JP4614876B2 - Latent crimped fiber - Google Patents

Description

  The present invention relates to a latent crimpable fiber. The present invention also relates to a nonwoven fabric using the latent crimpable fiber as a raw material.

  The applicant first has a first layer and a second layer adjacent to the first layer, and the first layer and the second layer are partially joined by a joint portion having a predetermined pattern. The first layer has a three-dimensional solid shape, and the second layer is made of a material exhibiting an elastomeric behavior, and the whole sheet has an elastomeric behavior and has a breathable three-dimensional sheet material (patented) Reference 1). This three-dimensional sheet material has a large number of irregularities on its surface. And this solid sheet material has sufficient recoverability when it is stretched in the plane direction and compression deformability when it is compressed in the thickness direction. For the purpose of enhancing the recoverability of the three-dimensional sheet material with respect to elongation and the deformability with respect to compression, the second layer of the sheet material contains latent crimpable fibers in a crimped state.

  Examples of latent crimpable fibers include polypropylene as the first component, ethylene-propylene random copolymer and ethylene-butene-propylene terpolymer as the second component, and both components are side-by-side type or core-sheath type. What comprises a composite fiber is known (refer patent document 2). This latent crimpable fiber is described as being bulky and exhibiting excellent performance in elastic recovery when crimped by heat treatment.

  However, when this latent crimpable fiber is used, for example, as the constituent fiber of the second layer of the above-described three-dimensional sheet material, the thickness of the lower layer cannot be said to be sufficient, and there has been a demand for a more bulky texture. One of the reasons why the thickness of the lower layer is not sufficient is due to the presence of a resin having high heat shrinkability in the fiber on the surface of the fiber. Specifically, in the heat shrinking process, the twisting force acts greatly due to the crimping so that the resin having a large shrinkage on the outside is located on the inside, and a fine coil shape having a relatively small radius. This is because crimps are easily developed. In addition, since the resin having a low melting point is on the outside, adjacent fibers are heat-bonded to each other, a fine coiled crimp with a small radius is developed, and the thickness of the fiber layer is reduced.

  Also, when the compatibility between the first component and the second component in the latent crimpable fiber is low, peeling occurs between the two components as shown in FIG. Since the degree of peeling greatly changes depending on the temperature, the extensibility changes greatly as the temperature changes. As a result, the extended physical properties greatly fluctuate due to fluctuations in production speed and fluctuations in the actual processing temperature due to the season, which is not preferable for stable production.

JP 2002-187228 A JP-A-2-191720

  Accordingly, an object of the present invention is to provide a latent crimpable fiber that can eliminate the above-mentioned drawbacks of the prior art.

  The present invention has the above object by providing a latently crimpable fiber having an eccentric core-sheath structure and using a resin having a thermal contraction rate larger than that of the resin constituting the sheath as the resin constituting the core. Achieved.

  Further, the present invention achieves the above object by providing a latent crimpable fiber having an eccentric core-sheath structure and using a resin having a melting point lower than that of the resin constituting the sheath as the resin constituting the core. It is a thing.

  The present invention also provides a nonwoven fabric using the latent crimpable fiber as a raw material.

  Since the latent crimpable fiber of the present invention tends to develop a gentle coiled crimp in the heat shrinking process, the nonwoven fabric using this has a large fiber layer thickness. Moreover, since the resin having a high melting point is on the outer side of the latent crimpable fiber of the present invention, a wide range of heat shrinkage temperatures can be set. Therefore, in the production of a nonwoven fabric using this, there are the advantages that the range of production conditions is widened and stable production can be achieved against temperature fluctuations. Furthermore, the nonwoven fabric using the latent crimpable fiber of the present invention is more bulky and feels better and has a good appearance.

  The present invention will be described below based on preferred embodiments with reference to the drawings. FIG. 1A shows the cross-sectional structure of the latent crimpable fiber of the present invention. The latent crimpable fiber of the present invention is a core-sheath type composite fiber composed of a core component and a sheath component each made of a thermoplastic resin. As shown to Fig.1 (a), the core component comprises the core part C of a fiber. On the other hand, the sheath component constitutes the sheath S of the fiber. The positions of the centers of gravity of the core part C and the sheath part S are shifted. That is, the composite fiber shown in FIG. 1A is an eccentric core-sheath fiber.

  As shown in FIG. 1A, the core C is substantially enclosed by the sheath S. Accordingly, the core component constituting the core C is not exposed on the surface of the fiber. However, it is not essential in the present invention that the core component constituting the core C is not exposed on the surface of the fiber, and a core-sheath structure is substantially formed by the core C and the sheath S. For example, as shown in FIG. 1B, the core component may be partially exposed on the surface of the fiber.

  The latent crimpable fiber of the present invention is characterized by the heat shrinkage of the core component and the sheath component. Specifically, when the thermal contraction rate of the core component and the thermal contraction rate of the sheath component are compared, the thermal contraction rate of the core component is larger than the thermal contraction rate of the sheath component. In contrast, in the conventional eccentric core-sheath-type latently crimpable fiber, the thermal contraction rate of the sheath component is larger than the thermal contraction rate of the core component. That is, in the latent crimpable fiber of the present invention, the magnitude relationship between the thermal shrinkage rates of the core component and the sheath component is opposite to that of the conventional latent crimpable fiber. The reason for this is as follows.

  The eccentric-type core-sheath type composite fiber uses a difference in heat shrinkability between the core component and the sheath component to cause the fiber to exhibit a three-dimensional coiled crimp. Conventionally, by using a resin with high heat-shrinkability for the sheath portion of latent crimpable fibers, the crimps that appear are made finer, the apparent shrinkage of the fibers is increased, and the three-dimensional coiled crimps It has been considered that the extensibility of the nonwoven fabric using latent crimpable fibers is increased by expressing the. However, when the compatibility between the core component and the sheath component is low, if a resin having high heat shrinkage is used for the sheath, peeling occurs between the two components during crimping, and only the resin having high heat shrinkage is linear. As a result of the study by the present inventors, it was found that the entire fiber length is less likely to develop a three-dimensional coiled crimp. In particular, when the fiber does not develop a three-dimensional coiled crimp over its entire length, the extensibility derived from the coiled crimp does not appear. Therefore, in the present invention, by using a resin having a large heat shrinkability for the core portion, the core component is contracted in the sheath component that is substantially not thermally contracted, thereby producing a three-dimensional coiled crimp. Occasionally, the core component and the sheath component are prevented from peeling, and a sufficient three-dimensional coiled crimp is developed over the entire fiber length. Furthermore, the crimped coil shape that appears throughout the length of the fiber is made loose.

As is clear from the above description, the effect of the latent crimpable fiber of the present invention is particularly remarkable when the compatibility between the core component and the sheath component constituting the fiber is low. From this viewpoint, in the present invention, a combination of resins having low compatibility is used as the core component and the sheath component on the condition that there is a sufficient difference in heat shrinkability between the core component and the sheath component in the fiber. preferable. Low compatibility means, for example, a combination of resins having a solubility parameter SP difference of 1.3 (cal / cm ³ ) ^1/2 or less, and in the case of such a combination, when the present invention is used, The core component and the sheath component are prevented from peeling off, and the effect that sufficient coiled crimp is developed becomes even more remarkable.

Examples of the combination of resins having a sufficient difference in heat shrinkage and low compatibility include a combination of linear low density polyethylene (LLDPE) and polypropylene (PP), LLDPE and polyethylene terephthalate (PET), and the like. . In the case of a combination of LLDPE and PP, the difference in the solubility parameter SP described above is 1.3 (cal / cm ³ ) ^1/2 .

  In the present invention, the degree of heat shrinkability of the core component and the sheath component is measured using a thermal stress measuring device (manufactured by Kanebo Engineering Co., Ltd.). Specifically, heating is performed at a heating rate of 1 ° C./sec using a fiber bundle of 110 dtex, and the shrinkage rate of the resin is measured.

  The latent crimpable fiber of the present invention is also characterized by the melting points of the core component and the sheath component. Specifically, when the melting point of the core component and the melting point of the sheath component are compared, the melting point of the core component is lower than the melting point of the sheath component. On the other hand, in the conventional eccentric type core-sheath-type latent crimpable fiber, for example, the fiber described in Patent Document 1, the melting point of the sheath component is lower than the melting point of the core component. . That is, in the latent crimpable fiber of the present invention, the relationship between the melting points of the core component and the sheath component is opposite to that of the conventional latent crimpable fiber. The reason for this is as follows.

  The latent crimped fiber, which is a conventional eccentric core-sheath type composite fiber, gives three-dimensional coiled crimps due to the difference in thermal shrinkage of its constituent resin by applying heat at a predetermined temperature. In addition, the apparent fiber length (that is, the distance between both ends of the free length) is shortened. The temperature (hereinafter referred to as heat shrink temperature) is generally a temperature in the vicinity of the melting point of the sheath component resin. Therefore, when a fiber assembly such as a nonwoven fabric using conventional latently crimped fibers is subjected to heat shrinkage treatment, the sheath of the fiber in the fiber assembly is softened or melted, so that adjacent fibers are thermally fused. Even if a sufficient three-dimensional coiled crimp is developed, the extensibility derived from the coiled crimp does not appear. Also, during crimping, the sheath of the fiber in the fiber assembly is softened or melted, resulting in significant separation between the two components, and the entire fiber length exhibits a three-dimensional coil shape. In addition, the extensibility derived from the coiled crimp is not expressed. In particular, when the compatibility between the core component and the sheath component is low, if heat shrinkage is caused in the vicinity of the melting point of the sheath component of the fiber in the fiber assembly, peeling between the two components is more likely to occur. Therefore, in the present invention, a resin having a low melting point is used for the core part, and the periphery thereof is surrounded by a resin having a high melting point, so that even when a state where the low melting point resin is softened or melted during heat shrinkage and peeling easily occurs, The high melting point resin surrounding the periphery of the low melting point resin prevents the peeling, and a sufficient coiled crimp is developed.

  In the present invention, there is an advantage that a wide range of heat shrinkage temperatures of the latent crimpable fibers can be set by using a resin having a low melting point for the core and surrounding the periphery with a resin having a high melting point. This brings about the advantage that the degree of freedom of the production conditions is increased in the production of the nonwoven fabric using the latent crimpable fiber of the present invention as a raw material. In a conventional latently crimpable fiber that uses a resin having a low melting point for the sheath and a resin having a high melting point for the core, if the heat shrinkage temperature is higher than the melting point of the sheath, the resin in the sheath may be softened or melted. It became severe and it was not easy to successfully develop a coiled crimp.

  There is no particular limitation on the difference between the melting point of the resin of the core component and the melting point of the resin of the sheath component, but 30 to 135 ° C., particularly 45 to 45 ° C., from the viewpoint of high expression of crimp and ease of fiber spinning. It is preferable that it is 120 degreeC.

  The melting point of each of the core component and the sheath component is measured using a differential scanning calorimeter DSC6200 (manufactured by Seiko Instruments Inc.). Specifically, thermal analysis of a finely cut fiber sample (sample mass 1 mg) is performed at a heating rate of 10 ° C./min, and the melting peak temperature of the resin is measured. The melting peak temperature is defined as the melting point.

  In some cases, a resin having a lower melting point has higher heat shrinkability. Accordingly, the present invention provides a latent crimpable fiber comprising an eccentric core-sheath composite fiber, wherein the core component has a higher heat shrinkage rate than the sheath component and the core component has a melting point of the sheath component. Lower embodiment.

  The latent crimpable fiber of the present invention is in a state where a three-dimensional coiled crimp is not expressed before contraction, and even if it is expressed, the number of crimps (the number of peaks per 25.4 mm) ) Has only a slight two-dimensional mechanical crimp of around 10-20. Therefore, it can be handled in the same manner as ordinary fibers, and a web can be formed. And it contracts by the heat | fever more than heat contraction temperature, and a three-dimensional coiled crimp is expressed. The manner of crimping varies depending on the area ratio and arrangement relationship between the core portion C and the sheath portion S, but the typical crimping manner is a manner of three-dimensional crimping in a coil shape. The latent crimpable fiber of the present invention expresses a three-dimensional coiled crimp having a number of crimps of about 40 to 100 after the shrinkage.

  The ratio of the core part C to the sheath part S in the latent crimpable fiber of the present invention (fiber cross-sectional area ratio, the former: latter) is 3: 7 to 7: 3, particularly 4: 6 to 6: 4. Is preferred. Within this range, the mechanical properties of the fiber are sufficient, and the fiber can withstand practical use. Further, the coiled crimp can be expressed without causing the core portion C and the sheath portion S to peel off.

  The latent crimpable fiber of the present invention is produced using a spinning device equipped with two systems of extrusion devices. As the thickness of the latent crimpable fiber, an appropriate value is selected according to the specific application. As a general range, the thickness before crimping is 1.0 to 10 dtex, particularly 1.7 to 8.0 dtex, the fiber spinnability and cost, card machine passability, productivity, It is preferable from the point of cost.

  The latent crimpable fiber of the present invention can be produced by a known melt spinning method. The spinning device includes two systems of extrusion devices and a spinneret. Each resin component melted by the extruder and the gear pump is controlled in discharge amount (volume), merges in the spinneret, and is discharged from the nozzle. As the shape of the spinneret, an appropriate shape is selected according to the form of the target composite fiber. A winding device is installed immediately below the spinneret, and the molten resin discharged from the nozzle is taken up at a predetermined speed.

  The latent crimped fiber of the present invention can be handled in the same manner as a normal fiber before the heat shrinkage, and a crimp of a predetermined shape occurs after the heat shrinkage. A nonwoven fabric is manufactured using latent crimpable fibers before heat shrink as a raw material, and heat is applied during or after the production of the nonwoven fabric to express crimps and shrink the latent crimpable fibers, thereby allowing the nonwoven fabric to Properties can be imparted.

  For example, FIGS. 2A and 2B schematically show a cross section of an example of a nonwoven fabric using the latent crimpable fiber of the present invention as a raw material. The nonwoven fabric 10 has a two-layer structure having a first layer 11 including one surface and a second layer 12 including the other surface. The first layer 11 and the second layer 12 are each composed of a fiber assembly. The latent crimpable fiber of the present invention is used as a raw material for the second layer 12. In the second layer 12, the latent crimped fiber is in a state in which the crimp is expressed (in the following description, the latent crimped fiber of the present invention in which the crimp is expressed is referred to as a crimped fiber). The first layer 11 and the second layer 12 are stacked on each other and partially joined. The joint portion 13 between the first layer 11 and the second layer 12 is consolidated as shown in the figure by the action of heat and / or pressure, and has a smaller thickness than other portions of the nonwoven fabric 10. As a result, on the first layer 11 side, there are a large number of convex portions 15 dispersedly arranged in a predetermined pattern and a large number of concave portions 14 formed at the positions of the joint portions 13. And the uneven | corrugated shape is formed in the surface of the 1st layer 11 of the nonwoven fabric 10 by the recessed part 14. FIG.

  The constituent fibers of the first layer 11 and the second layer 12 are joined at the intersection or are not joined. When the fibers are bonded at the intersection, examples of the bonding mode include heat fusion by an air-through method and adhesion by an adhesive. It is preferable that the crimped fibers contained in the second layer 12 are not joined to each other and are formed into a sheet by entanglement. This increases the degree of freedom between the crimped fibers and improves the compression recovery in the thickness direction and the extensibility in the planar direction.

  In the nonwoven fabric 10, it is preferable that the first layer 11 has a lower density (fiber density) than the second layer 12. That is, it is preferable that the first layer 11 has a sparser structure than the second layer 12. Thereby, the convex part 15 formed in the 1st layer 11 side becomes a bulky thing, the cushioning property as the nonwoven fabric 10 whole becomes favorable, and a texture improves. For example, when the nonwoven fabric 10 is used as the top sheet of the absorbent article and the first layer 11 is disposed on the skin contact surface side, the liquid discharged on the top sheet is quickly absorbed into the first layer 11. In addition, since the liquid absorbed in the first layer 11 smoothly moves to the second layer 12 due to the density gradient, the liquid is left on the surface of the surface sheet, causing stagnation, itchiness, rash, discomfort, etc. Can be effectively prevented.

  From the viewpoint of the texture and cushioning properties of the nonwoven fabric 10, the apparent thickness of the first layer 11 is preferably 0.5 mm to 2.0 mm, particularly preferably 1.0 mm to 2.0 mm. The apparent thickness of the second layer 12 is preferably 0.5 to 2.0 mm, particularly preferably 0.7 to 1.0 mm. The apparent thickness is measured by forming a cut surface of the nonwoven fabric 10 with a line parallel to the fiber orientation direction (flow direction during the production of the nonwoven fabric) and passing through the joint portion 13 in the nonwoven fabric 10. An enlarged photograph of the cut surface of the nonwoven fabric 10 is obtained using a digital HF microscope (VH-8000, manufactured by Keyence Corporation). A scale is matched with this enlarged photograph of the cut surface, and the thicknesses of the first layer portion and the second layer portion are measured, which are set as the apparent thicknesses of the first layer and the second layer, respectively.

Depending on the specific application, the nonwoven fabric 10 preferably has a basis weight of 40 to 110 g / m ² , particularly 50 to 90 g / m ² . Regarding each layer which comprises the nonwoven fabric 10, it is preferable that the basic weight of the 1st layer 11 is 20-55 g / m < ² >, especially 25-45 g / m < ² >. The basis weight of the second layer 12 is preferably ²⁰ to 55 g / m ² , particularly preferably 25 to 45 g / m ² .

  As described above, the second layer 12 includes crimped fibers. The second layer 12 may be composed only of crimped fibers, or may include other fibers. Examples of other fibers include ordinary thermoplastic fibers, regenerated fibers such as rayon, and natural fibers such as cotton. When other fibers are contained in addition to the crimped fibers, the blending amount of the other fibers is preferably 1 to 50% by weight, particularly 5 to 30% by weight, based on the entire second layer 12.

  On the other hand, examples of the constituent fibers of the first layer 11 include ordinary thermoplastic fibers, regenerated fibers such as rayon, and natural fibers such as cotton. A particularly preferable fiber is a concentric core-sheath type heat-fusible fiber. Moreover, the 1st layer 11 may contain the crimped fiber of the same kind or a different kind from the crimped fiber contained in a 2nd layer.

  The nonwoven fabric 10 shown in FIG. 2 is suitably manufactured by the method described below. First, the fiber assemblies constituting the first layer 11 and the second layer 12 are manufactured. As such a fiber assembly, for example, a web or a nonwoven fabric can be used. A nonwoven fabric is manufactured by the air through method, the heat roll method (heat embossing method), the airlaid method, the melt blown method etc., for example. The web is manufactured by a card machine, for example. In particular, it is preferable to use a nonwoven fabric as the fiber aggregate constituting the first layer 11 and to use a web as the fiber aggregate constituting the second layer 12. The web constituting the second layer 12 includes the latent crimped fiber of the present invention.

  Next, the fiber assembly constituting the first layer 11 is overlapped on the fiber assembly constituting the second layer 12, and these are partially joined in a predetermined pattern. Various methods can be used as a method of bonding the two as long as the bonding portion 13 in which the thickness of the first layer 11 is reduced more than other portions can be formed. For example, hot embossing or ultrasonic embossing is preferable. As shown in FIG. 2, the joints 13 may be in the form of scattered dots that are independent of each other, or may be linear, curved (including continuous waveforms, etc.), lattice, zigzag, or the like. good. The shape of each joint in the case where the joints 13 are arranged in the form of dots can be any shape such as a circular shape, a triangular shape, or a quadrangular shape.

  Heat is applied to the bonded first layer 11 and second layer 12 to cause the crimped fibers contained in the second layer 12 to crimp and shrink. By the expression of crimp, the constituent fibers of the second layer 12 located between the joint portions 13 contract, and the fiber density of the second layer 12 increases. With this shrinkage, the constituent fibers of the first layer 11 located between the joints 13 lose their place in the plane direction and move in the thickness direction. Thereby, the space between the joint portions 13 is raised, and a bulky convex portion 15 having a low fiber density is formed. Further, a concave portion having a high fiber density is formed between the convex portions 15, i. Thus, the nonwoven fabric 10 having a structure in which the surface on the first layer side has an uneven shape and the fiber density increases from the first layer 11 side to the second layer 12 side. Details of the method for producing such a nonwoven fabric are described in, for example, Japanese Patent Application Laid-Open No. 2002-187228 and Japanese Patent Application Laid-Open No. 2004-202890 related to the earlier application of the present applicant.

  When shrinking the latent crimpable fiber, the resin combination having the above-described heat shrinkage and / or melting point is used as the core component and the sheath component, so that these components are prevented from peeling off. The As a result, the second layer 12 is sufficiently contracted, and the bulky convex portion 15 having a low fiber density is easily formed. Moreover, sufficient extensibility is provided to the second layer due to the crimp of the latent crimpable fiber.

  The nonwoven fabric 10 thus obtained can be used for various applications such as surface sheets of various absorbent articles such as sanitary napkins, panty liners, and disposable diapers, surgical clothes, and cleaning sheets. When the nonwoven fabric 10 is used especially as a surface sheet of an absorbent article, it is possible to obtain an absorbent article having a good touch and an excellent wearing feeling. When using the nonwoven fabric 10 as a surface sheet, it is preferable that the 1st layer side is distribute | arranged so that a user's skin may be contacted from a viewpoint of making the touch still better.

  The above description relates to the nonwoven fabric having a two-layer structure using the latent crimpable fiber of the present invention, but the nonwoven fabric using the latent crimpable fiber of the present invention is not limited to the two-layer structure. For example, the nonwoven fabric can have a single layer structure, or a multilayer structure of three or more layers. In the case of a single layer structure, it is preferable that crimped fibers are contained in an amount of 50% by weight or more, particularly 70% by weight or more. You may be comprised from 100% of crimped fibers. In the case of a multilayer structure of three or more layers, it is preferable from the viewpoint of further improving the smoothness that crimped fibers are contained in at least the outermost layer.

  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.

[Examples 1-1 to 1-3 and Comparative Examples 2-1 to 2-3, 3-1 to 3-3, 4-1 to 4-3]
The latent crimpable fiber made of a composite fiber manufactured using a spinning device equipped with two systems of extrusion devices had an area ratio of the core portion to the sheath portion of 5: 5. The fiber diameter was 2.3 dtex. This fiber was cut into 51 mm short fibers. Details of the fibers are shown in Tables 1 and 2. Using this fiber, the two-layered nonwoven fabric shown in FIG. 2 was produced by the following methods (1) to (3).

(1) Production of first-layer fiber assembly A web having a basis weight of 20 g / m ² was produced by the card method using the fibers (2.3 dtex × 51 mm) shown in Tables 1 and 2 as raw materials. The web was hot embossed using a hot embossing roll (145 ° C. ± 10 ° C.) to produce a fiber assembly of the first layer. The embossed area ratio was 28%.

(2) Production of second-layer fiber aggregate A second-layer fiber aggregate having a basis weight of 20 g / m ² was produced by the card method using latent crimpable fibers shown in Tables 1 and 2 as raw materials.

(3) Production of Non-woven Fabric The first layer fiber assembly and the second layer fiber assembly were superposed and both fiber assemblies were partially joined by an ultrasonic embossing method to obtain a laminate. The shape of each joint by embossing was a circle with a diameter of 2 mm, and the embossing pattern was as shown in FIG. The distance between the centers of the joint portions adjacent in the longitudinal direction and the width direction was 7 mm. In the hot air furnace, the thermal contraction treatment was performed by blowing hot air having a temperature shown in Tables 1 and 2 on the laminate in an air-through manner for 5 to 10 seconds. As a result, the latent crimpable fibers contained in the fiber assembly of the second layer were crimped, and each fiber assembly was contracted in the in-plane direction. As a result, in the 1st layer formed from the fiber assembly of the 1st layer, many convex parts were formed between joining points. During the heat shrink treatment, the longitudinal direction and the width direction of the laminate were gripped and the shrinkage was regulated to 70% in both the longitudinal direction and the width direction so that the area after shrinkage was 49% of the area before shrinkage. The basis weight of the nonwoven fabric thus obtained was as shown in Tables 1 and 2.

[Evaluation]
About the nonwoven fabric obtained in this way, the crimped state of the fibers contained in the second layer was observed with a microscope. The case where the coiled crimp is expressed is “◯”, and the case where the coiled crimp is not expressed is “x”. Moreover, the presence or absence of peeling between the core component and the sheath component is confirmed, and a case where peeling occurs is set as “◯”, and a case where peeling does not occur is set as “X”. In addition, the 100 gf tensile elongation was measured in the longitudinal direction (MD) and the width direction (CD) of the nonwoven fabric by the following method, and the cross section of the nonwoven fabric was observed with a microscope, and the apparent thicknesses of the first layer and the second layer were determined first. Measurements were made as described. These results are shown in Tables 1 and 2. Furthermore, the microscope picture of the 2nd layer in the nonwoven fabric obtained in Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-3 is shown in FIG.3 and FIG.4.

[Measurement method of 100 gf tensile elongation]
Measurement was performed in a tensile mode using a tensile / compression tester (A & D Co., Ltd., RTA-100). First, the nonwoven fabric 10 is cut into a size of 80 mm × 25 mm, and a test piece is collected. Set the initial specimen length (distance between chucks) at 30 mm between the air chucks attached to the tensile / compression tester and the chuck attached to the load cell (rated output 5 kg) of the tensile / compression tester at 300 mm / The test piece is stretched at a rate of minutes. By this series of operations, the 100 gf tensile elongation in the longitudinal direction (MD) and the width direction (CD) is obtained.

  As is clear from the results shown in Tables 1 and 2, it can be seen that the nonwoven fabric of each example has a larger thickness of the second layer than the nonwoven fabric of the comparative example. Moreover, as is clear from the results shown in Tables 1 and 2 and FIGS. 3 and 4, in Comparative Examples 2-1 to 2-3 and 3-1 to 3-3, the core component and It can be seen that the degree of expression of the coiled crimp is different due to the change in the peeled state of the sheath component. Thereby, as is clear from the results shown in Tables 1 and 2, the extensibility of the nonwoven fabric is greatly changed. On the other hand, in Examples 1-1 to 1-3, peeling does not occur even if the heat shrink temperature is different, and as a result, the extensibility of the nonwoven fabric is stable. That is, due to the presence or absence of peeling, the nonwoven fabric of each example has a stable tensile elongation at a wide range of heat shrinkage temperatures and a large thickness of the second layer compared to the nonwoven fabric of the comparative example. I understand.

[Examples 5-1 to 5-3 and Comparative Examples 6-1 to 6-3, 7-1 to 7-3, 8-1 to 8-3]
The latent crimpable fiber made of a composite fiber produced by a spinning device equipped with two systems of extrusion devices had an area ratio of the core portion to the sheath portion of 5: 5. The fiber diameter was 2.3 dtex. This fiber was cut into 51 mm short fibers. Details of the fibers are as shown in Tables 3 and 4. Using this fiber as a raw material, a web having a basis weight of 20 g / m ² was produced by a card method. The web was embossed by ultrasonic embossing. The shape of each joint by embossing was a circle with a diameter of 2 mm, and the embossing pattern was as shown in FIG. The center-to-center distance of each joint adjacent in the longitudinal direction and the width direction was 7 mm. The embossed web was placed in a hot air oven, and hot air having a temperature shown in Tables 3 and 4 was blown by an air-through method for 5 to 10 seconds to perform heat shrinkage treatment. As a result, the latent crimpable fibers contained in the web were crimped to shrink the web in the in-plane direction. During the heat shrinking treatment, the longitudinal direction and the width direction of the web were gripped, and the shrinkage was restricted to 70% in both the longitudinal direction and the width direction, so that the area after shrinkage was 49% of the area before shrinkage. The nonwoven fabric thus obtained had a single-layer structure, and the basis weight was as shown in Tables 3 and 4.

[Evaluation]
About the nonwoven fabric of the single layer structure obtained in this way, the crimped state and the presence or absence of peeling of the fiber were observed in the same manner as in Example 1-1 and the tensile elongation (only MD) was measured. These results are shown in Tables 3 and 4.

  As is clear from the results shown in Table 3 and Table 4, in Comparative Examples 6-1 to 6-3 and 7-1 to 7-3, the peeled state of the core component and the sheath component changes depending on the difference in heat shrinkage temperature. As a result, the degree of expression of the coiled crimps is different, which greatly changes the stretchability of the nonwoven fabric. On the other hand, in Examples 5-1 to 5-3, peeling does not occur even if the heat shrink temperature is different, and as a result, the extensibility of the nonwoven fabric is stable. That is, due to the presence or absence of this peeling, the nonwoven fabric of each example has a stabilized tensile elongation at a wide range of heat shrinkage temperatures compared to the nonwoven fabric of the comparative example.

FIGS. 1A and 1B are schematic views showing the cross-sectional structure of the latent crimpable fiber of the present invention. 2 (a) is a perspective view showing a two-layered nonwoven fabric made from the latent crimpable fiber of the present invention, and FIG. 2 (b) is a sectional view in the thickness direction in FIG. 2 (a). is there. Fig.3 (a) thru | or (c) are the microscope pictures of the 2nd layer in the nonwoven fabric obtained in Examples 1-1 to 1-3. 4A to 4C are photomicrographs of the second layer in the nonwoven fabric obtained in Comparative Examples 1-1 to 1-3. FIG. 5 is a schematic diagram showing a state in which a latent crimpable fiber made of a conventional eccentric-type core-sheath composite fiber is peeled during crimping.

Explanation of symbols

C core portion S sheath portion 10 non-woven fabric 11 first layer 12 second layer 13 joint portion 14 concave portion 15 convex portion

Claims (4)

Has a core-sheath structure of an eccentric, as the resin constituting the core, rather large, the thermal shrinkage than the resin constituting the sheath, and the melting point using a low casting,
The thickness before crimps appear is 1.0 to 10 dtex,
The resin constituting the core is linear low density polyethylene,
A latent crimpable fiber having a number of crimps after shrinkage of 40 to 100 peaks / 25.4 mm . The latent crimpable fiber according to claim 1, wherein the difference in melting point between the resin constituting the core and the resin constituting the sheath is 30 to 135 ° C. A nonwoven fabric using the latent crimpable fiber according to claim 1 or 2 as a raw material. A first layer including one surface and a second layer including the other surface, wherein both layers are partially joined to form a plurality of convex portions and concave portions on the first layer side, The nonwoven fabric according to claim 3 , wherein the latent crimpable fiber is crimped into two layers.