JPH11179846A - White film for lamination of metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a white film for lamination of a metal which exhibits excellent opacifying properties and whiteness and hardly suffers scratches by a jig when a metal can is manufactured and has excellent slip properties and is pref. used for coating of a metal can. SOLUTION: A biaxially drawn film wherein a layer B consisting of a compsn. wherein a polyester consisting of 100-75 mole % ethylene terephthalate units and 0-25 mole % ethylene isophthalate units is compounded with 20-60 wt.% titanium oxide and a layer S consisting of a compsn. wherein a polyester consisting of 94-70 mole % ethylene terephthalate units, 5-25 mole % ethylene isophthalate units and 1-5 mole % diethylene tere(iso)phthalate units is compounded with at most 20 wt.% titanium oxide are laminated by a constitution of S/B/S is provided and the content of titanium oxide in the film is 20-50 wt.% and 0.01-0.5 wt.% lubricant with a mean particle diameter of 0.25-2.0 μm is incorporated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention has excellent heat laminating properties, moldability and tensile strength, excellent concealing properties and whiteness, less jig wear during metal can molding, and excellent printability. The present invention relates to a white film for metal lamination suitably 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. 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.

[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. Further, in recent years, the deep drawing ratio during can manufacturing and the processing speed have been increasing, and it has been required to enhance the slipperiness of the film surface more than ever.

As a conventional white film for metal lamination, for example, a film obtained by mixing titanium oxide with a copolyester in order to improve the moldability of cans is disclosed in
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 multilayer films in which titanium oxide is filled in a polyester resin have been proposed. However, improvement of whiteness and improvement of abrasion of a can-making jig, and further, increase of a deep drawing ratio And the excellent sliding property of the film surface corresponding to the increase in processing speed and none at the same time.

[0007]

SUMMARY OF THE INVENTION The present invention has excellent heat adhesion (heat laminating properties), moldability and strength, excellent concealing properties and whiteness, and is suitable for use in jigs for metal cans. An object of the present invention is to provide a white film for metal lamination which is preferably used for coating a metal can having less scratches and excellent slipperiness on the film surface.

[0008]

Means for Solving the Problems The present inventors used a polyester having a specific chemical structure as a raw material, constituted a film having a three-layer structure comprising a central layer B and layers S on both front and back sides, and furthermore, a titanium oxide film. Is unevenly distributed in the central layer B, and a specific amount of the lubricant in the layer S is mixed in the layer S to solve the above-mentioned problems, and further, a film having higher whiteness and concealing property is obtained. It was also found that the operability during production of this film was significantly improved, and the present invention was reached.

That is, the gist of the present invention is as follows. 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
Wherein the titanium oxide content in the film is 20 to 50% by weight and the lubricant having an average particle size of 0.25 to 2.0 μm is contained in the S layer. White film for metal lamination containing 0.1 to 0.5% by weight.

[0010]

BEST MODE FOR CARRYING OUT 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 concentration of titanium oxide and a layer (S) having a low concentration of titanium oxide on both sides thereof. The S layer is composed of 94 to 70 mol% of ethylene terephthalate units and ethylene isophthalate units. 5-
25 mol% and diethylene tere (iso) phthalate unit 1
B layer is composed of 100 to 75 mol% of ethylene terephthalate units and 0 to 75 mol% of ethylene isophthalate units.
~ 25 mol%.

The proportion of ethylene isophthalate units in the S layer is 5 to 25 mol%, preferably 8 to 15 mol%.
It is. If it is less than 5 mol%, the heat laminating property between the film and the metal plate and the processability of the laminated metal plate into 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 proportion 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 polyester of 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 copolyester, or a mixture of polyethylene terephthalate and copolyester,
Alternatively, two or more copolymerized polyesters may be melt-mixed.

The polyester raw material of the S layer and the B layer has an intrinsic viscosity of 0.5 or more, preferably 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,
Production costs increase, which is not desirable.

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. in the case of crystallinity and a glass transition temperature of 50 to 85 ° C. in the case of non-crystallineness. 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 that does not 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, Oxycarboxylic acids such as maleic anhydride, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, dicarboxylic acids such as cyclohexanedicarboxylic acid, 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 titanium oxide content of 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.

In the present invention, titanium oxide may be used after being subjected to any known surface treatment, if necessary.
The average particle size of the titanium oxide is preferably 0.1 to 0.5 μm, and more preferably 0.2 to 0.5 μm. Average particle size
If it exceeds 0.5 μm, the total surface area per unit weight of titanium oxide decreases, and the concealing property and whiteness of the film become insufficient, and the surface of the obtained film becomes uneven, resulting in low gloss. If the average particle size is less than 0.1 μm, the wavelength becomes smaller than the wavelength of visible light, and there is a possibility that visible light may pass through the film.

The film of the present invention contains 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 necessary. When the average particle size of the lubricant is less than 0.25,
The slipperiness of the film is reduced, and the film may be damaged or pinholes may be generated during drawing or squeezing 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 squeezing, which is not preferable. Also,
When the amount of the lubricant is less than 0.01% by weight, the slipperiness of the film is reduced. When the amount is more than 0.5% by weight, the film becomes too slippery and the appearance when the film is wound around a roll is poor. Become.

The thickness of the layer B of the film of the present invention is 5 to 20 μm, preferably 10 to 15 μm.
The thickness of each layer is 0.5 to 5 μm, preferably 1 to 3 μm.
And the total thickness is 9 to 25 μm, more preferably 12 to 25 μm.
１７17 μm. 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, 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, 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.

The film of the present invention has a coefficient of kinetic friction between the metal and the film of 0.05 to 0.25, preferably 0.1 to 0.2, and a coefficient of kinetic friction between the films of 0.25 to 0.25.
-0.55, preferably 0.3-0.5. If the coefficient of kinetic friction between the metal and the film is less than 0.05 or the coefficient of kinetic friction between the films is less than 0.25, the film becomes too slippery and the appearance when the film is wound up on a roll is poor. When the coefficient of kinetic friction between the metal and the film is greater than 0.25, or when the coefficient of kinetic friction between the films is greater than 0.55, the slipperiness of the film during drawing or squeezing when forming a can is reduced. Poorly, the film may be broken or a pinhole may be generated. In addition, when the cans are conveyed on a line, the slipperiness between the canned laminating films is poor, which causes troubles such as the cans protruding from the line, which is not preferable.

The film of the present invention has a heat shrinkage ratio at 150 ° C. for 30 minutes in the following range TD ≦ 6%, | MD−TD | ≧ 3%, more preferably the following range TD ≦ 5%, | MD− TD | ≧ 3.5%. When the heat shrinkage in the TD direction exceeds 6%, the heat laminating property to the steel sheet deteriorates, and when the difference between the heat shrinkage rates of the MD and TD is less than 3%, wrinkles occur during the heat laminating to the steel sheet. May not be desirable.

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 polyester thus obtained is
As it contains a relatively large amount of oligomers and acetaldehyde, in order to reduce these amounts, solid-phase polymerization is performed at a temperature of 200 to 240 ° C (temperature not exceeding the melting point of polyester) under reduced pressure or an inert gas flow. It is preferable that the film is further treated with steam or hot water as required, and then subjected to a film forming step.

The film of the present invention can be obtained by melting two resin compositions constituting each layer using separate extruders, superimposing them by a feed block method and extruding them from a die. A non-stretched sheet using a method of overlapping and extruding in a multi-manifold die, and a method combining the above-described methods, and then obtaining by stretching using a tenter-type biaxial stretching method or an inflation method. Can be. Further, a method of bonding two types of stretched films constituting each layer can also be used.

In the case of using a tenter type biaxial stretching method,
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 measuring method of the characteristic value of the film in the following Examples and Comparative Examples is as follows.

A. Intrinsic viscosity Phenol / Ethane tetrachloride
It was determined from the solution viscosity measured at a temperature of 20 ° C. B. 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. C. Dynamic friction coefficient According to ASTM D-1894, tensile speed 133.3
It was measured under the conditions of mm / min and a load of 200 g. D. 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. F. Drawing and canning of the can After laminating the film with tin-free steel, deep drawing of a 350 ml two-piece can was performed 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.

Examples 1 to 6 and Comparative Examples 1 to 4 The polyester resin compositions constituting the S layer shown in Table 1 were melt-extruded from the extruder 1 at a temperature of 280 ° C., and similarly the polyester resin compositions constituting the B layer Extruder 2 to temperature 2
It was melt extruded at 80 ° C. The two melted resins are superimposed in a multi-manifold die to form a three-layer structure of S / B / S having a thickness shown in Table 1, extruded from a T-die into a sheet, and a cooling drum having a surface temperature of 18 ° C. And then cooled to obtain an unstretched sheet having a thickness of 7 to 300 μm. The obtained unstretched sheet is supplied to a tenter-type simultaneous biaxial stretching machine, and is simultaneously biaxially stretched at a temperature of 90 ° C., a stretching ratio of MD 3.0 and TD 3.3, and a TD relaxation rate of 5%.
After performing a heat treatment at a temperature of 155 ° C. for 4 seconds, the film 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. Table 1
In the above, IPA represents isophthalic acid, and DEG represents diethylene glycol.

[0040]

[Table 1]

[0041]

According to the present invention, it has excellent heat adhesion (heat lamination properties), moldability and strength, excellent concealing properties and whiteness, and causes a jig scratch when a metal can is made. The present invention provides a white film for metal lamination, which is preferably used for coating a metal can having excellent slipperiness on the film surface.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI // B29K 67:00 B29L 9:00

Claims (6)

[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.
And the average particle diameter in the S layer is 0.25 to 2.0 μm.
a white film for metal lamination, containing 0.01 to 0.5% by weight of a lubricant. 2. The white film for metal lamination according to claim 1, wherein the B layer contains 1 to 4 mol% of diethylene tere (iso) phthalate units. 3. The film thickness of the layer B is 5 to 20 μm.
The white film for metal lamination according to claim 1, wherein the film thickness of the layer is 0.5 to 2 µm, and the total thickness of the film is 9 to 25 µm. 4. The coefficient of kinetic friction between the metal and the film is 0.4.
05 to 0.25, coefficient of dynamic friction between films is 0.25
The white film for metal lamination according to claim 1, wherein the thickness is from 0.5 to 0.55. 5. The white color for a metal laminate according to claim 1, wherein the dry heat shrinkage of the film in the machine direction (MD) and the transverse direction (TD) at 150 ° C. for 30 minutes is in the following range. the film. TD ≦ 6%, | MD−TD | ≧ 3% 6. The white film for metal lamination according to claim 1, which is produced by a simultaneous biaxial stretching method.