JP4830363B2 - Resin film-coated metal plate and resin film-coated metal can - Google Patents

Description

  The present invention relates to a resin film-coated metal plate and a resin film-coated metal can, and in particular, shows good processability and impact resistance, and particularly like carbonated beverages, especially beer and sparkling liquor. Resin film that has sufficient corrosion resistance and flavor as a container for filling highly demanding contents related to trace components, and has excellent foam generation characteristics such as foaming and foaming, which have a significant effect on quality. The present invention relates to a coated metal plate and a resin film-coated metal can.

  For metal cans, such as thin-walled deep-drawn cans and squeezed squeezed cans (DI cans), it prevents the deterioration of taste and flavor due to metal elution from metal plates, as well as the deterioration of contents. Therefore, a resin-coated metal plate provided with a resin layer on the inner surface of the can is generally used. As such a resin-coated metal plate, a metal plate coated with a thermoplastic polyester-based resin film has recently been used as an alternative to an epoxy-based coating layer that has been pointed out to be dangerous for environmental hormones.

  By the way, the resin film-coated metal can is often used for carbonated beverages such as juice and beer. However, when a resin film-covered metal can filled with a carbonated beverage and sealed is opened, there has been a problem that the contents are blown out from the opening and the contents are vented. On the other hand, Patent Literature 1 and Patent Literature 2 describe a method of reducing surface protrusions by containing particles having a small particle diameter in a resin film and reducing irregularities on the film surface after can molding. .

On the other hand, there is also an idea of actively generating bubbles to enhance the taste of carbonated beverages. For example, Patent Document 3 describes a polyester film that defines the degree of shape of particles contained in a resin. Patent Document 4 proposes a foamable liquid container in which a recess having a substantially V-shaped cross section is formed on the inner surface. Further, Patent Document 5 controls the size and density of particles in the resin and the base. The polyester film which prescribed | regulated the composition of the obtained polyester resin is described.
JP-A-6-238818 Japanese Patent Laid-Open No. 11-10724 JP-A-11-254625 Japanese Patent Laid-Open No. 5-97419 JP-A-2005-41217

  In carbonated beverages using fermentation, such as beer and sparkling liquor, foaming on the liquid surface suppresses the loss of carbonic acid and flavor components in the contents, and the contents deteriorate due to air oxidation. It has a great effect of preventing and maintaining the taste and aroma of beverages that are easily altered. In addition, since the foam part contains many bitter components of beer, there is an effect that the part other than the foam becomes mellow.

  However, since the techniques described in Patent Document 1 and Patent Document 2 have an effect of suppressing the generation of bubbles, it is not possible to expect an improvement in flavor due to the generation of bubbles as described above, and the taste is higher than that of a bottle or barrel filled. There was a problem that the smell was inferior.

  In Patent Document 3, the aim is to achieve both foamability and adhesiveness by adding particles having different shapes (flatness ratios) to the film. Without foaming sufficient to maintain the taste and fragrance, foaming properties are insufficient. Furthermore, since the part containing the particles serves as the starting point of generation of bubbles while serving as the adsorption point of the content component, the content flavor is lowered due to the adsorption of the flavor component to the container surface. Furthermore, there is a problem that it becomes a starting point of film cracking, which causes metal elution due to corrosion of the base metal and changes in taste and aroma.

  Patent Document 4 proposes a foamable liquid container in which a concave portion having a substantially V-shaped cross section is formed on the inner surface, but bubbles are very slowly generated only by a V-shaped hole, and defects in the resin are present. There is a possibility that problems such as corrosion resistance and flavor adsorption as a container may occur.

  In Patent Document 5, by controlling the size and density of the particles in the resin and defining the polyester resin composition, it is possible to generate dents suitable for the generation of foam, promote foaming, and have corrosion resistance and flavor properties. Although it was retained, some of the parts containing particles were defective during can molding, and were not satisfied with demands for strict corrosion resistance and flavor properties.

  The present invention has been made in view of such circumstances, and in carbonated beverages using fermentation such as beer and happoshu, while generating moderate foaming at the time of opening, it suppresses flavor adsorption to the container surface. In addition, by suppressing metal elution due to substrate corrosion, it has sufficient flavor and corrosion resistance as well as foaming and foam resistance as a container to fill strict quality requirements for trace components such as taste and aroma. An object is to provide an excellent resin film-coated metal plate and a resin film-coated metal can.

As a result of intensive studies in order to solve the above problems, the present inventors have found the following.
It has been found that the foaming property and foaming property are caused by the form of particles contained in the resin film coated on the metal plate, and the depressions or voids generated by the particles during can molding. However, on the other hand, such pores serve as adsorption points for the scent components of the can contents, and further, the adhesion to the metal plate is reduced, the occurrence of film cracks due to impact on the can, peeling, and contact with various contents It may cause corrosion and peeling at times. Thus, in order to promote the generation of foam, it is necessary to increase the amount of particles added, but on the other hand, increasing the amount added tends to cause a decrease in flavor and corrosion resistance due to adsorption of scent components. There was a problem.

  In order to improve the contradictory performance as described above, a new bubble generation mechanism is required regardless of the conventional idea. Therefore, further investigation was conducted. As a result, it has been found that by adding a polyolefin-based resin such as polyethylene or polypropylene resin together with the particles, sufficient foaming properties can be obtained even if the amount of particles added is kept low. And since it became possible to reduce the addition amount of particle | grains largely, it turned out that the bad influence which acts on flavor property and corrosion resistance is suppressed to the minimum.

  The effect of adding polyolefin is considered to be to reduce the surface free energy of the resin coated on the metal plate. When bubbles are generated on a smooth surface, generally the contact angle is large, that is, the surface tends to be generated more easily from the surface where the surface free energy is small and the contents are difficult to get wet. Since the surface pressure applied to the bubbles generated on the surface is expressed as 2γ / r (where γ is the surface tension and r is the bubble diameter), the pressure to compress the bubbles decreases as the surface free energy decreases, and the bubbles Since it becomes easy to grow stably, possibility that it will grow to the size of a bubble sufficient for the bubble diameter to grow large and to detach | desorb from the surface increases.

  However, when bubbles are generated from a gas dissolved in water, such as carbonated beverages, the energy for gas agglomeration is very large, so that uniform bubble nucleation is unlikely to occur on solid surfaces such as ordinary plastics. It is said. For this reason, bubbles are generated on the surface of a container for carbonated beverages, and not only the effect of reducing the surface free energy is sufficient, but a mechanism for reducing the energy for generating bubble nuclei is required. As a simple example, bubbles can be generated by introducing air bubbles by entrainment of air so that a large amount of bubbles are generated when pouring beer into a glass. However, in order to entrain air, it is necessary to apply mechanical energy such as pouring beer, and it is difficult to control foam generation.

  Therefore, as a method for controlling the generation of bubbles, it was examined that pores were imparted to the container surface whose surface free energy was reduced by adding polyolefin. When bubbles were imparted to the surface of various surface free energies and the foamability of beer was investigated, it was confirmed that the foamability was improved by several steps in a container having a low surface free energy. Although the mechanism is currently under investigation, the ease with which bubbles are generated in the pores is the shape in which the bubble surface is recessed when bubbles are generated in the holes when the surface free energy of the container surface is sufficiently small. In this case, the surface pressure in the direction in which the air bubbles are to be compressed is reduced by 2γ / r, and the air bubbles are very likely to be generated compared to the flat surface.

  In addition, the bubble nuclei that usually remain after the generation of bubbles is the starting point for the generation of the next bubble, and the bubbles are often generated continuously, but the surface free energy is large and the surface that is easily wetted by the contents is adsorbed on the container surface. Bubble nuclei tend to disappear and foam generation does not occur continuously, and foam generation decreases, while those that are hard to get wet with the contents tend to absorb air and continuously generate foam. It becomes a container with good property (foamability). Thus, the foam of carbonated beverages is overwhelmingly increased by reducing the surface free energy on the surface where the pores are present rather than just reducing the surface free energy of the container.

  From the above, in the present invention, by controlling the surface free energy and pore generation of the resin film on the inner surface of the can, it is characterized by achieving both foam generation and flavor component adsorption and suppression of film crack generation. It is a requirement. Then, in order to achieve both of the conflicting performances at a very high level, the present invention has been completed by controlling the surface free energy, the shape and amount of the pores, and the resin film state. In addition, a resin film-coated metal can with excellent adhesion to the metal plate that does not crack or peel off when impacted on the can and does not cause corrosion or peeling when in contact with various contents is obtained. It was also confirmed that the flavor component of the contents of the can was adsorbed to the film, and that the flavor of the contents was not impaired by the elution component and smell of the film.

  Furthermore, it has also been found that it is effective to heat-treat a resin film coated on a metal plate before can molding in order to sufficiently generate pores on the surface of the resin film during can molding.

The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] A resin film-covered metal plate in which a resin film mainly composed of a thermoplastic polyester having a single layer structure or a layer structure of two or more layers is coated on at least one side of the metal plate, (I) 0.01 to 0.5% by weight of particles having an average particle diameter of 0.5 to 5 μm, and (II) 0.01 to 2% by weight of polyolefin resin (film A) A resin film-coated metal plate for carbonated beverage cans, which is excellent in foaming property and foam holding property, characterized in that it has at least one side.

[2] Oite to [1], the surface of the resin film A, the particles having an average particle diameter of 0.5~5μm, characterized in that exposed 5-5000 per area 1 mm ² Resin film-coated metal plate for carbonated beverage cans with excellent foaming and foam retention .

[ 3 ] In the above [1] or [2] , the resin film A has an outermost resin film thickness of 2 to 10 μm, and the acid component in the polyester resin contained in the outermost resin is isophthalic acid A resin film-coated metal plate for carbonated beverage cans, which is excellent in foaming property and foam retention property , characterized in that 5 to 18 parts by weight and the balance are terephthalic acid.

[ 4 ] In any one of [1] to [ 3 ], the resin in the lowermost layer of the resin film A in contact with the metal plate contains 5 to 30% by weight of a carboxylic acid derivative-modified polyolefin granular resin. A resin film-coated metal plate for carbonated beverage cans, which has excellent foaming properties and foam holding properties .

[ 5 ] In any one of [1] to [ 4 ], the ratio of the resin film thickness of the outermost layer in the resin film A to the resin film thickness other than the outermost layer is 1:15 to 1: 2. A resin film-coated metal plate for carbonated beverage cans, which is characterized by having excellent foamability and foam retention .

[ 6 ] The resin film-coated metal plate according to any one of [1] to [ 5 ], wherein the resin film-coated metal plate is in a high temperature atmosphere of 80 ° C. or higher and 200 ° C. or lower after coating the resin film. A resin film-coated metal plate for carbonated beverage cans, which is excellent in foaming property and foam holding property, characterized in that it is heat-treated.

[ 7 ] In the above [ 6 ], a resin film-coated metal plate for a carbonated beverage can excellent in foaming property and foam holding property , wherein the crystallinity of the resin film is 15% or more.

[ 8 ] Foaming property and foam retention, wherein the resin film-coated metal plate according to any one of [1] to [ 7 ] is formed so that the resin film-coated surface is on the inner surface side of the can Resin film coated metal can for carbonated beverages with excellent properties .

In [9] the [8], the resin film surface, grain size particles of 0.5 to 5 [mu] m, foaming properties and which is characterized in that the exposed 10-10000 or a maximum area per 1 mm ² Foam Resin film-coated metal can for carbonated beverages with excellent durability .

In [10] the [8] or [9], the resin film surface, foaming holes with a pore diameter of 0.5~5μm, characterized in that it is present 1 to 1000 with a maximum area per 1 mm ² Resin film-coated metal cans for carbonated beverages with excellent properties and foamability .

[ 11 ] In any one of the above [ 8 ] to [ 10 ], the resin film surface has a maximum of ² to 500 holes formed by particles having a particle diameter of 0.5 to 5 μm per 1 mm ² area. A resin film-coated metal can for carbonated drinks, which is excellent in foaming property and foam holding property, characterized by being present.

[ 12 ] The resin film-coated metal can according to any one of [ 8 ] to [ 11 ] is heat-treated, whereby the crystallinity of the resin film is 30% or more, and the foaming property and foam retention Resin film coated metal can for carbonated beverages with excellent properties .

[ 13 ] In any of the above [ 8 ] to [ 12 ], the water contact angle of the resin film surface on the inner surface side of the resin film-coated metal can can be 80 degrees or more, and the foaming property and foaming property Resin film-coated metal can for carbonated beverages .

[ 14 ] In any of the above [ 8 ] to [ 13 ], the surface free energy of the resin film surface on the inner surface side of the can of the resin film-coated metal can is 35 mN / m or less, and the foaming property and foam retention Resin film coated metal can for carbonated beverages with excellent properties .

[ 15 ] In any one of the above [ 8 ] to [ 14 ], the polar component of the surface free energy of the resin film surface on the inner surface side of the resin film-coated metal can is 5 mN / m or less . And a resin film-coated metal can for carbonated beverages with excellent foam retention .
This problem can also be solved by the following means.
(A) A resin film-covered metal plate in which at least one surface of a metal plate is coated with a resin film mainly composed of a thermoplastic polyester having a single layer structure or a layer structure of two or more layers, and in the resin of the outermost layer of the resin film (I) 0.01 to 0.5% by weight of particles having an average particle diameter of 0.5 to 5 μm, and (III) 0.1 to 2% by weight of resin having a surface free energy of 35 mN / m or less. A resin film-covered metal plate having a film (film B) to be contained on at least one side.
(B) In any of the above, the resin film-covered metal plate, wherein the water contact angle of the outermost layer of the resin film A and / or B is 80 degrees or more.
(C) The resin film-covered metal plate according to any one of the above, wherein the surface free energy of the outermost layer of the resin film A and / or B is 35 mN / m or less.
(D) In any of the above, the resin film-covered metal plate, wherein the polar component of the surface free energy of the outermost layer of the resin film A and / or B is 5 mN / m or less.

  According to the present invention, it is possible to obtain a resin film-coated metal plate and a resin film-coated metal can that are excellent in foaming property and foam retention property while having good processability and impact resistance. And 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 the can, so use fermentation like beer and sparkling sake Ideal as a carbonated beverage can.

  Hereinafter, the resin film-coated metal plate and the resin film-coated metal can of the present invention will be described in detail.

  The resin film-coated metal can of the present invention can be obtained by subjecting a metal plate coated with a film having an appropriate resin composition to can molding. And the surface free energy of the inner surface of the can after molding is controlled, and furthermore, pores of appropriate shape and amount are generated on the surface of the resin film to generate appropriate foaming in the contents, and the amount of pores is minimal By being limited to the limit, it is possible to suppress flavor adsorption, impact cracking, corrosion, resin peeling, dissolution and the like due to pores.

  The resin film-coated metal plate of the present invention is a resin film-coated metal plate obtained by coating a resin film mainly composed of a thermoplastic polyester having a single layer structure or a layer structure of two or more layers on at least one surface of the metal plate. The resin film must satisfy at least one of the following conditions 1) or 2). That is, 1) 0.01 to 0.5% by weight of particles having an average particle diameter of 0.5 to 5 μm and (II) 0.01% of polyolefin-based resin in the resin of the outermost layer of the resin film 2% by weight, or 2) 0.01 to 0.5% by weight of (I) particles having an average particle diameter of 0.5 to 5 μm in the outermost resin layer of the resin film, and (III) the surface It contains 0.1 to 2% by weight of a resin having a free energy of 35 mN / m or less.

  Further, in the present invention, the resin film may be a single layer or may have a plurality of layer structures of two or more layers, so in the present invention, the outermost layer is the resin in the case of a single layer, In the case of having a plurality of layer structures of two or more layers, it is important that the resin of the outermost layer of the resin layers contains the above-described particles of the present invention and the specified resin, respectively. Thus, by controlling the outermost layer, it becomes easy to generate pores due to particles at the time of can production, which is preferable for foaming property and foam holding property.

  As described above, by using a resin film-coated metal plate coated with a resin film whose particle shape is in an appropriate range, fine pores are generated around the particles on the surface of the resin film during can molding. The generation of bubble nuclei in the portion becomes a generation point of bubbles, and stable fine bubbles are obtained, and appropriate foaming is generated when the can is opened. In order to obtain bubbles of such a stable size, the size, shape and amount of the pores need to be appropriate, which is only obtained within the scope of the present invention.

  In particular, unlike other carbonated beverages, beer foam has a large influence on the stability of the foam due to the size and amount of the foam. Also, if the amount is too small, the foam retention is poor. In beer, in order to maintain an appropriate amount of foam for a long time, the size of bubbles, gas components in the bubbles, and the like are important. It can be said that this invention is effective also in this point. In addition, by optimizing the size and shape of the pores, problems such as flavor adsorption, impact cracking, corrosion, resin peeling, and dissolution can be solved.

  The detailed reason for limitation will be described below.

  The first form of the basic constitution of the resin film used for the resin film-coated metal plate of the present invention is that 0.01 to 0 particles having an average particle diameter of 0.5 to 5 μm are contained in the resin of the outermost layer of the resin film. 5% by weight and 0.01 to 2% by weight of a polyolefin-based resin. As mentioned above, by combining fine particles with small particle size and polyolefin resin with low surface free energy, very fine foaming property can be obtained without film defects, but the particle size, amount, and amount of olefin resin There is an optimal range.

  The size and amount of particles added affect the size and shape of the pores generated on the surface of the resin film, which affect not only foaming of the contents but also flavor adsorption, impact cracking, dissolution, etc. . Considering the above, the average particle diameter of the particles is set to 0.5 to 5 μm. In the case of particles having an average particle size of less than 0.5 μm, pores having a size necessary for generating bubbles cannot be obtained. On the other hand, with respect to the particles having an average particle size exceeding 5 μm, the pore size is too large to obtain a bubble having a stable size, and mechanical properties such as workability and impact resistance of the film are deteriorated. Furthermore, it is preferably 1 μm or more, more preferably 2 μm or more, from the viewpoint of greatly promoting the generation of foaming. Moreover, since it is highly possible that particles of 4 μm or more are also defective, the average particle size is preferably 4 μm or less.

  In addition, the value represented by the number average particle diameter is used for the average particle diameter here. Therefore, as long as it does not impair the scope of the present invention, it may contain particles having a particle size of less than 0.5 μm and more than 5 μm. However, in order to degrade the mechanical performance of the film and increase the film cost, those having a ratio as small as possible are preferable, the particle size distribution is sharp, and the standard deviation is preferably 0.5 or less. Further, the shape of the particles is preferably close to a true sphere, and the ratio of major axis / minor axis is preferably 1.0 to 1.2. As for the particle diameter of the ellipsoidal shape, the average of the major axis and the minor axis is defined as the particle diameter.

  Further, the effect of obtaining bubbles having a stable size is exhibited when 0.01% by weight or more of particles having an average particle diameter of 0.5 to 5 μm is contained, and more preferably 0.02% by weight or more. On the other hand, the amount of particles is preferably 0.5% by weight or less so that deterioration of mechanical performance and accompanying deterioration of corrosion resistance and flavor properties do not occur. More preferably, it is 0.1 weight% or less.

  In addition, as particles contained in the resin film, it is easy to control the particle shape, so it is easy to obtain other performances such as anti-corrosion properties in addition to foaming properties, stability to the contents, high environmental compatibility and excellent flavor. Silicon oxide is most suitable from the standpoints of cost and cost.

  Thus, in this invention, foaming from a void | hole improves dramatically by reducing the surface free energy of a resin film. As a method of reducing the surface free energy, in addition to a method of adding a resin having a low surface free energy such as a polyolefin-based resin, the surface of the resin film is fluorinated by chemical treatment or physical vapor deposition, or wax is used. It is also possible to apply a low surface free energy paint or the like to the film surface, but from the viewpoint of ease of production, cost, uniformity, etc., there is a method of adding a resin having a low surface free energy such as a polyolefin resin. The best.

  As the resin having a low surface free energy, a polyolefin resin is optimal from the viewpoint of easy addition to polyester, cost, and safety. Polyolefin resins are resins obtained by vinyl polymerization of molecules containing carbon-carbon double bonds in the molecule, such as ethylene, propylene, butene, methylpentene, acrylic acid and esters thereof, and ethylene fluoride. Polyethylene, polypropylene, polybutene, polymethylpentene, polystyrene and the like. In particular, a polyethylene resin is preferable because it is appropriately dispersed in a polyester resin, and a high-density to low-density one or a linear low-density polyethylene resin (LLPDE) is preferable, and a mixture of a plurality of them is also suitable. .

  On the other hand, for the purpose of reducing the surface free energy, a low surface free energy resin other than a polyolefin-based resin can be applied as long as there is no problem in safety and dispersibility in the polyester resin which is the main component of the resin film. In that case, the surface free energy of the resin is set to 35 mN / m or less. That is, the second form of the basic structure of the resin film used for the resin film-coated metal plate of the present invention is that 0.01% of particles having an average particle diameter of 0.5 to 5 μm are contained in the resin of the outermost layer of the resin film. And 0.5 to 2% by weight of a resin having a surface free energy of 35 mN / m or less. Examples of resins having a surface free energy of 35 mN / m or less include fatty acid ester waxes, fats and oils, and paraffins.

  When the surface free energy of the outermost layer of the film becomes 35 N / m or less by adding a polyolefin resin or a resin having a surface free energy of 35 mN / m or less to the resin film, when the can is formed by the added particles as described above In combination with the generation of pores, very remarkable foaming properties are generated. When the surface free energy is higher than 35 mN / m, the stability of the bubble nuclei due to the reduction of the surface free energy is lowered and the foaming property is reduced.

Here, a method for measuring the surface free energy will be described. The surface free energy γs of the laminated metal plate 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, its dispersion component is γld, and its polar component is γlh, they 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), For each liquid, the contact angle θ is measured (humidity: 60 ± 5%, 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, since the surface free energy of the polyester resin is as high as about 43 mN / m, it is necessary to add a resin at least smaller than 35 mN / m. Dispersion in the polyester resin varies depending on the resin to be added, and there are those that uniformly cover the surface, those that become solid and only partially cover the surface, etc. Although it is difficult to predict, in the case of a polyolefin resin, the addition of 0.01 parts by weight or more reduces the surface free energy to a desired value, and more desirably 0.1 parts by weight or more. If it is less than 0.01 part by weight, the surface free energy will not be lowered sufficiently. On the other hand, the upper limit of the polyolefin resin is 2 parts by weight, and if it exceeds that, the effect of reducing the surface free energy is saturated and hardly changes, and it cannot be sufficiently dispersed in the polyester resin, causing surface defects and color unevenness. In addition, the adsorption of flavor components by polyolefin resin is not negligible, and the flavor deteriorates, or if a large amount of polyolefin resin is added, bubbles are likely to be formed too much, and large unstable bubbles that are not fine bubbles. Is likely to occur, and there is a possibility that the flavor of beer may be returned and damaged. Preferably, it is 1 part by weight or less. As described above, the content of the polyolefin resin is set to 0.01% by weight or more and 2% by weight or less.

  Similarly, the content in the case of a resin having a surface free energy of 35 mN / m or less is also 0.1 wt% or more and 2 wt% or less. The reason why the performance is impaired when the value is out of the range is the same as that of the polyolefin resin.

  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 wettability of beer in a resin film optimal for foaming with a surface free energy of 35 mN / m or less is expressed by a water contact angle, it is 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.

  In addition, since the proportion of the polar component in the beer liquid component is larger than that in the dispersed component, it is most effective to reduce the polar component of the surface free energy in order to reduce the wetting of the beer. Even if γs is higher than 35 mN / m, if the polar component γsh is 5 mN / m or less, wetting of beer can be sufficiently reduced and foaming properties are improved. Therefore, the polar component of the surface free energy of the outermost layer of the resin film is preferably 5 mN / m or less.

Moreover, in the resin film which contains the particle | grains prescribed | regulated above in resin of the outermost layer of a resin film, it is preferable that 5-5000 particle | grains are exposed on the surface per 1 mm < ² > area. Then, when the particles are exposed on the surface as described above, voids are generated around the exposed particles at the time of can molding, which becomes a starting point of bubble generation. Here, the particle exposure means that the outer surface of the particle does not necessarily have to be exposed when a part of the particle is exposed above the surface on the film surface, and even if the particle surface is covered with resin, the film surface It is assumed that the particles are exposed if the particles protrude above them. If the number of exposed particles is less than 5, the effect of obtaining bubbles of a stable size is insufficient. On the other hand, those having more than 5000 may cause excessive generation of foam depending on the contents, and the stability of the foam may be lowered. Therefore, the upper limit thereof is preferably not more than 5000 per 1 mm ² , more Preferably it does not exceed 1000.

  The resin film of the present invention is a resin film that directly contacts the contents of particles and polyolefin resin involved in foaming properties in order to improve film properties, improve production efficiency, or reduce film production costs. It is also possible to add only to the outermost layer. In the case of taking a two or more layer structure, at least the outermost layer is configured as described above, and the other layers may or may not contain particles and polyolefin resin. These may be judged from the aspects of film performance, manufacturing cost, and the like.

  Further, the resin film thickness of the outermost layer of the resin film in the present invention is 2 to 10 μm, and the acid component in the polyester resin contained in the outermost layer resin is 5 to 18 parts by weight of isophthalic acid and the remainder is terephthalic acid. It is preferable from the point of performance improvement. Details of the acid component in the polyester resin will be described later. In each layer of the polyester resin film, the number of layers containing particles is preferably as small as possible because it tends to cause flavor adsorption, impact cracking, dissolution and the like. Therefore, when the influence of the thickness of the particle-containing layer on foaming was investigated, the resin on the outermost layer on the side in contact with the contents was the particle-containing layer, and if the thickness was 2 μm or more, there were voids in the film surface layer. This was found to be effective for foaming. In addition, the effect of the outermost resin layer is effective when it is 2 μm or more, and the effect tends to increase as the thickness is thicker. However, the effect is saturated at 10 μm or more, and increasing the thickness further increases flavor adsorption, impact cracking, and dissolution. Degrading the performance. More preferably, it is 7 μm or less.

  Furthermore, it is preferable that the ratio of the resin film thickness of the outermost layer of the resin film to the resin film thickness other than the outermost layer is 1:15 to 1: 2. When the film thickness ratio is smaller than 1:15, the generation of surface vacancies is not sufficient, and the foaming property is lowered. On the other hand, when the film thickness ratio exceeds 1: 2, the impact resistance and workability are lowered.

  In addition, even if the resin film of this invention is a non-stretched manufacture and the hole prescribed | regulated to this invention produces | generates also in the film biaxially stretched, the effect of this invention will be expressed. In particular, pores may be generated around the particles during stretching, in which case foaming is promoted more than the unstretched film.

  Moreover, in this invention, after coat | covering a resin film to a metal plate, it heat-processes and crystallizes, A suitable void | hole becomes easy to produce | generate on the film surface at the time of can molding, and foamability expresses. That is, the heat treatment increases the brittleness of the film resin, increasing the number of pores generated around the particles during can molding. As a result, foaming at the time of opening the can is promoted.

  The heat treatment is performed in a temperature range of 80 ° C. to 200 ° C. Crystallization of the film resin proceeds by heat treatment, and the brittleness of the film increases. As a result, voids are easily generated in the film by processing. The heat treatment temperature at which such an effect occurs needs to be higher than the glass transition temperature of the polyester resin and lower than the melting point, and the temperature range is 80 ° C. to 200 ° C. Further, from the viewpoint of crystallization speed, it is preferable to perform the treatment at a temperature at which crystallization is easy: in the range of 80 ° C. to 180 ° C., and to finish it in a short time.

The crystallinity that sufficiently increases the brittleness is set to 15% or more as a guide. Below that, the brittleness may not be sufficient. Furthermore, it is preferably 20% or more, and the brittleness is sufficiently high. The calculation method of a crystallinity degree is calculated with the following formula | equation from the density of an object film, for example.
Xc = dc × (d−da) / d / (dc−da) × 100
Xc: degree of crystallinity (%), d: density of target film, dc: density when film resin is crystallized 100%, da: density when film resin is 100% amorphous state resin film is polyethylene terephthalate resin In the case of a single phase, since dc = 1.46 and da = 1.34, the density of the film having a crystallinity of 15% is 1.36.

  The heat treatment is performed in an atmosphere such as a dry atmosphere or a water vapor atmosphere. The heat treatment in a dry atmosphere is achieved, for example, by blowing high-temperature dry air in the air or increasing the temperature of the steel sheet by induction heating. On the other hand, the heat treatment in the steam atmosphere is achieved, for example, by spraying high-temperature and high-pressure steam on the film surface for several seconds, but an existing method such as retort sterilization may be used. In the case of a water vapor atmosphere, fine pores are generated during heat treatment, and can grow into large pores starting from that during can molding, so the effect is greater than in a dry atmosphere. In both the dry atmosphere and the steam atmosphere, a heat treatment temperature of about 80 ° C. is sufficient. The temperature when the heat treatment is performed in a water vapor atmosphere is preferably 80 ° C. or higher and 150 ° C. or lower because good foaming properties are exhibited by a treatment of 150 ° C. or lower.

  In both the dry atmosphere and the steam atmosphere, the treatment time is sufficient until the crystallinity rises to be within the above-mentioned range, for example, between 10 seconds and 10 minutes. Temperature and time conditions are determined by specifications. The treatment may be performed continuously with a coil or with a small sample of cut plates. Further, the cooling after the treatment may be any of air cooling, rapid cooling by water cooling, or slow cooling.

Next, the thermoplastic polyester that is the main component of the resin film will be described.
Polyester resin film used in applications such as carbonated beverage cans has excellent adhesion to metal plates, deformation such as elongation and compression of the film due to molding during canning, and deterioration of the film due to friction. There is no decrease in adhesion, and the coated film is crystallized or deteriorated by heating such as drying after can-making, printing baking, retort sterilization, etc., and no film peeling, shrinkage, cracks, pinholes, etc. The film is required to have performance such as that the film does not crack or peel off due to impact on the can, that it does not corrode or peel off when in contact with various contents, and that 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, the thermoplastic polyester used in the present invention includes various aromatic dicarboxylic acids and aliphatic dicarboxylic acids as the acid component, and various aliphatic diols and aromatic diols as the glycol component. Polymerized or copolymerized ones are used, and two or more types of copolymerized polyester resins having different compositions are used.

  Furthermore, the size and shape of the pores on the film surface after can molding are important from the viewpoint of foaming properties, other flavor properties, impact resistance, etc., and the composition of the resin film also affects the generation of such pores. The resin film must have moderate processability and strength. The composition of such a polyester resin is that the acid component is 5 to 18 parts by weight of isophthalic acid and the remainder is terephthalic acid. Is the best. By copolymerizing an appropriate amount of isophthalic acid with terephthalic acid, crystallization is suppressed and processability is improved, large cracks are less likely to occur, and mechanical performance deteriorates compared to terephthalic acid alone or with a low copolymer composition. It 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.

  Examples of acid components other than terephthalic acid and isophthalic acid include phthalic acid, 1,4-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, diphenic acid, diphenyl ether carboxylic acid, 5-sulfoisophthalic acid, diphenoxyethanedicarboxylic acid, adipic acid, oxalic acid, malonic acid, succinic acid, malic acid, citric acid, glutaric acid, dimer Acid, pimelic acid, speric acid, azelaic acid, sepacic acid, dodecadioic acid, trans-1,4-cyclohexanedicarboxylic acid and the like are used.

  On the other hand, as the glycol component, those obtained by arbitrarily polymerizing or copolymerizing various aliphatic diols and aromatic diols are used, such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,3-butanediol, , 2-butanediol, neopentyl glycol, pentamethylene glycol, hexamethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, trans-1,4-cyclohexanedimethanol, cis-1,4-cyclohexanedimethanol Bisphenols, p-xylene glycol, hydroquinone, 2,2-bis (4-β-hydroxyethoxyphenyl) propane, hydrogenated bisphenol A, and the like are used. In particular, those based on ethylene glycol and / or 1,4-butanediol and / or 1,4-cyclohexanedimethanol are preferred from the viewpoint of balance between mechanical properties and flavor properties.

  Therefore, terephthalic acid and ethylene glycol are the main components, and / or terephthalic acid and isophthalic acid and ethylene glycol are the main components, and / or terephthalic acid and ethylene glycol and 1,4-butanediol, and / or terephthalate Those containing acid, ethylene glycol and 1,4-cyclohexanedimethanol as main components are suitable as film components from the viewpoint of the balance between mechanical properties and flavor properties in a mixed resin state.

  Further, a small amount of a structural unit derived from a polyfunctional compound such as trimesic acid, pyromellitic acid, trimethylol ethane, trimethylol propane, trimethylol methane, pentaerythritol, or the like, as long as the object of the invention is not impaired. It may be included in the following amounts.

  Here, in the resin film, the fact that the thermoplastic polyester resin is the main component means that the polyester occupies 70% by weight or more in the resin component in the film. As other resin components, it is also possible to use resins having improved impact resistance by containing impact relaxation components such as modified polyolefins and elastomers in the range of 3 to 30 parts by weight, particularly carbonated beverages and lactic acid beverages. For applications that require such severe impact resistance, it is possible to ensure the required impact resistance by containing 5 to 30% by weight of the carboxylic acid derivative-modified polyolefin granular resin in the polyester resin.

  Further, in a film having a multilayer structure and containing particles and a polyolefin resin in the outermost layer, the resin in the lowermost layer in contact with the metal plate may contain 5 to 30% by weight of a carboxylic acid derivative-modified polyolefin granular resin. preferable. By adding the carboxylic acid derivative-modified polyolefin granular resin, it becomes possible to further suppress the occurrence of corrosion due to impact cracking, processing cracking, and adhesion deterioration of the resin film metal can.

  A modified polyolefin resin having a functional group derived from a carboxylic acid mixed in a polyester resin improves impact resistance and does not adversely affect other properties such as processability and heat resistance. It is preferable that the particle diameter is mainly present in the state of 0.1 to 5 μm particles by an equivalent sphere equivalent meter. Further, the weight ratio of the modified polyolefin resin in all resins needs to be in the range of 5 to 30% by weight. If it is less than 5% by weight, it is insufficient for improving impact resistance, and if it exceeds 30% by weight, performance such as workability and heat resistance is deteriorated.

The glass transition temperature of the modified polyolefin resin is preferably 0 ° C. or less by the same measurement method as that for the polyester resin. Preferably, it is -30 degrees C or less. Those having a glass transition temperature exceeding 0 ° C. are slightly inferior in impact resistance, particularly inferior in low-temperature impact resistance. Furthermore, it is more preferable that the Young's modulus at room temperature is 250 MPa or less and the elongation at break is 200% or more, more desirably the Young's modulus is 100 MPa or less and the elongation at break is 500% or more. The molecular weight is not particularly limited, but the number average molecular weight is preferably 2 × 10 ³ or more and 1 × 10 ⁶ or less. If it is less than 2 × 10 ³ or exceeds 1 × 10 ⁶ , the mechanical performance may be inferior and impact resistance may be lowered, and molding may be difficult.

  The functional group derived from carboxylic acid is contained in an amount of 2 to 20% by weight, more preferably 3 to 12% by weight in terms of weight ratio in terms of carboxylic acid. In this composition range, the affinity with the polyester resin and the dispersibility are maximized, so that the modified polyolefin resin has a stronger affinity with the matrix polyester resin, and the effect of mitigating interphase fracture between different resins at the time of impact is increased. As a result, the impact resistance is enhanced, and further, the aggregation of the modified polyolefin particles during the molding process is suppressed. As a result, the variation in performance due to the molding conditions is reduced. Such an effect is obtained when the weight ratio of the functional group in terms of carboxylic acid is 2% by weight or more. On the other hand, when the weight ratio exceeds 20% by weight, the affinity with the polyester resin is decreased, resulting in poor impact resistance.

  A method for producing the modified polyolefin resin will be described below. Functional groups derived from carboxylic acids include carboxylic acid groups, carboxylic ester groups, metal salts of carboxylic acid ions, etc., and monomers containing these functional groups are copolymerized, graft polymerized, or blocked in polyolefin resins. A carboxylic acid-modified polyolefin is obtained by polymerization.

  Specific examples of the monomer containing a functional group derived from carboxylic acid include 3 carbon atoms such as acrylic acid, methacrylic acid, vinyl acetate, vinyl propionate, maleic acid, maleic anhydride, itaconic acid, and maleic acid monomethyl ester. -8 unsaturated carboxylic acids, and metal salts in which all or part of these acids are neutralized with a divalent metal cation such as sodium, potassium, lithium, zinc, magnesium, calcium and the like. The degree of neutralization is preferably 20 to 80%, more preferably 30 to 70%, and the composition formed from the modified polyolefin resin having such a degree of neutralization is excellent in melt extrudability.

  Examples of the carboxylic acid ester include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isobutyl acrylate, isobutyl methacrylate, n-butyl acrylate, Examples include n-butyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, monomethyl maleate, glycidyl acrylate, glycidyl methacrylate, vinyl acetate, acrylic amine, and acrylamide.

  These carboxylic acid-derived functional group-containing monomers are copolymerized or blocked with carboxylic acid-derived functional group-free olefin monomers such as ethylene, propylene, 1-butene, 1-pentene, isobutene, isobutylene, butadiene, styrene, acrylonitrile, etc. Carboxylic acid-derived functional group-containing modified polyolefin resin can be obtained by polymerization or graft polymerization. Among these, in particular, those obtained by graft polymerization or copolymerization of a carboxylic acid group in a polyolefin resin exhibit high performance. A commercially available resin can also be used as such a modified polyolefin resin. For example, Modiper A (manufactured by Nippon Oil & Fats Co., Ltd.), Nucrel (manufactured by Mitsui DuPont Polychemical Co., Ltd.), Bondine (manufactured by Sumitomo Chemical Co., Ltd.), Admer (manufactured by Mitsui Chemicals Co., Ltd.), And Tuftec (manufactured by Asahi Kasei Corporation).

  Further, those obtained by partially neutralizing these carboxylic acids with metal salts can also be used. Although such a resin has a slightly reduced workability, a resin having a higher impact resistance can be obtained. Examples of commercially available resins include High Milan (Mitsui DuPont Polychemical Co., Ltd.). Furthermore, when zinc oxide, calcium hydroxide, or the like is added when the carboxylic acid-modified polyolefin resin is melt-dispersed in the polyester resin, the carboxyl groups in the modified polyolefin resin are neutralized with those metal ions, resulting in the carboxylic acid being A product having a structure in which a carboxylic acid-modified polyolefin resin partially neutralized with a metal salt is dispersed in a polyester resin is obtained.

  A mixed resin as a raw material is obtained by dispersing the modified polyolefin resin in the polyester resin. As a dispersion method, for example, two resins are melted and mixed, maintained at a temperature to become one phase, then cooled to a temperature at which the two phases are separated, and modified polyolefin resin in the polyester resin phase using phase separation. A method of dispersing phases, a method of evaporating a solvent after dissolving two resins in a common solvent, and a modified polyolefin resin whose primary particle size has been refined to 1 μm or less in advance is melted at a temperature that does not aggregate in the polyester resin. The polyester resin is produced by polymerizing a monomer in a solution containing a modified polyolefin resin and a polyester resin constituent monomer whose primary particle size is refined to 1 μm or less in advance, and the modified polyolefin resin is dispersed in the polyester. The method of making it into a state, and also two modified resins are melt-mixed and modified with a mechanical shear force There is a method of refining the olefin resin, and any method is possible.

  As a mixing and melting apparatus, a mixing apparatus such as a tumbler blender, a Henschel mixer, or a V-shaped blender, or a melt mixing apparatus such as a single or twin screw extruder, a kneader, or a Banbury mixer can be used. Temperature control such as temperature control and temperature change is made stricter than normal mixing method, mixing time is made 3 to 10 times longer than normal mixing time, mechanical shear rate at the time of mixing The thermoplasticity is increased by, for example, about 2 to 5 times faster than the normal speed, or by combining them, for example, mechanically mixing with a tumbler blender and then melt mixing with an extruder. A highly dispersible mixed resin is obtained in which a granular modified polyolefin resin having a particle size of 0.1 to 5 μm is dispersed in advance in a polyester resin. It is. By forming a film of a highly dispersible mixed resin obtained by melt-mixing with an extruder, a resin film having a more uniform particle diameter of the modified polyolefin resin can be obtained, and as a result, performance such as impact resistance is enhanced. The particle size distribution of the granular resin is much larger than that of dispersing the modified polyolefin resin while forming a film by melting and molding a mixed resin with such a uniform particle size and high dispersibility into an extruder. As a result, a film capable of exhibiting excellent performance in various performances can be obtained.

  On the other hand, the acetaldehyde content in the resin is preferably 10 ppm or less, more preferably 7 ppm or less, from the viewpoint of the flavor property of the polyester resin. If the acetaldehyde content exceeds this range, particularly 10 ppm, the flavor properties may be inferior. The method for setting the acetaldehyde content to 10 ppm or less is not particularly limited. For example, in order to remove acetaldehyde generated by thermal decomposition when a polyester resin is produced by polycondensation reaction or the like, the resin was obtained by a method of heat-treating the resin at a temperature below the melting point of the polyester under reduced pressure or in an inert gas atmosphere. Examples include a method of forming a polyester resin into a film, and a method of using a polyester resin obtained by solid-phase polymerization at a temperature of 150 ° C. or higher and a melting point or lower in a reduced pressure or inert gas atmosphere is preferable.

  Further, the polyester resin of the present invention preferably has fewer oligomers composed of a cyclic trimer or the like in the resin from the viewpoint of flavor. In particular, the content of the cyclic trimer is preferably 0.9% by weight or less, and more preferably 0.7% by weight or less. If the oligomer content in the resin exceeds this range, particularly 0.9% by weight, the flavor properties may be inferior. The method for setting the oligomer content to 0.9% by weight or less is not particularly limited, but can be achieved by adopting a method similar to the method for reducing the acetaldehyde content described above.

The intrinsic viscosity of the polyester resin used in the present invention is 0.3 to 2.0 dl / g, more preferably 0.3 to 1.5 dl / g, and still more preferably 0.5 to 1.0 dl / g. If it exceeds 2.0 dl / g, the viscosity is so high that mixing with particles having a particle size of 0.5 to 5 μm used in the present invention is extremely difficult, and the particles are not uniformly dispersed. On the other hand, if the intrinsic viscosity is less than 0.3 dl / g, the viscosity is low and the moldability becomes poor, making it difficult to produce a uniform film. There is sex. The intrinsic viscosity is measured by the method shown in JIS K7367-5, and is measured at a concentration of 0.005 g / ml in o-chlorophenol at 25 ° C. The intrinsic viscosity = (T−T ₀ ) / It is determined by the expression _(T 0 * c). In the formula, c represents the concentration of the resin per 100 ml of the solution expressed in grams, and T ₀ and T represent the flow time of the solvent and the resin solution in the capillary viscometer, respectively.

  Furthermore, it is desirable that the polyester resin used in the present invention has a glass transition temperature (Tg) of 50 to 100 ° C, more preferably 60 to 80 ° C. When the glass transition temperature is less than 50 ° C, the heat resistance of the polyester resin is inferior, so that the temperature rises at the time of molding, so that scratches and the like are likely to occur. May be inferior. The low-temperature crystallization temperature (Tc) is usually 120 to 210 ° C., preferably 140 to 200 ° C., and the melting point (Tm) is usually 210 to 265 ° C., preferably 220 to 260 ° C. . When the low temperature crystallization temperature is less than 120 ° C., crystallization is likely to occur, so that crystallization occurs during retort sterilization treatment (high temperature and high humidity treatment of about 120 ° C.), and the film is likely to crack or peel off. On the other hand, those having a low temperature crystallization temperature exceeding 210 ° C. may be inferior in mechanical strength such as processability and impact resistance of polyester. If the melting point is less than 210 ° C., the resin deteriorates due to heat during molding, and cracks and pinholes are likely to occur. On the other hand, when the melting point exceeds 265 ° C., crystallization proceeds by heat treatment such as drying at the time of molding and printing baking, and cracks and pinholes are likely to occur. The glass transition temperature, the low temperature crystallization temperature, and the crystal melting temperature are obtained by measuring the endothermic peak temperature at the time of temperature rise using a differential scanning calorimeter (DSC). The sample amount is 10 mg, the temperature rise rate is 10 ° C./min. It is a value measured under conditions.

  The resin film can further contain inorganic particles, organic particles, and organic polymer particles for the purpose of improving slipperiness, moldability, impact resistance, and the like. The inorganic particles, organic particles, and organic polymer particles may have a function as particles defined in the present invention. Inorganic particles include silica produced by dry and wet methods, porous silica, colloidal silica, titanium oxide, zirconium oxide, aluminum oxide, calcium carbonate, talc, calcium sulfate, barium sulfate, spinel, iron oxide, calcium phosphate Examples of organic particles or organic polymer particles include polystyrene particles, crosslinked polystyrene particles, styrene-acrylic crosslinked particles, acrylic crosslinked particles, styrene-methacrylic acid resin crosslinked particles, and methacrylic acid resin crosslinked particles. And vinyl polymer-based particles, and organic polymer particles containing silicone, benzoguanamine-formaldehyde, polytetrafluoroethylene, polyphenyl ester, phenol resin, and the like as constituent components. The particle diameter and content of these particles are not particularly limited, but in order to maximize performance, the particle diameter is preferably in the range of 0.01 to 5.0 μm, more preferably 0.1 to 2 A range of 0.5 μm is preferred. Their particle size distribution is sharp and a standard deviation of 0.5 or less is preferable. Further, the shape of the particles is preferably close to a true sphere, and the ratio of major axis / minor axis is preferably 1.0 to 1.2.

  Further, in the resin film, unless the effect of the present invention is hindered, a light stabilizer, an impact resistance improver, a compatibilizer, a lubricant, a plasticizer, an antistatic agent, a reaction catalyst, an anti-coloring agent, and a radical inhibitor. Further, additives such as a plasticizer, an antioxidant, a terminal blocking agent, a heat stabilizer, a release agent, a flame retardant, an antibacterial agent, and an antifungal agent may be further added. In the present invention, the content of these additives is preferably 0.005 parts by weight or more and 15 parts by weight or less with respect to 100 parts by weight of the resin. More preferably, it is 0.01 parts by weight or more and 2 parts by weight or less, and particularly preferably 0.05 parts by weight or more and 0.5 parts by weight or less. If the amount is less than 0.005 parts by weight, the effect is insufficient. On the other hand, if the amount exceeds 15 parts by weight, the additive becomes excessive and the mechanical performance of the resin layer is lowered. Further, heat resistance of 200 ° C. or higher is necessary so as not to deteriorate during resin molding.

  Examples of the reaction catalyst include an alkali metal compound, an alkaline earth metal compound, a zinc compound, a lead compound, a manganese compound, a cobalt compound, and an aluminum compound, and examples of the coloring inhibitor include a phosphorus compound.

  Examples of the radical inhibitor include one or more selected from phenol-based radical inhibitors, phosphorus-based radical inhibitors, sulfide-based radical inhibitors, and nitrogen-based radical inhibitors.

  As a plasticizer, a polybasic acid component having a molar ratio of an aromatic polybasic acid having 8 to 20 carbon atoms or an ester derivative thereof to a fatty acid polybasic acid having 2 to 20 carbon atoms or an ester derivative thereof is 0 to 2.0. And an aliphatic alcohol having 2 to 20 carbon atoms subjected to terminal polymerization with a monobasic acid having 2 to 20 carbon atoms or an ester derivative thereof and / or a monohydric alcohol having 1 to 18 carbon atoms. Mention may be made of plasticizers made of polyester.

  As an antistatic agent, an antistatic agent disclosed in JP-A No. 5-222357 is used for the purpose of preventing electrostatic troubles such as winding of a film around a roll in a film forming process and adhesion of dirt on the film surface. A method of kneading in a resin composition such as the above, or a method of applying an antistatic agent described in JP-A No. 5-1164 to the film surface can be applied as necessary.

  As the antibacterial agent, conventionally known antibacterial agents disclosed in JP-A-11-48431 and JP-A-11-138702 can be used as necessary.

  It is also possible to add a polyester resin polymerization catalyst into the resin. The polymerization catalyst preferably contains 1 ppm or more and 500 ppm or less of at least one element selected from germanium, antimony, and titanium. More preferably, it is 3 ppm or more, More preferably, it is 10 ppm or more. If the amount of at least one element selected from germanium, antimony, and titanium is less than 1 ppm, the effect of improving the flavor may not be sufficient, and if it exceeds 500 ppm, foreign matter is generated in the polyester, which becomes a crystal nucleating agent and easily crystallizes. Therefore, the impact resistance may be deteriorated or the heat resistance may be reduced. Of these elements, germanium is particularly preferred from the viewpoint of flavor.

  As the germanium compound, for example, germanium dioxide, germanium oxide such as germanium hydroxide containing crystal water, hydroxide, or germanium alkoxide compound such as germanium tetramethoxide, germanium tetraethoxide, germanium tetrabutoxide, germanium ethyleneglycoxide, Examples thereof include germanium phenoxide compounds such as germanium phenolate and germanium β-naphtholate, phosphorus-containing germanium compounds such as germanium phosphate and germanium phosphite, and germanium acetate.

  On the other hand, examples of the antimony compound include antimony trioxide, antimony trifluoride, antimony acetate, antimony borate, antimony formate, antimony acid and the like, and examples of the titanium compound include oxides such as titanium dioxide, water Hydroxides such as titanium oxide, alkoxide compounds such as tetramethoxy titanate, tetraethoxy titanate, tetrapropoxy titanate, tetraisopropoxy titanate, tetrabutoxy titanate, glycoxide compounds such as tetrahydroxyethyl titanate, compounds such as phenoxide compounds, acetates, etc. Can be mentioned.

  As described above, by forming a metal plate coated with the resin film having the above composition so that the target resin film is located on the inner surface side of the can, pores having an appropriate size and shape 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.

  It is possible to use the same film as the inner side as the outer side film, but in consideration of the film cost, etc., it covers a film that does not contain additives such as particles or polyolefin resin, or has reduced the amount added. It is preferable to do. 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.

Next, the metal plate that covers the resin film will be described. Although the metal plate of this invention is not specifically limited, The metal plate which uses iron 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 coat | covered the resin composition layer of this invention on the metal plate single side | surface or both surfaces is formed.

In the case of a metal plate made of iron, 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 as an adhesion layer between the metal plate and the resin film as long as the effects of the present invention are not hindered. The resin film-coated metal plate of the present invention is excellent in both primary adhesion and post-processing adhesion of the resin layer and the metal plate, but in a more severe 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 a more corrosive content causes the content to enter the interface with the metal plate through the resin layer, corrodes the metal plate, and deteriorates the adhesion to the film. there is a possibility. In such a case, it is possible to prevent the resin layer from peeling off by providing an appropriate primer layer.

  Although the kind of primer is not specifically limited, a well-known primer layer can also be used. For example, a polyester resin-based aqueous dispersant disclosed in JP-B-60-12233, an epoxy primer disclosed in JP-B-63-13829, and various functionalities disclosed in JP-A-61-149341. Examples thereof include a polymer having a group. The method for forming the primer layer is not particularly limited, but the primer coating may be applied to the metal plate and dried, or the primer coating may be applied to the film of the present invention and dried, or the primer may be applied to the metal plate. You may coat | cover a film and may coat | cover the film which bonded the film and primer layer of this invention together.

  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 in the range of a melting point of polyester resin from −70 ° 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 of the present invention so that the resin film-coated surface is on the inner surface side of the can. 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).

The resin film-coated metal can of the present invention has a maximum particle size of 0.5 to 5 μm per area of 1 mm ² on the resin film surface on the inner surface of the can from the viewpoint of appropriate foaming. Those having 10,000 exposed are suitable. In many cases, voids generated during can molding exist around the exposed particles, and become the starting point of foam generation. With respect to the density of the holes, those having a maximum of 1 to 1000 holes having a hole diameter of 0.5 to 5 μm per 1 mm ² are particularly suitable.

Here, the particle exposure means that the outer surface of the particle does not necessarily have to be exposed when a part of the particle is exposed above the surface on the film surface, and even if the particle surface is covered with resin, the film surface It is assumed that the particles are exposed if the particles protrude above them. If the number of exposed particles is less than 10, the effect of obtaining bubbles of a stable size is insufficient. On the other hand, if the number exceeds 10,000, the generation of bubbles may be excessive depending on the contents, and the stability of the bubbles may be reduced. Therefore, the upper limit of the number of exposed particles does not exceed 10,000 per 1 mm ² area. More preferably, it does not exceed 1000.

In addition, when the number of pores having a pore diameter of 0.5 to 5 μm is less than one, the effect of obtaining bubbles having a stable size is insufficient. The number is preferably 2 or more per 1 mm ² . On the other hand, if the number exceeds 1000 particles, the generation of bubbles may be excessive depending on the contents, and the stability of the bubbles may decrease, so the upper limit of the number of exposed particles does not exceed 1000 particles per 1 mm ² of area. Preferably, more preferably not more than 100.

In particular, the voids are generated not only by the periphery of the added particles but also by generation of irregularities due to surface shape change due to heat treatment, fine tearing of the film, generation of irregularities due to hitting the mold during can molding, and the like. However, as the starting point for the generation of bubbles, vacancies due to the added particles are most effective, and it is preferable that the ratio due to particles other than the former particles is as low as possible and the ratio due to particles is as high as possible. Therefore, the resin film surface on the inner surface side of the can preferably has a maximum of ² to 500 holes formed by particles having a particle size of 0.5 to 5 μm per 1 mm ^{2 of} area. When the number is less than 2, the foaming effect is insufficient. On the other hand, when the number exceeds 500, the generation of bubbles may be excessive depending on the contents, and the stability of the bubbles may be lowered.

  In addition, the void | hole prescribed | regulated here is a void | hole produced in the film surface of the side in contact with the contents of a can inner surface, and what was produced | generated in the film inside and the metal side is not included. The pore diameter is the average value of the major and minor diameters of the pores generated on the film surface. Such pores may be large or small, but in the present invention, the number of pores having a defined pore diameter of 0.5 to 5 μm is preferable, and in that case, the other diameter These holes are not counted in the number of holes.

  In addition, resin film-coated metal cans have places with a lot of holes and places with few holes depending on the forming means. In the case of two-piece cans, it is generally more in the part closer to the top of the can body than the bottom of the can. 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 holes and particles 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 by image processing by a computer. Further, the number of holes and particles in an area of 1 mm ² may be calculated by multiplying the total number in the range of 1 mm × 1 mm by 100 times the number in the range of 100 μm × 100 μm.

  Furthermore, in the above, the resin film can be made into two or more resin layers. In this case, however, the uppermost layer of the resin layer contains particles and is a resin film as defined above. Thus, by controlling the outermost surface layer on the side not in contact with the metal plate, pores due to particles are easily generated, which is preferable for foaming property and foam holding property.

  Regarding the surface free energy of the resin film surface on the inner surface side of the resin film-coated metal can, it is necessary to maintain the low surface free energy state before can molding. The surface free energy of the film surface is 35 N / m or less, and very remarkable foaming properties are generated in combination with the generation of pores during can molding by the added particles. When the surface free energy is higher than 35 mN / m, the stability of the bubble nuclei due to the reduction of the surface free energy is lowered and the foaming property is reduced. In addition, when the contact angle of water is 80 degrees or more and 80 degrees or more, foaming properties are promoted. However, when the contact angle is less than 80 degrees, the effect is small. Moreover, if a polar component is 5 mN / m or less, the wetting of beer can fully be reduced and foaming property will increase.

  Furthermore, when heat treatment is performed on the resin film-coated metal can, the performance is further improved. The heat treatment is preferably performed in a temperature range of 80 ° C. to 250 ° C. This is because the crystallization of the film resin proceeds by the heat treatment, and the pores generated at the time of can molding become larger and stabilized to have durability against impacts and cracks. Such an effect needs to be higher than the glass transition temperature of the polyester resin and lower than the melting point, and its temperature range is 80 ° C to 250 ° C. Further, from the viewpoint of the crystallization speed, the treatment is preferably performed in the range of 100 ° C. to 220 ° C. because the treatment is completed in a short time because crystallization is easy. The degree of crystallinity with which the performance is sufficiently enhanced is determined to be 30% or more. If it is lower than that, the stability may be insufficient. Furthermore, it is preferably 40% or more, and the stability is sufficiently high. The method for calculating the crystallinity is as described above.

  The heat treatment may be performed in either a dry atmosphere or a water vapor atmosphere. The heat treatment in a dry atmosphere is achieved, for example, by blowing high-temperature dry air in the air or increasing the temperature of the steel sheet by induction heating. On the other hand, the heat treatment in the steam atmosphere is achieved, for example, by spraying high-temperature and high-pressure steam on the film surface for several seconds, but an existing method such as retort sterilization may be used. In both the dry atmosphere and the steam atmosphere, the time required for the treatment is sufficient until the crystallinity rises to fall within the above-mentioned range.

  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 It is preferable that the plate thickness is reduced to 30 to 80%, more preferably 40 to 60% of the original metal plate.

  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.

  In the formulation shown in Table 1, spherical silica or calcium carbonate, barium sulfate, and an ethylene phthalate-ethylene isophthalate copolymer resin having a ratio of terephthalic acid to isophthalic acid of 90:10 (intrinsic viscosity 0.6 dl / g, Tg 70 ° C., Tc 170 C., Tm 230.degree. C., and Ge content 10 ppm) were supplied to an extruder, extruded from a T-die with a single screw extruder, and an unstretched resin film having a thickness of 25 .mu.m was prepared using a cooling drum.

  About Example 7, 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 biaxially stretched film. For Examples 17 and 18, two single screw extruders were used, one of which was spherical silica and another ethylene phthalate-ethylene isophthalate copolymer resin having a terephthalic acid and isophthalic acid ratio of 90:10. Is supplied with a mixture of 85 parts by weight of an ethylene phthalate-ethylene isophthalate copolymer resin having a terephthalic acid / isophthalic acid ratio of 90:10 and 15 parts by weight of a zinc-neutralized carboxylic acid-modified olefin (High Milan 1705 manufactured by Mitsui DuPont Polychemicals). Then, a two-layer unstretched film containing silica only in the upper layer was prepared by coextrusion using a feed block type T die. For Examples 19 and 20, two or three single-screw extruders were used, one of which was spherical silica and an ethylene phthalate-ethylene isophthalate copolymer resin having a terephthalic acid to isophthalic acid ratio of 90:10. Only the ethylene phthalate-ethylene isophthalate copolymer resin having a ratio of terephthalic acid and isophthalic acid of 90:10 is supplied to the remaining one or two units, and is coextruded using a feed block type T die and contains silica only in the upper layer. After forming a two- or three-layer unstretched film, the film was stretched three times in the longitudinal direction, three times in the transverse direction, biaxially stretched, and then heat treated at 170 ° C. to produce a biaxially stretched film.

  Moreover, as Examples 1-6, 8-18, and Comparative Examples 1-8 as outer films, unstretched films having a thickness of 15 μm (ethylene phthalate-ethylene iso-terephthalic acid / isophthalic acid ratio of 90:10) In Examples 7, 19, and 20, a biaxially stretched film (ethylene phthalate-ethylene isophthalate copolymer resin having a terephthalic acid and isophthalic acid ratio of 90:10) was used in Examples 7, 19, and 20. used.

A resin film-coated metal plate was prepared by coating the resin film obtained as described above on both surfaces of the 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.

  Here, the particle size of the particles dispersed in the resin film on the inner surface side is as follows. For the single layer film, the film is heated at 700 ° C. for about 5 hours, the PET is burned, and the residual particles are measured using the SEM. The minor axis was measured one by one and the particle size was calculated. For the two- and three-layer films, only the outermost layer was shaved with a cutting device, and only the particles in the outermost layer were measured by the above method.

The number of pores and particles is determined by observing the film surface with SEM, counting the corresponding number in the range of 100 μm × 100 μm at at least 10 locations on the surface of the arbitrary film, and multiplying the average value by 100 times in an area of 1 mm ² The number of holes and particles. 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 5 μm.

  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.

  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.

1. The canned resin-coated metal plate was subjected to first stage drawing and redrawing under the following conditions to obtain a thinned 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 ratio of the can body 45 to 60% of the thickness of the resin-coated metal plate before molding
2. The processing strain of the film introduced along with the strain-removing heat treatment can processing was heated and held for 30 seconds in a thermal environment having a film melting point of 230 ° C. and then rapidly cooled.
Here, regarding the number of holes and particles in the inner surface film of the thinned deep-drawn can, the part having the largest number of holes and particles was found by observing with a SEM in the can body, and the SEM was found for that part. The film surface was observed, and the corresponding number in the range of 100 μm × 100 μm was counted at at least 10 locations on any film surface, and the average value was multiplied by 100 to obtain the number of holes and particles 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 5 μm.

3. Evaluation of suitability of thinned deep-drawn cans and processability The following evaluations were made according to the limit that can be made without damaging the film. In addition, a pass is a thing of evaluation more than (circle).
Limiting degree of processing (thinning ratio): Molding with an evaluation thinning ratio of 45% is impossible: XX (poor)
Molding up to 45% thinning rate: × ↑
Moldable up to 50% thinning rate: △
Molding up to 55% thinning rate: ○ ↓
Moldable up to 60% thinning rate: ◎ (excellent)
・ Evaluation of impact resistance Neck processing was applied to a can body (thinning ratio 55%) subjected to heat treatment for removing strain, and after filling the can body with distilled water and attaching a lid and tightening, 30 cm at the bottom of the can A 0.5 kg iron ball was dropped from the height of the ball and shocked. Next, the lid is opened, 1% saline solution is filled inside the can so that the impacted part is immersed, and after immersion for 5 minutes, a 6V load is applied to the platinum electrode and the can metal part immersed in the liquid, Values were read and evaluated as follows. In addition, a pass is a thing of evaluation more than (circle).
Test result: Evaluation current value is 0.3 mA or more: XX (Inferior)
Current value is 0.1 mA to less than 0.3 mA: × ↑
Current value of 0.05 mA to less than 0.1 mA: Δ
Current value of 0.01 mA to less than 0.05 mA: ○ ↓
Current value is less than 0.01 mA: ◎ (excellent)
・ Corrosion-resistant strain relief heat treated can body (thinning ratio 50%) is necked, filled with beer (Sapporo black label), covered with lid, wrapped and cooled to 5 ° C After that, the can was dropped from a height of 30 cm with the bottom of the can facing down, and an impact was applied. Then, after maintaining for 30 days in an atmosphere of 40 ° C., the iron elution amount in the beer in the can was measured, and the corrosion resistance was evaluated by the elution amount. In addition, a pass is a thing of evaluation more than (circle).
Test result: Evaluated iron elution amount is 1.0 ppm or more: XX (Inferior)
Iron elution amount is 0.5 ppm or more to 1.0 ppm not yet: x ↑
Iron elution amount is 0.2 ppm or more and less than 0.5 ppm: Δ
Iron elution amount is 0.1 ppm or more and less than 0.2 ppm: ○ ↓
Iron elution amount is less than 0.1 ppm: ◎ (excellent)
・ After cleaning the inner surface of the can (thinning ratio: 50%) that has been heat treated to remove flavor, put a fragrance aqueous solution (d-limonene 20ppm aqueous solution), seal and leave it at 35 ° C for 20 days, then open Then, the amount of limonene extracted by ether immersion after washing the inside of the can with water was determined as the amount of adsorbed d-limonene per can by gas chromatography, and the taste characteristics were evaluated. A pass is a thing of evaluation more than (circle).
Test result: Evaluation adsorption amount exceeding 200 μg / can: × (poor)
Adsorption amount exceeds 100 μg / can and below 200 μg / can: Δ ↑
Adsorption amount of 30 μg / can and 100 μg / can or less: ○
Adsorption amount 10 μg / can over 30 μg / can: ◎ ↓
Adsorption amount 10μg / can or less: ◎◎ (excellent)

・ After washing the inner surface of the can body subjected to foaming strain relief heat treatment, filling with beer (Sapporo black label), filling with carbon dioxide gas so that the internal pressure becomes 1 kg / cm ^2, and cooling at 5 ° C. for 120 hours The can was opened in a room at 20 ° C., and the foamability of the beer surface after 5 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 cleaning the inner surface of the can subjected to foam-relieving heat treatment and filling with beer (Sapporo black label), it was charged with carbon dioxide so that the internal pressure became 1 kg / cm ² and cooled at 5 ° C for 120 hours. Thereafter, the container 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 10 minutes: △ ↑
More than 10 minutes to 20 minutes: ○
Over 20 minutes to 30 minutes: ◎ ↓
Over 30 minutes: ◎◎ (excellent)
The obtained results are shown in Table 1 together with the conditions.

  According to Table 1, in the present invention example, it is possible to obtain a resin film-coated metal can excellent in all of workability, impact resistance, corrosion resistance, flavor property, foaming property, and foam holding property. On the other hand, in the comparative example, any one or more of corrosion resistance, flavor property, foaming property, and foam retention property is inferior.

  In the formulation shown in Table 2, spherical silica and an ethylene phthalate-ethylene isophthalate copolymer resin having a ratio of terephthalic acid to isophthalic acid of 90:10 (inherent viscosity 0.6 dl / g, Tg 70 ° C., Tc 170 ° C., Tm 230 ° C., Ge A content of 10 ppm) was supplied to an extruder, extruded from a T-die with a single screw extruder, and an unstretched resin film having a thickness of 25 μm was prepared using a cooling drum.

  About Example 11, 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 biaxially stretched film. For Example 12, two single-screw extruders were used, one with spherical silica, and an ethylene phthalate-ethylene isophthalate copolymer resin with a terephthalic acid and isophthalic acid ratio of 90:10, and the other with A mixture of 85 parts by weight of an ethylene phthalate-ethylene isophthalate copolymer resin having a ratio of terephthalic acid and isophthalic acid of 90:10 and 15 parts by weight of a carboxylic acid-modified olefin (Nucrel N1108C manufactured by Mitsui DuPont Polychemical Co., Ltd.) A two-layer unstretched film containing silica only in the upper layer was produced by coextrusion using a T die. For Example 13, three uniaxial extruders were used, one of which was spherical silica and the other two phthalate-ethyleneisophthalate copolymer resins having a terephthalic acid / isophthalic acid ratio of 90:10. Is supplied with an ethylene phthalate-ethylene isophthalate copolymer resin having a ratio of terephthalic acid and isophthalic acid of 90:10, and is co-extruded using a feed block type T die to form a three-layer unstretched film containing silica only in the upper layer. After the preparation, the film was stretched three times in the longitudinal direction and three times in the transverse direction and biaxially stretched, and then heat treated at 170 ° C. to prepare a biaxially stretched film.

  Further, as Examples 1 to 10 and 12, as the outer surface film, an unstretched film having a thickness of 15 μm (ethylene phthalate-ethylene isophthalate copolymer resin having a terephthalic acid and isophthalic acid ratio of 90:10) is used. In Examples 11 and 13, a biaxially stretched film (ethylene phthalate-ethylene isophthalate copolymer resin having a ratio of terephthalic acid to isophthalic acid of 90:10) having a thickness of 15 μm was used.

A resin film-coated metal plate was prepared by coating the resin film obtained as described above on both surfaces of the 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.

  Here, the particle size of the particles dispersed in the resin film on the inner surface side is as follows. For the single layer film, the film is heated at 700 ° C. for about 5 hours, the PET is burned, and the residual particles are measured using the SEM. The minor axis was measured one by one and the particle size was calculated. For the two- and three-layer films, only the outermost layer was shaved with a cutting device, and only the particles in the outermost layer were measured by the above method.

  About the resin film coating metal plate of Examples 2-13, it heat-processed after resin film coating metal plate preparation. For a dry atmosphere, the resin-coated metal plate was placed in a baking furnace maintained at a predetermined temperature for a predetermined time, and then cooled in a room temperature atmosphere. On the other hand, the thing of water vapor | steam atmosphere was performed by using a retort sterilization processing equipment, putting the resin-coated metal plate in a retort equipment maintained at a predetermined temperature for a predetermined time, and then cooling in a room temperature atmosphere.

  The crystallinity after the heat treatment was measured by a density method. The film was peeled from the metal plate by immersing the film-coated metal plate in 10% hydrochloric acid soak, and the film density was measured using a density gradient tube. The method described above was used as a method for calculating the crystallinity from the film density.

The number of pores and particles is determined by observing the film surface with SEM, counting the corresponding number in the range of 100 μm × 100 μm at at least 10 locations on the surface of the arbitrary film, and multiplying the average value by 100 times in an area of 1 mm ² The number of holes and particles. 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 5 μm. 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.

  About the resin film-coated metal plate after heat treatment obtained from the above, a thinned deep drawn can is manufactured by the same method as in Example 1, and the suitability as a thinned deep drawn can is evaluated by the same method as in Example 1. did. The obtained results are shown in Table 2 together with the conditions.

  According to Table 2, in the example of the present invention, a resin film-coated metal can particularly excellent in foaming property and foam holding property can be obtained by each heat treatment.

Then, in Table 2, No. About 11 cans, after performing the distortion removal heat treatment (thinning rate 55%), the inner surface was washed, and beer (Sapporo black label) was poured along the can wall under the conditions shown in Table 3. The amount of beer foaming on the liquid surface 5 seconds after pouring beer was evaluated according to the following criteria.
Test result: Foam with an evaluation thickness of 30 mm or more is generated: x (poor)
Bubbles with a thickness of 5 mm or more and less than 30 mm are generated: △ ↑
Bubbles with a thickness of 1 mm or more and less than 5 mm are generated: ○
Bubbles less than 1mm in thickness are generated: ◎ ↓
No bubbles are generated: ◎◎ (excellent)
The obtained results are shown in Table 3 together with the conditions.

  According to Table 3, by cooling the can or beer to 8 ° C. or lower and filling it, bubbles are less likely to be generated and foaming during filling can be suppressed. Desirably, it is better to cool both the can and the beer. Moreover, if it is further lower temperature, foaming can be further suppressed, and filling at 5 ° C., further 2 ° C. or less is good. Moreover, when filling beer, it turns out that foaming can be suppressed further by filling after filling the inner surface of a can with water or beer.

  Since the resin film-coated metal can of the present invention is excellent for all, it can be used as a container filled with carbonated beverages such as beer and sparkling liquor, as well as excellent processability, impact resistance, corrosion resistance, flavor and foaming properties. It is also very useful in fields where foamability is required.

Claims (15)

A resin film-covered metal plate in which a resin film mainly composed of a thermoplastic polyester having a single layer or a layer structure of two or more layers is coated on at least one surface of the metal plate,
In the resin of the outermost layer of the resin film, (I) 0.01 to 0.5% by weight of particles having an average particle diameter of 0.5 to 5 μm, and (II) 0.01 to 2% of polyolefin resin A resin film-coated metal plate for carbonated beverage cans, which has excellent foaming properties and foam-holding properties, comprising a film containing 1% (film A) on at least one side. ^2. The foaming property and foam retention according to claim 1, wherein 5 to 5000 particles having an average particle diameter of 0.5 to 5 μm are exposed per 1 mm ^{2 on} the surface of the resin film A. 3. Resin film coated metal plate for carbonated beverage cans with excellent properties . The resin film thickness of the outermost layer of the resin film A is 2 to 10 μm, and the acid component in the polyester resin contained in the outermost layer resin is 5 to 18 parts by weight of isophthalic acid and the balance is terephthalic acid. The resin film-coated metal plate for carbonated beverage cans according to claim 1 or 2, which is excellent in foaming property and foam holding property . The resin in the lowermost layer of the resin film A in contact with the metal plate contains 5 to 30% by weight of a carboxylic acid derivative-modified polyolefin granular resin, according to any one of claims 1 to 3 . Resin film-coated metal plate for carbonated beverage cans with excellent foaming and foam retention . And the outermost layer of the resin thickness in the resin film A, the ratio of the resin film thickness other than the outermost layer, 1: 15 to 1: according to any one of claims 1-4, characterized in that the 2 Resin film-coated metal plate for carbonated beverage cans with excellent foaming and foam retention . The resin film-coated metal plate according to any one of claims 1 to 5 , wherein the resin film-coated metal plate is subjected to a heat treatment in a high-temperature atmosphere of 80 ° C or higher and 200 ° C or lower after the resin film is coated. A resin film-coated metal plate for a carbonated beverage can excellent in foaming property and foam holding property . 7. The resin film-coated metal plate for carbonated beverage cans according to claim 6 , wherein the resin film has a crystallinity of 15% or more. Carbonate excellent in foaming property and foam holding property, wherein the resin film-coated metal plate according to any one of claims 1 to 7 is formed such that the resin film-coated surface is on the inner surface side of the can. Resin film coated metal can for beverages . 9. The foaming property and foam holding property according to claim 8 , wherein a maximum of 10 to 10,000 particles having a particle size of 0.5 to 5 μm are exposed per 1 mm ^{2 on the} surface of the resin film. Excellent resin film coated metal can for carbonated beverages . 10. The foaming property and foam holding property according to claim 8 or 9 , wherein a maximum of 1-1000 pores having a pore diameter of 0.5-5 [mu] m are present on the surface of the resin film per 1 mm < ² > area . Resin film-coated metal can for carbonated beverages . The resin film surface, any particle size pores formed by particles of 0.5~5μm is, of claims 8 to 10, characterized in that is present from 2 to 500 pieces at maximum per area 1 mm ² foaming properties and carbonated beverage resin film-coated metal cans having excellent foam has properties according to or claim. Carbonate excellent in foaming property and foam holding property, wherein the resin film-coated metal can according to any one of claims 8 to 11 is heat-treated to make the crystallinity of the resin film 30% or more. Resin film coated metal can for beverages . The carbonic acid excellent in foaming property and foam holding property according to any one of claims 8 to 12, wherein the water contact angle of the resin film surface on the inner surface side of the resin film-coated metal can is 80 degrees or more. Resin film coated metal can for beverages . The surface free energy of the resin film surface on the inner surface side of the resin film-coated metal can is 35 mN / m or less, and is excellent in foaming property and foam holding property according to any one of claims 8 to 13. Resin film coated metal can for carbonated beverages . The foaming property and foam retention according to any one of claims 8 to 14, wherein the polar component of the surface free energy on the resin film surface on the inner surface side of the resin film-coated metal can is 5 mN / m or less. Resin film coated metal can for carbonated beverages with excellent properties .