JPH05320378A - Polyester film for metal plate laminating process - Google Patents

Abstract

(57) [Abstract] [Purpose] A metal can, such as a beverage can, which exhibits excellent moldability and is excellent in heat resistance and aroma retention when it is laminated with a metal plate and subjected to a drawing process such as drawing. Provided is a polyester film for laminating and forming metal plates, which can be used for manufacturing food cans and the like. [Structure] Copolymerized polyester (I) containing ethylene terephthalate as a main repeating unit having a melting point of 210 to 245 ° C. 99 to 60 wt% and polyester (II) 1 having a butylene terephthalate as a main repeating unit having a melting point of 180 to 223 ° C. -40% by weight of the polyester composition is blended, and the polyester composition has an average particle size of 0.01-2.5 μm and 0.005 of internally precipitated particles.
~ 3% by weight, the film surface orientation coefficient is 0.08 ~
A polyester film for laminating and molding metal plates, which has a heat shrinkage ratio at 0.16 and 150 ° C. of 10% or less and a density of less than 1.385 g / 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 laminating and forming metal plates, and more specifically, it shows excellent formability when it is laminated with a metal plate to perform can-making processing such as drawing and has heat resistance. Metal can with excellent fragrance and aroma 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 surfaces, but recently, for the purpose of simplifying the process, improving hygiene, and preventing pollution, rust prevention without using 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 for making a can by laminating a thermoplastic film on a metal plate such as tin plate, tin-free steel, or aluminum and then drawing it is under study.
Polyolefin and polyamide films have been tried as this thermoplastic resin film, but they have good moldability, heat resistance,
Not all of the fragrance-retaining properties are satisfied.

Therefore, a polyester film, particularly a polyethylene terephthalate film, has attracted attention because of its well-balanced properties, and several proposals based on this have been made. That is, (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 (Japanese Patent Laid-Open No. 56-10451).
No. 1/192546). (B) 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 which 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 a can-making process that involves large deformation.

Regarding (B), since it is an amorphous or extremely low crystalline aromatic polyester film, it has good moldability, but it has poor 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 may deteriorate due to an impact 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, the molding workability may be insufficient in a specific direction of the film when deformation is performed in all directions such as can manufacturing (deep drawing).

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

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 cans, for example, wrinkles are generated during lamination on a metal plate due to lack of slipperiness. In addition, lack of shaving resistance during drawing during can manufacturing causes pinholes, and in extreme cases causes film rupture, which does not serve as a coating for the inner and outer surfaces of a metal can.

In general, in order to improve the abrasion resistance of a film, a method of reducing the contact area between the film and the roll, processing tool, etc. by giving unevenness to the film surface, for example, a method of adding inert inorganic fine particles is used. It is used.
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 polyester are generated during the deformation. It becomes large and the shape of the protrusion becomes gentle, increasing the friction coefficient at the time of processing and causing particles to drop off due to small scratches (scratches) on the voids of the polyester film generated during processing, pinholes and film rupture Cause of. 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, etc. (JP-A-51-51). 34272, JP-A-52-7
8953, JP-A-52-78954, JP-A-53-
No. 41355, JP-A-53-71154, etc.), however, these particles inherently have the above-mentioned problems because they form large voids.

Therefore, as a polyester film which is better in slipperiness and abrasion resistance of the film and is suitable for can manufacturing, fine particles having a higher affinity with polyester than the above-mentioned fine particles and forming no voids around the particles. The development of those containing

[0015]

DISCLOSURE OF THE INVENTION The present inventors have 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.

[0016]

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 0.01 to 2.5 μm.
The content of internally precipitated particles of m is 0.005 to 3% by weight as a lubricant, and the plane orientation coefficient of the film is 0.08 to 0.1.
6. A polyester film for laminating and forming metal plates, which has a heat shrinkage at 10 ° C. of 10% or less 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 the kind thereof, but as a result, the melting point of the polymer is 210 to 245 ° C., preferably 215 to 240 ° C., more preferably 220 to 2 ° C.
It is the ratio in the range of 35 ° C. Polymer melting point is 210
If the temperature is lower than 0 ° C, the heat resistance is inferior, so that it cannot withstand the heating in the printing process after can making. On the other hand, the melting point of the polymer is 245 ° C.
If it exceeds, 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 the like, and examples of the copolymerization 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 to 223 ° C, preferably 200 to 223 ° C, more preferably 210 to 2 ° C.
It is a ratio in the range of 23 ° C. Polymer melting point 180
If the temperature is lower than ℃, the heat resistance is inferior, so that it cannot withstand the heating by printing after can making. The melting point of the polybutylene terephthalate homopolymer is 223 ° C.

The melting point of polyester is measured by Du P
Using ont Instruments 910DSC, heating rate 2 per minute
According to the method of obtaining a melting peak at 0 ° C. 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 reaction product obtained is subjected to a polycondensation reaction to obtain a copolyester, which is preferably used. In the production of polyester, if necessary, other additives such as lubricants, antioxidants, heat stabilizers, ultraviolet absorbers, antistatic agents and the like can also be added.

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 especially for a can to which internal pressure is applied, the film is easily cracked by the impact from the outside of the can and has excellent quality. Can't get When the content of the copolymerized polyester (I) is less than 60% by weight and the content of the polyester (II) exceeds 40% by weight, the heat resistance of the film is lowered and the impact resistance is insufficient.

The polyester composition of the present invention has an average particle size of 0.01 to 2.5 μm, preferably 0.05 to 1.5.
It contains internally precipitated particles that are .mu.m, more preferably 0.1-1.0 .mu.m. If the average particle size is less than 0.01 μm, the effect of improving the slipperiness is insufficient and the winding property deteriorates in the film manufacturing process, which is not preferable. If the average particle size exceeds 2.5 μm, the coarse particles (for example, 10 μm) in the portion deformed by processing such as deep drawing can manufacturing
(particles of m or more) as the starting point, causing pinholes,
It is not preferable because it breaks in some cases.

Such internally deposited particles are produced and deposited from a catalyst residue during the production of polyester and are contained in the polymer. For the inclusion and dispersion, a conventionally known method for forming internally deposited particles is used. You can For example, JP-A-48-61556 and JP-A-51-1.
12860, JP-A-51-115803,
JP-A-53-41355, JP-A-54-9039
The method disclosed in Japanese Patent Publication No. 7 can be used.

The internally deposited particles are preferably formed between the stage when the monomer formation reaction is substantially completed and the initial stage of the polycondensation reaction.

Preferred examples of the catalyst used in the monomer formation reaction and the compound added in this reaction stage include calcium compounds and lithium compounds. Further, examples of components forming the calcium compound and the lithium compound include aliphatic carboxylic acids such as acetic acid, propionic acid and butyric acid; aromatic carboxylic acids such as benzoic acid, p-methylbenzoic acid and naphthoic acid; methyl alcohol. Alcohols such as ethyl alcohol, propyl alcohol and butyl alcohol; glycols such as ethylene glycol and propylene glycol; chlorine and hydrogen. Explaining further, examples of the lithium compound include salts of the above-mentioned aliphatic carboxylic acids, salts of aromatic carboxylic acids, alcoholates, glycolates, chlorides, hydrides and the like.

The formation of the internally precipitated particles is usually carried out by adding a phosphorus compound to the system in which the above compound is present. Examples of the phosphorus compound include phosphoric acid, phosphorous acid, esters thereof (eg, alkyl ester, aryl ester, etc.) and the like. Further, other additives (for example, lithium phosphate) can be used for the generation, particle size, stabilization, etc. of the internally precipitated particles. Among the internally precipitated particles, those containing calcium, lithium and phosphorus have a relatively large particle size, and those containing lithium and phosphorus have a relatively small particle size, so that the composition can be changed depending on the desired particle size. As preferable internal deposit particles, lithium element 0.03 to 5% by weight, calcium element 0.03 to 5% by weight and phosphorus element 0.03 to
Mention may be made of particles containing 10% by weight.

The content of precipitated particles in the polyester composition must be 0.005 to 3.0% by weight, preferably 0.01 to 1.0% by weight. If the addition amount is less than 0.005% by weight, the effect of improving the slipperiness is insufficient, while if it exceeds 3.0% by weight, the film is often broken, which is not preferable. In addition, other lubricants may be added if necessary.

The internally precipitated particles in the present invention can be separated from the polymer by a known method and the particle size, amount, etc. can be determined.

In the internally deposited particles, trace amounts of other metal components, such as zinc, manganese, magnesium, cobalt, or antimony, within a range that does not impair the effects of the present invention,
It may contain germanium, titanium, or the like.

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. A method of precipitating particles on either one or both of the polyesters can be adopted.

In this way, the film is discharged from the melt extrusion die to be formed into 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, more preferably more than 0.10 and 0.1.
It must be 4 or less. If the surface orientation coefficient of the film is less than 0.08, problems such as cracking 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, more 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 1.3
It is required to be 55 g / cm ³ .

Here, the heat shrinkage rate was 150 at room temperature with two marks (intervals of about 10 cm) on the sample film.
Hold in a hot air circulation type oven at ℃ for 30 minutes, then return to room temperature and measure the interval between the gauge points to obtain the difference between before and after temperature holding at 150 ° C. Calculated from the point spacing. 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
When the temperature (° C.) Exceeds 10%, dimensional shrinkage is large when laminated on a metal plate, and defects such as wrinkles on the film occur, which is not preferable. When the heat shrinkage rate is 10% or less, more preferably 7% or less, and especially 6% or less, there are few defects such as wrinkles in the film when laminated on a metal plate, and good results can be obtained.

The above-mentioned plane orientation coefficient and heat shrinkage ratio (150
C.) and density to obtain a polyester film, for example, in 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 to 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 drawability during can making cannot be obtained even when the conditions of the film surface orientation coefficient, the heat shrinkage ratio at 150 ° C., and the 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. 10-75 μm
Is preferred. 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 above the melting point of the film, the films are pasted together and then rapidly cooled, and the surface layer portion (thin film portion) of the film in contact with the metal plate is made amorphous and brought into close contact. The film is pre-coated with the adhesive layer as a primer, and this surface is bonded to the metal plate. As the adhesive layer, known resin adhesives such as epoxy-based adhesives, epoxy-ester-based adhesives, and alkyd-based adhesives can be used.

[0044]

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

[0045]

Example 1 and Comparative Example 1 Dimethyl terephthalate,
To the mixture of dimethyl isophthalate and ethylene glycol, manganese acetate was added as a transesterification catalyst, and lithium acetate and calcium acetate dissolved in ethylene glycol were added, and the transesterification reaction was carried out by a conventional method. Trimethyl phosphate and antimony trioxide as a polymerization catalyst were added and polycondensed by a conventional method to obtain a polyethylene terephthalate copolyester (polyester (I)) having an intrinsic viscosity of 0.60 (o-chlorophenol, 35 ° C.). .. The ratio of the copolymerization component is as shown in Table 1.

The amount of the internally precipitated particles in the obtained polyester (I) was determined by a known particle separation method. The amount of the internally precipitated particles was as shown in Table 1. Further, when the polyester (I) was sandwiched between preparations, melted, and cooled and observed with a microscope, it was found that a large number of particles each having the average particle size shown in Table 1 were present.

This polyester (I) and polybutylene terephthalate (polyester (II)) were blended in the proportions shown in Table 1 to prepare a polyester composition, which was melt extruded at 280 ° C. and rapidly solidified. To obtain an unstretched film. Then, this unstretched film was longitudinally stretched 3.0 times at 90 ° C. and further at 100 ° C. for 3.
After transverse stretching to 1 time, heat set at 180 ° C for thickness 2
A 5 μm biaxially oriented film was obtained.

The characteristics of this film are shown in Table 1.

[0049]

Example 2 and Comparative Example 2 From the polyester composition obtained in the same manner as in Example 1 and Comparative Example 1 except that the polyester (I) obtained by copolymerizing the sebacic acid component in the ratio shown in Table 1 was used. A biaxially oriented film was obtained in the same manner as in Example 1 and Comparative Example 1, except that the longitudinal 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.

[0051]

Comparative Examples 3 and 4 Examples 1 and 2 except that lithium acetate, calcium acetate and trimethyl phosphate were not added when polyester (I) was obtained, and kaolin having an average particle size of 1.5 μm was added instead. A biaxially oriented film was obtained from the same polyester composition as in Example 1 and 2 by the same method. 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., and water-cooled to 150 mm. It was cut into a disk shape having a diameter, and deep drawing was performed in three 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 at a speed of 80 cans per minute or more.

The following observations and tests were carried out on this can, and each was evaluated according to the following criteria.

(1) Deep drawing workability- ○: The inner and outer surfaces of the film were processed without any abnormality, and no whitening or breakage was observed on the inner and outer surfaces of the can. Δ: Whitening is observed on the top and bottom of the film on the inside and outside of the can. X: A film breakage is recognized in a part of the film on the inside and outside of the can.

(2) Deep drawing workability- ○: The inner and outer surfaces were processed without any abnormality, and the rust prevention test of the film in the can (1% NaC1 water was put in the can, the electrode was inserted,
The current value is measured when a voltage of 6 V is applied with the can body as an anode. Hereinafter, it is less than 0.1 mA in the ERV test). X: There is no inner or outer surface, but current value is 0.1 mA in ERV test
As described above, when the energized portion is observed in an enlarged manner, pinhole-like cracks originating from the coarse lubricant are found in the film.

Table 1 shows the evaluation results of the above two types. From the results shown in Table 1, it can be seen that the films of Examples are excellent in deep drawing workability.

[0057]

[Table 1]

[0058]

EFFECTS OF THE INVENTION The polyester film for laminating and forming metal plates of the present invention has a deep drawing workability, a can-making process after 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 a polyester composition blended therein, the polyester composition having an average particle size of 0.01 to 2.5 μm and 0.005 of internally precipitated particles.
~ 3% by weight, the film surface orientation coefficient is 0.08 ~
A polyester film for laminating and forming metal plates, which has a thermal shrinkage of 0.16 or less at 150 ° C. of 10% or less and a density of less than 1.385 g / cm ³ .