JP2006070368A - Readily splittable and fibrillable acrylic short fiber assembly and wet nonwoven fabric - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a readily splittable and fibrillable acrylic short fiber assembly that is readily and finely splittable and a wet nonwoven fabric in which a plurality of microfibers having different fiber diameters ≤1 μm fiber diameters are interlaced. <P>SOLUTION: The readily splittable and fibrillable acrylic short fiber assembly comprises a wet short fiber that is composed of an acrylonitrile-based polymer, a methyl methacrylate-based polymer and/or a cellulose diacetate, has a plurality of cracks with at least one crack having length of 25-80% cross section width and has 1.5-3.0 apparent fineness ratio. The wet nonwoven fabric comprises an acrylic split fibrillated fiber that is obtained from the short fiber assembly as a raw material, is composed of a plurality of microfibers made of an acrylonitrile-based polymer containing ≥50 wt.% of acrylonitrile, a methyl methacrylate-based polymer and a cellulose diacetate and having different fiber diameters of ≤1 μm fiber diameters and amounting to at least 40% based on the total of microfibers having ≤0.5 μm fiber diameter. The microfibers are three-dimensionally interlaced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an easily split fiber / fibril acrylic short fiber aggregate and a nonwoven fabric using the short fiber aggregate, and more particularly, easily split or fibrillated by mechanical stress or impact force of high-pressure water jet. In particular, the present invention relates to an easily split and fibrillar acrylic short fiber aggregate that can be suitably used for producing a wiping sheet and the like, and a wet nonwoven fabric suitable as a wiping sheet using the short fiber aggregate.

  Acrylic fibers have been widely used in the clothing and bedding fields due to their excellent texture and dyeability, but as a textile material application, attention has been paid to the balance between the appropriate hydrophilicity and lipophilicity of acrylic fibers, Attempts have been made to develop various wiping materials, particularly wet wipers.

  In order to make the most of this hydrophilic / lipophilic balance, which is a characteristic of acrylic fibers, a technique has been adopted in which the fiber surface area is increased to improve wiping performance by making the acrylic fibers ultrafine fibers. Non-woven fabrics as wiping sheets are often used in a disposable manner, so reducing the cost of their production is a very big problem. By reducing the size of fibers that increase the fiber surface area that affects wiping performance, and processing non-woven fabrics. Therefore, there is a demand for a low-weight nonwoven fabric that reduces the amount of energy used and further reduces the amount of fiber used.

  One of the methods for obtaining ultrafine fibers of acrylic fiber is a direct spinning method, but the ultrafine fibers obtained by the direct spinning method have an industrially obtained fiber diameter of about 3 μm (fineness of about 0.1 dtex), The nonwoven fabric obtained by forming the ultrafine fiber into a sheet by a wet nonwoven fabric manufacturing method has a smaller fiber surface area than that obtained by the method in which the ultrafine fiber is split into fibrils, and has a limited wiping performance.

  On the other hand, as a method of obtaining ultrafine fibers of acrylic fibers, there is a method of splitting split fibers into split fibers, adding polyalkylene glycol to the spinning dope, eluting the polyalkylene glycol after fiber shaping, A method has been proposed in which a plurality of straw-shaped voids are formed to impart splitting properties (see Patent Document 1 and Patent Document 2).

  However, in these methods, not only the fiber production cost is increased by adding a process such as recovery of polyalkylene glycol, but the presence of voids inside the fiber is high for splitting the fiber in forming a sheet. It is disadvantageous in terms of cost because it is necessary to perform water jet with water pressure and to repeat the water jet treatment. In addition, the resulting sheet has insufficient split fiber fibrillation of the fibers constituting the sheet, and although the surface layer portion of the fiber is relatively split fiber fibrils, the entire fiber is finely split fiber fibrils. There is a limit to the wiping performance. In addition, when the pressure in the high-pressure water flow is increased, the degree of split fiber fibrillation is increased, but fine fiber waste (lint) is generated, which hinders the use as a wiping sheet.

  In addition, as a splitting fiber for obtaining ultrafine fibers of an acrylic fiber, a method for improving splitting by forming a phase separation structure of an acrylonitrile polymer and a different polymer other than the acrylonitrile polymer has been proposed. (See Patent Document 3). However, even in this method, split fiber fibrils can be formed by a high-pressure water stream at a relatively low pressure, but the fiber surface has a strong tendency to split into fibrils with the fiber trunk remaining, and split fiber fibrillarity is insufficient.

When these conventional splitting fibers are produced by wet papermaking, if they are disaggregated by stirring in order to open the fibers one by one, split fiber fibrillation will proceed, Entanglement causes entanglement defects increase or poor formation, or if the stirring force during the disaggregation process is lowered, the opening property becomes insufficient, and several to several tens of fibers are stuck and remain in a bundle In particular, it is difficult to use for producing a nonwoven fabric with a low basis weight which is lower than 50 g / m ² .

  In any case, there is a need for acrylic raw cotton suitable for the manufacture of wiping sheets that can provide excellent wiping performance, uniform texture, sheet strength, etc., and can be split into fibrils at low energy even at low weight. However, fibers that satisfy all the requirements have not been obtained.

JP-A 63-309614 Japanese Patent Laid-Open No. 2-200857 JP-A-7-82605

In view of such a situation, the present inventors have conducted intensive studies to obtain a non-woven fabric that can be used as a wiping sheet using an easily split fiber / fibril acrylic fiber that satisfies the required performance and the fiber. The present invention has been achieved. The object of the present invention is as follows.
The first purpose is a papermaking web that has good spreadability even with weak agitation force during wet papermaking and is uniform and has few defects due to fiber entanglement. After web formation, it is split and fibrillated even with low water flow energy, and has a high specific surface area. A second object of the present invention is to provide an easily split fiber / fibrillar acrylic short fiber assembly that can be obtained by using the easily split fiber / fibril acrylic short fiber assembly. Another object of the present invention is to provide a wet nonwoven fabric that has excellent sheet strength and excellent wiping performance.

The gist of the present invention is as follows.
The first invention is composed of 40 to 85% by weight of an acrylonitrile polymer containing 50% by weight or more of acrylonitrile and 60 to 15% by weight of a polymer selected from the group of methyl methacrylate polymer and cellulose diacetate. A plurality of cracks, at least one of which is a crack having a length of 25 to 80% of the cross-sectional width, the wet fiber having an apparent fineness ratio of 1.5 to 3.0 and a fiber length of 3 to 10 mm. It is an easy-fibre / fibrillar acrylic short fiber assembly made of short fibers.
The second invention includes a plurality of fine fibers having different fiber diameters of 1 μm or less, each composed of acrylonitrile-based polymer containing 50% by weight or more of acrylonitrile, methyl methacrylate-based polymer, and cellulose diacetate. Further, the present invention is a wet nonwoven fabric comprising 20% by weight or more of split fiber fibrillated fibers in which fine fibers having a fiber diameter of 0.5 μm or less occupy at least 40% of the total, and the split fiber fibrillated fine fibers are three-dimensionally entangled.

According to the present invention, the following excellent effects can be obtained.
1. The easily split fiber and fibrillar acrylic short fiber aggregate of the present invention is extremely excellent in water dispersibility, and a highly uniform web can be obtained during wet papermaking. It is an aggregate of short fibers that can be split into fibers at the same time as the split fibers are fibrillated.
2. The easily split fiber / fibrillar acrylic short fiber aggregate of the present invention is useful as a raw material for wet nonwoven fabrics, and can produce wet nonwoven fabrics without increasing the production cost of the nonwoven fabrics.
3. The wet nonwoven fabric of the present invention contains fine fibers having a fiber diameter of 1 μm or less and a fiber diameter of 0.1 μm, and is extremely excellent in wiping performance against not only water-based but also oil-based dirt. There is no spot of fiber entanglement and it has excellent formation.

  In the easily split fiber / fibril acrylic short fiber aggregate of the present invention, the short fiber is composed of an acrylonitrile polymer containing 50% by weight or more of acrylonitrile, and a polymer selected from the group of methyl methacrylate polymer and cellulose diacetate. Composed. The polymer selected from this group is a polymer that is incompatible or poorly compatible with the acrylonitrile-based polymer.

  The acrylonitrile-based polymer containing 50% by weight or more of acrylonitrile may be a homopolymer of acrylonitrile, or a copolymer containing 50% by weight or more of acrylonitrile and copolymerized with another vinyl monomer copolymerizable with acrylonitrile. May be. Other vinyl monomers used as the copolymerization component are not particularly limited, and examples thereof include acrylic acid, methacrylic acid, vinyl acetate, vinyl chloride, vinylidene chloride, acrylamide, and methacrylamide.

  The molecular weight of the acrylonitrile-based polymer is not particularly limited, but the molecular weight is preferably 50,000 to 1,000,000. If the molecular weight is less than 50,000, the spinnability in the spinning process is deteriorated and the fiber quality of the fiber is also deteriorated. If the molecular weight is more than 1,000,000, the polymer concentration in the preferred viscosity range of the spinning dope is lowered and the productivity is lowered.

  In the present invention, the methyl methacrylate polymer or cellulose diacetate is incompatible or poorly compatible with the acrylonitrile polymer, but is soluble in the solvent of the acrylonitrile polymer, and is a mixed solution with the acrylonitrile polymer. The stock solution can be used for spinning.

  The methyl methacrylate polymer may be a copolymer having polymethyl methacrylate or methyl methacrylate as a main component and another vinyl monomer copolymerizable with methyl acrylate. Examples of other vinyl monomers used as a copolymerization component include methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate and the like.

  The molecular weight of the methyl methacrylate polymer is not particularly limited, but the molecular weight is preferably 30,000 to 300,000. When the molecular weight is less than 30,000, dropout in the spinning process may be a problem, and when the molecular weight exceeds 300,000, the spinnability tends to decrease. Further, it is desirable that the methyl methacrylate polymer is hardly soluble in water. When the solubility in water is high, dropping into the coagulation bath occurs, and at the same time, fiber fluffing and yarn breakage tend to occur, and the spinning stability tends to decrease.

  Moreover, it is preferable that the cellulose diacetate in this invention is a cellulose diacetate whose average acetylation degree is 48.8% or more and less than 56.2%.

  The easily split fiber / fibril acrylic short fiber assembly of the present invention is composed of 40 to 85% by weight of acrylonitrile polymer and 60 to 15% by weight of methyl methacrylate polymer and / or cellulose diacetate. If the polymer is less than 40% by weight, excellent wiping performance due to the hydrophilic / lipophilic balance characteristic of acrylic fibers cannot be ensured, and if it exceeds 85% by weight, easy splitting and fibrillation are not exhibited.

  In the present invention, the methyl methacrylate polymer and cellulose diacetate constituting the fiber together with the acrylonitrile polymer may be present alone or both polymers may be present simultaneously. Furthermore, it may be a combination of different polymers with a methyl methacrylate polymer or a combination of different polymers with cellulose diacetate. Methyl methacrylate polymer is effective in reducing lint after split fiber fibrillation treatment, cellulose diacetate is effective in improving water absorption, methyl methacrylate polymer and cellulose diacetate are Depending on the intended use of the nonwoven fabric to be produced, it can be selected and combined as appropriate.

  In the easily split fiber acrylic short fiber assembly of the present invention, as a remarkable feature on the form of each short fiber, the fiber cross section has a plurality of cracks, and at least one of them is 25 to 80% of the cross section width. The crack is preferably a crack such that one other end reaches the fiber surface. The cross-sectional width of the fiber in the present invention refers to the diameter when the cross-sectional shape of the fiber is assumed to be a perfect circle.

  The occurrence of cracks in the fiber cross-section in the short fibers of the easy-split acrylic short fiber aggregate of the present invention is as follows: 1) When the spinning stock solution in which the different polymer solution is in a phase-separated state is extruded from the nozzle holes and solidifies in the coagulation bath The differences in the solidification characteristics of each polymer, 2) voids in the fibers that occur as a result of solvent removal during the coagulation / washing process, 3) interfacial debonding between different polymers due to stretching during or after coagulation, etc. It is estimated that it will occur.

  As the number of cracks observed in the fiber cross section increases, the greater the number of fibers observed in the fiber cross section, the smaller the split fiber fibrillation, and the longer the crack than the short crack, the more effectively the split fiber fibrillation. It is important that the length is 25 to 80% of the cross-sectional width of the fiber, and it is particularly preferable that the other end of the crack reaches the fiber surface. This long crack exerts the effect of a wedge being driven into the fiber, cracks inside the fiber, splits without leaving a thick fibrous trunk, and each is based on the interface of the polymer phase separation Fine fibrillation. If the length of the crack is less than 25% of the cross-sectional width, this effect is small, and if the length exceeds 80% of the cross-sectional width, split fiber fibrils can be easily formed with a slight shearing force. However, handling becomes difficult, which is not preferable.

And the easily split fiber / fibril acrylic short fiber aggregate of the present invention is in a wet state in which the apparent fineness ratio of the fiber calculated from the following formula is 1.5 to 3.0 and the fiber length is 3 to 10 mm. It consists of a certain short fiber. Further, the fineness of the short fiber is not particularly limited and may be any fineness generally used for the production of wet nonwoven fabrics, for example, 0.3 to 10 dtex.
Apparent fineness ratio = apparent fiber cross-sectional area / fineness-converted cross-sectional area Here, the apparent fiber cross-sectional area is the cross-sectional area of the wet fiber obtained as described later, and the fineness-converted cross-sectional area is the fiber in the wet state. Is a fiber cross-sectional area calculated from the specific gravity and mixing ratio of the polymer constituting the fiber, with the fineness calculated from the mass after drying to a constant weight at 20 ° C. and 65% RH.

  This apparent fineness ratio is related to the openability and water dispersibility of the easily split and fibrillar acrylic short fiber aggregates. If the apparent fineness ratio is 1.5 or more, the short fibers during wet papermaking It is easy to obtain a uniform papermaking web with a very good dispersion state. If the apparent fineness ratio is less than 1.5, the short fibers are difficult to open and paper making becomes difficult. If the apparent fineness ratio exceeds 3, the fiber opening and water dispersibility are good, but the yarn in spinning Cutting and winding around the roll occur frequently, making it difficult to manufacture the fiber itself.

  When the fiber length of the short fiber is less than 3 mm, the strength of the nonwoven fabric is reduced and the occurrence of lint from the nonwoven fabric after split fiber fibrillation is increased. When the fiber length exceeds 10 mm, uniform wet Paper making becomes difficult. Thus, the short fiber in the easily split fiber / fibril acrylic short fiber aggregate of the present invention has a phase separation structure that is very easily split into fibrils, and has excellent fiber opening and water dispersibility.

  The method for obtaining the split fiber / fibril acrylic short fiber aggregate of the present invention will be described. An acrylonitrile polymer containing 50% by weight or more of acrylonitrile, a polymer selected from the group of methyl methacrylate polymer and cellulose diacetate; Is dissolved in a common solvent to prepare a spinning stock solution, and the spinning method is spun into a coagulation bath and coagulated using a wet spinning method or a dry-wet spinning method to form a filamentous body. The short fiber assembly of the present invention can be obtained by removing the solvent and stretching it three times or more, collecting it in a wet state, and cutting it to a fiber length of 3 to 10 mm. Moreover, in order to reduce the residual shrinkage of the fiber before or after the fiber is cut, a relaxation treatment with hot water or pressurized steam may be performed.

  In the process of obtaining this short fiber aggregate, when subjected to a drying treatment with a hot roll or hot air, not only the number and length of cracks formed in the fiber cross section tends to be reduced, but the split fiber fibrillarity is lowered, Adhesion between the fibers occurs, and the openability and water dispersibility during wet papermaking tend to be lowered. It is necessary to collect the solvent removed and drawn in boiling water in a wet state.

  The solvent for preparing the spinning dope may be a common solvent that dissolves each polymer of acrylonitrile polymer, methyl methacrylate polymer, and cellulose diacetate, and examples thereof include dimethylformamide, dimethylacetamide, and dimethyl sulfoxide. . Further, an aqueous solution of a common solvent is preferably used for the coagulation bath.

  The wet nonwoven fabric of the present invention has a fiber diameter of 1 μm or less, which is composed of acrylonitrile-based polymer, methyl methacrylate-based polymer and / or cellulose diacetate each containing 50% by weight or more of acrylonitrile, or a mixture of two or more of them. 20-100% by weight of acrylic split fiber fibrillated fibers comprising a plurality of different fine fibers and having a fiber diameter of 0.5 μm or less occupying at least 40% of the total fine fibers, and 80-0% by weight of other fibers The fine fibers produced by splitting into fibrils are three-dimensionally entangled with each other. When the acrylic split fiber fibrillated fiber in the wet nonwoven fabric is less than 20% by weight, the amount of fine fibers is small, and excellent wiping performance cannot be obtained.

  The split fiber fibrillated fiber in the nonwoven fabric of the present invention is composed of 40 to 85% by weight of acrylonitrile polymer containing 50% by weight or more of acrylonitrile, 60 to 15% by weight of polymer selected from the group of methyl methacrylate polymer and cellulose diacetate. And has fine fibers produced by splitting into fibrils having a fiber diameter of 1 μm or less. In the present invention, each short fiber of the easily split and fibrillar acrylic short fiber aggregate preferably used for the production of wet nonwoven has easy split and fibril properties, so the nonwoven fabric has a fiber diameter of 1 μm or less. Contains a large amount of split fiber fibrillated fine fibers. Therefore, the more fine fibers that are split and fibrillated with a fiber diameter of 1 μm or less, the better the wiping performance, so the lower limit of the amount of easy split fiber and fibrillar acrylic short fiber aggregates used when manufacturing nonwoven fabrics It can be reduced to 20% by weight.

  In the non-woven fabric of the present invention, the fine fibers obtained by splitting the easily split and fibrillar acrylic short fibers into fibrillated fibers are composed of acrylonitrile-based polymer, methyl methacrylate-based polymer, or cellulose diacetate, or mixed with each other. The fine fibers having a fiber diameter of 1 μm or less are three-dimensionally entangled with each other or with the fibers that have been split into fibrils to form a nonwoven fabric. In the nonwoven fabric of the present invention, the split fiber fibrillated fiber is a fiber containing fine fibers generated by split fiber fibrillation, and the split fiber in a completely separated state or an incompletely separated state from the original easily split fiber / fibril short fiber. It is a fiber that includes fine fibers that have been fibrillated, and further includes fine fibers having different fiber diameters depending on the degree of progress of split fiber fibrillation.

  In the nonwoven fabric of the present invention, in addition to the acrylic split fiber fibrillated fiber containing fine fibers having a fiber diameter of 1 μm or less, the fiber length of 3 to 10 mm, particularly easily split fiber, is intended to improve the strength and bulkiness of the nonwoven fabric. Ordinary acrylic fiber, polyester fiber, nylon fiber, polypropylene fiber, vinylon fiber, rayon fiber, etc. may be mixed by blending cotton, blending, or the like. In particular, as the acrylic fiber to be mixed, an ultrafine acrylic fiber having a fineness of 0.05 to 0.4 dtex and an L / D (fiber length / fiber diameter) of 500 to 2000 made of an acrylonitrile polymer containing 50% by weight or more of acrylonitrile, It is preferably used in terms of improving the strength of the nonwoven fabric without reducing the wiping performance.

Nonwoven fabric of the present invention is particularly but not to limit its basis weight, preferably in the basis weight range of from a low basis weight of 10 g / m ² to high basis weight of 200 g / m ^2, and exhibits excellent wiping performance, nonwoven surface Forms a formation with excellent uniformity with no fiber tangles. The basis weight of less than 10 g / m ^2, the formation of 3-dimensional entangled structure of fine fibers Wari繊fibrillated becomes insufficient, the strength of the nonwoven fabric is lowered, if it exceeds 200 g / m ^2, Wari繊by water injection・ It becomes difficult to discharge water during fibrillation and three-dimensional entanglement, making it difficult to form a uniform formation.

  The method for producing a nonwoven fabric of the present invention comprises the easily split fiber / fibrillar acrylic short fiber aggregate and, if necessary, other fibers such as normal acrylic fibers or ultrafine acrylic fibers as a raw material. Using wet papermaking to form a papermaking web, a wet nonwoven fabric is obtained by water splitting the papermaking web by splitting fibrillation of easy splitting / fibrillar acrylic short fibers and three-dimensional entanglement processing of fine fibers It can also be dried with a hot roll or hot air if necessary.

  As a raw material for making paper, it is necessary to use 20% by weight or more of the easily split fiber / fibrillar acrylic short fiber aggregate. When other fibers are mixed, the splitting of easily split fiber / fibrillar acrylic short fiber is required. It is preferable to open and disperse in water so that fiber fibrillation does not progress. Along with other fibers, it is opened and dispersed in water with a weak stirring force, or each is separately opened and dispersed. A uniform papermaking web can be formed by mixing. In wet papermaking, heat-bonding binder fibers can be used to further improve the strength of the nonwoven fabric. In the case of using a heat-bonding binder fiber, the amount is 25% by weight or less based on the papermaking raw material so as not to make the nonwoven fabric rough.

   The water jet is applied to the paper web by supporting the paper web on a net or on a roller, preferably at a water pressure of 3 to 6 MPa, and jetting a water stream to split easily split / fibrillar acrylic short fibers to a fiber diameter of 1 μm or less. At the same time as the fiber fibrillation, it is three-dimensionally entangled with the fine fibers generated by split fiber fibrillation, the fibers having split fiber fibrillation, and other fibers used in combination. The water jet is appropriately selected and combined according to the intended use of the nonwoven fabric to obtain the shape and arrangement of the jet nozzle. When the split fiber / fibril acrylic short fiber aggregate of the present invention is used as a papermaking raw material, water jet is performed at a low pressure and with a small number of sprays due to the phase separation structure of the easy split fiber / fibril acrylic short fiber. Split fiber fibrillation and entanglement can be performed.

  Since the nonwoven fabric of the present invention contains a large amount of ultrafine fibers having a fiber diameter of 1 μm or less and a fiber diameter of 0.1 μm, the wiping performance for wiping and removing dirt is remarkably excellent, and fine fibers are included. Nevertheless, no linting occurs and the wiping sheet made of the nonwoven fabric of the present invention is useful as various wiping materials, and the nonwoven fabric of the present invention is useful as a filter material in addition to the wiping sheet.

  Hereinafter, the present invention will be specifically described by way of examples. In addition, the evaluation item in an Example was measured with the following method.

(Crack of fiber cross section)
Fill the tube of soft vinyl chloride resin with an inner diameter of 1.2 mm and a thickness of 0.3 mm to the extent that the fiber does not move. Cut the fiber with the razor blade in the vertical direction, and use a sputtering device to cut the fiber. The gold thin film was processed and observed with a scanning electron microscope 1400 times.

(Apparent fineness ratio)
The short fiber aggregate is immersed in liquid nitrogen, frozen, dried under reduced pressure while keeping the frozen state, and this is taken with a scanning electron microscope 500 times in the same manner as the observation of cracks in the fiber cross section. Using the image processing software, the cross-sectional area of 100 fibers was calculated from the photograph to obtain the apparent fiber cross-sectional area as an average value, and the apparent fineness ratio was calculated from this and the fineness-converted cross-sectional area.

(Opening, dispersibility (splitability))
Using a standard pulp disintegrator (manufactured by Kumagaya Riki Kogyo Co., Ltd., No 2530, JIS P8209 compliant device), water dropped into a fiber concentration of 1% by weight was stirred for 30 seconds at a propeller blade rotation speed of 1000 rpm, and this treatment 10 ml of the liquid was sampled and diluted 50 times with water in a 1000 ml glass beaker, and the fiber dispersion state was visually determined. Judgment criteria are as follows: even if there are no bundles or lumps of fibers of several to several hundred fibers at all, ○ is extremely minor, × is very large, and Δ is intermediate did.

(Split and fibril properties)
Using a household mixer (manufactured by Toshiba, MX-L20GA, 60 Hz AC power supply), measure the stirring time required for the freeness to drop to 300 ml or less, and use that time as a simple indicator for splitting and fibrillation. It was. The shorter the stirring time, the better the splitting and fibrillation properties with a small water jet energy. The time is within 3 minutes, ◎ within 10 minutes, ◯ within 20 minutes, and over 20 minutes as x. The freeness is measured by putting 3 g of fiber (in terms of dried fiber) in 700 ml of water and stirring with a mixer for a predetermined time, diluting this treatment solution with water to 1000 ml, and adding this solution to JIS P8121 Canadian standard drainage. The value was measured using a degree tester and the temperature was corrected to 20 ° C. from Appendix 1 of JIS P8121.

Example 1
A polymer stock solution A having a polymer concentration of 25% by weight, methyl methacrylate, obtained by heating and dissolving an acrylonitrile (AN) 92% by weight, vinyl acetate 8% by weight AN polymer having a molecular weight of 90000 (true specific gravity 1.16) in dimethylacetamide (DMAc). (MMA) 90% by weight, 10% by weight of methyl acrylate MMA polymer (manufactured by Mitsubishi Rayon Co., Ltd., Acrypet MDK, molecular weight 85000, glass transition temperature 90 ° C., true specific gravity 1.2) is heated and dissolved in DMAc to obtain a polymer concentration. 30% by weight of polymer stock solution B was prepared. Polymer stock solution A and polymer stock solution B were uniformly mixed with a static mixer immediately before the nozzle so that the polymer weight ratio was 50/50 to prepare a spinning stock solution.

  This spinning dope is heated to 60 ° C. and discharged by a wet spinning method into a 40 ° C. coagulation bath made of a DMAc 30 wt% aqueous solution from a spinneret having a nozzle shape of 75 μm in diameter and 30,000 nozzles. The yarn was taken out while being stretched, stretched 4.5 times simultaneously with solvent removal in 80 ° C hot water, subjected to 10% relaxation treatment in boiling water, cooled to 30 ° C, and the tow of the fiber bundle was wet. Collected at The tow was cut to a length of 1000 mm to prepare a sample, which was dried to a constant weight in an atmosphere of 20 ° C. and 65% RH. The average single fiber fineness was determined from the mass, and the average single fiber fineness was 3 dtex. It was. The collected tow was cut into a length of 6 mm with a guillotine cutter to obtain a short fiber aggregate.

  Table 1 shows the short fibers of the obtained short fiber aggregate and the evaluation results of the short fiber aggregate. As is clear from Table 1, it was confirmed that there were many cracks in the fiber cross section of each fiber, and three of them were 25% or more of the cross-sectional width at which the other end reached the fiber surface. The apparent fineness ratio of the fiber was 1.85, and it was excellent in splitting properties, and extremely excellent in splitting and fibrillation.

(Example 2)
AN polymer (92% by weight of AN and 8% by weight of vinyl acetate) and an AN polymer having a molecular weight of 90000 (true specific gravity of 1.16) are dissolved in DMAc by heating and dissolved in a polymer stock solution A having a polymer concentration of 25% by weight, cellulose diacetate having an average acetylation degree of 55% (Daicel Co., Ltd., cellulose diacetate MI flake, true specific gravity 1.32) was dissolved in DMAc by heating to prepare polymer stock solutions C each having a polymer concentration of 18% by weight. Polymer stock solution A and polymer stock solution C were uniformly mixed with a static mixer immediately before the nozzle so that the polymer weight ratio was 70/30 to prepare a spinning stock solution.

  This spinning dope is heated to 75 ° C. and discharged by a wet spinning method into a 35 ° C. coagulation bath made of DMAc 40% by weight aqueous solution from a spinneret having a nozzle shape of 60 μm in diameter and 20,000 nozzles. The yarn was taken out while being stretched, stretched 5 times at the same time as solvent removal in boiling water, cooled to 30 ° C., and the tow was collected in a wet state. The tow was cut to a length of 1000 mm to prepare a sample, which was dried to a constant weight in an atmosphere of 20 ° C. and 65% RH, and the average single fiber fineness was determined from the mass. The average single fiber fineness was 2.5 dtex. Met. The collected tow was cut into a length of 6 mm with a guillotine cutter to obtain a short fiber aggregate.

  Table 1 shows the short fibers of the obtained short fiber aggregate and the evaluation results of the short fiber aggregate. As is apparent from Table 1, it was confirmed that there were many cracks in the fiber cross section of each fiber, and one of the cracks was 25% or more of the cross-sectional width at which the other end reached the fiber surface. The apparent fineness ratio of the fiber was 1.93, and it was excellent in splitting properties and extremely excellent in splitting and fibrillation.

(Comparative Example 1)
An AN polymer (92% by weight of AN and 8% by weight of vinyl acetate) having a molecular weight of 90,000 (true specific gravity 1.16) was dissolved in DMAc by heating to prepare a polymer stock solution A having a polymer concentration of 25% by weight, and polyalkylene glycol (Sanyo Kasei). New Paul PE-78, EO-PO-EO polyether, EO / PO = 8/2, molecular weight 12000) was dissolved by heating in DMAc to prepare a solution D having a polymer concentration of 30% by weight. Polymer stock solution A and solution D were uniformly mixed with a static mixer immediately before the nozzle so that the solid content weight ratio was 90/10 to prepare a spinning stock solution.

  This spinning dope is heated to 60 ° C. and discharged by a wet spinning method into a 35 ° C. coagulation bath composed of a DMAc 55 wt% aqueous solution from a spinneret with a nozzle shape of 90 μm in diameter and 20,000 nozzles. The yarn was taken out while being stretched, stretched 6.0 times simultaneously with solvent removal in hot water at 80 ° C., cooled to 30 ° C., and the tow of the fiber bundle was collected in a wet state. The tow was cut to a length of 1000 mm, used as a sample, dried in an atmosphere of 20 ° C. and 65% RH until a constant weight was obtained, and the average single fiber fineness was determined from the mass. The average single fiber fineness was 2 dtex. It was. The collected tow was cut into a length of 6 mm with a guillotine cutter to obtain a short fiber aggregate.

  Table 1 shows the short fibers of the obtained short fiber aggregate and the evaluation results of the short fiber aggregate. As is clear from Table 1, although there are many fine straw-shaped holes in the fiber cross section of each fiber, no cracks are confirmed, and the apparent fineness ratio of the fiber is 1.76, which is excellent in the fiber separation property. The split fiber and fibril properties were very inferior.

(Comparative Example 2)
In Example 1, after spinning 4.5 times in the spinning process, a spinning oil was applied, and the fiber roll tow was collected after drying in contact with a 110 ° C. hot roll in tension. The tow was cut to a length of 1000 mm to prepare a sample, which was dried to a constant weight in an atmosphere of 20 ° C. and 65% RH, and the average single fiber fineness was determined from the mass. The average single fiber fineness was 2.7 dtex. Met. The collected tow was cut into a length of 6 mm with a guillotine cutter to obtain a short fiber aggregate.

  Table 1 shows the short fibers of the obtained short fiber aggregate and the evaluation results of the short fiber aggregate. As is apparent from Table 1, it was confirmed that there were many cracks in the fiber cross section of each fiber, and one of the cracks was 25% or more of the cross-sectional width at which the other end reached the fiber surface. However, the apparent fineness ratio of the fiber was 1.25, the splitting property was poor, and the split fiber / fibril property was inferior.

(Example 3)
The short fiber aggregate obtained in Example 1 was stirred for 30 seconds at a rotation speed of 1000 rpm of the propeller blade using a standard pulp disintegrator (manufactured by Kumagai Riki Kogyo Co., Ltd., No 2530, JIS P8209 compliant device), and the fiber concentration was 1 weight. % Aqueous dispersion 1 was obtained. On the other hand, an ultrafine acrylic fiber for papermaking (Mitsubishi Rayon Co., Ltd., Bonnell MVP-D122, fineness 0.1 dtex, fiber length 6 mm, L / D2000) was stirred for 3 minutes at a blade rotation speed of 3000 rpm, and the fiber concentration was 1% by weight. An aqueous dispersion 2 was obtained. The aqueous dispersion 1 and the aqueous dispersion 2 are stirred and mixed in a dispersion tank of a standard square sheet machine (No. 2555, manufactured by Kumagai Riki Kogyo Co., Ltd.) at a weight ratio of 50/50, and the papermaking basis weight becomes 35 g / m ² . Thus, a paper web was obtained by rolling up on a 100 mesh wire net.

  This papermaking web was placed on a support of a water jet treatment apparatus using a plastic net (manufactured by Nippon Filcon, model number FOL90) as a support, and arranged in a line on a straight line with a hole diameter of 0.12 mm and a hole pitch of 0.7 mm. Water flow was jetted onto the papermaking web while moving the support at a speed of 10 m / min from the nozzle at a water pressure of 5 MPa, then dehydrated with a nip roll and dried with a hot air heater at 110 ° C. to obtain a nonwoven fabric.

  When the obtained nonwoven fabric was observed with a scanning electron microscope 2000 times, the fiber diameter was split into a plurality of fine fibers having different fiber diameters of 1 to 0.1 μm, and the resulting fine fibers or fine fibers were formed. And finely fibrillated fibers, and mixed fine acrylic fibers are entangled three-dimensionally with each other, and among the fine fibers, fine fibers with a fiber diameter of 0.5 μm or less are about the entire fine fiber. 50% (fibers having a fiber diameter of 1 μm or less are about 85%). The measurement of the proportion of fine fibers having a fiber diameter of 0.5 μm or less is made by drawing vertical and horizontal lines with a length of 30 μm on an arbitrary part of a scanning electron microscope 2000 times photograph and measuring the fine fibers crossing each line. This was based on a method of measuring the number of fibers and determining the ratio of the number of fibers having a fiber diameter of 0.5 μm or less. In order to evaluate the wiping performance of the obtained non-woven fabric, fingerprints were imprinted on the glass plate, and when the dirt was wiped off, the wiping performance was extremely excellent.

Example 4
The short fiber aggregate obtained in Example 2 was stirred for 30 seconds at a rotation speed of 1000 rpm of the propeller blade using a standard pulp disaggregator (manufactured by Kumagai Riki Kogyo Co., Ltd., No2530, JIS P8209 standard apparatus), and the fiber concentration was 1 weight. % Aqueous dispersion 3 was obtained. On the other hand, an ultrafine acrylic fiber for papermaking (Mitsubishi Rayon Co., Ltd., Bonnell MVP-D122, fineness 0.1 dtex, fiber length 6 mm, L / D2000) was stirred for 3 minutes at a blade rotation speed of 3000 rpm, and the fiber concentration was 1% by weight. An aqueous dispersion 4 was obtained. The aqueous dispersion 3 and the aqueous dispersion 4 are stirred and mixed in a dispersion tank of a standard square sheet machine (No. 2555, manufactured by Kumagai Riki Kogyo Co., Ltd.) at a weight ratio of 50/50, and the papermaking basis weight becomes 35 g / m ² . Thus, a paper web was obtained by rolling up on a 100 mesh wire net.

  This papermaking web was placed on a support of a water jet treatment apparatus using a plastic net (manufactured by Nippon Filcon, model number FOL90) as a support, and arranged in a line on a straight line with a hole diameter of 0.12 mm and a hole pitch of 0.7 mm. Water flow was jetted onto the papermaking web while moving the support at a speed of 10 m / min from the nozzle at a water pressure of 5 MPa, then dehydrated with a nip roll and dried with a hot air heater at 110 ° C. to obtain a nonwoven fabric.

  When the obtained nonwoven fabric was observed with a scanning electron microscope 2000 times, the fiber diameter was split into a plurality of fine fibers having different fiber diameters of 1 to 0.1 μm, and the resulting fine fibers or fine fibers were formed. And fibrillated fibers, and mixed fine ultra-acrylic fibers are entangled three-dimensionally, and among the fine fibers, fine fibers with a fiber diameter of 0.5 μm or less are included in the entire fine fibers. It accounted for about 47% (about 78% of fibers with a fiber diameter of 1 μm or less). The ratio of fine fibers having a fiber diameter of 0.5 μm or less was measured by the same method as in Example 3. In order to evaluate the wiping performance of the obtained non-woven fabric, fingerprints were imprinted on the glass plate, and when the dirt was wiped off, the wiping performance was extremely excellent.

The present invention has the following applicability.
1. The easily split fiber / fibril acrylic short fiber assembly of the present invention comprises an acrylonitrile polymer and an acrylonitrile polymer that is incompatible with a methyl methacrylate polymer and / or cellulose diacetate. Can be obtained as well.
2. The easily split fiber / fibrillar acrylic short fiber aggregate of the present invention can be easily split into fine fibers having a fiber diameter of 1 μm or less by water jetting due to the structure of the fiber.
3. The easily split fiber / fibrillar acrylic short fiber aggregate of the present invention is useful as a papermaking raw material, and a wet nonwoven fabric can be obtained by wet papermaking alone or in combination with other fibers.
4). The wet nonwoven fabric of the present invention is composed of fine fibers having a fiber diameter of 1 μm or less composed of each polymer constituting easy-split / fibrillar acrylic short fibers, fine fibers and split fibers fibrillated fibers or other fibers. Consists of entanglement, and by the presence of extremely fine fine fibers, it can be used as a wiping sheet for wiping off not only water-based but also oil-based soils, and a filter material for removing soils.

2 is a cross-sectional photograph of the easily split fiber / fibrillar acrylic short fiber obtained in Example 1. FIG.

Claims (4)

  It is composed of 40 to 85% by weight of acrylonitrile polymer containing 50% by weight or more of acrylonitrile and 60 to 15% by weight of polymer selected from the group of methyl methacrylate polymer and cellulose diacetate, and has a plurality of cracks in the fiber cross section. However, at least one of them is a crack having a length of 25 to 80% of the cross-sectional width, and an easy-to-wet short fiber having an apparent fineness ratio of 1.5 to 3.0 and a fiber length of 3 to 10 mm. Split fiber, fibrillar acrylic short fiber assembly.   It includes a plurality of fine fibers having a fiber diameter of 1 μm or less, each composed of acrylonitrile-based polymer, methyl methacrylate-based polymer, and cellulose diacetate containing 50% by weight or more of acrylonitrile, and a fiber diameter of 0.5 μm. A wet nonwoven fabric comprising 20% by weight or more of split fiber fibrillated fibers in which the following fine fibers occupy at least 40% of the total, and the split fiber fibrillated fine fibers are three-dimensionally entangled.   A fiber in which split fiber fibrillated fiber is composed of 40 to 85% by weight of acrylonitrile polymer containing 50% by weight or more of acrylonitrile and 60 to 15% by weight of polymer selected from the group of methyl methacrylate polymer and cellulose diacetate The wet nonwoven fabric according to claim 2. The wet nonwoven fabric according to claim 2 or 3, wherein the ultrafine acrylic fiber having a fineness of 0.05 to 0.4 dtex composed of an acrylonitrile-based polymer containing 50% by weight or more of acrylonitrile is included within a range not exceeding 80% by weight.