JP4899745B2 - Resin film coated metal can - Google Patents

Description

  The present invention relates to a resin film-coated metal can, and more particularly, to a resin film-coated metal can for beer and other sparkling beverages.

In carbonated beverages using fermentation, such as beer and sparkling wine, it is said that the state that the liquid surface is poured so that the foam covers it is delicious. And by covering the liquid level with foam, it prevents the carbonic acid and flavor components in the contents from falling out, prevents the contents from deteriorating due to air oxidation, and maintains the taste and aroma of beverages that are easily altered. It is said to be effective. Moreover, since the bitter component of beer aggregates in foam, there is also an effect that the taste of parts other than foam becomes mellow. Therefore, when tasting beer, an effort is made to pour the beer liquid surface so that the foam is adequately covered.
When drinking beer by pouring into a glass from a bottled beer, the air is entrained during the pouring, and the carbon dioxide gas in the beer is liable to foam, so that sufficient foaming occurs and the above-described effects can be expected. However, in the case of canned beer, in many cases, the opening of the can is not moved to the cup, but it is directly drinkable with the can, so foam does not occur and the effect of enhancing the taste like the bottled beer described above is expected. Can not. Therefore, even in cans used for sparkling beverages such as beer, many attempts have been made to enhance the taste by generating bubbles when opened and drink.
For example, attempts have been made to generate bubbles when opened by devising the material and shape of the can. Patent Documents 1 to 3 describe a method in which irregularities are provided on the inner surface of a can and bubbles are generated starting from the irregularities.
Japanese Patent Laid-Open No. 5-97149 JP 2001-180671 A JP-A-2005-41217

  If fine irregularities are present on the inner surface of the can, it can be a starting point for foam generation. For example, when beer is poured into a container with fine irregularities on its surface, such as a ceramic cup, a phenomenon in which a large amount of foam is generated is observed. However, this is a phenomenon in which bubbles adsorbed in the irregularities on the inner surface of the container before filling with beer and bubbles are generated, and in such a container with fine irregularities on the surface If a lid is closed and sealed after filling with a beverage, and the lid is opened after a while, there is often little foam. This is because the air that becomes the starting point of the bubbles adsorbed on the irregularities on the inner surface of the container is filled and dissolves in the beverage for a while, and the core for generating bubbles disappears. Therefore, in the methods described in Patent Documents 1 and 2, since foam is generated by providing irregularities on the inner surface of the can, the foam is hardly generated when the can is opened after a while after being filled with beer. End up.

In Patent Document 3, by generating a lot of very fine holes on the inner surface of the can, it has succeeded in generating foam even when the can is opened after a while after filling the can. Since the surface energy in foam generation can be reduced in fine pores, the core of foam due to carbonic acid in beer is generated, and air that is the starting point of foam generation is not necessary. As a result, bubbles can be generated even after the air adsorbed on the inner surface of the can after being dissolved in the beer.
However, in the method of Patent Document 3, fine voids are generated by adding fine particles such as silicon oxide to the surface of the inner surface of the can and generating fine voids and cracks around the particles in the can molding. Therefore, the size and amount of the holes are difficult to control depending on the molding method. Even if an appropriate amount of pores is generated, the amount of bubbles generated is not so large due to the high surface energy. In order to generate a large amount of bubbles, the amount of pores on the surface must be very large. In addition, it is difficult to produce a large number of such holes on the inner surface, and manufacturing is difficult, and voids and cracks tend to be the starting point of film defects.

  The present invention has been made in view of such circumstances, and the pores from which bubbles are generated are stably generated without greatly changing the can manufacturing process, have no problems such as film defects, and have no complicated operations. An object of the present invention is to provide a resin film-coated metal can excellent in foaming property and foam holding property, which can generate fine bubbles by simply opening the can and enhance the taste of the beverage.

In order to solve the above-mentioned problems, the present inventors have intensively studied paying attention to the generation of holes. As a result, the following has been found and the present invention has been completed.
With the aim of generating fine pores on the film surface without adding fine particles, the additive to the resin film was devised to control the generation of pores on the film surface and the surface free energy. In a can coated with a film containing 0.01 to 1 part by weight of at least one kind of silicone resin and polyolefin resin in an amount of 0.01 to 1 part by weight with respect to 100 parts by weight of the film, foaming is very good, and only the can opening operation is sufficient. It was found that foaming properties can be obtained. In order to obtain sufficient foamability with only a can opening operation with good foamability, there is an appropriate size and amount of pores, and there is a relationship between foamability and surface free energy. It was also found that the foaming property was further improved by defining the surface free energy.

The present invention has been made based on the above findings and has the following characteristics.
[1] A metal can in which a polyester resin film is laminated on the inner surface of the can or the inner and outer surfaces of the can, the film on the inner surface of the can being a single layer or a multilayer, and the outermost film layer on the inner surface of the can being a silicone A polyester resin film containing 0.01 to 1 part by weight of at least one of a resin and a polyolefin-based resin with respect to 100 parts by weight of a polyester resin, and the surface free energy of the inner surface of the can is 20 to 35 mN / m In addition, the polar component of the surface free energy on the inner surface of the can inner surface is 5 mN / m or less, and the surface of the film on the inner surface of the can has 10 to 10 holes per 1 mm ^{2 with} a pore diameter of 0.5 to 10 μm. A resin film-coated metal can for sparkling beverages , characterized in that there are -10 ⁵ .

  As described above, according to the present invention, it is possible to obtain a resin film-coated metal can excellent in foaming property and foam holding property while having good corrosion resistance. And the void | hole used as the starting point of bubble generation | occurrence | production is stably produced without changing a can manufacturing process largely, and there are no problems, such as a film defect. As a result, it is possible to generate fine bubbles just by opening the can without complicated operations, and to enhance the taste of the beverage.

Hereinafter, the resin film-coated metal can of the present invention will be described in detail.
The resin film-coated metal can targeted by the present invention is a metal can obtained by laminating a polyester resin film on the inner surface of the can or the inner and outer surfaces of the can.
The film on the inner surface of the can is a single layer or multiple layers from the viewpoint of appropriate foaming, and the outermost layer of the film on the inner surface of the can is made of at least one of a silicone resin and a polyolefin resin. a polyester resin film containing 0.01 to 1 parts by weight per 100 parts by weight of the resin, furthermore, to the can inner surface side of the film surface, pore area 1 mm ² per pore size 0.5 to 10 [mu] m 10 to 10 There are ^five . Such a regulation on the inner surface side of the can is an important requirement in the present invention. These will be described in detail below.

On the inner surface side of the film surface, first pores having a pore diameter 0.5~10μm exists 10 to 10 ⁵ cells per area 1 mm ^2, and the pores defined in the present invention, contact with the contents of the can inner surface side These are pores generated on the surface of the film and do not include those penetrating the film or those generated inside the film or on the metal side. The depth of the holes is at most about 5 μm. The diameter is the average of the major and minor diameters of the pores generated on the film surface. Although there are large and small pores as described above, pores having a pore diameter of 0.5 to 10 μm defined in the present invention are most likely to generate bubble nuclei in the pores. Further, among these, those having a pore diameter of 1 to 5 μm have a particularly high foaming effect.
Pores of the pore diameter 0.5~10μm is required to be present 10 to 10 ⁵ up to per area 1 mm ^2. If the number of pores having a pore diameter of 0.5 to 10 μm is less than 10, the amount of bubbles generated is insufficient. The number is preferably 100 or more per 1 mm ² . On the other hand, if the number exceeds 10 ⁵ , the generation of bubbles may be excessive depending on the contents and the stability of the bubbles will decrease, so the upper limit of the number of pores must not exceed 10 ^{5 at the} maximum per area of 1 mm ^2. is there. More preferably not exceed 10 ^4.
The voids are generated in a can laminated with a film added with a specific resin. So, even if there are holes on the inner surface of the can before molding into the shape of the can, holes may be generated by molding, but by mixing a specific resin, fine dents are formed in the resin It can be expected that when it is generated and becomes a void by processing of can molding, or when a void is formed between the resins during can molding, it becomes a void after can molding.
In addition, resin film-coated metal cans have places with a lot of pores and places with few holes depending on the molding means. In the case of two-piece cans, it is generally more in the portion closer to the top of the can body than the bottom of the can. It is. In that case, the number of holes in the present invention is defined by the portion of the can body having the largest number of holes.
The number of vacancies can be determined by observing the film surface with an existing observation device such as an optical microscope or an electron microscope, and counting the number in a specified area or automatically counting by computer image processing. Further, the number of holes in an area of 1 mm ² may be calculated by a method such as multiplying the number in the range of 100 μm × 100 μm by 100, in addition to counting the total number in the range of 1 mm × 1 mm.
The outermost film layer on the inner surface of the can is a polyester resin film containing 0.01 to 1 part by weight of at least one kind of silicone resin and polyolefin resin with respect to 100 parts by weight of the polyester resin.
From the viewpoint of the shape and density of the generated holes, the film outermost layer is defined as described above. When 0.01 part by weight or more is added, the amount of pores necessary for foaming is generated. More desirably, the addition amount is 0.1 parts by weight or more. On the other hand, the upper limit is 1 part by weight, and if it exceeds that, the amount of generated pores is too much, and the physical properties such as film processability are impaired, and furthermore, the adsorption of flavor components by the added resin cannot be ignored. Deterioration is likely to occur or foam tends to be generated too much, and large unstable bubbles that are not fine bubbles are likely to be generated, which may impair the flavor of beer. Preferably, it is 0.5 parts by weight or less.

  As the silicone resin, dimethyl silicone, methylphenyl silicone, and those obtained by modifying fluorine or amino groups thereof can be used. In particular, those using polymer silicone or those in which polymer silicone is dispersed in polyethylene resin or PBT resin are preferable. For example, BY27 manufactured by Toray Dow Corning Co., Ltd. is preferable.

  Polyolefin-based resins are resins obtained by vinyl polymerization of molecules containing carbon-carbon double bonds in the molecule, such as ethylene and propylene, and include polyethylene, polypropylene, polybutene, polymethylpentene, polystyrene, etc. . In particular, a polyethylene resin is preferable because it is appropriately dispersed in a polyester resin, and a high-density to low-density one, a linear low-density polyethylene resin, or a mixture of a plurality of them is preferable. Further, a polyethylene resin having a MFR of 5 to 20 or a linear polyethylene resin is particularly suitable from the viewpoint of dispersion in the polyester resin.

The resin film-coated metal can is a film laminated metal plate obtained by laminating a resin film containing a polyester resin as a main component on at least one side, and the resin is molded into the shape of the can so that the resin is on the inner surface side of the can. It is preferable from the viewpoint of durability and productivity with respect to the contents.
As polyester-based resin film, it has excellent adhesion to the metal plate, there is no film deterioration or adhesion degradation due to deformation and friction due to film elongation and compression due to molding process at the time of can making, after can making Films coated by heating such as drying, printing and baking, retort sterilization, etc. will crystallize or deteriorate, and will not cause film peeling, shrinkage, cracks, pinholes, etc. Performance such that the film does not peel off or peel off, does not cause corrosion or peeling when in contact with various contents, and the film does not become cloudy. Furthermore, it is also required that the scent component of the contents of the can is adsorbed to the film, and that the flavor of the contents is not impaired by the elution component and odor of the film.
Satisfying the above requirements, as the polyester used in the present invention, various aromatic dicarboxylic acids and aliphatic dicarboxylic acids are optionally polymerized as the acid component, and various aliphatic diols and aromatic diols are optionally polymerized as the glycol component. Copolymerized ones are used, and two or more types of copolymerized polyester resins having different compositions are used.
Furthermore, from the viewpoints of foaming properties, other flavor properties, impact resistance, etc., the size and density of the pores formed on the film surface after can molding are important, and the composition of the resin film also contributes to the generation of such pores. Therefore, it is necessary that the resin film has appropriate processability and strength. As a composition of such a polyester resin, the acid component is 5 to 18 parts by weight of isophthalic acid and the rest is terephthalic acid. The one consisting of is optimal. By copolymerizing isophthalic acid with terephthalic acid in an appropriate amount, crystallization is suppressed and processability is improved compared to those of terephthalic acid alone or with a low copolymerization composition, process defects are less likely to occur, and mechanical performance is degraded. Is suppressed. If it is less than 5 parts by weight of isophthalic acid, such an effect is insufficient and mechanical performance may be inferior.
On the other hand, if the isophthalic acid component exceeds 18 parts by weight, the melting point is low and thermal degradation occurs during can processing, which may cause large cracks and impact degradation. Here, the balance being terephthalic acid means that at least 95% or more of the remaining components are terephthalic acid, and the amount of other acid components shown below is less than 5%. Moreover, when it has a several layer structure of two or more layers, it is appropriate for the outermost layer to have this composition.

The surface free energy of the can inner surface film surface is 20 to 35 mN / m
In the film having fine pores, it was found that the higher the foaming property, the lower the surface energy. On the other hand, the film surface energy tends to decrease due to the addition of polyolefin resin or silicone resin. In particular, the foaming property tends to increase when the surface energy of the film is reduced to an appropriate region by the addition of the above-mentioned MFR5-20 polyethylene resin or linear polyethylene resin, or a silicone resin using a high molecular weight silicone. there were. It is considered that these resins are appropriately dispersed in the polyester resin and contribute to the formation of appropriate fine pores, and also greatly promote the foamability by reducing the surface energy.
The mechanism of the relationship between surface energy and foaming properties is currently under investigation. For one thing, when the surface free energy of the film is small, the bubble surface has a concave shape when bubbles are generated in the pores. In this case, since the surface pressure applied to the bubbles is reduced by 2γ / r, it is considered that there is an effect that the bubbles are easily generated.
In addition, if the surface free energy is large and it is easy to get wet with the contents, the gas that becomes the starting point of the bubbles adsorbed on the surface of the container tends to disappear and the generation of bubbles is reduced. On the other hand, since the gas is easily adsorbed, there is an effect that when a bubble grows large and moves to the surface, a part is left on the surface and the bubble is generated again. In this way, bubbles are believed to increase by reducing the surface free energy at the surface where the voids are present.
In order to obtain the above effects, the surface free energy is preferably 20 to 35 mN / m. When the surface free energy of the outermost layer of the film is 35 N / m or less, very remarkable foaming property occurs. When the surface free energy is higher than 35 mN / m, the stability of bubble nuclei due to the reduction of the surface free energy is lowered, and the foaming property may be reduced. On the other hand, if the surface free energy is 20 mN / m or less, the film may not be produced stably.

Here, a method for measuring the surface free energy will be described. The surface free energy γs of the laminated metal can is divided into two components as follows.
γs = γsd + γsh
γsd is a dispersion component caused by van der Waals force or London force in the surface free energy, and γsh is a polar component related to forces such as hydrogen bonding of a polar group or acid / base interaction. When the contact angle when the liquid is dropped onto the surface of the laminated metal plate is θ, the surface free energy of the liquid is γl, the dispersion component is γld, and the polar component γlh, these satisfy the following relationship.
(Γsh) ^1/2 = − (γld / γlh) ^1/2 * (γsd) ^1/2 + γl / (γlh) ^1/2 * (1 + cos θ) / 2
Therefore, five liquids (pure water, glycerol, formamide, ethylene glycol, dimethylglycolol) having known surface free energies (γl, γlh, γld are known) are dropped on the surface of the measurement object (laminated metal plate), The contact angle θ of each liquid is measured and determined (humidity: 55 to 65%, temperature 20 ° C.). Then, the contact angle θ measured for each of the five liquids and the values of γl, γlh, and γld of each liquid are substituted into the above formula, and γsd and γsh are obtained by least square fitting. The surface free energy γs of the laminated metal plate is represented by the sum of γsd and γsh.

  In order to obtain a resin film surface having a surface free energy of 35 mN / m or less, the polyester resin has a high surface free energy of about 43 mN / m. As described above, the surface free energy is further reduced to a desired value by adding 0.1 part by weight or more. On the other hand, the upper limit of polyolefin resin or silicone resin is 1 part by weight as described above, and even if it is added in excess of it, the reduction of surface free energy is almost saturated and does not change, and it cannot be sufficiently dispersed in polyester resin. It is not suitable because it causes surface defects and uneven color tone. In addition, the adsorption of flavor components by polyolefin resin or silicone resin cannot be ignored, and the flavor deteriorates, and if a large amount of polyolefin resin is added, bubbles are likely to be formed too much, and large particles that are not fine bubbles are unstable. Bubbles are likely to occur, and the flavor of the beer may be lost and damaged. Preferably, it is 0.5 parts by weight or less. Further, it is needless to say that the foaming property is particularly improved by using the above-mentioned polyethylene resin of MFR5 to 20 or a linear polyethylene resin, or a silicone resin using a high molecular silicone.

  Furthermore, since the magnitude of the surface free energy is related to the wettability of beer on the surface of the resin film, a surface having a low surface free energy that is difficult to wet with beer is required. From this point, when the contact angle of beer in a resin film optimal for foaming with a surface free energy of 35 mN / m or less is converted to a water contact angle, it becomes 80 degrees or more, and if it is 80 degrees or more, foaming is promoted. If it is less than 80 degrees, the effect is small. Therefore, it is preferable that the water contact angle of the outermost layer of the resin film is 80 degrees or more.

The polar component of the surface free energy on the inner surface of the can inner surface is 5 mN / m or less The component of the beer liquid has a larger proportion of the polar component than the dispersed component. Is the most effective, and even if the total surface free energy γs is higher than 35 mN / m, the wetting of beer can be sufficiently reduced and the foaming property is improved if the polar component γsh is 5 mN / m or less. Therefore, the polar component of the surface free energy is preferably 5 mN / m or less for the outermost layer of the resin film.
In addition, the film on the inner surface side of the can may be a single layer or a multilayer.

As described above, by forming a metal plate coated with the resin film having the above composition so that the target resin film is on the inner surface of the can, pores having an appropriate size and density are formed on the film surface with controlled surface free energy. The resulting foaming properties are excellent, and the adhesion to the metal plate is excellent, and there is no deterioration of the film due to deformation, such as elongation or compression of the film due to molding during can making, and deterioration of adhesion due to friction. A can is obtained.
In addition, the film covered by heating such as drying after can-making, printing baking, retort sterilization treatment, etc. is prevented from crystallizing or deteriorating, thereby causing film peeling, shrinkage, cracks, pinholes, etc. In addition, a can is obtained in which the film is not cracked or peeled off by impact on the can, and further, the film does not corrode or peel off when in contact with various contents and the film does not become cloudy. Further, the scent component of the contents of the can is not adsorbed on the film, and the flavor of the contents is not impaired by the elution component or smell of the film.

On the other hand, the surface of the metal plate on the outer surface side of the can can also be used in a can as a double-sided laminated metal plate by covering the outer surface side with a film. It is also possible to perform can molding as a plate and then use it as a can by painting or printing as necessary.
As the film on the outer surface side, the same film as that on the inner surface side can be used, but considering the film cost, etc., a film that does not contain additives such as pores or polyolefin resins, or has a reduced amount of addition. It is preferable to coat. Regarding the resin type, it is possible to use the same polyester resin composition as that on the inner surface side, and a resin having a different composition may be used. However, when the inner surface film is an unstretched film, the outer surface side is also unstretched. When a film is used and the film on the inner surface side is a biaxially stretched film, it is preferable to use a biaxially stretched film on the outer surface side because the film physical properties on both surfaces are equivalent and defects during can molding are less likely to occur. Moreover, the film thickness of the outer surface side film is generally the same as or slightly thinner than the inner surface side.

Subsequently, the metal plate which laminates a resin film is demonstrated. Although the metal plate of this invention is not specifically limited, The metal plate which uses steel and aluminum as a raw material is preferable at the point of a moldability. In the case of a metal plate made of iron, in order to improve resin adhesion and corrosion resistance on the surface, an inorganic oxide film layer such as chromic acid treatment, phosphoric acid treatment, chromic acid / phosphoric acid treatment, electrolytic chromic acid treatment, You may provide the chemical conversion treatment coating layer represented by the chromium chromate process. Further, a spreadable metal plating layer, for example, a plating layer of nickel, tin, zinc, aluminum, gun metal, brass or the like may be provided. In the case of tin plating, 0.5 to 15 g / ^{m 2,} having a plating weight of the case of nickel or aluminum 1.8~20g / ^{m 2} is particularly preferable from the viewpoint of processability and resin adhesion. Such a metal plate has a thickness of usually 0.01 to 5 mm, preferably 0.1 to 2 mm. And the resin coating layer which laminated the resin composition layer of this invention mentioned above on the metal plate single side | surface or both surfaces is formed.
In the case of a metal plate made of steel, an electrolytic chromated steel plate is particularly preferable from the viewpoints of adhesion to the resin film of the present invention, corrosion resistance, and production cost. Metallic chromium amount of the metal chromium layer is suitably 50-200 mg / ^{m 2,} corrosion resistance is less than 50 mg / ^{m 2,} may post-process adhesion is insufficient, corrosion resistance exceeds 200 mg / ^{m 2,} after processing This is because the effect of improving the adhesion is saturated and the manufacturing cost is increased. Further, reckoned as metal chromium of chromium of chromium oxide is 3 to 30 mg / ^{m 2} is appropriate, may adhesiveness with less than 3 mg / ^{m 2} is inferior, color tone deterioration exceeds 30 mg / ^{m 2} This is because the adhesiveness is also poor.

In the present invention, a primer layer may be provided between the metal plate and the resin film in order to improve the adhesion between the resin film and the metal plate, as long as the effects of the present invention are not hindered. The resin film-coated metal can of the present invention is excellent in both the primary adhesion and post-processing adhesion of the resin layer and the metal plate, but in a severer corrosive environment or in an environment where better adhesion is required. A primer layer can be provided to provide characteristics according to requirements.
For example, when used as a metal can, filling with more corrosive contents causes the contents to enter the interface with the metal plate through the resin layer, corrode the metal plate, and deteriorate the adhesion to the film. there's a possibility that. In such a case, it is possible to prevent the resin layer from peeling off by providing an appropriate primer layer.

  As a method for producing a resin film-coated metal plate, a known method can be used. In particular, a resin film is pressed against a metal plate heated to a range of a melting point of a polyester resin from −150 ° C. to a melting point + 30 ° C. by a rotating roll. Is preferred.

Next, the resin film-coated metal can of the present invention will be described. The resin film-coated metal can of the present invention is formed by molding the above-described resin film-coated metal plate so that the resin film-coated surface is on the can inner surface side. Further, in the present invention, “can” refers to a case where any one or more of the can body, can lid and can bottom are used (including the case where all of them are used).
A known method can be used for the production of the resin film-coated metal can. Although it can be applied as a three-piece can with side seams, it is more preferably a seamless two-piece can, which is drawn and redrawn, bent and stretched by drawing and redrawing (stretching), and drawn and redrawed. It is possible to mold using bending / stretching / ironing, drawing / ironing, etc. In forming such as thinned deep-drawn cans and drawn irons (DI cans), which can bend and stretch by redrawing and / or ironing to thin the can body, the thinnest part of the can body The plate thickness is preferably reduced to 30 to 80% of the original metal plate, more preferably reduced to 40 to 60%.
The resin film-covered metal can of the present invention has a maximum number of pores having a particle diameter of 0.5 to 5 μm per 1 mm ² on the resin film surface on the inner surface of the can from the viewpoint of appropriate foaming. 10 to 10 are ^five existing set of cans, the pores become the starting point of the bubble generation.

As mentioned above, as the use of the obtained resin film-coated metal can, carbonated drinks, especially beverages using fermentation such as beer and sparkling liquor are used so that the characteristics of foaming when the filled drink opens can be maximized. It is preferable to fill and use for drinking. However, in such an application, when the resin film-coated metal can is filled with a beverage, foam may be generated and the filled beverage may overflow from the can. . Therefore, in this resin film-coated metal can, by cooling and filling the can or carbonated beverage to 8 ° C. or less, foam is less likely to be generated and foaming during filling can be suppressed. Desirably, it is better to cool both the can and the beverage. In addition, foaming can be further suppressed if the temperature is lower, and filling at 5 ° C., further 2 ° C. or lower is preferable.
Moreover, when filling the resin film-coated metal can with a carbonated beverage, foaming can be further suppressed by filling the can after wetting the inner surface of the can with a liquid. The liquid is preferably wetted with water, which is a component contained in a carbonated beverage, or ethanol in the case of an alcoholic beverage, or the beverage itself.
Further, since moderate foaming visually enhances the taste of beer, it is more preferable that the lid of the can is a full open type.

Resin films were prepared with the formulations shown in Table 1. The detailed manufacturing method and conditions for producing the resin film are as follows.
For Examples 1 to 5 and Comparative Examples 1 to 5, an ethylene terephthalate-ethylene isophthalate copolymer resin having a ratio of terephthalic acid to isophthalic acid of 90:10 (intrinsic viscosity 0.7 dl / g, Tg 70 ° C., Tc 170 ° C., Tm 230 The polyolefin resin or silicone resin was supplied to an extruder and extruded from a T-die with a single-screw extruder, and an unstretched film having a thickness of 26 μm was produced using a cooling drum. As the polyolefin resin, Hi-Zex 1300J as HDPE, Ultzex 2080C (both manufactured by Prime Polymer Co.) as LLDPE, and BY27 (manufactured by Toray Dow Corning) as the silicone resin were used. In addition, spherical silica having an average particle diameter of 2.5 μm was used as silicon oxide in the comparative example.
About Example 6, after making an unstretched film, it stretched | stretched 3 times longitudinally 3 times in the horizontal direction, biaxially stretched, and then heat-processed at 170 degreeC, and produced the biaxial stretched film.
For Examples 7 to 9 and Comparative Example 6, two single-screw extruders were used, and on one side, an ethylene terephthalate-ethylene isophthalate copolymer resin and an additive having a terephthalic acid and isophthalic acid ratio of 90:10 were used. The other unit is 85 parts by weight of an ethylene terephthalate-ethylene isophthalate copolymer resin having a 90:10 ratio of terephthalic acid and isophthalic acid, and 15 parts by weight of a zinc neutralized carboxylic acid-modified olefin resin (High Milan 1705, Mitsui DuPont Polychemical). A two-layer unstretched film containing an additive only in the upper layer was produced by supplying the mixture of the above and co-extrusion using a feed block type T die.
For Examples 10 to 12, two single-screw extruders were used, one of which was an terephthalic acid / isophthalic acid ratio of 90:10 ethylene terephthalate-ethylene isophthalate copolymer resin and an additive. Supplies a mixture of 85 parts by weight of an ethylene terephthalate-ethylene isophthalate copolymer resin having a 90:10 ratio of terephthalic acid to isophthalic acid and 15 parts by weight of zinc-neutralized carboxylic acid-modified olefin (High Milan 1705 manufactured by Mitsui DuPont Polychemical Co., Ltd.). After producing a two-layer unstretched film containing an additive only in the upper layer by coextrusion using a feed block type T die, the film is stretched three times in the horizontal direction and three times in the transverse direction, and then biaxially stretched at 170 ° C. A two-layer biaxially stretched film was produced by heat treatment.

  Further, as Examples 1 to 5, 7 to 9 and Comparative Examples 1 to 6, as non-stretched films having a thickness of 15 μm (ethylene terephthalate-ethylene isophthalate having a ratio of terephthalic acid to isophthalic acid of 90:10) A biaxially stretched film having a thickness of 15 μm (ethylene terephthalate-ethylene isophthalate copolymer resin having a ratio of terephthalic acid to isophthalic acid of 90:10) is used in Examples 6 and 10-12. did.

Subsequently, the resin film coated metal plate was produced by coat | covering the resin film obtained by the above on both surfaces of a metal plate. As the metal plate, tin-free steel (thickness 0.18mm, temper DR9, metal chromium layer 80mg / m ² , chromium oxide layer 15mg / m ² (metal chromium conversion) for thin-walled deep-drawn cans ( (Hereinafter abbreviated as TFS), and the resin film obtained as described above is thermocompression-bonded to both surfaces of each of the metal plates heated by the induction heating method, and then the resin film-coated metal plate is formed by a thermal bonding method in which it is quenched in water. Obtained.
About the resin-coated metal plate obtained as described above, a thinned deep drawn can was manufactured as follows, and the suitability of the thinned deep drawn can was evaluated.

<Can manufacturing>
The resin-coated metal plate was first-stage drawn and redrawn under the following conditions to obtain a thin-walled deep drawn can.
・ First stage blank diameter: 150-160mm
1st aperture stop: aperture ratio 1.65
-Re-drawing 1st re-drawing ... Aperture ratio: 1.25
Second re-drawing: Aperture ratio: 1.25
Curvature radius of die corner in redrawing process: 0.4mm
Wrinkle holding weight during redrawing ... 39227N (4000kg)
-Average thinning rate of the can body 50% of the thickness of the resin-coated metal plate before molding
-Neck / Flange Forming After trimming the open end of the can body, the neck part and the flange part were formed by spinning forming so as to match the size of the lid with a nominal diameter of 206.

<Evaluation of pores on surface of film and measurement of surface free energy>
Here, regarding the number of holes in the inner surface film of the thinned deep-drawn can, the part with the largest number of holes was found by observing with a SEM in the can body, and the film surface was observed with the SEM for that part. Then, the corresponding number in the range of 100 μm × 100 μm was counted at at least 10 locations on the surface of an arbitrary film, and the average value was multiplied by 100 to obtain the number of holes in an area of 1 mm ² . Moreover, the number of holes and the number of exposed particles were only counted from the surface where it was confirmed that the size was 0.5 to 10 μm. For reference, an example of an SEM photograph of the metal can inner surface is shown in FIG.
Further, regarding the surface free energy of the resin film and the can inner film, the surface free energy γs and its polar component γsh were measured by the method described in the text.

<Evaluation of beer can aptitude>
-Washing the inner surface of the can body (thinning ratio 50%) subjected to corrosion resistance strain relief heat treatment, pouring distilled water containing 1% sodium chloride into the can to 10 mm below the can opening, and into the solution A 6.3 V direct current was applied with the platinum electrode used as the anode and the can body as the cathode, and the flowing current value was measured and evaluated according to the following criteria. In addition, a pass is a thing of evaluation more than (circle).
Test result: Evaluation current value of 0.1 mA or more: × (poor)
Current value of 0.01 mA or more and less than 0.1 mA: Δ ↑
Current value 0.001 mA or more and less than 0.01 mA: ○ ↓
Current value less than 0.001 mA: ◎ (excellent)
・ After washing the inner surface of the can body (thinning ratio 50%) that has been subjected to foaming strain relief heat treatment, filled with beer (Sapporo black label), filled with carbon dioxide to an internal pressure of 0.1 MPa, and easily opened A can lid having a sex opening was provided by tightening to obtain a beer-filled can. The filled can was cooled at 5 ° C. for 120 hours, then opened in a room at 20 ° C., and the foamability of the beer surface after 10 seconds was evaluated according to the following criteria.
Test result: Evaluation foam does not completely cover the liquid level: x (poor)
Bubbles less than 2mm in thickness almost completely cover the liquid level: △ ↑
Bubbles with a thickness of 2 mm or more and less than 5 mm completely cover the liquid level: ○
Bubbles with a thickness of 5 mm or more and less than 10 mm completely cover the liquid level: ◎ ↓
Bubbles with a thickness of 10 mm or more completely cover the liquid level: ◎◎ (excellent)
・ After washing the inner surface of the can body (thinning ratio: 50%) that has been subjected to foam-relieving heat treatment and filling with beer (Sapporo black label), carbon dioxide is filled to an internal pressure of 0.1 MPa. A can lid having an openable mouth was provided by tightening to obtain a beer-filled can. After cooling the filled can for 120 hours at 5 ° C., the can was opened in a room at 20 ° C., and the time until foaming of the beer surface was broken in the liquid surface and was not completely covered was measured and evaluated according to the following criteria. .
Test result: Evaluation within 1 minute: × (Poor)
More than 1 minute to 5 minutes: △ ↑
More than 5 minutes to 10 minutes: ○
Over 10 minutes to 20 minutes: ◎ ↓
Over 20 minutes: ◎◎ (excellent)
The obtained results are shown in Table 1 together with the conditions.

  According to Table 1, in the example of the present invention, a resin film-coated metal can excellent in foaming property, foam holding property and corrosion resistance can be obtained. On the other hand, in the comparative example, one or more of foaming property and foam holding property is inferior. Furthermore, in Comparative Examples 5 and 6, the corrosion resistance is also inferior.

  The resin film-coated metal can obtained by the present invention can maintain a taste and aroma that have not been obtained so far by generating appropriate foaming at the time of opening, so that it can be fermented like juice, beer, sparkling liquor, etc. It is ideal as a carbonated beverage can.

It is a figure which shows an example of the SEM photograph of a metal can inner surface film surface. Example 1

Claims (1)

A metal can in which a polyester resin film is laminated on the inner surface or inner and outer surfaces of the can,
The film on the inner surface of the can is a single layer or multiple layers,
The outermost film layer on the inner surface of the can is a polyester resin film containing 0.01 to 1 part by weight of at least one kind of a silicone resin and a polyolefin resin with respect to 100 parts by weight of the polyester resin.
The surface free energy of the can inner surface film surface is 20 to 35 mN / m,
And, the polar component of the surface free energy on the inner surface of the can inner surface is 5 mN / m or less. Further, the film surface on the inner surface of the can has 10 to 10 pores per 1 mm ^{2 in} area of 0.5 to 10 μm. A resin film-coated metal can for sparkling beverages , characterized in that 10 ⁵ are present.

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