JPH04316608A - Thermo-splittable conjugated fiber - Google Patents

Abstract

PURPOSE:To provide the subject conjugated fiber having a crosssectional shape composed of a high-melting polymer and a low-melting polymer mutually bonded, having a difference in thermal shrinkage factor between both the polymers within a prescribed range, excellent in touch and useful for a nonwoven fabric, etc. CONSTITUTION:An objective conjugated fiber having a crosssectional shape composed of a high-melting polymer segment such as polyethylene terephthalate and a low-melting polymer segment such as an ethylene-propylene random copolymer mutually bonded and showing 50-75% difference in thermal shrinkage factor between the high-melting polymer and the low-melting polymer at a temperature 10 deg.C lower than the melting point of the low-melting polymer.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermally splittable conjugate fiber which is split by heat treatment to form ultrafine fibers, and a method for producing a nonwoven fabric using the same.

0002

BACKGROUND OF THE INVENTION Nonwoven fabrics made of thermoadhesive conjugate fibers do not require the use of binders during their manufacturing process, and have been used as surface materials for sanitary materials such as disposable diapers and napkins. To manufacture these nonwoven fabrics, two types of polymers with different melting points are spun into sheath-core type or side-by-side type composite fibers, which are then stretched, crimped, and cut and fed to a carding machine to form a uniform web. This web is hot air fused or hot roll fused at a temperature above the softening point of the low melting point component to form a nonwoven fabric. Many proposals have been made to improve the texture and feel of such thermal bond type nonwoven fabrics. However, making the fiber itself finer (ultra-fine), which is most effective, can only be done with single yarns up to 1 de because of the passability of the card machine.

0003

OBJECTS OF THE INVENTION The first object of the present invention is to provide a thermally splittable conjugate fiber suitable for producing a nonwoven fabric with excellent texture and feel. A second object of the present invention is to provide a method for producing a nonwoven fabric with excellent texture and feel from the heat-dividable fibers.

0004

SUMMARY OF THE INVENTION The thermally splittable fiber of the present invention, which achieves the above first object, has a cross-sectional shape in which a high melting point polymer segment and a low melting point polymer segment are bonded to each other. ℃The difference in thermal shrinkage between high melting point polymer and low melting point polymer at low temperature is 50-75%
It is characterized by In addition, a method for producing a nonwoven fabric that achieves the second object is to form the heat splittable conjugate fibers into a web using a carding machine, and then convert the web into a material that has a difference in heat shrinkage rate between a high melting point polymer and a low melting point polymer. After dividing and finely dividing the heat-dividable composite fiber into a web of ultra-fine fibers by heat treatment in a temperature range of 50% or more,
It is characterized in that the nonwoven fabric is obtained by thermal or mechanical entanglement means.

First, the thermally splittable composite fiber of the present invention will be explained. The thermally splittable fiber of the present invention has a cross-sectional shape in which a high melting point polymer segment and a low melting point polymer segment are bonded to each other. Such a cross-sectional shape is shown in Figure 1 (
High melting point polymer segment A as shown in a) to (g)
and low melting point polymer segment B are bonded to each other, and at least one part of high melting point polymer segment A and at least one part of low melting point polymer segment B are preferably exposed. Further, it is preferable that a total of four or more high melting point polymer segments and low melting point polymer segments are bonded. Polyethylene terephthalate (hereinafter referred to as PET), polyamide (hereinafter referred to as PA), etc. are used as polymers constituting the high melting point polymer segment, while ethylene propylene random copolymer (hereinafter referred to as EP) is used as the polymer constituting the low melting point polymer segment. (called random copolymer)
, ethylene propylene putene-1 random terpolymer (hereinafter referred to as EPB random terpolymer), etc. are used.

In the thermally splittable conjugate fiber of the present invention, the difference in thermal shrinkage between the high melting point polymer and the low melting point polymer at a temperature 10° C. lower than the melting point of the low melting point polymer is 50 to 75.
% is required. The reason why the difference in thermal shrinkage rate between both polymers is evaluated at a temperature 10° C. lower than the melting point of the low melting point polymer is that this temperature is the upper limit temperature at which stable operation can be performed while leaving the form of the low melting point polymer fiber.

[0007] Difference Δ in thermal shrinkage between a high melting point polymer and a low melting point polymer at a temperature 10°C lower than the melting point of the low melting point polymer
S is determined by the following formula. ΔS (%) = Slmp (%) - Shmp (%) where S
lmp and Shmp are low melting point polymers (l
mp) and high melting point polymer (hmp) at a temperature 10°C lower than the melting point of the low melting point polymer, and the fiber length when unshrinked (Llmp1, Lhmp1) and the temperature 10°C lower than the melting point of the low melting point polymer. It is determined by the following formula from the fiber length (Llmp2, Lhmp2) after heat shrinkage when heat treated for 15 minutes.

[0008]

[Math 1]

[0009] In the present invention, ΔS is 50 to 75%.
The reason for this limitation is that when ΔS is less than 50%, the splitting rate of the thermally splittable conjugate fiber is low, making it difficult to obtain ultrafine fibers by heating, and ultimately making it impossible to obtain a nonwoven fabric with good texture and feel. Close to the upper limit temperature that can maintain
This is because there is no existing low melting point polymer that exhibits a shrinkage rate difference of 75% or more at a temperature 10° C. lower than the melting point.

The thermally splittable composite fiber of the present invention having the above-mentioned configuration is produced by supplying a high melting point polymer and a low melting point polymer to a composite melt spinning device, and spinning a composite melt spinneret having a cross-sectional shape shown in FIG. The obtained undrawn yarn is stretched and crimped. In the production of thermally splittable conjugate fibers, various stresses are applied during mechanical processing such as stretching and crimping, but the high melting point polymer segment and the low melting point polymer segment are virtually not peeled and split. The single yarn denier must be maintained at 1 de or more. This is because both polymers have anti-thread, stretching,
This is because if peeling occurs during machining such as crimp, various troubles will occur. For example, during the stretching process, there may be fuzz and wrapping around rollers, and during the crimping process, there may be clogging at the crimper inlet. Furthermore, if the thermally splittable conjugate fibers are peeled off, the ultrafine fibers peeled off during the carding process for producing the web will get between the needles of the carding machine, interfering with the production of a uniform web. In order to suppress the occurrence of such troubles, to perform machining smoothly, and to obtain ultrafine fibers by thermal splitting and nonwoven fabrics with good texture and feel, the ratio of high melting point polymer and low melting point polymer is Ya■
EP random copolymer or E which is a low melting point polymer
It is necessary to select the content of components other than propylene and the MFR (melt flow rate) of the PB random terpolymer. That is, regarding the above item (2), the cross-sectional area ratio of high melting point polymer/low melting point polymer is preferably 3/7 to 7/3, more preferably 4/6 to 6/4, and particularly preferably 5/5 or its vicinity. Regarding (2) above, the EP random copolymer or EPB random terpolymer increases as the content of components other than propylene increases.
The heat shrinkage rate becomes large, making it suitable for the present invention. However, if the MFR becomes small, distortion during spinning or stretching becomes large, the peel strength at the interface between both polymers becomes low, and the troubles mentioned above during machining occur frequently, which is not preferable. On the other hand, when the content of components other than propylene is low, or when the MFR is large, the distortion that occurs between the two components during spinning and stretching is small, and there is no problem in the stretching, crimping, and carding processes, but distortion occurs due to heat treatment. The difference in shrinkage rate becomes small, and the heat treatment at a temperature approximately 10° C. lower than the melting point of the low melting point polymer cannot divide the polymer, making it necessary to raise the treatment temperature to a temperature higher than the melting point of the low melting point polymer. This is not preferable because the fibers lose their shape and the texture becomes hard. From this viewpoint, the content of components other than propylene in the EP random copolymer or EPB random terpolymer is preferably 2.0 to 8.0 wt%, and the MFR is preferably 5 to 30.

Next, the method for manufacturing the nonwoven fabric of the present invention will be explained. In the method for producing a nonwoven fabric of the present invention, the heat splittable conjugate fibers are formed into a web using a carding machine. This carding process is carried out in a conventional manner, but since the thermally splittable conjugate fibers do not peel off at this stage, there is no problem of ultrafine fibers getting between the needles of the carding machine. Next, the web is heat-treated in a temperature range where the difference in heat shrinkage rate between the high melting point polymer and the low melting point polymer is 50% or more, and the web is split into fine fibers using the difference in heat shrinkage rate between the two polymers to create ultra-fine fibers. Obtain a web of fibers. The thermally splittable conjugate fiber of the present invention has a thermal shrinkage rate difference ΔS of 50 between the two polymers.
Since it is as large as ~75%, the above-mentioned division and finerization can be carried out extremely smoothly. Next, this web is made into a nonwoven fabric by using thermal or mechanical entangling means. Thermal means include hot roll fusing or hot air fusing at a temperature above the softening point of one of the components constituting the web of ultrafine fibers, resulting in a thermal bond type nonwoven fabric, and mechanical means to form a web of ultrafine fibers. It is also possible to make a nonwoven fabric by entangling them by needle punching or water needles. Since the obtained nonwoven fabric is composed of ultrafine fibers, it has excellent texture and feel, and is preferably used as a surface material for sanitary materials.

0012

[Examples] Next, the present invention will be explained in detail with reference to Examples. In addition, the evaluation method of fibers and nonwoven fabrics performed in Examples is as follows.

(1) Difference in heat shrinkage rate (ΔS) The difference ΔS in heat shrinkage rate between a high melting point polymer and a low melting point polymer is the difference in heat shrinkage rate between a high melting point polymer and a low melting point polymer. It was determined from the shrinkage rate when heat treated for 15 minutes at a temperature 10° C. lower than the melting point of the polymer. Note that the calculation formula is as described above. (2) Division ratio Approximately 100 yarns were measured under a microscope, and the number X divided into single component yarns was divided by the number Y of single component yarns, and the result was expressed as a percentage. Division ratio = X ÷ Y × 100% (3) Peel strength The peel strength of both polymers is determined by peeling off one end of the sample approximately 2 cm in advance, holding both ends with clips, attaching the ends to a tensile tester, and applying the clip at a rate of 5 mm/min. Pull at a speed, measure the load at that time: W (g), and measure the diameter of the fiber using a microscope: D (μm). Peel strength: P (g/μm)
). P=W/D (4) Rupture length: means the length at which it breaks under its own weight, length 10
A sample with a diameter of 0 mm and a width of 25 mm was pulled at a tensile speed of 100 mm/min, and the breaking strength obtained was calculated using the following formula. (5) Tactile sensation (sensory test) Evaluation was carried out by a sensory test conducted by five adult women. That is, the sample is pressed against the inside of one forearm with the other hand and rubbed in multiple directions. The touch feeling was evaluated by five panelists, and on average, those with good contact feel were marked with ○, those with poor contact feeling were marked with ×, and those with very poor contact feeling were marked with XX.

Example 1 A high melting point polymer with a relative viscosity of 0.6 [a mixture of equal weights of phenol and tetrachloroethane was used as the solvent, and the solution concentration was 0.6].
5 g/100 ml, measured at a temperature of 20°C] PET (K101 manufactured by Kanebo Co., Ltd.), ethylene content as a low melting point polymer is 4.0 wt%, MFR is 24, melting point is 13
A random EP copolymer (Idemitsu Polypro Y2035G manufactured by Idemitsu Petrochemical Co., Ltd.) at 5°C was supplied to a composite melt spinning device at a volume ratio of high melting point polymer and low melting point polymer of 1:1, and the spinning temperature was 280°C. Take speed 12
It was wound up at 00 m/min. The obtained undrawn yarn was
℃, stretched 3.5 times, gave 14 crimps/inch with a push-in crimper, cut into 51 mm, and made a bonding mold 2 with the cross-sectional shape shown in Fig. 1(a) having a single yarn of 3.0 de. Component fiber I was obtained. The performance of this fiber is shown in Table 1. The difference in heat shrinkage rate of both polymers at 125° C., which is 10° C. lower than the melting point of the low melting point polymer, was 65.2%. The fibers were applied to a carding machine to obtain a web of 20 g/m2, but the fibers did not peel off in the carding machine, and the passing property was good, and a uniform web was obtained. This web was heat-treated for 10 seconds in a hot air oven set at 130°C. As a result, the high melting point polymer segment and the low melting point polymer segment constituting the fiber were peeled off due to the difference in thermal shrinkage rate, resulting in a web of ultrafine fibers. The fiber splitting ratio at this time is 10
It was 0%. Micrographs of the thermally splittable fibers before and after heat treatment are shown in FIGS. 2(a) and 2(b). Then the wind speed is 2m/se
c. The above-mentioned web was supplied to a hot air fusion device adjusted to 140° C. and heat treated for 5 seconds to obtain a hot air fusion bonded nonwoven fabric. The obtained nonwoven fabric had a soft texture as shown in Table 2.
It was also highly powerful.

Examples 2 to 8, Comparative Examples 1 to 2 Thermal splittable composite fibers II, III, IV, V, VI of the present invention and Comparative Examples were prepared in the same manner as in Example 1 using the combinations of raw materials shown in Table 1. Composite fiber VII was obtained. The performance of each fiber is shown in Table 1. The web made of each fiber was heat treated for 10 seconds at a temperature 10°C lower than the melting point of the low melting point polymer in the same manner as in Example 1, and then made into a nonwoven fabric under the conditions shown in Table 2 to improve its strength and texture. It was measured. As is clear from Table 2, the low melting point polymer has an ethylene content of 3 to 3.
Composite fiber I which is 5wt% EP random copolymer
In the case of Examples 1 to 8 using a web made of VI,
Nonwoven fabrics with high strength and good texture have been produced using hot air fusing, hot roll fusing, or needle punching. On the other hand, Comparative Example 1 using a web made of composite fiber VII in which the low melting point polymer is a propylene homopolymer containing no ethylene
In this case, the fibers were not divided before entanglement, so it became nothing more than an ordinary nonwoven fabric. In Comparative Example 2, in which the temperature of the hot air was raised to 170° C., which is higher than the melting point of polypropylene, in an attempt to increase the difference in shrinkage rate from PET, the fibers lost their shape and did not become a nonwoven fabric.

Example 9, Comparative Example 3 The high melting point polymer was manufactured by Ube Industries, Ltd. and had a relative viscosity of 1.
Using nylon 66 of 0 [measured using an equal weight mixture of phenol and tetrachloroethane as a solvent, a solution concentration of 0.5 g/100 ml, and a temperature of 20°C], fiber VIII and fiber IX were made using the raw material combinations shown in Table 1. Obtained. A web consisting of fibers VIII and IX was made into a nonwoven fabric in the same manner as in Example 1. Table 2 shows the performance of the nonwoven fabric. Example 9 from Table 2
The nonwoven fabric of Comparative Example 3 had high strength and excellent feel, but the nonwoven fabric of Comparative Example 3 was inferior in both strength and feel.

[0017]

[Table 1]

[0018]

[Table 2]

[0009]

[Effects of the Invention] By using the thermally splittable conjugate fiber of the present invention, a thermal bond type nonwoven fabric with a good feel that cannot be obtained with conventional adhesive fibers can be obtained. When this nonwoven fabric is used for sanitary materials such as napkins and disposable diapers, it has a good feel and can significantly increase added value. If the fiber of the present invention is used, like the water needle method,
There is no need for expensive equipment that generates high pressure in fluids, and nonwoven fabrics made of ultrafine fibers can be produced using equipment with a relatively simple structure, such as a hot air oven, and energy savings can also be achieved.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the cross-sectional shape of the thermally splittable conjugate fiber of the present invention.

[Figure 2] (a) and (b) are before heat treatment in Example 1;
This is a microscopic photograph of the resulting pyrolyzable composite fiber.

Claims (4)

[Claims] Claim 1: A cross-sectional shape in which a high melting point polymer segment and a low melting point polymer segment are joined to each other, and a difference in thermal shrinkage rate between the high melting point polymer and the low melting point polymer at a temperature 10° C. lower than the melting point of the low melting point polymer. is 50-7
5% thermally splittable composite fiber. 2. The thermally splittable composite according to claim 1, wherein the high melting point polymer segment consists of polyethylene terephthalate or polyamide, and the low melting point polymer segment consists of an ethylene propylene random copolymer or an ethylene propylene butene-1 random terpolymer. fiber. 3. The thermally splittable composite fiber according to claim 1, wherein a total of four or more high melting point polymer segments and four or more low melting point polymer segments are bonded together. 4. After forming the thermally splittable composite fiber according to any one of claims 1 to 3 into a web using a carding machine,
The web is heat-treated in a temperature range where the difference in thermal shrinkage rate between the high melting point polymer and the low melting point polymer is 50% or more, thereby splitting the heat splittable conjugate fibers into fine fibers to form a web of ultrafine fibers. 1. A method for producing a nonwoven fabric, characterized by obtaining the nonwoven fabric by thermal or mechanical entanglement means.