JP2882985B2 - 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 and covering metal can lids, and more particularly to a transparent film for laminating and covering metal can lids which does not cause white spots or white powder spots during retorting of metal cans.

[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-point polyester adhesive layer and used as a can-making material (JP-A-56-1045).
No. 1, JP-A-1-192546). (B) Amorphous or extremely low-crystalline aromatic polyester film is laminated on a metal plate and used as a can-forming material (Japanese Patent Laid-Open Nos. 1-192545 and 2-57).
339). (C) A biaxially oriented polyethylene terephthalate film having a low orientation and thermally fixed is laminated on a metal plate and used as a can-making material (Japanese Patent Application Laid-Open No. 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. . Further, at the time of this sterilization treatment, oligomers containing a trimer as a main component are precipitated from the film and adhere as white powder spots. These phenomena are called retort brushing or milky change, but they are very disliked because they impair the aesthetics of the product. It is rare.

[0005]

Means for Solving the Problems The present inventors have made intensive studies to develop a polyester film bonded and covered with a metal can lid which does not cause such retort brushing or milky change, and as a result, have reached the present invention. .

That is, the present invention provides a transparent film comprising 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 crystallization temperature of the polyester composition is 65 to 130 ° C., 130 ° C. in half-crystallization time is less than 100 seconds, the second order transition point of 40 ° C. or higher, and melting point of 260 ° C. or less, and 3 in the film Oligomers
It is a transparent film with a metal can lid laminated and coated, wherein the amount of the mer is 1.0% by weight or less .

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 I) is a copolymer, the proportion of the copolymer components depends on the kind thereof, but as a result, the crystallization temperature, the half-crystallization time, the second transition point and the melting point described later are satisfied. Is preferred. The mixing ratio of the polyester (I) and the polyester (II) is not particularly limited as long as it satisfies a crystallization temperature, a half-crystallization time, a second transition point and a melting point, which will be described later. It is preferable to mix the polyester (I) at a ratio of 80 to 30% by weight and the polyester (II) at a ratio of 20 to 70% by weight from the viewpoints of properties and impact resistance. In particular, it is preferable to mix the polyester (I) at a ratio of 70 to 40% by weight and the polyester (II) at a ratio of 30 to 60% 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 (or 1,4-butylene 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 method of dimethyl terephthalate, ethylene A method in which a glycol (or 1,4-butylene glycol) and a copolymer component are subjected to a transesterification reaction, and then the resulting reaction product is polycondensed to obtain a copolymerized polyester is preferably used.

It is preferable that the thus obtained melt-polymerized polyester is further subjected to solid-phase polymerization to obtain a polyester having a higher degree of polymerization, from the viewpoint of preventing white spots due to oligomers.

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, barium sulfate and the like, and examples of the organic lubricant include crosslinked silicone particles and crosslinked polystyrene 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. However, if the added amount of titanium dioxide, calcium carbonate, barium sulfate, etc. is too large, the film as a whole becomes white, so it is necessary to set the added amount to several percent or less.

In the production of polyester, for example, sodium montanate, T
It is also preferable to add a crystallization nucleating agent such as ALC (talc) or barium stearate.

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

The transparent film covered with a metal can lid of the present invention comprises a polyester composition containing the polyester (I) and the polyester (II), and has a crystallization temperature of 65 to 130 ° C. The half-crystallization time at 130 ° C. must be 100 seconds or less, preferably 60 seconds or less, the secondary transition point must be 40 ° C. or more, preferably 45 ° C. or more, and the melting point must be 260 ° C. or less. .

When the crystallization temperature is lower than 65 ° C., film formation,
In particular, it is difficult to successively stretch biaxially and it is easy to break. On the other hand, when the crystallization temperature exceeds 130 ° C., the crystallization speed of the film fused to the metal plate is extremely low, and the film is easily embrittled in an unstretched state.

If the half-crystallization time exceeds 100 seconds, a difference in crystallization occurs due to adhesion spots of water droplets during the retort sterilization treatment, and white spots occur in the film fused to the metal plate. If the half-crystallization time is 100 seconds or less, the crystallization speed of the polymer during the retort sterilization treatment is high, and a large number of fine crystals are generated in the film. As a result, vitiligo (retort brushing phenomenon) is significantly improved. Is done.

When the second order transition point is lower than 40 ° 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 when the film is fused and laminated on a metal plate is lowered. The melting point is preferably 230 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.

Here, the melting point of the polyester composition is D
u Pont Instruments 910 DS
The temperature is measured at a rate of 20 ° C./min using C, and the melting peak is determined. The crystallization temperature, secondary transition point and endothermic peak or inflection point were raised at a rate of 20 ° C./min, kept at 290 ° C. for 3 minutes, quenched, and then cooled again.
It is measured by raising the temperature at a rate of 0 ° C./min to determine a transition point, a crystallization peak, and an endothermic heak or inflection point. still,
The sample amount is about 15 mg.

The film made of the polyester composition has a trimer oligomer content of 1.0 % or less.
wt% or less, and preferably 0.8 wt% or less . The content of this oligomer is 1.0 wt.
%, The oligomer precipitates on the film surface due to heating during retort treatment or the like, causing white powder spots or contaminating the retort treatment cooling water. The oligomer content is 1.0 wt% or less. Thus, white powder spots and cooling water contamination do not occur.

Here, the content of the oligomer is measured by dissolving the film in a solvent composed of a mixture of hexafluoroisopropanol and chloroform, and then analyzing by GPC.

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.

[0025]

F = {(n _x + n _y ) / 2] −n _{z In the} above equation, f: plane orientation coefficient, n _x , n _y , n _z :
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 solution uses methylene iodide, and the measurement temperature is 25 ° C.

The transparent film of the present invention has a thickness of 6 to 20.
μm is preferred.

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 bonded, then quenched, and at least the surface layer (thin film) of the film in contact with the metal plate is melted and amorphized to be fused. preferable.

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

[0031]

The present invention will be further described below with reference to examples.

Example 1 Polyethylene terephthalate containing spherical silica having an average particle size of 1.5 μm, having an intrinsic viscosity of 0.8 and an oligomer amount of 1.0 wt%, and having an intrinsic viscosity of 1.1 and an oligomer amount of Was mixed with polybutylene terephthalate in a weight ratio of 50:50 to prepare a polyester composition.

This polyester composition is melt-extruded at 290 ° C. and solidified by quenching to obtain an unstretched film. The unstretched film is stretched in the machine direction at a stretching temperature of 72 ° C. and a draw ratio of 3.6 times. The film was stretched in the transverse direction at a stretching temperature of 85 ° C. and a stretching ratio of 3.6, and then heat-set at 190 ° C. to obtain a biaxially oriented film having a thickness of 12 μm. The plane orientation coefficient of this film is 0.156, and the secondary transition point (Tg) is 4
8 ° C., crystallization temperature (Tcc) 86 ° C., and melting point (T
m) is 252 ° C. and the half-crystallization time at 30 ° C. is 5
There was a second.

The obtained biaxially oriented film was bonded to tin-free steel (250 μm in thickness) heated at 200 ° C., and after cooling, the retort treatment was evaluated. As a result, as shown in Table 1, no white spots or white powder spots were found, and the quality of the film for the outer surface of the lid of a three-piece can was sufficiently satisfied.

Examples 2 to 10 and Comparative Examples 1 to 8 Instead of the polyester composition of Example 1, a polyester composition having the composition shown in Table 1 was used, and biaxial stretching was performed under the conditions shown in Table 1. A biaxially oriented film having the properties shown in Table 1 was obtained.

[0036]

[Table 1]

The white spots and white powder spots in the retort treatment in the table were evaluated by the following methods.

[0038] The film-laminated metal plate at 130 ° C was 3
A 0 minute retort treatment is performed, and changes in the appearance of white spots and white powder spots are observed.

Vitiligo: な し: no change in appearance…: slight haze in appearance ×: occurrence of white spot (brushing) ×: occurrence of roughness on the surface in addition to white spots White powder: ◎: no change in appearance ○: There is a slight cloudiness after the fingerprint. ×… White spots are observed after the fingerprint. ××… White spots occur on the entire surface.

Further, the intrinsic viscosity (IV) in the table indicates that the solvent is O
The measurement was performed at 35 ° C. using chlorophenol.

The half-crystallization time was measured by a depolarization method using a polymer crystallization rate measuring apparatus MK-701 manufactured by Kotaki Seisakusho.

From the results shown in Table 1, the film of the present invention contains:
It can be seen that white spots and white powder spots do not occur.

[0043]

EFFECTS OF THE INVENTION The transparent film coated with a metal can lid according to the present invention does not cause white spots (retort brushing) or white powder spots (oligomer precipitation) during retort sterilization, has no voids, and impairs the appearance of the product. Absent.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FIB29L 7:00 (72) Inventor Kinji Hasegawa 3-37-19 Koyama, Sagamihara-shi, Kanagawa Prefecture Teijin Limited Sagamihara Research Center (56) References JP-A-6-155660 (JP, A) JP-A-7-109363 (JP, A) JP-A-7-133358 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name ) C08J 5/00-5/02 C08J 5/12-5/22 B29C 55/00-55/30 B32B 1/00-35/00 C08L 1/00-101/00

Claims (3)

(57) [Claims] 1. A transparent film comprising 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. Crystallization temperature 65-130
° C., 130 ° C. in half-crystallization time is less than 100 seconds, the second order transition point of 40 ° C. or higher and a melting point of 260 ° C. or less der
And the amount of trimer oligomer in the film is 1.0 weight
% . 2. The metal can lid outer surface is bonded and covered.
The transparent film laminated with a metal can lid according to the above. 3. A 3-mer oligomer content in the off Irumu is 0.
2. The transparent film according to claim 1 , wherein the content is 8% by weight or less.