JPH07101013A - Polyester film for laminating and molding metal plates - Google Patents

Abstract

PURPOSE:To improve impact resistance and taste retentivity while holding excellent mold processability, heat resistance, retort resistance and perfume retentivity of copolymer polyester film. CONSTITUTION:A polyester film for laminating and molding metal plates comprises a copolymer polyester layer (A) having a melting point of 210-345 deg.C and glass transition temperature of 60 deg.C or higher, a polyester layer (B) made of polyester composition of a mixture of 80-45wt.% of copolymer polyester (I) having a main repetition unit of ethylene terephthalate having 210-245 deg.C and 20-55wt.% of polyester (II) having main repetition unit of butylene terephthalate having a melting point of 180-223 deg.C laminated, wherein surface roughness (Ra) of the layer (A) is 15nm or less, and surface roughness (Ra) of the layer (B) is l5nm or more.

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 specifically, it shows excellent forming processability when it is laminated with a metal plate to perform can forming processing such as drawing. Polyester film for metal plate laminating and forming process capable of producing metal cans having excellent properties and excellent in heat resistance, retort resistance, flavor retention, impact resistance, etc., such as beverage cans and food cans Regarding

[0002]

2. Description of the Related Art Metal cans are generally painted 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 the use of 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,
A method of making a can by drawing a thermoplastic resin film on a metal plate such as tin plate, tin-free steel, or aluminum is being studied. A polyolefin film or a polyamide film has been tried as the thermoplastic resin film, but it does not satisfy all of the molding processability, heat resistance, flavor retention, and impact resistance.

On the other hand, a polyester film, especially a polyethylene terephthalate film, has been noted as having 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 an adhesive layer of low melting point polyester and used as a can-making material (JP-A-56-1045).
No. 1, 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 and JP-A-2-57).
339). (C) A low orientation, heat-set, 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).

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

Regarding (A), the biaxially oriented polyethylene terephthalate film is excellent in heat resistance and aroma retention,
Molding processability is insufficient, and whitening of the film (generation of microcracks) and breakage occur in the can-making process involving large deformation.

As for (B), since it is an amorphous or extremely low crystalline aromatic polyester film, it has good moldability, but it is inferior in aroma retention, and printing after can making and retort sterilization treatment. After treatment such as the above, and further storage for a long period of time, the film is liable to become brittle, and there is a possibility that the film is deteriorated by a shock from the outside of the can.

Regarding (C), although it is intended to exert its effect in the intermediate region between the above (A) and (B), it has not yet reached the low orientation applicable to can manufacturing, and Even if it can be processed in a region with a low degree of deformation, subsequent printing,
As in the case of (B), another retort treatment for sterilizing the contents of the can makes the film more fragile and may be transformed into a film that is easily cracked by an impact from the outside of the can.

In order to solve such a problem, the present inventors have made various studies in consideration of using a film made of a copolyester. As a result, the copolyester film is excellent in molding processability, heat resistance, retort resistance, and aroma retention, but has good taste retention, impact resistance, especially impact resistance at a low temperature of 15 ° C or lower. It is insufficient, and it has been found that when a metal can to which this film is attached is dropped at low temperature and is given an impact, the film is likely to be cracked. Poor impact resistance at low temperatures is a serious problem for those handled in a cooled state such as juice and metal cans for soft drinks.

[0009]

The object of the present invention is to improve impact resistance while maintaining the excellent molding processability, heat resistance, retort resistance and aroma retention which the copolyester film has. Another object of the present invention is to provide a polyester film for metal plate laminating and forming, which is less likely to be cracked by impact, especially at low temperatures, and which does not deteriorate the taste of soft drinks and the like.

[0010]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that a film has a polyester containing ethylene as a main repeating unit and a polyester containing butylene terephthalate as a main repeating unit. By comprising two layers including a layer of the polyester composition blended in a specific ratio, and limiting the surface roughness of each layer to a specific range, the impact resistance and the taste retention at low temperatures are remarkably improved, and The present invention has been completed by finding that deterioration of winding property can be avoided.

That is, the present invention has a melting point of 210 to 245.
C., a copolymerized polyester layer (A) having a glass transition temperature of 60.degree. C. or more, and a copolymerized polyester (I) having a melting point of 210 to 245.degree. C. as a main repeating unit and having 80 to 45% by weight and a melting point of 180. ~ 223 ° C
And a polyester layer (B) composed of a polyester composition containing 20 to 55% by weight of polyester (II) containing butylene terephthalate as a main repeating unit, and a surface roughness of the copolymerized polyester layer (A). Sa (R
a) is 15 nm or less, and the surface roughness (Ra) of the polyester layer (B) is 15 nm or more, which is a polyester film for metal plate laminating and forming.

In the present invention, a typical example of the copolymerized polyester used as the copolymerized polyester (I) of the copolymerized polyester layer (A) and the polyester layer (B) is copolymerized polyethylene terephthalate. The 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 thereof, but as a result, the melting point is 210 to 245 ° C., preferably 215.
The ratio is in the range of ˜235 ° C. If the melting point is less than 210 ° C, the heat resistance will be poor. On the other hand, the melting point is 245 ° C.
When it exceeds, the crystallinity of the polymer is too large and the moldability is impaired.

Here, the melting point of the copolyester is measured by Du Pont Instruments 910.
According to a method of determining a melting peak at a temperature rising rate of 20 ° C./minute using DSC. The sample amount is about 20 mg.

The intrinsic viscosity of the copolyester is preferably 0.52 to 0.80, more preferably 0.54 to 0.70, and particularly preferably 0.57 to.
It is 0.65.

Further, the copolymerized polyester constituting the copolymerized polyester layer (A) in the present invention needs to have a glass transition temperature of 60 ° C. or higher, preferably 70 ° C. or higher. If the second-order transition temperature is lower than 60 ° C, satisfactory aroma-retaining property cannot be obtained. As such a copolymerized polyester, isophthalic acid copolymerized polyethylene terephthalate is particularly preferable because a copolymerized polyester having a high glass transition temperature can be obtained.

In the present invention, the polyester (II) constituting the polyester layer (B) is a polyester having butylene terephthalate as a main repeating unit, and may be a homopolymer or a copolymer.

The copolymerization component in the copolymer may be an acid component or an alcohol component. Examples of the copolymeric 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 fats such as cyclohexanedicarboxylic acid. Examples thereof include cyclic dicarboxylic acids, and examples of the copolymerized alcohol component include aliphatic diols such as ethylene glycol 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 thereof, but as a result, the melting point is 180 to 223 ° C., preferably 2
The ratio is in the range of 00 to 223 ° C, more preferably 210 to 223 ° C. If the melting point is less than 180 ° C, the heat resistance will be poor. The melting point of the polybutylene terephthalate homopolymer is 223 ° C.

The melting point of this polyester is measured in the same manner as the measurement of the copolyester described above by Du Pont.
Performed using Instruments 910 DSC.

In the polyester film of the present invention,
The polyester layer (B) is mainly composed of polyethylene terephthalate and has a melting point of 210 to 245 ° C. and is 80 to 45% by weight, preferably 70 to 45% by weight,
More preferably, it is 59 to 50% by weight, and polybutylene terephthalate or a copolyester 20 mainly composed of polybutylene terephthalate and having a melting point of 180 to 223 ° C.
55% by weight, preferably 30 to 55% by weight, more preferably 41 to 50% by weight. When the polybutylene terephthalate or polybutylene terephthalate copolymerized polyester is less than 20% by weight and the polyethylene terephthalate copolymerized polyester exceeds 80% by weight, impact resistance at low temperature cannot be improved. If the polybutylene terephthalate or polybutylene terephthalate copolymerized polyester exceeds 55% by weight and the polyethylene terephthalate copolymerized polyester is less than 45% by weight, the heat resistance of the film decreases and the impact resistance becomes insufficient.

In the present invention, the copolyester used in the copolyester (I) of the copolyester layer (A) and the polyester layer (B) and the polyester used in the polyester (II) of the polyester layer (B) are , The manufacturing method is not limited.
For example, in the case of a copolyester mainly composed of polyethylene terephthalate, 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 copolyester, or Is preferably a method in which dimethyl terephthalate, ethylene glycol and a copolymerization component are transesterified, and the resulting reaction product is subjected to polycondensation reaction to obtain a copolymerized polyester. In the production of each copolyester and polybutylene terephthalate, if necessary, other additives, such as antioxidants,
A heat stabilizer, a UV absorber, an antistatic agent, etc. can also be added.

The surface roughness (Ra) of the copolyester layer (A) must be 15 nm or less. Preferably 12 nm or less, more preferably 10 n
m or less. The copolyester layer (A) is a layer located on the side in contact with the contents of the can when it is attached to a metal can. By setting this surface roughness (Ra) to 15 nm or less, the contents, especially It can prevent the taste of the soft drink from becoming bad.

In order to reduce the surface roughness (Ra) to 15 nm or less, the average particle diameter and the amount of the lubricant added to the copolyester may be appropriately selected. For example, when silica is used as a lubricant, 0.04% by weight or less of silica having an average particle size of 1.5 μm and 0.36% by weight or less of silica having an average particle size of 0.8 μm may be added. . When the addition amount is 0.2% by weight, the average particle diameter of silica is 0.9
When the addition amount is 5 μm or less and the addition amount is 0.05% by weight, the average particle diameter of silica may be 1.33 μm or less. In this case, lubricants having different types and average particle sizes may be mixed and used.

Further, the polyester layer (B) must have a surface roughness (Ra) of 15 nm or more.
If the surface roughness (Ra) is less than 15 nm, the handling property (winding property) of the film is deteriorated, which is unsuitable.

The polyester layer (B) is a layer on the side adhered to the metal can when the film is laminated to the metal can.
Since it does not come into direct contact with the contents of the can, the surface roughness (R
Even if a) is 15 nm or more, the taste of the contents is not deteriorated.

Also in the case of the polyester layer (B), a desired surface roughness (Ra) can be obtained by appropriately controlling the average particle size and the amount of the lubricant added to the copolyester.

The lubricant added to the copolyester layer (A) and the polyester layer (B) may be inorganic or organic, but inorganic is preferred. As an inorganic lubricant,
Examples thereof include silica, alumina, titanium dioxide, calcium carbonate, barium sulfate, and the like, examples of the organic lubricant include silicone resin particles, crosslinked polystyrene particles, and the like. In particular, the preferable lubricant in terms of pinhole resistance is a monodispersed lubricant having a particle size ratio (major axis / minor axis) of 1.0 to 1.2. Examples of such a lubricant include true spherical silica and true spherical silicone particles.

The surface roughness (Ra) of the film is J
It is the center line average roughness obtained according to IS-B0601, and a portion of the measurement length L is extracted from the film surface roughness curve in the direction of the center line, and the center line of the extracted portion is taken as the X axis, and the vertical magnification is set. Is the Y axis, and the roughness curve is Y =
When represented by f (x), the value (R
a: nm) is defined as the film surface roughness.

[0030]

[Equation 1]

In the present invention, the reference length is 2.5 mm and 5
Ra is expressed as an average value of four measured values, one of which is the largest value.

The polyester film of the present invention has a structure in which a copolyester layer (A) and a polyester layer (B) are laminated, and the film having such a two-layer structure constitutes each layer, for example. Melting the copolyester and the polyester composition separately, coextruding, after laminating and fusion bonding before solidification, biaxial stretching, heat setting method, the copolyester and the polyester composition are separately melted and extruded It can be produced by a method of forming a film, unstretched or stretched, and then laminating and fusing both.

The polyester film has a surface roughness (R
a) When it is composed only of the copolyester layer (A) having a thickness of 15 nm or less, the impact resistance at low temperature becomes insufficient and the handleability (winding property) becomes worse. On the contrary, when the surface roughness (Ra) is composed of only the polyester layer (B) having a thickness of 15 nm or more, the taste retention property is deteriorated and the taste of the can contents is deteriorated, which is not suitable.

The polyester film of the present invention may be an unstretched film, but it is usually biaxially stretched and heat-set. In this case, the refractive index in the thickness direction of the copolyester layer (A) is 1.505 to 1.55.
It is preferably 0, more preferably more than 1.510 and 1.540 or less. If this refractive index is too low, moldability becomes insufficient, while if it is too high, the structure becomes close to amorphous, and the heat resistance may decrease.

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.

Thickness T of Copolyester Layer (A)
The ratio of the _A, and the thickness T _B of the polyester layer (B) (T _A /
T _B ) is preferably about 0.02 to 0.67, more preferably 0.04 to 0.43, and particularly preferably 0.04.
˜0.25. Specifically, for example, the thickness is 25 μm
In case of polyester film, polyester layer (B)
Has a thickness of 0.5 to 10 μm, preferably 1 to 7.5 μm
m, and more preferably 1 to 5 μm.

As the metal plate to which the polyester film of the present invention is stuck, particularly the metal plate for can manufacturing, tin, tin-free steel, aluminum and the like plates are 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 laminated and then cooled, and the surface layer portion (thin layer portion) of the film in contact with the metal plate is made amorphous and brought into close contact.

An adhesive layer is preliminarily coated on the film with a primer, and this surface is bonded to a metal plate. As the adhesive layer, a known resin adhesive, for example, an epoxy adhesive,
Epoxy-ester adhesives, alkyd adhesives, etc. can be used.

When the polyester film of the present invention is attached to a metal plate, the surface roughness (Ra) is 15 n.
The copolymerized polyester layer (A) having a size of m or less is laminated so as to come into contact with the contents. For example, when the polyester film of the present invention is attached to the inside of a metal can, the polyester layer (B) side is attached to the can.

Further, in the polyester film of the present invention, if necessary, another additional layer may be laminated between the copolyester layer (A) and the polyester layer (B) or on one side.

[0042]

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

[0043]

Examples 1 to 8 and Comparative Examples 1 to 7 Polyethylene terephthalate obtained by copolymerizing the components shown in Table 1 (intrinsic viscosity 0.6
4, containing 0.1% by weight of spherical silica having a particle size ratio of 1.1 and an average particle size of 0.3 μm) is a copolyester layer (A),
Similarly, the polyester composition shown in Table 1 (having a particle size ratio of 1.
1, containing 0.1% by weight of true spherical silica having an average particle diameter of 1.5 μm) as the copolyester layer (B),
Each of them was individually dried and melted by a conventional method, then coextruded from dies adjacent to each other, laminated, fused and rapidly cooled and solidified to prepare an unstretched laminated film.

Next, this unstretched film was longitudinally stretched at 110 ° C. to 3.0 times, and then transversely stretched at 125 ° C. to 3 times,
It was heat-set at 190 ° C. to obtain a biaxially oriented laminated film.

The thickness of the obtained film was 25 μm, the thicknesses of the copolyester layer (A) and the copolyester layer (B) were 5 μm and 20 μm, and the surface roughness (Ra) was 5 nm and 23 nm, respectively. Met.

The surface roughness (Ra) is a stylus surface roughness meter (SURFCORDERS S, manufactured by Kosaka Laboratory Ltd.).
E-30C), stylus radius 2 μm, measuring pressure 0.0
It was measured under the conditions of 3 g and a cutoff value of 0.25 mm.

[0047]

[Table 1]

[0048]

[Comparative Examples 8 to 9] In Example 2, only the copolyester layer (A) (Comparative Example 8) and the polyester layer (B) (Comparative Example 9) having a thickness of 25 μm were used without the two-layer laminated structure.
A single layer film of

[0049]

Examples 9 to 10 and Comparative Examples 10 to 11 Table 2 shows the average particle size and amount of spherical silica contained in the copolyester layer (A) and the copolyester layer (B) in Example 2. To change the surface roughness (R
A) was changed and the other conditions were the same as in Example 2 to obtain a biaxially oriented laminated film.

[0050]

[Table 2]

A total of 21 kinds of films obtained in Examples 1 to 10 and Comparative Examples 1 to 11 were laminated on both sides of tin-free steel heated to 230 ° C. and having a plate pressure of 0.25 mm.
After cooling with water, it was cut into a disk shape having a diameter of 150 mm, and deep drawing was performed in four 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 the cans, and the cans were evaluated according to the following standards.

(1) Deep drawing workability-1 ○: The film was processed without any abnormalities, and no whitening or breakage was observed in the film. Δ: Whitening is observed at the top of the film can. X: Film breakage is observed in a part of the film.

(2) Deep drawing workability-2 ○: Processed without any abnormality, rust resistance test of film surface in can (1% NaCl water was put in the can, an electrode was inserted, and the can body was used as an anode. The current value when a voltage of 6 V is applied is measured.
Hereinafter, it is 0.1 mA or less in the ERV test. X: There is no abnormality in the film, but the current value is 0.1 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.

(3) Impact resistance With respect to cans having good deep-drawing, after pouring water into them and cooling them to 0 ° C., 10 pieces for each test were dropped from a height of 30 cm onto the PVC tile floor. As a result of the ERV test in the can, ◯: 0.1 mA or less for all 10 pieces. (Triangle | delta): It was 0.1 mA or more about 1-5 pieces. X: 0.1 mA or more for 6 or more, or cracks of the film were already observed after dropping.

(4) Heat embrittlement resistance After the cans, which had been well drawn by deep drawing, were heated and held at 200 ° C. for 5 minutes, the impact resistance evaluation described in (3) was carried out. Was 0.1 mA or less. (Triangle | delta): It was 0.1 mA or more about 1-5 pieces. X: 0.1 mA or more for 6 or more or cracks were already observed in the film after heating at 200 ° C. for 5 minutes.

(5) Retort resistance The cans which were well formed by deep drawing were filled with water, retort-treated at 120 ° C. for 1 hour in a steam sterilizer, and then stored at 50 ° C. for 30 days. Ten of the obtained cans were dropped from the height of 30 cm for each test on the PVC tile floor surface, and then an ERV test in the cans was performed.

◯: 0.1 mA or less for all 10 pieces. (Triangle | delta): It was 0.1 mA or more about 1-5 pieces. ×: 0.1 mA or more for 6 or more, or cracks of the film were already observed after dropping.

(6) Taste Keeping A can that was well formed by deep drawing was filled with a cider and sealed. After holding at 37 ° C. for 30 days, the can was opened and the change in taste was examined by sensory test. ◯: There was no change in taste. Δ: A slight change in taste was observed. X: A change in taste was recognized.

The evaluation results and winding properties of the above 21 kinds of films are shown in Table 3.

[0061]

[Table 3]

As is clear from the results shown in Table 3, the can using the polyester film of the present invention is excellent in deep drawing workability, heat embrittlement resistance, retort resistance, and aroma retention, and also has impact resistance. In particular, it has excellent impact resistance at low temperatures, does not deteriorate the taste of soft drinks, and has good winding properties.

[0063]

EFFECT OF THE INVENTION The film for laminating and forming metal plates of the present invention has excellent forming processability, heat resistance, retort resistance, and aroma retention, and also has impact resistance, especially impact resistance at low temperature. Is improved, the taste of soft drinks is not deteriorated, and the winding property is good. Therefore, it is particularly suitable for being attached to a metal can for cooling soft drinks, which is often cooled and handled at low temperatures.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takafumi Kudo 3-37-19 Koyama, Sagamihara City, Kanagawa Teijin Limited Sagamihara Research Center

Claims (2)

[Claims] 1. A copolyester layer (A) having a melting point of 210 to 245 ° C. and a glass transition temperature of 60 ° C. or higher,
Copolyester (I) 80-having ethylene terephthalate having a melting point of 210 to 245 ° C. as a main repeating unit
Polyester (II) whose main repeating unit is butylene terephthalate having 45% by weight and a melting point of 180 to 223 ° C.
A polyester layer (B) made of a polyester composition blended with 20 to 55% by weight is laminated, and the surface roughness (Ra) of the copolyester layer (A) is 15 nm or less. ) Surface roughness (Ra) is 15
A polyester film for laminating and forming metal plates, which has a thickness of at least nm. 2. The polyester film for laminating and molding metal plates according to claim 1, wherein the copolyester layer (A) comprises isophthalic acid copolyethylene terephthalate.