A surface cross-linking agent for water-absorbing resin and water-absorbing resin modified by the same

Abstract

The present invention relates to the field of C08K5 / 00, and in particular to a special surface crosslinking agent for water-absorbing resin and a modified water-absorbing resin thereof; the surface crosslinking agent comprises: C2-C8 alcohol or C3-C10 epoxy substance, an active agent and water, and the weight ratios are respectively (2-10): (0.1-0.6): (90-97); the surface crosslinking agent can effectively solve the problem of cracking of the crosslinking layer or insufficient restriction of linear polymer migration to the outside caused by the difference in swelling capacity between the surface crosslinking layer and the internal crosslinking layer during the swelling process of the resin, and effectively reduce the soluble matter content of the water-absorbing resin; and by optimizing the preparation method of the water-absorbing resin, the water absorption performance and water retention performance of the water-absorbing resin are further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of resin synthesis, C08K5 / 00, and in particular to a surface crosslinking agent for water-absorbing resin and a water-absorbing resin modified by the surface crosslinking agent. Background Art

[0002] All absorbent resins have a three-dimensional network structure, including substituted and unsubstituted natural and synthetic polymers, such as cross-linked acrylic resins, polyvinyl alcohol, polyacrylonitrile, etc.; super absorbent resins are mainly used in sanitary napkins, diapers, panty liners, breast pads and other sanitary products. In the past, the absorbent materials used in these sanitary products were mainly cotton fibers, paper fibers, wood fibers, etc., which had low water absorption, were not pressure-resistant, and were inconvenient to use; the application of super absorbent resins makes these products lighter and more comfortable, but as sanitary products develop towards thinner shapes, their shortcomings are gradually revealed: after the diapers produced have absorbed liquid for a long time, they will feel greasy and sticky to the touch, causing discomfort or rashes when used, and seriously affecting the use effect of sanitary materials.

[0003] Chinese patent CN103910896B discloses a method for preparing a low re-osmosis polymer water-absorbing resin, which adds polymerization stabilizing agents such as sodium hypophosphite, styrene, xylene, etc. during the polymerization process to improve the polymerization stability; adds sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium carboxymethyl cellulose, sodium tripolyphosphate and other active agents before surface cross-linking, and adds tetrabutylammonium bromide, benzyltriethylammonium chloride and other phase transfer catalysts during surface cross-linking, so that the surface cross-linking solution can be evenly distributed on the particle surface, reducing the agglomeration phenomenon during surface cross-linking, and the liquid absorption capacity and anti-re-osmosis ability of the super absorbent resin are improved, but the above performance still has room for improvement. Chinese patent CN113943433B discloses a high-performance acrylic water-absorbing resin and a preparation method thereof, wherein the resin is polymerized and cross-linked in salt water to form a stable three-dimensional structure, and inorganic substances containing boron and cross-linking agents such as polyethylene glycol diacrylate and ethylene glycol diglycidyl ether are used to promote surface cross-linking of the resin and enhance liquid absorption performance; however, the polyethylene glycol diacrylate and ethylene glycol diglycidyl ether cross-linking agents used therein need to be stored at low temperatures and are easily ineffective in room temperature environments, and must be used as soon as possible after being prepared into a spray and cannot be left for a long time.

[0004] In actual use, if the water-absorbent resin is soluble in water, the gel becomes sticky after the liquid is swollen, and the sticky solubles are attached to the skin after dissolving, which greatly affects the sense of comfort and even causes rashes, and the safety of use decreases. At the same time, in terms of the performance of super absorbent resin, after the gel swells, a high content of solubles is separated out from the hydrogel, which greatly reduces the absorption rate of the water-absorbent resin and the liquid flow performance of the liquid. The overall performance will decrease during long-term use, especially causing the rewetting amount to increase. Therefore, it is inevitable to reduce the solubles in the resin and improve the anti-re-seepage performance. Summary of the invention

[0005] In order to solve the above technical problems, the present invention first provides a surface crosslinking agent for water-absorbing resin, the components of the surface crosslinking agent include: C2-C8 alcohol or C3-C10 epoxy substances, an active agent and water.

[0006] Furthermore, the C2-C8 alcohol includes but is not limited to at least one of C2-C8 monohydric alcohol, C2-C8 dihydric alcohol, and C2-C8 polyhydric alcohol.

[0007] Furthermore, the C2-C8 monohydric alcohol includes but is not limited to at least one of ethanol, propanol, butanol, pentanol, isobutanol, 2,2-dimethylpropanol, hexanol, isopentanol, heptanol and octanol.

[0008] Furthermore, the C2-C8 diol includes but is not limited to at least one of ethylene glycol, propylene glycol, 2-methyl-1,3-propanediol, butanediol, pentanediol, 2-methyl-2,4-pentanediol, neopentyl glycol, hexanediol, cyclohexanediol, dihydroxymethylcyclohexane, 2-ethyl-1,6-hexanediol, heptanediol, and neodiol.

[0009] Furthermore, the C2-C8 polyol includes but is not limited to at least one of propylene glycol, butanetriol, pentaerythritol, trimethylolpropane, pentanetriol, hexanetriol, heptanetriol, octantriol, xylitol, mannitol, sorbitol, and threitol.

[0010] Furthermore, the C3-C10 epoxy substances include but are not limited to at least one of cyclopentane, glycidyl acrylate, diglycidyl ether, allyl glycidyl ether, and vinyl carbonate.

[0011] Preferably, the surface cross-linking agent comprises C2-C8 diols; the C2-C8 diols are preferably hexanediol and butanediol.

[0012] Furthermore, the weight ratio of hexanediol to butanediol is (0.5-4):(0.8-5), preferably (0.74-3.6):(1.25-4); more preferably (2.4-3.6):(1.25-4).

[0013] Furthermore, the active agent includes but is not limited to at least one of anionic active agents, cationic active agents, nonionic active agents, amphoteric active agents, and organic metal active agents.

[0014] Furthermore, the active agent includes but is not limited to at least one of Span, Tween, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium carboxymethyl cellulose, octylphenol polyoxyethylene ether, and polyethylene glycol octylphenyl ether.

[0015] Preferably, the active agent comprises Tween and / or polyethylene glycol octylphenyl ether.

[0016] Further preferably, the active agent comprises Tween.

[0017] Furthermore, the Tween is selected from at least one of Tween 20, Tween 60 and Tween 80.

[0018] Preferably, the Tween is Tween 60.

[0019] Furthermore, the content of the active agent in the surface cross-linking agent is 20-400 ppm, preferably 20-200 ppm.

[0020] The surface crosslinking agent provided in the present application includes C2-C8 alcohol or C3-C10 epoxy substances, surfactants and water, wherein the C2-C8 alcohol or C3-C10 epoxy substances mutually promote their penetration and diffusion into the acrylic resin particles, so that they are evenly distributed in the surface structure of the particles; the hydroxyl groups generated after hydration and the carboxyl groups in the acrylic resin undergo intermolecular crosslinking reactions, strengthen the surface crosslinking of the resin, balance the crosslinking structure inside and outside the resin, and effectively solve the problem of swelling caused by the difference in swelling capacity between the surface crosslinking layer and the internal crosslinking layer during the swelling process of the resin. The invention relates to a method for controlling the cross-linking layer to crack or to solve the problem that the cross-linking layer is not cracked or is not sufficient to limit the migration of linear polymers to the outside; further providing that the weight ratios of C2-C8 alcohol or C3-C10 epoxy substance, surfactant and water are (2-10): (0.1-0.6): (90-97), respectively; the C2-C8 alcohol is 1,4-butanediol and 1,6-hexanediol; the surfactant is Tween 60; the stability and mutual synergy of the system are controlled, so that the surface-modified resin has better water absorption and water retention properties and has a lower soluble matter content.

[0021] Furthermore, in the surface cross-linking agent, the weight ratios of C2-C8 alcohol or C3-C10 epoxy substance, active agent and water are respectively (2-10): (0.1-0.6): (90-97), preferably (4-8): (0.2-0.5): (90-95).

[0022] In a preferred embodiment, in the surface cross-linking agent, the weight ratios of C2-C8 alcohol, the surfactant and water are (4.85-6.8):0.4:(93-95), respectively.

[0023] Secondly, the present application also provides a water-absorbing resin modified by the surface cross-linking agent.

[0024] Furthermore, during the surface cross-linking process of the water-absorbing resin, the spraying amount of the surface cross-linking agent accounts for 2-10% of the weight of the water-absorbing resin, preferably 3-8%; more preferably 4-6%.

[0025] Furthermore, the preparation method of the water-absorbing resin comprises the following steps:

[0026] S1, neutralization: adding acrylic acid, water, alkali solution, crosslinking agent solution and chelating agent solution into a reaction kettle;

[0027] S2, polymerization: after heating the reactor to a certain temperature, adding the initiator solution to generate a water-containing gel;

[0028] S3, granulation, drying and grinding;

[0029] S4. Surface crosslinking: spraying a surface crosslinking agent onto the ground water-absorbing resin, heating the mixture at 170-195° C. to react, and obtaining a surface crosslinked water-absorbing resin.

[0030] Furthermore, in the preparation method of the water-absorbing resin, by weight, 120-260 parts of acrylic acid, 50-200 parts of water, 180-300 parts of alkali solution, 1-10 parts of crosslinking agent solution, 0.5-6 parts of chelating agent solution, and 2-13 parts of initiator solution are included.

[0031] Furthermore, the alkali solution includes but is not limited to at least one of a sodium hydroxide solution, a potassium hydroxide solution, and a sodium carbonate solution; the mass fraction of the alkali solution is 25-40wt%.

[0032] In one embodiment, the alkali solution is a 32 wt % sodium hydroxide solution.

[0033] Furthermore, the crosslinking agent in the crosslinking agent solution is polyethylene glycol diacrylate and / or trimethylolpropane tri(meth)acrylate.

[0034] Preferably, the cross-linking agent is polyethylene glycol diacrylate.

[0035] Furthermore, the average molecular weight of the polyethylene glycol diacrylate is 200-1000, preferably 300-600.

[0036] In a preferred embodiment, the average molecular weight of the polyethylene glycol diacrylate is 400.

[0037] Furthermore, the mass fraction of the cross-linking agent solution is 6-15wt%, preferably 9-13wt%.

[0038] Furthermore, the chelating agent in the chelating agent solution is pentasodium diethylenetriamine pentaacetate.

[0039] Furthermore, the mass fraction of the chelating agent solution is 0.3-2wt%, preferably 0.7-1.5wt%.

[0040] Furthermore, the initiator in the initiator solution is selected from at least one of sodium persulfate, ammonium persulfate and hydrogen peroxide.

[0041] Preferably, the initiator is sodium persulfate.

[0042] Furthermore, the mass fraction of the initiator solution is 1-10wt%, preferably 2-6wt%.

[0043] Furthermore, when adding alkali solution in S1, the adding speed is controlled to ensure that the system temperature is 45-55°C.

[0044] Furthermore, the polymerization reaction in S2 is high temperature polymerization or low temperature polymerization; the reaction temperature of the high temperature polymerization is ≥80°C, and the starting temperature of the low temperature polymerization is 2-10°C.

[0045] Preferably, the polymerization reaction in S2 is high-temperature polymerization, and the high-temperature polymerization reaction temperature is preferably ≥88, more preferably 88-93°C. The higher the polymerization reaction temperature, the greater the internal crosslinking degree of the water-absorbing resin, and the greater the difference in the degree of crosslinking between the inner and outer surfaces; when the surface crosslinking agent of the present application is used in the water-absorbing resin semi-finished product obtained by polymerization at high temperature, the penetration and crosslinking promotion in the inner layer structure of its surface are more excellent, and the static extract content 4 hours after surface crosslinking is lower than the content of the stirred extract of the semi-finished product 16 hours before surface crosslinking.

[0046] Furthermore, in the drying step S3, the drying temperature is not more than 200°C, preferably not more than 190°C, until the water-absorbent resin content is less than 3%. When the drying temperature is too high, the degree of the surface cross-linking reaction of the water-absorbent resin will be affected, which is not conducive to the control effect of the surface cross-linking agent on the water absorption rate and the soluble matter content of the water-absorbent resin under pressure.

[0047] Furthermore, in S4, the spraying amount of the surface cross-linking agent accounts for 2-10% of the weight of the water-absorbing resin, preferably 3-8%; more preferably 4-6%.

[0048] Furthermore, the heating temperature in S4 is 190° C. and the heating time is 1 hour.

[0049] Furthermore, the preparation method further comprises a post-treatment step S5, in which an auxiliary agent is sprayed into the surface cross-linked water-absorbing resin, mixed evenly, and then heated at a certain temperature.

[0050] Furthermore, the auxiliary agent includes but is not limited to at least one of an anti-yellowing agent, a chelating agent, and a surfactant; it can be conventionally adjusted according to needs, and the present invention does not impose strict restrictions on the type and addition amount of the auxiliary agent.

[0051] Furthermore, the auxiliary agent comprises an anti-yellowing agent and a chelating agent, and the added amounts thereof are 0.02-0.2% and 0.01-0.1% of the weight of the water-absorbing resin respectively.

[0052] Preferably, the auxiliary agents are anti-yellowing agent and chelating agent, and the added amounts are 0.0675% and 0.05% of the weight of the water-absorbing resin respectively.

[0053] Furthermore, the present invention does not impose strict regulations on the anti-yellowing agent, and it can be selected according to needs.

[0054] Preferably, the anti-yellowing agent is 2-hydroxy-2-sulfinatoacetic acid and / or sodium 2-hydroxy-2-sulfinatoacetate.

[0055] Furthermore, in S5, the heating temperature is 70-85° C., and the heating time is 0.5-2 h.

[0056] Furthermore, unless otherwise specified in the present application, the solvent in the solution is water.

[0057] Beneficial Effects

[0058] 1. The present application optimizes the composition and content of the surface cross-linking agent, effectively improving the water retention performance of the water-absorbing resin modified by it and reducing the content of the latter's soluble matter;

[0059] 2. This application optimizes the preparation method of the water-absorbent resin, specifically defining it as a high-temperature polymerization reaction, with a polymerization temperature ≥ 80°C, and stipulates that the drying temperature of the hydrogel does not exceed 190°C, which not only enhances the effect of the surface cross-linking agent and reduces the content of the soluble matter of the water-absorbent resin, but also effectively improves the water-retaining pressure resistance and anti-reversion effect of the water-absorbent resin;

[0060] 3. The surface cross-linking agent of the present application does not require a special storage environment, has high stability at room temperature, is not prone to failure, and greatly saves the resin manufacturing cost. DETAILED DESCRIPTION

[0061] Example

[0062] Example 1

[0063] This embodiment first provides a surface cross-linking agent for water-absorbing resin, the components of the surface cross-linking agent are: 1,6-hexanediol, 1,4-butanediol, Tween 60 and water;

[0064] The mass ratio of 1,6-hexanediol, 1,4-butanediol, Tween 60 and water is 2.4:4:0.4:93.2; in the surface cross-linking agent, the concentration of Tween 60 is 100 ppm;

[0065] This embodiment also provides the water-absorbing resin modified by the surface cross-linking agent, and the preparation method comprises the following steps in parts by weight:

[0066] S1, neutralization: add 200 parts of acrylic acid, 92 parts of water, 245 parts of 32wt% sodium hydroxide solution, 4.66 parts of 11.3wt% polyethylene glycol diacrylate solution and 3.24 parts of 1wt% diethylenetriamine pentaacetic acid pentasodium solution into a reaction kettle; during the process, control the addition rate of the sodium hydroxide solution to ensure that the system temperature is 49°C;

[0067] S2, polymerization: after heating the reactor to 90°C, add 7.12 parts of 4 wt% sodium persulfate solution to generate a water-containing gel;

[0068] S3, granulation, drying, grinding: using a granulator to crush the water-containing gel, drying at 190° C. until the water-absorbent resin content is less than 3%, and then grinding until the water-absorbent resin particles have a diameter of 30-50 mesh;

[0069] S4. Surface crosslinking: spraying a surface crosslinking agent onto the ground water-absorbing resin, heating the mixture at 190° C. for 1 hour to obtain a surface crosslinked water-absorbing resin; the amount of the surface crosslinking agent sprayed is 5% of the weight of the water-absorbing resin.

[0070] S5, post-treatment: spray 2-hydroxy-2-sulfinic acid acetic acid and diethylenetriamine pentaacetic acid pentasodium into the surface cross-linked water-absorbing resin, mix well and heat at 80°C for 1h; the addition amounts of the 2-hydroxy-2-sulfinic acid acetic acid and diethylenetriamine pentaacetic acid pentasodium are 0.0675% and 0.05% of the weight of the water-absorbing resin respectively.

[0071] Example 2

[0072] This embodiment is basically the same as Embodiment 1, except that the mass ratio of 1,6-hexanediol, 1,4-butanediol, Tween 60 and water is 3.6:1.25:0.4:94.75.

[0073] Example 3

[0074] This embodiment is basically the same as Embodiment 1, except that: the mass ratio of 1,6-hexanediol, 1,4-butanediol, Tween 60 and water is 2.5:1.5:0.03:95.97; the spraying amount of the surface crosslinking agent accounts for 4.1% of the weight of the water-absorbing resin;.

[0075] Example 4

[0076] This embodiment is basically the same as Embodiment 1, except that: the weight ratio of the 1,6-hexanediol, 1,4-butanediol, Tween 60 and water is 3.6:4:0.4:92; the heating temperature in S4 is 180° C., and the heating time is 1 h.

[0077] Example 5

[0078] This embodiment is basically the same as Embodiment 1, except that: the components of the surface crosslinking agent are: 1,6-hexanediol, 1,4-butanediol and water; the weight ratio of 1,6-hexanediol, 1,4-butanediol and water is 2.5:1.5:96; the spraying amount of the surface crosslinking agent accounts for 4.1% of the weight of the water-absorbing resin.

[0079] Comparative Example 1

[0080] This embodiment is basically the same as Embodiment 1, except that: the components of the surface cross-linking agent are: 1,6-hexanediol, ethylene carbonate, Tween 60 and water; the weight ratio of 1,6-hexanediol, ethylene carbonate, Tween 60 and water is 3.6:1.25:0.4:94.75.

[0081] Comparative Example 2

[0082] This embodiment is basically the same as Comparative Example 1, except that: S2, polymerization: the initial temperature of the reactor is 9° C., 7.12 parts of 4 wt % sodium persulfate solution are added to generate a water-containing gel.

[0083] The average molecular weight of the polyethylene glycol diacrylate in the above examples and comparative examples is 400, purchased from Nantong Meiyuan, PEGDA400.

[0084] Performance Test:

[0085] The water-absorbent resin obtained in the above examples and comparative examples was tested for free swelling ratio (FSC), centrifugal water retention ratio (CRC), static extract content 4 hours after surface crosslinking (Extr 4h), stirred extract of semi-finished product 16 hours before surface crosslinking (Extr 16h), and 0.7psi pressurized water absorption ratio (0.7AUP). The test method refers to the Chinese patent CN115368497B authorized and published on August 8, 2023. The test results are shown in Table 1.

[0086] Table 1

[0087]

[0088] Summary: According to the above results, the water-absorbing resin modified by the surface cross-linking agent of the present application has more excellent water absorption and water retention properties. The ratio of the static extract content 4 hours after surface cross-linking to the stirred extract content of the semi-finished product 16 hours before surface cross-linking is 2 to 9%, indicating that the surface cross-linking agent can effectively solve the dissolution problem of soluble matter.

Claims

1. A water-absorbing resin modified by a surface crosslinking agent, characterized in that: During the surface crosslinking process of the water-absorbing resin, the spraying amount of the surface crosslinking agent accounts for 3-8% of the weight of the water-absorbing resin. The components of the surface crosslinking agent include: C2-C8 alcohol, an active agent and water. The C2-C8 alcohol is hexanediol and butanediol. The weight ratio of hexanediol to butanediol is (0.5-4): (0.8-5). The active agent is Tween 60. In the surface crosslinking agent, the weight ratios of C2-C8 alcohol, active agent and water are (4.85-6.8): 0.4: (93-95) respectively. The preparation method of the water-absorbing resin comprises the following steps: S1, neutralization: adding acrylic acid, water, alkali solution, crosslinking agent solution and chelating agent solution into a reaction kettle; S2, polymerization: after heating the reactor to a certain temperature, adding the initiator solution to generate a water-containing gel; S3, granulation, drying and grinding; S4, surface crosslinking: spraying a surface crosslinking agent onto the ground water-absorbing resin, heating the mixture at 170-195° C. to react, thereby obtaining a surface crosslinked water-absorbing resin; The polymerization reaction in S2 is high-temperature polymerization, and the high-temperature polymerization reaction temperature is 88-93°C; in the preparation method of the water-absorbing resin, by weight, 120-260 parts of acrylic acid, 50-200 parts of water, 180-300 parts of alkali solution, 1-10 parts of cross-linking agent solution, 0.5-6 parts of chelating agent solution, and 2-13 parts of initiator solution; the alkali solution is 32wt% sodium hydroxide solution, and the cross-linking agent is polyethylene glycol diacrylate.

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