JPH01229040A - Biaxially oriented polyester film - Google Patents

Abstract

PURPOSE:To obtain the title film suitable for magnetic tape, electrical insulation and condenser with an extremely small amount of low-molecular weight compound precipitated by copolymerizing a dicarboxylic acid component with a diol component having a specific molar volume. CONSTITUTION:(A) 1-20mol% diol component (e. g. 1,4-cyclohexanedimethanol) having >=70cm<3>/mol, preferably <=200cm<3>/mol molar volume of repeating structure unit and (B) a diol component such as ethylene glycol are polymerized with (C) a dicarboxylic acid component such as terephthalic acid to give pellets having >=0.75 intrinsic viscosity. The pellets are fed to a melt extruder, extruded into a sheet, and biaxially oriented to give the aimed film having >=0.70 intrinsic viscosity, 1.3600-1.3849g/cm<3> density and >=800kg/mm<2> sum of Young's moduli of longitudinal direction and width direction.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to biaxially oriented polyester films;
More specifically, the present invention relates to a biaxially oriented polyester film characterized by an extremely small amount of precipitated low molecular weight substances.

[Prior Art] As a biaxially oriented polyester film, a film is known in which the precipitation of low molecular weight substances is reduced by improving the physical properties such as the refractive index of a polyethylene terephthalate film (for example, JP-A-52 -69602
Publications, etc.).

[Problem to be solved by the invention] However, the above conventional biaxially oriented polyester film has the following problems:
Problems have arisen as a result of the dramatic increase in the speed of film processing, such as magnetic layer coating and calendering in magnetic media applications. That is, when the process temperature increases as the process speed increases, low molecular weight substances tend to precipitate on the film surface, which causes problems in the processing process and product performance.

An object of the present invention is to improve this problem and provide a biaxially oriented polyester film in which precipitation of low molecular weight substances on the film surface is extremely small.

[Means for Solving the Problems] The present invention provides a structure in which the molar volume of the repeating structural unit is 70 on/m
A film whose main component is polyester containing 1 to 20 mol % of a diol component of o1 or more, the film has an intrinsic viscosity of 0.70 or more and a density of 1.3600 to 1.
3849(]/a+f and the sum of Young's modulus in the longitudinal direction and the width direction is 800 kg/mm2 or more.

The polyester in the present invention includes ethylene prephthalate, ethylene α, β-bis(2-chlorophenoxy)ethane-4,4′-dicarboxylate, ethylene 2,6
- The main constituent is at least one structural unit selected from naphthalate units, and the molar volume is 70 crK/
The residual diol component of mo1 or more, preferably 100 cr4/no1 or more, is 1 to 20 mol%, preferably 1 to 1
It is necessary to contain 0 mol%, more preferably 1 to 5 mol%. be.). If the molar volume of the remaining diol component is smaller than the above range, the amount of low molecular weight substances precipitated on the film surface will increase, which is undesirable (hereinafter referred to as
A case in which a large amount of low molecular weight substances are precipitated on the film surface is referred to as poor oligomer precipitation prevention property, and a case in which a small amount of low molecular weight substances are deposited on the film surface is referred to as good oligomer precipitation prevention property).

The upper limit of the molar volume of the diol component residue is not particularly limited, but is 200 aK/not, preferably 17
0o4/mol, more preferably 150 cm/m.

If it exceeds 1, there will be a tendency for more tearing during stretching, so it is desirable that it is less than that. Preferred diol components satisfying the above molar volume include 1,4-cyclohexane dimetatool, butylene glycol neopentyl glycol, triethylene glycol, medylhydroquinone, naphthalene 2,7-diol, but are not limited to these. , and at least one type of structural unit selected from these is the main constituent, and the total amount may be within the range described. Furthermore, it is particularly desirable to use a diol component containing 1,4-cyclohexane dimetatool as a main component, since the ability to prevent oligomer precipitation will be even better. If the content of the above-mentioned diol component in the polyester is less than the above range, the oligomer precipitation prevention property will be poor, which is undesirable.On the other hand, if it is too much, the thermal properties will deteriorate, so it is not suitable for base films for magnetic media or films for electrical insulation. undesirable as such. In addition, the polyester in the present invention is within a range that does not impede the present invention, preferably 1
Other components may be copolymerized within 0 mol%. In addition, polyester containing ethylene terephthalate as a main component is particularly desirable because it provides even better oligomer precipitation prevention properties.

Further, it is preferable that the polyester used in the present invention contains inorganic particles because precipitation of low-molecular intermolecular bodies is further reduced. Although known particle types can be used, it is particularly preferable to use calcium carbonate particles, especially synthetic calcium carbonate particles, because they provide even better oligomer precipitation prevention properties.

The addition port of the particles is usually appropriately selected within the range of 0.1 to 20% by weight.

It is necessary that the intrinsic viscosity of the film in the present invention is 0.70 or more, preferably 0.75 or more, and more preferably 0.80 or more. If the intrinsic viscosity is smaller than the above range, the oligomer precipitation prevention properties will be poor, which is not preferable. The upper limit of the intrinsic viscosity is not particularly limited, but about 1.0 is the manufacturing limit.

The density of the film used in the present invention is 1.3600 to 1.3
849 [1/fan, preferably 1.3700 to 1.384
5g/reward, more preferably 1.3750 to 1.384
It must be 0(1/-).

If the density is lower than the above range, the dimensional stability will deteriorate, making it undesirable for use as a base film for magnetic media or as an electrically insulating film. Conversely, if the density is greater than the above range,
This is not preferable because the oligomer precipitation prevention property becomes poor.

The sum of Young's moduli in the longitudinal direction and width direction of the film in the present invention is 800 kg/mm2 or more, preferably 850 k
It is necessary that q/mtn2 or more.

If the sum of the Young's moduli is smaller than the above range, the oligomer precipitation prevention properties will be poor, which is not preferable. Although the upper limit of the sum of Young's moduli is not particularly limited, about 2000 kg/mm 2 is the manufacturing limit.

In addition, inorganic or organic additives such as antioxidants, heat stabilizers, lubricants, ultraviolet absorbers, and nucleating agents are added to the polyester used in the present invention to the extent that they do not impede the purpose of the present invention. may have been done.

Further, when the film of the present invention is thermally analyzed by DSC, it is desirable that the position of the endothermic peak detected in the range of melting temperature Tm - Tm - 100°C is 200 to 240°C, since the oligomer precipitation prevention property will be even better. .

The film of the present invention contains a diol component with a defined molar volume and has a defined intrinsic viscosity, density, and Young's modulus, but if any one of these is missing, the effects of the present invention cannot be obtained. First, a dramatic synergistic effect is achieved only when all of these conditions are simultaneously met, and a film in which precipitation of low-molecular m-forms on the film surface is extremely small can be obtained.

Next, a method for producing the film of the present invention will be explained.

First, the molar volume of the repeating structural unit in polyester is 7.
As a method for containing a diol component of 0 cm/mo1 or more, it may be copolymerized as part of the diol component of the polyester of the present invention from the beginning, or this diol component and the dicarboxylic acid component of the polyester used in the present invention may be mixed in advance. The polyester may be polymerized to form pellets, which may be mixed with the polyester pellets used in the present invention. At this time, in order to make the intrinsic viscosity of the film 0.70 or more, it is necessary to keep the intrinsic viscosity of the pellets at least 0.75 or more. This method may use only melt polymerization or in-phase polymerization, but the intrinsic viscosity is 0.5 to 0.
．． It is effective to solid-phase polymerize the polymer No. 65 to obtain a film intrinsic viscosity of 0.75 or more in the range of the present invention. The pellets thus produced are immediately fed to a melt extruder after being sufficiently dried by a known method. Setting the time from drying to extrusion within 60 minutes is effective in making the composition of the present invention have an intrinsic viscosity within the range of the present invention. The pellets supplied to the melt extruder were
It is extruded into a sheet through a slit-shaped die at 0°C, and cooled and solidified on a casting roll to produce an unstretched film. At this time, it is effective to keep the residence time in the melt extruder short, preferably 30 minutes or less, more preferably 20 minutes or less, in order to give the composition of the present invention an intrinsic viscosity within the range of the present invention. Further, in order to obtain a Young's modulus within the range of the present invention, it is desirable to use a filter with a 95% overaccuracy (measured value by a Coulter counter) of 2 to 4 μm to perform high-accuracy overaccuracy.

Next, this unstretched film is biaxially stretched and biaxially oriented. The stretching method may be any known method, such as a sequential two-wheel stretching method, a simultaneous two-wheel stretching method, or a method in which the film thus biaxially stretched is stretched again in either direction. The stretching area magnification (vertical magnification x horizontal magnification) is 24
It is effective to make the Young's modulus within the range of the present invention using the composition of the present invention. Heat treatment is 170-2
It is carried out for 0.5 to 60 seconds at a temperature of 40'C. The higher the heat treatment temperature, the better the film can be obtained in preventing oligomer precipitation. By setting the stretching ratio and heat treatment temperature in accordance with the type of polyester, a film having the density and Young's modulus of the present invention can be obtained. In addition, cooling after heat treatment is performed slowly (at 1.5° C./second or less) using the composition of the present invention to achieve a density within the range of the present invention.
This is effective for obtaining Young's modulus.

[Method for Measuring Characteristics and Evaluating Effects] Methods for measuring characteristic values and evaluating effects of the present invention are as follows.

(1) Intrinsic viscosity [η] (Unit: old/g) A value calculated from the following formula from the solution viscosity measured at 25° C. in orthochlorophenol is used.

That is, η, D/C=[η]+K[η]2・Nicodeη8. = (solution viscosity/solvent viscosity) -1, C is solvent 1
Dissolved polymer weight per 00ml (CI/100d, usually 1.2>, K is Huggins' constant (assumed to be 0,343).

In addition, solution viscosity and solvent viscosity were measured using an Ostwald viscometer.

(2) Density Value measured in a mixed solvent of n-hebutane and carbon tetrachloride at 25°C using density gradient piping.

(3) Young's modulus 2.
Measurement was performed at 5° C. and 65% RH.

(4) Amount of surface oligomer: Place the sample in an oven for 3 hours at 160°C to forcibly precipitate low molecular weight substances. Cut several pieces into 4.5 x 4.5 cm pieces and place them in an ethanol-based solvent. The low-molecular weight molecules were quantified using high-performance liquid chromatography. The unit was expressed as the weight of the low molecular weight substance precipitated on both sides of the film per Tr12.

(5) Endothermic peak Measured using a DSC (differential scanning calorimeter) type ■ manufactured by PerkinElmer. The measurement conditions for DSC are as follows. That is, 10 m9 of the sample was set in the DSC device,
The mixture was melted for 5 minutes at a temperature of 00'C and then quenched into liquid nitrogen. The temperature of this rapidly cooled sample is raised at 40'C/min, and the endothermic peak detected in the range of melting temperature Tm - Tm - 100°C is measured.

[Example] The present invention will be explained based on examples.

Example 1 Dimethyl terephthalate, 1,4-cyclohexane dimetatool, and ethylene glycol were mixed in a composition ratio shown in Table 1, Example 1, transesterified by a conventional method, and then melt-polymerized. Pellets with an intrinsic viscosity of 0.60 were obtained. Further, this pellet was subjected to solid phase polymerization at 230'C for 8 hours to obtain a pellet having an intrinsic viscosity of 0.87. The pellets were dried at 180'C for 3 hours under reduced pressure (3 Torr) and immediately fed into a melt extruder and melted at 300'C.
An unstretched film was produced by winding the film around a casting drum with a surface temperature of 30'C using an electrostatic casting method and cooling and solidifying it. At this time, the residence time in the extruder was 15 minutes. Further, during melt extrusion, a filter with a 95% filtration accuracy (measured by a Coulter counter) of 2 μm was used. This unstretched film was stretched 5.0 times in the longitudinal direction, then 5.0 times in the width direction at a stretching rate of 2000%/min using a stenter, and heat treated at 210° C. for 7 seconds under constant length. A biaxially oriented film with a thickness of 15 μm was obtained. As shown in Table 1, the parameters of the present invention of this film were within the range of the present invention, and the oligomer precipitation prevention property was very excellent.

Examples 2-3. Comparative Examples 1 to 6 Raw materials were mixed with various amounts charged so as to have the composition ratios shown in Table 1, and after transesterification, melt polymerization was performed to create pellets. These pellets were subjected to rough solid phase polymerization to obtain pellets having an intrinsic viscosity of 0.65 to 0.85. This pellet was heated at 180°C for 3 hours under reduced pressure (3TOI'r).
After drying, it was immediately fed into a melt extruder, melted at 300'C, wound around a casting drum with a surface temperature of 30'C using an electrostatic casting method, and cooled and solidified to produce an unstretched film. At this time, the residence time in the extruder is 1
It was set as 5 minutes. In addition, the 95% filtration accuracy (measured by Coulter counter) during melt extrusion is 2 to 15%.
A μm filter was used. This unstretched film was stretched 3 to 6 times in the longitudinal direction, then 3 to 6 times in the width direction at 95°C at a stretching rate of 2000%/min using a stenter, and then stretched at a constant length of 175 to 220°. Heat treated at C for 7 seconds,
A biaxially oriented film with a thickness of 15 μm was removed. The parameters of the present invention and the surface oligomer 1 of these films are as shown in Table 1, and when the parameters of the present invention are within the range of the present invention, the oligomer precipitation prevention property is good, but
It can be seen that if the parameters are outside the range of the present invention, a film with good oligomer precipitation prevention properties cannot be obtained.

[Effects of the Invention] The present invention contains a diol component with a molar volume within a specific range, and sets the intrinsic viscosity, density, and Young's modulus of the film within specific ranges, so that a film with good oligomer precipitation prevention properties can be obtained. This makes it possible to cope with increased film processing speeds in various applications. The use of the film of the present invention is not particularly limited, but it is particularly preferably used for magnetic tapes, electrical insulation, and capacitors.

Claims (1)

[Claims] A film whose main component is polyester containing 1 to 20 mol % of a diol component having a molar volume of repeating structural units of 70 cm^2/mol or more, the film having an intrinsic viscosity of 0.70 or more and a density of 1. 3600~1.384
9 g/cm^3 and a sum of Young's moduli in the longitudinal direction and width direction of 800 kg/mm^2 or more.