JPS6255524B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing polypropylene having excellent rigidity, heat resistance, and stretchability or extensibility. When polypropylene is stretched uniaxially or biaxially, its inherent mechanical strength is doubled, making it an important field for applications that require a stretching process, such as tapes, yarns, fibers, and films. It is becoming. In particular, it is well known that biaxially stretched film has been expanded to replace cellophane as a packaging material because it has excellent transparency, gloss, moisture resistance, heat resistance, cold resistance, oil resistance, electrical insulation, etc. It is also well known that it has been used as an insulating material for capacitor power cables and other products due to its excellent electrical properties. However, polypropylene is inferior to polyethylene terephthalate in terms of heat resistance and rigidity, so there are fields where its excellent moisture resistance and electrical insulation properties (particularly low dielectric loss) cannot be utilized, and polypropylene with excellent heat resistance and rigidity is in demand. It had been. In order to improve the heat resistance and stiffness of polypropylene, attempts have been made to improve the isotactic index, that is, to increase the proportion of the portion insoluble in boiling heptane, but the degree of improvement in heat resistance and stiffness achieved by such methods is relatively small. It was insufficient. Another method proposed is to mix a small amount of a nucleating agent such as a metal salt of a benzoic acid derivative with polypropylene (Japanese Patent Publication No. 14062/1983), but since such a nucleating agent does not dissolve in polypropylene, ,
There were drawbacks such as holes being easily formed during film formation and stretching, the transparency of the film being reduced, and the electrical properties of polypropylene being impaired. The present inventors have previously proposed a stretched polypropylene film using a particularly limited range of polypropylene (Japanese Patent Application No. 155,973/1982). However, when the above polypropylene is used, problems such as film cracking are likely to occur during stretching at a high magnification, and it is not possible to stretch stably, that is, the stretching ratio cannot be sufficiently increased. It was discovered that the drawback was that the excellent characteristics of the material could not be brought out to the fullest. The inventors of the present invention have conducted various studies to overcome these drawbacks, and have found that by decomposing and modifying polypropylene with a specific structure at a degree of decomposition within a specific range, heat resistance, rigidity, and stretchability can be improved. It was discovered that excellent polypropylene could be obtained, leading to the present invention. Furthermore, the polypropylene of the present invention has excellent oil resistance and rigidity, and has good spreadability during lamination. That is, the present invention is a method for modifying polypropylene, which is characterized in that polypropylene whose isotactic pentad fraction in the boiling heptane insoluble portion is 0.955 or more is decomposed within a degree of decomposition of 1.2 to 7.0. The polypropylene used in the present invention has an isotactic pentad fraction of the boiling heptane insoluble portion of 0.955 or more. If the isotactic pentad fraction is less than 0.955, it will be inferior in terms of heat resistance, rigidity, etc., like conventionally commercially available polypropylene. The preferred isotactic pentad fraction is 0.960 or more, more preferably 0.965 or more. The content of the boiling heptane soluble portion of the polypropylene used in the present invention is not particularly limited, but is preferably 2.0 to 9.0% by weight, more preferably 3.5 to 9.0% by weight.
It is 8.0% by weight. The content of the polymer soluble in xylene at 20°C is also not particularly limited, but is preferably 0.5 to 5.0% by weight, more preferably 1 to 3.0% by weight. When the polypropylene obtained by the present invention is used as an insulating material in oil-filled electrical equipment such as OF cables and OF condensers, the intrinsic viscosity of the polypropylene that is soluble in xylene at 20°C is 1.0 dl/g or less, In particular, it is preferably 0.5 dl/g or less. In the present invention, the isotactic pentad fraction of the boiling heptane insoluble portion, the content of the boiling heptane soluble portion, and the limiting viscosity of the polymer soluble in xylene at 20° C. are determined as follows. After completely dissolving 5 g of polypropylene in 500 ml of boiling xylene, the temperature was lowered to 20°C and left for 4 hours.
Thereafter, this is filtered to separate the xylene insoluble portion at 20°C. The filtrate is concentrated to dryness to evaporate the xylene, and further dried under reduced pressure at 60°C to obtain a polymer soluble in xylene at 20°C. The intrinsic viscosity measured in tetralin at 135°C is the intrinsic viscosity of a polymer soluble in xylene at 20°C. The xylene insoluble portion at 20° C. is dried and then Soxhlet extracted with boiling n-heptane for 8 hours. This extraction residue is called the boiling heptane insoluble part, and the value obtained by subtracting this dry weight from the weight of the prepared sample (5 g) divided by the weight of the prepared sample, expressed as a percentage, is the content of the boiling heptane soluble part. be. What is isotactic pentad fraction?A.
Macromolecules 6 , 925 by Zambell et al.
(1973), i.e. 13 _C -
It is an isotactic chain of pentad units in a polypropylene molecular chain measured using NMR, in other words, it is the fraction of propylene monomer units at the center of a chain in which five consecutive propylene monomer units are meso-bonded. However, regarding the attribution of NMR absorption peaks, the
Macromolecules 8 , 687 (1975). Specifically, the isotactic pentad fraction is measured as the area fraction of the mmmm peak among the total absorption peaks in the methyl carbon region of the 13 _C -NMR spectrum. By this method UK NATIONAL
NPL standard material of PHYSICAL LABORATORY
CRMNo.M19―14Poly propylene PP/MWD/2
When the isotactic pentad fraction was measured, it was 0.944. Polypropylene having an isotactic pentad fraction of 0.955 or more in the boiling heptane insoluble portion used in the present invention is disclosed in JP-A-53-33289 and JP-A-54.
- A method for decomposing polypropylene with an isotactic pentad fraction of 0.955 or more in the boiling heptane insoluble portion, which can be easily obtained by polymerizing propylene under appropriate conditions in the method disclosed in Publication No. 11985, is degree 1.2~7.0
Any decomposition method used for conventional polypropylene modification may be used as long as it can be used to modify the polypropylene. , (3) thermal decomposition method, and (4) radiation irradiation method for decomposition. These can also be used together. In any decomposition, the presence of air tends to cause coloring, so it is preferable to carry out the decomposition in an inert gas atmosphere. The decomposition methods (1) to (4) above will be described in detail below. (1) Peroxide decomposition This is a method in which a compound that can be thermally decomposed to generate radicals is mixed with the polypropylene and heated. Although it can be carried out in a solvent, industrially preferred is a method in which decomposition is carried out in an extruder in the substantial absence of a solvent. In order to improve mixing with the radical generator, the polypropylene is preferably in powder form, and is preferably in the form of polymer particles obtained by slurry polymerization or gas phase polymerization. The mixture may be stirred for several minutes using a Henschel mixer or the like. As the radical generator, known peroxides, diazo compounds, etc. can be used, but in the above-mentioned method of decomposing in an extruder, one having a half-life of about 2.0 to 10.0 hours at 130°C is preferable.
Examples of such radical generators include the following compounds. Radical generator: 2,5-dimethyl 2,5-
di(tertiarybutylperoxy)hexane,
Particularly preferred are 2,5-dimethyl 2,5-di(tert-butyl peroxy)hexyne-3, dicumyl peroxide, di-tert-butyl peroxide, and tert-butyl cumyl peroxide. They are dimethyl 2,5-di(tertiary butylperoxy)hexane and 2,5-dimethyl 2,5-di(tertiary butylperoxy)hexane-3. The mixing ratio of these radical generators varies depending on the type, decomposition temperature, decomposition time, other mixed additives, and especially the concentration of antioxidants that act as radical scavengers, but in general, polypropylene The amount is 0.0005 to 0.5% by weight. When cracking in an extruder, the set temperature of the extruder should be varied depending on the melt flow index of the polypropylene, but generally
The temperature is 180-280℃. The residence time of polypropylene in the extruder is generally 0.5 to 5 minutes. (2) Kneading and decomposition This is a method of decomposing polypropylene by applying high shear force to it. Decomposition is generally carried out in the molten state by applying high shear forces using multiple screws or rotors. Specifically, Banbury mixer, CIM extruder, ZSK extruder,
A kneader such as an FCM extruder can be used. The set temperature and residence time of the kneading machine vary depending on the type of kneading machine, the type and concentration of other additives mixed, but generally each is 180~
280°C for about 0.5 to 5 minutes. (3) Thermal decomposition Propylene polymers can be decomposed simply by heating, but this generally requires a high temperature of 300°C or higher, and is not necessarily a better method than other methods. Industrially, it can be carried out in a granulator. (4) Radiolysis This is a method of decomposing polypropylene by irradiating it with high-energy radiation. While other methods generally require high temperatures, this method can be performed at low temperatures. Of course, it may be done at high temperature. Preferred decomposition methods in the present invention are peroxide decomposition and kneading decomposition. The degree of decomposition (α) is calculated from the melt index MIO of polypropylene before decomposition and the melt index MI of polypropylene after decomposition using the following formula. α=MI/MIo Melt index is measured according to JISK6758. In order to prevent decomposition during the melt index measurement, 0.2% by weight of 2,6-dithyabutyl-4-methylphenol and 0.1% by weight of calcium distearate are added to the sample. In the present invention, the degree of resolution ranges from 1.2 to 7.0. If the degree of decomposition is smaller than this, the stretchability or extensibility will not be improved, while if the degree of decomposition is larger than this, the mechanical strength of the obtained polypropylene will be lowered or the stretching characteristics will be deteriorated. The preferred range of decomposition degree is 1.2 to 5.0, more preferably 1.5 to 3.0. The melt index of the decomposed polypropylene of the present invention is from 0.5 to 100, and preferably from about 0.5 to 10, particularly from about 1 to 5, for biaxially oriented polypropylene films. Further, it is preferably 0.5 to 15 for yarn, and 20 to 60 for lamination. Therefore, the melt index of the polypropylene subjected to decomposition may be appropriately selected so that the melt index of the polypropylene after decomposition falls within the above range. The present invention will be described in more detail below with reference to Examples, but the present invention is not limited thereto. Physical properties etc. in the following examples were measured by the following methods. Intrinsic viscosity: Measured with tetralin solution at 135℃ Young's modulus: ASTMD882 Swelling degree: Weight increase rate after 40 hours in xylene at 100℃ Example 1 (1) Preparation of catalyst (1) Preparation method 1 (reduction formation Preparation of products) After replacing the 200 reaction vessels with argon,
Add 40% dry hexane and 10% titanium tetrachloride, keep this solution at -5℃ and add 30% dry hexane.
, ethylaluminum sesquichloride
A solution consisting of 23.2 was prepared at a temperature of -3°C.
The dropwise addition was carried out under the following conditions. Stirring was then continued at the same temperature for 2 hours. After the reaction, the resulting reduced product was allowed to stand still and was subjected to solid-liquid separation at 0°C, and washed twice with 40 kg of hexane to obtain 16 kg of reduced product. (2) Preparation method The reduction product obtained by the preparation method was slurried in n-decalin, and the slurry concentration was adjusted to 0.2 g/
It was heat treated at 140°C for 2 hours as cc. After the reaction, the supernatant was extracted and washed twice with 40 ml of hexane to obtain a titanium trichloride composition (A). (3) Preparation method 11 kg of titanium trichloride composition (A) prepared according to the preparation method was slurried in 55% toluene,
Iodine and isoamyl ether were added so that the molar ratio of titanium trichloride composition (A)/iodine/diisoamyl ether = 1/0.1/1.0, and 80
Titanium trichloride solid catalyst (B) was obtained by reacting at ℃ for 1 hour. (2) Production of polypropylene After fully purging an autoclave with an internal volume of 200 with a stirrer with propylene, 2.6 g of the titanium trichloride solid catalyst (B), 51 g of diethylaluminum chloride, and 2.6 g of methyl methacrylate were charged. did. Next, 51Kg of liquefied propylene was supplied,
Polymerization was continued for 3 hours at a polymerization temperature of 70°C. Note that the molecular weight was adjusted using hydrogen. After the polymerization was stopped by adding isobutanol, the slurry was washed twice with 50 kg of liquefied propylene, and then dried to obtain 24 kg of powdered polymer. The polypropylene thus obtained has a melt index of 1.0 g/10 minutes and an isotactic pentad fraction of the insoluble part of boiling heptane.
0.960, content of boiling heptane soluble part is 7.5% by weight, content of 20℃ xylene soluble part is 2.5% by weight
It was from. The intrinsic viscosity of the xylene soluble portion at 20°C was 0.38 dl/g. (3) Decomposition and evaluation of polypropylene 0.2% by weight of a phenolic stabilizer and 0.01% by weight of 2,5-di(tert-butylperoxy)hexane were added and mixed to the above polypropylene, and a structure having a screw with a diameter of 65 mm was prepared. It was granulated using a granulator at a cylinder temperature of 230°C. The melt index of the obtained polypropylene was 2.5. This polypropylene is melt extruded at 290°C using a T-die extruder having a screw diameter of 65mm, and then rapidly cooled with a cooling roll at 35°C to obtain a sheet approximately 1.2mm thick. This sheet was stretched 7 times in the machine direction while heating it at 150℃ using a tenter manufactured by Japan Steel Works, and then stretched 7 times in the width direction while heating it with hot air at 165℃ until it was continuously stretched to a thickness of about 25μ. A biaxially stretched film was obtained. Processability and film characteristic values are shown in Table 1. Comparative Example 1 The propylene polymer used in Example 1 was granulated in the same manner as in Example 1, except that no radical generator was added. The melt index of the obtained polypropylene was 1.0. When this polypropylene was extruded and stretched in the same manner as in Example 1, stretching unevenness and breakage were likely to occur during stretching, and a normal biaxially stretched film could not be obtained in a stable manner. For this purpose, the film was stretched 4 times in the longitudinal direction while being heated at 150°C, and then stretched 7 times in the transverse direction while being heated with hot air at 165°C to obtain a biaxially stretched film with a thickness of about 40 μm. Processability and film characteristic values are shown in Table 1.

[Table] Examples 2 and 3 and Comparative Example 2 When only the degree of decomposition was changed under the same conditions as Example 1 (by changing the amount of radical generator added), the processability and film characteristic values were the same as in Example 1. It was as shown in the table. Example 4 Melt index is 1.5, isotactic pentad fraction of boiling heptane insoluble part is 0.967,
Polypropylene with a boiling heptane soluble content of 4.7% by weight was decomposed using 2,5-dimethyl-2,5-di(tertiarybutylperoxy)hexyne-3 by the method described in Example 1, The melt index was set to 2.8. This polypropylene was tested in a manner similar to Example 1. The results are shown in Table 2. Example 5 Using the polypropylene used in Example 4, 0.2% by weight of a phenolic stabilizer was added and mixed, and the mixture was kneaded and decomposed into granules at a cylinder temperature of 270°C using a ZSK granulator with twin screws of 55 mm in diameter. . The melt index of the polypropylene obtained was 2.3.
It was hot. This polypropylene was tested in a manner similar to Example 1. The results are shown in Table 2. Comparative Examples 3 and 4 Melt index is 1.5, isotactic pentad fraction of boiling heptane insoluble part is 0.940,
When polypropylene with a boiling heptane soluble content of 7.0% by weight was used under the same conditions as in Example 1 (by changing the amount of radical generator added), only the degree of decomposition was changed, the processability and film characteristic values were were as shown in Table 2. Comparative Example 5 Melt index is 2.6, isotactic pentad fraction of boiling heptane insoluble part is 0.960,
Polypropylene with a boiling heptane soluble content of 7.8% by weight was tested without decomposition. The results are shown in Table 2.

【table】

[Table] Example 6, Comparative Example 6 Polypropylene with a melt index of 26, an isotactic pentad fraction of the boiling heptane insoluble part of 0.970, and a boiling heptane soluble content of 6.3% by weight was used in Example 1. It was decomposed and granulated using the method described. The melt index of the obtained polypropylene was 55. This polypropylene was extrusion laminated onto 90μ thick kraft paper at a resin temperature of 280°C. The extrusion laminating device has a cylinder diameter of 90 mm, a die width of 580 mm, a screw rotation speed of 60 rpm, and an extrusion amount.
Processed at 1250g/min. The maximum take-up speed that allows stable lamination without surging and the oil resistance of the polypropylene layer were investigated. The results are shown in Table 3. For comparison, the melt index is 30,
The isotactic pentad fraction of the insoluble part of boiling heptane is 0.950, and the content of the soluble part of boiling heptane is
Polypropylene made by granulating 8.0% by weight polypropylene without the addition of a decomposing agent was similarly tested. The results are shown in Table 3.

【table】

Claims (1)

[Claims] 1. A method for modifying polypropylene, which comprises decomposing polypropylene having an isotactic pentad fraction of 0.955 or more in the boiling heptane-insoluble portion within a decomposition degree of 1.2 to 7.0.