JP2007203652A - Biaxially-oriented polyester film and package - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biaxially-oriented polyethylene terephthalate resin film which maintains practical characteristics without losing the excellent characteristics of a biaxially-oriented polyester resin film, which is equipped with proper twistability and foldability and which is useful as a twist-packaging film excellent in practicality, economical efficiency and productivity, and a package in which an article to be packaged is twist-packaged or fold-packaged. <P>SOLUTION: In this biaxially-oriented polyethylene terephthalate resin film which is composed of a resin substantially and mainly composed of polyethylene terephthalate, a film density is in the range of 1.350-1.364 g/cm<SP>3</SP>; a longitudinal elongation at break is in the range of 80-150%; a longitudinal stress at break is in the range of 200-300 MPa; and a twist maintaining angle is 240° or more. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a biaxially stretched polyethylene terephthalate resin film for twist packaging or folding packaging. More specifically, as a film for twist packaging or folding packaging, which has excellent twistability and bendability while maintaining the excellent characteristics of a biaxially stretched polyethylene terephthalate resin film, and is excellent in practicality, economy, and productivity. It is to provide.

  Conventionally, cellophane has been known as a film excellent in twistability and bendability. Cellophane is used as various packaging materials including twist packaging because of its excellent transparency, twistability, and bendability. However, on the other hand, cellophane has a hygroscopic property, and its characteristics fluctuate depending on the season, and it is difficult to supply it while maintaining a constant quality. Cellophane also has a problem in terms of environmental protection because it requires excessive energy for the manufacturing process. In contrast, a packaging material using polyethylene terephthalate as a base film is suitably used in various applications due to the excellent properties such as toughness, heat resistance, water resistance, and transparency of the stretched polyethylene terephthalate film. On the other hand, in applications where twistability and bendability are required, there is a problem that the shape cannot be maintained after packaging because it is stiff, and it is difficult to use as a cellophane substitute film.

  In addition, polypropylene and uniaxially stretched high-density polyethylene have been studied as cellophane substitutes so far, but twistability and bendability are significantly inferior to cellophane. That is, after packaging food or the like, the shape cannot be maintained during twist packaging or folding packaging, and a trouble occurs in which the packaged contents appear. In order to prevent such trouble, means for designing the film to a certain extent is used. However, for example, when square chocolate or candy is packaged using a hard film, there is a problem that the film tears at the corner and the packaging cannot be performed efficiently, and it is still not sufficient as a cellophane substitute film.

As a method for solving the above drawbacks, when the stress-strain curve has a yield point, the average refractive index of the unstretched film of the copolymer is N0, and the average refractive index of the biaxially stretched film is N1, 0 An easily bendable polyester film (for example, see Patent Document 1) characterized by satisfying .003 ≦ N1-N0 ≦ 0.021 has been reported.
Japanese Patent No. 2505474

However, in the above prior art, a biaxially stretched film made of a copolymer of polyethylene terephthalate, which has a yield point in the stress-strain curve, and the average refractive index of the unstretched film of the copolymer is N ₀ , When the average refractive index of the biaxially stretched film is N ₁ , the method of 0.003 ≦ N ₁ −N ₀ ≦ 0.021 is sufficient to obtain the required package shape after twisting or bending. In addition, although it is described that the use of a copolymer such as isophthalic acid and the thermal contraction rate are reduced in the heat treatment step after biaxial stretching, the use of the copolymer is cost, heat resistance, processing It is not preferable in terms of sex.

Further, the film is made of polyethylene terephthalate, the density is in the range of 1.35 to 1.375 g / cm ³ , the thermal shrinkage at 120 ° C. is at least 10%, and the film thickness is 6 to 30 μm. A food film for twist packaging (for example, refer to Patent Document 2) has been proposed.
Japanese Patent Publication No.59-12544

  The above-mentioned prior art makes it possible to maintain the packaging shape after twisting or folding, by making the film stiffer by reducing the density of the film, and by using polyethylene terephthalate for its toughness, it can be used for square chocolate and candy packaging. This makes it possible to prevent troubles that cause the film to tear. However, with the above prior art alone, when twist wrapping or folding wrapping is actually performed, the film breaking stress in the longitudinal direction is strong and the film elongation is large, so that trouble such as machine clogging due to film cutting failure just before individual packaging or Further, there was a problem that production efficiency was poor due to the early wear of the cutting blade and the considerable time required for machine maintenance, and further improvement was required.

  The present invention relates to a biaxially stretched polyethylene terephthalate resin film for twist packaging or folding packaging. More specifically, as a film for twist wrapping or folding wrapping which has excellent twistability and foldability while maintaining the excellent properties of the biaxially stretched polyethylene terephthalate resin film, and has excellent practicality, economy and productivity. It is to provide.

  In view of the above-mentioned problems of the prior art, the present inventors have a practicality, and are further advantageous in terms of cost, and are suitable for twist packaging consisting of a resin mainly composed of polyethylene terephthalate, which is advantageous in terms of cost and has good productivity. As a result of earnest research for the purpose of obtaining a film for folding packaging, the present invention has been achieved.

The present invention is a film substantially made of a resin mainly composed of polyethylene terephthalate, the film density is 1.350 to 1.364 g / cm ³ , and the elongation at break in the longitudinal direction of the film is 80. The biaxially oriented polyethylene terephthalate resin film is characterized in that it is ˜150%, the stress at break in the longitudinal direction of the film is 200 to 300 MPa, and the twist holding angle is 240 degrees or more.

In the present invention, if the film density exceeds 1.364 g / cm ³ , the bendability is lowered, which is not preferable. When the film density is less than 1.350 g / cm ³ , the heat resistance is lowered, which is not preferable. Further, it is preferably 1.360 g / cm ³ or more.
Moreover, when the twist holding angle is less than 240 degrees, it is not suitable for individual packaging such as chocolate and candy.

  The film density here means a value measured at 30 ° C. by means of a density gradient tube method (for example, a solution of calcium nitrate) or a floatation method. The stress at break and the elongation at break mean values measured according to JIS C-2318 method. Thus, using polyester having a specific composition, making the film density within the above specific range, and further making the film breaking point stress and breaking point elongation within the above specific range satisfy economics and productivity. In addition, it is excellent in practicality, is preferable for obtaining twistability and bendability, and is useful as a film for twist packaging or folding packaging.

  Here, the twist holding angle is a slight amount after the film is twisted 1.5 turns (540 degrees) at a speed of 200 pieces / min. It means a value obtained by measuring the angle at which the twist after the return is held. (Hereafter referred to as “Twist holding angle”)

In the present invention, when the breaking stress in the longitudinal direction of the film is less than 200 MPa, the film is easily cut between the unwinding portion and the cutting portion at the packaging speed, and trouble is likely to occur. On the other hand, when the stress at break exceeds 300 MPa, the cutter blade used at the cutting part is worn much, and the cutter blade is frequently replaced, resulting in a problem of poor economic efficiency.
Further, regarding the elongation at break in the longitudinal direction, if the elongation at break is less than 80%, the film may cause troubles between the unwinding portion and the cutting portion as described above. On the other hand, if the elongation at break exceeds 150%, it is difficult to cut at the cut portion, which causes a problem of many defective rates.
This is because the film that wraps solid objects found in twisted and folded packages must be easily handled by the packaging machine. In other words, when packaging 200 to 1000 solid objects per minute with one machine, adaptability to the process of cutting out the area required for packaging is required, and this must be satisfied as machine suitability. It is. Therefore, the film is required to have a characteristic that the cutting property at the packaging speed is good.

  In this case, the refractive index Nz in the thickness direction of the film is preferably 1.501 or more.

  In the present invention, when the refractive index Nz in the thickness direction of the film is less than 1.501, the plane orientation of the film is increased, and the film is torn in an angular chocolate or candy package.

Furthermore, in this case, it is preferable that the thermal contraction rate in the longitudinal direction and the lateral direction at 105 ° C. is 15% or more and 25% or less.
If the film has a thermal shrinkage rate in the longitudinal direction at 105 ° C. of 25% or more, the processability of the film is inferior. If it is about 15%, it can be used without any particular problem.

  Furthermore, in this case, it is preferably used for twisting or folding packaging.

  Furthermore, in this case, a packaging body in which the film is twisted or folded and wrapped is preferable.

  According to the present invention, a biaxially stretched polyethylene terephthalate resin film that has excellent twistability and bendability, and has excellent practicality with few troubles due to breakage or cutting failure during processing and tearing of the film after packaging. Can be provided.

The resin essentially comprising polyethylene terephthalate constituting the present invention is a resin obtained by direct esterification of terephthalic acid and ethylene glycol, and as a by-product, diethylene glycol, oligomer, cyclic oligomer, etc. Linear monomers and oligomers may be included as reactants. In addition, the intrinsic viscosity of the resin mainly composed of polyethylene terephthalate is preferably 0.55 to 1.30 dl / g, more preferably 0.60 to 1.20 dl / g. At this time, the resin density is preferably 1.350 to 1.450 g / cm ³ .

In this invention, the polyester which comprises a film can contain another copolymerization component in the range which does not inhibit the objective. Among other copolymerizable components that can be used, aromatic dicarboxylic acids such as naphthalenedicarboxylic acid, diphenylsulfone dicarboxylic acid, 5-sodium sulfoisophthalic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, decane Aliphatic dicarboxylic acids such as dicarboxylic acid, maleic acid, fumaric acid and dimer acid, oxycarboxylic acids such as p-oxybenzoic acid, and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid can be used. As glycol components, aliphatic glycols such as propanediol, butanediol, pentanediol, hexanediol and neopentylglycol, alicyclic glycols such as cyclohexanedimethanol, ethylene oxide adduct of bisphenol A, ethylene oxide of bisphenol S Aromatic glycols such as adducts, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like can be used. In addition, a small amount of a compound containing an amide bond, a urethane bond, an ether bond, a carbonate bond, or the like may be included.
As used herein, the resin having substantially polyethylene terephthalate as a main component means a resin in which 90 mol% or more of constituent components are preferably composed of ethylene terephthalate units, and more preferably 95 mol% or more.

  The resin having substantially polyethylene terephthalate as a main component can be produced by a conventional method. Examples include a direct esterification method in which an acidic component and a glycol component are directly reacted, and a transesterification method in which an ester as an acid component is reacted with a glycol component, but are not particularly limited.

  In the said composition, various additives may be contained as needed besides the resin which has polyethylene terephthalate as a main component. Additives such as titanium dioxide, fine particle silica, kaolin, calcium carbonate, and other inorganic lubricants, and fine particles made of acrylic cross-linked polymers, such as acrylic acid, methacrylic acid, acrylic ester, methacrylic ester, etc. Examples thereof include organic lubricants such as cross-linked polymers made of monomers. Moreover, an antistatic agent, an anti-aging agent, an ultraviolet light inhibitor, a colorant, a dye and the like may be contained alone, or two or more kinds may be used in combination.

The additive used in the present invention is preferably fine particle silica, but is not particularly limited. The composition of the fine-particle silica is mainly composed of silicon dioxide (SiO ₂ ), and the shape may be any shape such as indefinite shape, spherical shape, and agglomerated shape, but in the present invention, the indefinite shape having no crystal structure. Is preferred. Further, an average particle size (silica fine particles are dispersed in ion-exchanged water stirred at a predetermined rotational speed (about 5000 rpm) using a high-speed stirrer, and the dispersion is added to isotone (saline), an ultrasonic disperser. The particle size distribution was obtained by a Coulter counter method, and the particle size at 50% of the weight cumulative distribution was calculated as the average particle size.) Is preferably 1.4 to 4.5 μm, more preferably 1.8. ˜3.0 μm. If the average particle size is less than 1.4 μm, blocking occurs between the films, which becomes a problem. On the other hand, when the average particle size is larger than 4.5 μm, there arises a problem that fine particle silica is dropped during film processing and a problem that scratch resistance is deteriorated. In the present invention, silicia manufactured by Fuji Silysia Co., Ltd. (grade: 310P, shape: amorphous, average particle size: 2.7 μm) was used.

The resin film substantially comprising polyethylene terephthalate of the present invention is obtained by, for example, casting a resin melt-kneaded by an extruder to obtain an unstretched film, and then simultaneously biaxial stretching method or sequential biaxial stretching method, etc. A method of performing biaxial stretching and then heat setting is used.
Extrusion conditions can be selected as appropriate and are not particularly limited.

  In the present invention, a sheet obtained by cooling and solidifying a polyester melt-extruded by a known extruder is subjected to first-stage stretching 3.0 to 4.5 times in the transverse direction at a temperature equal to or higher than the glass transition temperature of the polyester, The second stage stretching is performed in the longitudinal direction 3.0 to 4.0 times at a temperature equal to or higher than the glass transition temperature of the glass, and further, a heat setting process in which the known width direction is a constant length (for example, both ends of the film are clipped). It is preferable to carry out the heat setting treatment by gripping at 80 to 130 ° C. for 1 to 20 seconds. Furthermore, it is preferable to control the product (M × HST) of the second stage draw ratio (M (magnification)) and the heat setting temperature (HST (° C.)) to 250 to 350.

  In the present invention, as the third stage stretching, re-stretching of 1.05 to 1.4 times may be performed at a temperature equal to or higher than the glass transition temperature of the polyester. Further, relaxation treatment (treatment of relaxing 0.5 to 8% in the width direction at 100 to 140 ° C.) may be performed in the width direction.

  The resin film essentially comprising polyethylene terephthalate of the present invention may be subjected to surface treatment by a conventionally known method such as corona discharge treatment, plasma treatment, ozone treatment, chemical treatment, etc., or a known anchor treatment depending on the purpose. An anchor treatment using an agent may be performed. The antistatic coating agent is not particularly limited as long as it is an alkylsulfonic acid, glycerin ester, polyglycene ester, or the like, and can impart antistatic properties. The coating method is not particularly limited as long as it is a conventionally known method such as a berth roll coating method, a roll knife coating method, a die coating method, or a gravure coating method. Furthermore, it may be a coating by in-line coating.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited by these Examples. In addition, the measuring method of the physical property of the film obtained by the Example and the comparative example is as follows.

Test method (1) Twist property Twist packaging was performed at a rate of 200 pieces / minute using a twist packaging machine TA300 type manufactured by Tenchi. The film is twisted 1.5 turns (540 degrees) into individual packages. Then measure the angle at which the twist was held after a slight return. (Hereafter referred to as “Twist holding angle”)
The twisting property is better as the holding angle is larger, and the evaluation is classified as follows.
○: Twist holding angle is 240 degrees or more Δ: Twist holding angle is 180 degrees or more and less than 240 degrees X: Twist holding angle is less than 180 degrees

(2) Bendability A 10 cm square film sample is lightly folded into four, and a load of 0.5 kg × 1 second is applied in the surface direction. Thereafter, the sample is placed on a glass plate as shown in FIG. Measured after 1 minute as opening angle = break angle. The smaller this angle, the better the bendability, and it was classified as follows.
○: Folding angle is less than 50 degrees Δ: Folding angle is 50 degrees or more and less than 80 degrees ×: Folding angle is 80 degrees or more

(3) Refractive index It measured with NaD ray light with the Abbe refractometer according to JIS-K-7142 except the state adjustment of the sample, and measurement temperature having been 30 degreeC. The mount solution was methylene iodide, and the refractive index (Nz) in the thickness direction was measured.

(4) Tm (melting point)
The measurement was performed by connecting a TA60WS disk station (manufactured by Shimadzu Corporation) to a robot DSC (differential scanning calorimeter) DSC-60 (manufactured by Shimadzu Corporation). After adjusting 10 mg of a sample to an aluminum pan, it was set in a DSC apparatus (reference: the same type of aluminum pan without a sample), and this sample was heated at a rate of 10 ° C./min. After heating at a temperature of 285 ° C. for 15 minutes, it was quenched with liquid nitrogen. The sample was then reheated at a rate of 10 ° C./min, and the melting point (Tm) was measured from the DSC chart.

(5) Heat shrinkage rate The heat shrinkage rate was measured according to the JIS C-2318 method except that the shrinkage conditions were 105 ° C and 15 minutes.

(6) Intrinsic Viscosity 0.1 g of the chip sample was precisely weighed, dissolved in 25 ml of a mixed solvent of phenol / tetrachloroethane = 6/4 (mass ratio), and measured at 30 ° C. using an Ostwald viscometer. The measurement was performed three times and the average value was obtained.

(7) Film density The film density was measured at 30 ° C. with a density gradient tube obtained by adjusting the concentration of a solution of calcium nitrate.

(8) Average particle diameter The volume median diameter of the sample aqueous dispersion was measured using a Coulter Counter Multisizer II (Beckman Coulter, Inc.).

(9) Strength at break and elongation at break The strength at break and elongation at break were measured according to JIS C-2381 method. At this time, the tensile speed of the test piece was 200 mm / min.

(10) Film thickness unevenness A continuous tape-shaped sample having a length of 3 m in the width (transverse stretching) direction and a length of 5 cm in the longitudinal (longitudinal stretching) direction is wound up, and the film thickness is continuously measured by an film thickness measuring machine (manufactured by Anritsu Corporation) The thickness was measured and recorded on a recorder. From the chart, the maximum value (dmax), the minimum value (dmin), and the average value (d) of the film thickness were determined, and the thickness unevenness (%) was calculated by the following formula. In addition, the measurement was performed 3 times and the average value was calculated | required. If the length in the width direction is less than 3 m, the pieces are joined together. The connecting part is deleted from the data.
Thickness unevenness (%) = ((dmax−dmin) / d) × 100

(11) Machine suitability Twist packaging machine The film running property from film unwinding to the cutting part was evaluated with a TA-700 type manufactured by Tench. The film running speed of the twist wrapping machine was 3.2 m / min. The results were classified and evaluated as follows. The evaluated film length is 320 m.
○: No film break ×: Film break occurred and there was a problem

Example 1
Silica (Silicia manufactured by Fuji Silysia Co., Ltd. (grade: 310P, shape: amorphous, average particle size: 2.7 μm) is added so as to be 0.03% by weight with respect to polyethylene terephthalate (inherent viscosity is 0.63 dl / g). A polyethylene terephthalate resin composition was obtained as an additive, melted and kneaded with an extruder, and the melted and kneaded product was supplied to a T die so that the resin temperature was 285 ° C. from the inside of the T die. Then, the film was cast with a casting roll at a temperature of 25 ° C., and the film was stretched 3.9 times in one direction (lateral direction) at 90 ° C. to obtain a uniaxially stretched polyester film. Biaxial elongation that is 3.3 times stretched at 80 ° C in the direction perpendicular to the stretching direction (longitudinal direction) and heat treated at 90 ° C to a thickness of 18 µm A stretched polyester resin film was obtained.

(Example 2)
A biaxially stretched polyethylene terephthalate resin film having a thickness of 18 μm was obtained in the same manner as in Example 1 except that the film was stretched 3.9 times in one direction (longitudinal direction) at 80 ° C. to obtain a uniaxially stretched polyester film. It was.

(Comparative Example 1)
The film was stretched 3.9 times in one direction (longitudinal direction) at 80 ° C. to obtain a uniaxially stretched polyester film. Subsequently, the film was stretched 4.0 times at 100 ° C. in the direction perpendicular to the stretching direction (transverse direction) and heat-treated at 100 ° C., and the thickness was 18 μm as in Example 1. An axially stretched polyethylene terephthalate resin film was obtained.

(Comparative Example 2)
The film was stretched 3.5 times in one direction (longitudinal direction) at 80 ° C. to obtain a uniaxially stretched polyester film. Subsequently, the film was stretched 4.0 times at 90 ° C. in a direction perpendicular to the stretching direction (transverse direction) and heat-treated at 100 ° C., and a thickness of 18 μm was obtained in the same manner as in Example 1. An axially stretched polyethylene terephthalate resin film was obtained.

(Comparative Example 3)
A biaxially stretched polyethylene terephthalate resin film having a thickness of 18 μm was obtained in the same manner as in Example 1 except that the heat treatment temperature was 110 ° C.

(Comparative Example 4)
A biaxially stretched polyethylene terephthalate resin film having a thickness of 18 μm was obtained in the same manner as in Example 1 except that the heat treatment temperature was 150 ° C.

(Comparative Example 5)
A biaxially stretched polyethylene terephthalate resin film having a thickness of 18 μm was obtained in the same manner as in Example 1 except that the film was stretched 2.4 times in one direction (longitudinal direction) at 80 ° C. to obtain a uniaxially stretched polyester film. It was.

  The present invention is a biaxially stretched polyethylene terephthalate resin film for twist wrapping or folding wrapping, which has excellent twistability and bendability while maintaining the excellent properties of the biaxially stretched polyethylene terephthalate resin film. It can be used in the field of packaging applications as a twist packaging film or a folding packaging film excellent in productivity and productivity, and contributes to the industry of twist packaging.

It is explanatory drawing of the measuring method of the folding angle of the biaxially-stretched polyester resin film of this invention.

Claims (5)

A film substantially composed of a resin mainly composed of polyethylene terephthalate, having a film density of 1.350 to 1.364 g / cm ³ and an elongation at break in the longitudinal direction of 80 to 150%, A biaxially stretched polyethylene terephthalate resin film characterized by having a breaking stress in the direction of 200 to 300 MPa and a twist holding angle of 240 degrees or more.   2. The biaxially stretched polyethylene terephthalate resin film according to claim 1, wherein a refractive index Nz in the thickness direction of the film is 1.501 or more.   2. A biaxially stretched polyethylene terephthalate resin film for twisting or folding packaging, characterized in that the thermal shrinkage in the longitudinal direction and the transverse direction at 105 [deg.] C. is 15% or more and 25% or less. .   The biaxially stretched polyethylene terephthalate resin film according to claim 1, wherein the film is used for twisting or folding packaging.   A package comprising the film according to claim 1 formed by twist-wrapping or folding-wrapping an article to be packaged.

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