JPH063346A - Hydrogel formed body for detecting free chlorine - Google Patents

Abstract

PURPOSE:To continuously detect free chlorine in swimming pool water or con tact lens cleaning and disinfecting solution by using a chlorine detecting reagent which reacts to free chlorine and changes in color and a hydrogel matrix. CONSTITUTION:The title formed body is obtained by using a chlorine detecting reagent which reacts to free chlorine and changes in color and a hydrogel matrix. A chlorine detecting reagent containing N,N'-diphenyl benzene by 0.001-0.2wt.%, reactive blue 163 by 0.001-0.5wt.%, etc., is preferably used. For the hydrogel matrix, a matrix composed mainly of a hydrophilic monomer, such as 2-hydroxyl ethyl methacrylate, etc., added with a hydrophobic monomer, such as methyl(meth) acrylate, etc., for adjusting the strength of the matrix when the matrix contains water is used. It is preferable to lightly crosslink the hydrogel matrix by using a crosslinking agent in order to prevent the eluation of an unreacted monomer or low-molecular weight polymer.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a hydrogel molded article for detecting free chlorine. More specifically, it relates to a hydrogel molded article that can be suitably used for detecting free chlorine in pool water, drinking water, treatment liquid for soft contact lenses, and the like.

[0002]

2. Description of the Related Art In recent years, attention has been paid to the occurrence of eye disorders such as tearing, conjunctival hyperemia, and corneal epithelial erosion after swimming in a pool infused with chlorine-disinfected water. These obstacles are caused by too high chlorine concentration in the water in the pool, and in order to prevent these obstacles, it is usually necessary to adjust the chlorine concentration to a predetermined concentration before swimming.
The exact concentration of chlorine cannot be known if it is measured immediately after it is put into the pool, so the concentration of free chlorine is continuously measured.

Conventionally, as a method for measuring the concentration of free chlorine, for example, a solution containing o-tolidine as an indicator for chlorine detection is used as it is, or a test paper is obtained by drying a filter paper impregnated with the solution. Used as
Although a method such as a method utilizing a color reaction of o-tolidine has been adopted, it is difficult to continuously measure the free chlorine concentration by such a method, and the free chlorine concentration is measured each time. In that case, it takes time and effort, so it can be fixed in the pool and permanently installed, and there is a long-awaited development of a reagent for detecting free chlorine that does not develop color when the concentration of free chlorine is low and that develops color only when it is high. There is.

As a preservative solution for soft contact lenses, conventionally, physiological saline and physiological saline are used as preservatives such as thimerosal, chlorohexidine, methylparaben, propylparaben and sorbic acid, and ethylenediaminetetraacetic acid, gluconic acid and citric acid. It is known that a liquid agent containing a sequestering agent such as an acid, a solvent in which a tablet of the compound is dissolved in purified water or distilled water at the time of use, and the like are known.

However, when soft contact lenses are immersed in these preservative solutions for soft contact lenses and a direct current is applied to wash and disinfect the soft contact lenses, chlorine ions present in the preservative solution are removed. It becomes free chlorine, and this free chlorine causes deterioration of the material of the soft contact lens, and there is a problem that the color soft contact lens and the soft contact lens marked by dyeing are discolored and bleached. When worn, free chlorine can cause serious injury.

Therefore, when such an electric treatment method is used for a contact lens, it is necessary to prevent free chlorine from being generated or to confirm to the user that the treatment liquid contains free chlorine. It is hoped that this will be possible.

As a method for analyzing free chlorine such as hypochlorous acid, conventionally, quantitative determination by a colorimetric method using N, N'-diethyl-p-phenylenediamine (DPD) and yellow coloring of o-tolidine are performed. There is a quantification method using a reaction, and it is possible to detect free chlorine in the treatment liquid of the soft contact lens, for example, by applying a method using a chlorine detection reagent such as DPD or o-tolidine. However, these chlorine detection reagents cannot be contained in the treatment liquid in advance, and it is determined whether or not free chlorine is contained in the treatment liquid when a direct current is applied to the treatment liquid. There is a problem that it is extremely complicated to check each time with a chlorine detection reagent.

Further, as a method of detecting free chlorine, a method of utilizing a sensor such as an electrode, an electrochemical detector or a semiconductor gas sensor (Japanese Patent Laid-Open No. 63-27745 and Japanese Patent Laid-Open No. 60-263).
Japanese Patent Laid-Open No. 852, Japanese Patent Laid-Open No. 2-52249, and Japanese Patent Laid-Open No. 2-28525.
No. 9) or a method of using a test piece in which a filter paper is impregnated with an indicator for chlorine detection (Japanese Patent Publication No. 54-3394 and Japanese Patent Publication No. 3394).
54-12360 publication) is known.

However, the method using the above-mentioned sensor has a problem that the cost is too high because such a sensor is expensive, and the method using the test piece elutes the chlorine detection indicator from the filter paper. Therefore, there is a problem that it is difficult to continuously use it while being immersed in the solution, and it cannot be said that any method is an appropriate method.

[0010]

The object of the present invention is that it can be permanently installed in, for example, a pool, and it develops color only for high-concentration free chlorine and is fixed in the processing container for soft contact lenses. It is an object of the present invention to provide a material that allows a user to recognize that free chlorine is contained in a treatment solution in which a lens is immersed when an electric current is applied to the treatment solution for cleaning and disinfecting the lens.

[0011]

That is, the present invention relates to a free chlorine detecting hydrogel molded product comprising a chlorine detecting reagent which changes color by reacting with free chlorine and a hydrogel base material.

[0012]

The hydrogel molded product for detecting free chlorine of the present invention is a reagent for detecting chlorine and a hydrogel group which changes color by reacting with free chlorine in pool water, drinking water, solutions for soft contact lenses, etc. It is made of wood.

Examples of general-purpose indicators for detecting chlorine which change color by reacting with free chlorine include, for example, o-tolidine, N, N'-diethyl-p-phenylenediamine (hereinafter referred to as DPD) which reacts with low concentration of free chlorine. , N,
Redox indicators such as N'-diphenylbenzidine, phenosafranine, and brilliant blue FCF, oil-soluble dyes that can detect free chlorine by gradually discoloring or fading, and reactive dyes such as Reactive Blue 163. Although various dyes can be used, in the present invention, among these, N, N'-diphenylbenzidine and Reactive Blue 163 are preferably used as chlorine detection reagents.

As described above, the hydrogel molded product of the present invention is used for detecting free chlorine in a specimen such as pool water, drinking water, and a treatment liquid for soft contact lenses. The free chlorine concentration required in such a sample varies depending on the type of the sample, but is, for example, about 0.4 to 1 ppm in the case of pool water, and about 0.1 to 1.5 ppm in the case of drinking water. Is. Therefore, it is preferable to select and use a chlorine detection test that can react at each free chlorine concentration depending on the type of these samples.

By the way, particularly when electrically cleaning and sterilizing a soft contact lens, since the soft contact lens is boiled while being in contact with the treatment solution, water is one of the general-purpose indicators for chlorine detection. A chlorine detection reagent that is insoluble and has excellent heat resistance must be used.

Further, these chlorine detecting reagents as powders are held in an electric treatment container for soft contact lenses, or they are present in a conventionally used treatment solution for soft contact lenses to continuously release free chlorine. Since it is extremely difficult to detect, such a reagent for detecting chlorine is contained in the hydrogel molded body, and in contact with the processing solution used for electroprocessing, and in a state where it can react when free chlorine is present, The hydrogel molded product is preferably held in the processing container by, for example, placing it on the bottom of the processing container, adhering it to the inner wall of the processing container, or embedding it in a contact lens holder.

The method for incorporating the chlorine detection reagent into the hydrogel molded body includes, for example, (a) immersing the hydrogel base material in a solution of the chlorine detection reagent and immersing the solution of the chlorine detection reagent inside the hydrogel base material. Water-insolubilization treatment after infiltration with (2) by adding a chlorine detection reagent in advance when polymerizing the hydrogel substrate and polymerizing, and by radical chain transfer to the chlorine detection reagent during polymerization. There is a method of covalently bonding to a hydrogel substrate.

Among the above-mentioned general-purpose indicators for detecting chlorine, there are those which develop color in the course of polymerization reaction and those which, when contained in the hydrogel molded body, lower the detection sensitivity. Further, in the present invention, water insolubility, heat resistance, durability, etc. may be required, and therefore, as satisfying these properties, among the general-purpose indicators for chlorine detection, as described above, N , N'-diphenylbenzidine and Reactive Blue 163 are preferably used as reagents for detecting chlorine.

The N, N'-diphenylbenzidine is
It is insoluble in water and can be contained in the hydrogel base material by adding it during the polymerization in the method (b). It does not dissolve or diffuse in water when the obtained hydrogel molded article is made to contain water. , It does not elute from the hydrogel molded body. In this case, if the free chlorine is not present, the hydrogel molded article is white, but if free chlorine is present, it is brown.

The reactive blue 163 is
Since it is a water-soluble reactive dye, the method of (a) above is used to impregnate the inside of the hydrogel base material in the form of an aqueous solution, and then add it to an alkaline solution such as an aqueous solution of sodium carbonate to insolubilize the water. Is preferably applied.
In this case, if the free chlorine is not present, the hydrogel molded product exhibits a blue color, but if free chlorine is present, even if this color fades, the original transparent hydrogel molded product is obtained.

The content of the chlorine detecting reagent in the molded hydrogel cannot be unconditionally determined because it depends on the type of the chlorine detecting reagent used, and it usually changes the color by reacting with free chlorine. A sufficient amount will do. As an example, when N, N'-diphenylbenzidine is used, its content is preferably 0.001 to 0.2% (% by weight, the same applies hereinafter), especially 0.02 to 0.06%. When the content is less than 0.001%, the color tends to be difficult to distinguish even when it reacts with free chlorine to change the color, and when it exceeds 0.2%, the content of free chlorine tends to increase. When the copolymer is polymerized, it tends to act as a polymerization inhibitor rather than the amount required for the reaction to discolor.

When Reactive Blue 163 is used as the chlorine detection reagent, its content is preferably 0.001 to 0.5%, more preferably 0.05 to 0.3%. When the content is less than 0.001%, the original blue color of the hydrogel molded product becomes lighter, and there is a tendency that there is no difference from when it is discolored by reacting with free chlorine, and when it exceeds 0.5%. In the meantime, it tends to take a long time to dye the hydrogel substrate.

Examples of the hydrogel base material used in the present invention include 2-hydroxyethyl methacrylate and 2
-Hydroxyalkyl methacrylates such as hydroxybutyl methacrylate and 2-hydroxypropyl methacrylate; N-vinyl lactams such as N-vinylpyrrolidone and N-vinylpiperidone; acrylic acid, methacrylic acid; Examples include polymers. The hydrophilic monomers may be used alone or in combination of two or more kinds. Among them, a material that does not give a very high water content is preferable because the reagent for detecting chlorine is contained in the hydrogel molded body. 2-hydroxyethyl methacrylate is preferably used in this respect.

Further, in the present invention, a hydrophobic monomer may be blended in order to adjust the strength of the hydrogel substrate when it contains water.

Specific examples of the hydrophobic monomer include (meth) acrylic acid alkyl esters such as methyl (meth) acrylate, ethyl (meth) acrylate and propyl (meth) acrylate; styrene; α-methylstyrene and the like. Alkyl styrene; vinyl esters of aliphatic carboxylic acids such as vinyl acetate and vinyl propionate. The above hydrophobic monomers may be used alone or in combination of two or more, and among these, alkyl esters of (meth) acrylic acid such as methyl (meth) acrylate and ethyl (meth) acrylate are It is preferably used because it has good copolymerizability with hydroxyethyl methacrylate.

When the hydrophilic monomer and the hydrophobic monomer are copolymerized, the ratio of the amount of each monomer used is
Hydrophilic monomer / hydrophobic monomer (weight ratio) is 100/0
It is preferable to adjust to -60/40, especially 90 / 10-70 / 30. When the proportion of the hydrophobic monomer is higher than the above range, the reaction between the chlorine detection reagent in the hydrogel molded body and the free chlorine present in the sample tends to be delayed.

In the present invention, in order to prevent the unreacted monomer and the low molecular weight polymer from eluting from the hydrogel base material, it is preferable that the hydrogel base material is lightly crosslinked with a crosslinking agent.

Examples of the cross-linking agent include ethylene glycol dimethacrylate, divinylbenzene, allyl methacrylate, trimethylolpropane trimethacrylate, etc. These may be used alone or in combination of two or more.

Thus, in order to lightly crosslink the hydrogel substrate, the amount of the crosslinking agent used is 0.001 to 0.5 with respect to 100 parts (parts by weight, the same applies hereinafter) of all monomer components to be subjected to polymerization. And preferably 0.01 to 0.2 part. When the amount used is less than 0.001 part, it tends to be impossible to prevent the unreacted monomer or low molecular weight polymer from eluting from the hydrogel base material, and when it exceeds 0.5 part, the hydrogel is not able to be prevented. Since the base material is excessively crosslinked, it tends to be rather brittle.

As a method for obtaining the hydrogel substrate,
For example, there may be mentioned a method in which the respective components such as the hydrophilic monomer, the hydrophobic monomer and the cross-linking agent are uniformly blended, a polymerization initiator is added thereto, and polymerization is carried out by a commonly used method to obtain a polymer.

The method for producing the above-mentioned polymer is not particularly limited, but, for example, after a polymerization initiator is added to the above-mentioned components, the temperature is from room temperature to 120 ° C., preferably 25 to 80 ° C. for several hours to several tens hours. Examples include a heat polymerization method in which the temperature is gradually raised to perform polymerization.

Examples of the polymerization initiator include 2,
2'-azobis (2,4-dimethylvaleronitrile),
2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile), azobisisobutyronitrile, benzoyl peroxide, t-butyl hydroperoxide, and other peroxides and redox initiators may be mentioned. These can be used alone or in admixture of two or more. Among these polymerization initiators, 2,2'-in order to allow polymerization at a relatively low temperature.
Azobis (2,4-dimethylvaleronitrile) and 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile) are preferred.

The amount of the above-mentioned polymerization initiator to be used may be an amount sufficient to initiate the polymerization, but it is usually about 0.001 to 0.3 part, especially about 0.01 part with respect to 100 parts of all the monomer components used for the polymerization. It is preferably about 0.1 part.

To obtain the molded product of hydrogel for detecting free chlorine of the present invention, for example, a method of incorporating the reagent for detecting chlorine of (a) or (b) in the molded product can be used. Which method should be adopted may be determined according to the characteristics of the above.

As an example, when N, N'-diphenylbenzidine is used, it is added with the respective components such as the hydrophilic monomer, the hydrophobic monomer and the crosslinking agent in the range of the compounding amount and polymerized. Thus, a hydrogel molded body can be obtained. When using Reactive Blue 163, for example, this aqueous solution is prepared in advance, and the polymer hydrogel base material obtained as described above is immersed in the aqueous solution and then taken out. Alternatively, it can be put into an alkaline solution such as an aqueous solution of sodium carbonate and subjected to water insolubilization treatment to obtain a hydrogel molded body.

In the present invention, the unreacted monomer may be eluted from the hydrogel molded product, if necessary, by boiling the hydrogel molded product, for example, in distilled water for 1 to 10 hours.

The thus obtained hydrogel molded product for detecting free chlorine of the present invention contains, for example, N, N'-diphenylbenzidine, Reactive Blue 163, etc. as a reagent for detecting free chlorine from hypohalous acid or the like. In particular, it can be suitably used for an electric cleaning and sterilizing apparatus for soft contact lenses. Also, in order to withstand high temperatures such as boiling and not to develop color if free chlorine does not exist even if it is used for a long period of time or to prevent the sensitivity from decreasing, the chlorine detection reagent is a hydrogel molding agent. It is contained in the body in a stable state.

Next, the hydrochlorinated molded article for detecting free chlorine of the present invention will be described in more detail with reference to Examples.
The invention is not limited to only such embodiments.

Production Examples 1 to 10 In a polypropylene test tube, each monomer was mixed with the composition shown in Table 1, and the crosslinking agent, the polymerization initiator and the chlorine detection reagent shown in Table 1 were mixed, and the mixture was placed in a nitrogen atmosphere. Polymerization was carried out by heating at 40 ° C for 12 hours, 60 ° C for 8 hours, and 100 ° C for 2 hours to obtain a colorless and transparent hydrogel molded product.

This hydrogel molded body has a diameter of 1 cm and a thickness of 1
After processing into a disc of mm size and boiling in distilled water for 8 hours to elute unreacted monomer, it is completely immersed in the treatment solution in the treatment container of the electric contact sterilization treatment device for soft contact lenses. Installed in.

[0041]

[Table 1]

The abbreviations used in this specification represent the following compounds, respectively.

2-HEMA: 2-hydroxyethyl methacrylate 2-HBMA: 2-hydroxybutyl methacrylate NVP: N-vinylpyrrolidone MMA: methyl methacrylate VAc: vinyl acetate EDMA: ethylene glycol dimethacrylate V-65: 2,2'- Azobis (2,4-dimethylvaleronitrile) NDB: N, N'-diphenylbenzidine Example 1 Using the above treatment container in which each hydrogel molded body obtained in Production Example 1 to 10 was installed, a normal sodium chloride concentration was obtained. Sodium chloride 0.45% (electrical conductivity: 8.2 mS / cm), 0.38% (electrical conductivity: 7.0 mS / cm), 0.225% (electrical conductivity: 4.2 mS / cm)
cm), 0.18% (electrical conductivity: 3.6 mS / cm) or 0.15%
The discoloration of the hydrogel molded article when the electric treatment was performed for 20 minutes in an aqueous solution containing (electrical conductivity: 2.9 mS / cm) was examined.

As a result, all of the hydrogel molded products of Production Examples 1 to 10 turned reddish brown when any of the sodium chloride aqueous solutions having the above respective concentrations were used, and free chlorine could be detected.

Example 2 Using the above-mentioned processing container in which each of the hydrogel moldings obtained in Production Examples 1 to 10 was installed, boric acid 1.3 W / V%, borax 0.1.
Electrical treatment is performed in a treatment solution (electric conductivity: 4.0 mS / cm) consisting of 06 W / V% and trisodium citrate 0.44 W / V%, and after boiling for 10 minutes, stop energizing and allow to cool. Then, the treatment solution was replaced with a new treatment solution, and the cycle of electrical treatment (boiling) was repeated again. After 100 cycles, the color of the hydrogel molding was the same as the beginning, and it did not discolor even after long-term use in a boiling state in which free chlorine was not present.

Also, using a hydrogel molded body after 100 cycles, sodium chloride 0.225% (electric conductivity: 4.2
The discoloration of the hydrogel molded article when the electric treatment was performed for 20 minutes in an aqueous solution containing mS / cm) was examined. As a result, it was confirmed that the hydrogel molded product turned reddish brown and reacted with free chlorine.

Comparative Examples 1 and 2 To the mixed solution of the monomers used in Production Example 1, o-tolidine 0.04% (Comparative Example 1) or DPD 0.04% (Comparative Example 2) was used as a chlorine detection reagent instead of NDB. Mixed and V-6
5 0.1% was added and polymerization was carried out in the same manner as in Production Example 1 to obtain a hydrogel molded body. The hydrogel molded body already obtained at this time turned yellow (Comparative Example 1) or red (Comparative Example 2). It was colored. Production Example 1 of this hydrogel molded article
In the same manner as above, the soft contact lens was installed in the processing container of the electric cleaning and sterilization processing device.

Using this processing container, sodium chloride 0.22
In an aqueous solution containing 5% (electrical conductivity: 4.2 mS / cm)
The discoloration of the hydrogel molded article after 20 minutes of electrical treatment was examined. As a result, it was found that the molded articles using either o-tolidine or DPD showed no discoloration and could not be used for detection of free chlorine.

Comparative Examples 3 and 4 Phenosafranine (manufactured by Wako Pure Chemical Industries, Ltd.) 0.04% (Comparative Example 3) or brilliant was added to the mixed solution of the monomers used in Production Example 1 instead of NDB as a chlorine detection reagent. Blue FCF (manufactured by Tokyo Chemical Industry Co., Ltd.) 0.04% (Comparative Example 4) was mixed, EDMA 0.2% and V-65 0.1% were added, and polymerization was carried out in the same manner as in Production Example 1 to obtain a hydrogel molded body. I got it.

This hydrogel molded body was made to have a diameter of 1 cm and a thickness of 1
I tried to elute unreacted monomer by boiling it in distilled water after processing it into a disc shape of mm, but phenosafranine or brilliant blue FCF continued to elute, and these were not sufficiently contained in the hydrogel molded body. I understood.

Example 3 A 5% sodium hypochlorite solution was diluted with distilled water to prepare a solution having a free chlorine concentration of 1 ppm (pool water quality standard) or 10 ppm. The hydrogel molded body obtained in Production Example 2 was immersed in these solutions, and the discoloration of the molded body was observed. As a result, it was confirmed that the hydrogel molded product dipped in the solution having a free chlorine concentration of 1 ppm did not discolor, but the hydrogel molded product dipped in the solution of 10 ppm had a reddish brown color and a high free chlorine concentration. Therefore, it is possible to easily know that the concentration of free chlorine in the pool water is high by permanently providing the hydrogel molded body in the pool.

Example 4 A colorless and transparent hydrogel substrate was obtained in the same manner as in Production Example 1 except that NDB was not added.

This hydrogel substrate is 1 cm in diameter and 1 mm in thickness
Was processed into a disc shape and was immersed in 100 ml of 0.01% aqueous solution of Reactive Blue 163 (Procion Blue MXG, manufactured by ICI Japan Co., Ltd.) at 60 ° C. for 30 minutes. After this, the hydrogel substrate was taken out and placed in a 1.0% sodium carbonate aqueous solution.
After soaking at 60 ° C. for 10 minutes, it was transferred into distilled water and boiled for 3 hours while exchanging the distilled water every hour to obtain a blue-colored hydrogel molded body. This hydrogel molded body was placed in the processing container of the electric cleaning and sterilizing apparatus for soft contact lenses in the same manner as in Production Example 1.

Using this treatment container, sodium chloride 0.15
% (Electrical conductivity: 2.9 mS / cm) in an aqueous solution containing 20
The discoloration of the hydrogel molded article when the electrical treatment was performed for a minute was examined. As a result, it was found that the hydrogel molded product changed from blue to transparent and the color disappeared due to free chlorine.

Example 5 A cycle of electrical treatment was carried out in the same manner as in Example 2 except that the treatment container in which the hydrogel molded product colored in blue obtained in Example 4 was installed as the treatment container in Example 2. Was repeated. After 100 cycles, the color of the hydrogel molding was the same as the beginning, and it did not discolor even after long-term use in a boiling state in which free chlorine was not present.

Also, using a hydrogel molded body after 100 cycles, sodium chloride 0.225% (electric conductivity: 4.2
The discoloration of the hydrogel molded article when the electric treatment was performed for 20 minutes in an aqueous solution containing mS / cm) was examined. As a result, it was confirmed that the hydrogel molded product changed from blue to transparent and reacted with free chlorine.

[0057]

EFFECTS OF THE INVENTION The hydrochlorinated molded article for detecting free chlorine according to the present invention can continuously detect free chlorine as it is by setting it once at a predetermined position. Therefore, the hydrogel molded article of the present invention is permanently installed in, for example, a pool to monitor the chlorine concentration of water in the pool, or is placed in a processing container for a soft contact lens and washed by applying an electric current to a processing solution in which the lens is immersed. It can be preferably used for detection of free chlorine in the solution when performing disinfection.

Further, the hydrogel molded article of the present invention does not develop color even under severe conditions such as boiling, unless free chlorine is present, and has a wide range of use. It has an effect that free chlorine can be detected at a low cost as compared with the detection method.

Claims (7)

[Claims] 1. A molded product of hydrogel for detecting free chlorine comprising a reagent for detecting chlorine which changes color by reacting with free chlorine and a hydrogel base material. 2. The molded product of hydrochlorine for detecting free chlorine according to claim 1, which contains 0.001 to 0.2% by weight of N, N'-diphenylbenzidine as a reagent for detecting chlorine. 3. A molded product of hydrogel for detecting free chlorine according to claim 1, which contains 0.001 to 0.5% by weight of Reactive Blue 163 as a reagent for detecting chlorine. 4. The hydrogel molded product for detecting free chlorine according to claim 1, 2 or 3, wherein the hydrogel base material contains a hydrophilic monomer as a main component. 5. The hydrogel molded product for detecting free chlorine according to claim 4, wherein the hydrophilic monomer is 2-hydroxyethyl methacrylate. 6. The hydrogel molded product for detecting free chlorine according to claim 1, 2, 3, 4, or 5, wherein the hydrogel substrate contains a hydrophobic monomer. 7. The hydrogel molded product for detecting free chlorine according to claim 1, 2, 3, 4, 5, or 6, wherein the hydrogel substrate is a lightly crosslinked copolymer.