JPH1060131A - White polyester film for metal lamination and process for preparing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a white polyester film for metal lamination which has excellent heat lamination and strength and in addition is excellent in opacifying effect and whiteness. SOLUTION: This white polyester film for metal lamination is a simultaneously biaxially stretched film comprising a compsn., the compsn. comprising: a polyester comprising 95 to 75mol% ethylene terephthalate units and 5 to 25mol% ethylene isophthalate units, the polyester having an intrinsic viscosity of not less than 0.5; and 20 to 40wt% white inactive particle having a particle diameter of not more than 0.5μm incorporated into the polyester, the white inactive particle being selected from among titanium dioxide, calcium carbonate and barium sulfate. The white polyester film satisfies the following property requirements: a tensile strength of not less than 15kgf/mm<2> , a heat shrinkage at 160 deg.C of not more than 5.0%, an optical density of not less than 0.3, a glossiness of not less than 10, a whiteness of not less than 81.0, and an adhesive power of not less than 300gf.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white polyester film for metal lamination having excellent heat laminating properties, moldability and tensile strength, excellent concealing properties, and excellent whiteness. It is about.

[0002]

2. Description of the Related Art Food and beverage packaging includes steel cans,
Metal cans such as aluminum cans are used in large quantities. Conventionally, these metal cans are provided with corrosion resistance, printability, etc.
It has been used by applying a solvent type paint mainly composed of a thermosetting resin. However, the application of such a paint has poor productivity and has a problem of environmental pollution, etc. Recently, a biaxially stretched plastic film or a laminated film based on the biaxially stretched plastic film is laminated. The use of metal lamination has increased.

A metal can covered with a plastic film is manufactured by laminating a plastic film on a metal plate such as a steel plate or an aluminum plate (including a plate that has been subjected to a surface treatment such as plating), and forming a laminated metal plate. You. And the plastic film used here has good laminability with a metal plate, and is excellent in moldability.
No peeling, cracks, cracks, and pinholes of the film during molding, do not impair the flavor of the contents of the can,
Numerous properties such as no water spots and white powder when retorted, excellent concealment properties and whiteness are required at the same time.

Therefore, in particular, as a film for the outer surface of a can,
Among plastic films, biaxially stretched film of polyethylene terephthalate or its copolymer filled with high concentration of titanium dioxide has excellent physical, mechanical and chemical properties, and has low production cost and excellent cost performance However, there are problems with respect to thermal laminating properties, strength, hiding properties, and whiteness.

To solve such a problem, for example, a polyester film having a specific pigment concentration (Japanese Patent Laid-Open No.
62-21428, JP-A-5-170942, 5-33
No. 9391), a polyester film having a specific viscosity (JP-A-6-271686), a polyester film having a specific degree of crystal orientation (JP-A-6-49234), and a multilayer polyester film (JP-A-7-52351). Gazette) has been proposed. But even with these films,
It was not possible to satisfy all the various required characteristics as described above.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides an inexpensive material which has excellent heat laminating properties (heat bonding properties), moldability and strength, and is suitable for coating metal cans having excellent concealing properties and whiteness. It is an object of the present invention to provide a white polyester film for metal lamination.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve this problem, and as a result, formed a film obtained by blending a specific polyester with a specific amount of inert particles in a specific amount under appropriate conditions. The present inventors have found that this object is achieved by doing so, and have completed the present invention.

That is, the gist of the present invention is as follows. 1. Polyester consisting of 95 to 75 mol% of ethylene terephthalate units and 5 to 16 mol% of ethylene isophthalate units and having an intrinsic viscosity of 0.5 or more is selected from titanium oxide, calcium carbonate and barium sulfate. What is claimed is: 1. A white polyester film for metal lamination, comprising a biaxially stretched film composed of a composition containing 20 to 40% by weight of active particles and having the following characteristics (1) to (6). (1) Tensile strength 15kgf / mm ² or more (2) Thermal shrinkage at 160 ° C 5.0% or less (3) Optical density 0.3 or more (4) Gloss 10 or more (5) Whiteness 81.0 or more (6) Adhesive strength 300gf or more 2. 2. The white polyester film for metal lamination according to the above item 1, produced by a simultaneous biaxial stretching method. 3. In producing the polyester film according to the above items 1 and 2, the ethylene terephthalate unit 80 to 50
A composition consisting of a copolyester having an intrinsic viscosity of 0.5 or more and 30% by weight or more of white inert particles in a copolyester having an intrinsic viscosity of 0.5 or more and 88 to 100 mol% of ethylene terephthalate units and ethylene A composition comprising 12 to 0 mol% of isophthalate units and having a limiting viscosity of 0.5 or more and a mixture of 0 to 15% by weight of white inert particles in a polyester is supplied to a melt extruder, extruded into a sheet, and extruded in a sheet form. And biaxially stretching in the transverse direction.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The polyester in the present invention may be a single copolyester or a mixture obtained by melting and mixing two or more kinds of polyesters. 95 to 75 mol% of ethylene terephthalate units and 95 to 75 mol of ethylene isophthalate units are used.
What is necessary is just what consists of 25 mol%. (For example, if polyethylene terephthalate and a copolyester composed of 80 mol% of ethylene terephthalate units and 20 mol% of ethylene isophthalate units are melt-mixed at an equal weight, 90 mol% of ethylene terephthalate units and 10 mol% of ethylene isophthalate units And a polyester consisting of

If the proportion of the ethylene isophthalate unit is less than 5 mol%, the polyester lacks heat laminating properties, and if it exceeds 25 mol%, the strength is insufficient, which is not preferable.

Further, the polyester in the present invention needs to have an intrinsic viscosity of 0.5 or more, and if the intrinsic viscosity is lower than this, the strength is insufficient. However, if the intrinsic viscosity is too large, not only the quality becomes excessive, but also the operability at the time of producing the film is deteriorated and the heat laminating property is deteriorated, which is not preferable. Particularly preferred are polyesters having an intrinsic viscosity of 0.6 to 1.2.

Further, the polyester is preferably a crystalline copolyester having a melting point of 200 to 240 ° C. and an amorphous copolyester having a glass transition point of 50 to 75 ° C. If the ratio is out of the range, the heat resistance is insufficient or the heat laminating property is deteriorated, which is not preferable.

The polyester has a content of oligomers (linear or cyclic 1- to 9-mers mainly composed of cyclic trimers) of 0.1 to 2% by weight, and a content of acetaldehyde of 5 to 5%.
A range of from 50 ppm to 50 ppm is preferable. If the range is out of these ranges, it is not preferable because it causes white powder, adversely affects taste, and increases production cost.

In the industrial production of polyester, a diethylene glycol component is inevitably produced as a by-product. However, it is desirable to control the content to be 1 to 3.5 mol% of the total glycol component. And the production cost becomes excessive, which is not preferable.

The polyester may be further copolymerized with components other than isophthalic acid within a range that does not impair the properties (usually 5 mol% or less). Specific examples of the copolymer component include phthalic acid, 2,6-naphthalenedicarboxylic acid,
-Dicarboxylic acids such as sodium sulfoisophthalic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, dodecane diacid, dimer acid, maleic anhydride, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, and cyclohexanedicarboxylic acid Acid, 4-hydroxybenzoic acid,
ε-caprolactone, hydroxycarboxylic acids such as lactic acid,
Examples include diols such as 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, cyclohexanedimethanol, and ethylene oxide adducts of bisphenol A and bisphenol S. A tri- or higher functional compound such as trimellitic acid, trimesic acid, pyromellitic acid, trimethylolpropane, glycerin, and pentaerythritol may be used in a small amount.

The polyester in the present invention can be produced by a conventional method. For example, a polyethylene terephthalate copolymer obtained by copolymerizing an isophthalic acid component is
It can be manufactured as follows.

First, a slurry of terephthalic acid and ethylene glycol is continuously supplied to an esterification tank in which bis (β-hydroxyethyl) terephthalate and / or its low polymer is present, and is heated at a temperature of about 250 ° C. for 8 hours. The esterification reaction rate is about 95% to continuously obtain an esterified product. Transfer this to a polymerization vessel, add the required amount of isophthalic acid or its ethylene glycol ester, and polycondensate at a temperature of about 280 ° C under a reduced pressure of 1.3 hPa or less in the presence of a catalyst such as antimony trioxide or germanium dioxide. Perform the reaction.

The polyester thus obtained is
Since oligomers and acetaldehyde are contained in relatively large amounts, solid-phase polymerization at a temperature of 200 to 240 ° C (a temperature not exceeding the melting point of polyester) under reduced pressure or an inert gas flow is used to reduce these amounts. Further, it is preferable that the film is treated with steam (hot water) as required, and then subjected to a film forming process.

In the present invention, it is necessary that the polyester film contains white inert particles selected from titanium oxide, calcium carbonate and barium sulfate.
The inert particles can be used after being subjected to any known surface treatment as necessary. Inert particles have a particle size
It is necessary that the particle size is 0.5 μm or less, preferably 0.1 to 0.5 μm.
The dispersibility in the polyester becomes poor, and the surface of the obtained film becomes uneven, resulting in low glossiness, which is not preferable.

The content of the inert particles is 20 to 40% by weight, preferably 25 to 35% by weight, and most preferably 27 to 33% by weight.
If the amount is less than 20% by weight, the concealing properties and whiteness of the film will be insufficient, and if it exceeds 40% by weight, the strength of the film will be undesirably reduced.

As a method for incorporating the inert particles into the film, any known method can be employed.
In particular, when the following method is adopted, a film excellent in various properties can be manufactured with good operability.

That is, ethylene terephthalate unit 90
~ 50 mol% and ethylene isophthalate unit 10 ~ 50 mol%
A composition A comprising a copolyester having an intrinsic viscosity of 0.5 or more and 30% by weight or more of inert particles, 88-100 mol% of ethylene terephthalate units and 12-0 mol% of ethylene isophthalate units. , Intrinsic viscosity 0.5
This is a method in which a composition B in which inert particles are mixed with the above polyester in an amount of 0 to 15% by weight is supplied to a melt extruder, extruded into a sheet, and biaxially stretched. At this time, the ratio of the composition A to the composition B is such that the composition of the polyester is 95 to 75 mol% of ethylene terephthalate units and 5 to 25 mol% of ethylene isophthalate units, and the content of inert particles is 20 to 40 mol%.
% By weight.

The amount of ethylene isophthalate units of the copolyester in the composition A is desirably 10 to 50 mol%, preferably 30 to 50 mol%, and if this amount is less than 10 mol%, the composition It is necessary to reduce the proportion of B, and the strength of the film decreases, and if it exceeds 50 mol%, the film-forming properties decrease. The amount of the inert particles in the composition A is 30% by weight or more, preferably 30 to 70% by weight.
When the amount is less than 30% by weight, it is necessary to reduce the proportion of the composition B, and the strength of the film is reduced. When the amount is too large, the dispersibility in the copolyester is deteriorated. However, the shape of the chip of the composition B is deteriorated, and poor biting in the extruder occurs, which is not preferable.

The amount of the ethylene isophthalate unit of the copolyester in the composition B is desirably 12 to 0 mol%, preferably 8 to 0 mol%, and when this amount exceeds 12 mol%, the strength of the film is reduced. Decrease. The amount of the inert particles in the composition B is preferably 0 to 15% by weight, more preferably 0 to 5% by weight.
If it exceeds 15% by weight, the strength of the film is reduced.

The film of the present invention must satisfy the following characteristics (1) to (6). (1) Tensile strength 15 kgf / mm ² or more, preferably 18-25 kgf / mm
² (2) Thermal shrinkage at 160 ° C of 5.0% or less, preferably
4.0% or less (3) Optical density 0.3 or more, preferably 0.4 to 0.7 (4) Gloss 10 or more, preferably 10 to 20 (5) Whiteness 81.0 or more, preferably 85.0 to 95.0 (6) Adhesive strength 300 gf or more

When the tensile strength is less than 15 kgf / mm ^{2, the} strength is practically insufficient. When the heat shrinkage is more than 5%, the printing properties are poor. When the optical density is less than 0.3, the concealing property is poor. When the gloss is less than 10, the appearance of the film becomes poor, and when the whiteness is less than 81.0, the whiteness is practically insufficient, and when the adhesive strength is less than 300 gf, the lamination with metal is performed. Poor. The larger the characteristic value that defines the lower limit,
It is preferable that the characteristic value defining the upper limit is smaller, but if the quality is excessive, not only the cost is increased, but also the operability at the time of film production deteriorates, it is preferable to set the degree as the preferable range described above. Appropriate. The elongation may be in the range of usually 80 to 160% (mechanical direction: MD and direction perpendicular thereto: average of TD).

The film of the present invention is obtained by feeding a polyester composition containing inert particles to a melt extruder,
It can be manufactured by extruding into a sheet at a temperature of 280 ° C., cooling it by closely contacting it on a cooling drum adjusted to a temperature of room temperature or lower, and biaxially stretching the obtained unstretched sheet in the longitudinal and transverse directions. As the biaxial stretching method, a simultaneous biaxial stretching method, a tenter type biaxial stretching method such as a sequential biaxial stretching method,
And an inflation method. In the present invention, the simultaneous biaxial stretching method is most suitable because a white film containing a high concentration of titanium oxide can be stably produced.

At this time, it is necessary to select film-forming conditions so that the obtained film satisfies the above-mentioned properties. For example, when the simultaneous biaxial stretching method is used, the MD is added to the MD as necessary. After pre-stretching to about 1.2 times, simultaneous biaxial stretching is performed with a tenter at a temperature of 50 to 150 ° C. so that the MD and TD stretching ratios become about 2 to 4 times, respectively. Heat treatment is performed at 80 to 220 ° C. for several seconds, and the temperature is gradually cooled to room temperature.

The heat treatment after stretching is a necessary step for reducing the heat shrinkage of the film.
It can be performed by a known method such as a method of blowing hot air, a method of irradiating infrared rays, or a method of irradiating microwaves, but the method of blowing hot air is optimal because heating can be performed uniformly and accurately.

The thickness of the film is suitably from 9 to 25 μm, and preferably from 12 to 17 μm, in order to secure the formability in drawing and ironing.

In order to improve the processability during film production and can production, an inorganic lubricant such as silica, alumina or kaolin is used as a masterbatch in advance, and a necessary amount of the masterbatch is added to form a film to form a film. Is desirably provided. Furthermore, in order to improve the appearance and printability of the film, for example, a silicone compound or the like can be contained.

The film of the present invention can be used for metal lamination as it is as a single-layer film. However, if necessary, a laminated film of polyethylene terephthalate, polybutylene terephthalate, and a film composed mainly of polyester or the like may be used. Can also be used.

In the case of a laminated film, the monolayer film of the present invention and another film may be laminated in different steps,
When forming the film of the present invention, another film may be simultaneously extruded and laminated.

Further, the film of the present invention may be subjected to in-line coating during film production or post-coating after film production in order to further improve laminating properties with metal and further increase strength.
An optional coating layer such as an adhesive layer may be formed.

The film of the present invention is used after being laminated with a metal. When the metal is a steel plate, a chemical conversion treatment such as chromic acid treatment, phosphoric acid treatment, electrolytic chromic acid treatment, chromate treatment, nickel, tin, zinc, Aluminum, gunmetal, brass, and those subjected to various other plating treatments are preferably used.

The method for measuring the characteristic values of the film in the present invention is as follows. Intrinsic viscosity Measured at 20 ° C using an equal weight mixture of phenol and ethane tetrachloride as a solvent. Tensile strength Measure according to ASTM D882 on a sample with a width of 10 mm and a length of 10 cm. In addition, data is shown by the average value of MD and TD. Heat shrinkage A sample with a width of 10 mm and a length of 10 cm is left in an atmosphere of 160 ° C. for 15 minutes, and the dimensional change before and after being left is measured to obtain a percentage of the original length. In addition, data is shown by the average value of MD and TD. Optical density For a film having a thickness of 13 μm, using a transmission density meter TD 932 manufactured by Macbeth, setting the transmission nozzle diameter to 3 mm, calculating the incident light amount I ₀ and the transmitted light amount I, and calculating the transmission density D by the following equation:
This is defined as the optical density. D = −log (I ₀ / I) Gloss Measured according to ASTM D523. Whiteness JIS L 1015 7.11 Whiteness is measured by C method (Hunter's method). Adhesive force (Heat laminating property) Between a metal roll heated to 240 ° C and a silicone rubber roll, a sample film and a tin-free steel plate are superposed and inserted, and heated and bonded at a linear pressure of 10 kgf / cm. Using an autograph manufactured by Shimadzu Corporation, a 180 ° peel test is performed on a 25 mm wide specimen at a peel speed of 10 mm / min to measure the peel strength. And the peel strength is 300gf
The above case is regarded as pass (○), and the case where the peel strength is less than 300 gf is rejected (×).

Next, the present invention will be specifically described with reference to examples.

Examples 1 to 12 and Comparative Examples 1 to 7 The composition A and the composition B shown in Table 1
At a weight ratio of B, the mixture is fed to a melt extruder, extruded in a sheet form from a T-die at a temperature of 280 ° C., closely contacted with a cooling drum controlled to a surface temperature of 18 ° C., and cooled to obtain a 130 μm thick unstretched sheet. Was. The obtained unstretched sheet is supplied to a tenter-type simultaneous biaxial stretching machine, and at a temperature of 80 ° C., a stretching ratio of MD 3.0,
After simultaneous biaxial stretching as TD 3.3, the relaxation rate of TD was 5
%, Heat-treated at a temperature of 210 ° C. for 4 seconds, cooled and wound up to obtain a 13 μm thick white film. In Example 7, the average particle diameter was used as particles (inert particles).
0.45 μm titanium dioxide, average particle size in Example 8 0.38 μm
m of calcium carbonate, Example 9 used barium sulfate having an average particle size of 0.36 μm, and in other examples, average particle size of 0.36 μm.
μm titanium dioxide was used. Table 1 shows the characteristic values and the like of the obtained film. [In Table 1, IP% is a ratio (mol%) of an ethylene isophthalate unit of the polyester.
Represents ]

[0040]

[Table 1]

[0041]

According to the present invention, an inexpensive metal which has excellent heat laminating properties (thermal adhesion), moldability and strength, and is preferably used for coating metal cans having excellent concealing properties and whiteness. A white polyester film for lamination is provided.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication location C08K 3/22 KJR C08K 3/22 KJR 3/24 3/24 3/26 3/26 C08L 67 / 02 LPD C08L 67/02 LPD // B29K 67:00 105: 16 B29L 7:00

Claims (3)

[Claims] 1. A polyester comprising 95 to 75 mol% of ethylene terephthalate units and 5 to 25 mol% of ethylene isophthalate units and having an intrinsic viscosity of 0.5 or more, titanium oxide,
Particle size selected from calcium carbonate and barium sulfate 0.5
A biaxially stretched film composed of a composition containing 20 to 40% by weight of white inert particles having a particle size of μm or less, the following (1)
A white polyester film for metal lamination, having the following characteristics: (1) Tensile strength 15kgf / mm ² or more (2) Thermal shrinkage at 160 ° C 5.0% or less (3) Optical density 0.3 or more (4) Gloss 10 or more (5) Whiteness 81.0 or more (6) Adhesive strength 300gf or more 2. The white polyester film for metal lamination according to claim 1, produced by a simultaneous biaxial stretching method. 3. The method for producing a polyester film according to claim 1, wherein the ethylene terephthalate unit is 90 units.
~ 50 mol% and ethylene isophthalate unit 10 ~ 50 mol%
A composition comprising a copolyester having an intrinsic viscosity of 0.5 or more and 30% by weight or more of white inert particles, 88-100 mol% of ethylene terephthalate units and 12-0 mol% of ethylene isophthalate units. , Intrinsic viscosity
A metal laminate characterized in that a composition in which 0 to 15% by weight of white inert particles are blended with a polyester of 0.5 or more is supplied to a melt extruder, extruded into a sheet shape, and biaxially stretched in the vertical and horizontal directions. For producing white polyester film for