JP2000141476A - Biaxially oriented white polyester film for laminating outer surface of metal can - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a white copolyester film for the lamination processing of the outer surface of a metal can excellent in white light shading properties and molding processability. SOLUTION: A biaxially oriented film comprises copolyester with an m.p. of 210-245 deg.C containing 1×108/mm3 more particles with an average particle size of 0.1-1.5 μm of white pigment and is obtained by stretching a non-stretched film by 2.7-3.6 times in its longitudinal direction and by 2.8-3.7 times in its lateral direction by a sequential biaxial stretching method and thermally fixing the stretched film at 150-205 deg.C and the degree of crystal orientation in the thickness direction of this biaxially oriented film is 0.25-0.55.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially oriented white polyester film for laminating the outer surface of a metal can, and more particularly to a biaxially oriented white copolyester useful for forming into a container after laminating on a metal plate. About film.

[0002]

2. Description of the Related Art Metal cans are generally coated to prevent corrosion of the inner and outer surfaces. Recently, for the purpose of simplifying the process, improving hygiene, and preventing pollution, coating with a thermoplastic resin film has been attempted as a method for imparting rust prevention without using an organic solvent.

[0003] That is, studies have been made on a method of laminating a thermoplastic resin film on a metal plate such as tinplate, tin-free steel, aluminum or the like, followed by drawing and the like to make a can.

Polyolefin films and polyamide films have been tried as such thermoplastic resin films.
It does not satisfy all of moldability, heat resistance and fragrance retention.

On the other hand, polyester films, especially polyethylene terephthalate films, have attracted attention as having balanced properties, and several proposals based on them 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-56-10451, JP-A-1-192).
546). (B) Amorphous or extremely low-crystalline aromatic polyester film is laminated on a metal plate and used as a can-making material (Japanese Patent Application Laid-Open Nos. 1-192545 and 2-57339). (C) Laminating a biaxially oriented polyethylene terephthalate film with low orientation and heat set on a metal plate and using it as a can-making material
No. 22530).

[0006]

However, the present inventors' studies have revealed that no satisfactory characteristics can be obtained in any case, and that each of them has the following problems. Regarding (A), the biaxially oriented polyethylene terephthalate film is excellent in heat resistance and fragrance retention, but has insufficient molding processability, and in the case of canning process involving large deformation, a minute crack is generated in the film. In such cases, breakage occurs. Regarding (B), since it is an amorphous or extremely low-crystalline aromatic polyester film, the moldability is good, but the fragrance retention is inferior, and after printing after can-making, retort sterilization, etc. There is a possibility that the film may be easily embrittled by the treatment and further stored for a long period of time, and the film may be easily broken by an impact from the outside of the can. As for (C), the effect is not exhibited in the intermediate region between the above (A) and (B), but it has not yet reached a low orientation applicable to can manufacturing.

[0007] In general, printing is performed on the outer surface of the metal container. When printing, a white paint is preliminarily applied for the purpose of shading before printing. By making the thermoplastic resin film to be laminated on the metal plate a white light-shielding film, the undercoating of the white paint can be omitted. However, in the above methods (A), (B) and (C), the white pigment is used. In the case of a white film produced by adding, the respective disadvantages cannot be solved and the purpose of the outer surface of the can cannot be achieved.

[0008] It is an object of the present invention to provide a white copolymer polyester film having excellent white light shielding properties and excellent moldability for metal can outer surface laminating.

[0009]

The present invention has the following arrangement to attain the object. Average particle size 0.1
White pigment in the range of ~ 1.5 µm as particles
Contains at least 10 × ⁸ particles / mm ³ and has a melting point of 210-245 ° C.
Wherein the unstretched film is stretched 2.7 to 3.6 times in the longitudinal direction by a sequential biaxial stretching method, After stretching 2.8 to 3.7 times in the direction, 150 to 20
A biaxially oriented biaxially oriented metal can, characterized in that the biaxially oriented film has been heat-set at 5 ° C. and the degree of crystal orientation in the thickness direction of the biaxially oriented film is in the range of 0.25 to 0.55. Oriented white polyester film.

A typical example of the copolymerized polyester in the present invention is copolymerized polyethylene terephthalate. The copolymer component may be an acid component or an alcohol component. Examples of the acid component include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decane dicarboxylic acid, and alicyclic groups such as cyclohexanedicarboxylic acid. Examples of the dicarboxylic acid include aliphatic alcohols such as butanediol and hexanediol, and alicyclic diols such as cyclohexanedimethanol. These can be used alone or in combination of two or more.

The proportion of the copolymer component depends on the type thereof, but as a result the polymer melting point is in the range of 210 to 245 ° C., preferably 215 to 235 ° C. When the melting point of the polymer is less than 210 ° C., the heat resistance is inferior, so that it cannot withstand the heating in printing after can production. On the other hand, when the polymer melting point is 2
If the temperature exceeds 45 ° C., the crystallinity of the polymer is too large and the moldability is impaired.

Here, the melting point of the copolyester was measured by Du Pont Instruments 910.
A method in which a melting peak is determined at a heating rate of 20 ° C./min using DSC. The sample amount is about 20 mg.

The copolyester of the present invention contains a white pigment having an average particle diameter in the range of 0.1 to 1.5 μm in an amount of 1 × 10 ⁸ particles / mm ³ or more in terms of the number of particles.

The white pigment may be inorganic or organic, but inorganic is preferred. Preferred examples of the inorganic pigment include alumina, titanium dioxide, calcium carbonate, barium sulfate and the like. In order to improve the white light-shielding property of the film, a pigment having a refractive index of 1.5 or more is preferable, and the average particle diameter of the pigment needs to be 0.1 μm or more. In addition, all white pigments need to have an average particle size of 1.5 μm or less. 1.5μ average particle size of white pigment
If it exceeds m, coarse particles (for example, particles of 10 μm or more) of a portion deformed by processing such as a deep drawing can become a starting point, and pinholes are formed or broken in some cases, which is not preferable.

Here, the average particle diameter of the white pigment is determined by first evaporating a metal on the particle surface, obtaining an area circle equivalent diameter from an image enlarged, for example, 10,000 to 30,000 times by an electron microscope, It is calculated by applying these to the following equation.

Average particle size = Total area equivalent circle diameter of measurement particles / Number of measurement particles The number of white pigment particles is determined by calculating the volume concentration of the pigment contained assuming spherical particles having a diameter of the average particle size. It is the value calculated by dividing the value.

The number of particles in the polyester is 1 × 10 ⁸
Pieces / mm ³ or more. If the number of particles is less than this, the white light-shielding properties will be insufficient, and the effect of the dispersed particles on lowering the crystal orientation of the film will not be sufficiently exhibited. The white pigments may be used alone or in combination of two or more.

The copolymerized polyester in the present invention is not limited by its production method. 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 method of transesterifying dimethyl terephthalate, ethylene glycol and a copolymer component. A method of reacting and then subjecting the resulting reaction product to a polycondensation reaction to form a copolymerized polyester is preferably used. In the production of the copolymerized polyester, if necessary, other additives such as an optical brightener, an antioxidant,
Heat stabilizers, ultraviolet absorbers, antistatic agents and the like can also be added. In particular, when the whiteness is to be improved, the addition of a fluorescent whitening agent is effective.

The polyester film of the present invention is obtained by melting the above-mentioned white pigment-containing copolymerized polyester, discharging it from a die, forming it into a film, and heat-setting biaxially. The degree of crystal orientation in the thickness direction of the film is in the range of 0.25 to 0.55. If the degree of crystal orientation exceeds 0.55, the formability becomes insufficient, and the film tends to break during deep drawing. On the other hand, when the degree of crystal orientation is less than 0.25, that is, when the orientation is excessively low, the heat resistance becomes insufficient.

The degree of crystal orientation is measured as follows. Crystal face of film using X-ray diffractometer (100)
The crystal orientation index <cos ² Φ _j , 100> in three directions (longitudinal direction MD, width direction TD, and thickness direction ND) is obtained, and the degree of crystal orientation f ^{i, k} is obtained from the following equation. f ^{i, k} = 2/3 <cos ² Φ _{j, k} > −1/2 (where i = MD, TD or ND, k = 100)

Here, the degree of crystal orientation in three directions is measured using a pole sample stand manufactured by Rigaku Corporation. However, when the white pigment is titanium dioxide, the reflection peak due to the titanium dioxide particles is close to the copolymerized polyester (100) with anatase (101) and rutile (110). _{Assuming that} the (100) reflection peak of the polymerized polyester is due to the reflection intensity of titanium dioxide (I _Tio2, α _{= 0} ), the intensity at all positions of α and β up to α = 90 ° is reduced by I _Tio2, α _{= 0} . Thus, the degree of crystal orientation is calculated. Here, I _Tio2, α _{= 0} = １ ／ (I _Tio2, α
_{= 0, MD} + I _Tio2, α _{= 0, TD} ).

In the above, α is a pole sample stage, and α = 9
0 ° indicates a case where (100) is arranged parallel to the film surface, and α = 0 ° indicates a case where (100) is arranged perpendicular to the film surface. Further, β represents the direction in the MD and TD planes of the film, β = 0 being the MD, and β = 90 ° being the TD direction. The degree of crystal orientation referred to in the present invention is the thickness direction N
Expressed by the value of D.

A film satisfying such requirements can be produced by using a sequential biaxial stretching method under the following conditions.

The above-mentioned copolyester is melted, discharged from a die, formed into a film, and immediately quenched to obtain a substantially amorphous copolyester sheet. Next, the sheet is heated in a roll, an infrared ray or the like and stretched in the longitudinal direction. At this time, the stretching temperature is 20 to 40 ° C. higher than the glass transition point (Tg) of the copolymerized polyester,
The draw ratio is set to 2.7 to 3.6 times. The lateral stretching is
Starting from a temperature 20 ° C. or higher than Tg, the temperature is raised while the temperature is lowered to 100 to 130 ° C. lower than the melting point (Tm) of the copolymerized polyester. The magnification of the transverse stretching is 2.8 to 3.7 times. The heat setting temperature is selected in the range of 150 to 205 ° C. to adjust the film quality according to the Tm of the copolymerized polyester polymer.

Before the white pigment in the present invention is incorporated into the copolymerized polyester, it is preferable to carry out particle size adjustment and coarse particle removal by a purification process. Industrial means of the refining process include, for example, a jet mill and a ball mill as pulverizing means, and examples of the classifying means include a dry or wet centrifuge. Of course, these means may be used in combination of two or more, and may be purified stepwise.

Various methods can be used for incorporating a white pigment into the copolymerized polyester. A typical method is as follows.
(A) A method of adding before the end of transesterification or esterification reaction at the time of synthesizing the copolyester, or adding before starting the polycondensation reaction. (A) A method of adding to the copolymerized polyester and melt-kneading. (C) The method of (a) or (b), wherein a master pellet containing a large amount of an additive is produced, kneaded with a copolymer polyester containing no particles, and a predetermined amount of the additive is contained.

In the case of using the method of (A) in which an additive is added during the synthesis of the polyester, it is preferable to add the additive to the reaction system as a slurry in which the additive is dispersed in glycol.

The object of the present invention is achieved only when all of the above three conditions of melting point, white pigment and degree of crystal orientation are satisfied. When all three conditions are satisfied, it becomes possible to obtain a polyester film for laminating the outer surface of a metal can having excellent light-shielding properties and excellent moldability.

The white polyester film of the present invention preferably has a thickness of 6 to 75 μm. 10-75 more
μm, particularly preferably 15 to 50 μm. If the thickness is less than 6 μm, breakage or the like is likely to occur during processing, while if it exceeds 75 μm, the quality is excessive and uneconomical.

The metal plate to which the white polyester film of the present invention is bonded, in particular, a metal plate for can making, is a tin plate,
Plates of tin-free steel, aluminum, etc. are suitable. The bonding of the polyester film to the metal plate can be performed, for example, by the following method. The metal plate is heated to a temperature equal to or higher than the melting point of the film, the film is bonded and then cooled, and the surface layer (thin layer) of the film in contact with the metal plate is made amorphous and adhered. The adhesive layer is primer-coated on the film in advance, and this surface is bonded to a metal plate. As the adhesive layer, a known resin adhesive such as an epoxy-based adhesive, an epoxy-ester-based adhesive, an alkyd-based adhesive, or the like can be used.

[0031]

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

Examples 1 to 5 and Comparative Examples 1 to 3
A titanium oxide having an average particle size of 0.27 μm and a density of 3.9 g / cm ³ was added to a copolymerized polyethylene terephthalate (intrinsic viscosity: 0.64) obtained by copolymerizing the components shown in (1) and (2), and a product shown in the table was added. It was melt-extruded under film conditions, quenched and solidified to form an unstretched film, and then the unstretched film was stretched longitudinally and transversely under the conditions shown in the same table, and then heat-set to a thickness of 2 mm.
A biaxially oriented film of 0 μm was obtained. Table 4 shows the characteristics of this film.

[0033]

[Table 1]

[Examples 6 to 8 and Comparative Examples 4 to 7] Table 2
In the copolymerized polyethylene terephthalate (intrinsic viscosity 0.64) obtained by copolymerizing the following components, barium sulfate (density 4.4 g / cm ³ ) and calcium carbonate (density 2.5 g / cm ³ ) having the average particle size shown in the same table , Silicon oxide (2.3 g density)
/ Cm ³ ) and titanium oxide (density: 3.9 g / cm ³ ) were added at the concentrations shown in the table, and were melt-extruded under the film forming conditions shown in the table.
It is quenched and solidified to form an unstretched film, and then the unstretched film is stretched longitudinally and transversely, and subsequently heat-set to a thickness of 20%.
A μm biaxially oriented film was obtained. Table 4 shows the characteristics of this film.

[0035]

[Table 2]

Comparative Examples 8 to 10 Average particle size 0.27 μm
m, melt-extruded copolymerized polyethylene terephthalate (intrinsic viscosity: 0.64) obtained by adding 12 wt% of titanium oxide having a density of 3.9 g / cm ³ and copolymerizing the components shown in Table 3, under the film forming conditions shown in the same table. It was quenched and solidified to form an unstretched film, and then the unstretched film was stretched longitudinally and transversely, and then heat-set to obtain a biaxially oriented film having a thickness of 15 μm. Table 4 shows the characteristics of this film.

[0037]

[Table 3]

A total of 18 kinds of films obtained in Examples 1 to 8 and Comparative Examples 1 to 10 were bonded to both sides of a 0.25 mm thick tin-free steel heated to 260 ° C.
After cooling with water, the plate was cut into a disk having a diameter of 150 mm and deep-drawn in three stages using a drawing die and a punch to prepare a 55 mm-diameter side seamless container (hereinafter abbreviated as a can).

The following observations and tests were performed on this container, and each was evaluated according to the following criteria. (1) Deep drawing workability -1 ○: Both inner and outer surfaces are processed without any abnormality on the film, and no fine cracks or breaks are found on the film on the inner and outer surfaces of the can. △: A part of the film on the inner and outer surfaces of the can is broken. Be

(2) Deep drawing workability-2 ○: Both inner and outer surfaces were processed without any abnormality, and rust prevention test of the film surface in the can (1% NaCl water was put in the can, electrodes were inserted, and the can was A current value when a voltage of 6 V is applied to the anode is measured.
×: The film has no abnormality on both the inner and outer surfaces, but the current value is 0.2 mA or more in the ERV test. When the energized portion is observed in an enlarged manner, cracks on the pinhole starting from the coarse lubricant are observed in the film.

(3) Impact cracking resistance Cans with good deep drawability were filled with water and 10 pieces of each test were dropped from a height of 30 cm onto a PVC tile floor for each test, and then subjected to an ERV test in the can. ○: 0.2 mA or less for all 10 pieces Δ: 0.2 mA or more for 1 to 5 pieces ×: 0.2 mA or more for 6 or more pieces, or
Cracks of the film are already observed after falling

(4) Heat Embrittlement Resistance The can which had been successfully deep drawn was heated and held at 210 ° C. for 5 minutes, and then subjected to impact cracking resistance evaluation described in (3). Δ: 0.2 mA or less for 10 pieces Δ: 0.2 mA or more for 1 to 5 pieces ×: 0.2 mA or more for 6 or more pieces, or
After heating at 210 ° C for 5 minutes, cracking of the film has already been observed.

(5) Can outer surface whiteness Before bonding the 18 kinds of white film and tin-free steel, the tin-free steel surface, which becomes the outer surface of the can after the can is made, has a length of 50 mm and a width of 0 mm each using a crow mouth. .1m
The black line was observed through a white film after making a can. Evaluation was performed as follows: ○: Neither black line of 1 mm and 0.1 mm width was observed. Δ: Black line of 1 mm width was slightly visible, but 0.1 mm width.
×: Black line having a width of 1 mm is visible and black line having a width of 0.1 mm is also slightly visible.

[0044]

[Table 4]

From the results shown in Table 4, it can be seen that the films of the examples are excellent in all of the deep drawability, impact cracking resistance, heat resistance and whiteness of the outer surface of the can.

[0046]

The biaxially oriented white polyester film for laminating the outer surface of a metal can according to the present invention can be processed into a can by, for example, deep drawing when forming a metal can by laminating a metal plate. It has excellent impact resistance, heat resistance and whiteness on the outer surface of the can after the can, and is extremely useful for bonding the outer surface of a metal can.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) // B29K 67:00 105: 16 B29L 7:00 C08L 67:00 (72) Inventor Gen Izumi, Sagamihara, Kanagawa 3-37-19 Koyama, Sagamihara Research Center, Teijin Limited (72) Inventor Yoji Murakami 3-37-19 Koyama, Sagamihara City, Kanagawa Prefecture, Sagamihara Research Center Teijin Limited

Claims (2)

[Claims] 1. A copolymer containing a white pigment having an average particle diameter in the range of 0.1 to 1.5 μm in a particle number of 1 × 10 ⁸ / mm ³ or more and a melting point in the range of 210 to 245 ° C. A biaxially oriented film made of polyester, which is obtained by stretching an unstretched film by 2.7 to 3.6 times in a longitudinal direction and 2.8 in a transverse direction by a sequential biaxial stretching method.
The film is heat-set at 150 to 205 ° C. after stretching to 3.7 times, and the degree of crystal orientation in the thickness direction of the biaxially oriented film is in the range of 0.25 to 0.55. Biaxially oriented white polyester film for laminating metal cans. 2. The biaxially oriented white polyester film for bonding the outer surface of a metal can according to claim 1, wherein after the film is bonded to a metal plate, the film is formed into a container such that the film is on the outer surface of the container.