JPS6231088B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a porous cellulose acetate fiber having a large number of fine pores inside the fiber, and a method for producing the same. Porous materials can be given various functions by utilizing their internal space and incorporating various substances within the pores.For example, they can be used to purify water by incorporating substances with ion exchange ability. I can do it. On the other hand, by utilizing the large internal surface area, it is possible to provide a material in which the surface properties of the material, such as the ability to adsorb a specific substance, are greatly improved. In particular, fibrous porous materials have the advantage of being easy to handle and mold into various shapes, and it is desirable to develop porous fibers using various materials, such as polyethylene, polypropylene, nylon, polyester, etc. Various porous techniques have been proposed for acrylic, acrylic, and the like. The present inventors have repeatedly conducted various studies regarding making cellulose acetate-based cells porous, particularly regarding methods for producing porous fibers. That is, the cellulose acetate fiber produced by the conventional dry method has a dense structure and has an extremely small surface area, so that it cannot be effectively used for the above-mentioned adsorbent applications. The present inventors focused on imprinting using a wet method, and as a result of their studies, they arrived at the present invention. That is, the present invention relates to cellulose acetate containing micropores or fibers mainly composed of cellulose acetate, which have an internal surface area of 15 m ² /g or more and are substantially free of macrovoids with a pore size of 5 μ or more. , and the average pore diameter of the micropores inside the fiber is 1
The purpose of this is to obtain porous cellulose acetate fibers characterized by having micropores uniformly throughout the interior of the fibers, the size of which is less than μ. Using a spinning dope in which a polymer mixture is dissolved in a solvent, an aqueous solution of the solvent maintained at a temperature of 25 to 75°C is used as a coagulant, and the effective draft ratio shown in the following formula (1) is in the range of 0.2 to 0.6. A method for producing porous cellulose acetate fiber characterized by wet spinning and then drying. Effective draft rate = Adopted draft / Maximum draft...(1
) However, maximum draft refers to the maximum spinning draft that can be applied without fiber breakage. The present invention will be explained in detail below. The cellulose acetate used in the present invention is composed of cellulose acetate such as cellulose diacetate and cellulose triacetate, a mixture thereof, or a cellulose acetate containing these acetates as a main component. The main component means that it may contain other polymers other than cellulose acetate, and these polymers are not limited in any way, but are preferably 20 wt% or less based on cellulose acetate.
May be present in amounts up to 10wt%. The action of these polymers serves to uniformly generate minute pores in the fibers. Further, this cellulose acetate is also formed from cellulose diacetate and cellulose triacetate alone or in combination. Especially the degree of acetylation is 58
% or more of cellulose triacetate provides porous fibers with a large surface area in which micropores are maintained uniformly even after drying. According to the method of the present invention, it does not contain macrovoids with a pore diameter of 5μ or more, and has an internal surface area of 15m ² /g.
As described above, it is possible to efficiently obtain porous cellulose acetate fibers in which the average diameter of micropores is 1 μm or less. FIG. 1 shows porous fibers other than the present invention shown for comparison, and FIG. 2 shows the fibers of the present invention. Both are electron micrographs of cross-sections of fibers, and they have fine pores uniformly throughout the inside of the fibers.
The fiber shown in Figure 1 contains two cavities (macrovoids) with a pore diameter of 5 μm or more inside, and such fibers have a small internal surface area and also have a reduced strength, making them difficult to use as adsorbents. It cannot be used effectively. On the other hand, the fiber of the present invention shown in FIG. 2 does not contain macrovoids inside and has a large surface area and strength. This surface area depends on the size of the pores and the porosity, but when the porosity is constant, the smaller the pore size, the larger the surface area. Regarding applications such as adsorbents, the larger the surface area that can act as an adsorption seat, the more effective it is. In the present invention, the average pore diameter is defined as 50% of the normalized integral curve of the pore volume measured by mercury intrusion method.
is defined as the value twice the hole radius. FIG. 3 is an integral curve of the normalized pore volume measured by the mercury intrusion method of the porous fiber shown in FIG. The pore radius corresponding to 50% of the integrated pore volume is 540 Å,
The average pore diameter is 540×2=1080 Å (0.108 μ).
When this average pore diameter is 1 μm or less, preferably 0.5 μm or less, the surface area becomes large, resulting in a porous fiber with high strength. Internal surface area of 15 m ² /g or more, and average pore size of 1
The porous cellulose acetate fiber of the present invention having a particle diameter of less than μ contains many fine pores as shown in FIG. 2, has strength, and can be used for various purposes other than fibers for clothing. In other words, the fiber can be used as an adsorbent for trace components contained in solutions or gases, as a support for the controlled release of medicines, agricultural chemicals, etc. by encapsulating them in micropores, and for other commonly thought of porous applications. It can be used while maintaining its shape. Next, the method for producing the fiber of the present invention will be described. A mixture of cellulose acetate or other polymers is dissolved in a solvent using a suitable device, and thoroughly filtered and defoamed to obtain a spinning stock solution. Examples of the solvent include acetone, ethylene carbonate, dioxane, dimethylacetamide (DMAc), dimethylformamide (DMF), dimethylsulfoxide (DMSO), and the like. Polymer concentration is 10~
30wt% is applied. The stock solution thus obtained is
It is kept at a temperature of 30 to 100°C and used for spinning. The coagulation bath is mainly composed of an aqueous solution of the solvent. The term "main body" means that it may contain small amounts of other dissolved components, such as organic substances such as alcohols, or inorganic salts, depending on the purpose. One of the features of the present invention is that the temperature of the coagulation bath is 25°C to 75°C.
℃, preferably 30℃ to 65℃. At temperatures below 25°C, the structure of the coagulated filaments becomes dense, making it difficult to form a fibrous structure with a large surface area. on the other hand
When the temperature exceeds 75° C., the solidification rate increases rapidly, and the volume shrinkage accompanying solidification does not occur, resulting in an extremely rough structure with large cavities, which ultimately does not contribute to the increase in surface area that is the aim of the present invention. The maximum draft defined in the present invention is a value uniquely determined by the type of cellulose acetate, the concentration of the spinning dope, the nozzle diameter of the spinneret, the discharge speed of the spinning dope in the nozzle, the concentration and temperature of the coagulation bath. It refers to the maximum spinning draft (ratio of the winding speed and the discharge speed of the spinning stock solution in the nozzle) that can be applied without breaking the fiber when wet spinning is performed with each of these factors determined, and this is the maximum spinning draft that can be applied without breaking the fiber when each of these factors is determined. It can be simulated by actually spinning the yarn under the specified conditions, gradually increasing the winding speed, and calculating the spinning draft from the winding speed at which yarn breakage occurs. In this way, the above-mentioned stock solution is subjected to wet spinning in the coagulation bath, and at this time, the draft is set to an effective draft ratio in the range of 0.2 to 0.6 as shown in the above formula (1). If this value is less than 0.2, sagging occurs in the spinning bath, making stable spinning difficult, and if it exceeds 0.6, a large amount of macrovoids similar to those caused by high-temperature coagulation described above will occur in the yarn, which is undesirable. The spun yarn is washed in warm water or hot water as necessary, or stretched, coated with a suitable oil, and then dried to produce the fiber of the present invention. The drying temperature range is from room temperature to about 200°C, but there is almost no change in the porous structure of the yarn formed by spinning during this drying process. In drying, it is particularly preferable to dry the fibers in a non-tensioned state, whereby porous fibers with high strength and elongation can be obtained. Although the main conditions of the present invention have been described above, other known conditions may be introduced as secondary conditions as long as the gist of the present invention is not impaired. The manufacturing method of the present invention is applicable not only to ordinary fibers but also to wet molding of hollow fibers, irregular cross-section fibers, and the like. The present invention will be explained below with reference to Examples. Example 1 Cellulose triacetate flakes having a degree of acetylation of 61.5% as a polymer were dissolved in a DMAc solvent by stirring at 110° C. for 120 minutes using a kneader. Temperature immediately
The temperature was lowered to 50°C, and the mixture was degassed to prepare a spinning stock solution with a polymer concentration of 15%. This stock solution was wet-spun into a DMAc 50% aqueous solution through a spinning nozzle with a hole diameter of 0.06 mmφ and 200 holes, and the yarn was drawn at a speed of 20 m/min (draft adopted).
1.34) Subsequently, the fibers were washed continuously, transferred onto a stainless steel wire mesh conveyor, and dried without tension in hot air at 110°C to obtain fibers with a fineness of 3 denier. In this experiment, the temperature of the coagulation bath was 30°C, 45°C, and 60°C. The properties of the obtained fibers are shown in Table 1. As a comparative example, fiber properties obtained at a coagulation bath temperature of 15°C and a spinning speed of 45 m/min at a bath temperature of 30°C (adopted draft 3.02, effective draft rate
The fiber properties of 0.70) are also shown in Table 1. Experiment No.2
Cross-sectional electron micrographs of the fibers obtained in 5 and 5 are shown in FIGS. 2 and 1. Furthermore, the pore radius distribution curve measured by the mercury intrusion method in Experiment No. 2 is shown in Figure 3.
The average pore diameter determined from Figure 3 was 0.108μ.

[Table] For reference, commercially available triacetate fiber Soalon (Mitsubishi Acetate
Co., Ltd.), the surface area of a fineness of 2.75 denier was measured.
It was 0.30m ² /g. Example 2 Cellulose triacetate porous fibers were spun and washed in the same manner as in Experiment No. 2 of Example 1. As a drying step, it was dried by passing it over a heated roller at 110°C in a fixed length. The resulting yarn is virtually free of macrovoids larger than 5μ, has an internal surface area of 21.5m ² /g,
The average pore diameter was 0.10μ, the yarn quality was 3.0 denier, dry strength: 0.5m ² /d, and dry elongation: 10%. Example 3 Cellulose triacetate flakes with a degree of acetylation of 61.5% were added to DMAc solvent using a kneader at 120°C.
Stir for a minute to dissolve. Immediately, the temperature was lowered to 80°C, filtered and defoamed to prepare a spinning stock solution with a polymer concentration of 20%. This stock solution was heated to DMAc50, which was kept at a temperature of 40℃.
% aqueous solution, taken up at a speed of 20 m/min, washed and dried in the same manner as in Example 1 to obtain fibers with a fineness of 3 denier. In this experiment, the effective draft rate was changed by changing the nozzle hole diameter. The obtained fiber properties are shown in Table 2. As a comparative example, the fiber properties in the case of an effective draft rate of 0.70 are also shown in Table 2.

[Table] Example 4 Cellulose diacetate flakes with a degree of acetylation of 55% were dissolved in a DMF solvent using a kneader by stirring at 110° C. for 120 minutes. Immediately lower the temperature to 60℃,
A spinning stock solution with a polymer concentration of 20% was prepared by defoaming. This stock solution was passed through a spinning nozzle with a nozzle diameter of 0.06 mmφ and a number of holes of 40% DMF maintained at a temperature of 45°C.
Wet spinning in an aqueous solution and taking it off at a speed of 20 m/min (adopted draft 1.70) and subsequent washing Example 1
In the same manner as above, it was dried to obtain a fiber having a fineness of 3 denier. The obtained fiber properties are shown in Table 3.

【table】 [Brief explanation of the drawing]

Figures 1 and 2 are cross-sectional electron micrographs of porous acetate fibers (3000x magnification), with Figure 1 showing a fiber other than the one according to the present invention, and Figure 2 showing a fiber according to the present invention. FIG. 3 is an integral curve of the pore distribution of the porous acetate fiber of the present invention.

Claims (1)

[Claims] 1. Using a spinning dope in which cellulose acetate or a polymer mixture containing cellulose acetate as a main component is dissolved in a solvent, and using an aqueous solution of the solvent maintained at a temperature of 25 to 75°C as a coagulant, the following ( 1) A method for producing porous cellulose acetate fibers, which comprises performing wet spinning at an effective draft ratio in the range of 0.2 to 0.6 as shown in the formula, and then drying. Effective draft rate = adopted draft/maximum draft...(1) However, maximum draft refers to the maximum spinning draft that can be applied without fiber breakage. 2. The method according to claim 1, wherein the porous cellulose acetate fiber obtained by wet spinning is stretched and then dried. 3. The method according to claim 1 or 2, characterized in that the fibers are dried in a non-tensioned state.