WO2024157679A1 - Silicone-modified epoxy resin, coating composition, and article coated with said coating composition - Google Patents

Abstract

Provided are a silicone-modified epoxy resin and a coating composition containing said resin, from which a cured product exhibiting high heat resistance can be obtained. Specifically provided is a silicone-modified epoxy resin having an epoxy equivalent weight in the range of 1,000-3,000 g/equivalent weight, and having an alkyl group with 10 or more carbon atoms.

Description

Silicone-modified epoxy resin, coating composition, and article coated with said coating composition

The present invention relates to a silicone-modified epoxy resin, a coating composition, and an article coated with the coating composition.

The method of applying a protective resin coating to the surface of metal components is widely used to impart heat resistance and corrosion resistance (weather resistance) to industrial metal components such as steel plates for automobiles, steel pipes for gas pipelines, and metal building materials, as well as household metal components such as frying pans and barbecue grills.

Epoxy resin protective coatings are commonly used for motorcycle mufflers and steel pipes for gas pipelines, which require particularly high heat and corrosion resistance.

　A silicone-modified epoxy resin, which is modified with silicone, is known as one of the above epoxy resins (for example, Patent Document 1), and this silicone-modified epoxy resin has improved heat resistance by introducing a siloxane bond, which has high bond strength, into the epoxy resin.

Special Publication No. 2020-521020

The epoxy resin in Patent Document 1 is a silicone-modified epoxy resin in which epoxy resin is modified with a reactive organosilane, but its heat resistance does not reach 500°C, and its performance cannot be said to be sufficient.

The heat resistance of the epoxy resin itself can be increased by making it highly cross-linked, but increasing the epoxy equivalent to achieve highly cross-linked resins also increases the viscosity, which poses the problem of significantly reducing compatibility with pigments that impart various functions to the coating, such as extender pigments and anti-rust pigments. If compatibility between the epoxy resin and the pigment cannot be guaranteed, voids will form in the resulting coating, compromising the heat resistance of the coating. For this reason, there is naturally an upper limit to the epoxy equivalent of epoxy resins for coating.

The problem that the present invention aims to solve is to provide a silicone-modified epoxy resin that can produce a cured product that exhibits high heat resistance, and a coating composition that contains the resin.

As a result of extensive research into solving the above problems, the inventors discovered that by introducing an alkyl group having 10 or more carbon atoms into a silicone-modified epoxy resin, it is possible to prevent the resin from becoming too viscous and ensure compatibility with pigments, thus completing the present invention.

That is, the present invention relates to the following silicone-modified epoxy resins, etc.
1. Silicone-modified epoxy resins having an epoxy equivalent in the range of 1,000 to 3,000 g/equivalent and having an alkyl group having 10 or more carbon atoms.
2. The silicone-modified epoxy resin according to 1, which has a bisphenol structure.
3. The silicone-modified epoxy resin according to 1 or 2, having an acid value in the range of 1 to 10 mgKOH/g.
4. The silicone-modified epoxy resin according to any one of 1 to 3, which comprises, as reaction components, an epoxy resin having a hydroxyl group, a silicone compound having a silanol group, and a fatty acid.
5. The silicone-modified epoxy resin according to 4, wherein the epoxy resin having a hydroxyl group is a bisphenol-type epoxy resin having a hydroxyl group.
6. The silicone-modified epoxy resin according to 4 or 5, wherein the silicone compound having a silanol group is a silicone compound having one or more siloxy units selected from R ₃ SiO _1/2 units (M units), SiO _4/2 units (Q units), R ₂ SiO _2/2 units (D units) and RSiO _3/2 units (T units) (R is an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a phenyl group or a hydroxyl group), has two or more silanol groups and the proportion of phenyl groups in R in the siloxy units is 50 mol % or more.
7. The silicone-modified epoxy resin according to any one of 4 to 6, wherein the fatty acid is a saturated fatty acid having 11 to 22 carbon atoms.
8. The silicone-modified epoxy resin according to any one of 4 to 7, wherein, in the reaction components, the epoxy resin is in the range of 30 to 60 parts by mass, the silicone compound having a silanol group is in the range of 20 to 50 parts by mass, and the fatty acid is in the range of 1 to 5 parts by mass.
9. A coating composition comprising the silicone-modified epoxy resin according to any one of 1 to 8 and a pigment.
10. A cured product of the coating composition described in 9.
11. An article coated with the cured coating composition described in 9.
12. A metal member coated with the cured product of the coating composition described in 9.

The present invention provides a silicone-modified epoxy resin that exhibits high heat resistance.
The present invention provides a coating composition that can provide a coating exhibiting high heat resistance.

An embodiment of the present invention will be described below. The present invention is not limited to the following embodiment, and can be implemented by making appropriate modifications within the scope that does not impair the effects of the present invention.
The compounds in the present specification may be derived from fossil resources or biological resources.

[Silicone-modified epoxy resin]
The silicone-modified epoxy resin of the present invention has an epoxy equivalent in the range of 1,000 to 3,000 g/equivalent and has an alkyl group having 10 or more carbon atoms.
In the silicone-modified epoxy resin of the present invention, despite its high epoxy equivalent, the introduction of an alkyl group having 10 or more carbon atoms can suppress an increase in viscosity. Furthermore, the introduction of an alkyl group having 10 or more carbon atoms can ensure compatibility with pigments, which will be described later.

In the present invention, "having an alkyl group having 10 or more carbon atoms" means that the silicone-modified epoxy resin has at least one alkyl group having 10 or more carbon atoms.
In the present invention, at least one of the terminal epoxy groups of the silicone-modified epoxy resin is preferably substituted with an alkyl group having 10 or more carbon atoms. That is, the silicone-modified epoxy resin of the present invention preferably has an alkyl group having 10 or more carbon atoms at at least one terminal.

The alkyl group having 10 or more carbon atoms contained in the silicone-modified epoxy resin of the present invention is preferably an alkyl group having 12 to 22 carbon atoms, and more preferably an alkyl group having 12 to 18 carbon atoms.
The alkyl group having 10 or more carbon atoms contained in the silicone-modified epoxy resin of the present invention may be either a branched alkyl group or a linear alkyl group, but is preferably a linear alkyl group.

The silicone-modified epoxy resin of the present invention may have an epoxy equivalent in the range of 1,000 to 3,000 g/equivalent, preferably in the range of 1,000 to 2,500 g/equivalent, and more preferably in the range of 1,000 to 2,200 g/equivalent.
The epoxy equivalent of the silicone-modified epoxy resin of the present invention is evaluated by the method described in the Examples.

The acid value of the silicone-modified epoxy resin of the present invention is, for example, in the range of 1 to 10 mgKOH/g, preferably in the range of 1 to 8 mgKOH/g, more preferably in the range of 1 to 7 mgKOH/g, and even more preferably in the range of 1 to 6 mgKOH/g.
The acid value of the silicone-modified epoxy resin of the present invention is evaluated by the method described in the Examples.

There are no particular limitations on the number average molecular weight of the silicone modified epoxy resin of the present invention, but it is, for example, in the range of 500 to 10,000, preferably in the range of 1,000 to 8,000, and more preferably in the range of 1,000 to 6,000.
There are no particular limitations on the weight average molecular weight of the silicone modified epoxy resin of the present invention, but it is, for example, in the range of 10,000 to 50,000, and preferably in the range of 20,000 to 40,000.
The number average molecular weight and weight average molecular weight of the silicone-modified epoxy resin of the present invention are evaluated by the method described in the Examples.

The silicone-modified epoxy resin of the present invention preferably comprises an epoxy resin having a hydroxyl group, a silicone compound having a silanol group, and a fatty acid as reaction components.
The term "reactive components" as used herein refers to components that constitute the structure of the silicone-modified epoxy resin, and does not include solvents or catalysts that do not constitute the structure of the silicone-modified epoxy resin.
Each component will be described below.

(Epoxy resin having hydroxyl group)
The epoxy resin is a resin having at least one epoxy group in the molecule, and examples thereof include bisphenol type epoxy resins such as bisphenol A type, bisphenol F type, bisphenol E type, bisphenol B type, bisphenol S type, bisphenol AD type, bisphenol AP type, bisphenol BP type, etc.; novolac type epoxy resins such as phenol novolac type and cresol novolac type; resorcinol type epoxy resins; aromatic epoxy resins such as trisphenolmethane triglycidyl ether; naphthalene type epoxy resins; fluorene type epoxy resins; and biphenyl type epoxy resins. The epoxy resin having a hydroxyl group of the present invention is, for example, the above-mentioned epoxy resin which further has a hydroxyl group.

The epoxy resin having a hydroxyl group is preferably a bisphenol A type epoxy resin having a hydroxyl group, and more preferably a compound represented by the following general formula (A-1).

（前記一般式（Ａ－１）中、
　Ｘは、下記一般式（Ａ－２）で表されるビスフェノール構造であり、
　ｎは繰り返し数である。）

(In the general formula (A-1),
X is a bisphenol structure represented by the following general formula (A-2):
n is the number of repetitions.)

（前記一般式（Ａ－２）中、
　Ｒ^１およびＲ^２は、それぞれ独立に、炭素原子数１～４のアルキル基又は炭素原子数１～４のアルコキシ基であり、
　ｎ１およびｎ２は、それぞれ独立に、０～４の範囲の整数であり、
　Ｌは、単結合、炭素原子数１～６のアルキレン基、エーテル結合（－Ｏ－）、ケトン結合（－Ｃ（＝Ｏ）－）、エステル結合（－Ｃ（＝Ｏ）Ｏ－、スルフィド結合（－Ｓ－）又はスルホニル結合（－ＳＯ_２－）である。）

(In the general formula (A-2),
R ¹ and R ² each independently represent an alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbon atoms;
n1 and n2 each independently represent an integer ranging from 0 to 4;
L is a single bond, an alkylene group having 1 to 6 carbon atoms, an ether bond (-O-), a ketone bond (-C(=O)-), an ester bond (-C(=O)O-, a sulfide bond (-S-) or a sulfonyl bond (-SO ₂ -).

In the general formula (A-2), when there are multiple R ¹ 's, the multiple R ¹ 's may be the same as or different from each other. Similarly, when there are multiple R ² 's, the multiple R ² 's may be the same as or different from each other.

When the epoxy resin having a hydroxyl group is, for example, a compound represented by the above general formula (A-1), the epoxy group of the compound represented by general formula (A-1) reacts with a fatty acid to introduce an alkyl group at the terminal.

The epoxy equivalent of the hydroxyl group-containing epoxy resin is preferably in the range of 300 to 3,000 g/equivalent, more preferably in the range of 450 to 3,000 g/equivalent, and more preferably in the range of 600 to 3,000 g/equivalent.
The epoxy equivalent is the weight of an epoxy resin required to obtain 1 mol of epoxy groups, and is measured by the method described in the examples.

In the present invention, it is recommended that the epoxy resins having hydroxyl groups used have an average epoxy equivalent in the range of 1,000 to 3,000 g/equivalent. For example, when using epoxy resins having two types of hydroxyl groups, it is recommended that they are used so that the average epoxy equivalent calculated by (total weight of epoxy resins)/{(amount of epoxy resin 1 used/epoxy equivalent of epoxy resin 1)+(amount of epoxy resin 2 used/epoxy equivalent of epoxy resin 2)} is in the range of 1,000 to 3,000.

The epoxy resin having a hydroxyl group may be a commercially available product, such as EPICLON 1055, EPICLON 3040, EPICLON 3050, EPICLON 4050, EPICLON 7050 (all manufactured by DIC Corporation), LAPOX P-62, LAPOX P-5 (all manufactured by ATUL INDIA), E-20 (epoxy equivalent: 455-555 g/Eq), E-21 (epoxy equivalent: 480-580 g/Eq), E-42 (epoxy equivalent: 230-280 g/Eq), E-44 (epoxy equivalent: 210-240 g/Eq), E-51 (epoxy equivalent: 184-194 g/Eq) (all manufactured by Sinopec Corporation).

(Silicone Compound Having Silanol Group)
In the silicone compound having a silanol group, the silanol group reacts with a hydroxyl group of an epoxy resin, and thereby a crosslinked structure is formed that crosslinks epoxy resins together.

The silicone compound having a silanol group is preferably a silicone compound having two or more silanol groups, and more preferably a silicone compound having one or more siloxy units selected from R ₃ SiO _1/2 units (M units), SiO _4/2 units (Q units), R ₂ SiO _2/2 units (D units) and RSiO _3/2 units (T units) (R is an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a phenyl group or a hydroxyl group), and is a compound having two or more silanol groups.

When the silicone compound having a silanol group is a silicone compound having one or more siloxy units selected from R ₃ SiO _1/2 units (M units), SiO _4/2 units (Q units), R ₂ SiO _2/2 units (D units) and RSiO _3/2 units (T units) (R is an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a phenyl group or a hydroxyl group) and has two or more silanol groups, the proportion of the phenyl groups in R in the siloxy units is preferably 50 mol % or more.

By making the ratio of phenyl groups in R in the siloxy unit 50 mol % or more, it is possible to improve heat resistance.
The proportion of phenyl groups in the siloxy units can be confirmed by Fourier transform infrared spectroscopy (FTIR), and the upper limit of the proportion of phenyl groups in the siloxy units is, for example, 80 mol %.

As the silicone compound having a silanol group, a commercially available product can be used, and examples of the commercially available product include DOWSIL RSN-6018, DOWSIL RSN-0220, and DOWSIL 3040 (all manufactured by The Dow Chemical Company).
The proportion of phenyl groups in R in the siloxy unit in the above commercially available products is 73 mol % for DOWSIL RSN-6018, 67 mol % for DOWSIL RSN-0220, and 50 mol % for DOWSIL 3040.

(fatty acid)
The fatty acid is preferably a saturated fatty acid having 11 to 22 carbon atoms, more preferably a straight-chain saturated fatty acid having 11 to 22 carbon atoms, and even more preferably a straight-chain saturated fatty acid having 11 to 18 carbon atoms.

Fatty acids may be used alone or in combination of two or more.

Specific examples of fatty acids include undecylic acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, nonadecylic acid, arachidic acid, heneicosylic acid, and behenic acid.

Oils containing fatty acids may also be used as reaction components.
Examples of the fats and oils include hydrogenated coconut oil fatty acids, hydrogenated palm kernel oil fatty acids, hydrogenated palm oil fatty acids, hydrogenated olive oil fatty acids, hydrogenated castor oil fatty acids, hydrogenated rapeseed oil fatty acids, etc. These are obtained by hydrolyzing and hydrogenating oils obtained from coconut, palm kernel, palm, olive, castor, and rapeseed, respectively, and all of them are mixtures of two or more types of long-chain aliphatic monocarboxylic acids.

The silicone-modified epoxy resin of the present invention preferably contains as reaction components an epoxy resin having a hydroxyl group, a silicone compound having a silanol group, and a fatty acid, and may further contain components other than these as long as the effects of the present invention are not impaired.
The silicone-modified epoxy resin of the present invention is preferably a reaction product of an epoxy resin having a hydroxyl group, a silicone compound having a silanol group, and a fatty acid.

The mixing ratio of the silicone compound having a silanol group is, for example, in the range of 50 to 100 parts by mass, preferably in the range of 60 to 90 parts by mass, and more preferably in the range of 70 to 85 parts by mass, per 100 parts by mass of the epoxy resin having a hydroxyl group.

The mixing ratio of the fatty acid is, for example, in the range of 1 to 10 parts by mass, preferably in the range of 1 to 7 parts by mass, more preferably in the range of 1 to 5 parts by mass, and even more preferably in the range of 3 to 4 parts by mass, per 100 parts by mass of the epoxy resin having a hydroxyl group.

The proportions of each component in the reaction components are preferably in the range of 30 to 60 parts by mass of epoxy resin having hydroxyl groups, 20 to 50 parts by mass of silanol-modified silicone compound, and 1 to 5 parts by mass of fatty acid.

The reaction of an epoxy resin having a hydroxyl group, a silicone compound having a silanol group, and a fatty acid can be carried out by a known method. For example, the silicone-modified epoxy resin of the present invention can be prepared by heating a reaction system containing an epoxy resin having a hydroxyl group, a silicone compound having a silanol group, and a fatty acid. The silicone-modified epoxy resin of the present invention can also be prepared by reacting an epoxy resin having a hydroxyl group with a silicone compound having a silanol group to form a silicone-modified epoxy resin, and then reacting the silicone-modified epoxy resin with a fatty acid.

[Coating composition]
The coating composition of the present invention contains the silicone-modified epoxy resin of the present invention and a pigment, and is used, for example, by dissolving it in a solvent.

Examples of the solvent for the coating composition of the present invention include alcohol solvents such as methanol, ethanol, propanol, n-butanol, iso-butanol, tert-butanol, and 3-methoxybutanol; glycol solvents such as ethylene glycol and propylene glycol; glycol ether solvents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol dimethyl ether, dipropylene glycol monomethyl ether, and dipropylene glycol dimethyl ether; glycol ester solvents such as ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, and diethylene glycol monobutyl ether acetate; ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; dimethylformamide, dimethylacetamide, N-methylpyrrolidone, dimethylsulfoxide, and tetrahydrofuran.
The solvent may be used alone or in combination of two or more kinds.

In the coating composition of the present invention, the solvent is used so that the solids concentration is, for example, 10 to 80 mass %, and preferably so that the solids concentration is 50 to 70 mass %.

The coating composition of the present invention can ensure sufficient pigment compatibility.
The above pigments include, for example, those called "extender pigments" and those called "anti-rust pigments." Extender pigments are pigments that are blended with the resin composition for the purpose of modifying the resin composition (increasing the amount, coloring properties, drying properties, etc.), while anti-rust pigments are pigments that are blended with the resin composition to increase the corrosion resistance.

Specific examples of extender pigments include barium sulfate, barium carbonate, calcium carbonate, magnesium oxide, magnesium carbonate, magnesium hydroxide, barium titanate, calcium hydroxide, calcium sulfite, calcium sulfate, calcium oxide, calcium silicate, titanium oxide, silica, zeolite, and talc.

Specific examples of anti-rust pigments include phosphates, hydrogen phosphates, phosphosilicates, borosilicates, borates, metaborates, molybdates, chromates, polyphosphates, etc., of one or more metals selected from the group consisting of calcium, strontium, barium, zinc, aluminum, and magnesium.

The coating composition of the present invention may contain at least one of an extender pigment and an anti-rust pigment.
The coating composition may contain one kind of extender pigment or two or more kinds of extender pigments. Similarly, the coating composition may contain one kind of rust-preventive pigment or two or more kinds of extender pigments.

When the coating composition of the present invention contains an extender pigment and/or an anti-rust pigment, the total content of the extender pigment and the anti-rust pigment (pigment content) is, for example, in the range of 20 to 80 parts by mass, and preferably in the range of 30 to 70 parts by mass, per 100 parts by mass of the silicone-modified epoxy resin of the present invention.

(Other ingredients)
The coating composition of the present invention may be in the form of a one-liquid paint that does not use a curing agent, or in the form of a multi-liquid paint that uses a curing agent.

The curing agent may be a polyisocyanate compound, a melamine compound, an epoxy compound, an oxazoline compound, a carbodiimide compound, or the like.

The coating composition of the present invention may further contain various additives, such as metal driers (which play a role in promoting the oxidative polymerization of carbon-carbon double bonds in the resin), waxes, surfactants, stabilizers, flow regulators, dyes, leveling agents, rheology control agents, UV absorbers, antioxidants, plasticizers, antistatic agents, defoamers, viscosity modifiers, light resistance stabilizers, weather resistance stabilizers, heat resistance stabilizers, pigment dispersants, thermosetting resins, and thermoplastic resins, as necessary. Publicly known additives can be used.

The coating composition of the present invention may be applied directly to the object to be coated, or a primer coating material suitable for the object to be coated may be applied first, and then the coating composition of the present invention may be applied.

　Materials of the items to be coated include various metals such as iron, copper, zinc, aluminum, magnesium, etc. and their alloys; plastic substrates such as polycarbonate (PC), acrylonitrile-butadiene-styrene copolymer (ABS), PC-ABS polymer alloy, polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polyamide (PA), polypropylene (PP), fiberglass, carbon fiber, etc., and fiber-reinforced plastic (FRP) containing fillers; glass, etc.

　Any known method can be used to apply the coating composition of the present invention, and the method will vary depending on the article to be coated. Examples include methods using a gravure coater, roll coater, comma coater, knife coater, air knife coater, curtain coater, kiss coater, shower coater, wheeler coater, spin coater, dipping, screen printing, spraying, applicator, bar coater, brush, roller, etc.

As a method for curing the coating composition of the present invention after application, a known method can be used.
The conditions are adjusted as appropriate depending on the presence or absence of a curing agent, the desired film thickness, and the like, but for example, a method of heating and curing for a certain period of time within a temperature range of about 120 to 350° C. can be used.

Examples of articles having a cured coating film of the coating composition of the present invention include the housings and internal parts of home appliances such as televisions, refrigerators, washing machines, and air conditioners; the housings and internal parts of electronic devices such as smartphones, mobile phones, tablet devices, personal computers, digital cameras, and game consoles; the housings of office equipment such as printers and facsimiles; leisure and sports goods; interior and exterior materials for various vehicles such as automobiles, ships, and railway cars; industrial machinery; interior and exterior materials for buildings such as exterior walls, roofs, glass, and decorative panels; and civil engineering materials such as soundproofing walls and drainage ditches.

The present invention will be specifically described below with reference to examples and comparative examples.
However, the present invention is not limited to the following examples.

In the examples of the present application, the acid value, hydroxyl value and epoxy equivalent were evaluated by the following methods.
[Method for measuring acid value]
The measurement was performed according to a method in accordance with JIS K0070-1992.
[Method for measuring hydroxyl value]
The measurement was performed according to a method in accordance with JIS K0070-1992.
[Method for measuring epoxy equivalent]
Measurement was performed according to a method in accordance with JIS K7236-2009.

In the examples of the present application, the number average molecular weight and weight average molecular weight of the epoxy resin are values calculated in terms of polystyrene based on GPC measurement, and the measurement conditions are as follows.
[GPC measurement conditions]
Measurement equipment: Tosoh Corporation's high-speed GPC equipment "HLC-8320GPC"
Column: "TSK GURADCLUMN SuperHZ-L" manufactured by Tosoh Corporation + "TSK gel SuperHZM-M" manufactured by Tosoh Corporation + "TSK gel SuperHZM-M" manufactured by Tosoh Corporation + "TSK gel SuperHZ-2000" manufactured by Tosoh Corporation + "TSK gel SuperHZ-2000" manufactured by Tosoh Corporation
Detector: RI (differential refractometer)
Data processing: Tosoh Corporation's "EcoSEC Data Analysis Version 1.07"
Column temperature: 40°C
Developing solvent: tetrahydrofuran Flow rate: 0.35 mL/min Measurement sample: 7.5 mg of a sample was dissolved in 10 ml of tetrahydrofuran, and the resulting solution was filtered through a microfilter to prepare a measurement sample.
Sample injection volume: 20 μl
Standard sample: In accordance with the measurement manual for the above-mentioned "HLC-8320GPC," the following monodisperse polystyrene with known molecular weight was used.

(Monodisperse polystyrene)
"A-300" manufactured by Tosoh Corporation
"A-500" manufactured by Tosoh Corporation
"A-1000" manufactured by Tosoh Corporation
"A-2500" manufactured by Tosoh Corporation
"A-5000" manufactured by Tosoh Corporation
"F-1" manufactured by Tosoh Corporation
"F-2" manufactured by Tosoh Corporation
"F-4" manufactured by Tosoh Corporation
"F-10" manufactured by Tosoh Corporation
"F-20" manufactured by Tosoh Corporation
"F-40" manufactured by Tosoh Corporation
"F-80" manufactured by Tosoh Corporation
"F-128" manufactured by Tosoh Corporation
"F-288" manufactured by Tosoh Corporation

(Synthesis Example 1: Preparation of Silicone-Modified Epoxy Resin A-1 Having Alkyl Groups)
A four-neck flask equipped with a stirrer, a thermometer, a temperature controller and a nitrogen inlet tube was charged with 17.0 parts by mass of bisphenol A type epoxy resin "EPICLON 3050" (DIC Corporation, epoxy equivalent 740-860 g/Eq), 11.0 parts by mass of bisphenol A type epoxy resin "EPICLON 7050" (DIC Corporation, epoxy equivalent 1750-2100 g/Eq), 1.0 parts by mass of lauric acid (Kao Corporation), 23.0 parts by mass of silanol-modified silicone compound "DOWSIL RSN 6018" (Dow Corning Corporation) and 16.0 parts by mass of ortho-xylene as a solvent. These were melted and heated to 130-140°C while stirring, and reacted for 3-4 hours while maintaining the same temperature and dehydrating. After the reaction was completed, the pressure was reduced to remove ortho-xylene, and the residue was diluted with methoxypropyl acetate to obtain a silicone-modified epoxy resin A-1 (non-volatile content 51% by mass) having alkyl groups at the ends.

The physical properties of the obtained silicone modified epoxy resin A-1 were as follows:
Acid value: 4.9 mg KOH / g
Epoxy equivalent: 2,000g/Eq
Number average molecular weight: 5,000
Weight average molecular weight: 35,000
Decomposition temperature: 420℃

(Synthesis Comparative Example 1: Preparation of Silicone Modified Epoxy Resin B-1)
A four-neck flask equipped with a stirrer, a thermometer, a temperature controller, and a nitrogen inlet tube was charged with 15.0 parts by mass of bisphenol A type epoxy resin "EPICLON 1055" (DIC Corporation, epoxy equivalent 450 to 500 g/Eq), 25.0 parts by mass of silanol-modified silicone compound "DOWSIL RSN 6018" (Dow Corning Corporation), and 25.0 parts by mass of a cyclohexanone/butyl acetate mixed solvent (cyclohexanone: butyl acetate = 50: 50 (mass)) as a solvent. These were melted and heated to 75 ° C. while stirring, 0.05 g parts by mass of zinc naphthenate was added as a catalyst, the temperature was raised to 125 ° C., and the reaction was continued for 5 hours while maintaining the same temperature and dehydrating to obtain a silicone-modified epoxy resin B-1 (non-volatile content 50% by mass).

The physical properties of the resulting silicone-modified epoxy resin B-1 were as follows:
Epoxy equivalent: 475g/Eq
Number average molecular weight: 1,200
Weight average molecular weight: 15,000
Decomposition temperature: 360℃

(Synthesis Comparative Example 2: Preparation of Silicone Modified Epoxy Resin B-2)
A four-neck flask equipped with a stirrer, a thermometer, a temperature controller and a nitrogen inlet tube was charged with 17.0 parts by mass of bisphenol A type epoxy resin (DIC Corporation "EPICLON 3050"), 11.0 parts by mass of bisphenol A type epoxy resin (DIC Corporation "EPICLON 7050"), 24.0 parts by mass of a silanol-modified silicone compound (Dow Corning Corporation "DOWSIL RSN 6018") and 16.0 parts by mass of ortho-xylene as a solvent. These were melted and heated to 130-140°C while stirring, and reacted for 3-4 hours while maintaining the same temperature and dehydrating. After the reaction was completed, the pressure was reduced to distill off ortho-xylene, and the mixture was diluted with methoxypropyl acetate to obtain a silicone-modified epoxy resin B-2 (non-volatile content 50% by mass).

The physical properties of the obtained silicone modified epoxy resin B-2 were as follows:
Epoxy equivalent: 1,996g/Eq
Number average molecular weight: 2,500
Weight average molecular weight: 10,000
Decomposition temperature: 300℃

(Example 1 and Comparative Examples 1-2: Preparation of Coating Composition, Formation of Coating Film, and Evaluation)
Using the silicone-modified epoxy resins produced, coating compositions were prepared according to the blending patterns shown in Tables 1 and 2, and the prepared coating compositions were applied to the substrates shown in Tables 1 and 2 to form coating films. The resulting coating films were evaluated as follows. The results are shown in Tables 1 and 2.

The coating film was formed by applying the coating composition to a substrate with a bar coater to a thickness of 20 μm, and then baking and heating at 270°C for 10 minutes to form a coating film. The coating film was evaluated after being left to stand for one day at room temperature of 25°C.

(Mixture Pattern I)
28.26 parts by mass of the silicone-modified epoxy resin shown in Tables 1 and 2, 28.26 parts by mass of titanium oxide ("Ti-Pure R-960" manufactured by Chemours) and 14.79 parts by mass of propylene glycol monomethyl ether acetate as a solvent were mixed and kneaded for 90 minutes with a paint shaker to obtain a kneaded base. 28.26 parts by mass of the silicone-modified epoxy resin shown in Tables 1 and 2, 0.43 parts by mass of a silicone-based leveling agent ("Modaflow 2100" manufactured by ALLNEX) and 14.79 parts by mass of propylene glycol monomethyl ether acetate were further added to the obtained kneaded base and mixed to prepare a coating composition with a non-volatile content of 57% by mass and a pigment mass concentration of 50% by mass.

(Mixing Pattern II)
28.22 parts by mass of the silicone-modified epoxy resin shown in Tables 1 and 2, 28.22 parts by mass of titanium oxide ("Ti-Pure R-960" manufactured by Chemours), 28.22 parts by mass of carbon black ("Carbon Black 1000" manufactured by Mitsubishi Chemical Corporation) and 14.77 parts by mass of propylene glycol monomethyl ether acetate as a solvent were mixed and kneaded for 90 minutes with a paint shaker to obtain a kneaded base. 28.22 parts by mass of the silicone-modified epoxy resin shown in Tables 1 and 2, 0.43 parts by mass of a silicone-based leveling agent ("Modaflow 2100" manufactured by ALLNEX) and 14.79 parts by mass of propylene glycol monomethyl ether acetate were further added and mixed to the obtained kneaded base to prepare a coating composition having a non-volatile content of 57% by mass and a pigment mass concentration of 50% by mass.

(Storage stability)
The prepared coating composition was stored at room temperature of 25° C. for 3 months, and a coating film was formed using the coating composition after storage by the above-mentioned method. The obtained coating film was visually evaluated according to the following criteria.
A: No blisters (bubble swelling) or discoloration (yellowing, etc.) are observed on the coating surface. B: Blisters (bubble swelling) and/or discoloration (yellowing, etc.) are observed on the coating surface. C: The coating does not adhere to the substrate.

(Gloss value)
The gloss of the coating film formed on the substrate was measured at any five points at an incident angle of 60° and a reflection angle of 60° using a gloss meter Micro-Tri-Gloss (manufactured by BYK), and the measured values were taken as gloss values.
The gloss value is an index of pigment dispersion, with a higher value indicating that the pigment is better dispersed.

(Adhesion to substrate)
The coating film formed on the substrate was evaluated for its adhesion to the substrate according to JIS K-5400:1990. Specifically, 1 mm-wide cuts were made on the coating film with a cutter to make 100 squares, and cellophane tape was applied so as to cover all the squares, which were then quickly peeled off. The number of squares remaining in contact after the test was expressed as a percentage.
In terms of substrate adhesion, 100% means that no coating film peeled off, and 0% means that the coating film was completely peeled off. Adhesion of 95% or more can be considered to be sufficient for practical use.

(Konig hardness)
The coating film formed on the substrate was measured for Koenig hardness in accordance with ISO1522.

(Pencil hardness)
The pencil hardness of the coating film formed on the substrate was measured in accordance with EN13523-4.

(Heat-resistant)
The coated substrate was placed in a ceramic oven and heated at 600° C. for 10 minutes. After heating, the coated substrate was immersed in water at room temperature. This process was repeated five times. After five cycles, the coating surface of the coated substrate was visually inspected and evaluated according to the following criteria:
A: No scratches, discoloration, or blisters on the coating surface. B: At least one of scratches, discoloration, and blisters on the coating surface. C: The coating is completely damaged.

(Adhesion to substrate after heating)
Those that were rated "A (no scratches, discoloration or blisters on the coating surface)" in the heat resistance evaluation were subjected to the above-mentioned substrate adhesion evaluation again.

Tables 1 and 2 show that high heat resistance is obtained for coatings made using a paint composition containing silicone-modified epoxy resin A-1 with an alkyl group. On the other hand, sufficient heat resistance is not obtained for coatings made using a paint composition containing silicone-modified epoxy resin B-1 (without an alkyl group). In coatings made using a paint composition containing silicone-modified epoxy resin B-2 (without an alkyl group), the high epoxy equivalent of silicone-modified epoxy resin B-2 results in insufficient compatibility with the pigment, causing the coating to lose gloss. In addition, due to insufficient pigment dispersion, voids are expected to form in the coating, and heat resistance is not obtained.

Claims (12)

A silicone-modified epoxy resin with an epoxy equivalent ranging from 1,000 to 3,000 g/equivalent and an alkyl group with 10 or more carbon atoms. The silicone-modified epoxy resin according to claim 1, which has a bisphenol structure. The silicone-modified epoxy resin according to claim 1 or 2, having an acid value in the range of 1 to 10 mgKOH/g. The silicone-modified epoxy resin according to claim 1 or 2, in which the reaction components are an epoxy resin having a hydroxyl group, a silicone compound having a silanol group, and a fatty acid. The silicone-modified epoxy resin according to claim 4, wherein the epoxy resin having a hydroxyl group is a bisphenol-type epoxy resin having a hydroxyl group. The silicone-modified epoxy resin according to claim 4, wherein the silicone compound having a silanol group is a silicone compound having one or more siloxy units selected from R ₃ SiO _1/2 units (M units), SiO _4/2 units (Q units), R ₂ SiO _2/2 units (D units) and RSiO _3/2 units (T units) (R is an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a phenyl group or a hydroxyl group), has two or more silanol groups, and the proportion of phenyl groups in R in the siloxy units is 50 mol % or more. The silicone-modified epoxy resin according to claim 4, wherein the fatty acid is a saturated fatty acid having 11 to 22 carbon atoms. The silicone-modified epoxy resin according to claim 4, wherein the reactive components include 30 to 60 parts by mass of the epoxy resin, 20 to 50 parts by mass of the silicone compound having a silanol group, and 1 to 5 parts by mass of the fatty acid. A coating composition containing the silicone-modified epoxy resin according to claim 1 or 2 and a pigment. A cured product of the coating composition according to claim 9. An article coated with the cured product of the coating composition according to claim 9. A metal member coated with a cured product of the coating composition according to claim 9.