JPH10180969A - White film for metal laminate and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a white polyester film for metal laminate having excellent heat laminating properties, strength, concealability and whiteness and a method for manufacturing it. SOLUTION: In a biaxially oriented film obtained by laminating a B layer formed of composition obtained by mixing 20 to 60wt.% of titanium oxide with polyester containing 100 to 75mol% of ethylene terephthalate unit and 0 to 25mol% of ethylene isophthalate unit, and an S layer formed of composition obtained by mixing 20wt.% or less of titanium oxide with polyester containing 94 to 70mol% of ethylene terephthalate unit, 5 to 25mol% of ethylene isophthalate unit and 1 to 5mol% of diethylene tere(iso)phthalate unit in a constitution of S-B-S layers, the titanium oxide content in the film is 20 to 50wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has an excellent thermal laminating property, moldability and tensile strength, excellent concealing property and whiteness, little occurrence of abrasion on a jig when forming a metal can, and improvement of printability. The present invention relates to a white film for metal lamination which is excellent and is preferably used for coating the outer surface of a metal can.

[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, and these metal cans are conventionally used to impart corrosion resistance, printability, etc.
It has been used by applying a solvent type paint mainly composed of a thermosetting resin to the surface of a can. However, the application of such a paint has poor productivity and has problems such as environmental pollution. Recently, a biaxially stretched plastic film or a laminate film obtained by laminating a heat-sealable film based on this film has been used. It is increasingly used for metal lamination.

[0003] 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 and processing a laminated metal plate. You. Plastic films used for such applications include:
Good lamination properties with metal plates, excellent moldability of cans, that is, no peeling, cracks, cracks, pinholes, etc. of the film during molding of the cans,
The flavor of the contents of the can is not impaired (when used on the inner surface of the can), and no water spot or white powder is generated when the retort treatment is performed. A phenomenon in which water droplets adhere to the film during retort treatment and crystallize to whiten, which impairs the aesthetics of the product.
A substance in which low molecular weight substances such as oligomers are deposited on the film surface.When a laminated film is used on the inner surface of the can, the flavor of the contents of the can is impaired. Spoil. ) Are required at the same time.

[0004] Normally, the surface of a can is printed. At this time, a white paint is undercoated for the purpose of concealing the metal color of the base, and the printing is performed thereon. In recent years, from the simplification of the manufacturing process (reduction in energy and cost) and measures against environmental problems (non-solvent), the production of a can body excellent in concealing properties, in which a white film is laminated, has been promoted.

As such a white film, a film obtained by blending a high concentration of titanium oxide with a polyester resin is used. However, the whiteness and hiding power of the conventional white film are insufficient, and it is desired to further increase the amount of titanium. However, due to the increase in the amount of titanium, the surface of the film becomes harder, and the problem that the jig for can making is worn out, and the shaved metal and titanium oxide adhere to the film surface, causing printing defects during printing, The problem that the heat laminating property with a steel sheet is deteriorated has been highlighted.

[0006] As such a white film for metal lamination, for example, a film obtained by mixing titanium oxide with a copolymerized polyester in order to improve the moldability of a can is disclosed in Japanese Patent Application Laid-Open No. 5-170942. JP-A-5-339391 discloses a mixture of a copolymerized polyester and rutile-type titanium oxide having a purity of 95% or more.
Japanese Patent Application Laid-Open No. 6-271686 discloses a mixture of a high-concentration titanium oxide master chip and a dilute polymer having a wide viscosity distribution in order to improve the processability and impact resistance of the can. Japanese Patent Application Laid-Open No. 6-49234 discloses a mixture of a titanium oxide master chip and a high-viscosity diluent polymer in order to improve impact resistance. A laminated polyester film in which two types of copolymerized polyesters having different pigment concentrations are laminated is disclosed in JP-A-6-399.
80 and JP-A-7-52351. As described above, various single-layer or multi-layer films in which titanium oxide is filled in a polyester resin have been proposed, but they have not been able to simultaneously improve whiteness and abrasion of a can jig. .

In recent years, there has been a demand for further increasing the whiteness and concealability of a film for a can, and further reducing the thickness of the film for cost reduction. In order to meet this demand, titanium oxide must be blended at a higher filling. However, when titanium oxide is further blended at a higher filling rate, (a) breakage is likely to occur during the production of a film, particularly during stretching, and the operability is impaired. (B) Laminability to a metal plate is deteriorated. When a laminated metal plate is formed, there is a problem that a jig made of metal or the like is easily damaged, and (d) printing on a laminated film surface is difficult (a defect is easily generated).

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide excellent heat adhesion to a metal plate (heat laminating property), moldability to a can, concealment and whiteness, and also to damage a jig during can making. An object of the present invention is to provide a white film laminated on a metal surface, which is suitable for coating of a metal can and which does not cause generation of a white film, and a method for producing the same.

[0009]

Means for Solving the Problems The inventors of the present invention used a polyester having a specific chemical structure as a raw material, and formed a film into a three-layer structure with a central layer B and a layer S on both the front and back sides different from each other. In addition, the compounding amount of titanium oxide is adjusted to the center layer B.
By unevenly distributing to, it was found that the above problems can be solved, furthermore, a film having higher whiteness and concealing property can be obtained, and that the operability during production of this film is remarkably improved. Reached.

That is, the gist of the present invention is as follows. 1. Layer B comprising a composition in which titanium oxide is blended with 20 to 60% by weight of a polyester comprising 100 to 75% by mole of ethylene terephthalate units and 0 to 25% by mole of ethylene isophthalate units, and 94 to 70% by mole of ethylene terephthalate units And ethylene isophthalate unit 5 to 2
5 mol% and diethylene tere (iso) phthalate unit 1 to 1
An S layer comprising a composition in which titanium oxide is blended in an amount of 20% by weight or less with a polyester comprising 5 mol% is S / B / S
2. A white polyester film for metal lamination, comprising: a biaxially stretched film laminated by the constitution described above, wherein the content of titanium oxide in the film is 20 to 50% by weight. 2. The unstretched sheet obtained by melt co-extrusion using a raw material resin having a limiting viscosity of the polyester constituting the B layer and the S layer of 0.5 or more is simultaneously biaxially stretched in the machine direction and the transverse direction. 2. The method for producing a white polyester film for metal lamination according to the above 1.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The white polyester film of the present invention comprises an intermediate layer having a high concentration of titanium oxide (layer B) and layers having a low concentration of titanium oxide (layer S) on both sides of the intermediate layer. The S layer contains 94 to 70 mol% of ethylene terephthalate units. The layer B is composed of 5 to 25 mol% of ethylene isophthalate units and 1 to 5 mol% of diethylene tere (iso) phthalate units, and the B layer contains 100 to 70 mol% of ethylene terephthalate units and 0 to 25 mol% of ethylene isophthalate units. It consists of

The proportion of ethylene isophthalate units in the S layer is 5 to 25 mol%, preferably 8 to 15 mol%.
It is. When the amount is less than 5 mol%, the heat laminating property between the film and a metal plate, for example, as a metal, and the processability from a laminated metal plate to a can are inferior. If it exceeds 25 mol%, there will be a problem in heat resistance at the time of heat setting or printing and baking after the can manufacturing process, and the crystallinity of the material will be lost. Of the film, the film becomes amorphous, the strength and heat resistance of the film are insufficient, and the metal plate on which the film is laminated is wrapped around a hot roll in a can making process.

The ratio of diethylene tere (iso) phthalate units in the S layer is 1 to 5 mol%, preferably 2 to 4 mol%.
Mol%. By introducing the diethylene tere (iso) phthalate unit as a polyester component within the above range, it is possible to adjust the balance between the amorphous imparting effect of the ethylene isophthalate unit and the crystallinity of the ethylene terephthalate unit. Laminating properties of metal and metal, processability into a can, heat resistance and strength are obtained.

The total of the ethylene terephthalate unit and the diethylene tere (iso) phthalate unit in the S layer is preferably in the range of 6 to 25 mol% in view of strength, heat resistance and heat laminating property. If it is less than 6 mol%, the heat laminating property between the polyester film and the metal and the processability of the laminated metal plate into a can are inferior. If it is more than 25 mol%, the crystallinity is lost, and it is difficult to sufficiently dry the pellets. Further, the strength and heat resistance of the film are insufficient, or the film becomes amorphous, and the metal plate on which the film is laminated is wound around a hot roll in a can making process.

The proportion of the ethylene isophthalate unit in the layer B is 0 to 25 mol%, preferably 5 to 15 mol%. If it exceeds 25 mol%, the crystallinity of the material will be lost, and it will be difficult to sufficiently dry the pellets. Further, the film becomes amorphous, and the strength and heat resistance of the film become insufficient, or the metal plate on which the film is laminated may be wound around a hot roll in a can making process.

The polyester in the layer B contains diethylene tere (iso) phthalate in an amount of 5 mol% or less, preferably 1 mol% or less.
The balance of crystallinity of the film can be adjusted by copolymerization of ４4 mol%.

In the present invention, the polyester used may be a single polyester or a mixture obtained by melt-mixing two or more polyesters. The polyester material of the S layer and the B layer has an intrinsic viscosity of 0.5 or more,
Preferably it is 0.6 to 1.2. When a polyester having an intrinsic viscosity of less than 0.5 is used, the operability at the time of film production deteriorates, and the strength of the obtained film is insufficient. However, if the intrinsic viscosity is too large, the production cost increases, which is not preferable.

The difference between the limiting viscosities of the polyesters in the S layer and the B layer is 0.1 or less, preferably 0.09 or less. When the difference in intrinsic viscosity exceeds 0.1, a flow mark is formed on the film during film formation. The flow mark refers to a flow variation of one kind of resin that occurs when two or more kinds of resins having different viscosities meet at a feed block or a T-die, that is, a flow pattern of the resin.

The polyester used in the present invention preferably has a melting point of 200 to 240 ° C. when it is crystalline, and has a glass transition temperature of 50 to 85 ° C. when it is amorphous. Outside of these ranges, heat resistance may be insufficient or thermal lamination properties may be reduced.

The polyester constituting the S layer and the B layer is as follows:
Any combination is possible as long as the above conditions are satisfied. Among them, it is a particularly preferred embodiment that the melting point of the polyester in the S layer (the glass transition temperature in the case of amorphous) is the same as or lower than that of the polyester in the B layer. This makes it possible to favorably balance the strength, heat resistance and thermal laminability of the film.

The polyester used in the present invention may be one obtained by further copolymerizing another component other than isophthalic acid and diethylene glycol within a range not to impair the properties (usually 5 mol% or less). Specific examples of the copolymer component include phthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, dodecane diacid, dimer acid, Examples thereof include maleic anhydride, maleic acid, fumaric acid, itaconic acid, dicarboxylic acids such as citraconic acid, mesaconic acid and cyclohexanedicarboxylic acid, and oxycarboxylic acids such as 4-hydroxybenzoic acid, ε-caprolactone and lactic acid. Also, 1,3
-Propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, cyclohexanedimethanol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, ethylene oxide adduct of bisphenol A or bisphenol S And the like. Further, a small amount of a trifunctional compound such as trimellitic acid, trimesic acid, pyromellitic acid, trimethylolpropane, glycerin, and pentaerythritol may be used.

The content of titanium oxide in the film of the present invention is 20 to 50% by weight, preferably 25 to 45% by weight, and most preferably 25 to 40% by weight as an average concentration in the whole film.
% By weight. When this content is less than 20% by weight,
The whiteness and hiding power of the film are insufficient. If it exceeds 50% by weight, the strength of the film is reduced even in a film having a specific three-layer structure as in the present invention, and the moldability of the film after lamination is inferior.

The titanium oxide content of the layer B is from 20 to 60.
% By weight, preferably 25-55% by weight, optimally 30-55% by weight.
50% by weight. If the amount is less than 20% by weight, the whiteness and hiding power of the film will be insufficient. If it exceeds 60% by weight, the strength of the film is reduced, and the moldability of the film after lamination is inferior.

The content of titanium oxide in the S layer is 20% by weight.
Or less, preferably 15% by weight or less, optimally 10% by weight
It is as follows. If the amount is more than 20% by weight, the jig will be worn when laminating on a metal plate or when making a metal plate on which a film is laminated, which has a great adverse effect on the manufacturing process, Worn metal or titanium oxide may adhere to the film surface during can processing, causing problems in printability.

Known single-layer white films having a titanium oxide content of about 20% by weight have insufficient whiteness and hiding power. As a countermeasure, if the titanium content is further increased to increase whiteness and concealment, there is a problem that the jig for cans is worn, and the scraped metal and titanium adhere to the film surface. Therefore, there is a problem that printing is omitted during printing, and further, there is a problem that thermal lamination property with a metal plate is deteriorated. On the other hand, in the film of the present invention, such various problems were solved by lowering the concentration of titanium oxide in the outer layer S and increasing the concentration of titanium oxide in the inner layer B. .

According to the present invention, the ratio Cb / Cs of the concentration Cb (wt%) of the titanium oxide compounded in the B layer to the concentration Cs (wt%) of the titanium oxide compounded in the S layer is set to 3 As described above, more preferably, when the number is 5 or more, the above various problems can be more effectively solved.

Further, assuming that the thickness of the S layer is Ts (μm) and the thickness of the B layer is Tb (μm), the relationship between the titanium oxide concentration in the S layer and the B layer and the thickness of each layer is as follows: When satisfying (Cb / Cs) × [Tb / (Tb + Ts)], it is possible to further improve the whiteness and the concealing property of the film while maintaining the mechanical properties and the moldability. That is, by increasing the titanium concentration of the inner layer B relative to the titanium concentration of the outer layer S, the thickness Tb of the inner layer film can be reduced while maintaining the concealing property and whiteness of the film. It becomes possible. When the value on the right side of the above formula is less than 3, the entire thickness of the film must be increased in order to improve the whiteness and the concealing property of the film, and thus not only the moldability is reduced, but also There is a risk of losing economy.

The titanium oxide can be used after being subjected to any known surface treatment, if necessary. The titanium oxide may be previously prepared into a master batch of 50 to 70% by weight using a kneading machine or the like, or may be directly added at the time of forming a film.

The titanium oxide has an average particle size of 0.1 to 0.5.
μm, preferably 0.2 to 0.5 μm.
When it is larger than 0.5 μm, the total surface area per unit weight of titanium oxide is reduced, and the concealing property and whiteness of the film may be insufficient. In addition, irregularities are formed on the surface of the obtained film, resulting in low glossiness and poor printability. If it is less than 0.1 μm, the average particle size becomes smaller than the wavelength of visible light, and visible light may pass through the film, and the concealing property and whiteness of the film may be insufficient.

The film of the present invention comprises the following (1) to (4)
It is preferable to satisfy the following characteristics. (1) Tensile strength is 10 kgf / mm ² or more, more preferably 13 kgf / mm ² or more. (2) The longitudinal direction of the film (M
D) and the heat shrinkage in the transverse direction (TD) are 6.0% or less, more preferably 0.5 to 5.0%. (3) The optical density is 0.3 or more, more preferably 0.4
~ 0.7. (4) Whiteness is 81.0 or more, more preferably 85.0.
that's all.

If the tensile strength is less than 10 kgf / mm ² , the practical strength tends to be insufficient. 6% heat shrinkage
If it is larger, the adhesiveness to the metal plate tends to deteriorate. When the optical density is less than 0.3, the concealability tends to be insufficient. When the whiteness is less than 81.0, the whiteness tends to be insufficient in practical use. It is desirable that the characteristic value defining the lower limit is larger, and the characteristic value defining the upper limit is smaller. However, excessive quality not only increases the cost but also deteriorates the operability at the time of film production. Therefore, it is preferable that the quality is in the above range.

The layer B has a thickness of 5 to 20 μm, preferably
10 to 15 μm, and the thickness of the S layer is 0.5 to 5 μm each.
, Preferably 1 to 3 μm each, and a total thickness of 6 to 30 μm.
μm is preferred. When the thickness of the layer B is less than 5 μm, the whiteness and the concealing property of the film tend to be insufficient.
If it exceeds 0 μm, the quality may be excessive and the cost performance may be lost. The thickness of the S layer is 0.5 μm.
If it is less than m, the jig may be worn during can making or the printability may be reduced. On the other hand, when the thickness exceeds 5 μm, the mechanical properties of the film are improved, but the whiteness and the concealing property are not high for the thickness of the film, and a peeling phenomenon easily occurs at the interface between the S layer and the B layer during the molding of the can. In order to secure the formability of drawing and squeezing,
More preferably, the thickness is 9 to 25 μm, and 12 to 17 μm.
m is even more preferred.

The heat shrinkage of the film of the present invention at 150 ° C. for 30 minutes is more preferably TD ≦ 6%, | MD-TD | ≧ 3%, and TD ≦ 5%, | MD-TD. | ≧ 3.5% is even more preferable because wrinkles can be prevented from occurring during thermal lamination to a steel sheet.

The polyester for forming the film of the present invention can be produced by a conventional method. For example, a polyethylene terephthalate copolymer in which an isophthalic acid component and diethylene glycol are copolymerized can be produced 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 a low polymer thereof is present, and reacted at a temperature of about 250 ° C. for about 8 hours. And the esterification reaction rate is 95
% Esterified product is continuously obtained. This is transferred to a polymerization vessel, and necessary amounts of isophthalic acid or its ethylene glycol ester and diethylene glycol are added. Then, a polycondensation reaction is performed 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 and germanium dioxide.

The film of the present invention can be produced by the following method. That is, a method in which two resin compositions constituting each layer are melted using separate extruders and then superimposed by a feed block method and extruded from a die, or a method in which two molten resin compositions are melted in a multi-manifold die An unstretched sheet is manufactured by using a method of overlapping and extruding in the above or a method combining the above two methods. Next, the unstretched sheet is stretched in the machine direction and the transverse direction using a tenter-type biaxial stretching method or an inflation method to obtain a film of the present invention. Alternatively, a method of laminating two types of stretched films constituting each layer can also be used.

When the tenter type biaxial stretching method is used,
For example, two types of polyester compositions containing titanium oxide constituting the S layer and the B layer are supplied to a melt extruder,
The extruded sheet is extruded into a sheet at a temperature of 220 to 280 ° C., and the extruded sheet is cooled by closely contacting it on a cooling drum whose temperature has been adjusted to room temperature or lower. Preliminarily stretched about 2 times, then biaxially stretched by a tenter at a temperature of 50 to 150 ° C to MD and TD so as to have a draw ratio of about 2 to 4 times each, and further, the relaxation rate of TD was 80 to 220 as%
By subjecting the film to a heat treatment at a temperature of several degrees Celsius for several seconds, the film of the present invention can be produced.

As a biaxial stretching method using a tenter, there are a simultaneous biaxial stretching method and a sequential biaxial stretching method. When the titanium oxide is highly filled, the film is easily broken at the time of stretching, but by using the simultaneous biaxial stretching method, the occurrence of the break can be significantly reduced. Is more preferable.

The heat treatment after stretching is a necessary step for reducing the heat shrinkage of the film. As the method of this heat treatment, there are known methods such as a method of blowing hot air, a method of irradiating infrared rays, and a method of irradiating microwaves.
Among them, the method of blowing hot air is optimal because heating can be performed uniformly and accurately.

In order to improve the processability during film production and can production, it is desirable to add a small amount of an inorganic lubricant such as silica, alumina, kaolin or the like to form a film to impart slip properties to the film surface. Furthermore, in order to improve the appearance and printability of the film, for example, the film may contain a silicone compound or the like. Also, in order to improve laminating properties with metal and further increase strength,
An optional coating layer such as an adhesive layer may be formed by in-line coating during film production or post-coating after film production.

When the metal plate on which the film of the present invention is laminated is a steel plate, a chemical treatment such as chromic acid treatment, phosphoric acid treatment, electrolytic chromic acid treatment, chromate treatment, nickel,
Tin, zinc, aluminum, gunmetal, brass, and other various types of plated steel plates can be preferably used.

Next, the present invention will be described specifically with reference to examples. The method for measuring the characteristic values of the films in the following Examples and Comparative Examples was as follows.

A. Intrinsic viscosity Phenol / Ethane tetrachloride
It was determined from the solution viscosity measured at a temperature of 20 ° C. B. Tensile strength The tensile strength was measured on a sample having a width of 10 mm and a length of 10 cm (n = 5 sheets) according to the measurement method specified in ASTM D882. In addition, data was shown by the average value of MD and TD. C. Heat shrinkage A sample of 10 mm in width and 10 cm in length was subjected to a load of about 0.4 g.
The sample was left for 30 minutes in an atmosphere of 50 ° C., the dimensional change before and after the measurement was measured, and the length was measured as a percentage of the original length after standing. The data is shown by the average value of three pieces in the MD direction and three pieces in the TD direction, and the average value of MD and TD. D. Optical density Using a transmission densitometer TD 932 manufactured by Macbeth,
With the diameter of the transmission nozzle set to 3 mm, the amount of incident light I ₀ and the amount of transmitted light I were determined, the transmission density D was calculated by the following equation, and this was used as the optical density. D = −log (I ₀ / I) Whiteness JIS L 1015 7.11 Whiteness was measured by the C method (Hunter's method).

F. Adhesive force (thermal laminating property) Between a metal roll heated to 240 ° C and a silicon rubber roll, a sample film and a tin-free steel plate having a thickness of 0.21 mm are superposed and supplied, and the speed is 20 m / mi.
n, and heated and bonded at a linear pressure of 50 kgf / cm. After water-cooling, a 180 ° peel test was performed on a 25 mm wide test piece at a peel speed of 10 mm / min using an autograph manufactured by Shimadzu Corporation to measure peel strength. Pass if peel strength or film breaking strength is 300 gf or more (indicated by ○), peel strength or film breaking strength is 300 gf
If less than, it was rejected (indicated by x). G. FIG. Film thickness A thin section was collected from the stretched film using a microtome, and the thickness of each layer of the thin section was measured using an electron microscope.

H. Abrasiveness of can-making jig Evaluated by the occurrence of scratches during can-making. After laminating the film with tin-free steel, deep drawing of a two-piece can equivalent to 350 ml was performed with the film side as the outer surface of the can body. This operation was carried out for 100 cans. At this time, the jig used for deep drawing was inspected for the presence or absence of flaws. If no flaws were found, it was good (indicated by a circle). If possible, it was determined to be defective (indicated by x). I. The composition of the polyester was determined by ¹ H-NMR analysis under the condition of 300 MHz using an analyzer manufactured by Varian. The content of ethylene terephthalate unit is the proportion of terephthalic acid in the total acid component, the content of ethylene isophthalate unit is the proportion of isophthalic acid in the total acid component, and the content of diethylene tere (iso) phthalate unit is the total The ratio was calculated by the ratio of diethylene glycol in the glycol component.

Examples 1 to 14, Comparative Examples 1 to 7 The polyester resin compositions constituting the S layer shown in Tables 1 and 2 were melt-extruded at a temperature of 280 ° C. from a first extruder. Similarly, the polyester resin composition constituting the layer B was melt-extruded at a temperature of 280 ° C. from the second extruder. The two kinds of melted resins were superimposed in a multi-manifold die, and the S / B / thickness of the thickness configuration shown in Tables 1 and 2 was obtained.
S was formed into a three-layer structure, and the three-layer structure was extruded into a sheet shape from a T-die, and was cooled by being in close contact with a cooling drum having a surface temperature of 18 ° C. to obtain an unstretched sheet having a thickness of 70 to 300 μm. The obtained unstretched sheet is supplied to a tenter-type simultaneous biaxial stretching machine at a temperature of 90 ° C., a stretching ratio of MD 3.0, and a TD.
As 3.3, simultaneous biaxial stretching was performed. Thereafter, a heat treatment was performed at a temperature of 155 ° C. for 4 seconds at a relaxation rate of TD of 5%. After cooling and winding, a white multilayer film having a thickness of 7 to 30 μm was obtained. Table 1 shows the characteristic values of the obtained film.
And Table 2. In Tables 1 and 2, "IPA" represents isophthalic acid and "DEG" represents diethylene glycol. The symbol A in the table indicates the value of the following equation. 3 ≦ (Cb / Cs) × [Tb / (Tb + Ts)]

[0046]

[Table 1]

[0047]

[Table 2]

As is clear from Tables 1 and 2, Example 1
All of Nos. To 14 were excellent in whiteness and concealing property, excellent in heat laminating property to a steel plate, and no damage of a jig during can making was observed. On the other hand, Comparative Example 1 was inferior in the heat laminating property because the content of the ethylene isophthalate unit in the S layer was as small as 4 mol%. Comparative Example 2
Means that the content of ethylene isophthalate units in the S layer is 27
Since the molar percentage was too large, the film strength was low and the heat laminability was poor. In Comparative Example 3, since the content of the ethylene isophthalate unit in the layer B was as large as 27 mol%, the film strength was low and the heat laminability was poor. In Comparative Example 4, since the content of the diethylene tere (iso) phthalate unit in the S layer was excessively large at 7.5 mol%, the film strength was low and the heat laminability was poor. In Comparative Example 5, since the content of titanium oxide in the B layer was excessively large at 65% by weight, the film strength was low. In Comparative Example 6, the whiteness of the film was insufficient because the content of titanium oxide in the layer B was as small as 16% by weight and the content of titanium oxide in the entire film was as small as 15% by weight. Met. In Comparative Example 7, since the content of titanium oxide in the S layer was as large as 25% by weight, scratches were found on the jig during can making.

[0049]

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. Provided are a white multilayer polyester film for lamination and a method for producing the same.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08L 67/02 C08L 67/02 // B32B 15/08 104 B32B 15/08 104A B29K 67:00 B29L 7:00 9:00

Claims (8)

[Claims] 1. An ethylene terephthalate unit of 100 to 7
5 mol% and ethylene isophthalate unit 0 to 25 mol%
A layer B comprising a composition in which titanium oxide is blended with 20 to 60% by weight of a polyester consisting of: 94 to 70 mol% of ethylene terephthalate units, 5 to 25 mol% of ethylene isophthalate units, and diethylene tere (iso) phthalate units An S layer comprising a composition in which titanium oxide is blended in an amount of 20% by weight or less with a polyester comprising 1 to 5% by mole,
A biaxially stretched film laminated in an S / B / S configuration, wherein the titanium oxide content in the film is 20 to 50% by weight.
A white polyester film for metal lamination, which is: 2. The titanium oxide concentration of the B layer, Cb wt.
2. The white polyester film for metal lamination according to claim 1, wherein the ratio of the titanium oxide concentration of the layer to the weight percentage of Cs satisfies the following expression. 3 ≦ Cb / Cs 3. The titanium oxide concentration in the B layer, Cb wt%
2. The white polyester film for metal lamination according to claim 1, wherein the ratio of the titanium oxide concentration of the layer to the weight percentage of Cs satisfies the following expression. 5 ≦ Cb / Cs 4. The ratio of the weight percentage of titanium oxide Cb blended in the B layer having a thickness Tb μm to the weight percentage of titanium oxide Cs blended in the S layer having a thickness Ts μm satisfying the following expression. The white polyester film for metal lamination according to any one of claims 1 to 3, wherein: 3 ≦ (Cb / Cs) × [Tb / (Tb + Ts)] 5. The white polyester film for metal lamination according to claim 1, which has the following characteristics (1) to (4). (1) Tensile strength 10 kgf / mm ² or more (2) Thermal shrinkage at 150 ° C. 6.0% or less (3) Optical density 0.3 or more (4) Whiteness 81.0 or more 6. The method according to claim 1, wherein the thickness of the B layer is 5 to 20 μm, the thickness of the S layer is 1 to 5 μm, and the total thickness is 6 to 30 μm. White polyester film for metal lamination. 7. The metal according to claim 1, wherein the thermal shrinkage in the transverse direction (TD) and the longitudinal direction (MD) of the film at 150 ° C. satisfies the following expression. White film for lamination. TD ≦ 6%, | MD−TD | ≧ 3% 8. An unstretched sheet obtained by melt co-extrusion using a raw material resin having an intrinsic viscosity of 0.5 or more of the polyester constituting the B layer and the S layer is simultaneously biaxially stretched in the machine direction and the transverse direction. The method for producing a white polyester film for metal lamination according to any one of claims 1 to 7, characterized in that: