JP3110712B2 - Easy tearing biaxially stretched polyester film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 Many packaging bags using various plastic films are used for packaging foods, medicines and miscellaneous goods. Two layers of a biaxially stretched plastic film and a heat-sealing non-oriented plastic are provided. Packaging bags laminated with three or more layers are widely used. Biaxially stretched polyester film is durable, moisture proof, mechanical strength,
It has excellent heat resistance and oil resistance, and biaxially stretched polyester films manufactured using the tubular method, flat simultaneous biaxial stretching method, flat sequential biaxial stretching method, etc. are widely used in the food packaging field, etc. I have.

[0003] However, a packaging bag using a biaxially stretched polyester film has a problem that tear-openability is poor. There is a method of adding a notch to improve the openability, but when tearing from the notch, a phenomenon that it does not tear linearly often occurs, not only is the content scattered and wasted, but also soft cookie etc. The confectionery may be broken at the time of opening, or may cause troubles such as staining clothes when the contents are liquid.

As an easy-opening material having excellent linearity when the film is torn, there is a material obtained by laminating a uniaxially stretched polyolefin film as an intermediate layer. Examples of such a film include a three-layer laminated film of a biaxially oriented polyester film / a uniaxially oriented polyolefin film / an unoriented polyolefin film,
An intermediate layer must be provided, which is costly, and its use is limited.

Therefore, as a method for imparting tear linearity to the biaxially stretched polyester film itself, a thermoplastic polyester resin (a) whose acid component is mainly composed of terephthalic acid or naphthalenedicarboxylic acid, and a phase-separated form from the polyester. A biaxially stretched polyester film using a mixture of a thermoplastic polyester resin (b) as a main raw material has been proposed (JP-A-8-169962). The above publication describes that PET is used as (a) and a polyether polyester block copolymer composed of polytetramethylene glycol and PBT is used as (b), but an extruder having a diameter of 200 mm or more is used. When produced on a scale of such mass production scale, the thickness unevenness of the film becomes large, and in some cases, it becomes difficult to form a film, or the tear linearity of the obtained film is reduced,
There is a problem that the haze of the film becomes high and the commercial value as a packaging bag decreases.

[0006]

DISCLOSURE OF THE INVENTION The present invention is intended to solve such problems, and has low moisture absorption, mechanical properties, transparency, fragrance retention, which are features of a biaxially stretched polyester film. Biaxial stretching with excellent heat resistance, oil resistance, and excellent productivity on a mass production scale with stable tear linearity, while maintaining dimensional stability in dry heat and wet heat environments required especially for food packaging materials. It is intended to provide a polyester film.

[0007]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve such problems, and as a result, PET was added to polytetramethylene glycol (P) having a specific molecular weight.
PBT containing a specific ratio of TMG) (modified PBT)
It has been found that the above-mentioned problems can be solved by forming a film using a composition containing the compound, and the present invention has been achieved.

That is, the gist of the present invention is as follows. Polybutylene terephthalate (modified PBT) containing 5 to 20% by weight of a polytetramethylene glycol unit having a molecular weight of 600 to 4,000 and polyethylene terephthalate (PET) were prepared by mixing PET / modified PBT = 70/30 to 95/5.
A biaxially stretched polyester film which is produced using raw materials mixed at a ratio of (weight ratio) and has tear linearity at least in a longitudinal direction.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION PET in the present invention can be prepared by a known production method, that is, an ester exchange reaction method between dimethyl terephthalate and ethylene glycol, or a direct esterification method from terephthalic acid and ethylene glycol. After being obtained, 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.

[0010] Other copolymerization components include isophthalic acid,
Phthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, succinic acid, adipic acid, sebacic acid, dodecane diacid, dimer acid, maleic anhydride,
Maleic acid, fumaric acid, itaconic acid, citraconic acid,
Mesaconic acid, dicarboxylic acids such as cyclohexanedicarboxylic acid, 4-hydroxybenzoic acid, ε-caprolactone, oxycarboxylic acids such as lactic acid, 1,3-propanediol, 1,6-hexanediol, glycols such as cyclohexanedimethanol, Trimellitic acid, trimesic acid, pyromellitic acid, trimethylolpropane,
Examples include polyfunctional compounds such as glycerin and pentaerythritol.

The PTMG used in the present invention has a molecular weight of from 600 to 4,000, preferably from 1,000 to 3,000.
0, and more preferably 1,000 to 2,000. Molecular weight
When it is less than 600, tear linearity cannot be obtained, and when it exceeds 4,000, performances such as mechanical strength, dimensional stability and haze are reduced, and stable tear linearity of the film is not exhibited.

In the film of the present invention, the content of the PTMG unit constituting the modified PBT is 5 to 20% by weight,
Preferably 10 to 20 (% by weight), more preferably 10 to 15
(% By weight). When the content of PTMG is less than 5% by weight, the resulting film does not exhibit tear linearity,
If the content exceeds 20% by weight, the mechanical strength, dimensional stability, haze and other properties of the obtained film are reduced.
It is difficult to obtain stable tear linearity of the film. When the content of PTMG exceeds 20% by weight, a phenomenon in which the film pulsates at the time of extrusion (a so-called ballast phenomenon) may be exhibited, particularly when produced on a mass production scale, and the thickness unevenness of the film increases. Problems arise.

In order to produce the film of the present invention, P
The mixing ratio of ET and modified PBT is expressed as PET / modified PBT =
70/30 to 95/5 (weight ratio), preferably 80/20 to 90/10
(Weight ratio), more preferably 85/15 to 90/10 (weight ratio). When the mixing ratio of the modified PBT is less than 5% by weight, the tear linearity cannot be obtained, and when it is more than 30% by weight, the variation in the thickness of the film becomes large or the tear linearity of the obtained film decreases. In addition, the performance such as mechanical strength, dimensional stability, and haze is reduced, and a problem occurs in practical performance. That is, in order to impart the tear linearity and practical performance of the film, it is necessary that the mixing ratio of PET and modified PBT be within the above range.

The modified PBT of the present invention can be obtained by polycondensation by adding PTMG in the polymerization step of PBT, but a simpler method is to use PBT and PTM.
G can also be obtained by melt-kneading with an extruder.

The raw material resin in the present invention may be mixed with other polymers such as polyethylene naphthalate and polycyclohexylene dimethylene terephthalate as long as the effects of the present invention are not impaired.

To produce the film of the present invention, first,
For example, a mixture of modified PBT and PET is charged into an extruder, heated and melted, and then extruded into a sheet shape from a die orifice of a T-die to produce an unstretched sheet. The sheet extruded from the die orifice of the T-die is wound tightly around a cooling drum by an electrostatic application casting method or the like, and cooled, and then vertically and horizontally at a temperature of 90 to 140 ° C. 3.
The film is stretched at a magnification of 0 to 5.0 times and further heat-treated at a temperature of 210 to 245 ° C to obtain a biaxially stretched film.

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., the crystallization of PET may be promoted and the transparency may be deteriorated. . When the stretching ratio is less than 3.0 times, the strength of the obtained stretched film is low, and pinholes are liable to be generated when the bag is formed. When the stretching ratio exceeds 5.0 times, stretching may be difficult. The heat treatment temperature is 21
When the temperature is lower than 0 ° C., the heat shrinkage of the obtained stretched film becomes large, and the bag after bag making may be deformed. On the other hand, when the heat treatment temperature is higher than 245 ° C., the film may be blown.

The biaxial stretching method may be any of a tenter simultaneous biaxial stretching method and a sequential biaxial stretching method using a roll and a tenter. Further, a biaxially stretched film may be manufactured by a tubular method.

The biaxially stretched polyester film of the present invention preferably has a tensile strength in the range of 17 to 35 kgf / mm ^{2. If} the tensile strength is smaller than this range, the practical strength is insufficient. However, not only is the quality too high, but also the operability during film production deteriorates, which is economically undesirable. 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 oriented polyester film of the present invention preferably has a dry heat shrinkage ratio of 3% or less (average value in the longitudinal and width directions) at 160 ° C. for 15 minutes.
%, It is not preferable because printability deteriorates.

Further, the biaxially stretched polyester film of the present invention preferably has a haze of 10% or less. If the haze exceeds 10%, the transparency of the film deteriorates and the commercial value is impaired.

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

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

(1) Raw material PET: relative viscosity 1.38 manufactured by Unitika Ltd. PBT: Novadur 5010 manufactured by Mitsubishi Engineering Plastics, relative viscosity 1.10 (measurement method is the same as above)

(2) Measurement method Relative viscosity: Relative viscosity was 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 performed for each of the left end, the center, and the right end of the film wound after the stretching heat treatment.

Haze (haze): The haze of a film having a thickness of 12 μm was measured according to ASTM D103-61. Tensile strength; ASTM-D using 10mm wide and 100mm long sample
It was measured according to 882. Thickness unevenness: Using a HEIDENHAIN micrometer, set the thickness at the center of the film in the width direction at a pitch of 10 cm in the MD direction.
The thickness at 20 points was measured, and the thickness unevenness (%) was determined using the following equation. [(Thickness maximum value-Thickness minimum value) / Thickness average value] x 100

Example 1 194 parts by weight of dimethyl terephthalate, 108 parts by weight of 1,4-butanediol, and 80 ppm of tetrabutyl titanate (a value converted into the weight of titanium metal with respect to the polymer) were added, and the temperature was raised from 150 ° C. to 210 ° C. The transesterification reaction was performed for 2.5 hours while heating. 90 parts by weight of the obtained transesterification reaction product was transferred to a polymerization reactor, and 40 ppm of tetrabutyl titanate was added. Then, 10 parts by weight of PTMG having a molecular weight of 1,100 was added, and the pressure was reduced, and finally the pressure was reduced to 1 hPa. ,twenty one
The temperature was raised from 0 ° C. and finally melt-polymerized at a temperature of 245 ° C. for 2 hours to obtain a modified PBT having a relative viscosity of 1.60. PET and modified P
Melt extruded BT and 85/15 weight ratio mixed chips at a resin temperature of 280 ° C using a 200mm φ extruder equipped with a coat hanger type T-die, and a cast roll temperature-controlled to 20 ° C Then, an applied voltage of 7 kV was applied to the pinning wire, followed by rapid contact cooling to obtain an unstretched sheet having a thickness of about 190 μm. The obtained unstretched sheet is rolled at 90 ° C with a longitudinal stretching machine.
Stretched 3.5 times at 120 ° C and 4.5 times at 120 ° C with a tenter transverse stretching machine, and then heat-treated at 235 ° C with a transverse relaxation rate of 3%, and cooled to room temperature to obtain a 12 µm-thick biaxially stretched film. I got The tear linearity of the obtained biaxially stretched film was measured, and the results are shown in Table 1.

Examples 2 to 12, Comparative Examples 1 to 8 The molecular weight of PTMG, the weight ratio of PTMG in the modified PBT,
A biaxially stretched film was obtained in the same manner as in Example 1, except that the weight ratio between PET and modified PBT was changed as shown in Tables 1 and 2. The tear linearity of the obtained biaxially stretched film was measured, and the results are shown in Tables 1 and 2. Examples 2 to 12
In the above, a biaxially stretched film excellent in transparency, strength, thickness accuracy and tear linearity was obtained. However, in Comparative Examples 1 and 2, since the copolymerization ratio of PTMG in the modified PBT was large, the thickness of the obtained film was large. Spots became large, and in Comparative Example 1, film formation became difficult. In Comparative Examples 3 and 4, since the copolymerization ratio of PTMG in the modified PBT was too small, tear linearity was not obtained. In Comparative Example 5, PTMG in the modified PBT was used.
Was too small in molecular weight to obtain tear linearity. In Comparative Example 6, the molecular weight of PTMG was too large to increase thickness unevenness and decrease tear linearity. Further, in Comparative Example 7, the tear linearity was not obtained because the amount of the modified PBT was too small, and in Comparative Example 8, the uneven thickness was increased because the amount of the modified PBT was too large, and the tear linearity was lowered. did.

Example 13 PBT and PTMG having a molecular weight of 2,000 were converted to PBT / PTMG.
= 85/15 (weight ratio) was melt-mixed with a twin-screw extruder to form chips, thereby preparing modified PBT (relative viscosity 1.36). Next, the resulting modified PBT and P
ET mixed with chips at a ratio of 15/85 (weight ratio), 200mm φ equipped with a coat hanger type T die
Using an extruder, the resin was melt-extruded at a resin temperature of 270 ° C. for a residence time of 5 minutes, and applied to a cast roll adjusted to a temperature of 20 ° C. by applying a voltage of 7 kV to a pinning wire and rapidly cooled.
An unstretched sheet of 90 μm was obtained. The obtained unstretched sheet is 3.5 times at 90 ° C. with a roll longitudinal stretching machine and 12 times with a tenter transverse stretching machine.
After stretching 4.5 times at 0 ° C, heat treatment is performed at 235 ° C with the relaxation rate in the transverse direction being 3%, and the film is gradually cooled to room temperature, and has a thickness of 12 µm.
m was obtained. The tear linearity of the obtained biaxially stretched film was measured, and the results are shown in Table 1.

[0030]

[Table 1]

[0031]

[Table 2]

Examples 14 to 24, Comparative Examples 9 to 16 Using the films obtained in Examples 1 and 7 and Comparative Examples 5 and 7, dry lamination was carried out in the configuration shown in Table 3, and the longitudinal direction of the polyester film was After making a four-sided seal bag having a length and width of 200 mm each made so as to be in the bag tearing direction, the tear linearity was evaluated. Table 3 shows the results of evaluating the tear linearity. In the evaluation, those that were torn almost linearly were considered acceptable, and those that could not be torn or were torn diagonally were rejected.

The abbreviations of the components of the packaging material are as follows. PT1: Biaxially oriented film obtained in Example 1 PT2: Biaxially oriented film obtained in Example 7 PT3: Biaxially oriented film obtained in Comparative Example 5 PT4: Biaxially obtained film in Comparative Example 7 Oriented 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: Unstretched polypropylene film (Toray) Made,
CPP2: Unstretched polypropylene film (Toray Co., Ltd.
AL: Aluminum foil (manufactured by Showa Aluminum Co., Ltd., thickness 7μm)

[0034]

[Table 3]

[0035]

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 the drawings]

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

FIG. 2 is a diagram showing the shape of a test piece after tearing in a tear test, wherein (a) is an example of a test piece after tearing of a sample having good tear linearity, and (b) is poor in tear linearity. 5 shows an example of a test piece after tearing of a sample.

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI // B29K 67:00 B29L 7:00 (56) References JP-A-8-169962 (JP, A) JP-A-1-165627 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C08L 67/03 C08J 5/18 CA (STN)

Claims (6)

(57) [Claims] 1. A polybutylene terephthalate (modified PBT) containing 5 to 20% by weight of a polytetramethylene glycol unit having a molecular weight of 600 to 4,000 and a polyethylene terephthalate (PET) are obtained by mixing PET / modified PBT = 70/30.
A biaxially stretched polyester film having a tear linearity at least in the longitudinal direction, which is produced using raw materials mixed at a ratio of about 95/5 (weight ratio). 2. The modified PBT obtained by a polycondensation reaction between a transesterification reaction product of dimethyl terephthalate and 1,4-butanediol and polytetramethylene glycol having a molecular weight of 600 to 4,000. The biaxially stretched polyester film according to claim 1, wherein 3. A modified PBT comprising a mixture of 80 to 95% by weight of polybutylene terephthalate (PBT) and 20 to 5% by weight of polytetramethylene glycol having a molecular weight of 600 to 4,000.
The biaxially stretched polyester film according to claim 1, which is produced by melt-kneading. 4. A tensile strength of 17 to 35 kgf / mm2 and a haze of 10
The biaxially stretched polyester film according to any one of claims 1 to 3, which has a characteristic of not more than%. 5. A laminated film using the biaxially stretched polyester film according to claim 1 for at least one layer. 6. An easily-openable packaging bag made from the laminated film according to claim 5 so that the direction of easy tearing is the direction of tearing of the bag.