KR102768409B1 - Blocked polyisocyanate and water-soluble clear coat composition comprising the same - Google Patents

Abstract

The present invention relates to a blocked polyisocyanate obtained from a polyisocyanate compound and a blocking agent, the blocked polyisocyanate containing a first block isocyanate group in which the isocyanate group is blocked by a silane-based blocking agent, a second block isocyanate group in which the isocyanate group is blocked by a polyalkylene polyol blocking agent, and a third block isocyanate group in which the isocyanate group is blocked by a pyrazole-based blocking agent.

Description

{BLOCKED POLYISOCYANATE AND WATER-SOLUBLE CLEAR COAT COMPOSITION COMPRISING THE SAME}

The present invention relates to a block polyisocyanate and a water-soluble clear coat composition comprising the same, and more particularly, to a one-component water-soluble block polyisocyanate and a water-soluble clear coat composition comprising the same.

In general, the body of a car should not deteriorate or rust, and should have durability to maintain the gloss and color of the coating. Therefore, the painting process of a car usually involves applying an intermediate (primer) coating to a car body that has undergone a pretreatment process, then applying an electrodeposition coating to improve adhesion and smoothness, and then applying a base coating to the intermediately painted car body for the appearance of the car body. After that, a clear coat is usually applied to protect the color of the base coat, improve the appearance, and protect the base coat from the outside.

In the case of clear coats, materials based on usability are usually used, but these are very environmentally unfriendly materials, so there is an increasing need to replace them with water-soluble ones.

Korean Patent No. 10-1310616 discloses a water-soluble topcoat composition for automobiles applicable to various clear coats, but this relates to a water-soluble topcoat composition for automobiles applicable as a base coat.

Korean Patent No. 10-1881216 discloses a water-based paint composition, but this relates to a water-based paint composition for an automobile body base coat that does not include an intermediate coat and a clear coat.

Accordingly, there is a continuing demand for a water-soluble clear coat composition to convert the conventional oil-based system applied to clear coats into an eco-friendly water-soluble system to prepare for environmental regulations and reduce VOCs.

Meanwhile, a coating film obtained by using a paint crosslinked with an isocyanate compound can exhibit excellent wear resistance, chemical resistance, and contamination resistance. In addition, a coating film using a non-yellowing polyisocyanate based on an aliphatic cycloaliphatic diisocyanate as an isocyanate component exhibits excellent weather resistance, and the demand for this is increasing.

Blocked polyisocyanate has a structure in which at least one isocyanate group is blocked through a chemical reaction with a blocking agent. Here, the blocking agent can be dissociated by heating and the isocyanate group can be regenerated, and such blocked polyisocyanate has the advantage of excellent processability.

However, although block polyisocyanates can be used in water-soluble paints by introducing hydrophilic functional groups, as functional groups are added, the chain is extended, and as the number of added functional groups increases, the molecular weight increases significantly, which is pointed out as a factor that deteriorates the paint properties.

Accordingly, there is a continuing demand for blocked polyisocyanates that can be used in water-soluble paints without deteriorating the paint properties, and in particular, there is an increasing demand for scratch-resistance-improving technology using blocked polyisocyanates.

Republic of Korea Patent No. 10-1310616 (2013.09.13.) Republic of Korea Patent No. 10-1881216 (July 17, 2018)

The present invention seeks to provide a one-component water-soluble blocked polyisocyanate having improved water dispersibility in one aspect and which can be used in the production of a water-soluble clear coat.

In another aspect, the present invention seeks to provide a one-component water-soluble clear coat composition comprising a blocked polyisocyanate.

The present invention provides a blocked polyisocyanate obtained from a polyisocyanate compound and a blocking agent, the blocked polyisocyanate containing a first block isocyanate group in which the isocyanate group is blocked by a silane-based blocking agent, a second block isocyanate group in which the isocyanate group is blocked by a polyalkylene polyol blocking agent, and a third block isocyanate group in which the isocyanate group is blocked by a pyrazole-based blocking agent.

According to one aspect of the present invention, a block polyisocyanate has improved water dispersibility and can be used in the production of a one-component water-soluble clear coat that can be diluted with water.

A one-component water-soluble clear coat composition according to another aspect of the present invention can be used by diluting it with water and can form a coating film having excellent appearance properties, gloss and scratch resistance.

The present invention is described in detail below.

1. Block polyisocyanate

The present invention provides a blocked polyisocyanate.

The block polyisocyanate of the present invention is obtained from a polyisocyanate compound and a blocking agent.

The block polyisocyanate of the present invention may contain a first block isocyanate group in which the isocyanate group is blocked by a silane-based blocking agent, a second block isocyanate group in which the isocyanate group is blocked by a polyalkylene polyol blocking agent, and a third block isocyanate group in which the isocyanate group is blocked by a pyrazole-based blocking agent.

Below, the above components are described in detail.

polyisocyanate compounds

Polyisocyanate compounds are a general term for compounds containing one or more isocyanate groups. The polyisocyanate compounds may be, for example, aliphatic polyisocyanate compounds, alicyclic polyisocyanate compounds, aromatic polyisocyanate compounds, etc., but are not limited thereto. Preferably, a polyisocyanate trimer may be used.

Aliphatic polyisocyanate compounds include, but are not limited to, trimethylene diisocyanate, 1,2-propylene diisocyanate, butylene diisocyanate (tetramethylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate), 1,5-pentamethylene diisocyanate (PDI), 1,6-hexamethylene diisocyanate (HMDI), 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, 2,6-diisocyanate methylcaprate, and the like.

As the alicyclic polyisocyanate compounds, for example, 1,3-cyclopentane diisocyanate, 1,3-cyclopentene diisocyanate, cyclohexane diisocyanate (1,3- or 1,4-cyclohexane diisocyanate), 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (isophorone diisocyanate, IPDI), methylenebis(cyclohexyl isocyanate) (4,4'-, 2,4'- or 2,2'-methylenebis(cyclohexyl isocyanate), trans, trans-isomer, trans, cis-isomer, cis, cis-isomer, or mixtures thereof) (H12MDI), methylcyclohexane diisocyanate (methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate), norbornene diisocyanate (NBDI), bis(isocyanatomethyl)cyclohexane (1,3- or 1,4-bis(isocyanatomethyl)cyclohexane or mixtures thereof) (H6XDI), etc., but are not limited thereto.

As aromatic polyisocyanate compounds, for example, tolylene diisocyanate (2,4- or 2,6-tolylene diisocyanate or mixtures thereof) (TDI), phenylene diisocyanate (m-, p-phenylene diisocyanate or mixtures thereof), 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate (NDI), diphenylmethane diisocyanate (4,4'-, 2,4'- or 2,2'-diphenylmethane diisocyanate or mixtures thereof) (MDI), 4,4'-toluidine diisocyanate (TODI), 4,4'-diphenylether diisocyanate, xylylene diisocyanate (1,3- or 1,4-xylylene diisocyanate or mixtures thereof) (XDI), tetramethylxylylene Diisocyanates (1,3- or 1,4-tetramethylxylylene diisocyanate or mixtures thereof) (TMXDI), ω,ω'-diisocyanate-1,4-diethylbenzene, etc., are not limited thereto.

As the polyisocyanate compound, a single compound or two or more types may be used in combination, but is not limited thereto.

In one embodiment, the polyisocyanate compound may be an aliphatic polyisocyanate compound or an alicyclic polyisocyanate compound, which may be preferred because of their superior weatherability.

In addition, among the aliphatic polyisocyanate compounds, an aliphatic polyisocyanate compound derived from an aliphatic diisocyanate is preferable. More specifically, the aliphatic diisocyanate may be preferably 1,6-hexamethylene diisocyanate trimer in terms of weather resistance and ease of industrial availability, but is not limited thereto.

In addition, by using a blocked polyisocyanate in which the isocyanate group is blocked by a blocking agent, a water-soluble clear coat composition exhibiting excellent physical properties such as appearance, water dispersibility, and scratch resistance can be provided.

The polyisocyanate compound may be included in an amount of 30 to 60 wt%, or 38 to 50 wt%, based on the total weight of the composition for producing a blocked polyisocyanate. When a clear coat composition including a blocked polyisocyanate having a polyisocyanate compound content within the above range is used, a coating film having excellent properties such as wear resistance, chemical resistance, contamination resistance, and scratch resistance can be formed. In addition, a water-soluble clear coat composition exhibiting excellent water dispersibility due to being blocked by a blocking agent can be provided.

blocking agents

The blocking agent used in the present invention forms a new bond with isocyanate (NCO) in the polyisocyanate compound to block the isocyanate group from reacting with other compounds, such as a resinous portion. In addition, the blocked isocyanate formed in this manner contains a blocked isocyanate group in that the blocking agent can be dissociated through a reaction such as heating, thereby allowing the isocyanate group to participate in the curing reaction again.

Here, the blocked polyisocyanate can be obtained from 30 to 60 parts by weight of a polyisocyanate compound and 15 to 60 parts by weight of a blocking agent, or 38 to 50 parts by weight of a polyisocyanate compound and 18 to 55 parts by weight of a blocking agent, but is not limited thereto.

Some of the isocyanate groups in the blocked polyisocyanate may be included unblocked. More specifically, the content of unblocked isocyanate groups based on the total isocyanate groups in the polyisocyanate compound may be 5 NCO% or less, for example, 1 NCO% or less, 0.5 NCO% or less, or 0 NCO% (i.e., not included).

When the content of the polyisocyanate compound and the blocking agent is within the above range, the desired water-soluble clear coat composition can be provided. When it is less than the above range, the degree of improvement in water dispersibility is minimal, and when it exceeds the above range, the problem of deterioration of the properties of the formed coating film may occur.

The blocking agent may include a silane-based blocking agent, a polyalkylene polyol blocking agent, and a pyrazole-based blocking agent. In this way, the three types of blocking agents can be used and reacted with each isocyanate trimer to obtain a blocked isocyanate group. By using these three types of blocking agents in combination, the water dispersibility of a water-soluble clear coat composition containing a blocked isocyanate can be improved, and the physical properties of a coating film formed using the same can be improved. Hereinafter, the three types of blocking agents will be described in detail.

<Silane blocking agent>

A silane blocking agent increases the curing density of a blocked polyisocyanate and improves the scratch resistance of a coating formed with a clear coat composition containing the same.

Silane blocking agents are compounds having a -Si(OR) _n group capable of reacting with isocyanates. The silane blocking agent can form a first block isocyanate group by combining with one of the isocyanate trimers. The -Si(OR) _n group combined with the isocyanate can form a -Si-O-Si- structure through a hydrolysis reaction and a self-condensation reaction, or can form an organic chemical bond of a -Si-O- structure by heat.

Silane blocking agents may be those having an epoxy group, an amino group, or a combination thereof, but are not limited thereto.

Silane blocking agents include gamma-aminopropyltrimethoxysilane (Silquest A-1100), bis(trimethoxysilylpropyl)amine (Silquest A-1170), bis(triethoxysilylpropyl)amine (Siquest Y-11699), organoalkoxysilane (Silquest Y-96699), 3-glycidoxypropyl trimethoxysilane, N-(2-aminoethyl)3-aminopropyltrimethoxysilane, bis-gamma-trimethoxysilylpropylamine, bis-gamma-triethoxysilylpropylamine, and It may include at least one selected from the group consisting of aminopropyltriethoxysilane.

The silane blocking agent may be included in an amount of 2 to 15 wt%, or 6 to 10 wt%, based on the total weight of the composition for producing a blocked polyisocyanate. When the silane blocking agent is included within the above content range, it has the effect of improving the adhesion and durability of the coating by generating an appropriate siloxane bond. When the content of the silane blocking agent is less than the above range, the number of siloxane bonds is small, which reduces the crosslinking density, resulting in problems such as reduced adhesion, gloss, and durability of the coating. When the content exceeds the above range, the paint storability may be reduced due to hydrolysis caused by increased reactivity with moisture due to an increase in the silane molecular weight, and thus the appearance and scratch resistance of the coating may be reduced.

<Polyalkylene polyol blocking agent>

Polyalkylene polyol blocking agents play a role in controlling the hydrophilicity of polyisocyanate.

The polyalkylene polyol blocking agent can combine with one of the isocyanate trimers to form a second block isocyanate group.

As the polyalkylene polyol blocking agent, for example, a polyol containing a polyoxyethylene group, more specifically, at least one selected from the group consisting of polyethylene glycol (PEG), polytetramethylene oxide (PTMO), polypropylene oxide (PPO), monoalkoxypolyethylene glycol, polyethylene triol, polypropylene triol alone, or copolymers thereof may be included. As the polyalkylene polyol blocking agent, it may be preferable to use polyethylene glycol in terms of hydrophilicity and chain control of blocked isocyanate. In particular, it may be more preferable to use methoxy polyethylene glycol in terms of being able to block isocyanate from the side and increasing the number of hydrophilic groups per molecule.

The polyalkylene polyol blocking agent may be a single polyalkylene polyol or a combination of two or more polyalkylene polyols, and the polyalkylene polyol copolymer may be a block copolymer, a graft copolymer, a star copolymer, or an alternating copolymer.

The polyalkylene polyol blocking agent can be used having a number average molecular weight of 200 to 800, for example, 300 to 700 or 400 to 600.

When the number average molecular weight of the polyalkylene polyol blocking agent is within the above range, the efficiency of blocking polyisocyanate can be improved. In addition, by maintaining appropriate hydrophilicity, excellent water dispersibility of the blocked polyisocyanate can be exhibited.

When the number average molecular weight of the polyalkylene polyol blocking agent is less than the above-mentioned range, the hydrophilicity decreases and the compatibility of the resin composition decreases. When the number average molecular weight exceeds the above-mentioned range, the hydrophilicity increases due to the increase in molecular weight, which decreases the water resistance and, accordingly, the appearance and scratch resistance decrease.

The polyalkylene polyol blocking agent may be included in an amount of 5 to 17 wt%, or 8 to 13 wt%, based on the total weight of the composition for producing a blocked polyisocyanate. When the polyalkylene polyol blocking agent is included within the above content range, it has the effect of improving storage stability and mechanical properties by generating an appropriate number of hydrophilic groups. When the content of the polyalkylene polyol blocking agent is less than the above range, there is a problem that the compatibility of the resin composition is reduced due to a small number of hydrophilic groups, and when it exceeds the above range, the water resistance of the coating is reduced due to moisture absorption according to increased hydrophilicity, and thus the appearance, gloss, and scratch resistance of the coating may be reduced.

<Pyrazole blocking agent>

A pyrazole blocking agent improves the storage stability of a blocked polyisocyanate and improves the appearance of a coating formed with a clear coat composition containing the same.

The pyrazole blocking agent can combine with one of the isocyanate trimers to form a third block isocyanate group.

As the pyrazole-based blocking agent, for example, at least one selected from the group consisting of pyrazole, 3-methylpyrazole, and 3,5-dimethylpyrazole may be included. In one embodiment, a blocked polyisocyanate was prepared using 3,5-dimethylpyrazole as the pyrazole-based blocking agent.

The pyrazole-based blocking agent may be included in an amount of 11 to 23 wt%, or 14 to 21 wt%, based on the total weight of the composition for producing a blocked polyisocyanate. When the pyrazole-based blocking agent is included within the above content range, the storage stability is excellent, so that shrinkage of the coating film due to an addition reaction upon reaction with the resin portion is reduced, thereby improving the appearance of the coating film. When the content of the pyrazole-based blocking agent is less than the above range, the isocyanate content after dissociation is small, so that the reactivity is lowered, and the crosslinking density is insufficient, so that the durability and weather resistance of the produced coating film may be lowered, and when it exceeds the above range, the content of the silane-based blocking agent and the polyalkylene polyol blocking agent is relatively reduced, so that compatibility with the resin composition is lowered and the crosslinking density is insufficient, so that the impact resistance, chipping resistance, and scratch resistance of the coating film may be lowered accordingly.

For example, the weight ratio of the silane-based blocking agent, the polyalkylene polyol blocking agent, and the pyrazole-based blocking agent may be 1:0.3 to 7:0.7 to 10 or 1:0.5 to 5:1 to 8. By using these three blocking agents in the above weight ratio, it is possible to maintain an appropriate crosslinking density with the resin composition due to increased reactivity, thereby providing a clear coat composition having excellent physical properties such as appearance, gloss, adhesion, impact resistance, and scratch resistance as well as water dispersibility.

Formation of block polyisocyanates

The block polyisocyanate of the present invention can be produced, for example, by mixing a polyisocyanate compound and a pyrazole-based blocking agent in a solvent to cause a first reaction, then adding a silane-based blocking agent to cause a second reaction, and then adding a polyalkylene polyol blocking agent to cause a third reaction. The first reaction of the polyisocyanate compound and the pyrazole-based blocking agent can be performed at 40 to 85°C, for example, 80°C, and the second and tertiary reactions can be performed at 60 to 85°C, for example, 80°C.

When the above reaction is carried out within the above range, the polyisocyanate can be blocked with each blocking agent in a desired amount. On the other hand, when the above reaction is carried out below the above range, the unblocked isocyanate may be included in an excess amount, for example, 5 NCO% or more, based on the total isocyanate groups, and when the reaction is carried out above the above range, a dissociation reaction of the formed blocked isocyanate may be carried out.

The solvent may be any solvent that is commonly used without limitation, but may include ketone solvents such as methyl ethyl ketone, methyl propyl ketone, methyl butyl ketone, ethyl propyl ketone, methyl isobutyl ketone, methyl aryl ketone, and diisobutyl ketone that do not react with polyisocyanate and do not affect water-soluble paints, acetate solvents such as methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, butyl acetate, methyl cellosolve acetate, cellosolve acetate, butyl cellosolve acetate, carbitol acetate, and propylene glycol methyl ether acetate (PMA), alcohol solvents such as butyl cellosolve, or mixed solvents thereof.

The blocked polyisocyanate according to the present invention may contain an organic chemical bond of a -Si-O-Si- structure or a -Si-O- structure by a silane-based blocking agent, may contain a urethane group by a polyalkylene polyol blocking agent, and may contain a urea group by a pyrazole-based blocking agent. The blocked polyisocyanate of the present invention has the technical characteristic of improving the water-dispersibility and the physical properties of a coating film formed with a clear coat composition used by the above three types of blocking agents and the content ratio thereof.

Additionally, the blocked polyisocyanate may have a weight average molecular weight (Mw) of 500 to 5,000, for example, 1,000 to 3,000.

When the weight average molecular weight of the block polyisocyanate is within the above range, an appropriate reaction rate is maintained, thereby improving the reactivity with the resin, thereby increasing the crosslinking density of the coating film, thereby improving the mechanical properties, appearance, and chemical resistance.

If the weight average molecular weight of the above-mentioned block polyisocyanate is less than the above-mentioned range, the reactivity is lowered, thereby deteriorating the compatibility and appearance of the resin composition, and if it exceeds the above-mentioned range, the side reaction of the isocyanate functional group increases due to the increase in molecular weight, thereby deteriorating the appearance and scratch resistance.

When forming a blocked polyisocyanate, the blocked polyisocyanate can be obtained in a mixed state with an unblocked polyisocyanate compound and/or three blocking agents used for isocyanate blocking and remaining. At this time, the obtained mixture can have a solid content of 70 to 90 wt%, or 75 to 85 wt% in the composition. In one example, a mixture having a solid content of 80% was prepared.

The blocked polyisocyanate may have an Si(OR ¹ ) ₃ content of 1 to 11%, or 2 to 10%, where R ¹ is an alkyl group having 1 to 2 carbon atoms.

Meanwhile, the Si(OR ¹ ) ₃ content can be obtained using the equation below.

Si(OR ¹ ) ₃ % = silane monomer equivalent × Si(OR ¹ ) ₃ molecular weight × F / total content × 100

Here, F = number of Si(OR ¹ ) ₃ in the polymer

When the Si(OR ¹ ) ₃ content of the block polyisocyanate is within the above range, it forms an appropriate siloxane bond, which has excellent storage stability and improves reactivity with resin, thereby increasing the crosslinking density of the coating film, thereby improving mechanical properties, appearance, and weather resistance.

If the Si(OR ¹ ) ₃ content of the above-mentioned block polyisocyanate is less than the above-mentioned range, the number of siloxane bonds is small, so that the crosslinking density of the coating film decreases, thereby lowering the weather resistance. If it exceeds the above-mentioned range, the paint storage property decreases due to hydrolysis caused by reaction with moisture as a result of the increase in the silane molecular weight, and thus the appearance, gloss, and scratch resistance decrease.

The blocked polyisocyanates may have an alkoxide (R ² O) content of 5 to 15%, or 7 to 12%, wherein R ² is an alkyl group having 1 to 4 carbon atoms.

Meanwhile, the alkoxide ( ^R2O ) content can be obtained using the formula below.

Alkoxide ( ^R2O ) content = polyalkylene polyol equivalent × ^R2O molecular weight × F / total content × 100

Here F = R ² O number of repeating units

When the alkoxide ((R ² O)) content of the block polyisocyanate is within the above range, an appropriate number of hydrophilic groups is generated, which provides excellent storage stability and improves reactivity with resin, thereby increasing the crosslinking density of the coating film, thereby improving mechanical properties, appearance, and weather resistance.

If the alkoxide ((R ² O)) content of the above-mentioned block polyisocyanate is less than the above-mentioned range, the number of hydrophilic groups is small, so that the reactivity is lowered, thereby lowering the compatibility of the resin composition. If it exceeds the above-mentioned range, the water resistance is lowered due to moisture absorption resulting from the increased hydrophilicity, and accordingly, the appearance, gloss, and scratch resistance are lowered.

When the solid content, Si(OR ¹ ) ₃ content, and alkoxide ((R ² O)) content of the blocked polyisocyanate are within the above ranges, it may be preferable in terms of crosslinking between the resin portion and the blocked polyisocyanate.

The block polyisocyanate according to the present invention can be used as a curing agent in a paint composition, an adhesive composition, an adhesive composition, a molding agent composition, and the like.

2. Water-soluble clear coat composition

The present invention can provide a water-soluble clear coat composition comprising a block polyisocyanate according to the present invention.

The water-soluble clear coat composition according to the present invention may contain a water-soluble resin portion together with the blocked polyisocyanate of the present invention. Specifically, the water-soluble clear coat composition according to the present invention may contain 5 to 15 parts by weight of the blocked polyisocyanate and 38 to 140 parts by weight of the water-soluble resin portion.

The water-soluble resin portion may include an acrylic dispersion resin, a water-soluble polyester resin, a urethane dispersion resin, an acrylic emulsion resin, and a melamine resin. Specifically, the water-soluble resin portion may include 20 to 50 parts by weight of an acrylic dispersion resin, 1 to 15 parts by weight of a water-soluble polyester resin, 1 to 15 parts by weight of a urethane dispersion resin, 1 to 15 parts by weight of an acrylic emulsion resin, and 10 to 30 parts by weight of a melamine resin.

Acrylic dispersion resin serves to improve the durability, appearance, and gloss of a coating formed from a water-soluble clear coat composition.

The acrylic dispersion resin may have a solid content of 40 to 50 wt% based on the total weight of the resin, a weight average molecular weight of 2,500 to 3,500 g/mol, a hydroxyl value of 100 to 150 mgKOH/g, an acid value of 10 to 20 mgKOH/g, and a glass transition temperature of 25 to 35°C.

The water-soluble polyester resin serves to improve the crosslinking density of the water-soluble clear coat composition.

The water-soluble polyester resin may have a solid content of 70 to 80 wt% based on the total weight of the resin, a number average molecular weight of 900 to 1,100 g/mol, a hydroxyl value of 100 to 150 mgKOH/g, an acid value of 15 to 30 mgKOH/g, and a viscosity at 25°C of V to W Gardner viscosity.

The urethane dispersion resin imparts elasticity to a coating film formed from a water-soluble clear coat composition and improves gloss, smoothness, and scratch resistance.

The urethane dispersion resin may have a solid content of 30 to 40 wt% based on the total weight of the resin, a weight average molecular weight of 20,000 to 30,000 g/mol, and a glass transition temperature of -20 to -10°C.

Acrylic emulsion resin serves to adjust the rheology of the water-soluble clear coat composition.

The acrylic emulsion resin may have a solid content of 35 to 45 wt% based on the total weight of the resin, a weight average molecular weight of 10,000 to 30,000 g/mol, a hydroxyl value of 10 to 100 mgKOH/g, an acid value of 5 to 30 mgKOH/g, a glass transition temperature of -10 to 45°C, and a viscosity at 25°C of 100 to 1,000 cps.

Melamine resin serves to control the degree of curing and improve the hardness of the water-soluble clear coat composition. In one embodiment, alkylated melamine resin (Luwipal072, BASF) was used as the melamine resin.

The blocked polyisocyanate may be included, for example, in an amount of from 5 to 15 wt %, or from 6 to 13 wt %, based on the total weight of the water-soluble clear coat composition. In one embodiment, the blocked polyisocyanate was mixed in an amount of 7 wt % based on the total weight of the water-soluble clear coat composition, thereby producing a water-soluble clear coat composition that forms a coating film having excellent physical properties.

The water-soluble clear coat composition according to the present invention contains the blocked polyisocyanate according to the present invention, so that the water dispersibility is improved and can be used by diluting with water. In addition, the storage stability and weather resistance can be improved, and the coating film formed using the same can exhibit excellent physical properties such as appearance, gloss, adhesion, impact resistance, hardness, and scratch resistance.

The water-soluble clear coat composition according to the present invention may further contain conventional components included in water-based paint compositions, together with the blocked polyisocyanate according to the present invention, within a range that does not impede the purpose of the present invention.

The water-soluble clear coat composition according to the present invention may contain, as additives, a rheology modifier (e.g., RM12W, DOW) added to adjust the rheological behavior of the composition, a light stabilizer (e.g., Tinuvin 1130 / Tinuvin 123 = 2/1) for suppressing ultraviolet absorption and radical chain reaction caused by ultraviolet light, an acid catalyst (e.g., dodecylbenzenesulfonic acid type acid catalyst, NACURE 5225, King Industries) for promoting the reaction and controlling the curing speed, a defoaming agent (e.g., BYKETOL AQ, BYK) for suppressing foaming, a wetting agent (e.g., BYK-348, BYK) for improving wettability, etc.

Meanwhile, the water-soluble clear coat composition according to the present invention may contain an organic solvent within a range that does not deteriorate the physical properties of the paint, and may contain, for example, butyl carbitol, dipropylene glycol n-butyl ether, butyl cellosolve, etc.

Additionally, the water-soluble clear coat composition according to the present invention may include deionized water (DIW) as an aqueous solvent.

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

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

<Manufacture of Examples and Comparative Examples>

Block polyisocyanate was prepared by the following method with the compositions shown in Tables 1 and 2 below.

division Example 1 2 3 4 5 6 7 8 9 10 11 12 13 Hexamethylene diisocyanate (HMDI) trimer 44.73 46.79 41.55 41.45 47.06 49.11 38.09 44.78 44.68 44.31 46.38 44.26 46.3 Dimethylpyrazole (DMP) 18.54 20.73 14.96 15.64 20.48 22.65 11.98 19.03 16.44 19.91 16.33 19.3 17.46 Silquest A-1100 　 　 　 　 　 　 　 　 9.26 　 　 　 　 Silquest A-1170 7.07 2.9 13.99 6.98 7.07 2.93 14.01 　 　 1.2 17.53 7 7.14 Silquest Y-11699 　 　 　 　 　 　 　 6.5 　 　 　 　 　 Methoxy polyethylene glycol 9.72 9.7 9.7 16.17 5.39 5.47 16.18 9.73 9.72 9.82 9.8 4.34 18.94 Propylene glycol methyl ether acetate (PMA) 9.97 9.94 9.9 9.88 10 9.92 9.87 9.98 9.95 12.38 4.98 12.55 5.08 Butyl cellosolve 9.97 9.94 9.9 9.88 10 9.92 9.87 9.98 9.95 12.38 4.98 12.55 5.08 Total 100 100 100 100 100 100 100 100 100 100 100 100 100

division Comparative example 1 2 3 Hexamethylene diisocyanate (HMDI) trimer 53.41 49.99 48.14 Dimethylpyrazole (DMP) 26.67 22.95 22.18 Silquest A-1100 　 　 　 Silquest A-1170 　 7.12 　 Silquest Y-11699 　 　 　 Methoxy polyethylene glycol 　 　 9.72 Propylene glycol methyl ether acetate (PMA) 9.96 9.97 9.98 Butyl cellosolve 9.96 9.97 9.98 Total 100 100 100

Example 1

A four-necked flask equipped with a stirrer, a thermometer, a condenser, and a nitrogen inlet tube was charged with HMDI trimer in the amount listed in Table 1, and the temperature was raised to 40°C. Dimethylpyrazole (DMP) was added, and the temperature was slowly raised. While controlling exotherm generation, the temperature was raised to 80°C and maintained until the primary NCO% became 2.4 to 2.7%. When the primary NCO% became 2.4 to 2.7%, a silane blocking agent (lquest A-1170) was added, and the temperature was maintained at 80°C. When the secondary NCO% became 0.9 to 1.2%, methoxy polyethylene glycol was added, and the temperature was maintained at 80°C. When the NCO% became 0%, solvents propylene glycol methyl ether acetate (PMA) and butyl cellosolve were added, the reaction was terminated, and cooling was performed.

As a result of the reaction, a blocked polyisocyanate having a solid content of 80%, a Si(OR ¹ ) ₃ content of 5 wt%, and an alkoxide ((R ² O)) content of 9 wt% was produced.

The measurement of NCO% was performed using the following method.

Weigh the sample containing isocyanate group in a beaker (250 mL). Then, add 25 mL of 0.1 N di-n-butylamine solution using a pipette. Add 25 mL of 1,4-dioxane (if the polymer does not dissolve, add 10 mL of reagent grade acetone). Stopper the flask. Then, continue to stir mechanically for 15 minutes to dissolve the prepolymer. Add 4–6 drops of bromphenol blue indicator solution, and rinse the beaker wall with 50 mL of isopropyl alcohol. Titrate with 0.1 N hydrochloric acid until the yellow endpoint is reached. Add all the reagents above under the condition of no sample and perform a blank test.

The isocyanate group content is calculated as follows:

Solution: NCO content (%) = {(B-V) × N × 0.4202} / W (g)}

Here,

B: The number of mL of hydrochloric acid consumed in the blank test

V: mL of hydrochloric acid consumed for titration of sample

0.4202: Milliequivalent weight of isocyanate group

W: Weight of the sample

Examples 2 to 13

Examples 2 to 13 were performed using the same process as Example 1 using the ingredients and contents described in Table 1.

Comparative examples 1 to 3

Comparative Examples 1 to 3 were performed using the same process as Example 1 using the ingredients and contents described in Table 2.

The properties of the block polyisocyanates manufactured according to the examples and comparative examples are presented in Table 3 below.

Physical properties Example (%) Comparative example (%) 1 2 3 4 5 6 7 8 9 10 11 12 13 1 2 3 NV (%) 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00 75.00 90.00 75.00 90.00 80.00 80.00 80.00 Si(OR ¹ ) ₃ (%) 5.00 2.00 10.00 5.00 5.00 2.00 10.00 5.00 5.00 0.90 12.40 5.00 5.00 0.00 5.00 0.00 R ² O (%) 9.00 9.00 9.00 15.00 5.00 5.00 15.00 9.00 9.00 9.00 9.00 4.00 17.50 0.00 0.00 9.00

<Preparation of clear coat composition>

Examples 1 to 13 and Comparative Examples 1 to 3 were prepared by mixing the block polyisocyanate, water-soluble resin, additives, and solvents, respectively.

The contents of water-soluble resin, additives, solvents and blocked polyisocyanate are presented in Table 4 below.

ingredient Content Water-soluble resin Acrylic dispersion resin 25% Water-soluble polyester resin 10% Urethane dispersion resin 8% Acrylic emulsion resin 11% Melamine resin 12% Additives rheology modifier 1.50% Light stabilizer (UVA/HALS) 1.20% Acid catalyst 0.70% parcel 0.30% Wetting agent 1.50% Butyl carbitol 2.40% solvent DIW 10.00% Dipropylene glycol n-butyl ether 2.40% Butyl cellosolve 7.00% Block isocyanate 7.00% total 100%

The water-soluble resin, additives, and solvents were added in the same amounts, and the block polyisocyanates of Examples 1 to 13 and Comparative Examples 1 to 3 were added as block polyisocyanates, and examples of manufacturing clear coat compositions and comparative manufacturing examples are presented in Table 5 below.

division ingredient Manufacturing example Comparative manufacturing example 1 2 3 4 5 6 7 8 9 10 11 12 13 1 2 3 block
Isocyanate Example 1 ○ 　 　 　 　 　 　 　 　 　 　 　 Example 2 　 ○ 　 　 　 　 　 　 　 　 　 　 Example 3 　 　 ○ 　 　 　 　 　 　 　 　 　 Example 4 　 　 　 ○ 　 　 　 　 　 　 　 　 Example 5 　 　 　 　 ○ 　 　 　 　 　 　 　 Example 6 　 　 　 　 　 ○ 　 　 　 　 　 　 Example 7 　 　 　 　 　 　 ○ 　 　 　 　 　 Example 8 　 　 　 　 　 　 　 ○ 　 　 　 　 Example 9 　 　 　 　 　 　 　 　 ○ 　 　 　 Example 10 ○ Example 11 ○ Example 12 ○ Example 13 ○ Comparative Example 1 　 　 　 　 　 　 　 　 　 ○ 　 　 Comparative Example 2 　 　 　 　 　 　 　 　 　 　 ○ 　 Comparative Example 3 　 　 　 　 　 　 　 　 　 　 　 ○

<Evaluation of the physical properties of the film>

A primer paint was applied to a steel plate specimen subjected to electroplating and cured at 140°C for 20 minutes to form a primer film with a thickness of 30 to 50 μm. Thereafter, a base coat was bell sprayed on the primer film and hot air was blown at 80°C for 3 minutes to evaporate the water remaining in the paint and form a base film with a thickness of 15 μm. Thereafter, a clear coat composition manufactured in each of the Manufacturing Examples and Comparative Manufacturing Examples was painted on the base film and cured at 140°C for 20 minutes to form a clear film with a thickness of 40 μm to manufacture the final film.

The appearance characteristics and physical properties of the final coating were measured using the following methods, and the results are shown in Table 6.

(1) Appearance

The gloss (LU), clarity (SH) and orange peel (OP) of the manufactured final coating were measured using an automotive exterior measuring device, Wave Scan DOI (BYK Gardner), and the measured properties were used to calculate the comprehensive exterior evaluation value (CF) using the following mathematical formula 1.

[Mathematical formula 1]

CF = LU × 0.15 + SH × 0.35 + OP × 0.5

CF was measured and calculated horizontally and vertically. Based on the horizontal/vertical values of CF, if CF was 79/74 or higher, it was evaluated as excellent (◎), if CF was 75/70 or higher but less than 79/74, it was evaluated as good (○), if CF was 72/67 or higher but less than 75/70, it was evaluated as average (△), and if CF was less than 72/67, it was evaluated as poor (×).

(2) Scratch resistance

This method measures the scratch resistance of the finished coating using an automotive scratch resistance measuring device (AMTEC-KISTER). The 20-degree gloss of the coating surface before and after the test is measured, and the gloss retention rate (%) is calculated and then evaluated. According to the measurement results, if the gloss retention rate (%) is 70% or more, it is evaluated as excellent (◎), if it is 60% or more but less than 70%, it is evaluated as good (○), if it is 50% or more but less than 60%, it is evaluated as average (△), and if it is less than 50%, it is evaluated as poor (×).

(3) Gloss

To measure the gloss (GLOSS, %) reflected from the coating, a gloss meter (BYK Gardner) was applied to measure the ^20o gloss of the final coating. According to the measurement results, if the gloss was 91% or higher, it was evaluated as excellent (◎), if it was 89% or higher but less than 91%, it was evaluated as good (○), if it was 87% or higher but less than 89%, it was evaluated as fair (△), and if it was less than 87%, it was evaluated as poor (×).

(4) Chipping resistance

After leaving the final coating at -20℃ for 3 hours, a 50g chipping stone (diameter 4mm) was struck at a ^45o angle under a pressure of 5 bar. Thereafter, foreign substances such as peeled coating remaining on the final coating were removed. Regarding the damaged areas of the final coating, if there were 10 or fewer damaged areas of 1mm or less, it was evaluated as excellent (◎), if there were 10 or fewer damaged areas of more than 1mm but less than 2mm, it was evaluated as good (○), if there were 10 or fewer damaged areas of 2mm or more but less than 3mm, it was evaluated as fair (△), and if there were more than 10 damaged areas of 2mm or more but less than 3mm, it was evaluated as poor (×).

(5) Hardness

The hardness of the clear coating was measured using the pencil hardness method. Specifically, the maximum hardness that did not damage the clear coating was measured using pencils 2B, B, HB, F, H, and 2H, respectively.

If the measurement result is HB or higher, it is evaluated as excellent (◎), if it is B, it is good (○), and if it is below B, it is evaluated as poor (×).

(6) Impact resistance

The impact resistance of the final coating was evaluated according to ASTM D2794. A DuPont impact tester was used, and the appearance of the coating was observed when a 500 g weight was dropped on the specimen while changing the dropping height from 30 cm to 50 cm.

As a result of the observation, if no cracks or peeling of the coating occurred when the drop height was 50 cm or more, it was evaluated as excellent (◎). If cracks or peeling of the coating occurred at a drop height of 30 cm or more but less than 50 cm, it was evaluated as good (○). If cracks or peeling of the coating occurred at a drop height of 20 cm or more but less than 30 cm, it was evaluated as average (△). If cracks or peeling of the coating occurred at a drop height of less than 20 cm, it was evaluated as poor (×).

(7) Water resistance

The final coating was immersed in a 40℃ constant temperature water bath for 240 hours and left at room temperature for 1 hour. The adhesion was evaluated using the baduk method and discoloration was visually confirmed.

Specifically, the Baduk method is a method in which 100 squares measuring 2 mm in width and 2 mm in length are made on the surface of a clear coating with a knife, and then the squares are removed using tape to measure the adhesion. Adhesion is evaluated as good (○) if 70% or more but less than 100% of the 100 squares remain, and as poor (×) if less than 70% remain.

If the measurement results showed good adhesion and no discoloration, it was evaluated as excellent (◎), if the adhesion was good but recovered after discoloration, it was evaluated as fair (△), and if the adhesion was poor or discolored, it was evaluated as poor (×).

(8) Content

A cotton cloth soaked in xylene solvent was placed on the surface of the final coating, and the time until the base coating surface appeared was measured by scratching it four times with a fingernail at a force of 2 kgf per minute.

The measurement results were evaluated as excellent (◎) for 10 minutes or longer, good (○) for 7 minutes or longer but less than 10 minutes, fair (△) for 5 minutes or longer but less than 7 minutes, and poor (×) for 5 minutes or less.

(9) Weather resistance

The final coating was tested for gloss retention (20 ^ㅇ gloss), adhesion, and color difference (X-Rite MA98) before and after 1,000 hours of exposure on a WOM, a weathering tester.

Specifically, the adhesion was evaluated using the checkerboard method of item (7), and if the remaining squares were 100%, the gloss retention rate was 95% or higher, and the color difference value (△E) was 1.0 or lower, it was evaluated as excellent (◎). If the remaining squares were 100%, the gloss retention rate was 90% or higher but lower than 95%, and the color difference value (△E) was 1.0 or lower, it was evaluated as good (○). If the remaining squares were less than 90%, the gloss retention rate was lower than 90%, and the color difference value (△E) was higher than 1.0, it was evaluated as poor (×).

Film properties Manufacturing example Comparative manufacturing example 1 2 3 4 5 6 7 8 9 10 11 12 13 1 2 3 appearance ◎ ○ ○ ○ ○ ○ ○ ◎ ◎ △ △ △ △ △ △ ○ Scratch resistance ◎ ○ ○ ○ ◎ ○ ○ ◎ ◎ △ ○ ◎ △ X ○ X gloss ◎ ○ ◎ ○ ○ ○ ◎ ◎ ◎ ○ ○ △ △ △ △ △ Chipping resistance ◎ ○ ◎ ◎ ◎ ○ ◎ ◎ ◎ △ ◎ ○ ◎ △ △ △ Impact resistance ◎ ○ ◎ ◎ ◎ ◎ ◎ ◎ ◎ △ ◎ ○ ○ X ○ X hardness ◎ ○ ◎ ○ ◎ ◎ ◎ ◎ ◎ ○ ◎ ◎ △ X ○ ○ Water resistance ◎ ◎ ◎ ○ ◎ ○ ○ ◎ ◎ ◎ ◎ ◎ △ X X ○ Content ◎ ◎ ◎ ◎ ○ ◎ ◎ ◎ ◎ ◎ ○ △ ○ ○ ○ ○ Weather resistance ◎ ○ ○ ◎ ◎ ○ ◎ ◎ ◎ △ △ ◎ ◎ X △ X Evaluation: ◎-Excellent, ○-Good, △-Average, X-Poor

As can be seen in Table 6, it was confirmed that silane-based blocking agents are effective in improving the scratch resistance, impact resistance, and weather resistance of paints, polyalkylene polyol blocking agents are effective in improving the appearance and water resistance, and pyrazole-based blocking agents are effective in improving the gloss of paints.

Although the present invention has been described in detail above only with respect to the described embodiments, it will be apparent to those skilled in the art that various modifications and variations are possible within the technical scope of the present invention, and it is natural that such modifications and variations fall within the scope of the appended claims.

Hereinafter, various embodiments of the present invention will be described.

(1) A blocked polyisocyanate obtained from a polyisocyanate compound and a blocking agent, the blocked polyisocyanate containing a first block isocyanate group in which an isocyanate group is blocked by a silane-based blocking agent, a second block isocyanate group in which an isocyanate group is blocked by a polyalkylene polyol blocking agent, and a third block isocyanate group in which an isocyanate group is blocked by a pyrazole-based blocking agent.

(2) A blocking agent, based on the total weight of the composition for producing a block polyisocyanate, comprises 2 to 15 wt% of a silane-based blocking agent, 5 to 17 wt% of a polyalkylene polyol blocking agent, and 11 to 23 wt% of a pyrazole-based blocking agent.

(3) A blocked polyisocyanate comprising at least one silane blocking agent selected from the group consisting of gamma-aminopropyltrimethoxysilane, bis(trimethoxysilylpropyl)amine, organoalkoxysilane, 3-glycidoxypropyl trimethoxysilane, N-(2-aminoethyl)3-aminopropyltrimethoxysilane, bis-gamma-trimethoxysilylpropylamine, bis-gamma-triethoxysilylpropylamine, and aminopropyltriethoxysilane.

(4) Block polyisocyanate comprising at least one polyalkylene polyol blocking agent selected from the group consisting of polyethylene glycol (PEG), polytetramethylene oxide (PTMO), polypropylene oxide (PPO), monoalkoxy polyethylene glycol, polyethylene triol, polypropylene triol alone, or copolymers thereof.

(5) A pyrazole-based blocking agent is a blocked polyisocyanate comprising at least one selected from the group consisting of pyrazole, 3-methylpyrazole, and 3,5-dimethylpyrazole.

(6) A blocked polyisocyanate having a solid content (NV) of 70 to 90 wt%, a Si(OR ¹ ) ₃ content of 1 to 11 wt%, and an alkoxide ((R ² O)) content of 5 to 15 wt%, based on the total weight of the blocked polyisocyanate.

(7) A water-soluble clear coat composition comprising a block polyisocyanate according to any one of items (1) to (6) and a water-soluble resin portion, wherein the water-soluble resin portion comprises an acrylic dispersion resin, a water-soluble polyester resin, a urethane dispersion resin, an acrylic emulsion resin, and a melamine resin.

(8) A water-soluble clear coat composition comprising 5 to 15 parts by weight of a block polyisocyanate and 38 to 140 parts by weight of a water-soluble resin.

(9) A water-soluble clear coat composition, wherein the water-soluble resin portion comprises 20 to 50 parts by weight of an acrylic dispersion resin, 1 to 15 parts by weight of a water-soluble polyester resin, 1 to 15 parts by weight of a urethane dispersion resin, 1 to 15 parts by weight of an acrylic emulsion resin, and 10 to 30 parts by weight of a melamine resin.

Claims (9)

A blocked polyisocyanate obtained from a polyisocyanate compound and a blocking agent,
It contains a first block isocyanate group in which the isocyanate group is blocked by a silane blocking agent, a second block isocyanate group in which the isocyanate group is blocked by a polyalkylene polyol blocking agent, and a third block isocyanate group in which the isocyanate group is blocked by a pyrazole blocking agent.
A blocked polyisocyanate, wherein the blocking agent comprises 6 to 10 wt% of a silane-based blocking agent, 8 to 13 wt% of a polyalkylene polyol blocking agent, and 14 to 21 wt% of a pyrazole-based blocking agent, based on the total weight of the composition for producing the blocked polyisocyanate. delete In claim 1,
A blocked polyisocyanate comprising at least one silane blocking agent selected from the group consisting of gamma-aminopropyltrimethoxysilane, bis(trimethoxysilylpropyl)amine, organoalkoxysilane, 3-glycidoxypropyl trimethoxysilane, N-(2-aminoethyl)3-aminopropyltrimethoxysilane, bis-gamma-trimethoxysilylpropylamine, bis-gamma-triethoxysilylpropylamine, and aminopropyltriethoxysilane. In claim 1,
A polyalkylene polyol blocking agent is a blocked polyisocyanate comprising at least one selected from the group consisting of polyethylene glycol (PEG), polytetramethylene oxide (PTMO), polypropylene oxide (PPO), monoalkoxypolyethylene glycol, polyethylene triol, polypropylene triol alone, or copolymers thereof. In claim 1,
A pyrazole blocking agent is a blocked polyisocyanate comprising at least one selected from the group consisting of pyrazole, 3-methylpyrazole and 3,5-dimethylpyrazole. In claim 1,
Based on the total weight of the block polyisocyanate, the solid content (NV) is 70 to 90 wt%, the Si(OR ¹ ) ₃ content is 1 to 11 wt%, and the alkoxide ((R ² O)) content is 5 to 15 wt%.
A blocked polyisocyanate wherein R ¹ is an alkyl group having 1 to 2 carbon atoms and R ² is an alkyl group having 1 to 4 carbon atoms. A water-soluble clear coat composition comprising a block polyisocyanate and a water-soluble resin part according to any one of claims 1, 3 to 6,
A water-soluble clear coat composition, wherein the water-soluble resin portion includes an acrylic dispersion resin, a water-soluble polyester resin, a urethane dispersion resin, an acrylic emulsion resin, and a melamine resin. In claim 7,
A water-soluble clear coat composition comprising 5 to 15 parts by weight of a block polyisocyanate and 38 to 140 parts by weight of a water-soluble resin. In claim 7,
A water-soluble clear coat composition, wherein the water-soluble resin portion comprises 20 to 50 parts by weight of an acrylic dispersion resin, 1 to 15 parts by weight of a water-soluble polyester resin, 1 to 15 parts by weight of a urethane dispersion resin, 1 to 15 parts by weight of an acrylic emulsion resin, and 10 to 30 parts by weight of a melamine resin.