JP2005178162A - Laminating polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low temperature thermal laminating braxially oriented polyester film excellent in barrier properties and taste/aroma retaining properties and capable of being thermally laminated to an adherend at 160-200°C. <P>SOLUTION: The low temperature thermal laminating biaxially oriented polyester film is a biaxially oriented laminated polyester film composed of at least two layers and the layer A constituting one side thereof is constituted of a polyester resin with a melting point of 245-280°C based on ethylene terephthalate while the layer B constituting the other surface thereof is constituted of a copolyester with a melting point of 200-240°C. The coefficients ΔPA and ΔPB of surface orientation of the respective layers satisfy the following formula (1):0.140≤ΔPA≤0.180 and the formula (2):0.020≤ΔPB≤0.080, and the thicknesses TA and TB of the respective layers satisfy the formula (3):0.08≤TB/TA≤0.50. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a biaxially stretched polyester film suitable for low temperature thermal lamination. More specifically, the present invention is a film suitable for surface protection of aluminum, steel, tinplate, paper, etc. processed into food containers, etc., and has excellent barrier properties and flavor retention, 160 ° C. to 200 ° C. The present invention relates to a biaxially stretched film for low-temperature heat laminating that can be laminated with the above.

  Conventionally, the surface protection of aluminum, steel, tinplate, paper, and the like used for food containers has been coated with various thermosetting resins such as epoxy and phenolic resins. In recent years, however, the technology has shifted from painting methods that require large amounts of organic solvents, water, and heat energy to the laminating method in which a thermoplastic resin film is laminated to a base material to cover the surface, mainly in beverage cans. Trends have changed. There are two methods for laminating a film: a method of laminating a film to a metal plate via an adhesive, and a method of laminating a film directly on a metal plate without using an adhesive, but the former is an adhesive. Since the process of applying and drying is necessary, the environmental load is large and not preferable. Regarding the latter, in addition to barrier properties and taste-retaining properties, thermal adhesiveness with non-adherents is required, which is technically difficult.

  As means for solving these problems, Patent Document 1 discloses a biaxially stretched polyester film for lamination in which a specific melting point and a plane orientation coefficient of a layer constituting one surface are defined. Since it is inferior in adhesiveness at a low temperature of ˜200 ° C., it cannot be used for applications requiring lamination at a low temperature such as paper and plated steel sheet.

JP-A-10-305541

  This invention is made | formed in view of the said actual condition, The solution subject is excellent in barrier property and a flavor retention property, and low temperature thermal laminating 2 which can be thermally laminated to a to-be-adhered body at 160 to 200 degreeC. It is to provide an axially stretched polyester film.

  As a result of intensive studies in view of the above problems, the present inventors have found that the above problems can be easily solved by a laminated polyester film having a specific configuration, and have completed the present invention.

That is, the gist of the present invention is a biaxially oriented laminated polyester film comprising at least two layers, and the A layer constituting one surface is a polyester resin mainly composed of ethylene terephthalate having a melting point of 245 to 280 ° C. The layer B that is configured and constitutes the other surface is composed of a copolymerized polyester resin having a melting point of 200 to 240 ° C., the plane orientation coefficients ΔPA and ΔPB of each layer satisfy the following formulas (1) and (2), and It exists in the polyester film for lamination characterized by the thickness TA and TB of each layer satisfy | filling following formula (3).
0.140 ≦ ΔPA ≦ 0.180 (1)
0.020 ≦ ΔPB ≦ 0.080 (2)
0.08 ≦ TB / TA ≦ 0.50 (3)

Hereinafter, the present invention will be described in detail.
The polyester resin used in the biaxially oriented polyester film for thermal lamination of the present invention (hereinafter sometimes simply referred to as “film”) is obtained by a polycondensation reaction of a polyvalent carboxylic acid and a polyhydric alcohol by a conventional method. Further, two or more kinds of polyester resins obtained in the same manner and having different melting points can be mixed to form a composition.

  Examples of the polyvalent carboxylic acid component include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, decanedicarboxylic acid, azelaic acid, dodecadicarboxylic acid, cyclohexanedicarboxylic acid, etc. Examples of the polyhydric alcohol component include ethylene glycol, propanediol, butanediol, pentanediol, hexanediol, neopentylglycol, 1,4-cyclohexanedimethanol, decanediol, 2-ethyl-butyl-1 -Propanediol, bisphenol A, etc. are mentioned, but it is not limited to these examples.

  Further, the polyester resin may be a copolymer of three or more kinds of polyvalent carboxylic acids or polyhydric alcohols, or may be a copolymer with a monomer or polymer such as diethylene glycol, triethylene glycol, or polyethylene glycol. Good.

  Next, the polyester constituting the A layer of the film will be described. The polyester constituting the A layer is required to have a melting point in the range of 245 to 280 ° C., preferably 245 to 270 ° C., more preferably 250 to 260 ° C., from the viewpoint of barrier properties and flavor retention. It is. When the melting point is less than 245 ° C., the barrier property is inferior under moist heat or acidity, and the low-molecular weight substance derived from the polyester is liable to precipitate, so the taste-retaining property is deteriorated. When the melting point exceeds 280 ° C., the productivity of the film decreases and the economic efficiency deteriorates, which is not preferable.

  Further, as the polyester component constituting the A layer, a polyester obtained by polycondensation of the above-mentioned polycarboxylic acid and polyhydric alcohol can be preferably used, and more preferably 95 mol% or more is an ethylene terephthalate unit. Are preferable in terms of barrier properties, taste-retaining properties, and abrasion resistance. When the ethylene terephthalate unit is 95 mol% or less, the crystal growth of ethylene terephthalate is inhibited, and the barrier property and the taste-retaining property may be deteriorated.

  The polyester constituting the B layer of the film of the present invention will be described. The polyester constituting the B layer is required to have a melting point of 200 to 240 ° C, preferably 210 ° C to 240 ° C, more preferably 215 ° C to 235 ° C, from the viewpoint of adhesion and heat resistance. A melting point of less than 200 ° C. is not preferable because the heat resistance and adhesion after laminating the film deteriorate. When the melting point exceeds 240 ° C., it is difficult to set the plane orientation coefficients of the A layer and B layer described later to predetermined values, and the laminating property is deteriorated.

  The polyester component constituting the B layer is, for example, a copolymerized polyester obtained by polycondensation using a component selected from the above-mentioned polycarboxylic acid and polyhydric alcohol.

  The film of this invention needs to be a laminated | multilayer film from which a layer which comprises the surface of a film consists of at least 2 layer which consists of A layer and B layer from a viewpoint of barrier property, a flavor retention property, and adhesiveness. The total thickness of the laminated film is preferably 5 to 50 μm, more preferably 8 to 30 μm from the viewpoints of barrier properties and economy.

  The thicknesses TA and TB of the A layer and the B layer must be 0.08 ≦ TB / TA ≦ 0.50, preferably 0.10, from the viewpoints of adhesion, barrier properties, and economy. ≦ TB / TA ≦ 0.40, more preferably 0.15 ≦ TB / TA ≦ 0.30. When TB / TA is less than 0.08, adhesion is deteriorated, which is not preferable. When TB / TA exceeds 0.50, the strength of the film is reduced and the number of breaks is increased in the heating step after the film is stretched vertically and horizontally, which is not preferable from the viewpoint of economy. In addition, such a configuration is not preferable because the thickness of the low-orientation layer is large, so that the slitting property of the film is poor and the curl is large, and the economic efficiency when laminating the film is also deteriorated.

  The plane orientation coefficient of the A layer of the film of the present invention needs to be 0.140 to 0.180, preferably 0.145 to 0.170, from the viewpoint of barrier properties and taste-retaining properties. Preferably it is 0.150-0.170. When the plane orientation coefficient of the A layer is less than 0.140, the barrier properties are deteriorated, and the low molecular weight component derived from the polyester is liable to precipitate on the surface of the A layer. When the plane orientation coefficient of the A layer exceeds 0.180, the number of breaks in the stretching process increases, and the economic efficiency deteriorates, which is not preferable.

  The plane orientation coefficient of the B layer of the film of the present invention is required to be 0.020 to 0.080 from the viewpoint of heat resistance and adhesiveness, preferably 0.020 to 0.070, more preferably 0.8. 025 to 0.060. If the plane orientation coefficient of the B layer is less than 0.020, the heat resistance is poor, and delamination or film shrinkage occurs in the heating step after laminating the film, which is not preferable. Moreover, since the adhesiveness deteriorates when the plane orientation coefficient of the B layer is 0.080 or more, it is not preferable.

  The method of setting the plane orientation coefficients of the A layer and the B layer in the above-mentioned range is not particularly limited. For example, a heat treatment is performed after making the difference in melting point between the raw materials used for the A layer and the B layer and stretching the film vertically and horizontally. A method of heat treatment at 220 to 245 ° C. for 0.3 seconds to 20 seconds during the process is simple and preferable.

  The film of the present invention is preferably blended with lubricant particles to impart slipperiness to the film. In particular, it is preferable to incorporate the following lubricant particles in the A layer because scratch resistance after lamination is improved. As the particles to be used, it is preferable to use one or two or more of inorganic particles, organic particles, and internally precipitated particles having an average particle diameter of 0.01 to 6.0 μm. The blending amount of the lubricant particles is preferably 0.1 to 3.0% by weight, more preferably 0.3 to 3.0% by weight. Moreover, you may contain 10-30 weight% of white pigments for the purpose of provision of concealment property. Although there is no restriction | limiting in particular in the particle | grains to be used, Usually, a rutile type titanium oxide, an anatase type titanium oxide, zinc sulfide, etc. are used.

  The haze of the film of the present invention is preferably 20 to 80%, more preferably 30 to 70%. Usually, after laminating the film, an optical method is used to check for defects such as pinholes and scratches. However, if the haze is 20% or less, not only the film defect but also the adherend defect Is also not preferable because the yield deteriorates. If the haze exceeds 80%, the number of breaks increases during film formation, which is economically undesirable.

  Although the manufacturing method of the film of this invention is not specifically limited, For example, the following methods are employ | adopted suitably. That is, the raw material polyester is melted in at least two extruders, coextruded from a T-die and laminated, and then rapidly cooled with a cooling roll to obtain an amorphous sheet, which is heated to 50 to 120 ° C. The film is stretched 3.0 to 5.0 times in the direction, and then heated to 100 to 150 ° C. and then stretched 3.0 to 5.0 times in the transverse direction. Finally, the film stretched vertically and horizontally is subjected to heat treatment at 220 to 245 ° C. for 0.3 to 20 seconds so that the plane orientation coefficients of the A layer and the B layer become the values described in claim 1. Further, during heat treatment, it is preferable to relax by 1 to 10% in the width direction of the film because dimensional stability can be improved.

  According to the present invention, it is excellent in barrier properties and taste-retaining properties, can be heat-laminated on an adherend at a low temperature of 160 to 200 ° C., and is suitable as a film for surface coating of food containers. A biaxially oriented polyester film is provided.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, this invention is not limited at all to these examples, unless the summary is exceeded. In addition, the evaluation method of the film of this invention is as follows.

(1) Intrinsic viscosity A measurement sample was dissolved in a solvent of phenol / tetrachloroethane = 50/50 (parts by weight) to prepare a solution having a concentration c = 0.01 g / cm ³ , and a relative viscosity with the solvent at 30 ° C. η _r was measured, and the intrinsic viscosity [η] was determined from the following formula.

(Η _r −1) / c = [η] + [η] 2 k′c
(However, in the above formula, k ′ is 0.33)

(2) Melting Point Using a DSC apparatus “MDSC2920 type” manufactured by TI Instruments, the measurement was performed at a temperature rising rate of 10 ° C./min, and the peak temperature of the heat of fusion was taken as the melting point.

(3) Haze measurement In accordance with JIS-K7105, haze measurement of the film was carried out with an integrating sphere turbidimeter NDH-20D manufactured by Nippon Denshoku Industries Co., Ltd.

(4) Degree of plane orientation An Atago Abbe refractometer was used. Methylene iodide is mounted, the sample film is closely attached to the prism so that the measurement surface is downward, and the refractive index in the longitudinal direction, the width direction, and the thickness direction (Nx, respectively) using a monochromatic light sodium D line (589 nm) as a light source Ny, Nz). From the obtained value, the plane orientation coefficient ΔP of each layer was determined by the following formula.
ΔP = (Nx + Ny) / 2−Nz

(5) Film thickness The cross section of the film was observed with a scanning electron microscope (SEM), and the thickness of each layer was measured.

(6) Adhesiveness Film using a table laminator VA-700 manufactured by Taisei Laminator Co., Ltd. under the conditions of a speed of 1 m / min, a nip roll temperature of 170 ° C., and a nip roll pressure of 0.3 MPa so that the B layer becomes an adhesive surface. Was laminated to a 0.2 mm thick TFS plate (manufactured by Nippon Test Panel Co., Ltd., standard test plate). The obtained sample was heat-treated in a hot air oven at 200 ° C. for 2 minutes in a nitrogen atmosphere to obtain a laminate material. Using a DuPont impact tester on the resulting laminate material, forming a dent so that the side coated with the film becomes the inner surface under the conditions of a striker tip R = 3/16 inch, a falling weight mass of 500 g, and a falling distance of 30 cm I let you. The obtained sample was subjected to a retort treatment at 125 ° C. for 30 minutes, and the following three-stage evaluation was performed according to the peeling state of the film in the dents part to obtain adhesiveness.
○: No peeling of the film is observed Δ: Film peeling is observed in a part of the dents ×: The film in the dents part is completely peeled off

(7) Taste-retaining fragrance Thickness 0.22mmX Length 15cmX Width 10cm The film of the present invention is laminated by the method of (6), and the steel sheet is such that the surface on which the film is laminated is inside The 3P can body was made by rounding and welding the joints and repairing the welded portion with an epoxy thermosetting resin. Next, a sample was prepared by winding a lid on the 3P can body, filling with mineral water, and finally closing the canopy. The obtained sample was subjected to high-temperature heat treatment at 125 ° C. for 30 minutes, and the flavor retention property after storage for 1 month at room temperature was judged according to the following criteria.
○: No change in taste and scent compared to before storage △: Slight change in taste and scent compared to before storage ×: Large change in taste and scent compared to before storage Can be seen

Next, the polyester raw material used for an Example is demonstrated.
Polyester A: Polyethylene terephthalate containing 1.5% by weight of calcium carbonate having an average particle diameter of 1.5 μm (Intrinsic viscosity 0.65 dl / g, melting point 253 ° C.)
Polyester B: Polyethylene terephthalate containing 1.3% by weight of agglomerated silica having an average particle size of 4.0 μm (intrinsic viscosity 0.68 dl / g, melting point 253 ° C.)
Polyester C: Polyethylene terephthalate containing 0.3% by weight of agglomerated silica having an average particle size of 2.5 μm (ultimate viscosity 0.63 dl / g, melting point 254 ° C.)
Polyester D: 11 mol% copolymerized polyethylene terephthalate with isophthalic acid (intrinsic viscosity 0.68 dl / g, melting point 230 ° C.)
Polyester E: Isophthalic acid 22 mol% copolymerized polyethylene terephthalate (Intrinsic viscosity 0.70 dl / g, melting point 190 ° C.)
Polyester F: 1,4-cyclohexanedimethanol 33 mol% copolymerized polyethylene terephthalate (Intrinsic viscosity 0.73 dl / g, no melting point)
Polyester G: Polybutylene terephthalate (Intrinsic viscosity 1.1 dl / g, melting point 224 ° C.)

  Polyester A is used as the A layer, and polyester D is used as the B layer, and they are melted by separate extruders, merged inside the T die, and rapidly cooled with a drum cooled to 25 ° C. to obtain a laminated amorphous sheet (laminated Thickness ratio TB / TA = 0.2). The obtained unstretched sheet was stretched 3.8 times in the machine direction at 105 ° C., then stretched 4.5 times in the transverse direction at 115 ° C., and then heat-treated at 240 ° C. for 5 seconds to form a film having a thickness of 12 μm. Obtained. The properties of the obtained film are as shown in Table 1 below and showed excellent properties.

  Polyester B was used as the A layer, and the raw material blended with 50 parts by weight of the polyester C and 50 parts by weight of the polyester E was used as the B layer, respectively, melted by separate extruders, merged inside the T die, and cooled to 25 ° C. The laminated amorphous sheet was obtained by quenching with a drum (TB / TA = 0.1). The obtained unstretched sheet was stretched 3.0 times in the longitudinal direction at 105 ° C., then stretched 3.5 times in the lateral direction at 115 ° C., and then heat treated at 237 ° C. for 4 seconds to form a 9 μm thick film. Obtained. The properties of the obtained film are as shown in Table 1, showing excellent properties.

  Polyester A was used as the A layer, and a raw material blended with 20 parts by weight of the polyester C and 80 parts by weight of the polyester E was used as the B layer, respectively, melted by separate extruders, merged inside the T die, and cooled to 25 ° C. The laminated amorphous sheet was obtained by quenching with a drum (TB / TA = 0.15). The obtained unstretched sheet was stretched 4.0 times in the longitudinal direction at 108 ° C., then stretched 4.5 times in the lateral direction at 112 ° C., and then heat treated at 238 ° C. for 5 seconds to form a film having a thickness of 12 μm. Obtained. The characteristics of the obtained film are as shown in Table 1. Although the adhesion was slightly inferior, the film exhibited good characteristics.

  A raw material obtained by blending 80 parts by weight of polyester A and 20 parts by weight of polyester E was used as the A layer, and polyester D was used as the B layer. Each layer was melted by a separate extruder, merged inside the T die, and cooled to 25 ° C. The laminated amorphous sheet was obtained by quenching with a drum (TB / TA = 0.2). The obtained unstretched sheet was stretched 3.5 times in the longitudinal direction at 115 ° C., then stretched 4.0 times in the transverse direction at 120 ° C., and then heat-treated at 235 ° C. for 6 seconds to obtain a film having a thickness of 25 μm. Obtained. The properties of the obtained film are as shown in Table 1, showing good properties although slightly inferior in flavor retention.

  A raw material blended with 90 parts by weight of polyester C and 10 parts by weight of polyester F is used as the A layer, and a raw material blended with 40 parts by weight of polyester C and 60 parts by weight of polyester F is used as the B layer. A laminated amorphous sheet was obtained by joining inside the die and quenching with a drum cooled to 25 ° C. (TB / TA = 0.4). The obtained unstretched sheet was stretched 3.0 times in the longitudinal direction at 115 ° C., then stretched 3.6 times in the transverse direction at 119 ° C., and then heat-treated at 228 ° C. for 7 seconds to form a film having a thickness of 20 μm. Obtained. The properties of the obtained film are as shown in Table 1, showing good properties although slightly inferior in flavor retention and film-forming properties.

(Comparative Example 1)
A film having a thickness of 12 μm was obtained in the same manner as in Example 1 except that the heat setting temperature was changed to 200 ° C. As shown in Table 2 below, since the plane orientation coefficient of the B layer was high, lamination could not be performed at 160 ° C.

(Comparative Example 2)
A film having a thickness of 12 μm was obtained in the same manner as in Example 1 except that polyester E was used as the B layer material. As shown in Table 2, the properties were inferior in adhesiveness because the plane orientation coefficient of the B layer was too low.
(Comparative Example 3)
A 9 μm film was obtained in the same manner as in Example 2 except that the lamination ratio TB / TA = 2.0. Although the properties were inferior to the taste properties as shown in Table 2, they showed good properties, but because the B layer was thick, film breakage occurred frequently at the time of heat treatment and at the time of slitting, and the economic efficiency deteriorated. In addition, the film curl was severe and the handling of the film deteriorated.
(Comparative Example 4)
A raw material blended with 50 parts by weight of polyester A and 50 parts by weight of polyester G is used as the A layer, and a raw material blended with 30 parts by weight of polyester C and 70 parts by weight of polyester E is used as the B layer. A laminated amorphous sheet was obtained by joining inside the die and quenching with a drum cooled to 25 ° C. (TB / TA = 0.25). The obtained unstretched sheet was stretched 3.5 times in the longitudinal direction at 68 ° C., then stretched 4.0 times in the transverse direction at 110 ° C., and then heat treated at 225 ° C. for 5 seconds to form a film having a thickness of 25 μm. Obtained. The properties of the obtained film are as shown in Table 2, and were inferior in flavor retention.

  The film of the present invention can be suitably used for surface protection of aluminum, steel, tinplate, paper and the like that are processed into food containers and the like.

Claims (1)

It is a biaxially oriented laminated polyester film consisting of at least two layers, and layer A constituting one surface is composed of a polyester resin whose main component is ethylene terephthalate having a melting point of 245 to 280 ° C., and constitutes the other surface The layer B is composed of a copolyester resin having a melting point of 200 to 240 ° C., the plane orientation coefficients ΔPA and ΔPB of each layer satisfy the following formulas (1) and (2), and the thicknesses TA and TB of the respective layers are as follows: A polyester film for laminating characterized by satisfying the formula (3).
0.140 ≦ ΔPA ≦ 0.180 (1)
0.020 ≦ ΔPB ≦ 0.080 (2)
0.08 ≦ TB / TA ≦ 0.50 (3)