JP2000108284A - Metal laminating polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film which is excellent in a thermal adhesion property to a metal plate and operating properties after coating the metal, free from injuries to environment and a human body, and suitable for, for example, an inner surface coating use or the like of a metallic container. SOLUTION: A metal laminating polyester film is a film comprising at least two layers of polyester layers, an in-plane mean refractive index of a layer A comprising one side surface is at most 1.580, an in-plane mean refractive index of a layer B comprising the other side surface is at least 1.630, and at least the layer B is composed of a polyester polymerized by using a titanium compound as a polymerization principal catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a polyester film for bonding to a metal plate.

[0002]

2. Description of the Related Art In recent years, the number of cases where a thermoplastic resin film is coated on a metal plate and used as a material for a metal can has been increasing. It is difficult to completely eliminate metal exposure due to pinholes even if the amount of paint applied is large or the coating is performed multiple times, even if the paint is applied to a conventional metal plate and the paint is applied and baked to form a film. On the other hand, in the case of a metal plate coated with a thermoplastic resin film, the metal exposure can be almost completely eliminated, and since the ductility is superior to that of a thermosetting resin-based coating, the processing characteristics are good. This is because there is an advantage. In addition, in the case of painting, a large amount of solvent is used in the application and drying and baking of the paint, so the environmental burden is high. In the case of epoxy resin, which is one of the common metal coatings, it is regarded as an endogenous endocrine disrupting substance. Since it contains bisphenol A, there is a concern about the effects not only on the environment but also on the human body. In contrast, coating with a thermoplastic resin film can suppress these environmental loads and exclude the effects on the human body.

[0003] Materials for the film to be used include polyolefin, polyvinyl chloride, polyester, fluororesin and the like. Polyolefin is inexpensive but has poor heat resistance, and is not suitable for beverages because of its resin odor and adsorption of aroma components. Applications are limited, such as not being suitable for containers. Polyvinyl chloride tends to suppress the use of the polymer material itself. Fluororesins are excellent in properties but very expensive, and their use is limited to special applications.
On the other hand, despite being relatively inexpensive, polyester is excellent in heat resistance, strength, and gas barrier properties, is widely used as a material for tableware and beverage containers, and is also widely used as a metal container coating film.

[0004] As described above, although a polyester film is suitable as a metal coating material, a film made of polyethylene terephthalate, which is the most common polyester material, has almost no heat-fusing property to metal, and thus is coated with an adhesive. It is essentially the same as painting in terms of environmental burden due to the use of large amounts of organic solvents. On the other hand, a method of introducing a copolymer component into polyethylene terephthalate and controlling the crystallinity of the film to obtain heat fusibility has been considered, but since the heat fusibility is high, the bonding process and In the heat molding process after bonding, the slipperiness of the polyester film coating layer with respect to the metal jig is extremely poor, and the coating layer may be damaged, or in extreme cases, each molding machine may be stopped or damaged.

[0005] Most of polyesters that are currently used industrially, such as for fiber, film and injection molding, are produced using an antimony compound as a main polymerization catalyst. The antimony compound inherent in the polyester does not precipitate in ordinary handling, but a very small amount of precipitation is observed in a wet heating state such as a retort treatment usually applied to beverages such as tea. The antimony element itself is a substance that is monitored by setting a standard value according to the Water Supply Law and the like, and it is required that the coating film has no deposition even in a trace amount.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to solve the problem of excellent heat adhesion to a metal plate and excellent operability after metal coating. An object of the present invention is to provide a film which is not harmful and is suitable for, for example, an inner surface coating of a metal container.

[0007]

Means for Solving the Problems As a result of intensive studies in view of the above problems, the present inventor has found that the above problems can be easily solved by using a film having a specific structure and a multilayer structure, and has completed the present invention. I came to. That is, the gist of the present invention is a film comprising two or more polyester layers, wherein the in-plane average refractive index of the A layer constituting one surface is 1.580 or less, and the B layer constituting the other surface. Wherein the in-plane average refractive index is 1.630 or more, and at least the B layer is made of a polyester polymerized by using a titanium compound as a main polymerization catalyst.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The polyester referred to in the present invention is a polymer in which a repeating unit having a carboxy group terminal and a hydroxy group terminal is polymerized through an ester bond. The repeating unit may be one in which a dicarboxylic acid or a dicarboxylic acid ester and a diol are condensed and have an ester bond inside the repeating unit. Examples of dicarboxylic acids include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid and 2,6-naphthalenedicarboxylic acid, and aliphatic dicarboxylic acids such as adipic acid, azelaic acid and sebacic acid. Examples of dicarboxylic esters include:
Examples thereof include dimethyl terephthalate and dimethyl isophthalate in which the terminal of the dicarboxylic acid described above is methoxide. Examples of the diol include ethylene glycol, trimethylene glycol, tetramethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol and the like.

In the polyester film of the present invention,
At least one surface of the layer B is formed by polymerizing the polyester using a titanium compound as a polymerization catalyst. Examples of titanium compounds include tetrapropyl titanate, tetraisopropyl titanate, tetrabutyl titanate, and the like. The main polymerization catalyst of the polyester is usually 1 to 50 ppm, preferably 1 to 25 ppm in terms of titanium element amount.
ppm, more preferably 1 to 15 ppm. If the amount of titanium is too small, a large amount of time is required for polymerization, so that it tends to be unsuitable for industrial production.

[0010] The polyester film of the present invention is desirably composed not only of the B layer but also of all layers of a polyester polymerized using a titanium compound. In the retort treatment, the elution target is not only the layer B that is in direct contact with the beverage, but in the case of a film of 20 μm or less, the entire layer is subject to elution of the catalyst compound by the retort. This is because there is a possibility that the polymerization main catalyst is eluted from the unexposed A layer or other intermediate layers.

The in-plane average refractive index of the layer A constituting one surface of the film of the present invention must be 1.580 or less. If the in-plane average refractive index of the layer A exceeds 1.580, the molecular orientation exists, so that the fluidity of the bonding interface with the metal during thermal bonding is insufficient, and the thermal adhesive force is insufficient. In addition, since the layer A has substantially no molecular orientation, it tends to be inferior in strength to a standard polyester film, and the ratio to the whole film is preferably not too high. Specifically, it is desirable that the thickness of the layer A is 30% or less of the total thickness. However, if the absolute value of the thickness of the layer A is less than 0.5 μm, the thermal adhesiveness itself may be insufficient. When the total thickness is small, the ratio of the layer A thickness to the total thickness may be 30% or more.

The in-plane average refractive index of the layer B constituting one surface of the present invention must be 1.630 or more. If the in-plane average refractive index of the B layer is less than 1.630, the molecular orientation of the B layer as the outermost layer during metal coating is insufficient, and a sufficient film strength, particularly a shear strength against surface friction, cannot be obtained. However, simply increasing the strength by imparting the molecular orientation does not necessarily completely prevent the film from being damaged by surface friction in the molding process, so that the surface roughness of the B layer is in the range of 0.5 to 2.0 μm. It is preferable that If the surface roughness is less than 0.5 μm, the film tends to have insufficient slipperiness, and the film may be damaged in the forming step. When the surface roughness exceeds 2.0 μm, the true contact area is too small, and stress concentration occurs on a small number of surface projections, so that the film tends to be easily worn.

In order to form such a surface, fine particles made of metal oxide or the like are contained in the layer B, and surface projections having the particles as nuclei are formed near the surface layer in a stretching step, a can making step, or the like. It is recommended to provide slipperiness. As the particles to be used, inorganic compounds such as silicon oxide, aluminum oxide, kaolin, talc, and calcium carbonate, and organic compounds such as polystyrene-based crosslinked polymer particles are preferable. If these particles are too small, the effect of imparting lubricity is thin, and if they are too large, they cause coating defects due to falling off of the particles. Therefore, it is desirable that the particles contained in the layer B have a particle size of 2 to 10 μm. When at least one kind of particles satisfies the above-mentioned particle size range,
Particles smaller than 2 μm may be contained depending on various other purposes such as coloring and antistatic purposes.

Further, the polyester film of the present invention comprises:
The heat shrinkage in the width direction at 200 ° C. is preferably 5% or less, more preferably 2% or less. The most common form of bonding a film to a metal is to unwind a metal plate and a film, each of which is in the form of a roll, and bond them together with a laminate nip roll. At this time, the metal plate is 200
Since the film is preheated to a temperature of at least ℃, heat shrinkage stress occurs immediately before the film comes into contact with metal. Unlike the tensioned longitudinal direction, the width direction can cause dimensional changes due to the stress.

[0015]

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 present invention. In the following examples, “parts” means parts by weight. Also,
The measurement method used for the evaluation is as follows.

(1) Evaluation of Catalyst The amounts of the respective elements were identified and quantified using a fluorescent X-ray spectrometer XRF1500. In the evaluation of the coating layer on the metal plate or the metal container, the solvent was distilled off from the solution in which the coating layer was dissolved and recovered using hexafluoroisopropanol to obtain a measurement sample piece. (2) Average refractive index in the plane of the film The main axis of the film molecular orientation was determined using a polarizing microscope.
The arithmetic average of the refractive index in the direction of the molecular orientation main axis and the refractive index in the direction perpendicular to the main axis was defined as the average refractive index in the film plane. The refractive index in each direction was measured using an Abbe refractometer. At the time of measurement, the layer B was brought into close contact with the prism,
The measurement was performed by placing a test piece having a refractive index of 1.92 on the layer. A sodium lamp was used as a light source. The refractive index of the layer A was determined from the first light-dark boundary line. Since the dark area was further present in the dark area in the measurement of the refractive index of the A layer, the refractive index at the boundary between the bright and dark areas was read and set as the refractive index of the B layer. Further, methylene iodide was interposed between the layer B and the prism, and between the layer A and the test piece, and they were sufficiently adhered to each other.

(3) Surface Roughness From the cross-sectional curve obtained by using a surface roughness measuring instrument SE-3F manufactured by Kosaka Laboratory Co., Ltd., the fifth from the highest in the cross-sectional curve of a portion extracted by a reference length of 2.5 mm. The difference between the average of the altitudes of the peaks up to and t and the average of the altitudes of the valley bottoms from the deepest to the fifth was calculated. The above difference was determined for ten different locations, and the arithmetic average was defined as the surface roughness. The radius of the stylus used at this time was 2.0 μm, and the load was 30 mg.
And the cutoff value was 0.08 mm. (4) Sb elution test A sample film of the same shape and the same size is bonded to one side of a 100 mm x 200 mm aluminum plate with a heating nip roll with the layer A as a bonding surface. The obtained film-coated aluminum plate was subjected to an inner diameter of 50 mm and a capacity of 300.
into a pressure-resistant tube with 300 ml of distilled water,
After being immersed in an oil bath at 30 ° C. for 30 minutes, it was gradually cooled at room temperature. The internal distilled water was measured by ICP, and the amount of Sb element was quantified.

(5) Observation of Content Particles A sample piece obtained by sectioning a film embedded in an epoxy resin with a microtome is subjected to cross-sectional observation with a scanning electron microscope to measure the particle size of the content particles. did. Further, the main constituent elements of the particles were evaluated by EDX irradiation. (6) Thermal Shrinkage Rate A sample having a width of 2 cm and a length of 100 cm was cut out, Nikka Rico made by Nikka Co., Ltd. was sprinkled on the surface of the film, and then subjected to free-end heat treatment at 200 ° C. for 5 minutes in a hot air oven. The heat shrinkage was calculated according to the following equation, where the length of the sample after the heat treatment was Lcm.

[0019]

## EQU1 ## Heat shrinkage (%) = 100-L The polyester used in Examples and Comparative Examples was produced by the following method.

(Production of polyester) Polyester A 100 parts of dimethyl terephthalate, ethylene glycol 6
0 parts and 0.1 part of calcium acetate-water salt were placed in a reactor and transesterified. That is, the reaction start temperature is set to 1
The temperature was raised to 70 ° C., and the reaction temperature was gradually raised with the distillation of methanol. After 4 hours, the temperature was raised to 230 ° C. to substantially end the transesterification reaction. Next, after adding 0.04 part of phosphoric acid, 0.005 part of tetrabutyl titanate was added, and a polycondensation reaction was performed. That is, the temperature is gradually increased and the pressure is gradually decreased.
C., the pressure was set to 0.3 mmHg, and after several hours, the reaction was stopped to obtain polyester A.

Polyester B 100 parts of dimethyl terephthalate, ethylene glycol 6
0 parts and 0.1 part of calcium acetate-water salt were placed in a reactor and transesterified. That is, the reaction start temperature is set to 1
The temperature was raised to 70 ° C., and the reaction temperature was gradually raised with the distillation of methanol. After 4 hours, the temperature was raised to 230 ° C. to substantially end the transesterification reaction. Next, an ethylene glycol slurry containing amorphous silica having a particle size of 2.5 µm and 0.04 part of phosphoric acid were added, and then 0.005 part of tetrabutyl titanate was added to carry out a polycondensation reaction. That is,
The temperature was gradually increased and the pressure was gradually decreased. After 2 hours, the temperature was set to 280 ° C. and the pressure was set to 0.3 mmHg. After several hours, the reaction was stopped to obtain Polyester B. The silica content in Polyester B was 2 parts.

Polyester C Polyester C was prepared in the same manner as polyester A except that 78 parts of dimethyl terephthalate and 22 parts of dimethyl isophthalate were used instead of 100 parts of dimethyl terephthalate.
I got Polyester D Polyester D was obtained in the same manner as polyester A, except that 0.05 parts of antimony trioxide was used instead of 0.005 parts of tetrabutyl titanate.

Polyester E Polyester E was obtained in the same manner as polyester C, except that 0.05 parts of antimony trioxide was used instead of 0.005 parts of tetrabutyl titanate. Polyester F 1.5μ particle size instead of 2.5μm amorphous silica
Polyester F was obtained in the same manner as polyester B except that amorphous silica was used. Polyester F obtained
The silica content therein was 0.6 part.

Example 1 A mixed polyester I and a polyester C each composed of 85 parts of polyester A and 15 parts of polyester B were melted in separate extruders, and coextruded from a T-die, immediately quenched to a temperature lower than the glass transition temperature, and substantially cooled. Thus, an amorphous polyester sheet was obtained. In the co-extrusion, the discharge ratio of the mixed polyester I and the polyester C was 5: 1.
And The obtained amorphous polyester sheet was stretched 3.5 times in the longitudinal direction at 83 ° C. using a roll stretching machine.
Next, using a tenter stretching machine, the film was stretched 4.2 times in the transverse direction at 110 ° C., and subsequently heat-fixed at 240 ° C. with the width fixed in the tenter to obtain a polyester film. The thickness of the obtained polyester film is 12 μm
was.

Example 1 A mixed polyester I and a polyester C each composed of 85 parts of polyester A and 15 parts of polyester B were melted by separate extruders, and coextruded from a T-die was immediately cooled to a temperature lower than the glass transition temperature. Thus, a substantially amorphous polyester sheet was obtained. In the co-extrusion, the discharge ratio of the mixed polyester I and the polyester C was 5: 1. The obtained amorphous polyester sheet was stretched 3.5 times in the longitudinal direction at 83 ° C. using a roll stretching machine. Next, using a tenter stretching machine, the film was stretched 4.2 times in the transverse direction at 110 ° C., and then heat-set at 240 ° C. while the width was fixed in the tenter to obtain a polyester film. The thickness of the obtained polyester film is 1
It was 2 μm.

Comparative Example 1 A polyester film was obtained in the same manner as in Example 1 except that polyester D was used instead of polyester A. The thickness of the obtained polyester film was 12 μm.

Example 2 A polyester film was obtained in the same manner as in Example 1 except that polyester E was used instead of polyester C. The thickness of the obtained polyester film was 12 μm. Comparative Example 2 A polyester film was obtained in the same manner as in Example 1 except that the heat setting temperature was 190 ° C. The thickness of the obtained polyester film was 12 μm.

Comparative Example 3 A polyester film was obtained in the same manner as in Example 1 except that the longitudinal stretching ratio was 2.5 and the transverse stretching ratio was 3.5. The thickness of the obtained polyester film was 12 μm. Example 3 A polyester film was obtained in the same manner as in Example 1 except that polyester F was used instead of polyester B. The thickness of the obtained polyester film was 12 μm. The results obtained above are summarized in Tables 1 and 2 below.
Shown in

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

The polyester film of the present invention is suitable for coating the inner surface of a metal container, has excellent heat adhesion to a metal plate and excellent operability after metal coating, and has a very high industrial value.

Claims (3)

[Claims] 1. A film comprising two or more polyester layers, wherein the in-plane average refractive index of the A layer constituting one surface is 1.580 or less and the in-plane average refractive index of the B layer constituting the other surface. A polyester film for metal bonding, wherein the polyester film has an average refractive index of 1.630 or more and at least the layer B is made of a polyester polymerized using a titanium compound as a main polymerization catalyst. 2. The surface roughness of the layer B is 0.5 to 2.0 μm.
The polyester film for metal bonding according to claim 1, wherein m is m. 3. The polyester film for metal bonding according to claim 1, wherein all the layers are made of a polyester polymerized by using a titanium compound as a main polymerization catalyst.