JPH02133607A - Porous polyolefin fiber - Google Patents

Abstract

PURPOSE:To provide the title lightweight fiber of opaquely white color with soft feel, having specific porous structure, large in surface area, consisting of a blend polymer comprising polyolefin and hydrophilic polyolefin. CONSTITUTION:The objective porous fiber consisting of a blend polymer comprising (A) 95-40wt.% of a polyolefin (e.g., PE, PP; being pref. with high degree of crystallinity) and (B) 5-60wt.% of a hydrophilic polyolefin (e.g., copolymer from ethylene and vinyl alcohol; pref. <=70 deg. in contact angle to water when determined in the form of a film). This fiber has such a porous structure that spaces surrounded by lamellae and numerous fibrils mutually connecting said lamellae are communicated over the entire range from the fiber surface to the center.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to porous polyolefin TA fibers.

(Prior art) In recent years, fibers for clothing and industrial materials have become increasingly diverse, and as part of this diversification, there has been an increasing demand for fibers 1 and 2 that are lightweight and have a soft texture, yet have appropriate strength. ing. ! One way to achieve lil weight and soft texture is to make it porous. For example, a blowing agent is blended with a thermoplastic polymer and melt-spun, and the blowing agent is decomposed during the spinning stage to make it porous. There are also those made by blending extractable substances (inorganic salts, organic low-molecular compounds, etc.) with thermoplastic polymers, spinning them, and then extracting them with an appropriate solvent to make them porous.

(Problems to be Solved by the Invention) However, it is difficult to create a uniform and fine foam structure in a product that is blended with a foaming agent and spun, and then foamed and made porous during the spinning stage. It is difficult to obtain fibers with high porosity, and attempts to increase the porosity result in frequent fiber breakage and a significant decrease in strength, making it difficult to obtain fibers with high porosity and low stability in the spinning process. The manufacturing process is complicated, and it is difficult to completely remove additives by extraction, so impurities tend to remain in the fiber product, which also affects the texture, making it difficult to obtain a product with a sufficiently good texture. In addition, if an attempt is made to increase the porosity, a significant decrease in strength occurs, so that this is also not completely satisfactory.

Under these circumstances, the applicant first spun polyethylene, heat-treated it, then cold-stretched it, and then hot-stretched it so that the space surrounded by a large number of fibrils connecting the lamellae was separated from the surface of the fiber to the center. proposed a porous polyethylene fiber that is continuous up to the
No. 7).

Although the IA fiber is made of polyethylene, it does not have the waxy feel characteristic of polyolefins, and is lightweight and has an excellent texture. As a raw material, it had no choice but to be of limited use.

In order to develop this fiber into uses that require hydrophilicity, we performed a lignophilic treatment using a lignophilic agent such as a surfactant, but found that the hydrophilicity could only be temporary. There is a problem that the hydrophilic agent falls off due to contact with wood and loses its wood-loving properties.Also, melt-spun products blended with wood-loving substances cannot be used with ordinary wood-loving substances as polyolefins. There was a problem in that fibers with good performance could not be obtained due to poor affinity for.

(Means for solving the problem) As a result of intensive study in view of the above situation, the present inventors found that
Blended polyolefins with polyolefins with specific performance properties can be made highly porous by melt spinning and stretching in the same way as ordinary crystalline polyolefins, resulting in lightness and excellent texture, as well as permanent wood-philicity. We have discovered that this is the case, and have arrived at the present invention.

That is, the gist of the present invention is that 95 to 40% by weight of polyolefin
and 5 to 60% by weight of a hydrophilic polyolefin.
A porous polyolefin fiber characterized by having a porous structure consisting of two interconnected spaces surrounded by lamellae and a large number of fibrils connecting the lamellae throughout the surface of the Ak fiber up to the center of the fiber. be.

Polyolefins used in the present invention include polyethylene, polypropylene, poly3-methylbutene-1
, poly-4-methylpentene-1, and the like. In addition, it is preferable to use a polyolefin with a high degree of crystallinity, and the degree of crystallinity of the undrawn yarn obtained by melt spinning a polyolefin blended with the wood-loving polyolefin described below is 40% or more, preferably 50%. It is preferable to select a polymer having a crystal orientation degree of 50% or more, preferably 60% or more. In addition, the wood-philic polyolefin blended with the polyolefin in the present invention has a contact angle with water of 8 when measured using a film.
It is often a polyolefin modified so that the angle is 0° or less, and more preferably a polyolefin modified so that the angle is 70" or less. Examples of such non-modified polymers Examples include those in which hydroxyl groups, carboxyl groups, amino groups, sulfonic acid groups, polyoxyethylene groups, etc. are bonded to the molecular chains of various polyolefins. Examples include copolymers of ethylene and maleic anhydride, copolymers of ethylene and polyoxyethylene chemically bonded, and metal ion crosslinked polyolefins.

Here, the reason why we limited the polymer blended with polyolefin to hydrophilic polyolefin is that when the polyolefin described above is blended with polyolefin, good affinity can be obtained between the two, and this can be melt-spun by kneading. The formation of a lamellar crystal structure in the undrawn yarn obtained by this process is not significantly inhibited, and furthermore, ff1l separation at the blend polymer interface is difficult to occur, so an excellent porous structure similar to that obtained when using a polyolefin monopolymer can be obtained. Moreover, because it has a hydrophilic group, it has permanent wood-philic properties, allowing water and moisture to penetrate into the fine pores of the fibers, making effective use of the extremely large surface area of the fibers. It has the excellent feature of being able to The mixing ratio of this polyolefin and wood-loving polyolefin is polyolefin 95 to 4.
5-60% by weight of hydrophilic polyolefin relative to 0% by weight
It must be. This means that when highly wood-philic polyolefins are used, they can exhibit hydrophilicity with a relatively small amount of blending, and conversely, when such wood-philic polyolefins are blended in large amounts, the polyolefin becomes It tends to inhibit the formation of lamellar crystals, making it difficult to obtain a good porous structure, and on the other hand, in the case of materials that have lower wood-philicity and more of the characteristics of polyolefin, they do not have sufficient hydrophilicity. In order to achieve this effect, it is necessary to blend a relatively large amount, and even when blended in a large amount, the polyolefin is 90 to 50% by weight and the hydrophilic polyolefin is 10%.
The combination is preferably 50% by weight. If the ratio of polyolefin is less than the above-mentioned lower limit, it tends to be difficult to obtain a sufficiently uniform porous structure, which is not preferable, and if it exceeds the above-mentioned upper limit, wood-philicity becomes insufficient, so it is not preferable.

The porous structure of the porous fiber of the present invention is obtained by stretching an undrawn yarn obtained by spinning a crystalline polymer, stretching the folded molecules between the lamellae of the undrawn yarn, and cleaving it into fibrils. Because it has a structure obtained by fibers, there is a space around the many fibrils arranged in the longitudinal direction of the fibers that connect the lamellae, and this structure is almost the same from the fiber surface to the center of the IA fiber. The space is connected from the surface of the fiber to the center, so the surface area of the fiber is very large, and the porous structure continues all the way to the center of the fiber. It is something that gives it a unique texture.

The porous 'Jt1M fiber of the present invention has a porosity of 30 to 8.
It is preferable that it is 0%, and the strength is 0.5 to 8 g/d,
It is preferable that the elongation is 1 to 300%. If the porosity is less than the lower limit above, does it affect lightness and texture? J tends to be insufficient, and if the upper limit is exceeded, strength tends to be insufficient. The strength and elongation are preferably within the above ranges when considering the use in clothing.

The method for producing porous fibers of the present invention will be explained below.

First, the above-mentioned polyolefin and wood-loving polyolefin are blended, but this blend needs to be sufficiently uniform.The above-mentioned polymers are either blended in advance using a blender such as a V-type blender, or melted using a melt extruder. Preferably, the blended and pelletized mixture is passed through an extruder for melt spinning. This is melt-spun using a conventional spinneret for fiber spinning to obtain a crystalline undrawn yarn. In this case, a length of 1-3 m is placed directly below the spinneret.
It is preferable to carry out melt spinning with a slow cooling section at an ambient temperature of 50 to 100° C., since undrawn yarn with a higher degree of crystallinity can be obtained. If the degree of crystallinity of the undrawn yarn is less than 40% or the degree of crystal orientation is less than 50%, the formation of a lamellar structure is insufficient, and even after the steps described below, a porous structure will not be formed at all, or even if it is formed, it will not be porous. The fiber structure becomes non-uniform, and a porous structure that communicates throughout from the fiber surface to the fiber center cannot be obtained, and the high porosity that is the object of the present invention cannot be obtained. The spinning temperature is 20% higher than the melting point (hereinafter referred to as mpH) of the polymer with a higher melting point among the polymers to be blended.
℃ higher temperature than this melting point (m p, )
The temperature is preferably 0° C. higher or lower. If the yarn is spun at a temperature lower than the lower limit of this temperature range, the resulting undrawn yarn will be highly oriented, but the maximum draw ratio will be low when the drawing process is performed in the later drawing step to make it porous. This is not preferable because the porosity becomes unfavorable. Conversely, spinning at a temperature exceeding the upper limit of the above temperature range is also not preferred, since it is difficult to obtain a high porosity. The spinning draft is 200~
The spinning draft is preferably 10,000, and more preferably 200 to 5,000.By taking the yarn in a molten state at such a high draft, the lamellae in which the lamellar crystals are highly oriented can be unstretched. It can be formed within the yarn, which allows the yarn to have a highly porous porous structure during the subsequent drawing process. If the length of the slow cooling section is less than 1 m or the ambient temperature thereof is less than 50° C., thread breakage immediately below the spinneret tends to occur frequently and process stability tends to decrease, which is not preferable. On the other hand, if the length of the slow cooling section exceeds 3 m or the ambient temperature exceeds 100°C, the cooling of the yarn becomes insufficient and the actual draft tends to decrease. Therefore, it is not preferable from the viewpoint of crystal orientation of the undrawn yarn obtained.

The undrawn yarn thus obtained may be drawn as is, but it may be annealed under a constant length or in a relaxed state at a temperature below m□ and which does not substantially damage the structure of the undrawn yarn. It may be stretched after that.

The porous fiber of the present invention can be obtained by stretching the unstretched system obtained in the above 2 to make it porous.
Preferably m, H-160°C to mp.

Cold stretching at -90°C followed by mpH-5o°C-m;
It is preferable to carry out a combination of hot stretching at -5° C., but the hot stretching may be a multi-stage stretching of two or more stages.

Cold drawing is an important process in producing the fibers of the present invention, and in this process microscopic racks are generated in the amorphous parts between the lamellar crystals of the highly oriented crystalline undrawn yarn, and in the subsequent hot drawing process. The above-mentioned specific porous structure is obtained by expanding it by thermoplastic stretching. The stretching ratio in cold stretching is preferably 5 to 100%, and the stretching ratio in hot stretching is such that the total stretching amount of cold stretching and hot stretching is 100 to 100%.
It is preferable to set it to 700%. If the hot drawing temperature is higher than m, -5°C, the fiber becomes transparent and the desired porous structure cannot be obtained. When the hot stretching temperature is lower than the above lower limit, it is not preferable because the lower the temperature, the lower the porosity. When the total stretching amount exceeds 700%,
This is not preferable because thread breakage occurs frequently during stretching. The porous polyolefin fiber obtained in this way has almost morphological stability ensured by hot drawing, but if necessary, it can be adjusted to mpH
Heat setting may be performed at a temperature of 60° C. to mpH-5° C. under tension or under relaxed conditions.

(Example) The present invention will be further explained below using Examples.
In one example, the crystallinity of the blend polymer was determined by integrating the diffraction intensities in all directions using a wide-angle X-ray diffraction device J and using the following formula.

Crystallinity χc = (integral value of total diffraction intensity - integral value of diffraction intensity of amorphous portion) / integral value of total diffraction intensity Also, the degree of crystal alignment can be determined by diffraction of the (110) plane using a wide-angle X-ray diffractometer. The half value of the distribution of strength in the fiber axis direction was determined using the following formula.

Crystal alignment degree = (Htth o+ / (180−Ht++
o+ )

Example 1 Gourd 0, 968 g/cm3 high density polyethylene (
Hyzex 2200J (manufactured by Mitsui Petrochemicals ■) and a cross-linked product of polyethylene and acrylic acid copolymer using zinc ions (Himilan-1702, manufactured by Mitsui Polychemicals ■, contact angle with water when made into a film: 69''). After blending in a mold blender at a ratio of 1=1 and drying, the pore size is 0.
The fibers were spun from an 8 mm, 36-hole nozzle at a spinning temperature of 200° C. and a spinning speed of 30011/...jn, and then wound up.

The obtained undrawn yarn was heat treated at 115° C. for 120 seconds under constant length. The degree of crystallinity of this undrawn yarn was 62%, and the degree of crystal orientation was 75%. This undrawn yarn was cold-stretched to 80% at 25°C, and then hot-stretched in a 2 m long heated rain bath heated to 115°C until the total stretching ratio reached 520%. Furthermore, grade heating setting was performed in a 2 m long heated rain shower heated to the same temperature so that the total stretching ratio was 400%.

The obtained porous fiber has a porous structure in which spaces formed by lamellae and many fibrils connecting between the lamellae are connected throughout the entire fiber from the surface to the center, making it extremely soft. It has a texture and a porosity of 6
The strength was 4°85 g/d, and the elongation was 38.9%.

Next, 200 c of this porous polyethylene woven Jl1g
After being immersed in ion-exchanged water (c) for 1 hour, it was dehydrated for 5 minutes using a centrifugal molecular 111 machine at 1000 x 11111, and the weight increase rate was measured to determine the water content, which was found to be 76%.

For comparison, porous polyethylene I/A fibers were prepared in the same manner as above using only high-density polyethylene with a density of 0 and 968 g/co+3, and the moisture content was measured to be 6%.
Met.

Example 2 High-density polyethylene (HIZEX 2200J manufactured by Mitsui Petrochemical Co., Ltd.) with a density of 0 and 968 g/cm3 and ethylene-vinyl alcohol copolymer (Soarnol D manufactured by Nippon Gosei Kagakuwa Co., Ltd.) and contact with water in a film 56°) in a ratio of 7:3 with a ■ type blender, and after drying,
Spinning temperature 200℃ from 6 holes, 0.6mm nozzle,
The fibers were spun and wound at a spinning speed of 300 m/win.

The resulting undrawn yarn was heat treated at 11'5° C. for 120 seconds under constant length. The degree of crystallinity of this undrawn yarn was 68%, and the degree of crystal orientation was 82%. This undrawn yarn was cold-stretched by 80% at 25°C, and then heated to 115°C to a length of 2 m.
Hot stretching was carried out in a heating box until the total stretching ratio reached 520%. Further, relaxation heat curing 1- was performed in a heating box 2 m long heated to the same temperature so that the total stretching ratio was 400%.

The obtained porous fiber has a porous structure in which spaces formed by lamellae and a large number of fibrils connecting the lamellae are connected throughout from the fiber surface to the center, and it is extremely soft and flexible. -lx texture, porosity was 52.4%, strength was 240 g/d, and elongation was 109%.

The moisture content of this fiber was measured in the same manner as in Example 1 and found to be 62%.

(Effects of the Invention) As described above, the porous polyolefin fiber of the present invention has a space surrounded by lamellae and a large number of fibrils connecting the lamellae from the fiber surface to the I center. Because it has a porous structure made up of interconnected pores, it has a large surface area, is extremely lightweight, has a soft texture, has a clean white color with no transparency, and has a high porosity. It shows excellent mechanical properties.

In addition, unlike those made porous by solvent or other extraction, it is made porous only by stretching, so it is a hygienic material that does not contain solvents or extraction additives, and has permanent hydrophilic properties. It has excellent sweat absorption properties, making it ideal for clothing that comes in direct contact with the skin, such as underwear, and for medical fabrics. In addition, it can be used for various industrial materials by taking advantage of its high water content and water content within the pores.

Patent applicant: Mitsubishi Rayon Co., Ltd.

Claims (1)

[Scope of Claims] 1) A porous fiber made of a blend polymer consisting of 95 to 40% by weight of polyolefin and 5 to 60% by weight of hydrophilic polyolefin, wherein the fiber is entirely covered from the fiber surface to the center of the fiber. A porous polyolefin fiber characterized in that it has a porous structure in which spaces formed by lamellae and a large number of fibrils connecting the lamellae communicate with each other. 2) The porous polyolefin fiber according to claim 1, wherein the hydrophilic polyolefin has a contact angle with water of 80° or less when measured in a film state. 3) The porosity of the porous fiber is 30-80% and the strength is 0.5
The porous polyolefin fiber according to claim 1, having an elongation of 1 to 300%.