JPH11199687A - White film for lamination onto metal plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a film having excellent moldability and strength, a low rate of change in thickness after thermal lamination onto a metal and slight unevenness of whiteness degree. SOLUTION: This white film for lamination onto a metal plate comprises a composition prepared by compounding a polyester composed of 95-75 mol.% ethylene terephthalate unit and 5-25 mol.% ethylene isophthalate unit with 20-40 wt.% titanium oxide. The resultant film has <=5% rate of change in thickness of the film after thermal lamination to that of a film before the thermal lamination after carrying out the thermal lamination of the film onto the metal plate so as to provide >=300 gf/25 mm adhesive strength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention has excellent thermal laminating properties, moldability and tensile strength and elongation, excellent concealing properties and whiteness, and has little whiteness unevenness and thickness unevenness after can production, and is stable. The present invention relates to a white film for metal plate lamination that can be produced as a product.

[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. Film-laminated cans using the same have come to be widely used.

[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.

As a film for the outer surface of a can, a biaxially stretched film of polyethylene terephthalate or a copolymer thereof filled with titanium oxide is excellent in physical, mechanical and chemical properties, has low production cost, and is cost-effective. It is used as an excellent material. However, there are problems to be improved in terms of heat laminating properties, mechanical strength, concealing properties, and whiteness. In particular, when beautiful printing is performed on the outer surface of a can, a higher whiteness is required. Further, when the processing deformation rate of the can is large, a film having high whiteness has been required to maintain the surface whiteness of the finally completed can.

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 JP-A-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 white films filled with titanium oxide in a polyester resin have been proposed.However, since the thickness change rate after heat laminating the film to a steel plate is high, whiteness after can production is high. There is a problem that spots are generated.

[0006]

DISCLOSURE OF THE INVENTION The present invention has excellent heat adhesion (heat lamination properties) and moldability of a can, and has a small rate of change in thickness after heat lamination on a metal plate. An object of the present invention is to provide a white film for metal plate lamination which is excellent in concealing properties and whiteness without white spots.

[0007]

Means for Solving the Problems As a result of diligent studies, the present inventors have found that a polyester comprising 95 to 75 mol% of ethylene terephthalate units and 5 to 25 mol% of ethylene isophthalate units contains 20 to 40% by weight of titanium oxide. % Of the composition after heat laminating the film to a metal plate so that the adhesive strength is 300 gf / 25 mm or more, and the change in thickness of the film after the heat lamination with respect to the film before the heat lamination. The present inventors have found that the above problems can be solved by using a white film having a ratio of 5% or less, and reached the present invention.

[0008]

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

[0009] The polyester in the present invention contains 95 to 75 mol%, preferably 90 to 90 mol% of ethylene terephthalate units.
８５85 mol% and ethylene isophthalate unit 5-25 mol%, preferably 10-15 mol%. If the ethylene isophthalate unit is less than 5 mol%, the suitability for thermal lamination to a metal plate is lacking, and if it is more than 25 mol%, there is a problem in heat resistance at the time of heat setting or printing baking after the can making process. In addition, the crystallinity of the material is lost, and it is difficult to dry the resin pellets sufficiently, causing troubles in the film forming process, the film becomes amorphous, the strength and heat resistance of the film are insufficient, and the film The laminated metal plate is wrapped around a hot roll in the can making process.

The polyester of the present invention contains 1 to 5 mol%, preferably 2 to 4 mol% of diethylene tere (iso) phthalate unit as a constituent component of the polyester, thereby imparting amorphousness by ethylene isophthalate unit. The balance between the effect and the crystallinity of the ethylene terephthalate unit can be adjusted, and the heat laminating property between the film and the metal, the processability into a can, the heat resistance and the strength can be obtained.

The intrinsic viscosity of the polyester raw material in the present invention is 0.5 or more, preferably 0.6 to 1.2. When the intrinsic viscosity is less than 0.5 polyester,
The operability during 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 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.

In the present invention, an oligomer of a polyester raw material (a linear or cyclic oligomer having a cyclic trimer as a center) may be used.
To 9-mer) in the range of 0.1 to 2.0% by weight. When the content of the oligomer is more than 2.0% by weight, it causes the generation of white powder. The acetaldehyde content of the polyester raw material is preferably 50 ppm or less in order to maintain the flavor of the contents of the can.

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 40% by weight, preferably 23 to 35% by weight. If the content of titanium oxide is less than 20% by weight, the whiteness and hiding properties of the film are insufficient. 40% by weight
If the ratio exceeds the above range, the strength of the obtained film is reduced, and stretching and cutting during film production frequently occur.

The titanium oxide used in the present invention is:
Rutile-type or anatase-type titanium oxide is used and may be used alone or as a mixture. 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. 0.1μ
If it is less than m 2, the average particle diameter 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 titanium oxide used in the present invention may be an inorganic treatment such as alumina, silica, zirconium oxide, titania, tin oxide, antimony oxide, zinc oxide, etc.
Alternatively, those which have been subjected to a surface treatment such as a polyol-based organic treatment such as pentatrierite and a silicone-based organic treatment such as an alkylchlorosilane-based are preferable.

In the film of the present invention, the rate of change in thickness of the film after heat lamination with respect to the film before heat lamination is 5% after heat lamination of the film to a metal plate so that the adhesive strength is 300 gf / 25 mm or more. It must be: In order to prevent the peeling of the film in the process of forming the can and the deterioration of the performance of the can, it is necessary to make the adhesive strength between the film and the metal plate 300 gf / 25 mm or more. If the rate exceeds 5%, unevenness of thickness and unevenness of whiteness after can making occurs, the appearance of the can deteriorates, and the commercial value decreases.

As a method for thermally laminating a film and a metal plate, for example, a film and a metal plate are passed through a metal roll heated to a high temperature and a heat-resistant rubber roll (for example, a silicon rubber roll) while being superposed. A bonding method can be used. As the temperature of the metal roll, usually, a temperature of (melting point of polyester −50) ° C. or more and a melting point or less is appropriate, and the pressure to be applied (linear pressure) is usually 5 to 100 kg / cm 2.

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) Tensile elongation is 70% or more. (3) The longitudinal direction of the film at 150 ° C. for 30 minutes (M
D) and the heat shrinkage in the transverse direction (TD) are 6.0% or less, more preferably 0.5 to 5.0%. (4) Whiteness is 81.0 or more, more preferably 85.0.
that's all.

The tensile strength is less than 10 kgf / mm ² , or
If the tensile elongation is less than 70%, the practical strength tends to be insufficient. When the heat shrinkage is more than 6%, the adhesiveness to the metal plate tends to deteriorate. When the optical density is less than 0.3, the concealability tends to be insufficient. Whiteness is 81.
If it is less than 0, the whiteness tends to be insufficient in practice. 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 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
Since it contains a relatively large amount of oligomers and acetaldehyde, in order to reduce these amounts, it is subjected to solid-state polymerization at a temperature of 200 to 240 ° C. under reduced pressure or an inert gas flow, and if necessary, steam or hot water. After processing with
It is preferable to provide for the film forming step.

In the present invention, a metal plate to be heat-laminated with a film is tin, tin-free steel (hereinafter, referred to as tin-free steel).
TFS), aluminum and the like.
Chemical conversion treatment of phosphate, chromic acid, electrolytic chromic acid, tin,
It may be plated with a metal such as zinc or nickel.

Next, a typical method for producing the film of the present invention will be described, but the present invention is not limited thereto. A polyester composition containing titanium oxide is supplied to a melt extruder, an unstretched sheet is extruded at a temperature of 220 to 280 ° C., and the resulting unstretched sheet is biaxially stretched in the longitudinal and transverse directions. Can be. As the biaxial stretching method, a tenter-type biaxial stretching method such as a simultaneous biaxial stretching method and a sequential biaxial stretching method, and an inflation method can be used. In the case of using a tenter-type simultaneous biaxial stretching method, for example, the unstretched sheet obtained as described above is cooled by closely contacting it on a cooling drum whose temperature has been adjusted to room temperature or lower. Pre-stretching about 1 to 1.2 times, and then using a tenter at a temperature of 90 to 120 ° C.
D and TD are preferably biaxially stretched so as to have a stretching ratio of about 2 to 4 times, and further subjected to a heat treatment at 80 to 220 ° C. for 1 to 10 seconds with a TD relaxation rate of 1 to 7%. . In order to produce a film having the properties defined in the present invention, it is particularly important to adjust the stretching temperature.

In the present invention, although the reason is not clear, the film produced by the simultaneous biaxial stretching method has a low rate of change in thickness of the film after heat lamination to a metal plate. Even when using a polyester composition containing a high concentration of titanium oxide, when using the simultaneous biaxial stretching method, it is difficult to cut the film because the stretching stress during stretching is low, and also in terms of production stability. Most preferred.

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

The thickness of the film must be 9 in order to secure the formability in drawing and squeezing when used as a metal can.
２５25 μm, preferably 10-1 μm.
7 μm.

In order to improve the processability during film production and can production, it is desirable to add a required amount of an inorganic lubricant such as silica, alumina, kaolin or the like to form a film to impart a slip property to the film surface. . Furthermore, in order to improve the printability of the film, for example, an antistatic agent or the like can be contained.

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

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

A. Intrinsic viscosity Phenol / Ethane tetrachloride
It was determined from the solution viscosity measured at a concentration of 0.5 g / dl and 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. Note that the data are represented by the average values of the three images in the MD direction and the three images in the TD direction, and the average values of the MD and TD. D. Whiteness Fix the film with a black presser plate, S
JIS L 1 using Z-RM80 COLORMEASURING SYSTEM
[0151] The measurement was carried out by the C method (Hunter method) of 7.11. E. FIG. Adhesive force (thermal lamination property) A sample film and a tin-free steel plate (TFS) having a thickness of 0.17 mm are superposed and supplied between a metal roll heated to 220 ° C and a silicon rubber roll, and the speed is 20 m / and heat bonding at a linear pressure of 10 kgf / cm. After water-cooling, 25%
A 180 ° peel test was performed on a test piece having a width of 10 mm at a peel speed of 10 mm / min, and the peel strength was measured. When the peeling strength or the breaking strength of the film was 300 gf / 25 mm or more, it was judged as pass (marked by ○), and when the peeling strength or the breaking strength of the film was less than 300 gf / 25 mm, it was judged unacceptable (marked with x). F. Thickness change rate The cross section of the film before and after heat laminating the film on TFS was observed with a scanning electron microscope, the thickness was measured, and calculated from the following equation. G. Thickness change rate (%) = (Ta−Tb) / Ta × 100 Ta: film thickness before heat lamination (μm) Tb: film thickness after heat lamination (μm) Thermal Lamination Suitability The situation when the film was thermally laminated to TFS was evaluated. A sample having good thermal laminating property was rated as ○, and a sample having poor thermal laminating property was rated as ×. H. Thickness unevenness (whiteness unevenness) Arbitrary 10 of heat-laminated steel plate (10 × 10 cm) after heat laminating a film to TFS having a thickness of 0.17 mm
The thickness (Tc) of the portion was accurately read by a dial gauge, and the case where the difference between the maximum value and the minimum value was less than 1.0 μm was evaluated as ○ (good), and the case where the difference was 1.0 μm or more was evaluated as x (defective). When the difference between the maximum value and the minimum value was less than 1.0 μm, the whiteness of the obtained laminated steel sheet was uniform.
When the particle size was not less than μm, white spots were visually observed.

Examples 1 to 7 and Comparative Examples 1 to 4 The polyester resin compositions shown in Table 1 were melt-extruded from an extruder at a temperature of 265.degree. Let cool, thickness 130
A μm unstretched sheet was obtained. According to the stretching conditions shown in Table 1, the obtained unstretched sheet was simultaneously biaxially stretched at a stretch ratio of 3.2 times in the longitudinal direction and 3.2 times in the transverse direction, and then the relaxation rate in the transverse direction was 5%. After performing a heat treatment at a temperature of 155 ° C. for 4 seconds, the resultant was cooled and wound up to obtain a white film having a thickness of 13 μm. The obtained film is superposedly supplied with a TFS having a thickness of 0.17 mm between a metal roll and a silicon rubber roll heated at 220 ° C., and is heated and bonded at a speed of 20 m / min and a linear pressure of 10 kgf / cm. did. Table 1 shows the characteristic values of the obtained film, the processability and the characteristics of the metal laminate plate. In Table 1, IPA represents isophthalic acid, and DEG represents a diethylene glycol component.

[0034]

[Table 1]

[0035]

According to the present invention, it has excellent heat laminating properties (thermal adhesion), moldability and strength, excellent concealing properties and whiteness, and a low rate of change in thickness after heat lamination to metal. Further, a white film for laminating a metal plate with less white spots after heat lamination is provided.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI // B32B 27/36 B32B 27/36 B29K 67:00 B29L 7:00

Claims (3)

[Claims] 1. An ethylene terephthalate unit of 95 to 75.
A film comprising a composition comprising 20% to 40% by weight of titanium oxide in a polyester comprising 5% to 25% by mole of an ethylene isophthalate unit and having an adhesive force of at least 300 gf / 25 mm to a metal plate. After the heat lamination, the change rate of the thickness of the film after the heat lamination with respect to the film before the heat lamination is 5
% Or less of a white film for metal plate lamination. 2. The white film for metal plate lamination according to claim 1, produced by a simultaneous biaxial stretching method. 3. The white film for metal plate lamination according to claim 1, which has the following performances (1) to (4). (1) Tensile strength 10 kgf / mm ² or more (2) Tensile elongation 70% or more (3) Thermal shrinkage at 150 ° C. 6.0% or less (4) Whiteness 81.0 or more