JP3323320B2 - 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 to a polyester film for laminating to a metal plate and exhibiting excellent formability when performing can forming such as drawing. The present invention relates to a polyester film for laminating and processing metal sheets which is hardly cracked by an impact from the outside of the can even if subjected to heat treatment such as retort sterilization treatment after the can and which has excellent scent retention of the contents.

[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 tinplate, tin-free steel, or aluminum, and then forming the can by drawing or the like. Polyolefin films and polyamide films have been tried as the thermoplastic resin film, but they do not satisfy the moldability, heat resistance and impact resistance.

On the other hand, polyester films, particularly polyethylene terephthalate films, have attracted attention as having balanced properties, and several proposals based on them 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-56-104
No. 51, JP-A-1-192546) (B) 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, JP-A-2-5
No. 7339) (C) A low-orientation, heat-fixed, biaxially stretched polyethylene terephthalate film is laminated on a metal plate and used as a can-making material. (Japanese Patent Application Laid-Open No. 64-22530)

[0004] However, none of these methods can provide sufficient characteristics, and it has been clarified that each has the following problems. Regarding (A), the biaxially oriented polyethylene terephthalate film is excellent in heat resistance, but is insufficient in moldability, and causes whitening (generation of minute cracks) and breakage of the film in canning with large deformation. .
(B) is an amorphous or extremely low-crystalline aromatic polyester film and thus has good moldability, but is easily embrittled by post-processing such as printing after can-making and retort sterilization. Transforms into a fragile film due to external impact. As for (C), the effect is not exerted in the intermediate region between the above (A) and (B). However, since the isotropy of the film surface is not ensured, it can be used as in can making (deep drawing). When the omnidirectional deformation is performed in a certain direction, the formability in a specific direction of the film may be insufficient.

The present inventors have studied the use of polybutylene terephthalate (hereinafter sometimes referred to as PBT) having a low second order transition point in order to improve impact resistance, and have investigated the use of polyethylene terephthalate (hereinafter referred to as PBT). , PET) was melt-blended with PBT to obtain a block copolymer film. However, the film obtained by this method has a fairly good impact resistance if an appropriate film forming condition can be selected, but the film characteristic is PE.
Since it greatly depends on the progress of the transesterification reaction between T and PBT, it is difficult to produce a homogeneous film with good reproducibility.

[0006]

SUMMARY OF THE INVENTION The present inventors have studied to develop a polyester film for can processing which does not have these problems. As a result, the use of a specific copolymerized polyester as a raw material for the film has led to the formation of a polyester film. The present inventors have found that a polyester film for can-making process excellent in processability, impact resistance after can-making, and fragrance retention of the contents can be obtained, and arrived at the present invention.

[0007]

That is, the present invention relates to a biaxially oriented film comprising a copolyester containing a lubricant having an average particle size of 2.5 μm or less, wherein the copolyester is 2,6-naphthalenedicarbon. An acid component comprising 80 to 95 mol% of an acid and 5 to 20 mol% of an aliphatic dicarboxylic acid represented by the following formula (I), and a glycol component mainly composed of ethylene glycol, and an intrinsic viscosity ([η]) A polyester film for laminating and processing metal plates, having a molecular weight of 0.5 to 0.7.

[0008]

Embedded image HOOC— (CH ₂ ) _n —COOH (I) (where n represents a positive integer of 2 to 10, preferably a positive integer of 4 to 8)

The copolymerized polyester in the present invention has an acid component of 80 to 95 mol% of 2,6-naphthalenedicarboxylic acid and an aliphatic dicarboxylic acid of the formula (I) of 5 to 20 mol%.
It is a copolyester consisting of mol% and a glycol component mainly consisting of ethylene glycol.

When the proportion of the aliphatic dicarboxylic acid component is less than 5 mol%, based on the total dicarboxylic acid constituting the polymer, the moldability and impact resistance are insufficient. The impact resistance tends to deteriorate.

As the aliphatic dicarboxylic acid, those having 2 to 10 methylene groups, preferably 4 to 8 methylene groups are used. Further, when an aromatic dicarboxylic acid such as isophthalic acid is used instead of the aliphatic dicarboxylic acid, the impact resistance cannot be improved.

The glycol component is mainly (about 90 mol% or more) ethylene glycol. When the amount of glycol components other than ethylene glycol increases, the melting point and the secondary transition point of the polymer decrease, which is not preferable.

The glycol components which can be used in combination with the ethylene glycol include aliphatic diols such as diethylene glycol, propylene glycol, neopentyl glycol, butanediol, pentanediol and hexanediol; and polyalkylene glycols such as polyethylene glycol and polypropylene glycol. And the like. These can be used alone or in combination of two or more.

The copolyester in the present invention preferably has a melting point in the range of 215 to 255 ° C. If the polymer melting point is lower than 215 ° C., the heat resistance is inferior, so that it cannot withstand the heating in printing after can-making, while if the polymer melting point exceeds 255 ° C., the crystallinity of the polymer is too high and the molding processability is impaired. become.

Here, the melting point of the copolyester was measured by 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.

The secondary transition point of the copolymerized polyester is preferably 100 ° C. or higher. Secondary transition point is 10
When the temperature is lower than 0 ° C., the fragrance retention of the polyester film becomes insufficient, which is not preferable.

Here, the secondary transition point of the polyester is determined by measuring the temperature distribution and tan δ with a “Vibron direct-reading dynamic viscoelasticity measuring device DDV-II type” manufactured by Toyo Baldwin Co., Ltd., and based on the tan δ measurement value. The dynamic loss modulus (E ″) is determined, and the temperature at which the E ″ value becomes the maximum is determined as the secondary transition point. The measurement condition at this time is a driving frequency of 110 cps.
At a temperature rising rate of 1 ° C./min from room temperature. Preparation of the measurement sample is to prepare a thin film of 5mm width, 20mm length, 0.2mm thickness from the molten polymer,
Immediately after the formation of the film, it is cooled and left at room temperature for 3 days or more. At this time, if there is unevenness in the thickness of the film, the measured values slightly vary. Therefore, five separately prepared sample films are measured, and the average value of the five measured values is determined as the secondary transition point.

The copolymerized polyester in the present invention must have a molecular weight in which the intrinsic viscosity ([η]) of the film is in the range of 0.5 to 0.7. This [η] is 0.5
If it is smaller than the value, the impact resistance is insufficient. On the other hand, if it is larger than 0.7, the molding processability is extremely poor, which is not preferable.

The copolymerized polyester in the present invention contains a lubricant having an average particle size of 2.5 μm or less. 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 as the organic lubricant, silicone resin particles and the like can be exemplified. In any case, the average particle size needs to be 2.5 μm or less. When the average particle size of the lubricant exceeds 2.5 μm, coarse lubricant particles (for example, 1 μm) of a portion deformed by processing of a deep drawing can or the like are used.
(A particle of 0 μm or more) becomes a starting point, and it is not preferable because a pinhole is generated or broken in some cases.

The amount of the lubricant in the copolymerized polyester is preferably determined depending on the winding property and the deep drawing processability in the film production process. Generally, it is preferable to add a small amount of particles having a large particle diameter and a large amount of particles having a small particle diameter. For example, in the case of silica having an average particle diameter of 2.0 μm, it is preferable to add about 0.05% by weight, and to add about 0.3% by weight of titanium dioxide having an average particle diameter of 0.3 μm. By intentionally adjusting the content of the lubricant, the film can be made opaque. For example, by adding 10 to 15% by weight of titanium dioxide,
It can be a white film.

The copolyester in the present invention can be produced by a conventionally known method. For example, a 2,6-naphthalenedicarboxylic acid component, an aliphatic dicarboxylic acid component, and an ethylene glycol are subjected to an esterification reaction or a transesterification reaction in the presence or absence of a catalyst to obtain a bisglycol ester and / or a precondensate thereof. Then, the bisphenol ester and / or a precondensate thereof can be easily obtained by a polycondensation reaction in the presence of a polycondensation catalyst.

The catalyst used in the polycondensation reaction of the copolymerized polyester in the present invention is not particularly limited.
Antimony compounds, titanium compounds, germanium compounds and the like are preferred.

Preferred examples of the antimony compound include antimony trioxide and antimony acetate.

Preferred examples of the titanium compound include titanium tetrabutoxide and titanium acetate. Further, as the germanium compound, (a) amorphous germanium oxide, (b) fine crystalline germanium oxide, and (c) germanium oxide dissolved in glycol in the presence of an alkali metal or an alkaline earth metal or a compound thereof. And a solution obtained by dissolving germanium oxide in water. The amount of the germanium compound is preferably from 40 to 200 ppm, more preferably from 60 to 150 ppm, as germanium atomic weight remaining in the copolymerized polyester.

In the production of the copolymerized polyester, if necessary, other additives such as an antioxidant, a heat stabilizer, an ultraviolet absorber and an antistatic agent can be added.

The polyester film of the present invention can be produced by melting the above-mentioned lubricant-containing copolymerized polyester, extruding it from a die to form a film, biaxially stretching and heat setting. For example, in the sequential biaxial stretching, the longitudinal stretching ratio is from 2.5 to 3.6 times, the transverse stretching ratio is from 2.7 to 3.6 times, and the heat setting temperature is 16
The temperature may be selected from the range of 0 to 230 ° C, preferably 170 to 220 ° C, and may be produced by combining these.

Further, the polyester film of the present invention comprises:
If necessary, a laminated film of two types of copolymerized polyesters having different copolymerization amounts and copolymerization types may be used. In this case, each layer of the laminate may be a polyester satisfying the requirements of the present invention, or only the outer layer portion may satisfy the requirements of the present invention.

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.

As the metal plate for cans to which the polyester film of the present invention is bonded, 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.

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 cooled. The surface layer (thin layer) of the film in contact with the metal plate is made amorphous and adhered.

The film is previously coated with an adhesive layer with a primer, and this surface is bonded to a metal plate. As the adhesive layer, a known resin adhesive such as an epoxy-based adhesive, an epoxy-ester-based adhesive, an alkyd-based adhesive, or the like can be used.

[0032]

The present invention will be further described below with reference to examples. In the examples, "parts" means parts by weight. The measurement of each characteristic value was performed according to the following method.

(1) Intrinsic viscosity [η] Measured at 30 ° C. using orthochlorophenol as a solvent.

(2) Film Formability, etc. The film was bonded to both sides of 0.25 mm thick tin-free steel heated to 260 ° C., cooled with water, and then cooled to 150 ° C.
It was cut into a disk having a diameter of mm and deep-drawn in two stages using a drawing die and a punch to prepare a 55 mm-diameter side seamless container (hereinafter abbreviated as can). The following observations and tests were performed on the cans, and the cans were evaluated according to the following standards.

(2-1) Formability-1 Good: Both inner and outer surfaces are processed into films without any abnormality, and no whitening or breakage is observed in the films on the inner and outer surfaces of the can. Δ: Whitening was observed on the top of the film inside and outside of the can. X: Film breakage is observed in a part of the film on the inner and outer surfaces of the can.

(2-2) Formability-2-Good: Both inner and outer surfaces are processed without any abnormality. Rust prevention test of the film surface in the can (1% NaCl water is put in the can, the electrode is inserted, and the can The current value is measured when a voltage of 6 V is applied with the anode as an anode.
The following is shown. ×: There is no abnormality in the film on both the inner and outer surfaces, but the current value is 0.1 mA or more in the ERV test, and when the energized portion is observed under magnification, pinhole-shaped cracks starting from the coarse lubricant are observed in the film.

(2-3) Impact Resistance For cans with good moldability, water was poured in, and 10 of each test were dropped from a height of 1 m onto a PVC tile floor for each test. As a result of the test, ○: 0.1 mA or less for all 10 samples. C: 0.1 mA or more for 1 to 5 pieces. X: The film was 0.1 mA or more for 6 or more pieces, or cracks of the film were already observed after dropping.

(2-4) Heat Embrittlement Resistance A can having good moldability was heated and held at 210 ° C. for 5 minutes, and then subjected to the above-mentioned impact resistance evaluation. It was 0.1 mA or less. C: 0.1 mA or more for 1 to 5 pieces. X: The film was 0.1 mA or more for 6 or more pieces, or cracks were already observed in the film after heating at 210 ° C. for 5 minutes.

(2-5) Flavor Retention For cans having good deep drawability, 10 cans of each of cider and mineral water were filled and sealed. After keeping at 37 ° C. for 4 months, the container was opened and the changes in aroma and taste were sensory-tested. A: There was no change in aroma and taste. ：: One or two fragrances and tastes were slightly changed. Δ: 5 or 6 pieces slightly changed in aroma and taste. ×: Changes in fragrance and taste were observed in all 10 tubes.

[0040]

Example 1 Production of copolymerized polyester: 1099 parts of dimethyl 2,6-naphthalenedicarboxylate, 115 of dimethyl sebacate
Parts, 620 parts of ethylene glycol and 0.74 part of manganese acetate as a transesterification catalyst were charged into a reactor equipped with a stirrer, a rectification column and a methanol distillation condenser,
The mixture was heated while the temperature was gradually raised from 130 ° C. to 240 ° C., and methanol produced as a result of the reaction was distilled out of the system to cause a transesterification reaction. 3 hours after the start of the reaction, the internal temperature was 23
The temperature reached 0 ° C., and 320 parts of methanol were distilled off.

Here, 0.49 parts of trimethyl phosphate as a stabilizer, 2.2 parts of spherical monodispersed silica having an average particle size of 1.5 μm as a lubricant, and 0.18 part of germanium dioxide as a polycondensation catalyst were added.

The reaction mixture was transferred to a reactor equipped with a stirrer and a glycol distilling condenser, and the temperature was gradually raised from 240 ° C. to 285 ° C. and 1 mmHg from normal pressure.
The polycondensation reaction was carried out while lowering the pressure to a high vacuum. This polymer has a secondary transition point (Tg) of 112 ° C. and a melting point (Tg) of
m) was 243 ° C.

Production of polyester film: The above-obtained copolyester was melt-extruded at 290 ° C. and solidified by quenching to obtain an unstretched film. Next, the unstretched film is longitudinally stretched at 130 ° C. by 3.0 times, further stretched by 3.2 times while increasing the temperature from 130 ° C. to 180 ° C., and then heat-set at 200 ° C. to obtain a thickness. A 25 μm biaxially oriented film was obtained. Table 1 shows the characteristics of this film.

[0044]

Example 2 Production of copolymerized polyester: The composition of the dicarboxylic acid component was changed as shown in Table 1, and titanium tetrabutoxide 0.3 was used instead of germanium dioxide as a polycondensation catalyst.
The procedure was the same as in Example 1, except that 4 parts were used. Table 1 shows Tg and Tm of the obtained polymer.

Production of polyester film: A biaxially oriented film having a thickness of 25 μm was obtained in the same manner as in the production of the film of Example 1, except that the copolymerized polyester obtained above was used. Table 1 shows the characteristics of this film.

[0046]

Example 3 Production of copolymerized polyester: The same procedure as in Example 1 was carried out except that 87 parts of dimethyl adipate was used instead of dimethyl sebacate. Table 1 shows Tg and Tm of the obtained polymer.

Production of polyester film: A biaxially oriented film having a thickness of 25 μm was obtained in the same manner as in the production of the film of Example 1, except that the copolymerized polyester obtained above was used. Table 1 shows the characteristics of this film.

[0048]

Example 4 Production of a copolyester: The same procedure as in Example 1 was carried out except that the composition of the dicarboxylic acid component was changed as shown in Table 1. Table 1 shows Tg and Tm of the obtained polymer.

Production of polyester film: A biaxially oriented film having a thickness of 25 μm was obtained in the same manner as in the production of the film of Example 1 except that the copolymerized polyester obtained above was used. Table 1 shows the characteristics of this film.

[0050]

Comparative Examples 1-2 Production of a copolyester was carried out in the same manner as in Example 1 except that the composition of the dicarboxylic acid component was changed as shown in Table 1. Table 1 shows Tg and Tm of the obtained polymer.

Production of polyester film: A biaxially oriented film having a thickness of 25 μm was obtained in the same manner as in the production of the film of Example 1 except that the copolymerized polyester obtained above was used. Table 1 shows the characteristics of this film.

[0052]

Comparative Examples 3 and 4 Production of copolymerized polyester: intrinsic viscosity [η] of film
Was carried out in the same manner as in Example 1 except that the polycondensation reaction was adjusted so that the values shown in Table 1 were obtained. Tg of these polymers,
Table 1 shows Tm.

Production of polyester film: A biaxially oriented film having a thickness of 25 μm was obtained in the same manner as in the production of the film of Example 1 except that the copolymerized polyester obtained above was used. Table 1 shows the characteristics of this film.

[0054]

Comparative Example 5 Production of copolymerized polyester: The same procedure as in Example 1 was carried out except that 97 parts of dimethyl isophthalate was used instead of dimethyl sebacate. Tg and Tm of the obtained polymer
Are shown in Table 1.

Production of polyester film: A biaxially oriented film having a thickness of 25 μm was obtained in the same manner as in the production of the film of Example 1 except that the copolymer polyester obtained above was used. Table 1 shows the characteristics of this film.

[0056]

Comparative Example 6 Example 1 was repeated except that 1.1 parts of spherical monodispersed silica having an average particle size of 2.8 μm was used as a lubricant. Table 1 shows the properties of the obtained film.

[0057]

[Table 1]

The symbols in the table are as follows.

NA: 2,6-naphthalenedicarboxylic acid SA: sebacic acid AA: adipic acid IA: isophthalic acid

[0060]

According to the present invention, it is possible to provide a polyester film for laminating and forming a metal plate, which is excellent in moldability, impact resistance after can making, fragrance retention of contents, and the like.

Continuation of front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C08J 5/18 C08L 67/00-67/02

Claims (1)

(57) [Claims] 1. A biaxially oriented film comprising a copolymerized polyester containing a lubricant having an average particle size of 2.5 μm or less, wherein the copolymerized polyester has 80 to 95 mol% of 2,6-naphthalenedicarboxylic acid and the following formula: An acid component comprising 5 to 20 mol% of the aliphatic dicarboxylic acid represented by (I),
A glycol component mainly composed of ethylene glycol, and an intrinsic viscosity ([η]) of 0.5 to 0.7.
Have a molecular weight, it is yet copolyester melting point
A polyester film for a metal plate laminating process, characterized in that the secondary transition point is 100 ° C or higher at 215 to 255 ° C. Embedded image HOOC— (CH ₂ ) _n —COOH (I) (where n is a positive integer of 2 to 10)