Background art:
The absorbent core is the most critical and important part of disposable absorbent products. The properties of disposable absorbent products, such as water absorption and water retention, largely depend on the absorbent core. In the prior art, the absorbent core generally comprises a surface layer, a bottom layer and an intermediate layer between the surface layer and the bottom layer, and the absorbent material is fixed on the surface of the intermediate layer by bonding and the like. When the absorbent core comes into contact with liquid such as water, the liquid reaches the intermediate layer through the surface layer, and is absorbed and held by the absorbent material fixed on the intermediate layer, thus playing the role of absorbing liquid. Therefore, the amount of liquid that can be absorbed by the absorbent core is determined by the amount of absorbent material. However, in this structure, first of all, the absorption material is usually only distributed between the surface layer and the middle layer, and between the bottom layer and the middle layer; Secondly, in order to make the surface material or the bottom material and the middle layer material have better adhesion, there should not be too much water-absorbing material, which is one of the disadvantages. The second disadvantage is that after absorbing a large amount of liquid, the absorbent material often separates the surface layer or bottom layer from the middle layer, and a large amount of absorbent material will escape from the side of the absorbent core. The third disadvantage is that when the absorption material absorbs a large amount of liquid, it will accumulate the absorbed liquid on the surface, forming a barrier, resulting in the internal absorption material being unable to contact with the liquid and the absorption efficiency being low. In another prior art (for example, China utility model patent CN200920 1947 14.5), in order to solve the problem of the distribution amount of the absorption material, the middle layer is made of a porous material, such as a fiber hot air nonwoven fabric, so that the absorption material is embedded in the holes of the porous material to increase the distribution amount of the absorption material. However, because the pores in the porous material are naturally formed and the shapes and sizes of the pores are irregularly distributed, the absorbent material is not easily embedded in these pores. A large amount of absorbing material is still distributed on the surface of the intermediate layer. Therefore, the increase of the distribution of the absorption material is limited, and the problems of separation of the surface layer or bottom layer from the middle layer and escape of the absorption material from the side are not solved. Technical realization factors: The purpose of the invention is to provide a composite absorbent core, which overcomes the problems existing in the traditional technology, can effectively improve the absorption capacity of liquid, shorten the absorption time of liquid, make full use of absorption materials and improve the absorption efficiency. At the same time, the structure of the composite absorbent core is simpler. According to the above purpose, the present invention provides a composite absorbent core, which comprises a bottom layer and a water-permeable layer, wherein the water-permeable layer is made of a material with a liquid-permeable function, and is characterized in that the longitudinal section of the water-permeable layer is wavy, and at least part of the wave troughs of the water-permeable layer are sealed with the bottom layer to form a cavity, and the cavity is filled with polymer water-absorbent resin. In the composite absorbent core, the cross section of the cavity is round, square, oval or diamond. In the composite absorbent core, sealing bonding is thermal bonding, adhesive bonding or ultrasonic bonding. In the composite absorbent core, the material with liquid permeation function is fluffy nonwoven fabric, polyurethane soft foam rubber or fluffy fiber paper. In the composite absorbent core, polymer water-absorbent resin is dispersed in the contact part between the groove and the bottom layer. In the composite absorbent core, the bottom layer is made of hydrophilic nonwoven fabric, dust-free paper, hydrophobic nonwoven fabric, cast film or breathable film. In the composite absorbent core, the cross section of the cavity is circular, and the radius range of the cross section of the cavity is 0.2-10 mm; The thickness of the permeable layer ranges from 0.5 to 6 mm; The number of cavities is 0.5-28/cm2; The mass of polymer water-absorbent resin is 40-450g/m2. In the composite absorbent core, the radius range of the cavity cross section is 0.5-4 mm; The thickness range of the permeable layer is1-3mm; The number of cavities is 1- 16 /cm2. As mentioned above, the composite absorbent core of the present invention adopts a wave-like structure, and the cavity formed by combining with the bottom layer can contain polymer absorbent resin, which increases the content and water absorption of polymer absorbent resin compared with the traditional structure. The structure is also simpler than the traditional one. Brief description of the drawings fig. 6 shows the structural schematic diagram of the composite absorbent core of the present invention; Fig. 2 shows a cross-sectional view of the composite absorbent core of the present invention; Fig. 3 shows the flow direction effect of the composite absorbent core of the present invention when absorbing liquid; Fig. 4 shows a state when the polymer water-absorbent resin in the composite absorbent core of the present invention starts to absorb liquid; Figs. 5A- 5B illustrate various embodiments of cavity distribution on the absorption layer; Fig. 6 shows an embodiment in which a polymer water-absorbent resin is dispersed in a contact portion between a tank and a bottom layer. Please refer to figure 1, which shows the structural schematic diagram of the composite absorbent core of the present invention. As shown in figure 1, the composite absorbent core includes a permeable layer 1 and a bottom layer 2. There are many protrusions on the permeable layer 1, which makes the longitudinal section of the permeable layer 1 wavy. For the specific structure, please refer to the cross-sectional view of Figure 2, which is the cross-sectional view along the direction A-A in Figure 1. It can be seen that at least a part of the trough 5 is sealed by the bottom layer 2 to form a cavity 3, and the cavity 3 is filled with polymer water-absorbing resin 4, and a depression 6 is formed on the peak side of the permeable layer 1. The absorption layer 1 is made of a material with liquid permeation function, such as water-permeable dust-free paper or water-permeable nonwoven fabric. The bottom layer 2 can be made of liquid permeable or liquid impermeable materials as required. When liquid needs to pass through the composite core, the bottom layer 2 is made of liquid-permeable materials, such as hydrophilic nonwoven fabric and dust-free paper. When there is no need for liquid to pass through the composite core, the bottom layer 2 is made of a liquid impermeable material, such as a waterproof nonwoven fabric, a cast film or a breathable film. The permeable layer 1 of the composite absorbent core of the present invention is wavy, and after contacting with the bottom layer 2, cavities 3 are formed, and polymer absorbent resin 4 can be filled in these cavities 3, so that the filling amount of polymer absorbent resin 4 is greatly improved. The liquid can directly enter the depression 6 and contact with the polymer water-absorbent resin 4 through the permeable layer 1, thus shortening the liquid absorption time. The specific absorption process is shown in Figure 3. Part of the liquid directly permeates the peak 6 of the permeable layer 1 and contacts with the polymer water-absorbent resin 4. Another part of the liquid accumulates in the recess 6 along the side wall of the recess 6, and at the same time, it contacts the polymer water-absorbent resin 4 through the side wall of the recess 6. The arrangement of the groove 6 can buffer the liquid to be absorbed in a short time, so that the peak edge 1 1 is quickly dried, and then the buffered liquid is gradually absorbed by the polymer water-absorbent resin 4. Compared with the prior art, the advantages of this structure include: the content of polymer water-absorbent resin 4 is increased, and there will be more space for adding polymer water-absorbent resin 4 in the cavity 3; The barrier formed by the polymer water-absorbent resin 4 after absorbing liquid is avoided, and unlike the prior art, the polymer water-absorbent resin 4 only absorbs liquid in the direction perpendicular to the absorbent core, but absorbs liquid in each normal direction on the surface of the cavity 3; The contact area between the polymer water-absorbent resin 4 and the liquid increases, and the liquid absorption time is shortened. In addition, since the polymer water-absorbent resin 4 is filled into the cavity 3. When the liquid absorbed by the polymer water-absorbent resin 4 expands, it also exists in the cavity 3, which avoids the problem that the polymer water-absorbent resin expands after absorbing water in the prior art, resulting in the escape of the side of the core. At the same time, thermal compounding or ultrasonic compounding can be selected for sealing bonding to prevent the bottom layer from separating from the permeable layer when the polymer meets liquid. Fig. 4 shows the state when the polymer water-absorbent resin in the composite absorbent core of the present invention starts to absorb liquid. As can be seen from fig. 4, in the lateral direction, due to the provision of the recess 6, when the polymer water-absorbent resin 4 in the cavity 3 absorbs liquid, it expands in the lateral direction and occupies the space of the recess 6. This structural arrangement effectively avoids the problem of polymer side leakage. When a large amount of liquid is absorbed, the polymer water-absorbent resin 12 will enter the absorption layer 1 through the cavity 3, and the material fiber of the absorption layer 1 will extend with the expansion of the polymer water-absorbent resin 12, and the polymer water-absorbent resin 12 will be fixed in the absorption core. Generally, the distribution of cavities 3 is preferably uniform and staggered, so that the composite absorbent core has uniform liquid absorption capacity. Figs. 5A and 5B show the distribution of cavities 3. In the embodiment of fig. 5A, the cavities 3 are distributed in a matrix in rows (or columns). The spacing of cavities 3 in each row (or column) is equal. In the embodiment of fig. 5B, the cavities 3 are distributed in rows (or columns). The spacing of cavities 3 in each row (or column) is equal, and adjacent rows are staggered. The cross section of the cavity 3 may be circular as shown in figs. 5A and 5B, but the shape is not limited to this, and the cross section of the cavity 3 may also be square, oval or diamond. . In addition, the invention also needs to be explained that it is difficult to accurately control the water-absorbent resin to be completely filled into the cavity in actual situations. And from the effect point of view, there is no need to do such precise control. Therefore, please refer to fig. 6, another embodiment of the present invention. According to the invention, the polymer water-absorbent resin 4 can also be dispersed in the contact part between the tank 5 and the bottom layer 2, and this small amount of dispersion will not cause the defects existing in the traditional technology. This situation should be regarded as included in the protection scope of the present invention. The following is the result of the comparative experiment between the absorbent cores of the present invention and the prior art: In the experiment, three absorbent cores of the prior art were selected for the comparative experiment. The absorbent layer of the core is fluffy nonwoven fabric with a density of 68g/m2, and the base material is 18g hydrophilic nonwoven fabric. The density of polymer water-absorbent material is 224g/m2, and the experimental cores of the same size are all 100mm long and 95mm wide. Use physiological saline containing 0.9% salt, 30ml each time, with an interval of 3 minutes each time, and conduct three ***90ml filling tests. The experimental results are shown in the following table: Note: "-"refers to normal saline that has not been drained after 5 minutes. Because the blind holes are arranged in the invention, the mass of the polymer water-absorbing resin that can be accommodated is far greater than that of the existing absorbent core, which directly leads to the larger liquid absorption capacity of the invention. It can be seen that the last 30 ml of liquid in the prior art cores 2 and 3 cannot be completely absorbed. At the same time, the thickness of the core of the invention is reduced by about 40% on average and the weight per square meter is reduced by 23%-40% compared with the absorbent core of the prior art, which highlights the advantages of lightness and thinness of the core of the invention. As the cavity is arranged in the invention, the quality of the polymer water-absorbent resin SAP that can be accommodated is much greater than that of the traditional absorbent core, which directly leads to a larger liquid intake of the invention. In terms of absorption time, the absorption time of 1 water injection decreased by about 25% on average, the absorption time of the second water injection decreased by more than 35%, and the absorption time of the third water injection decreased by more than 40% on average. As can be seen from the above results, compared with the traditional absorbent core, the absorbent core of the present invention has great advantages in both inhalation amount and inhalation time. The cross-sectional size of the cavity 3 can generally be selected by comprehensively considering the material and thickness of the permeable layer. In the preferred embodiment, the permeable layer 1 is made of fluffy non-woven fabric with a thickness of 2.0 mm, and the cavity 3 is cylindrical, with a bottom radius of 1 mm and a height of 1.8 mm. The number of circular holes distributed per square centimeter on the non-woven fabric is 12. The following table shows the range and typical examples of the dimension values of the bottom surface of the cavity 3. Scope priority scope: The radius of cavity bottom R (mm) is 0.2- 10.00.5-4 1 permeable layer thickness H (mm) is 0.5-6 1-32.0, and the number of cavities n (pieces /cm2) is 0.5-28/kloc-.