers, so it has excellent performance including heat resistance, and is also highly productive and economical. It becomes possible to realize a heat-resistant felt with good properties.

[Brief explanation of the drawing]

FIG. 1 shows thermogravimetric-differential thermal analysis (TG-differential thermal analysis) of a high-shrinkage polyimide fiber, which is an example of a high-shrinkage fiber according to the present invention.
FIG. 2 is a surface view and cross-sectional view of a microscopic photograph of sample A before heat treatment, and FIG. 3 is a surface view and cross-sectional view of a microscopic photograph of sample A after heat treatment. LIi Written amendment (voluntary) 1. Indication of the case 1986 Patent application No. 227266 2, Name of the invention Heat-resistant felt 3, Person making the amendment Relationship to the case Patent applicant address 2-14-15 Hongo, Bunkyo-ku, Tokyo Name
Ichikawa Keori Co., Ltd. Representative Kei Shimatani Part 4, Substitution Embedded ■ 151 6. Contents of the amendment (1) In the 10th line of page 4 of the specification, the phrase “comparatively low strength” was replaced with “relatively low strength.” correct. (2) On page 10, line 9 of the specification, the phrase "acid = anhydride" is corrected to "acid dianhydride." (3) “Increase hardening” on page 13, line 12 of the specification.
Correct the statement to "increase the effect." (4) "Aromatic polyamide fiber" on page 14, line 5 of the specification is deleted. (5) Table 1 on page 18 of the specification is corrected as shown in the attached sheet. (6) In lines 13 to 12 from the bottom of page 23 of the specification, the phrase "represents group C" is corrected to "represents group 0." (7) Delete "This will be heat treated" on page 28, lines 4 and 5 of the specification. 5-Object of correction 8r)

Claims (3)

[Claims] (1) A primary felt body is formed by laminating a web made of a heat-resistant fiber material with latent shrinkage that shrinks under a predetermined range of thermal atmosphere conditions, and pre-entangling it with a needle punch,
A heat-resistant felt characterized in that the felt body is heat-treated under the above-mentioned hot atmosphere conditions to tightly entangle the fibers. (2) The heat-resistant felt according to claim 1, wherein the predetermined range of thermal atmosphere conditions is between the glass transition point and maximum crystallization temperature of the fibers used. (3) The heat-resistant felt according to claim 1 or 2, wherein the latent shrinkable fiber has a shrinkage performance of 50% or more under the heat atmosphere conditions in the predetermined range.