JP2002037993A - Polyester film and polyester film for metal lamination - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film thermally adherable to a metal plate, excellent in molding processability, free from the generation of problems such as whitening, peeling or micro cracks even with crystallization treatment, and capable of easily obtaining a metal cane excellent in flavor property and shock resistance, under conditions of sufficient productivity. SOLUTION: The film comprises a polyester resin composition obtained by compounding (A) 10-70 wt.% of a polyethylene terephthalate resin and (B) 90-30 wt.% of a resin selected from polybutylene terephthalate and polyethylene 2,6-naphthalate. The film has >=2 melting peaks in a region of >=180 deg.C and <280 deg.C in a differential scanning calorimeter(DSC) after standing for 10 min in an atmosphere of 270 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film useful as a constituent material of a film-laminated metal plate, and to a metal can body and a can lid material manufactured using the laminated metal plate.

[0002]

2. Description of the Related Art Metal cans, which are one form of food and beverage packaging containers, have excellent mechanical strength, so that the contents can be stored for a long time, and the contents can be filled at a high temperature and sealed as it is. It is easy to perform sterilization treatment such as retort treatment, so it is highly reliable for safety and hygiene as a packaging container, and can store contents in a heated state, and can separate and collect cans after use relatively easily. Due to its many advantages, various contents have been filled and used in large quantities in recent years.

[0003] The inner and outer surfaces of a metal can for eating and drinking are conventionally made of a thermosetting resin for the purpose of maintaining the flavor of the contents and preventing corrosion of the metal can, or improving the aesthetics of the outer surface of the can and protecting the printed surface. Paints as the main component have been applied to metal cans. However, since such metal cans use a large amount of solvent during manufacturing, solvent removal during manufacturing affects the environment, residual solvents in the coating cause sanitary problems, and poor reaction during thermosetting. There are problems such as a decrease in flavor due to the remaining oligomer.

[0004] In order to overcome these problems, a method of laminating a plastic film to a metal has been proposed. As a metal plate obtained by laminating a polyester resin film on a metal plate, a so-called three-piece can (hereinafter referred to as 3P can) is used.
Cans and two-piece cans (hereinafter abbreviated as 2P cans) have been proposed. From the viewpoint of making cans seamless, the spread of 2P cans is desired.

[0005] As a general method for producing a 2P can, a metal plate on which a plastic film is laminated is punched by a can making machine, and a seamless can is formed by a drawing and ironing process. In this can-making process, the film is required to follow the spreading of the metal plate while being subjected to shearing by drawing and ironing.

[0006] In order to meet these required characteristics, canning performance is improved when a polyethylene terephthalate (PET) polyester resin having a specific intrinsic viscosity and a polybutylene terephthalate (PBT) polyester resin having a specific intrinsic viscosity are blended. An excellent film has been proposed (Japanese Patent No. 2882985, Japanese Patent No. 3020731).
JP, JP-A-10-195210, JP-A-10-195210
No. 11056).

[0007] When a film is formed of two types of polyesters, the film follows both the deformation of the metal during the molding of the can and the flavor of the contents of the can. For that purpose, it is necessary to have appropriate crystallinity. For that purpose, it is necessary to prevent copolymerization of different polyesters due to transesterification. For this reason, for example, measures have been taken to reduce the amount of heat applied to the film in the melting time of the resin and in the subsequent stretching and heat treatment steps. However, these methods have limitations when considering industrial production. That is, to increase the resin discharge rate to increase productivity, and to increase the capacity of the extruder to produce films with little quality fluctuation such as thickness unevenness,
In addition, it is necessary to lengthen the residence time of the resin in order to stabilize the discharge. For this reason, it has been difficult to obtain those satisfying the required characteristics and productivity.

[0008]

SUMMARY OF THE INVENTION In the present invention, the thermocompression bonding with a metal plate is possible even with a high degree of crystallinity because of its excellent mechanical properties. The quality of the laminated metal plate does not change easily due to fluctuations and is excellent in moldability, and even if the laminated metal plate or metal can film after thermocompression bonding or various molding processes is crystallized, the film will whiten or peel off A film, preferably a metal laminate, which can easily produce a metal can body having excellent flavor properties and impact resistance without causing problems such as generation of microcracks or microcracks and sufficiently considering productivity. To obtain a polyester film for use.

[0009]

In order to achieve the above object, the polyester film of the present invention comprises 10 to 70% by weight of a polyethylene terephthalate resin (A) and either polybutylene terephthalate or polyethylene 2,6 naphthalate. A film made of a polyester resin composition containing 90 to 30% by weight of a selected resin (B), which is placed in a 270 ° C. atmosphere for 10 minutes,
The melting point peak is 180 in a differential scanning calorimeter (DSC).
It is preferable that two or more polyester films are present in a region of not less than 280 ° C. and less than 280 ° C.

In this case, after being melted or softened and bonded to an aluminum plate, after being placed in an atmosphere of 270 ° C. for 10 minutes, a melting point peak of 180 ° C. or more and less than 280 ° C. in a differential scanning calorimeter (DSC) is obtained. It is preferable that the polyester film is characterized by having two or more in the region.

In this case, it is preferable that the above-mentioned polyester film is a polyester film for metal lamination.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The polyester (A) used in the present invention is obtained by subjecting a terephthalic acid component and an ethylene glycol component as main components to a melt polycondensation reaction or a subsequent solid-phase polymerization, and has an intrinsic viscosity of 0.1. 55-
0.90, preferably 0.5
8 to 0.80, and the molecular weight is 20 by weight average molecular weight.
2,000 to 200,000, the molecular weight distribution expressed by the ratio of the weight average molecular weight to the number average molecular weight is:
It is preferably in the range of 2.0 to 10.0.

When the intrinsic viscosity and the weight average molecular weight are smaller than these ranges, a film having mechanical strength that can be practically used cannot be obtained, and when it exceeds this range, the thermocompression bonding property of the film to a metal plate is impaired. It is not preferable. On the other hand, if the molecular weight distribution is smaller than this range, the ability of the film to follow the deformation of the metal plate during can making is impaired, and if the molecular weight distribution is larger than this range, the amount of oligomers is increased and flavor properties are impaired, which is not preferable.

The polyester (B) in the present invention is obtained by a melt polycondensation reaction or a solid phase polymerization reaction of a terephthalic acid component and a 1,4-butanediol component as main components. 0.60 viscosity
2.2, weight average molecular weight of 50,000 to 200,000,
The molecular weight distribution, which is the ratio between the weight average molecular weight and the number average molecular weight, is 1.5 to 5.0, or 2,6 naphthalenedicarboxylic acid and ethylene glycol as main components,
It is a polyethylene 2,6-dinaphthalate polymerized by an ordinary method.

If the intrinsic viscosity and the weight average molecular weight are smaller than these ranges, a film having mechanical strength that can be used practically cannot be obtained, and if it exceeds this range, the thermocompression bonding property of the film to a metal plate is impaired. It is not preferable. On the other hand, if the molecular weight distribution is smaller than this range, the ability of the film to follow the deformation of the metal plate during can making is impaired, and if the molecular weight distribution is larger than this range, the amount of oligomers is increased and flavor properties are impaired, which is not preferable.

As a method for producing polybutylene terephthalate, a known method can be employed. For example, dimethyl terephthalate, 1,4-butanediol and, if necessary, other copolymerization components are charged into a transesterification reactor and reacted at a temperature of about 230 ° C. for 5 hours to obtain a transesterification rate of about 95%. Get. Next, this is transferred to a polymerization vessel, and a known method can be used as a method for producing the polyester (A) in the presence of a catalyst such as tetra-n-butyl titanate or tetraisopropyl titanate. For example, the melt polycondensation reaction may be performed under reduced pressure of 1.3 hPa or less until a desired intrinsic viscosity, molecular weight, and molecular weight distribution at a temperature of 220 to 260 ° C. are obtained. Further, the polyester obtained by the above method may be further subjected to solid phase polymerization.

In the present invention, it is necessary to have can moldability and flavor, and to prevent whitening of the film after molding.

For this purpose, in order to control the crystallization rate and the degree of crystallization, it is necessary to suppress the transesterification reaction between the polyester (A) and the polyester (B) so as not to copolymerize.

When a transesterification reaction occurs between the polyester resins (A) and (B), the polyester resin (A)
And a copolymer of the polyester resin (B) and the ethylene terephthalate structure, which is the main component structure of the polyester resin (A), is randomized, and its rigidity is lost. The butylene terephthalate structure or 2,6 naphthalate structure, which is the main component structure of B), is randomized, and its characteristic high crystallinity is impaired.

In the present invention, various means are known for suppressing side reactions such as transesterification of the polyester resins (A) and (B) in the film composition. However, for application in industrial film production,
By adding a specific phosphorus compound, it is necessary to suppress a transesterification reaction caused by a catalyst, to preliminarily knead the phosphorus compound with polyethylene terephthalate, and to control the size of resin pellets when mixing.

As the phosphorus compound, it is most effective to use a pentaeristol type phosphorus compound and a phosphonic acid phosphorus compound in combination. Considering the stability in the extruder, those having a melting point of 200 ° C. or more and a molecular weight of 200 or more are preferred. Although the optimum amount of these phosphorus compounds varies depending on the type, from the viewpoint of suppression of the transesterification reaction, the amount of the phosphorus compound is 0.1.
It is preferable to mix an amount of from 01% by weight to 0.3% by weight. When used for food applications such as beverage cans, F
It must be used in compounds and amounts that meet standards such as the DA (United States Food and Drug Administration) and the Polyolefins Health Council.

More preferably, these phosphorus compounds are preliminarily kneaded with polyethylene terephthalate to form a master batch. By forming a master batch, the transesterification reaction suppressing effect is increased. Also,
The volume of one polyester resin pellet is 1.2 times or more, preferably 1.5 times or more the size of the other pellet.
It may be less than double. As a result, the melting timing of both polyester resins can be changed, and the effect of suppressing the transesterification reaction is further exhibited. In the present invention, it is more preferable to adopt the above-described method, but the method is not necessarily limited as long as the characteristics described later are satisfied by another method.

In the production of the film for metal lamination according to the present invention, the polyester resin (A), (B) and the specific organic phosphorus compound are prepared by converting the phosphorus compound into a masterbatch with one of the resins, Is most preferably dry blended. As the extruder, a twin screw type extruder in a single screw direction, same direction or different direction is preferable, and the shape and dimensions of the screw may be arbitrary. The extruder preferably has a melting time of 21 (time from the start of melting of any of the resins A and B to the close contact with the cooling roll after being extruded from the T-die) from the viewpoint of productivity and stability of quality. Minutes or more, more preferably 29 minutes or more. In less than 21 minutes, the stability in mass production is
Poor quality may result.

For the production of the film, first, after sufficiently drying the polymer, the extruder is used to raise the melting point of the polymer by 10 to 10%.
It is melt-extruded at a temperature higher by 80 ° C., and is discharged from the die in a sheet shape or a cylindrical shape using a T-shaped or circular die to obtain an unstretched film. Subsequently, the unstretched film is stretched in at least one direction. In the case of uniaxial stretching, it is preferable to continue stretching in the width direction of the oven, and in the case of biaxial stretching, successive stretching is performed in the longitudinal direction using a stretching roll or the like, and then in the width direction. Either axial stretching or simultaneous biaxial stretching in which stretching is performed substantially simultaneously in both directions may be used.

The stretched film may be subjected to a heat treatment, a surface treatment or the like to such an extent that the object of the present invention is not impaired. Also. The polyester film may be a single layer or a multilayer.

The polyester film of the present invention preferably has a thickness of 5 to 60 μm. The polyester film is usually formed into a film by adding a lubricant. Examples of the lubricant include silicon dioxide, kaolin, clay, calcium carbonate, calcium terephthalate, aluminum oxide, titanium oxide, calcium phosphate, silicone particles, and the like, and an inorganic lubricant is preferable. In addition, at the time of melt mixing, additives such as a stabilizer, a coloring agent, an antioxidant, an antifoaming agent, and an antistatic agent can be contained, if necessary, in addition to the lubricant.

The obtained polyester film is laminated on a metal plate to obtain a laminated plate. In this case, the roller or the metal plate is heated to 150 to 270 ° C., and after bonding the metal plate and the film via the roller, quenching is performed and at least the surface layer portion of the film in contact with the metal plate is melt-fused. Just do it. The laminating speed is 1 to 200 m / min. After laminating a polyester film, a metal plate may be laminated.

[0028]

The present invention will be specifically described below with reference to examples. still,
Each characteristic value of the polyester in the examples was measured as follows. 1. The intrinsic viscosity was measured at a temperature of 20 ° C. using an equal weight mixture of phenol and ethane tetrachloride as a solvent. 2. Melting peak of film Using DSC3100S manufactured by Rigaku Denki Co., put the film in a sample pan, cover the pan, melt under nitrogen gas atmosphere at 280 ° C for 10 minutes, quench, and cool from -20 ° C to 2 ° C.
The polyester resin (A) was measured at a heating rate of 0 ° C./min.
And the melting point (B) derived from the polyester resin (B). The film to be measured was a manufactured film and a film laminated under the following conditions. (Lamination conditions) Lamination temperature: 220 ° C Linear pressure 5 kgf / cm, 30 kgf / cm (two types) Molecular weight, molecular weight distribution (Sample preparation) 1 mg of a solution of 15 mg of each sample in hexafluoroisopropanol / chloroform = 2/3 (v / v)
, And then dissolve in chloroform (20 ml). Prepare a polystyrene (made by TOSHO) solution as a reference material,
Use as a sample for C calibration curve. (Analysis conditions) Column: gmhxl-gmhxl-g2000h
xl (TOSOH) Mobile phase: HFIP / Chlorof
orm = 2/98 (v / v) Flow rate: 0.7 ml / min Column Temp: 40 ° C. Detection Vol: 200 ml (apparatus used for measurement) GPC: SYDTEM-21 (Shodex) Data processing: SIC-480 (SIC) , System Instruments) 4. 1. Can-making film Laminated on an aluminum plate under the conditions of
After treatment at 0 ° C., the presence or absence of damage such as peeling, cutting, and cracking of the film after forming the can was visually observed and observed with a fluorescence microscope (magnification: 80 ×), and evaluated based on the following criteria. : 95 or more of the 100 cans were not damaged. Δ: 80 to 94 out of 100 cans were not damaged. ×: Some 21 or more of the 100 cans were damaged. Whitening After making the can under the conditions of 4, the surface on which the film was attached was 80 ° C.
Immersed in hot water for 10 minutes and observed whitening after pulling up ◎ ・ ・ ・ ・ ・ ・ No whitening before and after immersion ○ ・ ・ ・ ・ No substantial △ ・ ・ ・ ・ Whitening observed × ・ ・..Remarkably whitening

(Example 1) [Raw material resin] Polyester resin containing ethylene terephthalate as a main component (A) Polymerization method: melt solid phase Intrinsic viscosity: 0.75 Weight average molecular weight (Mw): 60000 Number average molecular weight (Mn) : 20,000 Molecular weight distribution (Mw / Mn): 3.0 Polyester resin containing butylene terephthalate as a main component (B) Polymerization method: Melt solid phase Intrinsic viscosity: 1.20 Weight average molecular weight (Mw): 103000 Number average molecular weight (Mn) ): 36000 Molecular weight distribution (Mw / Mn): 2.9 Ti content: (Wt%): 0.00004 [Production method] Polyester resin (B) and organic phosphorus compound (C1) (ADK STAB PEP-45: Asahi Denka Kogyo Co., Ltd.) (C2) (ethyl diphosphonoacetate: Johoku Chemical Co., Ltd.) and B / C1 / C2 = 60 /
The mixture was melt-extruded at a ratio of 0.07 / 0.03 (weight ratio) using a 45 mmφ twin screw extruder to prepare pellet chips having a diameter of 3 mm and a length of 5 mm. 4mm in diameter and 5m in length
m / polyester resin (A) and the above-mentioned master batch with A / B / C1 / C2 = 40/60/0.
Dry blending was performed so as to be 1 / 0.03 (weight ratio), and the mixture was put into an extruder in which two 185 mmφ extruders were connected in series. Thereafter, it was melted and extruded at 285 ° C. At this time, the time from the start of melting to flowing out of the T-die was about 31 minutes. After the extrusion, the film was rapidly cooled to obtain an unstretched film having a thickness of 190 μm. The film was stretched four times in the longitudinal direction at 90 ° C., and then stretched four times in the width direction at 235 ° C. After stretching,
Heat treatment was performed at 165 ° C., and the film was cooled to obtain a film having a thickness of 25 μm. The evaluation results of the obtained films are shown in Tables 1 and 2.

(Comparative Example 1) Films were obtained and evaluated in the same manner as in Example 1 except that the organic phosphorus compounds (C1, C2) were omitted. Tables 1 and 2 show the results. .

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

According to the present invention, mechanical properties are excellent,
Even with a high degree of crystallinity, thermocompression bonding with a metal plate is possible, and the quality of the laminated metal plate is unlikely to change due to changes in conditions during thermocompression bonding to the metal plate. Possible polyester film can be provided,
Excellent moldability, and even when crystallization of laminated metal plate or metal can film after thermocompression bonding or various molding processes, the film may be whitened or peeled off, or micro cracks may occur. It is possible to provide a polyester film capable of easily removing a metal can body having excellent flavor properties and impact resistance without using it, and it has a very high industrial value and greatly contributes to industry.

Continued on the front page (72) Inventor Hideki Shimizu 344 Kizu-Maebata, Inuyama-shi, Aichi Prefecture Toyo Spinning Co., Ltd. (72) Inventor Takashi Nagano 344 Loc. (72) Inventor Mitsuo Inoue 2-2-2-8 Dojimahama, Osaka City, Osaka Toyo Spinning Co., Ltd. Head Office (72) Inventor Shoichi Katamai 2-1-1 Katata, Otsu City, Shiga Prefecture Toyobo Co., Ltd. In-house F-term (reference) 4F071 AA45 AA46 AA84 AA87 AC15 AH05 BA01 BB06 BB07 BC01 4J002 CF06W CF07X CF08X EW086 EW126 FD170 FD206

Claims (3)

[Claims] 1. A polyester resin composition comprising 10 to 70% by weight of a polyethylene terephthalate resin (A) and 90 to 30% by weight of a resin (B) selected from either polybutylene terephthalate or polyethylene 2,6 naphthalate. 28. A film comprising
After 10 minutes in an atmosphere of 0 ° C., a differential scanning calorimeter (D
A polyester film, wherein two or more melting point peaks in SC) are present in a region of 180 ° C. or more and less than 280 ° C. 2. The polyester film according to claim 1, which is melted or softened and adhered to an aluminum plate, then placed in an atmosphere at 270 ° C. for 10 minutes, and then melted by a differential scanning calorimeter (DSC). Peak is 180 ° C or higher and 28
A polyester film, wherein two or more are present in a region below 0 ° C. 3. The polyester film for metal lamination according to claim 1 or 2.