JPH09324057A - Easily tearable polyester film and its prepare - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a biaxially stretched polyester film having a linear tearability at least on the longitudinal direction thereof and a package bag made by using the same. SOLUTION: This film is prepd. by using a starting material prepd. by mixing polyethylene terephthalate(PET) and a modified PET (A) contg. 10 to 40wt.% polyethylene glycol having a mol.wt. of 1,000 to 13,000 together in a PET to A wt. ratio of (50:50) to (80:20). In this case, the film has a tensile strength of 20 to 35kgf/mm<2> , a dry heat shrinkage of not more than 3% (160 deg.C×15min), and a haze value of not more than 5% and, in addition, has a linear tenability at least in the longitudinal direction.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a film having excellent tear linearity at least in the longitudinal direction and excellent strength,
Biaxially stretched polyester film that has heat resistance and dimensional stability and is useful as a packaging material for foods such as confectionery, pickles, miso, soups, jams, frozen, refrigerated, retort pouches, pharmaceuticals, daily necessities, cosmetics, etc. Things.

[0002]

2. Description of the Related Art Packaging of various plastic films is often used for packaging foods, pharmaceuticals and miscellaneous goods. Two layers or three layers of biaxially stretched plastic film and heat-sealable non-oriented plastic film are used. Packaging bags laminated with more than one layer are widely used. Biaxially stretched polyester film has excellent durability, moisture resistance, mechanical strength, heat resistance, and oil resistance, and is manufactured using the tubular method, flat simultaneous biaxial stretching method, flat sequential biaxial stretching method, etc. The biaxially stretched polyester film is widely used in the food packaging field and the like.

[0003] However, a packaging bag using a biaxially stretched polyester film has a problem that tear-openability is poor. There is a method of giving a notch to improve the openability, but when it is torn from the notch, the phenomenon that it does not tear linearly often occurs, not only is the contents scattered and wasted, but also soft such as cookies. When the confectionery is opened, it may crack, or if the contents are liquid, it may stain the clothes.

As an easy-open packaging material which is excellent in linearity when the film is torn, there is a uniaxially oriented polyolefin film laminated as an intermediate layer. Examples of such materials include a three-layer laminate film of biaxially stretched polyester film / uniaxially stretched polyolefin film / non-stretched polyolefin film, but it is necessary to provide an intermediate layer, and there is a problem in terms of cost, so that the application is difficult. It was limited.

[0005]

DISCLOSURE OF THE INVENTION The present invention is intended to solve such problems, and is a feature of the biaxially stretched polyester film, which is low hygroscopicity, mechanical properties, aroma retention, heat resistance, An object of the present invention is to provide a biaxially stretched polyester film having tear linearity while maintaining oil resistance and particularly dimensional stability under dry heat and wet heat environments required for food packaging materials.

[0006]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have solved the above problems by using a raw material prepared by mixing PET with a specific modified PET. It was found that the present invention has been reached.

That is, the gist of the present invention is as follows. Modified PET (A) containing 10 to 40% by weight of polyethylene glycol having a molecular weight of 1,000 to 13,000 in PET,
A film produced by using raw materials mixed at a ratio of PET / A = 50/50 to 80/20 (weight ratio), and having a tensile strength of 20.
~ 35kgf / mm ² , dry heat shrinkage less than 3% (160 ℃ x 15 minutes),
A biaxially stretched polyester film having tear linearity in at least a longitudinal direction, which has a characteristic of haze of 5% or less.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION PET in the present invention was obtained by a known method, that is, an ester exchange reaction method from dimethyl terephthalate and ethylene glycol, or a direct esterification method from terephthalic acid and ethylene glycol. After that, it can be obtained by melt polymerization or further solid phase polymerization, but other components can be copolymerized as long as the effects of the present invention are not impaired.

Other copolymerizable components include isophthalic acid,
Phthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, succinic acid, adipic acid, sebacic acid, dodecanedioic acid, dimer acid, maleic anhydride,
Maleic acid, fumaric acid, itaconic acid, citraconic acid,
Dicarboxylic acids such as mesaconic acid and cyclohexanedicarboxylic acid, 4-hydroxybenzoic acid, ε-caprolactone, oxycarboxylic acids such as lactic acid, glycols such as 1,3-propanediol, 1,6-hexanediol and cyclohexanedimethanol, Trimellitic acid, trimesic acid, pyromellitic acid, trimethylolpropane,
Examples thereof include polyfunctional compounds such as glycerin and pentaerythritol.

Further, as the raw material resin in the present invention,
Other polymers such as polybutylene terephthalate, polyethylene naphthalate, and polycyclohexylene dimethylene terephthalate can be mixed as long as the effects of the present invention are not impaired.

In the present invention, the molecular weight of polyethylene glycol (PEG) is required to be 1,000 to 13,000, preferably 2,000 to 10,000, and more preferably
It is between 4,000 and 8,000. When the molecular weight is less than 1,000, tear linearity cannot be obtained, and when it exceeds 13,000, mechanical strength, dimensional stability, haze and other performances deteriorate, and stable tear linearity of the film is developed. Hard to do.

In the film of the present invention, modified PET
The mixing ratio of PET and PEG constituting (A) is PET.
/ PEG = 60/40 to 90/10 (weight ratio), preferably 65/35 to 85/15 (weight ratio), more preferably 70/30
~ 80/20 (weight ratio). If the PEG content is less than 10% by weight or more than 40% by weight, the mechanical strength, dimensional stability, haze, and other performances are reduced, and stable linear tear properties of the film are difficult to develop.

In order to produce the film of the present invention, the mixing ratio of PET and modified PET (A) is PET /
A = 50/50 to 80/20 (weight ratio), preferably 55/45 to 75
/ 25 (weight ratio), and more preferably 60/40 to 70/30 (weight ratio). Modified PET (A) is 20
If the amount is less than 50% by weight, linear tearing is not obtained and 50% by weight
If it exceeds, the performance such as mechanical strength, dimensional stability, haze, etc. is deteriorated, causing a problem in practical performance.

The modified PET (A) in the present invention is PE
It can be obtained by melt-kneading T and PEG with an extruder, but as another method, P in the polymerization step of PET can be used.
It can also be obtained by adding EG and polycondensing.

As the method for producing the film of the present invention, for example, PET and PEG are blended in a predetermined compounding ratio and then melt-kneaded using a twin-screw extruder, and pelletized modified PET ( A mixture of A) and PET chips is put into an extruder, heated and melted, and then T
An unstretched sheet is manufactured by extruding a sheet from the die orifice of the die. The sheet extruded from the die orifice of the T-die is intimately wound around the cooling drum by an electrostatic applied casting method or the like to be cooled. Next, the unstretched sheet obtained was at a temperature of 90 to 140 ° C.
Biaxially stretched at a magnification of 3.0 to 5.0 times, and 210 to 250
Heat treated at ℃.

If the stretching temperature is lower than 90 ° C., it may not be possible to obtain a homogeneous stretched film. If the stretching temperature is higher than 140 ° C., crystallization of PET may be promoted, resulting in poor transparency. . If the draw ratio is less than 3.0 times, the strength of the obtained stretched film is low, and pinholes are likely to be formed in the bag. If it exceeds 5.0 times, stretching becomes difficult. Further, when the heat treatment temperature is lower than 210 ° C, the shrinkage rate of the obtained stretched film becomes large, and the bag after bag making may be deformed. On the other hand, when it is higher than 250 ° C, the film may melt and melt. is there.

The biaxial stretching method may be either a tenter simultaneous biaxial stretching method or a sequential biaxial stretching method using a roll and a tenter. Moreover, you may manufacture a biaxially stretched film by a tubular method.

The biaxially stretched polyester film of the present invention preferably has a tensile strength in the range of 20 to 35 kgf / mm ² , and if the tensile strength is less than the value in this range, the practical strength is insufficient, and if it exceeds this range. Not only is the quality excessive, but the operability during film production is rather reduced, which is economically unfavorable. The tensile elongation is preferably in the range of usually 80 to 160% (average value in the longitudinal direction and the width direction).

The biaxially stretched polyester film of the present invention preferably has a dry heat shrinkage ratio of 3% or less (average value in the longitudinal direction and the width direction) in a treatment at 160 ° C. for 15 minutes.
%, It is not preferable because printability deteriorates.

The haze of the biaxially stretched polyester film of the present invention is preferably 5% or less, and when the haze exceeds 5%, the transparency of the film deteriorates and the commercial value is impaired.

The biaxially stretched film of the present invention may be subjected to surface treatment by corona discharge treatment, surface hardening treatment, plating treatment, coloring treatment, or various coating treatments.

[0022]

In the present invention, not only the raw material obtained by melt-mixing PET and PEG is used, but the modified PET composed of PET and PEG is produced in advance, and then the raw material obtained by melt-mixing PET is used. PET
It is believed that a biaxially oriented polyester film having excellent tear linearity can be obtained due to its moderate dispersion in the matrix.

[0023]

EXAMPLES Next, the present invention will be specifically described with reference to examples. In addition, the raw materials and the measuring methods used for the evaluation of Examples and Comparative Examples are as follows.

(1) Raw material PET: manufactured by Unitika (relative viscosity 1.38 dl / g) PEG: manufactured by Sanyo Chemical Co., Ltd.

(2) Measurement method Relative viscosity: Measured at a concentration of 0.5 g / dl and a temperature of 20 ° C. using an equal weight mixture of phenol and ethane tetrachloride as a solvent. Tear linearity: Cut out a rectangular film piece of 205 mm in the longitudinal direction (MD direction) and 40 mm in the width direction (TD direction) from the biaxially stretched film, and a length of 5 mm is placed at the center of one short side of this film piece. Ten samples with the notch are prepared (FIG. 1). Next, tear by hand in the MD direction from the cut,
As shown in FIG. 2 (a), the number of samples whose tear propagation end reached the short side facing the cut side was used as the evaluation value of the tear linearity in the MD direction. (Evaluation value of 8 or more was regarded as acceptable.) The tear linearity in the TD direction was 205 m in the TD direction of the film.
The measurement was carried out in the same manner as described above, except that a sample obtained by cutting out a 40 mm strip of film in the m and MD directions was used as a sample. In addition,
The evaluation was carried out for each of the left end portion, the center portion and the right end portion of the film wound after stretching.

Haze (haze): The haze of a film having a thickness of 15 μm was measured according to ASTM D103-61. Dry heat shrinkage rate: Cut strip samples with marked lines in the MD and TD directions of the film, and cut in an oven 160
Treated at 15 ℃ for 15 minutes, and measure the distance between marked lines at 20 ℃, 65% R
It was measured at H equilibrium. The amount of shrinkage due to the treatment was expressed as a percentage of the dimension before treatment. Tensile strength; ASTM-D88 using a sample with a width of 10 mm and a length of 10 cm
Measured according to 2.

Example 1 PET and PEG having a molecular weight of 6,000 were used as PET / PEG = 75.
A mixture of chips at a ratio of / 25 (weight ratio) was melt-mixed with a twin-screw extruder and chipped to prepare modified PET (A) (relative viscosity 1.33 dl / g). Next, modified PET
(A) and PET were mixed in a chip ratio of 35/65 (weight ratio), and equipped with a coat hanger type T die.
Using a 50mmφ extruder, residence time 5 minutes, resin temperature 270
The mixture was melt extruded at a temperature of 20.degree. C., and a pinning wire was applied to a cast roll whose temperature was controlled at 20.degree. The resulting unstretched sheet was stretched 3.8 times at 90 ° C with a roll longitudinal stretching machine and 4.6 times at 120 ° C with a tenter transverse stretching machine, then subjected to a heat treatment at 230 ° C at a transverse relaxation treatment of 5%, and at room temperature. The mixture was cooled down to a biaxially stretched film having a thickness of 12 μm. The tear linearity of the obtained biaxially stretched film was measured, and the results are shown in Table 1.

Examples 2-8, Comparative Examples 1-7 Molecular weight of PEG in modified PET (A), PEG and PET
A biaxially stretched film was obtained in the same manner as in Example 1 except that the mixing ratio of modified PET (A) and the mixing ratio of PET were changed as shown in Table 1. The tear linearity of the obtained biaxially stretched film was measured, and the results are shown in Tables 1 and 2.

Example 9 Ethylene glycol and terephthalic acid were supplied to an esterification tank at a mixing ratio of 1.6 / 1.0 (molar ratio) at a temperature of 2
After reacting at 55 ° C for 6 hours, the bis-
β-Hydroxyethyl terephthalate (BHET) was obtained.
Next, this was transferred to a polymerization vessel, and 4 × 10 ⁻⁴ mol% of antimony trioxide was added as a catalyst to the acid component, and further,
PEG with a molecular weight of 6,000 has a composition ratio in modified PET (A)
Mix to 25% by weight, start depressurization, and finally
Polymerization was performed at a temperature of 280 ° C. for 5 hours under a reduced pressure of 1.3 hPa or less to obtain a modified PET (A) having a relative viscosity of 1.6. Next, modified PET
(A) and PET were mixed in a chip ratio of 35/65 (weight ratio), and equipped with a coat hanger type T die.
Using a 50mmφ extruder, residence time 5 minutes, resin temperature 270
The mixture was melt extruded at a temperature of 20.degree. C., and a pinning wire was applied to a cast roll whose temperature was controlled at 20.degree. The resulting unstretched sheet was stretched 3.8 times at 90 ° C with a roll longitudinal stretching machine and 4.6 times at 120 ° C with a tenter transverse stretching machine, and then subjected to heat treatment at 230 ° C at a transverse relaxation treatment of 5% and at room temperature. The mixture was cooled down to a biaxially stretched film having a thickness of 12 μm. The tear linearity of the obtained biaxially stretched film was measured, and the results are shown in Table 1.

Examples 10 to 11 and Comparative Examples 8 to 10 Molecular weight of PEG in modified PET (A), PEG and PET
A biaxially stretched film was obtained in the same manner as in Example 9 except that the mixing ratio of modified PET (A) and the mixing ratio of PET were changed as shown in Table 1. The tear linearity of the obtained biaxially stretched film was measured, and the results are shown in Tables 1 and 2.

[0031]

[Table 1]

[0032]

[Table 2]

Examples 12-19, Comparative Examples 11-18 The films obtained in Examples 1, 9 and Comparative Examples 1, 7 were
Dry laminating was performed with the configuration shown in Table 3, and after bag making, the tear linearity was evaluated. Table 3 shows the results of evaluating the tear linearity.

The abbreviations of the constituents of the packaging material are as follows. PT1: Biaxially stretched film obtained in Example 1 PT2: Biaxially stretched film obtained in Example 9 PT3: Biaxially stretched film obtained in Comparative Example 1 PT4: Biaxially stretched film obtained in Comparative Example 7 Stretched film LLDPE: Linear low-density polyethylene (Tokyo Cellophane Paper, TUX-TC, thickness 60 μm) ON: Biaxially stretched nylon 6 film (Unitika, thickness 15 μm) CPP1: Non-stretched polypropylene film (Toray) Made by
CPP2: Unstretched polypropylene film (Toray Co., Ltd.
AL: Aluminum foil (manufactured by Showa Aluminum, thickness 7μm)

[0035]

[Table 3]

[0036]

According to the present invention, there is provided a biaxially stretched polyester film having durability, moisture resistance, mechanical properties, heat resistance, oil resistance and tear linearity at least in the longitudinal direction. Further, by using the film of the present invention for at least one layer of the film constituting the packaging bag, a packaging bag having excellent opening properties can be obtained.

[Brief description of drawings]

FIG. 1 shows a shape of a test piece used for evaluation of tear linearity of a film.

FIG. 2 is a diagram showing a shape of a test piece after tearing in a tear test, (a) is an example of the test piece after tearing of a sample having good tear linearity, and (b) is poor tear linearity. An example of the test piece after tearing of the sample is shown.

[Explanation of symbols]

 1 notch

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display area B29K 67:00 B29L 9:00

Claims (3)

[Claims] 1. Polyethylene terephthalate (PET)
To polyethylene glycol with a molecular weight of 1,000 to 13,000
Modified PET (A) containing 10 to 40% by weight of PET / A
= 50/50 to 80/20 (weight ratio) A film produced using raw materials mixed in a ratio of 20 to 35 kgf / mm
² , dry heat shrinkage less than 3% (160 ℃ x 15 minutes), haze 5%
A biaxially stretched polyester film having tear linearity at least in the longitudinal direction, which has the following properties. 2. A laminated film using the biaxially stretched polyester film of claim 1 in at least one layer. 3. An easy-open packaging bag produced by using the laminated film according to claim 2 so that the easy tearing direction is the tearing direction of the bag.