Short fibers for airlaid and method for producing the same

Abstract

To provide an air-laid staple fiber with improved dispersibility, and a method for producing the staple fiber.SOLUTION: An air-laid staple fiber includes a stable fiber to which a fiber-treatment agent containing a hydrophilic oil solution and a silicone-containing oil solution is bonded by 0.7-2 wt.% of the staple fiber weight, the weight ratio of the hydrophilic oil solution and the silicone-containing oil solution contained in the fiber-treatment agent (weight of hydrophilic oil solution / weight of silicone-containing oil solution) being in a range from 60 / 40 to 90 / 10, and the moisture content being 2-13%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to short fibers for airlaid use and a method for producing the same. [Background technology]

[0002] Composite fibers with a sheath-core structure formed using two types of resin with different properties are used in a wide range of fields. For example, olefin-based composite fibers are used in nonwoven fabrics. Nonwoven fabrics are made by unidirectionally or randomly oriented chemical fibers, such as olefin-based fibers, which are bonded together by fusion or adhesive bonding to form a sheet. Nonwoven fabrics made with olefin-based composite fibers have excellent chemical resistance and are used in various filter materials and battery separators.

[0003] The above-mentioned composite fibers having a sheath-core structure are generally produced by forming undrawn fibers having a sheath-core structure by melt spinning and then drawing these undrawn fibers. Known methods for producing nonwoven fabrics include a dry method in which the drawn fibers obtained as described above are cut to a predetermined length to form short fibers (staples) and then opened, and a wet method in which the short fibers are dispersed in water to produce nonwoven fabrics.

[0004] Patent Document 1 discloses staple fibers for air-laid nonwoven fabrics, in which a fiber treatment agent containing an alkyl phosphate ester salt and a silicone compound is attached to the staple fibers. It describes that air-opening properties (dispersibility) can be improved by combining the monoalkyl phosphate ester salt content and polyphosphate ester salt content in the alkyl phosphate ester salt with a smoothing agent that is a silicone compound with an appropriate molecular weight.

[0005] Patent Document 2 discloses a method for producing drawn conjugated fibers by drawing undrawn fibers having a sheath-core structure, and the drawn conjugated fibers produced by this method. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5038848 [Patent Document 2] Patent No. 5938149 Summary of the Invention [Problem to be solved by the invention]

[0007] However, compared with fibers with a fineness of 1 dTex or less, short fibers of ultrafine fibers have a larger surface area and a higher fiber density per unit volume, which makes them more susceptible to static electricity and aggregation. Furthermore, the number of fibers per unit volume increases, making them more likely to become entangled. This can lead to poor dispersibility (air-spreadability). Furthermore, when the moisture content is high, the fibers become less likely to separate due to bundling caused by wetting, which can lead to poor dispersibility. Furthermore, when the moisture content is low, the frictional resistance between the fibers and the blade during cutting increases, reducing sharpness and causing the shape of the fibers at the cut cross section to become distorted, which can lead to poor dispersibility.

[0008] Therefore, an object of the present invention is to provide short fibers for airlaid use that can improve dispersibility and a method for producing the same. [Means for solving the problem]

[0009] The short fibers for airlaid according to the present invention comprise short fibers to which a fiber treatment agent containing a hydrophilic oil agent and a silicon-containing oil agent is attached in an amount of 0.7 to 2 weight % of the short fiber weight, the weight ratio of the hydrophilic oil agent to the silicon-containing oil agent contained in the fiber treatment agent (weight of hydrophilic oil agent / weight of silicon-containing oil agent) being within the range of 60 / 40 to 90 / 10, and the moisture content being 2 to 13%.

[0010] The method for producing staple fibers for airlaid according to the present invention comprises the steps of obtaining undrawn fibers by melt spinning, adhering a fiber treatment agent containing a hydrophilic oil agent and a silicon-containing oil agent to the undrawn fibers in an amount of 0.7 to 2% by weight of the fiber weight, drawing the undrawn fibers to form drawn fibers, and cutting the drawn fibers to a predetermined length, wherein the weight ratio of the hydrophilic oil agent to the silicon-containing oil agent contained in the fiber treatment agent (weight of hydrophilic oil agent / weight of silicon-containing oil agent) is within a range of 60 / 40 to 90 / 10, and the moisture regain of the drawn fibers after the step of cutting the drawn fibers is 2 to 13%. [Effects of the Invention]

[0011] The short fibers for airlaid of the present invention have an adjusted amount of fiber treatment agent attached, a weight ratio of the hydrophilic oil agent and the silicon-containing oil agent contained in the fiber treatment agent (weight of hydrophilic oil agent / weight of silicon-containing oil agent), and moisture content, which prevents the fibers from bundling due to wetting and prevents an increase in frictional resistance between the fibers and the blade during cutting, thereby improving dispersibility.

[0012] The method for producing short fibers for airlaid use of the present invention involves adjusting the amount of fiber treatment agent applied, the weight ratio of the hydrophilic oil agent and the silicon-containing oil agent contained in the fiber treatment agent (weight of hydrophilic oil agent / weight of silicon-containing oil agent), and the moisture content, thereby preventing the fibers from bundling due to wetting and suppressing an increase in frictional resistance between the fibers and the blade during cutting, making it possible to produce short fibers for airlaid use with improved dispersibility. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram illustrating a manufacturing apparatus for manufacturing short fibers for airlaid use according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram illustrating the configuration of a test device (for primary fiber-spreading evaluation) according to an example. [Figure 3] FIG. 1 is a schematic diagram illustrating the configuration of a test device (permeability evaluation) according to an example. [Figure 4] 1 is an SEM photograph showing a cross section of short fibers after cutting treatment in Example 1. [Figure 5] 1 is an SEM photograph showing a cross section of short fibers after cutting treatment in Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0015] 1. Composition of short fibers for airlaid The airlaid staple fiber according to this embodiment comprises staple fibers to which a fiber treatment agent containing a hydrophilic oil and a silicon-containing oil is attached in an amount of 0.7 to 2% by weight of the staple fiber. The weight ratio of the hydrophilic oil and the silicon-containing oil contained in the fiber treatment agent (weight of hydrophilic oil / weight of silicon-containing oil) is within the range of 60 / 40 to 90 / 10. The airlaid staple fiber according to this embodiment has a moisture regain of 2 to 13%.

[0016] (Textile treatment agent) The hydrophilic oil agent contained in the fiber treatment agent is, for example, an alkyl phosphate ester salt. The alkyl phosphate ester salt includes a monoalkyl phosphate ester salt, a dialkyl phosphate ester salt, a polyphosphate ester salt, or a mixture thereof. The alkyl phosphate ester salt has an average carbon number of 6 to 22, for example.

[0017] The silicon-containing oil contained in the fiber treatment agent contains, for example, polydimethylsiloxane; a siloxane compound in which some or all of the methyl groups of polymethylsiloxane have been substituted with substituents such as alkyl groups having two or more carbon atoms, phenyl groups, phenylalkyl groups, or amino groups; a siloxane compound obtained by graft polymerization of polyoxyalkylene, or the like; or a mixture of these.

[0018] (Weight ratio of oil in fiber treatment agent) The fiber treatment agent contains a hydrophilic oil and a silicon-containing oil. The amount of hydrophilic oil blended into the fiber treatment agent is 60 to 90% by weight based on the total weight of the fiber treatment agent. If the amount exceeds 90% by weight, the amount of silicon-containing oil used in combination will be small, which increases the frictional resistance between the fibers and the blade when cutting into short fibers, reducing sharpness, and the shape of the cut cross section will be crushed, resulting in reduced dispersibility, which is undesirable. If the amount is less than 60% by weight, the small amount of hydrophilic oil component will make static electricity more likely to be generated, causing the fibers to become charged and form clumps, reducing dispersibility, which is undesirable.

[0019] The remainder of the fiber treatment agent, excluding the hydrophilic oil, is a silicon-containing oil, excluding, for example, unavoidable ingredients. The amount of the silicon-containing oil is 10 to 40% by weight based on the total weight of the fiber treatment agent. The weight ratio of the hydrophilic oil to the silicon-containing oil contained in the fiber treatment agent (weight of hydrophilic oil / weight of silicon-containing oil) is within the range of 60 / 40 to 90 / 10. If the weight ratio of the hydrophilic oil to the silicon-containing oil contained in the fiber treatment agent exceeds 90 / 10, the frictional resistance between the fibers and the blade when cutting into short fibers increases, reducing cutting ability, crushing the shape of the cut cross section and reducing dispersibility, which is undesirable. If the ratio is less than 60 / 40, static electricity is likely to be generated, causing the fibers to become charged and form clumps, reducing dispersibility, which is undesirable.

[0020] The fiber treatment agent may contain components other than the hydrophilic oil and the silicon-containing oil as long as the desired antistatic properties and cutting properties are not impaired. Even in this case, the weight ratio of the hydrophilic oil to the silicon-containing oil is within the range of 60 / 40 to 90 / 10.

[0021] (Amount of fiber treatment agent attached) The amount of fiber treatment agent attached to the short fibers is 0.7 to 2% by weight based on the total weight of the short fibers. If the amount is less than 0.7%, static electricity is likely to be generated, causing the fibers to become charged and clump together, reducing dispersibility, which is not preferable. If the amount is more than 2% by weight, the bundling properties of the fiber treatment agent itself tend to result in unopened fiber bundles, which is not preferable.

[0022] (Short fiber moisture content) The moisture content of the staple fibers is 2 to 13% by weight based on the total weight of the staple fibers. Here, the moisture content of the staple fibers refers to the initial moisture content after the cutting process into staple fibers, which will be described later. A moisture content of less than 2% is undesirable because the frictional resistance between the fibers and the blade when cutting into staple fibers increases, reducing the sharpness, crushing the shape of the cut cross section, and reducing dispersibility. A moisture content of more than 13% by weight is undesirable because the fibers are highly wetted and tend to form unopened fiber bundles due to the fiber bundling. A more preferable range for the moisture content of the staple fibers is 5 to 10% by weight, which can improve dispersibility.

[0023] (fineness) The fineness of the short fibers is preferably 0.01 to 1.0 dTex. If the fineness is less than 0.01 dTex, significant deterioration in yarn quality, such as yarn breakage and fluffing, occurs during the spinning process, making it difficult to consistently produce high-quality fibers. This not only reduces the production volume per hour, but also increases production costs, which is undesirable. If the fineness exceeds 1.0 dTex, it becomes difficult to achieve the high strength and density of the nonwoven fabric in the low basis weight range that allows the characteristics of ultrafine fibers to be expressed, which is also undesirable. A more preferable range for the fineness of the short fibers is 0.1 to 0.8 dTex, which improves fiber quality, reduces production costs, and increases the strength and density of the nonwoven fabric.

[0024] (short fibers) The staple fibers are preferably composite fibers having a sheath-core structure, with a core made of a resin primarily composed of a crystalline propylene polymer and a sheath made of a resin primarily composed of an olefin polymer having a lower melting point than the core. A uniform nonwoven fabric can be obtained from the olefin composite staple fibers, and the excellent chemical resistance allows the production of nonwoven fabrics suitable for use in various filter materials and battery separators.

[0025] Examples of crystalline propylene polymers that are the main component of the core material include crystalline isotactic propylene homopolymers, ethylene-propylene random copolymers with a low ethylene unit content, propylene block copolymers composed of a homopolymer portion made of propylene homopolymer and a copolymer portion made of an ethylene-propylene random copolymer with a relatively high ethylene unit content, and crystalline propylene-ethylene-α-olefin copolymers in which each homopolymer or copolymer portion in the propylene block copolymer is further copolymerized with an α-olefin such as butene-1. Among these, isotactic polypropylene is preferred from the viewpoints of stretchability, fiber properties, and suppression of thermal shrinkage.

[0026] Examples of olefin polymers that are the main component of the sheath material include ethylene polymers such as high-, medium-, and low-density polyethylenes and linear low-density polyethylenes; copolymers of propylene with other α-olefins, specifically propylene-butene-1 random copolymers, propylene-ethylene-butene-1 random copolymers; amorphous propylene polymers such as flexible polypropylene; and poly(4-methylpentene-1). These olefin polymers may be used alone or in combination. Among these, high-density polyethylene is particularly preferred in terms of fiber properties. The various organic resins listed above may also be olefin compositions containing known additives, such as pigments, dyes, matting agents, antifouling agents, antibacterial agents, deodorizers, fluorescent whitening agents, antioxidants, flame retardants, stabilizers, UV absorbers, or lubricants.

[0027] (Sheath-core cross-sectional area ratio) The cross-sectional area ratio of the sheath material to the core material (sheath / core) is preferably within the range of 5 / 95 to 80 / 20. If it is less than 5 / 95, the sheath component will be insufficient, resulting in weak adhesion between the fibers when made into a nonwoven fabric, while if it exceeds 80 / 20, the core component will be insufficient, resulting in weak strength of the individual fibers, making it difficult to obtain the benefits of the composite fiber.

[0028] (Short fiber cut length) The fiber length of the short fibers is preferably 1 to 10 mm. If the fiber length is shorter than 1 mm, the nonwoven fabric strength is often not sufficient, and if the fiber length is longer than 10 mm, the fibers tend to entangle with each other, forming clumps and reducing dispersibility. A more preferred range for the fiber length of the short fibers is 2 to 5 mm, which improves dispersibility and ensures nonwoven fabric strength.

[0029] (additives) It is preferable that a nucleating agent be blended into the core material (a resin primarily composed of a crystalline propylene-based polymer). When a nucleating agent is added to the core material, the nucleating agent acts as a crystal nucleus itself or as a nucleating agent that induces crystal formation in the crystalline propylene-based polymer when the molten core material is discharged from the spinneret and cooled, thereby increasing the recrystallization temperature. This stabilizes the cooling during the spinning process and reduces unevenness in the fineness of the spun fiber (undrawn fiber), unevenness in the sheath-core ratio within the fiber, and uneven coverage of the sheath material, where the core material is partially exposed without being covered by the sheath material. The nucleating agent added to the core material can be inorganic or organic. Specific examples of inorganic nucleating agents include talc, kaolin, silica, carbon black, titanium oxide, zinc oxide, magnesium oxide, aluminum oxide, neodymium oxide, calcium sulfate, and barium sulfate. Specific examples of organic nucleating agents include metal benzoate nucleating agents such as sodium benzoate and calcium benzoate, metal oxalate nucleating agents such as calcium oxalate, metal stearate nucleating agents such as magnesium stearate and calcium stearate, metal benzoate nucleating agents such as aluminum benzoate, potassium benzoate, and lithium benzoate, metal phosphate nucleating agents, and dibenzylidene sorbitol nucleating agents. The nucleating agent may be one that melts together with the resin containing a crystalline propylene polymer as the core material when the resin is in a molten state, one that does not melt completely and disperses in the resin, or one that does not melt and forms a nucleus itself. In this embodiment, it is preferable to use a nucleating agent that melts together with the resin containing a crystalline propylene polymer as the core material and has an affinity therewith, or a nucleating agent that does not melt completely but has a portion that is compatible with the resin.

[0030] The use of such a nucleating agent effectively reduces variations in fineness (thickness) between fibers and variations in the core-sheath ratio within the fibers during cooling immediately after spinning, while the internal structure resulting from the formation of microcrystals further improves stretchability in the subsequent drawing step. Because inorganic nucleating agents do not melt, the amount of nucleating agent added must be carefully adjusted for each spinning and drawing condition. However, organic nucleating agents can be used in relatively low amounts and are adaptable to a wider range of spinning and drawing conditions. Therefore, it is preferable to use an organic nucleating agent, and in particular, it is more preferable to use an organic nucleating agent in relation to a resin primarily composed of a crystalline propylene polymer, since both are easily melted and compatible with each other.

[0031] Examples of organic nucleating agents that melt and have affinity with resins include dibenzylidene sorbitol-based nucleating agents. Specifically, dibenzylidene sorbitol (DBS), monomethyldibenzylidene sorbitol (e.g., 1,3:2,4-bis(p-methylbenzylidene)sorbitol (p-MDBS)), and dimethyldibenzylidene sorbitol (e.g., 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (3,4-DMDBS)) are preferably used.

[0032] 2.Airlaid staple fiber manufacturing equipment FIG. 1 is a schematic diagram illustrating the configuration of a production apparatus for producing short fibers for airlaid use according to this embodiment.

[0033] As shown in FIG. 1, the manufacturing apparatus 1 includes a spinning section 20, a fiber treatment agent application section 30, a first roller 40, a stretching section 50, a second roller 60, an adjustment section 72, an adjustment roller 80, and a cutter section 90.

[0034] The spinning section 20 is provided with a molten resin supply section (extruder cylinder) and a spinneret (nozzle), and extrudes, by melt spinning, a plurality of undrawn fibers 10A, 10B... each having a sheath-core structure in which a core material is a resin whose main component is, for example, a crystalline propylene polymer, and a sheath material is a resin whose main component is an olefin polymer whose melting point is lower than that of the core material. The obtained undrawn fibers 10A, 10B... are bundled together and conveyed as a tow 11.

[0035] The fiber treatment agent application section 30 applies the fiber treatment agent to the transported tow 11 using an application roller 31. Although Fig. 1 shows a configuration in which the transport roller 21 is provided between the spinning section 20 and the fiber treatment agent application section 30, the transport roller 21 may also be provided in other locations as appropriate. The fiber treatment agent used is a fiber treatment agent containing a hydrophilic oil agent and a silicon-containing oil agent in the weight ratio described above.

[0036] The first roller 40 conveys the tow 11 at a first conveying speed SP1. The first roller 40 includes a plurality of rollers 41.

[0037] The drawing unit 50 draws the tow 11, which is a bundle of undrawn fibers. The drawing is preferably performed at a high temperature, which enables drawing at a high ratio and produces drawn composite fibers with a finer fiber count. The heating and drawing process can be performed by contact heating and drawing with a high-temperature heating plate, radiant heating and drawing using far-infrared rays or the like, hot water heating and drawing, steam heating and drawing, or pressurized saturated steam heating and drawing. Steam heating and drawing is preferred because it allows heating the tow 11 uniformly and in a short time.

[0038] When steam heating and stretching is performed, the conditions are not particularly limited, but for example, heating is performed in a steam atmosphere at 100°C under normal pressure. When stretching is performed in pressurized saturated steam, the conditions are not particularly limited, but stretching is usually performed at 100°C or higher. As long as the temperature of the pressurized saturated steam is within a range in which the olefin polymer of the sheath material does not melt, a higher temperature is basically preferable. In consideration of the stretching ratio, stretching speed, and economic efficiency, the temperature range of the pressurized saturated steam is preferably 105 to 130°C, and more preferably 110 to 125°C.

[0039] The second roller 60 transports the stretched tow 11 at a second transport speed SP2. The second roller 60 includes a plurality of rollers 61. The stretching ratio in the stretching unit 50 can be adjusted by the ratio between the first transport speed SP1 and the second transport speed SP2. For example, when the second transport speed SP2 / the first transport speed SP1 is X times, the fineness can be reduced to 1 / X by the stretching process.

[0040] The draw ratio can be appropriately selected depending on the fineness of the undrawn fiber, but is usually 3.0 to 10.0 times, preferably 4.0 to 8.0 times, in total. The draw speed can be, for example, about 400 to 2000 m / min. In particular, when the spinning step and the drawing step are carried out continuously, a draw speed of 1000 m / min or more is preferable from the viewpoint of productivity.

[0041] The conditioning unit 72 is a processing unit that performs conditioning treatments such as drying or humidifying treatment on the tow 11. If conditioning treatments are not performed, the conditioning unit 72 can be omitted. While FIG. 1 shows a configuration in which two transport rollers 70, 71 are provided between the second roller 60 and the conditioning unit 72, transport rollers may not be provided if possible, or a configuration having one or three or more transport rollers may be used. Furthermore, such transport rollers may also be provided as appropriate in other locations in the manufacturing apparatus of FIG. 1.

[0042] The adjusting roller 80 adjusts the speed at which the tow 11 is supplied to the cutter section 90 by the rollers 81 that constitute the adjusting roller 80 .

[0043] The cutter section 90 has a flat cylindrical section 91, and a cutting blade 91A is provided facing outward on the side surface of the cylindrical section 91. When the tow 11 is wound around the cylindrical section 91 by driving the cutter section 90 around the rotation shaft 90A, the pressure during winding presses the tow 11 against the cutting blade 91A, and the tow 11 is cut into short fibers.

[0044] 1 shows an in-line type production apparatus in which the spinning section 20 to the cutter section 90 are continuously provided, but the production apparatus may be an outline type production apparatus consisting of a group of devices individually provided for each process. Also, the production apparatus may be configured so that a take-up roller is provided at any position to take up the tow 11, and the tow 11 is pulled out from the take-up roller and then the next or subsequent process is performed.

[0045] 3. Manufacturing method of short fibers for airlaid The method for producing short fibers for airlaid use according to this embodiment will be described with reference to FIG.

[0046] First, a plurality of undrawn fibers 10A, 10B... are discharged by melt spinning in the spinning section 20 shown in Fig. 1. The obtained undrawn fibers 10A, 10B... are bundled together and conveyed as a tow 11.

[0047] Next, in the fiber treatment agent application section 30 shown in Fig. 1, a fiber treatment agent is applied to the tow 11. As the fiber treatment agent, a fiber treatment agent containing a hydrophilic oil agent and a silicon-containing oil agent in the weight ratio described above is used.

[0048] Subsequently, the tow 11 is stretched in the stretching processing section 50 while the conveying speed is adjusted by the first roller 40 and the second roller 60 shown in Fig. 1. At this time, the stretching ratio is adjusted by the ratio of the second conveying speed SP2 / the first conveying speed SP1.

[0049] Next, the tow 11 is subjected to an adjustment process such as drying or humidifying in the adjustment unit 72 shown in Fig. 1. The adjustment process is performed as needed. In the examples described below, the tow 11 is subjected to a drying or humidifying process in the adjustment unit 72 to adjust the moisture content.

[0050] Next, after adjusting the speed with the adjusting roller 80 shown in FIG. 1, the material is cut into staple fibers in the cutter section 90. The cut staple fibers are subjected to an opening process. The opening process opens the staple fibers into a cotton-like state. In this way, staple fibers for airlaid can be produced.

[0051] The obtained short fibers for airlaid are processed into a nonwoven fabric by the airlaid method after being left (stored) for a predetermined period of time as necessary, or immediately after being opened into a cotton-like state.

[0052] 4. Action and Effects The short fibers for airlaid use in this embodiment are formed by adhering a fiber treatment agent to the short fibers in an amount of 0.7 to 2 weight % of the short fiber weight, with the weight ratio of hydrophilic oil and silicon-containing oil (weight of hydrophilic oil / weight of silicon-containing oil) being in the range of 60 / 40 to 90 / 10. Furthermore, the short fibers for airlaid use have a moisture regain of 2 to 13%.

[0053] With ultrafine fibers having a fineness of 1 dTex or less, the fiber density per unit volume is high, and the number of fibers per unit volume is large, which tends to deteriorate dispersibility. In the short fibers for airlaid of this embodiment, the moisture content is adjusted to 2 to 13%, which prevents an increase in frictional resistance between the fibers and the blade when cutting into short fibers and the likelihood of unopened fiber bundles being formed due to wetting of the fibers, thereby improving dispersibility.

[0054] In addition, since the weight ratio of the hydrophilic oil and silicon-containing oil in the fiber treatment agent is within the range of 60 / 40 to 90 / 10, the frictional resistance between the fibers and the blade when cutting into short fibers is prevented from increasing, and the fibers are prevented from becoming charged and forming clumps, thereby improving dispersibility.

[0055] In addition, since the amount of fiber treatment agent attached to the short fibers is 0.7 to 2% by weight, the fibers are prevented from becoming charged and forming clumps, and the fiber treatment agent's own bundling properties prevent the fibers from easily becoming unopened bundles, thereby improving dispersibility.

[0056] As described above, according to this embodiment, it is possible to provide short fibers for airlaid that can improve dispersibility.

[0057] 5. Variations In the above embodiment, the fiber treatment agent is applied between the melt spinning step and the drawing step, but this is not limiting and the fiber treatment agent may be applied at any timing between the melt spinning step and the cutting step. Furthermore, the staple fibers of this embodiment are preferably applicable to nonwoven fabric manufacturing methods using the airlaid method, but are also applicable to dry nonwoven fabric manufacturing methods that do not use the airlaid method.

[0058] 6. Evaluation Method (1) Fineness The fiber fineness of the undrawn fiber and drawn fiber was measured in accordance with JIS L1013.

[0059] (2) Oil adhesion rate The oil solution attached to the test fiber (weight 2g) was extracted with 20cc of ethanol / methanol (mixture ratio 2 / 1), the ethanol / methanol remaining on the fiber was dried by heat, and the weight of the fiber obtained as residue was measured. The weight loss (weight of the components extracted with ethanol / methanol) was calculated from the weight of the obtained residue, and this value was divided by the weight of the test fiber.

[0060] (3) Initial moisture content after cutting The moisture content of the test fiber (weight 3 g) was heated and dried using the built-in heater of the moisture content measuring device, and the value of the moisture content (wet basis) was measured using the built-in electronic balance.

[0061] (4) Dry dispersion test (4-1) Primary fiber opening evaluation Figure 2 is a schematic diagram illustrating the configuration of the test equipment used in the primary fiber-spreading evaluation test. The test equipment is configured with a sieve S1 with openings S1A of 250 μm and a sieve S2 with openings S2A of 250 μm. Test fiber F1 (weight 1 g) after cutting but before fiber-spreading was placed between the stacked sieves S1 and S2, and air W1 at a pressure of 0.4 MPa was applied evenly to the test fiber F1 from above the sieve S2 for 30 seconds. The test fiber F1 was evaluated for its ability to spread into a cotton-like state. In Table 1, cases where the fiber spread were indicated by "Good" and cases where the fiber did not spread were indicated by "Poor."

[0062] (4-2) Passability evaluation Figure 3 is a schematic diagram illustrating the configuration of the testing equipment used for the passability evaluation and the formation evaluation tests described below. A plastic funnel FN has a conical portion and a tubular portion extending from the conical portion, and a suction section SC is attached to the tip of the tubular portion. The funnel FN is configured with a sieve S1 with openings S1A of 250 μm, a sieve S3 with openings S3A of 2.36 mm, a tubular portion P1, and a sieve S2 with openings S2A of 250 μm. The staple fibers F2 (weight 1 g) opened to a cotton-like state in the primary opening evaluation described above were placed into the tubular portion P1, and the top of the tubular portion P1 was covered with the sieve S2. While the tip of the funnel FN was being sucked with a vacuum cleaner with a suction power of 160 W using the suction section SC, air W2 at 0.4 MPa was applied evenly to the staple fibers F2 from above the sieve S2 for 1 minute. The weight of the short fiber residue in the tubular portion P1 after the air W2 was applied (the short fiber that did not pass through the sieve S3) was measured, and the weight was divided by the weight (1 g) of the short fibers F2 added. The value for the passability evaluation is preferably 60% or less, and more preferably 40% or less.

[0063] (4-3) Evaluation of the ground In the test apparatus shown in Figure 3, staple fibers F2 (weight 1 g) opened to a cotton-like state in the above primary opening evaluation were placed in the tubular portion P1, the top of the tubular portion P1 was covered with sieve S2 to form a lid, and air W2 at 0.4 MPa was applied evenly to the staple fibers F2 from above the sieve S2 for 1 minute while suction was performed from the tip of the funnel FN using a vacuum cleaner with a suction power of 160 W through the suction portion SC. To evaluate the formation, the appearance of the web-like staple fibers (size φ200 mm) inside the sieve S1 after the air W2 application was visually observed and evaluated according to the following criteria.

[0064] Grade A indicates that "there are no fiber agglomerates or unevenness in basis weight (shade) of 3 mm or more in length, and the texture is uniform." Grade B indicates that "there are less than 10 fiber agglomerates of 3 mm or more in length, and unevenness in basis weight (shade) can be visually confirmed." Grade C indicates that "there are 10 or more fiber agglomerates of 3 mm or more in length, and unevenness in basis weight (shade) is noticeable, and the texture is non-uniform." Note that if short fibers do not pass through sieve S3 in the passability evaluation, the formation cannot be evaluated, and the evaluation is not possible, and this is indicated by the symbol "-." Grade A is preferable for the texture evaluation.

[0065] (5) Wet dispersion test (5-1) Primary variance evaluation The test fibers (weight 2 g) after cutting and before spreading were placed in a 100 L water tank, stirred at a stirring speed of 2800 rpm for 10 minutes, and the number of fiber agglomerates 3 mm or longer was counted. As a numerical value for evaluating primary dispersion, it is preferable that the number of fiber agglomerates be 40 or less.

[0066] (5-2) Second-order dispersion evaluation 300 mL of water was placed in a 500 mL beaker, and the fiber agglomerates with lengths of 3 mm or more obtained in the above primary dispersion test were placed in the water and stirred at a stirring speed of 5,000 rpm using a pencil mixer for 5 minutes, after which the number of fiber agglomerates with lengths of 3 mm or more was counted. As a numerical value for evaluating secondary dispersion, it is preferable that the number of fiber agglomerates is 0.

[0067] (6) Cut section The cut surface of the test fiber after cutting and before spreading was observed with an SEM. The deformation of the fiber shape in the cross section was evaluated visually. If the fiber shape in the cross section did not change (was not crushed), it was judged as "good," and if the fiber shape changed (was crushed), it was judged as "poor." It is preferable that the fiber shape in the cross section did not change (was not crushed).

[0068] 7. Working Example <Oil> In the following examples, the following oils were used as the oils used in the fiber treatment agents. Oil A: Hydrophilic oil (containing alkyl phosphate ester salt) manufactured by Takemoto Oil & Fat Co., Ltd. Oil B: Hydrophilic oil manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd. (contains alkyl phosphate ester salts, more polar than Oil A) Oil C: Silicon-containing oil (contains siloxane compounds) manufactured by Takemoto Oil & Fat Co., Ltd.

[0069] Example 1 (1) Preparation of sheath-core composite undrawn fibers The core material was a raw material prepared by blending 1.5% by mass of isotactic polypropylene "S119" manufactured by Prime Polymer Co., Ltd. with an additive ("Clearmaster PP-RM-NSA RMX50" manufactured by Dainichiseika Chemicals Co., Ltd.) with an additive of 1.5% by mass. The sheath material was a raw material prepared by blending 2.0% by mass of high-density polyethylene "J300" manufactured by Asahi Kasei Chemicals Corporation with an additive of 2.0% by mass ("Ultzex ​​IR-5" manufactured by Prime Polymer Co., Ltd.). Using the above core and sheath materials, undrawn fibers with a sheath-core structure were produced by melt spinning. A sheath-core composite spinneret was used, with the cross-sectional area ratio of the sheath and core (sheath / core) set to 50 / 50. The spinning conditions were an extruder cylinder temperature of 270°C, a spinneret temperature of 275°C, and a spinning speed of 180 m / min. An aqueous solution prepared by mixing oil agent A and oil agent C at a weight ratio of 80:20 at room temperature to adjust the oil agent solution concentration to 4 wt % was applied to the obtained undrawn fibers using an oiling roller (fiber treatment agent application unit 30). In this way, undrawn fibers with a fineness of 0.8 dTex were obtained.

[0070] (2) Preparation of drawn fibers In order to enable the drawing process to be carried out continuously from the spinning process described above, a drawing apparatus was used in which a steam heating drawing section (drawing section 50) using 100°C steam at atmospheric pressure was disposed between two rollers (an introduction roller (first roller 40) and a drawn fiber drawing roller (second roller 60)). The first roller 40 was driven at a speed of 180 m / min to introduce the undrawn fiber tow 11, and the second roller 60 was driven at a speed faster than the first roller 40 at a predetermined ratio to draw out the drawn fiber tow 11.

[0071] In the drawing process, when the speed of the drawing roller (second roller 60) was 781 m / min and the total draw ratio was 4.34, the drawn fiber could be obtained industrially stably without fiber breakage or drawing breakage. The drawn fiber of Example 1 had a fineness of 0.201 dTex.

[0072] (3) Preparation of short fibers The drawn fiber tow obtained in the drawing step was immediately cut to a fiber length of 3.0 mm using a rotary cutter (cutter unit 90, rotation speed 50 m / min) to obtain polyolefin staple fibers. The cutting pressure was 4.3 gf / dTex, the moisture content was 9.5 wt% relative to the weight of the polyolefin staple fibers, and the amount of oil applied was 1.2 wt% relative to the weight of the polyolefin staple fibers.

[0073] (4) Evaluation of short fibers In a dry dispersion test (primary dispersion evaluation) of the obtained polyolefin staple fibers, the fibers were dispersed into a cotton-like state, and the passability was evaluated as 30.2%. The formation evaluation showed no fiber clumps or unevenness in basis weight (shade), indicating a uniform formation. Furthermore, in a wet dispersion test (primary dispersion evaluation), the number of fiber clumps was 9, but after using a pencil mixer in the secondary dispersion evaluation, the number of fiber clumps was reduced to 0, indicating good dispersion. Figure 4 is an SEM photograph showing the cross section of the staple fibers after cutting treatment in Example 1. As can be seen from Figure 4, there was no deformation of the fiber shape (shape collapse) in the cross section in Example 1.

[0074] <Example 2> (1) Preparation of sheath-core composite undrawn fibers The same procedure as in Example 1 was carried out except that oil agent B was used instead of oil agent A when producing undrawn fibers having a sheath-core structure.

[0075] (2) Preparation of drawn fibers A drawn fiber was produced in the same manner as in Example 1. In the drawing process, the speed of the drawing roller (second roller 60) was 781 m / min, and the total draw ratio was 4.34 times. The drawn fiber was obtained industrially stably by drawing without fiber breakage or drawing breakage. The fineness of the drawn fiber of Example 2 was 0.200 dTex.

[0076] (3) Preparation of short fibers The cutting process, in which the pressure when cutting the drawn fibers was 4.8 gf / dTex, was carried out in the same manner as in Example 1. The moisture content of the obtained polyolefin short fibers was 9.1 wt %, and the amount of fiber treatment agent attached was 1.0 wt % relative to the weight of the polyolefin short fibers.

[0077] (4) Evaluation of short fibers In a dry dispersion test (primary dispersion evaluation) of the obtained polyolefin staple fibers, the fibers were dispersed into a cotton-like state, and the passability was evaluated as 28.1%. The formation evaluation showed no fiber clumps or unevenness in basis weight (shade), indicating a uniform formation. Furthermore, in a wet dispersion test (primary dispersion evaluation), the number of fiber clumps was 9, but after using a pencil mixer in the secondary dispersion evaluation, the number of fiber clumps was reduced to 0, indicating good dispersion. From the SEM photographs, there was no deformation of the fiber shape (shape collapse) in the cross section of Example 2.

[0078] Example 3 (1) Preparation of sheath-core composite undrawn fibers In the same manner as in Example 1, a sheath-core type composite undrawn fiber was produced.

[0079] (2) Preparation of drawn fibers A drawn fiber was produced in the same manner as in Example 1. In the drawing process, the speed of the drawing roller (second roller 60) was 781 m / min, and the total draw ratio was 4.34 times. The drawn fiber was obtained in an industrially stable manner without fiber breakage or drawing breakage. The fineness of the drawn fiber of Example 3 was 0.200 dTex.

[0080] (3) Preparation of short fibers The tow 11 containing the bundled stretched fibers was left standing (drying treatment) at room temperature for 6 hours in the adjustment section 72 to adjust the moisture content, and the stretched fibers were cut under a cutting pressure of 4.8 gf / dTex in the same manner as in Example 1. The resulting polyolefin staple fibers had a moisture content of 6.0 wt %, and the amount of fiber treatment agent attached was 1.2 wt % relative to the weight of the polyolefin staple fibers.

[0081] (4) Evaluation of short fibers In a dry dispersion test (primary dispersion evaluation) of the obtained polyolefin staple fibers, the fibers were dispersed into a cotton-like state, and the passability was evaluated as 29.8%. The formation evaluation showed no fiber clumps or unevenness in basis weight (shade), indicating a uniform formation. Furthermore, in a wet dispersion test (primary dispersion evaluation), the number of fiber clumps was 13, but after using a pencil mixer in the secondary dispersion evaluation, the number of fiber clumps was reduced to 0, indicating good dispersion. From the SEM photographs, there was no deformation of the fiber shape (shape collapse) in the cross section of Example 3.

[0082] <Comparative Example 1> (1) Preparation of sheath-core composite undrawn fibers The same procedure as in Example 1 was carried out to prepare undrawn fibers having a sheath-core structure, except that oil agent B was used instead of oil agent A and oil agents B and C were mixed at a weight ratio of 50:50.

[0083] (2) Preparation of drawn fibers A drawn fiber was produced in the same manner as in Example 1. In the drawing process, the speed of the drawing roller (second roller 60) was 781 m / min, and the total draw ratio was 4.34 times. The drawn fiber could be obtained industrially stably by drawing without fiber breakage or drawing breakage. The fineness of the drawn fiber obtained in Comparative Example 1 was 0.200 dTex.

[0084] (3) Preparation of short fibers The cutting process, in which the pressure when cutting the drawn fibers was 4.3 f / dTex, was carried out in the same manner as in Example 1. The moisture content of the obtained polyolefin short fibers was 7.1% by weight, and the amount of fiber treatment agent attached was 1.0% by weight based on the weight of the polyolefin short fibers.

[0085] (4) Evaluation of short fibers In a dry dispersion test (primary dispersion evaluation) of the obtained polyolefin short fibers, the fibers were dispersed into a cotton-like state, the passability evaluation was 95.1%, and the fibers aggregated into fiber clumps, did not pass through sieve S2, and the formation evaluation was not possible. In a wet dispersion test (primary dispersion evaluation), the number of fiber clumps was 0, indicating good dispersibility. Since no fiber clumps were observed in the primary dispersion evaluation, a secondary dispersion evaluation was not performed. From the SEM photograph, there was no deformation of the fiber shape (shape collapse) in the cross section in Comparative Example 1.

[0086] <Comparative Example 2> (1) Preparation of sheath-core composite undrawn fibers In the same manner as in Example 1, a sheath-core type composite undrawn fiber was produced.

[0087] (2) Preparation of drawn fibers A drawn fiber was produced in the same manner as in Example 1. In the drawing process, the speed of the drawing roller (second roller 60) was 781 m / min, and the total draw ratio was 4.34 times. The drawn fiber was obtained industrially stably by drawing without fiber breakage or drawing breakage. The fineness of the drawn fiber of Comparative Example 2 was 0.208 dTex.

[0088] (3) Preparation of short fibers The tow 11 containing the bundled drawn fibers was subjected to a drying treatment in an adjustment section 72 at 120°C in a drying oven length of 2 m to adjust the moisture content, and the drawn fibers were then cut at a pressure of 5.6 gf / dTex in the same manner as in Example 1. The resulting polyolefin short fibers had a moisture content of 0.4 wt %, and the amount of fiber treatment agent attached was 2.9 wt % relative to the weight of the polyolefin short fibers.

[0089] (4) Evaluation of short fibers In the dry dispersion test (primary dispersion evaluation) of the obtained polyolefin short fibers, the fibers were spread like cotton, the passability was 15.4%, and the formation evaluation showed that 8 fiber clumps and irregularities in basis weight (shade) were observed, indicating a slightly poor formation. In the wet dispersion test (primary dispersion evaluation), the number of fiber clumps was 10, but after using a pencil mixer in the secondary dispersion evaluation, the number of fiber clumps was 0, indicating good dispersibility. Figure 5 shows Comparative Example 2 5 is an SEM photograph showing the cross section of the short fibers after the cutting treatment of 1. From Fig. 5, deformation of the shape of the fibers in the cross section (deformation of the shape) was confirmed in Comparative Example 2.

[0090] <Comparative Example 3> (1) Preparation of sheath-core composite undrawn fibers The undrawn fibers having a sheath-core structure were produced in the same manner as in Example 1, except that only oil agent A was used.

[0091] (2) Preparation of drawn fibers A drawn fiber was produced in the same manner as in Example 1. In the drawing process, the speed of the drawing roller (second roller 60) was 781 m / min, and the total draw ratio was 4.34 times. The drawn fiber could be obtained industrially stably by drawing without fiber breakage or drawing breakage. The fineness of the drawn fiber of Comparative Example 3 was 0.201 dTex.

[0092] (3) Preparation of short fibers The cutting process, in which the pressure when cutting the drawn fibers was 5.1 gf / dTex, was carried out in the same manner as in Example 1. The moisture content of the obtained polyolefin short fibers was 4.2 wt %, and the amount of fiber treatment agent attached was 1.2 wt % relative to the weight of the polyolefin short fibers.

[0093] (4) Evaluation of short fibers In the dry dispersion test (primary dispersion evaluation) of the obtained polyolefin staple fibers, the fibers were spread out like cotton, the passability was 25.1%, and the formation evaluation showed that more than 10 fiber clumps and unevenness in basis weight (shade) were observed, indicating poor formation. Furthermore, in the wet dispersion test (primary dispersion evaluation), the number of fiber clumps was 50, but after using a pencil mixer in the secondary dispersion evaluation, the number of fiber clumps was reduced to 0, indicating that the fibers were difficult to disperse. From the SEM photograph, deformation of the fiber shape (deformation of the shape) was confirmed in the cross section of Comparative Example 1.

[0094] <Comparative Example 4> (1) Preparation of sheath-core composite undrawn fibers The same procedure as in Example 1 was carried out to prepare undrawn fibers having a sheath-core structure, except that oil agent B was used instead of oil agent A and oil agents B and C were mixed at a weight ratio of 20:80.

[0095] (2) Preparation of drawn fibers A drawn fiber was produced in the same manner as in Example 1. In the drawing process, the speed of the drawing roller (second roller 60) was 781 m / min, and the total draw ratio was 4.34 times. The drawn fiber could be obtained industrially stably by drawing without fiber breakage or drawing breakage. The fineness of the drawn fiber of Comparative Example 4 was 0.202 dTex.

[0096] (3) Preparation of short fibers The cutting process, in which the pressure when cutting the drawn fibers was 4.3 gf / dTex, was carried out in the same manner as in Example 1. The moisture content of the obtained polyolefin short fibers was 14.0 wt %, and the amount of fiber treatment agent attached was 1.1 wt % relative to the weight of the polyolefin short fibers.

[0097] (4) Evaluation of short fibers A dry dispersion test (primary spread evaluation) was conducted on the obtained polyolefin staple fibers, but the fibers had a high degree of bundling and did not spread into a cotton-like state. It was not possible to evaluate the passability or the formation. In a wet dispersion test (primary dispersion evaluation), the number of fiber agglomerates was 0, indicating good dispersibility. Since no fiber agglomerates were observed in the primary dispersion evaluation, a secondary dispersion evaluation was not conducted. From the SEM photograph, it was clear that there was no deformation (deformation) of the fiber shape in the cross section in Comparative Example 4.

[0098] <Comparative Example 5> (1) Preparation of sheath-core composite undrawn fibers The undrawn fibers having a sheath-core structure were produced in the same manner as in Example 1, except that an aqueous solution containing only oil agent A adjusted to a concentration of 1.5% by weight was used.

[0099] (2) Preparation of drawn fibers A drawn fiber was produced in the same manner as in Example 1. In the drawing process, the speed of the drawing roller (second roller 60) was 781 m / min, and the total draw ratio was 4.34 times. The drawn fiber could be obtained industrially stably without fiber breakage or drawing breakage. The fineness of the drawn fiber of Example 1 was 0.200 dTex.

[0100] (3) Preparation of short fibers Tow 11, which is a collection of drawn fibers obtained in the drawing process, was passed through a tank containing an aqueous solution of oil A at room temperature, adjusted to an oil solution concentration of 3% by weight, to apply a finishing oil to the drawn fibers. The drawn fibers were then cut to a fiber length of 3.0 mm using a rotary cutter (rotation speed 45 m / min) to obtain polyolefin staple fibers. The cutting pressure was 2.1 gf / dTex, the moisture content was 35% by weight based on the weight of the polyolefin staple fibers, and the amount of oil applied was 2.0% by weight based on the weight of the polyolefin staple fibers. The application of the finishing oil was essentially carried out to increase the moisture content in the fibers.

[0101] (4) Evaluation of short fibers A dry dispersion test (primary spread evaluation) was conducted on the obtained polyolefin staple fibers, but the fibers had a high degree of bundling and did not spread into a cotton-like state. It was not possible to evaluate the passability or the formation. In a wet dispersion test (primary dispersion evaluation), the number of fiber agglomerates was 0, indicating good dispersibility. Since no fiber agglomerates were observed in the primary dispersion evaluation, a secondary dispersion evaluation was not conducted. From the SEM photograph, it was clear that there was no deformation (deformation) of the fiber shape in the cross section in Comparative Example 5.

[0102] The above results are summarized in Table 1 below.

[0103] [Table 1]

[0104] As shown in Table 1 above, the airlaid staple fibers of Examples 1 to 3 obtained good results in the primary spread evaluation, passability evaluation, and formation evaluation in the dry dispersion test, confirming that short fibers with improved dispersibility were obtained. In Comparative Example 1, the fibers did not pass through sieve S3 in the passability evaluation, so formation evaluation was not possible. In Comparative Example 2, the formation evaluation was rated B, which was not good. In Comparative Example 3, the formation evaluation was rated C, which was not good. In Comparative Examples 4 and 5, the fibers did not spread in the primary spread evaluation.

[0105] The airlaid staple fibers of this embodiment can be preferably used as staple fibers for forming nonwoven fabrics by the airlaid method.

[0106] The airlaid staple fibers of this embodiment have excellent chemical resistance when formed into nonwoven fabrics, and can be preferably used as staple fibers for forming nonwoven fabrics used for various filter materials, battery separators, and the like.

[0107] The short fibers for airlaid of this embodiment can also be used as fibers for wet dispersion, as can be seen from the good secondary dispersion evaluation of wet dispersion. [Explanation of symbols]

[0108] 10A, 10B...Unstretched fiber 11...Tou 20...Spinning section 21...Transport roller 30... Fiber treatment agent attachment area 31...Adhesion roller 40...First roller 41...Roller 50...extension processing section 60...Second roller 61...Roller 70, 71...Transport rollers 72…Adjustment section 80...Adjusting roller 81...Roller 90...Cutter section 90A...Rotating shaft 91...Cylindrical part 91A...Cutting blade

Claims

1. The fiber treatment agent includes a hydrophilic oil agent and a silicon-containing oil agent, and the fiber treatment agent is attached to the fiber in an amount of 0.7 to 2% by weight of the weight of the short fibers. the weight ratio of the hydrophilic oil agent to the silicon-containing oil agent contained in the fiber treatment agent (weight of hydrophilic oil agent / weight of silicon-containing oil agent) is within a range of 60 / 40 to 90 / 10; The moisture content is 2 to 13%. The fineness of the short fibers is 0.1 to 0.8 dtex, the short fibers are composite fibers having a sheath-core structure, in which a core material is a resin containing a crystalline propylene-based polymer as a main component, and a sheath material is a resin containing an olefin-based polymer as a main component and having a melting point lower than that of the core material, The short fibers have a fiber length of 2 to 5 mm. Short fibers for airlaid.

2. The cross-sectional area ratio (sheath / core) of the sheath material and the core material is within a range of 5 / 95 to 80 / 20. The staple fiber for airlaid use according to claim 1.

3. The moisture content is 5 to 10%. The short fiber for airlaid use according to claim 1 or 2.

4. obtaining undrawn fibers by melt spinning; a step of applying a fiber treatment agent containing a hydrophilic oil agent and a silicon-containing oil agent to the undrawn fibers in an amount of 0.7 to 2% by weight of the fibers; a step of drawing the undrawn fibers to form drawn fibers; cutting the drawn fibers to a fiber length of 2 to 5 mm; Equipped with the weight ratio of the hydrophilic oil agent to the silicon-containing oil agent contained in the fiber treatment agent (weight of hydrophilic oil agent / weight of silicon-containing oil agent) is within a range of 60 / 40 to 90 / 10; the moisture regain of the drawn fibers after the step of cutting the drawn fibers is 2 to 13%; The drawn fiber has a fineness of 0.1 to 0.8 dtex, The short fibers are composite fibers having a sheath-core structure, in which a core material is a resin whose main component is a crystalline propylene polymer, and a sheath material is a resin whose main component is an olefin polymer whose melting point is lower than that of the core material. A method for producing short fibers for airlaid applications.

5. In the step of cutting the drawn fibers, the force per unit fineness applied to the drawn fibers is 0.049 N / dtex or less. The method for producing the short fibers for airlaid use according to claim 4.

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