JPH0680797A - Polyester film for lamination with metal sheet - Google Patents

Abstract

PURPOSE:To provide a polyester film which is excellent in workability indeep drawing and gives a can excellent in impact and heat resistances when used in application wherein it is laminated with a metal sheet and the laminate is fabricated, for example, deep drawn to form a metallic can. CONSTITUTION:The film is made from a copolyester having a melting point of 210-245 deg.C and containing 0.005-3wt.% particles of a metal salt of terephthalic acid or a metal salt containing an alkylene terephthalate component which have a mean particle diameter of 0.05-2.5mum, and it has a refractive index in the direction of film thickness of 1.505 to 1.550 and an intrinsic viscosity of the polymer part of 0.52 to 0.80.

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 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 coated 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 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, after laminating a thermoplastic resin film on a metal plate such as tin plate, tin-free steel, aluminum,
The method of making cans by drawing is being studied. Polyolefin and polyamide films have been tried as this thermoplastic resin film, but they do not satisfy all of molding processability, heat resistance, and aroma retention. Therefore, the polyester film is attracting attention because it is well balanced in physical, thermal, and chemical properties.

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

That is, if the slipperiness is insufficient, for example, wrinkles occur during the film winding process, and in the case of metal cans, for example, wrinkles occur 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 slipperiness 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, for example, a method of adding inert inorganic fine particles is used. Has been. Generally, the larger the size of the fine particles in the raw material polyester, 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 on the film surface needs to be as fine as possible. At present, there is a demand for satisfying these contradictory characteristics at the same time.

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-52-7
8953, JP-A-52-78954, and JP-A-53-
No. 41355, JP-A-53-71154, etc.), however, these particles inherently have the above-mentioned problems because they form large voids.

[0008]

Therefore, as a polyester film having better slipperiness and abrasion resistance of the film and suitable for can-making processing, the polyester film has a higher affinity with polyester than the above-mentioned fine particles, and has a high affinity for the particles. Development of particles containing fine particles in which voids are difficult to form is required.

[0009]

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

That is, the present invention has an average particle size of 0.05.
˜2.5 μm of terephthalic acid metal salt or alkylene terephthalate component containing metal salt particles 0.005
~ 3 wt%, the melting point of the polymer is 210 ~ 245 ℃
A metal plate having a refractive index in the thickness direction of the film of 1.505 to 1.550 and an intrinsic viscosity of the polymer portion of the film of 0.52 to 0.80. It is a polyester film for laminating and forming.

A typical example of the copolymerized polyester in the present invention is copolymerized polyethylene terephthalate. This 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, but as a result, the melting point of the polymer is in the range of 210 to 245 ° C., preferably 215 to 235 ° C. If the melting point of the polymer is less than 210 ° C., the heat resistance is poor, so that heating after printing after can-making cannot be endured. On the other hand, the polymer melting point is 24
When it exceeds 5 ° C, the crystallinity of the polymer is too large and the moldability is impaired.

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.

The copolymerized polyester in the present invention is not limited by its production method. 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 obtain 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,
If necessary, other additives such as antioxidants, heat stabilizers, UV absorbers, antistatic agents, etc. can be added.

The copolymerized polyester film used in the present invention is 35% as a solution in O-chlorophenol.
Those having an intrinsic viscosity of 0.52 to 0.80 obtained by measuring at 0 ° C are preferable.

Further, in the present invention, the polyester has an average particle size of 0.05 to 2.5 μm, preferably 0.1 to 2.5 μm.
Particles of a metal salt of terephthalic acid or a metal salt containing an alkylene terephthalate component having a size of 2.25 μm, more preferably 0.3 to 2 μm, are contained as a lubricant. 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. If the average particle size exceeds 2.5 μm, coarse particles (eg, particles of 10 μm or more) will be the starting point in the portion deformed by processing such as deep-drawing cans, causing pinholes and, in some cases, breaking. Therefore, it is not preferable.

Specific examples of such metal salt particles include:

[0018]

[Chemical 1]

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

The metal salt 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 terephthalic acid Calcium is dispersed in glycol such as ethylene glycol to form a slurry, and the slurry is subjected to a conventional particle size adjusting treatment, such as pulverizing treatment and classification treatment, to obtain a glycol slurry in which calcium terephthalate having a predetermined average particle diameter is dispersed. be able to. Further, particles of a metal salt containing an ethylene terephthalate component or a phosphorus component with the ethylene terephthalate 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 content of precipitated particles in the polyester is
It should be 0.005 to 3% by weight, preferably 0.01 to 1% by weight, and more preferably 0.05 to 0.
It is 5% 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% by weight, the film often breaks, which is not preferable. Also, if necessary, other lubricants may be added within a range that does not impair the effects of the present invention.

As a means for incorporating a lubricant into the polyester, any conventionally known means can be used and is not particularly limited, but a method of adding a lubricant at the time of producing the copolymerized polyester is preferable.

The polyester film of the present invention is obtained by melting the above-mentioned lubricant-containing copolyester, discharging it from a die to form a film, biaxially stretching and heat fixing. And this film needs to satisfy the following requirements (1) and (2).

(1) The refractive index in the thickness direction of the film is 1.
It is 505 or more and 1.550 or less, preferably more than 1.510 and 1.540 or less. When the refractive index is less than 1.505, the moldability becomes insufficient, while when it exceeds 1.550 (that is, when the orientation is excessively low), the structure is close to amorphous, so that the heat resistance is high. Will be insufficient.

The refractive index in the film thickness direction is measured as follows.

A polarizing plate analyzer is attached to the eyepiece side of the Abbe refractometer, and the refractive index of each is measured with a monochromatic NaD ray. Methylene iodide was used as the mount solution, and the measurement temperature was 25 ° C.

(2) The intrinsic viscosity of the polymer portion of the film is 0.52 or more and 0.80 or less, preferably 0.54 or more and 0.70 or less, and particularly preferably 0.57 or more and 0.65 or less. If the intrinsic viscosity is less than 0.52, other physical properties are suitable, for example, even if the product is laminated to a metal plate or canned by deep drawing, the retort can be sterilized after filling the can contents. The film tends to become brittle when subjected to a treatment or stored for a long period of time thereafter, and is easily broken by an impact from the outside of the can. On the other hand, those with an intrinsic viscosity of more than 0.80 are uneconomical because they are of excessive quality and the productivity of the raw material polymer is reduced.

To obtain such a polyester film,
For example, in sequential biaxial stretching, the longitudinal stretching ratio is 2.5 to
By selecting from the range of 3.6 times, the transverse draw ratio of 2.7 to 3.6 times, and the heat setting temperature of 150 to 220 ° C., preferably 160 to 200 ° C., and combining them. Good to do.

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.

As a 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 equal to or higher than the melting point of the film, the films are pasted together and then rapidly cooled, and the surface layer portion (thin layer portion) of the film in contact with the metal plate is made amorphous and adhered. The film is pre-coated with an adhesive layer as a primer, and this surface is attached to a metal plate. As the adhesive layer, a known resin adhesive such as an epoxy adhesive, an epoxy-ester adhesive, an alkyd adhesive, or the like can be used.

[0031]

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

[0032]

Examples 1 to 8 and Comparative Examples 1 to 5 Copolyethylene terephthalate obtained by copolymerizing an isophthalic acid component at a copolymerization ratio shown in Table 1 and calcium terephthalate having an average particle size shown in the same table are shown in the same table. The ingredients were blended in proportions, melt-extruded and rapidly solidified under the conditions shown in Table 2 to obtain an unstretched film.

Then, these unstretched films were sequentially biaxially stretched in the longitudinal and transverse directions under the conditions shown in Table 2 and heat-set to obtain biaxially oriented films having a thickness of 25 μm.

[0034]

[Comparative Examples 6 to 8] As a lubricant, a lubricant having the average particle size and content shown in Table 1 was added in the same manner as in Examples 2 and 7 except that bulk silica and kaolin were used instead of calcium terephthalate. An unstretched film of isophthalic acid copolymerized polyethylene terephthalate was obtained.

Then, this unstretched film was sequentially biaxially stretched in the longitudinal and transverse directions under the conditions shown in Table 2 and further heat set.
A biaxially oriented film having a thickness of 25 μm was obtained.

[0036]

Examples 9 to 11 In the same manner as in Examples 1 and 2 except that adipic acid component or sebacic acid component was used instead of isophthalic acid, calcium terephthalate having the average particle size and content shown in Table 1 was contained. An unstretched film made of copolymerized polyethylene terephthalate was obtained.

Then, this unstretched film was sequentially biaxially stretched in the longitudinal and transverse directions under the conditions shown in Table 2 and further heat-set.
A biaxially oriented film having a thickness of 25 μm was obtained.

[0038]

[Comparative Examples 9 and 10] A lubricant having the average particle size and content shown in Table 1 was added in the same manner as in Examples 9 and 11 except that bulk silica and kaolin were used as the lubricant instead of calcium terephthalate. An unstretched film made of copolymerized polyethylene terephthalate was obtained.

Then, the unstretched film was sequentially biaxially stretched in the longitudinal and transverse directions under the conditions shown in Table 2 and further heat-set.
A biaxially oriented film having a thickness of 25 μm was obtained.

[0040]

[Table 1]

[0041]

[Table 2]

Table 3 shows the characteristics of a total of 21 kinds of films obtained in Examples 1 to 11 and Comparative Examples 1 to 10.

Here, the winding property of the film is ◯ when no small protrusions on the roll surface due to poor slippage are observed when the film is wound into a roll in the manufacturing process of the film, and x when it is recognized. It was judged.

The film was laminated on both sides of 0.25 mm thick tin-free steel heated to 230 ° C., cooled with water, cut into a disc shape of 165 mm diameter, and deep-cut in four steps using a drawing die and punch. Drawn, 55m
A sideless seamless container (hereinafter, abbreviated as a can) having a diameter of m was prepared, and the following observation and test were performed on this can and evaluated according to the following criteria.

(1) Deep drawing workability- ○: The inner and outer surfaces of the film are processed without any abnormality, and no whitening or breakage is observed on the film on the inner or outer surface of the can.

X: Whitening of the film on the inside and outside of the can on the top of the can,
Fracture is observed.

(2) Deep drawing workability- ○: 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 made into an anode. Then, the current value is measured when a voltage of 6 V is applied, which is 0.08 in the ERV test.
Indicates less than mA.

X: There is no abnormality on the inner and outer surfaces, but the current value is 0.08 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.

[0049]

[Table 3]

From the results shown in Table 3, it can be seen that the films of Examples are excellent in deep drawability, impact crack resistance and heat resistance.

[0051]

INDUSTRIAL APPLICABILITY The polyester film for laminating and forming a metal plate of the present invention has a deep drawing workability after forming a metal can by, for example, deep drawing after forming a metal can after laminating with a metal plate. It has excellent impact 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 // B29C 51/14 7421-4F B29K 67:00 B29L 22:00 4F

Claims (1)

[Claims] 1. Containing 0.005 to 3% by weight of 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,
The polymer has a melting point of 210 to 245 ° C. and is made of copolyester, and the film has a refractive index of 1.505 in the thickness direction.
It is -1.550, and the intrinsic viscosity of the polymer part of a film is 0.52-0.80, The polyester film for metal plate lamination molding processing characterized by the above-mentioned.