JP2001139706A - Polyester film for lamination processing of metal plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a highly formable polyester film for lamination processing of a metal plate improved in deep draw forming processability while holding heat and retort resistances, aroma and taste retaining properties and operating efficiency. SOLUTION: This polyester film for lamination processing of a metal plate is characterized in that the polyester film is a biaxially oriented film comprising a polyester composed of an isophtalic acid-copolymerized polyethylene terephthalate as a main constituent component and having 210-245 deg.C melting point and comprises 0.5-20 ppm of a compound represented by the general formula (wherein R denotes a <=5C alkyl group).

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 formability when laminating to a metal plate and performing can forming such as drawing. The present invention relates to a polyester film for metal plate lamination molding capable of producing metal cans having excellent retort resistance, flavor retention and flavor retention, and the like, such as beverage cans and food cans.

[0002]

2. Description of the Related Art Metal cans are generally coated to prevent corrosion on the inner and outer surfaces. In recent years, for the purpose of simplifying the process, improving hygiene, and preventing pollution, rust prevention has been achieved without using organic solvents. The development of a method for obtaining a resin has been promoted, and as one of the methods, coating with a thermoplastic resin film has been attempted. That is, a method of laminating a thermoplastic resin film on a metal plate of tin, tin-free steel, aluminum, or the like, followed by drawing, etc., has been studied. As a thermoplastic resin film, a copolymerized polyester film has been tried, and a film satisfying the practical use standards in all of moldability, heat resistance, fragrance preserving property and impact resistance has been developed (for example, Japanese Patent Application Laid-Open No. 039979).

[0003] However, several problems were found in the practical use stage. First, there is a case where rejected products may be generated in a rust prevention test on a film surface in a can after being used as a lining of a beverage can and subjected to deep drawing.
Although the current product satisfies practical standards, the yield of non-defective products that can fully guarantee long-term rust resistance is not yet sufficient, and there is room for improvement.

Second, if the film does not have an appropriate slipperiness, workability such as generation of wrinkles during lamination with a metal plate is significantly deteriorated. On the other hand, it has been conventional to add inert particles as a lubricant in order to improve the slipperiness. However, when there are coarse particles and the high formability of the film is insufficient, drawing in metal can molding is performed. In a process involving large deformation as described above, a pinhole or breakage may occur in the film, which is a problem from the viewpoint of rust prevention.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, and further improves the deep drawing processability while maintaining heat resistance, retort resistance, fragrance retention and taste retention, and workability. An object of the present invention is to provide an improved polyester film for bonding a metal plate with high moldability.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that isophthalic acid copolymerized polyethylene terephthalate having a specific melting point is used and a specific compound is contained in a small amount. As a result, it has been found that the moldability can be improved while maintaining the flavor and fragrance retention, and the present invention has been achieved.

That is, the present invention provides an isophthalic acid copolymerized polyethylene terephthalate as a main component.
A biaxially stretched film made of a polyester having a melting point of 210 to 245 ° C., wherein the polyester contains a compound represented by the following general formula in an amount of 0.5 to 20 ppm. It is a polyester film.

[0008]

Embedded image

The polyester is an aggregate of primary particles having an average particle size of 0.001 to 0.1 μm, and has an average secondary particle size of 0.3 to 3 μm and a pore volume of 0.5 to 0.5 μm. ~ 2.
0 ml / g of porous silica particles of 0.02 to 0.8
It is preferable that the content be contained by weight.

<Polyester> In the present invention, among various polyesters, copolymerized polyethylene terephthalate (isophthalic acid copolymerized polyethylene terephthalate) having an excellent flavor retention and impact resistance and copolymerized with an isophthalic acid component is used. Hereinafter, it may be abbreviated as PET / I.). This PET / I is in a range where an acid component other than isophthalic acid and terephthalic acid or an alcohol component other than ethylene glycol does not impair the properties thereof, for example, 3% with respect to the total acid component or the total alcohol component.
It may be copolymerized at a ratio of not more than mol%. Examples of the copolymeric acid component include aromatic dicarboxylic acids such as phthalic acid and 2,6-naphthalenedicarboxylic acid, and aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and 1,10-decanedicarboxylic acid. Examples of the alcohol component include aliphatic diols such as 1,4-butanediol, 1,6-hexanediol, and neopentyl glycol, and alicyclic diols such as 1,4-cyclohexanedimethanol. These can be used alone or in combination of two or more.

The proportion of isophthalic acid and other copolymer components is such that the melting point of the polymer is in the range of 210 to 245 ° C., preferably 215 to 235 ° C. Melting point 21
If the temperature is lower than 0 ° C., the heat resistance is inferior. On the other hand, the melting point is 2
If the temperature exceeds 45 ° C., the crystallinity of the polymer is too large and the moldability is impaired. When the copolymer component is only isophthalic acid, the ratio at which the above melting point is obtained is approximately 6 to 18 mol.
%.

Here, the melting point of PET / I is measured by Du Pon
By using a Instruments 910 DSC and determining the melting peak at a heating rate of 20 ° C./min. The amount of the sample is about 20 mg.

The intrinsic viscosity of PET / I is 0.52 to
0.80, more preferably 0.54 to 0.70, especially 0.57 to
A range of 0.65 is preferred.

<Trace Additives> The polyester film of the present invention may contain 0.5 to 20 ppm, preferably 1 to 18 ppm, particularly preferably 2 to 16 ppm of a compound represented by the following general formula in PET / I. is necessary.

[0015]

Embedded image

In the above formula, the position of the R group on the benzene ring is not limited. In isophthalic acid copolymerized polyethylene terephthalate, the compound is not in a free state but in a state bound to a molecular terminal, but the content of the compound referred to herein means that the compound bound to the polyester is converted into a free carboxylic acid. Means the weight ratio (ppm) to the total polyester. If the content of the compound is less than 0.5 ppm, the deep drawability will be poor depending on the shape of the can. On the other hand, if it exceeds 20 ppm, the flavor and aroma retention may deteriorate.

The method of incorporating the compound into the polyester is not particularly limited. For example, a method of producing a copolymer with polyethylene terephthalate by condensation polymerization using isophthalic acid containing the compound is preferred. Can be

<Additive Lubricant Particles> The polyester film of the present invention contains lubricant particles, but the type thereof is not limited. As preferred lubricant particles from the viewpoint of taste and fragrance retention, porous silica particles which are aggregated particles can be exemplified.

The average particle size of the primary particles constituting the porous silica particles is preferably in the range of 0.001 to 0.1 μm. When the average particle size of the primary particles is less than 0.001 μm, ultrafine particles are generated by crushing in the slurry stage,
This is not suitable because it forms aggregates and causes pinholes, which deteriorates moldability. On the other hand, if the average particle size of the primary particles exceeds 0.1 μm, the porosity of the particles will be lost, and as a result, the flavor and fragrance retention will not be improved.

Further, the porous silica particles have a pore volume of 0.5 to 2.0 ml / g, more preferably 0.6 to 1.8.
It is preferably in the range of ml / g. When the pore volume is less than 0.5 m1 / g, the porosity of the particles is lost, and the effect of improving the flavor and fragrance retention is lost. On the other hand, if the pore volume is larger than 2.0 ml / g, agglomeration tends to occur due to crushing, which causes pinholes and deteriorates moldability.

The particle size and amount of the porous silica are as follows:
What is necessary is just to determine from the winding property of a film, pinhole resistance, and flavor retention. Usually, the average particle size of the porous silica particles is preferably in the range of 0.3 to 3 μm,
The addition amount is 0.02 to 0.8% by weight, and further 0.02 to 0.8% by weight.
Preferably it is in the range of 0.5% by weight.

The porous silica particles form aggregated particles, and the polyester film of the present invention has a number of coarse aggregated particles having a size of 50 μm or more of 10 / m ² or less.
Preferably it is 5 pieces / m ² or less, more preferably 3 pieces / m ^2.
It is desirable that: If the number of coarse aggregated particles having a size of 50 μm or more is too large, pinholes are likely to be generated, and the moldability tends to be poor.

In order to reduce the number of coarse agglomerated particles, an average opening of 10 to 30 μm, preferably 15 μm, made of a stainless steel fine wire having a wire diameter of 15 μm or less is used as a filter during film formation.
It is preferable to filter the molten polymer using a nonwoven fabric type filter having a size of 25 μm.

The porous silica particles are generally used at any time during the reaction for producing the polyester, for example, during the transesterification reaction or polycondensation reaction in the case of transesterification, or in the case of the direct polymerization method. At times, it is added to the reaction system (preferably as a slurry in glycol). In particular, at the beginning of the polycondensation reaction, for example, when the intrinsic viscosity is about O.D. It is preferable to add the porous silica particles to the reaction system before reaching 3.

<Production of polyester>
ET / I is not limited by its manufacturing method,
Terephthalic acid, ethylene glycol, isophthalic acid as a copolymer component and the above-mentioned alkylated benzoic acid as a minor component are mixed, esterified, and the resulting reaction product is subjected to polymerization until the desired degree of polymerization is attained. A condensation reaction to PET / I, or a transesterification reaction of dimethyl terephthalate, dimethyl isophthalate containing ethylene glycol and a predetermined amount of alkylated benzoic acid, and the reaction product obtained Polycondensation reaction until the polymerization degree reaches
A preferred method is ET / I. PET / I obtained by the above method (melt polymerization)
If necessary, a polymer having a higher degree of polymerization can be obtained by a polymerization method in the solid state (solid state polymerization).

The PET / I may contain, if necessary, an antioxidant, a heat stabilizer, a viscosity modifier, a plasticizer, a hue improver,
Additives such as lubricants, nucleating agents, and UV absorbers can be added.

The catalyst used for the polycondensation reaction includes:
Antimony compounds (Sb compounds), titanium compounds (Ti
Compound), a germanium compound (Ge compound) and the like are preferable. Among them, a titanium compound and a germanium compound are preferable in view of the taste and fragrance retention of the film. As the titanium compound, for example, titanium tetrabutoxide,
Preference is given to titanium acetate. Further, as the germanium compound, the following compounds are preferably exemplified. (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 (d) Germanium oxide in water Dissolved Solution <Film Physical Properties> The surface roughness (Ra) of the polyester film of the present invention is preferably 15 nm or less, particularly preferably 4 to 15 nm, from the viewpoint of the winding property and the flavor and fragrance retention of the film.

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, the roughness curve Y = f
When represented by (x), a value (Ra:
nm) is defined as the film surface roughness.

[0029]

(Equation 1)

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

The thickness of the film is preferably 10 to 75 μm, more preferably 15 to 40 μm. If it is less than 10 μm, breakage or the like is likely to occur during processing, and if it is more than 75 μm, it is uneconomical with excessive quality.

<Lamination with metal plate> The metal plate for cans to which the polyester film of the present invention is laminated may be tin,
Plates of tin-free steel, aluminum, etc. are suitable. The lamination of the polyester film to the metal plate can be performed by, for example, the following methods 1 and 2. 1. 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 rapidly cooled, and the surface layer (thin layer) of the film in contact with the metal plate is made amorphous and adhered. 2. 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.

[0033]

The present invention will be further described with reference to the following examples. The properties of the film were measured by the following methods. (1) Intrinsic viscosity of polyester Measured at 35 ° C. in orthochlorophenol. (2) Melting point of polyester Using Du Pont Instruments 910 DSC, heating rate 20 ° C /
In minutes to determine the melting peak. The sample size is 20 mg. (3) Trace additive content in polyester 0.5 g of film sample was dispersed in 2 ml of methanol,
After decomposing in an autoclave at 60 ° C and 90 kgf / cm ² (8.8 MPa) for 6 hours, dissolve in chloroform, and determine the content as a free compound in the film sample from the calibration curve obtained using a standard substance by gas chromatography. Find the quantity. (4) Deep drawing workability The film is laminated on both sides of a 0.25 mm thick tin-free steel heated at 230 ° C, cooled with water, cut into a 140 mm diameter disk, and drawn in four stages using a drawing die and punch. By deep drawing, a side-seamless container (hereinafter abbreviated as can) having a diameter of 55 mm was prepared.

The following observations and tests were performed on the cans, and the cans were evaluated according to the following standards. (4-1) Deep drawing workability -1 ○: Both inner and outer surfaces were processed into films without any abnormality, and no whitening or breakage was observed in the film on the inner and outer surfaces of the can.

△: whitening on the top of the film inside and outside of the can,
Breakage is observed or shavings are observed on the die or punch.

X: Film breakage is observed in a part of the film on the inner and outer surfaces of the can. (4-2) Deep drawing workability-2 ◎: The inner and outer surfaces were processed without any abnormality, and the rust prevention test of the film surface in the can (1% NaCl aqueous solution was put in the can, the electrode was inserted,
The current value is measured when a voltage of 6 V is applied using the can as an anode. In the following ERV test), less than 0.1 mA is shown.

Good: Both inner and outer surfaces were processed without any abnormality, and the ERV test on the film surface in the can showed 0.1 mA or more and less than 0.2 mA.

X: There is no abnormality on the inner and outer surfaces, but the current value is 0.2 mA or more in the ERV test. When the energized portion is observed under magnification, pinhole-shaped cracks starting from the coarse lubricant are observed in the film. (5) Heat-resistant embrittlement After the can which had been well drawn was heated and maintained at 200 ° C for 5 minutes, pour water into it and cool it to 0 ° C.
After dropping each piece from a height of 30 cm onto a PVC tile floor, an ERV test was performed in the can. As a result, ：: 0.2 mA or less for all 10 pieces.

Δ: 0.2 mA or more for 1 to 5 pieces.

X: 0.2 mA or more for 6 or more pieces, or cracking of the film was already observed after heating at 200 ° C. for 5 minutes. (6) Flavor retention and flavor retention-1 For cans with good deep drawing, fill with ion-exchanged water and store at room temperature (20 ° C) for 30 days. A tasting test is conducted by 30 panelists using the immersion liquid, and compared with ion-exchanged water for comparison, and evaluated according to the following criteria.

◎: 3 or less of 30 persons felt a change in taste and aroma as compared with the comparative solution.

：: Four to six out of thirty people felt a change in taste and aroma as compared with the comparative solution.

Δ: 7 to 9 out of 30 persons felt a change in taste and aroma as compared with the comparative solution.

×: Ten or more of the 30 persons felt a change in taste and aroma as compared with the comparative solution. (7) Flavor preservation and flavor retention-2 Cans with good deep drawability are filled with ion-exchanged water and retorted at 120 ° C for 1 hour in a steam sterilizer, and then at room temperature (20 ° C) 30 Store for days. A tasting test is conducted by 30 panelists using the immersion liquid, and compared with ion-exchanged water for comparison, and evaluated according to the following criteria.

◎: Three or less out of thirty felt changes in taste and aroma as compared with the comparative solution.

：: Four to six persons among 30 persons felt a change in taste and aroma as compared with the comparative solution.

Δ: 7 to 9 out of 30 persons felt a change in taste and aroma as compared with the comparative solution.

×: 10 or more out of 30 persons felt a change in taste and aroma as compared with the comparative solution.

[Examples 1-4 and Comparative Examples 1-4] Table 1
Containing 0.1% by weight of lubricant particles having an average particle size of
A copolymerized polyethylene terephthalate (intrinsic viscosity: 0.60) was prepared by copolymerizing the components shown in Table 1. When the lubricant particles are porous silica, the average particle size of the primary particles is 0.1.
The one having a pore volume of 1.3 ml / g having a pore size of 05 μm was used.

This copolymerized polyethylene terephthalate was melt-extruded and quenched and solidified to obtain an unstretched film. Next, this unstretched film was heated at 100 ° C. (Comparative Example 2
° C), stretched 3.1 times at 110 ° C (105 ° C for Comparative Example 2), and heat-set at 190 ° C (180 ° C for Comparative Example 2). A 25 μm biaxially oriented film was obtained. The surface roughness of these films (R
a) was 10 nm, and the number of coarse aggregated particles having a size of 50 μm or more in the film was 0 / m ² . Table 1 shows the evaluation results of these biaxially oriented polyester films.

[0051]

[Table 1]

As is clear from the results shown in Table 1, the polyester film of the present invention was satisfactory in all of the evaluation items. Furthermore, the film using the porous silica according to the second aspect is particularly excellent in flavor and fragrance retention. On the other hand, Comparative Examples 1 to 4, which did not satisfy the requirements of the present invention, could not satisfy all the evaluation items.

[0053]

The polyester film for laminating and processing a metal plate of the present invention is prepared by laminating a metal can with a metal plate after laminating the metal film with a metal plate. While maintaining excellent heat resistance, impact resistance, and retort resistance, high formability, especially in deep drawing, has been improved, and it has excellent flavor and fragrance retention properties, making it extremely useful as a film for metal containers. is there.

 ────────────────────────────────────────────────── ─── Continued on the front page F-term (reference) 4F071 AA45X AA46 AA84 AB26 AC09 AE22 AF53 AH05 BB07 BB08 BC01 4F100 AA20A AA20H AB01B AH02A AH02H AK42A AK42J AL01A BA01 BA02 CA19 DA01 DD07 J01J10J03J01J01J01J01J03 YY00A

Claims (2)

[Claims] An isophthalic acid-copolymerized polyethylene terephthalate as a main component and having a melting point of 210 to 24.
What is claimed is: 1. A polyester film for laminating and processing metal plates, comprising a biaxially stretched film made of a polyester at 5 [deg.] C., wherein the polyester contains a compound represented by the following general formula in an amount of 0.5 to 20 ppm. Embedded image 2. An aggregate of primary particles having an average particle size of 0.001 to 0.1 μm and an average secondary particle size of 0.3 to 3 μm.
2. The metal plate laminating process according to claim 1, wherein the porous silica particles having a pore volume of 0.5 to 2.0 ml / g are contained in an amount of 0.02 to 0.8% by weight. Polyester film.