HK1067389B - Polyester staple fiber and nonwoven fabric comprising same - Google Patents

Description

Polyester staple fiber and nonwoven fabric containing the same

Technical Field

The present invention relates to a polyester staple fiber and a nonwoven fabric comprising the same.

Background

Polyester staple fibers have excellent mechanical properties and chemical resistance and are therefore widely used in nonwoven fabrics. However, the nonwoven fabric containing the conventional polyester type staple fiber is disadvantageous in comparison with the nonwoven fabric containing nylon or polyolefin staple fiber because it undesirably rattles to the touch and is unsatisfactory in softness of touch.

It is known to produce nonwoven fabrics from staple fibers by a process in which the fabric is formed from the staple fibers by carding, wet-laid (wet-laid) or air-laid (air-laid) processes, and then the staple fibers in the fabric are entangled with each other by needle-punching or hydro-entangling processes, or thermally bonded under pressure by a calender or an embosser (heat-bonded), or impregnated with an adhesive emulsion and dried until mutual chemical bonding occurs between the staple fibers in the fabric. In the above-mentioned method, when the fabric is manufactured using the air-laid process, the polyester type staple fiber has a disadvantage in that the smoothness of the polyester type staple fiber is poor as compared with nylon or polyolefin staple fiber, and when it is crumpled, the resultant crumpled fiber is liable to occur with a high percentage of crumpling amount and the fiber spreading property under ambient air is poor, so that it is difficult to produce a non-woven fabric having a uniform texture from the polyester type staple fiber. This tendency is more clearly recognized when undrawn polyester fibers or copolyester fibers, which have a low degree of orientation and a low degree of crystallinity and are preferably used as binder fibers, are used to produce nonwoven fabrics. Therefore, there is a limitation in producing a nonwoven fabric having a uniform texture from a fabric formed by an air-laid process using binder fibers, particularly 100% binder fibers. Also, even if the carding method or the wet method is employed, it is very difficult to produce a nonwoven fabric having a uniform texture from polyester type staple fibers having a low surface smoothness and thus exhibiting poor fiber spreading properties.

This tendency is further enhanced when a fabric is made from the binder fibers by carding.

The difficulty in producing nonwoven fabrics seems to be caused by the high hardness of the polyester type staple fibers and the friction between the respective polyester type staple fibers. To solve this problem, Japanese examined patent publication No. 48-1480 discloses a method in which a dimethyl siloxane compound or an amine-modified siloxane compound is applied to the surface of a polyester fiber, and the applied compound is crosslinked by heating. However, when the treated polyester type staple fibers are formed into a fabric using, for example, a carding method, the staple fibers disclosed in this japanese laid-open publication have little inter-fiber friction and thus exhibit insufficient fiber entanglement, and the resulting fabric is easily broken. In this case, when the fabric is produced by a wet process, since the staple fibers in the japanese laid-open publication are not hydrophilic, the fibers cannot be uniformly dispersed in water. Further, when the fabric is produced by the air-laid method, the staple fibers in the japanese laid-open publication are unevenly distributed in the obtained fabric due to the generation of static electricity on the staple fibers. In addition, when the fiber in this japanese publication is used as a binder fiber, the surface treatment agent coated on the surface of the polyester type staple fiber forms a barrier against thermal bonding of the fiber.

Summary of The Invention

The invention solves the problems existing in the prior art. That is, an object of the present invention is to provide polyester staple fibers which can realize a soft hand and a uniform texture of a nonwoven fabric, and a nonwoven fabric comprising the same. Further, the present invention intends to provide a nonwoven fabric produced from a fabric which is produced from a polyester type staple fiber by an air-laid method and which has the above-mentioned excellent properties.

The present inventors have found that polyester type staple fibers, when a part of the outer surface thereof is made of a polymer blend of polyester and polyolefin mixed and dispersed in the polyester, are suitable for friction between the staple fibers, and when the content of polyolefin in the fibers is within a specific range, a nonwoven fabric having not only soft hand but also uniform texture can be obtained.

That is, the above object can be achieved by the polyester staple fiber of the present invention comprising a polymer blend comprising a matrix polyester polymer and 0.5 to 15 mass% of a polyolefin polymer, wherein the polyolefin polymer is blended and dispersed in the matrix polyester polymer, said polyester staple fiber having a concentric or eccentric core-in-shell type conjugate structure in which a shell portion is formed by the polymer blend, wherein 50% or more of the surface of the core-in-shell type conjugate staple fiber is formed by the shell portion formed by said polymer blend.

In the polyester type staple fiber of the present invention, the polyolefin polymer preferably contains at least one selected from the group consisting of: polyethylene, polypropylene, ethylene-propylene copolymers and polyethylene and polypropylene copolymers in which at least one ethylenically unsaturated monomer other than ethylene and propylene is block or graft copolymerized.

In the polyester type staple fibers of the present invention, the matrix polyester polymer is preferably selected from the group consisting of polyalkylene terephthalate and polyalkylene isophthalate-isophthalate (polyalkylene terephthalate-isophthalate) copolymers.

The polyester type staple fiber of the present invention preferably has a crystallinity of 20% or less or has a birefringence of 0.05 or less.

The polyester type staple fiber of the present invention preferably has a conjugated structure of concentric or eccentric core-in-sheath center (core-in-sheath), wherein the sheath (sheath) is partially formed of a polymerization mixture.

The polyester type staple fiber of the present invention preferably has a fiber length of 2 to 30mm, a zigzag or omega-shaped crimp of 3 to 13 crimps/25 mm, and a percentage of crimp of 3 to 15%.

The polyester type staple fiber of the present invention preferably has a fiber length of 30 to 200mm, a zigzag or omega-type crimp of 5 to 30 crimps/25 mm, and a crimp percentage of 3 to 30%.

The nonwoven fabric (1) of the present invention contains a plurality of polyester type staple fibers as described above and is produced by an air-laid fabric forming method.

The nonwoven fabric (1) of the present invention preferably contains 5% or less of undrawn (non-open) fibers.

The nonwoven fabric (2) of the present invention comprises a plurality of polyester staple fibers as described above and is produced by a wet-type fabric forming method.

The nonwoven fabric (3) of the present invention contains a plurality of polyester staple fibers as described above and is produced by a card fabric forming method.

The nonwoven fabric (1), (2) or (3) of the present invention preferably has a bending resistance of 70mm or less as measured by the cantilever method.

Best mode for carrying out the invention

The staple fibers of the present invention are polyester type staple fibers in which 50% of the surface area is comprised of a polymeric blend containing a polyolefin polymer mixed and dispersed in a matrix polyester polymer.

Polyester polymers suitable for use in the present invention include, for example, polyesters of aromatic dicarboxylic acids with aliphatic diols, such as polyalkylene terephthalates, in particular polyethylene terephthalate, polytrimethylene terephthalate and polybutylene terephthalate; polyalkylene naphthalates, particularly polyethylene naphthalates; polyesters of cycloaliphatic dicarboxylic acids and aliphatic diols, specifically polyalkylene cyclohexane-dicarboxylic acid esters; polyesters of aromatic dicarboxylic acids and cycloaliphatic diols, in particular polycyclohexane dimethanol terephthalate; polyesters of aliphatic dicarboxylic acids and aliphatic diols, specifically polyethylene succinate, polybutylene succinate, polyethylene adipate and polybutylene adipate; and polyhydroxycarboxylates, particularly cellulose acetate esters (polycact ester) and polyhydroxybenzoates. The polyesters suitable for use in the present invention may be copolyesters containing at least one copolymerized component selected from the group consisting of: acid components such as isophthalic acid, phthalic acid, adipic acid, sebacic acid, α, β - (4-carboxyphenoxy) ethane, 4-dicarboxyphenyl, sodium 5-sulfoisophthalate, 2, 6-naphthalenedicarboxylic acid and 1, 4-cyclohexanedicarboxylic acid and esters of the above acids; a diol component such as diethylene glycol, 1, 3-propanediol, 1, 4-butanediol, 1, 6-hexanediol, neopentyl glycol, 1, 4-cyclohexanedimethanol and polyalkylene glycol. These copolymerized components may be selected from compounds having three or more carboxyl groups or hydroxyl groups, such as pentaerythritol, trimethylolpropane, trimellitic acid, 1, 3, 5-trimellitic acid, so that the resulting copolyesters have branched chains. In the present invention, the above-mentioned polyester-based (co) polymers may be used alone or in combination as a mixture of two or more.

The polyester-based polymer and the polyolefin-based polymer may contain one or more additives, fluorescent brightening agent, stabilizer, flame retardant aid, ultraviolet absorber, antioxidant and pigment of various colors, as long as the effects of the present invention are not impaired.

In the polymer blend of the polyester type staple fibers used in the present invention, the content of the polyolefin polymer mixed and dispersed in the matrix polyester polymer must be in the range of 0.5 to 15% by mass, preferably 1 to 10% by mass, more preferably 2 to 7% by mass, further preferably 2 to 5% by mass, based on the mass of the polymer blend. If the content of the polyolefin polymer is less than 0.5% by mass, the object of the present invention, that is, a nonwoven fabric containing polyester staple fibers and having a soft hand and a uniform texture, cannot be obtained. Further, if the content of the polyolefin polymer is more than 15% by mass, not only the above-mentioned effects are saturated (saturated) or cannot be achieved, but also the fiber-forming property of the resulting polymer blend is lowered, so that the target staple fiber of the present invention cannot be obtained.

In the polyester type staple fibers of the present invention, 50% or more, preferably 70% or more, more preferably 90% to 100% of the surface of the fiber must be formed of the polymerization mixture. If the surface formed by the polymerization mixture is less than 50%, the resulting nonwoven fabric exhibits insufficient softness and unsatisfactory uniformity of texture. The staple fibers satisfying the above requirements include staple fibers formed of 100 mass% of the polymer blend, and conjugate staple fibers in which 50% or more of the surface of the fibers is formed of the polymer blend. The conjugate staple fibers include concentric shell-in-center type, eccentric shell-in-center type, shoulder-and-shoulder type, and sea-island type and partial-pie type conjugate staple fibers. The present invention preferably employs concentric and eccentric sheath-in-sheath center type conjugate staple fibers having 70% or more, more preferably 100% of the fiber surface formed by the sheath-in-portion of the polymeric blend.

The polyester staple fiber of the present invention may be a hollow fiber or a non-hollow fiber. The shape of the cross section of the polyester type staple fiber of the present invention is not limited to a circle but may be an irregular shape selected from the group consisting of an ellipse, a multilobal shape such as a trilobal to octalobal shape, and a polygonal shape such as a triangle to an octagon.

The effects of the present invention are clearly exhibited in polyester type staple fibers having a birefringence of 0.05 or less or a crystallinity of 20% or less.

In conventional polyester type staple fibers having a birefringence of 0.05 or less or a crystallinity of 20% or less, there is a tendency that inter-fiber friction increases, and thus the resulting nonwoven fabric may exhibit a reduced hand, a reduced fiber spreading property and an unsatisfactory uniformity of the texture of the fiber. This tendency seems to be more remarkable in a fiber having a low orientation (non-drawn fiber) which is produced by melt-spinning a polyalkylene terephthalate, particularly an isophthalic acid-copolymerized polyalkylene terephthalate, at a low take-out rate of 200 m/min or less. This tendency is very remarkable in non-drawn polyalkylene terephthalate fibers, in fibers formed of polyethylene terephthalate which has low crystallinity and has copolymerized polyethylene terephthalate copolymerized with 5 to 50 mol% of isophthalic acid based on the total number of moles of the acid component. The polyester staple fibers can be thermally bonded to each other under pressure, and can be used as binder fibers for nonwoven fabrics. When the above polyester polymer is used as the matrix polymer of the polyester staple fiber of the present invention, the resulting polyester staple fiber can be used as a binder fiber without causing the above problems. The polyester staple fibers obtained in the present invention are also useful for producing nonwoven fabrics having a desired soft hand and uniform texture.

There is no limitation on the thickness of the individual polyester staple fibers of the present invention. Generally, the thickness of the polyester staple fiber of the present invention is preferably in the range of 0.01 to 500 dtex.

The polyester type staple fiber of the present invention can be produced by, for example, the following method. A melt of the polymeric mixture of polyester polymer and polyolefin polymer is extruded through a (melt-) spinneret having a plurality of orifices of a conventional (melt-) spinning apparatus, cold air is blown against the molten stream and drawn off, the extruded filament stream of melt is cooled and solidified, and the solidified filaments are drawn off at a rate of 100-2000 m/min to obtain a non-drawn polyester multifilament yarn.

A melt of the polymerization mixture is prepared by: mixing a melt of the polyester polymer with a melt of the polyolefin polymer in a static mixer or a dynamic mixer, or mixing the polyester polymer and the particles of the polyolefin polymer in a desired mass ratio, subjecting the mixture to (melt-) kneading with a (melt-) extruder, and then feeding the resulting mixed melt to a (melt-) spinneret.

In the process of producing non-drawn polyester type conjugate filaments, the same procedure as above is carried out, except that a melt of the polymerization mixture and a melt of the polyester resin are fed separately to a (melt-) spinneret, and the melts of the polymerization mixture and the polyester resin are combined in the spinneret to form conjugate filaments between each other, 50% or more of the surface of the conjugate filaments being formed of the polymerization mixture.

The obtained undrawn filaments are drawn in hot water at a temperature of 70-100 ℃ or in steam at a temperature of 100-125 ℃ at a desired drawing rate, optionally the obtained drawn filaments are crumpled, oiled with a finish oil (finish oil) according to the use and purpose of the obtained staple fibers, dried and relaxed. The resultant filaments were cut into staple fibers having a desired fiber length to obtain the target polyester type staple fibers. In these steps, the oiling agent may contain a silicone compound of this type in an amount not interfering with the achievement of the object of the present invention. The polyester staple fiber of the present invention having a birefringence of 0.05 or less or a crystallinity of 2% or less is obtained by the same process steps as described above, but the process omits a drawing step by applying an overcoat finish to undrawn yarn, and drying the oiled undrawn yarn at room temperature for a period of time which does not cause the crystallinity of the dried yarn to exceed 20%. In the production of the nonwoven fabric from the polyester type staple fibers of the present invention, preferably, as described below, the staple fibers are adjusted in length to cause wrinkles according to the method of forming a fabric from the fibers.

For example, when the fabric is formed using the air-laid method, the length of the staple fiber is preferably adjusted to 2 to 30mm, more preferably 3 to 20 mm. By adjusting the fiber length to not less than 2mm, the desired staple fiber can be industrially produced under satisfactory process stability conditions, and by controlling the fiber length to not more than 30mm, the obtained staple fiber exhibits improved fiber spreading properties and high fiber blocking resistance. The polyester staple fibers may or may not be crimped fibers depending on the use of the resulting nonwoven fabric. That is, when the target nonwoven fabric must have high bulk, the staple fibers are preferably crimped fibers. When the target nonwoven fabric is to be improved in fiber spreading performance with respect to the air jet stream and the performance to be uniformly dispersed by the air jet stream is to be improved, the staple fibers may be wrinkle-free. When the crimped staple fibers are used in a web-forming airlaid process, the crimp count is preferably 3-13 crimps/25 mm, with a percent crimp content of 3-15%. When the number of wrinkles is adjusted to not more than 13 wrinkles/25 mm and the percentage of wrinkles is not more than 15%, the obtained nonwoven fabric shows satisfactory fiber spreading properties when air flows. Since the polyester staple fiber of the present invention easily has less wrinkle number and% wrinkle content than the conventional polyester staple fiber, it is easy to adjust the wrinkle number and% wrinkle content within the above ranges. In order to provide the polyester type staple fiber of the present invention with suitable bulk, it is preferable to adjust the number of wrinkles and the percentage of wrinkles to not less than 3 wrinkles/25 mm and not less than 3%, respectively. The mode of crimping is preferably a planar zigzag or omega type formed in a plane, not a three-dimensional spiral crimping mode, because the fiber spreading performance of the planar zigzag or omega, type crimped staple fibers is higher than that of the spiral crimped staple fibers.

Adjusting the number of wrinkles and the percentage of wrinkles as described above can reduce the content of non-open staple fibers in the fabric obtained by the air-laid method to 5 mass% or less.

When the fabric of the nonwoven fabric is produced using the wet textile forming method, the fiber length of the polyester type staple fiber is preferably 2 to 30mm, more preferably 30 to 20mm, for the above-described reasons. The staple fibers may be crimped or uncreped. I.e., imparting rugosities on staple fibers depending on the use and purpose of the target nonwoven fabric. However, crimped staple fibers are not preferred for wet web forming processes in view of the uniformity of distribution of the staple fibers dispersed in the aqueous slurry of staple fibers in the wet web forming process.

When the target nonwoven fabric is produced using the card fabric forming method, the length of the polyester type staple fiber is preferably adjusted to 30 to 200mm, more preferably 35 to 150mm, further preferably 40 to 100 mm. A fiber length of not more than 30mm prevents or reduces breakage of the resulting fabric due to insufficient entanglement of the staple fibers with each other. The fiber length of not more than 200mm can improve the spreading performance of the obtained staple fiber on a carding machine and improve the texture uniformity of the obtained fabric.

For improving the transfer properties of staple fibers through a carding machine, crimped staple fibers are preferably used. Preferably the staple fibres have a crimp count and percentage of 5-30 crimps per 25mm and 3-30% respectively. The adjustment of the number and percentage of wrinkles to not more than 30 wrinkles/25 mm and not more than 30%, respectively, makes it possible to obtain polyester staple fibers exhibiting good spreading properties on a carding machine and to obtain fabrics exhibiting satisfactory uniformity of texture. By adjusting the number and percentage of wrinkles to be not less than 5 wrinkles/25 mm and not less than 3%, respectively, it is possible to prevent or reduce the occurrence of breakage of the resulting fabric, which is caused by insufficient entanglement of the staple fibers with each other. The manner of the corrugations may be conventional planar zigzag or omega-shaped or three-dimensional spiral nodes.

The nonwoven fabric comprising the polyester type staple fiber of the present invention has a soft touch and good hand, and can exhibit a bending resistance of 700mm or less, which represents the softness of the fabric, as measured by the cantilever method.

The nonwoven fabric of the present invention includes a nonwoven fabric of the polyester staple fibers of the present invention mixed with the polyester staple fibers of the present invention and a nonwoven fabric laminate comprising at least one nonwoven fabric layer containing the polyester staple fibers of the present invention and at least one additional nonwoven fabric layer containing the staple fibers of the present invention, which are laminated with each other.

Specifically, the nonwoven fabric obtained solely from the polyester type staple fiber of the present invention exhibits a specific soft hand feeling by itself different from that of the nonwoven fabric containing the conventional polyester type staple fiber, and is therefore preferably used for various purposes.

In the polyester type staple fiber of the present invention, 50% or more of the outer surface of the individual staple fiber is formed of a specific polymer blend composed of a polyester polymer and 0.5 to 15 mass% of a polyolefin polymer. This feature of the present invention allows the reduction of inter-fiber friction of the obtained staple fibers and thus the improvement of fiber spreading properties, so that the obtained nonwoven fabric has a soft hand feeling and a high uniformity of texture.

The mechanism of the effect of the polyester type staple fibers and nonwoven fabrics of the present invention is not yet fully understood. However, assuming that in the polymer mixture used in the present invention, the polyolefin polymer is incompatible with the polyester polymer and therefore, when an appropriate amount of the polyolefin polymer is mixed and dispersed in the matrix composed of the polyester polymer, the polyolefin polymer is suspended in the form of a plurality of islands in the sea formed by the matrix polyester polymer, when the individual fibers are formed with the polymer mixture, a part of the islands appears on at least a part of the outer surface of each individual fiber to roughen the outer surface, and therefore the resulting individual fibers are mainly in contact with each other at the raised portions of the outer surface of the fiber, the friction coefficient between each other is low.

Examples

The invention is further illustrated by the following examples.

In examples and comparative examples, test items and measurement methods of the obtained staple fibers and nonwoven fabrics are as follows.

(a) Thickness of fiber

The fiber thickness was measured according to JIS 11015-1992, 7.5.1, method A.

(b) Length of fiber

The fiber length was measured by the direct method (method C) according to JIS L1015-.

(c) Number and percentage of wrinkles

The number and percentage of wrinkles of the crimped staple fibers were measured in accordance with JIS L1015-.

(d) Intrinsic viscosity of polyester polymer

The intrinsic viscosity (. eta.) of the polyester polymer was measured in o-chlorophenol at 35 ℃.

(e) Melt index (MFR) of polyester polymer or polyolefin polymer

The melt index of the polyester polymer or the polyolefin polymer was measured under condition 4 according to JIS K7210.

(f) Glass transition temperature (Tg) and melting temperature (Tm) of polyester polymer or polyolefin polymer

The glass transition temperature (Tg) and melting temperature (Tm) of the polyester polymer or polyolefin polymer were measured at a temperature rising rate of 20 ℃ per minute using a differential scanning calorimeter (model: DSC-7, manufactured by Parkin-Elmer Co.).

(g) Degree of crystallinity of fiber

Fiber density ρ (g/cm) was measured at 25 ℃ by using a density gradient tube³) The density gradient tube was charged with a mixture of n-heptane and carbon tetrachloride, and p was calculated from the density of the obtained fiber according to the following equation to calculate the crystallinity of the fiber.

xc＝ρc(ρ-ρa)/ρ(ρc-ρa)

Wherein xc represents the degree of crystallinity of the fiber in mass%, ρ c represents the crystal density of polyethylene terephthalate, i.e., 1.455g/cm³ρ a represents the amorphous density of polyethylene terephthalate, i.e., 1.335g/cm³And ρ represents the fiber density.

(h) Birefringence (DELTA n) of the fiber

The birefringence (Δ n) of the Fibers was determined by the retardation method as disclosed in Textile Institute Fibers, Manchester & London, w.e. morton and j.w.s.heart, Physical Properties of Textile Fibers, page 524-.

(i) Percentage of unextended fibres (u)

The 10g fabric produced by the air-laid method was subjected to taking of an undeveloped fiber cake, the mass (x) of the obtained fiber cake was measured, and the percentage content (u) of the undeveloped fibers in the fabric was calculated according to the following equation.

u(％)＝x/10×100

Where x represents the mass of the undeployed fiber cake taken from the fabric and u represents the percentage of undeployed fiber in the fabric.

(j) Bending resistance of nonwoven fabric

The bending resistance of the nonwoven fabric was measured in accordance with JIS L1085-. The lower the value, the higher the softness of the fabric.

(k) Evaluation of texture of nonwoven Fabric

The appearance of the fabric was observed with the naked eye and evaluated according to the following three classifications

Texture of grade fabrics

3 no lumps of undeployed fibers were found. No uneven mass distribution was found. The texture of the fabric is uniform

2 the undeveloped fibers do not clump significantly. The naked eye can find an uneven mass distribution.

1 the undeveloped fibers clump significantly. The uneven mass distribution is evident. The texture of the fabric is not uniform.

Example 1

Polyethylene terephthalate (PET) particles having an intrinsic viscosity [ eta ] of 0.61 and a melting temperature [ Tm ] of 256 ℃ dried at 120 ℃ under vacuum for 16 hours were mixed with each other in a mass ratio of 97: 3 with High Density Polyethylene (HDPE) particles having a melt index (MFR) of 20g/10 min and a melting temperature of 131 ℃. The mixture was melted in a twin-screw extruder and the resulting melt at a temperature of 280 ℃ was extruded at an extrusion rate of 200 g/min through a (melt-) spinneret with 600 spinneret holes having an inner diameter of 0.3 mm. The extruded filamentary melt stream was cooled with cold air at 30 ℃ and the cooled and solidified non-drawn multifilament yarn was wound at a rate of 1150 m/min. The undrawn multifilament yarn was crimped with a stuffing box crimper so that the number of in-plane zigzag crimp of the undrawn individual filaments of the multifilament yarn was 8 crimps/25 mm and the percentage of crimp was 4%. The crimped multifilament yarn was coated with 25% dry mass of a finish comprising 80/20 mass ratio of potassium alkylphosphate salt and polyoxyethylene-modified silicone based on the dry mass of the yarn, and then dried by blowing hot air at 45 ℃. The dried undrawn multifilament yarn was cut into a fiber length of 5 mm. The thickness of the obtained polyester staple fiber was 3.1 dtex, the crystallinity was 16%, and the birefringence was 0.0035.

The basis weight of the staple fiber obtained by the forming process of an air-laid fabric is 50g/m²The fabric of (1). The fabric was calendered at a linear pressure of 80KPa · m and a rate of 20 m/min using a pair of flat calendering rolls with a roll surface temperature of 200 ℃ to produce an air-laid nonwoven fabric. The nonwoven fabric had a 50mm bending resistance, the percentage (u) of non-spread fibers was 0.5%, and the uniformity of the texture of the nonwoven fabric was grade 3.

Example 2

Polyester staple fibers and air laid nonwoven fabrics were produced in the same procedure as in example 1, except that a polyethylene terephthalate-isophthalate copolymer containing 10 mol% of copolymerized isophthalic acid and having a melting point of 220 ℃ was used in place of PET. The thickness of the obtained polyester staple fiber was 3.4 dtex, the crystallinity was 9%, and the birefringence was 0.0027. The obtained nonwoven fabric had a bending resistance of 44mm, a percentage content of non-spread fibers of 0.8%, and a texture of grade 3.

Example 3

Amorphous polyethylene terephthalate-isophthalate copolymer particles (containing 40 mol% of copolymerized isophthalate, dried under vacuum at 50 ℃ for 24 hours and having an intrinsic viscosity [. eta. ] of 0.55 and a glass transition temperature (Tg) of 65 ℃) were mixed with particles of high-density polyethylene (HDPE) (having a melt index of 20g/10 minutes and a melt temperature of 131 ℃) in a mass ratio of 95: 5. The mixture was melted in a twin screw extruder to give a melt of the polymeric mixture at 250 ℃. Separately, PET particles dried at 120 ℃ for 16 hours and having an intrinsic viscosity [ eta ] of 0.61 were melted in an extruder to give a PET melt at 280 ℃.

A melt of the polymerization mixture and a PET melt were melt-spun by using a concentric in-shell center type conjugate filament forming spinneret having 1032 spinning holes with an inner diameter of 0.3mm to obtain an in-shell center type composite filament having a shell portion formed from the melt of the polymerization mixture and a center portion formed from the PET melt, the ratio (A/B) of the cross sections of the shell portion (A) and the center portion (B) being 50: 50.

The polymerization mixture and the in-shell core conjugate stream of the PET melt were extruded through a spinneret at a spinning temperature of 285 ℃ and an extrusion rate of 870 g/min, and cooled by blowing cold air at 30 ℃. The resulting undrawn core-in-shell conjugated multifilament yarn was wound at a rate of 1150 m/min. The undrawn conjugated multifilament yarn was drawn in hot water at 80 ℃ at a draw ratio of 3.75, then the drawn conjugated multifilament yarn was passed through a water bath at 30 ℃ to cool the yarn to prevent fusion between the drawn individual filaments, the cooled yarn was coated with 0.2% by dry mass of a finish comprising a potassium alkylphosphate salt and polyoxyethylene-modified silicone mixed in a dry mass ratio of 80: 20, and the oil-coated yarn was crimped in a stuffer type crimper so that the number of plane zigzag crimps per conjugated filament was 9 crimps/25 mm and the percentage of crimps was 12%. The crimped filaments were dried at 50 ℃ and cut to a fiber length of 5 mm. The thickness of the resulting staple fiber was 2.1 dtex.

The staple conjugate fiber was subjected to an air-laid fabric forming step to obtain a base mass (base mass) of 50g/m²The fabric of (1). The fabric was heat entangled with a stream of hot air at 150 c for 2 minutes to bond the individual staple fibers at the interdigitated portions. The obtained airlaid nonwoven fabric had a bending resistance of 53mm, the percentage of undeveloped fibers was 0.7%, and the texture of the nonwoven fabric was grade 3.

Comparative example 1

A polyester type staple composite fiber and air laid nonwoven fabric were produced in the same manner as in example 3 except that an amorphous polyethylene terephthalate and isophthalate copolymer (containing 40 mol% of copolymerized isophthalic acid, having an intrinsic viscosity [. eta. ] of 0.55 and a Tg of 65 ℃ C.) was used in place of the copolymerized mixture of the amorphous PET copolymer and HDPE used to form the shell portion of the conjugate fiber. The thickness of the resulting staple fiber was 2.1 dtex. The obtained nonwoven fabric had a bending resistance of 83mm, a percentage of non-spread fibers of 11%, and a texture of grade 1.

Comparative example 2

A polymerization mixture for forming a shell portion of a center-type conjugated filament in a shell was prepared according to the same method as in example 3, except that the mixing ratio of the amorphous PET copolymer particles to HDPE was changed from 95: 5 to 84: 16. The resultant polymerization mixture had poor filament-forming properties, and thus, the melt-spinning step could not be performed.

Example 4

Polyester type staple fibers and nonwoven fabrics were prepared according to the same method as in example 3, except for the following. In the polymerization mixture for the shell portion of the conjugate filaments, HDPE was replaced with an isotactic polypropylene resin having an MFR of 30g/10 min and a Tm of 160 ℃.

The thickness of the resulting staple fiber was 2.2 dtex. The obtained nonwoven fabric had a flexural strength of 58mm, a percentage of non-spread fibers of 1.3%, and a texture of grade 3.

Example 5

Polyester type staple fibers and nonwoven fabrics were prepared according to the same method as in example 3, except for the following.

In the polymerization mixture for the shell portion of the conjugated yarn, HDPE was replaced with an ethylene-propylene random copolymer (MFR 50g/10 min, Tm 135 ℃, copolymerization molar ratio of ethylene and propylene 37: 63).

The thickness of the resulting staple fiber was 2.2 dtex.

The obtained nonwoven fabric had a bending resistance of 58mm, a percentage of non-spread fibers of 1.3%, and a texture of grade 3.

Example 6

Polyester type staple fibers and nonwoven fabrics were prepared according to the same method as in example 3, except for the following.

In the polymerization mixture for the shell portion of the conjugated yarn, HDPE was replaced with linear low density polyethylene graft-copolymerized with 3.5 mass% maleic anhydride (MFR 8g/10 min, Tm 96 ℃ C.).

The thickness of the resulting staple fiber was 2.2 dtex.

The obtained nonwoven fabric had a bending resistance of 52mm, a percentage content of non-spread fibers of 0.8%, and a texture of 3 rd grade.

Example 7

Polyester type staple fibers and nonwoven fabrics were prepared according to the same method as in example 3, except for the following.

The PET used for the central portion of the conjugated filaments was replaced by nylon 6 having an intrinsic viscosity of 1.34 (measured in m-cresol at 35 ℃) and a Tm of 215 ℃. The nylon 6 chips were melted in an extruder to produce a nylon 6 melt having a temperature of 240 ℃. Melt spinning was carried out at a spinning temperature of 250 ℃ and an extrusion rate of 500 g/min to obtain a core-in-shell conjugate yarn. The obtained non-drawn multifilament yarn was drawn at a draw ratio of 2.1 at room temperature and then drawn at a draw ratio of 1.05 in hot water at 55 ℃. The drawn multifilament yarn was cooled by passing through a water bath and then oiled in the same manner as in example 3. A flat Z-shaped crease was produced on the oiled multifilament yarn with a number of 12 creases per 25mm and a percentage of 6.5% crease, and was then dried at 45 ℃. The crimped multifilament was cut into staple fibers in the same manner as in example 3.

The thickness of the resulting staple fiber was 2.2 dtex.

The obtained nonwoven fabric had a bending resistance of 52mm, a percentage of non-spread fibers of 1.6%, and a texture of grade 3.

Example 8

Polyester type staple fibers and nonwoven fabrics were prepared according to the same method as in example 3, except that the length of the staple fibers was changed from 5mm to 3 mm.

The obtained nonwoven fabric had a bending resistance of 57mm, a percentage content of non-spread fibers of 1.6%, and a texture of 3 rd grade.

Example 9

Polyester type staple fibers and nonwoven fabrics were produced according to the same method as in example 3, except that an eccentric in-shell center type conjugate filament forming spinneret was used instead of the concentric in-shell center conjugate filament forming spinneret. The percentage of wrinkles on the wrinkled fibers changed from 12% to 15%, the wrinkles being omega-shaped.

The thickness of the resulting staple fiber was 2.3 dtex.

The obtained nonwoven fabric had a bending resistance of 55mm, a percentage content of non-spread fibers of 0.9%, and a texture of 3 rd grade.

Example 10

Polyester type staple fibers and nonwoven fabrics were prepared according to the same method as in example 3, but without forming wrinkles on the stretch-composite multifilament yarns.

The obtained nonwoven fabric had a bending resistance of 53mm, a percentage content of non-spread fibers of 0.2%, and a texture of 3 rd grade.

Example 11

Polyester staple fibers and wood pulp fibers (mass ratio: 80: 20) prepared in the same manner as in example 10 were suspended in water while sufficiently stirring, and were produced from an aqueous mixed fiber slurry by using a rectangular sheet press to have a size of about 25cm by about 25cm and a dry basis mass of 50g/m²The sheet of (1). The sheet was dried at room temperature for 24 hours or more, and then placed on a porous polytetrafluoroethylene sheet, and subjected to a shrinkage treatment in a hot air circulation type dryer at 120 ℃ for 5 minutes, to obtain a wet-process nonwoven fabric.

The nonwoven fabric obtained had a bending resistance of 38mm and a texture of 3 rd grade.

Comparative example 3

Polyester type staple fibers and wet laid non-woven fabrics were prepared according to the same method as in example 11, except that the step of crimping the drawn multifilament yarns was omitted.

The nonwoven fabric obtained had a bending resistance of 38mm and a texture of grade 2.

Example 12

Polyester type staple fibers were prepared according to the same method as in example 3, except that the length of the staple fibers was changed from 5mm to 51 mm.

The staple fibers were fed to a carding step using a roller card to produce a carded web. During the carding step, staple fibers showed good card pass performance. Placing a plurality of carded fabrics on top of each other to obtain a dry basis mass of 50g/m²The laminated fabric of (1).

The laminated fabric was heat-entangled at the intersections of staple fibers with each other by the same heat-entangling method as in example 3 with a hot air flow to obtain a carded heat-entangled nonwoven fabric.

The nonwoven fabric obtained had a bending resistance of 58mm and a texture of grade 3.

Example 13

Polyester type staple fibers were prepared according to the same method as in example 10, except that the length of the staple fibers was changed from 5mm to 51 mm.

The staple fibers were fed to the carding step according to the procedure of example 12, producing a carded fabric. During the carding step, staple fibers showed good card pass performance. A plurality of carded webs were laid one on top of another and heat-entangled in the same manner as in example 12 to obtain a carded heat-entangled nonwoven fabric.

The nonwoven fabric obtained had a bending resistance of 51mm and a texture of 3 rd grade.

The present invention can provide a specific polyester type staple fiber for forming a nonwoven fabric having a soft hand feeling and a uniform texture. The present invention can also provide a nonwoven fabric having a uniform texture and a soft hand. In particular, the nonwoven fabric produced from the fabric formed of the polyester type staple fibers of the present invention by the air-laid fabric forming method has a low content of undeveloped fibers and excellent uniformity of texture.

Therefore, the specific polyester type staple fiber allows the nonwoven fabric made of the staple fiber to have more uses and thus higher industrial value.

Claims (10)

1. A polyester staple fiber comprising:

a polymeric mixture comprising a matrix polyester polymer and 0.5 to 15 mass% of a polyolefin polymer, wherein the polyolefin polymer is mixed and dispersed in the matrix polyester polymer,

the polyester staple fibers have a concentric or eccentric core-in-shell conjugate structure in which the shell portion is formed of a polymer blend,

wherein 50% or more of the surface of the center type conjugate staple fibers within the shell are formed by the shell portion formed by the polymeric mixture.

2. The polyester staple fiber according to claim 1, wherein the polyolefin polymer comprises at least one selected from the group consisting of polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene copolymer and polypropylene copolymer, wherein at least one ethylenically unsaturated monomer other than ethylene and propylene is block-copolymerized or graft-copolymerized.

3. The polyester staple fiber according to claim 1, wherein the matrix polyester polymer is selected from the group consisting of polyalkylene terephthalate and polyalkylene terephthalate-isophthalate copolymer.

4. The polyester staple fiber according to any one of claims 1 to 3, wherein the polyester staple fiber has a fiber length of 2 to 30mm and has wrinkles of 3 to 13 wrinkles/25 mm in number of wrinkles and a percentage of wrinkles of 3 to 15%.

5. The polyester staple fiber according to any one of claims 1 to 3, wherein the polyester staple fiber has a fiber length of 30 to 200mm and has wrinkles of 5 to 30 wrinkles/25 mm in number of wrinkles and a percentage of wrinkles of 3 to 30%.

6. A nonwoven fabric comprising a plurality of the polyester staple fibers of any one of claims 1 to 4 and produced by an air laid fabric forming process.

7. The nonwoven fabric of claim 6, wherein the percentage of undrawn fibers in the nonwoven fabric is 5% or less.

8. A nonwoven fabric comprising a plurality of the polyester staple fibers according to any one of claims 1 to 3 and produced by a wet forming method.

9. A nonwoven fabric comprising a plurality of polyester staple fibers according to any one of claims 1 to 3 and 5 and produced by a carded web forming process.

10. The nonwoven fabric according to any one of claims 6 to 9, wherein the nonwoven fabric has a bending resistance of 70mm or less as measured by a cantilever method.