JP2013056509A - Linearly-tearable biaxially-oriented polyester film that reduces oligomer foreign matter to be deposited thereon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a linearly-tearable biaxially-oriented polyester film which prevents deposition of an oligomer foreign matter, which cannot be solved by a conventional method.SOLUTION: The biaxially-oriented polyester film has a linearly-tearable property at least in a longitudinal direction. The film is formed of polybutylene terephthalate containing a polytetramethylene glycol unit, and polyethylene terephthalate. Ten or less oligomer-derived foreign matters having a diameter of 0.5 mm or more, and 50 or less oligomer-derived foreign matters having a diameter of 0.2 mm or more and less than 0.5 mm are contained per 10,000 mof the film.

Description

  The present invention is excellent in at least longitudinal tear linearity of the film, and has excellent strength, heat resistance, dimensional stability, confectionery, pickles, miso, soup, jam, frozen, refrigerated, retort pouch, etc. The present invention relates to a biaxially stretched polyester film useful as a packaging material for foods, pharmaceuticals, daily necessities, cosmetics and the like, and a method for producing the same.

  Many packaging bags using various plastic films are used for packaging foods, pharmaceuticals, and miscellaneous goods. Two or three or more layers of biaxially stretched plastic films and heat-sealable non-oriented plastics are laminated. Packaging bags are widely used. Biaxially stretched polyester film has excellent durability, moisture resistance, mechanical strength, heat resistance, and oil resistance. Manufactured using tubular method, flat simultaneous biaxial stretching method, flat sequential biaxial stretching method, etc. The biaxially stretched polyester film is widely used in the food packaging field.

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

  As an easily openable material that is excellent in linearity when the film is torn, there is one obtained by laminating a uniaxially stretched polyolefin film as an intermediate layer. Examples of such a film include a three-layer laminate film of a biaxially stretched polyester film / uniaxially stretched polyolefin film / non-stretched polyolefin film, but there is a problem in terms of cost because an intermediate layer must be provided. Was limited.

  Therefore, as a method of imparting tear linearity to the biaxially stretched polyester film itself, a thermoplastic polyester resin (I) whose acid component is mainly composed of terephthalic acid or naphthalenedicarboxylic acid, and a thermoplastic polyester exhibiting a phase separation form with this polyester A biaxially stretched polyester film using a mixture of resin (b) as a main raw material has been proposed (Patent Document 1). In the above publication, it is described that a polyether polyester block copolymer (hereinafter referred to as a modified PBT) composed of a polytetramethylene glycol unit and PBT is used as (b). .

  However, the biaxially stretched polyester film using the mixture as a raw material has a problem that the amount of oligomer attached to the film is large and the quality of the film is deteriorated as compared with the production of a polyester film of PET alone.

  If the oligomer adheres to the film, ink loss or dot loss may occur during printing, or the oligomer may dissolve in the ink and cause plate fogging.

  Conventionally, many studies have been made to prevent foreign substances such as oligomers. Examples thereof include a method of blowing air on the surface of the stretched film (Patent Document 2), a method of removing an adhesive roll by pressing it onto the film (Patent Document 3), and the like.

  However, in the conventional proposal as described above, adhered foreign substances derived from the oligomer could be suppressed, but it was not sufficient. This is because in the production process, there are foreign substances adhering to the oligomer that cannot be solved even by trying these conventional methods.

  Moreover, although the method which detects the film roll containing an adhesion foreign material with a foreign material inspection machine and does not commercialize this is also taken, compared with PET film, the amount of oligomers is large and it was not preferable from a viewpoint of productivity.

Japanese Patent Laid-Open No. 8-169962 JP 2009-72651 A JP 2010-179276 A

  An object of the present invention is to provide a tear linear biaxially stretched polyester film that suppresses oligomer-derived foreign matters that cannot be solved by conventional methods and has improved quality.

As a result of intensive studies, the inventors have melted the oligomer derived from the PBT component contained in the modified PBT and fused it to the stretched film, or adhered to the oligomer derived from the PET component and fused to the stretched film. I found out. For this reason, it is apparently not different from PET oligomer, but it was found that it could not be removed by the conventional air shower or adhesive roll. This is because the modified PBT oligomer has lower heat resistance than the PET oligomer, and therefore melts before the PET oligomer in the stretching zone in the tenter type stretching machine. That is, it is a problem peculiar to a mixture of modified PBT and PET.
Therefore, the present inventors have found that the above problem can be solved by controlling the oligomer gas concentration during tenter stretching in the production of a biaxially stretched polyester film, and have reached the present invention.
That is, the gist of the present invention is as follows.
(1) A film composed of polybutylene terephthalate containing a polytetramethylene glycol unit and polyethylene terephthalate, wherein there are 10 or less oligomer-derived foreign matters having a diameter of 0.5 mm or more per 10,000 m ^{2 of} the film, and a diameter of 0. A biaxially stretched polyester film having tear linearity at least in the longitudinal direction, wherein the number of foreign substances derived from oligomers of 2 mm or more and less than 0.5 mm is 50 or less.
(2) A laminated film using the biaxially stretched polyester film described in (1) in at least one layer.
(3) An easy-open packaging bag using the laminated film according to (2) and bag-making so that the direction showing tear linearity is the tear direction of the bag.
(4) A method for producing a biaxially stretched polyester film according to (1), wherein an unstretched sheet obtained from a mixture of polybutylene terephthalate and poly (ethylene terephthalate) containing a polytetramethylene glycol unit is used as a tenter stretching machine. The method for producing a biaxially stretched polyester film is characterized in that the stretching is carried out by controlling the oligomer gas concentration in the stretching zone in the tenter type stretching machine to be 0.2 mg / m ³ or less.

  ADVANTAGE OF THE INVENTION According to this invention, the adhesion amount of an oligomer is reduced and it can obtain the high quality tear linear polyester film which is hard to generate | occur | produce ink omission and dot omission when it uses for printing.

  Hereinafter, the present invention will be described in detail.

The tear linear biaxially stretched polyester film of the present invention has 10 or less oligomer-derived foreign matters having a diameter of 0.5 mm or more per 10000 m ² of the film, and 50 oligomer-derived foreign matters having a diameter of 0.2 mm or more and less than 0.5 mm. It is characterized by having no more than one. A method for measuring the oligomer-derived foreign matter will be described later.

Oligomer-derived foreign matter is a fatal defect in printing and is therefore desirably as small as possible. That is, the number of oligomer-derived foreign matters having a diameter of 0.5 mm or more needs to be 10 or less per 10000 m ^{2 of} the film, preferably 5 or less, more preferably 2 or less, and foreign matter of this size exists. Most preferably not.
In addition, the oligomer-derived foreign matter having a diameter of 2 mm or more and less than 5 mm needs to be 50 or less per 10,000 m ² of the film, preferably 30 or less, and most preferably 15 or less.
If the oligomer-derived foreign material has a diameter of less than 0.2 mm, problems such as missing ink or missing dots do not occur during printing.

In the present invention, it is important to reduce as much as possible the opportunity of contact between the stretched film and the modified PBT-derived oligomer generated in the tenter before the heat treatment zone in the tenter type stretching machine. For this reason, it is necessary to reduce the concentration of the oligomer gas, which is a low molecular weight polyester, so that it is not more than a certain value in the stretching zone in the tenter. Specifically, the oligomer gas concentration needs to be 0.2 mg / m ³ or less, preferably 0.1 mg / m ³ or less, and most preferably 0.05 mg / m ³ or less. That is.
If the oligomer gas concentration in the stretching zone in the tenter exceeds 0.2 mg / m ³ , it becomes an environment where oligomers derived from modified PBT are likely to be generated, and the size increases, so ink loss and dot loss during printing are likely to occur. .
The lower limit of the oligomer gas concentration is not particularly limited, but is not necessarily reduced to 0.03 mg / m ³ or less. This is because even if the oligomer gas concentration is further reduced, the influence on the reduction of the oligomer derived from the modified PBT is small, and it is technically difficult to measure a concentration lower than this.

  In the present invention, during the entire process of biaxially stretched polyester film production, by measuring the oligomer gas concentration in the stretching zone in the tenter type stretching machine with the highest oligomer gas concentration and controlling it within a predetermined range, as a result, Control the amount of oligomers deposited on the film.

  In the present invention, the method for reducing the oligomer gas concentration in the stretching zone in the tenter is not particularly limited. As an example, an unstretched film is obtained from a T-die in a molten polymer extrusion process, and this is a roll-type longitudinal stretching process. The production method of a biaxially stretched film in which the film is longitudinally stretched and then stretched in the tenter transverse stretching step will be described. In the production process of the biaxially stretched film, it is preferable to take measures for reducing the generation of oligomer gas in each of the three processes of the melt polymer extrusion process, the roll-type longitudinal stretching process, and the tenter-type lateral stretching process. In the present invention, the biaxial stretching method may be either a sequential biaxial stretching method using a roll and a tenter or a tenter simultaneous biaxial stretching method.

  In the melt polymer extrusion step, it is preferable to use a resin subjected to solid phase polymerization which is advantageous for suppressing the generation of oligomer gas. Further, since an oligomer is likely to be generated from a high-temperature molten polymer extruded from the T die, it is preferable to provide an exhaust duct in the vicinity of the T die.

  In the roll-type longitudinal stretching step, the temperature of the unstretched film is adjusted to Tg or higher, so that the oligomer in the film bleeds and easily contaminates the roll. Accordingly, it is preferable to provide means for cleaning the roll at the same time as production by niping an adhesive roll to the stretching roll. Furthermore, since the sublimated oligomer is likely to be deposited on the upper part of the longitudinal stretching step, it is effective to install an exhaust duct on the ceiling.

  In the tenter transverse stretching process, no matter where the oligomer is generated in the tenter, the oligomer will flow to the tenter inlet when it adheres to the tenter clip and is carried to the tenter inlet, or when the air flow in the tenter reaches the upstream direction of the film. Then, since there is a risk that the oligomer adheres to the film surface entering the tenter transverse stretching step, it is necessary to reduce the oligomer in all spaces in the tenter. In the tenter, the oligomer tends to sublimate from the film in the heat treatment zone, so that the oligomer is oxidatively decomposed by actively supplying and exhausting air to the heat treatment zone to reduce the oligomer gas concentration or by circulating platinum in the circulating hot air system. A method is conceivable. In order to prevent contamination of the tenter clip, it is effective to manage the surface temperature of the tenter clip at 90 ° C. or higher.

(Easily tearable biaxially stretched film)
PET used for the film of the present invention is obtained by a known production method, that is, an ester exchange reaction method from dimethyl terephthalate and ethylene glycol or a direct esterification method from terephthalic acid and ethylene glycol. Although obtained by melt polymerization or further solid phase polymerization, other components can be copolymerized as long as the effects of the present invention are not impaired.

  Other copolymer components include isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, succinic acid, adipic acid, sebacic acid, dodecanedioic acid, dimer acid, maleic anhydride, maleic Acids, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, dicarboxylic acids such as cyclohexanedicarboxylic acid, 4-hydroxybenzoic acid, ε-caprolactone, oxycarboxylic acids such as lactic acid, 1,3-propanediol, 1,6- Examples thereof include glycols such as hexanediol and cyclohexanedimethanol, and polyfunctional compounds such as trimellitic acid, trimesic acid, pyromellitic acid, trimethylolpropane, glycerin, and pentaerythritol.

  The molecular weight of the polytetramethylene glycol (hereinafter referred to as PTMG) unit used in the present invention is preferably in the range of 600 to 4000, more preferably 1000 to 30000, and still more preferably 1000 to 2000. When the molecular weight is less than 600, tearing linearity is hardly exhibited, and when it exceeds 4000, the performance such as mechanical strength, dimensional stability, and haze may be deteriorated.

  In the film of the present invention, the content of the PTMG unit constituting the modified PBT is preferably 5 to 20% by mass, more preferably 10 to 20% by mass from the balance such as tear linearity and mechanical strength. Preferably it is 10-15 mass%.

  In the film of the present invention, the mixing ratio of PET and modified PBT is preferably PET / modified PBT = 70/30 to 95/5 (mass ratio), more preferably, from the balance of tear linearity and mechanical strength. Is 80/20 to 90/10 (mass ratio), more preferably 85/15 to 90/10 (mass ratio).

  The modified PBT used in the present invention can be obtained by polycondensation by adding PTMG in the PBT polymerization step, but as a simpler method, it can also be obtained by melt-kneading PBT and PTMG with an extruder. Can do.

  In the raw material resin of the present invention, other polymers such as polyethylene naphthalate and polycyclohexylenedimethylene terephthalate can be mixed as long as the effects of the present invention are not impaired.

  To produce the film of the present invention, first, for example, a mixture of modified PBT and PET is put into an extruder, heated and melted, and then extruded into a sheet form from a die orifice of a T die to produce an unstretched sheet. To do. The sheet extruded from the die orifice of the T-die is cooled by being closely attached to a cooling drum by an electrostatic application casting method or the like, and then at a temperature of 90 to 140 ° C., 3.0 to 5. The film is stretched at a magnification of 0, and further heat treated at a temperature of 210 to 245 ° C. to obtain a biaxially stretched film.

  When the stretching temperature is less than 90 ° C, a homogeneous stretched film may not be obtained. When the stretching temperature exceeds 140 ° C, crystallization of PET is promoted and transparency may be deteriorated. When the draw ratio is less than 3.0 times, the strength of the obtained stretched film is low, and pinholes are likely to occur when formed into a bag. When the draw ratio exceeds 5.0 times, stretching becomes difficult. There is a case. Moreover, when the heat treatment temperature is lower than 210 ° C, the heat shrinkage rate of the stretched film obtained is increased, and the bag after bag making may be deformed. When the heat treatment temperature is higher than 245 ° C, the film is blown out. There is a case.

  The biaxially stretched polyester film of the present invention obtained as described above exhibits tear linearity at least in the longitudinal direction (MD). This biaxially stretched polyester film can be laminated with other films and used as a laminated film. In addition, by using this laminated film, an easy-open packaging bag can be produced by making a bag so that the direction of tear linearity is the tear direction of the bag.

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

Evaluation methods in Examples and Comparative Examples are as follows.

(Measurement method of oligomer-derived foreign matter)
The stretched film was passed through an optical foreign matter inspection apparatus to inspect a range of 1 m in the film width direction and 10,000 m in the film longitudinal direction. All the detected foreign matters having a diameter of 0.1 mm or more were sampled. The diameter of the foreign matter was the area average diameter calculated by the optical foreign matter inspection apparatus. Among the obtained foreign substances, those that were white and powdery were determined to be PBT-derived oligomers and counted as oligomer-derived foreign substances.

(Oligomer gas concentration measurement method)
The oligomer gas concentration in the stretching zone in the tenter was measured as follows.
(1) A hole was made in the wall of the stretching zone in the tenter, and a stainless steel pipe was passed through the hole. One end of the stainless steel pipe was set near the air inlet of the hot air circulation system, and the other end was connected to a gas cleaning bottle (Muenke type) installed outside the tenter. The gas washing bottle was filled with ethylene glycol for dissolving the oligomer component.
(2) Air was passed through the gas cleaning bottle for a certain period of time by a suction pump with a flow meter.
(3) The gas washing bottle was removed, and the inside of the gas washing bottle and the stainless steel pipe were washed with ethylene glycol.
(4) The absorbance was measured by applying the washed ethylene glycol and the ethylene glycol in the gas washing bottle to a UV spectrophotometer.
(5) Using a calibration curve prepared in advance, the measured absorbance was converted to the oligomer gas concentration.

(Evaluation method of tear linearity)
A sample in which a strip-shaped film piece of 205 mm in the longitudinal direction (MD) and 40 mm in the width direction (TD) is cut out from the biaxially stretched film, and a cut of 5 mm in length is made at the center of one short side of the film piece. 10 were produced. Next, the number of samples that were torn by hand from the notch to the MD and reached the short side where the tear propagation end faced the side where the notch was made was taken as the evaluation value of the tearing linearity of the MD, and an evaluation value of 8 or more was considered acceptable.
In addition, evaluation was implemented about each of the left end part of the film wound up after extending | stretching heat processing, a center part, and a right end part. The results are shown in Table 2.

(Evaluation method for printability)
The biaxially stretched film was subjected to a solid printing of 10,000 m ² with white ink (Fine Star R641AT white manufactured by Toyo Ink Co., Ltd.), and then passed through an optical foreign matter inspection apparatus to inspect for ink loss. The number of missing ink is shown in Table 2.

Example 1
194 parts by mass of dimethyl terephthalate, 108 parts by mass of 1,4-butanediol, and 80 ppm of tetrabutyl titanate (value converted to the mass of titanium metal with respect to the polymer) were added, and the temperature was increased from 150 ° C. to 210 ° C. while heating to 2.5 ° C. The transesterification reaction was performed for a time. After 90 parts by mass of the obtained transesterification reaction product was transferred to a polymerization vessel and 40 ppm of tetrabutyl titanate was added, 10 parts by mass of PTMG having a molecular weight of 1100 was added and pressure reduction was started, and finally the pressure was reduced to 1 hPa. The temperature was raised from 210 ° C. and finally melt polymerization was carried out at a temperature of 245 ° C. for 2 hours to obtain a modified PBT having a relative viscosity of 1.60.

  A simple chip mixture of PET and modified PBT with a mass ratio of 85/15 is melted in an extruder, then extruded from a T die, and adhered to a cooling drum whose surface temperature is controlled at 20 ° C. by an electrostatic application method. And rapidly cooled to obtain an unstretched film having a thickness of 190 μm. At this time, an exhaust device was installed between the T die and the cooling drum to suck the generated gas.

  Subsequently, the film was preheated with a preheating roll group whose temperature was adjusted to 90 ° C., and then stretched 3.5 times by changing the peripheral speed between the drawing rolls adjusted to 90 ° C. to obtain a longitudinally stretched film. At this time, the preheating roll and the drawing roll thoroughly wiped off with alcohol to completely remove the oligomer attached to the roll. In order to remove the oligomers deposited on the roll during production, the adhesive roll was nipped between the preheat roll and the stretching roll. Further, an exhaust duct was provided above the longitudinal stretching apparatus to prevent the oligomer cooled in the air from falling.

  Subsequently, the longitudinally stretched film was guided to a tenter type stretching machine, and transversely stretched 4.5 times at a stretching temperature of 120 ° C., followed by heat treatment at 235 ° C. with a transverse relaxation rate of 3%, and a thickness of 12 μm. A stretched film was obtained. At this time, the amount of air supply and exhaust in the heat treatment zone was increased, and the surface of the tenter clip was thoroughly wiped with alcohol to completely remove the oligomer attached to the tenter clip. Furthermore, the surface temperature of the tenter clip was controlled to 90 ° C. or higher to prevent oligomer precipitation. The evaluation results of the obtained biaxially stretched polyester film are shown in Table 1.

Example 2
A biaxially oriented polyester film was obtained in the same manner as in Example 2 except that a platinum catalyst was installed in the circulating hot air system of the tenter type stretching machine. The evaluation results of the obtained biaxially stretched polyester film are shown in Table 1.

Comparative Example 1
Exhaust between the T-die and the cooling drum is not performed, the nip between the preheating roll and the sticking roll of the drawing roll is removed, the exhaust duct above the longitudinal drawing device is not operated, and the surface temperature of the tenter clip is particularly controlled. First, a biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the supply / exhaust amount of the heat treatment zone of the tenter type stretching machine was not increased.
The evaluation results of the obtained biaxially stretched polyester film are shown in Table 1.

Comparative Example 2
A biaxially oriented polyester film was obtained in the same manner as in Comparative Example 1 except that the oligomer collected in advance was sprayed on an unstretched film immediately before entering the tenter-type stretching machine, and intentionally contaminated with the oligomer.
As a result of evaluating the obtained biaxially stretched polyester film, the number of foreign matter detected was large. Therefore, the range of 1 m in the film width direction and 5000 m in the film longitudinal direction was evaluated, and the number of foreign matters per 10000 m ² was obtained. The converted results are shown in Table 1.

Comparative Example 3
In Comparative Example 1, a biaxially oriented polyester film was obtained by further blowing off foreign matter by applying an air shower to the film surface at the tenter outlet.
The evaluation results of the obtained biaxially stretched polyester film are shown in Table 1.

Reference Example A biaxially oriented polyester film was obtained in the same manner as in Comparative Example 3 except that only PET was used as a raw material for the biaxially stretched polyester film.
The evaluation results of the obtained biaxially stretched polyethylene terephthalate film are shown in Table 1.

  In each Example of Table 1, a clean tear linear biaxially stretched polyester film having good printability could be prepared by satisfying the range of the oligomer-derived foreign matter defined in the present invention.

  On the other hand, in Comparative Examples 1 and 2, the adhesion amount of the oligomer is large, and ink loss or dot loss occurs even after printing.

  In Comparative Example 3, although the amount of oligomer-derived foreign matter is suppressed, it is not perfect.

  In the reference example, since the PBT-containing oligomer is not included, the conventional method is sufficiently effective, and the amount of oligomer adhesion is small.

Claims (4)

A film composed of polybutylene terephthalate and poly (ethylene terephthalate) containing a polytetramethylene glycol unit, and 10 or less oligomer-derived foreign matters having a diameter of 0.5 mm or more per 10,000 m ^{2 of} the film, and a diameter of 0.2 mm or more and 0 A biaxially stretched polyester film having tear linearity at least in the longitudinal direction, wherein the number of foreign substances derived from oligomers of less than 5 mm is 50 or less. A laminated film using the biaxially stretched polyester film according to claim 1 in at least one layer. An easy-open packaging bag using the laminated film according to claim 2, wherein the bag is formed such that the direction of tear linearity is the tear direction of the bag. A method for producing a biaxially stretched polyester film according to claim 1, wherein an unstretched sheet obtained from a mixture of polybutylene terephthalate and polyethylene terephthalate containing a polytetramethylene glycol unit is stretched by a tenter-type stretcher. At the time, the method for producing a biaxially stretched polyester film is characterized in that stretching is performed such that the oligomer gas concentration in the stretching zone in the tenter type stretching machine is 0.2 mg / m ³ or less.