JP2002052673A - Laminated polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated polyester film having heat sealability, capable of being easily opened linearly without scattering content and excellent to prevent the adhesion of a powder. SOLUTION: A biaxially oriented laminated polyester film comprising a co-extrusion laminated polyester film consisting of at least two layers, that is, a layer having a sea-island structure simultaneously satisfying formula (1): 50<=X/Y and formula (2): 5<=N<=200 [wherein, X is a mean value (μm) of the length on the longitudinal direction of the film of island parts, Y is a mean value (μm) of the length in the lateral direction of the film of island parts and N is the number of island parts per μm2 present in the cross section in the lateral direction of the film] and a layer constituted of polyester with a melting point of 220 deg.C or lower.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a laminated polyester film having excellent tear linearity in at least one direction and useful as a packaging material for foods such as confectionery, soups, pickles, retort pouches, and pharmaceuticals. is there.

[0002]

2. Description of the Related Art Biaxially stretched polyester films represented by polyethylene terephthalate are known for their excellent mechanical properties, electrical properties, chemical resistance, dimensional stability and the like.
It is used as a base material in many fields such as information recording materials, capacitors, packaging, plate making, discharging, and photographic films.

In recent years, these polyester films have been used as various packaging films by taking advantage of the excellent characteristics thereof, and as the awareness of the importance of environmental issues has been increasing, in particular, polyester films have reduced environmental pollution during their disposal. The scope of use is going to be further expanded in the future because it can be done.

[0004] The polyester film for packaging is widely used, and is required in various industrial fields such as foods, various electric / electronic parts, machines, equipment, building materials, chemicals and the like.

[0005] For packaging foods, medicines and miscellaneous goods, packaging bags using various plastic films are often used. For example, a heat-sealing film is used for a retort pouch or the like. However, since the tearability at the time of opening is poor and the tearing is not performed linearly, there are problems such as scattering of contents and soiling of clothes.

[0006] In addition, packaging bags using a plastic film having antistatic properties are often used for packaging powders. However, packaging bags having poor hand-cutting properties or packaging bags in a direction different from the intended direction are used. There is a case where tears occur and the contents scatter, causing trouble.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a heat-sealing property so that the contents can be easily and linearly opened without scattering. Another object of the present invention is to provide a laminated polyester film excellent in preventing powder adhesion.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that the above-mentioned problems can be easily solved by a film having a specific structure, thereby completing the present invention. Reached.

That is, the gist of the present invention is as follows:
A layer having a sea-island structure that simultaneously satisfies (2) and
A biaxially oriented laminated polyester film characterized by being a co-extruded laminated polyester film comprising at least two layers, including a layer composed of a polyester having a melting point of 220 ° C. or lower.

50 ≦ X / Y (1) 5 ≦ N ≦ 200 (2) (in the above formula, X is the average length (μm) of the length of the island in the film longitudinal direction, and Y is the film width of the island. Average length in the direction (μ
m) and N are the number of islands present in the cross section in the film width direction (pieces / μm ² ))

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The polyester in the present invention includes, for example,
A polymer containing an ester group obtained by polycondensation from a dicarboxylic acid and a diol or from a hydroxycarboxylic acid. Examples of dicarboxylic acids include terephthalic acid, succinic acid, isophthalic acid, adipic acid, azelaic acid, sebacic acid, dodecane diacid, 2,6-naphthalenedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid. Glycol, 1,3-
Propanediol, 1,6-hexanediol, 1,4
-Butanediol, diethylene glycol, triethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, polyethylene glycol and the like, and hydroxycarboxylic acids such as p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, respectively. Examples can be given.

Representative examples of such polymers include polyethylene terephthalate and polybutylene terephthalate. These polymers may be homopolymers or copolymers of the third component.

The film of the present invention is a co-extruded laminated biaxially oriented film having at least two layers, one of which is made of polyester having a melting point of 220 ° C. or less,
Those having a layer composed of polyester having a melting point of 200 ° C. or lower, more preferably 180 ° C. or lower are preferable. Melting point 22
A layer composed of polyester having a temperature higher than 0 ° C. is not practical in heat sealability, and a film composed only of such a layer is not practical due to poor tear straightness and uneven thickness.

The film of the present invention includes a layer having a sea-island structure, and such a layer must simultaneously satisfy the following formulas (1) and (2).

50 ≦ X / Y (1) 5 ≦ N ≦ 200 (2) (In the above formula, X is the average length (μm) of the island in the longitudinal direction of the film, and Y is the film width of the island. Average length in the direction (μ
m) and N are the number of islands present in the cross section in the film width direction (pieces / μm ² ). If X / Y is less than 50, the tear linearity of the film is impaired. On the other hand, if N is less than 5 (pieces / μm ² ), the tear linearity of the film is remarkably reduced, and 200 (pieces / μm ² ) is obtained.
When the number exceeds, the number of polyesters dispersed in the layer is too large, and it is difficult to perform linear tearing.

In the present invention, the layer having a sea-island structure is
Polyester units (preferably composed of a dicarboxylic acid component containing at least 50 mol% of an aromatic dicarboxylic acid and a glycol component containing 50 mol% or more of a glycol having 3 to 10 carbon atoms) and a polyalkylene glycol unit (the following formula) It is preferable to include a polyester D having (3) a polyester having a repeating unit structure) and a polyester A having ethylene terephthalate as a main repeating unit.

[0018]

HO— (CH ₂ ) _n —OH (3)
3 ≦ n ≦ 10 The mixing ratio of polyester D and polyester A is usually polyester D / polyester A = (30 to 5) / (70 to
95) (weight ratio), preferably (25-10) /
(75-90), more preferably (20-10) /
(80-90). If the mixing ratio of the polyester D is less than 5% by weight, the tear linearity of the film may be poor. On the other hand, when the mixing ratio of the polyester D exceeds 30% by weight, the mechanical strength of the film is reduced and the thickness unevenness is increased, which may be impractical.

As described above, the constituent components of the polyester D of the present invention are a polyester unit and a polyalkylene glycol unit, and the component ratio is usually polyester unit / polyalkylene glycol unit = (55 to 98) /
(45-2), preferably (5-30) / (95
To 70), more preferably (10 to 25) / (90 to
75). If the polyalkylene glycol unit content is less than 2% by weight, polyester D in polyester A
Tends to be less likely to occur in island form, and the tear linearity tends to be poor. In addition, 45 polyalkylene glycol units are used.
If the amount exceeds the weight percentage, the mechanical strength of the obtained film may be reduced.

To produce the polyester D used in the present invention, a method of melt-kneading a polymer having a polyester unit and a polymer having a polyalkylene glycol unit, or a method of preparing a copolymer having each of a polyester unit and a polyalkylene glycol unit, Although the method used is mentioned, another method may be used as long as the effect of the present invention is not impaired.

Further, in order to prevent the contents from adhering to the packaging bag, the film of the present invention preferably has an antistatic function. That is, the surface resistivity of the polyester film of the present invention is usually 5 × 10 ¹⁴ Ω / □ or less, preferably 1 × 10 ¹² Ω / □ or less, more preferably 5 × 10 ¹¹ Ω / □ or less.
Ω / □ or less. If the surface specific resistance is higher than 5 × 10 ¹⁴ Ω / □, adhesion of contents such as powder to a packaging bag is extremely undesirable.

As a method of imparting the antistatic effect, there are a method of kneading the antistatic agent into the film, and a method of applying the antistatic agent on the film.

The antistatic agent is not particularly limited as long as it reduces the surface resistivity. Examples thereof include glycerin fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, alkyldiethanolamine, and hydroxyalkylmonoethanolamine. , Polyoxyethylene alkylamine, alkyl diethanol amide, alkyl sulfonate, alkyl benzene sulfonate, alkyl phosphate, tetraalkyl ammonium salt, alkyl betaine, alkyl imidazolium betaine and the like.

Hereinafter, the method for producing the film of the present invention will be described in detail, but unless the gist of the present invention is exceeded.
The present invention is not particularly limited to the following examples.

The polyester chips dried by a known method are supplied to a melt extruder, and are heated and melted at a temperature not lower than the melting point of each polymer. Next, the molten polymer is extruded from a die and quenched and solidified on a rotary cooling drum so as to have a temperature equal to or lower than the glass transition temperature, to obtain a substantially amorphous unoriented sheet. In this case, in order to improve the flatness of the sheet, it is preferable to increase the adhesion between the sheet and the rotary cooling drum. In the present invention, the electrostatic application adhesion method and / or the liquid application adhesion method are preferably employed.

In the present invention, the sheet thus obtained is biaxially stretched to form a film. When the stretching conditions are specifically described, the unstretched sheet is preferably stretched 2 to 6 times at 70 to 145 ° C in the longitudinal direction to form a longitudinally uniaxially stretched film, and then at 90 to 160 ° C in the transverse direction. It is preferable to perform 6-fold stretching and perform heat treatment at 150 to 240 ° C. for 1 to 600 seconds. Further, at this time, in the maximum temperature zone of the heat treatment and / or the cooling zone at the outlet of the heat treatment, 0.times.
A method of relaxing 1 to 20% is preferred. Further, re-longitudinal stretching and re-lateral stretching can be added as necessary.

The polyester film of the present invention may be coated with a tenter, after finishing longitudinal stretching, if necessary, before the entrance of a transverse stretching tenter in order to improve, for example, adhesion, antistatic properties, weather resistance and surface hardness. A so-called in-line coating for drying in the inside may be performed. In addition, various coatings may be performed by offline coating after the production of the laminated film. Such a coat may be on one side or both sides.
As the material for the coating, any of an aqueous system and / or a solvent system may be used in the case of off-line coating, but an aqueous system or an aqueous dispersion system is preferable in the case of in-line coating.

Further, the thermoplastic resin such as polyethylene naphthalate and polytrimethylene terephthalate can be mixed with the polyester film of the present invention as long as the effects of the present invention are not impaired. Further, an ultraviolet absorber, an antioxidant, a surfactant, a pigment, a fluorescent whitening agent and the like can be mixed.

[0029]

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 addition, various physical properties,
Characteristics are measured or defined as follows. In Examples, "%" means "% by weight". (1) Melting Point Measurement The endothermic peak temperature due to crystal melting obtained at a heating rate of 16 ° C./min using a DSC7 type manufactured by PerkinElmer was defined as the melting point. (2) Surface specific resistance 50 mm inner electrode manufactured by Yokogawa Hewlett-Packard
1600 which is a concentric electrode with a diameter of 70 mm
8A is placed on the sample in an atmosphere of 23 ° C. and 50% RH,
A voltage of 100 V is applied, and 43
The surface resistivity of the sample was measured at 29A. (3) Ash test The test piece was rubbed back and forth 10 times with a flannel cloth, placed horizontally on tobacco ash in a 32-mesh bath, and the amount of attached ash was observed and evaluated according to the following criteria.

[0030] (4) Evaluation of cross-sectional shape After embedding the film in epoxy resin, cut it with a cutter in the longitudinal or width direction of the film, flatten the cross-section of the film with a microtome, apply oxygen plasma etching to prepare a sample, The shape of the portion dispersed in an island shape in the film was observed with an electron microscope (manufactured by JEOL Ltd.). By this observation, the average length X (μm) in the longitudinal direction and the average length Y (μm) in the width direction of the island-shaped portion were obtained, and X / Y was calculated.

In the cross section in the film width direction (100 μm
² ) The number of island-like dispersed portions observed in the above was counted, and the number per unit area (1 μm ² ) was calculated. (5) Tear linearity test A strip-shaped film of 300 mm in the longitudinal direction and 10 mm in the width direction was cut out, a cut of 3 mm in length was made on the short side of the film, the film was torn by hand, and the film was torn to the side opposite to the cut side. The case was defined as one point, and the measurement was performed ten times, and the total score was obtained. (6) Heat sealability Toyo Seiki Co., Ltd. 5-point heat sealer (HG-10)
0 type), heat sealing surfaces of each film are sealed with a seal size of 10 mm × 25 mm, a seal pressure of 20 Pa,
After heat-sealing under the conditions of a sealing time of 1 second and a temperature of 160 ° C., an adhesive strength (kg) per 1 cm width was used using a Tensilon UTM-4 type (manufactured by Orientec) at a peeling speed of 300 mm / min and a peeling width of 15 mm. / cm)
Classification was performed according to the following criteria, and heat sealability was evaluated.

Evaluation A: very excellent (adhesive strength is 1.5
kg / cm or more) Evaluation B: Excellent (adhesion strength is 1.0 or more and 1.5 kg / c)
Evaluation C: Poor (adhesive strength is less than 1.0 kg / cm) Example 1 (Method for producing polyester chip) 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, and 0.07 part of calcium acetate monohydrate were reacted. In a vessel, heated and heated, methanol was distilled off and transesterification was performed.
After the start of the reaction, it took about 4.5 hours to raise the temperature to 230 ° C., and the transesterification reaction was substantially completed.

0.04 parts of phosphoric acid and 0.035 parts of antimony trioxide were added and polymerized according to a conventional method. That is, gradually raise the reaction temperature to 280 ° C.
On the other hand, the pressure gradually decreased until finally 0.05 mmHg
And After 4 hours, the reaction was completed, and the mixture was formed into chips according to a conventional method to obtain polyester a. Polyester a obtained
Had a melting point of 255 ° C. and a solution viscosity IV of 0.66.

To 1.2 parts by weight of 1,4-butanediol was added 100 parts by weight of dimethyl terephthalate, and 106 ppm of tetrabutyl titanate (as titanium metal relative to dimethyl terephthalate) was added as a catalyst.
The transesterification was performed at 150 ° C. to 215 ° C. for 3.5 hours. Subsequently, the reaction product was placed under reduced pressure of 3 torr or less under 21 torr.
A melt polycondensation reaction was carried out at 5 to 245 ° C to obtain a polyester b. The melt viscosity IV of the obtained polyester chip was 0.85.

75% and 25% of polyester b and polytetramethylene ether glycol (molecular weight: 2,000)
Was melt-kneaded using a twin-screw extruder to obtain a polyester d.

Isophthalic acid was copolymerized with polyester a in an amount of 20 mol% to obtain polyester g. The melting point of polyester g was 210 ° C.

Polyester a was copolymerized with 25 mol% of isophthalic acid to obtain polyester h. The melting point of polyester h was 195 ° C.

Isophthalic acid was added to the polyester b in an amount of 35%.
By mol% copolymerization, polyester i was obtained. Polyester i had a melting point of 165 ° C.

The polyester g was mixed with 20% by weight of sodium alkyl sulfonate as an antistatic agent to obtain a polyester e.

Polyester f was obtained by adding 1000 ppm of amorphous silica having an average particle size of 2 μm to the above polyester g. (Production of polyester film) The above polyester g,
The mixed raw material 1 in which e and f were mixed at a ratio of 70%, 10%, and 20% and the mixed raw material 2 in which polyesters a and d were mixed at 70% and 30% were melted at 285 ° C., respectively. On the casting drum cooled to 20 ° C.
The seeds were co-extruded and cooled and solidified in a three-layer structure to obtain a non-oriented sheet (lamination thickness ratio: mixed material 1 / mixed material 2 / mixed material 1 = 1/4/1). Next, after stretching 4 times in the longitudinal direction at 90 ° C., a heat treatment of 4 times at 90 ° C., transverse stretching, and 230 ° C. for 10 seconds is performed through a preheating step in a tenter to obtain a thickness of 12 μm.
m polyester film was obtained.

The obtained polyester film was excellent in practicality and excellent in tear linearity, heat sealability and antistatic performance.

Examples 2 to 6 A polyester film was obtained in the same manner as in Example 1 except that the mixing ratios of the raw materials for the intermediate layer and the polyester d were changed, and the characteristics thereof were evaluated.

Examples 7 to 12 Polyester films were obtained in the same manner as in Example 1 except that the raw material for the outermost layer was changed, and the characteristics were evaluated.

Comparative Example 1 In Example 1, the raw material of the outermost layer was polyester a, f
A polyester film was obtained in the same manner as in Example 1 except that only the above was used, and the characteristics were evaluated.

The obtained polyester film was inferior in all of tear straightness, heat sealability and antistatic performance.

Comparative Example 2 A polyester film was obtained in the same manner as in Example 1 except that the raw material composition of the outermost layer and the intermediate layer was changed, and the characteristics were evaluated.

The obtained polyester film was inferior in heat sealability, antistatic performance, and linearity with easy tearing.

Comparative Example 3 A polyester film was obtained in the same manner as in Example 1 except that the raw material composition of the intermediate layer was changed, and its properties were evaluated.

The obtained polyester film was excellent in antistatic performance and heat sealability, but was poor in tear linearity.

Comparative Example 4 A polyester film was obtained in the same manner as in Example 1 except that the raw material composition of the surface layer was changed, and its properties were evaluated.

The resulting polyester film was excellent in tear linearity and antistatic performance, but was poor in heat sealability.

The results obtained are summarized in Tables 1 to 5 below.
It is shown in FIG.

[0053]

[Table 1]

[0054]

[Table 2]

[0055]

According to the present invention, there is provided a laminated polyester film having heat sealing properties, which can be easily and linearly opened without scattering contents, and which is excellent in preventing powder adhesion. And its industrial value is high.

 ──────────────────────────────────────────────────続 き Continuing on the front page F term (reference) 4F100 AK41A AK41B AK41C AK41K BA02 BA03 BA06 BA10B BA10C CA22 CA23 EH20 EJ38 GB23 GB66 JA04B JA04C JG04A JG04B JG04C JK03 JL05 JL05A JL12 YY00AYG01 QYYQAQQYYQAQQ QW06 4J002 CF05X CF10W GF00

Claims (7)

[Claims] 1. A co-extruded laminated polyester film comprising at least two layers, including a layer having a sea-island structure that simultaneously satisfies the following formulas (1) and (2) and a layer composed of polyester having a melting point of 220 ° C. or lower. A biaxially oriented laminated polyester film, characterized in that: 50 ≦ X / Y (1) 5 ≦ N ≦ 200 (2) (In the above formula, X is the average value (μm) of the length of the island in the film longitudinal direction, and Y is the length of the island in the film width direction. Average value (μ
m) and N are the number of islands present in the cross section in the film width direction (pieces / μm ² )) 2. The biaxial structure according to claim 1, wherein the layer having a sea-island structure contains a polyester D having a polyester unit and a polyalkylene glycol unit, and a polyester A having ethylene terephthalate as a main repeating unit. Oriented laminated polyester film. 3. The polyester unit constituting the polyester D comprises a dicarboxylic acid component containing 50 mol% or more of an aromatic dicarboxylic acid and a glycol having 3 to 10 carbon atoms.
A polyalkylene glycol having the following formula (3) (where 3 ≦
The biaxially oriented laminated polyester film according to claim 1 or 2, having a repeating unit structure of (n ≦ 10). HO- (CH ₂ ) _n -OH (3) 4. The biaxially oriented laminated polyester film according to claim 1, wherein the polyester D contains 2 to 45% by weight of a polyalkylene glycol unit. 5. The biaxially oriented laminated polyester film according to claim 1, comprising a layer composed of a polyester having a melting point of 200 ° C. or lower. 6. The biaxially oriented laminated polyester film according to claim 1, wherein the surface resistivity of at least one outermost layer is 5 × 10 ¹⁴ Ω / □ or less. 7. The biaxially oriented laminated polyester film according to claim 1, wherein at least one outermost layer has a surface resistivity of 5 × 10 ¹² Ω / □ or less.