JP2004162046A - Polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film having excellent mechanical strength, heat resistance, chemical resistance, insulating properties, dimensional stability, etc., and capable of being used in various fields, such as a field in which boiling or retorting treatment is required and therefore toughness, pinhole resistance, flexing resistance, strength in dropping as a bag, impact resistance, and other properties are requierd, another field in which thermoforming or vacumm forming of the film can be conducted, and the other field in which the film is used as a packaging bag or the like for a moisture-containing food, a chemical, etc. <P>SOLUTION: This polyester film has an initial modulus of 2.51-10 GPa in at least one direction, an impact strength of 40-10,000 J/mm, and a heat shrinkage percentage of ≤ 6% at 150°C in at least one direction. <P>COPYRIGHT: (C)2004,JPO

Description

  TECHNICAL FIELD The present invention relates to a polyester film suitable for food packaging and molding and processing, which has a small dimensional change in impact resistance, pinhole resistance, boil treatment and retort treatment.

  Polyester-based resin films (hereinafter, films include sheets) are excellent in mechanical strength, heat resistance, chemical resistance, insulation, dimensional stability, etc., and are used for packaging films, magnetic tape films, and photographic films. It is used for various applications, such as release films, optical films, and electronic component films.

  On the other hand, a biaxially stretched polyamide film or sheet is used for various applications such as packaging bags for water-containing foods and chemicals, which are fields requiring toughness, pinhole resistance, bending resistance, bag drop strength and impact resistance. (Hereinafter, represented by a film) is used. However, polyamide film may have poor surface flatness due to poor surface processing characteristics such as vapor deposition and coating compared to polyester, dimensional change due to moisture absorption, moisture absorption during boiling and retort processing, curl due to poor dimensional stability Demand for a polyester film that has toughness, pinhole resistance, bending resistance, bag drop strength and impact resistance, and has low dimensional stability and low moisture absorption has always been required since problems such as delamination are likely to occur. .

However, these films are obtained by mixing a copolymer polyester with a polyester such as polyethylene terephthalate as a base material (for example, see Patent Document 1), or using a part of a laminated film (for example, see Patent Document 2). By doing so, the crystallinity and molecular orientation of polyethylene terephthalate are slightly reduced, and pinhole resistance, bending resistance and impact resistance are imparted accordingly. Therefore, the problems of moisture absorption and dimensional stability in boiling and retorting treatments cannot be sufficiently solved.
JP-A-52-136276 JP-A-6-79776

  In the present invention, mechanical strength, heat resistance, chemical resistance, insulation, dimensional stability, etc. are excellent, and toughness, pinhole resistance, bending resistance, bag drop strength and impact resistance are required. It is an object of the present invention to obtain a polyester film used for various purposes such as a field requiring boil or retort treatment, a field capable of thermoforming or vacuum forming, and a packaging bag for water-containing foods and chemicals.

  In order to achieve the above object, the polyester film of the present invention has an initial elastic modulus in at least one direction of 2.51 GPa or more and 10 GPa or less, an impact strength of 40 J / mm or more and 10000 J / mm or less, and heat at 150 ° C. in at least one direction. The contraction rate is 6% or less.

  If the initial elastic modulus of the polyester film of the present invention is less than 2.51 GPa, it will be difficult to handle the film when it breaks or misaligns during printing at high speed, or when it is made into a bag. If the impact strength is less than 40 J / mm, the bag may be broken due to dropping when the bag is filled with the contents. On the other hand, if the heat shrinkage at 150 ° C. in at least one direction exceeds 6%, the film is undesirably deformed in a post-drying step such as printing.

  In this case, the polyester film may include at least terephthalic acid as an acid component and ethylene glycol as a glycol component.

  In this case, the polyester film is composed of a polyester resin composition in which 10 to 49% by weight of a polyester resin A made of a polyethylene terephthalate resin and 90 to 51% by weight of a polyester resin B other than the polyester resin A are blended. And a melting peak in a differential scanning calorimeter (DSC) at at least two places of 240 ° C. or more and 259 ° C. or less and 230 ° C. or less.

  Here, the melting peak in the differential scanning calorimeter (DSC) refers to the melting point of the polyester resin A and the polyester resin B measured by heating the film from room temperature to 280 ° C. at a rate of 20 ° C./min. It means the temperature at the peak top of the melting peak.

  In this case, the polyester resin B may be at least one resin selected from polytrimethylene terephthalate resin, polybutylene terephthalate resin, polypentamethylene terephthalate resin, and polyhexamethylene terephthalate resin. it can.

  In this case, the peak temperature of the recrystallization peak (Tc2) of the polyester film at the time of temperature decrease can be set to 180 ° C. or higher.

  Here, the recrystallization peak (Tc2) at the time of cooling refers to the temperature of the film being raised from room temperature to 280 ° C. at a rate of 20 ° C./min. / Min means the temperature at the peak top of the crystallization peak when the temperature is lowered to room temperature at a rate of / min.

  Further, in this case, the half width w height h ratio (w / h) of the recrystallization peak (Tc2) of the polyester film at the time of cooling can be 1.41 ° C./mW or less.

  Here, the half-width w height h ratio (w / h) of the recrystallization peak (Tc2) at the time of temperature drop is defined as the height of the crystallization peak from the base line L to the peak top t being h (mW). And the ratio w / h (° C./mW) between the half width w (° C.) and the height h (mW) when the half width at the height h / 2 is w (° C.).

  In this case, the reduced viscosity of the polyester film can be 0.80 or more.

  In this case, the boiling shrinkage of the polyester film in at least one direction at 95 ° C. for 30 minutes can be set to 6% or less.

  In this case, the retort shrinkage of the polyester film in at least one direction at 130 ° C. for 30 minutes can be set to 6% or less.

  In this case, the number of pinholes generated when the polyester film is bent 500 times at 5 ° C. as a Gelbo flex test can be reduced to 5 or less.

  The laminated polyester film may be a polyester film provided with a coating layer.

  Further, the laminated polyester film can be a polyester film provided with a gas barrier layer.

  Furthermore, the laminated polyester film may be a polyester film provided with a heat seal layer.

  In the present invention, mechanical strength, heat resistance, chemical resistance, insulation, dimensional stability, etc. are excellent, and toughness, pinhole resistance, bending resistance, dropping strength, impact resistance, etc. are required. Polyester films used in various applications such as a field requiring boil or retort treatment, a field capable of thermoforming and vacuum forming, and a packaging bag for water-containing foods and chemicals were obtained.

  The polyester that can be used in the present invention includes, as an acid component, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, aromatic dicarboxylic acids such as diphenic acid and phthalic acid, alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, and adipine. Acids, dimer acids, sebacic acids, aliphatic dicarboxylic acids such as dodecanedioic acid and eicoic acid, polyfunctional acids such as trimellitic acid and pyromellitic acid, and polylactic acid, polyglycolic acid, poly (2-oxybutyric acid) and the like There are derivatives of Examples of the alcohol component include ethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, 1,4-cyclohexanedimethanol and derivatives thereof. There is. The polyesters exemplified above can be used as a homopolymer or as a copolymer. It is also possible to use a blend of two or more homopolymers and / or copolymers. Examples of the homopolymer for this purpose include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyhexamethylene terephthalate, polypentamethylene terephthalate, polyethylene-2,6-naphthalate, and polylactic acid.

In particular, in order to provide mechanical strength, heat resistance, chemical resistance, insulation, dimensional stability, etc., as well as toughness, pinhole resistance, bending resistance, dropping strength and impact resistance, etc. Polyester terephthalate and its copolymer as polyester resin A, and polyesters other than polyethylene terephthalate and its copolymer as polyester resin B, for example, polytrimethylene terephthalate, polybutylene terephthalate, polypentamethylene terephthalate, polyhexamethylene terephthalate It is effective to prepare a polyester film composed of a polyester resin composition in which at least one or more of these copolymers are mixed. At this time, the polyester resin A and the polyester resin B preferably contain terephthalic acid as an acid component in an amount of 50 mol% or more, more preferably 70 mol or more, in all the acid components. Further, it is preferable that ethylene glycol is contained as a glycol component in a total amount of 10 mol% or more, more preferably 20 mol% or more.
Further, in order to prevent the film from whitening when the film is boiled or retorted or when the film is formed by heat molding, transesterification of the polyester resin A and the polyester resin B is performed so that the polyester resin A and the polyester resin B are not copolymerized. The present inventors have found that it is necessary to suppress the reaction, and it is important to control the crystallization rate and the degree of crystallization in order to suppress the transesterification reaction.

  When an ester exchange reaction occurs between the polyester-based resin A and the polyester-based resin B, a copolymer of the polyester-based resin A and the polyester-based resin B is generated, and a main component structure of the polyester resin (A) is formed. A certain ethylene terephthalate structure is randomized, and its rigidity is impaired. On the other hand, a high crystal which is a feature of a butylene terephthalate, trimethylene terephthalate, pentamethylene terephthalate or hexamethylene terephthalate structure which is a main component structure of the polyester resin B. It is presumed that the crystallinity is impaired, and as a result, the crystallization speed is reduced, and coarse spherulites causing whitening are likely to be generated. From this, the melting point of a film made of a polyester resin composition containing 10 to 49% by weight of a polyester resin A made of a polyethylene terephthalate resin and 90 to 51% by weight of a polyester resin B is determined by a differential scanning calorimeter (DSC). It is preferred that the melting peaks in at least two places of 240 ° C. or more and 259 ° C. or less and 230 ° C. or less.

  Means for suppressing side reactions such as transesterification of the polyester resin A and polyester resin B in the film composition include (1) adding a specific phosphorus compound to suppress a transesterification reaction caused by a catalyst. It is effective to (2) preliminarily knead the phosphorus compound with polyethylene terephthalate and (3) control the size of the resin pellets when mixing.

  Considering the stability in the extruder, the phosphorus compound preferably has a melting point of 200 ° C. or more and a molecular weight of 200 or more. The optimum amount of these phosphorus compounds varies depending on the type, but from the viewpoint of suppressing the transesterification reaction, it is preferable to mix 0.01 to 0.3% by weight. When used for food applications such as packaging and beverage cans, it is necessary to use compounds and amounts that meet the standards of the FDA (United States Food and Drug Administration), the Hygienic Council for Polyolefins, and the like.

Further, in order to further increase the crystallization rate, it is preferable to mix a substance serving as a crystallization nucleating agent in addition to suppressing the copolymerization.
Examples of the substance serving as a crystallization nucleating agent include polyethylene, polypropylene, polystyrene, a plasticizer such as a polyester polymer or a polyester copolymer having the above-mentioned monomer composition having a molecular weight of 20,000 or less, a fatty acid ester, calcium carbonate, and an amorphous zeolite. Particles, anatase type titanium dioxide, rutile type titanium dioxide, calcium phosphate, silica, kaolin, talc, clay, barium sulfate, zinc oxide, zinc sulfide, etc. % By weight or more and 1% by weight. However, the results vary greatly depending on the substance to be added, the amount of addition, the means of addition, the order of addition, the particle size, etc., and the conditions for melt extrusion of the film. Therefore, in order to preferably exhibit the effect stably, a master batch pellet is prepared by adding inorganic particles to a polyester copolymer having the above-mentioned monomer constitution having a molecular weight of 20,000 or less at the time of polymerization, and forming the master batch pellet at least. It is preferable to dry-blend, melt and extrude the pellets of the polyester resin A and polyester resin B serving as the base material and the master batch pellets. Compared with the case where inorganic particles are added to the polyester resin A or the polyester resin B at the time of polymerization, the dispersibility in the mixed resin becomes better, so that the crystallization speed is further improved. It is considered that the effect of suppressing whitening during thermoforming is improved.
In the present invention, it is preferable to adopt the above-described method, but the method is not necessarily limited as long as the characteristics described later are satisfied by another method.

The method of forming a film in the present invention will be described, but is not particularly limited thereto, but is preferably the method described below.
First, in the extrusion step, the above-mentioned polyester resin and other resin pellets are mixed, put into an extruder, melted, extruded using a T-die, brought into close contact with a cooling roll by an electrostatic adhesion method, and solidified by cooling. To obtain an unstretched sheet. At that time, the temperature of the extruder is preferably 262 ° C. or less for the feed section, the compression section and the measuring section, the filter, the resin flow path and the T-die.
Generally, when the temperature conditions for resin extrusion are described in the literature, the resin temperature immediately before the resin enters the T-die or immediately after the resin exits the T-die is often used as the extrusion temperature condition. Therefore, even if the resin temperature is controlled just before the resin enters the T-die or immediately after the resin exits the T-die, the resin temperature during the extrusion process up to that time is immediately before the resin enters the T-die or exits the T-die. It does not always coincide with the resin temperature immediately after. Due to the unique state of the machine such as the screw shape and the production speed and stability, the feed section, compression section and measuring section of the extruder, as well as the filter and resin flow path, are often changed intentionally. Are often different in practice.
That is, in the present invention, it is preferable to eliminate the zone at 270 ° C. or higher. It is considered that the reason is that the presence of a zone at 270 ° C. or higher accelerates the decomposition of the resin usable for the polyester resin B from around 270 ° C.

  The obtained unstretched sheet can be used as long as it satisfies the requirements of the present invention. Preferably, the unstretched sheet is stretched at least uniaxially, more preferably biaxially or more. Examples of the stretching method include tubular stretching, simultaneous biaxial stretching using a pantograph method, simultaneous or sequential biaxial stretching using a linear motor system, and sequential biaxial stretching using a combination of a heating roll and a tenter. In the case of the sequential biaxial method, stretching methods such as vertical-horizontal, horizontal-vertical, vertical-vertical-horizontal, vertical-horizontal-vertical, vertical-horizontal-horizontal, and vertical-vertical-vertical-horizontal are exemplified.

Here, a sequential biaxial stretching by a general vertical-horizontal method will be described as an example.
The obtained unstretched sheet is guided to a heated roll having a peripheral speed difference, where it is stretched 2 to 5 times in the longitudinal direction. The stretching temperature varies depending on the constituent resin, but is 50 to 120 ° C.
The sheet stretched in the longitudinal direction is guided to a tenter and stretched 3 to 6 times in the transverse direction. The stretching temperature varies depending on the constituent resin, but is usually 70 to 150 ° C.

  In order to obtain a film having a heat shrinkage at 150 ° C. in at least one direction of 6% or less in the present invention, heat setting is required after the completion of stretching. The heat setting is performed in a tenter at 200 ° C. to 235 ° C., preferably 210 ° C. to 225 ° C. after the completion of the transverse stretching. At 200 ° C. or lower, a film having a heat shrinkage of 6% or lower cannot be obtained. If the temperature exceeds 235 ° C., the heat shrinkage can be reduced, but the mechanical strength such as impact strength and piercing strength is reduced, and it is easy to break during film production and processing and break the packaging bag. Not a target. Preferably, the film is preferably relaxed by 2 to 7% in the horizontal direction during heat fixing, so that a film having a small heat shrinkage can be easily obtained. Note that the heat setting can be performed while relaxing the film coming out of the tenter in the vertical direction by using a roll or the like.

  The reduced viscosity (ηsp / c) of the film is preferably at least 0.80, more preferably at least 0.85, even more preferably at least 0.90. If it is less than 0.80, the impact strength is low, and the bag filled with the contents tends to be broken.

  Further, the peak temperature of the recrystallization peak at the time of cooling is preferably 180 ° C. or higher, more preferably 185 ° C. or higher, further preferably 190 ° C. or higher, more preferably 192 ° C. or higher. When the peak temperature of the recrystallization peak at the time of temperature fall is in the above range, because the crystallization speed of the film in the cooling process in the temperature fall from the melting point is fast, microcrystals that do not contribute to the scattering of visible light are quickly inside the film, Since the film can be formed in a large amount, it is effective in that the film is hardly whitened while maintaining the processing characteristics.

In the present invention, the half width w height h ratio (w / h) of the recrystallization peak (Tc2) at the time of temperature decrease in the differential scanning calorimeter (DSC) of the polyester film is preferably 1.41 ° C./mW or less, It is more preferably 1.20 ° C./mW or less, particularly preferably 1.10 ° C./mW or less.
The ratio (w / h) of the half width w to the height h of the recrystallization peak (Tc2) at the time of temperature decrease is obtained as follows. That is, as shown in FIG. 1, the scale of the DSC-temperature / caloric curve chart is such that the width of the vertical axis is 28 mW, the range of the horizontal axis (temperature, ° C.) is 30 to 281 ° C., and the actual length of the vertical axis is 120 mm. The DSC-temperature / caloric curve is plotted on a 193 mm actual length chart paper on the horizontal axis, and the height hs (mm) and the height hs / mm on the chart from the base line L of the crystallization peak to the peak top t are plotted. The length ws (mm) of the half width at 2 is actually measured, and the ratio ws / hs (mm / mm) is calculated.
In the polyester film of the present invention, when represented by the ratio ws / hs (mm / mm), ws / hs is preferably 0.25 or less, more preferably 0.22 or less, and particularly preferably 0.20 or less.
Then, based on the height h (mW) of the chart and the half-width w (° C.) at the height h / 2, the ratio is determined by the half-width w peak height h ratio of the crystallization peak (w / h (° C./mW). )).
Satisfying the above conditions is because the crystallization speed of the film in the cooling process at the temperature lowering from the melting point is fast, and microcrystals that do not contribute to the scattering of visible light can be quickly and abundantly formed in the film. This is effective in obtaining a film having an excellent design property in which the film is not whitened while being maintained.

  The polyester film of the present invention has an initial elastic modulus in at least one direction of at least 2.51 GPa, preferably at least 2.7 GPa, and more preferably at least 2.7 GPa in the longitudinal and transverse directions. If it is less than 2.51 GPa, it will be difficult to handle the film when it breaks during printing at high speed or when it is made into a bag.

  The polyester film in the present invention has an impact strength of 40 J / mm or more, preferably 50 J / mm or more, more preferably 60 J / mm or more. If it is less than 40 J / mm, the bag may be broken due to dropping when the bag is filled with the contents.

  The polyester film in the present invention has a heat shrinkage at 150 ° C. in at least one direction of 6% or less, preferably 4% or less, more preferably 3% or less, and further preferably 2% or less. If it exceeds 6%, the film is undesirably deformed in a post-drying step such as printing.

  The polyester film of the present invention has a shrinkage in at least one direction after boil treatment at 95 ° C. for 30 minutes of 6% or less, preferably 4% or less, more preferably 3% or less, and still more preferably 2% or less. If it exceeds 6%, it becomes impossible to use the food packaging bag which requires boil processing, since the bag is broken or the printing is deformed.

  The polyester film of the present invention has a shrinkage in at least one direction after retorting at 130 ° C. for 30 minutes of 6% or less, preferably 4% or less, more preferably 3% or less, and further more preferably 2% or less. If it exceeds 6%, the food packaging bag which requires retort treatment will be broken or deformed in printing, and cannot be used.

  Further, the polyester film of the present invention has a pinhole number of 5 or less, preferably 3 or less, more preferably 2 or less when bent 500 times at 5 ° C as a gelbo flex test. is there. When the number is six or more, the nylon film is not suitable for use as a food packaging material that requires pinhole resistance and bag breakage resistance.

  The film of the present invention has a thickness of 5 to 1000 μm, preferably 8 to 50 μm.

  The polyester film is usually formed into a film by adding a lubricant. Examples of the lubricant include silicon dioxide, kaolin, clay, calcium carbonate, calcium terephthalate, aluminum oxide, titanium oxide, calcium phosphate, silicone particles, and the like, and an inorganic lubricant is preferable. In addition, at the time of melt mixing, additives such as a stabilizer, a coloring agent, an antioxidant, an antifoaming agent, an antistatic agent, and the like can be contained, if necessary, in addition to the lubricant.

  By providing a coating layer, the film of the present invention can impart printability, easy adhesion, gas barrier properties, antistatic properties, and the like. As the base resin that can be used as the coating material, polyester, polyacryl, polyurethane, polyvinyl alcohol and their copolymers, graft copolymers, ethylene vinyl alcohol copolymers and the like can be used. Known coating methods can be used, for example, bar coating, gravure coating, microgravure coating, reverse coating, reverse kiss coating, large coating, curtain coating, spray coating and the like. Further, the coating can be carried out by either an off-line coating in which the film after the stretching is completed using a coater or an in-line coating in which coating is performed during film formation.

  The film of the present invention includes polyethylene such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, and ethylene-vinyl acetate copolymer, polypropylene, ethylene-acrylic acid copolymer, and ethylene-methacrylic acid copolymer. Thermal adhesion can be imparted by providing a heat seal layer made of a coalesced product, an ethylene / methyl acrylate copolymer, an ethylene / ethyl acrylate copolymer, an ethylene / methyl methacrylate copolymer, an ionomer, or the like. Examples of the method for providing the heat seal layer include extrusion lamination, film lamination, and a method in which a heat seal layer is applied during film formation by a coextrusion method.

The film of the present invention can be provided with gas barrier properties by providing an organic and / or inorganic gas barrier layer. The method is a known method, for example, a method of coating a gas barrier resin such as vinylidene chloride resin, or a metal or inorganic oxide deposited layer by a vacuum deposition method, a sputtering method, a physical deposition method such as an ion plate method, or a CVD method. And the like, and a method of forming it by using a chemical vapor deposition method or the like as appropriate.
The formation of

  The polyester film or the laminated polyester film of the present invention is used for a conventional nylon film, specifically, as a food packaging material in which pinhole resistance and bag-breaking resistance are required, particularly polyester is heat-resistant. It can be effectively used as a packaging material for processed marine products, pickles, prepared dishes, processed meat products, etc., which are subjected to boil treatment and retort treatment by utilizing the point of being excellent in moisture absorption dimensional stability. Furthermore, it can be effectively used for industrial food packaging such as pet food, agricultural chemicals, fertilizer, infusion pack, or semiconductor, precision material packaging such as medical, electronic, chemical and mechanical. In addition, by utilizing heat resistance, impact resistance, and crystallization characteristics, it is also useful as a material for packaging materials such as molded containers utilizing vacuum forming or pressure forming, cards, and electronic device cases.

  Hereinafter, specific examples will be described. In addition, each characteristic value was measured as follows.

1. Reduced viscosity (ηsp / c)
0.125 g of the polymer was dissolved in 25 mL of phenol / tetrachloroethane = 6/4 (weight ratio) and measured at 25 ° C. using an Ubbelohde viscosity tube. The unit is dL / g.

2. Initial elastic modulus, rupture elongation, rupture strength According to JIS-K7127-1989, the measurement was performed using Autograph AG-5000A (manufactured by Shimadzu Corporation).

3. Impact Strength Using a film impact tester (manufactured by Toyo Seiki Seisaku-Sho, Ltd., serial number T-84-3), the measurement film was pressed with a clamp, pierced with a 1/2 inch diameter hemispherical impact head, and the impact strength of the sample was measured. Ten samples were prepared, and the impact surface was changed, and five samples were measured. The sample was cut into 100 mm x 100 mm or more, and the ring for fixing the sample had an inner diameter of 30 mm. The average value of the determined impact strength of the sample was determined, and the value was converted to a value of about 1 mm in thickness to determine the impact strength (J / mm) of the film.

4. Heat shrinkage rate The sample is cut into 10 mm x 150 mm, and 10 samples with marking lines at 100 mm intervals are prepared. Thereafter, the sample was left in a gear oven at 150 ° C. for 30 minutes under no load, and after taking out, the interval between the marked lines was measured at room temperature. did.
Heat shrinkage = (AB) / A × 100
A: distance between marked lines before heating B: distance between marked lines after heating

5. Boil shrinkage The film is cut out to A4 size, and a square having a side of 180 mm is drawn on the surface as a mark line. The sample was immersed in hot water of 95 ° C. for 30 minutes, left at 23 ° C. and 65 RH% for 24 hours, then measured for the distance of the marked line again, and calculated in the same manner as in the above “4. Then, the boil shrinkage was determined.

6. Retort shrinkage rate The film is cut out to A4 size, and a square having a side of 180 mm is drawn as a mark on the surface.
The sample was immersed in a 0.19 MPa retort kettle at 130 ° C. for 30 minutes, left at 23 ° C. and 65 RH% for 24 hours, then measured again for the distance of the marked line, and the above equation of “4. The retort shrinkage was calculated in the same manner.

7. Gelbo test value For a film sample (distance between chucks: 178 mm, diameter: 89 mmφ) in which the ambient temperature was set to 5 ° C. in a gelbo flex tester (manufactured by Tester Sangyo Co., Ltd., manufacture number 27793) and the gelbo was repeated 500 times, The number of pinholes was compared (the number of ink-permeable portions on the filter paper was counted). The twist angle was 440 °.

8. Melting point of film (TmL, TmH), crystallization temperature (Tc2), half width of crystallization peak w peak height h ratio (w / h)
Using DSC3100S manufactured by Mac Science Co., put 8 to 10 mg of the film in a sample pan, cover the pan, measure in a nitrogen gas atmosphere from room temperature to 280 ° C at a heating rate of 20 ° C / min. The peak top temperatures of the melting peaks of the melting points derived from A) and the polyester resin (B) were defined as TmH and TmL, respectively.
Further, the sample at 280 ° C. was kept as it was for 1 minute, then cooled to room temperature at a rate of 20 ° C./min, and the temperature of the peak top t of the crystallization peak measured was defined as Tc2.
At this time, as shown in FIG. 1, the DSC-temperature / caloric curve chart has a scale of the vertical axis (heat amount, mW) based on an arbitrary value such that the entire Tc2 peak is included. The DSC-temperature / caloric curve was plotted on A4 paper with 28 mW and the range of the horizontal axis (temperature, ° C) was 30 to 281 ° C. The actual length of the vertical axis was 120 mm, and the actual length of the horizontal axis was 193 mm.
Then, in order to obtain the ratio w / h (° C./mW) of the half width w (° C.) of the crystallization peak to the height h (mW), the height on the chart from the base line L of the crystallization peak to the peak top t hs (mm) and the length ws (mm) of the half width at the height hs / 2 were actually measured, and the ratio ws / hs (mm / mm) was calculated.
Next, the height h (mW) from the base line L to the peak top t of the crystallization peak of the chart and the half-value width w (° C.) at the height h / 2 are determined, and the ratio is calculated. The peak height h ratio was defined as w / h (° C./mW).

9. Preparation of Laminated Film An unstretched polypropylene film (P1153, manufactured by Toyobo Co., Ltd .: 50 μm) was used as a sealant film for forming a heat seal layer on the obtained polyester film. An adhesive for dry lamination (“TM590 /” manufactured by Toyo Morton Co., Ltd.) Using CAT56 "), the laminate was dry-laminated with a solid coating thickness of 3 µm, and aged at 40 ° C for 3 days to produce a laminated film.

10. Dropping test An unstretched polypropylene film (P1153, manufactured by Toyobo Co., Ltd .: 50 μm) is used as a sealant film on the obtained polyester film using an adhesive for dry lamination (“TM590 / CAT56”, manufactured by Toyo Morton Co., Ltd.). Dry lamination with a thickness of 3 μm, seal on four sides with an impulse sealer, make 10 bags filled with water of 150 mm x 150 mm, and drop them repeatedly 20 times from the height of 1 m under 5 ° C environment It was expressed as the average value of the number of times of bag breakage or water leakage.

11. Boil test An unstretched polypropylene film (P1153, manufactured by Toyobo Co., Ltd .: 50 μm) was used as a sealant film on the obtained polyester film using a dry laminating adhesive (“TM590 / CAT56”, manufactured by Toyo Morton Co., Ltd.). Dry laminating with a coating thickness of 3 μm, sealing the four sides with an impulse sealer, making a bag filled with water of 150 mm x 150 mm, immersing in hot water of 95 ° C for 30 minutes, breaking the bag and appearance of the bag surface The presence or absence of defects (wrinkles, whitening) was evaluated.

12. Retort test An unstretched polypropylene film (Toyobo Co., Ltd. P1153: 50 μm) was used as a sealant film on the obtained polyester film using an adhesive for dry lamination (“TM590 / CAT56” manufactured by Toyo Morton Co., Ltd.). Dry laminating with a coating thickness of 3 μm, sealing the four sides with an impulse sealer, making a bag filled with water of 150 mm × 150 mm, retorting at 120 ° C. for 30 minutes, breaking the bag and poor appearance of the bag surface (wrinkles, (Whitening) was evaluated.

13. Printing test Using a three-color gravure printing machine manufactured by Modern Machinery Co., on one side of the obtained polyester film, three colors of blue, red, and white of gravure ink "Univia A" manufactured by Dainippon Ink and Chemicals, Inc. Gravure printing was performed, and visual evaluation was made for any appearance defects or printing deviations. Printing was performed at a speed of 50 m / min and a drying temperature of 90 ° C.

14． Vibration test Ten bags filled with water as described in the above section “10. Dropping bag test” were prepared, and one bag was placed in each of 10 cardboard boxes 200 mm wide × 200 mm deep × 40 mm high. As a model of actual product transportation in a state where five rows were stacked, vibration was performed in a 5 ° C. atmosphere at a vibration width of 50 mm and a vibration speed of 180 reciprocations / minute for 10 hours, and expressed as an average value of the number of generated pinholes.

15. Adhesive strength A 15 mm wide strip-shaped test piece was cut out from the laminated film described in the section “9. Preparation of a laminated film” and the bag subjected to the boil treatment described in the section “11. Using a graph AG-5000A (manufactured by Shimadzu Corporation), 180 ° peeling was performed while attaching water to the interface, and the adhesion strength between the polyester film and the sealant was measured.

16. Oxygen Permeability A test piece is cut out from the laminated film described in the item “9. Preparation of a laminated film” and the bag subjected to the boil treatment described in the item “11. The measurement was performed under the conditions of a temperature of 23 ° C. and a humidity of 65% using “OX-TRAN 10 / 50A” manufactured by Modern Controls.

(Example 1)
Polyethylene terephthalate resin (A1) (reduced viscosity 0.75) to which silicon dioxide (F) (Silicia 310 manufactured by Fuji Silysia) was added at the time of polymerization at 2000 ppm as polyester resin A, and polybutylene terephthalate resin (B1) as polyester resin B (Reduced viscosity 1.20), polybutylene terephthalate resin (B2) containing 1% of an organic phosphorus compound (ADEKA STAB PEP-45: manufactured by Asahi Denka Kogyo KK), and talc (D) ( Terephthalic acid / sebacic acid // ethylene glycol / 1,4-butanediol copolymer (C1) (90/10 // 60/40 (molar ratio) molecular weight obtained by adding 2% of an average particle size of 3.5 μm) during polymerization 2000) were prepared. They were introduced into a single screw extruder (65φ) so that A1 / B1 / B2 / C1 = 40/56/2/2 (parts by weight). The temperature setting of the extruder is as follows: the supply section (Ex1), the compression section (Ex2), the measuring section (Ex3) of the extruder, the flow path to the filter, the filter section, the flow path to the die, and the die temperature setting Ex1 The resin was supplied at 240 ° C., 260 ° C. from Ex2 to the filter section, and 255 ° C. thereafter. The temperature of the resin measured immediately after the resin came out of the T-die was 258 ° C. The filter used was a 200 mesh filter. The resin discharged from the T-die was quenched on a roll cooled to 20 ° C. by electrostatic contact to obtain an unstretched sheet having a thickness of about 200 μm. The sheet was fed to a roll stretching machine and stretched in the machine direction at 65 ° C. by 3.4 times. Subsequently, in a tenter, the polyester film is stretched laterally at 90 ° C. by 3.6 times, and is relaxed in the tenter at 200 ° C. for about 10 seconds, at 220 ° C. for about 10 seconds, and 4% in the transverse direction, while being about 16 μm polyester film. Got.

(Example 2)
A polyester film was obtained in the same manner as in Example 1 except that the raw materials were changed to A1 / B1 / B2 / C1 = 30/66/2/2 (parts by weight).

(Example 3)
Example 1 was the same as Example 1 except that polyhexamethylene terephthalate (B3) (reduced viscosity: 0.65) was polymerized to A1 / B1 / B2 / B3 / C1 = 40/51/5/2/2 (parts by weight). In exactly the same way, a polyester film was obtained.

(Example 4)
Exactly the same method as in Example 1 except that polytrimethylene terephthalate (B4) (reduced viscosity: 1.00) was polymerized to A1 / B4 / B2 / C1 = 30/66/2/2 (parts by weight) as a raw material. , A polyester film was obtained.

(Comparative Example 1)
A polyester film was obtained in exactly the same manner as in Example 1, except that the raw materials were changed to A1 / B1 / B2 / C1 = 75/21/2/2 (parts by weight).

(Comparative Example 2)
A polyester film was obtained in the same manner as in Example 1 except that the raw materials were changed to A1 / B1 / B2 / C1 = 3/93/2/2 (parts by weight).

(Comparative Example 3)
As the conditions of the extruder, only Ex2 was set to 295 ° C., and the other parts were prepared under the same conditions as in Example 1 to prepare a polyester film. At this time, the temperature of the resin immediately after leaving the T-die was 260 ° C.

(Comparative Example 4)
A polyester film was obtained in exactly the same manner as in Example 1 except that the raw materials were changed to A1 / B1 / B2 / C1 = 40/58/2/0 (parts by weight).

(Comparative Example 5)
A polyester film was obtained in the same manner as in Example 1, except that the raw materials were changed to A1 / B1 / B2 / C1 = 40/58/0/2 (parts by weight).

  The results are shown in Table 1.

(Example 5)
One side of the polyester film obtained in Example 1 was coated with an acrylic graft polyester resin so as to have a solid content thickness of about 0.1 μm to obtain a coated film. Then, on this coating layer, an unstretched polypropylene film (P1153, manufactured by Toyobo Co., Ltd .: 50 μm) as a sealant layer was used as an adhesive for dry lamination (“TM590 / CAT56”, manufactured by Toyo Morton Co., Ltd.), and a solid applied thickness of 3 μm. ) To obtain a laminated polyester film.

(Example 6)
The polyester film obtained in Example 1 was placed in a vacuum evaporation apparatus, the pressure in the chamber was maintained at 1 × 10 ⁻³ Pa, and a mixed oxide of 70% by weight of SiO ₂ and 30% by weight of Al ₂ O ₃ : 15 kW. To form a gas barrier layer made of a colorless and transparent inorganic oxide having a thickness of 190 ° on one surface of the polyester film to obtain an inorganic vapor-deposited film. Then, an unstretched polypropylene film (P1153, manufactured by Toyobo Co., Ltd .: 50 μm) was used as a sealant layer on the gas barrier layer made of the inorganic oxide, as an adhesive for dry lamination (“TM590 / CAT56” manufactured by Toyo Morton Co., Ltd.) Dry lamination was performed using a solid content coating thickness of 3 μm) to obtain a gas barrier laminated polyester film.

(Comparative Example 6)
One side of a biaxially stretched nylon film (N1100 manufactured by Toyobo Co., Ltd .: 15 μm) is coated with the same acrylic graft polyester resin as used in Example 5 so as to have a solid thickness of about 0.1 μm, and a coated film is formed. Obtained. Further, a sealant was dry-laminated on the coating layer in the same manner as in Example 5 to obtain a laminated nylon film.

(Comparative Example 7)
Using nylon 6 as a raw material, it is melt-extruded at 260 ° C. with a single screw extruder (65φ), discharged from a T-die, quenched on a roll cooled to 20 ° C. by electrostatic adhesion, and has a thickness of about 200 μm. An unstretched sheet was obtained. The sheet was supplied to a roll stretching machine and stretched 3.3 times at 70 ° C. in the machine direction. Subsequently, the film is stretched 3.8 times at 130 ° C. in a tenter and relaxed in the tenter at 200 ° C. for about 10 seconds, at 220 ° C. for about 10 seconds, and 4% in the transverse direction. Got. A gas barrier layer made of an inorganic oxide was formed on one surface of the obtained nylon film in the same manner as in Example 6 to obtain an inorganic vapor-deposited film. Further, a sealant layer was dry-laminated on the gas barrier layer made of this inorganic oxide in the same manner as in Example 6 to provide a sealant layer, and a gas-barrier laminated nylon film was obtained.

  The initial elastic modulus, impact strength, and heat shrinkage of the laminated polyester films, gas-barrier laminated polyester films, laminated nylon films, and gas-barrier laminated nylon films obtained in Examples 5 and 6 and Comparative Examples 6 and 7 were evaluated. The obtained laminated film and gas-barrier laminated film were evaluated for a gelbo test, a bag drop test, adhesion strength and oxygen permeability. Table 2 shows the evaluation results.

  As described above, the polyester film of the present invention has been described based on a plurality of examples. However, the present invention is not limited to the configurations described in the above examples, and appropriately combines the configurations described in each example. The configuration can be changed as appropriate without departing from the spirit of the invention.

  Since the polyester film of the present invention has properties such as excellent mechanical strength, heat resistance, chemical resistance, insulation properties, and dimensional stability, it has toughness, pinhole resistance, and bending resistance. In addition, it can be suitably used in fields requiring boil or retort treatment, which are fields requiring bag drop strength and impact resistance, etc., and fields in which thermoforming or vacuum forming is possible. It can also be used for various applications such as a field in which molding is possible and a packaging bag for water-containing foods and medicines.

How to determine the ratio w / h of the half width w to the height h of Tc2

Explanation of reference numerals

1 Recrystallization peak measured by DSC L Base line t Peak top h Temperature width (half width) at height w h / 2 from base line L to peak top t

Claims (13)

  Polyester characterized by having an initial elastic modulus in at least one direction of from 2.51 GPa to 10 GPa, an impact strength of from 40 J / mm to 10,000 J / mm, and a heat shrinkage at 150 ° C. of at least one direction of 6% or less. the film.   2. The polyester film according to claim 1, comprising at least terephthalic acid as an acid component and ethylene glycol as a glycol component.   A polyester resin composition comprising 10 to 49% by weight of a polyester resin (A) composed of a polyethylene terephthalate resin and 90 to 51% by weight of a polyester resin (B) other than the polyester resin (A); 3. The polyester film according to claim 1, wherein a melting peak in a differential scanning calorimeter (DSC) is present in at least two places of 240 ° C. or more and 259 ° C. or less and 230 ° C. or less. 4.   The polyester resin (B) is at least one resin selected from a polytrimethylene terephthalate resin, a polybutylene terephthalate resin, a polypentamethylene terephthalate resin, and a polyhexamethylene terephthalate resin. Item 10. The polyester film according to item 3.   5. The polyester film according to claim 1, wherein the peak temperature of the recrystallization peak (Tc2) at the time of temperature drop is 180 ° C. or higher.   The half-width w height-h ratio (w / h) of the recrystallization peak (Tc2) at the time of temperature drop is 1.41 ° C./mW or less, wherein the recrystallization peak (Tc2) is 1.41 ° C./mW or less. Polyester film.   The polyester film according to claim 1, 2, 3, 4, 5, or 6, wherein the reduced viscosity is 0.80 or more.   8. The polyester film according to claim 1, wherein a boil shrinkage in at least one direction at 95 ° C. for 30 minutes is 6% or less.   9. The polyester film according to claim 1, wherein the retort shrinkage at 130 ° C. for 30 minutes in at least one direction is 6% or less.   The number of pinholes generated when bending 500 times at 5 ° C. as a Gelboflex test is 5 or less, wherein the number of pinholes is 5 or less. 9. The polyester film according to item 9.   A laminated polyester film, wherein a coating layer is provided on the polyester film according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10.   A laminated polyester film, wherein a gas barrier layer is provided on the polyester film according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11.   A laminated polyester film, wherein a heat seal layer is provided on the polyester film according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12.

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