JPH0583642B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to a method for quickly and efficiently producing carbon fibers of excellent quality using arykyl fibers as raw materials. More specifically, the present invention relates to a method for producing a high-strength carbon fiber bundle in which fibers do not coalesce or fuse together during high-temperature firing treatment. [Background Art] Ever since it was discovered that acrylic fibers are useful as raw materials for high-strength, high-elastic carbon fibers, many proposals have been made regarding production methods on an industrial scale and others. In particular, when carbon fiber is used as a reinforcing material for a composite material, a high tensile strength is required, and it is desired that its performance can be stably obtained not only as a single fiber but also as a fiber bundle. In order to satisfy these demands, the firing process that converts the raw material acrylic fiber into the target carbon fiber, that is, the raw fiber is heated in an oxygen-containing air flow.
Pre-oxidation process in the temperature range of 200-300℃,
Next, the pre-carbonization process is carried out at temperatures up to 700℃ in an inert gas stream such as nitrogen gas, and then the carbonization process is carried out at temperatures up to 2000℃ in an inert gas stream such as nitrogen gas or argon gas. It is essential to operate under appropriate conditions, while finding fibrils that more easily achieve the targeted carbon fiber performance is also a particularly important challenge. However, since the firing process for converting acrylic fibers into carbon fibers involves extensive physical and chemical changes, the causal relationship between the two is not yet clear, and many unresolved problems remain. Therefore, it is necessary to study the conditions that the acrylic fiber for carbon fiber should have or the optimum firing method, especially from an industrial standpoint. The present inventors conducted intensive studies on a method for quickly and efficiently producing carbon fibers using acrylic fibers as a raw material, and as a result, they confirmed that the first preliminary oxidation step among the above-mentioned firing steps is extremely important. That is, this step has the role of advancing the cyclization reaction and crosslinking reaction of the molecules constituting the acrylic fiber, strengthening the intermolecular bonds, and modifying the molecular structure into one that is easily transferred to the carbonization reaction. Traditionally, the preliminary oxidation process is to process the fibrils in air at 200-300%
This is carried out by heat treatment at a temperature of °C, but in order for the above reaction to proceed sufficiently, a considerably long treatment time is required, and this is a major reason for the high price of carbon fiber. . The reactions in the preliminary oxidation step, mainly the cyclization reaction of the nitrile group and the oxidative crosslinking reaction accompanying oxygen absorption, are strongly influenced by the treatment temperature, and the higher the temperature, the faster the progress. Therefore, if the aim is to shorten the preliminary oxidation time as much as possible and perform rapid firing, an important research topic is the establishment of firing technology at higher temperatures. For example, according to the inventors' study, when preliminary oxidation is carried out at 240°C in an air stream, a firing time of 1 to 3 hours is required.
At 270℃, it can be shortened to 20 to 40 minutes. Pre-oxidation gradually increases the density of the fibers, reaching a preferred point of approx.
It becomes 1.35-1.40g/ ^cm3 . On the other hand, one of the biggest drawbacks of this method of shortening the preoxidation time by increasing the preoxidation temperature is that it significantly induces coalescence or fusion between the filaments of the fibrils during the firing operation. Although the degree of this phenomenon differs depending on the composition of the fibrils, the surface structure of the fibers, the number of constituent fibers, etc., it has been found that this phenomenon occurs in most cases with ordinary acrylic fibers. Moreover, the carbon fibers obtained by subsequent carbonization of oxidized fibers that have undergone coalescence or fusion phenomena have extremely large decreases in mechanical properties, especially tensile strength, and sometimes cause problems such as breakage during the carbonization process. , clearly recognized that coalescence or fusion phenomena have a significant negative impact on the performance of carbon fibers. [Object of the invention] The present invention shortens the processing time of the preliminary oxidation step,
As a result of intensive research into a method that does not cause coalescence or fusion during firing, we solved the above problems by attaching or containing a special polysiloxane water dispersant to acrylic fibers. This is something I have discovered that can be done. A method of producing carbon fiber by firing a precursor using aminosiloxane as an oil agent has been proposed, for example, in U.S. Pat. No. 4,378,343.
The aminosiloxane adhesion precursor shown in the above invention is not yet sufficiently effective in preventing fusion during the firing process as a precursor capable of producing carbon fibers with a high strength of 400 to 600 Kg/ ^mm2 . It is said. Therefore, the present inventors have conducted studies to produce high-performance carbon fibers as described above, and have found that a specific polysiloxane is useful as an oil agent for adhering to an acrylic fiber precursor, and that it is effective when treating fibers with an oil agent. The polysiloxane in the oil adheres uniformly to the fibers and is maintained in a state where migration does not occur on the fibers during drying, and the acrylic fibers treated with polysiloxane emulsion adhere to the fibers evenly when dried. We have discovered that the above object can be achieved by firing an acrylic fiber precursor that has certain requirements, such as being difficult to turn into tar and having the effect of preventing fiber fusion and adhesion. completed. [Structure of the Invention] The gist of the present invention is to convert a polysiloxane represented by the following general formula [] into a polysiloxane represented by the general formula []
In an oil agent dispersed in an aqueous solvent with an emulsifier represented by, the amount of the polysiloxane deposited is 0.01 to 10% by weight.
The objective is to make an acrylic fiber precursor obtained by treating acrylic fibers so as to make them flame resistant, and to carbonize them to produce carbon fibers. General formula []:

[Formula R ₁ , R ₂ , R ₄ : hydrogen, alkyl group, or aryl group R ₃ , R ₅ : hydrogen or

[Formula] (R ₆ , R ₇ , R ₈ : hydrogen, lower alkyl group or aryl group) X: alkylene group or arylene group Y:

【formula】

【formula】

[Chemical formula] (R ₉ : hydrogen or lower alkyl group, R ₁₀ : hydrogen,
Lower alkyl group or aminoalkyl group, p: An integer of 20 or less R ₁₄ , R ₁₅ : H or methyl group m, n: Indicates a positive integer such that m+n≧10 and the molecular weight of the polysiloxane is 100,000 or less] General formula []:

[Chemical formula] [R ₁₁ : alkyl group, R ₁₂ : H or alkyl group, R ₁₃ : H or methyl group, q: each represents an integer of 20 or less] The acrylic fiber used in carrying out the present invention contains 90 mol% It is made from a polymer obtained by polymerizing acrylonitrile. Fibers made from polymers containing more than 10 mol% of components other than acrylonitrile generally have difficulty preventing coalescence during the flame-retardant process, worsening firing operability, and making the target carbon fiber The physical properties of the material decrease rapidly. Examples of copolymerization components other than acrylonitrile include acrylic acid, methacrylic acid, itaconic acid, acrylic acid derivatives such as methyl acrylate and methyl methacrylate, acrylamide such as acrylamide, methacrylamide, N-methylolacrylamide, and N,N-dimethylacrylamide. Derivatives, alkyl vinyl ketones such as methyl vinyl ketone and ethyl vinyl ketone, acrolein derivatives such as acrolein and methacrolein, vinyl pyridine derivatives such as 2-vinylpyridine and 2-methyl-5-vinylpyridine, sodium methallylsulfonate, and styrene. Examples include sulfonic acid derivatives such as sodium sulfonate, vinyl acetate, methacrylonitrile, and the like. These may be used alone or in combination. The acrylonitrile copolymer can be prepared using conventional radical polymerization catalysts, such as azo compounds such as azobisisobutyronitrile, peroxides such as benzoyl peroxide and lauroyl peroxide, potassium persulfate/sodium hydrogen sulfite, and ammonium persulfate/hydrogen sulfite. It can be produced by conventionally known polymerization methods using a redox catalyst such as sodium, such as solution polymerization in dimethylformamide, aqueous suspension polymerization, and emulsion polymerization. The spinning dope is usually wet-spun or dry-wet spun using a solvent-water coagulation bath. The yarn that has left the coagulation bath is manufactured into acrylic fiber through main processes such as washing, stretching, drying and densification, and further post-stretching and relaxation as necessary. It is necessary to achieve a high degree of orientation. The method for producing the fibrils of the present invention involves spinning, washing fibers in a water-swollen state (that is, before drying and densification), or drying and densifying fibers in which a specific amount of polysiloxane is emulsified and dispersed. Let it adhere. The polysiloxane used in the present invention is a polysiloxane having a specific functional group as shown by the general formula The precursor obtained by treating acrylic fibers with an oil agent containing a polyaminosiloxane having a polyaminosiloxane dispersed with a specific emulsifier and drying it has polysiloxane attached to the surface of the acrylic fibers forming an appropriate cross-linked structure. This method is preferable because extremely high-performance carbon fibers can be produced without causing migration on the surface of the fibers over time, and without any disadvantageous phenomena such as fusion or adhesion of the fibers during firing. The amount of polysiloxane deposited on the fibers is preferably in the range of 0.01 to 10.0% by weight based on the weight of the fibers. On the other hand, the emulsifier used when dispersing polysiloxanes in an aqueous medium is a compound represented by the general formula []. In the general formula [],

Polyethylene glycols and polypropylene glycols in which the group represented by [Formula] or R ₁₂ is hydrogen have a good emulsifying effect in an aqueous medium of polysiloxanes, but the precursor treated with this oil agent generates tar. It is undesirable because the flame resistance is high and disadvantageous phenomena such as fusion and adhesion between fibers are observed during the flameproofing process. On the other hand, branched alkyl ether type emulsifiers have an excellent effect of uniformly emulsifying polysiloxane into an aqueous medium, improving the uniform adhesion of polysiloxane onto the fiber surface, and reducing problems such as migration over time. It can be a precursor without. Also,

[Formula] or emulsifiers in which R ₁₂ is derived from a primary alcohol cannot be said to have sufficient dispersion power of polysiloxane in an aqueous medium, and the emulsifying stability of the oil agent is insufficient. An oil agent in which a polysiloxane is emulsified in an aqueous medium using a more derived emulsifier exhibits excellent emulsion stability. In particular, emulsifiers derived from secondary alcohols are preferred because they exhibit excellent properties.

〔Example〕

EXAMPLES The present invention will be explained in more detail with reference to Examples below. The performance of carbon fiber strands is JIS R-7601.
This is the average value measured using 10 samples with a sample length of 200 mm. Example 1 An acrylonitrile polymer prepared by an aqueous suspension polymerization method has a composition of 98 wt% acrylonitrile, 2 wt% methacrylic acid, and a specific viscosity (measured at 25°C after dissolving 0.1 g of polymer in 100 ml of dimethylformamide) of 0.18. A 24wt% stock solution was prepared by dissolving in dimethylformamide. This stock solution was subjected to dry-wet spinning, washing and stretching through a spinning nozzle with a hole diameter of 0.15 mm and a number of holes of 2000, and the moisture content was 120.
% water-swollen acrylic fibers were obtained. Next, the water-swollen fibers are treated with an emulsification bath in which the aminosiloxane represented by the following formula (1) is emulsified in water with the EO-added alcohol represented by the following formula (2), so that the amount of the fibers is reduced to 1.1% (by weight). Fiber weight ratio) adhesion,
Subsequently, drying and densification were performed. A 1.3 denier fiber a was obtained.

[Molecular weight is 15,000 and N content is 0.7%. ] C _o H _2o+1 O−(CH ₂ CH ₂ O) _n H …(2) [This compound is a mixture of various compounds, and C _o
H _2o+1 O ⁻ refers to a group derived from a secondary alcohol, n is 12 as an average value, and m is 7 as an average value. ] In addition, for a separate comparative study, polysiloxane (3) was similarly deposited, dried and densified to obtain 1.3 denier fiber b. These fibers are single yarn fluff,
No problems such as thread breakage or spreading were observed.

[Molecular weight is 15,000] Next, these fibers a and b were heated at 220℃~
After flameproofing at 260℃ for 40 minutes, in _N2 ,
Carbon fibers A and B were prepared by carbonization treatment by applying a temperature increasing gradient from 500 to 1200°C. Table 1 shows the strand performance of the obtained carbon fibers.

[Table] The yarn was spun and taken off at a speed of 5 m/min to prepare an undrawn yarn. At this time, the number of holes in the nozzle is 6000.
It was hot. This undrawn yarn was stretched 5.5 times while being washed in hot water at 98°C, further washed thoroughly in boiling water, treated with an oil agent, and stretched on a heated roll with a surface temperature of 125°C.
After drying and densification treatment, the same polysiloxanes (1) and (3) as in Example 1 were subsequently applied in the same manner as in Example 1 to obtain acrylic fibers c and d. Next, these precursors are
Carbon fibers C and D were obtained by firing in the same process as in Example 1 except for 60 minutes. Table 2 shows the strand performance of the obtained carbon fibers.

Table 2 shows that high performance carbon fibers can be obtained using the polysiloxane and emulsifier according to the invention. Example 3 The following polysiloxanes (4), (5), and (6) were attached to water-swellable acrylic fibers obtained in the same manner as in Example 1, together with the emulsifier (2).

[Molecular weight is 20,000 and N content is 0.4%. ]

[Molecular weight is 10,000 and contains approximately 1% by weight of epoxy groups]

[Molecular weight is 18,000 and contains about 3% polyether group] Next, these fibers were dried to obtain acrylic fibers e, f, and g. These fibers were fired in the same process as in Example 1 to obtain carbon fibers E, F, and G. Table 3 shows the strand performance of the obtained carbon fibers.

[Table] It was found to be extremely effective in obtaining elementary fibers. Example 4 Acrylic fibers m, n, o, p, and q represented by formula (1) and having different amounts of aminosiloxane deposited were obtained using the same process as in Example 1. Example 1
The carbon fibers M, N, O, P, and Q shown in Table 6 were obtained by carbonization in the same process as above.

[Table] The texture of acrylic fiber m is a little hard, and it is presumed that adhesion between the fibers has already occurred, but this is probably due to the fact that the amount of siloxane adhered to the fibers was too small, resulting in uneven adhesion to the fibers. Seem. Furthermore, since the fiber q had a siloxane adhesion amount of more than 10%, the single fiber was wound around the roll during the fiber spinning and winding process, and the fiber could not be wound up. Therefore, from this experiment, the amount of polysiloxane deposited is
It turns out that 0.01 to 10% by weight is a suitable range. Comparative Example Precursor H. Carbon fiber H was obtained by the same process as in Example 1 except that the emulsifier was represented by formula (7). The performance of H is shown in Table 4.

[ka]

[Table] This result shows that the properties of the emulsifier have a large effect on the performance of carbon fibers.

Claims (1)

[Claims] 1. A polysiloxane represented by the following general formula [] is dispersed in an aqueous solvent with an emulsifier represented by the general formula [], and the amount of the polysiloxane adhered to is
A method for producing carbon fibers, which comprises making an acrylic fiber precursor obtained by treating acrylic fibers to a content of 0.01 to 10% by weight, making it flame resistant and carbonizing it. General formula []: [Formula] (R ₁ , R ₂ , R ₄ : hydrogen, alkyl group or aryl group, R ₃ , R ₅ : hydrogen or [formula] (R ₆ , R ₇ , R ₈ : hydrogen) , lower alkyl _group or aryl group ₎ p: An integer of 20 or less R ₁₄ , R ₁₅ : H or methyl group m, n: Indicates a positive integer such that m+n≧10 and the molecular weight of the polysiloxane is 100,000 or less] General formula []: [C] [R ₁₁ : Alkyl group, R ₁₂ : H or alkyl group, R ₁₃ : H or methyl group, q: each represents an integer of 20 or less] 2 As a polysiloxane, it is represented by the general formula [] where Y is an aminoalkyl group A method for producing carbon fiber according to claim 1, characterized in that polysiloxane is used. _3. The _polysiloxane is a polysiloxane in which Y is The method for producing carbon fibers according to claim 1, characterized in that organosiloxane is used.