JP2012001866A - Nonwoven fabric - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonwoven fabric, that is bulky and capable of increasing a flow speed of liquid in a thickness direction.SOLUTION: A nonwoven fabric comprises: first fibers made of fibers having thermal elongation property that elongates with heat; and second fibers made of heat-weldable conjugate fibers having nonthermal elongation property that do not substantially elongate with heat. The nonwoven fabric is obtained by thermal welding of fiber intersections of a web produced by a carding method. A mixing ratio (the former/latter) of the first fibers and the second fibers is 20/80 to 80/20 by weight ratio. Intersections between the first fibers, those between the second fibers, and those between the first fibers and the second fibers are thermally welded by an air-through method. A ratio (a flow direction/width direction) of orientation of fibers in the flow direction of the nonwoven fabric and orientation of fibers in the width direction of the nonwoven fabric is 1.0 to 1.3.

Description

  The present invention relates to a nonwoven fabric and a method for producing the same. The nonwoven fabric of the present invention is particularly preferably used as a constituent material of absorbent articles such as sanitary napkins and disposable diapers.

  Regarding a nonwoven fabric made of heat-extensible fiber, which is a fiber whose length is increased by heating, the present applicant has previously described a heat-fusible composite fiber composed of two components having different melting points, and a non-heat-fusible fiber. An intersection of the heat-fusible conjugate fibers is heat-sealed, and the heat-fusible conjugate fiber and the non-heat-fusible fiber are non-heat-bonded nonwoven fabrics, As a raw material of the conductive composite fiber, a material using a heat-extensible fiber having a resin orientation index in a specific range has been proposed (see Patent Document 1).

  Separately from this, regarding the nonwoven fabric made of heat-extensible fibers, the present applicant has a number of pressure-bonded portions to which the constituent fibers are pressure-bonded or bonded, and the constituent fibers in portions other than the pressure-bonded portions. Also proposed is a three-dimensional shaped non-woven fabric in which the intersecting points are joined by means other than pressure bonding, and the pressure bonding part is a concave part and the concave part is a convex part between at least one side. (See Patent Document 2). This nonwoven fabric has the advantage that it has a three-dimensional uneven shape, is flexible, and has a low basis weight, without using a special manufacturing method, by using heat-extensible fibers as a raw material.

  As a result of further investigations by the present inventors on the nonwoven fabric made of heat-extensible fibers, the heat-extensible fibers have a lower flexural modulus than that of ordinary heat-fusible fibers, which It was found that when a load is applied in the thickness direction, the bulk tends to decrease.

JP-A-2005-350835 JP 2005-350836 A

  Therefore, the subject of this invention is providing the nonwoven fabric which can eliminate the fault which the prior art mentioned above relates to the nonwoven fabric which uses a heat | fever extensible fiber as a raw material.

The present invention includes a first fiber made from a heat-extensible fiber whose length is increased by heating, and two components having different melting points, and is subjected to stretching treatment, and the length does not substantially increase by heating. A non-woven fabric obtained by heat-sealing the intersection of fibers in a web produced by the card method, including a second fiber made from a non-heat-extensible heat-fusible composite fiber,
The mixing ratio of the first fiber and the second fiber (the former / the latter) is 20/80 to 80/20 by weight ratio,
The intersection of the first fibers, the intersection of the second fibers, and the intersection of the first fibers and the second fibers are each heat-sealed by an air-through method,
A nonwoven fabric having a ratio (flow direction / width direction) of the degree of orientation of fibers along the flow direction of the nonwoven fabric and the degree of orientation of fibers along the width direction is 1.0 to 1.3.

In addition, the present invention includes a heat-extensible fiber that includes a heat-extensible fiber whose length is increased by heating and two components having different melting points and is subjected to a stretching treatment, and the heat-extensible heat that does not substantially extend its length by heating. Using a fusible composite fiber as a raw material, a web is manufactured by a card machine,
Hot air is blown onto the web by an air-through method to elongate the heat-extensible fibers, and the intersection points of the heat-extensible fibers, the intersection points of the heat-fusible composite fibers, and the heat-extensible fibers and the heat-melting fibers. Heat-bonding the intersection with the adhesive composite fiber, and producing a nonwoven fabric from the web,
In the production of the web using a card machine, there is provided a method for producing a nonwoven fabric in which the circumferential speed of condensation is set to 20 to 45% with respect to the circumferential speed of the doffer in the card machine.

  ADVANTAGE OF THE INVENTION According to this invention, the nonwoven fabric which is bulky and can raise the passage speed of the liquid in the thickness direction is provided.

1 (a) and 1 (b) are schematic views showing the state of changes in the constituent fibers of the web in the process of producing the nonwoven fabric of the present invention. FIG. 2 is a schematic view showing an apparatus suitably used for producing the nonwoven fabric of the present invention. FIG. 3 is a schematic diagram showing the structure of the card machine in the apparatus shown in FIG.

  Hereinafter, the present invention will be described based on preferred embodiments thereof. The non-woven fabric of the present invention includes, as constituent fibers, (a) a first fiber made from a heat-extensible fiber, which is a fiber whose length is extended by heating, and (b) two components having different melting points, and stretched It is characterized by including a second fiber that has been treated and is made from a non-heat-stretchable, heat-fusible composite fiber that does not substantially extend its length upon heating.

The nonwoven fabric of the present invention containing the first fiber and the second fiber can be obtained by heat-sealing an intersection of fibers in the web containing the heat-extensible fiber and the heat-fusible composite fiber by an air-through method. This web is manufactured by the card method. When a web is manufactured by the card method, in general, fibers are easily oriented in the flow direction of the web, and the fibers are not easily oriented in the width direction of the web. Therefore, also in the nonwoven fabric manufactured from the web obtained by the card method, the constituent fibers are in a state of being oriented in the flow direction rather than in the width direction. As a result, in a general nonwoven fabric, when the degree of fiber orientation in the flow direction is H _MD and the degree of fiber orientation in the width direction is H _CD , H _MD / H _CD (hereinafter referred to as H _MD / H _CD ). Is also a large value exceeding 1. On the other hand, in the nonwoven fabric of the present invention, although the value of H _MD / H _CD exceeds 1, although the card web is used as a raw material, the value is smaller than that of a general nonwoven fabric. Yes. Specifically, the nonwoven fabric of the present invention has a small value of H _MD / H _CD of 1.0 to 1.3, particularly 1.0 to 1.2. This also characterizes the nonwoven fabric of the present invention.

By the value of H _MD / H _CD card web of the nonwoven fabric of the present invention as a raw material is within the above range, the nonwoven fabric of the present invention, bulky, and has high rate of passage of the liquid in the thickness direction . The reason for this is as follows. In the card web which is a raw material of the nonwoven fabric of the present invention, the ratio H _MD / H _CD of the degree of fiber orientation in the flow direction and the width direction is substantially the same as that of the nonwoven fabric of the present invention. That is, it is within the above-mentioned range. In the web having such an orientation degree ratio, the degree of entanglement between the heat-extensible fibers and the heat-fusible composite fibers, which are constituent fibers, is high. On the other hand, in the web in which the orientation ratio is out of the above range, the fibers are preferentially oriented in either the flow direction or the width direction. The degree of entanglement with the composite fiber is lower than in the present invention. When heat-treating a web having a high degree of entanglement between the heat-extensible fiber and the heat-fusible composite fiber, for example, when viewed in the cross-section in the thickness direction of the web, as shown in FIG. Is stretched, and the stretch is effectively transmitted to the heat-fusible conjugate fiber intertwined with the heat-stretchable fiber. As a result, due to the elongation of the heat-extensible fiber, the heat-fusible conjugate fiber entangled with the heat-extensible fiber moves in a direction away from the heat-extensible fiber, and the inter-fiber distance increases. In addition, when the heat-extensible fiber is stretched as shown in FIG. 1B, the heat-fusible conjugate fiber is deformed so as to be convex upward, and thereby the heat-fusible conjugate fiber is It moves in the direction away from the heat-extensible fiber, and the inter-fiber distance increases. For these reasons, the non-woven fabric of the present invention has a large inter-fiber distance when viewed in the thickness direction, and at the same time, the fibers are more directed in the thickness direction of the non-woven fabric. As a result, the passage speed of the liquid in the thickness direction is increased. In particular, the passage speed of highly viscous liquids such as menstrual blood and loose stool is increased. Therefore, the nonwoven fabric of the present invention is a constituent material of absorbent articles such as sanitary napkins and disposable diapers, particularly as a surface sheet that comes into contact with the wearer's skin, or as an intermediate sheet disposed between the surface sheet and the absorbent body. Preferably used. Conventionally, controlling the orientation ratio of nonwoven fabric fibers itself has been carried out in the technical field, but such control exclusively has the same mechanical properties such as tensile strength and tensile elasticity in the flow direction and width direction. The purpose was to be. However, it has not been considered at all to make the nonwoven fabric bulky by controlling the orientation ratio of the fibers of the card web containing the heat-extensible fibers and non-heat-extensible fibers as in the present invention. Further, in the nonwoven fabric using the air-through method, the ratio of the orientation degree of the fiber along the flow direction of the nonwoven fabric and the orientation degree of the fiber along the width direction is as small as the present invention, as far as the present inventors know. It was.

  From the viewpoint of making the above-described bulky effect more remarkable, the mixing ratio (the former / the latter) of the first fiber and the second fiber in the nonwoven fabric of the present invention is 20/80 to 80/20 by weight ratio. In particular, it is preferable that the ratio is 50/50 to 70/30.

The degree of fiber orientation in the nonwoven fabric of the present invention can be measured using a high-precision molecular orientation meter MOA-6004 of Oji Scientific Instruments. The measurement is performed with GAIN = 1.0. The test piece is cut into a rectangle of 90 mm in the flow direction (MD) and 90 mm in the width direction (CD). Put it in a dedicated sample folder so that MD and CD face the specified direction, and attach it to the measuring instrument. At this time, a sample folder suitable for the thickness of the test piece is used. The value of H _MD / H _CD in the present invention is a MOR value obtained under these measurement conditions.

  As described above, the first fiber is made of a heat-extensible fiber as a raw material, and the heat-extensible fiber is composed of a fiber that is elongated by application of heat. Accordingly, the heat-extensible fibers contained in the card web and the first fibers contained in the nonwoven fabric obtained by heat-treating the card web are different when viewed as fibers. The second fiber contains two components having different melting points, is stretched, and is made from a non-thermally stretchable heat-fusible composite fiber whose length does not substantially extend by heating. This heat-fusible conjugate fiber has no substantial change before and after application of heat. That is, the heat-fusible conjugate fiber contained in the card web and the second fiber contained in the nonwoven fabric obtained by heat-treating the card web are substantially the same.

The nonwoven fabric of the present invention, which is characterized by being bulky, has a thickness of 0.5 to 3 mm, particularly 0.7 to 3 mm, when this is used as a top sheet of an absorbent article, for example. It is preferable. Further, the condition that the thickness is within this range, the nonwoven fabric of the present invention preferably has a basis weight of 10 to 80 g / m ^2, in particular 15 to 60 g / m ^2. The apparent density of the nonwoven fabric that is an index of bulkiness can be obtained by dividing the basis weight by the thickness. The thickness of the nonwoven fabric is measured by observing the longitudinal section of the nonwoven fabric. First, the nonwoven fabric is cut into a size of 100 mm × 100 mm, and a measurement piece is collected. A plate of 12.5 g (diameter 56.4 mm) is placed on the measurement piece, and a load of 49 Pa is applied. Under this state, the longitudinal section of the nonwoven fabric is observed with a microscope (manufactured by Keyence Corporation, VHX-900), and the thickness is measured.

  In the nonwoven fabric of the present invention, the intersections of the first fibers, the intersections of the second fibers, and the intersections of the first fibers and the second fibers are thermally fused by the air-through method. This heat-sealing reliably holds the three-dimensional network of constituent fibers, and the nonwoven fabric of the present invention is bulky, but it is difficult to reduce the thickness when a compressive force is applied in the thickness direction. Whether or not the intersection of the fibers is thermally fused by the air-through method can be determined by observing the nonwoven fabric with a scanning electron microscope.

  The nonwoven fabric of this invention has one of the characteristics also in the magnitude relationship of the fiber diameter of a 1st fiber and a 2nd fiber. Specifically, the first fiber has a fiber diameter larger than that of the second fiber. Thereby, the rough feeling of the surface of a nonwoven fabric reduces, and the touch of a nonwoven fabric becomes favorable. In general, the roughness of the surface of the nonwoven fabric depends on the thickness of the constituent fibers, and the roughness becomes more pronounced as the thickness increases. By the way, as a result of the study by the present inventors, when compared with the same thickness, the first fiber made from the heat-extensible fiber is more rough than the second fiber made from the heat-fusible composite fiber. It turned out to be difficult to perceive. In other words, when compared with the same thickness, the second fiber is more perceived as having a rough feeling than the first fiber. Therefore, in the present invention, the fiber diameter of the first fiber is made larger than the fiber diameter of the second fiber. The reason why it is difficult for the first fiber to perceive a rough feeling is that the first fiber made from the heat-extensible fiber has a lower elastic modulus than the second fiber made from the heat-fusible fiber. The inventors have speculated. In addition, in the nonwoven fabric of this invention, since the 1st fiber is comprised from the heat | fever extensible fiber after carrying out a heat | fever extension, the fiber diameter of the 1st fiber said here is the heat | fever extension after extending | stretching by heating. It refers to the fiber diameter of the conductive fiber. In general, when the heat-extensible fiber is stretched by heating, the fiber diameter becomes small.

  The nonwoven fabric of the present invention may contain fibers other than the above-described first fibers and second fibers. Examples of such fibers include fibers that are not inherently heat-fusible (for example, natural fibers such as cotton and pulp, rayon and acetate fibers), acrylic fibers, and the like. For example, in the case of cotton, these fibers are contained in the nonwoven fabric for the purpose of imparting the nonwoven fabric with properties such as hygroscopicity.

  In the nonwoven fabric of the present invention, the shape of the nonwoven fabric is maintained because the intersection of the constituent fibers is heat-sealed by the air-through method. You may make it keep the form of. Such means includes hot embossing. According to hot embossing, the constituent fibers of the nonwoven fabric are consolidated by consolidation with heat. The thickness of the embossed part formed in the nonwoven fabric by this consolidation is reduced compared to other parts of the nonwoven fabric. The embossed portion has, for example, a circular shape or a rectangular shape, and can be formed in a dotted shape over the entire area of the nonwoven fabric. Alternatively, a plurality of straight or curved embossed portions can be formed. A plurality of linear or curved embossed portions may be formed so as to cross each other.

  Next, the suitable manufacturing method of the nonwoven fabric of this invention is demonstrated, referring FIG. First, the card web 12 is produced using the card machine 11. The card web 12 includes a heat-extensible conjugate fiber and a heat-fusible conjugate fiber in a state before elongation.

  The web 12 is sent to a hot embossing device 13 where it is hot embossed. The hot embossing device 13 includes a pair of rolls 14 and 15. The roll 14 is a concavo-convex roll (engraving roll) whose peripheral surface is processed to be concavo-convex. On the other hand, the roll 15 is a smooth roll (anvil roll) having a smooth peripheral surface. Each roll 14 and 15 is heated to a predetermined temperature.

  The hot embossing is preferably performed at a temperature not lower than the melting point of the second resin component in the heat-extensible conjugate fiber in the web 12 -20 ° C or higher and lower than the melting point of the first resin component. Further, the heat embossing is preferably performed at a temperature of the melting point of the low-melting component in the heat-fusible conjugate fiber in the web 12 that is −20 ° C. or higher and lower than the melting point of the high-melting component. Furthermore, it is preferable that the heat embossing is performed at a temperature lower than the temperature at which the heat stretchable conjugate fiber exhibits heat stretch. When the melting points of the second component of the heat-extensible conjugate fiber and the heat-fusible conjugate fiber are different, the temperature range is set to the lower melting point. The heat-extensible conjugate fiber and the heat-fusible conjugate fiber in the web 12 are joined by hot embossing. As a result, a large number of embossed portions are formed on the web 12 to form the heat bond nonwoven fabric 16. In the embossed portion of the heat bond nonwoven fabric 16, the heat-extensible conjugate fiber and the heat-fusible conjugate fiber are consolidated and joined. In the part other than the embossed part, the heat-extensible conjugate fiber and the heat-fusible conjugate fiber are both in a non-bonded free state. Further, the elongation of the heat-extensible composite fiber has not yet occurred.

  Next, the heat bond nonwoven fabric 16 is conveyed to the air-through device 17. In the air-through device 17, the heat-bonding nonwoven fabric 16 is subjected to air-through processing. That is, the air through device 17 is configured such that hot air heated to a predetermined temperature penetrates the heat bond nonwoven fabric 16. The air-through process is performed at a temperature at which the heat-extensible conjugate fiber in the heat bond nonwoven fabric 16 is elongated by heating. And the crossing point of the heat extensible composite fibers of the free state which exists in parts other than the embossed part in the heat bond nonwoven fabric 16, the cross point of the heat fusible composite fibers, and the heat extensible composite fiber and the heat fusible composite fiber At the temperature at which the intersection with the However, the temperature needs to be set to a temperature lower than the melting point of the first resin component of the heat-extensible conjugate fiber and the high melting point component of the heat-fusible conjugate fiber.

  By such an air-through process, the heat-extensible composite fiber existing in a portion other than the embossed portion is elongated. Since a part of the heat-extensible fiber is fixed by the embossed portion, the stretched portion is a portion between the embossed portions. And since the part of the heat stretchable fiber is fixed by the embossed part, the stretched portion of the heat stretchable composite fiber loses its place in the plane direction of the heat bond nonwoven fabric 16, and Move in the thickness direction. Along with this movement, as described above with reference to FIGS. 1A and 1B, the heat-fusible conjugate fiber entangled with the heat-extensible fiber also moves in the thickness direction. These actions increase the bulk. Further, by air-through processing, the intersections of the heat-extensible conjugate fibers, the intersections of the heat-fusible conjugate fibers, and the intersections of the heat-extensible conjugate fibers and the heat-fusible conjugate fibers are respectively heat-melted at the convex portion of the nonwoven fabric 16. Join by wearing. Thus, the target nonwoven fabric 10 is obtained.

  In the above manufacturing method, in order to set the blending ratio of the constituent fibers of the nonwoven fabric 10 within the above-described range, for example, the following operation may be performed in the manufacture of the card web 12 that is a raw material of the nonwoven fabric 10.

  FIG. 3 schematically shows the structure of the card machine 11 for manufacturing the card web 12. The card machine 11 has a cylindrical member called a main cylinder 20 disposed at the center thereof. The main cylinder 20 is rotatable around its axis. In the figure, the main cylinder 20 rotates in the direction indicated by the arrow. A large number of comb teeth (not shown) are erected on the peripheral surface of the main cylinder 20. The extending direction of the comb teeth coincides with the radial direction of the main cylinder 20. The main cylinder 20 is used for temporarily loosening (opening) and aligning the lump-like fiber mixture 12 ′ by the action of comb teeth provided on the peripheral surface thereof.

  A cylindrical member called a feed 21 and a breast 22 is arranged on the upstream side of the main cylinder 20. The feed 21 and breast 22 rotate in the direction indicated by the arrow in FIG. The feed 21 and the breast 22 have a function of feeding a mixture 12 ′ of heat-extensible fibers and heat-fusible composite fibers to the main cylinder 20.

  The card machine 11 further includes a striper 23 and a worker 24. The striper 23 and the worker 24 are both cylindrical members, and are disposed at positions facing the peripheral surface of the main cylinder 20. Further, the striper 23 and the worker 24 are arranged along the peripheral surface of the main cylinder 20 so that the worker 24 is positioned on the downstream side of the rotation with respect to the stripper 23. A plurality of sets of strippers 23 and workers 24 may be arranged.

  The stripper 23 and the worker 24 have a large number of comb teeth (not shown) erected on the peripheral surfaces thereof. The extending direction of the comb teeth coincides with the radial direction of the striper 23 and the worker 24. The fiber mixture 12 ′ supplied to the card machine 11 is uniformly arranged by the worker 24 and the stripper 23 on the main cylinder 20. The worker 24 functions to remove excess fibers located on the main cylinder 20 and return the stripper 23 to the main cylinder 20.

  The fiber mixture 12 ′ coming out of the main cylinder 20 is delivered to the doffer 25. The doffer 25 is a cylindrical member, and is arranged so that the peripheral surface thereof faces the peripheral surface of the main cylinder 20. The doffer 25 is used to deliver the fiber mixture 12 ′ coming out of the main cylinder 20 to a condensation 26 located downstream of the doffer 25.

  A condensation 26 made of a cylindrical member is disposed downstream of the doffer 25. The condensation 26 is arranged so that the circumferential surface thereof faces the circumferential surface of the doffer 25. The condensation 26 is used to deliver the card web 12 to a subsequent process while adjusting the alignment of the fibers in the fiber mixture 12 ′ received from the doffer 25 and forming the card web 12.

  This manufacturing method is characterized in that the peripheral speed of the doffer 25 with respect to the peripheral speed of the condensation 26 is made faster than the conventional operating conditions. By setting such conditions, the amount of the fiber mixture 12 ′ supplied from the doffer 25 to the condensation 26 becomes larger than that in the conventional case, and the fibers are packed in the condensation 26. As a result, the proportion of fibers oriented in the width direction is relatively high compared to fibers oriented in the flow direction. From the viewpoint of making this effect more prominent, the ratio of the peripheral speed of the condensation 26 to the peripheral speed of the doffer 25 (peripheral speed of the condensation 26 when the peripheral speed of the doffer 25 is 100) is 45% or less, particularly 20 It is preferable to set it to ˜45%.

  Furthermore, in this manufacturing method, the ratio of the speed fed from the heat embossing device 13 to the speed at which the card web 12 is introduced into the air through device 17 (when the speed of the web 12 introduced into the air through device 17 is 100). The speed of the web 12 delivered from the hot embossing device 13) is preferably set to 90 to 100%, particularly 95 to 100%. This speed ratio is larger than the manufacturing conditions for the conventional air-through nonwoven fabric. By increasing the speed ratio, the tension applied to the card web 12 can be reduced. As a result, it is possible to prevent the fibers from being oriented in the flow direction in the card web 12. In the present invention, the card web may be made by a single card machine, or may be made by connecting a plurality of card machines. In the latter case, a part of the card web to be stacked may not be made by the method of the present invention.

  A hot embossing device 13 is installed between the card machine 11 and the air through device 17. In this hot embossing device 13, the heating temperature of the smooth roll 15 is set lower than the heating temperature of the uneven roll 14. It is preferable. Such a condition setting can also prevent the fibers from being oriented in the flow direction in the card web 12. The reason is as follows. The smooth roll 15 has a larger contact area with the card web 12 than the uneven roll 14. Therefore, if the smooth roll 15 and the uneven | corrugated roll 14 are set to the same heating temperature, it will become easy to stick the card web 12 of the smooth roll 15 which is a roll with a large contact area. Since the sticking of the card web 12 to the smooth roll 15 interferes with the production of the nonwoven fabric 10, conventionally, the card web 12 is sent out from the heat embossing device 13 in order to prevent this sticking from occurring. The ratio of the introduction speed into the air-through device 17 with respect to the speed was increased, and the card web 12 was forcibly peeled off from the smooth roll 15. However, such an operation contributes to the orientation of the fibers in the card web 12 in the flow direction, and should be avoided in the present invention. Therefore, in this manufacturing method, the card web 12 is prevented from sticking to the smooth roll 15 by setting the heating temperature of the smooth roll 15 lower than the heating temperature of the uneven roll 14. In addition, as described above, by reducing the ratio of the introduction speed to the air-through device 17 with respect to the speed at which the card web 12 is sent out from the card machine 11, it is possible to prevent an excessive tension from being applied to the card web. 12 is prevented from being oriented in the flow direction.

  From the above viewpoint, the heating temperature of the smooth roll 15 is preferably set to be 5 to 25 degrees lower than the heating temperature of the uneven roll 14, and more preferably set to be 10 to 20 degrees lower.

  The nonwoven fabric 10 obtained in this way can be applied to various fields that make use of its 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.

  Next, the heat-extensible fiber and the heat-fusible conjugate fiber that are the raw materials for the first fiber and the second fiber will be described. Examples of the heat-extensible fiber that is the raw material of the first fiber include a fiber that expands by changing the crystal state of the resin by heating. Particularly preferably used heat-extensible fibers include a first resin component and a second resin component having a melting point or softening point lower than the melting point of the first resin component, and the second resin component forms at least a part of the fiber surface. It is a composite fiber that exists continuously in the length direction (hereinafter, this fiber is referred to as “heat-extensible composite fiber”). 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 heat stretchable conjugate fiber is stretched by heating to a temperature lower than the melting point of the first resin component. In the production of the nonwoven fabric of the present invention, the heat-extensible conjugate fiber is elongated to produce the first fiber by performing a heat treatment at a temperature not lower than the melting point of the second resin component and lower than the melting point of the first resin component.

  The first resin component and the second resin component in the heat-extensible composite fiber preferably have a specific value for their orientation index from the viewpoint of sufficient heat-extensible expression. The orientation index of the resin is naturally different depending on the resin to be used. For example, when a polypropylene resin is used as the first resin component, the orientation index is preferably 60% or less, particularly 40% or less, and more preferably 25% or less. When the first resin component is polyester, the orientation index is preferably 25% or less, particularly 20% or less, and more preferably 10% or less. On the other hand, the second resin component preferably has an orientation index of 5% or more, particularly 15% or more, and more preferably 30% or more. 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 used in molding processes (plastics). 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 as 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. The heat-extensible conjugate fiber has a temperature of 10 to 20 ° C. higher than the melting point of the second resin component, and in the case of a resin having no melting point, the thermal elongation rate at a temperature 10 ° C. higher than the softening point is 0.5 to 20%, particularly It is preferably 3 to 20%, particularly 5.0 to 20%. When a nonwoven fabric is produced using fibers having such a thermal elongation rate as a raw material, the nonwoven fabric becomes bulky due to the elongation of the fibers.

  The melting points of the first resin component and the second resin component are measured using a differential scanning calorimeter (DSC6200 manufactured by Seiko Instruments Inc.). A finely cut fiber sample (sample weight 2 mg) is subjected to thermal analysis at a heating rate of 10 ° C./min, and the melting peak temperature of each resin is measured. The melting point is defined by its melting peak temperature. When the melting point of the second resin component cannot be clearly measured by this method, this resin is defined as “resin having no melting point”. In this case, the temperature at which the second resin component is fused to such an extent that the fusion point strength of the fiber can be measured is defined as the temperature at which the molecular flow of the second resin component begins.

The thermal elongation rate of the fiber is measured by the following method. A thermomechanical analyzer TMA / SS6000 manufactured by Seiko Instruments Inc. is used. As a sample, after preparing a plurality of fibers having a fiber length of 10 mm or more so that the total weight per 10 mm of the fiber length is 0.5 mg, and arranging the plurality of fibers in parallel, Mount on the device with 10mm distance between chucks The measurement start temperature is 25 ° C., and the temperature is increased at a temperature increase rate of 5 ° C./min with a constant load of 0.73 mN / dtex applied. The elongation amount of the fiber at that time is measured, and in the case of a resin having no melting point at a temperature 10 ° C. higher than the melting point of the second resin component, the elongation amount at a temperature 10 ° C. higher than the softening point is read. When the amount of elongation is Xmm, the thermal elongation rate is expressed by the following equation.
(X / 10) x 100 (%)
The reason why the thermal elongation rate is measured at the above-mentioned temperature is, as will be described later, when the nonwoven fabric is produced by thermally fusing the intersections of the fibers, and is higher than the melting point or softening point of the second resin component. It is because it is normal to manufacture in the range up to about 10 degreeC high temperature.

  In order for the heat-extensible composite fiber to achieve the above-described heat elongation rate, for example, a first resin component and a second resin component having different melting points are used, and melt spinning is performed at a low speed of less than 2000 m / min. After obtaining the fiber, the composite fiber may be heat-treated and / or crimped. In addition to this, the stretching process may be avoided.

  As the crimping process, it is convenient 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. Any aspect of crimping may be performed in the present invention. The crimping process may be accompanied by heating. Moreover, you may heat-process after a crimping process. Furthermore, in addition to the heat treatment after the crimping treatment, a separate heat treatment may be performed before the crimping treatment. Or you may perform a heat processing separately, without performing a crimping process.

  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.

  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 or polyester, and the sheath component is high-density polyethylene, the heating temperature is preferably 50 to 120 ° C., particularly preferably 70 to 115 ° C. The time is preferably 10 to 1800 seconds, particularly 20 to 1200 seconds. Examples of the heating method include hot air blowing and infrared irradiation. As described above, this heat treatment can be performed after the crimping treatment.

  There is no restriction | limiting in particular in the kind of 1st resin component and 2nd resin component, What is necessary is just resin with fiber formation ability. In particular, the difference in melting point between the two resin components, 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 more, particularly 25 ° C. or more. It is preferable because it can be easily performed. When the heat-extensible conjugate fiber is a core-sheath type, a resin having a melting point of the core component higher than the melting point or softening point of the sheath component is used. In particular, it is preferable to use a core-sheath type thermally stretchable conjugate fiber having a polyester such as polypropylene (PP) or polyethylene terephthalate (PET) as a core and a resin having a lower melting point than these as a sheath. 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 PP, the high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear Examples thereof include polyethylene such as low density polyethylene (LLDPE), ethylene propylene copolymer, and polystyrene. In addition, when a polyester resin such as PET or polybutylene terephthalate (PBT) is used as the first resin component, in addition to the example of the second resin component described above, PP, copolymer polyester, etc. may be used as the second resin component. Can be mentioned. 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.

  The ratio (weight ratio) between the first resin component and the second resin component in the heat-extensible composite fiber is 10:90 to 90: 10%, particularly 20:80 to 80: 20%, especially 50:50 to 70:30. % Is preferred. 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. Moreover, it is preferable that the ratio of the 1st resin component used as a core is large from a viewpoint of making the card | curd permeability favorable when it uses as a raw material of the nonwoven fabric manufactured with a card machine, without impairing extensibility.

  As the heat-extensible fiber, in addition to the above-described heat-extensible composite fiber, Japanese Patent No. 4131852, Japanese Patent Laid-Open No. 2005-350836, Japanese Patent Laid-Open No. 2007-303035, Japanese Patent Laid-Open No. 2007-204899, Japanese Patent The fibers described in 2007-204901 and JP-A-2007-204902 can also be used.

  The non-heat-extensible heat-fusible composite fiber used as a raw material together with the heat-extensible fiber includes two components having different melting points and is subjected to a drawing treatment. The heat-fusible conjugate fiber does not substantially extend its length even when heat is applied. The heat-fusible conjugate fiber is a bicomponent conjugate fiber that includes a high-melting-point component and a low-melting-point component, and the low-melting-point component continuously exists in the length direction at least part of the fiber surface. There are various forms of the composite fiber such as a core-sheath type and a side-by-side type, and any form can be used. The heat-fusible conjugate fiber is stretched at the raw material stage (that is, before being used for the nonwoven fabric). The stretching treatment referred to here is a stretching operation at a stretching ratio of about 2 to 6 times as described above.

  The fusing temperature of the heat-fusible composite fiber is preferably close to the fusing temperature of the heat-extensible fiber. Thereby, the heat-extensible fibers, the heat-fusible conjugate fibers, and the heat-extensible fibers and the heat-fusible conjugate fibers can be successfully fused. From this viewpoint, when the fusion temperature of the heat-fusible conjugate fiber is T1, and the fusion temperature of the heat-extensible fiber is T2, the difference between T1 and T2 is preferably within 20 ° C. Since it is not easy to strictly measure the fiber fusion temperature, the melting temperature of the resin involved in the fusion (that is, the low melting point resin) is replaced with the fusion temperature. The method for measuring the melting point uses the method described above.

  From the viewpoint of successfully fusing the heat-extensible fiber and the heat-fusible composite fiber, the low melting point component in the heat-fusible fiber and the second resin component in the heat-extensible composite fiber are the same type of resin. In the case of being different or different, it is preferable to have compatibility.

  In the heat-fusible conjugate fiber, the weight ratio of the high melting point component / low melting point component is preferably 6/4 to 2/8, particularly preferably 5/5 to 3/7. That is, it is preferable to contain a large amount of low melting point components. As a result, heat fusion by the air-through method occurs surely. This weight ratio can be calculated from the cross-sectional area of each of the high-melting component and the low-melting component measured by observing the cross-section of the heat-fusible conjugate fiber, and the density of each of the high-melting component and the low-melting component. As another means for surely causing the thermal fusion by the air-through method, it is possible to use one having a melt index of the low melting point component in the heat-fusible conjugate fiber of 10 to 40 g / 10 min, particularly 10 to 25 g / 10 min. preferable. The melt index is measured according to JIS K7210 under conditions of 190 ° C. and a load of 2.16 kg.

  As the resin of the heat-fusible composite fiber suitably used in relation to the above-described heat-extensible composite fiber, polypropylene or polyethylene terephthalate is used as a high melting point component, high density polyethylene (HDPE) as a low melting point component, and low density Examples thereof include combinations using polyethylene such as polyethylene (LDPE) and linear low density polyethylene (LLDPE), ethylene propylene copolymer, polystyrene, polypropylene, and copolyester.

  Both of the heat-extensible fiber and the heat-fusible composite fiber preferably have a fiber length of about 30 to 70 mm from the viewpoint of improving the passability of the card machine.

  As mentioned above, although this invention was demonstrated based on the preferable embodiment, this invention is not restrict | limited to the said embodiment. For example, in the manufacturing method described above, heat embossing is performed on the card web 12 to manufacture the heat bond nonwoven fabric 16, and air through processing is performed on the heat bond nonwoven fabric 16, but instead, heat embossing is performed. Instead, the card web 12 may be directly subjected to air-through processing.

  Moreover, the nonwoven fabric of this invention is not restricted to the thing of a single layer structure containing a 1st fiber and a 2nd fiber, The fiber layer containing a 1st fiber and a 2nd fiber, and 1 or 2 or more other fiber containing another fiber A non-woven fabric having a multilayer structure having a laminated structure with a fiber layer may be used. Further, it may be a composite nonwoven fabric obtained by laminating and integrating another nonwoven fabric with a single layer nonwoven fabric including the first fiber and the second fiber.

  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.

[Example 1]
A single-layer nonwoven fabric was produced using the apparatus shown in FIGS. The embossing roll 14 in the apparatus shown in FIG. 2 had a rhombus lattice-shaped convex part with a line width of 0.5 mm. The embossed area ratio in this nonwoven fabric was 14%. The heat-extensible fibers that are the raw materials of the first fibers and the heat-fusible conjugate fibers that are the raw materials of the second fibers were those shown in Table 1. The heat-extensible composite fiber is melt-spun at a take-up speed of 1300 m / min, then immersed in an aqueous solution of a hydrophilic oil agent to attach the oil agent, and then subjected to mechanical crimping, followed by heat treatment to dry the fiber. , And cut into short fibers (fiber length 51 mm). In addition, the extending | stretching process is not performed at the time of manufacture of this fiber (it is the same also in a following example and a comparative example). In addition, the extending | stretching process here means the extending | stretching operation of about 2-6 times normally performed with respect to the undrawn yarn obtained after melt spinning as mentioned above.

  Using these fibers as raw materials, nonwoven fabrics were produced under the conditions shown in Table 2. In the obtained nonwoven fabric, the intersections of the first fibers, the intersections of the second fibers, and the intersections of the first fibers and the second fibers were thermally fused by the air-through method.

[Comparative Examples 1 to 3]
The fibers shown in Table 1 were used, and the conditions shown in Table 2 were used. Except for these, a nonwoven fabric was obtained in the same manner as in Example 1.

[Evaluation]
About the nonwoven fabric obtained by the Example and the comparative example, the degree-of-orientation ratio of a fiber, a fiber diameter, basic weight, and thickness were measured by the above-mentioned method. Moreover, the liquid passing time of the nonwoven fabric was measured by the following method. These results are shown in Table 3 below.

[Measurement of liquid passage time]
Two tubes having an inner diameter of 35 mm are connected vertically, and a nonwoven fabric is sandwiched between the tubes. The apparatus assembled in this way is placed so that the sandwiched nonwoven fabric is horizontal. 10 cc of the test solution is dropped from the upper end of the upper tube toward the upper surface of the nonwoven fabric in 6 seconds, and the time from when the dropping is finished until the test solution enters the nonwoven fabric through the nonwoven fabric surface is visually confirmed. It was measured. The test solution was prepared by uniformly mixing glycerin and ion exchange water at a weight ratio of 1/9.

  As is apparent from the results shown in Table 3, it can be seen that the nonwoven fabric of the example has a lower apparent density and a higher bulk than the nonwoven fabric of the comparative example, and has a short liquid passing time. Therefore, the absorbent article using the nonwoven fabric of this example as a surface sheet that contacts the skin of the wearer or an intermediate sheet disposed between the surface sheet and the absorbent has a wearer speed of absorption. It becomes an excellent thing that you can feel.

10 Non-woven fabric 11 Card machine 12 Card web 20 Main cylinder 21 Feed 22 Breast 23 Striper 24 Worker 25 Doffer 26 Condensation

Claims (4)

Non-thermal extensibility that contains two components with different melting points and a first fiber made from a heat-extensible fiber whose length is increased by heating, and is stretched so that its length does not substantially increase by heating. A non-woven fabric obtained by heat-sealing the intersection of the fibers in the web produced by the card method, including the second fiber made from the heat-fusible conjugate fiber of
The mixing ratio of the first fiber and the second fiber (the former / the latter) is 20/80 to 80/20 by weight ratio,
The intersection of the first fibers, the intersection of the second fibers, and the intersection of the first fibers and the second fibers are each heat-sealed by an air-through method,
The nonwoven fabric whose ratio (flow direction / width direction) of the orientation degree of the fiber along the flow direction of a nonwoven fabric and the orientation degree of the fiber along the width direction is 1.0-1.3. It is a manufacturing method of the nonwoven fabric according to claim 1,
A heat-extensible fiber that includes a heat-extensible fiber whose length is increased by heating and a stretched fiber that includes two components having different melting points and that does not substantially extend when heated. Is used as a raw material, the web is manufactured by a card machine,
Hot air is blown onto the web by an air-through method to elongate the heat-extensible fibers, and the intersection points of the heat-extensible fibers, the intersection points of the heat-fusible composite fibers, and the heat-extensible fibers and the heat-melting fibers. Heat-bonding the intersection with the adhesive composite fiber, and producing a nonwoven fabric from the web,
In the production of the web using a card machine, a method for producing a nonwoven fabric, wherein the circumferential speed of condensation is set to 20 to 45% with respect to the circumferential speed of the doffer in the card machine. Between the card machine and the air-through device that blows hot air in the air-through method, using a manufacturing device in which a hot embossing device with an uneven roll and a smooth roll is arranged,
The manufacturing method according to claim 2, wherein a ratio of a speed of the web sent out from the heat embossing device to a speed of introduction of the web into the air through device is set to 90 to 100%.   The manufacturing method of Claim 3 which sets the heating temperature of the smooth roll in the said hot embossing apparatus lower than the heating temperature of an uneven | corrugated roll.

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