JPH0819246B2 - Polyester film for container molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a polyester film for molding a container, more specifically, it is excellent in deep-drawing moldability, bending property, etc.
Alternatively, the present invention relates to a container-forming polyester film useful for forming a container after being laminated with a metal plate.

<Prior Art and its Problems> It has been known in the past to manufacture a container by subjecting a plastic film to deep drawing. As the film, a polyolefin film, a polystyrene film, a polyvinyl chloride film, an unstretched polyethylene terephthalate film, etc. are usually used. However, the biggest drawback of polyolefins, polystyrene, and polyvinyl chloride is the lack of heat resistance, and many of them
Cannot be used above 100 ° C. Further, the unstretched polyethylene terephthalate film has the drawbacks that the crystallization phenomenon occurs at 100 ° C. or higher, the transparency is lost, and the film becomes brittle. Furthermore, many of the plastic materials that have hitherto been used have problems with gas barrier properties.

Also, metal containers are generally coated to prevent corrosion on the inside and outside, but recently, process simplification, hygiene improvement,
For the purpose of preventing pollution, the development of a method for obtaining rust-preventing property without using an organic solvent has been advanced, and as one of them, coating with a thermoplastic resin film has been attempted. That is, a method of making a can by laminating a thermoplastic resin film on a metal plate such as tin plate, tin-free steel, aluminum or the like and then making a can is under way. Polyolefin film and polyamide film have been tried as this thermoplastic resin film, but they have the molding processability, heat resistance,
Not all of the fragrance-retaining properties are satisfied.

On the other hand, a polyester film, especially a polyethylene terephthalate film, has been noted as having balanced properties, and several proposals based on this have been made. That is, (A) biaxially oriented polyethylene terephthalate film is laminated on a metal plate through an adhesive layer of low melting point polyester and used as a can-making material (JP-A-56-10451, JP-A-1-192546).

(B) An 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).

(C) A biaxially oriented polyethylene terephthalate film having low orientation and heat set is laminated on a metal plate and used as a material for can production (JP-A-64-22530).

However, none of these proposals has sufficient characteristics, and each has the following problems.

Regarding (A), the biaxially oriented polyethylene terephthalate film is excellent in heat resistance and aroma retaining property, but the moldability is insufficient, and the film is whitened (generation of microcracks) and ruptured in the can manufacturing process accompanied by large deformation. Occurs.

Regarding (B), since it is an amorphous or extremely low crystalline aromatic polyester film, the moldability is good, but the aroma retention is poor, and after printing after can making, after retort sterilization, etc. There is a possibility that the film is apt to become brittle by the treatment, and the film is likely to be fragile due to the impact from the outside of the can.

Regarding (C), the effect is not exhibited in the intermediate region between (A) and (B), but since the film surface isotropy is not guaranteed, deformation in all directions, such as in can manufacturing, is not possible. In some cases, the molding processability may be insufficient in a specific direction of the film.

<Means for Solving the Problem> The present inventors have arrived at the present invention as a result of extensive studies to solve the problem.

That is, the present invention has a melting point of 220 to 245 ℃ consisting of isophthalic acid copolymer polyethylene terephthalate, the surface orientation coefficient of 0.10 to 0.16, the thermal shrinkage at 150 ℃ is 10% or less, the density is less than 1.385 g / cm ^3. Is a polyester film for container molding.

The isophthalic acid copolymerized polyethylene terephthalate in the present invention has a polymer melting point of 220 to 245 ° C., preferably
It is a copolymerized polyethylene terephthalate in which an isophthalic acid component is copolymerized in a ratio of 220 to 240 ° C. If the melting point is less than 220 ° C, crazing (cracking) occurs during molding of the container, which is not preferable. In addition, printing is often performed on the container, and it is necessary to have a melting point of 220 ° C. or higher in order to withstand the heat during printing. On the other hand, if the melting point is higher than 245 ° C., the moldability into a container is not sufficient even if the film characteristics described later, for example, the surface orientation coefficient, the heat shrinkage ratio, etc. are within a predetermined range, which is not preferable. Here, the melting point of the polyester is measured by using a DSC-SSC / 580 manufactured by Seiko Denshi KK and determining a melting peak at a temperature rising rate of 10 ° C./min.

The isophthalic acid-copolymerized polyethylene terephthalate in the present invention contains a lubricant having an average particle size of 2.5 μm or less. This lubricant may be inorganic or organic, but is preferably inorganic. Examples of the inorganic lubricant include silica, alumina, titanium dioxide, calcium carbonate, barium sulfate, and the like, and examples of the organic lubricant include silicone particles. All require that the average particle size is 2.5 μm or less. If the average particle size of the lubricant exceeds 2.5 μm, the lubricant in the deep-drawn portion serves as the starting point, causing pinholes or even breaking, which is not preferable.

The amount of the lubricant in the isophthalic acid-copolymerized polyethylene terephthalate may be determined by the winding property in the film manufacturing process. Generally, it is preferable to add a small amount of particles having a large particle size and a large amount of particles having a small particle size. For example, average particle size 2.
It is preferable to add 0.05 wt% in the case of silica of 3 μm and about 1 wt% in the case of titanium dioxide having an average particle size of 0.3 μm.
Further, the film can be made opaque by intentionally adjusting the content of the lubricant. For example, titanium dioxide
A white film can be obtained by adding 10 to 15% by weight.

The isophthalic acid-copolymerized polyethylene terephthalate in the present invention may also contain other additives such as an antioxidant, a heat stabilizer, an ultraviolet absorber, a plasticizer, a pigment, an antistatic agent, if necessary, in a dispersed manner. it can.

The isophthalic acid-copolymerized polyethylene terephthalate in the present invention is not limited by its production method. For example, a method of subjecting terephthalic acid, ethylene glycol and isophthalic acid to an esterification reaction, and then subjecting the resulting reaction product to a polycondensation reaction to obtain isophthalic acid-copolymerized polyethylene terephthalate, transesterification of dimethyl terephthalate, ethylene glycol and dimethyl isophthalate. A method of reacting and then subjecting the obtained reaction product to a polycondensation reaction to obtain isophthalic acid-copolymerized polyethylene terephthalate is preferably used. Alternatively, a method in which polyethylene isophthalate is blended with polyethylene terephthalate, melted, and then copolymerized by a partition reaction may be employed.

The polyester film of the present invention is obtained by melting the above isophthalic acid-copolymerized polyethylene terephthalate, discharging it from a die to form a film, biaxially stretching and heat setting. The plane orientation coefficient of this film must be 0.10 or more and 0.16 or less, preferably more than 0.11 and 0.15 or less. If the film surface orientation coefficient is less than 0.10, problems such as cracking may occur when the deep drawing ratio in deep drawing becomes high, which is not preferable. On the other hand, if the surface orientation coefficient exceeds 0.16, fracture occurs during deep drawing, making deep drawing itself impossible.

Here, the plane orientation coefficient is defined by the following formula.

f = [(nx + ny) / 2] -nz In the above formula, f: plane orientation coefficient, nx, ny, nz: 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 polyester film of the present invention further has a heat shrinkage at 150 ° C. of 10% or less, preferably 7% or less, particularly preferably 6% or less, and a density of less than 1.385 g / cm ³ , preferably 1.380 to It needs to be 1.384 g / cm ³ .

Here, the heat shrinkage is 2% for the sample film at room temperature.
Mark the points (intervals of about 10 cm), keep them in a hot air circulation type oven at 150 ° C for 30 minutes, then return to room temperature and measure the intervals of the above-mentioned marks. Is calculated and calculated from this difference and the gauge interval before the temperature is kept at 150 ° C. The heat shrinkage rate in the longitudinal direction of the film is used as a representative. The density is measured with a density gradient tube.

When the heat shrinkage rate (150 ° C.) of the polyester film exceeds 10%, dimensional shrinkage is large when the container is subjected to printing after deep drawing and the container is distorted, which is not preferable. This heat shrinkage rate is 10% or less, further 7% or less, especially 6
When it is at most%, there is no or little distortion of the shape of the container during printing, and good results are obtained. Also the film density
If it exceeds 1.385 g / cm ³ , the deep drawability is poor and the film may crack, tear or break, which is not preferable.

To obtain a polyester film satisfying the above-mentioned plane orientation coefficient, heat shrinkage (150 ° C.) and density, for example, in sequential biaxial stretching, the longitudinal stretching ratio is from 2.5 to 4.0 times, and the transverse stretching ratio is from 2.7 to From 4.0 times the range,
150-220 ℃, preferably selected from the range of 180-200 ℃,
It is better to combine these.

The object of the present invention can be achieved only when all of the above-mentioned five conditions of polymer composition, melting point, plane orientation coefficient, thermal shrinkage (150 ° C.) and density are satisfied. For example, with polyethylene terephthalate homopolymer, sufficient deep drawability cannot be obtained even if the conditions of plane orientation coefficient, heat shrinkage at 150 ° C., and density are satisfied.

The container-forming polyester film of the present invention preferably has a thickness of 6 to 250 μm, more preferably 12 to 175 μm.

The polyester film for forming a container of the present invention is effective not only for forming a film alone, but also for forming a container by deep-drawing after laminating it with a metal plate such as an aluminum plate or a steel plate.

<Example> Hereinafter, the present invention will be further described with reference to Examples.

Example 1 and Comparative Examples 1 and 2 12 mol% isophthalic acid copolymerized polyethylene terephthalate (melting point 229 ° C., intrinsic viscosity 0.60) containing 0.07% by weight of silica having an average particle size of 2.0 μm was melt-extruded at 270 ° C. and rapidly cooled. It solidified and the unstretched film was obtained. Next, this unstretched film was longitudinally stretched, laterally stretched and then heat set under the conditions shown in Table 1 to obtain a biaxially oriented film having a thickness of 125 μm.

 Table 4 shows the characteristics of this film.

Comparative Examples 3 to 6 0.05% by weight of silica having an average particle diameter of 2.3 μm was added and contained,
The copolymerized polyethylene terephthalate (intrinsic viscosity 0.60) obtained by copolymerizing the isophthalic acid components in the proportions shown in Table 2
Melt extrusion was carried out at the temperature shown in the table and rapid solidification was carried out to obtain an unstretched film. Next, this unstretched film was longitudinally stretched, laterally stretched and then heat set under the conditions shown in Table 2 to obtain a biaxially oriented film having a thickness of 125 μm.

 Table 4 shows the characteristics of this film.

Examples 2 and 3 Isophthalic acid 12 mol% copolymerized polyethylene terephthalate (intrinsic viscosity 0.6
0) is melt-extruded at 270 ° C. and rapidly solidified to form an unstretched film, and the unstretched film is successively drawn at a longitudinal stretching temperature of 80 ° C., a longitudinal stretching ratio of 3.3 times, a transverse stretching temperature of 110 ° C. and a lateral stretching ratio of 3.5 times. It was axially stretched and then heat set at 210 ° C.

The properties of the obtained biaxially oriented film (thickness: 25 μm) are shown in Table 4.

A total of 9 types of films (each having a width of 600 mm) obtained in Examples 1 to 3 and Comparative Examples 1 to 6 were heated with an IR heater for 10 seconds to adjust the temperature of the film to 90 ° C., and then the caliber was 70 mm and the bottom was It was placed on a metal mold having a diameter of 55 mm and a depth of 120 mm, and was subjected to pressure molding at a pressure of 5 kg / mm ² . Next, the edge of the cup-shaped material was cut off, and curling processing was performed on the edge portion to mold the cup.

 In this molding, during pressure molding ◯: No cracks or breaks in the film ×: Cracks or breaks in the film In printing, ○: No distortion in the molded product ×: Molded product Table 4 shows the results of evaluation of the points at which strain occurred.

From the results shown in Table 4, it can be seen that the films of Examples 1 to 3 are excellent in deep drawing property, edging curling property and the like.

<Effects of the Invention> The polyester film of the present invention is excellent in deep drawability, bending workability, etc., and is excellent for forming a container, that is, for forming a single container or after deep-drawing a container after bonding with a metal plate. In particular, it is excellent in deep drawing workability, impact resistance and heat resistance after can making when forming a metal can by forming a metal can after laminating with a metal plate, and is useful as a metal container. is there.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location B29L 7:00 C08L 67:00 (72) Inventor Yoji Murakami 3-37-19 Koyama, Sagamihara City, Kanagawa Teijin Sagamihara Research Center Co., Ltd. (56) References JP-A-64-40400 (JP, A) JP-A-3-67629 (JP, A)

Claims (2)

[Claims] 1. An isophthalic acid copolymerized polyethylene terephthalate having a melting point of 220 to 245 ° C. and having a plane orientation coefficient of 0.10.
~ 0.16, thermal shrinkage at 150 ℃ less than 10%, density 1.385g /
A polyester film for forming a container, characterized by having a size of less than cm ³ . 2. The polyester film for forming a container according to claim 1, which is formed into a container after being bonded to a metal plate.