JPH11300916A - Easy-tearing polyester film and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a biaxially stretched polyester film having excellent gas barrier properties and good tear straightness. SOLUTION: An easy-tearing polyester film is obtained by laminating a polyvinylidene chloride copolymer layer on at least the single surface of a biaxially stretched polyester film produced by using a raw material prepared by mixing polybutylene terephthalate (modified PBT) containing 5-20 wt.% polytetramethylene glycol unit with a mol.wt. of 600-4,000 and polyethylene terephthate(PET) in a PET/modified PBT wt. ratio of 70/30-95/5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a polyester film having excellent strength, dimensional stability and transparency, and a high gas barrier property.
The present invention relates to an easily tearable biaxially stretched polyester film having tear straightness required for packaging materials such as miscellaneous goods.

[0002]

2. Description of the Related Art Various plastic film packaging bags are used in large quantities for packaging foods, pharmaceuticals, miscellaneous goods, etc., and it is required to preserve the expiration date and expiration date for a longer time. There is an increasing demand for films having the same. As a laminated film used for a packaging bag, a laminated film of a biaxially stretched plastic film and a heat-sealable non-stretched film is generally used. Biaxially stretched polyester film is excellent in strength, dimensional stability and fragrance retention, but for food packaging applications where long-term storage is required, it is necessary to improve oxygen and water vapor barrier properties, and polyvinylidene chloride copolymer (P
VDC) coated films are widely used.

[0003] In addition, as a characteristic required for a packaging bag, it is required that the packaging bag has two characteristics which are considered to be seemingly contradictory to strength and easy tearing when opened. There is a method of providing a notch to improve the opening property, 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,
A soft confectionery such as a cookie may break when opened, or may cause troubles such as staining clothes when the content is 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.

[0005]

DISCLOSURE OF THE INVENTION The present invention is intended to solve such problems, and provides a stretched film having excellent gas barrier properties and excellent tearability, and a stretched film thereof. An object of the present invention is to provide a packaging bag excellent in easy-opening properties.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to solve such problems, and as a result, have found that a PVDC layer is formed on a polyester film produced by using a composition obtained by mixing a specific polyester resin with PET. The inventors have found that the laminated film can solve the above-mentioned problems, and have reached the present invention.

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 = 70/3.
An easily tearable polyester film in which a polyvinylidene chloride-based copolymer layer is laminated on at least one surface of a biaxially stretched polyester film produced using raw materials mixed at a ratio of 0 to 95/5 (weight ratio).

[0008]

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.

Other copolymerization components include oxalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid,
5-sodium sulfoisophthalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, dimer acid, maleic anhydride, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, cyclohexanedicarboxylic acid, etc. Oxycarboxylic acids such as dicarboxylic acid, 4-hydroxybenzoic acid, ε-caprolactone, lactic acid, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, cyclohexanedimethanol, tricarboxylic acid Glycols such as ethylene glycol, polyethylene glycol, polypropylene glycol and polytetramethylene glycol, ethylene oxide adducts such as bisphenol A and bisphenol S, trimellitic acid, trimesic acid, pyromellitic acid, Ji roll propane, glycerin,
And polyfunctional compounds such as pentaerythritol.

The molecular weight of the polytetramethylene glycol (PTMG) used in the present invention is preferably 6
00 to 4,000, more preferably 1,000 to 3,
000. When the molecular weight is less than 600,
If it exceeds 0, the tear linearity of the film may not be reduced, and if the molecular weight exceeds 4,000, mechanical strength, dimensional stability, performance such as haze may be reduced, Moreover, stable tear linearity of the film is not exhibited.

In the film of the present invention, the content of PTMG units constituting the modified PBT is 5 to 20% by weight, preferably 10 to 20 (% by weight), and more preferably 10 to 15 (% by weight). . PTMG content is 5
If the amount is less than 20% by weight, the resulting film will not exhibit tear linearity, and if it exceeds 20% by weight, the resulting film will have poor mechanical strength, dimensional stability, haze and other properties, and It is difficult to obtain stable tear linearity of the film. The content of PTMG is 20% by weight.
In the case where the ratio exceeds 1, the phenomenon that the film pulsates at the time of extrusion (so-called a ballast phenomenon) may be exhibited particularly when the film is produced on a mass production scale, and a problem that the thickness unevenness of the film becomes large occurs.

In order to produce the polyester film of the present invention, the mixing ratio of PET and modified PBT is
ET / modified PBT needs to be 70/30 to 95/5 (weight ratio), preferably 80/20 to 90 /
10 (weight ratio), more preferably 85/15 to 90 /
10 (weight ratio). If the mixing ratio of the modified PBT is less than 5% by weight, the tear linearity cannot be obtained, and if it exceeds 30% by weight, the performance such as mechanical strength, dimensional stability, haze and the like is reduced, resulting in practical performance. A problem arises, and the thickness unevenness increases and tear linearity decreases.

The modified PBT in the present invention can be obtained by adding PTMG and conducting polycondensation in the polymerization step of PBT.
It can also be obtained by melt-kneading BT and PTMG.

In the film of the present invention, other thermoplastic resins such as polyethylene naphthalate and polycyclohexylene dimethylene terephthalate can be mixed as long as the effects of the present invention are not impaired. In addition, ultraviolet absorbers, antioxidants, antistatic agents, surfactants, pigments, fluorescent brighteners, etc., and inorganic particles such as silica, calcium carbonate, titanium oxide, etc., and organic materials containing acrylic acid, styrene, etc. Particles may be appropriately contained as necessary.

As the PVDC used in the present invention, one or more components such as vinylidene chloride homopolymer, vinylidene chloride, acrylic acid, acrylic acid ester, methacrylic acid, methacrylic acid ester, vinyl chloride, glycidyl methacrylate and methylol methacrylate are used. A polymerized product is used.

In the present invention, a method for forming a layer comprising PVDC includes a method in which a lubricant or an antistatic agent is blended with an organic solvent solution or an aqueous dispersion of PVDC, if necessary, as a solid content after drying of 0.1 to 0.1%. 5.0 g / m ^2, there is preferably a method of coating such that 0.2 to 2.0 g / m ^2. If the above coating thickness is less than 0.1 g / m ² , the gas barrier property under high humidity is insufficient, and the thickness is 5.0 g / m ^2.
If it exceeds g / m ² , there are problems in operability and cost. Examples of the coating method include a post-coating method in which a polyester film in the present invention is coated with an organic solvent solution or an aqueous dispersion of PVDC, or a pre-coating method in which an unstretched polyester film is coated and then stretched.

The polyester film of the present invention is manufactured by using the precoating method, whereby the adhesion between the base polyester film and the PVDC layer can be improved, and the thickness of the PVDC layer can be reduced. In addition, the tear linearity of the obtained laminated film is improved. Further, the precoat method has better productivity and is economically superior to the postcoat method.

As a specific example of producing the polyester film of the present invention, for example, after blending PBT and PTMG at a predetermined mixing ratio, melt-kneaded using a twin-screw extruder, and pelletized into chips. The resulting metamorphic PB
A mixture of T and PET chips is put into an extruder,
After being heated and melted, an unstretched film is extruded in the form of a sheet from a die orifice of a T-die and cooled by a cooling drum by an electrostatic application casting method or the like.

Subsequently, PVD is applied to the obtained unstretched film.
C, and after drying at 50-150 ° C, 70-180
At the same time or sequentially at a magnification of 3.0 to 5.0 times in the vertical and horizontal directions at a temperature of 210 ° C.
And a heat treatment and a relaxation treatment.

When the biaxially stretched film obtained in the present invention is used for packaging bags, it is called a sealant such as polyethylene, polypropylene, ethylene-vinyl acetate copolymer, and ionomer for imparting heat sealability. Used by laminating with an unstretched film. Further, a stretched nylon film, another plastic film, paper, a metal foil such as aluminum or the like can be laminated on the polyester film of the present invention.

Next, the present invention will be specifically described with reference to examples. The methods for evaluating various physical properties in Examples and Comparative Examples are as follows.

(1) Raw material N6: A1030BRF PVDC manufactured by Unitika Ltd. Saran latex L52 manufactured by Asahi Kasei Corporation
9B (2) Measuring method Tear linearity: From the laminated film, cut out a strip-shaped film piece of 205 mm in the longitudinal direction (MD direction) and 10 mm in the width direction (TD direction) of the polyester film, and cut one short side of this film piece. Ten samples having a cut of 5 mm in length at the center of the side are prepared (FIG. 1). Next, as shown in FIG. 2 (a), the number of samples whose tear propagation ends reached the short side facing the side where the cut was made was determined as the evaluation value of the tear linearity in the MD direction. did. Evaluation value 8
The above items were evaluated as 、, 7 to 5 as Δ, and 4 or less as ×. Oxygen permeability (cc / m ² · 24 hr · atm); JIS K-71
OX-TR manufactured by Modern Control Co., Ltd.
The measurement was performed using an AN100 model under the conditions of a temperature of 20 ° C and a humidity of 100% RH. Water vapor permeability (g / m ² · 24 hr); JIS K-7129
PARMATRA manufactured by Modern Control Co., Ltd.
Relative viscosity measured using NW3 / 31 at a temperature of 40 ° C. and a humidity of 90% RH; 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. did. Adhesive strength; a film obtained by laminating a polyester film having a PVDC layer and a sealant film laminated on the PVDC layer side to a size of 15 mm × 70 mm, peeling off the interface between the polyester film and the sealant film, and using an autograph manufactured by Shimadzu Corporation (AG10
Using 0), the measurement was performed under the conditions of a temperature of 20 ° C. and a humidity of 65% RH. Openability: tear by hand from the cut provided at the opening of the bag,
The one that was torn linearly was excellent, the one that was almost linearly torn was good, and one that could not be torn or was torn in an oblique direction was bad.

Examples 1 to 3 PBT and PTMG having a molecular weight of 2,000 were combined with PBT / PT
A mixture of chips mixed at a ratio of MG = 85/15 (weight ratio) is melt-mixed with a twin-screw extruder to form chips and denatured PB
T (relative viscosity 1.36) was adjusted. Next, the resulting modified PBT and PET obtained by mixing the chips at a ratio of 15/85 (weight ratio) were subjected to a residence time of 5 minutes using a 50 mmφ extruder equipped with a coat hanger type T-die. The resin was melt-extruded at a resin temperature of 270 ° C., closely adhered to a cast roll adjusted to a temperature of 20 ° C., and rapidly cooled to obtain an unstretched sheet having a thickness of 130 μm. Next, on one side of the obtained unstretched sheet, PV
After coating with DC latex, the sheet is dried, and the end of the sheet is held by clips of a tenter-type simultaneous biaxial stretching machine, stretched 3.3 times in MD and TD at a temperature of 100 ° C., and then relaxed in the TD direction. Rate of 5%, temperature about 23
Heat setting was performed at 0 ° C., and the resultant was gradually cooled to room temperature to obtain a 13 μm-thick biaxially stretched polyester film coated with PVDC having a thickness shown in Table 1. Table 1 shows the performance of the obtained film.

Example 4 The unstretched sheet obtained in Example 1 was biaxially stretched in the same manner as in Example 1 without coating PVDC latex, to obtain a biaxially stretched polyester film having a thickness of 12 μm. The obtained biaxially stretched film was coated with PVDC latex to obtain a biaxially stretched polyester film coated with PVDC having a thickness shown in Table 1. Table 1 shows the performance of the obtained film.

Comparative Example 1 A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that no PVDC latex was coated.
Table 1 shows the performance of the obtained film.

Comparative Examples 2 to 7 Biaxially stretched in the same manner as in Example 1 except that the composition of the modified PBT and the mixing ratio of the modified PBT and PET were changed as shown in Table 1, and the thickness was 13 μm. Was obtained. Table 1 shows the performance of the obtained film.

Examples 5 to 8, Comparative Examples 8 to 14 Unstretched polyethylene having a thickness of 60 μm was laminated on one surface of the biaxially stretched films obtained in Examples 1 to 4 and Comparative Examples 1 to 7 by a dry lamination method. Using this laminated film, a three-sided bag having a size of 15 mm × 20 mm was produced. Table 2 shows the results of evaluating the openability of the bag when a notch was inserted into the seal portion of the bag and tearing the bag in the MD direction, and measuring the adhesion strength between the polyester film and the sealant film.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

According to the present invention, the polyester has excellent strength, dimensional stability, transparency, and fragrance retention, has high gas barrier properties, and is used as a packaging material for foods, pharmaceuticals, miscellaneous goods and the like. A biaxially stretched polyester film having suitable tear straightness is obtained.

[Brief description of the drawings]

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

Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI // B29K 67:00 B29L 9:00 (72) Inventor Kazuhiro Kawaguchi 31-3 Ujiinosojiri, Uji-shi, Kyoto Unitika Inside Uji Plastic Factory Co., Ltd.

Claims (3)

[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 produced by mixing PET / modified PBT.
An easily tearable polyester film in which a polyvinylidene chloride-based copolymer layer is laminated on at least one side of a biaxially stretched polyester film produced using raw materials mixed at a ratio of 70/30 to 95/5 (weight ratio). 2. A film or a laminated film having the polyester film according to claim 1 in at least one layer,
An easy-open packaging bag formed by laminating a sealant film and then making a bag so that the longitudinal direction of the polyester film is in the tear direction. 3. 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 produced by mixing PET / modified PBT.
= 70/30 to 95/5 (weight ratio), after coating a polyvinylidene chloride-based copolymer latex on at least one surface of an unstretched film obtained by melt extrusion using a raw material mixed at a ratio of 70/30 to 95/5 (weight ratio), And a biaxially stretching in the transverse direction.