Polyamide curing agent for epoxy coating and preparation method thereof

Abstract

The present invention relates to a method for preparing a polyamide curing agent for an epoxy coating material, and a polyamide curing agent prepared thereby, the method comprising: a step of preparing a first mixture containing a first product by subjecting an amine group-containing compound and an alkyl group-containing acrylate to a Michael addition reaction; and a step in which a second mixture containing the first mixture, a fatty acid, and a dimer acid is heated and subjected to an amidation reaction, thereby producing a polyamide resin.

Description

Technical Field

[0001] This application claims priority based on Korean Patent Application No. 10-2022-0116928 filed on September 16, 2022, and all contents disclosed in the Korean patent application document are incorporated into this specification by reference.

[0002] The present invention relates to a polyamide curing agent for epoxy coatings which can be used as a low-solvent type, has excellent hydrophilicity, low equivalent weight and viscosity, and can be water-soluble and solvent-free, and a preparation method thereof. Background Art

[0003] Recently, many countries have restricted the content of organic solvents in paints containing organic solvents for environmental protection. South Korea also restricts paints containing organic solvents, especially for paints for ships that are painted on the outside. Therefore, shipyards install expensive solvent recovery equipment to recover the solvents generated when painting ships. However, shipyards that cannot install solvent recovery equipment have an increasing demand for high-solids type paints with low solvent content, solvent-free type paints, or water-soluble paints. Therefore, the demand for epoxy resins and epoxy resin curing resins, which are mainly used in ship paints, is increasing for high-solids, solvent-free, and water-soluble types.

[0004] Epoxy coatings suitable for other industrial fields besides heavy corrosion protection are also gradually moving towards water-soluble. Many parts of architectural coatings, container coatings, etc. have been converted to water-soluble.

[0005] In this regard, Japanese Patent No. 5348501 (Patent Document 1) discloses a polyamide amine curing agent obtained by reacting polyethylene polyamine (a1), aliphatic monocarboxylic acid (a2) and aromatic monocarboxylic acid (a3). The polyamide amine curing agent as in Patent Document 1 has a large molecular weight, a large number of amide groups, and thus a large number of hydrogen bonds and a high viscosity, so a solvent is required.

[0006] In addition, water-soluble conventional coatings are prepared by synthesizing fatty acids and / or dimer acids and amino-containing compounds, and the fatty acids and / or dimer acids contain excessive hydrophobic parts, so compared with conventional oil-soluble coatings, they contain emulsifiers, additives, etc., and when containing a large amount of the emulsifiers and / or additives, the hydrophilicity of the coating becomes too high. When the hydrophilicity of the coating becomes high, the prepared coating film has a problem of reduced physical properties such as swelling due to water, so it is necessary to improve this. For example, water-soluble conventional coatings containing emulsifiers have problems of insufficient physical properties such as rust resistance of the coating film due to the hydrophilicity of the emulsifier.

[0007] Therefore, it is necessary to develop a polyamide curing agent for epoxy coatings that can be used as a low-solvent type, has excellent hydrophilicity, low equivalent weight and viscosity, and can be water-soluble and solvent-free, and a preparation method thereof. Summary of the invention

[0008] (Problems to be solved by the invention)

[0009] Therefore, an object of the present invention is to provide a polyamide curing agent for epoxy paint which can be used as a low-solvent type, has excellent hydrophilicity, has low equivalent weight and viscosity, and can be water-soluble and solvent-free, and a method for preparing the same.

[0010] (Measures taken to solve the problem)

[0011] The present invention provides a method for preparing a polyamide curing agent for epoxy coatings, the method comprising: a step of preparing a first mixture containing a first product by subjecting an amine-containing compound to a Michael addition reaction with an alkyl-containing acrylate; and

[0012] The step of heating a second mixture including the first mixture, a fatty acid and a dimer acid to perform an amidation reaction, thereby preparing a polyamide resin.

[0013] In addition, the present invention provides a polyamide curing agent for epoxy coatings having a structure represented by Chemical Formula 1:

[0014]

Chemical formula 1

[0015]

[0016] In Chemical Formula 1,

[0017] R 1 To R 4 Each is independently selected from the group consisting of hydrogen, substituted or unsubstituted alkyl, aryl, amine and cycloalkyl.

[0018] (Effects of the Invention)

[0019] The polyamide curing agent according to the present invention has excellent hydrophilicity, low equivalent weight and viscosity, and can be solvent-free, so it is very suitable for use as an epoxy coating. In addition, the polyamide curing agent has the above-mentioned characteristics, and the coating film prepared therefrom has the same and / or better physical properties as the coating film prepared from the oil-soluble coating, for example, excellent physical properties such as rust resistance, chemical resistance, water resistance, repeated coating, and whitening resistance. DETAILED DESCRIPTION

[0020] Next, the present invention will be described in detail.

[0021] The "weight average molecular weight" in the present invention can be measured by a method known in the art, and can be expressed as a value measured by, for example, GPC (gel permeation chromatograph) method.

[0022] In addition, functional group values ​​such as "amine value" and "active hydrogen equivalent" can be measured by methods known in the art, for example, by titration method.

[0023] Preparation method of polyamide curing agent

[0024] The method for preparing a polyamide curing agent for epoxy coatings according to the present invention comprises: a step of preparing a first mixture containing a first product by subjecting an amine-containing compound and an alkyl-containing acrylate to a Michael addition reaction; and a step of heating a second mixture containing the first mixture, a fatty acid and a dimer acid and subjecting it to an amidation reaction to prepare a polyamide resin.

[0025] Michael Addition Reaction Steps

[0026] In this step, the amine-containing compound and the alkyl-containing acrylate are subjected to a Michael addition reaction to prepare a first mixture containing a first product.

[0027] The amine-containing compound may contain a primary amine group, for example, may contain more than one primary amine group. Specifically, the amine-containing compound may contain more than two primary amine groups. For example, the amine-containing compound may include: aliphatic amines such as butylamine, dibutylamine, diethylamine, hexylamine, isopropylamine, octylamine, tetrabutylamine, xylidine, aminobenzonitrile, aniline, benzylamine, ethylenediamine, trimethylenediamine, hexamethylenediamine, octamethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine and pentaethylenehexamine; aromatic amines such as o-xylene diamine, m-xylene diamine and p-xylene diamine; and alicyclic amines such as isophorone diamine, cyclohexane diamine and 1.3-bisaminomethylcyclohexane.

[0028] In addition, the alkyl-containing acrylate may specifically include an alkyl group having a carbon number of 1 to 6 or a carbon number of 1 to 4. For example, the alkyl-containing acrylate may include methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, tert-butyl acrylate, and the like.

[0029] At this time, the Michael addition reaction is a reaction between an amine group in an amine-containing compound and a vinyl group in an alkyl-containing acrylate, and can be carried out at 50 to 100° C. or 50 to 70° C. When the Michael addition reaction temperature is within the range, the Michael addition reaction can be carried out stably. On the contrary, when the Michael addition reaction temperature is less than the range, the reactivity is low and the reaction cannot be carried out normally, so it is difficult to form the first product. The Michael addition reaction is an exothermic reaction that generates heat during the reaction process. When the reaction temperature exceeds the range, the reaction is too fast and a large amount of heat is generated, making it difficult to adjust the temperature, and thus there may be a problem of reactant vaporization.

[0030] The first product may be a prepolymer containing an amine group and a carboalkoxy group.

[0031] In addition, the first mixture may include the first product and an amine-containing compound. In this case, the amine-containing compound in the first mixture is an amine-containing compound that remains without participating in the Michael addition reaction.

[0032] The first mixture can increase the molecular weight by Michael addition reaction, so that the coating composition containing the first mixture can achieve a high solid content. The first mixture can make the polyamide resin described later solubilized in water because it contains an alkyl group-containing acrylate having a small hydrophobic site in the structure.

[0033] Amidation reaction steps

[0034] In this step, the second mixture including the first mixture, fatty acid and dimer acid is heated to perform an amidation reaction, thereby preparing a polyamide resin.

[0035] Specifically, in this step, a variety of compounds can undergo amidation reaction, first, an amidation reaction between the alkoxy group of the first product and the amine group of the amine-containing compound; second, an amidation reaction between the carboxyl group of the fatty acid or dimer acid and the amine group of the amine-containing compound; and / or third, an amidation reaction between the carboxyl group of the fatty acid or dimer acid and the amine group of the first product.

[0036] The amidation reaction is a condensation reaction that produces alcohol during the reaction, and can be implemented at 150 to 250° C., 150 to 200° C., or 160 to 180° C. During the amidation reaction, when the temperature is within the range, the condensation reaction can be stably carried out. On the contrary, when the amidation reaction temperature is less than the range, the reaction temperature is low and the reaction cannot be carried out normally, so there is a problem of being difficult to obtain the final product. In addition, during the amidation reaction, when the temperature exceeds the range, in addition to the amidation reaction, side reactions such as imidazoline generation may also occur, and these side reactions are difficult to control, which may cause the problem of being difficult to obtain the final product.

[0037] The second mixture after the amidation reaction contains an amide group in the middle of the product, so that it can undergo a curing reaction with the epoxy resin.

[0038] The Michael addition reaction can be carried out at a low temperature, and the amidation reaction can be carried out at a high temperature. That is, the Michael addition reaction can be carried out at a low temperature and then the temperature can be raised, and the amidation reaction can be carried out at a high temperature, wherein the "low temperature" and "high temperature" are relative temperatures. Due to the temperature increase as described above, the content of the amide group can be reduced compared to the traditional amide curing agent, and the equivalent of the active hydrogen brought about by it can also be reduced. With the reduction of the equivalent of the active hydrogen, the amount of the curing resin used in the reaction with the epoxy resin can be reduced, and with the reduction of the hydrogen bonding site, the viscosity and molecular weight are reduced, which is conducive to water solubility and / or solvent-free.

[0039] The use of the fatty acid and dimer acid can be without any restriction as long as they are common fatty acids and / or dimer acids. For example, they can include one or more selected from the group consisting of soybean oil fatty acid, tall oil fatty acid, castor oil fatty acid, rice bran oil fatty acid, linseed oil fatty acid, coconut oil fatty acid, lauric acid, linolenic acid and fumaric acid. In addition, the dimer acid can include a dimerized fatty acid combined with two unsaturated fatty acids.

[0040] The second mixture may further contain a polyacid in addition to the fatty acid, for example, may include one or more selected from the group consisting of phthalic anhydride, maleic anhydride, isophthalic acid, adipic acid, tetrahydrophthalic anhydride, terephthalic acid, sebacic acid, succinic acid and citric acid.

[0041] For example, an alkyl-containing acrylate is added dropwise to a raw material mixture containing an amine-containing compound, a fatty acid and a dimer acid, and a Michael addition reaction is carried out at a low temperature of 50 to 100° C., and then the temperature is raised to a high temperature of 150 to 250° C. to carry out an amidation reaction, thereby preparing a polyamide resin.

[0042] In the present invention, the total equivalents of the number of double bonds of the alkyl-containing acrylate and the carboxyl groups of the alkoxy group and the fatty acid or dimer acid (number of double bonds + alkoxy group + carboxyl group) and the equivalents of the amine group in the amine-containing compound can be reacted in a ratio of 1:1.2 to 1:2.0 or 1:1.5 to 1:1.8. When the equivalent ratio of the number of double bonds and the total equivalents of the alkoxy group and the carboxyl group (number of double bonds + alkoxy group + carboxyl group) to the amine group is within the range, the prepared polyamide resin can be cured with the epoxy resin when it is applied to the coating, so that the mechanical properties can be excellent. On the contrary, when the equivalent ratio is less than the range, that is, when the equivalent ratio of the amine group relative to the number of double bonds and the total equivalents of the alkoxy group and the carboxyl group (number of double bonds + alkoxy group + carboxyl group) is insufficient, the molecular weight of the prepared polyamide resin is too large and has a high viscosity when it is applied to the coating, thereby limiting air spraying or water solubilization. In addition, when the equivalence ratio exceeds the range, that is, when the equivalence ratio of the amino group relative to the total equivalent of the number of double bonds and alkoxy and carboxyl groups (number of double bonds + alkoxy + carboxyl groups) is too large, unreacted amino-containing compounds will remain, resulting in insufficient physical properties of the prepared polyamide resin or reduced flexibility of the prepared coating film, and whitening may occur when immersed in water.

[0043] At this time, the equivalent of the double bond number and alkoxy group of the alkyl-containing acrylate (double bond number + alkoxy group) is 10% or more and less than 100%, or more than 20% and less than 100%, relative to the total equivalent of the double bond number and alkoxy group of the alkyl-containing acrylate and the carboxyl group of the fatty acid or dimer acid (double bond number + alkoxy group + carboxyl group). When the double bond number and alkoxy group equivalent of the alkyl-containing acrylate are less than the above range, the reduction range of the active hydrogen equivalent, viscosity and molecular weight is small, and the hydrophobicity of the fatty acid and / or dimer acid has a greater impact, so that the required physical properties of the prepared polyamide curing agent such as water solubility or solvent-free are difficult to achieve. In addition, when the double bond number and alkoxy group equivalent of the alkyl-containing acrylate exceed the above range, that is, when the fatty acid or dimer acid is not included, the coating film prepared using the polyamide resin may have problems of insufficient rust resistance and flexibility.

[0044] The second mixture is used to prepare a polyamide resin through an amidation reaction, so that the polyamide resin can be used as a curing agent for epoxy resin.

[0045] In addition, the present invention may further include, after the amidation reaction, a step of subjecting the polyamide resin to an addition reaction with an epoxy resin to prepare an epoxy addition polyamide resin.

[0046] Addition reaction steps

[0047] In the case of the epoxy adduct polyamide resin prepared by the addition reaction as described above, the drying property and the compatibility with the epoxy resin are improved, so that the reactivity at the time of coating can become excellent.

[0048] The epoxy resin may be exemplified by bisphenol-A epoxy resin, bisphenol-F epoxy resin, phenol novolac epoxy resin, alkyl diglycidyl ether, phenyl glycidyl ether, paratertiarybutyl phenylglycidyl ether, neopentane diglycidyl ether, neodecanoic acid glycidyl ether, etc. In addition, a commercially available product of the epoxy resin may be exemplified by bisphenol-A epoxy resin product YD-128 manufactured by Kukdo Corporation of Korea.

[0049] The polyamide resin and the epoxy resin may be reacted in a weight ratio of 100:0.1 to 100:30 or a weight ratio of 100:3 to 100:10. When the weight ratio of the polyamide resin to the epoxy resin is within the range, when the polyamide resin is applied to the coating, the compatibility with the epoxy resin as the main agent is improved, thereby having the effect of improving the drying property and the reaction speed. On the contrary, when the weight ratio is less than the range, it is difficult to obtain the effect of improving the drying property of the resin and the compatibility with the epoxy resin as the effect induced by the epoxy addition; when it exceeds the range, the viscosity and active hydrogen equivalent of the prepared epoxy addition polyamide resin are too high, so that it is difficult to achieve the problem of solvent-free.

[0050] The addition reaction may be carried out at 60 to 90° C. or 70 to 80° C. When the temperature during the addition reaction is within the above range, the epoxy group of the epoxy resin can stably react with the polyamide resin. On the contrary, when the temperature of the addition reaction is lower than the above range, the addition reaction slows down and generates latent heat, thereby causing a problem of uncontrollable heat generation; when the temperature exceeds the above range, the addition reaction proceeds too fast and reacts before the epoxy resin is evenly dispersed, thereby possibly causing a problem of forming small gel particles.

[0051] In addition, the present invention may further include the following after the amidation reaction and before the addition reaction:

[0052] The step of subjecting the polyamide resin to an imidazoline-forming reaction at a temperature of 200° C. or higher to prepare an imidazoline-containing polyamide resin.

[0053] For example, in the present invention, after the amidation reaction, the polyamide resin containing an imidazoline group can be prepared by an imidazoline formation reaction, and then an addition reaction can be performed.

[0054] Imidazoline formation reaction steps

[0055] The imidazoline group-containing polyamide resin prepared by the above-mentioned reaction further reduces the number of amide groups and reduces hydrogen bonds, thereby achieving an effect of further reducing the viscosity of the coating.

[0056] The imidazoline generation reaction can be carried out at a temperature of 200° C. or above or 200 to 250° C. During the imidazoline generation reaction, when the temperature is within the range, the imidazoline group generation can be effectively carried out. On the contrary, when the imidazoline generation reaction temperature is lower than the range, the generation of the imidazoline group slows down, resulting in a longer reaction time, thereby causing a problem of reduced productivity; when the temperature exceeds the range, the synthesized polyamide resin may be carbonized due to the high temperature.

[0057] Polyamide Curing Agent for Epoxy Coatings

[0058] In addition, the polyamide curing agent according to the present invention includes a structure represented by the following Chemical Formula 2.

[0059]

Chemical formula 2

[0060]

[0061] In chemical formula 2,

[0062] R 1 To R 4 Each is independently selected from the group consisting of hydrogen, substituted or unsubstituted alkyl, aryl, amine and cycloalkyl.

[0063] Specifically, R 1 To R 4 are each independently selected from hydrogen, substituted or unsubstituted C 1-20 Alkyl, C 6-20 The aromatic group, C 0-20 The amine group and C 3-20 In this case, the substitution is that one or more hydrogen atoms are independently replaced by non-hydrogen substituents, for example, by alkyl, cycloalkyl, aryl, heteroatom, halogen atom or the like.

[0064] More specifically, R 1 To R 4 are each independently selected from hydrogen, substituted or unsubstituted C 1-10 Alkyl, C 6-10 The aromatic group, C 0-10 The amine group and C 3-12 The group consisting of cycloalkyl.

[0065] For example, R 1 To R 4Each is independently selected from the group consisting of hydrogen, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, hexyl, octyl, t-butyl, phenyl, dimethylphenyl (e.g., o-xylene, m-xylene, p-xylene), cyanobenzyl, aminoethyl, aminopropyl, aminobutyl, aminohexyl, aminooctyl, (ethylenediamine)ethyl, (diethylenetriamine)ethyl, (triethylenetetramine)ethyl, (tetraethylenepentamine)ethyl, 3,5,5-trimethylcyclohexylamino-3-methyl, aminocyclohexyl and 4-[(4-cyclohexylamino)methyl]cyclohexylmethyl.

[0066] At this time, the alkyl group may be linear or branched.

[0067] The amine value of the polyamide curing agent may be 200 to 800 mgKOH / g, or 350 to 550 mgKOH / g.

[0068] In addition, the active hydrogen equivalent of the polyamide curing agent can be 80 to 200 g / eq, 90 to 180 g / eq, or 95 to 150 g / eq. When the active hydrogen equivalent of the polyamide curing agent is within the range, it is suitable for coatings and reacts with the epoxy group as the main agent to form a suitable crosslinking density, so that the target physical properties of the coating can be achieved. When the active hydrogen equivalent of the polyamide curing agent is less than the range, the crosslinking density becomes high and the coating becomes hard, so there is a problem of reduced impact resistance, etc.; when it exceeds the range, the weight average molecular weight of the polyamide curing agent becomes large, so there is a problem of difficulty in water solubility.

[0069] The viscosity of the polyamide curing agent at 25°C may be 200 to 5,000 cP, 500 to 2,500 cP or 1,000 to 2,500 cP. When the viscosity of the polyamide curing agent at 25°C is within the above range, the coating can be evenly coated due to the low viscosity when preparing the coating. When the viscosity of the polyamide curing agent at 25°C is less than the above range, the fluidity of the coating film becomes high, so there is a problem of poor sagging; when it exceeds the above range, the viscosity of the coating itself is too high, so that the problem of difficult spraying may occur.

[0070] In addition, the solid content of the polyamide curing agent may be 80 to 95 wt % or 80 to 90 wt %. The polyamide curing agent has a low viscosity at 25° C. and a high solid content, thereby being solvent-free and very suitable for epoxy coatings.

[0071] Thinner

[0072] The polyamide curing agent can be used as a solvent-free type due to its low viscosity. In addition, the polyamide curing agent can also be used by adding a diluent according to the purpose. For example, the polyamide curing agent can be used as an oil-soluble resin by adding an organic solvent, or can be used as a water-soluble resin by diluting it with distilled water or the like.

[0073] The organic solvent can be, for example, aromatic hydrocarbon solvents such as toluene and xylene; ketone solvents such as methyl ethyl ketone, methyl propyl ketone, methyl butyl ketone, methyl isobutyl ketone, methyl isoamyl ketone, ethyl propyl ketone and acetylacetone; ether or ester solvents such as methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, propylene glycol methyl ether, methoxypropanol and ethyl ethoxypropionate; and alcohol solvents such as 2-ethylhexanol, isobutanol, n-butanol, n-propanol, isopropanol and 1-methoxy-2-propanol, which can be appropriately selected and used according to the characteristics of the coating or the volatilization rate.

[0074] At this time, the diluent may be added in an amount of 30 wt% or less or 5 to 20 wt% relative to the total weight of the polyamide curing agent. When the content of the diluent exceeds the above range, the viscosity of the curing agent is too low, and the active hydrogen equivalent increases due to the diluent content, so that the water solubility problem may occur.

[0075] The polyamide curing agent of the present invention as described above has excellent hydrophilicity, low equivalent weight and viscosity, and can be solvent-free, so it is very suitable for epoxy coatings. In addition, the polyamide curing agent has the above-mentioned characteristics, and the coating film prepared therefrom has physical properties equivalent to and / or better than those prepared from oil-soluble coatings, for example, excellent physical properties such as rust resistance, chemical resistance, water resistance, recoatability, and whitening resistance.

[0076] (Methods for carrying out the invention)

[0077] The present invention is further described in detail below by way of examples. However, these examples are only for the purpose of helping to understand the present invention, and the protection scope of the present invention is not limited to these examples in any sense.

[0078] Example 1. Preparation of polyamide curing agent-1

[0079] 997g of dimer acid (Croda, Pripol 1017), 124g of tall oil fatty acid and 998g of triethylenetetramine were added to a 4-necked round-bottom flask, and a nitrogen tube, H-type separator, stirrer, thermometer and heater were set up, and the temperature was raised to 50°C. When the temperature reached 50°C, 171g of ethyl acrylate was added dropwise over 2 hours, and the Michael addition reaction was carried out under the condition that the temperature did not exceed 70°C. After the addition was completed, the temperature was raised to 160°C, and the amidation reaction was carried out. Water and ethanol were condensed and flowed out from the H-type separator. After maintaining at 160°C for 1 hour, the temperature was raised to 250°C and maintained for 3 hours, thereby carrying out the imidazoline formation reaction. After the imidazoline formation reaction, in order to remove the residual condensation water, the pressure was reduced to 600±100mmHg at 250°C and maintained for 1 hour to completely remove the moisture. Thereafter, the mixture was cooled to 80° C., and 100 g of bisphenol-A type epoxy resin (manufacturer: Kuodo Corporation, product name: YD-128) was added dropwise over 30 minutes, followed by reaction for 2 hours, thereby preparing a polyamide curing agent-1.

[0080] Preparation Example 1: Preparation of Oil-Soluble Curing Agent-1

[0081] 2242 g of the polyamide curing agent-1 prepared in Example 1 and 320 g of isopropyl alcohol were mixed to prepare an oil-soluble curing agent-1.

[0082] The prepared oil-soluble curing agent-1 had a transparent reddish brown appearance, an active hydrogen equivalent of 112 g / eq, an amine value of 410 mgKOH / g, and a viscosity of 1,800 cP at 25° C. (Brookfield).

[0083] Preparation Example 2: Preparation of water-soluble curing agent-1

[0084] 2242 g of the polyamide curing agent-1 prepared in Example 1 and 320 g of distilled water were mixed to prepare a water-soluble curing agent-1.

[0085] The prepared water-soluble curing agent-1 had a transparent reddish brown appearance, an active hydrogen equivalent of 112 g / eq, an amine value of 410 mgKOH / g, and a viscosity of 2,300 cP (Brookfield) at 25°C.

[0086] Example 2: Preparation of polyamide curing agent-2

[0087] 811 g of dimer acid (Croda, Pripol 1017), 102 g of tall oil fatty acid, 394 g of triethylenetetramine and 625 g of pentaethylenehexamine were added to a 4-necked round-bottom flask, and a nitrogen tube, H-type separator, stirrer, thermometer and heater were set up, and the temperature was raised to 50°C. When the temperature reached 50°C, 156 g of ethyl acrylate was added dropwise over 2 hours, and the Michael addition reaction was carried out under the condition that the temperature did not exceed 70°C. After the addition was completed, the temperature was raised to 160°C, and an amidation reaction was carried out. Water and ethanol were condensed and flowed out from the H-type separator. After maintaining at 160°C for 1 hour, the temperature was raised to 180°C and maintained for 3 hours, thereby carrying out an amidation reaction. After that, in order to remove the residual condensation water, the pressure was reduced to 600±100 mmHg at 180°C and maintained for 1 hour to completely remove the water. Thereafter, the mixture was cooled to 80° C., and 277 g of bisphenol-A type epoxy resin (manufacturer: Kuodo Corporation, product name: YD-128) was added dropwise over 30 minutes, followed by reaction for 2 hours to prepare a polyamide curing agent-2.

[0088] Preparation Example 3: Preparation of Oil-Soluble Curing Agent-2

[0089] 2236 g of the polyamide curing agent-2 prepared in Example 2 and 375 g of propylene glycol methyl ether were mixed to prepare an oil-soluble curing agent-2.

[0090] The prepared oil-soluble curing agent-2 had a transparent reddish brown appearance, an active hydrogen equivalent of 121 g / eq, an amine value of 499 mgKOH / g, and a viscosity of 1,400 cP (Brookfield) at 25°C.

[0091] Preparation Example 4: Preparation of water-soluble curing agent-2

[0092] 2236 g of the polyamide curing agent-2 prepared in Example 2 and 375 g of distilled water were mixed to prepare a water-soluble curing agent-2.

[0093] The prepared water-soluble curing agent-2 had a transparent reddish brown appearance, an active hydrogen equivalent of 121 g / eq, an amine value of 499 mgKOH / g, and a viscosity of 2,100 cP (Brookfield) at 25°C.

[0094] Example 3, Preparation of polyamide curing agent-3

[0095] 847g of dimer acid (Croda, Pripol 1017), 274g of tall oil fatty acid and 998g of triethylenetetramine were added to a 4-necked round-bottom flask. After setting up a nitrogen tube, an H-type separator, a stirrer, a thermometer and a heater, the temperature was raised to 50°C. When the temperature reached 50°C, 171g of ethyl acrylate was added dropwise over 2 hours. The Michael addition reaction was carried out while controlling the temperature not to exceed 70°C. After the addition was completed, the temperature was raised to 160°C, and an amidation reaction was carried out. Water and ethanol were condensed and flowed out from the H-type separator. After maintaining at 160°C for 1 hour, the reaction was carried out for 2 hours to prepare polyamide curing agent-3.

[0096] The prepared polyamide curing agent-3 had a transparent reddish brown appearance, an active hydrogen equivalent of 99 g / eq, an amine value of 540 mgKOH / g, and a viscosity of 55,500 cP (Brookfield) at 25°C.

[0097] Comparative Example 1: Preparation of polyamide curing agent-4

[0098] 1,413 g of dimer acid (Croda, Pripol 1017), 88 g of tall oil fatty acid and 684 g of triethylenetetramine were added to a 4-necked round-bottom flask. After setting up a nitrogen tube, an H-type separator, a stirrer, a thermometer and a heater, the temperature was raised to 160°C to carry out an amidation reaction, thereby condensing water and flowing out from the H-type separator. After maintaining at 160°C for 1 hour, the temperature was raised to 250°C for 3 hours to carry out an amidation reaction. After that, in order to remove the remaining condensation water, the pressure was reduced to 600±100 mmHg at 180°C and maintained for 1 hour to completely remove the water. After that, it was cooled to 80°C, and 103 g of bisphenol-A type epoxy resin (manufacturer: Guodu Company, product name: YD-128) was added dropwise over 30 minutes, and the reaction was carried out for 2 hours to prepare polyamide curing agent-4.

[0099] Preparation Example 5: Preparation of Oil-Soluble Curing Agent-4

[0100] 2195 g of the polyamide curing agent-4 prepared in Comparative Example 1 and 375 g of isopropyl alcohol were mixed to prepare an oil-soluble curing agent-4.

[0101] The prepared oil-soluble curing agent-4 has a transparent reddish brown appearance, an active hydrogen equivalent of 190 g / eq, an amine value of 265 mgKOH / g, and a viscosity of 21,500 cP (Brookfield) at 25°C.

[0102] Preparation Example 6: Preparation of water-soluble curing agent-4

[0103] 2195 g of the polyamide curing agent-4 prepared in Comparative Example 1 and 374 g of distilled water were mixed to prepare a water-soluble curing agent-4.

[0104] The prepared water-soluble curing agent-4 had a transparent reddish brown appearance, an active hydrogen equivalent of 190 g / eq, an amine value of 265 mgKOH / g, and a viscosity of 29,000 cP (Brookfield) at 25°C.

[0105] Comparative Example 2: Amine-added water-soluble curing agent

[0106] Anquamin 401 (product name) from Evonik was used as an amine addition water-soluble curing agent. The curing agent is a non-amidated amine resin.

[0107] Experimental Examples 1 to 8: Preparation of Coatings

[0108] The curing agents of Example 3, Preparation Examples 1 to 6 and Comparative Example 2 were mixed with the main agent of the coating so that the ratio of active hydrogen equivalent to epoxy equivalent was 0.8, thereby preparing the coating. At this time, as the main agent of the coating, KCC's EH2350 (product name) as an oil-soluble epoxy coating, KCC's WT3600 (product name) as a water-soluble epoxy coating, and KCC's EH3000 (product name) as a solvent-free epoxy coating were used.

[0109]

Table 1

[0110]

[0111] Test example: Evaluation of coating properties

[0112] The coatings of Experimental Examples 1 to 8 were airless coated so that the dry coating thickness was 100 μm, and left to stand at room temperature for 20 minutes to form coatings. Thereafter, the physical properties of the coatings were measured as follows. The results are shown in Table 2.

[0113] (1) Rust resistance

[0114] According to ASTM B117, the coating surface was X-cut and then subjected to salt spray. After 3,000 hours, the rust occurrence was measured to evaluate the rust resistance. At this time, the evaluation criteria were: no rust was evaluated as good (○), and rust was evaluated as poor (×).

[0115] (2) Chemical resistance

[0116] After the prepared coating film was immersed in a 5% KOH aqueous solution at 40°C for 7 days, the length (mm) of creep back on the sheet side was measured. At this time, the evaluation criteria were: when the length of creep back was less than 2 mm, it was evaluated as good (○), when it was more than 2 mm and less than 5 mm, it was evaluated as ordinary (△), and when it was more than 5 mm, it was evaluated as poor (×).

[0117] (3) Water resistance

[0118] After the prepared coating film was immersed in seawater for 14 days, the length (mm) of creep back on the sheet side was measured. At this time, the evaluation criteria were: when the length of creep back was less than 2 mm, it was evaluated as good (○), when it was more than 2 mm and less than 5 mm, it was evaluated as ordinary (△), and when it was more than 5 mm, it was evaluated as poor (×).

[0119] (4) Repeatability of coating

[0120] As described above, the coating film was coated once to prepare a primary coating film, and after 21 days, the coating was coated twice in the same manner as described above to prepare a secondary coating film. After 1 day, the adhesion between the primary coating film and the secondary coating film was measured.

[0121] The degree of adhesion was determined according to the ASTM D3359 tape adhesion test method. After 100 squares of 1 mm x 1 mm (horizontal x vertical) were formed on the secondary coating with a knife, the squares were subjected to a tape adhesion test and the degree of peeling was measured. At this time, the evaluation criteria were: no peeling was evaluated as good (○), 1 to 5 peelings were evaluated as normal (△), and 6 or more peelings were evaluated as poor (×).

[0122] (5) Whitening resistance

[0123] Half of the prepared coating film was immersed in seawater for 3 days, and the coating film conditions of the immersed part and the non-immersed part were compared. The evaluation criteria at this time were: no whitening was evaluated as good (○), and whitening was evaluated as bad (×).

[0124]

Table 2

[0125] Rust resistance Chemical resistance Water resistance Repeatability Whitening resistance Experimental Example 1 ○ ○ ○ ○ ○ Experimental Example 2 ○ ○ ○ ○ ○ Experimental Example 3 ○ ○ ○ ○ ○ Experimental Example 4 ○ ○ ○ ○ ○ Experimental Example 5 ○ ○ ○ ○ ○ Experimental Example 6 ○ △ ○ ○ ○ Experimental Example 7 - - - - - Experimental Example 8 × ○ ○ × ×

[0126] As shown in Table 2, the coating films prepared from the coating materials of Experimental Examples 1 to 5 were excellent in rust resistance, chemical resistance, water resistance, repeated coating resistance, and whitening resistance.

[0127] On the contrary, polyamide curing agent-4 is a polyamide resin that does not contain an alkyl-containing acrylate and does not undergo a Michael addition reaction. Although the coating films prepared from the coatings of Experimental Examples 6 and 7 containing this polyamide curing agent-4 have excellent physical properties in terms of oil solubility, they have the problem of being unable to be dissolved in water in water-soluble coatings.

[0128] The coating film prepared from the coating of Experimental Example 8 containing Evonik's Anquamin 401 (product name) as an amine addition water-soluble curing agent was very poor in rust prevention, recoatability, and blush resistance.

Claims

1. A method for preparing a polyamide curing agent for epoxy coatings, comprising: A step of preparing a first mixture containing a first product by subjecting an amine-containing compound to a Michael addition reaction with an alkyl-containing acrylate; and The step of heating a second mixture including the first mixture, a fatty acid and a dimer acid to perform an amidation reaction, thereby preparing a polyamide resin.

2. The method for preparing a polyamide curing agent for epoxy coating according to claim 1, wherein: The Michael addition reaction is carried out at 50 to 100°C. The amidation reaction is carried out at 150 to 250°C.

3. The method for preparing a polyamide curing agent for epoxy coating according to claim 1, wherein: After the amidation reaction, the method further comprises: subjecting the polyamide resin to an addition reaction with an epoxy resin to prepare an epoxy addition polyamide resin.

4. The method for preparing a polyamide curing agent for epoxy coating according to claim 3, wherein: After the amidation reaction and before the addition reaction, the method further comprises: The step of subjecting the polyamide resin to an imidazoline-forming reaction at a temperature of 200° C. or higher to prepare a polyamide resin containing an imidazoline group.

5. A polyamide curing agent for epoxy coatings, prepared by the method according to any one of claims 1 to 4, and comprising a structure represented by the following chemical formula 1, 【Chemical formula 1】 In Chemical Formula 1, R 1 To R 4 Each is independently selected from the group consisting of hydrogen, substituted or unsubstituted alkyl, aryl, amine and cycloalkyl.

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