JPWO1994024347A1 - Fibers with a network structure, nonwoven fabrics made from these fibers, and their manufacturing methods - Google Patents

Abstract

(57) [Abstract] This publication contains application data prior to electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] Reticulated Fibers, Nonwoven Fabrics Made from These Fibers, and Manufacturing Methods for the Same Field of the Invention The present invention relates to fibers composed of a mixture of mutually incompatible polymers and having an extremely fine reticulated structure, nonwoven fabrics made from these fibers with a dense structure, and methods for manufacturing the same.

BACKGROUND OF THE INVENTION One known method for obtaining ultrafine fibers and nonwoven fabrics using these fibers is to spin multicomponent seabird-type filaments, remove some of the polymer components with a solvent, and then bond the resulting fibers together to produce a nonwoven fabric. Another known method is the meltblown process, in which molten polymer is extruded through a spinning nozzle and attenuated by drawing with a heated fluid. However, removing some of the polymer components from multicomponent filaments with a solvent requires various steps to dissolve and remove the polymer. While the meltblown process can certainly produce extremely fine fibers, because attenuation is performed at the molten polymer stage, the meltblown process suffers from the drawback of limited stretch orientation and crystallization, resulting in extremely weak fibers.

Meanwhile, the so-called flash spinning method has been proposed as a method for obtaining ultrafine fibers from a polymer solution. As described in U.S. Patent No. 3,081,519, flash spinning involves extruding a polymer solution in a low-boiling solvent through a spinning nozzle, causing the solvent to vaporize instantaneously.

However, because the fibers obtained using this method are composed of a single polymer component, they have inherent disadvantages that limit the range of possible uses for the product. This issue is also true of the techniques disclosed in Japanese Patent Application Publication No. 41-6215 and Japanese Patent Application Publication No. 1-97256. Specifically, olefin polymers are lightweight, have low modulus, are comfortable to use or wear, and have a unique slimy feel. Ester polymers are inherently suitable for producing high-strength fibers and have high modulus, but high-strength fibers have not been obtained by flash spinning, and so they have not been put to practical use.

DISCLOSURE OF THE INVENTION The present invention aims to solve the above-mentioned problems and, in particular, to provide ultrafine network-structured fibers that offset the drawbacks of olefin-based polymers and ester-based polymers, thereby utilizing their respective advantages, as well as nonwoven fabrics made from these fibers and methods for their production.

The present inventors have conducted extensive research to solve the above problems and have arrived at the present invention.

The fiber having a network structure according to the present invention is made of a mixture at least consisting of an olefin polymer and an ester polymer which are incompatible with each other, and has a network structure.

The method for producing a network-structured fiber according to the present invention involves dissolving a blend of an olefin polymer and an ester polymer, which are incompatible with each other, in a solvent at high temperature and pressure to form a single-phase bath, and then spinning the resulting mixture through a nozzle while the polymer and solvent are in a phase-separated state.

The second fiber of the present invention is composed of an olefin polymer and an ester polymer. It possesses a network structure composed of unprecedentedly fine, ultrafine fibril fibers, exhibiting high strength and modulus. Therefore, it can be used as raw yarn for woven fabrics, knitted fabrics, dry-laid nonwovens, wet-laid nonwovens, and batting. It is also suitable for general-purpose applications such as clothing, thermal insulation, artificial leather, absorbent materials for hygiene products, protective clothing, curtains, sheets, wipers, filters, house wrap, and synthetic paper. Furthermore, because it contains a polyester polymer, it can be appropriately dyed in a post-processing step rather than using pigments.

The nonwoven fabric having a dense structure according to the present invention comprises a network of fibers, which are blended with a mixture of an incompatible olefin polymer and an incompatible ester polymer in a weight ratio of 5:95 to 9:15, and the fibers in the network are bonded together. The fibers in the network are bonded together either entirely or partially.

The method for producing a nonwoven fabric having a dense structure according to the present invention comprises preparing a mixture of incompatible olefin polymers and ester polymers in a weight ratio ranging from 5:95 to 9:15 to form a network of fibers, forming the fibers into a web, and then heat-pressing the web using a group of rolls to bond the interwoven fibers throughout the entirety of the mixed network of fibers.

Another method for producing a nonwoven fabric according to the present invention involves preparing a network of fibers containing a mixture of incompatible olefin polymers and ester polymers in a weight ratio ranging from 5/95 to 95/15, forming the fibers into a web, and then partially thermocompressing the web using an embossing machine to partially bond the inter-fibers of the mixed network.

Thus, the present invention provides a nonwoven fabric with a dense structure composed of highly fibrillated, ultrafine fibers. Nonwoven fabrics in which the fibers in the network structure are bonded together or throughout the entire network are suitable for general-purpose applications such as envelopes, packaging materials, floppy sleeves, waterproofing materials, labels, thermal insulation, synthetic paper, protective clothing for sanitary products, curtains, sheets, wipers, filters, and house wrap. Nonwoven fabrics in which the fibers in the network structure are partially bonded together are suitable for general-purpose applications such as clothing, thermal insulation, protective clothing for medical and sanitary products, curtains, sheets, wipers, filters, house wrap, tents, and artificial leather.

Next, the network structure fiber according to the present invention will be described in detail.

As used herein, a fiber having a network structure refers to a group of fibers in which fibril fibers of 0.01 to 10 μm are arranged in a three-dimensional network state and are endlessly arranged in the longitudinal direction of the yarn.

The components constituting the fiber of the present invention must be polymer components that are incompatible with each other. This incompatibility allows the mixed polymer components to exist independently, allowing the fiber to develop the essential fiber properties of each individual polymer. It is generally known that a mixed fiber of incompatible polymers is easily separated into its individual components by physical forces. Because the fibers of the present invention are incompatible with each other, they are primarily composed of extremely fine fibril fibers of single polymers. A specific combination of polymer components for this purpose is a combination of an olefin polymer and an ester polymer.

Of the polymer components constituting the fiber of the present invention, examples of the olefin polymer include polyethylene, polypropylene, copolymers mainly composed of ethylene, copolymers mainly composed of propylene, and the like.

Of these polymers, the viscosity of the ethylene polymer preferably has a melt index of 0.3 to 30 g/10 min, as measured by the method of ASTM-D-1238E. If the melt index is less than 0.3 g/10 min, the viscosity of the mixed solution becomes too high, making it difficult to obtain ultrafine fibril fibers. If the melt index is greater than 30 g/10 min, the strength of the fiber itself decreases and the fiber becomes slimy and sticky, tending to result in fibers that are difficult to handle.

The viscosity of the propylene polymer is preferably such that the melt flow rate, as measured by the method of ASTM-D-1238L, is 1 to 40 g/10 min. If the melt flow rate is less than 1 g/10 min, the viscosity of the mixed solution becomes too high, making it difficult to obtain ultrafine fibril fibers. If the melt flow rate exceeds 40 g/10 min, the strength of the fiber itself decreases and the fiber becomes slimy and sticky, resulting in fibers that are difficult to handle.

Examples of the ester polymer, which is the other polymer component constituting the fiber of the present invention, include polyethylene terephthalate and polybutylene terephthalate.

Furthermore, copolymers containing up to 40 mol% of isophthalic acid, phthalic acid, guar phthalic acid, adipic acid, sulfoisophthalic acid, diethylene glycol, propylene glycol, 1,4-butanediol, 2,2-bis(4-hydroxyquinoethoxophenyl)propane, bisphenol A, and polyalkynyl glycols are also suitable. Polymer viscosities range from fiber grades with a relative viscosity (ηrel) of 1.3-1.6 measured at 20°C and a concentration of 0.5% in a 1/1 (by weight) mixture of tetrachloroethane and phenol, to high-viscosity resins (relative viscosity 1.7) produced by solid-state polymerization. Higher polymer viscosity favorably increases fiber strength.

The components constituting the fibers of the present invention must be a mixed polymer component consisting of at least components that are incompatible with each other and have melting points of at least 100°C.

The reason that they must not be miscible with each other is as mentioned above. The reason that both polymer components must have melting points of 100°C or higher is due to practical regulations. Melting points below 100°C melt even in boiling water, significantly limiting their practical applications. Therefore, a melting point of 120°C or higher is even more preferable. Next, "composed of at least" means that the mixed polymer components account for 50% by weight or more of the fiber composition. A ratio of less than 50% by weight is undesirable because the characteristics of the olefin polymer and the ester polymer are lost.

In the fiber of the present invention, the blend specific gravity (specific gravity ratio) of the first olefin polymer and the ester polymer is preferably 5/95 to 95/15.

A blend ratio of olefin and ester polymers below this range is undesirable because the characteristics of each polymer are lost. Specifically, if the blend ratio of olefin polymer is less than 5% by weight, the lightness and fiber strength decrease. If the blend ratio of ester polymer is less than 5% by weight, the fiber modulus decreases, resulting in a loss of fabric stiffness and comfort when used and worn, and the characteristic slimy feel of olefin polymers develops. Therefore, a more preferable blend ratio is 5/85 to 85/15, and the most preferable blend ratio is 25/75 to 75/25.

Next, a method for producing the network-structured fibers of the present invention will be described. The commonly known frustrating spinning method can be used to produce the fibers of the present invention. The specific method will be described below.

First, a blend of an olefin polymer and an ester polymer is dissolved in a solvent that dissolves both polymers at high temperature and pressure, but not at low temperature. The resulting solution is then spun from a nozzle in a phase-separated state between the polymer and the solvent. This produces the above-mentioned fiber.

Examples of such solvents include commonly known aromatic hydrocarbons such as benzene and toluene, aliphatic hydrocarbons such as butane, pentane and their isomers and homologues, alicyclic hydrocarbons such as cyclohexane, and unsaturated hydrocarbons. Also included are halogenated hydrocarbons such as trichloromethane, methylene chloride, carbon tetrachloride, chloroform, 1,2-dichloro-2,2-difluoroethane, 1,2-dichloro-1,1-difluoroethane, methyl chloride, and ethyl chloride.

Further examples of suitable solvents include alcohols, ethers, ketones, nitriles, amides, and fluorocarbons. Furthermore, mixtures of the above-mentioned solvents may also be used. In recent years, with growing concern over global environmental issues, the use of solvents that deplete the ozone layer must be avoided. Taking environmental concerns into consideration, desirable solvents for the present invention include methylene chloride, 1,1-dichloro-2,2-difluoroethane, and 1,2-dichloro-1,1-difluoroethane.

The polymer concentration range cannot be universally limited, depending on the degree of polymerization of the polymer, the type of solvent, and the pressure applied. It is preferable to set the polymer concentration in the spinning mixture to 5 to 30% by weight and the solvent concentration to 70 to 95% by weight. A polymer concentration of less than 5% by weight makes it difficult to obtain continuous long fibers. A concentration of more than 30% by weight results in tubular fibers containing bubbles rather than fibrillation, making it difficult to obtain ultrafine, high-strength fibril fibers. A solvent concentration of less than 70% by weight increases the viscosity of the spinning mixture, making it difficult to dissolve the polymer uniformly. This tends to result in hollow fibers rather than ultrafine fibril fibers. Furthermore, a concentration of more than 95% by weight is undesirable because the network-structured fibers composed of fibril fibers are not continuous.

Adding an inert gas, such as nitrogen, before or after preparing the spinning mixture is highly desirable in order to increase the spinning pressure. Adding an inert gas before the temperature rise is particularly advantageous in that it prevents polymer degradation, improves temperature rise, promotes the solubility of the polymer in the solvent, and allows for the production of extremely fine fibril network-structured fibers.

When producing network-structured fibers according to the present invention, the fibers are drawn and oriented by the explosive force associated with solvent evaporation. Fiber strength is often determined by whether the fibers are sufficiently drawn and oriented. This explosive force is the instantaneous evaporation force. The solvent evaporates rapidly in less than 0.1 seconds, resulting in a rapid increase in polymer concentration, ultimately resulting in the precipitation of only the mixed polymer. The mixed polymer precipitated by the solvent evaporation is then cooled. This cooling process is crucial for fiber strength, and to obtain high-strength fibers, sufficient flash cooling and the rate-dependent stretching and orientation must be achieved. Because the manufacturing method of the present invention uses polymers that are incompatible with each other, the flash flow sufficiently promotes fibrillation, resulting in extremely fine fibrillar fibers.

When carrying out the manufacturing method of the present invention, the polymers used are incompatible with each other. Therefore, even if the polymers dissolve in the solvent, they tend to separate easily. Therefore, it is preferable to add a surfactant. The addition of this surfactant is effective in maintaining the stability of the spinning mixture in an emulsion state, and nonionic surfactants are generally applicable. Examples of surface lubricants include monoesters of lauric acid, stearic acid, and oleic acid, as well as polyoxyethylene adducts of lauryl alcohol, stearyl alcohol, and oleyl alcohol. The more homogeneous the mixture, the more likely it is that extremely fine fibril network-structured fibers will be obtained.

When carrying out the manufacturing method of the present invention, the melting and spinning temperatures of the spinning mixture are preferably 170°C or higher and 240°C or lower. Because ester polymers in particular experience a significant decrease in viscosity in the presence of a solvent, temperatures above 240°C are undesirable because they can cause discoloration of the fibers or accelerate decomposition, preventing the production of high-strength fibers. Temperatures below 70°C are also undesirable because they do not produce ultrafine fibril fibers but instead result in hollow, tubular fibers.

The duration of the molten state of the spinning mixture during the production method of the present invention cannot be generally limited because it depends on the melting and spinning temperatures. That is, at high temperatures, the duration of the molten state must be kept as short as possible, whereas at relatively low temperatures, a longer duration of the molten state is acceptable. If a duration of the molten state of the spinning mixture is specified, a duration of 5 to 90 minutes is preferred. If the duration of the molten state of the spinning mixture exceeds 90 minutes, the ester polymer may become discolored or thermally decompose, or the fiber strength may decrease. Furthermore, a duration of the molten state of less than 5 minutes is undesirable because the polymer may not be sufficiently dissolved, which can lead to problems such as clogging of the filter and problems in producing uniform fibers.

The pressure at which the polymer-dissolved mixed solution is spun is not limited to a specific value, depending on the amount of solvent, polymer concentration, and amount of inert gas added. A pressure of 60 kg/cm² or higher is generally preferred. Pressures below 60 kg/cm² result in a reduced explosive force during flash spinning, resulting in poor fiber orientation and failure to obtain high-strength fibers. Furthermore, non-uniform extrusion results, making it difficult to spin stable, highly fibrillated fibers. While the upper pressure limit is not particularly limited, 180 kg/cm² is preferred from the viewpoint of preventing a decrease in the viscosity of the polymer.

In flash spinning, the spinning mixture is spun under autogenous pressure or through a pressure letdown chamber. A commonly known nozzle can be used for spinning.

In addition, additives commonly used in fibers, such as matting agents, light resistance agents, heat resistance agents, pigments, fiber-opening agents, weather resistance agents, UV absorbers, heat storage agents, and stabilizers, can be added to the polymer or spinning mixture solution within the range that does not impair the effects of this invention.

Next, a nonwoven fabric having a dense structure in which fibers in a network structure are bonded throughout the entirety and a method for producing the same will be described in detail.

This nonwoven fabric is obtained by using the above-mentioned network structured fibers.

Here, a nonwoven fabric having a dense structure refers to a nonwoven fabric having an apparent density of 0.2 g/cm or more, in which the above-mentioned ultrafine network-structured fibers are densely bonded together.

Furthermore, the fibers that make up the nonwoven fabric of the present invention are incompatible with each other and are therefore primarily composed of extremely fine fibril fibers made from simple polymers. The finer the fibers, the denser the structure obtained when made into a nonwoven fabric, resulting in a high level of bacterial barrier properties that prevent even the smallest bacteria from penetrating compared to conventional nonwoven fabrics.

The nonwoven fabric of the present invention requires that the fibers in the network structure be bonded throughout. This means that the extremely fine fibril network fibers are closely bonded at their contact points, not just in spots. In other words, because the extremely fine fibril fibers are bonded at their contact points, the nonwoven fabric has an extremely dense structure and is excellent in strength, ductility, water pressure resistance, and breathability.

Therefore, the nonwoven fabric of the present invention preferably has a strength of 20 kg/5 cm or more, calculated per 100 g/m² of fabric weight. If the strength is less than 20 kg/5 cm+, the nonwoven fabric will not be usable for general purposes, and its uses will be extremely limited.

The moisture permeability, which indicates the ability to dissipate moisture, is preferably 100 g7 m2/hr or more.

If the moisture permeability rating is less than 100 g/m²/hr, moisture will not dissipate easily. Therefore, when used as clothing or a slat knob, moisture will build up, eventually resulting in condensation, discomfort, and even strain, making the area unsanitary. Therefore, the higher the moisture permeability rating, the better.

A water resistance of 50 cm or more is preferable. Water resistance is an indicator of the resistance to penetration of liquids such as water. If the water resistance is less than 50 cm, liquids such as water will pass through, along with bacteria, resulting in a significant decrease in resistance to bacteria. This makes the material unsuitable for use in sanitary protective clothing. The higher the water resistance value, the better.

The method for producing the nonwoven fabric will be described below.

In order to produce a nonwoven fabric according to the present invention, the network of fibers that constitute the nonwoven fabric must first be produced. In producing this network of fibers, the flash spinning method described above is applied.

When the spinning mixture is spun out of the nozzle, the flash stream and the precipitated fibers collide with a rotating plate, causing the network-like fibers to traverse and then open. The process of forming this network-like fiber is as described above. Opening methods include friction charging with a rotating plate and subsequent corona discharge, and either method may be used, or a combination of these methods may be used.

The opened reticular fibers are deposited on a conveyor to form a fiber web, which is then heat-pressed using a group of rolls. The heat-pressing conditions are preferably set to a temperature of at least 40°C below the melting point of the polymer with the lowest melting point among the polymers making up the fiber, and a linear pressure of at least 0.5 kg/cm and at most 20 kg/cm. Preliminary heat-pressing using a group of rolls at room temperature followed by further heat-pressing under the above conditions is preferred, as it results in stronger adhesion at the contact points of the fibril fibers.

If a temperature lower than 40°C below the melting point of the polymer is applied, the adhesion between the fibers as a whole will decrease, and the strength of the nonwoven fabric will decrease, which is undesirable. Also, if the heat-compression bonding is carried out at a temperature exceeding the melting point of the polymer, the fibers will melt, which will reduce the effect of obtaining ultrafine fibril fibers, which is undesirable.

On the other hand, if the linear pressure is less than 0.5 kg/cm, the adhesiveness between the fibers as a whole will decrease, and the strength of the nonwoven fabric will decrease, which is not preferable. Also, if the linear pressure exceeds 20 kg/cfD, the fiber layer will tend to turn into a film, which is not preferable.

The above-mentioned rolls may be a combination of steel rolls, rubber rolls, and resin rolls. When using steel rolls, it is preferable to coat them with fluoroethylene resin, rubber, or the like, to prevent the resulting nonwoven fabric from having an unusual gloss. Two to thirty rolls can be used. A common device for such rolls is most preferably a device called a calender roll machine.

In the nonwoven fabric of the present invention, the basis weight can be adjusted by changing the traverse state or conveyor speed, or significant changes in basis weight can be made by laminating the formed web or nonwoven fabric.

Next, a nonwoven fabric having a dense structure in which fibers in a network structure are partially bonded together and a method for producing the same, based on the present invention, will be described in detail.

This nonwoven fabric is also obtained by using the above-mentioned network-structured fibers.

In this case, the nonwoven fabric must have a network structure in which the fibers are partially bonded together. This means that the extremely fine fibril network fibers are intermixed and partially bonded in certain areas by the low-melting polymer, but are not bonded entirely. In other words, the extremely fine fibril fibers are partially bonded together by the low-melting polymer, thereby maintaining the shape of the nonwoven fabric.

The partially unbonded fibers are composed of extremely fine fibril network structures, resulting in a dense yet flexible nonwoven fabric with excellent strength, breathability, etc. Furthermore, this dense structure naturally provides a bacterial barrier.

This partially bonded state can be expressed as a bonded area ratio.

The bonded area ratio is measured by taking a small piece of nonwoven fabric, magnifying it with a scanning electron microscope, and measuring the ratio of the total area of the point-bonded portions to the area of the smallest repeating unit 10 times, based on the average value. A bonded area ratio of 50% or less is preferred. If it exceeds 50%, the number of bonded areas increases, restricting the freedom of the unfixed fibers in the nonwoven fabric, tending to make the nonwoven fabric feel stiff and lacking in flexibility. Furthermore, if the bonded area ratio is too low, the nonwoven fabric's shape deteriorates, so for practical purposes, a bonded area ratio of 4% or more is preferred. For these reasons, a ratio of 5% to 30% is most preferred.

This partially bonded state can also be expressed in terms of bond density. Bond density is determined by taking a small piece of fabric, magnifying it with a scanning electron microscope, calculating the ratio of the total number of bonded areas to the area of the smallest repeating unit, and converting it to the average of 10 individual measurements per square sennameter.

The bond density is preferably 15 or more and 120 or less bonds/cm². A density of less than 15 bonds/cm² reduces the formability of the nonwoven fabric, and further reduces the abrasion resistance of the nonwoven fabric, leading to problems such as pilling, which is undesirable. Therefore, the higher the bond density, the fewer practical problems there are, but if it is too high, the nonwoven fabric may become stiff and lack flexibility. Therefore, a bond density of 120 or less bonds/cm² is preferred. Based on the above, a more preferable range is 20 or more bonds/cm² and 100 or less bonds/cm², and the most preferable range is 30 or more bonds/cm² and 90 or less bonds/cm².

It is more preferable that both the adhesive area ratio and adhesive density are within the above ranges.

The adhesive portions may have any shape, such as a circle, oval, diamond, triangle, T-shape, cross, checkerboard, or grid.

The physical properties of this nonwoven fabric should preferably have a strength of 5 kg/5 cm or more, calculated per 100 g/r/m². A strength of less than 5 kg/5 cm can cause practical problems, significantly limiting the uses of the nonwoven fabric.

The compression stiffness is preferably 200 g or less. The compression stiffness indicates the flexibility of a nonwoven fabric; a lower value indicates greater flexibility. The compression stiffness was measured using the following method. First, a 50 mm sample width was taken in the machine direction (longitudinal direction) of the nonwoven fabric, and five 100 mm sample pieces were cut into 100 mm lengths in the direction perpendicular to this direction. Each sample piece was bent longitudinally to form a cylindrical shape, and both ends were joined to form a sample. The sample was then compressed radially at a compression rate of 50 mm/min using a Toyo Baldwin Tensolon UT M-4-1-100. The stress at the maximum load was measured, and the average value was divided by the basis weight of the nonwoven fabric (g/r/min) and converted to a value per 100 g/r/min. This value was taken as the compression stiffness. A compression stiffness of a nonwoven fabric exceeding 200 g is undesirable because it reduces flexibility and creates a rough, stiff feel. Therefore, a value of 160 g or less is more preferable, and 120 g or less is most preferable.

A moisture permeability of 100 g/m²/hr or higher is preferred. Moisture permeability indicates the ability of a material to dissipate moisture, with higher values indicating better performance. If the moisture permeability is less than 100 g/m²/hr, moisture will not dissipate easily. When used for clothing or house wrap, moisture will build up, leading to condensation, discomfort, and even mold growth, creating unsanitary conditions. Therefore, the higher the moisture permeability, the better.

The basis weight of this nonwoven fabric can be as thick as 500 g/m', but typically 20 to 200 g/m' is used.

The method for producing the nonwoven fabric will be described below.

To produce this nonwoven fabric, the network of fibers that make up the nonwoven fabric must first be produced, and the above-described frustule spinning method is used to produce this network of fibers.

When the spinning mixture is spun out of the nozzle, the flash flow and the precipitated fibers collide with the rotating plate, causing the network-like fibers to traverse and then open. The process of forming this network-like fiber is as described above. The opening method can be friction charging with a rotating plate or subsequent corona discharge, and either method can be used, or a combination of both.

The opened web of fibers is then deposited on a conveyor to form a fibrous web, which is then partially compressed using an embossing machine. Embossing machines include thermal embossing machines and ultrasonic embossing machines.

For thermal embossing, the preferred thermal compression conditions are a temperature of at least 40°C below the melting point and below the melting point of the polymer with the lowest melting point among the polymers constituting the fibers, and a linear pressure of at least 0.5 kg/cm and at most 50 kg/cm. Under this range of linear pressure, a clearance of 0.02 mm to 0.2 mm may be maintained. This clearance is used to prevent complete fusion of the fused points and the formation of a film. This clearance should be selected as appropriate for the application. Pre-compression with a roll at room temperature followed by embossing under the above conditions is also preferred, as it only disrupts the fibril fiber web. However, thermal compression at a temperature above the polymer's melting point during embossing can cause the fibers to melt, resulting in the web being caught by the roller and preventing sheet formation. Furthermore, this tends to be undesirable because the ultrafine network-like fibers fuse, reducing the benefits of obtaining ultrafine fibril fibers. On the other hand, if a temperature lower than the melting point of the polymer minus 40°C is applied in the final stage, the adhesion between the fibers will decrease, and the strength of the nonwoven fabric will decrease, which is not preferred.

On the other hand, if the linear pressure is less than 0.5 kg/cm, the adhesion between the fibers at the bonding points will decrease, and the strength of the nonwoven fabric will decrease, which is undesirable.

Furthermore, if the pressure exceeds 50 kg/cm, the pressure-bonded points tend to become filmy, and if the pressure exceeds this limit, the nonwoven fabric will have holes, which is undesirable.

The bonding conditions for the Pinsonic processing machine are, for example, ultrasonic vibrations at approximately 20 kHz, which partially fuse the fibers together and maintain the nonwoven fabric shape. The degree of fusion can be selected as desired by varying the amplitude of the ultrasonic waves. When using this ultrasonic fusion method, when bonding highly heat-sealable webs, areas other than the bonded areas are hardly affected by heat, so the heat shrinkability of the nonwoven fabric as a whole is maintained. This makes it even more effective when producing highly heat-shrinkable nonwoven fabrics.

The embossing patterns of these embossing machines are generally formed by an engraved roll with a raised pattern and a flat roll. The raised pattern can be created primarily by controlling the bonded area ratio and bonded point density described above. The tip shape of the raised portions of these engraved rolls can be any shape, including round, oval, diamond, triangular, T-shaped, cross-shaped, square, or lattice-shaped.

Furthermore, other embossing processes may be performed under different conditions or under the above conditions before or after embossing, and calendering may also be used in combination, without departing from the scope of the present invention.

EXAMPLES The present invention will now be described in detail with reference to the following examples. Measurements and evaluations of various properties in the following examples were carried out by the following methods.

Polymer melting point: The melting point was determined as the temperature at the extreme of the melting absorption curve measured using a Perkin-Elmer DSC-12J differential scanning calorimeter at a heating rate of 20°C/min.

Fiber fineness: Measured fineness according to JIS L-1090.

Fiber strength and elongation: Using a Toyo Baldwin Tensilon UTM-4-1-100, the strength and elongation were measured at a tensile speed of 5 cm/min, with a sample length of 10 cm, grip spacing of 5 cm, and 20 twists of 75 cm.

The tenacity thus obtained was divided by the fineness to obtain the fiber strength. For each of these formulations, 20 measurements were taken, and the values were expressed as average values.

Fiber Modulus: When measuring the strength and elongation of the above-mentioned fibers, the initial tensile resistance (g/d) was used as the modulus value in accordance with JTS L-1013710 "Initial Tensile Resistance Measurement."

Specific surface area: Nippon Hel Co., Ltd. (7) rBELsORP28J t [I], BET nitrogen adsorption method The specific surface area of the fiber was measured and calculated in m²/g.

Fiber Dyeability: After the following disperse dyeing or cationic dyeing was performed, reduction dyeing was performed, and the fibers were then rinsed and dried. The dyeability of the fibers was evaluated as follows:

◎ Excellent, ○ Good, △ Fair, X Poor Dispersion staining.

Disperse dye Blue E-FBL (Sumitomo Chemical) was used at 1% owf, dispersant Disper-TL (Meisei Chemical) was used at 1 g/L, and formic acid was used as an auxiliary agent at 0.1 g/L. The dye was boil-dyed for 60 minutes at a bath ratio of 1:50.

Cationic dyeing: ) 1% owf cationic dye Astrazon Blue FFR (Bayer) J, 0.5 g/L leveling agent Migregal WA-10 (Senryaku), and 10% owf sodium sulfate as an auxiliary were prepared. The liquor ratio was 1.50, and the fabric was boil-dyed for 60 minutes.

Reduction dyeing: - 1 g/L of Sunmol RL-100 (manufactured by Nicca Chemical Co., Ltd.) was used as a scouring agent, along with 2 g/L of hydrosulfide and 1 g/L of caustic soda. The solution was treated at a bath ratio of 1:50 at 80°C for 20 minutes.

KS strength and tensile elongation of nonwoven fabric: Ten specimens measuring 5 cm wide and 20 cm long were prepared using a Toyo Baldwin "Tensilon UTM-4-1-+00" according to the strip method described in JIS L-1096. Measurements were performed at a grip distance of 10 cm and a pulling speed of 10 cm/min. The individual maximum tensile strengths were averaged and converted to 100 g/m2 to determine the KS strength. The maximum elongations were also averaged to determine the tensile elongation of the nonwoven fabric.

Apparent density of nonwoven fabric: Five sample pieces, each 10 cm wide x 10 cm long, were prepared. The basis weight of each sample was measured. A load of 4.5 g/cm was applied to each sample using a thickness gauge manufactured by Daiei Scientific Instruments Co., Ltd., and the thickness was measured after 10 seconds. The apparent density was calculated using the following formula, and the average value was used as the apparent density of the nonwoven fabric.

Apparent density (g/cm') = basis weight (g/m") / thickness (1101) / 1000 Moisture permeability of 1000 nonwoven fabric: Moisture permeability (g/m"/hr) was measured in accordance with JIS-L 1099-A-1 under conditions of 40°C and 90% humidity.

Dyeability of nonwoven fabric: Processed and evaluated in the same manner as for fibers.

First, examples of fibers will be described below.

Example 1 A 500 cc autoclave was charged with 20 g of high-density polyethylene with a melting point of 132°C, a density of 0.96 g/cm², and a melt index of 0.8 g/10 min, 30 g of polyethylene terephthalate with a melting point of 256°C and a relative viscosity ηrel of 1.6, and methylene chloride as a solvent. Additionally, 0.2 wt% of a polyoxyethylene lauryl ether and isotridecyl stearate were added as surfactants to the polymer blend. The autoclave was then closed, and nitrogen was introduced to 40 kg/cm². Stirring and heating were initiated at a moderate speed. The solution concentrations of the components were 20 wt% for the polymer and 80 wt% for the solvent.

The time required for the temperature to reach 220°C after reaching 100°C was 25 minutes, and stirring was continued for 10 minutes after reaching 220°C to obtain a homogeneous solution. The gauge pressure at this time was 110 kg/cm. Next, while the autoclave pressure was maintained at 110 kg/cm using a continuous high-pressure nitrogen gas injection device, the valve was immediately opened and the mixture was spun into the atmosphere through a nozzle with a 0.75φ hole diameter and L/D = 1 and equipped with a pressure-reduction chamber. The pressure in the pressure-reduction chamber was 92 kg/cm.

The resulting fiber had excellent fibrillation, no discoloration, and high fiber strength and modulus. Furthermore, when this fiber was dyed with disperse dyes, it was confirmed that it could be dyed vividly. The properties of this fiber were as follows:

Strength: +4.85 g/d Elongation: 64% Modulus: 16.7 g/d Specific Surface Area: 31 m2/g [Example 2] Using the same autoclave as in Example 1, 20 g of polypropylene with a melting point of 162°C, a density of 0.910 g/cm⁻¹, and a melt flow rate of 4 g/10 min, 30 g of polyethylene terephthalate with a melting point of 256°C, a relative viscosity of ηrel of 1.7, and methylene chloride as a solvent were charged into the autoclave.

Furthermore, 0.2% by weight of lauryl ether having 3 moles of polyoxyethylene added thereto and isooctyl laurate were added as surfactants to the mixed polymer. The autoclave was then closed, and nitrogen was injected into the autoclave until the pressure reached 50 kg/cm. Stirring at a moderate speed and heating were then initiated.

The concentration of the mixed polymer in the solution was 20% by volume, and the concentration of the solvent was 80% by weight.

It took 30 minutes for the temperature to reach 200°C after reaching 100°C. After reaching 200°C, the mixture was stirred for 10 minutes to obtain a homogeneous solution. The pressure at this time was 105 kg/cm² gauge. Next, while continuously injecting high-pressure nitrogen gas to maintain the autoclave pressure at 105 kg/cm², the valve was immediately opened and the mixture was spun into the atmosphere through a nozzle with a 0.75φ orifice and an L/D = 1 ratio, equipped with a pressure-reduction chamber. The pressure in the pressure-reduction chamber was 85 kg/cm². The resulting fibers had excellent fibrillation, no fiber coloration, and high fiber strength and modulus. Furthermore, when the fibers were dyed with disperse dyes, vivid dyeing was confirmed. The fiber's properties were as follows:

Strength: 3.47 g/d Elongation: 50% Modules: 18.6 g/d Specific Surface Area: 29 rn2/g [Example 3] Fiber was produced using polyethylene terephthalate copolymerized with 5 mol% sulfoisophthalic acid, with a melting point of 247°C and a relative viscosity (ηrel) of 1.3. The melting and spinning temperatures were 200°C, but under the same conditions as in Example 2, except for this, the melting pressure was 105 kg/am², and the pressure in the drop chamber was 86 kg/cm².

The resulting fiber had excellent fibrillation, no coloration, and high fiber strength and modulus. Furthermore, when this fiber was dyed with a cationic dye, it was confirmed that only the polyester component could be dyed vividly. The properties of this fiber were as follows:

Strength: 4.53 g/d Elongation: 69% Modulus: 14.1 g/d Specific Surface Area: 38 m⁻¹/g [Examples 4-8, Comparative Examples 1.2] Using the autoclave described in Example 1, 200 g of methylene chloride was charged as a solvent under constant conditions while varying the blend ratio of high-density polyethylene (melting point 132°C, density 0.96 g/cm⁻¹, and melt index 0.6 g/10 min) and polyethylene terephthalate (melting point 256°C, relative viscosity ηrel 1.4). Additionally, 0.2 wt.% each of lauryl ether with 3 moles of polyoxyethylene added and isooctyl laurate was added as surfactants to the blend. The autoclave was then closed, and nitrogen was then injected into the autoclave at a rate of 50 kg/amt. Stirring was started at a moderate speed, and heating was initiated.

The solution concentrations of each component were as shown in Table 1. The time required for the temperature to reach 200°C after reaching 100°C was 35 minutes. After reaching 200°C, stirring was continued for 10 minutes to obtain a homogeneous solution. The pressure at this stage was approximately 110 kg/cm² (gauge pressure). Next, the autoclave was pressurized to maintain the pressure at 110 kg/cm² using a continuous high-pressure nitrogen gas injection device. The valve was immediately opened, and the solution was spun into the atmosphere through a nozzle with a hole diameter of 0 mm, 75φ, and L/D = 1, equipped with a pressure-drop chamber.

The results are shown in Table 1.

As is clear from Table 1, in the examples of the present invention, the dyeability with disperse dyes tends to improve as the blend ratio of polyester increases, and the obtained fibers were in an extremely good fibrillated state, and had high coloring, fiber strength, and modulus.

In Comparative Example 1, the resulting fiber was in a good fibrillated state and had relatively high fiber strength and modulus. However, because it contained no polyester, it had poor dyeability with disperse dyes. In Comparative Example 2, the resulting fiber contained no polyethylene, so it had good dyeability with disperse dyes, but it was in a poor fibrillated state and had low fiber strength and modulus.

Example 9 Fibers were produced under the same conditions as in Example 6, except that polybutylene terephthalate with a melting point of 228°C and a relative viscosity ηrel of 1.7 was used, and the melting and spinning temperatures were 200°C. The melting pressure was 112 kg/cm², and the pressure in the drop chamber was 93 kg/cm².

The resulting fiber had excellent fibrillation, was free of coloration, and had high fiber strength and modulus. Furthermore, when this fiber was dyed with disperse dyes, it was confirmed that it could be dyed well. The properties of this fiber were as follows:

Strength: 4.62 g/d Elongation: 263% Modulus: 3. 6 g/d Specific surface area: 38 m'/g [Example 10] A 10-liter autoclave was charged with 600 g of high-density polyethylene with a melting point of 132°C (density 0.96 g/cm) and a melt index of 0.8 g/10 min, 900 g of polyethylene terephthalate with a melting point of 256°C (density 0.96 g/cm) and a relative viscosity of ηrel 1.7, and methylene chloride as a solvent. Additionally, 0.2 wt.% of lauryl ether with 3 moles of polyoxyethylene added and isotridecyl stearate were added as surfactants to the polymer blend. The autoclave was then closed, and nitrogen was introduced to the autoclave until the pressure reached 20 kg/cm'. Stirring and heating were initiated at a moderate speed. The solution concentrations of the components were 20 wt.% polymer and 80 wt.% solvent.

It took 40 minutes for the temperature to reach 220°C after reaching 100°C. Stirring was continued for 10 minutes after reaching 220°C to obtain a homogeneous solution. The pressure at this point was 109 kg/cm² gauge. Next, the autoclave pressure was increased to 110 kg/cm² using a continuous high-pressure nitrogen gas injection device. The three valves were immediately opened, and the material was spun from three nozzles with a 0.75φ orifice diameter and an L/D ratio of 1 and equipped with pressure-drop chambers. The material was then collided with a rotating plate, opened, and deposited on a moving conveyor net to form a web.

The pressure in the pressure drop chamber was 92 kg/cm.

The webs were then laminated and passed through a hydraulic clearance calender with three pairs of rollers to produce a nonwoven fabric with a basis weight of 50 g/rn.

The upper rollers of this calender had urethane rubber surfaces, and the lower rollers were heated steel rollers with a fluororesin coating. The temperatures and linear pressures of the first through third pairs of rollers were 60, 120, 125°C, 10°F, 30, 8, and 1.5 kg/cm, respectively.

The resulting nonwoven fabric had excellent fiber fibrillation and no visible coloring. Furthermore, because the fibers were bonded across the entire surface, the nonwoven fabric had high strength, moisture permeability, and water pressure resistance. Furthermore, when this nonwoven fabric was dyed with disperse dyes, it was confirmed that it could be dyed vividly. The properties of this nonwoven fabric were as follows:

Specific Surface Area: +31 m2/g Nonwoven Fabric KS Strength (MD/CD): 38.4 / 39.8 kg/15 cm Nonwoven Fabric Elongation (MD/CD): 18 / 26% Apparent Density: 0.40 g/cm² Moisture Permeability: 280 g/m² /hr Water Pressure Resistance: 180 cmH tO Dyeability: Excellent [Example 11] Using the same equipment as in Example 10, an autoclave was charged with 400 g of polypropylene with a melting point of 162°C, a density of 0.910 g/cm³, and a melt flow rate of 4 g/l/min, 1100 g of polyethylene terephthalate with a melting point of 256°C and a relative viscosity y7rel of 1.6, and methylene chloride as a solvent. Additionally, 0.2% by weight of lauryl ether to which 3 moles of polyoxyethylene had been added and isooctyl laurate were added as surfactants relative to the mixed polymer. The autoclave was then closed, and nitrogen was introduced into the autoclave until the pressure reached 40 kg/cm. Stirring at a moderate speed and heating were then initiated. The mixed polymer concentration in the solution was 20% by weight, and the solvent concentration was 80% by weight.

It took 30 minutes for the temperature to reach 200°C after reaching 100°C. After reaching 200°C, the mixture was stirred for 10 minutes to obtain a homogeneous solution. The pressure at this time was 118 kg/cm² gauge. Next, the autoclave pressure was increased to 20 kg/cm² using a continuous high-pressure nitrogen gas injection device. Three valves were immediately opened, and the mixture was spun through three nozzles with a 0.75φ orifice and an L/D ratio of 1, each equipped with a pressure-reduction chamber. The fibers were collided with a rotating plate, opened, and deposited on a moving conveyor net to form a web. The pressure in the pressure-reduction chamber was 99 kg/cm². The webs were then stacked, and a nonwoven fabric with a basis weight of 100 g/m² was produced in the same manner as in Example 10, except that the temperatures of the first through third pairs of rollers in the calender were 60°C, 150°C, and 1155°C, respectively.

The resulting nonwoven fabric had excellent fiber fibrillation and no visible coloring. Furthermore, because the fibers were bonded across the entire surface, the nonwoven fabric had high strength, moisture permeability, and water pressure resistance. Furthermore, when this nonwoven fabric was dyed with disperse dyes, it was confirmed that it could be dyed vividly. The properties of the resulting nonwoven fabric were as follows:

Specific surface area: 29 m"/g Nonwoven fabric KS strength (MD/CD): 32.3/33.6 kg/5 cm Nonwoven fabric elongation (MD/CD'): 22/29% Absolute density: 0.47 g/cm Moisture permeability: 263 g/m"/hr Water pressure resistance: 159 cmH2O Dyeability: Excellent (Example 12) A nonwoven fabric was produced using polyethylene terephthalate copolymerized with 5 mol% sulfoisophthalic acid, which has a melting point of 247°C and a relative viscosity (ηrel) of 1.3. The melting and spinning temperatures were set to 200°C under the same conditions as in Example 11. The melting pressure was 119 kg/cm" and the pressure in the drop chamber was 100 kg/cm2.

The resulting nonwoven fabric had excellent fiber fibrillation and no visible coloring. Furthermore, because the fibers were bonded across the entire surface, the nonwoven fabric had high strength, moisture permeability, and water pressure resistance. Furthermore, when this nonwoven fabric was dyed with a cationic dye, it was confirmed that it could be dyed vividly. The properties of this nonwoven fabric were as follows:

Specific surface area: 28 m2/g Nonwoven KS strength (MO/CD): 29.2 / 30.1 kg/5 cm Nonwoven elongation (MD/CD'): 1.7 / 25% Apparent density: 0.39 g/cm' Moisture permeability: 278 g/m2/hr Water pressure resistance: 172 cmH2O Dyeability: Excellent [Examples 13-17, Comparative Example 3.4] Using the apparatus described in Example 10, the autoclave was filled with a constant amount of methylene chloride (6200 g) while varying the blend ratio of high-density polyethylene (melting point 132°C, density 0.96 g/cm', and melt index 0.6 g/10 min) and polyethylene terephthalate (melting point 256°C and relative viscosity ηrel 1.4). Lauryl ether with 3 moles of polyoxyethylene added and isooctyl laurate were added as surfactants at 0.2% by weight each to the mixed polymer, and the autoclave was closed. Nitrogen was then injected into the autoclave to a pressure of 40 kg/cm, and stirring at a moderate speed and heating were initiated.

The solution concentrations of each component were as shown in Table 2. The time required for the temperature to reach 200°C after reaching 00°C was 35 minutes. After reaching 200°C, stirring was continued for 10 minutes to obtain a homogeneous solution. The pressure during this time was approximately 110 kg/cm² gauge. Next, the pressure inside the autoclave was increased using a continuous high-pressure nitrogen gas injection device to maintain the pressure at 110 kg/cm². The three valves were immediately opened to allow spinning. A web was formed in the same manner as in Example 10, yielding a nonwoven fabric.

The results are shown in Table 2.

As is clear from Table 2, in Examples 13-17, while dyeability with disperse dyes tends to improve as the blend ratio of polyester increases, the resulting nonwoven fabrics were in an extremely good fibrillated fiber state and were free of coloration. Moreover, because the fibers were bonded over the entire surface, the nonwoven fabrics had high strength, moisture permeability, and water pressure resistance.

In Comparative Example 3, the nonwoven fabric obtained had a good fibrillated state and relatively high strength, but because it contained no polyester at all, its dyeability was poor.

In Comparative Example 4, which contained no polyethylene, the resulting nonwoven fabric exhibited good dyeability with disperse dyes, but the fibrillation state was not very good, and the nonwoven fabric strength, moisture permeability, and water pressure resistance were all low.

Example 18 A nonwoven fabric was produced under the same conditions as in Example 15, except that polybutylene terephthalate with a melting point of 228°C and a relative viscosity (ηrel) of 1.7 was used, and the melting and spinning temperatures were 200°C. The melting pressure was 112 kg/cm², and the pressure in the drop chamber was 93 kg/cm².

The resulting nonwoven fabric had excellent fiber fibrillation and no visible coloring. Furthermore, because the fibers were bonded over the entire surface, the nonwoven fabric had high strength, moisture permeability, and water pressure resistance. Furthermore, when this nonwoven fabric was dyed with disperse dyes, it was confirmed that it could be dyed vividly. The properties of this nonwoven fabric were as follows:

Specific surface area: 31 m'/g Nonwoven KS strength (MD/CD): 36.3 / 37.4 kg/5 cm Nonwoven elongation (MD/CD): 21 / 29% Apparent density: 0.3 7 g/cm' Breathability: 292 g/m'/hr Water resistance: 191 cm) (t.

Dyeability: Excellent [Example 9] A 10-liter autoclave was charged with 600 g of high-density polyethylene with a melting point of 132°C, a density of 0.96 g/cm², and a melt index of 0.8 g/10 min, 1-900 g of polyethylene terephthalate with a melting point of 256°C and a relative viscosity (ηrel) of 1.7, and methylene chloride as a solvent. Surfactants, 1% isooctyl stearic acid and 0.2% isostearyl ester, were added to the polymer blend. The autoclave was then closed, and nitrogen was introduced to a flow rate of 20 kg/cm². Stirring and heating were initiated at a moderate speed. The solution concentrations of the components were 20% by weight for the polymer and 80% by weight for the solvent.

It took 40 minutes for the temperature to reach 220°C after reaching 100°C. Stirring was continued for 10 minutes after reaching 220°C to obtain a homogeneous solution. The pressure at this point was 109 kg/cm² gauge pressure. Next, while the pressure was increased to 110 kg/am² from the autoclave pressure using a continuous high-pressure nitrogen gas injection device, three valves were immediately opened, and the material was spun from three nozzles with a 0.75φ orifice diameter and L/D = 1 and equipped with pressure-drop chambers. The material was then collided with a rotating plate, opened, and deposited on a moving conveyor (not shown) to form a web.

The pressure in the pressure drop chamber was 92 kg/cm 2 .

The webs were then stacked and passed through a hydraulic clearance embossing machine to produce a nonwoven fabric with a basis weight of 50 g/m2. The upper roll of this embossing machine was an engraved roll, and the lower roll was a flat roll, both of which were heated rolls. Embossing was performed without clearance between the upper and lower rolls, at a linear pressure of 20 kg/cm, a temperature of 125°C, and a speed of 10 m/s. The bonded area ratio of the engraved roll was 25%, and the bonded point density was 60/cm2.

The resulting nonwoven fabric had excellent fiber fibrillation and no discoloration was observed. Furthermore, because the fibers were composed of numerous small bonded points, the nonwoven fabric maintained practical strength while exhibiting excellent flexibility and moisture permeability. Furthermore, when this nonwoven fabric was dyed with disperse dyes, it was confirmed that it could be dyed vividly. The properties of this nonwoven fabric were as follows:

Specific surface area: 31 m²/g Nonwoven KS strength (MD/CD): 17.3 / 18.6 kg/5 cm Nonwoven tensile elongation (MD/CD): 28 / 31% Apparent density: 0.28 g/m² Compression stiffness: 125 g Moisture permeability: 250 g/m²/hr Dyeability: 20 [Example 20] Using the same equipment as in Example 19, an autoclave was charged with 400 g of polypropylene (melting point 162°C, density 0.910 g/cm², and melt flow rate 4 g/10 min), 1100 g of polyethylene terephthalate (melting point 256°C, relative viscosity y) of 1.6, and methylene chloride as a solvent. Additionally, surfactants, isooctyl stearate and isostearyl ester, each at 0.2 wt.% relative to the polymer blend, were added. The autoclave was then closed, and nitrogen was introduced into the autoclave until the pressure reached 40 kg/cm. Stirring at a moderate speed and heating were initiated. The polymer blend concentration in the solution was 20 wt.%, and the solvent concentration was 80 wt.%.

It took 30 minutes for the temperature to reach 200°C after reaching 00°C, and stirring was continued for 10 minutes after reaching 200°C to obtain a homogeneous solution. The pressure at this time was 118 kg/cm + a' gauge. Next, the autoclave pressure was increased to 120 kg/cm2 using a continuous high-pressure furnace gas injector. Three valves were immediately opened, and the material was spun from three nozzles with a 0.75φ orifice diameter and L/D = 1, each equipped with a pressure-reduction chamber. The fibers were collided with a rotating plate, opened, and deposited on a moving conveyor net to form a web. The pressure in the pressure-reduction chamber was 99 kg/cm2. These webs were then laminated, and a nonwoven fabric with a basis weight of 100 g/m' was produced in the same manner as in Example 19, except that the embossing temperature was changed to 120°C.

The resulting nonwoven fabric had excellent fiber fibrillation and no visible coloration. Furthermore, the fibers were composed of numerous small bonded points, resulting in practical strength while maintaining excellent flexibility and moisture permeability. Furthermore, when this nonwoven fabric was dyed with disperse dyes, it was confirmed that it could be dyed vividly. The properties of this nonwoven fabric were as follows:

Specific surface area: 29 m"/g Nonwoven fabric KS strength (MD/CD): 16.2/17.7 kg/cm Nonwoven fabric tensile elongation (MD/CD): 30/33% Absolute density: 0.29 g/cm Compression stiffness: 120 g Moisture permeability: 231 g/m2/hr Dyeability: Excellent [Example 21] A nonwoven fabric was produced under the same conditions as in Example 20, except that polyethylene terephthalate copolymerized with 5 mol% sulfoisophthalic acid, which has a melting point of 247°C and a relative viscosity ηrel of 1.3, was used. The melting and spinning temperatures were 200°C. The melting pressure was 119 kg/cm" and the drop chamber pressure was 100 kg/cm".

The resulting nonwoven fabric had excellent fiber fibrillation and no visible coloring. Furthermore, the fibers were composed of numerous small bonded points, resulting in excellent flexibility and moisture permeability while maintaining practical nonwoven strength. Furthermore, when this nonwoven fabric was dyed with cationic dyes, it was confirmed that it could be dyed vividly.

The properties of this nonwoven fabric were as follows:

Specific surface area: 2s m2/g Non-woven fabric KS strong (MD/CD): 14. 5/15. 7 kg/5 cm Nonwoven fabric tensile elongation (MD/CD　'): 37/39% Apparent density: 0 ．． Compression stiffness: 118 g Moisture permeability: 247 g/m²/hr Dyeability: Excellent [Examples 22-26, Comparative Examples 5.6] Using the apparatus described in Example 19, an autoclave was charged with a constant amount of 6200 g of methylene chloride as a solvent, while varying the blend ratio of high-density polyethylene (melting point 132°C, density 0.96 g/cm², and melt index 0.6 g/10 min) and polyethylene terephthalate (melting point 256°C, relative viscosity ηrel = 4). Surfactants, isooctyl stearate and isostearyl ester, were added at 0.2 wt.% each to the polymer blend, and the autoclave was closed. Nitrogen was then pumped into the autoclave to a pressure of 40 kg/cm², and stirring and heating were initiated at a moderate speed.

The solution concentrations of each component were as shown in Table 3. It took 35 minutes for the temperature to reach 200°C after reaching 100°C. Stirring was continued for 10 minutes after the temperature reached 200°C to obtain a homogeneous solution. The gauge pressure at this time was approximately 110 kg/cm. Next, the autoclave was continuously pressurized to maintain the pressure at 10 kg/cm using a continuous high-pressure nitrogen gas injection device. The three valves were immediately opened to begin spinning. A web was formed in the same manner as in Example 19, yielding a nonwoven fabric.

The results are shown in Table 3.

As is clear from Table 3, in Examples 22-26, the dyeability with disperse dyes tended to improve as the blend ratio of polyester increased. However, the resulting nonwoven fabrics were in an extremely good fibrillated fiber state, free of coloration, and because the fibers were composed of many small bonded points, they maintained practical nonwoven strength while exhibiting excellent flexibility and moisture permeability. Furthermore, when these nonwoven fabrics were dyed with disperse dyes, it was confirmed that they could be dyed vividly.

In Comparative Example 5, the nonwoven fabric obtained had a good fibrillated state and relatively high strength, but because it contained no polyester, its dyeability was completely poor.

In Comparative Example 6, which contained no polyethylene, the resulting nonwoven fabric exhibited good dyeability with disperse dyes, but the fibrillation state was not very good, and the nonwoven fabric strength and moisture permeability were both low.

Example 27 A nonwoven fabric was produced under the same conditions as in Example 24, except that polybutylene terephthalate with a melting point of 228°C and a relative viscosity (ηrel) of 1.7 was used, and the melting and spinning temperatures were 200°C. The melting pressure was 112 kg/cm², and the pressure in the drop chamber was 93 kg/cm².

The resulting nonwoven fabric had excellent fiber fibrillation and no visible coloration. Furthermore, the fibers were composed of numerous small bonded points, resulting in practical nonwoven fabric strength while also exhibiting excellent flexibility and moisture permeability. Furthermore, when this nonwoven fabric was dyed with disperse dyes, it was confirmed that it could be dyed vividly. The properties of this nonwoven fabric were as follows:

Specific surface area: 31 m"/g Nonwoven KS strength (MD/CD): 15.3/16.5 kg/5 Ca+ nonwoven tensile elongation (MO/CD): 37/39% Apparent density: 0. 27 g/cm" Compression stiffness: 109 g Moisture permeability: 262 g/m"/hr Dyeability: Excellent (Examples 28-34) When producing the nonwoven fabric of Example 25, the type of embossing roll was changed to alter the bonded area ratio and bonded point density as shown in Table 4.

The results are shown in Table 4.

As is clear from Table 4, the nonwoven fabrics of Examples 28 to 33 maintained practical nonwoven fabric strength while exhibiting excellent softness and moisture permeability, while the strength of the nonwoven fabric tends to increase and the softness to decrease with an increase in the bonded area ratio and bonded point density.

In Example 34, the bonded area ratio was 100% because the nonwoven fabric was pressed only by flat rolls, and although the resulting fabric was slightly inferior in flexibility, it still had practical nonwoven strength and excellent moisture permeability.

Claims (1)

[Claims] 1. A fiber having a network structure, comprising a mixture of at least an olefin polymer and an ester polymer that are incompatible with each other, and having a network structure. 2. The fiber of claim 1, wherein the olefin polymer is one of an ethylene polymer, a propylene polymer, an ethylene-based copolymer, and a propylene-based copolymer. 3. The fiber of claim 1 or 2, wherein the ester polymer is one of polyethylene terephthalate and polybutylene terephthalate. 4. The fiber of any one of claims 1 to 3, wherein the blend ratio of the olefin polymer to the ester polymer is in the range of 5/95 to 95/5 by weight. 5. The fiber of claim 4, wherein the blend ratio of the olefin polymer to the ester polymer is in the range of 15/85 to 85/15 by weight. 6. A method for producing a network-structured fiber, comprising dissolving a blend of incompatible olefin polymers and ester polymers in a solvent at high temperature and pressure to form a single-bath solution, and then spinning the blend through a nozzle while the polymers and solvent are in a phase-separated state. 7. A method for producing a network-structured fiber as set forth in claim 6, comprising adding an inert gas to the spinning mixture. 8. A method for producing a network-structured fiber as set forth in claim 6 or 7, comprising adding a surfactant to the spinning mixture. 9. A nonwoven fabric having a dense structure, comprising network-structured fibers blended with an incompatible olefin polymer and ester polymer in a weight ratio ranging from 5/95 to 95/5, and further comprising bonding the network-structured fibers together. 10. The nonwoven fabric of claim 9, wherein the olefin polymer is any one of an ethylene polymer, a propylene polymer, an ethylene-based copolymer, and a propylene-based copolymer. 11. The nonwoven fabric of claim 9 or 10, wherein the ester polymer is any one of polyethylene terephthalate and polybutylene terephthalate. 12. The nonwoven fabric of any one of claims 9 to 11, wherein the blend ratio of the olefin polymer to the ester polymer in the blend is in the range of 15/85 to 85/15 by weight. 13. The nonwoven fabric of any one of claims 9 to 12, wherein the network-structure fibers are bonded throughout, and the properties of the nonwoven fabric include a strength of 20 kg/5 cm or more, a water pressure resistance of 50 cm or more, and a moisture permeability of 100 g/m2/hr or more. 14. The nonwoven fabric according to any one of claims 9 to 12, wherein the network-structure fibers are partially bonded together, and the properties of the nonwoven fabric include a strength of 5 kg/5 cm or more, a compression stiffness of 200 g or less, and a moisture permeability of 100 g/m2/hr or more. 15. A method for producing a nonwoven fabric having a dense structure, comprising: preparing steel-structure fibers containing a mixture of incompatible olefin polymers and ester polymers in a weight ratio of 5/95 to 95/5; forming the fibers into a web; and then thermocompressing the web using a group of rolls to bond the mixed network fibers together throughout. 16. The method for producing a nonwoven fabric according to claim 15, wherein the temperature when thermocompressing the web using a group of rolls is in the range of from above minus 40°C the melting point of the polymer having the lowest melting point among the polymers constituting the fibers to below that melting point, and the linear pressure during thermocompression is in the range of from 0.5 kg/cm to 20 kg/cm. 17. A method for producing a nonwoven fabric having a dense structure, comprising: preparing a steel-structure fiber containing a mixture of an incompatible olefin polymer and an ester polymer in a weight ratio ranging from 5/95 to 95/5; forming the fiber into a web; and then partially thermocompressing the web using an embossing machine to partially bond the mixed mesh. 18. A method for producing a nonwoven fabric as recited in claim 17, wherein the concentration of the web when heat-bonded using an embossing machine is in the range of more than minus 40°C the melting point of the polymer having the lowest melting point among the polymers constituting the fibers but not exceeding that melting point, and the linear pressure during heat-bonding is in the range of 0.5 kg/cm to 50 kg/cm. 19. A method for producing a nonwoven fabric as recited in claim 17 or 18, wherein the bonded area ratio when partially bonding the mixed plexiform fibers is in the range of 4% to 50%. 20. A nonwoven fabric as recited in any one of claims 17 to 19, wherein the bonded area density when partially bonding the mixed plexiform fibers is in the range of 15/cm2 to 120/cm2.