JP3020731B2 - Metal can lid lamination coated transparent film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent film for laminating a metal can lid, and more particularly to a transparent film for laminating a metal can lid which does not cause white spots during retorting of the metal can.

[0002]

2. Description of the Related Art Metal cans for various drinks such as coffee and tea and foods are usually subjected to a retort sterilization treatment, and a negative pressure is applied to the can during this treatment. Since this negative pressure can cause can deformation, the metal can is made of thicker tin-free steel or the like. Such a metal can is usually formed as a three-piece can composed of a can body and a canopy, or a two-piece can composed of a can body and a lid, in terms of ease of production.

On the other hand, in order to prevent corrosion of metal cans, it has been attempted to bond and coat a thermoplastic resin film on the can surface instead of the conventional coating, and polyester films, especially polyethylene terephthalate films, have a good balance. Attention has been paid to its excellent properties, and several proposals based on this have been made. That is, (A) a biaxially oriented polyethylene terephthalate film is laminated on a metal plate via a low-melting polyester adhesive layer and used as a can-making material (JP-A-56-1045).
No. 1, JP-A-1-192546). (B) An amorphous or extremely low-crystalline aromatic polyester film is laminated on a metal plate and used as a material for can production (JP-A-1-92545, JP-A-2-573).
No. 39). (C) A biaxially oriented polyethylene terephthalate film having low orientation and heat set is laminated on a metal plate and used as a can-making material (JP-A-64-22530).

[0004]

However, in the canopy of a three-piece can in which such a conventional polyester film is fusion-bonded and laminated, a retort sterilization treatment (usually 120 parts) is performed.
At the time of steam treatment at ~ 130 ° C), water droplets adhere to the bottom of the can, and the film or its surface layer which has melted and became amorphous during lamination is crystallized at the portion where the water droplets adhere, thereby producing white spots. . This phenomenon is called retort brushing, but is very disliked because it impairs the beauty of the product.
There is a strong demand for the development of a film that does not cause such a phenomenon, especially a film that covers the outside of the canopy.

[0005]

Means for Solving the Problems The present inventors have made intensive studies to develop a polyester film coated with a metal can lid that does not cause retort brushing, and as a result, have reached the present invention.

That is, the present invention comprises a polyester composition comprising a polyester (I) having ethylene terephthalate as a main repeating unit and a polyester (II) having butylene terephthalate as a main repeating unit. The formation temperature is 65-120
C., a second transition point of 45 ° C. or higher and a melting point of 260 ° C. or lower.

In the present invention, the polyester (I) is a polyester having ethylene terephthalate as a main repeating unit, and may be a homopolymer or a copolymer.
In the case of a copolymer, the copolymer component may be an acid component or an alcohol component. As the copolymeric acid component, isophthalic acid, phthalic acid, aromatic dicarboxylic acids such as naphthalenedicarboxylic acid, adipic acid, azelaic acid, sebacic acid, aliphatic dicarboxylic acids such as decanedicarboxylic acid,
Alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid can be exemplified. Of these, aliphatic dicarboxylic acids are preferred. Examples of the copolymerized alcohol component include aliphatic diols such as butanediol and hexanediol, and alicyclic diols such as cyclohexanedimethanol. These may be used alone or in combination of two or more, but are preferably crystalline polyesters.

In the present invention, the polyester (II)
Is a polyester having butylene terephthalate as a main repeating unit, and may be a homopolymer or a copolymer. The copolymer component in the copolymer may be an acid component or an alcohol component. As the copolymeric acid component, isophthalic acid, phthalic acid, aromatic dicarboxylic acids such as naphthalenedicarboxylic acid, adipic acid, azelaic acid, sebacic acid, aliphatic dicarboxylic acids such as decanedicarboxylic acid,
Examples of alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid and the like, and examples of the copolymerized alcohol component include aliphatic diols such as ethylene glycol and hexanediol, and alicyclic diols such as cyclohexanedimethanol. These can be used alone or in combination of two or more.

The polyester (I) and the polyester (I
When the component (I) is a copolymer, the proportion of the copolymer component depends on the kind thereof, but as a result, it is preferable to satisfy the crystallization temperature, the secondary transition point, and the melting point described below. In addition, polyester (I) and polyester (II)
Is not particularly limited as long as it satisfies a crystallization temperature, a second transition point and a melting point, which will be described later. In terms of workability, heat resistance, impact resistance and the like, polyester (I) 8
0-30% by weight, polyester (II) 20-70% by weight
It is preferred to mix at the ratio of Particularly, 70 to 40% by weight of polyester (I) and 30 to 6% of polyester (II)
It is preferable to mix at 0% by weight.

The polyester (I) and the polyester (II) in the present invention are not limited by their production methods. For example, a method of subjecting terephthalic acid, ethylene glycol and a copolymer component to an esterification reaction, and then subjecting the resulting reaction product to a polycondensation reaction to form a copolymerized polyester, or a transesterification reaction of dimethyl terephthalate, ethylene glycol and a copolymer component. And then subjecting the resulting reaction product to a polycondensation reaction to form a copolymerized polyester. In the production of polyester, if necessary, other additives such as lubricants, antioxidants, heat stabilizers, ultraviolet absorbers,
An antistatic agent and the like can also be added.

[0011] The polyester composition of the present invention includes:
Usually, a lubricant of 4 μm or less is added. The lubricant may be inorganic or organic, but inorganic is preferred. Examples of the inorganic lubricant include silica, alumina, titanium dioxide, calcium carbonate, and barium sulfate, and examples of the organic lubricant include silicone particles. If the average particle size of the lubricant is too large, coarse particles (eg, particles having a size of 10 μm or more) serve as starting points, and pinholes are formed, or in some cases, they are broken during film formation, which is not preferable. In particular, spherical silica having an average particle size of 1.5 μm or less is preferable.

[0012] The metal can lid laminating coating film of the present invention comprises:
A polyester composition comprising the above polyester (I) and polyester (II), and the crystallization temperature of the polyester composition is 65 to 120 ° C., preferably 8 to 120 ° C.
0 ° C to 110 ° C, a secondary transition point of 45 ° C or higher, and a melting point of 26 ° C.
It is necessary that the temperature be 0 ° C. or less.

When the crystallization temperature is lower than 65 ° C., film formation,
In particular, biaxial stretching is difficult, and it is easy to break. On the other hand, if the crystallization temperature exceeds 120 ° C., the crystallization speed of the polymer during the retort sterilization treatment is slow, and the crystals grow slowly and become large, so that white spots occur on the film and the retort brushing deteriorates. By using a film made of the polyester composition having a crystallization temperature in the range of 65 to 120 ° C., the crystallization rate of the polymer during the retort sterilization treatment is high, and a large number of fine crystals are generated in the film. (Retort brushing phenomenon) is greatly improved, and film formation is easy.

When the secondary transition point is lower than 45 ° C.,
Moisture easily permeates the film, which may cause rust on the metal plate. Furthermore, stickiness occurs at the time of film formation, and handleability deteriorates. The appropriate second transition point is usually 45 to 70 ° C.

With respect to the melting point, if it exceeds 260 ° C., it is unsuitable because the adhesiveness at the time of fusing and laminating the film on the metal plate is lowered. The melting point is preferably from 240 to 260 ° C. from the viewpoint of easy adhesion treatment to the metal plate.
Further, the polyester composition has an endothermic peak or an inflection point in the range of 205 to 220 ° C depending on the polyester (II) component.

The melting point of the polyester composition is Du
The measurement is performed by raising the temperature at a rate of 20 ° C./min using a Pont Instruments 910 DSC and determining the melting peak. Further, the crystallization temperature, the secondary transition point, and the endothermic peak or inflection point were raised at a rate of 20 ° C./min,
After holding for 1 minute, the temperature is measured by quenching, raising the temperature again at a rate of 20 ° C./min, and determining the transition point, crystallization peak, endothermic peak or inflection point. The sample amount is about 15mg
And

The degree of polymerization of the polyester composition is preferably relatively low as long as it has a film-forming property, since the crystallization rate is high.

The polyester composition is discharged from a melt extrusion die in a conventional manner to form a film, and then biaxially stretched and heat-set to form a biaxially oriented film. The ratio of the biaxial orientation is preferably in a range where the plane orientation coefficient is 0.1 or more. The area stretch ratio is preferably 9 times or more. The biaxially oriented film is preferably a balanced type.

Here, the plane orientation coefficient is defined by the following equation. f = [(nx + ny) / 2] -nz In the above equation, f: plane orientation coefficient, nx, nY, nz:
These are the refractive index in the horizontal, vertical and thickness directions of the film, respectively.

The refractive index is measured as follows. A polarizing plate analyzer is attached to the eyepiece side of the Abbe refractometer, and each refractive index is measured with a monochromatic NaD line. The mounting liquid used was methylene iodide, and the measurement temperature was 2
5 ° C.

The transparent film of the present invention has a thickness of 12 to 3
It is preferably 0 μm.

The transparent film covered with the metal can lid is formed by laminating the biaxially oriented film on a metal plate to form a lid. For example, it is possible to use a method in which a metal plate is heated, a film is pasted, rapidly cooled, and at least a surface layer (thin film portion) of the film in contact with the metal plate is melt-amorphized and fused. preferable.

The transparent film of the present invention is laminated and covered on the top cover of a three-piece can or the lid of a two-piece can, and is particularly preferably laminated and covered on the outer surface of the lid.

[0024]

The present invention will be described in more detail with reference to the following examples.

[0025]

Examples 1 to 8 and Comparative Examples 1 to 4 Polyethylene terephthalate (PET) containing spherical silica having an average particle size of 1.5 μm and polybutylene terephthalate (PBT) were blended in the proportions shown in Table 1. Preparing a polyester composition, melt extruding the polyester composition at 280 ° C.,
It was quenched and solidified to obtain an unstretched film. Next, the unstretched film was stretched longitudinally and transversely under the conditions shown in Table 2, and then heat-set to obtain a biaxially oriented film having a thickness of 12 μm.
Table 3 shows the properties of this film.

The obtained biaxially oriented film was bonded to tin-free steel (250 μm in thickness) heated at 200 ° C., cooled with water, and then a lid was formed. The retort brushing was evaluated. The results were as shown in Table 3.

The retort brushing was evaluated by the following method. 3 at 130 ° C for film laminated metal plate
Perform a 0 minute retort treatment and observe the change in appearance.

◎ ・ ・ ・ ・ ・ ・ No change in appearance ○ ・ ・ ・ ・ There is a slight haze in appearance × ・ ・ ・ ・ Generation of white spots (brushing) ×× ・ ・ ・ Generation of roughness in addition to white spots

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

The intrinsic viscosity IV in the table was measured at 35 ° C. using O-chlorophenol as a solvent.

From the results in Table 3, the film of the present invention contains:
It can be seen that retort brushing does not occur.

[0034]

According to the transparent film of the present invention, there is no occurrence of white spots (retort brushing) at the time of retort sterilization, no voids, and the appearance of the product is not impaired.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoji Murakami 3-37-19 Koyama, Sagamihara City, Kanagawa Prefecture Inside the Sagamihara Research Center, Teijin Limited (72) Inventor Masayoshi Ono 2-1-1 Uchisaiwaicho, Chiyoda-ku, Tokyo In Teijin Limited (56) References JP-A-1-121335 (JP, A) JP-A-4-63836 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08J 5 / 00-5/24 B29B 11/16 B29B 15/08-15/14

Claims (3)

(57) [Claims] 1. A polyester composition comprising a polyester (I) having ethylene terephthalate as a main repeating unit and a polyester (II) having butylene terephthalate as a main repeating unit, and having a crystallization temperature of 65. ~ 120 ° C, secondary transition point is 40
A transparent film laminated and covered with a metal can lid, which has a melting point of 260 ° C. or higher and a melting point of 260 ° C. or lower. 2. The transparent film according to claim 1, wherein the outer surface of the metal can lid is laminated. 3. A polyester composition comprising a polyester (I) having ethylene terephthalate as a main repeating unit and a polyester (II) having butylene terephthalate as a main repeating unit, and having a crystallization temperature of 65. ~ 120 ° C, secondary transition point is 40
A transparent film for laminating and covering a metal can lid, wherein the transparent film has a melting point of not less than 260 ° C and a surface orientation coefficient of the film of not less than 0.1.