JPH10139897A - Polyester-based film for laminating three-piece can - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a polyester-based film for laminating three piece can having suppressed elution of an oligomer, causing no change in taste and flavor of foods, excellent in slipperiness and scratch resistance and useful for soft drink by setting the dynamic coefficient of friction between the film and a metal to a value under a prescribed value. SOLUTION: This polyester-based film for laminating three-piece is formed to have <=0.45 dynamic coefficient of friction between the film comprising polyethylene terephthalate (preferably having 0.55-0.85 intrinsic viscosity), etc., and a metal at 80 deg.C. An amount of ethylene terephthalate cyclic trimer is preferably <=0.7wt.% in the polyester-based film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-piece can laminating film mainly used for foodstuffs such as soft drinks, beer and canned foods. More specifically, the polyester film for lamination of three-piece cans, which has excellent scratch resistance of the film in the can making process and therefore has a good productivity of the can, and further has a good productivity of the can. And a film for laminating three-piece cans in which the elution of low molecular weight substances from the film by heat treatment after filling foodstuffs such as retort treatment is suppressed.

[0002]

2. Description of the Related Art A three-piece can refers to a can which is suitable for filling food items such as retort foods and coffee drinks and is manufactured by winding a top lid. Conventionally, a paint is generally applied to prevent corrosion of the inner and outer surfaces of a three-piece can, and a thermosetting resin is used for the paint.
As another method, there is a method using a thermoplastic resin.
For example, attempts have been made to laminate a polyolefin-based film on heated tin-free steel. Further, it has been studied to laminate a polyester film having good heat resistance on a metal plate and use the laminated metal plate as a three-piece can.

[0003]

Most of the thermosetting resin coatings are of a solvent type, and the formation of the coating film is 150 to 250.
Since heating at a high temperature of several degrees Celsius for a long time of several minutes is required, and a large amount of organic solvent is scattered during baking, improvements such as simplification of processes and prevention of pollution are demanded. Also, even when applied under the above conditions, it is inevitable that a small amount of organic solvent remains in the coating film. For example, when a food product is filled in a three-piece metal can having the coating film formed thereon, In such a case, the organic solvent migrates to the food, and adversely affects the taste and smell of the food. Furthermore, additives contained in the paint and low molecular weight substances resulting from incomplete crosslinking reaction migrate to foodstuffs, and have the same adverse effects as residual organic solvents.

[0004] The method using a thermoplastic resin film can solve the above problems, such as simplification of the process and prevention of pollution. However, among thermoplastic resin films,
For example, when a polyolefin-based film such as polyethylene or polypropylene is used, the film has low heat resistance and may be whitened by retort treatment and peeled off from a laminated metal plate or the like. Further, since the polyolefin-based film is soft, there is a problem that scratch resistance is inferior. If the scratch resistance of the film is poor, for example, in the case of a three-piece can, a process such as transferring and winding each leaf of the laminated metal plate in the can-making process is required. And the commercial value is reduced. Further, the method using a polyolefin-based film solves the problem caused by the migration of the residual solvent, which was observed in the method using a thermosetting resin coating, but the addition of a low molecular weight substance or a heat stabilizer generated during film formation. The transfer of agents to foodstuffs adversely affects the taste and odor of the foodstuffs. Further, the polyolefin-based film has a problem that it absorbs aroma components in foodstuffs and is inferior in flavor resistance.

On the other hand, a method using a polyester film among thermoplastic resin films is the most preferable method because the problems of the above-mentioned polyolefin film are improved. Polyester-based films have better scratch resistance than polyolefin-based films, but the level of ordinary polyester-based films is not sufficient, and improvements have been demanded. As a method of improving the scratch resistance, the surface of a polyester film is
A coating film method has been proposed in which an organic film having excellent lubricity and scratch resistance is formed by a coating method. Certainly, the scratch resistance is improved by this method, but it is necessary to use an organic solvent in the process of forming the organic film, and only a small part of the solvent remains in the organic film layer. When a food product is filled in a manufactured metal container, there is a problem that the organic solvent adversely affects the taste and odor of the food product. Further, there is a problem that a low molecular weight substance is eluted from the organic coating layer and has the same adverse effect as the residual organic solvent.

[0006] Further, polyester films have excellent heat resistance, do not require additives such as heat stabilizers, generate less low molecular weight substances, and have lower additive and lower molecular weight substances than polyolefin films. Food taste and odor problems due to migration are greatly improved. However, in the polyester-based film containing polyethylene terephthalate as a main component, an oligomer mainly composed of a so-called ethylene terephthalate cyclic trimer, which is a low molecular weight compound produced in a polymerization step or a film forming step, is sometimes referred to as an oligomer. There is a problem in that the oligomer is eluted from the film and migrates to foodstuffs, or the oligomer is deposited on the surface of the laminate film to impair the appearance, and a solution to the problem is desired.

As can be understood from the above, in the manufacturing process of a three-piece can, exceptional scratch resistance is required for the polyester film for lamination. An object of the present invention is to provide a three-piece can laminating film excellent in scratch resistance, in which the above problems have been solved.

[0008]

Means for Solving the Problems The present inventors have made intensive studies to achieve the above object, and as a result, have reached the present invention. That is, the present invention is characterized in that the coefficient of dynamic friction between the film and the metal at 80 ° C. is 0.45 or less.
It is a polyester film for piece can lamination.
The polyester film for laminating three-piece cans is characterized in that the content of ethylene terephthalate cyclic trimer in the polyester film is 0.7% by weight or less.

In the present invention, the scratch resistance is improved by setting the dynamic friction coefficient between the film and the metal at 80 ° C. to 0.45 or less, and the elution of oligomers is suppressed by using polyester.

[0010] The polyester used in the present invention is obtained mainly by polycondensation of a polycarboxylic acid and a polyhydric alcohol.

Examples of the polycarboxylic acid component include dicarboxylic acids, for example, aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid and diphenyldicarboxylic acid; adipic acid, azelaic acid, sebacic acid; Examples thereof include aliphatic dicarboxylic acids such as decanedicarboxylic acid, dodecanedicarboxylic acid, and dimer acid; and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid. Among the above, use of aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid and naphthalenedicarboxylic acid is preferred from the viewpoint of flavor resistance.

Examples of the polyhydric alcohol component include glycols, for example, aliphatic diols such as ethylene glycol, diethylene glycol, triethylene glycol, propanediol, butanediol, hexanediol, dodecanemethylene glycol, and neopentyl glycol; cyclohexanedimethanol And aromatic diols such as an ethylene oxide adduct of a bisphenol derivative. Preferably, it is ethylene glycol.

As the polyester, a system in which polyethylene terephthalate or a mixture of polyethylene terephthalate and a polyester-polyol block copolymer in an amount of 0.6 to 6% by weight in terms of a polyether component is particularly recommended. This configuration is preferable because the whitening phenomenon of the film caused by hot water treatment such as retort treatment is suppressed.

In the polyester, it is preferable that at least 70 mol% of the constituent components be composed of ethylene terephthalate units, more preferably 80 mol%.
That is all. 70 mol% ethylene terephthalate units
If it is less than 30, the heat resistance tends to decrease, for example, when the film is laminated to a metal can material, the film tends to be stretched, and the width tends to be reduced or wrinkles due to heat shrinkage. Or the productivity of processing may decrease, and the raw material cost of the polyester may increase, which may be economically disadvantageous.

The polyester is, from the viewpoint of mechanical properties,
The intrinsic viscosity is preferably 0.5 or more, more preferably 0.55 to 0.85.

The polyester film of the present invention has an 80
The coefficient of kinetic friction between the film and the metal at 0 ° C must be 0.45 or less, preferably 0.40 to 0.20,
More preferably, it is 0.35 to 0.20. When the kinetic friction coefficient is 0.45 or less, scratch resistance is at a practical level, a metal container having a good appearance can be obtained even when the can-making speed is increased, and the productivity of can-making can be increased.

In order to make the dynamic friction coefficient 0.45 or less, at least one selected from inorganic fine particles or crosslinked polymer particles having an average particle size of 0.5 to 5 μm and a thermoplastic resin incompatible with polyester. One component may be contained in the polyester such that the ratio to the total amount of the polyester is 0.3 to 5% by weight. The above components may be used alone or in combination of two or more, but a combined system is preferred.

The inorganic fine particles are not particularly limited as long as they are insoluble and inactive in the polyester. Specifically, metal oxides such as silica, alumina, zirconia, and titanium oxide; complex oxides such as kaolin, zeolite, sericite, and sepiolite; sulfates such as calcium sulfate and barium sulfate; calcium phosphates and zirconium phosphate; Phosphates; carbonates such as calcium carbonate; These inorganic fine particles may be either natural products or synthetic products, and the shape of the particles is not particularly limited. The inorganic fine particles may be used alone or in combination of two or more. In the case where only inorganic fine particles are used, a combined system of aggregated amorphous silica and spherical silica or zeolite is preferable.

The material of the crosslinked polymer particles is not particularly limited as long as it has heat resistance enough to withstand the temperature during melt molding of the polyester. For example, acrylic monomers such as acrylic acid, methacrylic acid, acrylic esters, and methacrylic esters; styrene monomers such as styrene and alkyl-substituted styrene; and divinylbenzene, divinylsulfone, and ethylene glycol dimethacrylate. Acrylate, trimethylolpropane trimethyl acrylate,
Copolymers with a crosslinkable monomer such as pentaerythritol tetramethyl acrylate; melamine resins; benzoguanamine resins; phenol resins; silicone resins. Among the above materials, a copolymer of an acrylic monomer and / or a styrene monomer and a crosslinkable monomer is particularly preferred. The crosslinked polymer particles may be used alone or in combination of two or more.

The method for producing the above-mentioned crosslinked polymer particles is not particularly limited, and can be produced by a conventionally known emulsion polymerization method, suspension polymerization method or the like. In addition, there is no restriction on incorporating means such as pulverization and classification for adjusting the particle diameter and the particle size distribution of the crosslinked polymer particles.

Examples of the thermoplastic resin incompatible with polyester include polyolefin resin, polystyrene resin, polyacrylic resin, polycarbonate resin, polyamide resin, polysulfonic acid resin, wholly aromatic polyester resin, and the like. Can be The thermoplastic resins may be used alone or in combination of two or more. The resin does not need to be in the form of particles.

When inorganic fine particles and crosslinked polymer particles are used, the average particle size must be 0.5 to 5 μm, and preferably 0.8 to 4 μm. 0.5μ
If it is less than m, the effect of improving the slipperiness between the film and the metal at high temperatures tends to be small, and the effect of improving the scratch resistance tends to be hardly exhibited. Conversely, if it exceeds 5 μm, the effect of improving the sliding property between the film and the metal at a high temperature is saturated, or the fine particles easily fall off due to friction,
When the film is formed, the film tends to break.

The content of the inorganic fine particles, the crosslinked polymer particles and the thermoplastic resin incompatible with the polyester is 0.3 to 5% by weight based on the total amount of the polyester based on the total amount of the components.
And preferably 0.5 to 3% by weight
It is. If the amount is less than 0.3% by weight, the effect of improving the slipperiness between the film and the metal at a high temperature is reduced, and the effect of improving the scratch resistance tends to be hardly exhibited. On the other hand, when the content exceeds 5% by weight, the effect of improving the slipperiness between the film and the metal at a high temperature tends to be saturated or the film-forming property of the film tends to decrease.

The addition of the inorganic fine particles, the crosslinked polymer particles, and the thermoplastic resin incompatible with the polyester may be carried out in the polyester production process, or may be carried out by adding the polyester and the above components and performing a melt kneading method. It doesn't matter. Further, it can be added as a master batch containing the above components at a high concentration.

In the polyester film of the present invention, the content of the ethylene terephthalate cyclic trimer generated in the polymerization step or the film forming step is preferably 0.7% by weight or less relative to the total amount of the polyester. ,
This makes it possible to further suppress the elution of the oligomer. More preferably 0.6% by weight or less;
Particularly preferably, it is 0.5% by weight or less. When the content of the ethylene terephthalate cyclic trimer exceeds 0.7% by weight, the elution of oligomers from the film tends to increase due to heat treatment (such as retort treatment) after filling the foodstuff. In the case of a laminated film on the inner surface of a can, oligomers tend to migrate to food products, which tend to adversely affect the taste and smell of the food products. In the case of a laminate film on the outer surface of a can, oligomers tend to precipitate on the film surface and the appearance tends to be impaired.

The method for reducing the content of the ethylene terephthalate cyclic trimer to 0.7% by weight or less is not particularly limited, and the ethylene terephthalate cyclic trimer is extracted and removed from the film after film formation with water or an organic solvent. And a method using a polyester having a low ethylene terephthalate cyclic trimer content as a raw material. The latter method is more economical and preferred. The method for producing a polyester raw material having a low ethylene terephthalate cyclic trimer content is not limited at all, and examples thereof include a reduced pressure heat treatment method, a solid phase polymerization method, an extraction method using water or an organic solvent, and a method combining these methods. be able to. In particular, after reducing the amount of ethylene terephthalate cyclic trimer by solid-state polymerization, the method of extracting with water and further reducing the ethylene terephthalate cyclic trimer is based on the ethylene terephthalate cyclic trimer content in the raw polyester. This is the most preferable method because the amount of ethylene terephthalate cyclic trimer in the film forming step is reduced and the amount of ethylene terephthalate cyclic trimer produced is suppressed.

If necessary, the polyester may contain an antioxidant, a heat stabilizer, an ultraviolet absorber, a plasticizer, a pigment, an antistatic agent, a lubricant, a crystal nucleating agent, and the like.

The method for producing the polyester is not particularly limited, and it can be produced by a conventionally known transesterification method, a direct polymerization method or the like. Further, in order to increase the molecular weight, it can be produced by a solid phase polymerization method. The solid phase polymerization method is a preferable method in that the content of the above-mentioned ethylene terephthalate cyclic trimer can be reduced.

The polyester film of the present invention may be either an unstretched film or a stretched film as long as it satisfies the above requirements. 1 for stretched film
Either axial stretching or biaxial stretching may be used, but a biaxially stretched film is preferred from the viewpoint of isotropy.

The method for producing the film is not limited at all. For example, in the case of a stretched film, a conventionally known method such as a T-die method and a tubular method can be applied.

The polyester film may be a single layer or a multilayer. Further, the thickness of the polyester film is preferably 4 to 50 μm, more preferably 5 to 30 μm.

In the three-piece can, a polyester-based film is first laminated on a metal plate to form a laminated metal plate, which is then wound around a top lid to form a three-piece can. Examples of the metal plate used include tin, tin-free steel, and aluminum.

The method of laminating the polyester film on the metal plate is not particularly limited, and a conventionally known dry laminating method, thermal laminating method or the like can be employed. As the lamination method, for example, there is a method in which an adhesive layer is laminated on a polyester-based film and then laminated with a metal plate, and the adhesive layer is formed on the film in a partially cured state, and a state in which the adhesive layer is laminated on the metal plate It is preferable to cure completely by using a method using heat, light, an electron beam, or the like. Also,
The adhesive used in the above method is, for example, an epoxy resin, a polyurethane resin, a polyester resin,
Examples thereof include a polyester polyurethane resin, an isocyanate resin, and various modified resins thereof. As another method, for example, there is a method in which a multilayer film in which a low melting point polyester resin layer is laminated on a polyester-based film is produced by a co-extrusion method, and thermal lamination is performed by heating a metal plate with electric current. preferable.

The lamination of the polyester film to the metal plate may be performed on one side or both sides. In the case of double-sided lamination, lamination may be performed simultaneously or sequentially.

[0035]

EXAMPLES Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, and may be practiced without departing from the above-mentioned purpose. Also fall within the technical scope of the present invention.

Experimental Example 1 Using the films and laminated steel sheets obtained in the following Examples and Comparative Examples, the dynamic friction coefficient, scratch resistance, ethylene terephthalate cyclic trimer amount, and elution of oligomer were measured. The method will be described below. (1) Dynamic friction coefficient Weight of 1.5 kg having a contact area of 50 mm x 70 mm
Was set on a slider, and the coefficient of kinetic friction when sliding on a tin-free steel plate at 80 ° C. at a speed of 250 mm / min was measured.

(2) Scratch Resistance Using a dyeing fastness friction tester manufactured by Toyo Seiki Co., Ltd.
A scratch on the film surface after rubbing on a tin-free steel plate at 80 ° C. for 1 minute at a reciprocation distance of 0 mm and 30 reciprocations / minute was visually observed and evaluated according to the following criteria. Note that △ and above are practical. ：: Almost no scratches were observed. Δ: Scratches are partially observed. ×: A scratch is observed on the entire surface.

(3) Ethylene terephthalate cyclic trimer amount The polyester film is dissolved in hexafluoroisopropyl alcohol / chloroform = 2/3 (V / V), the polyester is precipitated with methanol, and the precipitate is separated by filtration. The filtrate is evaporated to dryness, and the evaporated matter is dissolved in dimethylformamide. The solution was developed by liquid chromatography to determine the amount of ethylene terephthalate cyclic trimer in the polyester film.

(4) Elution of oligomer A laminated steel sheet of 10 cm square is subjected to a retort treatment at 120 ° C. for 30 minutes together with 500 cc of distilled water. The laminated steel sheet after the treatment was air-dried, the state of the film surface of the laminated steel sheet was observed with a magnifying glass, and the presence or absence of oligomer elution was determined according to the following criteria. Yes: oligomer crystals are observed on the film surface. None: No oligomer crystals are observed on the film surface.

Example 1 Polymethyl methacrylate particles (spherical; crosslinked with 0.1% by weight of agglomerated type silica (average particle size 1.5 μm) and trimethylolpropane trimethacrylate)
97 parts by weight of a polyethylene terephthalate containing 1.0% by weight of an average particle size, 1.0% by weight, low oligomerized by an extraction method, having an intrinsic viscosity of 0.70 and an ethylene terephthalate cyclic trimer amount of 0.33% by weight. And 3 parts by weight of a polyethylene terephthalate-polytetramethylene glycol ether block copolymer were melt-extruded by a T-die method to form an amorphous sheet.
The film was stretched 5 times and 3.5 times in the transverse direction, and heat-set at 200 ° C. to obtain a polyester film having a thickness of 12 μm. One side of the polyester film is coated with an adhesive (a mixture of a polyurethane adhesive “Adcoat” manufactured by Toyo Ink Co., Ltd. “Adcoat” and a curing agent) at a solid content of 4 g / m ² , dried and then aged at 40 ° C. for 24 hours. The resulting film was laminated on both sides of a cold-drawn steel sheet that had been degreased by a thermal lamination method to obtain a double-sided laminated steel sheet.

The properties of the obtained polyester film and laminated steel sheet are shown in Table 1. The polyester film and the laminated steel sheet obtained in this example have good slip resistance between the film and the metal at a high temperature, have excellent scratch resistance, and have no oligomer elution, as a metal lamination film and a laminated steel sheet. It was of high quality. When the polyester film obtained in this example was used for the inner surface of the can body and the inner and outer surfaces of the bottom lid, and was made as a three-piece can, the film was manufactured at a high speed without scratching the surface of the film during the can manufacturing process. I got a can. Also, even if the molding can is filled with coffee and subjected to retort treatment, there is no migration of the oligomer or organic solvent from the film, no change in taste or smell, and no precipitation of the oligomer on the outer surface of the bottom lid is observed. , With high commercial value.

Example 2 Instead of 97 parts by weight of polyethylene terephthalate used in Example 1, 0.3% by weight of coagulated silica having an average particle size of 1.5 μm and almost monodisperse particles having an average particle size of 3.0 μm A polyester film and a laminated steel sheet were obtained in the same manner as in Example 1, except that 97 parts by weight of polyethylene terephthalate containing 1.0% by weight of spherical zeolite having a diameter distribution was used. Table 1 shows these characteristics.
The polyester film and the laminated steel sheet obtained in this example were of high quality, as in Example 1.
Also, when making a 3-piece can and filling it with coffee,
As in Example 1, the product value was high.

Example 3 A polyester film and a laminated steel sheet were obtained in the same manner as in Example 1 except that 1.0% by weight of a polystyrene resin was used instead of 1.0% by weight of crosslinked polymethyl methacrylate particles. Table 1 shows these characteristics.
The polyester film and the laminated steel sheet obtained in this example were of high quality as in Example 1.
Also, when making a 3-piece can and filling it with coffee,
As in Example 1, the product value was high.

Comparative Example 1 A polyester film and a laminated steel sheet were obtained in the same manner as in Example 1 except that the crosslinked polymethyl methacrylate particles were not used. Table 1 shows these characteristics.
The polyester film and the laminated steel sheet obtained in this comparative example had poor sliding properties between the film and the metal at a high temperature and were inferior in scratch resistance, and were of low quality as a metal lamination film and a laminated steel sheet. Further, when a three-piece can was made in the same manner as in Example 1, a scratch was formed on the surface of the film during the can making process, and only a product having a low commercial value was obtained.

Comparative Example 2 Instead of 97 parts by weight of the polyethylene terephthalate used in Example 1, 0.1% by weight of agglomeration type silica having an average particle size of 1.5 μm was produced by a melt polymerization method, and the intrinsic viscosity was reduced. Polyethylene terephthalate 9 having an ethylene terephthalate cyclic trimer content of 0.65 and a content of 1.0% by weight
A polyester film and a laminated steel sheet were obtained in the same manner as in Example 1 except that 7 parts by weight was used. Table 1 shows these characteristics. The polyester film and the laminated steel sheet obtained in this comparative example were poor in slipperiness between the film and the metal at a high temperature, inferior in scratch resistance, and showed elution of oligomer, and were of low quality. Also,
When a three-piece can was made and filled with coffee in the same manner as in Example 1, scratches were made on the surface of the film during the can-making process, and oligomer precipitation was observed on the outer surface of the bottom lid by retort treatment. Was low.

Example 4 In place of 97 parts by weight of the polyethylene terephthalate used in Example 1, 1.0 part by weight of spherical polystyrene particles having an average particle diameter of 2.5 μm and having a substantially monodisperse particle size distribution crosslinked with divinylbenzene. %, And a polyester film and a laminated steel sheet were obtained in the same manner as in Example 1 except that 97 parts by weight of polyethylene terephthalate containing% was used. Table 1 shows these characteristics. The polyester film, laminated steel plate and metal can (3
The piece can was of high quality as in Example 1.

Example 5 Instead of 97 parts by weight of polyethylene terephthalate used in Example 1, polyethylene terephthalate 97 containing 0.6% by weight of agglomeration type silica having an average particle diameter of 1.5 μm was used.
A polyester film and a laminated steel sheet were obtained in the same manner as in Example 1 except that parts by weight were used. Table 1 shows these characteristics. The polyester film and the laminated steel sheet obtained in this example had good slipperiness between the film and metal at a high temperature, scratch resistance was at a practical level, and there was no elution of oligomers, and high quality was obtained. . Further, when a three-piece can was made and filled with coffee in the same manner as in Example 1, the product value was high as in Example 1.

Example 6 Instead of 97 parts by weight of polyethylene terephthalate used in Example 1, polyethylene terephthalate containing 0.3% by weight of aggregated silica having an average particle diameter of 1.5 μm and 1.0% by weight of low density polyethylene A polyester film and a laminated steel sheet were obtained in the same manner as in Example 1 except that 97 parts by weight were used. Table 1 shows these characteristics.
The polyester film and the laminated steel sheet obtained in this example had good sliding properties between the film and the metal at a high temperature, excellent scratch resistance, no elution of oligomers, and were of high quality. When a three-piece can was made and filled with coffee in the same manner as in Example 1,
As in Example 1, the product value was high.

Comparative Example 3 0.1% by weight of aggregated silica having an average particle size of 1.5 μm
Instead of using 0.1% by weight of the crosslinked polystyrene particles used in Example 4 in the same manner as in Comparative Example 2,
A polyester film and a laminated steel sheet were obtained. Table 1 shows these characteristics. The polyester film and the laminated steel sheet obtained in this comparative example were of low quality as in comparative example 2. Further, when a three-piece can was made and filled with coffee, the commercial value was low as in Comparative Example 2.

Example 7 Instead of 97 parts by weight of polyethylene terephthalate used in Example 1, 0.25% by weight of agglomeration type silica having an average particle diameter of 2.4 μm and an average particle diameter of 2.25% crosslinked with divinylbenzene. It contains 1.0% by weight of particles of butyl acrylate / methyl methacrylate / styrene having a particle size distribution of approximately 0 μm and having a substantially monodispersed particle size. A polyester film and a laminated steel sheet were obtained in the same manner as in Example 1, except that 97 parts by weight of polyethylene terephthalate having a monomer content of 0.4% by weight was used. Table 1 shows these characteristics. The polyester film and the laminated steel sheet obtained in this example were of high quality as in Example 1. Further, when a three-piece can was made and filled with coffee, the product was of high commercial value as in Example 1.

Examples 8 and 9 Instead of 1.0% by weight of particles of butyl acrylate / methyl methacrylate / styrene crosslinked with divinylbenzene, a spherical, almost monodisperse particle size distribution with an average particle size of 2.0 μm each. 1.0% by weight of spherical silica having
A polyester film and a laminated steel sheet were obtained in the same manner as in Example 7 except that 1.5% by weight of Nylon 6 and nylon 6 were used. Table 1 shows these characteristics. The polyester film, laminated steel plate and metal can obtained in this example were of high quality as in Example 7.

[0052]

[Table 1]

[0053]

The polyester film of the present invention has excellent slipperiness between the film and metal at a high temperature. Therefore, when a three-piece can is made using the film, the film surface resistance in the manufacturing process is reduced. It has good scratch resistance and can be made at high speed. Further, by setting the ethylene terephthalate trimer content of the film to 0.7% by weight or less, the elution of the oligomer from the film is suppressed even when a heat treatment (such as a retort treatment) is performed after filling the foodstuff. Therefore, there is no change in taste or smell of the foodstuff due to the transfer of the oligomer to the foodstuff, and no deterioration in the surface appearance due to the precipitation of the oligomer on the film surface. Thus, the polyester film for lamination of the present invention is particularly suitably used for producing a three-piece can suitable for filling beverages and foodstuffs.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08K 3/00 C08K 3/00 5/00 5/00 C08L 67/02 C08L 67/02 // B29K 67:00 105: 16 B29L 7:00 (72) Inventor Tsutomu Isaka 2-8-8 Dojimahama, Kita-ku, Osaka Toyobo Co., Ltd.

Claims (2)

[Claims] 1. A polyester film for laminating three-piece cans, wherein the coefficient of dynamic friction between the film and the metal at 80 ° C. is 0.45 or less. 2. The polyester film according to claim 1, wherein the content of the ethylene terephthalate cyclic trimer in the polyester film is 0.7% by weight or less.