JP3521938B2 - Polyester film for metal lamination - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a polyester film layer.
Regarding mine metal cans .

[0002]

2. Description of the Related Art In recent years, the number of cases in which a thermoplastic resin film is coated on a metal plate and used as a material for a metal can is increasing. It is difficult to completely eliminate metal exposure due to pinholes, etc., even with a large amount of paint applied or double coating with a coated plate in which a thermosetting resin paint is applied to a conventional metal plate and baked and cured. On the other hand, in the case of a coated metal plate coated with a thermoplastic resin, it is possible to almost completely eliminate the metal exposure, and since it is possible to select a resin that has superior stretchability compared to a coated plate, it is possible to improve workability. Because it is excellent. In addition, in the case of a coated plate, a large amount of solvent is used for coating and dry baking, whereas when coating a thermoplastic resin, it is generally done by thermal lamination and no solvent is used. Because there is an advantage of. As the thermoplastic resin used for these coatings, polyester having excellent heat resistance, processability and gas barrier property is generally used.

Polyethylene terephthalate, which is widely used as a raw material for plastic containers and stretched films, has excellent heat resistance, processability, gas barrier property, etc. as such a thermoplastic resin for metal coating, but depending on the metal used. For example, in the case of a chrome-plated steel plate, aluminum, etc., there are problems that bubbles are generated at the laminate interface in the thermal lamination temperature range set to reduce damage and sufficient adhesion cannot be obtained. Therefore, a copolyester was used as the coated polyester for improving the adhesion. However, depending on the copolymerization component, a phenomenon was observed in which low molecular weight substances were eluted during retort treatment. For example, a conventionally used film made of a copolyester having isophthalic acid as a co-polymerization component has an appropriate heat laminating property, but a low molecular weight substance is precipitated by heat treatment in the presence of water at a so-called heat sterilization level temperature. Therefore, the metal can coated with the polyester may impair the flavor of the filled contents, which is not preferable in terms of hygiene.

[0004]

Means for Solving the Problems As a result of intensive studies in view of the above problems, the present inventors have found that a biaxially stretched polyester film made of a specific polyester is suitable as a metal laminating film, Has been completed. That is, the gist of the present invention, polyester A smell constituting the surface of the person who is laminated to the metal
And copolymerized as a bifunctional acid component or glycol component
Laminating a polyester film copolymerization component is 10 to 40 mole% that is, a metal can formed by canning, the terminal carboxyl group after thermal lamination coating, can manufacturing the metal less than 50 equivalent / t And a low molecular weight substance extracted by retort treatment with pure water at 125 ° C. for 1 hour after coating the metal with a heat laminate and making a can is 2.0 μg or less per 1 cm ^{2 of the} coated surface.
It exists in a polyester film laminated metal can .

The present invention will be described in detail below. The term “metal can” as used in the present invention refers to a metal can obtained by subjecting a metal plate to one surface or both surfaces of which a polyester film is coated by thermal lamination, and by subjecting it to forming processing such as drawing or drawing and ironing. Examples of the metal plate used for such an application include a surface-treated steel plate and a light metal plate such as aluminum. In the case of the surface-treated steel sheet, examples thereof include coating with tin that has been passivated by a general chrome treatment, or nickel- or zinc-plated steel. In particular, electrolytic chromium-coated steel having two layers of chromium metal and chromium oxide is preferable. In the case of aluminum, pure aluminum may be used, but an alloy containing a small amount of manganese, magnesium, zinc, copper, or the like may be used. Also pure aluminum,
Any aluminum alloy may be treated with chromic acid or chromic acid / phosphoric acid.

As the polyester used in the present invention, an aromatic dicarboxylic acid or its ester-forming derivative as a difunctional acid component, specifically, terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid,
One or more of sebacic acid, phthalic acid or the like or an ester-forming derivative thereof, and ethylene glycol, diethylene glycol, butylene glycol, propylene glycol, polyethylene glycol as a glycol component, 1,4
-Polyester consisting of one or more of cyclohexanedimethanol and the like is preferable. Typical polyesters include polyethylene terephthalate (PET) and its copolymers, polyethylene-2,6-naphthalene dicarboxylate (PEN) and its copolymers, polycyclohexane dimethylene terephthalate (PCT) and its copolymers, and the like. Are exemplified.

In the present invention, polyester having excellent thermal laminating property is used. Specifically, when pressure-bonding a metal plate and a polyester film to be coated between heated lamination rolls, coating is performed without entraining air bubbles or the like at the laminate interface. It is easy to carry out the above process, and the one that has an adhesive force that does not peel off in the molding step after coating is used. That is, in the present invention, as the polyester constituting the surface laminated on the metal, the copolymerization component is 10 to 4
0 mol%, further 15-35 mol%, especially 18-3
3 mol% of copolymerized polyethylene terephthalate is used. If the copolymerization component is less than 10 mol%, the adhesion after thermal lamination will be insufficient. Moreover, when the copolymerization component exceeds 40 mol%, the fluidity at 100 to 150 ° C. increases,
When heated after coating, slight shear stress causes shearing or peeling.

The greatest feature of the polyester film of the present invention is that the amount of low molecular weight substance extracted by immersing in a water or various solvents and heating when the laminate-coated metal can is extremely small. That is, the amount of the low molecular weight substance extracted by retort treatment with pure water at 125 ° C. for 1 hour is 2.0 μg or less, preferably 1.5 μg or less, and more preferably 1.0 μg or less per 1 cm ^{2 of the} polyester-coated metal surface. When the amount of low-molecular-weight substances extracted by such retort treatment exceeds 2.0 μg per cm ^{2 of the} polyester-coated metal surface, the flavor of the filled contents is impaired when heated for the purpose of sterilization and the like, which is not preferable in terms of hygiene. .

Further, after the polyester film of the present invention is processed into a laminated metal can, the terminal carboxyl group of the polyester is less than 50 equivalents / t, preferably 40 equivalents / t,
More preferably, it is 30 equivalents / t. When the terminal carboxyl group exceeds 50 equivalents / t, it becomes a starting point of deterioration and decomposition of the polyester, the amount of low molecular weight substances inherent in the polyester increases, and the amount of low molecular weight substances extracted by the retort treatment increases, which is not preferable.

By the way, the parts of the polyester film of the present invention which are required to have the two properties of heat laminating property and small amount of low molecular weight extract are not necessarily the same surface. That is, the thermal laminating property is required for the contact surface with the metal, whereas the content of the low molecular weight intrinsic amount and the extraction amount thereof are required for the surface opposite to the laminating surface and a portion relatively close thereto. Therefore, the film of the present invention may be a single-layer film composed of polyester having both properties, but a laminated film in which a polyester excellent in thermal laminating property and a low-molecular-weight extracted polyester are laminated is particularly preferable. It is suitable.

When using a laminated polyester film,
The layer composed of polyester A (A layer) constituting the surface to be laminated on the metal is usually at least 1 μm or more, preferably 1.5 μm or more, and particularly preferably 2 μm or more. When the thickness of the polyester layer is less than 1 μm, sufficient adhesion may not be obtained after lamination. The thickness of layers other than the A layer is preferably at least twice the thickness of the A layer, more preferably 2.5 times, and particularly preferably 3 times or more. If the thickness ratio is less than twice, the coating layer tends to slip in the temperature range where the fluidity of the polyester A is remarkably increased in the metal can forming step after forming the coated metal plate.

The thickness of the polyester film of the present invention is usually 4 to 100 μm in both single layer and laminated layers. If the film thickness is less than 4 μm, the strength that can withstand the molding process after coating may be insufficient. When the film thickness is more than 100 μm, the coated polyester layer may not follow the deformed pattern of the metal plate and may peel off when the metal plate is coated.

In the laminated film suitable for the present invention, the copolymerization component of polyester A constituting the surface to be laminated on the metal is 10 to 40 mol%, further 15 to 35 mol%, and particularly 18 to 33 mol%. Copolymerized polyethylene terephthalate is preferred. If the copolymerization component is less than 10 mol%, the adhesion force after thermal lamination may be insufficient. Further, when the copolymerization component exceeds 40 mol%, 100
Increased fluidity at ~ 150 ° C and when heated after coating,
Shear or shearing may occur due to shear stress.

Further, the copolymerization component of polyester B constituting the other surface of the laminated film is preferably less than 10 mol%, more preferably less than 6 mol%. When the amount of the copolymerization component exceeds 10 mol%, the amount of low molecular weight substances inherent in the polyester tends to increase, and the amount of low molecular weight substances extracted by the retort treatment may increase. In the laminated polyester film suitable for the present invention, in addition to the polyester layer having a small extraction amount of low molecular weight substances and the polyester excellent in thermal laminating property, another kind of polyester is used as an intermediate layer.
It may be a layer or a laminate of a plurality of layers. For example, a laminate obtained by laminating an inexpensive polyester obtained by recycling scrap polyester generated in the polyester film manufacturing process as an intermediate layer is a film satisfying the two characteristics of the present invention, that is, excellent thermal laminating property and low amount of low molecular weight extract. Can be manufactured at low cost and is industrially suitable.

Polyethylene terephthalate having a reduced content of low molecular weight substances does not always have sufficient thermal laminating property, but it is laminated with polyester having excellent thermal laminating property to obtain a film satisfying the constitution of the present invention. be able to. As a method for reducing low molecular weight substances,
There is a method in which the polyester obtained by polymerization is heated in water or a solvent to extract the inherent low molecular weight substance into a film, and the film is formed by solid phase polymerization. There is also a method of reducing For example,
Normally, the polymerization condensation reaction is stopped at 0.40 to 0.50 while the polymerization condensation reaction is carried out until the intrinsic viscosity [η] becomes 0.60 or more, and the obtained resin is solid phase polymerized at 0.70 or more. The number of terminal carboxyl groups is reduced by increasing the intrinsic viscosity up to, and as a result, the amount of low molecular weight substances resulting from various deterioration reactions is reduced. As a method of laminating polyester, there are a method of laminating films formed separately, to form a laminated film, and a method of forming a laminated film by applying another polyester after or during the production process of the polyester film. Lamination by the coextrusion method, which is easy to manufacture and has few restrictions in lamination, is excellent. That is, it is a method of forming a laminated amorphous sheet by laminating the melted materials separately when extruding, and melt-extruding and rapidly solidifying, and this amorphous film is biaxially stretched according to a conventional method and then heat-set. A biaxially oriented film is obtained.

[0016]

EXAMPLES The present invention will be described in more detail with reference to examples, but the invention is not limited to the following examples without departing from the gist of the invention. The evaluation methods in the examples are as follows. In Examples and Comparative Examples, "part" means "part by weight". (1) Intrinsic viscosity [η] 1 g of a polymer was added to phenol / tetrachloroethane = 50
Dissolve in 100 ml of a mixed solvent of 50/50 (weight ratio) and
It was measured at 0 ° C. (2) Terminal carboxyl group concentration Makromol. chem. , 26, 226 (195
A. described in 8). It was measured according to the method of Conix.

(3) Evaluation of Laminating Property The sample film was temporarily attached to a pure aluminum flat plate at 100 ° C., and further finally bonded between laminating rolls at 270 ° C. and a stress of 300 N / m to obtain a polyester-coated aluminum flat plate. 5 cm x from the obtained aluminum flat plate
A 2 cm rectangular sample is cut out, and strain rate is 30 in the long side direction.
Tensile deformation was performed so that the length was 13 cm at 0% / min, and the evaluation was performed according to the following ranks. ◯: No air bubbles were generated due to air entrapment when the polyester-coated aluminum plate was used, and the film did not separate from the aluminum plate even in the tensile test. Δ: Air bubbles were entrained when air was entrapped when the polyester-coated aluminum plate was used. However, the film does not peel from the aluminum plate in the tensile test. ×: When the polyester-coated aluminum plate is used, air bubbles are generated due to air entrapment, and the film also peels from the aluminum plate in the tensile test.

(4) Low molecular weight extract amount (μg / cm ² ) A sample film was pressure-bonded to a pure aluminum flat plate between 270 ° C. and a laminating roll having a stress of 300 N / m to obtain a polyester-coated aluminum plate. However, only one side of the aluminum plate was coated with the resin. The polyester-coated aluminum plate was squeezed and ironed under the following molding conditions to produce a polyester-coated aluminum can with the polyester-coated surface facing inside. Blank diameter: 125 mm Drawing condition: Primary drawing ratio 1.75, Secondary drawing ratio 1.35 Ironing punch diameter: 52.65 mm Total ironing ratio: 68% High-purity water of 300 ml is filled in the above polyester-coated aluminum can, It heated so that it might become 125 degreeC, and performed the retort process for 30 minutes. A value M / S (was obtained by collecting the water after the retort treatment, distilling off the water, measuring the mass M (μg) of the obtained non-volatile matter, and dividing by the polyester coating area S (cm ² ) of the sample metal can used. μg / cm ² ) was defined as the amount of low molecular weight extract.

(5) Appearance of extract The water after the retort treatment was recovered, and the Tyndall phenomenon was observed using a xenon lamp as a light source, and ranked as follows. ◎: No turbidity of the optical path was observed immediately after the retort or after standing for 1 week. ○: No turbidity of the optical path was observed immediately after the retort. A Tyndall phenomenon is observed in △: It is transparent immediately after the retort under the amount of room light, but
A Tyndall phenomenon is observed in the xenon optical path, and water suspension is visually observed even under room light after standing for 1 week. ×: Underwater under room light under naked light both immediately after retort and after 1 week standing. Floating matter is observed

Example 1 [Production of Polyester] (Polyester a) 78 parts of dimethyl terephthalate, 22 parts of dimethyl isophthalate, 60 parts of ethylene glycol and 0.1 part of calcium acetate monohydrate were placed in a reactor and transesterified. went. That is, the reaction start temperature is 1
The temperature was raised to 70 ° C., the reaction temperature was gradually raised along with the distillation of methanol, and the temperature was raised to 230 ° C. 4 hours later to substantially end the transesterification reaction.

Then, an ethylene glycol slurry containing amorphous silicon oxide having an average particle diameter of 3 μm and phosphoric acid 0.0
After adding 4 parts, 0.04 part of antimony trioxide was added, and polycondensation reaction was carried out by a conventional method. That is, the temperature is gradually increased and the pressure is gradually reduced, the temperature is 280 ° C. after 2 hours, the pressure is 0.3 mmHg, the reaction is stopped after 2 hours, and 0.05 part of silicon oxide is contained.
Intrinsic viscosity 0.71, terminal carboxyl group is 40 equivalents /
A polyester of t was obtained. The melting point of the obtained polyester was 203 ° C.

(Polyester b) 96 parts of dimethyl terephthalate, 4 parts of dimethyl isophthalate, 60 parts of ethylene glycol and 0.1 part of calcium acetate monohydrate were placed in a reactor for transesterification. That is, the reaction start temperature was set to 170 ° C., the reaction temperature was gradually raised with the distillation of methanol, and the temperature was raised to 230 ° C. after 4 hours,
The transesterification reaction was substantially completed.

Next, an ethylene glycol slurry containing amorphous silicon oxide having an average particle size of 3 μm and phosphoric acid 0.0
After adding 7 parts, 0.04 part of antimony trioxide was added, and polycondensation reaction was carried out by a conventional method. That is, the temperature was gradually increased and the pressure was gradually decreased, and after 2 hours, the temperature was 280 ° C., the pressure was 0.3 mmHg, the reaction was stopped when 1 hour had passed, and 0.05 part of silicon oxide was contained. A polyester having an intrinsic viscosity of 0.48 was obtained. The obtained polyester is further processed at 225 ° C. and 0.3 mmHg.
After 10 hours of solid state polymerization, the intrinsic viscosity [η] is 0.8
5, a polyester having a terminal carboxyl group of 25 equivalent / t was obtained. The melting point of the obtained polyester was 256 ° C.

(Polyester c) 100 parts of dimethyl terephthalate, 60 parts of ethylene glycol and 0.1 part of calcium acetate monohydrate were placed in a reactor to carry out a transesterification reaction. That is, the reaction starting temperature was set to 170 ° C., the reaction temperature was gradually raised with the distillation of methanol, and after 4 hours, the temperature was raised to 230 ° C. to substantially end the transesterification reaction. Then, an ethylene glycol slurry containing amorphous silicon oxide having an average particle diameter of 3 μm and phosphoric acid of 0.1.
After adding 07 parts, 0.04 part of antimony trioxide was added, and polycondensation reaction was carried out by a conventional method. That is, the temperature was gradually increased and the pressure was gradually decreased, and after 2 hours, the temperature was 280 ° C., the pressure was 0.3 mmHg, the reaction was stopped after 1 hour and 30 minutes, and 0.05 part of silicon oxide was contained. Then, a polyester having an intrinsic viscosity of 0.45 was obtained. The obtained polyester is further treated at 225 ° C. and 0.3 m
Solid phase polymerization was carried out at mHg for 10 hours to obtain a polyester having an intrinsic viscosity [η] of 0.75 and a terminal carboxyl group of 18 equivalents / t. The melting point of the obtained polyester is 270 ° C.
Met.

(Polyester d) Polyester d was produced in the same manner as polyester a except that 88 parts of dimethyl terephthalate and 12 parts of dimethyl isophthalate were used. Intrinsic viscosity is 0.7
0 and the terminal carboxyl group were 53 equivalent / t. The melting point of the obtained polyester was 235 ° C.

(Polyester e) Polyester a and polyester d are used to recycle the polyester scrap generated when a film is produced, and blended with polyester b to obtain a polyester having 5 mol% of polyethylene isophthalate in all repeating units. Obtained. The obtained polyester has an intrinsic viscosity of 0.60 and a terminal carboxyl group of 5
It was 5 equivalent / t and the melting point was 244 ° C.

(Polyester f) Polyester f was produced in the same manner as polyester a except that 92 parts of dimethyl terephthalate and 8 parts of dimethyl isophthalate were used. Intrinsic viscosity is 0.70,
The terminal carboxyl group was 42 equivalents / t. The melting point of the obtained polyester was 245 ° C.

[Production of Polyester Film] Polyester a and polyester b were coextruded at 280 from a T die.
Melt extrusion was carried out at 0 ° C. and a residence time of 5 minutes. The discharge amount ratio of a and b per unit time was 3:22. After being extruded from the T-die, it was rapidly cooled to a temperature below the glass transition point on a cast drum to obtain a substantially amorphous sheet. This sheet was stretched 3.6 times in the machine direction at 80 ° C. using a roll stretching machine. Next, it was stretched 4.2 times in the transverse direction at 100 ° C. using a tenter stretching machine, and then 210
The film was heat set at 0 ° C. to obtain a film having a thickness of 25 μm. The layer structure of the obtained film was such that the layer composed of polyester a was 3 μm and the layer composed of polyester b was 22 μm.
The thickness was m. [Manufacture of laminated metal plate] A layer side of polyester is 1
Temporarily attached to a pure aluminum plate at 00 ° C, then 270
Main adhesion was performed between the laminate rolls at a temperature of 300 ° C. and a stress of 300 N / m to obtain a polyester-coated aluminum flat plate.

Example 2 A polyester-coated aluminum flat plate was obtained in the same manner as in Example 1 except that polyester b was changed to polyester c. Example 3 Polyester a, polyester e, and polyester c were melt-extruded by a coextrusion method so that polyester e was laminated on the intermediate layer, and polyester a and polyester c were laminated on different sides. The discharge rate ratio per unit time is 3:21:
A polyester laminated film (polyester a layer 3 μm, polyester e layer 21 μm, polyester c layer 1 μm) was obtained by the same method as in Example 1 except that the polyester coated aluminum plate was prepared in the same manner as in Example 1. Obtained.

Comparative Example 1 Polyester-coated aluminum was prepared in the same manner as in Example 1 except that a single-layer amorphous sheet of polyester c was obtained by melt extrusion under the conditions of 280 ° C. and residence time of 5 minutes without coextrusion. A flat plate was obtained. Comparative Example 2 Comparative Example 1 except that polyester c was changed to polyester d
A polyester-coated aluminum flat plate was obtained in the same manner as in.

Comparative Example 3 Example 1 except that polyester b was changed to polyester d
A polyester laminated film (polyester a layer: 3 μm, polyester d layer: 22 μm) was obtained in the same manner as in 1. and a polyester-coated aluminum flat plate was obtained in the same manner as in Example 1. Comparative Example 4 Example 2 except that polyester a was changed to polyester f
A polyester laminated film (polyester f layer: 3 μm, polyester c layer: 22 μm) was obtained in the same manner as in 1. and a polyester-coated aluminum flat plate was obtained in the same manner as in Example 1. The results obtained above are summarized in Table 1 below.

[0032]

[Table 1]

[0033]

EFFECT OF THE INVENTION Polyester film laminae of the present invention
When a metal container for foods and beverages is laminated and coated , the metal can has a small amount of components extracted by water or hot water, is excellent in hygiene, and has a high industrial value.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-6-228338 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B32B 27/36 B32B 15/08 B65D 6 / 14

Claims (2)

(57) [Claims] 1. A polyester A constituting a surface of a metal laminated to a metal, which comprises a difunctional acid component or a polyester .
10 to 4 copolymerized components as a recall component
Laminate a polyester film of 0 mol% ,
A metal can produced by can- making, wherein the metal has a terminal carboxyl group of less than 50 equivalents / t after heat lamination coating / making, and a pure metal of 125 ° C. after heat laminating coating / making. A low molecular weight substance extracted by retort treatment with water for 1 hour is 2.0 μg or less per 1 cm ^{2 of} coated surface, a polyester film lamine
Metal cans . 2. The copolymerization component of polyester B constituting the surface opposite to the surface laminated on the metal is 10
Laminate the laminated polyester film that is less than mol%
Sorted, can-making and the polyester film La of claim 1 comprising
Minated metal can .