JPH06285974A - Film for laminate - Google Patents

Abstract

PURPOSE:To obtain a film improving moldability, shock resistance and a property of keeping taste and smell and being suitable for sticking on a metal by a method wherein the degree of orientation in the crosswise direction intersecting the lengthwise direction of the film perpendicularly and the degree of orientation in the lenghtwise direction of the film and the crosswise direction in the central part of the direction of the thickness of the film are controlled to be in a specified relationship. CONSTITUTION:A heat-adhesive biaxially orientated polyester film. when the degrees of orientation in the lengthwise direction of the film in a surface layer part of this film and in corsswise direction intersecting this lengthwise direction of the film perpendicularly in this part are denoted by SMD and STD and the degrees of orientation in the lengthwise direction of the film and in the crosswise direction thereof in the central part in the direction of the thickness of the film by CMD and CTD, Disposition of the film is made so that the relationship of 0.5X SMD<CMD<SMD or and 0.5X STD<CTD<STD be satisfied on one side of the film at least and that this side of a surface be a non-thermal laminate side. It is preferable that the quantity of acetaldehyde in the biaxially orientated polyester film is 100ppm or below.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film for laminating comprising a biaxially oriented polyester film, and particularly to a beverage can, a food can, etc. which can be deep-drawn, folded, etc. by being attached to a metal plate. The present invention relates to a laminating film suitable for a can body, a can bottom, and a can lid.

[0002]

2. Description of the Related Art Conventionally, a metal is generally coated to prevent corrosion, but a method for obtaining a rust preventive property without using an organic solvent has been developed. That is, (1) a method of laminating a biaxially oriented polyethylene terephthalate film via an adhesive layer of low touch point polyester and using it as a can-making material (JP-A-56-10451, JP-B-1-192).
No. 546, etc.), (2) A method of laminating an amorphous or low crystalline aromatic polyester film on a metal plate and using it as a can-making material (JP-A-1-192545, JP-A-2-192545).
-57339), and (3) a method of laminating a low orientation polyethylene terephthalate film on a metal plate and using it as a can-making material (Japanese Patent Laid-Open No. 64-22530).
Have been proposed.

However, regarding the method (1), in terms of forming workability, particularly deep drawing workability in can making,
The method (2) is insufficient in impact resistance and aroma retention of the laminated films, and the method (3) is insufficient in impact resistance and aroma retention similar to the method (2). However, the reality is that it has not been put to practical use.

[0004]

In view of the above problems of the present invention, therefore, the present invention is particularly suitable for bonding to a metal which is excellent in moldability, impact resistance and aroma retention and can be sufficiently put to practical use. The purpose is to provide an optimal laminating film.

[0005]

A heat-bondable biaxially oriented polyester film for laminating films according to the present invention, which is intended for this purpose, wherein a film flow direction in a surface layer portion of the film and a transverse direction orthogonal to the film flow direction are provided. The degree of orientation of S _MD and S _TD , and the degree of orientation in the film flow direction and the transverse direction at the center of the film in the thickness direction are C _MD and C _TD , 0.5 × S _MD <C _MD <at least on one side of the film. S _MD or / and 0.5 × S _TD <C _TD <S _TD , and the surface side is the non-thermal laminating side.

The laminating film of the present invention comprises a heat-adhesive biaxially oriented polyester film, and the biaxially oriented polyester film preferably comprises a polyester resin, particularly a polyester copolymer. The copolymerized polyester is not particularly limited,
The following examples can be given as typical ones. As the acid component, terephthalic acid, isophthalic acid, aromatic dibasic acid such as naphthalenedicarboxylic acid, adipic acid,
Examples thereof include aliphatic dicarboxylic acids such as sebacic acid, azelaic acid, and dodecadioic acid. As the alcohol component, ethylene glycol, diethylene glycol,
Aliphatic diols such as butanediol and hexanediol can be mentioned. These are used in combination of one or more. For example, as a preferable example, a polyester copolymer having 65 mol% or more of terephthalic acid as a polyester acid component and 85 mol% or more of ethylene glycol as an alcohol component can be mentioned. Also,
The amount of acetaldehyde in the polyester is preferably 10 ppm or less. When the amount of diethylene glycol in the polyester is less than 1.5% by weight, preferably 0.85% by weight or less, more preferably 0.65% by weight or less, the impact resistance is good, which is preferable. Further, the carboxyl group in the polyester is less than 50 eq / t, preferably 4
When it is 0 eq / t or less, more preferably 30 eq / t or less, the impact resistance after retort is good, which is preferable.

The laminating film of the present invention is particularly suitable for being attached to a metal plate. That is, on a base material made of a metal plate, for example, a steel plate,
The biaxially oriented polyester film made of the above polyester resin is heat-bonded. The polyester flume is biaxially oriented by biaxial stretching, but in the present invention, the degree of orientation has a specific relationship with respect to the non-heat-bonding side (non-thermal laminating side) of the film and the central portion in the film thickness direction. Is controlled to satisfy. As a result, the desired values of both the molding processability, especially the deep drawing processability and the impact resistance, of the laminated body to which the films are attached are obtained, and the taste aroma is also satisfied. .

That is, the film flow direction in the surface layer portion of the film and the degree of orientation in the lateral direction orthogonal to the film flow direction are S _MD and S _TD , and the degree of orientation in the film flow direction and the lateral direction in the central portion in the film thickness direction are shown. When C _MD and C _TD , at least on one side of the film, the relationship of 0.5 × S _MD <C _MD <S _MD or / and 0.5 × S _TD <C _TD <S _TD is satisfied, and The surface side is the non-thermal laminating side.

That is, in the laminating film of the present invention, when the surface layer portion on the non-thermal laminating side is made to have a higher degree of orientation, the laminated layered body is formed, particularly the surface side during deep drawing. The durability is improved to improve the moldability, and the impact resistance of the surface side after molding is improved during the molding process. The degree of orientation of the central portion in the thickness direction of the film is set to a lower degree of orientation so that strains and the like during molding processing, particularly deep drawing processing, can be favorably absorbed, and molding processability is improved.

More preferably, the relation of the degree of orientation is 0.6 × S _MD <C _MD <0.85 × S _MD or / and 0.6 × S _TD <C _TD <0.85 × S _TD . is there.

Various lubricants may be added to the biaxially oriented polyester film of the present invention. The type of lubricant may be inorganic or organic. Suitable inorganic particles include agglomerated silica, spherical silica, alumina, titanium dioxide, calcium carbonate, barium sulfate, and zirconia. Examples of organic particles include silicone particles, crosslinked styrene particles, imide particles, and amide particles. Also its average particle size (by sedimentation method)
Is 2.0 μm or less, more preferably 1.5
The thickness may be less than or equal to μm, and most preferably less than or equal to 0.8 μm.

The method for producing the polyester resin in the present invention is not particularly limited, but when the laminated product of the film of the present invention and a metal is used as a container, the resin synthesized by the direct weight method is a taste-maintaining aroma. Is more preferable. Further, when the aldehydes are reduced by a method such as solid phase polymerization, it is more preferable in terms of taste-maintaining aroma. As described above, the amount of acetaldehyde is particularly preferably 10 ppm or less. Examples of the polymerization catalyst include antimony and germanium, and germanium is preferable from the viewpoint of taste-maintaining aroma. If desired, other additives such as antioxidants, heat stabilizers, ultraviolet absorbers, antistatic agents, colorants, pigments, whitening agents and the like may be added.

The thickness of the polyester film of the present invention is preferably in the range of 2 to 150 μm. The thickness is preferably 8 to 60 μm, more preferably 12 to 40 μm.

Typical examples of the metal plate to which the film of the present invention is attached include tin plate, tin-free steel, aminium, and the like. The surface of these metal plates may be subjected to organic or inorganic treatment as appropriate.

Next, a typical production method of the laminating film of the present invention will be explained, but the production method is not limited to this. Specified viscosity (usually 0.45 at intrinsic viscosity
400 ppm or less, preferably 80 ppm, after appropriately applying a lubricant formulation to a polyester resin having 1.50)
Dry below. The dry raw materials are melt mixed using an extruder. When an extruder having degassed holes is used, drying may be omitted, or various additives may be added during the extruder. After discharging the resin in a molten state from the die, it is once cooled on a cooling roll, and then stretched 2.0 to 6.0 times in the longitudinal direction in the range of 60 to 135 ° C., and then 60 to 140 ° C.
In the range of 2.0 to 6.0 times in the transverse direction and 120 to 2
Heat treatment is performed in the range of 40 ° C. while relaxing as necessary. In particular, by cooling the film surface immediately before longitudinal stretching (for example, by cooling with cooling air), the degree of orientation in the longitudinal direction (film flowing direction) can be increased particularly in the surface layer portion.

The biaxially oriented polyester film obtained as described above is attached to a metal plate as a base material, for example, a tin-free steel plate. The bonding conditions are, for example, heating a metal plate at 200 to 300 ° C.,
50-150 with the heating roll on the bonding surface of the film
Heat to 0 ° C. and laminate to the heated metal plate. Then, the non-heat-bonded surface of the film is removed by 15 to 50
By cooling with a cooling roll at a temperature of 0 ° C., the treatment can be performed without lowering the orientation degree on the non-heat-bonding side.

[Measurement method] (1) Orientation degree measuring device: FTS-15E / D (FT-IR manufactured by Bio Rad Digilab) Light source: Special ceramics detector: MCT auxiliary device: micro-ATR measuring auxiliary device (WILKS)
Incident angle: 45 ° IRE: KRS-5, using polarizer Measurement conditions: Decomposition ability = 4 cm ⁻¹ Cumulative number of times = 500 times As the degree of orientation, the absorption ratio of (νC—O trans band) and benzene ring (970 cm ⁻¹ / 790 cm ⁻¹ ) was obtained and used as the degree of orientation. In addition, the degree of orientation of the central portion is shaving the film with a grindstone, and after confirming that it is the central portion in the thickness direction,
It evaluated by the same method.

(2) Deep drawing workability A predetermined film is attached to tin-free steel heated to 265 ° C., then cooled from the film side with a cooling roll and then water-cooled. The film-bonded metal plate thus obtained is cut into a disk shape having a diameter of 250 mm, and then the film surface is formed into an inner surface using a heat molding machine to form a drawing ratio of 1.3. The can thus obtained is subjected to a visual judgment and a rust prevention test. Rust resistance is 1%
NaCl water was placed in a can, the can was used as an anode, and the cathode was inserted in NaCl. The current value was applied when a voltage of 6 V was applied. There was no appearance abnormality, and the current value was determined to be “◯” when the current value was 0.25 mA or less, and was determined to be “x” otherwise.

(3) Impact resistance-A A deep drawn can made under the conditions of (1) is filled with water and then sealed. About 50 canned products and those subjected to retort treatment at 120 ° C for 8 hours were dropped on a floor inclined at 15 ° from a height of 1.2 m, and then evaluated for rust prevention under the conditions described in (1). To do. Total number is 0.15 mA or less: ◎ Total number is 0.30 mA or less, half is 0.15 mA or less: ○ to ◎ Total number is 0.30 mA or less: ○ 8 or more is 0.30 mA or less: △ Other than that: ×, ◎, ○, It was determined that Δ is practically applicable.

(4) Impact resistance-B A deep drawn can made under the conditions of (1) is filled with water and then sealed. The canned product and the one that was heat-treated at 220 ° C. for 10 minutes were dropped on a floor inclined at 15 ° from a height of 1.2 m, and then evaluated according to the same criteria as described in (3).

(5) Taste-preserving aroma Orange drinks and coffees were enclosed, left for 1 week, and their aromas were evaluated. What feels equivalent to the coffee before inclusion: ○ Something that feels a little inferior in fragrance: △ Significantly inferior: × It was judged that ○ and △ could be put to practical use.

(6) Carboxyl group Using HIRANUMA COMTITE-7 REPORTING TITRETOR, a silver chloride composite electrode is used, and a supersaturated potassium chloride aqueous solution is filled, and the calculation is performed based on the following formula. COOH (eq / t) = [(A−B) × C × F] / S A: NaOH titer of sample (ml) (normality = N / 50−NaOH / methanol) B: NaOH titer of blank ( ml) C: 20 (20 = N / 50 × 1/1000 × 1)
0 ° F: Factor (determined by benzoic acid / methanol solution) S: Sampling amount (g)

[0023]

【Example】

Example 1 As a polyester resin, the acid component was terephthalic acid (T
PA), isophthalic acid (IPA), the alcohol component is ethylene glycol (EG), diethylene glycol (DEG), solid phase polymerized polyester (0.12% by weight of aggregated silica particles having an average particle diameter of 0.3 μm) ( IV = 0.78) was used.

The above resin was supplied to an extruder, melt-extruded at 260 ° C., discharged in a sheet form from a die, and cast on a cooling drum. This unstretched sheet is stretched at a stretching temperature of 10
Longitudinal stretching was performed at 2 ° C. and a stretching ratio of 3.0 times. However, both surfaces of the film immediately before stretching were cooled with air at 40 ° C. The obtained uniaxially stretched film is introduced into a tenter and stretched at a stretching temperature of 110.
The film was transversely stretched at a temperature of ℃ and a stretching ratio of 3.1 times. The biaxially stretched film was once cooled, and then heat set while being subjected to a relaxation treatment at 190 ° C. in the transverse direction at a relaxation rate of 1.5%.

The obtained film was heat-bonded on tin-free steel as a substrate as follows to obtain a laminate. First, tin-free steel was heated to 250 ° C., and the laminated surface of the film was heated with a heating roll at a temperature of 80 ° C. and then laminated.

When the degree of orientation of the film was measured and the resulting laminate was evaluated for deep drawing workability, impact resistance, and taste-maintaining aroma, the results shown in Table 1 were obtained. As shown in Table 1, each degree of orientation of the film was within the range specified in the present invention, and therefore good results were obtained in all of the deep-drawing processability, impact resistance, and taste retention.

Comparative Examples 1 and 2, Examples 2 to 5 (Table 1) Comparative Example 1 is the same as Example 1 except that it is heated with air at 95 ° C. immediately before longitudinal stretching. In Example 3, the same as Example 1 except that heating was performed with 110 ° C. air immediately before longitudinal stretching, and in Example 2, in the same manner as Example 1 except that heating was performed with 65 ° C. air immediately before longitudinal stretching. Is
Films were formed in the same manner as in Example 1 except that a liquid-weight polymer was used instead of the solid-state polymerization, and the laminated body laminated with the film and the metal plate was evaluated. In Examples 4 and 5, evaluation was performed by changing the amount of carboxyl groups.

[0028]

[Table 1]

[0029]

As described above, in the case of the laminating film of the present invention, the degree of orientation of the biaxially oriented polyester film to be laminated on the base material is set to
Since the middle part of the film in the thickness direction was controlled so as to satisfy a specific relationship, it is ideal for lamination, which is used for can-making laminates that are excellent in formability such as deep drawing, impact resistance, and taste-maintaining aroma. You can get a film.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kunio Shibatsuji 1-1-1, Sonoyama, Otsu City, Shiga Toray Co., Ltd. Shiga Plant

Claims (5)

[Claims] 1. A heat-adhesive biaxially oriented polyester film, wherein the film flow direction in the surface layer portion of the film and the degree of orientation in the transverse direction orthogonal to the film flow direction are S.
_{When MD} , S _TD , and the degree of orientation in the film flow direction and the lateral direction in the central portion of the film thickness direction are C _MD , C _TD , at least on one side of the film, 0.5 × S _MD <C _MD <S _MD or / and A laminating film, which satisfies the relationship of 0.5 × S _TD <C _TD <S _TD , and whose surface side is a non-thermal laminating side. 2. The relationship according to claim 1, wherein the relationship is 0.6 × S _MD <C _MD <0.85 × S _MD or / and 0.6 × S _TD <C _TD <0.85 × S _TD . Film for laminating. 3. The amount of acetaldehyde in the biaxially oriented polyester film is 10 ppm or less.
Or the laminating film of 2. 4. The laminating film according to claim 1, wherein the amount of diethylene glycol in the biaxially oriented polyester film is less than 1.5% by weight. 5. The laminating film according to claim 1, wherein the biaxially oriented polyester film has a carboxyl group of less than 50 (eq / t).