JPH04261826A - Polyester film for laminating metallic sheet - Google Patents

Abstract

PURPOSE:To provide the polyester film excellent in deep drawing workability, the impact resistance after can-making, heat resistance and retort treatment resistance when a metallic can is formed by can-making e.g. deep drawing after a metallic sheet has been stuck to said film. CONSTITUTION:The title polyester film contains the lubricant with the average diameter of at most 2.5mum, and is composed of the copolymerized polyester in which the melting point of polymer is 210-245 deg.C, and further has the refractive index of 1.505-1.55 in its thickness direction and the proper viscosity of 0.52-0.80 of the polymer part of said film.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a polyester film for laminating and forming metal plates, and more specifically, it exhibits excellent moldability when laminated with metal plates and is used in can-making processes such as drawing, and is heat resistant. The present invention relates to a polyester film for bonding and forming metal plates, which can be used to manufacture metal cans such as beverage cans and food cans, which have excellent properties such as durability, retort resistance, and aroma retention.

0002

[Prior Art] Metal cans are generally coated with paint to prevent corrosion on the inside and outside surfaces, but recently, for the purpose of simplifying processes, improving hygiene, and preventing pollution, rust prevention without the use of organic solvents has been applied. Development of methods to obtain this property is progressing, and one such method is coating with a thermoplastic resin film. That is,
Studies are underway on a method of laminating a thermoplastic resin film onto a metal plate such as tinplate, tin-free steel, or aluminum, and then producing cans by drawing or the like. Polyolefin films and polyamide films have been tried as this thermoplastic resin film, but these do not satisfy all of the moldability, heat resistance, and fragrance retention properties.

On the other hand, polyester films, particularly polyethylene terephthalate films, have attracted attention as having well-balanced properties, and several proposals have been made based on them. That is, (A) a biaxially oriented polyethylene terephthalate film is laminated to a metal plate via an adhesive layer of low melting point polyester and used as a can making material (Japanese Patent Application Laid-open No. 56-10451).
No., JP-A-1-192546). (B) An amorphous or extremely low crystallinity aromatic polyester film is laminated onto a metal plate and used as a can-making material (JP-A No. 1-192545, JP-A No. 2-573)
No. 39). (C) A heat-set biaxially oriented polyethylene terephthalate film with low orientation is laminated onto a metal plate and used as a can-making material (Japanese Patent Laid-Open No. 64-22530).

However, studies conducted by the present inventors revealed that neither of them had sufficient characteristics, and each had the following problems.

Regarding (A), biaxially oriented polyethylene terephthalate film has excellent heat resistance and fragrance retention, but
Molding processability is insufficient, and film whitening (minor cracks) and breakage occur during can-making processing that involves large deformation.

Regarding (B), since it is an amorphous or extremely low-crystalline aromatic polyester film, it has good moldability, but its aroma retention is poor, and it is difficult to print or retort sterilization after can manufacturing. There is a risk that the film will become brittle due to post-treatments such as the above, and furthermore, may become brittle due to long-term storage, and may deteriorate into a film that is easily broken by impact from outside the can.

Regarding (C), it is intended to be effective in the intermediate region between (A) and (B), but it has not yet reached a low orientation that can be applied to can manufacturing processing, and Even if processing is possible in an area with a small degree of deformation, subsequent printing and other retort processing to sterilize the contents of the can can easily cause the film to become brittle and deteriorate into a film that is more likely to break due to impact from the outside of the can. is the same as (B) above.

[0008]

[Problems to be Solved by the Invention] The present inventors have conducted intensive research to develop a polyester film for can manufacturing that does not have these problems, and as a result, they have arrived at the present invention.

[0009]

[Means for Solving the Problems] That is, the present invention comprises a copolymerized polyester containing a lubricant having an average particle size of 2.5 μm or less and having a polymer melting point of 210 to 245°C,
The refractive index in the film thickness direction is 1.505 to 1.550
and the intrinsic viscosity of the polymer part of the film is 0.52
This is a polyester film for metal plate lamination molding processing, characterized in that the polyester film has a polyester film of 0.80 to 0.80.

A representative 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. The acid component includes aromatic dibasic acids such as isophthalic acid, phthalic acid, and naphthalene dicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid, and alicyclic acids 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.

[0011] The proportion of the copolymerized components is such that the resulting polymer melting point is in the range of 210 to 245°C, preferably 215 to 235°C, although it depends on the type. If the polymer melting point is less than 210° C., the heat resistance will be poor and it will not be able to withstand heating during printing after can manufacturing. On the other hand, the polymer melting point is 2
If the temperature exceeds 45°C, the crystallinity of the polymer will be too large and moldability will be impaired.

[0012] Here, the melting point of the copolyester was measured using Du Pont Instruments 910.
The method is to determine the melting peak using DSC at a heating rate of 20°C/min. Note that the sample amount was approximately 20 mg.

The copolyester of the present invention contains a lubricant having an average particle size of 2.5 μm or less. This lubricant may be inorganic or organic, but inorganic lubricants are preferred. Inorganic lubricants include silica, alumina, titanium dioxide,
Examples include calcium carbonate and barium sulfate, and examples of organic lubricants include silicone particles. Both require an average particle size of 2.5 μm or less. If the average particle size of the lubricant exceeds 2.5 μm, coarse lubricant particles (for example, 10 μm) are
(particles larger than m) become the starting point, causing pinholes,
This is not preferable because it may break in some cases.

[0014] Particularly preferable lubricants from the point of view of pinhole resistance are monodisperse lubricants 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. be. Examples of such lubricants include true spherical silica and true spherical silicone particles.

Here, the average particle size and particle size ratio of the spherical monodisperse lubricant can be determined by first depositing metal on the particle surface and then using an electron microscope to obtain an image magnified 10,000 to 30,000 times. It is calculated by finding the minor axis and the area-circle-equivalent diameter, and then applying these to the following formula.

Average particle diameter = sum of area-circle-equivalent diameters of particles to be measured/ratio of several particle diameters of particles to be measured = average major diameter of particles/average minor diameter of the particles Also, the spherical lubricant particles must have a sharp particle size distribution. is preferable,
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 (Equation 1).

[0018]

[Math 1]

The amount of lubricant in the copolyester may be determined depending on the winding properties in the film manufacturing process. Generally, it is preferable to add a small amount of large particles and a large amount of small particles. For example, it is preferable to add about 0.05% by weight of silica with an average particle size of 2.0 μm, and about 0.3% by weight of titanium dioxide with an average particle size of 0.3 μm. It is also possible to make the film opaque by intentionally adjusting the pigment in the lubricant. For example, 1 titanium dioxide
By adding 0 to 15% by weight, a white film can be obtained.

The copolyester used in the present invention is not limited by its manufacturing method. For example, terephthalic acid, ethylene glycol, and a copolymer 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 copolymer component are transesterified. A method is preferably used in which the reaction product is reacted and then the resulting reaction product is subjected to a polycondensation reaction to obtain a copolymerized polyester. In the production of copolymerized polyester, other additives such as antioxidants, heat stabilizers, ultraviolet absorbers, antistatic agents, etc. can also be added as necessary.

The polyester film of the present invention is obtained by melting the above-mentioned lubricant-containing copolyester and extruding it from a die to form a film, which is then biaxially stretched and heat-set. This film must 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. If this refractive index is less than 1.505, moldability will be insufficient, while if it exceeds 1.550 (i.e., excessively low orientation), the structure will be close to amorphous, resulting in poor heat resistance. 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 using a monochromatic NaD line. The mounting liquid used was methylene iodide, 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, particularly preferably 0.57 or more and 0.65 or less. If the intrinsic viscosity is less than 0.52, even if the other physical properties are suitable and the lamination to a metal plate and the can manufacturing process by deep drawing are performed well, the can must be retorted for sterilization after filling the can contents. Due to the treatment or the subsequent long-term storage, the film tends to become brittle, making it more likely to break due to impact from outside the can. On the other hand, those having an intrinsic viscosity of more than 0.80 are of excessive quality and are not economical because the productivity of the raw polymer decreases.

[0025] Here, the intrinsic viscosity is a value measured at 25°C using orthochlorophenol as a solvent.

The polyester film of the present invention preferably has a thickness of 6 to 75 μm. Further 10-75 μm
, particularly preferably 15 to 50 μm. Thickness is 6
If it is less than μm, breakage etc. will easily occur during processing;
Anything larger than 5 μm is of excessive quality and is uneconomical.

[0027] Suitable metal plates for can manufacturing to which the polyester film of the present invention is laminated are plates made of tinplate, tin-free steel, aluminum, and the like. The polyester film can be laminated to the metal plate by, for example, the following methods (1) and (2).

(2) A metal plate is heated above the melting point of the film, a film is bonded to the metal plate, and then rapidly cooled to amorphize the surface layer (thin layer) of the film in contact with the metal plate to form a close contact.

(2) A film is coated with an adhesive layer in advance with a primer, and this surface is bonded to a metal plate. The adhesive layer may be a known resin adhesive such as an epoxy adhesive,
Epoxy-ester adhesives, alkyd adhesives, etc. can be used.

[0030]

[Examples] The present invention will be further explained below with reference to Examples.

[0031]

[Examples 1-4 and Comparative Examples 1-2] Average particle size 1.5μ
Copolymerized polyethylene terephthalate (intrinsic viscosity 0.67) containing 0.1% by weight of spherical monodispersed silica (particle size ratio 1.07, relative standard deviation 0.1) and copolymerized with the components shown in Table 1. ) was melt-extruded at the temperature shown in the same table and rapidly solidified to obtain an unstretched film.

Next, this unstretched film was longitudinally stretched and transversely stretched under the conditions shown in the same table, followed by heat setting treatment to obtain a biaxially oriented film having a thickness of 25 μm.

Table 5 shows the properties of this film.

[0034]

[Table 1]

[0035]

[Example 5 and Comparative Example 3] Polyethylene terephthalate copolymerized with 12 mol% isophthalic acid (intrinsic viscosity 0.67) containing the lubricant shown in Table 2 was melt-extruded at 280°C and rapidly solidified to form an unstretched film. Then, the unstretched film was subjected to longitudinal stretching at a temperature of 115°C and a longitudinal stretching ratio of 3.0 times.
Biaxial stretching was carried out successively at a transverse stretching temperature of 130°C and a transverse stretching ratio of 3.0 times, followed by heat setting at 190°C.

Table 5 shows the properties of the biaxially oriented film obtained.

[0037]

[Table 2]

[0038]

[Comparative Examples 4 and 5] 12 mol% isophthalic acid copolymerized polyethylene containing 0.1% by weight of spherical monodisperse silica with an average particle size of 1.5 μm (particle size ratio 1.07, relative standard deviation 0.1) Terephthalate (intrinsic viscosity 0.67) at 280℃
The film was melt-extruded and rapidly solidified to obtain an unstretched film.

Next, this unstretched film was longitudinally stretched and transversely stretched under the conditions shown in Table 3, followed by heat setting treatment to obtain a biaxially oriented film. Table 5 shows the properties of this film.

[0040]

[Table 3]

[0041]

[Comparative Examples 6 to 9] Contains 0.1% by weight of spherical monodisperse silica with an average particle size of 1.5 μm (particle size ratio 1.07, relative standard deviation 0.1), and contains the components shown in Table 4. Polymerized copolymerized polyethylene terephthalate (intrinsic viscosity: 0.67) was melt-extruded at the temperature shown in the same table and rapidly solidified to obtain an unstretched film.

Next, this unstretched film was longitudinally stretched and transversely stretched under the conditions shown in the same table, followed by heat setting treatment to obtain a biaxially oriented film with a thickness of 25 μm.

Table 5 shows the properties of this film.

[0044]

[Table 4]

A total of 14 types of films obtained in Examples 1 to 5 and Comparative Examples 1 to 9 were heated to 260° C. to a thickness of 0.
It was pasted on both sides of 25mm tin-free steel, cooled in water, cut into a disc shape with a diameter of 150mm, and deep-drawn in three stages using a drawing die and punch to form a container with seamless sides (hereinafter referred to as a can) with a diameter of 55mm. (abbreviated) was created.

The following observations and tests were performed on this can, and each was evaluated based on the following criteria.

(1) Deep drawing workability - 1○: The film was processed without any abnormalities on both the inner and outer surfaces of the can, and no whitening or breakage was observed in the film on the inner and outer surfaces of the can. △: Whitening is observed on the upper part of the film on the inner and outer surfaces of the can. ×: Film breakage was observed in part of the film on the inner and outer surfaces of the can.

(2) Deep drawing workability - 2○: Both the inner and outer surfaces were processed without any abnormalities, and the rust prevention test (1%
Put NaCl water into the can, insert an electrode, and measure the current value when a voltage of 6V is applied using the can as an anode. Below E
(abbreviated as RV test) shows 0.2 mA or less. ×: There is no abnormality in the film on both the inner and outer surfaces, but in the ERV test, the current value was 0.2 mA or more, and when the energized area was observed under magnification, pinhole-shaped cracks originating from the coarse lubricant were observed in the film.

(3) Impact cracking resistance Cans with good deep drawing were filled with water, and for each test, 10 cans were dropped from a height of 1 m onto the PVC tile floor, and then an ERV test was conducted inside the can. I did it. ○: 0.2 mA or less for all 10 pieces. Δ: 0.2 mA or more for 1 to 5 pieces. ×: The voltage was 0.2 mA or more for 6 or more pieces, or cracks in the film were already observed after being dropped.

(4) Heat embrittlement resistance After the cans that had been well deep-drawn were heated and held at 210°C for 5 minutes, the impact cracking resistance was evaluated as described in (3). ○: 0.2 mA or less for all 10 pieces. Δ: 0.2 mA or more for 1 to 5 pieces. ×: 0.2 mA or more for 6 or more pieces, or cracks in the film were already observed after heating at 210° C. for 5 minutes.

(5) Retort resistance Cans with good deep drawing were filled with water, retorted in a steam sterilizer at 130°C for 1 hour, and then stored at 50°C for 30 days. For each test, 10 of the obtained cans were dropped from a height of 1 m onto a PVC tile floor, and then an ERV test inside the can was conducted. ○: 0.2 mA or less for all 10 pieces. Δ: 0.2 mA or more for 1 to 5 pieces. ×: The voltage was 0.2 mA or more for 6 or more pieces, or cracks in the film were already observed after being dropped.

[0052]

[Table 5]

From the results in Table 5, it can be seen that the films of Examples are excellent in all of the deep drawing properties, impact cracking resistance, heat resistance, and retort resistance.

[0054]

Effects of the Invention The polyester film for laminating and forming metal plates of the present invention has good deep drawing workability when forming metal cans by performing can-making processing, for example, deep drawing, after laminating with metal plates. It has excellent impact resistance, heat resistance and retort resistance, and is extremely useful for metal containers.

Claims (1)

[Claims] [Claim 1] A copolymerized polyester containing a lubricant with an average particle diameter of 2.5 μm or less and a polymer melting point of 210 to 245°C, and a refractive index in the thickness direction of the film of 1.50.
5 to 1.550, and the polymer portion of the film has an intrinsic viscosity of 0.52 to 0.80.