KR920005720B1 - Absorbent products containing high density absorbent structures - Google Patents

Abstract

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Description

Products containing high density absorbent structures

The present invention relates to an article comprising a mixture of water insoluble discontinuous hydrogel particles and hydrophilic fibers and comprising a flexible absorbent structure that is substantially unbonded. Flexible absorbent structures, generally nonwoven sheets or fibrous webs, can significantly absorb fluids (eg, moisture and human secretions). For example, they are used as absorbent cores for disposable towels, cosmetic tissues, toilet paper, or absorbent products such as disposable diapers and sanitary napkins. Typically, such structures are made of inexpensive hydrophilic fibers, typically woodpulp fibers.

Water insoluble hydrogels are polymerizable materials capable of absorbing large amounts of water, typically at least 20 times its own weight. When these materials were first introduced, they were expected to revolutionize the field of disposable absorbent consumer materials (ie, disposable diapers, sanitary napkins, incontinence pads, etc.). However, to date, when water-insoluble hydrogels are used in disposable absorbent products, their performance cannot be tolerated.

One of the causes of poor performance of hydrogels is due to a phenomenon called gel blocking. Gel blocking means a phenomenon occurring when the hydrogel particles, the film, the fiber, etc. are wetted; The surface swells and inhibits the penetration of liquid into it. Subsequently, internal wetting occurs by a fairly slow diffusion process. In practical terms, it means that absorption is slower than release of the emulsion to be absorbed, so that the absorbent structure may not absorb before the hydrogel material in the diaper, sanitary napkin or other absorbent structure is sufficiently wetted.

Water insoluble hydrogels typically have a water absorption capacity (typically much greater than the difference in size) that far exceeds the water absorption capacity of woodpulp fibrous webs used in disposable absorbent consumer goods. The absorbing capacity of electrolyte containing fluids (eg urine) is much lower, but it is much higher than in fibrous webs. Accordingly, there has been attempt in the art to incorporate hydrogel materials into fiber webs made of wood pulp in order to increase the fluid absorption capacity of such webs. Initially, attempts were made to simply mix the hydrogel powder into a fibrous web. This method did not increase the volume absorption capacity of the web (R.E.Ericson, "1st International Absorbent Products Conference Proceedings", Section 6, Section 3 (1988.11)). Ericson reports that "the fluid retention under pressure increases, but the volume adsorption capacity is essentially the same." This phenomenon has been explained in several ways. Ericsson explained that the fibrous matrix prevents swelling of the hydrogel particles. Others consider the hydrogel's wicking characteristic to be quite poor, resulting in poor performance. Whatever the cause may be, it has become apparent that a simple mixture of hydrophilic fibers and hydrogel particles may not have the expected absorbing capacity based on the properties of each component in such mixture.

Because of the poor wicking properties of hydrogels, based on poor performance in disposable absorbent structures, some people in the art have attempted to improve hydrogel performance by introducing fibers into hydrogel particles. Introduction of the fibers into the hydrogel particles can be accomplished by wet-laying the mixture of hydrogel particles with hydrophilic fibers. During the wetting phase of this process the hydrogel swells. Hydrogels tend to shrink during the drying step. As a result, the gel extends over the fiber surface and forms fiber-fiber bonds in a way that is not different from the bonds that occur when using a binder (eg Radex). As a result of the wetting and bonding by the hydrogel, the resulting absorbent structure is quite stiff. It is described that the stiffness of such a structure can be reduced by treating the structure at high pressure. Even in this case, the stiffness of these structures is still high, especially when using a fiber / hydrogel ratio of 50:50 or more. However, this fiber / hydrogel ratio is most preferable in terms of cost; Hydrogels are, for example, much more expensive than wood pulp fibers. Moreover, the method described above comprises using a large amount of water and then drying. This has a significant impact on the manufacturing cost of the absorbent structure.

Another method is to place the hydrogel material layer on the material layer having good wicking properties by manufacturing the laminate structure. The wick layer diffuses the liquid over most of the surface of the hydrogel layer, allowing more hydrogels to be exposed to the liquid to be absorbed. Such structures have been claimed to have a higher absorption capacity than, for example, hydrogel particle mixtures in hydrophilic fibrous webs. Although the wick layer allows liquid to diffuse onto the hydrogel layer surface, there is no guarantee of permeation of the liquid into the hydrogel layer. Liquid permeation is still greatly limited by gel blocking. In other words, the absorbent structure does not fully exhibit the potential absorbency of the hydrogel as is known in the art.

Thus, there has been a continuing need for flexible absorbent structures that fully demonstrate the hydrogel's absorptive capacity. The absorbent structure of the present invention provides excellent absorbency and excellent wicking properties, yet is flexible, elastic and has good side integrity. These structures are extremely thin and comfortable, but are particularly suitable for use in disposable diapers which have at least the same absorption capacity as the much bulkier products on the market. Absorbent structures can be made by methods that do not use water or another solvent. Thus, the method does not involve solvent treatment and drying steps. The method is simple to allow the use of standard equipment, such as those typically used to make absorbent webs; The absorbent structure of the present invention can be manufactured at low manufacturing cost without any investment in money. Accordingly, it is an object of the present invention to provide a flexible absorbent structure comprising a water insoluble hydrogel with improved water absorption. A further object is to provide an improved disposable absorbent article (such as a diaper) that is substantially thinner and smaller in volume than conventional disposable absorbent articles. It is a further object of the present invention to provide a method of making such an absorbent structure.

Gel blocking phenomena have been described fully, and the results of poor properties of the absorbent structure containing hydrogels have been discussed (see E. Carus, "1st International Absorbent Products Conference Proceedings", Section V-1 (1988.11); And J.H. Field, "Pulp Parameters Affecting Product Performance", TAPPI, 65 (7), pp, 93-97 (1982).

Japanese Patent No. 56-65630 (published date: 1981. 6.3) describes a method for producing "tufted lumps" of cellulose fibers supporting water-insoluble resins. Lumps are prepared by dispersing the fibers and resin in methanol, wetting the mixture, and then drying off the solvent. Subsequently, the web is compressed to a density of at least 0.1 g / cm 3, preferably about 0.6 g / cm 3. The sheets thus obtained are cut into pieces each less than 0.5 g. Similar methods are described in US Pat. No. 4,354,901 (Patent Date: Oct. 19, 1982; Kopolow). This document describes a process for producing a slurry having less than about 0.1% by weight solids in water, which is a mixture of cellulose fibers and hydrocolloidal particulate material. The wet web is made from a slurry that is continuously dried and densified to at least 10%, preferably at least 50%. It is described that by the densification step, the stiffness of the absorbent structure is reduced (Gurley Stiffness: less than 40 g).

The present invention comprises a mixture of hydrophilic fibers and water-insoluble discontinuous hydrogel particles having a fiber / hydrogel ratio of about 30:70 to about 98: 2, wherein the density is about 0.15 to about 1 g / cm 3 and is substantially unbonded. To a flexible absorbent structure.

In addition, the present invention provides an air-laying method comprising (a) anhydrous web of hydrophilic fibers and water-insoluble hydrogel particles having a weight ratio of fiber / hydrogel of about 30:70 to about 98: 2, (b) compressing the web to a density of from about 0.15 to about 1 g / cm 3, wherein the web comprises a method for producing a flexible absorbent structure.

The present invention provides a mixture of hydrophilic fibers and water-insoluble hydrogel particles when the weight ratio of fiber / hydrogel is about 30:70 to about 98: 2 and the structure is densified to a density of about 0.15 to about 1 g / cm 3. It is based on the finding that it can be made of a highly absorbent flexible structure. The absorbent structure of the present invention is essentially a web of hydrophilic fibers in which water-insoluble discontinuous hydrogel particles are dispersed in the web. The hydrogel particles may be randomly dispersed or may be a pattern of the fiber / hydrogel ratio portion and the fiber / hydrogel ratio portion (including only the portion of the fiber only).

The term "substantially unbonded" means that the number of fiber / fiber bonds, fiber / hydrogel particle bonds, and hydrogel particle / hydrogel particle bonds is kept as low as appropriate as possible. Bonds that can occur include hydrogen bonds (eg paper-making bonds), between fibers and hydrogel particles, between hydrogel particles, and between certain types of fibers (eg thermoplastic fibers). And other forms of chemical bonds as may be included, and mechanical bonds. This is important because the large absorbency of the absorbent structure of the present invention is due to the considerable ability of the structure to recover volume quickly while the structure is initially wet. Many bonds between structural components will significantly impair this ability.

It is practically impossible to completely prevent the bond from forming the bond. However, to some extent binding did not appear to counteract the ability of the construct to recover volume quickly during initial wetting. Typically, the degree of bonding is minimized by preventing the fibers and hydrogel particles, or absorbent structures, from being exposed to water in liquid form and prolonged exposure to air with high relative humidity. The parameters of these processes are discussed in more detail below.

As used herein, "hydrogel" refers to an inorganic or organic compound that can absorb an aqueous fluid and retain it under normal pressure. To obtain good results, the hydrogel must be water insoluble. Examples include inorganic materials (eg silica gel) and organic compounds (eg crosslinked polymers). The crosslink can be a covalent bond, an ionic bond, a van der Waals bond, or a hydrogen bond. Examples of the polymer include polymers and copolymers of polyacrylamide, polyvinyl alcohol, ethylene maleic anhydride copolymer, polyvinyl ether, hydroxypropyl cellulose, carboxymethyl cellulose, polyvinyl morpholinone, vinyl sulfonate , Polyacrylates, polyacrylamides, polyvinyl pyridine and the like. Other suitable hydrogels are described in US Pat. No. 3,901,236 (patent date: August 26, 1975; Assarsson), which is incorporated herein by reference. Particularly preferred polymers for use herein are hydrolyzed acrylonitrile grafted starch, acrylic acid grafted starch, polyacrylates, and isobutylene maleic anhydride copolymers, or mixtures thereof.

Methods for preparing hydrogels are U.S. Patent Nos. 4,076,663 (Patent Date: February 28, 1978; Fusayoshi Masuda), 4,286,082 (Patent Date: Aug. 25, 1981; Tsuno Tsubakimoto et al.), 3,734,876, No. 3,661,815, 3,670,731, 3,664,343, 3,783,871, and Belgian Kingdom Patent No. 785,858, all of which are incorporated herein by reference.

As used herein, "particle" includes any form of particle (eg, hung, hemispherical, cube, rod, polyhedron, etc.), and also has a form with a maximum dimension / minimum dimension (eg, bed, Flaky, fibrous) particles. As used herein, "particle size" means the weight average of each particle of the initial dimension. It is also possible to use a hydrogel particle aggregate in which the weight average size of such a conglomerate is in the range described below.

While it is expected that the absorbent structures of the present invention will work well by using hydrogel particles with a wide variety of particle sizes, the elimination of the use of particles that are significantly smaller or considerably larger can be considered. Because of industrial hygiene, average particle sizes of (weight) below about 30 microns are less desirable. Particles having a minimum dimension of about 4 mm or more in length can give a rough feel in the absorbent structure, which is undesirable from the consumer's point of view. Preferred particles for use herein are particles having a (weight) average particle size of about 50 microns to about 1 mm.

The form of the hydrophilic fiber is non-limiting for use in the present invention. Any form of hydrophilic fiber suitable for use in conventional absorbent articles is also suitable for use in the absorbent structure of the present invention. Specific examples include cellulose fibers, rayon, polyester fibers. Examples of other suitable hydrophilic fibers are hydrophilized hydrophobic fibers such as surfactant treated or silica treated thermoplastic fibers. In addition, fibers that do not provide a web of sufficient absorbing capacity to be useful in conventional absorbent structures, but which provide good wicking properties, are suitable for use in the absorbent structures of the present invention. This is because, for the purpose of the present invention, the wicking properties of the fibers are much more important than the absorbency of the fibers. For reasons of availability and price, cellulose fibers, in particular woodpulp fibers, are preferred.

The relative amount of hydrophilic fibers and hydrogel particles is most simply represented by the weight ratio of fibers / hydrogels. These ratios can be about 30:70 to about 98: 2. The low ratio, i.e., fiber / hydrogel ratio of about 30:70 to about 50:50, indicates that when the hydrogel used has a low swelling capacity, that is, the ability of the hydrogel to absorb urine and other human secretions is about its own weight. It is practical only when less than 15 times (15X) (absorbency data can usually be purchased from the manufacturer of the hydrogel or can be conveniently measured by the absorption / discharge test described below). Hydrogels with a considerably high absorption capacity (i.e. 25 times, and thus highly swell after wetting) tend to gel-block when used in absorbent structures with low fiber / hydrogel ratios, thus undesirably slow-diffusing forms of absorption. Dynamics. On the other hand, a fairly high ratio of fiber / hydrogels (eg 95: 5 or more) provides significant performance only if the hydrogel used has a high absorption capacity (eg 25 times with respect to urine and other human secretions). . For the most commercially available hydrogels the optimum fiber / hydrogel ratio is about 50:50 to 95: 5.

Based on the analysis of price / performance, a fiber / hydrogel ratio of about 75:25 to about 90:10 is preferred. Of course, this preference is based on the relative price of hydrophilic fibers (eg woodpulp fibers) and hydrogels. For example, if wood pulp prices rise and / or hydrogel prices fall, the lower fiber / hydrogel ratio will be more cost effective.

The density of the absorbent structure is very important. When the hydrogel particles are dispersed into an absorbent web of hydrophilic fibers having a density of about 0.1 g / cm 3, the fluid absorption of these webs is slow, so that the hydrogel mixture is a fluid that is absorbed within a practically reasonable time (eg 10 minutes). The amount of is only increased in small amounts. When the absorbent structure is densified to a density of at least about 0.15 g / cm 3, it is observed that the absorbency is increased significantly. Moreover, fluid absorption is much faster during densification. The increase in absorbing capacity is surprising because by densifying the web the void volume in the anhydrous structure will be reduced. By densifying the web, the wicking of the fluid into the web becomes better, and as more hydrogel particles participate in the absorption process, the actual absorption capacity is considered to be higher. It is also contemplated that densified webs can be more effective in maintaining hydrogel particles separated from one another. In addition, by densifying the web from about 0.15 g / cm 3 to about 1 g / cm 3, the volume of the structure is reduced without loss of absorbency (which is desirable for the consumer for aesthetic reasons). However, further densification to a density of about 0.6 g / cm 3 or more does not reduce the volume further, because of the inverse relationship between volume and density. Thus, the density of the absorbent structure of the present invention is preferably about 0.15 to about 0.6 g / cm 3, more preferably about 0.25 to 0.4 g / cm 3.

The continuous flexible absorbent structure of the present invention comprises (a) air directing an anhydrous mixture of hydrophilic fibers and water-insoluble hydrogel particles having a weight ratio of about 30:70 to about 98: 2, and (b) It can be prepared by a method comprising the step of compressing to a density of about 0.15 to about 1 g / cm 3. Step (a) can be carried out by metering on the wire screen the air stream containing hydrophilic fibers and the air stream containing hydrogel particles. The fibers and hydrogel particles are mixed by turbulent flow of the two air streams as they contact each other. Alternatively, the fibers and hydrogels may be mixed in separate mixing chambers prior to air orientation.

For the purposes of the present invention, it is essential to use anhydrous hydrogel particles. In addition, the fibers, particles, or mixtures of fibers and particles, should not be exposed to liquid water or another solvent at any time during this or subsequent processes. When wet hydrogel particles are used, the fibers are entangled and / or bound with the particles, thereby giving the absorbent structure an undesirable stiffness. In particular, when cellulosic fibers (such as woodpulp fibers) are used as the hydrophilic fibers in the absorbent structures of the present invention, the flexibility of these structures is characterized by the small amount of chemical bond dissociating agents (cationic, nonionic or anionic surfactants). ) Can be enhanced by adding to the fibers. Examples of suitable binding dissociating agents are described in US Pat. No. 3,821,068 (patent date: June 28, 1974; Shaw), which is incorporated herein by reference. Particularly suitable binding dissociating agents are quaternary ammonium compounds of the type described in US Pat. No. 3,554,862 (patent date: Jan. 12, 1971; Hervey et al.), Which is incorporated herein by reference. Preferred quaternary ammonium compounds are compounds of the general formula

-

Wherein R ¹ and R ² are hydrocarbyl groups having from about 8 to about 22 carbon atoms, R ³ and R ⁴ are C _1-6 alkyl groups, n and m are integers from 2 to 10, and X is halogen .

Examples of such compounds are described in US Pat. No. 4,144,122 (patent date: March 13, 1979; Emanuelesson et al.), Which is incorporated herein by reference.

Typically, the amount of compatible bond dissociating agent in the absorbent structure is from about 0.01% to about 0.5% by weight of the hydrophilic fiber.

As used herein, "anhydrous" does not mean "absolute anhydrous". For example, under normal storage and handling conditions, the hydrogel particles absorb some moisture. Hydrophilic fibers also absorb some moisture during storage. Moreover, it may be desirable to use moist air during air transport of the fibers and hydrogel particles to prevent dust. Under these process conditions, the hydrogel particles and fibers will absorb much more moisture, but this does not reverse the practice of the present invention. However, the contact time between the hydrogel and the transport air is short, and the limited amount of absorption by the hydrogel during air transport with damp air will not produce substantial bonds in the structure. An important criterion is that the hydrogel particles should not be allowed to swell significantly and should not develop surface tack to the extent that the fibers are entangled and / or bound. Typically, this can be achieved by exposing the hydrophilic fibers and hydrogel particles to only water vapor, not liquid water. By simply exposing the hydrogel to moist air, if this exposure time is prolonged, substantial structural bonds can be created during subsequent processes, especially calendering. For example, US Pat. No. 4,252,761 (patent date: Feb. 24, 1981; Schoggen et al.) Exposes certain hydrogel materials to a certain level of water, which is an object of the present invention because of unacceptable initial absorption kinetics. To form an unacceptable combined structure. In order to keep the structure substantially unbound, the moisture content of the absorbent structure should be less than about 10% by weight of the anhydrous absorbent structure.

The absorbent structure can conveniently be produced by using conventional devices designed for air directing hydrophilic fibrous webs. In such devices, the web is typically formed by absorbing hydrophilic fibers in airflow and depositing the fibers on a wire mesh screen. Immediately upstream of the wire mesh screen, a desired mixture of hydrophilic fibers and hydrogel particles can be prepared by incorporating the desired amount of hydrogel particles into the air stream. The web formed on the screen is then passed through a calender roll fixed at nip pressure to obtain an absorbent structure of the desired density. It is evident that this embodiment of the present invention requires only a slight modification of the conventional apparatus (ie, installation of a metering apparatus for adding hydrogel particles) to produce an absorbent structure. In certain cases, it may be necessary to replace the standard wire mesh screen on the device with one or more fine mesh sizes. This need will arise when using relatively small hydrogel particles and / or when the mesh size of the standard screen is relatively coarse.

The absorbent structure of the present invention is very suitable for use in disposable absorbent articles because of its particular properties. As used herein, "absorbent product" means a consumer product capable of absorbing significant amounts of water and other fluids, such as human secretions. Examples of absorbent articles include disposable diapers, incontinence pads, paper towels, toilet paper, and the like.

The absorbent structure of the present invention has a higher absorbency than a normal hydrophilic fibrous web, has a high density, and has at least the same flexibility as that of a conventional fibrous web. For these reasons, these absorbent structures are particularly suitable for use in products (eg diapers, sanitary napkins, incontinence pads). Due to the high absorbency and high density, an absorbent product can be devised that is thin and has sufficient absorbency such that there is no fear that the absorbency will fail. Due to the flexibility of the structure, the comfort of the wearer and the wearability of the absorbent product can be devised. The flexibility of the structure makes the wearer comfortable and the wearability of the absorbent product good. In addition, the high density / low volume of the product will be important to the manufacturer in reducing packaging and transportation costs.

Disposable diapers comprising the absorbent structure of the present invention utilize conventional diaper manufacturing techniques, but the woodpulp fiber webs ("air-felt") cores typically used in conventional diapers are It can be prepared by replacing with an absorbent structure. That is, disposable diapers (top to bottom) may have a top sheet (hydrophobic nonwoven tissue (eg, knitted punched polyester)), an absorbent structure, and a flexible waterproof support sheet (eg, about 2.3 thick). mil embossed hard polyethylene). Optionally, the absorbent structure can be wrapped in envelope tissue (toilet paper with wet strength). Disposable diapers of this type are further described in U.S. Patent No. 3,952,745 (Patent Date: April 27, 1976; Duncan), and U.S. Patent No. 3,860,003 (Patent Date: January 14, 1975; Buell). It is described in detail.

Since the absorbent capacity of the absorbent structure of the present invention is larger than that of conventional woodpulp fiber webs, the woodpulp web can be replaced with the absorbent structure of the present invention having the same or less weight. The combined reduced weight and increased density add up to a volume lower than a factor of 3 to 12 (depending on the type of hydrogel used, the ratio of fibers / hydrogels, and the density).

It is convenient to express the amount of the absorbent structure used in the disposable diaper as the unit weight (g / cm 2) of the structure. Typically, the unit weight of the absorbent structure of the present invention as used in disposable diapers is about 0.01 to about 0.05 g / cm 2. One way in which the present invention can be used is to produce diapers with increased absorbency and reduced volume than conventional diapers. This can be obtained using an absorbent structure having a unit weight of about 0.018 to about 0.03 g / cm 2. Preferred unit weights are from about 0.019 to about 0.021 g / cm 2. The different method aims at an absorbent capacity substantially equal to that of a conventional diaper while fully exhibiting the capacity of volume reduction by the present invention. This is usually accomplished by using unit weights of about 0.01 to about 0.017 g / cm 2. Preferred unit weights are from about 0.014 to about 0.017 g / cm 2. The absorbent structure for use in disposable diapers preferably has a thickness of about 0.3 to about 2 mm, more preferably about 0.5 to about 1 mm.

Conventional disposable diapers are usually (top to bottom), top sheets (hydrophobic non-woven tissues (eg needle-punched polyester)), absorbent cores made of woodpulp fibers, and flexible waterproof support sheets (eg Embossed hard polyethylene with a thickness of about 2.3 mils). The absorbent capacity of such a diaper is substantially increased when the absorbent structure of the present invention is placed between the woodpulp fiber core and the support sheet. When using the absorbent structure in this method, a thickness of about 0.1 to about 1 mm is preferred. The absorbent structure used as the insert may be the same or different in size and shape from the woodpulp fiber core. In a particular embodiment, the woodpulp fiber core is hourglass (ie, the core width of the core is substantially smaller than the width at the distal end), and the absorbent structure is rectangular, the length of which is approximately equal to the length of the woodpulp fiber core. The width is about 1 to about 5 cm narrower than the width of the woodpulp fiber core at the narrowest point of the hourglass shape.

The absorbent structure of the present invention is very suitable for use in sanitary napkins because of its high absorbency, thinness and flexibility. As in the case of disposable diapers, sanitary napkins using the present absorbent structure may be derived from conventional sanitary napkins by simply replacing the absorbent core material (typically, a web of woodpulp fibers) with the absorbent structure of the present invention. Can be. Such substitution may be based on weight × weight, so that the volume is reduced and the absorption capacity is increased; It can be based on light weight, sacrificing the absorbency increase to further reduce the volume. The absorbent structure for use in a sanitary napkin preferably has a thickness of about 0.1 to about 2 mm, more preferably about 0.3 to about 1 mm.

One example of a sanitary napkin is a pad of the absorbent structure of the present invention; Hydrophobic upper sheet; And a fluid impermeable lower sheet. The upper sheet and the lower sheet are placed on opposite sides of the absorbent structure. Optionally, the absorbent structure is wrapped in skin tissue. Suitable materials for the top sheet, bottom sheet and skin tissue are well known in the art. Sanitary napkins and materials suitable for use are described in more detail in US Pat. No. 3,871,378 (Patent Date: March 18, 1975; Duncan et al.).

Performance test

A. Partitioning Test

Samples of the absorbent structure are subjected to a partitioning test described below in more detail. This test is designed to measure the absorbent performance of an absorbent structure as compared to conventional cellulose fibrous webs at both low and high liquid loading conditions. Absorbing liquid is “synthetic urine” (1% NaCl solution in distilled water); The surface tension of the solution is adjusted to 45 dyne / cm with about 0.0025% octylphenoxy polyethoxy ethanol surfactant (Triton X-100, Rohm and Haas Co.). This test was found to predict the absorbency under typical use conditions when using the absorbent structure as an absorbent core of a diaper.

The absorbent structure incorporates a predetermined amount of hydrogel particles into an air stream containing southern soft slash pine fibers; The mixture is prepared by air directing onto a wire mesh screen and densifying the resulting web to the required density between calender rolls. The structure has a unit weight of 0.04 g / cm 2. On the same apparatus, also a web of southern coniferous felled pine fibers having a unit weight of 0.04 g / cm 2 is prepared and calendered to a density of 0.1 g / cm 3. No hydrogel particles are added to the latter web. The latter web is used as a control in all tests. A circular sample 6 cm in diameter is punched out of a sheet of absorbent material for isolation testing.

Containment tests are performed as follows. That is, a piece of polyethylene sheet (usually a kind of material used as a support sheet for disposable diapers) is placed on a flat, nonabsorbable surface. A circular sample (diameter: 6 cm) of the absorbent structure to be tested is placed on a support sheet. Above it is usually placed a piece of paper tissue of the type that is used as a sheath tissue in disposable diapers. On the top of the skin tissue is placed a control (web on southern coniferous logging pine fibers, density 0.1 g / cm 3). The upper sample covered with another piece of support sheet weighted with 4.4 pounds (about 2 kg) of weight is wetted with a predetermined amount (about 1 g) of synthetic urine. This weight represents a limiting pressure of 1 psi (about 70 x 10 ³ N / m 2). After 5 minutes of equilibration, the weights are removed and two samples of absorbent material are weighed respectively. The "load" defined as the amount of synthetic urine absorbed in grams per gram of absorbent material is calculated for each sample. Subsequently, additional synthetic urine is added to the sample, placed again under limit weight, equilibrated and weighed. This is repeated several times (typically about 8 to 10 times) to obtain the relative absorbency of the test material for a wide range of total loads. The load of the lower test layer is then expressed as a function of the load in the upper layer, which is the control.

Of particular interest is the load of the test layer at points where the load of the control material is 2.0 g / g and 4.5 g / g, respectively. It has been found that the load of the test layer at the point where the load of the control material is 4.5 g / g can predict the failure of the load in normal use when the test material is used as the core of the disposable diaper. The test layer load at the point where the control layer load is 2.0 g / g represents the load of the diaper under typical conditions of use. All experimental results described herein are averaged over two or three tests.

B. Absorption / Exhaust Test

The absorbent properties of the absorbent structure are measured by its "synthetic urine" absorption and discharge. The basic procedure and device structure are described in Burgeni & Kapur, "Capillary Sorption Equilibria in Fiber Masses", Textile Research Journal, 37, 362 (1967), which is incorporated herein by reference. The test is particularly useful for measuring absorption kinetics.

An absorber consisting of a horizontal capillary tube about 120 cm long is connected to the fluid reservoir by a valve. The capillary ends are connected to a glass funnel comprising ASTM 4-8 micron frits on which absorbent web samples are placed by tygon tubing. The glass frit funnel is mounted on vertical struts. The frit height above the capillary tube determines the hydrostatic suction force applied on the sample. In a typical absorption / exhaust experiment, the volume of absorbent synthetic urine is determined as a function of hydrostatic suction force starting at 100 cm (corresponding to hydrostatic pressure of -100 cm).

Simplified tests have been developed to determine the useful absorbency of absorbent webs. In this test, the volume absorbed at -25 cm hydrostatic pressure is measured ("25 cm, absorbed"). The frit containing the sample is then lowered to zero hydrostatic pressure and the equilibrium value of the absorbed volume is measured ("0 cm, pore volume"). The frit is then raised to the 25 cm point again and the volume absorbed in the discharge form at -25 cm is measured ("25 cm, exit").

C. Gurley Stiffness Test

The stiffness of the absorbent structure is measured using a Gauley stiffness tester (product of W. and L.E.Gurley, Troy, NY). The use of this tester is described in US Pat. No. 4,354,901 (Patent Date: Oct. 19, 1982; Kopolow), which is incorporated herein by reference. In essence, the device measures the external force required to deflect a strip of material of a certain dimension to which one end is fixed and a load is applied to the other end. The result is obtained in units of g as the "Gulley stiffness". Each absorbent strip is 3.5 inches by 1 inch (about 8.9 cm by 2.5 cm).

The absorbent structure of the present invention has a Gulley stiffness of less than 2 g and preferably less than about 1 g when measured on a strip having a unit weight of 0.03 g / cm 2.

Example 1

In order to test the effect of the fiber / hydrogel ratio on the sequestering performance of the absorbent structure, the following absorbent structure was prepared. Southern coniferous felling pine fibers were made from acrylic acid grafted starch hydrogel ("Sanwet IM 1000", product of Sanyo Co., Ltd., Japan) and 100: 0 (i.e., hydrogel) having a weight average particle size of about 250 microns. None), 95: 5, 90: 10, 85: 15, and 80: 20 with anhydrous color mixing at a fiber / hydrogel ratio. Webs having dimensions of 41 × 30 cm and a unit weight of 390 g / m 2 are produced in a batch type air alignment device. The web is compressed to a dry density of 0.3 g / cm 3, corresponding to a thickness of 1.3 mm, using a flat hydraulic press. Samples of these webs were subjected to the above-described sequestration test to obtain the following results.

TABLE 1

TABLE 2

The data show that, compared to all fiber structures of the same density, the absorption capacity obtained by the absorbent structure of the present invention is dramatically increased over a wide range of conditions.

Example 2

For comparison, the absorbent structure is prepared using the wet orientation method described in US Pat. No. 4,354,901 (Patent Date: Oct. 19, 1982; Kopolow) as follows: Logging pine wood pulp fibers and acrylic acid grafted starch in the southern provinces. A mixture (fiber / hydrogel ratio = 80: 20) with a hydrogel material (Sanwet IM 1000, product of Sanyo Co., Ltd., Japan) is slurried in water with a consistency of 0.7%. The web is formed by straining the slurry on a wire mesh screen. The amount of the slurry is such that a unit weight of 0.034 g / cm 2 can be obtained. The web is dried in a 100 ° C. oven. The density of the dried web is about 0.2 g / cm 3. The web is then compressed to a density of 0.38 g / cm 3 by a hydraulic press. The resulting structure is stiff and board-like. The absorbency of this sample is determined by the quarantine test described above. The results are compared with the results of the air oriented structures prepared according to the method of the present invention (Table 3).

TABLE 3

1) The density of both structures is 0.3 g / cm 2.

2) according to the method of the invention.

3) a method as described in US Pat. No. 4,354,901.

The data shows that the absorbent structure according to the method of the present invention has much better absorption characteristics than the absorbent structure produced by the wet orientation method.

Example 3

The following structure is prepared by the above-described air orientation method: a web of 0.1 g / cm 3 in density consisting entirely of fibers (southern logging pine) (sample A) and a density of 0.3 g / cm 3 only consisting of fibers (southern logging pine) Web (sample B), fiber (southern logging pine) / hydrogel structure (fiber / hydrogel ratio = 80: 20) having a density of 0.3 g / cm 3 (sample C). The hydrogel is the same as used in Examples 1 and 2. All structures are soft and flexible. The sequestration performance of these samples is measured using the above-mentioned sequestration test, except that the equilibrium time is 1 minute.

TABLE 4

A structure according to the invention.

According to the sequestration data, densification of the entire structure (AB) consisting only of fibers increases the isolation performance under low load (because the wick characteristics are better), but the performance under low load decreases (reduced void volume). Caused by). The high density (0.3 g / cm 3) 80:20 fiber-hydrogel mixture (Sample C) has very good sequestration properties at both low and high loads.

Example 4

Absorbent structures containing different types of hydrogel particles are prepared by incorporating the dry hydrogel particles into a flow of southern coniferous felled pine fibers. All hydrogel samples have a weight average particle size of 100 microns to 1 mm. The mixture is formed on a wire screen into sheets with a unit weight of about 0.035 g / cm 2. The sheet is compressed to a dry density of 0.3 g / cm 3. The isolation performance of each sheet is tested by the isolation test described above. The results are shown in Table 5.

TABLE 5

1) A-100, product of grain processing.

2) A-200, product of grain processing.

3) Product of J-550, Grain Processing.

4) SGP 147, product of Henkel, USA.

5) SGP 502SB, product of Henkel, USA.

6) Akucell 3019, product of Enka, Germany.

7) Product of Foxorb 15, Avebe, France.

8) Sanwet IM 1000, product of Sanyo, Japan.

9) KI Gel 201, product of Kuraray, Japan.

From the results, it can be seen that the presence of hydrogel particles in the densified hydrophilic fibrous web significantly increases the sequestration capacity under both low and high load conditions. Similar structures are made by replacing southern softwood kraft pulp fibers with hardwood kraft pulp fibers, thermo-chemical mechanical softwood fibers, eucalyptus kraft pulp fibers, cotton fibers, polyester fibers. Substantially similar results are obtained.

Example 5

The absorbent structure is prepared by the batch process described in Example 1. Southern coniferous kraft pulp fibers are mixed with acrylic acid-crafted starch hydrogels ("Sanwet IM 1000, product of Sanyo Co., Ltd., Japan.) This type of hydrogel has a saturation capacity of about 25 for synthetic urine. Samples of various fiber / hydrogel ratios are prepared Synthetic urine absorption kinetics of these samples is studied in the absorption / exhaust device described above Synthetic urine used in this test is 1% NaCl, 0.06% MgCl in distilled water. ₂ · 6H ₂ O, and 0.03% CaCl ₂ · 2H ₂ O; the surface tension of the solution is about 0.0025% octyl phenoxy polyethoxy ethanol surfactant (“Triton X-100”, Rohm and Haas Co. All absorbent structures have a density of 0.3 g / cm 3 and a unit weight of about 0.04 g / cm 2 All absorption kinetics are limited to 1 psi (about 70 × 10 ³ N / m 2). Measured under pressure, which is close to the real-life conditions used for diapers. The.

TABLE 6

The data show that the equilibrium absorption capacity increases as the amount of hydrogel increases. However, the data show that as the amount of hydrogel increases, the rate of equilibrium absorption is also slowed down gradually. The optimum fiber / hydrogel ratio for this particular fiber-hydrogel system appears to be about 75:25 under these test conditions. Similar results were obtained with 0 cm-pore volume absorption kinetics, but interestingly different (Table 7). Since the wick properties are of little importance under these test conditions, the relative performance of the absorbent structures is measured to a considerable extent by the equilibrium absorbency of these structures. In addition, structures with very poor absorption kinetics (i.e., 40:60 fiber / hydrogel ratios) are defective at 60 minutes longer than 61/39 and 53:47 fiber / hydrogel samples even under hydrostatic pressure conditions of 0 cm. Indicates.

TABLE 7

If a similar sample, with a saturation capacity for "synthetic urine" of about 10 times, was made with southern coniferous kraft pulp fibers and hydrogels, the absorbency would be lower than in Table 7 for each fiber / hydrogel ratio. However, in these mixtures, contrary to the results obtained with the hydrogel with 25 times saturation capacity, the fiber / hydrogel ratio of 40:60 is 50:50 fiber / hydrogel at equilibrium time of 5 minutes and 10 minutes. It is expected to perform better than the ratio.

Example 6

The absorbent structure is prepared according to the method of the present invention, as described in Example 1. The fiber / hydrogel weight ratio is 80: 20. The Gurley stiffness of these structures is measured. For comparison, the Gurley stiffness values of the structures prepared according to the wet orientation method described in US Pat. No. 4,354,901 (see Example 2) are measured before and after the densification step (Table 8).

TABLE 8

This data confirms that initially significantly higher Gurley stiffness of wet oriented structures can be reduced by compressing the structures to higher density as described in US Pat. No. 4,354,901. The data also show that the Gurley stiffness of the air oriented structure of the present invention is lower by one decimal place than in the compressed wet orientation structure, and is lower than two decimal places than in the uncompressed wet orientation structure. .

Example 7

Disposable diapers using the absorbent structure according to the invention are prepared as follows:

When the absorbent structure prepared as in Example 1 was measured under a limit pressure of 0.1 psi (about 70 × 10 ³ N / m 2), the absorbent structure was calendered to a thickness of about 0.1 cm and a density of about 0.3 g / cm 3. The web is cut into pads 12 inches by 16 inches (about 30 by 40 cm). The pad has a unit weight of about 121 b / 3000 ft ² (about 20 g / m 2), a dry tensile strength of about 700 g / inch in the machine direction, and a dry tensile strength of about 300 g / inch wet strength in the direction crossing the machine. Seal with tissue paper.

The pad thus sealed is bonded to a 13 inch by 17 inch (about 33 cm by 43 cm) support sheet of embossed polyethylene film having a melt index of about 3 and a density of about 0.92 g / cm 3. The end of the support sheet is folded over the sealed pad and glued together. Finally, the absorbent pad is made of a hydrophobic but water and urine (Webline No. F 6211, a product of Kendall Co., Walpole, Mass., Consisting of a nonwoven rayon in combination with acrylic latex). Wrap it with the upper sheet.

Diapers have excellent absorbency, wicking properties, and retention on water and synthetic urine.

Example 8

Sanitary napkins using the absorbent structure according to the invention are prepared as follows:

The absorbent structure prepared as in Example 1 is calendered to a thickness of about 0.07 cm and a density of about 0.4 g / cm 3 when measured under a pressure limit of 0.1 psi (about 70 x 10 ³ N / m 2). The web is cut into 8 inch by 2 inch (approximately 20 x 50 cm) pads with tapered ends. A second pad (rectangular) of 5 inches by 2 inches (about 13 by 5 cm) is placed on top of the pad. The combined pad structure is placed opposite the waterproof support sheet (8 inches by 2 inches, tapered) of embossed hard polyethylene with an embossed thickness of 2.3 mils. The structure is covered with an upper sheet with a needle-punched 3 denier polyester nonwoven fabric having a density of about 0.03 g / cm 3 and a thickness of about 2.3 mm. This covered structure is placed on a 9 inch by 3 inch (about 23 by 7.5 cm) bottom sheet of hydrophobic spunbonded nonwoven polyester having a measured weight of about 15 g / m 2. The lower sheet folds upwards with the heat and pressure to join the overlapped sheets together. The absorbent structure thus produced is useful as a sanitary napkin and has excellent properties of absorbing and retaining menstrual fluid.

Example 9

The diaper containing the absorbent structure of the present invention was prepared as in Example 7. A control diaper of the same design is made using a web of wood pulp fibers having a density of 0.1 g / cm 3 in place of an absorbent structure having a density of 0.3 g / cm 3.

Wear diapers on normal infants. Infants should play in the nursery while wearing diapers during the test. The diaper will continue to be worn until it leaks. In order to accelerate the test, a predetermined amount of synthetic urine is preloaded into the diaper.

After leaking, take off the diaper and measure the amount of fluid absorbed. Calculate the load, X, defined as the amount of fluid absorbed (g) until leaking per gram of absorbent material. The results are shown in Table 9.

Absorbent cores (samples A, G and I) of conventional diapers contain about five times their own weight of fluid upon leakage. The absorbent structure of the present invention contains a fluid of 8.0 to 12.7 times its own weight upon leakage. In addition, the data show that the present invention can reduce the volume of the diaper core material to 1/7 (than conventional air felt diaper samples) while maintaining the absorbent capacity of the diaper (sample J is A, G and I). Compare with).

TABLE 9

Alternatively, the absorbent capacity is reduced even when the diaper core volume is reduced to less than 1/7 (e.g. 1/4 in Samples B, C and D; 1/5 in Sample F; or 1/6 in Samples E and H). Increase substantially than disposable diapers.

Example 10

A diaper is prepared as described in US Pat. No. 3,860,003 (patent date: 1975.1.14; Buell), which is incorporated herein by reference, provided that the absorbent body described in the literature (e.g., made from air oriented wood pulp) In addition, the hourglass absorbent structure of the present invention is inserted between the absorbent body and the support sheet. Absorbent structures are prepared as described in Example 1. The unit weight was 0.035 g / cm 2, the density was 0.03 g / cm 3, and the resulting thickness was 1.17 mm.

Example 11

Diapers are prepared as described in US Pat. No. 3,860,003 (patent date: 1975.1.14; Buell), which is incorporated herein by reference. The hourglass core made of conifer pulp is 15.5 inches (about 40 cm) long, 10.5 inches (about 27 cm) wide at the edge, and 3.75 inches (about 9.5 cm) thick at the center.

The absorbent structure of the present invention was prepared using the method of Example 1, using coniferous fiber and acrylic acid grafted starch hydrogel ("Sanwet IM 1000", Sanyo Co., Ltd., Japan) having a weight average particle size of about 25 microns. Product) with a fiber / hydrogel ratio of 85:15. The absorbent structure has a unit weight of 0.12 g / inch (0.019 g / cm 2), thickness of 0.03 inch (0.076 cm), and corresponds to a density of 0.25 g / cm 3. The structure is covered with a sheet of sheath tissue and cut to a size of 3.5 inches by 15.5 inches (about 9 by 40 cm). The structure is inserted longitudinally between the hourglass core in the diaper and the polyethylene support sheet, with the outer tissue placed opposite the hourglass core.

Additional diapers are made in the same manner except that the absorbent structure insert is 2.25 × 15.5 inches (about 6 × 40 cm).

The insert significantly raises the urine absorption capacity of the diaper.

Example 12

To a dry lap of conifer fibers obtained from a conventional papermaking process, a 10% solution of the quaternary ammonium compound of the following general formula is sprayed.

Wherein n and m are integers from 2 to 10, R ₁ is alkylaryl and R ₂ is C _1-6 alkyl ("Berocell 579", produced by Berol chemicals, Inc., LA, USA)

The dry wrap sprays at a rate of 10 g of solution per kg of dry fiber, which corresponds to a 0.1% quaternary ammonium compound on the fiber. The dry wrap was then disintegrated and the fibers were grafted with acrylic acid grafted starch hydrogel ("Sanwet 1M 1000", product of Sanyo Co., Ltd., Japan) with a weight average particle size of about 250 microns / 80: 20 fibers / Mix in hydrogel ratio.

From the fiber-hydrogel mixture, air oriented webs with a unit weight of 0.13 g / inch ² (about 200 g / m 2) are formed. The web is calendered to a density of about 0.2 g / cm 3, which corresponds to a thickness of about 0.038 inch (about 2 mm). The absorbent structure thus obtained is excellent in absorption characteristics and flexibility. Similar structures are prepared using nonionic and anionic softening agents in place of quaternary ammonium compounds. A structure having substantially similar characteristics is obtained.

The web containing the quaternary ammonium compound is cut into a pad of 11 7/8 × 16 inches (about 30 × 41 cm). The pad is used for the manufacture of disposable diapers as described in Example 7.

Claims (10)

(a) a liquid impermeable support sheet, (b) a hydrophobic top sheet, and (c) a hydrophilic fiber and a water-insoluble discontinuous cross-linked polymeric hydrogel particle located between the support sheet and the top sheet. An air-oriented substantially anhydrous mixture, wherein the weight ratio of fiber / hydrogel is about 30:70 to about 98: 2, the density is about 0.15 to about 1 g / cm 3, and the moisture content is about 10 weight of the anhydrous absorbent structure. A disposable diaper, comprising substantially unbonded, flexible absorbent structure having less than% and a Gurley Stiffness value of less than 2 g. About 0.01 to about 0.5 weight of hydrophilic fiber of (a) a liquid impermeable support sheet, (b) a hydrophobic top sheet, and (c) a quaternary-ammonium compound of the general formula located between the support sheet and the top sheet Disposable diaper, comprising an absorbent structure as described in claim 1 (c) further comprising%. Wherein R ₁ and R ₂ are hydrocarbyl groups having about 8 to about 22 carbon atoms, R ₃ and R ₄ are alkyl having 1 to 6 carbon atoms, n and m are integers from 2 to about 10, and X is halogen to be. The disposable diaper of claim 1 wherein the absorbent structure has a basis weight of about 0.01 to about 0.05 g / cm 2. The disposable diaper according to claim 1, wherein the absorbent structure is wrapped by envelope tissue. 5. The disposable diaper of claim 4 wherein the absorbent structure has a thickness of about 0.3 to about 2 mm. 5. The disposable diaper of claim 4 wherein the absorbent structure has a thickness of about 0.5 to about 1 mm. The disposable diaper according to claim 1, wherein the absorbent structure is an hourglass type. The disposable diaper according to claim 1, further comprising an absorbent core made of wood pulp fibers positioned between the hydrophobic upper sheet (b) and the absorbent structure (c). 9. The disposable diaper according to claim 8, wherein the absorbent core made of wood pulp fibers is an hourglass and the absorbent structure (c) is rectangular. (a) a liquid impermeable support sheet, (b) a hydrophobic top sheet, and (c) a hydrophilic fiber and a water-insoluble discontinuous cross-linked polymeric hydrogel particle located between the support sheet and the top sheet. An air-oriented substantially anhydrous mixture, wherein the weight ratio of fiber / hydrogel is about 30:70 to about 98: 2, the density is about 0.15 to about 1 g / cm 3, and the moisture content is about 10 weight of the anhydrous absorbent structure. A sanitary napkin characterized by comprising a substantially unbound flexible absorbent structure having less than% and a Gulley stiffness of less than 2 g.