JPS6014147B2 - Super absorbent sheet and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a highly absorbent sheet with excellent liquid absorbing properties, liquid retaining properties, and liquid diffusing properties, regardless of whether it is an aqueous liquid or an oil-based liquid, and a method for manufacturing the same.

Conventionally, absorbent sheets have been widely known as wadding webs or nonwoven fabrics made by depositing or entangling hydrophilic fibers such as pulp, cotton, and rayon. Because it exhibits water absorption by retaining water in the gaps between fibers, for example, when the sheet is compressed, most of the absorbed water is released to the outside of the sheet, resulting in no liquid retention. Since the sheet is so-called spot absorbent, it has no property of dispersing liquid along the surface of the sheet, so if you use it, for example, for omits, the area that comes into contact with your skin will remain sticky and uncomfortable. Ta. On the other hand, there are methods in which polyvinyl alcohol is impregnated into the base material and then coagulated and formalized, similarly, alkaline viscose xanthate solution is coagulated and regenerated with nitric acid, and carboxymethylcellulose and sodium alginate Methods are known in which the material is attached to Motomura as it is or after being gelled, but these methods improve the initial water absorption rate, but cannot improve the liquid dispersion and liquid retention properties. On the other hand, there is a method of attaching or dispersing water-insoluble and water-swellable polymers such as cross-linked polyethylene oxide, hydroxyalkyl methacrylate, etc. to the substrate, but even if water retention is improved, they still provide almost no liquid dispersion. It is. In view of this, the inventors of the present invention have conducted intensive research and found that the present inventors have developed absorbency that quickly absorbs not only water-based liquids but also oil-based liquids, liquid dispersibility that allows the absorbed liquid to immediately spread in a planar direction, and furthermore, They discovered and developed a superabsorbent sheet that satisfies all of the requirements for liquid retention, trapping liquid inside tissues and preventing it from being released outside the sheet, and a method for manufacturing the same.

That is, the present invention provides an aqueous composition obtained by adding a carbonate or a carbonate and a water-insoluble inorganic fine powder to an aqueous solution of a water-soluble monolithic polymer that becomes jelly-like upon infusibility, after impregnating or applying it to a fiber fleece. By applying an acidic treatment liquid such as a dilute acid solution or a mixed aqueous solution of an acid and a polyvalent metal salt to this, the aqueous composition is turned into a jelly, and at the same time, the carbonate in the aqueous composition and the acid in the treatment liquid are combined. This method involves generating fine carbon dioxide gas through a decomposition reaction to foam an aqueous composition in a fleece, and then drying the fleece. It satisfies all of the above characteristics due to the pore-capillary structure formed from the polymer xerogel and water-insoluble inorganic fine powder such as residual carbonate.

Examples of water-soluble polymers used in the present invention that can become jelly-like upon insolubilization (hereinafter referred to as jelly-formed polymers) include sodium alginate, ammonium alginate, carboxymethyl cellulose, and carboxyethyl cellulose soda salts. There are pectins, etc.

For example, in the case of alginates, the aqueous solutions of these gelatinized polymers can be prepared by dilute aqueous solutions of acids such as sulfuric acid and hydrochloric acid, and divalent and trivalent metal salts such as calcium chloride and aluminum nitrate, which are the gelatinized solutions of alginates. In the case of carboxyalkyl cellulose salts, they are made water insoluble by a jelly solution of trivalent metal salts such as aluminum chloride and ferric chloride, resulting in a transparent jelly-like hard material such as agar, which is known as food. It is known that a polymer jelly (hereinafter referred to as a polymer jelly) is formed as an intermediate product (hereinafter referred to as a polymer jelly, and a product obtained by drying this polymer jelly as it is is referred to as a polymer xerogel). This jelly-forming reaction is all an ion-exchange reaction of carboxyl groups in the jelly-formed polymer by the jelly-forming liquid, and as a result, the polymer becomes three-dimensional in an aqueous system, and at the same time, the micro three-dimensional network molecules It is thought that all the water is trapped inside without being dehydrated and becomes solid phase water (jelly). On the other hand, as a method for coagulating other water-soluble polymers that is distinguished from jelly-formed polymers having the above-mentioned properties,
Known methods include the aforementioned coagulation of polyvinyl alcohol with ramie nitrate, acid coagulation of polyvinyl formal, reed nitrate coagulation of alkali viscose xanthate, acid coagulation of hydroxyethylcellulose, and metal salt coagulation of sodium polyacrylate. However, the coagulation of these coagulable polymers is generally a dehydration coagulation mechanism called wet coagulation, and in this case, a transparent polymer aqueous solution becomes cloudy during coagulation. The mechanism is clearly distinguishable because a clear aqueous solution turns into an insoluble jelly without losing its transparency.

The reason why such a jelly-forming polymer is used in the present invention is that, first of all, when a composition containing a carbonate added to a fiber fleece base material is jelly-formed by a treatment liquid, carbonate, water-insoluble malignant substances, etc. The entire aqueous phase containing fine powder, etc. is solidified or jelly-formed, and since there is no outflow of water, carbonates, water-insoluble inorganic fine powder, etc. are completely immobilized in the composition.
Therefore, foaming due to reaction with acid can be performed uniformly and sufficiently.

In this respect, it is an alternative to jelly polymers! When using a coagulable polymer such as polyvinyl alcohol, the dehydration effect at the time of coagulation may cause carbonate, etc. to be pushed out of the composition along with water, and even if carbon dioxide gas is generated, the coagulation of the polymer may occur. The microfoamed structure is destroyed by the shrinkage of the foam, and a sufficient foaming effect cannot be expected.
Second, and this is important, the composition applied to the inter-fiber voids of the base material is not dehydrated and becomes a polymer jelly in the same state as when it was applied, so it continues into the fiber voids. It is fixed to the base material in a filled state. In other words, due to the adhesion properties of this jelly-formed polymer to the substrate, an extremely highly filled airtight sheet can be obtained even with a small amount of adhesion, and this extremely effectively improves the continuous capillary structure that is finally formed. However, in this respect as well, in the case of the conventional coagulable polymer, the dehydration shrinkage effect during coagulation causes it to move and adhere from the interfiber voids to the fiber surface and fiber intersection points, so there is no filling effect at all, and it becomes jelly. The capillary force was significantly inferior to that of polymers, and therefore high absorbency could not be obtained. Furthermore, as a third feature, which is particularly important in the present invention, the polymer jelly having open micropores filled in the interfiber voids of the Motomura fleece as described above can be heated. When the water in the jelly is dried and the water is removed, its volume is drastically reduced, and the remaining carbonate or other water-insoluble inorganic fine powders are interconnected and transformed into a micro-3D network-like porous polymer xerogel. However, since this is mainly attached to the voids of the fiber fleece, it acts synergistically with the constituent fibers to form a macroscopic network. In this case, the presence of water-impure inorganic fine powder such as residual carbonate not only serves as the nucleus for forming this microscopic network, but also softens and smooths the texture of the resulting sheet, or improves its texture. It is also an essential element for the present invention for this purpose. Fig. 1 shows an electron micrograph of the absorbent sheet according to the present invention, and Fig. 2 shows its model. A microporous structure composed of xerogel and residual carbonate or other water-insoluble inorganic fine powder, and also a fleece constituent fiber 2
and polymer xerogel 1 form a capillary structure. In exchange for the porous property, the fiber sheet as a whole has extremely high liquid absorption, liquid retention, and liquid dispersion properties, regardless of whether it is water-based or oil-based, as well as vagrancy absorption and wandering properties. Next, the present invention will be explained step by step.

First, in the application composition, the content of gelatinized polymers such as alginates and carboxyalkyl cellulose salts is usually 1% to 5%.
Used as a % concentration aqueous solution. An acid-foaming carbonate or, if necessary, a hydrophobic inorganic fine powder is added to this and uniformly dispersed and mixed. What should be noted here is that when water-soluble carbonates such as ammonium carbonate and sodium hydrogen carbonate are used as foaming agents, they all become water-soluble salts even after acid foaming, and can be easily extracted from the polymer jelly by washing with water. Therefore, in order to make the water-impossible inorganic fine powder remain in the polymer xerogel, it is essential to add other water-insoluble inorganic fine powders such as titanium oxide, colloidal silica, clay kaolin, etc. On the other hand, when water-insoluble carbonates such as barium carbonate, calcium carbonate, and magnesium carbonate are used, they may become water-soluble or water-insoluble depending on the type of acid used. For example, if calcium carbonate is completely foamed with hydrochloric acid, Calcium reacts and becomes all calcium chloride, which dissolves in water, but when this is foamed with sulfuric acid, it changes to calcium sulfate and produces water-insoluble salts.Therefore, in the case of water-soluble carbonates, the produced salts are completely water-soluble. As mentioned above, other water-insoluble inorganic fine powders are required for the carbonate, but even in this case, if the foaming is not completed and unreacted carbonate is left, the insoluble carbonate will be added to the polymer xerogel. The salt remains and a microporous structure is generated.In other words, what can become the water-insoluble inorganic fine powder in the polymer xerogel, which is essential for the present invention, is the remaining water-insoluble inorganic powder that does not contribute to foaming. These include carbonates, water-insoluble salts resulting from reaction changes of carbonates, water-insoluble inorganic fine powders such as titanium oxide and clay that do not take part in the reaction, or mixtures of these. When blending the above-mentioned fine powder into a jelly-formed polymer aqueous solution, it is necessary to make a decision after fully considering the type of acidic treatment liquid, treatment time, etc., but the amount of these additions is based on 10 parts by weight of the jelly-formed polymer aqueous solution. 2 parts to 5 parts, particularly 5 parts to 2 parts dark, is preferred.

In addition, a small amount of an aqueous binder such as adhesive polymer latex or emulsion, a dispersant, a coloring agent, a softening agent, etc. may be mixed as long as foaming by the carbonate is not inhibited. The applied composition prepared in this way may be applied as it is or made into a foam, and then uniformly impregnated into a fiber fleece base material by a known method such as a roll impregnation method, a knife coating method, or a roll printing method, or applied only to the surface of the base material. or printed in a fixed pattern.

The fiber fleeces used here include the Fairley method,
There are waddings and fiber webs obtained by the carding method, dry papermaking method, etc., so-called dry nonwoven fabrics obtained by bonding or bonding these, long fiber nonwoven fabrics obtained by the spunpond method, wet nonwoven fabrics produced by wet papermaking, etc. The constituent fibers of the base material include not only hydrophilic fibers such as ゞnoref〇, cotton, wool, rayon, and vinylon, but also polyamide, polyester,
Hydrophobic fibers such as polypropylene and polyacrylonitrile may be used, or mixtures thereof or composites in which these are laminated may be used. Next, the fiber fleece to which the aqueous composition has been applied is treated with a dilute aqueous acid solution such as hydrochloric acid or nitric acid, but as mentioned above, in the case of an alginate aqueous solution, it is turned into a jelly by the acid, so it is treated as an acid treatment solution. Although it is sufficient to use only the above acid aqueous solution, in the case of carboxyalkylcellulose salt, since it is not jelly-formed by acid, it is recommended to simultaneously perform jelly-formation and foaming by using a mixed aqueous solution in which a polyvalent metal salt is added to acid. preferable.

The acidic treatment solution is usually an aqueous solution with a concentration of 0.5% to 10%, and this is applied to the fleece applied by means such as dipping or spraying. As a result, the applied composition is immediately jelly-formed and, at the same time, extremely fine foamy carbon dioxide gas is generated, causing foaming. Coarsening is controlled, resulting in extremely uniform micropores. The diameter of the micropores is about one to several dozen pores. Next, remove the excess acidic treatment solution and wash thoroughly with water. Finally, the treated sheet is heated and dried to form a three-dimensional network of polymeric xerogel having the above-mentioned pores in the fiber sheet. Furthermore, by pressing this sheet with a fine embossed pattern, the texture of the sheet can be made even softer. In addition, when this absorbent sheet is used particularly in areas that come in direct contact with the skin, it is preferable to apply the polymeric xerogel to only one side of the fiber fleece, or to use a fiber fleece with no binder or with relatively little entanglement. By adhering polymeric xerogel to the inside of the fleece and further raising the surface fibers of the fleece, an absorbent sheet with good texture can be obtained. As described below, the nonwoven fiber sheet obtained by the present invention has liquid absorbing properties, liquid diffusing properties, liquid retaining properties, and moisture absorption/desorption properties, so that it can be used as a material for clothing, household use, etc. Industrial wiping, towels and other wiping cloths, disposable sheets, pillowcases, diapers, medical and sanitary diapers, diaper liners, napkins, absorbent pads, sheets, and drain materials for civil engineering. Can be applied to a wide range of applications such as curing sheets.

The present invention will be explained in more detail with reference to Examples below.

Example 1 Weight 45 polyester bonded with acrylic binder
Then, an aqueous composition having the following formulation was uniformly soaked into a nylon nonwoven fabric having an original size of 0.6 ribs so that the amount of solid content attached was 10%.

{Hajita Kishi Hirara Hair Aishinjo Aqueous Solution 19 Windows This was soaked in a 2% aqueous solution of hydrochloric acid for about 2 minutes to simultaneously form a jelly and foam the composition, and then washed with water and dried.

In the thus obtained sheet, alginate xerogel containing residual calcium carbonate was fixed in the form of a micro network. The water absorbency of this sheet is shown in Table 1.
Further, the liquid diffusivity is shown in Table 2. Measurement of water absorption is based on JIS/
It was carried out according to the Jirek method, and the tip of the sample in a 20c x 25 willow was submerged from the water surface for 5 willows, and the height of the rise of the absorbed water (willow) was measured after 2 minutes and after 1 powder. . In addition, liquid diffusivity was measured using 0.1 cc from the top of a sample of 10 skin x 10 cm.
After 2 minutes and 1 minute after dropping the water and machine oil, the area (ground) of the area where the water and machine oil were spread was measured. Here, in order to compare with the product of the present invention, the original untreated nonwoven fabric to which the above-mentioned composition was not applied was used as Comparative Product 1, and the nonwoven fabric to which the above-mentioned composition was applied was dried as it was without jelly foaming. These are listed as Comparative Product 2 in the table. Table 1: Water Absorbency Table 2: Liquid Diffusivity Although the shape was amorphous, the product of the present invention rapidly spread into a substantially circular shape centered at the point where the liquid was dropped, proving the uniformity of the treated sheet.

Furthermore, when the part of the sample where water and machine oil were absorbed was pressed by hand, most of the liquid was released to the outside for both comparison products, but for the product of the present invention, almost no water or oil was released. The liquid was trapped within the sheet structure, and the surface of the liquid-absorbing portion did not feel sticky and had excellent liquid retention. As described above, the sheet obtained in this example satisfied all of the properties of liquid absorption, liquid retention, and liquid dispersion, regardless of whether it was oil-based or water-based. Example 2 The nonwoven fabric base material used in Example 1 was uniformly impregnated with an aqueous composition having the following formulation.

After treating with a liquid to simultaneously form a jelly and foam the applied composition, the sample was washed with water and dried.

As a result of testing the obtained sheet, it showed almost the same tendency as in Example 1. Example 3 Mainly made of polyprofiber, weighing 120 ta' and having a thickness of 1.
A composition having the following formulation was applied to only one side of the needle-bonded nonwoven fabric.

After spraying this with a 2% mixed aqueous solution of hydrochloric acid and calcium chloride to sufficiently jelly-form and foam the coating composition,
Washed with water and dried.

To test the absorbency of the obtained sheet, colored water was dropped little by little from the side to which alginic acid was not applied, and the process of it penetrating into the back surface was observed. As a result, it was observed that water was quickly absorbed by the back side of the coated side at the same time as it was dropped, and the absorbed water quickly diffused in an approximately circular shape only through the back xerogel adhesion layer without appearing on the surface layer again. . Furthermore, even if you press the xerogel adhesion layer that has absorbed water by hand, there is almost no water flowing out, so even the absorbent layer does not feel sticky.
Furthermore, since there was no reverse osmosis to the surface, the surface side always remained dry. Almost the same good results were obtained for oil-based liquids. In this manner, a sheet having so-called one-point absorbency was obtained, which is suitable as a medical and sanitary textile material for, for example, omits, omulliners, sanitary napkins, surgical pads, bed sheets, and the like. Example 4 The nonwoven fabric used in Example 3 was uniformly impregnated with an aqueous composition having the following formulation.

This aqueous composition contains finely divided titanium powder which does not participate in foaming. Next, this was mixed with aluminum nitrate.
After being treated with a 3% mixed aqueous solution of nitric acid to simultaneously form a jelly and foam the applied composition, it was washed with water and dried. Finally, both surfaces of this sheet were buffed with sandpaper to form a raised layer. The obtained sheet has excellent liquid absorption properties, and the surface does not become sticky even after absorbing liquid.
It was extremely soft to the touch. Example 5 Print bonding was applied to both sides of a 60-th thick rayon fiber web bonded with polyvinyl alcohol fibers in the form of a lattice pattern using an aqueous composition having the following composition.

This aqueous composition includes a binder. Next, the coated and printed Motomura was sprayed with a 3% aqueous sulfuric acid solution to complete the jelly foaming of the print composition, followed by washing with water and drying.

Since the obtained sheet has excellent absorbency regardless of whether it is water-based or oil-based, it is particularly suitable as a household or industrial wiping material with good wiping properties.

[Brief explanation of the drawing]

Figure 1 is an electron micrograph of the product of the present invention, at a magnification of about 20 degrees. Figure 2 is a reproduction of Figure 1. 1 is polymer xerogel,
2 is the constituent fiber of fleece. ※　Kagaminofuji

Claims (1)

[Scope of Claims] 1. A superabsorbent sheet comprising a water-insoluble polymeric xerogel finely foamed by an acid decomposition reaction of carbonate and fixed to a fiber fleece in a form that includes water-insoluble inorganic fine powder. 2. The superabsorbent sheet according to claim 1, wherein the polymeric xerogel is adhered to only one side of the fiber fleece. 3. The superabsorbent sheet according to claim 1 or 2, wherein at least one surface is raised. 4. The superabsorbent sheet according to any one of claims 1 to 3, wherein the polymer xerogel is alginic acid, a polyvalent metal salt of alginic acid, or a mixed acid and polyvalent metal alginate. 5. The superabsorbent sheet according to any one of claims 1 to 3, wherein the polymer xerogel is a carboxyalkylcellulose polyvalent metal salt. 6. An aqueous composition obtained by adding a carbonate or a carbonate and a water-insoluble inorganic fine powder to an aqueous solution of a water-soluble polymer that becomes jelly-like upon insolubilization is applied to the fiber fleece, and then the water-soluble polymer is added to the fiber fleece. The aqueous composition is simultaneously foamed and jelly-formed by jelly-forming the aqueous solution of the polymer and applying an acidic treatment solution that reacts with the carbonate to generate carbon dioxide gas, followed by washing and drying the aqueous composition. A method for producing a superabsorbent sheet, characterized by: 7. The method for producing a superabsorbent sheet according to claim 6, wherein the water-soluble polymer is an alginate and the acidic treatment liquid is an aqueous acid solution. 8. The method for producing a superabsorbent sheet according to claim 6, wherein the water-soluble polymer is carboxyalkyl cellulose, and the acidic treatment liquid is a mixed aqueous solution of an acid and a polyvalent metal salt.