Water-absorbing resin and its manufacturing method

Abstract

This invention provides a water-absorbing resin and its manufacturing method. By adding calcined seashell powder to carry out a free radical polymerization reaction, a water-absorbing resin with more micropores can be obtained, thereby increasing the absorption performance and liquid permeability of the water-absorbing resin, and improving the diffusion and conductivity of the dried water-absorbing resin.

Description

Technical Field

[0001] This invention relates to a water-absorbing resin and a method for manufacturing the same, particularly to a water-absorbing resin with good absorption properties and a method for manufacturing the same. Background Technology

[0002] Absorbent polymers have a wide range of applications, such as water retention agents in agriculture or horticulture, anti-dew condensation agents in building materials, materials for removing water from petroleum, outer waterproof coatings in cables, and personal hygiene products (such as diapers, feminine hygiene products, and disposable wipes), with diapers being the most common.

[0003] The absorbency of disposable diapers depends on their absorption rate, absorbency, and dryness. In recent years, disposable diapers have focused on thinner designs, reducing the amount of pulp (hydrophilic fibers) and increasing the amount of absorbent resin. This increased proportion of absorbent resin in the absorbent core structure contributes to the thinner diaper. However, reducing the amount of hydrophilic fibers reduces the water storage space in a short time, slowing down liquid penetration and causing leakage. Furthermore, besides a good absorption rate, absorbent resin must also have high permeability to liquids. Poor permeability can cause the absorbent resin to clog the gaps between particles during absorption, creating a colloidal blockage that allows liquid to flow out of the diaper's absorbent core, thus reducing the diaper's absorbency.

[0004] Therefore, improving the absorption rate and permeability of superabsorbent polymers (SAPs) is currently a key research focus in this field. Existing methods utilize polyvalent metal cations for surface modification or aluminum dihydroxyacetate to enhance the liquid conductivity of SAPs. Alternatively, thermoplastic polymers such as polyethylene or polypropylene can be used in the heat treatment step, or amino-containing azo compounds can be added as blowing agents to the aqueous solution of acidic monomers to improve the liquid permeability of the SAP. Furthermore, adding encapsulated blowing agents or water-soluble alkoxysilane compounds to the aqueous solution of acidic monomers can respectively give the prepared SAPs better absorption rates or good colloidal stability. Moreover, existing methods can improve the diffusion and liquid permeability of SAPs after absorbing liquids by mixing water-soluble polyvalent metal powders, adhesives, and SAPs.

[0005] However, the absorption rate and liquid permeability of absorbent resins are evaluated after the resin has absorbed liquid. Research shows that compared to wet absorbent resins, dry absorbent resin particles are less likely to absorb liquid initially upon contact. This is because the diffusion and conductivity of liquids in dry absorbent resins are lower than in wet absorbent resins. Therefore, when existing absorbent resins are used in diapers, they are prone to causing side leakage during use.

[0006] In view of this, there is an urgent need to provide a water-absorbing resin and a method for manufacturing the same, so that the water-absorbing resin has excellent liquid diffusivity and conductivity when dry, while maintaining good absorption rate and liquid permeability. Summary of the Invention

[0007] One aspect of the present invention is to provide a method for manufacturing a water-absorbing resin, which involves adding calcined seashell powder to participate in a free radical polymerization reaction to obtain a water-absorbing resin that has excellent liquid diffusivity and conductivity when dry, while also maintaining good absorption rate and liquid permeability.

[0008] Another aspect of the present invention is to provide a water-absorbing resin, which is obtained by means of the above-described aspect.

[0009] According to one aspect of the present invention, a method for manufacturing a water-absorbing resin is provided. First, a water-absorbing resin composition and calcined seashell powder are subjected to a free radical polymerization reaction to obtain a gel. The water-absorbing resin composition comprises an aqueous solution of an unsaturated monomer, a polymerization initiator, and a free radical polymerization crosslinking agent. The calcined seashell powder has a core-shell structure. The particle size of the calcined seashell powder is 100 μm to 1 mm. Based on 100 wt% of the unsaturated monomer aqueous solution, the calcined seashell powder comprises 0.005 wt% to 10 wt%. Next, the gel is pulverized and sieved to obtain a plurality of water-absorbing resin particles. Then, the water-absorbing resin particles are subjected to a surface crosslinking reaction to obtain the water-absorbing resin.

[0010] According to one embodiment of the present invention, the core of the core-shell structure is micron-sized calcium oxide particles, and the shell layer of the core-shell structure is nano-sized to sub-micron-sized calcium oxide particles. The average particle size of the core layer is 7 μm to 500 μm, and the average particle size of the shell layer is no greater than 200 nm.

[0011] According to one embodiment of the present invention, the whiteness of the calcined seashell powder is at least 60.

[0012] According to one embodiment of the present invention, the specific surface area of ​​the calcined seashell powder is at least 8000 cm². 2 / g.

[0013] According to one embodiment of the present invention, the calcined seashell powder is added before, during or after the free radical polymerization reaction.

[0014] According to one embodiment of the present invention, the above method further includes drying the gel at a temperature of 100°C to 250°C before pulverizing and screening the gel.

[0015] According to one embodiment of the present invention, the average particle size of the above-mentioned water-absorbing resin particles is 0.06 mm to 1.00 mm.

[0016] According to another aspect of the present invention, a water-absorbing resin is provided, which is prepared by the above method, and the T20 value of this water-absorbing resin is not greater than 180 seconds.

[0017] According to an embodiment of the present invention, the high liquid flow conductivity of the above-mentioned water-absorbing resin is not less than 30 × 10⁻⁶. - 7 cm 3 -s / g.

[0018] According to one embodiment of the present invention, the free swelling rate of the above-mentioned water-absorbing resin is not less than 0.25 g / gs.

[0019] The water-absorbing resin and its manufacturing method of the present invention utilize calcined seashell powder added in a specific amount to participate in the free radical polymerization reaction. This causes the gas generated during the reaction to increase the micropores of the water-absorbing resin, thereby enabling the water-absorbing resin to have excellent liquid diffusivity and conductivity when dry, while maintaining good absorption rate and liquid permeability. Attached Figure Description

[0020] A better understanding of the features disclosed herein will be achieved by reading the following detailed description in conjunction with the accompanying drawings. It should be noted that, as is standard practice in the industry, many features are not drawn to scale. In fact, for clarity of discussion, the dimensions of many features may be arbitrarily scaled.

[0021] Figure 1 A flowchart illustrating a method for manufacturing a water-absorbing resin according to some embodiments of the present invention is shown.

[0022] Figure 2A and Figure 2B The images show scanning electron microscopy (SEM) images of the absorbent resins prepared with and without calcined seashell powder. Detailed Implementation

[0023] As used in this article, “around,” “about,” “approximately,” or “substantially” generally mean within 20 percent, 10 percent, or 5 percent of the stated value or range.

[0024] As described above, the present invention provides a water-absorbing resin and a method for manufacturing the same. By adding a specific amount of calcined seashell powder with a specific particle size to participate in a free radical polymerization reaction, the gas generated during the reaction causes an increase in the micropores of the water-absorbing resin, thereby enabling the water-absorbing resin to have excellent liquid diffusivity and conductivity when dry, while maintaining good absorption rate and liquid permeability.

[0025] Please see Figure 1 The diagram illustrates a flowchart of a method 100 for manufacturing a water-absorbing resin according to some embodiments of the present invention. First, operation 110 is performed, in which a water-absorbing resin composition and calcined seashell powder are subjected to a free radical polymerization reaction to obtain a gel. In some embodiments, the water-absorbing resin composition includes an unsaturated monomer aqueous solution, a polymerization initiator, and a free radical polymerization crosslinking agent. In some embodiments, the calcined seashell powder is added immediately before, during, or after the free radical polymerization reaction, but it is preferred to add it before the free radical polymerization reaction. However, if the calcined seashell powder is added after the free radical polymerization reaction is completed and a gel is obtained, or if the calcined seashell powder is added in any subsequent step, the desired effect of the present invention cannot be achieved. This is because during the free polymerization reaction, the calcined seashell powder, whose main component is calcium carbonate, can decompose to produce carbon dioxide, and bubbles can be dispersed in the resulting gel, thereby generating a large number of micropores. Therefore, the resulting water-absorbing resin can achieve the desired effect of the present invention.

[0026] In some examples, the amount of unsaturated monomer aqueous solution is 100 wt%, and the amount of calcined seashell powder is 0.005 wt% to 10 wt%, preferably 0.005 wt% to 5 wt%. If the amount of calcined seashell powder is less than 0.005 wt%, the liquid conductivity and liquid permeability of the subsequently prepared water-absorbing resin are poor. Conversely, if the amount of calcined seashell powder is greater than 10 wt%, not only does it increase the production cost, but also, since the main component of calcined seashell powder is inorganic salts without water absorption capacity, when excessive calcined seashell powder is added (e.g., greater than 10 wt%), unreacted calcined seashell powder remains in the subsequently prepared water-absorbing resin, thus reducing the absorption capacity of the water-absorbing resin and consequently reducing its absorption performance.

[0027] The calcined shell powder described above is obtained by processing monovalve and / or bivalve shells, and its main component is calcium carbonate. In some examples, the monovalve and / or bivalve shells may be, for example, but not limited to, oysters, clams, mussels, peacock clams, oyster mussels, abalone, pearl oysters, butterfly oysters, scallops, and any combination thereof. In this example, the monovalve and / or bivalve shells generally contain not less than 94 wt% calcium carbonate and other inseparable components.

[0028] The above processing steps include a pretreatment step for the shells, such as removing residual shell meat, surface cleaning, and coarse crushing to obtain shell powder. In some examples, the aforementioned surface cleaning can be, for example, a chemical mechanical cleaning method. For instance, a chemical mechanical cleaning method can be performed at room temperature using water or a dilute acid solution (e.g., hydrochloric acid with a concentration not exceeding 4N, or tartaric acid with a concentration not less than 12%), a chelating agent solution (e.g., saturated EDTA or EDTMP), or any combination thereof, combined with mechanical external force cleaning (e.g., brushing, ultrasonic vibration, etc.), or by pre-soaking the shells in the above solutions for 2 to 24 hours, followed by mechanical external force cleaning. After surface cleaning, the surface-cleaned shells are coarsely crushed using commercially available crushing equipment to obtain shell particles (with an average particle size not exceeding 500 μm). However, the above pretreatment is well known to those skilled in the art and will not be described further.

[0029] In some embodiments, the shell powder may be selectively subjected to an alkali coating step to obtain alkali-coated powder. In some embodiments, the alkali coating step involves coating the shell powder with a calcium salt slurry for 2 to 4 hours. The calcium salt slurry contains at least 2.5 wt% calcium salt, for example, containing 2.5 wt% to 20.0 wt% calcium salt, and the weight-to-volume ratio (g / mL) of the shell powder to the calcium salt slurry is 0.1 to 1. In some embodiments, the calcium salt is calcium hydroxide.

[0030] Next, the above processing steps also include a calcination step of the shell powder or alkali-coated powder at about 900°C to about 1200°C to obtain calcined shell powder. The calcination step can be carried out for about 3 hours to about 6 hours. In other embodiments, the calcination step can also be carried out at a temperature of 1000°C to 1100°C, for example, for 4 to 5 hours. It should be noted that carrying out the calcination step at the aforementioned temperature range can ensure that the effective calcium oxide content of the obtained calcined shell powder is not less than 93 wt%.

[0031] In some embodiments, after the calcination step, the calcined seashell powder may be selectively subjected to a grinding step to obtain a particle size of 100 μm to 1 mm, preferably 150 μm to 710 μm, and even more preferably 250 μm to 500 μm. If the particle size of the calcined seashell powder is greater than 1 mm, it is not easy to mix uniformly with the components of the water-absorbing resin composition and is not easy to participate in the free radical polymerization reaction; conversely, if the particle size of the calcined seashell powder is less than 100 μm, it may be suspended in the air of the factory, thereby harming the respiratory tract of operators and causing health hazards.

[0032] In some embodiments, the calcined seashell powder has a core-shell structure, wherein the core of the core-shell structure is micron-sized calcium oxide particles, and the shell layer is nano-sized to submicron-sized calcium oxide particles. In some embodiments, the shell layer of the core-shell structure is a discontinuous layer or a continuous layer. In the foregoing embodiments, the average particle size of the micron-sized calcium oxide particles in the core layer is 7 μm to 500 μm, and the average particle size of the nano-sized to submicron-sized calcium oxide particles in the shell layer is not greater than 200 nm, but preferably 60 nm to 150 nm. In some embodiments, the whiteness of the calcined seashell powder is at least 60, but preferably 60 to 88. In some embodiments, the zinc content of the calcined seashell powder is less than 1.67 ppm, the manganese content is less than 40 ppm, and the iron content is less than 350 ppm. In some embodiments, the specific surface area of ​​the calcined seashell powder is at least 8000 cm². 2 / g.

[0033] In some embodiments, the unsaturated monomer aqueous solution in the absorbent resin composition includes an acidic monomer having an unsaturated double bond, such as acrylic acid. In some embodiments, the unsaturated monomer aqueous solution may be methacrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, maleic acid (maleic acid), maleic anhydride, fumaric acid (trans-butenedioic acid), and trans-butenedioic anhydride. The unsaturated monomer aqueous solution may contain, but is not limited to, one monomer, and may also contain two or more of the above-mentioned monomer aqueous solutions.

[0034] In some embodiments, the concentration of the above-mentioned unsaturated monomer aqueous solution may be, but is not limited to, 20 wt% to 55 wt%, preferably 30 wt% to 45 wt%. Generally speaking, when the concentration of the acid monomer aqueous solution is 20 wt% to 55 wt%, the viscosity of the polymerized product is moderate, it is easier to machine, and the heat of reaction during free radical polymerization is easier to control.

[0035] In other embodiments, other hydrophilic monomers with unsaturated double bonds may be selectively added, such as acrylamide, methacrylamide, 2-carboxyethyl acrylate, 2-carboxyethyl methacrylate, methyl acrylate, ethyl acrylate, dimethylamine acrylamide, and chloroacrylamidotrimethylamine. However, the amount of the above-mentioned hydrophilic monomers added is based on the principle of not impairing the physical properties of the absorbent resin (e.g., holding power and absorption rate).

[0036] In some embodiments, water-soluble polymers may be selectively added to the absorbent resin composition to reduce preparation costs. These water-soluble polymers may be partially or fully saponified polyvinyl alcohol, polyethylene glycol, polyacrylic acid, polyacrylamide, starch, or starch derivatives (e.g., methylcellulose, methylcellulose acrylate, ethylcellulose), etc., preferably starch and partially or fully saponified polyvinyl alcohol used alone or in combination. In the foregoing embodiments, the molecular weight of the water-soluble polymer is not limited, and when the amount of the acid monomer aqueous solution is 100 wt%, the amount of water-soluble polymer added is based on the principle of not reducing the physical properties of the absorbent resin, typically not exceeding 20 wt%, preferably not exceeding 10 wt%, and more preferably not exceeding 5 wt%.

[0037] In some embodiments, the aqueous solution of the acid monomer can be directly subjected to polymerization; or it can be partially neutralized first using a neutralizing agent to make the aqueous solution of the acid monomer neutral or weakly acidic before polymerization. In these embodiments, the neutralizing agent comprises hydroxides or carbonates of alkali metals or alkaline earth metals (e.g., sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate), amines, and combinations thereof. In some embodiments, the neutralization concentration of the aqueous solution of the acid monomer is 45 mol% to 85 mol%. When the neutralization concentration is within the aforementioned range, the aqueous solution of the acid monomer has a suitable pH value and is less likely to cause harm if accidentally exposed to human body. It should be noted that the neutralization concentration described herein is defined as the ratio of the number of mol in the alkaline solution to the number of mol in the aqueous solution of the acid monomer, and can also be regarded as the percentage of acid groups in the aqueous solution of the acid monomer being neutralized. In some embodiments, the pH value of the aqueous solution of the acid monomer is 5.5 to 7.0, preferably 5.5 to 6.5. If the pH value of the aqueous solution of the acid monomer is between 5.5 and 7.0, it is less likely to leave a large amount of unreacted monomer in the aqueous solution after polymerization, and the water-absorbing resin obtained subsequently has better physical properties and a larger absorption capacity.

[0038] The prepolymerization reaction begins with the generation of free radicals from the decomposition of the polymerization initiator. In some embodiments, based on the amount of the unsaturated monomer aqueous solution being 100 wt%, the appropriate amount of the polymerization initiator is 0.001 wt% to 10 wt%, preferably 0.1 wt% to 5 wt%. If the amount of polymerization initiator is within the aforementioned range, the rate of the free radical polymerization reaction is more appropriate, the economic benefits are better, and the formation of a gel-like solid due to overpolymerization can be avoided.

[0039] In some embodiments, the polymerization initiator comprises a thermally decomposable initiator, a redox initiator, or a combination thereof. In some embodiments, the thermally decomposable initiator comprises peroxides [e.g., hydrogen peroxide, di-tert-butyl peroxide, peroxyamide, or persulfates (including ammonium and alkali metal salts)] and azo compounds [e.g., 2,2-azobis(2-amidinylpropane) dihydrochloride, 2,2-azobis(N,N-diethylmethylisobutylamidinyl) dihydrochloride]. In some embodiments, the redox initiator comprises acidic sulfites, ascorbic acid, or ferrous salts. The polymerization initiator is preferably used in combination with both the thermally decomposable and redox initiators, which first react the redox initiator to generate free radicals. When these free radicals transfer to the monomer, the polymerization reaction is initiated, and the large amount of heat released by the polymerization reaction raises the temperature. When a specific temperature is reached, the thermally decomposable initiator can be further decomposed to make the polymerization reaction more complete, thus avoiding leaving excessive unreacted monomers.

[0040] Free radical polymerization crosslinking agents in absorbent resin compositions can impart appropriate crosslinking degrees to the composition, thereby improving its processability after polymerization. In some embodiments, the free radical polymerization crosslinking agent may be a compound containing two or more unsaturated double bonds, such as N,N-bis(2-propenyl)amine, N,N-methylenebisacrylamide, N,N-methylenebismethylacrylamide, propylene acrylate, ethylene glycol diacrylate, polyethylene glycol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, glycerol trimethacrylate, glycerol-added ethylene oxide triacrylate or trimethacrylate, trimethyl... The crosslinking agents used include propane trimethacrylate, trimethylolpropane triacrylate, N,N,N-tris(2-propenyl)amine, ethylene glycol diacrylate, polyoxyethylene glycerol triacrylate, diethyl polyoxyethylene glycerol triacrylate, and dipropylene triethylene glycol ester. Compounds containing two or more epoxy groups, such as sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, and dipropylene glycol polyglycidyl ether, can also be used. Two or more free radical polymerization crosslinking agents can be used alone or in combination. In some embodiments, the acid monomer aqueous solution is 100 wt%, and the free radical polymerization crosslinking agent is 0.001 wt% to 5 wt%, preferably 0.01 wt% to 3 wt%. If the amount of free radical polymerization crosslinking agent added is within the aforementioned range, the viscosity of the polymer aqueous solution after the reaction is moderate, making it easier to mechanically process, and the absorbency of the subsequently obtained water-absorbing resin is large.

[0041] In some embodiments, the above-described free radical polymerization reaction can be carried out in a batch reaction vessel or a conveyor belt reactor.

[0042] In some embodiments, the gel is first shredded using a grinder to a particle size of no more than 20 mm, preferably no more than 10 mm, before undergoing a screening step. In some embodiments, the screening step first filters out gel particles with a particle size of less than 2.0 mm, preferably 0.05 mm to 1.50 mm. Gel particles with a diameter greater than 2.0 mm need to be returned to the reactor for further shredding. The particle size needs to be controlled within the aforementioned range to avoid generating a high amount of fine powder in subsequent processes and to ensure better thermal conductivity. Generally, the narrower the particle size distribution of the water-absorbing resin, the better its physical properties.

[0043] In some embodiments, the gel may be selectively dried before subsequent operations. In some embodiments, the drying process is carried out at a temperature of 100°C to 180°C. Using the aforementioned temperature range for the drying process allows for effective control of the drying time and the degree of crosslinking, thereby avoiding the retention of large amounts of unreacted monomers.

[0044] Next, step 120 is performed to pulverize and screen the gel to obtain absorbent resin particles. In some embodiments, the particle size of the absorbent resin particles is screened to be from 0.06 mm to 1.00 mm, preferably from 0.10 mm to 0.85 mm. Controlling the particle size of the absorbent resin particles to the aforementioned range can reduce the amount of fine powder in the finished product and can improve the absorption performance of the absorbent resin.

[0045] Then, step 130 is performed to conduct a surface crosslinking reaction on the water-absorbing resin particles to obtain a water-absorbing resin. Since the water-absorbing resin is a non-soluble hydrophilic polymer with a uniform bridging structure inside, generally, further bridging is performed on the resin surface to improve absorption rate, colloidal strength, anti-caking properties, and volume permeability. The surface crosslinking reaction is carried out using a surface crosslinking agent with functional groups that can react with acid groups. In some embodiments, the surface crosslinking agent includes a polyol, a polyamine, a compound having two or more epoxy groups, and a hydrocarbon ester, wherein the polyol may be, for example, glycerol, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, and propylene glycol; the polyamine may be, for example, ethylenediamine, diethylenediamine, and triethylenediamine; and the epoxy-containing compound may be, for example, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, and diglycerol. Polyglycidyl ether; hydrocarbon carbonates may include, for example, ethylene glycol carbonate, 4-methyl-1,3-dioxacyclopentan-2-one, 4,5-dimethyl-1,3-dioxacyclopentan-2-one, 4,4-dimethyl-1,3-dioxacyclopentan-2-one, 4-ethyl-1,3-dioxacyclopentan-2-one, 1,3-dioxacyclohexane-2-one, 4,6-dimethyl-1,3-dioxacyclohexane-2-one, and 1,3-dioxacycloheptane-2-one. The reaction can be carried out alone or in combination with two or more surface crosslinking agents. Furthermore, depending on the surface crosslinking agent selected, it can be added directly, or the surface crosslinking agent can be prepared into an aqueous solution or a hydrophilic organic solution before addition. Hydrophilic organic solvents include, but are not limited to, methanol, ethanol, propanol, isobutanol, acetone, dimethyl ether, and diethyl ether.

[0046] In some embodiments, the amount of water-absorbing resin particles is 100 wt%, and the amount of surface crosslinking agent added is 0.001 wt% to 10 wt%, preferably 0.005 wt% to 5 wt%. When the amount of surface crosslinking agent added is within the aforementioned range, the surface of the water-absorbing resin can have a crosslinked structure, thereby achieving better absorption performance.

[0047] The absorbent resin produced by the above-described method 100 can have a large number of micropores. Please refer to [link / reference]. Figure 2A and Figure 2B , Figure 2ATo obtain a scanning electron microscope image of the absorbent resin prepared by method 100, and Figure 2B This is a scanning electron micrograph of a water-absorbing resin prepared without the addition of calcined seashell powder. For example... Figure 2A and Figure 2B As shown, the present invention improves the absorption performance of the water-absorbing resin by adding calcined seashell powder to participate in the free radical polymerization reaction.

[0048] As described above, the absorbent resin obtained by method 100 can possess a superior absorption rate, which can be evaluated using the free swell rate (FSR). The free swell rate of the absorbent resin of the present invention is not less than 0.25 g / g / s, preferably not less than 0.27 g / g / s. It should be understood that absorbent resins with a high free swell rate can rapidly absorb liquids without the application of pressure.

[0049] Furthermore, the resulting absorbent resin also exhibits superior liquid permeability, thus reducing problems such as rewetting, poor drying properties, and leakage in the absorbent. Liquid permeability can be evaluated using saline flow conductivity (SFC), which indicates the absorbent resin's ability to pass through liquids under high pressure after absorption. This allows liquid to easily diffuse into other unabsorbed absorbent resins when more liquid enters the absorbent. The absorbent resin of this invention has a saline flow conductivity of not less than 30 × 10⁻⁶. -7 cm 3 -s / g, preferably not less than 40cm 3 -s / g.

[0050] Furthermore, the ability of a dry absorbent resin to absorb liquid upon initial contact with liquid can be expressed by the T20 value. A lower T20 value indicates that the dry absorbent resin readily absorbs liquid. The T20 value of the absorbent resin of the present invention is no greater than 180 seconds, preferably no greater than 160 seconds. It should be further noted that the T20 value is defined as the time required for 1 gram of absorbent resin to absorb 20 grams of physiological saline and 0.01 wt% of an aqueous solution of an alcohol ethoxylate compound at a pressure of 0.3 psi, wherein the alcohol ethoxylate compound has 12 to 14 carbon atoms. The absorbent resin of the present invention possesses both a low T20 value and a high liquid conductivity, which reduces rewetting of the absorbent and improves the dryness of the diaper.

[0051] The aforementioned absorbent is formed into a sheet shape using the absorbent resin and hydrophilic fibers of the present invention, which fixes the absorbent resin onto pulp fiber material and / or nonwoven fabric. The pulp fiber can be pulverized wood pulp, cross-linked cellulose fibers, cotton, wool, vinyl acetate fibers, etc. Generally, the content of absorbent resin in the absorbent is 20 wt% to less than 100 wt%, preferably 40 wt% to less than 100 wt%, and more preferably 50 wt% to less than 100 wt%. Using such a high content of absorbent resin in the core significantly enhances the effects of the present invention.

[0052] In practical applications, the absorbent can be placed on a liquid-impermeable polyethylene film, and then covered with a liquid-permeable non-woven fabric as the surface layer. Generally, the basis weight (weight per unit area) of the absorbent is 0.01 g / cm³. 2 Up to 0.30 g / cm 2 And the thickness is less than 30mm.

[0053] The following examples illustrate the application of the present invention, but are not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention.

[0054] Preparation of calcined seashell powder

[0055] Manufacturing Example 1

[0056] After removing the residual meat from discarded oyster shells (source: Wanggong, Changhua) and cleaning the surface, the shells were coarsely crushed into oyster shell particles using commercially available crushing equipment and sieved through a 40-mesh sieve. Next, the oyster shell particles (60g) were coated with a 2.5wt% calcium hydroxide slurry (aqueous suspension, 500mL) for 2 hours and then calcined at 1000℃ for 4 hours to obtain calcined shell powder (1) with a core-shell structure and an average particle size of 415μm.

[0057] Manufacturing Examples 2 and 3

[0058] Manufacturing Examples 2 and 3 were prepared using similar process steps to Manufacturing Example 1. The difference was that in Manufacturing Example 2, the concentration of the calcium hydroxide slurry was changed to 10 wt%, and the average particle size of the calcined shell powder (2) obtained was 450 μm. In Manufacturing Example 3, the oyster shell particles were sieved through a 140-mesh sieve, and the average particle size of the calcined shell powder (3) obtained was 95 μm.

[0059] Preparation of water-absorbing resin

[0060] Example 1

[0061] 503.12 g of a 48 wt% sodium hydroxide aqueous solution was slowly added to a 2000 c.c. conical flask containing 621.03 g of acrylic acid and 670.74 g of water. The sodium hydroxide / acrylic acid ratio was in the range of 0.85 to 0.95, and the addition time was 2 hours. The temperature of the neutralization reaction system in the flask was maintained in the range of 15°C to 40°C. An unsaturated monomer aqueous solution with a monomer concentration of 42 wt% was obtained, in which 70 mol% of the acrylic acid was neutralized to sodium acrylate, and the pH value was 5.69.

[0062] Next, 1.36 g of N,N'-methylenebisacrylamide (a crosslinking agent for free radical polymerization) was added to the unsaturated monomer aqueous solution, and the temperature was maintained at about 20°C. Then, 17.91 g of calcined seashell powder (1) was added to the aqueous solution. Then, 0.35 g of hydrogen peroxide, 4.15 g of sodium bisulfite and 4.15 g of ammonium persulfate were added as polymerization initiators to carry out free radical polymerization.

[0063] The resulting gel was then shredded using a shearing pulverizer, and gel particles with a diameter of less than 2 mm were screened out. Next, it was dried at 130°C for 2 hours. Finally, it was screened using a fixed particle size sieve of 0.1 mm to 0.85 mm to obtain water-absorbing resin particles.

[0064] Next, weigh 200g of water-absorbing resin particles, add 2.5g of ethylene glycol, aluminum sulfate and water in a volume ratio of 1:0.5:2 to form an aqueous solution as a surface crosslinking agent, and heat at 160℃ for 1 hour. After cooling, the water-absorbing resin can be obtained.

[0065] Examples 2 to 5

[0066] The water-absorbing resins of Examples 2 to 5 were prepared using a process similar to that of Example 1. The differences were that the amount of calcined seashell powder (1) used in Example 2 was 44.87 g; the amount of surface crosslinking agent (i.e., a mixed aqueous solution of ethylene glycol, aluminum sulfate and water) added in Example 3 was increased to 5.0 g; 4.63 g of polyethylene glycol 600 diacrylate (UM82-080, manufactured by Risheng Chemical) was used instead of N,N'-methylenebisacrylamide as the crosslinking agent for free radical polymerization in Example 4; and calcined seashell powder (2) was used instead of calcined seashell powder (1) in Example 5.

[0067] Comparative Examples 1 to 5

[0068] The water-absorbing resins of Comparative Examples 1 to 5 were also prepared using similar process steps as in Example 1. The difference was that in Comparative Example 1, sodium carbonate (Taiwan Plastics Corporation, product name: FP-100A) was used instead of calcined seashell powder (1); in Comparative Example 2, a foaming agent obtained by the method for manufacturing an encapsulating foaming agent as described in U.S. Patent No. 7,163,966 was used instead of calcined seashell powder (1); in Comparative Example 3, no calcined seashell powder (1) was added; in Comparative Example 4, calcined seashell powder (1) was added after the gel was shredded; and in Comparative Example 5, calcined seashell powder (3) was used instead of calcined seashell powder (1).

[0069] Evaluation method

[0070] To evaluate the properties of the absorbent resin of the present invention, its physical properties were analyzed by the following test methods. Unless otherwise specified, all measurements were performed at room temperature of 23±2°C and relative humidity of 45±10%. The absorbent resin should be thoroughly mixed before analysis.

[0071] Holding force

[0072] Centrifuge Retention Capacity (CRC) was tested according to the test method of WSP 241.2(12) specified by the European Disposables and Nonwovens Association (EDANA). The results of the retention capacity tests for the absorbent resin particles and the absorbent resin are shown in Table 1.

[0073] Water absorption ratio under pressure

[0074] The absorption against pressure (AAP) was tested according to the test method ERT442.3(10) specified by EDANA, and the AAP was tested for 60 minutes at a pressure of 4.9 kPa against a 0.9% sodium chloride aqueous solution. The test results of the water-absorbing resin are shown in Table 1.

[0075] Liquid flow conductivity

[0076] Saline flow conductivity (SFC, unit: 10) -7 cm 3 The flow conductivity (sec / g) was measured and calculated according to the method described in US Patent No. 5,562,646, which involved placing the absorbent resin in Jayco synthetic urine for 60 minutes and then measuring the flow conductivity of a 0.118M sodium chloride aqueous solution at a pressure of 0.3 psi. The flow conductivity of the absorbent resin is shown in Table 1.

[0077] T20 value

[0078] The T20 value (in seconds) was measured and calculated according to the method described in US Patent No. 9,285,302. It is the time required for 1 gram of the absorbent resin to absorb 20 grams of physiological saline and 0.01 wt% of an aqueous solution of an alcohol ethoxylate compound having 12 to 14 carbon atoms under a pressure of 0.3 psi. The average results of three repeated experiments are shown in Table 1.

[0079] Free swelling rate

[0080] The free swell rate (FSR, unit: g / g / s) was measured and calculated according to the method described in US Patent No. 10,028,867. First, 4 g of absorbent resin was dried at 23 ± 2 °C and a pressure not exceeding 0.01 torr for 48 hours. Then, approximately 1 g was weighed and placed in a beaker, dispersed at the bottom. Next, 20 g of a 0.9 wt% sodium chloride aqueous solution was poured in. The time elapsed from the moment the liquid came into contact with the absorbent resin until the liquid was completely absorbed by the resin was measured. The free swell rate was calculated by dividing the liquid volume by the weight of the absorbent resin, and then by the elapsed time. The average values ​​obtained from three repetitions are shown in Table 1.

[0081] Table 1

[0082]

[0083] Preparation of absorber

[0084] Using an absorbent molding machine, 10.0 g of water-absorbing resin and 10.0 g of crushed wood pulp were mixed and molded into a 400-mesh (38 μm) metal mesh, with an absorbent area of ​​160 square centimeters (8 cm × 20 cm). The molded absorbent was placed on top of a polyethylene film, and then non-woven fabric was placed on top. Next, the absorbent was pressed under a pressure of 18.39 kPa (160 square centimeters in area, 30 kg in weight) for 5 minutes, and then the edges were glued with white adhesive to obtain the absorbent for testing.

[0085] Examples 6 to 10 and Comparative Examples 6 to 10

[0086] Examples 6 to 10 were prepared using the absorbent resins of Examples 1 to 5, respectively, according to the above method; while Comparative Examples 6 to 10 were prepared using the absorbent resins of Comparative Examples 1 to 5, respectively, according to the same method. The basis weight and thickness of the absorbents are shown in Table 2.

[0087] Absorber reabsorption performance

[0088] A lower rewet (i.e., dryness) of the absorbent indicates better urine resistance of the absorbent resin. The test method involved placing a 4.8 kPa weight (160 square centimeters in area, 7.8 kg in weight) on the absorbents prepared in Examples 6 to 10 and Comparative Examples 6 to 10. 180 ml of synthetic urine (Jayco synthetic urine as described in US Patent Publication No. 20040106745) was added dropwise in three portions (30 minutes apart) at the center point. After the addition was complete, the weight was removed after another 30 minutes. Then, 30 sheets of filter paper (8 cm × 20 cm) with a pre-measured total weight W1 were placed on the absorbent, and the 4.8 kPa weight was immediately placed on the absorbent for 5 minutes to allow the filter paper to absorb the rewetted liquid. The weight W2 of the 30 sheets of filter paper was then measured. The synthetic urine rewet of the absorbent was (W2 - W1). The test results are shown in Table 2.

[0089] Table 2

[0090]

[0091] Based on the above test results, compared to Comparative Examples 1 to 5, Examples 1 to 5 all exhibit higher liquid flow conductivity and free swelling rate, and lower T20 values. In other words, the absorbent resins of Examples 1 to 5 more readily absorb liquid in a dry state, and also have better liquid diffusivity and conductivity. Furthermore, the absorbents prepared from the absorbent resins of Examples 1 to 5 have lower liquid re-seepage, thus improving their dryness.

[0092] Therefore, by applying the method for manufacturing the water-absorbing resin of the present invention, adding a specific amount of calcined seashell powder with a specific particle size to participate in the free radical polymerization reaction, a water-absorbing resin with more micropores can be obtained, thereby increasing the absorption performance and liquid permeability of the water-absorbing resin, and improving the diffusion and conductivity of the dried water-absorbing resin.

[0093] Although the present invention has been disclosed above with reference to several embodiments, it is not intended to limit the present invention. Anyone with ordinary knowledge in the art to which this invention pertains may make various modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

[0094] [Symbol Explanation]

[0095] 100: Method

[0096] 110, 120, 130: Operation.

Claims

1. A method for manufacturing a water-absorbing resin, characterized in that, Include: A gel is obtained by free radical polymerization of an absorbent resin composition and calcined seashell powder. The absorbent resin composition comprises an unsaturated monomer aqueous solution, a polymerization initiator, and a free radical polymerization crosslinking agent. The calcined seashell powder has a core-shell structure, with the core layer consisting of micron-sized calcium oxide particles and the shell layer consisting of nano- to submicron-sized calcium oxide particles. The average particle size of the core layer is 7 μm to 500 μm, and the average particle size of the shell layer is no greater than 200 nm. The particle size of the calcined seashell powder is 100 μm to 1 mm, and the composition is based on 100 wt% of the unsaturated monomer aqueous solution and 0.005 wt% to 10 wt% of the calcined seashell powder. The gel was crushed and sieved to obtain a plurality of absorbent resin particles; and The absorbent resin particles are subjected to a surface crosslinking reaction to obtain the absorbent resin.

2. The method for manufacturing the water-absorbing resin according to claim 1, wherein the whiteness of the calcined seashell powder is at least 60.

3. The method for manufacturing the water-absorbing resin according to claim 1, wherein the specific surface area of ​​the calcined seashell powder is at least 8000 cm². 2 / g.

4. The method for manufacturing the water-absorbing resin according to claim 1, wherein the calcined seashell powder is added before, during, or after the free radical polymerization reaction.

5. The method for manufacturing the water-absorbing resin according to claim 1, further comprising: Before crushing and screening the gel, the gel is dried at a temperature of 100°C to 250°C.

6. The method for manufacturing the water-absorbing resin according to claim 1, wherein the average particle size of the water-absorbing resin particles is from 0.06 mm to 1.00 mm.

7. A water-absorbing resin, characterized in that, The water-absorbing resin is prepared by the manufacturing method according to any one of claims 1 to 6, and the T20 value of the water-absorbing resin is not greater than 180 seconds.

8. The water-absorbing resin according to claim 7, wherein the liquid flow conductivity of the water-absorbing resin is not less than 30 × 10⁻⁶. -7 cm 3 -s / g.

9. The water-absorbing resin according to claim 7, wherein the free swelling rate of the water-absorbing resin is not less than 0.25 g / g / s.

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