WO2024018828A1

WO2024018828A1 - Ultrafine polyphenylene sulfide fiber, nonwoven fabric, and methods for producing same

Info

Publication number: WO2024018828A1
Application number: PCT/JP2023/023495
Authority: WO
Inventors: 大士勝田; 将太竹下; 匠平土屋; 有希二ノ宮; 茂俊前川
Original assignee: 東レ株式会社
Priority date: 2022-07-20
Filing date: 2023-06-26
Publication date: 2024-01-25

Abstract

Provided is an ultrafine polyphenylene sulfide fiber having an average fiber diameter of 0.2 μm to 5.0 μm and a crystallinity of 0% to 15%, as calculated by differential scanning calorimetry.　Provided are an ultrafine polyphenylene sulfide fiber having excellent adhesiveness and dispersibility, a nonwoven fabric comprising the same, and methods for producing the same.

Description

Ultrafine polyphenylene sulfide fibers and nonwoven fabrics, and methods for producing them

The present invention relates to ultrafine polyphenylene sulfide fibers having excellent adhesiveness and dispersibility, nonwoven fabrics made from the same, and methods for producing them.

In addition to having high heat resistance, chemical resistance, electrical insulation, and flame retardancy, polyphenylene sulfide also has excellent mechanical properties and moldability, making it suitable for use as a metal substitute and resistant to extreme environments. It is widely used as a material for obtaining Polyphenylene sulfide fibers made from polyphenylene sulfide are used in applications such as bag filters, papermaking canvas, electrical insulation paper, battery separators, and various diaphragms by taking advantage of the above properties. In particular, by combining the characteristics of polyphenylene sulfide, such as heat resistance and chemical resistance against high concentration alkaline solutions, with the ion permeability and gas separation properties of nonwoven fabric materials, we are creating hydrogen production equipment diaphragms, fuel cell diaphragms, and reinforcement of these diaphragms. Wet-laid nonwoven fabrics made of polyphenylene sulfide fibers are being developed for materials.

In recent years, nonwoven fabrics used for the above-mentioned applications are required to be thinner and have a lower basis weight for the purpose of making devices smaller, lighter, and higher in performance. In the case of thin, low basis weight nonwoven fabrics, there are problems such as the nonwoven fabrics being easily broken due to minute tension fluctuations during the manufacturing process, and being easily torn by contact with the edges or burrs of other components during the modularization process. be. Therefore, with the aim of improving the strength, various studies have been made to increase the strength and adhesiveness of binder fibers, which are components that contribute to adhesion between fibers that make up nonwoven fabrics. In addition, in a nonwoven fabric made of polyphenylene sulfide fibers, the binder fibers must also be made of polyphenylene sulfide in order not to impair the heat resistance and chemical resistance of polyphenylene sulfide.

Against this background, in order to obtain polyphenylene sulfide fibers for paper making that have a low heat shrinkage rate and good water dispersibility, undrawn polyphenylene sulfide fibers produced by melt spinning are immersed in hot water of 70°C or higher. A method for producing polyphenylene sulfide fibers for papermaking has been proposed, which is characterized by passing through a dry heat range of 70 to 90° C. in a relaxed state to undergo a relaxation heat treatment for 5 to 60 minutes. For example, see Patent Document 1).

On the other hand, with regard to improving the performance of a nonwoven fabric made of polyphenylene sulfide fibers, a nonwoven fabric characterized by containing ultrafine acid-resistant fibers A with a fiber diameter of 2 μm or less and acid-resistant fibers B with a fiber diameter larger than the acid-resistant fibers A. (See, for example, Patent Document 2), a nonwoven fabric characterized by containing polyphenylene sulfide fibers having an irregular cross section and polyphenylene sulfide fibers having a circular cross section with a fiber diameter of 5 μm or less has been proposed (for example, (See Patent Document 3).

In addition, there is also a method for producing filter cloth for bag filters using ultrafine fibers with a fiber diameter of 200 to 2000 nm, which are obtained by dissolving and removing the sea component of a sea-island type composite fiber composed of a sea component and an island component. It has been proposed (for example, see Patent Document 4).

Japanese Patent Application Publication No. 2010-174400 Japanese Patent Application Publication No. 2020-172729 JP2020-66818A International Publication No. 2017/086186

In the technique of Patent Document 1, polyphenylene sulfide undrawn fibers produced by a melt-spinning method are subjected to relaxation heat treatment to shrink within the manufacturing process, thereby making it possible to obtain polyphenylene sulfide fibers with a low heat shrinkage rate. However, since the polyphenylene sulfide undrawn fibers obtained by this method have a substantially large fiber diameter, it is difficult to obtain a thin fabric or a low basis weight nonwoven fabric.

Furthermore, the techniques of Patent Document 2 and Patent Document 4 relate to nonwoven fabrics using ultrafine polyphenylene sulfide fibers with a fiber diameter of 2 μm or less. Although this technology makes it possible to improve the performance of nonwoven fabrics, it is difficult to obtain thin fabrics or nonwoven fabrics with low basis weights because the binder fibers used are common undrawn polyphenylene sulfide yarns. Have difficulty. In addition, a manufacturing method for obtaining ultrafine polyphenylene sulfide fibers by removing the sea component of sea-island fibers using polyphenylene sulfide fibers as the island component is exemplified, but the ultrafine polyphenylene sulfide fibers obtained by this manufacturing method are Because crystallization progresses due to heating during sea removal, adhesiveness is insufficient when used as a binder fiber.

Furthermore, the technology of Patent Document 3 uses polyphenylene sulfide fibers with irregular cross sections and circular cross-sectional polyphenylene sulfide fibers with a fiber diameter of 5 μm or less, so that paper breakage does not occur during production using a wet papermaking method. It is possible to obtain a nonwoven fabric that is difficult to use. However, the effect of improving the strength of the nonwoven fabric obtained by this method is limited, and when trying to make a thin fabric or a low basis weight nonwoven fabric that is required in recent years, it is difficult to achieve a strength that can be used for practical purposes. It is.

SUMMARY OF THE INVENTION Therefore, an object of the present invention was to provide an ultrafine polyphenylene sulfide fiber having excellent adhesiveness and water dispersibility, a nonwoven fabric made from the same, and a method for producing the same. be.

The present inventors have conducted studies and found that in order to make nonwoven fabrics made of polyphenylene sulfide fibers thinner, lower in weight, and stronger, binder fibers that contribute to adhesion between fibers among the fibers that make up nonwoven fabrics should be used. It has been found that reducing the fiber diameter is effective. On the other hand, when trying to reduce the fiber diameter, methods are used such as drawing undrawn yarn or eluting and removing the sea component of sea-island fibers with a high-temperature solution, but crystallization progresses due to molecular orientation and exposure to heat. However, the binder fibers obtained had low adhesiveness.

Therefore, in order to achieve the above-mentioned problem, the present inventors conducted further intensive studies and found that even when the fiber diameter is reduced, the degree of crystallinity calculated by differential scanning calorimetry falls within a specific range. It was discovered that by doing so, ultrafine polyphenylene sulfide fibers having excellent adhesiveness and dispersibility could be obtained, and the present invention was completed.

The present invention aims to solve the above-mentioned problems, and the ultrafine polyphenylene sulfide fiber of the present invention has an average fiber diameter of 0.2 μm or more and 5.0 μm or less, and has a crystallization value calculated by differential scanning calorimetry. The degree of oxidation is 0% or more and 15% or less.

According to a preferred embodiment of the ultrafine polyphenylene sulfide fiber of the present invention, the ultrafine polyphenylene sulfide fiber is a fiber with a modified cross section, and has a degree of irregularity defined by the following formula of 1.2 or more.

Degree of irregularity = Minimum circumscribed circle diameter / Maximum inscribed circle diameter Here, the minimum circumscribed circle diameter is the diameter (μm) of the smallest circle that includes all of the fiber cross sections, and the maximum inscribed circle diameter is the diameter of the smallest circle that includes the entire fiber cross section. This is the diameter of a large circle (μm).

According to a preferred embodiment of the ultrafine polyphenylene sulfide fiber of the present invention, the average fiber length is 0.1 mm or more and 6.0 mm or less.

The method for producing ultrafine polyphenylene sulfide fibers of the present invention involves removing the sea component from an undrawn fiber having a sea-island composite cross section in which polyphenylene sulfide is arranged as an island component in an alkaline aqueous solution at a temperature of 70° C. or lower to obtain an average fiber diameter of This is a method for producing ultrafine polyphenylene sulfide fibers, in which fibers have a crystallinity of 0.2 μm or more and 5.0 μm or less and a crystallinity calculated by differential scanning calorimetry of 0% or more and 15% or less.

The method for producing a nonwoven fabric of the present invention includes mixing the ultrafine polyphenylene sulfide fibers and stretched polyphenylene sulfide fibers in a papermaking dispersion liquid to make paper, and then subjecting the nonwoven fabric to thermocompression bonding at a temperature of 130°C or higher and 250°C or lower. This is the manufacturing method.

According to the present invention, ultrafine polyphenylene sulfide fibers having excellent adhesiveness and dispersibility can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a conceptual diagram for explaining an example of the fiber cross section of the ultrafine polyphenylene sulfide fiber of the present invention and a method for measuring the degree of irregularity.

The ultrafine polyphenylene sulfide fiber of the present invention has an average fiber diameter of 0.2 μm or more and 5.0 μm or less, and a crystallinity calculated by differential scanning calorimetry of 0% or more and 15% or less. The constituent elements will be described in detail below, but the present invention is not limited to the scope described below unless it exceeds the gist thereof.

[Ultra-fine polyphenylene sulfide fiber]
The polyphenylene sulfide according to the present invention is a polymer composed of diphenylene sulfide units such as p-phenylene sulfide units represented by structural formula (1) and m-phenylene sulfide units as a main repeating unit.

The polyphenylene sulfide according to the present invention preferably contains 60 mol% or more of p-phenylene sulfide units. By controlling the content of p-phenylene sulfide units to preferably 60 mol% or more, more preferably 70 mol% or more, still more preferably 80 mol% or more, the fiber has excellent heat resistance. Moreover, when processed into a nonwoven fabric, it becomes a nonwoven fabric with excellent strength.

The polyphenylene sulfide according to the present invention may contain copolymerized units other than the above-mentioned diphenylene sulfide units as long as the effects of the present invention are not impaired. Examples of copolymerized units other than diphenylene sulfide units include aromatic sulfides such as triphenylene sulfide and biphenylene sulfide, and alkyl-substituted and halogen-substituted products thereof.

The polyphenylene sulfide according to the present invention includes inorganic substances such as titanium oxide, silica, barium oxide, and calcium carbonate, coloring agents such as dyes and pigments, flame retardants, and optical brighteners, to the extent that the effects of the present invention are not impaired. , antioxidants, and various additives such as ultraviolet absorbers.

The ultrafine polyphenylene sulfide fibers of the present invention may be not only monocomponent fibers but also composite fibers made of two or more types of resins. When the ultrafine polyphenylene sulfide fiber is a composite fiber, its composite form is not particularly limited as long as it does not impair the effects of the present invention, and may include a core-sheath type, a sea-island type, a side-by-side type, an eccentric core-sheath type, and a blend type. You can select as appropriate from among the following. In addition, when the above-mentioned ultrafine polyphenylene sulfide fiber is used as a composite fiber, the resin used together with the above-mentioned polyphenylene sulfide has a copolymerization ratio of m-phenylene sulfide units from the viewpoint of process stability and flexibility in the manufacturing process. Different polyphenylene sulfides are preferably used. For example, in the case of a core-sheath type composite fiber, the core component is polyphenylene sulfide made of only p-phenylene sulfide units, and the sheath component is polyphenylene sulfide copolymerized with m-phenylene sulfide units, or when the sea-island type composite fiber is used. In this case, the sea component may be polyphenylene sulfide consisting only of p-phenylene sulfide units, and the island component may be polyphenylene sulfide copolymerized with m-phenylene sulfide units.

The cross-sectional shape of the ultrafine polyphenylene sulfide fiber of the present invention is not limited in any way, and includes not only a round cross section but also a multilobal cross section such as a Y-shaped cross section and a triangular cross-section, a flat cross-section, an S-shaped cross section, a cross cross section, and a hollow cross section. It can be made into any irregular cross-sectional shape such as.

The ultrafine polyphenylene sulfide fiber of the present invention preferably has a degree of irregularity defined by the following formula of 1.2 or more. By setting the degree of irregularity to preferably 1.2 or more, more preferably 1.5 or more, and even more preferably 1.7 or more, the specific surface area of the fiber increases, so the adhesion area when used as a binder increases, The result is a nonwoven fabric with excellent strength. Further, the upper limit of the degree of irregularity is not particularly limited, but the upper limit that can be achieved in the present invention is about 500.

The degree of irregularity referred to here is measured by the method described below, and will be explained in detail using FIG. 1.

FIG. 1 shows an example of the fiber cross section of the ultrafine polyphenylene sulfide fiber of the present invention.

First, an image of the cross section of the fiber is taken using a scanning electron microscope at a magnification that allows observation of a single fiber. Using the photographed image, the minimum circumscribed circle and maximum inscribed circle in the cross section are plotted using image analysis software, and the degree of irregularity is calculated from the following formula. This is measured for 20 arbitrarily extracted fibers, a simple numerical average is obtained, and the result is rounded off to the second decimal place.

Degree of irregularity = Minimum circumscribed circle diameter / Maximum inscribed circle diameter Here, the minimum circumscribed circle diameter is the diameter (μm) of the smallest circle that includes the entire fiber cross section, and the maximum inscribed circle diameter is the diameter of the smallest circle that includes the entire fiber cross section. This is the diameter of a large circle (μm).

The average fiber diameter of the ultrafine polyphenylene sulfide fiber of the present invention is 0.2 μm or more and 5.0 μm or less. By setting the average fiber diameter to 0.2 μm or more, preferably 0.4 μm or more, and more preferably 0.5 μm or more, the fibers become less entangled and the dispersibility of the fibers improves. Improved uniformity. In addition, by setting the average fiber diameter to 5.0 μm or less, preferably 3.0 μm or less, more preferably 2.0 μm or less, the number of fibers constituting the same fineness and same basis weight increases, so when used as a binder. The number of bonding points increases, resulting in a nonwoven fabric with excellent strength.

The average fiber diameter (μm) of the fibers referred to here is determined as follows.
(1) An image of the cross section of the fiber is taken using a scanning electron microscope at a magnification that allows observation of a single fiber.
(2) Using the photographed image, use image analysis software to measure the area Af (μm ² ) formed by the cross-sectional outline of the single fiber, and calculate the diameter of a perfect circle that has the same area as this area Af. do.
(3) Measure this on 100 arbitrarily extracted fibers, obtain a simple numerical average, calculate the average fiber diameter (μm), and round to the second decimal place.

The ultrafine polyphenylene sulfide fibers of the present invention can be used as long fibers, but they can also be cut into short fibers by cutting the fibers to a certain length before being processed into nonwoven fabrics or the like.

When the ultrafine polyphenylene sulfide fiber of the present invention is used as short fibers, the average fiber length is preferably 0.1 mm or more and 6.0 mm or less. By setting the average fiber length to preferably 0.1 mm or more, more preferably 0.2 mm or more, and still more preferably 0.3 mm or more, the fibers are less likely to fall off during the processing step into a nonwoven fabric. In addition, by setting the average fiber length to preferably 6.0 mm or less, more preferably 4.0 mm or less, and even more preferably 2.0 mm or less, the fibers become less entangled with each other and the dispersibility of the fibers improves. The quality will improve when

The average fiber length of the fibers mentioned here is determined based on "8.4.1. Average fiber length (c direct method)" of JIS L1015:2010 "Chemical fiber staple test method".

The ultrafine polyphenylene sulfide fiber of the present invention has a degree of crystallinity calculated by differential scanning calorimetry of 0% or more and 15% or less. By setting the crystallinity to 0% or more, preferably 1% or more, the fiber can be easily handled in higher-order processes. In addition, by setting the crystallinity to 15% or less, preferably 12% or less, more preferably 10% or less, and still more preferably 9% or less, polyphenylene sulfide fibers with excellent adhesive properties, which are suitable for binder fibers, can be obtained. .

The crystallinity (%) of the fiber referred to here is determined as follows.
(1) After weighing out approximately 5 mg of fiber using an electronic balance, set the fiber in a differential scanning calorimeter and perform differential scanning under nitrogen, heating rate of 16°C/min, and measurement temperature range of 50 to 320°C. Perform calorimetry.
(2) Calculate the heat of crystallization ΔHc (J/g) from the area of the exothermic peak in the obtained measurement results (DSC curve), and calculate the heat of crystallization ΔHm (J/g) from the area of the endothermic peak. In addition, when multiple exothermic peaks or endothermic peaks are observed, ΔHc and ΔHm are calculated from the sum of the areas of all the peaks.
(3) Measure three times by changing the measurement position for each level, obtain a simple numerical average value, calculate ΔHc and ΔHm, and then calculate the degree of crystallinity (%) using the following formula (1). , round to the first decimal place.

Crystallinity (%) = (ΔHm-ΔHc)/ΔHm ⁰ ×100 (1)
Here, ΔHm ⁰ is the heat of fusion of a complete crystal (J/g), and in the case of polyphenylene sulfide, 140.1 J/g is generally used.

[Nonwoven fabric]
The nonwoven fabric of the present invention is a nonwoven fabric containing the above-mentioned ultrafine polyphenylene sulfide fibers. By including ultrafine polyphenylene sulfide fibers, the number of fibers constituting the nonwoven fabric increases, resulting in a nonwoven fabric that is resistant to tearing and has excellent strength. In addition, since the constituent fibers themselves become thinner, a thinner nonwoven fabric can be obtained.

The proportion of the ultrafine polyphenylene sulfide fibers in the nonwoven fabric of the present invention is preferably 10% by mass or more and 80% by mass or less. By setting the proportion of the ultrafine polyphenylene sulfide fibers to preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, the number of fibers constituting the nonwoven fabric increases, thereby improving adhesion between fibers. The number of dots increases, resulting in a nonwoven fabric with excellent mechanical properties. Furthermore, by setting the proportion of the ultrafine polyphenylene sulfide fibers to preferably 80% by mass or less, more preferably 75% by mass or less, and still more preferably 70% by mass or less, a nonwoven fabric with appropriate air permeability and flexibility can be obtained. .

Fibers other than the ultrafine polyphenylene sulfide contained in the nonwoven fabric of the present invention are not particularly limited, but include polyphenylene sulfide, polypropylene, polyethylene, poly-4-methylpentene-1, polycarbonate, polyacrylate, polyethylene terephthalate, polybutylene terephthalate, and Examples include fibers made of methylene terephthalate, polyethylene naphthalate, polylactic acid, aromatic polyester, polyamide, aromatic polyamide, thermoplastic polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, and copolymers thereof. Among these, fibers made of polyphenylene sulfide are preferably used from the viewpoint of chemical resistance, heat resistance, and adhesiveness with ultrafine polyphenylene sulfide fibers.

The basis weight of the nonwoven fabric of the present invention is preferably 2 g/m ² or more and 80 g/m ² or less. When the basis weight is preferably 2 g/m ² or more, more preferably 5 g/m ² or more, the nonwoven fabric has excellent strength. Further, by having a basis weight of preferably 80 g/m ² or less, more preferably 50 g/m ² or less, the nonwoven fabric has excellent flexibility.

The basis weight (g/m ² ) of nonwoven fabric mentioned here is measured by the following procedure in accordance with "6.2 Mass per unit area (ISO method)" of JIS L1913:2010 "General nonwoven fabric test method". , is the calculated value.
(1) Take a 20 cm x 25 cm test piece from the nonwoven fabric.
(2) For the sampled test piece, measure the mass (g) in a standard state and convert it to mass per 1 m ² of area (g/m ² ).
(3) For each level, the measurement is carried out three times by changing the sampling point of the test piece, and the value obtained by rounding off the arithmetic mean value to the first decimal place is calculated as the basis weight (g/m ² ).

The thickness of the nonwoven fabric of the present invention is preferably 170 μm or less. By setting the thickness of the nonwoven fabric to preferably 170 μm or less, more preferably 155 μm or less, the nonwoven fabric has appropriate air permeability and flexibility. Further, the lower limit of the thickness of the nonwoven fabric of the present invention is not particularly limited, but in order to obtain a nonwoven fabric with practical strength, it is preferably 2 μm or more, and more preferably 5 μm or more.

The thickness (μm) of the nonwoven fabric referred to here is based on JIS P8118:2014 "Paper and paperboard - Test method for thickness, density and specific volume". The thickness of 20 test pieces was measured one by one using a thickness meter (for example, "Micrometer" manufactured by Mitutoyo Co., Ltd.), and the thickness (μm) of the nonwoven fabric was calculated by taking a simple number average. , the value is rounded to the first decimal place.

The strength of the nonwoven fabric of the present invention is preferably 10 N/15 mm or more. By setting the strength of the nonwoven fabric to preferably 10 N/15 mm or more, more preferably 15 N/15 mm or more, and even more preferably 20 N/15 mm or more, the nonwoven fabric becomes tear-resistant and suitable for diaphragm applications and filter applications. Moreover, the upper limit of the strength of the nonwoven fabric of the present invention is not particularly limited, but the strength that the nonwoven fabric of the present invention can achieve is about 100 N/15 mm.

The strength of the nonwoven fabric (N/15mm) referred to here means that a nonwoven fabric cut into a sample width of 15mm is tested using a tensile tester Tensilon (for example, UTM-III-100 manufactured by Orientech Co., Ltd.). The value of the maximum point load was measured under the conditions of initial length 20 mm and tensile speed 20 mm/min, and the strength of the nonwoven fabric (N/15 mm) was calculated by taking the simple numerical average of the 5 measured values, and the first decimal place was calculated. This is a rounded value.

The strength per unit weight of the nonwoven fabric of the present invention is preferably 0.25 (N/15 mm)/(g/m ² ) or more. The strength of the nonwoven fabric is preferably 0.25 (N/15 mm)/(g/m ² ) or more, more preferably 0.38 (N/15 mm)/(g/m ² ) or more, and even more preferably 0.50. (N/15 mm)/(g/m ² ) or more provides a tear-resistant nonwoven fabric suitable for diaphragm applications and filter applications. Although the upper limit of the strength of the nonwoven fabric of the present invention is not particularly limited, the strength that the nonwoven fabric of the present invention can achieve is about 2.50 (N/15 mm)/(g/m ² ).

The strength per area of nonwoven fabric ((N/15mm)/(g/m ² )) referred to here is calculated by dividing the strength of the nonwoven fabric determined above by the area weight, and dividing the value to the third decimal place. This is a rounded value.

The ultrafine polyphenylene sulfide fiber of the present invention and the nonwoven fabric made from it not only have excellent long-term heat resistance, but also have chemical resistance, mechanical properties, electrical insulation properties, and flame retardancy. It can be used for diaphragm applications such as hydrogen production equipment diaphragms, fuel cell diaphragms, battery diaphragms, electrode diaphragms, and reinforcement materials for these diaphragms, bag filters, chemical filters, food filters, chemical filters, oil filters, engine oil filters, and air filters. Filter applications such as cleaning filters, paper applications such as electrical insulating paper, heat-resistant workwear applications such as firefighting uniforms, safety clothing, laboratory workwear, thermal clothing, flame-retardant clothing, papermaking felt, heat-resistant felt, mold release materials, It can be suitably used for various applications such as paper dryer canvas, heart patch, artificial skin, printed circuit board base material, copy rolling cleaner, ion exchange base material, oil retaining material, insulation material, cushioning material, net conveyor, etc. Although it can be preferably used for diaphragm applications and paper applications where thinning and low basis weight are required, it is not limited to these applications.

[Production method of ultrafine polyphenylene sulfide fiber and nonwoven fabric]
Next, preferred embodiments for producing the ultrafine polyphenylene sulfide fiber and nonwoven fabric of the present invention will be specifically described.

It is preferable to dry the polyphenylene sulfide used before applying it to melt spinning in order to improve spinnability in order to prevent water contamination and remove oligomers. As the drying conditions, vacuum drying at 100 to 200° C. for 1 to 24 hours is usually used.

In melt spinning, a melt spinning method using an extruder such as a pressure melter type, single screw extruder type, or twin screw extruder type can be applied. The extruded polyphenylene sulfide passes through piping, is measured by a metering device such as a gear pump, passes through a filter to remove foreign substances, and then is guided to a spinneret. At this time, the temperature from the polymer piping to the spinneret (spinning temperature) is preferably 290° C. or higher to improve fluidity, and preferably 380° C. or lower to suppress thermal decomposition of the polymer.

The ultrafine polyphenylene sulfide fiber of the present invention can be obtained by removing the polymer of the sea component of a sea-island composite fiber having a sea-island composite cross section in which polyphenylene sulfide is arranged as an island component. Note that the cross-sectional shape of the ultrafine polyphenylene sulfide fiber of the present invention is almost the same as the cross-sectional shape of the island component of the above-mentioned sea-island composite fiber, so the cross-sectional shape of the island component can be made into any shape. , it becomes possible to obtain ultrafine polyphenylene sulfide fibers having a desired cross-sectional shape. The method for controlling the cross-sectional shape of the island component is not particularly limited, but preferred methods include, for example, the methods disclosed in JP-A No. 2010-216042 and JP-A No. 2016-188454.

An easily soluble polymer is suitably used for the sea component of the above-mentioned sea-island composite fiber. The easily soluble polymers mentioned here include, for example, melt-molded polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polytrimethylene terephthalate, polypropylene, polyolefin, polycarbonate, polyacrylate, polyamide, polylactic acid, thermoplastic polyurethane, etc. selected from possible polymers and copolymers thereof. Among these, from the viewpoint of simplifying the elution process of the sea component, the sea component is preferably a copolymerized polyester, polylactic acid, polyvinyl alcohol, etc. that are easily eluted in aqueous solvents or hot water, and 5-sodium sulfoisophthalic acid is preferred. It is preferable to use a polyester obtained by copolymerizing a single polyester, or a polyester obtained by copolymerizing a polyethylene glycol in combination in order to further improve dissolution properties. On the other hand, if thermal decomposition of the easily eluted polymer progresses during spinning, the cross-sectional formability and spinnability of the conjugate fiber will deteriorate, so that it is required to be difficult to thermally decompose at the above-mentioned spinning temperature, that is, to have high heat resistance. From this point of view, a polyester obtained by homo-copolymerizing 5-sodium sulfoisophthalic acid is more preferable.

When using a polyester in which 5-sodium sulfoisophthalic acid is homopolymerized as the sea component, from the viewpoint of achieving both solubility in aqueous solvents and heat resistance, the copolymerized amount of 5-sodium sulfoisophthalic acid is 2 mol% or more and 20 mol% or less. is preferred. By setting the copolymerization amount of 5-sodium sulfoisophthalic acid to preferably 2 mol% or more, more preferably 3 mol% or more, solubility in aqueous solvents is improved, so when used as the sea component of a sea-island composite fiber, Sea components can be easily removed. Furthermore, by controlling the copolymerization amount of 5-sodium sulfoisophthalic acid to preferably 20 mol% or less, more preferably 15 mol% or less, a polymer with excellent heat resistance can be obtained.

The sea-island type composite fiber used in the present invention is produced by melting polyphenylene sulfide and other component polymers separately, then measuring them using a known measuring device such as a gear pump via polymer piping, and passing through a filter to remove foreign substances. , respectively leading to the spinneret. The respective polymers introduced into the spinneret are combined into an arbitrary composite form within the spinneret, and are discharged from the spinneret hole as sea-island composite fibers.

The spinneret used for discharging preferably has a diameter D of the spinneret hole of 0.1 mm or more and 0.6 mm or less, and a land length L of the spinneret hole (the length of the straight pipe part that is the same as the diameter of the spinneret hole). L/D, which is defined as the quotient obtained by dividing L) by the pore diameter, is preferably 1 or more and 10 or less.

The shape and cross-sectional area of the island component in the sea-island composite fiber may be the same as the area of the fiber cross-section calculated from the above-mentioned fiber shape and average fiber diameter. For example, by forming polyphenylene sulfide, which is an island component, into a round shape with a diameter of 2.0 μm, it is possible to produce a round cross-section fiber with an average fiber diameter of 2.0 μm. Therefore, in order to obtain ultrafine polyphenylene sulfide fibers having an average fiber diameter of 0.2 μm or more and 5.0 μm or less, the diameter of the island component may be set to 0.2 μm or more and 5.0 μm or less.

The number of island components in the sea-island composite fiber is not particularly limited, but is preferably 20 or more and 4000 or less. By setting the number of island components to preferably 20 or more, more preferably 100 or more, and even more preferably 200, the diameter of the island components can be reduced, and therefore the average fiber diameter of the ultrafine polyphenylene sulfide fiber can be reduced. It becomes possible. Further, by setting the number of island components to preferably 4000 or less, more preferably 3000 or less, the fiber cross-sectional formability becomes good, so that fibers with small variations in fiber diameter can be obtained.

The sea-island composite fibers discharged from the die hole are cooled and solidified by blowing cooling air (air) onto them. The temperature of the cooling air can be determined in balance with the cooling air speed from the viewpoint of cooling efficiency, but it is preferably 30° C. or lower. By setting the temperature of the cooling air to preferably 30° C. or lower, solidification behavior due to cooling is stabilized, resulting in fibers with high uniformity in fiber diameter.

Furthermore, it is preferable that the cooling air be allowed to flow through the undrawn fibers discharged from the die in a direction substantially perpendicular to the fiber axis. In this case, the speed of the cooling air is preferably 10 m/min or more from the viewpoint of cooling efficiency and uniformity of fineness, and preferably 100 m/min or less from the viewpoint of yarn spinning stability.

The undrawn fibers that have been cooled and solidified are taken up by a roller (godet roller) that rotates at a constant speed. The drawing speed is preferably 300 m/min or more in order to improve linear uniformity and productivity, and preferably 1500 m/min or less in order to prevent the orientation of molecular chains from proceeding.

The undrawn fibers thus obtained are subjected to the next step without being drawn.

The obtained undrawn fibers may be crimped using a crimper and fixed in shape using a setter at a temperature of 70° C. or lower, if necessary. By crimping, the fibers become entangled with each other, thereby increasing the adhesion area between the fibers, making it possible to obtain a nonwoven fabric with excellent mechanical strength.

The number of crimps in the above crimps is preferably 2 crimps/25 mm or more and 15 crimps/25 mm or less. By preferably setting the number of crimp to 2/25 mm or more, the fibers become entangled with each other more easily, resulting in a nonwoven fabric with excellent mechanical strength. Further, by setting the number of crimps to preferably 15 crimps/25 mm or less, the dispersibility of the fibers in the dispersion liquid is improved, resulting in a homogeneous nonwoven fabric.

Next, short fibers can be obtained by cutting the obtained sea-island composite fiber into a predetermined length with a cutter. The fiber length of the short fibers is preferably 0.1 mm or more and 6.0 mm or less. By setting the average fiber length to preferably 0.1 mm or more, more preferably 0.2 mm or more, and still more preferably 0.3 mm or more, the fibers are less likely to fall off during the processing step into a nonwoven fabric. In addition, by setting the average fiber length to preferably 6.0 mm or less, more preferably 4.0 mm or less, and even more preferably 2.0 mm or less, the fibers become less entangled with each other and the dispersibility of the fibers improves. When this happens, the uniformity of the basis weight improves.

Note that shortening using a cutter may be carried out after obtaining ultrafine polyphenylene sulfide fibers by the method described below.

In order to obtain the ultrafine polyphenylene sulfide fiber of the present invention, the sea-island composite fibers described above may be immersed in a solvent capable of dissolving the sea component to remove the sea component polymer. When the sea component polymer is copolymerized polyethylene terephthalate copolymerized with 5-sodium sulfoisophthalic acid, an alkaline aqueous solution such as an aqueous sodium hydroxide solution can be used as the solvent. At this time, the bath ratio of the sea-island composite fiber and the alkaline aqueous solution (mass of the sea-island composite fiber (g)/alkaline aqueous solution mass (g)) is preferably 1/10,000 or more and 1/5 or less, and 1/5,000 or more and 1/5 or less. It is more preferable that it is /10 or less. By setting it within this range, it is possible to suppress the ultrafine fibers from unnecessarily intertwining with each other when the sea component is dissolved.

At this time, the alkali concentration of the alkaline aqueous solution is preferably 0.1% by mass or more and 5.0% by mass or less, more preferably 0.5% by mass or more and 3% by mass or less. By setting it within this range, the dissolution of the sea components can be completed in a short time.

It is important that the temperature of the alkaline aqueous solution when removing sea components is 70°C or lower. By setting the temperature of the alkaline aqueous solution to 70°C or lower, preferably 65°C or lower, more preferably 60°C or lower, crystallization does not proceed during the elution process, resulting in ultrafine polyphenylene sulfide with low crystallinity and excellent adhesive properties. Fiber can be obtained.

The treatment time with the alkaline aqueous solution is preferably 10 minutes or more and 100 minutes or less. By setting the treatment time to preferably 10 minutes or more, more preferably 20 minutes or more, it becomes difficult for the sea component to remain undissolved, resulting in ultrafine polyphenylene sulfide fibers having excellent dispersibility. Further, by setting the treatment time to preferably 100 minutes or less, more preferably 70 minutes or less, crystallization is less likely to occur during the treatment, resulting in ultrafine polyphenylene sulfide fibers having excellent adhesive properties.

Furthermore, it is preferable to add a surfactant to the above alkaline aqueous solution as a dissolution promoter for the sea component. Examples of the surfactant include cationic surfactants, anionic surfactants, nonionic surfactants, etc., but when polyester is used as the easily soluble polymer, cationic surfactants are preferably used. . Further, the surfactant concentration in the alkaline aqueous solution is preferably 0.05% by mass or more and 2% by mass or less, and preferably 0.1% by mass or more and 1% by mass or less based on the weight of the alkaline aqueous solution. More preferred. By setting the temperature within this range, it is possible to complete the dissolution of sea components in a short time even at a temperature of 70° C. or lower.

A papermaking liquid can be prepared by using short fibers made of ultrafine polyphenylene sulfide fibers obtained as described above as binder fibers and dispersing them together with binder fibers in water. Note that polyphenylene sulfide drawn fibers are usually used as the binder fibers.

The ratio of binder fibers to binder fibers in the papermaking liquid is preferably 10% by mass or more and 80% by mass or less. By setting the ratio of the binder fiber to the binder fiber to preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, the number of bonding points between the fibers increases, resulting in excellent mechanical properties. It becomes a non-woven fabric. In addition, by setting the ratio of binder fibers to binder fibers to preferably 80% by mass or less, more preferably 75% by mass or less, and still more preferably 70% by mass or less, a nonwoven fabric with appropriate air permeability and flexibility can be obtained. Become.

A nonwoven fabric can be obtained by supplying the above papermaking liquid to a papermaking machine. Note that by adjusting the fiber concentration of the supplied papermaking liquid, the basis weight of the obtained nonwoven fabric can be changed.

The nonwoven fabric obtained as described above is preferably dried to remove moisture. The drying temperature is preferably 70° C. or lower to prevent a decrease in fusion properties due to crystallization of the amorphous portion.

The thus obtained nonwoven fabric is heat-pressed using a flat plate hot press machine or a calendar roll, whereby the ultrafine polyphenylene sulfide fibers of the present invention cause fusion between the binder fibers, resulting in a nonwoven fabric with excellent mechanical properties. Become. The thermocompression temperature is preferably 130°C or more and 250°C or less, and the compression time is preferably 10 minutes or less. By setting the thermocompression temperature to preferably 130° C. or higher, more preferably 150° C. or higher, and still more preferably 170° C. or higher, the ultrafine polyphenylene sulfide fibers of the present invention are fused to produce a nonwoven fabric with excellent mechanical properties. Further, by setting the thermocompression bonding temperature preferably to 250° C. or lower, it is possible to suppress the generation of wrinkles due to thermal contraction of the nonwoven fabric during thermocompression bonding. Furthermore, by setting the pressure bonding time to preferably 10 minutes or less, more preferably 5 minutes or less, it is possible to suppress a decrease in flexibility of the nonwoven fabric due to excessive crystallization.

Next, the present invention will be explained in detail based on Examples. However, the present invention is not limited only to these examples. In addition, in the measurement of each physical property, unless otherwise specified, the measurement was performed based on the method described above.

(1) Average fiber diameter Measurement was performed as described above using a scanning electron microscope "S-5500" manufactured by Hitachi High-Technologies Corporation as a scanning electron microscope and "WinROOF2015" manufactured by Mitani Shoji Co., Ltd. as an image analysis software. .

(2) Degree of irregularity Measurement was performed as described above using a scanning electron microscope "S-5500" manufactured by Hitachi High-Technologies Corporation as a scanning electron microscope and "WinROOF2015" manufactured by Mitani Shoji Co., Ltd. as an image analysis software.

(3) Average fiber length Measurement was performed as described above based on "8.4.1. Average fiber length (c direct method)" of JIS L1015:2010 "Chemical fiber staple test method".

(4) Crystallinity Measurement was performed as described above using a differential scanning calorimeter "DSC Q2000" manufactured by TA Instruments.

(5) Fabric weight Measurement was performed as described above in accordance with "6.2 Mass per unit area" of JIS L1913:2010 "General Nonwoven Fabric Test Methods".

(6) Thickness of nonwoven fabric Based on JIS P8118:2014 "Paper and paperboard - Test method for thickness, density and specific volume", measurement was performed as described above using a "micrometer" manufactured by Mitutoyo Co., Ltd. .

(7) Strength of nonwoven fabric The nonwoven fabrics produced in each of the practical and comparative examples were measured as described above using a tensile tester Tensilon (UTM-III-100 manufactured by Orientec).

(8) Quality of nonwoven fabric The quality of the obtained nonwoven fabric was evaluated on the following three levels.
A: There is no unevenness in the basis weight and the uniformity of the appearance is good. B: Fiber bundles, fiber aggregates, etc. are visible in the nonwoven fabric. C: Tears and pinholes have occurred in the nonwoven fabric.

[Reference example 1]
Polyphenylene sulfide consisting only of p-phenylene sulfide units was vacuum dried at 150°C for 12 hours, and then melt-spun at a spinning temperature of 330°C. In melt spinning, polyphenylene sulfide was melt-extruded by a twin-screw extruder, metered by a gear pump, and passed through a filter to remove foreign matter, and then fed into a spinning pack. Thereafter, polyphenylene sulfide was discharged from a die having 36 discharge holes at a single hole discharge rate of 0.2 g/min. The introduction hole located directly above the spinneret hole was a straight hole, and the connecting portion between the introduction hole and the spinneret hole was tapered. The polyphenylene sulfide discharged from the nozzle passed through a 50 mm heat-retaining area, and then was air-cooled over 1.0 m using a uniflow type cooling device at a temperature of 25° C. and a wind speed of 18 m/min. Thereafter, an oil agent was applied, and each of the 36 filaments was wound up with a winder through a first godet roller and a second godet roller at 1000 m/min to obtain an undrawn fiber.

Next, the obtained undrawn fibers were stretched 3.0 times between rollers heated to 90°C, and then heat set using rollers heated to 200°C to obtain polyphenylene sulfide drawn fibers.

Thereafter, the obtained stretched polyphenylene sulfide fibers were cut with a cutter to obtain short fibers with an average fiber length of 6 mm.

[Example 1]
Polyphenylene sulfide consisting only of p-phenylene sulfide units was used as the island component, polyethylene terephthalate copolymerized with 5.0 mol% of 5-sodium sulfoisophthalic acid was used as the sea component, and each polymer was vacuum-dried at 150°C for 12 hours. Melt spinning was carried out at a spinning temperature of 310°C. In melt spinning, the island component and the sea component were each melted separately, measured by a gear pump via polymer piping, passed through a filter to remove foreign substances, and then supplied to a spinning pack. Then, using a sea-island type composite mouthpiece (number of islands: 1000, D: 0.4 mm, L: 0.8 mm) in which the shape of the island component is round, the composite ratio of the sea/island component was set to 40/60 and melted and discharged. After cooling and solidifying the resulting yarn, an oil agent was applied thereto and the fiber was wound at a spinning speed of 1000 m/min to obtain an undrawn fiber having a sea-island composite cross section (single hole discharge rate: 2.6 g/min).

Next, the obtained sea-island composite fibers were cut with a cutter to obtain short fibers with an average fiber length of 0.5 mm. Thereafter, the obtained short fibers were dissolved for 40 minutes in a 3% by mass aqueous sodium hydroxide solution (bath ratio 1/100) heated to 50°C to obtain binder fibers made of ultrafine polyphenylene sulfide fibers. . In addition, "DY-1125K (quaternary ammonium salt type cationic surfactant)" manufactured by Lion Specialty Chemicals Co., Ltd. was added as a dissolution promoter to the sodium hydroxide aqueous solution based on the mass of the sodium hydroxide aqueous solution. The treatment was performed by adding 0.5% by mass.

50% by mass of the ultrafine polyphenylene sulfide fibers described above as binder fibers and 50% by mass of the drawn polyphenylene sulfide fibers obtained in Reference Example 1 as binder fibers were mixed into a papermaking dispersion liquid, and the fiber concentration was 0. The content was adjusted to 4% by mass. This paper making liquid was supplied to a simple paper machine to obtain a wet nonwoven fabric with a basis weight of 40 g/m ² . Further, the wet nonwoven fabric was put into a hot air dryer at 120°C, treated for 3 minutes, cooled in air, and then thermocompression bonded for 3 minutes at a press pressure of 1.5 MPa using a flat plate hot press at 200°C.

Table 1 shows the evaluation results of the obtained binder fibers and nonwoven fabrics.

[Example 2, 3]
A polyphenylene sulfide fiber for a binder and a nonwoven fabric were obtained in the same manner as in Example 1, except that the number of islands in the sea-island composite base was changed. Table 1 shows the evaluation results of the obtained binder fibers and nonwoven fabrics.

[Example 4]
Polyphenylene sulfide fibers for a binder and a nonwoven fabric were obtained in the same manner as in Example 1, except that short fibers with an average fiber length of 2.5 mm were used when cutting the sea-island composite fibers with a cutter. Table 1 shows the evaluation results of the obtained binder fibers and nonwoven fabrics.

[Comparative example 1]
A nonwoven fabric was obtained in the same manner as in Example 1, except that the undrawn fibers obtained in Reference Example 1 were used as binder fibers without being drawn. Table 1 shows the evaluation results of the obtained binder fibers and nonwoven fabrics.

[Comparative example 2]
Except that the undrawn fibers having a sea-island composite cross section obtained by the method of Example 1 were drawn 3.0 times between rollers heated to 90°C, and then heat set with rollers heated to 200°C. A polyphenylene sulfide fiber for a binder and a nonwoven fabric were obtained in the same manner as in Example 1. Table 1 shows the evaluation results of the obtained binder fibers and nonwoven fabrics.

[Example 5, Comparative Example 3]
Ultrafine polyphenylene sulfide fiber, and a nonwoven fabric was obtained. Table 1 shows the evaluation results of the obtained binder fibers and nonwoven fabrics.

[Example 6]
A binder material was prepared in the same manner as in Example 3, except that the island component shape of the sea-island composite fiber was Y-shaped, and the fiber cross section of the polyphenylene sulfide fiber after sea component elution was a Y-shaped cross section with a degree of irregularity of 1.7. Polyphenylene sulfide fibers and nonwoven fabrics were obtained. Table 1 shows the evaluation results of the obtained binder fibers and nonwoven fabrics.

[Example 7]
Polyphenylene sulfide for a binder was prepared in the same manner as in Example 3, except that the island component shape of the sea-island composite fiber was made flat, and the fiber cross section of the polyphenylene sulfide fiber after sea component elution was made into a flat cross section with a degree of irregularity of 3.8. Fibers and nonwoven fabrics were obtained. Table 1 shows the evaluation results of the obtained binder fibers and nonwoven fabrics.

[Example 8, 9]
Ultrafine polyphenylene sulfide fibers and nonwoven fabrics were obtained in the same manner as in Example 1, except that the basis weights of the nonwoven fabrics were changed to 10 g/m ² (Example 8) and 5 g/m ² (Example 9), respectively. Table 2 shows the evaluation results of the obtained binder fibers and nonwoven fabrics.

It can be seen that Examples 1 to 9 have a small average fiber diameter and a low degree of crystallinity, so it is possible to make the nonwoven fabric thinner, and the adhesiveness and quality are good.

On the other hand, in Comparative Example 1, the nonwoven fabric is thick because the fiber diameter is large, and in Comparative Examples 2 and 3, the adhesiveness of the binder fibers is low, so the strength and strength per area of the nonwoven fabric are low, and the quality is also inferior. there were.

1: Outline of fiber cross section 2: Minimum circumscribed circle 3: Maximum inscribed circle

Claims

Ultrafine polyphenylene sulfide fibers having an average fiber diameter of 0.2 μm or more and 5.0 μm or less, and a crystallinity calculated by differential scanning calorimetry of 0% or more and 15% or less.
The ultrafine polyphenylene sulfide fiber according to claim 1, wherein the ultrafine polyphenylene sulfide fiber is a modified cross-section fiber, and has a degree of irregularity defined by the following formula of 1.2 or more.
Degree of irregularity = Minimum circumscribed circle diameter / Maximum inscribed circle diameter Here, the minimum circumscribed circle diameter is the diameter (μm) of the smallest circle that includes all of the fiber cross sections, and the maximum inscribed circle diameter is the diameter of the smallest circle that includes the entire fiber cross section. This is the diameter of a large circle (μm).
The ultrafine polyphenylene sulfide fiber according to claim 1 or 2, having an average fiber length of 0.1 mm or more and 6.0 mm or less.
A nonwoven fabric comprising the ultrafine polyphenylene sulfide fiber according to claim 1.
An undrawn fiber with a sea-island composite cross section in which polyphenylene sulfide is arranged as an island component is removed in an alkaline aqueous solution at 70°C or lower, and the average fiber diameter is 0.2 μm or more and 5.0 μm or less and differentially scanned. A method for producing ultrafine polyphenylene sulfide fibers, which obtains fibers having a crystallinity of 0% or more and 15% or less as calculated by calorimetry.
A method for producing a nonwoven fabric, which comprises mixing the ultrafine polyphenylene sulfide fibers according to claim 1 or 2 and drawn polyphenylene sulfide fibers in a papermaking dispersion to make paper, and then subjecting the paper to thermocompression bonding at a temperature of 130°C or higher and 250°C or lower. .