JPH0441710A - Water-absorbing fiber and water-absorbing nonwoven fabric - Google Patents

Abstract

PURPOSE:To obtain the title fiber having excellent mechanical strength and useful in prevention of dropwise condensation of concrete by subjecting to melt spinning a polypropylene in which a granular water-absorbing resin is uniformly dispersed by polyethylene wax. CONSTITUTION:Polypropylene, in which a granular water absorbing resin (e.g. polyacrylic acid salt-based resin), preferably having <=30mum average grain diameter is uniformly dispersed by polyethylene wax, preferably at a volume ratio of resin/wax of (85.2/14.8) (78.1/21.9), is subjected to melt spinning to provide the objective fiber. Furthermore, a water absorbing nonwoven fabric having low tacky properties as well as excellent mechanical strength even in absorption of water is obtained from the above-mentioned fiber.

Description

[Detailed description of the invention] [Industrial application fields] The present invention relates to water absorbent fibers and water absorbent nonwoven fabrics.

[Prior art] Nonwoven fabrics (hereinafter referred to as water-absorbent non-woven fabrics) made of synthetic fibers with excellent water absorption capacity (hereinafter referred to as water-absorbent fibers) have traditionally been used for concrete curing sheets, dew prevention sheets, etc. There is.

As water-absorbing fibers that can be used as materials for such water-absorbing nonwoven fabrics, water-absorbing fibers made by chemically treating the surface of synthetic fibers made of acrylic polymers to form a hydrogel are widely used. In addition, as other water-absorbing fibers, a first component consisting of a crystalline polyolefin and a second component mainly consisting of a thermoplastic elastomer and a water-absorbing resin are used in parallel,
Also known is a water-absorbing fiber (Japanese Unexamined Patent Publication No. 62-28410) in which the first component is the core and the second component is the sheath.

[Problems to be Solved by the Invention] However, water-absorbing fibers made by chemically treating the surface of synthetic fibers made of acrylic polymers to form hydrogels deteriorate the mechanical strength of the fibers due to the gelation of the fiber surfaces due to water absorption. There is a problem that tackiness develops as well as decreases in viscosity. For this reason, water-absorbing nonwoven fabrics made of water-absorbing fibers also have the disadvantage that their mechanical strength decreases as they absorb water, and the fibers stick to each other when they absorb water, and even after drying, the nonwoven fabric does not return to its original shape. Since it does not return, it has the disadvantage that it cannot be used repeatedly.

In addition, a first component consisting of a crystalline polyolefin and a second component mainly consisting of a thermoplastic elastomer and a water-absorbing resin are used.
Water-absorbing fibers in which components are combined in a parallel type or sheath-core type have low tackiness when water is absorbed, but have the disadvantage that the mechanical strength of the fibers decreases as water is absorbed. Therefore, although water-absorbing nonwoven fabrics made of water-absorbing fibers can be used repeatedly, they have the disadvantage that their mechanical strength decreases as water is absorbed.

Therefore, an object of the present invention is to provide water-absorbing fibers and water-absorbing nonwoven fabrics that have low tackiness when water is absorbed and have substantially no decrease in mechanical strength due to water absorption.

[Means for Solving the Problems] The present invention has been made to achieve the above object, and the water-absorbing fiber of the present invention is made of polypropylene in which particulate water-absorbing resin is uniformly dispersed with polyethylene wax. It is characterized by being made by melt spinning.

Further, the water-absorbing nonwoven fabric of the present invention is characterized in that stable fibers made of the water-absorbing fibers of the present invention are mechanically entangled.

The present invention will be explained in detail below.

First, to explain the water absorbent fiber of the present invention, this water absorbent fiber contains polyethylene wax, particulate water absorbent resin (hereinafter simply referred to as water absorbent resin), and polypropylene, and polypropylene is the base polymer. The polyethylene wax corresponds to a dispersant.

The molecular weight and melting point of the polyethylene wax, which is a component of the water-absorbent fiber of the present invention, are not particularly limited as long as the water-absorbent resin can be uniformly dispersed in the polypropylene. It is desirable to have a small difference in melting point from a certain polypropylene.

Furthermore, the type of water-absorbing resin that is uniformly dispersed in the polypropylene by the polyethylene wax is not particularly limited, but it is preferably one that does not decompose or deteriorate its water-absorbing performance due to the heat history during the production of water-absorbent fibers. . Examples of such water-absorbing resins include polyacrylate-based water-absorbing resins. Note that the shape of the water-absorbing resin is not particularly limited, and the average particle size is preferably 30 μm or less in order to suppress deterioration in spinnability and stretchability.

The type of polypropylene that is the base polymer of the water-absorbing fiber of the present invention is not particularly limited, and is appropriately selected depending on the physical properties required of the intended water-absorbing fiber.

The water-absorbing fiber of the present invention is produced by first preparing a masterbatch using polyethylene wax as a dispersant, and then
It is obtained by tri-blending this masterbatch with polypropylene, which is a base polymer, and then melt-spinning. If a water-absorbing resin and polypropylene are directly mixed and spinning is attempted, the water-absorbing resin will aggregate and clog the nozzle, making spinning impossible.

A masterbatch can be obtained, for example, by kneading polyethylene wax and a water-absorbing resin using a masticating roller or the like, adding an appropriate amount of a melt-extrudable polymer to the resulting mixed wire mixture, and then kneading the mixture. The high molecular weight polymer at this time may be the same material as the polypropylene used as the base polymer, or may be a different material. The ratio of water absorbent resin to polyethylene wax in the masterbatch is 88.5:11.5 to 65.734.3 in volume ratio.
It is preferable that If the proportion of polyethylene wax is low, the water absorbent resin cannot be uniformly dispersed in the polypropylene. A particularly preferable ratio of water absorbent resin to polyethylene wax is 85. 2:14.
8 to 78.1+21.9.

When tri-blending the masterbatch and the base polymer polypropylene, the ratio of polypropylene to polyethylene wax is 2.4 by volume.
It is preferable to make it larger than /1. If the proportion of polyethylene wax is high, spinnability and drawability will decrease, and the mechanical strength of the resulting water-absorbing fiber will decrease.

The water-absorbing fiber of the present invention is obtained by dissolving and spinning polypropylene in which a water-absorbing resin is uniformly dispersed as described above. In addition, the water-absorbing fiber of the present invention means a fiber that has been subjected to stretching treatment, and the temperature during stretching is preferably higher than the melting point of the polyethylene wax used. It is difficult to stretch at temperatures lower than the melting point of polyethylene wax;
Stretch breakage occurs frequently. By stretching, the water-absorbing resin that was buried inside at the undrawn yarn stage is exposed on the fiber surface, and as schematically shown in Figure 1, lumps (water-absorbing resin 1) are attached to the surface. The fiber 2 will have a shape like this.

The amount of water absorbed by the water-absorbing fiber of the present invention formed in this way varies depending on the water-absorbing capacity of the water-absorbing resin, the ratio of the water-absorbing resin exposed on the fiber surface to the total amount of water-absorbing resin, etc. The proportion of the water-absorbing resin varies depending on the volume ratio of the water-absorbing resin and the polyethylene wax in the water-absorbing fibers, the ratio of the fiber diameter to the average particle size of the water-absorbing resin, and the like.

Further, the mechanical strength of the fiber depends on the stretching ratio, and the stretching ratio is limited by the volume ratio of the water-absorbing resin and the volume ratio of the polyethylene wax in the water-absorbing fiber, the fiber diameter, etc. Therefore, the volume ratio of the water-absorbing resin and polyethylene wax in the water-absorbing fiber of the present invention and the fiber diameter of the water-absorbing fiber are appropriately selected depending on the use.

A preferable ratio of the fiber diameter to the average particle diameter of the water absorbent resin in the water absorbent fiber of the present invention is 5:1 to 2:1. 5:1
The larger the size, the lower the water absorption efficiency. Further, when the ratio is less than 2:1, spinnability becomes low. The fiber diameter of the water-absorbing fibers herein means the fiber diameter of the portion of the water-absorbing fibers 2 where the water-absorbing resin 1 is not exposed on the surface, as shown in FIG. In FIG. 2, the same parts as in FIG. 1 are given the same reference numerals as in FIG. 1.

Next, the water-absorbing non-woven fabric of the present invention will be explained. As described above, this water-absorbing non-woven fabric is made by mechanically intertwining stable fibers made of the above-described water-absorbing fibers of the present invention.

The stable fibers that are the material for the water-absorbent nonwoven fabric of the present invention are prepared by mechanically crimping the water-absorbing fibers of the present invention at a rate of 12 to 18 crimp by a conventional method, and then cutting the fibers to a desired fiber length. can be easily obtained by In addition, in order to mechanically entangle the staple fibers thus obtained, for example, the obtained staple fibers are defibrated using a card machine to form a web, and the fibers within this web are three-dimensionally formed using a needle punch machine. The entanglement method can be applied to

[Function] In the water-absorbing fiber of the present invention, although most of the water-absorbing resin used as a material is exposed on the fiber surface, the entire fiber surface is not covered with the water-absorbing resin. Even if it absorbs water, its tackiness as a fiber is low. Furthermore, since polypropylene, which is the base polymer forming the fiber skeleton, does not swell, the mechanical strength of the fiber does not substantially decrease even when it absorbs water.

On the other hand, since the water-absorbing nonwoven fabric of the present invention is composed of the above-described water-absorbing fibers of the present invention, it has low tackiness even when water is absorbed, and there is substantially no decrease in mechanical strength due to water absorption.

[Examples] Examples of the present invention will be described below, but the present invention is not limited to these Examples.

In addition, the method of measuring the physical property values shown in the examples will be shown in advance.

・Single fiber strength JIS L 1 for each of the water absorbent fiber before water absorption and the water absorbent fiber after 24 hours immersion in pure water.
Single fiber strength was measured based on 069.

・Saturated water absorption of nonwoven fabric A nonwoven fabric dried for 12 hours in a vacuum dryer at 80°C is
A test piece is cut into 80 mm x 80 mm, and 5 test pieces (weight: W, g) are stacked and placed in a bag made of polyester filter cloth (200 mesh), and the bag containing the 5 test pieces is soaked in pure water. It was soaked in the water for 24 hours to absorb water. After this, the moisture between the fibers of the test piece was removed by dehydration using a centrifugal dehydrator, the weight (W2 g) of the five test pieces at this time was measured, and the number of times the own weight was calculated using the following formula. It was determined whether pure water was absorbed, and this value was taken as the saturated water absorption amount W of the nonwoven fabric.

Saturated water absorption amount W (times) = (W2 Wl ) /Wl Note that the saturated water absorption amount of the nonwoven fabric determined in this way was almost not different from the saturated water absorption amount of the fibers.

・Water absorption efficiency of nonwoven fabric The theoretical value (W times) of the saturated water absorption amount of the nonwoven fabric is calculated from the weight (theoretical value) of the water absorbent resin contained in the nonwoven fabric and the saturated water absorption amount (average value) of the water absorbent resin. The water absorption efficiency of the nonwoven fabric was determined from the value W and the actual saturated water absorption amount W using the following equation.

Water absorption efficiency (%) = W / w I asked for it.

As a result, the water absorption efficiency of the nonwoven fabric determined in this way had almost no difference from the water absorption efficiency of fibers.

Example 1 (1) Manufacture of water-absorbing fibers First, as a water-absorbing resin, a polyacrylic acid soda-based resin (trade name: Diawet, manufactured by Mitsubishi Yuka ■, average value of saturated water absorption of pure water + 118.36 g/ g, density 0.5g
/cm3) to an average particle size of 10 μm,
Polyethylene wax manufactured by Mitsui Petrochemical Industries, Ltd. (trade name: Hiwax, density 0.9) was used as the polyethylene wax.
6g/cm3) to prepare a masterbatch.

To create a masterbatch, mix water absorbent resin and polyethylene wax at a volume ratio of 88. 5:11. A mixture of 5:5 (4:1 by weight) was kneaded using a masticating roller heated to 190°C, and when the water-absorbent resin and polyethylene wax were uniformly kneaded, the water-absorbent resin and polyethylene wax were mixed together. Crystalline polypropylene (trade name UBE Polypro R31250, density 0.91 g/
cm3) until the volume ratio finally becomes 64.84:8.44:26.72 (4 = 3 in weight ratio) as shown in Table 1. This was done by adding the polypropylene in small portions.

When the state of dispersion of the water-absorbing resin in the masterbatch thus obtained was confirmed using a scanning electron microscope, it was found to be uniformly dispersed.

Next, the obtained masterbatch and crystalline polypropylene (trade name UBE Polypro R31250, density 0.91
g/cm3) in a weight ratio of 5 as shown in Table 1.
The mixture was mixed at a ratio of 0:50 and the resulting mixture was passed through a nozzle diameter of 0:50. Melt spinning was carried out at a spinning temperature of 220° C. using a single screw extruder equipped with a nozzle having a diameter of 6+ nm and 30 holes to obtain an undrawn yarn with a single fiber denier of 9.4 de (fiber diameter 37.9 μm). After this, the obtained undrawn yarn was heated to 2.5°C at 140°C.
The single yarn denier is 4.2 de (fiber diameter 25
．． A water absorbent fiber consisting of a drawn yarn of 3 urr+) was obtained.

Table 1 shows the composition ratios (volume ratio and weight ratio) of the water absorbent resin, polyethylene wax, and crystalline polypropylene in the water absorbent fibers thus obtained. Also,
The single fiber strength of this water-absorbing fiber before water absorption and the
Single fiber strength after 4 hours immersion (single fiber strength after water absorption)
Also shown in Table-1.

(2) Production of water-absorbent nonwoven fabric First, 15 fibers/
After the fibers were mechanically crimped, the fibers were cut to a fiber length of 51 mm to obtain a plurality of staple fibers.

Next, these multiple staple fibers are defibrated using a card machine to form a web, and the fibers within this web are three-dimensionally entangled using a needle punch machine, resulting in a fabric weight of 45 g/
A water absorbent nonwoven fabric of rrr was obtained.

Table 1 shows the saturated water absorption amount and water absorption efficiency of this water absorbent nonwoven fabric.
Shown below.

Examples 2 to 5 (1) Production of water absorbent fiber A masterbatch was prepared in the same manner as in Example 1 (1),
Example 1 (1
), water absorbent fibers were obtained.

・Example 2 (1) Weight ratio: 25 near 5, stretch ratio: 3.4 times ・Example 3 (1) Weight ratio: 40:60, stretch ratio: 2.8 times・Example 4 (1) Weight ratio...70:30, Stretching ratio...2.0 times ・Example 5(1) Weight ratio...80:20, Stretching ratio...1.8 times Table 1 shows the composition ratios (volume ratio and weight ratio) of the water absorbent resin, polyethylene wax, and crystalline polypropylene in each of the water absorbent fibers thus obtained. Table 1 also shows the single fiber strength before water absorption and the single fiber strength after water absorption of these water absorbent fibers.

(2) Production of water-absorbent nonwoven fabric Each water-absorbent fiber obtained in Examples 2 (1) to 5 (1) was
Staple fibers were prepared in the same manner as in Example 1 (2), and water-absorbing nonwoven fabrics were obtained in each Example in the same manner as in Example 1 (2).

Table 1 shows the saturated water absorption amount and water absorption efficiency of these water absorbent nonwoven fabrics.

Examples 6 to 11 (1) Production of water absorbent fibers Volume ratio of water absorbent resin, polyethylene wax, and crystalline polypropylene was 47.97+12.49:39.54
A masterbatch was prepared in the same manner as in Example 1 (1) except that the weight ratio was 2:1:3, and the weight ratio and stretching ratio of this masterbatch to crystalline polypropylene were as follows. Example 1 (
Water absorbent fibers were obtained in the same manner as in 1).

・Example 6 (1) Weight ratio...40:60, Stretching ratio...3.1 times ・Example 7(1) Weight ratio...50:50, Stretching ratio...2.8 times・Example 8 (1) Weight ratio...60:40, Stretching ratio...2.6 times ・Example 9(1) Weight ratio...80:20, Stretching ratio...2.1 times - Example 10 (1) Weight ratio...90:10, stretching ratio...2. 0x・
Example 11 (1) Weight ratio: 95:5, stretching ratio: 1.9 times Water absorbent resin in each water absorbent fiber thus obtained,
Table 1 shows the composition ratios (volume ratio and weight ratio) of polyethylene wax and crystalline polypropylene. Table 1 also shows the single fiber strength before water absorption and the single fiber strength after water absorption of these water absorbent fibers.

(2) Production of water-absorbent nonwoven fabric Each of the water-absorbent fibers obtained in Examples 6 (1) to 11 (1) was made into staple fibers in the same manner as in Example 1 (2), and the Water absorbent nonwoven fabrics were obtained in the same manner as in Example 1 (2).

Table 1 shows the saturated water absorption amount and water absorption efficiency of these water absorbent nonwoven fabrics.

Examples 6 to 11 (1) Production of water absorbent fibers Volume ratio of water absorbent resin, polyethylene wax, and crystalline polypropylene was 48.30:25.16:26.54
A masterbatch was prepared in the same manner as in Example 1 (1) except that the weight ratio was 1:1:1, and the weight ratio and stretching ratio of this masterbatch to crystalline polypropylene were as follows. Example 1 (
Water absorbent fibers were obtained in the same manner as in 1).

・Example 12 (1) Weight ratio...40:60, Stretching ratio...2.7 times ・Example 13(1) Weight ratio...50:50, Stretching ratio...2.4 times・Example 14 (1) Weight ratio: 60:40, stretching ratio: 2.1 times ・Example 15 (1) Weight ratio: 70:30, stretching ratio: 1.8 times Table 1 shows the composition ratios (volume ratio and weight ratio) of the water absorbent resin, polyethylene wax, and crystalline polypropylene in each of the water absorbent fibers thus obtained. Further, the single fiber strength before water absorption and the single fiber strength after water absorption of these water absorbent fibers are also shown in Table 1.

(2) Production of water-absorbent nonwoven fabric Each of the water-absorbent fibers obtained in Examples 12 (1) to 15 (1) was made into staple fibers in the same manner as in Example 1 (2), and the Water absorbent nonwoven fabrics were obtained in the same manner as in Example 1 (2).

Table 1 shows the saturated water absorption amount and water absorption efficiency of these water absorbent nonwoven fabrics.

For reference, water-absorbent fibers made by chemically treating the surface of synthetic fibers made of acrylic polymers to form hydrogels (product name: Lanseal, manufactured by Nippon Exlan, fiber diameter 2.
Table 1 also shows the single fiber strength before water absorption (5.4 μm), the single fiber strength after water absorption, and the saturated water absorption amount of the water absorbent nonwoven fabric made of this water absorbent fiber.

As is clear from Table 1, no decrease in single fiber strength due to water absorption was observed in the water absorbent fibers obtained in any of the Examples.

In addition, it was confirmed that in the water-absorbing nonwoven fabrics obtained in any of the examples, there was substantially no decrease in mechanical strength due to water absorption.

Furthermore, it was confirmed that both water-absorbent fibers and water-absorbent nonwoven fabrics have low stickiness when water is absorbed, and it was confirmed that water-absorbent nonwoven fabrics can be easily restored to their original shape by drying under reduced pressure. Ta.

[Effects of the Invention] As explained above, according to the present invention, it is possible to provide water-absorbing fibers and water-absorbing nonwoven fabrics that have low tackiness when water is absorbed and have substantially no decrease in mechanical strength due to water absorption. becomes. Moreover, since the water-absorbing nonwoven fabric of the present invention can be reused by drying under reduced pressure, it is possible to save resources and reduce waste by implementing the present invention.

[Brief explanation of drawings]

FIG. 1 is an enlarged view schematically showing the water-absorbing fiber of the present invention, and FIG. 2 is a sectional view taken along the line ■--■ in FIG. 1...Water absorbent resin, 2...Water absorbent fiber. Applicant Ube Nitto Kasei Co., Ltd. Agent Patent Attorney Shizuo Nakamura / Figure 2

Claims (2)

[Claims] (1) A water-absorbing fiber characterized by being made by melt-spinning polypropylene in which particulate water-absorbing resin is uniformly dispersed with polyethylene wax. (2) A water-absorbing nonwoven fabric characterized by mechanically intertwining staple fibers made of the water-absorbing fibers according to claim (1).