JP2018079318A - Liquid composition for stationary volatilization apparatus and method for improving the solubility of active ingredients in the liquid composition - Google Patents

Abstract

Disclosed is a liquid composition for use in an installation-type volatilization device, which can maintain good solubility of an active ingredient in the liquid composition and sustainability of the effect. The active ingredient comprises a surfactant and ethanol, isopropyl alcohol, n-propyl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol methyl ether acetate, ethylene glycol mono-n-propyl ether, ethylene glycol. A composition solubilized in water using at least one aqueous solvent selected from the group consisting of mono-iso-propyl ether, propylene glycol monomethyl ether, and propylene glycol monopropyl ether, which has the following formula (I ) Is a liquid composition for an installed volatilization apparatus having an optimization index defined by 15 to 75. [Equation 1] [Selection figure] None

Description

  The present invention relates to a liquid composition for an installed volatilization apparatus in which an active ingredient is solubilized in water under a specific condition, and a method for improving the solubility for the active ingredient in the liquid composition to be volatilized stably. About.

  Since oily substances are slightly soluble or sparingly soluble in water, conventionally, as a means for dissolving an oily substance as an active ingredient in water, a method using a surfactant or a method using an aqueous solvent has been used. It has been.

For example, Patent Document 1 describes a spray chemical containing at least one nonionic surfactant selected from the group consisting of polyoxyalkylene alkyl ethers and polyoxyalkylene polycyclic phenyl ethers.
Patent Document 2 describes a fragrance containing at least one nonionic surfactant selected from the group consisting of polyoxyethylene hydrogenated castor oil ether and polyoxyalkylene decyl ether.

JP 2012-75662 A JP 2013-59631 A

  As mentioned above, in order to stably dissolve the active ingredient that is an oily substance and to maintain the effect of the active ingredient by volatilization, the formulation of the liquid composition has been studied, but many materials are blended. If the compatibility with the components used is poor, various problems will occur.

  For example, when a surfactant is mainly used as a means for dissolving an oily substance in water, the formulation becomes complicated by using a large number of surfactants, and the composition is separated, precipitated, or colored. Such a problem may occur.

  In addition, even when the effect of the active ingredient due to volatilization is desired to be maintained for a certain period of time, there is a problem that the effect is not sustained due to the clogging of the absorbent core or the surfactant to the impregnated paper, etc. with the passage of time of use. is there.

  Furthermore, when an aqueous solvent is mainly used as a means for dissolving an oily substance in water, there are problems of danger due to ignition and a problem that a floor coating is dissolved in the case of liquid spillage.

  In particular, in a liquid composition used by being housed in an installation-type volatilization apparatus, the solubilization stability of the active ingredient and the sustainability of the effect of the active ingredient due to volatilization are important. However, there is no clear index for dissolving an active ingredient in a liquid composition, or for making a prescription having a long-lasting effect of an active ingredient, and the index has not been studied so far.

  Therefore, the present invention provides a liquid composition for use in an installation-type volatilization device, which can maintain good solubility of the active ingredient in the liquid composition and sustainability of the effect. Let it be an issue.

As a result of intensive studies, the present inventors have obtained a liquid composition in which an active ingredient is solubilized in water using a surfactant and an aqueous solvent so that the optimization index described below is within a certain range. However, the present inventors have found that the above problems can be solved, and have completed the present invention.
That is, the present invention relates to the following <1> to <4>.

<1> Surfactant and ethanol, isopropyl alcohol, n-propyl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol methyl ether acetate, ethylene glycol mono-n-propyl ether, ethylene glycol mono -A composition solubilized in water using at least one aqueous solvent selected from the group consisting of iso-propyl ether, propylene glycol monomethyl ether, and propylene glycol monopropyl ether, which has the following formula (I) The liquid composition for installation type volatilization apparatuses whose optimization index defined by 15 is 15-75.

<2> The liquid composition for an installed volatilization apparatus according to <1>, wherein the active ingredient is at least one selected from the group consisting of a fragrance, an insecticide, an insect repellent, and a bactericide.
<3> The liquid composition for an installed volatilization device according to <1> or <2>, wherein the installed volatilization device is an inverted volatilization device.
<4> Active ingredient, surfactant and ethanol, isopropyl alcohol, n-propyl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol methyl ether acetate, ethylene glycol mono-n-propyl ether, ethylene glycol mono- In a liquid composition for an installed volatilization device containing at least one aqueous solvent selected from the group consisting of iso-propyl ether, propylene glycol monomethyl ether, and propylene glycol monopropyl ether, the liquid composition is defined by the following formula (I): The method of improving the solubility of the active ingredient in a liquid composition by setting the optimization index to 15-75.

  ADVANTAGE OF THE INVENTION According to this invention, an active ingredient can be dissolved easily and the liquid composition with the sufficient sustainability of an effect (for example, the persistence of fragrance intensity | strength is a fragrance | flavor) can be provided. In addition, the liquid composition does not have a problem that the composition itself precipitates or generates unnecessary materials.

  Hereinafter, although this invention is explained in full detail, these show an example of a desirable embodiment, and this invention is not specified by these content.

  The liquid composition for the installation-type volatilization apparatus of the present invention comprises an active ingredient, a surfactant and ethanol, isopropyl alcohol, n-propyl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol methyl ether acetate, ethylene Solubilized in water using at least one aqueous solvent selected from the group consisting of glycol mono-n-propyl ether, ethylene glycol mono-iso-propyl ether, propylene glycol monomethyl ether, and propylene glycol monopropyl ether It is a composition, Comprising: The optimization index demonstrated below is 15-75, It is characterized by the above-mentioned.

  In addition, in this invention, an installation-type volatilization apparatus means the apparatus which installs indoors or outdoors and volatilizes active ingredients, such as a fragrance | flavor. For example, it is a device that is installed for a specific period such as one week, one month, two to three months, one year, etc., and continuously exerts its effect.

  In addition, the method for improving the solubility of the active ingredient of the present invention includes an active ingredient, a surfactant and ethanol, isopropyl alcohol, n-propyl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol methyl ether acetate, For an installation-type volatilization apparatus containing at least one aqueous solvent selected from the group consisting of ethylene glycol mono-n-propyl ether, ethylene glycol mono-iso-propyl ether, propylene glycol monomethyl ether, and propylene glycol monopropyl ether In the liquid composition, the optimization index described below is 15 to 75.

[Surfactant]
The surfactant used in the present invention may be any of a nonionic surfactant, an anionic surfactant, a cationic surfactant, and an amphoteric surfactant.

Nonionic surfactants include, for example, polyoxyalkylene hardened castor oil ethers such as polyoxyethylene hardened castor oil ether, polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene oleyl ether, and polyoxyethylene decyl ether. , Polyoxyalkylene alkyl ethers such as polyoxypropylene decyl ether, polyoxyalkylene fatty acid esters such as polyoxyethylene fatty acid esters, polyoxyalkylene glyceryl ether fatty acid esters such as polyoxyethylene glyceryl ether fatty acid esters, alkyl alkanolamides, alkyl poly Glucoside, sorbitan fatty acid ester, glycerin fatty acid ester, polyoxyethylene sorbitan fatty acid ester , Polyoxyethylene polyoxypropylene glycol, and the like.
Among these, polyoxyethylene hydrogenated castor oil ether, polyoxyethylene alkyl ether, and polyoxyethylene sorbitan fatty acid ester are preferable from the viewpoint of solubility of the active ingredient.

Examples of the anionic surfactant include alkyl sulfates, polyoxyethylene alkyl ether sulfates such as polyoxyethylene lauryl ether sulfate, sulfosuccinate, dialkylsulfosuccinate, alkyl glucoside sulfate, N-acyl. Examples include amino acid salts, carboxylate salts, sulfonate salts, and phosphate ester salts.
Among these, dialkyl sulfosuccinate and polyoxyethylene lauryl ether sulfate are preferable from the viewpoint of solubility of the active ingredient.

  Examples of the cationic surfactant include alkyl ammonium salts.

  Examples of amphoteric surfactants include alkylamidobetaines, alkyldimethylamine oxides, alkylbetaines, and cocamidoalkylhydroxysultaines.

  As the content ratio of the surfactant in the liquid composition of the present invention, from the viewpoint of the solubility of the active ingredient and the sustainability of the effect of the active ingredient, for example, 0.01 to 20% by mass with respect to the entire liquid composition, Preferably it is 0.1-10 mass%, More preferably, it is 0.5-5 mass%.

[Aqueous solvent]
The aqueous solvent used in the present invention is ethanol (boiling point 74 ° C.), isopropyl alcohol (boiling point 82 ° C.), n-propyl alcohol (boiling point 97 ° C.), ethylene glycol monomethyl ether (boiling point 125 ° C.), ethylene glycol monoethyl ether. (Boiling point 135 ° C.), ethylene glycol methyl ether acetate (boiling point 145 ° C.), ethylene glycol mono-n-propyl ether (boiling point 151 ° C.), ethylene glycol mono-iso-propyl ether (boiling point 142 ° C.), propylene glycol monomethyl ether ( And at least one selected from the group consisting of propylene glycol monopropyl ether (boiling point 150 ° C.).

  Among these, ethanol (boiling point 74 ° C.), isopropyl alcohol (boiling point 82 ° C.), propylene glycol monomethyl, which has a relatively low boiling point and is freely miscible with water, from the viewpoints of solubility and volatility of active ingredients and versatility. Ether (boiling point 121 ° C.) is preferred, and ethanol (boiling point 74 ° C.) is more preferred.

  In addition, 3-methoxy-3-methyl-1-butanol (boiling point 174 ° C.), propylene glycol (boiling point 188 ° C.) and ethylene glycol (boiling point 192 ° C.) may be used in the present invention because they may suppress volatilization. It is not suitable as an aqueous solvent.

  Furthermore, some of the above-mentioned series of aqueous solvents have a fungicidal and insect repellent enhancing effect, and can be supplementarily added for each purpose.

For example, propylene glycol monomethyl ether and propylene glycol monopropyl ether can be exemplified as those having a spatial disinfection effect.
Ethylene glycol monomethyl ether and ethylene glycol monoethyl ether can be exemplified as those having flying insect repellent performance.
Propylene glycol monopropyl ether and the like can be exemplified as those having the ability to kill eggs of clothing pests.

  Even if the aqueous solvent used in the present invention has the auxiliary effects and performance as described above, the aqueous solvent is not treated as an active ingredient of the present invention and used separately in the liquid composition of the present invention. It is done.

  In the liquid composition of the present invention, the content ratio of the aqueous solvent is, for example, 0.5 to 80% by mass, preferably 1 to 60% by mass with respect to the entire liquid composition from the viewpoints of solubility and volatility of the active ingredient. %, More preferably 2 to 50% by mass.

[Active ingredients]
Examples of the active ingredient of the liquid composition in the present invention include fragrances, deodorants, insecticides, insect repellents and bactericides. At least one selected from the group consisting of these can be arbitrarily used.

(Fragrance)
The fragrance used in the present invention is not particularly limited, but, for example, animal fragrance such as musk, reibyoukou, rysenkou, peppermint oil, abies oil, ajones oil, almond oil, angelica root oil, paging oil, bergamot oil, Perch oil, Boadrose oil, Kayabuchi oil, Gananga oil, Capsicum oil, caraway oil, cardamom oil, cassia oil, celery oil, cinnamon oil, citronella oil, cognac oil, coriander oil, cumin oil, camphor oil, jill oil, estgolan Oil, eucalyptus oil, fennel oil, garlic oil, ginger oil, grapefruit oil, hop oil, lemon oil, lemongrass oil, nutmeg oil, mandarin oil, peppermint oil, orange oil, sage oil, star anise oil, turpentine oil, lavender Plants such as oil, rosemary oil Mention may be made of the perfume.

  In addition, as the fragrance used in the present invention, artificial fragrance such as synthetic fragrance or extracted fragrance can be used, for example, hydrocarbon fragrance such as pinene and limonene, linalool, geraniol, citronellol, menthol, borneol, benzyl. Alcohol-based fragrances such as alcohol, anis alcohol, phenylethyl alcohol, dihydromyrsenol, phenol-based fragrances such as anethole, eugenol, n-butyraldehyde, isobutyraldehyde, hexyl aldehyde, citral, citronellal, benzaldehyde, hexyl cinnamamic aldehyde, etc. Aldehyde perfumes, Carbon, Menton, Camphor, Ketone perfumes such as acetophenone, Ionone, Lactone perfumes such as γ-Butyllactone, Coumarin, Cineol, Octyl acetate, Vetone Jill acetate, cinnamyl acetate, butyl propionate, methyl benzoate, hexyl acetate to Buchirushikuro, ester flavors such as linalyl acetate, Other Garakusorido the like also.

(Deodorants)
Deodorants include, for example, green tea dry-distilled extracts (eg, catechin, tannin, polyphenol, etc.), grapefruit extract, persimmon extract, perilla extract, mushroom extract, bamboo extract, champignon extract, and other plant extract, methacrylic acid Examples include lauryl, geranyl crotonate, and methylated cyclodextrin.

  In addition to the above, organic acids such as citric acid for neutralization of alkali odor, amines for neutralization of acid odor, and the like can be mentioned. Furthermore, what deodorizes with betaines for neutralization of an acid or an alkali is also mentioned.

(Insecticide)
Examples of insecticides include pyrethroid insecticides, organophosphorus insecticides, carbamate insecticides, insecticides derived from natural ingredients such as cypress, cedar and hiba essential oils, extracts from citrus peels and seeds, etc. Is mentioned. Among these, pyrethroid insecticides having a vapor pressure of 2 × 10 ⁻⁴ Pa (25 ° C.) or higher are preferable as those that volatilize naturally.

(Insect repellent)
As the insect repellent, for example, N, N-diethyl-m-toluamide, dimethyl phthalate, dibutyl phthalate, p-menthane-3,8-diol, 2-ethyl-1,3-hexanediol, di-n- Propyl isocincomellonate, p-dichlorobenzene, di-n-butyl succinate, caran-3,4-diol, 1-methylpropyl-2- (2-hydroxyethyl) -1-piperidinecarboxylate, 3- [ Acetyl (propylamino)] ethyl propionate, allyl isothiocyanate, menthyl acetate, butyl cyclohexyl acetate, butyl cycloheptyl acetate, peppermint oil, eucalyptus oil, peppermint oil, citronella oil, lavender oil, rosemary oil, chamomile oil, geranium oil Etc.

(Fungicide)
Examples of the disinfectant include hinokitiol, phenoxyethanol, isopropylmethylphenol, thiabendazole, p-chloro-m-xylenol, triclosan, thymol, allyl isothiocyanate, methylisothiazolinone, dichloroisocyanurate, chlorine dioxide, acetic acid, propion Examples thereof include organic acids such as acid, lactic acid, citric acid and malic acid, and antibacterial fragrances such as geraniol, citral, carvacrol and cinnamic aldehyde.

  In the liquid composition of the present invention, the content ratio of the active ingredient varies depending on the size of the room in which the volatilization device is installed and the period for which the effect is sustained. It is 0.01-20 mass%, Preferably it is 0.05-15 mass%, More preferably, it is 0.1-10 mass%.

[Other ingredients]
In the liquid composition of the present invention, in addition to the above-described various functional components, as long as the effects of the present invention are not impaired, an antiseptic, a UV absorber, an antifoaming agent, a pH adjuster, a chelating agent, A pigment | dye etc. can also be used. The above components are not particularly limited as long as they are components that are commonly used by those skilled in the art.

[Adjustment index]
In the present invention, the active ingredient is solubilized using the above-described surfactant and aqueous solvent, and a liquid composition is prepared so that the optimization index defined by the following formula (I) is 15 to 75.

  In addition, the present inventors set the active ingredient concentration (mass%), the surfactant concentration (mass%), the aqueous solvent concentration (mass%) of the liquid composition of the present invention, and the items composed thereof as a denominator or a numerator. The above formula (I) has been found by creating a formula for this and collating it with the test results regarding the solubility of the active ingredient in the liquid composition and the duration of the effect.

  In the above formula (I), the increase in numerical values of “aqueous solvent concentration” and “surfactant concentration” is a factor that promotes the solubility of the active ingredient, and the increase in numerical value of “active ingredient concentration” It is a factor that suppresses the solubility of. It is presumed that excellent solubility can be obtained when the ratio of these numerical values shows a specific value.

  Further, the increase in the numerical value of “surfactant concentration” is a factor that suppresses the volatility of the active ingredient because the surfactant itself does not volatilize. An increase in the numerical value of “aqueous solvent concentration” is a factor that promotes the volatility of the active ingredient, and an increase in the numerical value of “active ingredient concentration” is a factor that suppresses the volatility of the active ingredient. It is presumed that excellent volatility can be obtained when the ratio of these numerical values shows a specific value.

  That is, both the solubility and volatility of the active ingredient are adjusted for the numerical values of the promoting factor and the inhibitory factor (for example, if the numerical value of the promoting factor is high, the numerical value of the inhibitory factor acting in the opposite direction is also increased, etc.) Thus, the optimization index can be set to a specific value.

If the optimization index is 15 to 75, the liquid composition is uniformly transparent, so that good solubility of the active ingredient and sustained effect can be obtained.
The optimization index is more preferably 15 to 71, further preferably 18 to 71, particularly preferably 20 to 65, and most preferably 20 to 40.

  When the optimization index is less than 15, the solubility of the active ingredient in the liquid composition tends to deteriorate, and when the optimization index exceeds 75, the sustainability of the effect of the active ingredient tends to deteriorate.

[Method for preparing liquid composition]
The liquid composition of the present invention is produced by a conventional method. For example, each component can be obtained by mixing and stirring, and heating or the like may be performed as desired.

  By preparing the liquid composition by adjusting the concentrations of the active ingredient, the surfactant and the aqueous solvent so that the optimization index represented by the above formula (I) is 15 to 75, the desired effect of the present invention can be obtained. Can be obtained.

[Volatilizer]
The active ingredient of the liquid composition of the present invention is used in an upright type volatilization apparatus and an inverted type volatilization apparatus, and in particular, using an inverted type volatilization apparatus (for example, an apparatus described in JP 2010-51591 A). It is preferable to volatilize.

  By using the volatilization device, a sufficient amount of the active ingredient can be volatilized and diffused stably and uniformly in a space such as a room. Therefore, by using the volatilization apparatus, it is possible to enjoy a scent and the like if the active ingredient is a fragrance, and to obtain an insecticidal effect if the active ingredient is an insecticide.

  EXAMPLES The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these examples.

[Example 1]
As an active ingredient, lavender fragrance (trade name: S-4961, manufactured by Shiono Koryo Co., Ltd.), as a surfactant, polyoxyethylene hydrogenated castor oil ether (trade name: BROWNON RCW-60, manufactured by Aoki Oil & Fat Co., Ltd.), as an aqueous solvent Using 95% ethanol (manufactured by Wako Pure Chemical Industries, Ltd.), a liquid composition was prepared by stirring and mixing with ion-exchanged water for 10 minutes until the active ingredient was solubilized at the content shown in Table 1.

[Adjustment index]
The optimization index was calculated based on the following formula (I). The results are shown in Table 1.

[Solubility test]
A 350 mL clear container made of polyethylene terephthalate (PET) was filled with 300 mL of the liquid composition prepared above, sealed, and allowed to stand in storage at 5 ° C. and 50 ° C., respectively. Two weeks later, the appearance was visually checked for problems such as cloudiness, separation, and floating matter generation.

  In the above test, if the liquid composition has no white turbidity or separation, and there is no occurrence of suspended solids, it is confirmed that any one of the occurrence of white turbidity, separation, and suspended solids has excellent solubility of the active ingredient. Was evaluated as “x” inferior in solubility of the active ingredient. The results are shown in Table 1.

[Sustainability test]
400 ml each of the liquid composition prepared above is filled into a container used in “Toilet's Sticky! Sukiki-ri!” (Trade name) manufactured by Earth Pharmaceutical Co., Ltd., and the polyester absorbent used in the product is filled. A test specimen was prepared by attaching a liquid core and a volatile paper used in the same product. The test specimen was inverted and volatilized in a volatilization chamber at a temperature of 20 ° C. and a humidity of 55%.

  The number of days from the volatilization start date when 400 mL of the liquid composition in the test specimen was volatilized (except for 50 mL of the liquid remaining on the volatile paper or the like) was measured. The case where the number of days was 50 to 80 days was evaluated as “◯”, which is excellent in the sustainability of the effect of the active ingredient, and the case where it was out of the above range was evaluated as “x”, which was inferior in the sustainability of the effect of the active ingredient.

  The container used in the sustainability test is made on the assumption that it will be used for 65 days. If the number of days is less than 50 days, the volatilization of the active ingredient is fast and the sustainability of the effect of the active ingredient is weak. This is because when the amount exceeds 80 days, the amount of volatilization of the active ingredient per day is small and the effect of the active ingredient is weak. The results are shown in Table 1.

[Examples 2 to 15, Comparative Examples 1 to 7]
In Example 1, a liquid composition was prepared as shown in Table 1 with respect to the aqueous solvent, the active ingredient, the surfactant, and the content ratio thereof, and the same test as in Example 1 was performed. The results are shown in Table 1.

  In the examples, “FS-500M” manufactured by Shirai Matsushinyaku Co., Ltd. is used as the green tea dry distillation extract, “Phenoxyethanol-S” manufactured by Yokkaichi Gosei Co., Ltd. is used as the phenoxyethanol, and “Suzuki Hikaru Co., Ltd.” is used as the mint oil. "Light white oil" was used.

  Surfactant A in Examples and Comparative Examples is 50% by mass of polyoxyethylene hydrogenated castor oil ether (trade name: Marpon HC-60A, manufactured by Matsumoto Yushi Seiyaku Co., Ltd.), 40% by mass of polyoxyethylene. It consists of lauryl ether (trade name: Emulgen 109P, manufactured by Kao Corporation) and 10% by mass of dialkyl sulfosuccinate salt (trade name: Marpomace PT, manufactured by Matsumoto Yushi Seiyaku Co., Ltd.).

  Further, as 3-methoxy-3-methyl-1-butanol in Comparative Examples, “Solfit” manufactured by Kuraray Co., Ltd. was used.

  In Examples 1 to 15 and Comparative Examples 1 to 6 using 95% ethanol as the aqueous solvent, the concentration (mass%) of the aqueous solvent was 95% ethanol shown in Table 1 when determining the optimization index. A value obtained by multiplying the blending amount (% by mass) by 0.95 was used.

  In Table 1, “remainder” means that the total amount of the liquid composition is adjusted to 100 mass% by adding ion exchange water.

  From the above test results, in Comparative Examples 1, 2, 5 and 6, the liquid composition became turbid and there was a problem in appearance. Moreover, in Comparative Examples 3-7, the number of days from the volatilization start date when all 400 mL (excluding 50 mL of liquid remaining on the volatilization paper, etc.) volatilizes is longer than 80 days, and these all have sustained effects. The result was insufficient.

  On the other hand, in the examples where the optimization index is in the range of 15 to 75, both the solubility of the active ingredient in the liquid composition and the sustainability of the effect showed good results.

Claims (4)

Active ingredients include surfactants and ethanol, isopropyl alcohol, n-propyl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol methyl ether acetate, ethylene glycol mono-n-propyl ether, ethylene glycol mono-iso- A composition solubilized in water using at least one aqueous solvent selected from the group consisting of propyl ether, propylene glycol monomethyl ether, and propylene glycol monopropyl ether, which is defined by the following formula (I): The liquid composition for installation type volatilization apparatuses whose optimization index is 15-75.

  The liquid composition for an installation-type volatilization apparatus according to claim 1, wherein the active ingredient is at least one selected from the group consisting of a fragrance, an insecticide, an insect repellent, and a fungicide.   The liquid composition for an installed volatilization device according to claim 1 or 2, wherein the installed volatilization device is an inverted volatilization device. Active ingredient, surfactant and ethanol, isopropyl alcohol, n-propyl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol methyl ether acetate, ethylene glycol mono-n-propyl ether, ethylene glycol mono-iso-propyl In a liquid composition for an installation-type volatilization device containing at least one aqueous solvent selected from the group consisting of ether, propylene glycol monomethyl ether, and propylene glycol monopropyl ether, optimization defined by the following formula (I) A method for improving the solubility of an active ingredient in a liquid composition by adjusting the index to 15 to 75.