JPH11322969A - Polyester film for container molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polyester film which is excellent in moldability, heat resistance, flavor characteristics, and food hygiene and is suitable for high- impact metal cans prepd. by molding by blending two specific polyesters. SOLUTION: A polyester A in an amount of 1-30 pts.wt. formed by copolymerizing a dimerized fatty acid having an unsatd. bond or an ester- forming deriv. thereof and 70-99 pts.wt. polyester B of which at least 80 wt.% of the structural units are ethylene terephthalate units are blended. Polyester A of which 60-99 wt.% of the structural units are butylene terephthalate units is pref. in terms of impact strength, and polyester A which is prepd. by using a titanium compd. as a catalyst and contains 100-300 ppm titanium (based on the polymer) is pref. Polyester B of which 1-20 wt.% of the structural units are ethylene isophthalate units is pref. in terms of moldability and compatibility with polyester A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a polyester film for forming a container. More specifically, the present invention relates to a container-produced polyester film which is excellent in moldability, impact resistance and taste characteristics, and which is suitable for a container, particularly a metal can, which is produced by molding.

[0002]

2. Description of the Related Art Conventionally, the inner and outer surfaces of metal cans are coated with various thermosetting resins, such as epoxy and phenol, dissolved or dispersed in a solvent for the purpose of preventing corrosion. Has been widely practiced. However, such a method of coating the thermosetting resin requires a long time for drying the paint, and has unfavorable problems such as a decrease in productivity and environmental pollution due to a large amount of an organic solvent.

As a method of solving these problems, there is a method of laminating a film on a steel plate, an aluminum plate, or a metal plate obtained by subjecting the metal plate to various surface treatments such as plating, which is a material of a metal can. When a metal can is manufactured by drawing or ironing a laminated metal plate of a film, the film is required to have the following characteristics.

(1) It has excellent adhesion to a metal plate. (2) It is excellent in moldability and does not generate defects such as pinholes after molding. (3) The polyester film does not peel off, crack or pinhole due to impact on the metal can. (4) The scent component of the contents of the can adsorbs to the film,
The flavor of the contents is not degraded by the eluate from the film (hereinafter referred to as taste characteristics).

[0005] Many proposals have been made to solve these requirements. For example, Japanese Patent Application Laid-Open No. 64-22530 discloses a polyester film having a specific density and a plane orientation coefficient. Is a copolyester film having a specific crystallinity;
JP-A-895-895, JP-A-6-107815 and the like disclose polyester films containing specific particles.
In JP-A-156356, a film obtained by laminating a layer obtained by blending polyesters having different melting points on a copolymerized polyester film, and in JP-A-9-150492, a polyester film containing a long-chain aliphatic dicarboxylic acid component having an alkylene group is laminated. And the like are disclosed. However, these proposals do not comprehensively satisfy the above-mentioned various required properties, and in particular, have not only high moldability and impact resistance, but also excellent taste characteristics after retort treatment and food hygiene. It was not at a satisfactory level for the required applications.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and is excellent in moldability, heat resistance, taste characteristics, and food hygiene. An object of the present invention is to provide a polyester film for forming a container suitable for a metal can having excellent impact resistance.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a polyester A obtained by copolymerizing 1 to 40 parts by weight of a dimerized fatty acid having an unsaturated bond or an ester-forming derivative thereof and 80% of the constituent components of the polyester. This is achieved by a container-forming polyester film obtained by mixing polyester B whose ethylene terephthalate is at least part by weight in a weight ratio of 99: 1 to 70:30.

As a result of intensive studies, the present invention blends a polyester obtained by copolymerizing a specific compound with a polyester whose main component is ethylene terephthalate, thereby obtaining not only excellent moldability and taste characteristics, but also particularly after retort. However, they have found that a film having good impact resistance can be obtained.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, polyester A obtained by copolymerizing 1 to 40 parts by weight of a dimerized fatty acid having an unsaturated bond in terms of impact resistance after retort and moldability in a can-making process. When the amount of copolymerization is too small, a sufficient effect cannot be obtained. When the amount is too large, the heat resistance of the polymer tends to decrease. Therefore, the amount is preferably 5 to 35 parts by weight.

In the present invention, the dimerized fatty acid having an unsaturated bond or an ester-forming derivative thereof has 10 carbon atoms.
Obtained by dimerization of ~ 30 unsaturated fatty acids. Along with this dimerization reaction, monomers and trimers are produced,
From the viewpoint of the reactivity of the ester and the impact resistance, the ratio in each of the dimerized fatty acids is 3 parts by weight or less for the monomer, 95 parts by weight or more for the dimer, and 3 parts by weight or less for the trimer. It is preferable that the amount of the monomer be 1.5 parts by weight or less, the amount of the dimer be 97 parts by weight or less, and the amount of the trimer be 1.5 parts by weight or less.

As such a dimerized fatty acid, dimer acid which is a dimerized fatty acid having 36 carbon atoms is preferable in view of impact resistance and reactivity of the ester. As polyester A obtained by copolymerizing such a dimerized fatty acid having an unsaturated bond, polyethylene terephthalate, polytetramethylene terephthalate, polybutylene terephthalate, polyethylene isophthalate, It is preferable to use polycyclohexylene dimethylene terephthalate, polyethylene naphthalate, polyethylene-1,2-bis (2-chlorophenoxy) ethane-4,4'-dicarboxylate as a main component, and particularly from the viewpoint of impact resistance. And polybutylene terephthalate are preferred. In particular, when polybutylene terephthalate is used as a main component, a titanium compound is used as a catalyst in view of reactivity in a polymer production process and dispersibility after blending with polyester B,
100 to 300 ppm based on the polymer as titanium metal
It is preferred to contain.

Further, from the viewpoint of taste characteristics, it is necessary that at least 80 parts by weight of the constituent component of the polyester B is ethylene terephthalate, and it is particularly preferable that the amount is at least 85 parts by weight. Further, from the viewpoint of compatibility with the polyester A and moldability, 1 to 20 parts by weight of the constituent components of the polyester B is preferably ethylene isophthalate.

The mixing ratio of polyester A and polyester B must be 1:99 to 30:70 by weight. If the mixing amount of the polyester A is too large, the compatibility tends to be deteriorated. If the mixing amount is too small, a sufficient effect is not exhibited, which is not preferable.

As a method for blending the polyester A and the polyester B, specifically, from the viewpoint of taste characteristics, the kneading temperature is set to the melting point of the polyester B + 30 ° C. or lower, and further, the melting point +
The temperature is preferably set to 25 ° C. or lower, and in particular, kneading in a high vacuum state is preferable from the viewpoint of suppressing thermal decomposition. In addition, the kneading time is set at 20 to suppress thermal decomposition.
It is preferably within minutes. The kneading device may be either a twin screw or a single screw, but it is preferable to use a twin screw kneader from the viewpoint of uniformity of the polymer.

The average dispersion diameter (major diameter) of the polyester A in the film is preferably 5 μm or less, particularly preferably 3 μm or less from the viewpoint of impact resistance.

Such polyester A, polyester B
In the polyester film consisting of, from the viewpoint of laminating property, the particle concentration of 50 nm from the film surface is 1/50 to 1 / m with respect to the particle concentration of 1 μm from the film surface.
It is preferably 1,000, especially 1/50 to 1/5
00 is preferred.

The particles used in the present invention are not particularly limited in terms of composition regardless of whether they are organic or inorganic. However, they are not limited in terms of projection shape when formed into a film, abrasion resistance, workability, taste characteristics and the like. Therefore, the volume average particle diameter is preferably from 0.01 to 5 μm, and particularly preferably from 0.05 to 3 μm.

In order to sufficiently exhibit these effects, the particles are preferably contained in an amount of 0.01 to 40% by weight, and more preferably 0.05 to 30% by weight.

Specifically, examples of the inorganic particles include wet and dry silica, aluminum silicate, titanium oxide, calcium carbonate, calcium phosphate, barium sulfate, alumina, mica, kaolin, clay and the like. Preferred are wet silica, aluminum silicate, titanium oxide and the like from the viewpoints of properties, winding properties, affinity with polyester and the like.

As the organic particles, various organic polymer particles can be used, and the type of the organic particles is not particularly limited as long as the particles are at least partially insoluble in the polyester. Further, as a material of such particles, polyimide, polyamide imide,
Various materials such as polymethyl methacrylate, formaldehyde resin, phenol resin, cross-linked polystyrene, and silicone resin can be used, but vinyl-based cross-linked polymer particles having high heat resistance and easy to obtain uniform particle size distribution particles Is particularly preferred.

The polyester film in the present invention can be used in either a single layer or a laminate. A layer composed of polyester A and polyester B (hereinafter referred to as (I) layer) and another layer (hereinafter referred to as (I)
When the (I) layer) is laminated, in the (I) layer / (II) layer / metal plate, the polyester of the (II) layer is not particularly limited, but may contain polyester A and / or polyester B, The melting point is preferably from 200 to 260 ° C. In the (II) layer / (I) layer / metal plate,
The layer (II) preferably contains ethylene terephthalate and / or ethylene naphthalate as a main component, and preferably 90 parts by weight or more of ethylene terephthalate from the viewpoint of taste characteristics, and ethylene isophthalate from the viewpoint of moldability. Is preferably contained in an amount of 1 to 10 parts by weight. The lamination ratio of the (I) layer / (II) layer is 1
/ 30 to 30/1, particularly preferably 1/20 to 20/1. Further, (I) layer / (I
Three layers such as layer (I) / layer (I) and layer (II) / layer (I) / (II) may be stacked.

The thickness of the polyester film of the present invention is as follows:
The thickness is preferably from 3 to 50 μm, more preferably from 8 to 30 μm, from the viewpoint of moldability after lamination to metal, coatability to metal, impact resistance and taste characteristics.

The method for producing the polyester film in the present invention is not particularly limited. For example, after drying polyester as required, the polyester film is supplied to a known melt extruder, extruded from a slit die into a sheet shape, and then discharged. An unstretched sheet is obtained by bringing it into close contact with the casting drum by cooling or the like and solidifying it by cooling. The unstretched sheet is stretched in the longitudinal direction and width direction of the film and heat-treated to obtain a film having a desired thickness. Preferably, a tenter method is preferable in terms of film quality.After stretching in the longitudinal direction, a sequential biaxial stretching method in which the film is stretched in the width direction, a simultaneous biaxial stretching method in which the film is stretched almost simultaneously in the longitudinal direction and the width direction. Is desirable. The stretching ratio was 1. in each direction.
It is 5 to 4.0 times, preferably 1.8 to 3.5 times. Either the stretching ratio in the longitudinal direction or the stretching ratio in the width direction may be increased, and may be the same. The stretching speed is 1000% /
Min to 200,000% / min, and the stretching temperature can be any temperature as long as it is equal to or higher than the glass transition temperature of the polyester and equal to or lower than the glass transition temperature + 80 ° C, but is preferably the glass transition temperature + 20 ° C to 60 ° C. . After the biaxial stretching, the film is subjected to a heat treatment. This heat treatment can be carried out by any conventionally known method, such as in an oven or on a heated roll. The heat treatment temperature can be any temperature from 120 ° C. to 250 ° C., but is preferably from 150 to 240 ° C. The heat treatment time can be arbitrarily set, but is preferably 0.1 to 60 seconds, and more preferably 1 to 20 seconds. The heat treatment may be performed while relaxing the film in the longitudinal direction and / or the width direction. Further, re-stretching may be performed once or more in each direction, and then heat treatment may be performed.

Furthermore, when used on the inner surface of the can, the center line average roughness R of the surface of the polyester film inside the can is
a is preferably 0.003 to 0.05 μm, more preferably 0.005 to 0.03 μm. Further, the ratio Rt / Ra to the maximum roughness Rt is 4 to 50, preferably 6 to 50.
When it is 40, high-speed can-making properties are improved.

It is preferable to improve the adhesiveness by subjecting the film to a surface treatment such as a corona discharge treatment in order to further improve the characteristics.

Although the metal plate of the present invention is not particularly limited,
From the viewpoint of formability, a metal plate made of iron, aluminum, or the like is preferable. Further, in the case of a metal plate made of iron, an inorganic oxide coating layer on the surface thereof for improving adhesion and corrosion resistance, 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, a chromate treatment or a chromium chromate treatment may be provided. In particular, in terms of chromium metal, 6.5 to chrome
A chromium hydrated oxide of 150 mg / m ² is preferable, and a spreadable metal plating layer such as nickel, tin, zinc, aluminum, gunmetal, brass, etc. may be provided. It is preferable that tin plating has a plating amount of 0.5 to 15 mg / m ² , and nickel or aluminum has a plating amount of 1.8 to 20 g / m ² .

The biaxially stretched polyester film for forming a container of the present invention can be suitably used for coating the inner surface of a two-piece metal can manufactured by drawing or ironing. Further, it can be preferably used for covering the lid portion of a can because it has good metal adhesion and moldability.

[0028]

The present invention will be described in detail with reference to the following examples. The characteristics were measured and evaluated by the following methods.

(1) Melting Point of Polyester The polyester was dried, melted, quenched, and measured by a differential scanning calorimeter (DSC-2, manufactured by Perkin Elmer).
The measurement was performed at a heating rate of ° C./min.

(2) Measurement of Average Dispersion Diameter of Polyester A Particles were blended with polyester, cut into ultra-thin slices having a thickness of 0.2 μm, and then measured with a transmission electron microscope for at least 5 μm.
Observation and measurement were performed for 00 dispersion diameters.

(3) Analysis of metal content Analysis was performed by X-ray fluorescence analysis (FLX).

(4) Average Surface Particle Concentration of Polyester Film The surface particle concentration of the film is determined by a secondary ion mass spectrometer (SIMS: ATOM) using O ₂ ⁺ ions as primary ions.
The ratio was determined as the ratio of particle concentration at a depth of 0.5 μm from the surface / particle concentration at a depth of 1 μm from the surface using AKA-DIDA3000 manufactured by IKA Corporation.

The measurement conditions are as follows. Primary ion energy: 12 keV Primary ion current: 100 nA Detection secondary ion: positive ion Electrospray condition: ^{0.5 kV} -3.0 A Vacuum degree at measurement: 1.3 × 10 ^{−6 Pa}

(5) Formability After laminating a film on a TFS steel plate (thickness 0.20 mm) heated at a melting point of −20 ° C. to a melting point of + 50 ° C. at 60 m / min, cooled with warm water of 60 ° C., and then drawn. Two-stage molding with a molding machine (final molding ratio (maximum thickness / minimum thickness) = 1.4, 8)
At a moldable temperature range of 0 to 130 ° C).
Thereafter, the can was heat-treated at an optimum temperature of 200 to 250 ° C. for 30 seconds, and subjected to neck-in processing according to a conventional method. The obtained can was subjected to a retort treatment (treatment with pressurized steam at 120 ° C. for 30 minutes), and a neck portion (see FIG. 1) was observed.
It was determined as follows.

Class A: There is almost no change. Class B: A small whitened portion can be seen, but there is no problem. Class C: whitens. Class D: A small darkened portion is observed. Class E: The film was broken.

(6) Impact Resistance The can actually manufactured was filled with 350 g of water and the lid was wound. After that, the container was left at 5 ° C. for 48 hours. When the bottom of the container dropped, the container was dropped from a height of 40 cm at 45 ° with respect to the concrete ground to give an impact. Mask the inner surface with wax and put 1 in the cup
% Saline solution, left for one day, apply a voltage of 6 V to the electrode and the metal can in the saline solution, and read the current value 3 seconds later.
The average value after can measurement was determined.

Class A: less than 0.1 mA Class B: 0.1 mA or more and less than 0.3 mA Class C: 0.3 mA or more and 0.5 mA or less Class D: 0.5 mA or more

(7) Taste characteristics Fill a can (diameter 6 cm, height 12 cm) with water and
℃ × 30 minutes pressurized steam treatment, cooled to 20 ℃,
After standing for 24 hours, the change in turbidity of the solution was visually evaluated according to the following criteria.

Class A liquid is not turbid at all. Class B liquid is almost turbid. Class C liquid is slightly cloudy. Class D liquid is cloudy.

Example 1 An esterification reaction was carried out using terephthalic acid, 1,4-butanediol, and a dimer acid having an unsaturated bond (carbon number: 36) as a catalyst, and tetrabutoxytitanate was used as a polymerization catalyst. Then, phosphoric acid was added as a heat stabilizer, and a polycondensation reaction was carried out to obtain a polyester A in which 32 parts by weight of a dimer acid component having an unsaturated bond was copolymerized. At this time, the content of the titanium metal is 230 pp.
m, and no metals other than titanium and phosphorus were detected.

10 parts by weight of colloidal silica having a volume average particle diameter of 1.5 μm and 90 parts by weight of ethylene glycol were mixed and stirred at room temperature for 2 hours with a dissolver to obtain an ethylene glycol slurry of silica particles.

After transesterification by adding magnesium acetate and lithium acetate as catalysts to dimethyl terephthalate, dimethyl isophthalate and ethylene glycol, the reaction product is adjusted to the above-mentioned slurry, germanium dioxide as a polymerization catalyst, and heat stability. Phosphoric acid was added as an agent and a polycondensation reaction was performed to obtain a polyester B having an ethylene isophthalate component of 12 parts by weight.

Similarly, ethylene isophthalic acid component 6
A polyester for layer (II) lamination containing parts by weight was obtained.

After thoroughly drying 20% by weight of polyester A and 80% by weight of polyester B, the mixture was kneaded and extruded with a biaxial kneader to obtain a polyester for layer (I).

The polyester for the layer (I) obtained as described above is vacuum-dried at 120 ° C. for 4 hours, supplied to a single-screw extruder, discharged from a usual die, and cooled to a mirror surface while applying static electricity. It was solidified by cooling with a drum to obtain an unstretched film. This unstretched film is stretched 2.8 times in the longitudinal direction at a temperature of 110 ° C, cooled to 40 ° C, stretched 2.8 times in a width direction at a temperature of 110 ° C, and relaxed at 180 ° C by 3%.
Heat treated for 5 seconds.

Example 2 A polyester film was obtained in the same manner as in Example 1 except that a tin compound was used as a catalyst when polyester A was produced, and the amount of tetrabutoxytitanate was changed.

Example 3 A polyester film was obtained in the same manner as in Example 1 except that the polyester for the (II) layer was laminated. At this time, the layer (I) was used as a metal laminate surface.

Example 4 A polyester film was obtained in the same manner as in Example 3 except that the polyester type of the polyester A was changed to polyethylene terephthalate.

Example 5 A polyester film was obtained in the same manner as in Example 3 except that the polyester for the (II) layer was polyethylene terephthalate.

Example 6 A polyester film was obtained in the same manner as in Example 3, except that the particles of the polyester A were changed to aggregated silica.

Comparative Example 1 A polyester film was obtained in the same manner as in Example 3 except that the polyester A was changed to polyethylene terephthalate.

Comparative Example 2 A polyester film was obtained in the same manner as in Example 3 except that the amount of dimer acid was changed.

Comparative Example 3 A polyester film was obtained in the same manner as in Example 3, except that the amount of polyester A was changed.

[0054]

[Table 1]

[0055]

[Table 2]

[0056]

[Table 3]

The symbols in the table are as follows: PET: polyethylene terephthalate DMI: dimethyl isophthalate PBT: polybutylene terephthalate DA: dimer acid

[0058]

The biaxially stretched polyester film for forming a container of the present invention has not only excellent moldability and taste characteristics in forming into a can or the like, but also has particularly excellent characteristics in impact resistance after retort. However, it can be suitably used for metal cans manufactured by molding.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a metal can.

[Explanation of symbols]

 1: Thin wall 2: Neck

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B65D 25/36 B65D 25/36 C08K 3/00 C08K 3/00 5/00 5/00 C08L 67/02 C08L 67/02 // (C08L 67/02 67:06) B29K 67:00 B29L 9:00

Claims (10)

[Claims] 1 to 30 parts by weight of a polyester A obtained by copolymerizing 1 to 40 parts by weight of a dimerized fatty acid having an unsaturated bond or an ester-forming derivative thereof, and at least 80 parts by weight of a structural unit of the polyester are ethylene terephthalate. A polyester film for container molding obtained by blending 70 to 99 parts by weight of a polyester B comprising 2. 60 to 99 of the constituent components of the polyester A
The polyester film for forming a container according to claim 1, wherein the weight part is butylene terephthalate. 3. The polyester film according to claim 1, wherein the content of titanium metal in the polyester A is 100 to 300 ppm based on the polymer. 4. The container-forming polyester film according to claim 1, wherein 1 to 20 parts by weight of the structural unit of the polyester B is ethylene isophthalate. 5. The method according to claim 1, wherein the particle concentration at 50 nm from the film surface is 1/5 to 1 μm at 1 μm from the film surface.
The polyester film for forming a container according to any one of claims 1 to 4, wherein the ratio is / 1000. 6. The polyester film for forming a container according to claim 2, wherein the average dispersion diameter of the polyester A in the polyester film is 5 μm or less. 7. A laminated polyester film for forming a container, comprising at least one layer of the polyester film according to claim 6. 8. A laminated polyester film for forming a container, wherein the polyester film according to claim 6 is disposed on at least one of the outermost layers. 9. A container for forming a container according to claim 7, wherein at least a layer composed of a polyester film in which 90% by weight or more of the polyester component is ethylene terephthalate and a layer composed of the polyester film according to claim 6 are arranged. Laminated polyester film. 10. The polyester film for heat-laminate forming of a metal sheet according to claim 1.