JP4865216B2 - Bisphenol-free water-based paint - Google Patents

Description

  The present invention relates to a coating material that can form a coating film excellent in curability, processability and hygiene of the coating material and does not elute bisphenol A from the coating film, and is particularly suitable as a coating material for a can inner surface or a can outer surface. A coating composition, a method of printing an aluminum can using the same, and a printed aluminum can.

Conventionally, aluminum cans have been widely used as containers for beer, mineral water, juice, soft drinks and the like. As these paints for aluminum cans, solvent-type paints using polyvinyl chloride, phenolic resins, epoxy resins, acrylic resins, etc. as coating-type elements (vehicles) have been used as organic solvent-type paints. In particular, bisphenol A-type epoxy resin-added solvent-based paints have been widely used for adhesion to aluminum substrates.
However, because of the danger of fire and environmental pollution caused by solvent evaporation, water-based paints with polar resin have been developed. As a result, these resins were able to secure adhesion to the base aluminum metal, but in order to maintain the coating film hardness, in addition to these coating film form factors, epoxy resins, particularly bisphenol A type epoxy resins and phenols were used. Many water-based paints (for example, refer to Patent Documents 1 to 6) combined with a resin curing agent have been proposed.

  However, the coating film formed from these water-based paints contains bisphenol A, which is excellent in processability, adhesion, and corrosion resistance, but is suspected of being an exogenous endocrine disrupting chemical (environmental hormone). Therefore, the development of a paint that does not contain bisphenol A has become an urgent task, and various efforts have been made. As one of them, a system in which an acid-terminated polyester resin and a novolac type epoxy resin are combined has been studied. However, if sufficient curability of the coating film is obtained, the storage stability of the paint is lowered. was there.

JP-A-11-217538 Japanese Patent Application Laid-Open No. 11-263939 JP-A-11-343456 JP 2000-265108 A JP 2002-361784 A

An object of the present invention is to obtain a coating material having a high coating film hardness, excellent in curability, workability and hygiene of the coating material, and capable of forming a coating film in which bisphenol A is not eluted at all.
As a result of intensive studies to achieve the above object, the present inventors have developed a water-based paint with improved coating film hardness without deteriorating performance such as coating film hardness and adhesion of the coating film to the ground. It is in.

The present invention
[1] as a resin component, (A) a polyester resin 30 to 40 wt%, (B) an acrylic resin 5-16% by weight, (C) amino resin 52 to 60 wt% and (D) a high melting point waxes (A) Water-based paint comprising 1.3 to 2.5 parts by weight with respect to a total of 100 parts by weight of (C),
[2] The water-based paint according to the above [1], wherein the amino resin is 52 to 58% by weight,
[3] An aqueous paint using an aqueous medium having a solid content of 40 to 55% by weight and an organic solvent of 40 to 60% by weight, and the Ford Cup viscosity at 35 ± 3 ° C. is 30 to 45 seconds. The water-based paint according to the above [1] or [2],

[4] As the resin component, (A) 30 to 40% by weight of polyester resin, (B) 5 to 16 % by weight of acrylic resin, (C) 52 to 60% by weight of amino resin and (D) high melting point wax (A) Aluminum can characterized by printing using water-based paint comprising 1.3 to 2.5 parts by weight with respect to a total of 100 parts by weight of (C), and curing at a temperature of 150 to 210 ° C. for 20 to 45 seconds. How to print,

[5] An aluminum can printed on the outer surface of the aluminum can with the water-based paint for an aluminum can according to any one of [1] to [3] above,
By solving this problem, the above problems were solved.

Since the present invention is an aqueous paint that does not contain bisphenol A, which is a suspected exogenous endocrine disrupting chemical that can be used for printing aluminum cans, it is a non-hazardous material in the Fire Service Act compared to solvent-based paints that have been used in the past. Applicable and not applicable to the Industrial Safety Law, extremely safe, and low environmental pollution.
Since it is a water-based paint, it has a slightly faster volatility than solvent-based paints, and it is highly slippery because the blended wax bleeds, and also because it contains benzoguanamine. Excellent scratch resistance and high coating hardness due to abundant cross-linking system between functional groups. For this reason, the aluminum can printed with this water-based paint can provide an aluminum can having higher friction resistance than conventional solvent-based paints.

  The water-based paint for an aluminum can of the present invention comprises a polyester resin, an acrylic resin, an amino resin, (D) a high melting point wax, a dye or pigment, and a silicone resin or other compounding agent blended as necessary, a hydrophilic organic solvent and An aqueous paint dispersed as an emulsion in a dispersion medium composed of water.

  A wide range of polyester resins can be used as the polyester resin used in the present invention. For example, as one of them, there is a polyester made of an esterified product of a polybasic acid component and a polyhydric alcohol component. Examples of the polybasic acid component include one or more selected from phthalic anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, succinic acid, fumaric acid, adipic acid, sebacic acid, maleic anhydride, and the like. Dibasic acids and lower alkyl esterified products of these acids are mainly used, and if necessary, monobasic acids such as benzoic acid, crotonic acid, pt-butylbenzoic acid, trimellitic anhydride, methylcyclohexentricarboxylic acid , Tribasic or higher polybasic acids such as pyromellitic anhydride are used in combination. These polybasic acids are usually used by mixing two or more kinds of aromatic, alicyclic and aliphatic carboxylic acids.

  Examples of the polyhydric alcohol component include bivalent compounds such as ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, 3-methylpentanediol, 1,4-hexanediol, and 1,6-hexanediol. Alcohol is mainly used, and a trihydric or higher polyhydric alcohol such as glycerin, trimethylolethane, trimethylolpropane, pentaerythritol can be used in combination as necessary. These polyhydric alcohols can be used alone or in admixture of two or more.

In addition to the acid component and alcohol component of the polyester resin, oil fatty acid is reacted by a method known per se. Examples of the oil fatty acid include coconut oil fatty acid, soybean oil fatty acid, linseed oil fatty acid, Examples thereof include flower oil fatty acid, tall oil fatty acid, dehydrated castor oil fatty acid, and kiri oil fatty acid. In this case, the oil length of the alkyd resin is preferably 30% or less, particularly preferably about 5 to 20%.
Further, a low molecular weight polyester resin obtained by reacting an acid component and an alcohol component used in the production of these polyester resins may be reacted with a polyisocyanate compound by a method known per se.

  In order to impart adhesiveness, the polyester resin has a content in the resin component of 30 to 40% by weight, preferably ± 2% by weight. Although it will not be restrict | limited especially if it is said polyester resin, Usually, it is suitable that a number average molecular weight exists in the range of 1,000-20,000, Preferably it is 2,000-10,000. The polyester resin has an effect of increasing the coating film hardness. Although the blending amount is smaller than that of the solvent-based paint, film performance can be obtained if this is sufficient.

  The acrylic resin is one of the important components for maintaining the adhesion to the aluminum base without adding the bisphenol A type epoxy resin. This resin is composed of a copolymer resin containing a carboxyl group-containing polymerizable unsaturated monomer and other polymerizable unsaturated monomers as components. Examples of the polymerizable unsaturated monomer include one or a mixture of two or more of acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, etc. Among them, methacrylic acid is preferably used. Is done.

  The other polymerizable unsaturated monomer that is the monomer component of the acrylic resin may be any monomer that can be copolymerized with the carboxyl group-containing polymerizable unsaturated monomer, and may be appropriately selected and used depending on the required performance. For example, aromatic vinyl monomers such as styrene, vinyl toluene, 2-methyl styrene, t-butyl styrene, chlorostyrene; methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, N-, i- or t-butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, decyl acrylate, lauryl acrylate, cyclohexyl acrylate, methyl methacrylate, ethyl methacrylate, methacrylic acid n-propyl, methacrylate iso Carbon number of acrylic acid or methacrylic acid such as propyl, n-, i- or t-butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, decyl methacrylate, lauryl methacrylate, cyclohexyl methacrylate, etc. ~ 18 alkyl esters or cycloalkyl esters; 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, C2-C8 hydroxyalkyl esters of acrylic acid or methacrylic acid such as hydroxybutyl methacrylate; N-methylol acrylamide, N Name one or a mixture of two or more of N-substituted acrylamide or N-substituted methacrylamide monomers such as butoxymethyl acrylamide, N-methoxymethyl acrylamide, N-methylol methacrylamide, N-butoxymethyl methacrylamide, etc. Can do. As the other polymerizable unsaturated monomer, a mixture of (meth) acrylic acid esters and other comonomer such as styrene is particularly preferable.

The acrylic resin is not particularly limited in the constitution ratio and type of the monomer, but usually the carboxyl group-containing polymerizable unsaturated monomer is 15 to 60% by weight, preferably 20 to 50% by weight. It is preferred that the amount of the unsaturated monomer is 85 to 40% by weight, particularly 80 to 50% by weight.
The carboxyl group-containing acrylic resin can be easily prepared, for example, by solution polymerization of the above monomer composition in an organic solvent in the presence of a polymerization initiator. The acrylic resin has a resin acid value of 100 to 400 and a number average molecular weight of 2,000 to 100,000, preferably 5,000 to 30,000. The content of the acrylic resin in the resin component is 5 to 20% by weight, preferably 13 ± 3% by weight. This acrylic resin has the effect of increasing the coating film hardness by its blending. This is because, in the case of exterior paint, transport resistance is required to prevent the paint film from being peeled off by peeling between cans or between a can and a carton case (corrugated cardboard box) during transportation. It has to be effective. Moreover, water solubility comes out to the resin component by an acrylic resin.

The amino resin used in the present invention is a product obtained by adding formaldehyde to methylol and then condensing it to benzoguanamine or melamine, which are widely known, and adding an alcohol to the imino group, methylol group, or methylol group. Some of them have a methoxy group and a combination of these groups. Specific examples include benzoguanamine resin (condensate of benzoguanamine), melamine resin (condensate of melamine), and benzoguanamine / melamine co-condensation resin (co-condensate of benzoguanamine and melamine), such as benzoguanamine resin and / or benzoguanamine. / A melamine co-condensation resin is preferable, and it is more preferable to use both from the viewpoint of blocking resistance.
In addition, when a melamine type amino resin is used, a self-condensation reaction is accelerated | stimulated and there exists a tendency for sclerosis | hardenability and workability to fall.

As the benzoguanamine resin, a methoxylated benzoguanamine resin or a butoxylated benzoguanamine resin in which a part of methylol group is partially etherified with methanol or butanol is preferable. Furthermore, it is preferable to use an amino resin having 0.5 to 2.0 imino groups per benzoguanamine nucleus. When the number of imino groups is less than 0.5, odor-resistant adsorption, boiling water resistance, and curability tend to decrease due to a decrease in reactivity. On the other hand, when the number of imino groups exceeds 2.0, processability and adhesion tend to decrease.
Examples of the benzoguanamine / melamine cocondensation resin include resins obtained by etherifying a part or all of methylol groups as in the case of the benzoguanamine resin.
The functional group (—NH) group in the amino resin reacts with the functional group (—OH, —COOH) in the polyester resin and the functional group (—OH, —CONH, —COOH) in the acrylic resin to crosslink. Presumed to be.

The amino resin used in the present invention has a resin component content of 50 to 60% by weight, preferably 55 ± 3% by weight. When the content is less than 50% by weight, the formed coating film is soft, and when rubbed weakly against friction, the coating film peels off, resulting in poor scratch resistance and reduced hot water resistance, curability and hardness. On the other hand, when the content of the amino resin exceeds 60% by weight, the workability of the coating film formed is lowered, and cracking is likely to occur in the necking of the aluminum can, and the adhesion tends to be lowered.
When a benzoguanamine / melamine co-condensation amino resin is used in combination with a benzoguanamine single amino resin, the ratio of the benzoguanamine single / co-condensation system is preferably 100/0 to 50/50. When the ratio of the benzoguanamine single system / co-condensation system is smaller than 50/50, the solvent resistance is improved in short-time seizure, but the workability tends to be lowered.

  The coating composition of the present invention needs to contain a lubricity-imparting agent in order to smooth the surface flow state. Various waxes are used as the lubricity-imparting agent. The wax has a higher melting point pattern than that usually used. This may be natural or synthetic, and the natural wax may be either animal or plant. Further, as synthetic waxes, esterified products of polyol compounds and fatty acids can be used in addition to polyolefin-based, silicone-based wax and fluorine-based wax. Two or more kinds of lubricity imparting agents can be used in combination, and it is preferable to use animal and plant waxes, silicone waxes and fluorine waxes in combination.

The lubricity-imparting agent has a melting point of about 0.2 to 1.0 parts by weight and a melting point of about 100 ° C. or more with respect to a total of 100 parts by weight of (A) to ( C ). A mixture of 0.5 to 2.0 parts by weight, a total of 1.3 to 2.5 parts by weight is used. When silicone is further added, the wax is efficiently bleeded, so that a surface with good lubricity can be obtained.

  This paint uses a hydrophilic organic solvent to improve its compatibility with water. As the organic solvent, alcohol solvents, cellosolve solvents and carbitol solvents are preferable. Specific examples of the organic solvent include isopropanol, butyl alcohol, 2-hydroxy-4-methylpentane, 2-ethylhexyl alcohol, cyclohexanol, ethylene glycol, diethylene glycol, 1,3-butylene glycol, ethylene glycol monoethyl ether, ethylene Examples include glycol monobutyl ether, ethylene glycol-mono t-butyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, and N, N-dimethylaminoethanol. As the organic solvent, organic solvents that are difficult to mix with water other than the above can be used as long as they do not hinder the stability of the carboxyl group-containing reaction product in the aqueous medium. For example, aromatic hydrocarbons such as toluene and xylene, esters such as ethyl acetate and butyl acetate, ketones such as acetone and methyl ethyl ketone can be used.

  The resin component (organic solvent solution) and a small amount of a hydrophilic organic solvent are added, and the whole is heated to 50 to 100 ° C. to obtain a uniform solution, and then added to water to 50 to 60% by weight. Of water is added in small portions to emulsify. Further, the organic solvent component is removed by distillation under reduced pressure or the like to obtain an aqueous coating composition having a desired solid content concentration (35 to 55% by weight).

  The water-based paint of the present invention does not contain bisphenol A, which is suspected as an exogenous endocrine disrupting chemical, and is water-based, so that it is not flammable and can form a highly volatile and high hardness coating film. Since the temperature dependence of the viscosity is high, it is important to adjust the viscosity. Therefore, at the time of printing, it is preferable that the Ford cup viscosity, which is lower than that of the solvent-based paint, is adjusted to 30 to 45 seconds at 35 ± 3 ° C. When it is higher than this, smooth coating becomes difficult.

After coating (printing) the outer surface of the aluminum can, it is baked and cured at a temperature of 150 to 210 ° C. for 20 to 45 seconds, preferably about 180 to 200 ° C. for 20 to 45 seconds for baking the paint. In addition, aluminum cans used for beer, etc. are further coated on the inner surface of the can and subjected to secondary baking, but the temperature at this time may be higher than the baking temperature at the time of outer surface coating, but up to about 250 ° C. Is sufficiently heat resistant so there is no problem.
The water-based paint of the present invention has a higher viscosity than that of the solvent-based paint, but a conventional painting equipment can be used as it is for painting, and no special equipment is required.
Even if the water-based paint is thinner, a paint film having good film performance (coating hardness, peel resistance, slipperiness) particularly important as an aluminum can is formed.

[Evaluation methods]
(Ii) Coating film hardness Pencil hardness: Mitsubishi pencil Uni use, room temperature, 80 ° C in warm water x 30 minutes.
(B) Impact resistance: A DuPont impact value, a 1/2 inch impact core, a load of 300 g, and a recess when dropped from a height of 30 cm are evaluated.

(Ha) Bending-proof peeling: Evaluated by the state of the coating film when bent by 180 ° using a 1 mmφ shaft with a bending tester.
(Ii) Adhesiveness: Cross-cut peel test, confirmation of peel condition with cello tape (registered trademark).

(B) Sliding property: untreated, shower treatment (80 ° C. × 30 seconds + 50 ° C. × 180 seconds), retort treatment (125 ° C. × 30 minutes); Measure coefficient.

(F) Paint resistance a; Retort whitening: Water was measured on the can body, and the whitening after retort treatment (125 ° C. × 30 minutes) was visually measured.
b: Blister: Place a stainless steel case with cold water on the painted plate, apply steam directly through punch metal, and visually evaluate the blister.
c: Salt water corrosion test: The coating can was completely immersed in 1% saline, left at 40 ° C. for 1 week, taken out, and then the cellophane (registered trademark) was peeled off from the black ink portion, and the degree of peeling was visually evaluated.
(And) Abrasion resistance a: GV-cat: A paint can is cut open, a strip-shaped one is wound around a commercial can, and the coating is brought into contact with the GV-cat tester. Visually evaluate the scratches on the coating surface. (Amplitude: 3/8 inch, 2 Hz / 400 seconds, 125 ° C. × 30 minutes—after retorting)
b: Friction player: Evaluate the number of rotations until scratched using a friction player. Load 1000g, 1500rpm.

[Use paint]

[Coating conditions]
Use can size: 350ml
Paint weight: Aqueous BPA-free paint: 120 ± 15mg / can
Solvent paint (conventional product): 140 ± 15mg / can Coating temperature: 35 ± 3 ℃
Baking conditions: Temperature 200 × 30 seconds The physical properties of the coated film were measured. The results are shown in Tables 2-8.

Since the water-based paint of the present invention does not contain the bisphenol A type epoxy resin (environmental hormone) used in conventional solvent-based paints, there is little risk of environmental pollution, and the denseness, adhesion, and friction of the coating film. Since it is a paint with excellent strength and hardness, it is possible to stably coat aluminum cans.
The water-based paint composition of the present invention was developed for the purpose of coating the outer surface of an aluminum can, but various substrates other than an aluminum can, such as a metal plate, a heat-resistant plastic film, or a plastic film on a metal plate. It can apply | coat to what is laminated | stacked by well-known means, such as roll coating, coil coating, spray, and brush coating. Examples of the metal plate include an electroplated tin steel plate, an aluminum steel plate, and a stainless steel plate.

Claims (5)

As the resin component, (A) polyester resin 30 to 40% by weight, (B) acrylic resin 5 to 16 % by weight, (C) amino resin 52 to 60% by weight, and (D) high melting point wax (A) to (C Water-based paint comprising 1.3 to 2.5 parts by weight with respect to 100 parts by weight in total.
The water-based paint according to claim 1, wherein (C) the amino resin is 52 to 58% by weight. An aqueous paint using an aqueous medium having a solid content of 40 to 55% by weight and an organic solvent of 40 to 60% by weight, wherein the Ford cup viscosity at 35 ± 3 ° C is 30 to 45 seconds. Or the water-based coating material of 2 . As the resin component, (A) polyester resin 30 to 40% by weight, (B) acrylic resin 5 to 16 % by weight, (C) amino resin 52 to 60% by weight, and (D) high melting point wax (A) to (C ) Is printed using an aqueous paint comprising 1.3 to 2.5 parts by weight with respect to a total of 100 parts by weight, and an aluminum can is printed at a temperature of 150 to 210 ° C. and cured for 20 to 45 seconds. Method.
The aluminum can which the outer surface of the aluminum can was printed with the water-based paint for aluminum cans according to any one of claims 1 to 3 .