JP2005349691A - Thermoplastic resin-coated aluminum sheet for general can - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoplastic resin-coated aluminum sheet for a general can not lowered in adhesion even at the time of filling with highly corrosive content and excellent in adhesion and corrosion resistance. <P>SOLUTION: The thermoplastic resin-coated aluminum sheet is constituted by forming a non-porous anodic oxidation film with a porosity of 20% or below and a thickness of 40-300 nm at least on one side of a substrate body comprising aluminum or an aluminum alloy, coating the non-porous anodization film with a silane coupling agent within a range of 0.1-100 mg/m<SP>2</SP>and forming a resin coating layer comprising a thermoplastic resin with a thickness of 8-100 μm at least on one side of the substrate body. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is suitable for accommodating highly corrosive contents such as chemicals, paints, oils, etc., and is excellent in corrosion resistance, environmental protection and adhesiveness of a resin coating layer. The present invention relates to a coated aluminum plate.

Aluminum materials are widely used as metal containers such as cans, building materials, daily necessities, housings, or lids thereof because they are lightweight and have excellent formability.
Among these uses of aluminum materials, in the general can field such as 18 L cans, pail cans, drum cans, etc., highly corrosive chemicals, paints, seasonings, oils and the like are filled. In order to protect aluminum materials from such highly corrosive contents, surface treatment such as phosphoric acid chromate and zirconium chemical conversion treatment, anodizing treatment such as sulfuric acid alumite and phosphoric acid alumite, etc. is performed, and epoxy heat A can made of an aluminum plate coated with two layers of a curable resin paint is used. In recent years, a resin-coated aluminum plate on which a polyester-based thermoplastic resin film is laminated may be used.

By the way, the general chromate treatment as a base treatment of an aluminum plate material contains chromium harmful to the environment and the human body in the treatment liquid and the film to be formed, and also suitable for the chemical conversion treatment in the zirconium-based chemical conversion treatment film. Strict chemical management is necessary to obtain the proper characteristics.
As anodizing treatment applied to the aluminum plate material, sulfuric acid alumite and phosphoric acid alumite are generally used, but these are porous films, and the treatment liquid component contained in the pores forms a resin layer. When heated, it is released as a gas and may adversely affect the adhesion. There is a sealing treatment to prevent this, but there are problems such as a decrease in productivity and an increase in cost. Further, these base treatment layers cannot be said to have sufficient adhesion, and there is a problem that the resin layer peels off from the aluminum plate material when filled with a paint containing an organic solvent such as toluene or xylene.

By the way, the present inventors have been researching and developing aluminum materials for various uses. For example, as an aluminum molded body such as an outer casing of an electric component or an air conditioning fin material, a metal base material made of an aluminum alloy, and the metal base Corrosion resistance of a surface-treated aluminum material having a porous anodized film as part of the process of researching and developing a surface-treated aluminum material having a base layer made of an anodized film (so-called anodized oxide film) formed on the surface of the material For the purpose of improving gas release properties and adhesion to aluminum substrates, research and development on technology to obtain non-porous anodic oxide film with lower porosity than porous materials has been promoted. Is offered in. (See Patent Documents 1, 2, and 3)
JP-A-5-25694 JP-A-8-283991 JP-A-8-283990

The above-described resin coating on the surface of the aluminum plate material uses an organic solvent, so that the working environment is bad, and the paint is baked at a high temperature, so that an environmental load such as discharge of CO ₂ gas is large. Moreover, there is a problem that the cost is increased due to the two-layer coating.
Next, in the thermoplastic resin coating, the barrier property is lowered when the crystallization rate is lowered, and when the container is filled with a paint containing an organic solvent, problems such as peeling of the resin layer and occurrence of corrosion of the aluminum plate itself occur. Further, there has been a problem that the resin melted by heating during the lamination to the aluminum plate material is damaged and a pinhole is generated.

The present invention has been made in view of the above circumstances, and an object of the present invention is to obtain a resin-coated aluminum plate for general cans that has excellent adhesion and corrosion resistance, and does not deteriorate adhesion even when filled with highly corrosive contents. .
In addition, the present invention can suppress corrosion due to roll scratches and foreign matter contamination during bonding and contamination due to poor bonding, and does not contain harmful substances in the treatment liquid used for the base treatment or the film to be formed. The object is to provide a thermoplastic resin-coated aluminum plate for general cans that is excellent in safety and environmental protection.

In order to achieve the above object, according to the present invention, a nonporous anodic oxide film having a porosity of 20% or less and a film thickness of 40 to 300 nm is formed on at least one surface of a substrate body made of aluminum or an aluminum alloy. On the nonporous anodic oxide film, a silane coupling agent is applied in the range of 0.1 to 100 mg / m ² , and a thermoplastic resin having a thickness of 8 to 100 μm is applied to at least one surface of the substrate body. A resin coating layer is formed.

In the present invention, those having an amino group can be applied as the silane coupling agent.
In the present invention, it is preferable that the crystallization rate of the at least one resin coating layer is 40% or more.

In the present invention, the resin coating layer made of a thermoplastic resin formed on at least one surface of the substrate body can be composed of a single layer or a multilayer polyester film.
In the present invention, a substrate in which a sub-resin coating layer of a thermosetting resin is laminated on one surface of the substrate main body on which the contents are not contacted can be used.

According to the present invention, a nonporous anodic oxide film having a specific porosity and thickness, a specific coating amount of a silane-based coupling agent, and a resin coating layer of a thermoplastic resin having a specific range of thickness are provided on the substrate body. Since it is laminated, the can is constructed using the aluminum plate of the present invention for general cans, and even if the can is filled with highly corrosive contents, the adhesion of the resin coating layer does not decrease. There is an effect that can provide a general can excellent in corrosion resistance. Since the barrier property of the resin coating layer is greatly influenced by the crystallization rate, a sufficient barrier property can be secured by setting the crystallization rate to 40% or more.
Further, the present invention provides a substrate body with a nonporous anodic oxide film having a specific porosity and thickness, a specific coating amount of a silane coupling agent, and a resin coating layer of a thermoplastic resin having a specific range of thickness. Since it is laminated, it can suppress corrosion caused by roll scratches and foreign matter contamination during bonding and contamination due to poor bonding, and it does not contain harmful substances in the processing liquid used for the base treatment or the film to be formed. A general can excellent in safety and environmental protection can be provided.

In the first embodiment of the thermoplastic resin-coated aluminum plate for a general can according to the present invention, the aluminum plate A has no holes on the upper and lower surfaces of the substrate body 1 made of aluminum or an aluminum alloy, as shown in FIG. A porous anodic oxide film 2 is formed, a coupling layer 3 made of a silane coupling agent is formed on the outer surface side of the nonporous anodic oxide film 2, and a thermoplastic resin is formed on the outside of the coupling layer 3. The resin coating layer 5 is formed.
Further, in the second embodiment of the thermoplastic resin-coated aluminum plate for general cans according to the present invention, the aluminum plate B is formed on the upper and lower surfaces of the substrate body 1 made of aluminum or aluminum alloy as shown in the cross-sectional structure of FIG. A nonporous anodic oxide film 2 is formed, a coupling layer 3 made of a silane coupling agent is formed on the outer surface side of these nonporous anodic oxide films 2, and one (upper side in FIG. 2) coupling layer A resin coating layer 5 made of a thermoplastic resin is formed on the outside of 3, and a secondary resin coating layer 6 made of a thermosetting resin is formed on the outside of the other coupling layer 3 (the lower side in FIG. 2). It has been configured.

  The aluminum or aluminum alloy constituting the substrate body 1 means pure Al or Al alloy. Specifically, pure aluminum-based 1000 series, Al-Mn-based 3000 series alloys, Al-Mg-based 5000 series alloys and the like specified by JIS are listed, but not limited to these alloys. The thickness of the substrate body 1 varies depending on the application, but a substrate having a thickness of about 0.1 to 0.5 mm can be used.

  The nonporous anodic oxide film 2 formed on the outer surface side of the substrate body 1 can be formed by electrolytic treatment using aluminum as an anode in an electrolyte solution having low film solubility. Examples of the electrolyte include alkali metal salts, borates, silicates, tartrate, phosphates, and the like. Even with sulfuric acid having high film solubility, if the electrolytic treatment is stopped before the pores grow to become a porous film, the porosity can be lowered to the target range. The thickness of the anodic oxide film can be adjusted by the concentration and temperature of the electrolytic solution, the current and voltage during electrolysis, and the electrolysis time, and the porosity can also be controlled by these conditions.

The porosity of the nonporous anodic oxide film 2 is preferably 20% or less.
When the porosity of the nonporous anodic oxide film 2 is low, the treatment liquid component contained in the pores is small, and the treatment liquid component contained in the pores is not easily released to the outside by heating at the time of forming the resin layer. Moreover, since the adhesion area with respect to the resin layer of the nonporous anodic oxide film 2 becomes large, adhesiveness with a resin layer improves.
The thickness of the nonporous anodic oxide film 2 is preferably in the range of 40 nm to 300 nm.
If the nonporous anodic oxide coating 2 is thin, the uniformity and corrosion resistance of the coating are inferior, and if the nonporous anodic oxide coating 2 is thick, cracks occur during molding processing, and the work adhesion and corrosion resistance decrease. Among these ranges, it is more preferable to use a range of 50 nm to 200 nm.

The chemical structure of the silane coupling agent constituting the coupling layer 3 is represented by the following formula (1), for example.
Examples of the organic functional group include an amino group, a vinyl group, an epoxy group, and a methacryl group, and examples of the inorganic functional group include an ethoxy group and a methoxy group. The organic functional group is bonded to the organic substance, the inorganic functional group is bonded to the inorganic substance, or the silane coupling agents, and high adhesive strength is obtained. However, it is necessary to select an organic functional group that matches the type of organic matter from the viewpoint of compatibility, etc., and it is recommended that a silane coupling agent having an amino group as the organic functional group is most suitable for polyester resins. The inventor found out. Moreover, since the silane coupling agent having an amino group is easily soluble in water, there is an advantage that it is excellent in workability when diluted. Examples of the silane coupling agent having an amino group include γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β (aminoethyl) γ-aminopropyltriethoxysilane, and the like.
The silane coupling agent is applied by diluting with a volatile solvent such as water or alcohol. Examples of the application method include, but are not limited to, a dipping method, a spray method, and a roll coating method.
_{Y- (CH 2) -SiX 3 ...} (1) formula, Y: Organic functional group, X: Hydrolytic group

The coating amount of the silane coupling agent constituting the coupling layer 3 is in the range of 0.1-100 mg / ^{m 2} is preferred.
Since the silane coupling agent crosslinks the nonporous anodic oxide film 2 and the resin coating layer 5, the adhesion is improved. If the coating amount is less than 0.1 mg / m ² , uneven coating tends to occur, and the above effect cannot be obtained. When the coating amount exceeds 100 mg / m ² , cohesive failure of the coupling layer 3 is likely to occur, and the adhesion is deteriorated. A more preferable coating amount is in the range of 1 to 50 mg / m ² .

  The thermoplastic resin constituting the resin coating layer 5 is not particularly limited, and examples thereof include polyester resins, polypropylene resins, polyamide resins, and copolymerized polyester resins. From the viewpoint, a polyester resin is preferable. Specifically, a resin film obtained by biaxially stretching these resins is preferable from the viewpoint of handling properties. As this film, either a single layer or a multilayer of two or more layers made of the same or different resins can be selected, but it is more preferable to use a two-layer film having a layer having a low melting point on the side in contact with the aluminum surface. It is preferable because adhesion can be secured at a low temperature.

As a method for laminating the film constituting the resin coating layer 5, there is a method in which an aluminum plate is preheated by a heating band, the film is pressure-bonded to the aluminum plate using a pressure roll, and then heated by the heating band. Examples of the heating device include a heat roll, an electric furnace, a gas oven, an induction heating device, and an infrared heating device, but a non-contact heating device is preferable in order to maintain the appearance. In particular, an induction heating apparatus capable of heating to a predetermined temperature in a short time is preferable.
The crystallization ratio of the film can be adjusted by the stretching ratio of the film, the heating temperature and heating time after lamination, and the cooling rate. In particular, it can be easily changed by the heating temperature after lamination, and the crystallization rate decreases when the film is close to the melting point of the film, and the crystallization rate rapidly decreases when the melting point of the film is exceeded. However, if the heating temperature is lowered in order to reduce the crystallization rate of the film, the resin is insufficiently melted and sufficient adhesion cannot be obtained.

The thickness of the resin coating layer 5 is preferably in the range of 8 to 100 μm.
If the resin coating layer 5 of the thermoplastic resin coated on the aluminum substrate body 1 is thin, sufficient barrier properties cannot be obtained and the incidence of pinholes is increased. For example, when a film is bonded to the substrate body 1 by roll compaction, if the resin coating layer 5 is thin, foreign matter is present around the roll, or foreign matter is scratched by the foreign matter when pressed against the film. There is a risk of forming through holes. Therefore, the thickness of the resin coating layer 5 needs to be about 8 μm. On the other hand, if the resin coating layer 5 is too thick, heat is not easily transmitted to the entire resin coating layer 5 during lamination to the substrate body 1, and adhesion is reduced. In addition, the workability may be reduced.
When the resin coating layer 5 is a film, the crystallization rate is preferably 40% or more.
The crystallization rate of the film greatly affects the barrier property, and if the crystallization rate is lowered, the barrier property is lowered.

  In the case where a container such as a can is configured using the aluminum plate B of the second embodiment according to the present invention, when the auxiliary resin coating layer 6 is configured with a thermosetting resin coating on a surface that does not contact the contents, A method in which a thermoplastic resin is laminated on the surface in contact with the contents to form the resin coating layer 5, and then a sub-resin coating layer 6 of a thermosetting resin is coated on the surface not in contact with the contents, or thermosetting There is a method of forming the resin coating layer 5 by laminating a thermoplastic resin after coating the secondary resin coating layer 6 of the functional resin. The former is a method of forming the thermoplastic resin previously formed by increasing the baking temperature during coating. Since the crystallization rate of the resin film may be lowered, it is preferable to heat at a temperature lower than the melting point of the thermoplastic resin.

The thermosetting resin constituting the sub-resin coating layer 6 is preferably a polyester-based or epoxy-based resin from the viewpoint of content resistance, corrosion resistance, workability, and retort resistance. In order to impart adhesiveness and lubricity to these resins, polyolefin resins and synthetic oils may be added.
These resins are applied onto the coupling layer 3 on the front side or the back side of the substrate body 1 by a conventional method such as a dipping method, a spray method, or a roll coating method, and are baked at a temperature of 180 to 250 ° C. The final sub resin coating layer 6 can be obtained.

  The aluminum plate A or the aluminum plate B configured as described above is used as a container such as a can for storing highly corrosive contents such as chemicals, paints, seasonings and oils, or as a container lid such as a can lid. Can be used. If these aluminum plates A and B are provided with the resin coating layer 5 having an appropriate thickness on the surface side that comes into contact with the contents and having no defects such as pinholes, aluminum or There is no fear that the substrate body 1 made of an aluminum alloy corrodes, and a container having excellent corrosion resistance can be provided. In addition, since the treatment liquid and coating agent used for production in the anodized film 2 and the coupling layer 3 which are the bases of the resin coating layer 5 do not contain harmful substances, the safety management, hygiene and environmental protection are also improved. be able to.

A JIS 5052 aluminum alloy is rolled into an aluminum plate with a thickness of 0.3 mm, degreased and washed with caustic soda at 50 ° C. for 10 seconds, neutralized with 5% nitric acid at room temperature, and then the aluminum plate is made into an anode, carbon Electrolytic treatment was performed using the plate as a cathode. As the electrolytic solution, borate, silicate, phosphate, and sulfuric acid were used, and the thickness and porosity of the anodized film obtained were adjusted depending on the concentration, electrolysis time, electrolysis voltage, and the like. Further, chromate treatment was performed on some aluminum plate material samples so that the Cr amount was 15 mg / m ² .
For the aluminum plate material sample on which the anodized film was formed, a silane coupling agent having an organic functional group of amino group and epoxy group was used, and a predetermined amount was applied to the surface of each sample by roll coating.

Next, for each aluminum plate material sample, a resin coating layer is formed using a two-layer polyester film and a single-layer polyester film as the resin film to be coated. The bilayer polyester film is a biaxially stretched film obtained by copolymerizing ethylene terephthalate and isophthalate, and includes an adhesive layer on the side in contact with the aluminum plate (melting point 230 ° C.) and an orientation layer on the side in contact with the aluminum plate (melting point 260 ° C.). It has a two-layer structure, the adhesive layer has a thickness of 1 to 2 μm, and the alignment layer has an arbitrary thickness. The single-layer polyester film is a biaxially stretched film having a melting point of 250 ° C.
The aluminum plate obtained by applying the surface treatment of the base was heated to 170 ° C. with a heat roll, and then the material described above and the resin film having a laminated structure were pressure-bonded with a pressure roll at a linear pressure of 18 kg / cm ² . Subsequently, it heated and cooled with the high frequency induction heating apparatus, and formed the resin coating layer. The crystallization rate of the film here was adjusted by the temperature during the heat treatment.
Moreover, the aluminum plate material which performed the chromate process did not form an anodic oxide film, but the state which does not apply | coat a silane coupling agent WHEREIN: Only the film was crimped | bonded and it was set as the sample.

"Evaluation methods"
(1) Porosity of the anodic oxide film The surface of the anodic oxide film was observed with a scanning electron microscope at any 10 points of 50,000 times (minimum viewing area of 2.0 μm ² ) or more, and the area ratio of the holes was taken as an average value. Asked.
(2) Thickness of anodized film After the surface of the anodized film was cut with a super microtome equipped with a diamond blade, the cross section was observed with a transmission electron microscope and the film thickness was measured.
(3) Film Crystallization Rate First, the density ρ of the film before pressure bonding was measured with a density gradient tube, and substituted into the following equation to determine the crystallization rate C. C = (ρ−1.335) / (1.455−1.335) × 100
Next, the (100) crystal peak intensity appearing in the vicinity of 2θ = 26 ° of the film before and after pressure bonding is measured by X-ray diffraction. The strength of the film before pressure bonding is Ia, the strength of the film after pressure bonding is lb, and the crystallization rate C ′ is obtained from the following equation. C ′ = (Ib / Ia) × C

(4) Adhesiveness The sample whose edge was masked was immersed in toluene at 380 ° C. for 7 days, then subjected to DuPont impact processing so that the resin-coated surface became convex, and the tape was peeled off, and the peeled state was evaluated.
O: No peeling, Δ: Partial peeling, ×: Large peeling (5) Corrosion resistance A sample subjected to DuPont impact processing so that the resin-coated surface is convex, and masked at the end, is placed at 500 ° C. in a 5% NaCl aqueous solution. It was immersed for 7 days and evaluated by the corrosion state of the processed part.
O: No corrosion, △: Partial corrosion, ×: Most corrosion

(6) Presence / absence of pinholes Samples were cut into 100 mm squares, the end portions were masked, and 10 copper sulfate tests were conducted for each level. Evaluation was based on the number of discolored spots.
O: Less than 5, Δ: 5 or more and less than 20, ×: 20 or more In the production conditions for producing the aluminum plate sample, the electrolyte type, the porosity (%) of the anodic oxide film, the anode The thickness of the oxide film (μm), the coating amount of the silane coupling agent (mg / m ² ), the film thickness (μm), and the film crystallization rate (%) are shown in Table 1 below.
Moreover, each evaluation result described in the previous (1)-(6) about the previous aluminum plate sample is described in Table 2 below.

Sample No. 2 in Table 1 is a sample with a porosity set to 18% and a high porosity, but it was satisfactory for all the properties of adhesion, corrosion resistance, and pinholes. On the other hand, the sample No. 13 of the comparative example is a sample having a porosity of more than 20% and 25%, and the adhesion of the sample is greatly lowered and the corrosion resistance is also lowered.
In addition, all of sample Nos. 1 to 12 in Table 1 were formed with a nonporous anodic oxide film having a porosity of 20% or less and a film thickness in the range of 40 to 300 nm, and the silane coupling agent was 0. Aluminum coated with a thermoplastic resin having a thickness of 8-100 μm, coated in the range of 1-100 mg / m ² , but having good adhesion and corrosion resistance and having no pinhole film A plate was obtained.

Sample No. 14 is a sample in which the anodized film is thickened, and sample No. 15 is a sample in which the anodized film is made too thin. However, increasing the thickness of the anodized film significantly reduces the adhesion and reduces the corrosion resistance. When the anodic oxide film was made too thin, the corrosion resistance was greatly lowered and the adhesion was also lowered.
Sample No. 16 is a sample in which the coating amount of the silane coupling agent is excessively increased, and sample No. 17 is a sample in which the amount of the silane coupling agent is excessively decreased. .
Sample No. 18 was a sample in which the film was made too thick, but the adhesion was greatly lowered and the corrosion resistance was also lowered. Sample No. 19 was an example in which the film was made too thin, but pinholes were generated and the corrosion resistance was greatly reduced. Sample No. 20 is an example in which the crystallization rate of the film was lowered, but the corrosion resistance was lowered and pinholes were generated somewhat.

Sample No. 21 was an example in which no anodic oxide film was provided and no silane coupling agent was applied, but the film adhesion was poor.
As described above, a nonporous anodic oxide film having a porosity of 20% or less and a film thickness of 40 to 300 nm is formed, and a silane coupling agent is applied in a range of 0.1 to 100 mg / m ^2. It has been found that a sample obtained by removing any one of the above conditions has insufficient characteristics among adhesion, corrosion resistance, and presence / absence of pinholes.

FIG. 1 is a cross-sectional view showing a first embodiment of an aluminum plate according to the present invention. FIG. 2 is a cross-sectional view showing a second embodiment of an aluminum plate according to the present invention.

Explanation of symbols

A, B: aluminum plate, 1 ... substrate body, 2 ... anodized film, 3 ... coupling layer,
5 ... Resin coating layer, 6 ... Sub resin coating layer.

Claims (5)

A nonporous anodic oxide film having a porosity of 20% or less and a film thickness of 40 to 300 nm is formed on at least one surface of a substrate body made of aluminum or an aluminum alloy, and silane is formed on the nonporous anodic oxide film. A coupling agent is applied in the range of 0.1 to 100 mg / m ² , and a resin coating layer made of a thermoplastic resin having a thickness of 8 to 100 μm is formed on at least one surface of the substrate body. A thermoplastic resin-coated aluminum plate for general cans.   The thermoplastic resin-coated aluminum plate for general cans according to claim 1, wherein the silane coupling agent has an amino group.   The thermoplastic resin-coated aluminum plate for beverage can caps according to claim 1 or 2, wherein the crystallization ratio of the at least one resin coating layer is 40% or more.   The general can according to any one of claims 1 to 3, wherein the resin coating layer made of a thermoplastic resin formed on at least one surface of the substrate body is made of a single-layer or multi-layer polyester film. Thermoplastic resin coated aluminum plate. 5. The general substrate according to claim 1, wherein a sub-resin coating layer of a thermosetting resin is laminated on one surface of the substrate main body on the side where the contents are not contacted. Thermoplastic resin aluminum plate for cans.

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