JPH0790094A - Polyester film for laminating metal plate - Google Patents

Abstract

PURPOSE:To obtain a polyester film for laminating a metal plate, suitably useful as a metal can produced by molding and processing, having not only excellent adhesiveness, moldability, impact resistance and seasoning characteristics but extremely few film defects after molding.heat treatment, especially characteristic of repairing defects by heat treatment such as baking. CONSTITUTION:This polyester film for laminating a metal plate has at least two melting point peaks between 100 and 230 deg.C and contains 0.01-1wt.% of a diethylene glycol component.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a polyester film for laminating metal plates. More specifically, the present invention relates to a polyester film for laminating metal plates, which has excellent adhesiveness, moldability, impact resistance, and taste characteristics and is suitable for a metal can manufactured by molding.

[0002]

2. Description of the Related Art Conventionally, for the purpose of preventing corrosion, the inner and outer surfaces of metal cans are coated with various thermosetting resins such as epoxy or phenol dissolved or dispersed in a solvent to coat the metal surface. It has been widely practiced. However, such a coating method of a thermosetting resin has a problem that it takes a long time to dry the coating material, productivity is lowered, and environmental pollution is caused by a large amount of organic solvent.

As a method of solving these problems, there is a method of laminating a polyester film on a steel plate, an aluminum plate, or a metal plate which has been subjected to various surface treatments such as plating on the metal plate as a material for the metal can. When a laminated metal plate of a film is drawn or ironed to produce a metal can, the polyester film is required to have the following characteristics.

(1) Excellent adhesion to a metal plate.

(2) It has excellent moldability and does not cause defects such as pinholes after molding.

(3) The impact of a metal can does not cause the polyester film to peel off, crack, or pinhole.

(4) The scent component of the contents of the can is not adsorbed on the polyester film, and the odor of the polyester film does not impair the flavor of the contents (hereinafter referred to as taste characteristics).

Many proposals have been made to solve these requirements. For example, Japanese Patent Laid-Open No. 64-22530 discloses a polyester film having a specific density and plane orientation coefficient, and Japanese Laid-Open Patent Publication No. 2-57339. Discloses a copolyester film having a specific crystallinity. However, these proposals are not able to comprehensively satisfy the various required characteristics as described above, and in particular, do not cause defects such as pinholes after molding, impact resistance, and taste characteristics. I couldn't say it was at a satisfactory level.

[0009]

The object of the present invention is to eliminate the above-mentioned problems of the prior art, and is excellent in adhesiveness, moldability, heat resistance, impact resistance and taste characteristics, especially after molding. It is an object of the present invention to provide a copolyester and a film for a metal plate laminate, which does not cause defects such as pinholes and has excellent impact resistance and taste characteristics and which is suitable for a metal can produced by molding.

[0010]

The above-mentioned object of the present invention has at least two melting point peaks at 100 to 230 ° C. and a diethylene glycol component of 0.01 or less.
It can be achieved by a polyester film for laminating metal plates, which is characterized by containing ˜1% by weight.

The polyester in the present invention is a polymer composed of a dicarboxylic acid component and a glycol component, and examples of the dicarboxylic acid component include terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylsulfonedicarboxylic acid and diphenoxy. Aromatic dicarboxylic acids such as ethanedicarboxylic acid, 5-sodium sulfoisophthalic acid, phthalic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, fumaric acid and other aliphatic dicarboxylic acids, cyclohexanedicarboxylic acid Alicyclic dicarboxylic acids such as, and oxycarboxylic acids such as p-oxybenzoic acid, and the like. Among these dicarboxylic acid components, terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid are preferable from the viewpoint of impact resistance and taste characteristics. On the other hand, examples of the glycol component include ethylene glycol, propanediol,
Examples thereof include aliphatic glycols such as butanediol, pentanediol, hexanediol and neopentyl glycol, alicyclic glycols such as cyclohexanedimethanol, and aromatic glycols such as bisphenol A and bisphenol S. Among these glycol components, ethylene glycol is preferable from the viewpoint of impact resistance and taste characteristics. Two or more kinds of these dicarboxylic acid components and glycol components may be used in combination.

Further, a polyfunctional compound such as trimellitic acid, trimesic acid and trimethylolpropane may be copolymerized with the copolyester as long as the effect of the present invention is not impaired.

The polyester used in the present invention is required to have at least two melting point peaks at 100 to 230 ° C. in terms of adhesiveness, heat resistance and pinhole resistance. That is, by stacking or blending a polyester having a relatively high melting point and a polyester having a lower melting point, it becomes possible to make heat resistance and pinholes less likely to occur in the heat history during can making. In particular, when polyesters having different melting points are blended, it is preferable that the melting point difference is 5 ° C. or more because the pinhole resistance effect becomes good. As an example of the blend, generally, the drying temperature after the washing step at the time of can making is about 200 to 220 ° C. In that case, the melting point of the high melting point polyester is 21
The polyester having a temperature of 0 ° C. or higher is used, and the melting point of one of the low melting point polyesters is preferably 100 to 205 ° C., more preferably 100 to 200 ° C. The content of the low melting point polyester is not particularly limited, but from the viewpoint of pinhole resistance, it is preferably more than 20% by weight of the polyester film layer (A layer), further 25% by weight or more,
It is particularly preferably 30% by weight or more. In the case of a laminated film, the content of the low melting point polyester is preferably 21% by weight to 70% by weight of the polyester film layer (A layer) to be laminated, particularly preferably from the viewpoint of both impact resistance and pinhole resistance. It is 25% to 60% by weight. Also, the intrinsic viscosity [η] of the low melting point polyester to be blended
Is preferably 0.7 or more because the impact resistance is good.

It is considered that the improvement of the pinhole resistance is due to the effect that the low-melting point polymer becomes fluid due to heat during the molding process and the drying process so that pinholes are hard to occur, and that repair is performed if the holes are very small. To be

In the present invention, it is necessary to contain 0.01 to 1% by weight of a diethylene glycol component in order to improve impact resistance after receiving various heat histories in the can making process, and it is preferable. Is 0.01 to 0.8% by weight,
It is more preferably 0.01 to 0.6% by weight, and particularly preferably 0.01 to 0.5% by weight. When the content of the diethylene glycol component is less than 0.01, the polymerization process becomes complicated, which is not preferable in terms of cost. When it exceeds 1% by weight, the polyester is deteriorated due to the heat history in the can making process and the impact resistance of the film is increased. It is not preferable because it gets worse. Diethylene glycol is a by-product of polyester production,
To reduce the amount to 1% by weight or less, the polymerization time is shortened, the amount of antimony compound, germanium compound, etc. used as a polymerization catalyst is limited, the method of combining liquid phase polymerization and solid phase polymerization, and the alkali metal component are used. Although the method of making it contain, etc. are mentioned, the method is not particularly limited.

On the other hand, considering the scratch resistance in the contact between the inner surface of the can and the holder during baking coating in the can manufacturing process, the above A
In addition to the layers, polyester having a melting point of 230 to 300 ° C. is preferably laminated as the B layer. Preferably, polyethylene terephthalate, polyethylene naphthalate,
Examples thereof include polyethylene isophthalate and copolyesters thereof. Examples of preferred copolymerization components include isophthalic acid and butanediol, with isophthalic acid being particularly preferred in terms of taste characteristics.

The intrinsic viscosity [η] of the film is preferably 0.7 or more, more preferably the intrinsic viscosity [η].
Of 0.75 or more is preferable because impact resistance and taste characteristics can be further improved.

In order to improve the taste characteristics, the content of acetaldehyde in the polyester on the non-adhesive surface of the metal is preferably 50 ppm or less, more preferably 30 pp.
m or less, particularly preferably 20 ppm or less. If the acetaldehyde content exceeds 50 ppm, the taste characteristics are poor. The content of acetaldehyde in the film is 50
The method for controlling the pm or less is not particularly limited,
For example, in order to remove acetaldehyde generated by thermal decomposition when producing a polyester by a polycondensation reaction or the like, a method of heat treating the polyester under a reduced pressure or under an inert gas atmosphere at a temperature equal to or lower than the melting point of the polyester,
Preferably, the polyester is solid-state polymerized at a temperature of 150 ° C. or higher and a melting point or lower under reduced pressure or in an inert gas atmosphere, a method of melt film formation using a vent type extruder, and a method of extrusion during melt extrusion of polyester. Melting point +
A method of extruding within 30 ° C., preferably within a melting point + 25 ° C. in a short time, can be mentioned.

When the film of the present invention is used for beverages and food cans, at least the polyester on the side of the present invention which comes into contact with the contents has a germanium element content of 1 to 1 in terms of taste characteristics.
The content is preferably 500 ppm, more preferably 5 to 300 ppm, particularly preferably 10 to 100 pp.
m. When the amount of germanium element is less than 1 ppm, the effect of improving the taste characteristics is not sufficient, and when it exceeds 500 ppm, foreign matter is generated in the polyester, and the impact resistance is deteriorated, or the taste characteristics are deteriorated. The polyester of the present invention can have improved taste characteristics by containing the above-mentioned specific amount of germanium element in the polyester. The method of incorporating the germanium element into the polyester may be any conventionally known method and is not particularly limited, but usually, at any stage before the completion of the production of the polyester, a germanium compound may be added as a polymerization catalyst. preferable. Examples of such a method include a method of directly adding a powder of a germanium compound, or a method of dissolving a germanium compound in a glycol component which is a starting material of polyester, as described in JP-B-54-22234. And the like. Examples of the germanium compound, germanium dioxide, germanium hydroxide containing crystal water, or germanium tetramethoxide, germanium tetraethoxide, germanium tetrabutoxide, germanium alkoxide compounds such as germanium ethylene glycoloxide, germanium phenolate, germanium β-naphtholate, etc. Examples thereof include phosphorus-containing germanium compounds such as germanium phenoxide compounds, germanium phosphate and germanium phosphite, and germanium acetate. Of these, germanium dioxide is preferable.

The polyester of the present invention has a content of the oligomer in the polyester of 0.8% by weight from the viewpoint of taste characteristics.
The amount is preferably below, more preferably 0.7% by weight or less, and particularly preferably 0.6% by weight or less. Content of oligomer in copolymerized polyester is 0.8% by weight
If it exceeds, the taste characteristics are deteriorated, which is not preferable. The method for adjusting the content of the oligomer in the polyester to 0.8% by weight or less is not particularly limited, but the same method as the method for reducing the acetaldehyde content in the above-mentioned copolymerized polyester should be adopted. Can be achieved with.

The polyester of the present invention can be produced by any conventionally known method and is not particularly limited. For example, a case will be described where polyethylene terephthalate is copolymerized with an isophthalic acid component and germanium dioxide is added as a germanium compound. A terephthalic acid component, an isophthalic acid component and ethylene glycol are transesterified or esterified, and then germanium dioxide is added, followed by polycondensation reaction at a high temperature and reduced pressure until a constant diethylene glycol content is obtained, and a germanium element-containing polymer To get Then, the obtained polymer is subjected to a solid-state polymerization reaction at a temperature below its melting point under reduced pressure or in an inert gas atmosphere to reduce the content of acetadeldide to obtain a predetermined intrinsic viscosity [η] and a carboxyl end group. Etc. can be mentioned.

In producing the polyester of the present invention,
Conventionally known reaction catalysts and anti-coloring agents can be used, and examples of the reaction catalysts include alkali metal compounds, alkaline earth metal compounds, zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium. Examples of the anti-coloring agents such as compounds include phosphorus compounds.

In the present invention, a film obtained by laminating a layer A having at least two melting point peaks at 100 to 230 ° C. with a layer B mainly composed of polyester having a melting point of 230 ° C. to 300 ° C. The composition, catalyst, amount of diethylene glycol, and amount of carboxyl end groups in each layer may be different. When the edge of the film is collected, it is preferable to contain it in the layer A from the viewpoint of taste characteristics.

Further, the laminated film preferably has a ratio of the thickness of the A layer to the thickness of the B layer of 20: 1 to 1: 1 (A: B) from the viewpoint of taste characteristics and impact resistance, and particularly 1
It is preferably 5: 1 to 4: 1 (A: B) from the viewpoint of impact resistance.

The copolymerized polyester of the present invention contains 0 to 10% by weight of inorganic particles and / or organic particles having an average particle diameter of 0.1 to 10 μm in order to improve the handleability and processability of the film. In addition, it is preferable that the inorganic particles and / or the organic particles having an average particle diameter of 0.1 to 5 μm are contained in an amount of 0 to 3% by weight. The use of particles having an average particle size of more than 10 μm is not preferable because defects in the film are likely to occur. In particular, since it is not preferable to contain particles of 30 μm or more, it is preferable to use a filter capable of drastically reducing foreign matters of 30 μm or more as a film-forming filter. Examples of the inorganic particles and / or organic particles include wet and dry silica, colloidal silica, titanium oxide, calcium carbonate, calcium phosphate, barium sulfate, alumina, mica, kaolin, clay and the like inorganic particles and styrene, silicone, acrylic acid and the like. Examples thereof include organic particles having as a constituent. Among them, inorganic particles such as wet and dry colloidal silica and alumina, and organic particles having styrene, silicone, acrylic acid, methacrylic acid, polyester, divinylbenzene and the like as constituent components can be mentioned. Two or more kinds of these inorganic particles and / or organic particles may be used in combination.

The particles may be added to either the A layer or the B layer, but it is preferable to add the particles to the B layer for the ease of handling. On the other hand, particles may be added to the layer A as long as the characteristics are not impaired in terms of recovery. In addition, when particles are not contained, when the polymer is melt extruded and solidified by a casting drum, a method in which the layer B is on the drum surface is roughened and the film is pressed with air to solidify rapidly is adopted. May be.

Further, in producing the polyester film of the present invention, additives such as an antioxidant, a plasticizer, an antistatic agent, a weathering agent and a terminal blocking agent can be appropriately used if necessary. In particular, the combined use of an antioxidant is preferable because it prevents deterioration of the polyester due to heat history during the can making process.
The amount is 0.001-1 with respect to the total film weight.
About wt% is preferable.

The film made of the copolyester in the present invention may be an unstretched sheet or a uniaxially or biaxially stretched film.

In a molding method in which the moldability of the film is important such as ironing molding, an unstretched sheet, or
Refractive indices in the longitudinal direction, width direction, and thickness direction (Nx, Ny, N
z), the plane orientation coefficient fn = (Nx + Ny) / 2
A stretched film having a -Nz value of 0 to 0.12.

The thickness of the polyester film of the present invention is not particularly limited, but considering the processability, impact resistance and taste characteristics of the metal can, it is preferably 5 to 50 μm, more preferably 8 to 45 μm, and particularly preferably. 10-40 μm
Is.

The polyester film of the present invention can be formed by any conventionally known method. next,
The method for producing the film of the present invention will be described, but the present invention is not limited thereto.

Isophthalic acid 1 as polyester for layer A
7.5 mol% copolymerized polyethylene terephthalate ([η] = 0.85, diethylene glycol 0.7% by weight, melting point 213 ° C.) and isophthalic acid 22.5 mol% copolymerized polyethylene terephthalate ([η] = 0.63, Diethylene glycol 0.7% by weight, melting point 201 ° C), and polyester B as 5 mol% isophthalic acid copolymerized polyethylene terephthalate ([η] = 0.90, diethylene glycol 0.89% by weight, melting point 240 ° C) in a biaxial vent type. Separate extruders (extruder temperature is melting point + 25 ° C (A
Layer side is set to (melting point + 25 ° C for high-melting point polyester)) to melt, and then laminated in two layers with a feed block and discharged from a normal die, and then press the whole or part of the film with air. Then, the cast film is obtained by cooling and solidifying with a cooling drum roughened so that the layer B becomes the drum surface. The two-layer laminated film thus obtained is subjected to heat aging or surface activation treatment if necessary and wound up. Further, it is preferable to subject the film to a dust-proof treatment because defects in the film are less likely to occur.

The polyester cast film may be biaxially stretched simultaneously or successively. In the case of sequential biaxial stretching, it is possible to perform stretching in the longitudinal direction or the width direction two or more times. The stretching ratio in the longitudinal direction and width direction of the film can be arbitrarily set according to the degree of orientation, strength, elastic modulus, etc. of the target film, but preferably 2.5 to 2.5 in each direction.
It is 5.0 times. Either the stretching ratio in the longitudinal direction or the stretching ratio in the width direction may be increased or may be the same. The stretching temperature may be any temperature in the range of not less than the glass transition temperature of polyester and not more than the crystallization temperature, but it is usually preferably 80 to 150 ° C. Further, the film can be heat-treated after the biaxial stretching. This heat treatment can be performed by any conventionally known method such as heating in an oven or on a heated roll. The heat treatment temperature can be any temperature above the crystallization temperature of the polyester and below the softening point, but it is preferably 120 to 240 ° C. The heat treatment time may be arbitrary, but it is usually preferably 1 to 60 seconds. The heat treatment may be performed while relaxing the film in its longitudinal direction and / or width direction.

The metal plate of the present invention is not particularly limited,
A metal plate made of iron, aluminum or the like is preferable in terms of formability. Furthermore, in the case of a metal plate made of iron, an inorganic oxide coating layer that improves the adhesion and corrosion resistance on the surface of the metal plate, for example, chromic acid treatment, phosphoric acid treatment, chromic acid / phosphoric acid treatment, electrolytic chromic acid treatment A chemical conversion treatment coating layer represented by, for example, chromate treatment or chromium chromate treatment may be provided. Particularly, in terms of metallic chromium, 6.5 to 6.5 as chromium
A hydrated chromium oxide of 150 mg / m ² is preferable, and a spreadable metal plating layer such as nickel, tin, zinc, aluminum, gun metal or brass may be further provided. For tin plating 0.5-15 / m ^2, it is preferable to have a plating amount when nickel or aluminum 1.8~20g / m ^2.

The metal laminating film of the present invention can be preferably used for coating the inner and outer surfaces of a two-piece metal can produced by drawing or ironing. Also, good metal adhesion for covering the lid part of a two-piece can, or the body, lid, and bottom of a three-piece can,
Since it has moldability, it can be preferably used. In particular, the colored film of the present invention can be used for coating the outer surface. Therefore, a colorant can be blended in the polyester layer, and a white colorant, a red colorant or the like is preferably used as the colorant, and a colorant selected from titanium oxide, zinc white, an inorganic or organic pigment, etc. It is desirable to add 50% by weight, preferably 15-40% by weight. If the addition amount is less than 5% by weight, the color tone and the whiteness are inferior, which is not preferable. You may use together a pinking agent, a bluing agent, etc. as needed.

[0036]

[Characteristic Measuring Method and Evaluation Method] The characteristics of the polyester film are measured and evaluated by the following methods.

(1) Content of diethylene glycol component in polyester It was measured by NMR (13 C-NMR spectrum).

(2) Content of germanium element in polyester The content of germanium element in the polyester composition and the peak intensity were quantified by fluorescent X-ray measurement.

(3) Intrinsic viscosity of polyester Dissolve polyester in orthochlorophenol and prepare
It was measured at ° C.

(4) Melting point of polyester Crystallized polyester chips were subjected to a differential scanning calorimeter (DSC-2 type manufactured by Perkin-Elmer Co., Ltd.) at 10 ° C. /
It was measured at a temperature rising rate of min.

(5) Content of Acetaldehyde in Polyester or Film 2 g of fine powder of polyester film was sampled and put in a pressure resistant container together with ion-exchanged water, extracted with water at 120 ° C. for 60 minutes, and quantified by high sensitivity gas chromatography.

(6) Carboxyl terminal group (equivalent / ton) The polyester was dissolved in o-cresol / chloroform (weight ratio 7/3) at 90 to 100 ° C. for 20 minutes, and potentiometric titration was carried out with an alkali to obtain the value.

(7) Content of Oligomer in Polyester Film 100 mg of polyester film was dissolved in 1 ml of orthochlorophenol, and liquid chromatograph (Varia) was used.
The cyclic trimer was measured with a model 8500 manufactured by N. Co. to obtain the amount of oligomer.

(8) Plane orientation coefficient It was measured using an Abbe refractometer with sodium D line (wavelength 589 nm) as a light source. The plane orientation coefficient fn = (Nx + Ny) / 2-Nz obtained from the refractive indices (Nx, Ny, Nz) in the longitudinal direction, the width direction, and the thickness direction was calculated and obtained.

(9) Adhesion property Between the metal roll heated to 180 to 230 ° C. and the silicone rubber roll, the polyester film surface of the present invention and Sn
The plate was joined with a plated tin plate, pressure-bonded at a pressure of 4 kg / cm, and cooled in air after bonding. The adhesive strength of the laminated plate was determined by a peeling test at an angle of 180 °, and the adhesive strength of 250 g / cm or more was regarded as acceptable.

(10) Film Defects The adhesive surface of a polyester film and a tin-plated tin metal plate are heated and pressure-laminated at a temperature of 180 to 230 ° C., and a press molding machine (VAS-made by Semba Iron Works Co., Ltd.) is used.
33P type) was cold-formed at a pressure of 100 kg / cm ² to obtain a cup having a diameter D of 100 mm and a depth h of 130 mm and a drawing ratio (h / D) of 1.3. Further, this cup was baked under the conditions of 220 ° C. for 10 minutes, and defects of the film before and after the baking were examined by the following method.

A 1% saline solution was placed in the cup, and a voltage of 6 V was applied to the electrode in the saline solution and the metal can to read the current value.

Class A: less than 0.5 mA Class B: 0.5 mA or more and less than 1 mA Class C: 1 mA or more and less than 3 mA Class D: 3 mA or more

(11) Impact resistance After can making in the above (8) and (9), heat treatment was performed at 200 ° C. for 10 minutes, carbonated water was filled, and carbon dioxide bubbling was performed at 0 ° C. for 24 hours. Then, after punching 5 points from the outside of the can bottom with punches, the contents were removed and the inside of the can was masked with wax, and 1% saline solution was put into the cup, and the electrodes in the saline solution and the metal can were placed. A current value was read by applying a voltage of 6V.

Class A: less than 0.3 mA Class B: 0.3 mA or more and less than 0.5 mA Class C: 0.5 mA or more and less than 1 mA Class D: 1 mA or more

(12) Taste characteristics The polyester film was allowed to stand for 7 days while being in contact with the perfume aqueous solution (20 ppm aqueous d-limonene) only on the layer B side (contact area: 314 cm ² ), and then the film was subjected to 80
The components that are heated and expelled in a nitrogen stream for 30 minutes at
D per 1 g of film by gas chromatography
-The amount of limonene adsorbed was quantified to assess the taste properties of the film.

Further, a fragrance aqueous solution (d-
Limonene (20 ppm aqueous solution) was added, and the mixture was sealed, left for 1 month, and then opened, and sensory inspection was performed to evaluate changes in odor according to the following criteria.

Class A: No change in odor is observed Class B: Almost no change in odor C Class: Change in odor is observed.

[0054]

The present invention will be described in detail below with reference to examples.

Example 1 17.5 mol% of isophthalic acid as the polyester for the layer A
Copolyethylene terephthalate (antimony element amount 330 ppm, [η] = 0.85, diethylene glycol 0.70% by weight, melting point 216 ° C., acetaldehyde amount 12 ppm, carboxyl terminal group 21 equivalent / ton) and isophthalic acid 22.5 mol% Polymerized polyethylene terephthalate (antimony element amount 330 ppm, [η] = 0.
73, diethylene glycol 0.70% by weight, melting point 20
1 ° C., acetaldehyde amount 12 ppm, carboxyl terminal group 35 equivalent / ton) were blended in a weight ratio of 7: 3, and 5 mol% of isophthalic acid copolymerized polyethylene terephthalate (germanium element amount 42 ppm, as a polyester of layer B, [ppm] η] = 0.90, diethylene glycol 0.89% by weight, melting point 240 ° C., acetaldehyde amount 10 ppm, carboxyl terminal group 20 equivalent / ton,
Silicon oxide particles with an average particle diameter of 4 μm 0.2% by weight) were used as separate extruders of a twin-screw vent type (extruder temperature was melting point + 25 ° C.).
(A layer side has melting point + 25 ° C for high melting point polyester)
And set to 2) to melt, and then two layers (polyester A layer / polyester B layer = 9 / in a feed block).
After being laminated on 1) and discharged from a normal die, the film is pressed with air so that the layer B becomes the drum surface, and cooled and solidified by a cooling rough surface drum (surface roughness 8S) to obtain a cast film of 30 μm. It was The obtained film was 0.72% by weight of diethylene glycol and 14 pp of acetaldehyde.
m, [η] = 0.80, and the oligomer was 0.59% by weight.

Table 1 shows the physical properties of the thus obtained two-layer laminated cast film, and the results of canning after laminating the layer A on a metal plate. As you can see from the table, 100-230
The film of the present invention having two or more melting points at 0 ° C. was excellent not only in adhesiveness, impact resistance and taste characteristics, but also had a small current value showing defects in the film after air baking and was good.

Example 2 As polyester, dimethyl terephthalate and dimethyl isophthalate were used in an amount of 10 mo based on the total acid components of the polyester.
It was charged so as to be 1%, ethylene glycol and manganese acetate were charged into a flask equipped with a rectification column and a distillation condenser, and transesterification was performed while heating to 150 to 235 ° C. while stirring and distilling methanol. . After distilling out almost the theoretical amount of methanol, trimethyl phosphate 0.
Ethylene glycol slurry containing 03 parts by weight, germanium dioxide 0.04 parts by weight, and silicon dioxide particles having an average particle diameter of 1.5 μm was added so that the content of silicon oxide particles in the polymer would be 0.2% by weight. The reaction mass was transferred to a reactor equipped with a distillation condenser. Then, while stirring, the pressure inside the reactor was gradually reduced by 0.5 mmHg and was reduced to 29
The polycondensation reaction is performed by raising the temperature to 0 ° C and the intrinsic viscosity [η]
0.61 of copolyester was obtained. Then, the copolyester was subjected to a solid phase polymerization reaction at 190 ° C. under N ₂ flow according to a conventional method to obtain an intrinsic viscosity [η] of 0.68 and a melting point of 233.
° C, diethylene glycol component amount 0.90% by weight, germanium element amount 51 ppm, acetaldehyde content 3
A copolyester having a ppm and an oligomer content of 0.55% was obtained. Using this polyester as the B layer and the A layer as the polyester of Example 1, melt extrusion was performed in the same manner as in Example 1 and melt-extruded onto a casting drum while applying electrostatic to obtain an unstretched film. The unstretched film was stretched 3.2 times in the longitudinal direction at 95 ° C. and then 3.3 times in the width direction at 105 ° C. Further, this biaxially stretched film was heat-treated at a constant length of 185 ° C. to obtain a polyester film having a thickness of 25 μm. The obtained film was 0.73% by weight of diethylene glycol and 17 p of acetaldehyde.
pm, [η] = 0.74, and the oligomer was 0.72% by weight.

The physical properties of the film thus obtained are shown in Table 1. As can be seen from the table, the film of the present invention having two or more melting points at 100 to 230 ° C. had good adhesiveness and a small current value showing defects of the film after air baking. On the other hand, since the [η] of the low melting point polymer of the A layer was slightly small, the impact resistance was slightly low.

Examples 3 to 6 Polyester cast films were obtained in the same manner as in Example 1, except that the kind of polymer, the molecular weight, the blending amount of polymer, the conditions of added particles and the like were changed. The results are shown in Table 1 and Table 2.

In Example 3, the B layer was thick and the impact resistance was slightly lowered. Example 4 is excellent in adhesiveness by blending a polymer having a lower melting point, but the adsorbed amount of d-limonene is increased because it contains a butanediol residue component. In Example 5, since the [η] of the B layer was small and the amount of aldehyde and the amount of oligomer were large, impact resistance,
The taste characteristics were slightly degraded. In Example 6, the melting point of the blended polymer was low, and the pinhole resistance was particularly good.

As a result, the polyester film of the present invention was characterized by excellent adhesiveness, impact resistance, taste characteristics, and few defects in the film after molding and heat treatment.

Comparative Example 1 As layer A, isophthalic acid 17.5 mol% copolymerized polyethylene terephthalate (germanium element amount 50 ppm,
[Η] = 0.65, diethylene glycol 1.50% by weight, melting point 210 ° C., acetaldehyde amount 37 ppm, carboxyl terminal group 41 equivalent / ton), 5 mol% isophthalic acid copolymerized polyethylene terephthalate as layer B (germanium element amount 42 ppm, [Η] = 0.64, diethylene glycol 1.20% by weight, melting point 239 ° C., acetaldehyde amount 38 ppm, carboxyl end group 39 equivalent / ton, silicon oxide particles having an average particle size of 6 μm 0.1% by weight) At 285 ° C., a copolyester film was obtained in the same manner as in Example 1. The results are shown in Table 3.

Since this polyester film was not blended with the low melting point polymer, there were many defects in the film after molding and heat treatment.

Comparative Example 2 The polyester of layer B used in Example 2 was used as layer B, and the polyester of layer A of Comparative example 1 was used as layer A. Melting point + 25 ° C.
Was melt extruded and solidified on a casting drum while applying static electricity to obtain an unstretched film. This unstretched film was stretched at 90 ° C. in the longitudinal direction by 3.6 times and then at 105 ° C. in the width direction by 3.6 times. Further, this biaxially stretched film was heat-treated under a constant length at 190 ° C. for 7 seconds to obtain a polyester film having a thickness of 25 μm. The obtained film was 1.45% by weight of diethylene glycol and 5 of acetaldehyde.
4 ppm, [η] = 0.62, oligomer 0.89% by weight
Became.

The physical properties of the film thus obtained are shown in Table 3. As can be seen from the table, the impact resistance was low, and the current value showing defects in the film after molding / heat treatment became large.

[0066]

[Table 1]

[Table 2]

[Table 3]

[0067]

EFFECTS OF THE INVENTION The polyester film for laminating metal sheets of the present invention not only has excellent adhesiveness, impact resistance and taste characteristics, but also has very few defects in the film after molding and heat treatment. Since it has a feature of repairing defects, it can be suitably used for a metal can manufactured by a molding process.

Claims (3)

[Claims] 1. At least 2 at 100-230 ° C.
A polyester film for laminating metal plates, which has three or more melting point peaks and contains 0.01 to 1% by weight of a diethylene glycol component. 2. At least 2 at 100-230 ° C.
A layer having three or more melting point peaks has a melting point of 230 ° C.
B whose main constituent is polyester at 300 ° C
Layers are laminated and the diethylene glycol component is added to 0.0
A polyester film for laminating metal plates, characterized by containing 1 to 1% by weight. 3. The polyester film for laminating metal plates according to claim 1, wherein the intrinsic viscosity [η] is 0.7 or more.