Film-forming aid and aqueous emulsion composition comprising the same

Abstract

To provide a film-forming aid that can sufficiently lower the lowest film-forming temperature of an aqueous emulsion composition even with a small amount of addition of the film-forming aid.SOLUTION: A film-forming aid comprises a compound represented by formula (1): R1-O-(CH2-CH(R3)-O)n-R2, where R1 and R2 each denote a C1-8 linear or branched alkyl group, where at least one of R1 and R2 is a C3-8 branched alkyl group, with the total number of carbon atoms of R1 and R2 being 6 or more, R3 is hydrogen, a methyl group or an ethyl group, and n denotes an average added mol number of -(CH2-CH(R3)-O)-, which is a number from 2 to 4.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a coalescent and an aqueous emulsion composition containing the same. [Background technology]

[0002] Traditionally, the mainstream paint industry has been organic solvent-based paints, which are used by evaporating organic solvents such as toluene and xylene to form a film. However, there is a strong demand for a shift to water-based paints due to concerns about work safety and reducing environmental pollution. A typical example of a water-based paint is a paint using an aqueous emulsion composition (hereinafter referred to as "water-based emulsion composition" or "water-based emulsion paint"), in which resin particles are dispersed in an aqueous medium. Regarding the film-forming mechanism of water-based emulsion paints, which use an aqueous medium as the solvent, while organic solvent-based paints form a continuous film upon evaporation of the organic solvent, water-based emulsion paints do not form a continuous film by evaporation alone. Instead, after water evaporation, resin particles come into contact with each other, deform, and fuse together, forming a smooth, gap-free film. To promote the fusion of resin particles, additives commonly known as coalescence aids are used. Coalescence aids also have the effect of lowering the minimum film-forming temperature (MFT) of the paint and improving film-forming properties.

[0003] Currently, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (Texanol (registered trademark, the same applies hereinafter)) is widely used as a coalescence aid. Patent Document 1 discloses the preparation of an aqueous acrylic resin dispersion (corresponding to a paint) by adding an alkylene glycol dialkyl ether having a boiling point of 150 to 220°C as a coalescence aid to an acrylic resin dispersion. Examples of alkylene glycol dialkyl ethers having a boiling point of 150 to 220°C include diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, and dipropylene glycol dimethyl ether. Meanwhile, the same document also discloses a comparative example in which diethylene glycol di-n-butyl ether having a boiling point of 255°C is used as a coalescence aid, as an alkylene glycol dialkyl ether having a boiling point other than 150 to 220°C. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-193252 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (Texanol) or the alkylene glycol dialkyl ether described in Patent Document 1 is used as a coalescence aid, there is still room for improvement in terms of lowering the minimum film-forming temperature of the water-based emulsion paint. In other words, in this case, in order to sufficiently lower the minimum film-forming temperature of the water-based emulsion paint, a relatively large amount of coalescence aid must be added, which has the problem of adversely affecting the hardness and smoothness of the paint film that is formed.

[0006] Therefore, an object of the present invention is to provide a film-forming aid that can sufficiently lower the minimum film-forming temperature of an aqueous emulsion composition even when added in a small amount. [Means for solving the problem]

[0007] As a result of extensive research, the present inventors have discovered the following formula (1):

[0008] [ka]

[0009] In the above formula (1), R 1 and R 2 is a linear or branched alkyl group having 1 to 8 carbon atoms, and R 1 and R 2 At least one of R is a branched alkyl group having 3 to 8 carbon atoms, and 1 and R 2 The total number of carbon atoms is 6 or more, R 3 is hydrogen, a methyl group, or an ethyl group, n is -(CH-CH(R 3 )-O)-, which represents the average number of moles added, and is a number of 2 to 4. The present invention has been accomplished based on the discovery that the above problems can be solved by a film-forming aid containing a compound represented by the following formula: [Effects of the Invention]

[0010] When the coalescent of the present invention is applied to an aqueous emulsion composition, the minimum film-forming temperature of the aqueous emulsion composition can be sufficiently lowered even when the amount of the coalescent added is small. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a graph plotting the relationship between the amount of each film-forming aid added to an aqueous acrylic resin emulsion composition and the minimum film-forming temperature, as evaluated in the Examples section. [Figure 2]1 is a graph plotting the relationship between the amount of each film-forming aid added to the aqueous emulsion composition of acrylic styrene resin and the minimum film-forming temperature evaluated in the Examples section. [Figure 3] 1 is a photograph taken with a digital camera of a coating film formed from an aqueous emulsion composition of an acrylic resin, which was evaluated in the Examples section. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to only the following embodiments. In this specification, "(meth)acrylate" is a general term for acrylate and methacrylate. Similarly, compounds containing (meth), such as (meth)acrylic, are a general term for compounds having "meth" in their names and compounds not having "meth." Furthermore, unless otherwise specified, "%" and "parts" mean "% by mass" and "parts by mass," respectively, and "boiling point" means the boiling point at normal pressure. Furthermore, in the following examples, unless otherwise specified, operations were performed under conditions of room temperature (25°C) and relative humidity of 40 to 50% RH.

[0013] <Film-forming agent> The film-forming aid of the present invention contains a compound represented by the following formula (1).

[0014] [ka]

[0015] In the above formula (1), R 1 and R 2 is a linear or branched alkyl group having 1 to 8 carbon atoms, and R 1 and R 2 At least one of R is a branched alkyl group having 3 to 8 carbon atoms, and 1 and R 2 The total number of carbon atoms is 6 or more, R 3 is hydrogen, a methyl group, or an ethyl group, n is -(CH-CH(R 3 )-O)- and is a number of 2 to 4.

[0016] In one embodiment, the film-forming aid of the present invention includes a compound represented by the above formula (1) having a boiling point of more than 220°C.

[0017] When this coalescent is used in an aqueous emulsion composition, the minimum film-forming temperature of the aqueous emulsion composition can be sufficiently lowered even when the amount of coalescent added is small. The mechanism by which this effect is achieved is unknown, but is presumed to be as follows.

[0018] In aqueous emulsion compositions, the evaporation of water alone does not result in the formation of a continuous film. Instead, after the evaporation of water, resin particles come into contact with each other and fuse together, forming a smooth, gap-free film. To promote this process, a coalescence aid is used. However, when using currently commonly used coalescence aids, such as 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (Texanol) or the alkylene glycol dialkyl ether described in Patent Document 1, a relatively large amount of coalescence aid must be added to lower the minimum film-forming temperature of the aqueous emulsion composition. When a large amount of coalescence aid is contained in an aqueous emulsion composition, the hardness and smoothness of the resulting coating film are adversely affected. This is thought to be due to the plasticization of the coating film caused by the large amount of coalescence aid remaining in the coating film.

[0019] Therefore, the present inventors conducted extensive research into the design of coalescents and found that the above-mentioned problems can be solved by using a compound having at least one branched alkyl group having 3 to 8 carbon atoms at its terminal, as represented by the above formula (1). Generally, the use of a hydrophobic coalescent is considered advantageous in that it penetrates into resin particles, swelling their surfaces, promoting fusion between resin particles after application, and lowering the minimum film-forming temperature. However, when a hydrophobic coalescent is incorporated into an aqueous emulsion composition (paint), the resin particles dispersed in the aqueous medium can become unstable and aggregate, making application of the composition itself difficult. In contrast, the compound represented by the above formula (1) contains an oxyalkylene group that imparts hydrophilicity and at least one branched alkyl group having 3 to 8 carbon atoms that imparts hydrophobicity in an appropriate balance. In particular, since the compound represented by formula (1) has a branched alkyl group having 3 to 8 carbon atoms at its terminal, a coalescing agent containing the compound represented by formula (1) can efficiently reduce the surface tension of water in an aqueous emulsion composition. As a result, even when added in small amounts, the coalescing agent of the present invention can efficiently penetrate into resin particles, suppressing aggregation of the resin particles while swelling the surfaces of the resin particles. Furthermore, since the coalescing agent efficiently reduces the surface tension of water in an aqueous emulsion composition, the wettability of the aqueous emulsion composition to the substrate is improved. Therefore, an aqueous emulsion composition containing the coalescing agent of the present invention has good applicability to the substrate.

[0020] Specifically, when an aqueous emulsion composition containing the coalescing aid of the present invention is applied to a substrate, the presence of the coalescing aid allows it to penetrate the resin, and the resin particles whose surfaces have swelled due to the action of the coalescing aid facilitate fusion in the coating. In this case, the compound represented by formula (1) efficiently reduces the surface tension of water, allowing the coalescing aid to penetrate the resin particles efficiently, thereby efficiently promoting swelling and fusion between the resin particles. As a result, even a small amount of the coalescing aid of the present invention can sufficiently lower the minimum film-forming temperature of the aqueous emulsion composition. Furthermore, because only a small amount of the coalescing aid of the present invention is required to be added to the aqueous emulsion composition, only a small amount of the coalescing aid remains in the resulting coating, thereby preventing plasticization of the coating. Therefore, the coalescing aid of the present invention minimizes adverse effects on the hardness and smoothness of the resulting coating. Therefore, when the aqueous emulsion composition is used as a paint, for example, the effects on the inherent properties of the paint (e.g., hardness, smoothness, etc.) can be minimized.

[0021] It should be noted that the present invention is not limited to the above mechanism.

[0022] As described above, the coalescence aid of the present invention contains a compound represented by the following formula (1). The coalescence aid may contain only one type of compound represented by the following formula (1), or two or more types of compounds. Hereinafter, the compound represented by the following formula (1) will also be referred to as "compound (1)."

[0023] [ka]

[0024] In the above formula (1), R 1 and R 2 is a linear or branched alkyl group having 1 to 8 carbon atoms, and R 1 and R 2 At least one of R is a branched alkyl group having 3 to 8 carbon atoms, and 1 and R 2 The total number of carbon atoms is 6 or more.

[0025] Examples of the linear or branched alkyl group having 1 to 8 carbon atoms include alkyl groups such as a methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, tert-pentyl group, neopentyl group, 1,2-dimethylpropyl group, n-hexyl group, isohexyl group, 1,3-dimethylbutyl group, 1-isopropylpropyl group, 1,2-dimethylbutyl group, n-heptyl group, 1,4-dimethylpentyl group, 3-ethylpentyl group, 2-methyl-1-isopropylpropyl group, 1-ethyl-3-methylbutyl group, n-octyl group, 2-ethylhexyl group, 3-methyl-1-isopropylbutyl group, 2-methyl-1-isopropyl group, 1-t-butyl-2-methylpropyl group, and 3,5,5-trimethylpentyl group. The linear or branched alkyl group having 1 to 8 carbon atoms is preferably a linear or branched alkyl group having 1 to 6 carbon atoms, and more preferably a linear or branched alkyl group having 1 to 5 carbon atoms.

[0026] In the present invention, R 1 and R 2 At least one of R is a branched alkyl group having 3 to 8 carbon atoms. 1 and R 2As the branched alkyl group having 3 to 8 carbon atoms that at least one of the alkyl groups has, any of the above-mentioned alkyl groups can be used. Among these, from the viewpoint of further lowering the minimum film-forming temperature of the aqueous emulsion composition, the branched alkyl group having 3 to 8 carbon atoms is preferably an isopropyl group, an isobutyl group, a tert-butyl group, a 2-ethylhexyl group, a tert-pentyl group, a 1,2-dimethylpropyl group, a 1,3-dimethylbutyl group, a 1,2-dimethylbutyl group, a 1,4-dimethylpentyl group, a 3-ethylpentyl group, a 2-methyl-1-isopropylpropyl group, or a 1-ethyl-3-methylbutyl group, more preferably an isopropyl group, an isobutyl group, a tert-butyl group, or a 2-ethylhexyl group, and even more preferably an isopropyl group, an isobutyl group, or a tert-butyl group. As the branched alkyl group having 3 to 8 carbon atoms, a branched alkyl group having 3 to 5 carbon atoms is more preferred. 1 and R 2 Either one of R has a branched alkyl group having 3 to 8 carbon atoms, but both may have branched alkyl groups having 3 to 8 carbon atoms. 1 and R 2 When both of R and R have a branched alkyl group having 3 to 8 carbon atoms, 1 and R 2 is preferably an isopropyl group, an isobutyl group, a tert-butyl group, or a 2-ethylhexyl group, and more preferably an isopropyl group, an isobutyl group, or a tert-butyl group. 1 and R 2 When one of R has a branched alkyl group having 3 to 8 carbon atoms, R 1 and R 2 The other of R is preferably a linear alkyl group having 1 to 6 carbon atoms, and more preferably a linear alkyl group having 1 to 5 carbon atoms. 1 and R 2 is a linear or branched alkyl group having 1 to 5 carbon atoms, and R 1 and R 2 At least one of them is a branched alkyl group having 3 to 5 carbon atoms.

[0027] In the present invention, R 1 and R 2 The total number of carbon atoms in R1 and R2 is 6 or more. 2 The total number of carbon atoms in R and R is preferably 7 or more, and more preferably 8 or more, from the viewpoint of further lowering the minimum film-forming temperature of the aqueous emulsion composition. 2 The upper limit of the total number of carbon atoms is not particularly limited and is theoretically 16, but from the viewpoint of practical application, it is preferably 15 or less, more preferably 12 or less, and even more preferably 10 or less.

[0028] In the above formula (1), R 3 is hydrogen, a methyl group, or an ethyl group. Here, in formula (1), "-(CH-CH(R 3 )-O)-" represents an oxyalkylene group, and "-(CH-CH(R 3 )-O)-" is, for example, R 3 When R is hydrogen, it represents an oxyethylene group (-(CH2CH2-O)-); 3 When R is a methyl group, it represents an oxypropylene group (-(CH2-CH(CH3)-O)-); 3 When R is an ethyl group, it represents an oxybutylene group (-(CH2-CH(CH2CH3)-O)-). In one embodiment, from the viewpoint of further improving the effects of the present invention, R 3 is hydrogen or a methyl group.

[0029] In the above formula (1), "-(CH-CH(R 3 )-O) n "-" represents a polyoxyalkylene chain. n is -(CH-CH(R 3 n represents the average number of moles of )-O)- added, and is a number from 2 to 4. From the viewpoint of further lowering the minimum film-forming temperature of the aqueous emulsion composition, n is preferably a number from 3 to 4.

[0030] In the above formula (1), -(CH-CH(R 3 )-O) nWhen - has a plurality of oxyalkylene groups, the plurality of oxyalkylene groups may be the same or different. 3 )-O) n When - has two or more kinds of oxyalkylene groups, the arrangement may be either random or block.

[0031] The boiling point of the compound represented by formula (1) contained in the coalescent of the present invention is not particularly limited, but is preferably above 220°C. By having a boiling point above 220°C, when a coating film is formed from the aqueous emulsion composition, even if the water evaporates, the coalescent can remain in the coating film without volatilizing, thereby efficiently promoting swelling and fusion of the resin particles. This allows the minimum film-forming temperature of the aqueous emulsion composition to be sufficiently lowered. The boiling point of the compound represented by formula (1) is preferably 225°C or higher, more preferably 230°C or higher, even more preferably 240°C or higher, particularly preferably 245°C or higher, and most preferably 250°C or higher. By having the boiling point of the compound represented by formula (1) within the above range, the desired effects of the present invention can be more effectively achieved. Furthermore, the boiling point of the compound represented by formula (1) is preferably 400°C or lower, more preferably 380°C or lower, even more preferably 350°C or lower, and particularly preferably 330°C or lower. When the boiling point of the compound represented by formula (1) is within the above range, the film-forming aid volatilizes after the fusion of the resin particles is completed, and the influence on the inherent properties of the coating material (e.g., hardness, smoothness, etc.) can be minimized.

[0032] Examples of the compound represented by the formula (1) include ethylene glycol dialkyl ethers such as ethylene glycol diisopropyl ether, ethylene glycol ethyl ether mono-tert-butyl ether, ethylene glycol mono-n-propyl ether mono-tert-butyl ether, ethylene glycol monoisopropyl ether mono-tert-butyl ether, and ethylene glycol di-tert-butyl ether; diethylene glycol dialkyl ethers such as diethylene glycol diisopropyl ether, diethylene glycol ethyl ether mono-tert-butyl ether, diethylene glycol mono-n-propyl ether mono-tert-butyl ether, diethylene glycol monoisopropyl ether mono-tert-butyl ether, and diethylene glycol di-tert-butyl ether; triethylene glycol diisopropyl ether, triethylene glycol monomethyl mono-tert-butyl ether, triethylene glycol monoethyl ether mono-tert-butyl ether, triethylene glycol mono-n-propyl ether mono-tert-butyl ether, and triethylene glycol mono-n-propyl ether mono-tert-butyl ether. Examples of the alkyl ethers include triethylene glycol dialkyl ethers such as propylene glycol diisopropyl ether, propylene glycol ethyl ether mono-tert-butyl ether, propylene glycol mono-n-propyl ether mono-tert-butyl ether, propylene glycol monoisopropyl ether mono-tert-butyl ether, and triethylene glycol di-tert-butyl ether; propylene glycol dialkyl ethers such as propylene glycol diisopropyl ether, propylene glycol ethyl ether mono-tert-butyl ether, propylene glycol mono-n-propyl ether mono-tert-butyl ether, propylene glycol monoisopropyl ether mono-tert-butyl ether, and propylene glycol di-tert-butyl ether; and dipropylene glycol dialkyl ethers such as dipropylene glycol diisopropyl ether, dipropylene glycol ethyl ether mono-tert-butyl ether, dipropylene glycol mono-n-propyl ether mono-tert-butyl ether, dipropylene glycol monoisopropyl ether mono-tert-butyl ether, and dipropylene glycol di-tert-butyl ether. These alkyl ethers may be used alone or in combination of two or more.

[0033] The method for producing the compound represented by the above formula (1) is not particularly limited. For example, 1 -OH(R 1 is R in the above formula (1) 1 (same meaning as R) to form an alkylene oxide. 1 -(CH2-CH(R 3 )-O) n -H(R 1 and R 3 are the R in the above formula (1), 1 and R 3 After obtaining an alkylene glycol monoalkyl ether represented by the formula (same meaning as above), an alkyl group is introduced at the end of the alkylene glycol monoalkyl ether to form R 1 -(CH2-CH(R 3 )-O) n -R 2 (R 1 ~R 3 are the R in the above formula (1), 1 ~R 3 Examples of the method include a method for obtaining an alkylene glycol dialkyl ether represented by the following formula (same meaning):

[0034] Specifically, an alkylene oxide is added to an alcohol in the presence of a catalyst. In this case, by using an alkylene oxide such as ethylene oxide, propylene oxide, or butylene oxide as the alkylene oxide, an alkylene glycol monoalkyl ether in which an oxyalkylene group is introduced into the alcohol can be obtained. For example, by using propylene oxide or the like in addition to ethylene oxide as the alkylene oxide to be added, an alkylene glycol monoalkyl ether in which an oxyalkylene group is introduced into the alcohol can be obtained. 1 Multiple oxyalkylene groups can be introduced to the -OH. When two or more types of alkylene oxides are added, either random addition or block addition may be used. In the above method, the crude product after the reaction may be purified using a purification means such as distillation.

[0035] Next, the alkylene glycol monoalkyl ether obtained by the above method and an alkene can be used to obtain an alkylene glycol dialkyl ether by a known method (for example, the method described in Chinese Patent Application Publication No. 106928032).

[0036] <Water-based emulsion composition> The present invention also provides an aqueous emulsion composition comprising the above-mentioned coalescent, a resin, and an aqueous medium. The aqueous emulsion composition has a sufficiently low minimum film-forming temperature and can form a coating film with good hardness and smoothness.

[0037] In the aqueous emulsion composition of the present invention, the content of the coalescing aid is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, even more preferably 0.1 parts by mass or more, and particularly preferably 0.2 parts by mass or more, per 100 parts by mass of the resin. When the content is equal to or greater than the above-mentioned lower limit, the minimum film-forming temperature can be sufficiently lowered, and a desirable effect of improving film-forming properties can be obtained. Furthermore, in the aqueous emulsion composition of the present invention, the content of the coalescing aid is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, even more preferably 15 parts by mass or less, even more preferably 10 parts by mass or less, particularly preferably 7 parts by mass or less, and most preferably 5 parts by mass or less, per 100 parts by mass of the resin. When the content is equal to or less than the above-mentioned upper limit, the minimum film-forming temperature of the aqueous emulsion composition can be sufficiently lowered, and adverse effects on the hardness and smoothness of the coating film formed can be minimized.

[0038] [resin] The resin used in the aqueous emulsion composition of the present invention is not particularly limited, and examples thereof include acrylic resin, acrylic-styrene resin, vinyl acetate resin, polyvinyl alcohol resin, vinyl acetate acrylic resin, vinyl acetate VEOVA resin, ethylene vinyl acetate resin, synthetic rubber latex, urethane resin, epoxy resin, phenol resin, alkyd resin, polyester resin, vinyl chloride resin, and vinylidene chloride resin. These may be used alone or in combination of two or more. As the resin, for example, acrylic resin or acrylic-styrene resin is preferred.

[0039] Acrylic resins are resins obtained by polymerizing (meth)acrylic monomers. Examples of (meth)acrylic monomers include (meth)acrylic acid; (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate; 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 2-hydroxycyclohexyl (meth)acrylate. (meth)acrylic acid hydroxyalkyl esters such as hydroxydecyl (meth)acrylate; (poly)oxyethylene (meth)acrylates such as ethylene glycol (meth)acrylate, diethylene glycol (meth)acrylate, propylene glycol (meth)acrylate, and dipropylene glycol (meth)acrylate; (meth)acrylamides such as (meth)acrylamide, N-methylol (meth)acrylamide, N-butoxymethyl (meth)acrylamide, and diacetone acrylamide; and epoxy group-containing (meth)acrylates such as glycidyl (meth)acrylate. These may be used alone or in combination of two or more.

[0040] Acrylic styrene resins are resins obtained by polymerizing (meth)acrylic monomers and styrene monomers. Examples of (meth)acrylic monomers are as described above. Examples of styrene monomers include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-phenylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-tert-butylstyrene, pn-hexylstyrene, pn-octylstyrene, pn-nonylstyrene, pn-decylstyrene, and pn-dodecylstyrene. These may be used alone or in combination of two or more.

[0041] The glass transition temperature of the resin used in the aqueous emulsion composition of the present invention is not particularly limited, but is, for example, 10 to 35°C.

[0042] The content of the resin in the aqueous emulsion composition of the present invention is not particularly limited, but is, for example, 30 to 80 mass %. The resin may be blended in the aqueous emulsion composition as a resin emulsion, for example.

[0043] [Aqueous medium] In this specification, the aqueous medium refers to a medium containing water as a main component (preferably containing 50% by mass or more), and may further contain components other than water. Examples of components other than water include organic solvents that dissolve in water, such as methanol, ethanol, isopropanol, ethylene glycol, diethylene glycol, propylene glycol, and dipropylene glycol. Preferably, only water is used as the aqueous medium.

[0044] [Optional ingredients] In addition to the film-forming aid, resin, and aqueous medium, the aqueous emulsion composition of the present invention may further contain known additives to the extent that the effects of the present invention are not impaired. Examples of additives include pigments, plasticizers, dispersants, thickeners, antifoaming agents, preservatives, UV absorbers, and fragrances. The content of such additives is not particularly limited, but is preferably 0.1 to 30% by mass relative to the resin.

[0045] [Method for producing aqueous emulsion composition] The method for producing the aqueous emulsion composition of the present invention is not particularly limited. For example, a method may be used in which the monomer components constituting the resin are emulsion-polymerized in an aqueous medium in the presence of a polymerization initiator and an emulsifier to prepare a resin emulsion, followed by the addition of additives such as a film-forming aid. Examples of emulsion polymerization include (1) a method in which the monomer components are polymerized dropwise into an emulsifier and an aqueous medium (monomer drop method); (2) a method in which the raw materials (monomer components, emulsifier, and aqueous medium) are mixed together and polymerized all at once (monomer bulk charge method); and (3) a method in which a seed emulsion is produced by prepolymerizing a portion of the raw materials (one or more of the monomer components, an emulsifier, an aqueous medium, and a polymerization initiator), followed by adding the remaining raw materials to the seed emulsion and carrying out emulsion polymerization (seed emulsion method). Among these, method (3) is preferred as a method for obtaining emulsions with good particle size control and polymerization stability. In the above method, the emulsifier and polymerization initiator may be any known emulsifier and polymerization initiator that is commonly used in emulsion polymerization.

[0046] [Uses of aqueous emulsion compositions] The aqueous emulsion composition of the present invention has a sufficiently low minimum film-forming temperature and can form a coating film with good hardness and smoothness, and therefore can be suitably used as a coating material. The aqueous emulsion composition of the present invention may also be used as a pressure-sensitive adhesive, adhesive, etc. [Example]

[0047] The present invention will be described in more detail using the following examples and comparative examples, although the technical scope of the present invention is not limited to the following examples.

[0048] <Synthesis of film-forming agents> [Synthesis Example 1-1] Synthesis of triethylene glycol mono-n-butyl ether mono-tert-butyl ether (BTG-tBu) (1) Synthesis of triethylene glycol mono-n-butyl ether A 3000 mL autoclave equipped with a stirrer and temperature controller was charged with 700 parts by mass of n-butanol (Tokyo Chemical Industry Co., Ltd.) and 0.7 parts by mass of caustic potash (Fujifilm Wako Pure Chemical Industries, Ltd.) (0.1% by mass relative to n-butanol). The pressure in the vessel was purged with nitrogen (0.1 MPa ⇔ 0.5 MPa) five times to remove air from the vessel. Then, 1247 parts by mass of ethylene oxide (Nippon Shokubai Co., Ltd.) (3.0 mol relative to n-butanol) was intermittently introduced into the autoclave at 120-140°C over a period of 3 hours, and the reaction was continued at 140°C for 1 hour. The reaction was then continued for 2 hours at a reaction temperature of 135-145°C. After completion of the reaction, the temperature was lowered to room temperature, yielding the crude product (triethylene glycol mono-n-butyl ether).

[0049] Next, the obtained crude product (triethylene glycol mono-n-butyl ether) was charged into a glass flask equipped with a packed column, a thermometer, and a condenser, and purification was carried out under the following distillation conditions. Specifically, the distillation temperature and pressure were set to 110-120°C and 170-200 mmHg, and an initial distillate was obtained. Next, the distillation temperature and pressure were set to 130-140°C and 20-40 mmHg, and a fraction containing triethylene glycol mono-n-butyl ether was obtained. The purity of the triethylene glycol mono-n-butyl ether obtained by distillation was confirmed (99% or higher) by gas chromatography (GC).

[0050] ≪GC conditions≫ The gas chromatography conditions were as follows: Equipment: Shimadzu Gas Chromatograph GC-2025 Detector: Hydrogen ionization detector (FID) Sample introduction amount: Split injection method Column: ZB-1 (length: 30 m, inner diameter: 0.32 mm, film thickness: 0.25 μm) Injection volume: 0.2μl Linear speed: 30cm / sec Carrier gas: Helium Temperature increase conditions: increase temperature from 100°C to 340°C at 20°C / min, and hold at 340°C for 1 minute.

[0051] (2) Synthesis of BTG-tBu BTG-tBu was synthesized using triethylene glycol mono-n-butyl ether and isobutylene as raw materials by a known method (for example, the method described in Chinese Patent Application Publication No. 106928032). The resulting BTG-tBu was confirmed to have a purity of 95% or higher by gas chromatography (GC) (GC conditions described above). The boiling point of BTG-tBu was 270°C.

[0052] [Synthesis Example 1-2] Synthesis of triethylene glycol monomethyl ether mono-tert-butyl ether (MTG-tBu) (1) Synthesis of triethylene glycol monomethyl ether Triethylene glycol monomethyl ether was synthesized in the same manner as in [Synthesis Example 1-1](1) above, except that n-butanol was changed to methanol.

[0053] (2) Synthesis of MTG-tBu MTG-tBu was synthesized in the same manner as in [Synthesis Example 1-1](2) above, except that triethylene glycol mono-n-butyl ether was replaced with triethylene glycol monomethyl ether. The resulting MTG-tBu was confirmed to have a purity of 95% or higher by gas chromatography (GC) under the above-mentioned GC conditions. The boiling point of MTG-tBu was 254°C.

[0054] <Synthesis of resin emulsion> [Synthesis Example 2-1] Synthesis of acrylic resin emulsion (resin emulsion A) A 300 ml Erlenmeyer flask was charged with 49.5 parts by mass of butyl acrylate (Fujifilm Wako Pure Chemical Corporation, special grade reagent), 49.5 parts by mass of methyl methacrylate (Fujifilm Wako Pure Chemical Corporation, special grade reagent), and 1 part by mass of acrylic acid (Fujifilm Wako Pure Chemical Corporation, special grade reagent), and mixed. A separate 500 ml Erlenmeyer flask was charged with 43.4 parts by mass of deionized water and 6.6 parts by mass of Newcol 707-SF (Nippon Nyukazai Co., Ltd., polyoxyethylene polycyclic phenyl ether sulfate ester ammonium salt, 30% pure content) as an emulsifier, and mixed with a stirrer. The monomer mixture from earlier was added to the flask in five separate portions. After thorough mixing, 10% by mass of ammonium persulfate (Fujifilm Wako Pure Chemical Corporation, A pre-emulsion was prepared by adding 5 parts by mass of an aqueous solution of (special grade reagent). A four-neck flask equipped with a stirrer, thermometer, nitrogen inlet, reflux condenser, and dropping funnel was charged with 50 parts by mass of deionized water and 5.58 parts by mass (5% of the prepared pre-emulsion), and the temperature was raised to 80°C. The temperature was maintained at 80°C for 30 minutes to allow for initial polymerization. After initial polymerization, the remaining pre-emulsion was added dropwise over 3 hours to allow for polymerization. The mixture was then aged at 80°C for 1 hour and then cooled to room temperature. The pH was adjusted to 8.0 with a 25% by mass aqueous ammonia solution to obtain Resin Emulsion A (butyl acrylate / methyl methacrylate / acrylic acid = 49.5 / 49.5 / 1 (mass ratio)) with a solids content of 49.4% by mass.

[0055] [Synthesis Example 2-2] Synthesis of acrylic styrene resin emulsion (resin emulsion B) A 300 ml Erlenmeyer flask was charged with 40 parts by mass of butyl acrylate (Fujifilm Wako Pure Chemical Corporation, special grade reagent), 30 parts by mass of methyl methacrylate (Fujifilm Wako Pure Chemical Corporation, special grade reagent), 30 parts by mass of styrene (Fujifilm Wako Pure Chemical Corporation, special grade reagent), and 2 parts by mass of acrylic acid (Fujifilm Wako Pure Chemical Corporation, special grade reagent). A separate 500 ml Erlenmeyer flask was charged with 45.4 parts by mass of deionized water and 4.1 parts by mass of Newcol CMP-11-SN (Nippon Nyukazai Co., Ltd., polyoxyethylene cumylphenol ether sulfonate ester sodium salt, 50% pure content) as an emulsifier, and mixed with a stirrer. The monomer mixture from earlier was added to the flask in five separate portions. After thorough mixing, 5.1 parts by mass of a 10% by mass aqueous solution of ammonium persulfate (Fujifilm Wako Pure Chemical Corporation, special grade reagent) was added to prepare a pre-emulsion. A four-neck flask equipped with a stirrer, thermometer, nitrogen inlet tube, reflux condenser, and dropping funnel was charged with 50 parts by mass of deionized water and 7.83 parts by mass (5% of the prepared pre-emulsion), and the temperature was raised to 80°C. The temperature was maintained at 80°C for 30 minutes to allow for initial polymerization. After initial polymerization, the remaining pre-emulsion was added dropwise over 3 hours to allow for polymerization. The mixture was then aged at 80°C for 1 hour and then cooled to room temperature. The pH was adjusted to 8.0 with a 25% by mass aqueous ammonia solution to obtain Resin Emulsion B (butyl acrylate / methyl methacrylate / styrene / acrylic acid = 40 / 30 / 30 / 2 (mass ratio)) with a solids content of 50.7% by mass.

[0056] <Preparation of Water-Based Emulsion Composition> [Water-based emulsion composition of acrylic resin] To Resin Emulsion A synthesized in Synthesis Example 2-1 above, the compound obtained in Synthesis Example 1-1 or 1-2 above or the comparative compound shown below was added as a film-forming aid in an amount of 5, 10 or 20 parts by mass per 100 parts by mass of the resin of the resin emulsion, and the mixture was mixed and stirred at 25°C for 180 minutes, and then allowed to stand for 24 hours to prepare an aqueous emulsion composition.

[0057] [Water-based emulsion composition of acrylic styrene resin] To Resin Emulsion B synthesized in Synthesis Example 2-2 above, the compound obtained in Synthesis Example 1-1 or 1-2 above or the comparative compound shown below was added as a film-forming aid in an amount of 1, 2.5, 5, or 10 parts by mass per 100 parts by mass of the resin in the resin emulsion, and the mixture was mixed and stirred at 25°C for 180 minutes, and then allowed to stand for 24 hours to prepare an aqueous emulsion composition.

[0058] [Comparative compounds] DBDG (Diethylene glycol di-n-butyl ether, boiling point 255°C, manufactured by Nippon Nyukazai Co., Ltd.) TX-IB (2,2,4-trimethyl-1,3-pentanediol diisobutyrate, boiling point 282°C, manufactured by Eastman Chemical Co.) Texanol (2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, boiling point 240°C, manufactured by Eastman Chemical Co.).

[0059] <Evaluation of Water-Based Emulsion Compositions> The film-forming properties and coating physical properties of the aqueous emulsion compositions were evaluated. Table 1 shows the minimum film-forming temperature and hardness results for aqueous emulsion compositions using acrylic resin, and Table 2 shows the minimum film-forming temperature and hardness results for aqueous emulsion compositions using acrylic styrene resin. Table 3 shows the results for smoothness for aqueous emulsion compositions using acrylic resin. In Tables 1 to 3, the "content (parts by mass)" of the coalescing agent indicates the amount of coalescing agent added per 100 parts by mass of resin in the aqueous emulsion composition. In Tables 1 to 3, the notation "-" next to a coalescing agent means that the agent was not added, and the notation "-" next to a coating physical property means that the agent was not measured.

[0060] Graphs plotting the relationship between the amount of each coalescent added and the minimum film-forming temperature for the aqueous emulsion compositions are shown in Figures 1 and 2 (Figure 1: Aqueous emulsion composition of acrylic resin, Figure 2: Aqueous emulsion composition of acrylic styrene resin). For the evaluation of smoothness, the coating surface used for the gloss evaluation was photographed with a digital camera (at 1x magnification) and the results are shown in Figure 3 (Figure 3 (a) Example 1, (b) Example 4, (c) Comparative Example 4, (d) Comparative Example 10).

[0061] [Film forming property (minimum film forming temperature)] The aqueous emulsion composition prepared above was measured using a minimum film-forming temperature measuring instrument (manufactured by Tester Sangyo Co., Ltd.). The minimum film-forming temperature (MFT) was measured under the conditions of a measurement temperature range of 0°C to 50°C, a coating film thickness of 0.2 mm, and a drying time of 1 hour.

[0062] [Coating film properties] The hardness and smoothness of the coating film of the aqueous emulsion composition prepared above were evaluated by the following methods.

[0063] (hardness) The aqueous emulsion composition prepared above was applied to a glass plate using an applicator to a wet film thickness of 75 μm, and then dried (110°C x 3 minutes, then room temperature x 24 hours) to obtain a coating film. The obtained coating film was measured using a pendulum hardness tester (Cotec Co., Ltd., SP0500) starting from a pendulum angle of 6° and counting the number of swings until the pendulum angle reached 3° or less. If the dried coating film does not reach the required hardness, it is said to have insufficient hardness, which can cause problems such as the coating film surface being easily scratched.

[0064] (smoothness) The smoothness was evaluated by visually inspecting the coating film formed from the aqueous emulsion composition and by measuring the gloss.

[0065] The aqueous emulsion composition prepared above was applied to a glass plate using an applicator to a wet film thickness of 75 μm, and then dried (0°C x 24 hours) to obtain a coating film. The gloss of the coating film (incident angle: 60°, 20°) was measured using a gloss meter (GROSS METER IG-331 manufactured by HORIBA, Ltd.). The gloss represents the degree of regular reflection of light hitting the surface and indicates the smoothness of the coating film surface. The higher the gloss, the flatter the coating film surface.

[0066] [Table 1]

[0067] [Table 2]

[0068] [Table 3]

[0069] [Film forming property] As shown in Table 1, in the acrylic resin emulsion system, the compositions of Examples 1 to 6, which contained the film-forming aid of the present invention, had significantly lower MFTs than the compositions of Comparative Examples 1 to 9, which contained a film-forming aid (comparative compound) outside the scope of the present invention, and the composition of Comparative Example 10, which did not contain any film-forming aid.

[0070] Furthermore, as shown in Table 2, in the acrylic styrene resin emulsion system, the compositions of Examples 7 to 14, to which the film-forming aid of the present invention was added, had significantly lower MFTs than the compositions of Comparative Examples 11 to 14, to which a film-forming aid (comparative compound) outside the scope of the present invention was added, and the composition of Comparative Example 15, to which no film-forming aid was added.

[0071] These results demonstrate that the film-forming aid of the present invention, even when added in a small amount, can sufficiently lower the minimum film-forming temperature of the aqueous emulsion composition and improve film-forming properties.

[0072] [Coating film properties] The hardness and smoothness of the coating film formed were checked for the aqueous emulsion compositions containing the film-forming aid in an amount that showed the effect of lowering the minimum film-forming temperature in the above [Film-forming properties].

[0073] As shown in Tables 1 and 2, the coating films formed from compositions containing the film-forming aids of the present invention in Examples 1 to 14 were found to exhibit superior results in terms of hardness when compared with coating films formed from compositions containing film-forming aids outside the scope of the present invention, depending on the amount of film-forming aid added.

[0074] As shown in Table 3, the coating films formed from the compositions containing the coalescing aid of the present invention in Examples 1 and 4 exhibited higher gloss and better smoothness than the coating films formed from the compositions of Comparative Examples 1 and 10. Furthermore, as shown in Figure 3, the coating films formed from the compositions containing the coalescing aid of the present invention in Examples 1 and 4 had significantly fewer white thread-like spots and were superior in smoothness than the coating films formed from the compositions of Comparative Examples 1 and 10.

[0075] As shown in Figures 1 and 2, the coalescence aid of the present invention is highly effective in reducing the minimum film-forming temperature even when added in small amounts. Therefore, when comparing compositions containing the coalescence aid of the present invention at various addition amounts with compositions containing coalescence aids outside the scope of the present invention, it is clear that the composition containing the coalescence aid of the present invention has a lower minimum film-forming temperature. In other words, when attempting to achieve a certain minimum film-forming temperature, the use of the coalescence aid of the present invention allows for a significantly reduced amount of addition compared to the use of a coalescence aid outside the scope of the present invention. Thus, as the amount of coalescence aid added decreases, the effects of adding the coalescence aid on the coating film (e.g., hardness and smoothness) can also be reduced.

[0076] From the above results, it was confirmed that the coalescence aid of the present invention can sufficiently lower the minimum film-forming temperature while suppressing adverse effects on the hardness and smoothness of the coating film formed. Furthermore, the coalescence aid of the present invention can sufficiently lower the minimum film-forming temperature even when added in small amounts, thereby providing an aqueous emulsion composition in which adverse effects on the hardness and smoothness of the coating film formed are suppressed.

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