JP2818315B2 - Polyester film for laminating metal plates - Google Patents

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 a metal plate, and more particularly to a polyester film for laminating to a metal plate and exhibiting excellent formability when performing can forming such as drawing. TECHNICAL FIELD The present invention relates to a polyester film for metal plate laminating and forming capable of producing metal cans, such as beverage cans, food cans, and the like, having excellent properties and fragrance retention.

[0002]

2. Description of the Related Art Metal cans are generally coated to prevent corrosion of the inner and outer surfaces. Recently, for the purpose of simplifying the process, improving hygiene, and preventing pollution, rust is prevented without using an organic solvent. Development of a method for obtaining the property has been advanced, and as one of the methods, coating with a thermoplastic resin film has been attempted. That is,
A method of laminating a thermoplastic resin film on a metal plate of tin, tin-free steel, aluminum or the like and then making the can by drawing or the like is being studied. Polyolefin films and polyamide films have been tried as this thermoplastic resin film, but they do not satisfy all of the moldability, heat resistance and fragrance retention.

[0003] On the other hand, polyester films, particularly polyethylene terephthalate films, have attracted attention as having balanced properties, and several proposals based on these have been made. That is, (A) a biaxially oriented polyethylene terephthalate film is laminated on a metal via an adhesive layer of a low-melting polyester and used as a can-forming material (JP-A-56-10451).
No. JP-A-1-192546). (B) Amorphous or extremely low-crystalline aromatic polyester film is laminated on a metal plate and used as a can-forming material (Japanese Patent Application Laid-Open Nos. 1-192545 and 2-573).
No. 39). (C) A biaxially oriented polyethylene terephthalate film having a low orientation and thermally fixed is laminated on a metal plate and used as a material for can production (Japanese Patent Laid-Open No. 64-22530).

[0004]

However, the present inventors' studies have revealed that no satisfactory characteristics can be obtained in any case, and that each of them has the following problems.

As for (A), the biaxially oriented polyethylene terephthalate film is excellent in heat resistance and fragrance retention.
Molding is inadequate, and whitening (generation of minute cracks) and breakage of the film occur in can making with large deformation.

As for (B), since it is an amorphous or extremely low-crystalline aromatic polyester film, the moldability is good, but the aroma retention is inferior, and the printing and retort sterilization treatment after can-making are performed. Such a film may be easily embrittled by post-treatment or storage for a long time, and may be transformed into a film which is easily broken by an impact from the outside of the can.

As for (C), the effect is not exhibited in the intermediate region between the above (A) and (B), but it has not yet reached the low orientation applicable to can processing. Since the isotropy of the film surface is not ensured, when the omnidirectional deformation is performed as in the case of a can making process, the formability in a specific direction of the film may be insufficient.

[0008]

Means for Solving the Problems The inventors of the present invention have made intensive studies to develop a polyester film for processing cans free of these problems, and as a result, have reached the present invention.

That is, according to the present invention, the average particle size is 2.5 μm.
Polymer containing the following lubricant has a melting point of 210-245 ° C
Having a refractive index in the film thickness direction of 1.515 to 1.550, a subpeak by DSC of 150 to 205 ° C., and a protrusion on the film surface having the following formula: 0.1 ≦ Nd / A polyester film for laminating metal plates, characterized by satisfying N ≦ 0.5 [where, N: total number of projections on the film surface, Nd: projections having depressions depressed around the core with lubricant]. .

A typical example of the copolymerized polyester in the present invention is copolymerized polyethylene terephthalate. This copolymer component may be an acid component or an alcohol component. As the acid component, isophthalic acid, phthalic acid,
Examples thereof include aromatic dibasic acids such as naphthalenedicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid, and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid. Examples thereof 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, but as a result the polymer melting point is in the range of 210 to 245 ° C., preferably 215 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, when the polymer melting point is 2
If the temperature exceeds 45 ° C., the crystallinity of the polymer is too large and the moldability is impaired.

The measurement of the melting point and the measurement of the sub-peak temperature of the copolyester were carried out by DuPont Instrument.
temperature 910 DSC, heating rate 20 ° C
/ Min to determine the melting peak. The sample amount was about 20 mg. Details of each peak are shown in FIG.

The copolymerized polyester in the present invention contains a lubricant having an average particle size of 2.5 μm or less. The lubricant may be inorganic or organic, but inorganic is preferred. As inorganic lubricants, silica, alumina, titanium dioxide,
Calcium carbonate, barium sulfate and the like can be exemplified. As the organic lubricant, crosslinked polystyrene particles, silicone particles and the like can be exemplified. In any case, the average particle size needs to be 2.5 μm or less. When the average particle size of the lubricant exceeds 2.5 μm, coarse lubricant particles (for example, particles of 10 μm or more) of a portion deformed by processing such as deep drawing can serve as a starting point,
It may cause pinholes or break in some cases,
Not preferred.

A lubricant which is particularly preferable from the viewpoint of pinhole resistance is a monodisperse lubricant having an average particle size of 2.5 μm or less and a particle size ratio (major axis / minor axis) of 1.0 to 1.2. is there. Examples of such a lubricant include spherical silica, spherical titanium oxide, spherical zirconium, and spherical silicone particles.

Here, the average particle diameter and the particle diameter ratio of the spherical monodispersed lubricant can be determined from the image obtained by evaporating a metal on the particle surface and then enlarging the particle diameter by, for example, 10,000 to 30,000 times using an electron microscope. The short diameter and the area circle equivalent diameter are calculated, and then they are applied to the following equation to calculate the diameter.

Average particle diameter = total area equivalent circle diameter of measurement particles / number of measurement particles Particle diameter ratio = average major axis of particles / average minor axis of particles The spherical lubricant particles have a sharp particle size distribution. Preferably, the relative standard deviation representing the steepness of the distribution is 0.5
Hereinafter, it is more preferably 0.3 or less.

This relative standard deviation is expressed by the following equation.

[0018]

(Equation 1) The amount of the lubricant in the copolymerized polyester may be determined depending on the winding property in the film production process. Generally, it is preferable to add a small amount of particles having a large particle diameter and a large amount of particles having a small particle diameter. For example, in the case of silica having an average particle size of 2.0 μm, the ratio is set to 0.1.
It is preferable to add about 0.3% by weight of titanium dioxide having an average particle diameter of 0.3% and a weight of 0.05% by weight. By intentionally adjusting the content of the lubricant, the film can be made opaque. For example, a white film can be obtained by adding 5 to 20% by weight, preferably 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 of subjecting terephthalic acid, ethylene glycol and a copolymer component to an esterification reaction and then subjecting the resulting reaction product to a polycondensation reaction to obtain a copolymerized polyester, or a method of transesterifying dimethyl terephthalate, ethylene glycol and a copolymer component. A method of reacting and then subjecting the resulting reaction product to a polycondensation reaction to form a copolymerized polyester is preferably used. In the production of the copolymerized polyester, if necessary, other additives such as an antioxidant, a heat stabilizer, an ultraviolet absorber, an antistatic agent and the like can be added.

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. This film has the following requirements (1) and (2)
And (3). (1) The refractive index in the thickness direction of the film is 1.515 or more and 1.550 or less, preferably more than 1.520 and 1.54.
0 or less. If the refractive index is less than 1.515, the moldability becomes insufficient, while if it exceeds 1.550 (that is, if the orientation is excessively low), the structure becomes almost amorphous. Becomes 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 each refractive index is measured with a monochromatic NaD line. The mounting solution uses methylene iodide, and the measurement temperature is 25 ° C. (2) DSC has a subpeak of 150 ° C. or higher and 205
° C or lower, preferably higher than 160 ° C and lower than 200 ° C, more preferably higher than 170 ° C and lower than 195 ° C.

Since this copolymerized polyester film is laminated on a metal plate by heating, it is necessary to control the DSC subpeak temperature in the above range in order to secure the stability of the quality of the laminated film.

Only by adjusting the laminating temperature and the sub-peak temperature during the heating lamination, the film quality after can making becomes satisfactory. If the sub-peak temperature exceeds 205 ° C., the film may break during can making even if the lamination temperature is adjusted to any lamination temperature.
If the temperature is lower than ℃, raising the laminating temperature will make the film at the bottom of the can with small deformation brittle, and lowering the laminating temperature will break the film at the top of the side of the can with large deformation. I can't make it. (3) The number of projections having depressions depressed around the film surface lubricant as a nucleus exceeds 10% of the total number of projections and is 50%.
%, Preferably more than 15% and not more than 45%, more preferably more than 20% and not more than 40%. This “projection having a depression depressed around the periphery with a lubricant as a nucleus” (hereinafter sometimes referred to as a projection having a depression) is formed by a stretching process, and is different from, for example, the formation of unevenness by satin finish processing.

When the number of the projections having the depressions is less than 10%, the film breaks at the time of can making, or the film has poor impact cracking resistance after can making. On the other hand, when the number of the projections is 50
% Of the film is difficult to form a film, and during the first stretching, the unevenness of the stretching is severe, and the biaxially stretched film has remarkable step-like unevenness, which impairs the uniformity of quality as the film. .

FIG. 2 is a schematic view of the projection having the depression. 2A is a plan view and FIG. 2B is a cross-sectional view. On the other hand, FIG. 3 shows a schematic view of a projection having no depression (normal projection). 3A is a plan view, and FIG. 3B is a cross-sectional view. 4 and 5 show enlarged photographs of the film surface. FIG. 4 shows that the projections on the film surface are ordinary projections, and FIG. 5 shows that the projections on the film surface are ordinary projections and projections having depressions. As an example of a method for producing a film satisfying the above requirements (1), (2), and (3), a method using biaxial stretching, particularly sequential biaxial stretching, will be described below. It is not limited to only.

As described above, the copolyester is melted, discharged from a die, formed into a film, and immediately quenched to obtain a substantially amorphous copolyester sheet. Next, the sheet is heated in a roll, an infrared ray or the like and stretched in the longitudinal direction. At this time, the stretching temperature is preferably 30 to 50 ° C. higher than the glass transition point (Tg) of the copolymerized polyester, and the stretching ratio is preferably 2.5 to 3.5 times. The stretching in the transverse direction is started at a temperature 20 ° C. or more higher than Tg, and is 80 ° C. higher than the melting point (Tm) of the copolyester.
It is preferable to perform the heating while raising the temperature to a temperature lower by about 130 ° C. The magnification of the transverse stretching is preferably set to 2.7 to 3.6 times. The heat setting temperature is selected in the range of 150 to 205 ° C. to adjust the film quality according to the Tm of the copolymerized polyester polymer. The heat setting temperature corresponds to the DSC sub-peak temperature.

Of the above film forming conditions, the stretching temperature is high,
By lowering the stretching ratio, the number of projections having the depressions described in the above (3) increases. At the same time, the orientation can be reduced without increasing the difference in physical properties in the width direction of the biaxially stretched film, and a film excellent in subsequent formability can be obtained.

[0029] The polyester film of the present invention preferably has a thickness of 6 to 75 µm. 10-75μ
m, more preferably 10 to 75 μm, 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, the quality is excessive and uneconomical.

As a metal plate to which the polyester film of the present invention is bonded, in particular, a metal plate for can making, a plate of tin, tin-free steel, aluminum or the like is suitable.
The bonding of the polyester film to the metal plate can be performed, for example, by the following method. 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 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-based adhesive, an epoxy-ester-based adhesive, an alkyd-based adhesive, or the like can be used.

[0031]

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

[0032]

Examples 1-5 and Comparative Examples 1-3 Average particle size 1.5 μm
Copolymerized polyethylene terephthalate (intrinsic viscosity 0.60) obtained by adding 0.1% by weight of spherical monodispersed silica (particle size ratio 1.07, relative standard deviation 0.1) and copolymerizing the components shown in Table 1. Was melt-extruded at the temperatures shown in the same table and quenched and solidified to obtain an unstretched film.

Next, the unstretched film was stretched longitudinally and transversely under the conditions shown in the same table, and then heat-set to obtain a biaxially oriented film having a thickness of 25 μm.

Table 4 shows the characteristics of this film.

[0035]

[Table 1]

[0036]

Example 6 and Comparative Example 4 A 12 mol% copolymerized polyethylene terephthalate (intrinsic viscosity: 0.60) containing a lubricant shown in Table 2 was melt-extruded at 280 ° C., quenched and solidified to obtain an unstretched film. Then, the unstretched film was subjected to a longitudinal stretching temperature of 115 ° C., a longitudinal stretching ratio of 3.0 times,
The film was successively biaxially stretched at a transverse stretching temperature of 130 ° C and a transverse stretching magnification of 3.0, and then heat-set at 190 ° C.

Table 4 shows the properties of the obtained biaxially oriented film.

[0038]

[Table 2]

[0039]

Comparative Examples 5 to 8 Copolymer of 12% by mole of isophthalic acid containing 0.1% by weight of spherical monodispersed silica having an average particle size of 1.5 μm (particle size ratio: 1.07, relative standard deviation: 0.1) Polyethylene terephthalate (melting point: 228 ° 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.

[0041]

[Table 3] A total of 14 kinds of films obtained in the above Examples 1 to 6 and Comparative Examples 1 to 8 were stuck on both sides of a 0.25 mm thick tin-free steel heated to 260 ° C., and after cooling with water, 150 mm
Cut into a circular disk with a diameter, and deep-drawn in three stages using a drawing die and a punch.
Abbreviated as can).

The following observations and tests were conducted on this container, and each was evaluated according to the following criteria. (1) Deep drawing workability-1 ○: Both inner and outer surfaces are processed into films without any abnormality, and no whitening or breakage is observed in the films on the inner and outer surfaces of the can.

△: Whitening is observed on the top of the film inside and outside the can.

X: Film breakage is observed in a part of the film on the inner and outer surfaces of the can. (2) Deep drawing workability-2 加工: Both inner and outer surfaces were processed without any abnormality, and rust prevention test of the film surface in the can (1% NaCl water was put in the can, an electrode was inserted, and the can body was used as an anode. A current value when a voltage of 6 V is applied is measured.
The following is shown.

×: There is no abnormality in the film on both the inner and outer surfaces,
In the ERV test, the current value was 0.2 mA or more, and when the energized portion was observed under magnification, pinhole-shaped cracks starting from the coarse lubricant were observed in the film. (3) Impact cracking resistance For cans with good deep draw forming, water was fully poured, and 10 pieces of each test were dropped on a PVC tile floor from a height of 1 m for each test, and then an ERV test in the can was performed. Result: ０．２: 0.2 mA or less for all 10 samples.

Δ: 0.2 mA or more for 1 to 5 pieces.

X: The film was 0.2 mA or more for 6 or more pieces, or cracks of the film were already observed after dropping. (4) Heat embrittlement resistance The can which had been subjected to good deep drawing was heated and maintained at 210 ° C. for 5 minutes, and then subjected to impact cracking resistance evaluation described in (3). It was 0.2 mA or less.

Δ: 0.2 mA or more for 1 to 5 pieces.

X: The film was 0.2 mA or more for 6 or more pieces, or cracks of the film were already observed after heating at 210 ° C. for 5 minutes.

Table 4 shows the above four types of evaluation results.

[0051]

[Table 4] From the results in Table 4, it can be seen that the films of the examples are excellent in all of the deep drawing workability, impact cracking resistance and heat resistance.

[0052]

The polyester film for laminating and forming a metal plate according to the present invention can be subjected to can drawing after laminating with a metal plate, for example, in deep drawing to form a metal can. It has excellent impact resistance and heat resistance,
Very useful for metal containers.

[Brief description of the drawings]

FIG. 1 is a DSC measurement chart of a film, showing a sub-peak melting point peak.

FIG. 2 is a schematic view of a projection in which a depression is formed around a particle as a core in the polyester film of the present invention, wherein A is a plan view and B is a cutaway view.

FIG. 3 is a schematic diagram showing a situation around a particle when stretched by a conventional method, wherein A is a plan view and B is a cross-sectional view.

FIG. 4 shows the surface shape of a conventional polyester film ( thin film ).
It is a differential interference microscope photograph (magnification 650 times) which shows a shape .

FIG. 5 shows the surface of the polyester film ( thin film ) of the present invention.
It is a differential interference microscope photograph (650 times magnification) which shows a shape . .

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI C08L 67:02 (72) Inventor Yoji Murakami 3-37-19 Koyama, Sagamihara-shi, Kanagawa Prefecture Teijin Limited Sagamihara Research Center (56) References JP-A-3-87249 (JP, A) JP-A-4-117427 (JP, A) JP-A-3-86729 (JP, A) JP-A-2-242738 (JP, A) JP-A-2 -57339 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C08J 5/18 B29C 55/00-55/30 B32B 1/00-35/00

Claims (1)

(57) [Claims] 1. A copolyester containing a lubricant having an average particle size of 2.5 μm or less and having a melting point of 210 to 245 ° C., and having a refractive index of 1.5 in the thickness direction of the film.
15 to 1.550, and the number of
The temperature is 50 to 205 ° C., and the protrusions on the film surface are represented by the following formula: 0.1 ≦ Nd / N ≦ 0.5, where N is the total number of protrusions on the film surface, and Nd is a depression depressed around the lubricant as a nucleus. Having the following characteristics]: A polyester film for bonding metal plates.