JPH0739555B2 - Aqueous coating composition for outer surface of can - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of use) The present invention relates to a highly water-based paint for external surfaces of cans, and particularly to an external surface of a can which can be applied onto printing ink by a wet-on-wet system. Aqueous coating composition for use.

(Prior Art) The outer surface of the can is printed on the undercoat metal plate and then top-coated. In recent years, from the viewpoint of reducing coating cost, a wet-on-wet coating process has been adopted in which the final drying process of the printing ink is omitted and top coating is performed. Water-dilutable paint is used as the top coating paint. For example, an aqueous top coating paint containing an aqueous acrylic resin as a main component is known (JP-A-49-115125 and JP-A-
53-94362, JP-A-57-209963, JP-A-58
-755 publication). However, these water-based paints have not yet been made sufficiently water-based in terms of hygiene for workers involved in painting work. In particular, the acrylic resin obtained by ordinary emulsion polymerization has a particle size of 0.2-
Since it is about 0.5 micron, there were defects in the fluidity and gloss of the paint. In terms of fluidity, the viscosity is too low as it is and roll coater coating is difficult. Although some organic solvents show a tendency to increase in viscosity when added, they have a drawback that the stability of the coating composition is poor and gelation occurs in 2 to 3 days. Regarding the gloss of the coating film, the coating becomes thixotropic in some cases, resulting in a semi-glossy coated surface.

Further, when the amount of the organic solvent in the paint is set to a level that does not cause a problem in terms of hygiene, the coating film may be repelled or the gloss of the coating film may be significantly reduced.

(Problems to be Solved by the Invention) The present invention has been made in view of the above circumstances, solves the problem of work hygiene, and has fluidity of paint, gloss of paint film, storage stability of paint, etc. Is an improvement of.

[Structure of Invention]

(Means for Solving Problems) That is, the present invention is based on 100 parts by weight of a total amount of 50 to 80 parts by weight of an acrylic resin obtained by emulsion polymerization and 50 to 20 parts by weight of a water-soluble polyester resin. Amino resin 10 to 80 parts by weight is added as a resin component, and most of water and 5 to 10% by weight of hydrophilic organic solvent based on the coating composition are used as solvent components. Particle size
It is a water-based coating composition for an outer surface of a can, which is characterized by having a size of 0.1 micron or less.

The particle size of the acrylic resin emulsion of the present invention is 0.1 μm or less, which is considerably smaller than that of the ordinary acrylic resin emulsion. Therefore, its fluidity exhibits characteristics close to those of a resin solution (flow characteristics similar to Newtonian flow). The monomer composition of the acrylic resin emulsion is acrylic acid, methacrylic acid or its alkyl ester, acrylamide, methylol acrylamide styrene, α-methyl styrene and the like. An acrylic resin emulsion is obtained by emulsifying a mixture of the above monomers with an anionic surfactant or a nonionic surfactant and using ammonium persulfate or potassium persulfate as a polymerization catalyst. It is available as the commercially available John Krill series.

In the present invention, the water-soluble polyester resin is added in order to improve the cissing of the paint or the gloss of the coating film when top-coating on the undried printing ink layer.

The water-soluble polyester resin of the present invention includes, as constituent components of the resin, for example, phthalic acid, maleic acid, trimellitic acid or its acid anhydride, isophthalic acid, terephthalic acid,
Polybasic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, and ethylene glycol, 1,3-propylene diol, diethylene glycol, dipropylene glycol, neopentyl glycol, 1,6-hexanediol, trimethylol It is a combination of polyhydric alcohols such as ethane, trimethylolpropane, glycerin, and pentaerythritol, but soybean oil fatty acid, coconut oil fatty acid, dehydrated castor oil fatty acid, benzoic acid, para, for adjusting the molecular weight and selecting physical properties. It may contain a small amount of a monobasic acid such as tert-butylbenzoic acid.

As a method for producing a water-soluble polyester resin, a mixture of the above raw materials is reacted in an inert gas stream with stirring at a temperature of 160 to 250 ° C. until a desired acid value is reached, and then a hydrophilic solvent and water are added, In addition to alkylamines such as trimethylamine, triethylamine, butylamine, 2-dimethylethanolamine, diethanolamine, triethanolamine, aminomethylpropanol, morpholine and other monovalent amines, and polyhydric amines such as diethyleneamine, diethylenetriamine, etc. Let As the water-soluble polyester resin, a water-based oil-free alkyd resin or a water-based eponester resin may be used.

Water-soluble polyester resin is acrylic resin emulsion 50 ~
Combine with 80 parts by weight to add up to 100 parts by weight. If the amount of water-soluble resin is less than 20 parts by weight, wet-on-wet coating suitability and the gloss of the coating film are inferior, and if it is more than 50 parts by weight, the proportion of the organic solvent used during the production of water-soluble resin and for making it water-based is large. Therefore, it is difficult to reduce the amount of organic solvent in the coating composition.

Examples of the amino resin in the present invention include hexamethylolmelamine resin, methylolated benzoguanamine resin, methylolated melamine resin, methylolated urea resin and etherified products thereof. Amino resin is added 10 to 80 parts by weight to 100 parts by weight of acrylic resin emulsion and water-soluble resin, and if less than 10 parts by weight,
The curing speed and the hardness of the coating film are inferior. If the amount is more than 80 parts by weight, the formation of the coating film will be unsatisfactory, which is not practical.

In the present invention, a self-emulsifying epoxy resin can be blended in addition to the above-mentioned essential resin component. The self-emulsifying epoxy resin includes, for example, a bisphenol A type epoxy resin and a carboxyl group-containing acrylic resin which are esterified and dispersed in water with an amine. Epoxy resin having an epoxy equivalent of about 500 to 1000 is preferable.

In the present invention, the aqueous resin is dispersed and dissolved in water and a small amount of hydrophilic organic solvent. As a hydrophilic organic solvent,
It contains organic amines used for water solubilization of water-soluble resins and organic solvents necessary for forming a uniform coating film without cissing in wet-on-wet coating. The amount of organic solvent in the coating composition is in the range of 5-10% by weight. Hydrophilic organic solvents required to obtain coating suitability include cellosolve solvents such as methyl cellosolve, ethyl cellosolve, propyl cellosolve, butyl cellosolve, and hexyl cellosolve, and methyl carbitol, ethyl carbitol, methyl cellosolve acetate, ethyl cellosolve. A high-boiling point solvent such as acetate or diacetone alcohol is preferable, but low-boiling point alcohols such as methyl alcohol, ethyl alcohol, and butyl alcohol may be added thereto.

As a wet-on-wet coating method according to the present invention, for example, a metal plate coated with white coating is printed with an alkyd-based or polyester-based printing ink, and then a top-coating paint is applied to form a printing ink and a top-coating paint. Are simultaneously dried and cured.

The water-based paint composition for external surfaces of a can of the present invention can be used as a top coating paint suitable for wet-on-wet coating, or can be used as a base coat paint or a color varnish by incorporating a pigment.

Additives such as a surface smoothing agent, an antifoaming agent, and a pigment dispersion aid can be added to the water-based coating composition for an outer surface of a can of the present invention.

Roll coating is the most preferable coating method, but air spray coating, airless spray coating, electrostatic spray coating, dip coating, electrodeposition coating, etc. are also possible.

The water-based coating composition for an outer surface of a can of the present invention can be baked at a temperature of 150 to 250 ° C. for a time of 5 seconds to 20 minutes.

Hereinafter, the present invention will be specifically described with reference to examples. In the examples, "part" and "%" mean "part by weight" and "% by weight", respectively.

(Example) Example 1 Acrylic resin emulsion of particle system 0.1 micron or less John Cryl 540 (trade name of SCS Johnson & San Co., solid content 45%) 156 parts Water-soluble polyester resin (65% solid content) 47 parts Amino Resin Cymail 303 (trade name of Mitsui Toatsu Kagaku Co., Ltd.) 20 parts Catalyst 3006B (trade name of Mitsui Toatsu Co., Ltd.) 0.6 part Hexyl cellosolve 8 parts Butyl cellosolve 3 parts Deionized water 70 parts Mixing the above components well After that, adjust the pH to 7.3 with dimethylethanolamine and add an aqueous silicone solution.
0.5% was added to obtain a semi-transparent aqueous varnish having a solid content of 39.5%, an organic solvent content of 7.5% and a viscosity of 305 cps.

The water-soluble polyester resin used here was made from neopentyl glycol, isophthalic acid, and trimellitic anhydride as raw materials, and was reacted at 220 ° C for 6 hours. It is a clear solution with a solid content of 65% and a pH of 7.2, obtained by adding an equimolar number to the acid component and neutralizing.

After printing the above water-based varnish on a tin plate with a thickness of 0.24 mm with a printing ink of oily alkyd type, and applying it with a roll coater to a dry coating film with a wet-on-wet method to a thickness of 10 μm It was baked and dried at 180 ℃ for 10 minutes. The smoothness of the obtained coating film was equivalent to that of the conventional solvent-based varnish, the measured value of 60 ° reflectance was 100, and the pencil hardness of the coating film was 2H.

Comparative Example 1 Manufacture of delayed acrylic compound Methacrylic acid 150 parts Ethyl acrylate 620 parts Styrene 100 parts Methyl methacrylate 100 parts 2-Hydroxyethyl methacrylate 30 parts Ammonium persulfate 2 parts Liponox NCY (Lion Co., Ltd. trade name ) 20 parts Sannor NES (Lion Co., Ltd. product name) 20 parts Ion-exchanged water and one-third of the mixed monomer are charged into a four-necked flask replaced with nitrogen gas, and the mixture is heated to 65 ° C and the rest of the mixture is maintained. Two-thirds of the monomer was added dropwise over 2 hours, and the reaction was continued for another hour. A white opaque acrylic resin emulsion having a solid content of 46.6% was obtained. The particle size of this emulsion was 0.2 microns on average.

Preparation of aqueous varnish 140 parts of the above acrylic resin emulsion Water-soluble polyester resin used in Example 1 46.2 parts Amino resin Cymel 303 20 parts Catalyst 3006B 0.6 parts Butyl cellosolve 11 parts Ion-exchanged water 81.3 parts Dimethylethanolamine 1 part Mix, solid content 39.8%, viscosity 1075 cps (25
An opaque aqueous varnish having a pH of 7.2) was obtained. The organic solvent content in this paint is 7.6%.

When this water-based varnish was applied under the same conditions as in Example 1, the resulting baked coating film had a noticeable flow pattern in the coating direction, and repelling occurred in the printing ink portion. The gloss value of this coating film was 87, and the pencil hardness was H to 2H.

Next, when 23 parts of butyl cellosolve was added to this paint, a smooth paint film was obtained, and the amount of organic solvent in the paint in this case was 14.2%.

〔The invention's effect〕

The water-based coating composition for an outer surface of a can of the present invention uses a combination of an emulsion of an acrylic resin having an average particle size of 0.1 micron or less and a water-soluble resin with good fluidity characteristics, and therefore an organic solvent necessary for coating suitability. Can be reduced to the extent that there is no problem in hygiene. In addition, it has good wet-on-wet paintability, processability and gloss of the coating film, so it is useful as a clear top coating paint on the outer surface of the can. It also has good pigment dispersibility, so it can also be used as a base coat paint for the outer surface of a can. Target.

Continuation of the front page (56) References JP-A-56-84766 (JP, A) JP-A-57-209963 (JP, A)

Claims (1)

[Claims] 1. An acrylic resin 50 obtained by emulsion polymerization.
-80 parts by weight and 50-20 parts by weight of water-soluble polyester resin are added as a resin component to 10 to 80 parts by weight of amino resin to 100 parts by weight, and most of the water and the coating composition are used as a standard. A can characterized by comprising 5 to 10% by weight of a hydrophilic organic solvent as a solvent component, the acrylic resin having a number average particle size of 0.1 micron or less, and being applied on a printing ink by a wet-on-wet method. External water-based coating composition.