JP4059966B2 - White film for metal lamination - Google Patents

Description

【００４１】
【発明の効果】
本発明によれば、優れた熱接着性（熱ラミネート性）、成形性及び強度を有し、隠蔽性、白度に優れ、金属缶製缶時に治具の傷が発生しにくく、さらに、フィルム表面の優れた滑り性を有する金属缶の被覆に好適に用いられる金属ラミネート用白色フィルムが提供される。[0001]
BACKGROUND OF THE INVENTION
The present invention has excellent heat laminating properties, moldability and tensile strength, excellent concealment and whiteness, less wear on jigs when forming metal cans, and suitable for coating outer surfaces of metal cans with excellent printability It is related with the white film for metal laminates used for.
[0002]
[Prior art]
For food and beverage packaging, metal cans such as steel cans and aluminum cans are used in large quantities. These metal cans have conventionally been coated with thermosetting resin to provide corrosion resistance and printability. It has been used by applying a solvent-type paint as a main component.
However, the application of such a paint has poor productivity and problems such as environmental pollution. Recently, a biaxially stretched plastic film or a laminated film obtained by laminating a heat-sealable film based thereon. It is becoming increasingly common to use metal to laminate metal.
[0003]
A metal can covered with a plastic film is manufactured by laminating a plastic film on a metal plate (including those subjected to surface treatment such as plating) such as a steel plate or an aluminum plate, and molding the laminated metal plate.
The plastic film used for such applications includes (1) good laminating properties with metal plates, and (2) excellent can moldability, that is, film peeling, cracking, No cracks, pinholes, etc., (3) The taste of the contents of the can is not impaired (when used on the inner surface of the can), (4) Water spots and white powder are generated when retorting is performed. (Water spot is a phenomenon in which a film melted and amorphized at the time of laminating adheres to water and drops to crystallize and whiten during retort processing, which impairs the appearance of the product. White powder is an oligomer. When the laminated film is used on the inner surface of the can, the flavor of the can contents is impaired and the product is used on the outer surface of the can. To impairs the aesthetic properties of the can.) A number of characteristics such as are required simultaneously.
[0004]
Usually, the surface of the can is printed, and at that time, a white paint is primed for the purpose of concealing the metal color of the base, and the printing is performed thereon. In recent years, production of cans excellent in concealment properties laminated with a white film has been promoted from the viewpoint of simplification of manufacturing processes (reduction in energy and cost) and measures against environmental problems (non-solventization).
[0005]
As such a white film, the thing which mix | blended high concentration titanium oxide with the polyester resin is used. However, the conventional white film has insufficient whiteness and hiding properties, and it is desired to further increase the amount of titanium. However, due to the increase in the amount of titanium, the film surface becomes hard and the jig for canning wears, scraped metal or titanium oxide adheres to the film surface, and printing breakage occurs during printing, The problem that the heat laminating property with a steel plate is deteriorated has been highlighted.
Further, in recent years, the increase in the deep drawing ratio at the time of can making and the processing speed have been increased, and there is a demand for improving the slipperiness of the film surface more than ever.
[0006]
As a conventional white film for metal lamination, for example, JP-A-5-170942 discloses a mixture of a copolyester and titanium oxide in order to improve the moldability of a can. JP-A-5-339391 discloses a mixture of a copolyester and a rutile type titanium oxide having a purity of 95% or more. JP-A-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 workability and impact resistance of the can. JP-A-6-49234 discloses a titanium oxide master chip mixed with a high viscosity diluted polymer in order to improve impact resistance. Also, a laminated polyester film obtained by laminating two types of copolymer polyesters having different pigment concentrations is disclosed in JP-A-6-39980 and JP-A-7-52351.
As mentioned above, various single-layer or multi-layer films in which polyester resin is filled with titanium oxide have been proposed, but the whiteness is improved, the wear of the can making jig is improved, and the deep drawing ratio is increased. In addition, none of the films satisfy the excellent slipperiness of the film surface corresponding to the increased processing speed.
[0007]
[Problems to be solved by the invention]
The present invention has excellent thermal adhesiveness (thermal laminating property), moldability and strength, excellent concealability and whiteness, is less likely to cause damage to jigs during metal cans, and is a film. An object of the present invention is to provide a white film for metal laminate which is suitably used for coating a metal can having excellent slipperiness on the surface.
[0008]
[Means for Solving the Problems]
The inventors of the present invention use polyester having a specific chemical structure as a raw material, and the film is formed into a three-layer structure with the central layer B and the layers S on both sides, and the blending amount of titanium oxide is changed to the central layer B. By making it unevenly distributed and blending a specific amount of lubricant with a specific shape in the layer S, the above problems can be solved, and a film with higher whiteness and concealment can be obtained, and at the time of production of this film It was found that the operability was remarkably improved and the present invention was reached.
[0009]
That is, the gist of the present invention is as follows.
B layer which consists of a composition in which 20 to 60% by weight of titanium oxide is blended with 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 S layer composed of a composition in which 20% by weight or less of titanium oxide is blended in a polyester composed of 5 to 25 mol% of ethylene isophthalate units and 1 to 5 mol% of diethylene tere (iso) phthalate units, S / B / A biaxially stretched film laminated with a structure of S, wherein the titanium oxide content in the film is 20 to 50% by weight, and a lubricant having an average particle diameter of 0.25 to 2.0 μm is contained in the S layer. White film for metal laminate containing 0.01 to 0.5% by weight.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
The polyester in the present invention comprises an intermediate layer (B) having a high titanium oxide concentration and layers (S) having a low titanium oxide concentration on both sides thereof, and the S layer comprises 94 to 70 mol% of ethylene terephthalate units and ethylene isophthalate units. It consists of 5 to 25 mol% and 1 to 5 mol% of diethylenetere (iso) phthalate units, and layer B consists of 100 to 75 mol% of ethyleneterephthalate units and 0 to 25 mol% of ethyleneisophthalate units.
[0011]
The proportion of ethylene isophthalate units in the S layer is 5 to 25 mol%, preferably 8 to 15 mol%. When the amount is less than 5 mol%, the heat laminating property between the film and the metal plate and the processability from the laminated metal plate to the can are inferior. If it exceeds 25 mol%, there will be problems with heat resistance during heat setting and printing baking after the can making process, and the crystallinity of the material will be lost, making it difficult to sufficiently dry the resin pellets. Troubles occur, the film becomes amorphous, the film strength and heat resistance are insufficient, or a metal plate laminated with the film is wound around a hot roll in the can making process.
[0012]
Moreover, the ratio of the diethylene tere (iso) phthalate unit of S layer is 1-5 mol%, Preferably, it is 2-4 mol%.
By introducing the diethylene tere (iso) phthalate unit as a polyester component within the above range, the balance between the amorphousness imparting effect by the ethylene isophthalate unit and the crystallinity of the ethylene terephthalate unit can be adjusted, and the film And heat laminating properties of metal and metal, processability to cans, heat resistance and strength are obtained.
[0013]
Moreover, it is preferable from the point of intensity | strength, heat resistance, and heat laminating property that the sum total of the ethylene isophthalate unit and diethylene tere (iso) phthalate unit in S layer is the range of 6-25 mol%.
When the amount is less than 6 mol%, the heat laminating property between the polyester film and the metal and the processability from the laminated metal plate to the can are inferior. When the amount is more than 25 mol%, the crystallinity is lost and it is difficult to sufficiently dry the pellets. Moreover, the strength and heat resistance of the film are insufficient, the film becomes amorphous, and the metal plate laminated with the film is wound around the hot roll in the can making process.
[0014]
In addition, the balance of crystallinity of the film can be adjusted by copolymerizing diethylene tere (iso) phthalate with 5 mol% or less, preferably 1 to 4 mol% in the polyester of the B layer.
[0015]
In the present invention, the polyester used may be a single copolymer polyester, a mixture of polyethylene terephthalate and copolymer polyester, or a mixture of two or more copolymer polyesters melt-mixed.
[0016]
The polyester raw materials for the S layer and the B layer have an intrinsic viscosity of 0.5 or more, preferably 0.6 to 1.2. If a polyester having an intrinsic viscosity of less than 0.5 is used, the operability during film production is deteriorated and the strength of the resulting film is insufficient. However, if the intrinsic viscosity is too large, the production cost increases, which is not preferable.
[0017]
The difference in intrinsic viscosity between the polyester of 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 enters the film during film formation. A flow mark refers to a flow variation of a kind of resin that occurs when two or more kinds of resins having different viscosities are joined together by a feed block or a T die, that is, a flow pattern of the resin.
[0018]
The polyester used in the present invention preferably has a melting point of 200 to 240 ° C. when crystalline and a glass transition temperature of 50 to 85 ° C. when amorphous. Outside these ranges, the heat resistance is insufficient or the heat laminating properties are reduced.
[0019]
The polyester constituting the S layer and the B layer can be arbitrarily combined as long as the above conditions are satisfied. Among them, it is a particularly preferable embodiment that the melting point (the glass transition temperature in the case of amorphous) of the polyester of the S layer is the same as or lower than that of the polyester of the B layer. This makes it possible to satisfactorily balance the strength, heat resistance, and heat laminating properties of the film.
[0020]
The polyester used in the present invention may be one obtained by further copolymerizing other components other than isophthalic acid and diethylene glycol within a range not impairing the characteristics (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, dodecanedioic acid, dimer acid, Examples thereof include dicarboxylic acids such as maleic anhydride, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid and cyclohexanedicarboxylic acid, and oxycarboxylic acids such as 4-hydroxybenzoic acid, ε-caprolactone and lactic acid.
In addition, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, cyclohexanedimethanol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, bisphenol A and bisphenol And glycols such as an ethylene oxide adduct of S.
Further, a small amount of trifunctional compounds such as trimellitic acid, trimesic acid, pyromellitic acid, trimethylolpropane, glycerin, pentaerythritol, and the like may be used.
[0021]
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 entire film.
When the content is less than 20% by weight, the whiteness and hiding properties of the film are insufficient. If it exceeds 50% by weight, the strength of the film is lowered even if it is a film having a specific three-layer structure as in the present invention, and the film formability after lamination is inferior.
[0022]
The content of titanium oxide in the B layer is 20 to 60% by weight, preferably 25 to 55% by weight, and optimally 30 to 50% by weight. When the blending amount is less than 20% by weight, the whiteness and hiding property of the film are insufficient. When it exceeds 60% by weight, the strength of the film is lowered, and the film formability after lamination is inferior.
[0023]
The content of titanium oxide in the S layer is 20% by weight or less, preferably 15% by weight or less, and optimally 10% by weight or less. When this blending amount exceeds 20% by weight, jigs are worn when laminating to a metal plate or when a metal plate laminated with a film is produced, and the production process is greatly adversely affected. Worn metal or titanium oxide may adhere to the film surface during can processing and cause problems in printability.
[0024]
In the present invention, titanium oxide can be used after performing any known surface treatment as required.
The average particle size of titanium oxide is 0.1 to 0.5 μm, preferably 0.2 to 0.5 μm. When the average particle size exceeds 0.5 μm, the total surface area per unit weight of titanium oxide decreases, resulting in insufficient film concealment and whiteness, and unevenness on the surface of the resulting film, resulting in low gloss. It is not preferable. When the average particle diameter is less than 0.1 μm, the wavelength is smaller than the wavelength of visible light, and there is a possibility that visible light may pass through the film, which is not preferable because the concealability and whiteness of the film are insufficient.
[0025]
The film of the present invention must contain 0.01 to 0.5% by weight, preferably 0.05 to 0.1% by weight, of a lubricant having an average particle size of 0.25 to 2.0 μm in the S layer. is there.
When the average particle size of the lubricant is less than 0.25, the slipperiness of the film is lowered, and the film may be damaged or pinholes may be generated during drawing or squeaking when forming a can. On the other hand, if the average particle size is larger than 2.0 μm, stress is concentrated on the particles, and the film may be broken during drawing or squeaking, which is not preferable.
In addition, when the amount of the lubricant added is less than 0.01% by weight, the slipperiness of the film decreases, and when it exceeds 0.5% by weight, the film becomes too slippery and the appearance when the film is wound on a roll. Becomes worse.
[0026]
The thickness of the B layer of the film of the present invention is 5 to 20 μm, preferably 10 to 15 μm, the thickness of the S layer is 0.5 to 5 μm, preferably 1 to 3 μm, and the total thickness is 9 -25 μm, more preferably 12-17 μm.
When the thickness of the B layer is less than 5 μm, the whiteness and hiding property of the film are likely to be insufficient, and when it exceeds 20 μm, the quality may be excessive and the cost performance may be lost.
If the thickness of the S layer is less than 0.5 μm, the jig may be worn during can making or the printability may be reduced. On the other hand, if it exceeds 5 μm, the mechanical properties of the film are improved, but the whiteness and hiding properties are not high for the thickness of the film, and a peeling phenomenon is likely to occur at the interface between the S layer and the B layer during can molding.
[0027]
The film of the present invention has a dynamic friction coefficient between the metal and the film of 0.05 to 0.25, preferably 0.1 to 0.2, and a dynamic friction coefficient between the films of 0.25 to 0.55, preferably Is preferably 0.3 to 0.5.
When the dynamic friction coefficient between the metal and the film is less than 0.05 or the dynamic friction coefficient between the films is less than 0.25, the film becomes too slippery and the appearance when the film is wound on a roll is deteriorated.
In addition, when the dynamic friction coefficient between the metal and the film is larger than 0.25, or when the dynamic friction coefficient between the films is larger than 0.55, the slipperiness of the film during drawing or squeezing when forming a can is formed. The film may be broken and pinholes may occur. Further, when the can is transported by the line, the slipperiness between the can laminate films is poor, which causes a trouble such as the can protruding from the line, which is not preferable.
[0028]
In the film of the present invention, the thermal shrinkage rate after treatment at 150 ° C. for 30 minutes has the following range TD ≦ 6%, | MD-TD | ≧ 3%
More preferably, the following range TD ≦ 5%, | MD-TD | ≧ 3.5%
It is.
When the thermal shrinkage rate in the TD direction exceeds 6%, the thermal lamination property to the steel sheet is deteriorated, and when the difference between the thermal shrinkage rates of MD and TD is less than 3%, wrinkles occur during the thermal lamination to the steel plate. It may not be preferable.
[0029]
The polyester for forming the film of the present invention can be produced by a conventional method. For example, a polyethylene terephthalate copolymer obtained by copolymerizing an isophthalic acid component and diethylene glycol 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 the reaction is performed at a temperature of about 250 ° C. for about 8 hours. Thus, an esterified product having an esterification reaction rate of around 95% is continuously obtained. This is transferred to a polymerization can and the required amount 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 or germanium dioxide.
[0030]
Since the polyester thus obtained contains a relatively large amount of oligomers and acetaldehyde, in order to reduce these amounts, a temperature of 200 to 240 ° C. (the melting point of the polyester is adjusted under reduced pressure or inert gas flow). It is preferable to subject it to a film forming step after solid-state polymerization at a temperature not exceeding) and, if necessary, treatment with water vapor or hot water.
[0031]
The film of the present invention is a method in which two types of resin compositions constituting each layer are melted by using separate extruders, are superposed by a feed block method and extruded from a die, and the two types of melted resin compositions are multi-manifolded. It can be obtained by producing an unstretched sheet using a method of superposing and extruding in a die, a method combining the above methods, and then stretching using a tenter biaxial stretching method or an inflation method.
Moreover, the method of bonding 2 types of stretched films which comprise each layer can also be used.
[0032]
When the tenter type biaxial stretching method is used, for example, two kinds of polyester compositions containing titanium oxide constituting the S layer and the B layer are supplied to a melt extruder, and the sheet is formed at a temperature of 220 to 280 ° C. The extruded sheet was cooled in close contact with a cooling drum whose temperature was adjusted to room temperature or lower, and the obtained unstretched sheet was pre-stretched about 1 to 1.2 times on MD as necessary. Then, biaxial stretching is performed by a tenter at a temperature of 50 to 150 ° C. so that the stretching ratio of MD and TD is about 2 to 4 times, respectively, and further, the relaxation rate of TD is set to several percent, and 80 to 220 ° C. The film of the present invention can be produced by performing a heat treatment for several seconds.
[0033]
Examples of the biaxial stretching method using a tenter include a simultaneous biaxial stretching method and a sequential biaxial stretching method. When titanium oxide is highly filled, the film is likely to break during stretching, but the occurrence of this breakage can be significantly reduced by using the simultaneous biaxial stretching method. Is more preferred.
[0034]
The heat treatment after stretching is a process necessary for reducing the thermal shrinkage rate of the film. As the heat treatment method, there are known methods such as a method of blowing hot air, a method of irradiating infrared rays, and a method of irradiating microwaves. Of these, the method of blowing hot air is optimal because it can be heated uniformly and accurately.
[0035]
In order to improve the process passability during film production and can making, 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 film appearance and printability, for example, the film can contain a silicone compound or the like.
Moreover, in order to improve the laminating property with a metal or to further increase the strength, an arbitrary coating layer such as an adhesive layer may be formed by in-line coating during film production or post coating after film production.
[0036]
When the metal plate for laminating the film of the present invention is a steel plate, chemical treatment such as chromic acid treatment, phosphoric acid treatment, electrolytic chromic acid treatment, chromate treatment, nickel, tin, zinc, aluminum, gunmetal, brass, other A steel plate subjected to various plating treatments can be preferably used.
[0037]
Next, the present invention will be described specifically by way of examples.
The measuring method of the characteristic value of the film in the following examples and comparative examples is as follows.
[0038]
A. It calculated | required from the solution viscosity measured at the temperature of 20 degreeC using the equal weight mixed solvent of intrinsic viscosity phenol / ethane tetrachloride.
B. A sample with a heat shrinkage width of 10 mm and a length of 10 cm is left in an atmosphere of 150 ° C. for 30 minutes under a load of about 0.4 g, and the dimensional change before and after being left is measured. Asked. The data is shown by the average values of 3 sheets in the MD direction and 3 sheets in the TD direction, and the average values of MD and TD.
C. Coefficient of dynamic friction was measured in accordance with ASTM D-1894 under conditions of a tensile speed of 133.3 mm / min and a load of 200 g.
D. A thin slice was collected from the stretched film using a microtome, and the thickness of each layer of the thin slice was measured using an electron microscope.
F. Can drawing and squeezing workability film were bonded to tin-free steel, and then 350 ml two-piece can was deep drawn with the film side as the outer surface of the can body. This operation was carried out for 100 cans, and the presence or absence of scratches on the film was observed.
[0039]
Examples 1-6 and Comparative Examples 1-4
The polyester resin composition constituting the S layer shown in Table 1 was melt-extruded from the extruder 1 at a temperature of 280 ° C., and the polyester resin composition constituting the B layer was similarly melt-extruded from the extruder 2 at a temperature of 280 ° C.
Two types of molten resin are stacked in a multi-manifold die to form a three-layer structure of S / B / S with the thickness shown in Table 1, extruded from a T-die into a sheet, and a cooling drum with a surface temperature of 18 ° C And cooled to obtain an unstretched sheet having a thickness of 7 to 300 μm.
The obtained unstretched sheet was supplied to a tenter-type simultaneous biaxial stretching machine and simultaneously biaxially stretched at a temperature of 90 ° C. and a stretching ratio of MD3.0 and TD3.3, and then the relaxation rate of TD was set to 5%. After heat treatment at 155 ° C. for 4 seconds, it was cooled and wound up to obtain a white multilayer film having a thickness of 7 to 30 μm.
Table 1 shows the characteristic values and the like of the obtained film.
In Table 1, IPA represents isophthalic acid, and DEG represents diethylene glycol.
[0040]
[Table 1]

[0041]
【The invention's effect】
According to the present invention, it has excellent thermal adhesiveness (thermal laminating property), moldability and strength, excellent concealability and whiteness, and is less likely to cause jig damage when it is made of a metal can. Provided is a white film for metal laminate which is suitably used for coating a metal can having excellent slipperiness on the surface.

Claims (6)

Layer B comprising a composition comprising 20 to 60% by weight of titanium oxide in 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 S layer composed of a composition in which 20% by weight or less of titanium oxide is blended in a polyester composed of 5 to 25 mol% of ethylene isophthalate units and 1 to 5 mol% of diethylene tere (iso) phthalate units, S / B / A biaxially stretched film laminated in the structure of S, wherein the titanium oxide content in the film is 20 to 50% by weight, and a lubricant having an average particle diameter of 0.25 to 2.0 μm is contained in the S layer. White film for metal laminate containing 0.01 to 0.5% by weight. The white film for metal laminates according to claim 1, wherein the B layer contains 1 to 4 mol% of diethylene tere (iso) phthalate units. The white film for a metal laminate according to claim 1, wherein the film thickness of the B layer is 5 to 20 µm, the film thickness of the S layer is 0.5 to 2 µm, and the total thickness of the film is 9 to 25 µm. The white film for metal laminate according to claim 1 or 2, wherein a dynamic friction coefficient between the metal and the film is 0.05 to 0.25, and a dynamic friction coefficient between the films is 0.25 to 0.55. The white film for metal laminate according to any one of claims 1 to 3, wherein a dry heat shrinkage rate by a treatment at 150 ° C for 30 minutes in the machine direction (MD) and the transverse direction (TD) of the film is in the following range.
TD ≦ 6%, | MD-TD | ≧ 3% The white film for metal laminate according to any one of claims 1 to 4, which is produced by a simultaneous biaxial stretching method.