JPH0478520A - Molding of syndiotactic polypropylene - Google Patents

Abstract

PURPOSE:To obtain a drawn product of syndiotactic polypropylene with excellent transparency by drawing a molded item of polypropylene with syndiotactic structure and treating it with a gaseous hydrocarbon compd. CONSTITUTION:A polypropylene with syndiotactic structure, if necessary mixed with a stabilizer such an antioxidant as is used in the case of molding of isotactic polypropylene, is molded and then drawn. As a molded item to be drawn, a product with a relatively low degree of crystallinity is pref. as it is easily drawable and it is drawable at a high draw ratio. For example, a product with a relatively small strength of a diffraction line observed at a face distance of about 7.1 Angstrom is pref. used. A molded item satisfying this condition exhibits a larger cooling speed after heat melt molding. As the heating temp., a temp. which is 10 deg.C or lower than the m.p. of polypropylene used is pref. The drawn product as it is and under loaded condition is heated with a gaseous hydrocarbon compd. to make the lowered transparency better.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for stretching polypropylene.

Specifically, the present invention relates to a method for stretching polypropylene having a substantially syndiotactic structure.

[Prior art]

Polypropylene is a lightweight and inexpensive polymer, and especially when stretched, it has excellent strength and is used for seeding purposes.

[Problem to be solved by the invention]

Isotactic polypropylene is relatively easy to stretch,
A molded product with relatively high crystallinity (usually 50 to 60%) molded under normal molding conditions is heated to a temperature lower than the melting point, usually 10%.
By stretching the film while heating it to 0 to 160°C, it can be easily stretched to about 3 to 20 times. On the other hand, syndiotactic polypropylene is said to have elastomeric properties when produced using conventional methods, is soluble in hydrocarbon compounds at room temperature, and is used as crystalline polypropylene molded products, especially stretched products. Although this was difficult to imagine, it was recently discovered by J,^, 4EN et al. (J,^-, Che, Soc, 1988.
110.6255-6256) Syndiotactic polypropylene obtained by a catalyst consisting of a transition metal compound having an asymmetrical ligand and an aluminoxane has a toughness such that the syndiotactic benfluoride fraction exceeds 0.7. It is a good polypropylene and is a crystalline polypropylene with a high melting point. This polypropylene with high syndiotacticity has relatively good physical properties, and it can be expected that the physical properties will be improved by further stretching. However, the method used for the above-mentioned isotactic polypropylene in which the molded product is stretched at a temperature slightly lower than the melting point has the problem that it can only be stretched approximately twice as fast at a sufficient speed, and the stretched product has extremely poor transparency. Ta.

[w, no way to solve the problem]

The present inventors conducted intensive studies on a method for stretching syndiotactic polypropylene that solved the above problems, and completed the present invention.

That is, the present invention is a method for molding syndiotactic polypropylene, which comprises stretching a polypropylene molded product having a substantially syndiotactic structure and then treating the product with vapor of a hydrocarbon compound.

In the present invention, substantially syndiotactic polypropylene means a syndiotactic pentad fraction that can be produced using a catalyst consisting of aluminoxane and a transition metal compound having an asymmetrical ligand discovered by J. A. EWEN et al. (A.

Zambelli et al. Macromolecules v
ol 6687 (1973) + same vol 8925
(1975)) shows not only homopolymers of propylene with high tacticity exceeding 0.7, but also copolymers with small amounts of other α-olefins, and other α-olefins used in copolymerization. Examples of olefins include ethylene and α-olefins having 4 to 20 carbon atoms, specifically butene-1, pentene-1, hexene-1, octene-1
, 4-methylpentene-1 and the like. The polymerization ratio to propylene is usually 20 wtZ or less, more preferably 10 wtZ or less of other olefins are copolymerized. 1,2.4- for copolymers)
The intensity of the peak observed at about 20.2 pp- based on tetramethylsilane in C-NMR measured with a dichlorobenzene solution is 0.3 or more of the peak intensity attributed to all the methyl groups of propylene. Those having a highly syndiotactic structure are preferably used.

As a catalyst for producing polypropylene having a substantially syndiotactic structure, in addition to the compounds described in the above-mentioned literature, compounds having a different structure may also be used, even if they have a syndiotactic structure when propylene is homopolymerized. Any catalyst system that can produce polypropylene with a pentad fraction of 0.7 or more can be used. Specific examples of transition metal compounds containing asymmetrical ligands include isopropyl (cyclobankgenyl-1-fluorenyl) hafnium dichloride and isopropyl (cyclopentagenyl-1-fluorenyl) zirconium dichloride described in the above-mentioned literature. Examples of aluminoxane include compounds represented by RR (wherein R is a hydrocarbon residue having 1 to 3 carbon atoms), particularly methylaluminoxane where R is a methyl group and n is 5 or more. , preferably 10 or more. The ratio of aluminoxane used to the above transition metal compound is 10 to 1,000,000 times, usually 50 to 5,000 times by mole.

There are no particular restrictions on the polymerization conditions, and solvent polymerization using an inert medium, bulk polymerization without an inert medium, or gas phase polymerization can also be used. , the polymerization pressure is normal pressure to 10
It is common to carry out at 0 kg/cj. Preferably the temperature is -100 to 100°C and normal pressure to 50 kg/cd.

This catalyst system has a narrow molecular weight distribution when the polymerization is substantially carried out in one step, and the ratio of the weight average molecular weight to the number average molecular weight (hereinafter abbreviated as MW/MN) measured by gel permini-silane chromatography at 135°C. is 1.5-3
Usually, a narrow one of about 85 is obtained, but it is possible to use two types of transition metal compounds (it is effective to use two types of metals such as zirconium and hafnium) or two or more types of transition metal compounds with different molecular weights. 3. by mixing etc.
It is also possible to produce compounds with a wide molecular weight distribution of 5 or more, and compounds with any molecular weight distribution can be used in the present invention. The preferred molecular weight is 13
The intrinsic viscosity (hereinafter referred to as η) measured with a 5° C. tetralin solution is generally 0.5 to 20.0 degrees.

In the present invention, the polypropylene having a substantially syndiotactic structure obtained by the above method is then treated with a stabilizer such as an antioxidant, which is used in conjunction with the molding of isotactic polypropylene, if necessary. It is mixed, shaped and then stretched. The molded product to be stretched is preferably one with a relatively low degree of crystallinity, which is easy to stretch and can be stretched at a high magnification. Relatively small ones are preferably used. A molded product that satisfies this condition is obtained by increasing the cooling rate after heating and melt molding.

There is no particular restriction on the molding method, and extrusion molding, press molding, injection molding, etc. can be employed.

The molded article thus obtained is then stretched. There is no particular restriction on the temperature during stretching, but stretching can be performed even at room temperature, and by slowing down the stretching speed, the stretching ratio can be increased. However, it is of course possible to heat and stretch in order to reduce the stretching stress. The heating temperature is preferably at least 10°C lower than the melting point of the polypropylene used, particularly preferably at least 20°C lower. Here, the shape of the molded product may be any shape as long as it can be stretched, such as a sheet, a film, or a thread, and stretching can be carried out not only by uniaxial stretching but also by two-wheel stretching. Other methods such as roll stretching may also be used, and the stretching ratio can be 3 times or more, particularly several tens to 100 times if the stretching is carried out slowly near room temperature.

In the present invention, the drawn product obtained by the above method is then preferably treated with steam of a hydrocarbon compound under an applied load in the stretched state. By processing and stretching in this way, the decreased transparency can be improved. Further, if necessary, heat treatment can be performed to remove the vapor of the hydrocarbon compound, thereby making it possible to improve the physical properties. Here, as the hydrocarbon compound, in addition to saturated or unsaturated hydrocarbons having about 5 to 20 carbon atoms, halogenated hydrocarbons in which one or all of the hydrogen atoms in these compounds are replaced with halogen atoms can also be used.

Preferably pentane, hexane, heptane, octane,
Saturated hydrocarbon compounds such as nonane and decane, benzene,
Aromatic hydrocarbon compounds such as toluene, xylene, ethylbenzene, cumene, and cymene, or compounds in which some hydrogen atoms thereof are replaced with halogen atoms are preferably used. During this treatment, it is preferable that the stretched product be in a stretched state, that is, in a loaded state, so that deformation can be avoided. This treatment can be carried out at room temperature, but it can also be heated to shorten the treatment time. The heating temperature is usually preferably 100"C or lower to avoid deformation of the molded product, and the treatment time is 1 second to 100"C, although it varies depending on the temperature during treatment.
Usually, after this treatment, blowing with nitrogen, air, etc., vacuum treatment, or heat treatment is performed to remove hydrocarbon compounds contained in the molded product. However, the physical properties can be improved by heat treatment at a temperature below the melting point of syndiotactic polypropylene, preferably under an applied load.

〔Example〕

The present invention will be further explained with reference to Examples below.

Example 1 Isopropyl (cyclopentadienyl-1-fluorenyl) zirconium dichloride 0.0.0. Using 2g and 30g of methylaluminoxane (polymerization degree 16.1) manufactured by Toyo Akzo ■, the internal volume was 200.
! ! Tolu 17801 was added in an autoclave and polymerized for 2 hours at 20'C at a polymerization pressure of 3 kg/cj-G, followed by deashing with methanol and methyl acetoacetate, washing with an aqueous hydrochloric acid solution, and filtration to obtain 5.6 kg of Syndiotactic polypropylene was obtained. According to I″C-NMR, this polypropylene has a syndiotactic bentaside fraction of 0.935, and η measured in a tetralin solution at 135° C. is 1.45.

2.4-) Measured with dichlorobenzene? IW/MN
was 2.2. A known stabilizer was added to this polypropylene, the mixture was granulated using an extruder, and then melted and fluoresced at 200"C to form a l- sheet. The following physical properties were measured on this sheet.

Bending rigidity: kg/d ASTM D-747 (
23°C) Tensile yield strength: kg/d ASTM
D-638 (23°C) Elongation at break: % 45
7M D-638-(23°C) Izot (notched) Impact strength: kg-cm/cm ASTM D-638
(23°C, -10°C) Haze: % A
According to STM [11003.

Bending rigidity 5300kg/ej, tensile yield strength 240k
g/c, elongation at break 520χ, Izotsu impact strength 1
4.2.3°6 (23°C1-10°C, respectively), and the haze was 28%. This sheet was stretched 3 times at 30°C to form a stretched film and its physical properties were measured. The following measurements were made regarding the physical properties of this film.

Haze: % 457M Tensile strength according to 01003: kg/cd 50mm x 20 from stretched film
A test piece of mm in diameter was cut out and its tensile strength at break was determined using a tensile tester at a tensile speed of 200 mm/in.

Elongation: % Elongation of a test piece at break when determining tensile strength.

The tensile strength was 650 kg/cj, the elongation was 78%, and the haze was 32%. This stretched product was placed in a sealed container and treated with toluene vapor at 30°C for 6 hours, then the stretched state was kept at 80°C for 5 hours, and its physical properties were measured. The tensile strength was 690 kg/cj, and the elongation was 60. %, and haze was 12%. It can be seen that treatment with toluene vapor improves transparency.

On the other hand, when stretched and heat treated without being treated with toluene, the tensile strength is 680 kg/cj and the elongation is 5.
5%, haze was 35%, and transparency was not improved.

Example 2 The same procedure as Example 1 was carried out except that the stretching was carried out at 120°C and the treatment with toluene was carried out at 50°C for 30 minutes. The tensile strength was 680 kg/d, the elongation was 85%, and the haze was 18%.
Met. The haze before treatment with toluene was 38%.

Example 3 The same procedure as Example 1 was performed except that xylene was used instead of toluene, and the tensile strength was 685 kg/cd and the elongation was 70%.
, haze was 14%.

〔Effect of the invention〕

By the method of the present invention, a stretched product of syndiotactic polypropylene with excellent transparency can be obtained, which is extremely valuable industrially.

Patent applicant Mitsui Toatsu Chemical Co., Ltd.

Claims (1)

[Claims] 1. A method for molding syndiotactic polypropylene, which comprises stretching a polypropylene molded product having a substantially syndiotactic structure and then treating it with vapor of a hydrocarbon compound. 2. The method according to claim 1, wherein the treatment with hydrocarbon compound vapor is carried out under load conditions.