JPH093757A - Water absorbing nonwoven fabric - Google Patents

Abstract

PURPOSE: To produce a water absorbing nonwoven fabric simultaneously having a biodegradability and a high water absorption property. CONSTITUTION: This water absorbing nonwoven fabric is obtained by melt- spinning an aliphatic polyester resin having a thermoplasticity, decomposable with microorganisms, and containing a glycol and an aliphatic dicarboxylic acid or their derivatives as constructing units, making a web by capturing many long fiber filaments, providing regular and intermittent self melted adhesion regions in the web to obtain a spun bonded nonwoven fabric, laminating a paper sheet consisting of pulp fibers on the one side of the spun bonded nonwoven fabric, then penetrating through a high pressure flow of a column of water from the paper sheet side to the spun bonded nonwoven fabric side to unify by intertwining the pulp fibers with the long fibers in the nonwoven fabric. The pulp fibers contain cross-linked carboxyalkyl groups.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-absorbent non-woven fabric having a high water absorbency and capable of being completely decomposed by microorganisms in compost, wet soil, water containing activated sludge, sea water and the like. More specifically, the present invention relates to a nonwoven fabric in which a biodegradable spunbonded nonwoven fabric and a pulp fiber having a crosslinked carboxyalkyl group are entangled and integrated with each other, which is a disposable paper diaper, a sanitary article. It can be widely used as a sanitary material field such as, a soil water retention material, an agricultural material field such as a nursery sheet, a food field such as a food freshness-retaining material and a dehydrating material, and a medical material such as a building material, dressing, and gauze.

[0002]

2. Description of the Related Art In recent years, many studies have been conducted on polymers as resins used for biodegradable nonwoven fabrics. Examples of the degradable polymer include polysaccharides such as cellulose and chitin, proteins such as regenerated collagen, poly-3-hydroxybutyrate and poly-3 produced by microorganisms.
-Hydroxy valerate, polyester such as poly-3-hydroxycaprate, etc. are known, but a non-woven fabric made by using any resin is an absorbent material for an aqueous solution containing water or salts such as saline. Is difficult to use. On the contrary, cotton, pulp, paper, cloth, sponge and the like are known as traditional biodegradable absorbent materials.
However, these water absorption capabilities are due to the capillary phenomenon and cannot absorb a large amount of water. It also has a drawback that water is easily released again when pressure is applied in a water absorbing state.

In recent years, a group of materials called super-absorbent resins have been known, and these resin materials basically have a chemical structure in which a water-soluble polymer is slightly crosslinked to make it insoluble in water. I have. Examples of such a highly water-absorbent material include, for example, starch obtained by graft-polymerizing acrylonitrile and then hydrolyzing it, starch obtained by graft-polymerizing an acrylic acid metal salt, and acrylic acid polymerized with a copolymerizable cross-linking agent. Cross-linked resin, methyl methacrylate-
Many products such as hydrolysates of vinyl acetate copolymers have been proposed.Since these superabsorbent resins have the principle of water absorption as osmotic pressure, they can absorb much more water than capillary action. it can. In addition, the super absorbent resin has the excellent feature that it does not easily re-release water even if pressure is applied in the water-absorbed state, but it has the drawback of not being biodegradable, and it is landfilled for disposal. Then, the superabsorbent resin is not decomposed by microorganisms and remains in the soil for a long period of time, and in recent years, cases of causing environmental problems are increasing.

On the other hand, a highly water-absorbent material composed of cellulose fibers having a crosslinked carboxyalkyl group is also known. Since it has biodegradability unlike the above-mentioned synthetic polymer-based water-absorbent resin, it is used in the field of disposable hygiene materials. Are particularly suitable. However, such a material has a drawback in that when it absorbs a liquid in the form of a fiber mat or a sheet, it cannot maintain its shape because it has no wet strength and is poor in handling suitability. Further, a spunbonded nonwoven fabric obtained by melt-spinning a thermoplastic resin into a web and a paper sheet composed of cellulose fibers are laminated, and a water column flow is jetted from the surface of the paper sheet at a high pressure to penetrate the synthetic fiber, The composite non-woven fabric obtained by entanglement and integration of cellulose fibers is flexible, has strength in a wet state and is suitable as a wiping cloth, and the present inventors have found that glycol and an aliphatic dicarboxylic acid are used as the thermoplastic resin. Alternatively, a biodegradable nonwoven fabric comprising a biodegradable aliphatic polyester resin composed of a derivative thereof has been proposed (Japanese Patent Application No. 6-272287).

[0005]

Therefore, the present inventors have found that the biodegradable non-woven fabric as described above has extremely weak water absorption, and it is not sufficient that the liquid is absorbed by the pulp fiber used as it is. Therefore, it is examined to give the pulp fiber further improved water absorption,
The inventors have found that the above object can be achieved by providing a pulp fiber of a biodegradable nonwoven fabric with a crosslinked carboxyalkyl group, and completed the present invention. The purpose of the present invention is
Carboxyalkylating agent for pulp fiber of biodegradable composite nonwoven fabric consisting of long fiber spunbonded nonwoven fabric and pulp fiber,
An aqueous reaction solution containing an alkali metal hydroxide, a cross-linking agent, and water is contained, and then heated to form cross-linked carboxyalkyl groups in pulp fibers, thereby providing a nonwoven fabric having both biodegradability and high water absorption performance. Especially.

[0006]

The present invention comprises a glycol and an aliphatic dicarboxylic acid or derivative component thereof, which has thermoplasticity and can be decomposed by microorganisms, as constituent units.
After melt-spinning an aliphatic polyester resin and collecting a large number of long-fiber filaments into a web, one side of a spunbonded nonwoven fabric obtained by providing the web with regular and intermittent self-fusing zones is used. After laminating a paper sheet made of fibers, a high pressure water column flow is penetrated from the paper sheet side to the spunbonded nonwoven fabric side, and the pulp nonwoven fabric and the continuous filaments of the nonwoven fabric are entangled and integrated into one another. Is a water-absorbent nonwoven fabric having a crosslinked carboxyalkyl group.

Examples of the aliphatic dicarboxylic acid or its derivative which is a constituent unit of the aliphatic polyester resin usable in the present invention include succinic acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid and their derivatives. These anhydrides can be mentioned, and at least one kind is used appropriately selected from these. If necessary, malic acid, tartaric acid, oxycarboxylic acid such as citric acid may be added to the constituent units. Among these dicarboxylic acids, succinic acid and its derivatives are preferable because they are excellent in biodegradability and productivity. Examples of the glycol which is a constituent unit of the aliphatic polyester resin usable in the present invention include ethylene glycol, butanediol, hexanediol, decamethylene glycol, neopentyl glycol, cyclohexanedimethanol, and the like. At least 1 appropriately selected from
Seeds are used.

In the present invention, the long fibers constituting the biodegradable spunbonded nonwoven fabric are extruded from a large number of die after heating and melting an aliphatic polyester resin containing glycol and an aliphatic dicarboxylic acid or its derivative component as a constituent unit. Then, it is produced by stretching with high-speed high-pressure air by an ejector. The melt flow rate of the aliphatic polyester resin usable in the present invention at a load of 2.16 Kg and a temperature of 190 ° C. measured by the method shown in JIS K 7210 is 15 to 70 g / 10 minutes, preferably 20 to 60 g. / 10 minutes. If the melt flow rate is less than 15 g / 10 minutes, it is necessary to raise the melt spinning temperature in order to improve the fluidity of the resin, which not only causes a cost increase but also makes the produced sheet hard and the texture is suitable, which is suitable. Absent. On the other hand, if the melt flow rate exceeds 70 g / 10 minutes, yarn breakage frequently occurs during drawing with high-pressure air, which is not suitable.

The resin temperature during melt spinning is set to 50 to 135 ° C., preferably 50 to 120 ° C., higher than the melting point of the resin. When the resin temperature during melt spinning is higher than the melting point by less than 50 ° C., the viscosity of the molten resin is high and it is not suitable for spinning. On the other hand, when the temperature of the resin is higher than the melting point by more than 135 ° C., the temperature deviates from the melting point of the resin too much, so that it becomes difficult to cool the resin when spinning the resin from a large number of spinnerets, and the fusion of fibers is Not only is yarn breakage likely to occur, the stability of the resin is reduced, and there is a risk of partial resin decomposition, which is not suitable. The water content of the resin before spinning measured by the Karl Fischer method is 0.2% or less, preferably 0.05% or less. When the water content of the resin is more than 0.2%, not only the number of yarn breaks during melt spinning but also
In an extreme case, the resin is decomposed and spinning becomes impossible, which is not suitable.

In the present invention, a large number of long fibers accumulated on the support are provided with self-bonding regions of the fibers at regular intervals for the purpose of maintaining the shape and strength of the nonwoven fabric.
The self-bonding area is composed of a large number of long fibers accumulated on a support,
It is formed by being introduced between a heated concavo-convex roll and a smooth roll, and subjected to heating and pressure treatment, so that the sheet portion corresponding to the convex part of the concavo-convex roll is fused.
In this case, the temperature of the roll is 5 to 50 ° C., preferably 5 to 40 ° C. lower than the melting point of the resin constituting the long fibers used. If the difference between the roll temperature and the melting point of the resin is less than 5 ° C., the fibers adhere to the roll during thermocompression bonding by the roll, which causes manufacturing troubles. On the other hand, if the difference between the roll temperature and the melting point of the resin exceeds 50 ° C., the self-bonding portion is not sufficiently formed, the sheet strength is notably lowered, and fuzzing becomes severe, which is not suitable. The linear pressure when performing thermocompression bonding with an uneven roll and a smooth roll is 10
-80 kg / cm, preferably 20-60 kg / cm. If the linear pressure is less than 10 kg / cm, the formation of the self-fused area by the thermocompression bonding becomes insufficient, and
When it is larger than m, it is not suitable because it causes breakage in the fusion-bonded area, the texture of the nonwoven fabric is deteriorated, and the strength is lowered. As a method of forming the self-fusion area, the continuous continuous fibers that have been accumulated are introduced between the concavo-convex roll and the ultrasonic horn, and subjected to ultrasonic treatment to form a point fusion portion corresponding to the convex portion. It is also possible.

In the present invention, the area of each self-bonding zone is preferably in the range of 0.03 to ⁴ mm ² . If the area of the self-bonding area is less than 0.03 mm ² , the strength of the nonwoven fabric is insufficient, and conversely, if the area of self-bonding area exceeds 4 mm ² , the nonwoven fabric becomes hard and unsuitable. The total area of the self-bonding area is 2 to the surface area of the long fiber non-woven fabric.
20%. If the total area of the self-fusing area is less than 2%, the strength is insufficient, and conversely, if the self-fusing area exceeds 20%, the nonwoven fabric becomes hard, which is not suitable. The basis weight of the spunbonded nonwoven fabric made of long fibers thus produced has a basis weight of 5 to 30 g / m ² , preferably 5 to 20 g.
/ M ² . The basis weight of spunbonded non-woven fabric is 30 g / m ²
If it exceeds, the paper sheet made of pulp fiber will be laminated on one side of the spunbonded non-woven fabric, and even if it is applied so as to penetrate the high pressure water column flow from the paper sheet side to the spunbonded non-woven fabric side, It becomes difficult to pass through the bonded non-woven fabric, and the entanglement between the long fibers forming the spun-bonded non-woven fabric and the pulp fibers forming the paper sheet is hindered, and integration cannot be achieved.

Further, since the ability to suck and remove water on the surface of the laminate of the spunbonded nonwoven fabric and the paper sheet through the spunbonded nonwoven fabric from the suction nozzle located under the support net is reduced, a high pressure water column flow is applied. A water pool is generated on the surface of the laminated body, and the energy of the high-pressure water column flow is used for splashing the water on the surface, so that not only energy loss occurs but also the texture of the nonwoven fabric deteriorates. Conversely, if the basis weight of the spunbond nonwoven fabric is less than 5 g / m ² ,
The strength of the resulting composite non-woven fabric becomes low, the gap between the long fibers becomes large, and when a high pressure water column flow is applied,
Pulp fibers are washed away from the gaps and are wasted. Also, when used waste water is collected, a large amount of pulp fibers are mixed therein, which makes it difficult to treat the wastewater.

On one surface of the spunbonded non-woven fabric prepared as described above, a paper sheet made of a large number of pulp fibers is laminated. As this paper sheet, various known arbitrary ones can be used. The grammage of the paper sheet is also a matter that can be arbitrarily determined, and in particular, a paper sheet having a grammage measured by the method of JIS P 8124 in the range of 10 to 200 g / m ² is preferably used. Paper sheet basis weight is 10g
If it is less than / m ² , the absolute amount of pulp fibers will be small, and the bulkiness of the resulting water absorbent nonwoven fabric will not be sufficient.
On the other hand, if the basis weight of the paper sheet exceeds 200 g / m ² , the absolute amount of pulp fibers is too large, and even if a high pressure water column flow is applied to the paper sheet, spunbonded nonwoven fabric will be added to each pulp fiber. It is not suitable because it is difficult to give momentum to the extent that it can be entangled with the constituent long fibers. Furthermore, the flexibility of the resulting water absorbent nonwoven fabric is reduced.

The pulp fibers that make up the paper sheet include
Crafting softwood and hardwood wood, sulfite method,
Soda method, digested by polysulfite method, etc., unbleached pulp fiber or bleached pulp fiber obtained as required, or ground pulp fiber from the softwood wood, mechanical pulp fiber such as thermomechanical pulp fiber alone, Can be used together or as a mixture. The weight mixing ratio of the softwood pulp fiber and the hardwood pulp fiber is in the range of softwood pulp fiber: hardwood pulp fiber = 100: 0 to 20:80, preferably 100: 0 to 40:60. If the hardwood pulp fiber exceeds 80% by weight of the total pulp fiber, not only the loss of pulp increases when the high pressure water column flow is applied to the paper sheet, but also the flexibility of the composite sheet after entanglement decreases. As a result, the resulting water-absorbent nonwoven fabric also becomes hard.

JIS P of the paper sheet used in the present invention
The density according to 8118 is 0.65 g / cm ³ or less. When the density of the paper sheet exceeds 0.65 g / cm ³ ,
When the high pressure water column flow is applied from above the paper sheet, the movement of the pulp fibers is suppressed, so that the entanglement of the long fibers and the pulp fibers becomes insufficient, and the flexibility of the composite sheet after the entanglement decreases. However, there is a limit in reducing the density of the paper sheet, and the lower limit is about 0.20 g / cm ³ in a soft state like tissue paper. The paper sheet is usually obtained by using a pulp fiber slurry to make a paper in a known wet paper machine and drying it with a drier. During paper making, for example, polyamide epichlorohydrin resin or its modified product, polyamine epichlorohydrin resin. A wet paper strength enhancer such as melamine resin or urea resin may be added to the slurry before use.

This paper sheet is laminated on one side of a spunbonded non-woven fabric sheet prepared in advance.
The basis weight ratio of the spunbonded non-woven fabric sheet and the absolute dry basis weight of the paper sheet according to P8124 are adjusted so that spunbonded non-woven fabric: paper sheet = 1: 1 to 1:19. When the ratio of spunbonded non-woven fabric: paper sheet is less than 1: 1, the amount of pulp fiber becomes relatively small with respect to the amount of long fiber, and the bulkiness of the resulting composite non-woven fabric decreases.
The bulkiness of the resulting water-absorbent nonwoven fabric is also low. In addition, the amount of inexpensive pulp fibers is smaller than that of long fibers, which increases the manufacturing cost of the obtained composite sheet itself, which is not suitable. On the contrary, when the ratio of spunbonded non-woven fabric: paper sheet exceeds 1:19 and the ratio of the paper sheet increases, it becomes difficult for all of the pulp fibers constituting the paper sheet to be entangled firmly, and when the water absorption treatment is performed, This is not suitable because the fibers will easily fall off. Furthermore, the flexibility of the resulting water absorbent nonwoven fabric is reduced.

After a paper sheet is laminated on one side of the spunbonded nonwoven fabric, when a high-pressure water column flow is applied from the surface of the paper sheet to the spunbonded nonwoven fabric side, high pressure is applied from the paper sheet side of the laminate to the spunbonded nonwoven fabric side. A high-pressure water column flow is ejected so that the water column flow penetrates. This high pressure water column flow has a high water pressure, for example, 20 to 180 kg / cm ² through a fine hole diameter, for example, a nozzle hole having a diameter of 0.01 to 0.3 mm.
It is obtained by ejecting water at the pressure of. When this high-pressure water column flow is applied to the laminate, the high-pressure water column flow first collides with the paper sheet to bring the paper sheet into close contact with the spunbonded nonwoven fabric, and then, in this close contact state, partial destruction of the paper sheet is caused. Then, the pulp fibers constituting the paper sheet of that portion are isolated, the pulp fibers are deformed such as bent and twisted, and the pulp fibers are sufficiently given kinetic energy to cause random movement. As a result, the pulp fibers and the long fibers in the spunbonded non-woven fabric are entangled with each other due to their composite action, and further, the pulp fibers also entangle the long fibers with each other.

To make the composite non-woven fabric obtained by entanglement of the pulp fibers and long fibers into a water-absorbent non-woven fabric, the pulp fibers constituting the composite non-woven fabric are mixed with a carboxyalkylating agent,
It is necessary to contain an aqueous reaction solution composed of an alkali metal hydroxide and a crosslinking agent to carry out the reaction of crosslinking and carboxyalkylation. As the carboxyalkylating agent used in this aqueous reaction solution, an alkali metal salt of halocarboxylic acid is used. As the halocarboxylic acid alkali metal salt, monochloroacetic acid alkali metal salt, monobromoacetic acid alkali metal salt, α-chloropropionic acid alkali metal salt,
β-chloropropionic acid alkali metal salts, α-bromopropionic acid alkali metal salts, β-bromopropionic acid alkali metal salts and the like having 3 or less carbon atoms are preferable, and these may be used alone or appropriately selected and mixed. used. In terms of cost, sodium monochloroacetate is cheap, so it is recommended to use it.

Sodium hydroxide is most preferred as the alkali metal hydroxide, but other alkali metal hydroxides such as lithium hydroxide, potassium hydroxide, rubidium hydroxide and cesium hydroxide can also be used. As the cross-linking agent, a cross-linking agent that cross-links with pulp fibers in an alkaline aqueous reaction solution, has a boiling point as high as possible, and is almost non-volatile. Since the present invention includes a step of allowing the composite non-woven fabric containing pulp fibers to contain the aqueous reaction solution and then removing the water by evaporating the water, a crosslinking agent having a low boiling point that volatilizes during this step is not suitable. .

Examples of the cross-linking agent usable in the present invention include ethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, polyethylene glycol diglycidyl ether, polyepoxy compounds such as diepoxybutane, divinyl sulfone and methylene. Divinyl compounds such as bisacrylamide, dichloropropanol, dibromopropanol,
Examples thereof include polyvalent halogen compounds such as dichloroacetic acid, and polyvalent aziridine compounds. At least one of them is appropriately selected from these. Epichlorohydrin, which is often used for crosslinking a cellulose derivative and can impart excellent pure water absorption performance, is not suitable for the present invention because of its low boiling point.

The above-mentioned carboxyalkylating agent, alkali metal hydroxide and cross-linking agent are dissolved in water to prepare an aqueous reaction solution. The proportion of water based on the total weight in this aqueous reaction solution cannot be uniquely specified because the solubility in water varies depending on the type of carboxyalkylating agent or alkali metal hydroxide used, but water within the range of solubility A smaller ratio is advantageous because the energy cost for evaporating water in the subsequent evaporation of water after the composite nonwoven fabric is allowed to contain the aqueous reaction solution is advantageous. However, if the concentration is too high, the aqueous reaction solution itself becomes unstable and handling becomes difficult. Therefore, in the present invention, the ratio of water to the total weight of the aqueous reaction solution is 60 to 90% by weight when sodium hydroxide is used. A carboxyalkylating agent, an alkali metal hydroxide, and a cross-linking agent are added so as to be within the range of%, and dissolved in water. The ratio of this water is the carboxyalkylating agent used as described above,
Since the respective solubilities in water differ depending on the types of the alkali metal hydroxide and the crosslinking agent, the lower limit value varies slightly.

The mixing molar ratio of the carboxyalkylating agent and the alkali metal hydroxide is adjusted within the range of 0.8 to 1.2 of alkali metal hydroxide / carboxyalkylating agent. The more outside this range, one of the chemicals remains unreacted, which is uneconomical. The amount of the crosslinking agent added varies depending on the type of the crosslinking agent and the reaction conditions,
It is 0.1 to 30% by weight based on the weight of cellulose. Next, the aqueous reaction solution prepared as described above is added to the pulp fibers of the composite non-woven fabric composed of long fibers and pulp fibers prepared in advance, to the pulp fibers of the part containing the aqueous reaction solution, Carboxyalkylation and crosslinking reaction are performed.

On the other hand, when the composite non-woven fabric contains an aqueous reaction solution, a coating method such as a comma coater, a roll coater, a lip coater, a slit die coater may be used, or an impregnation method, a size press method, various types. It is also possible to employ the printing method, the spray application method, or the like. The content of the aqueous reaction liquid contained in each of the above-mentioned various systems is such that the molar ratio of the carboxyalkylating agent to the glucose residue of the pulp fiber is 0.7 to carboxyalkylating agent / glucose residue (mol / mol). Suitably 2.0 is obtained. When the molar ratio is less than 0.7, it is 0.
A substitution degree higher than 35 cannot be obtained, and a water-absorbent nonwoven fabric having a high water absorption cannot be obtained. Conversely, the molar ratio is 2.
Even if it is 0 or more, the degree of substitution hardly increases, which is economically disadvantageous.

Next, the composite non-woven fabric containing the aqueous reaction liquid is heated at 50 to 150 ° C. for a few ten seconds to 8 minutes with air blowing, and the composite non-woven fabric contained in the composite non-woven fabric is heated. A part of water is removed by evaporation, and the ratio of water to the total weight of the contained aqueous reaction solution is 20 to 60.
It is adjusted to be in the range of weight%. The method of evaporating water is not particularly limited, but it is desirable to evaporate water in the shortest time possible. Since the reaction rate of carboxyalkylation is fairly fast, when evaporating water, if carboxyalkylation progresses or finishes during the evaporation of water if the temperature range is too long, for example, 30 minutes or more. Therefore, the effect of the present invention cannot be obtained.

Carboxyalkylation hardly progresses under the above-mentioned water evaporation conditions (degree of substitution is 0.1 or less),
For such evaporation, a method of evaporating water in a dryer or in a reaction vessel while applying hot air in the above temperature range is convenient. When the proportion of water in the aqueous reaction liquid contained in the composite non-woven fabric after partially evaporating water in this way is less than 20% by weight, the degree of substitution is rapidly reduced, and the resulting water absorption is obtained. It is necessary to avoid the non-woven fabric because it will turn yellow significantly. Further, when the proportion of water is higher than 60%, the effect of the present invention becomes small.

Immediately after the proportion of water in the aqueous reaction solution contained in the composite non-woven fabric is adjusted in this manner, as described above, almost no carboxyalkylation has occurred yet, so that the composite non-woven fabric is further added. By heating, carboxyalkylation and crosslinking reaction are carried out. In this case, it is necessary to prevent the water from evaporating during heating and to escape to the outside of the system, or even if the water escapes to the outside of the system, the proportion of water in the aqueous reaction solution should be maintained within the above range. is there. This operation is carried out by continuously passing a composite nonwoven fabric containing an aqueous reaction liquid in which the proportion of water is adjusted, through a heating device, or covering the whole with a water-impermeable sheet, and then sealing the batch. It can be easily carried out by heating so that the reaction temperature is maintained at 50 to 110 ° C. according to the formula.

When the reaction temperature is lower than 50 ° C., it takes a long time to complete the reaction. On the contrary, when the reaction temperature exceeds 110 ° C. and becomes high, the degree of substitution and water absorption performance of the resulting water absorbent nonwoven fabric are low. It is not suitable because the water-absorbent non-woven fabric itself is significantly yellowed. The heating may be performed from the outside of the composite non-woven fabric, but when the amount of the composite non-woven fabric is large, the temperature may naturally reach the above temperature range due to the heat of reaction of carboxyalkylation in the case of stacking. The object can be achieved only by leaving it under a closed condition or under an open condition. The reaction time cannot be determined regardless of the reaction temperature, but is in the range of 10 minutes to 4 hours. If the reaction time is less than 10 minutes, the reaction will not be completed sufficiently even if the temperature is raised, and if the reaction time is longer than 4 hours, the reaction will be completed, so it is meaningless to spend more reaction time. .

The pure water absorption of the pulp fibers in the composite nonwoven fabric to which the cross-linking bond and the carboxyalkyl group have been added as described above is mainly determined by the substitution degree of the carboxyalkyl group and the cross-linking density. The water absorption performance of the pulp fiber is theoretically higher as the substitution degree of the carboxyalkyl group is higher, but the substitution degree is practically 0.35 to 0.35.
A range of 0.8 is suitable. The upper limit of the degree of substitution that can be actually used is about 1.2, and even if the degree of substitution exceeds 1.2, the water absorption reaches almost saturation and is meaningless. And
A high degree of substitution exceeding 0.8 cannot be achieved unless the reaction using the aqueous reaction solution is repeated at least twice, which is economically disadvantageous. If the degree of substitution is less than 0.35, sufficient pure water is obtained. Water absorption cannot be obtained. The degree of substitution within the scope of the present invention described above is the total amount of the carboxyalkylating agent and the alkali metal hydroxide added to cellulose, the proportion of water in the aqueous reaction solution after evaporation of water, the reaction temperature, the reaction time, and the like. It is determined by the effect, and if necessary, these factors are appropriately selected, combined and adjusted to obtain a suitable degree of substitution.

On the other hand, the water absorption of pure water increases as the crosslink density decreases, but if it is too small, the gel strength upon water absorption is weak, and a water-soluble carboxyalkylcellulose salt remains, which causes stickiness. Absent. On the contrary, if the crosslink density is too high, the amount of water absorption decreases, so it is necessary to set the optimum crosslink density depending on the application. In the present invention, the crosslinking density is adjusted by adjusting the addition rate of the crosslinking agent.
The composite non-woven fabric which has completed the carboxyalkylation and the crosslinking reaction still contains a large amount of inorganic salts and decomposed products of the carboxyalkylating agent, and therefore it is necessary to remove them for purification, but any known method can be used. You may use. For example, a method of removing impurities by washing with a mixture of water and an organic solvent compatible with water such as lower aliphatic alcohols such as methanol, ethanol and isopropyl alcohol can be preferably used.

As described above, according to the present invention, an aliphatic polyester resin composed of glycol and an aliphatic dicarboxylic acid or its derivative, which has thermoplasticity and can be decomposed by microorganisms, is melt-spun to obtain a continuous length. After stacking a paper sheet made of pulp fiber on one side of a so-called spunbonded nonwoven fabric, which is made up of fiber filaments and collected as a web, a high-pressure water column flow is ejected from the paper sheet side toward the spunbonded nonwoven fabric side. After entangled pulp fibers and long fibers to form a composite non-woven fabric, the pulp fibers of this composite non-woven fabric contain and react an aqueous reaction liquid containing a carboxyalkylating agent, an alkali metal hydroxide, and a cross-linking agent, The pulp fiber has cross-linked carboxyalkyl groups, so it has excellent water absorption and water absorption rate, and it can be Soil, water containing activated sludge, can be completely decomposed by microorganisms in seawater, etc., disposable paper diapers, sanitary material fields such as sanitary products, soil water retention materials, agricultural material fields such as nursery sheets, food freshness retention materials, It can be used as a water-absorbent nonwoven fabric that can be widely used in the field of foods such as dehydrating materials, and also as medical materials such as building materials, dressings, and gauze.

[0031]

The present invention will be described in more detail with reference to the following examples, but of course the present invention is not limited thereto. In the examples and comparative examples,% means% by weight.

Example 1 An aliphatic polyester resin (trade name: Bionore, Showa High Polymer Co., Ltd.) having biodegradability was prepared using glycol and an aliphatic dicarboxylic acid derivative as constitutional units. The melting point of this resin was 114 ° C., and the melt flow rate at 190 ° C. was 30 g / 10 minutes. This resin was dried in a dryer before use, and the water content per unit weight was 0.
It was 02%. Next, melt this resin at 220 ° C.,
After extruding from a large number of fine holes, it was drawn by an ejector with high-speed air to form a continuous filament filament group, which was collected and deposited on a moving wire to form a web. The fineness of this long fiber was 2.4 denier. Then, this long-fiber deposit was introduced at a roll linear pressure of 40 kg / cm between a concavo-convex roll heated to 100 ° C. and a smooth roll, and the portion corresponding to the convex part of the concavo-convex roll was fused to give a basis weight of 12 g. A spunbonded nonwoven fabric of / m ² was obtained.
The area of each self-bonding area obtained was 0.12 mm ² , and the total area of the self-bonding areas was 4 per total area of the nonwoven fabric.
%Met.

On the surface of this spunbonded nonwoven fabric, a paper sheet obtained by wet papermaking using bleached softwood kraft pulp fibers was laminated. This paper sheet has a basis weight of 76 g / m.
² and the density was 0.52 g / cm ³ . Then, the paper sheet is placed on the upper side, the spunbond nonwoven fabric is placed on the lower side, and the sheet is placed on a transfer conveyor formed of wire mesh,
After forming the laminated body, while conveying the laminated body at a speed of 20 m / min, a nozzle hole having a hole diameter of 0.12 mm is 0.64 m.
A high-pressure water column flow is ejected at a water pressure of 40 kg / cm ² using a high-pressure water column flow ejection device arranged in a zigzag pattern at m intervals.
High-pressure water column flow treatment was applied from the surface of the paper sheet to the non-woven fabric side. As described above, the pulp fibers constituting the paper sheet and the long fibers constituting the spunbonded nonwoven fabric are entangled with each other to obtain a composite nonwoven fabric having a basis weight of 80 g / m ² integrated with each other. It was

This composite non-woven fabric was cut into a size of 20 cm × 30 cm (weight 4.8 g), which was cut with 8.38% sodium hydroxide and 24.40% sodium monochloroacetate.
Ethylene glycol diglycidyl ether 0.68%,
After soaking in an aqueous reaction solution consisting of 66.54% of water for 1 minute, taken out, sandwiched between filter papers and pressed, 2 g of aqueous reaction solution (carboxyalkylating agent / glucose residue (mol /Mole)=1.3). Then, the thermoelectric hot air dryer equipped with an exhaust facility was kept at 50 ° C., and while exhausting, the composite nonwoven fabric containing the aqueous reaction solution was put in this dryer for 5 minutes to evaporate water. The water content in the aqueous reaction solution contained in the composite nonwoven fabric was 42%. This composite non-woven fabric was placed in a polyethylene bag and placed in a dryer kept at 50 ° C. for 3 hours to carry out carboxymethylation and crosslinking of pulp fibers. Next, after the reaction, the composite nonwoven fabric was dipped in a 70% aqueous methanol solution, then taken out, sandwiched between filter papers and pressed to remove the aqueous methanol solution. This operation was repeated 4 times to thoroughly wash the composite non-woven fabric. Finally, this composite nonwoven fabric was immersed in a 100% methanol solution, taken out, sandwiched between filter papers, pressed, and air-dried to obtain a water-absorbent nonwoven fabric.

The degree of substitution of the resulting water-absorbent nonwoven fabric
The pure water absorption and microbial degradability were tested and their quality was evaluated. Test and evaluation method (1) Degree of substitution 1 g of a test sample was put in a flask and methanol-
50 ml of hydrochloric acid solution (mixed aqueous solution prepared by dissolving hydrogen chloride in 70% methanol aqueous solution to a concentration of 1 mol / l) was added, left for 1 hour, and thoroughly washed with methanol to completely remove hydrochloric acid. Removed and air dried. Then, the air-dried sample was placed in a 300-ml Erlenmeyer flask, 20 ml of 0.1N sodium hydroxide solution and 100 ml of pure water were added, and the mixture was slowly stirred for 1 hour, and then, the mixture was added to 0.
Phenolphthalein was titrated with a 1N hydrochloric acid solution as an indicator, and the substitution degree was calculated by the formulas (1) and (2). Y = 0.1A-0.1B ... (1) Substitution degree = 162Y / (1000W-80Y) ... (2) However, A: The amount of 0.1N sodium hydroxide solution (m
l) B: amount of 0.1 N hydrochloric acid (ml) Y: amount of carboxymethyl group (milliequivalent) W: weight of carboxymethyl cellulose (g)

(2) Absorption of pure water A test sample of 1 g was put in a size of 10 cm × 10 cm in 250
It is sealed in a mesh nylon net bag, and this is deionized through an ion-exchange resin to distill the water.
Immerse the sample for a minute to allow it to absorb water, then hang it up and hang it for 10 minutes to drain the water, and then weigh the sample to be tested, and measure the pure weight (g) absorbed per 1 g of the absolutely dried sample to be tested. It was defined as the amount of pure water absorbed. (3) Microbial degradability Three pieces of the obtained water-absorbent nonwoven fabric having a size of 10 cm × 30 cm were placed in the open soil of Tokyo Commodity Research Institute, Shinoji Paper Co., Ltd., 1-10-6 Shinonome, Koto-ku, Tokyo. It was embedded at a depth of 25 cm, and the morphological change of the water-absorbent nonwoven fabric after 6 months was visually observed and evaluated. The evaluation was performed in the following two stages. X ... Decomposition of the pulp fiber portion of the sheet was observed, but decomposition of the spunbonded nonwoven fabric portion was not observed. ◯: Degradation is recognized in both the pulp fiber portion and the spunbonded nonwoven fabric portion of the sheet.

Example 2 A composite non-woven fabric was allowed to contain an aqueous reaction solution, which was then dried in a drier 1
A water-absorbent nonwoven fabric was obtained in the same manner as in Example 1 except that the water was evaporated by heating for a minute to adjust the proportion of water in the aqueous reaction solution contained in the composite nonwoven fabric to 58%. ,
The quality was evaluated. Example 3 The composite non-woven fabric was allowed to contain an aqueous reaction solution, and then dried in a dryer.
A water-absorbent nonwoven fabric was obtained by performing the same operation as in Example 1 except that the water was evaporated by heating for a minute to adjust the ratio of water in the aqueous reaction liquid contained in the composite nonwoven fabric to 22%. ,
The quality was evaluated.

Comparative Example 1 Water contained after impregnating a composite nonwoven fabric with an aqueous reaction solution
Without changing the proportion of water in the sexual reaction solution, that is, the proportion of water
Same as Example 1 except 66.54%
Carboxymethylation of pulp fiber and crosslinking reaction
80g / m ^TwoOf water absorbent non-woven fabric and evaluate its quality
did. Comparative Example 2 A composite non-woven fabric was impregnated with an aqueous reaction solution and then dried with a drier.
Aqueous reaction liquid contained in the composite non-woven fabric by evaporating water for a minute
The water content of the aqueous reaction liquid
The paper was adjusted to 18% without changing the ratio.
Except for this, the basis weight is the same as in Example 1 except that the pulp fiber is
Carboxymethylation and cross-linking are performed, and the basis weight is 80 g /
m^TwoThe water-absorbent non-woven fabric was obtained and its quality was evaluated. Comparative Example 3 Polypropylene resin was melt-spun at 220 ° C. and self-fused
Set the temperature of the uneven roll and the smooth roll to set the area to 1
A water-absorbent nonwoven fabric was obtained in the same manner as in Example 1 except that the temperature was 40 ° C.
A cloth was obtained and its quality was evaluated.

The results obtained in Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 1.

[0040]

[Table 1]

As can be seen from Table 1, according to the present invention, it is possible to obtain a water-absorbent non-woven fabric having a degree of substitution in the range of 0.35 to 0.8 and having an excellent water absorption of pure water and excellent biodegradability (Example 1). ~
3). On the other hand, if the composite non-woven fabric contains an aqueous reaction solution for carboxyalkylation and crosslinking, and if the proportion of water in the reaction solution is not adjusted, a predetermined degree of substitution cannot be obtained, resulting As a result, the water absorption capacity of the water absorbent nonwoven fabric is small (Comparative Example 1). Further, when the water in the reaction liquid is excessively evaporated and the water content is less than a predetermined ratio, a water absorbent nonwoven fabric having a small water absorption amount is obtained (Comparative Example 2). If the spunbonded nonwoven fabric is composed of long fibers from the conventionally used polypropylene pyrene resin, the water absorption will be extremely excellent if the degree of substitution is increased, but only the pulp fiber portion is decomposed by microorganisms. However, since the polypropylene resin does not decompose the long fibers, it has no biodegradability and is not suitable for the purpose of the present invention (Comparative Example 3).

[0042]

INDUSTRIAL APPLICABILITY The present invention relates to the field of sanitary materials such as disposable paper diapers and sanitary products, the field of agricultural materials such as soil water retention materials, sheets for raising seedlings, the field of food products such as food freshness-retaining materials and dehydration materials,
Furthermore, it is effective in providing a water-absorbent nonwoven fabric having biodegradability, which can be widely used as a building material or the like.

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Claims (1)

[Claims] 1. An aliphatic polyester resin, which has thermoplasticity and can be decomposed by microorganisms and contains glycol and an aliphatic dicarboxylic acid or a derivative component thereof as constituent units, is melt-spun to collect a large number of long fiber filaments. After forming a web, the web is provided with regular and intermittent self-bonding areas, and a paper sheet made of pulp fiber is laminated on one surface of the spunbond nonwoven fabric. In a composite non-woven fabric in which a high pressure water column flow is penetrated toward the side, and pulp fibers and long fibers of the non-woven fabric are entangled and integrated, the pulp fibers have crosslinked carboxyalkyl groups. .