JPS6261202A - Polystyrene film for electric insulation - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to improvements in polystyrene films used as insulators or dielectrics in capacitors, cables, transformers, etc.

<Prior art> Traditionally, oriented polystyrene films suffer from dielectric loss (ta
Since its dielectric properties (nδ) are extremely small at 0.02% and its frequency dependence is small, it is used as a dielectric material in capacitors for communication equipment, which particularly requires precision. However, because the raw materials used are atactic and do not crystallize.

Thermal dimensional stability is poor, and when the temperature exceeds 80°0, extremely large thermal contraction occurs. For this reason, the temperature conditions for use as a capacitor are limited, and if you try to manufacture a metal vapor deposition type capacitor, the film may shrink significantly during metal vapor deposition, deform the film, or cause cracks in the vapor deposited metal film, making it difficult to put it into practical use. The current situation was that it could not be provided.

In addition, isotactic polystyrene has been studied academically and technically since ancient times (for example, Journal of the Japan Society of Fibers and Textiles Vol. 23, No. 1, 1967, PlB-p 24. ), l, as a drawback of isotactic polystyrene.

(1) The crystallization speed is extremely slow, and a long annealing time is required for crystallization, which causes an increase in cost.

(2) When an amorphous oriented film is crystallized, it becomes extremely brittle.

There were other problems.

<Problems to be Solved by the Invention> A. The object of the present invention is to provide a polystyrene film for electrical insulation which has good heat resistance and U-solvent property using crystalline polystyrene film forming technology.

Means for Solving All Problems> In order to solve the above problems, the present invention has the following configuration: an oriented film mainly made of isotactic polystyrene, the film having an isotactic index of 85 or more. , the degree of crystallinity is 65 or more and 55 or less,
It is characterized by being a polystyrene film for electrical insulation having a plane orientation of 6 x 10 to +5 to 12 x 10 and an internal haze of 2 or less.

In the present invention, the resin mainly composed of isotactic polystyrene is an isotactic polystyrene homopolymer or a blend or copolymer with other resins, and the resin to be blended is α-polyolefin,
Polyphenylene ether, the monomer to be copolymerized is
Examples include α-methylstyrene, maleic anhydride, etc.
In order to improve solvent resistance, the weight fraction of isotactic polystyrene is preferably 90% or more, preferably 95% or more. Furthermore, the isotactic index (hereinafter abbreviated as II) of the resin is 8.
It is necessary that it is 5% or more, and preferably 95% or more. If II is below the range 1, the degree of crystallinity will be low even if highly oriented, the thermal dimensional stability will be poor, and high temperature (
Particularly at temperatures below 80'o), large thermal contraction occurs, causing dielectric breakdown.

Further, the crystallinity of the film of the present invention needs to be 35% or more and 55% or less, and preferably 40% or more and 55% or less. If the crystallinity is less than the above range, the thermal dimensional stability will be poor. On the other hand, if it is larger than the above range, the dimensional stability will be good, but the film will become brittle, prone to cracks, etc., and the electrical properties will deteriorate.

Furthermore, it is preferable that the intrinsic viscosity of the film of the present invention is c or less (abbreviated as [η]) of 1 or more and 6 or less.

More preferably, it is 1.2 or more and 24 or less, [η]
When it is within the above range, not only film forming properties such as extrusion properties and stretchability will be good, and a uniform film will be obtained, but also mechanical properties will be good.

Furthermore, there are two melting peaks observed by DEC of the film of the present invention, near 220° 0 and near 200°C, and the ratio of these peak areas r = A20o/A22o (A2
oo, A2□. (peak areas at 200° C. and 220° C., respectively) are preferably 0.05 or more and 1'5 or less because thermal dimensional stability is good.

The film of the present invention needs to be at least uniaxially oriented in order to have good biaxial mechanical properties, and preferably biaxially oriented.

At this time, when the refractive index in the longitudinal direction of the film is 'feNX* and the refractive index in the thickness direction of the film is N2, plane orientation (hereinafter abbreviated as Δn.Δn-[Nx + Nx]/2
-Nz) is 3 x 10-5 or more 12 x 10-3
It must be less than or equal to, and greater than or equal to 4x1()-',
It is preferably 10 x 10-' or less. If the plane orientation is smaller than the above range, the film will not be brittle and the dielectric breakdown voltage will decrease.

On the other hand, if the plane orientation is larger than the above range, the film is likely to have folds, resulting in cracks and a decrease in dielectric breakdown voltage.

In addition, the internal haze of the film of the present invention must be 2% or less, preferably 1% or less.The internal haze is related to light scattering at voids or crystal boundaries in the film. Especially in the latter case), the more these are present in the film or the crystal size is larger, the larger the internal haze will be. The internal haze is within the above range.

Decrease in mechanical properties due to crystallization can be reduced, and electrical properties such as dielectric breakdown voltage can also be improved.

Furthermore, an organic or inorganic crystal nucleating agent may be added to the film of the present invention. When a nucleating agent is added, the crystals are finely dispersed9.
This is preferable because it further improves the mechanical properties, but on the other hand, it causes deterioration of the electrical properties, so it is preferable that the amount added is 1 part by weight or less. Further, in the film of the present invention, a heat stabilizer, an antioxidant, etc. may be added to the extent that the electrical properties are not deteriorated.

Furthermore, the ash content contained in the film of the present invention is 1[10pp].
m or less, preferably 60 ppm or less, the dielectric breakdown voltage is high and it is particularly good as a capacitor film.

Next, a method for manufacturing the polystyrene film of the present invention will be described.

First, intactic polystyrene is obtained by dissolving styrene monomer in an aromatic hydrocarbon and polymerizing it using a Ziegler-Natsuta catalyst.The polymer is obtained as a precipitate by adding a mixture of methanol and hydrochloric acid to the polymerization system. The precipitate is thoroughly washed with methanol to remove the catalyst.

Furthermore, in order to remove amorphous components (atactic components), extraction such as methyl ethyl ketone is performed to remove the necessary 1. Let I be. The raw material powder thus obtained is melt-extruded using an extruder and extruded into gut-shaped pellets.

Next, the isotactic polystyrene pellet thus obtained is melt-extruded into a sheet form through a T-shaped die using an extruder at a temperature of 250° C. or more and 520° C. or less, and is tightly attached to a cooling drum and cooled and solidified. Alternatively, a circular die may be used for cooling and solidifying with a cooling mandrel. At this time, it is preferable to maintain the temperature of the cast film at 80°C or higher, preferably 90°C or lower, since this will prevent the film from cracking.
C or higher and 160″C or lower, preferably 115°C or higher and 15
゛0'.

2 times or more and 10 times or less in at least one direction.

Preferably, the stretching is 2.5 times or more and 6 times or less. If the stretching temperature is lower than the above range, cracks will occur during stretching.

It cannot be stretched more than 1.5 times. Moreover, if it exceeds the above range, not only will effective orientation not be obtained due to draw stretching, but in some cases crystallization will progress and stretching will not be possible. The stretching method may be -axial stretching, simultaneous biaxial stretching, or sequential biaxial stretching, but in order to improve film properties, a biaxial stretching method in which the film is oriented biaxially is preferred. Further, if the stretching ratio is 2 times or less, preferably 25 times or less, sufficient planar orientation cannot be obtained and the film after heat treatment becomes brittle and easily cracks.

Furthermore, if the stretching ratio is 10 times or more, preferably 6 times or more, the film tends to crack in the stretching direction, resulting in poor mechanical properties.

The stretched film thus obtained is subsequently stretched at a temperature higher than the stretching temperature and lower than 200°C, preferably higher than 160'a19
At 0°C or less, in at least one direction of the stretching direction,
Heat setting is performed while stretching to 1 inch or more and 20% or less. If the heat setting temperature is lower than the stretching temperature, preferably lower than 160°C, the crystallinity of the film will hardly increase and the thermal dimensional stability will deteriorate.

On the other hand, if the heat setting temperature exceeds 2D D'o, preferably higher than 190°C, orientation relaxation will occur due to the activation of the movement of the nine molecular chains compared to the crystallization rate of the stretched film. However, the film becomes equivalent to that of an unstretched film, resulting in poor mechanical properties, and the film especially melts during heat setting. Furthermore, if the stretching ratio during heat setting is smaller than the above range, the orientation relaxation will be large and the crystal soybean size will also become large, resulting in high internal haze and deterioration of mechanical properties. In addition, if it is larger than the above range, the film is likely to tear,
It is not possible to form a stable film, and the longer the heat setting time, the more crystallization progresses and stable quality can be obtained.9 In the present invention, the degree of crystallinity is saturated in about 10 minutes under the above conditions, so it is possible to form a film within 10 minutes. is sufficient.

In addition, as a method of heat fixation, after performing the first stage heat treatment in a two-step method, * at a temperature between the lowest peak temperature (Tm) of the crystal melting point of DSC and the first stage heat treatment temperature,
If the second stage heat treatment is performed while the relaxation is less than 210%, the strain in the film is removed and the thermal dimensional stability becomes even better.

<Effects of the Invention> The present invention provides a polystyrene film with I and I of 85 or more, crystallinity of 35% or more and J255% or less, and diagonal orientation of 5 x 10-3 or more and 12 x 10-' or less. By controlling the internal haze to 2% or less, the following effects can be obtained.

(1) Excellent thermal dimensional stability and solvent resistance.

(2) Small change in crystallinity over time, cracks,
No dimensional changes occur.

(3) The drop in dielectric breakdown voltage at high temperatures is small.

It is therefore suitable for electrical insulation applications such as capacitors, cables, and transformers, and is particularly suitable as an insulating film for capacitors that requires low tan δ and high dielectric breakdown voltage.

Here, the terms and measurement methods used in the present invention will be summarized and explained below.

(1) II: Sample W (mg) was placed in a Soxhlet extractor, extracted with boiling methyl ethyl ketone for 6 hours, and then thoroughly dried, where W' (mg) is the weight, and II is determined by the following formula.

II (%) - 100xW'/W (2) Intrinsic viscosity ([η]): Measured in tetralin at 135°C according to ASTM D-1601. Unit dj/g (3) Crystallinity (Xc): The sample density d8 is measured according to ASTM-D 1505, and the amorphous density d of isotactic polystyrene is
A, crystal density d. dA = 1.052 (g/meter 3) doe = 1.127 (g/cm ), respectively.

is calculated.

(4) DSC melting peak area ratio (F): 5 mg of DSC-'f manufactured by PerkinElmer (Test I) was placed in a mold, and the atmosphere was replaced with nitrogen. Next, when the temperature is raised at a heating rate of 20'O/min, the crystalline melting point of isotactic polystyrene reaches an endothermic peak P2 of around 200'o. . and 220
It is observed as an endothermic peak P220 near 'o. The peak area ratio is calculated as A200/A2/[+ as the ratio of the peak area A2oo of 2[10 and the peak area A2□ of P220 measured from the baseline.

(5) Planar orientation (Δ0): The refractive index in the longitudinal direction of the film (NY9) and the refractive index in the width direction (NX
) # and the refractive index (N2) in the thickness direction were measured.

Determined as Δn (Nx + Ny K Nz). Note that sodium D line is used as the light source during measurement, and methylene iodide is used as the mounting liquid.

(6) Heat shrinkage rate: From film, length 200nxn.

Cut a sample with a width of 10 mm (the direction in which the heat shrinkage rate is measured is the length direction). The sample was kept in a hot air circulation oven at 120°C for 15 minutes, then taken out to room temperature.
Measure its length. If the length is f L (mm), the thermal shrinkage rate can be determined by the following formula.

Thermal shrinkage rate (%) - 10Qx (200-L)/200 (force) Breakdown voltage (BDV): Measured at 20°C according to ASTM-D-149.

(8) If the residual oil film dissolves or cracks occur when it is immersed in vegetable oil for condensers at 80°C for 24 hours, it will be ranked C.
1 If there is almost no dissolution, the sample weight before oil immersion is W +
(g) eWhen the sample weight after oil immersion is W2 (g), weight increase ΔW (%) = 100x defined by the following formula
'- is 0% or more and 6 inches or less is ranked A, and all cases that are thicker than 6% are ranked B. Rank A for capacitors
can be used, but cannot be used in ranks B and C.

(9) Ash content (Ash) was measured according to JIS-C-2560.

(10) Internal Haze According to the ASTM D-1003-52 method, the film is immersed in liquid halafine and the film haze is measured. The standard thickness of the film was 12 μm, and the film haze different from this thickness was converted to 12 tt/thick umbrella and was defined as film haze.

<Example> Next, the present invention will be explained based on examples.

Example 1 Styrene monomer was dissolved in toluene and titanium tetrachloride was dissolved in toluene.
triethylaluminum as a catalyst.

Polymerization was carried out. After the polymerization, a mixed solution of methanol and hydrochloric acid was added to the polymerization solution to obtain a precipitate of one polymer. The polymer powder thus obtained was washed with methanol.

It was further washed with acetone to obtain isotactic polystyrene powder.

The powder was melt-extruded into pellets at 300° C. using a twin-screw extruder.

The isotactic polystyrene pellets thus obtained had an isotactic index of 11-96.
Intrinsic viscosity [η] = 2.0 d ll g * Ash content 80
It was ppm.

Next, the pellet was extruded into a sheet using an extruder at 290.degree. C., adhered to a drum at 95.degree. C. using air pressure, and solidified by cooling. Next, the sheet was heated at 160°C for 3 times in the longitudinal direction.
．． Stretch it three times, then feed it into a stenter,
The film was stretched 6.0 times in the transverse direction at 140° C., and then heat-set at 175° C. for 60 seconds while being stretched by 3 times in the width direction. As a result, the film thickness was 12 μm, the crystallinity was 40%,
A biaxially stretched film with a melting peak area ratio r-0, an 11-plane orientation of 6×10, and an internal haze D of 5% was obtained. The heat shrinkage rate of the film is 1.0% in the longitudinal direction (hereinafter abbreviated as MD)9
It has a small BDV of 0.5% in the width direction (hereinafter abbreviated as TD) and is suitable for electrical insulation with a BDV of 360 V/)t.
It was found that the oil resistance was also rank A, and that it could be used for oil-immersed electrical insulation. The main conditions are shown in Table 1.

The film characteristics and evaluation results are summarized.

Comparative Example 1 Stretching was performed in the same manner as in Example 1, and heat treatment was performed at 100° C. for 90 seconds while stretching 2 inches in the width direction. The crystallinity of the film is as low as 5%, and it is F-0, and the heat shrinkage rate is high (and the BDV is low. Ta.

See Table 1.

Example 2 Using the same raw materials as in Example 1, a similar unstretched film was cast, and then the unstretched film was fed into a simultaneous biaxial stretching stenter to undergo simultaneous biaxial stretching of 3×3 times at 130′a. Do it, then MD.

Heat treatment was performed at 180°C for 60 seconds while stretching 2% in both TD directions. As shown in Table 1, the properties of the film thus obtained are that the degree of crystallinity is 40, the plane orientation is 8, and the internal haze is 0. Filtering staff, heat shrinkage is 2 for both MD and TD.
．． It was small with 0 staff. Also, the dielectric breakdown voltage is 380kv/
It was found that it was extremely high in mm, making it suitable for use in capacitors. See Table 1 Example 6 The stretching process was carried out in the same manner as in Example 1, and heat setting was carried out at 175
After 30 seconds at 20% tension in TD at 195°C, heat setting was carried out at 195°C for 30 seconds at 0°. The crystallinity of the film was measured and was 45%.
In addition, the heat shrinkage rate was good at 0 in both MD and TD, and the p and BDV were high at 380 V/μ, making it suitable for electrical insulation.See Table 1.

Example 4 pxI=90% [η)-2 by the same polymerization method as Example 1
, 5 dl/g of isotactic polystyrene pellets were obtained.

The pellet 'i was extruded into a sheet using an extruder at 500°C, and cooled and solidified in close contact with air pressure on a cooling drum at 95°C. Next, the sheet is M
It was stretched 6 times in both D and TD directions at 160°C, and heat-set at 175°C for 60 seconds while elongating by 2%. As a result, a film having a thickness of 10 μm was obtained. The properties of the film are as shown in Table 1, and it had good properties for electrical insulation, and was also excellent in oil resistance, ranking A.

Comparative Examples 2 and 3 Commercially available atactic polystyrene pellets (II=20
%, [η] = 2.0 (d7/3)), extrusion, stretching, and heat setting were performed in the same manner as in Example 4, but the film melted during heat setting and could not be formed (Comparative Example 2), a stretched film was obtained without heat setting.

The film has a crystallinity of 0% and a heat shrinkage rate of 3.
Not only is it large at 0%, but its BDV is low and oil resistance is rank C.
It was bad. See Table 1.

Example 5 The isotactic polystyrene obtained by the polymerization method of Example 1 was further increased to 11-9 by a solvent extraction method.
8, [η] x 2.2 d 17g.

After melt extrusion at 300°0, cooling and solidifying on a cooling drum, it was stretched 35 times in the MD at 130°C, then stretched 3°0 times at 140°C in a stenter, and then 175 A biaxially oriented film was obtained by heat treatment for 60 seconds at a stretching ratio of 5%.

The film has a high crystallinity of 48% and a heat shrinkage rate of 0%.
The BDV was also good at 390 V/μ.

See Table 1.

Example 6 An unstretched film was produced in the same manner as in Example 5, and this time the film was stretched 5 times in the MD direction at 140°C.
Heat setting was carried out for 60 seconds at 75° C.9 and a stretching ratio of 0%.

The uniaxially stretched film thus obtained is easier to avoid in the MD force direction than the biaxially stretched film, but has a crystallinity of 5.
It has a high coefficient of 0 and a heat shrinkage rate of MD 2.5%.

'['D-1,0%! l, BD V 350V/
μ was also high, and the oil resistance was also good with rank A. Table 1
reference.

Comparative Example 4' An unstretched film was obtained in the same manner as in Example 5, and this time heat setting was performed at 175'a for 1.20 seconds without stretching.

The crystallinity of the film thus obtained was as low as 30%.
The internal haze was 5% and the film was extremely brittle. Also, the BDV is low at 200V/lz.

Even in the 1ij oil test, it swelled greatly in oil and was ranked C. See Table 1.

Example 7 and Comparative Example 5 Foil-wrapped capacitors Example 7 and Comparative Example 5 were prepared using the biaxially stretched films obtained in Example 1 and Comparative Example 1 as dielectrics and using A7 foil as electrodes.

Note that the capacitance of each capacitor was set to 0.01 μF.

Example 7. Twenty capacitors of Comparative Example 5 were each prepared, and a life test was conducted at 80° C. by applying an AC voltage (5 DHZ) that was 1.5 times the corona discharge starting voltage.

The results are shown in the figure. The horizontal axis shows the electrification time (hr), and the vertical axis shows the number of capacitors that did not break down as the survival rate (ch). As is clear from the figure, in Comparative Example 5, about half of the capacitors were destroyed immediately after the start of energization, but in Example 7,
It can be seen that there is very little damage in the capacitor, and it has stable performance as a capacitor.

[Brief explanation of the drawing]

The figure shows Example 7. 3 is a characteristic curve showing the survival rate of the capacitor prepared in Comparative Example 5.

Claims (1)

[Claims] An oriented film mainly made of isotactic polystyrene, the film having an isotactic index of 85% or more and a crystallinity of 35% or more and 55% or less,
A polystyrene film for electrical insulation having a plane orientation of 3 x 10^-^3 or more and 12 x 10^-^3 or less, and an internal haze of 2% or less.