Aqueous coating composition for metal packaging material and metal packaging material using the same

Abstract

To provide an aqueous coating composition for a metal packaging material capable of forming a coating film which does not cause coating defects such as sagging, mixing air and blistering without pre-treatment or post-treatment during spray coating and does not cause spilling when opening without adding a defoaming agent to a beverage.SOLUTION: There is provided an aqueous coating composition for a metal packaging material which comprises an aqueous dispersion of an acrylic modified epoxy resin (A), a phenol resin (B) and a wax, wherein the viscosity ηH at a shear rate of 10000 s-1 at 25°C is 10 to 50 mPa s, the ratio ηL / ηH between the viscosity ηL at a shear rate of 0.1 s-1 and the viscosity ηH at a shear rate of 10000 s-1 is 8 to 18 and the surface free energy of a cured coating film formed is 40 to 60 mN / m.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aqueous paint for metal packaging materials for forming a resin layer on the inner surface of a can body or a can bottom.

Background Art

[0002] The body portion of a beverage can called a two-piece can has a bottomed cylindrical structure made of an aluminum material as an example of a metal material, and a resin coating film layer is usually provided inside the can for the purpose of corrosion prevention of the metal material. Spray coating is generally applied to the coating of the paint for forming this coating film layer. Spray coating is a high-speed coating that enables coating 100 to 300 cans per minute per spray machine. Therefore, many problems of coating defects have become apparent. For example, "mixing air" caused by bubbles generated by the impact when the atomized paint adheres to the object to be coated, "sagging" in which uneven film thickness occurs due to the flow of the paint after coating, "blister" caused by foaming of the coating film during baking, etc. are mentioned. In many cases, these coating defects occur when the viscosity characteristics of the paint used are not appropriate. When such coating defects occur inside the can, it causes a decrease in the corrosion prevention function of the coating film, so suppression of the occurrence of coating defects is required.

[0003] In addition, as a filling form of a two-piece beverage can made of an aluminum material, a so-called positive pressure can in which the internal pressure is much higher than the external pressure is generally known. When opening a positive pressure can, since the internal pressure is suddenly released, unexpected spills or sudden foaming may occur, which hinders drinking, so improvement is required.

[0004] Patent Document 1 discloses a coating method in which a basic neutralizing agent is previously applied on a base material and then an anionic aqueous paint is applied when applying an anionic aqueous paint, and it is described that there are no coating film defects in the coated can after baking, no blisters or mixing air occur, and a film thickness of a certain level or more is ensured over the entire can.

[0005] Patent Document 2 describes a method of spray coating an aqueous paint on the inner surface of a metal can and preheating the outer surface of the bottom of the can and the lower part of the can body in advance before baking and drying the paint to prevent foaming (blistering) of the paint during baking and drying.

[0006] Also, Patent Document 3 discloses that in the production of carbonated beverages, by adding an antifoaming agent or the like to the carbonated beverage raw material, spillage during the production of carbonated beverages and when opening the drink for consumption is suppressed.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, in the manufacturing methods of Patent Documents 1 and 2, although no coating defects such as coating defects occur and a good coating surface can be obtained, the pre-treatment and post-treatment before and after coating complicate the production process, resulting in problems such as a decrease in production efficiency and an increase in manufacturing costs. Also, in modern times when a variety of flavors such as ready-to-drink are required for beverages, the method of Patent Document 3 may damage the flavor of the beverage even in a small amount due to an antifoaming agent or the like.

[0009] An object of the present invention is to provide an aqueous paint for metal packaging materials that can form a coating film that does not cause coating defects such as "dripping", "mixing air", and "blistering" without pre-treatment or post-treatment during spray coating, and does not cause spillage or the like when opened without adding an antifoaming agent to the beverage.

Means for Solving the Problems

[0010] The aqueous coating for metal packaging materials of the present invention is composed of an aqueous dispersion of an acrylic-modified epoxy resin (A), a phenolic resin (B), and a wax, and has a viscosity η at a shear rate of 10,000 s -1 at 25°C of 10 to 50 mPa·s, and the ratio η H of the viscosity ηL at a shear rate of 0.1 s -1 to the viscosity η at a shear rate of 10,000 s -1 is 8 to 18, and is an aqueous coating characterized in that H the surface free energy of the formed cured coating film is 40 to 60 mN / m. L / η H is 8 to 18, and is characterized in that the surface free energy of the formed cured coating film is 40 to 60 mN / m.

Advantages of the Invention

[0011] According to the present invention described above, coating defects such as "dripping" and "mixing air" do not occur during spray coating, and even when a can having a coating film formed from the aqueous coating for metal packaging materials of the present invention on its inner surface is filled with a beverage or the like, unexpected splashing or abnormal foaming does not occur upon opening.

Embodiments for Carrying Out the Invention

[0012] Embodiments of the present invention will be described. The present invention is not limited to the following embodiments, and the following examples do not limit the present invention. In this specification, "aqueous coating for metal packaging materials" may sometimes be simply referred to as "aqueous coating" or "coating".

[0013] The aqueous paint of the present invention contains an aqueous dispersion of an acrylic-modified epoxy resin (A), a phenolic resin (B), and wax, has a viscosity within a specific range under a high shear rate at 25°C, and is characterized in that the ratio of the viscosities at low and high shear rates is within a specific range. Therefore, this aqueous paint has excellent paintability during spray coating, and its cured coating film has no coating defects and can obtain a good surface quality. Further, this paint is also characterized in that the surface free energy of the cured coating film formed is 40 to 60 mN / m. Thereby, even if the filling of the can having the coating film formed from this paint on the inner surface is a carbonated beverage or the like, there is no spillage or abnormal foaming during opening.

[0014] It is important that the viscosity characteristics of the aqueous paint of the present invention are within a specific range. Specifically, under the conditions of 25°C and a high shear rate of 10000 s -1 it is important that the viscosity η H is 10 to 50 mPa·s, and preferably 15 to 40 mPa·s. The viscosity under a high shear rate affects the atomization property in spray coating, and an aqueous paint with η H in the range of 10 to 50 mPa·s has good atomization property and exhibits excellent paintability. By setting the viscosity η -1 at 10 mPa·s or more at a shear rate of 10000 s H the spray pattern will not become overly wide, a sufficient film thickness can be ensured to exhibit the coating film function, and coating film defects such as unevenness and peeling on the coating surface will not occur. Furthermore, sagging will not occur after coating on the object to be coated, a homogeneous coating film can be obtained, and coating film functions such as corrosion resistance will be improved. By setting the viscosity η H at 50 mPa·s or less, the spray pattern will not become overly narrow, and it will be possible to spray the paint sufficiently onto the object to be coated. Also, since no mixing air will be generated during coating, the resulting coating film will not contain bubbles, and coating film functions such as corrosion resistance will be further improved.

[0015] The aqueous paint of the present invention has a viscosity η -1 under the low shear rate condition of 0.1 s Land the viscosity η -1 at the shear rate of 10,000 s H and the viscosity ratio η L / η H is importantly 8 to 18. The paint with the viscosity ratio within this range shows excellent paintability in spray painting, and the surface of the formed cured paint film is smooth and uniform without surface defects. η L / η H When it is 8 or more, sagging and blistering after spray painting can be suppressed. η L / η H When it is 18 or less, the leveling property immediately after painting is improved, and a paint film with a uniform film thickness can be obtained. Moreover, it also contributes to the stability of the paint itself, and aggregation and gelation are less likely to occur during long-term storage.

[0016] In addition, various methods can be mentioned to adjust η L / η H of the aqueous paint of the present invention. As an example, resin structure control of the acrylic-modified epoxy resin (A), addition of various rheology control agents, composition adjustment of the solvent contained in the aqueous paint, etc. can be shown. η L / η H To increase η L / η H for example, regarding the resin structure of the acrylic-modified epoxy resin (A), means such as increasing the acid value of the acrylic resin part, increasing the glass transition temperature of the acrylic resin part, decreasing the mass ratio of the acrylic resin part to the epoxy resin part, and decreasing the dispersion particle size of the acrylic-modified epoxy resin (A) can be mentioned. On the other hand, to adjust η L / η H to be low, it is effective to perform the opposite actions to the above. In addition, when obtaining the acrylic-modified epoxy resin (A), according to the "graft polymerization method" described later, η L / η H tends to be low compared with other methods. In addition, among rheology control agents, the use of so-called thixotropic agents is effective in increasing η L / η H and examples include celluloses, polyurethanes, polyacrylic acids, polyamides, etc.

[0017] In the present invention, the viscosity at a specific shear rate was measured at 25°C using a cone rotor with a diameter of 50 mm and a cone angle of 1° by a rheometer "Physica MCR301" manufactured by Anton Paar. η L is the shear rate of 0.1 s -1 after holding for 60 seconds, and η H is the viscosity after holding for 10 seconds at a shear rate of 10,000 s -1 respectively measured.

[0018] Furthermore, the aqueous paint of the present invention is characterized in that the surface free energy of the cured coating film surface to be formed therefrom is within a specific range. Specifically, it is important that it is 40 to 60 mN / m, and preferably 43 to 58 mN / m. As factors affecting the surface free energy of the coating film, there are chemical factors inherent to the material and structural factors due to the surface shape of the coating film. For example, if a low-polarity polytetrafluoroethylene or waxes cover the surface layer of the coating film as a chemical characteristic, its surface free energy decreases, and it is clear from Wenzel's wetting equation that if there is a surface structure such as unevenness, its surface free energy further changes. Although it is not particularly limited whether the surface free energy of the cured coating film formed from the aqueous paint of the present invention is due to chemical factors or structural factors, it is important for the coating film function that the value is 40 to 60 mN / m. When the surface free energy of the coating film is 40 mN / m or more, abnormal foaming or spilling during opening of the can provided with this coating film on the inner surface is suppressed. When the surface free energy of the coating film is 60 mN / m or less, the coating film has appropriate lubricity and scratch resistance, and it becomes possible to improve the molding defect rate during can manufacturing or suppress the occurrence of corrosion starting from scratches on the coating film.

[0019] In the present invention, the surface free energy of the cured coating film is calculated by measuring the contact angle between the coating film and a liquid sample. For the measurement, an automatic contact angle meter "DM-501Hi" manufactured by Kyowa Interface Science Co., Ltd. was used, and water, methylene iodide, and n-hexadecane were used as liquid samples, and the respective contact angles were measured.

[0020] <Acrylic-modified epoxy resin (A)> The acrylic-modified epoxy resin (A) used in the present invention is a composite resin having an acrylic resin part and an epoxy resin part. The acrylic resin constituting the acrylic resin part is obtained by polymerizing an ethylenically unsaturated monomer, and as the ethylenically unsaturated monomer used in the present invention, it is preferable to use a carboxyl group-containing monomer and other ethylenically unsaturated monomers. Examples of the carboxyl group-containing monomer include (meth)acrylic acid [“acrylic acid” and “methacrylic acid” are collectively referred to as “(meth)acrylic acid”. The same applies hereinafter.], maleic acid, itaconic acid, fumaric acid and the like. Examples of other ethylenically unsaturated monomers include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, hexyl (meth)acrylate, and ethylhexyl (meth)acrylate, ethylenically unsaturated monomers having a hydroxyl group such as hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, hydroxypentyl (meth)acrylate, and hydroxyhexyl (meth)acrylate, aromatic monomers such as styrene and methylstyrene, N-hydroxyalkyl (meth) acrylamides such as N-hydroxymethyl (meth) acrylamide, N-hydroxyethyl (meth) acrylamide, N-hydroxybutyl (meth) acrylamide, N-alkoxyalkyl (meth) acrylamides such as N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, N-(n-, iso) butoxymethyl (meth) acrylamide, N-methoxyethyl (meth) acrylamide, N-ethoxyethyl (meth) acrylamide, N-(n-, iso) butoxyethyl (meth) acrylamide, and amide monomers such as (meth) acrylamide can be mentioned.

[0021] As the epoxy resin constituting the epoxy resin part of the acrylic-modified epoxy resin (A), epoxy resins such as bisphenol type, novolak type, naphthalene type, and biphenyl type are preferable. Among these, considering the processability, retort resistance, and metal adhesion of the resulting cured coating film, bisphenol A type epoxy resin is more preferable.

[0022] The epoxy resin preferably has a weight average molecular weight of 2500 to 80000, more preferably 15000 to 70000. By setting the weight average molecular weight to 2500 or more, the residual amount of unreacted substances such as bisphenol A can be reduced, and the processability and retort resistance can be improved. When the weight average molecular weight is 80000 or less, the adhesion to metal is improved.

[0023] Examples of commercially available epoxy resins include jER1007, jER1009, jER1010, jER1256, jER4250, etc. manufactured by Mitsubishi Chemical Corporation.

[0024] As described above, the acrylic-modified epoxy resin (A) is a composite resin of an acrylic resin and an epoxy resin. Representative examples of its production method include (a) graft polymerization method, (i) esterification method, (u) direct polymerization method, etc. That is, (A) Graft polymerization method: A method of obtaining an acrylic-modified epoxy resin (A) in which an acrylic resin is grafted onto an epoxy resin by polymerizing an ethylenically unsaturated monomer using a radical polymerization initiator in the presence of an epoxy resin. (B) Esterification method: A method of obtaining an acrylic-modified epoxy resin (A) by copolymerizing an ethylenically unsaturated monomer to obtain an acrylic resin (a) having a carboxyl group, and subjecting a part of the carboxyl group and a part of the epoxy groups in the epoxy resin to an esterification reaction in the presence of a basic compound. That is, an acrylic-modified epoxy resin (A) can be obtained by an addition reaction between an acrylic resin (a) having a carboxyl group and an epoxy resin. (C) Direct polymerization method: A method of obtaining an acrylic-modified epoxy resin (A) in which an acrylic resin is added to an epoxy resin by reacting a part of the epoxy groups in the epoxy resin with the carboxyl groups of a carboxyl group-containing monomer such as (meth)acrylic acid, and polymerizing an ethylenically unsaturated monomer using a radical polymerization initiator in the presence of the resulting reaction product. In the present invention, among the above three methods, it is preferable to use the method (B).

[0025] Also, the acrylic-modified epoxy resin (A) can be obtained by combining the above methods. For example, a method in which an ethylenically unsaturated monomer is polymerized in the presence of an epoxy resin to perform graft polymerization, and then a basic compound is added to perform an esterification reaction, or a method in which an ethylenically unsaturated monomer is copolymerized in the presence of a reaction product of an epoxy resin and (meth)acrylic acid or the like to perform direct polymerization, and then an esterification reaction is performed, etc. can be mentioned.

[0026] In the above method, as the radical polymerization initiator used for the polymerization of the ethylenically unsaturated monomer, for example, it is preferable to use an organic peroxide, a persulfate, an azobis compound, and a redox system in which these are combined with a reducing agent. In the present invention, a peroxide-based initiator is preferable, and benzoyl peroxide is particularly preferable.

[0027] The radical polymerization initiator is preferably used in an amount of 1 to 10 parts by mass, more preferably 1 to 6 parts by mass, based on 100 parts by mass in total of the ethylenically unsaturated monomers. Incidentally, the reaction conditions such as the temperature and time during polymerization are not special, and known conditions can be used. It is important to appropriately adjust the reaction conditions so that the viscosity characteristics when made into an aqueous paint become optimal to obtain the acrylic-modified epoxy resin (A).

[0028] In addition, in the above method, as the basic compound used in the esterification reaction, Examples include alcohol amines such as dimethylethanolamine, ethanolamine, diethanolamine, and aminomethylpropanol, alkyl amines such as trimethylamine, triethylamine, and butylamine, morpholine, ammonia, and the like. The basic compound is preferably used in the reaction in a proportion of 5 to 70 mol%, more preferably 10 to 60 mol%, based on 100 mol% of the carboxyl group-containing monomer. Incidentally, the reaction conditions such as the temperature and time during the esterification reaction are not special and can be carried out using known conditions, but it is important to appropriately adjust the reaction conditions so that the viscosity characteristics of the resulting aqueous paint become optimal to obtain the acrylic-modified epoxy resin (A).

[0029] In obtaining the acrylic-modified epoxy resin (A), the mass ratio of the total amount (Wm) of the ethylenically unsaturated monomers to the total amount (We) of the epoxy resin is preferably Wm / We = 10 / 90 to 50 / 50, more preferably 15 / 85 to 45 / 55. If the proportion of Wm is 10 or more, the stability of the paint is improved and aggregates and gelation do not occur. On the other hand, if the proportion of Wm is 50 or less, the processability, metal adhesion, and retort resistance of the resulting coating film are improved. Also, it becomes easier to keep the viscosities under low shear rate and high shear rate within an appropriate range, and as a result, a good coating film surface can be obtained.

[0030] The acid value of the acrylic-modified epoxy resin (A) is preferably 40 to 200 mgKOH / g, more preferably 55 to 185 mgKOH / g. When the acid value is 40 mgKOH / g or more, the storage stability of the aqueous paint is improved, and the surface smoothness of the formed paint film is improved. When the acid value is 200 mgKOH / g or less, the water resistance of the formed paint film is improved. For example, even when subjected to retort treatment under high temperature and high pressure, deterioration such as whitening does not occur in the paint film. In addition, since hydrolysis of the paint film itself can be suppressed, it is difficult to elute into beverages or the like in contact with the paint film, so its hygiene and flavor can be maintained. The acid value of the acrylic-modified epoxy resin (A) is adjusted by the amount of the carboxyl group-containing monomer used above. When the blending ratio of the carboxyl group-containing monomer is increased, the acid value increases, and when the blending ratio is decreased, the acid value decreases. In addition, the acid value of the acrylic-modified epoxy resin (A) in the present invention is a theoretical value calculated based on the amounts of the ethylenically unsaturated monomers and epoxy resin constituting it.

[0031] To disperse the obtained acrylic-modified epoxy resin (A) in an aqueous medium, a conventional method may be used. Specifically, the carboxyl groups present in the acrylic-modified epoxy resin (A) are neutralized with a basic compound or the like to impart hydrophilicity. More specifically, after adding a basic compound to the acrylic-modified epoxy resin (A), a method of adding an aqueous medium such as water to form an aqueous dispersion, or a method of adding an aqueous medium such as water containing a basic compound to the acrylic-modified epoxy resin (A) to form an aqueous dispersion can be exemplified.

[0032] The aqueous dispersion of the acrylic-modified epoxy resin (A) in the present invention preferably has a D50 particle size of 0.05 to 1 μm, more preferably 0.1 to 0.8 μm. When the D50 particle size is 0.05 to 1 μm, the viscosity η H is 10 to 50 mPa·s, and η L / η HIt is more likely to fall within the range of 8 to 18, and has viscosity characteristics suitable for spray coating properties, so that a good coating surface can be easily obtained. Further, if the D50 particle size is 0.05 μm or more, the viscosity stability of the paint increases, and if it is 1 μm or less, aggregation, gelation, etc. are less likely to occur during storage of the paint, and the storage stability is good. In addition, the D50 particle size of the dispersion in the present invention refers to the particle size at which the cumulative frequency of the particle size distribution becomes 50%, and was measured using "NANOTRAC WAVE" manufactured by Microtrac Bell Co., Ltd.

[0033] <Phenolic resin (B)> The phenolic resin (B) used in the present invention includes 4-functional phenol compounds such as bisphenol A and bisphenol F, 3-functional phenol compounds such as phenol, m-cresol, and 3,5-xylenol, and 2-functional phenol compounds such as o-cresol, p-cresol, and p-tert-butylphenol reacted with formaldehyde in the presence of a basic catalyst, and the like. In this case, the phenol compounds are used alone or in combination of two or more. Here, the functionality of the phenol compound indicates the number of carbon atoms in the benzene ring to which an aldehyde can be added. That is, for example, a 4-functional phenol compound is a phenol compound having 4 carbon atoms in the benzene ring to which an aldehyde can be added. As the phenolic resin (B), those in which part or all of the methylol groups formed by the addition of formaldehyde are etherified with alcohols having 1 to 12 carbon atoms can be preferably used. Thereby, the adhesion of the coating film to the base material can be further improved. The phenolic resin (B) functions as a curing agent for the paint.

[0034] The phenolic resin (B) is preferably used in an amount of 0.3 to 15 parts by mass, more preferably 0.3 to 10 parts by mass, based on 100 parts by mass of the acrylic-modified epoxy resin (A). When the phenolic resin (B) is 0.3 parts by mass or more, the metal adhesion and curability of the formed coating film are good, and when it is 15 parts by mass or less, the processability of the coating film is good.

[0035] The phenolic resin (B) is preferably compounded during the reaction for obtaining the acrylic-modified epoxy resin (A). Thereby, the processability, metal adhesion, and retort resistance of the formed coating film become further better. Explaining the specific compounding method in light of the above-described method for producing the acrylic-modified epoxy resin (A), for example, (a) In the graft polymerization method, an ethylenically unsaturated monomer is polymerized in a state where an epoxy resin and the phenolic resin (B) coexist. (b) In the esterification method, the phenolic resin (B) is compounded during the esterification reaction (addition reaction) of the acrylic resin (a) and the epoxy resin. (c) In the direct polymerization method, a part of the epoxy groups in the epoxy resin is reacted with the carboxyl groups of a carboxyl group-containing monomer such as (meth)acrylic acid, and an ethylenically unsaturated monomer is polymerized in the coexistence of the obtained reaction product and the phenolic resin (B).

[0036] <Wax> Examples of the wax used in the present invention include natural waxes and synthetic waxes. Examples of the natural waxes include animal and plant waxes such as beeswax, lanolin wax, spermaceti wax, candelilla wax, carnauba wax, rice wax, wood wax, and jojoba oil, minerals such as montan wax, ozokerite, ceresin, paraffin wax, microcrystalline wax, and petrolatum, and petroleum waxes. Among these, considering the slipperiness and abrasion resistance of the formed coating film, carnauba wax, candelilla wax, rice wax, lanolin wax, and microcrystalline wax are preferable.

[0037] Examples of the synthetic waxes include synthetic hydrocarbon waxes such as Fischer-Tropsch wax, polyethylene wax, oxidized polyethylene wax, and oxidized polypropylene wax, modified waxes such as montan wax derivatives, paraffin wax derivatives, and microcrystalline wax derivatives, Hydrogenated waxes such as hardened castor oil and hardened castor oil derivatives, Polytetrafluoroethylene (PTFE) waxes, etc. may be mentioned. Considering the slipperiness and abrasion resistance of the coating film, polyethylene waxes and microcrystalline wax derivatives are preferred.

[0038] As a method of blending wax, there are a method of directly blending powdery wax and a method of blending after previously preparing a wax dispersion. Among these, the latter method is preferred in terms of suppressing the generation of aggregates. The wax dispersion can be prepared by a known method such as a method of mixing wax and water and forcibly emulsifying, or a method of dripping water little by little while stirring a liquid obtained by heating and melting wax or a solution obtained by dissolving wax in a solvent to carry out phase inversion emulsification. A dispersant such as a surfactant may be used as necessary when obtaining the wax dispersion.

[0039] Commercially available products of the wax dispersion in the present invention include Hydrocer100 (polyethylene wax), Hydrocer257 (polyethylene wax), Hydrocer600 (microcrystalline / polyethylene mixed wax), Hydrocer901 (polyethylene / paraffin mixed wax), Hydrocerf9174 (PTFE), Fluoro AQ60 (PTFE), Hydrocer EC98 (emulsified carnauba wax), Hydrocer EE95 (emulsified polyethylene wax), Hydrocer EM08 (emulsified microcrystalline wax), Hydrocer EP91 (emulsified paraffin wax) manufactured by Shamrock Technologies, CERACOL39 (polyethylene wax), CERACOL79 (carnauba wax), CERACOL601 (carnauba wax), AQUACER498 (emulsified paraffin wax), AQUACER507 (emulsified polyethylene wax), AQUACER1547 (emulsified polyethylene wax) manufactured by BYK, SL506 (carnauba wax), SL508 (carnauba wax), SL19 (polyethylene wax), SL145E (emulsified paraffin wax), SL535E (emulsified carnauba wax), SL330E (emulsified polyethylene wax) manufactured by Elementis Japan Co., Ltd. HYTEC E-5403P (emulsified polyethylene wax), HYTEC E-8237 (emulsified polyethylene wax), E-1000 (emulsified polyethylene wax), HYTEC E-4A) manufactured by Toho Chemical Industry Co., Ltd. Microspersion215-50 (polyethylene wax), Microspersion250 (polyethylene wax), Microspersion930 (polyethylene wax), Microspersion190-50 (polyethylene / PTFE mixed wax), Microspersion411 (polyethylene / PTFE mixed wax) manufactured by MICRO POWDERS Aquaslip5071 (oxidized polyethylene wax), Aquaslip656 (oxidized polyethylene wax), Aquaslip671 (oxidized polyethylene wax), Aquaslip677 (modified paraffin wax), Aquaslip912 (carnauba wax), Aquaslip942 (carnauba wax), Aquaslip952 (carnauba wax), etc. manufactured by Lubrizol

[0040] In order to ensure the stability of the wax used in the present invention in the paint and the slipperiness of the formed paint film, it is preferable that the D50 particle size of the dispersion is 0.01 to 5 μm. When it is 0.01 μm or more, the slipperiness of the formed paint film is improved, and when it is 5 μm or less, the surface of the cured paint film becomes smooth, there are no surface defects, and good surface quality can be obtained.

[0041] The wax content in the present invention is preferably 0.01 to 1 part by mass with respect to a total of 100 parts by mass of the acrylic-modified epoxy resin (A) and the phenol resin (B). When it is 0.01 part by mass or more, the slipperiness of the formed coating film becomes good, and when it is 1 part by mass or less, the surface state of the coating film becomes smooth and uniform, and a can having a coating film formed from the said coating material on the inner surface is less likely to cause spillage or abnormal foaming during opening.

[0042] The aqueous coating material of the present invention preferably has a kinetic friction coefficient of the formed cured coating film of 0.35 or less. The kinetic friction coefficient can be adjusted by appropriately setting the wax content. When the kinetic friction coefficient is 0.35 or less, the coating film has appropriate slipperiness, and the moldability during can manufacturing and the corrosion resistance of the coating film are improved. The preferable lower limit value is about 0.07.

[0043] The coating material may contain an arbitrary liquid medium such as an organic solvent or water in addition to the resin, and is preferably adjusted to a viscosity suitable for the coating method. As the organic solvent, those capable of dissolving or dispersing the resin can be used. Specifically, for example, hexane, heptane, octane, decane, amylbenzene, isopropylbenzene, ethylbenzene, o-xylene, m-xylene, p-xylene, 1,2-diethylbenzene, 1,3-diethylbenzene, 1,4-diethylbenzene, cyclohexylbenzene, 2,6-dimethylnaphthalene, p-cymene, styrene, tetralin, α-pinene, β-pinene, dodecylbenzene, toluene, mesitylene, etc. In addition, hydrocarbon solvents such as Swazol 1000, Swazol 1500 (manufactured by Maruzen Petrochemical Co., Ltd.), T-SOL100FLUID, T-SOL150FLUID (manufactured by JXTG Energy Co., Ltd.), ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methylcyclohexanone, isophorone, In addition to ethyl acetate, butyl acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, dimethyl succinate, dimethyl glutarate, dimethyl adipate, etc., ester solvents such as FlexiSolv DBE esters (manufactured by INVISTA), alcohol solvents such as methanol, ethanol, n-amyl alcohol, s-amyl alcohol, t-amyl alcohol, isoamyl alcohol, isobutyl alcohol, isopropyl alcohol, 2-ethylbutanol, 2-ethylhexanol, 2-octanol, n-octanol, neopentyl alcohol, n-butanol, s-butanol, t-butanol, 1-propanol, n-hexanol, 2-heptanol, 3-heptanol, n-heptanol, 3-pentanol, 2-methyl-1-butanol, 3-methyl-2-butanol, 4-methyl-2-pentanol, etc., ether alcohol solvents such as ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monoethyl ether, ethylene glycol monophenyl ether, ethylene glycol monohexyl ether, ethylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, propylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monomethyl ether, etc. These can be used alone or in admixture of two or more.

[0044] The aqueous paint of the present invention may contain curing aids such as amino resins and isocyanate compounds for the purpose of improving the curability and metal adhesion of the coating film as necessary. Examples of the amino resin include those obtained by addition reaction of formaldehyde to amino compounds such as urea, melamine, and benzoguanamine. Examples of the isocyanate compound include blocked isocyanates using active methylene, MEK oxime, or ε-caprolactam as a blocking agent, and MEK oxime type aqueous isocyanates. These curing aids can be used alone or in combination of two or more kinds.

[0045] It is also possible to blend a surfactant and an antifoaming agent in the aqueous paint of the present invention as necessary.

[0046] The aqueous paint of the present invention can be applied to various substrates, and a metal packaging material having a coating film layer formed from the aqueous paint on a metal plate can be obtained. Examples of the substrate include various untreated or surface-treated metal plates such as aluminum plates, steel plates, and tin plates, metal plates coated with a primer on these metal plates, or PET-coated metal plates obtained by laminating a polyethylene terephthalate (PET) film on these metal plates. Examples of the use of the metal packaging material of the present invention include metal cans for containing beverages, foods, etc., and the types thereof include DI cans (cans manufactured by the Drawing&Ironing method), DR cans (cans manufactured by the Drawing&Redrawing method), various three-piece cans, film-laminated cans, etc. Further, the shape of the substrate may be plate-like or bottomed cylindrical. After applying and curing the aqueous paint for the metal packaging material of the present invention to these substrates, further deformation processing may be applied. Through various processing steps, a beverage container as a packaging material can be obtained.

[0047] As a method for coating the aqueous paint for metal packaging materials of the present invention on a substrate, various known methods can be applied, such as roll coater coating, spray coating, dip coating, electrocoating, etc. Among them, it has particularly excellent spray applicability. As the drying and curing conditions of the applied paint, usually, the conditions of 10 seconds to 30 minutes at a substrate surface temperature of 120 to 300 °C are preferable.

[0048] The amount of the coating film after drying may be appropriately selected depending on the application, but usually 5 to 200 mg / dm 2 is preferable. In particular, when used as the inner surface of a two-piece can body such as a DI can, 10 to 100 mg / dm 2 is preferable.

Examples

[0049] Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited only to the following Examples. In addition, the following "parts" and "%" are values based on "parts by mass" and "mass%" respectively, unless otherwise specified.

[0050] [Production Example 1] <Acrylic resin solution (a1)> Into a reaction vessel equipped with a stirrer, thermometer, reflux condenser, dropping tank, and nitrogen gas inlet tube, 1 / 4 of a mixture consisting of 20.0 parts of styrene, 10.0 parts of methyl methacrylate, 20.0 parts of ethyl acrylate, 50.0 parts of methacrylic acid, 83.0 parts of ethylene glycol monobutyl ether, 70.0 parts of n-butanol, and 2.3 parts of benzoyl peroxide was charged. Under a nitrogen gas atmosphere, it was heated to 80 to 90 °C and the remaining total amount was dropped over 2 hours while maintaining the temperature. After stirring for 2 hours from the end of dropping, it was cooled to obtain an acrylic resin solution (a1) with a non-volatile content concentration of 40%.

[0051] [Production Example 2] <Acrylic resin solution (a2)> An acrylic resin solution (a2) with a non-volatile content concentration of 40% was obtained in the same manner as in Production Example 1, except that the amount of styrene was 5.0 parts, the amount of methyl methacrylate was 5.0 parts, and the amount of methacrylic acid was 70.0 parts.

[0052] [Production Example 3] <Acrylic resin solution (a3)> An acrylic resin solution (a3) with a non-volatile content concentration of 40% was obtained in the same manner as in Production Example 1, except that the amount of styrene was 35.0 parts and the amount of methacrylic acid was 35.0 parts.

[0053] [Production Example 4] <Acrylic resin solution (a4)> An acrylic resin solution (a4) with a non-volatile content concentration of 40% was obtained in the same manner as in Production Example 1, except that the amount of ethyl acrylate was 40.0 parts, the amount of styrene was 5.0 parts, and the amount of methyl methacrylate was 5.0 parts.

[0054] [Production Example 5] <Acrylic resin solution (a5)> Into a reaction vessel similar to that in Production Example 1, 1 / 4 of a mixture consisting of 60.0 parts of methyl methacrylate, 25.0 parts of 2-ethylhexyl acrylate, 15.0 parts of acrylic acid, 83.0 parts of ethylene glycol monobutyl ether, 70.0 parts of n-butanol, and 2.3 parts of benzoyl peroxide was charged. It was heated to 80 - 90 °C under a nitrogen gas atmosphere and while maintaining that temperature, the remaining total amount was added dropwise over 2 hours. After stirring for 2 hours from the end of the dropwise addition, it was cooled to obtain an acrylic resin solution (a5) with a non-volatile content concentration of 40%. [Production Example 6] <Phenolic resin solution (B-1)> Into a reaction vessel similar to that in Production Example 1, 94.0 parts of phenol and 284 parts of 37% formalin were charged. While stirring, 24.0 parts of a 25% aqueous sodium hydroxide solution was added, and after reacting at 80 °C for 3 hours, 180 parts of n-butanol was added and cooled. 29.2 parts of 20% hydrochloric acid was added to neutralize sodium hydroxide. The aqueous layer was separated, the solution layer of the phenolic resin was taken out, washed with water, dehydrated, concentrated, and then n-butanol was added as necessary to obtain a phenolic resin solution (B-1) with a non-volatile content concentration of 50%.

[0055] [Production Example 7] <Acrylic-modified epoxy resin (A-1)> Into a reaction vessel similar to that of Production Example 1, 75.0 parts of jER1009 (bisphenol A type epoxy resin manufactured by Mitsubishi Chemical Corporation), 15.4 parts of ethylene glycol monobutyl ether, 18.6 parts of n-butanol, and 62.5 parts of acrylic resin solution (a1) were charged. Under a nitrogen gas atmosphere, the temperature was raised to 120 °C to dissolve the epoxy resin. After confirming dissolution, it was cooled to 80 °C. Subsequently, 4.5 parts of dimethylaminoethanol and 4.5 parts of water were mixed and added, and the mixture was stirred at 80 °C for 2 hours to carry out the reaction between the epoxy resin and the acrylic resin. After completion of the reaction, it was cooled, and 300 parts of water was added dropwise over 1 hour to obtain an aqueous dispersion of an acrylic-modified epoxy resin (A-1) with a non-volatile content concentration of 21%.

[0056] [Production Example 8] <Acrylic-modified epoxy resin (A-2)> Into a reaction vessel similar to that of Production Example 1, 75.0 parts of jER1009, 15.4 parts of ethylene glycol monobutyl ether, 18.6 parts of n-butanol, and 62.5 parts of acrylic resin solution (a2) were charged. Under a nitrogen gas atmosphere, the temperature was raised to 120 °C to dissolve the epoxy resin. After confirming dissolution, it was cooled to 80 °C. Subsequently, 4.3 parts of dimethylaminoethanol and 4.3 parts of water were mixed and added, and the mixture was stirred at 80 °C for 2 hours to carry out the reaction between the epoxy resin and the acrylic resin. After completion of the reaction, it was cooled, and 301 parts of water was added dropwise over 1 hour to obtain an aqueous dispersion of an acrylic-modified epoxy resin (A-2) with a non-volatile content concentration of 21%.

[0057] [Production Example 9] <Acrylic-modified epoxy resin (A-3)> Into a reaction vessel similar to that in Production Example 1, 75.0 parts of jER1009, 15.4 parts of ethylene glycol monobutyl ether, 18.6 parts of n-butanol, and 62.5 parts of an acrylic resin solution (a3) were charged. The temperature was raised to 120°C under a nitrogen gas atmosphere to dissolve the epoxy resin. After confirming dissolution, it was cooled to 80°C. Subsequently, 4.9 parts of dimethylaminoethanol and 4.9 parts of water were mixed and added, and the mixture was stirred at 80°C for 2 hours to carry out the reaction between the epoxy resin and the acrylic resin. After completion of the reaction, it was cooled, and 300 parts of water was added dropwise over 1 hour to obtain an aqueous dispersion of an acrylic-modified epoxy resin (A-3) with a non-volatile content concentration of 21%.

[0058] [Production Example 10] <Acrylic-modified epoxy resin (A-4)> An aqueous dispersion of an acrylic-modified epoxy resin (A-4) with a non-volatile content concentration of 21% was obtained in the same manner as in Production Example 7, except that the acrylic resin solution (a4) was used instead of the acrylic resin solution (a1).

[0059] [Production Example 11] <Acrylic-modified epoxy resin (A-5)> Into a reaction vessel similar to that in Production Example 1, 75.0 parts of jER1009, 15.4 parts of ethylene glycol monobutyl ether, 18.6 parts of n-butanol, and 25.0 parts of an acrylic resin solution (a5) were charged. The temperature was raised to 120°C under a nitrogen gas atmosphere to dissolve the epoxy resin. After confirming dissolution, it was cooled to 80°C. Subsequently, 4.9 parts of dimethylaminoethanol and 4.9 parts of water were mixed and added, and the mixture was stirred at 80°C for 1 hour. Then, 37.5 parts of the acrylic resin solution (a1) was charged and stirred at 80°C for an additional 2 hours to carry out the reaction between the epoxy resin and the acrylic resin. After completion of the reaction, it was cooled, and 300 parts of water was added dropwise over 1 hour to obtain an aqueous dispersion of an acrylic-modified epoxy resin (A-5) with a non-volatile content concentration of 21%.

[0060] [Production Example 12] <Acrylic-modified epoxy resin (A-6)> Into a reaction vessel similar to that of Production Example 1, 60.0 parts of jER1009, 3.2 parts of ethylene glycol monobutyl ether, 8.3 parts of n-butanol, and 100.0 parts of an acrylic resin solution (a1) were charged. The temperature was raised to 120°C under a nitrogen gas atmosphere to dissolve the epoxy resin. After confirming dissolution, it was cooled to 80°C. Subsequently, 4.3 parts of dimethylaminoethanol and 4.3 parts of water were mixed and added, and the mixture was stirred at 80°C for 2 hours to carry out the reaction between the epoxy resin and the acrylic resin. After completion of the reaction, it was cooled, and 301 parts of water were added dropwise over 1 hour to obtain an aqueous dispersion of an acrylic-modified epoxy resin (A-6) with a non-volatile content concentration of 21%.

[0061] [Production Example 13] <Acrylic-modified epoxy resin (A-7)> Into a reaction vessel similar to that of Production Example 1, 60.0 parts of jER1009, 3.2 parts of ethylene glycol monobutyl ether, 8.3 parts of n-butanol, and 100.0 parts of an acrylic resin solution (a2) were charged. The temperature was raised to 120°C under a nitrogen gas atmosphere to dissolve the epoxy resin. After confirming dissolution, it was cooled to 80°C. Subsequently, 3.9 parts of dimethylaminoethanol and 3.9 parts of water were mixed and added, and the mixture was stirred at 80°C for 2 hours to carry out the reaction between the epoxy resin and the acrylic resin. After completion of the reaction, it was cooled, and 301 parts of water were added dropwise over 1 hour to obtain an aqueous dispersion of an acrylic-modified epoxy resin (A-7) with a non-volatile content concentration of 21%.

[0062] [Production Example 14] <Acrylic-modified epoxy resin (A-8)> Into a reaction vessel similar to that of Production Example 1, 85.0 parts of jER1009, 23.5 parts of ethylene glycol monobutyl ether, 25.4 parts of n-butanol, and 37.5 parts of an acrylic resin solution (a1) were charged. The temperature was raised to 120°C under a nitrogen gas atmosphere to dissolve the epoxy resin. After confirming dissolution, it was cooled to 80°C. Subsequently, 4.6 parts of dimethylaminoethanol and 4.6 parts of water were mixed and added, and the mixture was stirred at 80°C for 2 hours to carry out the reaction between the epoxy resin and the acrylic resin. After completion of the reaction, it was cooled, and 300 parts of water were added dropwise over 1 hour to obtain an aqueous dispersion of an acrylic-modified epoxy resin (A-8) with a non-volatile content concentration of 21%.

[0063] [Production Example 15] <Acrylic-modified epoxy resin (A-9)> Into a reaction vessel similar to that in Production Example 1, 75.0 parts of jER1010 (bisphenol A type epoxy resin manufactured by Mitsubishi Chemical Corporation), 15.4 parts of ethylene glycol monobutyl ether, 18.6 parts of n-butanol, and 62.5 parts of acrylic resin solution (a1) were charged. The temperature was raised to 120°C under a nitrogen gas atmosphere to dissolve the epoxy resin. After confirming dissolution, it was cooled to 80°C. Subsequently, 4.0 parts of dimethylaminoethanol and 4.0 parts of water were mixed and added, and the mixture was stirred at 80°C for 2 hours to carry out the reaction between the epoxy resin and the acrylic resin. After completion of the reaction, it was cooled, and 301 parts of water were added dropwise over 1 hour to obtain an aqueous dispersion of acrylic-modified epoxy resin (A-9) with a non-volatile content concentration of 21%.

[0064] [Production Example 16] <Acrylic-modified epoxy resin (A-10)> Into a reaction vessel similar to that in Production Example 1, 75.0 parts of jER1009, 35.7 parts of ethylene glycol monobutyl ether, and 35.7 parts of n-butanol were charged, and the temperature was raised to 120°C to dissolve the epoxy resin. While maintaining the temperature inside the reaction vessel at 120°C, a mixture consisting of 12.5 parts of methacrylic acid, 5.0 parts of styrene, 2.5 parts of methyl methacrylate, 5.0 parts of ethyl acrylate, and 0.8 part of benzoyl peroxide was continuously added dropwise from a dropping tank over 1 hour. One hour and 2 hours after completion of the dropping, 0.1 part of benzoyl peroxide was added respectively, and the reaction was continued for 3 hours after completion of the dropping, and then it was cooled to 90°C. Subsequently, 4.5 parts of dimethylaminoethanol were added and stirred for 10 minutes, and then 300 parts of water were added dropwise over 1 hour to obtain an aqueous dispersion of acrylic-modified epoxy resin (A-10) with a non-volatile content concentration of 21% having part of acrylic resin (a6).

[0065] [Production Example 17] <Acrylic-modified epoxy resin (A-11)> Into a reaction vessel similar to that in Production Example 1, 75.0 parts of jER1009, 15.4 parts of ethylene glycol monobutyl ether, 18.6 parts of n-butanol, 62.5 parts of acrylic resin solution (a1), and 6.0 parts of solution of phenolic resin (B-1) were charged. Except that the temperature was raised to 120 °C and dissolved under a nitrogen gas atmosphere, in the same manner as in Production Example 7, an aqueous dispersion of a mixture of an acrylic-modified epoxy resin (A-11) with a non-volatile content concentration of 21% and a phenolic resin was obtained.

[0066] [Production Example 18] <Acrylic-modified epoxy resin (A-12)> An aqueous dispersion of a mixture of an acrylic-modified epoxy resin (A-12) with a non-volatile content concentration of 21% and a phenolic resin was obtained in the same manner as in Production Example 17, except that 6.0 parts of CKS-3898 (a phenolic resin solution manufactured by Aica Kogyo Co., Ltd.: non-volatile content concentration 50%) was used instead of the solution of phenolic resin (B-1).

[0067] [Production Example 19] <Acrylic-modified epoxy resin (A-13)> The reaction was carried out in the same manner as in Production Example 16, except that 8.8 parts of methacrylic acid, 8.7 parts of styrene, 2.5 parts of methyl methacrylate, and 5.0 parts of ethyl acrylate were used as monomers. After the reaction, it was cooled to 90 °C, and then 5.5 parts of dimethylaminoethanol was added and stirred for 10 minutes. Subsequently, 301 parts of water was added dropwise over 1 hour to obtain an aqueous dispersion of an acrylic-modified epoxy resin (A-13) with a non-volatile content concentration of 21% having (a7) parts of acrylic resin.

[0068] The compositions, acid values, and D50 particle diameters of the acrylic-modified epoxy resins (A-1) to (A-13) obtained in Production Examples 7 to 19 are shown in Table 1.

[0069] [Examples 1 to 18] While stirring the aqueous dispersion of the acrylic-modified epoxy resin obtained in the above Production Example, a phenolic resin and a wax were added at the ratios shown in Tables 2 to 3, and water was added as necessary to obtain aqueous paints with a non-volatile content concentration of 20% shown in Examples 1 to 18. Regarding Examples 11, 14, 16, and 18, the phenolic resin solution (B-1) was already compounded at the stage of Production Example 17, and in Example 12, CKS-3898 was already compounded at the stage of Production Example 18.

[0070] [Comparative Example 1] To 100 parts of the aqueous paint obtained in Example 1, 0.3 part of dimethylaminoethanol was further added to obtain an aqueous paint with a non-volatile content concentration of 20%.

[0071] [Comparative Example 2] To 100 parts of the aqueous paint obtained in Example 2, 0.2 part of dimethylaminoethanol was further added to obtain an aqueous paint with a non-volatile content concentration of 20%.

[0072] [Comparative Examples 3 - 6] While stirring the aqueous dispersion of the acrylic-modified epoxy resin obtained in the above Production Example, the phenolic resin solution (B-1) and wax were added at the ratios shown in Table 3. Also, water was added as necessary to obtain aqueous paints with a non-volatile content concentration of 20% shown in Comparative Examples 3 - 6 (in Comparative Example 5, the phenolic resin solution (B-1) was not added, and in Comparative Example 6, the wax was not added).

[0073] [Evaluation of Physical Properties] The physical properties of the aqueous paints obtained in Examples 1 - 18 and Comparative Examples 1 - 6 were evaluated. When evaluating the physical properties of the paint films formed from each aqueous paint, the paint was applied to form a paint can or a test panel, and the following items were evaluated. For the paint can, the entire inner wall surface of an aluminum bottomed cylindrical can with an inner diameter of about 7.5 cm, a height of about 12 cm, and a capacity of about 350 ml was coated with each aqueous paint by airless spraying so that the dry film weight per can was 130 mg. Then, the can was laid on its side and tumbled at 60 rpm for 30 seconds, and then baked in an oven set at 200°C for 2 minutes while standing upright. For the test panel, a flat plate was used by cutting open the body part of this paint can.

[0074] [Viscosity of Paint] The viscosity of each aqueous paint was measured at 25 °C using a cone rotor with a diameter of 50 mm and a cone angle of 1° by a rheometer "Physica MCR301" manufactured by Anton Paar. η L is the shear rate of 0.1 s -1 after holding for 60 seconds, and η H is the shear rate of 10,000 s -1 after holding for 10 seconds, and the viscosities were measured respectively. η L / η H is η L divided by η H .

[0075] <Spray paintability> The paint can was filled with 1% saline solution. Using an enamel meter (electrical conductivity tester), with the can body as the anode and the cathode inserted into the saline solution, the current value was measured when a voltage of 6 V was applied for 30 seconds. The smaller the current value, the more uniformly and densely the paint film is formed, and it can be evaluated accordingly. ◎: The current value is less than 0.5 mA. Good ○: The current value is 0.5 mA or more and less than 3 mA. No problem in practical use. △: The current value is 3 mA or more and less than 10 mA. Cannot be used. ×: The current value is 10 mA or more. Cannot be used.

[0076] <Evaluation of sagging> Each aqueous paint was applied on an aluminum plate with a thickness of 0.26 mm, a length of 20 cm, and a width of 5 cm using a bar coater so that the dry film weight was 50 mg / dm 2 . After that, the undried painted plate was fixed at an angle of 90° to the horizontal for 1 minute, and then baked in an oven set at 200 °C for 2 minutes. The film thickness of the cured paint film on the obtained painted plate was measured at 1 cm intervals in the longitudinal direction. ◎: The difference between the maximum value and the minimum value is less than 0.5 μm. No sagging and good ○: The difference between the maximum value and the minimum value is 0.5 μm or more and less than 1 μm. No problem in practical use. △: The difference between the maximum value and the minimum value is 1 μm or more and less than 3 μm. Sagging occurs. Cannot be used. ×: The difference between the maximum value and the minimum value is 3 μm or more. Significant sagging occurs. It cannot be used.

[0077] <Surface free energy> The contact angles of the coating film surfaces of the test panels were measured using an automatic contact angle meter "DM-501Hi" manufactured by Kyowa Interface Science Co., Ltd., with water, methylene iodide, and n-hexadecane as liquid samples. The obtained contact angle values were inserted into the formula of Kitazaki, Hata, etc. to determine the surface free energy of the cured coating film surfaces of each test panel.

[0078] <Coefficient of kinetic friction> A 1 kg weight with three steel balls was placed so that the steel balls were in contact with the coating film surfaces of each test panel, and this weight was pulled at a speed of 150 cm / min to measure the coefficient of kinetic friction at this time. The smaller the coefficient of kinetic friction, the better the slipperiness.

[0079] <Scratch measurement> Using a tribogear HEIDON-22H (manufactured by Shinto Kagaku Co., Ltd.), under the conditions of a scratch needle diameter of 100 μm, a scratch length of 50 mm, and a scratch speed of 300 mm / min, a scratch measurement was continuously performed by applying a load from 0 to 500 g. The load at the time when scratches occurred on the coating film and reached the aluminum substrate was measured. ◎: Load 350 g or more. Good. ○: Load 300 g or more and less than 350 g. No problem in practical use. △: Load 200 g or more and less than 300 g. It cannot be used. ×: Load less than 200 g. It cannot be used.

[0080] <Resistance to splashing> The difficulty of splashing from the container due to abnormal foaming when opening the stopper was evaluated by the following substitute test. 350 mL of beer cooled to 4°C was poured into a glass bottle with an inner volume of 450 mL, and each test panel with a size of 4 cm × 7 cm coated on both sides was slowly immersed therein. The foaming property of the beer after immersion was visually confirmed. ◎: No bubbles are generated from the test panel. Good ○: Slight foaming occurred from the test panel. The beer surface was not covered with foam. There is no problem in practical use. △: Foaming occurred from the test panel. Part of the beer surface was covered with foam. It cannot be used. ×: Considerable foaming occurred from the test panel. The entire beer surface was covered with foam. It cannot be used.

[0081] <Water resistance> With the test panel immersed in water, retort treatment was carried out in a retort autoclave at 130 °C for 1 hour, and the appearance of the coating film was visually evaluated. ◎: No change compared to the untreated coating film. Good. ○: Extremely slight whitening. There is no problem in practical use. △: Slight whitening. It cannot be used. ×: Considerable whitening. It cannot be used.

[0082] <Corrosion resistance> Potassium metabisulfite was dissolved in cola so that the sulfurous acid concentration became 80 ppm, 350 mL of the solution was filled into each painted can, the lid was immediately tightened, and it was stored statically at 37 °C for 3 months. After storage, the contents of each painted can were sampled, the aluminum elution amount from the can body was measured, and the corrosion resistance was evaluated according to the following criteria. ◎: Aluminum elution amount less than 1.0 ppm. Good. ○: Aluminum elution amount 1.0 ppm or more and less than 3.0 ppm. There is no problem in practical use. △: Aluminum elution amount 3.0 ppm or more and less than 5.0 ppm. It cannot be used. ×: Aluminum elution amount 5.0 ppm or more. It cannot be used.

[0083] Table 2 and 3 show the painting properties of the water-based paints obtained in Examples 1 to 18 and Comparative Examples 1 to 6, and the evaluation results of the coating film physical properties obtained from these water-based paints.

[0084]

Table 1

[0085]

Table 2

[0086]

Table 3

[0087] As shown in Tables 2 and 3, all of the physical properties of the water-based paints of Examples 1 to 18 were good, while in the water-based paints of Comparative Examples 1 to 6, any one of the physical properties was poor, and none of them could achieve all good properties.

[0088] The product names and contents of the waxes in Tables 2 and 3 are as follows. Aquaslip952: Carnauba wax dispersion manufactured by Lubrizol, D50 particle size 0.14 μm CERACOL79: Carnauba wax dispersion manufactured by BYK, D50 particle size 2.2 μm

Claims

1. An aqueous dispersion of an acrylic-modified epoxy resin (A), a phenolic resin (B), and a wax, The viscosity η at a shear rate of 10,000 s at 25°C －１ is 10 to 50 mPa·s, and the viscosity η Ｈ at a shear rate of 0.1 s －１ and the viscosity η Ｌ at a shear rate of 10,000 s －１ and the ratio η Ｈ / η Ｌ is 8 to 18, and is an aqueous paint Ｈ ​ characterized in that the surface free energy of the formed cured coating film is 40 to 60 mN / m, an aqueous paint for metal packaging materials.

2. The aqueous paint for metal packaging materials according to Claim 1, characterized in that the kinetic friction coefficient of the formed cured coating film is 0.35 or less.

3. The aqueous paint for metal packaging materials according to Claim 1 or 2, wherein the D50 particle size of the wax is 0.01 to 5 μm, and the content of the wax is 0.01 to 1 part by mass with respect to 100 parts by mass in total of the acrylic-modified epoxy resin (A) and the phenolic resin (B).

4. The aqueous paint for metal packaging materials according to Claim 1 or 2, wherein the acrylic-modified epoxy resin (A) is an addition reaction product of an acrylic resin (a) having a carboxyl group and an epoxy resin, and has an acrylic resin part and an epoxy resin part.

5. The aqueous paint for metal packaging materials according to Claim 4, characterized in that the phenolic resin (B) is blended during the addition reaction of the acrylic resin (a) having a carboxyl group and the epoxy resin.

6. A metal packaging material having a coating film layer formed from the aqueous paint for metal packaging materials according to Claim 1 or 2 on a metal plate.

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