Application of halogenated hydantoin in preparation of special disinfectant for infant SPA pool

Abstract

The application discloses application of halogenated hydantoin in a special disinfectant for infant SPA pools and belongs to the technical field of water body disinfection. In view of the technical problems of traditional SPA disinfectants, such as fast drug loss, large concentration fluctuation and high irritation of disinfection by-products, the halogenated hydantoin is prepared into three-layer gradient composite microparticles, the microparticles comprise a halogenated hydantoin inner core, a temperature-sensitive hydrogel intermediate layer and a porous outer layer protective shell, and the three-stage self-adaptive drug release is realized by relying on the temperature reversible phase change characteristics of the hydrogel, and the drug release rate can be automatically regulated according to the water temperature. The application can stably control the effective halogen and chloramine concentrations of the water body without adding auxiliary medicaments, effectively reduces the harm of disinfection by-products and is suitable for the safe disinfection scene of infant SPA pools.

Description

Technical Field

[0001] This invention relates to the field of disinfectant technology, specifically to the application of halogenated hydantoin in the preparation of disinfectants for infant SPA pools, and particularly to a three-layer gradient composite microparticle disinfectant with temperature-adaptive three-stage release function and its application in the disinfection of water in infant SPA pools. Background Technology

[0002] Infant spa pools are specially designed for infants aged 0-6 years, providing opportunities for swimming, fitness, and water play. Compared to adult swimming pools, infant spa pools have several unique operational requirements. For example, the water temperature is typically maintained at 32-34℃ to ensure the comfort of infants, the water volume per pool is generally 0.5-2 tons, and while the usage load is lower, the water age is longer. This places special demands on the use of disinfectants in this setting. Disinfectants need to achieve stable and continuous release of active ingredients in the high-temperature water of 32-34℃, avoiding significant concentration fluctuations. Simultaneously, the types and concentrations of disinfection byproducts must be strictly controlled at extremely low levels to ensure the safety of infants. In recent years, with changing family childcare concepts, the number of infant swimming venues has grown rapidly, becoming an important segment of the maternal and infant service industry. Infants have thinner skin stratum corneum, weaker barrier function, and their immune systems are still developing. Their resistance to pathogenic microorganisms in water is far lower than that of adults, and their sensitivity to chemical disinfectants and their byproducts is also significantly higher. Therefore, the water quality and safety requirements for infant spa pools are far higher than those for ordinary adult swimming pools.

[0003] Currently, infant spa pools mainly employ two disinfection methods. One method involves directly adding chlorine-based disinfectants, including sodium hypochlorite, sodium dichloroisocyanurate (dichloroisocyanurate), and trichloroisocyanuric acid (trichloroisocyanuric acid). While chlorine-based disinfectants have advantages such as a broad bactericidal spectrum and low cost, their use in infant spa pools has significant drawbacks. First, the hypochlorous acid produced by the hydrolysis of these disinfectants in water decomposes more rapidly in high-temperature water (32-34°C), leading to rapid disinfectant consumption and large concentration fluctuations. In practice, it often requires replenishment 2-3 times daily to barely maintain residual chlorine levels. Second, chlorine-based disinfectants react with organic nitrogen compounds such as urea and amino acids present in the water to produce inorganic chloramine products such as monochloramine, dichloramine, and nitrogen trichloride. Dichloramine and nitrogen trichloride can be clearly detected by smell even at concentrations as low as 0.1 mg / L, not only producing an irritating odor that triggers complaints but, more importantly, irritating the delicate respiratory mucosa of infants and young children, and even inducing asthma attacks. Secondly, the addition of sodium dichloroisocyanurate and trichloroisocyanuric acid will produce cyanuric acid, which has a stable molecular structure and accumulates in water without being naturally degraded. When its concentration exceeds a certain threshold, it will have a "lock-in" effect on free chlorine, significantly weakening the disinfection efficiency. More importantly, cyanuric acid has a similar structure to melamine and poses a potential health risk to the kidneys and urinary system of infants and young children. Several states in the United States have set strict limits on the concentration of cyanuric acid in infant swimming pools.

[0004] Another type is on-site disinfection methods, represented by hypochlorous acid water or acidic electrolyzed water. While this method can reduce the risks associated with the storage and transportation of disinfectants, the equipment relies on electricity and salt consumables, resulting in high operating costs. Furthermore, the generated disinfectant solution has extremely poor stability, with active ingredients decaying significantly within hours, making it difficult to maintain long-lasting disinfection capabilities during continuous operation of an infant spa pool.

[0005] In recent years, halogenated hydantoin disinfectants have attracted attention due to their excellent sustained-release properties and low irritation. Halogenated hydantoins (including dichlorohydantoin, bromochlorohydantoin, and dibromohydantoin) slowly hydrolyze in water to release active halogens, exhibiting advantages such as good bactericidal effect and long-lasting action. However, when halogenated hydantoins are directly added to infant spa pools, their release rate is still significantly affected by temperature—high temperatures accelerate hydrolysis, leading to excessively rapid release, while low temperatures result in excessively slow release. Furthermore, the small volume of water is extremely sensitive to concentration changes, making it difficult to achieve precise control of the effective halogen concentration through simple addition. In addition, existing sustained-release formulation technologies mostly use fixed-pore-size frameworks or coating structures to control the release rate. Their release behavior does not adjust with changes in ambient temperature and lacks the ability to adapt to fluctuations in spa pool water temperature, failing to meet the differentiated needs of infant spa pools for "high-temperature sustained release and low-temperature suppressed release." Currently, there are no halogenated hydantoin formulations with temperature-responsive intelligent release functions specifically designed for infant spa pool scenarios.

[0006] In summary, the existing disinfection technology for infant SPA pools has the following shortcomings: (1) Traditional chlorine-based disinfectants hydrolyze quickly and are consumed rapidly in high-temperature water bodies of 32~34℃, requiring frequent addition and making concentration control difficult; (2) Chloramine byproducts are produced in large quantities and have a strong irritating odor, posing a health threat to the respiratory tract of infants; (3) Dichloro or trichloroisocyanuric acid disinfectants pose a risk of cyanuric acid accumulation; (4) Existing halogenated hydantoin preparations lack a temperature response release mechanism that adapts to the temperature fluctuations of SPA pool water, making it impossible to achieve precise disinfection by "releasing on demand".

[0007] Based on this, the present invention provides a solution for making halogenated hydantoin into three-layer gradient composite microparticles. By using the phase change characteristics of the thermosensitive hydrogel intermediate layer to drive the reversible opening and closing of the shell pores, a temperature-adaptive three-stage intelligent release is achieved, aiming to solve the above-mentioned multiple technical problems at the same time. Summary of the Invention

[0008] The purpose of this invention is to provide an application of halogenated hydantoin in the preparation of a special disinfectant for infant SPA pools. It addresses the shortcomings of existing disinfection technologies, such as poor water temperature adaptability, large fluctuations in drug concentration, and low safety of byproducts. Through structural optimization design, it achieves temperature-adaptive intelligent drug release disinfection, which is suitable for the high safety requirements of infant SPA pools.

[0009] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: An application of halogenated hydantoin in the preparation of a disinfectant for infant SPA pools is characterized in that the halogenated hydantoin is made into three-layer gradient composite microparticles for addition and use, wherein the composite microparticles include, from the inside out, a core layer, a middle layer and an outer protective shell.

[0010] The core layer is a halogenated hydantoin powder with a particle size of 200–300 μm, which is the core disinfection active component of the present invention. The halogenated hydantoin is specifically selected from any one of dichlorohydantoin, bromochlorohydantoin, or dibromohydantoin. It has stable bactericidal properties, low irritation, and is suitable for disinfection scenarios in water bodies for infants and young children.

[0011] The intermediate layer is a thermosensitive hydrogel layer, prepared by copolymerization and crosslinking of N-isopropylacrylamide (NIPAM) and butyl acrylate (BA), with the degree of crosslinking controlled at 3–8 mol%, and the minimum critical dissolution temperature (LCST) precisely controlled at 32 ± 0.5 °C. This structure possesses excellent and stable thermosensitive reversible phase transition properties, undergoing regular swelling and contraction deformation with water temperature, providing structural driving force for the controlled release of drugs. When the water temperature is below the LCST, the hydrogel molecular chains extend, fully swell and absorb water, with a volume expansion rate of 120%–150%; when the water temperature is above the LCST, the hydrogel molecular chains contract, rapidly expelling water, and the volume drastically decreases to 40%–60% of the swollen state. This phase transition response window is less than 2 °C, exhibiting abrupt temperature threshold changes. After repeated heating and cooling cycles (e.g., multiple cycles from 25 °C to 40 °C), its LCST and swelling ratio show no significant decay, ensuring long-term reliability.

[0012] The outer protective shell has a porous structure, and its material is selected from polydopamine, chitosan or silica. According to the film-forming characteristics of the selected material, the shell thickness and porosity are controlled by adjusting the amount of pore-forming agent and curing conditions, so that its pore size and porosity parameters are precisely matched with the phase change volume expansion rate of the intermediate layer near LCST. It can follow the temperature-sensitive phase change of the intermediate layer to realize the reversible opening and closing of the microporous structure.

[0013] Based on the aforementioned three-layer composite structure, this invention achieves temperature-adaptive segmented drug release. When the water temperature is ≤32℃, the middle layer hydrogel swells, the outer protective shell channels close, and the halogenated hydantoin is essentially not released, effectively avoiding ineffective drug loss during low-temperature settling. When the water temperature is in the conventional operating range of 33–35℃, the channels are partially open, and the halogenated hydantoin is released stably and uniformly, maintaining the basic disinfection concentration of the water. When the water temperature is ≥35℃, the middle layer fully contracts, the channels are fully open, and the halogenated hydantoin is released rapidly, achieving enhanced disinfection under high-temperature conditions and adaptively matching the disinfection load requirements at different water temperatures.

[0014] Furthermore, by adding the aforementioned three-layer gradient composite microparticles, the effective halogen concentration in the infant SPA pool water can be stably maintained at 0.4–1.0 mg / L, while the chloramine concentration in the water is controlled at 0.08 mg / L or below. This significantly reduces the irritation and safety risks posed by disinfection byproducts, meeting the stringent hygiene and safety standards for infant water. The above concentration range can be achieved by adjusting the dosage and particle size distribution of the microparticles.

[0015] In the overall application process, this invention does not require the addition of various auxiliary agents such as chelating agents, adsorbents, surfactants, pH adjusters, enzyme preparations, and redox agents to the water. It can achieve precise disinfection by relying on the structural characteristics of the microparticles themselves, thus avoiding the problem of secondary pollution of water bodies caused by auxiliary agents from the source. It is safe to use and easy to operate and maintain.

[0016] As an optional supporting structure, this invention can be used in conjunction with a floating perfluorocarbon gel layer. The perfluorocarbon gel layer is a porous foam sheet (2–5 mm thick, 3–8 cm in diameter) with a density less than water, obtained by cross-linking polymerization and foaming of perfluorocarbon monomers (such as perfluorooctylethylene), with a specific surface area of ​​200–500 m² / g. During use, it floats directly on the surface of the SPA pool, and through its hydrophobic and aerophilic properties, it physically adsorbs trace amounts of volatile halogens (such as bromine, chlorine, and halogenated hydrocarbons) escaping from the water, further reducing odor and irritation, and improving the water play experience and safety for infants and young children. This floating perfluorocarbon gel layer is an optional auxiliary structure and is not essential for achieving the basic disinfection function of this invention; its use can be selected based on actual needs.

[0017] The preparation method of the above-mentioned three-layer gradient composite microparticles includes, but is not limited to, the following steps: (1) Core preparation: The halogenated hydantoin raw material was crushed, graded and sieved, and powder with a particle size of 200–300 μm was selected as the core material; (2) Intermediate layer coating: NIPAM monomer, BA monomer, crosslinking agent (such as N,N'-methylenebisacrylamide, BIS) and initiator are dissolved in solvent in proportion, and a temperature-sensitive hydrogel layer is formed on the core surface by spray coating or in-situ polymerization. The degree of crosslinking is controlled to be 3–8 mol%, the polymerization reaction temperature is 60–70℃, and the reaction time is 4–8 hours. (3) Construction of outer protective shell: A pore-forming agent is introduced into the porous shell material by means of interfacial polymerization, layer-by-layer self-assembly or phase separation to form a porous shell with specific pore size and porosity. The shell thickness and porosity are optimized according to the phase change expansion rate of the intermediate layer.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) Through the synergistic effect of the three-layer gradient composite structure, the three-stage precise drug release with temperature self-adaptation is realized, which effectively solves the problems of poor water temperature adaptability and large concentration fluctuation of traditional disinfectants; (2) The LCST is well-suited to the water temperature of the infant SPA pool, and the temperature-sensitive response has threshold mutation characteristics with a response window of less than 2℃, making the switching sensitive and reliable. (3) No additives are required, and the concentration of chloramine byproducts is low, which meets the high safety requirements for infants and young children. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Conventional modifications and substitutions made by those skilled in the art based on the core technical solutions of the present invention are all within the scope of protection of the present invention.

[0020] To ensure the objectivity and comparability of the experimental data, a standardized simulation test system for infant SPA pools was established, closely matching actual application scenarios: each pool had a water volume of 1 ton, an initial pH of 7.2-7.4, and initial organic impurity content (urea, amino acids, etc.) simulating the typical load of infants playing in water (total organic nitrogen 0.15 mg / L). Water temperature could be precisely controlled, and the test period was 7 days. The test indicators included the effective halogen concentration, chloramine concentration, average daily chemical consumption rate, sterilization rate, and the level of irritant odor in the water. The odor level was divided into 0-4 grades, with 0 being odorless, 1 being slightly odorless, 2 being a weak odor, 3 being a noticeable irritating odor, and 4 being a strong, pungent odor.

[0021] The present invention provides a unified standard process for the preparation of three-layer gradient composite microparticles: the core is made of 200~300μm halogenated hydantoin powder; the middle layer is a thermosensitive hydrogel copolymerized with N-isopropylacrylamide and butyl acrylate, with LCST precisely controlled at 32±0.5℃; the outer protective shell is matched with the pore size and porosity according to the phase change expansion rate of the middle layer, and no auxiliary agents are added throughout the process. Example 1

[0022] In this embodiment, the disinfectant is a dichlorohydantoin-based three-layer gradient composite microparticle with specific parameters: the core is 200~300μm dichlorohydantoin powder; the middle layer hydrogel has a crosslinking degree of 5mol%, LCST 32.2℃; and the porosity of the outer polydopamine porous shell is precisely matched with the swelling expansion rate of the middle layer of 120%~150%.

[0023] Dosage: 5g / t of water, with a floating perfluorocarbon gel layer (3mm thick, 350m² / g specific surface area), no additional additives required throughout the process. Three stages of water temperature testing were conducted: ① Low-temperature settling stage (≤32℃, constant temperature 31.5℃); ② Regular use stage (33~35℃, constant temperature 34℃); ③ High-temperature load stage (≥35℃, constant temperature 35.5℃). Each stage was tested continuously for 48 hours, and the cycle was repeated for 7 days.

[0024] Experimental results: During the low-temperature phase, the effective halogen concentration remained stable at 0.38~0.42 mg / L, with virtually no ineffective release of the agent and a daily loss rate of 1.2%; during the routine use phase, the effective halogen concentration remained stable at 0.55~0.75 mg / L, with fluctuations ≤0.05 mg / L, and the chloramine concentration was 0.05~0.06 mg / L; during the high-temperature load phase, the effective halogen concentration rapidly increased to 0.85~0.98 mg / L, meeting the requirements for enhanced disinfection, with a maximum chloramine concentration of 0.07 mg / L; the water body had no irritating odor throughout the process (Grade 0), and the sterilization rate against Escherichia coli and Staphylococcus aureus was ≥99.95%, requiring no additional agent addition within 7 days. Example 2

[0025] In this embodiment, the disinfectant is a bromochlorohydantoin-based three-layer gradient composite microparticle with the following specific parameters: the core is 200~300μm bromochlorohydantoin powder; the middle layer hydrogel has a crosslinking degree of 3mol% (lower limit of the claim) and an LCST of 31.8℃; the outer shell material is chitosan, with porosity matching the phase change parameters.

[0026] Dosage: 5g / t of water, without a perfluorocarbon gel layer, without any auxiliary agents, simulating actual normal use scenarios, with dynamic water temperature fluctuations of 31~36℃ (matching the daily water temperature changes of infant SPA pools), and continuous operation for 7 days.

[0027] Experimental results: When the water temperature is ≤32℃, the drug release rate is extremely low, and the effective halogen concentration fluctuates slightly from 0.39 to 0.43 mg / L; the drug release is stable in the range of 33 to 35℃, with an effective halogen concentration of 0.52 to 0.72 mg / L; when the temperature is ≥35℃, the drug release is rapid, and the concentration can reach 0.82 to 0.95 mg / L; the total chloramine concentration is 0.04 to 0.07 mg / L, the odor level is 0, the sterilization rate is ≥99.92%, the average daily drug loss rate is 1.5%, and the concentration fluctuation range is ≤0.06 mg / L. Example 3

[0028] In this embodiment, the disinfectant is a dibromohydantoin-based three-layer gradient composite microparticle with specific parameters: the core is 200~300μm dibromohydantoin powder; the middle layer hydrogel has a crosslinking degree of 8mol% (upper limit of claims) and an LCST of 32.3℃; the outer shell material is silica, precisely matching the phase change pore parameters.

[0029] Dosage: 6g / t of water, with a matching perfluorocarbon gel layer, dynamic water temperature circulation of 25~40℃, simulating extreme temperature difference conditions, continuous operation for 7 days.

[0030] Experimental results: After multiple rounds of temperature change cycles, the hydrogel phase change performance did not decrease, and the three-stage drug release characteristics remained stable; the effective halogen concentration was precisely maintained at 0.45~0.96 mg / L throughout the process, completely covering the optimal range defined by the patent; the highest chloramine concentration was 0.06 mg / L, far below the limit of 0.08 mg / L; there was no volatile halogen odor, the sterilization rate was ≥99.96%, the average daily loss rate of the agent under extreme temperature differences was only 1.8%, and there was no large fluctuation in concentration. Example 4

[0031] In this embodiment, the disinfectant is a dichlorohydantoin-based three-layer gradient composite microparticle with specific parameters: the core is 200~300μm dichlorohydantoin powder; the middle layer hydrogel has a crosslinking degree of 6mol% and an LCST of 32.0℃; the outer protective shell is made of silica porous structure with pore size and porosity precisely matched to the 120%~150% phase change swelling expansion rate of the middle layer.

[0032] Dosage: 5g / t of water, without a floating perfluorocarbon gel layer, without any auxiliary agents, simulating the normal use conditions of an infant SPA pool, with a constant water temperature of 32~34℃ (industry standard water temperature for playing), and continuous stable operation for 7 days.

[0033] Test results: The three-stage drug release response is sensitive. When the water temperature is ≤32℃, the channel closes, resulting in extremely low ineffective drug loss, with a daily average loss rate of 1.3%. During the normal operating range of 33~34℃, the channel remains partially open, and the effective halogen concentration is maintained at 0.50~0.70mg / L with a concentration fluctuation range of ≤0.04mg / L. The chloramine concentration remains stable at 0.04~0.06mg / L throughout the process, without producing any irritating odor (Grade 0). The sterilization rate against pathogenic bacteria in the water is ≥99.94%, and no additional drug is required for the entire 7-day process, with the water quality consistently meeting the standards. Example 5

[0034] In this embodiment, the disinfectant is a bromochlorohydantoin-based three-layer gradient composite microparticle with specific parameters: the core is 200~300μm bromochlorohydantoin powder; the middle layer hydrogel has a crosslinking degree of 4mol% and an LCST of 32.1℃; the outer shell adopts a chitosan porous structure, which is precisely matched with the phase change parameters of the thermosensitive hydrogel.

[0035] Dosage: 4g / t of water (lower limit of conventional dosage), no perfluorocarbon gel layer or any auxiliary additives throughout the process, simulating low load and low dosage economic use scenarios, with dynamic water temperature fluctuation of 30~37℃, covering all working conditions of low temperature stagnation, normal use and high temperature overload, and continuous operation for 7 days.

[0036] Experimental results: Stable three-stage drug release can still be achieved even with low dosage. The effective halogen concentration is 0.37~0.41 mg / L during the low-temperature settling stage, which meets the basic disinfection threshold. The effective halogen concentration is 0.48~0.68 mg / L during the normal water temperature range. The concentration rises to 0.80~0.92 mg / L during the high-temperature overload stage, with good enhanced disinfection effect. The highest concentration of chloramine throughout the process is 0.07 mg / L, which meets the standard of ≤0.08 mg / L. The water body has no odor, the sterilization rate is ≥99.90%, the average daily loss rate of the agent is 1.6%, and there are no problems such as excessive concentration or disinfection failure. Comparative Example 1

[0037] The infant SPA pool uses commercially available sodium hypochlorite disinfectant, added according to the industry standard dosage, without adding any special slow-release or controlled-release additives. The water temperature fluctuates dynamically between 31 and 36 degrees Celsius, and the pool is operated continuously for 7 days, with routine daily inspections and replenishment.

[0038] Experimental results: Under high-temperature conditions, hypochlorite rapidly hydrolyzes and becomes ineffective, with a daily average loss rate of 12.5%, requiring twice-daily replenishment; the effective residual chlorine concentration in the water fluctuates greatly, ranging from a minimum of 0.12 mg / L to a maximum of 1.35 mg / L, making stable controlled release impossible; the chloramine concentration continuously increases, remaining stable at 0.15~0.22 mg / L for 7 days, far exceeding the limits of this invention; the water has a distinct irritating odor (level 3), which intensifies during high-temperature periods; the average sterilization rate is 95.2%, but the disinfection stability is poor. Comparative Example 2

[0039] Dichlorohydantoin powder of the same specifications as in Example 1 was selected and added directly to water. There was no temperature-sensitive hydrogel intermediate layer or outer porous protective shell. All other test conditions were completely consistent with those in Example 1.

[0040] Test results: The agent lacks temperature-adaptive release characteristics. Release is slow at water temperatures ≤32℃, with the lowest effective halogen concentration at only 0.21 mg / L, failing to meet disinfection standards. At water temperatures ≥35℃, rapid hydrolysis and release of the agent result in a burst release of the agent, with the peak effective halogen concentration reaching 1.42 mg / L, exceeding the safe range. The concentration fluctuated drastically throughout the test, ranging from 0.8 to 1.2 mg / L. The highest chloramine concentration was 0.11 mg / L, exhibiting a slight irritating odor (Level 2). The average daily loss rate of the agent was 8.3%, requiring two replenishments within 7 days. The sterilization rate fluctuated greatly, ranging from 92.5% to 99.8%, indicating extremely poor stability. Comparative Example 3

[0041] The conventional coated slow-release dichlorohydantoin disinfectant was used. The outer shell is a fixed-pore-size polymer coating with no temperature-sensitive phase change structure, so it cannot adjust the release rate in response to changes in water temperature. The content of the effective components is the same as in Example 1, and the test conditions are the same.

[0042] Test results: The formulation has a fixed drug release rate and lacks a three-stage adaptive function; drug release is too rapid during low-temperature static placement, resulting in significant ineffective losses, with a daily average loss rate of 6.8%; the drug release rate cannot be increased during high-temperature use, leading to insufficient disinfection load, with the lowest effective halogen concentration at 0.32 mg / L, which cannot meet the requirements for high-temperature enhanced disinfection; the chloramine concentration is 0.09~0.12 mg / L, exceeding the patent-limited standard; there is a slight odor in the water (Level 1); the sterilization rate is only 96.8% under fluctuating water temperature conditions, indicating poor adaptability. Comparative Example 4

[0043] Based on the formulation of Example 1, the crosslinking degree of the intermediate layer hydrogel was adjusted to 10 mol% (exceeding the range of 3-8 mol% in claim 3), while the remaining structure, parameters, and test conditions remained completely unchanged.

[0044] Test results: The hydrogel's thermosensitive phase change properties failed, the reversibility of swelling and shrinkage was significantly reduced, and the pore opening and closing response was delayed; at low temperatures, the pores could not be completely closed, resulting in ineffective release of the agent and an average daily loss rate of 5.2%; at high temperatures, the pores did not open sufficiently, the release rate was insufficient, the highest effective halogen concentration was only 0.78 mg / L, and the high-temperature disinfection load was insufficient; the chloramine concentration rose to 0.085~0.09 mg / L, exceeding the safety limit, resulting in a slight irritating odor, and the sterilization rate dropped to 98.5%, with overall performance significantly deteriorating. Comparative Example 5

[0045] Through comparisons with multiple embodiments and comparative examples, it is clear that this invention achieves precise, three-stage drug release adapted to water temperature by defining a three-layer gradient composite microparticle structure, temperature-sensitive hydrogel crosslinking degree, LCST threshold, and pore matching parameters. Compared to traditional chlorine-based disinfectants, ordinary halogenated hydantoin powders, and conventional sustained-release formulations, the disinfectant of this invention exhibits significantly reduced drug loss, minimal concentration fluctuations, strictly controlled disinfection byproduct content, and no irritating odor. Furthermore, it is demonstrated that optimal temperature-sensitive phase change controlled-release effects can only be achieved within the parameter range defined by this invention. Exceeding the parameter range or lacking the composite structure leads to a significant decrease in disinfection stability and safety, fully verifying the innovation and practicality of this invention's technical solution, perfectly meeting the high-safety and high-stability disinfection requirements of infant SPA pools.

Claims

1. The application of halogenated hydantoin in the preparation of a special disinfectant for infant SPA pools, characterized in that, The disinfectant is a three-layer gradient composite microparticle, comprising, from the inside out: (1) Core layer, wherein the core layer is halogenated hydantoin powder with a particle size of 200-300 μm; (2) Intermediate layer, wherein the intermediate layer is a thermosensitive hydrogel layer with a crosslinking degree of 3-8 mol%, wherein the thermosensitive hydrogel is formed by crosslinking N-isopropylacrylamide and butyl acrylate, and its minimum critical dissolution temperature is 32±0.5℃; (3) Outer protective shell, wherein the outer protective shell is a porous structure, and its pore size and porosity are matched with the phase change volume expansion rate of the intermediate layer near the minimum critical dissolution temperature.

2. The application according to claim 1, characterized in that, The halogenated hydantoin is selected from any one of dichlorohydantoin, bromochlorohydantoin, or dibromohydantoin.

3. The application according to claim 1, characterized in that, The three-layer gradient composite microparticles drive the reversible opening or closing of the pores in the outer protective shell through the temperature-sensitive phase change of the middle layer, achieving temperature-adaptive segmented release. Specifically, when the water temperature is ≤32℃, the pores in the outer protective shell are closed, and halogenated hydantoin is basically not released; when the water temperature is 33–35℃, the pores are partially open, and halogenated hydantoin is stably released to maintain the basic disinfection concentration. When the water temperature is ≥35℃, the channels are fully open, and halogenated hydantoin is rapidly released to achieve enhanced disinfection.

4. The application according to claim 1, characterized in that, After adding the three-layer gradient composite microparticles, the effective halogen concentration in the infant SPA pool water is maintained at 0.4-1.0 mg / L, and the chloramine concentration does not exceed 0.08 mg / L.

5. The application according to claim 1, characterized in that, No chelating agents, adsorbents, surfactants, pH adjusters, enzymes, or redox agents need to be added to the water during the application process.

6. The application according to claim 1, characterized in that, It also includes a matching floating perfluorocarbon gel layer, which is used to physically adsorb volatile halogens in water.