Organopolysiloxane, adhesion-imparting agent, aqueous coating material composition, and primer composition

Abstract

Provided is a water-soluble organopolysiloxane which is represented by formula (1) and exhibits excellent storage stability. (In the formula, R1 is a monovalent hydrocarbon group having 1-10 carbon atoms, R2 moieties are each independently a monovalent hydrocarbon group having 1-10 carbon atoms which may be substituted with a glycidyloxy group, R3 is a methyl group or an ethyl group, a, b, c and d are numbers that satisfy the relationships a ≥ 0.5, b ≥ 0, c > 0, d ≥ 0, and a+b+c+d=1, and x and y are numbers that satisfy the relationships x ≥ 1 and y ≤ 0.5.)

Description

Organopolysiloxane, adhesion promoter, aqueous coating composition, and primer composition

[0001] The present invention relates to an organopolysiloxane, an adhesion promoter, an aqueous coating composition, and a primer composition; more specifically, the present invention relates to an organopolysiloxane that contains, as constituent units, a 3-glycidyloxypropyl group-containing siloxane unit and a diorganosiloxane unit and that has a silanol group; an adhesion promoter comprising the organopolysiloxane; and an aqueous coating composition and a primer composition that contain the organopolysiloxane.

[0002] Compounds having two or more different reactive functional groups in one molecule are known as coupling agents that bond different types of materials. Among these, silane coupling agents that have a hydrolyzable silyl group such as an alkoxysilyl group as one of the reactive groups and further have various organic reactive groups such as a primary amino group, a secondary amino group, a glycidyl ether group, a methacryl group, a ureido group, a vinyl group, a mercapto group, or an isocyanate group are known as primers that improve the adhesion of paints and as adhesion promoters that are added to paint compositions.

[0003] Furthermore, compositions have been reported that use a silane coupling agent as a monomer and add a reactive organopolysiloxane obtained by hydrolyzing and condensing a hydrolyzable silyl group. For example, Patent Document 1 proposes a coating material and an adhesive sheet that contain an organosilsesquioxane having an epoxy group, and Patent Documents 2 to 4 propose the use of a relatively low molecular weight oligomer obtained by partially hydrolyzing and condensing a silane coupling agent having an epoxy group as an adhesion improver.

[0004] The advantages of using oligomers and / or polymers obtained by hydrolysis and condensation of silane coupling agents compared to silane coupling agents include, firstly, that they have a high molecular weight and low volatility, eliminating concerns about the reduction of active ingredients during processes such as drying. Another advantage is that they generate less volatile organic compounds (VOCs), and from the perspective of reducing the environmental impact of recent trends such as the shift from solvent-based paints to water-based and solvent-free paints, oligomers that have been partially hydrolyzed in advance generate less alcohol per unit mass of active ingredient compared to silane coupling agents that generate alcohol through hydrolysis, making them a material that is suited to such needs.

[0005] Aiming to further reduce VOCs, aqueous solutions containing hydrolysis condensates obtained by completely hydrolyzing a silane coupling agent and removing the generated alcohol have also been proposed. Patent Documents 5 to 7 propose aqueous silane compositions containing hydrolysis condensates containing functional groups such as amino groups, mercapto groups, and carboxy groups, while Patent Document 8 proposes an aqueous silane composition containing a hydrolysis condensate having an ethylene glycol group.

[0006] In all of these aqueous silane compositions, the hydrolysis condensation product of the silane coupling agent is highly active, and from the viewpoint of handling and stability, it is essential to prepare them as aqueous solutions, but their storage stability is insufficient.

[0007] JP 2019-143161 A, International Publication No. 2018 / 34232, JP 2018-127507 A, JP 2022-27097 A, European Patent No. 0675128, JP 2016-44278 A, JP 2015-34097 A, JP 2017-114852 A

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a water-soluble organopolysiloxane that has organic functional groups and exhibits excellent storage stability.

[0009] As a result of extensive research aimed at solving the above problems, the present inventors have found that an organopolysiloxane having specific amounts of siloxane units having 3-glycidyloxypropyl groups and diorganosiloxy units, and having silanol groups, has excellent storage stability, and that an aqueous composition containing this organopolysiloxane has excellent adhesion and is suitable as a primer, which led to the completion of the present invention.

[0010] That is, the present invention provides: 1. an organopolysiloxane represented by the following formula (1): (In the formula, R 1 is a monovalent hydrocarbon group having 1 to 10 carbon atoms, and R 2 are each independently a monovalent hydrocarbon group having 1 to 10 carbon atoms which may be substituted with a glycidyloxy group, and R 3 is a methyl group or an ethyl group, a, b, c, and d are numbers that satisfy a≧0.5, b≧0, c>0, d≧0, and a+b+c+d=1, and x and y are numbers that satisfy x≧1, y≦0.5. 2. The organopolysiloxane according to 1, wherein a, b, c, and d are numbers that satisfy 0.5≦a≦0.9, b=0, 0.1≦c≦0.5, and d=0; 3. An adhesion promoter comprising the organopolysiloxane according to 1 or 2; 4. An aqueous coating composition containing the organopolysiloxane according to 1 or 2; 5. A primer composition containing the organopolysiloxane according to 1 or 2.

[0011] The organopolysiloxane of the present invention contains highly reactive epoxy groups, which are effective in modifying organic resins and improving adhesion to resin substrates, and also has excellent stability, thereby achieving a long usable period. Furthermore, the organopolysiloxane of the present invention contains silanol groups, which not only provide excellent reactivity with inorganic substrates but also exhibit high water solubility, making it useful as an additive for aqueous coating compositions.

[0012] Organopolysiloxane Ep1 obtained in Example 1-1 1 1H-NMR spectrum.

[0013] The present invention will be described in detail below. (1) Organopolysiloxane The organopolysiloxane according to the present invention is represented by the following general formula (1).

[0014]

[0015] In the above formula, R 1 is a monovalent hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, which may be linear, branched, or cyclic, and specific examples thereof include alkyl groups such as methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, and n-decyl groups; cycloalkyl groups such as cyclopentyl and cyclohexyl groups; alkenyl groups such as vinyl, allyl, butenyl, hexenyl, and octenyl groups; and aryl groups such as phenyl and naphthyl groups. Of these, methyl, ethyl, n-propyl, and phenyl groups are preferred, methyl and ethyl groups are more preferred, and methyl groups are even more preferred.

[0016] R 2 are each independently a monovalent hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, which may be substituted with a glycidyloxy group, and specific examples thereof include the above-mentioned R 1 and glycidyloxy-substituted alkyl groups such as a glycidyloxypropyl group. Among these, methyl, ethyl, n-propyl, glycidyloxypropyl, and phenyl groups are preferred, methyl and ethyl groups are more preferred, and methyl group is even more preferred.

[0017] R 3 is a methyl group or an ethyl group.

[0018] a, b, c, and d represent the molar ratios of each siloxane unit and are numbers that satisfy the equation a + b + c + d = 1. a is a number equal to or greater than 0.5 and preferably a number from 0.5 to 0.9. If a is less than 0.5, the amount of available epoxy groups is reduced, making it impossible to expect improved adhesion. In addition, the organopolysiloxane represented by formula (1) becomes highly viscous, gummy, or solid, resulting in poor handleability and reduced water solubility. b is a number equal to or greater than 0, but is preferably 0 in terms of the amount of epoxy groups contained in the organopolysiloxane of the present invention. c is a number greater than 0 and is preferably a number from 0.1 to 0.5. If c is 0, the organopolysiloxane will have a structure composed only of trisiloxane units and tetrasiloxane units, and the silanol groups contained therein will be highly reactive, resulting in insufficient storage stability and making the organopolysiloxane unsuitable for practical use. d is a number of 0 or more, but is preferably 0 from the viewpoint of the reactivity of the silanol group.

[0019] x and y respectively represent the number of moles of hydroxy groups and alkoxy groups bonded to 1 mole of Si atoms. x is a number of 1 or more, and from the viewpoint of storage stability, a number of 1 to 2 is preferred. If x is less than 1, the water solubility of the organopolysiloxane and its reactivity with inorganic substrates will be poor. y is a number of 0.5 or less, and from the viewpoint of reducing the amount of alcohol generated by hydrolysis, a number of 0.4 or less is preferred.

[0020] The organopolysiloxane of the present invention is preferably one represented by the following formula (1a):

[0021]

[0022] In formula (1a), R 2 and R 3 are the same as above, a1 and c1 are numbers that satisfy 0.5≦a1≦0.9, 0.1≦c1≦0.5, and a1+c1=1, and x1 and y1 are numbers that satisfy x1≧1, y1≦0.5.

[0023] The weight-average molecular weight of the organopolysiloxane of the present invention is preferably 500 to 10,000, more preferably 500 to 1,000, from the viewpoints of water solubility and ease of handling. The weight-average molecular weight in the present invention is a value calculated in terms of standard polystyrene by gel permeation chromatography (GPC). The kinematic viscosity of the organopolysiloxane of the present invention is 100 to 500 mm 2 / s is preferred, and 200 to 450 mm 2 The kinematic viscosity is a value measured at 25°C using a Cannon-Fenske viscometer.

[0024] The organopolysiloxane of the present invention preferably contains 1% by mass or less of water and free alcohol as impurities. Although water does not fall under the category of VOCs, if present in excess it can react with epoxy groups, and therefore, when the organopolysiloxane of the present invention is to be stored for long periods of time, it is desirable to minimize its content.

[0025] (2) Method for Producing Organopolysiloxane The method for producing the organopolysiloxane of the present invention is not particularly limited, and can be produced, for example, by co-hydrolytic condensation under acidic conditions of alkoxysilanes containing one or more of 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropyltriethoxysilane, or a mixture thereof, represented by the following formula (i), diorganodimethoxysilane, diorganodiethoxysilane, or a mixture thereof, represented by the following formula (iii), and, if necessary, organotrimethoxysilane, organotriethoxysilane, or a mixture thereof, represented by the following formula (ii), and tetramethoxysilane, tetraethoxysilane, or a mixture thereof, represented by the following formula (iv).

[0026] (In the formula, R 1 ~R 3 is the same as above.)

[0027] Specific examples of the diorganodimethoxysilane and diorganodiethoxysilane represented by the above formula (iii) include dimethyldimethoxysilane, dimethyldiethoxysilane, diethyldimethoxysilane, diethyldiethoxysilane, methylethyldimethoxysilane, methylethyldiethoxysilane, methylpropyldimethoxysilane, methylpropyldiethoxysilane, 3-glycidyloxypropylmethyldimethoxysilane, 3-glycidyloxypropylmethyldiethoxysilane, cyclopentylmethyldimethoxysilane, cyclopentylmethyldiethoxysilane, cyclohexylmethyldimethoxysilane, cyclohexylmethyldiethoxysilane, methylphenyldimethoxysilane, methylphenyldiethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, methyloctyldimethoxysilane, and methyloctyldiethoxysilane.

[0028] Specific examples of the organotrimethoxysilane and organotriethoxysilane represented by the above formula (ii) include trialkoxysilanes such as methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, cyclohexyltrimethoxysilane, cyclohexyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, octyltrimethoxysilane, octyltrimethoxysilane, decyltrimethoxysilane, and decyltriethoxysilane.In addition, hydrolysis condensation products of the above silane compounds may be used.These may be used alone or in combination of two or more.

[0029] The amount of these silane monomers used is preferably adjusted according to the molar ratio of each siloxane unit constituting the desired organopolysiloxane (the values ​​of a to d in formula (1)).

[0030] The amount of water used for hydrolysis of the alkoxysilane monomer is preferably 0.8 to 1.1 times, more preferably 1 to 1.1 times, by mole per mole of alkoxysilyl group, from the viewpoint of suppressing the reaction with the epoxy group and reducing the amount of residual alkoxysilyl groups.

[0031] The acid component used to adjust the acidic conditions during the hydrolysis reaction is not particularly limited as long as it is a commercially available Brønsted acid, but from the viewpoint of ease of availability, formic acid, acetic acid, citric acid, hydrochloric acid, and nitric acid are preferred. The amount of acid used is preferably 0.0001 to 0.01 moles per mole of silane monomer, from the viewpoint of suppressing an increase in the molecular weight of the organopolysiloxane obtained by an excessive dehydration condensation reaction between silanols and a decrease in water solubility due to a decrease in the amount of silanol groups.

[0032] In the hydrolysis reaction, an organic solvent may be used, if necessary, to the extent that it does not inhibit the reaction. The organic solvent used is preferably one that is compatible with water, which is the reaction raw material, and alcohols, esters, ketones, ethers, etc. are preferred. Furthermore, taking into consideration the distillation conditions for removing the generated alcohol, the organic solvent preferably has a low boiling point, and a solvent having a boiling point of 150°C or less under atmospheric pressure is desirable. Specific examples of alcohols include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, pentyl alcohol, neopentyl alcohol, hexyl alcohol, cyclohexyl alcohol, etc. Specific examples of esters include ethyl acetate and butyl acetate. Specific examples of ketones include acetone, methyl ethyl ketone, cyclohexanone, etc. Specific examples of ethers include tetrahydrofuran, tetrahydropyran, dioxane, etc.

[0033] The hydrolysis reaction temperature is preferably 55 to 70° C., and the reaction time is preferably 1 to 5 hours. After the hydrolysis reaction of the silane monomer, it is preferable to carry out a step of distilling off water, the alcohol produced by hydrolysis of the alkoxysilyl group, and the organic solvent under reduced pressure at a temperature in the range of 30 to 80° C.

[0034] The organopolysiloxane of the present invention can be used as an adhesion promoter in curable compositions such as paints, and because of its excellent water solubility, it can also be used in aqueous paint compositions.

[0035] (3) Aqueous Coating Composition The aqueous coating composition of the present invention contains the organopolysiloxane described above. The organopolysiloxane may be used singly or in combination of two or more. The aqueous coating composition of the present invention preferably contains water as a solvent, and is particularly preferably an aqueous solution containing only water as a solvent. The amount of the organopolysiloxane in the composition is preferably 5 to 50% by mass, more preferably 10 to 40% by mass.

[0036] Specific examples of aqueous coating compositions include compositions containing aqueous resins such as aqueous epoxy resin compositions and aqueous urethane resin compositions, and the organopolysiloxane of the present invention can be used as one component of these aqueous resin compositions. Specific examples of aqueous resins include aqueous epoxy resins, aqueous polyurethane resins, aqueous polyester resins, aqueous acrylic resins, etc. Furthermore, the aqueous coating composition of the present invention may contain any additives such as organic solvents, antioxidants, UV absorbers, light stabilizers, thickeners, dispersants, and adhesion promoters, as long as the effects of the present invention are not impaired.

[0037] There are no particular restrictions on the method for producing the aqueous coating composition of the present invention, and examples include a method in which the organopolysiloxane, solvent, and optionally an aqueous resin and other additives are mixed in a conventional manner.

[0038] The resulting aqueous coating composition can be applied to a predetermined substrate directly or via another layer such as a primer layer, and then dried for 1 to 60 minutes in an environment of 20 to 50°C and 30 to 60% RH to form a coating film. The substrate is not particularly limited, but examples include plastic molded bodies, wood-based products, ceramics, glass, metals, and composites of these. The method for applying the aqueous coating composition is not particularly limited and can be appropriately selected from conventionally known methods, including various application methods such as brush coating, wiping, spraying, dipping, bar coating, flow coating, roll coating, curtain coating, spin coating, and knife coating.

[0039] (4) Primer Composition The organopolysiloxane of the present invention can be suitably used as a coupling component or aqueous reactive binder in an aqueous primer composition (paint). The primer composition of the present invention contains the above-described organopolysiloxane. The organopolysiloxane may be used singly or in combination of two or more. The primer composition of the present invention preferably contains water as a solvent, and is preferably an aqueous solution containing only water as a solvent. The amount of the organopolysiloxane in the composition is preferably 5 to 50% by mass, more preferably 10 to 40% by mass. Furthermore, the primer composition of the present invention may contain any additives within a range that does not impair the effects of the present invention. Specific examples of such additives include those exemplified for the aqueous paint composition.

[0040] There are no particular limitations on the method for producing the primer composition of the present invention or the method for forming the primer layer, and examples thereof include the same methods as those for the aqueous coating composition.

[0041] Further, other layers may be formed on the surface of the primer layer, and examples of such other layers include a coating layer made of a cured coating of an aqueous resin composition containing an aqueous acrylic resin, an aqueous polyester resin, an aqueous epoxy resin, an aqueous urethane resin, etc. Among these, a coating layer made of a cured coating of an aqueous urethane resin composition is preferred. The coating layer can also be formed by the same method as for the aqueous paint composition.

[0042] The present invention will be specifically described below using examples and comparative examples, but the present invention is not limited to these. In the following examples, unless otherwise specified, "parts" and "%" mean "parts by mass" and "% by mass", respectively. In addition, GPC measurement and proton nuclear magnetic resonance spectrum ( 1 The H-NMR measurement conditions are as follows, and the kinematic viscosity is a value measured at 25°C using a Cannon-Fenske viscometer.

[0043] (1) GPC Measurement Conditions Apparatus: HLC-8320GPC manufactured by Tosoh Corporation Developing solvent: tetrahydrofuran (THF) Flow rate: 0.6 mL / min Detector: differential refractive index detector (RI) Column: TSK Guard column Super H-H TSKgel Super HM-N (6.0 mm I.D. × 15 cm × 1) TSKgel Super H2500 (6.0 mm I.D. × 15 cm × 1) (all manufactured by Tosoh Corporation) Column temperature: 40°C Sample injection volume: 50 μL (2.0% THF solution) Standard: monodisperse polystyrene (2) 1 H-NMR measurement conditions: Apparatus: BURKER AVANCE III 400 Solvent: CDCl3 Internal standard: tetramethylsilane (TMS)

[0044] [1] Synthesis of Organopolysiloxane [Example 1-1] 425 g (1.8 mol) of 3-glycidyloxypropyltrimethoxysilane and 24 g (0.2 mol) of dimethyldimethoxysilane were placed in a 1 L three-neck flask equipped with a stirrer, a condenser, a dropping funnel, and a thermometer. 104.4 g of 0.2% hydrochloric acid (5.8 mol as water) was added dropwise thereto (the internal temperature was controlled at 20-40°C during the dropping). After the dropping was completed, the mixture was stirred at 70°C for 1 hour, and then distilled under reduced pressure at 70°C to remove the alcohol generated by the hydrolysis reaction and excess water, yielding a colorless, transparent liquid organopolysiloxane (Ep1). The kinematic viscosity of the resulting organopolysiloxane at 25°C was 429 mm 2 The epoxy functional group content was 202 g / mol and the weight average molecular weight was 610.1 As a result of analysis by H-NMR and GPC measurement, it was found that organopolysiloxane (Ep1) had a structure represented by the following formula (2). 1 The H-NMR spectrum is shown in FIG.

[0045]

[0046] Example 1-2 The same procedure as in Example 1-1 was carried out, except that the amounts of 3-glycidyloxypropyltrimethoxysilane were changed to 236 g (1.0 mol), dimethyldimethoxysilane to 120 g (1.0 mol), and 0.2% hydrochloric acid to 90 g (5.0 mol as water), to obtain a colorless, transparent liquid organopolysiloxane (Ep2). The kinematic viscosity of the obtained organopolysiloxane at 25°C was 218 mm 2 The epoxy functional group content was 258 g / mol and the weight average molecular weight was 700. 1 As a result of analysis by H-NMR and GPC measurement, it was found that organopolysiloxane (Ep2) had a structure represented by the following formula (3).

[0047]

[0048] Example 1-3: 425 g (1.8 mol) of 3-glycidyloxypropyltrimethoxysilane and 44 g (0.2 mol) of 3-glycidyloxypropylmethyldimethoxysilane were placed in a 1 L three-neck flask equipped with a stirrer, a condenser, a dropping funnel, and a thermometer. 104.4 g of 0.2% hydrochloric acid (5.8 mol as water) was added dropwise thereto (the internal temperature was controlled between 20 and 40°C during the dropping). After the dropping was completed, the mixture was stirred at 70°C for 1 hour, and then distilled under reduced pressure at 70°C to remove the alcohol generated by the hydrolysis reaction and excess water, yielding a colorless, transparent liquid organopolysiloxane (Ep3). The resulting organopolysiloxane had a kinematic viscosity of 361 mm at 25°C. 2 The epoxy functional group content was 200 g / mol and the weight average molecular weight was 510. 1As a result of analysis by H-NMR and GPC measurement, it was found that organopolysiloxane (Ep3) had a structure represented by the following formula (4).

[0049]

[0050] Comparative Example 1-1: 472 g (2.0 mol) of 3-glycidyloxypropyltrimethoxysilane was placed in a 1 L three-neck flask equipped with a stirrer, a condenser, a dropping funnel, and a thermometer. 108 g of 0.2% hydrochloric acid (6.0 mol as water) was added dropwise thereto (the internal temperature was controlled at 20-40°C during the dropping). After the dropping was completed, the mixture was stirred at 70°C for 1 hour, and then distilled under reduced pressure at 70°C to remove the alcohol generated by the hydrolysis reaction and excess water, yielding a colorless, transparent liquid organopolysiloxane (Ep4). The kinematic viscosity of the resulting organopolysiloxane at 25°C was 726 mm 2 The epoxy functional group content was 189 g / mol and the weight average molecular weight was 830. 1 As a result of analysis by H-NMR and GPC measurement, organopolysiloxane (Ep4) had a structure represented by the following formula (5).

[0051]

[0052] Comparative Example 1-2 The same procedure as in Example 1-1 was carried out, except that the amounts of 3-glycidyloxypropyltrimethoxysilane were changed to 141.6 g (0.6 mol), dimethyldimethoxysilane to 168 g (1.4 mol), and 0.2% hydrochloric acid to 82.8 g (4.6 mol as water), to obtain a colorless, transparent liquid organopolysiloxane (Ep5). The kinematic viscosity of the obtained organopolysiloxane at 25°C was 181 mm 2 The epoxy functional group content was 288 g / mol and the weight average molecular weight was 930. 1 Analysis by H-NMR and GPC measurements revealed that organopolysiloxane (Ep5) had a structure represented by the following formula (6): Organopolysiloxane (Ep5) was incompatible with ion-exchanged water, turned cloudy, and had poor water solubility.

[0053]

[0054] [2] Storage Stability Evaluation [Examples 2-1 to 2-3, Comparative Example 2-1] The organopolysiloxanes (Ep1 to Ep4) synthesized in Examples 1-1 to 1-3 and Comparative Example 1-1 were stored at room temperature (25°C) and 5°C, and the kinematic viscosity and water solubility were evaluated immediately after production, and after 1 month, 2 months, and 3 months. The results are shown in Table 1. The water solubility was evaluated by assigning "Good" to the case where each organopolysiloxane was mixed with ion-exchanged water at 25°C to a concentration of 10% and uniformly dissolved, and assigning "Poor" to the case where cloudiness occurred.

[0055]

[0056] As shown in Table 1, Comparative Example 2-1, which used organopolysiloxane Ep4, which contains no disiloxane units and is composed only of trisiloxane units, exhibited high silanol activity, and the condensation reaction progressed, resulting in a significant increase in viscosity and a decrease in water solubility over time. Such materials can only be handled immediately after production and are of a quality unsuitable for practical use. In contrast, the organopolysiloxanes Ep1 to Ep3 obtained in Examples 1-1 to 1-3 exhibited similar behavior over time at 25°C, but the magnitude of the change was small, and it was clear that they showed almost no change when stored at 5°C.

[0057] [3] Preparation and Evaluation of Primer Compositions [Examples 3-1 to 3-3, Comparative Examples 3-1 to 3-5] The primer components listed in Table 2 below were diluted with ion-exchanged water to a solids content of 30%, and the resulting compositions were wiped onto polished steel sheets and dried for 30 minutes at 25°C and 50% RH. Subsequently, 100 parts of water-based paint resin BURNOCK WD-551 (manufactured by DIC Corporation) and 30 parts of isocyanate curing agent BURNOCK DNW-5500 (manufactured by DIC Corporation) were mixed and diluted with water to form an aqueous urethane paint, which was applied using a No. 14 bar coater and allowed to stand for 3 days at 25°C and 50% RH before being cured at 80°C for 4 hours.

[0058] The coating films obtained above were evaluated as follows. The results are shown in Table 2. (1) Coating Appearance: The coating films were visually inspected for abnormalities. ○: No abnormalities ×: Abnormalities such as foreign matter, unevenness, or cloudiness were observed. (2) Initial Adhesion: According to JIS K5600, 25 grids were created by cutting six vertical and six horizontal cuts at 2 mm intervals into the coating film using a razor blade. Cellotape (registered trademark, manufactured by Nichiban Co., Ltd.) was firmly adhered to the grids, and the grids were then rapidly peeled off at a 90° angle toward the user. The number of grids (X) in which the coating film remained unpeeled was expressed as X / 25. (3) Boiling Adhesion: The adhesion of the evaluation samples after immersion in boiling water for 10 hours was evaluated in the same manner as for the initial adhesion. (4) Pencil Hardness: Measured by applying a load of 750 g according to the pencil scratch test method described in JIS K5600-5-4.

[0059] KBM403: 3-glycidyloxypropyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd.) KBE903: 3-aminopropyltriethoxysilane (Shin-Etsu Chemical Co., Ltd.) MP200: hydrolysis condensate of 3-glycidyloxypropyltrimethoxysilane (Momentive Performance Materials, CoatOSil MP200 Silane) Eg-Pr: [3-(2,3-dihydroxyprop-1-oxy)propyl]silanol oligomer-containing composition described in Example 4 of JP 2017-114852 A

[0060] As shown in Table 2, Examples 3-1 to 3-3, in which organopolysiloxanes Ep1 to Ep3 obtained in Examples 1-1 to 1-3 were used as primer components, demonstrated excellent urethane coating film appearance, adhesion, and hardness. These results demonstrate that the organopolysiloxanes of the present invention are useful as adhesion-contributing components for environmentally friendly water-based coatings, and demonstrate their potential application not only in primers but also as internal coating adhesion promoters. On the other hand, Comparative Examples 3-1 and 3-3, in which 3-glycidyloxypropyltrimethoxysilane and its hydrolysis condensate were used as primer components, resulted in insufficient adhesion. Comparative Example 3-2, which uses a primer component containing amino groups highly reactive with urethane coatings, resulted in favorable adhesion improvement, but tended to be too reactive, significantly deteriorating the coatability of the urethane coating and impairing the coating film appearance. Comparative Example 3-4 resulted in poor adhesion, likely due to insufficient reactivity between the ethylene glycol structural group and the urethane coating.

Claims

1. An organopolysiloxane represented by the following formula (1): (In the formula, R 1 is a monovalent hydrocarbon group having 1 to 10 carbon atoms, and R 2 are each independently a monovalent hydrocarbon group having 1 to 10 carbon atoms which may be substituted with a glycidyloxy group, and R 3 is a methyl group or an ethyl group, a, b, c, and d are numbers that satisfy a≧0.5, b≧0, c>0, d≧0, and a+b+c+d=1, and x and y are numbers that satisfy x≧1 and y≦0.

5.

2. The organopolysiloxane of claim 1, wherein a, b, c, and d are numbers that satisfy the following conditions: 0.5≦a≦0.9, b=0, 0.1≦c≦0.5, and d=0.

3. An adhesion promoter comprising the organopolysiloxane of claim 1 or 2.

4. An aqueous coating composition containing the organopolysiloxane of claim 1 or 2.

5. A primer composition containing the organopolysiloxane of claim 1 or 2.