JPH01266170A - Water-base paint composition - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Field of Application) The present invention relates to a water-based paint composition containing a water-based acrylic resin, a bisphenol A alkylene oxide adduct, and an amine formaldehyde condensate, and particularly relates to a water-based paint composition that has excellent water resistance. , relates to an aqueous coating composition that has excellent processability and can reduce the content of solvent.

The outer surface of beverage cans for storing soft drinks, etc. and food cans for packaging food products prevents corrosion of the can material, increases the aesthetic value of the product,
Moreover, it is coated with a coating film that can withstand the heat treatment process during food sterilization. Traditionally, these paints are epoxy/
A method is used in which an organic solvent solution of amino resin, acrylic/amino resin, polyester/amino resin, etc. is applied using a roll coater, and then baked and hardened in a gas oven. However, these paints cause a large amount of solvent loss during baking.

It causes air pollution and is undesirable from the point of view of resource conservation, so there is a desire for a water-based paint that can solve these problems.

There are two types of known water-based paints: water-dispersible and water-soluble.
Water-dispersible resins are usually synthesized by emulsion polymerization using a surfactant, but the surfactant used remains in the coating after it is formed, reducing water resistance. Ta. On the other hand, there is a method of synthesizing a resin containing an acid content (carboxyl group) without using a surfactant in an organic solvent, and then neutralizing it with a volatile base to make it a dispersion or water-soluble.
These water-based paints have an acid value of 20 in the basic resin structure.
This method requires a higher acid content and has the drawback of poor performance such as water resistance and alkali resistance. In order to improve these drawbacks, a method of mixing a large amount of aqueous amino resin such as hexamethoxymethylmelamine or methylated benzoguanamine has been used, but the processability has been greatly reduced. When water-based amino resin is reduced.

Paint film hardness tends to decrease, water resistance, paint film hardness.

It was difficult to balance the processability and processability.

In addition, conventional water-soluble paints contain 10% by weight or more of organic solvents to improve the storage stability of the paint and the leveling of the paint film formation. It was insufficient.

(Problem to be solved by the invention) The present invention has been made in view of the above-mentioned current situation.

The goal is to create a product that is water resistant enough to withstand the heat treatment process used to sterilize a single beverage can, has high hardness that will not be damaged during the transportation process of nine cans, and has excellent workability that can be processed into various can shapes. The present invention provides an aqueous coating composition for the external surface of a can that forms a coating film and has a low organic solvent content.

[Structure of the invention]

(Means for solving problems) In other words, the present invention is as follows.

a) Based on copolymer.

Aromatic vinyl monomer wt5-45wt% ethyl acrylate or butyl acrylate
15-60 匈L% α/β monoethylenically unsaturated carboxylic acid 2-15 wt% and.

32 to 70% water-based acrylic resin made by dissolving or dispersing a copolymer of vinyl monomer containing 5 to 35% by weight of hydroxyalkyl acrylate or methacrylate having 1 to 5 carbon atoms in water with a volatile base b) Bisphenol A Polyalkylene oxide adduct
5~18w
t% and.

C) A water-based coating composition characterized by containing 10 to 50 wt% of an amine formaldehyde condensate as a resin component.

Examples of the aromatic vinyl monomer in the present invention include styrene, vinyltoluene, and α-methylstyrene, with styrene being particularly preferred. The aromatic vinyl monomer is used in an amount of 15 to 45 wt% in the copolymer; if it is less than 15 wt%, the water resistance and hardness of the coating film will decrease, and if it is more than 45 wt%, the flexibility of the coating film will be poor.

Ethyl acrylate or butyl acrylate.

A necessary component to improve the flexibility of the coating film.

It is used in an amount of 15 to 60 wt% in the copolymer.

α/β monoethylenically unsaturated carboxylic acids include acrylic acid,
These include methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, and especially acrylic acid.

Methacrylic acid is preferred. The α/β monoethylenically unsaturated carboxylic acid is used in an amount of 2 to 15 wt% in the copolymer,
If it is less than 2 wt%, it becomes difficult to make it water-based, and if it is more than 15 wt%, the water resistance of the coating film becomes poor.

Hydroxyalkyl acrylates or methacrylates having 1 to 5 carbon atoms include hydroxymethyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyamyl acrylate, hydroxybutyl acrylate and corresponding methacrylates, preferably hydroxymethyl acrylate, hydroxyethyl acrylate or Methacrylate is good. These monomers account for 5 to 35 wt% of the copolymer.
If the amount is less than 5 wt%, there will be fewer crosslinking points, resulting in poor water resistance of the coating film, and lack of hydrophilic groups, resulting in poor paint stability.On the contrary, if it is more than 35 wt%, there will be too many crosslinking points. As a result, the flexibility of the coating film is poor.

The acrylic copolymer of the present invention contains the above-mentioned monomers as essential components, but other copolymerizable vinyl monomers may also be used. These vinyl monomers include, for example, alkyl esters of acrylic acid or methacrylic, such as 2-ethylhexyl acrylate, cyclohexyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, stearyl methacrylate, cyclohexyl methacrylate, or vinyl acetate.

Examples include vinyl ethyl ether, N-alkoxyalkyl-substituted amides such as N-(methoxymethyl)acrylamide, and N-(n-butoxy)acrylamide.

The acrylic copolymer of the present invention can be obtained by a conventional solution polymerization method. That is, the above monomer mixture is subjected to radical polymerization in an organic solvent using a peroxide such as benzoyl peroxide or an azo compound such as 2,2' azobisisobutyronitrile as a catalyst.

To obtain a water-based acrylic resin, water and a volatile base such as ammonia or an organic amine are added to a solution of the copolymer obtained by solution polymerization. The volatile base may be used in an amount that at least partially neutralizes the carboxylic acid in the acrylic copolymer. As an organic amine.

For example, monoethanolamine, dimethylamine.

Examples include diethylamine, triethylamine, triethanolamine, and diethylethanolamine.

Then, the organic solvent in the solution is distilled off at a temperature of 40 to 80°C under reduced pressure to obtain an aqueous acrylic resin that is soluble or dispersed in water. For this reason, the organic solvent used during synthesis preferably has a boiling point of 150° C. or less, taking into account distillation in the subsequent step.1 Taking into account the temperature during synthesis and the solubility of the synthesized copolymer in the organic solvent.

Isopropyl alcohol, n-butanol, isobutyl alcohol with a boiling point within the range of 80 to 150°C.

Alcohol solvents such as n-amyl alcohol and iso7myl alcohol, and ester solvents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and ethylene glycol monoisopropyl ether are preferred.

The water-based acrylic resin of the present invention is used in an amount of 32 to 70 wt% of the resin solids in the entire coating composition, and if it is less than 32 wt%, the adhesion to the metal base material will decrease.

The gloss of the paint film decreases.

The bisphenol A polyalkylene oxide adduct of the present invention is made by adding about 2 to 30 moles (=1) of ethylene oxide or propylene oxide to bisphenol A.A mixture of ethylene oxide and propylene oxide may also be used.Bisphenol A poly The alkylene oxide adduct is contained in 5-1% of the resin solid content of the total coating composition.
8 wt% is used; if it is less than 5 wt%, no improvement in the processability of the coating film will be observed, and if it exceeds 18 wt%, the water resistance of the coating film will decrease.

The amine formaldehyde condensate of the present invention includes alkyl etherified melamine resin, alkyl etherified urea resin,
Alkyl etherified resins of diguanazine in which two triazine rings are bonded to a phenylene nucleus, alkyl etherified glycol resins, and the like are used alone or in combination of two or more. Preferably, fully etherified hexamethoxymelamine is used. The amine formaldehyde condensate is used in an amount of 10 to 50 wt% based on the resin solid content of the total coating composition, and if it is less than 10 wt%, crosslinking is insufficient and water resistance is impaired. , the hardness of the coating film decreases.

If it exceeds 50 wt%, the processability of the coating film will decrease.

The coating composition of the present invention may optionally contain an amine-blocked acid catalyst as a curing aid, such as p-)luenebenzenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenedisulfonic acid, etc., at a resin solid content of 100 parts. 0.1 wt part is added to form a paint. It is also possible to mix water-soluble resins and water-dispersible resins commonly used as resins for water-based paints, such as water-soluble polyester resins, maleated fatty acids, and water-soluble or water-dispersible epoxy resins. . Further, a leveling agent, an antifoaming agent, and a lubricant can also be added in the same way. Alternatively, the pigment can be kneaded with the solvent-free copolymer resin solution to prepare a pigment paste, which can be made into a paint in the same manner as described above.

The water-based paint of the present invention can be applied to a substrate by known means such as roll coating, spraying, and brushing. Examples of the base material include metal base materials such as electro-tinned steel plate, tin free tail, and aluminum.

Furthermore, the water-based paint of the present invention can be cured under a wide range of baking conditions, from baking at 150 to 200°Cw for about 0 minutes to baking at a high temperature and short time at about 250'Cwt for 0 seconds.

The present invention will be explained below with reference to Examples. In the examples, 1 part means part by weight, and 1% means % by weight.

(Example) Production Example 1 (Production of aqueous acrylic resin solution A1) 100 parts of n-butanol was charged into a four-eye flask equipped with a thermometer, a stirrer, a reflux condenser, one dropping tank, and a nitrogen gas blowing tube, and nitrogen gas was added. While stirring while introducing
17 parts of styrene, 45 parts of ethyl acrylate, and 61.8 parts of acrylic were added from a drop tank kept at 5°C.

A mixture of 10 parts of 2-hydroxyethyl acrylate, 19 parts of methyl acrylate, and 3 parts of benzoyl peroxide was added dropwise over 3 hours.6Then, the mixture was kept at 105°C and reacted for 1 hour, and 0.3 parts of benzoyl peroxide was added for 1 hour. The reaction was completed. Cool to below 40°C, add 9.9 parts of dimethylethanolamine and 200 parts of water, and heat to 80°C under reduced pressure.
At °C, n-butanol was distilled off together with water, and the solid content was 6
A transparent and viscous aqueous acrylic resin solution A1 containing 0% residual n-butanol and 10% residual n-butanol was obtained.

Production Examples 2 to 7 Aqueous acrylic resin solutions A2 to A5 were obtained according to the same method as Production Example A1 using the monomer composition shown in Table 1 wt and dimethylethanolamine.

Production example B1 125 parts of aqueous acrylic resin solution A, rutile type titanium white 5
0 parts and 25 parts of water were mixed and dispersed with an attritor to obtain pigment dispersion paste B1.

Production Example B2 225 parts of water-based acrylic resin A, 50 parts of rutile titanium white and 25 parts of water were mixed and dispersed with an attritor to obtain pigment dispersion paste B2.

Example 1 40 parts of aqueous acrylic resin solution A1, bisphenol A
4 parts of 10 mole ethylene oxide adduct, 12 parts of hexamethoxymelamine (Imel 303 manufactured by Mitsui Toatsu Chemical Co., Ltd.; the same applies to the following examples), amine-blocked paratoluenesulfone eI! , 0.5 part of ethylene glycol monobutyl ether, 43.42 parts of water, and 0.1 part of a silicone leveling agent were mixed to form a paint.

Examples 2-10. Comparative Examples 1 to 3 Coating compositions were obtained according to the same method as in Example 1 and using an aqueous acrylic resin solution, a polyalkylene oxide adduct of bisphenol A, and hexamethoxymelamine according to the formulation shown in Table 1-2.

Example 11 13.75 parts of aqueous acrylic resin solution Al, 55.0 parts of pigment dispersion paste Bl, 2.75 parts of 10 mole ethylene oxide adduct of bisphenol A, 8.25 parts of hexamethoxymelamine, amine-blocked paratoluenesulfone A white paint was obtained by mixing 0.05 parts of acid, 1.75 parts of ethylene glycol monobutyl ether, and 45 parts of 1 B of water.

Example 12 A white paint was obtained according to the same method as in Example 11 and the formulation shown in Table 1-2.

Paint test of paints obtained in each example and comparative example.

A coating film physical property test and a paintability test were conducted.

The results are shown in Table-3.

Each test method is as follows.

Paint test - Paint stability test; After the paint was stored at room temperature for two months, the state of gelation and separation of the resin was observed.

- Organic solvent content test in paint; The paint was diluted with methyl ethyl ketone and directly quantified by gas chromatography.

Coating film physical property test An electroplated tin plate with a thickness of 0.23 mm was coated with a roll coat so that the film thickness after drying was 7 μm.

A baked painted panel was prepared at an ambient temperature of 190° C. for 10 minutes with a gas open. The scratch resistance was evaluated by forming a 3-piece can by molding a painted plate with the painted surface facing the outside of the can.

○Water resistance test; After the painted panel was immersed in water and heat treated at 100°C for 30 minutes, the whitening state of the paint film was evaluated.

○Workability test; An Erichsen test was performed.

○Impact resistance; The test was conducted using DuPont type 1/2 inch and 500g load.

0 Pencil hardness test: Evaluation was performed using a pencil hardness test method in accordance with JIS standards.

○Adhesion test; A #IN test was conducted.

- Scratchability A can was filled with contents, and the outside surface of the can was brought into contact with the contents in 80'C hot water to evaluate the extent of damage to the paint on the outside of the can.

Paintability Test - Flow; Immediately after coating with a roll coater, it was baked in a gas oven to evaluate the flow state.

〔Effect of the invention〕

The water-based paint composition for the external surface of cans of the present invention has water resistance that can withstand the heat treatment process during food sterilization of single-serve beverage cans, etc., and has high hardness that prevents damage during the transportation process of three cans.

It forms a coating film with excellent processability that can be processed into various can shapes, and has excellent coating stability and flow coating suitability even when the organic solvent content is 5% or less in the coating material.

Claims (1)

[Claims] 1. a) Based on the copolymer, 15 to 45 wt% of aromatic vinyl monomer ethyl acrylate or butyl acrylate 15 to 45 wt%
A copolymer of a vinyl monomer containing 60 wt% α/β monoethylenically unsaturated carboxylic acid 2 to 15 wt% and 5 to 35 wt% hydroxyalkyl acrylate or methacrylate having 1 to 5 carbon atoms is dissolved in water with a volatile base. Dissolved or dispersed water-based acrylic resin 32~70w
t% b) Bisphenol A polyalkylene oxide adduct 5
18 wt% and c) 10 to 50 wt% of an amine formaldehyde condensate as resin components.