JPH026847B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an acrylic precursor fiber bundle (precursor) that is a raw material for producing carbon fiber or graphitized fiber.
Regarding. Conventionally, acrylic fibers have been widely used as raw materials for producing carbon fibers, and many attempts have been made to improve the performance, quality, and cost reduction of these carbon fibers. That is, carbon fibers are generally made by heating acrylic fibers under tension in an oxidizing atmosphere at 200 to 400°C to convert them into so-called flame-resistant yarns, and then carbonizing them by heating them in a high-temperature inert atmosphere at at least 1000°C. If desired, the acrylic fibers are further heated in an inert atmosphere at a high temperature and graphitized to produce carbon fibers or graphitized fibers. Because carbon fiber undergoes rapid chemical changes, it is usually difficult to produce large quantities of carbon fiber of constant quality and performance in a short period of time. In the above manufacturing process, the heating step in an oxidizing atmosphere, that is, the flameproofing step, oxidizes the polymer chains constituting the acrylic fibers and cyclizes the nitrile groups, thereby thermally stabilizing the structure of the fibers. As the chemical structure changes during this process, the fibers generate heat, causing fusion between single filaments and defects in the internal structure of the fibers, which may cause problems in the mechanics of the final carbon fiber. It is said that it causes not only physical properties but also quality deterioration such as fuzz and thread breakage. Therefore, in order to prevent the above-mentioned fusion or the manifestation of defects in this flame-retardant process, we have developed an acrylic fiber that is resistant to such defects by adjusting the copolymer composition of the fiber constituent polymer, spinning conditions, various oil agents, and flame-retardant fibers. Various proposals have been made regarding pretreatment, etc. One example is the firing of acrylic fibers that reduce cracks, voids, etc. that occur in the fibers by reducing the amount of residual solvent in the fibers obtained by dry-wet spinning to a certain amount or less. There are methods such as (Japanese Patent Publication No. 51-34488) and a method of attaching silicon to acrylic fibers and firing them (Japanese Patent Publication No. 12739/1983). Although each of these proposals represents a solution to the problems in charcoal fiber production, they are not necessarily sufficient. For example, in order to industrially produce carbon fiber at low cost, it is desirable to simultaneously fire multiple fiber bundles with a large number of single filaments, but in this case, it is difficult to uniformly fire the fiber bundles, and A large amount of thermal decomposition products such as tar are generated, reducing the physical properties of the carbon fiber obtained.
Otherwise, there are problems such as significant variation. In addition, an increase in the number of single yarns and fiber bundles tends to cause fusion between single yarns, generation of fuzz, and heat accumulation during firing.
As a result, it is usually difficult to stably produce carbon fibers with excellent quality and performance. It is known that the precursor to which silicone, especially silicone-based oil, is applied is effective in preventing fusion between single filaments during firing, but according to the studies of the present inventors, it is true that silicone-based oil Although it is effective in preventing inter-fusion adhesion, its adhesion to the precursor,
It was discovered that depending on the impregnation state, it does not contribute to improving the physical properties of the obtained carbon fiber. The object of the present invention is to provide an acrylic precursor fiber bundle that can be easily flame-resistant during firing, especially in an oxidizing atmosphere, has excellent mechanical properties, and has stable quality. Another object of the present invention is to provide an acrylic fiber bundle coated with a silicone oil agent, which has less mutual fusion between single yarns and less deterioration in physical properties or performance. The object of the present invention is to provide a fiber made of an acrylonitrile polymer containing at least 92% by weight of acrylonitrile and treated with a silicone oil, which has iodine adsorption as determined by the measurement method described below. The amount is approximately 1 to 3 per fiber weight.
% by weight, and the thickness of the skin layer as detected by the iodine adsorption is within the range of about 0.5 to 3μ, a single yarn fineness of 0.5 to 1.5D and a total denier of 1000 to 30000D, an acrylic precursor. This can be achieved by body fiber bundles. In the present invention, if the iodine adsorption amount exceeds about 3%, defects such as mutual fusion between single fibers and voids in the fibers are likely to occur during the flameproofing process, and on the other hand, if the iodine adsorption amount exceeds about 3%,
If the carbon fiber is less than 100%, the drawability becomes poor during the tensioning or elongation oxidation treatment in the flame-retardant process, resulting in frequent breakage of single filaments and structural defects in the flame-retardant yarn, making it difficult to produce carbon fibers with excellent mechanical properties. become. In addition, even if the skin layer thickness of the iodine-adsorbing yarn is less than 0.5μ, similar to the case where the iodine adsorption amount is less than 1%, single fiber breakage during tension or elongation oxidation treatment in the flame-retardant process, flame-retardant This causes structural destruction of the yarn, resulting in a decrease in the strength and elongation of the carbon fiber and an increase in the occurrence of fuzz. On the other hand, when the skin layer becomes large, when the swollen yarn is treated with an oil agent, the oil agent penetrates into the single fiber through the fibrils unique to acrylic fibers, inhibiting drying and densification, resulting in structural defects inside the fiber, and carbon This results in a decrease in fiber strength and elongation and an increase in fluffing. Therefore, the thickness of the skin layer should be limited to 3μ or less. Here, the amount of iodine adsorption and the thickness of the skin layer detected by iodine adsorption of the present invention are values measured by the following measuring method. (1) Measuring method of iodine adsorption amount Accurately weigh approximately 0.5 g of the dry sample and transfer it to a 200 ml Erlenmeyer flask with a stopper. Add 100 ml of iodine solution (50.76 g of I ₂ , 10 g of 2,4-diclophenol, 90 g of acetic acid and 100 g of potassium iodide, transfer to a 1 L volumetric flask and dissolve with water to make a constant volume), and add 50℃
Perform adsorption treatment while permeating for minutes. The iodine-adsorbed sample is washed under running water for 30 minutes and then dehydrated by centrifugation. Place the dehydrated sample in a 200ml beaker and dissolve with 100ml of dimethyl sulfoxide. After dissolving, the amount of iodine adsorbed is determined by potentiometric titration with an N/10 silver nitrate aqueous solution. In addition, as a method of determining the amount of iodine adsorption, the color value of the iodine adsorption sample, for example, the L value indicated by the Hunter color value may be used. However, in this case, it is necessary to calibrate the relationship between the amount of iodine adsorption and the color value. (2) Measuring method for the skin layer of iodine-adsorbing yarn After embedding 50 to 100 iodine-adsorbing yarns (filaments) in paraffin, which is a standard method for microscopic observation, the cross section of the fibers was cut using a microtome to a thickness of 6 to 9 microns. Cut it and measure the average thickness of the skin layer, which has become dark brown due to adsorption of iodine, under a 200x microscope. The reason why the amount of iodine adsorption and the thickness of the skin layer determined by the above measurement method are closely related to the performance as an acrylic precursor fiber bundle is not fully clear, but at least the amount of iodine adsorption determined by the iodine adsorption is closely related to the performance as an acrylic precursor fiber bundle. The presence of the skin layer prevents fusion between single fibers during the flameproofing process, and the double structure of such fibers is related to ease of tension or elongation during flameproofing, which is the object of the present invention. It is thought that this has an advantageous effect on the production of carbon fibers with excellent physical properties.
Furthermore, what is important is that the iodine adsorption amount and the thickness of the skin layer serve as criteria for determining the quality and performance of the precursor, and facilitate the manufacturing process of the acrylic precursor fiber bundle and the setting of its conditions. In particular, as in the present invention, the single yarn fineness is 0.5 to 1.5d,
In fiber bundles with a total denier of 1,000 to 30,000 D, it is difficult to measure the variation in physical properties among the single fibers that make up the fiber bundle, so the performance as a precursor is determined by the amount of iodine adsorbed and the presence of a skin layer. What can be done is extremely advantageous industrially. In general, as the fineness of single fibers decreases and the total denier increases, it becomes difficult to eliminate the aforementioned troubles in carbon fiber production, especially fuzzing during tension or elongation flame resistance, occurrence of yarn breakage, and fusion. As long as an acrylic precursor fiber that satisfies the iodine adsorption amount and skin layer thickness specified in the invention is used, these troubles will be resolved and the conditions for each process of flame resistance and carbonization will be easy to set. The acrylic precursor fiber bundle of the present invention is a fiber made of a homopolymer or copolymer containing at least 92% by weight of acrylonitrile (AN),
Copolymerizable components include, for example, acrylic acid, itaconic acid, crotonic acid and their lower alkyl esters, α-methylacrylonitrile, acrylamide, methacrylamide, β-hydroxyethyl methacrylate, and other unsaturated substances that are copolymerizable with AN. Examples include vinyl monomers. These AN-based polymers are those having an intrinsic viscosity [η] of at least 1.4 measured as a dimethylformamide (DMF) solution at 25°C. The method for producing the acrylic precursor fiber bundle of the present invention includes using DMF, dimethyl sulfoxide (DMSO), and the like in which the AN polymer solution has a concentration of 18 to 21% by weight.
Obtained by wet or dry-wet spinning using various solutions such as organic solvent solutions such as dimethyl acetamide (DMAC), concentrated aqueous solutions of inorganic salts such as rhodan salt and zinc chloride, and concentrated aqueous solutions of inorganic acids such as nitric acid as spinning stock solutions. However, the fiber bundle of the present invention has a single yarn fineness of 0.5 to
Since the fiber bundle has a fiber bundle of 1.5D and a total denier of 1000D or more, the wet spinning method is advantageous as the spinning method. As for the spinning conditions, the spinning stock solution is about 50 to 80%
The actual draft ratio is controlled to 2.5 to 6, preferably 2.5 to 4.5 in a spinning bath (coagulation bath) that is controlled at a temperature of 2.5 °C and kept at substantially the same temperature as the spinning stock solution temperature.
It is discharged from a spinneret and coagulated within the range of . At this time, if the temperature of the spinning dope is less than 50°C, the stretching tension in the stretching process will be excessive, and the iodine adsorption amount of the obtained precursor and the thickness of the skin layer will be small, which will fall outside the specified limits of the present invention. Not only does the strength and elongation properties of the carbon fiber obtained by firing the carbon fiber decrease, but also the occurrence of fuzz increases. Furthermore, partial structural destruction of the fibers occurs, resulting in stretching breakage and single filament breakage. On the other hand, when the temperature exceeds 80°C, the precipitated structure of the coagulated thread becomes coarse, large voids occur inside the single fiber, and the amount of iodine adsorbed in the resulting precursor and the thickness of the skin layer increase, which exceeds the specified limits of the present invention. Therefore, the strength and elongation characteristics of the carbon fiber obtained by firing the carbon fiber decrease. Furthermore, by setting the spinning bath temperature to substantially the same temperature as the spinning solution temperature, coagulation spots are reduced, the uniformity of the fiber internal structure is improved, and as a result, the performance of the carbon fiber is improved. Further, if the effective draft ratio is less than 2.5, uneven fineness occurs and single fiber breakage increases during drawing. On the other hand, if it exceeds 6, yarn breakage occurs on the spinneret surface, and the density of the coagulated yarn decreases, resulting in an excessive amount of iodine adsorption in the precursor and an excessive thickness of the skin layer. The physical properties of the carbon fibers deteriorate. The coagulated yarn formed in the spinning bath is processed as usual.
After stretching approximately 3 to 7 times in a hot water bath or hot water bath at approximately 30 to 98°C and washing with water, a silicone oil treatment is performed. must be maintained within the range of 100 to 250% by weight, preferably 150 to 200% by weight, based on the weight of dry fiber. In other words, if the silicone oil treatment is performed when the moisture content of the wet yarn is 250% by weight or more, the homogeneity of the fiber will deteriorate due to excessive penetration of the oil, and the iodine adsorption amount of the obtained precursor and the skin layer will deteriorate. The thickness becomes so large that it falls outside the specified limits of the present invention. On the other hand, if the silicone oil treatment is performed when the water content is less than 100%, insufficient penetration of the oil will cause structural destruction inside the fiber during stretching, resulting in a decrease in the physical properties of the carbon fiber. As mentioned above, this silicone oil treatment is related to the amount of iodine adsorbed in the fibers and the thickness of the skin layer, which are the characteristics of the present invention. Therefore, sufficient consideration should be given to the type of silicone oil and the amount of the silicone oil applied. In other words, silicone oils include, for example, polyether-modified polysiloxane (polydimethylpolysiloxane ethylene oxide copolymer), alcohol-modified polysiloxane, amino-modified polysiloxane, dimethylpolysiloxane used in combination with some emulsifiers, and alkyl-modified polysiloxane. etc. is desirable. Also, the amount of silicone oil adhered is usually about 0.1 to 5.
It is preferably within the range of % by weight. The wet yarn that has been treated with a silicone oil agent needs to be subsequently subjected to drying and densification treatment, but the means and conditions for this may be the same as conventional methods. For example, at about 100 to 200 ° C. This is carried out using a plurality of heated rolls (or heated drums) or hot air, and at that time, it may be relaxed by about 0 to 10% if necessary. Next, the dried and densified yarn is subjected to secondary stretching in pressurized steam, and further dried if necessary. As for the stretching conditions at that time, the steam pressure should be about 1 to 6 kg/cm ² G, and the stretching ratio should be in the range of at least 8 times as a total stretching ratio, preferably 8 to 16 times. At this time, if the stretching ratio is 8 times or less, the degree of fiber orientation of the precursor decreases, the amount of iodine adsorbed and the thickness of the skin layer become excessive, and the strength and elongation of the carbon fiber obtained from the precursor decreases. On the other hand, if it is 16 times or more, single filament breakage occurs frequently during drawing, which is inappropriate as an operating condition. In addition, regarding the detailed conditions of the above yarn spinning process, the tensile strength and elongation is at least 6 g/d and 10 to 13
It is preferable to select the fiber bundle so as to form a fiber bundle of . As mentioned above, the acrylic precursor fiber bundle of the present invention thus obtained is a carbon fiber manufacturing fiber material,
In other words, it has many excellent properties as a precursor, and can be easily subjected to oxidation treatment during flame resistance and carbonization processes, especially under tension or elongation to improve physical properties. Since the occurrence of fusion, fuzz, and thread breakage can be effectively prevented, carbon fibers with excellent mechanical properties can be stably produced. An example of the physical properties of the carbon fibers stably obtained from the acrylic precursor fiber bundle of the present invention is that the tensile strength and elongation of the resin-impregnated strands of the carbon fibers are at least 380 Kg/mm ² and 1.7% or more, respectively. be. Hereinafter, the present invention will be explained in more detail with reference to Examples. Example 1 Acrylonitrile (AN) 99.7% and acrylic acid
A copolymer consisting of 0.3% was dissolved in dimethyl sulfoxide (DMSO) to give a polymer concentration of 19.5% by weight.
A spinning stock solution with a temperature of 65℃ was prepared, and
It was discharged at an effective draft ratio of 3.5 into a coagulation bath of a 55% aqueous solution of DMSO maintained at 65°C. At this time, the spinneret has a diameter of 0.06 mmφ,
A hole with 1500 holes was used. After washing the coagulated yarn with water and stretching it in hot water, the wet yarn was stretched 4.5 times so that the moisture content of the wet yarn was approximately 200%, and then immersed in a silicone oil bath with a silicone oil concentration of 8%. Then, it was dried and densified on a heated drum with a surface temperature of 130°C. The obtained dried yarn bundle was stretched 2.8 times in pressurized steam at a pressure of 4 kg/ ^cm2 ,
Dry again to obtain single yarn fineness of 1d and total denier.
A fiber bundle of 3000D was obtained. This fiber bundle is 6.3g/d
It has a tensile strength of 12.3% and an elongation of 12.3%, and when this fiber bundle is air-treated, it is easily separated and opened into single fibers, and there is no fusion or pseudo-fusion between the single fibers. It turned out that. Next, the amount of iodine adsorbed in the fiber bundle and the presence of a skin layer were examined, and the thickness thereof was measured. As a result, the amount of iodine adsorbed was 2.0% and the thickness of the skin layer was 2 μm. The fiber bundle thus obtained was heated to 230°C, 240°C and
Heat it for about 40 minutes under a tension of 0.2 g/d in a three-stage hot air circulation heating furnace maintained at a temperature of 250°C to make it flame resistant, then heat it from 300°C to 1250°C in a nitrogen atmosphere at a rate of 800°C. Carbonization took 5 minutes at a speed of 5 minutes. The physical properties of the resin-impregnated carbon fibers were
Measured according to JIS-R-7601. The results are shown below. Tensile strength (Kg/mm ² ) 468 Elongation (%) 1.86 Initial elastic modulus (ton/mm ² ) 25.1 Example 2 Acrylic fibers were prepared in the same manner as in Example 1 except that the coagulation bath temperature was changed. Created a bundle. Table 1 shows the physical properties of the obtained fiber bundle, the amount of iodine adsorbed, and the thickness of the skin layer of the iodine adsorbed yarn. Table 1 also shows the physical properties of carbon fiber bundles obtained by firing these fiber bundles in the same manner as in Example 1.

[Table] *During drawing, spinning was impossible due to frequent single yarn breakages.
Example 3 An acrylic fiber bundle was produced in the same manner as in Example 1 except that the spinning draft ratio was changed. Table 2 shows the physical properties of the obtained fiber bundle, the amount of iodine adsorbed, and the thickness of the skin layer of the iodine adsorbed yarn. Table 2 also shows the physical properties of charcoal fiber bundles obtained by firing these fiber bundles in the same manner as in Example 1.

【table】

[Table] * Large unevenness in fineness and frequent breakage of single filaments during drawing.
Example 4 An acrylic fiber bundle was created in the same manner as in Example 1, except that the secondary draw ratio under pressurized steam was changed in Example 1 (however, the primary draw ratio in a hot water bath was 4.5 ). Table 3 shows the physical properties of the obtained fiber bundle, the amount of iodine adsorbed, and the thickness of the skin layer of the iodine adsorbed yarn. Table 3 also shows the physical properties of carbon fiber bundles obtained by firing these fiber bundles in the same manner as in Example 1.

[Table] *During drawing, spinning was impossible due to frequent single yarn breakages.
Comparative Example 2 Table 4 shows the physical properties, iodine adsorption amount, and yarn skin layer thickness of the fiber bundle in which 2% of the organic oil stearyl alcohol ethylene oxide adduct (20 mol) was attached instead of the silicone oil in Example 1. Table 5 also shows the quality of the charcoal fiber bundles obtained from the fiber bundles.

【table】

【table】

Claims (1)

[Claims] 1 Fibers made of an acrylonitrile polymer containing at least 92% by weight of acrylonitrile and treated with a silicone oil, with an iodine adsorption amount of about 1 to 3% by weight per fiber weight, and Single yarn fineness 0.5 with skin layer thickness detected by adsorption within the range of approximately 0.5-3μ
Acrylic precursor fiber bundles of ~1.5d and total denier 1000-30000D.