JP2007301846A - 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, has good twisting properties and folding properties, and is useful as a twist-wrapping film excellent in practicality, economical properties, and productivity, and also to provide a package formed by twist-wrapping or fold-wrapping an article to be wrapped by using the film. <P>SOLUTION: The biaxially oriented polyethylene terephthalate resin film is made of a resin containing polyethylene terephthalate substantially as a main component. The density of the film is 1.358-1.364 g/cm<SP>3</SP>, the coefficient of friction is 0.25-0.90, and the twist holding angle is at least 250°. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a biaxially stretched polyethylene terephthalate resin film or roll 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 and uses a copolyester, the average refractive index of the unstretched film is N0, and the average refractive index of the biaxially stretched film is N1, An easy-folding polyester film (for example, see Patent Document 1) characterized by satisfying 0.003 ≦ N1-N0 ≦ 0.021 has been reported.
Japanese Patent No. 2505474

  However, although the above prior art is good in bendability, when used for twisting, an antistatic coat is applied for antistatic properties required for a film as mechanical suitability. Reduces the coefficient of friction between the films or causes slippage between the film and the nail of the twist wrapping machine, resulting in insufficient twisting. As a result, the return angle after twisting increases and the twisting property deteriorates, resulting in a high defect rate. There is a problem of becoming. In addition, when heat is received in processing steps such as printing, the use of copolymers such as isophthalic acid and the heat treatment step after biaxial stretching can reduce the thermal shrinkage rate for the problem that film flatness deteriorates. Although described, there is a problem that the use of a copolymer is high in cost and is not preferable as productivity, and it is difficult to say as a sufficient technique, and further improvement is required.

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, when only the above conventional technology is actually used for twist wrapping or folding wrapping, the film breaking strength in the longitudinal direction becomes too strong, the cutting blade wears quickly, and a considerable time is required for machine maintenance. In addition, if the film elongation is large, film cutting defects occur immediately before individual packaging, causing problems such as machine clogging and poor production efficiency. There is a need for improvement.

  The present invention relates to a biaxially stretched polyethylene terephthalate resin film for twist packaging or folding packaging. In more detail, while maintaining the excellent properties of the biaxially stretched polyethylene terephthalate resin film, it solves the problems that have been considered difficult with the prior art, and has a good twist and bendability, and is practical and economical. Further, it is provided as a twist packaging film or a folding packaging film or a roll film excellent in productivity.

  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 consisting essentially of a resin mainly composed of polyethylene terephthalate, wherein the film has a density of 1.358 to 1.364 g / cm ³ , a friction coefficient of 0.25 to 0.90, A biaxially stretched polyethylene terephthalate resin film having a twist holding angle of 250 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. If the film density is less than 1.358 g / cm ³ , the heat resistance is undesirably lowered. Furthermore, it is preferably 1.360 g / cm ³ or more.

A film density here means the value calculated | required based on the density gradient tube method JISK-7112-1980. For example, the concentration is adjusted using a solution of calcium nitrate, and a density gradient solution is first prepared so that a desired density is obtained. Next, this density gradient liquid is put into a 85 cm long gradient tube and a float with a known specific gravity is put in. After checking whether the position of the whole float and the difference between the floats are normal, it is checked whether the gradient of the liquid is broken. It is confirmed that the prepared density gradient liquid is in a state where a desired density is obtained. Then, it sets to the thermostat for density measurement, and it sets so that it may become 30 degreeC. The film density is set to 16 hours after the sample is loaded, and the gravity center position of the sample sample and the position of the float immediately above and below the sample sample are read from the density gradient tube scale from the density gradient tube. The density (film density) is obtained up to the fourth decimal place.
X = position of sample specimen A = upper float position B = lower float position P = specific gravity of upper float position Q = specific gravity of lower float position

Q = [(X−B) × (Q−P)] / (A−B) = film density

  Moreover, it is preferable that the friction coefficient in the environment of 23 degreeC x 65% RH of the film obtained in this invention is 0.25-0.90. When the friction coefficient in an environment of 23 ° C. × 65% RH is less than 0.25, slipping occurs between the nails of the twist packaging machine and sufficient twisting cannot be performed. Furthermore, when twisting is performed, the return after twisting becomes large, and sufficient twisting properties cannot be obtained, which is not preferable. On the other hand, when the friction coefficient in an environment of 23 ° C. × 65% RH exceeds 0.90, wrinkles are mixed when the film is wound in a roll form or slit to the required width. Furthermore, vertical wrinkles are generated in the film by the guide rolls during printing, vapor deposition, and antistatic coating, which are subsequent processes, which causes a problem. At this time, the friction coefficient is preferably 0.25 to 0.60. More preferably, it is 0.30-0.40.

  The coefficient of friction means a value measured under an environment of 23 ° C. × 65% RH according to ASTM-D1894.

  It is preferable that the twist holding angle of the film obtained in the present invention is 250 degrees or more. Further, it is preferably 270 ° or more, particularly preferably 280 ° or more. When individual packaging such as chocolate or candy is used, the packaging shape cannot be maintained, and the packaged contents appear, which is not preferable because it is not practical. Furthermore, when the film twist retention angle obtained in the present invention is less than 250 degrees, the packaging shape cannot be maintained when the individual packaging such as chocolate or candy is carried out, and the packaged contents come out, which is not preferable because it is not practical. .

  The twist holding angle means that the film is wound by 1.5 turns (540 degrees) by using a twist packaging machine TA300 type manufactured by Tenchi Co., Ltd. at a speed of 200 pieces / minute. After a slight return after that, it means a value obtained by measuring the angle at which the twist is held as the twist holding angle.

  The folding angle of the film obtained in the present invention is preferably less than 50 degrees. When the folding angle is 50 degrees or more, the packaging shape cannot be maintained when the gum or candy is folded and packaged, and the packaged contents come out, which is not preferable because it is not practical.

The bending angle is that 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. It means a value measured after 1 minute as an opening angle = a folding angle. The smaller this angle, the better the bendability, and the evaluation results were 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

  In the present invention, when the breaking strength in the longitudinal direction of the film is less than 200 MPa, the film strength is weak at the above wrapping speed, which causes a trouble that the film breaks from the unwinding roll part to the cutting part through the guide roll. It's easy to do. In addition, if the strength at break exceeds 300 MPa, it cannot be cut unless the blade alignment of the cutter blade used in the cutting part is set strongly due to its strong strength, so the wear of the cutter blade increases and the life is shortened. Become. Accordingly, there is a problem that the cutter blade is frequently replaced and the economy is deteriorated.

In the present invention, it is preferable that the surface specific resistance of at least one surface of the film is 1 × 10 ⁷ (Ω / □) to 1 × 10 ¹⁴ (Ω / □). If the surface resistivity exceeds 1 × 10 ¹⁴ (Ω / □), the antistatic effect is lost, and static electricity generated by the metal guide roll or metal guide plate during twist packaging cannot be removed. As a result, after the film meanders or is cut to a desired size, the film clings to the cutting blade or the twist packaging machine itself, causing film clogging, resulting in a significant decrease in productivity, which is not preferable.

  The surface specific resistance herein means a value obtained by measuring the surface specific resistance (Ω / □) of the obtained film surface in accordance with ASTM D257. The measurement temperature and humidity were 23 ° C. × 65% RH and were used as indicators of the antistatic effect.

  Furthermore, it is preferable that the refractive index Nz in the thickness direction of the film is 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.

  The refractive index Nz as used herein was measured with NaD line light using an Abbe refractometer according to JIS-K-7142 except that the condition of the sample was adjusted and the measurement temperature was 30 ° C. The mounting liquid means a value obtained by measuring the refractive index (Nz) in the thickness direction using methylene iodide.

  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%, the film is stretched at the time of cutting, and 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 characteristics compatible with the cutting property at the packaging speed.

  The strength at break and the elongation at break here mean values measured according to the JIS C-2318 method.

  In the present invention, the film is preferably a biaxially stretched polyethylene terephthalate resin roll film which is wound as a roll along the longitudinal direction after film formation. The roll film here means a roll form used for printing / vapor deposition or twist packaging.

  Furthermore, the film or roll film of the present invention is preferably used for twisting or folding packaging.

  Furthermore, the film of the present invention is preferably used as a package in which the film is twisted or folded and wrapped.

The present invention is a film consisting essentially of a resin mainly composed of polyethylene terephthalate, wherein the film has a density of 1.358 to 1.364 g / cm ³ , a friction coefficient of 0.25 to 0.90, By having the twist holding angle of 250 degrees or more, it has excellent twistability and heat resistance, and further improved troubles due to breakage and cutting failure during processing, and tearing of the film after packaging. A biaxially stretched polyethylene terephthalate resin film or roll film and a package comprising the same 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 the present invention, the polyester constituting the film may contain other copolymerization components as long as the purpose is not impaired. 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 process by gripping at 60 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 200 to 400.

  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.

  In addition, the resin film substantially comprising polyethylene terephthalate of the present invention is not particularly limited with respect to the film thickness. For example, as a twist packaging film, 5 to 30 μm is preferable, and 10 to 25 μm is more preferable. preferable. When the film thickness is less than 5 μm, the film is torn off at the twisted portion during twist packaging. On the other hand, if the film thickness exceeds 30 μm, the return angle after twist packaging becomes large, which is not preferable.

  The resin film substantially comprising polyethylene terephthalate as a main component of the present invention preferably has a thermal shrinkage in the longitudinal direction and the width direction at 105 ° C. for 15 minutes of 15% or more and 25% or less. If the thermal shrinkage rate of the film exceeds 25%, the film shrinks during printing, other coating, and processing such as vapor deposition, and a predetermined printing pitch cannot be obtained. Further, if the thermal shrinkage of the film is less than 15%, a phenomenon such that the twisting property deteriorates due to the progress of crystallization of the film is not preferable.

  The resin film containing polyethylene terephthalate as a main component of the present invention includes, for example, alkylsulfonic acid, glycerin ester, polyglycene ester, etc. as an antistatic coating agent, and can impart the antistatic property of the present invention. If it is a thing, it will not specifically limit. The coating amount is not particularly limited as long as it is an optimum amount that can impart the antistatic property of the present invention. Further, 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.

  The resin film having polyethylene terephthalate as a main component in the present invention is handled in a processing step or the like that a film having a width of 0.2 m or more is wound around a winding core (core) with a length of 300 m or more. Above preferred. A roll made of a film having a width of less than 0.2 m has a low industrial value and is inappropriate. Also, rolls made of film with a length of less than 300 m have a short film winding length, so that it takes too much time to replace the roll when used for printing, slitting or twisting wrapping. Deteriorate. The roll width of the film of the present invention is more preferably 0.3 m or more, and further preferably 0.4 m or more. The roll length of the film is more preferably 400 m or more, and further preferably 500 m or more.

  The upper limit of the width and winding length of the film roll of the present invention is not particularly limited. However, from the viewpoint of ease of handling, generally, the width is 1.5 m or less, and the winding length is 8000 m or less when the film thickness is 18 μm. Is preferred. Moreover, as a winding core, a paper tube core, a plastic core, a metal core, etc. of 3 inches, 6 inches, 8 inches, etc. can be used normally.

  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 250 degrees or more Δ: Twist holding angle is 180 degrees or more and less than 250 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) Intrinsic viscosity After 0.1 g of a chip sample was precisely weighed, it was 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.

(6) Film density The film density here means a value determined in accordance with the density gradient tube method JIS K-7112-1980. As a measuring method in the present invention, concentration adjustment was performed using a calcium nitrate solution, and a density gradient solution was first prepared so that a desired density was obtained. Next, this density gradient liquid is put into a 85 cm long gradient tube and a float with a known specific gravity is put in. After checking whether the position of the whole float and the difference between the floats are normal, it is checked whether the gradient of the liquid is broken. It was confirmed that the prepared density gradient solution was in a state where a desired density was obtained. Then, it set to the thermostat for density measurement, and set it to become 30 degreeC. The film density is set to 16 hours after immersion of the sample sample. The center of gravity of the sample sample and the position of the float immediately above and below the sample sample are read from the scale of the density gradient tube from the density gradient tube. The density (film density) was determined up to the fourth decimal place.
X = position of sample specimen A = upper float position B = lower float position P = specific gravity of upper float position Q = specific gravity of lower float position

Q = [(X−B) × (Q−P)] / (A−B) = film density

(7) Average particle diameter Disperse silica fine particles in ion-exchanged water stirred at a predetermined rotational speed (about 5000 rpm) using a high-speed stirrer, and add the dispersion to Isoton (saline) to disperse ultrasonically. After further dispersion by a machine, a particle size distribution was obtained by a Coulter counter method using a Coulter counter Multisizer II (Beckman Coulter Co.), and a particle size at 50% of the weight cumulative distribution was calculated as an average particle size.

(8) 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. A longitudinal direction means the direction (longitudinal direction) which unwinds with respect to a roll. The width direction means a direction perpendicular to the roll unwinding direction (lateral direction).

(9) Mechanical suitability Twist packaging machine Tench TA-700 type was used to evaluate film running performance from film unwinding to cutting part. 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 breakage or clogging △: Film breakage or clogging is available, but usable level ×: Film breakage or clogging occurs frequently and cannot be used

(10) Film tearing Twist wrapping was performed at a rate of 200 pieces / min. The film is twisted 1.5 turns (540 degrees) into individual packages. Thereafter, it is visually evaluated whether or not the 100 individually wrapped films are torn due to their contents. The number of torn pieces was counted and evaluated as a tear rate (%).

(11) Surface resistivity The surface resistivity (Ω / □) of the obtained film surface was measured in accordance with ASTM D257. The measurement temperature and humidity were 23 ° C. × 65% RH. It was used as an index of the antistatic effect.

(12) Heat resistance The heat resistance evaluation was measured in both the longitudinal direction and the width direction in accordance with the JIS C-2318 method except that the thermal shrinkage rate was 105 ° C. × 15 minutes as a shrinkage condition. The results were classified and evaluated as follows.
○: 15% or more and 25% or less in both the longitudinal direction and the width direction Δ: Either the longitudinal direction or the width direction is 15% or more and 25% or less ×: Both the longitudinal direction and the width direction are less than 15% or more than 25%

Example 1
Silica (Fuji Silysia Corp. Silicia (grade: 310P, shape: amorphous, average particle size: 2.7 μm) to 1000 ppm relative to polyethylene terephthalate (Toyobo Co., Ltd .: RE553, intrinsic viscosity: 0.63 dl / g) Was added as an additive to obtain a polyethylene terephthalate resin composition, which was melt-kneaded with an extruder and supplied to a T die, and extruded from the inside of the T die to a resin temperature of 285 ° C. Furthermore, after casting with a casting roll at a temperature of 25 ° C., the film was stretched 3.9 times in one direction (lateral direction) at 90 ° C. to obtain a uniaxially stretched polyester film. In contrast, the film was stretched 3.3 times at 80 ° C. in a perpendicular direction (longitudinal direction) and heat treated at 90 ° C. to a thickness of 18 μm A biaxially stretched polyester resin film was obtained and rolled up as a 4000 m roll, and then sodium alkyl sulfonate (manufactured by Matsumoto Yushi Seiyaku Co., Ltd .: TB214 (solid content 40%)) was used as the antistatic agent, and IPA = The liquid concentration was adjusted so that the solid content was 1.6% by diluting 30% and the remainder with water, and then after coating with a gravure roll so that the wet coating amount was 4.5 g / m ^2. It was dried with a dryer at 0 ° C., and the antistatic coating was carried out so that the coating amount after drying was 0.007 g / m ² .

(Example 2)
Except that the film was stretched 3.8 times in one direction (transverse direction), then stretched 3.1 times in the perpendicular direction (longitudinal direction) and heat treated at 70 ° C., it was carried out in the same manner as in Example 1.

(Example 3)
The film was stretched 3.9 times in one direction (transverse direction), then stretched 3.5 times in the perpendicular direction (longitudinal direction) and sodium alkyl sulfonate was used as an antistatic agent, and the coating amount after drying was 0.00. The same procedure as in Example 1 was performed except that the antistatic coating was applied with a gravure roll so as to be 011 g / m ² .

Example 4
Except that the film was stretched 3.9 times in one direction (transverse direction) and then stretched 3.8 times in the perpendicular direction (longitudinal direction), and was not coated with an antistatic agent, it was carried out in the same manner as in Example 1.

(Comparative Example 1)
Except that the film was stretched 3.9 times in one direction (longitudinal direction), then stretched 4.0 times in the right-angle direction (transverse direction) and heat treated at 100 ° C., it was carried out in the same manner as in Example 1.

(Comparative Example 2)
Silica was added as an additive so as to be 2000 ppm with respect to polyethylene terephthalate to obtain a polyethylene terephthalate resin composition. The film was stretched 4.1 times in one direction (longitudinal direction) to obtain a uniaxially stretched polyester film. Subsequently, the film was stretched 4.0 times in the direction perpendicular to the stretching direction (transverse direction) and heat treated at 100 ° C., and the same procedure as in Example 1 was performed.

(Comparative Example 3)
Silica was added as an additive so as to be 2000 ppm with respect to polyethylene terephthalate to obtain a polyethylene terephthalate resin composition. The film was stretched 3.9 times in one direction (lateral direction) to obtain a uniaxially stretched polyester film. Next, the film is stretched 3.3 times in a direction perpendicular to the stretching direction (longitudinal direction), sodium alkylsulfonate is used as an antistatic agent, and the coating amount after drying becomes 0.003 g / m ^2. Thus, it carried out like Example 1 except having applied the antistatic coat with the gravure roll.

(Comparative Example 4)
Except that the film was stretched 3.9 times in one direction (transverse direction), then stretched 3.1 times in the perpendicular direction (longitudinal direction) and heat treated at 150 ° C., it was carried out in the same manner as in Example 1.

  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 (7)

A film consisting essentially of a resin mainly composed of polyethylene terephthalate, having a density of 1.358 to 1.364 g / cm ³ , a friction coefficient of 0.25 to 0.90, and a twist holding angle. A biaxially stretched polyethylene terephthalate resin film characterized by being at 250 ° 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. The biaxially stretched polyethylene according to claim 1, wherein the film has a surface resistivity of 1 × 10 ⁷ (Ω / □) to 1 × 10 ¹⁴ (Ω / □) on at least one side of the film. Terephthalate resin film.   The biaxially stretched polyethylene terephthalate according to claim 1, wherein the film has an elongation at break of 80 to 150% in the longitudinal direction and a strength at break of 200 to 300 MPa in the longitudinal direction. Resin film.   The biaxially stretched polyethylene terephthalate resin roll film according to claim 1, wherein the film is wound up as a roll after film formation.   6. A biaxially stretched polyethylene terephthalate resin film or a biaxially stretched polyethylene terephthalate resin roll film according to claim 1, which is used for twisting or folding packaging.   A package formed by twisting or folding-wrapping an article to be packaged using the film or roll film according to claim 1.

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