JPH11209681A - Water-based coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-based coating which does not cause roll marks to appear in high-speed roll coating. SOLUTION: This water-based coating is prepd. by dissolving or emulsifying, in an aq. medium, a copolymer which comprises 20-45 wt.% arom. vinyl monomer units, 0.5-10 wt.% t-amino-group-contg. vinyl monomer units, 1-30 wt.% α,β-ethylenically unsatd. carboxylic acid monomer units, and 15-78.5 wt.% other free-radically polymerizable monomer units (the sum of these monomer units being 100 wt.%) and in which the molar number of carboxyl groups contained is higher than that of t-amino groups contained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aqueous coating composition comprising an anionic polymer, and more particularly to an aqueous coating composition having excellent dispersibility of pigments, especially titanium oxide, and excellent coating leveling properties. is there.

[0002]

2. Description of the Related Art Conventionally, organic solvent-based paints (hereinafter simply referred to as solvent-based paints) are often used for coating metal cans, automobiles, home appliances or steel furniture for packaging soft drinks or processed foods. However, for the purpose of saving petroleum resources or preventing environmental pollution, water-based paints using an aqueous medium have recently been used for a wide range of applications.
Water-based paints are generally inferior in water resistance, gloss and hardness of the coating film as compared with solvent-based paints.Moreover, due to their thixotropy, when coating metal plates with high-speed rotating rolls. In addition, there is a problem that a stripe generally called a roll line is easily generated on a painted surface in parallel with the painting direction.

[0003] In order to solve the above-mentioned problems, there have been many proposals regarding water-based paints. For example, water-based paints comprising a graft copolymer obtained by a macromonomer method have excellent water resistance and excellent workability of metal after coating. It is known that a film can be obtained (JP-A-7-300573, JP-A-7-305022, JP-A-8-73804, etc.). However, the water-based paint described in the above-mentioned patent publication tends to generate the above-mentioned streaks in a coating method using a high-speed roll, and this tendency was particularly remarkable in a water-based paint containing titanium oxide as a white pigment.

[0004] On the other hand, it has been proposed to introduce an amino group together with a carboxyl group into an anionic polymer to be used as a film forming material in order to disperse the pigment in a white water-based paint containing titanium oxide [Yokoyuki Kageyama et al. , Journal of the Society of Color Materials, No. 64
Vol. 9, No. 572-579 (1991)]. Kageyama et al. Describe that the amino groups introduced into the anionic polymer interact electrostatically with the titanium oxide, resulting in improved dispersibility of the titanium oxide in the paint. However, even with the amino group-containing anionic polymer disclosed in the above-mentioned literature, the above-mentioned problem of streaks or rolls has not been solved yet.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to obtain a water-based paint which does not cause rolls in high-speed rotation roll coating. As a result, the present inventors have found that aromatic vinyl monomer units and tertiary amino group-containing According to the aqueous coating composition comprising an anionic polymer containing a specific amount of a vinyl monomer unit, it has been found that the roll does not occur, and the present invention has been completed. That is, the present invention relates to an aromatic vinyl monomer unit, a tertiary amino group-containing vinyl monomer unit, an α, β-ethylenically unsaturated carboxylic acid monomer unit and other radically polymerizable monomer units. Wherein the proportion of each monomer unit based on the total amount of all the constituent units is an aromatic vinyl monomer unit; 20 to 45% by weight, and a tertiary amino group-containing vinyl monomer. Unit: 0.5 to 10% by weight, α, β
-Ethylenically unsaturated carboxylic acid monomer units; 1 to 30% by weight and other radically polymerizable monomer units;
An aqueous coating obtained by dissolving or emulsifying and dispersing a copolymer having a molar number of 78.5% by weight and containing more carboxyl groups than the number of containing tertiary amino groups in an aqueous medium. This is a white water-based paint obtained by dispersing titanium oxide as a pigment in the water-based paint. Hereinafter, the present invention will be described in more detail.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The copolymer according to the present invention comprises an aromatic vinyl monomer unit, a tertiary amino group-containing vinyl monomer unit, an α, β-ethylenically unsaturated carboxylic acid monomer unit and other units. Is an anionic copolymer having the above radical polymerizable monomer units as essential components and having each of the above ratios in the above-mentioned ratio. When the proportion of the aromatic vinyl monomer unit in the copolymer is less than 20% by weight, the pigment dispersibility and leveling property of the obtained water-based coating material are poor. On the other hand, when the content exceeds 45% by weight, the viscosity of the coating material is remarkably increased, and it is difficult to obtain an aqueous coating material suitable for coating. When the proportion of the tertiary amino group-containing vinyl monomer unit is less than 0.5% by weight, pigment dispersibility and leveling property are poor, while 10% by weight
If it exceeds, the viscosity of the paint increases. If the proportion of the α, β-ethylenically unsaturated carboxylic acid monomer unit is less than 1% by weight, it is difficult to make the copolymer aqueous, while if it exceeds 30% by weight, the water resistance of the coating film is poor. .

Further preferred copolymers are those having the following constitution. Aromatic vinyl monomer unit; 30 to 40% by weight Tertiary amino group-containing vinyl monomer unit; 1 to 5% by weight α, β-ethylenically unsaturated carboxylic acid monomer unit; 3 to 10% by weight Monomer unit of 45 to 66% by weight

[0008] The above copolymer is an aromatic vinyl monomer,
It can be produced by copolymerizing a vinyl monomer having a secondary amino group, an α, β-ethylenically unsaturated carboxylic acid monomer and other radically polymerizable monomers. As the aromatic vinyl monomer, styrene or α-methylstyrene,
p-tert-butylstyrene, o-methylstyrene,
Examples include a styrene derivative of p-methylstyrene and benzyl (meth) acrylate.

As the tertiary amino group-containing vinyl monomer,
N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, N, N-dimethyl-p
-Styrene sulfonamide, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-diethylaminopropyl (meth) acrylate N- [2- (meth) acryloyloxyethyl] piperidine, N- [2- (meth) acryloyloxyethyl] pyrrolidine, N- [2
-(Meth) acryloyloxyethyl] morpholine, 4
-(N, N-dimethylamino) styrene, 4- (N, N
-Diethylamino) styrene, 4-vinylpyridine, 2
-Dimethylaminoethyl vinyl ether, 2-diethylaminoethyl vinyl ether, 4-dimethylaminobutyl vinyl ether, 4-diethylaminobutyl vinyl ether, 6-dimethylaminihexyl vinyl ether and the like.

The α, β-ethylenically unsaturated carboxylic acids include (meth) acrylic acid, crotonic acid, maleic acid,
Fumaric acid, itaconic acid, maleic anhydride, itaconic anhydride and the like. In the relationship between the carboxyl group and the amino group in the copolymer of the present invention, it is necessary that the number of moles of the carboxyl group be present in excess of the number of moles of the amino group. It is preferably about 4 times the amount of the group.

Other radically polymerizable monomers are those which impart a film-forming function to the copolymer, and specifically include methyl (meth) acrylate, ethyl (meth) acrylate,
n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate,
Isobutyl (meth) acrylate, t-butyl (meth)
Acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, perfluorooctyl (meth) acrylate, cyclohexanediol mono (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) Acrylate, 2-hydroxyethyl (meth) acrylate with ε-
Compound to which caprolactone is added [eg, Placcel F, manufactured by Daicel Chemical Industries, Ltd.], polycarbonate diol mono (meth) acrylate, N-methoxymethyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide, N-iso Butoxymethyl (meth)
Acrylamide, vinyl acetate, vinyl cyclohexanecarboxylate, vinyl benzoate and the like can be mentioned.

Further, a macromonomer can also be used as another radical polymerizable monomer. Specific examples of the macromonomer include one-terminal methacryloxy group polymethyl methacrylate, one-terminal methacryloxy group polydimethylsiloxane, and one-terminal methacryloxy group poly ( Methyl methacrylate / 2-hydroxyethyl methacrylate) and one-terminal methacryloxy group poly (2-ethylhexyl methacrylate / 2-hydroxyethyl methacrylate). As the number average molecular weight of the macromonomer,
1,000 to 30,000 is preferred.

The film formed from the water-based paint of the present invention comprises:
It may or may not be cured. When curing, N- as another radical polymerizable monomer
A self-crosslinkable copolymer obtained by using a self-reactive monomer under heating such as methoxymethyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide and N-isobutoxymethyl (meth) acrylamide Use or as other radical polymerizable monomers,
By using a hydroxyl group-containing monomer such as 2-hydroxyethyl (meth) acrylate, a method of obtaining a hydroxyl group-containing copolymer and using it in combination with an amino resin described below can be employed.

The radical polymerization of the above monomer can be carried out under the following conditions. Polymerization conditions in which isopropyl alcohol, n-butanol, isobutyl alcohol or butyl cellosolve is used as a polymerization solvent, a radical generating compound such as azobisisobutyronitrile is used as a polymerization initiator, and a temperature of 60 to 150 ° C. can be preferably employed. . The preferable ratio of the monomer and the polymerization solvent in the polymerization is 20 to 60% by weight as the monomer concentration in the solution. Further, the preferred average molecular weight of the copolymer in the present invention is 2,000 to 20,000, more preferably 3,000 to 15,000, in number average molecular weight.
The molecular weight can be controlled by adjusting the amount of the polymerization initiator used. In the radical polymerization under the above-mentioned conditions, all the components polymerize at a polymerization rate of almost 100%. Therefore, it is preferable that the copolymerization ratio of each monomer is approximately equal to the ratio of each monomer unit in the target copolymer.

After the majority of the organic solvent in the obtained copolymer solution is removed from the solution by distillation or the like, water is added as a medium to obtain the aqueous coating composition of the present invention. The amount of the organic solvent to be removed from the copolymer solution is preferably 50 to 100% of the organic solvent used. In the present invention, the above-mentioned copolymer can be used as it is as a film-forming material in an aqueous paint, but an unneutralized carboxyl group in the above-mentioned copolymer is neutralized with an organic amine as described below. Copolymers can be more preferably used. Such a completely neutralized copolymer is excellent in water solubility, and hardly causes viscosity increase or the like even after a long period of time in an aqueous medium.

The neutralizing organic amine has a pKb of 4.
6 or more, specifically, ethanolamine (pKb; 4.6), dimethylethanolamine (pKb;
b; 4.8), diethanolamine (pKb; 5.1)
And triethanolamine (pKb; 6.3). Particularly preferred are dimethylethanolamine, diethanolamine and mixtures thereof.

When it is desired to obtain a cured film by using a hydroxyl group-containing copolymer as a copolymer for forming a film, it is preferable to use an amino resin in combination. Examples of the amino resin include alkyl etherified melamines such as methyl etherified melamine and butyl etherified melamine; alkyl etherified urea resins; and alkyl etherified benzoguanamines such as methyl etherified benzoguanamine and ethyl etherified benzoguanamine. The preferred amount of the amino resin used is 3 to 80 parts by weight (amino resin solid content) per 100 parts by weight of the copolymer.

The water-based paint of the present invention can be used as a clear paint and forms a coating film having excellent flowability and leveling property. However, according to the white water-based paint obtained by dispersing titanium oxide in the clear paint, high-speed In the rotating roll coating, a remarkable effect that a roll is not generated on the coating surface is exerted. In the water-based paint of the present invention, in addition to pigments such as titanium oxide, various additives such as a silicone-based lubricity imparting agent or a film-forming auxiliary may be added. Metal plates such as stainless steel, tin and zinc treated steel plates are preferred. In addition to painting directly on the metal surface, you may paint on ink or primer,
Any use of undercoating, intermediate coating or topcoating is possible. Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

[0019]

Examples and Comparative Examples Copolymers 1 to 6 were produced by polymerizing the monomers shown in Table 1 by the following method. The abbreviations used below indicate the following compounds, respectively. MMA; methyl methacrylate, S
t; styrene, DMA; N, N-dimethylaminoethyl methacrylate, EA; ethyl acrylate, BA; butyl acrylate, NMMA; N-methoxymethyl acrylamide, AA; acrylic acid, HEMA; 2-hydroxyethyl methacrylate Rate, CR-90; titanium dioxide [manufactured by Ishihara Sangyo Co., Ltd.].

[0020]

Example 1 A stirrer, reflux condenser, two dropping funnels,
A glass flask equipped with a gas inlet tube and a thermometer was charged with 1/3 of the mixture of the monomers described in Table 1 (the unit of the numerical value is gram), 18.0 g of butyl cellosolve and 42.0 g of isopropyl alcohol, and 87 The temperature was raised to ° C. Then, a mixture of the remaining 2/3 of the above mixture and 0.38 g of mercaptoethanol was dropped from one dropping funnel over 3 hours, and simultaneously, butyl cellosolve was added from the other dropping funnel. 0 g, 14.0 g of isopropyl alcohol (hereinafter referred to as IPA) and 2,
2'-azobis (2-methylbutyronitrile) (hereinafter A
BN-E) (3 g)
It was dropped over time. Thereafter, further 6.0 g of butyl cellosolve, 14.0 g of IPA and 0.4 ABN-E;
6 g was added dropwise over 2 hours to synthesize the desired copolymer. The number average molecular weight of the polymer was 7,900. The obtained copolymer solution is heated to 40 ° C., and IPA is
After distilling off, a copolymer A solution having a solid content of 80% by weight was obtained.

Solution of copolymer A (solid content 100 g)
9.8 g of dimethylethanolamine and CR
After adding 120 g of -90 and mixing with three rolls, 74 g of water and 38 g of butyl cellosolve were added to obtain a white aqueous paint having a solid concentration of 60% by weight. Using the above white paint, the surface of the electroplated tin plate was coated by a high-speed roll coating method (coating thickness after drying: 5 μm). Next, the coated plate is dried at 200 ° C. for 10 minutes to form a cured coating film by the reaction of NMMA, which is a self-crosslinkable monomer, and then subjected to pressure steam treatment (leaved in 130 ° C. steam for 30 minutes). Were evaluated for physical properties. The results are as shown in Table 2.

[0022]

Example 2 A white water-based paint was produced in the same manner as in Example 1, except that the copolymer B shown in Table 1 was used as the copolymer.

[0023]

[Table 1]

[0024]

Comparative Examples 1-2 A white water-based paint was produced in the same manner as in Example 1, except that the copolymer C (Comparative Example 1) or the copolymer D (Comparative Example 2) was used. Incidentally, the copolymer C is a copolymer in which the ratio of the styrene monomer unit is lower than the lower limit in the present invention, and the copolymer D does not contain a monomer unit having a tertiary amino group. Things.

[0025]

[Table 2]

In the physical properties of the coating film shown in Table 2, all of the properties except for the roll were measured in accordance with the method specified in JIS K5400. a. Roll eyes: The presence or absence of roll eyes of the coating film after baking and curing is visually judged, and when there are almost no roll eyes,
In the following, △, Δ, and × were given according to the degree of occurrence of roll eyes. b. Paint viscosity ........ Using ford cup # 4, 12
0 seconds or less were evaluated as ◎, and 120 to 150 seconds as ○. c. Impact resistance ········· Drug-type impact test method. d. Hardness: The coated plate was immersed in hot water at 80 ° C. to measure the pencil hardness. e. Adhesion ・ ・ ・ ・ ・ ・ ・ ・ ・ Method in accordance with the cross-cut tape test method (evaluated by the residual ratio of the coating film after the tape is peeled off)

As is clear from Table 2, Comparative Example 1 using copolymer C in which the proportion of styrene monomer units is lower than the lower limit in the present invention, or a copolymer containing no tertiary amino group-containing monomer units In Comparative Example 2 using D, a roll occurs. On the other hand, according to the present invention, the roll is almost non-existent or slightly present,
Moreover, physical properties such as impact resistance and hardness are maintained at a high level.

[0028]

The water-based paint of the present invention is excellent in water resistance, leveling property and pigment dispersibility. According to the water-based paint, a roll is hardly generated in coating with a high-speed roll. It is suitable for coating metal plates, and is suitable not only for coating metal plates used for PCM and home appliances, but also for coating metal cans for food packaging because of its high water resistance.

Claims (2)

[Claims] 1. An aromatic vinyl monomer unit, a tertiary amino group-containing vinyl monomer unit, an α, β-ethylenically unsaturated carboxylic acid monomer unit and other radically polymerizable monomer units. A copolymer, wherein the ratio of each monomer unit based on the total amount of all the constituent units is an aromatic vinyl monomer unit; 20 to 45% by weight; a tertiary amino group-containing vinyl monomer unit 0.5 to 10% by weight, α, β-ethylenically unsaturated carboxylic acid monomer units; 1 to 30% by weight and other radically polymerizable monomer units; 15 to 78.5% by weight; And an aqueous coating material obtained by dissolving or emulsifying and dispersing a copolymer in which the number of moles of the carboxyl group contained exceeds the number of moles of the tertiary amino group. 2. A white aqueous coating obtained by dispersing titanium oxide as a pigment in the aqueous coating according to claim 1.