JP2022183490A - Cationic electrodeposition coating composition, electrodeposited material and method for producing electrodeposited material - Google Patents

Abstract

To provide a cationic electrodeposition coating composition capable of forming a coating layer that has high storage stability and can be cured at low temperatures.SOLUTION: A cationic electrodeposition coating composition contains an aminated epoxy resin (A) and a blocked polyisocyanate curing agent (B). The aminated epoxy resin (A) has a tertiary amination rate of 85% or more. The blocked polyisocyanate curing agent (B) results from the reaction between an oxime compound and an aromatic polyisocyanate. The tertiary amination rate of the aminated epoxy resin (A) is preferably 95% or more.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a cationic electrodeposition coating composition, an electrodeposition coating, and a method for producing an electrodeposition coating.

Cationic electrodeposition paints are often used as undercoat paints to impart corrosion resistance to industrial products such as automobiles. In recent years, low-temperature curable cationic electrodeposition paints have been proposed to reduce energy costs. For example, U.S. Pat. No. 5,900,001 teaches a cationic electrodeposition coating comprising a low-temperature curing blocked polyisocyanate compound, an amino group-containing epoxy resin and a pigment dispersion paste.

WO2017/138445

The cationic electrodeposition paint of Patent Document 1 is inferior in storage stability. In general, low-temperature curability and storage stability are contradictory effects, and it is difficult to make them compatible.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a cationic electrodeposition coating composition which is excellent in storage stability and capable of forming a low-temperature curable coating film.
Another object of the present invention is to provide an electrodeposition-coated article obtained using the cationic electrodeposition coating composition and a method for producing the electrodeposition-coated article.

Specifically, the present invention provides the following aspects:
[1]
an aminated epoxy resin (A);
a blocked polyisocyanate curing agent (B),
The tertiary amination rate of the aminated epoxy resin (A) is 85% or more,
The blocked polyisocyanate curing agent (B) is a cationic electrodeposition coating composition obtained by reacting an oxime compound and an aromatic polyisocyanate.

[2]
The cationic electrodeposition coating composition according to [1] above, wherein the aminated epoxy resin (A) has a tertiary amination rate of 95% or more.

[3]
The cationic electrodeposition coating composition according to [1] or [2] above, wherein the aromatic polyisocyanate contains 4,4′-diphenylmethane diisocyanate and/or a polymer thereof.

[4]
The cationic electrodeposition coating composition according to any one of [1] to [3] above, wherein the oxime compound contains methyl ethyl ketoxime.

[5]
The aminated epoxy resin (A) is obtained by reacting an amine compound and an epoxy resin,
The amine compound is a combination of two types of primary amine and secondary amine,
The primary amine has the formula:
_NH2- ( _CH2 ) ⁿ - ^NR1R2 (1)
(In formula (1), R ¹ and R ² each independently represent an alkyl group having 1 to 6 carbon atoms which may have a terminal hydroxyl group, and n represents an integer of 2 to 4.)
is represented by
The secondary amine has the formula:
^{R3R4NH (} 2)
(In formula (2), R ³ and R ⁴ each independently represent an alkyl group having 1 to 4 carbon atoms and having a terminal hydroxyl group.)
The cationic electrodeposition coating composition according to any one of [1] to [4] above, represented by

[6]
The cationic electrodeposition coating composition according to any one of [1] to [5] above, wherein the aminated epoxy resin (A) has a molecular weight distribution of 3.0 or less.

[7]
The cationic electrodeposition coating composition according to any one of [1] to [6] above, wherein the content of the curing catalyst is less than 0.5% by mass based on the solid content of the cationic electrodeposition coating composition.

[8]
The cationic electrodeposition coating composition according to any one of [1] to [7] above, wherein the curing catalyst content is less than 0.25% by mass of the solid content of the cationic electrodeposition coating composition.

[9]
After immersing the object to be coated in the cationic electrodeposition coating composition according to any one of [1] to [8] above, a voltage is applied between the object to be coated and the counter electrode to A step of forming an uncured coating film on the coating;
a step of heating the coating film at a temperature of 140° C. or less to obtain a cured cationic electrodeposition coating film.

[10]
an object to be coated;
An electrodeposition-coated article having, on the article to be coated, a cationic electrodeposition coating film formed from the cationic electrodeposition coating composition according to any one of [1] to [8] above.

INDUSTRIAL APPLICABILITY The cationic electrodeposition coating composition of the present invention is excellent in storage stability and can form a coating film that can be cured at a low temperature. The electrodeposition-coated article of the present invention is excellent in oil repellency resistance.

[Cationic electrodeposition coating composition]
Primary amino groups are generally highly reactive. Therefore, in the cationic electrodeposition coating composition (hereinafter sometimes simply referred to as the electrodeposition coating composition), if the aminated epoxy resin has many primary amino groups, it becomes easier to react with the curing agent, Cures at low temperatures. That is, the low-temperature curability is improved. However, in an electrodeposition coating composition, an aminated epoxy resin having a primary amino group tends to undergo a curing reaction even during storage, resulting in poor storage stability.

In this embodiment, in order to achieve both low-temperature curability and storage stability, the reactivity of the aminated epoxy resin is suppressed and a highly reactive curing agent is used. That is, the proportion of primary amino groups in the aminated epoxy resin used in the present embodiment is reduced, and the tertiary amination ratio is set to 85% or more. Furthermore, as a curing agent, a blocked polyisocyanate curing agent obtained by reacting an oxime compound and an aromatic polyisocyanate is used.

Since the aminated epoxy resin having a tertiary amination rate of 85% or more and relatively low reactivity is used, the storage stability is improved. A blocked polyisocyanate curing agent obtained by reacting an oxime compound with an aromatic polyisocyanate dissociates at a low temperature. Therefore, aminated epoxy resins with low reactivity can be cured at low temperatures (for example, 120° C. or lower).

The tertiary amination ratio is a percentage obtained by dividing the tertiary amine value by the total amine value (100×(tertiary amine value)/(total amine value)). The tertiary amine value refers to mg of potassium hydroxide equivalent to perchloric acid required to neutralize the tertiary amine contained in 1 g of sample. Each amine value can be obtained by the following method according to ASTM D2073.

Tertiary amine value test method (1) Weigh aminated epoxy resin in a 100 ml beaker.
(2) Add 0.5 g of pure water.
(3) Dissolve the aminated epoxy resin in 50 g of THF.
(4) Stir for 5 minutes.
(5) Next, add 7.5 ml of acetic anhydride and 2.5 ml of acetic acid and stir at about 40° C. for 5 minutes.
(6) Titrate with 0.1N perchloric acid acetic acid solution using an automatic potentiometric titrator.
(7) Measure the tertiary amine value by the following formula.
Tertiary amine value = (titration amount (mL) x factor x 10) / (aminated epoxy resin amount (g) x solid content)

Total amine value test method (1) Accurately weigh 500 mg of aminated epoxy resin in a 200 ml Erlenmeyer flask.
(2) Add about 50 ml of glacial acetic acid and dissolve uniformly.
(3) Add 5 to 6 drops of indicator (methyl violet solution) and stir evenly.
(4) Titrate with a 0.1N perchloric acid-acetic acid solution, and the end point is when the solution becomes bright green.
((3) and (4) above may be replaced by potentiometric titration.)

Since it can be cured at a low temperature, repelling due to splashed oil is less likely to occur. Repelling is a phenomenon in which the coated surface is uneven and its distribution and degree are not uniform. Repelling due to splashed oil is said to be caused by a difference in surface tension between the electrodeposition coating film (that is, the cationic electrodeposition coating composition) before curing and the splashed oil.

Electrodeposition coating is performed by immersing an object to be coated in a water-soluble coating composition. Before and after electrodeposition coating, the object to be coated is usually washed with water. Therefore, moisture tends to remain on the surface of the coating film. On the other hand, depending on the coating environment, mist containing oil may scatter and the oil may adhere to the surface of the coating film. In addition, silicon particles and the like contained in tap water used for washing may remain on the surface of the coating film as oil. When water and oil are present on the surface of the electrodeposition coating film before curing, the water content evaporates first when the electrodeposition coating film is heated for curing. With this evaporation, the oil bursts. This is splashed oil. When the splashed oil lands on the surface of the uncured coating film, craters are formed on the coating film surface due to the difference in surface tension between the two. This phenomenon is cissing caused by the splashed oil.

The coating film formed from the electrodeposition coating composition according to the present embodiment has already begun to harden in the vicinity of the temperature at which water evaporates (approximately 100° C.). Therefore, even if the splashed oil lands on the coating film surface, craters are less likely to be formed. Hereinafter, this is referred to as being excellent in oil cissing resistance.

The oil repellency resistance of the electrodeposition coating film can be evaluated as follows.
First, after the object to be coated is subjected to electrodeposition coating, the coating film is naturally dried at room temperature (20° C. to 25° C.). After that, the object to be coated is placed horizontally, and an aluminum cup is fixed in the center with double-sided tape. Drop one drop of water into the aluminum cup using a dropper. Then, drop one drop of oil onto the water droplet. In this state, the object to be coated is heated at 110° C. to 220° C. (preferably 120° C. to 200° C.) for 10 minutes to 30 minutes to cure the electrodeposition coating film. At this time, the oil in the aluminum cup bursts as the water evaporates and scatters outside the aluminum cup. After that, the surface of the cured electrodeposition coating film is visually observed. When the number of craters formed on the surface of the cured electrodeposition coating film is 5 or less and the diameter of all the craters is 1 mm or less, the oil cissing resistance is excellent, the number of craters is 10 or less, and If the diameter of all craters is 3 mm or less, it can be evaluated as suitable for practical use. The diameter of a crater is the diameter of a circle having the same area as the crater (equivalent circle).

Since the coating film formed from the electrodeposition coating composition according to the present embodiment is excellent in oil crater resistance as described above, it does not require a so-called oil crater inhibitor, or the amount added can be reduced. . Therefore, deterioration in adhesion between the cured electrodeposition coating film and other members is suppressed.

The solid content of the electrodeposition coating composition is preferably 1% by mass or more and 30% by mass or less with respect to the total amount of the electrodeposition coating composition. When the solid content is within the above range, a sufficient amount of the electrodeposition coating film is deposited, so the corrosion resistance is likely to be improved. Furthermore, throwing power and coating appearance are easily improved.

The pH of the electrodeposition coating composition is preferably 4.5 or more and 7 or less. When the pH is within the above range, an appropriate amount of acid is present in the electrodeposition coating composition, so that the coating film appearance and coating workability are likely to be improved. Furthermore, since the filterability of the electrodeposition coating composition is also enhanced, the horizontal appearance of the cured electrodeposition coating film is likely to be improved. The pH of the electrodeposition coating composition can be set within the above range by adjusting the amount of neutralizing acid, the amount of free acid added, and the like. The above pH is more preferably 5 or more and 7 or less. The above pH can be measured using a commercially available pH meter with a temperature compensation function.

The milligram equivalent (MEQ(A)) of the acid per 100 g of the solid content of the electrodeposition coating composition is preferably 10 mEq or more and 50 mEq or less. MEQ (A) is an abbreviation for mg equivalent (acid), which is the sum of mg equivalents of all acids per 100 g of the solid content of the electrodeposition coating composition. MEQ(A) can also be adjusted by the amount of neutralized acid and the amount of free acid. MEQ (A) is obtained by dissolving about 10 g of the solid content of the electrodeposition coating composition in about 50 ml of a solvent (THF: tetrahydrofuran), and then performing potentiometric titration with a 0.1 N NaOH solution. It is obtained by quantifying the amount of acid contained in.

The milligram equivalent (MEQ (B)) of the base per 100 g of the solid content of the electrodeposition coating composition is preferably 50 mEq or more and 350 mEq or less. MEQ (B) is an abbreviation for mg equivalent (base), which is the sum of mg equivalents of all bases (typically amino groups of aminated epoxy resins) per 100 g of solid content of the paint. When the MEQ (B) is within the above range, the storage stability is likely to be improved. Moreover, the storage stability of the electrodeposition coating composition can be evaluated from the change in MEQ (B) over time. MEQ (B) can be adjusted depending on the type and amount of amine compound used to prepare the aminated epoxy resin. MEQ (B) was obtained by dissolving about 5 g of the solid content of the electrodeposition coating composition in about 50 ml of THF, and performing potentiometric titration with a 0.1 N perchloric acid solution to determine the base contained in the electrodeposition coating composition. Determined by quantifying the amount.

<Amine epoxy resin (A)>
The aminated epoxy resin (A) is a coating film-forming resin that constitutes an electrodeposition coating film. The aminated epoxy resin is included in the electrodeposition coating composition in the form of a resin emulsion together with the blocked polyisocyanate curing agent. The tertiary amination rate of the aminated epoxy resin (A) is 85% or more. A tertiary amination rate of 85% or more means that the amount of primary amino groups is small, so that the resulting electrodeposition coating composition has improved storage stability. The tertiary amination rate of the aminated epoxy resin (A) is preferably 95% or more, more preferably 96% or more.

The degree of tertiary amination of the aminated epoxy resin (A) is also related to the electrical conductivity of the electrodeposition coating composition. When the tertiary amination rate decreases, the electrical conductivity increases and the gas pinning property tends to decrease. The electrical conductivity of the electrodeposition coating composition is preferably 1500 μS/cm ² or more and 2000 μS/cm ² or less. When the electrical conductivity is within the above range, the throwing power is improved, and the gas-pin property is enhanced, so that the appearance of the coating film surface is likely to be improved. Conductivity can be measured using a commercially available conductivity meter.

The number average molecular weight of the aminated epoxy resin (A) is preferably 1,000 or more and 7,000 or less. When the number average molecular weight is 1,000 or more, physical properties such as solvent resistance and corrosion resistance of the resulting cured electrodeposition coating film are improved. When the number average molecular weight is 7,000 or less, the viscosity of the aminated epoxy resin (A) can be easily adjusted, enabling smooth synthesis. In addition, it facilitates emulsification and dispersion of the resulting aminated epoxy resin (A). The number average molecular weight of the aminated epoxy resin (A) is more preferably 1,500 or more and 4,000 or less.

The molecular weight distribution of the aminated epoxy resin (A) is preferably 3.0 or less, more preferably 2.7 or less, and particularly preferably 2.5 or less. When the molecular weight distribution of the aminated epoxy resin (A) is within the above range, it can be said that side reactions are suppressed in the reaction between the starting material epoxy resin and the amino compound. performance is easily demonstrated.

In order to control the molecular weight distribution of the aminated epoxy resin (A) to 3.0 or less, the reaction temperature, reaction time, etc. may be adjusted. For example, when the reaction temperature is less than 120°C or exceeds 180°C, the molecular weight distribution tends to be high. Alternatively, a method using a combination of a primary amine and a secondary amine, which will be described later, can be used as the amine compound.

The amine value of the aminated epoxy resin (A) (same as the above total amine value) is preferably 20 mgKOH/g or more and 100 mgKOH/g or less. When the amine value of the aminated epoxy resin (A) is 20 mgKOH/g or more, the emulsified dispersion stability of the aminated epoxy resin (A) in the electrodeposition coating composition is improved. On the other hand, when the amine value is 100 mgKOH/g or less, the amount of amino groups in the cured electrodeposition coating film becomes appropriate, and the decrease in water resistance of the coating film is suppressed. The amine value of the aminated epoxy resin (A) is more preferably 20 mgKOH/g or more and 80 mgKOH/g or less.

The hydroxyl value of the aminated epoxy resin (A) is preferably 150 mgKOH/g or more and 650 mgKOH/g or less. When the hydroxyl value is 150 mgKOH/g or more, the curability of the electrodeposition coating composition is enhanced and the appearance of the coating film is improved. When the hydroxyl value is 650 mgKOH/g or less, the amount of hydroxyl groups remaining in the cured electrodeposition coating film becomes appropriate, and the water resistance of the coating film is easily improved. The hydroxyl value of the aminated epoxy resin is more preferably 150 mgKOH/g or more and 400 mgKOH/g or less.

In particular, the aminated epoxy resin (A) has a number average molecular weight within the range of 1,000 to 7,000, an amine value of 20 to 100 mgKOH/g, and a hydroxyl value of 150 to 650 mgKOH/g (preferably is 150 to 400 mgKOH/g), the corrosion resistance of the object to be coated is likely to be further improved by the electrodeposition coating composition.

The electrodeposition coating composition may contain a plurality of aminated epoxy resins (A) having different amine values and/or hydroxyl values. In this case, the average amine value and the average hydroxyl value calculated based on the mass ratio of the plural aminated epoxy resins (A) are preferably within the above range. Among them, the plural aminated epoxy resins (A) are composed of an aminated epoxy resin having an amine value of 20 to 50 mgKOH/g and a hydroxyl value of 50 to 300 mgKOH/g and an amine value of 50 to 200 mgKOH/g. and an aminated epoxy resin having a hydroxyl value of 200 to 500 mgKOH/g. As a result, the core portion of the emulsion becomes more hydrophobic and the shell portion becomes more hydrophilic, so that the corrosion resistance of the object to be coated can be more easily improved.

The aminated epoxy resin (A) is obtained by modifying the oxirane ring (also referred to as "epoxy group") of the epoxy resin with an amine compound, that is, by aminating it. However, as the amine compound, it is preferable to use an amine compound having at least one of a primary amino group, a secondary amino group and a tertiary amino group, excluding ketimine (including diketimine).

Ketimine has a structure in which the active primary amino group is protected with a ketone, and is easily hydrolyzed to produce a primary amino group. Therefore, the use of ketimine tends to lower the tertiary amination rate of the aminated epoxy resin.

A primary amino group as a raw material is consumed in the amination reaction of the epoxy resin to form a branched chain of the aminated epoxy resin (A). Therefore, it is difficult to reduce the tertiary amination rate of the resulting aminated epoxy resin (A).

At the time of amination, the amine compound is preferably used in an amount of 0.9 equivalent or more and 1.2 equivalent or less with respect to 1 equivalent of the epoxy group of the starting material epoxy resin. The reaction conditions for amination can be appropriately selected according to the reaction scale and the like. For example, the reaction may be carried out at 80° C. or higher and 150° C. or lower for 0.1 hour or longer and 5 hours or shorter, more preferably 120° C. or higher and 150° C. or lower for 0.5 hour or longer and 3 hours or shorter.

(amine compound)
Amine compounds other than ketimine used for amination of epoxy resins include, for example, primary amines such as butylamine, octylamine and monoethanolamine; secondary amines such as diethylamine, dibutylamine, methylbutylamine, diethanolamine and N-methylethanolamine; Amine; tertiary amine such as triethylamine, N,N-dimethylbenzylamine, N,N-dimethylethanolamine; complex amine such as diethylenetriamine; N,N-dimethyl-1,3-propanediamine, N,N-dimethylethylenediamine diamines having a primary amino group and a tertiary amino group such as N-(3-aminopropyl)diethanolamine; and diamines having a primary amino group, a tertiary amino group and a hydroxyl group such as N-(3-aminopropyl)diethanolamine. Amine compounds may be used alone or in combination of two or more. Among them, when a diamine having a hydroxyl group is used, the adhesion and curability of the coating film are likely to be improved.

The number of primary amino groups in the amine compound is not particularly limited as long as it is 1 or 2 or more. Among them, from the viewpoint of reaction control, the number of primary amino groups is preferably one. The number of hydroxyl groups is not particularly limited as long as it is 1 or 2 or more.

Among them, as the amine compound, a combination of two kinds of the following primary amine and secondary amine is preferably used. As a result, the emulsification and dispersion stability of the aminated epoxy resin (A) in the electrodeposition coating composition is improved, and the molecular weight distribution is easily controlled. For example, the molecular weight distribution of the aminated epoxy resin (A) can be easily controlled to 2.7 or less. Molecular weight distribution means the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn): Mw/Mn. Each average molecular weight and molecular weight distribution are polystyrene conversion values measured by gel permeation chromatography.

A primary amine has the formula:
_NH2- ( _CH2 ) ⁿ - ^NR1R2 (1)
(In formula (1), R ¹ and R ² each independently represent an alkyl group having 1 to 6 carbon atoms which may have a terminal hydroxyl group, and n represents an integer of 2 to 4.)
is represented by

A secondary amine has the formula:
^{R3R4NH (} 2)
(In formula (2), R ³ and R ⁴ each independently represent an alkyl group having 1 to 4 carbon atoms and having a terminal hydroxyl group.)
is represented by

When these amine compounds are used, the primary amino group of the primary amine is first reacted with the epoxy resin and consumed. Therefore, the remaining reactive amino groups are only secondary amino groups for both primary and secondary amines. The secondary amino group reacts with the epoxy group of the epoxy resin to obtain an aminated epoxy resin (A). Since the reactive amino group is only a secondary amino group, there is no superiority in reactivity, the reaction proceeds evenly, and the molecular weight distribution of the resulting aminated epoxy resin (A) is controlled.

A tertiary amino group or a tertiary amino group produced by the reaction of a secondary amino group present in the primary amine may react with an epoxy group to form a quaternary ammonium group, but this reaction is unlikely to occur. it is conceivable that.

In the above formula (1), R ¹ and R ² are specifically methyl, ethyl, propyl or butyl, and may have a terminal hydroxyl group. n is an integer of 2 to 4, preferably 3; R ¹ and R ² may be the same or different. Specific examples of primary amines include N-(3-aminopropyl)diethanolamine, N,N-dimethyl-1,3-propanediamine (DMAPA), and N,N-diethyl-1,3-propanediamine (DEAPA). , N,N-dibutyl-1,3-propanediamine and the like.

In formula (2) above, R ³ and R ⁴ both have a C 1-4 alkyl group having a hydroxyl group. R ³ and R ⁴ may be the same or different. The secondary amine is a secondary amine, and specific examples thereof include dimethanolamine and diethanolamine (DETA).

The primary amine is preferably 30% by mass or more and 80% by mass or less, more preferably 40% by mass or more and 70% by mass or less of the total of the primary amine and the secondary amine. When the ratio of the primary amine is within the above range, an excessive increase in the viscosity of the aminated epoxy resin (A) is suppressed, and the stability of the emulsion containing the aminated epoxy resin (A) tends to be improved. .

(Raw material epoxy resin)
The epoxy resin that is the raw material of the aminated epoxy resin (A) is, for example, a polyphenol polyglycidyl ether type epoxy resin. A polyphenol polyglycidyl ether type epoxy resin is generally obtained by reacting a polycyclic phenol compound and epichlorohydrin. Examples of polycyclic phenol compounds include bisphenol A, bisphenol F, bisphenol S, phenol novolak, and cresol novolak.

Polyphenol polyglycidyl ether type epoxy resins include epoxy resins obtained by chain extension reaction of polyphenol polyglycidyl ether type epoxy resins with polycyclic phenol compounds. The conditions for the chain extension reaction can be appropriately selected according to the stirrer to be used, the reaction scale, and the like. The reaction conditions are, for example, 85 to 180° C. for 0.1 to 8 hours, more preferably 100 to 150° C. for 2 to 8 hours. The stirring device is not particularly limited, and a general stirring device in the paint field can be used.

As the raw material epoxy resin, an oxazolidone ring-containing epoxy resin described in JP-A-5-306327 can also be mentioned. This epoxy resin is obtained by reacting a diisocyanate compound or a bisurethane compound obtained by blocking the isocyanate group of the diisocyanate compound with a lower alcohol such as methanol or ethanol, with epichlorohydrin.

Some of the oxazolidone ring-containing epoxy resins undergo a chain extension reaction with bifunctional polyester polyols, polyether polyols (e.g., polyols having a polyethylene oxide group, polyols having a polypropylene oxide group, etc.), dibasic carboxylic acids, etc. may have been The raw material epoxy resin may contain, for example, a polypropylene oxide group-containing epoxy resin obtained by a chain extension reaction using a polyol having a polypropylene oxide group. The content of the polypropylene oxide group-containing epoxy resin is preferably 1 part by mass or more and 40 parts by mass or less, more preferably 15 parts by mass or more and 25 parts by mass or less with respect to 100 parts by mass of the total amount of the raw material epoxy resin.

<Blocked Polyisocyanate Curing Agent (B)>
The blocked polyisocyanate curing agent (B) (hereinafter sometimes simply referred to as curing agent (B)) also constitutes the electrodeposition coating film. The blocked polyisocyanate curing agent (B) preferentially reacts with the amine groups of the aminated epoxy resin (A) and further reacts with hydroxyl groups to cure the aminated epoxy resin (A).

A curing agent (B) is obtained by reacting an oxime compound and an aromatic polyisocyanate. A blocking agent that blocks an aromatic polyisocyanate dissociates more easily at a lower temperature than a blocking agent that blocks an aliphatic polyisocyanate. Furthermore, since an oxime compound is used as a blocking agent, the dissociation temperature is further lowered. Therefore, the electrodeposition coating composition containing the curing agent (B) cures at a low temperature in spite of using the aminated epoxy resin (A) with relatively low reactivity.

(aromatic polyisocyanate)
The aromatic polyisocyanate is not particularly limited as long as it has one or more aromatic rings and two or more isocyanate groups (-N=C=O) bonded to the aromatic rings. Aromatic polyisocyanates include, for example, tolylene diisocyanate, xylylene diisocyanate, phenylene diisocyanate, diphenylmethane diisocyanate (MDI), and polymers thereof. MDIs include 2,4'-diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate. Polymeric MDI is typically exemplified as the polymer. Among them, MDI and/or its polymer (particularly, polymethylene polyphenyl polyisocyanate (polymeric MDI)) is preferable from the viewpoint of excellent corrosion resistance and reactivity. Commercially available polymeric MDI is typically a mixture of MDI monomers and MDI oligomers.

(blocking agent)
The oxime compound that blocks the isocyanate group has the following formula (1):

(In formula (1), R ¹ is hydrogen or an alkyl group having 1 to 4 carbon atoms, and R ² is an alkyl group having 1 to 4 carbon atoms.)
is represented by

The alkyl group having 1 to 4 carbon atoms may be linear or branched. Examples of alkyl groups having 1 to 4 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group and t-butyl group.

Both R ¹ and R ² are preferably alkyl groups having 1 to 4 carbon atoms, more preferably alkyl groups having 1 to 3 carbon atoms, and both are 1 carbon atoms, in that corrosion resistance is unlikely to be affected. An alkyl group of ∼2 is particularly preferred. Specifically, methyl ethyl ketoxime (MEKO) in which R ¹ is a methyl group and R ² is an ethyl group is preferred.

The blocking rate of the curing agent (B) is preferably 100%. This makes it easier to further improve the storage stability of the electrodeposition coating composition.

The content of the curing agent (typically the curing agent (B)) is set in consideration of the amount, structure, etc. of the curable resin (typically the aminated epoxy resin (A)). Specifically, a curing agent is used in an amount sufficient to react with active hydrogen-containing functional groups such as primary amino groups, secondary amino groups and hydroxyl groups possessed by the curable resin. The curing agent is, for example, such that the solid content mass ratio of the curable resin and the curing agent (curable resin/curing agent) is 90/10 to 50/50, more preferably 80/20 to 65/35. blended. The fluidity and curing speed of the electrodeposition coating composition are controlled by the solid content mass ratio of the curable resin and the curing agent.

<Curing catalyst>
The electrodeposition coating composition may contain a curing catalyst. The curing catalyst is not particularly limited, and those known in the field of coatings can be used. Examples of curing catalysts include organic tin and bismuth compounds. Examples of organic tin include dibutyltin oxide, dioctyltin oxide, dioctyltin dilaurate, dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, dibutyltin dibenzoate, and dioctyltin dibenzoate. Bismuth compounds include bismuth oxide and bismuth hydroxide.

However, since the electrodeposition coating composition according to the present embodiment is excellent in low-temperature curability, the use of a curing catalyst can be omitted or the amount used can be reduced. As a result, the amount of metal contained in the electrodeposition coating composition is reduced, thereby reducing the environmental load. For example, the curing catalyst content may be less than 0.5% by weight, and may be less than 0.25% by weight, based on the solids content of the electrodeposition coating composition.

As used herein, the term "solid content of the electrodeposition coating composition" means the mass of all the components contained in the electrodeposition coating composition that remain solid after removal of the solvent. . Specifically, the aminated epoxy resin (A), the blocked polyisocyanate curing agent (B), and the optionally contained pigment dispersing resin, pigment, and other solid components contained in the electrodeposition coating composition means the total solid mass of

<Pigment>
The electrodeposition coating composition may contain a pigment if necessary. Pigments are usually added to the electrodeposition coating composition as a pigment dispersion paste containing a pigment dispersion resin and a pigment.

Pigments are pigments commonly used in electrodeposition coating compositions. Examples of pigments include coloring pigments such as titanium white (titanium dioxide), carbon black and red iron oxide; extender pigments such as kaolin, talc, aluminum silicate, calcium carbonate, mica and clay; iron phosphate, aluminum phosphate, calcium phosphate , aluminum tripolyphosphate, and antirust pigments such as aluminum phosphomolybdate and aluminum zinc phosphomolybdate.

(Pigment dispersion resin)
A pigment dispersing resin is a resin for dispersing a pigment, and is used by being dispersed in an aqueous medium. Pigment dispersing resins include, for example, pigment dispersing resins having cationic groups, such as modified epoxy resins having at least one selected from quaternary ammonium groups, tertiary sulfonium groups and primary amino groups. Specific examples of pigment dispersion resins include quaternary ammonium group-containing epoxy resins and tertiary sulfonium group-containing epoxy resins. Examples of the aqueous solvent include ion-exchanged water and water containing a small amount of alcohol.

<Other ingredients>
The electrodeposition coating composition optionally contains components other than the aminated epoxy resin (A), the blocked polyisocyanate curing agent (B), and the curing catalyst.

(Curable resin)
The electrodeposition coating composition may optionally contain an aminated resin having a tertiary amination rate of less than 85%. The electrodeposition coating composition may also contain aminated resins other than the aminated epoxy resin (A), such as aminated acrylic resins and aminated polyester resins, if necessary. However, from the viewpoint of storage stability, 80% by mass or more, further 90% by mass or more, particularly 100% by mass of all aminated resins contained in the electrodeposition coating composition has a tertiary amination rate of 85. % or more of the aminated epoxy resin (A).

The electrodeposition coating composition may contain curable resins other than the aminated resin. Examples of other coating film-forming resins include hydroxyl group-containing acrylic resins, hydroxyl group-containing polyester resins, urethane resins, butadiene resins, phenol resins, and xylene resins. Among them, phenol resin and xylene resin are preferable. Specifically, xylene resins having 2 to 10 aromatic rings are preferred. However, from the viewpoint of low-temperature curability, 80% by mass or more, further 90% by mass or more, particularly 100% by mass of all the curable resins contained in the electrodeposition coating composition has a tertiary amine conversion rate. It is preferably 85% or more aminated epoxy resin (A).

(Other curing agents)
The electrodeposition coating composition may optionally contain polyisocyanate curing agents other than the curing agent (B), such as aliphatic diisocyanates, alicyclic polyisocyanates, blocked products thereof, and blocked compounds other than oxime compounds. It may also contain an agent-blocked aromatic polyisocyanate.

Examples of aliphatic diisocyanates include hexamethylene diisocyanate (including trimers), tetramethylene diisocyanate, and trimethylhexamethylene diisocyanate. Alicyclic polyisocyanates include, for example, isophorone diisocyanate and 4,4'-methylenebis(cyclohexyl isocyanate).

Blocking agents include monovalent alkyl (or aromatic) alcohols such as n-butanol, n-hexyl alcohol, 2-ethylhexanol, lauryl alcohol, phenol carbinol and methylphenyl carbinol; ethylene glycol monohexyl ether , Cellosolves such as ethylene glycol mono-2-ethylhexyl ether; Polyether type double-ended diols such as polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol phenol; Diols such as ethylene glycol, propylene glycol, 1,4-butanediol and polyester type double-ended polyols obtained from dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, suberic acid and sebacic acid; phenols such as para-t-butylphenol and cresol; and ε-caprolactam, γ- Examples include lactams represented by butyrolactam.

The electrodeposition coating composition may contain curing agents other than the polyisocyanate curing agent, such as organic curing agents such as melamine resins and phenolic resins, silane coupling agents, and metal curing agents.

However, from the viewpoint of low-temperature curability, 80% by mass or more, further 90% by mass or more, particularly 100% by mass of all the curing agents contained in the electrodeposition coating composition is the curing agent (B). is preferred.

(Nitrite metal salt)
The electrodeposition coating composition may further contain a nitrite metal salt. The metal nitrite salt tends to improve the corrosion resistance of the coating film to be obtained, especially the corrosion resistance of the edge portion (edge rust prevention). The nitrite metal salt is preferably an alkali metal nitrite or an alkaline earth metal nitrite, more preferably an alkaline earth metal nitrite. Nitrite metal salts include, for example, calcium nitrite, sodium nitrite, potassium nitrite, magnesium nitrite, strontium nitrite, barium nitrite, and zinc nitrite.

The content of the nitrite metal salt is, for example, 0.001% by mass or more and 0.2% by mass or less in terms of the metal element of the metal component with respect to the total mass of the curable resin and the curing agent.

(other ingredients)
The electrodeposition paint composition may optionally contain additives commonly used in the paint field, such as organic solvents, anti-drying agents, surfactants such as antifoaming agents, acrylic resin fine particles, etc., for viscosity adjustment. agents, anti-repellent agents, inorganic rust inhibitors. Examples of organic solvents include ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monoethylhexyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, and propylene glycol monophenyl ether. Examples of inorganic rust inhibitors include vanadium salts, copper, iron, manganese, magnesium and calcium salts.

Furthermore, in addition to the above, known auxiliary complexing agents, buffering agents, smoothing agents, stress relieving agents, brightening agents, semi-brightening agents, antioxidants, ultraviolet absorbers, and the like may be contained depending on the purpose.

These additives may be added during the production of the resin emulsion, during the production of the pigment dispersion paste, or during or after mixing the resin emulsion and the pigment dispersion paste. good.

<Preparation of cationic electrodeposition coating composition>
The electrodeposition coating composition is prepared by mixing a resin emulsion containing an aminated epoxy resin (A) and a blocked polyisocyanate curing agent (B), a pigment dispersion paste, additives, etc. by a commonly used method. be able to.

(Preparation of resin emulsion)
The resin emulsion is prepared by dissolving each of the aminated epoxy resin (A) and other curable resins, and the blocked polyisocyanate curing agent (B) and other curing agents in an organic solvent. and by mixing these solutions and then neutralizing with a neutralizing acid.

Examples of neutralizing acids include organic acids such as methanesulfonic acid, sulfamic acid, lactic acid, dimethylolpropionic acid, formic acid, and acetic acid. Among them, neutralization with one or more acids selected from the group consisting of formic acid, acetic acid and lactic acid is more preferable.

The solid content of the resin emulsion is usually 25 to 50% by mass, preferably 35 to 45% by mass, based on the total amount of the resin emulsion. Here, the term "solid content of the resin emulsion" means the mass of all the components contained in the resin emulsion that remain solid even after the solvent is removed. Specifically, it means the total weight of aminated epoxy resin, curing agent and other solid components added as necessary, contained in the resin emulsion.

The neutralizing acid is preferably used in an amount of 10 to 100%, more preferably 20 to 70%, as the equivalent ratio of the neutralizing acid to the amino group equivalents of the aminated epoxy resin. preferable. In the present specification, the equivalent ratio of the neutralizing acid to the amino group equivalent of the aminated epoxy resin is defined as the neutralization rate. When the neutralization rate is 10% or more, affinity for water is ensured, and water dispersibility is improved.

(Method for preparing pigment dispersion paste)
A pigment dispersion paste is prepared by mixing a pigment dispersion resin and a pigment. The content of the pigment-dispersing resin in the pigment-dispersing paste is not particularly limited.

The solid content of the pigment dispersion paste is, for example, 40% by mass or more and 70% by mass or less, and 50% by mass or more and 60% by mass or less with respect to the total amount of the pigment dispersion paste.

As used herein, the term “solid content of the pigment dispersion paste” means the mass of all the components contained in the pigment dispersion paste that remain solid even after the solvent is removed. Specifically, it means the total weight of the pigment dispersion resin, the pigment, and other solid components added as necessary, contained in the pigment dispersion paste.

The method of adding the nitrite metal salt to the electrodeposition coating composition is not particularly limited. For example, an aqueous solution of the nitrite metal salt is prepared in advance and added to the electrodeposition coating composition. Alternatively, the nitrite metal salt is premixed with the pigment to prepare a pigment paste, which is added to the electrodeposition coating composition.

[Manufacturing method of electrodeposition coating]
An electrodeposition coating film is formed by subjecting an article to be coated to electrodeposition coating using the electrodeposition coating composition. An electrodeposition coated article having an electrodeposition coating film is prepared by immersing the article to be coated in the above electrodeposition coating composition and then applying a voltage between the article to be coated and the counter electrode to obtain an uncured surface on the article to be coated. and heating the coating film at a temperature of 140° C. or less to obtain a cured electrodeposition coating film.

(1) Application step In this step, a voltage is applied between the object to be coated as a cathode and a counter electrode (anode). As a result, an uncured coating film is deposited on the object to be coated. The voltage is, for example, 50 V or more and 450 V or less. The bath liquid temperature may be, for example, 10° C. or higher and 45° C. or lower. The voltage application time is not particularly limited, and is, for example, 2 minutes or more and 5 minutes or less.

The material of the object to be coated is not particularly limited as long as it is electrically conductive. Examples of objects to be coated include cold-rolled steel sheets, hot-rolled steel sheets, stainless steel, electrogalvanized steel sheets, hot-dip galvanized steel sheets, zinc-aluminum alloy plated steel sheets, zinc-iron alloy plated steel sheets, and zinc-magnesium alloy plated steel sheets. Steel plate, zinc-aluminum-magnesium alloy plated steel plate, aluminum plated steel plate, aluminum-silicon alloy plated steel plate, tin plated steel plate, and surface treatment thereof (e.g., chemical conversion treatment using phosphate, zirconium salt, etc.) ) is applied. The shape of the object to be coated is also not particularly limited, and may be a flat plate shape or a complicated three-dimensional shape.

(2) Curing Step After the applying step, the formed uncured coating film is washed with water if necessary, and then heated at a temperature of 140° C. or less. Thereby, the coating film is cured to obtain a cured electrodeposition coating film. Since the electrodeposition coating composition according to this embodiment can be cured at a low temperature, it can be cured at such a low temperature.

The curing temperature may be, for example, 135° C. or lower, or 130° C. or lower. The curing temperature is preferably 100° C. or higher, more preferably 110° C. or higher. The heating time is not particularly limited, and is, for example, 10 to 30 minutes.

[Electrodeposition coating]
The electrodeposition coated article has an article to be coated and a cationic electrodeposition coating film formed on the article from the above cationic electrodeposition coating composition. The cationic electrodeposition coating is cured. The electrodeposition-coated article is produced, for example, by the method described above.

The film thickness of the electrodeposition coating film after curing is preferably 5 μm or more and 60 μm or less, more preferably 10 μm or more and 25 μm or less, from the viewpoint of rust prevention.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these. In the examples, "parts" and "%" are based on mass unless otherwise specified.

[Production Example 1-1] Production of aminated epoxy resin (A1) 12 parts of butyl cellosolve, 940 parts of bisphenol A type epoxy resin (Ep, trade name DER-331J, manufactured by Dow Chemical Co.), bisphenol A (BPA) 330 parts of phenol, 30 parts of phenol, and 2 parts of N,N-dimethylbenzylamine were added, the temperature in the reaction vessel was maintained at 120° C., and the reaction was allowed to proceed until the epoxy equivalent reached 650 g/eq. Cool until the temperature reaches 110°C. To this, a mixture of 50 parts of N,N-dimethyl-1,3-propanediamine (DMAPA) and 100 parts of diethanolamine (DETA) was added and reacted at 160° C. for 1 hour to obtain an aminated epoxy resin ( A1) was obtained.

[Production Example 1-2] Production of aminated epoxy resin (A2) 12 parts of butyl cellosolve, 940 parts of bisphenol A type epoxy resin (Ep, trade name DER-331J, manufactured by Dow Chemical Co.), 330 parts of bisphenol A (BPA) parts, 5 parts of phenol, and 2 parts of N,N-dimethylbenzylamine are added, the temperature in the reaction vessel is maintained at 120 ° C., and the reaction is performed until the epoxy equivalent becomes 620 g / eq. was cooled to 110°C. To this, a mixture of 110 parts of diethanolamine (DETA) and 70 parts of N,N-diethyl-1,3-propanediamine (DEAPA) was added and reacted at 140° C. for 1 hour to obtain an aminated epoxy resin ( A2) was obtained.

[Production Example 1-3] Production of aminated epoxy resin (A3) 12 parts of butyl cellosolve, 940 parts of bisphenol A type epoxy resin (Ep, trade name DER-331J, manufactured by Dow Chemical Co.), 370 parts of bisphenol A (BPA) parts, 45 parts of phenol, and 2 parts of N,N-dimethylbenzylamine are added, the temperature in the reaction vessel is maintained at 120 ° C., and the reaction is performed until the epoxy equivalent becomes 620 g / eq. was cooled to 110°C. To this, a mixture of 70 parts of diethanolamine (DETA) and 50 parts of N-methylethanolamine (MMA) was added and allowed to react at 140° C. for 1 hour to obtain aminated epoxy resin (A3).

[Production Example 1-4] Production of aminated epoxy resin (A4) 12 parts of butyl cellosolve, 900 parts of bisphenol A type epoxy resin (Ep, trade name DER-331J, manufactured by Dow Chemical Co.), 320 parts of bisphenol A (BPA) Parts, 60 parts of polypropylene glycol diglycidyl ether (trade name EP400P, manufactured by Sanyo Kasei Co., Ltd.), 30 parts of phenol, and 2 parts of N,N-dimethylbenzylamine were added, and the temperature in the reaction vessel was maintained at 120 ° C. , until the epoxy equivalent reached 600 g/eq, and then cooled until the temperature in the reaction vessel reached 110°C. To this, a mixture of 110 parts of diethanolamine (DETA) and 70 parts of N,N-diethyl-1,3-propanediamine (DEAPA) was added and reacted at 140° C. for 1 hour to obtain an aminated epoxy resin ( A4) was obtained.

[Production Example 1-5] Production of aminated epoxy resin (X1) 26 parts of butyl cellosolve, 940 parts of bisphenol A type epoxy resin (Ep, trade name DER-331J, manufactured by Dow Chemical Co.), 365 parts of bisphenol A (BPA) 45 parts of phenol and 2 parts of dimethylbenzylamine were added, the temperature in the reaction vessel was maintained at 120°C, and the reaction was allowed to proceed until the epoxy equivalent reached 1100 g/eq. cooled until To this, 70 parts of diethanolamine (DETA), 25 parts of N-methylethanolamine (MMA), and 85 parts of diethylenetriamine diketimine (diketimine) were added and reacted at 140° C. for 1 hour to obtain an aminated epoxy resin (X1). got

[Production Example 1-6] Production of aminated epoxy resin (X2) 26 parts of butyl cellosolve, 1010 parts of bisphenol A type epoxy resin (Ep, trade name DER-331J, Dow Chemical Co.), 390 parts of bisphenol A (BPA) and 2 parts of dimethylbenzylamine were added, the temperature in the reaction vessel was maintained at 120°C, and the reaction was allowed to proceed until the epoxy equivalent reached 800 g/eq. To this, 160 parts of diethanolamine (DETA) and 65 parts of diethylenetriaminediketimine (diketimine) were added and reacted at 140° C. for 1 hour to obtain aminated epoxy resin (X2).

[Production Example 1-7] Production of aminated epoxy resin (X3) 26 parts of butyl cellosolve, 1190 parts of bisphenol A type epoxy resin (Ep, trade name DER-331J, Dow Chemical Co.), 342 parts of bisphenol A (BPA) and 2 parts of dimethylbenzylamine are added, the temperature in the reaction vessel is maintained at 120°C, and the reaction is allowed to proceed until the epoxy group concentration reaches 0.27 mmol/g, after which the temperature in the reaction vessel reaches 110°C. cooled to To this, 167 parts of diethylenetriaminediketimine (diketimine) was added and reacted at 140° C. for 1 hour to obtain an aminated epoxy resin (X3).

[Production Example 2-1] Production of blocked polyisocyanate curing agent (B1) 360 parts of polymeric MDI (MDI) was charged into a reaction vessel and heated to 60°C. 240 parts of methyl ethyl ketoxime (MEKO) was added dropwise at 60° C. over 2 hours. After further heating at 75 ° C. for 4 hours, in the measurement of the IR spectrum, it was confirmed that the absorption based on the isocyanate group disappeared, and after cooling, 27 parts of methyl isobutyl ketone (MIBK) was added to block polyisocyanate curing agent. (B1) was obtained.

[Production Example 2-2] Production of blocked polyisocyanate curing agent (Y1) 1400 parts of polymeric MDI (MDI) was charged into a reaction vessel and heated to 60°C. A mixture of 330 parts of butyl diglycol ether (BDG) and 950 parts of butyl cellosolve (BC) was added dropwise thereto at 60° C. over 2 hours. After further heating at 75 ° C. for 4 hours, in the measurement of the IR spectrum, it was confirmed that the absorption based on the isocyanate group disappeared, and after cooling, 27 parts of methyl isobutyl ketone (MIBK) was added to block polyisocyanate curing agent. (Y1) was obtained.

[Production Example 2-3] Production of blocked polyisocyanate curing agent (Y2) 50 parts of hexamethylene diisocyanate (HDI) was charged into a reaction vessel and heated to 60°C. A mixture of 10 parts of trimethylolpropane (TMP) and 30 parts of methyl ethyl ketoxime (MEKO) was added dropwise thereto at 60° C. over 2 hours. After further heating at 75 ° C. for 4 hours, in the measurement of the IR spectrum, it was confirmed that the absorption based on the isocyanate group disappeared, and after cooling, 27 parts of methyl isobutyl ketone (MIBK) was added to block polyisocyanate curing agent. (Y2) was obtained.

[Production Example 2-4] Production of blocked polyisocyanate curing agent (Y3) 270 parts of polymeric MDI (MDI) was charged into a reaction vessel and heated to 60°C. A mixture of 118 parts of butyl cellosolve (BC) and 25 parts of methyl isobutyl ketone (MIBK) was added dropwise thereto at 60° C. over 2 hours. After further heating at 75 ° C. for 4 hours, in the measurement of the IR spectrum, it was confirmed that the absorption based on the isocyanate group disappeared, and after cooling, 27 parts of methyl isobutyl ketone (MIBK) was added to block polyisocyanate curing agent. (Y3) was obtained.

[Production Example 3] Preparation of Pigment Dispersion Paste In a sand grind mill, 106.9 parts of a pigment dispersion resin obtained as follows, 1.6 parts of carbon black, 40 parts of kaolin, 55.4 parts of titanium dioxide, molybdenum phosphorous were added. 3 parts of aluminum oxide and 13 parts of deionized water were added and dispersed until the particle size became 10 μm or less to obtain a pigment-dispersed paste (solid content: 60%).

(Preparation of pigment dispersion resin)
2220 parts of isophorone diisocyanate and 342.1 parts of methyl isobutyl ketone were charged into a reaction vessel equipped with a stirrer, condenser, nitrogen inlet tube and thermometer, and the temperature was raised to 50°C. Subsequently, 2.2 parts of dibutyltin laurate was added, and 878.7 parts of methyl ethyl ketone oxime was charged at 60°C. After that, the temperature was maintained at 60° C. for 1 hour, and after confirming that the NCO equivalent was 348, 890 parts of dimethylethanolamine was added. Further, the temperature was maintained at 60° C. for 1 hour, and it was confirmed by IR that the NCO peak had disappeared. 1872.6 parts of 50% lactic acid and 495 parts of deionized water were then charged while cooling not to exceed 60°C. Thus, a quaternizing agent was obtained.

Separately, another reactor was charged with 870 parts of tolylene diisocyanate and 49.5 parts of methyl isobutyl ketone. The temperature was raised so as not to exceed 50° C., and 667.2 parts of 2-ethylhexanol was added dropwise over 2.5 hours. After completion of dropping, 35.5 parts of methyl isobutyl ketone was added and the temperature was maintained for 30 minutes. After that, it was confirmed that the NCO equivalent was 330-370. A half-blocked polyisocyanate was thus obtained.

Separately, 940 parts of bisphenol A type epoxy resin (trade name DER-331J, manufactured by Dow Chemical Company) and 38.5 parts of methanol were charged in another reaction vessel, and then 0.1 part of dibutyltin dilaurate was added. . After raising the temperature to 50° C., 87.1 parts of tolylene diisocyanate was added and the temperature was further raised. 1.4 parts of N,N-dimethylbenzylamine was added at 100°C and the mixture was kept at 130°C for 2 hours. At this time, methanol was fractionated with a fractionating tube. This was cooled to 115° C. and methyl isobutyl ketone was charged until the solid content concentration reached 90%. Subsequently, 270.3 parts of bisphenol A and 39.2 parts of 2-ethylhexanoic acid were charged. After stirring at 125° C. for 2 hours, 516.4 parts of the above half-blocked polyisocyanate was added dropwise over 30 minutes. After that, the mixture was heated and stirred for 30 minutes. Subsequently, 1506 parts of polyoxyethylene bisphenol A ether was gradually added and dissolved. After cooling to 90° C., the above quaternizing agent was added, and the temperature was maintained at 70 to 80° C., and the acid value was confirmed to be 2 or less. Thus, a pigment dispersion resin was obtained (resin solid content: 30%).

[Example 1]
(1) Preparation of Resin Emulsion (EmA1) 400 g (solid content) of aminated epoxy resin (A1) and 160 g (solid content) of blocked polyisocyanate curing agent (B1) are mixed, and ethylene glycol mono-2-ethylhexyl is mixed. Ether was added at 3% (12 g) on solids. Next, formic acid was added to neutralize to a neutralization rate of 40%. Subsequently, ion-exchanged water was gradually added for dilution to obtain a resin emulsion (EmA1).

(2) Preparation of electrodeposition coating composition Into a stainless container were added 1,394 g of ion-exchanged water, 560 g of resin emulsion (EmA1), and 41 g of the above pigment dispersion paste. After that, it was aged at 40° C. for 16 hours to prepare an electrodeposition coating composition C1.

(3) Preparation of electrodeposition coated product A cold-rolled steel sheet (JISG3141, SPCC-SD) was degreased by immersing it in a surf cleaner EC90 (manufactured by Nippon Paint Surf Chemicals Co., Ltd.) at 50°C for 2 minutes. Next, the cold-rolled steel sheet was immersed at 40° C. for 90 seconds in a zirconium chemical treatment solution containing 0.005% ZrF and adjusted to pH 4 using NaOH to perform zirconium chemical treatment. Thus, the article to be coated was obtained.

A necessary amount of 2-ethylhexyl glycol (an amount that gives a cured electrodeposition coating film having a film thickness of 20 μm) was added to the electrodeposition coating composition C1, and the object to be coated was immersed therein. A voltage was applied between the electrodes under the condition that the voltage was raised for 30 seconds to reach 180 V and then maintained for 150 seconds to deposit an uncured coating film on the object to be coated. The resulting uncured coating film was cured by baking at 120° C. for 25 minutes to obtain an electrodeposition coating having a cured electrodeposition coating film.

[Example 2]
An electrodeposition coating resin emulsion (EmA2) and an electrodeposition coating composition C2 were prepared in the same manner as in Example 1, except that the aminated epoxy resin (A2) was used, to produce an electrodeposition coating.

[Example 3]
An electrodeposition coating resin emulsion (EmA3) and an electrodeposition coating composition C3 were prepared in the same manner as in Example 1, except that the aminated epoxy resin (A3) was used, to produce an electrodeposition coating.

[Example 4]
An electrodeposition coating resin emulsion (EmA4) and an electrodeposition coating composition C4 were prepared in the same manner as in Example 1, except that the aminated epoxy resin (A4) was used, to produce an electrodeposition coating.

[Comparative Example 1]
An electrodeposition paint was prepared in the same manner as in Example 1, except that an aminated epoxy resin (X1) and a blocked polyisocyanate curing agent (Y1) were used, and 12 parts of dioctyltin oxide was added as a curing catalyst. A resin emulsion (EmX1) and an electrodeposition coating composition Z1 were prepared to produce an electrodeposition coating.

[Comparative Example 2]
An electrodeposition coating resin emulsion (EmX2) and an electrodeposition coating composition Z2 were prepared in the same manner as in Example 1, except that an aminated epoxy resin (X2) and a blocked polyisocyanate curing agent (Y2) were used. , to produce an electrodeposition coating.

[Comparative Example 3]
An electrodeposition paint resin emulsion (EmX3) and an electrodeposition paint composition Z3 were prepared in the same manner as in Example 1, except that the aminated epoxy resin (X3) and the blocked polyisocyanate curing agent (Y3) were used. , to produce an electrodeposition coating.

[evaluation]
The aminated epoxy resin, the electrodeposition coating composition, and the electrodeposition coating were evaluated as follows. The results are listed in Table 1.

(1) Tertiary Amination Ratio of Aminated Epoxy Resin A tertiary amine value and a total amine value were determined according to the above method. A tertiary amination rate (%) was calculated by dividing the tertiary amine value by the total amine value.

(2) Molecular Weight Distribution of Aminated Epoxy Resin Using gel permeation chromatography, the weight average molecular weight (Mw), number average molecular weight (Mn) and molecular weight distribution were measured under the following conditions.
Equipment: alliance2695S separations module
Column: Tosoh TSKgel ALPHA-M
Flow rate: 0.05ml/min
Detector: Alliance 2414 Refractive Index Detector
Moving bed: N,N'-dimethylformamide Standard sample: TSK STANDARD POLYSTYRENE (manufactured by Tosoh), A-500, A-2500, F-1, F-4, F-20, F-80, F-700, 1 -Phenylhexane (manufactured by Aldrich)

(3) Gel fraction (curability) of the electrodeposition coating composition
Using the electrodeposition coating composition, a coating film was deposited on a test plate (tin plate) whose weight (W ₀ ) had been measured in advance. Then, the coating film was cured by baking at 120° C. for 25 minutes to form a cationic electrodeposition coating film on the test plate. The film thickness of the cured coating film was 20 μm. The mass (W ₁ ) of the test panel with the cured coating was measured.

Subsequently, this test plate was immersed in acetone and refluxed for 6 hours, and then dried at 105° C. for 20 minutes. The mass (W ₂ ) of the test plate after drying was measured, and the gel fraction was determined by the following formula (1).
Gel fraction (%) = ( _W2 - _W0 )/( _W1 - _W0 ) x 100

The gel fraction was evaluated according to the following criteria. The higher the gel fraction, the better the curability.
Good: Gel fraction 90% or more Acceptable: Gel fraction 85% or more and less than 90% Poor: Gel fraction less than 85%

(4) Rubbing property (curing property) of cured electrodeposition coating film
The surface of the cured electrodeposited coating was rubbed 50 times with gauze soaked in methyl isobutyl ketone (MIBK), and the changes in the coating and the gauze were visually observed.

Visual observation results were evaluated according to the following criteria.
Good: No change in paint film Acceptable: Streaks on the surface of the paint film Poor: Color transfer to gauze

(5) Storage stability of electrodeposition coating composition (MEQ (B) evaluation)
After about 10 g of the solid content of the electrodeposition coating composition was dissolved in about 50 ml of THF, 7.5 ml of acetic anhydride and 2.5 ml of acetic acid were added. Subsequently, using an automatic potentiometric titrator (manufactured by Kyoto Electronics Industry Co., Ltd., APB-410), potentiometric titration was performed with a 0.1N perchloric acid acetic acid solution to measure the base content in the electrodeposition coating composition. and MEQ (B ₀ ) was determined.
Separately, the MEQ (B ₁ ) of the electrodeposition coating composition stored at 40° C. for 28 days was similarly measured. Change (%) in MEQ (B) before and after the storage test: MEQ (B ₁ )-MEQ (B ₀ ) was calculated.

The amount of change (%) was evaluated according to the following criteria. The smaller the change (%), the better the storage stability.
Good: Less than 5% Acceptable: 5% or more and less than 20% Bad: 20% or more

(6) Oil Repelling Resistance of Electrodeposition Coating Film An uncured electrodeposition coating film was deposited on the object to be coated in the same manner as in "(3) Formation of cured electrodeposition coating film" in Example 1. The coating was then air dried at room temperature (20°C to 25°C). After that, the object to be coated was placed horizontally, and an aluminum cup was fixed in the center thereof with double-sided tape. One drop of water was dropped into the aluminum cup using a dropper, and then one drop of oil was dropped on the water drop. In this state, the object to be coated was heated at 120° C. for 25 minutes to cure the electrodeposition coating film. The surface of the obtained cured electrodeposition coating film was visually observed. The diameter of the crater was taken as the diameter of a circle having the same area as the crater (equivalent circle).

Visual observation results were evaluated according to the following criteria. If more than one criterion is met, the better criterion is adopted.
Good: 5 or less craters and all craters with a diameter of 1 mm or less Acceptable: 10 or less craters and all craters with a diameter of 3 mm or less Poor: 1 crater with a diameter of more than 3 mm more than one

The electrodeposition coating compositions of Examples 1 to 4 containing the aminated epoxy resin (A) and the blocked polyisocyanate curing agent (B) are excellent in both storage stability and low-temperature curability. On the other hand, the electrodeposition coating composition of Comparative Example 1, which used diketimine as the amine compound, had a low tertiary amination rate and poor storage stability. Furthermore, in Comparative Example 1, since a blocking agent other than the oxime compound was used, the low-temperature curability was low. The electrodeposition coating composition of Comparative Example 2 used a curing agent derived from an aliphatic polyisocyanate, and thus was inferior in low-temperature curability. The electrodeposition coating composition of Comparative Example 3 also had low low-temperature curability because a blocking agent other than the oxime compound was used.

The cationic electrodeposition coating composition of the present invention is particularly suitable for use as an undercoat for coating automobile bodies.

Claims (10)

an aminated epoxy resin (A);
a blocked polyisocyanate curing agent (B),
The tertiary amination rate of the aminated epoxy resin (A) is 85% or more,
The blocked polyisocyanate curing agent (B) is a cationic electrodeposition coating composition obtained by reacting an oxime compound and an aromatic polyisocyanate. 2. The cationic electrodeposition coating composition according to claim 1, wherein said aminated epoxy resin (A) has a tertiary amination rate of 95% or more. 3. The cationic electrodeposition coating composition according to claim 1, wherein said aromatic polyisocyanate contains 4,4'-diphenylmethane diisocyanate and/or a polymer thereof. The cationic electrodeposition coating composition according to any one of claims 1 to 3, wherein the oxime compound comprises methyl ethyl ketoxime. The aminated epoxy resin (A) is obtained by reacting an amine compound and an epoxy resin,
The amine compound is a combination of two types of primary amine and secondary amine,
The primary amine has the formula:
_NH2- ( _CH2 ) ⁿ - ^NR1R2 (1)
(In formula (1), R ¹ and R ² each independently represent an alkyl group having 1 to 6 carbon atoms which may have a terminal hydroxyl group, and n represents an integer of 2 to 4.)
is represented by
The secondary amine has the formula:
^{R3R4NH (} 2)
(In formula (2), R ³ and R ⁴ each independently represent an alkyl group having 1 to 4 carbon atoms and having a terminal hydroxyl group.)
The cationic electrodeposition coating composition according to any one of claims 1 to 4, represented by The cationic electrodeposition coating composition according to any one of claims 1 to 5, wherein the aminated epoxy resin (A) has a molecular weight distribution of 3.0 or less. The cationic electrodeposition coating composition according to any one of claims 1 to 6, wherein the content of the curing catalyst is less than 0.5 mass% of the solid content of the cationic electrodeposition coating composition. The cationic electrodeposition coating composition according to any one of claims 1 to 7, wherein the content of the curing catalyst is less than 0.25 mass% of the solid content of the cationic electrodeposition coating composition. After immersing the object to be coated in the cationic electrodeposition coating composition according to any one of claims 1 to 8, a voltage is applied between the object to be coated and the counter electrode, and the object to be coated forming an uncured coating;
a step of heating the coating film at a temperature of 140° C. or less to obtain a cured cationic electrodeposition coating film. an object to be coated;
An electrodeposition-coated article having, on the article to be coated, a cationic electrodeposition coating film formed from the cationic electrodeposition coating composition according to any one of claims 1 to 8.