JP2007107143A - High strength fusing conjugate fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing high strength fusing conjugate fiber industrially at a low cost. <P>SOLUTION: The fusing conjugate fiber comprises crystalline propylene-based polymer as the core component and olefinic polymer having lower melting point than that of the core component as the sheath component, wherein the conjugate fiber has a ratio of the core component weight-average molecular weight measured by cross fractionation chromatograph to the sheath component weight-average molecular weight (core component weight-average molecular weight/sheath component weight-average molecular weight) in a specific range. By properly selecting melt flow rate of the both sheath and core components after discharged from nozzles to obtain undrawn fiber, the undrawn fiber can be drawn at a high magnification and as the strength development to the draw ratio is high, so the high strength fusing conjugate fiber can be obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a heat-fusible conjugate fiber. More specifically, it is a heat-fusible conjugate fiber having a sheath-core structure, which has high strength and can be manufactured industrially at low cost with high productivity, and is a wet nonwoven fabric such as a dry nonwoven fabric or a battery separator. It is related with the heat-fusible composite fiber suitable for uses, such as.

  The physical properties of polymer products such as synthetic fibers and films that are stretched are strongly influenced by their higher order structure (structure formed by molecular chain aggregates: molecular orientation, crystallinity, etc.) The higher order structure depends on the stretching process and the method and degree of heat treatment. In general, by performing the stretching treatment, the molecular chain is uniaxially oriented in the stretching direction, and mechanical properties such as strength in the stretching direction and Young's modulus are improved. Therefore, if it is intended to obtain a polymer product having excellent mechanical properties, it is preferable to perform a stretching process at a higher magnification, and a heat treatment is performed as necessary after the stretching process.

  In order to obtain a polymer product having excellent mechanical properties, the stretching process is particularly important, and various measures have been taken to perform stretching at a high magnification. Largely, to obtain an undrawn yarn that can be drawn at a high magnification, and to adopt a drawing method that can be drawn at a high magnification.

  Generally, in order to obtain an undrawn yarn that can be drawn at a high magnification, it is effective to obtain an undrawn yarn that suppresses the molecular orientation of the polymer chain by reducing the stress acting on the spinning line during the spinning process. It is. Examples of a method for reducing the spinning line stress include a method of increasing the discharge resin temperature and decreasing the molecular weight of the discharge resin. However, these methods may cause a decrease in tension just below the nozzle, causing yarn swaying, and may lead to deterioration of spinnability. Further, when the molecular weight is extremely reduced, the physical properties of the final fiber product may be deteriorated.

  In addition, reducing the take-up speed from the spinneret as much as possible or reducing the hole diameter of the spinneret as much as possible is effective for obtaining an undrawn yarn that can be drawn at a high magnification. However, lowering the take-off speed causes a decrease in productivity. Further, if the hole diameter is too small, clogging of the resin or the like may be caused, leading to a decrease in productivity.

  As methods for drawing these undrawn yarns, contact heating drawing using a metal heating roll or metal heating plate, or non-contact heating drawing using hot water, boiling water, pressurized saturated steam, hot air, far infrared rays, carbon dioxide laser, etc. Is mentioned. In general, in order to obtain a stretched synthetic fiber having higher fiber strength by performing a stretching process at a high magnification, non-contact heating stretching is effective. Among these, from the viewpoint that the temperature of the stretched object can be instantaneously increased to a temperature at which stretching can be performed at a high magnification, stretching by pressurized saturated water vapor (see Patent Document 1) or carbon dioxide laser (see Patent Document 2) is suitable. is there. However, these stretching methods also have problems that a large amount of capital investment is required, a running cost is high, and operability is difficult.

On the other hand, a sheath-core type heat-fusible composite fiber in which a high-melting-point component is arranged in the core component and a lower-melting-point component is arranged in the sheath component is used for the heat-bonding nonwoven fabric (patent) Reference 1). For example, a sheath-core type heat-fusible composite fiber with polypropylene as the core component and polyethylene as the sheath component has excellent heat-sealing properties, cost, safety, and low environmental impact. Widely used. And this heat-fusible conjugate fiber is subjected to a stretching treatment in order to increase the fiber strength.
JP 2002-180330 A JP 2002-115117 A

  In recent years, there has been an increasing demand for heat-fusible composite fibers having higher fiber strength, and there is a constant demand for improvement in strength characteristics. In order to obtain a high-strength heat-fusible conjugate fiber, a measure for obtaining an undrawn yarn that can be drawn at a high magnification is adopted, and a drawing method that can be drawn at a high magnification is adopted. In general, the fiber strength strongly depends on the draw ratio and is in a proportional relationship. Therefore, how to draw at a high magnification is important for obtaining a high-strength heat-fusible conjugate fiber. However, forcibly stretching causes problems such as stretching breakage, and the stretching ratio while maintaining industrial-level operability and productivity is naturally limited. That is, there is an upper limit to the fiber strength.

  Under such circumstances, the problem to be solved by the present invention is a heat-fusible conjugate fiber having a sheath-core structure, which has high strength and is industrially inexpensive and manufactured with high productivity. The object of the present invention is to provide a heat-fusible conjugate fiber suitable for applications such as dry nonwoven fabrics and wet nonwoven fabrics such as battery separators.

  As a result of intensive studies to solve the above problems, the present inventors have arranged a crystalline propylene polymer as a core component and an olefin polymer having a melting point lower than that of the core component as a sheath component. The ratio of the weight average molecular weight of the core component and the weight average molecular weight of the sheath component measured by cross-fractionation chromatography of the heat-fusible conjugate fiber obtained by drawing an undrawn yarn obtained by melt spinning It has been found that by controlling (core component weight average molecular weight / sheath component weight average molecular weight) within a specific range, a high-strength heat-fusible conjugate fiber can be obtained, and the present invention has been completed.

The present invention has the following configuration.
(1) A heat-fusible composite obtained by drawing an undrawn yarn in which a crystalline propylene polymer is arranged in a core component and an olefin polymer having a melting point lower than that of the core component is arranged in a sheath component. The ratio of the weight average molecular weight of the core component to the weight average molecular weight of the sheath component (core component weight average molecular weight / sheath component weight average molecular weight) measured by cross-fractionation chromatography of the heat-fusible conjugate fiber. A heat-fusible conjugate fiber characterized by being 2.5 or less.

(2) The heat-fusible conjugate fiber according to claim 1, wherein the resin raw material of the sheath component has an MFR at 190 ° C. of 3 to 18 g / 10 min.
(3) The heat-fusible conjugate fiber according to (1) or (2) above, wherein the MFR of the core component resin raw material at 230 ° C. is 5 to 60 g / 10 min.
(4) The heat-fusible conjugate fiber according to any one of (1) to (3), wherein the fiber breaking strength is 6.0 cN / dtex or more.
(5) The heat-fusible conjugate fiber according to (4), wherein the dry heat shrinkage at 145 ° C. is 20% or less.
(6) The heat-fusible conjugate fiber according to any one of (1) to (3), wherein the core component is isotactic polypropylene and the sheath component is high-density polyethylene.
(7) The heat-fusible conjugate fiber according to (6), wherein the core component isotactic polypropylene has a Q value (molecular weight distribution: weight average molecular weight / number average molecular weight) of 4 or less.

  The heat-fusible conjugate fiber of the present invention was obtained by disposing a crystalline propylene polymer as a core component, an olefin polymer having a melting point lower than that of the core component as a sheath component, and melt spinning. A drawn fiber obtained by drawing an undrawn yarn. The MFR of the core component after discharging the spinneret and the sheath component so that the core component weight average molecular weight / sheath component weight average molecular weight measured by the cross-fractionation chromatograph of the heat-fusible conjugate fiber is 2.5 or less. By appropriately selecting MFR and the like, it is possible to increase the strength development property with respect to the draw ratio while securing the drawability, and thus, a high-strength and heat-strengthening conjugate fiber can be obtained industrially. This high-strength heat-fusible conjugate fiber is suitable for the purpose of improving productivity and bulking of the nonwoven fabric in dry nonwoven fabrics, and for improving the piercing strength in wet nonwoven fabrics such as battery separators. Used.

Hereinafter, the present invention will be described in detail according to embodiments of the invention.
The heat-fusible conjugate fiber of the present invention was obtained by disposing a crystalline propylene polymer as a core component and an olefin polymer having a melting point lower than that of the core component as a sheath component and melt spinning. The ratio of the weight average molecular weight of the core component to the weight average molecular weight of the sheath component (core component) obtained by drawing an undrawn yarn and measured by cross-fractionation chromatography of the heat-fusible conjugate fiber (Weight average molecular weight / sheath component weight average molecular weight) is 2.5 or less. If the core component weight average molecular weight / sheath component weight average molecular weight is 2.5 or less, the effect of the present invention is sufficiently exerted, more preferably 2.3 or less, and still more preferably 2.1 or less.

  Here, the cross-fractionation chromatograph is a combination of the temperature rise elution fractionation method (TREF) and the gel permeation chromatography (GPC) method, and is a method that can simultaneously know the crystallinity distribution and molecular weight distribution of the polymer. is there. The heat-fusible conjugate fiber of the present invention has a high-melting-point component in the core and a low-melting-point component in the sheath. However, the core component and the sheath component are separated by the difference in elution temperature due to this melting-point difference. Each weight average molecular weight can be measured. The resin discharged from the spinneret becomes an undrawn yarn through a melt spinning process, and becomes a heat-fusible conjugate fiber through a drawing process and a heat treatment process. In this melt spinning process, drawing process, and heat treatment process, the molecular weight changes. It can be regarded as almost none. Therefore, controlling the core component weight average molecular weight / sheath component weight average molecular weight of the heat-fusible conjugate fiber to a specific range means, in other words, the MFR of the core component resin and the MFR of the sheath component resin after discharging the spinneret. It means controlling the ratio to a specific range.

  The ratio of the weight average molecular weight of the core component and the weight average molecular weight of the sheath component (core component weight average molecular weight / sheath component weight average molecular weight) measured by the cross-fractionation chromatograph of the heat-fusible conjugate fiber of the present invention is as described above. In order to achieve this range, it is preferable to decrease the weight average molecular weight of the core component and increase the weight average molecular weight of the sheath component. The weight average molecular weight of the core component is 100,000 to 160,000, and the weight average molecular weight of the sheath component is 40,000 to 40,000, provided that the core component weight average molecular weight / sheath component weight average molecular weight is 2.5 or less. A range of 80,000 is preferable, and a weight average molecular weight of the core component is preferably 120,000 to 150,000, and a weight average molecular weight of the sheath component is preferably 50,000 to 70,000.

  The ratio of the weight average molecular weight of the core component and the weight average molecular weight of the sheath component (core component weight average molecular weight / sheath component weight average molecular weight) measured by the cross-fractionation chromatograph of the heat-fusible conjugate fiber of the present invention is described above. Examples of the range method include the following methods. By appropriately combining these methods, the weight average molecular weight ratio can be adjusted to a specific range of the present invention.

  The weight average molecular weight of both sheath core components measured by the cross-fractionation chromatograph of the conjugate fiber of the present invention is, for example, the value of the melt flow rate (MFR) of the core component resin and sheath component resin discharged from the spinneret. It is a correlated numerical value. When the weight average molecular weight is large, the MFR is small, and when the weight average molecular weight is small, the MFR is large. Therefore, it is preferable to decrease the weight average molecular weight of the core component and increase the weight average molecular weight of the sheath component. In other words, it is preferable to increase the MFR of the core component and decrease the MFR of the sheath component.

  Even when a resin material having a relatively low MFR is used, it is possible to increase the MFR of the resin discharged from the nozzle by adjusting the degree of molecular weight drop by changing the extrusion temperature during spinning. Accordingly, the ratio of the weight average molecular weight of the present invention (core component weight average molecular weight / sheath component weight average molecular weight) of 2.5 or less is selected by appropriately selecting the MFR of the resin raw material for both sheath core components and the spinning extrusion conditions. Can be.

  The MFR of the resin raw material to be used is not particularly limited, but the MFR at 230 ° C. of the resin raw material of the core component is preferably 5 to 60 g / 10 min, and more preferably 8 to 40 g / 10 min. The extrusion temperature during spinning is not particularly limited, but is preferably in the range of 200 to 350 ° C, more preferably 260 to 330 ° C. Similarly, the MFR at 190 ° C. of the resin raw material for the sheath component is preferably 3 to 30 g / 10 min, more preferably 8 to 18 g / 10 min. The extrusion temperature during spinning is not particularly limited, but is preferably in the range of 180 to 300 ° C, more preferably 220 to 260 ° C.

  Generally, the drawability of an undrawn yarn obtained by melt spinning is strongly influenced by the stress that it receives during the spinning process. This is because the molecular chain is oriented along the fiber axis due to the stress acting on the spinning line, and the unstretched yarn in which the molecular chain is highly oriented by the high spinning line stress is low in elongation and stretched at a high magnification. I can't do it. Here, in the case of a composite fiber, it is necessary to consider the solidification temperature of both components. For example, in the case of a sheath-core type composite fiber, when one of the components is cooled to the solidification temperature in the spinning process, the deformability as the composite fiber is lost, and thus the other component cannot be deformed. That is, the component that solidifies at a lower temperature is solidified in a state where the composite fiber is not thinned, and in this case, a large stress does not act, and thus the molecular chain orientation of the component is kept low.

  Solidification of the polymer material is caused by glass transition or crystallization, but in the case of a polyolefin-based resin, the glass transition temperature is generally not more than room temperature, and thus solidification is caused by crystallization. The crystallization temperature tends to correlate with the melting point, and it can be said that the high melting point polyolefin resin has a higher crystallization temperature. That is, in the case of the sheath-core type heat-fusible fiber of the present invention, a high melting point component is disposed in the core and a lower melting point component is disposed in the sheath. The solidification of the component completes the thinning of the composite fiber, followed by the solidification of the sheath component having a low melting point. That is, the core component has a highly oriented unstretched yarn structure and the sheath component has a low orientation.

  When the undrawn yarn obtained in this way is drawn, the drawability of the core component that is highly oriented becomes rate-limiting, and the draw ratio is limited. In other words, it can be said that the stretchability of the sheath component that is low-oriented can be stretched only at a stretch ratio with a sufficient margin, that is, the strength expression of the sheath component is not sufficient.

  Here, it is important that the core component weight average molecular weight / sheath component weight average molecular weight of the heat-fusible conjugate fiber is 2.5 or less. This means that the weight average molecular weight of the core component is decreased and the weight average molecular weight of the sheath component is increased, that is, the MFR of the core component after nozzle discharge in the spinning process is increased and the MFR of the sheath component is decreased. . This makes it possible to control the degree of orientation of the core component and the sheath component of the undrawn yarn obtained in the spinning process so that the fiber strength is easily developed in the drawing process. When melt spinning is performed under such a resin composition and extrusion conditions, a large spinning line stress does not act on the core component, so molecular orientation is suppressed, and conversely, a large spinning line stress acts on the sheath component. As a result, molecular orientation is promoted.

  The core component MFR after nozzle discharge in the spinning process is increased and the sheath component MFR is decreased so that the core component weight average molecular weight / sheath component weight average molecular weight of the heat-fusible conjugate fiber is 2.5 or less. Leads to an improvement in spinning stability. As described above, in order to obtain an undrawn yarn that can be drawn at a high magnification, generally, a method of increasing the temperature of the discharged resin or decreasing the molecular weight of the discharged resin (increasing MFR) is employed. If the discharge resin temperature is remarkably increased or the molecular weight of the discharge resin is remarkably reduced, the tension is lowered directly under the nozzle, causing yarn swinging, which may lead to deterioration of spinnability. However, the MFR of the core component after nozzle discharge in the spinning process is increased so that the core component weight average molecular weight / sheath component weight average molecular weight of the heat-fusible conjugate fiber of the present invention is 2.5 or less. By adopting a resin configuration with a reduced MFR and extrusion conditions, the spinning line tension contracted by the core component is small, but the spinning line tension contracted by the sheath component is increased. This large tension acting on the sheath component leads to an increase in the overall tension of the composite fiber, which suppresses yarn fluctuations due to turbulence in the atmosphere and fluctuations in the speed of the cooling air, and minimizes deterioration of spinnability. And an undrawn yarn having excellent drawability can be obtained.

  This resin composition intended to suppress the orientation of the core component and promote the orientation of the sheath component, and the extrusion conditions are suitable as an undrawn yarn for obtaining a high-strength drawn fiber. This is because it is possible to stretch at a high magnification by suppressing the orientation of the core component that governs stretchability, and further, by enhancing the orientation of the sheath component in the unstretched yarn, it is possible to increase the strength expression by the stretching treatment. Because.

  The cross-sectional composite ratio of the core component and the sheath component is not particularly limited, but is preferably in the range of core / sheath = 40/60 to 70/30 vol%. When the ratio of the core component is high, the stretchability tends to slightly decrease, but the strength expression with respect to the draw ratio is increased, so the strength of the stretched fiber finally obtained is about the same. Become. Further, if importance is attached to suppression of thermal shrinkage of the drawn fiber, it is effective to increase the ratio of the core component. The fiber cross-sectional shape may be any of circular and elliptical round shapes, triangular and square square shapes, key shapes and different types such as an eight-leaf shape, and hollow shapes.

  As the crystalline propylene-based polymer as the core component, an isotactic polypropylene-based resin is desirable, and among them, the Q value (weight average molecular weight / number average molecular weight) is preferably 4 or less, more preferably 3.5 or less, More preferably, it is 3.0 or less. Here, selecting an isotactic polypropylene resin having a Q value of 4 or less is to select a resin having a small amount of a high molecular weight component that significantly impairs stretchability, and is preferable because high stretchability is obtained. The isotactic pentad fraction (IPF: mol%) is not particularly limited, but is preferably 90% or more, more preferably 95% or more. Here, IPF means high stereoregularity, and it can be said that the higher the IPF, the higher the crystallinity. The crystallinity of the drawn fiber is closely related to the heat shrinkage characteristics of the fiber, and the higher the crystallinity of the drawn fiber, the more the heat shrinkage tends to be suppressed.

  The crystalline propylene polymer used as the core component may be a homopolymer of propylene or a copolymer of propylene and an α-olefin (ethylene, butene-1, etc.). Among these, a homoisotactic polypropylene polymer is preferable from the viewpoint that thermal contraction of the drawn fiber can be suppressed.

  On the other hand, the olefin polymer having a lower melting point than the crystalline propylene polymer disposed as a sheath component includes ethylene-based polymers such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, and linear low-density polyethylene. A low crystalline propylene polymer which is a polymer and a copolymer of propylene and another α-olefin can be exemplified. These olefin-based polymers may be used alone or in combination of two or more, but no particular problem is posed, but among these, high-density polyethylene is desirable from the viewpoint of fiber strength characteristics and heat-sealing characteristics.

  In addition, the crystalline propylene polymer used for the core component related to the present invention and the olefin polymer used for the sheath component may be variously modified as necessary within the range not hindering the effects of the present invention. Additives for exhibiting performance, such as antioxidants, light stabilizers, UV absorbers, neutralizers, nucleating agents, epoxy stabilizers, lubricants, antibacterial agents, deodorants, flame retardants, antistatic agents, You may add a pigment, a plasticizer, etc. suitably.

  The undrawn yarn used in the present invention is composed of the core component and the sheath component described above, and the core component weight average molecular weight / sheath component weight average of the heat-fusible conjugate fiber of the present invention measured by cross fractionation chromatography. It is obtained by selecting the MFR of the resin raw material and selecting the extrusion conditions so that the molecular weight is 2.5 or less. The melt spinning method is not particularly limited, and a known method is used. I can do things.

  The spinning temperature (discharge resin temperature) is preferably 200 to 350 ° C, more preferably 260 to 300 ° C. When the spinning temperature is 200 ° C. or higher, the resin viscosity can be discharged from the spinneret in a moderately low state, and a large spinning line stress is difficult to act in the process of thinning the composite fiber, and the molecular orientation of the core component is suppressed. It is preferable because it is easy. In addition, when the spinning temperature is 350 ° C. or lower, it is preferable that a high-strength drawn fiber can be obtained by the subsequent drawing treatment without causing deterioration or thermal decomposition of the resin and without significantly destabilizing the spinning process. If the spinning temperature is in the range of 260 to 300 ° C., the balance between the effect of suppressing the orientation of the core component, the stability of the spinning process, and the strength development by the stretching treatment is particularly preferable.

  When the fibrous resin discharged from the spinneret is cooled, it can be cooled to a solidification temperature or lower in a conventional method, for example, a medium such as air, water, glycerin, and the like. In order to suppress the molecular orientation of the components, it is desirable to cool slowly with air rather than rapidly cooling. Air temperature and wind speed can be set arbitrarily, but in order to further suppress molecular orientation, it is desirable that the wind speed is low and the temperature is not too low. When the temperature of the resin discharged from the spinneret is high and the cooling rate is appropriate, the crystalline higher order structure of the crystalline propylene polymer that is the core component of the undrawn yarn is changed to a pseudo hexagonal crystal that has excellent drawability. It is possible to control.

  The take-up speed of the undrawn yarn can be set at an arbitrary speed. When the take-up speed is lower than the free fall speed of the melted undrawn yarn, a uniform undrawn yarn cannot be obtained, leading to a reduction in drawability. Furthermore, the reduction in the take-up speed leads to a decrease in productivity. In addition, when the take-up speed is extremely high, the deformation speed at the position where the composite fiber is thinned is increased, and an undrawn yarn having advanced molecular orientation of the core component is obtained. This leads to a decrease in stretchability. Accordingly, in consideration of productivity, spinning stability, and stretchability in the subsequent stretching process, the take-up speed is preferably in the range of 200 to 1500 m / min, and more preferably in the range of 300 to 1000 m / min.

  Next, the drawing method of the sheath-core type heat-fusible conjugate fiber of the present invention will be described. The stretching method is not particularly limited, and even if any known stretching method is adopted, the effect of the present invention, that is, the core component weight average molecular weight / sheath component weight average molecular weight of the heat-fusible conjugate fiber is By selecting the MFR of the resin raw material for both the sheath and core components and selecting the extrusion conditions so as to be 2.5 or less, an unstretched yarn that can be stretched at a high magnification and has high strength expression with respect to the stretch ratio is obtained. As a result, the effect of obtaining a high-strength heat-fusible conjugate fiber is obtained.

  Among them, rather than contact heating stretching using metal heating rolls and metal heating plates, non-contact heating stretching using hot water, boiling water, pressurized saturated steam, hot air, far infrared rays, carbon dioxide laser tends to be able to stretch at a higher magnification. And preferred. In particular, from the viewpoint of simplicity and operability, non-contact heating stretching using warm water, boiling water, hot air, and far infrared rays is preferable. The stretching temperature is desirably as high as possible below the melting point of the sheath component used. In this case, high-strength drawing is possible, and thus a high-strength heat-fusible conjugate fiber can be obtained. Therefore, stretching from boiling water or pressurized saturated steam is more preferable from the viewpoint that the temperature of the stretched object can be increased to a high temperature and can be instantaneously increased to that temperature. In this case, the stretching speed can be increased, and the effect of improving productivity can be obtained. In addition, as a method of using pressurized saturated steam for a heating medium, a labyrinth type pressurized saturated steam stretching machine may be used, and a pressurized saturated steam stretching machine with both ends sealed by a pressurized water tank (see Patent Document 1). There may be.

  The undrawn yarn of the present invention is characterized by high strength development with respect to the draw ratio. However, by increasing the draw ratio as much as possible, the strength of the heat-fusible conjugate fiber can be further increased. The draw ratio can be appropriately selected according to the fineness of the undrawn yarn, the sheath core ratio, and the resin configuration, but the effective draw ratio is preferably 4.0 times to 8.0 times, more preferably 5.0. Double to 7.0 times. The stretching speed is not particularly limited, but considering productivity, it is preferably 50 m / min or more, and more preferably 100 m / min or more.

  The stretching step may be either one-stage stretching or multi-stage stretching. When performing multi-stage stretching, it is possible to combine the above-described stretching methods. For example, the first stage is hot roll stretching, two-stage stretching. The eye can also employ a stretching method such as pressurized saturated steam stretching.

  A heat treatment step can be provided as necessary after the above-described stretching step. The heat treatment method is not particularly limited, and any known stretching method can be employed. In general, drawn fibers drawn at a high magnification often exhibit a high thermal shrinkage rate, but thermal shrinkage can be reduced by undergoing a heat treatment step. The heat treatment temperature is preferably not higher than the melting point of the sheath component and as high as possible because heat shrinkage can be further suppressed.

  In order to satisfy processing suitability and physical properties of the product, it is desirable to attach a surfactant to the surface of the sheath-core type heat-fusible conjugate fiber of the present invention. The type of the surfactant is not particularly limited, and a known method such as a roller method, a dipping method, a spraying method, or a pad drying method can also be adopted as an adhesion method.

  The heat-fusible conjugate fiber of the present invention employs the above-described resin composition of the sheath core, the spinning method, the stretching method, and the heat treatment method, and the core component weight average molecular weight / sheath component weight average molecular weight of the heat fusible conjugate fiber is determined. By setting it to 2.5 or less, it becomes a drawn fiber having both high fiber strength and excellent heat shrinkage resistance. The fiber breaking strength is 6.0 cN / dtex or more, more preferably 6.3 cN / dtex, and still more preferably 6.5 cN / dtex. Further, the dry heat shrinkage at 145 ° C. is 20% or less, preferably 18% or less, more preferably 15% or less.

  The sheath-core type heat-fusible conjugate fiber of the present invention can be used for various applications, and can be made into various fiber forms according to the application. For example, in the case of the fiber for card nonwoven fabric, the fiber form of the staple which gave the crimp is preferable. The sheath-core type heat-fusible conjugate fiber of the present invention has high fiber strength and heat-fusibility, and is particularly suitable because it can increase the bulk and strength of nonwoven fabrics and improve card productivity. It is thought that. The fineness, the number of crimps, and the fiber length are not particularly limited and can be appropriately selected. In the case of fibers for woven fabric filters, fibers for winding filters, fibers for woven fabric sheets, fibers for knitted nets, etc., the fiber form of filaments is preferred. The fineness is not particularly limited and can be appropriately selected. In the case of an airlaid nonwoven fabric, a shortcut chop is preferred. The fineness is not particularly limited, and may be crimped or may not be crimped. The fiber length can be appropriately selected in consideration of the type of processing machine, required physical properties, productivity, and the like. In the case of a fiber for concrete reinforcement or a fiber for papermaking nonwoven fabric, the fiber form of a shortcut chop is preferable. It may be crimped or may not be crimped, and the fiber length can be appropriately selected in consideration of processing methods, required physical properties, productivity, and the like. Although the fineness is not particularly limited, for example, in the case of a wet nonwoven fabric such as a battery separator, it is preferable that the fineness is small, preferably 2.2 dtex or less, more preferably 1.5 dtex or less. More preferably, it is 1.0 dtex or less. When a battery separator wet nonwoven fabric is produced using the sheath-core type heat-fusible conjugate fiber of the present invention, it has a high fiber strength, and also has a high heat-sealing power when made into a nonwoven fabric by heat treatment, This is particularly suitable because it has a high effect of preventing sharp hard objects such as metals from penetrating the nonwoven fabric.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by them. In addition, the measuring method or definition of the physical-property value shown in the Example is shown below.

(1) Single yarn fineness The undrawn yarn and the drawn yarn were measured according to JIS-L-1015.
(2) MFR
Measurements were performed under the following conditions for the fibrous materials of each of the pellet core and the sheath core discharged from the spinneret.
In the case of a polypropylene resin raw material: measured at a test temperature of 230 ° C. and a test load of 21.18 N.
(Test condition 14 of JIS-K-7210 “Table 1”)
For polyethylene resin raw material: Measured at a test temperature of 190 ° C. and a test load of 21.18N.
(Test condition 4 of JIS-K-7210 “Table 1”)
In the case of fibrous material after nozzle discharge: measured at a test temperature of 230 ° C. and a test load of 21.18 N.
(Test condition 14 of JIS-K-7210 “Table 1”)

(3) Weight average molecular weight With respect to the heat-fusible conjugate fiber subjected to the stretching treatment, the weight average molecular weight of each of the core component and the sheath component was measured by cross fractionation chromatography. A high-temperature sample solution in which the heat-fusible conjugate fiber of the present invention is completely dissolved in orthodichlorobenzene is injected into a column filled with an inert carrier such as glass beads, and the sample is dropped by lowering the column temperature. After adhering to the surface of the packing material, while flowing orthodichlorobenzene into the column, the temperature of the column is gradually increased to detect the concentration of the components eluted at each temperature, and the elution is performed at each temperature simultaneously. The components are sent to the GPC device on-line for each fraction, and the weight average molecular weight of each component is obtained from the chromatogram obtained there.

  The measuring apparatus used was a CFC apparatus (T150A type, filler: glass beads (Shodex GPC AD-806MS manufactured by Showa Denko)) manufactured by Mitsubishi Chemical Corporation under the following conditions. After injecting 4 mL of the sample solution (solvent: orthodichlorobenzene, sample concentration: 40 mg / 10 mL) into the column heated to 140 ° C., the sample polymer is cooled to 0 ° C. at a rate of 1 ° C./min, and the sample polymer is placed on the packing surface. Adsorbed (deposited). Next, while the orthodichlorobenzene was flowed at a flow rate of 60 mL / h, the column was gradually heated up to 140 ° C., and the polymer eluted from the surface of the filler at each temperature was sequentially sent to the GPC column on-line. The weight average molecular weights of both sheath core components were obtained from the chromatogram obtained there.

(4) Effective draw ratio It calculated from the formula of undrawn yarn fineness / drawn yarn fineness.
(5) Single yarn strong elongation It measured according to JIS-L-1015.
(6) Dry heat shrinkage rate Measured according to JIS-L-1015. The heat treatment temperature was 145 ° C. and the heat treatment time was 10 minutes.
(7) Nonwoven fabric piercing strength Using a short-cut chop with a fiber length of 5 mm that has not been crimped, a web was produced by a papermaking method, and this was heat-sealed at 136 ° C. to obtain a nonwoven fabric with 50 basis weight. . The puncture strength of this was measured according to the method described in JIS-Z-1707.

Example 1
Isotactic polypropylene “SA2D” (manufactured by Nippon Polypro Co., Ltd., resin raw material MFR = 14 g / 10 min, Q value = 3.1) is used as the core component, and high-density polyethylene “M6800” (Kyoyo Polytech Co., Ltd.) is used as the sheath component. ), Resin raw material MFR = 8 g / 10 min), using a sheath core type composite spinneret so that the cross-sectional composite ratio of the sheath core is 50/50, the extruder cylinder temperature of the core component is 300 ° C., A heat-fusible conjugate fiber having an undrawn yarn fineness of 4.2 dtex was spun under the conditions of an extruder cylinder temperature of the sheath component of 240 ° C., a spinneret temperature of 250 ° C., and a winding speed of 920 m / min. The MFR of the core component discharged from the spinneret was 54.1 g / min, and the MFR of the sheath component was 11.1 g / 10 min. Then, in a roll stretching machine having a hot water tank between the rolls, the first stage roll temperature is set to room temperature and the hot water tank temperature is set to 102 ° C. to bring it into a boiling state (100 ° C.), and the second stage roll temperature is 110 ° C. The stretching process was performed under the conditions. The maximum effective draw ratio that can be drawn industrially stably was 4.7 times, and the strength of the obtained drawn fiber was 6.4 cN / dtex, and the dry heat shrinkage at 145 ° C. was 16.9%. When the molecular weight of the drawn fiber was measured by a cross-fractionation chromatograph, the weight average molecular weight of the core component was 1280,000, and the weight average molecular weight of the sheath component was 64,600. Moreover, when this was cut into 5 mm and the puncture strength of the 50-weight nonwoven fabric produced by heat-sealing the paper web was measured, it was 13.0 N. Thus, the heat-fusible conjugate fiber obtained by the method of Example 1 had high fiber strength, and the dry heat shrinkage rate was kept low.

Example 2
An undrawn yarn of a heat-fusible conjugate fiber was spun in the same manner as in Example 1 except that the cross-sectional composite ratio of the sheath core was 40/60. The MFR of the core component discharged from the spinneret was 55.0 g / min, and the MFR of the sheath component was 11.5 g / 10 min. Thereafter, a roll stretching machine having a hot water tank between the rolls was subjected to a stretching process under the conditions that the first stage roll temperature was room temperature, the hot water tank temperature was 95 ° C., and the second stage roll temperature was 110 ° C. The maximum effective draw ratio at which it can be drawn industrially stably was 4.2 times. The strength of the obtained drawn fiber was 6.3 cN / dtex, and the dry heat shrinkage at 145 ° C. was 15.1%. When the molecular weight of the drawn fiber was measured by a cross-fractionation chromatograph, the weight average molecular weight of the core component was 125,000, and the weight average molecular weight of the sheath component was 63,000,000. Moreover, when this was cut into 5 mm and the puncture strength of the 50-weight nonwoven fabric produced by heat-sealing the papermaking web was measured, it was 12.2N. Thus, the heat-fusible conjugate fiber obtained by the method of Example 2 had high fiber strength and the dry heat shrinkage rate was kept low.

Example 3
An undrawn yarn of a heat-fusible composite fiber having an undrawn yarn fineness of 5.8 dtex was obtained in the same manner as in Example 2 except that the extruder cylinder temperature of the core component was 290 ° C. and the winding speed was 670 m / min. Spinned. The core component MFR discharged from the spinneret was 37.6 g / min, and the sheath component MFR was 10.8 g / 10 min. Thereafter, in a roll stretching machine having a pressurized saturated steam stretching tank between the rolls, the first stage roll temperature is room temperature, the hot water tank temperature is 125 ° C., and the second stage roll temperature is 110 ° C. went. The pressurized saturated steam stretching tank is provided with a labyrinth structure at both ends of the stretching tank, thereby suppressing the leakage of pressurized steam. The maximum effective draw ratio that can be drawn industrially stably was 5.3 times, and the strength of the obtained drawn fiber was 6.8 cN / dtex, and the dry heat shrinkage at 145 ° C. was 14.1%. When the molecular weight of the stretched fiber was measured by a cross-fractionation chromatograph, the weight average molecular weight of the core component was 146,000 and the weight average molecular weight of the sheath component was 650,000. Moreover, when this was cut into 5 mm and the puncture strength of the 50-weight nonwoven fabric produced by heat-sealing the paper web was measured, it was 13.7 N. Thus, the heat-fusible conjugate fiber obtained by the method of Example 3 had high fiber strength, and the dry heat shrinkage rate was kept low.

Example 4
Isotactic polypropylene “SA04D” (manufactured by Nippon Polypro Co., Ltd., resin raw material MFR = 40 g / 10 min, Q value = 3.0) is used as the core component, and high-density polyethylene “3S01A” (Tosoh Corp.) is used as the sheath component. Made of resin raw material MFR = 13 g / 10 min), using a sheath-core type composite spinneret so that the cross-sectional composite ratio of the sheath core becomes 60/40, the core temperature of the extruder cylinder of the core component is 260 ° C. Spinning unstretched yarn of heat-fusible conjugate fiber with unstretched yarn fineness of 7.8 dtex under the conditions that the extruder cylinder temperature is 220 ° C, the spinneret temperature is 240 ° C, and the winding speed is 720 m / min. did. The MFR of the core component discharged from the spinneret was 59.0 g / min, and the MFR of the sheath component was 24.3 g / 10 min. Then, in a roll stretching machine having a hot water tank between the rolls, the first stage roll temperature is set to room temperature and the hot water tank temperature is set to 102 ° C. to bring it into a boiling state (100 ° C.), and the second stage roll temperature is 110 ° C. The stretching process was performed under the conditions. The maximum effective draw ratio at which industrially stable drawing was possible was 5.2 times, and the strength of the obtained drawn fiber was 6.3 cN / dtex, and the dry heat shrinkage at 145 ° C. was 18.2%. When the molecular weight of the stretched fiber was measured by a cross-fractionation chromatograph, the weight average molecular weight of the core component was 123,000 and the weight average molecular weight of the sheath component was 521,000. Moreover, when this was cut into 5 mm and the piercing strength of the 50-weight nonwoven fabric produced by heat-sealing the paper web was measured, it was as low as 7.8 N because of its large fineness. Thus, the heat-fusible conjugate fiber obtained by the method of Example 4 had high fiber strength, and the dry heat shrinkage rate was kept low.

Example 5
Isotactic polypropylene “SA03D” (manufactured by Nippon Polypro Co., Ltd., resin raw material MFR = 30 g / 10 min, Q value = 2.8) is used as the core component, and high-density polyethylene “S6900” (Kyoyo Polyethylene Co., Ltd.) is used as the sheath component. ), Resin raw material MFR = 16.5 g / 10 min), and a sheath core type composite spinneret is used so that the cross-sectional composite ratio of the sheath core is 50/50, and the extruder cylinder temperature of the core component is 310. Unstretched heat-fusible conjugate fiber with unstretched yarn fineness of 3.6 dtex under the conditions of ℃, sheath cylinder extruder cylinder temperature is 220 ℃, spinneret temperature is 260 ℃, and winding speed is 940 m / min The yarn was spun. The core component MFR discharged from the spinneret was 62.6 g / min, and the sheath component MFR was 27.6 g / 10 min. Thereafter, in a roll stretching machine having three sets of rolls and a hot water tank between the rolls, the first stage roll temperature is room temperature, the first hot water tank temperature is 90 ° C., the second stage roll temperature is 90 ° C., Two-stage stretching treatment was performed under the condition that the temperature of the two warm water tanks was 95 ° C and the temperature of the third-stage roll was 120 ° C. The maximum effective draw ratio at which it can be drawn industrially stably was 5.1 times, and the strength of the obtained drawn fiber was 6.1 cN / dtex, and the dry heat shrinkage at 145 ° C. was 15.2%. When the molecular weight of the stretched fiber was measured by a cross-fractionation chromatograph, the weight average molecular weight of the core component was 122,000, and the weight average molecular weight of the sheath component was 51 million. Further, the puncture strength of a 50-percent nonwoven fabric produced by cutting this into 5 mm and thermally fusing the papermaking web was 16.0 N. Thus, the heat-fusible conjugate fiber obtained by the method of Example 5 had high fiber strength, and the dry heat shrinkage rate was kept low.

Example 6
Implemented except that polypropylene “SA2E” (manufactured by Nippon Polypro Co., Ltd., resin raw material MFR = 16.0 g / 10 min, Q value = 5.3) was used as the core component, and the extruder cylinder temperature of the core component was set to 330 ° C. In the same manner as in Example 1, an undrawn yarn was spun. The MFR of the core component discharged from the spinneret was 38.4 g / min, and the MFR of the sheath component was 11.1 g / 10 min. The stretching process was also the same as in Example 1. As a result, the maximum effective stretch ratio that enables industrially stable stretching was 4.2 times, and the strength of the obtained stretched fiber was 6.0 cN / dtex and a dryness at 145 ° C. The heat shrinkage rate was 14.5%. When the molecular weight of the drawn fiber was measured by a cross-fractionation chromatograph, the weight average molecular weight of the core component was 143,000, and the weight average molecular weight of the sheath component was 64.40 million. In addition, the puncture strength of a 50-weight non-woven fabric produced by cutting this into 5 mm and heat-sealing the paper web was 12.6 N. Thus, the heat-fusible conjugate fiber obtained by the method of Example 6 had high fiber strength, and the dry heat shrinkage rate was kept low.

Example 7
Example 1 except that linear low-density polyethylene “M60” (manufactured by Tosoh Corporation: resin raw material MFR = 8.0 g / 10 min) was used as the sheath component, and the extruder cylinder temperature of the sheath component was 200 ° C. In the same manner as above, an undrawn yarn was spun. The MFR of the core component discharged from the spinneret was 54.6 g / min, and the MFR of the sheath component was 13.2 g / 10 min. The stretching process was also the same as in Example 1. As a result, the maximum effective draw ratio at which industrially stable stretching was possible was 4.2 times, and the strength of the obtained drawn fiber was 6.1 cN / dtex and a dryness at 145 ° C. The heat shrinkage rate was 16.1%. When the molecular weight of the stretched fiber was measured by a cross-fractionation chromatograph, the weight average molecular weight of the core component was 128,000 and the weight average molecular weight of the sheath component was 63,990. Further, the puncture strength of a 50-percent nonwoven fabric produced by cutting this into 5 mm and thermally fusing the papermaking web was 9.9 N. Compared with Example 1, the piercing strength is low, which is because the sheath component is a linear low-density polyethylene, and therefore the thermal fusion force at the fiber entanglement point of the nonwoven fabric is low. Thus, the heat-fusible conjugate fiber obtained by the method of Example 6 had high fiber strength, and the dry heat shrinkage rate was kept low.

Comparative Example 1
Heat-sealability of unstretched yarn fineness of 4.2 dtex in the same manner as in Example 1 except that high-density polyethylene “S6920” (manufactured by Keiyo Polyethylene Co., Ltd., pellet MFR = 26 g / 10 min) was used as the sheath component. Composite fiber was spun. The core component MFR discharged from the spinneret was 54.9 g / min, and the sheath component MFR was 42.2 g / 10 min. Then, the extending | stretching process was performed by the method similar to Example 1. FIG. The maximum effective draw ratio that can be drawn industrially stably was 4.7 times, and the strength of the obtained drawn fiber was 5.0 cN / dtex, and the dry heat shrinkage at 145 ° C. was 16.5%. When the molecular weight of the stretched fiber was measured by a cross-fractionation chromatograph, the weight average molecular weight of the core component was 1290,000, and the weight average molecular weight of the sheath component was 44,600. In addition, when the puncture strength of a 50-mesh non-woven fabric prepared by cutting this into 5 mm and heat-sealing the paper web was measured, it was as low as 9.4 N despite the same fineness as in Example 1. It was. Thus, although the heat-fusible conjugate fiber obtained by the method of Comparative Example 1 was drawn at the same effective draw ratio as Example 1, the fiber strength was low.

Comparative Example 2
Heat fusion of unstretched yarn fineness of 4.2 dtex in the same manner as in Example 1 except that high density polyethylene “J302” (manufactured by Tosoh Corporation, pellet MFR = 41.5 g / 10 min) was used as the sheath component. Conjugated composite fiber was spun. The MFR of the core component discharged from the spinneret was 54.1 g / min, and the MFR of the sheath component was 72.6 g / 10 min. Then, the extending | stretching process was performed by the method similar to Example 1. FIG. The maximum effective draw ratio that can be drawn industrially stably was 4.7 times, and the strength of the obtained drawn fiber was 5.0 cN / dtex, and the dry heat shrinkage at 145 ° C. was 16.0%. When the molecular weight of the drawn fiber was measured with a cross-fractionation chromatograph, the weight average molecular weight of the core component was 12.9 million, and the weight average molecular weight of the sheath component was 391,000. Further, when the puncture strength of a 50-percent nonwoven fabric prepared by cutting this into 5 mm and heat-sealing the paper web was measured, it was as low as 8.0 N despite the same fineness as in Example 1. It was. Thus, although the heat-fusible conjugate fiber obtained by the method of Comparative Example 1 was drawn at the same effective draw ratio as Example 1, the fiber strength was low.

Comparative Example 3
A heat-fusible conjugate fiber having an undrawn yarn fineness of 5.8 dtex was obtained in the same manner as in Example 3 except that “S6920” (manufactured by Keiyo Polyethylene Co., Ltd., pellet MFR = 26 g / 10 min) was used as the sheath component. Spinned. The core component MFR discharged from the spinneret was 37.6 g / min, and the sheath component MFR was 43.0 g / 10 min. Then, the extending | stretching process was performed by the method similar to Example 3. FIG. The maximum effective draw ratio at which it can be industrially drawn stably was 4.8 times, and the strength of the obtained drawn fiber was 5.8 cN / dtex, and the dry heat shrinkage at 145 ° C. was 14.2%. When the molecular weight of the stretched fiber was measured by a cross-fractionation chromatograph, the weight average molecular weight of the core component was 142,000, and the weight average molecular weight of the sheath component was 44,000. Further, the puncture strength of a 50-percent nonwoven fabric produced by cutting this into 5 mm and thermally fusing the papermaking web was 8.8N. Thus, although the heat-fusible conjugate fiber obtained by the method of Comparative Example 1 was drawn at substantially the same effective draw ratio as Example 3, the fiber strength was low.

Comparative Example 4
A heat-fusible conjugate fiber having an undrawn yarn fineness of 7.8 dtex in the same manner as in Example 4 except that “J302” (manufactured by Tosoh Corporation, pellet MFR = 41.5 g / 10 min) was used as the sheath component. Was spun. The MFR of the core component discharged from the spinneret was 59.0 g / min, and the MFR of the sheath component was 74.1 g / 10 min. Then, the extending | stretching process was performed by the method similar to Example 4. FIG. The maximum effective draw ratio at which it can be drawn industrially stably was 5.2 times, and the strength of the obtained drawn fiber was 5.2 cN / dtex, and the dry heat shrinkage at 145 ° C. was 20.6%. When the molecular weight of the stretched fiber was measured with a cross-fractionation chromatograph, the weight average molecular weight of the core component was 1240,000 and the weight average molecular weight of the sheath component was 38,880. Further, the puncture strength of a 50-percent nonwoven fabric produced by cutting this into 5 mm and heat-sealing the paper web was 6.1 N. Thus, although the heat-fusible conjugate fiber obtained by the method of Comparative Example 4 was drawn at the same effective draw ratio as Example 4, the fiber strength was low.

Comparative Example 5
A heat-fusible conjugate fiber having an undrawn yarn fineness of 4.2 dtex was spun in the same manner as in Example 1 except that the extruder cylinder temperature of the core component was 260 ° C. The core component MFR discharged from the spinneret was 20.9 g / min, and the sheath component MFR was 10.1 g / 10 min. Then, the extending | stretching process was performed by the method similar to Example 1. FIG. The maximum effective draw ratio at which the fiber can be drawn industrially stably was 3.2 times, and the strength of the obtained drawn fiber was 3.4 cN / dtex, and the dry heat shrinkage at 145 ° C. was 12.1%. When the molecular weight of the drawn fiber was measured with a cross-fractionation chromatograph, the weight average molecular weight of the core component was 174,000, and the weight average molecular weight of the sheath component was 65,600. Moreover, when this was cut into 5 mm and the piercing strength of a 50-percent nonwoven fabric produced by heat-sealing the paper web was measured, the fineness was greater than in Example 1 and the fiber strength was low. It was as low as 9.0N. Thus, the heat-fusible conjugate fiber obtained by the method of Comparative Example 5 could be drawn only at a lower draw ratio than Example 1, and the fiber strength was low. This is presumably because the core component MFR discharged from the spinneret was too low.

Claims (7)

  This is a heat-fusible conjugate fiber obtained by drawing an undrawn yarn in which a crystalline propylene polymer is arranged in the core component and an olefin polymer having a melting point lower than that of the core component is arranged in the sheath component. The ratio of the weight average molecular weight of the core component to the weight average molecular weight of the sheath component (core component weight average molecular weight / sheath component weight average molecular weight) measured by cross-fractionation chromatography of the heat-fusible conjugate fiber is 2. A heat-fusible conjugate fiber characterized by being 5 or less.   The heat-fusible conjugate fiber according to claim 1, wherein the resin raw material of the sheath component has an MFR at 190 ° C of 3 to 18 g / 10 min.   The heat-fusible conjugate fiber according to claim 1 or 2, wherein the resin raw material of the core component has an MFR at 230 ° C of 5 to 60 g / 10 min.   The heat-fusible conjugate fiber according to any one of claims 1 to 3, which has a fiber breaking strength of 6.0 cN / dtex or more.   The heat-fusible conjugate fiber according to claim 4, wherein the dry heat shrinkage at 145 ° C is 20% or less.   The heat-fusible conjugate fiber according to any one of claims 1 to 3, wherein the core component is isotactic polypropylene and the sheath component is high-density polyethylene.   The heat-fusible composite fiber according to claim 6, wherein the core component isotactic polypropylene has a Q value (molecular weight distribution: weight average molecular weight / number average molecular weight) of 4 or less.