JPH0345769A - Highly water absorbing sheet - Google Patents

Abstract

PURPOSE:To obtain the subject then sheet, containing water absorbing fiber having fresh water absorptivity and heat bonding fiber, having a high tenacity and shape stability of the sheet, good in handleability and excellent in water absorption rate and absorptivity and useful as paper diapers, etc. CONSTITUTION:The objective highly water absorbing sheet, composed of 20-80wt.% water absorbing fiber having >=100 times fresh water absorptivity and 80-20wt.% other fibers, containing >=20wt.% (based on the nonwoven fabric) heat bonding fibers as the other fibers in the aforementioned nonwoven fabric, interstices between the water absorbing fiber and/or other fibers being bonded by at least partially softening or melting the heat bonding fibers. Furthermore, the above-mentioned water absorbing fiber is preferably a polycarboxylic acid- based fiber or isobutylene/maleic anhydride copolymer-based fiber having >=200 times fresh water absorptivity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to sheets having high water absorption performance and various products using them.

``Traditional techniques 1 Recently, paper diapers, sanitary napkins, etc. have become widely popular and diversified due to the development of polymeric absorbents.

These polymer absorbents include, for example, polyacrylic acid in which some of the carboxyl groups are alkali metal salts or amine salts, isobutylene/maleic anhydride copolymers, hydrolysates of acrylonitrile polymers, and modified acrylonitrile polymers. Powders such as starch are used. However, these powders cannot be converted into acid form by themselves, nor are they easy to handle, so they are mixed into valves and used as absorbents in paper diapers and the like. For this reason, in applications that require large amounts of water absorption and liquid absorption, from the point of view of providing morphological stability to the absorbent layer,
As the amount of polymeric absorbent increases, the amount of pulp must be increased, making it difficult to make the absorbent layer thinner or more compact.

On the other hand, it has been proposed that the polymeric absorbent be made into fibers and made into sheets such as non-woven fabrics. For example, JP-A-63-28
No. 912 and JP-A No. 63-101457 disclose polyacrylic acid, isobutylene/
A method has been proposed for producing fibers made of a polycarboxylic acid such as dry spinning of an aqueous solution containing a polycarboxylic acid such as maleic anhydride and a polyhydric alcohol as a crosslinking agent, and partially crosslinked by heat treatment. However, these fibers generally have a low fiber strength of less than Ig/d, and it is not only difficult to make sheets such as nonwoven fabrics using these fibers alone, but also the fibers often fall off from the sheet and the sheet itself is damaged. It is not easy to handle because it is not strong enough. Moreover, the strength of the sheet that swells and gels after absorbing water is extremely low, and in some cases cannot maintain its shape, which may make subsequent handling, for example, recovery difficult, depending on the application.

[Problem to be Solved by the Invention 1] The present invention is made of water-absorbing fibers as described above, and has a thin sheet with high strength and shape stability, and has good handling properties.
The purpose of the present invention is to provide a super absorbent sheet with excellent water absorption speed and ability, and a compact water absorbent product using the same.

[Means for Solving the Problems] The present invention has a fresh water absorption capacity of 100 times or more, preferably 2
It is a nonwoven fabric consisting of 20 to 80% by weight of water-absorbing fibers that are 00 times or more and 80 to 20% by weight of other fibers, and the other fibers in the nonwoven fabric include thermally adhesive fibers of 201L or more (relative to the nonwoven fabric). The super absorbent sheet is characterized in that the water absorbent fibers and/or other fibers are bonded to each other by at least partial softening or melting of thermoadhesive fibers.

The present invention also provides paper diapers, sanitary napkins, and
Baby pants, breast milk pads, and other products include incontinence pads.

The water absorbent fibers forming the super absorbent sheet of the present invention have a fresh water absorption capacity of 100 times or more, preferably 200 times the weight of m fibers.
It is a fiber that is more than twice
No. 2, JP-A No. 63-101457, fibers made of polycarboxylic acid in which at least a portion of the carboxyl groups are alkali metal salts or monovalent amine salts are used. can. Note that these fibers have low strength and elongation.

Examples of the polycarboxylic acid include maleic acid, crotonic acid,
7 Maric acid, itaconic acid, acrylic acid, methacrylic acid,
These alkali metal salts or monovalent amine salts, and heptad homopolymers such as maleic anhydride, fumaric anhydride, and itaconic anhydride, or these and ethylene,
Copolymers of propylene, isobutylene, cI~ with alkyl methacrylates, vinyl acetate, methyl vinyl ether, inbutyl vinyl ether, styrene compounds, etc., as well as acrylonitrile, acrylamide, etc., hydrolyzed in the presence of alkali. There is. Among them,
It has a carboxyl group of about 10 meq/g or more, and its 20
Polyhydric alcohols for fibers made of isobutylene/maleic anhydride copolymer and polyacrylic acid in which ~80% is an alkali metal salt or monovalent amine salt include, for example, ethylene glycol, propylene glycol, 1.4
-Butanediol, diethylene glycol, pentaerythritol, glycerol, etc. are used.

Other fibers used in combination with the water-absorbing fibers include various synthetic fibers, recycled fibers, natural fibers, etc., but in the present invention, it is necessary that at least these fibers contain heat-adhesive fibers. Thermal adhesive fibers include polyethylene,
Fibers made of a single polymer with a relatively low melting point such as polyester copolymerized with sodium sulfoisophthalate (hereinafter referred to as SIP modified); bimetallic or core-sheath fibers made of these and other polymers with a high melting point, such as polyethylene terephthalate, boriflohylene, etc. Conventionally known fibers, such as type composite fibers, can be used.

In the super absorbent sheet of the present invention, the amount of water absorbent fibers is 2
It is desirable to contain 0 to 80% by weight, and 20% by weight.
If it is less than 80, the water absorption capacity as a sheet is insufficient.
If it exceeds % by weight, it is difficult to form a sheet easily due to insufficient strength of the fibers, and it is also difficult to obtain sufficient strength and morphological stability of the sheet. In addition, the thermoadhesive fibers bond other fibers including the water absorbent fibers and/or the thermoadhesive fibers by at least partially melting or softening the fibers, thereby ensuring sufficient strength and form stability of the sheet. It is necessary to mix 20% by weight or more (based on the nonwoven fabric) in order to provide the water-absorbent fibers, and in some cases, it is also possible to make all the other fibers mixed with the water-absorbent fibers thermally bondable fibers. If the content of heat-adhesive fibers is less than 20%, adhesion between the fibers will be insufficient, and especially if the strength of the water-absorbing fibers is low, it will be difficult to obtain strong strength and form stability of the sheet. Further, the shape retention of the sheet upon water absorption was not observed.

The methods of mixing these fibers into a sheet include preparing each fiber in a stable, mixing them using a commonly known cotton blending method to make a card or a web in a random unit, or The method is to prepare filament in the form of a filament, form it into a sheet using a spunbond method, perform needle punching if necessary, heat it in a heat calendar or heat furnace, and heat press it. However, some water-absorbing fibers have low strength or do not have sufficient elongation depending on their composition. This can be shaken out onto a support to form a sheet, and then hot pressed.

Alternatively, short fibers of water-absorbing fibers may be dispersed in a secondary air stream in the melt-blowing method to directly form a sheet of mixed fibers of melt-blown fibers and water-absorbing fibers.

By further integrating a so-called facing material made of a thin layer of hydrophobic fibers on the surface of the sheet obtained in this way, it is possible to further enhance the shape stability and the effect of preventing the water-absorbing fibers from falling off. . Further, a moisture-permeable waterproof layer (for example, a microporous film, etc.) can be integrated on at least one surface of the sheet.

[Example 1] Next, embodiments of the present invention will be described using specific examples, but the present invention is not limited to these examples. Note that parts and percentages in the examples are by weight unless otherwise specified.

In addition, the water absorption capacity of fibers is measured as follows.

Take 5 g of fiber and place it in a test basket made of copper wire with a diameter of 0.4 mm, with a diameter of 50 mm, a depth of 80 mm, a distance between wires of 20 mm, and a weight of 3.0 g, and the water temperature is 24 to 26 ° C. from a height of 12mm above the water surface to a depth of 200m with the basket on its side.
It falls silently into the water at a depth of m. After leaving the basket on the bottom of the water for 3 minutes, gently take it out of the water while keeping it on its side.
The sample was left on a wire mesh of a No. 0 sieve for 1 minute, excess water was dripped, and the weight was measured in a beaker, and the water absorption capacity was calculated from the change in weight before and after.

Example 1 Propylene glycol was added as a crosslinking agent to an aqueous polycarboxylate solution in which 50% of the carboxyl groups of an isobutylene/maleic anhydride copolymer (Isopan 10 manufactured by Kuraray Co., Ltd.) was converted into sodium salt with sodium hydroxide. Water-absorbing fiber (51 mm x 10 d, strength 0.5 g/d) that has a water absorption capacity of 295 times in fresh water and 45 times in 0.9% saline obtained by dry spinning and rough heat treatment.60
% by weight and 40% by weight of polyethylene/polyester composite heat-adhesive fiber (51 mm x 3 d) were shaken out onto a mesh support together with air to form a web, which was then heated and pressed for a short time using a calendar roll at 140°C. and make it into a water-absorbing sheet. This sheet has a basis weight of 40g/m.
It has good morphological stability, less water-absorbing fibers come off, and can be cut appropriately and used as a thin liquid-absorbing layer for paper diapers, napkins, etc.

Example 2 Water-absorbing fiber 1 was produced in the same manner as in Example 1 except that 1,4-butanediol was used as a crosslinking agent, and had a water absorption capacity of 280# in fresh water and 43 times as much in 0.9% saline. l(51mm
A web was made by mixing 40% by weight of XIOd1 strength 0.6g/d), 20% by weight of polyethylene terephthalate fiber (50mm x 2d), and 40% by weight of the heat-adhesive fiber used in Example 1, and heated and pressed to obtain a fabric weight of 200g. /
m" water-absorbing sheet. This sheet can be used as an oil-water separation material by rolling it into a roll and putting it into an oil-water mixture and absorbing water. After absorbing water, the sheet can be used as an oil-water separating material. It can be recovered stably afterwards.

[Effect of the invention 1 As stated above; The super absorbent sheet is extremely thin compared to the conventional water absorbing layer made of a mixture of water absorbent resin powder and pulp;
It has strength and form stability as a sheet, and its water absorption capacity is high. In addition, depending on the fiber mixing ratio and product form, heat-adhesive fibers or other fibers exist as reinforcing materials in the gelled sheet even after water absorption, which suppresses fluidity, so it is difficult to recover it. Processing can be performed easily.

Such sheets are used as paper diapers, sanitary napkins, baby (training) pants, breast pads, and incontinence pads in the form of a layered layer between a water-impermeable backsheet and a facing material made of hydrophobic fibers, for example. . In this case, the water absorption layer made of the sheet is thin and has a large absorption capacity, so the product can be made significantly more compact. Moreover, since the sheet is easy to handle and process due to its shape stability and strength, the productivity of the above-mentioned product can be improved.

Claims (10)

[Claims] (1) Water absorbent fiber 2 with fresh water absorption capacity of 100 times or more
It is a nonwoven fabric consisting of 0 to 80% by weight of other fibers and 80 to 20% by weight of other fibers, and contains 20% by weight or more (based on the nonwoven fabric) of heat-adhesive fibers as other fibers, water absorbent fibers and/or A super absorbent sheet characterized in that other fibers are bonded to each other by at least partial softening or melting of heat-adhesive fibers. (2) The super absorbent sheet according to claim 1, wherein the water absorbent fibers are polycarboxylic acid fibers having a fresh water absorption capacity of 200 times or more. (3) The super absorbent sheet according to claim 1 or 2, wherein the water absorbent fiber is an isobutylene/maleic anhydride copolymer fiber having a fresh water absorption capacity of 200 times or more. (4) The superabsorbent sheet according to claim 1, 2 or 3, which has a facing material made of a thin layer of hydrophobic fibers on the surface. (5) Claim 1 having a moisture-permeable waterproof layer on at least one surface
, 2, 3 or 4. (6) A paper diaper comprising the superabsorbent sheet according to claim 1, 2, 3, 4 or 5 as an absorbent layer. (7) A sanitary napkin comprising the superabsorbent sheet according to claim 1, 2, 3, 4 or 5 as an absorbent layer. (8) Baby pants comprising the super absorbent sheet according to claim 1, 2, 3, 4 or 5 as an absorbent layer. (9) A breast milk pad comprising the super absorbent sheet according to claim 1, 2, 3, 4 or 5 as an absorbent layer. (10) An incontinence pad comprising the super absorbent sheet according to claim 1, 2, 3, 4 or 5 as an absorbent layer.