JPH08208950A - Biaxially oriented polyester film and its production - Google Patents

Abstract

PURPOSE: To obtain a polyester film excellent in mechanical properties, resistances to heat, oil and thermal posttreatment such as boiling or retorting and also in straight tearability in the longitudinal and transverse directions. CONSTITUTION: This film is formed from a mixture comprising 50-95wt.% thermoplastic polyester resin (P1) and 50-5wt.% polyamide resin (P2) and satisfies the relations: 0.1<=LT<=5.0, 0.3<=LM/LT<3.0, and N>=10 [wherein LM (μm) is the number - average length of dispersed P2 particles observed in the longitudinal section of the film; LT (μm) is the number - average length of dispersed P2 particles observed in the transverse section; and N is the number of dispersed P2 particles per 10μm<2> observed in the transverse section].

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is excellent in straightness when it is torn in a longitudinal direction and a width direction and is made of a thermoplastic polyester resin (referred to as P1) and a polyamide resin (referred to as P2), and is excellent. Has strength and dimensional stability,
Including foods such as soups, jams, and retort pouches,
The present invention relates to a biaxially oriented polyester film useful as a packaging material for medicines, daily necessities, toiletries and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Various plastic film packaging bags are often used for packaging foods, pharmaceuticals, miscellaneous goods, etc. Two layers of a biaxially stretched plastic film and a heat-sealable non-oriented plastic film are used. Three
Packaging bags laminated with more than one layer are widely used. Especially in the food packaging field where moisture proof performance, mechanical performance, heat resistance, and oil resistance are required, high strength products manufactured by using the flat simultaneous biaxial stretching method, the flat sequential biaxial stretching method, etc. as the biaxially oriented film. A polyester biaxially oriented film is used.

However, the packaging bag made from these polyester biaxially oriented films has a problem that the tearing and unsealing property is poor, and notches are often provided as a device for improving the unsealing property. However, even when tearing from the notch, there often occurs a phenomenon that the packaging bag is not torn linearly in the vertical or horizontal direction. In such a case, not only is the contents scattered and wasted at the same time as the package is opened, but also when the contents are liquid, an accident such as staining clothes is likely to occur. Especially in the case of polyester biaxially oriented film, such a problem occurs. Therefore, a non-oriented plastic film capable of heat sealing is laminated, the sealing strength is weakened to form a bag, and the bag is opened from the sealing portion. Although the method has been adopted, the phenomenon that the bag cannot be opened and the phenomenon that the contents are scattered from the seal portion during handling such as transportation often occurs, and therefore improvement thereof is strongly demanded.

Further, as an easy-opening material which is excellent in straightness when the film is torn, there is a uniaxially stretched polyolefin film laminated as an intermediate layer. For example, 3 of biaxially stretched polyester film / uniaxially stretched polyolefin film / non-oriented polyolefin film
There is a layer laminate film. But according to this
Although the tear straightness in the stretching direction of the axially stretched film is improved, a multilayer structure in which a new intermediate layer is provided only for improving the straight tear straightness has a problem that the cost is high and the application is limited. It had been.

[0005]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and is highly effective as a moisture proof performance, mechanical performance, heat resistance and oil resistance of polyester film, especially as a packaging material for foods. A biaxially oriented film suitable for an easy-open packaging material that has the required dimensional stability in a dry heat or wet heat environment and is excellent in straightness when torn in the longitudinal direction and the width direction of the film, and a method for producing the same. Is to provide.

[0006]

The present inventors have arrived at the present invention as a result of intensive studies to solve such problems.

That is, the gist of the present invention is as follows.

1. Weight ratio of P1 and P2 50 to 95/5
A biaxially oriented polyester film composed of a mixture of 0 to 5, wherein the number average value of the lengths in the longitudinal direction of the film of the P2 dispersed particle cross section observed on the longitudinal section of the film is L
M (μm), P2 observed on the widthwise cross section of the film
L is the number average value of the length of the cross section of the dispersed particles in the film width direction.
When T (μm) and the number of P2 dispersed particles observed on the cross section of the film in the width direction is N (number / 10 μm ² ), the following formulas (1) to (3) are satisfied. A biaxially oriented polyester film having a linear tearing property in both the longitudinal direction and the width direction. 0.1 ≦ LT ≦ 5.0 (1) 0.3 ≦ LM / LT <3.0 (2) N ≧ 10 (3) 2. It consists of P1 and P2, and their weight ratio is 50-9.
The melt viscosity ratio of P2 to P1 at 5/50 to 5 (M
A mixture having R) of 0.1 to 4.0 is extruded into a sheet form from the lip gap of the die under the condition that the draft ratio (ratio of the gap size of the die and the thickness of the solidified sheet) is 1 or more and less than 5, and the mixture is cooled. The sheet thus obtained is at least 1.5 times as much as 2 times at a temperature within the range from the glass transition temperature of P1 to the crystallization temperature.
A method for producing a biaxially oriented polyester film having a linear tearing property in both a longitudinal direction and a width direction, which comprises axially stretching and subsequently heat treating at a temperature lower than a crystal melting temperature.

The present invention will be described in detail below.

P1 used in the present invention is a polyester containing a dicarboxylic acid or its ester-forming derivative and a diol or its ester-forming derivative as main components.

Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, bisbenzoic acid, bis (p-carboxyphenyl) methane, anthracene dicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 4,4'-diphenoxyethanedicarboxylic acid, adipic acid, sebacic acid, azelaic acid, dodecanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid,
Examples thereof include 1,4-cyclohexanedicarboxylic acid and the like, alone or in a mixture.

As the diol, ethylene glycol,
Propylene glycol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,
6-Hexanediol, decamethylene glycol, cyclohexanedimethanol, cyclohexanediol, diethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and mixtures thereof.

Preferred P1 in the present invention is polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polypropylene terephthalate, polycyclohexylene dimethylene terephthalate, polyhexamethylene terephthalate, poly (ethylene terephthalate / ethylene isophthalate) copolymer. However, these can be used alone or as a mixture of two or more kinds, and it is also possible to use a copolymer of other components.

Particularly preferred as P1 in the present invention are polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate and polycyclohexane dimethylene terephthalate.

P2 in the present invention is a polyamide obtained from lactam, amino acid or diamine and dicarboxylic acid.

As the lactam, ε-caprolactam,
Examples of ω-laurolactam and amino acids include 6-aminocaproic acid, 11-aminoundecanoic acid, 12-aminododecanoic acid, and paraaminomethylbenzoic acid.

As the diamine, tetramethylenediamine, hexamethylenediamine, undecamethylenediamine, dodecamethylenediamine, 2,2,4- / 2,4,4.
4-trimethylhexamethylenediamine, 5-methylnonamethylenediamine, metaxylylenediamine, paraxylylenediamine, 1,3-bis (aminomethyl) cyclohexane, 1,4-bis (aminomethyl) cyclohexane, 1-amino- 3-aminomethyl-3,5,5-trimethylcyclohexane, bis (4-aminocyclohexyl) methane, bis (3-methyl-4-aminocyclohexyl) methane, 2,2-bis (4-aminocyclohexyl) propane, bis (Aminopropyl) piperazine,
Aminoethylpiperazine and the like can be mentioned.

As the dicarboxylic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, terephthalic acid, isophthalic acid, 2-chloroterephthalic acid, 2-methylterephthalic acid, 5-methylterephthalic acid, 5- Methyl isophthalic acid, 5-sodium sulfoisophthalic acid, hexahydroterephthalic acid, hexahydroisophthalic acid and the like can be mentioned.

Examples of P2 used in the present invention include nylon 6, nylon 66, nylon 610, nylon 11, nylon 12, MXD6 (polyamide obtained by polymerizing metaxylylenediamine and adipic acid), and copolymers thereof. In particular, MXD6 is particularly preferable.

The film of the present invention must be composed of a mixture of P1 and P2 in a weight ratio of 50 to 95/50 to 5. If the proportion of P2 is less than 5% by weight, straightness of tearing cannot be obtained, and if it exceeds 50% by weight, mechanical properties such as strength of the film and heat resistance are unfavorably deteriorated. P1
The weight ratio of P2 to P2 is more preferably 70 to 90/30 to 10.

The film of the present invention has P2 in P1.
Must be dispersed in an island shape so as to satisfy the above formulas (1) to (3).

Formula (1) is expressed by P2 in the film width direction.
Shows the size of dispersed particles, and when LT is finely dispersed to less than 0.1 μm, tear straightness cannot be obtained,
A coarse dispersion state of more than 5.0 μm is not preferable because the mechanical properties and transparency of the film deteriorate.

Formula (2) shows the shape of the particles of P2, and when the formula (2) is satisfied, the film has tear straightness in both the longitudinal direction and the width direction of the film.

Equation (3) shows the number of dispersed particles of P2 existing in P1, which is a certain number or more, that is,
If there are not more than 10 pieces / 10 μm ² , the straightness of tearing does not appear.

Further, various additives and other polymers can be blended in the film of the present invention within a range that does not impair the straightness of tearing. Examples of the additive include an inorganic or organic crystal nucleating agent, a lubricant such as silica and calcium carbonate, a heat stabilizer, an antioxidant, a filler, a plasticizer, a pigment and a dye.

Next, the method for producing the film of the present invention will be described.

In the present invention, both P1 and P2 resins are
The melt viscosity ratio (MR) of P2 to P1 is 0.1 to
It must be chosen to be 4.0. MR is 4.
If it is larger than 0, the dispersed particles of P2 become large, and the number of dispersed particles becomes insufficient to develop the linear tear property, and the film of the present invention cannot be obtained. On the other hand, when the MR is less than 0.1, the dispersed particles of P2 become too small and the linearity of tearing decreases, and the viscosity difference between the two is too large.
The film cannot be formed well.

The glass transition temperature of P2 is preferably lower than the crystallization temperature of P1 by 10 ° C. or less. If the glass transition temperature of P2 is higher than the above range, P1 may be stretched.
However, P2 becomes difficult to be stretched, voids are likely to be generated at the interface, and the mechanical properties of the film may deteriorate.

As a film forming method, an inflation method,
Although a known manufacturing method such as the T-die method can be used,
The T-die method is preferred.

In the T-die method, a mixture of predetermined amounts of P1 and P2 is put into an extruder, heated and melted, and then extruded into a sheet from a lip of a die. The sheet extruded from the die is wound around a cooling drum and rapidly cooled. At this time, it is desirable to set DR to be 1 or more and less than 5, preferably 1.5 to 4. When DR is set to 5 or more, the tear straightness in the width direction of the film becomes difficult to develop, and
Making DR less than 1 causes a problem in production stability. P
The dispersed particle shape of 2 is the flow of the polymer in the molten state,
It occurs due to the tensile deformation of the molten sheet between the die and the cooling roll, but the latter deformation has a large effect. DR indicates the amount of apparent deformation between the die and the cooling roll,
The larger the DR, the more elongated the shape of the P2 particles in P1.

Then, the obtained unstretched sheet is biaxially stretched to obtain a biaxially oriented film. The biaxial stretching method may be a tenter simultaneous biaxial stretching method or a sequential biaxial stretching method using a roll and a tenter. The stretching is carried out at a temperature not lower than the glass transition temperature of P1 and not higher than the crystallization temperature, and is biaxially stretched at least 1.5 times in both longitudinal and transverse directions, followed by heat treatment.

In the case where the biaxially oriented film produced as described above is required to have easy surface adhesion, it may be subjected to a physicochemical surface treatment such as corona discharge treatment or coating on one side or both sides. Good.

The film of the present invention has not only excellent mechanical properties but also excellent dimensional stability and linear tearability in the longitudinal direction and width direction of the film, so that it is an easy-open packaging material for foods, pharmaceuticals, sundries, etc. Is suitable as

When the film of the present invention is used for a packaging bag, it is usually polypropylene, polyethylene, ethylene-vinyl acetate copolymer, polyester, etc. in order to impart heat sealability and gas barrier property. It is used by being laminated with other plastic film, paper, metal foil such as aluminum. In this case, the film of the present invention is used for at least one layer, and the number of laminated layers is not particularly limited as long as the laminated film has a linear tearing property.

By making a bag of such a laminated film, an easily openable packaging bag is obtained. Since this packaging bag has excellent tear straightness, it is useful as a packaging bag for foods such as soups, jams and retort pouches, as well as pharmaceuticals, daily necessities, toiletries and the like.

[0036]

EXAMPLES Next, the present invention will be specifically described with reference to examples. The raw materials and measuring methods used in Examples and Comparative Examples are as follows.

(1) Raw material Polyethylene terephthalate (PET): DE-BR polybutylene terephthalate (PBT) manufactured by Unitika Ltd .: Novador 5020S polyethylene naphthalate (PEN) manufactured by Mitsubishi Chemical Co .: SPE107 nylon 6 (N6) manufactured by Mitsubishi Gas Chemical Co., Inc. : Unitika BRL Nylon 66 (N66): Asahi Kasei Leona 1500 Nylon 610 (N610): Showa Denko D316 Nylon 11 (N11): Toray
Rilsan BMNO Nylon 12 (N12): manufactured by EMS, L20G polymethaxylylene adipamide (MXD6): manufactured by the following method. 8 of a salt consisting of metaxylylenediamine and adipic acid
A 0% by weight aqueous solution was placed in a 30 liter autoclave, and under a nitrogen atmosphere, the temperature was 270 ° C. and the pressure was 17.5 kg / c.
After the polymerization reaction was carried out at m ² for 2 hours, the water vapor was slowly discharged, and the pressure release was completed in about 1 hour.
The reaction was continued at 1.5 ° C. for 1.5 hours. After that, pressure was applied with nitrogen to expel the resin into a strand shape, cool with a water bath, and cut the strand with a pelletizer to obtain a pellet (MXD-1). Furthermore, by changing the polycondensation time, three types of MXD6 having different melt viscosities were produced (M
XD-2-4).

Table 1 shows the melt viscosities of the above raw materials.

[0039]

[Table 1]

(2) Measuring method (a) Melt viscosity A flow tester (CFT-500 manufactured by Shimadzu Corporation) equipped with a nozzle having a diameter of 0.5 mm and a length of 2.0 mm was used.
At a temperature of 260 to 290 ° C. and a preheating time of 150 seconds, the load was changed and measurement was performed at four points. The apparent melt viscosity at a shear rate of 1000 sec ⁻¹ was read from the obtained shear rate-melt viscosity curve.

(B) Size of Dispersed Particles A scanning electron microscope (JSM-15, manufactured by JEOL Ltd.) was used to take electron micrographs of the longitudinal fracture surface and the transverse fracture surface of the film. Using this photograph, the sizes of all the dispersed particles observed in the range of 50 μm ² were measured, and the number average values thereof were taken as LM and LT.

(C) Number of dispersed particles From the photograph of the above cross section, 50 μm of the fracture surface in the film width direction is shown.
Count the number of all dispersed particles observed in the range of ² and 1
It was converted to the number per 0 μm ² .

(D) Tear rectilinearity of film A strip-shaped film piece having a length of 205 mm in the longitudinal direction (MD) and a width of 20 mm in the width direction (TD) and a strip shape having a length of 205 mm in the width direction and a length of 20 mm from the stretched film. The film pieces are cut out, and 10 samples each having a 5 mm-long cut in the center of the short side of one of these film pieces are prepared (FIG. 1). Next, the number of samples reached by tearing by hand in the direction of the long side from the notch and reaching the short side where the tear propagation end faces the notched side as shown in FIG. 2A was taken as the evaluation value. (Evaluation value: 0 to 10) The evaluation was performed on the left end portion of the film wound after stretching.

Example 1 A composition was prepared by mixing PET and MXD-1 in a weight ratio of 80/20. A resin temperature of 280 ° C.,
Extrusion film formation was performed with DR4. The edge of the obtained sheet was held in a clip of a tenter type simultaneous biaxial stretching machine and stretched 3.5 times in both longitudinal and transverse axial directions under the condition of 95 ° C., and then the relaxation rate in the transverse direction was set to 5%. Heat treatment was performed to obtain a stretched film having a thickness of 15 μm. The tear straightness of the obtained film was measured, and the results are shown in Table 2.

Examples 2 to 3 Stretched films were obtained in the same manner as in Example 1 except that PET and MXD-1 were mixed in a weight ratio of 92/8 or 55/45. The tear straightness of the obtained film was measured, and the results are shown in Table 2.

Example 4 PET and MXD-1 were mixed in a weight ratio of 80/20,
An unstretched sheet was formed under the conditions of DR3. This unstretched sheet is sequentially stretched by using a biaxial stretching machine at 90 ° C. in the machine direction.
After stretching 7 times and then 4.6 times in the transverse direction at 120 ° C.,
Heat treatment is applied with a lateral relaxation rate of 5% and a thickness of 15μ
A stretched film of m 2 was obtained. The tear straightness of the obtained film was measured, and the results are shown in Table 2.

Examples 5 to 11 Stretched films were obtained in the same manner as in Example 1 except that the resins shown in Table 2 were used as P2. The tear straightness of the obtained film was measured, and the results are shown in Table 2.

Example 12 A composition was prepared by mixing PBT and MXD-1 in a weight ratio of 80/20. A resin temperature of 260 ° C.
Extrusion film formation was performed with DR4. The edge of the obtained sheet was held in a clip of a tenter type simultaneous biaxial stretching machine and stretched 3.5 times in both longitudinal and transverse axial directions under the condition of 65 ° C., and then the relaxation rate in the transverse direction was set to 5%. Heat treatment was performed to obtain a stretched film having a thickness of 15 μm. The tear straightness of the obtained film was measured, and the results are shown in Table 2.

Example 13 A stretched film was obtained in the same manner as in Example 12, except that N6 was used as P2 and the film was formed by extrusion at a resin temperature of 240 ° C. The tear straightness of the obtained film was measured, and the results are shown in Table 2.

Example 14 A composition was prepared by mixing PEN and MXD-1 in a weight ratio of 80/20. A resin temperature of 290 ° C.
Extrusion film formation was performed with DR4. The edge of the obtained sheet was held in a clip of a tenter type simultaneous biaxial stretching machine and stretched 3.5 times in both longitudinal and transverse axial directions under the condition of 135 ° C., and then the relaxation rate in the transverse direction was set to 5%. Heat treatment was performed to obtain a stretched film having a thickness of 15 μm. The tear straightness of the obtained film was measured, and the results are shown in Table 2.

[0051]

[Table 2]

Comparative Example 1 A stretched film was obtained in the same manner as in Example 1 except that only PET was used. The tear straightness of the obtained film was measured, and the results are shown in Table 3.

Comparative Examples 2 to 3 A stretched film was obtained in the same manner as in Example 1 except that PET and MXD-1 were mixed in a weight ratio of 97/3 or 45/55. The tear straightness of the obtained film was measured, and the results are shown in Table 3. In Comparative Example 3, MXD-1 was not dispersed in the form of particles.

Comparative Example 4 A stretched film was obtained in the same manner as in Example 1 except that DR was changed to 10. The tear straightness of the obtained film was measured, and the results are shown in Table 3.

Comparative Example 5 A stretched film was obtained in the same manner as in Example 1 except that MXD-4 was used as P2. The tear straightness of the obtained film was measured, and the results are shown in Table 3.

Comparative Example 6 A stretched film was obtained in the same manner as in Example 12, except that only PBT was used. The tear straightness of the obtained film was measured, and the results are shown in Table 3.

Comparative Example 7 A stretched film was obtained in the same manner as in Example 14, except that only PEN was used. The tear straightness of the obtained film was measured, and the results are shown in Table 3.

[0058]

[Table 3]

Examples 15 to 22 and Comparative Examples 8 to 13 Laminated films having the packaging material constitution shown in Table 4 were produced by the dry laminating method, and 200 each in the longitudinal direction and the width direction.
A 4-sided sealed bag made of mm was prepared, and the straightness of tearing was evaluated when the bag was torn from both the vertical and horizontal directions. The abbreviations of the constituent packaging materials indicate the following. PET1: Film obtained in Example 1 PET6: Film obtained in Example 6 PET (1): Film obtained in Comparative Example 1 PET (5): Film obtained in Comparative Example 5 LLDPE: Linear Low-density polyethylene film (Tokyo Cellophane Paper Co., TUX-TC, thickness 60 μm) ON: N6 biaxially oriented film (Unitika, thickness 1)
5 μm) CPP: unstretched polypropylene film (Toray, thickness 60 μm) AL: aluminum foil (Showa Aluminum, thickness 7 μm) Table 4 shows the results of evaluation of straightness of tearing.

[0060]

[Table 4]

[0061]

According to the present invention, mechanical properties, heat resistance,
Provided is a film having excellent oil resistance and excellent performance for post-heat treatment such as boiling and retorting, and having excellent tear straightness in both the longitudinal direction and the width direction of the film. In addition, an excellent easy-open packaging bag can be obtained by using this in one or more films constituting the packaging bag.

[Brief description of drawings]

FIG. 1 is a view showing the shape of a test piece used for evaluation of tear straightness of a film.

FIG. 2 is a diagram showing the shape of a test piece after tearing in a tear test, where (a) is an example of a test piece with good tear straightness and (b) is an example of a test piece with poor tear straightness. Show.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Keizo Yoda 23, Uji Kozakura, Uji City, Kyoto Prefecture Unitika Co., Ltd. Central Research Institute (72) Inventor, Atsuhiro Ishikawa 23, Uji Kozakura, Uji City, Kyoto Unitika Co., Ltd. Central Research Company In-house

Claims (5)

[Claims] 1. A weight ratio of a thermoplastic polyester resin (referred to as P1) to a polyamide resin (referred to as P2) of 5
A biaxially oriented polyester film comprising a mixture of 0 to 95/50 to 5, wherein the number average value of the length of the P2 dispersed particle cross section observed in the film longitudinal direction cross section is LM (μm). , LT (μm) is the number average value of the lengths of the P2 dispersed particles observed in the widthwise cross section of the film in the width direction of the film, and the number of P2 dispersed particles observed in the widthwise cross section of the film. N (pieces / 10μ
m ² ), a biaxially oriented polyester film having tear straightness in both the longitudinal direction and the width direction, which satisfies the following formulas (1) to (3). 0.1 ≦ LT ≦ 5.0 (1) 0.3 ≦ LM / LT <3.0 (2) N ≧ 10 (3) 2. The biaxially oriented polyester film according to claim 1, wherein P2 is a polyamide containing 90 mol% or more of structural units formed by a polycondensation reaction of metaxylylenediamine and adipic acid. 3. A laminated film having a linear tearing property, wherein the biaxially oriented polyester film according to claim 1 or 2 is used in at least one layer. 4. The laminated film according to claim 3 is used,
Easy-open packaging bag made. 5. A draft comprising a mixture of P1 and P2 having a weight ratio of 50 to 95/50 to 5 and a melt viscosity ratio (MR) of P2 to P1 of 0.1 to 4.0. Ratio (ratio of die gap size and solidified sheet thickness) is 1
The sheet obtained by extruding into a sheet form from the lip gap of the die under the above condition of less than 5 and cooling the sheet at a temperature within the range of the glass transition temperature of P1 to the crystallization temperature and at least 1 in both the longitudinal and lateral directions. . A method for producing a biaxially oriented polyester film having a linear tearing property in both the longitudinal direction and the width direction, which comprises biaxially stretching 5 times and subsequently heat treating at a temperature lower than a crystal melting temperature.