Background:
The absorbent core is the most critical and important part of disposable absorbent articles. The performance of disposable absorbent articles, such as water absorption and retention, is largely determined by the absorbent core. In the prior art, an absorbent core generally comprises a surface layer, a bottom layer and an intermediate layer arranged between the surface layer and the bottom layer, and absorbent materials are fixed on the surface of the intermediate layer by means of 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, firstly, absorbent materials are usually only distributed between the surface layer and the middle layer and between the bottom layer and the middle layer; Second, 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-absorbent material, which is one of the shortcomings. The second disadvantage is that after the absorbent material absorbs a large amount of liquid, it often causes the separation between the surface layer or the bottom layer and 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 absorbent material absorbs a large amount of liquid, it will accumulate the absorbed liquid on the surface, forming a barrier, which causes the internal absorbent material to be unable to contact with the liquid, and the absorption efficiency is low. In another prior art (for example, China utility model patent CN292194714.5), in order to solve the problem of the distribution amount of absorbent materials, a porous material such as fiber hot air nonwoven fabric is adopted as the middle layer, so that the absorbent materials are embedded in the holes of the porous materials to increase the distribution amount of the absorbent materials. However, because the holes in porous materials are naturally formed and the shapes and sizes of the holes are irregularly distributed, it is not easy for absorbent materials to be embedded in these holes. A large amount of absorbent material is still distributed on the surface of the intermediate layer. Therefore, the increase of the distribution of absorbent materials is limited, and the problems of separation of the surface layer or bottom layer from the middle layer and the escape of absorbent materials from the side are not solved. Technical realization factors: The purpose of the invention is to provide a composite absorption 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, wherein 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, the sealing bonding is thermal bonding, adhesive bonding or ultrasonic bonding. In the composite absorbent core, the material with the liquid seepage function is fluffy nonwoven fabric, polyurethane soft foamed rubber or fluffy fiber paper. In the composite absorbent core, the polymer water-absorbent resin is dispersed in the contact part between the trough and the bottom layer. In the composite absorbent core, the bottom layer is made of hydrophilic nonwoven fabric, dust-free paper, water-repellent 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 .2-1 mm; The thickness of the permeable layer ranges from .5 to 6 mm; The number of the cavities is .5-28/cm2; The mass of the polymer water-absorbent resin is 4-45g/m2. In the composite absorbent core, the radius range of the cavity cross section is .5-4 mm; The thickness of the permeable layer ranges from 1 to 3 mm; The number of the 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 water-absorbent resin, which increases the content of polymer water-absorbent resin and water absorption compared with the traditional structure. The structure is also simpler than the traditional one. Brief description of the drawings fig. 1 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 the state when the polymer water-absorbent resin in the composite absorbent core of the present invention starts to absorb liquid; Figs. 5A- 5B show various embodiments of the distribution of cavities on the absorption layer; Fig. 6 shows an embodiment in which polymer water-absorbent resin is dispersed in the contact part between the trough and the bottom layer. Please refer to fig. 1, which shows the structural schematic diagram of the composite absorbent core of the present invention. As shown in fig. 1, the composite absorbent core comprises a water 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 also refer to the cross-sectional view of Figure 2, which is the cross-sectional view along the direction of A-A in Figure 1. It can be seen that at least some wave troughs 5 are sealed with the bottom layer 2 to form a cavity 3, which is filled with polymer water-absorbent resin 4, and a depression 6 is formed on the peak side of the water-permeable layer 1. The absorption layer 1 is made of a material with liquid seepage 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-tight material, such as a water-repellent 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 water-absorbent resin 4 can be filled in these cavities 3, so that the filling amount of polymer water-absorbent resin 4 is greatly improved. The liquid can directly enter the depression 6 and contact the polymer water-absorbent resin 4 through the permeable layer 1, thus shortening the liquid absorption time. Refer to fig. 3 for the specific absorption process. A part of the liquid directly permeates through the wave crest 6 of the permeable layer 1 and contacts with the polymer water-absorbent resin 4. Another part of the liquid accumulates in the depression 6 along the side wall of the depression 6, and at the same time, it contacts with the polymer water-absorbent resin 4 through the side wall of the depression 6. The arrangement of the recess 6 can buffer the liquid to be absorbed in a short time, so that the peak side 11 can be dried quickly, 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 in the cavity 3 to add polymer water-absorbent resin 4; The barrier formed by the polymer water-absorbent resin 4 after absorbing the liquid is avoided, which is different from the prior art that only absorbs the liquid in the direction perpendicular to the absorbent core, but absorbs the 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 is increased, 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, thus avoiding the problem that the polymer water-absorbent resin expands after absorbing water in the prior art, so that the side edge of the core escapes. At the same time, thermal compounding or ultrasonic compounding can be selected for sealing and bonding to prevent the bottom layer from being separated from the permeable layer when the polymer meets the 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 escape. When there is a large amount of absorbed liquid, the polymer water-absorbent resin 12 will pass through the cavity 3 and enter the absorption layer 1 after expansion, and the material fibers of the absorption layer 1 will be elongated 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 the cavities 3. In the embodiment of fig. 5A, the cavities 3 are distributed in a matrix in rows (or columns). The spacing of the 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 can 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 can also be square, oval or diamond. . In addition, the invention also needs to be explained that it is difficult to accurately control the water-absorbing resin to be completely filled into the cavity in actual situations. Moreover, from the effect point of view, it is not necessary to make such precise control. Therefore, please refer to fig. 6, another embodiment of the present invention. The present invention can also allow the polymer water-absorbent resin 4 to be dispersed in the contact part between the trough 5 and the bottom layer 2, and this small amount of dispersion will not produce 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 a comparative experiment between the present invention and the absorbent cores in the prior art: In the experiment, three absorbent cores in the prior art were selected for the comparative experiment. The absorbent layer of the core of the invention is made of fluffy nonwoven fabric, the density of which is 68g/m2, and the bottom layer is made of 18g hydrophilic nonwoven fabric. The density of polymer water-absorbing material is 224g/m2, and the experimental cores of the same size are all 1mm long and 95mm wide. Use physiological saline containing .9% salt, 3ml each time, with an interval of 3 minutes each time, and carry out three ***9ml filling tests. The experimental results are shown in the following table: Note: "-"refers to the 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-absorbent resin that can be accommodated is far greater than that of the existing absorbent core, which directly leads to the larger liquid intake of the invention. It can be seen that the last 3ml of liquid in the prior art core 2 and the prior art core 3 cannot be completely absorbed. At the same time, the thickness of the core of the invention is reduced by about 4% on average compared with the absorbent core of the prior art, and the weight per square meter is reduced by 23%-4%, which highlights the light and thin advantages of the core of the invention. As the cavity is arranged in the invention, the mass of the polymer water-absorbent resin SAP that can be accommodated is far 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 the first water injection decreased by about 25% on average, the absorption time of the second water injection decreased by more than 35% on average, and the absorption time of the third water injection decreased by more than 4% on average. From the above results, it can be seen that compared with the traditional absorbent core, the absorbent core of the present invention has great advantages in both inhalation amount and inhalation time. Generally, the size of the cross section of the cavity 3 can be selected by comprehensively considering the materials and thickness of the permeable layer 1. In a preferred embodiment, the permeable layer 1 is made of fluffy non-woven fabric with a thickness of 2.mm, and the cavity 3 is cylindrical with a bottom radius of 1mm and a height of 1.8 mm.. The number of circular holes distributed on each square centimeter of non-woven fabric is 12. The following table shows the range and typical examples of the size values of the bottom surface of the cavity 3. Scope priority scope Example The radius of cavity bottom R (mm) is .2-1..5-41, the thickness of permeable layer H (mm) is .5-61-32., and the number of cavities N (pieces/cm2) is .5-281-1612.