JPH0752242A - Polyester film to be laminated on metal, laminated metal sheet, and metal container - Google Patents

Abstract

PURPOSE:To obtain a polyester film to be laminated on a metal without deterioration in appearance caused by separation of an oligomer and transfer to food. CONSTITUTION:A polyester film contains ethylene units by 70mol% or more of polyester components. In the polyester film, the content of an ethylene terephthalate cyclic trimer is not more than 0.7wt.%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminating film used as a metal material mainly for food products such as soft drinks, beer and canned foods, a laminated metal plate laminated with the film, and the laminated metal plate. The present invention relates to a metal container formed by forming a can into a can. More specifically, a laminating film in which the elution amount of oligomers from the laminating film is suppressed by a heat treatment such as a retort treatment after filling the food product, a laminated metal plate laminated by the film, and the laminated metal plate can The present invention relates to a metal container formed into a shape.

[0002]

2. Description of the Related Art A paint is generally applied to prevent corrosion of the inner and outer surfaces of a metal can, and a thermosetting resin is used as the paint. There is also a method of using a thermoplastic resin.
For example, it has been attempted to laminate polyolefin fill to heated tin-free steel or to laminate polypropylene resin. Further, it is being studied to laminate a polyester film having a better heat resistance on a metal plate and use it for a metal can using the laminated metal plate.

[0003]

Many of the methods for coating a thermosetting resin paint are solvent-based, and a high temperature of 150 to 250 ° C. and a long time of several minutes of heating are required to form a coating film. In addition, a large amount of organic solvent is scattered during baking, and it is desired to improve the process by simplifying it and preventing pollution. In addition, even when applied under the above-mentioned conditions, when a small amount of an organic solvent remains in the coating film and a food product is filled, the organic solvent is transferred to the food product, which adversely affects the taste and smell of the food product. In addition, additives contained in paints and low molecular weight substances due to incomplete crosslinking reaction migrate to food products and have the same adverse effects as residual organic solvents.

The method using a thermoplastic resin film can solve the problems of the above-mentioned problems such as the simplification of the process and the prevention of pollution. However, for example, when a polyethylene or polypropylene olefin resin film is used, heat resistance is improved. It has low properties and may be whitened and peeled off by retort treatment. In addition, the problem of adversely affecting the taste and odor of foodstuffs due to the transfer of residual solvent can be solved, but olefin resin film is the transfer of additives such as low molecular weight substances and heat stabilizers generated during film formation to foodstuffs. It adversely affects the taste and smell of food products. Further, the olefin resin film is inferior in flavor resistance and has a problem that the aroma component in the food product is adsorbed. On the other hand, the method of using the polyester film among the thermoplastic resin films is the most preferable method because the problems of the above-mentioned polyolefin resin film are improved. Certainly, polyester-based films have excellent heat resistance and do not require the addition of additives such as heat stabilizers.They also have good heat resistance and produce less low-molecular-weight substances. The problems of food taste and odor due to the migration of low molecular weight substances are greatly improved. However, the polyester film containing polyethylene terephthalate as a main component contains the ethylene terephthalate cyclic trimer produced in the polymerization step or the film forming step, and there is a problem that the ethylene terephthalate cyclic trimer is transferred to food products. The solution was desired.

[0005]

Means for Solving the Problems The present invention has been achieved as a result of extensive studies to solve the above-mentioned problems.
That is, the present invention provides 7 of the constituent components of polyester.
A polyester film for metal laminating, wherein the content of the ethylene terephthalate cyclic trimer in a film formed of a polyester having 0 mol% or more ethylene terephthalate units is 0.7% by weight or less. Then, a laminated metal plate can be obtained by laminating this film on a metal plate such as tin plate or aluminum. Further, this laminated metal plate is a metal container obtained by making a can by a conventional method.

In the polyester used in the present invention, it is necessary that 70 mol% or more of the constituent components be composed of ethylene terephthalate units. It must consist of ethylene terephthalate units. If the ethylene terephthalate unit content is less than 70 mol%, the heat resistance is lowered and the film may be stretched during processing when laminating to a metal can material, for example, and the width may be reduced due to heat shrinkage, and wrinkles may occur. However, it is not preferable because the production efficiency is lowered and the productivity of processing is reduced, or the raw material cost of polyester is increased, which is economically disadvantageous.

Dicarboxylic acids used for copolymerization other than terephthalic acid include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, naphthalene dicarboxylic acid and diphenyl dicarboxylic acid, adipic acid, azelaic acid, sebacic acid, decane dicarboxylic acid. Examples thereof include aliphatic dicarboxylic acids such as dodecanedicarboxylic acid and dimer acid, and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid.

As glycols used for copolymerization other than ethylene glycol, diethylene glycol, triethylene glycol, propanediol, butanediol, hexanediol, dodecane methylene glycol,
Examples thereof include aliphatic diols such as neopentyl glycol, alicyclic diols such as cyclohexanedimethanol, and aromatic diols such as ethylene oxide adducts of bisphenol derivatives.

Among the above-mentioned copolymer components, it is preferable to use aromatic dicarboxylic acids such as isophthalic acid and naphthalenedicarboxylic acid from the viewpoint of less deterioration in flavor resistance. The polyester preferably has an intrinsic viscosity of 0.5 or more. In addition, these polyesters may contain, if necessary, a lubricant composed of inorganic or organic fine particles, an antioxidant, a heat stabilizer, an ultraviolet absorber, a plasticizer, a pigment, an antistatic agent, a lubricant, a crystal nucleating agent, etc. There is no limitation in blending. Further, the method for producing the polyester is not particularly limited, and the polyester may be produced by either a transesterification method or a direct polymerization method. Also,
It may be produced by a solid phase polymerization method to increase the molecular weight. The use of the solid phase polymerization method is a preferable method in the sense that the content of the ethylene terephthalate cyclic trimer described below is reduced.

The polyester film of the present invention has an ethylene terephthalate cyclic trimer content of 0.
It should be 7% by weight or less. The amount is preferably 0.6% by weight or less, more preferably 0.5% by weight or less. When the content of the ethylene terephthalate cyclic trimer exceeds 0.7% by weight, the amount of oligomers eluted from the film increases due to heat treatment after filling food products such as retort treatment. It is not preferable because it migrates to an oligomer and adversely affects the taste of food.
Further, in the case of a can outer surface laminated film, oligomers are deposited on the surface of the film and the appearance is impaired, which is not preferable.

The method for reducing the content of the ethylene terephthalate cyclic trimer to 0.7% by weight or less is not particularly limited, and the ethylene terephthalate cyclic trimer is extracted and removed from the film after film formation with water or an organic solvent. Or a polyester having a low ethylene terephthalate cyclic trimer content may be used as a raw material. It is economical and recommended to use the latter method. There is no limitation on the method for producing a polyester raw material having a low ethylene terephthalate cyclic trimer content, and examples thereof include a reduced pressure heat treatment method, a solid phase polymerization method, an extraction method with water or an organic solvent, and a method combining these methods. You can In particular, after reducing the amount of ethylene terephthalate cyclic trimer by the solid phase polymerization method, the method of further extracting with water to further reduce the ethylene terephthalate cyclic trimer has a small content of ethylene terephthalate cyclic trimer in the raw material polyester. Moreover, it is the most preferable method because the production amount of the ethylene terephthalate cyclic trimer in the film forming step can be suppressed.

The polyester film of the present invention may be either an unstretched film or a stretched film as long as the above requirements are satisfied. In the case of a stretched film, either uniaxial stretching or biaxial stretching may be used, but a biaxially stretched film is preferred because of its isotropic property. The manufacturing method of the film is not limited. For example, in the case of a stretched film, either the T-die method or the tubular method can be applied. The polyester film may be a single layer or a multi-layer.

The method of laminating the above-mentioned polyester film on a metal plate is not particularly limited, and a dry laminating method, a thermal laminating method or the like can be adopted. Specific examples of the adhesive layer include epoxy resin, polyurethane resin,
Examples thereof include polyester resins, polyester polyurethane resins, isocyanate resins, and various modified resins thereof. A method in which a multilayer film in which a polyester resin layer having a low melting point is laminated on an upper layer of the polyester film is manufactured by a co-extrusion method, and thermal lamination is performed by electrically heating a metal plate is recommended. In the method of laminating an adhesive layer on a polyester film and then laminating it on a metal plate, an adhesive layer is formed on the film in a partially cured state so that it is completely cured in a laminated state on the metal plate. Method is recommended. As a curing method, a method such as heat or photoelectron beam is recommended.

The film laminate may be single-sided or double-sided. In the case of double-sided laminating, they may be laminated simultaneously or sequentially. The method of forming a metal container using the laminated metal plate is not limited. It can be applied to both 2-piece and 3-piece cans. Also, in the case of 2-piece cans, there are 3 such as shallow drawn cans, re-drawn cans, drawn and ironed cans, and drawn stretch cans.
In the case of a piece can, it can be applied to any method such as a solder can, a welding can, and an adhesive can.

Next, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and any implementation is possible within the scope of the above-mentioned gist. Also falls within the technical scope of the present invention. The measuring method used in the examples is as follows. (1) Method for quantifying ethylene terephthalate cyclic trimer in polyester film Dissolve polyester film in hexafluoroalcohol / chloroform = 2/3 (V / V), precipitate the polyester with methanol, and filter the precipitate. . The filtrate is evaporated to dryness and the evaporated dry matter is dissolved in dimethylformamide. The solution was developed by liquid chromatography to quantify the amount of ethylene terephthalate cyclic trimer.

(2) Elution amount of oligomer of metal plate laminate film A metal plate laminate film of 10 cm square is subjected to retort treatment with 500 cc of distilled water at 120 ° C. for 30 minutes. The treated metal plate laminated film was air dried, and the state of the film surface was visually observed to determine the presence or absence of oligomer elution. When the surface became whitish and the gloss decreased, it was judged that the oligomer was eluted.

Example 1 A 97-polymerized portion of polyethylene terephthalate having an intrinsic viscosity of 0.70 and an ethylene terephthalate cyclic trimer content of 0.33% by weight, which was oligomerized by the extraction method, and a polyethylene terephthalate-polytetramethylene glycol ether block copolymer were used. A mixture of the polymer 3 and the polymerized portion was melt extruded, and a 12 μm-thick polyester film was obtained by successive biaxial stretching. The content of the ethylene terephthalate cyclic trimer in the polyester film was 0.40% by weight. One side of the polyester film was coated with an adhesive (a mixture of a polyurethane-based adhesive “Adcoat” manufactured by Toyo Ink Co., Ltd.) and a curing agent in an amount of 4 g / m ^{2 in} terms of solid content, and dried 4
Aging was performed at 0 ° C. for 24 hours to obtain a laminating film. The obtained film for lamination was laminated on both sides of a degreased cold-rolled steel sheet by a thermal lamination method to obtain a double-sided laminated steel sheet. The obtained double-sided laminated steel plate was put in a pressure vessel containing distilled water and heat-treated at 120 ° C. for 30 minutes to evaluate the model of the retort treatment. The treated laminated steel sheet was taken out of the pressure vessel and the surface of the film was observed, but the gloss of the film surface was good and no oligomer surface precipitation was observed.

Example 2 97 parts by weight of polyethylene terephthalate having an intrinsic viscosity of 0.75 and an ethylene terephthalate cyclic trimer content of 0.4% by weight produced by a solid phase polymerization method and a polyethylene terephthalate-polytetramethylene glycol ether block copolymer A mixture with 3% by weight of the polymer was melt extruded and subjected to sequential biaxial stretching to obtain a polyester film having a thickness of 12 μm. The content of the ethylene terephthalate cyclic trimer in the polyester film was 0.52% by weight. An alkyd resin was coated on one surface of the polyester film so as to have a solid content of 4 g / m ² and cured to form a cured heat resistant layer. An adhesive (a mixture of a polyurethane adhesive "Adcoat" and a curing agent manufactured by Toyo Ink Co., Ltd. and a curing agent) on the surface opposite to the cured heat-resistant layer of the film was coated at a solid content of 4 g / m ² and dried to 40 Aging was performed at 24 ° C. for 24 hours to obtain a laminating film. The obtained laminating film was laminated on both sides of a degreased cold-rolled steel sheet by a thermal lamination method to obtain a double-sided laminated steel sheet. The obtained double-sided laminated steel sheet was put in a pressure vessel containing distilled water and heat-treated at 120 ° C. for 30 minutes to evaluate the model of the retort treatment. The treated laminated steel sheet was taken out from the pressure vessel and the surface of the film was observed, but the gloss of the film surface was good and no oligomer surface precipitation was observed.

Comparative Example 1 Ethylene terephthalate obtained by the same method as in Example 1 except that polyethylene terephthalate having an intrinsic viscosity of 0.65 and an ethylene terephthalate cyclic trimer amount of 1.0 wt% produced by a melt polymerization method is used. A polyester film having a cyclic trimer content of 0.98% by weight was used to obtain a laminating film in the same manner as in Example 1. Using the laminating film, a double-sided laminated steel sheet was obtained in the same manner as in Example 1, and the retort treatment model was evaluated in the same manner as in Example 1. The film surface of the treated laminated steel sheet was inferior in gloss, and oligomers were deposited on the film surface.

Example 3 90 parts by weight of polyethylene terephthalate having an amount of ethylene terephthalate cyclic trimer of 0.4% by weight as an A layer resin and 0.7% by weight of ethylene terephthalate cyclic trimer.
Of terephthalic acid / isophthalic acid (molar ratio 70/30) and ethylene glycol (10 parts by weight) of polyester copolymer A (polyester A) as the B layer resin are melted by separate extruders, respectively, and then coextruded. Melt extrusion, then sequential biaxial stretching method, total thickness 20 μm
A biaxially stretched composite polyester film (A layer thickness 17 μm, B layer thickness 3 μm) was obtained. The ethylene terephthalate cyclic trimer in the obtained polyester film was 0.5.
It was 5% by weight. The layer B surface of the composite polyester film was placed on a tin plate and passed through a 170 ° C. metal roll to obtain a laminated steel plate. A model evaluation of the retort treatment was performed on the laminated steel sheet in the same manner as in Example 1. The gloss of the film surface of the treated laminated steel sheet was good and no oligomer surface precipitation was observed.

Comparative Example 2 A biaxially stretched composite film was obtained in the same manner as in Example 1 except that polyethylene terephthalate having an ethylene terephthalate cyclic trimer content of 1.0% by weight was used. The amount of ethylene terephthalate cyclic trimer in the composite film was 0.90% by weight. Example 2 of the composite film
It was laminated on a tin plate by the same method as described above, and the model evaluation of the retort treatment was performed. The film surface of the treated laminated steel sheet was inferior in gloss, and oligomers were deposited on the film surface.

Example 4 Layer A consisting of polyethylene terephthalate, layer B consisting of a copolymer of terephthalic acid / dimer acid having 36 carbon atoms (molar ratio 85/15) and ethylene glycol, and terephthalic acid / isophthalic acid (mol Ratio 83/17) and C consisting of a copolyester from ethylene glycol
The amount of ethylene terephthalate cyclic trimer consisting of layers is 0.
An unstretched composite polyester film having a total thickness of 47% by weight of 32 μm (A layer thickness of 9 μm, B layer thickness of 20 μm, C layer thickness of 3 μm) was laminated on the C layer and the surface was laminated with a tin plate at 230 ° C.
A laminated steel plate was obtained by passing it between the metal roll and the rubber roll heated to above. The laminated steel sheet is molded by a molding machine at 100k.
Press forming is performed with a pressure of g / cm ^{2 and} the diameter is 100 mm,
A cup with a depth of 70 mm was obtained. The cup was subjected to model evaluation of retort treatment in the same manner as in Example 1. The gloss of the film surface of the treated cup was good and no oligomer surface precipitation was observed.

Comparative Example 3 Ethylene terephthalate cyclic trimer content was 0.80% by weight
The same unstretched composite polyester film as in Example 3 was used, and a cup made of a laminated steel sheet obtained in the same manner as in Example 3 was subjected to the model evaluation of the retort treatment in the same manner as in Example 1. The film surface of the treated cup was inferior in gloss, and an oligomer was deposited on the film surface.

[0024]

EFFECT OF THE INVENTION In the polyester film for metal laminate of the present invention, the amount of oligomers eluted from the laminate film is suppressed by heat treatment such as retort treatment after food filling. It is extremely useful as a metal plate or a metal container because it does not deteriorate the surface appearance due to the deposition of oligomers on the film or film surface.

Claims (4)

[Claims] 1. A polyester for metal laminating, wherein the content of ethylene terephthalate cyclic trimer in a polyester film in which 70 mol% or more of the constituent components of polyester is ethylene units is 0.7% by weight or less. System film. 2. A laminated metal plate obtained by laminating the film according to claim 1 on a metal plate. 3. A metal container formed by using the laminated metal plate according to claim 2. 4. A polyester film for metal laminating, wherein the content of the ethylene terephthalate cyclic trimer according to claim 1 is 0.5% by weight or less.