JPH05320377A - Polyester film for metallic plate cladding processing - Google Patents

Abstract

PURPOSE:To obtain the film having specific characteristics, excellent in forming processability and heat resistance, capable of giving e.g. metallic cans with good scent holding ability by incorporating metal salt fine particles as lubricant in a composition comprising a copolyester and a polyester. CONSTITUTION:The film can be obtained by incorporating (A) a polyester composition comprising (1) 99-60wt.% of a copolyester 210-245 deg.C in melting point with the main recurring unit being ethylene terephthalate unit and (2) 1-40wt.% of a polyester 180-223 deg.C in melting point with the main recurring unit being butylene terephthalate with (B) 0.005-3wt.% of fine particles of terephthalic acid metal salt or alkylene terephthalate component-contg. metal salt 0.05-2.5mum in mean diameter [e.g. a compound of formula I or II (n is 0-3)]. This film has the following characteristics: (a) planar orientation coefficient: 0.08-0.16; (b) thermal shrinkage rate at 150 deg.C: <=10%; and (c) density: <1.385g/cm<3>.

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 forming and laminating metal plates, and more specifically, it shows excellent forming processability when it is laminated with a metal plate to perform can-making processing such as drawing and heat resistance. Metal can with excellent fragrance and aroma retention,
For example, the present invention relates to a polyester film for laminating and forming metal plates which can be used for producing beverage cans, food cans and the like.

[0002]

2. Description of the Related Art Metal cans are generally painted to prevent corrosion on the inner and outer surfaces, 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 laminating a thermoplastic film on a metal plate such as tin plate, tin-free steel, aluminum or the like and then making a can is under way.
Polyolefin and polyamide films have been tried as this thermoplastic resin film, but the moldability, heat resistance,
Not all of the fragrance-retaining properties are satisfied.

Therefore, a polyester film, especially a polyethylene terephthalate film, has attracted attention because of its well-balanced characteristics, and several proposals based on this have been made. That is, (A) a biaxially oriented polyethylene terephthalate film is laminated on a metal via an adhesive layer of low melting point polyester and used as a can-making material (JP-A-56-10451).
No. 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-2-573).
39). (C) A low orientation, heat-set, biaxially oriented polyethylene terephthalate film that is heat-fixed is laminated on a metal plate and used as a can-making material (Japanese Patent Laid-Open No. 64-22530). (D) A copolymerized polyester film having a specific plane orientation coefficient, heat shrinkage ratio, and density is laminated on a metal plate and used as a can-making material (JP-A-3-86729).

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

Regarding (A), the biaxially oriented polyethylene terephthalate film is excellent in heat resistance and aroma retention,
Molding processability is insufficient, and whitening of the film (generation of microcracks) and breakage occur in the can-making process involving large deformation.

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.

Regarding (C), although it is intended to exert its effect in the intermediate region between the above (A) and (B), it has not yet reached the low orientation applicable to can manufacturing, and Since the isotropy of the film surface is not guaranteed, when omnidirectional deformation is performed as in can-making processing (deep drawing processing), moldability may be insufficient in a specific direction of the film.

Regarding (D), when used in a can to which internal pressure is applied, the film is easily broken by an impact from the outside of the can, so that a can of excellent quality may not be obtained.

Further, in the 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, in order to improve the abrasion resistance of a film, a method of reducing the contact area with a roll, a processing tool or the like by giving unevenness to the film surface is roughly classified into (i) the film. There are used a method of precipitating inactive fine particles from a polymer catalyst residue used as a raw material and a method (ii) of adding inactive inorganic fine particles. In general, the larger the size of the fine particles in the raw material polymer, the greater the effect of improving the slipperiness.

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 the polyester become large. , The shape of the protrusions becomes gradual, the friction coefficient at the time of processing is increased, and particles are dropped due to small scratches (scratches) on the voids of the polyester film generated during processing, causing pinholes and film breakage. Becomes
Therefore, the unevenness of the film surface needs to be as fine as possible, and under the present circumstances, there is a demand for simultaneously satisfying these contradictory characteristics.

As the inert fine particles, it has been often practiced to add one kind or two or more kinds (combination of large particles and small particles) of calcium carbonate, titanium oxide, kaolin and the like (JP-A-51-51). 34272, JP-A-52-78953, JP-A-52-78954, JP-A-53-41355, JP-A-53-71154, etc.), but since these fine particles form large voids, The problem is inherent. In addition, the precipitated particles (for example, polyester oligomer metal salt) precipitated during the production of polyester have small voids and good shaving property, but have drawbacks such as poor scratch resistance.

[0014]

DISCLOSURE OF THE INVENTION The present inventor has solved these inconveniences, the voids around the inert fine particles are small, and the film surface is appropriately roughened to improve the slipperiness and abrasion resistance of the film. The present invention has been achieved as a result of intensive research to develop a polyester film suitable for can manufacturing.

[0015]

That is, according to the present invention, a copolymerized polyester (I) 99-60 containing ethylene terephthalate having a melting point of 210-245 ° C. as a main repeating unit.
Polyester (II) 1 containing mainly butylene terephthalate having a weight% and a melting point of 180 to 223 ° C. as a main repeating unit
A polyester composition blended with 40% by weight,
The polyester composition has an average particle size of 0.05 to 2.5 μ.
m of terephthalic acid metal salt or metal salt containing alkylene terephthalate component is added in an amount of 0.005 to 3% by weight, and the plane orientation coefficient of the film is 0.08 to 0.
16. A polyester film for metal sheet laminating and forming, which has a heat shrinkage ratio at 10% or less at 16, 150 ° C. and a density of less than 1.385 g / cm ³ .

In the present invention, the copolyester (I)
Is a copolyester having ethylene terephthalate as a main repeating unit, and the copolymerization component may be an acid component or an alcohol component. Examples of the copolymerization component include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid and 2,6-naphthalenedicarboxylic acid; aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and decanedicarboxylic acid; cyclohexanedicarboxylic acid. Examples thereof include alicyclic dicarboxylic acids and the like, and examples of the copolymerization alcohol component include aliphatic diols such as butanediol and hexanediol, and alicyclic diols such as cyclohexanedimethanol. These are alone or 2
More than one species can be used.

The proportion of the copolymerization component depends on its kind, but as a result, the melting point of the polymer is 210 ° C. to 245 ° C., preferably 215 to 240 ° C., more preferably 220 to 240 ° C.
The ratio is in the range of 235 ° C. Polymer melting point is 21
If the temperature is lower than 0 ° C, the heat resistance is poor, and thus heating after printing after can-making cannot be endured. 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.

Further, in the present invention, polyester (II)
Is a polyester containing 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 copolymerization component include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid; aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid; and cyclohexanedicarboxylic acid. Examples thereof include alicyclic 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 thereof, but as a result, the melting point of the polymer is 180 ° C to 223 ° C, preferably 200 to 223 ° C, more preferably 210 to 210 ° C.
It is a ratio in the range of 223 ° C. Polymer melting point is 18
If the temperature is lower than 0 ° C, the heat resistance is inferior, and therefore, it cannot withstand the heating during printing after can making. The melting point of the polybutylene terephthalate homopolymer is 223 ° C.

Here, the melting point of polyester is measured by Du
Pont Instruments 910 DSC
And a melting peak at a temperature rising rate of 20 ° C./min. The sample amount is about 20 mg.

Copolyester (I) in the present invention
The polyester (II) and the polyester (II) are not limited by their manufacturing methods. For example, a method of subjecting terephthalic acid, ethylene glycol and a copolymerization component to an esterification reaction, and then subjecting the resulting reaction product to a polycondensation reaction to form a copolymerized polyester, or a transesterification reaction of dimethyl terephthalate, ethylene glycol and a copolymerization component. Then, the resulting reaction product is subjected to a polycondensation reaction to obtain a copolyester, which is preferably used. In the production of polyester, other additives such as antioxidants, heat stabilizers, ultraviolet absorbers and antistatic agents may be added, if necessary.

The polyester composition in the present invention is a composition in which 99-60% by weight of the copolyester (I) and 1-40% by weight of the polyester (II) are blended. When the content of the copolymerized polyester (I) is more than 99% by weight and the content of the polyester (II) is less than 1% by weight, when the film is used for a can to which internal pressure is applied, the film is easily cracked by an impact from the outside of the can and has excellent quality. Can't get Further, the copolymerized polyester (I) is less than 60% by weight, and the polyester (II) is
If it exceeds 40% by weight, the heat resistance of the film decreases and the impact resistance becomes insufficient.

The polyester composition of the present invention has an average particle size of 0.05 to 2.5 μm, preferably 0.1 to 2.25.
Further, fine particles of a metal salt of terephthalic acid or a metal salt containing an alkylene terephthalate component having a thickness of μm, more preferably 0.3 to 2.0 μm are additionally contained. If the average particle size is less than 0.05 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 exceeds 2.5 μm, coarse particles (for example, particles of 10 μm or more) in a portion deformed by processing such as deep drawing can are used as a starting point to generate pinholes or, in some cases, break. Therefore, it is not preferable.

Specific examples of such metal salt particles include:

[0025]

[Chemical 1]

[0026]

[Chemical 2]

[0027]

[Chemical 3]

[0028]

[Chemical 4]

[0029]

[Chemical 5]

[0030]

[Chemical 6]

Examples include the following: Preferable examples of the metal forming the metal salt fine particles include alkali metals and alkaline earth metals.

The metal salt fine particles are not limited by the manufacturing method. As a typical example, a production example of calcium terephthalate particles will be described. An aqueous solution of terephthalic acid was added to an aqueous solution of calcium chloride to precipitate calcium terephthalate, the calcium terephthalate was separated, washed with water and dried, and then anhydrous calcium terephthalate was added. Is dispersed in glycol such as ethylene glycol to form a slurry, and the slurry is subjected to a conventional particle size adjusting treatment, for example, pulverizing treatment and classification treatment to obtain a glycol slurry in which calcium terephthalate having a predetermined average particle diameter is dispersed. You can Further, particles of an ethylene terephthalate component, or particles of a metal salt containing the same and a phosphorus component can be produced by a known method for preparing internally precipitated particles, but the production of these particles is different from the system for producing the polyester in the present invention. System.

The amount of lubricant added to the polyester composition is
It is necessary to make it 0.005 to 3.0% by weight, preferably 0.01 to 1.0% by weight, more preferably 0.05.
Is 0.5% by weight. This addition amount is 0.005% by weight
When it is less than 3.0, the effect of improving the slipperiness is insufficient, while 3.0
If it exceeds 5% by weight, the film often breaks, which is not preferable. In addition, other lubricants may be added if necessary.

Means known in the art can be used as a means for incorporating a lubricant into the polyester composition, and it is not particularly limited, but a lubricant may be used during the production of the copolyester (I) and / or the polyester (II). The method of addition is preferred.

In the production of the polyester film of the present invention, the copolyester (I) and the polyester (II) are each mixed in a predetermined amount and melt-extruded. At this time, the above polyester is mixed so as to have a predetermined lubricant content. Either one or both of them may be added with a lubricant, or a method of blending a predetermined amount at the time of extrusion and extruding may be employed.

In this way, the film is extruded from the melt extrusion die to form a film, and then biaxially stretched and heat set to obtain a biaxially oriented film. The plane orientation coefficient of this film is 0.08 or more and 0.16 or less, preferably more than 0.09 and 0.15 or less, and more preferably more than 0.10 and 0.1.
It must be 4 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 surface 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.

F = [(nx + 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 further has a heat shrinkage ratio at 150 ° C. of 10% or less, preferably 7%.
% Or less, particularly preferably 6% or less, and the density is less than 1.385 g / cm ³ , preferably 1.380 to
1.350 g / cm ³ , more preferably 1.375 to
It is required to be 1.355 g / cm ³ .

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

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

The above-mentioned plane orientation coefficient and thermal shrinkage (150
C) and a polyester film satisfying the density, for example, in the sequential biaxial stretching, the longitudinal stretching ratio is 2.
From the range of 5 to 3.6 times, the transverse stretching ratio is 2.7 to 3.6.
It is advisable to select the heat setting temperature from the range of 150 to 220 ° C., preferably 160 to 200 ° C. from the double range and combine them.

The object of the present invention is achieved only when all of the above five conditions of the blending ratio of polyester, melting point, surface orientation coefficient, thermal shrinkage (150 ° C.) and density are satisfied. For example, with polyethylene terephthalate homopolymer, sufficient deep drawing workability at the time of can making cannot be obtained even if the conditions of surface orientation coefficient, heat shrinkage at 150 ° C., and density are satisfied. Further, with the above-mentioned copolymerized polyester (I) alone, particularly in a can to which internal pressure is applied, the can is easily cracked by an impact from the outside of the can, and a product excellent in can quality cannot be obtained.

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, it is uneconomical because of excessive quality.

As the metal plate for can making to which the polyester film of the present invention is laminated, a plate of tin plate, tin-free steel, aluminum or the like is 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 not lower 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 preliminarily coated on the film with a primer, and this surface is bonded 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.

[0049]

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

[0050]

Example 1 and Comparative Example 1 Polyethylene terephthalate-based copolyester copolymerized with an isophthalic acid component containing calcium terephthalate having an average particle size shown in Table 1 (intrinsic viscosity 0.60: polyester (I)) And polybutylene terephthalate (polyester (II)) at a ratio shown in Table 1 to prepare a polyester composition, and the polyester composition is melt extruded at 280 ° C.
It was rapidly cooled and solidified to obtain an unstretched film.

Next, this unstretched film was longitudinally stretched 3.0 times at 90 ° C., further horizontally stretched 3.1 times at 100 ° C., and then heat-set at 180 ° C. to be biaxially oriented with a thickness of 25 μm. I got a film.

The characteristics of this film are shown in Table 1.

[0053]

Example 2 and Comparative Example 2 A polyester composition obtained in the same manner as in Example 1 and Comparative Example 1 was used, except that polyethylene terephthalate copolymerized with a sebacic acid component was used as the polyester (I). A biaxially oriented film was obtained in the same manner as in Example 1 and Comparative Example 1 except that the stretching was performed at 85 ° C. and the transverse stretching was performed at 95 ° C.

The characteristics of the obtained film are shown in Table 1.

[0055]

Comparative Examples 3 and 4 Polyester compositions obtained in the same manner as in Examples 1 and 2 except that kaolin having an average particle size of 1.5 μm was added instead of calcium terephthalate were used. A biaxially oriented film was obtained by the same method as described above. The characteristics of this film are shown in Table 1.

A total of 6 films obtained in Examples 1 and 2 and Comparative Examples 1 to 4 were laminated on both sides of a 0.25 mm thick tin-free steel heated to 230 ° C.,
After cooling with water, cut it into a disk with a diameter of 150 mm, and perform deep drawing in three stages using a drawing die and punch, and create a sideways seamless container (hereinafter abbreviated as a can) with a diameter of 55 mm at a speed of 80 cans per minute or more. did.

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- ○: The film was processed without any abnormality on both the inner and outer surfaces, and no whitening or breakage was observed on the film on the inner and outer surfaces of the can. Δ: Whitening was found on the upper part of the film on the inner and outer surfaces of the can. X: Film breakage is observed in part of the film on the inside and outside of the can

(2) Deep drawability- ○: The inner and outer surfaces were processed without any abnormality, and the rust prevention test of the film surface inside the can (1% NaCl water was put in the can, the electrode was inserted, and the can body was The current value is measured when a voltage of 6 V is applied as an anode, which is 0.1 mA in the ERV test.
Shown below x: There is no abnormality on the inner and outer surfaces, but the current value is 0.
It is 1 mA or more, and pinhole-like cracks originating from the coarse lubricant are observed in the film when the energized portion is enlarged and observed.

Table 1 shows the evaluation results of the above two types. The results in Table 1 show that the films of Examples are excellent in deep drawing workability, impact crack resistance after can making, and heat resistance.

[0061]

[Table 1]

[0062]

EFFECTS OF THE INVENTION The polyester film for laminating and forming a metal plate of the present invention has a deep drawing workability and a post-can making process in forming a metal can by laminating with a metal plate, for example, deep drawing. It has excellent impact resistance and heat resistance and is extremely useful for metal containers.

Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location B29K 67:00 C08L 67:02 8933-4J (72) Inventor Kinji Hasegawa 3-37-19 Oyama, Sagamihara City, Kanagawa Prefecture No. Teijin Limited Sagamihara Research Center (72) Inventor Yoji Murakami 3-37-19 Koyama, Sagamihara City, Kanagawa Teijin Limited Sagamihara Research Center

Claims (1)

[Claims] 1. A copolymerized polyester (I) having a melting point of 210 to 245 ° C. and a main repeating unit of ethylene terephthalate (I), and a polyester (II) having a melting point of 180 to 223 ° C. and a butyrene terephthalate as a main repeating unit. 1 to 40% by weight of the polyester composition, wherein the polyester composition contains fine particles of a metal salt of terephthalic acid or a metal salt containing an alkylene terephthalate component having an average particle diameter of 0.05 to 2.5 μm. 0.005 to 3% by weight is added, the plane orientation coefficient of the film is 0.08 to 0.16, and the heat shrinkage rate at 150 ° C. is 10.
% And a density of less than 1.385 g / cm ³ , a polyester film for metal plate laminating and forming.