JP2021098848A - Polyester film, printing base paper, method for producing polyester film, and method for producing heat-sensitive stencil printing paper - Google Patents

Abstract

To provide a polyester film having productivity, and flatness and workability.SOLUTION: A polyester film has a softening initiation temperature of 80-130°C measured by nano thermoanalysis (nano TA).SELECTED DRAWING: None

Description

The present invention relates to a polyester film having productivity and flatness / processability (transportability / perforation), a base paper for printing, a method for producing a polyester film, and a method for manufacturing a heat-sensitive stencil printing base paper.

Polyester is used in various industrial fields because of its good processability. In addition, these polyester processed products play an important role in today's life such as industrial use, optical product use, and packaging use. In the field of electronic information equipment devices, the digitization of information is progressing, and the number of printed matter using paper as a medium tends to decrease, but plate making by thermal stencil is widespread and still in high demand. Conventionally, as a film for thermal stencil printing base paper, a film obtained by laminating a porous support such as porous tissue paper on a film such as polyester has been used. The thermoplastic resin film used for such applications is perforated by flash irradiation with a thermal head, halogen lamp, xenon lamp, flash lamp, etc., infrared irradiation, or pulse irradiation such as a laser beam, and is porous such as porous thin leaf paper. The support has ink retention and passability and is used as a plate. The plate-making method using a thermal head is a method in which a document is read by a sensor, and an image corresponding to the document is perforated in a dot shape in a film portion of a base paper by the thermal head to perform plate-making. In such a plate-making method using a thermal head, it is necessary to reduce the energy supplied to the head in order to suppress damage to the thermal head and extend its life. A film for heat-sensitive stencil printing base paper, which has good printability (resolution, print quality) at the time of printing, is desired because the ink held in a porous support such as tissue paper surely passes through the perforated holes.
For the purpose of improving printability, a film (for example, Patent Document 1 and Patent Document 2) in which the composition of a polyester film constituting a printing base paper is adjusted to lower the melting point of the film has been proposed. Further, a technique for improving the perforation property by using a film having a reduced glass transition temperature (for example, Patent Document 3) has been proposed.

Japanese Unexamined Patent Publication No. 9-99666 Japanese Unexamined Patent Publication No. 2013-202961 Japanese Unexamined Patent Publication No. 2011-020404

However, the methods described in Patent Documents 1 and 2 have a problem that the film-forming property at the time of producing a polyester film is remarkably lowered and the productivity is poor. Further, in the method as described in Patent Document 3, when the polyester film shrinks in the process of processing the polyester film into a base paper for printing and cannot maintain the flatness, or when the film is embrittled, the roll transportability is improved. It could be reduced. Further, there is a problem that the perforation property is lowered because the characteristics of the film change before and after the base paper is formed due to the heat during processing.
An object of the present invention is to solve the above-mentioned problems. That is, by providing a polyester film having productivity and flatness / processability (transportability / perforation), a base paper for printing using the polyester film, a method for manufacturing a polyester film, and a method for manufacturing a heat-sensitive stencil printing base paper. is there.

The polyester film of the present invention has the following features in order to solve the above problems. That is, it is a polyester film having a softening start temperature of 80 to 130 ° C. measured by nanothermal analysis (nano TA).
Further, the present invention is a base paper for printing containing the polyester film described above.
Further, the present invention is a method for producing a polyester film, in which two or more kinds of polyester resins are melt-kneaded with an actual measurement value of a resin temperature of 240 ° C. or higher and 280 ° C. or lower and a kneading time of 5 minutes or more and 60 minutes or less. After that, a step of molding into a film is included, and as diol constituents of the two or more kinds of polyester films, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,4 -Cyclohexylene dicarboxylic acid Containing at least two selected from methanol, at least two selected from terephthalic acid, isophthalic acid, adipic acid, 1,4-cyclohexanedicarboxylic acid, and 2,6-naphthalenedicarboxylic acid as dicarboxylic acid constituents. It is a method for producing a polyester film containing.
Further, the present invention is a method for producing a heat-sensitive stencil printing base paper, which includes a step of producing a polyester film by the manufacturing method described above and a step of adhering the polyester film to a porous support. This is a method for manufacturing base paper.

Since the polyester film of the present invention is excellent in productivity, flatness, and processability, it is used for magnetic recording, packaging film, electrical insulation, condenser, adhesive, and printing (heat-sensitive stencil printing base paper, photo, photo. It can be suitably used as a film for various industrial materials such as for plate making and for thermal transfer ribbons).

This is an example schematically showing a chart obtained when nanothermal analysis measurement is performed on a polyester film.

The polyester referred to in the present invention is a resin obtained by polycondensation of a diol component and a dicarboxylic acid component. In the present invention, the constituent component indicates the smallest unit that can be obtained by hydrolyzing polyester. Examples of the diol component include ethylene glycol, propanediol, butanediol, pentanediol, trimethylene glycol, tetramethylene glycol, cyclohexanedimethanol, and spiroglycol. The components of the dicarboxylic acid include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid and naphthalenedicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid, sebacic acid and cyclohexanedicarboxylic acid, or ester derivatives thereof. However, it is not limited to this. Specific examples of polyester include polymethylene terephthalate, polyethylene terephthalate, polypropylene terephthalate, polyethylene isophthalate, polytetramethylene terephthalate, poly-1,4-cyclohexylene methylene terephthalate, and polyethylene-2,6-naphthalate. Can be done. The polyester used in the present invention may be a homopolymer or a copolymer. Further, two or more kinds of the above polyesters may be blended and used.

Among the above polyesters, the polyester film of the present invention preferably contains polyethylene terephthalate (PET) as a main component from the viewpoint of productivity. Here, the main component refers to a component that accounts for 60% by weight or more of the components constituting the film. The PET used as the main component here represents a polyester containing the largest amount of terephthalic acid as a dicarboxylic acid component and the largest amount of ethylene glycol as a diol component.
When PET is used as the main component of the polyester film of the present invention, ethylene glycol is contained as a diol component, but a glycol component other than ethylene glycol may be contained. As glycol components other than ethylene glycol, for example, chlorohydroquinone, methylhydroquinone, 4,4'-dihydroxybiphenyl, 4,4'-dihydroxydiphenylsulphon, 4,4'-dihydroxydiphenylsulfide, 4,4'-dihydroxybenzophenone, p. Aromatic diols such as -xylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, etc. Examples thereof include aliphatic and alicyclic diols such as 1,4-butanediol, 1,6-hexanediol, and neopentyl glycol. Among them, it is preferable to contain at least one selected from 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, and 1,4-cyclohexylene dimethanol.

When PET is used as the main component of the polyester film of the present invention, terephthalic acid is contained as a dicarboxylic acid component, but it is preferable that a dicarboxylic acid component other than terephthalic acid is further contained. Examples of the components of the dicarboxylic acid other than terephthalic acid include aromatics such as naphthalenedicarboxylic acid, isophthalic acid, diphenylsulphondicarboxylic acid, benzophenonedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, and 3,3'-diphenyldicarboxylic acid. Dicarboxylic acids such as dicarboxylic acid, adipic acid, succinic acid, azelaic acid, sebacic acid, dodecandioic acid, hexahydroterephthalic acid, 1,3-adamantandicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2,6- Examples thereof include alicyclic dicarboxylic acids such as naphthalenedicarboxylic acids. It is preferable to mix and use or copolymerize with a polyester containing at least one selected from the above. Among the above, containing at least one selected from isophthalic acid, adipic acid, 1,4-cyclohexanedicarboxylic acid, and 2,6-naphthalenedicarboxylic acid is the crystallinity of the resin constituting the polyester film and the softness of the film described later. Is particularly preferable because it can be controlled efficiently.

In addition to the above-mentioned dicarboxylic acid constituents and diol constituents, aromatic hydroxycarboxylic acids such as p-hydroxybenzoic acid, m-hydroxybenzoic acid, 2,6-hydroxynaphthoic acid, and p-aminophenol, A small amount of p-aminobenzoic acid or the like may be further contained as long as it does not impair the object of the present invention.

When PET is used as the main component of the polyester film of the present invention and a polyester containing a dicarboxylic acid component other than terephthalic acid is used in combination as a dicarboxylic acid component, or when a dicarboxylic acid component other than terephthalic acid is copolymerized with PET, terephthal is used. The composition ratio of the dicarboxylic acid other than the acid is preferably 18 to 35 mol%, more preferably 19 to 35 mol%, and 20 to 30 mol% when the total dicarboxylic acid component of the polyester resin is 100 mol%. Is more preferable. By setting the composition ratio as described above, the crystallinity of the resin constituting the polyester film and the softness of the film described later can be efficiently controlled, and the range suitable for film formation and processing can be obtained. If the composition ratio of the dicarboxylic acid other than terephthalic acid is less than 18 mol%, sufficient processability may not be exhibited when the polyester film is put into practical use, or the processability of the film may be deteriorated. If the composition ratio of the dicarboxylic acid other than terephthalic acid is more than 35 mol%, the film-forming property may be deteriorated and the productivity may be lowered. The composition in the polyester film can be analyzed by ^{proton nuclear magnetic resonance spectroscopy (1} H-NMR) or carbon nuclear magnetic resonance spectroscopy ( ¹³ C-NMR) after extracting the film itself with a solvent.

The polyester film of the present invention may contain organic particles, inorganic particles, or both as long as the effects of the present invention are not impaired.

The polyester film of the present invention can also be used by blending an additive with the resin composition constituting the film as long as the effects of the present invention are not impaired. Specific examples of such additives include organic compounds, thermal decomposition inhibitors, thermal stabilizers, light stabilizers and antioxidants.

The polyester film of the present invention contains PET as a main component and is preferably used in combination with polybutylene terephthalate (PBT). The blending amount of polybutylene terephthalate (PBT) is preferably 1 to 40% by weight, more preferably 5 to 30% by weight, still more preferably 15 to 30% by weight. The method of blending PBT with the polyester film of the present invention is not particularly limited, and examples thereof include a method of blending PET and PBT. The term "blending" as used in the present invention means that the resins of the composition constituting the film are polymerized, and the polymerized resins are mixed by melt kneading. PBT-derived components can be present in the polyester film by adding and copolymerizing the components constituting PBT during the polymerization of PET used as the main component of the polyester film, but the crystallinity and flexibility peculiar to PBT Resin properties such as sex are less likely to be expressed. Therefore, by mixing by blending instead of copolymerization, different properties of each resin can be exhibited even when a film is formed. If the PBT is less than 1% by weight, the crystallinity of the polyester film may be insufficient and the film-forming property may be poor, or the effect of the resin blend may be weak and the workability may be lowered. Further, when the PBT is more than 40% by weight, the polyester film may have an increase in shrinkage and a decrease in flatness. The presence or absence of the PBT blend in the polyester film and its concentration can be confirmed by infrared spectroscopic analysis described later.

_{The polyester film of the present invention has a ratio (I 1268} / I ₁₂₅₀ ) of the spectral intensity at 1268 cm- ^{1 and the spectral intensity at 1250 cm-1} detected by infrared spectroscopic analysis in the method described later being 1.05 to 1.30. It is preferably 1.10 to 1.30. ^{The spectral intensity at 1268 cm-1} detected by infrared spectroscopic analysis is the CO expansion and contraction of the ester bond when terephthalic acid or isophthalic acid is used as the dicarboxylic acid component and 1,4-butanediol is used as the diol component. ^{The spectral intensity at 1250 cm -1} detected by infrared spectroscopic analysis is C- of the ester bond when terephthalic acid or isophthalic acid is used as the dicarboxylic acid component and ethylene glycol is used as the diol component. It represents O expansion and contraction. By having the above peak ratio, it can be confirmed that the polyester film is dry-blended with PET and PBT and melt-mixed under the optimum conditions described later, and the concentration of PET and PBT is within the above-mentioned preferable range. Indicates that When the ratio of spectral intensities (I ₁₂₆₈ / I ₁₂₅₀ ) is smaller than 1.05, the concentration of PBT is lower than the optimum range, and the film-forming property of the film may be deteriorated. When the ratio of spectral intensities (I ₁₂₆₈ / I ₁₂₅₀ ) is larger than 1.30, the concentration of PBT becomes higher than the optimum range, and flatness and perforation may be deteriorated.

The ratio of spectral intensities in infrared spectroscopic analysis of polyester film (I ₁₂₆₈ / I ₁₂₅₀ ) can be evaluated by the method described later. The ratio of the spectral intensities of infrared spectroscopic analysis can be achieved in the above range by blending the PBT concentration with the above-mentioned method and concentration.

The polyester film of the present invention preferably has one or more melting peaks (Tm) in the 1st run temperature rise process of differential scanning calorimetry (DSC) required in the measurement method described later. Further, the total calorific value ΔHm _{total 1st} of the melting peak is preferably 5 to 35 J / g, and more preferably 11 to 28 J / g. The melting peak in the 1st run temperature rise process of differential scanning calorimetry (DSC) is an index showing the progress of crystallization of the polyester film in the film forming process or the degree of formation of microcrystals (crystal nuclei) that are the starting points of crystals. Become. If the film does not have a melting peak or if the ΔHm _{total 1st} is less than 5 J / g, the flatness and workability may be impaired when the polyester film is put into practical use. Further, when ΔHm _{total 1st} exceeds the above range, the crystallinity of the film is too high, so that the film may become brittle and the film forming property may be lowered, or the processability may be lowered.

In the polyester film of the present invention, when a melting point peak (Tm) is detected in the region of 200 ° C. or higher in the 1st run temperature rise process of differential scanning calorimetry (DSC) required by the measurement method described later, ΔHm _{≧ of the peak. The calorific value of 1st melting at 200 ° C.} is preferably 1 to 30 J / g or less, more preferably 5 to 20 J / g or less, and particularly preferably 10 to 20 J / g. By having the above characteristics, the crystallinity of the polyester film can be controlled within a range suitable for processing. The calorific value of the melting peak detected in the region of 200 ° C. or higher correlates with the content ratio of the high melting point substance in the composition contained in the polyester film. We, the present inventors have assiduously studied the results, since the content of the refractory material affects the crystallinity of the film required for softening behavior and film formation at low temperatures of the film, the heat of .DELTA.Hm _{≧ 200 ° C. 1st} Found that an optimal range exists. If _{the amount of heat of ΔHm ≧ 200 ° C. 1st} is less than the above range, the crystallinity of the film cannot be maintained, and the flatness may be lowered or the workability may be lowered in practical use. Further, if ΔHm _{≧ 200 ° C. 1st} exceeds the above range, the crystallinity may be too high and the perforation property may decrease.

The polyester film of the present invention has a highest melting point (peak top temperature of melting point peak) observed in the 1st run temperature rise process of differential scanning calorimetry (DSC) required by the measurement method described later, which is 250 ° C. or less. preferable. Workability can be improved by setting the highest melting point to 250 ° C. or lower. It is more preferably 245 ° C. or lower, further preferably 240 ° C. or lower, and particularly preferably 180 ° C. or higher and 235 ° C. or lower.

The polyester film of the present invention preferably has a melting point (peak top temperature of melting point peak) of 2 or more observed in the 1st run temperature rise process of differential scanning calorimetry (DSC) obtained in the measurement method described later, and is preferably 180. It is more preferable to have at least one melting point in the range of ~ 210 ° C. and the range of 210 to 240 ° C., respectively. By having a melting point in such a range, it is possible to achieve both improvement in workability and flatness.

The polyester film of the present invention has a melting point detected in a region of 200 ° C. or lower in the 2nd Run temperature rise process, which is measured after melting / quenching with 1st Run of differential scanning calorimetry (DSC) obtained by a measurement method described later. The peak (Tm) heat of fusion ΔHm _{≤ 200 ° C. 2nd} is preferably 10 J / g or less, and more preferably 5 J / g or less. By having the above characteristics, the crystallinity of the polyester film can be controlled within a range suitable for processing. _{The calorific value of the melting peak ΔHm ≤ 200 ° C. 2nd} detected in the region of 200 ° C. or lower in the 2nd Run temperature rise process of differential scanning calorimetry (DSC) is the crystal of the low melting point component in the resin composition contained in the polyester film. It reflects the sex. For example, when PET and PBT are used as raw materials and PET and PBT are blended at the time of polymerization of PET, or when the resin is modified by performing melt extrusion at a high temperature during raw material kneading and film formation, the polyester film contains The crystallinity of the low melting point component of is increased, and ΔHm _{≤ 200 ° C. 2nd} may be increased. As a result of diligent studies, the present inventors have found that the crystallinity of this low melting point component has a large effect on the softening behavior of the film at low temperatures, and that the calorific value of the melting peak in this region has an optimum range. .. If ΔHm _{≤ 200 ° C. 2nd} exceeds the above range, the crystallinity may increase and the workability, particularly the drilling property due to heat, may decrease. The minimum value of ΔHm _{≤ 200 ° C. 2nd} is 0 J / g. In order _{to control ΔHm ≤ 200 ° C. 2nd} within the above range, when PET and PBT are used, a formulation in which the above-mentioned raw materials are blended is used, or the extrusion conditions (temperature at the time of melt extrusion, etc.) described later are controlled. Can be achieved with.

The polyester film of the present invention is preferably a biaxially oriented film stretched biaxially in an arbitrary direction and in a direction perpendicular to the biaxial direction. Biaxial orientation can improve the flatness and heat resistance of the film and improve workability. As a method for obtaining a biaxially oriented film, a sequential biaxial stretching method (a stretching method combining stretching in each direction such as a method of stretching in the longitudinal direction and then stretching in the width direction) and a simultaneous biaxial stretching method (longitudinal). A method of simultaneously stretching in the direction and the width direction), or a method in which they are combined can be mentioned. Of these, the sequential biaxial stretching method is particularly preferable from the viewpoint of productivity.

The polyester film of the present invention preferably has a thickness of 0.5 to 5.0 μm, more preferably 0.5 μm or more and 3.0 μm or less. Within the above range, both film forming property and processability (perforation property and transportability) can be achieved. If the thickness is less than the above range, the film-forming property and the handling in practical use may be deteriorated. If the thickness exceeds the above range, the workability may decrease. The thickness of the film can be adjusted according to the film forming conditions. The thickness can be evaluated by the method described later.

In the polyester film of the present invention, the melt flow rate (MFR) of the resin composition constituting the polyester film at 250 ° C. is preferably 5 to 40 g / 10 min, and more preferably 15 to 35 g / 10 min. MFR is an index showing the fluidity of the resin that constitutes the film, but as a result of diligent studies, the present inventors have conducted diligent studies and found that the ease of movement of the resin when the film softens, especially the flexibility of the amorphous chain contained in the resin. Found to have a correlation with MFR at 250 ° C. When the MFR at 250 ° C. is within the above range, the resin has flexibility when it reaches the softening start temperature, and the amorphous chains flow as the softening starts to pierce the film, resulting in a film having excellent piercing properties. can do. Further, when the MFR at 250 ° C. is within the above range, the amorphous chains have an intermolecular force to a certain extent even when softened, so that embrittlement is suppressed and the film forming property and processability are excellent. It can be a film. If the MFR is smaller than 5 g / 10 min, the flexibility of the resin when it reaches the softening point is low, and the amorphous chain may not flow even when heat is applied, and the perforation property may decrease. If the MFR is larger than 40 g / 10 min, the intermolecular force between the amorphous chains when softened is low and the amorphous chains are liable to become brittle, so that the film-forming property and processability may be deteriorated. MFR can be evaluated by the method described later. The method of setting the MFR in the above range is not particularly limited, but for example, the type of resin constituting the polyester film, the degree of polymerization and molecular weight of the polyester can be adjusted, and resins having different MFRs can be blended. Can be mentioned.

The polyester film of the present invention needs to have a softening start temperature of 80 to 130 ° C., which is observed by measurement using a nano-thermal analyzer (nano TA) described later. The softening start temperature is more preferably 80 to 120 ° C, and particularly preferably 80 to 110 ° C. The softening start temperature observed by measurement using a nano-thermal analyzer (nano TA), which will be described later, is due to the movement of the amorphous component contained in the resin that constitutes the film while the polyester film maintains the film state. It refers to the point where the flexibility of the film increases. In thermal analysis using nano TA, a cantilever with a nano-sized probe (thermal probe) having a heating function attached to the tip is used for analysis. Therefore, a ^{very narrow region of 100 nm 2} or less is locally measured at 10 ° C./sec. Since it can be rapidly heated with, it is possible to evaluate the softening behavior of the resin excluding the influence of crystallization due to the heat of the evaluation sample. In general, the softening behavior of a polyester film due to heating is due to the flow of amorphous molecules of the resin constituting the film. Conventionally, the glass transition point Tg obtained by differential scanning calorimetry (DSC) is used as an index for measuring that molecules become easy to move (resulting in softening) when the resin is heated to a certain temperature or higher. Was being done. The glass transition point Tg of the polyester resin constituting the polyester film detected by DSC is the temperature at which the amorphous molecules contained in the polyester resin constituting the polyester film start to move. However, as a result of diligent studies by the present inventors, the polyester film, particularly the biaxially oriented polyester film, has a small proportion of flowing amorphous molecules, so that the film is formed at the glass transition point Tg temperature detected by DSC. It was found that the correlation between the film characteristics (perforation property) and Tg in practical use was low because the softening was not sufficient. Further, conventionally, as an index for measuring that the resin is in a softened state when the resin is heated to a certain temperature or higher, needle insertion using thermal analysis (TMA) as described in Japanese Patent Application Laid-Open No. 2004-58485 is used. The softening temperature evaluation by mode is known. In such softening temperature evaluation, the needle diameter of the probe used for the measurement is large (in JIS K7196 referred to in the softening start temperature measurement described in JP-A-2004-58485, the needle diameter (indenter) of the probe is the diameter. 0.5 ± 0.05 mm or 1.0 ± 0.05 mm in diameter), and the temperature rise of the ambient temperature is evaluated at a rate of rise of about 20 ° C./min. As a result of diligent studies by the present inventors, crystallization of the resin occurs during the temperature rise at the rate of temperature rise in the softening temperature evaluation, so that the evaluation result is greatly affected by the crystallization of the resin. It was found that the correlation with the film characteristics (perforability) was low. Therefore, the movement of amorphous molecules contained in the film can be observed in an environment that is not affected by crystallization as in practical use, and the temperature indicating the flexibility due to the heat of the film is defined as the above-mentioned nano-thermal analyzer (nano TA). ) Was found to be suitable for the softening start temperature, and it was found that this temperature shows a strong correlation with the perforation property in practical use. By controlling this temperature within the above range, both film productivity and workability can be achieved, and practicality can be enhanced. When the softening start temperature is lower than 80 ° C., the film easily shrinks due to the heat generated during film formation, and the flatness and productivity of the film deteriorate. If the softening start temperature exceeds 130 ° C., the processability of the film deteriorates. The method for controlling the softening start temperature of the polyester film is not particularly limited, and examples thereof include using the above-mentioned composition as the resin constituting the polyester film and forming a film under the production conditions described later.

The polyester film of the present invention preferably has an average shrinkage rate of 0 to 20% when heated at 65 ° C. for 1 hour, which is measured in an arbitrary direction and in an orthogonal direction thereof by a measurement method described later, and is 0 to 15%. More preferably. The shrinkage rate when heated to 65 ° C. is related to the softening start temperature and crystallinity of the film. By setting the shrinkage rate of the film within the above range, the workability of the film can be improved. If the shrinkage rate when heated at 65 ° C. exceeds 20%, deformation at low temperature is likely to occur, and the flatness of the film and durability in practical use may decrease.

The polyester film of the present invention preferably has an average shrinkage rate of 20 to 60% when heated at 130 ° C. for 30 minutes, which is measured in an arbitrary direction and in an orthogonal direction thereof by a measuring method described later, and is preferably 30 to 50%. More preferably. The shrinkage when heated at 130 ° C. is related to the softening start temperature, melting point and crystallinity of the film. If the shrinkage rate when heated at 130 ° C. is less than 20%, the processability of the film, particularly the perforation property when used as a film for printing base paper, may decrease. If the shrinkage of the film when heated at 130 ° C. exceeds 60%, the film is significantly deformed by heat, and the flatness when the film is put into practical use may be lowered or the productivity at the time of film production may be lowered. The method for controlling the shrinkage rate of the film is not particularly limited, and for example, it can be achieved by using the above-mentioned composition as the resin constituting the film and manufacturing under the film-forming conditions described later.

The polyester film of the present invention may be composed of a single layer, or may have a laminated structure of two or more layers. When having two or more layers, if they are composed of different compositions, for example, composition (I) and composition (II), the laminated structure is two layers (I) / (II), (I) / (II) /. (I), (II) / (I) / (II), (II) / (I) / (II) / (I), (II) / (I) / (II) / (I) / (II) ), Etc., but not limited to this. Further, it is possible to form a layer structure in which a layer having a composition different from that of (I) to (II) is further added.

The method for producing a polyester film of the present invention will be described with reference to a formulation example in which PET and PBT are used as resins constituting the polyester film, but the present invention is not limited to this example.

As a method for obtaining the polyester used in the present invention, a polymerization method by a conventional method can be adopted. For example, a dicarboxylic acid component such as terephthalic acid or an ester-forming derivative thereof, a diol component such as ethylene glycol or an ester-forming derivative thereof, and a mixture of a plurality of types thereof are subjected to a transesterification reaction or a known method. It can be obtained by carrying out a melt polymerization reaction after an esterification reaction. Further, if necessary, the polyester obtained by the melt polymerization reaction may be subjected to a solid phase polymerization reaction at a temperature equal to or lower than the melting point temperature of the polyester.

The polyester obtained by the above method is dried at 110 to 180 ° C. for 3 hours under reduced pressure as needed, then fed to a heated full-flight single-screw extruder, passed through a filter, and then the molten polymer thereof. Is ejected into a sheet using the mouthpiece of the T-die. At this time, the cylinder filter temperature and screw arrangement are adjusted, and the measured value of the resin temperature of the resin extruded from the T-die is 5 to 30 from the highest melting point observed in the 1st run temperature rise process of differential scanning calorimetry (DSC). ℃ It is preferable to raise the temperature. The measured value of the resin temperature is preferably 240 to 280 ° C., more preferably 240 to 260 ° C., and even more preferably 240 to 250 ° C. Further, the kneading time in the molten state of the resin is preferably 5 minutes or more and 60 minutes or less. By adjusting the measured value of the resin temperature and the kneading time within the above range, changes in thermal characteristics before and after melt extrusion of the resin can be suppressed. This sheet-like material is brought into close contact with a cooling drum having a surface temperature of 20 to 70 ° C. and cooled and solidified to obtain an unstretched film in a substantially non-oriented state. Next, the unstretched film obtained above is biaxially stretched and then subjected to one-stage or multi-stage heat treatment to obtain a biaxially oriented film. As a method of biaxial stretching, a sequential biaxial stretching method (a stretching method combining stretching in each direction such as a method of stretching in the longitudinal direction and then stretching in the width direction) and a simultaneous biaxial stretching method (longitudinal direction). And a method of stretching in the width direction at the same time), or a method combining them can be used. Here, a sequential biaxial stretching method in which stretching is performed first in the longitudinal direction and then in the width direction will be illustrated. After preheating the unstretched film in the range of {(polyester Tg} -10 ° C)} to Tg, while heating with a heating roll in the range of Tg to (Tg + 30) ° C, preferably (Tg) to (Tg + 15) ° C. The film is stretched 3.0 to 6.0 times, more preferably 3.5 to 5.0 times in the longitudinal direction (MD direction) in one step or two or more steps (MD stretching). Then, it is cooled by a group of cooling rolls at 20 to 50 ° C.

As a stretching method in the width direction (TD direction) following MD stretching, for example, a method using a tenter is common. Both ends of the uniaxially stretched film are gripped with clips, guided to a tenter, and stretched in the width direction (TD stretching). The stretching temperature is preferably Tg to (Tg + 30) ° C., more preferably 3.0 to 6.0 times in the range of (Tg) to (Tg + 15) ° C., from the viewpoint of sufficiently aligning during stretching and improving flatness. Is preferably stretched 3.5 to 5.0 times.

Next, an operation of heat-fixing the stretched film under tension (heat-fixing treatment) is performed. The temperature of the heat-fixing treatment is either one-stage heat-fixing, in which heat treatment is performed at the same temperature at the beginning and end of the heat treatment zone, or multi-stage heat-fixing, in which heat treatment is performed at different temperatures in the first half and the second half of the heat treatment zone. The heat fixing temperature is Tg of polyester + 10 to the highest melting point of polyester −10 ° C., preferably Tg + 20 ° C. of polyester to the highest melting point −20 ° C. of polyester. By setting the temperature as described above, the heat shrinkage rate of the polyester film can be efficiently reduced and good flatness can be maintained. When the heat fixing temperature exceeds the highest melting point of polyester, -10 ° C, the polyester constituting the polyester film melts, fuses to the clips that fix both ends of the film during film formation, and the film is collected from the stretching device. May be difficult. Further, when the heat fixing temperature is lower than Tg + 10 ° C. of polyester, crystallization of the film does not proceed during the heat fixing treatment, and the flatness of the film may deteriorate. After the heat-fixing treatment, the film is cooled and wound to obtain a biaxially oriented film while subjecting the film to room temperature, preferably 0 to 15% in the longitudinal and width directions, if necessary.

Since the polyester film of the present invention is excellent in productivity, flatness, and processability, it is used for magnetic recording, packaging film, electrical insulation, condenser, adhesive, and printing (heat-sensitive stencil printing base paper, photo, photo. It can be suitably used as a film for various industrial materials such as for plate making and for thermal transfer ribbons).
Further, as a preferable embodiment using the polyester film of the present invention having excellent productivity, flatness and processability, a printing base paper such as a thermal stencil printing base paper containing the polyester film of the present invention can be mentioned.

The thermal stencil printing base paper preferably contains the polyester film described above and further contains a porous support. The thermal stencil printing base paper is preferably a laminate in which a polyester film is bonded to a porous support.
The porous support is preferably a porous support containing fibers, and specific examples thereof include thin paper such as Japanese paper and woven fabrics such as screen gauze. The fibers contained in the porous support are not particularly limited and can be selected from, for example, synthetic fibers, natural fibers and the like, and one or more of these fibers may be combined. As the porous support, for example, Japanese paper made by papermaking short fibers containing synthetic fibers (for example, mainly composed of synthetic fibers) is preferably used.

The average fiber diameter and fiber length of the fibers contained in the porous support are not particularly limited. The average fiber diameter of the synthetic fiber is preferably 0.1 to 20 μm, more preferably 1 to 15 μm. The fineness of the synthetic fiber is preferably 0.0001 to 4 dtex, more preferably 0.1 to 2.5 dtex. The fiber length of the synthetic fiber is preferably 0.1 to 5 mm. The average fiber diameter of the natural fiber is preferably 0.1 to 60 μm, more preferably 1 to 20 μm. The fiber length of the natural fiber is preferably 0.1 to 10 mm.
As the synthetic fiber, for example, polyester, polyamide, polyphenylene sulfide, polyacrylonitrile, polypropylene, polyethylene, a copolymer thereof, or the like is used. These synthetic fibers may be used alone or in combination of two or more. Among these synthetic fibers, polyester and polyacrylonitrile are preferable, and polyester is more preferable, from the viewpoint of strength or water resistance. Examples of the polyester include polyethylene terephthalate, a copolymer of ethylene terephthalate and ethylene isophthalate, polyethylene naphthalate, polyhexamethylene terephthalate, and a copolymer of hexamethylene terephthalate and 1,4-cyclohexanedimethylene terephthalate. As the polyester fiber, generally, an amorphous copolymer polyester having polyethylene terephthalate-based stretched polyester fiber, unstretched polyester fiber, and polyethylene terephthalate-based polyester as a core component and composed of terephthalic acid, isophthalic acid, ethylene glycol, diethylene glycol, etc. is used as a sheath. Examples thereof include polyester-based composite fibers as components.

As the synthetic fiber, fibers having various fiber diameters can be appropriately used depending on the quality required for the heat-sensitive stencil printing base paper, and synthetic fibers having a single fiber diameter may be used, but two or more kinds of fibers may be used. Synthetic fibers of diameter can be used together. For example, thick fibers may be blended to improve rigidity and printing resistance, and fine fibers may be blended to improve image quality.
Examples of natural fibers include kozo, mitsumata, hemp, and kenaf.

The porous support can be blended with a flame retardant, a heat stabilizer, an antioxidant, an ultraviolet absorber, a pigment, a dye, a fatty acid ester, an organic lubricant such as wax, an antifoaming agent such as polysiloxane, and the like. ..
The thickness of the porous support is preferably 10 to 250 μm, more preferably 20 to 200 μm.
The porous support can be produced by a papermaking method such as a wet papermaking method. In the wet papermaking method, for example, the fibers can be dispersed and filtered and then scooped, dehydrated and dried on the wire to produce a porous support.

The method for producing a heat-sensitive stencil printing base paper includes a step of producing a polyester film by the above-mentioned production method and a step of adhering the above-mentioned polyester film to a porous support. Although not particularly limited, it can be produced, for example, by applying an adhesive to a porous support and adhering it to a polyester film.
Examples of the adhesive for adhering the porous support and the polyester film include heating of vinyl acetate (vinyl acetate resin, etc.), (meth) acrylic, vinyl chloride vinyl acetate copolymer, polyester, urethane, etc. Photo-curable (preferably UV-curable) adhesives such as mold adhesives, (meth) acrylates, polyester (meth) acrylates, urethane (meth) acrylates, epoxy (meth) acrylates, and polyol (meth) acrylates. Agents can be mentioned.

In the thermal stencil printing base paper, a mold release agent may be applied to the surface of the polyester film on the side opposite to the side to be adhered to the porous support. The release agent can improve the slippage of the film surface of the thermal stencil printing base paper that slides with respect to the thermal head during perforation. When drilling with the thermal head, the polyester film melted by heat may remain on the thermal head and fuse, resulting in poor drilling. By applying a mold release agent, such poor drilling can be achieved. Can be prevented. As the release agent, for example, one kind or two or more kinds of silicone type, fluorine type, wax type, and surfactant type can be used.

[Characteristic measurement method]
(1) Glass transition point Tg (° C), melting point Tm (° C), heat of fusion (g / J) of polyester resin and film
According to JIS K7121-1987, a DSC (RDC220) manufactured by Seiko Instruments Inc. is used as a differential scanning calorimeter, and a disk station (SSC / 5200) manufactured by Seiko Instruments Inc. is used as a data analyzer. The temperature is raised from room temperature to 300 ° C. at a heating rate of 10 ° C./min on the saucer (1st Run). The sample is taken out and rapidly cooled, and then the temperature is raised from room temperature to 300 ° C. at a heating rate of 10 ° C./min (2nd Run).
Read the glass transition point Tg (° C), the peak top temperature of the heat absorption peak of melting (melting point Tm (° C)), and the amount of heat of fusion (ΔHm _{total 1st} , ΔHm _{≥ 200 ° C 1st} (g / J)) from the DSC chart of 1st Run. _{The heat of fusion (ΔHm ≤ 200 ° C. 2nd} , (g / J)) was read from the DSC chart of 2nd Run.

(2) Thickness (μm)
The film thickness was measured at arbitrary 5 locations with 10 films stacked in accordance with the JIS K7130 (1992) A-2 method using a dial gauge. The average value was divided by 10 to obtain the film thickness.
(3) Melt flow rate (MFR, g / 10min)
After the resin pellets constituting the film or the flakes of the film (the film is freeze-milled into granular resin having a diameter of 1 mm or less), the film is dried under vacuum at 140 ° C. for 3 hours. Next, a melt indexer (manufactured by Toyo Seiki Seisakusho Co., Ltd., F-F01) was used for measurement in accordance with JIS K7210-1: 2014 at a temperature of 250 ° C. and a load of 1 kgf.

(4) Amount of constituent components of the film ECA-400 (manufactured by JEOL RESONANCE Co., Ltd.) using a solution obtained by weighing 50 mg of a sample and adding 0.21 ml of deuterated hexafluoroisopropanol / 0.49 ml of deuterated chloroform as a measurement sample. ¹ H-NMR is measured using. The molar ratio is calculated from the area of the proton peaks assigned to each component, and the amount of the component (mol%) is determined so that the total of the diol components and the total of the dicarboxylic acid components are 100 mol%.
(5) Infrared spectroscopy (IR)
Infrared spectroscopic spectra are collected by FT-IR (PerkinElmer, Fourier GOLD) under the following conditions by the transmission method and 128 times of integration. Intensity at 1268cm ^-1 in the spectra obtained, and obtains the spectral intensity at 1250 cm ^-1, and calculating the ratio _(I 1268 _/ I _1250).

(6) Film shrinkage (%)
The measurement is performed according to JISC2151: 2019. A sample piece having a sample length of 100 mm and a sample width of 10 mm obtained by cutting out a thermoplastic resin film in an arbitrary direction of the film and in a direction perpendicular to the film was placed in a hot air oven set at 65 ° C. and set to 1 hour or 130 ° C. The sample was placed in a hot air oven and heat-treated for 30 minutes, and the heat shrinkage was calculated from the average value of the dimensional changes of the sample pieces. The shrinkage rate was n = 10 in any direction.
Shrinkage rate (%) = {[Dimension of sample piece before heat treatment (mm)]-[Dimension of sample piece after heat treatment (mm)] / [Dimension of sample piece before heat treatment (mm)] x 100

(7) Film softening start temperature (° C.) by nanothermal analysis (nano TA)
A sample of 10 mm × 10 mm is cut out from an arbitrary part of the polyester film and attached to a metal pedestal with double-sided tape to prepare a sample. This sample was subjected to an atmospheric atmosphere using a nanothermal analyzer (TA device: NanoTA2 manufactured by Anasys Instruments, AFM device: Nano-R manufactured by PACIFIC NANOTECHNOLOGY, probe: Anasys Instruments / PNI-AN2-300). Heat under the heating condition of 25 ° C. to 10 ° C./sec, and obtain a chart in which the displacement amount of the probe is plotted on the vertical axis and the temperature is plotted on the horizontal axis. As shown in FIG. 1, the measurement sample is slightly displaced in the positive direction (probe is pushed up) due to expansion as the temperature rises, but when a certain temperature is reached, the displacement starts to decrease. The temperature at which the displacement starts to decrease is defined as the softening start temperature. The measurement was carried out at n = 5 per sample, and the average value of the obtained values was taken as the softening start temperature (° C.) of the sample.

(8) Flatness After cutting the film into squares in any direction so that each side is 40 cm, and applying an acrylic adhesive (3M, SP7533) to one side with a bar coater so that the thickness at the time of drying is 1 μm. , Japanese paper (manufactured by Miki Special Paper Co., Ltd., T-25, thickness 25 μm, grain size 16 g / m ² ) and dried at 80 ° C. to prepare a laminate. After that, it was cut out from the center of the laminate so as to be parallel to the side of the sample, and the average value (mm) of the lift of the four corners when the film was placed on a horizontal table with the film on the upper side was measured. did. The evaluation was performed with n = 5, and the average value was used as the characteristic value of the level and judged according to the following criteria.
A: Less than 5 mm B: 5 mm or more and less than 10 mm C: 10 mm or more

(9) Workability a. Punchability A laminated product of film and Japanese paper produced in (8) is supplied to "RISOGRAPH" (registered trademark) GR275 manufactured by Riso Kagaku Corporation as a base paper for printing, and a drilling test is performed by a thermal head plate making method (400 dpi). Was done. At this time, the energy input to the thermal head is 60%, and the perforated sample is perforated by observing 50 perforated parts of the film at a magnification of 500 times using a scanning microscope (JSM6700F manufactured by JEOL Ltd.). The equivalent circle diameter of the hole diameter was measured, and the average value of the hole diameter was calculated. The obtained average value was evaluated according to the following criteria.
AA: Perforation diameter is 25 μm or more A: Perforation diameter is 20 μm or more and less than 25 μm B: Perforation diameter is 10 μm or more and less than 20 μm C: Perforation diameter is less than 10 μm b. Transportability The film is slit to a length of 3000 m / width of 300 mm and heated to a temperature of 80 ° C. while being transported by a roll-to-roll heating device (manufactured by Nippon Gaishi Co., Ltd.) at a speed of 50 m / min and a tension of 50 N / m. The transportability when all 3000 m was transported was evaluated according to the following criteria.
A: No film tear during transportation B: Film tear during transportation 1 to 3 times C: Film tear during transportation 4 times or more

(10) Film-forming property (productivity) of the film
The film formation described in Examples and Comparative Examples was continuously carried out for 10 hours, and the number of times of film tearing (including both fracture and transverse stretching during longitudinal stretching and heat fixing treatment) was determined according to the following criteria for production. I confirmed the sex.
A: No tear B: The frequency of tears is 1 to 5 times C: The frequency of tears is 6 times or more

(Reference Example 1) PET / I-1
Using 100 parts by weight of ethylene glycol, 102 parts by weight of dimethyl terephthalate, and 55 parts by weight of dimethyl isophthalate as starting materials, 0.11 part by weight of magnesium acetate / tetrahydrate was used as a catalyst in a reactor, and the reaction start temperature was set to 150 ° C. The reaction temperature was gradually increased with the distillation of methanol to 230 ° C. after 3 hours. After 4 hours, 0.04 part by weight of trimethyl phosphate and 0.04 part by weight of antimony trioxide were added to the reaction mixture in which the transesterification reaction was substantially completed, and the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from the normal pressure, and finally adjusted to 0.3 mmHg, and the transesterification reaction was carried out. The reaction was stopped 4 hours after the start of the reaction, and the polymer was discharged under nitrogen pressure to obtain a PET / I-1 chip having an isophthalic acid component content of 35 mol% with respect to the entire dicarboxylic acid component. The intrinsic viscosity of polyester was 0.60 dl / g, and the MFR at 250 ° C. was 40 g / 10 min.

(Reference example 2) PET / I-2
The content of the isophthalic acid component with respect to the total dicarboxylic acid component was 25 mol% in the same manner as in Reference Example 1 except that 100 parts by weight of ethylene glycol, 117 parts by weight of dimethyl terephthalate, and 39 parts by weight of dimethyl terephthalate were used as starting materials. A PET / I-2 chip was obtained. The intrinsic viscosity of polyester was 0.60 dl / g, and the MFR at 250 ° C. was 40 g / 10 min.

(Reference Example 3) PET / I-3
The polycondensation reaction was carried out in the same manner as in Reference Example 2 except that the reaction was stopped 5 hours after the start of the reaction. I got a tip. The intrinsic viscosity of polyester was 0.75 dl / g, and the MFR at 250 ° C. was 10 g / 10 min.

(Reference Example 4) PET / I-4
The content of the isophthalic acid component with respect to the total dicarboxylic acid component was 22 mol% in the same manner as in Reference Example 1 except that 100 parts by weight of ethylene glycol, 122 parts by weight of dimethyl terephthalate, and 35 parts by weight of dimethyl terephthalate were used as starting materials. PET / I-4 chips were obtained. The intrinsic viscosity of polyester was 0.60 dl / g, and the MFR at 250 ° C. was 40 g / 10 min.

(Reference Example 5) PET-1
A PET-1 chip was obtained in the same manner as in Reference Example 1 except that 100 parts by weight of ethylene glycol and 155 parts by weight of dimethyl terephthalate were used as starting materials. The intrinsic viscosity of polyester was 0.60 dl / g, and the MFR at 250 ° C. was not measurable.

(Reference Example 6) PET / I-5
The content of the isophthalic acid component with respect to the total dicarboxylic acid component was 10 mol% in the same manner as in Reference Example 1 except that 100 parts by weight of ethylene glycol, 141 parts by weight of dimethyl terephthalate, and 16 parts by weight of dimethyl terephthalate were used as starting materials. PET / I-5 chips were obtained. The intrinsic viscosity of polyester was 0.60 dl / g, and the MFR at 250 ° C. was 40 g / 10 min.

(Reference Example 7) PET / I-6
The content of the isophthalic acid component with respect to the entire dicarboxylic acid component was 38.2 mol in the same manner as in Reference Example 1 except that 100 parts by weight of ethylene glycol, 97 parts by weight of dimethyl terephthalate, and 60 parts by weight of dimethyl terephthalate were used as starting materials. % PET / I-6 chips were obtained. The intrinsic viscosity of polyester was 0.60 dl / g, and the MFR at 250 ° C. was 40 g / 10 min.

(Reference Example 8) PET / N-1
Similar to Reference Example 1 except that 100 parts by weight of ethylene glycol, 110 parts by weight of dimethyl terephthalate, and 52 parts by weight of dimethyl 2,6-naphthalenedicarboxylic acid were used as starting materials, the naphthalene dicarboxylic acid component with respect to the entire dicarboxylic acid component was prepared. A PET / N-1 chip having a content of 30 mol% was obtained. The intrinsic viscosity of polyester was 0.65 dl / g, and the MFR at 250 ° C. was unmeasurable.

(Example 1)
Weigh 50% by weight of PBT-1 (manufactured by Toray Industries, Inc., "Trecon" (registered trademark) 1100M, MFR 30g / 10min), 50% by weight of PET / I-1, dry blend, and rotate in the same direction with a vent. It is supplied to a shaft kneading extruder (manufactured by Japan Steel Works, screw diameter 30 mm, screw length / screw diameter = 45.5), and the measured value of the resin temperature in the molten state of the resin discharged from the die becomes 250 ° C. The extrusion conditions are adjusted as described above, and the mixture is discharged in a strand shape, pelletized with water at 25 ° C., cooled with water at a temperature of 25 ° C., and then immediately cut to obtain pellets. The obtained pellets were dried under reduced pressure at 140 ° C. for 3 hours and then supplied to a full-flight single-screw extruder. Next, the polymer melted by the extruder is filtered through a 10 μm cut filter, melt-extruded from the mouthpiece of the T-die, and then adhere-cooled and solidified while applying an electrostatic charge to a cast drum having a surface temperature of 25 ° C., and unstretched to a thickness of 38 μm. A sheet was prepared. The melt-kneading time was 15 minutes. At this time, the temperature of the extruder / filter was adjusted so that the measured value of the resin temperature in the molten state of the resin discharged from the mouthpiece was 250 ° C. Next, the obtained unstretched sheet was preheated with a plurality of heating rolls heated to a surface temperature of 60 ° C., and then the heating roll heated to a surface temperature of 75 ° C. It was stretched 4.0 times in the longitudinal direction (MD direction) with different cooling rolls at 30 ° C. The uniaxially stretched sheet thus obtained is stretched 4.0 times at a temperature of 80 ° C. in the longitudinal direction and the direction perpendicular to the longitudinal direction (TD direction) using a tenter, and subsequently heat-treated at 100 ° C. A polyester film having a thickness of 1.5 μm stretched on a shaft was produced.

(Example 2)
Weigh 20% by weight of PBT-2 (manufactured by Toray Industries, Inc., "Trecon" (registered trademark) 1200M, MFR 8g / 10min) and 80% by weight of PET / I-2 so that the thickness of the unstretched sheet becomes 90 μm. A polyester film having a thickness of 3.5 μm stretched biaxially was produced in the same manner as in Example 1 except for the adjustment.

(Example 3)
Biaxial in the same manner as in Example 1 except that 20% by weight of PBT-2 (manufactured by Toray Industries, Inc., "Trecon" (registered trademark) 1200M, MFR8g / 10min) and 80% by weight of PET / I-2 were weighed. A polyester film having a thickness of 1.5 μm was prepared.

(Example 4)
A polyester film having a thickness of 1.5 μm stretched biaxially was produced in the same manner as in Example 1 except that PET / I-3 was weighed in an amount of 80% by weight.

(Example 5)
PBT-3 (manufactured by Toray Industries, Inc., "Trecon" (registered trademark) 1400S, MFR 4g / 10min) 10% by weight and PET / I-4 90% by weight were weighed in the same manner as in Example 1. A stretched polyester film having a thickness of 1.5 μm was prepared.

(Example 6)
PBT-2 (manufactured by Toray Industries, Inc., "Trecon" (registered trademark) 1200M, MFR 8g / 10min) 20% by weight and PET / I-4 80% by weight were weighed in the same manner as in Example 1. A stretched polyester film having a thickness of 1.5 μm was prepared.

(Example 7)
Using the formulation of Example 3, the same as in Example 1 except that the temperature of the extruder / filter was adjusted so that the measured value of the resin temperature in the molten state of the resin discharged from the mouthpiece was 280 ° C. A biaxially stretched polyester film having a thickness of 1.5 μm was produced.

(Comparative Example 1)
PBT-1 (manufactured by Toray Industries, Inc., "Trecon" (registered trademark) 1100M, MFR 30g / 10min) 60% by weight and PET / I-1 40% by weight were weighed in the same manner as in Example 1. A stretched polyester film having a thickness of 1.5 μm was prepared.

(Comparative Example 2)
PET-1 was dried under reduced pressure at 140 ° C. for 3 hours and then supplied to a full-flight single-screw extruder. Next, the polymer melted by the extruder is filtered through a 10 μm cut filter, melt-extruded from the mouthpiece of the T-die, and then adhere-cooled and solidified while applying an electrostatic charge to a cast drum having a surface temperature of 25 ° C., and unstretched to a thickness of 38 μm. A sheet was prepared. At this time, the temperature of the extruder / filter was adjusted so that the measured value of the resin temperature in the molten state of the resin discharged from the mouthpiece was 280 ° C. Next, the obtained unstretched sheet was biaxially stretched in the same manner as in Example 1 to prepare a polyester film having a thickness of 1.5 μm.

(Comparative Example 3)
PET / I-5 was dried under reduced pressure at 140 ° C. for 3 hours and then fed to a full-flight single-screw extruder. Next, the polymer melted by the extruder is filtered through a 10 μm cut filter, melt-extruded from the mouthpiece of the T-die, and then adhere-cooled and solidified while applying an electrostatic charge to a cast drum having a surface temperature of 25 ° C., and unstretched to a thickness of 38 μm. A sheet was prepared. At this time, the temperature of the extruder / filter was adjusted so that the measured value of the resin temperature in the molten state of the resin discharged from the mouthpiece was 250 ° C. Next, the obtained unstretched sheet was biaxially stretched in the same manner as in Example 1 to prepare a polyester film having a thickness of 1.5 μm.

(Comparative Example 4)
PET / I-6 was dried under reduced pressure at 140 ° C. for 3 hours and then fed to a full-flight single-screw extruder. Next, the polymer melted by the extruder is filtered through a 10 μm cut filter, melt-extruded from the mouthpiece of the T-die, and then adhere-cooled and solidified while applying an electrostatic charge to a cast drum having a surface temperature of 25 ° C., and unstretched to a thickness of 38 μm. A sheet was prepared. At this time, the temperature of the extruder / filter was adjusted so that the measured value of the resin temperature in the molten state of the resin discharged from the mouthpiece was 250 ° C. Next, the obtained unstretched sheet was biaxially stretched in the same manner as in Example 1 to prepare a polyester film having a thickness of 1.5 μm.

(Comparative Example 5)
Using the formulation of Example 3, the same as in Example 1 except that the temperature of the extruder / filter was adjusted so that the measured value of the resin temperature in the molten state of the resin discharged from the mouthpiece was 290 ° C. Although melt extrusion was performed, it was difficult to form an unstretched sheet because the resin discharged from the T-die foamed, so the film collection was abandoned.

(Comparative Example 6)
PET / N-1 was dried under reduced pressure at 140 ° C. for 3 hours and then supplied to a full-flight single-screw extruder. Next, the polymer melted by the extruder is filtered through a 10 μm cut filter, melt-extruded from the mouthpiece of the T-die, and then adhere-cooled and solidified while applying an electrostatic charge to a cast drum having a surface temperature of 25 ° C., and unstretched to a thickness of 38 μm. A sheet was prepared. At this time, the temperature of the extruder / filter was adjusted so that the measured value of the resin temperature in the molten state of the resin discharged from the mouthpiece was 280 ° C. Next, the obtained unstretched sheet was biaxially stretched in the same manner as in Example 1 to prepare a polyester film having a thickness of 1.5 μm.

Table 1 shows the evaluation results of the polyester films collected in Examples 1 to 7 and Comparative Examples 1 to 6.

Claims (16)

A polyester film having a softening start temperature of 80 to 130 ° C. as measured by nanothermal analysis (nano TA). The polyester film according to claim 1, wherein the softening start temperature measured by nanothermal analysis (nano TA) is 80 to 110 ° C. The polyester film according to claim 1 or 2, wherein the highest melting point in the 1st run heating process of differential scanning calorimetry (DSC) is 250 ° C. or lower. The polyester film according to any one of claims 1 to 3, which has a thickness of 0.5 to 5 μm. Any of claims 1 to 4, wherein the _{heat of fusion ΔHm ≤ 200 ° C. 2nd} of the melting point peak detected in the region of 200 ° C. or lower in the 2nd run temperature raising process of differential scanning calorimetry (DSC) is 10 J / g or less. The polyester film described in. Any of claims 1 to 5, wherein the _{heat of fusion ΔHm ≧ 200 ° C. 1st} of the melting point peak detected in the region of 200 ° C. or higher in the 1st run temperature raising process of differential scanning calorimetry (DSC) is 1 to 30 J / g. The polyester film described in the crab. Any of claims 1 to 6, wherein the _{heat of fusion ΔHm ≥ 200 ° C. 1st} of the melting point peak detected in the region of 200 ° C. or higher in the 1st run temperature raising process of differential scanning calorimetry (DSC) is 5 to 20 J / g. The polyester film described in the crab. The polyester film according to any one of claims 1 to 7, wherein the melt flow rate (MFR) of the resin composition constituting the polyester film at 250 ° C. is 5 to 40 g / 10 min. A spectral intensity at 1268cm ^-1, which is detected by infrared spectroscopy, the ratio of the spectral intensity at ^{_{1250cm -1 (I 1268 / I 1250}} ) is 1.05 to 1.30, more of claims 1 to 8 The polyester film described in the spectrum. At least selected from ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, and 1,4-cyclohexylene diethanol as the diol constituents of the polyester resin constituting the polyester film. Claim 1 containing two types and at least two types selected from terephthalic acid, isophthalic acid, adipic acid, 1,4-cyclohexanedicarboxylic acid, and 2,6-naphthalenedicarboxylic acid as the dicarboxylic acid constituents of the polyester resin. The polyester film according to any one of 9. The polyester film according to any one of claims 1 to 10, which is biaxially oriented. The polyester film according to any one of claims 1 to 11, which is used for printing. A base paper for printing containing the polyester film according to any one of claims 1 to 12. A method for producing a polyester film, in which two or more types of polyester resins are melt-kneaded at a measured value of a resin temperature of 240 ° C. or higher and 280 ° C. or lower for a kneading time of 5 minutes or longer and 60 minutes or lower, and then formed into a film. Including the step, the polyester film comprises at least selected from ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, and 1,4-cyclohexylene diethanol as diol constituents. A method for producing a polyester film containing two types and at least two types selected from terephthalic acid, isophthalic acid, adipic acid, 1,4-cyclohexanedicarboxylic acid, and 2,6-naphthalenedicarboxylic acid as dicarboxylic acid constituents. The polyester film contains 50 to 99 mol% of ethylene glycol and 1 to 50 mol% of 1,4-butanediol with respect to all diol constituents, and 65 to 82 mol% of terephthalic acid and isophthalic acid with respect to all dicarboxylic acid constituents. The method for producing a polyester film according to claim 14, which contains 18 to 35 mol% of an acid. A method for producing a heat-sensitive stencil printing base paper, which comprises a step of manufacturing a polyester film by the manufacturing method according to claim 14 or 15 and a step of adhering the polyester film to a porous support. Production method.

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