JPH0367630A - Biaxially oriented polyester film - Google Patents

Abstract

PURPOSE:To improve heat resistance, strength, continuity in film making and a draw ratio of a longitudinal direction, by a method wherein the subject film is made into a polyester film wherein at least specific ratio of an acid ingredient and glicol ingredient are constituted respectively of terephthalic acid and 1,4- cyclohexanedimethanol, and density, a birefringent index and Young's modulus of a longitudinal direction of the film are limited. CONSTITUTION:At least 80 mol% of an acid ingredient of a film is constituted of terephthalic acid, preferably at least 90 mol%, preferably further at least 95 mol%. Then at least 90 mol% in a glycol ingredient is constituted of 1,4- cyclohexanedimethanol, preferably at least 95 mol%, preferably further at least 97 mol%. Density of the film is made so as to fall within a range of 1.220-1.250 g/cm<2>, preferably a range of 1.224-1.240 g/cm<2>. A birefringence index (DELTAn) and Young's modulus of a longitudinal direction of the film are made so as to fall respectively within range of 0.010-0.040 and 310-370 kg/mm<2>.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a biaxially oriented polyester film that has excellent heat resistance, mechanical strength, and film formation continuity.

[Prior art and problems to be solved by the invention] Poly(1,4-cyclohexane dimethylene terephthalate)
(hereinafter abbreviated as PCT) has a melting point (Tm) of 5 to 35° compared to polyethylene terephthalate (hereinafter abbreviated as PET).
It has been reported that the glass transition temperature (Tg) is 5 to 25°C higher (J, Polymer Sc
i, C06, 17, (1964)). That is, P.C.T.
The film has better heat resistance than PET film.

However, in terms of strength, PCT film is comparable to PET film.
It is much lower than that of film, for example, when comparing Young's modulus, PET film has 6.8X105 psj (= 4
80 kg/mm”), while PCT film has a 4.OX 10’ psi (>280 kg/mm”)
), and it is reported that the strength is about 60% that of PET (Soc, Plastics Engrs
, J. Yu 1083 (1961)). film strength,
In particular, Young's modulus is a very important factor when continuously processing films industrially, and if Young's modulus is small, the tension applied during unwinding, winding, or various processing may cause irreversible damage to the film. It may even stretch.

For this reason, the Young's modulus in the longitudinal direction of the film is preferably as large as possible;
Only those having a Young's modulus of about /n++i'' were known.

[Means to solve the problem]

The present inventors conducted studies to solve the above problems, and found that a film having a certain density and birefringence index is
The present inventors have discovered that the film has excellent heat resistance and has higher strength than conventionally known PCT films, leading to the completion of the present invention.

That is, the gist of the present invention is that 80 mol% or more of the acid component is terephthalic acid, and 90 mol% or more of the glycol component is 1,4
- A polyester film composed of cyclohexanedimethanol, the film having a density of 1.220 to
1.250 g/d, birefringence 0.010-0.04
0, and the Young's modulus in the longitudinal direction of the film is 310~
4"OOkg/ms".

The present invention will be explained in detail below.

The polyester film of the present invention is a film in which 80 mol% or more of the acid component is composed of terephthalic acid,
Preferably 90 mol% or more, more preferably 95 mol%
The above is a film made of terephthalic acid. If the terephthalic acid content in the acid component is less than 80 mol%, the crystallinity of the polymer will be reduced, which will have an adverse effect on heat resistance. In addition, as long as the above range is satisfied, aromatic dicarboxylic acids such as isophthalic acid, 2,6- or 2,7-naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, or p-hydroxybenzoic acid can be used as the third component. Aromatic hydroxy acids such as acids may be contained in the polymer as a copolymerization component.

Further, in the polyester film of the present invention, it is necessary that 90 mol% or more of the glycol component is composed of cyclohexanedimethanol, and the content of cyclohexanedimethanol in the glycol component is preferably 95% by mole.
It is mol% or more, more preferably 97 mol% or more. If the content of cyclohexanedimethanol in the glycol component is less than 90 mol %, the crystallinity of the polymer decreases, as in the case of the acid component, and the heat resistance is adversely affected.

The cis-trans fraction of 1,4-cyclohexanedimethanol in the present invention is preferably 50 mol% or more trans.If the cis-trans fraction is large, the melting point will be particularly low, and the heat resistance at high temperatures will be reduced. will be in short supply.

The method of polymerizing the PCT polymer in the present invention can be a known polyester melt polymerization method, but in order to minimize thermal deterioration, a method of combining melt polymerization and solid phase polymerization to achieve the desired degree of polymerization is also possible. Can be adopted. The degree of polymerization of the film of the present invention is determined by its intrinsic viscosity, which is 0.45 when measured at 30°C in a solution of phenol:tetrachloroethane=1:1 (weight ratio) and assuming Higgins' constant as 0.33. More preferably, it is 0.60 or more. If the intrinsic viscosity is less than 0.45, it is not preferable because the stretchability is poor when attempting to obtain a biaxially oriented film.

The polyester film of the present invention can contain fine particles that are inactive with respect to polyester, if necessary. These fine particles can be selected from inorganic or organic particles, specifically kaolin, talc, silicon dioxide, calcium carbonate, lithium fluoride, titanium dioxide, zeolite, calcium terephthalate, crosslinked polymers, etc. The amount and average particle size can also be selected as appropriate depending on the application and necessity.

The polyester film of the present invention has a density of 1.22
The range is 0 to 1.250 g/aA, preferably 1
．． The range is 224 to 1.240 g/cj. If the density is less than 1.220 g/d, sufficient heat resistance cannot be obtained due to insufficient crystallization.

Although it is usually difficult to exceed 1,250 g/c+a, even if it is produced, crystallization will progress too much and the film itself will become brittle, making it impractical.

The birefringence index (Δn) of the polyester film of the present invention is 0
．． It needs to be in the range of 0.010 to 0.040.

This birefringence (Δn) can be determined by measuring the refractive index of the film in the longitudinal direction and in the direction perpendicular thereto using an ABBE refractometer, and calculating the difference therebetween. Birefringence (Δ
When n) is smaller than 0.010, the strength in the longitudinal direction is insufficient, and when the birefringence index (Δn) exceeds 0.040, the stretchability in the width direction is insufficient during film formation. This is a significant decrease, which is not desirable. The birefringence (Δn) of the polyester film of the present invention is 0.015 to 0°030
The range is more preferable.

Next, the method for producing biaxially oriented polyester of the present invention will be described in detail.

Since it is necessary for the polyester film of the present invention to have sufficient molecular orientation in the longitudinal direction, stretching in this direction is usually carried out in two stages, but it can also be carried out in more stages. For example, two-stage stretching formulations can be broadly classified into two types. First, one method is to perform two-stage stretching when stretching an unstretched sheet in the longitudinal direction by roll stretching. In this case, in the first stage of stretching, the film is heated so that the actual temperature of the film is in the range of 100 to 120°C, and the film is stretched 1.5 to 3.0 times. Next, the second stage of stretching is carried out at a temperature lower than that of the first stage and the actual temperature of the film is 9.
Heat to a temperature in the range of 0 to 105°C, 1.4 to 2
．． Stretch 5 times. At this time, it is preferable to set the overall stretching ratio in the longitudinal direction to 3.3 to 5.0 times; if it exceeds 5.0 times, the stretchability in the width direction will deteriorate, and if it is less than 3 times, it will be insufficient. molecular orientation cannot be obtained. The distribution of the stretching ratios in the first and second stages is such that if the stretching ratio in the second stage, which is stretched at a lower temperature, is increased, small ranks or voids are likely to be formed in the film, so the ratio in the second stage should be Stretching ratio of 5
It is not preferable to set it above 0%. Further, the optimum actual temperature of the film during stretching differs depending on the thickness of the film, line speed, etc., but in general, when the film is thick and the line speed is fast, it is better to set the temperature a little higher. Immediately after the first stage of stretching is completed, the film is cooled to a temperature below the glass transition temperature.
Next, it is preferable to perform preheating for the second stage of stretching in terms of ease of temperature control and prevention of crystallization of the film.

Also, during stretching, if the heating roll is at a high temperature, the film may stick to the roll, but in such cases it is also possible to change the material of the roll to a non-adhesive material and stretch. It is.

As the non-adhesive roll, a hard chrome plated roll with a matte surface, a ceramic roll, an elastomer roll, a fluororesin roll, etc. can be used.

The thus obtained film after being stretched in two steps in the longitudinal direction has a birefringence index (Δn) of 0.070-0.1.
00, and the average refractive index of the film is 1,5550-1
．． It is preferably in the range of 5610. A film within this range, after being stretched in the width direction as described below, will not only have excellent strength but also excellent uniformity in thickness and good stretchability in the width direction.

Stretching in the width direction is usually carried out by the so-called tenter method, the set magnification is selected from the range of 3.5 to 4.0 times, and the stretching temperature is preferably determined so that the actual magnification after stretching is as close to the set magnification as possible. . This stretching temperature is usually 95-115°C
You can choose from a range of , but generally speaking, the thicker the film, the
High stretching temperatures are required.

The biaxially oriented polyester film obtained in this manner can be then heat-set to dramatically improve its heat resistance. Heat setting is generally carried out by the tenter method, similar to the width direction stretching, and the conditions are 1.
Apply hot air at a temperature of 80 to 260°C, preferably 220 to 250°C, for 1 second to 5 minutes to reduce the density of the film to 1.
．． 220~1゜250g/c+a, preferably 1.22
It is carried out so that it is in the range of 4 to 1.240 g/c+ll. Further, at this time, for the purpose of improving the heat shrinkage rate in the width direction, it is also possible to perform a relaxation treatment of 3 to 5% in the width direction while heat setting. As for the heat setting temperature, since the melting point of PCT is higher than that of PET, PCT film can be heated up to about 250"C due to the film's planar orientation (described later).
Heat fixation can be performed without reducing ΔP). PET
It is known that film plane orientation (ΔP) begins to decrease at a heat setting temperature of 240″C, and PC
In the case of T film, the heat setting temperature can be set high as described above, so it is thought that good heat resistance can be obtained.

The biaxially oriented polyester film thus obtained has a Young's modulus in the longitudinal direction of 310 to 370 kg/m,
The strength is about 10 to 30% better than conventionally known PCT films.

Another method for imparting molecular orientation in the longitudinal direction of a film is to perform two-wheel stretching, then heat set at a low temperature, and then stretch the film again in the longitudinal direction (hereinafter referred to as re-stretching). be. In this case, the orientation of the two-wheel stretched film for re-stretching is a vertically and horizontally balanced film with a birefringence index (Δn) of -0, oio to 0,030, or a slightly predominant orientation in the longitudinal direction. Preferably. In a two-wheel stretched film with a birefringence index (Δn) of less than -0,010, the Young's modulus may not exceed 310 kg/mn+'' even after re-stretching, and
A two-wheel stretched film having a birefringence index (Δn) exceeding 0.030 is already highly oriented in the longitudinal direction, and further re-stretching results in a film that is extremely susceptible to tearing in the longitudinal direction, which is undesirable. The two-wheel stretched film for re-stretching may be produced by conventionally known final biaxial stretching or simultaneous two-wheel stretching performed in one vertical and one horizontal step, or as described above. Alternatively, it may be a two-wheel stretched film that is stretched in two stages in the longitudinal direction.

In particular, when a film with a birefringence (△n) of 0.010 to 0.020 is re-stretched using the latter method, the continuity of film formation including re-stretching is good, and the strength in the longitudinal direction and the This is preferable since it becomes a film with excellent ratio.

In order to improve the strength and Young's modulus by re-stretching, it is necessary to heat set the biaxially stretched film in advance at a low temperature of 120 to 140'C for 1 second to 1 minute.

If this heat setting temperature is less than 120°C, the crystallization of the film will be insufficient and the effect of re-stretching will be insufficient;
If it exceeds C, on the contrary, crystallization is promoted too much and re-stretching becomes impossible.

It is preferable to use a roll stretching method for re-stretching. In this case, the film is heated or cooled to a temperature 5 to 15°C lower than the above-mentioned low temperature heat-setting temperature, and then 1 It is preferable to stretch in the longitudinal direction at a magnification of .05 to 1.30 times. At this time, due to stress during stretching,
If the phenomenon of the film slipping on the surface of the stretching roll is observed, install a counter roll made of rubber material at an appropriate position on the stretching roll, or install an electrostatic application device to prevent the film from sliding on the stretching roll. It is necessary to bring them into close contact and re-stretch them. Among the above methods, the method of adhesion by electrostatic application is particularly preferable because it causes less damage to the film surface.

The re-stretched film is then heated to 180° in a tenter.
at a temperature of ~260°C, preferably 220-250°C,
Heat-fix by applying hot air for 1 second to 5 minutes. At this time, the density of the film after heat setting is 1.220 to 1.250 g/
Heat setting is performed so that the ctA is preferably in the range of 1.224 to 1.240 g/c+a. Also, if necessary,
Relaxation treatment can also be performed in the width direction of the film.

The thus obtained biaxially oriented polyester film has a longitudinal Young's modulus of 310 to 400 kg/III+
2, which is 10 times higher than the conventionally known PCT film.
It has a high strength of about 40%. In addition, when the Young's modulus in the longitudinal direction is improved by re-stretching, the decrease in the Young's modulus in the transverse direction is smaller than when the Young's modulus is improved by performing two-step stretching in the longitudinal direction as described above. It is preferable because there are many.

Since the biaxially stretched polyester film of the present invention has a large Young's modulus, it is industrially advantageous, especially for thin films with a thickness of 25 μm or less, but even films with a thickness of 25 μm or more have no effect. is fully demonstrated.

〔Example〕

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

The method for evaluating the characteristics of the film of the present invention is shown below.

(1) Birefringence (Δn) degree of one-plane orientation (ΔP), average refractive index n) Using an ABBE refractometer manufactured by Atago Optical Co., Ltd., the refractive index in the longitudinal direction in the film plane is nMD, and the direction perpendicular to it (width The refractive index in the film thickness direction was measured as nto, and the refractive index in the thickness direction of the film as nc, and each parameter was determined from the following equation. Note that the refractive index was measured using sodium D line at 23°C.

Birefringence (Δn) - n, nTD plane orientation degree (ΔP) = ((nMD+nTD)/2
) n & average refractive index (n) = (n, t++ny
o+nz)/3(2) Film density Measured at 25°C using a density gradient tube filled with a mixture of n-hebutane and carbon tetrachloride.

(3) Young's Modulus of Film Using a tensile tester Intesco Model 2001 manufactured by Intesco Co., Ltd., a sample film with a length of 300 mm and a width of 20 mm was tested at 10% Tensile at a strain rate of min, tensile stress -
It was calculated using the following formula using the first straight line part of the helix curve.

In addition, the sample film was incubated at the same temperature and humidity as during the measurement.
The temperature and humidity were controlled for at least 4 hours before use.

(4) Breaking strength of film Using a tensile tester Intesco Model 2001 manufactured by Intesco ■, a sample film with a length of 50 mm1 and a width of 151 mm was tested in a room controlled at a temperature of 23° C. and a humidity of 50% RH. It was calculated from the following formula by pulling at a speed of /min.

Breaking strength - F/S (kg/mm2) (5) Heat shrinkage rate Heat treated in an atmosphere of 200°C (±2°C) for 10 minutes under no tension, measured the length of the sample before and after that, and then It was calculated using the formula.

×l Oo Example 1 (Preparation of polymer) 95 mol% of terephthalic acid unit as dicarboxylic acid component
, using 5 mol% of isophthalic acid units, 100% of 14-cyclohexanedimethanol with a cis:trans ratio of 1:3 as the glycol component, and adding 0.06 mol% of titanium oxide to the oxidized component as a catalyst. Esterification was carried out by heating in a polymerization tank while stirring. Here, as a lubricant, 0.20w of thyroid with an average particle size of 1°30μm was added to the polymer.
After adding so that it becomes t%, polycondensation is performed, [η]=
A poly(1,4-cyclohexane dimethylene terephthalate) copolymer of 0.65 was obtained. After this polymer is made into chips, it is subjected to solid phase polymerization under a nitrogen stream and finally [η]
=1.05 polyester was obtained.

(Film production) After drying the above polyester, it was melt-extruded at 305°C and adhered to a casting drum maintained at 40°C using an electrostatic cooling method to form an unstretched sheet with a thickness of approximately 80 μm. Obtained. This unstretched sheet was brought into contact with a roll whose surface was treated with a non-adhesive fluororesin and was adjusted to 110'C and preheated, and then heated at 2.50°C between the rolls with a difference in circumferential speed while irradiating with an infrared heater. Stretched twice in the longitudinal direction.

At this time, the actual temperature of the film in the stretching section was measured with a radiation thermometer and found to be 110°C. After this stretched film was once cooled to below the glass transition temperature, it was again brought into contact with a metal roll adjusted to 90°C to preheat it, and further stretched 1°80 times in the longitudinal direction while irradiating it with an infrared heater. . The actual temperature of the film at this time is 90'
It was C. The birefringence index (Δ
n) is 0.096 and the average refractive index (n) is 1.5581
Met. Next, this stretched film is introduced into a tenter and 1
The film was stretched 3.60 times in the width direction at 00°C. Continuing further, 2
Heat setting was performed at 50'C for about 10 seconds to obtain a biaxially oriented film with a thickness of 5 μm. Further, during heat setting, a 3% relaxation treatment was performed in the width direction. The physical properties of this film are shown in Table 1.

Example 2 Using the polymer used in Example 1, Example 1
Melt extrusion and sheeting were carried out in the same manner as above, and the thickness was approximately 70t1m.
An unstretched sheet was obtained. This unstretched sheet was prepared in Example 1.
After preheating at 110"C using the non-adhesive roll used in 2.2.
00 times stretched. At this time, the actual temperature of the film in the stretching section was 110"C. After the stretched film was once cooled to below Tg, it was again brought into contact with a metal roll adjusted to 90"C and preheated, and an infrared heater was turned on. While irradiating
It was further stretched 2.00 times in the longitudinal direction. The actual temperature of the film at this time was 90°C. The birefringence index (Δn) of the film after this two-step stretching was 0.091, and the average refractive index (
n) was 1.5583. Next, this stretched film was introduced into a tenter and stretched 3.times.60 times in the width direction at 110.degree. Further, heat setting was carried out at 250''C for about 10 seconds to obtain a biaxially oriented film with a thickness of 5 μm.Furthermore, during heat setting, a relaxation treatment of 3% in the width direction was performed.The physical properties of this film were It is shown in Table 1.

Example 3 Using the polymer used in Example 1, Example 1
Melt extrusion and sheet formation were carried out in the same manner as above to obtain an unstretched sheet with a thickness of about 60 μm. This unstretched sheet was brought into contact with a metal roll adjusted to 100''C and preheated, and then stretched 3,00 times in the longitudinal direction while being irradiated with an infrared heater.

At this time, the actual temperature of the film in the stretching section was 100°C. Moreover, the birefringence index (Δn) of this stretched film is 0.
081, and the average refractive index (n) was 1.5586.
Next, this film was introduced into a tenter and stretched at 110°C by 3°60 times in the width direction. Further, heat fixation was continued at 130° C. for about 5 seconds. The birefringence of the film at this time is -
It was 0,002. In order to further re-stretch this biaxially stretched film in the longitudinal direction, it was preheated with a metal roll adjusted to 120°C and then stretched 1.15 times. At this time, an electrostatic adhesion method was used to bring the film into close contact with the stretching roll so that it would not slip. Further, the actual temperature of the film in the stretching section of the re-stretching was 120°C. This re-stretched film was introduced into the tenter again and heat-set at 250° C. for about 10 seconds to obtain a biaxially oriented film with a thickness of 5 pm. Further, during heat setting, relaxation treatment was performed at a rate of 3% in the width direction. Table 1 shows the physical properties of this film.

Comparative Example 1 In Example 3, after the stretching in the width direction was completed without re-stretching in the longitudinal direction, the stretching was continued at 250°C in a tenter.
Heat setting was performed for about 10 seconds to obtain a biaxially oriented film with a thickness of 5.8 μm. Further, during heat setting, a 3% relaxation treatment was performed in the width direction.

Table 1 shows the physical properties of this film.

Comparative Example 2 In Example 1, the heat setting temperature after two-wheel stretching was set at 160°.
A biaxially oriented film having a thickness of 5 μm was obtained by carrying out everything in the same manner as in Example 1 except for using C.

Table 1 shows the physical properties of this film.

Comparative Example 3 Thyroid with an average particle size of 1.30 μm was mixed into a polymer with a diameter of 0.2 μm.
0 wt % was added, and 100% polyethylene terephthalate was polymerized according to a conventional method.

The intrinsic viscosity [η] of this polymer was 0.66.

Using this polymer, melt extrusion and sheet formation were performed in the same manner as in Example 1 at a resin temperature of 290°C.
An unstretched sheet of 5 μm was obtained. This unstretched sheet was preheated with a metal roll whose surface temperature was adjusted to 84° C., and then stretched 3.80 times in the longitudinal direction while being irradiated with an infrared heater. At this time, the actual temperature of the film in the stretching section was 84°C, and the birefringence index (△n) of the film after stretching was 0.1
It was 20.

Next, this stretched film was introduced into a tenter and stretched 3.94 times in the width direction at 110°C. Further, heat setting was performed at 235° C. for about 10 seconds to obtain a biaxially oriented film with a thickness of 5 μm. Note that during heat setting, a 3% relaxation treatment was performed in the width direction. Table 1 shows the physical properties of this film.

〔Effect of the invention〕

The biaxially oriented polyester film of the present invention has excellent heat resistance, and its strength is about 10 to 40% higher than that of conventionally known PCT films, so it is less likely to elongate during continuous processing. , which is advantageous as an industrial film.

Furthermore, the biaxially oriented polyester film of the present invention has good film forming continuity and can increase the stretching ratio in the longitudinal direction, so it has advantages in terms of productivity, and its industrial value is high.

Applicant: Diafoil Co., Ltd.

Claims (1)

[Claims] (1) A polyester film in which 80 mol% or more of the acid component is terephthalic acid and 90 mol% or more of the glycol component is 1,4-cyclohexanedimethanol, and the film has a density of 1.220 to 1.22%. 250g/cm
^3, the birefringence is 0.010 to 0.040, and the Young's modulus in the longitudinal direction of the film is 310 to 400 kg/m
A biaxially oriented polyester film characterized in that m^2.