CN110713566B - Fine powder reconstituted pellet and method for producing super absorbent resin - Google Patents
Fine powder reconstituted pellet and method for producing super absorbent resin Download PDFInfo
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- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
- C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
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- C08F220/06—Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
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Abstract
Disclosed are a method for producing a fine powder reconstituted pellet and a super absorbent resin. The fine powder regranufacturing material is obtained by regranulating acrylic polymer fine powder and at least one hydroxycarboxylic acid additive. The method comprises 1) providing an acrylic polymer hydrogel, drying and pulverizing; 2) classifying the pulverized polymer into a conventional binder having a particle size of 150 to 710 μm and a fine powder of not more than 150 μm; 3) mixing the fine powder with an aqueous solution containing a hydroxycarboxylic acid additive to prepare a reconstituted grain wet material, drying, crushing and grading to obtain reconstituted grains; 4) mixing the conventional base material obtained in the step 2) and the reconstituted grains obtained in the step 3), and carrying out surface crosslinking to obtain a super absorbent resin product, wherein the amount of the polymer derived from the reconstituted grains in the super absorbent resin product is not more than 15 wt%.
Description
Technical Field
The present invention relates to a method for producing a super absorbent resin and a super absorbent resin produced by the method. Specifically, the present invention relates to recycling of fine powder generated in the production step of a super absorbent resin, which has substantially equivalent liquid permeability and water absorbency under high pressure as a super absorbent resin produced without using the fine powder.
Background
Super Absorbent Polymer (SAP) is a water-swellable, water-insoluble Polymer gelling agent that can absorb an aqueous solution several times or more its weight, and is widely used in various applications such as sanitary products such as diapers, sanitary napkins, and incontinence pads, and water retention agents for agriculture and forestry, and industrial water-stopping agents, based on its property.
In most cases, these super absorbent resins have been widely used in the field of sanitary materials such as diapers or sanitary napkins. For these applications, it should exhibit high water absorbability, it should not release absorbed water even under external pressure, and in addition it should well maintain the shape even in a state of volume expansion (swelling) by absorbing water, and thus exhibit excellent liquid permeability.
In the field of water-absorbent resins, particles having a particle diameter of not more than 150 μm are generally referred to as fine powders. One requirement for a super absorbent resin is to have a low fine powder content because fine powder may be a cause of a decrease in liquid permeability of an absorbent article such as a diaper due to clogging, and also may reduce the surface crosslinking effect of the super absorbent resin (even if it is subjected to surface crosslinking, it becomes difficult to improve various physical properties such as load absorption capacity and the like). In addition, since it is easily thrown off when incorporated into an absorbent article such as a diaper, it may cause a problem of loss and deterioration of working environment due to dust.
Therefore, a process of eliminating fine powder is required so that fine powder is not included in the final product, or a re-granulation process of aggregating fine powder into a normal particle size is required. At this point, it is important to have a high pelletizing strength so that the pellets do not re-crush during the re-pelletizing process. Insufficient granulation strength causes deterioration in properties such as liquid permeability of the product.
Chinese patent CN 1847289B discloses a method for recovering fine powder by a step of adding an aqueous liquid containing at least one additive selected from the group consisting of a thermal initiator, an oxidizing agent and a reducing agent to the fine powder to obtain a granulated wet mass, and a step of drying while allowing the granulated wet mass to coexist with a polymer gel. The method can effectively reduce the residual monomer content of the product, but the further addition of the oxidizing agent causes the reduction of the chroma of the product. Furthermore, it does not improve the deterioration of the liquid permeability of the final product due to the recovery of fines.
Chinese patent CN107074996B discloses a method for recovering fine powder. Which incorporates an additive of disodium hydroxysulfoacetate in an aqueous solution for granulation, which results in reconstituted pellets exhibiting reduced residual monomer content, high water retention capacity and low color change.
Accordingly, there remains a need in the art to provide a method for utilizing fine powders that require superabsorbent resins incorporating the fine powders to have properties, particularly liquid permeability, substantially equivalent to conventional superabsorbent resins.
Disclosure of Invention
The object of the present invention is to provide a method for utilizing a fine powder, a high-absorbency resin incorporating the fine powder having properties, particularly liquid permeability, substantially equivalent to those of conventional high-absorbency resins.
Accordingly, in one aspect of the present invention, a fine powder regrind is provided that is obtained from a regrind process of an acrylic polymer fine powder having a particle size of no greater than 150 μm and at least one hydroxycarboxylic acid additive selected from the group consisting of aliphatic hydroxyacids, aromatic hydroxyacids, or mixtures thereof.
Another aspect of the present invention relates to a method for preparing a super absorbent resin, comprising:
(1) providing an acrylic polymer hydrogel, drying and pulverizing it;
(2) classifying the pulverized polymer into a conventional binder having a particle size of 150 to 710 μm and a fine powder having a particle size of not more than 150 μm;
(3) mixing the fine powder with an aqueous solution containing a hydroxycarboxylic acid additive selected from aliphatic hydroxy acids, aromatic hydroxy acids or a mixture thereof, thereby preparing a reconstituted grain wet mass, followed by drying, pulverizing and classifying to obtain a reconstituted grain material;
(4) mixing the conventional base material obtained in the step (2) and the reconstituted grains obtained in the step (3), and carrying out surface crosslinking to obtain a super absorbent resin product, wherein the amount of the polymer derived from the reconstituted grains in the super absorbent resin product is not more than 15 wt%.
Another aspect of the present invention relates to a super absorbent resin obtained by the method for preparing the super absorbent resin.
Still another aspect of the present invention relates to the use of the fine powder reconstituted pellets of the present invention in the preparation of a superabsorbent resin.
Detailed Description
The inventors of the present invention have found that if a hydroxycarboxylic acid additive is added to a fine powder and a fine powder reconstituted pellet is formed, such fine powder re-granulation can be used as a raw material for forming a super absorbent resin, and the properties of the resulting super absorbent resin are substantially equivalent to those of a super absorbent resin obtained without blending the fine powder reconstituted pellet. The present invention has been completed based on this finding.
1. Fine powder reconstituted aggregates
One aspect of the present disclosure relates to a fines reconstituted pellet. The fine powder reconstituted pellet of the present invention contains acrylic polymer fine powder and a hydroxycarboxylic acid additive.
In the present invention, the term "acrylic" compound includes acrylic acid, methacrylic acid, C thereof1-4Alkyl esters, and mixtures of two or more thereof.
The method for forming the acrylic polymer fine powder is not particularly limited and may be a conventional method known in the art, and for example, polymerization, pulverization and formation of the polymer fine powder may be carried out by the method disclosed in chinese patent CN107074996B (which is incorporated herein by reference as part of the present invention).
In one embodiment of the invention, the fine powder is formed as follows: polymerizing an acrylic compound monomer solution to form a polymer hydrogel; the hydrogel is dried, crushed and classified to obtain the fine powder. In one embodiment of the present invention, the fine powder has a particle size of not more than 150 μm.
The fine powder reconstituted pellets of the present invention comprise a hydroxycarboxylic acid additive selected from the group consisting of aliphatic hydroxyacids, aromatic hydroxyacids, or mixtures thereof. In one embodiment of the invention, the aliphatic hydroxy acid is selected from lactic acid, glycolic acid, malic acid, glyceric acid, tartaric acid, citric acid or a mixture of two or more thereof; the aromatic hydroxy acid is selected from salicylic acid, vanillic acid, syringic acid, dihydroxybenzoic acid, gallic acid, or a mixture of two or more thereof.
In one embodiment of the present invention, the molecular weight of the additive is 60 to 1000, preferably 80 to 800, more preferably 90 to 600, and most preferably 100 to 500.
In a preferred embodiment of the present invention, the hydroxycarboxylic acid additive has a solubility in 100g of deionized water of 1g or more, preferably 5g or more, more preferably 10g or more at 23. + -. 2 ℃.
In one embodiment of the present invention, the hydroxycarboxylic acid additive is contained in an amount of 0.3 to 1 part by weight, preferably 0.35 to 0.9 part by weight, more preferably 0.4 to 0.8 part by weight, still more preferably 0.45 to 0.7 part by weight, and most preferably 0.4 to 0.6 part by weight, based on 100 parts by weight of the fine powder. When the content is less than the above range, the re-granulation effect cannot be sufficiently exhibited, and the liquid permeability of the final product is not improved. In contrast, when the content exceeds the above range, the effect of improving physical properties to be obtained is small in consideration of the amount of the compound used. Therefore, it is economically undesirable.
The method for forming the fine powder reconstituted pellets of the present invention is not particularly limited, and may be a conventional method known in the art. In one embodiment of the invention, the hydroxycarboxylic acid additive is dissolved using an aqueous liquid as a solvent, and this solution is then mixed with a fine powder to form a reconstituted pellet.
Suitable solvents are not particularly limited, and non-limiting examples thereof include, for example, water or an aqueous solution of a hydrophilic organic solvent (e.g., a lower alcohol such as methanol, ethanol, etc.)). The water content of the solvent is preferably in the range of 90 to 100 wt%, preferably 99 to 100 wt%, and a pure water solvent is most preferable in terms of physical properties and strength of re-granulation.
When the fine powder is mixed with the aqueous solution containing the hydroxycarboxylic acid additive, the amount of the solution is 20 to 200 parts by weight, preferably 40 to 180 parts by weight, more preferably 60 to 160 parts by weight, and preferably 80 to 120 parts by weight, based on 100 parts by weight of the fine powder. When the amount of the solution exceeds 200 parts by weight, a large amount of large-agglomerated granulated wet material is formed, which may cause difficulties in requiring further granulation at high speed mixing and a large amount of load for drying. In contrast, when the amount of the dispersion is less than 20 parts by weight, the strength of granulation may be insufficient, so that the excellent characteristics of the final product may be lost, and granulation may be incomplete due to non-uniform mixing.
In one embodiment of the invention, the aqueous solution and the fines are mixed at high speed at a speed of 600 rpm. High speed mixing means that the time period required to complete mixing of the aqueous solution and the fines to produce a granulated wet mass is short. The mixing time is preferably not more than 3min, more preferably not more than 1min, most preferably 1 to 60 sec. When the mixing time is long, it may become difficult to uniformly mix the aqueous solution and the fine powder, and a large amount of large-agglomerated wet material is liable to be generated. Further, when mixing is continued for a long time after complete mixing, the resulting water-absorbent resin may be deteriorated in properties, specifically, increased water extractables of the water-absorbent resin, decreased water absorption capacity under load, and the like.
The fine powder granulation wet material of the present invention may be a granule comprising a plurality of fine powders and having a median particle diameter of not more than 15mm, preferably 0.3 to 10mm, more preferably 0.35 to 5 mm.
2. Preparation method of high water absorption resin
(i) The method for producing a super absorbent resin of the present invention comprises the steps of providing an acrylic polymer hydrogel, drying and pulverizing the same.
The step of providing the acrylic polymer hydrogel is not particularly limited and may be a conventional step in the art. The acrylic polymer hydrogel can be obtained commercially or obtained by polymerizing acrylic monomers, for example, by the method for producing the polymer hydrogel disclosed in CN 107074996B.
In one embodiment of the present invention, the steps of providing the acrylic polymer hydrogel and drying and pulverizing comprise:
(a) step of polymerization
In this embodiment, a resin composition containing a super absorbent resin having an internal cross-linked structure obtained by polymerizing a water-soluble unsaturated monomer is used. The water-absorbent resin is preferably a polycarboxylic acid-based water-absorbent resin, for example, a partially neutralized polymer of polyacrylic acid, a hydrolysate of a starch-acrylonitrile graft polymer, or the like.
Preferably, a polyacrylic acid (salt) polymer, which is also referred to as a polyacrylic acid (salt) -based super absorbent resin, is used, which is obtained by polymerizing/crosslinking a monomer containing acrylic acid and/or a salt thereof as a main component.
In one embodiment of the present invention, the polymerization step is carried out under the following conditions: the concentration of the aqueous solution of the monomer is 35 wt% or more, and the amount of the internal crosslinking agent is 0.05 mol% or more based on the monomer(ii) a Introducing N into the aqueous monomer solution2And removing oxygen. The polymerization method is preferably aqueous solution polymerization;
the neutralization rate of acid radicals of the monomers is 40-90 mol%, preferably 50-85 mol%, more preferably 60-80 mol%;
the water-absorbent resin must have a crosslinked structure, and is preferably a water-absorbent resin obtained by copolymerization or reaction with a crosslinking agent (internal crosslinking agent) having 2 (or more) polymerizable unsaturated groups (or reactive groups) in one molecule;
specific examples of these internal crosslinking agents include: n, N' -methylenebis (meth) acrylamide, polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, and the like;
the amount of the internal crosslinking agent is usually 0.04 mol% or more, preferably 0.04 to 0.5 mol%, more preferably 0.05 to 0.15 mol% based on the monomer (excluding the internal crosslinking agent). If the amount of the internal-crosslinking agent is less than 0.04 mol%, the water-absorbing agent as claimed in the present invention may not be obtained.
When the monomer is prepared as an aqueous solution, the concentration of the monomer in the aqueous monomer solution is not particularly limited depending on the temperature of the aqueous solution and the kind of the monomer, but the concentration of the aqueous monomer solution in the polymerization step is preferably 30 wt% or more, more preferably, in the range of 35 to 50 wt%. If it deviates from the above range, for example, if the concentration of the aqueous solution is less than 30% by weight, the water-absorbing agent as claimed in the present invention may not be obtained;
the polymerization initiator used for the polymerization is not particularly limited as long as it is generally used for the preparation of a super absorbent resin. Specifically, a thermal decomposition type polymerization initiator may be used, for example: persulfates such as sodium persulfate and potassium persulfate; peroxides such as hydrogen peroxide and t-butyl peroxide; azonitrile compounds, azoamidine compounds, and photodecomposition type polymerization initiators. In addition, a reducing agent that promotes the decomposition of the polymerization initiator may be used in combination, and the redox-type polymerization initiator may be constituted by a combination of the polymerization initiator and the reducing agent.
In the present invention, the aqueous solution polymerization method is preferably employed, and for example, when the heat-dissipating polymerization is carried out by a double arm kneader or the like, it is preferable to use a redox polymerization initiator in combination with a reducing agent. In addition, when the aqueous solution of the monomer is supplied to a predetermined vessel or a driven conveyor to carry out the boiling polymerization, it is preferable to use a thermal decomposition type polymerization initiator.
N2The addition of (A) is not particularly limited, but N is preferably added in the pipe2After the reaction mixture is merged with the reaction mixture, additional stirring, particularly forced stirring, is performed. In this case, the time from the point of confluence to the additional stirring is preferably 10 seconds or less, more preferably 5 seconds or less.
(b) Drying and pulverizing step
The polymer gel obtained in the polymerization step is usually dried in the form of particles of about 0.1 to 5 mm. The specific drying method is not particularly limited, and may be any drying method known in the art, for example, drying using a general dryer or heating furnace.
The drying temperature is generally 100-250 ℃, preferably 120-220 ℃, and more preferably 150-200 ℃.
The drying time is not particularly limited, and may be a time period for obtaining a dried product having a desired moisture content. In view of easy pulverization, it is preferable that the water content (loss on drying after heating at 180 ℃ for 3 hours) of the dried matter obtained in the drying step is not more than 5% by weight. Generally, it is preferable that the drying time is within 2 hours in terms of production efficiency, although it may vary depending on the particle size of the polymer gel and the granulated wet mass, drying temperature, air flow rate, and the like.
The above drying step is also used for drying the re-granulated wet material.
The pulverization step is a step of pulverizing the polymer gel. Although the pulverization can be usually carried out on the dried product of the polymer gel obtained in the drying step, it can also be carried out on the wet polymer gel obtained in the polymerization step before drying. The pulverization is preferably carried out so as to obtain more particles having a desired particle diameter (preferably a weight average particle diameter of 150 to 710 μm). The method of pulverization is not particularly limited, and any known method can be employed.
(ii) The pulverized polymer is classified into a conventional binder having a particle size of 150 to 710 μm and a fine powder having a particle size of not more than 150 μm.
The classification step is a step of classifying the pulverized material obtained in the pulverization step. In the classification step, the target water absorbent resin is prepared by screening particles having a desired particle diameter (preferably a weight average particle diameter of 150 to 710 μm), and obtaining a polymer fine powder obtained as a remaining substance. The classification method is not particularly limited, and any known method can be used, for example, screening.
(iii) Mixing the fine powder with an aqueous solution containing a hydroxycarboxylic acid additive to thereby prepare a reconstituted grain wet material, followed by drying, pulverizing and classifying to obtain a reconstituted grain material.
Hydroxycarboxylic acid additives suitable for use in the process of the present invention are selected from aliphatic hydroxy acids, aromatic hydroxy acids or mixtures thereof. In one embodiment of the invention, the aliphatic hydroxy acid is selected from lactic acid, glycolic acid, malic acid, glyceric acid, tartaric acid, citric acid or a mixture of two or more thereof; the aromatic hydroxy acid is selected from salicylic acid, vanillic acid, syringic acid, dihydroxybenzoic acid, gallic acid, or a mixture of two or more thereof.
In one embodiment of the present invention, the molecular weight of the additive is 60 to 1000, preferably 80 to 800, more preferably 90 to 600, and most preferably 100 to 500.
In a preferred embodiment of the present invention, the hydroxycarboxylic acid additive has a solubility in 100g of deionized water of 1g or more, preferably 5g or more, more preferably 10g or more at 23. + -. 2 ℃.
In one embodiment of the present invention, the hydroxycarboxylic acid additive is used in an amount of 0.3 to 1 part by weight, preferably 0.35 to 0.9 part by weight, more preferably 0.4 to 0.8 part by weight, preferably 0.45 to 0.7 part by weight, and preferably 0.4 to 0.6 part by weight, based on 100 parts by weight of the fine powder. When the amount is less than the above range, the re-granulation effect cannot be sufficiently exhibited, and the liquid permeability of the final product is not improved. In contrast, when the amount exceeds the above range, the effect of improving physical properties to be obtained is small in consideration of the amount of the compound used. Therefore, it is economically undesirable.
The method for mixing the two is not particularly limited and may be a conventional method known in the art. In one embodiment of the invention, the hydroxycarboxylic acid additive is used dissolved in water to form a solution, which is then mixed with fine powder to form a re-granulated wet mass.
Suitable solvents are not particularly limited, and non-limiting examples thereof include, for example, water or an aqueous solution of a hydrophilic organic solvent (e.g., a lower alcohol such as methanol, ethanol, etc.)). The water content of the solvent is preferably in the range of 90 to 100 wt%, preferably 99 to 100 wt%, and a pure water solvent is most preferable in terms of physical properties and strength of re-granulation.
When the fine powder is mixed with an aqueous solution containing a hydroxycarboxylic acid additive, the amount of the dispersion is 20 to 200 parts by weight, preferably 40 to 180 parts by weight, more preferably 60 to 160 parts by weight, and preferably 80 to 120 parts by weight, based on 100 parts by weight of the fine powder. When the amount of the aqueous solution exceeds 200 parts by weight, a large amount of large-agglomerated granulated wet material is formed, which may cause difficulties in requiring further high-speed mixing granulation, and a large amount of load is required for drying. In contrast, when the amount of the aqueous solution is less than 20 parts by weight, the strength of granulation may be insufficient, so that the excellent characteristics of the final product may be lost, and granulation may be incomplete due to non-uniform mixing.
In one embodiment of the invention, the aqueous solution and the fines are mixed at high speed at a speed of 600 rpm. High speed mixing means that the time period required to complete mixing of the aqueous liquid and the fines to produce a granulated wet mass is short. The mixing time is preferably not more than 3min, more preferably not more than 1min, most preferably 1 to 60 sec. When the mixing time is long, uniform mixing of the aqueous liquid and the fine powder may become difficult, and a large amount of large-lump wet material is liable to be generated. Further, when mixing is continued for a long time after complete mixing, the resulting water-absorbent resin may be deteriorated in properties, specifically, increased water extractables of the water-absorbent resin, decreased water absorption capacity under load, and the like.
The method of the present invention includes the steps of drying, pulverizing and classifying a regranulated wet mass formed by mixing an aqueous solution and fine powder. The method of drying, pulverizing and reclassifying is not particularly limited and may be a conventional method in the art. In one embodiment of the present invention, the drying, pulverization and reclassification are carried out by drying, pulverizing and classifying the foregoing polymer hydrogel.
In one embodiment of the invention, the reclassified particles having a particle size of 150-710 μm are used as a conventional binder for the manufacture of the final product, while particles having a particle size of less than 150 μm are re-granulated as a fine powder.
(iv) Mixing the conventional base material obtained in the step (ii) and the reconstituted pellets obtained in the step (iii), and carrying out surface crosslinking to obtain a super absorbent resin product, wherein the amount of the polymer derived from the reconstituted pellets is not more than 15 wt%.
The method of mixing the conventional binder with the reconstituted pellets is not particularly limited and may be a conventional method known in the art as long as the amount of the reconstituted pellets is not more than 20 wt%, more preferably not more than 18 wt%, and preferably not more than 15 wt%, based on the total weight of the super absorbent resin product.
The crosslinking agent used in the surface crosslinking step of the present invention may be any of various crosslinking agents, and from the viewpoint of physical properties, organic surface crosslinking agents such as polyol compounds, epoxy compounds, polyamine compounds, or polycondensates of polyamine compounds and halogenated epoxy compounds, inorganic surface crosslinking agents such as polyvalent metal salts, and the like are generally used.
To obtain the particulate water-absorbent resin of the present invention, it is preferable to carry out surface crosslinking with a plurality of organic surface-crosslinking agents, and at least 1 of the surface-crosslinking agents used contains a polyvalent hydroxyl group. It is also possible to use a plurality of organic surface-crosslinking agents to form an optimum crosslinked layer depending on the permeability and reactivity of different surface-crosslinking agents with respect to the water-absorbent resin, thereby providing the particulate water-absorbing agent of the present invention.
The amount of the surface cross-linking agent to be used depends on the compound used and the combination thereof, but is preferably 0.1 to 10 wt%, more preferably 0.5 to 5 wt%, based on the mass of the pellets before surface cross-linking.
The water-absorbent resin mixed with the surface-crosslinking agent is preferably subjected to a heat treatment. In the heat treatment, the temperature of the water-absorbent resin mixed with the surface cross-linking agent, that is, the temperature of the mixture of the water-absorbent resin and the surface cross-linking agent is preferably 100 to 250 ℃, more preferably 150 to 210 ℃. The heating time is preferably 20-70 min.
In a preferred embodiment of the present invention, the method for producing the super absorbent resin of the present invention comprises:
-charging acrylic acid, deionized water and aqueous NaOH solution into a reaction vessel. During the addition of the NaOH solution, precipitates were observed, but gradually dissolved to form a transparent homogeneous solution. When the addition is completed, the temperature of the neutralized solution rises due to the heat of neutralization. Subsequently, an internal crosslinking agent and an aqueous solution of diethyltriaminepentaacetic acid pentasodium salt were added. Pumping the obtained reaction solution out through a stainless steel pipeline under the action of a quantitative pump, and continuously mixing Na on line at a position which is about 50mm away from the outlet of the pipeline2S2O8Aqueous solution, and N is introduced at the junction2；
-feeding said aqueous monomer solution to a continuous polymerization machine, and starting the polymerization reaction over a period of time. During the polymerization reaction, the polymer tape expands and foams in all directions while generating water vapor, and then shrinks and collapses to a size slightly larger than the width of the polymer tape. After 3min from the start of the polymerization reaction, the crosslinked polymer containing the ribbon-like hydrogel was taken out from the tail end of the polymerization belt;
-disintegrating the aqueous gel obtained by the above-mentioned polymerization reaction using a gel disintegrator to obtain a particulate aqueous gel, drying, crushing, and classifying using a standard sieve to obtain a conventional base material and a fine powder;
putting the obtained fine powder into a mechanical stirring type mixer for fast rotation, spraying an aqueous solution containing a hydroxycarboxylic acid additive into the fine powder to form a reconstituted grain wet material, and drying and grading the reconstituted grain wet material to obtain a reconstituted grain material with the grain size of 150-710 microns; and
-mixing the re-granulated pellets with a conventional base material, feeding the pre-surface cross-linked particles obtained into a stirred tank, spraying a surface cross-linking agent solution into the stirrer, and obtaining the surface cross-linked superabsorbent resin.
The super absorbent resin as claimed in claim 8, which is prepared by the method of the present invention, wherein the conductivity SFC of physiological saline is 50X 10-7cm3S/g or more; the free swelling rate is more than 0.3 g/g.s; the water absorption capacity under high pressure of 4.8kPa is 24g/g or more.
The invention uses at least one hydroxycarboxylic acid additive in the fine powder re-granulation process, and the obtained super absorbent resin has improved high liquid permeability compared with the super absorbent resin without the additive. Since the fine powder is recycled, the process cost can be reduced, resulting in economic benefits.
The present invention is further illustrated by the following examples.
Examples
Measurement of physical Properties of super absorbent resin
(i) Centrifuge Capacity for Water retention (CRC)
The centrifugal water retention capacity (CRC) of the super absorbent resin was measured according to EDANA method (ERT 441.2-02). "ENANA" is an abbreviation of European non-woven fabrics industry Association. "ERT" is an abbreviation for the European standard superabsorbent polymer determination method. In the present invention, the physical properties of the super absorbent resin were measured in accordance with ERT standards (2002 revised edition/publicly known literature) unless otherwise specified.
Specifically, 0.2g of a super absorbent resin was uniformly put into a tea bag (60 mm. times.85 mm) and heat-sealed, and then immersed in a far excess (usually about 500 ml) of 0.90 wt% NaCl aqueous solution at 23 (. + -. 2). degree.C.. After 30 minutes, the bag was lifted, and water was removed by a centrifugal force of 250G for 3 minutes using a centrifugal separator (model H-122, manufactured by Kokusan Co., Ltd., Japan), and the weight W of the bag was measured1g. The same operation was carried out without using the super absorbent resin, and the weight W at that time was measured2g, CRCg/g is calculated from the following formula.
(ii) Water absorption Rate under high pressure (AAP0.7)
The water absorption capacity (AAP) of the super absorbent resin under a pressure of 4.8kPa was measured by EDANA method (ERT 442.2-02).
(iii) Weight average particle diameter D50
The weight-average particle diameter D50 of the super absorbent resin was measured by the measurement method disclosed in U.S. Pat. No. 7638570.
Specifically, 100g of a super absorbent resin was sieved through an ASTM standard sieve having a mesh opening of 710. mu.m, 600. mu.m, 500. mu.m, 425. mu.m, 300. mu.m, 212. mu.m, or 150. mu.m at room temperature (23. + -. 2 ℃ C.) and a humidity of 50 RH%, and the residual weight percentage R was plotted on a logarithmic probability paper. The classifier used was a Retsch vibratory classifier AS200 in germany.
In this way, the particle diameter corresponding to R ═ 50% was read as a weight average particle diameter (D50).
(iv) Saline Flow Conductivity (SFC)
The SFC of the super absorbent resin of the present invention is measured based on the measurement method disclosed in U.S. Pat. No. 5669894.
(v) Free Swell Rate (FSR)
The FSR of the super absorbent resin of the present invention is measured based on the measurement method disclosed in International publication No. 2009/016055. Specifically, 0.02 part by weight of indigo as a food additive was added to 1000 parts by weight of a 0.90 wt% NaCl aqueous solution prepared in advance, and the liquid temperature was adjusted to 23 ℃. The sample was weighed as 1.000. + -. 0.01g in a 25ml beaker, and 20g of a 0.90 wt% aqueous NaCl solution colored blue was weighed and poured into the sample beaker. The time was started after the solution was completely added, and the stopwatch was stopped when the liquid surface was completely covered with the resin, and the time was recorded.
Where FSR is the sample expansion rate, WFIs the weight of 0.9% NaCl solution, tsFor the swelling time, WDIs the net weight of the sample.
Production example 1：
5kg of acrylic acid, 4345g of deionized water and 4159g of a 50 wt% aqueous NaOH solution were placed in a stainless steel container having a capacity of 20L at a rate of 832 g/min. During the addition of the NaOH solution, precipitates were observed, but gradually dissolved to form a transparent homogeneous solution. When the addition was completed, the temperature of the neutralized solution was raised to 91 ℃ by the heat of neutralization. Subsequently, 686g of polyethylene glycol 400 diacrylate (manufactured by taiwan chang materials industries ltd.) having a concentration of 4% and 14g of an aqueous solution of diethyltriaminepentaacetic acid pentasodium (basf) having a concentration of 5 wt% were added as an internal crosslinking agent, and the temperature of the reaction solution was lowered to 88 ℃ under the action of a circulating water bath in a jacket of a vessel.
The reaction solution is pumped out through a stainless steel pipeline at a speed of 4735g/min under the action of a quantitative pump, and Na with the continuous online mixing flow rate of 110g/min and the concentration of 3 percent is continuously mixed at a position which is 50mm away from the outlet of the pipeline2S2O8Aqueous solution, and N with the flow rate of 0.75L/min is introduced into the junction2。
A continuous polymerization machine having a polymerization belt in which the above-mentioned aqueous monomer solution was continuously fed at 4845 g/min. The temperature of the reaction solution at the inlet of the polymerizer was 82 ℃. The polymerization was started over a period of time. During the polymerization reaction, the polymer tape expands and foams in all directions while generating water vapor, and then shrinks and collapses to a size slightly larger than the width of the polymer tape. After 3 minutes had elapsed from the start of the polymerization reaction, the crosslinked hydrogel polymer in a tape form was taken out from the tail end of the polymerization belt.
The aqueous gel obtained by the above polymerization reaction was disintegrated using a meat chopper (JY-22M, model No. 8mm, manufactured by Jienging mechanical Equipment Co., Ltd., south Jiangsu, Jiangsu) to obtain a particulate aqueous gel (1). In the gel disintegration process, the input amount of the gel is 1453g/min, and deionized water heated to 75 ℃ at 161.5g/min is sprayed in parallel.
The granular hydrogel obtained in the above manner was spread on a stainless steel wire mesh having a mesh opening of 850 μm, and dried by blowing hot air at 180 ℃ for 30min at an average speed of 1m/s, with a thickness of 45 mm. Subsequently, the dried polymer obtained by the drying operation was pulverized by a roll mill and classified by a standard sieve having a mesh size of 710 μm and 150 μm. Obtaining a conventional base material A with the particle size of 150-710 mu m and a fine powder B with the particle size of less than 150 mu m. At this time, the amount of the obtained fine powder was 15 wt% of the dry polymer.
Reference example 1：
500g of the conventional base A obtained above was charged into a 10L vertical V-type stirring tank, and subsequently, 20g of the surface cross-linking agent solution prepared in advance was spray-added to the mixer and mixed, thereby obtaining a coated wet material. Here, the surface cross-linking solution used was a solution obtained by mixing 0.6 parts by weight of 1, 2-propanediol, 0.4 parts by weight of ethylene carbonate, and 3 parts by weight of deionized water with respect to 100 parts by weight of the intermediate base powder. The stirring speed of the mixer was 500rpm, and the spraying acceleration of the surface-crosslinking solution was 20 g/min. The coated wet mass was then charged into an 8L vertical V-blender kettle, which was stirred in a ribbon blender at 250 rpm. Here, the jacket oil temperature of the heating kettle was 200 ℃ and the heating treatment time was 50min, whereby surface crosslinking was carried out to obtain a super absorbent resin.
Example 1：
The fine powder B100g obtained in production example 1 was put in a mechanical stirring mixer and rapidly rotated at 600rpm, and a mixed solution containing 0.5g of malic acid and 100g of water was sprayed thereto for 30 seconds to form a wet reconstituted grain of about 0.3 to 5 mm.
Then, the above regranulated wet mass was spread on a metal screen and dried with hot air at 180 ℃ for 30 minutes. The resulting mixture was crushed by a roll crusher and then classified by using a standard sieve having a mesh size of 710 μm and 150. mu.m. The re-granulated particles B1 having a particle size of 150 to 710 μm are obtained.
The re-granulated granules B1 thus obtained were mixed with a classified conventional base material a (B1 content: 15 wt% of the total amount) to obtain pre-surface cross-linked granules.
500g of the pre-surface cross-linked particles obtained by the above-mentioned method was put into a 10L vertical V-type stirring tank, and then 20g of the pre-prepared surface cross-linking agent solution was sprayed and added to the mixer to mix, thereby obtaining a coated wet material. Here, the surface cross-linking solution used was a solution obtained by mixing 0.6 parts by weight of 1, 2-propanediol, 0.4 parts by weight of ethylene carbonate, and 3 parts by weight of deionized water with respect to 100 parts by weight of the intermediate base powder. The stirring speed of the mixer was 500rpm, and the spraying acceleration of the surface-crosslinking solution was 20 g/min. The coated wet mass was then charged into an 8L vertical V-blender kettle, which was stirred in a ribbon blender at 250 rpm. Here, the jacket oil temperature of the heating kettle was 200 ℃ and the heating treatment time was 50min, whereby surface crosslinking was carried out to obtain a super absorbent resin.
Comparative example 1：
The procedure of example 1 was repeated to convert the malic acid-containing aqueous liquid to pure water and obtain reconstituted pellets B2. The same operation as in example 1 was carried out except that the obtained regranulated pellets B2 were mixed with the base pellets a obtained in production example 1 (the content of B2 was 15 wt% of the total amount) to obtain pre-surface-crosslinked particles, and surface-crosslinking was carried out to obtain a finished super absorbent resin.
Comparative example 2：
The procedure was the same as in example 1 except that the malic acid content was changed to 0.25 g. Otherwise, the same operation as in example 1 was carried out, and surface crosslinking was carried out to obtain a finished super absorbent resin.
Comparative example 3：
The same procedure as in example 1 was repeated except that the re-granulated pellet B2 obtained was mixed with the base pellet A obtained in production example 1 (the content of B2 was changed to 20% by weight of the total amount) to obtain pre-surface-crosslinked particles, and surface-crosslinking was carried out to obtain a finished product of a super absorbent resin in the same manner as in example 1.
TABLE 1 CRC before and after Table Cross product Properties of reference example 1, example 1 and comparative examples 1 to 3
As can be seen from Table 1, in comparative reference example 1 and comparative example 1, when no additive was used, the properties were deteriorated with re-granulation of fine powder, except that the liquid-suction rate was increased.
In example 1, however, when the malic acid-containing additive was used in an amount of 0.5% by weight and the fine powder was contained in an amount of up to 15% by weight, the other properties, particularly the saline flow conductivity, were comparable to those of the product of reference example 1 in which no fine powder was used, except that the liquid absorption rate was increased. And in comparative examples 2 and 3, when the content of malic acid was reduced to 0.25 wt% or the content of fine powder was increased to 20 wt%, the properties except the rate were deteriorated.
The polyacrylic acid (salt) super absorbent resin has excellent performances such as high liquid permeability and rapid water absorption, and can be applied to sanitary absorbent articles such as paper diapers.
Claims (8)
1. A fines regranufacture comprising acrylic polymer fines having a particle size of no greater than 150 μm and a hydroxycarboxylic acid additive selected from aliphatic hydroxyacids, aromatic hydroxyacids, or mixtures thereof;
the hydroxycarboxylic acid additive accounts for 0.3-1 part by weight based on 100 parts by weight of the fine powder.
2. The fines regranufacture pellet of claim 1, wherein the hydroxycarboxylic acid additive is selected from the group consisting of lactic acid, glycolic acid, malic acid, glyceric acid, tartaric acid, citric acid, or salicylic acid, vanillic acid, syringic acid, dihydroxybenzoic acid, gallic acid, and mixtures of two or more thereof.
3. A preparation method of a high water absorption resin comprises the following steps:
(1) providing an acrylic polymer hydrogel, drying and pulverizing it;
(2) classifying the pulverized polymer into a conventional binder having a particle size of 150 to 710 μm and a fine powder having a particle size of not more than 150 μm;
(3) mixing the fine powder with an aqueous solution containing a hydroxycarboxylic acid additive selected from aliphatic hydroxy acids, aromatic hydroxy acids or a mixture thereof, thereby preparing a reconstituted grain wet mass, followed by drying, pulverizing and classifying to obtain a reconstituted grain material; the hydroxycarboxylic acid additive accounts for 0.3-1 part by weight based on 100 parts by weight of the fine powder;
(4) mixing the conventional base material obtained in the step (2) and the reconstituted grains obtained in the step (3), and carrying out surface crosslinking to obtain a super absorbent resin product, wherein the amount of the polymer derived from the reconstituted grains in the super absorbent resin product is not more than 15 wt%.
4. The method according to claim 3, characterized in that the hydroxycarboxylic acid additive is selected from lactic acid, glycolic acid, malic acid, glyceric acid, tartaric acid, citric acid, or salicylic acid, vanillic acid, syringic acid, dihydroxybenzoic acid, gallic acid, or a mixture of two or more thereof.
5. The method according to claim 3 or 4, wherein the step (3) is carried out to obtain the reconstituted pellets with the particle size of 150-710 μm and the fine powder with the particle size of less than 150 μm, and the fine powder obtained in the step (2) are subjected to granulation treatment.
6. A super absorbent resin obtained by the method according to any one of claims 3 to 5.
7. The super absorbent resin according to claim 6, wherein the flow conductivity SFC of physiological saline is 50X 10-7cm3S/g or more; the free swelling rate is more than 0.3 g/g.s; the water absorption capacity under high pressure of 4.8kPa is 24g/g or more.
8. Use of the fine powder reconstituted pellets according to any one of claims 1 to 2 for producing a super absorbent resin.
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| EP2057228A1 (en) * | 2006-08-31 | 2009-05-13 | Nippon Shokubai Co., Ltd. | Particulate water absorbing agent and production method thereof |
| CN106795253A (en) * | 2015-06-09 | 2017-05-31 | 株式会社Lg化学 | Prepare the fine powder comprising super-absorbert the resin method of the super-absorbert resin of assembly and the super-absorbert resin for thus preparing again |
| CN107074996A (en) * | 2014-12-10 | 2017-08-18 | 株式会社Lg化学 | The method for preparing super absorbent polymer |
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| EP2057228A1 (en) * | 2006-08-31 | 2009-05-13 | Nippon Shokubai Co., Ltd. | Particulate water absorbing agent and production method thereof |
| CN107074996A (en) * | 2014-12-10 | 2017-08-18 | 株式会社Lg化学 | The method for preparing super absorbent polymer |
| CN106795253A (en) * | 2015-06-09 | 2017-05-31 | 株式会社Lg化学 | Prepare the fine powder comprising super-absorbert the resin method of the super-absorbert resin of assembly and the super-absorbert resin for thus preparing again |
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