JPH1044317A - Polyester-coated aluminum plate, laminated lid and laminated can body made by molding plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To be excellent in the storage of contents and the retention of fragrance and to make the metallic gloss of a can raw material be utilized by a method in which when a can lid and a can main body are formed from an aluminum sheet which is used as a raw material of metal cans, both sides of the sheet are coated with polyester, and the haze of the polyester layer to be an outside surface is adjusted to be a specified value or below. SOLUTION: Both sides of an aluminum sheet are coated with a polyester film, and the haze of a coating layer to be the outside surface of a can is adjusted to be 4% or less. When the haze exceeds 4%, the metallic gloss of a metallic raw material becomes dull. For example, polyethylene terephthalate and heat-laminating copolyethylene terephthalate are melted and co-extruded by an extruder, cooled rapidly, stretched at a temperature higher than or equal to the glass transition temperature by a roll drawing machine and tenter drawing machine in sequence and heat-set at a temperature lower than the melting point. The polyester film is pressed and laminated on the aluminum sheet by induction-heating. The obtained coated aluminum sheet is molded into a laminated lid and a laminated can body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal sheet coated with polyester, a laminated lid formed by molding the same, and a laminated can body.

[0002]

2. Description of the Related Art In recent years, metal cans coated with a thermoplastic resin film, particularly a polyester film, have been widely used, especially for beverage cans. Conventionally, it has been difficult to completely eliminate metal exposure due to pinholes in the coating of the inner surface of a metal can.However, it is easy to completely eliminate metal exposure by coating a film. This is because each modification due to the interaction between the object and the metal can be prevented.

On the other hand, a polyester film which has been widely used for coating a metal outer surface is a white film containing titanium dioxide. This hides the color of the metal, especially steel, to provide a variety of prints on the outer surface of the metal can,
This is because the purpose is to substitute for white printing as a base. However, in beer filling applications and the like, in order to impart a refreshing feeling, on the contrary, in many cases, printing utilizing the silvery metallic luster of the can material is used as a base, and not only the above-mentioned white film but also pigments are contained. It has been difficult to use even a normal polyester film that has not been used because the color tone of the can material is reduced.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to improve the preservability of the contents and the fragrance retention, and to provide a design that utilizes the metallic luster of the can material. It is an object of the present invention to provide a polyester-coated aluminum plate for realizing a polyester-coated metal can excellent in quality.

[0005]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventor has found that the above problems can be easily solved by using polyester satisfying specific characteristics. It was completed.
That is, the gist of the present invention is that an aluminum plate used for a metal can material is coated on both sides with a polyester, and the haze of a polyester coating layer which is an outer surface when the can is formed into a can lid and a can body is 4% or less. The present invention resides in a polyester-coated aluminum plate, a laminated lid and a laminated can formed by molding the same.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The polyester referred to in the present invention means a polymer obtained by polycondensing a dicarboxylic acid such as terephthalic acid or isophthalic acid with a diol such as ethylene glycol, diethylene glycol or 1,4-butanediol.

As the above-mentioned polyester, polyethylene terephthalate, polyethylene naphthalate or a copolymer thereof, which has a proven track record as a material for beverage containers such as bottles and is relatively inexpensive and excellent in food hygiene, are preferred. Since the polyester film used in the present invention is also used for coating a drawn and ironed can body, it is preferable that the polyester film can follow large deformation. For this reason, adhesion by a thermosetting resin is not appropriate, and it is preferable to make the polyester film itself have adhesiveness by copolymerizing polyester. In addition, if the surface opposite to the surface to be bonded to aluminum has adhesiveness, the surface of the coating layer is easily scratched by sticking to a metal processing device in a can making process or the like, so that the adhesiveness is increased. And a film in which a polyester having relatively low adhesiveness and a polyester having relatively low adhesion are laminated.

As the polyester having relatively low adhesiveness, the above-mentioned polyethylene terephthalate can be mentioned.
Further, as the adhesive polyester, a copolymer derivative of polyethylene terephthalate is preferable. Industrially suitable copolymerization components include relatively inexpensive diethylene glycol, isophthalic acid, etc., but the change in glass transition temperature is small, and the deformation behavior during can-making is similar to that of a low-adhesion polyethylene terephthalate layer. Acids are particularly good.

[0009] Among the ester units constituting the adhesive polyester, the ester unit containing a copolymer component is one.
0 to 50%, further 18 to 30%, especially 20 to 27
% Is desired. If the copolymerized ester unit does not reach 10%, the adhesion becomes insufficient, and if it exceeds 50%, the properties of polyethylene terephthalate suitable as a can coating material may be lost.

The term "ester unit" as used in the present invention means a repeating unit in which one of a dicarboxylic acid and one of a diol are condensed. As the aluminum material of the present invention, pure aluminum may be used, but manganese, magnesium, iron, copper and the like may be alloyed in a small amount, or a multilayer structure in which pure aluminum is laminated on an aluminum alloy layer. You may have.

The aluminum plate of the present invention is coated on both sides with a polyester film. The coating layer on the surface to be the outer surface of the can has a haze of 4% or less, preferably 3% or less.
%, More preferably 2% or less. If the haze of the coating layer constituting the outer surface of the can exceeds 4%, the metallic luster of the metal material is undesirably dull. The polyester film constituting the inner surface of the can can be coated with anything known in the art, but there is an advantage that coating can be performed under the same conditions on both surfaces of aluminum during lamination, so that the same as the outer surface is used. It is recommended that the film also be used for interior coating.

The aluminum plate coated with the polyester film of the present invention can be produced, for example, by the following method. First, polyethylene terephthalate and heat laminating copolymerized polyethylene terephthalate, which are the raw materials of the main constituent layers, are melt-coextruded and rapidly cooled by an extruder,
Further, using a roll stretching machine and a tenter stretching machine, sequential biaxial stretching is performed at a temperature equal to or higher than the glass transition temperature.
Heat setting is performed at a temperature lower by about 50 ° C.

The obtained polyester film is bonded to an aluminum plate heated to 240 ° C. by induction heating by a thermocompression bonding method using a laminating roll. If necessary, heat treatment may be performed to such an extent that the crystallinity of the polyester film becomes 8 to 10%. Subsequently, the polyester layer is rapidly cooled to a temperature lower than the glass transition temperature so that spherulites are not generated in the polyester layer, to obtain a polyester-coated aluminum plate. The coated aluminum plate thus obtained can be formed into a laminated can lid or a laminated can body by a conventional method.

[0014]

EXAMPLES Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist. In the following examples, “parts” means parts by weight. Also,
Haze evaluation was performed as follows.

(Haze Evaluation) A coating layer (a layer constituting the inner surface of the can) on the opposite side of the coating layer (a layer constituting the outer surface of the can) of the sample metal plate is sanded with sandpaper to expose the metal. This is immersed in 2N-HCl to dissolve the metal to obtain a target coating layer. The obtained coating layer was coated with liquid paraffin on the side that had been bonded to the metal plate, and measured with a spectroscopic turbidimeter NDH-20D manufactured by Nippon Denshoku Industries Co., Ltd. according to JIS-K6714. Haze. In addition, when the film to be evaluated is printed, the plain part without the colored printing is applied.
Measure haze as described above.

(Production of Polyester) Production Example 1 (Production of Polyester A) 100 parts of dimethyl terephthalate, ethylene glycol 6
0 parts and 0.1 part of calcium acetate-water salt were placed in a reactor and subjected to 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, thereby substantially terminating the transesterification reaction.

Next, an ethylene glycol slurry containing amorphous silica having an average secondary aggregation particle diameter of 1.3 μm and 0.04 part of phosphoric acid are added, and 0.04 part of antimony trioxide is added to carry out a polycondensation reaction. Was. That is, the temperature was gradually increased and the pressure was gradually decreased. After 2 hours, the temperature was set to 280 ° C. and the pressure was set to 0.3 mmHg. After 2 hours, the reaction was stopped, and the polyester containing 0.5 part of silica was added. A was obtained.

Production Example 2 (Production of Polyester B) In Production Example 1, polyester B was obtained without adding amorphous silica. Production Example 3 (Polyester C) Polyester C was obtained in the same manner as in Production Example 1, except that 75 parts of dimethyl terephthalate and 25 parts of dimethyl isophthalate were used instead of 100 parts of dimethyl terephthalate. .

Example 1 Mixed polyester I and polyester C in which 1 part of polyester A and 99 parts of polyester B were mixed were melted in separate extruders, and coextruded at a discharge ratio of 10: 2 (mixed polyester I: polyester C). After being extruded by the method, the mixture was rapidly cooled to a glass transition temperature or lower to obtain an amorphous film. The obtained sheet was stretched three times in the longitudinal direction at 80 ° C. by a roll stretching machine.

Subsequently, the film was stretched four times in the transverse direction at 100 ° C. by a tenter stretching machine, and heat-set at 220 ° C. in the width direction to obtain a laminated polyester film having a thickness of 12 μm. The surface of the obtained laminated polyester film on the polyester C side was used as a metal bonding surface, and bonded to both surfaces of an aluminum plate induction-heated to 240 ° C. using a laminating roll, and then heat-fixed at 260 ° C. It was quenched by a cold water bath to obtain a laminated aluminum plate. The haze of the coating layer of the obtained laminated aluminum plate was 1.5%.

The obtained laminated aluminum plate was punched out into a circular shape, formed into a panel, compounded and scored, and a tab was attached to the laminated aluminum plate to form a laminated lid. In addition, the obtained laminated aluminum plate was punched into a circle, drawn between the drawing die and the punch to form a cup, and the cup wall was thinned between the ironing ring and the punch. After printing, necking flanging was performed to obtain a laminated can. The resulting aluminum can having the lid and the can had an excellent metallic luster appearance.

Comparative Example 1 An aluminum plate covered with a laminated polyester film was obtained in the same manner as in Example 1, except that Polyester A was used instead of Mixed Polyester I. The haze of the coating layer of the obtained aluminum plate was 10% or more. Using the resulting polyester-coated aluminum plate, a lid and a can were formed in the same manner as in Example 1. The resulting aluminum can comprising the lid and the can had a dull metallic luster and had a refreshing appearance.

Comparative Example 2 The haze of the outer surface coating layer (white polyester film base) on the bottom of a commercially available polyester-coated beverage can was found to be 10% or more. The polyester-coated beverage can did not have an appearance utilizing the metallic luster.

[0024]

According to the present invention described above, a highly transparent polyester film is coated on an aluminum material for a can, and when molded into a metal can, has an excellent appearance utilizing the metallic luster of aluminum. Metal cans can be obtained without painting, and their industrial value is very high.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B65D 77/20 B65D 77/20 M

Claims (3)

[Claims] 1. An aluminum plate coated on both sides with a polyester, which is used for a metal can material, wherein a haze of a polyester coating layer which is an outer surface when the can is formed into a can lid and a can body is 4% or less. Characterized polyester coated aluminum plate. 2. A laminated lid formed by molding the polyester-coated aluminum plate according to claim 1. 3. A laminated can formed by molding the polyester-coated aluminum plate according to claim 1.