JP3676107B2 - Polyester film for metal plate lamination molding - Google Patents

Description

【００４５】
【表２】

【００４６】
【表３】

【００４７】
表３の評価結果から明らかなように、本発明のフィルムは、成形加工性、耐衝撃性、耐熱性、保味保香性に優れたものである。
【００４８】
【発明の効果】
本発明の金属板貼合せ成形加工用ポリエステルフィルムは、金属板と貼合わせた後製缶加工、例えば深絞り加工して金属缶を成形するにあたり、共重合ポリエステルが持っている優れた耐熱性、耐衝撃性、耐レトルト性を保持しながら、保味保香性、特にレトルト後の保味保香性に優れ、かつ成形加工性が改善されたものであり、金属容器用フィルムとして極めて有用である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polyester film for metal plate laminating processing, and more specifically, it exhibits excellent molding processability when it is bonded to a metal plate to make cans such as drawing, and has heat resistance, retort resistance, and retention. The present invention relates to a polyester film for laminating and processing metal plates, which can produce metal cans excellent in taste-retaining properties, impact resistance, etc., such as beverage cans and food cans.
[0002]
[Prior art]
Metal cans are generally painted to prevent corrosion on the inside and outside surfaces. Recently, for the purpose of simplifying the process, improving hygiene, and preventing pollution, there is a method of obtaining rust prevention without using organic solvents. Development is progressing, and as one of them, coating with a thermoplastic resin film is attempted. That is, a method for making a can by drawing or the like after laminating a thermoplastic resin film on a metal plate such as tinplate, tin-free steel, or aluminum has been studied.
[0003]
As this thermoplastic resin film, it is becoming clear that a copolymerized polyester film is suitable in terms of moldability, heat resistance, impact resistance, and flavor retention. However, this polyester film does not always have sufficient flavor retention, when it contains beverages that have an extremely delicate taste, such as green tea, and mineral water that requires tasteless and odorless. Changes to are sensed.
[0004]
On the other hand, Japanese Patent Laid-Open No. 6-116376 proposes a metal film forming polyester film having improved flavor properties made of a copolyester containing a specific amount of alkali metal element and germanium element. However, when this film is used, it shows excellent flavor retention in a process where heat is not applied at the stage where the contents such as the cold pack system are filled, but at the stage where the contents such as retort treatment are filled. In the process in which heat treatment is performed, sufficient flavor retention properties are not always obtained.
[0005]
On the other hand, in the present inventors' previous studies, if a copolymer polyethylene terephthalate having a specific melting point is used and a film having a specific glass transition temperature and dynamic viscoelasticity is used, the taste-retaining property can be improved. (Japanese Patent Laid-Open No. 10-166440). However, it has been found that sufficient moldability cannot always be obtained depending on the can manufacturing conditions.
[0006]
[Problems to be solved by the invention]
The object of the present invention is to solve the problems of the prior art and maintain the excellent heat resistance and impact resistance of the copolymerized polyester film, while retaining the flavor retention, particularly after retorting. An object of the present invention is to provide a polyester film for metal plate laminating and molding which has excellent fragrance retention and improved moldability.
[0007]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above object, the present inventors have used a copolymerized polyethylene terephthalate having a specific melting point, a specific glass transition temperature, a dynamic viscoelasticity, and a specific compound. It has been found that the addition of a trace amount can improve the flavor retention and molding processability, leading to the present invention.
[0008]
That is, the present invention is a biaxially oriented film comprising a polyester having a melting point of 210 to 245 ° C., the main component being 2,6-naphthalenedicarboxylic acid copolymerized polyethylene terephthalate, and the loss elastic modulus of the film is Maximum temperature peak temperature (Te) and glass transition temperature (Tg) in DSC measurement satisfy the following formulas (1) and (2), and naphthoic acid and / or lower alkyl ester of naphthoic acid is added to the polyester. It is a polyester film for metal plate lamination molding processing characterized by containing 0.5-100 ppm in conversion as naphthoic acid methyl ester.
Tg ≧ 78 (1)
Te−Tg ≦ 30 (2)
(Here, Tg is the glass transition temperature (° C.) in DSC measurement after 290 ° C. heat melting and quenching, and Te is the maximum temperature peak temperature (° C.) of the loss elastic modulus of the film.)
[0009]
Moreover, it is preferable that the amount of extraction when this film is extracted with ion-exchanged water at 121 ° C. for 2 hours is 0.078 mg / cm ² or less.
[0010]
In the present invention, among various polyesters, while maintaining excellent heat resistance and impact resistance, it is possible to improve the taste-retaining property, particularly the retentive flavor-retaining property. 1,6-Naphthalene dicarboxylic acid copolymerized polyester is used as the main component. The polyester may be further copolymerized with other components, and the component may be a dicarboxylic acid component or a diol component.
[0011]
Examples of copolymer components other than 2,6-naphthalenedicarboxylic acid include the following components. Dicarboxylic acid components include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid and 2,7-naphthalenedicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and decanedicarboxylic acid, and cyclohexanedicarboxylic acid. And alicyclic dicarboxylic acids such as 1,4-butanediol, 1,6-hexanediol, diethylene glycol and the like, and alicyclic such as 1,4-cyclohexanedimethanol. Examples thereof include aromatic diols such as diol and bisphenol A.
[0012]
The proportion of 2,6-naphthalenedicarboxylic acid and other copolymer components is a proportion that results in a polymer melting point of 210-245 ° C, preferably 215-240 ° C, depending on the type. When the melting point is less than 210 ° C., the heat resistance is poor. On the other hand, if the melting point exceeds 245 ° C., the crystallinity of the polymer is too large and the moldability is impaired.
[0013]
Here, the melting point of the polyester is measured by using a Du Pont Instruments 910 DSC and obtaining a melting peak at a heating rate of 20 ° C./min. The sample amount is 20 mg.
[0014]
Furthermore, the intrinsic viscosity (orthochlorophenol, 35 ° C.) of the polyester used in the present invention is preferably 0.52 to 1.50, more preferably 0.57 to 1.00, particularly preferably 0.60. 0.80. When this intrinsic viscosity is less than 0.52, impact resistance may be insufficient, which is not preferable. On the other hand, when the intrinsic viscosity exceeds 1.50, molding processability may be impaired.
[0015]
The polyester in the present invention is not limited by its production method, but polycondensates until terephthalic acid, ethylene glycol and a copolymer component are esterified and then the obtained reaction product has a desired degree of polymerization. Preferable examples include a method of reacting or a method of subjecting terephthalic acid dimethyl ester, ethylene glycol and a copolymer component to a transesterification reaction, and then subjecting the obtained reaction product to a polycondensation reaction until a desired degree of polymerization is achieved. In addition, the polyester obtained by the above method (melt polymerization) can be made into a polymer having a higher degree of polymerization by a polymerization method (solid phase polymerization) in a solid phase state as necessary.
[0016]
If necessary, additives such as antioxidants, heat stabilizers, viscosity modifiers, plasticizers, hue improvers, lubricants, nucleating agents, and ultraviolet absorbers can be added to the polyester.
[0017]
Preferred examples of the catalyst used in the polycondensation reaction include an antimony compound (Sb compound), a titanium compound (Ti compound), and a germanium compound (Ge compound). Among these, the titanium compound and the germanium compound are used to maintain the film. More preferable in terms of flavor retention. Preferred examples of the titanium compound include titanium tetrabutoxide and titanium acetate. As germanium compounds, (a) amorphous germanium oxide, (b) fine crystalline germanium oxide, and (c) germanium oxide were dissolved in glycol in the presence of an alkali metal, an alkaline earth metal, or a compound thereof. A solution, (d) a solution in which germanium oxide is dissolved in water, and the like are preferable.
[0018]
The polyester film of the present invention contains naphthoic acid and / or a lower alkyl ester of naphthoic acid in the polyester in an amount of 0.5 to 100 ppm, preferably 1 to 80 ppm, particularly preferably 2 to 50 ppm in terms of naphthoic acid methyl ester. It is necessary to. Here, the naphthoic acid and / or the lower alkyl ester of naphthoic acid includes not only free naphthoic acid contained in the polyester and lower alkyl ester of free naphthoic acid but also naphthoic acid bonded to the terminal of the polyester chain. The content of the naphthoic acid and / or the lower alkyl ester of naphthoic acid in the polyester is such that the free naphthoic acid contained in the polyester, the lower alkyl ester of free naphthoic acid, and the naphthoic acid bonded to the terminal of the polyester are released. It is expressed as a weight ratio (ppm) of the total weight of the naphthoic acid methyl ester to the polyester. Furthermore, lower alkyl represents an alkyl group having 1 to 6 carbon atoms.
[0019]
If the naphthoic acid and / or the lower alkyl ester of naphthoic acid is less than 0.5 ppm, the moldability becomes poor depending on the shape of the can. On the other hand, if it exceeds 100 ppm, the flavor-retaining property is deteriorated. Therefore, it is not preferable.
[0020]
The method for incorporating naphthoic acid and / or a lower alkyl ester of naphthoic acid into the polyester is not particularly limited. For example, naphthoic acid is added to 2,6-naphthalenedicarboxylic acid and / or its lower alkyl ester added as a copolymerization component. The method using what contains the lower alkyl ester of an acid and / or a naphthoic acid is mentioned preferably. As a method of obtaining 2,6-naphthalenedicarboxylic acid and / or a lower alkyl ester thereof containing such naphthoic acid and / or a lower alkyl ester of naphthoic acid, 2,6-naphthalenedicarboxylic acid and / or a lower alkyl ester thereof may be used. A method of adding a predetermined amount of naphthoic acid and / or a lower alkyl ester of naphthoic acid, or a recovery 2,6-containing naphthoic acid methyl ester by-produced in a process of recovering a 2,6-naphthalenedicarboxylic acid component from a polymer Examples thereof include a method of using naphthalenedicarboxylic acid methyl ester as it is.
[0021]
The polyester film of the present invention is used in a biaxially stretched and heat-set state. At this time, the maximum temperature peak temperature (Te) of the loss elastic modulus of the polyester film and the glass transition temperature (Tg) in DSC measurement need to satisfy the following formulas (1) and (2).
Tg ≧ 78 (1)
Te−Tg ≦ 30 (2)
(Here, Tg is the glass transition temperature (° C.) in DSC measurement after 290 ° C. heat melting and quenching, and Te is the maximum temperature peak temperature (° C.) of the loss elastic modulus of the film.)
[0022]
When the Tg of the film is less than 78 ° C., the heat resistance becomes inferior, and the flavor-retaining property after the retort treatment is deteriorated. For this reason, when a copolymerization component other than 2,6-naphthalenedicarboxylic acid is used as the polyester copolymerization component, the rate of decrease in the glass transition temperature is small or does not change when the proportion of the copolymerization component is increased. It is preferable to use such a component that increases.
[0023]
Here, Tg of polyester puts a 20 mg film sample in a pan for DSC measurement, heats and melts on a 290 ° C. heating stage for 5 minutes, and then quickly solidifies rapidly on an aluminum foil in which the sample pan is laid on ice, By using a Du Pont Instruments 910 DSC, the glass transition point is determined at a heating rate of 20 ° C./min.
[0024]
Furthermore, when the value of Te-Tg exceeds 30, the molecular orientation and crystallinity of the film become too high, so that the moldability is remarkably lowered. Although the value of Te depends on the copolymerization component and the amount of copolymerization, a method of adjusting the biaxial stretching ratio, stretching temperature, and heat setting temperature is particularly preferred depending on the film forming conditions.
[0025]
Here, Te is obtained using a dynamic viscoelasticity measuring device under conditions of a measurement frequency of 10 Hz and a dynamic displacement of ± 25 × 10 ⁻⁴ cm.
[0026]
Since the polyester film of the present invention is particularly used for food cans or beverage cans, it is better that there are less substances that are eluted or scattered from the film, but it is difficult to eliminate these substances at all. Therefore, for use in the food can or beverage can applications, such as ion exchange 121 ° C. in water, 2 hours, the extracted amount of the film 1 square cell per inch when the extracted that is 0.078 mg or less and preferably More preferably, it is 0.016 mg or less.
[0027]
In order to reduce the extraction amount, the glass transition temperature of the film may be increased. The glass transition temperature of the film is determined by the glass transition temperature and the degree of orientation of the polymer constituting the film, but it is preferable to increase the glass transition temperature of the polymer (polyester) because the moldability deteriorates when the degree of orientation is increased. .
[0028]
Further, the refractive index in the thickness direction of the film is preferably from 1.500 to 1.540, and more preferably from 1.505 to 1.530. If the refractive index is too low, the moldability becomes insufficient. On the other hand, if the refractive index is too high, the structure is close to amorphous, and the heat resistance may be lowered.
[0029]
Here, the refractive index in the thickness direction of the film is measured with a monochromatic light NaD line by attaching a polarizing plate analyzer to the eyepiece side of Abbe's refractometer. The mounting solution uses methylene iodide, and the measurement temperature is 25 ° C.
[0030]
The film of the present invention preferably has a thickness of 6 to 75 μm. Furthermore, it is preferable that it is 8-75 micrometers, especially 10-50 micrometers. If the thickness is less than 6 μm, tearing or the like is likely to occur during processing, while those exceeding 75 μm are excessive quality and uneconomical.
[0031]
As a metal plate to which the film of the present invention is bonded, particularly a metal plate for canning, a plate made of tin, tin-free steel, aluminum or the like is suitable. The polyester film can be bonded to the metal plate by the following methods (1) and (2), for example.
(1) The metal plate is heated to the melting point of the film or higher, and the film is bonded and then cooled, and the surface layer portion (thin layer portion) of the film in contact with the metal plate is amorphized and adhered.
{Circle around (2)} An adhesive layer is preliminarily coated on the film, and this surface is bonded to a metal plate. As the adhesive layer, known resin adhesives such as epoxy adhesives, epoxy-ester adhesives, alkyd adhesives, and the like can be used.
[0032]
【Example】
The following examples further illustrate the present invention. The film characteristics were measured by the following method.
(1) Intrinsic viscosity of polyester Measured at 35 ° C. in orthochlorophenol.
[0033]
(2) Melting | fusing point of polyester By the method of calculating | requiring a melting peak with the temperature increase rate of 20 degree-C / min using Du Pont Instruments 910 DSC. The sample amount is 20 mg.
[0034]
(3) Glass transition temperature (Tg) of polyester
A 20 mg film sample was placed in a DSC measurement pan, heated and melted on a 290 ° C. heating stage for 5 minutes, and then quickly solidified on an aluminum foil laid on ice, using a Du Pont Instruments 910 DSC, According to a method for obtaining a glass transition point at a temperature rising rate of 20 ° C./min.
[0035]
(4) Maximum temperature peak temperature (Te) of loss elastic modulus of the film
The loss elastic modulus is determined using a dynamic viscoelasticity measuring device at a measurement frequency of 10 Hz and a dynamic displacement of ± 25 × 10 ⁻⁴ cm, and the maximum temperature peak temperature at this time is indicated.
[0036]
(5) Naphthoic acid and / or lower alkyl ester content of naphthoic acid in polyester 0.5 g of a film sample was dispersed in 2 ml of methanol and decomposed in an autoclave (90 kgf / cm ² ) at 260 ° C. for 6 hours. It is dissolved in chloroform, naphthoic acid and lower alkyl esters of naphthoic acid are quantified by gas chromatography, and the weight is converted to naphthoic acid methyl ester to determine the content.
[0037]
(6) A deep drawing processable film is laminated on both sides of tin-free steel with a plate pressure of 0.25 mm heated to the melting point of polyester, water-cooled, then cut into a 140 mm diameter disc, and using a drawing die and punch Deep drawing is performed in four stages to create a 50 mm diameter side seamless container (hereinafter abbreviated as a can). The cans are observed and tested as follows, and evaluated according to the following criteria.
(1) Deep drawability-1
A: No whitening or breakage is observed in a film processed without abnormality in the film.
(Triangle | delta): Whitening is recognized by the can upper part of a film.
X: Film breakage is observed in a part of the film.
(2) Deep drawability-2
○: Processed without abnormality, rust prevention test for film surface in can (1% NaCl aqueous solution is put in can, electrode is inserted, current value when voltage of 6V is applied with can body as anode is measured. Hereinafter, 0.2 mA or less is shown in the ERV test.
X: Although there was no abnormality in the film, the current value exceeded 0.2 mA in the ERV test, and pinhole-like cracks starting from the coarse lubricant of the film were observed when the energized part was enlarged and observed.
[0038]
(7) For impact-resistant deep-drawn cans, after water is fully poured and cooled to 0 ° C, 10 pieces for each test are dropped from a height of 30 cm onto the PVC tile floor, then inside the can The results of the ERV test are evaluated according to the following criteria.
○: It was 0.2 mA or less for all 10 pieces.
(Triangle | delta): It exceeded 0.2 mA about 1-5 pieces.
X: It exceeded 0.2 mA about 6 or more, or the crack of the film was already recognized after dropping.
[0039]
(8) Heat resistance embrittlement After the can with good deep drawing was heated and held at 200 ° C. for 5 minutes, the results of the above-described impact resistance evaluation were evaluated according to the following criteria.
○: It was 0.2 mA or less for all 10 pieces.
(Triangle | delta): It exceeded 0.2 mA about 1-5 pieces.
X: It exceeded 0.2mA about 6 or more pieces, or the crack of the film was already recognized after heating at 200 degreeC x 5 minutes.
[0040]
(9) Retort resistance The can with good deep-draw molding was filled with water, subjected to a retort treatment at 120 ° C. for 1 hour in a steam sterilizer, and then stored at 50 ° C. for 30 days. After dropping 10 cans obtained from a height of 50 cm onto a PVC tile floor surface for each test, the results of the ERV test in the cans are evaluated according to the following criteria.
○: It was 0.2 mA or less for all 10 pieces.
(Triangle | delta): It exceeded 0.2 mA about 1-5 pieces.
X: It exceeded 0.2 mA about 6 or more, or the crack of the film was already recognized after dropping.
[0041]
(10) Flavor retention 1
A can with good deep drawing is filled with ion exchange water and stored at room temperature (20 ° C.) for 30 days. Using the immersion liquid, a tasting test was conducted with 30 panelists, and compared with comparative ion-exchanged water, and evaluated according to the following criteria.
A: Less than 3 out of 30 felt changes in taste and aroma compared to the comparative solution.
◯: 4 to 6 out of 30 felt changes in taste and aroma compared to the comparison solution.
(Triangle | delta): 7-9 people among 30 felt the change of taste and fragrance compared with the comparison liquid.
X: 10 or more people out of 30 felt changes in taste and aroma compared with the comparative solution.
[0042]
(11) Preservative flavor retention-2
A can with good deep drawing is filled with ion exchange water, subjected to a retort treatment at 120 ° C. for 1 hour in a steam sterilizer, and then stored at room temperature (20 ° C.) for 30 days. Using the immersion liquid, a tasting test was conducted with 30 panelists, and compared with comparative ion-exchanged water, and evaluated according to the following criteria.
A: Less than 3 out of 30 felt changes in taste and aroma compared to the comparative solution.
◯: 4 to 6 out of 30 felt changes in taste and aroma compared to the comparison solution.
(Triangle | delta): 7-9 people among 30 felt the change of taste and fragrance compared with the comparison liquid.
X: 10 or more people out of 30 felt changes in taste and aroma compared with the comparative solution.
[0043]
[Examples 1-7 and Comparative Examples 1-6]
Polyethylene terephthalate copolymerized with the copolymer components shown in Table 1 in the proportions shown in Table 1, and containing naphthoic acid and / or lower alkyl esters of naphthoic acid in the amounts shown in Table 1 (inherent viscosity 0.64, average The resultant was dried, melt-extruded, and rapidly cooled and solidified to obtain an unstretched film. Next, this unstretched film was longitudinally stretched at the temperature and magnification shown in Table 1, and then horizontally stretched at the temperature and magnification shown in Table 1, and further heat-set at 180 ° C. to obtain a biaxially oriented film.
The resulting film had a thickness of 25 μm and a surface roughness (Ra) of 26 nm. Table 2 shows the glass transition temperature (Tg) of the film, the maximum temperature peak temperature (Te) of the loss modulus, the refractive index in the film thickness direction, and the amount of ion-exchanged water extracted. Table 3 shows the other evaluation results. .
[0044]
[Table 1]

[0045]
[Table 2]

[0046]
[Table 3]

[0047]
As is apparent from the evaluation results in Table 3, the film of the present invention is excellent in molding processability, impact resistance, heat resistance, and flavor retention.
[0048]
【The invention's effect】
The polyester film for metal plate laminating molding processing of the present invention has excellent heat resistance that the copolyester has in forming a metal can by, for example, deep drawing after laminating with a metal plate, While retaining impact resistance and retort resistance, it has excellent flavor retention, especially after retort, and improved moldability, making it extremely useful as a metal container film. is there.

Claims (2)

A biaxially oriented film comprising a polyester having a melting point of 210 to 245 ° C., the main component of which is 2,6-naphthalenedicarboxylic acid copolymerized polyethylene terephthalate, and the maximum temperature peak temperature (Te ) And a glass transition temperature (Tg) in DSC measurement satisfy the following formulas (1) and (2), and naphthoic acid and / or a lower alkyl ester of naphthoic acid in the polyester as naphthoic acid methyl ester: The polyester film for metal plate lamination molding processing characterized by containing 0.5-100 ppm in conversion.
Tg ≧ 78 (1)
Te−Tg ≦ 30 (2)
(Here, Tg is the glass transition temperature (° C.) in DSC measurement after 290 ° C. heat melting and quenching, and Te is the maximum temperature peak temperature (° C.) of the loss elastic modulus of the film.) The polyester film for metal plate lamination molding processing according to claim 1, wherein the extraction amount when the film is extracted with ion-exchanged water at 121 ° C for 2 hours is 0.078 mg / cm ² or less.