JP7790255B2 - Nonwoven fabric, manufacturing method of nonwoven fabric - Google Patents

Description

The present invention relates to nonwoven fabrics and methods for manufacturing nonwoven fabrics.

Nonwoven fabrics have a wide range of applications in various industrial fields, including clothing, cosmetics, hygiene products, and medical supplies. For example, Patent Document 1 proposes a water-decomposable nonwoven fabric in which pulp fibers and regenerated cellulose fibers are entangled by high-pressure water jet processing, as a nonwoven fabric suitable for wet products such as wet tissues, baby wipes, and wipes.

International Publication No. 2019/150964

Not only wet products and water-decomposable nonwoven fabrics, but also nonwoven fabrics used in applications that come into contact with human skin, such as tissue paper, are required to have a new and unique pleasant feel that meets consumer preferences, demands, trends, etc.
The present invention provides a nonwoven fabric having a novel and uniquely pleasant feel against the skin and a method for producing the same.

The inventors attempted to obtain nonwoven fabrics from slurries containing dissolving pulp in order to achieve a new and unique feel in nonwoven fabrics. Dissolving pulp has very little hemicellulose, which means that the interfiber bonds are weak, and it was expected that this unique feel would be achieved.
However, the inventors' tests revealed that simply making paper from a slurry containing dissolving pulp did not provide sufficient sheet strength because the interfiber bonds of dissolving pulp were extremely weak. As a result, a sheet-like nonwoven fabric could not be obtained. Attempts were made to use chemicals to increase sheet strength, but the use of chemicals resulted in the nonwoven fabric becoming stiffer and the unique pleasant feel of dissolving pulp being lost.
Therefore, the present inventors came up with the idea of subjecting a wetlaid web obtained by blending chemical fibers such as rayon or vinylon into a slurry to high-pressure water jet treatment in order to avoid impairing the pleasant feel that is unique to dissolving pulp and to supplement the sheet strength required to obtain a nonwoven fabric. By subjecting a wetlaid web obtained from a slurry containing dissolving pulp and chemical fibers to high-pressure water jet treatment, sufficient strength was achieved to obtain a nonwoven fabric. In addition, the obtained nonwoven fabric was able to achieve a new and unique pleasant feel to the skin, particularly flexibility.

The present invention has the following aspects.
[1] A nonwoven fabric comprising dissolving pulp and chemical fibers, the dissolving pulp and the chemical fibers being entangled.
[2] The nonwoven fabric of [1], wherein the average fiber length of the chemical fibers is 3 to 20 mm.
[3] The nonwoven fabric according to [1] or [2], wherein the chemical fiber is rayon.
[4] A method for producing a nonwoven fabric, comprising subjecting a wet-laid web obtained from a slurry containing dissolving pulp and chemical fibers to a high-pressure water jet treatment.
[5] The manufacturing method of [4], wherein the chemical fiber is rayon.

The present invention provides a nonwoven fabric with a novel and uniquely pleasant feel, and a method for producing the same.

FIG. 2 is a schematic diagram for explaining the high-pressure water jet treatment carried out in the examples.

In this specification, the term "bone-dry nonwoven fabric" means a nonwoven fabric having a moisture content of 1% by mass or less relative to the total mass of the nonwoven fabric.
In this specification, the use of "to" to indicate a range of values means that the values before and after it are included as the lower and upper limits.
The lower and upper limits of the ranges disclosed in this specification can be combined in any way to create new ranges.

<Nonwoven fabric>
The nonwoven fabric of the present invention contains dissolving pulp and chemical fibers. In the nonwoven fabric of the present invention, the dissolving pulp and the chemical fibers are integrated by being entangled with each other. The state in which the dissolving pulp and the chemical fibers are entangled and integrated with each other in the nonwoven fabric can be understood by observing the surface of the nonwoven fabric under magnification, and seeing that the fibers are randomly oriented and entangled.
Generally, nonwoven fabrics obtained by entangling fibers with each other through high-pressure water jet processing are called spunlace nonwoven fabrics. The nonwoven fabric of the present invention can also be said to be a spunlace nonwoven fabric in which dissolving pulp and chemical fibers are hydroentangled with each other through high-pressure water jet processing.

The nonwoven fabric of the present invention is made by entangling and integrating dissolving pulp and chemical fibers through high-pressure water jet processing. As a result, continuous streak-like jet marks are formed on the nonwoven fabric in the flow direction (MD) of the production line. In the nonwoven fabric of the present invention, the presence of streak-like jet marks formed by high-pressure water jet processing on the surface of the nonwoven fabric indicates that the dissolving pulp and chemical fibers are hydroentangled. The jet marks are fine marks created by the high-pressure water jet. In the jet marks, the density of the fibers making up the nonwoven fabric is higher than the density of areas other than the jet marks, which were not affected by the high-pressure water jet.

(dissolving pulp)
The nonwoven fabric of the present invention contains dissolving pulp. Dissolving pulp is usually used as a cellulose raw material. Dissolving pulp is commonly used as a raw material for various industrial products, such as rayon, cellophane, pharmaceutical excipients, food additives, civil engineering materials, artificial fibers, cigarette filters, and liquid crystal films. One of the features of the present invention is that dissolving pulp is used as a raw material for the nonwoven fabric.
The presence of dissolving pulp in the nonwoven fabric can be confirmed by the proportion of α-cellulose in the nonwoven fabric.

The proportion of α-cellulose to the total amount of all dissolving pulp in the nonwoven fabric is preferably 92% by mass or more, more preferably 94% by mass or more, and even more preferably 96% by mass or more. When the proportion of α-cellulose is 92% by mass or more, it is thought that a nonwoven fabric having a smooth feel and flexibility is easily obtained.
The ratio of α-cellulose to pulp in the nonwoven fabric is measured in accordance with JIS P8101.

Dissolving pulp is a cellulose raw material obtained by selectively removing hemicellulose and lignin from lignocellulosic materials contained in raw chips. The raw chips for dissolving pulp may be wood (coniferous trees, broad-leaved trees, etc.) or non-wood (plants such as kenaf, bagasse, and bamboo), and are not particularly limited.
Considering production efficiency, wood with a high volumetric density is preferably used. Examples of suitable hardwoods include Eucalyptus globulus, Eucalyptus grandis, Eucalyptus eurograndis, Eucalyptus pelita, Eucalyptus camaldulensis, Eucalyptus brassiana, and Acacia melansi. Examples of suitable coniferous trees include radiata pine, Caribbean pine, Douglas fir, hemlock, redwood, and larch. One type of hardwood, coniferous tree, or non-wood may be used alone, or two or more types may be used in combination, with no particular limitation on the combination.

The content of α-cellulose in the dissolving pulp is preferably 92% by mass or more, more preferably 94% by mass or more, and even more preferably 96% by mass or more. When the content of α-cellulose in the dissolving pulp is equal to or more than the lower limit, it is thought that a nonwoven fabric having a smooth feel and flexibility is easily obtained.
The content of α-cellulose in the dissolving pulp is measured in accordance with JIS P8101.

The viscosity of the dissolving pulp is preferably 6 to 13 mPa·s, more preferably 6 to 11 mPa·s, and even more preferably 6 to 10 mPa·s. The viscosity of the dissolving pulp is the relative viscosity measured in accordance with J TAPPI No. 44. The viscosity of the dissolving pulp is the relative viscosity when the dissolving pulp is dissolved in an aqueous solution of copper ethylenediamine, and is also used as an indicator of the degree of polymerization of cellulose in the dissolving pulp. When the viscosity of the dissolving pulp is equal to or greater than the lower limit of the above numerical range, the sheet strength of the wetlaid web and nonwoven fabric is likely to be improved. When the viscosity of the dissolving pulp is equal to or less than the upper limit of the above numerical range, the fluidity of the slurry is sufficiently high, making wetlaid papermaking easier.

The dissolving pulp may be produced by an acidic sulfite cooking method or an alkaline cooking method, and any dissolving pulp obtained by either method can be used.
The alkaline cooking method includes, for example, kraft cooking, polysulfide cooking, soda cooking, and alkali sulfite cooking, and any of these methods may be used without any particular limitation. In consideration of the quality of the dissolving pulp, energy efficiency, etc., the kraft cooking method is preferably used.
Hereinafter, a method for producing dissolving pulp by the kraft cooking method will be described, but the dissolving pulp is not limited to that produced by the kraft cooking method.

To produce dissolving pulp using the kraft cooking method, wood chips or other materials are heated in the presence of water to undergo prehydrolysis. The strength of the prehydrolysis is preferably a P factor of 200 to 1000. The temperature is preferably 160 to 170°C. The treatment temperature can be determined based on the treatment time. The P factor is calculated from the temperature and time during prehydrolysis. There are no particular restrictions on the equipment used for prehydrolysis, but general-purpose continuous digesters, batch cookers, etc. are preferably used.

Next, the wood chips after prehydrolysis are subjected to an alkaline cooking treatment. There are no particular restrictions on the equipment used for alkaline cooking, but general-purpose continuous digesters, batch digesters, etc. are preferably used. When kraft cooking wood, the sulfidity of the kraft cooking liquor is preferably 20-35%. The effective alkali addition rate of the kraft cooking liquor is preferably 10-25% by mass per bone-dry mass of wood. The cooking temperature is preferably 140-170°C. The kraft cooking method can be either a cooking method in which white liquor is added in portions or a cooking method in which white liquor is added all at once, and there is no particular restriction on the kraft cooking method.

The kappa number of the unbleached pulp obtained by alkali cooking is not particularly limited. In consideration of the quality of the dissolving pulp and subsequent bleachability, the kappa number is preferably 6 to 18 when hardwood is used as the raw material, and 20 to 35 when softwood is used as the raw material.
The unbleached pulp is washed, roughly screened, and screened, and then delignified, preferably by oxygen delignification, and then bleached to obtain bleached pulp. Specific embodiments of the oxygen delignification and bleaching are not particularly limited and can be appropriately selected by those skilled in the art.
The bleaching treatment is generally a multi-stage bleaching treatment that combines bleaching stages such as chlorine dioxide, alkali, oxygen, hydrogen peroxide, and ozone. The unbleached pulp is finally bleached to a brightness of 87 to 92% ISO, preferably 89 to 92% ISO, to obtain dissolving pulp.

The main components of bleached pulp are cellulose and hemicellulose. Bleached pulp may contain impurities such as lignin and resin. Regarding bleached pulp, general dissolving pulp contains 95-99% by mass of cellulose and 1-5% by mass of hemicellulose. In contrast, general papermaking pulp contains approximately 85% by mass of cellulose and 15% by mass of hemicellulose. General cotton contains 99% or more by mass of cellulose and less than 1% by mass of hemicellulose.

The dissolving pulp may be mercerized (alkaline). The mercerized dissolving pulp contains alkali cellulose. Various mercerization treatment solutions (such as alkaline solutions) can be used for the mercerization reaction. A surfactant may be used as a mercerization accelerator for the mercerization reaction. Examples of surfactants that can be used as mercerization accelerators include the surfactant (A) disclosed in WO 2016/170857. However, the surfactant is not limited to this example.
The temperature and time of the mercerization reaction are not particularly limited, and can be set or changed as appropriate by those skilled in the art.

The average fiber length of the dissolving pulp in the nonwoven fabric is preferably 0.3 to 4 mm, more preferably 0.5 to 3 mm, and even more preferably 0.5 to 1 mm. When the average fiber length of the dissolving pulp is equal to or greater than the lower limit of the above-mentioned numerical range, the strength of the nonwoven fabric is likely to be improved. In addition, a smooth feel and suppleness are likely to be obtained. When the average fiber length of the dissolving pulp is equal to or less than the upper limit of the above-mentioned numerical range, the dissolving pulp is less likely to become tangled in the manufacturing equipment, making it easier to manufacture the nonwoven fabric.
The average fiber length of the dissolving pulp is measured in accordance with JIS P8226.

The fiber width of the dissolving pulp in the nonwoven fabric is preferably 10 to 30 μm, more preferably 10 to 25 μm, and even more preferably 10 to 20 μm. When the fiber width of the dissolving pulp is equal to or greater than the lower limit of the above-mentioned numerical range, the strength of the nonwoven fabric is likely to be improved. When the fiber width of the dissolving pulp is equal to or less than the upper limit of the above-mentioned numerical range, the dispersibility of the dissolving pulp in the slurry when producing the nonwoven fabric is likely to be improved.
The fiber width of dissolving pulp is measured using an image analysis technique such as Valmet FS5.

(chemical fiber)
The chemical fiber is not particularly limited. Regenerated fiber, semi-synthetic fiber, or synthetic fiber can be used. One type of chemical fiber may be used alone, or two or more types may be used in combination.
Examples of regenerated fibers include rayon, viscose rayon, polynosic rayon, cupra (cuprammonium rayon), lyocell, and Tencel, but the regenerated fibers are not limited to these examples.
Examples of semi-synthetic fibers include acetate, triacetate, and promix, but the semi-synthetic fibers are not limited to these examples.
Examples of synthetic fibers include nylon, vinylon, vinylidene, polyester, polyolefin (e.g., polyethylene, polypropylene, etc.), polyurethane, acrylic, polyvinyl chloride, and aramid, but are not limited to these examples.
The regenerated fibers, semi-synthetic fibers, and synthetic fibers may be used singly or in combination of two or more kinds.

Among these, recycled fibers are preferred as chemical fibers, with rayon and vinylon being more preferred, and rayon being even more preferred. When the chemical fiber is rayon, it is easier to obtain nonwoven fabrics that feel softer to the touch. Rayon is biodegradable, and dissolving pulp is also biodegradable, so there is also the advantage that biodegradable nonwoven fabrics can be obtained.

The rayon may be flat rayon, which has a flat fiber cross-sectional shape. The fiber cross-sectional shape refers to the shape of a cut surface perpendicular to the longitudinal direction of the fiber. A flat shape refers to a shape in which the fiber cross-sectional shape has a major axis defined by the maximum length passing through the center point and a minor axis defined by the minimum length passing through the center point, and the ratio of the major axis to the minor axis of the cross section is 2 or more. The ratio of the major axis to the minor axis of the fiber cross section can be calculated by observing the flat cross sections of 10 different flat rayon samples under a microscope from the perpendicular direction and averaging the major axis and minor axis measured using a microscale as a reference.
Examples of flat shapes include cocoon-shaped, oval-shaped, and elliptical-shaped, but the flat shape is not limited to these examples.

As the flat rayon, either solid flat rayon or hollow flat rayon may be used. Hollow flat rayon has a flat fiber cross section when wet. This increases the contact area between fibers, generating adsorption and frictional forces due to the surface tension of the fibers, making it easier to achieve high strength. Furthermore, hollow flat rayon swells and becomes easily unraveled in the presence of a large amount of water during washing. This is thought to facilitate the hydrolysis of the nonwoven fabric. Commercially available hollow flat rayon may also be used. An example of a commercially available hollow flat rayon is SBH manufactured by Daiwabo Rayon Co., Ltd.

The fineness of the chemical fiber is preferably 0.3 to 7.0 dtex, more preferably 0.5 to 5.0 dtex, and even more preferably 0.8 to 2.0 dtex. When the fineness of the chemical fiber is equal to or greater than the lower limit of the above-mentioned range, the sheet strength is likely to be improved. When the fineness of the chemical fiber is equal to or less than the upper limit of the above-mentioned range, the dispersibility of the chemical fiber in the slurry during the production of the nonwoven fabric is likely to be improved. Furthermore, re-agglomeration after disintegration in water is likely to be suppressed. Therefore, the water-decomposability is likely to be improved.
The fineness of the chemical fiber is measured in accordance with JIS L-1015.

The average fiber length of the chemical fibers is preferably 3 to 20 mm, more preferably 3 to 15 mm, and even more preferably 5 to 10 mm. When the average fiber length of the chemical fibers is equal to or greater than the lower limit of the above-mentioned range, the sheet strength is likely to be improved. When the average fiber length of the chemical fibers is equal to or less than the upper limit of the above-mentioned range, the chemical fibers are less likely to become entangled in the manufacturing equipment, making it easier to manufacture a nonwoven fabric. In addition, the smooth feel and suppleness inherent in the dissolving pulp are less likely to be lost.
The average fiber length of the chemical fibers is measured in accordance with JIS L-1015.

(Other fibers)
The nonwoven fabric of the present invention may further contain fibers other than dissolving pulp and chemical fibers, as long as the pleasant feel that is unique to dissolving pulp is not significantly impaired.
Examples of other fibers include cellulose fibers such as wood pulp and non-wood pulp, and natural fibers such as cotton, wool, silk, hemp, etc. The wood pulp may be beaten or unbeaten.

Examples of wood pulp other than dissolving pulp include chemical pulp, semi-chemical pulp, and mechanical pulp.
Examples of chemical pulps include hardwood pulp (hardwood kraft pulp (LBKP)), softwood pulp (softwood kraft pulp (NBKP)), sulfite pulp (SP), soda pulp (AP), unbleached kraft pulp (UKP), and oxygen bleached kraft pulp (OKP).
Examples of semi-chemical pulps include semi-chemical pulp (SCP) and chemi-groundwood pulp (CGP).
Examples of mechanical pulp include groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP).
Examples of non-wood pulps other than dissolving pulp include cotton pulps such as cotton linter and cotton lint, non-wood pulps such as hemp, straw and bagasse, cellulose isolated from sea squirts, seaweed and the like, chitin, chitosan, etc. As deinked pulp, deinked pulp made from recycled paper may be used.

(Other ingredients)
The nonwoven fabric of the present invention may further contain other components in addition to the dissolving pulp, chemical fibers and other fibers, as long as the good feel that is unique to the dissolving pulp is not significantly impaired.
Examples of other components include dry strength agents, wet strength agents, and softeners.
Examples of dry paper strength agents include cationized starch, polyacrylamide (PAM), and carboxymethyl cellulose (CMC).
Wet strength agents include polyamide epichlorohydrin, urea, melamine, and thermally crosslinkable polyacrylamide.
Examples of the softening agent include anionic surfactants, nonionic surfactants, and cationic surfactants.
The other components may be used alone or in combination of two or more.

(Composition of nonwoven fabric)
The content of dissolving pulp in the nonwoven fabric is preferably 40 to 95% by mass, more preferably 50 to 90% by mass, and even more preferably 60 to 80% by mass, relative to the total mass of the nonwoven fabric (100% by mass). When the content of dissolving pulp is equal to or greater than the lower limit of the above-mentioned range, it is easy to obtain the water-decomposability, good feel to the touch, and flexibility that are characteristic of dissolving pulp. When the content of dissolving pulp is equal to or less than the upper limit of the above-mentioned range, it is easy to obtain the sheet strength during production and the strength of the nonwoven fabric.

The chemical fiber content in the nonwoven fabric is preferably 5 to 60% by mass, more preferably 10 to 50% by mass, and even more preferably 20 to 40% by mass, based on the total mass of the nonwoven fabric (100% by mass). When the chemical fiber content is at or above the lower limit of the above numerical range, the sheet strength during production and the strength of the nonwoven fabric are likely to be achieved. When the chemical fiber content is at or below the upper limit of the above numerical range, the water-decomposability and the pleasant feel and flexibility characteristic of dissolving pulp are likely to be achieved.

The content of other fibers is preferably 0 to 30% by mass, more preferably 0 to 25% by mass, and even more preferably 0 to 20% by mass, relative to the total mass of the nonwoven fabric (100% by mass). If the content of other fibers is at or above the lower limit of the above numerical range, the properties and feel of the other fibers are more likely to be expressed in the nonwoven fabric. If the content of other fibers is at or below the upper limit of the above numerical range, the good feel and suppleness unique to dissolving pulp are more likely to be obtained.

The content of other components is preferably 0 to 15% by mass, more preferably 0 to 12.5% by mass, and even more preferably 0 to 10% by mass, relative to the total mass of the nonwoven fabric (100% by mass). If the content of other components is equal to or greater than the lower limit of the above numerical range, the properties of the other components are more likely to be expressed in the nonwoven fabric. If the content of other components is equal to or less than the upper limit of the above numerical range, the good feel and suppleness unique to dissolving pulp are less likely to be lost.

(Properties of nonwoven fabric)
The basis weight of the nonwoven fabric is not particularly limited. It can be changed appropriately depending on the application of the nonwoven fabric. For example, the basis weight of the nonwoven fabric is preferably 15 to 90 g/ ^m² , more preferably 20 to 85 g/ ^m² , and even more preferably 25 to 80 g/ ^m² . When the basis weight of the nonwoven fabric is equal to or greater than the lower limit of the above-mentioned numerical range, the strength of the nonwoven fabric is likely to be improved. When the basis weight of the nonwoven fabric is equal to or less than the upper limit of the above-mentioned numerical range, the softness and flexibility of the nonwoven fabric are less likely to be impaired.
The basis weight of the nonwoven fabric is measured in accordance with JIS P 8124.

The thickness of the nonwoven fabric is not particularly limited and can be changed as appropriate depending on the application of the nonwoven fabric.

The density of the nonwoven fabric is not particularly limited. It can be changed appropriately depending on the application of the nonwoven fabric. The density of the nonwoven fabric is preferably 0.1 to 0.35 g/ ^cm3 , more preferably 0.11 to 0.32 g/ ^cm3 , and even more preferably 0.12 to 0.30 g/ ^cm3 . When the density of the nonwoven fabric is equal to or greater than the lower limit of the above-mentioned numerical range, the strength of the nonwoven fabric is likely to be improved. When the density of the nonwoven fabric is equal to or less than the upper limit of the above-mentioned numerical range, a pleasant feel and flexibility are likely to be obtained.
The density of the nonwoven fabric is measured in accordance with JIS P8118.

The tensile strength of the nonwoven fabric is not particularly limited. It can be changed as appropriate depending on the application of the nonwoven fabric. The tensile strength of the nonwoven fabric is preferably 0.05 kN/m or more, more preferably 0.08 kN/m or more, and even more preferably 0.1 kN/m or more. If the tensile strength of the nonwoven fabric is above the above lower limit, the nonwoven fabric can be easily used in applications requiring tensile strength, such as wet tissues, cleaning sheets, and face masks. The upper limit of the tensile strength of the nonwoven fabric is not particularly limited. For example, the upper limit is about 1.0 kN/m.

The tensile strength of a nonwoven fabric is measured using a tensile tester in both the MD direction and the CD direction (perpendicular to the MD direction), and the geometric mean value of the tensile strength in the MD direction and the tensile strength in the CD direction is calculated. The tensile strength in both the MD direction and the CD direction is measured under the following conditions: sample width 15 mm, span length 100 mm, and tensile speed 100 mm/min. An AUTOGRAPH tester manufactured by Shimadzu Corporation can be used as the tensile tester.

The tensile elongation of the nonwoven fabric is not particularly limited. It can be changed as appropriate depending on the application of the nonwoven fabric. The tensile elongation of the nonwoven fabric is preferably 5% or more, more preferably 7% or more, and even more preferably 10% or more. If the tensile elongation of the nonwoven fabric is above the above-mentioned lower limit, the nonwoven fabric can be easily used in applications requiring tensile elongation, such as face masks. The upper limit of the tensile elongation of the nonwoven fabric is not particularly limited. For example, the upper limit is about 20%.

The tensile elongation of a nonwoven fabric is measured using a tensile tester in both the MD direction and the CD direction perpendicular to the MD direction, and the geometric mean value of the tensile elongation in the MD direction and the tensile elongation in the CD direction is calculated. The tensile elongation in both the MD direction and the CD direction is measured under the following conditions: sample width 15 mm, span length 100 mm, and tensile speed 100 mm/min. An AUTOGRAPH tester manufactured by Shimadzu Corporation can be used as the tensile tester.

The fresh wet strength of the nonwoven fabric is not particularly limited. It can be changed as appropriate depending on the application of the nonwoven fabric. The fresh wet strength of the nonwoven fabric is preferably 0.2 kgf/50 mm or more, more preferably 0.25 kgf/50 mm or more, and even more preferably 0.3 kgf/50 mm or more. If the fresh wet strength of the nonwoven fabric is above the above lower limit, the nonwoven fabric can be easily used in applications requiring fresh wet strength, such as wet tissues, cleaning sheets, and face masks. The upper limit of the fresh wet strength of the nonwoven fabric is not particularly limited. For example, the upper limit is about 1.5 kgf/50 mm.

The wet strength of a nonwoven fabric is determined as follows. Specifically, a nonwoven fabric is impregnated with pure water so that the mass ratio of bone-dry nonwoven fabric to water is 1:2 (bone-dry nonwoven fabric:water), resulting in a wet nonwoven fabric. The wet strength of a nonwoven fabric is calculated as the geometric mean value of the tensile strength in the MD and CD directions of the wet nonwoven fabric. For the wet nonwoven fabric, a sample width of 50 mm is folded in half to 25 mm, and the tensile strengths in the MD and CD directions are measured under conditions of a span length of 100 mm and a pulling speed of 100 mm/min. An AUTOGRAPH tester manufactured by Shimadzu Corporation can be used as the tensile tester.

The fresh wet elongation of the nonwoven fabric is not particularly limited. It can be changed as appropriate depending on the application of the nonwoven fabric. The fresh wet elongation of the nonwoven fabric is preferably 10% or more, more preferably 15% or more, and even more preferably 20% or more. If the fresh wet elongation of the nonwoven fabric is above the above lower limit, the nonwoven fabric can be easily used in applications requiring fresh wet elongation, such as face masks. The upper limit of the fresh wet elongation of the nonwoven fabric is not particularly limited. For example, the upper limit is about 40%.

The fresh wet elongation of a nonwoven fabric is determined as follows. Specifically, a nonwoven fabric is impregnated with pure water so that the mass ratio of bone-dry nonwoven fabric to water is 1:2 (bone-dry nonwoven fabric:water), resulting in a wet nonwoven fabric. The fresh wet elongation of a nonwoven fabric is calculated as the geometric mean value of the tensile elongation in the MD and CD directions of the wet nonwoven fabric. For the wet nonwoven fabric, a sample width of 50 mm is folded in half to 25 mm, and the tensile elongation in each of the MD and CD directions is measured under conditions of a span length of 100 mm and a pulling speed of 100 mm/min. An AUTOGRAPH testing machine manufactured by Shimadzu Corporation can be used as the tensile tester.

In one embodiment of the present invention, TS7 may be used as an index of the flexibility of a nonwoven fabric.
TS7 can be obtained using a tissue softness analyzer (TSA) manufactured by emtec. In a nonwoven fabric according to one embodiment of the present invention, relatively stiff fibers may cause strong vibrations when subjected to the TSA blade during measurement, while relatively soft fibers may cause weak vibrations when subjected to the blade. These vibrations are measured at frequencies in the acoustic spectrum, and after processing by the software provided with the TSA, TS7 is obtained.
Generally, it is said that the larger the TS7 value of a nonwoven fabric, the harder the nonwoven fabric is. In one embodiment of the present invention, it is believed that the smaller the TS7 value, the softer the feel of the nonwoven fabric.

It is considered that TS7 is preferably 20 or less, more preferably 18 or less, and even more preferably 15 or less. The lower limit of TS7 is not particularly limited, but is considered to be about 5. When TS7 is the above upper limit or less, it is considered that a soft feel is easily obtained.
The TS7 of a nonwoven fabric is the average value of the TS7 of the front surface and the TS7 of the back surface. The front surface of the nonwoven fabric is the surface that was directly sprayed with the water flow of the high-pressure water jet treatment in the production line. Therefore, the front surface of the nonwoven fabric has streaky jet marks formed by the high-pressure water jet treatment. The back surface of the nonwoven fabric is the surface opposite to the front surface.

<Method of manufacturing nonwoven fabric>
The method for producing a nonwoven fabric of the present invention comprises subjecting a wet-laid web obtained from a slurry containing dissolving pulp and chemical fibers to a high-pressure water jet treatment.
The method for preparing the slurry containing dissolving pulp and chemical fibers is not particularly limited. The details and preferred embodiments of the dissolving pulp and chemical fibers are the same as those described above in the section <Nonwoven fabric>.
Furthermore, other fibers and other components may be further blended into the slurry as needed, provided that the good feel that is unique to dissolving pulp is not significantly impaired. Details of the other fibers and other components are the same as those explained above in the section on <Nonwoven fabric>.

The proportion of dissolving pulp in the slurry is preferably 40 to 95% by mass, more preferably 50 to 90% by mass, and even more preferably 60 to 80% by mass, relative to 100% by mass of the slurry. When the proportion of dissolving pulp in the slurry is equal to or greater than the lower limit of the above numerical range, the characteristic good feel and suppleness of dissolving pulp are more likely to be achieved. When the proportion of dissolving pulp in the slurry is equal to or less than the upper limit of the above numerical range, the sheet strength during production and the strength of the nonwoven fabric are more likely to be achieved.

The proportion of chemical fibers in the slurry is preferably 5 to 60% by mass, more preferably 10 to 50% by mass, and even more preferably 20 to 40% by mass, relative to 100% by mass of the slurry. When the proportion of chemical fibers in the slurry is equal to or greater than the lower limit of the above numerical range, the sheet strength during production and the strength of the nonwoven fabric are more likely to be achieved. When the proportion of chemical fibers in the slurry is equal to or less than the upper limit of the above numerical range, the good feel and flexibility characteristic of dissolving pulp are more likely to be achieved.

The proportion of other fibers in the slurry is preferably 0 to 30% by mass, more preferably 0 to 25% by mass, and even more preferably 0 to 20% by mass, relative to 100% by mass of the slurry. When the proportion of other fibers in the slurry is equal to or greater than the lower limit of the above numerical range, the properties and feel of the other fibers are easily imparted to the nonwoven fabric. When the proportion of other fibers in the slurry is equal to or less than the upper limit of the above numerical range, the good feel and suppleness characteristic of dissolving pulp are easily obtained.

The proportion of other components in the slurry is preferably 0 to 15% by mass, more preferably 0 to 12.5% by mass, and even more preferably 0 to 10% by mass, relative to the total mass of the slurry (100% by mass). When the proportion of other components is equal to or greater than the lower limit of the above numerical range, the properties of the other components are more easily imparted to the nonwoven fabric. When the proportion of other components is equal to or less than the upper limit of the above numerical range, the characteristic good feel and flexibility of dissolving pulp are more easily obtained.

In one aspect of the present invention, for example, a sheet-like wet-laid web can be obtained by wet-laid papermaking using a slurry containing dissolving pulp and chemical fibers. The papermaking process can be carried out using a variety of papermaking machines, including a cylinder papermaking machine, a short-wire papermaking machine, an inclined wire papermaking machine, and a Fourdrinier papermaking machine. A thickener such as polyethylene oxide may be added to the slurry during papermaking, and the fiber orientation of the wet-laid web may be controlled by adjusting the ratio of the papermaking liquid speed to the wire speed in the wire part during papermaking.

Next, the wetlaid web is subjected to a high-pressure water jet treatment. In the nonwoven fabric of the present invention, the structure in which the dissolving pulp and chemical fibers are integrated is formed by subjecting the wetlaid web to a high-pressure water jet treatment. By subjecting the wetlaid web to a high-pressure water jet treatment, the dissolving pulp and chemical fibers are twisted, bent, and turned, causing the fibers to intertwine and integrate.
High-pressure water jet processing is also called water punch processing or water jet processing. In both processes, high-pressure water is sprayed onto a layer of accumulated fibers to entangle the fibers.

The specific method of high-pressure water jet treatment is not particularly limited as long as it can entangle the dissolving pulp and chemical fibers with the water flow. For example, a wetlaid web is placed on a porous support, and high-pressure water is sprayed from the upper surface of the wetlaid web through a nozzle having an array of many fine pores with a pore diameter of about 0.08 to 0.30 mm at a water pressure of 15 to 150 kg/ ^cm2 , thereby entangling the dissolving pulp and chemical fibers in the wetlaid web with each other.
The high-pressure water jet treatment can be carried out by various methods. The number of nozzle holes, nozzle hole diameter, water pressure of each nozzle, and nozzle passing speed are not particularly limited as long as they can entangle the fibers with each other.

High-pressure water jet treatment may be carried out online immediately after forming a web by wet papermaking, or the wet-made web may be dried and then subjected to high-pressure water jet treatment online or offline. Furthermore, high-pressure water jet treatment may be carried out once or multiple times. In order to ensure sufficient entanglement of the dissolving pulp and chemical fibers, it is preferable to carry out high-pressure water jet treatment multiple times.

The high-pressure water jet energy used in the high-pressure water jet treatment is preferably 0.01 to 0.50 kWh/kg/m, more preferably 0.02 to 0.40 kWh/kg/m, even more preferably 0.03 to 0.30 kWh/kg/m, and particularly preferably 0.05 to 0.20 kWh/kg/m. When the high-pressure water jet energy is equal to or greater than the lower limit of the above-mentioned range, the sheet strength during production and the strength of the nonwoven fabric are likely to be achieved. When the high-pressure water jet energy is equal to or less than the upper limit of the above-mentioned range, the water disintegrability of the nonwoven fabric is likely to be improved.

The high-pressure water jet energy is calculated by the following formula (1): When the high-pressure water jet treatment is carried out multiple times, the high-pressure water jet energy is the total value of the high-pressure water jet treatments.
E=P×(F/100)×0.163...Formula (1)
In equation (1), E is the high-pressure water jet energy (kWh/kg/m), P is the water pressure at the nozzle (kgf/cm ² ), and F is the flow rate of water ejected from one hole of the nozzle (cm ³ /min).

F in formula (1) is calculated by the following formula (2).
F=(A/100)×V×100...Formula (2)
In equation (2), F is the flow rate (cm ³ /min) of water ejected from one hole of the nozzle portion, A is the area (mm ² ) of one nozzle hole, and V is the flow velocity (m/min) of water ejected from the nozzle.

V in the formula (2) is calculated by the following formula (3).
V=(2×g×(P-Ap)×10000/(ρ×1000)) ^1/2 ×60...Formula (3)
In equation (3), V is the flow velocity (m/min) of water ejected from the nozzle, g is the acceleration of gravity (=9.8 m/s ² ), P is the water pressure at the nozzle (kgf/cm ² ), A is the area of one nozzle hole (mm ² ), p is the atmospheric pressure (kgf/cm ² ), and ρ is the density of water (g/cm ³ ).

In the method for producing the nonwoven fabric of the present invention, in addition to the high-pressure water jet treatment, other entanglement treatments may be used in combination, as long as a new feel on the skin can be obtained.
Other entanglement processes include, for example, needle punching, thermal bonding, and chemical bonding. In the needle punching method, a layer of fibers is repeatedly pierced with a needle that moves up and down at high speed, and the fibers can be entangled by the protrusions engraved on the needle. In the thermal bonding method, the fibers can be bonded to each other by passing a layer of fibers mixed with low-melting-point heat-fusible fibers between heated rolls to thermocompress the layer, or by applying hot air to the layer. In the chemical bonding method, an emulsion-based adhesive resin is applied to the layer of fibers by impregnation, spraying, or the like, and then the layer is heated and dried to bond the intersections of the fibers.
The other entanglement treatment may be carried out on either the wet-laid web before the high-pressure water jet treatment or the wet-laid web after the high-pressure water jet treatment.

The wet-laid web that has been subjected to the high-pressure water jet treatment is then dried to obtain a nonwoven fabric. Before drying, the wet-laid web that has been subjected to the high-pressure water jet treatment may be pressed or dehydrated as necessary. It may also be adjusted to the desired thickness by pressing.

<Mechanism of action>
The nonwoven fabric according to the present invention as described above is made by entangling dissolving pulp and chemical fibers. Nonwoven fabrics made from dissolving pulp are novel. Therefore, the nonwoven fabric according to the present invention provides a novel and uniquely pleasant feel to the touch.
In the present invention, a wet-laid web obtained from a slurry containing dissolving pulp and chemical fibers is subjected to high-pressure water jet treatment. This allows the characteristic pleasant feel of dissolving pulp to be preserved, while also developing sufficient sheet strength to produce a nonwoven fabric. The resulting nonwoven fabric has a novel and unique pleasant feel, particularly flexibility.

<Application>
The uses of the nonwoven fabric are not particularly limited, and examples thereof include daily necessities such as tea bags and draining sheets, industrial uses such as various filters, agricultural materials such as vinyl greenhouse sheets, clothing-related products such as interlinings, medical products, and hygiene products.
The nonwoven fabric of the present invention is suitable for use as cosmetics such as wet sheets and face masks, wet products such as hand towels, wet tissues, baby wipes and wipers, and hygiene products. The nonwoven fabric may be impregnated with a humectant such as water or propylene glycol, an antibacterial agent such as alcohol or a parabenzoic acid ester, an antifungal agent, a fragrance, a drug having a desired medicinal effect, or the like.
The nonwoven fabric can also be used as a surface material for sanitary materials. In this case, the nonwoven fabric may be subjected to treatment to enhance its hydrophilicity or water repellency, if desired.

The present invention will be specifically explained below using examples, but the present invention is not limited to the following description.

<Raw materials>
(dissolving pulp)
In each example, dissolving pulp (hereinafter referred to as "DP") derived from hardwood obtained by the kraft cooking method was used. The α-cellulose content of the DP used was 96.4% by mass. The viscosity of the DP according to J TAPPI No. 44 was 8.9 mPa s.

(chemical fiber)
Rayon: Rayon fibers with a fineness of 1.1 dtex, an average fiber length of 7 mm, and a fiber diameter of 10 μm were used.
Vinylon: Vinylon fiber with a fineness of 1.1 dtex, an average fiber length of 7 mm, and a fiber diameter of 11 μm was used.

(Other fibers)
NBKP: Softwood kraft pulp with a freeness of 705 ml measured in accordance with JIS P 8121-2:2012 was used. The average fiber length of the NKP was 2.3 mm and the fiber diameter was 24 μm.
- Hemp: Hemp fibers with an average fiber length of 3.79 mm and a fiber width of 19.6 μm were used.

Example 1
DP and rayon were blended in a mass ratio of DP/rayon = 90/10 to obtain a slurry. A wetlaid web was obtained from the slurry by wetlaid papermaking using a handsheet machine. The wetlaid web was then subjected to high-pressure water jet treatment using a water jet device (high-pressure water jet treatment device).
The high-pressure water jet treatment was performed as shown in Figure 1. That is, a 25 cm x 25 cm wet web 1 was placed on a 30 cm x 30 cm plastic wire 2 and line-treated in the machine direction (MD) indicated by the arrow in the figure. A high-pressure water jet was sprayed onto the wet web 1 moving along with a line belt 5 using a first sprayer 3 equipped with nozzles having a hole diameter of 0.1 mm, a pitch of 1 mm, and an array of 1 nozzle at a water pressure ^of 20.0 kgf/cm². Subsequently, a high-pressure water jet was sprayed using a second sprayer 4 equipped with nozzles having a hole diameter of 0.1 mm, a pitch of 1 mm, and an array of ¹ nozzle at a water pressure of 19.0 kgf/cm². The total high-pressure water jet energy from the first sprayer 3 and the second sprayer was 0.100 kWh/kg/m² (hereinafter, the high-pressure water jet treatment conditions in Example 1 will be referred to as "Condition A").
Immediately after the high-pressure water jet was sprayed from the second sprayer 4, the wetlaid web 1 was peeled off from the plastic wire support 2 and collected. Thereafter, the wetlaid web was pressed against filter paper for dewatering, and then dried in a cylinder dryer at 120°C for 2 minutes to obtain the nonwoven fabric of Example 1.

Example 2
The nonwoven fabric of Example 2 was obtained in the same manner as in Example 1, except that the first injector ³ sprayed a high-pressure water jet stream at a water pressure of 16.0 kgf/ ^cm2 , and the second injector 4 sprayed a high-pressure water jet stream at a water pressure of 15.0 kgf/cm2. The total high-pressure water jet energy in Example 2 was 0.070 kWh/kg/m (hereinafter, the high-pressure water jet treatment conditions in Example 2 will be referred to as "Condition B").

<Examples 3 to 10, Comparative Examples 1 to 7>
Nonwoven fabrics of each example were obtained in the same manner as in Example 1, except that the slurry composition and high-pressure water jet treatment conditions were changed as shown in Table 1. However, in Comparative Example 1, the dissolving pulp was not entangled sufficiently even after the high-pressure water jet treatment, and the fibers were stuck in the plastic wire. Therefore, the wet-laid web after the high-pressure water jet treatment could not be recovered from the plastic wire, and no nonwoven fabric was obtained. Therefore, for the slurry with 100% DP, high-pressure water jet treatment under condition B, in which the high-pressure water jet energy was weaker than that under condition A, was not performed.

<Measurement and evaluation>
(Basic weight)
The basis weight (g/m ² ) of the nonwoven fabric was measured in accordance with JIS P 8124.

(Thickness)
The thickness (μm) of the nonwoven fabric was measured in accordance with JIS P8118.

(density)
The density (g/cm ³ ) of the nonwoven fabric was measured in accordance with JIS P8118.

(Tensile strength)
The tensile strength (kN/m) of the nonwoven fabric was measured in both the MD and CD directions using an AUTOGRAPH testing machine manufactured by Shimadzu Corporation under conditions of a sample width of 15 mm, a span length of 100 mm, and a pulling speed of 100 mm/min, and the geometric mean value of these values was calculated.

(Tensile elongation)
The tensile elongation (%) of the nonwoven fabric was measured in each of the MD and CD directions using an AUTOGRAPH testing machine manufactured by Shimadzu Corporation under conditions of a sample width of 15 mm, a span length of 100 mm, and a pulling speed of 100 mm/min, and the geometric mean value of these values was calculated.

(wet strength)
The fresh wet strength (kgf/50 mm) of the nonwoven fabric was measured as follows for a wet nonwoven fabric obtained by impregnating a nonwoven fabric with pure water so that the mass ratio of bone-dry nonwoven fabric to water was 1:2 (bone-dry nonwoven fabric:water). The tensile strength of the wet nonwoven fabric was measured in both the MD and CD directions using an AUTOGRAPH testing machine manufactured by Shimadzu Corporation, with a sample width of 50 mm folded in half to 25 mm, a span length of 100 mm, and a pulling speed of 100 mm/min, and the geometric mean value of these values was calculated.

(wet elongation)
The fresh wet elongation (%) of a nonwoven fabric was measured for a wet nonwoven fabric obtained by impregnating a nonwoven fabric with pure water so that the mass ratio of bone-dry nonwoven fabric to water was 1:2 (bone-dry nonwoven fabric:water) as follows: The wet nonwoven fabric was measured for tensile elongation in both the MD and CD directions using an AUTOGRAPH testing machine manufactured by Shimadzu Corporation, with a sample width of 50 mm folded in half to 25 mm, a span length of 100 mm, and a pulling speed of 100 mm/min, and the geometric mean value of these values was calculated.

(Flexibility)
The suppleness of the nonwoven fabric was evaluated by a sensory test based on the sensation of the fingertips when gripped by the fingers of engineers involved in the nonwoven fabric manufacturing. Five engineers each evaluated the suppleness of the nonwoven fabric using the following eight-point scale. The average score of the five engineers' results was calculated.
1 point: Very rough to the touch and very poor in flexibility.
2 points: Rough to the touch and not very flexible.
3 points: Rough to the touch and less flexible, but better than lower points.
4 points: Neither excellent nor inferior in terms of smoothness or suppleness.
5 points: Neither excellent nor inferior in smoothness or suppleness, but better than the lower points.
6 points: Smooth and supple to the touch, but inferior to the higher points.
7 points: Smooth to the touch and highly flexible.
8 points: Very smooth to the touch and extremely flexible.

(TS7)
The TS7 of the nonwoven fabric was measured using a tissue softness measuring device (manufactured by emtec, algorithm: TPII). TS7 is an index of the softness of the nonwoven fabric.

<Results>
The results for each example are shown in Table 1.

In Examples 1 to 10, sheet-shaped nonwoven fabrics were obtained by subjecting a wet-laid web obtained from a slurry containing dissolving pulp and chemical fibers to high-pressure water jet processing. The nonwoven fabrics of Examples 1 to 10 had a unique suppleness and a new, unique, pleasant feel to the touch derived from the dissolving pulp. In contrast, in Comparative Examples 2 to 7, sheet-shaped nonwoven fabrics were obtained, but the pleasant feel and suppleness characteristic of dissolving pulp were not obtained.
In Examples 1 to 10, compared with Comparative Examples 2 to 7, the wet web after the high-pressure water jet treatment was easier to recover from the plastic wire, and the nonwoven fabric was easier to obtain.

Regarding flexibility, a comparison of the results of Examples 7 and 9 with Comparative Example 6 confirms that increasing the blending ratio of DP in the slurry composition tends to result in good flexibility. The same tendency can also be confirmed by comparing the results of Examples 8 and 10 with Comparative Example 7.
Good flexibility was obtained in Examples 1 to 6, which used rayon, especially in Examples 1 and 2. In contrast, as shown in the results of Comparative Examples 2 to 5, when hemp was used, flexibility was difficult to obtain and the surface was noticeably rough.
Among Examples 1 to 10, the nonwoven fabrics obtained from the slurries of Examples 3 and 4 in which DP/rayon were blended at a mass ratio of 70/30 had the best balance of flexibility and strength.

The present invention provides a nonwoven fabric with a novel and uniquely pleasant feel, and a method for producing the same.

1 Wet web 2 Support (plastic wire)
3 First injector 4 Second injector 5 Line belt

Claims (5)

A nonwoven fabric comprising dissolving pulp and chemical fibers, wherein the dissolving pulp and the chemical fibers are entangled ,
The nonwoven fabric has a dissolving pulp content of 70 to 95% by mass, relative to 100% by mass of the total mass of the nonwoven fabric . The nonwoven fabric according to claim 1, wherein the average fiber length of the chemical fibers is 3 to 20 mm. The nonwoven fabric according to claim 1 or 2, wherein the chemical fiber is rayon. A method for producing a nonwoven fabric, comprising:
The method comprises subjecting a wet web obtained from a slurry containing dissolving pulp and chemical fibers to a high-pressure water jet treatment,
A method for producing a nonwoven fabric , wherein the content of the dissolving pulp is 70 to 95% by mass, relative to 100% by mass of the total mass of the slurry . The manufacturing method described in claim 4, wherein the chemical fiber is rayon.