JP2001047579A - Thermal adhesion multilayer polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film useful as a corrosion resistant film of a metal material such as, for example, a beverage can or the like having excellent adhesive properties and scarcely-peeled-off properties even by heating or water containing. SOLUTION: In the multilayer film made of a plurality of polyester layers, the polyester layer for constituting at least one surface has less than 10 deg.C/min of a temperature raising speed capable of being detected at a crystal melting peak in the case of measuring the temperature raising by a DSC from an amorphous state and a melting point(MP) to be detected of 190 to 245 deg.C. Then, a constituting layer occupied by a thickness of 60% or more of an overall thickness of the multilayer film is constituted of a polyester having a melting point of MP+10 deg.C or higher.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film useful as a base material of a composite material bonded to other materials such as plastic, metal, paper, cloth and wood.

[0002]

2. Description of the Related Art Polyester films are widely used as composite materials bonded to various materials. For example,
In the field of beverage cans, in order to enhance the corrosion resistance of metals, cans are made from a laminated metal plate on which a polyester film is laminated as an organic coating.

Heretofore, a method of laminating a polyester film to another material has generally used an adhesive, particularly a non-aqueous adhesive, but from the viewpoint of reducing the environmental burden due to the use of a large amount of an organic solvent. More and more examples have been given in which a polyester film is provided with thermal adhesiveness and directly adhered to an adherend. Polyethylene terephthalate, which is the most widely used polyester as a film material, does not have sufficient thermal adhesiveness.Therefore, a general method is to impart thermal adhesiveness by copolymerizing other components such as isophthalic acid. is there. For example, Japanese Unexamined Patent Publication (Kokai) No. 2-305827 discloses a polyethylene terephthalate copolymerized with 12 mol% of isophthalic acid and a polyethylene terephthalate copolymerized with 9 mol% of sebacic acid.

[0004] However, copolymerized polyethylene terephthalate, in which about 10 mol% of other components are copolymerized, satisfies a certain level of properties as a polyester constituting a heat bonding layer, but has relatively high crystallinity. ,
It was not necessarily suitable for industrial mass production, as it required a high degree of temperature and pressure control when bonding with other materials. On the other hand, a method of lowering crystallinity by further increasing the copolymerization amount of other components is not a fundamental improvement method because heat resistance becomes insufficient.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has as its object to solve the problem. It has excellent adhesiveness and is difficult to peel off even by heating or hydration. An object of the present invention is to provide a polyester film useful as a corrosion-resistant coating on a material.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies in view of the above problems, and as a result, have found that a multilayer polyester film having a specific structure can easily solve the above problems, and have completed the present invention. I came to. That is, the gist of the present invention is a multilayer film comprising a plurality of polyester layers, wherein at least one of the polyester layers constituting the surface is capable of detecting a crystal melting peak when measuring the temperature from amorphous to DSC. The speed is 10 ° C /
Min, and the detected melting point (MP) is 190 to 245 ° C, and the constituent layer occupying 60% or more of the total thickness of the multilayer film has a melting point of MP + 10 ° C or more. The present invention relates to a heat-adhesive multilayer polyester film characterized by being composed of polyester.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The polyester in the present invention is a polymer in which repeating units are polycondensed with an ester bond. The repeating unit may have an ester bond. Rather, most of widely used polyesters use a condensate of a dicarboxylic acid and a diol as a repeating ester unit. Examples of dicarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid,
Examples thereof include aromatic dicarboxylic acids such as 2,7-naphthalenedicarboxylic acid, and aliphatic dicarboxylic acids such as adipic acid, azelaic acid, and sebacic acid. Examples of the diol include ethylene glycol, trimethylene glycol, tetramethylene glycol, 1,4-cyclohexanedimethanol, polyethylene glycol, polytetramethylene glycol, and the like. In addition to these dicarboxylic acids and diols, those capable of independently forming an ester unit, for example, p-hydroxybenzoic acid and the like may be polycondensed. Moreover, the structure of the ester repeating unit obtained by condensing polyhydric carboxylic acids, such as trimellitic acid and pyromellitic acid, or polyhydric alcohols, such as glycerin, may be sufficient.

The film of the present invention preferably has at least one surface formed of a polyester layer having a thermal adhesive property. The term "thermal adhesion" as used herein means that after being pressed and adhered to a target adherend at a temperature sufficiently higher than the glass transition temperature, for example, a metal, the temperature is lowered to room temperature. This refers to the property that the bonded state continues.
Specific examples of the heat-adhesive polyester include copolymerized polyesters obtained by copolymerizing the above-mentioned various dicarboxylic acids or diols. For example, 90% of all acid components
Copolymerized polyethylene terephthalate in which 70 mol% is terephthalic acid, 10 to 30 mol% is isophthalic acid, and the diol component is ethylene glycol is an example of a widely used heat-adhesive polyester.

The polyester constituting at least one surface of the film of the present invention is melted once and then rapidly cooled to obtain an amorphous state. When the DSC temperature is measured, the crystal melting peak is less than 10 ° C./min. It cannot be detected unless the heating rate is high. In order to exhibit sufficient adhesiveness to other materials such as metal, it is necessary that at least the polyester in the vicinity of the interface with the other material be melted and amorphous. Therefore, 10 ° C /
If the crystal melting peak is detected at a heating rate of more than one minute, the crystallization rate is too high, and the polyester at the interface of the laminate will easily crystallize if it goes through the heat history in various molding steps after lamination. It is not preferable because the force is reduced.

The melting point (MP) of the polyester having a low crystallization rate used in the present invention is 190 to 24.
It is in the range of 5 ° C, preferably in the range of 200 to 235 ° C. As mentioned above, in order to achieve sufficient adhesion,
Although the crystallization rate must be sufficiently suppressed, on the other hand, in the case of an amorphous polyester that does not crystallize at all or a low-melting polyester whose melting point is less than 190 ° C. even if it can be crystallized, the crystallization rate is sufficiently low. For example, the adhesive layer may be remarkably softened and peeled off after passing through a heat history of about 200 ° C. in the can-making process, which is not preferable. Further, even if the crystallization speed is sufficiently low, the melting point is
If it exceeds 5 ° C., it is not preferable because it is easy to peel off even if it is brought into close contact with heat, and it becomes difficult to make it heat-bonded.

The method for reducing the crystallization rate without lowering the melting point is not particularly limited, but examples include a method for significantly reducing the remaining amount of the catalyst functioning as a nucleating agent. In ordinary polymerization of polyester, antimony trioxide, germanium dioxide, or the like is used as a main catalyst, and its content is several tens to several hundreds pp in terms of a metal element.
m, and functions as a nucleating agent to a considerable extent, so that the crystallization rate is high. However, if the amount of the catalyst is reduced, the polymerization rate is also reduced, so that the catalyst type conventionally used for industrial production is not feasible as a business. Therefore, it is recommended to use a titanium compound having high polymerization activity even in a small amount. As the titanium compound used as a polymerization catalyst,
Tetrabutyl titanate, tetrapropyl titanate, etc., and the amount of titanium metal in polyester is 1%.
When the content is 0 ppm or less, the nucleating agent effect of the remaining catalyst can be significantly suppressed.

The low crystallization rate polyester used in the present invention may be a mixture of a plurality of polyesters.
For example, in the case of copolymerized polyethylene terephthalate in which 20 to 30 mol% of other components are copolymerized, the crystallization rate can be sufficiently reduced even if it is a general polymerization main catalyst system. Therefore, by mixing a polyester with a reduced amount of catalyst, for example, polyethylene terephthalate homopolymer, and a copolymerized polyethylene terephthalate, which is a normal catalyst system, but sufficiently reduced in crystallization rate by copolymerization, the crystallization rate and the melting point are both reduced. It may be suitable as the heat-adhesive polyester according to the present invention.

In the film of the present invention, the total thickness of 60
% Of the polyester has a melting point of 10 ° C. or higher, preferably 20 ° C. or higher than the melting point (MP) of the low crystallization rate polyester. For example, when bonded to a metal, the vicinity of the interface of the laminated metal must be amorphous, so that at least the metal plate is heated to the melting point of the thermo-adhesive polyester or higher. For this reason, if the melting point of the main constituent layer having the strength and function as a structure is not higher than MP by 10 ° C. or more, the molecular orientation of the main constituent layer is reduced at the time of bonding, and in extreme cases, the crystal is melted. Reach. When there is only an amorphous or extremely low molecular orientation, embrittlement proceeds due to a decrease in free volume with time, cracks occur due to internal tension due to residual strain in the processed portion, and corrosion resistance decreases, which is preferable. Absent.

It is desirable that the low crystallization rate polyester constituting at least one surface of the film of the present invention is already amorphous at the film stage. Therefore, 2
After axial stretching, it is recommended to heat set at a temperature higher than MP and lower than the melting point of the main polyester constituent layer. The film of the present invention may have a multilayer structure of three or more layers. For example, the polyester constituting the surface opposite to the surface made of the low crystallization rate polyester is blended with lubricant particles, and in order to enhance the transparency of the intermediate layer, there is an example in which the intermediate layer does not contain any additives. Can be Even in such a case, it is sufficient that these high melting point polyester layers account for 60% or more as a whole and have sufficient strength.

As a standard for maintaining the strength of the main high-melting polyester constituent layer, the in-plane refractive index of the film is usually 1.590 or more, preferably 1.600 or more. If the refractive index in the film plane is 1.590 or more in any direction, the plane orientation of the polyester is sufficiently high and the mechanical properties, especially the impact resistance, are excellent. As long as the properties of the film of the present invention are not impaired,
Various organic compounds and inorganic compounds can be added.
For example, silica, alumina, titanium oxide, kaolin, as a core of surface projections formed to impart slipperiness,
Particles such as inorganic particles such as calcium carbonate, calcium phosphate, and clay, and organic particles containing styrene, acrylic acid, and the like as constituents may be added. Further, coloring agents such as dyes and pigments, antistatic agents, plasticizers, and ultraviolet absorbers may be added.

[0016]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention. The evaluation method and the method for producing a raw material in the present invention are as follows. In the examples, “parts” means “parts by weight”. (1) Heating rate, melting point Differential scanning calorimeter M manufactured by TA Instruments
Use DSC2920. Sample polyester 10mg
Was sealed in an aluminum pan, equilibrated at 300 ° C., taken out, immersed in liquid nitrogen and rapidly cooled to obtain an amorphous sample. This is put into the apparatus again and equilibrated at 0 ° C., and the measurement is performed up to 300 ° C. at each heating rate. The value of the fastest heating rate at which the crystal melting peak was detected was determined. Further, the peak temperature of the endothermic peak of crystal melting at the heating rate was defined as the melting point. (2) Thickness of each layer Gold-deposited on both sides of the film is embedded in epoxy resin and sectioned with an ultramicrotome. The cross section of the obtained sample piece was observed with a scanning electron microscope (SEM), and the thickness of each layer was measured. (3) In-plane refractive index of an film An Abbe refractometer manufactured by Atago was used. Methylene iodide was mounted and the sample film was adhered to the prism, and the in-plane refractive index was measured using monochromatic sodium D-ray as a light source. The prism was brought into close contact with the side opposite to the heat-adhesive polyester layer. (4) Adhesiveness A 200-mm-thick aluminum film having a thickness of 200 μm and a nip roll temperature of 170 ° C. and a nip roll pressure and air pressure of 0.3 MPa was applied at a laminating speed of 1 m / min with a table laminator VA-700 manufactured by Taisei Laminator Co., Ltd. The plate was pressed and adhered. The obtained sample was subjected to a heat treatment at 230 ° C. for 2 minutes in a nitrogen atmosphere in a hot air oven to obtain a laminate.

Dent was formed on the obtained laminate using a DuPont impact tester. Dent formation was performed with the tip R = 3/16 inch, the weight of the falling weight 500 g, and the falling distance 30 cm, so that the surface covered with the film was inside the dents. This was subjected to a heat treatment at 180 ° C. for 3 minutes in a hot air oven, and the following three-stage evaluation was carried out according to the peeling state of the film at the dents portion to obtain adhesiveness.

：: No peeling of the film was observed. ：: Peeling of the film was observed at a part of the dents. X: The film at the dents part was completely peeled. The dents were formed again so that the film became the outer surface of the dents, and after a heat treatment at 60 ° C. for 24 hours in a hot air oven, the film surface at the top of the dents was observed with a scanning electron microscope and cracks were observed. The presence or absence was checked.

Next, a method for producing the raw material polyester used in the examples will be described. [Production of Polyester] Polyester A 85 parts of terephthalic acid, 15 parts of isophthalic acid, and 48 parts of ethylene glycol were charged into a reactor, and transesterification was performed. That is, the reaction start temperature was 225 ° C., and the internal pressure was 0.9.
The reaction was started at a pressure of kg / cm ^3, and then the reaction temperature was gradually raised. After 4 hours, the temperature was raised to 260 ° C. to terminate the transesterification reaction.

Then, orthophosphoric acid was adjusted to 23 ppm as a phosphorus atom with respect to the theoretical yield of the polyester resin, and then cobalt acetate tetrahydrate was adjusted to 20 ppm as a cobalt atom with respect to the theoretical yield of the polyester resin.
Further, tetra-n-butyl titanate was added sequentially so as to be 5 ppm as a titanium atom with respect to the theoretical yield of the polyester resin.
An ethylene glycol slurry in which m amorphous silica was dispersed was added, and a polycondensation reaction was performed.

That is, the reaction temperature is gradually increased from 260 ° C. and the pressure is gradually reduced from normal pressure. After 2 hours, the temperature is decreased to 280 ° C. and the pressure is reduced to 1 mmHg or less. Polyester A was obtained.
The particle content in Polyester A was 0.1 part. Polyester B Polyester B was obtained in the same manner as in the production of polyester A, except that 100 parts of terephthalic acid was used instead of 85 parts of terephthalic acid and 15 parts of isophthalic acid. Polyester C Easter Copolyester 6763 manufactured by Eastman Chemical Japan Co., Ltd. was used as polyester C. Polyester D Polyester D was obtained in the same manner as in the production of polyester A, except that germanium dioxide was used instead of tetra-n-butyl titanate and the germanium atom was set to 50 ppm based on the theoretical yield of the polyester resin.

Example 1 Polyester A and polyester B were melt-extruded in separate extruders at 280 ° C., and T:
They were joined in a die and extruded. The extruded molten sheet was quenched below the glass transition temperature on a cast drum to form a substantially amorphous sheet. Subsequently, the amorphous sheet was 3.6 mm long at 80 ° C.
Double stretching was performed to obtain a uniaxially stretched film. 3. This uniaxially stretched film is transversely drawn at 100 ° C. with a tenter stretching machine.
The film was stretched 0-fold, heat-fixed at 235 ° C. while keeping the width fixed, relaxed 5% in the width direction at 200 ° C., cooled to room temperature and wound up to obtain a film having a total thickness of 9 μm.

Example 2 A mixed polyester obtained by mixing polyester B and polyester C at a weight ratio of 1: 1 was mixed with polyester A
Was used in the same manner as in Example 1 except that the total thickness was 9 μm.
m polyester film was obtained. Comparative Example 1 Except that polyester C was used instead of polyester A,
A polyester film having a total thickness of 9 μm was obtained in the same manner as in Example 1.

Comparative Example 2 A polyester film having a total thickness of 9 μm was obtained in the same manner as in Example 2 except that the mixing ratio of polyester B and polyester C was changed to 1: 2 by weight. Comparative Example 3 A polyester film having a total thickness of 9 μm was obtained in the same manner as in Example 2, except that the mixing ratio of polyester B and polyester C was changed to 5: 1 by weight. The resulting film could not be bonded due to lack of thermal adhesion.

COMPARATIVE EXAMPLE 4 The procedure of Example 2 was repeated except that polyester B was used in place of polyester B as the main constituent layer, and that the mixture ratio of polyester B and polyester C was 5: 4 by weight. An attempt was made to obtain a polyester film having a total thickness of 9 μm in the same manner as in Example 2. However, the film was melt-ruptured in the heat fixing step, and the film could not be collected.

Comparative Example 5 A polyester film was obtained in the same manner as in Comparative Example 4 except that the heat setting temperature was 210 ° C. At the time of bonding, the metal contracted remarkably and the metal was exposed at the end. Adhesion due to the formation of the dents was good at places where the metal was not exposed, but cracks occurred at the dents over time.

Comparative Example 6 A polyester film having a total thickness of 9 μm was obtained in the same manner as in Example 1 except that the discharge amount ratio between polyester A and polyester B was 7: 2. The film was very easily torn and easily broken when tension was applied to the film during lamination, so that lamination could not be performed without air entrapment or lamination wrinkles.

The results obtained above are summarized in Tables 1 to 3 below.
3 is shown.

[0029]

[Table 1] * In Table 1, ET stands for ethylene terephthalate unit, EI stands for ethylene isophthalate unit, and CT stands for cyclohexylene dimethylene terephthalate unit.

[0030]

[Table 2]

[0031]

[Table 3]

[0032]

Industrial Applicability The heat-adhesive polyester film of the present invention has excellent adhesiveness and is hard to be peeled off by heating or hydration, and is particularly useful as a corrosion-resistant coating for metal materials such as beverage cans and has a high industrial value. .

 ──────────────────────────────────────────────────の Continued on the front page F term (reference) 4F100 AB01C AK41A AK41B BA02 BA03 BA10B BA10C BA25 BA26 EH20 EJ38 GB16 JA04A JA04B JA12A JK06

Claims (1)

[Claims] 1. A multilayer film comprising a plurality of polyester layers, wherein at least one of the polyester layers constituting the surface has a heating rate at which a crystal melting peak can be detected when measuring a heating temperature from amorphous to DSC. C./min and the detected melting point (MP) is 190
~ 245 ° C, 60 times the total thickness of the multilayer film.
%, Wherein the constituent layer occupying at least 0.3% of the thickness is composed of a polyester having a melting point of not less than MP + 10 ° C.