JP2528204B2 - Polyester film for metal laminating molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to a polyester film for metal laminating and forming, and more specifically, an excellent forming process for forming a can by laminating with a metal plate. The present invention relates to a polyester film for metal laminating and forming, which is capable of producing metal cans, such as beverage cans and food cans, which have excellent heat resistance and aroma retention.

<Prior art and its problems> Metal cans are generally coated to prevent corrosion on the inner and outer surfaces, but recently, for the purpose of process simplification, hygiene improvement, pollution prevention, etc., no organic solvent was used. The development of a method for obtaining anticorrosive properties has been advanced, and as one of them, coating with a thermoplastic resin film has been attempted. That is, studies are underway on a method of laminating a thermoplastic resin film on a metal plate such as tin plate, tin-free steel, or aluminum, and then making a can by drawing or the like. Polyolefin films and polyamide films have been tried as the thermoplastic resin films, but they do not satisfy all of the molding processability, heat resistance, and aroma retention.

On the other hand, a polyethylene terephthalate film has attracted attention as a polyester film and the like because of its 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 a low-melting-point polyester adhesive layer and used as a can-making material (JP-A-56-10451, 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, JP-A-2-57339).

(C) A biaxially oriented polyethylene terephthalate film having low orientation and heat set is laminated on a metal plate and used as a material for can production (JP-A-64-22530).

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

Regarding (A), the biaxially oriented polyethylene terephthalate film is excellent in heat resistance and fragrance retention, but is insufficient in moldability and whitening of the film (generation of minute cracks) in canning with large deformation. Breakage occurs.

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 after printing after can making, after retort sterilization, etc. There is a risk that the film will be easily embrittled by the treatment and that the film will be easily broken by the impact from the outside of the can.

Regarding (C), the effect is not exhibited in the intermediate region between (A) and (B), but since the film surface isotropy is not guaranteed, deformation in all directions, such as in can manufacturing, is not possible. When the above is performed, the moldability may be insufficient in a specific direction of the film.

<Means for Solving Problems> The present inventors have further earnestly studied to develop a polyester film for can manufacturing without these problems,
The present invention has been reached.

That is, the present invention comprises a copolyester containing a lubricant having an average particle diameter of 2.5 μm or less, a melting point of 210 to 245 ° C., a refractive index in the film thickness direction of 1.505 to 1.545, and a refractive index in the film surface direction. Rate is 1.61 to 1.66 in all directions
Is a polyester film for metal 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 dibasic acids such as isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid; aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decane dicarboxylic acid; and alicyclic rings such as cyclohexanedicarboxylic acid. Examples of the alcohol component include aliphatic diols such as butanediol and hexanediol, and alicyclic diols such as cyclohexanedimethanol. These can be used alone or in combination of two or more.

The proportion of the copolymer component depends on the type thereof, and as a result, the polymer melting point is in the range of 210 to 245 ° C, preferably 215 to 240 ° C, and more preferably 220 to 235 ° C. When the melting point of the polymer is less than 210 ° C., the heat resistance is inferior, so that it cannot withstand the heating in printing after can production. On the other hand, the polymer melting point
When the temperature exceeds 245 ° C., the crystallinity of the polymer is too large and the moldability is impaired.

Here, the melting point of the polyester is measured by using a DSC-SSC / 580 manufactured by Seiko Denshi KK and determining a melting peak at a temperature rising rate of 20 ° C./min.

The copolymerized polyester in the present invention has an average particle size of 2.5.
It contains a lubricant of not more than μm. This lubricant is inorganic. It does not matter whether it is organic or not, but it 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 particles. Both have an average particle size of 2.5
It must be less than μm. Average particle size of lubricant is 2.5μ
If it exceeds m, coarse lubricant 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, and pinholes are generated or, in some cases, broken, which is not preferable.

Particularly preferred in terms of pinhole resistance is a lubricant having an average particle size.
2.5 μm or less and a particle size ratio (major axis / minor axis) of 1.0
It is a monodisperse lubricant that is ~ 1.2. Examples of such a lubricant include true spherical silica, true spherical titanium oxide, true spherical zirconium, true spherical silicone particles and the like.

Here, the average particle size and particle size ratio of the spherical monodispersed lubricant are
First, a metal is vapor-deposited on the surface of the particles, and then the long diameter, the short diameter, and the area equivalent circle diameter are obtained from an image magnified 10,000 times to 30,000 times with an electron microscope, and then these are applied to the following formulas to be calculated. To be done.

Average particle size = 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, it is preferable that the spherical lubricant particles have a sharp particle size distribution, The relative standard deviation that indicates the steepness of the distribution is 0.5
It is preferably below 0.3.

 This relative standard deviation is expressed by the following equation.

Here, Di: area circle equivalent diameter of each particle (μm): average value of area circle equivalent diameter n: represents the number of particles.

The amount of the lubricant in the copolyester may be determined by the winding property in the film manufacturing process. Generally, it is preferable to add a small amount of particles having a large particle size and a large amount of particles having a small particle size. For example, 0.05 for silica with an average particle size of 2.0 μm
% By weight, 0.3% by weight for titanium dioxide with an average particle size of 0.3 μm
It is preferable to add a certain amount. Further, the film can be made opaque by intentionally adjusting the content of the lubricant. For example, a white film can be obtained by adding 10 to 15% by weight of titanium dioxide.

The copolymerized polyester in the present invention is not limited by its production method. For example, a method in which terephthalic acid, ethylene glycol and a copolymerization component are subjected to an esterification reaction, and then the resulting reaction product is subjected to a polycondensation reaction to obtain a copolymerized polyester, or dimethyl terephthalate, ethylene glycol and a copolymerization component are transesterified. A method of reacting and then subjecting the obtained reaction product to a polycondensation reaction to obtain a copolyester is preferably used. In the production of the copolyester, other additives such as an antioxidant, a heat stabilizer, an ultraviolet absorber and an antistatic agent may be added if necessary.

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

(1) The refractive index in the thickness direction of the film is 1.505 or more and 1.545 or less, preferably more than 1.510 and 1.540 or less, and more preferably more than 1.510 and 1.530 or less. If this refractive index is less than 1.505, the moldability will be insufficient, while if it exceeds 1.545 (that is, if the orientation is excessively low), the structure will be close to amorphous, resulting in insufficient heat resistance. Become.

(2) The refractive index in the film surface direction is 1.61 or more and 1.66 or less, preferably 1.615 or more and 1.655 or less in all directions. Deep drawing and drawing often used in can manufacturing-
In ironing, the deformation must be uniform in all directions, and any part of the film must be able to follow this deformation. When the film surface refractive index is less than 1.61, molding processability is good, but heat resistance is poor,
On the other hand, in the direction where the refractive index exceeds 1.66, the whiteness and breakage of the film occur during deep drawing due to poor moldability.

In addition, the refractive index in the film thickness direction and the surface direction is measured as follows.

Attach a polarizing plate analyzer to the eyepiece side of the refractometer of Appe, and measure the refractive index of each with a monochromatic NaD ray.
The mounting solution uses methylene iodide, and the measurement temperature is 25 ° C.

In order to obtain such a refractive index in the thickness direction and a refractive index in the film plane direction, the longitudinal stretching ratio is 2.5 to 3.6 times, the transverse stretching ratio is 2.7 to 3.6 times, and the heat setting temperature in biaxial stretching, particularly sequential biaxial stretching. The stretching heat treatment may be performed at 150 to 230 ° C. More preferably, from such conditions, the refractive index in the thickness direction is 1.
505 or more and 1.545 or less, the refractive index distribution of the film surface is 1.61 or more
The film density is 1.66 or less, and the film density is less than 1.385 g / cm ³ ,
Furthermore, it is advisable to perform the biaxially stretched heat-setting treatment by finding the condition of 1.380 to 1.384 g / cm ³ .

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

A tin plate, tin-free steel plate, aluminum plate, or the like is suitable as the metal plate for can manufacturing to which the polyester film of the present invention is laminated. 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 film is bonded, and then rapidly cooled, and the surface layer (thin layer) of the film in contact with the metal plate is made amorphous and adhered.

The adhesive layer is primer-coated on the film in advance, and this surface is bonded 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.

<Examples> The present invention will be further described with reference to Examples.

Examples 1 to 4 and Comparative Examples 1 to 3 Spherical monodisperse silica having an average particle size of 1.5 μm or 2.0 μm (particle size ratio 1.07, relative standard deviation 0.1) was added and the components shown in Table 1 were copolymerized. The copolymerized polyethylene terephthalate (intrinsic viscosity: 0.60) was melt-extruded at the temperature shown in the same table and solidified rapidly to obtain an unstretched film.

Next, this unstretched film was longitudinally stretched under the conditions shown in the same table, laterally stretched, and then heat set to obtain a biaxially oriented film.

 Table 4 shows the characteristics of this film.

Example 5 and Comparative Example 4 Isophthalic acid 12 mol% copolymerized polyethylene terephthalate (intrinsic viscosity 0.6
0) is melt-extruded at 280 ° C and rapidly solidified to form an unstretched film, and the unstretched film is successively drawn at a longitudinal stretching temperature of 100 ° C, a longitudinal stretching ratio of 3.0 times, a transverse stretching temperature of 110 ° C and a lateral stretching ratio of 3.1 times. It was axially stretched and then heat-set at the temperature shown in the table.

 The characteristics of the obtained biaxially oriented film are shown in Table 4.

Comparative Examples 5-8 12 mol% isophthalic acid copolymerized polyethylene terephthalate (melting point) containing 0.05% by weight of spherical monodisperse silica having an average particle size of 2.0 μm (particle size ratio 1.07, relative standard deviation 0.1)
(229 ° C, intrinsic viscosity 0.60) was melt-extruded at 280 ° C and quenched and solidified to obtain an unstretched film. Next, the unstretched film was stretched longitudinally and transversely under the conditions shown in Table 3 and then heat-set to obtain a biaxially oriented film.

 Table 4 shows the characteristics of this film.

A total of 13 kinds of films obtained in Examples 1 to 5 and Comparative Examples 1 to 8 were laminated on both sides of a 0.25 mm thick tin-free steel heated to 260 ° C., water-cooled, and then a disc having a diameter of 150 mm. It was cut into a shape and deep-drawn in two 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 this container, and each container was evaluated according to the following criteria.

(1) Deep drawing workability-1 ◯: Both the inner and outer surfaces of the film were processed without any abnormality, and no whitening or breakage was found on the film on the inner or outer surface of the can.

Δ: Whitening was observed on the top of the film inside and outside of the can.

X: Film rupture is recognized in a part of the film inside and outside the can.

(2) Deep drawing workability-2 ○: Both 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 used as the anode. Measure the current value when a voltage of 6 V is applied, which is 0.2 mA or less in the ERV test.

×: There is no abnormality in the film on both the inner and outer surfaces, but the current value is 0.2 mA or more in the ERV test. When the energized portion is observed under magnification, pinhole-shaped cracks starting from the coarse lubricant are observed in the film.

(3) Impact crack resistance With respect to cans with good deep drawing, water was fully poured, and 10 pieces for each test were dropped from a height of 1 m onto the PVC tile floor surface, and then an ERV test inside the can was performed. Results: Good: 0.2 mA or less for all 10 pieces.

Δ: 0.2 mA or more for 1 to 5 pieces.

X: 0.2 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 subjected to good deep drawing were heated and held at 210 ° C for 5 minutes, the impact crack resistance evaluation described in (3) was performed. It was 0.2 mA or less.

Δ: 0.2 mA or more for 1 to 5 pieces.

×: 0.2mA or more for 6 or more or 210 ° C
After heating for 5 minutes, cracks in the film were already observed.

Table 4 shows the above four types of evaluation results.

From the results shown in Table 4, the film of the example was found to have deep drawability,
It turns out that it is excellent in all of the impact cracking resistance and the heat resistance.

<Effects of the Invention> The polyester film for metal laminating / molding processing of the present invention has a deep drawing workability and a post-can making resistance when forming a metal can by, for example, deep drawing and then forming a metal can after laminating with a metal plate. It has excellent impact resistance and heat resistance, and is extremely useful for metal containers.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location B29L 7:00 B29L 7:00 (72) Inventor Yoji Murakami 3-37-19 Oyama, Sagamihara City, Kanagawa Prefecture Sagamihara Research Center, Teijin Limited

Claims (1)

(57) [Claims] 1. A copolymer containing a lubricant having an average particle size of 2.5 μm or less and having a melting point of 210 to 245 ° C., a refractive index in the film thickness direction of 1.505 to 1.545, and a refractive index in the film surface direction. Is 1.61 to 1.66 in all directions, and is a polyester film for metal laminating processing.