JP2006001033A - Polyester film for use in coating metal sheet, polyester film-coated metal sheet and polyester film-coated metal container - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film for use in coating a metal sheet which is not blocked when wound in a roll form, does not damage a metal gloss feeling even if the metal sheet is coated with the printed film and the coated metal sheet is formed into a can, does not cause the delamination between ink or an adhesive and the film and a trouble such as the shift of a printing pitch and can be subjected to short-time retort treatment at a high temperature. <P>SOLUTION: The polyester film is formed using a polyester resin, wherein the compositional ratio of ethylene terephthalate is 80 mol% or above, as a raw material and characterized in that the heat shrinkage factor in the longitudinal direction of the polyester film at 190°C is 5% or below, the heat shrinkage factor in the lateral direction thereof is 2% or below, the content of a lubricant is 0.03-0.2 wt.% and the haze thereof is 2.0% or below. At least one side of the polyester film is coated with a coating film comprising a composition mainly containing a water-soluble polyester polyurethane. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is mainly for the outer surface of a metal can body, and is coated on the outer surface of a can for the purpose of preventing corrosion of metal containers for foodstuffs such as soft drinks, beer, and canned foods. TECHNICAL FIELD The present invention relates to a highly transparent polyester-based film for coating a metal plate used in applications requiring a glossy surface, a polyester-based film-coated metal plate obtained by coating the polyester-based film on the metal plate, and the polyester-based film-coated metal plate The present invention relates to a polyester film-covered metal container formed by molding.

  Conventionally, a method of coating a thermoplastic resin film has been carried out as a method for preventing corrosion of the inner surface and outer surface of a metal can for foodstuffs. For example, a polyolefin film such as polyethylene or polypropylene, or a polyester film such as polyethylene terephthalate is coated on a heated metal plate such as tin-free steel, and the film-coated metal plate is used for a metal can.

  However, among the thermoplastic resin films, for example, when a polyolefin-based film such as polyethylene or polypropylene is used, the heat history in the can making process or the heat history such as retort treatment after can making is inferior in heat resistance. When receiving, there may be a problem that the film peels off from the film-coated metal plate.

  On the other hand, a method using a polyester film as the thermoplastic resin film is a more preferable method because the problems of the polyolefin film are improved.

  The polyester-based film has a drawback that it is easy to cause blocking (blocking phenomenon) when the film is wound into a roll, and generally a lubricant is added to the film for preventing blocking. However, when the lubricant in the film is added more than necessary, the lubricant may inhibit transparency, or the lubricant itself may cause foreign matter.

  When it is required that the beverage can itself has a metallic luster due to design requirements, etc., it is possible to print on a commonly used film for coating a metal plate and apply it to the metal plate. Because the feeling is insufficient, after all, it prints directly on the metal plate, applies a clear coat, pulls out a part of the film surface and shows the metal plate surface, and presents a metallic luster. .

  Further, in a polyester film, delamination (delamination phenomenon) occurs at the interface between the film and the adhesive and between the film and the ink, which may be a problem. In particular, if high temperature retort treatment is applied, delamination is likely to occur at the interface between the film and adhesive, and the film and ink, and retort treatment cannot be performed at high temperatures in a short time. This is the current situation.

  The present invention has been made against the background of the problems of the prior art. In a polyester film for coating a metal plate, the film wound on a roll is not blocked, and the printed film is coated on a metal plate and canned. No loss of metallic luster, no delamination between the ink or adhesive and the film, no problems such as printing pitch misalignment, etc., and the ability to perform retorting at high temperatures for a short time. This is a problem.

The present invention
(1) A polyester film made from a polyester resin having a composition ratio of ethylene terephthalate of 80 mol% or more, wherein the polyester film has a heat shrinkage rate of 190% or less in the longitudinal direction of 5% or less, and the transverse direction. The heat shrinkage ratio is 2% or less, the lubricant content is 0.03 to 0.2% by weight, the haze is 2.0% or less, and at least one surface of the polyester film is mainly water-soluble polyester. A polyester-based film for coating a metal plate, characterized by being coated with a coating film comprising a composition containing polyurethane;
(2) A polyester film-coated metal plate obtained by coating the polyester film according to (1) with at least one surface of a metal plate coated with the coating film, the polyester film-coated metal plate A polyester film-coated metal plate, wherein the film surface side has a light reflectance of 70% or more at wavelengths of 450 nm, 550 nm and 700 nm,
(3) A polyester film-coated metal container formed by molding the polyester film-coated metal plate according to (2),
It is.

  The polyester film for coating a metal plate according to the present invention is a film excellent in adhesiveness, transparency and heat resistance, and when used as a film for the outer surface of a metal can that requires a metallic luster, a more beautiful metal container There is an advantage that can be.

The present invention is described in detail below.
The polyester film of the present invention may be a single layer film or a laminated film.

  The polyester resin used as a raw material for the polyester film in the present invention is a polyester resin mainly composed of ethylene terephthalate. The term “ethylene terephthalate as a main component” means that, in the present invention, at least the composition ratio of ethylene terephthalate is configured to be 80 mol% or more. When an ethylene terephthalate component is comprised in the range shown above, there is almost no problem in heat resistance as a metal plate coating film. When the ethylene terephthalate component is less than 80 mol%, the heat resistance is inferior, and troubles such as whitening and delamination may occur in the process after high-temperature heat treatment.

  To the polyester resin used in the present invention, a component other than ethylene terephthalate may be copolymerized or a polyester resin composed of these components may be added without departing from the gist of the present invention. For example, aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, and biphenyldicarboxylic acid; aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dodecanedicarboxylic acid, and dimer acid An alicyclic dicarboxylic acid such as cyclohexanedicarboxylic acid, an aliphatic diol such as ethylene glycol, diethylene glycol, triethylene glycol, propanediol, butanediol, hexanediol, dodecamethylene glycol, neopentyl glycol; cyclohexanedimethanol, etc. Aromatic diols; aromatic diols such as ethylene oxide adducts of bisphenol derivatives may be copolymerized or polyester resins composed of these components may be added. The blending amount of these components needs to be 20 mol% or less in order to ensure the composition ratio of the ethylene terephthalate of 80 mol% or more.

  The melting point of the polyester resin used in the present invention is preferably 240 to 260 ° C, more preferably 245 to 258 ° C. If the melting point is less than 240 ° C., the heat resistance becomes insufficient, and it is often not preferred. In addition, if the melting point exceeds 260 ° C., the production cost is increased and it is economically disadvantageous, which is often not preferred.

  Moreover, it is preferable that the intrinsic viscosity (IV) of the polyester-type resin used in this invention is the range of 0.5-0.8. If the intrinsic viscosity (IV) is less than 0.5, it is not preferable because the oligomer is likely to precipitate. Further, if the intrinsic viscosity (IV) exceeds 0.8, the production cost increases, which is economically disadvantageous.

  The polyester resin used in the present invention needs to contain a lubricant. As described above, the polyester film has the disadvantage that it is likely to cause blocking when the film is wound into a roll, and in order to prevent this blocking, a lubricant is added to the polyester resin used as a raw material. Is common.

  The content of the lubricant is required to be 0.03 to 0.2% by weight, preferably 0.05 to 0.1% by weight, based on the total amount of the polyester resin. If it is less than 0.03% by weight, the slipping property such as blocking resistance of the film is inferior, and the film is easily wrinkled. If it exceeds 0.2% by weight, the transparency of the film is lowered, This is because when the metal plate is coated, the metallic luster is inferior. In order to maintain the metallic luster, it is necessary to suppress the haze of the film described later to 2% or less, and to suppress the haze to 2% or less, the content of the lubricant needs to be 0.2% by weight or less. is there. Here, as the lubricant, inert inorganic particles such as silica, alumina, kaolin, clay, titanium oxide, calcium phosphate, calcium carbonate, lithium fluoride, barium sulfate, and carbon black are preferable. In particular, silica is preferred as the lubricant. The average particle size of the lubricant is preferably 1 to 3 μm. This is because if it is less than 1 μm, the slipping property such as blocking resistance is inferior, whereas if it exceeds 3 μm, the lubricant is likely to fall off, and the film may be broken when the metal plate is coated.

  The blending of the lubricant into the polyester resin may be performed in the production process of the polyester resin, or the above components may be added to the polyester resin and melt-kneaded. It is also possible to produce a polyester-based resin containing the above components at a high concentration, and use this as a master batch to melt-knead with a polyester-based resin containing no or a small amount of the above components.

  Moreover, the polyester resin in the present invention can contain an antioxidant, a heat stabilizer, an ultraviolet absorber, a plasticizer, a pigment, an antistatic agent, a lubricant, a crystal nucleating agent, and the like, if necessary.

  Although it does not specifically limit as a manufacturing method of the polyester-type film of this invention, For example, dryers, such as a hopper drier and a paddle drier, or a vacuum so that the residual moisture content may be 150 ppm or less It can be manufactured by a method of drying using a dryer and extruding into a film at a temperature of 200 to 300 ° C. using an extruder. Or you may employ | adopt the method of extruding an undried polyester-type resin raw material similarly to a film form, removing a water | moisture content in a vent type extruder. In any case, if the residual moisture content exceeds 150 ppm, the viscosity of the obtained film is lowered, and troubles such as breakage occur at the time of film stretching, which is not preferable. When extruding, any existing method such as T-die method or tubular method may be adopted. After extrusion, it is cooled rapidly to obtain an unstretched film.

  The polyester film of the present invention is preferably a biaxially stretched film obtained by stretching the unstretched film in the longitudinal and transverse directions. By biaxially stretching the polyester film, the barrier property is increased, and metal rust caused by moisture in the air can be prevented. The biaxial stretching method is not particularly limited, but it is preferable to use the sequential biaxial stretching method because the range of thickness that can be produced is widened. In this case, the stretching ratio in the longitudinal direction is preferably 2 to 5 times, more preferably 2.5 to 4 times, and the stretching temperature is preferably 100 to 150 ° C, more preferably 110 to 140 ° C. is there. The stretching ratio in the transverse direction is preferably 2 to 5 times, more preferably 2.5 to 4 times, and the stretching temperature is preferably 120 to 160 ° C, more preferably 125 to 150 ° C.

  The residual shrinkage stress due to biaxial stretching of the polyester film is preferably reduced or removed by a heat setting method or the like. This is because the dimensional change due to the heat history in the can manufacturing process or the like can be reduced. Reduction or removal of residual shrinkage stress by biaxial stretching of the film is preferably at a temperature not higher than 10-30 ° C. below the melting point of the film, more preferably at a temperature not higher than 20-30 ° C. below the melting point of the film. Heat fixing.

  The thickness of the polyester film of the present invention is preferably in the range of 5 to 25 μm. If the thickness is less than 5 μm, the barrier property is inferior and the corrosion resistance may be deteriorated. On the other hand, if the thickness exceeds 25 μm, the cost for production increases, which is economically disadvantageous. Because.

  The polyester film of the present invention has at least one surface mainly water-soluble from the viewpoint of adhesiveness, specifically, from the viewpoint of adhesiveness between the polyester film and the adhesive and between the polyester film and the printing ink. It is necessary to be coated with a coating film made of a composition containing the polyester polyurethane. In particular, from the viewpoint of adhesion after retorting, the coating film needs to be a composition containing a water-soluble polyester polyurethane resin.

  The polyester polyurethane resin is a resin having an ester bond and a urethane bond in the main chain.

  In the polyester polyurethane resin, a urethane bond in the main chain is formed by a reaction between an isocyanate component and a polyol component. As the isocyanate component, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, 1, There are 5-naphthalene diisocyanate, hexamethylene diisocyanate, hydrogenated diphenylmethane diisocyanate, etc., and these may be used alone or in combination of two or more. Good. Examples of the polyol component include, as diols, aliphatic glycols such as ethylene glycol, propanediol, pentanediol, hexanediol and neopentyl glycol, alicyclic glycols such as cyclohexanedimethanol, and aromatic glycols such as bisphenol A and bisphenol S. These may be used alone or in combination of two or more.

  In the polyester polyurethane resin, the ester bond in the main chain is formed by the reaction of a dicarboxylic acid component and a diol component. Dicarboxylic acid components include terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, decanedicarboxylic acid, maleic acid, fumaric acid, other oxycarboxylic acids, and alicyclic dicarboxylic acids. There are acids, etc., and these may be used alone or in combination of two or more. Examples of the diol component include aliphatic glycols such as ethylene glycol, propanediol, pentanediol, hexanediol and neopentyl glycol, alicyclic glycols such as cyclohexanedimethanol, and aromatic glycols such as bisphenol A and bisphenol S. These may be used alone or in combination of two or more.

  As described above, the polyester polyurethane resin used in the polyester film of the present invention needs to be water-soluble, and it is preferably applied in a water-soluble form from the viewpoint of handleability. In order to impart water solubility to the polyester polyurethane resin, for example, it is preferable to copolymerize a compound having a hydrophilic group such as a sulfonic acid group or a carboxyl group in the side chain as a part of the diol component. Specific examples of the compound having a hydrophilic group include dimethylolpropionic acid, dimethylolbutanoic acid, dihydroxyfumaric acid, sodium 2-sulfonate-1,4-butanediol, and the like.

  As described above, at least one surface of the polyester film of the present invention needs to be coated with a coating film made of the above composition. The coating film is preferably applied by so-called coating and is controlled to a thickness of 0.001 μm to 1 μm. If the coating thickness is 0.001 μm or less, the adhesiveness is not sufficient, and delamination is caused at the interface of the printing ink, and if the coating thickness exceeds 1 μm, it is excessive quality, This is because it is not economically preferable. This coating treatment may be either a stretched film during film formation (in-line) or a film after film formation (off-line).

  The polyester film of the present invention needs to have high transparency in order to obtain a metallic luster when the film is coated on a metal plate, and its haze is such that the film is coated with the above-mentioned polyester polyurethane resin coating film. It is necessary to be 2% or less in the state. When the haze exceeds 2%, when the film is coated on the metal plate, the metallic gloss is clearly inferior to the metal plate not coated with the film, which is not preferable. This is because the lubricant contained in the film absorbs or diffuses light.

  When the polyester-based film of the present invention is coated on a metal plate to form a film-coated metal plate, the light reflectance measured by the measurement method described later to obtain a sufficient metallic luster, that is, the film coating It is preferable that the light reflectance at wavelengths of 450 nm, 550 nm, and 700 nm from the film surface side of the metal plate is 70% or more, but the haze is 2% or less for the light reflectance to be 70% or more. It is necessary.

  The polyester film of the present invention is required to have a heat shrinkage rate in the longitudinal direction at 190 ° C. of 5% or less and a heat shrinkage rate in the transverse direction of 2% or less. If the temperature is outside this range, for example, to prevent damage to the surface of the beverage can, printing with a cured heat-resistant layer that crosslinks at a high temperature as described later on a polyester film causes shrinkage due to thermal history. However, this causes a trouble that the printing pitch of each can shifts, which is not preferable.

  The method for setting the thermal shrinkage in the longitudinal direction at 190 ° C. of the polyester film to 5% or less and the thermal shrinkage in the transverse direction to 2% or less is not particularly limited. As a film having a high degree of crystallinity by copolymerizing butanediol and increasing the crystallization rate, or when the polyester film is the above-mentioned biaxially stretched film, the temperature conditions as described above And a method of suppressing heat shrinkage by heat fixing, or a method of suppressing heat shrinkage by providing a relaxation step after stretching when the polyester film is a stretched film described later.

  The polyester film is preferably subjected to a wettability improving treatment in advance on at least the surface opposite to the coated surface in order to improve the adhesion to the printing ink or the adhesive. For example, by performing a corona discharge treatment, the surface tension of the film surface is set to 40 mN / m or more, more preferably 45 mN / m or more.

  When the polyester film of the present invention is used for so-called gravure printing, it is preferable to provide a cured heat-resistant layer in advance on the opposite side of the film from the coated surface of the polyester polyurethane resin coating film. The cured heat-resistant layer plays a role in preventing film damage and threading in each process including the can making process, and also for heat treatment and retort after seam welding at the time of can making and content filling. It also serves to suppress the softening and whitening phenomenon of the film during processing.

  The material used for the cured heat-resistant layer is a curable resin, such as an epoxy resin, a melamine resin, a benzoguanamine resin, an acrylic resin, a urethane resin, a polyester resin, a phenoxy resin, an oxazoline resin, and Various curing reactive resins such as those various modified resins are used. These curable reactive resins may be used alone or in combination of two or more. Moreover, since it is requested | required that it is excellent in heat resistance, it is preferable that melting | fusing point or decomposition temperature is 250 degreeC or more, and it is more preferable that it is 300 degreeC or more.

  The curing reaction of the curing reactive resin may be a curing reaction by heat, light, electron beam or the like, or a conventionally known low molecular type curing agent may be used. Examples of the low molecular type curing agent include melamine compounds such as hexamethylol melamine and alkoxy derivatives thereof, and isocyanates such as tolylene diisocyanate.

  A method for forming the cured heat-resistant layer is not particularly limited, but a so-called coating method in which a curing reactive resin is dissolved in a solvent, applied to a film, and dried and cured is a preferred embodiment.

The coating amount of the cured heat resistant layer is preferably controlled to be 0.3 to 10 g / m ² in a dried / cured state. More preferably in the range of 0.3 to 5 g / ^{m 2.} When the coating amount (dried / cured state) is less than 0.3 g / m ² , the protective effect on the surface of the polyester film is often insufficient, and conversely when it exceeds 10 g / m ² , the coated metal plate is bent. Cracks are likely to occur in the cured heat-resistant layer during processing.

  The polyester film-coated metal plate of the present invention is provided with an adhesive layer on the ink layer side after providing a multicolor printing ink layer such as gravure printing on the coated surface of the polyester polyurethane resin coating film of the polyester film, It can be obtained by coating a polyester film on a metal plate via the adhesive layer. By covering the polyester film with the metal plate via the adhesive layer, the polyester film and the metal plate can be firmly adhered to each other, so that the dimensional change of the polyester film due to thermal history can be reduced. In addition, barrier properties and corrosion resistance can be further improved.

  As a coating method using the above-mentioned adhesive, for example, it is preferable to form an adhesive layer on a film in a partially cured state, and to completely cure in a state where it is coated on a metal plate. A method using light or an electron beam is preferred. Examples of the adhesive used in the above method include epoxy resins, polyurethane resins, polyester resins, polyester polyurethane resins, isocyanate resins, and various modified resins thereof. Further, a conventionally known low molecular type curing agent may be used in combination. Examples of the low molecular type curing agent include melamine compounds such as hexamethylol melamine and alkoxy derivatives thereof, and isocyanates such as tolylene diisocyanate.

  A method for forming the adhesive layer is not particularly limited, but a so-called coating method in which an adhesive resin is dissolved in a solvent and applied is a preferred embodiment.

  The adhesive layer is preferably controlled so that the thickness after curing is 0.5 to 5 μm. More preferably, it is the range of 1-3 micrometers. When the thickness after curing is less than 0.5 μm, the adhesive force between the polyester film and the metal plate is often insufficient, and conversely, when the thickness after curing exceeds 5 μm, the production cost increases. In addition, cracks tend to occur when stress such as bending is applied, which is often not preferable.

  The metal plate used for the film-coated metal plate is not particularly limited, but it is particularly preferable to use tin-free steel from the viewpoint of metallic luster. Further, the thickness is not particularly limited, but is preferably 100 to 500 μm, more preferably 150 to 400 μm from the viewpoint of economical efficiency represented by the cost of materials and canning processing speed, etc., while ensuring the material strength. It is.

  In order to obtain a metallic luster, the polyester film-coated metal plate obtained as described above has a light reflectance measured by a measurement method described later, that is, 450 nm from the film surface side of the film-coated metal plate. The light reflectance at wavelengths of 550 nm and 700 nm is preferably 70% or more. In order to obtain a metallic luster on the film surface of the film-coated metal plate, all wavelengths in the visible spectrum need to be transmitted through the film and reflected on the surface of the metal plate. As described above, the haze needs to be 2% or less. By making the light reflectance of wavelengths of 450 nm, 550 nm, and 700 nm particularly 70% or more among all wavelengths in the visible spectrum, the specific absorptions of the three primary colors of blue, green, and red can be balanced, A sufficient metallic luster can be obtained on the film surface of the polyester film-coated metal sheet.

  The polyester-based film-coated metal plate obtained as described above is beautiful and has excellent surface wear resistance, and the coated metal plate can be used as various panel materials and cosmetic outer plate materials as they are. Not only that, but if this can be made into a desired shape according to a conventional method with the cured heat-resistant layer as the outside, a very beautiful and highly-designed metal container can be obtained. For example, metal cans such as soft drinks, beer, and canned foods It can be suitably used as a material.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and the content and effect of this invention are demonstrated concretely, this invention is not limited to a following example, unless it deviates from the summary.

  In addition, the measuring method of each characteristic of the film in an Example and a comparative example is described below.

(1) Method for measuring intrinsic viscosity In a mixed solvent of phenol / tetrachloroethane (weight ratio: 6/4), the polyester resin as a raw material of Example 1 and Comparative Example 1 is adjusted to a concentration of 0.4 g / dl. It melt | dissolved and measured at the temperature of 30 degreeC using the Ubbelohde type | mold viscosity tube.

(2) Melting | fusing point measuring method The polyester-type resin as a raw material of Example 1 and the comparative example 1 was heat-melted for 5 minutes at 300 degreeC, Then, it rapidly_cool | quenched with liquid nitrogen. Using 10 mg of the sample as a sample, the endothermic peak temperature based on crystal melting that appears when the temperature was raised at a rate of 20 ° C./min was measured with a differential scanning calorimeter (DSC-60) manufactured by Shimadzu Corporation.

(3) Moisture content measuring method The polyester resin raw material chips of Example 1 and Comparative Example 1 immediately after finishing the drying process are sampled in containers, respectively, and sealed until the moisture content is measured. About 2 g of raw material chips were weighed and measured at a vaporization temperature of 180 ° C. using a Karl Fischer moisture meter (MKC-210) with a moisture vaporizer (ADP-351) manufactured by Kyoto Electronics Industry Co., Ltd.

(4) Haze measurement method The polyester film obtained in Example 1 and Comparative Example 1 was covered with a polyester polyurethane resin coating film by the haze (cloudiness) measurement method shown in JIS K7105. Measured with

(5) Measuring method of thermal contraction rate Based on JIS C-2318, the thermal contraction rate of the polyester film obtained in Example 1 and Comparative Example 1 after 190 ° C. and 30 minutes was measured. The measurement direction was two directions, the vertical direction and the horizontal direction.

(6) Measuring method of film wettability (surface tension) According to JIS K6768 polyethylene and polypropylene film wetting test method, the surface tension of the corona discharge-treated surface of the polyester film obtained in Example 1 and Comparative Example 1 was measured. It was measured.

(7) Gravure printability (print sharpness) evaluation Coating liquid composed of polyester resin / epoxy resin / melamine resin on the corona discharge-treated surface of the polyester film obtained in Example 1 and Comparative Example 1 (MA310 (product) Name), manufactured by Sakuranomiya Chemical Co., Ltd.), and the polyurethane test pattern gravure printing was performed on the polyester polyurethane resin coating surface. confirmed.
○: No problem △: Poor print clarity ×: Print missing / ink skip

(8) Light reflectance Using a Hitachi High-Technologies spectrophotometer (U-3310 type spectrophotometer), a sample obtained by cutting a film-covered metal plate obtained in the same manner as in the above (7) into approximately 40 mm squares was 280 to 800 mm. The light reflectance was measured between 780 nm. The reflected light intensity relative to the incident light intensity was expressed as a percentage.

(9) Adhesion evaluation The polyester-based film-coated metal plate obtained in Example 1 and Comparative Example 1 was cut into a size of 130 mm × 190 mm, the film-coated metal plate was formed into a cylindrical shape, and then covered with a lid. A film-coated metal container was obtained, and the situation of the lid molding part at that time and the situation of the lid molding part after performing the retort treatment at 125 ° C. for 30 minutes were evaluated.
○: No change ×: Delamination occurs in the molded part

(10) Metallic glossiness The metallic glossiness when direct sunlight was applied to the polyester film-coated metal container was evaluated according to the following criteria.
○: Metal gloss is sufficient ×: Metal gloss is inferior

[Example 1]
(Manufacture of polyester film)
Polyethylene terephthalate (RE553 / ST553 (both trade names) (manufactured by Toyobo Co., Ltd.) at a weight ratio of 25/75) having an intrinsic viscosity of 0.62 and a melting point of 254 ° C. as a raw material polyester resin The amount of silica was adjusted so that it contained 0.05% by weight of agglomerated silica having an average particle size of 1.5 μm, and pressed to form a chip. This raw material chip was dried with a paddle dryer, and the water content was measured to be 39 ppm. The dried raw material chips were melted with an extruder at 285 ° C. This melt was extruded from a die onto a cooling drum at 35 ° C. to obtain an amorphous sheet. Thereafter, the amorphous sheet was stretched 3.3 times in the machine direction at 120 ° C. and 4.0 times in the transverse direction at 130 ° C., and heat-set at 235 ° C. to produce a polyester film having a thickness of 12 μm. For the film, as a composition containing a water-soluble polyester polyurethane resin, a coating solution (Hydran HW340 (trade name), Dainippon Ink & Chemicals, Inc.) adjusted to have a coating layer thickness of 0.05 μm. Manufactured by the gravure coating method and dried at 235 ° C. At the same time, a corona discharge treatment was performed on the surface opposite to the coated surface. The film was measured for haze, heat shrinkage at 190 ° C. (longitudinal and transverse directions) and surface tension, respectively 1.8%, 1.7%, 0.3%, 51 mN / m. Met. The results are shown in Table 1.

  Moreover, the corona discharge treatment surface of the obtained polyester film is clear coated with a coating liquid (MA310 (trade name), manufactured by Sakuranomiya Chemical Co., Ltd.) composed of polyester resin / epoxy resin / melamine resin, and polyester polyurethane resin. When a multicolor test pattern was printed on the coating surface side by the gravure printing method, problems such as printing omission and ink skipping did not occur. Also, the print clarity was sufficient. The results are shown in Table 1.

(Manufacture of film-coated metal plates)
A polyester-based adhesive (Byron-300 (trade name), Toyobo Co., Ltd.) made of linear saturated polyester as an adhesive on the coating liquid (hydran HW340) coating surface (printing surface) of the polyester-based film of Example 1. And a curing agent (Coronate L (trade name), manufactured by Nippon Polyurethane Industry Co., Ltd.) (weight ratio: 93/7) was applied so that the thickness after curing was 1.5 μm. Next, a 190 μm-thick metal plate (tin-free steel, L-type bright finish, surface roughness 0.3 to 0.5 μm, manufactured by Nippon Steel Corporation) preheated at 200 ° C. The plate and the surface of the polyester film on the adhesive layer side are matched, and the film is coated with a pressure of 500 N / cm between the rubber roll and the rubber roll at a speed of 10 m / min. A metal plate was obtained. The light reflectances of wavelengths of 450 nm, 550 nm, and 700 nm on the film surface side of the obtained film-coated metal plate were 78.2%, 82.8%, and 95.1%, respectively. The results are shown in Table 1.

(Manufacture of metal containers)
A three-piece can was manufactured using the obtained polyester film-coated metal plate. During the production of cans, no problems such as film delamination occurred. Moreover, even if it performed the retort process of 125 degreeC x 30 minutes, adhesive evaluation was (circle). Furthermore, when the metal glossiness of the obtained metal container was evaluated, it was (circle). The results are shown in Table 1.

[Comparative Example 1]
In Example 1, a polyester film was produced in the same manner as in Example 1 except that the content of the aggregation type silica was 0.25% by weight. In addition, the moisture content of the raw material chip | tip immediately after complete | finishing a drying process was 45 ppm.

  The haze, the heat shrinkage (longitudinal direction and transverse direction) at 190 ° C., and the surface tension of the polyester film of Comparative Example 1 are 4.6%, 1.8%, 0.2%, and 51 mN / m, respectively. Met. Moreover, in the gravure printing evaluation of the multicolor test pattern, problems such as printing omission and ink skipping did not occur, but the printing clarity was inferior. The results are shown in Table 1.

  The polyester film was coated on a metal plate in the same manner as in Example 1 to obtain a polyester film-coated metal plate, and light reflection at wavelengths of 450 nm, 550 nm, and 700 nm on the film surface side of the obtained polyester film-coated metal plate. When the rate was measured, they were 52.1%, 68.6%, and 88.3%, respectively. The results are shown in Table 1.

  A three-piece can was manufactured using the obtained polyester film-coated metal plate. During the production of cans, no problems such as film delamination occurred. Moreover, even if it performed the retort process of 125 degreeC x 30 minutes, adhesive evaluation was (circle). Furthermore, when the metal glossiness of the obtained metal container was evaluated, it was x. The results are shown in Table 1.

注）ＥＴＰ；エチレンテレフタレート

Note) ETP; ethylene terephthalate

By using the polyester-based film for coating a metal plate of the present invention, there is no delamination between the ink and the adhesive and the film, and troubles such as printing pitch deviation do not occur, and the beverage is retorted at a high temperature in a short time. In addition, it is possible to manufacture a metal container with a film-coated metal plate that can obtain a sufficient metallic luster.

Claims (3)

  A polyester film made from a polyester resin having a composition ratio of ethylene terephthalate of 80 mol% or more, wherein the polyester film has a heat shrinkage in the vertical direction at 190 ° C. of 5% or less and a heat shrinkage in the horizontal direction. The rate is 2% or less, the content of the lubricant is 0.03 to 0.2% by weight, the haze is 2.0% or less, and at least one surface of the polyester film mainly contains a water-soluble polyester polyurethane. A polyester film for coating a metal plate, which is coated with a coating film comprising the composition.   A polyester film-covered metal plate comprising the polyester film according to claim 1 coated on at least one surface of the metal plate in contact with the metal plate on the surface coated with the coating film, A polyester film-coated metal sheet, wherein the light reflectance on the film surface side of the film-based metal sheet is 70% or more at wavelengths of 450 nm, 550 nm, and 700 nm, respectively. A polyester film-coated metal container formed by molding the polyester film-coated metal plate according to claim 2.