JPH01280075A - Absorbent - Google Patents

Abstract

PURPOSE:To provide a soft absorbent having a fast ulcer-absorbing performance by molding one part of a resin in grooves formed on the surface of a fiber substrate to form fine fibrous resin moldings when an acrylic acid monomer for highly absorbable resins is coated on the fiber web and subsequently polymerized. CONSTITUTION:An aqueous solution of an acrylic acid monomer for highly absorbable resin, e.g., acrylic acid or a mixture of the acrylic acid and methacrylic acid, especially a treating solution prepared by mixing the solution of a monomer having carboxylic acid groups neutralized with an alkali metal, etc., in a neutralization degree of 20-90% based on the total carboxyl groups with a crosslinkable monomer having two or more double bonds copolymerizable with monomer in the molecule, is coated on a fiber web preferably comprising polyester fibers having modified cross-sections and subsequently polymerized. The treated web is irradiated with electron beams and/or UV light to polymerize remaining monomers. Since one part of the resin forms fine fibrous resin molding while using grooves thus produced on the surface of the modified cross- section fiber substrate as molds, the absorbent has a high ulcer-absorbing rate and is soft, thereby being suitable as a disposable diaper.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an absorbent material suitable for disposable diapers containing a superabsorbent resin. This article relates to a thin and compact bag-shaped absorbent material that provides performance and can absorb large amounts of urine in a short period of time.

"Prior Art" Recently, with the spread of superabsorbent resins, the market for so-called disposable sanitary materials such as disposable diapers has rapidly expanded.

Disposable diapers typically consist of a water permeable top sheet that contacts the skin of a user such as an infant, an intermediate liquid absorbing and retaining layer, and an outer water impermeable packing sheet. Conventionally, the liquid absorption and retention layer has been made of an absorbent material made by mixing or layering crushed wood pulp fibers and particulate superabsorbent resin. Because it is inferior, use super absorbent resin instead! &
An absorbent material fixed to a cloth base material has been proposed (Japanese Unexamined Patent Publication No. 5
9-1351149, etc.).

"Problem to be Solved by the Invention" By the way, the conventional absorbent material is formed by applying a large amount of a superabsorbent resin monomer solution to a fiber web, and then polymerizing it. Due to its low viscosity, the monomer solution cannot be supported by the fiber base material alone, so it slides down along the fiber axis and is trapped by the fiber base material at the intertwining point between the fibers and the fibers or at the point where the fibers are close to each other. to form large droplets. Therefore, in the polymerization method in which polymerization is initiated by spraying a polymerization initiator onto the surface of a monomer solution droplet, the polymerization reaction does not proceed uniformly to the center of the droplet inner layer, resulting in a resin with low absorption performance. There was a big drawback. Furthermore, the resin thus formed is
■ Specific surface area is small and urine absorption rate is slow; ■ When it comes in contact with urine, a gel is formed on the resin surface layer, and this gel makes it difficult for urine to penetrate inside (gel block); ■ A fiber base material that supports the resin or / If the swelling of the resin is hindered by the surrounding resin, it may stop absorbing urine, or the texture may become hard, resulting in poor adhesion to the skin of users such as infants. there were.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide an absorbent material that is soft and has good absorption performance by composing at least a part of a superabsorbent resin with a fine fibrous resin. It is.

"Means for Solving the Problems" The absorbent material according to the present invention is an absorbent material obtained by applying an acrylic acid-based superabsorbent resin monomer solution to a fiber web and polymerizing the same. It is characterized in that at least a portion of the superabsorbent resin that adheres to the fiber base material is composed of a fibrous resin that is formed using a groove provided on the surface of the fiber base material as a template.

Hereinafter, the present invention will be explained in detail using figures. FIG. 1 is a diagram for explaining an example of manufacturing the absorbent material of the present invention. The fiber web 1 is coated with a monomer solution 3 containing one of the redox type polymerization initiators and a crosslinking monomer by a nip type coating roll 2,
Subsequently the other initiator solution 4 is sprayed and then 60-
It is led to a polymerization tank 5 maintained at 100°C. The polymerization initiator added to the monomer solution 3 contacts the other sprayed initiator 4 to initiate a radical polymerization reaction. Polymerization starts from the beginning and the reaction ends in a few seconds. The superabsorbent resin 6 obtained in this way has a water content of approximately 10 to 30%.
Since it is a water-containing polymer containing a large amount of unreacted residual acid monomer, it is then irradiated with electron beam 7 and/or ultraviolet ray 8 to complete the polymerization. In electron beam and ultraviolet irradiation, if the moisture content is adjusted to 25 to 35% in advance, unreacted residual acid monomer can be efficiently reduced. In the middle, water is sprayed using a suitable means such as a rotating brush 9 to control the humidity. In addition, in Figure 1, the code 1
0 is a heater, and 11 is a blower.

Thereafter, as shown in FIG. 2, a solution of a crosslinking agent having 2 g or more of a functional group capable of reacting with a carboxylic acid group in its molecule is sprayed onto the hydrous polymer using a suitable means such as a rotating brush 12, and a heating device is applied. 13 to form crosslinks on the resin surface at 100 to 200°C to improve absorption performance.

FIG. 3 is a schematic diagram showing the adhesion state of superabsorbent resin in a conventional absorbent material, in which reference numeral 14 indicates a fiber base material and 15 indicates a resin portion. FIG. 4 explains the state of adhesion of the superabsorbent resin in the absorbent material of the present invention. In the figure, reference numeral 15 indicates the resin part attached in the same manner as before, and 16 indicates the resin part in the form of fine fibers of the present invention. The resin part to be attached is shown. Furthermore, since FIG. 5 is for explaining the fibrous resin of the present invention in more detail, in the figure, reference numeral 17a indicates a groove disposed on the surface of the fiber 17 along the fiber axis, and I8 indicates a groove formed into a mold. This shows the resin formed.

As shown in Figures 4 and 5 above, the monomer solution applied to the fiber web rapidly spreads through the grooves provided on the surface of the fiber base material by capillary action, polymerizes in the grooves, and forms a fibrous material. of resin is formed.

Figures 6(a), (b), (c), and (d) show surface diagrams of a fiber base material 19 having grooves 19a continuous along the fiber axis on the fiber surface, other than those shown in Figure 5. Give an example.

The fine fibrous resin 20 formed on the Tl4t7a or 19a hardens or shrinks when dried, and as shown in FIG.
Is it possible to separate from Ml9a (17a)?
Is there anything that can hinder the action of the present invention? In this way, the absorbent material of the present invention is composed of two types: the conventional relatively large-sized superabsorbent resin and the fine fibrous superabsorbent resin formed on the surface of fibers with irregular cross sections. Since the latter fine fibrous resin has an extremely large specific surface area, it has the effect of compensating for the disadvantage of superabsorbent resins, which have a slow absorption rate, and significantly improving the initial absorption rate. Furthermore, if a portion of the superabsorbent resin is converted into such fine fibers, urine can penetrate deep into the resin, thereby increasing its absorption capacity. Moreover, the above structure further improves the flexibility of the absorbent material, thereby improving the feeling of wearing the sanitary material.

The fine fibrous superabsorbent resin according to the present invention preferably has a fineness of 500 deniers or less and a composition ratio of 5% by weight or more based on the total amount of resin. If the absorbent material of the present invention does not satisfy these values, it will be difficult to obtain excellent effects such as improved initial absorption rate, increased absorption capacity, and softening.

Here, the fineness of the fine fibrous superabsorbent resin is determined by the following formula from the cross-sectional area A (cm'') of the resin obtained from a microscopic photograph and the specific gravity P (g/cm3) of the resin.

Fineness (denier) - AX9000XP The specific gravity P (g/co+3) of the superabsorbent resin in the absorbent material of the present invention determined in this way is approximately 1.2, although it depends on the water content.

The fibers with irregular cross sections used in the present invention as described above can be obtained by melt-spinning a thermoplastic polymer by devising spinneret holes.
can be obtained easily. For example, by using the spinneret hole 2I shown in FIG. 8, a fiber 22 having an irregular cross section shown in FIG. 9 can be obtained.

The fibers 17 and 19 having irregular cross sections shown above are examples of the deaf-like shape of the present invention, and are not limited thereto.

Furthermore, the fibers with such irregular cross-sections are not limited to the base fibers that form the main body of the fibrous web, but may also be applied to the binder fibers that also serve as a heat-sealing agent.

The irregular cross-section fibers that make up the base fibers and/or binder fibers do not necessarily have to be of the same type.
It may be composed of two or more types of fibers with irregular cross sections. The size of the grooves provided on the fiber surface may also be different between the fibers, and furthermore, the grooves provided on the surface of each fiber may be provided with grooves of different sizes and shapes. The size of the grooves of the irregular cross-section fibers may be such that the fineness force of the fine fibrous superabsorbent resin formed by polymerization therein does not exceed 100 denier. For example, in the groove 19a shown in FIGS. 1θ (a) and (b), the radius of curvature R is 2 to 200×10
ms, and the cross-sectional area A (shaded area) of groove +9a is 2 to I O
If it is selected within the range of ``O00X I O-@mts'', it is possible to easily obtain a fine fibrous resin of 100 deniers or less.The cross-sectional area A (shaded area) of the groove 19a is
A tangent line is drawn between adjacent convex portions, and the area defined by this tangent line and 1119a is referred to as the area.

Further, there is no particular restriction on the shape of the grooves in the fiber base material used in the present invention. A shape in which the resin is embedded as shown in Figure 1+ (a), a shape in which the resin is held to a certain extent to prevent it from falling off as shown in Figure 11 (b), or a shape in which the resin is prevented from falling off as shown in Figure 11 (C). As shown, any shape that allows the resin to adhere, but allows the resin to easily fall out of the grooves due to the bending of the fibers, may be used.

In addition, in the figure, the code|symbol 23 shows a fiber base material, and 24 shows a super absorbent resin.

In the present invention, the composition ratio of the irregular cross-section fibers in the total fiber base material is preferably at least 25% by weight of the total fiber base material, although it depends on the number and size of the grooves that the irregular cross-section fibers have. . If the amount is less than 25% by weight, the fine fibrous resin base formed by the irregular cross-section fibers will be insufficient, and the absorption capacity and absorption rate of the absorbent material will not be sufficiently improved, and the softening of the absorbent material will be insufficient.

Furthermore, in the present invention, when the fiber surface is made hydrophilic, the monomer solution easily adheres to the fiber base material and spreads over the fiber base material, so that the monomer solution can be applied efficiently. In addition, when the surface of the fiber base material is made wet, it becomes possible to quickly wet and spread urine within the absorbent material and retain a large amount of urine within the absorbent material.

In particular, in the present invention, the monomer solution applied to the fiber web is easily guided into the grooves provided on the fiber surface by making the fiber surface hydrophilic, and quickly moves through the grooves by the action of capillarity. It is particularly preferred because it spreads. Such hydrophilization of the fiber surface can be easily achieved by applying a known surfactant having a large wetting effect to the fiber surface.

Examples include:

(a) Nonionic surfactants such as polyoxine ethylene alkyl ether, polyoxyethylene alkyl phenol ether, polyoxine ethylene sorbitan resin acid ester, polyoxine ethylene alkyl resin ester, polyoxyethylene oxypropylene block polymer, etc. (b) R' Anionic surfactants such as tt fatty acid salts, alkylnaphthalene sulfonates, dialkyl succinates, alkyl sulfate salts, higher alcohol sulfate salts, etc. (C) Cations such as alkylamine salts, alkyl quaternary ammonium salts, etc. Among the surfactants listed above, it is desirable to use one or more surfactants selected from the group of nonionic surfactants and/or the group of anionic surfactants.

When the absorbent material of the present invention is used in disposable diapers, it is necessary to repeatedly transport and diffuse urine, so durable hydrophilicity is desirable. As such a hydrophilic treatment agent, it is preferable to use a parent wood group-containing oligomer. For polyester fibers, parent wood group-containing polyester oligomers are applied. In this case, the molecular weight of a part of the oligomer is 300 to 6, considering the bonding with the polyester fiber polymer substrate and the dispersibility in the hydrophilic treatment liquid.
Preferably, it is in the range of 000. A portion of the oligomer is preferably made into a copolymer containing, for example, terephthalic acid and isophthalic acid as the nocarboxylic acid component so as to melt and eutecticize at a relatively low temperature.

As the hydrophilic group, hydratable polyoxyalkylene groups: acidic groups consisting of sulfonic acid, phosphonic acid, carboxylic acid, etc., or ionizable salts thereof; nitrogenous basic salts, or ionizable salts thereof, etc. can be used. Of these, those based on polyoxyalkylene groups are the best. Since hydrophilic group-containing oligomers having water resistance generally have a slightly poor wetting effect, a preferable hydrophilic effect can be obtained if necessary in combination with the above-mentioned known surfactant having a large wetting effect. The amount of these hydrophilic treatment agents attached to the fiber is 0.05~
It is sufficient if it is within the range of 2.0% heavy crushing.

The liquid diffusivity of irregular cross-section fibers with grooves arranged along the fiber axis on the fiber surface, that is, the effect of capillarity within the grooves, is determined by the effect of the capillary phenomenon in the grooves, which is obtained by using a square of 15 ca+ on each side (the directions of the sides correspond to the machine direction and the width direction, respectively). The test piece 25 cut into
As shown in Figure 2, the thickness is 61 m and the density is 0.020.
Adjust the number of stacked test pieces 25 so that the thickness is ~0.025 g/cm3, sandwich them between methyl methacrylate resin plates 26, and then leave them horizontally. A hole 27 with a diameter of 3I is drilled in the center of the upper resin plate. A colored test solution (physiological saline; 0.9% by weight Nac4) ice was dropped onto the test piece 25, and the state of wetting and spreading after 8 hours was observed. When measured in this way, the fibrous web in the present invention is
It is desirable that the area of wetting and spreading is 10C or more.

In addition, the reference numeral 28 in the figure indicates the part wetted with the colored test liquid;
9 indicates a spacer for adjusting the gap between the resin plates.

The fiber web used in the present invention has a basis weight of 10 to 100 g/
Preferably it is m'. If it is less than 10 g/m", it is difficult to attach the amount of superabsorbent resin required as an absorbent material for disposable diapers. If it exceeds 100 g/m", it is economically disadvantageous.

The bulkiness of the fibrous web used in the present invention is defined as the fibrous web volume cc per 1 g of fibrous base material, that is, the specific volume (cc/g) of 0.
．． 8 to 2.4 x l O' (cc/g) is preferred. This is because if the monomer solution is less than 0.8 X I O"cc/g, the monomer solution will form a film and adhere to the fiber substrate, and if it exceeds 2.4 X I O"cc/g, the resulting absorption This is because the thickness of the material becomes too large, making it difficult to handle in subsequent processes.

The fibrous web used for the skeleton of the absorbent material of the present invention has excellent bulkiness, compression recovery, and compression elasticity in order to recover the bulk after applying the monomer solution and to prevent urine from getting wet back from the wet absorbent material. required. Therefore, in the absorbent material of the present invention, a bulky, highly elastic base fiber is the main component, and a carded web is formed by dispersing and mixing binder fibers made of heat-sealable composite spun fibers that are melt-bonded at a relatively low temperature. Then, a fibrous web is used, which is then heat-treated in a dry state to form a so-called dry nonwoven fabric. The reason why a dry nonwoven fabric method is adopted is that this method does not impair the excellent bulk and high elasticity of the fiber base material, and it is hygienic because no chemicals are used as a binder.

Here, the base fiber preferably has a thermoplastic synthetic fiber having a fineness of 2 to 20 deniers and a fiber length of 32 to 128 IIm as a main component. Specifically, polyester,
One or more thermoplastic synthetic fibers may be selected from among polyamide, polypropylene fibers, etc., and polyester fibers are particularly preferred since they provide large voids and high compressive elasticity to the fiber web.

It is of course possible to blend water-soluble fibers such as Cotton #a or rayon fibers into the base fibers for the purpose of improving the performance of the fibrous web. By blending these hydrophilic fibers, it is possible to increase the amount of monomer applied to the fiber web, or it is preferable to suppress the amount to 30% by weight or less based on the total fiber base material. These fibers have low bulk and compressive elasticity when wet, so if the amount is too large, the recovery of the bulk of the fiber web after applying the monomer solution will be reduced, and the prevention of urine wet back from the wet absorbent material will be less effective. Because it will disappear. The bulkiness and high elasticity required for the base fiber can be easily obtained by providing a hollow section in the cross section of the fiber and adjusting the number of crimps in the range of 5 to 25 crimps/inch.

The binder fibers used together with the base fibers to form the fibrous web cannot stabilize the form of the fibrous web if the entire fibers are fused and cut by heat treatment. It is preferable to use composite spun fibers that combine polymer components that do not.

Heat-fused composite spun fibers may be core-sheath type, side-by-side type, or other types, and the softening point of the polymer component with a lower melt softening point is lower than the softening point of other polymer components. There is no particular restriction as long as the temperature is at least 30°C or lower. Examples of such thermoplastic polymer combinations include:
For example, many combinations are possible, such as low melting point polyester polymer and polyethylene terephthalate, polyethylene and polyethylene terephthalate, polyethylene and polyamide, polyethylene and polypropylene, polypropylene and polyethylene terephthalate, polypropylene and polyamide, but are of course limited to these. Not yours. Furthermore, the binder fibers may be composed of two or more types of fibers selected from among these combinations. For example, combinations of composite spun fibers made of a low melting point polyester polymer and polyethylene terephthalate and composite spun fibers made of polyethylene and polyethylene terephthalate can be mentioned.

When using polyester fibers as the base fiber, use composite spun fibers made of a low-melting point polyester polymer and polyethylene terephthalate.The polyester polymers become compatible with each other through heat treatment, resulting in a bulky fiber web with good shape stability. You can get it.

Such a low melting point polyester polymer has good fiber forming properties and melts and softens at 80 to 180°C.
There are no particular restrictions. That is, dicarboxylic acid components such as terephthalic acid, isophthalic acid, phthalic acid, P-hydroxybenzoic acid, 5-sodium sulfoisophthalic acid, naphthalene dicarboxylic acid, oxalic acid, adipic acid, sebacic acid, and cyclohexanedicarboxylic acid, and ethylene glycol and diethylene glycol. , triethylene glycol, propanediol, butanediol, bentanediol, hexanediol, neopentyl glycol, polyethylene glycol, and other diol components that satisfy the above-mentioned melt softening point can be used.

In terms of ease of fiber production and fiber properties, it is preferable to use a copolymer of terephthalic acid, isophthalic acid and ethylene glycol as the low melting point polyester polymer.

The ratio of the low melting point polymer component disposed in the IV spun yarn fiber sheath to the polymer disposed in the core may be from 10:90 to 90:10. If it is less than 10290, it will be difficult to perform core-sheath type summer joint spinning, and if it exceeds 90.1O, the fiber performance will deteriorate.

By making the binder fiber finer or increasing its amount,
The binder fibers should have a fineness of between 1.5 and 1.5, since increasing the number of entangled bonding points gives the fibrous web superior dimensional stability, but at the same time detracts from the required bulk and compressive elasticity of the fibrous web.
8 denier, and the fineness is preferably in the range of 32 to 1281. Further, the composition ratio of the binder ml in the fiber web is preferably in the range of 5 to 50% by weight based on the total fiber base material. If the binder fiber content is less than 5% by weight, the dimensional stability of the fibrous web will be impaired, while if it exceeds 50 weight %, the bulk and compressive elasticity necessary for the fiber web will be lost.

The fibrous web in the present invention can be formed using carding, air laying, other known techniques, or a combination of these techniques. The method using Nakadera carding is: ■ It is possible to obtain a fiber web with large voids and high compressive elasticity, ■ It is possible to obtain a wide sheet with high speed and excellent productivity, and ■ It is possible to obtain a web with two or more layers. Sheets can be easily laminated, ■ The basis weight can be easily adjusted, ■ A condensing roll (or compression roll), etc. is attached to the tick-off device (card web take-out device) to adjust the degree of orientation of each fiber base material. It is most preferred because it has many advantages such as: (1) the resulting fibrous web is homogeneous; Carded webs that can be laminated with two or more thin web sheets are particularly preferred for the present invention because they are extremely homogeneous.

Note that a known roller card, flat card, etc. can be used as the card opening machine.

Further, the heat treatment of the carded web can be performed using a known air-through type dryer for dry nonwoven fabrics in which hot air penetrates the web in the thickness direction.

The dry nonwoven fabric method involves mixing and dispersing heat-fusible binder fibers that melt and bond to base fibers at a relatively low temperature, and then heat-treating them in a completely dry state. Compared to a method in which the fibers are heat-treated in a wet state, it is possible to form a fibrous web with greater bulk and high elasticity (compressive elasticity), and it has the advantage that there are no health and safety problems for drugs on the skin.

The heat treatment conditions were as follows: The temperature was set to between the softening point of the low melting point polymer of the binder fiber and the softening point +80°C, and the hot air speed of the air through was selected to be 0.5 to 3.0 s/sec, and the heat treatment time was 1 to 3.
A range of 0 seconds is sufficient.

The acrylic acid-based highly absorbent FAT 41 monomer solution used in the present invention is preferably an aqueous solution of acrylic acid or a mixture of acrylic acid and methacrylic acid, in which 20 to 95% of all carboxyl groups are converted to alkali metal salts or ammonium salts. Partially neutralized ones are better. If the degree of partial neutralization is too high, it will be difficult to increase the 6°C of the aqueous solution, and as a result, the crosslinking reaction will be suppressed and the proportion of water-soluble resin will increase, resulting in the formation of an occlusive gel film on the resin surface. Furthermore, if the degree of partial neutralization is too high, the swollen gel will exhibit weak alkalinity, which is unfavorable in terms of safety and hygiene. Conversely, if the degree of partial neutralization is too low, the absorption capacity of the resin will drop significantly. Whether acrylic metal hydroxide, bicarbonate, ammonium salt, etc. can be used to neutralize the acrylic acid monomer, depending on industrial availability, price, etc.
Sodium hydroxide or potassium hydroxide is preferred from the viewpoint of safety, and potassium hydroxide is particularly preferred since it can increase the concentration of the aqueous solution of the acrylic acid monomer. The concentration of these acrylic acid monomer solutions is preferably at least 35% by weight, and the higher the concentration, the higher the degree of resin polymerization, and the more the amount of monomer attached to the fiber web can be increased, which may cause other problems. Unless otherwise specified, it is preferable to use a concentration slightly lower than the saturation concentration at the operating temperature.

The absorbent material of the present invention has an effective urine absorption 11 (under 0.5 psi pressure) of Ig
If 15 to 45 cc of superabsorbent resin is fixed to each diaper, the absorbency normally used for disposable diapers (O is approximately RL)
Rectangular notebook with l15cm and length 40CI11 (area 0
．． 06 m''), and in order to repeatedly absorb and retain about 50 cc of the user's urine 4 to 5 times each time, the amount of superabsorbent resin needs to be at least twice the weight of the fibrous web itself.

In the present invention, as a crosslinking agent, 0.0I to 10% by weight of a crosslinkable monomer having two or more type 2 packings in the molecule that can be copolymerized with an acrylic acid monomer based on the monomer is added to the monomer solution to achieve intermolecular crosslinking. Avoiding this formation can stabilize the morphology of the swollen gel. This crosslinking monomer is not particularly limited as long as it is water-soluble, and examples include ethylene glycol noacrylate, ethylene glycol noacrylate, noethylene glycol diacrylate, diethylene glycol no methacrylate, polyethylene glycol noacrylate, polyethylene glycol noacrylate, and polypropylene glycol noacrylate. Acrylate, polypropylene glycol no methacrylate, glycerin triacrylate, glycerin trimethacrylate, NN'
-methylenebisacrylamide, NN'-methylenebismethacrylamide, diallyl phthalate, noaryl fumarate, diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, triallylphophate, among others, polyethylene Glycol (meth)acrylate and NN'-methylenebisacrylamide are preferred. If the amount of crosslinking monomer added is less than 0.01 m% by weight relative to the monomer, the absorption performance will be extremely high, but the swollen gel will become paste-like and flow, resulting in poor shape retention of the gel, making it impossible to use it in disposable diapers. Moreover, if it exceeds 1.0 tonne weight, the shape retention of the gel will be improved, but the absorption performance will deteriorate.

In the present invention, the absorption performance of the superabsorbent resin may be improved by adding a high molecular weight polysaccharide to the monomer solution and performing graft polymerization using this polysaccharide as a backbone polymer. The resulting graft polymer has a structure in which polysaccharide is used as a backbone and polyacrylic acid is branched, and it has a three-dimensional structure that is self-crosslinked without using a crosslinking agent. The polymer quantum class 11 used as the trunk polymer is not limited to natural polysaccharides,
Including modified products thereof, such as starches such as potato starch and corn starch, hydroquine ethylcellulose, cellulose, guar gum, locust peat gum, mannan, and hydrolysates, oxides, and alkyl ethers of their polysaccharides. , aryl ether compound,
It includes various modified products such as oquin alkylated products, carboxymethylated products, aminoethyl etherified products, organic acid esterified products, etc., and these compounds are used alone or in combination of two or more. For example, mention may be made of various starches, carboxymethyl cellulose which is not easily soluble in cold water, low-conversion methyl cellulose, high molecular weight hydroxyethyl cellulose and mixtures of these polysaccharides with other polysaccharides. It is preferable that the amount of these polysaccharides added is in the range of l:0.02 to l:0, o5 in units of monomers to monosaccharides. The reaction temperature may be 60 to 100°C, and the use of crosslinking monomers as necessary does not hinder the present invention.

The present invention uses water-soluble polymers such as sodium polyacrylate, polyvinylpyrrolidone, polyvinyl alcohol, hydroxyethyl cellulose, etc. as viscosity modifiers in the monomer solution.
Improving the adhesion of the monomer solution to the fiber base material by using at least one compound selected from high molecular weight polysaccharides such as carboxymethyl cellulose, ultrafine particle inorganic compounds such as colloidal silica as a thixotropic agent, etc. It is possible. The monomer solution has a viscosity of 2 to 200 c
It is preferable that the monomer solution is in the range of 2 cps, and if it is less than 2 cps, the monomer solution once attached to the fiber base material will immediately slide down along the fiber axis, and a thin, thin film that envelops the fiber base material in a sheath shape will not be formed. On the other hand, if it exceeds 200 cps, the monomer solution applied to the fiber web will form a film, which is not preferable.

In the present invention, radicals are generated by using an acrylic acid-based superabsorbent resin monomer in combination with a peroxide substance and a reducing substance,
The resin is formed by a so-called oxidation-reduction type (redox type) polymerization method that initiates polymerization, but this polymerization method requires less energy for radical generation and activation than a thermal decomposition type radical polymerization method, and requires relatively low temperature. Since it is possible to carry out explosive polymerization in a continuous manner, it is extremely suitable for producing absorbent materials by coating a monomer solution on a fiber web sheet and completing polymerization in an extremely short period of time (several seconds). .

The peroxide substances used in the present invention are hydroperoxide compounds such as t-butyl hydroperoxide and cumene hydroperoxide, azobisisobutyronitrile, 2-2'' azobis(aminonepropane) dibasic acid salts, etc. It is preferable to consist of at least one compound selected from compounds, hydrogen peroxide, and persulfate compounds such as potassium persulfate and ammonium persulfate, and the reducing substance is a sulfite compound such as sodium bisulfite. , reducing organic acid compounds such as L-ascorbic acid, salt compounds such as ferrous sulfate, etc.
Of course, it is not limited to these types of compounds. These polymerization initiators are preferably those with high water solubility, and the amount used varies depending on the combination of initiators and polymerization temperature. Good to use. 0
If it is less than 0.01% by weight, the polymerization reaction will not proceed sufficiently;
If the amount exceeds 0% by weight, the effect cannot be obtained even if the amount of the initiator is increased.

Methods for applying the monomer solution to the fibrous web include kiss coating using a coating roll and scattering using a rotating brush.The monomer solution can be applied efficiently to the fibrous web running at high speed, and the amount of application can be easily controlled. I can do it. In particular, a nip type coating roll is most preferred. The fibrous web is sandwiched between a pair of coating rolls rotating at the same speed as the fibrous web, and a monomer solution is applied to both the front and back surfaces.

In the present invention, after a monomer solution is applied to a fibrous web, an initiator is added over the monomer solution to initiate polymerization.

At this time, it is preferable to add the aqueous solution of the initiator to the surface of the monomer solution in the form of fine particles using a spray device. The higher the concentration of the opening agent, the better, but it is better to keep it lower than the saturation concentration at a given temperature to avoid clogging the holes in the spray nozzle.Also, in order to spray uniformly over the entire fiber web, It is preferable to provide a large number of initiators.It is sufficient that the amount of initiator added is 0.01 to 2.0% by weight based on the monomer.The monomer solution applied to the fibrous web is then heated at 60-100°C. led to a polymerization tank maintained at
A polymerization reaction takes place.

There are no particular restrictions on the shape of the reaction tank, but if polymerization is to be completed in a short time while the fiber web is running continuously, the fiber web may be run from top to bottom or from bottom to top as shown in Figure 1. The reaction is preferably carried out in a polymerization tank in which the temperature is maintained at 60 to 100° C. and the humidity is 80% or more using hot air saturated with water. If the temperature of the reaction tank is less than 60°C,
Although the basic molecular weight of the obtained resin increases and the absorption performance of the resin improves, it takes a long time to complete the polymerization reaction, so the temperature is preferably 60° C. or higher. Further, if the temperature exceeds 100°C, a self-crosslinking type polymerization reaction occurs, which deteriorates the absorption performance of the resin, which is not preferable. Normally, in the polymerization of acrylic acid monomers, a large amount of reaction heat is generated as the reaction progresses, and it is not uncommon for local rapid temperature increases to occur and abnormal reactions. Since a fiber web with good air permeability is used, water in the monomer solution efficiently evaporates outside the system during polymerization, and the reaction heat is cooled by the latent heat of vaporization, making the temperature distribution uniform and localized. It is possible to prevent problems such as self-crosslinking progressing to a high degree in that portion due to a temperature increase, resulting in a decrease in absorption performance.

In the present invention, the polymerization reaction accompanied by rapid heat generation is completed homogeneously in an extremely short period of time, but as mentioned above, this is only possible by using a bulky and breathable fiber web as a carrier for the monomer solution. becomes.

The polymerization reaction is usually completed in a few seconds (3 to 15 seconds), and about 9 seconds.
0-85% of the acid monomer is converted to superabsorbent resin. The resin thus obtained is a hydrous polymer containing 20% water and 5 to 10% of unreacted residual acid monomer inside. Residual acrylic acid or a mixture monomer of acrylic acid and methacrylic acid not only reduces the absorption performance of the superabsorbent resin, but also irritates the user's skin and causes itching and sores, which is undesirable from a health and safety perspective. .

The residual monomer in the water-containing polymer can be efficiently reduced by irradiating it with electron beams and/or ultraviolet rays. Among these, electron beam irradiation is particularly useful because it forms appropriate crosslinks in superabsorbent resins obtained through redox polymerization, reduces water-soluble resin components, and suppresses stickiness during swelling. It is. The reaction by electron beam irradiation proceeds most efficiently when the water content of the hydrous polymer is around 20%. Further, since radicals are generated by irradiation, it is not necessary to add an initiator. Stickiness can be sufficiently suppressed if the irradiation dose is in the range of 2 to 20 megarads. Several liters of residual monomer are removed by electron beam irradiation.
It is possible to reduce the residual monomer to 11,000 ppm, but if left as it is, the characteristic odor of acrylic acid monomers will still remain, and there is a danger that it will irritate the skin of users such as babies, so UV rays are further irradiated to reduce the residual monomer to 11,000 ppm or less. It is desirable to reduce it to The presence of a photodecomposition type radical initiator is required to initiate the reaction of residual monomers in a hydrous polymer by ultraviolet irradiation.
When hydrogen peroxide is used as the peroxide substance of the polymerization initiator, this hydrogen peroxide effectively acts as a photodegradable radical initiator, so there is no need to add an initiator again before ultraviolet irradiation. Furthermore, when the hydrous polymer is irradiated with an electron beam prior to ultraviolet irradiation, the addition of an initiator can be omitted since a sufficient amount of hydrogen peroxide is generated in the hydrous polymer by the electron beam irradiation. The reaction caused by ultraviolet irradiation proceeds most efficiently when the water content of the hydrated polymer is around 30%.
It is desirable to adjust the humidity by spraying water as appropriate. If the amount of ultraviolet ray irradiation is in the range of 5 to 500 millijoules/cva'', it is possible to reduce the amount of residual monomer to 1000 ppm or less.

When the crosslinking density of the surface layer of the superabsorbent resin of the present invention is increased, so-called gel block, which is formed by a paste-like gel on the surface layer, is suppressed, and urine quickly penetrates into the resin, allowing urine to be absorbed. Performance can be further improved. Examples of such crosslinking agents include polydacidyl ethers such as ethylene glycol dignnor ether and polyethylene glycol dignnor ether, which have two or more functional groups that react with carboxylic acid in the molecule, diethylene glycol, triethylene glycol, and propylene glycol. , polyols such as glycerin, polyglycerin, and pentaerythritol, and polyamines such as ethylenenoamine. When these crosslinking agents are added to a hydrous polymer and heated, it is possible to form extremely uniform intermolecular crosslinks on the surface layer of the hydrous polymer, and the size of the mesh structure formed by crosslinking can be controlled to some extent. can do. The crosslinking agent is 0°0I to 2 to the monomer.
．． It is sufficient to use 0% by weight. 0. If the OI weight is less than 1%, the effect will be small, and if it exceeds 2.0 weight%, the effect will not improve even if the amount of the crosslinking agent is increased further. The most convenient and preferred method for adding the crosslinking agent solution to the hydrous polymer is spraying with a rotating brush.

In addition, since crosslinking reactions such as esterification between carboxyl groups and hydroxyl groups and amidation between carboxyl groups and amine groups proceed more easily at higher temperatures,
It is best to heat treat at ℃.

The properties of the fibrous web used in the present invention are measured as follows.

The bulk height (cc/g) is calculated by cutting four test pieces obtained by cutting the fiber web into squares with sides of 10+ m (the directions of the sides are aligned with the machine direction and the center direction, respectively). are stacked alternately, and methyl methacrylate resin plates and weights are placed on top of them to give a weight of 0.5 g/
A load of ca' is applied for 10 minutes, the volume V, (cc) of the fiber web layer at that time is measured, and this value (1) is divided by the weight of the fiber web layer that has been weighed in advance.

The compressive elastic modulus (%) is determined by applying a load of 35 g/am' to the fiber web layer whose bulkiness V, (cc) was measured, and measuring the volume V, (cc) when left for IO minutes.
, calculate the compressive elastic modulus (%) according to the formula below.

Compressive modulus (%) = 7'x I 00■1 The tensile strength and elongation of the fiber web are determined by
Measurement is performed using a test piece cut into a rectangle of 5 cm and width 2.5 cm (long sides aligned with machine direction and width direction). Using "Tensilon", clamp both ends of the test piece with chucks and adjust the sample length to 10 cm.

Next, the sample is stretched at a stretching rate of 100%/min to obtain a stress-elongation relationship curve. From this relationship curve, read the strength (g/25 m@) and elongation (%) when the test piece breaks.

The absorption rate of the absorbent material obtained by the present invention is determined by a test piece prepared by cutting a sample into a circle with a diameter of 5c+a after vacuum drying at 80°C for 2 hours and conditioning the humidity in an atmosphere of 60 R8% at 25°C for 8 hours. Measure using. A filter paper (Toyo Roshi No. 2, diameter 5.5 cm) 31. Place the resin frame 32. Here, the test liquid (physiological saline, 0.9% by weight Nacfl 33) is adjusted by changing the height of the burette 34 so that the surface of the glass filter is wetted.Next, the absorbent test piece 35 0,1 g/
Apply a load of 36 ctn' and immediately start absorbing the test liquid, and the absorption of the test liquid per 1 g of resin f)i (g/g
) versus absorption time (minutes).

The absorption performance of the absorbent material obtained in the present invention, that is, the absorption capacity and water retention capacity, was determined by vacuum drying at 80°C for 2 hours,
A sample that has been conditioned for 8 hours in an R8% atmosphere is 10cm on each side.
Measurement is performed using a test piece cut into a square of m (the directions of the sides are aligned with the machine direction and the middle direction, respectively). First, the weight of the test piece (I Ca) (g) was weighed, and then the test piece was placed in a bag made of 250 nylon cloth with a length of 20c+n and a medium size of 15c+e. Salt solution, 0.9% N by weight
acl) in a shallow container to absorb the test liquid. After soaking for 1 hour, take out the test piece along with the nylon cloth bag, place it on a 10-mesh wire mesh, and place a methyl methacrylate resin plate and weight on top of it to give a 35 g/c
Draining is carried out under a pressure of m2 for 15 minutes. Then, take out the test piece and weigh it to a weight of 11t (b) (g). Return the test piece to the nylon cloth bag, place it together with the nylon cloth bag on the side wall of the rotating tank of the centrifugal dehydrator, and apply a centrifugal force of 150G to
After performing centrifugal dehydration for 0 seconds, remove the test piece from the nylon cloth and weigh 1 (c) (g).

Obtain the absorption capacity and water retention capacity from (a), (b), and (c) according to the following formula.

Water retention ratio (g / g) = (b) Ca) - 1 chou r [Example J The present invention will be explained in detail below with reference to Examples.

(Example-1) Polyethylene terephthalate (intrinsic viscosity 0°65) consisting essentially of a constituent unit of ethylene terephthalate was
Using a spinneret with holes shown in the figure, melt spinning was carried out at 280°C, followed by cooling and applying an oil agent according to a conventional method.
I picked it up in minutes, bundled it up and put it in a can. The bundled tow of the undrawn yarn fibers obtained in this way was drawn using a horizontal drawing machine,
Stretched by 4°0 times at a speed of 1.5 m/min, passed through a pressing and crimping device consisting of a crimper roll and a crimper box, crimped by machine 1, and heated to 130°C in an autoclave.
After being heat treated for 0 minutes, it was cut into short fibers. The irregular cross-section fiber thus obtained has a cross section shown in FIG. 9, where R is 8.5 x I O-3 mm.

The cross-sectional area A of the groove was 64 X l O-'am', and the fiber properties were shown in Table 1.

Table 1 (Example 2) 70% by weight of the irregular cross-section fiber obtained in Example 1 was used as the base fiber, a low melting point polyester polymer (intrinsic viscosity 0.35) was used as the binder fiber, and polyethylene terephthalate (intrinsic viscosity 0.57) in the core, add 30% by weight of core-sheath type composite spun fibers with a sheath-to-core volume ratio of 1:1, and use an opener to uniformly mix and open the cotton. After that, the card is fed to two flat card opening machines arranged in series and carded at a speed of 50 m/min. Two thin webs are taken out from each card, and these are laminated to form one homogeneous card. Formed a web. here,
The core-sheath type composite spun fiber has a fineness of 4 denier and a fiber length of 5.
The polyester polymer with a low melting point disposed in the sheath contains 60 mol% of terephthalic acid and 40 mol% of isophthalic acid as a dicarphonic acid component.
Short fibers were used which were polyester copolymers containing mol % and having a melt softening point of approximately 110°C.

The printed card web is then guided to a flat belt type air-through type heat treatment equipment, and 16
Hot air at 0° C. was passed through for 10 seconds to melt the binder fibers and bond the fibers together, forming a fibrous web with good shape stability. The performance of the fiber s (1 web obtained in this manner is shown in Table 2) Table 2 (Example 3) While running the fiber web obtained in Example 2 at 50 m/min, Hydrogen peroxide was added to the fiber web at a concentration of 1.67% by weight based on the monomer using a mold coating roller, and the monomer solution heated to 40°C was added to the fibrous web so that the monomer weight was 200 g/m''. After coating, a 5% by weight aqueous solution of L-ascorbic acid was sprayed onto the fiber web at a concentration of 0.34% by weight based on the monomer, and immediately introduced into a polymerization tank where the atmosphere was kept at 80°C and humidity above 80%. The monomer solution was a partially neutralized acrylic acid monomer aqueous solution with a concentration of 65 in which 60% of the total carboxyl groups of acrylic acid were neutralized with potassium hydroxide, and NN'-methyl was added as a crosslinking monomer. A resin containing 0.085% by weight of bisacrylamide based on the monomer was used.The polymerization reaction started immediately after the monomer solution was applied to the fiber web, and the reaction was completed in about 8 seconds with heat generation. The absorbent material obtained in this way became a fine fibrous resin in the grooves on the fiber surface of the superabsorbent resin or irregular cross-section fibers.The properties of the obtained absorbent material are shown in Table 3. show.

[Comparative Example-1] The same operation as in Example-1 was performed except that a hollow fiber spinneret with a normal circular cross section was used.

The properties of the obtained fibers are shown in Table -■.

[Comparative Example-2] The same operation was carried out in Example-2 except that the hollow fibers obtained in Comparative Example-1 were used instead of the irregular cross-section fibers obtained in Example-1 as the heath fibers. The properties of the obtained fibrous web are shown in Table 2.

[Comparative Example-3] In Example-3, the same operation was performed except that the fibrous web obtained in Comparative Example-2 was used instead of the fibrous web obtained in Example-2. The properties of the obtained absorbent material are shown below.
Shown in 3.

Table 3 "Effects of the Invention" As explained above, since the absorbent material of the present invention contains fine fibrous superabsorbent resin, the absorption rate of urine is fast.
It is possible to provide an absorbent material that can efficiently bring out the latent absorption capacity of the resin and is suitable for soft disposable diapers. Furthermore, since the absorbent material of the present invention is soft and capable of quickly absorbing a large amount of urine, sanitary materials such as disposable diapers that are comfortable to wear and do not easily leak can be obtained.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an absorbent manufacturing device, Figure 2 is a diagram showing a crosslinking agent treatment device, and Figures 3 and 4 are fibers of superabsorbent resin in a conventional absorbent material and the absorbent material of the present invention. A schematic diagram of the state of adhesion to a base material, FIG. 5 is a diagram showing the fibrous superabsorbent resin of the present invention, and FIGS. 6(a) to (d) are diagrams showing grooves continuous along the fiber axis on the fiber surface. FIG. 7 is a diagram showing an example of the fiber base material arranged, FIG. 7 is a diagram showing the fibrous superabsorbent resin peeled off from the fiber surface, FIG. 8 is a diagram showing an example of the spinneret hole, and FIG. 9 is a diagram showing an example of the spinneret hole. A diagram of the cross-sectional shape of the fiber obtained from the spinneret hole in Figure 8,
FIG. 10 is a diagram showing grooves arranged on the fiber surface, FIG. ), (b), and (c) are explanatory diagrams of the method for evaluating liquid diffusivity of fibrous webs, Figure 13 is a diagram showing an apparatus for measuring absorption rate of absorbent material, and Figure 14 is an illustration of the method for evaluating liquid diffusivity of a fibrous web. It is a graph showing the absorption rate of each absorbent. 1... Fiber web, 2... Coating roller, 3... Monomer solution, 4...
- Initiator, 5... Polymerization tank, 6... Fiber web with super absorbent resin attached, 7... Electron beam irradiation device, 8... Ultraviolet irradiation device, 9...
...Water spray device, 10...Heater, 11...
...Blower 112 ...Rotating brush, 13
... Heating device, 14 ... Fiber base material, 1
5... Conventional super absorbent resin, 16...
Fibrous superabsorbent resin of the present invention, 17... Fibrous superabsorbent resin formed using grooves on the fiber surface, +8... grooves as a mold, 19.22...・Fiber, 19a・
...Groove, 20...Resin, 21...
・Spinneret hole, 23...Fiber base material, 24...
Super absorbent resin, 25...Test piece, 26...
... Methyl methacrylate resin plate, 27 ... Hole, 28 ... Part wet with colored test liquid, 29
...Spacer, 30...Glass filter support stand, 3! ... Filter paper, 32 ... Resin frame, 33 ... Test liquid, 34 ... Buret, 35 ... Absorbent test piece, 36 ...・・・・・・
load. Applicant Mitsubishi Rayon Co., Ltd. Figure 1 Figure 2 Figure 5 Figure 6 (0) (b) (C) Figure 10 (0) (b) Figure 11 (0) (b) (c) Figure 1
Figure 2 (a) (b) (C)

Claims (1)

[Scope of Claims] An absorbent material obtained by applying an acrylic acid-based superabsorbent resin monomer solution to a fiber web and polymerizing the same, comprising: An absorbent material characterized in that at least a portion thereof is made of a fibrous resin formed by using grooves provided on the surface of a fiber base material as a mold.