JPH089707B2 - Inner coating can using water-based paint - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inner coating can using an O / W emulsion water-based paint, and more specifically, it has an excellent combination of hot water resistance (retort resistance) and extraction resistance. The present invention relates to an inner coating can using a water-based paint.

[0002]

2. Description of the Related Art Conventionally, in the production of canned cans, various paints have been used to coat metal materials and the can itself in order to prevent metal elution into the contents and to prevent metal corrosion. Has been done. Not only in the case of drawing and ironing cans using unpainted metal materials, but also drawing cans using painted metal materials,
Even in the three-piece can, various paints are spray-painted and baked on the can body and the can lid in order to correct the damage of the coating film that enters in the can manufacturing process and to form the top coat.

From the viewpoint of adhesion to a metal substrate, corrosion resistance, flavor characteristics and coating film processability, a paint composed of a combination of an epoxy resin and a curing agent resin and a vinyl-based paint are excellent. When these paints are applied in the form of an organic solvent solution, good performance is exhibited, but during spray coating, the solvent volatilizes into the work environment, causing air pollution and environmental hygiene problems.

In order to eliminate these drawbacks, water-based paints,
That is, the development of an aqueous dispersion paint has already been carried out. The first type of such water-based paint is one in which the paint resin is atomized by some means, and a surfactant or a water-soluble or hydrophilic resin is dispersed in water as a dispersant (for example, JP-B-44). -18076). The second type is
A coating material having a functional group such as an epoxy resin is modified by reacting it with a resin having a carboxyl group such as an acrylic resin, and the modified resin is neutralized with ammonia or amines so that it is self-exposed in an aqueous medium. It is emulsified (for example, JP-A-59-213718).

Japanese Patent Laid-Open No. Sho 63-1 proposed by the present inventors
No. 83968 discloses that a coating film-forming resin component contains an epoxy resin component, a resole-type phenol resin component, and a carboxyl group-containing acrylic resin component, and the carboxyl group in the acrylic resin is in the form of an ammonium salt or an amine salt. It is described that an O / W emulsion water-based coating composition is prepared by the phase inversion method.

[0006]

However, in the former type of water-based paint, the dispersion particle diameter of the coating resin component tends to be generally coarse or uneven, and the water-based paint has poor dispersion stability. The performance of the obtained coating film is inferior to that of the solvent type paint.

Further, although the latter type of coating is superior in dispersibility and the like to the former type of coating, it is greatly restricted by the coating resin composition. For example, in the case of epoxy resin coating, Since it is difficult to take a sufficiently large amount of the curing agent, it is not possible to sufficiently cure the coating film, and therefore the adhesion of the coating film and the hardness, denseness of the coating film,
This causes a problem that the barrier property against corrosive components cannot be improved to a satisfactory level.

In the prior art proposed by the present inventors,
Epoxy resin component and curing agent resin component such as resol-type phenol resin, etc., at an arbitrary ratio, were excellent in terms of producing a water-based paint by phase-inversion emulsification utilizing the surface-active effect of the neutralized acrylic resin. However, a cured coating film formed from a coating material using a carboxyl group-containing acrylic resin component as a dispersant, the coating film tends to whiten somewhat during high temperature hot water treatment such as retort sterilization and the coating film. Some of the resin components therein tend to be extracted into hot water.

[0009] It can be said that the carboxyl group-containing acrylic resin component has a surface active action in the state of an ammonium salt or an amine salt, and becomes insoluble in the free state.
It is considered that a part of the resin component migrates into the aqueous phase under the condition that water acts under high temperature and high pressure.

Therefore, the object of the present invention is to eliminate the above-mentioned drawbacks of the conventional water-based coating composition comprising an epoxy resin component, a resol-type phenol resin component and a carboxyl group-containing acrylic resin component, and to perform high temperature hot water treatment such as retort sterilization. Another object of the present invention is to provide an inner coating can using an aqueous coating material in which whitening of the coating film and extraction from the coating film are prevented.

Another object of the present invention is to use an aqueous coating composition which is excellent in combination of coating workability, adhesion of coating film, retort sterilization, corrosion resistance with the passage of time thereafter and extraction resistance of coating film. It is to provide the inner coating can.

[0012]

According to the present invention, a metal can barrel and an epoxy resin component, a resole-type phenol resin component and a carboxyl group-containing acrylic resin component-containing aqueous solution provided on at least the inner surface side of the can barrel. An inner coating can comprising a cured coating film of a paint, wherein the cured coating film comprises a continuous matrix phase composed of a curing reaction product of an epoxy resin component and a resol-type phenol resin component, a carboxyl group-containing acrylic resin component and a resol-type phenol resin component. An inner surface coating can comprising a dispersed particle phase composed of a cured reaction product of

The water-based paint used for the inner coating can of the present invention comprises the above-mentioned three resin components, the epoxy resin component is 90 to 40% by weight, the resol type phenol resin component is 3 to 40% by weight, and The carboxyl group-containing acrylic resin component is preferably present in an amount ratio of 5 to 40% by weight.

In the coating film of this inner coating can, in the cross section of the cured coating film, the continuous matrix phase is present in an area fraction of 98 to 80% and the dispersed particle phase is present in an area fraction of 2 to 20%, and The average length of the dispersed particle phase in the major axis direction is preferably in the range of 0.5 to 5.0 μm, and the cured coating film has a dynamic storage modulus-temperature curve of 90 to 1 μm.
It is preferable to have two shoulders at 10 ° C. and a temperature of 140 to 170 ° C.

[0015]

The aqueous coating composition for an inner coating can of the present invention contains an epoxy resin component, a resol-type phenol resin component and a carboxyl group-containing acrylic resin component as a coating film forming resin component, and the carboxyl group in the acrylic resin is ammonium. It is in line with conventional water-based paints in that it forms an O / W emulsion in the form of salt or amine salt, but some of the epoxy resin component and resol type phenol resin component are dispersed particle phase. The other part of the resol-type phenol resin component and at least most of the acrylic resin component are present in the aqueous phase (including the part of the dispersed particle interface) from the structural viewpoint. Is a remarkable feature of.

That is, the presence of a part of the resol-type phenolic resin component in addition to the carboxyl group-containing acrylic resin component in the form of ammonium salt or amine salt in the aqueous phase causes a cross-linking reaction between them to form a thermosetting resin. In addition, the cured reaction product has a completely new and unexpected effect of being incorporated in the final cured coating film in the form of dispersed particles.

The cured coating film of the inner coating can of the present invention comprises a continuous matrix phase composed of a curing reaction product of an epoxy resin component and a resol-type phenol resin component, a carboxyl group-containing acrylic resin component and a resol-type phenol resin component. The dispersed particle phase consisting of the curing reaction product, the dispersed particle phase consisting of a part of the epoxy resin component and the resol-type phenolic resin component in the water-based paint is the continuous matrix phase in the coating film, and This shows a very interesting behavior that a continuous aqueous phase composed of the other part of the resol type phenol resin component and the acrylic resin component is phase-converted into the dispersed particle phase in the coating film.

FIG. 1 is an electron micrograph showing a dispersed particle structure of an aqueous paint, in which black spherical particles are dispersed particles composed of an epoxy resin component and a resol type phenol resin component. The composition of the dispersed particle phase and the continuous aqueous phase of the water-based paint can be confirmed by separating these and analyzing each separated component.

FIG. 2 is a gel permeation chromatogram (GPC) of the resin component contained in the continuous aqueous phase separated from the water-based coating material in this way, and the lowest numerical value is the polystyrene-based weight average molecular weight. Is. In FIG. 2, the large peak A on the left side is due to the acrylic resin, while the small peak P on the right side is due to the resol-type phenol resin component. In FIG. 2, the reason why such a double peak appears is that the carboxyl group-containing acrylic resin component and the resol-type phenol resin component originally have a large difference in molecular weight, and the acrylic resin is present as a condition that they exist in the aqueous phase. However, the resol type phenol resin component is limited to a considerably low molecular weight.

FIG. 3 is an electron micrograph of a cross section of a coating film showing a dispersed particle structure in a cured coating film formed from the water-based paint of FIG. 1, in which a black background indicates an epoxy resin component and a resol-type phenol resin component. Shows a continuous matrix phase composed of a cured product of, and the white portion shows a dispersed particle phase containing an acrylic resin. Comparing FIG. 1 and FIG. 3, the characteristic that the acrylic resin, which was present in the continuous phase in the state of the coating material, was taken into the continuous matrix as dispersed particles in the state of the coating film, resulting in phase conversion. Will be revealed.

FIG. 4 shows a conventional organic solvent type paint I containing an epoxy resin component and a resole-type phenol resin component, a conventional water-based paint II and a water-based paint III of the present invention (see the examples described later for details). It is a dynamic storage elastic modulus-temperature curve calculated | required about the obtained cured coating film. From FIG. 4, the cured coating film formed from the conventional paint has a temperature of 90 to 11
While it only has a single shoulder at 0 ° C,
The surprising feature that the coating film of the inner coating can of the present invention has a shoulder at a temperature of 140 to 170 ° C. in addition to the shoulder in the above temperature range becomes apparent.

Although the graph of FIG. 4 shows that the cured coating film of the inner surface coating can of the present invention has a phase-separated structure, it also shows facts of further interest. That is, the glass transition point (Tg) of the uncured acrylic resin used here is 1
Although it is about 10 ° C. and does not appear as another shoulder in the curve of FIG. 4, having a shoulder at a temperature of 140 to 170 ° C. indicates the fact that this acrylic resin is crosslinked.

The low molecular weight resol type phenolic resin component present in the water phase of the paint used for the inner surface coating can of the present invention has a high reactivity with the acrylic resin and exhibits a high degree of crosslinking and curing action. , Very specific. From this point of view, the resole-type phenol resin component in the aqueous phase has a weight average molecular weight of 200 to 500 (GPC method).
In addition, the acrylic resin component and the resol-type phenol resin component are preferably present in the aqueous phase in a weight ratio of 99: 1 to 80:20 in view of the stability of the coating material and the physical properties of the coating film.

The water-based paint used in the inner coating can of the present invention contains an acrylic resin component containing a carboxyl group, and the carboxyl group in the acrylic resin is in the form of an ammonium salt or an amine salt to form an O / W emulsion. Since it is formed, it has excellent storage and storage stability and coating workability, and since it contains the epoxy resin component and the resol-type phenolic resin component in a predetermined ratio, it has excellent curing performance. Not only the advantages are achieved, but the cured coating film formed is such that the acrylic resin component is completely crosslinked and cured, and the cured product is incorporated in the continuous matrix of the coating film in the form of dispersed particles. Therefore, there is an effect that the whitening of the coating film and the extraction from the coating film are prevented even in the high temperature hot water treatment such as retort sterilization. Thus, this paint is excellent in the combination of coating workability, adhesion of the coating film, retort sterilization, and further corrosion resistance over time and extraction resistance of the coating film.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION The water-based paint used in the present invention contains an epoxy resin component, a resol-type phenol resin component, and a carboxyl group-containing acrylic resin as coating film forming components, and the carboxyl group-containing acrylic resin component is It is neutralized to the form of ammonium salt and amine salt.

(Epoxy Resin Component) As the epoxy resin, a bisphenol type epoxy resin obtained by polycondensation of bisphenols such as bisphenol A and epihalohydrin is suitable, and the epoxy equivalent thereof is generally 400 to 20,000, particularly 1,000 to 5,0
The range of 00 and the number average molecular weight are 1,000 to 20,000, especially
Those in the range of 2,000 to 13,000 are preferred.

(Resol-Type Phenolic Resin Component) As described above, the resol-type phenol resin component used in the present invention has a part existing as a dispersed particle phase and a part existing in the water phase in the aqueous paint. The distribution of these naturally depends on the molecular weight, but the resol-type phenol resin component used must have a molecular weight distribution corresponding to these. Generally, a low molecular weight component having a weight molecular weight of 200 to 500 and a weight molecular weight of 500
The high molecular weight portion exceeding 80:20 to 20:80,
In particular, it is preferably contained in a weight ratio of 60:40 to 30:70. However, it should be noted that although it is the low molecular weight components that are present in the aqueous phase, not all of the low molecular weight components are contained in the aqueous phase.

This resol type phenol resin component is produced by a method known per se except that the molecular weight distribution is within the above range. This resole resin contains p-substituted phenol and formaldehyde or a functional derivative thereof in a ratio of formaldehyde of 2 mol or more per mol of the phenol in the presence of an ammonia catalyst, an alkali metal catalyst or an alkaline earth metal catalyst to 80 to 80 mol. It can be obtained by heating at a temperature of 130 ° C. for about 1 to 10 hours. It is also obtained by reacting at a temperature lower than 50 ° C. to form a monomer dimethylol compound, and then condensing the resulting monomer dimethylol compound at a high temperature so as to obtain a desired molecular weight distribution. be able to. As a measure of the low molecular weight resin component, a bisphenol monomer and a p-cresol binuclear body (dimer) fall within this molecular weight range.

Suitable examples of p-substituted phenols include, but are not limited to, p-cresol, p-ethylphenol, p-tertbutylphenol, p-tertamylphenol, pn-octylphenol, pn-nonylphenol. , P-methoxyphenol, p-phenylphenol, p-cyclohexylphenol, p-benzylphenol and the like. Particularly, p-cresol, p-ethylphenol, p-tert-butylphenol and p-phenylphenol are preferable.

Suitable examples of p-substituted polynuclear phenols which may be used alone or in combination are 2,2'-bis (4-hydroxyphenyl) propane (bisphenol A), 2,2 '.
-Bis (4-hydroxyphenyl) butane (bisphenol B), 1,1'-bis (4-hydroxyphenyl) ethane, bis (4-hydroxyphenyl) methane (bisphenol F), 4-hydroxyphenyl ether, p-
Polycyclic phenols such as (4-hydroxy) phenol.

In the present invention, all phenol components are p
It is preferably composed of substituted phenols, but other phenols can be combined provided that they do not exceed 30 mol% based on total phenol. Examples of such other phenols include bifunctional phenols such as o-cresol, 2,3-xylenol, and 2,5-xylenol, phenol (carbolic acid), m-cresol, m-ethylphenol, and 3, Examples include trifunctional phenols such as 5-xylenol and m-methoxyphenol.

In the synthesis, as the other raw material, in addition to formaldehyde, a functional derivative thereof, that is, a derivative which acts as formaldehyde under the reaction conditions, such as paraformaldehyde, polyoxymethylene and the like can be used.

The condensation reaction is carried out in a suitable reaction medium, especially an aqueous medium, in the presence of an ammonia catalyst, an alkali metal catalyst or an alkaline earth metal catalyst. Examples of the catalyst include ammonia, caustic soda, caustic potash, alkali metal hydroxides and alkaline salts such as sodium carbonate, magnesium hydroxide, calcium hydroxide, barium hydroxide, calcium oxide, basic magnesium carbonate, basic magnesium chloride, A hydroxide, oxide or basic salt of an alkaline earth metal such as basic magnesium acetate is preferably used. These basic catalysts have a catalytic amount in the reaction medium,
In particular, it may be present in an amount of 0.01 to 0.5 mol%.

The resin produced can be purified by a means known per se, for example, the resin component as a reaction product is extracted and separated from the reaction medium with, for example, a ketone, alcohol, a hydrocarbon solvent or a mixture thereof, and optionally water. It is possible to obtain a resol-type phenol aldehyde resin in a form that can be mixed with an epoxy resin or the like by removing unreacted materials by washing with and further removing water by an azeotropic method or a precipitation method.

Of course, at least a part of the methylol group in the resole resin may be reacted with an alcohol such as butyl alcohol to preliminarily modify it into the etherified methylol group.

The water-based paint used for the inner surface coating can of the present invention is obtained by emulsifying and dispersing the paint resin into a fine dispersed particle diameter even when the composition ratio of the epoxy resin and the curing agent resin is within an arbitrary range. Obtaining is a salient feature.

(Carboxyl Group-Containing Acrylic Resin Component) The acrylic resin as the polymer dispersant is preferably present in an amount of an acid value of 2 to 30, particularly 5 to 20 based on the coating resin component. . When the acid value is below the above range, it becomes difficult to disperse the resin component in the form of an O / W type emulsion, and even if the resin component is strongly dispersed, the dispersion stability is poor. Further, when the acid value exceeds the above range, the hot water resistance of the coating film is lowered and the corrosion resistance after retort sterilization is lowered, even when cured.

The acrylic resin itself to be used preferably has an acid value of 35 to 350, particularly 70 to 330, and the acrylic resin is used in an amount of 3 to 30% by weight, particularly 5 to 25% by weight relative to the resin as a coating film forming component. It is preferably used in an amount of% by weight.

As the acrylic resin, any acrylic resin can be used as long as the acid value is within the above range. This acrylic resin is an ethylenically unsaturated carboxylic acid or an anhydride thereof which gives the resin a carboxyl group having the above-mentioned acid value, an acrylic acid ester or a methacrylic acid ester, and other ethylene copolymerizable therewith. It is composed of a copolymer with an unsaturated monomer. Examples of the ethylenically unsaturated carboxylic acid or its anhydride include acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, and itaconic anhydride.

Examples of the esters of acrylic acid and methacrylic acid include methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, and isobutyl (meth) acrylate. , (Meth) acrylic acid n-amyl, (meth) acrylic acid isoamyl, (meth) acrylic acid n-hexyl,
Examples include 2-ethylhexyl (meth) acrylate and n-octyl (meth) acrylate. However, the above-mentioned (meth) acrylic acid means acrylic acid or methacrylic acid.

Examples of the other monomer copolymerized with these monomers include styrene, vinyltoluene, acrylonylolyl, methacrylonitrile and the like.

The acrylic resin used should have a molecular weight sufficient to form a film, generally 10,000 to
It is desirable to have a molecular weight in the range of 200,000, especially 20,000 to 150,000. Examples of suitable combinations of acrylic copolymers are: (1) Methyl methacrylate / acrylic acid 2
-Ethylhexyl / acrylic acid, (2) Styrene / methyl methacrylate / ethyl acrylate / methacrylic acid, (3)
Styrene / ethyl acrylate / methacrylic acid, and (4) methyl methacrylate / ethyl acrylate / acrylic acid.

These acrylic resins can be easily obtained by polymerizing these monomers in an organic solvent in the presence of azobisisobutyronitriles and peroxides.

(Neutralizer) Ammonia or amine is used as a neutralizer for converting the acrylic resin into a salt. As the amine, alkylamines such as isopropylamine, sec-butylamine, tert-butylamine, isoamylamine, etc., particularly branched-chain alkylamines are preferably used, and alcohol amines such as mono-, di- or tri-ethanolamine. , Heterocyclic amines such as pyrrolidine, piperidine, piperazine and morpholine, and aromatic amines such as dimethylaniline are used. The amines are preferably used in an amount of at least 0.3 chemical equivalent, particularly 0.7 to 1.3 chemical equivalent based on the carboxyl group of the acrylic resin.

(Paint and its manufacturing method) The thermosetting resin O / W emulsion is prepared by mixing amine-containing water with an organic solvent solution containing an epoxy resin component, a resol-type phenol resin component and an acrylic resin. Alternatively, it can be formed by a so-called phase conversion method in which a melt containing an epoxy resin component, a resol-type phenol resin component and an acrylic resin is mixed with amine-containing water.

In this paint, the epoxy resin component is present in an amount of 90 to 40% by weight, the resol type phenolic resin component is present in an amount of 3 to 40% by weight, and the carboxyl group-containing acrylic resin component is present in an amount of 5 to 40% by weight. Good.

When amine water is added to the organic solvent solution or melt containing the above resin component, the viscosity of the system increases at the initial stage of the addition, but the viscosity of the system gradually decreases as the addition is continued. Get started. At this stage, the addition is interrupted, the whole system is homogenized by stirring, and if the addition of amine water is continued again, the viscosity of the system is drastically lowered by the addition of a predetermined amount of amine water. At the initial stage when the amine water is added to the resin solution, the aqueous phase exists in the form of a dispersed phase, but at the stage where the viscosity of the system is drastically decreased, the aqueous phase containing the specific resin component is continuously (dispersed medium). ) The O / W type emulsion in which the phase and the specific other resin component are dispersed is stably formed.

In the case of the solution phase conversion method, an organic solvent solution (A) of an epoxy resin component and a resol-type phenol resin component and an organic solvent solution (B) of an acrylic resin are prepared, and these solutions (A) and (B) are prepared. ) Is uniformly mixed to obtain a raw material solution. Examples of the organic solvent for this solution include aromatic hydrocarbon solvents such as toluene and xylene; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohol solvents such as ethanol, propanol, butanol; ethyl cellosolve, One or more of cellosolve solvents such as butyl cellosolve; ester solvents such as ethyl acetate and butyl acetate can be used. The resin component concentration in the raw material solution is
It is generally in the range of 5 to 80% by weight, preferably 20 to 70% by weight. This raw material solution contains known compounding agents for paints such as plasticizers, lubricants, pigments, fillers,
Stabilizers and the like may be added if desired.

The amount of water used for phase inversion varies depending on the type of resin and the concentration of the raw material solution, but generally 0.5 to 2.0 times by weight, particularly 0.7 to 1.5 times by weight of water is recommended per raw material solution. To be done. The resin solution and the amine water are mixed at room temperature, but may be heated up to about 100 ° C. if desired. The addition and mixing can be carried out in a reaction vessel equipped with an ordinary stirrer, but if desired, a high shear stirrer such as a homomixer or irradiation of ultrasonic vibration can be used.

Due to the phase inversion, the aqueous dispersion contains both water and an organic solvent. By subjecting this aqueous dispersion to azeotropic vacuum distillation, the organic solvent can be removed azeotropically with water, and the aqueous dispersion can be concentrated. It should be understood that the azeotropic distillation of the organic solvent can be performed while replenishing water from the outside.

The concentration of the coating resin solids in the final water-based paint is preferably in the range of 10 to 70% by weight, particularly 20 to 60% by weight, and the content of the organic solvent in the water-based coating is 15% by weight or less. It is particularly desirable that the amount is 5% by weight or less. Further, for the purpose of improving the dispersion stability of the resin component in the paint, it is acceptable to add a slight amount of a surfactant or a polymer dispersant to the system at any stage. The dispersed particle size of this water-based paint is 0.1-10 μm, especially 0.3-5 μm.
It is desirable to be in the range of m.

In the case of the melt phase inversion method, a melt containing a coating resin and an acrylic resin is prepared. The melt viscosity of this melt is generally 10 to 100,000 centipoise, especially
It is suitable to be in the range of 100 to 30,000 centipoise, and if the viscosity is higher than the above range, uniform and uniform kneading of both may be difficult. The temperature of the melt is 10
It is suitable to be in the range of from 150 to 150 ° C., particularly from 20 to 120 ° C. When the temperature is higher than the above range, partial gelation or premature gelation of the coating resin component is likely to occur, which is not preferable. The organic solvent described above can be used for the purpose of lowering the kneading temperature and lowering the melt viscosity.

The amount of the organic solvent used is suitably 30% by weight or less, particularly 15% by weight or less, based on the resin content. Of course, one or both resin components may be supplied to the kneading in the form of an organic solvent solution.

The melt-kneading can be carried out using a kneader, Banbury mixer, single-screw or twin-screw extrusion-type kneader. The amount of water added and the removal of the organic solvent are the same as in the solution phase conversion method.

(Use) The water-based paint used in the inner coating can of the present invention has a viscosity suitable for coating, and can be used for coating various metal materials, cans, cans or other members. This water-based paint can be used not only for ordinary spray paint and electrostatic coating, but also for coating work with various coaters such as roller coating, brush coating, doctor coater, air knife coater and reverse coater.

The water-based paint for use in the inner coating can of the present invention is particularly useful as a paint for metal containers, and can be applied as a coating film at any stage from the stage of metal material to the stage of metal container. In particular, it is possible to perform continuous coating on a coil-shaped metal plate or metal foil, or spray-coat on the inner surface of a re-drawing can or a drawing and ironing can, or roll-coat on a metal plate.

For example, in the case of a three-piece can having a side seam, a black plate, various coated steel plates, for example, a plated steel plate whose surface is plated with tin, chromium, aluminum, zinc or the like, or chromic acid and / or phosphoric acid on the surface thereof. Steel plate or foil chemically treated or cathodic electrolyzed with etc .; Light metal plate or foil such as aluminum; Composite metal material etc. in which aluminum foil etc. is adhered and laminated on the surface of organic substrate such as resin film such as polyolefin or paper board The material is preliminarily applied, the above-mentioned coating is applied, and after baking, the material is joined by means such as soldering, welding, joining with an adhesive or the like to form a can.

Alternatively, the material for the paint can is punched, press-formed, or scored, button-formed, tabs are attached, and the like to form a can lid or an easy open can lid. Of course, the order may be reversed, and the above-mentioned paint may be applied to the can body, the can lid or the can after baking and baked, and this paint may be provided as a single coat or a double coat.

In the case of a seamless can (two-piece can), the can material is subjected to squeezing processing or squeezing-ironing processing, and the coating material is applied to the molded can and baked. Alternatively, the order may be reversed and the coating material may be applied to the can material before processing and baked.

The solution type paint used for the inner coating can of the present invention may be any means such as dip coating, roller coating, spray coating, brush coating, electrostatic coating, electrodeposition coating, wire coating, flow coating and doctor coating. It can be applied to canning materials, canisters, can lids or cans. The paint thickness can generally range from 1 to 50 microns, especially from 2 to 40 microns on a dry matter basis.

The heating for baking and curing the paint includes, for example, an atmosphere heating method using an electric heating oven, a gas combustion oven, a hot air oven generated from various heat sources, or resistance heating or induction heating from the side of the substrate to be coated. Any method may be used, such as a method or heating by conduction heat for press-bonding an object to be coated on a hot plate, a method of directly heating a coating film by a flame generated by burning gas, or heating by infrared rays or far infrared rays.

[0062]

The invention is explained in more detail in the following examples. In addition, unless otherwise indicated, a part represents a weight part. [Example 1] Resol type phenol resin derived from bisphenol A, p-cresol and formaldehyde using an ammonia catalyst (bisphenol A / p-
Cresol = 80/20, weight average molecular weight 650) 20
Part was dissolved in 40 parts of a mixed solvent of xylene, methylisobutylketone, cyclohexanone and n-butanol (xylene / methylisobutylketone / cyclohexanone / n-butanol = 1/1/1/1) to prepare a solution.
As a result of analysis by gel permeation chromatography (hereinafter abbreviated as GPC), a ratio of a low molecular weight component having a weight average molecular weight of 200 to 500 and a high molecular weight component having a weight average molecular weight of more than 500 in this resol type phenol resin. Was 45:55.

Separately, 80 parts of a bisphenol A type epoxy resin having a number average molecular weight of 3750 and an epoxy equivalent of about 3000 was dissolved in 160 parts of a mixed solution of butyl acetate and butyl cellosolve (butyl acetate / butyl cellosolve = 3/1) to prepare a solution. Of phenol resin solution.

On the other hand, a mixture of 20 parts of ethyl acrylate, 20 parts of methyl methacrylate, 40 parts of methacrylic acid, 20 parts of styrene and 1 part of benzoyl peroxide was prepared, and a stirrer, a thermometer, a dropping funnel, a reflux condenser and an inert gas were prepared. A flask equipped with an inlet was charged with 50 parts of ethyl cellosolve and 25 parts of the above mixture, heated to 90 ° C. with stirring under a nitrogen stream, and then left in the flask kept at the same temperature for the remaining amount of the mixture. Was added dropwise over 3 hours for copolymerization, 0.1 part of benzoyl peroxide was added and stirring was continued for 3 hours at the same temperature, then 50 parts of ethyl cellosolve was added and cooled to complete the reaction. It was The weight average molecular weight of the obtained acrylic resin was about 120,000, the acid value was 123, and the solid content of the resin solution was 50%.

Next, after 300 parts of the mixed solution of the epoxy resin solution and the phenol resin solution was precondensed at 115 ° C. for 4 hours, 20 parts of the acrylic resin solution was added and stirred until uniform. Further, ammonia water prepared by dissolving 30 parts of 28% concentration of ammonia water in 450 parts of deionized water was prepared, and gradually the mixture of the epoxy resin solution, the phenol resin solution and the acrylic resin solution was vigorously stirred. Dropped. The system becomes a white cream at the beginning of the addition of aqueous ammonia, but the viscosity of the system gradually decreases as the aqueous ammonia is added. At this stage, the addition of aqueous ammonia was interrupted, stirring was continued, and the addition of aqueous ammonia was restarted after the whole was in a state of being uniformly dispersed. As a result, the viscosity of the system dropped sharply. The addition of aqueous ammonia was continued under stirring, and 500 parts of deionized water was further added. A stable O / W type emulsion was formed after the addition of the entire amount was completed.

This emulsion was concentrated by a rotary evaporator to a solid content of 40% and filtered through a # 1 glass filter to obtain an emulsified water-based paint. In this emulsified water-based paint, the average particle size of the resin particles is 0.58 μm,
It contains 3.5% organic solvent per paint. FIG. 1 shows the morphology of the resin particles observed with a transmission electron microscope (hereinafter abbreviated as TEM).

The emulsion-type water-based paint was applied to an ultracentrifugal separator to settle the resin particles to obtain a supernatant. A few drops of concentrated hydrochloric acid were added to 2 ml of this supernatant, and the mixture was dried. Tetrahydrofuran 5 ml was added to dissolve the resin component, and the mixture was filtered. The result of GPC analysis of the filtrate is shown in FIG. here,
The molecular weight represents the molecular weight of monodisperse polystyrene. Further, it was confirmed by infrared spectroscopy that the component of peak A was mainly acrylic resin and the component of peak P was mainly phenol resin. The area ratio of peak A to peak P is 90: 1.
It was 0.

100 ml of this emulsified water-based paint was used as the content 1
When placed in a 00 ml glass wide-mouthed bottle, sealed and stored in a constant temperature bath at 50 ° C. for 1 month and then opened and investigated,
No skinning occurred on the liquid surface. In addition, neither the viscosity of the emulsified water-based paint nor the average particle size of the resin particles changed as compared with those before storage.

The emulsion-type water-based paint was applied to a tin plate using a # 30 bar coater and baked at 200 ° C. for 10 minutes, and then the coating film was peeled from the tin plate. This coating film was embedded in polystyrene resin, a thin piece was cut in a direction perpendicular to the coating film surface with an ultramicrotome, stained with ruthenium tetroxide, and then observed with a TEM. The results are shown in Fig. 3. here,
The black part is a cured product of an epoxy resin and a phenol resin, and the white part is a cured product of an acrylic resin and a phenol resin. The average length of the white portion in the long axis direction is about 1 μm.

The dynamic viscoelasticity of this coating film was evaluated by Rheovlon D
Using DV-II-EA (manufactured by Orientec Co., Ltd.),
It was observed at a measurement frequency of 110 Hz. The temperature dependence of the dynamic storage modulus is shown in Fig. 4 (Paint III). The results of Comparative Example 1 are also shown in the figure. The glass transition temperature (hereinafter abbreviated as Tg) of the acrylic resin alone shown in this example was found to be about 110 ° C. by differential thermal analysis, and the results of Comparative Example 1 (Paint I and Paint II) are also shown. Considering it, the shoulder on the low temperature side (about 95 ° C.) is derived from the cured product of the epoxy resin and the phenol resin, and the shoulder on the high temperature side (about 160 ° C.).
It is considered that the shoulder of (.degree. C.) is derived from the cured product obtained by reacting the acrylic resin and the phenol resin.

Further tests were conducted for the purpose of confirming that the curing reaction between the acrylic resin and the phenol resin had occurred. The acrylic resin solution (9 parts) and the phenol resin solution (1 part) were mixed and applied to TFS and baked. On the other hand, an acrylic resin solution was separately coated and baked on TFS to prepare. These coated plates were extracted in toluene at boiling temperature for 1 hour under reflux. A coating film remained on the coated plate coated with the resin solution containing the phenol resin, but the coating film did not remain on the coated plate coated with the resin solution containing no phenol resin and was completely dissolved. From this, it was confirmed that the acrylic resin and the phenol resin reacted with each other to form a cured product insoluble in the solvent.

On the other hand, the above-mentioned emulsion type water-based paint was applied to an electrolytic chromic acid-treated steel plate (hereinafter abbreviated as TFS) using a roll coater, and baked at 210 ° C. for 10 minutes to cure. The coated plate was bonded by pressing it for 2 minutes with a hot press using a nylon adhesive. When the peel strength was measured by T-peel, the initial peel strength immediately after adhesion was 6.8 kg / 5 mm width, and the time-dependent peel strength after immersion in warm water at 90 ° C. for 1 week was 4.6 kg / 5 mm.
It was wide. Further, when this adhesion test piece was subjected to retort treatment at 125 ° C. for 30 minutes and evaluated, whitening of the coating film was not observed and the peel strength of 4.5 kg / 5 mm width or more was retained.

A roll coater was used to coat one side of the TFS with the above-mentioned emulsified water-based paint, which was baked at 210 ° C. for 10 minutes, and then the other side was similarly painted and baked to prepare a double-sided coated plate. . Using this coated plate and nylon adhesive, an adhesive can body of 202 diamonds (both ends are neck-in processed to 200 diamonds) was prepared, and the bottom lid was double-wound, and then coffee was The beverage was filled and the canopy was double-wound to make a canned coffee beverage. The canned coffee beverage was retort sterilized at 125 ° C. for 30 minutes, cooled, air-dried, and stored in a warehouse. When the cans were opened and evaluated after storage for 6 months, no abnormalities such as whitening of the coating film and corrosion of the inner surface of the can were observed. Further, after filling and sealing the distilled water in the can, the retort sterilization treatment was performed at 125 ° C. for 30 minutes, and the potassium permanganate (KMnO ₄ ) consumption amount of the content liquid was measured. Potassium permanganate consumption is about 10ppm,
The amount of organic substances eluted was suppressed to a low level.

Comparative Example 1 70 parts of the epoxy resin solution of Example 1 and 30 parts of the acrylic resin solution of Example 1 were reacted in the presence of dimethylaminoethanol at 90 ° C. for 30 minutes to give an epoxy resin and an acrylic resin. A composite resin bound by an ester bond was prepared. Furthermore, after adding 20 parts of the phenol resin solution of Example 1, 3 parts of dimethylaminoethanol was added to neutralize the carboxyl groups in the acrylic resin, and 100 parts of deionized water was added dropwise with stirring to emulsify. A water-based paint (Paint II) was prepared. On the other hand, a mixture obtained by precondensing a mixture of the epoxy resin solution and the phenol resin solution of Example 1 was used as it was as a solvent type paint (paint I).

Using these paints, a coating film was prepared according to the method described in Example 1 and the dynamic viscoelasticity was measured. The results are shown in Fig. 4. Only one shoulder corresponding to Tg is present in any of the coating films, and it can be seen that the entire film forms a uniform system. Further, according to the method of Example 1, the cross-sectional structure of the coating film was observed by TEM. All of these coating films had a uniform structure and no phase separation structure was observed. The potassium permanganate consumption measured according to Example 1 was about 15 ppm in all cases.

Example 2 According to the method shown in Example 1, five kinds of resole type phenolic resins derived from bisphenol A, p-cresol and formaldehyde using an ammonia catalyst were prepared. Furthermore, bisphenol A and p-
Three types of resol-type phenolic resins derived from cresol and formaldehyde using magnesium hydroxide as a catalyst were prepared. In synthesizing these resol-type phenolic resins, the average molecular weight and the weight average molecular weight are adjusted to 200 by varying the addition amount of formaldehyde.
Resol type phenolic resins having different ratios of the low molecular weight component of 500 to the high molecular weight component of which the weight average molecular weight exceeds 500 were obtained.

On the other hand, p-cresol and formaldehyde were reacted at 45 ° C. using a magnesium hydroxide catalyst to form a dimethylol compound of p-cresol monomer,
Then, the resulting dimethylol compound of the p-cresol monomer was condensed at 120 ° C. to further obtain one kind of resol-type phenol resin. The monomer composition of the resol-type phenol resin and the average molecular weight and weight-average molecular weight of the obtained resol-type phenol resin are 200 to 500.
Table 1 shows the ratio of the low molecular weight component of the above and the high molecular weight of which the weight average molecular weight exceeds 500.

Using these 9 kinds of resole type phenolic resins, the epoxy resin solution, acrylic resin solution and morpholine used in Example 1, 9 kinds of emulsion type aqueous paints were prepared according to the method shown in Example 1. did. Let the resin particles in these emulsion-type water-based paints settle by a centrifugal separation method,
The supernatant was analyzed by the method described in Example 1. The results are also shown in Table 1.

These emulsion type water-based paints were applied to a tin plate to obtain cured coating films, and the cross-sectional structures of these coating films were observed by TEM and the dynamic viscoelasticity was measured. It was confirmed that the coating film of any of the emulsion type water-based paints had a structure in which the dispersed particle phase was present in the continuous matrix phase. Table 1 shows the area fractions of the continuous matrix phase and the dispersed particle phase, and the average size of the dispersed particle phase in the major axis direction. Furthermore, it was confirmed by dynamic viscoelasticity measurement that each coating film had two shoulders in its dynamic storage elastic modulus-temperature curve. Table 1 also shows the temperatures at the beginning of the shoulder on the low temperature side and the high temperature side of each coating film.

Further, these emulsified water-based paints were applied to TFS to evaluate the adhesive performance, an adhesive can body was prepared, and canned milk coffee was prepared and evaluated according to the method of Example 1. Table 1 shows the results of evaluating the amount of potassium permanganate consumed. Moreover, no abnormality was observed in can performance using any of the emulsion-type water-based paints.

Comparative Example 2 p-cresol and formaldehyde were reacted at 45 ° C. using a magnesium hydroxide catalyst to form a dimethylol compound of p-cresol monomer. The weight average molecular weight of this phenol resin was about 180.
Using this phenol resin, an emulsified water-based paint was produced according to the method of Example 1. As a result of analyzing this emulsion-type water-based paint, the weight average molecular weight of the phenol resin dissolved in the aqueous phase was about 170, and the ratio of the acrylic resin to the phenol resin was 55:45. The potassium permanganate consumption measured according to Example 1 was about 25 ppm.

Comparative Example 3 p-cresol and formaldehyde were reacted at 45 ° C. using a magnesium hydroxide catalyst to form a dimethylol compound of the p-cresol monomer, and then the p-cresol monomer produced was reacted. 1 dimethylol compound
Resol type phenol resin was obtained by condensing at 20 ° C.

An emulsified water-based paint was produced by using 45 parts of this phenol resin, 45 parts and 10 parts of the epoxy resin solution and the acrylic resin solution of Example 1 in terms of solid content, respectively. As a result of analyzing this emulsion type water-based paint, the weight average molecular weight of the phenol resin dissolved in the water phase is about 290,
The ratio of acrylic resin to phenol resin was 70:30. As a result of preparing a coating film of this emulsified water-based paint and observing the cross-sectional structure with a TEM, the average size of the dispersed particle phase in the major axis direction was 6.3 μm. The temperature of the high temperature side shoulder obtained by the dynamic viscoelasticity measurement was 175 ° C. The potassium permanganate consumption measured according to Example 1 was about 20 ppm.

Example 3 Seven kinds of emulsion types were prepared using the epoxy resin solution of Example 1, the acrylic resin solution and the phenol resin solution,
An aqueous paint was prepared. Epoxy resin, acrylic resin,
Table 2 shows the ratio of phenolic resin (solid content conversion).
Analysis results of the obtained emulsified water-based paint, TEM observation results,
Table 2 also shows the measurement results of dynamic viscoelasticity. Furthermore,
These emulsified water-based paints were applied to TFS to evaluate the adhesive performance, an adhesive can barrel was prepared, and canned milk coffee was prepared and evaluated according to the method of Example 1. As a result, no abnormality was observed in the adhesive performance and the can performance with any of the emulsified water-based paints. The potassium permanganate consumption measured according to Example 1 is 10
To 14 ppm.

[Comparative Example 4] Four types of emulsion-type aqueous coating materials were prepared using the epoxy resin solution of Example 1, the acrylic resin solution, and the phenol resin solution. Table 3 shows the ratio of the epoxy resin, the acrylic resin, and the phenol resin (in terms of solid content). Table 3 also shows the analysis results, the TEM observation results, and the dynamic viscoelasticity measurement results of the obtained emulsified water-based paint. Further, these emulsified water-based paints were applied to TFS to evaluate the adhesive performance, an adhesive can barrel was prepared, and a canned milk coffee was prepared and evaluated according to the method of Example 1. Table 3 shows the evaluation results of potassium permanganate consumption. No abnormality was observed in the can performance using any of the emulsion type water-based paints.

Example 4 Five kinds of carboxyl group-containing acrylic resins having the monomer compositions shown in Table 4 were synthesized according to the method shown in Example 1. The acid value of the obtained acrylic resin is shown in Table 4. The acrylic resin, the epoxy resin and the phenol resin used in Example 1 were used in an amount of 1 per solid content.
Using 5:85:15 ratio, and according to the method of Example 1, 5 types of emulsion type aqueous coating materials were prepared. Table 4 shows the evaluation results obtained by coating these paints.

[Example 5] Five epoxy resins having the molecular weights and epoxy equivalents shown in Table 5 were used, and the acrylic resin and phenol resin of Example 1 were used in a ratio of 85:15:15 based on the solid content of the epoxy resin. According to the method of Example 1, 5 types of emulsion type water-based paints were prepared. Table 5 shows the evaluation results obtained by coating these paints.
Are also shown.

[0088]

[Table 1]

[0089]

[Table 2]

[0090]

[Table 3]

[0091]

[Table 4]

[0092]

[Table 5]

[0093]

INDUSTRIAL APPLICABILITY In the water-based paint used for the inner coating can of the present invention, in addition to the carboxyl group-containing acrylic resin component in the form of ammonium salt or amine salt, a part of the resol-type phenol resin component is present in the aqueous phase. By doing so, both of them undergo a cross-linking reaction to form a thermosetting resin, and this curing reaction product is incorporated in the final cured coating film in the form of dispersed particles, that is, the epoxy resin component and the resol type phenol resin in the water-based paint. The dispersed particle phase consisting of a part of the components is the continuous matrix phase in the coating film, and the continuous aqueous phase consisting of the other part of the resol type phenolic resin component and the acrylic resin component in the aqueous coating is the dispersed particles in the coating film. It is possible to change the phase to a phase, which has the effect of preventing whitening of the coating film and extraction from the coating film even during high temperature hot water treatment such as retort sterilization. It is. Thus, this paint is excellent in the combination of coating workability, adhesion of the coating film, retort sterilization, and further corrosion resistance over time and extraction resistance of the coating film. It is possible to obtain a painted inner can.

[Brief description of drawings]

FIG. 1 is an electron micrograph showing a dispersed particle structure of an aqueous paint.

FIG. 2 is a gel permeation chromatogram (G) of a resin component contained in a continuous aqueous phase separated from an aqueous paint.
PC).

FIG. 3 is an electron micrograph of a cross section of a coating film showing a dispersed particle structure in a cured coating film formed from the water-based paint of FIG.

FIG. 4 is a conventional organic solvent-based paint I containing an epoxy resin component, a resol-type phenol resin component and a carboxyl group-containing acrylic resin component, a conventional water-based paint II, and a water-based paint III used for the inner coating can of the present invention. It is a dynamic storage elastic modulus-temperature curve calculated | required about the cured coating film obtained from (the details refer to an Example).

Claims (3)

[Claims] 1. An inner coating can comprising a metal can barrel and a cured coating film of an epoxy resin component, a resol type phenol resin component and a carboxyl group-containing acrylic resin component-containing water-based paint provided on at least the inner surface side of the can barrel. A continuous matrix phase composed of a cured reaction product of an epoxy resin component and a resol-type phenol resin component, and a dispersed particle phase composed of a curing reaction product of a carboxyl group-containing acrylic resin component and a resol-type phenol resin component. Inner surface coating can. 2. In the cross section of the cured coating film, the continuous matrix phase has an area fraction of 98 to 80% and the dispersed particle phase is 2%.
2. The inner coating can according to claim 1, wherein each of the particles is present in an area fraction of 20 to 20%, and the dimension of the dispersed particle phase in the major axis direction is in the range of 0.5 to 5.0 μm on average. 3. The cured coating has its dynamic storage modulus-temperature curve at a temperature of 90 to 110 ° C. and a temperature of 140 to 170.
The inner coated can according to claim 1, which has two shoulders at ℃.