JP2908193B2 - Polyester film for metal plate lamination processing - 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, it shows excellent moldability when laminating to a metal plate for can forming such as drawing. Good adhesion to metal plate, and good windability, and heat resistance, retort resistance, fragrance retention, impact resistance,
Further, the present invention relates to a polyester film for a metal plate laminating process capable of producing a metal can having excellent taste 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 tin, 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 moldability, heat resistance, fragrance preservation, and impact resistance.

On the other hand, polyester films, particularly polyethylene terephthalate films, have been attracting attention as having balanced properties, and some proposals based on these have been made. That is, (A) a biaxially oriented polyethylene terephthalate film is laminated on a metal plate via a low-melting-point polyester adhesive layer and used as a can-making material (JP-A-56-10451).
No. 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-forming material (Japanese Patent Laid-Open No. 1-192545, Japanese Patent Laid-Open No. 2-573).
No. 39). (C) A biaxially oriented polyethylene terephthalate film having low orientation and heat set is laminated on a metal plate and used as a material for can production (Japanese Patent Application 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 has the following problems.

Regarding (A), a biaxially oriented polyethylene terephthalate film is excellent in heat resistance and fragrance retention,
In the process of making cans with insufficient molding workability and large deformation, whitening (generation of minute cracks) and breakage of the film occur.

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 the printing and retort sterilization after can-making are performed. Such a film may be easily embrittled by post-treatments or storage for a long period of time, and may be changed to 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. Even if it can be processed in a region with a small degree of deformation, subsequent printing,
Similar to the above (B), the other retort treatment for sterilizing the contents of the can may easily cause embrittlement and may be transformed into a film which is easily broken by an impact from the outside of the can.

In order to solve such a problem, the present inventors have considered various uses of a film made of a copolymerized polyester and have made various studies. As a result, the copolymerized polyester film is excellent in molding workability, heat resistance, retort resistance, and fragrance retention, but has an impact resistance, particularly
It has been found that the impact resistance at a low temperature of 5 ° C. or less is insufficient, and when a metal can to which this film is bonded is dropped at a low temperature to give an impact, the film is easily cracked. Poor impact resistance at low temperatures poses a major problem when handled in a cooled state, such as metal cans for juices and soft drinks.

Further, the adhesion between the film and the metal plate is not always sufficient, and under severe conditions, there is a problem that the film may peel off.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to maintain the excellent moldability, heat resistance, retort resistance, and fragrance retention of a copolyester film, while retaining the taste retention and impact resistance. It is an object of the present invention to provide a polyester film for metal plate laminating and forming, which has improved properties and is less likely to cause cracks due to impact particularly at low temperatures.

[0011]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above-mentioned object, and as a result, the film is composed of two layers of a copolyester and the melting point of both copolyesters. By differentiating
Preferably, the use of a germanium catalyst as a polycondensation catalyst for both copolymerized polyesters improves the impact resistance at low temperatures, and further improves the taste retention if the surface roughness of each layer is in a specific range. As a result, it has been found that the winding property can be prevented from being deteriorated, and the present invention has been completed.

That is, the present invention has a melting point of 210 to 24.
5 ° C. of isophthalic acid copolymerized polyester layer (A), the melting point is by laminating a copolyester layer of 210~245 ℃ (B), the isophthalic acid copolymerized polyester layer
(A) having a surface roughness (Ra) of 15 nm or less;
The surface roughness (Ra) of the ester layer (B) is 15 nm or more
, And the and the isophthalic acid copolymerized polyester layer is the melting point of (A), the copolymerized polyester layer (B) higher than the melting point of the combined molding bonded metal plates, characterized in that the difference is 2 ℃ or more It is a polyester film for use.

In the present invention, copolymerized polyethylene terephthalate is a representative example of the copolymerized polyester used in the copolymerized polyester layer (B). This copolymer 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 decane dicarboxylic acid, and alicyclic groups such as cyclohexanedicarboxylic acid. Examples of the dicarboxylic acid include aliphatic alcohols such as butanediol and hexanediol, and alicyclic diols such as cyclohexanedimethanol. These can be used alone or in combination of two or more. Above all, isophthalic acid is particularly preferred.

The copolyester used in the isophthalic acid copolyester layer (A) of the present invention has excellent scent retention, and therefore, among the above copolyesters used in the copolyester layer (B). ,
It is a copolymerized polyester using isophthalic acid as an acid component, and a typical example is isophthalic acid copolymerized polyethylene terephthalate. In the isophthalic acid copolymerized polyester, as a copolymerizing component other than isophthalic acid, the copolymerizing component as exemplified as the copolymerizing component of the copolymerized polyester in the copolymerized polyester layer (B) does not impair its properties. It may be copolymerized at a ratio of 3 mol% or less to the acid component or all the alcohol components.

Isophthalic acid copolymerized polyester layer (A)
And the melting point of the copolymerized polyester layer (B) is 210 to 24.
5 ° C, preferably in the range of 221-240 ° C. If the melting point is lower than 210 ° C., the heat resistance will be poor. On the other hand, when the melting point exceeds 245 ° C., the crystallinity of the polymer is too large and the moldability is impaired.

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.

Further, in the present invention, the melting point of the isophthalic acid copolymerized polyester layer (A) must be higher than the melting point of the copolymerized polyester layer (B), and the difference must be 2 ° C. or more. It is preferably at least 3 ° C, more preferably at least 5 ° C. If this requirement is not satisfied, the impact resistance will not be improved.

The intrinsic viscosity of each copolymerized polyester of the isophthalic acid copolymerized polyester layer (A) and the copolymerized polyester layer (B) is preferably 0.52 to 0.80, more preferably 0.1 to 0.80. 54 to 0.70, particularly preferably 0.57 to 0.65.

Further, in the polyester film of the present invention, the isophthalic acid copolymerized polyester layer (A) comprises:
Its surface roughness (Ra) is 15 nm or less, preferably 12 nm or less.
nm or less, more preferably Ru 2~10nm der. The isophthalic acid copolymerized polyester layer (A) is a layer located on the side in contact with the contents of the can when bonded to a metal can. By setting the surface roughness (Ra) to 15 nm or less,
It is possible to improve the taste retention of the contents and to improve the impact resistance at low temperatures. If the surface roughness (Ra) is less than 2 nm, the surface of the film is easily damaged.

In order to reduce the surface roughness (Ra) to 15 nm or less, the average particle size and the amount of the lubricant to be added to the isophthalic acid copolymerized polyester may be appropriately selected. The lubricant may be inorganic or organic, but inorganic is preferred. As the inorganic lubricant, silica, alumina, titanium dioxide,
Calcium carbonate, barium sulfate and the like can be exemplified, and examples of the organic lubricant include silicone resin particles and cross-linked polystyrene particles. In particular, a lubricant which is preferable 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 spherical silica, spherical silicone resin particles, and spherical cross-linked polystyrene particles.

For example, when silica is used as a lubricant, 0.04% by weight or less for silica having an average particle size of 1.5 μm, and 0.36% for silica having an average particle size of 0.8 μm.
What is necessary is just to add below weight%. When the addition amount is 0.2% by weight, the average particle size of the silica is 0.95 μm or less.
When the addition amount is 0.05% by weight, the average particle size of the silica may be set to 1.33 μm or less.

On the other hand, the copolyester layer (B) has a surface roughness (Ra) of Ru der than 15 nm. If the surface roughness (Ra) is less than 15 nm, the handling (winding) of the film deteriorates, which is not appropriate.

When the film is bonded to a metal can, the copolyester layer (B) is a layer adhered to the metal can and does not come into direct contact with the contents of the can. Even if Ra) is 15 nm or more, the taste of the contents is not deteriorated.

In the case of the copolyester layer (B), the desired surface roughness (Ra) can be obtained by appropriately selecting the average particle size and the amount of the filler to be added to the copolyester within the above ranges. ) Can be obtained.

The surface roughness (Ra) of the film is J
This is the center line average roughness determined according to IS-B0601, and a portion of the measured length L is extracted from the film surface roughness curve in the direction of the center line, the center line of the extracted portion is defined as the X axis, and the longitudinal magnification 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.

[0026]

(Equation 1)

In the present invention, when the reference length is 2.5 mm, 5
The number is measured, and Ra is represented as an average of four values excluding one from the larger value.

The isophthalic acid copolymerized polyester and the copolymerized polyester in the present invention are not limited by the production method. For example, terephthalic acid, ethylene glycol and isophthalic acid or a copolymer component is subjected to an esterification reaction, and then the obtained reaction product is subjected to a polycondensation reaction to give an isophthalic acid copolymerized polyester or a copolymerized polyester, or dimethyl terephthalate,
A method of subjecting ethylene glycol and isophthalic acid or a copolymer component to a transesterification reaction and then subjecting the resulting reaction product to a polycondensation reaction to obtain an isophthalic acid copolymerized polyester or a copolymerized polyester is preferably used. As the transesterification catalyst, a manganese compound (for example, manganese acetate) or a titanium compound (for example, titanium acetate or titanium tetrabutoxide) is preferable. In the polymerization step, a germanium compound is used as a polycondensation catalyst.
Examples of the germanium catalyst include (a) amorphous germanium oxide (b) fine crystalline germanium oxide (c) a solution of germanium oxide dissolved in glycol in the presence of an alkali metal or alkaline earth metal or a compound thereof. A solution in which germanium oxide is dissolved in water is used.

The amount of the germanium compound catalyst is from 40 to 40 as the amount of germanium remaining in the copolymerized polyester.
200 ppm is preferable, and 60 to 150 ppm is more preferable.

In the production of the isophthalic acid copolyester or copolyester, other additives such as a fluorescent whitening agent, an antioxidant, a heat stabilizer, an ultraviolet absorber, an antistatic agent and the like are added as required. be able to.

The polyester film of the present invention has a laminated structure of an isophthalic acid copolymerized polyester layer (A) and a copolymerized polyester layer (B). Isophthalic acid copolymerized polyester and copolymerized polyester constituting the layer are separately melted and co-extruded from a die, laminated and fused before solidification, then biaxially stretched, heat-fixed, and each copolymerized polyester is separated. And then extruded into a film, in an unstretched state or after stretching, and then laminating and fusing them.

The polyester film of the present invention may be an unstretched film, but is usually used in a state of being biaxially stretched and heat set. In this case, the refractive index in the thickness direction of the isophthalic acid copolymerized polyester layer (A) is 1.490.
１．５1.550, more preferably more than 1.505 and not more than 1.540. If the refractive index is too low, the moldability will be insufficient, while if it is too high, the structure will be 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 is likely to occur during processing, while if it exceeds 75 μm, the quality is excessive and uneconomical.

Isophthalic acid copolymerized polyester layer (A)
The thickness T _S of the thickness T _A, copolyester layer (B)
The ratio of the (T _A / T _S) is preferably about 0.02 to 1.5, more preferably 0.04 to 0.67, particularly preferably 0.04 to 0.25. Specifically, for example, in the case of a polyester film having a thickness of 25 μm, the thickness of the isophthalic acid copolymerized polyester layer (A) is set to 0.5 to 15 μm.
μm, preferably 1 to 10 μm, more preferably 1 to 5
μm.

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. After the metal plate is heated above the melting point of the film and the films are bonded together, the film is cooled, and the surface layer (thin layer) of the film in contact with the metal plate is made amorphous and adhered. An 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.

When the polyester film of the present invention is bonded to a metal plate, the copolymerized polyester layer (B)
Side to the metal plate.

Further, in the polyester film of the present invention, if necessary, another additional layer may be laminated between the isophthalic acid copolymerized polyester layer (A) and the copolymerized polyester layer (B). Good.

[0038]

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

[0039]

Examples 1 to 6 and Comparative Examples 1 to 5 Polyethylene terephthalate prepared by copolymerizing the components shown in Table 1 (using antimony oxide as a polymerization catalyst, an intrinsic viscosity of 0.64, and a particle size ratio of 1.
1. 0.1% by weight of spherical silica having an average particle diameter of 0.3 μm
Is the isophthalic acid copolymerized polyester layer (A), and polyethylene terephthalate (antimony trioxide used as a polymerization catalyst, intrinsic viscosity 0.64, particle size ratio 1.1, average particle size) copolymerized with the components shown in Table 1 Each is dried and melted by a conventional method so that the spherical polyester having a diameter of 1.5 μm (containing 0.1% by weight of spherical silica) becomes a copolymerized polyester layer (B), and then co-extruded from dies adjacent to each other.
Laminating, fusing, and quenching and solidifying were performed to produce an unstretched laminated film.

Next, the unstretched film was longitudinally stretched 3.0 times at 110 ° C., and then transversely stretched 3 times at 120 ° C.
It was heat-set at 190 ° C. to obtain a biaxially oriented laminated film.

The thickness of the obtained film is 25 μm, the thickness of the isophthalic acid copolymerized polyester layer (A) and the copolymerized polyester layer (B) are 5 μm and 20 μm, respectively, and the surface roughness (Ra) is 5 nm and 5 nm, respectively. 23
nm.

The surface roughness (Ra) was measured by a stylus type surface roughness meter (SURFCORDER S manufactured by Kosaka Laboratory Co., Ltd.).
E-30C) using a stylus radius of 2 μm and a measurement pressure of 0.0
The measurement was performed under the conditions of 3 g and a cutoff value of 0.25 mm.

[0043]

[Table 1]

[0044]

Comparative Examples 6 and 7 In Example 2, only the isophthalic acid copolymerized polyester layer (A) (Comparative Example 6) and the copolymerized polyester layer (B) alone (Comparative Example 7) were not used as the two-layer laminated structure. Was prepared as a single-layer film having a thickness of 25 μm.

[0045]

Examples 7 to 8 and Comparative Examples 8 to 9
The average particle size and content of spherical silica contained in the isophthalic acid copolymerized polyester layer (A) and the average particle size and content of spherical silica contained in the copolymerized polyester layer (B) are shown in Table 3. The biaxially oriented laminated film was obtained in the same manner as in Example 2 except that the surface roughness (Ra) was changed.

[0046]

[Table 2]

[0047]

Examples 9 to 14 and Comparative Examples 10 to 12 Polyethylene terephthalate copolymerized with an isophthalic acid component shown in Table 3 (using germanium oxide as a polymerization catalyst, intrinsic viscosity 0.64, particle size ratio 1.1, average particle size) Isophthalic acid copolymerized polyester layer (A) containing 0.3% by weight of spherical silica (containing 0.1% by weight), polyethylene terephthalate copolymerized with the components shown in Table 3 (using germanium oxide as a polymerization catalyst, intrinsic viscosity 0.64, particle diameter ratio 1.1, containing 0.1% by weight of spherical silica having an average particle diameter of 1.5 μm)
Are dried and melted separately by a conventional method so that each becomes a copolymerized polyester layer (B), then co-extruded from dies adjacent to each other, laminated, fused and quenched and solidified to form an unstretched laminated film did.

Next, the unstretched film was longitudinally stretched 3.0 times at 110 ° C., and then transversely stretched 3 times at 120 ° C.
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 isophthalic acid copolymerized polyester layer (A) and the copolymerized polyester layer (B) were 5 μm and 20 μm, respectively, and the surface roughness (Ra) was 5 nm and 5 nm, respectively. 23
nm.

[0050]

[Table 3]

A total of 27 kinds of films obtained in Examples 1 to 15 and Comparative Examples 1 to 12 were coated on both sides of a tin-free steel sheet having a thickness of 0.25 mm heated at 230 ° C. to form a copolymer polyester layer (B). ) Is bonded in such a way that the surface thereof contacts the tin-free steel, cooled with water, cut into a disk having a diameter of 150 mm, deep-drawn in four stages using a drawing die and a punch, and a 55 mm-diameter side seamless container ( Hereinafter, it is abbreviated as can).

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

(1) Deep drawing processability -1 ○: The film was processed without any abnormality, 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 prevention test on film surface in can (1% NaCl water was put in the can, electrodes were inserted, and the can body was used as an anode. The current value when a voltage of 6 V is applied is measured.
Hereinafter, abbreviated as ERV test) shows 0.1 mA or less. ×: There is no abnormality in the film, but the current value is 0.1 mA or more in the ERV test, and pinhole-shaped cracks starting from the coarse lubricant are recognized in the film when the energized portion is observed under magnification.

(3) Impact resistance For cans having good deep-drawing properties, water was fully poured, cooled to 10 ° C., and 10 pieces of each test were dropped from a height of 30 cm on a PVC tile floor. As a result of performing an ERV test in the can, the results were as follows: A: 0.2 mA or less for all 10 samples. ：: 0.3 mA or less for all 10 samples. Δ: 1 mA or more was 0.3 mA or more. X: 0.3 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 200 ° C. for 5 minutes, and then subjected to the impact resistance evaluation described in (3). Was 0.3 mA or less. Δ: 1 mA or more was 0.3 mA or more. C: Cracks were already observed in the film after heating for 6 or more at 0.3 mA or more or at 200 ° C. for 5 minutes.

(5) Retort Resistance Cans with good deep drawability were filled with water, retorted in a steam sterilizer at 120 ° C. for 1 hour, and then stored at 50 ° C. for 30 days. After dropping 10 cans obtained for each test from a height of 1 m onto a PVC tile floor, an ERV test in the cans was performed. ：: 0.3 mA or less for all 10 samples. Δ: 1 mA or more was 0.3 mA or more. X: 0.3 mA or more for 6 or more pieces, or cracks of the film were already observed after dropping.

(6) Preservation of Taste A can that had good deep drawing was filled with cider and sealed. After keeping at 37 ° C. for 30 days, the can was opened and the change in taste was examined by a sensory test. ：: There was no change in taste. Δ: Slight change in taste was observed. ×: A change in taste was observed.

The results of the above six evaluations and the winding properties are as shown in Table 4.

[0060]

[Table 4]

As is clear from the results in Table 4, cans using the polyester film of the present invention are excellent in deep drawing workability, heat embrittlement resistance, retort resistance, taste retention, and impact resistance. In particular, it has excellent impact resistance at low temperatures, and also has good adhesion to a metal plate.

In particular, when the surface roughness (Ra) of the isophthalic acid copolymerized polyester layer (A) is 15 nm or less and the surface roughness (Ra) of the copolymerized polyester layer (B) is 15 nm or more, the content of the The taste is not changed, and the winding property is good.

[0063]

According to the present invention, the copolyester has excellent moldability, heat resistance, retort resistance,
It is possible to provide a polyester film for a metal plate laminating process which has improved flavor retention and impact resistance while maintaining its fragrance retention, and is particularly resistant to cracking at low temperatures under impact.

Continuation of the front page (56) References JP-A-5-42643 (JP, A) JP-A-5-338103 (JP, A) JP-A-6-172556 (JP, A) JP-A-5-154497 (JP) , A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B32B 1/00-35/00

Claims (2)

(57) [Claims] 1. An isophthalic acid copolymerized polyester layer (A) having a melting point of 210 to 245 ° C., and a melting point of 210 to 245 ° C.
Formed by laminating ℃ copolyester layer and (B), the
Surface roughness of isophthalic acid copolymerized polyester layer (A)
(Ra) is 15 nm or less, the copolymerized polyester layer
(B) has a surface roughness (Ra) of 15 nm or more, and the isophthalic acid copolymerized polyester layer (A) has a melting point of:
A polyester film for a metal plate laminating process, wherein the melting point is higher than the melting point of the copolymerized polyester layer (B) and the difference is 2 ° C. or more. 2. A copolyester according to claim 1 Symbol mounting metal plate bonded polyester film for combined molding a copolyester using a germanium compound as a polycondensation catalyst.