Hydrogel nested structure as well as preparation method and application thereof

Abstract

The invention discloses a hydrogel nested structure as well as a preparation method and application thereof. The hydrogel nested structure comprises a hollow hydrogel shell and a built-in substance arranged in the hydrogel shell, the hydrogel shell is polymerized and formed by a reaction aqueous solution consisting of a water-soluble monomer, alkali, a cross-linking agent, an initiator, a reinforcing agent, a humectant, a water-soluble additive and a water-soluble pigment in a reaction forming device; after polymerization molding, the built-in substance is completely wrapped by the hydrogel shell. According to the invention, the hydrogel shell is endowed with excellent mechanical properties through a special material formula and a forming process; the hydrogel nested structure prepared by the preparation method is high in toughness, high in strength and not broken all the time in the whole process of water absorption expansion and transparency transformation, so that the hydrogel nested structure can be applied to the field of blind boxes, the application field of hydrogel materials is greatly widened, and higher commercial value is realized.

Description

Technical Field

[0001] This invention relates to the field of hydrogel technology, and more specifically to a nested hydrogel structure, its preparation method, and its application. Background Technology

[0002] Blind boxes, a popular trendy product, are primarily appealing due to the anticipation of discovering an unknown doll before opening, the surprise after opening, and the resulting collecting and social enjoyment. Currently, blind box products mainly take the form of static plastic dolls or models, with relatively limited interactive options after opening. Meanwhile, toys made from highly absorbent resin (hydrogel) offer unique appeal due to their dynamic properties of swelling and changing shape when wet.

[0003] The core function of currently available superabsorbent resin toys lies in their expansion upon contact with water, creating visual changes. However, after swelling in water, these toys are prone to structural loosening, breakage, and even disintegration due to the sharp decrease in the strength of the resin network, resulting in poor aesthetics and durability. If existing hydrogel toy materials are directly incorporated into the hydrogel nested structure as the hydrogel shell, two problems arise: firstly, under stress, the hydrogel shell, after absorbing water, is highly susceptible to cracking at weak points, which rapidly propagates and leads to shell breakage; secondly, current technologies do not offer guidance on how to seamlessly mold the hydrogel shell within the interior to form a wrapping structure. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a hydrogel nested structure, its preparation method, and its applications. The goal is to endow the hydrogel shell with excellent mechanical properties through a special material formulation and molding process, ensuring that it maintains high toughness, high strength, and does not break throughout the entire process of water absorption, swelling, and transparency transformation.

[0005] The technical solution adopted by this invention to solve the technical problem is: a hydrogel nested structure, comprising a hydrogel shell and an embedded component placed within the hydrogel shell; the hydrogel shell is polymerized in a reaction molding apparatus from a reaction aqueous solution composed of water-soluble monomers, alkali, crosslinking agent, initiator, reinforcing agent, humectant, water-soluble auxiliary agent, and water-soluble pigment; after polymerization, the embedded component is completely enclosed by the hydrogel shell. The hydrogel nested structure includes, but is not limited to, spherical, cylindrical, cubic, cuboid, pyramidal, and other irregular shapes.

[0006] Furthermore, in the aforementioned hydrogel nested structure, the hydrogel shell is a soft, water-containing elastic colloid with a certain strength. Initially opaque, it expands into a transparent or translucent hydrogel after absorbing water. The water absorption ratio of the hydrogel shell is 10-30 times. The hydrogel shell is not a completely sealed shell; its surface has two symmetrical small holes (one formed by the injection molding hole and the other by the positioning point). During water absorption, water enters the gap between the gel layer and the embedded material through these small holes until the internal and external water pressures reach equilibrium. Because the contact area between the outer surface of the gel layer and water is much larger than that between the inner surface and water, the outward expansion force is greater than the inward compression force. As the hydrogel shell expands after absorbing water, the space between the hydrogel shell and the embedded material gradually increases, thus preventing compression of the embedded material during the expansion process.

[0007] Further, by weight percentage, the aqueous reaction solution comprises: 15% to 35% water-soluble monomer, 5% to 20% alkali, 0.01% to 1% crosslinking agent, 0.01% to 1% initiator, 0.1% to 5% reinforcing agent, 0.1% to 25% humectant, 0% to 5% water-soluble additive, 0% to 0.5% water-soluble pigment, with the balance being water, and the total weight percentage of all the above components is 100%.

[0008] Further, the water-soluble monomer is one or more of acrylic acid, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, hydroxyethyl acrylate, and hydroxypropyl acrylate; the base is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate.

[0009] Further, the crosslinking agent is composed of a compound containing multiple double bond groups and a compound containing multiple epoxy groups; the compound containing multiple double bond groups includes any one or more of polyethylene glycol di(meth)acrylate, diethylene glycol dimethacrylate, allyl methacrylate, 1,1,1-trimethylolpropane triacrylate, triallylamine, N'N-methylenebisacrylamide, and tetraallyloxyethane; the compound containing multiple epoxy groups includes one or more of ethylene glycol diglycidyl ether and polyethylene glycol diglycidyl ether.

[0010] Furthermore, the initiator is one or more of the following: an azo water-soluble initiator, persulfate, persulfate-sodium bisulfite system, persulfate-organic amine system, or hydrogen peroxide-ascorbic acid system.

[0011] Further, the reinforcing agent is one or more of polyvinyl alcohol, high molecular weight polyethylene glycol, polyoxyethylene monovinyl ether, and nano-silica. Specifically, it can be one or more of polyethylene glycol 400 diacrylate, polyethylene glycol 600 diacrylate, TPEG2400 (isoprenol polyoxyethylene ether), SPEG2400 (methyl allyl polyoxyethylene ether), and PEG6000.

[0012] Furthermore, the humectant is one or more of diols, polyols, or low molecular weight polyethylene glycol; specifically, it can be one or more of glycerol, propylene glycol, PEG200, PEG300, and PEG400.

[0013] Furthermore, the water-soluble additive is one or more of the following: bittering agent, flavoring agent, antibacterial agent, water-soluble surfactant, and thickener.

[0014] The working principle of reinforcing agents: Polyvinyl alcohol (PVA) is rich in hydroxyl groups, has strong hydrophilicity, and has long molecular chains. It can form physical entanglement and hydrogen bonding with the crosslinking network of hydrogels, share stress, effectively improve the toughness and strength of the gel, and prevent the gel from cracking when it absorbs water and swells or dries. Polyethylene glycol 400 diacrylate and polyethylene glycol 600 diacrylate both contain two double bonds and can be used as crosslinking agents to copolymerize with water-soluble monomers to form interpenetrating / hybrid crosslinking networks. The PEG chains in the structure act as long-chain crosslinking points, giving the network internal mobility and making the polymer have good flexibility, strength and elongation. TPEG2400 and SPEG2400 can copolymerize with water-soluble monomers as terminal hydrophilic groups to improve the hydrophilicity of the polymer and improve the dispersibility of the polymer in water. The polyoxyethylene chains, as hydrophilic long chains, can extend in water to improve the flexibility and strength of the gel.

[0015] PEG6000, as a hydrophilic long chain, can insert into the polymer network segments, increasing the chain mobility, making the gel softer, and improving its flexibility and strength. At the same time, it can improve the fluidity and wettability of the reaction solution, making it easier to mold. Nano-silica, through the large number of silanol groups on the surface of nano-sized SiO2 particles, can form strong hydrogen bonds with polar groups (-COOH, -OH, etc.) in the hydrogel polymer network, thereby forming physical cross-linking points in the gel network and increasing the cross-linking density. At the same time, nano-SiO2 can act as a "nanofiller" and be uniformly dispersed in the gel, effectively absorbing impact energy, hindering crack propagation, and improving gel strength.

[0016] The working principle of humectants: The hydroxyl groups (-OH) in glycerol and propylene glycol molecules can form strong hydrogen bonds with water molecules, significantly reducing the evaporation rate of water and absorbing moisture from the air to a certain extent. In the gel network, they act as "moisture anchoring points," possessing strong water-locking capabilities. Glycerol and propylene glycol also have strong antifreeze properties; at certain concentrations, they can withstand ambient temperatures below -18°C, effectively improving the performance of the nested gel structure. PEG200, PEG300, and PEG400 have similar moisturizing properties to glycerol and propylene glycol, primarily by binding firmly to water molecules through hydrogen bonds, thereby absorbing and fixing moisture.

[0017] Furthermore, this invention also discloses a method for preparing the above-mentioned hydrogel nested structure, the method comprising the following steps: S1, mixing water-soluble monomers, alkali, and water in a certain proportion, and cooling the mixture to below 25°C; S2, mixing the mixture from step S1 with crosslinking agent, reinforcing agent, moisturizing agent, water-soluble auxiliary agent, and water-soluble pigment in a certain proportion to obtain reaction solution A; S3, preparing the required initiator into solutions B and C respectively; S4, preheating the reaction molding machine to the reaction temperature, placing the embedded material at the positioning point in the mold cavity, and closing the mold; S5, mixing the three reaction solutions A, B, and C in a certain proportion in the storage cavity through a metering system; S6, injecting the uniformly mixed reaction solution into the mold cavity through the injection port according to the set feeding amount through the metering system; S7, polymerizing and molding according to the set reaction temperature and reaction time; S8, after the reaction is completed, cooling, opening the mold, and demolding, the formed hydrogel nested structure can be obtained.

[0018] Furthermore, to avoid prepolymerization of the reaction solution and ensure that the polymerization reaction occurs precisely and controllably only within the mold cavity, the reaction molding device employs a multi-channel metering feeding method, using metering pumps to precisely meter and add different reaction solutions proportionally. The mold cavity surface of the reaction molding device is sprayed with a release agent, resulting in a smooth, flawless gel shell surface. The polymerization reaction temperature is 20~50℃, and the reaction time is 5~50 minutes. Considering the exothermic polymerization, a polymerization temperature below 50℃ is preferred to prevent explosive polymerization. Simultaneously, an oxidation-reduction initiation system is used to initiate polymerization at a low temperature, combined with a thermal initiator for maturation.

[0019] Furthermore, the heat distortion temperature (HDT) of the portion of the embedded material in contact with the hydrogel shell is at least 10°C higher than the highest temperature of the hydrogel polymerization reaction or the temperature of the subsequent heat treatment, to prevent thermal deformation of the embedded material during the polymerization and molding process of the hydrogel shell. The material of the embedded material (the external portion in contact with or adjacent to the hydrogel shell) includes, but is not limited to, plastic, glass, and metal. When the external material of the embedded material is plastic, the plastic can be polar or non-polar, wherein the non-polar plastic is a non-polar plastic whose surface has been modified by plasma treatment, corona treatment, flame treatment, or chemical etching treatment.

[0020] In addition, the present invention also limits the application of the aforementioned hydrogel nested structure, which is mainly applied to the blind box field. Blind boxes include, but are not limited to, one or more of the following: figurine blind boxes, toy blind boxes, card blind boxes, stationery blind boxes, and beauty blind boxes.

[0021] The beneficial effects of this invention are as follows: Compared with the prior art, the hydrogel nested structure provided by this invention, through a specific monomer, auxiliary agent system and polymerization process, makes the hydrogel shell opaque in the dry state, effectively hiding the internal blind box; after absorbing water and swelling, it uniformly and stably transforms into a transparent / semi-transparent state, clearly displaying the contents, realizing a visual interactive experience from "hiding" to "revealing"; the hydrogel shell is not only a packaging, but also a component with independent functions (water absorption change, fragrance, color change) and aesthetics, forming a high-value whole together with the internal blind box. By introducing reinforcing components such as PVA, TPEG2400, and nano silica, combined with specific multi-type crosslinking agents, a "rigid and flexible" interpenetrating / hybrid network is constructed, enabling the hydrogel shell to maintain high toughness, tear resistance and structural integrity after absorbing water and swelling, completely solving the core defect of traditional water-absorbing toys that "break upon contact with water". The molding reactor adopts an A / B / C three-channel metering feeding system to separate the active components, avoid pre-polymerization of the reaction liquid, and ensure that the polymerization reaction occurs precisely and controllably only within the mold cavity. Pre-set positioning points within the mold cavity ensure that the built-in blind box always remains in the center of the shell. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the upper and lower mold cavities of the reaction molding machine in Example 1.

[0023] Figure 2 This is a schematic diagram of the structure of the hydrogel nested spheres provided in Example 1.

[0024] Among them, 1-lower mold; 2-upper mold; 3-upper mold cavity; 4-injection port; 5-positioning point; 6-lower mold cavity; 7-hydrogel shell; 8-inner part. Detailed Implementation

[0025] The present invention will be further illustrated below with specific embodiments. However, these examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0026] Example 1 Add 20g sodium hydroxide and 75g water to a mixing vessel, cool to 25℃, add 40g acrylic acid, cool to 25℃, add 5g 2-acrylamido-2-methylpropanesulfonic acid, 0.4g N'N-methylenebisacrylamide, 0.15g polyethylene glycol diglycidyl ether, 1g polyethylene glycol 600 diacrylate, and 0.007g bittern, stir until homogeneous to obtain reaction solution A. Prepare a 1%~10% aqueous solution of potassium persulfate as reaction solution B, and prepare a 1%~10% aqueous solution of tetramethylethylenediamine as reaction solution C. Heat the reaction molding machine to 40~50℃, spray a release agent, place the inserts, and close the mold. Mix reaction solutions A, B, and C in proportion using a metering pump through a three-channel system in the storage chamber. The mixed reaction solution is then precisely injected in proportion using a metering pump. The reaction time is 20~40 minutes. After cooling, demold to obtain a gel nested structure. In this embodiment, the mold cavity is spherical, which can be used to prepare gel-nested spheres.

[0027]

[0028] In the above embodiments: the concentration of PVA aqueous solution is 1%~10%, the concentration of TPEG2400 aqueous solution is 10%~50%, the concentration of potassium persulfate is 1%~10%, and the concentration of tetramethylethylenediamine is 1%~10%.

[0029]

[0030] In the above embodiments: the concentration of PVA aqueous solution is 1%~10%, the concentration of potassium persulfate is 1%~10%, and the concentration of tetramethylethylenediamine is 1%~10%.

[0031] Performance testing methods: 1) Hydrogel shell strength test Soak the nested hydrogel bulbs in 3L of deionized water at 20~30℃ for 24 hours. If the hydrogel shell does not break after absorbing water and expanding, the strength of the hydrogel shell meets the qualified standard.

[0032] 2) Hydrogel shell water absorption ratio test Weigh the embedded material and record the weight as m0; weigh the gel-nested spheres and record the weight as m1; soak the gel-nested spheres in 3L of deionized water at 20~30℃ for 24 hours, drain the water, weigh them, and record the weight as m2. The water absorption ratio formula is as follows: Water absorption ratio = (m2-m1) / (m1-m0) times.

[0033] 3) Gel nested sphere water loss test Weigh the nested gel spheres and record the weight as m0. Pack the nested gel spheres in a sealed bag and place them in a 50℃ constant temperature and humidity chamber for 7 days of aging. After removing and cooling, weigh them and record the weight as m1. The formula for water loss rate is as follows: Water loss rate = (m0-m1) / m0×100%.

[0034] The test results are shown in the table below:

[0035] Based on Examples 2, 3, 4, 11, 12, 13, and 14, it can be concluded that adding a certain proportion of PVA can effectively improve the flexibility and strength of the hydrogel shell. Based on Examples 5, 6, and 7, it can be concluded that adding a certain proportion of TPEG2400 can also improve the strength of the gel. Based on Examples 8, 9, and 10, it can be concluded that adding a certain proportion of nano-silica can also enhance the gel strength. Based on Examples 11, 12, 13, and 14, it can be concluded that adding a certain proportion of glycerol and propylene glycol can effectively reduce the water loss rate of the hydrogel shell and achieve a certain moisturizing effect.

[0036] A simplified schematic diagram of the reactive forming apparatus used in this invention is shown below. Figure 2 As shown, the system mainly includes an upper mold and a lower mold, each containing at least one hemispherical cavity, designated as the upper mold cavity and lower mold cavity, respectively. The upper mold cavity has an injection port connected to an external A / B / C three-channel metering and feeding system. After the upper and lower molds are closed, the polymerization reaction liquid enters each mold cavity through the injection port for polymerization. The lower mold cavity has positioning points, primarily consisting of support pillars connected to the inner wall of the lower mold cavity. The other end of each support pillar is connected to a placement platform for placing the internal contents, ensuring the internal blind box remains centered within the shell. The volume of the support pillar can be minimized to reduce its impact on the molded hydrogel shell; the height of the support pillar can be adjusted according to the required thickness of the hydrogel shell.

[0037] The above embodiments are only used to illustrate the present invention and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions also fall within the scope of the present invention, and the patent protection scope of the present invention should be defined by the claims.

Claims

1. A hydrogel nested structure, characterized in that: It includes a hydrogel shell and an embedded part placed inside the hydrogel shell; the hydrogel shell is polymerized in a reaction molding apparatus by a reaction aqueous solution composed of water-soluble monomers, alkali, crosslinking agent, initiator, reinforcing agent, moisturizer, water-soluble auxiliary agent and water-soluble pigment; after polymerization molding, the embedded part is completely enclosed by the hydrogel shell.

2. The hydrogel nested structure as described in claim 1, characterized in that, In the aforementioned hydrogel nested structure, the hydrogel shell is a soft, water-containing elastic colloid with a certain strength. It is initially opaque and expands into a transparent or translucent hydrogel after absorbing water. The water absorption ratio of the hydrogel shell is 10 to 30 times.

3. The hydrogel nested structure as described in claim 1, characterized in that, The aqueous reaction solution comprises, by weight percentage: 15% to 35% water-soluble monomer, 5% to 20% alkali, 0.01% to 1% crosslinking agent, 0.01% to 1% initiator, 0.1% to 5% reinforcing agent, 0.1% to 25% humectant, 0% to 5% water-soluble additive, 0% to 0.5% water-soluble pigment, with the balance being water, and the total weight percentage of all the above components is 100%.

4. The hydrogel nested structure as described in claim 1, characterized in that: The water-soluble monomer is one or more of acrylic acid, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, hydroxyethyl acrylate, and hydroxypropyl acrylate; the base is one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate.

5. The hydrogel nested structure as described in claim 1, characterized in that: The crosslinking agent is composed of compounds containing multiple double bond groups and polyepoxy groups; the compounds containing multiple double bond groups include any one or more of polyethylene glycol di(meth)acrylate, diethylene glycol dimethacrylate, allyl methacrylate, 1,1,1-trimethylolpropane triacrylate, triallylamine, N'N-methylenebisacrylamide, and tetraallyloxyethane; the compounds containing polyepoxy groups include one or more of ethylene glycol diglycidyl ether and polyethylene glycol diglycidyl ether; the initiator is one or more of azo water-soluble initiators, persulfates, persulfate-sodium bisulfite systems, persulfate-organic amine systems, or hydrogen peroxide-ascorbic acid systems.

6. The hydrogel nested structure as described in claim 1, characterized in that: The reinforcing agent is one or more of polyvinyl alcohol, high molecular weight polyethylene glycol, polyoxyethylene monovinyl ether, and nano silica; the humectant is one or more of diol, polyol, or low molecular weight polyethylene glycol; and the water-soluble additive is one or more of bittering, fragrance, antibacterial agent, water-soluble surfactant, and thickener.

7. A method for preparing a hydrogel nested structure as described in any one of claims 1 to 6, characterized in that, The preparation method includes the following steps: S1, mixing water-soluble monomers, alkali, and water in a certain proportion, and cooling the mixture to below 25°C; S2, mixing the mixture from step S1 with crosslinking agent, reinforcing agent, humectant, water-soluble auxiliary agent, and water-soluble pigment in a certain proportion to obtain reaction solution A; S3, preparing the required initiator into solutions B and C respectively; S4, preheating the reaction molding machine to the reaction temperature, placing the built-in material at the positioning point in the mold cavity, and closing the mold; S5, mixing the three reaction solutions A, B, and C in a certain proportion in the storage cavity through a metering system; S6, injecting the uniformly mixed reaction solution into the mold cavity through the injection port according to the set feeding amount through the metering system; S7, polymerizing and molding according to the set reaction temperature and reaction time; S8, after the reaction is completed, cooling, opening the mold, and demolding, the formed hydrogel nested structure can be obtained.

8. The method for preparing a nested hydrogel structure as described in claim 7, characterized in that: The reaction molding machine adopts a multi-channel metering feeding method, and uses metering pumps to accurately meter and add different reaction liquids according to the proportion; the mold cavity surface of the reaction molding machine is sprayed with a release agent; the reaction temperature of the polymerization molding is 20~50℃, and the reaction time is 5~50 minutes.

9. The method for preparing a nested hydrogel structure as described in claim 7, characterized in that: The heat distortion temperature (HDT) of the portion of the embedded part that contacts the hydrogel shell is more than 10°C higher than the highest temperature of the hydrogel polymerization reaction or the temperature of the subsequent heat treatment.

10. The application of a hydrogel nested structure as described in any one of claims 1 to 6, characterized in that, The aforementioned hydrogel nested structure is applied in the blind box field, including but not limited to one or more of the following: figurine blind boxes, toy blind boxes, card blind boxes, stationery blind boxes, and beauty blind boxes.

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