JP7232617B2 - Wet-laid nonwoven fabric containing polyphenylene sulfide fiber - Google Patents

Description

The present invention relates to a wet-laid nonwoven fabric containing polyphenylene sulfide fibers.

Polyphenylene sulfide (PPS) fiber is a high-performance fiber with excellent heat resistance, chemical resistance, hydrolysis resistance, dimensional stability when absorbing moisture, insulation, flame retardancy, and heat retention, so its applications are expanding. are doing. For example, filters used for high-temperature gas dust collection, canvas for dryers used in the drying process of industrial products, roll wiping materials for office copiers, insulating materials for electrical equipment, molding materials, cushioning materials (cushion materials), and heat insulating cloths. , battery separators, and the like.

As a heat-resistant nonwoven fabric made of PPS fibers, a heat-resistant wet-laid nonwoven fabric manufactured by a wet papermaking method is known. For example, heat-resistant wet-laid nonwoven fabrics using both stretched PPS fibers and unstretched PPS fibers are known (see, for example, Patent Documents 1 to 3). When a wet nonwoven fabric is produced by a wet papermaking method, there are a wet press section for squeezing water from the wet paper produced by the papermaking net, a step for conveying the wet paper to a dryer, and the like. A heat-resistant wet-laid nonwoven fabric containing stretched PPS fibers and unstretched PPS fibers has a problem that paper breakage is likely to occur in the wet press section and the conveying process. It is also known that a nonwoven fabric with high heat-resistant dimensional stability can be obtained even with a low basis weight by lowering the dry heat shrinkage of PPS fibers. (See Patent Document 4, for example). In this case, there is a problem that the wet paper web and the nonwoven fabric cannot have sufficient specific tensile strength. It is known to use polyvinyl alcohol fibers or polyester fibers as binder fibers in order to ensure sufficient tensile strength of wet paper webs and nonwoven fabrics (for example, Patent Documents 5 and 6). In this case, there is a problem that the chemical resistance is lowered.

JP-A-1-272899 JP 2010-24574 A JP 2011-106043 A JP 2004-285536 A JP 2017-218693 A JP 2017-226928 A

An object of the present invention is to provide a polyphenylene sulfide fiber-containing wet-laid nonwoven fabric that is less likely to break during production by a wet-laid papermaking method and has excellent chemical resistance.

The above problems can be solved by the following inventions.

(1) Containing only polyphenylene sulfide fiber, polyphenylene sulfide fiber having an irregular cross section (excluding flat shape) and polyphenylene sulfide fiber having a circular cross section with a fiber diameter of 5 μm or less, and having a basis weight of 8 g/m ² or more , 200 g/m ² or less.

(2) The polyphenylene sulfide fiber content according to (1) above, wherein the content of the polyphenylene sulfide fiber having a circular cross-sectional shape with a fiber diameter of 5 μm or less is 5% by mass or more and 70% by mass or less based on the total fiber. Wet-laid nonwoven fabric.

According to the present invention, it is produced by a wet papermaking method by containing only polyphenylene sulfide fibers and containing polyphenylene sulfide fibers having an irregular cross section and polyphenylene sulfide fibers having a circular cross section having a fiber diameter of 5 μm or less. It is possible to provide a wet-laid nonwoven fabric containing polyphenylene sulfide fibers, which hardly causes paper breakage and has excellent chemical resistance.

The polyphenylene sulfide fiber-containing wet-laid nonwoven fabric of the present invention is characterized by comprising only polyphenylene sulfide fibers and containing PPS fibers having an irregular cross section and PPS fibers having a circular cross section with a fiber diameter of 5 μm or less. The wet-laid nonwoven fabric containing PPS fibers of the present invention preferably contains drawn PPS fibers as main fibers and undrawn PPS fibers as binder fibers. Undrawn PPS fibers have a predominantly amorphous structure and can be melted by the application of heat and act as a binder. A drawn PPS fiber has high single fiber strength and excellent dimensional stability by being subjected to drawing in the fiber manufacturing process. In the present invention, when the drawn PPS fiber and the undrawn PPS fiber are used in combination, it becomes easy to provide a nonwoven fabric having excellent chemical resistance and heat resistance.

A polyphenylene sulfide fiber is a synthetic fiber composed of a polymer (PPS polymer) having -(C ₆ H ₄ -S)- as a main structural unit as a polymer structural unit. Representative examples of PPS polymers include polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfide ketone, and the like. Also included are random copolymers and block copolymers thereof. Furthermore, mixtures of the above polymers are mentioned. A particularly preferred PPS polymer is a PPS polymer containing preferably 90% by mass or more of p-phenylene units represented by —(C ₆ H ₄ —S)— as the main structural unit of the polymer.

In the PPS fiber having a modified cross section, the modified cross section means that the cross-sectional shape when cut perpendicular to the length direction of the fiber is other than a circular cross-sectional shape, such as a triangular shape, a Y shape , a dogbone shape, and a trefoil shape. It means a thing having a cross section such as For example, these can be obtained by a method of direct spinning using an irregular mold, a method of dissolving or splitting a composite fiber, etc. PPS fibers having an irregular cross section obtained by direct spinning using an irregular mold are It is preferably used in the present invention. Although the cross-sectional shape is not particularly limited, PPS fibers having a Y-shaped or trefoil-shaped cross-sectional shape are more preferable from the viewpoint of strength improvement. The Y-shaped or trefoil shape has a larger specific surface area than a circular cross-sectional shape, increases the number of adhesion points between fibers, and not only improves the strength of the wet paper and the strength of the base paper after the papermaking process, Since the nonwoven fabric is deformed and adhered so as to enter the space, it can contribute to improving the strength of the nonwoven fabric.

Wet-laid nonwoven fabrics made only of PPS fibers have extremely low water retention in the state of wet paper when they are made into sheets by the wet papermaking method. There was a problem that it is likely to occur. The PPS fiber-containing wet-laid nonwoven fabric of the present invention contains PPS fibers having an irregular cross-section and PPS fibers having a circular cross-section having a fiber diameter of 5 μm or less, so that paper breakage occurs during production by a wet paper-making method. It has the effect of being difficult. More specifically, by including PPS fibers having an irregular cross section and PPS fibers having a circular cross section with a fiber diameter of 5 μm or less, the specific surface area of the fibers is improved, and the adhesion points between the fibers are increased. The strength of the wet paper increases, making it less likely that the fibers will peel off or break in the wet press section of the paper machine. , can suppress paper breaks. Furthermore, the strength of the base paper after drying with a dryer is improved, and post-processing properties are also excellent.

In the PPS fiber-containing wet-laid nonwoven fabric of the present invention, the content of PPS fibers having an irregular cross section is preferably 10% by mass or more and 95% by mass or less, more preferably 30% by mass or more and 90% by mass or less. preferable. If the content of the PPS fibers having an irregular cross section is less than 10% by mass, the strength of the base paper after drying and the strength of the nonwoven fabric after heat calendering may not be sufficiently improved. Moreover, when the content of the PPS fibers having an irregular cross section is more than 95% by mass, the wet paper strength is not sufficiently improved, and there is a possibility that the paper breaks easily.

In the PPS fiber-containing wet-laid nonwoven fabric of the present invention, the content of PPS fibers having a circular cross-sectional shape with a fiber diameter of 5 μm or less is preferably 5% by mass or more and 70% by mass or less, and more preferably 10% by mass or more and 40% by mass. % or less. If the content of PPS fibers having a circular cross-section with a fiber diameter of 5 μm or less is less than 5% by mass, the wet paper web strength is not sufficiently improved, and there is a risk that the paper breaks easily. In addition, when the content of PPS fibers with a circular cross-section having a fiber diameter of 5 μm or less exceeds 70% by mass, the strength of the base paper after drying with a dryer is not sufficiently improved, and the post-processability is deteriorated. There is The diameter of the fiber with a circular cross-sectional shape was obtained by cutting the PPS fiber-containing wet-laid nonwoven fabric with a sharp blade, observing the cross section with a scanning electron microscope (SEM) at a magnification of 2000, and randomly extracting 100 fibers. Average of diameter measurements.

In the PPS fiber-containing wet-laid nonwoven fabric of the present invention, the content of PPS unstretched fibers is preferably 30% by mass or more and 90% by mass or less, more preferably 40% by mass or more and 80% by mass, based on the total fiber amount. % or less. When the content of the PPS unstretched fibers is less than 30% by mass, the binder effect of bonding the fibers together is insufficient, and sufficient tensile strength as a nonwoven fabric may not be obtained. Moreover, when the content of the PPS undrawn fibers exceeds 90% by mass, shrinkage in the width direction increases during heat calendering, which may deteriorate the profile.

Considering the production efficiency in the wet papermaking method, the diameter of the PPS fibers is preferably 0.1-30 μm, more preferably 1.0-25 μm, still more preferably 2-20 μm. If the fiber diameter is less than 0.1 μm, it may drop out of the papermaking net of the wet paper machine. On the other hand, when the fiber diameter exceeds 30 μm, the degree of entanglement between the fibers in the slurry becomes insufficient, the effect of suppressing paper breakage in the wet papermaking process is not sufficient, and the contact points between the fibers become too small. strength may become difficult to maintain. In addition, when PPS fibers having a circular cross section with a fiber diameter of 5 μm or less are not contained, the wet paper strength is not sufficiently improved, and paper breakage is likely to occur. The diameter of the PPS fiber having an irregular cross section was obtained by cutting the PPS fiber-containing wet-laid nonwoven fabric with a sharp knife, observing the cross section with an SEM at a magnification of 2000, and measuring the area of 100 randomly selected fibers. It is the average value calculated as the diameter of a circle.

The fiber length of the fibers used in the PPS fiber-containing wet-laid nonwoven fabric of the present invention is preferably 1 to 20 mm, more preferably 2 to 15 mm, still more preferably 3 to 10 mm. If it is less than 1 mm, it may fall out of the papermaking net during wet papermaking, and sufficient strength may not be obtained. On the other hand, if the thickness exceeds 20 mm, tangling or the like may occur when dispersed in water, and a uniform texture may not be obtained.

In the present invention, a wet-laid nonwoven fabric containing PPS fibers is produced by a wet-laid papermaking method. First, fibers are uniformly dispersed in water, and then a slurry is prepared through processes such as screening (removal of foreign matters, lumps, etc.). The final fiber concentration of the slurry is preferably 0.01-0.50% by weight. The slurry is made up by a paper machine to obtain wet paper. During the process, chemicals such as dispersants, antifoaming agents, hydrophilic agents, antistatic agents, polymer adhesives, release agents, antibacterial agents, and bactericides may be added.

As a paper machine, for example, a paper machine using a single paper making net such as a fourdrinier, a circular net, or an inclined wire, or a combination paper machine in which two or more paper making nets of the same type or different types are installed online, etc. are used. be able to. In the case where the nonwoven fabric has a multi-layered structure of two or more layers, a method of laminating wet paper made by each paper machine, or forming one layer and then dispersing fibers on that layer. A non-woven fabric can be produced by a casting method or the like in which the prepared slurry is cast and laminated. When the slurry in which the fibers are dispersed is cast, the layer previously formed may be in a wet paper state or in a dry state. Also, two or more dry layers can be heat-sealed to form a multi-layered nonwoven fabric.

In the wet papermaking process, the wet paper produced in the papermaking net and squeezed in the wet press section is dried with dryers such as Yankee dryers, air dryers, cylinder dryers, suction drum dryers, and infrared dryers. , a wet-laid nonwoven base paper is obtained. When the wet paper is dried, it is brought into close contact with a hot roll such as a Yankee dryer and dried under heat and pressure, thereby improving the smoothness of the contacted surface. Hot and pressure drying means drying by pressing the wet paper against a hot roll with a touch roll or the like. The surface temperature of the hot roll is preferably 100-180°C, more preferably 120-160°C. The pressure is preferably 50-1000 N/cm, more preferably 100-800 N/cm.

The PPS fiber-containing wet-laid nonwoven fabric of the present invention is preferably subjected to heat calendering. Calender units used for thermal calendering of PPS fiber-containing wet-laid nonwoven fabrics include roll combination calender units such as metal roll-metal roll, metal roll-elastic roll, metal roll-cotton roll, and metal roll-silicon roll. mentioned. These calender units can be used alone or in combination of two or more.

During hot calendering, the surface temperature of the metal roll is preferably 100-260°C, more preferably 150-250°C. If the temperature of the metal roll is lower than 100° C., the melting of the unstretched PPS fibers may not progress and the binding between the fibers may not progress. Moreover, if the temperature of the metal roll is higher than 260° C., the fibers constituting the PPS fiber-containing wet-laid nonwoven fabric may stick to the metal roll, impairing the uniformity of the surface of the nonwoven fabric.

The nip pressure of the nip during hot calendering is preferably 190-1800 N/cm, more preferably 390-1500 N/cm. The processing speed is preferably 5-150 m/min, more preferably 10-80 m/min.

In the present invention, when the PPS fiber-containing wet-laid nonwoven fabric has a multi-layer structure, it may have a multi-layer structure in which each layer has the same fiber composition, or may have a multi-layer structure in which each layer has a different fiber composition. In the case of a multilayer structure, the density of fibers in the slurry can be lowered by lowering the basis weight of each layer, so that the texture of the PPS fiber-containing wet-laid nonwoven fabric is improved, resulting in a uniform texture of the PPS fiber-containing wet-laid nonwoven fabric. improve sexuality. Moreover, even if the formation of each layer is uneven, it can be compensated for by stacking. Furthermore, the papermaking speed can be increased, and the effect of improving the workability is also obtained.

The wet-laid nonwoven fabric containing PPS fibers of the present invention has a basis weight of 8 to 200 g/m ² , more preferably 12 to 150 g/m ² , as measured according to JIS P 8124:2011. If the basis weight is less than 8 g/m ² , the uniformity and tensile strength of the PPS fiber-containing wet-laid nonwoven fabric will be insufficient. If the basis weight exceeds 200 g/m ² , it becomes difficult to apply heat uniformly to the PPS fiber-containing wet-laid nonwoven fabric during heat calendering.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples. All parts and percentages in the examples are by mass unless otherwise specified.

<PPS fiber 1>
PPS fiber 1 was a drawn PPS fiber having a trefoil cross-section, a fineness of 1.3 decitex, a diameter of 11 μm, and an irregular cross-section of a fiber length of 5 mm.

<PPS fiber 2>
A drawn PPS fiber having a circular cross-sectional shape, a fineness of 1.1 decitex, a diameter of 10 μm and a fiber length of 5 mm was designated as PPS fiber 2 .

<PPS fiber 3>
A PPS fiber 3 was an undrawn PPS fiber having a trefoil cross section, a fineness of 2.6 decitex, a diameter of 16 μm, and an irregular cross section of 5 mm in fiber length.

<PPS fiber 4>
A PPS fiber 4 was an undrawn PPS fiber having a circular cross section, a fineness of 1.7 decitex, a diameter of 13 μm, and a fiber length of 5 mm.

<Small diameter PPS fiber>
A PPS drawn fiber having a circular cross-sectional shape, a fineness of 0.2 decitex, a diameter of 4 μm and a fiber length of 3 mm was used as a small diameter PPS fiber.

<PVA fiber>
Polyvinyl alcohol fibers having a fineness of 1.1 decitex and a fiber length of 3 mm were used as PVA fibers.

<PET fiber>
The core is polyethylene terephthalate (melting point: 260°C), and the sheath is amorphous copolymerized polyester (glass transition point: 72°C) composed of polyethylene terephthalate with isophthalic acid as a copolymer component, and the fineness is 1.1 decitex. , a polyester core-sheath fiber having a fiber length of 5 mm was used as a PET fiber.

<Examples 1 to 11, Comparative Examples 1 to 6>
With the fiber formulation shown in Table 1, the fibers were dispersed in water at a dispersion concentration of 0.2% by mass for 10 minutes, and a wet paper was formed using a cylinder paper machine, and then subjected to a Yankee dryer with a surface temperature of 150 ° C. It was dried under heat and pressure to obtain a wet-laid nonwoven base paper.

(Heat calendering)
The wet-laid nonwoven base paper is subjected to heat calendering twice by a metal roll-elastic roll calender unit at a metal roll temperature of 230° C. and a processing speed of 10 m/min so that both the front and back sides are nipped in contact with the metal rolls. A contained wet-laid nonwoven fabric was obtained.

In Examples and Comparative Examples, the basis weight and thickness were measured, and the productivity and alkali resistance were evaluated.

(Metsuke)
In accordance with JIS P 8124:2011, the PPS fiber-containing wet-laid nonwoven fabric was cut into 100 mm × 100 mm test pieces, and 20 pieces were measured using an electronic analysis balance (manufactured by Shimadzu Corporation). and

(thickness)
Based on JIS P 8118:2014, 20 specimens were measured one by one from the test specimens sampled at the time of basis weight measurement using a micrometer (manufactured by Mitutoyo), and the average value of each value was taken as the thickness.

(Productivity)
The following indices were used to evaluate the productivity in the production of the wet-laid nonwoven base paper.

"5": The running properties of the wet paper and the wet-laid nonwoven base paper in each part of the paper machine were stable, and no paper breakage occurred. Speed up is also possible.
"4": The running properties of the wet paper and the wet-laid nonwoven base paper in each part of the paper machine are stable. No paper break occurs, but slight fiber peeling is observed.
"3": The running properties of the wet paper and the wet-laid nonwoven base paper in each part of the paper machine are stable. No paper break occurred, but more fiber peeling than "4".
"2": The strength of the wet paper web at the press part is weak, but production is possible if the speed is lower than that of "3". Occasionally, paper breaks may occur at the exit of the dryer.
"1": The strength of the wet paper web at the press part is weak, and paper breaks occur frequently.

(alkali resistance)
In accordance with JIS P 8113: 2006, using a constant-speed tension type tensile tester "Tensilon desktop material testing machine, model number: STA-1150" (manufactured by Orientec), 15 mm × 150 mm with the MD direction as the long side It was cut into strips and used as test pieces. The distance between chucks was set to 100 mm, the moving speed of the chuck was set to 100 mm/min, and tension was performed at a constant speed. After immersing the PPS fiber-containing wet-laid nonwoven fabric in a 10% NaOH aqueous solution at room temperature for 50 hours, it was thoroughly washed with water and air-dried. rate was calculated.

Strength retention rate = tensile strength 2 / tensile strength 1 x 100

The alkali resistance of the PPS fiber-containing wet-laid nonwoven fabric was evaluated using the following indices.

"5": 100%
"4": 97% or more, less than 100% "3": 93% or more, less than 97% "2": 90% or more, less than 93% "1": less than 90%

By comparing Examples 1 to 12 with Comparative Examples 1 to 6, it is found that PPS fibers made only of PPS fibers and having a modified cross section and PPS fibers having a circular cross section with a fiber diameter of 5 μm or less are included, and the basis weight is The PPS fiber-containing wet-laid nonwoven fabrics of Examples 1 to 12, which have a weight of 8 g/m ² or more and 200 g/m ² or less, are less productive than the PPS fiber-containing wet-laid nonwoven fabric of Comparative Example 1, which does not contain PPS fibers having an irregular cross section. I know you're good. In addition, it can be seen that the wet-laid nonwoven fabrics containing PPS fibers of Comparative Examples 2 and 3, which contain PVA fibers or PET fibers as part of the binder fibers, are superior in alkali resistance. In addition, it can be seen that the productivity is superior to the PPS fiber-containing wet-laid nonwoven fabric of Comparative Example 4, which does not contain PPS fibers having a circular cross section and a fiber diameter of 5 μm or less. In addition, the PPS fiber of Comparative Example 5, which is composed only of PPS fibers and includes PPS fibers having an irregular cross section and PPS fibers having a circular cross section with a fiber diameter of 5 μm or less, has a basis weight of less than 8 g/m ² . It can be seen that the productivity is superior to the wet-laid nonwoven fabric containing PPS fibers and the wet-laid nonwoven fabric containing PPS fibers of Comparative Example 6 having a basis weight of more than 200 g/m ² .

From the comparison of Examples 1 to 5, it can be seen that the productivity is more excellent when the basis weight is 12 g/m ² or more and 150 g/m ² or less.

From the comparison of Examples 6 to 9, when the content of PPS fibers having a circular cross-sectional shape with a fiber diameter of 5 μm or less is 5% by mass or more and 70% by mass or less with respect to the total fibers, the productivity is more excellent. I know there is.

From a comparison of Examples 8, 9, and 10, the PPS fiber-containing wet-laid nonwoven fabric of Example 8, which has a PPS undrawn fiber content of 30% by mass or more, has a PPS undrawn fiber content of less than 30% by mass. It can be seen that the PPS fiber-containing wet-laid nonwoven fabrics of Examples 9 and 10 are superior in productivity.

From the comparison of Examples 1, 11 and 12, when the content of PPS fibers with a circular cross section with a fiber diameter of 5 μm or less is the same, the content of PPS fibers with a circular cross section with a fiber diameter of more than 5 μm is higher than the content of PPS fibers with a circular cross section with a fiber diameter of 5 μm or less. Also, it can be seen that the higher the content of the PPS fiber having a modified cross section, the more excellent the productivity.

The wet-laid nonwoven fabric containing PPS fibers of the present invention can be used as a filter for high-temperature gas dust collection, as a canvas for dryers used in the drying process of industrial products, as a roll wiping material for office copiers, as an insulating material for electrical equipment, as a molding material, as a shock absorber. It can be used as a material (cushion material), a heat insulating cloth, and the like.

Claims (2)

A polyphenylene sulfide fiber consisting only of polyphenylene sulfide fibers and having a modified cross section (excluding a flat shape) and a polyphenylene sulfide fiber having a circular cross section with a fiber diameter of 5 μm or less, and having a basis weight of 8 g / m ² or more, 200 g / A polyphenylene sulfide fiber-containing wet-laid nonwoven fabric having a m ² or less. The polyphenylene sulfide fiber-containing wet-laid nonwoven fabric according to claim 1, wherein the content of the polyphenylene sulfide fibers with a circular cross-section having a fiber diameter of 5 μm or less is 5% by mass or more and 70% by mass or less based on the total fibers.