MXPA99006644A - Absorbent structure having improved absorption properties - Google Patents

Abstract

An absorbent, porous structure (4), intended for use in an absorbent article, wherein the structure (4) exhibits a first region (19), primarily consisting of a first material, which stands in direct connection with a second region (20), primarily consisting of a second material. The receding wetting angle&thgr;r is larger for the first material than for the second material, whereby liquid transport between the two regions (19, 20) takes place in a direction from the first region (19) to the second region (20), at least when the porous structure (4) is wet.

Description

ABSORBENT STRUCTURE WHICH HAS IMPROVED ABSORPTION PROPERTIES TECHNICAL FIELD The invention relates to a porous, absorbent structure, intended for use in an absorbent article, wherein the structure has a first region, consisting primarily of a first material, which is direct connection to a second region, which consists primarily of a second material. BACKGROUND OF THE INVENTION A great problem, in relation to the construction of absorbent bodies for absorbent articles of the type mentioned, is to achieve an optimal combination of a sufficiently large capacity for liquid acquisition, a sufficient local and total absorption capacity as well as a capacity of sufficient distribution of liquid. In addition, it is essential that the absorbent article can retain bodily fluids absorbed in such a way that rewetting is avoided, ie the liquid exit of the article. Another important property, especially in the case of diapers and incontinence guards, is that the article can repeatedly receive and absorb relatively large amounts of liquid emitted over a short period of time. One type of absorbent bodies commonly used for absorbent articles consists of one or more layers of cellulose fluff pulp. When an absorbent body of this type is moistened, the region of the absorbent body initially reached by the liquid absorbs essentially all of the liquid. In this way, this region becomes saturated with liquid and, when subsequent wetting occurs, the absorbent body no longer has sufficient capacity to receive all the excreted body fluid. Accordingly, the liquid flows on the surface of the article and leaks around the edges of the article. In order to solve any leakage, it has been suggested to equip the absorbent body with compression patterns of different types and therefore increase the liquid distribution capacity of the article. An example of a compression pattern of this type is the presence of grooves extending in the longitudinal direction of the article. In this way, it is possible to achieve a certain drainage of the initially unidified region in the absorbent body, since the finer capillaries in the compressed portions of the absorbent body better transport the liquid than the adjacent portions of the absorbent body. Said capillary transport, however, is relatively slow and the drainage of the unidified liquid region is therefore frequently incomplete and insufficient. Another problem, in relation to compressed fiber structures, is that the compressed regions swell when wetted, while the less compressed neighboring regions frequently collapse. Accordingly, the initial differences in capillary size in the structure are matched, and the liquid distribution capacity of the fiber structure is reduced. One way to prevent the flow of liquid on the surface of the absorbent body is to fix two or more absorbent layers with mutually different properties on top of each other. For example, in accordance with document O93 / 15702, a top layer, intended to face the user during use, therefore consists of a cellulose fluff pulp with a high critical volume and a network of comparatively thick capillaries, while that a lower layer consists of a layer of cellulose fluff with a lower critical volume and finer capillaries. The critical volume refers to the volume in which the pulp de noras swells or collapses when wetted. The intention of such a construction is that the liquid must be able to penetrate quickly into the upper, more porous layer, and then be gradually drained by means of draining the upper layer by the finer capillaries in the lower layer. It is expected that the upper layer is emptied sufficiently of liquid in order to prevent leakage when the absorbent body is subjected again to the arrival of body fluid. Nevertheless, in practice, it has been found that this does not work in the expected way. This is because the surface properties of the fibers in the two layers of cellulose fluff are such that the drainage of the liquid from the upper layer to the lower layer is not carried out in the expected magnitude based on the difference of size of capillaries. One type of cellulose fluff pulp with a high critical volume is a chemisermomechanically manufactured fluff pulp, known as CTMP. In a structure of the type presented in document O93 / 15702, CTMP is combined with a chemically manufactured fluff pulp, called CP, which has a lower critical volume. Such pulps also initially have a difference in terms of hydrophilicity, or wetting capacity, where CTMP is less hydrophilic than CP. Such a difference in hydrophilicity facilitates the transport of the liquid in one direction from a region consisting of CTMP to a region consisting of CP. During wetting, however, the surface properties of the cellulose fibers change, such that all cellulose fluff pulp which is in a dry state has a lower wetting capacity instead of becoming more hydrophilic. The reason for this situation among other things, is that the surface chemical properties of the pulp fibers change since a reorientation occurs on the fiber surfaces in such a way that hydrophilic groups are concentrated, as a result of which the fiber surfaces are they become more humid. Another reason that contributes to the properties of the charged surface is that there is a change in resins and other components such as, for example, because certain components dissolve while others more hydrophilic migrate to the fiber surfaces. SUMMARY OF THE INVENTION Throughout the present invention, however, an absorbent structure of the type mentioned in the introduction has been achieved wherein the problems of liquid transfer between the regions in the absorbent body, consisting of absorption materials with properties different surface, have been eliminated to a large extent. An absorbent structure in accordance with the present invention is primarily characterized in that the return wetting angle thetar is greater for the first material than for the second material, as a result of which liquid transport between the two regions is carried out at an address from the first region to the second region when the porous structure is wet.

In accordance with a beneficial embodiment, the advance wetting angle thetaa is greater for the first material than for the second material, as a result of which liquid transport is carried out from the first region to the second region, regardless of If the structure is dry or wet. It is advantageous for the transfer of liquid between the regions in the absorbent structure that the average pore size in the absorbent structure be greater within the first region with the first material than within the second region with the second material. For example, since a porous fiber material has pores, or hollows of different sizes within a range of sizes, it is possible to define an exact pore size. The term "pore average" refers to an average pore size in the absorbent structure, so it is desirable that most pores have a size close to the average pore size. The pore size is small and the liquid transport properties of the structure are easier to predict, based on the knowledge of average pore size According to one embodiment of the present invention, the first region consists of a first layer in the absorbent structure, and the second region consists of a second layer in the absorbent structure, where the two layers are in direct connection between them through the surfaces of the layers resting on each other. they can be constituted by layer parts of the same material, therefore, the division of the material layer into different regions can be such that the first layer n and the second region are arranged side by side in the plane of the material layer. However, it is also possible to design an absorbent structure in accordance with the present invention which shows a layer of material where the two regions of material are different surface properties are arranged side by side in the thickness direction of the material layer . Another possibility, within the scope of the present invention, is to arrange several regions with mutually different retraction wetting angles in such a way that a wetting angle gradient is formed in the absorbent structure, said gradient of wetting angles can occur in a substantially flat absorbent structure, showing one thickness direction and two opposite major surfaces. Thus, a gradient of wetting angles in the direction of thickness of the structure can be achieved by means of the integrated multilayer structure, where the receding wetting angle decreases in one direction from one surface of the structure to the other surface. Correspondingly, a moistening angle gradient can be created in the plane of the structure by arranging regions with different moistening angles receding side by side in the plane. It is obviously also possible within the scope of the present invention to design a structure that shows a gradient of wetting angles both in the thickness direction and in the plane. It is an additional advantage if the regions in the structure also have a gradient in the advance wetting angle. According to another embodiment of the present invention, the first material itself has a receding wetting angle that is essentially equally large, or equally small, than the backward wetting angle of the second material. In order to achieve the desired difference in wetting angles between the two regions of material in the absorbent structure, the first material is treated with an agent in order to raise the back wetting angle above the value of the angle of rewet wetting of the second material. The invention is well suited in relation to absorbent structures where the first region consists primarily of chemithermomechanical cellulose fluff pulp (CTMP), and the second region consists of chemical cellulose fluff pulp (CP) and where the surface of the CTMP fibers have been treated with an agent in order to increase the back wetting angle. With such a treatment of the CTMP fibers, it has been found that it was possible to increase the back wetting angle from 0 ° -10 ° to about 40 °, which gives the absorbent structure some liquid transport properties considerably improved by means of improving liquid transfer between adjacent regions with a different fiber structure. Other absorption materials that can be used when designing an absorbent structure in accordance with the present invention are different types of absorbent foams, absorbent structures, bonded or unbound fibers consisting wholly or partially of absorbent fibers such as cotton, viscose, peat, flax, or similar. A useful agent for raising the back wetting angle is ethylhydroxyethylcellulose (EHEC) which is applied to the absorbent structure, for example, by spraying or coating with a liquid containing the agent, for example, in the form of a solution or suspension, or by any other known method of surface treatment. The absorbent structure according to the present invention can also constitute all or a part of a body absorbed in an absorbent article, such as a diaper, sanitary napkin, or incontinence protector. Said absorbent article has a liquid permeable coating layer, a liquid impermeable coating layer, an absorbent body enclosed between the two coating layers. In a case in which the first region is constituted by a first layer in the absorbent body and the second region is constituted by a second layer in the absorbent body, the first layer suitably faces the liquid permeable coating layer and the second layer faces the liquid impervious coating layer. As a general rule, an absorbent article has an elongated shape with two end portions and a crotch portion, arranged between the end portions, intended to be placed in the crotch of a wearer during the use of the article and therefore to serve as a region. of reception for the body fluid emitted towards the article. Thus, it is advantageous that the first region consisting of the first material substantially coincides with the crotch portion of the article.

Making sure that the regions of material in the absorbent structure show differences in wetness angles at least in a wet state, but preferably also in a dry state, it is possible to obtain a controlled and predictable distribution of liquid in the absorbent structure. When a small drop of liquid is placed on a regular surface in a solid state, one of two possible events occurs depending on the properties of the liquid and the solid material, respectively. The liquid can either be spread on the surface or can remain in the form of a drop in the solid material. In this last case, the small drop will form a definite angle with the surface of the solid material. Theoretically, the theta contact angle can adopt values between 0 ° and 180 °. In practice, however, the contact angle never reaches 180 ° since the force of gravity distorts the shape of the small drop. A contact angle theta = 0 ° implies that the liquid spreads spontaneously on the surface. The contact angle theta = 90 ° constitutes the wetting limit. When the contact angle is less than 90 °, the liquid will be absorbed spontaneously in the pores of the material, while a contact angle greater than 90 ° implies that a pressure must be applied in order to make the liquid penetrate in the pores. However, the 90 ° limit is true only for capillaries that have parallel walls. The dynamic contact angle refers to the angle presented when a liquid front is moving. The terms "advancing and receding wetting angle" are intended to specify whether the dynamic contact angle is measured when a liquid advances on a dry surface, or when the liquid recedes in a recently wetted area. The importance of the recoil dampening angle to achieve good liquid transfer between two components in an absorbent structure was not previously known. By providing a sufficiently large difference between the backward dampening angles of adjacent regions in an absorbent structure, it is, therefore, by means of the present invention, possible to construct an absorbent fiber structure where the liquid transfer properties do not change when The fiber structure is moistened. As a result of the difference in the receding wetting angle, between the different regions in the fiber structure, the region having the smallest wetting angle also has the ability to drain liquid from a region in the fiber structure with a higher recoil dampening angle.

The liquid transfer between two adjacent regions in a fiber structure also depends on the pore size in the two regions. If the regions have the same pore size, the difference in the backward dampening angle should be greater than the smallest of the pores. This implies that a structure very strongly compressed with small pores, in some cases can drain a more hydrophilic, less compressed structure. In practice, however, it has been found that differences in pore size are compensated after wetting. The reason for this situation is that wet structures swell or collapse in such a way that the two fiber structures that initially had different pore sizes become relatively similar after wetting. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be described in more detail with reference to the figures shown in the accompanying drawings, wherein Figure 1 shows a plan view of a diaper seen from the side intended to face the user. during its use; Figure 2 shows a cross section through the diaper of Figure 1, along the line II-II; Figure 3 shows a plan view of an incontinence protector, observed from the side intended to face the user during use; Figure 4a shows a cross section on the side of the line IV-IV through the incontinence protector in figure 3, and presenting an absorbent body according to a first embodiment of the present invention; Figure 4b shows a. cross section along the line IV-IV through the incontinence protector in figure 3, and having an absorbent body according to a second embodiment of the invention; Figure 5 is a schematic illustration of an instrument arrangement for the determination of contact angle. Figures 6a-c show examples of the graphs recorded during the determination of the contact angle. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The diaper 1 illustrated in FIGS. 1 and 2 comprises a first liquid-permeable coating layer 2, a second liquid-impermeable coating layer 3, and an absorbent body 4 enclosed between the coating layers. . The two coating layers 2,3 have a slightly greater extension in the plane than the absorbent body 4 and project beyond the absorbent body 4 around its entire periphery. The coating layers 2, 3 are mutually connected within the projection portions 5, for example, by means of glue or either heat welding or ultrasonically.The liquid-permeable coating layer 2 is constituted for example by a layer of non-woven fiber fabric, which is known as a non-woven material or by a perforated plastic film, a gauze material or the like. The coating layer 2 may also obviously consist of a laminated film of two or more layers of any of the listed materials. The liquid-impermeable coating layer 3 may consist of a liquid-impermeable plastic film, a protected layer that has been coated by a liquid barrier material, or any other layer of easily foldable material having the capacity to resist the penetration of liquids. As a general rule, it is advantageous if the liquid-impermeable coating layer 3 has a certain restoring capacity, that is, if it allows the passage of water vapor through the layer 3. The diaper 1 has an elongated shape, with front and rear portions 6,7 wider and a narrower crotch portion 8. The front portion 6 is the part of the diaper 1 intended to face the wearer when the diaper is employed and the back portion 7 is the part of the diaper facing backward in the wearer. In addition, the diaper 1 has two longitudinally concave curved side edges, 9, 10, a front edge 11 and a trailing edge 12. The diaper 1 is of the type which is fixed together during use in such a manner that, similarly a trouser covers the lower portion of the user's torso. For this purpose, a tape flap 13, 14 is arranged which projects from each side edge 9, 10 near the trailing edge 12 of the diaper. The tape flaps 13, 14 have the purpose of interacting with a receiving area 15, which is located in the liquid impermeable coating layer 3, on the front portion 6 of the diaper 1. Said receiving area 15 presents in a Some type of reinforcement is suitable, for example, in the form of an additional plastic layer or a coating applied in the liquid-impermeable coating layer 3. Alternatively, it is obviously possible to conceive the use of other types of fixing devices for the diaper 1, such as buttons and eyelets, hooks and eyelets, pressure fasteners, hook and loop closure devices, or the like. The diaper 31 is further equipped with longitudinal elastic members 16, 17, applied with pretension, arranged in a substantially V-shaped pattern with the V directed towards the front edge 11 of the diaper and the two legs directed towards the trailing edge 12. of the diaper. The elastic members 16, 17 form the diaper 1 and constitute their leg elastics during the use of the diaper. Consequently, the elastic members 16, 17 serve to maintain the lateral edges 9, 10 of the diaper resting on the user's legs, in order to avoid the formation of gaps between the diaper and the user's body in use, through said gaps the body fluid could leak from the diaper. Correspondingly, an elastic member 18 is arranged along the trailing edge 12 of the diaper in order to achieve an elastic seal around the wearer's waist. The absorbent body 4 consists of two absorption layers 19, 20 with a mutually different position. The first absorption layer 19 is immediately arranged inside the liquid-permeable coating layer 2, and the second absorption layer 20 is arranged close to the liquid-impermeable coating layer 3. The absorption layers have a shape and mutually different sizes, whereby the first absorption layer 19 is smaller than the second absorption layer 20 and has a substantially rectangular shape, while the second absorption layer has a T-shape with the transverse bar of the T in the front portion 6 of the diaper. The first absorption layer 19 consists primarily of cellulose fluff pulp manufactured chemometrically., known here as CTMP. A layer of said fluff pulp has a relatively open structure with relatively large capillaries, since the CTMP fibers are rigid and relatively thick. The structure also remains largely after wetting, since the fibers retain a large part of their stiffness. Accordingly, an absorption layer 19 of CTMP fibers has a high instantaneous liquid acquisition capacity, a good liquid holding capacity, but a relatively low liquid wicking capacity. The second absorption layer 20 consists primarily of chemically manufactured cellulose fluff pulp, known here as CP. The fibers in a fluff pulp of this type are thin and foldable and form a fiber structure with relatively small capillaries when formed in a layer. A CP fiber absorption layer has a high liquid wicking capacity, but the absorption in the layer 20 is carried out slowly due to the small size of the capillaries. In addition, the volume of liquid that can be absorbed in a CP fiber structure is limited, especially since the fibers collapse when wetted. By means of their mutually different properties, the two absorption layers 19, 20 fulfill different functions, thus, the first absorption layer serves as a reception layer for the liquid emitted towards the diaper 1. The first absorption layer 19 must be able to receive rapidly large amounts of liquid during a short period of time, that is, said layer must have a high capacity of instantaneous absorption of liquids. The layer 19 must also be able to retain the liquid until its successful absorption by the second absorption layer 20. Thus, the second absorption layer 20 constitutes a layer for storage and distribution of the liquid. The liquid absorbed by the second absorption layer 20 is distributed through the capillary structure of the layer, away from the region of the layer initially wetted by the liquid. As a result of this, a new liquid can be absorbed gradually from the first absorption layer, ie, from the first absorption layer 19 to the second absorption layer 20. In order to make possible the use of the construction with two absorption layers 19, 20 having different absorption properties in a predicted manner, it is essential that the liquid is always transferred from the first absorption layer to the second absorption layer. This implies that the affinity of the liquid of the second absorption layer 20 must be greater than the affinity of the liquid of the first absorption layer 19, in order to ensure that the transfer of the liquid between the layers 19, 20 is always carried out in the right direction. The fibers of untreated CTMP usually have an advance wetting angle, thetaa which during wetting with water is between 40 ° and 60 °, while the reverse wetting angle, thetar, is between 0 ° and 20 ° . The corresponding values for CP fibers (chemical pulp) are thetaa between 20 ° and 30 °, and thetar of about 0 °. This implies insofar as the fiber structure is dry, liquid transport occurs in a direction towards the second absorption layer 20, since the advance wetting angle is greater in the second absorption layer 20 than in the second absorption layer 20. first absorption layer 19. As soon as the layers are wet, however, there is no difference as to the wetting angle and the liquid transport between the layers stops accordingly. Thus, the expected drainage of liquid from the first absorption layer 19 to the second absorption layer 20 is not carried out. In order to ensure the realization of the transport of liquid in a direction from the first absorption layer 19 to the second absorption layer 20, the CTMP fibers of the first absorption layer 19, in accordance with the present invention, have been treated in order to increase the back wetting angle thetar said increase in thetar can, for example, be achieved by the treatment of fibers of cellulose with an agent that increases thetar. Some examples of agents that can be used for the thetar increase are polymers such as ethylhydroxyethyl cellulose, abbreviated below as EHEC, polyvinyl alcohol (PVA) and poly-n-isopropylacrylamide.

(PNIPAM). Other useful agents are different polysaccharides, cellulose derivatives, surfactants anchored on the surface of the absorption material as well as polymeric surfing agents. As mentioned above, the agent that increases the wetting angle can be applied to the fibers by means of any known technique for surface treatment of the fibers. Accordingly, the agent can, for example, be sprayed or otherwise applied to the fibers in the form of a liquid containing the agent. The increase of the thetar back wetting angle that is obtained when dealing with CTMP with EHC, is of a magnitude of 40 °. Since the CP fibers have a thetar back shrinkage angle which is 0 °, the transport of liquid in the absorbent body 4 will always be carried out in a direction from the first absorption layer 19 to the second absorption layer. The incontinence guard 30 illustrated in Figures 3,4a and 4b, comprises a liquid permeable coating layer 32, a liquid impermeable coating layer 33, and an absorbent body 34 enclosed between the coating layers 32, 33. The liquid-permeable coating layer consists, for example, of a layer of non-woven fiber fabric, which is known as a non-woven material, or of a perforated plastic film, a gauze material or the like. . The liquid-impermeable coating layer 33 may consist of a liquid-impermeable plastic film, a nonwoven layer that has been coated with a liquid barrier material, or any other layer of easily foldable material having the ability to resist the penetration of liquids. It is generally an advantage if the liquid impervious coating layer 33 shows a certain breathing capacity, that is, if it allows the passage of water vapor through the layer 33. The two coating layers 32, 33 have an extension slightly greater in the plane than the absorbent body 34 and extends over a distance away from the absorbent body 34 around its entire periphery. The coating layers 32, 33 are mutually connected within the projection portions 35, for example, by glue or welding with application of heat or ultrasound. On the outside of the liquid-impermeable coating layer 33, a fixing member 36 is arranged in the form of two transverse regions with self-adhesive glue. Prior to use, the fixation member 36 is suitably coated with a peelable protective layer, not illustrated in the drawing, of paper treated with release agent, plastic film, or the like. Instead of the illustrated glue pattern, in the form of the two transverse glue regions, numerous other glue patterns can be used, such as for example one or more longitudinal regions, dots, full coating, etc. Alternatively, other types of fastening members may be used, such as for example hook and loop surfaces, snaps, bands, special trusses, or the like. An incontinence guard 30 of the type illustrated in the figures has the primary purpose of being used by people with relatively mild incontinence disorders and therefore has a size that can be easily accommodated within normal trusses. Accordingly, the fastening member 36 serves to hold the incontinence guard in place within the truss. The incontinence guard 30 is substantially in the shape of an hourglass, with wider end portions 37, 38 and a narrower crotch portion 39, located between the end portions 37, 38. The crotch portion 39 is the portion of the incontinence protector intended for application in the wearer's crotch during use and serves as a reception area for excreted body noise towards the 30 incontinence protector., the incontinence guard 30 shows two transverse rounded end edges 40.41 and two longitudinal curved side edges 42, 43 extending between the end edges 40, 41. Two alternative constructions of the absorbent body 34 are shown in Figures 4a and 4b. of the incontinence guard 30 in Figure 3. The absorbent body 34 shown in Figure 4a is formed of a coherent absorption layer that shows a first region 49, consisting primarily of a first type of fibers, and a second region 50. , which consists primarily of a second type of fibers. The first region 49 has essentially an oval shape and lies in the plane of the absorbent body 34 located substantially in the crotch portion 39 of the incontinence guard 30. In the direction of the thickness of the absorbent body, the first region 49 extends from the liquid-permeable coating layer 32 of the incontinence guard 30, up to a distance in the direction toward the liquid-impermeable coating layer 33, but not until reaching the liquid-impermeable coating layer 33. Thus, the first region 49 is encompassed by the second region 50 throughout, except on the surface 51 of the first region 49 facing towards the liquid permeable coating layer 32. The first region 49 of the absorbent body consists primarily of a material of fiber, which, compared to the second region 50, has a higher wetting angle, both in state wet as in dry state. This implies that both the thetaa advance wetting angle and the thetar backward wetting angle are higher for the first region 49 than for the second 50 region. Such a difference in wetting angle can be achieved either by choosing materials that from one principle shows a sufficient difference in terms of the magnitude of the wetting angles. Alternatively, the difference can be achieved by treating the material in one or both regions 49.50 with an agent in order to change the wetting angles. Agents suitable for this purpose have been described in connection with the diaper shown in Figures 1 and 2. It is not necessary that the material in the regions 49, 50 be constituted of different types of materials, but the absorbent body may be constituted by a single material layer where the difference at least in terms of the back wetting angle of the different regions has been achieved by treating the material in one or both regions 49.50, so that the surface properties of the absorption material have changed Also, the absorbent body 34 ', illustrated in Figure 4b, shows a first region 49' and a second region 50 '. The only difference between the absorbent bodies 34, 34 'in Figures 4a and 4b is that the first region 49' in Figure 4b extends through the entire thickness of the absorbent body 34 '. Determination of wetting angles The different wetting angles that are important for the present invention were determined by means of the apparatus illustrated in Figure 5. Thus, the Wihelmy method was employed. The balance that was used for the determination of the contact angles in relation to the invention is manufactured by Cahn Instruments in California, United States of America. The model number is DCA-322, where DCA represents * Dynamic Contact Angle. "A Compaq 386/20 personal computer was used to control the instrument, the same computer was also used to record data from the measurements and to carry out the subsequent calculations During a measurement, a fiber 65 is suspended vertically on an extremely sensitive balance 60. A liquid container 64 is placed on a moving table 61, directly below the fiber 65. By means of the elevation of the table 61, the liquid surface 69 moves upwards towards the fiber 65. When the fiber 65 is immersed in the liquid 68, a meniscus of the liquid, which affects the partially submerged fiber with a vertical force is formed around the fiber 65. The force arising between the liquid 68 and the fiber 65 can be either positive or negative, depending on the surface properties of the liquid and the fiber. An attractive force, that is, a positive force arises when the contact angle between the fiber and the liquid is less than 90 °. When the system shows a contact angle greater than 90 °, on the other hand, the liquid and the fiber will reject each other and the force becomes negative. The latter is valid, for example in the case of a polypropylene fiber immersed in distilled water. The force of attraction or repulsion is measured by means of the balance. The force is related to the contact angle in accordance with: F = Yt- P cos? + mg - pL 1 g A; where F = measured force (N)? L = the surface energy of the liguid (J / m2) p = the circumference of the fiber? = contact angle at the fiber / liquid-air interface (°) m = the mass of the moted fiber (kg) g = the gravity constant (m / s2) pL = the density of the liquid (kg / m3) 1 = the length of the wetted fiber (m) A = the cross-sectional area of the fiber (m2) ) The contact angle can vary along the fiber and around said fiber, and an average calculated over the entire periphery of the fiber is contemplated in the equation. The second term in the equation represents the weight of the mounted fiber, while the third term of the equation is what is known as the "floating force", that is, the weight loss that arises as a result of the volume of the displaced liquid. In a computer (not illustrated) equipped with a calculation program for the determination of the contact angle, these two terms are usually taken into account, thus simplifying in some way the equation a: F =? L p eos theta When the fiber 65 is immersed in the liquid 68, the value of the advancing contact angle thetaa is obtained In order to obtain a value of the return contact angle thetar, the fiber 65 is raised from the liquid 68 by means of lowering the moving table 61. Theta contact angles, thetar are dependent on the speed of the liquid front, and therefore it is important that the moving table 61 is raised and lowered with a constant speed. moreover, the speed must be sufficiently low to allow the system to have the time necessary to reach equilibrium at each point during the measurement. In addition, both the temperature and the humidity in the sample chamber must be controlled. Balance 60 has three balance plates (see figure 5). A first plate A has a precision of 10"dg, and therefore is suitable for the measurement of contact angle in fibers, however, the balance can also be used for measurements of surface energy in liquids, where a second plate is used B less precise The balance is stopped by placing counterweights on a third plate C. In order to prevent drafts, dust, or the like from disturbing the measurement, the plates and the moving table 61 are protected by structures sliding glass 62. These also allow the control of humidity and air temperature.In order to avoid vibrations during the course of measurement, the balance is placed on a base (not shown) .The table where the container is placed of liquid 64 is raised and lowered through a motor (not shown) The speed of table 61 is controlled by the connected computer and displayed before the start of the measurement.

Other parameters that must be fed before the start of the measurement are the surface energy of the liquid and the circumference of the fiber 65. A fiber is mounted on a piece of fiber 66 in such a way that a part of the fiber 65 is free. The assembled fiber 65 is fixed in a metal staple 67 and suspended in the first platen A. The scale 60 has already been stopped with only the metal staple 67 suspended in the platen A. A test liquid 68, which has a surface energy The fiber 65 is suspended perpendicularly in relation to the surface of the liquid 69 and must be completely immobile before the start of the measurement in such a way that the balance present a stable value. Table 61 with the liquid container 64 is raised in such a manner that the liquid surface 61 is approximately 1 mm from the fiber 65. When the measurement is started, the computer records a baseline, after which the table 61 it is raised at a predetermined speed. Thus, the fiber 65 must have sufficient rigidity to remain vertical also after it has penetrated the surface of the liquid 69. When (depending on the length of the fiber) one millimeter or a few millimeters of the fiber 65 have been immersed in the liquid 68, the computer is given an order to stop the mixture 61. Subsequently, the mixture 61 is lowered. During the course of the test, variations in force along the fiber 65 are displayed on the computer screen. Examples of the appearance of the obtained graphs are shown in Figures 6a-c. When the measurement is completed, representative portions of the advance 71 and reverse 72 graphs are selected. Subsequently, the computer calculates the contact angles with the help of the ilhelmy equation. The invention should not be considered as limited to the modalities described herein. Accordingly, the invention includes all types of absorbent structures comprising at least two regions in communication of which at least the back wetting angle is different.

Claims (1)

1. CLAIMS l.An absorbent, porous structure (4) intended for use in an absorbent article, wherein the structure (4) shows a first region (19), consisting primarily of a first material, which is in direct connection with a second one. region (20), which consists primarily of a second material, wherein the first material in an untreated condition shows a theta back wetting angle essentially equal to or smaller than the theta back wetting angle of the second material, characterized in that the first material has been treated with an agent in order to raise the thetar backward dampening angle of the first material above the thetar backward dampening angle value of the second material, whereby the thetar backward dampening angle is greater for the first material than for the second material, and therefore liquid transport is observed between the two regions (19, 20) in a direction from the first region (19) to the second region (20) at least when the porous structure (4) is wet. . An absorbent structure (4) according to claim 1, characterized in that the advance wetting angle thetaa is greater for the first material than for the second material, so that the liquid transport between the two regions (19, 20) it is carried out in a direction from the first region (19) to the second region (20), regardless of whether the structure (4) is dry or wet. An absorbent structure (4) according to claim 1 or 2, characterized in that the average pore size in the absorbent structure (4) is greater within the first region (19) than within the second region (4). 4) . 4. An absorbent structure (4) according to claim 1,2 or. 3, characterized in that the first region is constituted by a first layer (19) in the absorbent structure (4), and in that the second region is constituted by a second layer (20) in the absorbent structure (4), and where both layers (19,20) are in direct connection between them through the surfaces of the layers resting against each other. . An absorbent structure according to claim 1, 2 or 3, characterized in that the two regions (49, 50, 49 ', 50') are formed from parts of the same material layer (34). . An absorbent structure according to claim 5, characterized in that the first region (49 ') and the second region (50') are arranged one along the other in the plane of the material layer (34). An absorbent structure according to claim 5, characterized in that the two regions (49, 50) are arranged one along the other in the thickness direction of the material layer (34). An absorbent structure according to any of the preceding claims, characterized in that it presents additional regions with absorbent material, wherein the materials in the different regions comprised in the absorbent structure show different thetar back wetting angles therebetween. An absorbent structure according to claim 8, characterized in that the fiber structure is substantially planar with a first surface and a second surface parallel to the plane of the structure and with a direction of thickness perpendicular to the plane, where the different regions are arranged mutually in such a way that the structure shows a gradient of wetting angle in the thickness direction and / or the plane of the structure. . An absorbent structure according to any one of the preceding claims, characterized in that the first region (19; 49) consists primarily of a cellulose fluff pulp manufactured chemometrically (CTMP), and because the second region (20; 50) consists of of cellulose fluff pulp chemically (CP). . An absorbent structure according to claim 10, characterized in that the agent for raising the thetar back wetting angle is ethylhydroxy-ethyl cellulose (EHEC). . An absorbent structure according to claim 10, characterized in that the agent for raising the back wetting angle thetar is poly-n-isopropylacrylamide (PNIPAM). . An absorbent structure according to any of the preceding claims, characterized in that the agent for raising the back wetting angle thetar is applied to the structure by means of spraying. . An absorbent structure according to any of claims 1-12, characterized in that the agent for raising the back wetting angle thetar is applied to the fiber structure by means of the coating of material with a liquid containing the agent. . An absorbent article such as a diaper, a sanitary napkin, or an incontinence protector showing a liquid-permeable cover layer (2).; 32), a liquid impervious coating layer (3; 33) and an absorbent body (4; 34) enclosed between the two coating layers (2, 3; 32, 33), wherein the absorbent body (4; ) shows a first region (19; 49), consisting primarily of a first material, which is in direct connection with a second region (20; 50), consisting primarily of a second material, where the first material in a condition untreated shows a theta back wetting angle essentially equal to or smaller than the theta back wetting angle of the second material, characterized by the fact that the first material has been treated with an agent in order to raise the back wetting angle thetar of the first material above the value for the theta retraction wetting angle of the second material so that the thetar retraction wetting angle is greater for the first material than for the second all material and so the liquid transport is carried out between the two regions (19, 20; 49, 50) in a direction from the first region (19; 49) to the second region (20; 50) at least when the absorbent body (4; 34) is wet. . An absorbent article according to claim 15, characterized in that the advancing wetting angle thetaa is greater for the first material than for the second material so that the transport of liquids is carried out between the two regions (19, 20; 49, 50) in a direction from the first region (19; 49) to the second region (20; 50) regardless of whether the absorbent body (4; 34) is dry or wet. 17. An absorbent article according to claim 15 or according to claim 16, characterized in that the first region (19) is constituted by a first layer (19) in the absorbent body (4), the second region (20). ) is constituted by a second layer (20) in the absorbent body (4), where the two layers (19,20) are in direct connection between them through the surfaces in the layers (19, 20) that are supported one against the other, and where the first layer (19) faces towards the permeable coating layer, the liquids (12) and the second layer (20) faces towards the liquid impermeable coating layer (3). 18. An absorbent article according to claim 15 or 16, characterized in that the two regions (49, 50, 49 ', 50') are constituted by parts of the same layer of material in the absorbent body (34). 19. An absorbent article according to claim 18, characterized in that the first region and the second region (49 ', 50') are arranged along one another in the plane of the material layer. . An absorbent article according to claim 18, characterized in that the two regions (49, 50) are arranged along one another in the thickness direction of the material layer. . An absorbent article according to any of claims 15-20, and further having two end portions (6,7; 37, 38) and a crotch portion (8; 39), arranged between the end portions (8).; 39), intended to be received in the crotch of a user during use, and to serve in this way as a reception region for the body fluid emitted towards the article, characterized in that the first region (19; 49), which presents the first material, is located primarily in the crotch portion (8; 39) of the article.