JPH07101018A - Polyester film for laminating and molding metal plates - Google Patents

Abstract

PURPOSE:To obtain impact resistance at a low temperature by laminating a specific copolymer polyester layer containing specific small and large particle lubricants, and a polyester layer containing a mixture of a specific copolymer polyester and a specific polyester and a containing specific lubricant. CONSTITUTION:One copolymer polyester layer of a two-layer structure contains 0.01-3wt.% of a lubricant A having a mean particle size of 0.05- less than 0.6mum and 0.001-0.2wt.% of lubricant B having a mean particle size of 0.3 to 2.5mum in such a manner that mean particle size of the lubricants A and B is 2.5mum or more, its melting point is 210-245 deg.C and its glass transition temperature is 60 deg.C or higher, and a germanium compound is used as a polycondensation catalyst. The other polyester layer contains a polyester composition of a mixture of 80-45wt.% of a copolymer polyester having a repetition unit of ethylene terephthalate which has a melting point of 210-245 deg.C and containing the germanium compound as the polycondensation catalyst and 20-55wt.% of polyester having the repetition unit of butylene terephthalate having a melting point of 180-223 deg.C, and 0.3-0.5wt.% of a lubricant having a mean particle size of 0.8- less than 2.5mum.

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 metal plates, and more particularly, it shows excellent forming processability when it is laminated with a metal plate to perform a can forming process such as drawing process, and it is heat resistant. Metal can with excellent qualities and taste retention,
For example, the present invention relates to a polyester film for metal plate laminating and forming which can produce beverage cans, food cans and the like.

[0002]

2. Description of the Related Art Metal cans are generally painted to prevent corrosion on the inside and outside, but recently, for the purpose of simplifying the process, improving hygiene, and preventing pollution, rust prevention without the use of organic solvents The development of a method for obtaining the property has been advanced, and as one of them, coating with a thermoplastic resin film has been attempted. That is,
A method of making a can by drawing a thermoplastic resin film on a metal plate such as tin plate, tin-free steel, or aluminum is being studied. Polyolefin films and polyamide films have been tried as this thermoplastic resin film, but they do not satisfy all of the moldability, heat resistance, taste retention, and impact resistance.

On the other hand, a polyester film, especially a polyethylene terephthalate film, has been noted as having balanced properties, and several proposals based on this have been made. That is, (A) a biaxially oriented polyethylene terephthalate film is laminated on a metal plate via an adhesive layer of low melting point polyester and used as a can-making material (JP-A-56-1045).
No. 1, JP-A-1-192546). (B) An amorphous or extremely low crystalline aromatic polyester film is laminated on a metal plate and used as a can-making material (JP-A-1-192545 and JP-A-2-57).
339). (C) A low orientation, heat-set, 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).

However, the studies by the present inventors have revealed that none of them has sufficient characteristics and have the following problems.

Regarding (A), the biaxially oriented polyethylene terephthalate film is excellent in heat resistance, but the moldability is insufficient, and the film is whitened (generation of microcracks) and ruptured in the can manufacturing process accompanied by large deformation. Occurs.

As for (B), since it is an amorphous or extremely low crystalline aromatic polyester film, it has good moldability, but it is inferior in aroma retention, and printing after can making and retort sterilization treatment. After treatment such as the above, and further storage for a long period of time, the film is liable to become brittle, and there is a possibility that the film is deteriorated by a shock from the outside of the can.

Further, in a polyester film, its slipperiness and abrasion resistance are major factors affecting the workability of the film manufacturing process and the processing process in each application, and further the quality of the product.

That is, for example, if the slipperiness is insufficient, wrinkles are generated in the film winding process, and in the case of metal can applications, for example, wrinkles are generated during lamination on a metal plate due to lack of slipperiness. In addition, lack of abrasion resistance during drawing during can making causes pinholes and, in extreme cases, breaks the film, so that the inner and outer surfaces of the metal can are not covered.

Generally, the slipperiness of a magnetic recording film,
In order to improve the abrasion resistance, a method of reducing the contact area with a roll, a processing tool or the like by adding inactive fine particles to give unevenness to the film surface is taken.
In general, the larger the size of the fine particles in the raw material polymer, the greater the effect of improving the slipperiness.

For example, it has been frequently practiced to add, as the inert fine particles, one kind or two or more kinds (combination of large particles and small particles) of calcium carbonate, titanium oxide, kaolin, etc. 51-34272, JP-A-52-78953, JP-A-52-78954, JP-A-53-41355, and JP-A-53-71154).

However, in a process involving large deformation such as drawing in metal can forming, as the size of the fine particles increases, voids formed at the boundary between the fine particles and polyester increase during the deformation. , The shape of the protrusions becomes gradual, the friction coefficient during processing is increased, and particles are also dropped due to small scratches (scratches) on the voids of the polyester film generated during processing, causing pinholes and film breakage. The problem arises that

[0012]

The object of the present invention is to improve the taste retention and impact resistance while maintaining the excellent molding processability, heat resistance and retort resistance of the copolyester film. Another object of the present invention is to provide a polyester film for metal sheet laminating and forming, which is unlikely to be cracked by impact at low temperatures.

[0013]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to achieve the above object, and as a result, found that a film was prepared from a copolymerized polyester containing ethylene terephthalate as a main repeating unit and a butylene terephthalate as a main repeating unit. By using a germanium catalyst as a polycondensation catalyst for the copolyester and specifying a lubricant to be added to each of the two layers, the taste-preserving property is improved. The inventors have found that the impact resistance at low temperatures is remarkably improved and completed the present invention.

That is, in the present invention, the average particle size (d _A ) is 0.
It contains 0.01 to 3% by weight of lubricant A having a particle diameter of 05 μm or more and less than 0.6 μm, and 0.001 to 0.2% by weight of lubricant B having an average particle size (d _B ) of 0.3 μm or more and 2.5 μm or less, Moreover, the ratio (d _B / d _A ) of the average particle size (d _A ) of the lubricant _A and the average particle size (d _B ) of the lubricant B is 2.5 or more, and the melting point is 2
10 to 245 ° C, a glass transition temperature of 60 ° C or higher,
A copolyester layer (A) using a germanium compound as a polycondensation catalyst, and a copolyester using a germanium compound as a polycondensation catalyst with ethylene terephthalate having a melting point of 210 to 245 ° C as a main repeating unit (I) ) 80-45% by weight and melting point 180-22
A polyester composition containing 20 to 55% by weight of a polyester (II) containing butylene terephthalate as a main repeating unit at 3 ° C., and having an average particle diameter (dc) of 0.8.
It is a polyester film for metal sheet laminating and forming, which is formed by laminating a polyester layer (B) containing 0.03 to 0.5% by weight of a lubricant C having a size of from μm to less than 2.5 μm.

In the present invention, a typical example of the copolymerized polyester used as the copolymerized polyester (I) of the copolymerized polyester layer (A) and the polyester layer (B) is copolymerized polyethylene terephthalate. The copolymerization component may be an acid component or an alcohol component. Examples of the acid component include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid and naphthalenedicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and decanedicarboxylic acid, and alicyclic compounds such as cyclohexanedicarboxylic acid. Examples thereof include dicarboxylic acid, and examples of the alcohol component include aliphatic diols such as butanediol and hexanediol, and alicyclic diols such as cyclohexanedimethanol. These may be used alone or in combination of two or more.

The proportion of the copolymerization component depends on the kind thereof, but as a result, the melting point is 210 to 245 ° C., preferably 215.
The ratio is in the range of ˜235 ° C. If the melting point is less than 210 ° C, the heat resistance will be poor. On the other hand, the melting point is 245 ° C.
When it exceeds, the crystallinity of the polymer is too large and the moldability is impaired.

Here, the melting point of the copolymerized polyester is measured by Du Pont Instruments 910.
According to a method of determining a melting peak at a temperature rising rate of 20 ° C./minute using DSC. The sample amount is about 20 mg.

The intrinsic viscosity of the copolyester is preferably 0.52 to 0.80, more preferably 0.54 to 0.70.

In the present invention, the copolyester used as the copolyester (I) of the copolyester layer (A) and the polyester layer (B) is produced by either the direct weight method or the DMT method (transesterification method). In the case of the DMT method, a manganese compound (eg manganese acetate) or a titanium compound (eg titanium acetate, titanium tetrabutoxide, etc.) is preferable as the transesterification catalyst. In the polymerization stage, a germanium compound is used as a polymerization catalyst. Examples of the germanium catalyst are (a) amorphous germanium oxide (b) fine crystalline germanium oxide (c) a solution of germanium oxide dissolved in glycol in the presence of an alkali metal or alkaline earth metal or a compound thereof (d) A solution obtained by dissolving germanium oxide in water is used.

The amount of the germanium compound catalyst is 40 to 40 as the amount of germanium atom remaining in the copolyester.
200 ppm is preferable and 60 to 150 ppm is more preferable.

The above-mentioned copolyester has a methyl terminal concentration in the polyester of preferably 15 eq mol / 10 ⁶ g or less, more preferably 10 eq mol / 10 ⁶ g or less. If the concentration of the methyl end in the polyester is too high, phenomena such as easy generation of white powder from the copolyester during the molding process, or poor taste retention when used in a container are observed.

Further, the copolyester constituting the copolyester layer (A) in the present invention needs to have a glass transition temperature of 60 ° C. or higher, preferably 70 ° C. or higher. If the glass transition temperature is less than 60 ° C,
Satisfactory taste retention cannot be obtained. As such a copolymerized polyester, isophthalic acid copolymerized polyethylene terephthalate is particularly preferable because a copolymerized polyester having a high glass transition temperature can be obtained.

Further, in the present invention, the polyester (II) constituting the polyester layer (B) is a polyester having butylene terephthalate as a main repeating unit, and may be a homopolymer or a copolymer.

The copolymerization component in the copolymer may be an acid component or an alcohol component. Examples of the copolymeric acid component include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid and naphthalenedicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and decanedicarboxylic acid, and fats such as cyclohexanedicarboxylic acid. Examples thereof include cyclic dicarboxylic acids, and examples of the copolymerized alcohol component include aliphatic diols such as ethylene glycol and hexanediol, and alicyclic diols such as cyclohexanedimethanol. These may be used alone or in combination of two or more.

The proportion of the copolymerization component depends on the kind, but as a result, the melting point is 180 to 223 ° C., preferably 200.
〜223 ° C., and more preferably 210 to 223 ° C. If the melting point is less than 180 ° C, the heat resistance will be poor. The melting point of the polybutylene terephthalate homopolymer is 223 ° C.

The melting point of this polyester is also measured in the same manner as the measurement of the copolyester described above by Du Pont.
Performed using Instruments 910 DSC.

In the polyester film of the present invention,
The polyester layer (B) contains 80 to 45% by weight of a copolymerized polyester (I) having ethylene terephthalate as a main repeating unit and a melting point of 210 to 245 ° C., and a melting point of polybutylene terephthalate or butylene terephthalate as a main repeating unit of 180. It is necessary to comprise 20 to 55% by weight of the copolyester (II) at 223 ° C. When polybutylene terephthalate or polybutylene terephthalate copolyester (II) is less than 20% by weight and polyethylene terephthalate copolyester (I) exceeds 80% by weight, impact resistance at low temperature cannot be improved. . When the polybutylene terephthalate or polybutylene terephthalate copolyester (II) exceeds 55% by weight and the polyethylene terephthalate copolyester (I) is less than 45% by weight, the heat resistance of the film decreases and the impact resistance Will be insufficient.

In the present invention, the copolyester used in the copolyester (I) of the copolyester layer (A) and the polyester layer (B) and the polyester used in the polyester (II) of the polyester layer (B) are , The manufacturing method is not limited.
For example, in the case of a copolyester having ethylene terephthalate as a main repeating unit, terephthalic acid, ethylene glycol and a copolymerization component are subjected to an esterification reaction,
Then, the obtained reaction product is subjected to a polycondensation reaction to obtain a copolyester, or dimethyl terephthalate,
A method in which ethylene glycol and a copolymerization component are subjected to a transesterification reaction and then the resulting reaction product is subjected to a polycondensation reaction to obtain a copolymerized polyester is preferably used. In the production of each copolyester and polybutylene terephthalate, other additives such as an antioxidant, a heat stabilizer, an ultraviolet absorber and an antistatic agent may be added, if necessary.

In the present invention, the copolyester constituting the copolyester layer (A) has an average particle size (d _A ) of 0.05 μm or more and less than 0.6 μm, preferably 0.08 to 0.5 μm. , And more preferably 0.1 to 0.
4 μm of lubricant A (small particle lubricant) in an amount of 0.01 to 3% by weight,
Preferably 0.1 to 1.0% by weight, more preferably 0.1.
2 to 0.5 and containing by weight%, further the average particle size (d _B) is 0.
3 μm or more and 2.5 μm or less, preferably 0.5 to 2.0
[mu] m, more preferably 0.6-1.8 [mu] m of lubricant B (large particle lubricant), 0.001-0.2% by weight, preferably 0.002-0.1% by weight, more preferably 0.005%.
~ 0.05% by weight.

The average particle size (d _A ) of the small particle lubricant is 0.05.
When it is less than μm, the effect of improving the slipperiness is insufficient, and the winding property deteriorates in the film manufacturing process, which is not preferable. When the average particle size (d _A ) exceeds 0.6 μm, the portion deformed by processing such as deep drawing can is
Coarse particles (for example, particles of 10 μm or more) are the starting points,
This is not preferable because it causes pinholes and sometimes breaks.

If the content of the small particle lubricant is less than 0.01% by weight, the effect of improving the slipperiness is insufficient, while 3
If it exceeds 5% by weight, the film often breaks, which is not preferable.

Further, in the present invention, the large particle lubricant is contained in the copolyester together with the small particle lubricant, whereby the slipperiness can be further improved. When the average particle size of this large particle lubricant is less than 0.3 μm,
Sliding property cannot be further improved, while 2.5 μm
If it exceeds, when it is deformed by deep drawing, particles fall off, pinholes are formed, or the film is broken, resulting in poor abrasion resistance.

The content of the large particle lubricant is 0.001
If the amount is less than%, the slipperiness does not change from the case of using only small particle lubricant,
If it exceeds 0.2% by weight, abrasion resistance deteriorates, so it is not suitable.
Is. Furthermore, the average particle size (d_A) And large grains
Average particle size of lubricant (d_B) Ratio (d_B/ D_A) Is 2.5
Or more, preferably 3.0 or more. Average particle size ratio (d _B
/ D_AIs less than 2.5, slipperiness due to addition of large-particle lubricant
The improvement effect does not appear. Lubricants used in the present invention
Both small-particle lubricants and large-particle lubricants include inorganic and organic lubricants.
However, the inorganic type is preferable. Inorganic lubricant
As silica, alumina, titanium dioxide, calcium carbonate
Examples include sium and barium sulfate, and as an organic lubricant
Examples include silicone resin particles and cross-linked polystyrene particles
it can.

These lubricants can be used alone or in combination of two or more. Also,
Other lubricants can be added as required.

In particular, the small particle and large particle lubricants which are preferable in terms of pinhole resistance have a particle size ratio (major axis / minor axis) of 1.0 to.
A monodispersed lubricant of 1.2. Examples of such lubricant include true spherical silica, true spherical tatin dioxide, true spherical silicone resin particles, and true spherical crosslinked polystyrene particles.

Here, the average particle diameter and particle diameter ratio of the spherical monodisperse lubricant are as follows. First, a metal is vapor-deposited on the surface of the particle, and then the image is magnified 10,000 to 30,000 times with an electron microscope. It is calculated by obtaining the minor axis and the area equivalent circle diameter, and then applying these to the following equation.

Average particle size = total sum of area-circle equivalent diameters of measured particles / number of measured particles Particle size ratio = average major axis of particles / average minor axis of the particles Further, the spherical lubricant particles have a sharp particle size distribution. Is preferable, and the relative standard deviation representing the steepness of the distribution is 0.5.
Hereafter, it is preferably 0.3 or less.

This relative standard deviation is expressed by the following equation (Equation 1).

[0039]

[Equation 1]

In the present invention, the polyester composition constituting the polyester layer (B) has an average particle diameter (d
c) is 0.8 μm or more and less than 2.5 μm, preferably 1.
The lubricant C of 0 to 2.3 μm is contained in an amount of 0.03 to 1.0% by weight, preferably 0.05 to 0.5% by weight.

When the average particle diameter (dc) of the lubricant C is less than 0.8 μm, the slipperiness is insufficient and the winding property is deteriorated in the film manufacturing process, which is not preferable. Further, when the average particle diameter (dc) exceeds 2.5 μm, coarse particles serve as a starting point in a portion deformed by processing such as deep drawing can making pin holes or breaking the film, which is not preferable. .

If the content of the lubricant C is less than 0.03% by weight, the lubricity is insufficient. On the other hand, if it exceeds 1.0% by weight, the film is broken by the processing such as deep drawing can manufacturing. It is not preferable because it occurs frequently.

Further, the lubricant C may be inorganic or organic, but is preferably inorganic. Examples of the inorganic lubricant include silica, alumina, titanium dioxide, calcium carbonate, barium sulfate and the like, and examples of the organic lubricant include silicone resin particles and crosslinked polystyrene particles.

These lubricants may be used alone or in combination of two or more. Also,
Other lubricants can be added as required.

Particularly preferred in view of pinhole resistance is a lubricant having the same particle diameter ratio (major axis / minor axis) of 1 as the above-mentioned lubricant as a lubricant for the copolymerized polyester constituting the copolymerized polyester layer (A). It is a monodispersed lubricant having a value of 0 to 1.2.

As a means for incorporating a lubricant into the (copolymerized) polyester, a conventionally known means can be used and is not particularly limited, but a method of adding a lubricant during the production of the (copolymerized) polyester is preferable.

In the production of the polyester film of the present invention, first, the (copolymerized) polyester is melt extruded. At this time, the above-mentioned polyester is made to contain a lubricant so that a predetermined lubricant content is obtained, or a predetermined amount is used at the time of extrusion. It is possible to employ a method of blending the amounts of and extruding.

In the present invention, by incorporating the above-mentioned small particle lubricant and large particle lubricant in the copolyester, the lubricant particles do not fall off even if they are greatly deformed (deep drawing process) during can making, and the resistance is improved. Since a polyester film having good scraping property can be obtained, when it is contained in a homopolyester such as polyethylene terephthalate, the slipping property is improved, but the scraping resistance is not improved.

The polyester film of the present invention has a structure in which the copolyester layer (A) and the polyester layer (B) are laminated, and the film having such a two-layer structure constitutes each layer, for example. Melting the copolyester and the polyester composition separately, coextruding, after laminating and fusion bonding before solidification, biaxial stretching, heat setting method, the copolyester and the polyester composition are separately melted and extruded It can be produced by a method of forming a film, unstretched or stretched, and then laminating and fusing both.

When the polyester film is composed only of the copolyester layer (A), the impact resistance at low temperature becomes insufficient, and conversely, when it is composed only of the polyester layer (B), it is not protected. It is not suitable because it deteriorates the taste and rust resistance.

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 tends to occur during processing, while if it exceeds 75 μm, it is uneconomical because of excessive quality.

Thickness T of Copolyester Layer (A)
The ratio of the _A, and the thickness T _B of the polyester layer (B) (T _A /
T _B ) is preferably about 0.02 to 0.67, more preferably 0.04 to 0.43, and particularly preferably 0.04.
˜0.25. Specifically, for example, the thickness is 25 μm
In case of polyester film, polyester layer (B)
Has a thickness of 0.5 to 10 μm, preferably 1 to 7.5 μm
m, and more preferably 1 to 5 μm.

The plane orientation coefficient of the copolyester layer (A) of the film of the present invention is 0.08 or more and 0.16 or less, more preferably 0.09 or more and 0.15 or less, and particularly 0.10 or more and 0. It is preferably 14 or less. If the plane orientation coefficient of the film is less than 0.08, problems such as cracking may occur when the deep drawing ratio in deep drawing becomes high, which is not preferable. On the other hand, if the plane orientation coefficient exceeds 0.16, fracture occurs during deep drawing, making deep drawing itself impossible.

Here, the plane orientation coefficient is defined by the following formula.

[0055]

## EQU00002 ## f = [(nx.times.ny) / 2] -nz In the above formula, f: plane orientation coefficient, nx, ny, nz:
These are the refractive indices in the horizontal, vertical and thickness directions of the film, respectively. The refractive index 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 ray. Methylene iodide was used as the mount solution, and the measurement temperature was 25 ° C.

The polyester film of the present invention has a heat shrinkage ratio at 150 ° C. of 10% or less, further 7%.
It is particularly preferably 6% or less.

Here, the heat shrinkage rate was 15 at the room temperature with 15 mark points on the sample film (at intervals of about 10 cm).
It is kept in a hot air circulation type oven at 0 ° C for 30 minutes, then returned to room temperature and the interval between the above-mentioned mark points is measured to obtain the difference before and after the temperature is kept at 150 ° C, and before the temperature is kept at 150 ° C. It is calculated from The heat shrinkage rate in the longitudinal direction of the film is representative.

Heat shrinkage of polyester film (150
(° C) exceeds 10%, dimensional shrinkage is large when laminated on a metal plate, and defects such as wrinkles are formed in the film.
Not preferable. This heat shrinkage rate is 10% or less, further 7%
Below, particularly, if it is 6% or less, there are few defects such as wrinkles in the film when laminated to a metal plate, and good results can be obtained.

The above-mentioned plane orientation coefficient and thermal shrinkage (15
In order to obtain a polyester film satisfying 0 ° C.), for example, in the sequential biaxial stretching, the longitudinal stretching ratio is 2.5 to 3.
From the range of 6 times, the transverse stretching ratio is from 2.7 to 3.6 times, and the heat setting temperature is from 150 to 220 ° C., preferably 16
It may be carried out by selecting from the range of 0 to 200 ° C. and combining them.

As the metal plate to which the polyester film of the present invention is stuck, particularly the metal plate for can making, tin, tin-free steel, aluminum, etc. are suitable.
The polyester film can be attached to the metal plate by the following method, for example.

The metal plate is heated to a temperature equal to or higher than the melting point of the film, the films are laminated and then rapidly cooled, and the surface layer portion (thin layer portion) of the film that is in contact with the metal plate is made amorphous and brought into close contact.

An adhesive layer is coated on the film with a primer in advance, and this surface is attached to a metal plate. As the adhesive layer, a known resin adhesive, for example, an epoxy adhesive,
Epoxy-ester adhesives, alkyd adhesives and the like can be used.

When the polyester film of the present invention is attached to a metal plate, in order to improve impact resistance,
It is preferable that the polyester layer (B) is laminated on the side that receives the impact. For example, when the polyester film of the present invention is attached to the inside of a can, the polyester layer (B) may be attached to the can.

Further, in the polyester film of the present invention, both polyester layers (A),
Other additional layers may be laminated between (B) or on one side.

[0066]

EXAMPLES The present invention will be further described below with reference to examples.

[0067]

[Examples 1 to 8 and Comparative Examples 1 to 8] Average particle size is 0.2μ
0.4% by weight of titanium dioxide with an average particle size of 1.3μ
m spherical silica (particle size ratio 1.07, relative standard deviation 0.
1) 0.01% by weight, copolymerized polyethylene terephthalate obtained by copolymerizing the components shown in Table 1 (using tetrabutyl titanate as an ester exchange catalyst and germanium oxide as a polycondensation catalyst, an intrinsic viscosity of 0.64) The copolyester layer (A) and the polyester composition shown in Table 1 (containing, as a lubricant, true spherical silica having an average particle size of 1.5 μm and a particle size ratio of 1.1) as the polyester layer (B). So that each is dried separately by a conventional method,
After being melted, they were coextruded from dies adjacent to each other, laminated, fused and rapidly cooled and solidified to prepare an unstretched film.

Next, this unstretched film was longitudinally stretched at 110 ° C. to 3.0 times, and then transversely stretched at 125 ° C. to 3 times,
Heat treatment was performed at 190 ° C. to obtain a biaxially oriented laminated film.

The thickness of the obtained film was 25 μm, and the thicknesses of the copolyester layer (A) and the polyester layer (B) were 5 μm and 20 μm, respectively.

[0070]

[Table 1]

[0071]

[Example 9 and Comparative Examples 9 to 11] The average particle size is 0.3 μm.
True spherical silica (particle size ratio 1.1, relative standard deviation 0.1)
Of 0.3% by weight and 0.05% by weight of spherical silica (particle size ratio 1.1, relative standard deviation 0.1) having an average particle size of 0.5 μm, and the components shown in Table 2 are copolymerized. The copolymerized polyethylene terephthalate formed is a copolymerized polyester layer (A),
Similarly, each of the polyester compositions shown in Table 2 is separately dried by a conventional method so as to form the polyester layer (B),
After being melted, they were coextruded from dies adjacent to each other, laminated, fused and rapidly cooled and solidified to prepare an unstretched film.

Next, this unstretched film was longitudinally stretched at 110 ° C. to 3.0 times, transversely stretched at 125 ° C. to 3.1 times and heat-set at 180 ° C. to obtain a biaxially oriented laminated film. .

The thickness of the obtained film was 25 μm, and the thicknesses of the copolyester layer (A) and the polyester layer (B) were 5 μm and 20 μm, respectively.

[0074]

[Table 2]

[0075]

Examples 10 to 25 and Comparative Examples 12 to 19 Biaxially oriented films were prepared by changing the kind, particle size and content of the lubricant as shown in Table 3 in Example 2.

[0076]

[Table 3]

[0077]

[Comparative Examples 20 to 21] In Example 10, the copolyester layer (A) (Comparative Example 2) was used without forming a two-layer laminated structure.
0) and a polyester layer (B) (Comparative Example 21) only were prepared as monolayer films.

A total of 46 types of films obtained in Examples 1 to 25 and Comparative Examples 1 to 21 were laminated on both sides of 0.25 mm thick tin-free steel heated at 250 ° C.,
After cooling with water, it was cut into a disk shape having a diameter of 150 mm, and deep drawing was performed in four steps using a drawing die and a punch to prepare a side surface seamless container (hereinafter abbreviated as a can) having a diameter of 55 mm.

The following observations and tests were carried out on the cans, and the cans were evaluated according to the following standards.

(1) Deep drawing processability-1 ○: The film was processed without any abnormality, and no whitening or breakage was observed in the film. Δ: Whitening is observed at the top of the film can. X: Film breakage is observed in a part of the film.

(2) Deep drawing workability-2 ○: Processed without any abnormality, rust prevention test of film surface in can (1% NaCl water was put in the can, an electrode was inserted, and the can body was used as an anode. The current value when a voltage of 6 V is applied is measured.
Hereinafter, it is less than 0.1 mA in the ERV test. X: There is no abnormality in the film, but the current value is 0.1 mA or more in the ERV test, and pinhole-like cracks originating from the coarse lubricant are observed in the film when the energized portion is enlarged and observed.

(3) Impact resistance With respect to cans having good deep drawing, water was fully poured and after cooling to 10 ° C., 10 pieces for each test were set to a height of 50 cm.
After dropping it to the PVC tile floor surface, the result of the in-can ERV test was ◯: 0.1 mA or less for all 10 pieces. (Triangle | delta): It was 0.1 mA or more about 1-5 pieces. X: 0.1 mA or more for 6 or more, or cracks of the film were already observed after dropping.

(4) Heat embrittlement resistance After the cans that had been well-formed by deep drawing were heated and held at 200 ° C. for 5 minutes, the impact resistance evaluation described in (3) was performed. Was 0.1 mA or less. (Triangle | delta): It was 0.1 mA or more about 1-5 pieces. X: 0.1 mA or more for 6 or more or cracks were already observed in the film after heating at 200 ° C. for 5 minutes.

(5) Retort resistance A can with good deep-drawing was filled with water, retorted at 120 ° C. for 1 hour in a steam sterilizer, and then stored at 50 ° C. for 30 days. Ten of the obtained cans were dropped from the height of 30 cm for each test on the PVC tile floor surface, and then an ERV test in the cans was performed. ◯: 0.1 mA or less for all 10 pieces. (Triangle | delta): It was 0.1 mA or more about 1-5 pieces. ×: 0.1 mA or more for 6 or more, or cracks of the film were already observed after dropping.

(6) Taste retention A can which was well formed by deep drawing was filled with a cider and sealed. After holding at 37 ° C. for 30 days, the can was opened and the change in taste was examined by sensory test. ◯: There was no change in taste. Δ: A slight change in taste was observed. X: A change in taste was recognized.

The evaluation results and winding properties of the above 46 kinds of films are shown in Table 4.

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[Table 4]

As is clear from the results in Table 4, the can using the polyester film of the present invention is excellent in deep-drawing workability, heat embrittlement resistance, and retort resistance, and at the same time, has taste retention and impact resistance. Excellent impact resistance especially at low temperature.

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INDUSTRIAL APPLICABILITY The polyester film for laminating and molding metal plates according to the present invention has excellent moldability, heat resistance and retort resistance, as well as taste retention and impact resistance, especially impact resistance at low temperatures. The properties are remarkably improved and the rust resistance is also good.
Therefore, it is particularly suitable for being stuck to a metal can that is often cooled and handled at a low temperature such as for juice or soft drink.

Front page continued (72) Inventor Takafumi Kudo 3-37-19 Koyama, Sagamihara City, Kanagawa Teijin Limited Sagamihara Research Center

Claims (1)

[Claims] 1. _A lubricant A having an average particle size (d _A ) of 0.05 μm or more and less than 0.6 μm is 0.01 to 3% by weight, and an average particle size (d _B ) is 0.3 μm or more and 2.5 μm or less. The lubricant B is contained in an amount of 0.001 to 0.2% by weight, and the ratio of the average particle diameter (d _A ) of the lubricant _{A to} the average particle diameter (d _B ) of the lubricant B (d _B / d)
_A ) is 2.5 or more, and the melting point is 210 to 245.
C., a glass transition temperature of 60.degree. C. or higher, a copolymerized polyester layer (A) using a germanium compound as a polycondensation catalyst, and ethylene terephthalate having a melting point of 210 to 245.degree. A polyester composition in which 80 to 45% by weight of a copolyester (I) containing a germanium compound and 20 to 55% by weight of a polyester (II) having a melting point of 180 to 223 [deg.] C. butylene terephthalate as a main repeating unit are blended. And a polyester layer (B) containing 0.03 to 0.5% by weight of a lubricant C having an average particle size (dc) of 0.8 μm or more and less than 2.5 μm. Polyester film for laminating and forming boards.