DE69431745T2 - FIBER WITH NETWORK STRUCTURE, FLEECE MADE THEREOF, AND METHOD FOR PRODUCING THE FIBER AND THE FLEECE - Google Patents

Description

The present invention relates to a fine-denier filament with a braid-like structure, which consists of a mixture of polymers that are not miscible with one another, a nonwoven fabric comprising this filament and having a finely fibrillated structure, and their production, which are known for example from US-A-5147,586.

Background of the invention

To produce fine-denier filaments and nonwovens using these filaments, the process of spinning Sea Island multicomponent filaments, then removing part of the polymer components from them with a solvent and solidifying the resulting filaments to obtain a nonwoven fabric is known. The use of the so-called melt-blowing process is also known, in which a molten polymer is spun from spinnerets and then stretched with a heated liquid to fibrillate it. However, a process in which part of the polymer components of the multicomponent filaments are removed with a solvent requires various steps. Although the melt-blowing process produces very fine filaments because fibrillation takes place in the phase in which the polymer is molten, the process has the disadvantage that stretch orientation and crystallization are low, so that the resulting filaments have only low mechanical strength.

The so-called flash spinning process, which is used to produce very fine filaments from a polymer solution, is also known. As described in US Patent 3,081,519, the flash spinning process involves spinning a polymer solution in a low-boiling solvent from spinnerets in order to immediately evaporate the solvent.

However, the filaments produced with such a formulation consist of only a single polymer component for all materials, and therefore they have a disadvantage due to the polymer that the development of applications for the product is limited. The process described in Japanese Unexamined Patent Publication 41/006,215-B and Japanese Laid-Open Publication 01/097,256-A has the same problem. To be more specific, while polyolefins are excellent in terms of low mass but have a low modulus so that they do not have a good feel when worn and put on, and have a special smoothness, polyesters are polymers that are naturally suitable for producing filaments with high tear strength and have a high modulus but do not have a good modulus when flash spinning. Filaments with a high tear resistance, so they have not actually been used until now.

EP-A-0.093.021 describes fibrillated bicomponent fibers produced by flash spinning with an inner core consisting of an olefin polymer and an outer sheath consisting of a corresponding amount of hydrophilic polymer, as well as filaments consisting of aggregates of such individual fibers.

US-A-5,147,586 describes a flash-spun filament with a braid-like structure comprising a polyolefin component with a braid-like structure.

Description of the invention

The present invention is intended to provide a fine-denier filament with a braid-like structure in which the aforementioned problems are solved, in particular the disadvantages of polyolefins and polyesters are mutually canceled out and their advantages are fully exploited, as well as a nonwoven fabric with this filament and a method for its production.

The inventors have made extensive efforts to solve the above-mentioned problems and have arrived at the present invention according to the main claims 1, 5, 8, 14 and 16.

The filament according to the invention consists of a mixture comprising at least polyolefin and polyester which are immiscible with each other and it has a braid-like structure.

The process according to the invention for producing a filament with a braid-like structure comprises dissolving a mixture of polyolefin and polyester, which are immiscible with each other, in a solvent at high temperature and high pressure and spinning the resulting dissolved phase from nozzles, wherein the polymer phases and the solvent are separated.

The filament of the present invention is made of polyolefin and polyester, has a previously unavailable braid-like filament structure with very fine denier fibrillated filaments, and has high tear strength and high modulus. Therefore, it can be used as a material for textiles, knitwear, dry-process nonwovens, wet-process nonwovens, etc., and compressed staple fibers, and is also suitable for various purposes such as clothing fabrics, insulation materials, artificial leather, absorbents used as hygiene materials, protective clothing, curtains, bed sheets, cleaning cloths, filters, household packaging, synthetic paper, etc. Since the filament If it contains polyester, it is not only dyed with pigments, but is also dyed accordingly during post-treatment.

The nonwoven fabric of the present invention having a fine fibrillated structure contains filaments having a braided structure containing a mixture of polyolefin and polyester which are not miscible with each other in a mass ratio in a range of 5:95 to 95:5, wherein the filaments having a braided structure are bonded to each other. The filaments having a braided structure are bonded to each other over the entire area in the nonwoven fabric or are bonded to each other in such a way that numerous heat bonding areas are formed which are spaced apart from each other by a certain distance.

The method of the invention for producing the nonwoven fabric with the finely fibrillated structure comprises producing filaments with a braid-like structure, wherein polyolefin and polyester, which are not miscible with each other, are mixed in a mass range of 5:95 to 95:5, producing pile from the filaments and solidifying the pile by applying heat and pressure so that all the mixed braid-like structures of the filaments are bonded together.

Another method according to the invention for producing nonwoven fabric comprises producing filaments with a braid-like structure, wherein polyolefin and polyester, which are not miscible with each other, are mixed in a mass range of 5:95 to 95:5, producing pile from the filaments and partially solidifying the pile by applying heat and pressure with an embossing device so that the mixed filaments with a braid-like structure are partially bonded.

In this way, nonwoven fabric having a fine fibrillated structure with highly fibrillated fine denier filaments can be produced according to the present invention. Among these nonwoven fabrics, the nonwoven fabrics in which the filaments having a braid-like structure are bonded together over the entire area are suitable for various purposes such as envelopes, packaging materials, elastic cuffs, waterproof materials, labels, thermal insulation materials, synthetic paper, materials for medical and hygienic protective clothing, curtains, bed sheets, cleaning cloths, filters, household packaging, etc. Nonwoven fabric in which the filaments having a braid-like structure are bonded partially is suitable for various purposes such as clothing, thermal insulation materials, materials for medical and hygienic protective clothing, curtains, bed sheets, cleaning cloths, filters, household packaging, tents, artificial leather, etc.

The filament with a braid-like structure according to the invention is explained in more detail below.

The braided filament structure according to the invention means that fibrillated filaments with a diameter of 0.01-10 μm are formed three-dimensionally and endlessly in the longitudinal direction.

The components forming the filament of the present invention must be polymer components that are immiscible with each other. Due to the fact that they are immiscible with each other, the mixed polymer components exist individually so that the resulting filament exhibits the fibrousness inherent in each of the polymer components. As is known, a fiber made of mixed polymers that are immiscible with each other is easily disintegrated into its components when a physical force is applied. In the filament of the present invention, since the polymers are immiscible with each other, each polymer exists predominantly in the form of fine-denier fibrillated filaments. The specific combination of polymer components is therefore a combination of polyolefin and polyester.

Examples of the polyolefin which is a polymer component constituting the filaments of the present invention are polyethylene, polypropylene, copolymer consisting mainly of ethylene, copolymer consisting mainly of propylene, etc.

The viscosity of the ethylene polymers among the above polymers is preferably 0.3-30 g/10 min in terms of the melt index value measured by the method of ASTM-D-1238E. If the melt index value is less than 3 g/10 min, the viscosity of the mixed solution becomes too high, so that fine-denier fibrillated filaments are hardly obtained. If the melt index value is greater than 30 g/10 min, the tensile strength of the filaments themselves decreases and at the same time the smoothness and stickiness of the filaments increase, so that the filaments do not have a good grip.

Preferably, the viscosity of the propylene polymers is 1-40 g/10 min in terms of the melt index value measured by the method of ASTM-D-1238L. If the melt index value is less than 1 g/10 min, the viscosity of the solution mixture becomes too high, so that fine-denier fibrillated filaments are hardly obtained. If the melt index value is greater than 40 g/10 min, the tensile strength of the filaments themselves decreases, and at the same time, the smoothness and stickiness of the filaments increase, so that the filaments do not have a good grip.

Examples of the polyester which is the other polymer component constituting the filament of the present invention are polyethylene terephthalate and polybutylene terephthalate. In addition, copolymers in which the above are the main components containing up to 40 mol% of the copolymerization monomers, such as isophthalic acid, phthalic acid, glutaric acid, adipic acid, sulfoisophthalic acid, diethylene glycol, propylene glycol, 1,4-butanediol, 2,2-bis(4-hydroxyethoxyphenyl)propane, bisphenol A, polyalkylene glycol, etc. can be used. The usable viscosity of the polymer in terms of relative viscosity measured with a 0.5% solution in a mixture of tetrachloroethane and phenol in a mass ratio of 1:1 at 20°C is about 1.3-1.6 (filament grade) to 1.7 (a high-viscosity resin prepared by solid-state polymerization). The higher the viscosity of the polymer, the greater the tear strength of the filament, which is the better.

The components constituting the filament of the present invention must form a mixture of polymers consisting of at least the immiscible components and having a melting point of at least 100°C. The reason why they should be immiscible has already been mentioned. The reason why the polymer components must have a melting point of at least 100°C is a practical determination. If the melting point is less than 100°C, the polymer will be melted by boiling water and the application possibilities are extremely limited. Therefore, the melting point should better be at least 120°C. The phrase "polymers consisting of at least the immiscible components" means that the aforementioned mixed polymer components account for at least 50% by mass in the filaments. If the proportion is less than 50% by mass, the properties of the polyolefin and polyester are lost, so such a proportion is not preferred.

In the filament of the present invention, the mass ratio of the polyolefin to the polyester should be 5:95 to 95:5. If the proportion of the polyolefin or the polyester is less than the above proportion, the properties of the polymer are lost, and therefore such a proportion is not preferred. More specifically, if the proportion of the polyolefin is less than 5 mass %, the brightness/lightness and tear strength of the filament decrease, and if the proportion of the polyester is less than 5 mass %, the modulus of the filament decreases, the rigidity and the feel during use and wear are not achieved, and the smooth feeling characteristic of polyolefin is not obtained. Therefore, the range of the blend ratio should be better between 15:85 and 85:15, and preferably between 25:75 and 75:25.

One of the methods of producing a filament with a braided structure according to the invention is explained below. The known flash spinning method can be used to produce the filament according to the invention. This method is explained in more detail below.

First, a mixture of polyolefin and polyester is dissolved at high temperature and high pressure in a solvent in which both polymers are insoluble at low temperatures but soluble at high temperatures and high pressure. After producing a single-bath phase, this is spun from nozzles under phase separation, so that the aforementioned filaments are created.

Examples of the solvent used for this purpose are known aromatic hydrocarbons such as benzene and toluene; aliphatic hydrocarbons such as butane, pentane and isomers and their homologues; alicyclic hydrocarbons such as cyclohexane; and unsaturated hydrocarbons. Other examples are halogenated hydrocarbons such as trichloromethane, methylene chloride, carbon tetrachloride, chloroform, 1,1-dichloro-2,2-difluoroethane, 1,2-dichloro-1,1-difluoroethane, methyl chloride, Ethyl chloride, etc. Other examples are alcohols, ethers, ketones, nitriles, amides, fluorocarbons, etc. Other examples are mixtures of the above solvents. In view of the new situation that global environmental pollution is a major problem, the use of solvents that could destroy the ozone layer should be particularly avoided. Also taking this environmental aspect into account, solvents that are preferably used for carrying out the present invention include methylene chloride, 1,1-dichloro-2,2-difluoroethane, 1,2-dichloro-1,1-difluoroethane, etc.

The range of polymer concentrations is not so definitely limited as it depends on the polymerization degree of the polymer, the type of solvent, pressure application, etc. However, they should be adjusted so that the concentration of polymers and solvent in the spinning solution is 5-30 mass% and 95-70 mass%, respectively. If the concentration of polymers is less than 5 mass%, it is difficult to obtain continuous filaments, and if it is more than 30 mass%, fibrillation does not occur, resulting in cylindrical filaments containing foam, so it is difficult to obtain fine-denier fibrillated filaments with high tear strength. When the concentration of the solvent is less than 70 mass%, the viscosity of the spinning solution becomes too high to dissolve the polymers homogeneously, so that fine-density fibrillated filaments tend to fail to form and the filaments have voids, and when the concentration of the solvent is more than 95 mass%, endless fibrillated threads with braid-like structure do not form, so such concentrations are not preferred.

To increase the spinning pressure, inert gas, such as nitrogen gas, should preferably be injected before or after the spinning solution is prepared. It is best to add the inert gas before the temperature is increased, as this prevents the degradation of the polymers and improves the ability to increase the temperature, which accelerates the solubility of the polymers in the solvent, resulting in very fine-titer filaments with a fibrillated, braid-like structure.

In the manufacture of the braided structure filament according to the present invention, elongation and orientation of the filament are carried out by means of the explosive force associated with the evaporation of the solvent, and the tensile strength of the filament is often determined by whether the filament is well stretched and oriented. The explosive force at this time is the evaporation force due to the speed at that time. The solvent is evaporated at a time within a period of not more than 0.1 second, and thereby an increase in the concentration of the polymers is achieved within a short time, and finally only the mixed polymers are precipitated. The mixed polymers precipitated by the evaporation of the solvent are cooled. For the tensile strength, this cooling step is extremely important, and in order to obtain filaments with high tensile strength, attention should be paid to fast flow cooling and elongation and orientation depending on the cooling rate. In a manufacturing process according to the invention, polymers that are not miscible with each other are used so that fibrillation is promoted by the fast flow, resulting in fine-denier fibrillated filaments.

Since immiscible polymers are used to carry out the process according to the invention, the polymers can be easily separated even when dissolved in the solvent, which is why a surfactant is preferably added. The addition of the surfactant serves to keep the spinning solution stable in the emulsified state. A non-ionic surfactant is normally used. Examples of surfactants are adducts of polyoxyethylene with lauryl alcohol, stearyl alcohol, oleyl alcohol, etc. and monoesters of lauric, stearic or oleic acid. The more homogeneous the solution mixture or the spinning solution is, the finer the titer of the fibrillated filaments with a braid-like structure.

When carrying out the process according to the invention, the dissolving and spinning temperature of the spinning solution is preferably in the range of 170 to 240°C. A reduction in viscosity in the presence of a solvent is particularly important for polyesters. If the temperature is greater than 240°C, the filaments may discolor or degradation may be accelerated, so that filaments with high tear strength cannot be obtained, so such temperatures are not preferred. If the temperature is lower than 170°C, very fine-denier fibrillated filaments are not produced, but cylindrical filaments with voids, so such temperatures are not preferred.

The duration of keeping the spinning solution in the dissolved state when carrying out the production process of the present invention is not definitely determined because it depends on the above-mentioned dissolving and spinning temperatures. At a high temperature, the holding time for dissolution must be kept as short as possible, and when the temperature is relatively low, the holding time for dissolution may be long. The holding time is preferably about 5 to 90 minutes. If the holding time for dissolving the spinning mixture is longer than 90 minutes, discoloration or heat degradation of the polyester is possible, so that the tensile strength of the filaments may decrease, and if this time is shorter than 5 minutes, the dissolution of the polymers is insufficient, resulting in the problem of clogging of the filter or problems in producing uniform filaments, so such times are not recommended.

The pressure for the spinning solution in which the polymers are dissolved is not usually specified, as it depends on the amount of solvent, the concentration of the polymers and the amount of inert gas introduced. It should generally be However, the pressure should not be less than 5884 kPa (60 kgf/cm²). If the pressure is lower than 5884 kPa (60 kgf/cm²), the explosive force during flash spinning is too low, so that the orientation of filaments is poor and filaments with high tensile strength cannot be obtained. In addition, spinning becomes uneven and there is a problem that highly fibrillated filaments are not continuously produced. Although there is no particular limitation on the upper limit of the pressure, it is preferably 17652 kPa (180 kgf/cm²) to avoid a decrease in the viscosity of the polymers.

When carrying out the flash spinning process, the spinning solution is spun under a self-generated pressure or via a pressure reduction chamber. Conventional spinnerets can be used as spinnerets.

To the polymers or the spinning solution, the agents normally used for filaments such as anti-glass agents, light stabilizers, heat stabilizers, pigments, fibril opening agents, weather stabilizers, UV absorbers, heat blockers, stabilizers, etc. may be added to the extent that they do not impair the effect of the present invention.

The nonwoven fabric with the finely fibrillated structure, in which the filaments are bonded over the entire surface in a braid-like structure, and a process for its production are explained in more detail below.

The nonwoven fabric is manufactured using the filaments with the aforementioned braid-like structure.

The term "nonwoven fabric with a dense structure" used here refers to a nonwoven fabric in which the apparent density is at least 0.2 g/cm³ and the aforementioned very fine-denier braid-like structure is densely consolidated.

The filaments that form the nonwoven fabric according to the invention are not miscible with one another, so that mainly fibrillated filaments made of very fine-density simple polymers are formed. The finer the filaments, the more densely structured the resulting nonwoven fabric is. As a result, the product according to the invention has a greater ability to act as a bacterial barrier, which does not allow smaller bacteria to pass through, than conventional nonwoven fabrics.

The nonwoven fabric according to the invention must be such that the filaments with a braid-like structure are bonded together over the entire surface. This means that the filaments with the very fine-density fibrillated structure are densely bonded in the bonded areas and the bonding does not only occur at specific points. In other words, the bonding occurs in the bonded areas of the very fine-density filaments, so that a nonwoven fabric with a high-density structure is created and this nonwoven fabric has excellent properties in terms of strength, bacterial barrier capacity, water impermeability pressure and moisture permeability.

The nonwoven fabric according to the invention preferably has a strength of at least 20 kgf/5 cm at a basis weight of 100 g/m². If the strength is lower than 20 kgf/5 cm, various areas cannot be used and the application possibilities of the nonwoven fabric are greatly limited.

Preferably, the moisture permeability, that is, the ability to disperse moisture, is at least 100 g/m²/h. If the moisture permeability is less than 100 g/m²/h, moisture is hardly dispersed, so when the nonwoven fabric is used as a garment or household packaging, moisture penetrates, causing water droplets to form, an unpleasant feel, or fungi to form, causing an unhygienic condition. Therefore, the higher the moisture permeability, the better.

The waterproofing pressure is preferably at least 50 cm. The waterproofing pressure is a parameter of how poorly a liquid such as water is allowed to pass through. If it is lower than 50 cm, liquids such as water and bacteria will penetrate the nonwoven fabric, so the bacterial barrier ability will be poorer and the product cannot be used as a material for hygienic protective clothing. Therefore, the higher the waterproofing pressure value, the better.

A method for producing the above-mentioned nonwoven fabric is described below.

In the production of the nonwoven fabric according to the invention, the filaments with a braid-like structure that form the nonwoven fabric should first be produced, whereby the aforementioned flash spinning process should be used.

When the mixed solution or dope is spun from the nozzles, the flash liquid and the deposited filaments impact the rotating plate, and after the filaments are vibrated in a net structure like twill, fibril opening occurs. The process of forming the filaments with a net-like structure has already been described. There are two ways for fibril opening. One is frictional electrification with the rotating plate and the other is subsequent corona discharge, and either of these ways or both may be used.

The filaments thus opened with a braid-like structure are collected on a conveyor belt and the resulting filament pile is solidified by applying heat and pressure with a group of rollers. The solidification conditions are as follows. The temperature must be at least as high as the difference "melting point of the polymer with the lowest melting point among the polymers forming the filaments - 40ºC" and must not be higher than this melting point, with the squeezing pressure in the axial direction of the rollers being 0.5 to 20 kp/cm. The exact conditions are finally determined accordingly. Solidification with pressure using a group of rollers at room temperature is more preferred and further Consolidation with pressure under the above conditions, as this achieves a strong bond in the bonding area between the filaments.

If a temperature lower than the difference "melting point of the polymer - 40ºC" is used in the final stage, the adhesion or bonding of all the filaments will decrease, so the tear strength of the nonwoven fabric will decrease, and if the consolidation with heat and pressure is carried out at a temperature higher than the melting point, the filaments will melt and the effect of the fine-denier fibrillated filaments produced will decrease. These temperatures are therefore not preferred.

If the squeezing pressure in the axial direction of the rollers is less than 0.5 kgf/cm, the adhesion of all filaments deteriorates and the tear strength of the nonwoven fabric decreases, and if it is greater than 20 kgf/cm, the filament layer tends to become paper-thin. Therefore, these pressures are not preferred.

For the above-mentioned roller group, steel, rubber and resin rollers are used together. When steel rollers are used, coating with fluoroethylene resin, rubber, etc. should be carried out to prevent abnormal gloss from being produced on the resulting nonwoven fabric. Two to thirty rollers can be used. It is best to use a conventional device called a calender roller device for this roller group.

In the nonwoven fabric according to the invention, the basis weight can be adjusted by changing the aforementioned vibration-like twill and the speed of the conveyor belt. The basis weight can be changed significantly by laying the formed pile or the nonwoven fabric.

Then, a nonwoven fabric with a fine fibrillated structure is produced according to the process described in detail below, in which the filaments with a braid-like structure are bonded together in such a way that numerous heat-bonded areas with certain distances between them are formed.

This nonwoven fabric can also be produced using the aforementioned filaments with a braid-like structure.

In this nonwoven fabric, the filaments with a braid-like structure must be partially bonded. This means that the very fine-denier filaments with a fibrillated network structure must be partially bonded to each other and also by a polymer, which is a low-melting component, in certain areas during mixed spinning. They are therefore not completely bonded. In other words, very fine-denier fibrillated filaments are partially bonded by the polymer, which is a low-melting component, so that the shape of the nonwoven fabric is maintained. The filaments where no partial bonding occurs consist of very fine-denier filaments with a fibrillated braid-like structure. Therefore, the resulting nonwoven fabric is, despite its dense structure, soft and has excellent tear resistance and moisture permeability. In addition, due to this dense structure, it is naturally bacteria-proof.

This state of partial bonding can be expressed by the proportion of the bonded areas to the total area of the nonwoven fabric obtained. This proportion is determined as follows. Namely, a small piece of the nonwoven fabric is photographed using a scanning electron microscope, and ten measurements of the proportion of the sum of the bonded areas to the area of the minimum repeat unit are averaged. Preferably, the proportion of the bonded areas to the total area is not more than 50%. If the proportion is more than 50%, the bonded area becomes too large, which limits the freedom of the unfixed filaments in the nonwoven fabric and tends to make the nonwoven fabric hard, i.e., lack softness. On the other hand, if the proportion is too low, the shape of the nonwoven fabric deteriorates. Therefore, from a practical point of view, the proportion should be at least 4%. Taking the above into account, the range is preferably 5 to 30%.

The state of this partial bonding can also be expressed by the density of the bonding areas. The density of the bonding areas is calculated as follows. Namely, a small piece of the nonwoven fabric is photographed using a scanning electron microscope, and the ratio of the sum of each bonding area to the area of the minimum repeat unit is determined in cm2; this measurement is repeated ten times and the average is calculated. The density of the bonding areas is preferably 15 to 120/cm2. If it is less than 15/cm2, the shape of the nonwoven fabric is unfavorable and, in addition, the rubbing fastness of the nonwoven fabric decreases, which leads to the problem of furring. Therefore, the higher the density of the bonding areas, the fewer the practical problems and the better it is. However, if the density is too high, the nonwoven fabric may have a hard touch and no softness. The preferred density is therefore not more than 120/cm². In view of the above, the range is better 20 to 100/cm² and most preferably 30 to 90/cm².

Both the proportion of bonding areas in the total area and the density of the bonding areas should ideally be in the aforementioned ranges.

The bonding areas can be circular, elliptical, diamond-shaped, triangular, T-shaped, I-shaped, parallel-crossed or grid-shaped.

The preferred property of the nonwoven fabric is that the strength calculated for 100 g/m² is at least 5 kgf/5 cm. If the strength is less than 5 kgf/5 cm, there may be problems in practical use and the application possibilities of the nonwoven fabric are quite limited.

The compression softness is preferably not more than 200 g. The compression softness represents the softness of the nonwoven fabric, and the lower its value is, the softer the product is. This compression softness is determined as follows. Namely, five samples of the nonwoven fabric with a width of 50 mm in the direction of the device (longitudinal direction) and a length of 100 mm perpendicular to this direction are prepared, each sample is bent sideways to form a hollow cylinder, the two ends of which are glued, the resulting sample is compressed with a Tensilon UTM-4-1-100 (Toyo Baldwin) in the axial direction at a speed of 50 mm/minute, the tension at maximum load is measured, the average value of which is divided by the mass of the nonwoven fabric, and the value calculated for 100 g/m2 is the compression softness. The softness when squeezing the non-woven fabric should not be more than 200g, otherwise the softness will decrease and the non-woven fabric will become hard. It is better not to be more than 160g, or preferably not to be more than 120g.

The preferred moisture permeability is at least 100 g/m²/h. Moisture permeability shows the ability to disperse moisture, and the higher the value, the better the property. If the moisture permeability is less than 100 g/m²/h, moisture is hardly dispersed, so when the nonwoven fabric is used as clothing or household packaging, moisture will penetrate, causing water droplets to condense, causing an unpleasant touch or fungi to form, causing an unhygienic condition. Therefore, the higher the moisture permeability, the better.

The basis weight of the nonwoven fabric can be up to 500 g/m² and is normally between 20 and 200 g/m².

A method for producing the nonwoven fabric is described below.

When producing the nonwoven fabric, the filaments with a braid-like structure that form the nonwoven fabric must first be produced. The aforementioned flash spinning process is used to produce the filaments with a mesh structure.

When the spinning solution is spun from the nozzles, the flash liquid and the deposited filaments hit the rotating plate, the braid-like filaments are vibrated like twill and fibril opening takes place. The process of forming the braid-like filaments has been described previously. There are two ways for fibril opening. One is frictional electrification with the rotating plate and the other is subsequent corona discharge, and either or both of these ways can be used.

The filaments thus opened with a braid-like structure are collected on a conveyor belt and the resulting filament pile is Embossing rolling device partially solidifies by applying heat and pressure. Examples of embossing rolling devices are the heat embossing device and the pin sonic processing device operating on the basis of ultrasonic waves.

The conditions for heat and pressure bonding using a heat embosser are as follows. The temperature must be at least as high as the difference of "melting point - 40ºC" and must not be higher than the melting point of the polymer with the lowest melting point among the polymers forming the filaments. The squeezing pressure in the axial direction of the rollers is in the range of 0.5 to 50 kgf/cm. Processing can be carried out at the squeezing pressure in the above range with a gap of 0.02-0.2 mm. The gap is determined according to the purpose of use to avoid thinning by completely fusing the bonding area with the roller. In addition, embossing under the above conditions should be carried out after pre-bonding with heat and pressure using rollers at room temperature to avoid irregularity in the fibrillated filament pile. In embossing, if the consolidation is carried out with heat and pressure at a temperature higher than the melting point of the polymer, the filaments are sometimes melted, causing the pile to wrap around the roller and not forming a web. In addition, there is an undesirable tendency for the very fine denier filaments to fuse with a braid-like structure, thus reducing the effect of the very fine denier fibrillated filaments. On the other hand, in the final stage, the use of a temperature lower than the difference "melting point of the polymer - 40ºC" is not preferred, since it reduces the bonding between the filaments, thus reducing the strength of the nonwoven fabric.

For the squeezing pressure in the axial direction of the rollers, a value lower than 0.5 kp/cm is not preferred, as this reduces the bonding between the filaments in the bonding areas, which reduces the strength of the nonwoven fabric. A pressure of more than 50 kp/cm is also not preferred, as the bonding area becomes extremely thin and, in the worst case, the nonwoven fabric becomes full of holes.

For example, the conditions for heat and pressure bonding using a pin sonic processing device are that the filaments are partially bonded by vibrating them with ultrasonic waves of about 20 kHz, so that the state of the nonwoven fabric is maintained. The degree of heat bonding can be changed appropriately by changing the amplitude of the ultrasonic waves. By using the method of heat bonding with ultrasonic waves, when the pile is bonded with high heat bonding ability, areas other than the bonding areas are hardly affected, and therefore the nonwoven fabric as a whole can be kept in such a state that the heat shrinkage properties can still be maintained. Thus, when producing a nonwoven fabric with high heat shrinkage, the effect can be achieved even more effectively.

The embossing shape of these embossing devices is usually formed by an embossing roller with a projecting pattern and a smooth roller. The projecting pattern can be formed by controlling the aforementioned ratio of the bonding area and the density of the bonding area. The final shape of the projecting area of the engraved roller can be circular, ellipse-like, diamond-shaped, triangular, T-shaped, I-shaped, parallel-crossed or lattice-shaped.

Other embossings may be carried out under the above or other conditions before or after the above embossing or calendering may be carried out simultaneously if these processes do not lie outside the scope of the present invention.

Detailed description of the preferred embodiments

The present invention is explained in more detail below with reference to the following examples. Measurements and evaluations of various properties in the following examples were carried out by the following methods. Melting point of the polymer:

A differential scanning calorimeter (DSC-2, Parkin Elmer) was used and the temperature giving the polar value of the melt absorption curve measured at a ramp rate of 20ºC/min was set as the melting point.

Filament fineness:

The degree of fineness based on the corrected basis weight was measured according to JIS L-1090.

Tensile strength and elongation of the filament:

A Tensilon (UTM-4-1-100 from Toyo Baldwin) was used. A specimen with a length of 10 cm was twisted 20 times/5 cm for a clamping length of 5 cm and the strength and elongation were measured at a pulling speed of 5 cm/min. The measured strength was divided by the above-mentioned fineness to obtain the strength of the filament. The measurements were carried out twenty times and the average was determined.

Filament module:

When measuring the above strength and elongation of the filament, the initial tensile strength (g/dtex) was determined according to JIS L-1013 7.10 (Measurement of initial tensile strength) and set as the modulus value.

Specific surface:

The specific surface area (m2/g) of the filament was measured by BET nitrogen absorption using a Belsorp 28 from Nippon Bel KK.

Dyeability of the filament:

The filament was dyed by the dispersion dyeing or cationic dyeing method described below, then reduced dyed, washed with water and dried, and the dyeability of the filament was evaluated as follows: : very good, ○: good, Δ: relatively good, x: poor.

Dispersion dyeing: Blue E-FBL (a disperse dye from Sumitomo Chemical) (1 mass%), 1 g of dispersant (Disper-TL, from Meisei Kagaku) per liter and 0.1 g of formic acid (as a complementary agent) per liter were mixed and the filament was dyed by boiling for 60 minutes at a volume ratio of 1:50.

Cationic dyeing: Astrazon Blue FFR (a cationic dye from Bayer) (1 mass%), 0.5 g of mixed dye (Migregal WA-10, from Senka) per liter and 10 mass% sodium sulfate (as a complementary agent) were mixed and the filament was dyed by boiling for 60 minutes at a volume ratio of 1:50.

Reduced dyeing: Sanmole RL-100 (a refining agent from Nikka Kagaku KK) (1 g/l), 2 g of hydrosulfite per liter and 1 g of sodium hydroxide per liter were mixed and the filament was treated with the mixture at 80ºC for 20 minutes in a volume ratio of 1:50.

KS strength and tensile elongation of the nonwoven fabric:

A Tensilon (UTM-4-1-100, made by Toyo Baldwin) was used. Ten specimens each with a width of 5 cm and a length of 20 cm were prepared according to a peeling method specified in JIS L-1096, and the measurement was carried out with a clamping length of 10 cm and a pulling speed of 10 cm/min. The maximum tensile strength for each specimen was averaged and calculated for 100 g/m² to obtain the KS strength. Then, the average value of the maximum elongation was determined. This average value was the tensile elongation of the nonwoven fabric.

Apparent density of the nonwoven fabric:

Five specimens each with a width of 10 cm and a length of 10 cm were prepared, the mass of each specimen was determined, then a load of 4.5 g/cm2 was applied, the thickness was measured with a thickness gauge (made by Daiei Kagaku Seiki Seisakusho) after standing for 10 minutes, the apparent density was calculated using the following formula, and the average value was the apparent density of the nonwoven fabric:

Apparent density (g/cm³) = Basis mass (g/m²)/Thickness (mm)/1000

Moisture permeability of the nonwoven fabric:

According to the provisions of JIS L-1099-A-1, the moisture permeability (g/m²/h) was measured at a temperature of 40ºC and a humidity of 90%. Dyeability of the nonwoven fabric:

The procedures for dyeing and evaluating the nonwoven fabric were the same as for the filament.

Examples of filaments are given below.

example 1

Into a 500 cc autoclave were charged 20 g of high density polyethylene having a melting point of 132°C, a density of 0.96 g/cm3 and a melt index of 0.8 g/10 min, 30 g of polyethylene terephthalate having a melting point of 256°C and a relative viscosity of 1.6 and methylene chloride (a solvent). In addition, 0.2 mass % each (based on the above polymer mixture) of polyoxyethylene (POE, 3 mol) lauryl ether and isotridecyl stearate were added as surfactants. Then, the autoclave was closed, nitrogen was introduced into the autoclave until the pressure became 3923 kPa (40 kgf/cm2), and the mixture was stirred at an appropriate rate while heating. The concentration in the solution was 20 mass% for the polymers and 80 mass% for the solvent.

The time required for the temperature to rise from 100 to 220ºC was 25 minutes. When the temperature reached 220ºC, the mixture was further stirred for 10 minutes to obtain a homogeneous solution. The gauge pressure at this time was 10787 kPa (110 kgf/cm²). The valve on a continuous injector was then immediately opened to supply compressed nitrogen gas to maintain the pressure in the autoclave at 10787 kPa (110 kgf/cm²). The solution was then spun into the air from the nozzles provided with a pressure-reducing chamber (hole diameter: 0.75 mm, L (length)/D (diameter): 1). The pressure in the pressure-reducing chamber was 9022 kPa (92 kgf/cm²).

The resulting filaments were very well fibrillated. No discoloration of the filaments was observed and the strength and modulus were high. The filaments were dyed with a disperse dye and were found to be well dyed. The filaments had the following properties:

Tensile strength: 4.36 g/dtex (4.85 g/d)

Elongation: 64%

Module: 15 g/dtex (16.7 g/d)

Specific surface: 31 m²/g

Example 2

In the same autoclave as in Example 1 were added 20 g of polypropylene with a melting point of 162ºC, a density of 0.910 g/cm3 and a melt index of 4 g/10 min, 30 g of polyethylene terephthalate with a melting point of 256ºC and a relative viscosity of 1.7 and methylene chloride (a solvent).

In addition, 0.2 mass % (based on the polymer mixture) of POE (3 mol) lauryl ether and isooctyl laurate were added as surfactants. Then, the autoclave was closed, nitrogen was introduced into the autoclave until the pressure was 4903 kPa (50 kgf/cm2), and the mixture was stirred at an appropriate rate while heating. The concentration in the solution was 20 mass % for the mixed polymer and 80 mass % for the solvent.

The time required for the temperature to rise from 100 to 200ºC was 30 minutes. When the temperature reached 200ºC, the mixture was further stirred for 10 minutes to obtain a homogeneous solution. The gauge pressure at this time was 10297 kPa (105 kgf/cm²). The valve on a continuous injector was then immediately opened to supply compressed nitrogen gas to maintain the pressure in the autoclave at 10297 kPa (105 kgf/cm²) and the solution was spun into the air from the nozzles with a diameter of 0.75 mm and a UD ratio of 1, equipped with a pressure-reducing chamber. The pressure in the pressure-reducing chamber was 8336 kPa (85 kgf/cm²).

The resulting filaments were well fibrillated and not discolored and had high strength and high modulus. The filaments were dyed with a disperse dye and were found to be well colored. The filaments had the following properties:

Tensile strength: 3.12 g/dtex (3.47 g/d)

Stretch: 50%

Module: 16.74 g/dtex (18.6 g/d)

Specific surface area: 29 m²/g

Except that polyethylene terephthalate copolymerized with 5 mol% of sulfoisophthalic acid (melting point: 247°C, relative viscosity: 1.3) was used and that the dissolving and spinning temperature for preparing filaments was 200°C, the same steps as in Example 2 were carried out. The pressure at dissolving was 10297 kPa (105 kgf/cm²) and the pressure in the pressure-reducing chamber was 8434 kPa (86 kgf/cm²).

The resulting filaments were well fibrillated and not discolored and had high strength and modulus. The filaments were dyed with a cationic dye and it was found that only the polyester component was well colored. The filaments had the following properties:

Tensile strength: 4.01 g/dtex (4.53 g/d)

Stretch: 69%

Module: 12.7 g/dtex (14.1 g/d)

Specific surface area: 38 m²/g

Examples 4-8 and comparative examples 1-2

In the same autoclave as in Example 1, high-density polyethylene (melting point: 132ºC, density: 0.96 g/cm³, melt index: 0.6 g/10 min) and polyethylene terephthalate (melting point: 256ºC, relative viscosity: 1.4) were added in various mixing ratios and 200 g of methylene chloride (a solvent). In addition, 0.2 mass % each (based on the above polymer mixture) of POE (3 mol) lauryl ether and isooctyl laurate were added as surfactants. Then, the autoclave was closed, nitrogen was introduced into the autoclave until the pressure became 4903 kpA (50 kp/cm²), and the mixture was stirred at an appropriate rate while being heated.

The concentrations of each component are shown in Table 1. The time required for the temperature to rise from 100 to 200ºC was 35 minutes. When the temperature reached 200ºC, the mixture was further stirred for 10 minutes to obtain a homogeneous solution. The gauge pressure at this time was 10787 kPa (110 kgf/cm²). The valve on a continuous injector was then immediately opened to supply compressed nitrogen gas to maintain the pressure in the autoclave at 10787 kPa (110 kgf/cm²), and the solution was spun into the air from the nozzles (diameter: 0.75 mm, L/D = 1) equipped with a pressure-reducing chamber.

The results are presented in Table 1. Table 1

PET: Polyethylene terephthalate

PE: High density polyethylene

It is clear from Table 1 that in the examples of the present invention, there was a tendency that the higher the content of polyester, the better the dyeability with a disperse dye, and the resulting filaments were very well fibrillated and not discolored, and had high strength and high modulus.

In Comparative Example 1, the resulting filaments were well fibrillated and their strength and modulus were relatively high, but since it did not contain any polyester, they could not be dyed well with a disperse dye. In Comparative Example 2, on the other hand, since it did not contain any polyethylene, the filaments could be dyed well, but they were not so well fibrillated and their strength and modulus were low.

Example 9

Filaments were prepared under the same conditions as in Example 6, except that polybutylene terephthalate (melting point: 228ºC, relative viscosity: 1.7) was used and the dissolving and spinning temperature was 200ºC. The pressure at dissolving was 10983 kPa (112 kgf/cm²) and the pressure in the pressure-reducing chamber was 9120 kPa (93 kgf/cm²).

The resulting filaments were very well fibrillated and not discolored and had high strength and high modulus. The filaments were dyed with a disperse dye and were found to be well colored. The filaments had the following properties:

Tensile strength: 4.16 g/dtex (4.62 g/d)

Stretch: 63%

Module: 12.2 g/dtex (13.6 g/d)

Specific surface area: 38 m²/g

Example 10

In a 10-liter autoclave, 600 g of high-density polyethylene (melting point: 132°C, density: 0.96 g/cm³, melt index: 0.8 g/10 min), 900 g of polyethylene terephthalate (melting point: 256°C, relative viscosity: 1.7) and methylene chloride (a solvent) were charged. In addition, 0.2 mass % (based on the above polymer mixture) each of POE (3 mol) lauryl ether and isotridecyl stearate were added. Then, the autoclave was closed, nitrogen was introduced into the autoclave until the pressure became 1961 kPa (20 kgf/cm²), and the mixture was stirred at an appropriate rate while heating. The concentration in the solution was 20 mass % for the polymers and 80 mass % for the solvent.

The time required for the temperature to rise from 100 to 220ºC was 40 minutes. When the temperature reached 220ºC, the mixture was further stirred for 10 minutes to obtain a homogeneous solution. The gauge pressure at this time was 10689 kPa (109 kgf/cm²). Three valves were then opened on a continuous injector to supply compressed nitrogen gas to maintain the pressure in the autoclave at 10787 kPa (110 kgf/cm²). The solution was then spun from three nozzles (diameter: 0.75 mm, L/D = 1) equipped with a pressure-reducing chamber. The filaments were impacted on a rotating plate, opened and collected on a moving conveyor belt net to obtain pile. The pressure in the pressure reduction chamber was 9022 kPa (92 kp/cm²).

Then, the web was laid and passed through an oil pressure spacer calendering machine with three pairs of rollers to obtain a nonwoven fabric with a basis weight of 50 g/m². All surfaces of the upper rollers of this calender were made of polyurethane rubber, while the lower rollers were heating rollers whose steel surface was coated with fluorine resin. For the first, second and third rollers, the temperature was 60, 120 and 125ºC, respectively, and the squeezing pressure in the axial direction of the roller was 0.3, 0.8 and 1.5 kgf/cm, respectively.

The resulting nonwoven fabric had very good filament fibrillation without discoloration. In addition, the filaments were solidified over the entire area, so the strength of the nonwoven fabric was high, and the moisture permeability and waterproofing pressure were also high. It was also found that the nonwoven fabric had good dyeability when dyed with a disperse dye. The nonwoven fabric had the following properties:

Specific surface: 31 m²/g

KS strength of the nonwoven fabric (MR/QR): 38.4/39.8 kp/5 cm (MR: machine direction, QR: cross direction)

Elongation of the nonwoven fabric (MR/QR): 18/26%

Apparent density: 0.40 g/cm³

Moisture permeability: 280 g/m²/h

Waterproofing pressure: 180 cm H₂O

Dyeability:

Example 11

In the same autoclave as in Example 10, 400 g of polypropylene (melting point: 162ºC, density: 0.910 g/cm³, melt index: 4 g/10 min), 1100 g of polyethylene terephthalate (melting point: 256ºC, relative viscosity: 1.6) and methylene chloride (a solvent) were added. In addition, 0.2 mass % (based on the POE(3 mol) lauryl ether and isooctyl laurate were added as surfactants to the polymer mixture. The autoclave was then closed, nitrogen was introduced into the autoclave until the pressure was 3923 kPa (40 kp/cm²), and the mixture was stirred at an appropriate rate while being heated. The concentration in the solution was 20% by mass for the polymer mixture and 80% by mass for the solvent.

The time required for the temperature to rise from 100 to 200ºC was 30 minutes. When the temperature reached 200ºC, the mixture was further stirred for 10 minutes to obtain a homogeneous solution. The gauge pressure at this time was 11572 kPa (118 kgf/cm²). Three valves were then immediately opened on a continuous injector to supply compressed nitrogen gas to maintain the pressure in the autoclave at 11768 kPa (120 kgf/cm²). The solution was then spun from three nozzles (hole diameter: 0.75 mm, L/D = 1) equipped with a pressure-reducing chamber. The filaments were impacted on a rotating plate, opened and collected on a moving conveyor belt net to obtain pile. The pressure in the depressurization chamber was 9709 kPa (99 kgf/cm²). Then the web was laid and the same steps as in Example 10 were carried out, except that for the first, second and third rollers, the temperature was 60, 150 and 155ºC, respectively, to produce nonwoven fabric having a basis weight of 100 g/m².

The resulting nonwoven fabric had very good filament fibrillation without discoloration. In addition, the filaments were bonded over the entire area, so the strength of the nonwoven fabric was high, and the moisture permeability and waterproofing pressure were also high. It was also found that the nonwoven fabric had good dyeability when dyed with a disperse dye. The nonwoven fabric had the following properties:

Specific surface area: 29 m²/g

KS strength of the nonwoven fabric (MR/QR): 32.3/33.6 kp/5 cm

Elongation of the nonwoven fabric (MR/QR): 22/29%

Apparent density: 0.47 g/cm³

Moisture permeability: 263 g/m²/h

Waterproofing pressure: 159 cm H₂O

Dyeability:

Example 12

Except that polyethylene terephthalate copolymerized with 5 mol% sulfoisophthalic acid (melting point: 247ºC, relative viscosity: 1.3) was used and that the dissolving and spinning temperature was 200ºC, Nonwoven fabric was prepared under the same conditions as in Example 11. The pressure during dissolution was 11670 kPa (119 kgf/cm²) and the pressure in the pressure reduction chamber was 9807 kPa (100 kgf/cm²).

The resulting nonwoven fabric had very good filament fibrillation without discoloration. In addition, the filaments were bonded over the entire area, so the strength of the nonwoven fabric was high, and the moisture permeability and waterproofing pressure were also high. It was also found that the nonwoven fabric had good dyeability when dyed with a cationic dye. The nonwoven fabric had the following properties:

Specific surface area: 28 m²/g

KS strength of the nonwoven fabric (MR/QR): 29.2/30.1 kp/5 cm

Elongation of the nonwoven fabric (MR/QR): 17/25%

Apparent density: 0.39 g/cm³

Moisture permeability: 278 g/m²/h

Waterproofing pressure: 172 cm H₂O

Dyeability:

Examples 13-17 and comparative examples 3-4

In the same autoclave as in Example 10, high density polyethylene (melting point: 132°C, density: 0.96 g/cm³, melt index: 0.6 g/10 min) and polyethylene terephthalate (melting point: 256°C, relative viscosity: 1.4) were added in various mixing ratios and 6200 g of methylene chloride each as a solvent. In addition, 0.2 mass % (based on the above polymer mixture) of POE (3 mol) lauryl ether and isooctyl laurate each were added. Then, the autoclave was closed, nitrogen was introduced into the autoclave until the pressure was 3923 kpA (40 kp/cm²), and the mixture was stirred at an appropriate rate while heating.

The concentrations of each component in the solution are shown in Table 2. The time required for the temperature to rise from 100 to 200ºC was 35 minutes. When the temperature reached 200ºC, the mixture was further stirred for 10 minutes to obtain a homogeneous solution. The gauge pressure at this time was 10787 kPa (110 kgf/cm²). Three valves on a continuous injector were then immediately opened to supply compressed nitrogen gas to maintain the pressure in the autoclave at 10787 kPa (110 kgf/cm²). The solution was then spun, and in the same manner as in Example 10, pile was prepared and nonwoven fabric was obtained.

The results are presented in Table 2. Table 2

PET: Polyethylene terephthalate

PE: High density polyethylene

From Table 2, in Examples 13-17, there was a tendency that the higher the proportion of polyester was, the better the dyeability with a disperse dye was, and the resulting nonwoven fabrics had very good filament fibrillation and were not discolored. In addition, the filaments were bonded over the entire area, so the strength of the nonwoven fabric was high, and the moisture permeability and waterproof pressure were also high.

In Comparative Example 3, the resulting nonwoven fabric had good filament fibrillation and its strength was relatively high, but since it did not contain any polyester at all, it did not dye well.

On the other hand, in Comparative Example 4, although the resulting nonwoven fabric could be dyed well with a disperse dye because it did not contain any polyethylene at all, it was not so well fibrillated and its strength, moisture permeability and waterproof pressure were low.

Example 18

Except that polybutylene terephthalate (melting point: 228°C, relative viscosity: 1.7) was used and the dissolving and spinning temperature was 200°C, nonwoven fabric was prepared under the same conditions as in Example 15. The pressure at dissolving was 10983 kPa (112 kgf/cm²) and the pressure in the pressure-reducing chamber was 9120 kPa (93 kgf/cm²).

The resulting nonwoven fabric had very good filament fibrillation without discoloration. In addition, the filaments were bonded over the entire area, so the strength of the nonwoven fabric was high, and the moisture permeability and waterproofing pressure were also high. It was also found that the nonwoven fabric had good dyeability when dyed with a disperse dye. The nonwoven fabric had the following properties:

Specific surface: 31 m²/g

KS strength of the nonwoven fabric (MR/QR): 36.3/37.4 kp/5 cm

Elongation of the nonwoven fabric (MR/QR): 21/29%

Apparent density: 0.37 g/cm³

Moisture permeability: 292 g/m²/h

Waterproofing pressure: 191 cm H₂O

Dyeability:

Example 19

In a 10-liter autoclave, 600 g of high-density polyethylene (melting point: 132°C, density: 0.96 g/cm³, melt index: 0.8 g/10 min), 900 g of polyethylene terephthalate (melting point: 256°C, relative viscosity: 1.7) and methylene chloride (a solvent) were charged. In addition, 0.2 mass % (based on the above polymer mixture) of isooctyl stearate and isostearyl ester were added as surfactants. Then, the autoclave was closed, nitrogen was introduced into the autoclave until the pressure became 1961 kPa (20 kgf/cm²), and the mixture was stirred at an appropriate rate while heating. The concentration in the solution was 20 mass % for the polymers and 80 mass % for the solvent.

The time required for the temperature to rise from 100 to 220ºC was 40 minutes. When the temperature reached 220ºC, the mixture was further stirred for 10 minutes to obtain a homogeneous solution. The gauge pressure at this time was 10689 kPa (109 kgf/cm²). Three valves were then opened on a continuous injector to supply compressed nitrogen gas to maintain the pressure in the autoclave at 10787 kPa (110 kgf/cm²). The solution was then spun from three nozzles (hole diameter: 0.75 mm, L/D = 1) equipped with a pressure-reducing chamber. The filaments were impacted on a rotating plate, opened and collected on a moving conveyor belt net to obtain pile. The pressure in the pressure reduction chamber was 9022 kPa (92 kp/cm²).

Then, the pile was laid and passed through an oil pressure spaced embossing machine to obtain a nonwoven fabric with a basis weight of 50 g/m². The upper roller of the embossing machine was an engraved roller while the lower one was a smooth roller, and both were heating rollers. With a squeezing pressure in the axial direction of the roller of 20 kgf/cm, a temperature of 125ºC and a speed of 10 m/min, the pile was embossed without a space between the upper and lower rollers. The proportion of the area bonded by the engraved roller was 25% and the density of the bonded area was 60/cm².

The resulting nonwoven fabric had very good filament fibrillation without discoloration. In addition, the filaments were in a structure with numerous small pressure-bonded areas, so that the nonwoven fabric had excellent softness and moisture permeability with practically sufficient strength. It was also found that the nonwoven fabric was easily dyeable when dyed with a disperse dye. The nonwoven fabric had the following properties:

Specific surface: 31 m²/g

KS strength of the nonwoven fabric (MR/QR): 17.3/18.6 kp/5 cm

Tensile elongation of the nonwoven fabric (MR/QR): 28/31%

Apparent density: 0.28 g/cm³

Softness when squeezed: 125 g

Moisture permeability: 250 g/m²/h

Dyeability:

Example 20

In the same autoclave as in Example 19, 400 g of polypropylene (melting point: 162°C, density: 0.910 g/cm³, melt index: 4 g/10 min), 1100 g of polyethylene terephthalate (melting point: 256°C, relative viscosity: 1.6) and methylene chloride (a solvent) were charged. In addition, 0.2 mass % (based on the above polymer mixture) of isooctyl stearate and isostearyl ester were each added as surfactants. Then, the autoclave was closed, nitrogen was introduced into the autoclave until the pressure became 3923 kpA (40 kgf/cm²), and the mixture was stirred at an appropriate rate while heating. The concentration in the solution was 20 mass % for the polymer mixture and 80 mass % for the solvent.

The time required for the temperature to rise from 100 to 200ºC was 30 minutes. When the temperature reached 200ºC, the mixture was further stirred for 10 minutes to obtain a homogeneous solution. The gauge pressure at this time was 11572 kPa (118 kgf/cm²). Three valves were then opened on a continuous injector to supply compressed nitrogen gas to maintain the pressure in the autoclave at 11768 kPa (120 kgf/cm²). The solution was then spun from three nozzles (hole diameter: 0.75 mm, L/D = 1) equipped with a pressure-reducing chamber. The filaments were impacted on a rotating plate, opened and collected on a moving conveyor belt net to obtain pile. The pressure in the depressurization chamber was 9709 kPa (99 kgf/cm²). Then, the web was laid and treated in the same manner as in Example 19 except that the embossing temperature was 150ºC, to obtain nonwoven fabric having a basis weight of 100 g/m².

The resulting nonwoven fabric had very good filament fibrillation without discoloration. In addition, the filaments were in a structure with numerous small pressure-bonded areas, so that the nonwoven fabric had excellent softness and moisture permeability with practically sufficient strength. It was also found that the nonwoven fabric was easily dyeable when dyed with a disperse dye. The nonwoven fabric had the following properties:

Specific surface area: 29 m²/g

KS strength of the nonwoven fabric (MR/QR): 16.2/17.7 kp/5 cm

Tensile elongation of the nonwoven fabric (MR/QR): 30/33%

Apparent density: 0.29 g/cm³

Softness when squeezed: 120 g

Moisture permeability: 231 g/m²/h

Dyeability:

Example 21

Except that polyethylene terephthalate copolymerized with 5 mol% of sulfoisophthalic acid (melting point: 247°C, relative viscosity: 1.3) was used and that the dissolving and spinning temperature was 200°C, nonwoven fabric was prepared under the same conditions as in Example 20. The pressure at dissolving was 11670 kPa (119 kgf/cm²) and the pressure in the pressure-reducing chamber was 9807 kPa (100 kgf/cm²).

The resulting nonwoven fabric had very good filament fibrillation without discoloration. In addition, the filaments were in a structure with numerous small pressure-bonded areas, so that the nonwoven fabric had excellent softness and moisture permeability with practically sufficient strength. It was also found that the nonwoven fabric was easily dyeable when dyed with a cationic dye. The nonwoven fabric had the following properties:

Specific surface area: 28 m²/g

KS strength of the nonwoven fabric (MR/QR): 14.5/15.7 kp/5 cm

Tensile elongation of the nonwoven fabric (MR/QR): 37/39%

Apparent density: 0.30 g/cm³

Softness when squeezed: 118 g

Moisture permeability: 247 g/m²/h

Dyeability:

Examples 22-26 and comparative examples 5-6

In the same autoclave as in Example 19, high density polyethylene (melting point: 132ºC, density: 0.96 g/cm³, melt index: 0.6 g/10 min) and polyethylene terephthalate (melting point: 256ºC, relative viscosity: 1.4) were added in various mixing ratios and 6200 g of methylene chloride each as a solvent. In addition, 0.2 mass % (based on the above polymer mixture) of isooctyl stearate and isostearyl ester each as a surfactant were added. Then, the The autoclave was closed, nitrogen was introduced into the autoclave until the pressure was 3923 kpA (40 kp/cm²), and the mixture was stirred while heated at an appropriate rate.

The concentrations of each component are shown in Table 3. The time required for the temperature to rise from 100 to 200°C was 35 minutes. When the temperature reached 200°C, the mixture was further stirred for 10 minutes to obtain a homogeneous solution. The gauge pressure at this time was 10787 kPa (110 kgf/cm²). Three valves on a continuous injector were then immediately opened to supply compressed nitrogen gas to maintain the pressure in the autoclave at 10787 kPa (110 kgf/cm²). The solution was then spun and pile was formed in the same manner as in Example 19 to produce nonwoven fabric.

The results are presented in Table 3. Table 3

PET: Polyethylene terephthalate

PE; high density polyethylene

From Table 3, in Examples 22-26, there was a tendency that the higher the proportion of polyester was, the better the dyeability with a disperse dye was, and the resulting nonwoven fabrics had very good filament fibrillation and were not discolored. In addition, the filaments were in a structure with numerous small pressure-bonded areas, so that the nonwoven fabrics had excellent softness and moisture permeability with practically sufficient strength. It was also found that the nonwoven fabrics had good dyeability when dyed with a disperse dye.

In Comparative Example 5, the resulting nonwoven fabric had good filament fibrillation and its strength was relatively high, but since it did not contain any polyester at all, it did not dye well.

In contrast, in Comparative Example 6, although the resulting nonwoven fabric could be dyed well with a disperse dye since it did not contain any polyethylene at all, it was not so well fibrillated and its strength and moisture permeability were low.

Example 27

Except that polybutylene terephthalate (melting point: 228°C, relative viscosity: 1.7) was used and the dissolving and spinning temperature was 200°C, nonwoven fabric was prepared under the same conditions as in Example 24. The pressure at dissolving was 10983 kPa (112 kgf/cm²) and the pressure in the pressure-reducing chamber was 9120 kPa (93 kgf/cm²).

The resulting nonwoven fabric had very good filament fibrillation without discoloration. In addition, the filaments were in a structure with numerous small pressure-bonded areas, so that the nonwoven fabric had excellent softness and moisture permeability with practically sufficient strength. It was also found that the nonwoven fabric was easily dyeable when dyed with a disperse dye. The nonwoven fabric had the following properties:

Specific surface: 31 m²/g

KS strength of the nonwoven fabric (MR/QR): 15.3/16.5 kp/5 cm

Tensile elongation of the nonwoven fabric (MR/QR): 37/39%

Apparent density: 0.27 g/cm³

Softness when squeezed: 109 g

Moisture permeability: 262 g/m²/h

Dyeability:

Examples 28-34

When producing the nonwoven fabric in Example 25, the type of embossing roll was changed so that the ratio and density of the bonding areas changed. The results are shown in Table 4.

From Table 4, it is clear that the nonwoven fabrics of Examples 28-33 had excellent softness and moisture permeability with practically sufficient strength, with a tendency that the larger the ratio and density of the bonding area, the higher the strength and the lower the softness.

In Example 34, the proportion of the bonded area was 100% because the compression bonding was only carried out with a smooth roller. As a result, the resulting nonwoven fabric had a slightly lower softness, but still showed practically sufficient strength and moisture permeability. Table 4

PET: Polyethylene terephthalate

PE: high density polymer

Claims (19)

1. A filament having a fine fibrillated structure, which is a flash-spun filament having a braid-like structure and comprising a polyolefin component having a braid-like filament structure, characterized in that it further comprises a polyester component having a braid-like filament structure which is immiscible with the polyolefin component having the braid-like filament structure, wherein the polyolefin and the polyester are present in a mass ratio in the range of 5:95 to 95:5. 2. Filament according to claim 1, characterized in that the polyolefin is a polyethylene, polypropylene, a copolymer consisting mainly of ethylene or a copolymer consisting mainly of propylene. 3. Filament according to claim 1 or 2, characterized in that the polyester is polyethylene terephthalate or polybutylene terephthalate. 4. Filament according to claim 1, characterized in that the mass mixing ratio of the polyolefin to the polyester in the polymer mixture is in the range of 15:85 to 85:15. 5. A method for producing a filament having a fine fibrillated structure according to claim 1, characterized in that a mixture of polyolefin and polyester is dissolved in a solvent at high temperature and high pressure in a mass ratio in the range of 5:95 to 95:5 to obtain a solution phase and then spun by flash spinning so that the filament has a polyolefin component having a braid-like filament structure and a polyester component having a braid-like filament structure which are not miscible with each other. 6. Process according to claim 5, characterized in that an inert gas is introduced into the spinning solution. 7. Process according to claim 5 or 6, characterized in that a surfactant is added to the spinning solution. 8. Nonwoven fabric with a finely fibrillated structure, which has filaments according to claim 1, characterized in that the filaments are glued together. 9. Nonwoven fabric according to claim 8, characterized in that the polyolefin is a polyethylene, polypropylene, a copolymer consisting mainly of ethylene or a copolymer consisting mainly of propylene. 10. Nonwoven fabric according to claim 8 or 9, characterized in that the polyester is polyethylene terephthalate or polybutylene terephthalate. 11. Nonwoven fabric according to one of claims 8 to 10, characterized in that the mass mixing ratio of the polyolefin to the polyester in the polymer mixture is in the range of 15:85 to 85:15. 12 Nonwoven fabric according to one of claims 8 to 11, characterized in that the filaments are bonded together with a finely fibrillated structure over the entire surface of the nonwoven fabric obtained and that the nonwoven fabric has the properties of a strength of at least 20 kp/5 cm, a water impermeability pressure of at least 50 cm and a moisture permeability of at least 100 g/m²/h. 13. Nonwoven fabric according to one of claims 8 to 11, characterized in that the filaments with a finely fibrillated structure are heat-bonded to one another in such a way that spatially separated heat-bonding areas are created and that the nonwoven fabric has the properties of a strength of at least 5 kp/5 cm, a softness when compressed of at most 200 g and a moisture permeability of at least 100 g/m²/h. 14. A method for producing a nonwoven fabric with a finely fibrillated structure, with which filaments according to claim 1 are produced, characterized in that pile is produced from the resulting filaments and the pile is then consolidated with heat and pressure using a group of rollers so that the filaments are bonded together over the entire surface of the nonwoven fabric. 15. A method for producing a nonwoven fabric according to claim 14, characterized in that the temperature during heat and pressure bonding of the pile using a group of rollers is higher than the difference "melting point of the polymer having the lowest melting point among the polymers forming the filaments minus 40°C" and not higher than this melting point, and that the squeezing pressure in the axial direction of the rollers during heat and pressure bonding is in the range of 0.5 to 20 kg/cm. 16. A method for producing a nonwoven fabric with a finely fibrillated structure, with which filaments according to claim 1 are produced, characterized in that pile is produced from the resulting filaments and the pile is then consolidated with heat and pressure using a group of rollers so that filaments are bonded to one another in such a way that spatially separated heat bonding areas are created. 17. A method for producing a nonwoven fabric according to claim 16, characterized in that the temperature when consolidating the pile with heat and pressure using an embossing device is higher than the difference "melting point of the polymer having the lowest melting point among the polymers forming the filaments minus 40°C" and not higher than this melting point, and that the squeezing pressure in the axial direction of the rollers is in the range of 0.5 to 50 kg/cm. 18. A method for producing a nonwoven fabric according to claim 16 or 17, characterized in that the proportion of the bonding areas in the total area of the nonwoven fabric is 4 to 50%. 19. A process for producing a nonwoven fabric according to one of claims 16 to 18, characterized in that the density of the bonding areas is 15 to 120/cm².