JP2008101285A - Nonwoven manufacturing method - Google Patents

Abstract

An object of the present invention is to provide a method for producing a nonwoven fabric that can increase the strength of the nonwoven fabric while maintaining a good texture.
In the method for producing a nonwoven fabric of the present invention, a hot air treatment is applied to a web containing a heat-fusible conjugate fiber to fuse the intersections of the fibers. The composite fiber is composed of a first resin component and a second resin component having a melting point or a softening point lower than the first resin component, and the second resin component is present continuously in the length direction at least at a part of the fiber surface. The web is treated with hot air at a temperature T3 that is lower than the melting point T1 of the first resin component and equal to or higher than the melting point T2 of the second resin component to fuse the intersections of the fibers, and is further higher than the temperature T3 and lower than T1. Hot air treatment is performed at temperature T4, which is a temperature.
[Selection] Figure 1

Description

  The present invention relates to a method for producing a nonwoven fabric.

  There is known a method of manufacturing a nonwoven fabric by blowing hot air onto a web containing a heat-fusible conjugate fiber to fuse the intersections of the fibers. For example, a card web composed of a core-sheath type composite short fiber having a sheath part of an ethylene polymer as a main component and a core part of a propylene polymer, and a single yarn fineness of 0.2 to 1 denier. There has been proposed a method for producing a heat-bonded nonwoven fabric that is heat-treated with hot air to bond contact points between fibers (see Patent Document 1). According to the description of Patent Document 1, the nonwoven fabric produced by this production method is composed of a core-sheath type composite short fiber having a fineness, resulting in high nonwoven fabric strength, bulkiness and excellent water retention. It is said that

  Aside from the above technique, a method for producing a nonwoven fabric using heat-stretched fibers as constituent fibers is known (see Patent Document 2). In this production method, a web of high-shrinkage polyester fiber having latent spontaneous elongation is subjected to entanglement treatment and then subjected to shrinkage heat treatment to increase the entanglement density. According to the description in Patent Document 2, the sheet strength is increased by increasing the confounding density. However, on the other hand, the increase in the entanglement density causes the texture of the sheet to become hard. Therefore, in Patent Document 2, the draping property of the sheet is improved by subjecting the sheet to a spontaneous extension heat treatment after the shrink heat treatment.

JP-A-7-70899 JP-A-53-58074

  The objective of this invention is providing the manufacturing method of the nonwoven fabric which the various characteristics of the obtained nonwoven fabric improved rather than the method of the prior art mentioned above.

The present invention provides a nonwoven fabric manufacturing method in which a hot air treatment is applied to a web containing a heat-fusible conjugate fiber to fuse the intersections of the fibers,
The composite fiber is composed of a first resin component and a second resin component having a lower melting point or softening point than the first resin component, and the second resin component is present continuously in the length direction at least part of the fiber surface,
The web is treated with hot air at a temperature T3 that is lower than the melting point T1 of the first resin component and equal to or higher than the melting point T2 of the second resin component to fuse the intersections of the fibers, and is further higher than the temperature T3 and lower than T1. The manufacturing method of the nonwoven fabric which hot-air-processes at temperature T4 which is temperature is provided.

  According to the production method of the present invention, the strength of the nonwoven fabric can be increased while maintaining a good texture. In particular, when a heat-extensible composite fiber is used as a constituent fiber of the nonwoven fabric, the strength of the nonwoven fabric can be increased and the nonwoven fabric can be made bulky. Further, the surface of the nonwoven fabric has a three-dimensional appearance.

  Hereinafter, the present invention will be described based on preferred embodiments thereof. The manufacturing method of the nonwoven fabric of this embodiment includes (a) a web forming step, (b) a pressure bonding portion forming step, (c) a first hot air treatment step, and (d) a second hot air treatment step. Broadly divided. Hereinafter, each process will be described.

  As the web forming means used in the web forming step, an appropriate one is appropriately selected according to the constituent fibers of the web. When the web is made of short fibers, for example, a card method in which the short fibers are opened using a card machine, or a method in which the short fibers are transported in an air stream and deposited on a net (air array method) may be employed. it can. In the case of a card, the fiber length of the short fiber is suitably 30 to 70 mm. In the case of the air array method, it is appropriate that the short fiber has a fiber length of 3 to 30 mm. On the other hand, when the web is made of, for example, long fibers, a spun bond method, a melt blown method, a spinning blow method, or the like can be employed.

  The web contains a heat-fusible conjugate fiber as a constituent fiber. The web may be composed only of heat-fusible fibers, or may be composed of heat-fusible fibers and other types of fibers. When the web contains fibers other than heat-fusible conjugate fibers as its constituent fibers, the proportion of heat-fusible conjugate fibers in the web (this proportion is also the proportion of heat-fusible conjugate fibers in the target nonwoven fabric) Is preferably 50 to 95% by weight, particularly 70 to 95% by weight. On the other hand, the ratio of fibers other than the heat-fusible composite fiber is preferably 5 to 50% by weight, more preferably 20 to 30% by weight. Examples of fibers other than the heat-fusible composite fibers include fibers that do not inherently have heat-fusibility (for example, natural fibers such as cotton and pulp, rayon, and acetate fibers).

  The web is generally of a single layer structure containing heat-fusible conjugate fibers. However, this does not mean that the web is limited to a single layer structure. For example, the web may have a multilayer structure in which one or more layers containing heat-fusible conjugate fibers and one or more layers not containing heat-fusible conjugate fibers are appropriately overlapped. Alternatively, the web has a multilayer structure in which one or more layers containing a heat-fusible conjugate fiber and one or more layers containing a different type of heat-fusible conjugate fiber are appropriately stacked. It may be. Further, the web includes one or more layers including a heat-fusible conjugate fiber, one or more layers including a different type of heat-fusible conjugate fiber, and a heat-fusible conjugate fiber. It may have a multilayer structure in which one or more layers not containing fibers are appropriately overlapped.

As for the basis weight of the web, an appropriate range is selected according to the specific use of the target nonwoven fabric. The basis weight of the web is preferably 10 to 80 g / m ² , particularly preferably 15 to 60 g / m ² . The basis weight of the web is substantially the same as the basis weight of the finally obtained nonwoven fabric.

  The heat-fusible conjugate fiber contained in the web is composed of two or more kinds of materials. The heat-fusible conjugate fiber is a bicomponent conjugate fiber that is generally composed of two kinds of materials. When the heat-fusible conjugate fiber is a two-component conjugate fiber, the conjugate fiber includes a first resin component and a second resin component having a melting point or a softening point lower than the first resin component, and the second resin component is on the fiber surface. At least a part is in the form of being continuously present in the length direction. Examples of the composite fiber having such a form include a core-sheath type composite fiber and a type of composite fiber in which the first resin component and the second resin component are alternately arranged in the circumferential direction of the fiber. The former conjugate fiber can be classified into a concentric type and an eccentric type. The latter composite fiber can be classified into a side-by-side type and a split type.

  There is no restriction | limiting in particular in the fineness of a heat-fusible composite fiber. An appropriate value is selected according to the specific use of the target nonwoven fabric. A general range is 1.0 to 10 dtex, particularly 1.7 to 8.0 dtex, from the viewpoints of fiber spinnability and cost, card machine passability, productivity, cost, and the like.

  Various resins capable of forming fibers can be used as the first resin component and the second resin component constituting the heat-fusible conjugate fiber. For example, polyolefin resins such as polyethylene, polypropylene, ethylene-α olefin copolymer, polyester resins such as polyethylene terephthalate and polybutylene terephthalate, polyamide resins, acrylic resins, etc., depending on their melting point or softening point They can be used in appropriate combinations.

  In particular, when a heat-stretchable conjugate fiber that can be stretched by heat at a temperature lower than the melting point of the first resin component is used as the heat-fusible conjugate fiber, the strength of the resulting nonwoven fabric can be increased. In addition, the nonwoven fabric can be made bulky, and the surface of the nonwoven fabric can have a three-dimensional appearance, which is preferable. Details of the heat-extensible conjugate fiber will be described later.

  The web obtained in the web forming step is then sent to a heat embossing device 21 as shown in FIG. 1, where heat embossing is performed. The heat embossing device 21 includes a pair of rolls 22 and 23. The roll 22 is a smooth roll having a smooth peripheral surface. On the other hand, the roll 23 is an engraving roll having a large number of convex portions formed on the peripheral surface. Each roll 22, 23 can be heated to a predetermined temperature.

The heat embossing is performed at a temperature not lower than the melting point T2 of the second resin component and lower than the melting point T1 of the first resin component in the heat-fusible conjugate fiber in the web 20. The heat-fusible conjugate fibers in the web 20 are pressure-bonded by heat embossing. As a result, a large number of pressure bonding portions are formed on the web 20. Each pressure-bonded portion is a circle, triangle, rectangle, other polygon, or a combination thereof having an area of about 0.1 to 3.0 mm ² and is regularly formed over the entire area of the web 20. . Further, the pressure-bonding portion may be a continuous straight line or a curve having a width of about 0.1 to 3.0 mm, and can be appropriately selected according to the purpose. In order to express the three-dimensional shape in the target nonwoven fabric using heat-extensible conjugate fibers as the heat-fusible conjugate fibers, there are some heat-fusible conjugate fibers that are not pressure bonded. There is a need. From this viewpoint, the embossing rate is preferably 1 to 25%, more preferably 2 to 15%.

  The pressure bonding portion refers to a bonding portion formed by pressure bonding or bonding of the constituent fibers of the web 20. Examples of means for crimping the fibers include embossing with or without heat, and ultrasonic embossing. On the other hand, as a means for adhering fibers, bonding with various adhesives can be mentioned. In the present embodiment, the pressure bonding portion is formed by embossing with heat.

  FIG. 2A schematically shows a cross-sectional state of the web 20 after heat embossing. A number of pressure-bonding portions 26 are formed on the web 20 by heat embossing. In the pressure bonding part 26, the heat-extensible conjugate fiber is pressure-bonded by the action of heat and pressure, or melted, solidified and fused. On the other hand, in the portions other than the pressure bonding portion 26, the heat-extensible conjugate fiber is in a free state in which no pressure bonding or fusion occurs.

  Returning to FIG. 1 again, the web 20 is conveyed to the first hot air blowing device 24 and subjected to the first hot air treatment step. In the hot air blowing device 24, the web 20 is subjected to hot air treatment at a temperature T3 which is lower than the melting point T1 of the first resin component and higher than the melting point T2 of the second resin component in the heat-fusible conjugate fiber contained therein. Specifically, the hot air heated to the temperature T3 is blown onto the web by a blower (not shown) such as a blower. The hot air blown to the web 20 passes through the web and is sucked by a suction box (not shown) installed therebelow. The sucked hot air is heated to the original temperature T3 and circulated to the blower. As described above, in the present embodiment, the hot air is blown to the web by a penetration method, that is, an air-through method. By blowing hot air of temperature T3, the second resin component in the heat-fusible conjugate fiber is melted and the intersection of the conjugate fibers is fused.

  Conditions such as the hot air blowing pressure, the wind speed, and the blowing time in the first hot air blowing device 24 are selected in accordance with the type of the heat-fusible conjugate fiber constituting the web, the basis weight of the web, and the like.

  The web 20 subjected to the first hot air treatment step in the first hot air blowing device 24 is continuously conveyed to the second hot air blowing device 25 and subjected to the second hot air treatment step. The second hot air blowing device 25 has the same structure as the first hot air blowing device 24 described above. In the second hot air blowing device 25, the web 20 is heat-treated at a temperature T4 that is higher than the temperature T3 in the previous hot air treatment step and lower than the melting point T1 of the first resin component. In FIG. 1, the first hot air spraying device 24 and the second hot air spraying device 25 are represented as separate devices, but the present invention is not limited to this. For example, in one spraying device, It is also possible to perform the first hot air treatment step and the second hot air treatment step continuously by separately setting the hot air blowing temperature. When the hot air treatment is performed continuously, the temperature may change stepwise from the first hot air treatment step to the second hot air treatment step, or may change continuously.

  The web 20 before being subjected to the first hot-air spraying step previously performed is in a free state in which the constituent fibers are not fused. When the hot air treatment is performed on the web 20 in this free state, the bulk of the web 20 becomes lower than that before the hot air treatment due to the blowing pressure of the hot air. That is, the fibers are clogged and the fibers are close to each other. When the web 20 in such a state is subjected to the second hot air blowing step, the fibers constituting the web are more clogged due to the hot air blowing pressure, and the fibers are brought closer to each other. As a result, the number of intersections between the fibers further increases, and the number of fusion points further increases. Thereby, the strength of the resulting nonwoven fabric 10 is improved. As described above, in the present embodiment, the hot air treatment is performed in at least two stages, thereby increasing the number of fusion points between the constituent fibers and improving the strength of the nonwoven fabric. Moreover, since air-through hot air blowing is employed for fusing the constituent fibers together, it is possible to prevent the resulting nonwoven fabric from becoming too hard.

  In particular, when a heat-extensible conjugate fiber is used as the heat-fusible conjugate fiber, the web 20 is given bulkiness in the second hot air treatment step. The reason for this is as follows. When the hot air treatment is performed at the temperature T4 on the web 20 after being subjected to the first hot air spraying step, the heat-extensible conjugate fiber existing in a portion other than the pressure bonding portion 26 in the web 20 is stretched. Since a part of the heat-extensible conjugate fiber is fixed by the pressure bonding portion 26, it is the portion between the pressure bonding portions 26 that extends. Further, since a part of the heat-extensible conjugate fiber is fixed by the pressure bonding portion 26, the stretched portion of the elongated heat-extensible conjugate fiber loses its place in the plane direction of the web 20, and the web 20 Move in the thickness direction. As a result, convex portions are formed between the pressure bonding portions 26. As a result, the nonwoven fabric 10 finally obtained becomes bulky. Moreover, the surface of a nonwoven fabric comes to show a three-dimensional external appearance by formation of this convex part. This state is shown in FIG. As is apparent from this figure, the three-dimensional appearance means that the surface of the nonwoven fabric 10 has an uneven shape.

  When a heat-extensible composite fiber is used as the heat-fusible composite fiber, the difference between the temperature T3 and the temperature T4 is preferably 5 ° C. or more, particularly 5 to 15 ° C. The reason is that the fibers are fused by melting the second resin component, that is, the fusion of the intersections of the fibers in the first hot air blowing process, and the thermal expansion of the fibers, that is, the intersection of the second hot air blowing process. This is because it becomes easy to individually control the thermal expansion of the fiber.

  In this manufacturing method, as shown in FIG. 1, when the second hot air treatment step is performed separately from the first hot air treatment step, the second hot air treatment step is performed in the first hot air treatment step. Since the two resin components are once melted, the internal strain that causes the second resin component to shrink the fiber is removed. Since it is attached to the second hot air treatment step under this state, there is an advantage that the thermal extensibility of the first resin component is not inhibited.

  On the other hand, when the first hot air treatment step and the second hot air treatment step are continuously performed, the second hot air treatment step leaves the second resin component in a molten state by the first hot air treatment step. Therefore, there is an advantage that heat energy can be used efficiently.

  The nonwoven fabric 10 obtained by this manufacturing method is shown in FIG. The non-woven fabric 10 has a substantially flat surface on one side 10 a and a concavo-convex shape on the other side 10 b having a large number of convex portions 11 and concave portions 12. The concave portion 12 includes a pressure bonding portion formed by pressing or bonding constituent fibers of the nonwoven fabric 10. The convex portion 11 is located between the concave portions 12. The inside of the convex portion 11 is filled with the constituent fibers of the nonwoven fabric 10. The convex part 11 and the recessed part 12 are alternately arrange | positioned over one direction (X direction in FIG. 3) of a nonwoven fabric. Further, they are alternately arranged in a direction (Y direction in FIG. 3) orthogonal to the one direction. Since the convex portion 11 and the concave portion 12 are arranged in this way, when the nonwoven fabric 10 is used with a surface sheet in the field of disposable hygiene articles such as disposable diapers and sanitary napkins, The contact area is reduced, and stuffiness and rash are effectively prevented.

  As is apparent from the above description, in the nonwoven fabric 10 using the heat-extensible conjugate fiber as the heat-fusible conjugate fiber, the heat-extensible conjugate fiber is pressure-bonded at the pressure-bonding portion 26, and pressure-bonded. The portions other than the portion 26, specifically, mainly the convex portions, are joined by heat fusion by an air-through method in which the intersection of the heat-extensible conjugate fibers is a means other than pressure bonding. As a result, the nonwoven fabric 10 has a three-dimensional concavo-convex shape and is flexible, but has high bonding strength between fibers at the convex portions, and is less likely to fluff. In addition, the present manufacturing method is a combination of a heat bonding method and an air-through method, which are extremely general methods for manufacturing nonwoven fabrics, and does not include any special process. Therefore, the manufacturing process is simple and the manufacturing efficiency is high. Furthermore, if the above-mentioned manufacturing method is used, even if the nonwoven fabric 10 has a low basis weight, a three-dimensional uneven shape can be easily formed. Further, unlike a conventional uneven nonwoven fabric, a three-dimensional shape can be easily formed even if the nonwoven fabric is a single layer.

  From the viewpoint of making the uneven shape of the nonwoven fabric 10 containing the heat-extensible nonwoven fabric more prominent, at least the first hot air blowing step and the hot air blowing step in the first hot air blowing step, It is preferable to carry out from the surface facing the smooth roll used in the heat embossing.

  The nonwoven fabric 10 obtained in this way can be applied to various fields utilizing its texture and high strength. In particular, when the nonwoven fabric 10 contains a heat-extensible composite fiber, the nonwoven fabric 10 can be applied to various fields that make use of the uneven shape, bulkiness, and high strength. For example, surface sheets in the field of disposable hygiene articles such as disposable diapers and sanitary napkins, second sheets (sheets disposed between the surface sheet and the absorber), back sheets, leak-proof sheets, or personal wipes, It is suitably used as a skin care sheet, and further as an objective wiper.

When used for such applications, the nonwoven fabric 10 preferably has a basis weight of 15 to 60 g / m ² , particularly 20 to 50 g / m ² . Moreover, it is preferable that the thickness is 1-5 mm, especially 2-4 mm. However, since the appropriate thickness varies depending on the application, it is appropriately adjusted according to the purpose.

  Next, the heat extensible composite fiber used suitably for this manufacturing method is demonstrated. The 1st resin component in a heat | fever extensible composite fiber is a component which expresses the heat | fever extensibility of this fiber, and a 2nd resin component is a component which expresses heat-fusibility. The first resin component preferably has an orientation index of 30 to 60%, more preferably 35 to 55%. On the other hand, the second resin component has an orientation index of preferably 40% or more, and preferably 50% or more. There is no restriction | limiting in particular in the upper limit of the orientation index of a 2nd resin component, but it is so preferable that it is high, but if it is about 70%, the effect which can be fully satisfied is acquired. The orientation index is an index of the degree of orientation of the polymer chain of the resin constituting the fiber. And when the orientation index of a 1st resin component and a 2nd resin component is each said value, a heat | fever extensible composite fiber comes to expand | extend by heating.

The orientation index of the first resin component and the second resin component is expressed by the following formula (1), where A is the birefringence value of the resin in the heat-extensible conjugate fiber, and B is the intrinsic birefringence value of the resin. expressed.
Orientation index (%) = A / B × 100 (1)

  Intrinsic birefringence refers to birefringence in the state where the polymer polymer chains are perfectly oriented. The values are, for example, the first edition of “Plastic Materials in Molding”, and the typical plastic materials (plastic Edited by the Japan Society for Molding and Processing, Sigma Publishing, published on February 10, 1998).

The birefringence in the heat-extensible composite fiber is measured under polarization in a direction parallel to and perpendicular to the fiber axis by attaching a polarizing plate to an interference microscope. As the immersion liquid, a standard refraction liquid manufactured by Cargille is used. The refractive index of the immersion liquid is measured with an Abbe refractometer. From the interference fringe image of the composite fiber obtained by the interference microscope, the refractive index in the direction parallel and perpendicular to the fiber axis is obtained by the calculation method described in the following document, and the birefringence that is the difference between the two is calculated.
“Fiber structure formation in high-speed spinning of core-sheath type composite fiber”, page 408 (Journal of the Fiber Society, Vol. 51, No. 9, 1995)

  The heat stretchable conjugate fiber can be stretched by heat at a temperature lower than the melting point of the first resin component. And it is preferable that the heat | fever extensible composite fiber is 0.5 to 20%, especially 3 to 20% in the heat | fever elongation rate in the temperature 10 degreeC higher than melting | fusing point or softening point of a 2nd resin component. When a nonwoven fabric is produced using fibers having such an elongation rate as a raw material, the nonwoven fabric becomes bulky or exhibits a three-dimensional appearance due to the elongation of the fibers. For example, the uneven shape on the surface of the nonwoven fabric becomes remarkable.

  Moreover, it is preferable that the elongation rate (%) at the temperature T4 is 3 points or more, especially 3.5 points or more larger than the elongation rate (%) at the temperature T3. The reason is that the fibers are fused by melting the second resin component, that is, the fusion of the intersections of the fibers in the first hot air blowing process, and the thermal expansion of the fibers, that is, the intersection of the second hot air blowing process. This is because it becomes easy to individually control the thermal expansion of the fiber.

  The thermal elongation rate is measured by the following method. Using a thermomechanical analyzer TMA-50 (manufactured by Shimadzu Corp.), parallel fibers are mounted at a distance between chucks of 10 mm, and a constant load of 0.025 mN / tex is applied, and a temperature increase rate of 10 ° C./min. Raise the temperature at. The change in the elongation rate of the fiber at that time is measured, and the elongation rate at a temperature 10 ° C. higher than the melting point or softening point of the second resin component is read to obtain the thermal elongation rate of the fiber. The reason for measuring the thermal elongation at the above-mentioned temperature is that, when a nonwoven fabric is produced by thermally fusing the intersections of fibers, the temperature is higher than the melting point or softening point of the second resin component and about 10 ° C. higher than them. It is because it is normal to manufacture in the range. In the present invention, a fiber having a positive thermal elongation rate (elongated by heat) is called a thermally extensible fiber, and other fibers that are not elongated by heat are normal fibers.

  In order to achieve the orientation index as described above for each resin component in the thermally stretchable conjugate fiber, for example, the first resin component and the second resin component having different melting points are used, and melt spinning is performed at a low speed of less than 2000 m / min. Then, after obtaining the composite fiber, the composite fiber may be heat-treated and / or crimped. In addition to this, the stretching process may be avoided.

  As shown in FIG. 4, the melt spinning method is performed using a spinning device provided with two systems of extrusion devices 1 and 2 including extruders 1 </ b> A and 2 </ b> A and gear pumps 1 </ b> B and 2 </ b> B and a spinneret 3. The resin components melted and measured by the extruders 1A and 2A and the gear pumps 1B and 2B are merged in the spinneret 3 and discharged from the nozzle. As the shape of the spinneret 3, an appropriate shape is selected according to the shape of the target composite fiber. A winding device 4 is installed immediately below the spinneret 3, and the molten resin discharged from the nozzle is taken down at a predetermined speed. The take-up speed of the spun yarn in the melt spinning method of this embodiment is preferably less than 2000 m / min, more preferably 1000 to 1800 m / min. The temperature of the die (spinning temperature) depends on the type of resin used. For example, when polypropylene is used as the first resin component and polyethylene is used as the second resin component, the temperature is 200 to 300 ° C., particularly 220 to It is preferable to set it as 280 degreeC.

  Since the fiber thus obtained is spun at a low speed, it is in an undrawn yarn state. The undrawn yarn is subjected to heat treatment and / or crimping treatment.

  Appropriate conditions for the heat treatment are selected according to the types of the first and second resin components constituting the composite fiber. The heating temperature is lower than the melting point of the second resin component. For example, when the heat-extensible conjugate fiber is a core-sheath type, the core component is polypropylene and the sheath component is high-density polyethylene, the heating temperature is preferably 50 to 120 ° C., particularly preferably 70 to 115 ° C., and the heating time Is preferably 10 to 1800 seconds, more preferably 20 to 1200 seconds. Examples of the heating method include hot air blowing and infrared irradiation.

  On the other hand, as the crimping process, it is simple to perform mechanical crimping. There are two-dimensional and three-dimensional forms of mechanical crimping. In addition, there are three-dimensional manifested crimps found in the eccentric type core-sheath type composite fiber and side-by-side type composite fiber. In the present invention, any type of crimping may be performed. The crimping process may be accompanied by heating. In that case, the heat treatment and the crimping treatment are performed simultaneously. Further, in addition to the heating in the crimping process, a separate heat treatment may be performed.

  In the crimping process, the fiber may be somewhat stretched, but such stretching is not included in the stretching process referred to in the present invention. The drawing treatment referred to in the present invention refers to a drawing operation with a draw ratio of 2 to 6 times that is usually performed on undrawn yarn.

  The melting point of the first resin component and the second resin component in the thermally stretchable conjugate fiber are such that the difference between the melting points of both resin components or the softening point of both resin components is 20 ° C. or more, particularly 25 ° C. or more. It is preferable from the viewpoint that the nonwoven fabric can be easily manufactured by heat fusion. Moreover, it is desirable that the first resin component has crystallinity. Resin having crystallinity is a general term for resins that are melt-spun and stretched to the extent that they are normally carried out, and it is a general term for resins that produce sufficient orientation and crystals. Is a resin that can be defined. As a preferable combination of the first resin component and the second resin component, as the second resin component when the first resin component is polypropylene (PP), high-density polyethylene (HDPE), low-density polyethylene (LDPE), Examples thereof include polyethylene such as linear low density polyethylene (LLDPE), ethylene propylene copolymer, and polystyrene. When a polyester resin such as polyethylene terephthalate (PET) or polybutylene terephthalate (PBT) is used as the first resin component, polypropylene (PP) is added as the second component in addition to the above-described example of the second resin component. And copolyester. Furthermore, examples of the first resin component include polyamide-based polymers and two or more types of copolymers of the first resin component described above, and examples of the second resin component include two or more types of the second resin component described above. Copolymers are also included. These are appropriately combined.

  A particularly preferred combination of the first resin component and the second resin component is a combination in which the first resin component is polypropylene and the second resin component is polyethylene, particularly high-density polyethylene. This is because the non-woven fabric can be easily manufactured because the difference in melting point between both resin components is in the range of 20 to 40 ° C. In addition, since the specific gravity of the fiber is low, a nonwoven fabric that is lightweight and excellent in cost and can be incinerated and discarded with a low heat quantity is obtained. Further, by using this combination, the heat stretchability of the heat stretchable conjugate fiber is also increased. The reason for this is as follows. The heat-extensible conjugate fiber has a structure in which the orientation coefficient of the first resin component is suppressed within a specific range and the orientation coefficient of the second resin component is increased. Polyethylene, which is the second resin component, particularly high-density polyethylene, is a substance having high crystallinity. Therefore, until the heat-extensible composite fiber is heated and the temperature reaches the melting point of polyethylene, the heat elongation of the fiber is restrained by the polyethylene. When the fiber is heated to the melting point of polyethylene or higher, the polyethylene starts to melt and the restriction is released, so that the first resin component, polypropylene, can be stretched, and the entire fiber stretches.

  The melting point of the first resin component and the second resin component was determined by using a differential scanning thermal analyzer DSC-50 (manufactured by Shimadzu Corporation) and performing thermal analysis of a finely cut fiber sample (sample mass 2 mg) at a heating rate of 10 ° C. / The melting peak temperature of each resin is measured and defined by the melting peak temperature. When the melting point of the second resin component cannot be clearly measured by this method, the temperature at which the second resin component is fused to such an extent that the fiber fusion point strength can be measured as the temperature at which the second resin component begins to flow. Is the softening point.

  The ratio (weight ratio) between the first resin component and the second resin component in the heat-extensible composite fiber is preferably 10:90 to 90: 10%, particularly 30:70 to 70: 30%. Within this range, the mechanical properties of the fiber are sufficient, and the fiber can withstand practical use. Further, the amount of the fusion component is sufficient, and the fibers are sufficiently fused.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples.

[Production of fiber]
Prior to Examples and Comparative Examples, the production of fibers used in Examples and Comparative Examples will be described.
(1) Fiber A
Melt spinning was performed under the conditions shown in Table 1 to obtain a concentric core-sheath composite fiber. The obtained conjugate fiber was not subjected to stretching treatment and subjected to mechanical crimping. Furthermore, it was set as the short fiber of fiber length 51mm. About the obtained fiber, the orientation index and melting | fusing point of resin, and the elongation ratio of the fiber were measured by the above-mentioned method (thermally-stretched fiber).
(2) Fiber B
Similarly, melt spinning was performed under the conditions shown in Table 1 to obtain a concentric core-sheath type composite fiber. The resulting composite fiber was subjected to a double stretching process and mechanical crimping. Furthermore, it was set as the short fiber of fiber length 51mm. About the obtained fiber, the orientation index and melting | fusing point of resin, and the elongation rate of the fiber were measured similarly (normal fiber).
All these results are shown in Table 1. Although not shown in the table, all fiber thicknesses were 3.3 dtex.

[Examples 1-3 and Comparative Examples 1-4]
Using the fiber A and the fiber B, a nonwoven fabric was manufactured by the method shown in FIG. A specific manufacturing method is as follows. First, the web formed using the card machine was embossed. The embossing was performed such that a circular pressure-bonding portion was formed and the area ratio of the pressure-bonding portion was 3%. The processing temperature was 130 ° C. Next, air-through processing was performed. In the air-through process, heat treatment of blowing hot air from the surface facing the smooth roll in embossing was performed twice under the conditions shown in Table 2. Table 2 also shows the fiber elongation at each heat treatment temperature in air-through processing. This elongation rate is a value obtained by reading the elongation rate at each temperature from the change in the elongation rate of the fiber measured by the method described above. The thickness, basis weight, specific volume, and strength per unit basis weight of the obtained nonwoven fabric were measured by the following methods. Further, the three-dimensional formability was evaluated by the following method. The results are shown in Table 2.

[Thickness, basis weight, specific volume]
A 12 cm × 12 cm plate is placed on the measurement table, and the position of the upper surface of the plate in this state is used as a measurement reference point A. Next, the plate is removed, a non-woven fabric test piece to be measured is placed on the measurement table, and the plate is placed thereon. The position of the upper surface of the plate in this state is B. From the difference between A and B, the thickness of the nonwoven fabric specimen to be measured is determined. The weight of the plate can be variously changed depending on the purpose of measurement. Here, the plate was measured using a plate having a weight of 54 g. A laser displacement meter (manufactured by Keyence Corporation, CCD laser displacement sensor KL-080) was used as a measuring instrument. Instead of this, a dial gauge thickness gauge may be used. However, when using a thickness meter, it is necessary to adjust the pressure applied to the nonwoven fabric test piece. Moreover, the thickness of the nonwoven fabric measured by the above-mentioned method greatly depends on the basis weight of the nonwoven fabric. Therefore, a specific volume (cm ³ / g) calculated from the thickness and basis weight is adopted as an index of bulkiness. The measurement of the basis weight is optional, but the weight of the test piece itself for measuring the thickness is weighed and calculated from the measured size of the test piece.

〔Strength〕
A strip having a length of 100 mm and a width of 25 mm is cut out from the nonwoven fabric to be measured in the direction perpendicular to the machine flow direction (MD direction) (CD direction) and used as a test piece. This test piece is attached to a Tensilon tensile tester with a chuck spacing of 75 mm and a tensile test is performed at a tensile speed of 300 m / min. The maximum strength at that time is defined as the strength of the nonwoven fabric. Here, since the nonwoven fabric strength greatly depends on the basis weight, the value obtained by dividing the nonwoven fabric strength by the basis weight is used as an index representing the strength of the nonwoven fabric as the strength per unit basis weight.

[Three-dimensional shaping]
The nonwoven fabric was visually observed and judged according to the following criteria.
◎: Clear three-dimensional shape ○: Three-dimensional shape Δ: Almost no three-dimensional shape is recognized ×: Not three-dimensional shape

  From the results shown in Table 2, it can be seen that the nonwoven fabric produced by the method of the example is not only bulky and high in strength, but also excellent in three-dimensional formability.

[Examples 4 and 5 and Comparative Examples 5 and 6]
Using the fiber B, a nonwoven fabric was produced under the conditions shown in Table 3. A specific manufacturing method is as follows. First, a web was formed using a card machine. This web was subjected to air-through processing. In the air-through process, heat treatment for blowing hot air was performed twice under the conditions shown in Table 3. The thickness, basis weight, specific volume, and strength per unit basis weight of the obtained nonwoven fabric were measured by the above-described methods, and the texture was evaluated by the following methods. The results are shown in Table 3.

[Texture]
The texture was evaluated in five stages by a sensory test with five monitors (5: very soft, 4: soft, 3: normal, 2: hard, 1: very hard), and the average value was calculated.

  From the results shown in Table 3, it can be seen that the non-woven fabric produced by the method of the example can exhibit strength while maintaining bulkiness and texture.

FIG. 1 is a schematic view showing an apparatus used in an embodiment of the production method of the present invention. FIG. 2 is a schematic view showing a state in the process of manufacturing a nonwoven fabric using the apparatus shown in FIG. FIG. 3 is a perspective view showing an example of a nonwoven fabric manufactured according to an embodiment of the manufacturing method of the present invention. FIG. 4 is a schematic view showing an apparatus used in the melt spinning method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 Extruder 1A, 2A Extruder 1B, 2B Gear pump 3 Spinneret 4 Winding device 10 Nonwoven fabric 11 Convex part 12 Concave part 20 Web 21 Heat embossing apparatus 22, 23 Roll 24 1st hot air spraying apparatus 25 2nd hot air spraying apparatus 26 Pressure bonding part

Claims (6)

In a method for producing a nonwoven fabric in which a hot air treatment is applied to a web containing a heat-fusible composite fiber to fuse the intersections of the fibers,
The composite fiber is composed of a first resin component and a second resin component having a lower melting point or softening point than the first resin component, and the second resin component is present continuously in the length direction at least part of the fiber surface,
The web is treated with hot air at a temperature T3 that is lower than the melting point T1 of the first resin component and equal to or higher than the melting point T2 of the second resin component to fuse the intersections of the fibers, and is further higher than the temperature T3 and lower than T1. The manufacturing method of the nonwoven fabric which hot-air processes at temperature T4 which is temperature.   The composite fiber has an orientation index of the first resin component of 30 to 60% and an orientation index of the second resin component of 40% or more, and is subjected to heat treatment or crimping treatment. The production method according to claim 1, wherein the composite fiber is a heat-extensible composite fiber that can be stretched by heat at a temperature lower than the melting point.   The method according to claim 2, wherein the difference between the melting point of the first resin component and the melting point of the second resin component, or the difference between the melting point of the first resin component and the softening point of the second resin component is 20 ° C or higher.   4. The method according to claim 2, wherein the thermally stretchable conjugate fiber has an elongation rate (%) at a temperature T <b> 4 that is 3 points or more larger than an elongation rate (%) at a temperature T <b> 3.   The manufacturing method according to any one of claims 2 to 4, wherein a difference between the temperature T3 and the temperature T4 is 5 ° C or more.   After the web is partially crimped or bonded to form a number of pressure-bonding portions, the web is hot-air treated at temperature T3 to fuse the intersections of the fibers, and then hot-air treatment is performed at temperature T4 between the intersections. The production method according to any one of claims 2 to 5, wherein the fibers are elongated.

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