JP5067919B2 - Absorbent composite and method for producing the same - Google Patents

Description

  The present invention relates to an absorbent composite suitably used in the field of sanitary materials such as disposable diapers and sanitary napkins, and a method for producing the same.

As an absorbent used in the field of sanitary materials such as disposable diapers and sanitary napkins, an absorbent composite composed of a substrate and a water absorbent resin is known.
In recent years, demand for disposable diapers for elderly people has increased, and more water retention is required for absorbent composites. In addition, demands for thinner and lighter absorbent composites are increasing due to distribution / garbage problems.
In order to cope with these, in the absorbent composite, it has been studied to reduce the amount of the base material and increase the water-absorbent resin, but the amount of the base material is reduced to increase the water-absorbent resin. The body has a problem that a large amount of water-absorbing resin becomes a soft gel due to water absorption as compared with the base material, and so-called gel blocking causes a phenomenon of preventing liquid diffusion and lowers water retention.
As a means for preventing gel blocking, a method using two types of absorbent resins having different absorption performances (for example, see Patent Document 1), a composition comprising a cationic ion-exchange hydrogel-forming polymer and an anionic ion-exchange hydrogel-forming polymer (For example, refer to Patent Document 2), a method using an absorbent resin having a high surface crosslinking density (for example, refer to Patent Document 3), and a mixture of the absorbent resin and the thermoplastic resin is foam-extruded to form a sheet. Although a method (for example, refer to patent document 4) etc. is proposed, since gel blocking is prevented by using the absorptive resin which reduced absorption performance in any case, it is sufficient in terms of absorption performance. I can't say that.
Thus, in the absorbent composite, sufficient improvement in absorption performance and reduction in thickness and weight have not been realized.
JP 2001-252307 A International Publication No. 98/037149 Pamphlet Japanese Patent Laid-Open No. 06-057010 International Publication No. 01/64153 Pamphlet

  An object of the present invention is to provide a thin, lightweight, and highly absorbent absorbent composite that does not cause gel blocking even when the amount of the substrate is reduced and the water-absorbing resin is increased.

As a result of intensive studies to achieve the above-mentioned problems, the absorbent composite composed of the base material and the water-absorbent resin particles bonded to the base material is selected as a water-absorbent resin particle by a specific method. The present inventors have found that the above problems can be solved by using the large particles made at a specific ratio, and have reached the present invention.
That is, the present invention is as follows.
An absorbent composite composed of at least a base material and water-absorbing resin particles bonded to the base material, wherein 50% by weight or more of the water-absorbing resin particles cannot pass through a sieve having an opening of 500 μm. Some absorbent complex.

When the present inventors researched about gel blocking, it turned out that the cause is that water absorption resin swells by water absorption, and the space | gap part between resin becomes small, and as a result, the spreading | diffusion of a liquid is prevented. Therefore, it is considered that the gel blocking phenomenon can be prevented if the water-absorbing resin particles are arranged so as to reduce the contact between the particles and secure the particle gap. The present inventors have paid attention to the fact that when the same weight of the water-absorbing resin particles is supported on the substrate, the larger the particles, the lower the packing density of the water-absorbing resin particles, and the particle gap can be secured.
However, if large particles are selected using the particle size obtained by the usual measurement method, long particles and thin and flat particles may be included in the large particles, which can surely reduce the packing density. Can not. Therefore, in the present invention, large particles are selected by sieving.

According to the present invention, since the gap between the water-absorbent resin particles is ensured, even if the amount of the base material is reduced and the water-absorbent resin is increased, gel blocking does not occur, and the absorbency is thin, light, and has good absorption performance. A complex can be provided.
Moreover, since the particle | grain space | interval also becomes a channel | path for a liquid, a liquid can be rapidly sent to a base material and an absorption speed improves.
Furthermore, since the particle gap promotes the diffusion of the liquid in the lateral direction, the utilization efficiency of the absorbent composite can be increased, and the fit and wearing feeling can be improved.

The present invention is described in detail below.
In the present invention, a material including a base material and water absorbent resin particles bonded to the base material as a constituent element is referred to as an absorbent composite. At this time, the bonding form is not particularly limited, and the water-absorbing resin particles may be bonded to the surface of the base material, the water-absorbing resin particles may be entangled with the base material, or just mixed. The base material and the water-absorbing resin particles may be combined one by one or in combination.

  The ratio of the water absorbent resin to the total weight of the base material and the water absorbent resin is preferably 60% by weight or more, more preferably 70% by weight or more and 99% by weight or less, and still more preferably 80% by weight. It is 99 weight% or less.

If the proportion of the water-absorbent resin is too low, the amount of absorption as an absorber is reduced, which is not preferable. However, if the ratio of the water-absorbing resin is simply increased, contact between the water-absorbing resins at the time of water absorption increases and blocking occurs. When blocking occurs, the water absorption capacity and absorption speed of the water absorbent resin cannot be exhibited, so that the water absorption capacity and the absorption speed are reduced.
Therefore, in the conventional absorbent composite, it is difficult to increase the ratio of the water absorbent resin to the total weight of the base material and the water absorbent resin to 40% by weight or more. However, in the present invention, since the gap between the water-absorbing resin particles is secured using the large particles selected by a specific method, the ratio of the water-absorbing resin can be increased without causing blocking.

The size of the water absorbent resin particles will be described.
In the present invention, it is essential that 50% by weight or more of all water-absorbing resin particles cannot pass through a sieve having an opening of 500 μm. Preferably, the ratio of water-absorbing resin particles that cannot pass through a sieve having an opening of 600 μm is 50% by weight or more, and more preferably, the ratio of water-absorbing resin particles that cannot pass through a sieve having an opening of 710 μm is 50% by weight or more. More preferably, the ratio of the water-absorbent resin particles that cannot pass through a sieve having an opening of 850 μm is 50% by weight or more.
Further, the proportion of particles that cannot pass through a sieve having an opening of 500 μm is preferably 55% by weight or more, and more preferably 60% by weight or more. On the other hand, particles that cannot pass through a sieve having an opening of 1400 μm are preferably 50% by weight or less, and more preferably 30% by weight or less. Further, the particles that cannot pass through a sieve having an opening of 3000 μm are preferably 20% by weight or less, more preferably 10% by weight or less, and further preferably 5% by weight or less.
The weight ratio of the water-absorbent resin particles that cannot pass through the sieve having a specific opening is determined according to JIS standard K0069.

  In addition, when the particles are used alone, if the particle diameter is too large, the absorption rate is slowed down. However, this point is appropriately compensated by a composite effect such as using a fiber having a high absorption rate as a base material. Can do.

The weight average particle diameter of the water-absorbent resin particles is preferably 400 to 2000 μm, more preferably 450 to 1800 μm, still more preferably 500 to 1600 μm, and most preferably 600 to 1300 μm.
The average particle size is also determined by sieving according to JIS standard K0069. A sieve having an aperture of 106 μm, 212 μm, 300 μm, 425 μm, 500 μm, 600 μm, 710 μm, 850 μm, 1000 μm, 1180 μm, 1400 μm, 1700 μm, 2500 μm is used.

Furthermore, the particle size distribution of the water-absorbent resin particles preferably has two or more peaks.
The two peaks are preferably two times or more different in particle diameter, more preferably three times or more, and most preferably four times or more. If there is a difference in particle size, the gap between particles can be secured, but close to close packing can be achieved, and large and small particles have less contact when swollen and can exhibit each other's performance. .

The shape of the water-absorbing resin particles is not limited, and examples thereof include spherical powder, irregular powder, short fiber shape, long fiber shape, and sheet shape widely used in the absorbent composition.
A powder is preferable in terms of form stability after water absorption and water absorption speed.

Next, adhesion between the base material and the water-absorbent resin particles will be described.
If the water-absorbent resin particles are not fixed, the water-absorbent resin is biased in the absorbent composite, and it becomes easy to block. Therefore, in the absorbent composite of the present invention, the absorbent resin particles are bonded to the base material. And fix it. However, it is not necessary that all the water-absorbing resin particles are bonded to the substrate, and the water-absorbing resin particles that are not bonded may be included.
In the present invention, that the water-absorbent resin particles are bonded to the base material means that a treatment for bonding is performed in the manufacturing process of the absorbent composite, and as a result, some of the particles are bonded. This includes cases where there is no

There are no particular restrictions on the bonding method, bonding with an adhesive, bonding with a chemical bond between the substrate and the water-absorbing resin particles, bonding by physical interaction between the substrate and the water-absorbing resin particles, in the water-absorbing resin particles Adhesion in a form in which a part of the base material (fibers) enters is preferable, but it is preferable that the fibers are bonded in a form in which the fibers are taken into the water-absorbent resin particles.
The form in which the fibers are contained in the water-absorbent resin particles represents a state in which the fibers in the substrate are present in the water-absorbent resin matrix. The shape and length of the fibers that enter are not particularly limited. When bonded in this form, water can be taken into the water-absorbent resin through the fiber, so that excellent performance is exhibited in terms of absorption amount and absorption speed. It can be confirmed with an electron microscope whether or not the fibers are bonded in the form of entering the water-absorbent resin.

  On the other hand, it is preferable to avoid the use of an adhesive that remarkably impedes liquid flow from the fiber to the water absorbent resin on the adhesive surface between the water absorbent resin particles and the substrate. Inhibition of liquid flow from the fiber to the water-absorbent resin is caused by the presence of a large amount of hydrophobic components on the adhesive surface between the water-absorbent resin and the substrate. An amount of hydrophobic adhesive that does not significantly impede the flow of liquid from the fiber to the water-absorbent resin, or a hydrophilic adhesive that does not impede the flow of liquid may be used. Adhesives that may impede liquid permeability include hydrophobic thermoplastic polymers and hydrophobic emulsion binders. It is more preferable not to use a hydrophobic adhesive, and it is more preferable not to use a hydrophilic adhesive.

  A preferred bonding method is a method of dehydrating the substrate and the water-absorbing water-containing resin in contact with each other. Bonding by this method is preferable because it is not necessary to use an adhesive. Moreover, since adhesion | attachment is carried out by this method, since a part of fiber is taken in into a water absorbing resin, it is preferable at the point of an absorption speed or an absorptive power.

The water content of the water-absorbent resin particles is preferably performed by applying 10 to 3000 parts by weight of water to the water-absorbent resin and / or the substrate with respect to 100 parts by weight of the water-absorbent resin.
The larger the amount of water, the higher the adhesiveness and the better. However, if the amount is too high, drying takes too much time, which is inefficient.
The water to be hydrated may contain impurities. Examples of the impurities include cations such as sodium ion, ammonium ion and iron ion, anions such as chlorine ion, water-soluble organic compounds such as acetone, alcohols, ethers and amines. For adjusting the pH of the water-absorbent resin and / or the absorbent composite, an acidic or basic one may be used. From the viewpoint of the contact between the water-absorbent resin and the nonwoven fabric and the absorption capacity, it is preferable to use distilled water or ion-exchanged water free from these impurities alone.
In addition, it is a preferable method to impart a function to the absorbent composite produced by dissolving and / or dispersing a substance having a function such as deodorization in water. Examples of deodorants that can be used here include organic and inorganic deodorants. When using a deodorant insoluble in water, it is preferable to use a dispersant or a surfactant as necessary. In addition, inorganic deodorants can be dispersed in water without using a dispersant by reducing the particle size to the nano level. It is preferable to use without.
There is no restriction | limiting in particular in the water-containing method. For example, a method of attaching to a water bath, a method of spraying water, a method of contacting with a water-containing body, a method of exposing to a humidified state and the like can be mentioned. Of these, the water spray method, which is industrially simple and easily adjusts the water content, is a preferred method. In spraying water, it is preferable to adopt a method in which the moisture content of the substrate is uniform. If there is a large variation in the moisture content at each location in the substrate, the amount of water absorbed by the water-absorbent resin before the dehydration drying process after contacting the water-absorbent resin will vary depending on the location, which may lead to dehydration during the drying process. The accompanying foaming behavior is different, and the resin size in the absorbent composite after drying becomes heterogeneous. Absorbent composites in which resin particles having heterogeneous sizes are arranged may deteriorate the texture.

The contact between the water-absorbent resin particles and the substrate may be carried out after one or both of them are hydrated, or before that. If the water-absorbent resin particles contain water, they will easily stick to parts other than the base material, so the water-absorbent resin particles before contact are dried to the extent that there is no adhesion to other substances or adhesion between particles. It is preferable.
Examples of the contact method include a method in which water-absorbing resin particles are sprayed from above on a substrate, a method in which water-absorbing resin particles scraped with a drum are discharged and brought into contact with each other, and water-absorbing resin particles in a drum roll. And a method of discharging and contacting with pressure. A method in which the water-absorbent resin particles can be arranged so that they do not come into contact with each other when the water-absorbent resin particles swell is preferable because the performance of the water-absorbent resin is easily exhibited without waste.

Any method of dehydration may be used.
Specific examples include drying by heating, drying by heating gas circulation, methods of spraying dry air or nitrogen, vacuum drying, freeze drying, azeotropic dehydration, fluidized drying, microwave drying, etc., drying by heating, Drying by heating gas circulation is preferable. The heating condition is preferably 70 to 350 ° C. for 1 second to 1000 seconds, more preferably 100 to 340 ° C. for 1 second to 1000 seconds, and still more preferably 120 to 330 ° C. for 1 second to 1000 seconds. Most preferably, it is 150 to 300 ° C. for 1 to 1000 seconds. The higher the temperature, the shorter the drying time is. However, when the heating is performed for a long time at a high temperature, the absorption performance may be lowered depending on the type of the resin. Simultaneously with the drying, a surface treatment such as surface crosslinking may be performed.
The dehydration may be performed at any time until the final product is obtained, but it is preferable to perform the dehydration promptly after hydration from the viewpoint of deterioration of the water absorbent resin.

  The arrangement of the bonded water-absorbing resin particles is not particularly limited, and the water-absorbing resin particles may be bonded to only one side of the substrate or may be bonded to both sides of the substrate. Adhering to both sides is preferable because the amount of absorption per area increases.

Moreover, it is preferable to arrange | position so that a resin area filling rate may be 3-90 (%), More preferably, it is 5-80, More preferably, it is 7-70, Most preferably, it is 9-60. If the area filling rate is too high, the water-absorbent resins come into contact with each other when the water-absorbent resin swells, and blocking is likely to occur. Moreover, when the resin area filling rate is too low, the amount of absorption per area in the composite absorbent body is reduced, which is not preferable.
The resin area filling factor is an index representing the ease with which particles contact each other when the water-absorbing resin absorbs the liquid.
The resin area filling factor is measured as follows.
The photograph of the surface of a composite_body | complex is measured with an optical microscope or an electron microscope. At this time, the measurement condition and the magnification are selected so that the water-absorbent resin and the substrate can be distinguished, and a photograph can be taken with 10 or more water-absorbent resin particles in one photograph. The photograph is enlarged and copied, and the area of the water-absorbent resin particle portion is measured and calculated according to the following formula. 5 or more arbitrary points in the absorber are photographed, and the average value is defined as the area filling rate. In the case where the water-absorbent resin is adhered to both surfaces of the substrate, the measurement is performed separately on each surface.
Resin area filling rate (%) = area of water-absorbing resin particle portion / weight of entire photographing location × 100

Next, the base material will be described.
In the present invention, the base material refers to a material that can maintain a sheet shape.
The material of the substrate may be any material as long as it is in sheet form, but is preferably paper or cloth.
Paper refers to paper in a broad sense defined by JIS standard P0001, and cloth is a general term for sheet-like fiber products defined by JIS standard L0206. The cloth is classified into a woven fabric, a knitted fabric, a braided fabric, a lace, a net, and a non-woven fabric according to the means for forming the sheet. The fabric used in the present invention is preferably a woven fabric, a knitted fabric, or a non-woven fabric, and most preferably a non-woven fabric. Paper and / or cloth is preferable because it has excellent shape stability unlike short fibers such as pulp. Nonwoven fabric is defined by JISL0222.

The shape of the substrate is not particularly limited.
The thickness is preferably 0.001 mm to 1 cm, more preferably 0.01 mm to 5 mm, still more preferably 0.05 mm to 3 mm, and most preferably 0.1 mm to 1 mm.
Weight is preferably ^{0.1g / m 2 ~1kg / m 2} , more preferably from ^{0.5g / m 2 ~500kg / m 2} , more preferably ^{1g / m 2 ~100g / m 2} . Those that are too thin or light are not preferred from the standpoint of strength.

The tensile strength at break of the substrate after physiological saline is preferably 0.6 to 5000 N / 20 mm, more preferably 0.7 to 500 N / 20 mm, and further preferably 0.85 to 100 N / 20 mm. It is preferably 1 to 100 N / 20 mm.
The tensile strength at break after absorption of physiological saline means the tensile strength at break after absorption of physiological saline by the base material.
In sanitary materials, they may be used as they are without being replaced immediately after liquid absorption. Moreover, after liquid absorption, liquid absorption over several times may be calculated | required. If the use is continued after absorbing once, a load is applied in a state where moisture exists in the absorber. If the substrate breaks due to the load, the liquid permeability and liquid diffusibility are lowered, and the performance of the absorber is deteriorated. Therefore, it can be said that a base material that maintains high strength even after absorption of physiological saline is preferable in terms of durability of the absorbent body. Further, in the case of a production process in which the base material contains water, there may be a problem if the strength at the time of water inclusion is low, and it can be said that the higher the strength of the base material, the better. However, the strength may be a certain level or higher, and even if the strength is higher than that, there is substantially no difference in performance.

The tensile strength at break after absorption of physiological saline by the substrate is determined as follows.
Sample: 15 cm × 2 cm rectangular base material (preparing several types by changing direction)
Equipment: Tensile tester (Shimadzu autograph)
Method: 700 g of 0.9% saline is taken in a 1 L beaker and the substrate is immersed for 10 minutes. The substrate is pulled up, left on a Kim towel for 1 minute, and a portion of 2.5 cm is set from both ends so that the distance is 10 cm, and the substrate is pulled until it breaks at a speed of 10 mm / min. The force at this time is recorded, and the maximum value is the strength N / 20 mm. If there is a direction, change the direction and make several points, and use the lowest value as the strength.

  The ratio of the tensile breaking elongation in the machine direction and the transverse direction of the substrate is 1: 1.2 to 1:10, and the tensile breaking strength ratio in the machine direction and the transverse direction is 1.2: 1 to 10: 1. Is preferred.

There are no particular limitations on the raw material of the substrate, and a plurality of combinations of substrates may be used, but it is preferable that fibers are included. The fiber may be a natural fiber or a synthetic fiber, and may be a combination of a plurality of fibers. The length of the fiber may be either a short fiber or a long fiber, but a continuous long fiber is more preferable than a short fiber because it has better liquid permeability.
Treatment may be performed for strengthening or imparting hydrophilicity.
Hydrophilic materials are more preferable than hydrophobic materials because they are superior in liquid absorption and water permeability. Of the hydrophilic substrates, cellulose-based substrates are particularly preferable. The cellulosic substrate in the present invention refers to a cloth or paper made mainly of cellulose. The proportion of cellulose in the substrate is preferably 50% or more, more preferably 70% or more, further preferably 90% or more, and most preferably 99% or more. Cellulose may be derivatized by treatment such as esterification or etherification. Moreover, what mixed other fiber may be used. Examples of cellulose include natural fibers such as cotton and hemp, and regenerated fibers such as rayon, polynosic, lyocell, and cupra. Recycled fibers are preferred as the fibers.

The substrate absorption rate is preferably 2 g / g or more and 200 g / g or less, more preferably 4 g / g or more and 100 g / g or less, still more preferably 8 g / g or more and 50 g / g or less, and most preferably It is 12 g / g or more and 30 g / g. In the absorbent composite, the base material absorbs faster than the water-absorbent resin, so that the base material absorbs at the initial stage of absorption and the water-absorbent resin absorbs at the later stage. Therefore, the higher the absorption ratio of the base material, the faster the initial liquid absorption rate, which is preferable. Usually, the absorption of the base material is due to capillary action, and when the load is applied, the liquid may return or may cause stuffiness during use, but in the absorbent composite of the present invention, Since the water-absorbent resin particles are adhered to the base material, the water-absorbent resin absorbs the liquid from the base material. For this reason, it is unlikely that the liquid will return due to the load or stuffy during use.
The absorption rate of the base material is a value obtained by measuring how many times the base material absorbs 0.9% physiological saline in 60 minutes and becomes a weight, and is expressed by the following formula.
Absorption capacity of substrate (g / g) = weight after absorption (g) / weight before absorption (g)
Specifically, the measurement is performed by the following method.
The substrate is cut into a circle having a diameter of 59.5 mm, and the weight is recorded. Then, a wire is passed through the circumferential portion at a distance of 1 cm. 500 g or more of 23 ° C. physiological saline is prepared in a 1 L beaker, and the substrate is dipped in the physiological saline together with the wire. After 60 minutes, the substrate together with the wire is taken out from the physiological saline and suspended for 10 minutes so that the substrate does not come into contact with the other. Ten minutes later, the wire is removed and the total weight of the water-containing base material and the attached water is measured.

The absorption rate of the substrate is preferably 0.35 mg / second or more and 100 mg / second or less, more preferably 0.45 mg / second or more and 50 mg / second or less, further preferably 0.55 mg / second or more and 30 mg / second or less, Most preferably, it is 0.65 mg / second or more and 10 mg / second or less.
The absorption rate of the substrate represents the rate at which the substrate having a width of 2 cm absorbs 0.9% physiological saline in the vertical direction.
Specifically, the measurement is performed as follows.
Sample: 10 cm x 2 cm rectangular base material (If there are vertical and horizontal directions, change the direction and prepare two or more points)
Apparatus: Electronic balance, petri dish with a diameter of 90 mm Method: Place a petri dish on the electronic balance, and suspend the substrate vertically from 10 cm above the petri dish. The petri dish is taken from the electronic balance, and 60 g of 0.9% physiological saline is weighed with another balance. Hold the lower part of the base material by hand and place the petri dish again on the electronic balance so as not to touch the physiological saline, and set the value of the balance to 0 point. The substrate is gently soaked in physiological saline, and the value of the electronic balance is recorded over time. The time (second) and the absolute value (mg) of the value of the electronic balance are plotted on a graph, and the slope (mg / second) between 120 seconds and 240 seconds is taken as the absorption rate. If there are directions with different absorption speeds, change the direction and measure several points, and use the earliest value as the absorption speed. In the case of a material that absorbs water up to 10 cm or more before 240 seconds, the length may be measured at 10 cm or more.

The suction speed of the substrate is preferably 0.001 cm / second or more, more preferably 0.002 cm / second or more, still more preferably 0.003 cm / second or more, and 0.004 cm / second. The above is most preferable. The higher the suction speed of the base material, the better the diffusing capacity, so that the utilization efficiency of the absorbent composite can be increased.
The suction speed of the substrate is the speed at which suction is performed in the vertical direction per unit time.
It can calculate using the following formula | equation 1 from the absorption rate of a base material, the water absorption magnification of a base material, and a fabric weight.
(Formula 1)

The initial suction speed of the substrate is preferably 1 cm or more, more preferably 2 cm or more, further preferably 4 cm or more, and most preferably 6 cm or more.
The initial suction speed represents the height rising from the water surface after 1 minute when the base material is vertically immersed in physiological saline. When the absorption speed and diffusivity are particularly strongly required, the initial suction speed is important.
Specifically, it can be calculated from the value after 1 minute at the time of absorption rate measurement using the following formula 2.
(Formula 2)

It is preferable that the substrate has directions with different absorption rates.
If there are directions with different absorption rates in the base material, the liquid permeability in a specific direction is excellent and the liquid is easily diffused in the specific direction, so that the balance of absorption in the absorber can be controlled. In particular, when used for sanitary materials such as paper diapers, urine pads, sanitary products, etc., the absorbent body often has a shape having a longitudinal direction and a transverse direction, and can be diffused preferentially in the longitudinal direction. It is preferable because the utilization efficiency of the absorber is increased and leakage from the side is less likely to occur.

The strength ratio between the longitudinal direction and the lateral direction of the substrate is preferably 1.2 times or more, more preferably 1.5 times or more, and most preferably 2 times or more.
The ratio of the longitudinal and lateral elongation of the substrate is preferably 1.2 times or more, more preferably 1.5 times or more, and most preferably 2 times or more.
In the present invention, the direction having the maximum intensity is defined as the longitudinal direction, and the direction perpendicular thereto is defined as the lateral direction.
The elongation and strength of the base material can be determined by conducting a tensile test in a dry state without being immersed in physiological saline in the same manner as the strength of the base material after absorption of physiological saline. The tensile test is performed until the base material breaks, and the force at the maximum strength is defined as the strength of the base material, and the distance stretched at that time is defined as the elongation.

The contact angle of the substrate is preferably 130 degrees or less, more preferably 120 degrees or less, still more preferably 110 degrees or less, and most preferably 100 degrees or less.
The smaller the contact angle, the better the affinity between the substrate and the liquid, which is preferable in that the liquid can be quickly diffused and absorbed. Moreover, when the contact angle is small, the affinity between the base material and the water-absorbing resin is increased, which is preferable in terms of absorbability and adhesiveness.
The contact angle is defined as an angle formed after 10 seconds of contact of a 44% ammonium polyacrylate aqueous solution having a viscosity of 74 cp at 25 ° C. with the substrate.
The measurement is performed using a contact angle meter (CA-X150 type) manufactured by FACE (Kyowa Interface Science Co., Ltd.). The liquid is a Wako Pure Chemicals 44% ammonium polyacrylate aqueous solution (70 to 110 cp), which is used after adjusting the viscosity with water. Viscosity is measured using a rotating disk viscometer.

Next, the water absorbent resin constituting the water absorbent resin particles will be described.
There is no limitation on the type of water-absorbing resin, and any water-absorbing resin may be used.
The side chain preferably has an acid group, and more preferably a resin having a side chain having a carboxylic acid group.
Further, 50% or more of the acid groups are preferably neutralized in the form of a salt, and more preferably 50% of the acid groups are neutralized in the form of an ammonium salt.
A water-absorbent resin having an acid group in the side chain is preferable because an electrostatic repulsion between acid groups occurs during liquid absorption and the absorption rate is increased. It is preferable that the acid group is neutralized because the liquid is absorbed into the water-absorbent resin by osmotic pressure. When neutralized in the form of an ammonium salt, the ammonium salt is preferable because of its high affinity for water and an increased amount of absorption.

Monomers constituting the water-absorbing resin include (meth) acrylic acid, ethacrylic acid, itaconic acid, maleic acid, crotonic acid, fumaric acid, sorbic acid, cinnamic acid, their anhydrides, and unsaturated carboxylic acids. Although the neutralized salt of a monomer is mentioned, The neutralized salt of (meth) acrylic acid is preferable. The type of the neutralized salt is preferably an alkali metal salt such as lithium, sodium or potassium, or a nitrogen-containing basic substance such as ammonia.
Other monomers may be copolymerized, and unsaturated monomers that may be copolymerized include (meth) acrylic acid, ethacrylic acid, itaconic acid, maleic acid, crotonic acid, sorbic acid, cinnamic acid, Their anhydrides, vinyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, vinyl toluene sulfonic acid, 2- (meth) acrylamide-2-methylpropane sulfonic acid, 2- (meth) acryloylethane sulfonic acid, 2- ( Anionic unsaturated monomers such as (meth) acryloylpropane sulfonic acid, 2-hydroxylethylacryloyl phosphate, 2-hydroxylethyl methacryloyl phosphate, phenyl-2-acryloyloxyethyl phosphate, vinyl phosphate and salts thereof; acrylamide , Methacrylamide, N-ethyl (Meth) acrylamide, Nn-propyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, Nonionic hydrophilic group-containing unsaturated monomers such as methoxypolyethylene glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate, N-vinylpyrrolidone, N-acryloylpipediline, N-acryloylpyrrolidine; You may use the hydrophilic monomer which forms a water absorbing resin by hydrolysis of the functional group after superposition | polymerization like meth) acrylate, ethyl (meth) acrylate, vinyl acetate.
Examples of the hydrophobic monomer that can be used in combination include styrene, vinyl chloride, butadiene, isobutene, ethylene, propylene, stearyl (meth) acrylate, lauryl (meth) acrylate, and the like. More than one type can be added.

A crosslinking agent may be allowed to coexist in the monomer. As a crosslinking method, a method in which a condensation type crosslinking agent is used to react with a functional group in the resin to crosslink, a polymerizable crosslinking agent is used. Examples include a method of crosslinking by copolymerizing with an unsaturated monomer, a method of crosslinking by irradiating the resin with an electron beam or radiation, etc., preferably a method using condensation type crosslinking, most preferably a functional group of the resin. This is a method in which a polymerizable crosslinking agent and an unsaturated monomer are copolymerized in the presence of a condensation type crosslinking agent that reacts with.
As the condensation type crosslinking agent, ethylene glycol diglycidyl ether, trimethylolpropane triglycidyl ether, (poly) glycerin polyglycidyl ether, diglycerin polyglycidyl ether, glycidyl ether compounds such as propylene glycol diglycidyl ether; (poly) glycerin, (Poly) ethylene glycol, propylene glycol, 1,3-propanediol, polyoxyethylene glycol, triethylene glycol, tetraethylene glycol, diethanolamine, triethanolamine and other polyhydric alcohols; ethylenediamine, diethylenediamine, polyethyleneimine, hexa Multivalent amines such as methylenediamine; Multivalent ions such as zinc, calcium, magnesium, and aluminum Which may be used those crosslinking agents of two or more.
Examples of the polymerizable crosslinking agent include diethylene glycol diacrylate, N, N′-methylenebisacrylamide, polyethylene glycol diacrylate, polypropylene glycol diacrylate, trimethylolpropane diallyl ether, allyl glycidyl ether, pentaerythritol triallyl ether, and pentaerythritol diester. Examples include acrylate monostearate, bisphenol diacrylate, isocyanuric acid diacrylate, tetraallyloxyethane, diallyloxyacetate, and the like. Two or more of these crosslinking agents may be used.

  The solvent of the monomer solution at the time of synthesizing the water absorbent resin is not particularly limited as long as it has excellent solubility. Particularly preferred is water alone, but hydrophilic solvents such as ethanol, methanol, acetone and the like may be used alone or in combination. If necessary, salts such as sodium chloride, basic compounds such as ammonia for pH control, and a suspending agent may be added in the case of reverse phase suspension polymerization.

The polymerization method of the monomer at the time of synthesizing the water-absorbent resin is not particularly limited, and (water) solution polymerization, reverse layer suspension polymerization, reverse phase emulsion polymerization, spray polymerization, belt polymerization and the like are widely used. Is applicable. The polymerization initiation method is not particularly limited, and polymerization with a radical polymerization initiator, polymerization by irradiation with radiation, electron beam, or ultraviolet polymerization with a photosensitizer can be performed. Examples of the initiator used for such radical polymerization include persulfates such as potassium persulfate, ammonium persulfate and sodium persulfate; hydrogen peroxide; organics such as cumene hydroperoxide, t-butyl hydroperoxide and peracetic acid. Examples thereof include known initiators such as oxide oxides. When an oxidizing radical polymerization initiator is used, a reducing agent such as L-ascorbic acid or Rongalite may be used in combination.
It is preferable to perform a deoxygenation operation in the monomer solution in advance before the start of polymerization. As a specific method, there is a method of removing dissolved oxygen by bubbling with an inert gas for a sufficient time.
In addition, it is preferable that the atmosphere in the reactor is replaced with an inert gas such as nitrogen or helium. The inside of the reactor may be any of reduced pressure, normal pressure, and increased pressure.
The polymerization initiation temperature is usually preferably in the range of 0 to 70 ° C. More preferably, it is the range of 10-40 degreeC. If the starting temperature is too high, polymerization by heat occurs before the initiator is added, which is not preferable. On the other hand, if the starting temperature is too low, it takes too much time to start the reaction, which is not preferable. The temperature in the reactor during the reaction may depend on the outcome, and the temperature may be controlled by cooling or heating from the outside. The temperature rising rate and the maximum temperature during the polymerization are not particularly problematic, and there is no problem even if the maximum temperature exceeds 100 ° C. The maximum temperature during polymerization is usually 20 to 140 ° C, preferably 40 ° C to 120 ° C.
The concentration of the monomer solution is preferably 10 to 70%, and most preferably 30 to 50%. If the concentration is too high, the reaction tends to run away, which is not preferable. If the concentration is too low, it takes too much time for the reaction, and the subsequent drying process is also burdened, which is not preferable.
The polymerization time is preferably set in the vicinity of the time when heat generation from the reaction solution stops. Since there are heating processes such as a drying process and a post-crosslinking process as post-processes after the polymerization, the polymerization may be terminated before the heat generation from the reaction solution stops. Further, after completion of heat generation, it may be heated and kept for several hours.
When the polymer obtained after the polymerization is a hydrogel, it is preferable to perform drying. Although this drying method is not particularly limited, for example, azeotropic dehydration, fluidized drying, hot air drying, vacuum drying and the like are preferably used, and hot air drying and vacuum drying are particularly preferable. Dry to a moisture content of 30% by weight or less, preferably 10% by weight or less. Drying may be performed with any form of hydrogel, but it is preferable to dry after coarsely crushing to increase the surface area. The drying temperature is preferably in the range of 70 ° C to 180 ° C, particularly preferably 100 to 140 ° C.
The particle size of the polymer after drying is adjusted by operations such as pulverization and classification as required.

For water-absorbent resins, deodorants, fragrances, various inorganic powders, foaming agents, pigments, dyes, antibacterial agents, hydrophilic short fibers, plasticizers, adhesives, surfactants, fertilizers, oxidizing agents, A reducing agent, a chelating agent, an antioxidant, a heat stabilizer, an ultraviolet absorber, a light stabilizer, water, salts and the like may be added.
Examples of the inorganic powder include fine particles of various inorganic compounds that are inert to water and hydrophilic organic solvents, fine particles of clay mineral, and the like. In particular, the inorganic powder preferably has an appropriate affinity for water and is insoluble or hardly soluble in water, such as metal oxides such as silicon dioxide and titanium oxide, natural zeolite, synthetic zeolite, etc. Silicic acid (salt), kaolin, talc, clay, bentonite and the like.
The usage-amount of the said inorganic powder is 0.001-10 weight part normally with respect to 100 weight part of water absorbing resin, Preferably it is 0.01-5 weight part. There is no restriction | limiting in particular in the mixing method of water absorbing resin and inorganic powder, It carries out by the dry blend method, the wet mixing method, etc.

The water-absorbent resin is preferably polymerized until the residual monomer amount is 1% by weight or less.
When there are many residual monomers, the elution from an absorber will increase and it is unpreferable in performance. Residual monomer can also be reduced by heat treatment at the time of manufacturing or after completion of the absorbent composite to complete the polymerization, but the water-absorbent resin as the starting material has been polymerized to a residual monomer content of 10% by weight or less. Is preferred. A large amount of residual monomer in the starting material is not preferable because it is difficult to complete polymerization on the substrate and a large amount of residual monomer tends to remain in the end.
The amount of the residual monomer is filtered after adding a water-absorbing resin cut to a size of 2 to 3 mm or less to 0.9% physiological saline, which is 250 times the weight of the resin, and stirring for about 6 hours. The filtrate is quantified using a liquid chromatography method.

Specific examples of the water-absorbing resin include a crosslinked polyacrylic acid partially neutralized product (for example, see JP-A-55-84304) and a hydrolyzate of starch-acrylonitrile graft polymer (for example, JP-B-49-43395). ), Neutralized product of starch-acrylic acid graft polymer (for example, see JP-A-51-125468), saponified product of vinyl acetate-acrylic acid ester copolymer (for example, see JP-A-52-14689) ), Hydrolyzate of acrylonitrile copolymer or acrylamide copolymer (for example, see JP-B-53-15959), polyglutamate (for example, see JP-A-2003-192794), and so on.
From the viewpoint of absorption performance, cost, etc., a polyacrylic acid partial neutralized product crosslinked product that is usually used for hygiene materials is preferred.

Below, the polyacrylic acid partial neutralized material crosslinked body is demonstrated.
In the crosslinked polyacrylic acid partially neutralized product, preferably 50 mol% or more of the repeating units in the polymer molecular chain are carboxyl group-containing units. More preferably, it is 80 mol% or more, and most preferably 90 mol% or more. When the number of carboxyl group-containing units among the repeating units is small, it is not preferable because a decrease in absorption performance is observed.
The carboxyl group in the polymer molecular chain is preferably partially neutralized, and examples of the salt include alkali metals such as sodium, potassium and lithium, and nitrogen-containing basic substances such as ammonia. 50% or more of the carboxyl groups are preferably neutralized, and more preferably 70% or more are neutralized.
As a kind of salt, it is preferable to be partially neutralized with at least one kind including ammonia, and most preferably partially neutralized with ammonia alone.
From the viewpoint of absorption performance, 50 mol% or more of the carboxyl group neutralized salts in the polymer molecular chain are preferably ammonium salts, more preferably 70 mol% or more, still more preferably 90 mol% or more, and most preferably all ammonium salts. Neutralized with A high proportion of the ammonium salt is preferable in terms of absorption capacity and adhesion to the substrate.
In addition, the ratio of the ammonium salt in a water absorbing resin can be calculated by calculating | requiring the total amount of nitrogen atoms in a water absorbing resin. The total amount of nitrogen atoms in the water absorbent resin can be determined by the Kjeldahl method.

The crosslinked polyacrylic acid partially neutralized product may be heated after drying controlled to a predetermined particle size. In the heat treatment, it is preferable that a compound having two or more functional groups capable of reacting with the carboxyl group to be used coexists. A compound having two or more functional groups capable of reacting with a carboxyl group may be added before polymerization, or may be added to particles before heat treatment. When put before heat processing, it is preferable to dissolve in hydrophilic solvents, such as water, alcohols, and ethers, and to spread on the surface. Although the temperature of heat processing is not specifically limited, Preferably it is the range of 120-250 degreeC. Preferably it is 150-240 degreeC, More preferably, it is 170-230 degreeC. The heat treatment may be performed continuously in the same apparatus after completion of drying, or may be a step independent of the drying step.
For the above heat treatment, a normal dryer or a heating furnace can be used. For example, a groove type mixer / dryer, a rotary dryer, a disk dryer, a fluidized bed dryer, an airflow dryer, an infrared dryer, etc. Can be mentioned.

Next, other physical properties of the water absorbent resin particles will be described.
The surface salt concentration of the water-absorbent resin particles before adhering to the substrate is preferably 50 mol% or more, more preferably 60 mol% or more, further preferably 70 mol%, and most preferably 80 mol% or more. If the surface salt concentration before adhering onto the substrate is too low, the adhesion of the particles will be reduced.

The surface salt concentration of the water-absorbent resin portion in the composite after final adhesion to the substrate is not particularly limited, but is preferably 90 mol% or less, more preferably 80 mol% or less, and most preferably 60 mol%. It is as follows. A lower surface salt concentration of the water-absorbent resin in the final composite is advantageous because it hardly causes stickiness even when exposed to moist air.
The surface salt concentration refers to the proportion of neutralized groups in the surface portion of the water absorbent resin.
The surface salt concentration can be determined by measuring by a microscopic ATR method which is one of infrared absorption analysis methods. The neutralization rate of the resin surface can be directly measured by the microscopic ATR method. The internal portion is measured by a micro ATR method after cleaving the resin by using an ultramicrotome (ULTRACUT N manufactured by Reichert) to expose the central portion. As a measuring device, FTS-575 manufactured by Bio-Rad is used.
Hereinafter, the method for measuring the surface salt concentration will be specifically described with reference to a polyacrylic acid water-absorbing resin as an example. As an indicator for defining the composition ratio of carboxylic acid and carboxylate, 1,695 cm ^-1 (carboxylate νC = 0 Baseline 1774~1616cm ^-1) and 1558cm ^{-1 -} peak of (carboxylate νCOO baseline 1616~1500cm ^-1) An area ratio (1695/1558 cm ⁻¹ ) was calculated, and separately prepared by measuring and preparing 10 mol%, 30 mol%, 50 mol%, 70 mol%, 90 mol%, 100 mol% partially neutralized polyacrylic acid neutralized with ammonia as a standard sample The composition ratio is obtained from the line.

The surface strength of the water-absorbent resin particles is preferably 0.1 to 5.5N, more preferably 0.1 to 5N, still more preferably 0.2 to 4N, and most preferably 0.2 to 3N. .
The surface strength is a parameter representing the ease of deformation of the particle surface.
A high surface strength indicates that the water-absorbent resin particles are not easily deformed. The fact that it is difficult to deform means that the water-absorbing resin absorbs and swells, whereas the negative force is strong, and consequently the absorption capacity is lowered. Further, if the surface is not easily deformed, it is not preferable because the adhesion surface becomes small and particles are likely to be detached from the composite.
The surface strength is obtained as follows.
Equipment: Shimadzu Autograph AG-1
Sample: 0.10 g of water-absorbing resin particles are precisely weighed, and uniformly placed in the bottom of a cylindrical container having an inner diameter of 20.5 mm and a height of 50 mm, with a nylon sheet having a pore size of 75 μm attached to the bottom surface. A 50φ petri dish is prepared, 0.90 g of physiological saline is added, and the cylindrical container containing the water-absorbent resin particles is allowed to stand, and is absorbed and swollen for 1 hour.
Measurement: A 1 kN load cell was used, and a cylindrical shaft having a diameter of 19.7 mm was attached. The measurement range is set to 0.2 kN, and is set so that the load cell is lowered at a constant speed of 0.6 mm / min according to the height at which no load is applied to the load cell. The pressure applied to the load cell is recorded over time, and the load (N) at the time when the actual volume is reached is defined as the surface strength. The actual volume of the water-absorbent resin is calculated using the following formula using the specific gravity of physiological saline 1.010 g / cm ³ and the specific gravity of the water-absorbent resin.
Actual volume (cm ³ )
= 0.1 / specific gravity of resin (g / cm ³ ) + 0.9 / specific gravity of physiological saline (g / cm ³ )

The absorption capacity of the water absorbent resin particles without pressure is preferably 55 g / g or more. More preferably, it is 60 g / g or more, and 70 g / g or more is the most preferable.
A higher absorption capacity of the water absorbent resin is preferable because the amount of the water absorbent resin to be used can be reduced.
The non-pressurized absorption rate is an amount capable of freely swelling and absorbing 0.9% physiological saline in a state where no load is applied to the water absorbent resin.
The non-pressure absorption capacity of the water absorbent resin is measured by the following method.
The weight of a non-woven tea bag-type bag (60 × 40 mm) is measured, 0.05 g of water-absorbing resin particles are uniformly placed, and immersed in 0.9% physiological saline at 23 ° C. After 180 minutes, the bag is taken out, the corner of the tea bag is fixed, suspended for 10 minutes in an oblique state, drained, and then weighed. The same operation is performed without using the water absorbent resin, the weight is measured, and the water absorption ratio of the tea bag is obtained. Absorption capacity is calculated according to the following formula. The measurement is performed three times, and the average value is defined as the non-pressurized absorption ratio (1).
Non-pressure absorption capacity (g / g) of water-absorbent resin particles
= {(Weight of tea bag after absorption)-(weight of tea bag before absorption x water absorption ratio of blank tea bag)} / (weight of water absorbent resin particles)

The absorption capacity under pressure at 0.8 psi of the water-absorbent resin particles is preferably 20 g / g or more, more preferably 25 g / g or more, and most preferably 30 g / g or more.
The absorption capacity under pressure is measured by the following method.
Put 0.02 g of water-absorbing resin particles in an acrylic resin cylinder with an inner diameter of 25 mm, a height of 30 mm, and a 250 mesh nylon nonwoven fabric at the bottom, and put a smoothly moving cylinder inside the cylinder to make a measuring device and measure the weight. To do. A load of 278.33 g corresponding to 0.8 psi is placed on the upper part of the cylinder of the measuring device to obtain a load, which is placed in a petri dish with an inner diameter of 120 mm containing 60 g of 0.9% physiological saline. It is taken out after 60 minutes, left on a Kim towel for 3 seconds, drained, the weight of the device after removing the load is measured, and the absorption capacity under pressure is calculated according to the following formula.
Absorption capacity under pressure of water-absorbent resin particles (g / g) = (weight of device after absorption (g) −weight of device before absorption (g)) / (weight of water-absorbent resin particles)

  Tensile strength at break composed of water-absorbing resin particles having an absorption ratio of 70 g / g or more under no pressure and an absorption ratio of 20 g / g or more under 0.8 psi pressure is 0.6 (N / 20 mm) or more. Absorbent composites are preferable for sanitary materials such as paper diapers because they exhibit excellent absorption characteristics both under pressure and without pressure. At this time, the absorbent composite is preferably composed of water-absorbent resin particles and paper or cloth, and more preferably, the water-absorbent resin particles are separated so that the water-absorbent resins are not blocked.

In addition, 70% or more of the water-absorbent resin particles having a non-pressurized absorption ratio of 70 g / g or more and an absorption ratio of 20 g / g or more under a 0.8 psi load is acrylic acid, and 50% of the carboxyl groups. % Or more is neutralized as an ammonium salt, and it can be obtained by polymerizing unsaturated carboxylic acid monomers having a total of 70% or more neutralized. At this time, a monomer containing 0.01 to 0.1 mol% of a compound having two or more unsaturated groups in one molecule serving as a crosslinking agent is used. You may use 0.1-3 weight part of compounds which have two or more functional groups which can react a carboxyl group before superposition | polymerization or in any process after superposition | polymerization. Radical polymerization is performed using a redox initiator, and 0.01 to 0.5 mol% is used as the radical polymerization initiator with respect to the amount of the unsaturated monomer. A reducing agent shall be 0.0001-1g with respect to 1 mol of monomers. If necessary, heating is performed under heating conditions that satisfy the following formula. This heating is preferably performed at the same time as the production of the absorbent composite rather than the water absorbent resin alone.
Y ≦ −1.6X + 345
Where Y is the heating time (minutes) and X is the heating temperature (° C.)

Next, an example of the manufacturing method of an absorptive composite is demonstrated.
FIG. 1 is a schematic view of a preferred production apparatus for producing the absorbent composite of the present invention. Each code | symbol in FIG. 1 shows the following.
a: Raw fabric roll (cloth-like hydrophilic substrate), b: water sprayer, c: cloth and / or paper, d1, d2: water absorbent resin particle hopper, e1, e2: drum for particle adhesion, f: water absorption Resin particles, g: drying device, h: composite roll, i: hopper for spraying small particle size particles The cloth-like hydrophilic substrate taken out from the raw fabric roll (a) is a water sprayer (b), etc. The device is used to form a water-containing cloth-like hydrophilic substrate (c), and then sprayed onto the water-containing cloth-like hydrophilic substrate from the particle-adhering drum (e1) in which the particles are placed in the recessed portion on the drum. Then, particles are sprayed from the particle bonding drum (e2) in which the particles are adhered to one side of the cloth-like hydrophilic substrate, and then the particles are placed in the recessed portion on the drum even on the surface where the particles are not bonded. Furthermore, particles with a small particle size were more uniformly dispersed than (i), and the particles were adhered to both sides. The cloth-like hydrophilic substrate is dried through a drier to produce a composite in which particles are firmly bonded.

The drum structure in which the water-absorbing resin particles are arranged on the cloth-like hydrophilic substrate is an important point. On the surface of the drum, there is a recess where a water-absorbing resin cannot be inserted in an arbitrarily determined portion.
It is preferable that the depressions are arranged so as to reduce the probability that the water-absorbing resin particles to be installed come into contact with each other. In order to improve the absorption performance of the absorbent composite, there is an optimal dent arrangement. That is, the water-absorbing resin is spaced from neighboring resin particles so that the water-absorbing resin can swell by absorption, and more water-absorbing resin is placed on the cloth-like hydrophilic substrate.
The outer diameter of the entrance of the dent needs to have a size of 1 to 3 times the particle size of the large particle size of the water absorbent resin used. Preferably it is 1.2 to 2 times. The outer diameter of the recess entrance is the distance between the longest points on the edge of the drum surface at the entrance of the recess. Here, the particle size of the large particle size means an average particle size of particles taken out by 20% by weight from the larger particle size side of the entire absorbent resin particle placed on the absorbent composite. The particle diameter measuring method here uses the upper limit, the lower limit, and the average value of the particles passing through the upper limit interval sieve and remaining on the lower limit interval sieve as the particle size of the particles. However, it is preferable that the difference between the upper limit and the lower limit of the interval between the sieve meshes to be used is 400 μm or less.
The structure of the recess may be any shape, such as a non-square shape represented by a circle, an ellipse, etc., a square shape represented by a triangle, a quadrangle, a pentagon, etc., or an indefinite shape not defined as a specific shape. Absent. From the viewpoint of drum production, a non-square or square fixed shape is preferable. The rectangular shape is preferable because of ease of manufacturing the drum and ease of insertion and discharge of the particles into the recess.

In addition, the structure of the indentation from the edge of the drum surface toward the inside is such that the space is narrowed from the surface to the inside, even if the indentation structure does not have the same space from the surface to the inside, or the indentation structure so that the space extends from the surface to the inside. A hollow structure may be used. From the viewpoint of easy insertion and discharge of the water-absorbent resin particles, it is preferable to have a hollow structure in which the space is narrowed from the surface to the inside.
If the outer diameter of the recess entrance is too large, there is an increased probability that a large number of water-absorbing resin particles will be inserted into the recess, or the water-absorbing resin particles after insertion will easily fall out of the recess, Stable operation becomes difficult. In addition, when the outer diameter of the drum entrance is too small, a process of removing water absorbent resin particles adhering to a place other than the dent due to static electricity or the like even if the dent water absorbent resin particles are sucked using suction force. Even the water-absorbent resin particles present in the depression may be removed.

Moreover, it is preferable that the depth of the hollow of this drum is 0.3 to 2 times the average particle diameter of the granular water-absorbing resin used. More preferably, it is 0.5-1.5 times, More preferably, it is 0.7-1.2 times.
If the depth of the dent is shallow, use a suction force to remove the water-absorbent resin particles adhering to places other than the dent due to static electricity, etc. Even existing water-absorbent resin particles may be removed. In addition, if the depth of the dent is too deep, it is difficult to adjust the amount of resin to be adhered on the manufactured absorbent composite because a large number of water-absorbing resin particles are inserted into the dent, or after insertion. The water-absorbent resin particles are not easily discharged, and stable operation becomes difficult.

  The drum preferably has a hole at the bottom of the indentation on the drum surface through which the water-absorbing resin particle blowing gas can pass. The inner diameter of the hole is preferably smaller than the particle diameter of the small particle diameter of the water absorbent resin to be used. If the hole is larger than the small particle, the particle having a particle size smaller than the hole often passes through the hole and enters the drum and is not sprayed onto the cloth-like hydrophilic composite. In many cases, it may cause problems in operation. Further, the hole structure may be any structure as long as it substantially fulfills the function of blowing gas from the inside of the drum to the outside of the drum. In order to prevent the water-absorbing resin particles from clogging into the hole as much as possible, it is preferable that the hole is widened toward the inside of the drum.

  Further, when the water-absorbing resin particles are inserted into the drum, it is preferable that the inside of the drum is in a reduced pressure state and is inserted in a suction state. At this time, the pressure difference between the outside and inside of the drum is preferably in the range of 0.01 to 500 Torr. If this pressure difference is too small, particles inserted into the recess may easily fall off, while if too large, many particles may enter the recess and be difficult to discharge. Therefore, the preferable range of this pressure difference is 0.05 to 100 Torr, more preferably 0.1 to 50 Torr, and most preferably 0.5 to 5 Torr. This suction effect not only improves the establishment of the insertion of the water-absorbent resin particles into the recess, but also after the water-absorbent resin particles are inserted into the recess and before the spray onto the cloth-like hydrophilic substrate, This is a very preferable method because it is possible to prevent the water-absorbing resin particles from dropping out of the depression due to the operation of removing the water-absorbing resin particles attached to a place other than the depression.

  Provide equipment to remove water-absorbing resin particles adhering to the drum other than the recesses after the water-absorbing resin particles are inserted into the recesses on the drum and before being sprayed onto the cloth-like hydrophilic substrate. Is preferred. The removal method is not particularly limited, but examples of specific methods include a method of scraping with a brush, a method of blowing a gas, a method of applying vibration, and the like. Among these methods, the method of blowing gas is the most preferable method.

Moreover, since the drum generates static electricity during operation and may destabilize the movement of the water-absorbent resin particles, it is preferable to install a device for removing static electricity.
After arranging the resin having a large particle diameter by the drum, it is preferable to spray the resin having a small particle diameter so as to satisfy the total surface area coefficient. The spraying may be performed on only one side, and it is also preferable to spray on both sides with the cloth reversed. In order to reduce detachment, it is preferable to spray the substrate again with water before spraying the small particle size. The method for spraying the small particle diameter is not particularly limited, but a method that can be controlled as uniformly as possible is preferable.

  It is preferable to move the cloth-like hydrophilic substrate. The moving method at this time is not particularly limited. As a specific example of the moving method, there are a method in which the upper and lower portions of the cloth-like hydrophilic base material are not supported, and a method in which the lower portion has a support such as a belt conveyor and moves according to the movement of the support. When the water-absorbing resin is bonded to both surfaces of the cloth-like hydrophilic substrate, it is preferable to adopt a belt conveyor type moving method when passing the drum surface in the bonding process to the surface to be bonded last. This is because the resin adhering to the back surface of the cloth-like hydrophilic base material is prevented from falling off when water-absorbing resin particles are sprayed from the drum. Moreover, it is preferable to employ | adopt a belt conveyor type moving method at the time of the dehydration drying process of the last process. This is because some cloth-like hydrophilic substrates shrink during dehydration and drying, so that the shrinkage is minimized.

  Specific examples and comparative examples of the present invention are shown below, but the present invention is not limited to the following examples.

ここで、Ｓは複合体の面積（ｃｍ²）、Ａは面積充填率（％）、ｒは粒子径（ｃｍ）、
Ｗ_rは粒子径ｒの粒子の重量、ρ_rは粒子径ｒの吸水性樹脂のかさ比重（ｇ／ｃｍ³）を表
す。
ここで、粒子径ｒは、目の開きが１０６μｍ、２１２μｍ、３００μｍ、４２５μｍ、５００μｍ、６００μｍ、７１０μｍ、８５０μｍ、１０００μｍ、１１８０μｍ、１４００μｍ、２０００μｍ、２５００μｍの篩を使用して篩い分けすることによって求めた。通過することのできた篩の目の開きと通過することのできない篩の目の開きの中間の値を粒子径とした。なお、１０６μｍの篩を通過したものについては、５３μｍとし、２５００μｍの篩の上に残ったものについては、２７００μｍとした。この操作により、５３μｍ、１５９μｍ、２５６μｍ、３６２．５μｍ、４６２．５μｍ、５５０μｍ、６５５μｍ、７８０μｍ、９２５μｍ、１０９０μｍ、１２９０μｍ、１７００μｍ、２２５０μｍ、２７００μｍの粒径へと分類した。
また、かさ比重ρ_rは、２ｃｍ³のメスフラスコを使用して２ｃｍ³分の吸水性樹脂を測
り取り、その重量を計量し、重量を２で割ることによって求めた。測定は５回行い、平均値を取った。かさ比重は、篩い分け後のそれぞれの粒径において測定した。 In Examples and Comparative Examples, samples were evaluated by the following methods.
(1) Overlap index The overlap index is a coefficient representing the degree of contact between the water absorbent resins in the vertical direction. And overlap index smaller again, easily blocking due to a large overlap of the particles with each other, since undesirable from the viewpoint of water absorbing performance, the overlap index is preferably 0.3 to 1.5.
The overlap index was calculated by collecting the water-absorbent resin particles used in the sample, dividing the particles into predetermined particle sizes, measuring the particle weight and bulk specific gravity for each particle size, and using the following Equation 3.
(Formula 3)

Here, S is the area (cm ² ) of the composite, A is the area filling rate (%), r is the particle diameter (cm),
W _r represents the weight of the particle having the particle diameter r, and ρ _r represents the bulk specific gravity (g / cm ³ ) of the water absorbent resin having the particle diameter r.
Here, the particle diameter r was determined by sieving using a sieve having an opening of 106 μm, 212 μm, 300 μm, 425 μm, 500 μm, 600 μm, 710 μm, 850 μm, 1000 μm, 1180 μm, 1400 μm, 2000 μm, 2500 μm. . The intermediate value between the opening of the sieve that could pass and the opening of the sieve that could not pass was taken as the particle size. In addition, about what passed the 106 micrometers sieve, it was set to 53 micrometers, and about what remained on the 2500 micrometers sieve, it was set to 2700 micrometers. By this operation, the particle size was classified into 53 μm, 159 μm, 256 μm, 362.5 μm, 462.5 μm, 550 μm, 655 μm, 780 μm, 925 μm, 1090 μm, 1290 μm, 1700 μm, 2250 μm, and 2700 μm.
The bulk density [rho _r is weighed using volumetric flask 2 cm ³ 2 cm ³ min of the water-absorbent resin was weighed and the weight was divided by two weight. The measurement was performed 5 times and the average value was taken. The bulk specific gravity was measured at each particle size after sieving.

(2) Non-Pressure Absorption Capacity The non-pressure absorption capacity of the sample was the amount absorbed after 3 hours when 0.9% physiological saline was freely absorbed. Specifically, a circular composite absorbent body having a diameter of 59.5 mm was prepared, and measurement was performed using the same method as the above-described substrate absorption capacity. However, when water-absorbing resin particles that are not adhered are contained or when detachment occurs, the water-absorbing resin particles are collected by filtration and left on a Kimwipe for 10 seconds or longer to drain water. We will calculate it by adding its weight. Moreover, in the case of the sample in which the water-absorbent resin particles are not fixed at all, in accordance with the method for measuring the absorption capacity of the water-absorbent resin, the measurement was carried out by putting an absorber in the T-Bag.

(3) Return amount and suction speed The return amount is an index representing a feeling of use when the body fluid absorbent article is used. If the amount of return is large, the skin gets wet and the attachment is uncomfortable. It can be said that the smaller the return amount, the better because the surface of the article dries and becomes comfortable.
The suction speed is an index indicating the ease with which the liquid can be taken into the absorbent body. A higher suction speed is preferable because it enables quick liquid absorption.
The return amount and the suction speed were measured by the following methods.
The same situation as when using a polyethylene sheet on the bottom of the sample and a top sheet collected from the uni-charm children's paper diaper mooney's top fit and secured with a thumbtack, and using the absorbent composite as a sanitary material Was reproduced.
A cylindrical pipe having a diameter of 60 mm and a weight of 53.5 g was installed at the center of the sample. 80 g of physiological saline warmed to 37 ° C. was weighed and dropped through a pipe at the center of the sample at a rate of 7 to 8 ml / second. The suction speed was defined as the time from the start of dropping the liquid until the time when the physiological saline inside the pipe disappeared from the top sheet. Five minutes after the start of dropping the droplet, Advantech No. 2 filter paper with a diameter of 150 mm cut into a square with a side of 10 cm is placed on the sample so that it is about 90 g, and is left at the bottom of the droplet. A 3.5 kg load was applied to the top. Three minutes after applying the load, the load was removed, the filter paper was removed from the sample, and the weight was measured. At this time, the weight increased from the weight of the original filter paper was taken as the return amount.

The water-absorbent resin particles used in Examples and Comparative Examples were produced by the following method.
(Production Example 1)
Acrylic acid was manufactured by Wako Pure Chemical Industries, Ltd. and was used after being purified by distillation. 100 g of reagent acrylic acid was dissolved in 91.02 g of water. The aqueous solution was cooled in an ice bath, and while maintaining the liquid temperature at 30 ° C. or lower, 117.94 g of a 25 wt% aqueous ammonia solution was gradually added with stirring to obtain a 40 wt% aqueous ammonium acrylate solution (neutralization rate). 100%).
90 g of this 40 wt% ammonium acrylate aqueous solution and 0.0187 g of N, N′-methylenebisacrylamide were added to a 300 ml separable flask. The flask was bathed in a water bath so that the liquid temperature was maintained at 30 ° C. The aqueous solution was deaerated by bubbling with nitrogen gas, and the reaction system was purged with nitrogen. Next, 0.43 g of a 42 wt% glycerin aqueous solution was added with a syringe, and after stirring well, 0.0917 g of a 30 wt% aqueous hydrogen peroxide solution and 0.0415 g of Rongalite each dissolved in 1 g of water were added to initiate polymerization. The internal temperature started from 30 ° C and increased to 100 ° C within 5 minutes from the start of the reaction. Then, it heated for 3 hours with the water bath so that internal temperature might be maintained at 70 degreeC. Thereafter, the gel was taken out from the Separa flask and roughly crushed, and then dried at 100 ° C. for 4 hours using an inert oven. After the drying, the mixture was pulverized with a homogenizer and classified using a sieve of 106 μm, 212 μm, 300 μm, 425 μm, 500 μm, 600 μm, 710 μm, 850 μm, 1000 μm, 1180 μm, 1400 μm, 2000 μm and 2500 μm. This was designated as water absorbent resin particles 1. The resin particles had a surface strength of 0.5 N and a surface salt concentration of 90%.

(Production Example 2)
The water absorbent resin produced in Production Example 1 was subjected to a heat treatment at 180 ° C. for 10 minutes using an inert oven. This was designated as water absorbent resin particles 2. The surface salt strength was 2.7N. The total ammonium salt concentration was 70% and the surface salt concentration was 30%.
(Production Example 3)
To a 300 ml flask, 81.73 g of reagent acrylic acid (manufactured by Wako Pure Chemical, special grade reagent), 185.71 g of water, and 31.78 g of sodium hydroxide were slowly added while cooling with ice so that the liquid temperature did not exceed 30 ° C. (Salt concentration 70%). 90 g of this monomer solution and 0.0561 g of N, N′-methylenebisacrylamide were added to a 300 ml separable flask. The flask was bathed in a water bath so that the liquid temperature was maintained at 30 ° C. The aqueous solution was deoxygenated by bubbling with nitrogen gas, and the reaction system was purged with nitrogen. Polymerization was started by adding 0.0826 g of 30 wt% dissolved in 1 g of water and 0.0518 g of Rongalite respectively. The internal temperature started from 30 ° C and increased to 70 ° C in 10 minutes from the start of the reaction. Five minutes after reaching the maximum temperature, the mixture was heated in a water bath for 3 hours so that the internal temperature was maintained at 75 ° C. After elapse of a predetermined time, the gel was taken out from the separable flask and roughly crushed and then dried at 100 ° C. using an inert oven for 4 hours. After drying, the mixture was pulverized with a homogenizer, and classified using sieves of 106 μm, 212 μm, 300 μm, 425 μm, 500 μm, 600 μm, 710 μm, 850 μm, 1000 μm, 1180 μm, 1400 μm, 2000 μm, and 2500 μm. This was designated as water absorbent resin particles 3. The surface strength of the resin particles was 0.9N.

(Production Example 4)
A mixed solution of 0.6 g of isopropyl alcohol, 0.02 g of glycerin, and 0.06 g of water was made and sprayed uniformly on 2 g of the water absorbent resin produced in Production Example 3. This was heated at 180 ° C. for 10 minutes using an inert oven. This was designated as water absorbent resin particles 4. The surface strength of the resin particles was 5.9N.

Samples of Examples and Comparative Examples were prepared by the following method.
Example 1
“Benlyse” (registered trademark) manufactured by Asahi Kasei Fibers Co., Ltd. was cut into a length of 35 cm and a width of 14 cm. Benrise is a continuous long fiber nonwoven fabric made of 100% cellulose. It is a cellulose-based nonwoven fabric with excellent water absorption characteristics. Moreover, since it is a continuous long fiber, it has sufficient strength when it contains water, and it has excellent liquid diffusibility. Similarly, cut a sheet of Teflon (registered trademark) into a length of 35 cm and a width of 14 cm, and draw a line of 33 cm in length and 12 cm in width. Two of these were prepared. 2.6 g of the resin remaining on the 1000 μm sieve of Production Example 1 was uniformly sprayed inside the line of one Teflon sheet so as to avoid contact between particles as much as possible. Further, 2 g of the resin remaining on the 212 μm sieve was uniformly sprayed using a 300 μm sieve. Using a spray bottle, 5 g of water was sprayed on the Benize and then contacted on the particles. On another Teflon sheet, 2.6 g of the resin remaining on the 1000 μm sieve was sprayed in the same manner. Using a spray bottle, 3 g of water was sprayed onto the Benize on the Teflon sheet, and the particle-free surface was brought into contact with the Teflon sheet particles prepared later. From the state in which the Teflon sheets were in contact with the top and bottom of the cloth, the particles and the cloth were brought into close contact with each other by applying a light load by hand. The top Teflon sheet was removed, and a weight was placed on the resin-free portion and fixed, and drying was performed at 180 ° C. for 10 minutes using an inert oven while suppressing shrinkage of Benlyse.
(Example 2)
In the same manner as in Example 1, an absorbent composite was prepared using 2.9 g of the resin remaining on the 850 μm sieve on both sides.

(Example 3)
In the same manner as in Example 1, 1 g of the resin remaining on the 710 μm sieve was used on both sides, and after drying, 0.6 g of the resin remaining on the 300 μm sieve was prepared on both sides of the resin of Production Example 2. Scattered. Since the small particle size resin was not adhered, the problem of unevenness occurred, but since the large particle size resin was adhered, the minimum performance could be exhibited.
Example 4
In the same manner as in Example 1, 1.5 g of the resin remaining on the 600 μm sieve was used on both sides to prepare an absorbent composite.
(Example 5)
In the same manner as in Example 1, 1 g of the resin remaining on the 500 μm sieve was used on both sides and 0.8 g of the resin remaining on the 106 μm sieve was used on both sides to prepare an absorbent composite.

(Example 6)
“Benlyse” (registered trademark) manufactured by Asahi Kasei Fibers Co., Ltd. was cut into a length of 35 cm and a width of 14 cm. A line was drawn 1 cm from the end to draw a rectangle 33 cm long and 12 cm wide. The Benize is placed on a Teflon (registered trademark) sheet cut to the same size as the Benize. After spraying 3 g of water using a spray bottle, 2.6 g of the resin remaining on the 1000 μm sieve of Production Example 1 was sprayed evenly with a spoon from a height of 20 cm on the inside of the rectangle. Thereafter, 2 g of water was further sprayed, and 2 g of the resin remaining on the 212 μm sieve was sprayed. After spraying 1 g of water with a mist sprayer, a Teflon sheet cut out to the same size as Benlyse was placed on top and lightly pressed by hand. The entire Teflon sheet was turned upside down and the Teflon sheet without particles was peeled off. After spraying 3 g of water again using a spray bottle, 2.6 g of particles remaining on the 1000 μm sieve were sprayed. The Teflon sheet was put on again, and a light load was applied by hand to hold it down, and the Teflon sheet was peeled off. A weight was placed on the resin-free portion and fixed, and drying at 180 ° C. for 10 minutes was performed using an inert oven while suppressing shrinkage of Benlyse. Compared with Example 1, there was much overlap of particles.
(Example 7)
A composite was produced in the same manner as in Example 1 except that the resin of Production Example 3 was used. Compared to the water-absorbent resin of Production Example 1, since it is not an ammonium salt, the amount of absorption as a resin is small, so that the amount of absorption as a composite is slightly reduced. Moreover, since the surface salt concentration was slightly lower than that of the ammonium salt, there were particles that were detached after fabrication.
(Example 8)
A composite was prepared in the same manner as in Example 1 except that “Oji Kinocross KS-40” registered trademark manufactured by Oji Kinocross Co., Ltd. was used instead of Benrise. Oji Kinocloth is a dry pulp nonwoven fabric. Since the strength of the pulp was weak, the adhesive strength was such that when the particles were grasped with tweezers, the pulp fibers could be easily detached.
Example 9
A composite was produced in the same manner as in Example 1 except that the heat drying temperature was 60 ° C. and the drying time was 6 hours. It takes a long time to dry at low temperatures.
(Example 10)
A composite was produced in the same manner as in Example 1 except that 0.8 g of the resin remaining on the 500 μm sieve was used on both sides of the resin of Production Example 1. Since the resin ratio was low, the water absorption performance was low.

(Comparative Example 1)
A mixture of pulp and water-absorbent resin was taken out from the “Pamper Perth Cotton Care” (registered trademark) M size absorbent part manufactured by P & G, and used as Comparative Example 1. The pulp and the water-absorbent resin were not adhered, and the pulp was also cottony and could not keep its shape.
(Comparative Example 2)
A composite was produced in the same manner as in Example 1 except that 5 g of the resin remaining on the 212 μm sieve of the resin of Production Example 1 was used only on one side. Since only a small particle size is used, the gap between particles is not sufficient, and the liquid diffusibility and suction are poor.
(Comparative Example 3)
A composite was produced in the same manner as in Example 1 except that the adhesion treatment was not performed. Since no adhesion treatment was performed, most of the particles were detached at the time of evaluation as an absorber, so that the stability as an absorber was lacking, and the performance was hardly exhibited. The returnability and the suction speed were measured without intentional deviation of particles. When particles were solidified near the bottom of the droplet, the suction speed was slow, and when the particles were biased toward the edges, the returnability deteriorated.

Table 3 shows the evaluation results of the absorbent composites obtained in Examples 1 to 10 and Comparative Examples 1 to 3 . Table 1 shows the characteristics of the water-absorbent resin used in the absorbent composite, and Table 2 shows the characteristics of the base material of the absorbent composite.
It was confirmed that the absorptive complex of the present invention was excellent in absorption capacity, return amount, and suction speed.

Explanatory drawing of the manufacturing apparatus of the absorptive composite of this invention.

Claims (13)

An absorbent composite comprising at least a substrate and water-absorbent resin particles adhered to the substrate,
The substrate is cloth or paper;
The water absorbent resin particles are composed of a resin having a carboxylic acid group in the side chain,
The surface strength of the water-absorbent resin particles is 0.1 to 5.5 N,
All SANYO more than 50% by weight of the water-absorbent resin particles can not pass through the 500μm sieve opening of eyes,
The following overlap index represented by the formula Ru der 0.3-1.2 absorbent composite.

(In the formula, S is the area (cm ² ) of the absorbent composite , A is the area filling rate (%), r is the particle diameter (cm), W _r is the weight of the particle having the particle diameter r, and ρ _r is the particle diameter. The bulk specific gravity (g / cm ³ ) of the water-absorbent resin of r is represented.
The area filling factor A is a value calculated according to the following formula using an enlarged copy of each photograph obtained by photographing an arbitrary five points on the surface of the absorbent composite with an optical microscope or an electron microscope.

Area filling rate A (%) = area of water-absorbing resin particle portion / area of entire photographing location × 100

The particle diameter r is determined when the water-absorbent resin particles are sieved using sieves having openings of 106 μm, 212 μm, 300 μm, 425 μm, 500 μm, 600 μm, 710 μm, 850 μm, 1000 μm, 1180 μm, 1400 μm, 2000 μm and 2500 μm. The intermediate value of the opening of the sieve that could pass and the opening of the sieve that could not pass (however, those that passed through the 106 μm sieve remained on the 53 μm and 2500 μm sieves) Is 2700 μm).
The bulk specific gravity ρ _r is 2 for the water absorbent resin particles having the respective particle diameters r after the sieving.
weighed 2 cm ³ min using a volumetric flask cm ^3, were weighed and the weight is a value obtained by dividing by 2 the weight. )   The absorptive composite according to claim 1, wherein the water-absorbent resin particles occupy 60% by weight or more of the total weight of the base material and the water-absorbent resin particles. The absorptive composite according to claim 1 or 2 whose weight average particle diameter of said water-absorbent resin particles is 400 micrometers or more and 2000 micrometers or less. The absorptive composite according to any one of claims 1 to 3 , wherein the water-absorbent resin particles include a polyacrylate copolymer. The absorptive composite according to any one of claims 1 to 4 , wherein 50% or more of the total acid groups in the resin constituting the water-absorbent resin particles are neutralized in the form of an ammonium salt. The absorptive composite according to any one of claims 1 to 5 , wherein the substrate contains 50% or more of cellulose or a cellulose derivative. The absorptive composite according to any one of claims 1 to 6 , wherein the substrate is cloth or paper. The tensile breaking elongation ratio in the machine direction and the transverse direction of the base material is 1: 1.2 to 1:10, and the tensile breaking strength ratio in the machine direction and the transverse direction is 1.2: 1 to 10: 1. The absorptive complex according to any one of claims 1 to 7 . The absorptive composite according to any one of claims 1 to 8 , wherein a contact angle of an aqueous solution of ammonium polyacrylate having a solution viscosity of 74 cps of the substrate is 130 degrees or less. A method for producing an absorbent composite comprising at least a base material and water-absorbing resin particles bonded to the base material, wherein the base material and water-absorbing water-absorbing resin particles are in contact with each other and dehydrated The manufacturing method of the absorptive composite_body | complex of any one of Claim 1 to 9 made to adhere by. The water content is provided by adding 10 to 3000 parts by weight of water to 100 parts by weight of the absorbent resin particles to the water absorbent resin particles, the base material, or both the water absorbent resin particles and the base material. The method for producing an absorbent composite according to claim 10 . The method for producing an absorbent composite according to claim 10 or 11 , wherein the dehydration is performed under heating at 70 to 350 ° C for a treatment time of 1 to 1000 seconds. Absorbent complex produced by the method according to any one of claims 10 to 12.

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