JP3016943B2 - 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 a metal plate, and more particularly, it shows excellent moldability when laminating a metal plate and performing can making such as drawing. Also, the present invention relates to a polyester film for laminating a metal plate which can produce a metal can having excellent scent retention, for example, a beverage can, a food can and the like.

[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 prevention is performed 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,
Studies have been made on a method of laminating a thermoplastic resin film on a metal plate such as tinplate, tin-free steel, or aluminum, and then forming the can by drawing or the like. 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.

On the other hand, polyester films, particularly polyethylene terephthalate films, have attracted attention as having balanced properties, and several proposals based on them 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-making 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 material for can production (Japanese Patent Application Laid-Open Nos. 1-192545 and 2-573).
No. 39). (C) A low-orientation, heat-fixed, biaxially oriented polyethylene terephthalate film is laminated on a metal plate and used as a can-making material (Japanese Patent Laid-Open No. 64-22530). (D) A copolymer polyester film having a specific plane orientation coefficient, heat shrinkage, and density is laminated on a metal plate and used as a can-making material (Japanese Patent Laid-Open No. 3-86729).

[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.

Regarding (A), a 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 fragrance retention is inferior, and printing and retort sterilization 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 omnidirectional deformation is performed as in canning (deep drawing), the formability in a specific direction of the film may be insufficient.

[0008] Regarding (D), especially when used for a can subjected to internal pressure, the film is liable to be broken by an impact from the outside of the can, and a can of excellent quality may not be obtained.

[0009]

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, the present invention relates to 99 to 60% by weight of a copolymerized polyester mainly composed of polyethylene terephthalate and having a melting point of 210 to 245 ° C., and polybutylene terephthalate or a copolymer mainly composed of polybutylene terephthalate having a melting point of 180 to 223 ° C. It contains a lubricant having an average particle diameter of 2.5 μm or less, a plane orientation coefficient of 0.08 to 0.16, a heat shrinkage at 150 ° C. of 10% or less, and a density of 1 to 40% by weight of a polymerized polyester. Is less than 1.385 g / cm ³ , and the projections on the film surface satisfy the following formula:

[0011]

(Equation 2)

With respect to the copolymer polyester mainly composed of polyethylene terephthalate used in the present invention, the copolymer 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, but as a result, the melting point of the polymer is from 210 to 245 ° C., preferably from 215 to 240 ° C., more preferably from 220 to 235 ° C.
It is the ratio which becomes the range of. 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, if the polymer melting point exceeds 245 ° C,
The crystallinity of the polymer is too large and the moldability is impaired.

On the other hand, with respect to the copolymerized polyester mainly composed of polybutylene terephthalate used in the present invention, the copolymerized 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 ethylene glycol and hexane diol, and alicyclic diols such as cyclohexane dimethanol. 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 melting point of the polymer is from 180 to 223 ° C, preferably from 200 to 223 ° C, more preferably from 210 to 223 ° C.
It is the ratio which becomes the range of. When the melting point of the polymer is less than 180 ° C., the heat resistance is inferior, so that it cannot withstand the heating in printing after can-making. The melting point of polybutylene terephthalate homopolymer is 223 ° C., and it is difficult to obtain a copolyester having a higher melting point.

Here, the melting point of the copolyester was measured by using Du Pont Instruments 910.
A method in which a melting peak is determined at a heating rate of 20 ° C./min using DSC. The sample amount is about 20 mg.

The copolymerized polyester mainly composed of polyethylene terephthalate and the copolymerized polyester mainly composed of polybutylene terephthalate or polybutylene terephthalate used in the present invention are not limited by the production method. For example, in the case of a copolymer polyester mainly composed of polyethylene terephthalate,
A method in which terephthalic acid, ethylene glycol and a copolymer component are subjected to an esterification reaction, and then the obtained reaction product is subjected to a polycondensation reaction to form a copolymerized polyester, or a dimethyl terephthalate, an ethylene glycol and a copolymer component are subjected to a transesterification reaction. Then, a method of subjecting the resulting reaction product to a polycondensation reaction to obtain a copolymerized polyester is preferably used. In the production of each copolymerized polyester and polybutylene terephthalate, if necessary, other additives such as antioxidants, heat stabilizers, ultraviolet absorbers,
An antistatic agent and the like can also be added.

The polyester film of the present invention mainly comprises polyethylene terephthalate and has a melting point of 210 to 24.
It must be composed of 99 to 60% by weight of a copolymerized polyester at 5 ° C and 1 to 40% by weight of a copolymerized polyester mainly composed of polybutylene terephthalate or polybutylene terephthalate and having a melting point of 180 to 223 ° C. Polybutylene terephthalate or a copolymer mainly composed of polybutylene terephthalate is less than 1% by weight and a copolymer mainly composed of polyethylene terephthalate exceeds 99% by weight. It is easily cracked by external impacts and can not provide excellent quality cans. Further, the content of polybutylene terephthalate or the copolymer polyester mainly composed of polybutylene terephthalate exceeds 40% by weight, and the proportion of the polyethylene terephthalate copolymerized polyester is 60% by weight.
If it is less than 1, the heat resistance of the film decreases, and the impact resistance becomes insufficient.

Further, the polyester film of the present invention comprises:
It 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. Examples of the inorganic lubricant include silica, alumina, titanium dioxide, calcium carbonate, barium sulfate and the like, and examples of the organic lubricant include crosslinked polystyrene particles and silicone particles. 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 a deep drawing can or the like serve as a starting point, and pinholes are generated, and in some cases, It is not preferable because it breaks.

A lubricant which is preferable from the viewpoint of pinhole resistance is a monodisperse lubricant having an average particle diameter of 2.5 μm or less and a particle diameter ratio (major axis / minor axis) of 1.0 to 1.2. It is a lubricant. Examples of such a lubricant include spherical silica, spherical tatatin 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 by evaporating a metal on the surface of the particles and then using an electron microscope to enlarge, for example, 10,000 to 30,000 times. 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 size = total area equivalent circle diameter of measurement particles / number of measurement particles Particle size ratio = average major axis of particles / average minor axis of the particles

The spherical lubricant particles preferably have a sharp particle size distribution, and the relative standard deviation representing the steepness of the distribution is preferably 0.5 or less, more preferably 0.3 or less. This relative standard deviation is expressed by the following equation.

[0024]

(Equation 3)

The amount of the lubricant in the polyester film may be determined according to 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, it is preferable to add about 0.05% by weight for silica having an average particle size of 2.0 μm and about 0.3% by weight for titanium dioxide having an average particle size of 0.3 μm. 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 polyester film of the present invention is prepared by blending a predetermined amount of the above-mentioned copolymerized polyester mainly composed of polyethylene terephthalate and a copolymerized polyester mainly composed of polybutylene terephthalate or polybutylene terephthalate, and melt-extruding the film. It can be manufactured by forming into a shape, biaxially stretching and heat setting. At this time, the above-mentioned lubricant, for example, a spherical monodispersed lubricant, is used in one or both of polyethylene terephthalate copolymerized polyester and polybutylene terephthalate or polybutylene terephthalate copolymerized polyester,
It may be contained during polymerization or may be added and mixed during melt extrusion.

The thus obtained polyester film of the present invention has a plane orientation coefficient of 0.08 or more and 0.16 or less,
Preferably, it should be more than 0.09 and 0.15 or less, more preferably more than 0.10 and 0.14 or less. If the plane orientation coefficient of the film is less than 0.08, if the deep drawing ratio of the deep drawing becomes high, problems such as cracks occur, which is not preferable. On the other hand, when the plane orientation coefficient exceeds 0.16, breakage occurs during deep drawing, and deep drawing itself becomes impossible.

Here, the plane orientation coefficient is defined by the following equation.

[0029]

(Equation 4)

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 light NaD line. The mounting solution uses methylene iodide, and the measurement temperature is 25 ° C.

The polyester film of the present invention further comprises:
The heat shrinkage at 150 ° C. is 10% or less, preferably 7% or less, particularly preferably 6% or less, and the density is 1.3.
Less than 85 g / cm ³ , preferably 1.380 to 1.35
0 g / cm ³ , more preferably 1.375 to 1.355
g / cm ³ .

Here, the heat shrinkage rate was determined by setting two points (approximately 10 cm) on the sample film at room temperature.
Hold in a hot air circulating oven at 0 ° C. for 30 minutes, then return to room temperature, measure the distance between the mark points, find the difference before and after holding the temperature at 150 ° C., and compare this difference with the temperature before holding at 150 ° C. Calculated from the reference point interval. The film is represented by the heat shrinkage in the longitudinal direction of the film. The density is measured with a density gradient tube.

The heat shrinkage (150 ° C.) of the polyester is 1
If it exceeds 0%, the size shrinks greatly when bonded to a metal plate, and disadvantages such as wrinkling of the film occur, which is not preferable. This heat shrinkage rate is 10% or less, further 7% or less,
In particular, when the content is 6% or less, good results can be obtained with few defects such as generation of wrinkles in the film when bonded to a metal plate. On the other hand, when the film density exceeds 1.385 g / cm ³ , the deep drawability is inferior and the film may be cracked, torn or broken, which is not preferable.

Further, the polyester film of the present invention comprises:
The number of projections having depressions depressed around the film surface lubricant as a nucleus is more than 10% of the total number of projections and 50% or less,
Preferably more than 15% and not more than 45%, more preferably 2%
It is necessary to be more than 0% and 40% or less. This “protrusion with a depression depressed around the lubricant core”
(Hereinafter, a projection having a depression may be formed) by a stretching process, and is different from, for example, the formation of unevenness by satin finishing.

If the number of projections having the depressions is less than 10%, the film will break during can making, or the film will have 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. 1 is a schematic view of the projection having the depression. 1A is a plan view and FIG. 1B is a cross-sectional view. On the other hand, FIG. 2 shows a schematic view of a projection having no depression (normal projection). 2A is a plan view and FIG. 2B is a cross-sectional view. 3 and 4 show enlarged photographs of the film (thin film) surface. 3 are those projections of the film (thin film) surface is from the normal projections, Fig. 4 is a film (thin
The projection on the surface of the film is composed of ordinary projections and projections having depressions.

The plane orientation coefficient and the heat shrinkage ratio (150
° C), to obtain a polyester film that satisfies the projections having the density and the depressions, for example, the following biaxial stretching, in particular, the sequential biaxial stretching method is used, but the polyester film of the present invention is obtained by this method. However, the present invention is not limited to such films.

First, a copolymerized polyester mainly composed of polyethylene terephthalate and polybutylene terephthalate or a copolymerized polyester mainly composed of polybutylene terephthalate are blended in a predetermined ratio, melted, and discharged from a die to form a film. Then, the mixture is 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 40 to 55 ° 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 preferably started at a temperature 40 ° C. or more higher than Tg, and is performed while increasing the temperature to 70 to 110 ° C. lower than the melting point (Tm) of the copolymerized polyester. 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 220 ° C. to adjust the film quality according to the Tm of the polymer.

Of the above film forming conditions, the stretching temperature is high,
By lowering the stretching ratio, the number of projections having the above-mentioned depressions 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.

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, the quality is excessive and uneconomical.

As the 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, for example, an epoxy adhesive, an epoxy-ester adhesive, an alkyd adhesive, or the like can be used.

[0042]

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

[0043]

Examples 1-6 and Comparative Examples 1-8 Average particle size 1.5 μm
0.1% by weight of a monodispersed spherical silica (particle size ratio 1.07, relative standard deviation 0.1) of the following, and copolymerized with the components shown in Table 1 and composed mainly of polyethylene terephthalate (polyethylene terephthalate) Hereinafter, abbreviated as PET copolymerized polyester) and polybutylene terephthalate (hereinafter referred to as P
BT) or a copolymerized polyester mainly composed of polybutylene terephthalate obtained by copolymerizing the components shown in Table 1 (hereinafter abbreviated as BBT copolymerized polyester) at a ratio shown in Table 1 and mixed at 280 ° C. It was melt-extruded and quenched and solidified to obtain an unstretched film.

Next, the unstretched film was stretched longitudinally and transversely under the conditions shown in the table, and then heat-set to obtain a film having a thickness of 2 mm.
A biaxially oriented film of 5 μm was obtained.

[0045]

[Table 1]

Table 2 shows the surface orientation coefficient, heat shrinkage, density and occurrence rate of projections having depressions of this film.

[0047]

[Table 2]

[0048]

Example 7 and Comparative Example 9 A biaxially oriented film was obtained in the same manner as in Example 5 except that the lubricants shown in Table 3 were used and the other conditions were the same as in Example 5.

[0049]

[Table 3]

Plane orientation coefficient of the obtained biaxially oriented film,
Table 4 shows the heat shrinkage, the density, and the incidence of protrusions having depressions.

[0051]

[Table 4]

[0052]

Comparative Examples 10 and 11 The unstretched film obtained in Example 3 was stretched longitudinally and transversely under the conditions shown in Table 5 and then heat-set to obtain a biaxially oriented film.

[0053]

[Table 5]

Plane orientation coefficient of the obtained biaxially oriented film,
Table 6 shows the heat shrinkage, the density, and the incidence of protrusions having depressions.

[0055]

[Table 6]

A total of 18 kinds of films obtained in Examples 1 to 7 and Comparative Examples 1 to 11 were bonded to both sides of a 0.25 mm thick tin-free steel heated to 230 ° C.
After cooling with water, the plate was cut into a disk having a diameter of 150 mm and deep-drawn in four stages using a drawing die and a punch to prepare a side-seamless container (hereinafter abbreviated as can) having a diameter of 55 mm.

The following observations and tests were performed on the cans, and the cans were evaluated according to the following standards.

(1) Suitability for lamination ○: Laminable without wrinkles Δ: Significant shrinkage in width during lamination ×: Wrinkles during lamination

(2) Deep drawing workability -1 ○: Both 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 and outer surfaces of the can. △: Whitening on the upper part of the film on the inner and outer surfaces of the can. Recognized ×: Film rupture is recognized on a part of the film on the inner and outer surfaces of the can

(3) Deep drawing workability-2 ○: Both inner and outer surfaces were processed without any abnormality, and rust prevention test of the film surface inside the can (1% NaCl water was put in the can, electrodes were inserted, and the can was The current value when a voltage of 6 V is applied to the anode is measured.
X: The film has no abnormality on both the inner and outer surfaces, but the current value is 0.1 mA or more in the ERV test, and when the energized portion is observed under magnification, pinhole-shaped cracks starting from the coarse lubricant are observed in the film.

(4) Impact cracking resistance Cans with good deep drawing were filled with water, 10 pieces of each test were dropped from a height of 30 cm on a PVC tile floor for each test, and ERV test in the cans was performed. As a result, ○: 0.1 mA or less for all 10 pieces Δ: 0.1 mA or more for 1 to 5 pieces ×: 0.1 mA or more for 6 pieces or more, or already after dropping Cracked film was found

(5) Heat Embrittlement Resistance The can which had been subjected to good deep drawing was heated and maintained at 200 ° C. for 5 minutes, and then subjected to impact cracking resistance evaluation described in (4). C: 0.1 mA or less for 10 pieces Δ: 0.1 mA or more for 1 to 5 pieces X: 0.1 mA or more for 6 pieces or more, or after heating at 200 ° C. for 5 minutes, Cracks were found

Table 7 shows the results of the above five evaluations.

[0064]

[Table 7]

From the results shown in Table 7, it can be seen that the films of the examples are excellent in lamination suitability, deep drawing workability, impact cracking resistance and heat resistance.

[0066]

The polyester film for laminating a metal plate of the present invention can be formed into a metal can by laminating a metal plate after laminating the metal plate with a metal plate. It is excellent in impact resistance and heat resistance after can making, and is extremely useful for metal containers.

[Brief description of the drawings]

FIG. 1 is a schematic view of a projection of a polyester film (thin film) of the present invention, in which dents are formed around particles formed on the surface , A is a plan view, and B is a cutaway view. It is.

FIG. 2 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. 3 is a differential interference micrograph (at a magnification of 650) showing the surface shape of a conventional polyester thin film .

FIG. 4 is a differential interference micrograph (at a magnification of 650) showing the surface shape of the polyester thin film of the present invention.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI // B29K 7:00 67:00 C08L 67:02 (56) References JP-A-5-186612 (JP, A) JP-A Heisei 5-156040 (JP, A) JP-A-3-86729 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08J 5/18 B32B 15/08 104 B29C 55/12

Claims (1)

(57) [Claims] A copolymer polyester mainly composed of polyethylene terephthalate and having a melting point of from 210 to 245 ° C.
60% by weight and a melting point of mainly polybutylene terephthalate or polybutylene terephthalate of 180 to 22
Consisting of 1 to 40% by weight of a copolymerized polyester at 3 ° C,
It contains a lubricant having an average particle diameter of 2.5 μm or less, a plane orientation coefficient of 0.08 to 0.16, and a heat shrinkage at 150 ° C. of 10%.
A polyester film for laminating metal sheets, wherein the density is less than 1.385 g / cm ³ and the projections on the film surface satisfy the following formula. (Equation 1)