JPH11106526A - Metal plate-laminating polyester film and preparation thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal plate-laminating film having excellent mechanical characteristics and heat resistance, capability of contact-bonding by heat at relatively low temp., a low content of CTET of the main, responsible substance for the white powder occurring on retort treating, besides fine processability as well as excellent tight-windability and feathering resistance in case of an application as a cover material, and little occurrence of water spots even on the retort treatment; and a preparing process thereof. SOLUTION: A film-constituting polyester resin, comprising an acid component of, based on the whole acid components, 60-95 mole % of terephthalic acid and 40-5 mole % of isophthalic acid, and a glycol component consisting mainly of ethylene glycol, satisfies the following properties of (a) an intrinsic viscosity of 0.45-1.0 dl/g, (b) an m.p. Tm only one existing in the range of 240-253 deg.C, (c) a sum of the melting heat [Δ Hm] resulting from the crystalline portions of the polyester resin, of 15-35 J/g, and (d) a degree of surface orientation of 0.11-0.16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film useful as a constituent material of a film-laminated metal plate and a method for producing the same, and further relates to a metal can and a can lid produced using the laminated metal plate.

[0002]

2. Description of the Related Art Metal cans, which are one form of food and beverage packaging containers, have excellent mechanical strength and excellent sealing properties, so that the contents can be stored for a long time, and the contents can be filled at a high temperature. It can be sealed as it is, and sterilization treatment such as retort treatment can be easily performed, so it is highly reliable for safety and health as a packaging container.Furthermore, contents can be stored in a heated state and cans after use In recent years, various types of contents have been filled and used in large quantities because of their many advantages that separation and collection are relatively easy.

[0003] The inner and outer surfaces of a metal can for food and drink are intended to maintain the flavor of the contents and to prevent corrosion of the metal can, or to improve the aesthetics of the outer surface of the can and to protect the printed surface. Heretofore, a solvent-type paint mainly containing a thermosetting resin has been applied. However, such a paint can has the following problems. (A) When a heating treatment such as a retort treatment is performed after filling and sealing the content, low molecular weight substances such as a residual solvent in the coating film migrate into the content, and the flavor of the content is significantly reduced.
(Inferior in flavor) (b) As the diameter of the can lid becomes smaller and the thickness of the can becomes thinner, workability and impact resistance of the paint film are required more than before, while the paint film becomes white after retort treatment. Although retort resistance is required for problems such as film formation and peeling of the coating film, it is difficult to obtain a coating film satisfying these performances. (C) A large amount of an organic solvent is used, and a large amount of thermal energy is required for drying and baking the coating film.

In recent years, a metal can manufactured using a film-laminated metal plate obtained by laminating a single-layer or multi-layer plastic film on a metal plate has attracted attention. In particular, polyester films have the advantages of being excellent in mechanical strength, workability, heat resistance, hardly causing pinholes and cracks, hardly impairing the flavor of the contents (excellent in flavor), and being relatively inexpensive. Yes, it is being actively put into practical use.

[0005] As a method of laminating a plastic film to a metal plate, an adhesive layer is provided in advance on at least one of the plastic film and the metal plate, and a heat bonding method is used. And the like. As in the former method, when an adhesive made of a solution in which an uncured thermosetting resin is dissolved in an organic solvent is used, the above-mentioned problems (A) and (C), and the problem of the adhesive layer and film. Since an interface is generated between them, there is a problem in workability of the laminated metal plate and impact resistance of the laminated can. On the other hand, when the latter method is used, the above problems (a) to (c) are solved, and the productivity of the metal can is improved.

A laminated metal plate obtained by laminating a polyester resin film on a metal plate is a three-piece can (hereinafter referred to as a three-piece can).
P cans), or two-piece cans (hereinafter abbreviated as 2P cans), but they have been put to practical use, but at present the application to lid materials constituting metal cans has not advanced. is there. In particular, the main characteristics required for the film laminated on the outer surface of the lid material include adhesiveness to a metal plate, moldability when forming the lid material from the laminated metal plate (pressing and curling processability), and lid. In the tightening process in which the material and the body member are wound and brought into close contact with each other, the film should not be damaged when it comes in contact with the winding roll at high load while rotating at high speed (hereinafter, abbreviated as winding property), retort treatment Occasionally, white powder, which is considered to be derived from the low molecular weight material of the polyester resin, is generated, or the spots where water droplets formed by condensation of steam adhere are white spots (water spots).
In addition, when the laminated metal plate is applied as an easy open lid (EOE) material, the film is cut following the metal plate when the tab is opened, and the film is cut from the metal plate. It can be cited that the film does not peel off, and no film residue is observed at the cut portion (feathering property).

JP-A-5-331302, JP-A-7
Japanese Patent Publication No. 145252 discloses a polyester film in which water spots are unlikely to occur during retort, and Japanese Patent Publication No. 7-80253 discloses a film suitable for EOE. However, in any case, there is no detailed description of the tightness which seems to be the most difficult to solve among the above required performances, and the above-mentioned ~
Techniques for satisfying all of the required performances have not been known so far, and for those skilled in the art, a film capable of sufficiently withstanding a winding process in which particularly severe processing is performed and a film laminated with the film. The development of such a lid material has been strongly desired.

[0008]

DISCLOSURE OF THE INVENTION The present invention relates to a polyester which can be laminated on a metal plate by thermocompression bonding and has not only excellent winding properties but also all of the above-mentioned requirements. It is an object of the present invention to provide a film and a metal can body and a lid member obtained by laminating the film on a metal plate. Another object of the present invention is to provide a method for producing such a polyester film.

[0009]

Means for Solving the Problems The present inventors have developed an excellent crimping property by using a biaxially stretched polyester film having a specific chemical structure and physical properties, thereby solving the problems of the present invention. The inventors have found that the present invention has been achieved.

That is, the gist of the present invention is as follows. (1) The acid component is terephthalic acid 60 to the total acid component.
A biaxially stretched polyester film for metal plate lamination, comprising 95 mol% and isophthalic acid 40 to 5 mol%, wherein the glycol component is mainly composed of ethylene glycol and satisfies the following characteristics (a) to (d). (A) The limiting viscosity of the polyester resin constituting the film is 0.45 to 1.0 dl / g. (B) It has only one melting point Tm in the range of 240 to 253 ° C. (C) The sum of heats of fusion [ΔHm] derived from crystal parts of the polyester resin is 15 to 35 J / g. (D) The degree of plane orientation is 0.11 to 0.16. (2) PET and isophthalic acid copolymerized polyethylene terephthalate are mixed, and the both ends of an unstretched sheet obtained by melt-extrusion with an extruder are gripped, preheated at a temperature of 40 to 120 ° C, and then at a temperature of 50 to 130 ° C. After being biaxially stretched at a stretching ratio of 2 to 4 times in each of the longitudinal and transverse directions, 120 to 200
The method for producing a polyester film according to the above (1), wherein the polyester film is heat-set at ℃.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

In the biaxially oriented polyester film for laminating a metal plate of the present invention, the acid component is 60 to 95 mol% of terephthalic acid and 40 to 5 mol% of isophthalic acid with respect to the total acid component, and the glycol component is mainly ethylene. It consists of a polyester made of glycol. When the proportion of the terephthalic acid component is less than 60 mol%, it is difficult to orientate and crystallize the obtained film, and as a result, there arises a problem that the operability particularly in the stretching step is deteriorated. Also,
When the obtained film is applied as a material for a lid material, there is a problem that feathering property is poor. On the other hand, when the proportion of the terephthalic acid component exceeds 95% by mole, there arises a problem that a high temperature is required for thermocompression bonding to a metal plate and that the crimpability is poor. The ratio of the terephthalic acid component to the total acid component is preferably 70 to 90 mol%, more preferably 75 to 88 mol%.

The intrinsic viscosity of the polyester resin constituting the film in the present invention is 0.45 to 1.0 dl / g, preferably 0.50 to 0.90 dl / g, more preferably 0.55 to 0.80 dl / g. It is. When the intrinsic viscosity of the film is less than 0.45 dl / g, it is difficult to obtain a film having mechanical strength that can be practically used,
If it exceeds 1.0 dl / g, the thermocompression bonding of the film to the metal plate will be impaired.

The biaxially stretched film of the present invention has only one melting point Tm as measured by differential scanning calorimetry (DSC).
m is 240 to 253 ° C, preferably 240 to 250 ° C,
More preferably, it is in the range of 243 to 250 ° C. Even if the composition of the polyester resin constituting the film satisfies the above conditions, the film has two or more Tm,
When the temperature exceeds 53 ° C., since the polyester resin in the film is non-uniform or has high crystallinity, the resulting film has a problem that the thermocompression bonding property, the moldability, and the tightening property are deteriorated. In addition, as described later, when an unstretched sheet is manufactured by mixing PET and isophthalic acid copolymerized PET and melt-extruding, an irregular pattern called a flow mark occurs in the unstretched sheet, or during stretching, Cuts occur frequently, and the operability during film production may be impaired. On the other hand, when Tm is less than 240 ° C., the orientation crystallization of the film becomes insufficient, and when this film is applied to a lid material, the film has poor retort resistance (particularly, water spot) and poor feathering property. There is.

The film of the present invention has a heat of fusion [ΔHm] derived from its crystal part of 15 to 35 J / g, preferably 18 to 33 J / g, more preferably 20 to 30 J / g.
It is necessary to be. If it exceeds 35 J / g, the adhesiveness to the metal plate may decrease, or the tightness of the laminated metal plate on which this film is laminated may decrease. Further, when ΔHm is less than 15 J / g, it is difficult for the resin composition to be oriented and crystallized, so that it is difficult to form a uniform stretched film. In addition, when a lid material is formed using this film, a water spot is generated during retort treatment. It is easy to occur.

The degree of plane orientation f of the film of the present invention must be 0.11 to 0.16. Where f
Is defined by the following formula. f = {(nx + ny) / 2} -nz where nx and ny are the maximum and minimum values of the refractive index in the plane direction of the film, and nz represents the refractive index in the thickness direction of the film. When the degree of plane orientation is less than 0.11, the mechanical properties and heat resistance of the film are not sufficient, and there is a problem that the film shrinks during thermocompression bonding with a metal plate. When the degree of plane orientation exceeds 0.16, the thermocompression bonding property with a metal plate is reduced, or when a lid material is formed using a laminated metal plate, micro cracks are generated in the film or the film is easily broken. Cause problems.

As the polyester resin raw material used in the present invention, a copolymerized polyester satisfying the ratio of the constituent components in the present invention can be used.
By using a method (blending method) of melt-extruding a resin in which PET and isophthalic acid copolymerized PET are mixed so as to satisfy the above component ratio, it is possible to easily and more stably produce a film having the characteristics of the present invention. it can. For example, when a copolymerized polyester satisfying the above component ratio is used as a starting material,
In some cases, blocking occurs in the resin drying step, causing a problem of handling, and since it is difficult to be oriented and crystallized, necking or fusing is likely to occur in the step of stretching the film.

PE used in the above blending method
T is substantially composed of a terephthalic acid component and an ethylene glycol component, and is obtained by performing a melt polycondensation reaction, preferably a solid phase polymerization reaction. By performing the solid-phase polymerization reaction, the content of low molecular weight substances, particularly terephthalic acid-ethylene glycol cyclic trimer (CETET), in the resin can be significantly reduced. We have confirmed that CTET causes white powder generated during retort treatment, and PET and isophthalic acid copolymerized PE obtained by such a solid-state polymerization reaction.
By using a raw material in which T is mixed so as to have the ratio of the above constituent components, the content of CTET in the obtained film can be remarkably reduced, so that generation of white powder can be prevented. large.

Known methods can be applied to the production of PET. For example, a slurry of terephthalic acid, ethylene glycol and, if necessary, other copolymerization components is continuously supplied to an esterification reactor in which bis (β-hydroxyethyl) terephthalate and a low polymer thereof are present. The reaction is carried out at a temperature of about 3 to 8 hours to continuously obtain an esterified product having an esterification reaction rate of about 95%.
Next, this was transferred to a polymerization vessel, and germanium dioxide,
The melt polycondensation reaction may be performed in the presence of a catalyst such as antimony trioxide under a reduced pressure of 1.3 hPa or less at a temperature of 250 to 280 ° C. until a polyester resin having a desired intrinsic viscosity is obtained. For the solid-phase polymerization reaction, the melt polycondensation reaction is terminated at a stage of intrinsic viscosity lower than the target, and an inert gas flow is performed so that the obtained resin is in a lump and has an atmosphere of 180 to 235 ° C. Alternatively, the treatment is performed under reduced pressure for 2 to 20 hours.

The PET may be appropriately copolymerized with other components as long as the effects of the present invention are not impaired. Isophthalic acid, (phthalic anhydride), phthalic acid,
Aromatic dicarboxylic acids such as 2,6-naphthalenedicarboxylic acid and 5-sodium sulfoisophthalic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, dodecanedicarboxylic acid, maleic anhydride, fumaric acid, itacone Aliphatic dicarboxylic acids such as acid, citraconic acid and mesaconic acid; alicyclic dicarboxylic acids such as (anhydrous) hexahydrophthalic acid and hexahydroterephthalic acid;
0 dimer acid, p-hydroxybenzoic acid, lactic acid, β-
Hydroxybutyric acid, hydroxycarboxylic acids such as ε-caprolactone, (anhydrous) trimellitic acid, trimesic acid,
Polyanhydrides such as (anhydrous) pyromellitic acid can be mentioned. Examples of the alcohol component as a copolymer component include diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-pentanediol. Aliphatic diols such as hexanediol, neopentyl glycol, polyethylene glycol having a molecular weight of 200 to 2,000, polypropylene glycol and polytetramethylene glycol, and fats such as 1,4-cyclohexanedimethanol and 1,4-cyclohexanediethanol Examples include cyclic diols, aromatic diols such as ethylene oxide or propylene oxide adducts of bisphenol A and bisphenol S, and polyfunctional alcohols such as trimethylolpropane, glycerin and pentaerythritol. . In PET, a diethylene glycol component (DEG) is by-produced at the time of polymerization, and this structure is contained in the resin skeleton. The total of the copolymer components including DEG is 5 mol% or less, more preferably 3 mol% or less of the total acid components. preferable. If it exceeds 5 mol%, the crystallinity of PET is impaired, and the desired film performance of the present invention cannot be obtained.

The isophthalic acid copolymerized PET used in the present invention can be obtained by the same melt polycondensation reaction as PET. The isophthalic acid copolymerized PET may be copolymerized with 5 mol% or less, more preferably 3 mol% or less of other components of the total acid component. When the proportion of the other copolymer component exceeds 5 mol%, the compatibility with PET decreases,
The tightening property and feathering property are deteriorated.

The content of CTET in the film of the present invention is preferably 0.6% by weight or less. The lid material of the metal can body is required not to generate white powder at the time of retort, but there is no clear relationship between the total amount of low molecular weight substances in the film and the amount of white powder generated. CET is the main causative substance of white powder, and the above problem can be prevented by setting the content of CTET to 0.6% by weight or less. As a method for suppressing the content of CTET in the film to 0.6% by weight or less, a solid-phase-polymerized PE is used.
This can be achieved by using T or increasing the amount of solid-state polymerization PET added as much as possible.

The film for laminating a metal plate of the present invention can be manufactured by a known method such as a flat type or tubular type film forming method. A flat type is preferable, and as a stretching method, a simultaneous or sequential two-stage biaxial stretching method can be used.

When the film of the present invention is produced by the flat biaxial stretching method, for example, a resin composition comprising PET and copolymerized PET blended so as to have a target composition is provided with a T die. Using an extruder, a temperature of 230 to
The mixture is melted and mixed at 280 ° C., extruded into a sheet shape from a T-die, and brought into close contact with a casting roll whose temperature has been adjusted to 40 ° C. or lower and quenched to obtain an unstretched sheet having a desired thickness. In order to sufficiently melt-mix the raw material resin composition, a raw material that has been previously melt-kneaded may be used. The degree of kneading of the resin composition is determined by the screw shape of the extruder, the extrusion temperature, the residence time of the resin, and the like. However, if the residence time is increased unnecessarily or the extrusion temperature is increased, CTET is increased.
May occur.

Next, the unstretched sheet is gripped at both ends with clips and preheated by blowing hot air at a temperature of 40 to 120 ° C. from the upper and lower surfaces of the sheet. It is biaxially stretched about 2 to 4 times. Thereafter, the relaxation rate in the vertical and / or horizontal direction is set to several percent, and 1
After heat-treating the film by heat treatment at 20 to 200 ° C. for several seconds to several tens of seconds, the film is cooled to room temperature, and 20 to 500 m / mi
The film is wound at a speed of n to obtain a film having a desired thickness. If the preheating temperature is less than 40 ° C. or the stretching temperature is less than 50 ° C., the stretching stress increases and necking easily occurs.On the other hand, if the preheating temperature is 120 ° C. or the stretching temperature exceeds 130 ° C., fusing or In some cases, the crystallization of the film proceeds to whiten, and the degree of plane orientation of the film decreases. If the heat setting temperature is lower than 120 ° C.,
A film having sufficient mechanical properties and heat resistance cannot be obtained, and if the temperature exceeds 200 ° C., the thermocompression bonding property of the obtained film to a metal plate is reduced. When the stretching ratio is out of the above range, the degree of plane orientation f is 0.11 to 0.1.
It becomes difficult to obtain 16 films.

As a heat treatment method after the stretching, a conventionally known method can be adopted, for example, a method of blowing hot air to the stretched film, a method of irradiating the stretched film with infrared rays, and a method of irradiating the stretched film with microwaves. Although a method etc. are mentioned, the method of blowing hot air to a stretched film is preferable in that heating can be performed uniformly and accurately. Also,
JP-B-35-11774, JP-B-43-5557
As disclosed in Japanese Unexamined Patent Application Publication No. H10-205, a heat buffer zone may be provided between the stretching step and the heat fixing step.

The film of the present invention has one or more average particle diameters selected from inorganic lubricants such as silica, alumina, kaolin, calcium carbonate, titanium dioxide, barium sulfate and the like, or organic lubricants such as silicone particles. 2.
A required amount of a lubricant of 5 μm or less can be added to impart a slip property to the film surface, thereby improving the processability during film production and thermocompression bonding with a metal plate. Further, a high concentration (for example, 10 to 30% by weight) of titanium dioxide, barium sulfate, a silicone compound, or the like is added to impart concealing properties, and the appearance of the can body and the lid can be improved. Furthermore, the film has a coloring agent, an antioxidant, an antistatic agent,
An antifoaming agent, a flame retardant and the like can be contained.

The film of the present invention has a thickness of 5 to 50 μm.
m, preferably 8 to 25 μm, more preferably 10 to
20 μm. When the thickness is less than 5 μm, breakage or the like is apt to occur during processing, and when the thickness exceeds 50 μm, the winding property deteriorates.

The film of the present invention may be provided with an adhesive layer by coextrusion, lamination, or coating in order to improve the adhesion to the metal plate. The dry thickness of the adhesive layer is preferably 0.5 μm or less.

On the other side of the film which is thermocompression-bonded to the metal plate, one or two types are used to improve the appearance and printability of the metal can body and to improve the heat resistance and retort resistance of the film. The above resin layer can be provided. These layers can be provided by a coextrusion method, a lamination or a coating process.

As a method of laminating the film and the metal plate of the present invention, the metal plate is preheated to a predetermined temperature in advance, and the film and the film are pressed against each other by a temperature-controllable roll and thermocompressed. It is manufactured continuously. Examples of the method of heating the metal plate include a heater roll heat transfer method, an induction heating method, a resistance heating method, and a hot air transfer method. preferable. Also,
As a cooling method after lamination, a method of dipping in a coolant such as water or a method of contacting with a cooling roll can be used. In the present invention, the lamination conditions are not particularly limited, especially when used for a lid material,
Excessive amorphization of the film during the lamination process should be avoided. This is because the non-crystallized part is partially crystallized during the retort treatment to generate a water spot or to deteriorate the feathering property.
Preferred lamination conditions are [Tm-50 ° C] to [Tm with respect to the melting point Tm of the resin composition constituting the film.
−10 ° C.] on a metal plate, at room temperature to [Tm −1
00 ° C] with a linear pressure of 5 to 100k
After the film is pressed and thermocompressed at g / cm, the film is quenched in cold water.

As the metal plate used in the present invention, a sheet-shaped or band-shaped steel plate and an aluminum plate, or those obtained by subjecting their surfaces to various plating treatments or chemical conversion treatments are preferable. In particular, those having a chromium hydrated oxide film on the surface layer or a film having a two-layer structure of chromium metal chromium in the lower layer and chromium hydrated oxide in the upper layer are excellent in adhesion to the film. In addition, tin, nickel, zinc, one or two or more types of multi-layer plating of aluminum,
Alloy plating, chromium hydrate oxide film on the upper layer,
Alternatively, a film having a two-layer structure as described above,
Specifically, tinplate, tin-free steel (TF
S), nickel-plated steel sheet, ultra-thin tin-plated steel sheet (LT
S) and the like can be used. For aluminum plate, pure aluminum, Al-Mn alloy, Al-Mg alloy, chromate treatment, phosphate treatment, anodizing treatment,
Those subjected to a boehmite treatment or the like, or those obtained by forming a chromium hydrated oxide film or a film having the above two-layer structure on the surface thereof can be used.

In the case where the laminated metal plate obtained as described above is used as a cover material, press forming, curling forming, in the case of EOE, forming such as score processing or rivet processing for tab setting, and resin Lining is applied. The polyester film of the present invention is laminated on the outer surface of the metal can, but may be laminated on the inner surface of the can.

In the case where a heat treatment is performed after the above-mentioned lid material forming process to relax the residual stress of the film,
It is preferable to satisfy the following characteristics (e) to (h). (E) The limiting viscosity of the polyester resin constituting the film is 0.45 to 1.0 dl / g. (F) It has only one melting point Tm in the range of 240 to 253 ° C. (G) Sum of heat of fusion [ΔHm] derived from crystal part of polyester resin is 10 to 35 J / g. (H) The degree of plane orientation is 0.05 to 0.16. When any of the above conditions is not satisfied, any of the performances of the tightening property, the retort resistance property, and the feathering property is inferior. In particular, [ΔHm] is less than 10 J / g and the plane orientation degree is 0.05. If it is less than 1, a water spot is generated during the retort treatment, or the feathering property is reduced.

Since the metal can and the lid using the film of the present invention are excellent in retort resistance, they can be used for filling beer, fruit juice, carbonated beverage, coffee, green tea, black tea, processed food and the like. Are suitable.

[0036]

Next, the present invention will be described more specifically with reference to examples. The method of analyzing and measuring each characteristic value used in Examples and Comparative Examples is as follows.

Composition of polyester resin: 230 ° C. in sealed tube
, And subjected to gas chromatogram analysis for quantitative analysis.

Intrinsic viscosity [η] of resin: phenol / 1,
It measured at 20 degreeC using the 1,2,2- tetrachloroethane equal weight mixed solvent. The unit is dl / g.

The degree of plane orientation f of the film: manufactured by Atago Optical Co., Ltd.
Using an Abbe refractometer, the value was obtained from the following equation. f = {(nx + ny) / 2} -nz where nx and ny are the maximum and minimum values of the refractive index in the plane direction of the film, and nz represents the refractive index in the thickness direction of the film. The refractive index is a value obtained by attaching a polarizing plate analyzer to the eyepiece side of an Abbe refractometer and measuring the temperature with a monochromatic NaD line using methylene iodide as a mounting solution at a temperature of 25 ° C. The width of the film used for the measurement was 20
cm, 3 cm from the center and both ends of the film were measured, and the average value was defined as the degree of plane orientation. Regarding the film of the lid material, ten lid materials were measured, and the average value was defined as the degree of plane orientation.

Thermal properties of the film: 10 to 12 mg of each sample was taken from the film and the lid material film.
Using Perkin Elmer DSC-7, heating rate 2
The temperature was increased to 25 to 280 ° C. under the conditions of 0 ° C./min and measured. The melting point Tm of the polyester was defined as the peak top temperature of the melting peak. Incidentally, for example, Japanese Patent Application Laid-Open No. 4-117
In the case where a subpeak derived from a heat-setting treatment performed at the time of producing a film described in Japanese Patent No. 427, etc., this was excluded. The heat of fusion [ΔHm] derived from the crystalline portion of the polyester was calculated by taking into account factors such as crystallization during temperature rise and the like.

CTET amount of film: A predetermined amount of a sample was collected from the film, dissolved in a mixed solvent of hexafluoroisopropanol / chloroform at an equal volume ratio, and dropped into acetonitrile with stirring to precipitate the resin. Was. Next, this was filtered with a membrane filter, and the obtained filtrate was analyzed using a high performance liquid chromatograph (600E, manufactured by Waters). Note that C
A calibration curve of TET and an internal standard substance was prepared, and the content of CTET contained in the film was determined based on the curve.

Lamination property: The condition after lamination was visually evaluated according to the following criteria. ：: The film laminated with metal has no defects such as scratches and wrinkles, and the part which is well thermocompressed is 98% of the entire area.
that's all. Δ: The above portion is 80% or more and less than 98% of the entire area. ×: The above portion is less than 80% of the entire area.

Adhesiveness: The above laminating property is ○ or Δ
A strip-shaped test piece having a width of 18 mm was cut out from the laminated metal plate determined to be. The film was not laminated on the end of the metal plate, and the length of the laminated portion was 8c.
m or more. Using an autograph manufactured by Shimadzu Corporation, the film was cut at a speed of 10 mm / nin.
An 80 ° peel test was performed to measure the peel strength, and the peel strength was evaluated according to the following criteria. ：: Peel strength of 10 or more test specimens out of 11 specimens was 30
The film was broken at 0 gf or more or 300 gf or more. Δ: Peeling strength of 5 to 9 test pieces is 300 gf or more,
The film was broken at 300 gf or more. C: Peeling strength or four or less test pieces having a breaking strength of 300 gf or more when the film is broken.

Formability: A laminated metal plate is formed into a 202-diameter lid material using a press machine (manufactured by Onuma Iron Works, NFL-25) and a curling machine (manufactured by Tokyodo Machine Co., Ltd.), and the film is peeled and cut. The presence or absence of damage such as cracks was visually observed and observed with a fluorescence microscope (magnification: 80), and evaluated according to the following criteria. Good: 95 or more of the 100 lids were not damaged. Δ: Out of 100 lid materials, 80 to 94 were not damaged. ×: Some damage is observed in 21 or more of the 100 lid materials.

Retort resistance: The lid material obtained as described above was autoclaved (BS325, manufactured by Tommy Seiko Co., Ltd.).
And subjected to a retort treatment in steam at 125 ° C. for 30 minutes. The appearance of water spots and white powder on the appearance of the film was visually observed and used as an index of retort resistance according to the following criteria. ：: good. Δ: Water spot or white powder was observed in less than 5% of the film surface area. ×: Water spots or white powder were observed in 5% or more of the film surface area.

Winding property: After a resin lining (PVC sol) is applied to the inner surface of the lid material, a winding machine (manufactured by Chujo Can Co., Ltd.)
Semi-automatic seamer) and commercially available 190g 3P can (welded can)
Was used for tightening. In the winding step, since the film is not damaged or does not occur even by subtle differences in conditions, prepare 100 lid materials created under each condition, arrange them randomly, and continuously It was tightened and evaluated according to the following criteria. ：: 95 or more of the 100 lids were not damaged. Δ: Out of 100 lids, 80 to 94 were not damaged. ×: Some damage is observed in 21 or more of the 100 lid materials.

Feathering property: aluminum plate (505)
2H34 material) were used to obtain 100 pieces each of a stainless steel tab (SOT) type EOE from the laminated metal plate obtained.
Then, ten people were asked to open 10 plugs each, and the cut surfaces were visually observed and evaluated according to the following criteria. ：: Out of 100 EOEs, 95 or more had no abnormality such as peeling of the film or whiskers. Δ: Out of 100 EOEs, 80 to 94 did not show abnormalities such as peeling of the film or whiskers. ×: Abnormalities such as peeling of the film and whiskers were observed in 21 or more out of 100 EOEs.

(Production of Polyester Resin) Polyester resin A: In the presence of a small amount of bis (β-hydroxyethyl) terephthalate and its low polymer, the molar ratio of terephthalic acid (TPA) and ethylene glycol (EG) is 1/1. .6 slurry and an average particle size of 1.0 μm
Was charged into an esterification reaction tank, and the system was stirred at 250 ° C. and 4.9 × 10 ⁵ Pa to obtain an esterified product having an esterification reaction rate of 95.2%. . Next, this was transferred to a polycondensation reaction tank, and 2 × 10 ⁻² mol% of germanium dioxide was added to all the acid components, and the temperature was raised to 280 ° C. while stirring the inside of the system.
It took 1 hour to reduce the pressure in the system to 60 Pa, and stirring was continued for 1.5 hours while maintaining this state. Next, the inside of the system was returned to normal pressure by a nitrogen gas flow, discharged in a strand form, cooled with water, and pelletized polyester resin A was obtained with a pelletizer. Table 1 shows the results of analysis after sufficiently drying the polyester resin A. As a result of analyzing the ash content of the pellet, the content of silica was 0.01% by weight.
Met.

Polyester resin B: polyester resin A
Was preliminarily dried at 70 ° C. for 2 hours, sufficiently crystallized at 130 ° C., heated to 220 ° C., and subjected to solid-state polymerization for 8 hours while maintaining the inside of the system at a reduced pressure of 78 Pa to obtain a polyester resin. B was obtained. Table 1 shows the analysis results.

Polyester resins CG and J: Various copolymerized polyester resins CG and J were obtained in the same manner as polyester resin A or B. In addition, isophthalic acid (I
PA) In the case of copolymerized PET, IPA having a molar ratio of 1/2
An esterification reaction was performed using the / EG slurry. In the case of diethylene glycol (DEG) copolymerized PET, a predetermined amount of DEG was added into the system at the start of the polycondensation reaction. Table 1 shows the analysis results of the obtained resins. In addition, each resin was prepared by adding silica having an average particle size of 1.0 μm to 0.1 μm.
It contained 0.1% by weight.

Polyester resin H: Dry-blended sufficiently dried polyester resins B and E in an equal weight ratio,
This was melt-mixed at 270 ° C. using a twin-screw extruder (PCM45, manufactured by Ikegai Ironworks Co., Ltd.), extruded into strands (discharge rate: 350 g / min), cooled with water, and pelletized to obtain a polyester resin H.

Polyester resin I: In the above method for obtaining polyester resin H, polyester resin E was melt-mixed without drying sufficiently to obtain polyester resin I.

[0053]

[Table 1]

Example 1 (Production of Film a) 75 parts by weight of a sufficiently dried polyester resin B and 25 parts by weight of a polyester resin E were dry blended, and an extruder (75 mm) equipped with a T die was used.
Using a gentle compression type single screw having a diameter of L / D = 45), the sheet was extruded at 270 ° C. at a discharge rate of 500 g / min. Subsequently, this was brought into close contact with a casting roll adjusted to a surface temperature of 18 ° C. and rapidly cooled to obtain an unstretched sheet having a thickness of 100 μm. The end of the unstretched sheet is gripped by a clip of a tenter-type stretching machine, and
After running through the preheating zone, the longitudinal direction (M
After stretching in D) three times and subsequently running in a preheating zone at 80 ° C, the film was stretched 3.5 times in the transverse direction (TD) at a temperature of 100 ° C. Next, after heat-setting at 160 ° C. with a TD relaxation rate of 5%, the film was cooled to room temperature and wound up at a speed of 50 m / min to obtain a film having a thickness of 10 μm. The obtained film was slit to obtain a roll-shaped film a having a width of 20 cm. Next, Table 2 shows the results of various property evaluations using this film.

(Manufacture of lid) Sheet thickness 0.19 mm, sheet width 2
A 2 cm roll-shaped TFS (temper degree T-4) is heated to 208 ° C. by an induction heating roll, and the above-mentioned roll-shaped film “a” is coated on both sides thereof with a pair of silicone rolls whose surface temperature is adjusted to 50 ° C. 20m nip length using
After laminating under conditions of m and a line speed of 20 m / min (lamination time: 0.06 seconds), after 3 seconds, the laminate was immersed and cooled in ice water to obtain a laminated metal plate. Table 2 shows the obtained laminated metal plate and various evaluation results when a lid material was manufactured using the laminated metal plate. Note that E
The evaluation of the feathering property of the OE was performed using a commercially available rolled aluminum (5052H34, 0.26 mm thick).
Lamination was carried out in the same manner as above, except that this was heated with a heater roll.

Example 2 After running in a preheating zone of 70 ° C., MD at a temperature of 90 ° C.
A film b and a laminated metal plate were obtained under the same conditions as in Example 1 except that the film was simultaneously biaxially stretched by a factor of 3 and a TD by a factor of 3.3. Table 2 shows the properties of the film b, the laminated metal plate, and various evaluation results when a lid material was manufactured using the laminated metal plate.

Examples 3 to 10 and Comparative Examples 1 to 9 As shown in Tables 2 and 3, films were produced by the simultaneous biaxial stretching method while changing the type and blending ratio of the polyester resin and the film production conditions. Using the obtained film, a laminated metal plate was prototyped under the same conditions as in Example 1, and its performance was evaluated. Tables 2 and 3 show the obtained results.

[0058]

[Table 2]

[0059]

[Table 3]

Comparative Example 10 55 parts by weight of a sufficiently dried polyester resin B and 45 parts by weight of a polyester resin G were dry-blended.
An unstretched sheet having a thickness of 180 μm was obtained in the same manner as in Example 1. Next, the unstretched sheet is subjected to MD, T under various conditions.
D was attempted to be stretched three times, but rupture frequently occurred during stretching, and a film having a uniform thickness could not be continuously produced.

Comparative Example 11 Using polyester resin I, a film having a thickness of 10 μm was obtained in the same manner as in Example 2. However, this film was brittle, could be easily broken by hand, and was not practical. Thus, a stretched film was prepared with various thicknesses, but the same result was obtained. The intrinsic viscosity of each of the obtained films was 0.45 dl /
g.

Examples 11 to 13 and Comparative Examples 12 to 16 Table 4 shows the evaluation results when the lamination temperature on the metal plate was changed using the above various films. In addition, the intrinsic viscosity and the melting point of the film after the lid material was formed were the same values as those of the film before the lamination.

[0063]

[Table 4]

[0064]

According to the present invention, (1) excellent in mechanical properties and heat resistance, (2) thermocompression bonding can be performed at a relatively low temperature, a wide range of laminating conditions can be applied, and (3) retort processing occurs. Low content of CTET, which is the main cause of white powder, and (4) excellent workability for various forms after lamination, even when applied as a lid material, (5) crimpability and feathering (6) It is possible to provide a film for laminating a metal plate and a method for producing the same, which have many advantages that water spots are less likely to occur even after retort treatment. In particular, the present invention has found a film formulation that overcomes this problem, which is a major cause of the fact that a film-laminated metal plate could not be used as a lid material until now, and at the same time, a film that satisfies other required properties. It can be said that the present invention has created the possibility that a film-laminated metal plate can be applied as a lid material for the first time in terms of finding a production method of the present invention.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI C08L 67/02 C08L 67/02 // B29K 67:00 B29L 7:00 (72) Inventor Yoshihiro Umemura 23 Uji Kozakura 23 Uji City, Kyoto Prefecture Unitika Corporation Central Research Laboratory

Claims (5)

[Claims] 1. The following (a) to (d) wherein the acid component is 60 to 95 mol% of terephthalic acid and 40 to 5 mol% of isophthalic acid with respect to the total acid component, and the glycol component is mainly composed of ethylene glycol. Biaxially oriented polyester film for metal plate lamination that satisfies the characteristics of (A) The limiting viscosity of the polyester resin constituting the film is 0.45 to 1.0 dl / g. (B) It has only one melting point Tm in the range of 240 to 253 ° C. (C) The sum of heats of fusion [ΔHm] derived from crystal parts of the polyester resin is 15 to 35 J / g. (D) The degree of plane orientation is 0.11 to 0.16. 2. The polyester film according to claim 1, wherein the content of the terephthalic acid-ethylene glycol cyclic trimer contained in the film is 0.6% by weight or less. 3. A laminated metal plate obtained by laminating the film according to claim 1 or 2 and a metal plate, and a metal can body and a can lid material using the laminated metal plate. 4. Polyethylene terephthalate (PET)
And isophthalic acid copolymerized polyethylene terephthalate, and the both ends of an unstretched sheet obtained by melt-extrusion with an extruder are gripped and preheated at a temperature of 40 to 120 ° C, and then at a temperature of 50 to 130 ° C in the vertical and horizontal directions. The method for producing a polyester film according to claim 1, wherein the polyester film is biaxially stretched at a stretching ratio of 2 to 4 times, and then heat-set at 120 to 200 ° C. 4. 5. The method for producing a polyester film according to claim 4, wherein the PET has been subjected to solid-state polymerization.