KR102643078B1 - Pyrazole based block isocyanate capable of radical reaction for low temperature curing and composition comprising the same - Google Patents

Abstract

The present invention relates to a low-temperature crosslinkable pyrazole-based block isocyanate capable of radical reaction and a composition containing the same. More specifically, a pyrazole derivative functionalized with meth(acrylate) is an isocyanate. ) is a low-temperature crosslinking type pyrazole-based block isocyanate used as a blocking group to control the reactivity of , and crosslinking is possible through deblocking of the isocyanate group and subsequent reaction with the hydroxyl group at a relatively low temperature of 100 to 130 ℃, and meta Blocking agents with (a) acrylate groups are present in the crosslinked film and can participate in additional radical polymerization during the heat curing process, and as a result of this radical polymerization, the crosslink density can be improved during the deblocking process at the corresponding heat curing temperature conditions. It relates to a low-temperature cross-linking pyrazole-based block isocyanate capable of radical reaction and a composition containing the same. The low-temperature crosslinking composition according to one embodiment of the present invention is not only capable of double curing, but can also be potentially applied to various coating materials due to the low curing temperature and improved surface mechanical properties of the coating layer.

Description

Low-temperature cross-linking pyrazole-based block isocyanate capable of radical reaction and composition comprising the same {Pyrazole based block isocyanate capable of radical reaction for low temperature curing and composition comprising the same}

The present invention relates to a low-temperature crosslinkable pyrazole-based block isocyanate capable of radical reaction and a composition containing the same. More specifically, a pyrazole derivative functionalized with meth(acrylate) is an isocyanate. ) is a low-temperature cross-linking type pyrazole-based block isocyanate used as a blocking group to control the reactivity of ), enabling cross-linking through deblocking of the isocyanate group and subsequent reaction with the hydroxyl group at a relatively low temperature of 100 to 130 ℃. In addition, the blocking agent having a meta(acrylate) group is present in the crosslinked film and can participate in additional radical polymerization during the heat curing process, and as a result of this radical polymerization, the crosslink density increases during the deblocking process under the corresponding heat curing temperature conditions. It relates to a low-temperature crosslinking pyrazole-based block isocyanate capable of radical reaction that can improve and a composition containing the same.

Polyurethanes have been developed for various uses such as adhesives, coatings, packaging materials, insulation materials, and flame retardants through reactions with isocyanate compounds and hydroxyl group-containing compounds. Despite the rapid progress in the synthesis of isocyanates, polyols and catalysts in the production of polyurethane, the moisture sensitivity and toxicity of isocyanates have been an obstacle in the industrial aspect, requiring careful storage of isocyanate compounds, and solving these problems has become an obstacle. To this end, much research has been conducted on the development of blocked isocyanates, in which isocyanates are blocked with compounds with specific chemical structures having active hydrogen, such as oximes, imidazoles, pyrazoles, triazoles, amines, phenols, and malonates. It has been done.

This blocking reaction of isocyanate is possible at room temperature or relatively low temperature, resulting in inertness and low toxicity to moisture and nucleophiles, and the deblocking reaction of this blocked isocyanate is possible at elevated temperature, allowing accurate deblocking reaction. The blocking reaction can be controlled based on the steric effect and electronegativity of the blocking agent and the chemical structure of the isocyanate.

Meanwhile, this blocked isocyanate could be used as a one-component (1K) composition in the automobile clear coat layer that protects the outer surface of the automobile body from external damage or provides gloss and transparency, and a typical automobile clear coat is used at 150°C. The thermal crosslinking process is carried out under conditions of 25 to 30 min, and these crosslinking conditions consume high energy, leading not only to economic problems but also to environmental and ecological problems such as carbon dioxide emissions. The heavier the car body, the more energy it requires to move. To solve this problem, it is essential to convert the car body to a plastic material rather than a metal-based material to lighten the car. In order to improve fuel efficiency and save energy, various studies are currently being conducted to reduce the weight of automobiles by applying high-performance engineering polymers that can replace metal materials as automobile materials.

Common automobile materials consist of the car body and chassis frame. Most of them are metal materials and can withstand cross-linking reaction without sufficient deformation even at a high temperature of 150℃, so the car body is painted using a high-temperature curing coating process. However, lightweight plastic materials have the physical and chemical properties of polymer materials. Due to its nature, deformation and distortion occur at high temperatures, so it is required that curing reaction and crosslinking occur below the glass transition temperature of the plastic substrate of the automobile body.

Currently, most low-temperature curing coating technologies are approaching isocyanate, which is highly reactive with hydroxyl groups, stored in a separate storage tank in a two-component form and mixed separately only at specific times of use. It is partially applied to parts painting and repair processes, but its application is limited because it requires a temperature condition of over 120℃ and the mechanical properties provided are not high.

Looking at the patented technologies for forming low-temperature curing coatings and paints as described above, Korean Patent Registration No. 10-0409152 (announced on January 6, 2003) shows excellent appearance smoothness and water resistance, as well as low-temperature curing and chipping resistance. A method for manufacturing an improved one-component urethane resin composition for automotive anti-chipping primer and intermediate coating is disclosed, wherein a monomer polyol with a molecular weight of 500 or less and an oligomer polyol with a molecular weight of 2,000 or less are mixed so that the mixing ratio of the monomer polyol and the oligomer polyol is adjusted to an equivalent ratio. 0.2~0.8: A technique for producing a compound having an amino functional group or a resin having a hydroxyl functional group by mixing to 0.8~0.2 and blocking the isocyanate functional group by adding and stirring a blocking agent for the isocyanate functional group to the resulting mixture. , technology for paints manufactured using pigments, additives, and solvents is disclosed.

In addition, Korean Patent Publication No. 10-0484060 (announced on December 28, 2005) states that polyethylene glycol containing a polyethylene oxide group as the main resin is 0.3 to 10.0% of the solid content, and the acid value before neutralization with dimethylolpropionic acid is 16 to 36 mgKOH/ g, a hydroxyl value of 60 to 120 mgKOH/g, a water-dispersed polyurethane polyol resin with a weight average molecular weight of 300 to 6,000, and a water-soluble amino resin as a curing resin, and an acid value of 25 to 50 mgKOH/g before neutralization with dimethylolpropionic acid, block A method for a low-temperature curing and high-solids water-soluble paint composition comprising a resin composition composed of a water-dispersed block polyisocyanate resin with an isocyanate group content of 4.0 to 15.0% by weight and a weight average molecular weight of 1,500 to 5,000. This is disclosed.

In addition, Korean Patent Publication No. 10-1859813 (announced on May 18, 2018), which is the inventor's earlier registered patent of the present invention, is about a new block isocyanate with a dual curing reactive structure with different dissociation temperature, block isocyanate Fast work is possible by first forming a curing reaction on the surface and interface as the blocking group, which can be dissociated at low temperature, is dissociated. Afterwards, internal crosslinking occurs as the temperature rises and the deblocked pre-isocyanate progresses, making it a process-friendly solution. It has shown the advantage of being highly usable in coatings, paints, and adhesive technologies where surface hardening must occur quickly.

As previously explained, the deblocking temperature of blocking agents for automotive clearcoat materials must be lower than 150°C, so the inventors of the present invention reported on the reactivity and curing efficiency of isocyanate crosslinking agents blocked by imidazole groups and found that the larger imidazole It has been demonstrated that derivatives can lower the unblocking temperature more efficiently (Coatings, 2020, 10, 974), and also that pyrazoles with bulky three-dimensional configurations have lower deblocking temperatures. It has been reported (Coatings, 2020, 10, 961) that it can contribute to higher curing speeds and greater efficiency.

However, although bulkier blocking agents provide lower deblocking temperatures, they may remain in the crosslinked film or evaporate from the film, undesirably affecting the mechanical properties of the film. To overcome the poor mechanical properties of thermosetting polyurethane films, the inventors of the present invention have made extensive efforts to improve both mechanical properties and storage modulus by introducing a dual-cure clearcoat system. As an example, this system consists of a polyol binder containing a radical reactive double bond and a hydroxyl group along with an isocyanate curing agent (Prog. Org. Coat. 2012, 74, 257?269 and Prog. Org. Coat. 2018, 125, 160? 166), it was confirmed that although the overall mechanical properties were improved, the dissociated blocking agent still remained in the crosslinked film, which could have a negative effect on the appearance of the film.

In the present invention, DFT (Density Functional Theory) simulation is performed to predict the activation energy (Ea) of the deblocking process and the H-N distance of the pyrazole molecule, and the isocyanate blocking agent enables deblocking at low temperatures by meta(acrylate)-functionalization. developed pyrazole derivatives. According to the present invention, due to the presence of the meta(acrylate) group, the blocking agent can participate in additional radical polymerization during the heat curing process, and as a result of this radical polymerization, the blocking agent remains in the crosslinked film, thereby maintaining the corresponding heat curing temperature. The present invention was completed by confirming that crosslinking density could be improved during the deblocking process under these conditions.

Korean Patent Publication No. 10-0409152 (announced on January 6, 2003). Korean Patent Publication No. 10-0484060 (announced on December 28, 2005). Korean Patent Publication No. 10-1859813 (announced on May 18, 2018).

Coatings, 2020, 10, 974. Coatings, 2020, 10, 961. Prog. Org. Coat. 2012, 74, 257-269. Prog. Org. Coat. 2018, 125, 160-166.

In order to solve the above problems, the present invention provides a low-temperature cross-linking block isocyanate capable of deblocking isocyanate groups at a relatively low temperature of 100 to 130 ° C. and a low-temperature cross-linking composition containing the same. We would like to provide

In addition, the present invention seeks to provide an isocyanate blocking agent and a low-temperature crosslinking composition in which the deblocked isocyanate blocking agent remains in the crosslinked film or evaporates from the film and does not have an undesirable effect on the mechanical properties of the film.

In addition, the present invention seeks to provide a low-temperature crosslinking composition in which a blocking agent is present in the composition after the deblocking reaction and additional radical polymerization is possible, thereby improving the crosslinking density.

In order to solve the above problems, the present invention provides a low-temperature crosslinking pyrazole-based blocked isocyanate using a pyrazole derivative functionalized with a meta(acrylate) group as a blocking group to control the reactivity of isocyanate. .

In addition, in the present invention, a low-temperature crosslinking type pyrazole-based block isocyanate capable of radical reaction; and a polyol.

Due to the presence of a meta(acrylate) group in the low-temperature crosslinking pyrazole-based blocked isocyanate according to the present invention, the blocking agent can participate in additional radical polymerization during the heat curing process, and as a result of this radical polymerization, the blocking agent is crosslinked. Remaining in the film, the crosslinking density can be further improved during the deblocking process at the corresponding heat curing temperature conditions.

In addition, the low-temperature crosslinking composition according to the present invention is capable of forming a methacrylate-functionalized pyrazole derivative through an efficient deblocking reaction at a lower temperature due to additional radical polymerization resulting in bond dissociation energy (BDE) and higher crosslinking density. Isocyanate balllocked by can improve the mechanical properties of the surface of the crosslinked composition.

The present invention complements the shortcomings of the one-component coating system based on a high temperature curing process, which is commercialized and applied in the automotive industry, and the two-component coating system, which has problems with low workability and recycling, and is expected to transition to a lightweight material. It has the advantage of being a coating system that can be cured in the temperature range of 100~130℃, suitable for automobile body, and provides better mechanical properties on the surface of automobile body even in low temperature range, while saving energy and reducing greenhouse gas emissions through low-temperature curing reaction. It has the advantage of being able to significantly reduce.

Figure 1 shows a method for producing a pyrazole-based isocyanate blocking agent according to an embodiment of the present invention, and shows the synthesis method of (a) Example and (b) Comparative Example.
Figure 2 shows (a) 1H-NMR spectrum of a pyrazole-based isocyanate blocking agent and (b) FTIR spectrum of hexamethylene diisocyanate trimer (HDI Trimer) blocked with a pyrazole-based blocking agent according to an embodiment of the present invention. .
Figure 3 shows the blocking reaction of hexamethylene diisocyanate trimer (HDI Trimer) using a pyrazole-based blocking agent according to an embodiment of the present invention.
Figure 4 shows the results of the RPT test (rigid-body pendulum test) of the clear coat cured at different curing temperatures (a) 110 ℃, (b) 120 ℃ and (C) 130 ℃ according to an embodiment of the present invention. will be.
Figure 5 shows rheological curing behavior by real-time storage modulus at different curing temperatures (a) 110 °C, (b) 120 °C and (C) 130 °C according to an embodiment of the present invention.
Figure 6 shows the urethane reaction and radical reaction under thermal crosslinking conditions between hexamethylene diisocyanate trimer (HDI Trimer) and polyester polyol blocked with a pyrazole-based blocking agent capable of radical reaction according to an embodiment of the present invention.
Figure 7 compares the thermal properties of a clear coat film cured at 130°C according to an embodiment of the present invention, showing (a) thermal stability by TGA and (b) glass transition temperature by secondary heating DSC. .
Figure 8 compares the thermal properties of clear coat films cured at 130°C according to an embodiment of the present invention, showing (a) DMA for storage modulus and (b) tan δ.
Figure 9 shows the indentation curve of a clear coat film cured at (a) 120 and (b) 130 ° C. according to an embodiment of the present invention, and (c) is the indentation hardness (HIT) value based on the Oliver and Pharr method. It represents.
Figure 10 shows the indentation curve of the cured clear coat film according to the solvent used when manufacturing the clear coat according to an embodiment of the present invention, and the indentation hardness (HIT) value based on the Oliver and Pharr method.

Hereinafter, the present invention will be described in detail. Terms or words used in this specification and claims should not be construed as limited to their common or dictionary meanings, and the inventor may appropriately define the concept of terms in order to explain his or her invention in the best way. It must be interpreted with meaning and concept consistent with the technical idea of the present invention based on the principle that it is.

In order to solve the above problems, the present invention provides a pyrazole-based isocyanate blocking agent capable of radical reaction, which has the chemical structure of the following formula (A).

<Formula A>

In Formula A, R is hydrogen or a methyl group, and R1 is an alkyl group having 1 to 8 carbon atoms.

In addition, the present invention provides a low-temperature crosslinkable pyrazole-based block isocyanate capable of radical reaction, which is prepared through a urea bond formation reaction between a compound of the following formula (A) and a polyisocyanate compound.

<Formula A>

In Formula A, R is hydrogen or a methyl group, and R1 is an alkyl group having 1 to 8 carbon atoms.

According to one embodiment of the present invention, the compound of Formula A may be any one of Formulas 1 to 3 below.

<Formula 1>

<Formula 2>

<Formula 3>

According to one embodiment of the present invention, the polyisocyanate compound may be an aliphatic, aromatic, alicyclic, or araliphatic compound containing two or more isocyanate groups in the molecular structure, and in this case, the polyisocyanate compound may be a dimer. It may have a multimer form such as a dimer or trimer, and a representative trimer form includes hexamethylene diisocyanate trimer.

According to one embodiment of the present invention, the polyisocyanate compound is ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), octamethylene diisocyanate, nonamethylene diisocyanate, and dodecamethylene diisocyanate. Isocyanate, 2,2-dimethylpentane diisocyanate, 2,2,4-trimethyl hexamethylene diisocyanate, decamethylene diisocyanate, butene diisocyanate, 1,3-butadiene-1,4-diisocyanate, 2,4,4 -Trimethyl hexamethylene diisocyanate, 1,6,11-undecane triisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2,6-diisocyanate methyl caproate, bis(2-isocyanate ethyl) ) fumarate, bis (2-isocyanate ethyl) carbonate, 2-isocyanate ethyl-2,6-diisocyanate hexanoate, 1,3,6-hexamethylene triisocyanate, 1,8-diisocyanato -4-Isocyanatomethyl octane, 2,5,7-trimethyl-1,8-diisocyanato-5-isocyanatomethyl octane, bis(isocyanatoethyl) carbonate, bis(isocyanatoethyl) ether , 1,4-butylene glycol dipropyl ether-ω,ω'-diisocyanate, lysine diisocyanato methyl ester, lysine triisocyanate, 2-isocyanatoethyl-2,6-diisocyanato ethyl-2,6 -Diisocyanato hexanoate, 2-isocyanato propyl-2,6-diisocyanato hexanoate, 2,6-di(isocyanatomethyl) furan, 1,3,-bis(6-isocy) It may be one or more aliphatic isocyanates selected from the group consisting of anatohexyl)-uretidine-2,4-dione and 1,3,5-tris(6-isocyanatohexyl)isocyanurate.

Alternatively, the polyisocyanate compound may be thiodiethyl diisocyanate, thiopropyl diisocyanate, thiodihexyl diisocyanate, dimethyl sulfone diisocyanate, dithio dimethyl diisocyanate, dithio diethyl diisocyanate, dithio propyl diisocyanate, dicyclo It may be one or more sulfur-containing aliphatic isocyanates selected from the group consisting of hexyl sulfide-4,4'-diisocyanate.

Alternatively, the polyisocyanate compound may be diphenyl sulfide-2,4'-diisocyanate, diphenyl sulfide-4,4'-diisocyanate, 3,3'-dimethoxy-4,4'-diisocyanato dibenzyl thio. Aromatic sulfide isocyanates such as ether, bis(4-isocyanatomethyl benzene) sulfide, 4,4'-methoxy benzene, thioethylene glycol-3,3'-diisocyanate, and diphenyl disulfide-4,4'-di. Isocyanate, 2,2'-dimethyldiphenyl disulfide-5,5'-diisocyanate, 3,3'-dimethyldiphenyl disulfide-5,5'-diisocyanate, 3,3'-dimethyldiphenyl disulfide-6, 6'-diisocyanate, 4,4'-dimethyldiphenyl disulfide-5,5'-diisocyanate, 3,3'-dimethoxy diphenyl disulfide-4,4'-diisocyanate, 4,4'-dimethoxy It may be one or more aromatic disulfide-based isocyanates selected from the group consisting of diphenyl disulfide-3,3'-diisocyanate.

According to one embodiment of the present invention, the polyisocyanate compound is 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 2,4-tolylene diisocyanate (TDI), 2,6-tolylene Diisocyanate, 4,4'-diphenylenemethane diisocyanate (MDI), 2,4-diphenylmethane diisocyanate, ethyl phenylene diisocyanate, 4,4'-diisocyanate biphenyl, 3,3'-dimethyl- 4,4'-diisocyanate biphenyl, 3,3'-dimethyl-4,4'-diisocyanate diphenylmethane, naphthalene diisocyanate, methyl naphthalene diisocyanate, trizine diisocyanate, bis(isocyanatophenyl) ethylene , 3,3'-dimethoxybiphenyl-4-4'-diisocyanate, isopropylenephenylene diisocyanate, dimethylphenylene diisocyanate, diethylphenylene diisocyanate, diisopropylphenylene diisocyanate, trimethyl Benzene triisocyanate, benzene triisocyanate, triphenylmethane triisocyanate, naphthalene triisocyanate, diphenylmethane-2,4,4'-triisocyanate, 3-methyl diphenylmethane-4,6,4'-triisocyanate, 4 -Methyl-diphenylmethane-3,5,2',4',6'-pentaisocyanate, xylylene diisocyanate, bis(isocyanatoethyl)benzene, bis(isocyanatopropyl)benzene, α,α , α',α'-tetramethyl xylylene diisocyanate, bis(isocyanatobutyl)benzene, bis(isocyanatomethyl)naphthalene, bis(isocyanatomethyl)diphenyl ether, bis(isocyanatoethyl) ) It may be one or more aromatic isocyanates selected from the group consisting of phthalates.

Alternatively, the polyisocyanate compound may be diphenyl sulfone-4,4'-diisocyanate, diphenyl sulfone-3,3'-diisocyanate, diphenylmethane sulfone-4,4'-diisocyanate, or 4-methyl diphenylmethane. Sulfone-2,4'-diisocyanate, 4,4'-dimethoxy diphenyl sulfone-3,3'-diisocyanate, 3,3'-dimethoxy-4,4'-diisocyanate dibenzyl sulfone, 4, 4'-Dimethyldiphenylsulfone-3,3'-diisocyanate, 4,4'-di-tert-butyl diphenyl sulfone-3,3'-diisocyanate, 4,4'-methoxy benzene ethylene disulfone- It may be one or more aromatic sulfone isocyanates selected from the group consisting of 3,3'-diisocyanate and 4,4'-dichlorophenylsulfone-3,3'-diisocyanate.

According to one embodiment of the present invention, the polyisocyanate compound is isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (HMDI), cyclohexylene diisocyanate, methylcyclohexylene diisocyanate, Bis(2-isocyanateethyl)-4-cyclohexene-1,2-dicarboxylate, 2,5-norbornane diisocyanate, 2,6-norbornane diisocyanate, 2,2-dimethyl dicyclohexyl Methane diisocyanate, 2-isocyanatomethyl-3-(3-isocyanato propyl)-5-isocyanatomethyl-bicyclo[2,2,1]-heptane, 2-isocyanatomethyl-3- (3-isocyanatopropyl)-6-isocyanatomethyl-bicyclo[2,2,1]-heptane, 2-isocyanatomethyl-2-(3-isocyanatopropyl)-5-isocyanate Nattomethyl-bicyclo[2,2,1]-heptane, 2-isocyanatomethyl-2-(3-isocyanatopropyl)-6-isocyanatomethyl-bicyclo[2,2,1]- Heptane, 2-isocyanatomethyl-3-(3-isocyanatopropyl)-6-(2-isocyanatoethyl)-bicyclo [2,2,1]-heptane, 2-isocyanatomethyl- 3-(3-isocyanatopropyl)-6-(2-isocyanatoethyl)-bicyclo[2,1,1]-heptane, 2-isocyanatomethyl-2-(3-isocyanatopropyl )-5-(2-isocyanatoethyl)-bicyclo [2,1,1]-heptane, 2-isocyanatomethyl-2-(3-isocyanatopropyl)-6-(2-isocyanate It may be one or more alicyclic isocyanates selected from the group consisting of natoethyl)-bicyclo[2,2,1]-heptane and norbornane bis(isocyanatomethyl).

According to one embodiment of the present invention, the polyisocyanate compound is 1,3-bis (isocyanatomethyl) benzene (m-xylene diisocyanate, m-XDI), 1,4-bis (isocyanatomethyl) benzene (p-xylene diisocyanate, p-XDI), 1,3-bis(2-isocyanato propan-2-yl)benzene (m-tetramethyl xylene diisocyanate, m-TMXDI), 1,4-bis( 2-Isocyanato propan-2-yl) benzene (p-tetramethyl xylene diisocyanate, p-TMXDI), 1,3-bis(isocyanatomethyl)-4-methylbenzene, 1,3-bis(iso Cyanatomethyl)-4-ethylbenzene, 1,3-bis(isocyanatomethyl)-5-methylbenzene, 1,3-bis(isocyanatomethyl)-4,5-dimethylbenzene, 1,4- Bis(isocyanatomethyl)-2,5-dimethylbenzene, 1,4-bis(isocyanatomethyl)-2,3,5,6-tetramethylbenzene, 1,3-bis(isocyanatomethyl) -5-tert-butyl benzene, 1,3-bis(isocyanatomethyl)-4-chlorobenzene, 1,3-bis(isocyanatomethyl)-4,5-dichlorobenzene, 1,3-bis( Isocyanatomethyl)-2,4,5,6-tetrachlorobenzene, 1,4-bis(isocyanatomethyl)-2,3,5,6-tetrachlorobenzene, 1,4-bis(isocyanate) Natomethyl)-2,3,5,6-tetrabromo benzene, 1,4-bis (2-isocyanatoethyl) benzene, 1,4-bis (isocyanatomethyl) naphthalene selected from the group consisting of It may be one or more aromatic aliphatic isocyanates.

According to one embodiment of the present invention, the block isocyanate may be a pyrazole-based low-temperature crosslinking block isocyanate capable of radical reaction, which is characterized by having the chemical structure of the following formula (3).

<Formula 3>

In Formula 3, R is hydrogen or a methyl group, and R1 is an alkyl group having 1 to 8 carbon atoms.

In addition, in the present invention, a low-temperature crosslinking type pyrazole-based block isocyanate capable of the radical reaction; and a polyol.

According to one embodiment of the present invention, the polyol may be one or more selected from polyester polyol, polyacrylate polyol, polycarbonate polyol, polyether polyol, polyurethane polyol, melamine polyol, and mixtures thereof.

Additionally, in the present invention, the low-temperature crosslinking composition preferably has a crosslinking reaction temperature of 100 to 130°C.

Additionally, in the present invention, 10 to 35% by weight of at least one polyol having a hydroxyl group; A pyrazole-based low-temperature cross-linking block isocyanate capable of radical reaction, which is prepared through a urea bond formation reaction between a compound of the following formula (A) and a polyisocyanate compound; and 25 to 35% by weight of a mixture containing a reactive diluent, an ultraviolet absorber or stabilizer, a leveling agent, and a solvent.

<Formula A>

In Formula A, R is hydrogen or a methyl group, and R1 is an alkyl group having 1 to 8 carbon atoms.

In the low-temperature crosslinking one-component clear coat composition for automobiles according to the present invention, the polyisocyanate compound may be an aliphatic, aromatic, alicyclic, or araliphatic compound containing two or more isocyanate groups in the molecular structure. The polyol may be one or more selected from polyester polyol, polyacrylate polyol, polycarbonate polyol, polyether polyol, polyurethane polyol, melamine polyol, and mixtures thereof.

In the low-temperature crosslinking one-component clear coat composition for automobiles according to the present invention, the polyol has a hydroxyl value in the range of 150 to 300 mg KOH per gram of polyol and an acid value of 8 to 25 mg KOH or less per gram of polyol. desirable.

In the low-temperature crosslinking one-component clear coat composition for automobiles according to the present invention, the mixture may further include any one or more of a tin compound, a zinc compound, or an amine compound as a reaction accelerator, and in this case, the tin compound is dibutyltin. Dibutlytin dilaurate (DBTDL) is more preferred.

In the low-temperature crosslinking one-component clear coat composition for automobiles according to the present invention, the composition is characterized in that it contains xylene as a solvent.

In the low-temperature cross-linking one-component clear coat composition for automobiles according to the present invention, the low-temperature curing reaction is characterized in that the reaction temperature is 100 to 130 ° C.

Hereinafter, as shown in the accompanying drawings showing preferred embodiments of the present invention, implementation examples and embodiments of the present invention will be described in detail so that those with general knowledge in the technical field to which the present invention belongs can easily implement it. In particular, the technical idea of the present invention and its core structure and operation are not limited by this. In addition, the content of the present invention can be implemented in various other types of equipment, and is not limited to the implementation examples and embodiments described herein.

<Preparation example> Preparation of pyrazole-based blocking agent

The methacrylate-functionalized pyrazole derivative according to one embodiment of the present invention was prepared by a two-step reaction.

Figure 1 shows a method for synthesizing a pyrazole-based blocking agent according to an embodiment of the present invention, including (a) Examples and (b) Comparative Examples.

First, pyrazole containing a hydroxyl group at the 5-position was synthesized by reacting a 1,3-diketone derivative with hydrazine monohydrate. The methacrylate-functionalization reaction was successfully prepared by the reaction of methacrylic acid and pyrazole-5-ol in the first step via the DCC/DMAP coupling reaction described in Figure 1. Details of the manufacturing method are described below.

<Preparation Example 1> Preparation of 3-Methyl-1H-pyrazole-5-ol(PyOH-1)

Ethyl acetoacetate (11.82 g, 0.09 mol, 1 equiv) was dissolved in ethanol (EtOH, 11 mL) in a one-neck round bottom flask (100 mL) equipped with a stir bar. Hydrazine monohydrate (5 g, 0.999 mol, 1.1 equiv) was added slowly using a syringe.

While the reaction solution was stirred at room temperature for 2 hours while a white precipitate was formed, the precipitate was filtered, washed several times with cold ethanol, and the white powder was dried in a vacuum oven to obtain the product as a white powder (yield: 78%, 6.77 g). ).

1H NMR of PyOH-1 (300 MHz, DMSO-d6, TMS standard, r.t.): δ = 5.24(s; 1H), 2.1(s;3H).

<Preparation Example 2> Preparation of 3-Isopropyl-1H-pyrazole-5-ol(PyOH-2)

Ethyl isobutyryl acetate (14.36 g, 0.0908 mol, 1 equiv) dissolved in ethanol (15 mL) and hydrazine monohydrate (5 g, 0.0999 mol, 1.1 equiv) was added to a one-neck round bottom flask (100 mL) equipped with a reflux condenser. ) and heated at 70°C for 4 hours to react, then cooled to room temperature and observed crystallization. The flask was stored in the refrigerator until the solution was completely recrystallized. The slightly pink crystals formed were filtered and washed several times with cold ethanol, and the obtained light pink powder was dried in a vacuum oven (yield: 77%, 8.82 g).

1H NMR of PyOH-2 (300 MHz, DMSO-d6, TMS standard, r.t.): δ = 5.21 (s; 1H), 2.76 (m; 1H), 1.13 (d; 6H).

<Preparation Example 3> Preparation of 3-(tert-Butyl)-1H-pyrazole-5-ol(PyOH-3)

Ethyl pivaloiacetate (15.63 g, 0.0908 mol, 1 equiv) was dissolved in ethanol (16 mL) and hydrazine monohydrate (5 g, 0.0999 mol, 1.1 equiv) and then dissolved in a one-neck round bottom flask (100 mL) equipped with a reflux condenser. mL), heated at 70°C for 4 hours, cooled to room temperature, and observed crystallization. The flask was stored in the refrigerator until the solution was completely recrystallized. The white crystals formed were filtered and washed several times with cold ethanol, and the obtained white crystals were dried in a vacuum oven (yield: 82%, 10.4 g).

1H NMR of PyOH-3 (300 MHz, DMSO-d6, TMS stnadard, r.t.): δ= 5.22 (s, 1H), 1.2 (s, 9H).

<Preparation Example 4> Preparation of 3-Methyl-1H-pyrazole-5-yl methacrylate (PyA-1)

PyOH-1 (6.91 g, 0.07 mol, 1.2 equivalent) prepared in Preparation Example 1 was added to a one-neck round bottom flask (100 mL) with dichloromethane (50 mL) and methacrylic acid (5.05 g, 0.059 mol, 1 equivalent). After adding DMAP (1.43 g, 0.012 mol, 0.2 equiv), it was cooled to 0°C and DCC (12 g, 0.059 mol, 1 equiv) was slowly added to the round bottom flask while stirring.

After 30 minutes, the ice bath was removed and the reaction was kept at room temperature with stirring overnight, then the dicyclohexylurea (DCU) by-product was filtered and the organic layer was washed with 0.1 M aqueous HCl solution, saturated NaHCO3 and brine. The organic layer was collected and dried over MgSO4. After filtration, the organic layer was concentrated by vacuum evaporation and further purified by silica gel column chromatography using a mixture of ethyl acetate and hexane (3:7, v/v) as an eluent to obtain the product as a white solid. (Yield: 30%, 2.925 g)

1H NMR of PyA-1 (300MHz, CDCl3, TMS standard, r.t.): δ =12.29(s, 1H), 6.35(m, 1H), 5.94(s, 1H), 5.76(m, 1H), 2.29(s) , 3H), 2.04(s, 3H). 13C NMR (300MHz, CDCl3, TMS standard, r.t.): 164.99, 155.86, 140.98, 135.59, 128.14, 95.30, 19.01, 11.26.

<Preparation Example 5> Preparation of 3-Isopropyl-1H-pyrazole-5-yl methacrylate (PyA-2)

PyOH-2 (8.88 g, 0.07 mol, 1.2 equivalent) prepared in Preparation Example 2 was added to a one-neck round bottom flask (100 mL) with dichloromethane (60 mL), DMF (20 mL), and methacrylic acid (5.05 g, After adding 0.059 mol, 1 equiv) and DMAP (1.43 g, 0.012 mol, 0.2 equiv), it was cooled to 0°C and DCC (12.107 g, 0.059 mol, 1 equiv) was slowly added to the round bottom flask while stirring.

After 30 minutes, the ice bath was removed and the reaction was kept at room temperature with stirring overnight, then the dicyclohexylurea (DCU) by-product was filtered and the organic layer was washed with 0.1 M aqueous HCl solution, saturated NaHCO3 and brine. The organic layer was collected and dried over MgSO4. After filtration, the organic layer was concentrated by vacuum evaporation and further purified by silica gel column chromatography using a mixture of ethyl acetate and hexane (4:6, v/v) as an eluent to obtain the product as a white solid. (Yield: 39%, 4.44 g)

1H NMR of PyA-2 (300 MHz, CDCl3, TMS standard, r.t.): δ = 10.67 (s; 1H), 6.34 (m; 1H), 5.97 (s; 1H), δ = 5.75 (m , 1H), δ = 2.97 (m; 1H), δ = 2.04 (s; 3H), 1.25 (d; 6H). 13C NMR (300 MHz, CDCl3, TMS standard, r.t.): 164.62, 155.27, 151.72, 135.40, 127.81, 92.25, 26.34, 22.35, 18.28.

<Preparation Example 6> Preparation of 3-(tert-Butyl)-1H-pyrazole-5-yl methacrylate (PyA-3)

PyOH-3 (9.87 g, 0.07 mol, 1.2 equivalent) prepared in Preparation Example 3 was added to a one-neck round bottom flask (100 mL) with dichloromethane (50 mL), DMF (15 mL), and methacrylic acid (5.05 g, After adding 0.0587 mol, 1 equiv) and DMAP (1.433 g, 0.0117 mol, 0.2 equiv), it was cooled to 0°C and DCC (12.1 g, 0.0587 mol, 1 equiv) was slowly added to the round bottom flask while stirring.

After 30 minutes, the ice bath was removed and the reaction was kept at room temperature with stirring overnight, then the dicyclohexylurea (DCU) by-product was filtered and the organic layer was washed with 0.1M aqueous HCl solution, saturated NaHCO3 and brine. The organic layer was collected and dried over MgSO4. After filtration, the organic layer was concentrated by vacuum evaporation and further purified by silica gel column chromatography using a mixture of ethyl acetate and hexane (4:6, v/v) as an eluent to obtain the product as a white solid. (Yield: 42%, 2.41 g)

1H NMR of PyA-3 (300 MHz, CDCl3, TMS standard, r.t.): δ = 10.50 (s; 1H), 6.33 (m; 1H), 5.99 (s; 1H), δ = 5.74 (m) , 1H), δ = 2.02 (s; 3H), 1.3 (s; 9H). 13C NMR (300 MHz, CDCl3, TMS standard, r.t.): 164.79, 155.61, 154.66, 135.62, 127.95, 92.50, 31.60, 30.14, 18.52.

<Preparation Example 7> Preparation of 3,5-Di-tert-butyl-1H-pyrazole (DtBPy)

2,2,6,6,-Tetramethylheptane-3,5-dione (50 g, 0.27 mol, 1 equiv) and hydrazine hydrate (18.6 g, 0.37 mol, 1.37 equiv) were dissolved in methanol (100 mL). This was stirred at room temperature for 1 hour to produce a white solid adduct, which was filtered, washed several times with cold ethanol, purified, and dried in a vacuum oven to obtain the product as a white powder with a yield of about 96% (47.18 g).

1H NMR of DtBPy (300 MHz, CDCl3, TMS standard, r.t.): δ = 5.89 (s; 1H), 1.32 (s; 18H).

<Examples and Comparative Examples> Synthesis of block isocyanate and production of clear coat

The synthesis of block isocyanate and the preparation of the clear coat according to one embodiment of the present invention were performed as follows.

First, Desmodur N3300, a commercially available hexamethylene diisocyanate (HDI) trimer, with 21.8 wt% NCO (this means that 1 g of N3300 contains 0.218 g (0.0052 mol) of NCO) was placed in a vial with a stir bar. 1 g of the isocyanate blocking agent (0.0054 mol) prepared in Preparation Examples 4 to 7 was dissolved in an organic solvent in a separate vial. At this time, the molar equivalent of NCO in HDI trimer and blocking agent was 1:1.1.

The solution containing the prepared blocking agent was slowly added to the HDI trimer solution at room temperature and stirred for 24 hours.

The blocking reaction was confirmed by observing the disappearance of the NCO (2250-2280 cm-1) peak using FT-IR, as shown in Figure 2, and as a result of the blocking reaction by the pyrazole derivative, the reactive isocyanate is easily converted to urea under mild conditions. It could be transformed into , and the reaction conversion rate was high, so no separate purification process was needed.

<Analysis Example 1> Confirmation of chemical structure

The chemical identity and purity of the compounds prepared according to one embodiment of the present invention were confirmed using 1H and 13C NMR spectra (300 MHz NMR spectrometer, Bruker, Ultrashield). CDCl3 (δ = 7.26 ppm for 1H NMR, 77.36 ppm for 13C NMR) and DMSO-d6 (δ = 2.5 ppm for 1H NMR) were used as deuteration solvents.

Fourier transform infrared (FT-IR) spectra of blocked isocyanates were analyzed using a FT-IR spectrometer (Thermo Fisher Scientific Inc., Nicolet 6700/Nicolet Continuum).

<Analysis Example 2> Simulation using density functional theory (DFT)

The degree of chemical bonding of the HDI trimer blocked by a pyrazole-based blocking agent prepared according to an embodiment of the present invention was determined by density functional theory (DFT) using Gaussian 09 software at the B3LYP/6-31G(d) level. Simulated and analyzed using . Geometric optimization and frequency calculation of each blocked isocyanate and blocking agent were first performed to obtain the formation enthalpy of the stable structure, and using the obtained formation enthalpy, the bond dissociation energy (BDE) was calculated from the HDI trimer block isocyanate. The bond dissociation energy (BDE) for dissociating the pyrazole-based blocking agent was calculated, and bond dissociation energy (BDE) generally refers to the enthalpy difference between the product and reactant.

Based on DFT simulation, the reactivity of isocyanate blocked with a pyrazole-based blocking agent prepared according to an embodiment of the present invention is predicted at the molecular level, and the bond dissociation energy (BDE) is calculated from the optimized chemical structure. are summarized in Table 1 below.

Block isocyanate Bond Dissociation Energy (BDE)
(kcal/mol) CN bond length
(Å) HDI-BL-PyA-1 10.31 1.448 HDI-BL-PyA-2 10.39 1.447 HDI-BL-PyA-3 10.36 1.447 HDI-BL-DtBPy 16.98 1.436 Desmodur PL350 20.78 1.429

Bond dissociation of blocked isocyanates (HDI-BL-PyA-1, HDI-BL-PyA-2, and HDI-BL-PyA-3) by methacrylate-functionalized pyrazole according to one embodiment of the present invention The energy (BDE) was lower than the bond dissociation energy (BDE) of the isocyanate blocked by DtBPy (HDI-BL-DtBPy).

As can be seen in Table 1, the bond dissociation energy (BDE) was lowered by the repulsion between the O atom of the ester and the -NCO functional group, and the effect was shown to increase the C-N bond length.

However, the bulkier alkyl group at the 3-position of pyrazole did not lower the bond dissociation energy, so the bond dissociation energies between PyA-1, PyA-2, and PyA-3 were similar.

Meanwhile, in another test conducted by researchers of the present invention, when an imidazole group was used as a blocking agent, it was confirmed that an imidazole derivative with a bulky alkyl group right next to the 1-position of the imidazole ring had a lower bond dissociation energy ( Coatings, 2020, 10, 974.), and one interpretation of the reason for this difference is that steric effects affect adjacent atoms more strongly than two atoms that are separated.

There is no significant difference between the bond dissociation energies between the three types of methacrylate-functionalized pyrazole-based block isocyanates prepared according to one embodiment of the present invention, but they show different solvent affinities, and this dissimilarity is one embodiment of the present invention. It was expected that the HDI trimers blocked by three different methacrylate-functionalized pyrazoles prepared according to the example would exhibit different curing behavior, thermal and surface mechanical properties, and based on this, the preparation and physical properties of clear coats containing them were analyzed. It came down to this.

The specific composition of the clear coat manufactured according to one embodiment of the present invention is summarized in Table 2 below.

clear coat sample Example 1
CC-PyA-1 Example 2
CC-PyA-2 Example 3
CC-PyA-3 Comparative Example 1
CC-DtBPy Comparative Example 2
CC-PL350 Block isocyanate HDI 1g - PyA-1 0.95g - - - - PyA-2 - 1.108g - - - PyA-3 - - 1.19g - - PyA-4 - - - 1.03g - PL350 - - - - 1.647 g menstruum 3.07 g
(BA) 2.11g
(xylene) 2.19g
(xylene) 4.73 g
(BA) - polyester polyol
(OH value: 270 mg KOH/g) 1.07 g

The formulation of the clearcoat sample containing blocked isocyanate dissolved in organic solvent was mixed with 1.07 g of polyester polyol (OH value = 270 mg KOH/g, non-volatile fraction = 60%) as described in Table 2 above. Clearcoat samples prepared and formed from a mixture of blocked isocyanate and polyester polyols were Example 1 (CC-PyA-1), Example 2 (CC-PyA-2), and Example 3 (CC-PyA-3). ), Comparative Example 1 (CC-DtBPy), and Comparative Example 2 (CC-PL350).

<Analysis Example 3> Viscoelastic analysis of crosslinking behavior

Clear coat samples containing isocyanate blocked with a pyrazole-based blocking agent along with polyester polyol according to an embodiment of the present invention (CC-PyA-1, CC-PyA-2, CCPyA-3, CC-DtBPy and CC The curing behavior of -PL350) was analyzed in real time using an oscillatory rheometer (MARS III, HAAKE, Thermo Scientific, Waltham, WA, USA) equipped with a controlled temperature chamber (CTC).

The storage modulus (G') was measured in real time in small-amplitude oscillatory shear (SAOS) mode to determine the rheological cross-linking behavior of the clearcoat material, and reliable rheological data were obtained from the gap (250 μm) between the top and bottom plates. As a standard, it was obtained at an angular frequency of 5 Hz and a strain rate of 0.1%. The clear coat sample was placed on a parallel plate with a diameter of 25 mm and then surrounded by a controlled temperature chamber.

The temperature was increased from 30°C to the target temperature (110, 120, 130°C) at a heating rate of 5°C/min and then maintained at the target temperature for 30 minutes.

The unique cross-linking behavior of various clearcoats using different pyrazole-based blocking agents was analyzed using a rigid pendulum tester (RPT, PRT-3000 W, AND, Japan).

After manufacturing the sample by applying the clear coat solution to the tin substrate and bar-coating it evenly with an applicator, for the RPT test, place the RBP-006 edge attached to the vibrating pendulum (FRB-300) on the clear coat film and use the vibrating pendulum during the curing process. Real-time curing behavior was monitored periodically, and the temperature was increased from 30°C to the target temperature at a heating rate of 5°C/min and then maintained at the target temperature for 30 minutes.

<Analysis Example 4> Analysis of thermal properties of cured film

The thermal stability of the clearcoat film cured at 130°C was analyzed using thermogravimetric analysis (TGA: TA Instruments, TGA Q500), and measurements were performed up to 600°C at a heating rate of 10°C/min in an N2 atmosphere.

Differential scanning calorimetry (DSC, TA Instruments, DSC Q2000) measurements were made by heating to 120°C at RT, cooling to -40°C under N at a rate of 10°C/min, and heating a second time to 120°C at a rate of 5°C/min. The glass transition temperature (Tg) of the cured polymer was determined.

Additionally, the Tg value of the cured polymer film was also determined by dynamic mechanical analysis (DMA, TA Instruments, DMA Q800) by scanning the temperature in the range of 60°C to 180°C at a heating rate of 5°C/min, where the applied Strain rate and frequency were 0.5% and 1 Hz, respectively. Samples for DMA were prepared in Teflon molds (5.6 cm × 1.1 cm × 0.1 cm) and cured in a convection oven at 130°C for 4 hours. These samples were also used for TGA and DSC measurements.

<Analysis Example 5> Analysis of surface mechanical properties of cross-linked film

The clear coat film was manufactured on a tin plate through bar coating, and the manufacturing method was the same as the preparation for RPT measurement. Coated samples of tin plates were cross-linked for 40 minutes in a convection oven at 120 and 130 °C. The prepared samples were left at room temperature overnight.

The load-displacement curve of the cross-linked membrane was obtained using a nano-indentation tester (NHT3, Anton Paar, Austria) with a Berkovich-type indenter, and the force was applied at a rate of 60 mN/min from 0 to 10 mN and maintained at 10 mN for 10 seconds. Afterwards, the loading process was reversed and unloaded.

In addition, the indentation hardness (HIT) and indentation elastic modulus (EIT) values were calculated from the permanent penetration depth (final depth, hf), maximum displacement (hmax), and elastic unloading stiffness (S=dP/dh), five times per sample. Surface hardness was measured and averaged using NHT3 software, and the differences between each measurement were small and negligible.

Figure 1 shows a method for synthesizing a pyrazole-based blocking agent according to an embodiment of the present invention, including (a) Examples and (b) Comparative Examples.

In the present invention, a methacrylate-functionalized pyrazole derivative as an isocyanate blocking agent was designed and prepared through a two-step reaction as shown in FIG. 1.

First, pyrazole containing a hydroxyl group at the 5th position of the pyrazole ring was prepared through a reaction between hydrazine monohydrate and a 1,3-diketone derivative with an ethyl ester group on one side. At this time, the reaction temperature varied greatly depending on the carbon number of the alkyl group (CH3, CH(CH3)2, C(CH3)3), which is a substituent of the pyrazole group. 3,5-di-tert-butyl pyrazole (DtBPy) was prepared using a previously reported method for comparison.

Overall, the pyrazole reaction was able to obtain products of high yield and excellent purity, and a DCC/DMAP coupling esterification reaction was additionally performed to functionalize methacrylate into the pyrazole ring.

PyOH-1, PyOH-2, and PyOH-3 according to one embodiment of the present invention had low solubility in dichloromethane, so addition of additional DMF as a solvent was inevitable, and methacrylic acid was used in pyrazole (PyOH-1, Because it can react with both -OH and -NH groups of PyOH-2 and PyOH-3), the yield (~30%) was low because the pure product that reacted only with OH instead of NH had to be separated using column chromatography.

Figure 2 shows (a) 1H-NMR spectrum of a pyrazole-based blocking agent and (b) FTIR spectrum of hexamethylene diisocyanate trimer (HDI Trimer) blocked with a pyrazole-based blocking agent according to an embodiment of the present invention.

The structure was confirmed because the characteristic peaks of the vinyl group of methacrylate (-C=CH2) appeared at 5.72 and 5.74 ppm in the 1H NMR spectrum.

Figure 3 shows a blocking reaction between a pyrazole-based blocking agent and hexamethylene diisocyanate trimer (HDI Trimer) according to an embodiment of the present invention.

Methacrylate-functionalized pyrazoles (PyA-1, PyA-2, PyA-3) prepared according to one embodiment of the present invention and methacrylate-free DtBPy were dissolved in different solvents to form HDI trimers (N3300). It was used for block formation, and its specific composition is summarized in Table 1.

At this time, PyA-1 was soluble only in dichloromethane (DCM), chloroform, DMF, DMSO, and butylacetate (BA), but not in xylene, and for thermosetting systems, solvents with higher boiling points (>110 °C) are generally used. DCM and chloroform are not ideal solvents in the present invention, and DMF and DMSO are not suitable solvents in the coating industry due to health concerns.

Therefore, in the present invention, it is preferable to use a solvent that is acceptable in the coating industry and has good affinity with polyol dissolved in xylene, so PyA-1 was used by dissolving it in butyl acetate.

Isocyanates blocked with PyA-1, PyA-2, PyA-3 and DtBPy according to one embodiment of the present invention were viscous opaque white, transparent and colorless, transparent yellow and transparent colorless solutions, respectively. The NCO blocking reaction was confirmed by observing the disappearance of the -NCO peak at 2250 to 2270 cm-1 in the FT-IR spectrum, as shown in (b) of Figure 2.

As can be seen in (b) of Figure 2, except for HDI-BL-DtBPy, the three HDI trimers blocked by PyA-1, PyA-2, and PyA-3 have a C of methacrylate at 1580 cm-1. =C, and all blocked HDI trimers also showed a peak at 1750 cm-1, which corresponds to C=O of urea as a result of NCO blocking.

This blocked curing agent solution was mixed with 1.07 g of polyester polyol (OH value = 270 mg KOH/g) with a molar ratio of -NCO to -OH of 1:1 equivalent, and a solution of blocked isocyanate and polyol (CC-PyA-1 , CC-PyA-2, CC-PyA-3, CC-DtBPy and CC-PL350) were slightly viscous and prepared cured films for investigation of thermal properties by TGA, DSC and DMA and surface mechanical properties using a nanoindentation tester. In addition, it was used to investigate real-time thermal curing behavior using RPT and rheometer.

The thermal curing behavior of a bar-coated thin film of a clear coating sample containing isocyanate and polyester polyol blocked with a pyrazole-based blocking agent according to an embodiment of the present invention was measured using RPT and a rheometer at three target temperatures (110 , 120 and 130 oC).

Figure 4 shows the results of an RPT test (rigid-body pendulum test) of a clear coat cured at different curing temperatures (a) 110 ℃, (b) 120 ℃ and (C) 130 ℃ according to an embodiment of the present invention. will be.

As can be seen in Figure 4, the oscillating pendulum period for the clear coating film decreased during the heating procedure as the cured coating formed a cross-linked network, and all clearcoat samples at 110, 120, and 130 °C showed similar curing patterns.

CC-PyA-2 showed the earliest cross-linking initiation, followed sequentially by CC-PyA-1, CC-DtBPy, CC-PyA-3, and CC-PL350. The degree of crosslinking of the two clearcoats containing CC-PyA-2 and CC-PyA-1 was greater than the other, as indicated by the observed decrease in pendulum period when cured at 110 and 120 °C.

In particular, clearcoat samples containing a commercial blocked isocyanate (Desmodur PL350) did not cure at the same temperature and, interestingly, CC-DtBPy showed a relatively slow onset and less decrease in pendulum period, a result that suggests that CC-DtBPy With a higher bond dissociation energy (BDE) of 16.98 kcal/mol, which can be explained by the absence of methacrylate functional groups, this result suggests that deblocked DtBPy is capable of chemically binding within the cross-linked film. It showed that it was impossible.

Figure 5 shows rheological curing behavior by real-time storage modulus at different curing temperatures (a) 110 °C, (b) 120 °C and (C) 130 °C according to an embodiment of the present invention.

Clearcoat samples were placed between the top and bottom plates spaced 250 μm apart on an oscillating rheometer to evaluate the thermal setting behavior and storage modulus (G') of the samples at the target temperature.

Measurements of rheological properties are compatible with RPT experiments in that the heating conditions for both measurements were the same, with a heating rate of 5°C/min and a target temperature held for 30 min.

As can be seen in Figure 5, CCPyA-2 showed the fastest curing onset time, followed by CC-PyA-1, CC-PyA-3, CC-DtBPy, and CC-PL350. A reverse curing onset time was observed between CCPyA-3 and CC-DtBPy. CC-PyA-3 with lower BDE and methacrylate functional groups showed a much higher storage modulus than CC-DtBPy, which was due to the addition of additional radicals of methacrylate-functionalized pyrazole during thermal curing due to supplementation of the urethane reaction. It appears to be due to polymerization.

Rheological curing behavior of real-time storage modulus at different curing temperatures (a) 110 °C, (b) 120 °C and (c) 130 °C, slower onset of cure leads to higher storage modulus with the help of a less restrictive molecular mobility environment. You can.

Figure 6 shows the urethane reaction and radical reaction under thermal crosslinking conditions between hexamethylene diisocyanate trimer (HDI Trimer) and polyester polyol blocked with a pyrazole-based blocking agent capable of radical reaction according to an embodiment of the present invention.

On the other hand, the clearcoat sample containing commercial blocked isocyanate (CC-PL350) did not cure at the same temperature, similar to the RPT results, and measurements of rheological properties showed that it reacted slower than CC-PyA-2 and CC-PyA-1. Despite its initiation, it showed a relatively high storage modulus (G') for CC-PyA-3.

As discussed earlier, urethane formation during the deblocking process initiated similar cross-linking between CC-PyA-1, CC-PyA-2, and CC-PyA-3 due to similar BDEs, but the initiation time of radical polymerization was different between these systems. That is, in terms of radical initiation, PyA-2 blocking derivative showed initiation first, followed by PyA-1 and PyA-3, and the difference in the initiation time of these three blocking agents is due to molecular weight, stacking ability, etc. ), which may be due to differences in solvent affinity.

Figure 7 compares the thermal properties of a clear coat film cured at 130°C according to an embodiment of the present invention, showing (a) thermal stability by TGA and (b) glass transition temperature by secondary heating DSC. .

As can be seen in (a) of Figure 7, the decomposition onset temperature of 5% weight loss (Td) for the cured films of CC-PyA-1, CC-PyA-2, CC-PyA-3, and CCDtBPy, respectively. The temperatures were 253.5, 272.2, 254.5, and 195°C, and interestingly, it was found that the blocking agent containing a methacrylate group had greater thermal stability. This is because the pyrazole derivative with a methacrylate group remaining in the cured film is not decomposed after diblocking and participates in additional radical polymerization. On the other hand, the cross-linked film of CC-DtBPy showed relatively lower thermal stability and larger weight loss (~23 wt%) at 195-281 °C, and this weight loss was related to the wt% of DtBPy (~33 wt%) in the cured film. %). These TGA results confirmed the improved thermal stability of cured films containing methacrylate-functionalized pyrazole derivatives.

The Tg value of the cured film was determined from DSC and DMA analysis, and as can be seen in (b) of Figure 7, the Tg value after secondary heating at a rate of 5 ℃/min was confirmed to be in the range of 77 to 82 ℃. , the Tg values for the cured films of CC-PyA-1, CC-PyA-2, CC-PyA-3 and CC-DtBPy were 82, 80.5, 77 and 78.7 °C, respectively.

A series of DSC data also showed that crosslinked films containing methacrylate-functionalized pyrazole showed relatively similar or slightly higher Tg values than films without methacrylate.

Figure 8 compares the thermal properties of a clear coat film cured at 130°C according to an embodiment of the present invention, showing (a) DMA for storage modulus and (b) tan δ.

The viscoelastic properties of cured films containing methacrylate-functionalized pyrazole were evaluated by DMA, and the storage modulus (E′) and loss tangent (tan δ) were ? Measurements were made in a temperature range of 60 to 180°C. E' for all samples decreased in the temperature range from 45 to 55 °C, and the peaks of tanδ values were at 100, 90, and 88.7 °C for CC-PyA-1, CC-PyA-2, and CC-PyA-3, respectively. was observed.

For DMA measurements, cured CC-DtBPy clearcoat samples were not prepared successfully at 130°C, resulting in thin films with voids, and the samples were too thin to perform DMA measurements. Overall, the Tg of the three cured clearcoat samples (CC-PyA-1, CC-PyA-2, and CC-PyA-3) ranged from 88 to 100 °C, and these results are based on the pyrazole blocking group as prepared. It was shown that the clear coat sample was able to fully participate in the crosslinking reaction.

The degree of crosslinking (Xc) and molecular weight between crosslinks (Mc) of the clear coat prepared according to one embodiment of the present invention were calculated using the following equations.

where G0N is the modulus of the rubbery plateau, ρ is the density of the film, R is the gas constant (8.3145 J/(mol·K)), and T is the absolute temperature.

In general, a larger G0N in DMA means a larger , The thermal properties of the clear coat according to one embodiment of the present invention, including Xc and Mc determined by DMA, are summarized in Table 3.

CC-PyA-1 CC-PyA-2 CC-PyA-3 CC-DtBPy T _g , D S C
(℃) 82 80.5 77 78.7 T _g , D M A
(℃) 100 90 88.7 - T _d , T G A
(℃) 253.3 272.2 254.5 195 X _c
(10 ^-3 mol/g) 0.062 0.031 0.008 - M _c
(g/mol) 16.22 31.76 128 - Mw of blocking group
(g/mol) 166.18 194.23 208.26 180.3

Figure 9 shows the indentation curve of a clear coat film cured at (a) 120 and (b) 130 ° C. according to an embodiment of the present invention, and (c) is the identification hardness (HIT) value based on the Oliver and Pharr method. It represents.

In general, differences in Tg values need to be compared with differences in surface mechanical properties between clearcoat samples, so the surface mechanical properties of films cured at 120 and 130 °C were evaluated using a nano-indentation tester.

Since clear coat films containing DtBPy or DMP (Desmodur PL-350) as blocking agent were not fully cured at 120 and 130 °C, methacrylate functionalized pyrazoles (CC-PyA-1, CC-PyA-2 and CC- The surface mechanical properties were investigated only for PyA-3).

As can be seen in Figures 9 (a) and (b), the normal force versus indentation penetration depth curve indicates that, unlike the curing temperature of 120 °C, the curing temperature of 130 °C is high enough to completely cure all samples, and both temperatures The same trend appeared in all conditions. Films containing CC-PyA-3 exhibited significantly lower indentation penetration depths than films with CC-PyA-1 or CC-PyA-2 at a given curing temperature, indicating that CC-PyA-3 films were resistant to external stresses. This can be seen as showing greater resistance to

Meanwhile, the indentation depth profile of the clear coat film cured at 120 °C showed more distinguishable results depending on the type of pyrazole derivative.

The HIT value, which represents the representative surface indentation hardness of the cured film against external force, was calculated from the indentation depth curve using the Oliver and Pharr method, and the results for two different curing temperatures are shown in Figure 9 (c).

The HIT value for the CC-PyA-3 sample cured at 120 °C (201.3 MPa) was similar to the HIT value for the CC-PyA-3 sample cured at 130 °C (210.3 MPa), and this HIT value was It was much higher than the HIT value of the Desmodur PL350 sample cured with the same polyol at 150 ℃ reported in another study by (Coatings, 2020, 10, 974.).

Although CC-PyA-3 showed a slow onset of thermal curing according to the RPT in Figure 5 and the rheological analysis results in Figure 6, it exhibited the highest surface mechanical properties among the clear coat samples. This discrepancy appears to result from dissociated blocking groups participating in radical polymerization rather than urethane formation.

As previously described in Table 2, the blocked isocyanates by PyA-1, PyA-2 and PyA-3 have similar bond dissociation energy (BDE) and activation energy (Ea) values of the deblocking process, CC- There are several possible explanations for the excellent surface mechanical properties of PyA-3:

From the perspective of chemical reaction, introducing a tert-butyl group into the pyrazole ring can suppress intermolecular π-π stacking, effectively increasing molecular solubility and reducing aggregation, PyA-3 compared to PyA-1 and PyA-2. Because it is most soluble in xylene, it has high compatibility with polyols dissolved in xylene, showing better performance in chemical reactions.

Figure 10 shows the indentation curve of the cured clear coat film according to the solvent used when manufacturing the clear coat according to an embodiment of the present invention, and the indentation hardness (HIT) value based on the Oliver and Pharr method. At this time, HDI-BL-PyA-3 was used as a blocked block isocyanate mixed with polyol, and the solvents used in preparing the clear coat composition were xylene, butyl acrylate (BA), and methyl ethyl ketone ( MEK) and propylene glycol methyl ether acetate (PMA), which are most commonly used to increase the strength of the film in the coating industry, were used, and the indentation curve of the cured clear coat film is shown after curing at 120 ℃ for 30 minutes. , and indentation hardness (HIT) values based on the Oliver and Pharr method are shown. From Figure 10, it can be seen that the type of solvent used in preparing the clear coat can have a significant effect on the final surface hardness. In particular, the mechanical properties of the clear coat surface cured using xylene as a solvent affect the strength of the film in the coating industry. It was confirmed that the surface hardness was significantly improved compared to the case of using propylene glycol methyl ether acetate (PMA), which is the most commonly used material to increase

As described above, a methacrylate-functionalized pyrazole derivative according to an embodiment of the present invention was newly designed and manufactured as an isocyanate blocking agent, and the isocyanate blocked by the prepared pyrazole was used as a thermosetting crosslinking agent to form a polyester polyol (OH value = 270 mg KOH/g), the bond dissociation energies of the isocyanates blocked by PyA-1, PyA-2 and PyA-3 due to the ester group of methacrylate were as follows: It was successfully lowered compared to the BDE of blocked isocyanates by DtBPy and commercial Desmodur PL-350.

Additionally, despite similar bond dissociation energies, the three clearcoat samples (CC-PyA-1, CC-PyA-2, and CC-PyA-3) showed different cure behavior during RPT and rheometry tests, overall Clear coats containing methacrylate-functionalized pyrazole as a blocking agent were shown to cure at significantly lower temperatures than the comparative examples CC-DtBPy and CC-PL350. In addition, it was found that methacrylate-functionalized pyrazoles exhibited different solvent affinities and steric hindrance, which could affect radical polymerization reactivity. Among the three different clear coat samples, CC-PyA-3 was found to exhibit different solvent affinities and steric hindrance at 130 °C. Although it showed the slowest cure onset, the storage modulus was similar to CC-PyA-1 and CC-PyA-2 cured at 130°C.

Additionally, CC-PyA-3 cured at 120 °C and 130 °C showed the highest surface indentation hardness, which may be due to the slower reaction due to the bulkier structure of PyA-3, which retards the radical reaction and thus has less restricted molecular mobility. This is interpreted to promote more subsequent reactions and higher reaction conversion.

That is, the low-temperature crosslinking composition according to one embodiment of the present invention is not only capable of double curing, but can also be potentially applied to various coating materials due to the low curing temperature and improved surface mechanical properties of the coating layer, and more preferably in the automobile industry. It complements the shortcomings of the one-component coating system based on the high-temperature curing process that has been commercialized and applied in the field and the two-component coating system that has problems with low workability and recycling, while at the same time being suitable for automobile bodies that are expected to transition to lightweight materials. It has the advantage of being suitable as a coating system that can be cured in the temperature range of ~ 130 ℃, and can provide better mechanical properties on the surface of the car body even in the low temperature range, while saving energy and significantly reducing greenhouse gas emissions due to low-temperature curing reaction. There is an advantage.

Claims (13)

delete 25 to 35% by weight of a mixture containing a pyrazole-based block isocyanate capable of radical reaction prepared through a urea bond formation reaction between a compound of the following formula (A) and a polyisocyanate compound and a solvent;
A dual-curable low-temperature crosslinking composition comprising 10 to 35% by weight of at least one type of polyol:
<Formula A>

In Formula A, R is hydrogen or a methyl group, and R ₁ is an alkyl group having 1 to 8 carbon atoms. In claim 2,
The compound of Formula A is a dual-curable low-temperature crosslinking composition, characterized in that any one of the following Formulas 1 to 3:
<Formula 1>

<Formula 2>

<Formula 3>
In claim 2,
The polyisocyanate compound is an aliphatic, aromatic, alicyclic, or aromatic aliphatic compound, and is a dual-curable low-temperature crosslinking composition, characterized in that it contains two or more isocyanate groups in its molecular structure. In claim 2,
The polyisocyanate compounds include ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), octamethylene diisocyanate, nonamethylene diisocyanate, dodecamethylene diisocyanate, and 2,2-dimethylpentane diisocyanate. Isocyanate, 2,2,4-trimethyl hexamethylene diisocyanate, decamethylene diisocyanate, butene diisocyanate, 1,3-butadiene-1,4-diisocyanate, 2,4,4-trimethyl hexamethylene diisocyanate, 1, 6,11-undecane triisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2,6-diisocyanate methyl caproate, bis(2-isocyanate ethyl)fumarate, bis(2-isocyanate) Ethyl) carbonate, 2-isocyanate ethyl-2,6-diisocyanate hexanoate, 1,3,6-hexamethylene triisocyanate, 1,8-diisocyanato-4-isocyanatomethyl octane, 2,5,7-trimethyl-1,8-diisocyanato-5-isocyanatomethyl octane, bis(isocyanatoethyl) carbonate, bis(isocyanatoethyl) ether, 1,4-butylene glycol di. Propyl ether-ω,ω'-diisocyanate, lysine diisocyanato methyl ester, lysine triisocyanate, 2-isocyanatoethyl-2,6-diisocyanato ethyl-2,6-diisocyanato hexanoate, 2 -Isocyanato propyl-2,6-diisocyanato hexanoate, 2,6-di(isocyanatomethyl) furan, 1,3,-bis(6-isocyanato hexyl)-uretidine- At least one aliphatic isocyanate selected from the group consisting of 2,4-dione, 1,3,5-tris (6-isocyanato hexyl) isocyanurate or thiodiethyl diisocyanate, thiopropyl diisocyanate, ti At least one selected from the group consisting of odihexyl diisocyanate, dimethylsulfone diisocyanate, dithio dimethyl diisocyanate, dithio diethyl diisocyanate, dithio propyl diisocyanate, and dicyclohexyl sulfide-4,4'-diisocyanate. Sulfur-containing aliphatic isocyanate or diphenyl sulfide-2,4'-diisocyanate, diphenyl sulfide-4,4'-diisocyanate, 3,3'-dimethoxy-4,4'-diisocyanato dibenzyl thioether, bis (4-isocyanatomethyl benzene) sulfide, 4,4'-methoxy benzene, aromatic sulfide isocyanates such as thioethylene glycol-3,3'-diisocyanate, diphenyl disulfide-4,4'-diisocyanate, 2 ,2'-dimethyldiphenyl disulfide-5,5'-diisocyanate, 3,3'-dimethyldiphenyl disulfide-5,5'-diisocyanate, 3,3'-dimethyldiphenyl disulfide-6,6'- Diisocyanate, 4,4'-dimethyldiphenyl disulfide-5,5'-diisocyanate, 3,3'-dimethoxy diphenyl disulfide-4,4'-diisocyanate, 4,4'-dimethoxy diphenyl disulfide A dual-curable low-temperature crosslinking composition, characterized in that it is at least one aromatic disulfide isocyanate selected from the group consisting of -3,3'-diisocyanate. In claim 2,
The polyisocyanate compounds include 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 2,4-tolylene diisocyanate (TDI), 2,6-tolylene diisocyanate, and 4,4'-diisocyanate. Phenylenemethane diisocyanate (MDI), 2,4-diphenylmethane diisocyanate, ethyl phenylene diisocyanate, 4,4'-diisocyanate biphenyl, 3,3'-dimethyl-4,4'-diisocyanate biphenyl , 3,3'-dimethyl-4,4'-diisocyanate, diphenylmethane, naphthalene diisocyanate, methyl naphthalene diisocyanate, trizine diisocyanate, bis (isocyanatophenyl) ethylene, 3,3'-dimethoxy ratio. Phenyl-4-4'-diisocyanate, isopropylenephenylene diisocyanate, dimethylphenylene diisocyanate, diethylphenylene diisocyanate, diisopropylphenylene diisocyanate, trimethylbenzene triisocyanate, benzene triisocyanate, tri Phenylmethane triisocyanate, naphthalene triisocyanate, diphenylmethane-2,4,4'-triisocyanate, 3-methyl diphenylmethane-4,6,4'-triisocyanate, 4-methyl-diphenylmethane-3, 5,2',4',6'-pentisocyanate, xylylene diisocyanate, bis(isocyanatoethyl)benzene, bis(isocyanato propyl)benzene, α,α, α',α'-tetramethyl 1 selected from the group consisting of xylylene diisocyanate, bis(isocyanatobutyl)benzene, bis(isocyanatomethyl)naphthalene, bis(isocyanatomethyl)diphenyl ether, and bis(isocyanatoethyl)phthalate More than one type of aromatic isocyanate or diphenyl sulfone-4,4'-diisocyanate, diphenyl sulfone-3,3'-diisocyanate, diphenylmethane sulfone-4,4'-diisocyanate, 4-methyl diphenylmethane sulfone- 2,4'-diisocyanate, 4,4'-dimethoxy diphenyl sulfone-3,3'-diisocyanate, 3,3'-dimethoxy-4,4'-diisocyanate dibenzyl sulfone, 4,4'-Dimethyldiphenylsulfone-3,3'-diisocyanate,4,4'-di-tert-butyl diphenyl sulfone-3,3'-diisocyanate, 4,4'-methoxy benzene ethylene disulfone-3, A dual-curable, low-temperature crosslinking composition comprising at least one aromatic sulfone isocyanate selected from the group consisting of 3'-diisocyanate and 4,4'-dichlorophenylsulfone-3,3'-diisocyanate. In claim 2,
The polyisocyanate compounds include isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (HMDI), cyclohexylene diisocyanate, methylcyclohexylene diisocyanate, and bis(2-isocyanate ethyl)-4. -Cyclohexene-1,2-dicarboxylate, 2,5-norbornane diisocyanate, 2,6-norbornane diisocyanate, 2,2-dimethyl dicyclohexylmethane diisocyanate, 2-isocyanato Methyl-3-(3-isocyanato propyl)-5-isocyanatomethyl-bicyclo[2,2,1]-heptane, 2-isocyanatomethyl-3-(3-isocyanatopropyl)- 6-Isocyanatomethyl-bicyclo[2,2,1]-heptane, 2-isocyanatomethyl-2-(3-isocyanatopropyl)-5-isocyanatomethyl-bicyclo[2,2 ,1]-heptane, 2-isocyanatomethyl-2-(3-isocyanatopropyl)-6-isocyanatomethyl-bicyclo [2,2,1]-heptane, 2-isocyanatomethyl- 3-(3-isocyanatopropyl)-6-(2-isocyanatoethyl)-bicyclo[2,2,1]-heptane, 2-isocyanatomethyl-3-(3-isocyanatopropyl )-6-(2-isocyanatoethyl)-bicyclo [2,1,1]-heptane, 2-isocyanatomethyl-2-(3-isocyanatopropyl)-5-(2-isocyanate Natoethyl)-bicyclo[2,1,1]-heptane, 2-isocyanatomethyl-2-(3-isocyanatopropyl)-6-(2-isocyanatoethyl)-bicyclo[2, A dual-curable, low-temperature crosslinking composition comprising at least one alicyclic isocyanate selected from the group consisting of 2,1]-heptane and norbornane bis(isocyanatomethyl). In claim 2,
The polyisocyanate compound is 1,3-bis (isocyanatomethyl) benzene (m-xylene diisocyanate, m-XDI), 1,4-bis (isocyanatomethyl) benzene (p-xylene diisocyanate, p- XDI), 1,3-bis (2-isocyanato propan-2-yl) benzene (m-tetramethyl xylene diisocyanate, m-TMXDI), 1,4-bis (2-isocyanato propan-2- 1) Benzene (p-tetramethyl xylene diisocyanate, p-TMXDI), 1,3-bis(isocyanatomethyl)-4-methylbenzene, 1,3-bis(isocyanatomethyl)-4-ethylbenzene , 1,3-bis(isocyanatomethyl)-5-methylbenzene, 1,3-bis(isocyanatomethyl)-4,5-dimethylbenzene, 1,4-bis(isocyanatomethyl)-2 ,5-dimethylbenzene, 1,4-bis(isocyanatomethyl)-2,3,5,6-tetramethylbenzene, 1,3-bis(isocyanatomethyl)-5-tert-butyl benzene, 1 ,3-bis(isocyanatomethyl)-4-chlorobenzene, 1,3-bis(isocyanatomethyl)-4,5-dichlorobenzene, 1,3-bis(isocyanatomethyl)-2,4 ,5,6-tetrachlorobenzene, 1,4-bis(isocyanatomethyl)-2,3,5,6-tetrachlorobenzene, 1,4-bis(isocyanatomethyl)-2,3,5 Characterized by being at least one aromatic isocyanate selected from the group consisting of 6-tetrabromo benzene, 1,4-bis (2-isocyanatoethyl) benzene, and 1,4-bis (isocyanatomethyl) naphthalene. A low-temperature cross-linking composition capable of double curing. In claim 2,
The block isocyanate is a dual-curable low-temperature crosslinking composition, characterized in that it has the chemical structure of the following formula (3):
<Formula 3>

In Formula 3, R is hydrogen or a methyl group, and R ₁ is an alkyl group having 1 to 8 carbon atoms. delete In claim 2,
The polyol is a dual-curable low-temperature crosslinking composition, characterized in that at least one selected from polyester polyol, polyacrylate polyol, polycarbonate polyol, polyether polyol, polyurethane polyol, melamine polyol, and mixtures thereof. In claim 2,
The composition is a dual-curable low-temperature crosslinking composition, characterized in that it contains xylene as a solvent. In claim 2,
The composition is a low-temperature cross-linking composition capable of double curing, characterized in that the cross-linking reaction temperature is 100 to 130 ° C.