TW202419579A - Cellulose fibers, resin composition, molded article, and method for producing cellulose fibers - Google Patents

Abstract

Provided are a resin composition, a molded article, and a method for producing cellulose fibers. When dyed by a dye, the cellulose fibers have a ratio (L'/L) of the skin layer brightness (L') and the core layer brightness (L) of 0.70 or less. The skin layer brightness (L') and the core layer brightness (L) of the cellulose fiber cross section are obtained by measuring the R, G, and B values of each of the layers, and calculating using the formula of [(maximum value of the R, G, and B values)/255] * 100 [%].

Description

Cellulose fiber, resin composition, molded product, and method for producing cellulose fiber

The present invention relates to cellulose fiber, resin composition, molded product, and method for producing cellulose fiber.

In order to improve the strength and rigidity of plastics, fiber composites made by mixing high-strength and high-elastic fibers such as glass fibers are used in various fields such as automotive parts, sporting goods, building materials, and groceries.

Glass fiber reinforced resin materials used as lightweight and high-strength materials have excellent properties in use. However, if glass fiber is used as a reinforcing fiber, there is a problem of heavy environmental burden due to the residues generated when it is discarded.

In addition, printed wiring boards also use glass fiber as a base material to improve insulation and rigidity. However, if glass fiber is also used in these, there is a problem of heavy environmental burden due to the residues generated when discarded.

Therefore, for the reinforcing fibers used in fiber-reinforced resin materials and the base materials of printed wiring boards, there is a review of using cellulose fibers having excellent properties such as high mechanical properties, dimensional stability, low thermal expansion, electrical insulation, and low specific gravity.

For example, Patent Document 1 discloses a cellulose fiber containing cellulose type II and an imidazolium salt content of 1 mass % or less. [Prior Art Document] [Patent Document]

[Patent Document 1] International Publication No. 2021/241539

[The problem that the invention wants to solve]

Although the cellulose fiber described in the above-mentioned patent document 1 is excellent, with the increasing demand for cellulose fibers in recent years, further development of cellulose fibers is required. In particular, cellulose fibers with high elastic modulus and excellent stretching are required. However, elastic modulus and stretching are opposite functions and it is difficult to take both into account. The purpose of the present invention is to solve this problem, and the purpose is to provide excellent cellulose fibers with a good balance between elastic modulus and stretching, as well as resin compositions, molded products, and cellulose fiber manufacturing methods using the cellulose fibers. [Means for solving the problem]

Based on the above-mentioned problem, the inventor of this case has found that the above-mentioned problem can be solved by adjusting the density of the cellulose in the surface layer and the core layer of the cellulose fiber. Specifically, the above-mentioned problem is solved by the following means. ＜1＞ A cellulose fiber, wherein the ratio (L’/L) of the lightness (L’) of the surface layer and the lightness (L) of the core layer when dyed with a dye is 0.70 or less, and the lightness (L’) of the surface layer and the lightness (L) of the core layer of the cross section of the cellulose fiber are the values calculated by measuring the R, G, and B values of each layer according to [(the maximum value among the R, G, and B values)/255]*100[%]. <2> The cellulose fiber as described in <1>, wherein the degree of crystallization measured by X-ray diffraction (XRD) is 40% or more. <3> The cellulose fiber as described in <1> or <2>, which is stretched. <4> The cellulose fiber as described in <1>, wherein the degree of crystallization measured by X-ray diffraction (XRD) is 40% or more, and the fiber is stretched. <5> The cellulose fiber as described in any one of <1> to <4>, wherein the number average fiber length is 1 mm or more and less than 10 mm. <6> The cellulose fiber as described in any one of <1> to <5>, which is a chopped strand. <7> A cellulose fiber as described in any one of <1> to <4>, which is a continuous fiber. <8> A resin composition comprising a cellulose fiber as described in any one of <1> to <7> and a resin. <9> A molded product is formed from the resin composition as described in <8>. <10> A method for producing cellulose fiber, comprising: immersing a cellulose solution containing a raw material cellulose in a coagulation liquid, spinning, and then washing with a washing liquid containing water. <11> A method for producing cellulose fiber as described in <10>, wherein the ratio (L'/L) of the lightness of the surface layer (L') to the lightness of the core layer (L) of the cellulose fiber when dyed with a dye is less than 0.70, the lightness of the surface layer (L') and the lightness of the core layer (L) of the cross section of the cellulose fiber are the values calculated by measuring the R, G, and B values of each layer according to [(the maximum value among the R, G, and B values)/255]*100[%], and the crystallinity of the cellulose fiber measured by X-ray diffraction (XRD) is more than 40%, and the cellulose fiber is stretched. [Effects of the invention]

According to the present invention, it is possible to provide an excellent cellulose fiber having a good balance between elastic modulus and elongation, a resin composition using the cellulose fiber, a molded product, and a method for producing the cellulose fiber.

The following is a detailed description of the form in which the present invention is implemented (hereinafter also referred to as "this embodiment"). In addition, the following embodiment is an example for explaining the present invention, and the present invention is not limited to this embodiment. In addition, "~" in this specification is used to indicate that the numerical values described before and after it are included as lower limits and upper limits. In this specification, various physical property values and characteristic values are at 23°C unless otherwise specified. In the case where the measurement methods described in the standards displayed in this specification vary depending on the year, unless otherwise specified, they are based on the standards as of January 1, 2022.

The cellulose fiber of this embodiment is a cellulose fiber in which the ratio (L'/L) of the lightness of the surface layer (L') and the lightness of the core layer (L) when dyed with a dye is 0.70 or less. The lightness of the surface layer (L') and the lightness of the core layer (L) of the cross section of the cellulose fiber are the values calculated by measuring the R, G, and B values of each layer according to [(the maximum value among the R, G, and B values)/255]*100[%]. In this way, by making the structure of the surface layer denser than the core layer, an excellent cellulose fiber with a good balance between elastic modulus and stretch can be obtained. It is beneficial in terms of having both elastic modulus and stretch as physical properties in a trade-off relationship. That is, in this embodiment, the cellulose fiber is dyed, washed, and then observed with a digital microscope. Here, low brightness means that the dye is difficult to remove, indicating that the cellulose exists densely. In contrast, high brightness means that the dye is easy to remove, indicating that the cellulose is relatively loose. It is speculated that by forming a structure in which the surface layer is relatively denser than the core layer, it is not easy to produce phase separation inside the fiber, which can make the fiber crystallization degree high, thereby achieving high rigidity.

The above-mentioned brightness ratio (L'/L) is below 0.70, preferably below 0.68, and further can be below 0.66, below 0.64, below 0.62, and below 0.60. The lower limit of the above-mentioned brightness ratio (L'/L) is preferably above 0.30, more preferably above 0.35, further preferably above 0.40, further preferably above 0.45, further preferably above 0.49, and can also be above 0.51, above 0.53, above 0.54, above 0.55, above 0.56, above 0.57, above 0.58, above 0.59, and above 0.60. By being above the above-mentioned lower limit, there is a tendency to more effectively exert the effect of the present invention. The brightness ratio is measured by the method described in the embodiment. In addition, when the fiber surface is treated, the surface treatment agent is removed by a known method and then the measurement is performed. As for the method of adjusting the lightness ratio (L'/L), for example, when a cellulose solution containing raw cellulose is immersed in a coagulation liquid and spun to produce cellulose fibers, after spinning, the cellulose fibers are washed for a long time (for example, more than 6 hours or less than 24 hours) with a washing liquid containing water. By washing, the proportion of cellulose on the surface can be made denser.

In the cellulose fiber of this embodiment, the lightness of the surface layer (L') is preferably 20% or more, more preferably 25% or more, more preferably 30% or more, further preferably 35% or more, further preferably 40% or more, and may be 41% or more, 43% or more. By being above the above lower limit, a higher elongation at break can be tended. In addition, the lightness of the surface layer (L') is preferably 65% or less, more preferably 60% or less, further preferably 55% or less, further preferably 50% or less, further preferably 48% or less, and further preferably 45% or less. By being below the above upper limit, a higher rigidity can be tended.

In the cellulose fiber of this embodiment, the brightness of the core layer (L) is preferably more than 60%, more preferably more than 65%, more preferably more than 68%, further preferably more than 70%, further preferably more than 73%, further preferably more than 75%. By being above the lower limit, there is a tendency to achieve higher rigidity. In addition, the brightness of the core layer (L) is preferably less than 95%, more preferably less than 90%, more preferably less than 85%, further preferably less than 83%, further preferably less than 81%, and can also be less than 79%. By being below the upper limit, there is a tendency to achieve higher elongation at break.

In the cellulose fiber of the present embodiment, the difference in brightness (L-L') between the core layer (L) and the surface layer (L') is preferably 15% or more, more preferably 20% or more, more preferably 25% or more, further preferably 30% or more, and preferably 45% or less, more preferably 40% or less, further preferably 35% or less.

The cellulose fiber of this embodiment preferably has a high degree of crystallization. With a high degree of crystallization, a cellulose fiber with a higher modulus of elasticity can be obtained. The degree of crystallization of the cellulose fiber of this embodiment measured by X-ray diffraction (XRD) is preferably 40% or more, more preferably 50% or more, further preferably 52% or more, further preferably 55% or more, 60% or more, 65% or more, 70% or more, 75% or more, 80% or more. In addition, the upper limit of the degree of crystallization of the above cellulose fiber is actually 90% or less, and further preferably 88% or less, 85% or less, 84% or less, 80% or less, 75% or less, 70% or less, 65% or less, 60% or less, 55% or less.

The crystal orientation of the cellulose fiber of this embodiment is preferably 85% or more, more preferably 87% or more, further preferably 90% or more, further preferably 91% or more, and further preferably 92% or more. The upper limit of the crystal orientation can be 100%, but is actually 99% or less, 98% or less, 97% or less, 96% or less, and 95% or less.

The cellulose fiber of this embodiment is preferably stretched. By stretching, the orientation of the cellulose in the cellulose fiber is aligned, the hydrogen bond ratio is increased, and the surface layer can be made denser. The stretching ratio (stretching ratio) is preferably 10 times or more, and further, depending on the application, it can also be 20 times or more, 30 times or more, 35 times or more, or 50 times or more. By becoming above the lower limit, there is a tendency that the elastic modulus of the fiber becomes higher due to the increase in the orientation of the cellulose chain. In addition, the above stretching ratio is preferably 100 times or less, more preferably 80 times or less, further preferably 70 times or less, further preferably 60 times or less, and further preferably 50 times or less. Depending on the application, it can also be 40 times or less, 30 times or less, 25 times or less, 20 times or less, or 15 times or less. By keeping the value below the upper limit, it tends to be possible to effectively achieve both stable continuous production and maintenance of physical properties.

The cellulose fiber of the present embodiment is a cellulose fiber in which the ratio (L'/L) of the lightness of the surface layer (L') to the lightness of the core layer (L) when dyed with a dye is 0.70 or less. The lightness of the surface layer (L') and the lightness of the core layer (L) of the cross section of the cellulose fiber are values calculated by measuring the R, G, and B values of each layer according to [(the maximum value among the R, G, and B values)/255]*100[%]. In particular, it is preferable that the crystallinity degree measured by X-ray diffraction (XRD) is 40% or more, and the fiber is stretched.

The cellulose fiber of this embodiment contains cellulose. There is no particular limitation on the cellulose, and it can be natural cellulose raw materials such as wood pulp, cotton, cotton linter, hemp, bamboo, abaca, or regenerated cellulose fibers such as rayon, cupra, lyocell, and regenerated cellulose such as paper or clothing made from these. As an example of this embodiment, the cellulose can be exemplified by regenerated cellulose.

The cellulose used in this embodiment preferably has a degree of polymerization of 200 or more, more preferably 400 or more, more preferably 600 or more, further preferably 800 or more, and further preferably 1000 or more. By being above the above lower limit, there is a tendency to further improve the effect of high fiber strength. In addition, the cellulose used in this embodiment preferably has a degree of polymerization of 5000 or less, more preferably 3000 or less, more preferably 2000 or less, further preferably 1500 or less, and further preferably 1200 or less. By being below the above upper limit, there is a tendency to further improve the effect of improving physical properties caused by high concentration of cellulose. The degree of polymerization is measured by particle size screening stratification.

The cellulose content of cellulose fibers is usually 90% by mass or more, preferably 95% by mass or more, and more preferably 97% by mass or more. In addition, only one type of cellulose may be used, or two or more types may be used. When two or more types are used, the total amount is preferably within the above range.

The cellulose fiber of this embodiment may also contain components other than cellulose. Specifically, examples include additives such as antioxidants or ionic liquids used in spinning cellulose as described in detail below. Examples of ionic liquids include imidazolium salts.

In the cellulose fiber of this embodiment, the content of imidazolium salt is preferably 1% by mass or less, more preferably 0.8% by mass or less, more preferably 0.7% by mass or less, and further preferably 0.65% by mass or less. By being below the above upper limit, the heat resistance of the cellulose fiber can be improved. In the cellulose fiber of this embodiment, the content of imidazolium salt is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, more preferably 0.05% by mass or more, further preferably 0.08% by mass or more, and further preferably 0.1% by mass or more. As described above, by containing a trace amount of imidazolium salt in the cellulose fiber, the smoothness of the surface is effectively maintained, and the handling property tends to be improved. The cellulose fiber of this embodiment may contain only one imidazolium salt or two or more. When containing two or more, the total amount is preferably within the above range.

The fiber diameter of the cellulose fiber of this embodiment is preferably 5 μm or more, more preferably 7 μm or more, more preferably 8 μm or more, further preferably 9 μm or more, and further preferably 10 μm or more. By being above the lower limit, there is a tendency to further improve the effect of maintaining spinnability. In addition, the fiber of the cellulose fiber of this embodiment is preferably 30 μm or less, more preferably 17 μm or less, more preferably 16 μm or less, further preferably 15 μm or less, and further preferably 14 μm or less. By being below the upper limit, there is a tendency to improve the reinforcing effect when making a fiber-reinforced resin. The fiber of the cellulose fiber is measured according to the description of the embodiment described later.

The form of the cellulose fiber of this embodiment is not particularly limited. The first embodiment of the cellulose fiber of this embodiment is continuous fiber. Continuous fiber refers to a fiber having a number average fiber length exceeding 10 mm, preferably 10 cm or more, and more preferably 1 m or more. The upper limit is not particularly limited, but is 100,000 m or less. The continuous fiber is preferably wound around a core material (including a winding bobbin, etc.) as a winding body for storage and transportation. The continuous fiber may be a spun yarn obtained by spinning short fibers or long fibers, and is preferably not a spun yarn. The continuous fiber is preferably a fiber-like fiber obtained by spinning.

The second embodiment of the cellulose fiber of this embodiment is long fibers. Long fibers are, for example, continuous fibers cut into strands of a certain length. The fiber length of the long fibers is preferably 1 mm or more, more preferably 2 mm or more, preferably less than 10 mm, more preferably 9 mm or less, and further preferably 8 mm or less. The number average fiber length is the average value of the lengths of each fiber, and is usually equivalent to the shear length in the case of strand cutting.

The tensile modulus of elasticity of the cellulose fiber of the present embodiment is preferably 20 GPa or more, more preferably 25 GPa or more, further preferably 30 GPa or more, further preferably 32 GPa or more, and further preferably 35 GPa or more. In addition, the upper limit of the tensile modulus of elasticity of the cellulose fiber of the present embodiment is not particularly limited, and is actually 50 GPa or less. The elongation at break of the cellulose fiber of the present embodiment is preferably 3% or more, more preferably 4% or more, further preferably 5% or more, further preferably 6% or more, further preferably 6.5% or more, and further preferably 10% or more. In addition, the upper limit of the elongation at break of the cellulose fiber of the present embodiment is not particularly limited, and is actually 20% or less, and even 15% or less is sufficient to meet the required performance. The above tensile modulus and elongation at break are measured according to the description of the following embodiments.

<Method for producing cellulose fiber> Next, the method for producing cellulose fiber of this embodiment is described. The cellulose fiber of this embodiment can be produced by a known method, preferably by a method comprising the following steps: immersing a cellulose solution containing raw material cellulose and a solvent in a coagulation liquid, spinning, and then washing with a washing liquid containing water. By washing the cellulose fiber with a washing liquid containing water after spinning, the cellulose on the surface becomes dense, making it easier to achieve the desired brightness ratio. In addition, the brightness ratio can also be adjusted by adjusting the production scale. In this embodiment, it is more preferable to manufacture by a method including the following steps: immersing a cellulose solution containing raw cellulose and imidazolium salt in a coagulation liquid, spinning, and then washing with a washing liquid containing water.

The cellulose content (cellulose concentration) in the above-mentioned cellulose solution is preferably 1% by mass or more, more preferably 3% by mass or more, further preferably 5% by mass or more, and further preferably 7% by mass or more. By being above the above lower limit, the cellulose solution has a viscosity that easily produces molecular orientation during spinning, and a tendency to obtain fibers with a higher modulus of elasticity can be obtained. In addition, the cellulose content in the cellulose solution is preferably 20% by mass or less, more preferably 17% by mass or less, and further preferably 14% by mass or less. Depending on the application, it can also be 11% by mass or less. By being below the above upper limit, the viscosity of the cellulose solution will not be too high, which can further reduce the burden on the device during spinning. The details of other raw material cellulose are the same as those described in the above cellulose fiber items.

The solvent of the cellulose solution in this embodiment can be an ionic liquid, a tertiary amine oxide, dimethylsulfoxide, dimethylacetamide, preferably an ionic liquid, a tertiary amine oxide, and more preferably an ionic liquid. As the ionic liquid, an imidazolium salt is preferred, and a salt composed of a cation and an anion having an imidazole ring is preferred. As anions, chloride anions, bromide anions, acetate anions, phosphate anions, propionate anions, and formate anions are exemplified, and chloride anions and bromide anions are preferred, and chloride anions are more preferred. As a tertiary amine oxide, N-methylthiophene-N-oxide is preferred. The imidazolium salt in this embodiment preferably has a molecular weight of 100 to 500. Specific examples of the imidazolium salt in this embodiment include 1-alkyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium diethyl-phosphate, 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium propionate, 1-butyl-3-methylimidazolium formate, 1-butyl-3-methylimidazolium phosphate, and 1-butyl-3-methylimidazolium propionate. 1-ethyl-3-methylimidazolium dimethyl phosphate, 1,3-dimethylimidazolium acetate, 1-ethyl-3-methylimidazolium propionate, 1-ethyl-3-methylimidazolium formate, 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium dimethyl phosphate, 1-allyl-3-methylimidazolium chloride, etc., preferably 1-alkyl-3-methylimidazolium chloride. The carbon number of the alkyl group in the 1-alkyl-3-methylimidazolium chloride is preferably 2 or more and 6 or less. The alkyl group of the 1-alkyl-3-methylimidazolium chloride is preferably butyl. The butyl group may be any of tert-butyl, n-butyl, sec-butyl, and isobutyl, and is preferably n-butyl. The 1-alkyl-3-methylimidazolium chloride is more preferably 1-butyl-3-methylimidazolium chloride.

In this embodiment, the method for obtaining imidazolium salts such as 1-alkyl-3-methylimidazolium chloride is not particularly limited, and known techniques can be used. For example, 1-alkyl-3-methylimidazolium chloride can be obtained from the reaction product of 1-methylimidazole and RCl (R is an alkyl group with 2 to 6 carbon atoms). In this embodiment, when using imidazolium salts such as 1-alkyl-3-methylimidazolium chloride, it is preferable to remove the acid component by alkali.

The cellulose solution may also contain an aprotic polar solvent. Examples of the aprotic solvent include dimethyl sulfoxide, pyridine, N,N-dimethylacetamide, N,N-dimethylformamide, and N-methyl-2-pyrrolidone.

In the method for producing cellulose fibers of this embodiment, in a cellulose solution containing raw cellulose and a solvent (preferably an imidazolium salt) (hereinafter sometimes referred to as "cellulose solution"), the content of the solvent (preferably an imidazolium salt and/or an oxidized tertiary amine, more preferably an imidazolium salt) is preferably 80% by mass or more, more preferably 83% by mass or more, and further preferably 86% by mass or more. In addition, the content of the solvent (preferably an imidazolium salt and/or an oxidized tertiary amine, more preferably an imidazolium salt) in the above-mentioned cellulose solution is preferably 99% by mass or less, more preferably 97% by mass or less, further preferably 95% by mass or less, and further preferably 93% by mass or less. In addition, in the above-mentioned cellulose solution, the imidazolium salt and/or tertiary amine oxide (preferably imidazolium salt) preferably accounts for more than 90 mass% of the solvent contained in the cellulose solution, more preferably more than 95 mass%, further preferably more than 98 mass%, and further preferably more than 99 mass%. Only one imidazolium salt may be used, or two or more may be used. When two or more are used, the total amount should be within the above range.

The cellulose solution may further contain a stabilizer in addition to the above. Examples of the stabilizer include o-catechol, gallol, gallic acid, methyl gallate, ethyl gallate, propyl gallate, isopropyl gallate, ellagic acid, oxalic acid, phosphoric acid, sodium hexametaphosphate, tannin, and tannic acid.

The following is a description of the method for producing cellulose fibers according to the present embodiment with reference to FIG1. It is self-evident that the method for producing cellulose fibers according to the present embodiment is not limited to the above.

FIG. 1 is an example of a schematic diagram of an apparatus for producing cellulose fibers of the present embodiment, wherein 1 represents a cellulose solution, 2 represents a nozzle, 3 represents cellulose fibers, 4 represents a coagulation liquid, and 5 represents a winding machine. Furthermore, in the present embodiment, the apparatus or an apparatus other than the apparatus preferably has a cleaning bath into which a cleaning liquid is added for cleaning the produced cellulose fibers. In the present embodiment, a cellulose solution 1 is sprayed from a nozzle 2. When the cellulose solution 1 is sprayed from the nozzle, it tends to have a high viscosity and poor fluidity. Therefore, in order to improve fluidity, it is preferable to heat the solution for spraying. The temperature of the cellulose solution during spraying is preferably 70°C or higher, more preferably 80°C or higher. By reaching 70°C or higher, the fluidity of the cellulose solution tends to be further improved. In addition, the upper limit of the temperature of the cellulose solution during spraying is preferably 130°C or lower, more preferably 120°C or lower. By reaching 130°C or lower, the decomposition of cellulose can be more effectively suppressed. In addition, the nozzle diameter during spraying can be, for example, 0.1 to 0.5 mm. The fibrous cellulose solution sprayed from the nozzle 2 is immersed in the coagulation liquid 4. By immersing in the coagulation liquid, the fibrous cellulose solution is spun. Spinning can be either continuous, where the concentration of the solvent is kept below a certain amount while adding coagulation liquid, or batch, where the coagulation liquid is replaced when the concentration of the solvent in the coagulation liquid exceeds a certain level. The solvent dissolved in the coagulation liquid can be recovered and recycled for use in the manufacture of cellulose fibers. The air gap from the fibrous cellulose ejected from the nozzle 2 to the coagulation liquid 4 is preferably 3 to 30 cm.

The spraying speed from the nozzle during spinning is preferably 0.015cc/min or more per hole, more preferably 0.025cc/min or more, further preferably 0.03cc/min or more, further preferably 0.05cc/min or more, and further preferably 0.08cc/min or more. By being above the above lower limit, there is a tendency to further improve productivity. In addition, the spraying speed is preferably 1cc/min or less per nozzle, more preferably 0.8cc/min or less, more preferably 0.5cc/min or less, further preferably 0.2cc/min or less, and further preferably 0.12cc/min or less. By being below the above upper limit, the desolventizing agent in the coagulation bath can be effectively carried out. The number of nozzles can be 5,000 or more, or 10,000 or more, depending on the production scale. The spinning speed (winding speed) is preferably 50 m/min or more, more preferably 60 m/min or more, more preferably 70 m/min or more, further preferably 80 m/min or more, and further preferably 90 m/min or more. By being above the lower limit, productivity tends to be further improved. In addition, the spinning speed is preferably below 1000 m/min, more preferably below 500 m/min, more preferably below 300 m/min, further preferably below 200 m/min, and further preferably below 100 m/min. By being below the upper limit, the desolventizing agent in the coagulation bath can be more effectively performed.

The coagulation liquid may be water at a temperature in the range of 0°C to 100°C, or a low-grade alcohol, polar solvent, or non-polar solvent at a temperature in the range of -40°C to 100°C. If the economy and the working environment are taken into consideration, a solvent containing water is preferred. During the immersion in the coagulation liquid or by subsequent washing, the solvent is released from the spun cellulose solution, and cellulose fibers can be obtained. In this embodiment, the immersion time in the coagulation liquid is also dependent on the volume, temperature, and other conditions of the liquid, but in total, for example, it is preferably 0.1 seconds or more, and more preferably 6 seconds or more. By being above the above lower limit, the amount of solvent (imidazolium salt, etc.) in the obtained cellulose fiber can be effectively reduced. In addition, the upper limit of the time of immersion in the coagulation liquid is preferably less than 48 hours, more preferably less than 24 hours, and further less than 10 hours, less than 3 hours, and less than 2 hours. By being below the above upper limit, a trace amount of solvent (especially imidazolium salt) remains in the cellulose fiber, the fiber surface can maintain a lubricated state, and the handling tends to be improved.

In this embodiment, the cellulose fibers spun are washed with a washing liquid containing water. By washing with the washing liquid, the surface of the cellulose fibers can be made dense. In addition, the crystallization degree of the cellulose fibers can be increased. As for the washing liquid containing water, examples include a liquid consisting only of water and a washing liquid containing water and at least one polar solvent. In this embodiment, the washing liquid containing water preferably has water accounting for more than 90% by mass of the whole, more preferably accounting for more than 95% by mass, and further preferably accounting for more than 98% by mass. In this embodiment, for example, after the cellulose fibers spun are wound, the entire winding body is immersed in the washing liquid. The time for cleaning with a cleaning solution is preferably 3 hours or more, more preferably 5 hours or more, further preferably 10 hours or more, further preferably 15 hours or more, and further preferably 20 hours or more. By being above the above lower limit, the residual solvent can be removed more appropriately and the surface layer can be made tighter. In addition, the time for cleaning with a cleaning solution is preferably 10 days or less, more preferably 5 days or less, and further preferably 3 days or less. By being below the above upper limit, there is a tendency to further improve productivity. The temperature of the cleaning solution is preferably 5°C or more, more preferably 9°C or more, further preferably 11°C or more, further preferably 13°C or more, and further preferably 15°C or more. By being above the above lower limit, there is a tendency to further improve the desolventizing rate. The temperature of the cleaning liquid is preferably below 100°C, more preferably below 90°C, further preferably below 80°C, further preferably below 70°C, and further preferably below 60°C. By being below the above upper limit, there is a tendency to effectively suppress the destruction of the cellulose structure.

In addition, the temperature difference between the coagulation liquid and the cleaning liquid (absolute value, preferably the temperature of the cleaning liquid - the temperature of the coagulation liquid) is preferably 0°C or more, more preferably 1°C or more, further preferably 2°C or more, further preferably 3°C or more, and further preferably 4°C or more. By being above the above lower limit, there is a tendency to be able to more effectively clean impurities and the like in the cellulose fiber. In addition, the temperature difference between the coagulation liquid and the cleaning liquid (absolute value, preferably the temperature of the cleaning liquid - the temperature of the coagulation liquid) is preferably 90°C or less, more preferably 80°C or less, further preferably 70°C or less, further preferably 60°C or less, and further preferably 50°C or less. By being below the above upper limit, there is a tendency to be able to effectively suppress the destruction of the cellulose structure.

The cellulose fiber immersed in the coagulation liquid is wound on the winding machine 5. By adjusting the winding speed of the winding machine, the obtained cellulose fiber can be stretched and the fiber diameter of the cellulose fiber can be adjusted. In addition, a stretching roller can be provided in addition to the winding machine for stretching. When the winding speed relative to the ejection speed of the cellulose fiber from the nozzle is adjusted for stretching, the ratio (winding speed/ejection speed) is preferably 10 to 100 times, and more preferably 30 to 70 times.

<Application of cellulose fiber> The cellulose fiber of this embodiment can be widely used in known applications, and is preferably used as a resin composition containing a resin and cellulose fiber. As the resin composition, there are examples of the cellulose fiber of this embodiment impregnated with a resin (e.g., a prepreg), and the cellulose fiber of this embodiment kneaded with a resin (e.g., a resin pellet). When the resin composition is a pellet, it is preferably a long-fiber pellet. The long-fiber pellet refers to a pellet having a pellet length equal to the average fiber length of the cellulose fiber contained in the pellet. The so-called equivalent means that the average fiber length of the cellulose fiber contained in the pellet is 95-105% of the pellet length, preferably 99-101%. Such long fiber pellets can be produced, for example, by spinning and opening the cellulose fiber bundle, impregnating the cellulose fiber with a molten resin component, extracting the strands, and shearing them to the desired pellet length (for example, 1 mm or more, or 30 mm or less, or further less than 10 mm). On the other hand, when the resin composition contains a thermosetting resin, the resin composition includes a prepreg in which the thermosetting resin is semi-cured, in addition to a fiber-reinforced resin material in which the thermosetting resin is completely cured. The resin contained in the above-mentioned resin composition may be a thermoplastic resin or a thermosetting resin. As for the thermoplastic resin, polyamide resin (nylon), polyacetal resin, polycarbonate resin, polyvinyl chloride resin, ABS resin, polyester resin, polyethylene resin, polyolefin resin, polystyrene resin, (meth) acrylic resin, fluororesin may be exemplified, and as for the thermosetting resin, unsaturated polyester resin, epoxy resin, melamine resin, phenolic resin may be exemplified. As for the polyolefin resin, polypropylene resin may be exemplified. Furthermore, when a polyolefin resin is used, it is preferable that a part of the polyolefin resin is an acid-modified polypropylene resin. As for the acid-modified polypropylene resin, it is preferably an acid-modified polyolefin resin modified by maleic anhydride and/or maleic acid (preferably maleic anhydride acid-modified polypropylene resin). In addition, the resin composition may also contain additives such as low shrinkage agent, flame retardant, flame retardant auxiliary, plasticizer, antioxidant, ultraviolet absorber, colorant, pigment, filler, etc. according to the needs. The molded product of this embodiment is formed from the resin composition of this embodiment. For details of the resin composition using the cellulose fiber of this embodiment, please refer to International Publication No. 2019/066069 and International Publication No. 2019/066070, and these contents are incorporated into this specification.

The molded product of this embodiment is formed from the resin composition of this embodiment. The resin composition of this embodiment can be used, for example, in transparent resin materials, 3D shaping materials, buffer materials, repair materials, adhesives, adhesives, sealants, heat insulation materials, sound absorbing materials, artificial leather materials, coatings, electronic materials, packaging materials, automotive parts, and fiber composites. The shape of the molded product can be a sheet or a film like a coating. The above-mentioned molded product can be manufactured by a known method, such as the method described in paragraphs 0092 to 0114 of Japanese Patent Publication No. 2019-119983, and these contents are incorporated into this specification. [Example]

The present invention is described in more detail with the following examples. The materials, usage amounts, ratios, processing contents, processing sequences, etc. shown in the following examples can be appropriately changed without exceeding the scope of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below. If the measuring equipment used in the examples is difficult to obtain due to discontinuation of production, other equipment with equivalent performance can be used for measurement.

Example 1 ＜Spinning＞ 1 mass % of KYOWAAD 500SN (manufactured by Kyowa Chemical Industry Co., Ltd.) was added to a 60 mass % aqueous solution of 1-butyl-3-methylimidazolium chloride (BmimCl, manufactured by Kinkai Processing Products, product number: 20042301 (ionic liquid)), and stirred at room temperature for 5 hours. After filtering through No. 4A hard filter paper, the filtrate was dehydrated to obtain BmimCl for spinning. To the BmimCl, a raw material slurry (manufactured by Georgia-Pacific Cellulose, product number: V-81) was added, and stirred at 100°C to prepare a cellulose solution with a concentration of 9 mass %. Cellulose fibers were produced from the cellulose solution prepared as described above using the apparatus shown in FIG1 . That is, cellulose solution 1 was put into a syringe, and was ejected from a nozzle 2 having a nozzle diameter of 0.26 mm at 0.1 cc/min, and was wound at a winding speed to obtain a draw ratio shown in Table 1, and the cellulose fibers were passed (immersed) in 15° C. water (coagulation liquid 4) for 0.7 seconds and coagulated, and were wound around a winding reel by a winding machine 5. Thereafter, the winding reel (winding body) was immersed in 20° C. water (cleaning liquid) for 1 day for cleaning. Furthermore, the winding speed is adjusted so as to achieve the above-mentioned draw ratio, thereby stretching the cellulose fiber. The obtained cellulose fiber is measured and evaluated as follows.

<Staining> The cellulose fibers wound on the reel were released and embedded in epoxy resin (Epomount main agent: Epomount hardener II = 10:2 (mass ratio)) manufactured by Refine Tec Ltd. After complete hardening, 1 μm thick ultra-thin sections were prepared using an ultra-thin slicer (Leica, EM UC7) and a SYM knife XAC model (SYMX3055), and bonded to a glass sample using a silicone adhesive. 0.15 mL of a staining aqueous solution containing 1% by mass of BrilliantBlueR (Tokyo Chemical Industry, product number: C0700) and 10% by mass of sodium chloride (Fuji Film Wako Pure Chemical Industries, Ltd., product number: 191-01665) was added dropwise to the ultra-thin sections, and heated at 70°C on a hot plate for 3 minutes. After heating, the fibers are cleaned by washing them for 1 minute in the order of pure water, ethanol, glycerin, and ethanol. Figure 2 is a schematic diagram of a cross-sectional view of a dyed fiber, 10 represents the cross-sectional view of the fiber, 11 represents the surface layer, and 12 represents the core layer. The surface layer 11 still has color residue after dyeing and washing. In contrast, the core layer 12 loses color if it is washed.

<Brightness measurement> The cross section of the ultra-thin slice of the cellulose fiber that was dyed and washed was observed by a digital microscope. The observation was performed by transmitting light 225, mixed irradiation light 100 (coaxial 100%), and magnification 1500 times, and the image was obtained by manual depth synthesis. In addition, the sampling of cellulose fiber was performed on the cross section of 5 places after excluding the 5% part of the length direction of the winding start and winding end of the fiber wound on the winding reel, and the average value was calculated. In addition, the fiber whose cross section can be clearly observed when observing with a digital microscope was used as the measurement object. When observing under a microscope, the core layer is selected to measure the RGB value at the central part of the fiber cross section, and the surface layer is selected to measure the RGB value at the almost central part of the surface part of the fiber (i.e., the dyed part). From the measured values, the brightness of the surface layer (L') and the core layer (L) is calculated by the following formula. Brightness = [(maximum value among R, G, B values)/255]*100[%] From the brightness of the surface layer and the core layer, the brightness ratio (L'/L) of the surface layer (L') and the core layer (L) is calculated. The digital microscope used is KEYENCE VHX-7000. A cross-sectional photograph of Example 6 is shown in FIG3. Figure 3(a) is a partial enlargement of an image observed through a digital microscope. The object of measurement is a beautiful shape such as that shown in Figure 3(b).

<Degree of crystallization of cellulose fiber> The cellulose fiber (undyed) wound on the winding reel was released, cut into fibers of about 1 mm in length with scissors, dispersed in water and filtered by vacuum to make a fiber sheet. The degree of crystallization of the obtained fiber sheet was measured by X-ray diffraction analysis (XRD). The degree of crystallization was calculated by the Segal method based on the intensity value of the (002) plane peak and the intensity value of the amorphous peak. The measurement was performed using MiniFlex600 manufactured by Rigaku. The unit of the degree of crystallization of cellulose fiber is expressed in %.

<Fiber diameter of cellulose fiber> Released cellulose fiber was wound on a 0.1g weight and the fiber length was 2.5cm and the fiber diameter was measured by an automatic vibration fiber meter (DENICON DC-21 manufactured by SEARCH CO., LTD.). The fiber diameter (dtex) value was converted into fiber diameter (μm) using the fiber specific gravity of 1.52, and this value was used in the subsequent tensile test.

<Tensile test> For the cellulose fiber with measured fiber density, the weight is maintained and installed in the tensile tester (SHIMADDU small table tester EZTest) through the fixture. According to the provisions of JIS L 1013, the tensile test is carried out to measure the tensile modulus of elasticity (unit: GPa) and the elongation at break (unit: %). For a sample, a total of 15 times are measured, and the average value after excluding the maximum and minimum values is adopted. The fiber sample is obtained by vacuum drying at 60℃ for 24 hours, and the tensile test is carried out in a constant temperature and humidity chamber at 22℃50%RH. Evaluation is carried out according to the following categories. ＜＜Tensile elastic modulus＞＞ S: 30GPa or more A: 20GPa or more but less than 30GPa B: less than 20GPa (not up to practical level) ＜＜Elongation at break＞＞ S: 10% or more A: 5% or more but less than 10% B: less than 5% (not up to practical level)

Example 2 In Example 1, the ionic liquid was changed to 1-ethyl-3-methylimidazolium diethyl phosphate (EmimDEP), and the same method was used. Example 3 In Example 1, the draw ratio was changed to 13 for winding, and the fiber was produced in the same manner.

Example 4 In Example 2, the fiber was produced in the same manner except that the draw ratio was changed to 13 for winding.

Example 5 In Example 1, the fiber was produced in the same manner except that the concentration of the cellulose solution was changed to 10 mass % and the draw ratio was changed to 51 for winding.

Example 6 In Example 1, the fiber is produced in the same manner except that the concentration of the cellulose solution is changed to 10 mass % and the stretch ratio is changed to 40. In addition, the crystal orientation is measured according to the following method. <<Crystal orientation>> The fiber is fixed to a sample holder with the fiber axis direction (fiber length direction) as the reference axis, and the X-ray diffraction spectrum is measured. The azimuthal distribution intensity of the diffraction angle of the strong diffraction intensity obtained in the X-ray diffraction spectrum is measured by penetration measurement. In the azimuthal distribution curve, orientation peaks are observed near 0° and 180°, and the average value Φ _1/2 of the half-value width of these peaks is calculated. The crystal orientation is calculated by the following formula. Crystal orientation (%) = [1-(Φ _1/2 /180°)] × 100 The measurement was performed using EMPYREAN manufactured by Spectris.

Example 7 In Example 1, the concentration of the cellulose solution was changed to 8.7 mass % and the stretch ratio was changed to 51, and fibers were prepared in the same manner.

Example 8 In Example 1, the concentration of the cellulose solution was changed to 8.7 mass % and the stretch ratio was changed to 40, and fibers were prepared in the same manner. In addition, the crystal orientation was measured in the same manner as in Example 6.

Example 9 In Example 1, the ionic liquid was changed to (NMMO monohydrate, N-methyl thiophene-N-oxide-hydrate, manufactured by Angene, product number: ANG-05911), the concentration of the cellulose solution was changed to 12 mass %, the draw ratio was changed to 40, and 0.5 mass % of propyl gallate (manufactured by Fuji Film & Wako Pure Chemical Industries, Ltd., Wako First Grade) was added to the raw material slurry when the solvent was added to the raw material slurry. In addition, the fiber was prepared in the same manner. In addition, the crystal orientation was measured in the same manner as in Example 6. In addition, the step of obtaining BmimCl for spinning in Example 1 was not performed.

Comparative Example 1 In Example 1, the addition amount of KYOWAAD 500SN (manufactured by Kyowa Chemical Industry Co., Ltd.) was changed to 3% by mass, and the winding reel after winding was not immersed in water (cleaning liquid), and the same method was used.

Comparative Example 2 Several strands of commercially available rayon fiber bundles (manufactured by Cordenka, product number: RT700, number average fiber diameter 12 μm) were taken out. After being immersed in acetone for 6 hours to remove the surface treatment agent, they were dyed in the same manner as in Example 1 and the brightness was calculated. In addition, the tensile modulus of elasticity and elongation at break were measured in the same manner as in Example 1. In addition, the crystal orientation was measured in the same manner as in Example 6.

[Table 1] Embodiment 1 Embodiment 2 Embodiment 3 Embodiment 4 Embodiment 5 Embodiment 6 Lightness of surface layer (L')/core layer (L) 40/80 42/77 48/76 44/77 42/72 45/78 Lightness ratio (L'/L) 0.50 0.55 0.63 0.57 0.58 0.58 Degree of crystallization of cellulose fiber (%) 83 74 57 53 83 80 Crystal orientation of cellulose fiber (%) 93.0 Cellulose degree of polymerization 1180 1180 1180 1180 1180 1180 Fiber concentration (mass%) 9 9 9 9 10 10 Ionic liquids BmimCl EmimDEP BmimCl EmimDEP BmimCl BmimCl Stretch ratio 65 40 13 13 51 40 Fiber diameter (μm) 9 12 20 twenty four 13 12 Tensile modulus of elasticity (GPa) S A S A S S Elongation at break (%) A A S S A A [Table 2] Embodiment 7 Embodiment 8 Embodiment 9 Comparison Example 1 Comparison Example 2 Lightness of surface layer (L')/core layer (L) 40/72 45/76 41/70 83/95 62/71 Lightness ratio (L'/L) 0.56 0.59 0.59 0.88 0.87 Degree of crystallization of cellulose fiber (%) 82 81 52 35 53 Crystal orientation of cellulose fiber (%) 92.5 88.0 90.5 Cellulose degree of polymerization 1180 1180 1180 1180 - Fiber concentration (mass%) 8.7 8.7 12 9 - Ionic liquid BmimCl BmimCl NMMO monohydrate BmimCl - Stretch ratio 51 40 40 65 - Fiber diameter (μm) 14 12 14 10 12 Tensile modulus of elasticity (GPa) S S A B B Elongation at break (%) A A S A S

In Table 1 and Table 2, the polymerization of cellulose indicates the degree of polymerization of the cellulose raw material. From the results of Table 1 and Table 2 above, it is clear that the cellulose fiber of the present invention can improve the physical properties of elastic modulus and elongation in a well-balanced manner. In contrast, the elastic modulus of the fiber of the comparative example is evaluated as "B", and the elastic modulus and elongation cannot be improved in a well-balanced manner.

1: Cellulose solution 2: Nozzle 3: Cellulose fiber 4: Coagulation liquid 5: Winding machine 10: Fiber cross section 11: Surface layer 12: Core layer

[Figure 1] Figure 1 is an example of a schematic diagram showing an apparatus and steps for producing cellulose fibers. [Figure 2] Figure 2 is a schematic diagram showing a cross section of cellulose fibers after dyeing and washing. [Figure 3] Figures 3 (a) and (b) are photographs of a cross section of cellulose fibers of Example 6 after dyeing and washing.

1: Cellulose solution

2: Nozzle

3: Cellulose fiber

4: Coagulation liquid

5: Winding machine

Claims (11)

A cellulose fiber, wherein the ratio (L'/L) of the lightness of the surface layer (L') to the lightness of the core layer (L) when dyed with a dye is less than 0.70, and the lightness of the surface layer (L') and the lightness of the core layer (L) of a cross section of the cellulose fiber are values calculated by measuring the R, G, and B values of the respective layers according to [(the maximum value among the R, G, and B values)/255]*100[%]. The cellulose fiber of claim 1, wherein the degree of crystallization measured by X-ray diffraction (XRD) is greater than 40%. The cellulose fiber of claim 1 or 2, which is stretched. The cellulose fiber of claim 1, wherein the degree of crystallization measured by X-ray diffraction (XRD) is greater than 40%, and the fiber is stretched. The cellulose fiber of claim 1 or 2, wherein the number average fiber length is greater than 1 mm and less than 10 mm. The cellulose fiber of claim 1 or 2, which is a chopped strand. The cellulose fiber of claim 1 or 2 is a continuous fiber. A resin composition comprising the cellulose fiber according to any one of claims 1 to 7, and a resin. A molded article is formed from the resin composition of claim 8. A method for producing cellulose fiber includes: immersing a cellulose solution containing raw material cellulose in a coagulation liquid, spinning, and then washing with a washing liquid containing water. The method for producing cellulose fiber of claim 10, wherein the ratio (L'/L) of the lightness of the surface layer (L') to the lightness of the core layer (L) of the cellulose fiber when dyed with a dye is less than 0.70, the lightness of the surface layer (L') and the lightness of the core layer (L) of the cross section of the cellulose fiber are the values calculated by measuring the R, G, B values of the respective layers according to [(the maximum value among the R, G, B values)/255]*100[%], the crystallinity of the cellulose fiber measured by X-ray diffraction (XRD) is greater than 40%, and the cellulose fiber is stretched.

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