JP3351158B2 - Stretched polyester film for packaging - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a packaging oriented polyester film of the ethylene 2,6-naphthalate as a main constituent. More specifically, the present invention relates to a stretched polyester film for packaging having good moldability, heat resistance, and tear resistance.

[0002]

2. Description of the Related Art Conventionally, a polyester biaxially stretched film represented by polyethylene terephthalate (hereinafter sometimes abbreviated as PET) has mechanical properties, electrical properties, chemical resistance, dimensional stability, and transparency. It is excellent in various properties such as, and is widely used in various fields. Particularly in the field of packaging materials, they are more environmentally friendly and have better mechanical properties than halogen-containing polymers such as polyvinyl chloride, and are relatively inexpensive. It has come to be used as a general packaging material mainly for applications.

On the other hand, in polyethylene terephthalate,
Of the packaging materials, applications where barrier properties are important are still insufficient, and barrier properties have been improved by laminating aluminum foil and barrier resin or by providing a metal thin film by vapor deposition. Not only is it complicated, but also the recovery of the packaging material is poor.

In recent years, compared to PET, mechanical properties, heat resistance,
Polyethylene naphthalate films have attracted attention because of their excellent gas barrier properties. An unstretched polyethylene naphthalate film has moldability but has low strength and is difficult to be made into a thin film. On the other hand, a biaxially stretched polyethylene naphthalate film is easy to be formed into a thin film and has high strength, but is liable to be broken and lacks reliability as a packaging material, and has not been used particularly in molding applications.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in the prior art, to have transparency, barrier properties, heat resistance and tear resistance, suitable for packaging materials, and to have good moldability. An object of the present invention is to provide a good stretched polyester film.

[0006]

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided
The stretched polyester film for packaging is composed of ethylene terephthalate containing 70 to 95% by weight of a polyester in which at least 80 mol% of the repeating structural units are ethylene-2,6-naphthalate units and particles having an average particle diameter of 0.001 to 5 µm. Polyester 5 to 3 as main constituent
0% by weight, containing 0.001 to 5% by weight of the particles in the whole polyester composition, and having a heat treatment temperature of 15 %.
0 to 300 ° C., and the refractive index in the thickness direction is 1.50 to
1.63.

[0007] The stretched polyester film of the present invention is composed essentially of ethylene-2,6-naphthalate, and comprises a polyester having a repeating unit of at least 80 mol% of ethylene-2,6-naphthalate in an amount of 70 to 70%.
It is necessary to contain 95% by weight. Further, the repeating structural unit is preferably at least 85 mol%, more preferably 90 mol%. If the amount of the ethylene-2,6-naphthalate unit is less than 80% by mole of the repeating structural unit, dimensional stability and mechanical properties are unfavorably poor. If it is 20 mol% or less, it may be modified by the following copolymer components.

As the copolymerization component, dibasic acid components such as terephthalic acid, 2,7-naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylsulfondicarboxylic acid, diphenyletherdicarboxylic acid, diphenoxyethanedicarboxylic acid, and 5-sodium Aromatic dicarboxylic acids such as sulfoisophthalic acid, 5-lithium sulfoisophthalic acid, 4-sodium sulfo-2,6-naphthalenedicarboxylic acid, phthalic acid, diphenyldicarboxylic acid, diphenylthioetherdicarboxylic acid, diphenylketonedicarboxylic acid, and phenylindanedicarboxylic acid acid,
Oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, aliphatic dicarboxylic acids such as fumaric acid,
Alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid,
Examples thereof include oxycarboxylic acids such as p-oxybenzoic acid, and polyether dicarboxylic acids such as polyethylene oxide dicarboxylic acid and polytetramethylene oxide dicarboxylic acid.

Further, as the glycol component, for example,
Aliphatic glycols such as ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol and neopentyl glycol, alicyclic glycols such as cyclohexanedimethanol, aromatic glycols such as bisphenol A and bisphenol S, polyethylene glycol, polypropylene glycol And polyalkylene glycols such as polytetramethylene glycol and polyethylene glycol-polypropylene glycol copolymer. The average molecular weight of the polyalkylene glycol or polyether dicarboxylic acid is preferably from 400 to 40,000, more preferably from 600 to 20,000, and still more preferably from 1,000.
〜１０10000.

In particular, 2,7-naphthalenedicarboxylic acid,
It is preferable that the isophthalic acid component be contained in an amount of 5 to 15 mol%, since the tear resistance and the moldability are improved. Of course, a plurality of dibasic acids or a plurality of glycols may be copolymerized, and as long as the effects of the present invention are not impaired, trimellitic acid, trimesic acid, and polyfunctional compounds such as trimethylolpropane are copolymerized. A thing may be used.

Furthermore, the average particle diameter is 0.001 to 5 μm
By mixing a polyester mainly composed of ethylene terephthalate containing particles of the above with the polyester, the tear resistance of the stretched film is improved, and the moldability in the process of forming the stretched film into a container or the like, Excellent releasability from mold. When the average particle diameter is less than 0.001 μm, the releasability from the mold is poor, and the average particle diameter is 5 μm.
If it exceeds m, not only the transparency deteriorates, but also the particles easily fall off. Here, the polyester having ethylene terephthalate as a main constituent component means that at least 80 mol% of the repeating structural units is ethylene terephthalate,
Further, the above copolymerization may be performed.

In the present invention, the particle content of the entire polyester composition is from 0.001 to 5% by weight. If the content of the particles is less than 0.001% by weight, the composition becomes sticky to the mold and causes molding failure, which is not preferable. On the other hand, when the content of the particles exceeds 5% by weight, the transparency is greatly deteriorated.

After the particles are thus contained in the polyester mainly composed of ethylene terephthalate, at least 80 mol% of the repeating structural units are ethylene-terminated.
It is presumed that by mixing with 2,6-naphthalate polyester, the crystallinity and orientation around the particles are close to those of PET, so that tear resistance and moldability are greatly improved.

Examples of the particles include so-called internal particles produced in a polymerization system, and external particles composed of inorganic, organic, or a composite thereof. As the internal particles, known internal particles can be suitably used, and as the external particles, for example, wet silica, dry silica, colloidal silica, titanium oxide, calcium carbonate, calcium phosphate, calcium fluoride, lithium fluoride, barium sulfate, Examples include inorganic particles such as zirconia, alumina, mica, talc, kaolin, and clay, and organic particles containing styrene, silicone, acrylic acid, and the like as constituent components. Among them, inorganic particles such as wet or dry silica or colloidal silica, alumina, and the like, and organic particles containing styrene, silicone, acrylic acid, methacrylic acid, polyester and the like as constituents are preferred. In particular, for packaging, particles of calcium carbonate, silica, crosslinked polystyrene, or polyester having a refractive index relatively close to polyester are preferable. The shape of these particles is not particularly limited, but is preferably spherical. Typical examples thereof include spherical silica and crosslinked polystyrene particles. In addition, two or more of these particles may be used in combination.

A method for incorporating particles into a polyester containing ethylene terephthalate as a main component is as follows.
There is a method using internal particles for precipitating a catalyst or the like to be added at the time of polyester polymerization reaction, a method of adding inert particles to a polyester synthesis reaction system, a method of melting and mixing polyester chips and particles with a twin-screw extruder, and the like. Either method may be used.

In the present invention, the refractive index in the thickness direction is required to be 1.50 to 1.63 in order to improve moldability and tear resistance. Preferably, the thickness direction refractive index is 1.52 to 1.62, more preferably 1.54 to 1.64.
1.61 is desirable in terms of moldability and tear resistance.

The stretched polyester film of the present invention may have a single-layer structure or a multilayer structure (laminated structure).
If at least one layer is made of a polyester having the characteristics described above, the tear resistance may be improved.
Other layers include polyethylene naphthalate layer, PET
Or a layer such as copolymerized polyester, or lubricity, coloring,
A layer for imparting antistatic properties and adhesiveness can also be provided.

In the present invention, when performing molding such as drape molding, straight molding, vacuum molding, cavity molding and drawing molding, the heat shrinkage at 120 ° C. for 30 minutes is 0.5% or less, preferably 0%. When it is not more than 0.4%, the shape of the corner after molding becomes sharper, which is preferable.

The production of a polyester in which at least 80 mol% of the repeating structural units of the present invention is ethylene-2,6-naphthalate can be carried out by any conventionally known method, and is not particularly limited. For example, 2,6-naphthalenedicarboxylic acid and optionally a small amount of other dicarboxylic acid component are directly transesterified with ethylene glycol and optionally a small amount of other glycol component, or dialkyl ester of dicarboxylic acid component is used. In this case, a polyester can be obtained by transesterification with a glycol component and heating it under reduced pressure to remove an excess glycol component.
At this time, it is preferable to use a transesterification reaction catalyst or a polymerization reaction catalyst as necessary, or to add a stabilizer and a coloring inhibitor. As the reaction catalyst, for example, an alkali metal compound, an alkaline earth metal compound, a zinc compound, a lead compound, a manganese compound, a cobalt compound, an aluminum compound, an antimony compound, a germanium compound, a titanium compound, among which an antimony compound and a germanium compound are preferable, Examples of the stabilizer and the coloring inhibitor include a phosphorus compound. Examples of antimony compounds include antimony trioxide, antimony pentoxide, antimony acetate, antimony glycolate, and germanium compounds such as germanium dioxide, germanium acetate, germanium tetramethoxide, germanium tetraethoxide, germanium tetrabutoxide, and germanium ethylene glycoloxide. Germanium alkoxide compounds, water-containing germanium hydroxide, phosphorus-containing germanium compounds such as germanium phosphate,
Germanium phenoxide compounds such as germanium phenolate are exemplified. Examples of the phosphorus compound include phosphoric acid and its ester, phosphorous acid and its ester, phosphonic acid and its ester, phosphinic acid and its ester, and those having a small reducing action such as phosphoric acid and a phosphoric acid ester Is preferred.
The polymerization temperature is preferably as low as possible as long as the polymerization state can be maintained. Of course, coloring inhibitors,
An antioxidant, a nucleating agent, a lubricant, an antiblocking agent, an ultraviolet absorber, an antifoaming agent, an antistatic agent and the like may be added.

Further, the production of a polyester containing ethylene terephthalate as a main component is also carried out by a known method, but it is necessary to incorporate external particles as necessary. When adding external particles to the reaction system, it is preferable to add them in the form of an ethylene glycol slurry.

The oriented polyester film of the present invention is preferably produced by melt extrusion. Polyester is
At the time of vacuum drying, a predetermined amount of a specific particle master polymer is added and mixed, and after vacuum drying, it is supplied to a melt extruder and discharged from a slit-shaped ordinary die. The melt is cooled and solidified on a rotating cooling drum having a mirror-finished surface or a roughened surface to obtain a substantially amorphous cast film. When cooling on a rotating cooling drum, it is preferable to adopt an electrostatic application casting method from the viewpoint of uniformity of thickness.

The polyester film of the present invention may be a uniaxially stretched film, but is preferably biaxially stretched in order to impart mechanical strength, and an ordinary polyester biaxial stretching method can be employed. It is performed by simultaneous biaxial stretching by a tenter method or sequential biaxial stretching. In the case of sequential biaxial stretching, stretching in the longitudinal direction or the width direction can be performed twice or more.

The stretching temperature is at least 80 for the repeating structural units.
Any temperature can be used as long as it is in the range of not less than the glass transition temperature of the polyester in which mol% is ethylene-2,6-naphthalate and not more than the temperature-raising crystallization temperature. The temperature is preferably 110 to 180 ° C and 120 to 200 ° C in the case of stretching in the width direction. The stretching ratio in the longitudinal and width directions of the film can be arbitrarily set according to the desired degree of orientation, strength, elastic modulus, etc. of the film.

Further, after the biaxial stretching, the film is subjected to a heat treatment. This heat treatment can be performed by any conventionally known method such as in an oven or on a heated roll. The heat treatment temperature is 150 to 300 ° C. Although the heat treatment time can be arbitrarily set, it is usually preferable to perform the heat treatment for 0.5 to 60 seconds. The heat treatment causes the film to move in its longitudinal direction and / or
Alternatively, it may be performed while relaxing in the width direction.

The intrinsic viscosity of the polyester film of the present invention is preferably in the range of 0.4 to 1.2, more preferably 0.5 to 1.1, particularly preferably 0.6 to 1.0.

The haze value of the film is preferably 10% or less, more preferably 5% or less. Haze value is 10%
If it exceeds, transparency as a packaging material is lacking.

The surface condition of the stretched polyester film of the present invention is such that the center line average roughness Ra is 0.030 μm or less and the maximum roughness Rt is 0.5 μm in order to maintain good transparency and maintain good transparency. The following is preferred. The center line average roughness Ra is more preferably 0.020.
μm or less, particularly preferably 0.015 μm or less.
Further, the maximum roughness Rt is more preferably 0.3 μm or less, particularly preferably 0.2 μm or less.

The thickness of the film is 1 to 1000 μm
m, preferably 1 to 100 μm. In the production of the stretched polyester film of the present invention, additives such as an antioxidant, a plasticizer, an antistatic agent, a weathering agent, an unsealed blocking agent, and a dye can be used as needed.

The stretched polyester film of the present invention is subjected to various surface treatments such as corona discharge treatment, chemical treatment, flame treatment, ultraviolet treatment, plasma treatment, etc., as required, in order to improve the adhesiveness and ink adhesion. be able to.

[Method of measuring and evaluating properties] The properties of the polyester film were measured and evaluated by the following methods. (1) Intrinsic viscosity Measured at 25 ° C. using o-chlorophenol as a solvent.

(2) Thermal Shrinkage A film sample having a width of 10 mm and a length of 250 to 300 mm is marked at intervals of 200 mm, fixed on a sample support plate under a constant tension, and used as a universal projector (manufactured by Nippon Kogaku Co., Ltd.).
V16A), the original length of the marking interval was measured.
A load was applied to the measured sample using a 3 g clip, and the sample was processed while rotating in a hot air oven set at 100 ° C. for 30 minutes. The treated sample was left for 2 hours in the atmosphere in which the original length was measured, and then the marking interval was measured in the same manner as in the original length measurement method to determine the shrinkage.

(3) Refractive index in thickness direction Measured using an Abbe refractometer with sodium D line (wavelength 589 nm) as a light source.

(4) Tear Propagation Resistance Using a light load type tear tester (manufactured by Toyo Seiki Co., Ltd.),
It was measured according to STM-D-1922. The sample size was 51 × 64 mm, a 13 mm cut was made in the longitudinal direction, and the indicated value when the remaining 51 mm was torn was read, and the smaller value in the film longitudinal direction and the width direction was used.

(5) Film haze Film haze was measured according to ASTM-D1003-52.

(6) Average particle size of particles The polyester portion is removed from the sample by a plasma low-temperature incineration method (for example, PR-503, manufactured by Daiwa Chemical Co., Ltd.) to expose the particles. The processing conditions are selected such that the polyester is ashed but the particles are not damaged. This is observed with a SEM, and the image of the particles is analyzed with an image analyzer (for example, QTM90 manufactured by Cambridge Instruments).
0), the frequency distribution of 500 or more observed particles is obtained, and the particle diameter showing the peak value is defined as the average particle diameter. When two or more peak values appear, it is determined that two or more types of particles having different average particle diameters are added based on the respective peak values. In the case of internal particles, a cross section of the polymer is cut to form an ultrathin section having a thickness of about 0.1 to 1 μm, and a photograph is taken using a transmission electron microscope at a magnification of about 5000 to 20,000 times (10 sheets: 25 cm × 25 cm), and the average particle diameter of the internal particles was determined from the equivalent circle diameter.

(7) Content of particles The polyester is dissolved, and the sample is dissolved using a solvent (eg, o-chlorophenol or the like) that does not dissolve the particles, and the particles are centrifuged from the solution to obtain the total weight of the sample. The weight ratio (% by weight) of the particles with respect to is defined as the particle content. In the case where two or more types of particles having different average particle diameters are added, the peak height of the frequency distribution is considered as the addition ratio of each particle, and the weight ratio is calculated from the average particle diameter and the specific gravity. The values converted into are used as the respective particle contents.

(8) Center line average roughness Ra, maximum roughness Rt A high-precision thin film step measuring device ET-10 manufactured by Kosaka Laboratory Co., Ltd.
It measured using. The conditions were as follows, and the value was an average value of 20 measurements.・ Stylus tip radius: 0.5 μm ・ Stylus load: 5 mg ・ Measurement length: 1 mm ・ Cutoff value: 0.08 mm Note that Ra and Rt are defined, for example, by Jiro Nara, “Surface roughness measurement / evaluation”. Law "(General Technology Center, 1983)
Is shown.

(9) Formability a. Elongation The elongation at break was measured at a speed of 200 mm / min using Tensilon, and the smaller value was taken in the longitudinal direction and the width direction of the film. b. Vacuum Formability At 100 to 200 ° C., draw forming (forming ratio (height /
(Diameter) = 0.15), and the moldability was determined by the following evaluation. Class A: Having sharp corners and a molding zone with good transparency in a temperature range of 10 ° C. or higher. Class B: Has sharp corners and a molding zone with good transparency in a temperature range of 5 ° C. or more and less than 10 ° C. Class C: The temperature range having sharp corners and molding zones with good transparency is less than 5 ° C., and molding stability is poor. Class D: stable molding cannot be obtained.

[0039]

The present invention will be described in detail with reference to the following examples, but the present invention is not limited to these examples. Example 1 100 parts by weight of dimethyl 2,6-naphthalenedicarboxylate and ethylene glycol (hereinafter abbreviated as EG) 51 were placed in a transesterification reactor equipped with a stirrer, a rectification column, and a condenser.
Parts by weight, 0.06 parts by weight of calcium acetate and 0.025 parts by weight of antimony trioxide were added.
The temperature was gradually raised to ° C., and the transesterification reaction was carried out while simultaneously distilling the produced methanol out of the reaction system. 0.04 parts by weight of trimethyl phosphate was added to the reaction product thus obtained, and the mixture was reacted for 5 minutes. Subsequently, while continuously distilling ethylene glycol, 28
The temperature was raised to 5 ° C., and simultaneously the pressure was reduced to 0.2 mmHg to carry out a polycondensation reaction, thereby obtaining polymer pellets having an intrinsic viscosity of 0.67.

On the other hand, as a particle master, an average particle diameter of 0.1 was used.
A particle master A (first particle) composed of polyethylene terephthalate containing 2% by weight of 5 μm SiO ₂ and a particle master B composed of polyethylene terephthalate containing 1% by weight of SiO ₂ having an average particle diameter of 2 μm (second particle) ) Was prepared. Then, add the above polymer pellets to 1
Precrystallized at 50 ° C. Next, the above-mentioned two types of particle masters A and B prepared in advance were added to the polymer pellets in an amount of 0.01% for the first particles.
The mixture was added and mixed so that the amount of the second particles became 15% by weight and the amount of the second particles added was 0.006% by weight, followed by vacuum drying at 180 ° C.

Then, it was fed to an extruder, melted at 295 ° C., discharged from a usual die, cooled and solidified by a cooling drum to prepare an unstretched sheet. The obtained unstretched sheet is
3.5 times vertically at 35 ° C, 3.5 times horizontally at 140 ° C
After biaxial stretching twice, the relaxation rate was set to 3%, and 18%.
Heat treatment was performed at 0 ° C. for 2 seconds to obtain a biaxially stretched film having a thickness of 25 μm. Table 1 shows the properties of the obtained film. Both tear resistance and moldability were excellent.

Example 2 A film was obtained in the same manner as in Example 1 except that the particle master was changed and the stretching ratio was 2.0 times in both the vertical and horizontal directions. Table 1 shows the properties of the obtained film. Both tear resistance and moldability were excellent.

Example 3 In Example 1, the particle master B was changed to an internal particle-containing master (in which internal particles were formed by adding calcium acetate, lithium acetate, trimethyl phosphate, phosphorous acid, and antimony trioxide). , Heat treatment temperature 140 ° C,
A film was obtained in the same manner as in Example 1 except that the relaxation rate was set to 0%. Table 1 shows the properties of the obtained film.
Although both tear resistance and moldability were good, the heat shrinkage was large and the moldability was slightly reduced.

Example 4 In Example 1, isophthalic acid was added in an amount of 10
Mole% copolymerized polyethylene naphthalate (A), polyethylene naphthalate (B), and polyethylene terephthalate (C) containing particles were used, and each resin was melted by a plurality of extruders, and (B + C) ) / (A + C) / (B + C) was obtained in the same manner as in Example 1, except that the heat treatment temperature was 210 ° C. Was. Table 2 shows the properties of the obtained film. Particularly excellent in both tear resistance and moldability were obtained.

Comparative Example 1 A film was obtained in the same manner as in Example 1, except that the stretching ratio was 4.9 times vertically and 4.2 times horizontally and the heat treatment temperature was 200 ° C. Table 2 shows the properties of the obtained film. Both the tear resistance and the moldability were greatly reduced.

Comparative Example 2 A film was obtained in the same manner as in Example 1, except that only polyethylene naphthalate containing particles was used.
Moldability and tear resistance were greatly reduced.

[0047]

[Table 1]

[0048]

[Table 2]

[0049]

According to the present invention, ethylene-2,6-
By mixing a polyester mainly composed of naphthalate and a polyester mainly composed of ethylene terephthalate containing particles to produce a stretched film, the moldability, tear resistance, heat resistance and barrier properties are particularly good. it can be obtained Do oriented polyester film can be suitably used in the fields of packaging materials.

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Claims (3)

(57) [Claims] 1. 70 to 95% by weight of a polyester in which at least 80 mol% of the repeating structural units are ethylene-2,6-naphthalate units, and an average particle size of 0.001 to 5 μm.
m to 5% to 30% by weight of a polyester mainly composed of ethylene terephthalate containing particles having a particle size of 0.001 to 5%.
% By weight, the heat treatment temperature is 150 to 300 ° C.,
A stretched polyester film for packaging , having a thickness direction refractive index of 1.50 to 1.63. 2. A stretched polyester film for packaging having a laminated structure in which at least one layer is the film layer according to claim 1. 3. The heat shrinkage at 120 ° C. for 30 minutes is 0.5
% Or less of the stretched polyester film for packaging according to claim 1 or 2.