WO2020141733A1 - Clear coating composition - Google Patents

Abstract

The present invention relates to a clear coating composition comprising a silicone-modified polyester polyol resin, an acrylic polyol resin, a polyester resin, and an isocyanate resin.

Description

Clear paint composition

The present invention relates to a clear coating composition.

In general, the outer plate of the vehicle body should be free from deterioration and rust of the coating film, and must have durability to maintain the gloss or color of the coating film. Therefore, in the coating process of a vehicle, after the electrodeposition coating of a vehicle body that has been subjected to a pre-treatment process, an intermediate coating is applied to improve adhesion and smoothness, and a base coating is applied to the vehicle body that has been coated in the middle for aesthetic appearance of the vehicle body. Thereafter, it is common to apply a clear coating film to protect the color of the base coating film, improve the appearance, and protect the base coating film from the outside.

Conventionally, as a clear paint for automobiles, a thermosetting coating composition of a resin containing amino groups and an amino resin has been widely used. However, when using a conventional thermosetting coating composition, parts made of plastic materials such as bumpers and rearview mirrors may deform or distort when the components are cured under high temperature curing conditions, so they must be separated from the vehicle body and separately painted. There was a hassle. In addition, there was a disadvantage in that the color of the plastic material parts separated from the vehicle body and the color of the vehicle body are different. Accordingly, a low temperature curable transparent coating composition having lowered the curing temperature so that the plastic material parts are integrally bonded to the vehicle body can be performed.

As an alternative, Korean Patent No. 1,655,621 (Patent Document 1) discloses a clear coating composition comprising two types of acrylic polyol resin, polyester polyol resin, reactive silicone additive and isocyanate curing agent. However, the conventional low-temperature curing type clear coating composition, such as the clear coating composition of Patent Literature 1, has insufficient mechanical properties of the coating film prepared therefrom, and thus can be applied only for repair or coating of parts, and is limited to application for vehicle body coating. There was.

Therefore, it is possible to cure at a low temperature of 120° C. or less, but it is necessary to research and develop a clear coating composition suitable for application for vehicle body coating because of excellent mechanical properties of the coating film prepared therefrom.

Accordingly, the present invention is to provide a clear coating composition capable of producing a coating film that is capable of curing at a low temperature of 120° C. or lower, but has excellent mechanical properties.

The present invention provides a clear coating composition comprising a silicone-modified polyester polyol resin, an acrylic polyol resin, a polyester resin and an isocyanate resin.

The clear coating composition according to the present invention can be cured at a low temperature of 120° C. or lower, thereby reducing the cost required during the coating process, and is economical. The color can prevent different problems. In addition, since it is possible to coat both the vehicle body and the parts in one coating process, it is possible to reduce process hassle and cost loss. Furthermore, the coating film prepared from the clear coating composition is excellent in mechanical properties such as hardness, adhesion, water resistance, acid resistance, scratch resistance, and solvent resistance, and thus can be usefully used for painting a body.

The clear coating composition according to the present invention includes a silicone-modified polyester polyol resin, an acrylic polyol resin, a polyester resin, and an isocyanate resin.

Silicone-modified polyester polyol resin

The silicone-modified polyester polyol resin serves to improve the scratch resistance of a coating film prepared from a composition comprising the same.

The silicone-modified polyester polyol resin may include a first repeating unit derived from an organic polysiloxane, a second repeating unit derived from a polyfunctional alcohol, and a third repeating unit derived from a polyfunctional carboxylic acid. For example, the silicone-modified polyester polyol resin may be composed of a first repeating unit derived from an organic polysiloxane, a second repeating unit derived from a polyfunctional alcohol, and a third repeating unit derived from a polyfunctional carboxylic acid. That is, the silicone-modified polyester polyol resin may be prepared by reacting an organic polysiloxane, a polyfunctional alcohol monomer, and a polyfunctional carboxylic acid monomer. As another example, the silicone-modified polyester polyol resin may be prepared by condensation reaction of an organic polysiloxane, a polyfunctional alcohol monomer, and a polyfunctional carboxylic acid monomer.

The organic polysiloxane may include functional groups and non-functional organic groups. For example, the organic polysiloxane may include at least one functional group selected from the group consisting of silanol and alkoxy groups, and may include at least one non-functional organic group selected from the group consisting of methyl, propyl and phenyl groups. Examples of the alkoxy group include methoxy, ethoxy and butoxy groups.

The organic polysiloxane may have a number average molecular weight of 100 to 5,000 g/mol. For example, the organic polysiloxane may have a number average molecular weight of 200 to 5,000 g/mol, 300 to 5,000 g/mol, or 500 to 5,000 g/mol.

Commercially available products of the organic polysiloxane include Dow Corning's DC-3037, DC-3074, RSN-0217, RSN-0220, RSN-0233, RSN-0255 and RSN-6018, Wacker's SILRES series, SY300, IC836, REN168 , SY409, IC232, SY231, IC368, IC678, 601, 603, 604 and the like.

The polyfunctional alcohol monomer is, for example, ethylene glycol (EG), propylene glycol (PG), trimethylolpropane (TMP), trimethylolethane (TME), cyclohexanedimethanol, neopentyl glycol (NPG), 2 -Butyl-2-ethyl-1,3-propanediol, 1,6-hexanediol, diethylene glycol, dipropylene glycol, tripropylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentane It may be one or more selected from the group consisting of diol, triethylolpropane, glycerin and pentaerythritol.

The polyfunctional carboxylic acid monomer is, for example, phthalic anhydride (PA), hexahydrophthalic anhydride (HHPA), methyl hexahydrophthalic anhydride, tetrahydrophthalic anhydride, It may be one or more selected from the group consisting of methyltetrahydrophthalic anhydride, succinic anhydride, isophthalic acid, azlaic acid, maleic anhydride and trimellitic anhydride.

The silicone-modified polyester polyol resin may be prepared by reacting 100 parts by weight of an organic polysiloxane, 300 to 800 parts by weight of a polyfunctional alcohol monomer, and 300 to 600 parts by weight of a polyfunctional carboxylic acid monomer. For example, the silicone-modified polyester polyol resin is 100 parts by weight of an organic polysiloxane, 400 to 700 parts by weight, or 500 to 650 parts by weight of a polyfunctional alcohol monomer and 350 to 550 parts by weight, or 400 to 500 parts by weight of polyfunctionality It can be prepared by reacting a carboxylic acid monomer. When the silicone-modified polyester polyol resin is prepared using the monomers in the above content range, there is an effect of improving appearance characteristics and scratch resistance of the coating film prepared from the coating composition containing the same.

The silicone-modified polyester polyol resin has a hydroxyl value (OHv) of 150 to 350 mgKOH/g, an acid value (Av) of more than 0 mgKOH/g and 30 mgKOH/g or less, a number average molecular weight (Mn) of 100 to 10,000 g/mol, and It may have a glass transition temperature (Tg) of -50 ℃ to 30 ℃. For example, the silicone-modified polyester polyol resin may have a hydroxyl value of 150 to 300 mgKOH/g, or 200 to 300 mgKOH/g, 1 to 30 mgKOH/g, or 1 to 20 mgKOH/g acid value, 100 to 5,000 g/mol, or a number average molecular weight of 100 to 2,000 g/mol, and a glass transition temperature of -30°C to 30°C, or greater than 0°C and 20°C or less.

When the hydroxyl value of the silicone-modified polyester polyol resin is within the above range, curability can be improved, and when the acid value is within the above range, the reactivity is controlled to improve the appearance characteristics, and when the number average molecular weight is within the above range, appearance When a coating film having excellent properties can be formed, and the glass transition temperature is within the above range, the appearance properties of the coating film are improved, and there is an effect of satisfying the paint SVR (Solid Volume Ratio).

The silicone-modified polyester polyol resin may be included in an amount of 1 to 30 parts by weight based on 1 to 30 parts by weight of acrylic polyol resin. For example, the silicone-modified polyester polyol resin may be included in an amount of 5 to 20 parts by weight, or 5 to 15 parts by weight based on 1 to 30 parts by weight of the acrylic polyol resin. When the content of the silicone-modified polyester polyol resin is within the above range, it is possible to prevent a problem that the gloss of the coating film prepared from the coating composition containing the same is lowered, and a problem that the appearance characteristics and curing density of the coating film are lowered.

Acrylic polyol resin

The acrylic polyol resin serves to impart coating properties to the composition.

The acrylic polyol resin may include a repeating unit derived from an ethylenically unsaturated monomer and a repeating unit derived from an acrylic monomer containing a hydroxyl group. That is, the acrylic polyol resin may be prepared by reacting an ethylenically unsaturated monomer and an acrylic monomer containing a hydroxyl group. For example, the acrylic polyol resin may be prepared by reacting an ethylenically unsaturated monomer, an acrylic monomer containing a hydroxyl group, and a radical polymerization initiator under a solvent. As another example, the acrylic polyol resin may be prepared by reacting an ethylenically unsaturated monomer, an acrylic monomer containing a hydroxyl group, a non-functional acrylic monomer, a radical polymerization initiator, and a molecular weight modifier under a solvent.

The ethylenically unsaturated monomer may be at least one selected from the group consisting of styrene and derivatives thereof, butadiene, C _1-12 alkyl (meth)acrylic and C _1-12 alkyl (meth)acrylic acid esters.

The acrylic monomer containing the hydroxyl group is hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, kaduraacrylate, kaduramethacrylate, capro Lactone acrylate, caprolactone methacrylate, 2,3-dihydroxypropylacrylic, 2,3-dihydroxypropylmethacrylate, polypropylene modified acrylate, polypropylene modified methacrylate, 4-hydroxymethyl It may be one or more selected from the group consisting of cyclohexyl-methylacrylate, 4-hydroxymethylcyclo-methylmethacrylate and ethylenically unsaturated beta-hydroxy ester.

The ethylenically unsaturated beta-hydroxy ester may be prepared by reacting an ethylenically unsaturated acid monomer with an epoxy compound. As said ethylenically unsaturated acid monomer, monocarboxylic acid, such as (meth)acrylic acid, is mentioned, for example. Further, the epoxy compound is not involved in radical polymerization, and examples thereof include glycidyl ether and glycidyl ester.

The non-functional acrylic monomer may be at least one selected from the group consisting of alkyl (meth) acrylate, cycloalkyl (meth) acrylate, and bicycloalkyl (meth) acrylate. For example, the non-functional acrylic monomer is methyl methacrylate, ethyl methacrylate, iso-butyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, n-hexyl methacrylate, 2- Ethyl hexyl methacrylate, iso-carbonyl methacrylate, cyclohexyl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate, iso-butyl acrylate, n-butyl acrylate, tert-butyl acrylate, 2 It may be one or more selected from the group consisting of -ethylhexyl acrylate, n-octyl acrylate, iso-carbonyl acrylate, and cyclohexyl acrylate.

The solvent is not particularly limited as long as it is a common solvent used in radical polymerization, and examples include aromatic hydrocarbon-based solvents such as toluene and xylene; Ketone solvents such as methyl ethyl ketone, methyl propyl ketone, methyl butyl ketone, and ethyl propyl ketone; Ester solvents such as methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate and ethyl ethoxypropionate; And alcohol-based solvents such as n-butanol, propanol and 1-methoxy-2-propanol; and the like.

In addition, commercially available products of the aromatic hydrocarbon-based solvent include cocosol #100, cocosol #150, and the like.

The radical polymerization initiator is not particularly limited as long as it is a conventional polymerization initiator used in radical polymerization. For example, 2,2'-azobis(2-methylbutylonitrile), 2,2'-azobisisobutyl Nitrile, dibenzoyl peroxide, tert-butylperoxy benzoate, ditert-butylperoxide, tert-butylperoxy-2-ethylhexanoate, tert-butylperoxy acetate, tert-amylperoxy-2- It may be one or more selected from the group consisting of ethyl hexanoate, ditert-amyl peroxide, cumyl hydroperoxide and dicumyl peroxide.

The molecular weight modifier is not particularly limited as long as it is a common one used in the production of acrylic polyols. For example, mercaptans such as n-dodecyl mercaptan, n-decyl mercaptan, and t-dodecyl mercaptan; And alpha methyl styrene dimers; And the like.

The acrylic polyol resin has a hydroxyl value of 80 mgKOH/g to 200 mgKOH/g, an acid value of more than 0 mgKOH/g and 30 mgKOH/g or less, a number average molecular weight of 1,000 to 10,000 g/mol, and a glass transition temperature of 0°C or more and 70°C or less. Can have In another example, the acrylic polyol resin has a hydroxyl value of 100 mgKOH/g to 200 mgKOH/g, an acid value of 1 mgKOH/g to 25 mgKOH/g, or an acid value of 5 mgKOH/g to 15 mgKOH/g, 1,500 to 7,000 g/mol, or 2,000 to 5,000 g It may have a number average molecular weight of /mol, and a glass transition temperature of 10°C to 70°C, or 20°C to 60°C.

When the hydroxyl value of the acrylic polyol resin is within the above range, the curability of the composition containing the same may be improved, and when the acid value is within the above range, the reactivity of the composition containing the same may be controlled to adjust the appearance characteristics of the coating film prepared therefrom. When the number average molecular weight is within the above range, the appearance properties and physical properties of the prepared coating film are appropriate, and when the glass transition temperature is within the above range, the initial hardness of the prepared coating film may be improved.

The acrylic polyol resin may be included in an amount of 1 to 30 parts by weight based on 1 to 30 parts by weight of the silicone-modified polyester polyol resin. For example, the acrylic polyol resin may be included in an amount of 5 to 20 parts by weight, or 5 to 15 parts by weight based on 1 to 30 parts by weight of the silicone-modified polyester polyol resin. When the content of the acrylic polyol resin is within the above range, it is possible to prevent a problem that the gloss of the coating film prepared from the coating composition containing it is lowered, and a problem that the appearance characteristics and curing density of the coating film are lowered.

Polyester resin

The polyester resin serves to improve the curing speed of the composition containing it.

The polyester resin may be synthesized directly according to a known method, or a commercially available product may be used. For example, the polyester resin can be prepared by reacting a carboxylic acid with a polyol.

At this time, the carboxylic acid is adipic acid (AA), isophthalic acid (IPA), phthalic anhydride (TMA), hexahydrophthalic anhydride (HHPA), cycloaliphatic acid, phthalic anhydride, isophthalic acid, terephthalic acid, succinic acid, ah It may be one or more selected from the group consisting of dipic acid, fumaric acid, maleic anhydride, tetrahydrophthalic anhydride, hexahydro phthalic anhydride, and derivatives thereof. In addition, the polyol is methoxypolyethylene glycol, neopentyl glycol (NPG), trimethylol propane (TMP), 1,6-hexanediol (1,6-HD), ethylene glycol, propylene glycol, diethylene glycol, butanediol, It may be one or more selected from the group consisting of 1,4-hexanediol and 3-methylpentanediol.

In addition, the polyester resin may be in a liquid form having a solids content (NV) of 50 to 90% by weight based on the total weight of the resin. As another example, the polyester resin may be in a liquid form having a solids content (NV) of 55 to 80% by weight, or 60 to 75% by weight based on the total weight of the resin. When a polyester resin is used in a liquid form, the composition has excellent workability and leveling properties, and when a polyester resin in a liquid form having a solid content is within the above range, the volatile organic compound (VOC) content in the composition is reduced. Therefore, there is an effect of improving the eco-friendliness.

Furthermore, the polyester resin may have an acid value (Av) of 1 to 30 mgKOH/g, and a hydroxyl value (OHv) of 100 to 400 mgKOH/g. As another example, the polyester resin may have an acid value of 10 to 30 mgKOH/g, or 15 to 25 mgKOH/g, and a hydroxyl value of 150 to 350 mgKOH/g, or 200 to 320 mgKOH/g. When the acid value of the polyester resin is within the above range, water resistance of the prepared coating film is improved, and when the hydroxyl value is within the above range, chemical resistance and mechanical properties of the produced coating film are improved.

In addition, the polyester resin may have a number average molecular weight (Mn) of 100 to 700 g/mol. For example, the polyester resin may have a number average molecular weight of 200 to 600 g/mol, or 250 to 500 g/mol. When the number average molecular weight of the polyester resin is within the above range, there is an effect of excellent curing density.

In addition, the polyester resin may be included in the composition in an amount of 5 to 40 parts by weight based on 1 to 30 parts by weight of the silicone-modified polyester polyol resin. For example, the polyester resin may be included in the composition in an amount of 10 to 30 parts by weight, or 15 to 25 parts by weight based on 1 to 30 parts by weight of the silicone-modified polyester polyol resin. When the content of the polyester resin is within the above range, the appearance and chipping properties of the prepared coating film are excellent, and it is possible to cure at a low temperature of 120°C or lower.

Isocyanate resin

The isocyanate resin serves to form a coating film by crosslinking the components in the composition and curing the composition.

The isocyanate resin is composed of an isocyanurate group, an uretdione group, a biuret group, a urethane group, an allophanate group, and an iminooxadiazinedione group. It may include one or more functional groups selected from the group. That is, the isocyanate resin is an isocyanurate group, an uretdione group, a biuret group, a urethane group, an allophanate group, and an iminooxadiazinedione It may be an isocyanate containing at least one functional group selected from the group consisting of groups.

The isocyanate resin may be prepared from aliphatic or alicyclic isocyanates. For example, the isocyanate resin includes aliphatic isocyanates such as 1,6-hexamethylene diisocyanate; And 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane (isophorone diisocyanate, IPDI), bis-(4-isocyanatocyclohexyl)-methane, Alicyclic isocyanates such as 1-isocyanato-1-methyl-4(3)-isocyanatomethyl cyclohexane, 2,4-hexahydrotoluylene diisocyanate and 2,6-hexahydrotoluylene diisocyanate ; Can be prepared from. For example, the isocyanate resin is 1,6-hexamethylene diisocyanate, 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane and bis-(4-isocy Anatocyclohexyl)-methane.

The isocyanate resin may be included in an amount of 10 to 40 parts by weight based on 1 to 30 parts by weight of the silicone-modified polyester polyol resin. For example, the isocyanate resin may be included in an amount of 15 to 35 parts by weight, or 20 to 30 parts by weight based on 1 to 30 parts by weight of the silicone-modified polyester polyol resin. When the content of the isocyanate resin is within the above range, it is possible to prevent a problem that a composition has insufficient reactivity, resulting in a decrease in curing density, and an unreacted substance in the coating film after curing, resulting in deterioration in properties of the coating film.

Organic solvent

The coating composition may further include an organic solvent. At this time, the organic solvent serves to improve the workability of the composition by adjusting the viscosity of the coating composition.

The organic solvent may include one or more selected from the group consisting of aromatic, acetate-based, alcohol-based and propionate-based. For example, the organic solvent is an aromatic solvent such as toluene and xylene; Acetate-based solvents such as 1-methoxy-2-propyl acetate, methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, dimethyl glutarate, dimethyl succinate and dimethyl adipate; alcohol solvents such as n-butanol, propanol and 1-methoxy-2-propanol; And propionate-based solvents such as ethyl ethoxy propionate. In addition, commercially available products of the aromatic solvent include cocosol #100, cocosol #150, and the like. Furthermore, commercially available products of the acetate solvent include Rhodiasolv RPDE from Solvay.

The organic solvent may be included in an amount of 5 to 60 parts by weight based on 1 to 30 parts by weight of the silicone-modified polyester polyol resin. For example, the organic solvent may be included in an amount of 10 to 50 parts by weight, or 10 to 45 parts by weight based on 1 to 30 parts by weight of the silicone-modified polyester polyol resin. When the organic solvent is included within the content range, the coating composition containing the same has an effect of having excellent workability during painting.

additive

The clear coating composition may further include one or more additives selected from the group consisting of flow control agents, curing catalysts, wetting agents, light stabilizers, ultraviolet absorbers, antifoaming agents, surface conditioners and leveling agents.

The additive may be included in an amount of 1 to 40 parts by weight based on 1 to 30 parts by weight of the silicone-modified polyester polyol resin. For example, the additive may be included in an amount of 1 to 35 parts by weight, or 1 to 30 parts by weight based on 1 to 30 parts by weight of the silicone-modified polyester polyol resin.

The flow modifier serves to improve the workability of the composition by regulating the composition's sagging. In addition, the flow control agent may be, for example, an acrylic resin having a diurea group. In another example, the flow-rate modifier is a needle-shaped diurea group obtained by reacting an alkyl acrylate such as butyl acrylate or an alkyl methacrylate such as butyl methacrylate with 1,6-hexamethylene diisocyanate and benzyl amine. It may be an acrylic polyol resin having a containing structure.

The curing catalyst serves to prevent the incomplete curing of the coating composition, thereby improving the mechanical properties of the coating film prepared therefrom. Further, the curing catalyst may be at least one selected from the group consisting of dibutyltin dilaurate, triethyl amine, diethylenetriamine, bismuth carboxylate, and zirconium chelate.

Wetting agents serve to improve the leveling properties and wettability of a coating film prepared from a composition comprising the same, and are not particularly limited as long as they are commonly used in coating compositions. For example, the wetting agent may be a silicone acrylate-based or acetylene alcohol-based wetting agent.

The light stabilizer serves to improve weather resistance. The light stabilizer may be used without particular limitation, as long as it is a conventional one that can be used in the coating composition, for example, hindered amine-based. For example, the hindered amine light stabilizer is 2,4-bis[N-butyl-N-(1-cyclohexyloxy-2,2,6,6-tetramethylpiperidin-4-yl) Amino]-6-(2-hydroxyethylamine)-1,3,5-triazine, bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate and the like. have.

The ultraviolet absorber absorbs ultraviolet rays to prevent discoloration of the coating composition, and serves to prevent swelling, delamination, and loss of gloss of the coating film prepared from the coating composition. In addition, the ultraviolet absorber may be used without particular limitation as long as it is a common one that can be used in the coating composition, and examples thereof include benzotriazole-based hydroxyphenyl benzotriazole. Moreover, as a commercial item of the said ultraviolet absorber, Tinuvin 384 of BASF is mentioned.

The anti-foaming agent serves to suppress the generation of air bubbles generated during the preparation of the coating composition and to suppress or remove phenomena such as pinholes or popping caused when the coating film is formed. The antifoaming agent may be used without particular limitation as long as it is a conventional one that can be used in the coating composition. For example, commercial products of the antifoaming agent include BYK-011, BYK-015, BYK-072 from BYK, DF-21 from Air Product, agitan 281 from Munzing, and Foamster-324 from Sannovko.

The surface adjuster serves to control the smoothness of the coating layer by adjusting the surface tension after application of the coating composition, and can be used without particular limitation, as long as it is a common one that can be used in the coating composition. For example, the surface modifier may be a surfactant, for example, a silicone-based surfactant.

The leveling agent imparts smoothness to the coating composition, thereby improving the appearance characteristics of the coating film prepared therefrom, thereby suppressing the occurrence of orange peel. In addition, the leveling agent can be used without particular limitation as long as it is a conventional one that can be used in the coating composition.

2-liquid coating composition

The clear coating composition may be a two-component coating composition comprising a main portion and a curing agent portion. Thus, the clear coating composition may be used after mixing the main part and the curing agent part before application. In this case, the main part includes a silicone-modified polyester polyol resin, an acrylic polyol resin, a polyester resin and an organic solvent, and the curing agent part includes an isocyanate resin and an organic solvent, and an additive is included in at least one of the main part or the curing agent. can do.

The clear coating composition may have a solid content (NV) of 40% to 70% by weight. For example, the clear coating composition may have a solid content of 40% to 65% by weight, for example, 45% to 61% by weight. When the solid content of the clear coating composition is within the above range, the coating workability of the composition may be improved.

The clear coating composition can be cured at 60 ℃ to 120 ℃. For example, the clear coating composition may be cured at 70 ℃ to 110 ℃, or 80 ℃ to 110 ℃. Since the clear coating composition is curable within the temperature range, it is economical to reduce the cost required during the painting process, and it is economical, and it is possible to integrally coat the vehicle body and material parts coupled thereto, so that the color of the parts and the vehicle body after painting Different problems can be avoided. In addition, since it is possible to coat both the vehicle body and the parts in one coating process, it is possible to reduce process hassle and cost loss.

The clear coating composition may have a viscosity of 10 to 40 seconds based on the number 4 pod cup. For example, the clear coating composition may have a viscosity of 15 to 35 seconds, or 20 to 35 seconds based on the number 4 pod cup. When the viscosity of the clear coating composition is less than 10 seconds, problems such as vertical surface flow may occur, and if it is more than 40 seconds, the viscosity of the composition is high, thereby deteriorating the appearance characteristics of the coating film produced therefrom or the load on the sprayer. It can cause a sprayer malfunction.

The clear coating composition according to the present invention as described above can be cured at a low temperature of 120° C. or lower, thereby reducing the cost required during the coating process, and is economical. After that, it is possible to prevent the problem of different colors of the parts and the body. In addition, since it is possible to coat both the vehicle body and the parts in one coating process, it is possible to reduce process hassle and cost loss. Furthermore, the coating film prepared from the clear coating composition has excellent mechanical properties such as appearance properties, adhesion, water resistance, acid resistance, scratch resistance, and solvent resistance, and thus can be usefully used for car body coating.

Hereinafter, the present invention will be described in more detail through examples.

However, these examples are only for the understanding of the present invention, and the scope of the present invention is not limited to these examples in any sense.

In the present invention, functional groups such as'acid value' and'hydroxyl value' of the resin can be measured by methods well known in the art, and for example, may represent a value measured by a titration method.

In addition, the'number average molecular weight' of the resin may be measured by a method well known in the art, for example, may represent a value measured by a method of gel permeation chromatograph (GPC).

In addition, the'glass transition temperature' of the resin may be measured by a method well known in the art, for example, may indicate a value measured by a differential scanning calorimetry (DSC) method.

Synthesis Example 1. Preparation of silicone-modified polyester polyol resin

123 parts by weight of neopentyl glycol, 317 parts by weight of trimethylolpropane, 170 parts by weight of cyclohexane dimethanol, DC-3074 (manufactured by Dow Corning) in a four-necked flask equipped with a thermometer, stirring device, condenser, filling column and separation tube 114 parts by weight, and 474 parts by weight of hexahydrophthalic anhydride were added and heated to 230° C. while removing condensed water under a nitrogen atmosphere. Then, when the acid value of the prepared resin reached 20 mgKOH/g, the filling column was removed and the reaction was continued. Thereafter, when the acid value of the prepared resin reached 7 mgKOH/g, the mixture was cooled to 130° C., and then diluted with 480 parts by weight of butyl acetate to prepare silicone-modified polyester polyol resin-1.

The obtained silicone-modified polyester polyol resin-1 had a number average molecular weight of 928 g/mol, a hydroxyl value of 250 mgKOH/g, an acid value of 10 mgKOH/g, a glass transition temperature of 10°C, a solid content of 70% by weight, and a Gardner viscosity Y property. Had.

Synthesis Example 2. Preparation of silicone-modified polyester polyol resin

306 parts by weight of neopentyl glycol, 87 parts by weight of trimethylolpropane, 141 parts by weight of cyclohexane dimethanol, 141 parts by weight of DC-3074 (manufactured by Dow Corning) in a four-necked flask equipped with a thermometer, agitating device, condenser, filling column and separation tube 132 parts by weight, and 550 parts by weight of hexahydrophthalic anhydride were added and heated to 230° C. while removing condensed water under a nitrogen atmosphere. Then, when the acid value of the prepared resin reached 20 mgKOH/g, the filling column was removed and the reaction was continued. Thereafter, when the acid value of the prepared resin was 7 mgKOH/, the mixture was cooled to 130° C., and then diluted with 480 parts by weight of butyl acetate to prepare a silicone-modified polyester polyol resin-2.

The obtained silicone-modified polyester polyol resin-2 had a number average molecular weight of 1,018 g/mol, a hydroxyl value of 133.7 mgKOH/g, an acid value of 35 mgKOH/g, a glass transition temperature of -10°C, a solid content of 70% by weight, and a Gardner viscosity Y. Had physical properties.

Synthesis Example 3. Preparation of acrylic polyol resin

Into a four-necked flask equipped with a thermometer, stirring device, condenser and heating equipment, 155 parts by weight of Cocosol #100, 15 parts by weight of ethyl ethoxypropionate and 148 parts by weight of glycidyl ester (HEXION, CADURA E10P) were purchased. The temperature was raised to 150°C. Thereafter, when the temperature was stable to isothermal, the monomer mixture was added dropwise for 300 minutes, and then isothermal was maintained for 120 minutes. At this time, the monomer mixture was prepared by mixing 208 parts by weight of styrene, 125 parts by weight of hydroxyethyl methacrylate, 54 parts by weight of acrylic acid and 20 parts by weight of tertiary butyl peroxide.

Thereafter, the reaction product was cooled to 80° C., and 100 parts by weight of butyl acetate and 100 parts by weight of Cocosol #100 were added and diluted to prepare an acrylic polyol resin.

The obtained acrylic polyol resin had a physical content of 60% by weight, a Gardner viscosity Z, a hydroxyl value of 150mgKOH/g, an acid value of 10mgKOH/g, a glass transition temperature of 40°C, and a number average molecular weight of 2,030g/mol in the total weight of the acrylic polyol resin.

Synthesis Example 4. Preparation of polyester resin

345 parts by weight of neopentyl glycol, 74 parts by weight of trimethylolpropane and 375 parts by weight of hexahydrophthalic anhydride were added to a four-necked flask equipped with a thermometer, stirrer, condenser, filling column, and separation tube, and condensation was performed under a nitrogen atmosphere. It was heated up to 230 ℃ while removing. After that, when the acid value of the prepared resin reached 25 mgKOH/g, the filling column was removed and the reaction was continued. Thereafter, when the acid value of the prepared resin was 7 mgKOH/g, the mixture was cooled to 130° C., and then 250 parts by weight of butyl acetate was added and diluted to prepare a polyester resin.

The obtained polyester resin had physical properties of a number average molecular weight of 350 g/mol, a hydroxyl value of 255 mgKOH/g, an acid value of 20 mgKOH/g, a solids content of 75% by weight of the total weight, and a Gardner viscosity Z.

Examples 1 to 9 and Comparative Examples 1 to 3. Preparation of clear coating composition

To prepare a clear coating composition, each component was stirred and mixed for 20 minutes at 1,500 rpm with a composition as described in Tables 1 and 2 below.

Ingredient (parts by weight)		Example 1	Example 2	Example 3	Example 4	Example 5	Example 6
Silicone-modified polyester polyol resin-1		10	10	15	5	25	7
Silicone-modified polyester polyol resin-2		-	-	-	-	-	-
Acrylic polyol resin		10	10	5	15	8	10
Polyester resin		20	28	23	22	16	35
Isocyanate resin		25	20	27	28	21	20
additive	Curing catalyst	0.1	0.1	0.1	0.1	0.1	0.1
	Surface modifier	0.2	0.2	0.2	0.2	0.2	0.2
	Flow modifier	2.1	2.1	2.1	2	2	2
	Light stabilizer	0.6	0.6	0.6	0.6	0.6	0.6
	UV absorber	1.1	1.1	1.1	1.1	1.1	1.1
Organic solvent	Cocosol #100	18	18	14	14	14	12
	Cocosol #150	12.9	9.9	11.9	12	12	12
Total		100	100	100	100	100	100

Ingredient (parts by weight)		Example 7	Example 8	Example 9	Comparative Example 1	Comparative Example 2	Comparative Example 3
Silicone-modified polyester polyol resin-1		33	8	-	-	28	13
Silicone-modified polyester polyol resin-2		-	-	10	-	-	-
Acrylic polyol resin		7	6	10	25	-	28
Polyester resin		15	45	20	24	16
Isocyanate resin		20	20	25	19	22	33
additive	Curing catalyst	0.1	0.1	0.1	0.1	0.1	0.1
	Surface modifier	0.2	0.2	0.2	0.2	0.2	0.2
	Flow modifier	2.3	2.1	2.1	2.1	2.1	2.1
	Light stabilizer	0.6	0.6	0.6	0.6	0.6	0.6
	UV absorber	1.1	1.1	1.1	1.1	1.1	1.1
Organic solvent	Cocosol #100	11	9	18	15	16	13
	Cocosol #150	9.7	7.9	12.9	12.9	13.9	8.9
Total		100	100	100	100	100	100

Hereinafter, manufacturers and product names of each component used in Comparative Examples and Examples are as follows.

-Isocyanate resin: 1,6-hexamethylene diisocyanate (1,6-HMDI) trimer, unreacted NCO content: 21.5 wt%

-Flow control agent: acrylic polyol resin having hydroxyl and diurea groups, Setalux 81198 SS-55 from Akzo Nobel,

-Surface modifier: Silicone surfactant (BYK-331)

-Curing catalyst: Cocosol #100 containing 10% by weight of dibutyltin dilaurate (TL-1)

-Light stabilizer: Hindered amine light stabilizer (BAu's Tinuvin 123)

-UV absorber: Tinuvin 384 from BASF

Test Example: Measurement of physical properties of the coating film prepared from the coating composition

The top coat (manufacturer: KCC, product name: WT3090) was applied to the specimen and dried to form a top coat of 15 µm thickness. Thereafter, the clear coating compositions of Examples and Comparative Examples were coated on the top coat and cured at 100° C. for 25 minutes to form a clear coat having a thickness of 40 μm. The physical properties of the specimens were measured in the following manner, and the results are shown in Tables 3 and 4.

Specifically, the clear coating film using a handgun spray (nozzle diameter: 1.5mm, air pressure: 4.5kgf / ㎠ to maintain a constant), while maintaining a constant distance between the nozzle inlet and the specimen 30cm horizontally 40 ~ It was applied while moving at a speed of 50 cm/sec.

(1) Hardness

The hardness of the clear coating film was measured by the pencil hardness method. Specifically, 3B, 2B, B, HB, F, H, 2H and 3H were used to measure the maximum hardness without damaging the clear coating film (3B, 2B, B, HB, F, H, 2H) , 3H: thirteen ⇔ excellent).

(2) Adhesion

After the specimens were heat-treated and left at room temperature for 24 hours, the adhesion was evaluated by the Go method.

Specifically, in the Go method, 100 squares having a width of 2 mm and a width of 2 mm were made with a knife on the surface of the clear coating film, and then the square was removed using a tape to measure adhesion. At this time, the measured adhesiveness is M-1 (very good) when 100 squares are 100% intact, M-2 (excellent) when the remaining square is 70% or more and less than 100%, M- when 50% or more and less than 70% 3 (normal), M-4 (bad) when 30% or more and less than 50%, M-5 (very bad) when less than 30%.

In addition, the heat treatment was repeated for a total of 3 cycles in one cycle, which was allowed to stand at room temperature for 20 minutes after heat treatment at 150°C for 20 minutes.

(3) Water resistance

The specimen was immersed in a constant temperature water bath at 40° C. for 240 hours and left at room temperature for 1 hour, and then a peeling test was performed in the same manner as in the Go method of item (2), and the evaluation criteria were also applied.

(4) Acid resistance

0.2 ml of 0.1 N sulfuric acid was added dropwise to the surface of the coated film of the specimen, and then treated in an oven preheated to 30° C. or higher for 150 minutes. At this time, the appearance of etching, staining or swelling of the portion where sulfuric acid was dropped on the specimen was visually observed to determine the highest temperature at which the specimen was not damaged as the acid resistance temperature.

(5) Scratch resistance

The 20° gloss of the specimen was measured (initial gloss measurement), and the surface of the specimen was reciprocated 10 times using a wash resistance tester (manufactured by Amtec Kistler), and then the 20° gloss was measured. Subsequently, the initial gloss and the gloss after the surface treatment were calculated by using the following equation (1).

[Equation 1]

Gloss retention rate = gloss after surface treatment / initial gloss × 100

(6) Solvent resistance

After placing a cotton cloth with xylene on the coating film of the specimen, the time at which the lower coating surface appeared was scratched 4 times with 2Kg force every 1 minute.

Item	Example 1	Example 2	Example 3	Example 4	Example 5	Example 6
Solid content in total weight (% by weight)	52.6	50.4	56	51	61	52
Hardness	F	HB	F	F	HB	HB
Adhesion	M-1	M-2	M-1	M-1	M-1	M-1
Water resistance	M-1	M-1	M-1	M-1	M-1	M-2
Acid resistance	45℃	41℃	44℃	43℃	43℃	40℃
Scratch resistance (gloss retention rate)	65%	60%	64%	63%	61%	60%
Solvent resistance	10 minutes	9 minutes	10 minutes	10 minutes	10 minutes	8 minutes
Initial gloss	89%	84%	88%	89%	84%	85%

Item	Example 7	Example 8	Example 9	Comparative Example 1	Comparative Example 2	Comparative Example 3
Solid content in total weight (% by weight)	54	54	45	38	42.7	39
Hardness	HB	HB	B	2B	B	3B
Adhesion	M-1	M-1	M-2	M-2	M-5	M-3
Water resistance	M-2	M-2	M-2	M-3	M-2	M-3
Acid resistance	41℃	41℃	38℃	38℃	36℃	37℃
Scratch resistance (gloss retention rate)	59%	59%	57%	52%	54%	53%
Solvent resistance	7 minutes	7 minutes	7 minutes	6 minutes	5 minutes	5 minutes
Initial gloss	84%	84%	83%	82%	82%	81%

As shown in Tables 3 and 4, the coating films prepared from the clear coating compositions of Examples 1 to 9 were all excellent in hardness, adhesion, water resistance, acid resistance, scratch resistance, solvent resistance, and initial gloss.

On the other hand, the coating film prepared from the composition of Comparative Example 1 which does not contain a silicone-modified polyester polyol resin and Comparative Example 3 that does not contain a polyester resin lacks hardness and solvent resistance. Further, the coating film prepared from the clear coating composition of Comparative Example 2, which did not contain an acrylic polyol resin, had very poor adhesion and poor solvent resistance.

As described above, the clear coating composition according to the present invention can be cured at a low temperature of 120° C. or lower, thereby reducing the cost required during the painting process, and is economical. It is possible to prevent the problem of different colors of the parts and the body after. In addition, the coating film prepared from the clear coating composition has excellent mechanical properties such as hardness, adhesion, water resistance, acid resistance, scratch resistance, and solvent resistance, and thus can be usefully used for coating the body.

Claims (5)

1. A clear coating composition comprising silicone-modified polyester polyol resin, acrylic polyol resin, polyester resin, and isocyanate resin.
2. The method according to claim 1,

   The silicone-modified polyester polyol resin has a hydroxyl value of 150 to 350 mgKOH/g, an acid value of more than 0 mgKOH/g and 30 mgKOH/g or less, a number average molecular weight of 100 to 10,000 g/mol and a glass transition temperature of -50 to 30°C Having, clear coating composition.
3. The method according to claim 1,

   The acrylic polyol resin has a hydroxyl value of 80 to 200 mgKOH/g, an acid value of more than 0 mgKOH/g and 30 mgKOH/g or less, a number average molecular weight of 1,000 to 10,000 g/mol and a glass transition temperature of more than 0°C and 70°C or less, Clear paint composition.
4. The method according to claim 1,

   The polyester resin has a number average molecular weight of 100 to 700 g/mol, a hydroxyl value of 100 to 400 mgKOH/g, and an acid value of 1 to 30 mgKOH/g, a clear coating composition.
5. The method according to claim 1,

   The clear coating composition comprises 1 to 30 parts by weight of silicone-modified polyester polyol resin, 1 to 30 parts by weight of acrylic polyol resin, 5 to 40 parts by weight of polyester resin, and 10 to 40 parts by weight of isocyanate resin, clear coating composition .