JPH0252654B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to polyethylene compositions for blow molding. More specifically, the present invention relates to a polyethylene composition for blow molding that has excellent drawdown resistance and environmental stress cracking resistance. Blow molding is one of the methods for molding thermoplastic resins, and is widely used for molding detergent bottles, shampoo bottles, cosmetic bottles, kerosene cans, industrial chemical cans, and the like. However, in the blow molding method, once a cylindrical molten resin called a parison is extruded from an extruder, air is blown into the parison in a mold to create a product, so the larger the product, the more it must be held between the molds. Previously, the phenomenon of drooping (drawdown) due to the parison's own weight was severe, making molding difficult. Methods to reduce parison drawdown include lowering the molding temperature, increasing the extrusion speed, or using a resin with a low melt flow rate, but all of these methods increase the load on the extruder. It also has the disadvantage that the extrusion surface of the parison becomes large and the appearance of the resulting molded product also deteriorates. On the other hand, the drawdown of the parison is correlated with the melt tension of the resin, and resins with high melt tension have small drawdowns. As a method for improving the melt tension of resin during inflation film molding, a method has been proposed in which a small amount of radical generator is added to polyolefin resin (Japanese Patent Application Laid-Open No. 57-38837). Even when applied to improve the melt tension of polyethylene for molding, drawdown is not improved. Therefore, the present inventors have studied the development of polyethylene for blow molding that has excellent drawdown resistance and environmental stress cracking resistance, and as a result, has arrived at the present invention. That is, the present invention is a blow molded product obtained by adding 0.002 to 0.10 parts by weight of a radical generator and 0 to 0.05 parts by weight of a crosslinking aid to 100 parts by weight of polyethylene () satisfying the following (A) to (E). Polyethylene composition for use. (A) Melt tension (MT) is within the range specified by formula (1) and formula (2), [η]≦3.23, 3.14log ₁₀ [η]−0.529≦log ₁₀ (MT)≦3
.11log ₁₀ [η]−0.267……(1) At [η]＞3.23 0.749log ₁₀ [η]+0.690≦log ₁₀ (MT)≦
0.150log ₁₀ [η]+1.24……(2) [η]: Decalin solvent, intrinsic viscosity at 135℃ (B) Melt flow rate (ASTM D 1238:
E) 0.01 to 5.0 g/10 min, (C) density 0.915 to 0.970 g/cm ³ , (D) melt flow rate ratio 8 to 50, and (E) HSFR 30 to 600 sec ^-1 . It provides: The polyethylene used in the present invention is a homopolymer of ethylene or ethylene mainly composed of ethylene and other α-olefins, such as propylene, 1-butene, 1-pentene, 1-hexene,
4-methyl-1-pentene, 1-octene, 1-
It is a copolymer with decene etc. The polyethylene () used in the present invention has the formula MT
This is the range defined by (1) and formula (2). When [η]≦3.23, 3.14log ₁₀ [η]−0.529≦log ₁₀ (MT)≦3
.11log ₁₀ [η]−0.267……(1) At [η]＞3.23 0.749log ₁₀ [η]+0.690≦log ₁₀ (MT)≦
0.150log ₁₀ [η] + 1.24...(2) [η]: Decalin solvent, intrinsic viscosity at 135℃ Polyethylene whose MT is outside the range of the above formula and whose MT exceeds the upper limit is often used in practical use. Not on target. In addition, all polyethylenes below the lower limit have extremely narrow molecular weight distributions, causing rough skin of the parison during molding, making it impossible to obtain a product with a good appearance. MT in the present invention uses a melt tension tester manufactured by Toyo Seiki Co., Ltd. to melt polyethylene in a cylinder (inner diameter: 9.55 mm) at a melting temperature of 190°C through a nozzle (hole diameter: 2.10 mm, length: 8.00 mm). mm)
More constant speed (piston descending speed: 10mm/min)
This is the stress (g) generated when the molten strand extruded through a load cell is taken up by a roller (outer diameter: 5.0 cm) rotating at a constant speed (100 rpm). The rotation speed of the roller is 100 rpm.
If the strand melts and breaks before reaching , the stress (g) at that point is defined as MT. The polyethylene used in the present invention has a melt flow rate (ASTM D 1238: E hereinafter abbreviated as MFR ₂ ) of 0.01 to 5.0 g/10 min, preferably
It is within the range of 0.01 to 1.0g/10min. _MFR2
is less than 0.01g/10min, when molding with the addition of the radical generator and crosslinking aid described below,
MFR ₂ becomes small and formability decreases significantly.
On the other hand, when MFR ₂ exceeds 5.0 g/10 min, it is necessary to add a large amount of radical generator to improve MT, which results in the formation of gel and also reduces environmental stress cracking resistance. The polyethylene () used in the present invention has a density of
0.915 to 0.970g/cm ³ , preferably 0.915 to 0.970g/cm 3
It is within the range of 0.965g/ ^cm3 . Those with a density of less than 0.915 g/cm ³ have low rigidity, and those with a density of more than 0.970 g/cm ³ have poor environmental stress cracking resistance. The polyethylene used in the present invention has a melt flow rate ratio (ASTM D 1238: value in N: MFR ₁₀ and value in ASTM D 1238, E:
Ratio to MFR ₂ : MFR ₁₀ /MFR ₂ ; hereinafter abbreviated as FRR)
ranges from 8 to 50, preferably from 10 to 30. If the MRR is less than 8, the surface of the parison will be rough during extrusion molding, making it impossible to obtain a product with a good appearance, and if it exceeds 50, the strength of the product will be significantly reduced. The polyethylene () used in the present invention has an HSFR of
30 to 600sec ^-1 , preferably 40 to 500sec ^-1
is within the range of Those with HSFR less than 30sec ^-1 are
The surface of the parison becomes rough during extrusion molding, making it impossible to obtain a product with a good appearance, and those exceeding 600 sec ^-1 are undesirable because the elongation at break decreases. In addition, HSFR in the present invention is a constant shear stress (2.4 × 10 ⁶ dyne/cm ² ) and the shear rate (sec ^-1 ). If the polyethylene used in the present invention is a composition consisting of a high-density, low-molecular-weight ethylene polymer and a low-density, high-molecular-weight ethylene copolymer, a hollow molded article with even better environmental stress cracking resistance can be obtained. preferable. Polyethylene () having the above properties used in the present invention
Using a so-called Ziegler catalyst, which is composed of two components: a compound of a transition metal in group - of the periodic table and an alkyl metal consisting of a metal in group -, ethylene alone or ethylene and α-olefin are mixed within the above range at low pressure. It is obtained by polymerizing in such a way that it enters the High-pressure polyethylene obtained by radically polymerizing ethylene under high temperature and high pressure, and medium-pressure polyethylene obtained by polymerizing ethylene under medium pressure using a Phillips catalyst consisting of chromium oxide with silica-alumina as a carrier, are free from radical generation. When mixed with additives, the environmental stress cracking resistance further decreases,
The purpose of the present invention cannot be achieved. The polyethylene used in the present invention includes antioxidants, ultraviolet absorbers, lubricants, antistatic agents, flame retardants, pigments, dyes, inorganic or organic fillers, blowing agents, and low-crystalline or amorphous ethylene. - Various compounding agents commonly used for polyolefins, such as 1-butene copolymer and ethylene-propylene copolymer, may be added to the extent that the purpose of the present invention is not impaired. The radical generator used in the present invention preferably has a decomposition temperature of 150 to 270°C at which the half-life is 1 minute, and specific examples include cumene hydroperoxide, diisopropylbenzene hydroperoxide, 2,5-dimethyl-2, Hydroperoxides such as 5-dihydroperoxyhexane, 2,5-dimethyl-2,5-dihydroperoxyhexine-3, di-t-butyl peroxide, di-t-
amyl-peroxide, t-butyl-cumyl-peroxide, dicumyl-peroxide, 2,5-
Dimethyl-2,5-di(t-butyl-peroxy)hexane, 2,5-dimethyl-2,5-di(t-butyl-peroxy)hexane-3,α,
α′-bis(t-butyl-peroxy)diisopropyl-benzene, 2,2-bis(4,4-di-t
Dialkyl peroxides such as -butyl-peroxy-cyclohexyl)propane, peroxy esters such as t-butyl-peroxy-acetate, t-butyl-peroxy-laurate, t-butyl-peroxy-benzoate, and di-t-butyl-diperoxy-phthalate. etc. The radical generator is polyethylene (): 100
It is necessary to add an amount in the range of 0.002 to 0.10 parts by weight, preferably 0.005 to 0.03 parts by weight, based on the parts by weight. If the amount added is less than 0.002 parts by weight, the effect of improving drawdown properties will not appear, and if it exceeds 0.10 parts by weight, the environmental stress cracking resistance of the composition will decrease, and furthermore, gel will be generated and the appearance of the product will deteriorate. . In addition to the radical generator, the polyethylene () of the present invention further contains 0 to 0 crosslinking aids.
You may add 0.05 parts by weight. By adding such a crosslinking aid, the amount of radical generator can be reduced and branching can be efficiently caused. Specific examples of the crosslinking aid include triaryl cyanurate, triaryl isocyanurate, 1,3,5-triacryloylhexahydrotriazine, tris(2-hydroxyethyl)isocyanuracrylate, tris(2-hydroxyethyl) ethyl) isocyanuric methacrylate,
1,2-polybutadiene, ethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol diacrylate, trimethylolpropane trimethacrylate, etc. can be mentioned. In order to obtain the polyethylene composition for blow molding of the present invention, the polyethylene (), a radical generator, and a crosslinking aid are mixed using various known methods within the above ranges, such as a Henschel mixer, a V-blender, a ribbon blender, and a tumbler blender. Furthermore, after mixing, the mixture is kneaded and granulated using a single-screw extruder or multi-screw extruder, or by melt-kneading using a Banbury mixer, kneader, single-screw extruder, or multi-screw extruder. can get. When kneading in the above method, the drawdown properties of the parison are improved in the blow molding method described below by kneading at a temperature higher than the decomposition temperature of the radical generator, that is, usually at a temperature of 150 to 280°C. The above-mentioned kneading is not necessarily necessary, and even if the composition is simply mixed with a Henschel mixer etc., the temperature of the extruder is set at a temperature higher than the decomposition temperature of the radical generator, that is, usually 150°C, in the blow molding described later. By keeping the temperature between 280℃ and 280℃,
The drawdown properties of the parison are improved. By heat-treating the polyethylene composition of the present invention, the modified composition has a large MT as shown in the following formulas (3) and (4). That is, by improving the drawdown property, blow molding becomes easier. At [η]≦3.23, 3.11log ₁₀ [η]−0.267＜log ₁₀ (MT)……(3) At [η]＞3.23, 0.150log ₁₀ [η]+1.24＜log ₁₀ (MT)……(4 ) The method for blow molding using the polyethylene composition for blow molding of the present invention is not particularly limited, and is a general blow molding method. extrusion blow molding method,
Examples include a blow molding method with an inline screw plunger and a blow molding method with an accumulator chamber. When performing hollow molding using the above method, both
This can be done by extruding the parison from a die after melting at a temperature of 190 to 260°C, and cooling it by blowing air into the mold. The polyethylene composition for blow molding of the present invention has improved drawdown properties compared to conventional polyethylene and also has excellent environmental stress cracking resistance, so it can be used for gasoline tanks, industrial chemical cans, kerosene cans, lorry tanks, etc. It is particularly suitable for large containers such as solar heat collectors and mesh ends. Next, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples unless the gist thereof is exceeded. Examples 1 to 3 (1) Catalyst synthesis 5 mol of anhydrous magnesium chloride was suspended in dehydrated and purified hexane 10 in a nitrogen stream, and 25 mol of ethanol was added dropwise over 1 hour with stirring, followed by reaction at room temperature for 1 hour. 12 mol of diethylaluminium chloride was added dropwise to this at room temperature, and the mixture was stirred for 2 hours. Next, titanium tetrachloride
After adding 10 mol, the temperature was raised to 60°C and the reaction was carried out with stirring for 3 hours. The produced solid portion was separated by decantation, washed repeatedly with purified hexane, and then made into a hexane suspension. The titanium concentration in the hexane suspension was determined by titration. Further, when a portion of the obtained solid was dried under reduced pressure and the catalyst composition was examined, it was found that 74 mg of titanium, 202 mg of magnesium, and 618 mg of chlorine were present per gram of solid. (2) Polymerization Add 50 ml of hexane to the first stage polymerization vessel with an internal volume of 200 ml.
/hr, triethylaluminum 140mmol/
2.8 mmol/hr supported catalyst in terms of titanium atoms
Ethylene was fed continuously at a rate of hr and the contents of the polymerization vessel were discharged at the required rate at 80°C.
Introducing hydrogen at a rate of 15Kg/hr and 250/hr,
The first stage polymerization is carried out continuously under the conditions of a total pressure of 7 Kg/cm ² and an average residence time of 2 hours. Suspension solution of hexane containing polyethylene produced by polymerization (ethylene polymer content 300g/, MFR of polyethylene ₂
= 50g/10min, intrinsic viscosity [η] = 0.92dl/g,
Density = 0.972 g/cm ³ ) was introduced into a flash drum at the same temperature, and after separating the hydrogen contained in the solution, the entire amount was introduced as it was into the second stage polymerization vessel with an internal volume of 200, without adding any catalyst. While supplying purified hexane 50/hr and discharging the contents of the polymerization vessel at the required rate, ethylene was produced at 70°C.
15Kg/hr, 1-butene 150g/hr, hydrogen 5
The second stage polymerization is carried out continuously under conditions of a total pressure of 3.5 Kg/cm ² and a residence time of 2 hours. The effluent from the second stage polymerization reactor contains 300 g/hr of ethylene polymer composition;
PE-I) MFR ₂ is 0.05g/10min,
[η] is 3.32dl/g, FRR is 19, HSFR is
60sec ^-1 , MT was 14g, and density was 0.956g/cm ³ . (3) Production of polyethylene composition for blow molding 2,5 dimethyl-2,5-di(t-butylperoxy)hexane was added as a radical generator to 100 parts by weight of PE obtained by the above polymerization. 1, 3, 5 triacryloylhexahydrotriazine as a crosslinking aid
A composition was obtained by adding and mixing the ingredients in the proportions shown in the table and melting and granulating them using a 20 mmφ extruder (resin temperature: 280°C). Next, the composition was evaluated by the following method. Environmental stress cracking resistance (ESCR): ASTM D 1693
Test piece thickness: 2 mm, temperature: 50°C, and surfactant: Antarox.
Measured under the conditions of a 10% CO-630 solution. Drawdown property: resin temperature using hollow molding
Evaluation was made by extruding a parison of a constant weight at 220°C and measuring the distance (cm) that the tip of the parison hangs down in 10 seconds. The results are shown in Table 1. Comparative Examples 1 and 2 The results of evaluating the PE obtained in Example 1 without adding any radical generator etc.
Table 1 shows the evaluation results for each of the following. Examples 4 and 5 In a similar manner to the polymerization method described in Example 1,
The physical properties of the first stage polyethylene are MFR ₂ = 150g/
10min, [η] = 0.74dl/g and density = 0.974g/cm ³
, and the effluent from the second stage polymerization vessel is MFR ₂ =
0.34g/10min, [η]=2.30dl/g, FRR=16,
HSFR=430sec ^-1 , MT=6g and density=0.959g/
cm ³ of a polymer (hereinafter referred to as PE-) was obtained. Next, a composition obtained by adding PE and the radical generator and crosslinking aid used in Example 1 in the proportions shown in Table 1 was evaluated in the same manner as in Example 1. The results are shown in Table 1. Comparative Examples 3 and 4 The results of evaluating the PE obtained in Example 4 without adding any radical generator etc.
Table 1 shows the evaluation results for each of the following.

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Claims (1)

[Claims] 1. Polyethylene () that satisfies the following (A) to (E): 100
0.002 to 0.002 to part by weight of radical generator
A polyethylene composition for blow molding, which contains 0.10 parts by weight and 0 to 0.05 parts by weight of a crosslinking aid. (A) Melt tension (MT) is within the range specified by formula (1) and formula (2), [η]≦3.23, 3.14log ₁₀ [η]−0.529≦log ₁₀ (MT)≦3.1
1log ₁₀ [η]−0.267……(1) When [η]＞3.23, 0.749log ₁₀ [η]+0.690≦log ₁₀ (MT)≦0.
150log ₁₀ [η] + 1.24...(2) [η]: Decalin solvent, intrinsic viscosity at 135℃ (B) Melt flow rate (ASTM D 1238:
E) 0.01 to 5.0 g/10 min, (C) density 0.915 to 0.970 g/cm ³ , (D) melt flow rate ratio 8 to 50, and (E) HSFR 30 to 600 sec ^-1 .