MXPA00007563A - Absorbent structure and product based on raw materials having a high degree of renewability - Google Patents

Abstract

The invention relates to an absorbent structure and an absorbent product, such as a nappy, an incontinence shield, a sanitary towel or the like, which product includes the absorbent structure. The absorbent structure includes a superabsorbent which has been produced from one or more hydrophilic monomers by free radical copolymerization in the presence of starch and/or chemically modified starch. During production of the superabsorbent, use has been made of a free radical initiator which forms three or more radical sites per molecule. The absorbent structure furthermore includes hydrophilic and/or hydrophobic fibres which, together with the superabsorbent, impart a hydrophilic character to the absorbent structure. In the dry state, the superabsorbent constitutes between 10 and 75%of the dry weight of the absorbent structure. The absorbent structure and the product are based on raw materials having a high degree of renewability.

Description

"ABSORBENT STRUCTURE AND PRODUCT BASED ON RAW MATERIALS HAVING A HIGH DEGREE OF R? NOVABI IDAD" TECHNICAL FIELD The invention relates to an absorbent structure that includes a highly absorbent polymer, that is, a superabsorbent, which has been produced from one or more hydrophilic monomers by free radical copolymerization in the presence of chemically modified starch and / or starch. Furthermore, the invention relates to an absorbent product, such as a diaper, an incontinence protector, a sanitary napkin or the like, which product includes the absorbent structure. The absorbent structure and the product are based on raw materials that have a high degree of renewability and are derived mainly from sources of non-fossil raw material.

BACKGROUND OF THE INVENTION In recent times, it has become even more usual to use highly absorbent polymers frequently referred to as superabsorbents, in absorbent structures for use, for example, in absorbent products that are intended to absorb body fluids. The examples of - These products are diapers, incontinence pads and sanitary napkins. In this context, the superabsorbent materials are understood as being polymers that are capable of absorbing several times their own weight of fluid to be absorbed and which, during absorption, form gels containing fluid. The use of superabsorbent materials, or materials having superabsorbent properties, in absorbent structures present in absorbent products, provides a number of advantages. As a result of using a superabsorbent material, the volume of an absorbent product can be considerably reduced compared to the volume of an absorbent product that only uses conventional absorptive materials, such as, for example, cellulose-based fluff, soft paper , non-woven material and the like. This reduction in volume can be obtained without deteriorating the absorption properties. Another advantage of the superabsorbent materials is that they have a superior capacity, in comparison with many of the other absorptive materials to retain the fluid absorbed under pressure. The good ability to retain the fluid is an advantage when an absorptive material is based on diapers, incontinence protector or sanitary napkins, since the fluid of the absorbed body is retained in the product and is not pressed out of the product when, for example , a user sits down. In recent times, a great deal of effort has been applied to develop different degradable plastic materials to be used, for example, as barrier surface materials in absorbent products. This should be evident, for example, from patent specifications numbers EP 0 408 503 A2, WO 90/10671 and US Patent Number 3,952,347 which all describe plastic materials that have been made at least partially degradable by adding starch. As a result, there are now a number of different plastic materials that are less partially degradable and that are available for use in absorbent products such as diapers, incontinence guards and sanitary napkins. Several of these materials are based on combinations of synthetic polymers and biologically degradable starch. Even if there are now usable barrier surface materials that can at least be partially biologically degradable, it is more difficult to find degradable replacement materials for the superabsorbent materials, which until now have generally been biologically non-degradable.

- - A particularity of many of the superabsorbent materials that have been used to date that can be considered as being a disadvantage is, therefore, that these superabsorbent materials are not biologically degradable and that they are not based either on renewable raw materials. The superabsorbent materials that have been used to date have commonly made use of synthetic polymers, such as acrylic acid as the main raw material. Due to this reason, it has recently been proposed that superabsorbent materials based on various renewable raw materials, such as various polysaccharides and in particular, starch, should be used. A particularity of these previously known polysaccharide-based superabsorbent materials which can be considered as being a disadvantage is the tendency of these superabsorbent materials to give rise to so-called gel blocking in association with fluid absorption in an absorptive body containing this superabsorbent material . Especially constructed absorptive bodies having separate "cavities" for the superabsorbent material, for example, of the type described in US Pat. No. 5,433,715, have therefore been developed to prevent gel blockage from occurring.

However, since it is a relatively complicated matter to form these specially constructed absorptive bodies, there is a need for absorbent structures and products that do not require any special constructions and that are based largely on renewable raw arteries that exhibit high biological degradability. US Pat. No. 5,549,590 discloses a high performance absorbent particle containing a non-colloidal water-resistant solid core encapsulated by a hydrogel-forming polymer and wherein the solid core, for example, is starch. A process for making these absorbent particles and an absorbent article comprising these particles are also disclosed in U.S. Patent Number 5,549,590. Patent Number DE 196 19 680 discloses a method for producing a superabsorbent polymer with hydrophilic monomers in the presence of bulk starch. Since no solvent is used in the polymerization process in Patent Number DE 196 19 680, organophilic radical initiators must be used in the process.

COMPENDIUM OF THE INVENTION - A first object of the present invention, therefore, is that of providing an absorbent structure that is based on a high degree of renewable raw materials that exhibit high biological degradability and, however, do not require any special configuration processes during their production. This first object is achieved by the absorbent structure according to the invention, according to Claim 1 of the appended patent, including a superabsorbent which has been produced from one or more hydrophilic monomers by copolymerization of free radical in the presence of starch and / or chemically modified starch, and through the use that has been made during the production of the superabsorbent, of a free radical initiator that forms three or more radical sites per molecule and, through the absorbent structure that includes hydrophilic and / or hydrophobic fibers , together with the superabsorbent, impart a hydrophilic character to the absorbent structure, and also by the superabsorbent which constitutes, in the dry state, between 10 percent and 75 percent of the dry weight of the absorbent structure. Furthermore, a second object of the present invention is that of using the absorbent structure according to the invention to provide a product - - Absorbent having excellent absorption properties, whose product is based to a high degree on renewable raw materials that exhibit high biological degradability. This second object of the invention is achieved by the absorbent product according to the invention, according to Claim 13 of the appended patent, which includes an absorptive body that is enclosed by a wrapping material that is at least partially fluid permeable. , with the absorptive body including an absorbent structure including a superabsorbent that has been produced from one or more hydrophilic monomers by free radical polymerization in the presence of chemically modified starch and / or starch and, having been used, during the production of the superabsorbent, of a free radical initiator that forms three or more radical sites per molecule, and by the absorbent structure that includes hydrophilic and / or hydrophobic fibers that, together with the superabsorbent, impart a hydrophilic character to the absorbent structure and also by superabsorbent constituting , in the dry state, between 10 percent and 75 percent of the dry weight of the absorbent structure.

BRIEF DESCRIPTION OF THE FIGURES - Next, the invention will be described in greater detail with reference to the accompanying drawings, in which Figure 1 shows a diagrammatic cross section of an absorbent structure in accordance with an embodiment of the invention, Figure 2 shows a diagrammatic cross section of an absorbent structure in accordance with a particularly preferred embodiment of the inventionFigure 3 shows a plan view of an absorbent product in accordance with a preferred embodiment of the invention, as seen from the side that, during use, is intended to be oriented towards a user, and Figure 4 shows a cross section through the line II- -II through the absorbent product in Figure 3.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Figure 1 shows a diagrammatic cross section of an absorbent structure in accordance with a first embodiment of the invention. In this case, the structure 1 comprises a single layer 2, consisting of a mixture of fluff pulp, ie native cellulose fibers and a superabsorbent and a type which is specific to the invention. In Figure 1, the elongated cellulose fibers and the granulated superabsorbent particles have been indicated diagrammatically. In the first embodiment, the ratio in which the cellulose fibers and the superabsorbent are mixed is essentially constant throughout the absorbent structure 1. In this embodiment, the dry superabsorbent preferably constitutes between 20 percent and 30 percent by weight of the dry weight of the absorbent structure, while the rest consists mainly of cellulose fibers that, together with the superabsorbent, impart a character hydrophilic with a high level of ability to absorb and retain body fluids, to absorbent structure 1. Figure 2 shows a second, particularly preferred embodiment of an absorbent structure 3 according to the invention. In this embodiment, the structure 3 comprises several layers 4, 5, 6 of which at least one first layer 4 has a higher content of the superabsorbent which is specific to the invention of the other layers 5, 6. In this regard, the superabsorbent preferably constitutes between 40 percent and 60 percent by weight of the dry weight of the first layer 4, with two opposite sides of the first layer 4 - advantageously being in contact with the second layer 5 and the third layer 6, respectively, of the different layers. In this way, a situation is achieved in which the first layer 4, which has a higher content of the superabsorbent, is covered on the two opposite sides by the layers 5, 6 having a lower content of the superabsorbent. A modality of this nature has several advantages. An advantage is that the absorptive properties of the different layers 4, 5, 6 can be set to be different, depending on the association to which it is intended. Another advantage when using the absorbent structure in an absorbent product according to the invention, is that the superabsorbent is placed farther from the surface of the product, as a result of which the gel that is formed when the superabsorbent absorbs the fluid from the Body becomes less visible and perceptible. This can be an advantage since it has been found that users who sometimes think that this jelly-like substance, which is visible or can be perceived from the outside of the product, may seem unpleasant or be considered as a sign of a defect in the quality of the absorbent product. The specific superabsorbent which is used in the structure of the absorbent material in the absorbent product according to the present invention can be said to be a hybrid superabsorbent which is based on a combination of a synthetic polymer and a natural polymer in the form of a starch and / or a starch derivative. The superabsorbent is based on a hydrophilic polymer composition which can be produced by (free radical) co-polymerization of the monomers remaining below the synthetic polymer in the presence of starch and / or starch derivative. The polymerization is characterized by the use of a free radical initiator that can form triradicals or polyradicals. Even when the ratio of the weight of the components of the synthetic polymer and the starch or components of the starch derivative is between 90:10 and 10:90, it is preferably between 60:40 and 30:70. The monomers which are suitable for forming the basis for the synthetic polymer component and which may be mentioned are a number of polymerizable acids such as acrylic acid, methacrylic acid, caproic acid, vinylsulfonic acid, vinylphosphonic acid, maleic acid, including its anhydride, fumaric acid, itaconic acid, 2-acrylamido-2-methylpropanesulfonic acid and its amides, hydroxyalkyl ester and, esters and amides containing amine or ammonium groups, and also water-soluble N-vinyl amides or diallylmethylammonium chloride.

- The superabsorbent preferably contains hydrophilic monomers according to the formulas: RJ R-1- CH = C wherein R is hydrogen, methyl or ethyl; R is composed of groups of -COOR, sulfonyl groups, phosphonyl groups, phosphonyl groups which are esterified with (C1-C4) alkanol or a group having the formula O CH3 - C - NH - CH2 R = CH3 and R is hydrogen, methyl or ethyl or carboxyl groups; R is hydrogen or amino- or hydroxy- (C 1 -C 4) -alkyl; and R is sulfonyl groups, phosphonyl groups or carboxyl groups. Acrylic acid and methacrylic acid are particularly preferred hydrophilic monomers to be used as the base for the synthetic polymer component.

In principle, all types of starch that occur naturally as the base for the natural polymer component, such as corn starch, wax-corn starch, potato starch, wheat starch, amyl starch corn, can be used. and tapioca starch. These can be used both natively and pregelatinized. In this context, pregelatinized maize starch and pregelatinized potato starch are particularly suitable. A number of different chemically modified starches or starch derivatives can also be used for the natural polymer component, such as catalytically acid, enzymatically or thermally degraded starches, oxidized starches, starch ether such as allyl ether or hydroxyalkyl starches such as starches of 2-hydroxyethyl, 2-hydroxypropyl starches or 2-hydroxy-3-trimethylammoniopropyl starches, or carboxyalkyl starches such as carboxymethyl starches, starch esters such as, for example, starch monocarboxylic ester such as starch formate, starch acetate, starch acrylate, starch methacrylate or starch benzoate, starch ester of dicarboxylic or polycarboxylic acids, such as starch succinate or starch maleate, starch carbamic ester (starch urethane), dithiocarbon starch ester (starch xanthate) or starch ester of inorganic acids such c such as starch sulfate, starch nitrate or starch phosphate, starch ester ether such as, for example, 2-hydroxyalkyl starch acetate, or complete starch acetals, such as those formed, for example, by reacting the starch with an aliphatic or cyclic vinyl ether. In this context, carboxymethyl starch, succinate starch or starch maleate are particularly preferred. In principle, all compounds that with or without the influence of additional activators such as light, radiation, heat, ultrasound, reducing agents, etc. they give rise to three or more radical sites per molecule, they can be used as free radical initiators. This implies that these free radical initiators contain three, four or more groups that can form free radicals. Even when radical sites can be formed simultaneously in this context, they usually form one after the other. Examples of suitable compounds are those containing at least three hydroperoxide units, peroxide units or azo units. Suitable compounds of this nature are the polyhydroxy peroxides which can be obtained by the anodic oxidation of the polycarboxylic acids, in particular of the polyacrylic acid and the polymethacrylic acid, in the presence of oxygen.

- Peroxide units may be present, for example, such as percarbonate, perketal or peryester units. The agents of the compounds of this nature are the dioxetane compounds and tertiary butyl esters, such as, for example, tertiary butyl methacrylate-peracrylate copolymers. When the superabsorbent which is used according to the invention is produced, it is preferred to use free radical initiators containing peroxide units together with a reducing agent. The examples of the appropriate reductive agents in this context are Fe2 +, ascorbic acid, sulfinic acid, sulfite and formamidinosulfinic acids and their salts. Suitable compounds containing three or four azo units, which may be mentioned by way of example, are the reaction products of azodicarboxylic acids with compounds containing more than two oxirane functions, with a preferred azodicarboxylic acid being 4,4 '- azobis (4-cyanovaleric acid), which forms suitable free radical initiators with, for example, polyglycerol-polyglycidyl ethers. Other suitable compounds within this group are the products of the reaction of the hydroxy- and amino-functional azo compounds with compounds containing more than two oxirane groups. Examples of suitable compounds of - this nature is 2, 2'-azobis (N, N-dimethylene-isobutylamidine) or its corresponding dihydrochloride, 2,2'-azobis (2-aminopropane) dihydrochloride, 2,2 r -zobis (2-methyl-N- (1, 1-bis (hydroxymethyl) -2-hydroxyethyl) propionamide), 2,2'-azobis (2-methyl-N- (1,1-bis (hydroxymethyl) ethyl) propionamide) or 2, 2'-azobis (2- methyl-N- (2-hydroxyethyl) prop? onamide), which form suitable free radical initiators with, for example, polyglycerol-polyglycidyl ethers. Azobisnitriles with tri- or poly-alcohols can also be mentioned. In this regard, the products of the 2,2'-azobisisobutyronitrile reaction with glycerol, trimethylolpropane, threitol, erythritol, pentaerythritol, arabitol, adonitol, xylitol, sorbitol, mannitol or dulcitol are particularly preferred. When the superabsorbent in question is produced, the free radical initiators mentioned above can be used by themselves or in arbitrary mixtures with each other. It is added in this context from 0.001 percent to 20 percent by weight and, preferably from 0.05 percent to 3.0 percent by weight of the free radical initiator, calculated on the total amount of the monomer. Even though the molecular weight that is appropriate for the free radical initiators employed can vary within wide limits, in particular it falls within the range of 100-10,000,000.

When the superabsorbent in question is produced, it is particularly preferred to use free radical initiators whose free radical-forming functions possess different reactivities, that is, they are activated by different mechanisms. These initiators consequently also contain both azo and peroxide or hydroperoxide functions, for example, whose functions are activated one after the other in a predetermined manner and can consequently be used, for example, to produce block polymers. In addition, it is advantageous to use initiators whose radical-forming functions are placed at different distances from one another in the molecule. When the superabsorbent in question is produced, it is also possible to use appropriate crosslinking agents, ie, compounds which possess at least two double bonds and which can be polymerized in the network that is formed by the synthetic polymer component. Suitable crosslinking agents are, in particular, methylenebisacrylamide and methylenemethacrylamide, respectively, unsaturated mono- or polycarboxylic esters of such polyols, such as diacrylate or triacrylate, e.g. diacrylate or butanediol methacrylate or ethylene glycol, trimethylolpropane triacrylate, as well as - vinyl methacrylate and allyl compounds such as allyl (meth) acrylate, triallyl cyanurate, diallyl maleate, polyallyl esters, allyl ethers or polyols, such as, for example, pentaerythritol diallyl ether and pentaerythritol triallyl ether , tetraalyloxetane, triallylamine, tetraalylethylenediamine, allyl esters of phosphoric acid and also vinylphosphonic acid derivatives. It is added in this context from 0 percent to 20 percent by weight and preferably from 0 percent to 3 percent by weight of the crosslinking agent calculated in the total monomer fraction. Using the aforementioned starting materials, the superabsorbent in question can be produced using previously known polymerization processes, for example, by polymerization in the aqueous phase in accordance with a reverse suspension polymerization process in the free radical initiator mentioned above. Specific preference is given in this context to the polymerization in a solution containing water, ie the so-called gel polymerization, with the content of the dry matter in the solution containing water, being between 50 percent and 60 percent by weight, the temperature being between 0 ° C and 130 ° C, preferably between 10 ° C and 100 ° C, and it being possible for the pressure to be an atmospheric pressure or - a pressure greater than this one. In addition, the polymerization can also be carried out under a protective gas atmosphere, for example, a nitrogen atmosphere. The basic polymerization process will not be described in greater detail in the present document, since it is well known to those skilled in the art and is beyond the scope of the present invention. The superabsorbent in question can also be subsequently crosslinked, in a manner known per se, in the gel phase containing water and / or finally crosslinked as ground polymer particles and screened. Compounds containing at least two groups which can form covalent bonds with the carboxyl groups and / or hydroxyl groups of the polymer composition are suitable crosslinking agents for these objects. Examples of suitable compounds which may be mentioned are the di- or polyglycidyl compounds, such as diglycidyl ester of phosphoric acid, alkoxysilyl compounds, polyaziridine, polyamine, polyamidoamine and their reaction products with epichlorohydrin, di- or polyalcohols, divinyl sulfone, or di- or poly-aldehydes such as glyoxal, for example. The glycidyl ether of phosphoric acid and the polyamidoamine-epichlorohydrin adducts are particularly preferred in this context.

After the polymerization has been completed, the quality properties of the polymerized material can be further improved by the polymerized gel containing water that is heat treated for a number of hours at a temperature of 50 ° C to 130 ° C, preferably at a temperature of 70 ° C. ° C to 100 ° C. After being mechanically divided using an apparatus that is appropriate for the object, the gelatinous superabsorbent thus obtained can be removed by means of a previously known drying process in order to provide a superabsorbent in solid form which is suitable for use . A particularly preferred drying process in this context in cylinder drying that allows the product to dry under mild conditions. After the superabsorbent has been obtained in solid, dry form, they are ready for use in an absorbent structure in accordance with the present invention. The superabsorbent used in the absorbent structures according to the invention imparts absorptive properties which are entirely satisfactory for the proposed applications. Due to the fact that both the superabsorbent used and the other components in the absorbent structures and products according to the invention are at least partly biologically degradable and at least partly based on renewable raw materials, the absorbent structures and the products in accordance with the invention offer great advantages compared to absorbent structures and conventional products, which are often based on high grade synthetic raw materials that are not degradable and are often based on crude oil or oil. These advantages are particularly evident with regard to disposable absorbent products such as diapers, incontinence guards, sanitary napkins or the like. The absorbent structures and products according to the invention preferably comprise mixtures or combinations of the specific superabsorbent and various fibers such as fluff pulp consisting of cellulose, rayon, peat, cotton, henequen, flax or the like. In addition, various synthetic fibers such as polyethene, polypropene, polyester, nylon, bicomponent fibers, split fibers or the like can be mixed. It is therefore possible to use both hydrophobic and hydrophilic fibers, which can be valuable with respect to ensuring the different absorption properties in the different layers in the absorbent structures according to the invention.

In addition, the absorbent structure according to the invention can be bonded or consolidated in different ways, for example, by melting the thermoplastic fibers that are included in the absorbent structure or by adding a special bonding agent. In addition, the absorbent structure according to the invention may have undergone additional processing such as pressing, embossing, calendering, hydroentanglement, mechanical smoothing or the like. Figures 3 and 4 show an absorbent product 11 in accordance with a preferred embodiment of the invention. In Figure 3, the absorbent product 11 is shown as seen from the side on which it is intended, during use, to be oriented towards the body of a user. In the described embodiment, the absorbent product is a diaper 11 and includes a fluid-permeable surface material 12 on the side which is intended to be oriented towards the user, during its use. In addition, the diaper 11 includes a barrier material 13 impermeable to the fluid on the side that is intended to be oriented away from the user during use. The fluid-permeable surface material 12 and the fluid impermeable barrier material 13 together enclose an absorbent structure 3 of - according to the invention and can be said to constitute a wrapping material for the diaper 11. In the described embodiment, the diaper 11 has an elongated shape with the front and rear sections 15, 16 wide and a narrower crotch section 17. The front section 15 is that part of the diaper 11 which, during use is intended to be applied on the front side of the wearer while the back section 16 is that part of the diaper 11 which during use is applied to the back side of the wearer. In addition, the diaper 11 has two longitudinal inwardly curved side edges 18, 19, a front edge 20 and a rear edge 21. The diaper 11 is of the type that, in use, is held together to enclose in this manner the lower part of the user's body in the manner of a pair of underpants. For this purpose, a tape tab 22, 23 is placed and projects from each side edge 18, 19 in the vicinity of the rear edge 21 of the diaper. The tape tabs 22, 23 are designed to interact with a clamping surface 24, which is placed in the fluid impermeable barrier material 13 in the front section 15 of the diaper 11. The clamping surface 24 preferably includes a certain shape of reinforcement, such as for example an additional layer of plastic and a liner which has been applied to the barrier material impervious to fluid 13. The types of alternative arrangements for holding together the diapers such as buttons and buttonholes, hooks and badges, buttons of pressure or similar, of course can also be used. Furthermore, in the described embodiment, the diaper 11 is provided with longitudinal elastic elements 25, 26 which are advantageously positioned along the lateral edges 18, 19. The elastic elements 25, 26 form the diaper 11 and function during use as the elastic of the leg. This means that the elastic elements 25, 26 retain the lateral edges 18, 19 of the diaper 11 in contact with the user's legs during use and prevent the formation of clearances between the diaper and the body of the user whose free spaces could lead through the rest to the escape of the fluid from the diaper 11. It is also possible to obtain embodiments of the product according to the invention where the elastic elements are placed in another way that is appropriate for the application. In a corresponding manner, the elastic elements 27, 28 are placed along the front edge 20 and the rear edge 21, with the aim of creating elastic seals around the user's waist. The absorbent structure 3 according to the invention can be said to constitute an absorptive core - in the described diaper 11, as is evident from the attached Figure 4. In the described embodiment, the second layer 5 mentioned above, immediately inside the fluid-permeable surface material 12 can be said to constitute a separating layer of the fluid whose task is to rapidly transport the fluid to the first layer 4 mentioned above, which has a higher content of superabsorbent than the other layers 5, 6. In this context, the task of the first layer 4 is to absorb, store and bind the fluid. In the described modality, in the third layer 6 of the absorbent structure 3 functions as a dispersion layer whose task is to transport the fluid towards the unusable parts of the first layer 4, in order to allow renewed absorption in those parts of the first layer 4 from where the fluid has been transported by handling with the aid of the third layer 6. This effect can be achieved in a manner that is well known to a person skilled in the art, for example, by selecting the raw fiber material and the content of the superabsorbent in the different layers in order to influence in this way, for example, the capillary forces and the hydrophilicity in the different layers in the desired manner. It is also possible to conceive of embodiments of the invention wherein the fluid receiving layer and the dispersion layer are not included in the absorbent structure 3, but instead are provided as separate material layers. A separate fluid receiving layer suitable in this embodiment advantageously consists of a relatively thick bulky fiber material which exhibits high resilience in both dry and wet states in order to avoid crushing in the wet state. Examples of suitable fiber materials in this context are non-woven materials, which are based on stiffened cellulose fibers and / or synthetic fibers such as polyethene fibers, polypropylene fibers, polyester fibers or the like. In the embodiments of the product according to the invention having separate layers of fluid reception and fluid dispersion, the absorbent structure is advantageously of the type that has been described above with reference to the accompanying Figure 1, that is to say comprising a single layer with essentially the same mixing ratio between the superabsorbent and the fibers. The dispersion layer in this embodiment advantageously consists of a powerfully compressed layer separated from hydrophilic fibers which provide small capillaries and, as a result, strong capillary forces and good dispersibility. The materials which have been found to be particularly suitable for this application and which may be mentioned are those which are described in Patent Numbers WO 94/10953 and WO 94/10956. The invention can be varied in many ways within the scope of the appended patent claims. As will already be apparent, it is possible to conceive both embodiments of absorbent products according to the invention wherein the absorbent structure according to the invention in principle consists of a complete absorptive body and also of embodiments in which the absorbent structure is combined with layers of dispersion or reception of separate fluids consisting of materials that are appropriate for these objects.

EXAMPLES With a scope to illustrate the invention, the absorptive bodies were manufactured in a normal manner using a pilot scale configuration device, a so-called sheet former in accordance with a technique that is well known to a skilled person. The resulting absorptive bodies were then evaluated using test methods that have been found to be suitable for absorbent structures that are intended for use with absorbent products to absorb body fluids.

- - The absorptive bodies were made by lint paste, which consists of soft bleached chemistry wood pulp that is mixed with different superabsorbents in a device intended for the object and subsequently configured in the sheet former in an absorptive core having one or more layers, after which the absorptive core was provided with a surface material in order to form an absorptive body to evaluate the absorptive properties. In the experimental series, the absorptive bodies were manufactured having four different absorptive cores in accordance with the following four experimental series: REF MIX: a layer of fluff paste containing a homogeneous mixture of 25 weight percent of the superabsorbent based on conventional acrylic acid, INV Mixture: a layer of fluff paste containing a homogeneous mixture of 25 weight percent of the superabsorbent, containing 30 weight percent starch, which was used according to the invention, CAPA REF; two identical external layers of 100 percent by weight of fluff pulp with an internal intervention layer containing a homogeneous mixture of 50 percent by weight of the conventional acrylic acid-based superabsorbent, with the content of the superabsorbent calculated on the weight of the set of absorptive core, being 33 weight percent, and CAPA INV; two identical outer layers of 100 percent by weight of the slurry with an internal intervention layer containing a homogeneous mixture of 50 weight percent of the superabsorbent, containing 30 weight percent of starch used according to the invention , with the content of the superabsorbent calculated in the weight of the whole absorptive group, being 33 weight percent. The absorptive bodies were provided with conventional surface materials, namely a fluid-impermeable polyethene film on the outside of the absorptive core on that side which, in an absorbent product, must be oriented towards the user during use, while the opposite side of the absorptive core, ie, the front side was provided with a thin hydrophobic nonwoven material, but permeable to the fluid. The absorptive bodies having four different types of absorptive cores were then evaluated with respect to the absorptive properties that were important for the application using the following test methods: Admission time and rewetting The test method is intended primarily to evaluate the different superabsorbents in an absorptive body. In principle, the method comprises adding the fluid retention capacity of the absorptive body during charging and also measuring the absorption time. The test method is carried out in the following manner: 1. The absorptive bodies having dimensions of x, and 28 x 10 centimeters are manufactured in the sheet former mentioned above, with the weight of the area being approximately 1000 grams. per square meter from which the weight of pulopa area constitutes approximately 750 grams per square meter. The volume of the pulp is adjusted so that it is finally about 8 cubic centimeters per gram. As has been evident previously, the core of the absorptive bodies also contains the desired content of the superabsorbent. 2. Before being tested, the absorptive bodies are conditioned at 23 ° C and relative humidity of 50 per cent for 24 +. 2 hours. 3. Before being tested, the absorptive bodies are weighed, with the weight of the surface material being subtracted before the weight of the absorptive core area is calculated. The absorptive bodies are marked at the proposed wetting point. 4. The thickness of the absorptive bodies is measured in a thickness gauge that is appropriate for the object, and the exact volume is calculated. If the volume is too high, the absorptive body is pressed into a pressing device that is appropriate for the object. Absorptive bodies whose volume is too low are discarded. 5. A volume of 60 milliliters of test liquid is measured. The test fluid used consists of the so-called synthetic urine, that is, a salt / water solution that adapts to resemble human urine. 6. A Plexiglas tube having an internal diameter of 23 millimeters is placed on top of the mark of the wetting point in the absorptive body. 7. The test liquid is added through the Plexigl tube in such a way that a column of liquid of 20 mm is maintained during the addition. The time (ti) for the entire volume of the liquid to be absorbed is determined using a stopwatch that is accurate to 0.01 s. 8. The dry weight of the bundle of fifteen pieces of filter paper is determined to an accuracy of 0.01 g. 9. 10 minutes after beginning the absorption, the bundle of filter papers plus a loading weight of 2550 grams are placed in the upper part of the absorbed body moistened. 10. After the load has been applied on the upper part of the absorptive body and the intervention filter papers for 15 seconds, the weight of the load and the bundle of filter papers is removed with the wet weight of the filter paper. determined to an accuracy of 0.01 g. After this, rewetting (rl) is calculated as a difference between the wet and dry weights of the filter papers. 11. Then add an additional 60 milliliters of the test liquid plus compensation for the previously calculated rewet (rl). 12. Repeating the aforementioned articles 7 to 11 twice, the additional absorption times (t2 and t3) and the additional re-wetting (r2 and r3) are determined in association with repeated wetting. In conclusion, ti, t2 and t3 are recorded up to an accuracy of ls and rl, r2 and r3 are recorded up to an accuracy of 0.1 gram. TABLE 1 provides the values of ti, t2 and t3, and rl, r2 and r3, for four different absorptive bodies in the example.

TABLE 1 Experiment Admission time, Rewet, second grams ti t2 t3 rl r2 r3 MIX REF 14 11 15 0.4 7.3 14.1 MIX INV 13 18 28 1.1 11.3 20.6 CAPA REF 33 42 50 0.6 7.0 19.5 CAPA INV 31 38 48 1.5 9.1 25.0 As can be seen from the results of the test obtained, the differences in the time of admission ti between MIX REF and MIX INV and between CAPA REF and CAPA INV, respectively, are relatively small. Therefore, it seems as if the absorptive bodies according to the invention (INV) exhibit an initial admission time ti, which is of the same order as that of the corresponding conventional absorptive body (REF). With respect to t2 and t3 for the two absorptive bodies containing a homogeneous mixture of slurry and the superabsorbent (REF MIX and INV Mixture), it seems as if the absorptive body according to the invention (INV Mixture) exhibits times of admission something - more prolonged (t3 and t3) than the corresponding conventional absorptive body (REF MIX). However, the results of the test for the two two-layer absorptive bodies (CAPA REF and INV CAPA) show that it is possible to produce absorptive bodies according to the invention (INV CAPA) having admission times (t2, t3) in association with repeated wetting that are as good as those for a corresponding conventional absorptive body (REF CAPA). All rewetting measures (rl, r2 and r3) provide higher values for the absorptive bodies according to the invention (INV MIX and INV CAPA) than for the corresponding conventional absorptive bodies (REF MIX and REF CAPA). However, the results of the test show that all the absorptive bodies produced in the experiments possess sufficiently good values with respect to both the intake and rewet times to be able to function extremely well in the absorbent product, such as a diaper, a protector of incontinence or a sanitary towel. Liquid dispersion Another important property of absorptive bodies is the ability to disperse liquid. A measure of this property that is meaningful to the application can be obtained by a test method, as described below: 1. The absorptive bodies to be evaluated are conditioned as described above, and are provided with a signal indicating a distance of 11 centimeters from one of the short ends. 2. A liquid container is placed on the side of a scale that is accurate to 0.1 gram as much as the liquid container as the scale has been carefully adjusted to the horizontal plane using a level of bubble. 3. An oblong Plexiglas plate is placed using support devices that are appropriate for the object on an upper part of the scale such that the Plexiglas plate is inclined 30 degrees with respect to the horizontal plane and in such a way that the number from the short ends of the Plexiglas plate projects downward towards the liquid container. At the same time, the inclined Plexiglas plate is not allowed to touch the edge of the liquid container. 4. The test liquid, ie synthetic urine, is added to the container up to 2 centimeters from the length of the inclined Plexiglas plate, which projects below the surface of the liquid.

. The absorptive body to be evaluated is weighed to an accuracy of 0.1 gram in order to provide 6. The absorptive body is placed on the inclined Plexiglas plate with the fluid permeable side up in this position and does not come in contact with Test liquid in the liquid container, and then the scale is subjected tied. 7. After that, the absorptive body is fixed with a clamp in a predetermined position using the aforementioned 11 centimeter mark and a mark or signal corresponding to the Plexiglas plate on the top of the inclined Plexiglas plate, without Let the absorptive body be placed in contact with the test liquid. 8. The absorptive body is now dropped down over the top of the inclined Plexiglas plate and, when doing so, one of its short ends is immersed in the test liquid in the liquid container. 9. Using a computer, the reading of the scale is recorded continuously for 60 min., While the level of test liquid in the liquid container remains constant, after which the measurement is discontinued from the absorptive body is removed from its position at the top of the inclined Plexiglas plate.

- . The wetting length of the wet region in the longitudinal direction of the absorptive body is measured in centimeters. 11. The dispersion capacity of the absorptive body liquid after 5 and 60 minutes of measurement, respectively, is calculated in a unit of gram / gram, according to the formula; liquid dispersion = m2 / m ?, where m is the dry weight of the absorptive body, while m2 is the weight read from the scale at the respective time point. TABLE 2 presented below provides the results obtained from the measurement of the liquid dispersion carried out in four absorptive bodies, described above. TABLE 2 Experiment Liquid dispersion, gr / gr Wetting length 60 min. cm min 60 min MIX REF 9. .3 14. .2 28 MIX INV 8, .2 11. .1 26.7 LAYER R? F 8. .9 15. .9 28 LAYER INV 8. .1 14, .4 28 As can be seen from the TABLE 2 above, the absorptive bodies according to the invention (INV MIX and INV CAPA, respectively) each exhibited a somewhat lower liquid dispersion capacity than the corresponding conventional absorptive body (REF MIX and REF CAPA, respectively). In summary, the absorbent structures according to the invention offer completely satisfactory absorptive properties for use in absorbent products, without any specially adapted configuration processes and the like being required during manufacture. In addition, the invention offers additional advantages such as the fact that the absorbent structures and the products according to the invention to a high degree are based on renewable raw materials that exhibit high biological degradability. In the foregoing, the invention has been described with reference to the appended figures, preferred embodiments and examples. However, the invention must somehow be considered as being fed to that to which it refers in this context; on the contrary, its scope is defined by the subsequent patent claims. In this way, the content of starch or starch derivatives in the superabsorbent employed by the invention, for example, can be varied within wide limits. Taking into account the fact that one of the main purposes of the invention is to provide absorbent structures and products that are based on raw materials having high renewability, the modalities are particularly advantageous in which the dry superabsorbent contains more than 30 percent by weight. weight of the starch and / or chemically modified starch, and wherein at the same time, the dry superabsorbent constitutes between 15 percent and 65 percent of the dry weight of the absorbent structure. In the particularly preferred embodiments of the absorbent productsIn accordance with the invention, the enclosing material is also at least partially biologically degradable in order to improve the compositional capacity and at least partially based on raw materials exhibiting high renewability. In this regard, the content of the biologically degradable material, preferably the starch, is preferably greater than 10 weight percent of the weight of the shell material.

Claims (15)

- R E I V I N D I C A C I O N S

1. An absorbent structure containing a superabsorbent which has been produced from one or more hydrophilic monomers by copolymerization of free radical in the presence of chemically modified starch and / or starch, characterized in that use has been made, during the production of the superabsorbent, of an initiator of free radical that forms three or more radical sites per molecule, and free radical copolymerization has been carried out in the aqueous phase, and in which the absorbent structure (1, 3) includes hydrophilic and / or hydrophobic fibers which, together with The superabsorbent imparts a hydrophilic character to the absorbent structure and in that, in the dry state, the superabsorbent constitutes between 10 percent and 75 percent of the dry weight of the superabsorbent structure.

The absorbent structure according to claim 1, characterized in that the dry superabsorbent contains more than 30 weight percent of starch and / or chemically modified starch, and in that, at the dry end, the superabsorbent constitutes between 15 one hundred and 65 weight percent dry weight of the absorbent structure (1).

3. The absorbent structure according to claim 1 or 2, characterized in that the absorbent structure (1) comprises a single layer (2) exhibiting essentially a constant mixing ratio between the fibers and the superabsorbent, and in that, in the dry, the superabsorbent constitutes between 20 percent and 30 percent by weight of the dry weight of the absorbent structure (1). .

The absorbent structure according to claim 1 or 2, characterized in that the absorbent structure (3) includes several layers (4, 5, 6) of which, at least one layer (4) has a higher content of the superabsorbent than the other layers (5, 6), and in that, in the dry state, the superabsorbent [in this context] constitutes between 40 percent and 60 percent by weight of the dry weight of the first layer (4).

The absorbent structure according to claim 4, characterized in that the first layer (4) remains in contact, on two opposite sides, with the layers (5, 6) of the different layers having a lower content in superabsorbent in the first layer (4).

6. The absorbent structure according to any of the preceding claims, characterized in that the superabsorbent includes hydrophilic monomers according to the general formula: R3 R1 I I CH = C I R2 wherein R1 is hydrogen, methyl or ethyl; R2 is a group of -COOR4, sulfonyl groups, phosphonyl groups, phosphonyl groups which are esterified with (C1-C4) -alkanol or a group having the formula _O CH3 NH C - CH2 - R and R is hydrogen, methyl, ethyl or carboxyl groups; R is hydrogen or amino- or hydroxy- (C 1 -C 4) -alkyl; and R is sulfonyl groups, phosphonyl groups or carboxyl groups.

The absorbent structure according to any of the preceding claims, characterized in that the starch that is included in the superabsorbent is native starch or pregelatinized maize starch, native or pregelatinized wax maize starch, native or pregelatinized potato starch, native or pregelatinized wheat starch, native or pregelatinized amyl maize starch or native or pregelatinized tapioca starch and / or in which the chemically modified starch that is included in the superabsorbent is degraded into catalytic acid, enzymatically or thermally, oxidized starch, starch ether such as allyl starch or hydroxyalkyl starch such as 2-hydroxyethyl starch, 2-hydroxypropyl starch or 2-hydroxy-3-trimethylammonium propyl starch, or carboxyalkyl starch such as carboxymethyl starch, starch ester such as starch formate, starch acetate, starch acrylate, starch methacrylate or starch benzoate, starch ester such as starch succinate or starch maleate, carbamic starch ester (starch urethane), starch dithiocarbon ester (starch xanthate), or starch ester of inorganic acids such as starch sulfate, starch nitrate or starch phosphate, starch ester ether such as 2-hydroxyalkyl acetate starch, or complete starch acetals such as the reaction products of starch with aliphatic or cyclic vinyl ether.

8. The absorbent structure according to any of the preceding claims, characterized in that the starch that is included in the superabsorbent is pregelatinized maize starch or pregelatinized potato starch, and / or because the chemically modified starch that is included in the superabsorbent is starch of carboxymethyl, starch succinate or starch maleate.

The absorbent structure according to any of the preceding claims, characterized in that the free radical initiator employed when the superabsorbent is produced is a compound containing at least three hydroperoxide units, peroxide units or azo units.

10. The absorbent structure according to any of the preceding claims, characterized in that the free radical initiator employed when the superabsorbent is produced is a reaction product of azobisbutyronitrile and trimethylolpropane.

11. The absorbent structure according to any of the preceding claims characterized in that the free radical initiator employed when the superabsorbent is produced is a polyhydroxy peroxide which has been obtained by the anodic oxidation of a piolicarboxylic acid in the presence of oxygen.

The absorbent structure according to any of the preceding claims, characterized in that the superabsorbent has been produced by polymerizing a solution containing between 15 percent and 60 percent by weight of one or more hydrophilic monomers, in the presence of starch and / or chemically modified starch, by means of a gel polymerization process in the presence of a free radical initiator that is capable of forming triradicals or polyradicals.

13. The absorbent product (11) such as a diaper, an incontinence protector or a sanitary napkin including an absorptive body enclosed by a sheath material at least partially permeable to the fluid, characterized in that the absorptive body includes an absorbent structure of according to any of claims 1 to 12. 1.

The absorbent product according to claim 13, wherein the wrapping material includes a fluid permeable surface material (12) on the side of the absorbent structure (3) which is intended to be oriented towards a user during the use of a material of fluid impermeable barrier (13) on the side of the absorbent structure (3) which is intended to be oriented towards the user during use, characterized in that the fluid-permeable surface material (12) and / or the barrier material ( 13) includes one or more biologically degradable materials that have a high degree of renewability in a mixture that is greater than about 10 weight percent of the total weight of the wrapping material.

15. The absorbent product according to claim 14, characterized in that the starch is included in the biologically degradable material.