JP7665973B2 - Hydrophilizing agents for elastomers - Google Patents

Description

The present invention relates to a hydrophilizing agent, and in particular to a hydrophilizing agent that has the effect of imparting hydrophilicity to elastomers and has excellent heat resistance and stability of hydrophilicity over time.

Elastomers have excellent heat resistance, abrasion resistance, and elasticity, and are therefore used in a wide range of applications, including everyday items, construction and civil engineering materials, electrical appliance parts, and automobile parts. It is common for elastomers to be modified to meet the required characteristics for each application.

One of the modifications of elastomers is hydrophilization treatment. By hydrophilizing an elastomer, it is possible to modify the surface and interior of the elastomer. The effects of surface modification include improved wettability, improved adhesion, anti-fogging properties, and anti-soiling properties. The effects of internal modification include improved dispersibility of pigments. For example, Patent Document 1 discloses a composition in which a pigment is dispersed inside an elastomer.

One method of hydrophilization is treatment by plasma irradiation or ultraviolet irradiation. Patent Document 2 discloses a method of hydrophilizing the surface of an ethylene propylene elastomer by irradiating it with plasma or ultraviolet light.

Another known method of hydrophilization is to add a hydrophilizing agent to an elastomer. Patent Document 3 discloses that adding a polyethylene glycol ester as a hydrophilizing agent to an acrylonitrile butadiene elastomer results in a rubber composition with excellent hydrophilicity and stain resistance. Patent Document 4 discloses a hydrophilizing agent that is an ester of an alkylene oxide adduct and a monocarboxylic acid having 1 to 24 carbon atoms.

JP 2010-043401 A JP 2013-123975 A JP 2018-53160 A JP 2017-171815 A

The hydrophilization method using plasma or ultraviolet light disclosed in Patent Document 2 requires an irradiation device in the manufacturing facility, and is not suitable for use on large products or products with complex shapes.

On the other hand, in the hydrophilization method using a hydrophilizing agent, if the hydrophilizing agent has low heat resistance, the hydrophilizing agent may decompose and lose its function when a manufacturing process of a product using an elastomer includes a step in which heating is performed (e.g., a vulcanization step or a melt-kneading step). The hydrophilizing agent disclosed in Patent Document 4 has a problem in that it is easily thermally decomposed under high temperature conditions.
The hydrophilizing agent described in Patent Document 3 can be said to have heat resistance in that it exhibits hydrophilicity even after a vulcanization process. However, Patent Document 3 does not consider changes in properties such as a decrease in hydrophilicity over time. Therefore, there is a problem with the stability of the effect of the hydrophilizing agent over time.
Moreover, in neither Patent Document 3 nor Patent Document 4 was evaluation carried out from the viewpoint of dispersibility of the dye.

The present invention aims to provide a hydrophilizing agent that has excellent heat resistance, is effective in imparting hydrophilicity to elastomers, and also has excellent stability over time and pigment dispersibility.

As a result of intensive investigations, the present inventors have found that the above-mentioned problems can be solved by using a polymer having a specific structure as a hydrophilizing agent. That is, the present invention provides the following items <1> to <6>.
<1> A hydrophilizing agent comprising a copolymer obtained by polymerizing a monomer component containing an epoxy group-containing monomer (A1) and a (meth)acrylic acid alkyl ester (A2) represented by the following general formula (1), in which the proportion of the epoxy group-containing monomer (A1) is 10 to 95 mol % and the proportion of the (meth)acrylic acid alkyl ester (A2) is 5 to 90 mol % in the monomer component:

(In formula (1), R1 represents a hydrogen atom or a methyl group, and R2 represents an alkyl group having 9 to 22 carbon atoms.)
<2> The hydrophilizing agent according to <1>, wherein the epoxy group-containing monomer (A1) is glycidyl (meth)acrylate.
<3> The hydrophilizing agent according to <1> or <2>, wherein the monomer component further contains a hydroxyl group-containing monomer (A3).
<4> The hydrophilizing agent according to <3>, wherein the proportion of the hydroxyl group-containing monomer (A3) is 60 mol % or less.
<5> The hydrophilizing agent according to <3> or <4>, in which the hydroxyl group-containing monomer (A3) is glycerin mono(meth)acrylate or 2-hydroxyethyl (meth)acrylate.
<6> The hydrophilizing agent according to any one of <1> to <5>, wherein the copolymer has a weight average molecular weight in terms of polystyrene of 3,000 to 50,000.

By using the hydrophilizing agent of the present invention, it is possible to obtain a hydrophilizing agent that has high heat resistance and can impart hydrophilicity to an elastomer. Furthermore, by using the hydrophilizing agent of the present invention, it is possible to obtain an elastomer composition that has even better stability of hydrophilicity over time and high dispersibility of pigments.

The hydrophilizing agent of the present invention will be described in detail below. In this specification, the numerical range "AA-BB" means "AA or more and BB or less."

[Hydrophilic Agent (Copolymer P)]
The hydrophilizing agent of the present invention is obtained by polymerizing a monomer component containing an epoxy group-containing monomer (A1) and a (meth)acrylic acid alkyl ester (A2) represented by the following general formula (1), and contains a copolymer in which the proportion of the epoxy group-containing monomer (A1) in the monomer component is 10 to 95 mol %, and the proportion of the (meth)acrylic acid alkyl ester (A2) is 5 to 90 mol %:

(In general formula (1), R1 represents a hydrogen atom or a methyl group, and R2 represents an alkyl group having 9 to 22 carbon atoms.)
In the present invention, the term "(meth)acrylate" is a general term including acrylate and methacrylate.

The copolymer (P) in the present invention may be composed only of structural units derived from the epoxy group-containing monomer (A1) and the (meth)acrylic acid alkyl ester (A2). Alternatively, in addition to the structural units derived from these monomers, it may also contain structural units derived from other monomers.

The copolymer (P) may be in any form, such as a random copolymer, a block copolymer, or an alternating copolymer. A random copolymer is particularly preferred.

The hydrophilizing agent of the present invention may contain other components in addition to the copolymer (P). The content of the copolymer (P) in the hydrophilizing agent of the present invention is preferably 70 to 100% by mass, and more preferably 80 to 100% by mass.

<Epoxy Group-Containing Monomer (A1)>
The copolymer (P) contains a structural unit derived from the epoxy group-containing monomer (A1). By containing the epoxy group-containing monomer as a monomer component, the copolymer (P) can be imparted with hydrophilicity to the elastomer.

It is preferable that the epoxy group-containing monomer (A1) has a functional group that can be polymerized with the (meth)acrylic acid alkyl ester (A2). Examples of such functional groups include an acrylic group, a methacrylic group, and a vinyl group. In the present invention, it is particularly preferable that the epoxy group-containing monomer (A1) has an acrylic group or a methacrylic group.

The epoxy group-containing monomer (A1) is preferably a monomer having a molecular weight of 50 to 500, preferably 100 to 300. By using a monomer with the above molecular weight, it is possible to impart hydrophilicity to the elastomer.

Examples of the epoxy group-containing monomer (A1) include glycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate glycidyl ether, etc. In view of the effect of imparting hydrophilicity to the elastomer and ease of availability, the epoxy group-containing monomer (A1) is preferably glycidyl (meth)acrylate or 3,4-epoxycyclohexylmethyl (meth)acrylate, and more preferably glycidyl (meth)acrylate.
The epoxy group-containing monomer (A1) may be used alone or in combination of two or more. When two or more types are used in combination, (meth)acrylates having different main chains may be combined, or a methacrylate and an acrylate having the same main chain may be combined.

The ratio of the epoxy group-containing monomer (A1) in the monomer components of the copolymer (P) (the content ratio of the epoxy group-containing monomer (A1) to the total monomers) is 10 to 95 mol%. If the content ratio of the epoxy group-containing monomer (A1) is less than 10 mol%, the hydrophilicity and pigment dispersibility of the elastomer are reduced. On the other hand, if the content ratio of the epoxy group-containing monomer (A1) exceeds 95 mol%, it becomes difficult to express hydrophilicity and the stability over time is reduced. From the viewpoint of imparting appropriate hydrophilicity to the elastomer, the content ratio of the epoxy group-containing monomer (A1) is preferably 15 to 50 mol%, and more preferably 20 to 40 mol%.

<(Meth)acrylic acid alkyl ester (A2)>
The copolymer (P) contains a structural unit derived from the (meth)acrylic acid alkyl ester (A2). When the copolymer (P) contains the (meth)acrylic acid alkyl ester (A2) as a monomer component, the stability over time of the hydrophilizing agent and the dispersibility of the dye can be improved.
The (meth)acrylic acid alkyl ester (A2) in the present invention is represented by the following general formula (1).

In the general formula (1), R1 is a hydrogen atom or a methyl group. From the viewpoint of polymerizability, a methyl group is preferable.
R2 is an alkyl group having 9 to 22 carbon atoms. Examples of the alkyl group having 9 to 22 carbon atoms include a nonyl group, a decyl group, a dodecyl group, a lauryl group, and a stearyl group. From the viewpoint of imparting hydrophilicity to the elastomer, the number of carbon atoms in the alkyl group constituting R2 is preferably 12 to 22. Furthermore, from the viewpoint of the heat resistance and stability over time of the hydrophilizing agent, the number of carbon atoms in the alkyl group constituting R2 is more preferably 16 to 18, and particularly preferably 18.
R2 may be a branched alkyl group or a linear alkyl group, but is particularly preferably a linear alkyl group. When R2 is a branched alkyl group, it is preferable that the main chain portion of R2 has 9 or more carbon atoms.

Examples of the (meth)acrylic acid alkyl ester (A2) applicable to the present invention include stearyl (meth)acrylate, lauryl (meth)acrylate, and behenyl (meth)acrylate. Among these, stearyl (meth)acrylate is preferred, and stearyl methacrylate is particularly preferred.

The (meth)acrylic acid alkyl ester (A2) may be used alone or in combination of two or more types.

The proportion of the (meth)acrylic acid alkyl ester (A2) in the monomer components of the copolymer (P) (the content of the (meth)acrylic acid alkyl ester (A2) relative to the total monomers) is 5 to 90 mol%. If the content of the (meth)acrylic acid alkyl ester (A2) is less than 5 mol%, it is difficult to impart hydrophilicity, heat resistance, and stability over time to the elastomer. On the other hand, if the content of the (meth)acrylic acid alkyl ester (A2) is more than 90 mol%, the pigment dispersibility and hardness of the elastomer may decrease. In consideration of hydrophilicity, heat resistance, stability over time, and pigment dispersibility, the content of the (meth)acrylic acid alkyl ester (A2) is more preferably 7 to 50 mol%, and even more preferably 10 to 30 mol%.

The ratio of the content of the (meth)acrylic acid alkyl ester (A2) to the total content of the epoxy group-containing monomer (A1) and the (meth)acrylic acid alkyl ester (A2) is preferably 0.30 to 0.70, more preferably 0.30 to 0.65, and particularly preferably 0.30 to 0.60. By increasing the content of the (meth)acrylic acid alkyl ester (A2) within the above range, it is possible to obtain a copolymer (P) that can be made into an elastomer with good hydrophilicity, heat resistance, stability over time, and pigment dispersion.

<Hydroxyl Group-Containing Monomer (A3)>
The copolymer (P) may further contain a structural unit derived from a hydroxyl group-containing monomer (A3). By containing the hydroxyl group-containing monomer (A3) as a monomer component in the copolymer (P), the hydrophilicity and pigment dispersibility of the elastomer can be further improved, and the elastomer can have an appropriate hardness.

The hydroxyl group-containing monomer (A3) preferably has a functional group polymerizable with the (meth)acrylic acid alkyl ester (A2). Examples of such functional groups include an acrylic group, a methacrylic group, and a vinyl group. In the present invention, it is particularly preferable that the hydroxyl group-containing monomer (A3) has an acrylic group or a methacrylic group.

The hydroxyl group-containing monomer (A3) is preferably a monomer having a molecular weight of 50 to 1000, preferably 100 to 300. By using a monomer with the above molecular weight, it is possible to impart appropriate hydrophilicity, pigment dispersibility, and hardness to the elastomer.

Examples of the hydroxyl group-containing monomer (A3) include glycerin mono(meth)acrylate, 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, hydroxyphenyl (meth)acrylate, etc. From the viewpoints of compatibility with elastomers and hydrophilicity-imparting effect, glycerin mono(meth)acrylate and 2-hydroxyethyl (meth)acrylate are preferred, 2-hydroxyethyl (meth)acrylate is more preferred, and 2-hydroxyethyl (meth)acrylate is particularly preferred.

In the monomer components of the copolymer (P), the proportion of the hydroxyl group-containing monomer (A3) (the content ratio of the hydroxyl group-containing monomer (A3) to the total monomers) is preferably 60 mol% or less. By making the proportion of the hydroxyl group-containing monomer (A3) 60 mol% or less, an elastomer having good hydrophilicity, pigment dispersibility, and hardness can be obtained. The proportion of the hydroxyl group-containing monomer (A3) is more preferably 55 mol% or less, and even more preferably 50 mol% or less. From the viewpoint of obtaining the above-mentioned effects of the hydroxyl group-containing monomer (A3), the proportion of the hydroxyl group-containing monomer (A3) is preferably 20 mol% or more, and more preferably 30 mol% or more.

The ratio (molar ratio) of the content of the hydroxyl-containing monomer (A3) to the total content of the epoxy-containing monomer (A1) and the hydroxyl-containing monomer (A3) is preferably 0.30 to 0.80, more preferably 0.40 to 0.70. The ratio (molar ratio) of the content of the hydroxyl-containing monomer (A3) to the total content of the (meth)acrylic acid alkyl ester (A2) and the hydroxyl-containing monomer (A3) is preferably 0.40 to 0.80, more preferably 0.50 to 0.70. By setting the ratio within the above range, it is possible to obtain a copolymer (P) that can be made into an elastomer having good hydrophilicity, pigment dispersibility, and hardness.

<Other Monomers>
The copolymer (P) may contain, in addition to the structural units derived from the above (A1) to (A3), structural units derived from monomers polymerizable with (A1) to (A3). By incorporating other monomer components into the copolymer (P), various physical properties of the hydrophilizing agent can be adjusted. Examples of the other monomers include alkyl (meth)acrylates having 1 to 8 carbon atoms. Examples of the alkyl groups having 1 to 8 carbon atoms include methyl groups, ethyl groups, butyl groups, and octyl groups. In this case, the ratio of other monomers in the monomer components of the copolymer (P) (the content ratio of monomers other than A1 to A3 relative to the total monomers) is preferably 30 mol% or less, more preferably 15 mol% or less, and even more preferably 10 mol% or less, from the viewpoint of obtaining the effects of the above monomer components (A1) to (A3).

<Molecular weight of copolymer (P)>
The copolymer (P) of the present invention has a weight average molecular weight (Mw) in terms of polystyrene of preferably 3,000 to 50,000, more preferably 4,000 to 30,000, and even more preferably 5,000 to 15,000. By making the Mw of the copolymer (P) 3,000 or more, it is possible to ensure stability over time when added to an elastomer. In addition, by making the Mw of the copolymer (P) 50,000 or less, it is possible to improve the compatibility between the elastomer and the copolymer (P).

The copolymer (P) of the present invention preferably has a dispersity [Mw/Mn (weight average molecular weight/number average molecular weight)] of 1.5 to 4.0, more preferably 1.5 to 2.5. By setting the dispersity of the copolymer (P) within the above range, the above-mentioned effects of the present invention can be imparted in a well-balanced manner.

The weight average molecular weight (Mw), number average molecular weight (Mn) and dispersity (Mw/Mn) of the copolymer (P) are determined by gel permeation chromatography (GPC) using polystyrene as a standard substance.

[Method for producing copolymer (P)]
Next, the method for producing the copolymer (P) of the present invention will be described.
The copolymer (P) can be obtained by radical polymerization of a monomer mixture containing at least an epoxy group-containing monomer (A1), an alkyl (meth)acrylate ester (A2), and a hydroxyl group-containing monomer (A3).
The polymerization can be carried out by a known method, such as solution polymerization, suspension polymerization, emulsion polymerization, etc. Solution polymerization or suspension polymerization is preferred in that the weight average molecular weight (Mw), number average molecular weight (Mn), and dispersity (Mw/Mn) of the copolymer (P) can be easily adjusted to within the above ranges.

As the polymerization initiator, a known one can be used. For example, organic peroxides such as 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate and azo-based polymerization initiators such as 2,2'-azobisisobutyronitrile can be used. Only one type of polymerization initiator may be used, or two or more types may be used in combination.
The amount of the polymerization initiator used can be appropriately set depending on the combination of monomers used, reaction conditions, and the like.
The polymerization initiator may be added all at once, or a part of it may be added all at once and the rest may be added dropwise, or the entire amount may be added dropwise. It is preferable to add the polymerization initiator dropwise together with the monomer mixture, since this makes it easier to control the reaction. Furthermore, it is preferable to add the polymerization initiator after the monomer mixture is added dropwise, since this can reduce the amount of residual monomers.

The polymerization solvent used in the solution polymerization can be one in which the monomer and the polymerization initiator are soluble, such as methanol, ethanol, 1-propanol, acetone, methyl ethyl ketone, and propylene glycol monomethyl ether.
The concentration of the monomer mixture relative to the polymerization solvent is preferably 10 to 60% by mass, more preferably 20 to 50% by mass. If the concentration of the monomer mixture is too low, the monomers tend to remain after the reaction, and the molecular weight of the resulting copolymer may decrease. On the other hand, if the concentration of the monomers is too high, it may become difficult to control heat generation.
When the monomer is added to the polymerization solvent, the entire amount may be added at once, or a part of the monomer may be added at once and the rest may be added dropwise, or the entire amount may be added dropwise. From the viewpoint of ease of controlling heat generation, it is preferable to add a part of the monomer at once and the rest may be added dropwise, or to add the entire amount dropwise.

The polymerization temperature can be set appropriately depending on the type of polymerization solvent, etc., but is preferably within the range of 50°C to 110°C. The polymerization time can be set depending on the type of polymerization initiator and the polymerization temperature. For example, when 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate is used as the polymerization initiator, a polymerization time of about 6 hours is appropriate when polymerization is carried out at a polymerization temperature of 90°C.

By carrying out the above polymerization reaction, copolymer (P), which is the active ingredient of the hydrophilizing agent of the present invention, is obtained. The obtained copolymer (P) may be used as it is, or it may be isolated by removing the solvent, filtering, or purifying the reaction liquid after the polymerization reaction.

[Elastomer composition]
When the copolymer (P) of the present invention is prepared into an elastomer composition, it is suitably used as a hydrophilizing agent for the elastomer.
The above-mentioned elastomers include thermosetting elastomers and thermoplastic elastomers. Examples of the thermosetting elastomers include diene-based rubbers such as natural rubber, isoprene rubber, butadiene rubber, and styrene-butadiene rubber; and non-diene rubbers such as urethane rubber, silicone rubber, and fluororubber. Examples of the thermoplastic elastomers include polystyrene-based elastomers such as polystyrene and styrene-butadiene elastomers, olefin/alkene-based elastomers such as polyethylene and ethylene-vinyl acetate elastomers, and polyvinyl chloride-based elastomers.

When the polymer (P) of the present invention is present in a thermosetting elastomer, it is preferable to mix the rubber composition before vulcanization with the copolymer (P) and then vulcanize the mixture.

The content of the copolymer (P) of the present invention in the elastomer composition is preferably 0.5 parts by mass to 30 parts by mass, more preferably 1 part by mass to 20 parts by mass, and even more preferably 2 parts by mass to 10 parts by mass, when the mass of the elastomer is 100 parts by mass. By setting the content of the copolymer within the above range, it is possible to appropriately impart hydrophilicity to the elastomer.

The elastomer composition may also contain various components that are generally added to adjust physical properties, as necessary. Examples of such components include plasticizers, crosslinking agents, softeners, tackifiers, antistatic agents, fillers, antioxidants, silane coupling agents, zinc oxide, vulcanization accelerators, vulcanizing agents, stearic acid, workability improvers, resins, waxes, oils, and solvents, which may be appropriately selected and contained within a range that does not impair the object of the present invention.

The elastomer composition can be produced by mixing the above-mentioned components and kneading them by a known method.

The present invention will now be described more specifically with reference to examples and comparative examples.
[Polymerization of copolymer (P)]
Copolymers P1 to P7 and comparative copolymers P'1 to P'3 were obtained according to the following polymerization examples. The proportions of monomer components in each copolymer are shown in Table 1. In Table 1, the proportions of monomer components are in mol %.

(Polymerization Example 1)
A 1 L separable flask (reaction vessel) equipped with a stirrer, a thermometer, a condenser, a dropping funnel and a nitrogen inlet tube was charged with 210.0 g of methyl ethyl ketone (product name: MEK, manufactured by Maruzen Petrochemical Co., Ltd.), and the atmosphere in the flask was replaced with nitrogen to create a nitrogen atmosphere. A monomer solution was prepared by mixing 50.0 g of glycidyl methacrylate (product name: Blenmer G, manufactured by NOF Corp., described as "GMA" in Table 1), 80.0 g of stearyl methacrylate (product name: Blenmer SMA, manufactured by NOF Corp., described as "SMA" in Table 1), 70.0 g of 2-hydroxyethyl methacrylate (product name: Blenmer E, manufactured by NOF Corp., described as "HEMA" in Table 1), and 40.0 g of methyl ethyl ketone. Also, a polymerization initiator solution was prepared by mixing 50.0 g of t-butyl peroxyneodecanoate (product name: Perbutyl ND, manufactured by NOF Corporation) and 50.0 g of methyl ethyl ketone.
The temperature inside the reaction vessel was raised to 75° C., and the monomer solution and the polymerization initiator solution were simultaneously dropped over two hours, respectively, and then the reaction was carried out for three hours at 75° C. After the reaction was completed, methyl ethyl ketone was distilled off to obtain a copolymer P1.

(Polymerization Example 2)
A copolymer P2 was obtained in the same manner as in Polymerization Example 1, except that the monomers were changed to 30.0 g of glycidyl methacrylate, 120.0 g of stearyl methacrylate, and 50.0 g of 2-hydroxyethyl methacrylate.

(Polymerization Example 3)
A copolymer P3 was obtained in the same manner as in Polymerization Example 1, except that the monomers were changed to 50.0 g of glycidyl methacrylate, 80.0 g of lauryl methacrylate (product name: Blenmer LMA, manufactured by NOF Corporation, referred to as "LMA" in Table 1), and 70.0 g of 2-hydroxyethyl methacrylate.

(Polymerization Example 4)
A copolymer P4 was obtained in the same manner as in Polymerization Example 1, except that the monomers were changed to 50.0 g of glycidyl methacrylate, 80.0 g of stearyl methacrylate, and 70.0 g of glycerin monomethacrylate (product name: Blenmer GLM, manufactured by NOF Corporation; referred to as "GLM" in Table 1).

(Polymerization Example 5)
Polymer P5 was obtained in the same manner as in Polymerization Example 1, except that the monomers were changed to 50.0 g of glycidyl methacrylate, 70.0 g of stearyl methacrylate, 70.0 g of 2-hydroxyethyl methacrylate, and 10.0 g of methyl methacrylate (product name: MMA monomer, manufactured by Kuraray Co., Ltd., referred to as "MMA" in Table 1).

(Polymerization Example 6)
A copolymer P6 was obtained in the same manner as in Polymerization Example 1, except that the monomers were changed to 80.0 g of glycidyl methacrylate, 50.0 g of stearyl methacrylate, and 70.0 g of 2-hydroxyethyl methacrylate.

(Polymerization Example 7)
A copolymer P7 was obtained in the same manner as in Polymerization Example 1, except that the monomers were changed to 40.0 g of glycidyl methacrylate and 160.0 g of stearyl methacrylate.

(Polymerization Example 8)
Comparative copolymer P'1 was obtained in the same manner as in Polymerization Example 1, except that the monomers were changed to 50.0 g of glycidyl methacrylate, 70.0 g of 2-hydroxyethyl methacrylate, and 80.0 g of methyl methacrylate.

(Polymerization Example 9)
Comparative copolymer P'2 was obtained in the same manner as in Polymerization Example 1, except that the monomer was changed to 200.0 g of glycidyl methacrylate.

(Polymerization Example 10)
Comparative copolymer P'3 was obtained in the same manner as in Polymerization Example 1, except that the monomer was changed to 200.0 g of 2-hydroxyethyl methacrylate.

[Measurement of weight average molecular weight and dispersity of copolymer]
The weight average molecular weight (Mw) and number average molecular weight (Mn) of copolymers P1 to P7 and P'1 to P'3 were measured by gel permeation chromatography (GPC) under the following conditions. The weight average molecular weight (Mw) and dispersity (Mw/Mn) are shown in Table 1.
Apparatus: Tosoh Corporation, HLC-8220
Column: Shodex LF-804
Standard material: polystyrene Eluent: THF (tetrahydrofuran)
Flow rate: 1.0ml/min
Column temperature: 40°C
Detector: RI (Differential Refractive Index Detector)

[Preparation of Elastomer Composition]
(Examples 1 , 3 to 6, 8, Reference Examples 1 and 2 , Comparative Examples 1 to 3)
0.5 g of each of the copolymers P1 to P7 and P'1 to P'3 was weighed out and mixed with 10 g of an olefin/alkene-based elastomer (product name: Ultrathene 685, manufactured by Tosoh Corporation) and 39.5 g of toluene to prepare toluene solutions of the elastomer compositions of Examples 1 , 3 to 6, and 8, Reference Examples 1 and 2 , and Comparative Examples 1 to 3.

(Example 8)
3.0 g of copolymer P2 was weighed out, and mixed with 10 g of ethylene propylene elastomer (product name: EP912, manufactured by JSR Corporation) and 39.5 g of toluene to prepare a toluene solution of the elastomer composition of Example 8.

(Reference example)
A polyoxyethylene alkyl ether (product name: Nonion E-202S, manufactured by NOF Corporation) was used as a hydrophilizing agent and mixed with an olefin/alkene-based elastomer and toluene in the same manner as in Example 1 to prepare a toluene solution of the elastomer composition of the Reference Example.

Table 2 shows the compounding ratios of the hydrophilizing agent and elastomer for each Example, Comparative Example, and Reference Example. The amount of each component in Table 2 is in "parts by mass."

[evaluation]
(1) Evaluation of hydrophilicity (initial hydrophilicity) Toluene solutions of the elastomer compositions of Examples 1 , 3 to 6, and 8, Reference Examples 1 and 2 , Comparative Examples 1 to 3, and Reference Example were each applied onto a glass substrate using a bar coater, and dried on a hot plate at 100° C. for 30 minutes. This resulted in the formation of a resin film having a thickness of 1 μm.
The contact angle of the obtained resin film was measured by the tangent method in accordance with JIS R3257. The hydrophilicity of the resin film was evaluated according to the following indices. The evaluation results and the contact angle are shown in Table 2.
A (very good hydrophilicity): contact angle is less than 30° B (good hydrophilicity): contact angle is 30° or more and less than 45° C (slightly poor hydrophilicity): contact angle is 45° or more and less than 75° D (poor hydrophilicity): contact angle is 75° or more

(2) Evaluation of heat resistance 10 g of each of the toluene solutions of the elastomer compositions of Examples 1 , 3 to 6, 8, Reference Examples 1 and 2 , Comparative Examples 1 to 3, and Reference Example was weighed out and dried in a vacuum drying oven at 120°C and -0.1 kPa or less for 1 hour to prepare a sample. 10 mg of the obtained sample was placed in an aluminum pan and heated to 300°C at a rate of 10°C/min in an air atmosphere using a thermogravimetric analyzer (STA7200, Hitachi High-EcScience Co., Ltd.), and the thermal weight loss rate was measured.
The heat resistance of the copolymer (hydrophilizing agent) was evaluated using the temperature (Td5) at which the thermal weight loss rate reached 5% according to the following index. The evaluation results and Td5 values are shown in Table 2.
A (very good heat resistance): Td5 is 270°C or more. B (good hydrophilicity): Td5 is 250°C or more and less than 270°C. C (slightly poor hydrophilicity): Td5 is 240°C or more and less than 250°C. D (poor hydrophilicity): Td5 is less than 240°C.

(3) Evaluation of stability over time The glass substrate on which the resin film obtained in (1) was formed was stored at 80° C. and 70% humidity for one week. The resin film was then washed with water and dried at room temperature for one day. The contact angle of the dried resin film (contact angle over time) was measured in the same manner as in (1). The rate of change in the contact angle was calculated using the following formula based on the contact angle (initial contact angle) measured in (1).
Rate of change (%) = |(initial contact angle) - (contact angle over time)|/(initial contact angle) x 100
The stability of the resin film was evaluated according to the following indices. The evaluation results and the rate of change are shown in Table 2.
A (very good stability): rate of change is 3.0% or less. B (good stability): rate of change is more than 3.0% and less than 5.0%. C (slightly poor stability): rate of change is 5.0% or more and less than 10.0%. D (poor stability): rate of change is 10.0% or more.

(4) Evaluation of pigment dispersion 0.1 g of Green No. 3 was added as a pigment to 50 g of a toluene solution of the elastomer composition of Examples 1 , 3 to 6, 8, Reference Examples 1 and 2 , Comparative Examples 1 to 3, and Reference Example, and mixed for 60 minutes. The pigment-containing elastomer composition was applied onto a glass substrate with a bar coater, and dried on a hot plate at 100°C for 30 minutes. This formed a resin film with a thickness of 1 μm.
The obtained resin film was observed with an optical microscope (magnification: 10 times) and visually. The dispersibility of the pigment was evaluated according to the following indices. The results are shown in Table 2.
A (good dispersibility): When observed under a microscope, the coating film was uniform and free of unevenness, and the surface was evaluated as being almost smooth. B (fairly good dispersibility): When observed under a microscope, unevenness was confirmed, but not by visual inspection. C (poor dispersibility): Unevenness or roughness was confirmed by visual inspection.

As shown in Table 2, the elastomer compositions of Examples 1 to 8 had excellent initial hydrophilicity, and even after storage under high temperature and high humidity conditions, the change in hydrophilicity was small, and excellent stability over time was obtained. Furthermore, the dispersibility of the pigment was also good. Furthermore, the results of the heat resistance evaluation showed that the copolymers P1 to P7 of the present invention had excellent heat resistance.
On the other hand, in Comparative Examples 1 to 3, the initial hydrophilicity was insufficient, and the stability over time was also poor. Also, in Comparative Examples 1 to 3, the dispersibility of the dye was poor.
The Reference Examples are conventional products having a structure different from that of the Examples, but they do not satisfy all of the requirements for hydrophilicity, heat resistance, stability and pigment dispersibility.

Claims (4)

A hydrophilizing agent for elastomers , comprising a copolymer obtained by polymerizing a monomer component including an epoxy group -containing monomer (A1), a (meth)acrylic acid alkyl ester (A2) represented by the following general formula (1), and a hydroxyl group-containing monomer (A3 ), wherein, in the monomer component, a ratio of the epoxy group-containing monomer (A1) is 15 to 50 mol %, a ratio of the (meth)acrylic acid alkyl ester (A2) is 7 to 50 mol % , and a ratio of the hydroxyl group-containing monomer (A3) is 42.6 to 60 mol % .

(In formula (1), R1 represents a hydrogen atom or a methyl group, and R2 represents an alkyl group having 9 to 22 carbon atoms.) The hydrophilizing agent for elastomers according to claim 1, wherein the epoxy group-containing monomer (A1) is glycidyl (meth)acrylate. 3. The hydrophilizing agent for elastomers according to claim 1 , wherein the hydroxyl group-containing monomer (A3) is glycerin mono(meth)acrylate or 2-hydroxyethyl(meth)acrylate. The hydrophilizing agent for elastomers according to any one of claims 1 to 3 , wherein the copolymer has a weight average molecular weight in terms of polystyrene of 3,000 to 50,000.