Thermoplastic cellulose acetate fiber and manufacturing method therefor

Abstract

To provide a thermoplastic cellulose acetate fiber having excellent fiber cross-section circularity and fiber uniformity.SOLUTION: The thermoplastic cellulose acetate fiber is made of a thermoplastic cellulose acetate resin mainly composed of cellulose acetate and a plasticizer, and has the fiber cross-section circularity of 0.50 or more. An acetyl group average substitution degree of the cellulose acetate is preferably 1.0 or more and 2.8 or less. A content of the plasticizer in the thermoplastic cellulose acetate resin is 10 mass% or more and 40 mass% or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a thermoplastic cellulose acetate fiber comprising cellulose acetate and a plasticizer, and a method for producing the same. [Background technology]

[0002] In recent years, biodegradable plastics have been attracting attention due to concerns about the impact of microplastics on ecosystems. Ordinary plastics are synthesized from petroleum, and there are no microorganisms in the natural environment that can decompose them. Ordinary plastics can be broken down into smaller pieces by exposure to water and ultraviolet light, but they do not decompose and become microplastics, which are difficult to recover. Microplastics in the aquatic environment are particularly problematic, but only a small number of plastics are biodegradable in the aquatic environment.

[0003] One of the plastics that shows biodegradability in the aqueous environment is cellulose acetate. Cellulose acetate, which is produced from cellulose, the main component of wood and cotton, and acetic acid, the main component of vinegar, is an environmentally friendly biomass material. Therefore, it is widely used in films, sheets, fibers, paints, etc. However, cellulose acetate has low thermal fluidity, and if the temperature is raised to a level that gives it sufficient fluidity, it will exceed the heat resistance temperature of cellulose acetate and will undergo thermal decomposition. Therefore, when producing fibers, it is necessary to dissolve it in a specific solvent such as acetone or methylene chloride, which places a large burden on the environment. In addition, after the solvent evaporates from the surface of the yarn discharged from the nozzle and a skin layer is formed on the fiber surface, the solvent inside the fiber evaporates, so that the skin layer collapses in the fiber cross-sectional direction, resulting in a multi-lobed cross-section and making it impossible to form a cross-section with a high circularity. If the circularity is low, the strength and elongation and yarn quality are likely to decrease.

[0004] In order to overcome these problems associated with fibers using cellulose acetate, various studies have been carried out. For example, a biodegradable cellulose acetate fiber with excellent melt spinnability and a method for producing the same have been disclosed, which is produced by adding caprolactone tetraol as a plasticizer to cellulose acetate to improve thermal fluidity and reduce the rate of yarn breakage during spinning (Patent Document 1). In addition, a thermoplastic cellulose acetate propionate fiber that is made of a thermoplastic cellulose acetate propionate composition containing cellulose acetate propionate and a polyether compound and has excellent melt spinnability, strength and elongation properties, and uniformity of fineness has been disclosed (Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-317228 [Patent Document 2] JP 2004-182979 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, although it is described that the fiber described in Patent Document 1 exhibits good melt spinnability and can give cellulose acetate fibers having excellent biodegradability and fiber strength, the rate of fiber breakage is more than five times per hour, which is not at a level suitable for industrial production.Furthermore, there is no description of the cross-sectional shape or uniformity of the fiber. Patent Document 2 also describes that cellulose acetate (cellulose acetate) substituted only with acetyl groups has insufficient thermoplasticity, and therefore cellulose acetate propionate, in which at least a portion of the hydroxyl groups of cellulose are substituted with acetyl groups and propionyl groups, is used. However, cellulose acetate propionate is produced by esterifying cellulose with two types of acid, acetic acid and propionic acid, and is less versatile than cellulose acetate. Therefore, an object of the present invention is to provide a thermoplastic cellulose acetate fiber excellent in cross-sectional circularity and fiber uniformity, and a method for producing the same, by using cellulose acetate, which is the most versatile of cellulose esters. [Means for solving the problem]

[0007] That is, the gist of the present invention is, firstly, a fiber made of a thermoplastic cellulose acetate resin mainly composed of cellulose acetate and a plasticizer, and having a circularity of 0.50 or more in a fiber cross section. Among them, the average degree of acetyl group substitution of the cellulose acetate is preferably 1.0 to 2.8, the content of the plasticizer is preferably 10 to 40% by mass, and U% (fineness unevenness) is preferably 3.5% or less. Secondly, there is provided a method for producing thermoplastic cellulose fibers, in which thermoplastic cellulose acetate resin is melt spun at a temperature of 300°C or higher and 340°C or lower, the temperature is maintained between 0 cm and 20 cm directly below the spinneret, and the melt spinning is carried out at a spinning speed of 300 to 2000 m / min. Effect of the Invention

[0008] According to the present invention, it is possible to provide a thermoplastic cellulose acetate fiber mainly composed of cellulose acetate, which is the most versatile of cellulose esters. Also, according to the present invention, it is possible to provide a thermoplastic cellulose acetate fiber having a high degree of circularity in the fiber cross section. Also, according to the present invention, it is possible to provide a thermoplastic cellulose acetate fiber having little variation in fineness and excellent fiber uniformity. Furthermore, according to the present invention, it is possible to provide a thermoplastic cellulose acetate fiber which can be produced continuously and stably and has a high degree of circularity in the cross-sectional shape of the fiber and little variation in fineness, and a method for producing the same. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 shows an example of the cross-sectional shape of the thermoplastic cellulose acetate fiber of the present invention. [Diagram 2] FIG. 2 shows an example of the cross-sectional shape of the thermoplastic cellulose acetate fiber of the present invention. [Diagram 3] FIG. 3 is an example of a cross-sectional shape of a fiber outside the scope of the present invention. [Figure 4] FIG. 4 is a schematic diagram showing a method for spinning thermoplastic cellulose acetate fibers of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] In the present invention, the thermoplastic cellulose acetate fibers are made of a thermoplastic cellulose acetate resin.

[0011] In the present invention, the thermoplastic cellulose acetate resin comprises cellulose acetate and a plasticizer.

[0012] The cellulose acetate of the present invention preferably has a weight-average molecular weight (Mw) of 50,000 or more and 250,000 or less. If the weight-average molecular weight is lower than 50,000, the melt viscosity during spinning is low, thread breakage is likely to occur, and continuous stable production tends to be difficult. It is preferably 70,000 or more, more preferably 90,000 or more. If the weight-average molecular weight is higher than 250,000, the thermal fluidity during spinning is low, and it tends to be difficult to obtain fibers. It is preferably 200,000 or less, more preferably 180,000 or less.

[0013] The weight average molecular weight in the present invention refers to a value measured by gel permeation chromatography (GPC) and calculated in terms of polystyrene.

[0014] The cellulose acetate of the present invention preferably has an average degree of acetyl group substitution of 1.0 or more and 2.8 or less. If the average degree of acetyl group substitution is lower than 1.0, the water resistance decreases, and problems tend to occur easily in later processes such as dyeing. It is preferably 1.6 or more, more preferably 2.2 or more. If the average degree of acetyl group substitution is higher than 2.8, the biodegradation rate tends to decrease. It is preferably 2.7 or less, more preferably 2.6 or less.

[0015] The plasticizer used in the present invention may be appropriately selected from known plasticizers suitable for cellulose acetate. For example, phthalic acid esters such as dimethyl terephthalate, diethyl terephthalate, dibutyl terephthalate, bis(2-ethylhexyl)phthalate, and diisodecyl phthalate; aliphatic dibasic acid esters such as dibutyl adipate, diisodecyl adipate, bis[2-(2-butoxyethoxy)ethyl]adipate, bis(2-ethylhexyl)azelate, dibutyl sebacate, and diethyl succinate; phosphate esters such as trimethyl phosphate, triethyl phosphate, tributyl phosphate, tris(2-ethylhexyl)phosphate, and triphenyl phosphate; glycerin fatty acids such as glycerin triacetate, glycerin diacetate monostearate, glycerin diacetate monolaurate, and glycerin diacetate monooleate; polyalkylene glycols such as polyethylene glycol and polypropylene glycol; and polyesters such as polylactic acid and polybutylene succinate. The plasticizers may be used alone or in combination.

[0016] The thermoplastic cellulose acetate resin in the present invention preferably has a plasticizer content of 10% by mass or more and 40% by mass or less. If the plasticizer content is less than 10% by mass, the thermal fluidity during spinning tends to decrease, making it difficult to obtain fibers. It is preferably 15% by mass or more, more preferably 20% by mass or more. If the plasticizer content is more than 40% by mass, the strength of the obtained fibers tends to decrease. It is preferably 37% by mass or less, more preferably 35% by mass or less.

[0017] The thermoplastic cellulose acetate resin in the present invention preferably has a melt flow rate (MFR) at 230°C and a load of 2.16 kg of 3 g / 10 min or more and 30 g / 10 min or less. If the MFR is lower than 3 g / 10 min, the thermal fluidity during spinning decreases, and it tends to be difficult to obtain fibers. It is preferably 4 g / 10 min or more, more preferably 5 g / 10 min or more. If the MFR is higher than 30 g / 10 min, the strength of the obtained fibers tends to decrease. It is preferably 20 g / 10 min or less, more preferably 15 g / 10 min or less.

[0018] The thermoplastic cellulose acetate resin in the present invention may be modified by adding additives within the range that does not impair the effects of the present invention. Examples of additives include heat stabilizers, antioxidants, fluorescent whitening agents, infrared reflectors, and infrared absorbers. The additives may be used alone or in combination.

[0019] The thermoplastic cellulose acetate fiber of the present invention preferably has a single yarn fineness of 1.0 dtex or more and 100 dtex or less. If the single yarn fineness is lower than 1.0 dtex, the yarn tends to be easily broken and troubled in the post-processing such as yarn processing, weaving, and knitting. It is preferably 1.2 dtex or more, more preferably 1.5 dtex or more, and even more preferably 1.8 dtex or more. If the single yarn fineness is higher than 100 dtex, it becomes difficult to maintain the uniformity of the fiber, and there is a tendency for the fineness unevenness and strength variation to become large. It is preferably 90 dtex or less, more preferably 80 dtex or less.

[0020] The thermoplastic cellulose acetate fiber of the present invention preferably has a strength of 0.5 cN / dtex or more and 4.0 cN / dtex or less. If the strength is lower than 0.5 cN / dtex, yarn breakage is likely to occur in later processes such as yarn processing, weaving, and knitting, and the processability tends to deteriorate. It is preferably 0.6 cN / dtex or more, more preferably 0.7 cN / dtex or more. If the strength is higher than 4.0 cN / dtex, the elongation tends to be easily reduced. It is preferably 3.5 cN / dtex or less, more preferably 3.0 cN / dtex or less, and even more preferably 2.5 cN / dtex or less.

[0021] The thermoplastic cellulose acetate fiber of the present invention preferably has an elongation of 15% or more and 70% or less. If the elongation is lower than 15%, yarn breakage is likely to occur in subsequent processes such as yarn processing, weaving, and knitting, and processability tends to deteriorate. It is preferably 20% or more, more preferably 25% or more. If the elongation is higher than 70%, the strength tends to decrease. It is preferably 60% or less, more preferably 50% or less.

[0022] The thermoplastic cellulose acetate fiber of the present invention preferably has a U% value, which is an index of fineness unevenness, of 3.5% or less. If U% exceeds 3.5%, it becomes difficult to maintain the uniformity of the fiber, and fineness unevenness and strength variation tend to become large. Furthermore, fluff and yarn breakage tend to occur in the post-processing, and processability tends to deteriorate. It is preferably 3.3% or less, and more preferably 3.0% or less.

[0023] In the present invention, U% refers to the average deviation rate of fiber diameter. The average deviation rate of fiber diameter is a value that represents the unevenness of fiber thickness obtained by measuring the capacitance of thermoplastic cellulose acetate fibers over 100 m using a continuous yarn unevenness tester, calculating the variation in fiber diameter from the variation in capacitance, and then calculating the variation in fiber diameter from the calculated variation in fiber diameter. The lower the average deviation rate, the less uneven the fineness is, meaning that the fiber is more uniform.

[0024] The cross-sectional shape of the fiber of the present invention will be described below.

[0025] The thermoplastic cellulose acetate fiber of the present invention has a circularity of 0.50 or more in the fiber cross section (fiber cross section perpendicular to the fiber length direction). If the circularity is lower than 0.50, the strength tends to decrease. In addition, the yarn breakage tends to occur easily in the post-processing such as yarn processing, weaving, and knitting, and the processability tends to deteriorate. The circularity is preferably 0.55 or more, and more preferably 0.60 or more.

[0026] The circularity in the present invention is calculated by the following formula, and the closer it is to 1, the closer the fiber cross-sectional shape is to a perfect circle. Formula: Circularity = 4πS / C 2 where S is the cross-sectional area of ​​the fiber (μm 2 ), C is the circumference of the fiber cross section (μm), and π is the circular constant.

[0027] 1 and 2 are diagrams showing an example of the cross-sectional shape of the fiber in the thermoplastic cellulose acetate fiber of the present invention. In this example, the circularity is 0.50 or more, and a decrease in strength and fiber breakage in a post-processing step are unlikely to occur.

[0028] Next, a preferred example of the method for producing the thermoplastic cellulose acetate fiber of the present invention will be described.

[0029] An example of a schematic diagram of a spinning device for melt spinning is shown in Figure 4. The thermoplastic cellulose acetate resin is melted and extruded from a spinneret (a) so that the circularity is 0.50 or more, and then the resin is kept warm by a heater (b) directly below the spinneret, cooled by cooling air (c), taken up by a godet roller (d), and wound up by a winder (e) to obtain the thermoplastic cellulose acetate fiber of the present invention.

[0030] The spinning temperature is preferably 210°C or higher and 260°C or lower. If the spinning temperature is lower than 210°C, the thermal fluidity decreases, and it tends to be difficult to obtain fibers. It is preferably 220°C or higher, and more preferably 230°C or higher. If the spinning temperature is higher than 260°C, it exceeds the heat resistance temperature of the thermoplastic cellulose acetate resin, and thread breakage due to thermal decomposition tends to occur, making continuous stable production difficult. It is preferably 255°C or lower, and more preferably 250°C or lower.

[0031] The temperature of the heater (b) directly below the spinneret, which keeps the cellulose acetate resin extruded in a fibrous form from the spinneret (a) warm, is 300°C or higher and 340°C or lower. If the heater temperature is lower than 300°C, it becomes difficult to maintain the uniformity of the fibers, and there is a tendency for unevenness in fineness and strength to increase. The heater temperature is preferably 305°C or higher, and more preferably 310°C or higher. If the heater temperature is higher than 340°C, it exceeds the heat resistance temperature of the thermoplastic cellulose acetate resin, and thread breakage due to thermal decomposition tends to occur, making continuous stable production difficult. The heater temperature is preferably 335°C or lower, and more preferably 330°C or lower.

[0032] The spinning speed is preferably 300 m / min or more and 2000 m / min or less. If the spinning speed is slower than 300 m / min, the strength decreases, and yarn breakage tends to occur easily in later processes such as yarn processing, weaving, and knitting, and the processability tends to deteriorate. It is preferably 350 m / min or more, and more preferably 400 m / min or more. If the spinning speed is faster than 2000 m / min, the elongation decreases, and yarn breakage tends to occur easily in later processes such as yarn processing, weaving, and knitting, and the processability tends to deteriorate. It is preferably 1800 m / min or less, and more preferably 1600 m / min or less.

[0033] In this way, the present invention makes it possible to continuously and stably produce thermoplastic cellulose acetate fibers that are excellent in the circularity of their cross sections and in the uniformity of the fibers, while suppressing unevenness in fineness. EXAMPLES

[0034] The present invention will be described in detail below with reference to examples, but the following examples are merely illustrative of the present invention and are not intended to limit the present invention. The methods for measuring and evaluating various physical properties are as follows.

[0035] (1) Weight average molecular weight (Mw) Measurement was performed using a gel permeation chromatography (GPC) manufactured by Nippon Waters under the following conditions. Column 1: ACQUITY APC XT 900 2.5μm 4.6×75mm Column 2: ACQUITY APC XT 200 2.5μm 4.6×75mm Column 3: ACQUITY APC XT 45 1.7μm 4.5×150mm Eluent: chloroform:methanol=4:1 Flow rate: 0.5ml / min Column temperature: 40℃ Detector: RI Sample concentration: 1w / v% Injection volume: 10μl

[0036] (2) Spinning stability The spinning stability was evaluated based on the average number of yarn breaks when 10 kg of fiber was spun. ○: The thread breakage occurred less than once ×: Thread breakage occurs once or more

[0037] (3) Circularity The obtained thermoplastic cellulose acetate fibers were cut perpendicular to the length of the fibers, and the cut surfaces were observed under an optical microscope at 100x magnification. The cross-sectional area and circumference of the fiber cross section were measured, and the circularity was calculated using the following formula. Formula: Circularity = 4πS / C 2 where S is the cross-sectional area of ​​the fiber (μm 2 ), C is the circumference of the fiber cross section (μm), and π is the circular constant.

[0038] (4) Fineness According to JIS L 1013, a 100m sample yarn length was taken using a measuring machine, and the weight was calculated.

[0039] (5) Strength and elongation A tensile test was carried out in accordance with JIS L 1013 using an Autograph (registered trademark) AGS manufactured by Shimadzu Corporation. The breaking strength and breaking elongation at the time when the fiber broke were each measured five times under conditions of a measurement length of 200 mm and a tensile speed of 200 mm / min, and the average values ​​were calculated.

[0040] (6) Unevenness of fineness A Zellweger UsterTester4 Model C was used as a continuous yarn unevenness tester, and U% was measured in normal mode while feeding the fiber at a speed of 100 m / min.

[0041] Example 1 Thermoplastic cellulose acetate (NEQAS (registered trademark) OCEAN OCN100E-R027, MFR: 6.7 g / 10 min, Mw: 140,000, manufactured by NEQAS) was used, and the fiber was spun from a spinneret at a spinning temperature of 245° C. so as to have a cross-sectional shape as shown in FIG. 1 . The fiber was kept warm for 15 cm from the spinneret face with a heater directly below the spinneret at 325° C., and wound up at 1500 m / min to produce a thermoplastic cellulose acetate fiber of 53 dtex / 12 f. The thermoplastic cellulose acetate fiber obtained had a cross-sectional circularity of 0.91, a U% of 1.5%, and good spinning stability.

[0042] Example 2 Thermoplastic cellulose acetate fibers were produced in the same manner as in Example 1, except that the spinning temperature was 240°C, the heater temperature immediately below the spinneret was 315°C, and the resulting thermoplastic cellulose acetate fibers were 84 dtex / 12f. The resulting thermoplastic cellulose acetate fibers had a cross-sectional circularity of 0.89, a U% of 0.9%, and good spinning stability.

[0043] Example 3 Thermoplastic cellulose acetate fibers were produced in the same manner as in Example 1, except that the spinning temperature was 230°C, the heater temperature immediately below the spinneret was 315°C, and the resulting thermoplastic cellulose acetate fibers were 75 dtex / 1f. The resulting thermoplastic cellulose acetate fibers had a cross-sectional circularity of 0.90, a U% of 1.0%, and good spinning stability.

[0044] Example 4 Thermoplastic cellulose acetate fibers were produced in the same manner as in Example 1, except that the spinning speed was 400 m / min. The obtained thermoplastic cellulose acetate fibers had a cross-sectional circularity of 0.91, a U% of 1.7%, and good spinning stability.

[0045] Example 5 Thermoplastic cellulose acetate fibers were produced in the same manner as in Example 1, except that the temperature of the heater immediately below the spinneret was set to 315° C. The thermoplastic cellulose acetate fibers obtained had a cross-sectional circularity of 0.90, a U% of 2.0%, and good spinning stability.

[0046] Example 6 Thermoplastic cellulose acetate fibers were produced in the same manner as in Example 2, except that the cross-sectional shape was as shown in Figure 2. The obtained thermoplastic cellulose acetate fibers had a cross-sectional circularity of 0.63, a U% of 2.1%, and good spinning stability.

[0047] Example 7 Thermoplastic cellulose acetate fibers were produced in the same manner as in Example 1, except that the spinning temperature was 270° C. The obtained thermoplastic cellulose acetate fibers had a cross-sectional circularity of 0.89 and a U% of 2.7%, but the number of yarn breakages was high and spinning stability was poor.

[0048] Example 8 Thermoplastic cellulose acetate fibers were produced in the same manner as in Example 1, except that the heater immediately below the spinneret was set to 295°C. The obtained thermoplastic cellulose acetate fibers had a cross-sectional circularity of 0.90 and good spinning stability. However, the U% was 5.7%, which meant that the fiber uniformity was poor, and there were variations in fineness and strength and elongation, making the fibers insufficient for yarn processing, weaving, and knitting.

[0049] Example 9 Thermoplastic cellulose acetate fibers were produced in the same manner as in Example 1, except that the temperature of the heater immediately below the spinneret was set to 345° C. The obtained thermoplastic cellulose acetate fibers had a cross-sectional circularity of 0.90 and a U% of 2.4%, but the number of yarn breakages was high and the spinning stability was poor.

[0050] Example 10 Thermoplastic cellulose acetate fibers were produced in the same manner as in Example 1, except that the spinning speed was 200 m / min. The obtained thermoplastic cellulose acetate fibers had a cross-sectional circularity of 0.89, a U% of 1.3%, and good spinning stability. However, the strength was low at 0.3 cN / dtex, and the fibers were not capable of withstanding yarn processing, weaving, and knitting.

[0051] Example 11 The same method as in Example 1 was used to produce the thermoplastic cellulose acetate fiber, except that the spinning speed was 2300 m / min. The cross-sectional circularity of the obtained thermoplastic cellulose acetate fiber was 0.90, U% was 1.2%, and spinning stability was good. However, the elongation was low at 9%, and the fiber was not able to withstand yarn processing, weaving, and knitting.

[0052] Comparative Example 1 Spinning was performed in the same manner as in Example 1, except that the spinning temperature was 200° C. The molten thermoplastic cellulose acetate could be formed into threads, but had low fluidity and could not be wound up into fibers.

[0053] Comparative Example 2 Thermoplastic cellulose acetate fibers were produced in the same manner as in Example 2, except that the cross-sectional shape was as shown in Figure 3. The obtained thermoplastic cellulose acetate fibers had good spinning stability. However, the circularity of the cross-sectional shape was 0.42, and U% was 7.4%, so the fiber uniformity was poor, and there were variations in fineness and strength and elongation, and the fiber was not suitable for yarn processing, weaving, and knitting.

[0054] [Table 1]

[0055] The thermoplastic cellulose acetate fibers obtained in Examples 1 to 5 were good in terms of fiber uniformity, spinning stability, circularity, and strength and elongation, whereas the thermoplastic cellulose acetate fibers obtained in Examples 6 to 11 and the Comparative Example were poor in at least one of fiber uniformity, spinning stability, circularity, and strength and elongation. [Industrial Applicability]

[0056] The thermoplastic cellulose acetate fiber of the present invention can be made into various fiber structures and can be suitably used not only for clothing such as innerwear and sportswear, but also for industrial materials such as weed control sheets, tree cover sheets, and Ecobags (registered trademark). [Explanation of symbols]

[0057] a. Spinneret b Heater directly below the cap c Cooling air d Godet roller e Winder

Claims

1. A thermoplastic cellulose acetate fiber made of a thermoplastic cellulose acetate resin mainly composed of cellulose acetate and a plasticizer, wherein the circularity of the fiber cross-section is 0.50 or higher.

2. The thermoplastic cellulose acetate fiber according to claim 1, wherein the average degree of acetyl group substitution of cellulose acetate is 1.0 or more and 2.8 or less.

3. The thermoplastic cellulose acetate fiber according to claim 1 or 2, wherein the plasticizer content in the thermoplastic cellulose acetate resin is 10% by mass or more and 40% by mass or less.

4. The thermoplastic cellulose acetate fiber according to claim 1 or 2, wherein the U% (fineness variation) is 3.5% or less.

5. The thermoplastic cellulose acetate fiber according to claim 3, wherein the U% (fineness variation) is 3.5% or less.

6. A method for producing thermoplastic cellulose acetate fibers, comprising melting the thermoplastic cellulose acetate resin, introducing it to a die, maintaining a temperature of 0 cm to 20 cm directly below the die with a heater at 300°C to 340°C, and melt spinning at a spinning speed of 300 to 2000 m / min.

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