JP2000313755A - Polyester film for metal plate laminate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a film for a metal plate laminate excellent in hot laminating properties to the metal plate and formability of a can without embrittling even after heat treatment or retort sterilizing treatment, etc., scarcely causing cracks or peeling even in a shock such as dropping and suitable for coating a metal can. SOLUTION: This biaxially oriented polyester film for a metal plate laminate has (80-50)/(20-50) wt.% ratio (A)/(B) of (A) a polyester consisting essentially of polybutylene terephthalate (PBT) to (B) a polyester consisting essentially of polyethylene terephthalate (PET) and further the melting point of the polyester (B) within the range of ±20 deg.C based on the melting point of the polyester (A) and <=120 deg.C heating crystallization temperature Tc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film for laminating a metal plate, and more particularly to a metal for manufacturing a metal can body by subjecting a laminated metal plate obtained by laminating a film to a metal to a process such as drawing or ironing. The present invention relates to a polyester film for plate lamination.

[0002]

2. Description of the Related Art Conventionally, to prevent corrosion of the inner and outer surfaces of a metal can,
A solvent-type paint mainly composed of a thermosetting resin has been applied. However, solvent-based paints generate a large amount of solvent when heated at a high temperature to form a coating film, and thus have problems in terms of work safety and the environment. Therefore, recently, as a corrosion prevention method using no solvent, metal coating with a thermoplastic resin film has been proposed. Among thermoplastic resins, polyester is particularly excellent in workability and heat resistance. The development of laminating films is in progress.

[0003] A film-coated metal can is manufactured by forming a laminated metal plate by laminating a thermoplastic resin film on a metal plate such as a steel plate or an aluminum plate (including a plate subjected to a surface treatment such as plating). . The thermoplastic resin film used for such applications has a good heat lamination property with a metal plate, and has excellent moldability of a can,
In other words, various properties such as no peeling, cracking, pinholes, etc. of the film when forming the can, and no embrittlement during printing, retort sterilization and long-term storage after can formation are required at the same time. You.

The outer surface of the can is usually subjected to printing. At this time, a white paint is undercoated for the purpose of concealing the metal color of the base, and the printing is applied thereon. That is, the film for the outer surface of the can is required to have further concealing properties and printability in addition to the required physical properties. However, in recent years, development of a white film in which a white pigment is kneaded has been promoted due to a demand for simplification of a manufacturing process (reduction of energy and cost) and non-solvent use of a white paint.

[0005] In order to satisfy the required performance as described above, there have been proposed some copolymerization or blending of other components for the purpose of maintaining the heat laminating property and improving the moldability of the can. For example, (a) PET obtained by copolymerizing isophthalic acid or (JP-B-8-19245, JP-B-8-19)
No. 246, Japanese Patent No. 2528204), (b) PET blended with PBT (JP-A-5-156040),
Alternatively, (c) a composition in which a colorant is added to a composition in which PBT is mixed with PET (Japanese Patent Application Laid-Open No. 7-238176) is disclosed.

[0006] However, in (a), the copolymerization lowers the melting point and lowers the crystallinity, thereby improving the heat laminability and moldability with metal. There is a problem that embrittlement occurs during sterilization and impact resistance is poor. In (b) and (c), there is no problem with heat treatment at a relatively low temperature such as retort sterilization, but heat at a higher temperature accompanying printing etc. In particular, in (c), when a large amount of a coloring agent is blended, there is a problem that the strength of the film is reduced.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide excellent heat lamination properties with a metal plate and moldability of a can, and to be embrittled even after heat treatment near the melting point associated with printing or retort sterilization. An object of the present invention is to provide a polyester film for laminating a metal plate suitable for coating a metal can, wherein the polyester film is free from cracks and peeling even upon impact such as dropping of the metal can.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that a polyester (A) mainly composed of PBT having a specific range of melting point difference and specific crystallization characteristics. The present inventors have found that a film composed of a specific proportion of the PET-based polyester (B) achieves the object of the present invention, and has reached the present invention.

That is, the gist of the present invention is as follows. Polybutylene terephthalate (PBT) -based polyester (A) and polyethylene terephthalate (PE)
T) The proportion of the main polyester (B) is (A) / (B) = 80-
50/20 to 50 (% by weight), polyester (B)
A biaxially stretched polyester film for laminating a metal plate, wherein the melting point of the polyester is in the range of ± 20 ° C. with respect to the melting point of the polyester (A), and the crystallization temperature Tc is 120 ° C. or less.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. Examples of the polyester (A) mainly composed of PBT in the present invention include PBT and those obtained by copolymerizing PBT with other components. Examples of the polyester (B) mainly composed of PET in the present invention include PET and PET. And those obtained by copolymerizing other components.

The terephthalic acid component in the polyester (A) and the polyester (B) is preferably at least 80 mol% based on the total acid component. 8 terephthalic acid component
If it is less than 0 mol%, the melting point of the polyester decreases, and the heat resistance of the obtained film decreases. The alcohol component in the polyester (A) is at least 80 mol%, more preferably 90 mol%, based on the total alcohol component.
% Or more is 1,4-butanediol. If the amount of 1,4-butanediol is less than 80 mol%, the crystallinity, particularly the crystallization rate, is reduced, and the impact resistance of the obtained film is reduced. Further, it is preferable that 80 mol% or more of the alcohol component in the polyester (B) is ethylene glycol based on all alcohol components. When the amount of ethylene glycol is less than 80 mol%, the crystallinity is reduced, and the heat resistance of the obtained film is reduced.

The copolymerization component in the polyester (A) and the polyester (B) is not particularly limited.
Acid components include isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, oxalic acid, succinic acid, adipic acid, sebacic acid,
Azelaic acid, dodecane diacid, dimer acid, maleic anhydride, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, dicarboxylic acids such as cyclohexanedicarboxylic acid, 4-hydroxybenzoic acid, ε-caprolactone, lactic acid and the like. No. Further, as the alcohol component, ethylene glycol, diethylene glycol,
1,3-propanediol, neopentyl glycol,
Examples include 1,6-hexanediol, cyclohexanedimethanol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and ethylene oxide adducts of bisphenol A and bisphenol S. In addition, trimellitic acid, trimesic acid, pyromellitic acid, trimethylolpropane, glycerin, pentaerythritol, etc.
A small amount of a functional compound or the like may be used. Two or more of these copolymer components may be used in combination.

As the other copolymer component in the polyester (B), a copolymer of isophthalic acid as an acid component is preferably 5 to 20 mol%, more preferably a copolymer of 7 to 15 mol%. The one using isophthalic acid as a copolymer component has a good balance between heat resistance and crystallinity, and can obtain a film excellent in heat lamination property with metal and moldability of a can.

In the present invention, the mixing ratio of the polyester (A) and the polyester (B) is (A) / (B) = 80
To 50/20 to 50 (% by weight), and more preferably (A) / (B) = 70 to 50/3.
0 to 50 (% by weight). Polyester (A) is 80
If the content is more than 10% by weight, a highly crystalline polyester (A)
Characteristic is remarkably exhibited, the moldability of the laminated metal sheet is reduced, and the impact resistance is deteriorated. On the other hand, when the content of the polyester (A) is less than 50% by weight, the crystallization speed of the obtained film is reduced, and the film becomes brittle by heat treatment at a relatively low temperature such as retort sterilization. That is, in the film of the present invention, maintaining the crystallinity of the polyester (A) is important for achieving the object of the present invention.

Further, in the film of the present invention, the melting point of the polyester (B) needs to be in the range of ± 20 ° C., more preferably ± 10 ° C., with respect to the melting point of the polyester (A). If the melting point difference is out of the range of ± 20 ° C., the melting behavior of the polyester (A) and the polyester (B) near the melting point is different. Progression,
The resulting film becomes brittle. The embrittlement of the film is particularly remarkable as the heat treatment temperature approaches the melting point.

Further, the film of the present invention needs to have a temperature-increased crystallization temperature Tc of 120 ° C. or less when the film is melted and then heated from a rapidly cooled amorphous state. 110 ° C. is preferred. Tc is 120 ° C
If it exceeds 300, embrittlement or partial whitening occurs during the retort sterilization treatment, resulting in poor film appearance.

The polyester (A) in the present invention
The polyester (B) may be a single polymer or a blend of two or more.

As the polymerization method of the polyester (A) and the polyester (B) in the present invention, for example, a transesterification method or a direct polymerization method can be used. As transesterification catalysts, Mg, Mn, Zn, Ca, Li, T
oxides and acetates of i. Examples of the polycondensation catalyst include compounds such as Sb, Ti, Ge oxide, and acetate. Since the polyester after polymerization contains monomers and oligomers, by-products such as acetaldehyde and tetrahydrofuran, it is preferable to carry out solid phase polymerization at a temperature of 200 ° C. or more under reduced pressure or an inert gas flow.

In the polymerization of the polyester, if necessary, additives such as an antioxidant, a heat stabilizer, an ultraviolet absorber,
An antistatic agent or the like can be added. As antioxidants, hindered phenol compounds, hindered amine compounds, etc., as heat stabilizers, phosphorus compounds, etc., as ultraviolet absorbers, benzophenone compounds,
Benzotriazole compounds and the like can be mentioned.

The film in the present invention can be made into a white film by containing 10 to 50% by weight, preferably 20 to 40% by weight of titanium oxide.
If the amount is less than 10% by weight, the whiteness and concealability of the film will be insufficient, and if it exceeds 50% by weight, the strength of the film will decrease, and the moldability of the film and the moldability of the film after lamination will decrease. Inferior.

Titanium oxide can be used after being subjected to a 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 decreases, 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 may be 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 not be improved.

The film of the present invention is biaxially stretched in order to impart well-balanced properties such as dimensional stability, high elongation, heat resistance, heat laminating properties and moldability required for a laminated can. When an inorganic substance such as titanium oxide is added to the polymer, voids are generally formed at the interface between the polymer and the inorganic substance during stretching, and the strong elongation of the film is reduced. If there are too many voids in the film, the moldability of the can may be reduced, or impact resistance such as dropping may be reduced. Therefore, when the titanium oxide is highly filled, the stretching condition is selected to reduce the porosity to 10%.
Below, it is more preferable to make it 8% or less.

The film of the present invention can be produced by a known method such as a flat type or tubular type film forming method, but a flat type is preferred for producing a film having a small thickness unevenness.

When the film of the present invention is produced, the polyester (A) and the polyester (B) may be dry-blended or melt-mixed in advance using a conventional single-screw or twin-screw extruder. When using a flat film forming method, the polymer is supplied to an extruder equipped with a T-die, extruded into a sheet at a temperature of 220 to 280 ° C, and the extruded sheet is cooled to a room temperature or lower. The obtained unstretched sheet is pre-stretched about 1 to 1.2 times in the machine direction (MD) as necessary, and then MD and 50 ° C. to 50 ° C. It is biaxially stretched in the transverse direction (TD) so as to have a stretching ratio of about 2 to 4 times each, and further subjected to a heat treatment at 80 to 220 ° C. for several seconds with the TD relaxation rate being several percent. It can be a film.

As the biaxial stretching method using a tenter, an ordinary simultaneous biaxial stretching method or a sequential two-stage stretching method can be used. When using a polymer highly filled with titanium oxide, the film tends to break during stretching, but by using the simultaneous biaxial stretching method, it is possible to suppress the occurrence of voids in the film and reduce the occurrence of breakage. Therefore, the simultaneous biaxial stretching method is more preferable.

Heat treatment after stretching is a necessary step for imparting dimensional stability to the film. Examples of the method include a method of blowing hot air, a method of irradiating infrared rays, and a method of irradiating microwaves. There are known methods. 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 or kaolin 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. Further, in order to improve the laminating property with 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.

The polyester film of the present invention comprises a steel plate,
It is heat-laminated on a metal plate such as aluminum, but the metal plate to be laminated is chemically treated such as chromic acid treatment, phosphoric acid treatment, electrolytic chromic acid treatment, chromate treatment, nickel, tin, zinc, aluminum, gunmetal, brass Alternatively, a steel plate subjected to various other plating treatments or the like can be preferably used.

Next, the present invention will be described specifically with reference to examples. The method for measuring the characteristic values in the examples and comparative examples is as follows:
It is as follows.

A. Intrinsic Viscosity (IV) Using an equal weight mixed solvent of phenol / tetrachloride,
It was determined from the solution viscosity measured at a temperature of 20 ° C. B. Melting point (Tm) and temperature rise crystallization peak temperature (Tc) Using PerkinElmer DSC, 20 ° C./m
In, the melting point and the crystallization peak temperature at the time of temperature rise were measured. Tc is 100 ° C./m after melting the stretched film.
An amorphous sample quenched at a rate of at least in was used. C. 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. D. Whiteness JIS L 1015 7.11 Whiteness was measured by the C method (Hunter's method). E. FIG. Porosity B (%) Ligroin (specific gravity 0.7) manufactured by Ishizu Pharmaceutical Co., Ltd. and Daifoil (specific gravity 1.9) manufactured by Daikin Industries, Ltd. were mixed to prepare a density gradient tube, and the film specific gravity was measured at 23 ° C. Assuming that the specific gravity of the polymer after stretching was 1.36, the porosity was calculated by the following equation. B = [1- (film specific gravity) / (theoretical specific gravity)] × 100 Here, the theoretical specific gravity is calculated from the following equation. Theoretical theoretical gravity = 1 / [(titanium oxide content) / (titanium oxide specific gravity) + (1-titanium oxide content) /1.36] Heat laminating property A sample film and a tin-free steel plate having a thickness of 0.21 mm are superposed and supplied between a heated metal roll and a silicon rubber roll, and the speed is 20 m / min and the linear pressure is 50 k.
It was bonded by heating under the condition of gf / cm, immersed in ice water after 2 seconds, and cooled to obtain a laminated metal plate. From the obtained laminate, a strip-shaped test piece having a width of 18 mm (the end in the length direction was not laminated, and the laminated portion was 8 mm in the length direction)
cm or more) were cut out.
Next, JIS Z-152 was applied to the film surface of the test piece.
Adhesive tape specified in No. 2 was affixed, a 180 ° peel test was performed at a speed of 10 mm / min with an autograph manufactured by Shimadzu Corporation, and the peel strength was measured to evaluate the adhesiveness according to the following criteria. did. A: Peeling strength of 10 or more test specimens out of 11 specimens was 30
The film was broken at 0 gf or more, or at 300 gf or more. ：: Peeling strength of 5 to 9 test pieces out of 11 was 300
The film was broken at a gf of 300 gf or more. Δ: 7 or more test pieces having a peel strength of less than 300 gf. G. FIG. Formability The film side of the laminated metal sheet is taken as the outer surface of the can body, and 35
Deep drawing was performed on a two-piece can corresponding to 0 ml, and a case where no peeling (floating) or whitening of the film was observed was evaluated as ○, and a case where it was observed was evaluated as ×. H. Impact resistance -1 When a laminated metal plate was retorted at 125 ° C for 30 minutes, a weight of 1 kg (the tip was a spherical surface having a diameter of 1/2 inch) was dropped from a height of 50 cm onto the film side at 5 ° C. The state of the film was observed. The evaluation was XX if peeling or breakage was visually observed, but not visually observed, but × if metal corrosion was observed by immersing in copper sulfate aqueous solution, and metal corrosion was observed even if immersed in copper sulfate aqueous solution. A sample in which no was observed was evaluated as ○. I. Impact resistance-2 The laminated metal plate was heat-treated at the temperature shown in Table 2 for 60 seconds, allowed to cool to room temperature, retorted at 125 ° C for 30 minutes, and evaluated in the same manner as F above.

Raw Materials The copolymer components of polyester (A) and polyester (B), intrinsic viscosity (IV), and melting point (Tm) used in Examples and Comparative Examples are shown in Table 1, respectively. As the polyester resin, silica having an average particle size of 1.1 μm was used in a concentration of 0.1 μm.
1% by weight was charged. In Examples 6 to 10 and Comparative Examples 8 to 12, a white film was produced by mixing a master chip containing a higher concentration of titanium oxide with the polyester (A) and the polyester (B). The contents of the master chip are shown below. MB; Pm at Tm 223 ° C., average particle size 0.22 μm
(IV 1.16 dl)
/ G). ME1: Tm 230 ° C. IPA 10 mol% copolymerized PE
In T, titanium oxide having an average particle size of 0.20 μm is 60% by weight.
Charged (IV 0.60 dl / g). ME2; IPA 6mol% copolymer PET with Tm 240 ° C
Was filled with 60% by weight of titanium oxide having an average particle size of 0.25 μm (IV 0.65 dl / g). In addition, IPA represents isophthalic acid, and SEA represents sebacic acid.

Example 1 60 parts by weight of polyester (A) and polyester (B)
40 parts by weight were dry-blended and melt-extruded at 260 ° C. using an extruder equipped with a T-die. Subsequently, this was brought into close contact with a cooling drum having a surface temperature of 18 ° C. to be cooled, and the thickness was reduced to 1 mm.
An unstretched sheet of 10 μm was obtained. The end of the obtained unstretched sheet was gripped by a clip of a tenter-type simultaneous biaxial stretching machine, and after traveling in a preheating zone of 60 ° C., it was 3.0 times in the MD at a temperature of 80 ° C. and 3 times in the TD. Simultaneous biaxial stretching was performed at a magnification of 3 times. Thereafter, a heat treatment was performed at a temperature of 150 ° C. for 4 seconds at a relaxation rate of TD of 5%, and then cooled to room temperature and wound up to obtain a film having a thickness of 12 μm. The production conditions of the film and the performance of the obtained film are shown in Tables 1 and 2.

Examples 2 to 3 and Comparative Examples 1 to 4 Biaxially stretched films were prepared in the same manner as in Example 1 except that the raw material resin, the compounding ratio and the film production conditions were changed as shown in Table 1. Obtained. Table 2 shows the performance of the obtained film.
It was shown to.

Example 4 70 parts by weight of the polyester (A) shown in Table 1 and 30 parts by weight of the polyester (B) were dry-blended and melt-extruded at 260 ° C. using an extruder equipped with a T-die. . Subsequently, this was brought into close contact with a cooling drum having a surface temperature of 18 ° C. and cooled to obtain an unstretched sheet having a thickness of 140 μm. The obtained unstretched sheet is roll-stretched 2.8 times in the MD direction at a temperature of 80 ° C., and the end is gripped by a clip, and the sheet is 3.0 in the TD direction.
The film was successively biaxially stretched at twice the magnification. Thereafter, a heat treatment was performed at a temperature of 150 ° C. for 4 seconds at a relaxation rate of TD of 5%, and then cooled to room temperature and wound up to obtain a film having a thickness of 12 μm. The production conditions of the film and the performance of the obtained film are shown in Tables 1 and 2.

Example 5, Comparative Examples 5 to 7 A biaxially stretched film was obtained in the same manner as in Example 4, except that the starting resin, the compounding ratio and the film production conditions were changed as shown in Table 1. . Table 2 shows the performance of the obtained film.
It was shown to.

[0037]

[Table 1]

[0038]

[Table 2]

Examples 6 to 10 and Comparative Examples 8 to 10 A white biaxially stretched film was produced in the same manner as in Example 1 except that the raw resin, the compounding ratio and the film production conditions were changed as shown in Table 3. I got Table 4 shows the performance of the obtained film.

Comparative Examples 11 to 12 A white biaxially stretched film was obtained in the same manner as in Example 4, except that the raw material resin, the compounding ratio and the film production conditions were changed as shown in Table 3. Table 4 shows the performance of the obtained film.

[0041]

[Table 3]

[0042]

[Table 4]

As shown in Tables 2 and 4, each of the examples was excellent in thermal lamination properties, moldability and impact resistance. However, in Comparative Examples, particularly, those satisfying the impact resistance after the retort sterilization treatment were not obtained, and the impact resistance of the film filled with titanium oxide at a high concentration was remarkably reduced.

[0044]

According to the present invention, it has excellent heat laminating properties and moldability, does not become brittle even after heat treatment at high temperature such as during printing, or retort sterilization, and furthermore, does not suffer from impact such as dropping. Provided is a film which is less likely to crack or peel and is suitable for coating a metal can.

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[Procedure amendment]

[Submission date] February 10, 2000 (2000.2.1
0)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction contents]

In the film of the present invention, the melting point of the polyester (B) needs to be within a range of ± 20 ° C., more preferably ± 10 ° C., with respect to the melting point of the polyester (A). If the difference in melting point is out of the range of ± 20 ° C., the melting behavior of the polyester (A) and the polyester (B) near the melting point is different, and the printing on the surface of the can, etc.,
In the heat treatment process at a high temperature of 200 ° C. or higher , incompatibility proceeds or crystallization proceeds, and the resulting film becomes brittle. Embrittlement of the film, Chikazukuho etc. Author arbitrariness in particular heat treatment temperature is the melting point.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) B32B 27/36 B32B 27/36 B65D 1/09 C08K 3/22 C08K 3/22 C08L 67/02 C08L 67 / 02 B65D 1/00 B // B29K 67:00 B29L 7:00 F term (reference) 3E033 BA07 BA18 BB01 BB04 BB08 EA10 4F071 AA45 AA46 AA83 AA84 AB18 AF23 AF45 AH05 BB08 BC01 BC02 4F100 AA21A AB03 J0538 JL01 JL12 YY00A 4F210 AA24C AA25 AB16 AG01 QA02 QC07 QG01 QG18 QW12 4J002 CF062 CF071 DE136 FD050 FD060 FD070 FD170 GG01 GH00

Claims (3)

[Claims] 1. Polybutylene terephthalate (PBT)
The ratio of the main polyester (A) and the main polyethylene (B) polyethylene terephthalate (PET) is (A) /
(B) = 80-50 / 20-50 (% by weight), and the melting point of the polyester (B) is ± 2 with respect to the melting point of the polyester (A).
A biaxially stretched polyester film for laminating a metal plate, wherein the temperature is in the range of 0 ° C and the temperature-rise crystallization temperature Tc is 120 ° C or less. 2. The polyester film according to claim 1, wherein the polyester (B) is mainly composed of PET copolymerized with isophthalic acid. 3. The polyester film according to claim 1, which contains 10 to 50% by weight of titanium oxide.