JP2005096444A - Polyester film for 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 coating a metal sheet not producing the shaving refuse of the film at the time of seaming processing and not containing Sb having a control value, a polyester film coated metal sheet excellent in can making processability and a polyester film coated metal container excellent in corrosion resistance and the protectivity of food becoming content. <P>SOLUTION: The polyester film has a two-layered constitution of layer A/layer B wherein the layer A comprises a polyester resin with a melting point Tma of 240-260°C and an intrinsic viscosity IVa of 0.55-0.75 and the layer B comprises a polyester resin with a melting point Tmb of 220-235°C and an intrinsic viscosity IVb of 0.55-0.75. The maximum values of shrinkage stress in the flow direction and width direction of the polyester film when the polyester film is measured by a thermomechanical analyzer (TMA) are 1.2-3.0 MPa. Each of the maximum values of shrinkage stress satisfies the formula: Fx >Fy (wherein Fx is the maximum value of the shrinkage stress in the flow direction of the film and Fy is the maximum value of the shrinkage stress in the width direction of the film). This polyester film contains no Sb element substantially. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a polyester film used for the purpose of preventing corrosion of metal containers for foodstuffs such as soft drinks, beer, and canned foods, a polyester film-coated metal plate obtained by coating the polyester film on a metal plate, and The present invention relates to a polyester film-coated metal container formed by molding the polyester film-coated metal plate.

  Conventionally, paint is generally applied to prevent corrosion of the inner and outer surfaces of metal cans, and various thermosetting resins such as epoxy and phenol are used as the paint.

  Most of the methods for applying a thermosetting resin paint use a solvent-type paint. Formation of the coating requires heating at 150-250 ° C for several minutes at a high temperature and for a long time, and since a large amount of organic solvent is scattered during baking, improvements such as simplification of the process and prevention of pollution are desired. Has been.

  Further, in the coating film formed under the above-described conditions, it is inevitable that a small amount of the organic solvent remains as a result. For example, the metal can on which the coating film is formed is filled with food. In some cases, organic solvents can migrate to foodstuffs, adversely affecting the taste and smell of foodstuffs. Furthermore, additives contained in the paint and low molecular weight substances resulting from imperfect cross-linking reaction may migrate to food products and have the same adverse effects as in the case of the residual organic solvent described above.

  Another method for preventing corrosion on the inner and outer surfaces of the metal can is to use a thermoplastic resin film. For example, a polyolefin film such as a polypropylene film or a polyester film is coated on a heated metal plate such as tin-free steel, and the film-coated metal plate is used for a metal can.

  Among the above-mentioned problems, problems such as simplification of the process and prevention of pollution can be solved by the method using the thermoplastic resin film.

  However, among the thermoplastic resin films, for example, when a polyolefin-based film such as polyethylene or polypropylene is used, the heat resistance is inferior, so the heat history in the can making process, the heat such as the retort treatment after can making, etc. When a history is received, the film may peel 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.

  In addition, on the inner surface side of the can, the polyester film is excellent in heat resistance and produces less low molecular weight substances, so that the taste and smell of foodstuffs are deteriorated due to migration of the low molecular weight substances compared to polyolefin films. Hard to occur. It is excellent in so-called flavor resistance.

The polyester used for such a polyester film is produced by a polycondensation reaction between a polycarboxylic acid and a polyhydric alcohol, which will be described later. At the polycondensation reaction, antimony trioxide (Sb ₂ O ₃₎ is used as a polymerization catalyst. ) Is widely used. Therefore, it is inevitable that a trace amount of Sb element remains as a result in the polyester produced under such conditions.

Antimony trioxide (Sb ₂ O ₃ ) is a polymerization catalyst that is inexpensive and has excellent catalytic activity. However, in recent years, there has been a movement to establish restrictions on Sb, which is a heavy metal, for example. , EU will comply with its own laws in each EU member country, with a limit value of 0.02mg / kg as the limit value (SML) for the concentration of migration into food for plastic materials and products that come into contact with food It is said. Accordingly, there is a demand for polyesters produced using catalysts that do not contain Sb elements.

In addition, when a film-coated metal plate in which a polyester film is coated on a metal plate is formed into a so-called three-piece can, there may be a problem that the film is scraped during the tightening process in the process. (For example, refer to Patent Document 1.) Although there is no problem when forming a can with a relatively small capacity of 190 ml or 250 ml, when a can with a capacity of 350 ml or more or a can with a large diameter is formed, there is a relatively small amount of squeeze. Since it is large, film scraps are likely to be generated during the tightening process, which may be mixed in the beverage, which is a problem.
JP 2000-143841 A

  The present invention has been made against the background of the above-described prior art, and provides a polyester film for coating a metal plate that does not contain scraping scraps of the film and does not contain Sb having a regulation value during the tightening process. It is an object of the present invention to provide a polyester film-coated metal plate excellent in workability and a polyester film-coated metal container excellent in corrosion resistance and food product protection.

The present invention
(1) A layer consists of polyester resin of melting | fusing point Tma; 240-260 degreeC, intrinsic viscosity IVa; 0.55-0.75, B layer has melting | fusing point Tmb; 220-235 degreeC, intrinsic viscosity IVb; 0.55 A polyester film having a two-layer structure of A layer / B layer composed of a polyester resin of ˜0.75, and when the polyester film is measured with a thermomechanical analyzer (hereinafter abbreviated as TMA) The maximum value of shrinkage stress in the flow direction or width direction is 1.2 to 3.0 MPa, and the maximum value of the shrinkage stress is the following formula, Fx> Fy {where Fx is the maximum shrinkage stress in the flow direction of the film. The value (MPa) and Fy indicate the maximum value (MPa) of the shrinkage stress in the width direction of the film. }, And is substantially a polyester-based film for coating a metal plate, characterized by not containing an Sb element,
(2) A polyester film-covered metal plate, wherein the polyester film according to (1) is coated on at least one surface of a metal plate, and the B layer is a surface adjacent to the metal plate, Also,
(3) A polyester-based film-covered metal container formed by molding the polyester-based film-coated metal plate according to (2).

  The polyester-based film for coating a metal plate according to the present invention is excellent in heat resistance and stable in the surface of a metal plate even after heat treatment such as a can manufacturing process, while exhibiting good handling properties without film breakage during coating processing. In addition to being able to be coated, it has excellent barrier properties, corrosion resistance, flavor resistance, etc., so there is no surface exposure of the metal plate, the finish of the can is good, and cans of 350 ml or more are compared. It is possible to provide a metal container that is beautiful in a metal container having a large target size and excellent in corrosion resistance and the protection of foodstuffs as contents.

The present invention is described in detail below.
The film of the present invention has a two-layer structure of A layer / B layer. Further, when forming a polyester film-coated metal container from a polyester film-coated metal plate obtained by coating the polyester film on a metal plate, the A layer is a layer in contact with the foodstuff as the contents or a layer that becomes the surface of the container. The B layer is preferably a layer coated on the metal plate side. Accordingly, the A layer is required to have heat resistance in the can manufacturing process, and the B layer is required to have coating adhesion by thermocompression in addition to the same heat resistance as the A layer.

  In the present invention, the polyester-based resin used for the A layer is preferably a polyester-based resin having a composition ratio of polyethylene terephthalate of 80 mol% or more. By using the above-described components, the metal plate can be used without causing the film to shrink or excessively squeeze even when heat treatment is performed for the purpose of repairing with a belt-shaped film during can manufacturing. Can be completely covered.

  The melting point (Tma) of the polyester resin used for the A layer needs to be 240 to 260 ° C, preferably 245 to 255 ° C. A melting point (Tma) of less than 240 ° C. is not preferable because the heat resistance in the can-making repair process and the like becomes insufficient. On the other hand, if the melting point exceeds 260 ° C., it is not preferable because the production cost increases and this is economically disadvantageous.

  Moreover, the intrinsic viscosity (IVa) of the polyester-type resin used for the said A layer needs to be the range of 0.55-0.75. When the intrinsic viscosity (IVa) is less than 0.55, the mechanical strength in the case of a film is insufficient, and the film forming operability is adversely affected, such as frequent breakage. Absent. Further, when the intrinsic viscosity (IVa) exceeds 0.75, the film is easily scraped when subjected to special processing such as winding when the metal plate coated with the film is formed into a can. Etc., which may impair the workability. In addition, the manufacturing cost is increased, which is economically disadvantageous. In view of economy and the like, the intrinsic viscosity (IVa) is preferably 0.65 or less.

  In the present invention, the polyester resin used as the A layer may be copolymerized with components other than ethylene terephthalate or added with a polyester resin composed of these components 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 is preferably adjusted so that the composition ratio of the ethylene terephthalate is 80 mol% or more. As will be described later, when butanediol is copolymerized in order to control crystallinity and shrinkage stress, the ratio is preferably 15 mol% or less.

  Moreover, when determining the blending of the polyester-based resin of the A layer, a resin obtained by collecting the polyester-based film having a two-layer structure of the present invention can be blended and reused. In this case, it is preferable to adjust the blending ratio of each component of the polyester film within the range of the present invention in total including the components from the recovered resin.

  It does not specifically limit about the manufacturing method of the polyester-type resin of the said A layer. That is, it may be produced by either a transesterification method or a direct polymerization method. Further, it may be produced by a solid phase polymerization method in order to increase the molecular weight. Furthermore, from the viewpoint of reducing the amount of precipitated oligomers from the polyester resin in the paste rise treatment, retort treatment, etc. performed after filling and sealing the contents in the obtained metal can, it was produced by a reduced pressure solid phase polymerization method. It is preferable to use a polyester resin having a low oligomer content. However, it is preferably produced without using an Sb compound catalyst.

  The polyester film of the present invention preferably has a dynamic friction coefficient within the following range. Since the A layer becomes a surface layer when the film-coated metal plate is formed as described above, the film surface in the measurement of the dynamic friction coefficient of the film surface at 80 ° C. is the surface of the A layer. The dynamic friction coefficient of the surface of the A layer at 80 ° C. is preferably 0.45 or less, more preferably 0.43 or less, and particularly preferably 0.40 or less. When the coefficient of dynamic friction is 0.45 or less, it becomes possible to prevent contamination of the can making process due to film wrinkling or film scraping in the can making process or the like.

  Examples of a method of setting the dynamic friction coefficient of the film surface to 0.45 or less include a method of containing crosslinked polymer particles and / or inorganic fine particles described later in the film, a method of forming fine spherulites of a polyester resin, and the like. Can be mentioned. By these methods, can-making processability can be improved, and scratch resistance (scratch resistance) can be imparted. These may be used alone or in combination of two or more.

  The crosslinked polymer particles are not particularly limited as long as they have heat resistance capable of withstanding the temperature at the time of melt molding of the polyester resin. Examples of the material for forming such crosslinked polymer particles include acrylic monomers such as acrylic acid, methacrylic acid, acrylic ester, and methacrylic ester, and styrene such as styrene and alkyl-substituted styrene. Copolymers of monomers, etc., and crosslinkable monomers such as divinylbenzene, divinylsulfone, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetramethacrylate; melamine resin; benzoguanamine resin; phenol Resin; Examples thereof include silicone resins. The crosslinked polymer particles can be produced from these materials by a conventionally known emulsion polymerization method or suspension polymerization method. Moreover, in order to adjust the particle diameter and particle size distribution of the crosslinked polymer particles, pulverization, classification, or the like may be performed.

  The inorganic fine particles are not particularly limited as long as they are insoluble and inactive in the polyester resin. Specific examples include metal oxides such as silica, alumina, zirconia, and titanium oxide; complex oxides such as kaolin, zeolite, sericite, and sepiolite; sulfates such as calcium sulfate and barium sulfate; calcium phosphate, zirconium phosphate, and the like. Phosphate; carbonates such as calcium carbonate can be mentioned. These inorganic fine particles may be natural products or synthetic products. The shape of the particles is not particularly limited.

  The particle diameter of the crosslinked polymer particles and / or inorganic fine particles is preferably 0.5 to 5.0 μm, more preferably 0.8 to 4.0 μm. If the particle size is less than 0.5 μm, the effect of improving the slipperiness between the film and the metal at high temperature is reduced, and the film is easily wrinkled. On the other hand, if the particle size exceeds 5.0 μm, the above effect is obtained. This is because saturation tends to occur and the particles are likely to fall off, which tends to cause breakage of the film at the time of film formation, and to reduce impact strength.

  The content of the crosslinked polymer particles and / or inorganic fine particles in the polyester film A layer is preferably 0.3 to 5.0% by weight, more preferably 0.5%, based on the total amount of the polyester film A layer. -3.0 wt%. If the amount is less than 0.3% by weight, the effect of improving the slipperiness between the film and the metal at high temperature is reduced, and the film is easily wrinkled. If the amount exceeds 5.0% by weight, the above effect is saturated. This is because there is a tendency that the film-forming property of the film is lowered and the impact strength is lowered. In addition, moderate haze, that is, processing defects of the metal-coated plate in which the film is coated on the metal plate by appropriately adding crosslinked polymer particles and / or inorganic fine particles that make the haze of the polyester film 25 to 60% It is also possible to prevent malfunction of a defect detector that detects

  The above-mentioned crosslinked polymer particles and / or inorganic fine particles may be blended in the polyester film A layer in the production process of the polyester resin, or the above components may be added to the polyester resin and melt kneaded. Moreover, the polyester-type resin which contains the said component in high concentration can be manufactured, and it can also be melt-kneaded with this as a masterbatch with the polyester-type resin which does not contain the said component or contains a small amount.

  The layer A preferably contains a small amount of ethylene terephthalate cyclic trimer so as not to impair the protective effect of foodstuffs and the beauty of the can. Therefore, it is preferable to use a polyester-based resin used in the A layer having a low ethylene terephthalate cyclic trimer content. The ethylene terephthalate cyclic trimer content in the polyester resin used for the A layer is preferably 0.70% by weight or less, more preferably 0.50% by weight or less. The polyester-based resin having a low cyclic trimer content is, for example, a method for producing a polyester-based resin having a low cyclic trimer content, such as a reduced pressure heat treatment method or a solid-phase polymerization method, Or a method of extracting the cyclic trimer with an organic solvent, a method combining these, and the like.

  In the present invention, the polyester-based resin used for the B layer is preferably a mixed polyester-based resin obtained by mixing a polyester resin composed of polyethylene terephthalate-based polyester b1 and polybutylene terephthalate-based polyester b2. More preferably, the composition ratio is suitably adjusted so as to be within the range of the melting point (Tmb) of the B layer described later within the range of polyester b1 / polyester b2 = 85-100 / 15-0 mol%. preferable. By using the above components, sufficient coating adhesion can be obtained when coating a metal plate, and the coating process can be performed at a lower temperature and at a higher speed.

  The melting point (Tmb) of the mixed polyester resin used for the B layer needs to be 220 to 235 ° C, preferably 225 to 235 ° C, and more preferably 225 to 233 ° C. A melting point (Tmb) of less than 220 ° C. is not preferable because the fluidity of the B layer increases due to the thermal history in the can manufacturing process or the like, and the dimensional change of the A layer may increase. On the other hand, when the melting point exceeds 235 ° C., it approaches the melting point of the A layer. Therefore, if it is attempted to ensure adhesion to the metal plate by heat fusion, excessive heat is applied to the A layer, which is not preferable.

  The intrinsic viscosity (IVb) of the mixed polyester resin used for the B layer needs to be in the range of 0.55 to 0.75. When the intrinsic viscosity (IVb) is less than 0.55, the mechanical strength in the case of a film is insufficient, and the film forming operability is adversely affected such as frequent breakage. Absent. In addition, if the intrinsic viscosity (IVb) exceeds 0.75, sufficient coating adhesion cannot be obtained when coating the metal plate, and the metal plate may be peeled off, and the manufacturing cost is increased. This is economically disadvantageous and undesirable. In view of economy and the like, the intrinsic viscosity (IVa) is preferably 0.65 or less.

  In addition, in the polyester-type resin used for B layer, when using the said polybutylene terephthalate-based polyester b2, the intrinsic viscosity becomes like this. Preferably it is 0.55-1.00. When the polyester b2 having an intrinsic viscosity greater than 1.00 is used, sufficient coating adhesion to the metal plate cannot be obtained as described above, and the polyester b2 is easily peeled off from the metal plate. When the polyester b2 having an intrinsic viscosity of less than 0.55 is used, the film forming operability tends to be very bad because the mechanical strength in the case of a film is insufficient and breakage frequently occurs.

  Even in the polyester resin used as the B layer in the present invention, a component other than ethylene terephthalate and butylene terephthalate may be copolymerized or a polyester resin composed of these components may be added without departing from the scope of the present invention. Good. 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 or the like, or an aliphatic diol such as ethylene glycol, diethylene glycol, triethylene glycol, propanediol, butanediol, hexanediol, dodecamethylene glycol, or neopentyl glycol; a fat such as cyclohexanedimethanol Cyclic 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 method for producing the polyester resin of the B layer is not particularly limited. That is, it may be produced by either a transesterification method or a direct polymerization method. Further, it may be produced by a solid phase polymerization method in order to increase the molecular weight. Furthermore, from the viewpoint of reducing the amount of precipitated oligomers from the polyester resin in the paste rise treatment, retort treatment, etc. performed after filling and sealing the contents in the obtained metal can, it was produced by a reduced pressure solid phase polymerization method. It is preferable to use a polyester resin having a low oligomer content. However, it is preferably produced without using an Sb compound catalyst.

  The polyester-based film having a two-layer constitution of A layer / B layer of the present invention includes an antioxidant, a heat stabilizer, an ultraviolet absorber, a plasticizer, a pigment, an antistatic agent, and a lubrication as necessary for each of the two layers. Agents, crystal nucleating agents, and the like.

  The polyester resin used in the polyester film having a two-layer structure of A layer / B layer of the present invention is mainly obtained by polycondensation of a dicarboxylic acid component and a diol component without using an Sb compound catalyst.

The above “polycondensation without using an Sb compound catalyst” means polycondensation without using an Sb compound catalyst such as antimony trioxide (Sb ₂ O ₃ ), for example, using a Ge compound catalyst, a Ti compound catalyst, or the like. However, it is not limited to the catalysts described here.

  The method of laminating the polyester film having a two-layer structure of layer A / layer B of the present invention is not particularly limited. For example, the raw materials of layer A and layer B are melted using separate extruders, Each molten resin is merged, extruded onto a cooling roll in layers from a T-die and cooled and solidified to obtain an unstretched sheet of laminated resin, and then subjected to stretching treatment and heat treatment to be laminated. At this time, it is preferable to adjust the amount of the molten resin extruded from each extruder so that the ratio of the thickness of the A layer / B layer falls within a preferable range described later.

  The polyester film having a two-layer configuration of the A layer / B layer is preferably a biaxially stretched film. By biaxially stretching the polyester film, the flavor resistance of the polyester film can be improved.

  The polyester film of the present invention is required to have a maximum shrinkage stress of 1.2 to 3.0 MPa in the flow direction of the film or in the width direction when measured by TMA measured by the measurement method described later. . Specifically, the maximum value Fx of the shrinkage stress in the flow direction of the film is preferably 1.5 to 3.0 MPa, and the maximum value Fy of the shrinkage stress in the width direction is preferably 1.3 to 3.0 MPa. The relationship between Fx and Fy needs to be Fx> Fy.

  The maximum value of the shrinkage stress in the flow direction or the width direction of the film is 1.2 to 3.0 MPa, and the relationship between the maximum value Fx of the shrinkage stress in the flow direction of the film and the maximum value Fy of the shrinkage stress in the width direction is By setting Fx> Fy, a larger shrinkage stress remains in the film flow direction in the polyester film. Therefore, when heat treatment is performed in the coating process, the flow direction is determined by applying an appropriate temperature. It becomes possible to contract only. Thereby, after the flange processing, it is possible to perform the tightening processing without generating scraps of the film.

  The maximum value of the shrinkage stress in the flow direction of the film or the width direction when measured by the TMA of the film is 1.2 to 3.0 MPa, the maximum value Fx of the shrinkage stress in the flow direction of the film and the width direction. For example, when the polyester film is a biaxially stretched film to be described later, the relationship of the maximum value Fy of shrinkage stress is Fx> Fy. A method of enlarging and heat-fixing under the temperature conditions as described below, reducing the shrinkage stress, and slightly increasing the shrinkage stress in the longitudinal direction, if the polyester film is a stretched film described later, a relaxation step after stretching A method of reducing the shrinkage stress by providing the above, a method of controlling the crystallinity and the shrinkage stress by copolymerizing butanediol as a component of the polyester resin at a ratio described later, etc. Mentioned, it may be combined therewith or the like.

  As the biaxial stretching method, it is preferable to use a sequential biaxial stretching method. In this case, the stretching ratio in the longitudinal direction is preferably 3.5 to 5 times, more preferably 3.5 to 4.5 times, and the stretching temperature is preferably 80 to 120 ° C., more preferably. Is 95-120 ° C. In order to control the shrinkage stress by biaxial stretching and obtain the relationship of Fx> Fy, it is necessary to set it higher than the normal longitudinal stretching ratio. The stretching ratio in the transverse direction is preferably 2.5 to 5 times, more preferably 3 to 4.5 times, and the stretching temperature is preferably 80 to 130 ° C, more preferably 100 to 130 ° C. It is.

  In order to satisfy the above characteristics, when the sequential biaxial stretching method is used, either the A layer or the B layer of the polyester-based film of the present invention having a two-layer configuration of A layer / B layer, or A layer / Among the constituent components of the polyester resin in both layers of the B layer, when the butanediol component is contained in an amount of 15 mol% or less of the total diol component, the stress during stretching is reduced, and a higher stretching ratio in the longitudinal direction. Is preferable, and it becomes easy to maintain Fx> Fy, which is the relationship of the above-mentioned shrinkage stress.

  In addition, by using a polyester resin containing a butanediol component in a range not exceeding 15 mol% as the polyester resin constituting the A layer / B layer as described above, many processes such as drying and mixing can be performed. Even if there is some variation in the composition ratio due to passing through, there is obtained an effect that the variation in stress during transverse stretching is small and it is difficult for a stop due to breakage to occur.

  It is preferable that the residual shrinkage stress due to biaxial stretching of the A layer of the polyester film having a two-layer configuration of A layer / B layer is reduced or removed by a heat setting method or the like when the metal plate is coated. This is because the dimensional change due to the heat history in the can manufacturing process or the like can be reduced. Further, the B layer is preferably made amorphous or non-orientated due to its thermal history or the like when the residual shrinkage stress is reduced or removed by heat fixing the A layer. This is because, when the polyester film is coated on the preheated metal plate, sufficient coating adhesion can be obtained without preheating the metal plate to the melting point of the B layer, and the coating process can be performed at a low temperature. This is because higher speed can be realized. The reduction or removal of residual shrinkage stress by biaxial stretching of the A layer and the amorphization or non-orientation of the B layer are preferably performed at a temperature 5 ° C. lower than the melting point of the polyester constituting the B layer. The temperature is 15 ° C. or lower than the melting point of the polyester constituting the A layer, more preferably 2 ° C. lower than the melting point of the polyester constituting the B layer, or 20 ° C. or lower than the melting point of the polyester constituting the A layer. Can be achieved including securing of the impact strength, so-called coating operability or handling properties. Further, the melting point of the A layer and the melting point of the B layer are determined within a range in which the temperature condition can be set.

  The total thickness of the two-layer polyester film of A layer / B layer of the present invention is preferably in the range of 4 to 65 μm, more preferably in the range of 5 to 30 μm. This is because if the thickness is less than 4 μm, the barrier property is inferior and the corrosion resistance may be deteriorated, and further, the low molecular weight substance from the metal container permeates into the food or beverage, which is often inconvenient. On the other hand, if the thickness of the film exceeds 65 μm, it is often disadvantageous economically.

  The thickness of the layer A is 3 to 50 μm from the viewpoint of canning processability, dimensional stability due to heat history during canning process, coating operability and handling of the film, barrier properties, corrosion resistance, economy, etc. The range is preferable, and the range of 4 to 40 μm is more preferable. On the other hand, the thickness of the B layer is preferably in the range of 1 to 15 μm, and more preferably in the range of 1 to 10 μm, from the viewpoints of adhesion, heat resistance against heat history during can manufacturing, and the like. Further, the ratio of the thickness of the A layer / B layer is preferably in the range of A / B = 1/1 to 20/1, and more preferably in the range of 2/1 to 10/1.

  The film-coated metal plate of the present invention is obtained by coating the polyester film on at least one surface of the metal plate, and has excellent can-making processability.

  Although it does not specifically limit as a metal plate used for the said film coating metal plate, For example, tin, tin free steel, aluminum etc. are mentioned. Also, 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. is there.

  In addition, as a method of laminating the polyester-based film on at least one surface of the metal plate, a conventionally known method can be applied, and is not particularly limited, but preferably includes a thermal coating method, and particularly preferably, the metal plate is heated by energization. And thermal coating. Moreover, the polyester-type film may be coat | covered on both surfaces of the metal plate. When the polyester film is coated on both surfaces of the metal plate, they may be coated simultaneously or sequentially.

  In addition, when the polyester film having the two-layer configuration of the A layer / B layer is coated on at least one surface of the metal plate, it is used as a layer for coating the B layer on the metal plate side as described above. In order to improve the barrier properties and corrosion resistance of the layer and to further improve the coating adhesion, a conventionally known adhesive mainly composed of a thermosetting resin is applied to the B layer in advance to carry out the coating. May be.

  The metal container of this invention is obtained by shape | molding using the above-mentioned film covering metal plate. Although the shape of a metal container is not specifically limited, For example, it can be set as a can shape, bottle shape, barrel shape, etc. Also, a method for forming the metal container is not particularly limited, and known methods such as a drawing method, an ironing method, and a drawing ironing method can be used.

  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) Moisture content measurement method The polyester raw material chips for layers A and B of Examples 1 and 2 and Comparative Examples 1 to 3 immediately after finishing the drying process are sampled in containers and sealed until the moisture content is measured. Keep it. 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.

(2) Measuring method of melting | fusing point It measured using the differential scanning calorimeter (DSC-60) of Shimadzu Corporation. The polyester resins as raw materials for layer A / layer B of Examples 1 and 2 and Comparative Examples 1 to 3 were heated and melted at 300 ° C. for 5 minutes, and then rapidly cooled with liquid nitrogen. Using 10 mg as a sample, the endothermic peak temperature (melting point) based on crystal melting that appears when the temperature was raised at a rate of 20 ° C./min was measured.

(3) Intrinsic Viscosity Measuring Method Polyester system as raw material for layer A / layer B of Examples 1 and 2 and Comparative Examples 1 to 3 in a mixed solvent of phenol / tetrachloroethane (6/4 by weight) The resin was dissolved to a concentration of 0.4 g / dl and measured at a temperature of 30 ° C. using an Ubbelohde type viscosity tube.

(4) Measuring method of maximum value of shrinkage stress Samples having a width of 4 mm and a length of 20 to 30 mm were cut out from the polyester films obtained in Examples 1 and 2 and Comparative Examples 1 to 3, and a thermal machine manufactured by Shimadzu Corporation. Using a analyzer (TMA-60), the maximum value with shrinkage was determined in a load curve obtained by raising the temperature at a rate of 10 ° C./min from 30 ° C. with a sample holder interval of 10 mm, an initial load of 49 mN. Sample cutting and measurement directions were two directions of the film flow direction and the width direction.

(5) Method for quantifying ethylene terephthalate cyclic trimer About 100 mg of the polyester film obtained in Examples 1 and 2 and Comparative Examples 1 to 3 was precisely weighed, and hexafluoroisopropyl alcohol / chloroform = 2/3 (V / V, volume ratio) The polyester was dissolved by immersion in 3 ml. Subsequently, 20 ml of chloroform was added, the polyester was precipitated with 10 ml of methanol, the precipitated polyester was filtered off and dried, and the amount was measured. Further, the filtrate obtained when the precipitated polyester was filtered off was evaporated to dryness, and then the evaporated dry product was dissolved in 10 ml of N, N-dimethylformamide. The solution obtained by centrifugal filtration of the solution was analyzed by HPLC (LC-100) manufactured by Hewlett Packard. The main analysis conditions are shown below.
Column: μ-Bondasper C ¹⁸ 5μ 100 3.9 mm × 15 cm (manufactured by Waters)
Eluent A: 2% acetic acid / water (v / v)
Eluent B: Acetonitrile gradient B%: 10 → 100% (0 → 55 min) Linear flow rate: 0.8 ml / min Detection wavelength: UV-258 nm

(6) Haze Measurement Method The polyester films obtained in Examples 1 and 2 and Comparative Examples 1 to 3 were measured by the haze (cloudiness) measurement method shown in JIS K7105.

(7) Method of measuring dimensional change rate of polyester film in heat treatment of polyester film coated metal sheet Degreased metal plate with 190 μm thickness (tin-free steel, L type bright finish, surface roughness 0.3-0. 5 μm, manufactured by Nippon Steel Co., Ltd.) is preheated to 200 ° C., and the B layer is a metal plate of the metal plate and one side of the polyester film obtained in Examples 1 and 2 and Comparative Examples 1 and 2. The film is covered with a polyester film-coated metal plate [thickness 202 μm (polyester)] by passing between a rubber roll and a rubber roll with a pressure of 500 N / cm at a speed of 10 m / min. System film / metal plate = 12 μm / 190 μm). The obtained polyester-based film-coated metal plate was cut into a square of 60 mm × 60 mm with the film sample portion and the metal plate portion having the same area so that one side was parallel to the film longitudinal stretching direction. Next, the film-coated metal plate sample was hung from the ceiling so as to be in the middle of the oven in a hot-air oven adjusted to a wind speed of 1 to 10 m / sec and a temperature of 230 ° C., and subjected to heat treatment for 2 minutes. The sample was taken out of the oven and immediately immersed in water at 25 ° C. or lower for 1 second or longer and rapidly cooled with water. Next, in the film portion of the sample, the length in the direction perpendicular to the transverse direction of the film was read and used as the dimension after heat treatment (I: unit mm). The dimensional change rate was calculated from the obtained I by the following formula.
Dimensional change rate (%) = (| 60−I | / 60) × 100

(8) Method for measuring dynamic friction coefficient The polyester film-coated metal plates of Examples 1 and 2 and Comparative Examples 1 and 2 obtained as described in (7) above have long sides parallel to the film longitudinal stretching direction. Then, the areas of the film sample part and the metal plate part were jointly cut into a rectangle of 150 mm × 100 mm to obtain a sample. Next, a 1.5 kg weight slider having a contact area of 50 mm × 70 mm is set with the film sample as the surface so that the longitudinal direction of the film is parallel to the sliding direction, and on a 80 ° C. tin-free steel plate. The dynamic friction coefficient when sliding at a speed of 250 mm / min was measured.

(9) Determination Method of Oligomer Precipitation One side of the polyester film-coated metal plate of Examples 1 and 2 and Comparative Examples 1 and 2 obtained as described in (7) above is parallel to the film longitudinal stretching direction. Then, the areas of the film sample part and the metal plate part were jointly cut into a square of 100 mm × 100 mm to obtain a sample. This sample was retorted with 500 cc of distilled water at 120 ° C. for 30 minutes. The film-coated metal plate after the treatment was air-dried, the state of the film surface was observed with a loupe, and the presence or absence of oligomer precipitation was determined based on the following criteria.
Existence: Oligomer crystals are observed on the film surface.
No: Oligomer crystals are not observed on the film surface.

(Production example of polyester resin)
Polyester A: Ethylene terephthalate cyclic containing 0.3% by weight of agglomerated silica with an average particle size of 1.5 μm, and having a reduced amount of ethylene terephthalate cyclic trimer by extraction method (method of extraction with water or organic solvent) Polyethylene terephthalate (trade name: SU554, manufactured by Toyobo Co., Ltd.) polymerized with a Ge catalyst having a trimer content of 0.33% by weight, an intrinsic viscosity of 0.62, and a melting point of 254 ° C. was used.
Polyester B: Melt spherical polymethyl methacrylate particles (trade name: TN200, manufactured by Nippon Shokubai Co., Ltd.) 5.0% by weight with 95% by weight of polyester A and crosslinked with trimethylolpropane trimethacrylate having an average particle size of 3.0 μm. A mixed resin was used.
Polyester C: Copolymerized polyester of terephthalic acid / isophthalic acid (molar ratio 90/10) and ethylene glycol polymerized with Ge catalyst (melting point 233 ° C., intrinsic viscosity 0.63, trade name: RF230, manufactured by Toyobo Co., Ltd.) Was used.
Polyester D: Polybutylene terephthalate (trade name: NOVADURAN 5008L, manufactured by Mitsubishi Engineering Plastics) having an intrinsic viscosity of 0.70 and a melting point of 222 ° C. polymerized with a Ti catalyst was used.
Polyester E: Ethylene terephthalate cyclic trimer obtained by solid-phase polymerization of a polyester containing 0.3% by weight of agglomerated silica having an average particle size of 1.5 μm, obtained by the same method as the production method of polyester A Polyethylene terephthalate polymerized with a Ge catalyst having an ethylene terephthalate cyclic trimer content of 0.33% by weight, an intrinsic viscosity of 0.80, and a melting point of 255 ° C. was used.
Polyester F: By the same method as the production method of polyester A, the content of ethylene terephthalate cyclic trimer is 0.80% by weight, containing 0.3% by weight of agglomerated silica having an average particle size of 1.5 μm, and the intrinsic viscosity. Of polyethylene terephthalate polymerized with a Ge catalyst having a melting point of 0.50 and a melting point of 253 ° C. was used.

[Example 1]
(Manufacture of polyester film)
Polyester A / polyester B = 80/20 (parts by weight) was used as the polyester resin for the A layer (Tma; 254 ° C., IVa; 0.62). On the other hand, polyester C = 100 parts by weight was used as the polyester-based resin for the B layer. The polyester-based resin for the A layer was dried with a paddle dryer. The moisture content after drying was 48 ppm. Further, the polyester after drying was melted with a single screw extruder at a resin temperature of 280 ° C. and a residence time of 10 minutes while being fed with a quantitative screw feeder. The polyester-based resin for the B layer was melted at a resin temperature of 280 ° C. and a residence time of 15 minutes while removing moisture in a vent-type extruder without being dried. The melt of polyester resin for layer A / layer B was merged in a die, and then extruded onto a cooling drum (35 ° C.) to obtain an amorphous sheet. Thereafter, the amorphous sheet was stretched 3.7 times in the machine direction at 120 ° C. and 3.8 times in the transverse direction at 130 ° C. and heat-set at 230 ° C., and the A layer thickness was 9.5 μm and the B layer thickness was A polyester film having a thickness of 2.5 μm (total thickness: 12 μm) was obtained. The maximum value of the shrinkage stress at the time of TMA measurement of the film by the above-described method was 2.5 MPa in the film flow direction (Fx) and 1.5 MPa in the width direction (Fy). Further, haze and ethylene terephthalate cyclic trimer content in the film were measured and found to be 48% and 0.41% by weight, respectively. The results are shown in Table 1.

(Manufacture of film-coated metal plates)
A degreased metal plate having a thickness of 190 μm (tin-free steel, L-type bright finish, surface roughness 0.3 to 0.5 μm, manufactured by Nippon Steel Corp.) is preheated to 200 ° C., The polyester film is combined with the surface on the B layer side, passed between a rubber roll having a pressure of 500 N / cm and a rubber roll at a speed of 10 m / min, and then rapidly cooled with water to form a film-coated metal plate [thickness 202 μm (Polyester film (A layer / B layer) / metal plate = 12 μm (9 μm / 3 μm) / 190 μm)). At this time, there was no problem in handling properties such as film breakage, and the film was good. When the dimensional change rate by the heat processing of the polyester film shown above was measured about the obtained polyester film covering metal plate, the vertical direction was 1.0% and the horizontal direction was 0.3%. Moreover, it was 0.39 when the dynamic friction coefficient in 80 degreeC of the film surface was measured. Furthermore, when the presence or absence of oligomer precipitation was observed, oligomer deposition was not observed on the film surface. The results are shown in Table 1. Moreover, when the film-coated metal plate obtained in this way was applied to the above-described defect detector, the above-mentioned appropriate haze value caused no defect misidentification, and the defect part including wrinkles was recognized as a defect. I was able to.

(Manufacture of metal containers)
Using the above-mentioned film-coated metal plate, a can was made as a three-piece can for 500 ml, and can can be made at a high speed in the can making process. There were no problems such as plate surface exposure. In addition, the film could be processed without generating scraps during film tightening after flange processing. In addition, the can thus obtained was filled with foodstuffs, subjected to a retort treatment at 125 ° C. for 30 minutes, and a storage test was conducted at 40 ° C. for 6 months. It was excellent. The results are shown in Table 1.

[Example 2]
As polyester resin for A layer, in addition to polyester A / polyester B, recycled resin raw material R of the two-layer film obtained in Example 1 (when the two-layer film prepared in Example 1 was coated on a metal plate) A mixture (Tma; 250 ° C., IVa; 0.59) in which the resin obtained by remelting the cut film is blended at a ratio of polyester A / polyester B / regenerated resin raw material R = 64/16/20 (part by weight). Using. As the polyester resin for the B layer, a mixture (Tmb; 232 ° C., IVb; 0.61) blended at a ratio of polyester C / polyester D = 95/5 (parts by weight) was used. Each polyester resin for layer A was dried with a separate paddle dryer. The moisture content of the dried polyethylene terephthalate (polyesters A and B) and the recycled resin material R of the film was 44 ppm and 35 ppm, respectively. In addition, the polyester-based resins after drying are mixed in the hopper while continuously feeding separately with a quantitative screw feeder so as to have the ratio described in the funnel-shaped hopper directly above the extruder, and the resin temperature It was melted by a single screw extruder at 280 ° C. and a residence time of 8 minutes. A polyester film and a polyester film-coated metal plate were produced in the same manner as in Example 1 except that the A layer thickness was 10 μm and the B layer thickness was 2 μm.

  Maximum value of shrinkage stress when measured by TMA of the polyester film (film flow direction and width direction), haze, ethylene terephthalate cyclic trimer content, rate of dimensional change in heat treatment of polyester film coated metal sheet ( The longitudinal and transverse directions) and the dynamic friction coefficients were 2.5 MPa, 1.5 MPa, 48%, 0.39 wt%, 0.9%, 0.3%, and 0.40, respectively. Moreover, when the presence or absence of precipitation of the oligomer on the surface of the polyester film-coated metal plate was observed, the precipitation of the oligomer was not observed. The results are shown in Table 1.

  In addition, when a three-piece can for 500 ml was produced using the polyester-based film-coated metal plate, the can can be produced at a high speed in the can-making process, and even after heat treatment in the process, the film is uneven. There were no problems such as surface exposure of the metal plate. Moreover, the film can be processed without generating scraps during the tightening after the flange processing, and the storage test of the resulting can also has good corrosion resistance and excellent food product protection. The results are shown in Table 1.

[Comparative Example 1]
In Example 1, a polyester film and a polyester film-coated metal plate were produced in the same manner as in Example 1 except that the stretching ratio in the longitudinal direction under the film forming conditions was set to 3.0 times.

  Maximum value of shrinkage stress when measured by TMA of the polyester film (film flow direction and width direction), haze, ethylene terephthalate cyclic trimer content, rate of dimensional change in heat treatment of polyester film coated metal sheet ( The longitudinal and transverse directions) and the dynamic friction coefficients were 1.0 MPa, 1.6 MPa, 45%, 0.38 wt%, 0.3%, 0.3%, and 0.38, respectively. Moreover, when the presence or absence of precipitation of the oligomer on the film-coated metal plate surface was observed, the precipitation of the oligomer was not observed. The results are shown in Table 1.

  In addition, when a three-piece can for 500 ml was produced using the polyester-based film-coated metal plate, the can can be produced at a high speed in the can-making process, and even after heat treatment in the process, the film is uneven. There were no problems such as surface exposure of the metal plate. However, the film was scraped during the tightening after the flange processing, and a beautiful container could not be manufactured. Therefore, a storage test of the resulting can was not performed. The results are shown in Table 1.

[Comparative Example 2]
As the polyester resin for layer A, polyester B was used in the same manner as in Example 1 except that a mixed resin of polyester B / polyester E = 20/80 (parts by weight) (Tma; 255 ° C., IVa; 0.77) was used. -Based film and polyester-based film-coated metal plate were produced.

  Maximum value of shrinkage stress when measured with TMA of the polyester film (film flow direction and width direction), haze, ethylene terephthalate cyclic trimer content, rate of dimensional change in heat treatment of polyester film coated metal sheet ( The longitudinal and transverse directions) and the dynamic friction coefficients were 3.0 MPa, 1.8 MPa, 48%, 0.37 wt%, 1.5%, 0.5%, and 0.39, respectively. Moreover, when the presence or absence of precipitation of the oligomer on the film-coated metal plate surface was observed, the precipitation of the oligomer was not observed. The results are shown in Table 2.

  In addition, when a three-piece can for 500 ml was produced using the polyester-based film-coated metal plate, the can can be produced at a high speed in the can-making process, and even after heat treatment in the process, the film is uneven. There were no problems such as surface exposure of the metal plate. However, the film was scraped during the tightening after the flange processing, and a beautiful container could not be manufactured. Therefore, a storage test of the resulting can was not performed. The results are shown in Table 2.

[Comparative Example 3]
As the polyester resin for layer A, polyester B was used in the same manner as in Example 1 except that a mixed resin of polyester B / polyester F = 20/80 (parts by weight) (Tma; 253 ° C., IVa; 0.52) was used. Based films were produced.

The maximum value of shrinkage stress when measured by TMA of the polyester film (flow direction and width direction of the film), haze, ethylene terephthalate cyclic trimer content is 2.0 MPa, 1.2 MPa, 48%, It was 0.77% by weight. Since the polyester film was unstable in film formation and ruptured, and an industrially satisfactory film could not be obtained, the production test of the film-coated metal plate was not performed. The results are shown in Table 2.

＊再生樹脂Ｒ；実施例１で作成した二層構成フィルムを金属板に被覆した際に切り落としたフィルムを再溶融した樹脂。
＊ＥＴＰ；エチレンテレフタレート

* Recycled resin R; a resin obtained by remelting a film cut off when the two-layer film prepared in Example 1 was coated on a metal plate.
* ETP; ethylene terephthalate

＊再生樹脂Ｒ；実施例１で作成した二層構成フィルムを金属板に被覆した際に切り落としたフィルムを再溶融した樹脂。
＊ＥＴＰ；エチレンテレフタレート

* Recycled resin R; a resin obtained by remelting a film cut off when the two-layer film prepared in Example 1 was coated on a metal plate.
* ETP; ethylene terephthalate

The polyester-based film for coating a metal plate of the present invention is suitable for use as a metal container for foods, beverages, etc. because it does not cause scraping of the film during tightening and is excellent in hygiene. It is great to contribute.

Claims (3)

A layer consists of polyester resin of melting | fusing point Tma; 240-260 degreeC, intrinsic viscosity IVa; 0.55-0.75, B layer has melting | fusing point Tmb; 220-235 degreeC, intrinsic viscosity IVb; 0.55-0. A polyester film having a two-layer structure of A layer / B layer made of 75 polyester resins, and the flow direction of the film when the polyester film is measured with a thermomechanical analyzer (hereinafter abbreviated as TMA), Alternatively, the maximum value of the shrinkage stress in the width direction is 1.2 to 3.0 MPa, the maximum value of the shrinkage stress satisfies the following formula, and substantially does not contain an Sb element. Polyester film.
Fx> Fy
{In the formula, Fx represents the maximum value (MPa) of shrinkage stress in the flow direction of the film, and Fy represents the maximum value (MPa) of shrinkage stress in the width direction of the film. }   A polyester film-covered metal plate, wherein the polyester film according to claim 1 is coated on at least one surface of a metal plate as the surface where the B layer is in contact with the metal plate. A polyester film-coated metal container formed by molding the polyester film-coated metal plate according to claim 2.