JPS6143379B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polyethylene resin composition for injection molding, and more specifically, a low density polyethylene resin composition composed of ethylene having a relatively high molecular weight and a density of 0.91 to 0.95 g/cm ³ and an α-olefin having 4 or more carbon atoms. It is made by mixing an ethylene copolymer with a relatively low molecular weight and a high density of 0.950 g/cm ³ or more, or a copolymer of ethylene and α-olefin. This invention relates to a polyethylene resin composition with excellent environmental stress cracking resistance (hereinafter abbreviated as ESCR). Polyethylene is used for a variety of purposes, but injection molded products used for machine parts and the like tend to crack over time during use, which poses a major practical problem. This phenomenon is called environmental stress cracking, and is a phenomenon in which a molded product cracks and breaks over time when it is under stress from the outside or when processing strains from molding remain. Furthermore, this phenomenon occurs when the molded product is destroyed in a shorter time depending on the environment in which it is used. Proposed methods for improving the ESCR of polyethylene include mixing polyethylene with rubbers such as natural rubber and butyl rubber, and mixing polybutene-1, polycarbonate, and low-molecular-weight, low-melting-point paraffin wax. but,
These methods have the following problems: ESCR is not practically satisfactory, the mechanical strength of the molded product is reduced, the mixture dissolves into certain solvents at low temperatures, and the materials to be mixed are expensive and economically disadvantageous. It has some drawbacks and is not satisfactory. In addition, as mentioned above, ESCR of polyethylene can be achieved without mixing other polymers.
Methods to improve this include copolymerizing ethylene and α-olefin to lower the density, increasing the molecular weight (that is, generally decreasing the melt index), and modification by grafting, crosslinking, etc. method is known. However, these methods have problems such as insufficient ESCR, reduced mechanical strength, and reduced moldability, and are not practically satisfactory. In recent years, as the use and demand for polyethylene has increased, comprehensive and higher performance physical properties are required, and ESCR
It is required to have good hardness, high mechanical strength, good processing characteristics, and a certain level of quality. Generally, the lower the density or the lower the melt index (higher molecular weight), the better the ESCR of polyethylene. However, when the density is lowered, the mechanical strength decreases, and on the other hand, when the melt index is lowered (the molecular weight is increased), the fluidity during processing deteriorates, making processability difficult. Undesirable. I was tired,
Good ESCR, high density, and good processing properties are contradictory to each other. The present inventors solved the above problems,
As a result of various studies in order to obtain a polyethylene resin composition suitable for injection molding, we found that (A) ethylene and an α-olefin having 4 or more carbon atoms are combined with at least one of a chromium compound and a titanium compound. Polymerized in the presence of a catalyst system containing species and hydrogen, with a density of 0.91 to 0.95 and a number of branches per 1000 skeletal carbon atoms of 3 or more, obtained without substantial removal of the catalyst and low molecular weight polymer. , and this and the skeletal carbon atoms of the boiling cyclohexane extraction residue
The ratio of the number of branches per 1000 is 1:1 to 1:0.1
10 to 75% by weight of an ethylene copolymer with a degree of branching distribution in the range of 1.0 to 75% by weight and an intrinsic viscosity of less than 1.0 to 2.5 measured in tetralin at 130°C, and (B) ethylene alone or ethylene and α-olefin. Polymerized in the presence of hydrogen and a catalyst system comprising at least one of a chromium compound and a titanium compound, with a density greater than 0.950, obtained without substantial removal of the catalyst and low molecular weight polymer, in tetralin at 130°C A polyethylene resin composition having a melt index of 2.0 to 30 and a density of 0.935 to 0.960, which is prepared by mixing 90 to 25% by weight of an ethylene polymer with an intrinsic viscosity of 1.3 or less as measured by ESCR, density and It was discovered that it has good processability and is extremely suitable as a polyethylene resin composition for injection molding, and the present invention was achieved. The present invention will be explained in more detail below.
ASTM-D1693-70 is used as an indicator for ESCR evaluation.
Although the bent-stop method specified in
Proposed an evaluation method and device for ESCR (Unexamined Japanese Patent Publication No. 1983
-109988), and as a result of various studies on ESCR of olefin polymers and olefin polymer compositions using this apparatus and method, the following facts were discovered. 1. When two types of olefin polymers exhibiting mutually different ESCRs are mixed, the ESCR has additivity. For example, as shown in Figure 1, polyethylene A
(Melt index 0.53, density 0.944, ESCR
F ₅₀ 202) and polyethylene B (melt index 8.1, density 0.962, ESCR F ₅₀ 8.4), the F ₅₀ value of the mixture (the time it takes for 50% of the sample to break, an indicator of ESCR quality) The logarithm of is equal to the sum of the products of the logarithm of the F ₅₀ value of each component and its polymerization rate. 2 In the case of olefin polymer alone, ethylene and α
-The ESCR of copolymers with olefins is superior to that of ethylene homopolymers with the same molecular weight. Furthermore, even if the copolymer of ethylene and α-olefin has the same molecular weight and density, it differs depending on the type of α-olefin to be copolymerized. ESCR is excellent. For example, as shown in Table 1,
Ethylene-propylene copolymer and ethylene-butene copolymer with almost the same intrinsic viscosity and density
When comparing ethylene-hexene-1 copolymer and ethylene-hexene-1 copolymer, the ESCR of the copolymers becomes better as α-olefin with a larger number of carbon atoms is used as a comonomer. That is, when 1-butene, 1-hexene, or the like having 4 or more carbon atoms is used as the α-olefin to be copolymerized, the ESCR of the copolymer is dramatically improved. However, when the comonomer is propylene, the rate of improvement in ESCR is small.

According to [Table].
3 The copolymer of ethylene and α-olefin is
The higher the molecular weight, the better the ESCR. For example, as shown in FIG.
Science) Vol. 34, p. 569 (1959). ] Even if it is increased, the ESCR improvement effect is small, but high molecular weight copolymers dramatically improve the ESCR even if the degree of branching is small. 4. The distribution of short chain branches with respect to molecular weight (branching degree distribution) is closely related to ESCR, and olefin copolymers with more branches in the high molecular weight portion have better ESCR. For example, as shown in Table 2, in boiling cyclohexane

[Table] There are many branches in the low molecular weight part that can be extracted.
Copolymer B, which has few branches in the extraction residue, has poor ESCR, while copolymer A, which has many branches in the extraction residue, has improved ESCR. In addition, copolymers A and B shown in Table 2 were separated by column fractionation.
J.H. ElIiot, “Polymer Fractionation”
Molecular weight fractionation was performed according to the method described in M. J. R. Cantow, ed., Academic Press, pp. 67-93 (published in 1967), and the distribution of the degree of branching was determined. The results are shown in Figure 3. Figure 3 shows that copolymer A, which has a uniform branching degree distribution and many branches exist even in the molecular weight portion of 100,000 or more, has an uneven branching degree distribution. ,
The ESCR is better than copolymer B, which has almost no branches in the molecular weight part of 100,000 or more, indicating that the branches in the high molecular weight part dramatically improve the ESCR. The present invention was achieved based on the above findings, and the high molecular weight and low density ethylene copolymer (hereinafter abbreviated as component A) used in the present invention is composed of ethylene and 4 or more carbon atoms. A copolymer with α-olefin having a density of 0.91 to 0.95 is preferable. Also, producing an ethylene copolymer with too large a molecular weight is not necessarily advantageous, as it tends to gel or is difficult to mix with other polyolefins; therefore, the intrinsic viscosity should be less than 1.0-2.5. is preferred. Furthermore, when an ethylene copolymer produced without hydrogen in the presence of a catalyst containing at least one of a chromium compound and a titanium compound is mixed with other polyolefins, substantial mixing is difficult and gelation tends to occur. Preference is given to copolymers prepared in the presence of hydrogen. Further, a copolymer with a non-uniform branching degree distribution is undesirable because it contains a large number of low molecular weight partial branches which are less effective in improving ESCR, and undesirably lowers the density. Therefore, 1000 skeletal carbon atoms
The ratio of this to the number of branches per 1000 skeletal carbon atoms of the boiling cyclohexane extraction residue is preferably from 1:1 to 1:
A branching degree distribution of 0.1, more preferably 1:1 to 1:0.5 is used. Such copolymers are made by combining ethylene and α-olefins such as butene-1, pentene-1, 4-methylpentene-1, hexene-1, octene-1, etc. as catalysts in medium pressure or low pressure processes, especially up to high molecular weight components. It is obtained by copolymerizing in the presence of a carrier-supported catalyst that copolymerizes uniformly and hydrogen. Examples of such catalyst systems include so-called Phillips type catalysts and Ziegler type catalysts. To give a concrete example,
Catalysts whose main component is 0.5 to 6% by weight of chromium oxide supported on silica, silica/alumina, and titanium halides such as titanium tetrachloride and titanium trichloride are combined with magnesium chloride, magnesium alkoxide, and hydroxide. Catalysts supported on magnesium compounds such as magnesium, or catalysts whose main components are reaction products of these and organic aluminum compounds such as triethylaluminum and triisobutylaluminum, reaction products of titanium tetrachloride and metallic aluminum and organic Examples include catalysts containing aluminum compounds as a main component. On the other hand, the low molecular weight and high density ethylene polymer (hereinafter abbreviated as component B) used as another component in the present invention is a combination of ethylene alone or ethylene and α-olefin with a chromium compound and a titanium compound. It can be produced by polymerizing in the presence of a catalyst containing at least one of the above and hydrogen by a generally well-known medium pressure method or low pressure method. This component B preferably has a density of 0.950 or more and an intrinsic viscosity of 1.3 or less, more preferably an intrinsic viscosity of 1.0 or less. If the intrinsic viscosity is 1.3 or more, a composition with good fluidity during processing cannot be obtained. Therefore, the polyethylene resin composition of the present invention, which is a mixture of component A and component B, must have a melt index in the range of 2.0-30 and a density in the range of 0.935-0.960 in order to be used for injection molding. It is desirable that In the present invention, there are no particular limitations on the mixing method used to produce the polyethylene resin composition, and various mixing methods that provide a uniform composition can be used. Furthermore, the mixing ratio and combination of component A and component B are related to the ESCR, density, and processability of the components. Therefore, as for the mixing ratio, it is desirable that component A, which has a high intrinsic viscosity, accounts for 10 to 75% by weight of the entire composition. When the ethylene-based resin composition of the present invention obtained in this manner is subjected to injection molding, it has excellent ESCR, so there is no risk of environmental stress failure, and it has a wide molecular weight distribution, so it does not flow easily during processing. It has good properties and can obtain a high extrusion amount at low pressure, and there is no risk of roughening on the surface of the molded product even when processed at high extrusion speed. The composition of the present invention may contain conventional additives such as antioxidants, ultraviolet absorbers, color pigments, and lubricants. Next, the method of 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. In addition, in the examples and comparative examples, the outflow ratio is
In the melt index measurement method specified in JISK-6760, it is defined as the ratio of the flow rate when a load of 21.60 kg is applied to the flow rate when a load of 2.16 kg is applied, and this flow rate ratio is This is an index showing the pressure dependence of the material, and those with a large value have excellent fluidity at high pressures and do not cause roughness even at high shear rates. Example 1 Aluminum chloride, dimethyldiethoxysilane, diethoxymagnesium (mole ratio 2:2:
A solid component was obtained by stirring and mixing 1) in toluene. This solid component and titanium tetrachloride are combined into n-
Mixing in hexane gave the reaction product as a solid component. This solid component, triethylaluminum and isobutane were charged into an autoclave No. 3, the temperature was raised to 85°C, and 20 kg/cm ³ of ethylene, 4.5 g of butene-1 and 4 kg of hydrogen were introduced under pressure to carry out polymerization. After the polymerization was completed, the monomer and solvent were removed by distillation under heating, and the sample was used as it was without particularly removing the catalyst and low-molecular components. Similar treatments were carried out in the following Examples and Comparative Examples. The thus obtained ethylene-butene-1 copolymer had an intrinsic viscosity of 2.10, a density of 0.938, a degree of branching of 4.6 pieces/1000°C, a degree of branching of the residue extracted with boiling cyclohexane of 4.2 pieces/1000°C, and a The ratio was 1:0.91. On the other hand, without using butene-1, the ratio of hydrogen to ethylene was 17Kg/cm 2 and hydrogen was 7Kg/cm ² .
The above polymerization was carried out except that the amount was changed to Kg/cm ² . The obtained polyethylene has an intrinsic viscosity of 0.78 and a density of
It was 0.963. 55% by weight of the copolymer of ethylene and butene-1 thus obtained and 45% by weight of polyethylene were mixed by roll kneading at 145° C. for 10 minutes. When the physical properties of the obtained polyethylene resin composition were measured, the results shown in Table 3 were obtained. Table-3 Melt index 5.1 Density 0.950 Outflow ratio 45 ESCR (F ₅₀ hr) 52 Example 2 1 activated in air at 730℃ for 10 hours
A chromium-titanium-silica alumina catalyst containing 2.5% by weight of chromium oxide and 2.5% by weight of a titanium compound and isobutane were placed in a 1.5 autoclave, heated to 101°C, and 34 kg/cm ² of ethylene and 1 butene of ethylene were charged. Polymerization was carried out by injecting 0.5% by weight of hydrogen at 1 kg/cm ² . The thus obtained ethylene-butene-1 copolymer had an intrinsic viscosity of 2.0, a density of 0.949, a degree of branching of 3.4 pieces/1000C,
The degree of branching of the boiling cyclohexane extraction residue is 3.0/
The temperature was 1000C, and the ratio was 0.88. On the other hand, a chromium-titanium-silica-alumina catalyst containing 1% by weight of chromium oxide and 4% by weight of a titanium compound, which had been activated at 850°C for 10 hours, and isobutane were placed in a 1.5 autoclave and heated to 105°C. Ethylene was polymerized by pressurizing 34 kg/cm ² of ethylene and 1 kg/cm ² of hydrogen. The polyethylene thus obtained has an intrinsic viscosity of 0.92,
The density was 0.963. 72% by weight of the copolymer of ethylene and butene-1 thus obtained and 28% by weight of polyethylene were mixed by roll kneading at 145° C. for 10 minutes. When the physical properties of the obtained composition were measured, the results shown in Table 4 were obtained. Table-4 Melt index 2.9 Density 0.959 Flow rate ratio 76 ESCR (F ₅₀ hr) 17 Comparative example 1 Titanium tetrachloride, triethyl ethylaluminum and isobutane were charged into autoclave 3 and heated to 85℃, and ethylene, butene-1, Hydrogen was introduced under pressure to a total pressure of 26 kg/cm ² to carry out polymerization. The copolymer of ethylene and butene-1 thus obtained has an intrinsic viscosity of 1.9, a density of 0.943, and a degree of branching.
The branching degree of the boiling cyclohexane extraction residue was 0.8 pieces/1000C, and the ratio was 1:0.08. 55% by weight of this copolymer and 45% by weight of the polyethylene having an intrinsic viscosity of 0.92 and a density of 0.963 used in Example 2 were mixed by roll kneading at 145° C. for 10 minutes. When the physical properties of the obtained composition were measured, the results shown in Table 5 were obtained. Table-5 Melt index 4.8 Density 0.953 Flow rate ratio 62 ESCR 3.5 Example 3 Using the same catalyst and equipment as used in Example 2, ethylene was 34 kg/cm ² and butene-1 was 0.7% by weight based on the weight% of ethylene. , 1 kg/cm ² of hydrogen was injected under pressure and copolymerization of ethylene and butene-1 was carried out at a temperature of 101°C. The obtained copolymer A has an intrinsic viscosity of
1.9, density is 0.945, degree of branching is 4.3/1000C, degree of branching of boiling cyclohexane extraction residue is 3.6/
1000C, the ratio was 1:0.84. On the other hand, using the same catalyst and equipment as used in Example 2, using isobutane as a solvent, 34 kg/cm ² of ethylene, 2.4% by weight of butene-1 based on the weight of ethylene, and 1 kg/cm ² of hydrogen were introduced under pressure, and the temperature Polymerization was carried out at 105°C. The obtained copolymer B had an intrinsic viscosity of 0.88 and a density of 0.950. 55% by weight of the thus obtained copolymer A and 45% by weight of copolymer B were mixed by roll kneading at 145°C for 10 minutes. When the physical properties of the obtained composition were measured, the results shown in Table 6 were obtained. Table-6 Melt index 3.7 Density 0.947 Outflow ratio 65 ESCR F ₅₀ 13 Examples 4 to 6 Contains 1% by weight chromium oxide and 4% by weight titanium compound activated in air at 800°C for 10 hours A chromium-titanium-silica-alumina catalyst and isobutane were placed in a 1.5-liter autoclave, heated to 90°C, and 34 kg of ethylene and butene were added.
Copolymer 1 was obtained by injecting 0.7% by weight of Copolymer 1 based on the weight of ethylene and 1 kg/cm ² of hydrogen, and polymerization was carried out at a temperature of 97°C. Also, ethylene 34Kg/
cm ² , butene-1 to 0.8% by weight of ethylene
Copolymer 2 was obtained by carrying out polymerization in the same manner as described above, except that the weight percent and hydrogen content were 1 Kg/cm ² and the polymerization temperature was 98°C. The physical properties of these copolymers 1 and 2 are shown in the table below.
7 was correct.

[Table] On the other hand, using the same catalyst and equipment as used in Example 1, 17.5 kg/cm ² of ethylene and 3 kg/cm of butene-1 were used.
Polymerization was carried out at a temperature of 95° C. by injecting 6 kg/cm ² of hydrogen. The intrinsic viscosity of the obtained polymer 3 was 1.0,
The density was 0.955. Next, copolymer 1 or 2 and copolymer 3 are listed.
The mixture was mixed using a roll at the ratio shown in 8. The physical properties of each composition obtained were as shown in Table 8.

【table】 [Brief explanation of the drawing]

Figure 1 shows the ESCR when polyethylene A and polyethylene B, which have different ESCRs, are mixed.
Figure 2 shows the degree of branching and the difference in molecular weight of ethylene copolymers.
This is a relationship diagram of ESCR, and Figure 3 shows the molecular weight and ESCR of ethylene and butene-1 copolymers with different ESCR.
It is a relationship diagram.

Claims (1)

[Scope of Claims] 1 (A) Polymerizing ethylene and an α-olefin having 4 or more carbon atoms in the presence of hydrogen and a catalyst system containing at least one of a chromium compound and a titanium compound, and a density of 0.91 to 0.95 g/cm ³ , obtained without substantial removal of low molecular weight polymers, skeletal carbon atoms
The number of branches per 1000 is 3 or more, and this and the skeletal carbon atoms of the boiling cyclohexane extraction residue 1000
An ethylene copolymer with a branching degree distribution in the range of 1:1 to 1:0.1 and an intrinsic viscosity of 1.0 to less than 2.5 dl/g when measured in tetralin at 130°C. (B) Polymerize ethylene alone or ethylene and α-olefin in the presence of hydrogen and a catalyst system containing at least one of a chromium compound and a titanium compound to form a catalyst and a low molecular weight polymer. Density obtained without substantial removal
A melt index of 2.0 to 30 g/10 min, made by mixing 90 to 25% by weight of an ethylene polymer larger than 0.950 g/cm ³ and having an intrinsic viscosity of 1.3 dl/g or less as measured in tetralin at 130°C. , the density is
A polyethylene resin composition for injection molding with excellent environmental stress cracking resistance of 0.935 to 0.960 g/cm ³ .