JPS6351469B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to new and useful aqueous thermosetting coating compositions, and more particularly to aqueous one-component polyurethane coating compositions comprising specific water-soluble blocked isocyanate compounds as the isocyanate component. It is. It has been well known that blocked isocyanate compounds are used in place of free polyisocyanate compounds as curing agents for paints and other applications.・Free from life (pot life) problems, easy to store as a paint, no viscosity change during work, less solvent selectivity, and improved pigment dispersibility. However, the usage form of one-component polyurethane resin using such a blocked material is usually to mix and dissolve a solvent-based polyol resin and a solvent-based blocked isocyanate compound in a solution to form a thermosetting resin solution. It is. In recent years, many examples have been reported in which such blocked isocyanate compounds are used as crosslinking components of water-soluble resins using water as a medium.
All of these are aqueous block polyisocyanate compounds in which the blocks are simply emulsified or suspended in water, and none have been found in which they are completely dissolved to form an aqueous solution. Incidentally, such an aqueous dispersion of a block body has the great feature that water can be used as a medium, but the aqueous dispersion of a solvent-type block polyisocyanate compound is mixed with a water-soluble resin as an aqueous medium. When the water-based resin mixture obtained in this way is used as a paint, it is difficult to form a uniform emulsion or suspension system.For example, when the water-based resin mixture obtained in this way is used as a paint, the coating film formed there is unevenly composed of the blocked isocyanate compound and the resin. Because it is a polyurethane resin, it has drawbacks such as low gloss, insufficient curing reaction, and poor coating performance. Apart from this, there is also a method in which a blocked isocyanate compound is dissolved in an aqueous dispersion of a water-soluble resin as described above, or a method in which a block body is mixed in advance as one of the resin compositions and then dispersed in water. Although these methods have been carried out, they all involve dispersion in water, and it is difficult to obtain a uniform system. However, the present inventors focused on the existence of various drawbacks as mentioned above in this type of one-component polyurethane coating composition, and as a result of intensive research to obtain a uniform aqueous coating composition, a specific water-soluble polyurethane coating composition was found. The present inventors have discovered that a composition comprising a polyhydroxyl blocked isocyanate compound and an aqueous polyhydroxyl compound as main components meets these objectives, and has completed the present invention. That is, the present invention comprises, as main components, a bishydroxypiperazine derivative (a-1), a di- to hexafunctional polyisocyanate compound (a-2), and at least one polyisocyanate compound in the molecule as a blocking agent component.
Compound (a-3) having active hydrogen [hereinafter,
This is abbreviated as a blocking agent. ], first,
The above derivative (a-1) and the above compound (a-2) are reacted, and then the isocyanate-terminated prepolymer thus obtained is reacted with the above blocking agent (a-
3) or block some of the isocyanate groups in the compound (a-2) with the blocking agent (a3) above, and then react the remaining isocyanate groups with the blocking agent (a3). General formula obtained by reacting the above derivative (a-1) with [However, Z in the formula represents the residue of the blocking agent (a-3),

[Formula] is a residue of a difunctional polyisocyanate, that is, a diisocyanate, in the polyisocyanate compound (a-2) (A represents a divalent organic group.)
of,

[Formula] is a residue of the bishydroxypiperazine derivative (a-1) [However, R and R' may be the same or different, and are divalent compounds having 2 to 6 carbon atoms. Hydrocarbon group (however, C in the main chain of this hydrocarbon group
An oxygen atom may be present in the -C bond. )
shall represent. 〕of,

[Formula] is two to two of the polyisocyanate compound (a-2) above.
Represents a hexafunctional polyisocyanate, that is, a di-, tri-, tetra-, penta-, and/or hexaisocyanate residue (B represents a divalent to hexavalent organic group) and n is an integer from 1 to 6, x represents the degree of functionality of the polyisocyanate compound (a-2) and is an integer from 2 to 6, and y is 0 or 1. It is assumed that it is an integer of ~5, but at the same time, it is assumed that the relationship x>y≧0 must be satisfied. ] Blocked isocyanate compound (A-
A water-soluble blocked isocyanate compound (A) obtained by neutralizing 1) with an acidic substance (A-2) such as acetic acid, lactic acid, crotonic acid, formic acid, propionic acid, malonic acid, tartaric acid, citronic acid or phosphoric acid. and a nonionic or cationic aqueous polyhydroxyl compound (B) in a ratio such that the equivalent ratio of effective active isocyanate groups to hydroxyl groups is 5:95 to 95:5. This is what we provide. Here, the above bishydroxypiperazine derivative (a-1) has the general formula (However, R and R′ in the formula are as described above.)
In this formula, R and R' are each -CH ₂ -
CH ₂ −,

[Formula] -CH ₂ -CH ₂ - CH ₂ -, -CH ₂ -CH ₂ -O-CH ₂ -CH ₂ -,

【formula】

[Example of preparation of water-soluble blocked isocyanate compound (A)]

N,N'-bishydroxyisopropyl-2-
108 parts of methylpiperazine was heated to 50°C, and 168 parts of 1,6-hexamethylene diisocyanate was gradually added dropwise thereto over 5 hours with sufficient stirring. After the dropwise addition was completed, the mixture was reacted at 60° C. for 4 hours to obtain an isocyanate-terminated prepolymer. The content of isocyanate groups in this prepolymer was 7.3%.
Next, 43 parts of methyl ketoxime was added and reacted at the same temperature for 5 hours to obtain a blocked isocyanate compound. This compound was then dissolved in 95 parts of isopropyl alcohol and neutralized with 65% acetic acid to give a non-volatile content of 71.2% and a pH of 71.2%.
A clear water soluble solution of 6.3 was obtained. Hereinafter, this will be referred to as curing agent H-1. Reference Example 2 [Preparation example of water-soluble blocked isocyanate compound (A)] 1 mole of trimethylolpropane and 3 moles of 1,6-hexamethylene diisocyanate were added to 96 parts of N,N'-bishydroxyethyl-2-methylpiperazine. 1342 parts of a polyisocyanate compound having an isocyanate group content of 16.7%, which is an adduct of the above, were reacted in the presence of 447 parts of ethyl acetate and 75 parts of methyl ethyl ketone to obtain an isocyanate-terminated prepolymer. The content of isocyanate groups in this prepolymer was 5.7%. Next, 112 parts of ε-caprolactam was added and reacted at 70°C for 2 hours to obtain a blocked isocyanate compound. Thereafter, this compound was desolventized under reduced pressure, dissolved in 664 parts of isopropyl alcohol, and then neutralized with lactic acid to obtain a blocked isocyanate compound, which was transparent and soluble in water with a nonvolatile content of 67.1% and a pH of 6.6. It was a hot solution. Hereinafter, this will be referred to as curing agent H-2. Reference example 3 [Example of preparation of water-soluble polyhydroxy compound (B)] "Epicron 1050" (Dainippon Ink Chemical Co., Ltd.)
Bisphenol A type epoxy resin: 244 parts of epoxy equivalent (470), 52 parts of diethanolamine and 125 parts of isopropyl alcohol were added under reflux at 80°C.
A liquid aminoepoxy resin was obtained by reacting for a period of time. The hydroxyl value of the resin was then adjusted to pH 6 with acetic acid and was 246. Hereinafter, this will be referred to as polyol P-
It is called 1. Reference Example 4 [Preparation example of water-soluble polyhydroxy compound (B)] reflux 30 parts of isopropyl alcohol and 2 parts of azobisisobutyronitrile, and further add 40 parts of glycidyl methacrylate, 20 parts of hydroxyethyl methacrylate, and butyl acrylate. A mixture consisting of 40 parts of azobisisobutyronitrile and 2 parts of azobisisobutyronitrile was added dropwise over a period of 2 hours, and even after the addition was completed, the reaction was continued under reflux for an additional 3 hours to obtain a copolymer solution. Next, 15 parts of diisopropanolamine and 30 parts of isopropyl alcohol were added to this, and the mixture was reacted at reflux temperature for 3 hours. After that, add 50 parts of 10% phosphoric acid aqueous solution, 20 parts of butyl cellosolve and deionized water at room temperature.
The solution to which 750 parts were added was a colorless and transparent aqueous solution with a hydroxyl value of 193. Hereinafter, this will be referred to as polyol P
-2. Reference example 5 [Preparation example of water-soluble polyhydroxy compound (B)] Formate of dimethylaminoethyl methacrylate
3.5 parts of 2-dimethylaminoethanethiol hydrochloride, 0.2 parts of t-butyl hydroperoxide, and 95 parts of deionized water were reacted at 80° C. for 1 hour under a nitrogen stream. Next, 30 parts of styrene, 29 parts of methyl methacrylate,
A monomer mixture consisting of 20 parts of 2-ethylhexyl acrylate, 20 parts of hydroxyethyl methacrylate, 1 part of methacrylic acid, and 4 parts of formate of dimethylaminoethyl methacrylate, and hydrogen peroxide as a polymerization catalyst were added dropwise to a reaction vessel at 65°C. Then, they were copolymerized to obtain an emulsion with a solid content concentration of 50%. Hereinafter, this will be referred to as polyol P-3. Reference Example 6 [Preparation example of water-soluble polyhydroxy compound (B)] 37 parts of phthalic anhydride, 25 parts of polyether polyol (addition of 4 moles of ethylene oxide on average to 1 mole of pentaerythritol), 24 parts of glycerin, 10 parts of pentaerythritol and 10 parts of rice bran oil fatty acid were charged and heated at 180°C for 2 hours, then gradually raised to 220°C over 1.5 hours and held at the same temperature for 5 hours. After that, the product was cut to 80% with isopropyl alcohol and had a Gardner viscosity of T-U and a hydroxyl value of 364.
Hereinafter, this will be referred to as P-4. Example 1 30 parts of curing agent H-1 and polyol P-1
70 parts were mixed and diluted to 35% with water to obtain a transparent baking paint. By applying this onto a tin plate using a No. 1 bar coater and baking it at 150°C for 30 minutes, a strong coating film with excellent gloss as shown in Table 1 was obtained. Example 2 A transparent aqueous resin solution was obtained by blending 2 parts of curing agent H-2 and 98 parts of polyhydroxyl compound P-2. Next, this was applied onto a glass plate using a 76μ applicator and baked at 160°C for 30 minutes, resulting in a transparent and tough coating film with the properties shown in Table 1. . Example 3 95 parts of polyol P-3 and curing agent H-1
A stable emulsion solution was prepared by blending 5 parts. Next, this was applied onto a glass plate using a 76μ applicator and baked at 150° C. for 20 minutes to obtain a strong coating film with excellent water resistance as shown in Table 1. Example 4 60 parts of polyol P-4 and curing agent H-2
40 parts were mixed and the nonvolatile content was adjusted to 65% with deionized water to obtain a transparent aqueous resin solution. After coating this on a tin plate using a No. 1 bar coater, it was heated to 160℃.
By baking for 30 minutes, a strong coating film with excellent gloss was obtained as shown in Table 1.

[Table] (Note) “Gloss” is expressed as 60° specular reflectance (%). "Coating film strength" is "Tensilon" at 20℃
Measurements were made using a bulging tester manufactured by Toyo Baldwin Co., Ltd. at a bulging speed of 200 mm/min, and expressed as tensile strength. "Adhesion" refers to the coating surface of the baked hardened coating formed on glass or tinplate.
After drawing 100 goblets with a size of mm x 10 mm, they were peeled off using cellophane tape and the number of goblins that remained without being peeled off was displayed. tin,
Examples 2 and 3 are cases of glass. "Water resistance" is a visual judgment of the condition of the painted surface after being immersed in warm water at 50℃ for one week, and a "◎" indicates that no change was observed and was evaluated as "excellent". This is what I did.

Claims (1)

[Scope of Claims] 1 As main components, (A) a bishydroxypiperazine derivative (a-1), a di- to hexafunctional polyisocyanate compound (a-2), and at least one compound in the molecule as a blocking agent component. From a compound (a-3) having one active hydrogen, first, the above derivative (a-1) and the above compound (a-2) are reacted,
Next, the isocyanate-terminated prepolymer obtained in this way is reacted with a blocking agent (a-3), or a part of the isocyanate groups in the above compound (a-2) is reacted with a blocking agent (a-3) in advance.
General formula obtained by blocking the remaining isocyanate groups with 3) and then reacting the above derivative (a-1) with the remaining isocyanate groups. [However, Z is a compound having at least one active hydrogen in the molecule (a-
The residue of 3), [Formula] is a di- to hexa-functional polyisocyanate compound (a
-2) residues of diisocyanate (however,
A represents a divalent organic group. )of,
[Formula] is a residue of the bishydroxypiperazine derivative (a-1) [However, R and R' may be the same or different, and each is a divalent group having 2 to 6 carbon atoms. Hydrocarbon group (However, C-C in the main chain of this hydrocarbon group
An oxygen atom may be present in the bond. ). ], [Formula] is a di-, tri-, tetra-, penta- and /
or a hexaisocyanate residue (where B represents a di- to hexavalent organic group), and n is an integer from 1 to 6, and x
is a di- to hexa-functional polyisocyanate compound (a-
2) represents the degree of functionality, and shall be an integer from 2 to 6, and y shall be an integer from 0 or 1 to 5, but at the same time the relationship x>y≧0 is satisfied. shall be required. ] Blocked isocyanate compound (A-
A water-soluble blocked isocyanate compound obtained by neutralizing 1) with an acidic substance (A-2) and (B) a nonionic or cationic aqueous polyhydroxy compound at an equivalent ratio of effective active isocyanate group/hydroxyl group. is contained in a ratio of 5:95 to 95:5,
Aqueous thermosetting coating composition.