ABSORBENT MATERIAL

Disclosed is an absorbent material which is used as ink pads of ink-jet and bubble-jet printers, various building materials and materials for civil engineering work, said absorbent material comprising a non-woven fabric containing water-absorptive fibers, wherein a water absorption percentage is not less than 400% by weight and a change in volume is less than 10% in a state where water is absorbed in the amount of not less than 400% by weight.

EXAMPLE 1 5% by weight of highly water-absorptive fibers (OASIS manufactured by Technical Absorbent Co.) having a fineness of 9 denier and a fiber length of 51 mm and 85% by weight of flame-retardant modacrylic fibers (LUFNEN BR manufactured by Kanebo Ltd.) having a fineness of 3 denier and a fiber length of 51 mm were mixed, and then carding, cross-laid and needle punching were performed in a conventional production process of felt to obtain a felt having a thickness of 15 mm, a weight of 2500 g/m 2 and a density of 0.17 g/cm 3 as an absorbent material of the present invention. In the preliminary stage of the production of the felt, 2% by weight of an anionic hydrophilic oily agent was added to the above flame-retardant modacrylic fibers and fiber blending was performed, thereby to improve the water absorption rate of the resulting absorbent material. The resulting felt was cut into pieces having a width of 3 cm and a length of 10 cm to produce a test material. Using this test material, the water absorption percentage and water absorption rate were measured by the method described above. As a result, the water absorption percentage was 490% by weight and the water absorption rate was 3.9 seconds. Furthermore, the thickness of the test material was 16 mm in a state where water was absorbed in the amount of 490% by weight. After water absorption, only the thickness changed without changing the area, and the volume changed by &plus;6.7%. Then, the water retention percentage of the test material was measured by the method described above in a state where the test material absorbed water in the amount of 490% by weight. As a result, it was confirmed that the water retention percentage after dropping is 470% by weight and the water retention is 96%, that is, the water retention properties are excellent. Even after this dropping test, no fibers were removed from the cut surface of the felt. Furthermore, this felt was put in a desiccator containing water at the bottom and allowed to stand in a temperature controlled bath at 30 at 100% RH. Then, the weight after 72 hours was measured. The moisture absorption percentage was calculated from a difference between the measured weight and absolute dry weight. As a result, high moisture absorption percentage such as 25% was shown. 
 EXAMPLE 2 Absorbent materials No. 1 to 6 were produced in the same manner as in Example 1 except that a mixing ratio of the highly water-absorptive fibers (A) to the flame-retardant modacrylic fibers (B) used in Example 1 is set as shown in Table 1. With respect to the respective absorbent materials, the water absorption percentage, the change in volume (change in thickness, area does not change) before and after water absorption, the water retention percentage, and the water absorption rate were measured. The results are shown in Table 1. All of the above absorbent materials No. 1 to 6 passed VO in accordance with UL Standards. 1 TABLE 1 No. A (%) B (%) Water Change in Water retention Water 1 2 98 410 9 91 6.1 2 4 96 480 4 95 3.3 3 9 91 620 7 98 4.2 4 14 86 850 9 96 6.5 5 1 99 230 3 73 7.1 6 21 79 1030 16 90 10.5 As is apparent from these results, the absorbent materials No. 1 to 4 show high water absorption percentage and high water retention percentage, small change in volume (change in thickness) before and after water absorption, and small water absorption rate(second). To the contrary, the absorbent material No. 5 was insufficient in water absorption percentage because the amount of the highly water-absorptive fibers used is small such as 1% by weight. Furthermore, since the absorbent material No. 6 contains a large amount of the highly water-absorptive fibers, the water absorption percentage was sufficient. However, the change in volume (change in thickness) was large and the water absorption rate(second) was large. As described above, when the absorbent material of the present invention is composed of a felt comprising the highly water-absorptive fibers and flame-retardant modacrylic fibers of the above Examples, the content of the highly water-absorptive fibers is preferably adjusted within a range from 2 to 20% by weight, and more preferably from 3 to 10% by weight, based on the total weight. The felt thus obtained described above was cut into various complicated shapes. As a result, it could be easily cut into any shape without causing a problem. That is, it was confirmed that this felt has excellent cutting processability. Furthermore, a change in water absorption change on repeated water absorption was examined by using the above absorbent material No. 3. As a result, the water absorption percentage was 600% by weight in the fifth water absorption, 540% by weight in the tenth water absorption, and 530% by weight in the twentieth water absorption, respectively, and the water absorption was reduced to only 500% by weight even in the fiftieth water absorption. That is, it was confirmed that the water absorption percentage is not largely reduced even if water absorption is repeated. 
 EXAMPLE 3 An absorbent material was produced in the same manner as in Example 1 except that highly water-absorptive fibers (fineness: 5 denier, fiber length: 51 mm) obtained by hydrolyzing the surface layer portion of acrylic fibers were used in place of the highly water-absorptive fibers used in Example 1 and that polyester fibers (Regular/full dull, fineness: 3 denier, fiber length: 76 mm) were used in place of the flame-retardant modacrylic fibers. As this absorbent material, two kinds of an absorbent material wherein 20% by weight of the above highly water-absorptive fibers and 80% by weight of the above polyester fibers are mixed (No. 7) and an absorbent material wherein 30% by weight of the above highly water-absorptive fibers and 70% by weight of the above polyester fibers are mixed (No. 8) were produced. With respect to two kinds of these absorbent materials, the water absorption percentage, the change in volume (change in thickness) before and after water absorption, the water retention percentage, and the water absorption rate were measured in the same manner as in the above Examples. The results are shown in Table 2. 2 TABLE 2 No. Water Change in Water retention Water 7 720 9 68 6.1 8 880 4 75 4.8 It was confirmed that the absorbent materials of this Example are inferior in water retention percentage to those of Examples 1 and 2, but show high water absorption percentage and small change in volume (change in thickness). Industrial Applicability As described above, the absorbent material of the present invention shows high water absorption percentage and high water retention percentage as well as small change in volume on water absorption, and is superior in cutting processability. Therefore, the absorbent material of the present invention can be widely as an absorbent material required to have excellent water absorption properties, water retention properties, form stability and easily processing in various fields.