JP2001287264A - Biaxially stretched polyester film and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially stretched polyester film having excellent tear rectilinearity and tear strength while holding dynamic characteristics, aroma retention, heat resistance, oil resistance, low moisture absorption and, especially, dimensional stability under dry and moist heat environment required in a food packaging material. SOLUTION: The biaxially stretched polyester film comprises a mixture consisting of 90-70 weight % of a crystalline polyester resin (A) containing 80 mol% or more of terephthalic acid and 10-30 weight % of block copolyester (B) consisting of a crystal segment with a melting point of 170 deg.C or higher and a soft polymer with a melting or softening point of 100 deg.C or lower and a molecular weight of 400-8,000 and is excellent in tear rectilinearity in a machine direction and characterized by that a ratio of tear strength in a machine direction to that in the direction crossing the machine direction at a right angle is 0.7 or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a confectionery, pickle, miso, soup, jam, frozen, refrigerated, and has excellent tear straightness, excellent tear strength, heat resistance, and dimensional stability.
Including foods such as retort pouches, pharmaceuticals, daily necessities,
The present invention relates to a film useful as a packaging material for cosmetics and the like.

[0002]

2. Description of the Related Art In the packaging of foods, medicines and miscellaneous goods, packaging bags using various plastic films are often used. Two or three layers of a biaxially stretched plastic film and a heat-sealable non-oriented plastic film are used. The packaging bags laminated as described above are widely used.

[0003] The biaxially stretched polyester film is durable,
It is excellent in moisture resistance, mechanical strength, heat resistance and oil resistance, and biaxially stretched polyester film manufactured using tubular method, flat simultaneous biaxial stretching method, flat sequential biaxial stretching method etc. is used for food packaging. Widely used in the field.

[0004] However, a packaging bag using a biaxially stretched polyester film has a problem that tear-openability is poor. There is a method of providing a notch to improve the openability, but when tearing from the notch, a phenomenon that it does not tear linearly often occurs, and not only is the content scattered but wasted, but also cookies etc. The soft confectionery may break when opened, or may cause troubles such as soiling clothes when the contents are liquid.

[0005] As an easy-open packaging material excellent in straightness 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 had to be provided, which was problematic in terms of cost, and its use was limited. In order to solve such problems with a single-layer film and complete the opening,
It is not enough to have tear straightness, and auxiliary means such as providing a lead tape or tear tape for guiding the tearing direction or performing scoring is required. In addition, the conventional polyester film with excellent straightness of tearing has low tear strength in the direction to be torn, and inappropriate tearing occurs during the manufacturing process or converting, or after the bag is sealed and the contents are filled. Due to various stresses, there is a disadvantage that unscheduled spontaneous unsealing is likely to occur in a direction having a tear straightness.

[0006]

DISCLOSURE OF THE INVENTION The present invention is intended to solve such a problem, and it is intended to solve the problems of the mechanical properties, fragrance retention, heat resistance, oil resistance and low mechanical properties which are characteristic of biaxially stretched polyester films. While maintaining moisture absorption and dimensional stability under the dry heat and wet heat environment required especially for food packaging materials, it has improved tear strength in the direction that has been weak to tear, and has excellent tear straightness. Another object of the present invention is to provide a biaxially stretched polyester film having a large tear strength in a direction to be torn.

[0007]

Means for Solving the Problems The present inventors have made intensive studies to solve such problems, and as a result, have reached the present invention. That is, the biaxially stretched polyester film of the present invention is characterized in that the ratio of the tear strength in the machine flow direction to the tear strength in the orthogonal direction is 0.7 or more, and excellent tear straightness in the machine flow direction. It is a polyester film.

In this case, a biaxially stretched polyester film having excellent tear straightness in the machine flow direction and having a tear strength in the direction equal to or higher than the tear strength in the orthogonal direction is preferred.

In this case, the crystalline polyester resin (A) containing at least 80 mol% of terephthalic acid is used.
90-70 wt%. Crystal segment having a melting point of 170 ° C. or more and a melting point or softening point of 100 ° C. or less, and a molecular weight of 400 to 8
A biaxially stretched polyester film composed of a mixture of 10 to 30% by weight of a block copolymer polyester (B) composed of 000 soft polymers is preferred.

Further, in this case, the intrinsic viscosity of the crystalline polyester resin (A) is 0.68 or more and 0.9 or more.
A biaxially oriented polyester film having a value of 0 or less is preferable.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the polyester film of the present invention will be described below.

The biaxially oriented polyester film of the present invention has a tear strength of 2.20 g in the machine flow direction (MD direction).
That is all. It is preferably at least 2.50 g. When the tear strength is less than 2.20 g, the tear resistance in the direction of the straight tearing property is poor. If the tear strength exceeds 5.00 g, it is difficult to develop tearing straightness in the machine flow direction.

The biaxially stretched polyester film of the present invention has a value obtained by dividing the tear strength in the machine flow direction (MD direction) by the tear strength in the orthogonal direction (TD direction): R is 0.7.
0 or more. Preferably, R is not less than 0.80 and not more than 2.00. When R is less than 0.70, the tear resistance in the straight tear direction is poor as in the case of the conventional straight tear film. Further, when R exceeds 1.00, a very excellent film in which the direction of easy tearing and the direction of straight tearing are different is obtained. When R exceeds 2.00, it is difficult to develop tearing straightness in the machine flow direction.

In the present invention, the crystalline polyester (A)
The blending ratio of the block copolymer polyester (B) to the crystalline polyester (A) is preferably 90 to 70 wt%, and the block copolymer polyester (B) is blended at a ratio of 10 to 30 wt%, more preferably. 90 to 75% by weight of the crystalline polyester (A), 10 to 25% by weight of the block copolymerized polyester (B), more preferably 90 to 80% by weight of the crystalline polyester (A) and 10 to 20% by weight of the block copolymerized polyester (B). . If the amount of the block copolymer polyester (B) is less than 10% by weight, tearing straightness cannot be obtained. If the amount of the block copolymerized polyester (B) exceeds 30% by weight, the tensile strength of the biaxially stretched polyester film is reduced, and the dimensional stability and rigidity are reduced, so that it cannot be used.

The crystalline polyester (A) in the present invention
Is a polyester having ethylene terephthalate as a main repeating unit, and polyethylene terephthalate (P
ET) is optimal, but a copolymer of PET and polybutylene terephthalate (PBT), PET and polyethylene naphthalate (PEN), or a mixture thereof can be used.

The polyester has an intrinsic viscosity of 0.6.
Those having 8 dl / g or more are preferable, and those having 0.70 dl / g or more and 0.9 dl / g or less are suitable. When the one having an intrinsic viscosity of less than 0.68 dl / g is used, both impact strength and tear straightness are not excellent. When the intrinsic viscosity is larger than 0.9 dl / g, the extrusion moldability is poor. Although the polymerization method of the crystalline polyester (A) is not particularly limited,
A solid-state polymerization method can be used in combination to set the intrinsic viscosity in a suitable range.

In the block copolymer polyester (B) of the present invention, the crystal segment having a melting point of 170 ° C. or higher has a melting point of 170 ° C.
° C or higher, for example, residues of aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid, and ethylene glycol, propylene glycol, butanediol, pentamethylene glycol, and P-xylene glycol And polyesters comprising residues of aliphatic, aromatic and alicyclic diols such as cyclohexanedimethanol, etc., and it is particularly desirable that terephthalic acid residues account for 80 mol% or more.

A soft polyester having a molecular weight of 400 to 8000 has a melting point or softening point of 100 ° C. or lower when measured only with the segment constituents. When a molecular weight of 400 or less is used, the obtained block copolymerized polyester has a low melting point and a high tackiness,
It becomes difficult to process it into a film. When the molecular weight exceeds 8,000, the soft polymer undergoes layer separation, exhibits an extremely high melt viscosity, becomes hard and brittle, and becomes difficult to remove from the polymerization vessel after the copolymerization reaction. When a polymerized polyester is used for film formation, transparency is poor, which is not preferable. Particularly preferably, those having a molecular weight of 800 to 4000 are good.

The proportion of the low melting point soft polymer in the block copolymerized polyester is in the range of 1 to 12 mol%. When the amount is less than 1 mol%, the properties as a soft polymer cannot be obtained. When the amount exceeds 12 mol%, the dispersion of the block copolymerized polyester (B) becomes large at the time of mixing and melting with the crystalline polyester (A), and the tearing straightness is reduced. It cannot be obtained, and the transparency deteriorates. Particularly preferably, it is 3 to 8 mol%. Examples of such a low-melting soft polymer include polyethylene oxide glycol, polytetramethylene oxide glycol, polypropylene oxide glycol,
Polyethers such as copolymerized glycols of ethylene oxide and propylene oxide, copolymerized glycols of ethylene oxide and tetrahydrofuran, aliphatic polyesters such as polyneopentyl azelate, polyneopentyl adipate, polyneopentyl sepacate, poly-
Examples thereof include polylactones such as ε-caprolactone and polypivalolactone. Preferably, polyethylene oxide glycol, polytetramethylene oxide glycol and the like are practical.

These block copolymerized polyesters can be produced by a usual condensation polymerization method. Specific examples of the block copolymer polyester used in the present invention include polyethylene terephthalate-polyethylene oxide block copolymer, polyethylene terephthalate-polytetramethylene oxide block copolymer, polybutylene terephthalate-polyethylene oxide block copolymer, and polybutylene. Terephthalate-
Polytetramethylene oxide block copolymer, polyethylene terephthalate-polyethylene oxide, polypropylene oxide block copolymer, polytetramethylene terephthalate / isophthalate-polytetramethylene oxide block copolymer, polyethylene terephthalate-poly-ε-caprolactone block copolymer Coalesce, polyethylene terephthalate-polyneopentylseparate block copolymer, block copolymer of polyester from di (4-carboxyphenoxy) ethane and ethylene glycol and polyethylene glycol,
A block copolymer of a polyester from bis (N-paracarboethoxyphenyl) adipamide and ethylene glycol and polyethylene glycol can be exemplified.

In producing the film of the present invention, it does not matter at all if an appropriate additive such as an antioxidant, an antiblocking agent, an ultraviolet absorber or a lubricant is added in advance.

As a method of forming the film of the present invention, for example, a mixture of crystalline polyester (A) and block copolymerized polyester (B) in the form of chips is charged into an extruder, heated and melted. The sheet is extruded and discharged from the die orifice of the die into a sheet. In this case, the shear rate of the resin at the die orifice is preferably 200 sec-1 or more. If the shear rate is less than 200 sec-1, straight cutting properties cannot be obtained. Next, the sheet in this softened state
It is wound tightly around the cooling drum and cooled.

Subsequently, the obtained unstretched sheet is 90 to 1
The film is stretched at a temperature of 10 ° C. in the machine direction at a stretch ratio of 3 to 4 times. Subsequently, at a temperature of 80 to 110 ° C., 3.5 in the lateral direction.
The film is stretched at a stretching ratio of up to 4.5 times. When the stretching ratio is lower than the respective temperatures, a uniform stretched film may not be obtained. On the other hand, when the respective stretching temperatures exceed the respective temperatures, crystallization of the crystalline polyester (A) is promoted, resulting in poor transparency. May be. The biaxially stretched film is subsequently heat treated at a temperature of 210-250 ° C. If the heat treatment temperature is lower than 210 ° C., the shrinkage of the film increases, which causes deformation when used as a bag. On the other hand, when the temperature is higher than 250 ° C., the film melts and it becomes difficult to form a film. The biaxial stretching method is preferably a sequential biaxial method using a roll and a tenter, and it is desirable that the film be stretched in the longitudinal direction and then stretched in the horizontal direction. When the longitudinal stretching is performed after the transverse stretching, it is difficult to obtain a straight tearing property.

The heat shrinkage of the biaxially stretched polyester film of the present invention is preferably 3% or less in both the machine flow direction (MD direction) and the width direction (TD direction) at 150 ° C. for 30 minutes. When the heat shrinkage exceeds 3%, printability deteriorates, which is not preferable. The haze of the biaxially stretched film of the present invention is preferably 4% or less. 4%
Exceeding the range deteriorates the transparency of the film and impairs the commercial value.

The biaxially stretched film of the present invention can be subjected to a corona discharge treatment, a flame treatment, a surface hardening treatment, or a surface treatment by various coatings. Next, the present invention will be specifically described with reference to examples. In addition, the measuring method of an Example and a comparative example is as follows.

[0026]

【Example】

(Measurement method) Tear strength A strip of 30 mm in width and 10 mm in width is cut out in the tearing direction. Using a razor, pull 12 from the center of the short side 5mm in the tearing direction.
Make a notch of mm. Using an Instron-type tensile tester equipped with a 100 g measurement load cell and a sample chuck that is as light as possible, using a 5 mm-end of each sample as a margin, a tear strength of 500 mm / min.
Take a chart of the chuck moving distance and read the tear strength when the chuck moving distance is 20 mm. MD direction tear,
The measurement is performed three times each in the TD direction, and the average is taken. 2. Reduced viscosity and intrinsic viscosity Using an Ubbelohde type viscosity tube, a sample was dissolved at a solution concentration of 0.4 g / dl in a mixed solvent of phenol / tetrachloroethane at a weight ratio of 6/4, and reduced from the value measured at a temperature of 30 ° C. The viscosity is determined and, if necessary, converted to the intrinsic viscosity. 3. Tear straightness From a biaxially stretched film, a sample in which a strip-shaped film piece of 200 mm in the MD direction and 40 mm in the TD direction was cut out, and a cutout of 5 mm in length was cut into the center of one short side of one side of this film piece. Create 10 books. Next, the hand was torn in the MD direction from the cut, and the tear propagation end reached within 5 mm from the center of the short side facing the cut side. Those that did not reach the side were marked as x. 4. Haze A film having a thickness of 12 μm was measured according to JIS K-7105. 5. Heat shrinkage A strip sample with marked lines in the MD and TD directions of the film was cut out and treated in an oven at 150 ° C. for 30 minutes. After the treatment, the distance between the marked lines was 23 ° C. and 65% RH equilibrium. Was measured. The amount of shrinkage due to the treatment was shown as a percentage of the dimension before the treatment.

Example 1 As a crystalline polyester (A), SR553 manufactured by Toyobo Co., Ltd. (intrinsic viscosity 0.75 dl / g)
Using, as a block copolymerized polyester (B),
Modified P composed of 100 mol% of terephthalic acid as a dicarboxylic acid component, 96.7 mol% of butanediol and 3.3 mol% of polytetramethylene glycol as a diol component
A mixture was prepared by mixing BT (reduced viscosity: 1.33 dl / g) at a ratio of 90/10 wt%. This was melt-extruded from a T-die at a resin temperature of 280 ° C. using a 65 mmφ extruder, and closely quenched to a cast roll adjusted to 25 ° C.
An unstretched sheet having a thickness of about 200 μm was obtained. At this time, the shear rate at the die was 360 sec-1. Next, the obtained unstretched sheet is stretched 3.7 times at 100 ° C. by a roll type longitudinal stretching machine and 4.5 times at 105 ° C. by a tenter type transverse stretching machine, and then relaxed by 5% in the transverse direction. Treat at 240 ° C
And cooled to room temperature to obtain a biaxially stretched film having a thickness of 12 μm. The tear straightness of the obtained biaxially stretched film was measured, and the results are shown in Table 1.

[0029]

[Table 1]

Example 2 Example 1 was repeated except that the proportions of PET and modified PBT used in Example 1 were changed as shown in Table 1 as the crystalline polyester (A) and the block copolymerized polyester (B). In the same manner as in the above, a biaxially stretched film was obtained.

Comparative Example 1 A biaxially stretched film was obtained in the same manner as in Example 1, except that simultaneous biaxial stretching was performed as a stretching method.

Comparative Example 2 Polyethylene Terephthalate
(Intrinsic viscosity: 0.63 dl / g), melt extruded from a T-die at a resin temperature of 280 ° C. using a 65 mm φ extruder, tightly and rapidly cooled to a cast roll adjusted to 25 ° C. An unstretched sheet having a thickness of about 200 μm was obtained. At this time, the shear rate at the die was 270 sec-1. Then, the obtained unstretched sheet was rolled by a roll-type longitudinal stretching machine to 10
After stretching 3.7 times at 0 ° C. and 4.5 times at 105 ° C. with a tenter-type transverse stretching machine, a 5% relaxation treatment in the transverse direction was performed.
Heat treatment at 240 ° C, cool to room temperature, thickness 12μ
m biaxially stretched film was obtained.

[0033]

According to the present invention, the biaxially stretched polyester film has the following characteristics: durability, moisture resistance, mechanical properties,
A biaxially stretched polyester film having heat resistance and oil resistance, high tear strength in the MD direction of the film, and tear straightness in the MD direction is provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of evaluation of tear straightness.

[Explanation of symbols]

 1 Notch with 5mm length

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B29L 7:00 B29L 7:00 (72) Inventor Kazumoto Imai 344 Mazuhata, Kizu, Oaza, Inuyama City, Aichi Prefecture Toyo Toyo Spinning Co., Ltd. Inuyama Plant (72) Inventor Keiji Mori Inuyama City, Aichi Prefecture Inoyama Kizu character Maehata 344 Toyo Spinning Co., Ltd. Inuyama Plant F term (reference) 3E064 BA54 BC01 BC15 BC20 EA30 FA01 FA04 FA05 4F071 AA45 AA45X AA46X AA47 AA47X AA75 AA81 AF16 AF45 AF54 AH04 BA01 BB06 BB08 BC01 BC10 4F210 AA24A AA24C AA24F AG01 QA02 QA03 QC05 QC06 QD16 QG01 QG18 QW12 4J002 CF05W CF06X CF07X CF10X CF18X GG02

Claims (4)

[Claims] 1. A biaxially stretched polyester film, wherein the ratio of the tear strength in the machine flow direction to the tear strength in the orthogonal direction is 0.7 or more and 2 or less, and the tear straightness in the machine flow direction is excellent. . 2. The biaxially stretched polyester film according to claim 1, wherein the ratio of the tear strength in the machine flow direction to the tear strength in the orthogonal direction is 1.0 or more and 2.0 or less. 3. The crystalline polyester resin (A) according to claim 1, wherein the polyester contains at least 80 mol% of terephthalic acid. Crystal segment of melting point 170 ° C or higher and melting point or softening point of 100 ° C or lower,
A biaxially stretched polyester film comprising a mixture of 10 to 30% by weight of a block copolymer polyester (B) comprising a soft polymer having a molecular weight of 400 to 8000. 4. The axially stretched polyester film according to claim 3, wherein the intrinsic viscosity of the crystalline polyester resin (A) is 0.68 or more and 0.90 or less.