Method for preparing carboxymethyl cellulose particles, carboxymethyl cellulose particles prepared by the method, and water-absorbent article comprising the same

Abstract

The present invention relates to a method for preparing carboxymethyl cellulose particles, cellulose derivative particles prepared by the method, and a water-absorbent article comprising the same. The method comprises: step 1, reacting a cellulose raw material with an alkalizing agent to obtain alkalized cellulose; step 2, reacting the alkalized cellulose with a carboxymethylating agent to obtain carboxymethyl cellulose; step 3, which is a primary crosslinking step, reacting the carboxymethyl cellulose with a core crosslinking agent to obtain a carboxymethyl cellulose crosslink in a slurry state; step 4, filtering the carboxymethyl cellulose crosslink in a slurry state, washing and dehydrating; step 5, which is a secondary crosslinking step, reacting the carboxymethyl cellulose crosslink obtained in step 4 with a surface crosslinking agent to obtain a carboxymethyl cellulose having a core-shell structure; and step 6, drying and pulverizing the carboxymethyl cellulose having a core-shell structure to obtain carboxymethyl cellulose particles having a core-shell structure.

Description

Technical Field

[0001] The present invention relates to a method for preparing carboxymethyl cellulose (hereinafter referred to as "CMC") particles, CMC particles prepared by the method and water-absorbent articles comprising the same, and more particularly, to a method for preparing CMC particles comprising the step of reacting a CMC crosslinked product subjected to a core crosslinking reaction step with a surface crosslinking agent to obtain CMC having a core-shell structure, CMC particles prepared by the method and water-absorbent articles comprising the same. Background Art

[0002] Super absorbent polymer (SAP) is a functional raw material that can absorb water several dozen to several thousand times its own weight. It is widely used as a material for absorbent articles such as diapers for infants and young children, sanitary napkins for women, incontinence products for adults, pet products such as defecation pads, as well as medical absorbents, waterproof materials for civil engineering and construction, seedling cloths, and preservatives in the food distribution field.

[0003] Since the SAP is mainly used as a disposable material, it is required to be easy to manufacture and low in cost, among which physical properties such as the ability to absorb water from a substrate containing an aqueous liquid, liquid permeability, and swollen gel strength are considered to be important properties.

[0004] Conventionally, acrylic water-absorbent resins as such SAPs have been widely used due to their high water absorption and low process costs. However, acrylic water-absorbent resins are obtained from the petroleum industry and may be toxic due to residual monomers. Therefore, when used in diapers or sanitary products, they may cause erythema or itching in parts of the body that come into contact with them for a long time. Therefore, studies have been conducted on the use of CMC derived from cellulose, a natural plant material, into highly absorbent particles and their application in water-absorbent products.

[0005] As a conventional method of this kind, Patent Document 1 (Korean Patent Gazette No. 2001-0105311) describes a method for preparing a highly water-absorbent polysaccharide derivative, which comprises the following steps: (a) cross-linking one or more polysaccharides containing acidic groups such as CMC by a cross-linking agent to form a gel; (b) adjusting the pH of the polysaccharide to a value of 3.5 to 5.5 when necessary; (c) pulverizing the acidified polysaccharide gel; and (d) drying the pulverized polysaccharide at a high temperature.

[0006] The following is recorded in the patent document 1: The highly absorbent polysaccharide derivative can be used to absorb liquids composed of body fluids containing various salts and non-ionic substances, and is particularly suitable for the manufacture of absorbent sanitary products such as diapers and sanitary napkins. In essence, the highly absorbent polysaccharide derivative is mainly used as a water-absorbent raw material used in urine-absorbing diapers. However, the absorbency to blood is relatively low, and it is difficult to use it as a female product for absorbing blood. This is because the physical properties of urine and menstrual blood are very different. Specifically, menstrual blood contains water, salts, proteins, cells, etc., and its viscosity is higher than that of urine, and its diffusion rate is very slow. Moreover, larger cell blocks contained in the blood cannot be absorbed by the previous SAP such as the highly absorbent polysaccharide derivative, and a film is formed on the surface to hinder blood absorption.

[0007] As a method for solving this problem, Patent Document 2 (Japanese Patent Publication No. 2005-263858) describes a method for preparing a water-absorbing material, which comprises the following steps: (i) providing an aqueous solution containing polyvalent metal ions and a surfactant; (ii) adding a cellulose derivative and / or alginic acid or a salt thereof to the aqueous solution, crosslinking the solution, and performing gelation by swelling and hydration; (iii) contacting the crosslinked gel obtained in the step (ii) with a hydrophilic volatile solvent to dehydrate the gel; and (iv) drying. In this case, the method for preparing a water-absorbing material further comprises a step of treating the solid component obtained in the step (iii) or the step (iv) with a surface crosslinking agent.

[0008] According to the embodiment of the patent document 2, CMC powder is used as the cellulose derivative and / or alginic acid or its salt, and CMC powder is added to the aqueous solution provided by the step (i) to swell and crosslink to obtain a crosslinked gel. However, according to the method, in the initial stage of the step (ii) of obtaining the crosslinked gel, the CMC powder rapidly absorbs water and swells, has a high viscosity, and may produce an uneven crosslinking reaction. In addition, when considering the wearing feel when applied to sanitary napkins for women or adult urinary incontinence products, the reality is that there is still a need to improve the blood absorption capacity and water retention capacity of the absorbent material. In addition, the absorption rate under load is also an important factor affecting the wearing feel, which also needs to be improved. The absorption rate under load is the degree of absorption of physiological saline measured under pressure.

[0009] Patent document 1: KR1020010105311A

[0010] Patent Document 2: JP2005263858A Summary of the invention

[0011] The present invention is proposed to solve the above problems, and its purpose is to provide a method for preparing CMC particles, which comprises the step of reacting a CMC cross-linked product that has undergone a core cross-linking reaction step with a surface cross-linking agent to obtain CMC having a core-shell structure, so that the blood absorption capacity, centrifuge retention capacity (Centrifuge Retention Capacity, CRC) and absorbency under load (Absorbency Under Load, AUL) are excellent.

[0012] Another object of the present invention is to provide CMC particles prepared by the method and an absorbent article comprising the same.

[0013] One embodiment of the present invention provides a method for preparing CMC particles, the method comprising: step 1, reacting a cellulose raw material with an alkalizing agent to obtain alkalized cellulose; step 2, reacting the alkalized cellulose with a carboxymethylating agent to obtain CMC; step 3, which is a primary crosslinking step, reacting the CMC with a core crosslinking agent to obtain a CMC crosslinked product in a slurry state; step 4, filtering the CMC crosslinked product in a slurry state, washing and dehydrating; step 5, which is a secondary crosslinking step, reacting the CMC crosslinked product obtained in step 4 with a surface crosslinking agent to obtain CMC with a core-shell structure; and step 6, drying and pulverizing the CMC with a core-shell structure to obtain CMC particles with a core-shell structure.

[0014] Another embodiment of the present invention provides CMC particles prepared according to the preparation method.

[0015] Another embodiment of the present invention provides a water-absorbent article comprising CMC particles prepared according to the preparation method.

[0016] According to the present invention, modified CMC particles having high water absorption can be prepared by including the step of reacting a CMC crosslinked product subjected to a core crosslinking reaction step with a surface crosslinking agent to obtain CMC having a core-shell structure.

[0017] The CMC particles thus prepared can have excellent gel strength and AUL by surface crosslinking, and can exhibit excellent blood absorption capacity due to the increase in bulk density by the secondary crosslinking step. Further, according to the present invention, CMC particles having excellent water retention capacity measured under harsh conditions, such as CRC, can be provided, wherein CRC represents the water retention capacity of physiological saline measured after centrifugation. Therefore, the CMC particles of the present invention can be preferably used in feminine products for absorbing blood.

[0018] Furthermore, according to the present invention, gelation of CMC does not proceed during the core cross-linking process, thereby eliminating the problem of uneven cross-linking caused by high viscosity generated during the process. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a photograph of blood applied to CMC particles prepared according to Example 1.

[0020] Figure 2 For the Figure 1 Photograph of the Petri dish after shaking off the CMC particles that were not in contact with blood.

[0021] Figure 3 This is a photograph of blood applied to CMC particles prepared according to Example 8.

[0022] Figure 4 Shown from the Figure 3 Photograph of the Petri dish after shaking off the CMC particles that were not in contact with blood.

[0023] Figure 5 It is a device used to measure AUL of CMC particles. DETAILED DESCRIPTION

[0024] Next, the present invention will be described in detail.

[0025] In the present specification, when it is mentioned that a certain part “includes” a certain component, unless there is a particular description to the contrary, this means that other components may be further included, and other components are not excluded.

[0026] In this specification, the term "core crosslinking" refers to the crosslinking formed on the main chain of CMC by the reaction of CMC with a crosslinking agent. The crosslinking agent used at this time is called a "core crosslinking agent", and the reaction of CMC with the core crosslinking agent is called a "core crosslinking reaction".

[0027] In this specification, the term "surface crosslinking (or shell crosslinking)" means crosslinking formed on the surface of a CMC crosslinked product having core crosslinking by reacting with a crosslinking agent. The crosslinking agent used in this case is called a "surface crosslinking agent (or shell crosslinking agent)", and the reaction of the CMC crosslinked product with the surface crosslinking agent is called a "surface crosslinking reaction".

[0028] One embodiment of the present invention provides a method for preparing CMC particles, the method comprising: step 1, reacting a cellulose raw material with an alkalizing agent to obtain alkalized cellulose; step 2, reacting the alkalized cellulose with a carboxymethylating agent to obtain CMC; step 3, which is a primary crosslinking step, reacting the CMC with a core crosslinking agent to obtain a CMC crosslinked product in a slurry state; step 4, filtering the CMC crosslinked product in a slurry state, washing and dehydrating; step 5, which is a secondary crosslinking step, reacting the CMC crosslinked product obtained in step 4 with a surface crosslinking agent to obtain CMC with a core-shell structure; and step 6, drying and pulverizing the CMC with a core-shell structure to obtain CMC particles with a core-shell structure.

[0029] The following is a detailed description of the method for preparing CMC particles of the present invention in steps.

[0030] 1. Step of obtaining alkalized cellulose (alkalization reaction step)

[0031] This step is a step of reacting the cellulose raw material with an alkalizing agent to obtain alkalized cellulose.

[0032] As the cellulose raw material, conventional pulp commonly used in the art can be used without length restrictions, but specifically, pulp of 1 μm or more and less than 8 mm can be used, and more specifically, pulp of 0.15 mm or more and 0.5 mm or less can be used. More specifically, the cellulose raw material can be a raw material prepared by cutting one or more pulps selected from raw cotton, linter, and wood into a length of 0.15 mm or more and 0.5 mm or less. In the case of using the cellulose raw material cut in this way, the entanglement of the cellulose raw material and the mixer can be reduced, and the lumps generated by the tiny pulps can be suppressed to carry out a uniform reaction, and the operation time can be shortened, and the workability and fluidity can be ensured to improve productivity. As a result, compared with the case of using a cellulose raw material that has not undergone a cutting process, more than 30% of the preparation cost can be saved.

[0033] The step of obtaining the alkalized cellulose may use conventional methods commonly used in the art. For example, the following method may be used: after adding the cellulose raw material and the reaction solvent into the reactor, an alkalizing agent is added thereto, and the reaction is carried out while stirring at a temperature of 20° C. to 30° C. at a speed of 100 rpm to 200 rpm for 90 minutes to 150 minutes, thereby converting the cellulose into the alkalized cellulose.

[0034] The reaction solvent may include one or more selected from water, acetone, isopropyl alcohol, tert-butyl alcohol, and dimethyl ether. In this case, the amount of the reaction solvent used may be 50 parts by weight or more and 2,000 parts by weight or less relative to 100 parts by weight of the cellulose raw material.

[0035] The alkalizer may include an alkali metal hydroxide. For example, the alkalizer may include one or more selected from sodium hydroxide, potassium hydroxide and lithium hydroxide, and may be used in an aqueous solution state. The amount of the alkalizer added may be 5 parts by weight or more and 600 parts by weight or less relative to 100 parts by weight of the cellulose raw material. When the amount of the alkalizer added is within the range, in the step 2 described later, the carboxymethyl group can be uniformly substituted into the entire cellulose, thereby increasing the reactivity of the carboxymethylating agent and obtaining a CMC with a desired degree of substitution.

[0036] The purpose of adding the alkalizing agent is to weaken the crystal structure of cellulose so that the carboxymethylating agent described later and the cellulose can react easily. That is, the alkalizing agent promotes the reaction between the cellulose and the carboxymethylating agent. The alkalized cellulose needs to be stirred at room temperature (20°C to 30°C) for a specified time to uniformly weaken its crystal structure.

[0037] 2. Steps for obtaining CMC (carboxymethylation reaction step)

[0038] This step is a step of reacting the alkalized cellulose obtained in step 1 with a carboxymethylating agent to obtain CMC.

[0039] The step of obtaining CMC may be carried out by a conventional method commonly used in the art, for example, the following method may be used: a carboxymethylating agent is added to a reactor containing the alkalized cellulose obtained in step 1, and the reaction is carried out while the temperature is raised.

[0040] According to one embodiment of the present invention, step 2 may include: step 2-1, which is a primary carboxymethylation reaction step performed at a temperature above 40°C and below 55°C for a period of more than 90 minutes and less than 150 minutes; and step 2-2, which is a secondary carboxymethylation reaction step performed at a temperature above 65°C and below 75°C for a period of more than 30 minutes and less than 90 minutes.

[0041] Specifically, the carboxymethylating agent may include any one selected from chloroacetic acid, sodium chloroacetate, and mixtures thereof, and may be used in the form of a mixed solution dissolved in a reaction solvent. In this case, the reaction solvent may include one or more selected from water, acetone, isopropyl alcohol, tert-butyl alcohol, and dimethyl ether.

[0042] According to one embodiment of the present invention, the degree of substitution DS of the carboxymethyl group of the CMC prepared according to the step 2 may be greater than 0.7 and less than 2.0, and the degree of polymerization DP of the CMC may be greater than 800 and less than 4,000. In the present specification, the degree of substitution DS of the carboxymethyl group represents the average number of hydroxyl groups on each anhydroglucose unit in the cellulose molecule replaced by carboxymethyl groups. When the degree of substitution DS of the carboxymethyl group is within the range, a uniform reaction can be performed, and thus it is preferred. Moreover, the degree of polymerization of the CMC is a factor that affects the viscosity of the CMC. When the degree of polymerization is within the range, CMC particles having excellent bulk density can be prepared, and thus it is preferred.

[0043] According to one embodiment of the present invention, before the step 3 described later, a step 2.5 may be further included, in which the CMC obtained according to the step 2 is neutralized. The neutralization step may be performed according to a conventional method commonly used in the art, such as adding a neutralizing agent to the CMC for neutralization. Here, the neutralizing agent may be any oxidizing agent, mainly nitric acid, acetic acid, hydrochloric acid, etc. These neutralizing agents may be used in a state of being diluted to an aqueous solution with a concentration of 40% by weight or more and 99% by weight or less.

[0044] 3. Primary cross-linking step (core cross-linking reaction step)

[0045] This step is a step of reacting the CMC obtained in step 2 with a core crosslinking agent to obtain a CMC crosslinked product in a slurry state. Here, the slurry state means a low-fluidity liquid state containing a high concentration of suspended matter (CMC crosslinked product), and gelation does not occur in this step.

[0046] The steps 1 to 3 can be performed in a continuous or discontinuous manner. For example, when the steps 1 to 3 are performed continuously in the same reactor, there may be CMC that has completed or is undergoing a carboxymethylation reaction in the reactor after the step 2, and a core crosslinking agent can be added thereto to continuously perform the core crosslinking reaction. That is, according to the present invention, after the step 2 (carboxymethylation reaction step), no additional drying or pulverization process is performed, and a core crosslinking agent can be added to the inside of the reactor containing wet type CMC, and the CMC in the wet state is directly involved in the core crosslinking reaction to form a CMC crosslinked product. Through the reaction of the wet CMC with the core crosslinking agent, a core crosslink can be formed on the backbone of the CMC, thereby obtaining a CMC crosslinked product in a slurry state.

[0047] On the other hand, when the steps 1 to 3 are performed discontinuously, the drying and pulverizing process may be performed after the step 2, and the dry type CMC, the core crosslinking agent and the reaction solvent which have undergone such process may be added to the reactor. Then, the core crosslinking is formed on the backbone of the CMC through the reaction between the CMC and the core crosslinking agent in the reactor, thereby obtaining a CMC crosslinked product in a slurry state.

[0048] In this case, the case where the steps 1 to 3 are continuously performed in the same reactor is preferred because the process is simple and economical compared to the case where the steps are performed discontinuously. The use of core-crosslinked CMC in this way can ensure dispersibility and water absorption relative to 0.9% saline.

[0049] According to an embodiment of the present invention, the core cross-linking agent may include at least one selected from epoxy compounds and polyols. Specifically, examples of the epoxy compound include epichlorohydrin, glycerol diglycidyl ether, polyethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, ethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, propylene glycol diglycidyl ether, and glycidol. Examples of the polyol include glycerin, glycerol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, and the like. glycol), dipropylene glycol, polypropylene glycol, etc.

[0050] According to an embodiment of the present invention, the content of the core crosslinking agent may be greater than 0.1 parts by weight and less than 40 parts by weight based on 100 parts by weight of the cellulose raw material. When the content of the core crosslinking agent is within the range, the core crosslinking reaction efficiency is excellent, an appropriate core crosslinking density is exhibited, and the centrifuge retention capacity (CRC) of the CMC particles finally provided can be increased.

[0051] According to an embodiment of the present invention, step 3 can be performed by stirring at a temperature of 65°C to 75°C for 30 minutes to 90 minutes at a speed of 100 rpm to 300 rpm. When the reaction temperature, reaction time and stirring speed are within the range, core cross-linking is performed without gelation, and the cross-linking reaction efficiency is high and economical relative to the energy invested. In addition, step 3 can be performed at a pH of 6 to 8, in which case the cross-linking reaction can be easily controlled to improve the efficiency of the cross-linking reaction.

[0052] 4. Filtration, cleaning and dehydration steps

[0053] This step is a step of filtering the CMC cross-linked product in a slurry state obtained in step 3, and then washing and dehydrating it.

[0054] Specifically, after the CMC cross-linked product in slurry state obtained in step 3 is discharged from the reactor, it can be filtered according to a conventional known filtering method. For example, the filtration can be performed by sieving, suction filtration, ultrafiltration, filter pressing, etc., and suction filtration can be used specifically, but is not limited thereto.

[0055] According to an embodiment of the present invention, in the cleaning in step 4, one or more selected from water and volatile hydrophilic organic solvents can be used, and specifically, an aqueous solution containing a volatile hydrophilic organic solvent can be used. Although the volatile hydrophilic organic solvent is not particularly limited, as specific examples, lower alcohols such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, and tert-butyl alcohol can be listed; ketones such as acetone and methyl ethyl ketone; ethers such as 1,4-dioxane and tetrahydrofuran; amides such as N,N-dimethylformamide; sulfoxides such as dimethyl sulfoxide, etc., more specifically, methanol, ethanol or isopropyl alcohol can be used. After the cleaning process, impurities can be removed and a CMC cross-linked product with a purity of more than 99% can be obtained.

[0056] 5. Secondary cross-linking step (surface cross-linking reaction step)

[0057] This step is a step of reacting the CMC cross-linked product obtained in step 4 with a surface cross-linking agent to obtain CMC having a core-shell structure.

[0058] According to an embodiment of the present invention, the surface cross-linking agent may include at least one selected from polyepoxides and polyols. Specifically, examples of the epoxy compound include epichlorohydrin, glycerol diglycidyl ether, polyethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, ethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, propylene glycol diglycidyl ether, and glycidol. Examples of the polyol include glycerin, glycerol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, and the like. glycol), dipropylene glycol, polypropylene glycol, etc.

[0059] According to an embodiment of the present invention, the content of the surface crosslinking agent may be 0.1 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the CMC crosslinked product obtained in step 4. When the content of the surface crosslinking agent is within the above range, the surface crosslinking reaction efficiency is excellent, and CMC particles having good absorption under load can be provided.

[0060] On the other hand, in the method for preparing CMC particles of the present invention, the step 5 may use one method selected from the following two methods.

[0061] As a first method, step 5 may be a secondary crosslinking step, in which the CMC crosslinked product obtained in step 4 is reacted with the surface crosslinking agent and the foaming agent to obtain a porous CMC having a core-shell structure. At this time, the foaming agent and the surface crosslinking agent may react with the CMC crosslinked product in a solution state. Specifically, in step 5, a foaming agent solution and a surface crosslinking agent solution may be added to the CMC crosslinked product, or a mixed solution of a foaming agent solution and a surface crosslinking agent solution may be added.

[0062] According to an embodiment of the present invention, the foaming agent may include a carbonate compound, specifically, one or more carbonate compounds selected from magnesium carbonate, calcium carbonate, sodium bicarbonate and potassium bicarbonate. The foaming agent is a water-soluble compound and may be added in the form of an aqueous solution.

[0063] According to an embodiment of the present invention, the content of the foaming agent may be greater than 0.03 parts by weight and less than 20 parts by weight, and specifically greater than 0.3 parts by weight and less than 15 parts by weight, based on 100 parts by weight of the CMC cross-linked product obtained in step 4. When the content of the foaming agent is within the above range, the bulk density can be increased, thereby providing CMC particles having excellent blood absorption capacity.

[0064] In addition, in the first method, the surface crosslinking agent solution may contain a volatile hydrophilic organic solvent as a solvent. Examples of the volatile hydrophilic organic solvent include lower alcohols such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, and tert-butyl alcohol; ketones such as acetone and methyl ethyl ketone; ethers such as 1,4-dioxane and tetrahydrofuran; amides such as N,N-dimethylformamide; sulfoxides such as dimethyl sulfoxide, etc., and specifically alcohols, more specifically methanol, ethanol, or isopropyl alcohol.

[0065] According to an implementation of the present invention, in the first method, step 5 can be performed by stirring at a temperature of 50° C. to 90° C. at a speed of 100 rpm to 300 rpm for 120 minutes to 270 minutes. When step 5 is performed under the reaction conditions, the CMC cross-linked product, the foaming agent and the surface cross-linking agent can be evenly distributed, thereby improving the surface cross-linking efficiency.

[0066] As a second method, step 5 may be a secondary cross-linking step, in which a surface cross-linking agent solution prepared by dissolving the surface cross-linking agent in an organic solvent and water are added to the carboxymethyl cellulose cross-linked product after step 4, so that the carboxymethyl cellulose cross-linked product is surface cross-linked and gelled at the same time, thereby obtaining a gel-like carboxymethyl cellulose having a core-shell structure.

[0067] According to an embodiment of the present invention, in the second method, the organic solvent may include a volatile hydrophilic organic solvent having a boiling point lower than that of water, and specifically may include alcohols having a boiling point lower than that of water. Examples of the volatile hydrophilic organic solvent having a boiling point lower than that of water include lower alcohols such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, and tert-butyl alcohol; ketones such as acetone; ethers such as tetrahydrofuran, and examples of alcohols having a boiling point lower than that of water include methanol, ethanol, and isopropyl alcohol.

[0068] According to one embodiment of the present invention, in the second method, the content of the organic solvent added in the step 5 may be more than 200 parts by weight and less than 2,000 parts by weight based on 100 parts by weight of water. In the step 5 (surface crosslinking reaction step), the relative amounts of water and the organic solvent are very important. Specifically, when the amount of the organic solvent is relatively greater than the amount of water in the initial stage of the surface crosslinking reaction step, the rapid viscosity increase caused by the expansion of CMC can be suppressed, thereby achieving uniform surface crosslinking. Then, as the surface crosslinking reaction is carried out while the temperature is raised, the amount of the organic solvent may be relatively less than the amount of water due to volatilization, thereby carrying out the surface crosslinking reaction of the CMC crosslinked product having the core crosslinking, and the CMC crosslinked product can swell and hydrate in water to gel.

[0069] According to an implementation state of the present invention, in the second method, the step 5 may include a process of stirring for more than 120 minutes and less than 360 minutes at a speed of more than 100 rpm and less than 300 rpm while heating at a temperature above "the boiling point of the organic solvent" or "the azeotropic point of water and the organic solvent" and less than 100°C. When the step 5 is performed under the reaction conditions, as the reaction progresses to the later stage, the organic solvent with a boiling point lower than the boiling point of water can be volatilized first. According to the change in the solution equilibrium of the organic solvent and water generated during this heating process, gelation can be achieved while performing a uniform surface cross-linking reaction. As an example, when ethanol is used as an organic solvent, when the temperature is lower than the azeotropic point of water and ethanol (78.1°C), the solution equilibrium is "amount of organic solvent>amount of water", and when the temperature is gradually increased to a temperature higher than the azeotropic point, the solution equilibrium can become "amount of water>amount of organic solvent". That is, in the initial stage of the temperature increase process (the amount of organic solvent>the amount of water), a uniform surface crosslinking reaction is mainly carried out, and when the solution equilibrium changes due to the temperature increase (the amount of water>the amount of organic solvent), gelation can be gradually carried out together with the surface crosslinking reaction, thereby carrying out a uniform surface crosslinking reaction and smoothly carrying out gelation, and an excellent CMC having a core-shell structure can be obtained. On the contrary, when CMC is crosslinked and gelated in the presence of water alone without an organic solvent, the viscosity increases due to the rapid expansion of CMC in the initial stage of the reaction, and thus an uneven crosslinking reaction may be carried out.

[0070] 6. Steps to obtain CMC particles

[0071] This step is a step of obtaining CMC particles having a core-shell structure by drying and pulverizing the CMC having a core-shell structure obtained in step 5. At this time, the CMC having a core-shell structure may be dried and pulverized after a dehydration process.

[0072] The drying may be carried out in any conventional known drying manner without limitation, for example, natural drying, hot air drying or high temperature drying may be used.

[0073] In addition, the pulverization may be performed using a conventionally known pulverizer, for example, a cutting mill, a hammer mill, a pin mill, a screw mill, a roll mill, a disc mill, or the like.

[0074] According to an embodiment of the present invention, the bulk density of the CMC particles having a core-shell structure obtained in step 6 may be 0.5 g / ml or more and 0.9 g / ml or less, and in this case, particles having excellent blood absorption capacity and dispersibility can be provided. In particular, when the bulk density is within the above range, when an absorbent article including the CMC particles absorbs liquid, gel blocking due to the particles floating to the upper layer of the absorbent article or a decrease in initial water absorption due to the particles being densely packed to the lower layer of the absorbent article can be eliminated.

[0075] The preparation method of CMC particles of the present invention may further include: a classification step, sieving the porous CMC particles having a core-shell structure obtained according to step 6 to obtain particles of 150 μm or more and 850 μm or less. When the size of the CMC particles is included in the range, the gel blocking phenomenon and the problem of decreased water absorption can be eliminated, wherein the gel blocking phenomenon is caused by decreased dispersibility due to the smaller particle size, and the problem of decreased water absorption is caused by excessive liquid permeability due to the larger particle size. When considering both dispersibility and water absorption, the size of the CMC particles can be 250 μm or more and 500 μm or less.

[0076] Another embodiment of the present invention provides CMC particles prepared according to the preparation method and a water-absorbent article comprising the same.

[0077] According to an embodiment of the present invention, the blood absorption capacity of the CMC particles obtained by the following calculation formula may be greater than or equal to 130 mg and less than or equal to 155 mg.

[0078] Calculation formula 1

[0079] Blood absorption capacity (mg) = W2-W1

[0080] In the calculation formula 1, W1 is the weight of the Petri dish, and W2 is the weight of the Petri dish measured after 1.0 g of CMC particles are uniformly sprinkled on the Petri dish, 0.1 ml of blood is continuously dripped drop by drop into the center of the dish containing the CMC particles, and the blood is coagulated at room temperature for two hours, and then all the CMC particles in a clean state that have not contacted the blood are shaken off.

[0081] Thus, the CMC particles prepared according to the present invention have excellent AUL, CRC and blood absorption capacity, and thus can be preferably used in sanitary napkins for women, which are female products for absorbing blood. In addition, water-absorbing articles selected from sanitary products such as disposable diapers and adult incontinence products and pet products such as defecation pads can be prepared, and can also be used as materials such as medical water absorbents, water-stopping materials for civil engineering and construction, seedling cloths, and preservatives in the field of food distribution, and can be applied in various forms.

[0082] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0083] Example 1

[0084] First, pulp (Ethenier-F, Rayonier) was cut into a length of 0.15 mm to 0.5 mm to prepare a cellulose raw material.

[0085] Next, 90 g of the cut cellulose raw material was added to a pressure reactor (Lodige, Druvatherm series), and after adding 1231 g of an 80 wt % isopropanol aqueous solution as a reaction solvent, 158 g of a 50 wt % sodium hydroxide aqueous solution as an alkalizing agent was added, and the mixture was reacted while stirring at 150 rpm for 120 minutes at 25° C. to obtain alkalized cellulose.

[0086] Next, 360 g of a 45 wt % sodium chloroacetate aqueous solution as a carboxymethylating agent was added to the reactor to prepare CMC. At this time, the CMC was prepared by a primary carboxymethylation reaction step and a secondary carboxymethylation reaction step, wherein the alkalized cellulose and the carboxymethylating agent in the reactor were stirred at 50° C. and 200 rpm for 120 minutes to react in the primary carboxymethylation reaction step, and the temperature was raised to 70° C. and reacted for 60 minutes in the secondary carboxymethylation reaction step. The CMC prepared in this way had a degree of substitution DS of carboxymethyl of 1.0 and a degree of polymerization DP of 1,400.

[0087] Next, 4 g of glycerol diglycidyl ether as a core crosslinking agent was added to the reactor containing CMC, and a core crosslinking reaction (primary crosslinking reaction) was performed while stirring at 70° C. and 200 rpm for 60 minutes to prepare a CMC crosslinked product in a slurry state. At this time, the CMC crosslinked product did not gel.

[0088] Next, the CMC cross-linked product in a slurry state was discharged from the reactor and filtered using a suction filter (LK LabKorea, WJ-110), and then 900 g of a 70 wt % ethanol aqueous solution was added for primary washing, and 900 g of an 80 wt % ethanol aqueous solution was added for secondary washing and dehydration.

[0089] Next, 30 g of the CMC cross-linked product after the dehydration process was transferred to the pressure reactor again, and 270 g of a 1 wt % polyethylene glycol diglycidyl ether solution (solvent: ethanol) and 90.45 g of a foaming agent aqueous solution prepared by dissolving 0.45 g of sodium bicarbonate (foaming agent) in 90 g of water were added thereto. The internal temperature of the reactor was raised to 70° C., and then a surface cross-linking reaction (secondary cross-linking reaction) was carried out while stirring at 70° C. at a speed of 150 rpm for 180 minutes to prepare a porous CMC having a core-shell structure.

[0090] Next, after the surface cross-linking reaction is completed, the porous CMC with a core-shell structure is dehydrated, hot-air dried at 70°C for 360 minutes, and then crushed using a cutter (Fritsch Company, pulverisette 19) to prepare porous CMC particles with a core-shell structure (hereinafter referred to as "the first particle"). At this time, the first particle has a particle size ranging from 250 μm to 500 μm. In addition, the first particle is obtained in the following manner, which uses a standard sieve of 60 mesh (250 μm) for sieving, and after obtaining particles with a size of more than 250 μm, uses a standard sieve of 35 mesh (500 μm) for sieving to exclude particles with a size of more than 500 μm.

[0091] Example 2

[0092] CMC particles having a core-shell structure (hereinafter referred to as "second particles") were prepared in the same manner as in Example 1 except that 90.09 g of a foaming agent aqueous solution prepared by dissolving 0.09 g of sodium bicarbonate (foaming agent) in 90 g of water was added.

[0093] Example 3

[0094] CMC particles having a core-shell structure (hereinafter referred to as "third particles") were prepared in the same manner as in Example 1 except that 90.27 g of a foaming agent aqueous solution prepared by dissolving 0.27 g of the sodium bicarbonate (foaming agent) in 90 g of water was added.

[0095] Example 4

[0096] CMC particles having a core-shell structure (hereinafter referred to as "fourth particles") were prepared in the same manner as in Example 1 except that 90.9 g of a foaming agent aqueous solution prepared by dissolving 0.9 g of the sodium bicarbonate (foaming agent) in 90 g of water was added.

[0097] Example 5

[0098] CMC particles having a core-shell structure (hereinafter referred to as "fifth particles") were prepared in the same manner as in Example 1 except that 94.5 g of a foaming agent aqueous solution prepared by dissolving 4.5 g of the sodium bicarbonate (foaming agent) in 90 g of water was added.

[0099] Example 6

[0100] CMC particles having a core-shell structure (hereinafter referred to as “sixth particles”) were prepared in the same manner as in Example 1 except that the time of the surface cross-linking reaction was adjusted to 240 minutes.

[0101] Example 7

[0102] CMC particles having a core-shell structure (hereinafter referred to as "seventh particles") were prepared in the same manner as in Example 1 except that the time of the secondary carboxymethylation reaction was adjusted to 80 minutes.

[0103] Example 8

[0104] The CMC cross-linked product in the slurry state which was not gelled and discharged from the reactor according to the above-mentioned Example 1 was filtered, washed and dehydrated in the same manner as the above-mentioned Example 1.

[0105] Next, 30 g of the CMC crosslinked product after the dehydration process was transferred to the pressure reactor again, 270 g of a 1 wt % polyethylene glycol diglycidyl ether solution (solvent: ethanol) and 90 g of water were added thereto, and the internal temperature of the reactor was raised to 88° C. while stirring at a speed of 150 rpm for 240 minutes, so that a surface crosslinking reaction (secondary crosslinking reaction) was carried out and gelation was carried out to prepare a gel-like CMC having a core-shell structure. At this time, the azeotropic point of ethanol and water as the solvent of the surface crosslinking agent solution was 78.1° C. When the temperature was lower than the azeotropic point, the amount of ethanol in the reactor was greater than the amount of water, and when the temperature was raised to above the azeotropic point, the solution equilibrium changed and the amount of ethanol was less than the amount of water.

[0106] Next, after the surface crosslinking reaction is completed, the gel-like CMC is dehydrated and hot-air dried in the same manner as in Example 1, and then pulverized to prepare CMC particles having a core-shell structure and a size of 250 μm or more and 500 μm or less (hereinafter referred to as "eighth particles").

[0107] Example 9

[0108] CMC particles having a core-shell structure (hereinafter referred to as "9th particles") were prepared in the same manner as in Example 8, except that during the surface crosslinking reaction (secondary crosslinking reaction), the internal temperature of the reactor was raised to 88° C. and stirred at a speed of 150 rpm for 300 minutes, thereby performing a surface crosslinking reaction (secondary crosslinking reaction) and gelling simultaneously to prepare a gel-like CMC having a core-shell structure.

[0109] Example 10

[0110] CMC particles having a core-shell structure (hereinafter referred to as "the tenth particle") were prepared in the same manner as in Example 8, except that after the CMC was prepared through the primary and secondary carboxymethylation reaction steps, the temperature of the reactor containing the CMC was cooled to 30° C. and 60 ml of a 35% HCl solution was slowly dripped therein for 20 minutes to neutralize to pH 8.5 before the core crosslinking reaction (primary crosslinking reaction) was carried out.

[0111] Comparative Example 1

[0112] CMC particles having a core-shell structure (hereinafter referred to as "11th particles") were prepared in the same manner as in Example 1 except that 90 g of water was added instead of the aqueous blowing agent solution in the absence of a blowing agent.

[0113] Comparative Example 2

[0114] CMC particles having a core-shell structure (hereinafter referred to as “12th particles”) were prepared in the same manner as in Comparative Example 1 except that the time of the surface cross-linking reaction was adjusted to 240 minutes.

[0115] Comparative Example 3

[0116] CMC particles having a core-shell structure (hereinafter referred to as “13th particles”) were prepared in the same manner as in Comparative Example 1 except that the time of the secondary carboxymethylation reaction was adjusted to 80 minutes.

[0117] Comparative Example 4

[0118] The CMC cross-linked product in a slurry state discharged from the reactor according to Example 8 was filtered, washed and dehydrated in the same manner as in Example 8, and then water was added thereto and stirred to obtain a paste of the CMC cross-linked product. At this time, the amount of water added was 1,000 parts by weight based on 100 parts by weight of the CMC cross-linked product in a slurry state that had undergone the dehydration process.

[0119] Next, the paste of the cross-linked CMC was formed into a spherical shape with a diameter of 2 cm, dried in a dryer at a temperature of 70° C. for 360 minutes, and then pulverized using a cutter (Fritsch, pulverisette 19) to prepare a cross-linked CMC granular product. At this time, the cross-linked CMC granular product had a particle size ranging from 250 μm to 500 μm, and had only core cross-linking.

[0120] Next, 30 g of the granular CMC cross-linked product was transferred to the pressure reactor again, and 270 g of a 1 wt % polyethylene glycol diglycidyl ether solution (solvent: ethanol) and 90 g of water were added thereto as a surface cross-linking agent solution, and then a surface cross-linking reaction was performed by immersion. At this time, the surface cross-linking reaction temperature was 70°C and the reaction time was 1,440 minutes. Here, the immersion method refers to a method in which the surface cross-linking of the CMC cross-linked product is performed in a state where the CMC cross-linked product is immersed in the polyethylene glycol diglycidyl ether solution and water without a stirring process.

[0121] After the surface cross-linking reaction was completed, dehydration, drying and pulverization were performed in the same manner as in Example 8 to prepare CMC particles having a core-shell structure (hereinafter referred to as "the fourteenth particle").

[0122] Comparative Example 5

[0123] CMC particles having a core-shell structure (hereinafter referred to as "15th particles") were prepared in the same manner as in Comparative Example 4, except that uncut pulp (length 8 mm or more) was used as the cellulose raw material, and the reaction time of the first carboxymethylation reaction step was adjusted to 180 minutes and the reaction time of the second carboxymethylation reaction step was adjusted to 120 minutes.

[0124] Comparative Example 6

[0125] A CMC crosslinked product having core crosslinking was prepared by the same method as in Comparative Example 4, through core crosslinking reaction, washing and dehydration processes, except that uncut pulp (length of 8 mm or more) was used as the cellulose raw material, and the reaction time of the first carboxymethylation reaction step was adjusted to 180 minutes and the reaction time of the second carboxymethylation reaction step was adjusted to 120 minutes.

[0126] Then, the CMC cross-linked product after the dehydration process was directly dried at 70°C for 360 minutes without a surface cross-linking reaction step, and then pulverized using a cutter (Fritsch, pulverisette 19) to prepare CMC particles having only core cross-linking (hereinafter referred to as "16th particles").

[0127] <Evaluation method>

[0128] 1. Blood absorption capacity

[0129] The blood absorption capacity of the first to sixteenth particles obtained in Examples 1 to 10 and Comparative Examples 1 to 6, respectively, was evaluated in the following manner.

[0130] First, measure the weight W1 of a petri dish with an inner diameter of 3 cm, sprinkle 1.0 g of particles in the petri dish, and tap the bottom plate so that the particles are evenly spread on the surface of the dish. Next, put 0.1 ml of blood into a 1 ml plastic syringe, insert a 21G needle, and then drip it drop by drop slowly and continuously into the center of the particles in the petri dish. At this time, horse blood is used as the blood. Next, after the blood is coagulated at room temperature for two hours, shake off all the particles in a clean state that have not contacted the blood, and measure the weight W2 of the petri dish containing the coagulated blood and the particles entangled therewith. Using the measured weight, the blood absorption capacity is calculated according to the following formula (1), and the results are recorded in the following Table 1.

[0131] Blood absorption capacity (mg) = W2-W1 (1)

[0132] In the above formula (1), W1 is the weight of an empty Petri dish, and W2 is the weight of the Petri dish containing coagulated blood and particles entangled therewith.

[0133] Specifically, Figure 1 A photograph showing the application of blood on CMC particles prepared according to Example 1, Figure 2 Shown from the Figure 1 A photo of a petri dish after shaking off the CMC particles that did not come into contact with blood. Figure 3 A photograph showing the application of blood on CMC particles prepared according to Example 8, Figure 4 Shown from the Figure 3 Photograph of a Petri dish after shaking off the CMC particles that were not in contact with blood.

[0134] 2. Absorbency Under Load (AUL)

[0135] Use Figure 5 The device shown measures the absorbance under load of the first to sixteenth particles obtained according to Examples 1 to 10 and Comparative Examples 1 to 6, respectively.

[0136] First, a 400-mesh metal mesh 5 is installed on the bottom plate of a cylindrical PMMA (polymethyl methacrylate) cylinder 7 (inner diameter: 60 mm, height: 50 mm). At room temperature, 0.9 g of the particles 6 (W3) are evenly placed on the metal mesh 5, and a plastic piston 8 with a 0.7 psi metal weight 9 is placed on the particles 6 to construct an AUL measuring device.

[0137] In addition, a glass ceramic filter plate 2 (diameter: 80 mm, thickness: 7 mm) with a porosity #0 is set on the inner side of the Petri dish 1 (diameter: 118 mm, height: 12 mm), and a physiological saline solution 3 composed of a 0.9 wt % sodium chloride aqueous solution is added to the Petri dish 1 so that the height of the physiological saline solution 3 is equal to the height of the ceramic filter plate 2, and then a filter paper 4 is placed above the ceramic filter plate 2.

[0138] Next, the AUL measuring device was placed on the filter paper 4, and after the physiological saline was absorbed under pressure for 60 minutes, the weight W4 of the particles in the measuring device was measured. The AUL was calculated according to the following formula (2) using the weight thus measured, and the results are recorded in the following Table 1.

[0139] AUL(g / g)=(W4-W3) / W3 (2)

[0140] In the above formula (2), W3 is the weight of the initial particles (0.9 g), and W4 is the weight of the particles after absorbing physiological saline under pressure (0.7 psi) for 60 minutes.

[0141] 3. Centrifuge Retention Capacity (CRC)

[0142] The centrifuge retention capacities of the first to sixteenth particles respectively obtained according to Examples 1 to 10 and Comparative Examples 1 to 6 were measured in the following manner.

[0143] After 0.2 g (W5) of each of the particles is uniformly loaded into a tea bag and sealed, it is immersed in a physiological saline solution consisting of a 0.9 wt% sodium chloride aqueous solution at room temperature for 30 minutes. Next, water is removed from the sealed tea bag at 250 G for three minutes using a centrifuge, and the weight W6 of the sealed tea bag is measured. In addition, for the tea bag without particles, the immersion and centrifugal separation operations are performed in the same manner, and its weight W7 is measured. Using the weight measured in this way, CRC is calculated according to the following formula (3), and the results are recorded in the following Table 1.

[0144] CRC(g / g)=(W6-W7-W5) / W5 (3)

[0145] In the formula (3), W5 is the weight of the initial particles (0.2 g), W6 is the weight of the tea bag filled with particles and sealed after immersion and centrifugation, and W7 is the weight of the tea bag without particles after immersion and centrifugation.

[0146] [Table 1]

[0147] AUL(g / g) CRC(g / g) Blood absorption capacity (mg) Example 1 9.51 33.0 150 Example 2 9.46 32.7 133 Example 3 9.48 32.8 140 Example 4 9.50 33.0 151 Example 5 9.50 33.2 151 Example 6 9.51 32.9 150 Example 7 9.51 32.9 149 Example 8 9.51 32.2 148 Example 9 9.52 33.1 153 Example 10 9.51 32.7 150 Comparative Example 1 9.41 31.5 123 Comparative Example 2 9.42 31.0 123 Comparative Example 3 9.42 31.4 122 Comparative Example 4 9.42 30.9 124 Comparative Example 5 9.39 31.3 120 Comparative Example 6 8.38 30.5 75

[0148] It can be confirmed from Table 1 that the 1st to 10th particles prepared according to Examples 1 to 10 exhibited excellent AUL, CRC and blood absorption capacity, and in particular, significantly excellent blood absorption capacity, compared with the 11th to 16th particles prepared according to Comparative Examples 1 to 6. The above embodiments disclosed in the present invention are not intended to limit the technical concept of the present invention, but to illustrate the present invention. The scope of rights of the present invention should be interpreted by the attached claims, and all technical concepts within the scope equivalent to the contents of the claims should be interpreted as included in the scope of rights of the present invention.

[0149] Description of Reference Numerals

[0150] 1: Petri dish

[0151] 2: Ceramic filter plate

[0152] 3: NaCl solution

[0153] 4: Filter paper

[0154] 5: Metal mesh

[0155] 6: Superabsorbent particles

[0156] 7: PMMA cylinder

[0157] 8: Plastic piston

[0158] 9: Metal weight

Claims

1. A method for preparing carboxymethyl cellulose particles, comprising: Step 1, reacting a cellulose raw material with an alkalizing agent to obtain alkalized cellulose; Step 2, reacting the alkalized cellulose with a carboxymethylating agent to obtain carboxymethyl cellulose; Step 3, which is a primary cross-linking step, reacting the carboxymethyl cellulose with a core cross-linking agent to obtain a carboxymethyl cellulose cross-linked product in a slurry state; Step 4, filtering the carboxymethyl cellulose cross-linked product in a slurry state, and then washing and dehydrating it; Step 5, which is a secondary cross-linking step, reacting the carboxymethyl cellulose cross-linked product obtained in step 4 with a surface cross-linking agent to obtain carboxymethyl cellulose having a core-shell structure; and Step 6, drying and crushing the carboxymethyl cellulose having a core-shell structure to obtain carboxymethyl cellulose particles having a core-shell structure, wherein the step 5 is a secondary crosslinking step as follows: while heating the carboxymethyl cellulose crosslinked product after the step 4 at a temperature higher than the "boiling point of the organic solvent" or the "azeotropic point of water and the organic solvent" and lower than 100°C, a surface crosslinking agent solution prepared by dissolving the surface crosslinking agent in an organic solvent and water are added to the carboxymethyl cellulose crosslinked product after the step 4, so that the carboxymethyl cellulose crosslinked product is surface crosslinked and gelled to obtain a gel-like carboxymethyl cellulose having a core-shell structure; or the step 5 is a secondary crosslinking step as follows: the carboxymethyl cellulose crosslinked product after the step 4 is reacted with the surface crosslinking agent and a foaming agent to obtain a porous carboxymethyl cellulose having a core-shell structure, The organic solvent includes a volatile hydrophilic organic solvent having a boiling point lower than that of water.

2. The method for preparing carboxymethyl cellulose particles according to claim 1, characterized in that: The cellulose raw material is prepared by cutting one or more pulps selected from raw cotton, linter, and wood into a length of 0.15 mm to 0.5 mm.

3. The method for preparing carboxymethyl cellulose particles according to claim 1, characterized in that: The step 2 comprises: step 2-1, which is a primary carboxymethylation reaction step performed at a temperature of 40°C to 55°C for 90 minutes to 150 minutes; and step 2-2, which is a secondary carboxymethylation reaction step performed at a temperature of 65°C to 75°C for 30 minutes to 90 minutes.

4. The method for preparing carboxymethyl cellulose particles according to claim 1, characterized in that: The carboxymethyl cellulose prepared according to step 2 has a degree of substitution DS of carboxymethyl groups of 0.7 to 2.0, and a degree of polymerization DP of 800 to 4,000.

5. The method for preparing carboxymethyl cellulose particles according to claim 1, characterized in that: Before the step 3, the method further comprises a step 2.5, in which the carboxymethyl cellulose obtained according to the step 2 is neutralized.

6. The method for preparing carboxymethyl cellulose particles according to claim 1, characterized in that: The core crosslinking agent includes at least one selected from epoxy compounds and polyols.

7. The method for preparing carboxymethyl cellulose particles according to claim 1, characterized in that: The content of the core crosslinking agent is 0.1 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the cellulose raw material.

8. The method for preparing carboxymethyl cellulose particles according to claim 1, characterized in that: The step 3 is performed by stirring at a temperature of 65° C. to 75° C. at a speed of 100 rpm to 300 rpm for 30 minutes to 90 minutes.

9. The method for preparing carboxymethyl cellulose particles according to claim 1, characterized in that: In the washing in step 4, at least one selected from water and a volatile hydrophilic organic solvent is used.

10. The method for preparing carboxymethyl cellulose particles according to claim 1, characterized in that: The surface crosslinking agent includes at least one selected from polyepoxides and polyols.

11. The method for preparing carboxymethyl cellulose particles according to claim 1, characterized in that: The content of the surface crosslinking agent is 0.1 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the crosslinked carboxymethyl cellulose obtained in step 4.

12. The method for preparing carboxymethyl cellulose particles according to claim 1, characterized in that: The foaming agent includes at least one carbonate compound selected from the group consisting of magnesium carbonate, calcium carbonate, sodium bicarbonate and potassium bicarbonate.

13. The method for preparing carboxymethyl cellulose particles according to claim 1, characterized in that: The content of the foaming agent is 0.03 parts by weight or more and 20 parts by weight or less based on 100 parts by weight of the carboxymethyl cellulose cross-linked product obtained in step 4.

14. The method for preparing carboxymethyl cellulose particles according to claim 1, characterized in that: The step 5 is performed by stirring at a temperature of 50° C. to 90° C. at a speed of 100 rpm to 300 rpm for 120 minutes to 270 minutes.

15. The method for preparing carboxymethyl cellulose particles according to claim 1, characterized in that: The organic solvent includes alcohols having a boiling point lower than that of water.

16. The method for preparing carboxymethyl cellulose particles according to claim 1, characterized in that: The content of the organic solvent added in the step 5 is 200 parts by weight or more and 2,000 parts by weight or less based on 100 parts by weight of water.

17. The method for preparing carboxymethyl cellulose particles according to claim 1, characterized in that: The step 5 includes: heating to a temperature above the boiling point of the organic solvent or the azeotropic point of water and the organic solvent and below 100° C., and stirring at a speed of 100 rpm to 300 rpm for 120 minutes to 360 minutes.

18. The method for preparing carboxymethyl cellulose particles according to claim 1, characterized in that: The bulk density of the carboxymethyl cellulose particles obtained in step 6 is 0.5 g / ml or more and 0.9 g / ml or less.

19. Carboxymethyl cellulose particles prepared according to the preparation method selected from any one of claims 1 to 18.

20. The carboxymethyl cellulose particles according to claim 19, characterized in that The blood absorption capacity of the carboxymethyl cellulose particles obtained by the following calculation formula is 130 mg or more and 155 mg or less, Calculation formula 1 Blood absorption capacity (mg) = W2-W1 In the calculation formula 1, W1 is the weight of the Petri dish, and W2 is the weight of the Petri dish measured after 1.0 g of carboxymethyl cellulose particles are evenly sprinkled on the Petri dish, 0.1 ml of blood is continuously dripped drop by drop into the center of the dish containing the carboxymethyl cellulose particles, and the blood is coagulated at room temperature for two hours, and then all the clean carboxymethyl cellulose particles that have not contacted the blood are shaken off.

21. An absorbent article comprising carboxymethyl cellulose particles produced according to the production method selected from any one of claims 1 to 18.

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