JPH0791749B2 - Dense carbonaceous fiber structure - Google Patents

Abstract

A fibrous structure comprising a multiplicity of nonflammable, nonlinear, substantially irreversibly heat-set, first carbonaceous polymeric fibers, and at least one second nonflammable carbonaceous polymeric fiber, yarn or tow in an interlocking relationship with said first fibers; the fibrous structure is preferably densified and has a bulk density of from 4.8 to 32 kg/m<3>, and a process for producing the interlocked, fibrous structure useful as a thermal insulating and/or sound absorbing structure.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a first multiplicity of non-combustible, non-linear elastic, extensible, substantially irreversibly heat-set carbonaceous polymer fibers, which are carbonaceous polymer precursor materials. Of entangled second fibers and then heat treating the entire structure to heat set the second fibers to produce a fibrous structure.

The fibrous structure of the present invention has thermal insulation and / or sound insulation applications and overwhelming utility. These structures are preferably concentrated and have good shape and volume retention properties and are structurally stable to multiple compression and load release cycles. These structures, which have a relatively high densification (compared to non-structures), have a surprisingly felt-like appearance and very low breaking fibres.

This large number of carbonaceous fibers are used to make wooly, pilus-like materials, felts, webs, blankets, butterings, etc., and these fibers are hereinafter referred to as "fibrous structures". When a fibrous structure is densified by planting with a second fiber, the structure is referred to herein as a "densified fiber structure" or simply "densified structure".

The term "planting" as used herein generally refers to the method by which fibers are entangled, intermingled with each other, or entangled with each other. Preferably, the fibrous structure of the first fiber is sewn together with the second fiber by stitching the fibrous structure.

For many high temperature insulation applications, highly densified fibrous structures (ie wool-like fimbriae or butting)
It is desirable to manufacture so that it retains its integrity and its densification over extended exposure to high temperatures. The densified structure is useful at elevated temperatures above 400 ° C and retains good mechanical and physical properties.

The non-combustible non-linear elastic carbonaceous fiber suitable for producing the fibrous structure of the present invention is EP 0199567 (issued October 29, 1986; title of invention: Carbonaceous Fibers with Spring-L).
ike Reversible Deflection and Method of Manufactur
e; Inventor Matsukarafu et al.). Prior to the present invention, it was not possible to permanently densify the fibrous structure of the non-linear carbonaceous fibers and to maintain the integrity of the densified fibrous structure at temperatures above 400 ° C. .

At temperatures above 400 ° C., fibers made from the above carbonaceous polymeric materials (including non-combustible p-aramid fibers) will decompose, thus causing the fibrous structure to lose its integrity. Therefore, it is of considerable advantage to be able to permanently densify and retain a fibrous structure with polymer fibers that do not lose their physical structure at elevated temperatures.

U.S. Pat. No. 4,628,846 (Inventor Vibes) describes an apparatus that can be utilized to manufacture the fibrous structure of the present invention.

The present invention provides a number of non-combustible, non-linear, substantially irreversibly heat-set, elastic, shape-reproducible and extensible 1.2: 1.
First with greater deflection ratio and aspect ratio greater than 10: 1
A carbonaceous polymer fiber and at least one second non-combustible, substantially irreversibly heat-set, which is planted in entangled relationship with the first fiber to form an entangled fibrous structure. And a carbonaceous polymer fiber, yarn or tow.

Preferably, the present invention is directed to at least one of a wooly, pilus-like material, butting or web wherein the first carbonaceous fiber has a sinusoidal or coiled form and the fibrous structure is non-woven.
In the form of layers and in a fibrous structure in which the second carbonaceous fibers, yarns or tows have a linear or non-linear morphology and a higher denier than the first carbonaceous fibers.

Advantageously, the second entanglement carbonaceous fiber is chemically similar to or the same as the first carbonaceous fiber of the fibrous structure.

The invention further relates to a densified fibrous structure having a bulk density of 4.8 to 32 Kg to m ³ .

The present invention also relates to a method of making a fibrous structure from a number of non-combustible, non-linear, substantially irreversibly heat-set first carbonaceous polymer fibers, the method comprising: Planting at least one non-heat-set second carbonaceous polymer fiber, yarn or tow in entangled relationship with the first fiber and then heat treating the fibrous structure in an inert atmosphere. And heat setting the entangled second fibers, yarns or tows.

The method of the present invention also enables the fibrous structure of the first fiber to be seeded and blended with a large diameter second carbonaceous polymer precursor fiber that has high shear resistance to, for example, needle punching operations. . Carbonaceous fibers having a relatively high denier can also provide high mechanical strength.

According to a preferred embodiment of the present invention, the first heat-set non-linear carbonaceous polymer fiber is planted by needle punching with a second fiber, yarn or tow produced from a carbonaceous precursor material. Increase the bulk density and mechanical strength of the fibrous structure. The needle punch causes the second fiber to make a loop in the fibrous structure.

Heat treatment of the fibrous structure creates a hook in the loop seam.
Advanced needle punches can be used to create densified structures with a felt-like feel and appearance after heat treatment.

According to a further aspect of the invention, more than one fibrous structure, such as a batting, can be joined together. One of the battings can be used as the entanglement fiber of the other batting.

The first carbonaceous fibers preferably have a sinusoidal or coiled morphology or have a complex structural combination with the two. These first fibers may include linear heat-set carbonaceous polymer fibers.

The carbonaceous fibers used in the present invention have a carbon content of at least 65% and a nitrogen content of 5-35%. These fibers are specifically identified for their degree of carbonization and / or their electrical conductivity in determining the most suitable application.

The first carbonaceous fiber or fiber matrix is derived from a suitable stabilized carbonaceous polymer precursor material; eg, a stabilized polyacrylonitrile (PAN) based material, or a pitch based material, ie petroleum or coal tar pitches. Produced by heat treating a carbonaceous precursor material derived from a non-combustible, thermally stable carbonaceous fiber or other polymeric material that can be converted into a fibrous structure.

For example, in the case of PAN substrate fibers, these fibers are made by melting or wet spinning a suitable fluid of precursor material and have a nominal diameter of 4 to 25 microns. These fibers are collected as an aggregate of multiple carbonaceous filaments in the form of tows and, in the case of PAN-based fibers, stabilized by conventional methods. Stabilized fibers, tows or staple yarns (made from cut or stretch-broken fiber samples) are then coiled and / or sine by knitting the fibers, tows, or yarns into a woven fabric or cloth. Formed in a wave shape (it will also be appreciated that other textile and coil forming methods may be used).

The fabric or fiber thus produced is then heat-treated in an inert atmosphere at a temperature of 525-750 ° C. for a time in a relaxed or unstressed state to cause a heat-induced heat setting reaction, Cross-linking and / or cross-chain cyclization reactions occur between the original polymer chains. 150-525
525-750, although at low temperatures of ℃, the fibers are given various degrees of fixation, from temporary to permanent fixation.
At elevated temperatures of 0 ° C., the fibers are imparted with a substantially permanent or irreversible heat setting morphology. The term "permanent" or "irreversible heat setting" also means that once a non-linear fiber has been stretched into a substantially linear shape without exceeding its original internal tensile strength, it releases its stress. It means that it has an irreversibility of returning to a non-linear shape with. The fibers heat treated by the above method can be stretched into a substantially linear shape, yet relieve the stress and return to the non-stretched, non-linear shape. Such stretching of the fibers can be done over many cycles without breaking the fibers, and imparts additional tension (without exceeding the tensile strength of the fibers) to a substantially linear form. The same is true even when added to a fiber.

If the heat treatment is carried out while the coiled and / or sinusoidal fibers are relaxed or stress-free and under an inert, non-oxidizing atmosphere, the fibers may initially be heat treated at a temperature in the high temperature range. Of course it should be understood. As a result of the high temperature treatment in the range of 525-750 ° C, a permanently fixed sinusoidal or coiled morphology is imparted to the fiber, tow or yarn. The resulting fibers, tows or yarns having a non-linear structural morphology (which can be derived by unraveling a knitted fabric) are subjected to other processing methods known in the art to open, ie, tow or fabric. It is possible to separate the fibers into entangled wool-like pili-like materials and to make a method in which the individual fibers retain their coiled or sinusoidal morphology resulting in a fairly lot of fibrous structure.

Stabilized fibers that have been permanently fixed in the desired structural form, for example by knitting and then heating at temperatures above 525 ° C in a relaxed and unstressed state, retain their elastic and reversible flexural properties. To do. High temperatures up to about 1500 ° C can be used, but when carding the fibers to make a fluffy material, the most flexible fibers and the minimum fiber breakage loss is in fibers heat treated to a temperature of 525-750 ° C. It should be understood that it is found in.

The second carbonaceous fibers used in the present invention include fibers that can be entangled with the first fibers of the fibrous structure and that can withstand the high temperatures described above. The second fiber can be derived from another yarn, can be a fiber of adjacent battering, or can be blended with the first fiber to form a wool-like pilus-like material or battering. It can be hot and can be used for densification.

Preferably, the entangled second fibers can be made from the same or similar stabilized carbonaceous polymer precursor material as the first fibers. For example, suitable stabilizing precursor materials are PAN or Pitch-based materials (eg, petroleum or coal tar), or other polymeric materials that are thermally stable to the high temperatures of interest described above, such as aramid fibers and especially aromatic polyaramids. It can be selected from KEVLAR (trademark of E-I-Deupon de Nemours & Company, Incorporated).

PAN-based fibers can be collected as an aggregate of multiple continuous filament tows and stabilized by conventional oxidation. The stabilized second fiber, tow or staple yarn (cut or stretch-broken fiber staple) is then planted on the first carbonaceous fiber by the method of the present invention to form a fibrous or densified structure. Can be made.

When planted in a carbonaceous fiber structure, the second carbonaceous fiber can be incorporated into the structure as linear or non-linear fibers before it is permanently heat set.

The second non-linear fibers are these fibers in an inert atmosphere 150
It can be produced in the same manner as the first fiber by imparting temporary fixing to the fiber by heat-treating it in a relaxed or unstressed state in the temperature range of ˜525 ° C. These fibers are provided with varying degrees of temporary to permanent fixation with increasing temperature in a particular temperature range. These fibers are then permanently fixed by chemical treatment or by heat treatment of the fibrous structure after the entanglement step. Preferably, the heat treatment is performed at a temperature of 525 ° C. or above to provide the fiber with a permanent set.

When the second carbonaceous fiber is permanently heat set, the first
And a second carbonaceous fiber, which provides integrity and handleability to the fibrous structure.

As with the first fiber, temperatures up to about 1500 ° C can be used to provide permanent fixation to the second fiber,
The most pliable and the least fiber breakage loss is found in fibers heat treated to temperatures of 525-750 ° C.

Entangled fibrous structures are utilized in high temperature insulating and sound absorbing structures and can be classified into three groups depending on the particular application and environment in which the structure is encased.

In the first group, the carbonaceous fibers used in the fibrous structure of the present invention are electrically non-conductive. Non-conductive refers to resistance greater than 4 x 10 ⁶ ohms / cm when measured on 6K tow fibers each having a diameter of 7-20 microns. The specific resistance of each fiber is about
Greater than 10 ² ohm / cm. A 6K tow is a tow made up of 6,000 fibers.

In the second group, the carbonaceous fibers used in the fibrous structure of the present invention are classified as partially electrically conductive (ie having low electrical conductivity) and have a carbon content of less than 85%. Hold. When the precursor stabilizing fiber is an acrylic fiber, that is, a PAN base fiber, the nitrogen content is 5 to 35%, preferably 16 to 20%. These partially electrically conductive fibers are excellent for use as aerospace vehicle insulation, as well as insulation in areas of public safety interest. Structures made from these are lightweight, have low moisture absorption, good attrition strength, and good appearance and handleability.

The higher the carbon content in the carbonaceous fiber, the higher the electrical conductivity. Such fibers, when formed into a dense structure,
Especially when most of the fibers are non-linear or coiled,
It still retains a wooly appearance. Also, the greater the percentage of coiled fibers in the structure, the greater the elasticity of the structure. As a result of the high carbon content, structures made using these partially conductive fibers also have high sound absorption,
And it provides a more effective thermal barrier at high temperatures. These fibers are 4 × when measured on 6K tow fibers where each fiber has a diameter of 7-20 microns.
It has an electrical resistance of 10 ⁶ to 4 × 10 ³ ohm / cm.

The third group are carbonaceous fibers with a carbon content of at least 85%. These fibers have excellent thermal insulation and sound absorption properties as a result of their high carbon content. The coiled or sinusoidal features of the fibers in the fibrous structure provide good compressive and elastic insulation while retaining improved insulation efficiency. Fibrous structures made with the third group of fibers have particular application in furnace insulation and high temperature and noise areas.

Preferably, the third group of fibers used is derived from stabilized acrylic fibers and has a nitrogen content of less than 10%.
As a result of the higher carbon content, the fibrous structure is more electrically conductive. That is, its electrical resistance is less than 4 × 10 ³ ohms / cm as measured on 6K tow fibers where each fiber has a diameter of 7-20 microns.

Precursor-stabilized acrylic fibers that are advantageously used in the production of fibrous structures are selected from acrylonitrile homopolymers, acrylonitrile copolymers and acrylonitrile terpolymers. The copolymer preferably comprises at least about 85 mol% acrylonitrile units and up to 15 mol% of one or more monovinyl units copolymerized with styrene, methyl acrylate, methyl methacrylate, vinyl chloride, vinylidene chloride, vinyl pyridine and the like. . The acrylic filament may also consist of a terpolymer with acrylonitrile units preferably at least about 85 mol%.

It is also possible that the carbonaceous precursor starting material may have electrical conductivity on the order of metallic conductors attached thereto by heating the fibrous structures to temperatures above about 1000 ° C. in a non-oxidizing atmosphere. It should be further understood. Electrically conductive starting materials such as Pitch (petroleum or coal tar), polyacrylonitrile copolymer (PANOX
Alternatively, it can be obtained from GRAFIL-01), polyphenylene, polyvinylidene chloride (Saran; trademark of The Dow Chemical Company), or the like.

According to a feature of the invention, antistatic fibers, i.e. fibers capable of dissipating electrostatic charge, can be inserted into the fibrous structure and also serve as entanglement and densification fibers. .

The preferred precursor fibers are made by melt or wet spinning the precursor material in a well known manner to produce a monofilament or multifilament tow. These fibers, yarns or tows can then be woven or knitted by any of a number of commercially available techniques. The woven or knitted material is then heated to a temperature above about 525 ° C., preferably above 550 ° C., after which it is knitted, carded, and used in the fibrous structure of the present invention for wool-like pilus-like materials. Is generated.

If desired, the densified fibrous structure can be heat treated to a carbon or graphite structure. The method of the present invention allows the production of carbon or graphite structures without complicated knitting operations.

It should be understood that all percentages used herein are percentages by weight.

The carbonaceous fiber preferably used in the present invention has the test method ASTM D2.
With LOI value greater than 40 as measured by 863-77. This test method is also known as the "oxygen index" or "limited oxygen index" (LOI). This test method determines the oxygen concentration in an O ₂ / N ₂ mixture as a vertically mounted sample ignites and burns at its upper end. The dimensions of the sample are 0.65 x 0.35 cm and the length is 7-15 cm. LOI is calculated by the following formula.

Specific embodiments of the present invention are shown in the following examples.

Example 1 A. Tow of non-linear carbonaceous fibers heat-treated at 550 ° C. was opened with a Shearley opener and obtained from RK Carbon Fibers Inc. of RK Carbon Fibers Incorporated of Philadelphia, PA, USA. Oxidized PAN fiber) blended with 25%. Dog bone OPF is 200 before blending
It had a temporary crimp fixed at a temperature of ° C. The battering was mixed and run on a needle punch machine to densify the precursor fiber from a thickness of 7.5 cm to a thickness of 1.8 cm.

B. Producing thickened butting or felt from A above, including sewing with dog bone type OPF entangled, under nitrogen atmosphere 70
Heat treatment was performed at 0 ° C. for 60 minutes. The resulting thickened butting or felt has good permanent integrity at 400 ° C.
It was stable at the above temperatures.

Example 2 A densified batting was prepared according to the method of Example 1, A. The batting formed is then 60 at a temperature of 1500 ° C.
After heat treatment for a minute, a uniform carbon structure suitable as a soundproofing and heat insulating material was obtained.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Goswami, Bubenssee South Carolina, United States 29631 Clemson Strawberry Lane 200 (56) References JP-A-55-101224 (JP, A) JP 60-52207 (JP, B2) JP 58-51056 (JP, B2) JP 1-503243 (JP, A)

Claims (24)

[Claims] 1. A number of non-combustible, non-linear, substantially irreversibly heat-set, elastic, shape-reproducible and extensible 1.2:
First carbonaceous fibers having a deflection ratio greater than 1 and an aspect ratio greater than 10: 1 and having a sinusoidal or coiled morphology, and fibers entangled in entangled relationship with the first fibers Comprising at least one second non-combustible substantially irreversibly heat-set carbonaceous fiber, yarn or tow forming a quality structure, the first and second carbonaceous fibers being stable A fibrous structure which is derived from a modified polymer precursor material. 2. The structure according to claim 1, wherein the entangled fibrous structure is densified and has a density of 4.8 to 32 kg / m ³ . 3. The structure of claim 1 wherein the first and second carbonaceous fibers are derived from a stabilized polymer precursor fiber or pitch substrate precursor fiber having a diameter of 4 to 25 microns. 4. Polymer precursor fibers are acrylic fibers selected from acrylonitrile homopolymers, acrylonitrile copolymers and acrylonitrile terpolymers, the copolymers and terpolymers being at least 85.
A structure according to claim 3 comprising mol% acrylonitrile units and up to 15 mol% of one or more monovinyl units copolymerized with another polymer. 5. A structure according to claim 1, wherein the carbonaceous fibers have a carbon content of more than 65% and a limiting oxygen index value (LOI value) of more than 40. 6. A 6K tow fiber consisting of 6,000 fibers, the carbonaceous fibers being electrically conductive, having a carbon content of at least 85%, and each fiber having a nominal diameter of 7 to 20 microns. The structure of claim 5 having an electrical resistance of less than 4 x 10 ³ ohms / cm. 7. The carbonaceous fibers are electrically non-conductive or non-static dissipative, have a carbon content of less than 85%, and each fiber has a nominal diameter of 7-20 microns. 6,
6. An electrical resistance of greater than 4 × 10 ³ ohms / cm when measured on a 6K tow fiber consisting of 000 fibers.
The described structure. 8. A 6K carbon fiber having low electrical conductivity and low static dissipative properties, and a carbon content of less than 85%, and each fiber having a nominal diameter of 7-20 microns and 6,000 more fibers. 4 × 10 ⁶ when measured on tow fiber
4 × 10 ³ ohms / cm claim 5 Structure according with the electrical resistor. 9. The fibrous structure is in the form of a non-woven wool-like fluff, batting or web, and the second carbonaceous fiber is in a linear or non-linear form and the first carbonaceous fiber. A structure according to any one of claims 1 to 8 having a higher denier. 10. A structure according to claim 1, wherein the carbonaceous fibers have a nitrogen content of 5 to 35%. 11. A method of making a fibrous structure from a first carbonaceous fiber having a number of non-combustible non-linear, substantially irreversibly heat-set and having a sinusoidal or coiled morphology. And a second carbonaceous polymer fiber derived from at least one non-heat-set and stabilized polymer precursor material to a first fiber derived from a stabilized polymer precursor material , Planting the yarn or tow in entangled relationship with the first fiber, and then heat treating the fibrous structure in an inert atmosphere to heat set the entangled second fiber, yarn or tow. A method for producing a fibrous structure, comprising the steps of: 12. A second fiber, yarn or tow is irreversibly heat set to form a carbonaceous fiber, yarn or tow which is similar or identical in composition to the first heat set carbonaceous fiber. 12. The method of claim 11 made from a possible precursor carbon polymer material. 13. The second fiber is heat treated at a temperature above 525 ° C. in an inert atmosphere, wherein the fiber structure is an acrylic fiber and the second non-heat set entangled fiber is heat treated. 13. A method according to claim 11 or 12 including the step of imparting permanent fixation to the yarn or tow. 14. The fibrous structure is in the form of a wooly fluff, mat, felt or batting, and the second fiber, yarn or tow is 4.8-32K.
13. The structure is present in a structure so as to be enriched in g / m ³ to give the structure integrity and manageability.
Or the method described in 13. 15. The method according to claim 11, wherein the implantation of the second fibers into the first fibers is achieved by needle punching. 16. The second carbonaceous fiber is selected from fibers having the same or different composition as the first carbonaceous fiber.
15. The method according to any one of 15 to 15. 17. A method according to any one of claims 11 to 16, wherein the second planted fibers are derived from battering. 18. The method according to claim 11, wherein the second fibers are linear or non-linear fibers. 19. The method according to claim 11, wherein the fibrous structure comprises a plurality of buttings. 20. The at least one butting comprises carbonaceous fibers having a carbon content of at least 85%.
The method described. 21. The method of claim 19, wherein at least one butting comprises linear fibers. 22. The method according to claim 10, wherein the carbonaceous fibers have a nitrogen content of 5 to 35%. 23. A first sine wave or coil derived from oxidized polyacrylonitrile having a reversible deflection ratio greater than 1.2: 1, an aspect ratio greater than 10: 1, and a limiting oxygen index value greater than 40. Providing a first butting of a non-linear elastic shape reproducible stretchable non-combustible heat-set carbonaceous fiber having a linear morphology;
Overlaying at least one second batting of polyacrylonitrile fibers on the first batting as described above; entanglement of polyacrylonitrile fibers from the second batting with heat set fibers of the first batt; and thereafter. A step of heat treating the entire densified structure to heat set the second battering substantially permanently. 24. The method of claim 23, wherein the carbonaceous fibers have a nitrogen content of 5-35%.