TWI807852B - Superabsorbent polymers and method of fabricating the same - Google Patents

Abstract

A superabsorbent polymer and a method of forming the same are provided. The method includes performing a free radical polymerization reaction to a superabsorbent polymer components to obtain a colloid gel. The colloid gel is smashed and screened to obtain superabsorbent polymer particles. The superabsorbent polymer particles are performed a surface cross-linking reaction with surface cross-linking agent and ionomer to obtain the superabsorbent polymer. The superabsorbent polymer has a great saline flow conductivity.

Description

Water absorbent resin and its production method

The present invention relates to a water-absorbing resin and its manufacturing method, in particular to a water-absorbing resin with better liquid flow conductivity and its manufacturing method.

Water-absorbent resins have a wide range of applications, such as water retaining agents in agriculture or gardening, anti-dew condensation agents in building materials, materials for removing moisture in petroleum, outer waterproof coating agents in cables, personal hygiene products (such as diapers, feminine hygiene products, and disposable wipes, etc.), among which diapers are the bulk.

The absorbent performance of diapers depends on the absorption rate, absorption capacity and dryness. In recent years, the goal of thinning diapers is to reduce the amount of pulp (hydrophilic fiber) and increase the amount of water-absorbent resin, so as to achieve thinner diapers by increasing the proportion of water-absorbent resin in the absorbent structure of diapers. However, the reduction in the amount of hydrophilic fibers will reduce the water storage space in a short period of time, and the liquid infiltration speed will slow down, making it too late for the liquid to be absorbed and leak out. In addition, the water-absorbent resin must have high permeability to liquids in addition to a good absorption rate. If the liquid permeability is not good, it will cause the water-absorbent resin to block the gaps between the particles when absorbing liquid, forming a colloidal blocking phenomenon and causing the liquid to flow out of the absorbent body of the diaper, thereby reducing the absorption performance of the diaper.

Therefore, improving the absorption rate and permeability of water-absorbent resins is one of the current research priorities in this field. In conventional methods, polyvalent metal cations can be used for surface modification or aluminum dihydroxyacetate can be used to improve the liquid flow conductivity of the water-absorbent resin. It is also possible to use thermoplastic polymers such as polyethylene or polypropylene in the heat treatment step, or add an amino group-containing azo compound as a foaming agent to the aqueous solution of acid-containing monomers to improve the liquid permeability of the water-absorbent resin. In addition, adding an encapsulated blowing agent or a water-soluble alkoxysilane compound to the acid-group-containing monomer aqueous solution can make the prepared water-absorbent resin have better absorption rate or good colloidal stability, respectively. Furthermore, it is known that the diffusibility and liquid permeability of the water-absorbent resin after absorbing liquid can be improved by mixing water-soluble polyvalent metal powder, adhesive and water-absorbent resin.

In addition, the conventional water-absorbent resin will be subjected to surface cross-linking treatment to further bridge the surface of the water-absorbent resin to achieve the effects of increasing absorption rate, improving colloid strength, anti-caking and liquid permeability. For example, conventional methods include dispersing water-absorbent resin and cross-linking agent in an organic solvent for surface cross-linking treatment; or mixing inorganic powder into water-absorbing resin for cross-linking treatment; or adding a cross-linking agent and then treating it with steam; or using organic solvents, water and polyols for surface treatment; or using organic solvents, water and ether compounds for surface treatment, etc. However, although the conventional surface treatment method can increase the absorption rate and the water absorption capacity under pressure, it may cause a significant decrease in the retention force of the water-absorbent resin, thereby reducing the effect of practical application.

In view of this, there is an urgent need to provide a water-absorbent resin and a manufacturing method thereof, so as to simultaneously increase the liquid flow conductivity and the water absorption capacity under pressure of the water-absorbent resin, and still maintain a high retention force.

One aspect of the present invention is to provide a method for producing a water-absorbent resin, which is to increase the liquid flow conductivity of the prepared water-absorbent resin by participating in a surface cross-linking reaction with a reactive polymer.

Another aspect of the present invention is to provide a water-absorbent resin produced by the above-mentioned aspect.

According to one aspect of the present invention, a method for producing a water-absorbent resin is provided. The method includes performing radical polymerization on the water-absorbing resin composition to obtain a gel. The water-absorbent resin composition includes an aqueous unsaturated monomer solution, a polymerization initiator and a radical polymerization cross-linking agent. Then, pulverizing and screening the gel to obtain a plurality of water-absorbing resin particles; and performing a surface cross-linking reaction on the water-absorbing resin particles, a surface cross-linking agent and a reactive polymer to obtain a water-absorbing resin, wherein the reactive polymer includes polyethylene segments and polyacrylic acid segments.

According to one embodiment of the present invention, the above-mentioned reactive polymer is an ethylene acrylic acid polymer, and the ethylene acrylic acid polymer comprises a polyethylene segment represented by the following formula (1) and a polyacrylic acid segment represented by the following formula (2),

其中M為氫原子、IA族元素或IIA族元素；且基於乙烯丙烯酸聚合物為100wt%，聚乙烯鏈段為80wt%至99wt%，聚丙烯酸鏈段為1wt%至20wt%。

Wherein M is a hydrogen atom, a group IA element or a group IIA element; and based on 100wt% of the ethylene acrylic acid polymer, the polyethylene segment is 80wt% to 99wt%, and the polyacrylic acid segment is 1wt% to 20wt%.

According to an embodiment of the present invention, when the weight of the polyethylene segment in the reaction polymer is 100 wt%, the weight of the polyacrylic acid segment is 8 wt% to 20 wt%.

According to an embodiment of the present invention, when the weight of the above-mentioned water-absorbent resin particles is 100wt%, the amount of the reactive polymer added is 0.01wt% to 10wt%.

According to another aspect of the present invention, there is provided a water-absorbent resin produced by the above method, and the T20 value of the water-absorbent resin is not greater than 180 seconds.

According to an embodiment of the present invention, the liquid flow conductivity of the above-mentioned water-absorbent resin is not less than 30×10 ^-7 cm ³ -s/g.

According to an embodiment of the present invention, the retention force of the water-absorbent resin is greater than 20 g/g.

By applying the water-absorbent resin and its manufacturing method of the present invention, the reaction polymer participates in the surface cross-linking reaction to achieve the effect of improving the liquid flow conductivity of the water-absorbent resin and the water absorption rate under pressure, and at the same time maintain a high retention force of the water-absorbent resin, so it can be practically applicable.

As used herein, "around", "about", "approximately" or "substantially" generally means within 20 percent, or within 10 percent, or within 5 percent of the stated value or range.

Based on the above, the present invention provides a water-absorbent resin and its manufacturing method. By participating in the surface cross-linking reaction of the reactive polymer, the effect of improving the liquid flow conductivity of the water-absorbent resin and the water absorption rate under pressure can be achieved, and at the same time, the high retention force of the water-absorbent resin can be maintained, so it can be practically applicable.

The manufacturing method of the water-absorbent resin provided by the present invention includes performing free-radical polymerization on the water-absorbent resin composition to obtain a gel. In some embodiments, the water-absorbent resin composition includes an aqueous solution of an unsaturated monomer, a polymerization initiator, and a free radical polymerization crosslinking agent.

In some embodiments, the aqueous unsaturated monomer solution in the water-absorbent resin composition includes an acid-based monomer having an unsaturated double bond, such as acrylic acid. In some embodiments, the aqueous unsaturated monomer solution can be methacrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, maleic acid (maleic acid), maleic anhydride, fumaric acid (fumaric acid), and fumaric anhydride. The unsaturated monomer aqueous solution may include but not limited to one kind of monomer, and two or more kinds of the above-mentioned monomer aqueous solutions may also be selected.

In some embodiments, the concentration of the unsaturated monomer aqueous solution may be but not limited to 20 wt% to 55 wt%, preferably 30 wt% to 45 wt%. Generally speaking, if the concentration of the acid-based monomer aqueous solution is 20 wt% to 55 wt%, the viscosity of the polymerized product is moderate, it is easier to process mechanically, and the reaction heat during free radical polymerization is also easier to control.

In other embodiments, other hydrophilic monomers with unsaturated double bonds can be optionally added, such as acrylamide, methacrylamide, 2-carboxyethyl acrylate, 2-carboxyethyl methacrylate, methyl acrylate, ethyl acrylate, dimethylamine acrylamide, and acrylamidotrimethylamine chloride. However, the addition amount of the above-mentioned hydrophilic monomer is based on the principle that the physical properties (such as holding power and absorption rate) of the water-absorbing resin are not damaged.

In some embodiments, the acid-based monomer aqueous solution can be directly polymerized; or first partially neutralized with a neutralizing agent to make the acid-based monomer aqueous solution neutral or weakly acidic, and then polymerized. In these embodiments, the neutralizing agent includes alkali metal or alkaline earth metal hydroxides or carbonates (such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate), amine compounds, and combinations thereof. In some embodiments, the neutralization concentration of the acid-based monomer aqueous solution is 45 mol% to 85 mol%. When the neutralization concentration of the acid-based monomer aqueous solution is within the above-mentioned range, the acid-based monomer aqueous solution can have a pH value more suitable for free radical polymerization, and if it accidentally contacts with a human body, possible damage can be reduced. It should be added that the neutralization concentration described herein is defined as the ratio of the number of moles of the alkaline solution to the number of moles of the acid-based monomer aqueous solution, and can also be regarded as the percentage of neutralized acid groups in the acid-based monomer aqueous solution.

In some embodiments, the pH of the acid-based monomer aqueous solution is not less than 5.5, preferably 5.5 to 7.0, more preferably 5.5 to 6.5. If the pH value of the acid-based monomer aqueous solution is 5.5 to 7.0, it is less likely that a large amount of unreacted monomer will remain in the aqueous solution after polymerization, and the subsequent water-absorbent resin will have better physical properties and higher absorption capacity.

In some embodiments, water-soluble polymers may also be selectively added to the water-absorbent resin composition to reduce production costs. In some embodiments, the water-soluble polymer comprises partially saponified or fully saponified polyvinyl alcohol, polyethylene glycol, polyacrylic acid, polyacrylamide, starch or starch derivatives (such as methyl cellulose, methyl cellulose acrylate, ethyl cellulose, etc.), preferably starch and partially or fully saponified polyvinyl alcohol alone or in combination. In the aforementioned embodiments, the molecular weight of the water-soluble polymer is not limited, and when the amount of the unsaturated monomer aqueous solution is 100 wt%, the amount of the water-soluble polymer added is based on the principle of not reducing the physical properties of the water-absorbent resin, usually 0 wt% to 20 wt%, preferably 0 wt% to 10 wt%, and even more 0 wt% to 5 wt%.

The pre-polymerization reaction starts with the generation of free radicals by the decomposition of the polymerization initiator. In some embodiments, based on 100 wt% of the unsaturated monomer aqueous solution, 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 the polymerization initiator is within the aforementioned range, the rate of free radical polymerization is more appropriate, the economic benefits are better, the reaction heat is easier to control, and the formation of gel-like solids due to excessive polymerization can be avoided.

In some embodiments, the polymerization initiator comprises a thermal decomposable initiator, a redox initiator, and combinations thereof. In some embodiments, the thermally decomposing initiator includes peroxides [such as hydrogen peroxide, di-tert-butyl peroxide, amide peroxide or persulfate (including ammonium salts and alkali metal salts)] and azo compounds [such as 2,2-azobis(2-amidinopropane) dihydrochloride, 2,2-azobis(N,N-dimethyleneisobutylamidine) dihydrochloride]. In some embodiments, the redox initiator comprises an acidic sulfite, ascorbic acid, or ferrous salt. The polymerization initiator is preferably used in combination with a thermal decomposition type initiator and a redox type initiator. First, the redox type initiator reacts to generate free radicals. When the free radicals are transferred to the monomer, the polymerization reaction is initiated, and the large amount of heat released by the polymerization reaction will increase the temperature of the reaction system. When the reaction system reaches a specific temperature, the thermal decomposition type initiator can be further decomposed to make the polymerization reaction more complete, so it can avoid leaving too much unreacted monomer.

The radical polymerization cross-linking agent in the water-absorbent resin composition can make the water-absorbent resin composition have an appropriate degree of cross-linking, and improve the workability of the water-absorbent resin composition after polymerization. In some embodiments, the free radical polymerization crosslinking agent can be a compound containing two or more unsaturated double bonds, such as N,N-bis(2-propenyl)amine, N,N-methylenebisacrylamide, N,N-methylenebismethacrylamide, propylene acrylate, ethylene glycol diacrylate, polyethylene glycol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, glycerin trimethacrylate, glycerin trimethacrylate, triacrylate of glycerol with ethylene oxide, or Trimethacrylate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, N,N,N-tris(2-propenyl)amine, ethylene glycol diacrylate, polyoxyethylene glycerol triacrylate, diethylpolyoxyethylglycerol triacrylate, dipropylene triethylene glycol ester, etc. In some embodiments, the radical polymerization crosslinking agent can be a compound containing two or more epoxy groups, such as sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, diglycerol polyglycidyl ether, etc. The radical polymerization reaction crosslinking agent can be used individually or in mixture of 2 or more types.

In some embodiments, the amount of the acid-based monomer aqueous solution is 100 wt%, and the radical polymerization reaction 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 polymer aqueous solution after reaction will have a moderate viscosity, which is easier to process mechanically, and the subsequent absorption of the water-absorbent resin is larger, that is, the performance of the water-absorbent resin is better.

In some embodiments, the free radical polymerization described above can be performed in a batch reaction vessel or a conveyor belt reactor.

In some embodiments, the gel can be optionally cut into a particle size of not greater than 20 mm, preferably not greater than 10 mm, by a grinder, and then the screening step is performed. In some embodiments, the screening step is to screen out gels with a particle size of less than 2.0 mm, preferably 0.05 mm to 1.50 mm. Gels with a particle size greater than 2.0 mm must be returned to the reactor for re-shredding. The particle size must be controlled within the above-mentioned range to avoid the high amount of fine powder produced in the back-end process, and it can have better heat conduction properties to avoid excessive residual monomer in the finished product. Generally speaking, the narrower the particle size distribution of the gel, the better the physical properties, and it is beneficial to the subsequent drying process.

In some embodiments, the gel may optionally be dried before subsequent operations. In some embodiments, the drying process is performed at a temperature of 100°C to 180°C. Using the aforementioned temperature range to carry out the drying process can effectively control the drying time and effectively control the degree of crosslinking so as to avoid remaining a large amount of unreacted monomers.

Next, the production method of the water-absorbent resin includes pulverizing and sieving the gel to obtain water-absorbent resin particles. In some embodiments, the particle size of the water-absorbent resin particles is selected to be 0.06 mm to 1.00 mm, preferably 0.10 mm to 0.85 mm. Controlling the particle size of the water-absorbent resin particles to the aforementioned range can reduce the amount of fine powder in the finished product and improve the absorption performance of the water-absorbent resin. Similarly, the narrower the particle size distribution of the water-absorbent resin, the better the physical properties.

Then, the water-absorbent resin particles, the surface crosslinking agent, and the reactive polymer are subjected to a surface crosslinking reaction to obtain a water-absorbent resin. Since the water-absorbing resin is a hydrophilic polymer that will not dissolve, the resin has a uniform bridging structure inside. In order to improve the absorption rate, improve the colloid strength, improve the anti-caking and body permeability and other characteristics, further bridging must be done on the surface of the resin. The surface crosslinking reaction is carried out by utilizing a surface crosslinking agent having a functional group capable of reacting with an acid group. In addition, in the present invention, in order to further improve the liquid flow conductivity of the prepared water-absorbent resin, a reactive polymer such as ionomer is added to jointly carry out surface crosslinking reaction.

In some embodiments, the surface crosslinking agent includes polyols, polyamines, compounds with two or more epoxy groups, and alkylene carbonate, wherein the polyols can be, for example, glycerol, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, and propylene glycol; the polyamines can be, for example, ethylenediamine, diethylenediamine, and triethylenediamine; Ethylene glycol diglycidyl ether and diglycerol polyglycidyl ether; alkylene carbonate can be, for example, ethylene glycol carbonate, 4-methyl-1,3-dioxolane-2-one, 4,5-dimethyl-1,3-dioxolane-2-one, 4,4-dimethyl-1,3-dioxolane-2-one, 4-ethyl-1,3-dioxolane-2-one, 1,3-dioxolane alkan-2-one, 4,6-dimethyl-1,3-dioxan-2-one and 1,3-dioxepan-2-one. The surface crosslinking agent can be reacted individually or in mixture of 2 or more types. In addition, according to the selected surface cross-linking agent, the surface cross-linking agent can be added directly, or the surface cross-linking agent can be prepared into an aqueous solution or a hydrophilic organic solution first, and then added. Hydrophilic organic solvents include but are not limited to methanol, ethanol, propanol, isobutanol, acetone, methyl ether, and diethyl ether.

In some embodiments, the amount of the surface crosslinking agent added is 0.001 wt% to 10 wt%, preferably 0.005 wt% to 5 wt%, based on 100 wt% of the water absorbent resin particles. When the added amount of the surface crosslinking agent is in the aforementioned range, the surface of the water-absorbent resin can have a bridging structure, thereby achieving better absorption performance.

The water-absorbent resin and the reactive polymer must be mixed evenly to effectively achieve the effect of the present invention, so a mixing device with better mixing effect is required. In some embodiments, the mixing device can be a V-shaped mixer, a column mixer, a high-speed agitating mixer, a helical mixer, an airflow mixer, a double-arm kneader, a double-arm conical mixer, a ribbon mixer, a close-wall mixer, a pulverizing kneader, a rotary mixer, or a screw extruder.

The ionic polymers described above are polymers comprising repeating units composed of ionic units within a macromolecule of electrically neutral repeating units, wherein the ionic groups are part of the actual polymer backbone. In some embodiments, the ionic groups can be, for example, carboxylic acid groups. In these embodiments, the ionic polymer can be ethylene-acrylic acid copolymer (EAA), which is a compound comprising a polyethylene segment with the following formula (1) and a polyacrylic acid segment with the following formula (2), (1) (2) wherein M is a hydrogen atom, a group IA element (such as lithium, sodium or potassium) or a group IIA element (such as calcium or magnesium). In this embodiment, based on 100 wt% of the ethylene acrylic acid polymer, the polyethylene segment is 80 wt% to 99 wt%, and the polyacrylic acid segment is 1 wt% to 20 wt%.

其中M為氫原子、IA族元素(例如鋰、鈉或鉀)或IIA族元素(例如鈣或鎂)。在一些實施例中，M較佳為IA族元素。 In other embodiments, the ionic polymer may be an ethylene acrylic acid compound having the following formula (3):

Wherein M is a hydrogen atom, a group IA element (such as lithium, sodium or potassium) or a group IIA element (such as calcium or magnesium). In some embodiments, M is preferably a Group IA element.

In some embodiments, in the ethylene acrylic acid compound, when the weight of the polyethylene segment (ie the formula (1)) is 100 wt%, the weight of the polyacrylic acid segment (ie the formula (2)) is 8 wt% to 20 wt%. In ethylene acrylic acid compounds, the polyethylene segment is a hydrophobic group, while the polyacrylic acid segment is a hydrophilic group, so it is easier to absorb water. Therefore, if there are too many polyethylene segments (for example, the weight of the polyacrylic acid segment is less than 8wt%), the absorption capacity of the water-absorbent resin will decrease; on the contrary, if the polyacrylic acid segment is too much (for example, the weight of the polyacrylic acid segment is greater than 20wt%), then the ionic polymer itself will absorb moisture in the atmosphere to form agglomerates, resulting in poor mixing effect with the water-absorbent resin particles, and the desired effect of the present invention cannot be achieved.

In some embodiments, when the weight of the water-absorbent resin particles is 100 wt%, the amount of the reactive polymer added is 0.01 wt% to 10 wt%. When the amount of the reactive polymer added is in the aforementioned range, the effect of improving the absorption capacity of the water-absorbent resin (eg, water absorption capacity under pressure) can be effectively achieved.

In some embodiments where the ionic polymer is ethylene acrylic acid compound, the surface crosslinking reaction includes heat treatment at a temperature of 150°C to 210°C. Heat treatment at the aforementioned temperature can completely melt the ethylene acrylic acid compound, and can produce a water-absorbent resin with better quality, that is, a water-absorbent resin with better water-absorbing ability.

As mentioned above, the present invention can produce a water-absorbent resin having saline flow conductivity (SFC), which can be used to evaluate liquid permeability. When the water-absorbent resin has better liquid permeability, the problems of rewet, poor dryness and leakage of the absorbent body can be reduced. Liquid flow conductivity means that after the water-absorbent resin absorbs liquid, it has the permeability of liquid under high pressure, so that when the liquid enters the absorber again, it is easy to pass through the water-absorbent resin that has absorbed the liquid and diffuse into other non-absorbed water-absorbent resins. The liquid flow conductivity of the water absorbent resin of the present invention is not less than 30×10 ^-7 cm ³ -s/g, preferably not less than 40×10 ^-7 cm ³ -s/g.

Furthermore, the water-absorbent resin needs to have good retention capacity (Centrifuge Retention Capacity, CRC) and absorption against pressure (AAP), so as to ensure that the water-absorbent resin will not be damaged or affect the ability to absorb liquid due to the external pressure applied to the absorber after absorbing liquid. In some embodiments, the retention force of the water-absorbent resin of the present invention is not less than 20 g/g, preferably not less than 25 g/g. In some embodiments, the water absorption capacity under pressure of the water-absorbent resin of the present invention is greater than 15 g/g, preferably greater than 20 g/g, more preferably greater than 23 g/g.

In addition, the ability of a dry water-absorbent resin to absorb liquid when it first comes into contact with liquid can be expressed by the T20 value. When the water-absorbent resin has a lower T20 value, it means that the dry water-absorbent resin easily absorbs liquid. The T20 value of the water-absorbent resin of the present invention is not greater than 180 seconds, preferably not greater than 160. It is added that the T20 value is defined as the time required for 1 gram of water-absorbent resin to absorb 20 grams of physiological saline and 0.01 wt% aqueous solution of alcohol ethoxylate under a pressure of 0.3 psi, and the alcohol ethoxylate has 12 to 14 carbon atoms. In some embodiments, the T20 value of the water-absorbent resin of the present invention is less than 180 seconds, preferably less than 160 seconds. The water-absorbent resin of the present invention has both a lower T20 value and a higher liquid flow conductivity, which can reduce the rewet amount of the absorbent body and improve the dryness of the diaper.

Absorption System The absorbent resin and hydrophilic fibers of the present invention are used to form a sheet-like absorbent body. In practical application, the above-mentioned absorber can be placed on a liquid-impermeable polyethylene (PE) film, and a liquid-permeable non-woven fabric can be used as the surface layer; or the water-absorbent resin can be fixed on pulp fiber material (airlaid) and/or non-woven fabric. Pulp fibers may be comminuted wood pulp, cross-linked cellulose fibers, cotton, wool, vinyl acetate fibers, and the like. Generally speaking, based on 100 wt% of the absorber, the content of the water-absorbent resin (or core concentration) in the absorber is 20 wt% to less than 100 wt%, preferably 40 wt% to less than 100 wt%, more preferably 50 wt% to less than 100 wt%. The use of such a high content of water-absorbent resin in the core body concentration can significantly exert the effect of the present invention. Generally, the basis weight (weight per unit area) of the above-mentioned absorbent body is 0.01 g/cm ² to 0.30 g/cm ² , and the thickness of the absorbent body is not more than 30 mm.

Several examples are used below to illustrate the application of the present invention, but they are not intended to limit the present invention. Those with ordinary knowledge in the technical field of the present invention can make various changes and modifications without departing from the spirit and scope of the present invention. Preparation of Reactive Polymer Production Example 1

Take 1180 g of ethylene acrylic acid compound (CAS No. 9010-86-0, purchased from Aldrich-Sigma, containing 18 wt% polyacrylic acid segment), 118 g of sodium hydroxide and 5 g of pure water, and mix them with a Banbury mixer at 150° C. for 30 minutes to obtain an ethylene acrylic acid compound (A) that neutralizes sodium ions. Manufacturing example 2-3

Production Example 1 was repeated, and the difference from Production Example 1 was that the ethylene acrylic acid compound in Production Example 2 contained 15 wt% polyacrylic acid segment (CAS No. 9010-77-9, purchased from Aldrich-Sigma, containing 15 wt% polyacrylic acid segment); Production Example 3 used 172 g of magnesium hydroxide instead of sodium hydroxide to obtain ethylene acrylic acid compound (B) with neutralizing sodium ions and ethylene acrylic acid compound (C) with neutralizing magnesium ions, respectively. Manufacturing example 4-5

Manufacturing example 1 was repeated, except that ethylene acrylic acid compounds (available from Exxon) were used, wherein manufacturing example 4 was Escor ^TM 5080 containing 10 wt% polyacrylic acid segment, and manufacturing example 5 was Escor ^TM 5020 containing 7.5 wt% polyacrylic acid segment, so as to prepare ethylene acrylic acid compounds (D) and (E) with neutralizing sodium ions, respectively. Preparation of Water Absorbent Resin Example 1

Take 503.12 g of 48 wt% sodium hydroxide aqueous solution and slowly add it into a 2000 c.c. Erlenmeyer flask containing 621.03 g of acrylic acid and 670.74 g of water. The dropping ratio of sodium hydroxide/acrylic acid is in the range of 0.85 to 0.95, and the dropping time is 2 hours. The mol% of acrylic acid is partially neutralized to sodium acrylate, and the pH value is 5.69.

Next, 1.36 g of N,N'-methylenebisacrylamide (free radical polymerization crosslinking agent) was added to the unsaturated monomer aqueous solution, and the temperature was maintained at about 20°C. 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 perform free radical polymerization.

The gel body obtained by the reaction was chopped by a cutter pulverizer, and the gel body whose particle size was less than 2 mm in diameter was screened out. Next, it dried at the temperature of 130 degreeC for 2 hours. Then sieve with a sieve with a fixed particle size of 0.1 mm to 0.85 mm to obtain water-absorbent resin particles.

Next, weigh 200 g of the water-absorbent resin particles obtained above, add 2.5 g of surface cross-linking agent, which is an aqueous solution mixed with ethylene glycol, aluminum sulfate, and water at a volume ratio of 1:0.5:2, and add 0.1 g of ethylene acrylic acid compound (A) capable of neutralizing sodium ions, heat treatment at 160° C. for 1 hour, and after cooling, the water-absorbent resin can be obtained. Examples 2 to 6

The water-absorbent resins in Examples 2 to 6 were prepared by the same process steps as in Example 1. The difference is that the amount of ethylene acrylic acid compound (A) in Example 2 is 1.0 g; in Example 3, 0.1 g of ethylene acrylic acid compound (B) is used instead; in Example 4, 0.1 g of ethylene acrylic acid compound (C) is used instead; in Example 5, 0.1 g of ethylene acrylic acid compound (D) is used; Bisacrylamide was used as a free radical polymerization crosslinking agent. Comparative Examples 1 to 6

The water-absorbent resins of Comparative Examples 1 to 6 were also prepared using the same process steps as in Example 1. The difference is that in Comparative Example 1, an unneutralized ethylene acrylic acid compound (CAS No. 9010-86-0, purchased from Aldrich-Sigma, containing 18 wt% polyacrylic acid segment) was used instead of the ethylene acrylic acid compound (A) with neutralizing sodium ions; in Comparative Example 2, 0.1 g of ethylene acrylic acid compound (E) was used; in Comparative Example 3, no ethylene acrylic acid compound was added; in Comparative Example 4, 5 g of ethylene acrylic acid compound (E) was used; in Comparative Example 5, heat treatment was performed at a temperature of 140 °C ; Comparative Example 6 was heat-treated at a temperature of 250°C. Evaluation method

In order to evaluate the properties of the water-absorbent resin of the present invention, its physical properties are analyzed by the following test methods. Unless otherwise specified, the following measurement conditions are all carried out at room temperature 23±2°C and relative air humidity 45±10%. The water-absorbent resin should be thoroughly mixed before analysis. Retentivity

Centrifuge Retention Capacity (CRC) is tested according to the test method of ERT 441.3(10) stipulated by the European Disposables and Nonwovens Association (EDANA). Table 1 shows the retention test results of the water-absorbent resins. Water absorption ratio under pressure

Absorption against pressure (AAP) is tested according to the test method of ERT442.3 (10) stipulated by EDANA. Under the pressure of 4.9 kPa, the water absorption under pressure is tested for 60 minutes for 0.9% sodium chloride aqueous solution. Table 1 shows the test results of the water absorption capacity under pressure of the water-absorbent resin. liquid flow conductivity

The liquid flow conductivity (saline flow conductivity, SFC, unit: 10 ^-7 cm ³ -sec/g) is measured and calculated according to the method described in US Patent No. 5,562,646, which is to measure the flow conductivity of a 0.118M sodium chloride aqueous solution under a pressure of 0.3 psi after placing the water-absorbent resin in Jayco synthetic urine for 60 minutes. Table 1 shows the flow conductivity of the water-absorbent resin. T20 value

The T20 value (unit: second) is measured and calculated according to the method described in US Patent No. 9,285,302. It is the time required for 1 gram of water-absorbent resin to absorb 20 grams of physiological saline and 0.01 wt% aqueous solution of alcohol ethoxylates under a pressure of 0.3 psi, and the alcohol ethoxylates have 12 to 14 carbon atoms. The average results of three repeated experiments are shown in Table 1.

Table 1 Preparation of absorber

Using an absorber forming machine, 10.0 grams of water-absorbent resin and 10.0 grams of pulverized wood pulp are mixed and formed. The forming mesh is 400 mesh (38 μm) metal mesh, and the area of the absorber is 160 cm2 (8 cm×20 cm). Place the formed absorbent body on top of the polyethylene film, and then place the non-woven fabric. Next, the absorber was pressed with a pressure of 18.39 kPa (area 160 cm2, weight 30 kg) for 5 minutes, and the surrounding area was stuck with white glue to obtain the absorber for testing. Examples 7 to 12 and Comparative Examples 6 to 10

Examples 7 to 12 are absorbent bodies prepared by the above-mentioned method using the water-absorbent resins of Examples 1-6 respectively; and Comparative Examples 7-12 are respectively used the water-absorbent resins of Comparative Examples 1-6 to prepare absorbent bodies by the above-mentioned method. Table 2 shows the basis weight and thickness of the absorber. Absorbent rewetting performance

The lower the rewet (that is, the dryness) of the absorbent body, the better the urine resistance of the water-absorbent resin. The test method is to place a weight of 4.8 kPa (area 160 cm2, weight 7.8 kg) on the absorber prepared in Examples 7 to 12 and Comparative Examples 7 to 12 above, add 180 ml of synthetic urine (the Jayco synthetic urine described in U.S. Patent Publication No. 20040106745) at the center point dropwise in 3 times (30 minutes each time), and remove the weight on the absorber 30 minutes after the addition. Then, place 30 pieces of filter paper (8 cm x 20 cm) with a pre-measured total weight W1 on the absorber, and immediately place a weight of 4.8 kPa on the absorber for 5 minutes to make the above filter paper absorb the rewetting liquid. Then, the weight W2 of 30 filter papers was measured. The synthetic urine rewet amount of the absorbent body is (W2-W1). The test results are shown in Table 2.

Table 2

According to the above test results, compared with Comparative Examples 1 to 6, Examples 1 to 6 use a specific amount of ethylene acrylic acid compound that neutralizes metal ions to participate in the surface crosslinking reaction, and can obtain water-absorbent resins with both higher liquid flow conductivity and lower T20 value. In other words, the water-absorbent resins of Examples 1 to 6 not only have excellent liquid flow conductivity, but also have better liquid diffusivity and conductivity in a dry state. Furthermore, according to Examples 7 to 12, the absorbent body made with the water-absorbent resin of Examples 1 to 6 can have a liquid rewet amount of less than 3.0 g, which is significantly lower than that of Comparative Examples 7 to 12, indicating that the dryness is also excellent.

Therefore, applying the method for producing a water-absorbent resin of the present invention, utilizing the reactive polymer to participate in the surface crosslinking reaction of the water-absorbent resin particles, can effectively improve the liquid flow conductivity and the liquid diffusivity of the produced water-absorbent resin in a dry state, and at the same time maintain a high retention force of the water-absorbent resin, so it can be practically applicable.

Although the present invention has been disclosed as above with several embodiments, it is not intended to limit the present invention. Anyone with ordinary knowledge in the technical field of the present invention can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be as defined by the scope of the appended patent application.

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Claims (5)

A method for producing a water-absorbing resin, comprising: performing a radical polymerization reaction on a water-absorbing resin composition to obtain a gel, wherein the water-absorbing resin composition includes an aqueous solution of an unsaturated monomer, a polymerization initiator, and a free-radical polymerization crosslinking agent; pulverizing and screening the gel to obtain a plurality of water-absorbing resin particles; Water-based resin, wherein when the weight of the water-absorbing resin particles is 100wt%, the amount of the reaction polymer added is 0.01wt% to 10wt%, and the reaction polymer is an ethylene acrylic acid polymer, and the ethylene acrylic acid polymer comprises a polyethylene segment represented by the following formula (1) and a polyacrylic acid segment represented by the following formula (2)

Wherein M is a group IA element or a group IIA element; and when the weight of the polyethylene segment in the reaction polymer is 100wt%, the weight of the polyacrylic acid segment is 8wt% to 20wt%. The method for producing a water-absorbent resin according to claim 1, Wherein based on 100wt% of the ethylene acrylic acid polymer, the polyethylene segment is 80wt% to 99wt%. A water-absorbent resin produced by the manufacturing method described in claim 1 or 2, wherein the T20 value of the water-absorbent resin is not greater than 180 seconds. The water-absorbent resin according to claim 3, wherein the water-absorbent resin has a liquid flow conductivity of not less than 30×10 ^-7 cm ³ -s/g. The water-absorbent resin according to claim 3, wherein a retention force of the water-absorbent resin is greater than 20 g/g.