JP2908119B2 - Polyester film for metal plate lamination processing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film for laminating and forming a metal plate, and more particularly to a polyester film for laminating to a metal plate and exhibiting excellent formability when performing can forming such as drawing. The present invention relates to a polyester film for metal plate lamination molding capable of producing metal cans, such as beverage cans and food cans, having excellent properties, retort resistance, fragrance retention and the like.

[0002]

2. Description of the Related Art Metal cans are generally coated to prevent corrosion of the inner and outer surfaces. Recently, for the purpose of simplifying the process, improving hygiene, and preventing pollution, rust prevention is performed without using an organic solvent. Development of a method for obtaining the property has been advanced, and as one of the methods, coating with a thermoplastic resin film has been attempted. That is,
Studies have been made on a method of laminating a thermoplastic resin film on a metal plate such as tinplate, tin-free steel, or aluminum, and then forming the can by drawing or the like. Polyolefin films and polyamide films have been tried as this thermoplastic resin film, but they do not satisfy all of the moldability, heat resistance and fragrance retention.

[0003] Therefore, polyester films, especially polyethylene terephthalate films, have attracted attention as having balanced properties, and several proposals based on these have been made. That is, (A) a biaxially oriented polyethylene terephthalate film is laminated on a metal plate via a low-melting-point polyester adhesive layer and used as a can-making material (JP-A-56-10451).
No. JP-A-1-192546). (B) Amorphous or extremely low-crystalline aromatic polyester film is laminated on a metal plate and used as a material for can production (Japanese Patent Application Laid-Open Nos. 1-192545 and 2-573).
No. 39). (C) A low-orientation, heat-fixed, biaxially oriented polyethylene terephthalate film is laminated on a metal plate and used as a can-making material (Japanese Patent Laid-Open No. 64-22530).

[0004] However, the present inventors' studies have revealed that no satisfactory characteristics can be obtained in any case, and that each has the following problems.

Regarding (A), a biaxially oriented polyethylene terephthalate film is excellent in heat resistance and fragrance retention.
Molding is inadequate, and whitening (generation of minute cracks) and breakage of the film occur in can making with large deformation.

As for (B), since it is an amorphous or extremely low-crystalline aromatic polyester film, the moldability is good, but the fragrance retention is inferior, and printing and retort sterilization after can-making are performed. Such a film may be easily embrittled by post-treatment or storage for a long time, and may be transformed into a film which is easily broken by an impact from the outside of the can.

As for (C), the effect is not exhibited in the intermediate region between the above (A) and (B), but it has not yet reached the low orientation applicable to can processing. Even if it can be processed in a region with a small degree of deformation, subsequent printing,
As in the above (B), there is a possibility that the retort treatment for sterilizing the contents of the can makes the film brittle easily and may be transformed into a fragile film by an impact from the outside of the can.

[0008]

DISCLOSURE OF THE INVENTION The present inventors have intensively studied to develop a polyester film for processing cans which does not have these problems, and as a result, have reached the present invention.

[0009]

That is, the present invention provides a polymer having a melting point of 210 to 245 ° C. and a glass transition temperature of 50.
℃ or more , and the terminal carboxyl group concentration is 35 equivalent / 10
^A polyester film for laminating and processing a metal plate, comprising a copolymerized polyester of ⁶ g or more , wherein the acetaldehyde content of the film is 20 ppm or less.

A typical example of the copolymerized polyester in the present invention is a copolymerized polyethylene terephthalate. The copolymer component may be an acid component or an alcohol component. Examples of the copolymeric acid component include aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and decane dicarboxylic acid, isophthalic acid, phthalic acid, 2,6
Preferred are aromatic dicarboxylic acids such as -naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, and 1,5-naphthalenedicarboxylic acid. Further, as the copolymerized alcohol component, diethylene glycol, propylene glycol, neopentyl glycol,
Aliphatic diols such as butanediol, pentanediol and hexanediol, and polyalkylene glycols such as polyethylene glycol and polypropylene glycol can be preferably exemplified. These can be used alone or in combination of two or more.

The proportion of the copolymer component depends on the type thereof, but the melting point of the polymer is from 210 to 245 ° C., preferably from 21 to 245 ° C.
The temperature is 5 to 240 ° C, and the glass transition temperature of the polymer is 50 ° C or higher, preferably 60 ° C or higher.
When the melting point of the polymer is less than 210 ° C., the heat resistance is inferior, so that it cannot withstand the heating in printing after can-making. On the other hand, when the melting point of the polymer exceeds 245 ° C., the crystallinity of the polymer is too large, and the moldability is impaired. If the glass transition temperature is less than 50 ° C., the strength of the polyester film is reduced by heat treatment (such as boiling water treatment) of the formed metal plate. Problems such as poor performance occur.

Therefore, it is necessary to determine the type and amount of the copolymer component in consideration of both the melting point and the glass transition temperature of the polymer.

Here, the melting point and glass transition temperature of the copolymerized polyester are measured by Du Pont Instruments 910.
Using a DSC, a melting peak and a glass transition temperature peak are determined at a heating rate of 20 ° C./min. The sample amount is about 20 mg.

The copolyester of the present invention further has a terminal carboxyl group concentration of 35 equivalents / 10 ^6.
g or more, preferably Ru der 40 eq / 10 ⁶ g or more. The concentration of the terminal carboxyl group is related to the fragrance retention and the adhesion to the metal plate, and it is necessary to satisfy the above values.

The range of the terminal carboxyl group concentration is as follows:
It is in a range larger than the value of the terminal carboxyl group concentration in a normal polyester. The reason why excellent fragrance retention and adhesion to the metal plate are recognized in this range is not clear, but the reduction of adsorption and the like due to the interaction between the terminal carboxyl group and the scent component, and the contact with the metal plate by the terminal carboxyl group are also unknown. It is thought that the improvement in affinity was caused.

Such a copolyester having a terminal carboxyl group concentration can be produced by employing the following special reaction conditions in a transesterification method (DMT method) or an esterification method (direct weight method). For example, a polyester is obtained by using a larger amount of a compound such as a metal compound used at the time of transesterification or esterification, such as Mg, Mn, Zn, Ca, Li, and Ti, than usual.
In the latter part of the polymerization reaction, the polymerization reaction proceeds while maintaining the temperature higher than usual and / or for a long period of time, and copolymerizes a monomer relatively susceptible to thermal decomposition, such as an aliphatic carboxylic acid or aliphatic glycol having 4 to 12 carbon atoms It can be manufactured by a method such as Also, a polyester having the above terminal carboxyl group concentration may be obtained by blending a certain amount of a so-called regenerated polymer which has been relatively thermally decomposed.

Further, a method of reacting an acid anhydride such as phthalic anhydride or succinic anhydride with a copolymerized polyester polymer can be employed. However, although this method can certainly increase the terminal carboxyl group concentration to a large value, the presence of unreacted acid anhydride may deteriorate the fragrance retention, and it is necessary to optimize the reaction conditions.

Therefore, the amount of the low molecular weight compound in the copolyester is preferably very small. For example, the amount of extraction when n-heptane is extracted at 66 ° C. for 2 hours is 0.5%.
mg / inch ² or less, preferably 0.1 mg / inch
² or less is more preferable. Here, mg / inch ² represents the amount of extraction per square inch of the film when the film was extracted with n-heptane.

The catalyst used in the polycondensation of the copolymerized polyester in the present invention is not particularly limited, but preferably includes an antimony compound, a titanium compound, a germanium compound and the like, and particularly, a titanium compound and a germanium compound are obtained. It is preferable from the aspect of the fragrance retention of the polyester film.

Preferred examples of the titanium compound include titanium tetrabutoxide and titanium acetate. Examples of the germanium compound include (a) amorphous germanium oxide, (b) fine crystalline germanium oxide,
(C) A solution in which germanium oxide is dissolved in glycol in the presence of an alkali metal or an alkaline earth metal or a compound thereof, and (d) a solution in which germanium oxide is dissolved in water are preferable.

The amount of the germanium compound is from 40 to 40 as the amount of germanium remaining in the copolymerized polyester.
200 ppm is preferable, and 60 to 150 ppm is more preferable.

The copolyester in the present invention preferably contains a lubricant having an average particle size of 2.5 μm or less. The lubricant may be inorganic or organic, but inorganic is preferred. Examples of the inorganic lubricant include silica, alumina, titanium dioxide, calcium carbonate, and barium sulfate, and examples of the organic lubricant include silicone particles. In any case, the average particle diameter is preferably 2.5 μm or less. When the average particle size of the lubricant exceeds 2.5 μm, coarse lubricant particles (eg, particles having a size of 10 μm or more) of a portion deformed by processing such as a deep-drawing can become a starting point, and pinholes are generated, and in some cases, It is not preferable because it breaks.

A lubricant which is particularly preferable from the viewpoint of pinhole resistance is a monodisperse lubricant having an average particle size of 2.5 μm or less and a particle size ratio (major axis / minor axis) of 1.0 to 1.2. is there. Examples of such a lubricant include spherical silica, spherical silicone, and spherical calcium carbonate.

The amount of the lubricant in the copolymerized polyester may be determined depending on the winding property in the film production process. Generally, it is preferable to add a small amount of particles having a large particle diameter and a large amount of particles having a small particle diameter. For example, it is preferable to add about 0.05% by weight in the case of silica having an average particle diameter of 2.0 μm, and about 0.3% by weight in the case of titanium dioxide having an average particle diameter of 0.3 μm. Also, by intentionally adjusting the pigment of the lubricant, the film can be made opaque. For example, titanium dioxide
By adding 0 to 15% by weight, a white film can be obtained.

The lubricant is not limited to the above-mentioned externally added particles. For example, internal precipitated particles obtained by depositing a part or all of the catalyst used in the production of polyester in the reaction step can be used. It is also possible to use externally added particles and internally precipitated particles in combination.

The polyester film of the present invention comprises:
It is necessary that the acetaldehyde content is 20 ppm or less. It is preferably at most 10 ppm, more preferably at most 5 ppm. Acetaldehyde content is 20
When the content exceeds ppm, a large amount of acetaldehyde is eluted in the content when the metal can is used, and the fragrance retention deteriorates. In addition, since the copolymerized polyester usually contains 100 ppm or more of acetaldehyde when the polycondensation reaction is completed, for example, the following method is used to reduce the acetaldehyde content to a low value of 20 ppm or less. Is required. The copolyester chip is heat-treated at a temperature of about 150 to 200 ° C. for a long time to sufficiently disperse acetaldehyde, and then melt-extruded in a short time to form a film. When stretching and heat-treating the unstretched film obtained by melting and extruding, acetaldehyde is scattered while blowing a large amount of hot air.

The polyester film of the present invention is obtained by melting the above-mentioned copolymerized polyester, discharging it from a die, forming it into a film, biaxially stretching and heat setting. The film preferably satisfies the following requirements (1), (2) and (3).

(1) The refractive index in the thickness direction of the film is 1.
It is preferably from 505 to 1.550, more preferably from 1.510 to 1.540. If the refractive index is less than 1.505, the moldability is insufficient, while if it exceeds 1.550 (that is, if the orientation is excessively low), the structure becomes almost amorphous, so that the heat resistance is high. Tends to be insufficient.

The refractive index in the thickness direction of the film is measured as follows. A polarizing plate analyzer is attached to the eyepiece side of the Abbe refractometer, and each refractive index is measured with a monochromatic NaD line. The mounting solution uses methylene iodide, and the measurement temperature is 25 ° C.

(2) The refractive index in the plane direction of the film is preferably 1.610 to 1.660 in all directions. The refractive index in the film surface direction is preferably as uniform as possible in all directions, and the value of the refractive index is 1.610 to
When the ratio is out of the range of 1.660, the film has anisotropy, so that the moldability tends to deteriorate. The refractive index in the surface direction of the film is also measured by Abbe's refractometer in the same manner as described above.

(3) The intrinsic viscosity of the polymer portion of the film is 0.52 or more and 0.80 or less, and more preferably 0.54 or more and 0.5 or less.
It is preferably 70 or less, particularly preferably 0.57 or more and 0.65 or less. When the intrinsic viscosity is less than 0.52, other physical properties are suitable, and even if lamination to a metal plate and can-making by deep drawing are performed well, retort for sterilization after filling the can contents. By performing the treatment or by storing the film for a long time thereafter, the film is easily embrittled and easily broken by an impact from the outside of the can. On the other hand, those having an intrinsic viscosity of more than 0.80 are of excessive quality and are not economical because the productivity of the raw material polymer is lowered.

Further, the polyester film of the present invention may be a laminated film of two types of copolymerized polyesters having different copolymerization amounts and copolymerization types, if necessary. In this case, each layer of the laminate may be a polyester satisfying the requirements of the present invention, or only the outer layer portion may satisfy the requirements of the present invention.

The polyester film of the present invention preferably has a thickness of 6 to 75 μm. 10-75μ
m, particularly preferably 15 to 50 μm. If the thickness is less than 6 μm, breakage or the like is likely to occur during processing, while if it exceeds 75 μm, the quality is excessive and uneconomical.

As a metal plate for cans to which the polyester film of the present invention is bonded, a plate of tin, tin-free steel, aluminum or the like is suitable. The bonding of the polyester film to the metal plate can be performed, for example, by the following method.

The metal plate is heated to a temperature equal to or higher than the melting point of the film, the film is bonded, and then rapidly cooled, and the surface layer (thin layer) of the film in contact with the metal plate is made amorphous and adhered.

The film is previously coated with an adhesive layer with a primer, and this surface is bonded to a metal plate. As the adhesive layer, a known resin adhesive such as an epoxy-based adhesive, an epoxy-ester-based adhesive, an alkyd-based adhesive, or the like can be used.

[0037]

The present invention will be further described below with reference to examples. In the examples, "parts" means parts by weight. The measurement of each characteristic value was performed according to the following method.

(1) Terminal carboxyl group concentration CONIX method (Makromol, Chem. 26 , 226 (195
8)).

(2) Acetaldehyde Content The amount of acetaldehyde generated when the film was heat-treated at 160 ° C. for 20 minutes was determined by gas chromatography.

(3) Deep drawing workability ：: The film was processed without any abnormality, and no whitening or breakage was observed in the film on the inner and outer surfaces of the can. Δ: Whitening is observed at the top of the film can. X: Film breakage is observed in a part of the film.

(4) Impact cracking resistance For cans with good deep drawing, pour water thoroughly, drop 10 pieces for each test from a height of 1 m onto a PVC tile floor, and then perform ERV test in the can. Was done. (ERV test: 1%
NaCl water is put in a can, an electrode is inserted, and a current value when a voltage of 6 V is applied using the can as an anode is measured). ：: 0.1 mA or less for all 10 samples. C: 0.1 mA or more for 1 to 5 pieces. ×: 0.1 mA or more for 6 or more pieces, or cracks of the film were already observed after dropping.

(5) Retort Resistance Cans with good deep drawability were filled with water and retorted at 130 ° C. for 1 hour in a steam sterilizer, and then stored at 50 ° C. for 30 days. After dropping 10 cans obtained for each test from a height of 1 m on a PVC tile floor, an ERV test in the cans was performed. ：: 0.1 mA or less for all 10 samples. C: 0.1 mA or more for 1 to 5 pieces. ×: 0.1 mA or more for 6 or more pieces, or cracks of the film were already observed after dropping.

(6) Perfume Retention For cans having good deep drawing, 10 bottles of cider or mineral water were filled and sealed. After keeping at 37 ° C. for 4 months, the container was opened and the changes in aroma and taste were sensory-tested. A: There is no change in aroma and taste. ：: One or two fragrances and tastes were slightly changed. Δ: 5 or 6 pieces slightly changed in aroma and taste. ×: Changes in fragrance and taste were observed in all 10 tubes.

[0044]

Examples 1 to 7 and Comparative Examples 1 to 3 Polyethylene terephthalate obtained by copolymerizing the components shown in Table 1 was obtained by changing the catalyst under the polycondensation reaction conditions, the reaction temperature and the reaction time.

Next, the copolymerized polyethylene terephthalate was dried, melted, extruded from a die, and cooled with a cooling drum to obtain an unstretched film. Then, after stretching in the longitudinal direction,
After stretching in the transverse direction was performed while changing the temperature and the amount of hot air blown, the film was heat-fixed to obtain a biaxially oriented film having a thickness of 25 μm.

The refractive index of each film in the thickness direction is 1.
The refractive index in the plane direction was in the range of 1.620 to 1.650 in all directions.

The evaluation results of the films are shown in Table 1. All the films satisfying the requirements of the present invention showed good results.

[0048]

[Table 1]

[0049]

According to the present invention, the can processability after lamination with a metal plate, for example, the deep drawing processability, the impact resistance after the can process, and the fragrance retention of the contents are excellent. Polyester film can be provided.

Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI // B29K 67:00 B29L 7:00 C08L 67:02 (56) References JP-A-3-86729 (JP, A) JP-A-3-3 87249 (JP, A) JP-A-2-191627 (JP, A) JP-A-5-339348 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C08J 5/00-5 / 02 B29C 55/12 B32B 1/00-35/00

Claims (3)

(57) [Claims] 1. A polymer having a melting point of 210 to 245 ° C., a glass transition temperature of 50 ° C. or higher , and a terminal carboxyl group concentration.
Of a copolyester having a degree of 35 equivalents / 10 ⁶ g or more , and an acetaldehyde content of the film of 20 p.
pm or less, a polyester film for laminating and forming a metal plate. 2. A copolyester according to claim 1 Symbol mounting metal plate laminating molding for polyester film are those prepared by using a germanium compound as a catalyst for the polycondensation reaction. 3. The amount of extraction when the film is extracted with n-heptane at 66 ° C. for 2 hours is 0.5 mg / inch ^2.
The polyester film for laminating and processing a metal plate according to claim 1 or 2, wherein: