JP7715519B2 - Epoxy resin coating composition - Google Patents

Description

This invention relates to an epoxy resin coating composition containing an epoxy resin-containing base agent and an amine-based curing agent. More specifically, it relates to an epoxy resin coating composition that is a high-solids epoxy resin coating with a low solvent content, yet is less likely to cause abnormalities in appearance when applied.

In two-component curing paints, which are produced by a reaction between the base epoxy resin and the curing agent amine compound, the coating film can become sticky or crack after curing in low-temperature environments, and whitening can occur when the paint gets wet. These are phenomena that often occur in high-solid paints with low solvent content.

Reducing the amount of volatile organic solvents emitted from paint is one of the paint industry's major goals, from the perspective of reducing the burden on the environment and workers. High-solid paints offer a solution, but the problems with paint film quality mentioned above pose a major obstacle to their widespread adoption.

The stickiness and abnormal appearance of the coating are thought to be caused by the fact that the reaction rate between the amine compound and the moisture and carbon dioxide in the ambient atmosphere is faster than the curing reaction rate between the epoxy resin and the amine compound, resulting in the formation of large amounts of carbamate in the epoxy resin coating. In particular, if the temperature (air temperature) in the environment in which the coating is applied is low, the reaction rate between the epoxy resin and the amine compound slows, making such abnormal appearance more likely to occur.

Generally, in paints with low solvent content, epoxy resins and amine compounds with relatively small molecular weights are used. In particular, amine compounds commonly used in two-component curing paints, such as 1,3-bis(aminomethyl)cyclohexane, 4,4'-methylenebis(cyclohexylamine), xylylenediamine, and isophoronediamine, tend to appear on the surface of the paint film due to the effects of surface tension, and the reactions of the amine compounds mentioned above can cause abnormal appearances such as whitening.

For this reason, in the past, poor appearances have been prevented by suppressing reactivity through modification of amine compounds or by increasing the molecular weight to suppress bleeding onto the coating surface. Specific examples include (i) modification through the Mannich reaction with phenolic compounds and aldehyde compounds, (ii) adduct modification through reaction with epoxy resins, (iii) modification through reaction with compounds containing carboxyl groups, and (iv) modification through the Michael reaction with acrylic compounds.

However, these modifications increase the viscosity of the amine-based compound. This ultimately requires an increase in the amount of diluting solvent, making it difficult to develop a high-solids paint with a low solvent content. Non-reactive diluents (plasticizers) are sometimes used instead of diluting solvents, but this poses the problem of impairing the corrosion resistance that is important for paints.

Therefore, epoxy resin coating compositions are known that combine a polyamine compound, such as 1,3-bis(aminomethyl)cyclohexane, xylylenediamine, or a modified product thereof, with an alkylamine compound (see Patent Documents 1 to 3). By combining a conventionally used polyamine compound with an alkylamine compound, these epoxy resin coating compositions can eliminate the tackiness of the coating surface and prevent stickiness, and can also prevent whitening that occurs when water droplets adhere to the coating.

Japanese Patent Application Publication No. 8-3282 Japanese Patent Application Publication No. 8-104738 JP 2001-163955 A

The epoxy resin coating compositions described in Patent Documents 1 to 3 mentioned above have been used relatively widely to date, and are known to be effective in suppressing poor appearance such as stickiness and whitening.

However, while these effects are effective under certain circumstances, their effectiveness is limited in unsuitable environments, specifically high humidity environments. This is because water acts as a catalyst when amine compounds appear on the coating surface and react with carbon dioxide in the air, making it difficult to prevent the reaction between amine compounds and carbon dioxide in high humidity environments. Furthermore, the addition of alkylamine compounds can actually worsen the appearance of the coating.

The inventors therefore conducted extensive research into the above-mentioned problems and surprisingly discovered that by using a lower alcohol as a solvent, which had not previously been used in epoxy resin coating compositions, it was possible to suppress poor appearance such as stickiness, cracking, and whitening of the coating film, even in low-temperature and high-humidity environments, and thus completed the present invention.

Therefore, the object of the present invention is to provide an epoxy resin coating composition that can reliably prevent poor appearance of the coating film regardless of the usage environment.

That is, the present invention is an epoxy resin coating composition containing a base agent having an epoxy resin and an amine-based curing agent, characterized in that the content of a solvent having a boiling point of less than 200°C is 1 to 15 mass %, and 50 mass % or more of the solvent is a lower alcohol having 1 to 5 carbon atoms.

In the present invention, the solvent used in the epoxy resin coating composition is a lower alcohol having 1 to 5 carbon atoms, accounting for at least 50% by mass, preferably at least 80% by mass, more preferably at least 90%, and even more preferably at least 99% of the solvent. The use of such lower alcohols is intended to promote compatibility of the amine curing agent with the epoxy resin, particularly to achieve good compatibility with the cyclic aliphatic polyamines preferably used in the present invention, as described below. This prevents bleeding of the amine curing agent in the epoxy resin coating composition of the present invention without being affected by the environment.

Such lower alcohols having 1 to 5 carbon atoms are not particularly limited, but examples of primary alcohols include methanol, ethanol, propan-1-ol, butan-1-ol, and pentan-1-ol, and examples of secondary alcohols include propan-2-ol, butan-2-ol, pentan-2-ol, and 1-methoxy-2-propanol. One or more of these can be used. Of these, primary alcohols are preferred.

In addition, in the present invention, solvents other than lower alcohols having 1 to 5 carbon atoms can be included as long as the above-mentioned quantitative restrictions are met. There are no particular restrictions on these other solvents, except that they must have a boiling point of less than 200°C. However, since lower alcohols are relatively poor solvents for epoxy resins, the following are preferred: ketone-based organic solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; ester-based organic solvents such as methyl acetate, ethyl acetate, and butyl acetate; and hydrocarbon solvents such as toluene and xylene.

The present invention is a two-component epoxy resin paint composition containing an epoxy resin-containing base and an amine-based curing agent. Taking into account typical use as a paint, the solvent has a boiling point of less than 200°C. In particular, the epoxy resin paint composition of the present invention is a high-solids paint, and the solvent content in the epoxy resin paint composition is 1 to 15% by mass. This solvent content is preferably 1 to 10% by mass, and more preferably 1 to 5% by mass. While this definition may vary, paints with a solvent content of 30% or less are generally referred to as high-solids paints. However, the present invention is an epoxy resin paint composition with an even lower solvent content.

There are no particular restrictions on the amine curing agent used in the epoxy resin coating composition of the present invention, and any amine compound, either an aliphatic amine or an aromatic amine, commonly used as an amine curing agent can be used. However, because they can ensure excellent corrosion resistance and workability, an amine curing agent containing an amine compound made from a cyclic aliphatic polyamine or an aliphatic polyamine having two or more amino groups is preferred, or an amine curing agent containing both of these amine compounds is preferred.

Specific examples of cyclic aliphatic polyamines include 1,3-bis(aminomethyl)cyclohexane, 4,4'-methylenebis(cyclohexylamine), xylylenediamine, and isophoronediamine, and one or more of these can be used. Specific examples of aliphatic polyamines include polyoxypropylenediamine and tetraethylenepentamine, and one or more of these can be used. The amine compound used as the amine curing agent may be modified, as long as the viscosity of the paint is within a range that allows application. In particular, those modified with phenolic compounds, aldehyde compounds, epoxy resins, acrylic compounds, etc. can be used, taking into account the curing reaction speed and the performance of the resulting coating film.

The above-mentioned amine-based curing agents may also contain a plasticizer component for purposes such as viscosity adjustment. Non-reactive diluents such as benzyl alcohol and high-boiling-point hydrocarbons are commonly used as plasticizer components.

On the other hand, the epoxy resin constituting the base component of the epoxy resin coating composition of the present invention can be any epoxy resin that has two or more epoxy groups per molecule and can react with an amine-based curing agent to form a crosslinked coating film. Examples include bisphenol-type epoxy resins such as bisphenol A epoxy resin, bisphenol F epoxy resin, and bisphenol AD epoxy resin, as well as special epoxy resins such as chelate-modified epoxy resin, dimer acid-modified epoxy resin, propylene oxide-modified epoxy resin, and sulfide-containing epoxy resin. These epoxy resins can be used alone or in combination of two or more. Representative examples of commercially available epoxy resins include the YD series manufactured by Nippon Steel Chemical & Material Co., Ltd. and the jER series manufactured by Mitsubishi Chemical Corporation.

In particular, in this invention, lower alcohols, which are not good solvents for epoxy resins, are the main solvent. Therefore, taking into consideration their solubility, it is preferable to use an epoxy resin with an epoxy equivalent weight of 100 to 1,000. Even more preferable is an epoxy resin with an epoxy equivalent weight of 100 to 300. Additionally, from the perspective of the corrosion resistance and workability of the coating film, the weight-average molecular weight of the epoxy resin is preferably 200 to 4,000, and more preferably 300 to 2,000.

There are no particular restrictions on the ratio of base agent to amine curing agent in the epoxy resin coating composition of the present invention, and it can be approximately the same as the formulation used in general epoxy resin coating compositions. However, as a guideline, the amount of amine curing agent used should be such that the ratio of the amount of active hydrogen in the amine compound to the epoxy groups in the epoxy resin is in the range of 0.3 to 1.5, and preferably, from the perspective of coating film performance, this ratio should be in the range of 0.5 to 1.0. Furthermore, as described below, when the epoxy resin coating composition of the present invention contains an aliphatic monoamine, it is advisable to consider the ratio of the amount of active hydrogen in the amine compound to the epoxy groups in the epoxy resin, including the amount of active hydrogen in this aliphatic monoamine.

The epoxy resin coating composition of the present invention may also contain an aliphatic monoamine having 10 to 20 carbon atoms. This aliphatic monoamine is preferably a monofunctional amine compound, specifically a compound having a primary amine such as stearylamine or tallow alkylamine. The incorporation of such an aliphatic monoamine can enhance the effect of suppressing appearance defects. However, if an excessive amount of aliphatic monoamine is incorporated into the epoxy resin coating composition, there is a risk of poor interlayer adhesion when coatings are reapplied. Therefore, when an aliphatic monoamine is incorporated, it is preferable to adjust the amount of the aliphatic monoamine to 2% by mass or less in the epoxy resin coating composition, preferably 1% by mass or less, and more preferably 0.5% by mass or less. Furthermore, to enhance the effect of suppressing appearance defects, it is preferable to incorporate 0.01% by mass or more of the aliphatic monoamine into the epoxy resin coating composition.

The epoxy resin paint composition of the present invention may contain a pigment. Pigments that can be used include various extender pigments, color pigments, and anti-rust pigments commonly used in paints. Typical extender pigments include calcium carbonate, barium sulfate, talc, and silica. Color pigments include titanium oxide, red iron oxide, yellow iron oxide, and carbon black. Anti-rust pigments include zinc chromate, strontium chromate, zinc phosphate, zinc phosphomolybdate, and aluminum phosphate. However, it is preferable to use phosphate-based protective pigments, which are safer than anti-rust pigments containing heavy metals such as chromium and lead that are harmful to health. From the perspectives of the corrosion resistance of the paint film and the usable life of the paint, the total amount of these pigments contained is preferably 50 to 200 parts by mass, and more preferably 60 to 150 parts by mass, per 100 mass of the resin components (epoxy resin and amine compound combined).

In addition, various additives can be blended into the epoxy resin coating composition of the present invention to improve coating performance, etc. Representative examples of such additives include commonly used silane coupling agents, pigment dispersants, anti-settling agents, and anti-foaming agents.

The epoxy resin coating composition of the present invention eliminates the drawbacks of amine-based curing agents made from cycloaliphatic polyamines such as 1,3-bis(aminomethyl)cyclohexane, 4,4'-methylenebis(cyclohexylamine), xylylenediamine, and isophoronediamine, such as stickiness, cracking, and whitening, resulting in an epoxy resin coating with excellent water resistance. The applications of this epoxy resin coating composition are not particularly limited, and it can be used, for example, as a coating for coating the roofs and walls of steel structures and the indoor steel frames of structures, or as a coating material for corrosion prevention of metal and concrete in flooring materials, etc. It is particularly effective in outdoor coating applications that are prone to exposure to low-temperature and high-humidity environments.

The epoxy resin coating composition of the present invention can reliably prevent poor appearance of the coating film regardless of the usage environment.

The present invention will be explained below based on examples, but the present invention is not limited to these examples. Furthermore, "parts" and "%" in the examples are based on mass unless otherwise specified.

(Preparation of epoxy resin coating composition)
The base agent and amine-based curing agent were prepared in the mass proportions shown in Table 1, and mixed at the respective mixing ratios to prepare epoxy resin coating compositions according to Examples 1 to 7 and Comparative Examples 1 to 7. Details of the components used are as follows:

Epoxy resin: Epotohto YDF-170 (product name of Nippon Steel Chemical & Material Co., Ltd., epoxy equivalent weight 170)
Talc: Talc PS-85 (trade name, manufactured by Fukuoka Talc Kogyo Co., Ltd., oil absorption capacity 50 ml/100 g, average particle size 4.5 μm)
Titanium oxide: TITONE R-5N (product name, manufactured by Sakai Chemical Industry Co., Ltd., average particle size 0.26 μm)
Carbon black: MA-100 (product name of Mitsubishi Chemical Corporation)
Solvents (methanol, ethanol, propylene glycol monomethyl ether, 1-hexanol, benzyl alcohol, toluene)
Amine compound A: a mixture of epoxy-modified isophorone diamine, isophorone diamine, and 1,6-hexanediamine, 2,2,4-trimethyl (trade name: Sanmaid IM-544, manufactured by Evonik Japan Co., Ltd., active hydrogen equivalent: 100)
Amine compound B: a mixture of 4,4'-methylenebis(cyclohexylamine) and modified 4,4'-methylenebis(cyclohexylamine) (trade name: Ancamine 2143, manufactured by Evonik Japan Co., Ltd., active hydrogen equivalent: 118)
Amine compound C: stearylamine (active hydrogen equivalent: 135)

To prepare these, the base resin was prepared by adding the specified amounts of epoxy resin, solvent, various pigments, and various additives, and then dispersing for 60 minutes until the pigments were thoroughly dispersed. Meanwhile, the amine-based curing agent was prepared by adding amine compound C (stearylamine) to either amine compound A or B, and stirring thoroughly until uniformly dissolved. The amount of amine-based curing agent added to the base resin was adjusted so that the ratio of the NH group (active hydrogen) equivalent in the amine compound (including amine compound C) to the epoxy equivalent in the base resin (active hydrogen/epoxy equivalent) was 0.8 to 1.0. The base resin and curing agent were thoroughly mixed in the mass proportions shown in Table 1 to prepare an epoxy resin coating composition.

(Observation of the appearance of the coating film)
The gray-colored base resin was thoroughly mixed with the curing agent, and the mixture was applied to a tin plate using an applicator with a gap of 600 μm. The paint was then cured for four days in a thermo-hygrostat at 10°C and 30% RH, 10°C and 80% RH, or 23°C and 30% RH, after which the paint was visually observed for appearance and evaluated on a three-point scale. The evaluation criteria are as follows, and the results are summarized in Table 1.
○: No abnormalities (no appearance abnormalities such as cracks or quality abnormalities such as stickiness).
△: Minor abnormalities present (appearance abnormalities such as yuzu peel or slight cracks, or minor quality abnormalities such as stickiness).
×: Abnormal (Abnormal appearance such as wrinkles or cracks, or quality abnormality such as stickiness).

As can be seen from the results shown in Table 1, the epoxy resin coating compositions of Comparative Examples 1 to 7, which used 1-hexanol, benzyl alcohol, or toluene as the main solvent, did not cause any problems with the appearance of the coating film at room temperature and in a low-humidity environment, but at lower temperatures or higher humidity, abnormal appearance became apparent. On the other hand, the epoxy resin coating compositions of Examples 1 to 7, which used a lower alcohol as the main solvent, were able to suppress abnormal appearance compared to the comparative examples. In other words, it was possible to obtain epoxy resin coating compositions that reduced appearance defects and were resistant to environmental changes.

Claims (4)

An epoxy resin coating composition comprising a base agent having an epoxy resin, an amine-based curing agent, and a pigment , wherein the content of a solvent is 1 to 15 mass %, the boiling point of the solvent is less than 200°C, and 50 mass % or more of the solvent is a lower alcohol having 1 to 5 carbon atoms, the amine-based curing agent contains an amine compound consisting of a cyclic aliphatic polyamine and/or an aliphatic polyamine, and an aliphatic monoamine having 10 to 20 carbon atoms , and the epoxy resin coating composition contains the aliphatic monoamine in an amount of 0.01 mass % or more and 2 mass % or less . The epoxy resin coating composition according to claim 1, wherein the epoxy resin has an epoxy equivalent of 100 to 1,000. The epoxy resin coating composition according to claim 1 or 2, wherein the lower alcohol is one or more selected from the group consisting of methanol, ethanol, propan-1-ol, butan-1-ol, pentan-1-ol, propan-2-ol, butan-2-ol, pentan-2-ol, and 1-methoxy-2-propanol. The epoxy resin coating composition according to any one of claims 1 to 3, which is for outdoor coating applications.