JPH0312562B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polypropylene resin for stretched films with excellent electrical properties. Stretched polypropylene films have good tensile strength and rigidity, as well as excellent heat resistance, oil resistance, and electrical properties, so they are widely used in electrical applications such as capacitors and power cables. One measure of electrical properties is breakdown voltage. When voltage is applied to a film, the voltage at which the insulation resistance decreases and a relatively large current can pass through is called breakdown voltage, and is calculated by voltage/film thickness. It is indicated by. Therefore, in order to withstand high voltage, it is better to make the film thicker, but conversely, if the insulator has good performance, the film can be made thinner, which means less material is required, and the product quality is improved. It is also possible to reduce the size. Therefore, it is desired to improve the electrical properties of the film. As a result of various studies, the present inventors discovered that a polypropylene resin having specific physical properties satisfies the conditions for extremely excellent electrical properties when made into a stretched film, particularly a biaxially stretched film. Completed the invention. An object of the present invention is to provide a polypropylene resin for biaxially stretched films with excellent electrical properties. The polypropylene resin of the present invention is produced by polymerizing propylene using a stereoregular catalyst,
A stereoregular polymer of propylene obtained by removing catalyst residue, which has (a) a kerosene soluble content of 2 wt% or less at 30°C, and (b) a kerosene insoluble content of boiling n at 30°C. - The heptane extraction residue is 92wt% or more, and (c) the melt flow index is 10 to 0.01g/
10 min, and (iv) a polypropylene resin for stretched films with improved electrical properties, characterized in that the total ash content is 20 ppm or less. The polypropylene resin specified in the present invention will be described in detail below. Polymerizing propylene using a stereoregular catalyst,
For example, 10 g of the stereoregular propylene polymer obtained by removing the catalyst residue is decomposed into 200 ml of kerosene,
Stir at 130-150℃ to completely dissolve. At this time, it is preferable to add an antioxidant such as 2,6-di-t-butyl-p-cresol in order to obtain correct values. After completely dissolving the
While slowly lowering the temperature to precipitate the polymer,
Keep at ℃ for 5 hours. After this, kerosene soluble parts and kerosene insoluble parts are separated by filtration. Next, the kerosene insoluble part
The procedure of thoroughly dispersing in 200 ml of room temperature n-heptane and separating the washing liquid from the kerosene-insoluble part was repeated twice. The kerosene-soluble part and the washing liquid are put together in a large amount of methanol (more than 10 times the amount of kerosene) to precipitate the polymer. The obtained polymer is dried at 80°C and 40mmHg and weighed. This is called kerosene soluble polymer. The kerosene-insoluble portion separated from the washing liquid is extracted with n-heptane (boiling n-heptane) at 98°C for 10 hours using a Soxhlet extractor, and the extracted portion is dissolved in a large amount of methanol (more than 10 times the amount of kerosene). The polymer is precipitated, and after excessive separation, it is dried and weighed in the same manner as above. This is called boiling heptane extracted polymer. The extraction residue is similarly dried and weighed. This is called boiling heptane extraction residue polymer. As mentioned above, the weight of the kerosene soluble polymer, boiling heptane extracted polymer, and boiling heptane extracted residual polymer separated into three parts is in the range of 99.5 to 100.5 wt% compared to the charged polymer. After checking, determine the proportion of each part as follows. Kerosene soluble content at 30℃ = Kerosene soluble polymer weight / Charged polymer weight x 100 Boiling n-heptane extraction residue = Boiling heptane extraction residue polymer weight / (Prepared polymer weight) - (Kerosene soluble polymer weight) x 100 Above The kerosene soluble content at 30°C is 2wt% or less, preferably 1wt% or less, determined as follows,
Moreover, the boiling n-heptane extraction residue is over 92wt%.
It is an essential condition for the resin of the present invention that the content is preferably 93 wt% or more (and less than 98 wt%). The value calculated by directly extracting the powder obtained by polymerization without using the above-mentioned method for determining the boiling n-heptane extraction residue does not necessarily correlate with the electrical properties of the resin, and the present invention It is not suitable for specifying the resin. (a) In the limitations of the present invention, the kerosene soluble content at 30℃ is
If it is more than 2wt%, not only will the electrical properties be bad, but the Young's modulus and tensile strength of the film will be insufficient, making it unfavorable for stretched films.Furthermore, when the film is made, oil-like polymers will rise to the surface and the appearance will deteriorate. Not only is this defective, but the films also stick together, which makes it difficult to pull out the film after the film is rolled up, which is undesirable. (b) If the boiling n-heptane extraction residue is less than 92wt%, the electrical properties, especially the breakdown voltage, are low and undesirable; if it is more than 98wt%,
When made into a film, the impact resistance is greatly reduced, which is undesirable. Also, (c) melt flow index (JIS
K-7210) is 10 to 0.01 as it is necessary to form a film.
is preferably in the range of 8 to 0.1. Regarding additives such as stabilizers, it is of course preferable that the ash content is low, especially in the resin referred to in the present invention, and in particular, it is desirable to keep this value below 20 ppm in order to increase the electrical properties, especially the breakdown voltage. preferable. The polypropylene resin of the present invention can be produced by various methods, but usually it is polymerized using a catalyst that gives highly stereoregular polypropylene, and then the catalyst residue is removed very strictly, and then n-
It is obtained by strictly removing heptane soluble components, but using a highly stereoregular catalyst, the removal of catalyst residue and n-heptane soluble components are performed under extremely well-controlled conditions. There is a need. Examples will be shown below and more specifically explained. The stereoregular propylene polymer obtained by polymerizing propylene using the stereoregular catalyst used in the present invention and removing the catalyst residue is, for example,
It was obtained according to the following reference example according to Publication No. 56-90806. Reference example Titanium tetrachloride was reduced and ground with aluminum in the presence of aluminum chloride in a vibrating mill with an internal volume of 600 ml containing 80 steel balls with a diameter of _{12 mm} . 30 g of a eutectic of titanium chloride and aluminum trichloride, 1.5 g of diphenyl ether, and 0.6 g of titanium tetrachloride were added, and the mixture was pulverized at room temperature under a nitrogen atmosphere for 14 hours. The contents were separated from the steel balls under a nitrogen atmosphere to obtain a titanium trichloride composition. 20g of this titanium trichloride composition was mixed with n-heptane.
After stirring for 30 minutes at 80° C. using 200 ml, n-heptane was removed by decantation. next,
100 ml of n-heptane was added to this to prepare a titanium trichloride catalyst slurry. n-heptane in an autoclave with an internal volume of 500
150, add 0.5 kg of titanium trichloride catalyst obtained by repeating the above operation, 0.9 kg of diethyl aluminum chloride, and 0.05 di-n-butyl ether,
At 70°C, propylene was introduced and polymerization was carried out for 5 hours at a total pressure of 5 kg/cm ² gauge and 7 vol% hydrogen. After the polymerization reaction, 100% of methanol was added and heated at 100°C for 1 hour, then 50% of water was added, stirred at 100°C, left to stand, and the aqueous layer was removed. The slurry was further washed 5 times at 90° C. with 100 g of water. Then n-heptane 100
Add and heat to 80℃, filter at 80℃ and remove the powder.
Wash with n-heptane 100 °C at 80 °C to remove catalyst residue,
Polypropylene from which atactic polypropylene was sufficiently removed was obtained. Example 1 Using the polypropylene obtained in Reference Example (i), the n-heptane extraction residue (1) was extracted by immediately extracting the powder with boiling n-heptane for 10 hours using a Soxhlet extractor without treating the powder with kerosene. Calculated as weight of residue/weight before extraction x 100, (ii) n-heptane extraction residue (2), as described above, at 30°C
This is the result of extraction after removing the kerosene soluble content (iii) The breakdown voltage is obtained by adding 0.1% by weight of a phenolic stabilizer to polypropylene and melt extruding at 280°C using a T-die extractor with a screw of 65 mm in diameter. Then, after rapidly cooling with a cooling roll at 40°C to obtain a sheet with a thickness of 1 mm, it was heated to 140 to 160°C.
Stretched 5 times in the longitudinal direction and 6 times in the transverse direction,
A biaxially stretched film with a thickness of about 40 μm was obtained by heat treatment at 150°C. The dielectric breakdown voltage of this product was measured according to the method of ASTM=149 and expressed in units of V/μ. Example 2 Polypropylene polymerized according to Reference Example was used and treated in the same manner as in Example 1, except that the hydrogen concentration during polymerization was 8 vol %. Example 3 The same procedure as Example 2 was carried out except that the polymerization temperature was 65°C. Comparative Example 1 The amount of methanol was 80, the heating was 85°C, the water washing temperature was 85°C, the sample was filtered at 70°C without adding n-heptane, and it was dried without washing with n-heptane. The same treatment as in Example 1 was carried out using polypropylene polymerized according to the reference example. Comparative Example 2 The same procedure as Comparative Example 1 was carried out except that the hydrogen concentration during polymerization was 8 vol%. Comparative Example 3 The same procedure as Comparative Example 2 was carried out except that the polymerization temperature was 65°C. The results obtained in Examples and Comparative Examples are shown in tables and drawings. Note that the ash content of the polymer shown in the examples is 20 ppm or less. Boiling n-heptane extraction residue
(2) and the breakdown voltage are clearly correlated (curve 1), and it can be seen that the breakdown voltage sharply increases at a bending point near 92wt% of boiling n-heptane extraction residue, that is, at 93% or more. On the other hand, the boiling n-heptane extraction residue (1) does not correlate with the breakdown voltage (curve 2), and the limit is not clear. The kerosene soluble content at 30°C (curve 3) is shown in the figure, but there is no significant difference within the above range. The polymers of Examples and Comparative Examples whose physical properties are shown in the table are all manufactured by the method described in the text, and if the physical properties of the polymer do not satisfy the values specified in the present invention. It is clear that the physical properties of the film do not satisfy the desired electrical properties.

[Front] Out

[Brief explanation of the drawing]

The drawings are examples (including those not shown in the table)
Relationship between physical properties of polypropylene resin used in polypropylene resin (breakdown voltage/boiling n-heptane extraction residue (2), breakdown voltage/boiling n-heptane extraction residue (1), 30℃ kerosene soluble content/boiling n -Heptane extraction residue (2)).

Claims (1)

[Scope of Claims] 1. A stereoregular polymer of propylene obtained by polymerizing propylene using a stereoregular catalyst and removing the catalyst residue, which polymer is (a) compatible with kerosene at 30°C. The soluble content is 2wt% or less, (b) the residue after boiling n-heptane extraction of kerosene insolubles at 30°C is 92wt% or more, and (c) the melt flow index is 10 to 0.01g/
10 min, and (iv) a polypropylene resin for stretched films with improved electrical properties, characterized in that the total ash content is 20 ppm or less.