JP4543313B2 - Polyester film - Google Patents

Description

  The present invention relates to a polyester film suitable for various uses such as food packaging, general industrial use, optical use, electric material use, molding processing and the like, and useful as a constituent material of a film laminate metal plate.

  Polyester films represented by polyethylene terephthalate have been developed for various uses because of their mechanical properties and heat resistance. However, since the polyester film is inferior in flexibility and moldability, there are some uses that cannot be used. On the other hand, polyamide films represented by 6-nylon are often used for food packaging and the like because they are excellent in flexibility, pinhole resistance and gas barrier properties. However, since the polyamide film has poor dimensional stability against moisture absorption, it is difficult to use it for boiled or retort food applications or industrial applications.

  Therefore, it has been studied to impart flexibility, which is one of the characteristics of the polyamide film, to the polyester film. Most of these impart flexibility to the film by using a copolyester as the whole or a part of the base resin. However, the use of the copolyester may cause a problem during processing such as printing because the mechanical strength and elastic modulus of the film are lowered.

  In addition, studies have been made to impart flexibility to the film using crystalline polyester. For example, JP-A-2002-37993 and JP-A-2003-2987 disclose films obtained by blending polyethylene terephthalate and polybutylene terephthalate.

  In addition, a film in which polyethylene terephthalate and polybutylene terephthalate are blended has been studied as a can laminate film. For example, Japanese Patent No. 2882885, Japanese Patent No. 3020731, Japanese Patent Laid-Open No. 10-195210, Japanese Patent Laid-Open No. 10-110046, Japanese Patent Laid-Open No. 2003-20348, etc. include polyethylene terephthalate (PET) polyester resin and poly A polyester film blended with butylene terephthalate (PBT) polyester resin has been proposed. By optimizing the thermal characteristics and plane orientation of the film, the film follows the deformation of the metal plate and heat treatment after lamination The flavor property by (crystallization treatment) is improved. At this time, since the degree of crystallinity cannot be increased if the transesterification reaction between the two kinds of polyesters in the film proceeds excessively, the resin melting time during film formation and subsequent stretching and heat treatment steps Is devised to reduce the amount of heat applied to the film.

  Further, JP-A-2002-179892 and JP-A-2002-321277 also propose a blend film of PET and PBT, which can be used for molding transfer, molding container, metal bonding, and the like. Has been. Although these are blend films, the PET phase and the PBT phase have independent crystals, so that heat fusion and formability can be maintained. Extruding is disclosed.

  However, in the known polyester blend film described above, when the temperature is lowered after the film is melted at a temperature close to or higher than the melting point and bonded to a metal plate or the like, whitening occurs in the film. The problem that the designability of the film was impaired was unavoidable. Further, even when the film is molded as it is, when the film is melted at a temperature near or higher than the melting point of the film, the film is whitened with cooling, and the problem that the design property of the film is impaired can be avoided. There wasn't.

JP 2002-37993 A JP 2003-2987 A Japanese Patent No. 2882985 Japanese Patent No. 3020731 JP 10-195210 A Japanese Patent Laid-Open No. 10-110046 JP 2003-20348 A JP 2002-179892 A JP 2002-321277 A

  The problem of the whitening in the known polyester blend film is assumed as follows. In the production of the above-mentioned known polyester blend film, a plurality of types of polyester resin chips to be blended are mixed (dry blended) before melting, and the resulting mixed chips are put into an extruder and melted and mixed. Therefore, melting of a plurality of types of polyester resin chips starts substantially at the same time, and is melted and mixed for a long time. Due to melting and mixing for a long time, copolymerization (progress of transesterification reaction) has occurred, or even if no copolymerization has occurred, a plurality of substantially compatible polyesters are very finely dispersed. It is considered to be in a state. Even if a plurality of kinds of polyesters are not copolymerized and have crystallinity in a dispersed state substantially independent of each other, they are easily affected by each other in a very finely dispersed state. Therefore, the independence of the crystallinity at a higher level is not maintained for each polyester, and as a result, it is presumed that the crystallization hardly progresses when the temperature is lowered from the molten state, and the film is whitened.

  In order to solve the problem of whitening, it is desired to increase the crystallization speed of individual polyesters by roughening the dispersion state of a plurality of polyesters to be blended, for example, PET and PBT. However, if the dispersion state is too rough, it may be considered that the film is cleaved or the piercing strength is inferior. Accordingly, there is a demand for a film that is controlled to a moderately coarse dispersion state and balances them all.

  The object of the present invention is excellent in mechanical properties, has high crystallinity, has excellent design properties without being whitened even when heat-treated near or above the melting point of the film in laminating with a metal plate, and is capable of cleaving the film. And providing a polyester film having good piercing strength. The object of the present invention is a polyester that is excellent in the above-mentioned properties, is suitable for various uses such as food packaging, general industrial use, optical use, electrical material use, molding processing and the like, and is useful as a constituent material for film-laminated metal plates. To provide a film.

As a result of the study, the present inventors used a streak length in a Fourier image obtained by a transmission electron microscope in the film cross-sectional direction as an index representing the dispersion state of the resin inside the film, and this streak length is 30 nm ⁻¹ or more. It has been found that the purpose is achieved by a film.

The present invention includes the following inventions.
(1) Polyethylene terephthalate resin (A) and a crystalline polyester resin (B) different from the resin (A), based on the total amount of the resin (A) and the resin (B), the resin (A) 10 An index representing a dispersion state of a resin inside a film by a transmission electron microscope in a film cross-sectional direction, which is a film made of a polyester resin composition blended at a ratio of ˜90 wt% and resin (B) 90-10 wt% A polyester film characterized in that a half value of a streak length in a Fourier image is 30 nm ^-1 or more.
(2) The polyester film according to (1), wherein the crystalline polyester resin (B) is selected from a polybutylene terephthalate resin and a polytrimethylene terephthalate resin.
(3) The polyester film according to (1) or (2), wherein the reduced viscosity of the polyester film is 0.80 or more.
(4) The polyester film according to any one of (1) to (3), which is for metal plate lamination.
(5) The polyester film according to any one of (1) to (3), which is for molding.

According to the present invention, it has excellent mechanical properties, has high crystallinity, is excellent in design without whitening even when heat-treated near or above the melting point of the film when bonded to a metal plate, and has no cleavage of the film. A polyester film having good puncture strength is provided.
The polyester film of the present invention is excellent in the above-mentioned properties, mechanical properties, heat resistance, flexibility and molding processability, so it can be used for various food packaging, general industrial, optical, electrical material, molding, metal Or it is suitable for various uses, such as an object for vapor deposition of a metal oxide, and is especially useful as a constituent material of a film laminate metal plate.

  The polyester film of the present invention includes a polyethylene terephthalate resin (A) and a crystalline polyester resin (B) different from the resin (A), based on the total amount of the resin (A) and the resin (B). (A) It is comprised from the polyester-type resin composition mix | blended in the ratio of 10 to 90 weight% and resin (B) 90 to 10 weight%.

  The polyethylene terephthalate resin (A) used in the present invention is composed mainly of polyethylene terephthalate, and may be a homopolymer of polyethylene terephthalate (PET), and other copolymerizable components are copolymerized. It may be a copolymer. In the case of a copolymer, the polyethylene terephthalate component is preferably contained in an amount of 80 mol% or more, more preferably 90 mol% or more of the polyester component. Examples of copolymerizable acid components include aromatic dicarboxylic acids such as isophthalic acid, naphthalenedicarboxylic acid, diphenic acid, and phthalic acid, alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, adipic acid, dimer acid, and sebacin. Examples thereof include aliphatic dicarboxylic acids such as acid, dodecanedioic acid and eicoic acid, polyfunctional acids such as trimellitic acid and pyromellitic acid, polylactic acid, polyglycolic acid, poly (2-oxybutyric acid), and derivatives thereof. . Examples of the copolymerizable alcohol component include propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, 1,4-cyclohexanedimethanol, and their Derivatives.

  The reduced viscosity of the polyethylene terephthalate resin (A) is preferably 0.55 to 1. 10, more preferably 0.58 to 1.00. When the reduced viscosity of the resin (A) is less than 0.55, it becomes difficult to obtain a film having mechanical strength that can be practically used. On the other hand, when the reduced viscosity of the resin (A) exceeds 1.10, The thermocompression bonding property of the film to the metal plate tends to be impaired.

  The crystalline polyester resin (B) used in the present invention may be copolymerized PET, but is preferably selected from polybutylene terephthalate (PBT) resins and polytrimethylene terephthalate (PTT) resins. It is also possible to use a plurality of these resins.

  The polybutylene terephthalate (PBT) -based resin may be a homopolymer of polybutylene terephthalate or a copolymer obtained by copolymerizing other copolymerizable components. In the case of a copolymer, in order not to impair the high crystallinity of the polyester, the polybutylene terephthalate constituent component is preferably contained in an amount of 80 mol% or more, more preferably 90 mol% or more of the polyester component. Similarly, the polytrimethylene terephthalate (PTT) resin may be a homopolymer of polybutylene terephthalate or a copolymer obtained by copolymerizing other copolymerizable components. In the case of a copolymer, in order not to impair the high crystallinity of the polyester, the polytrimethylene terephthalate constituent component is preferably contained in an amount of 80 mol% or more, more preferably 90 mol% or more of the polyester component.

  For PBT resins and PTT resins, copolymerizable acid components include isophthalic acid, naphthalenedicarboxylic acid, diphenic acid, phthalic acid and other aromatic dicarboxylic acids, and 1,4-cyclohexanedicarboxylic acid and other alicyclic dicarboxylic acids. Acid, adipic acid, dimer acid, sebacic acid, dodecanedioic acid, eicoic acid and other aliphatic dicarboxylic acids, trimellitic acid, pyromellitic acid and other polyfunctional acids, polylactic acid, polyglycolic acid, poly (2-oxybutyric acid) ), And their derivatives. Examples of copolymerizable alcohol components include ethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, 1,4-cyclohexanedimethanol, And their derivatives.

  The reduced viscosity of the resin (B) is preferably 0.80 to 2.20, more preferably 0.85 to 1.30. When the reduced viscosity of the resin (B) is less than 0.80, it is difficult to obtain a film having mechanical strength that can be practically used. On the other hand, when the reduced viscosity of the resin (B) exceeds 2.20, the film The thermocompression bonding property to the metal plate is likely to be impaired.

  Further, if the difference between the reduced viscosity of the PET resin (A) and the reduced viscosity of the PBT resin and / or the PTT resin (B) is reduced, cleavage (peeling) of the blend film is difficult to occur. As a standard for that, the difference between the two reduced viscosities is preferably from 0.0 to 0.45, more preferably from 0.0 to 0.3. If it exceeds 0.45, the film may be easily cleaved.

  In the polyester film of the present invention, the blending ratio of the polyethylene terephthalate resin (A) and the crystalline polyester resin (B) is 10 to 10 based on the total amount of the resin (A) and the resin (B). 90 wt% and resin (B) 90-10 wt%, preferably resin (A) 10-70 wt% and resin (B) 90-30 wt%, more preferably resin (A) 35-65 % By weight and resin (B) 65-35% by weight. When the resin (A) is more than 90% by weight (that is, the resin (B) is less than 10% by weight), the moldability of the film is deteriorated, and in particular, the laminated metal plate in which the film is laminated on the metal plate. A can-making defect occurs during can-making, and the film is easily damaged. On the other hand, when the resin (A) is less than 10% by weight (that is, the resin (B) is more than 90% by weight), when the film is cooled at a temperature close to or higher than its melting point, The film tends to be whitened.

In the polyester film of the present invention, the value of ½ of the streak length in the Fourier image, which is an index representing the dispersion state of the resin inside the film by a transmission electron microscope in the film cross-sectional direction, is 30 nm ⁻¹ or more.

  The streak length is an index representing the dispersion state of the polyester resins (A) and (B) in the film, and is obtained as follows. By dyeing the cross section of the cut polyester film with a dye and photographing with a transmission electron microscope, one of polyester (A) and (B) becomes the sea and the other becomes an island from the difference in dyeing degree. Sea island structure can be confirmed. However, this sea-island structure is very difficult to see because the physical properties and molecular structure of polyesters (A) and (B) are close to each other, and the boundary between polyesters (A) and (B) is not clear. Therefore, an image taken with a transmission electron microscope is taken into a computer as a difference in density due to a difference in staining degree and subjected to Fourier transform to obtain a Fourier image, and the length of streaks expressed in the Fourier image is obtained. In the present invention, it is defined by a value that is ½ of the streak length.

The presence or absence of this streak depends on the presence of the phase structure, the degree of dispersion (structure size), the strength of the electron micrograph between the two phases, and the like. As an outline, when the degree of dispersion is coarser than a certain level, the streak length is inversely proportional to the size of the phase structure. The streak length takes a smaller value as the degree of dispersion becomes coarser (the phase structure present becomes larger), but the streak length gradually increases as the degree of dispersion becomes smaller (the phase structure present becomes smaller). However, if the degree of dispersion becomes finer until it becomes closer to molecular dispersion, the two-phase structure that causes streak scattering on the electron microscope photograph cannot be distinguished, and ultimately it becomes impossible to distinguish. Since the scattering theoretical treatment is equivalent to the case of a scattering pattern consisting of one phase (when the structure is very large), the streak length takes a smaller value as the degree of dispersion gets closer to the molecular dispersion and becomes finer. In summary, streaks can be observed when the degree of dispersion of the polyesters (A) and (B) in the film system is appropriate. The magnitude of the streak length can be considered as an index reflecting the appropriateness of dispersion within the film system. The streak length is expressed in units of nm- ¹ . Although this is not necessarily an appropriate expression, this notation is used herein according to convention. Further, the streak length value can be obtained by taking data with an image as the number of pixels and performing a Fourier transform, so that it is possible to maintain arbitraryness.

The value of 1/2 of the streak length of the polyester film of the present invention is 30 nm ⁻¹ or more, preferably 50 nm ⁻¹ or more, more preferably 70 nm ⁻¹ or more. If the value of ½ of the streak length is 30 nm ⁻¹ or more, a moderately coarse dispersion of the polyesters (A) and (B) is achieved in the film system, and the individual polyesters (A) and (B ) Is increased, whitening is greatly suppressed even when heat-treated near or above the melting point of the film, and the piercing strength of the film is good. The good puncture strength is considered to be due to the effect of PBT and / or PTT in (B) by maintaining the independence of polyesters (A) and (B). Further, the degree of dispersion of the polyesters (A) and (B) is not too coarse, and the problem of cleavage of the film does not occur. When the value of 1/2 of the streak length is less than 30 nm ⁻¹ , the fine dispersion and / or copolymerization of the polyesters (A) and (B) has progressed too much. It becomes defective.

The upper limit of the value of 1/2 of the streak length is not particularly limited, but in the blend from the polyesters (A) and (B) whose physical characteristics and molecular structure are approximate, it is 1/2 of the streak length. It is considered very difficult to obtain a film with a value exceeding 2000 nm- ¹ . Therefore, 1/2 of the streak length of the polyester film is a 30 nm ^-1 or 2000 nm ^-1 or less, for example, at 30 nm ^-1 or 500 nm ^-1 or less, preferably 50 nm ^-1 or 500 nm ^-1 or less More preferably, it is 70 nm ⁻¹ or more and 500 nm ⁻¹ or less.

In addition, a layer structure may be confirmed inside a film. That is, after the resins A and B are melted, they are led to a static mixer, preferably in a molten state. A static mixer, for example, manufactured by Noritake Co., is an element in which rectangular plates are twisted 180 degrees in a resin flow path, and the number of layers doubles each time one element is passed. Become. Therefore, theoretically, when passing through n elements, it becomes a 2n layer, but in reality, it may change depending on the relationship between the flow path diameter, the discharge amount, the viscosity and surface tension of each resin, and the like. In the present invention, at least the central part in the thickness direction of the film, the number of layers in the 2 μm-thick region is 5 or more, preferably 30 or more, more preferably 100 or more, particularly 400 or more, and further 2000 or more. It is preferable that
Moreover, although an upper limit does not exist theoretically, it is actually 100,000 layers or less. Even if polyesters A and B are used as separate raw materials, if they are copolymerized or highly uniformly mixed in an extruder or a subsequent melting tube, they appear as one layer, which is inappropriate in the present invention. It is. When it appears as one layer, the value of ½ of the streak length is 30 nm ⁻¹ .

  Further, the reduced viscosity (ηsp / c) of the polyester film of the present invention is preferably 0.80 or more, more preferably 0.85 or more, further preferably 0.90 or more, and most preferably 0.95 or more. By setting the reduced viscosity of the film to 0.80 or more, the scratch resistance of the film is improved. If the reduced viscosity of the film is less than 0.80, the hardness of the film after laminating to the metal plate will be insufficient, it will be easily damaged when processing the laminated metal plate, and the aluminum or steel plate may be deformed when making cans. Cause destruction. The upper limit of the reduced viscosity of the polyester film is not particularly limited, but is, for example, 1.50 or less, preferably 1.30 or less.

Next, production of the polyester film of the present invention will be described.
In order to produce the polyester film of the present invention, it is preferable to take the following production method in order to achieve an appropriately coarse dispersion of the polyesters (A) and (B) in the film system.

  In the present invention, PET (A) and PBT and / or PTT (B) are individually melted, and molten PET (A) and PBT and / or PTT (B) are mixed at a predetermined blending ratio. Then, the obtained mixed resin is molded. Specifically, (A) and (B) are put into separate extruders and individually melted at respective appropriate temperatures (melting point + 30 ° C. or lower), and (A) and (B) in a molten state are predetermined. This is a method of mixing at a blending ratio, guiding the obtained mixed resin to a die, and melt extrusion.

  In the production of a conventional general polyester film, materials constituting a single film layer are put into a single extruder, melted and extruded to form a film. In the patent document exemplified in the background art, two or more different polyester materials are used. However, a single extruder is used as the extruder, and the two or more different polyester materials are collectively used. Melt mixed. This is presumed to be the result of considering the stability and economics during film formation. Therefore, it seems difficult to produce higher quality films.

  In the conventional method, for example, in the case of producing a blend film of PET (melting point 255 ° C.) and PBT (melting point 220 ° C.) using only a single extruder having a single screw or a twin screw, the melting points of both are used. Since the difference between the two is 30 ° C. or higher, when the two are blended from the resin chip stage, the temperature of the extruder must be set to the melting point of PET or higher, and usually 280 ° C. or higher in consideration of production stability. Set to PBT begins to decompose at 260 ° C. or higher, and further, the decomposition rate becomes higher from around 280 ° C. Therefore, the molecular weight of PBT decreases due to the heat of the extruder set at 280 ° C. or higher. As a result, the compatibility between PBT and PET is improved and the process proceeds in a more uniform direction, so that copolymerization (transesterification reaction) is facilitated. Alternatively, even if PBT and PET are not copolymerized and have crystallinity in an almost independent state, they are easily affected by each other in a very finely dispersed state, and crystallinity at a higher level Independence is not maintained. For this reason, it is presumed that crystallization is difficult to proceed when the temperature is lowered from the molten state, and as a result, whitening cannot be prevented at a higher level.

  When a transesterification occurs between the PET resin (A) and the PBT and / or PTT resin (B), a copolymer of the resin (A) and the resin (B) is generated, and the PET resin ( The ethylene terephthalate structure which is the main component structure of A) is randomized and the characteristic rigidity is impaired, while the butylene terephthalate structure or trimethylene terephthalate which is the main component structure of PBT and / or PTT resin (B). The structure is randomized and the high crystallinity that is characteristic of the structure is impaired. As a result, the crystallization rate is slow, and coarse spherulites that cause whitening are likely to occur.

  In the conventional method, particularly when a slow compression type extruder is used, when an extruder having a large compression ratio (for example, a compression ratio larger than 2.0) is used, and when L / D is large (for example, larger than 35) L / D) When an extruder is used, the apparent set temperature can be lowered, but the amount of self-heating in the compression section (compression zone) of the extruder increases, and the resin temperature becomes higher than the set temperature. Therefore, it seems that PTT, PBT, etc. with a low melting point are easily decomposed.

  In order to solve such problems of the conventional method, in this method, PET (A) and PBT and / or PTT (B) are individually melted, and the melted (A) and (B) are mixed. To do. By adopting this production method, copolymerization (transesterification) of (A) and (B) and fine dispersion can be suppressed, and a film with improved quality while maintaining film formation stability. It turns out that it is obtained.

  In the individual melting step of PET (A) and PBT and / or PTT (B), it is preferable to use two or more extruders in parallel. As such an extruder, various known ones can be used. In addition, instead of using two or more extruders in parallel, it is possible to perform individual melting using a single extruder.

  However, when individual melting is performed using a single extruder, the screw compression part (compression zone) in the single screw extruder is of a double flight type, and is a rapid compression type with a small compression ratio. (Compression ratio of 2.0 or less) must be used. Here, the “double flight type” means a structure in which the compression part (compression zone) of the screw has a double helix structure and a subflight having an outer diameter slightly smaller than the outer diameter of the main flight is provided between the main flights. The solid phase part and the molten part of the polymer are separated by the subflight. If the compression part of a screw is a double flight type, PBT (and / or PTT) (B) which started melting previously and PET (A) which is maintaining solid at that time are the first half of the compression part. Since they are separated by flight, individual melting of (A) and (B) is performed. And it is thought that the contact time in the molten state of (A) and (B) becomes short, and moderately coarse dispersion is achieved. Examples of an extruder having such a compression section (compression zone) having a double flight type screw include UB series (trade name) manufactured by Mitsubishi Heavy Industries, Ltd., all of which are polyester films that meet the present invention. However, it is not always achieved, and the above-mentioned conditions must be satisfied. In the method of using a single extruder, since the allowable range of conditions is narrow, a method of using two or more extruders in parallel is preferable.

  In the mixing step of the melted state (A) and (B), as a machine base for mixing the melted polyester, ordinary single-screw extruder, twin-screw extruder, dynamic mixer, static mixer (manufactured by Noritake Company, etc.) Etc. are used. At this time, when using a normal single-screw extruder or twin-screw extruder so that the melted state (A) and (B) are not mixed so uniformly and not so much compatibilized, those having a small compression ratio ( For example, 1.1 to 3.8, preferably 1.3 to 3.0), L / D of the entire extruder screw is small (for example, 20 to 35, preferably 20 to 30), and L / D of the compression section. Is small (for example, 5 to 25, preferably 10 to 20).

In this mixing step, it is preferable to use a static mixer in order to obtain a more optimal degree of dispersion of (A) and (B). The number of elements of the static mixer is preferably 9 or more and 32 or less, and more preferably 12 or more and 28 or less.
By using such a static mixer having the number of elements, it is easy to obtain a moderately coarse dispersity, no whitening occurs, a good puncture strength, and a good film that does not cause cleavage. When the number of elements is less than 12, polyesters (A) and (B) tend to exhibit an extreme phase structure, and the film may be cleaved. On the other hand, when the number of elements exceeds 32, the mixing of the polyesters (A) and (B) proceeds too much and fine dispersion proceeds too much, so that whitening and puncture strength are liable to occur.

  Moreover, in this invention, in order to suppress side reactions, such as transesterification, in a film composition containing resin (A) and resin (B), it is also preferable to add a specific phosphorus compound. Conventionally, various means have been known as means for suppressing side reactions such as transesterification in a film composition containing a polyethylene terephthalate resin and other crystalline polyester resins. However, for application in the field of industrial film production, it is preferable to suppress a transesterification reaction by catalysis by adding a specific phosphorus compound to the film composition. It is also preferable to control the size of the resin chip when mixing.

  As such a phosphorus compound, it is preferable that the melting point is 200 ° C. or more and the molecular weight is 200 or more in consideration of the stability in the extruder. For example, dimethyl methylphosphonate, diphenyl methylphosphonate, dimethyl phenylphosphonate, diethyl phenylphosphonate, diphenyl phenylphosphonate, benzyl phosphonate, diethyl benzylphosphonate, diphenylphosphinic acid, methyl diphenylphosphinate, phenyl diphenylphosphinate, phenyl Examples include phosphinic acid, methyl phenylphosphinate, phenyl phenylphosphinate, diphenylphosphine oxide, methyldiphenylphosphine oxide, and triphenylphosphine oxide. One or more of these organophosphorus compounds can be used. The phosphorus compound is preferably pre-kneaded with the resin in advance, and more preferably pre-kneaded with a polyethylene terephthalate resin chip.

  Although the addition amount of a phosphorus compound changes with kinds of phosphorus compound, about 0.01 to 0.3 weight% is preferable with respect to the total amount of resin (A) and resin (B) from a viewpoint of transesterification suppression. . In addition, when using a polyester film for food uses, such as a drink can, it is necessary to use it by the compound and quantity which satisfy | fill standards, such as FDA (US Food and Drug Administration) and polyolefin hygiene council.

  In the present invention, it is more preferable to add a crystallization nucleating agent to the film composition containing the resin (A) and the resin (B). As the nucleating agent, either organic fine particles or inorganic fine particles can be used, and examples thereof include silica, kaolin, calcium carbonate, titanium dioxide, polyethylene glycol, and talc. Talc is preferable. One or more of these crystal nucleating agents can be used. In general, the addition amount of the crystal nucleating agent is suitably about 0.0001 to 0.1% by weight based on the total amount of the resin (A) and the resin (B).

  The molten mixed resin obtained is extruded. In the resin extrusion conditions, it is necessary that the resin temperature is 265 ° C. or lower and that a region of 275 ° C. or higher, preferably 270 ° C. or higher is not formed in the temperature setting from the cylinder part to the T-die. When the temperature is increased, the compatibility of the polyester resin (A) and the resin (B) is increased and a finely dispersed state is obtained. As a result, the film is likely to be whitened, causing a decrease in viscosity, and the film hardness is likely to decrease.

  The polyester film of the present invention can be produced by an inflation method, a simultaneous biaxial stretching method, a sequential biaxial stretching method, or the like with a normal film production facility if the above conditions are satisfied. Further, the melt-extruded sheet may be used without being stretched, or may be stretched only by one axis.

  In the present invention, the heat treatment is preferably performed at 140 to 270 ° C., preferably 200 to 270 ° C. after the stretching is completed. At this time, a heat treatment while relaxing 2% or more in the vertical direction and / or the horizontal direction yields a polyester film having good adhesion to the metal plate and operability during canning.

  The thickness of the polyester film of the present invention is preferably 3 to 1000 μm, more preferably 5 to 70 μm. Moreover, normally, in melt mixing, a lubricant is added to the polyester composition to form a film. Examples of lubricants include inorganic lubricants such as silica, kaolin, clay, calcium carbonate, calcium terephthalate, aluminum oxide, titanium oxide, and calcium phosphate, and organic lubricants such as silicone particles, but inorganic lubricants are preferred. The amount of lubricant added is generally about 0.01 to 5% by weight, preferably 0.02 to 0.2% by weight, based on the total amount of the resin (A) and the resin (B). In addition, in addition to the lubricant, various additives such as a stabilizer, a colorant, an antioxidant, an antifoaming agent, and an antistatic agent can be included in the melt mixing.

By the above manufacturing method, the polyester film of the present invention in which the value of ½ of the streak length is 30 nm ⁻¹ or more can be obtained.

  The obtained polyester film is laminated on a metal plate to obtain a laminated metal plate. In this case, the roller or the metal plate is heated to 150 to 270 ° C., the metal plate and the polyester film are bonded together by the roller, and then rapidly cooled to melt and fuse at least the surface layer portion of the film in contact with the metal plate. That's fine. The laminating speed is, for example, 1 to 200 m / min, preferably 2 to 150 m / min. Further, after the polyester film is placed on the metal plate, the film may be laminated on the metal plate.

The polyester film of the present invention can be used not only for metal plate laminating but also for various uses such as food packaging, general industrial use, optical use, electric material use and molding processing. More specifically, for general packaging, antistatic, gas barrier, heat sealing, anti-fogging, metal deposition, easy tearing, easy opening, bag making packaging, retort packaging, boil packaging, drug packaging, easy Can be used for various applications such as adhesiveness, magnetic recording, capacitor, ink ribbon, transfer, adhesive label, stamping foil, gold and silver thread, tracing material, mold release, shrink film, etc. . Among these, the polyester film of the present invention is particularly suitable for molding processing (molding material when a single film is molded into a target article) and for metal plate laminating (a constituent material of a film laminated metal plate). is there.
At this time, the piercing strength at 0 ° C. is 0.7 N / μm or more, preferably 0.9 N / μm or more and 10 N / μm or less. At 20 ° C., 1.2 N / μm or more, preferably 1.3 N / μm or more and 10 N / μm or less is desired.
The piercing strength here means a value obtained by the following measurement.
A sample is cut into a strip of 20 mm width and 160 mm length and fixed to the upper chuck of a tensile tester (manufactured by Shimadzu Corp., Autograph AG-5000A) so that a ring with a circumference of about 100 mm is formed downward. A steel needle having a tip curvature radius of 0.35 mm is fixed to the upper part so that the needle tip faces downward and the needle tip hits the center of the test piece. The test piece was pulled upward at a pulling speed of 50 mm / min to puncture the test piece, and the maximum load until the needle penetrated was measured. Ten test pieces were prepared, and the piercing surface was changed, and five test pieces were measured. The average value of the obtained maximum loads was determined, and the value was converted per 1 μm thickness to obtain the puncture strength (N / μm) of the film.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In the examples, each characteristic value of polyester was measured as follows.

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

2. The cross-sectional phase structure of the film having a half streak length as an index of dispersion was observed using a transmission electron microscope. First, the sample film was embedded in an epoxy resin. As the epoxy resin, a mixture of Luavec 812, Luavec NMA (manufactured by Nacalai Tesque) and DMP30 (TAAB) in a weight ratio of 100: 89: 3 was used. After embedding the sample film in an epoxy resin, the sample film was left in an oven adjusted to a temperature of 60 ° C. for 16 hours to cure the epoxy resin and obtain an embedded block.

  The obtained embedding block was attached to an ultra cut N manufactured by Nissan Sangyo, and an ultrathin section was prepared. First, trimming was performed using a glass knife until a cross section of a portion desired to be observed for the film appeared on the resin surface. Next, an ultrathin section was cut out using a diamond knife (Sumitomo Electric, Sumiknife SK2045). The cut ultrathin sections were collected on a mesh, and then stained by standing in a ruthenium tetroxide vapor for 30 minutes at room temperature, and thinly deposited with carbon.

  The electron microscope observation was carried out using JEM-2010 manufactured by JEOL under the condition of an acceleration voltage of 200 kV. An image obtained by electron microscopic photography of the film cross section was recorded on an imaging plate (FDL UR-V, manufactured by Fuji Photo Film). The signal recorded on the imaging plate was read out using digital luminography (Pixsys TEM manufactured by JEOL Ltd.) and recorded as digital image information on a Windows personal computer.

After transferring this image file to a Macintosh personal computer, a Fourier image was calculated using a software NIH image. The calculation was performed using an FFT (two-dimensional fast Fourier transform) routine assembled with a macro built in the NIH. In the Fourier image, it was recognized that streaks appeared in a direction perpendicular to the direction in which the phase seen in the real image was running. A value (nm ⁻¹ ) which is half the streak length was determined. This streak appears due to the presence / absence of a phase, contrast, and the strength of correlation between phases seen in a real image.

3. 1. Number of layers inside the film In the region of 2 μm × 2 μm at the center with respect to the cross-sectional direction of the film, The number of layers confirmed from the difference in dyeing degree of polyesters A and B when observed with an electron microscope was counted.

4). Film Whitening The film was laminated to an aluminum plate under the following conditions and left in a gear oven at 280 ° C. for 1 minute. Then, it cooled by applying 25 degreeC air to the film surface of a laminated board at a wind speed of 20 m / min. The cooled film was visually determined as follows.

(Lamination condition)
Lamination temperature: 220 ° C
Linear pressure: 10 N / cm

◎: No whitening and high gloss on the film surface ○: Slight whitening is observed, but the glossiness on the film surface is high Δ: Whitening is observed, and the glossiness on the film surface is low ×: Whitening is remarkable In the present invention, where the glossiness of the film surface is low, the evaluation ○ is necessary from a practical viewpoint, and preferably the evaluation ◎ is required.

5). Piercing strength A sample was cut into a strip with a width of 20 mm and a length of 160 mm and fixed on the upper chuck of a tensile tester (Shimadzu Corporation Autograph AG-5000A) so as to form a ring with a circumference of about 100 mm downward. A steel needle having a tip curvature radius of 0.35 mm is fixed to the upper side of the side chuck so that the needle tip faces downward and the needle tip hits the center of the test piece. The test piece was pulled upward at a pulling speed of 50 mm / min to puncture the test piece, and the maximum load until the needle penetrated was measured. Ten test pieces were prepared, and the piercing surface was changed, and five test pieces were measured. The average value of the obtained maximum loads was determined, and the value was converted per 1 μm thickness to obtain the puncture strength (N / μm) of the film.
Moreover, measurement temperature was implemented at 0 degreeC and 20 degreeC.
In the present invention, at 0 ° C., 0.7 N / μm or more, preferably 0.9 N / μm or more and 10 N / μm or less is desired. At 20 ° C., 1.2 N / μm or more, preferably 1.3 N / μm or more and 10 N / μm or less is desired.

6). Film cleavage index A so-called cross cut test was conducted. The sample film surface was cut into a grid pattern with an interval of 1 mm, and 100 divided areas were produced. When cellophane tape (manufactured by Nichiban Co., Ltd.) is applied to the surface of this sample film, a load of 1 kg / cm ² is applied to the entire surface for 10 seconds, and then the applied cellophane tape is peeled off in a direction perpendicular to the film to form a grid pattern. Of 100 divided areas, the number of film surfaces attached to the cellophane tape side was determined. This number was taken as the film cleavage index. In the present invention, the film cleavage index needs to be 5 or less, preferably 3 or less, more preferably 1 or less.

[Examples 1 to 4]
Polyethylene terephthalate resin (reduced viscosity 0.85, manufactured by Toyobo Co., Ltd.) as polyester resin (A) was charged into 60 mmφ extruder (I) (L / D = 29, compression ratio 4.2) and melted at 275 ° C. On the other hand, polybutylene terephthalate resin (NV5010AS, manufactured by Mitsubishi Engineering Plastics, reduced viscosity 1.10) as polyester resin (B) is put into another 60 mmφ extruder (II) (L / D = 29, compression ratio 4.2). And melted at 240 ° C. Thereafter, both extruders (I) and Extruder (II) were mixed in a static mixer (N20, manufactured by Noritake Co., N20) in a molten state so that polyethylene terephthalate / polybutylene terephthalate = 5/5 (weight ratio). It was led in, mixed, melted, extruded from a T-die, and an unstretched sheet having a thickness of 200 μm was obtained. The number of elements of the static mixer was four levels of 6 (Example 1), 12 (Example 2), 18 (Example 3), and 24 (Example 4). At this time, the temperature of the cylinder portion and the filter portion (200 mesh) of the static mixer is 260 ° C., the temperature from the filter portion to the T-die is 255 ° C., and the temperature of the resin discharged from the T-die is 257 ° C. I made it.

This unstretched sheet is guided to a roll stretching machine, stretched 3.3 times at 70 ° C in the longitudinal direction, and further stretched 3.5 times at 95 ° C in the transverse direction with a tenter, and then in the transverse direction in the tenter. The film was heat-set at 150 ° C. while relaxing 3% to obtain a film having a thickness of 17 μm.
[Example 5]
A polyester film was obtained in the same manner except that the number of elements was 9 in Comparative Example 1.

[Comparative Example 1, Examples 6-7]
Polyethylene terephthalate resin (reduced viscosity 0.70, manufactured by Toyobo Co., Ltd.) as polyester resin (A) was put into 60 mmφ extruder (I) (L / D = 29, compression ratio 4.2) and melted at 275 ° C. On the other hand, a polybutylene terephthalate resin (manufactured by Toray, 1200S, reduced viscosity 1.30) as a polyester resin (B) is charged into another 60 mmφ extruder (II) (L / D = 29, compression ratio 4.2). Melted at 240 ° C. Thereafter, both extruders (I) and Extruder (II) were mixed in a static mixer (N20, manufactured by Noritake Co., N20) in a molten state so that polyethylene terephthalate / polybutylene terephthalate = 5/5 (weight ratio). It was led in, mixed, melted, extruded from a T-die, and an unstretched sheet having a thickness of 200 μm was obtained. The number of elements of the static mixer was three levels of 6 (Comparative Example 1), 12 (Example 6), and 18 (Example 7). At this time, the temperature of the cylinder portion and the filter portion (200 mesh) of the static mixer is 260 ° C., the temperature from the filter portion to the T-die is 255 ° C., and the temperature of the resin discharged from the T-die is 257 ° C. I made it.

  This unstretched sheet is guided to a roll stretching machine, stretched 3.3 times at 70 ° C in the longitudinal direction, and further stretched 3.5 times at 95 ° C in the transverse direction with a tenter, and then in the transverse direction in the tenter. The film was heat-set at 150 ° C. while relaxing 3% to obtain a film having a thickness of 17 μm.

[Examples 8 to 9]
Except for Example 3 except that the weight mixing ratio of Resin (A) to Resin (B) was (A) / (B) = 25/75 (Example 7) and 75/25 (Example 8). A polyester film was obtained in the same manner.

[Comparative Example 2]
Polyethylene terephthalate resin (reduced viscosity 0.85, manufactured by Toyobo) as the polyester resin (A), and polybutylene terephthalate resin (Mitsubishi Engineering Plastics, NV5010AS, reduced viscosity 1.10) as the polyester resin (B), Chip blending was performed at a mixing ratio (A) / (B) = 5/5, and the mixture was introduced into a 60 mmφ extruder (II) (L / D = 29, compression ratio 4.2) and melted at 270 ° C. Thereafter, a film was formed in the same manner as in Example 1 to obtain a polyester film.

[Example 10]
A polyester film was obtained in exactly the same manner as in Example 3 except that polytrimethylene terephthalate (reduced viscosity 0.92) was used instead of polybutylene terephthalate.

[Example 11]
In Example 2, a polyester film was obtained in the same manner except that the reduced viscosity of PET was 0.75.

[Example 12]
A polyester film was obtained in the same manner as in Example 2, except that PET (reduced viscosity 0.80) copolymerized with polyethylene glycol having a molecular weight of 2000 was used instead of PBT.

  The characteristic results of the obtained polyester films are shown in Table 1.

From Table 1, all the polyester films (Examples 1 to 11) of the present invention in which the value of ½ of the streak length is 30 nm ⁻¹ or more have no whitening problem, and are excellent in piercing strength and cleavage strength. It was. In particular, the polyester films of Examples 2 to 4 and 7 to 10 in which the half value of the streak length is 70 nm ⁻¹ or more showed very good characteristics.

  In Comparative Example 2, although the same polyethylene terephthalate and polybutylene terephthalate as in Examples 1 to 4 were used, significant whitening was observed because the chips were blended and then melted together.

  Moreover, the reduced viscosity difference (0.60) of PET and PBT used in Comparative Example 1 and Examples 6 to 7 is smaller than the reduced viscosity difference (0.25) of PET and PBT used in Examples 1 to 3. It was a big one. Therefore, when a static mixer with the same number of elements was used, PET and PBT had a larger phase structure and dispersion was insufficient, and the streak length was reduced. In order to obtain a better polyester film, it has become clear that PET and PBT (and / or PTT) should be selected so that the reduced viscosity difference between PET and PBT (and / or PTT) is reduced. .

Claims (5)

Polyethylene terephthalate resin (A) and crystalline polyester resin (B) different from the resin (A), resin (A) 10 to 90 weight based on the total amount of resin (A) and resin (B) % And resin (B) is a film composed of a polyester-based resin composition blended at a ratio of 90 to 10% by weight, which is an index representing the dispersion state of the resin inside the film by a transmission electron microscope in the film cross-sectional direction. A polyester film characterized in that a half value of streak length in an image is 50 nm-1 or more, and the number of layers inside the film observed by a transmission electron microscope in the film cross-sectional direction is 100 or more .   The polyester film according to claim 1, wherein the crystalline polyester resin (B) is selected from a polybutylene terephthalate resin and a polytrimethylene terephthalate resin. The reduced viscosity of the polyester film is 0.80 or more, a polyester film according to any one of claims 1-2. The polyester film according to any one of claims 1 to 3 , which is for metal plate lamination. The polyester film according to any one of claims 1 to 3 , which is used for molding processing.