JPH09194537A - Resin for rotation molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a resin for rotation molding, comprising a specific ethylene.α-olefin random copolymer, having a prescribed particle diameter, little in curvature and contraction after the rotation molding, good in the balance between rigidity and stretch crack resistance, and excellent in mechanical strength and low temperature characteristics. SOLUTION: This resin comprises the random copolymer of ethylene with an α-olefin such as 1-hexene, having a density of 0.920-0.955(g/cm<3> ), a melt flow rate(MFR) of 1-20(g/10min) and a mol.wt. distribution (Mw/Mn) of 2-3. The particle size of the resin is <=30 meshes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin suitable for producing a hollow molded product, a molded product having a complicated shape and the like, and more particularly to a resin for rotational molding which has an excellent balance of stress cracking property and impact strength.

[0002]

2. Description of the Related Art Conventionally, products such as tanks, containers, daily necessities, furniture, horticultural products, and outdoor products have been produced by using the rotational molding method. Materials used therefor are required to have high mechanical strength, particularly high impact strength, and excellent stress crack resistance.

[0003]

Polyethylene has been mainly used in the rotational molding so far, but the obtained product has one of impact strength, rigidity, or stress cracking property, or Although two are better,
There are few resins that have excellent physical properties, and there has been a demand for a product having a better balance of physical properties. Therefore, it is an object of the present invention to provide a resin capable of producing a product in which those physical properties are appropriately balanced.

[0004]

That is, the present invention has a density of 0.920 to 0.955 (g / cm ³ ) and a melting index (M
FR) 2 to 10 (g / 10 min) and a molecular weight distribution (Mw / Mn) consisting of a random copolymer of ethylene and α-olefin having a molecular weight of 2 to 3, and a resin for rotomoulding having a particle size of 30 mesh or less. .

[0005]

DETAILED DESCRIPTION OF THE INVENTION The resin according to the present invention is a random copolymer of ethylene and α-olefin. α-
The olefin has 4 to 10 carbon atoms, preferably 4 to
8 olefins, such as 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-
Octene and the like and mixtures thereof can be mentioned. The α-olefin content of the copolymer is 0.5 to 1
By adjusting the amount to 5, preferably 1.0 to 10 mol%, preferable practical physical properties, particularly rigidity, impact strength, and stress crack resistance can be exhibited.

Such polyethylene is composed of ethylene and α-
It can be produced by random copolymerization with an olefin, in which case, for example, a metallocene olefin polymerization catalyst, which is a combination of a metallocene compound of a transition metal and an organoaluminum oxy compound, an organoaluminum compound if necessary, and an organic boroso compound is used. Used.
They are the international publication WO-91 / 04257,92.
The catalyst system described in / 01723 etc. can be used. As an example, in the presence of bis (n-propylcyclopentadienyl) zirconium dichloride, ethylene-bis (4,5,6,7-tetrahydroindenyl) zirconium dichloride and methylaluminoxane, It can be obtained by copolymerizing ethylene and α-olefin in a gas phase, a slurry state or a solution state. The copolymer obtained here has a linear molecular structure, and has a relatively narrow molecular weight distribution and narrow composition distribution as compared with linear polyethylene obtained by polymerizing with a conventional Ziegler catalyst system. It is known to show.

This polyethylene is based on ASTM D-12
Measured under the conditions of 190 ℃ and load of 2160g
Has a melting index (MFR) of 1 to 20, preferably 2
It is 10 (g / 10 minutes). See also ASTM D-15
The density measured according to 05 is 0.920 to 0.9
55, preferably 0.925 to 0.950 (g / c
m ^Three). Further gel permeation chromatography
Raffy uses o-dichlorobenzene solvent 13
Weight average molecular weight (Mw) and number average molecular weight measured at 5 ° C
Average molecular weight distribution (Mw / Mn) represented by the ratio of (Mn)
Is 2 to 3, preferably 2 to 2.5. density,
Melt index and molecular weight distribution must be within the above numerical range
Has excellent moldability, high mechanical strength, especially impact strength
And rigidity and stress crack resistance can be obtained. Inside
Also has an average molecular weight distribution of 2 to 3
Molded products with less stickiness and excellent stress crack resistance
can get. Also, by being in the above density range,
A molded product with excellent flexibility and mechanical strength.

In the rotational molding, the resin powder is put in a heated mold, and the resin powder is adhered and welded to the surface of the mold while rotating the whole mold. Will be an important factor in raising the. By adjusting the melting index to 1 to 20 (g / 10 min) as described above, the molten resin does not drip and easily flows along the irregularities of the mold, resulting in uniform wall thickness and a clean appearance. With a particle size of 30 mesh or less,
Since it is preferably 40 to 100 mesh, a pinhole-free molded film is formed during melting.

In the present invention, other resins, elastomers, organic or inorganic fillers, antioxidants, heat stabilizers, ultraviolet absorbers, etc. are used within the range that does not impair the moldability of rotational molding and the physical properties of products. A flame retardant, an antistatic agent, a lubricant, a foaming agent, a cross-linking agent, a coloring agent, a release agent and the like can be added. Examples of the filler include glass fiber, glass flakes, glass beads, silica, mica, talc, alumina, barium sulfate, magnesium oxide, calcium oxide, hydrotalcite and the like. Also, high-pressure polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, crystalline or amorphous ethylene-propylene copolymer, ethylene-propylene-diene copolymer, ethylene-butene-1 copolymer. Resins or elastomers such as polymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-vinyl acetate copolymer and the like can be blended.

The above-mentioned other resins, elastomers, additives such as fillers and various stabilizers and compounding agents are added to the resin according to the present invention by using a Henschel mixer, ribbon blender, tumbler, extruder, Banbury mixer, kneader and the like. After mixing by mixing, it is pulverized by means such as freeze pulverization and mechanical pulverization so as to have a particle size suitable for rotational molding. After that, the resin powder is put into a mold that rotates around one axis or two axes that intersect at right angles, a mold that swings and rotates, and the resin powder is adhered to the mold surface in a sealed state, melted, and cooled and taken out. The product can be obtained. When powders having different color tones are mixed during this molding, a product having a characteristic appearance can be obtained.

[0011]

The resin according to the present invention makes it possible to produce a rotomoulded article excellent in mechanical strength, low temperature characteristics and stress crack resistance. In particular, it has an excellent balance of impact strength, rigidity and stress crack resistance, has little warpage after molding, has little shrinkage, and has a property of being resistant to scratches.

Therefore, it is suitable for manufacturing hollow products and products having complicated shapes, and is suitable for manufacturing large tanks, containers, balls, garden products, furniture, machine parts, hollow bodies having irregular cross sections, outdoor products and the like. It can be used.

[0013]

EXAMPLES Next, the present invention will be described through examples. Examples 1 to 4 Copolymers of ethylene and 1-hexene were produced using a metallocene olefin polymerization catalyst containing zirconium. The 1-hexene content in the copolymer was 5.3 mol%, the average molecular weight distribution was 2.5, and its melting index and density are shown in Table 1. Freeze-pulverize this copolymer,
A powder having a particle size of 30 mesh or less is produced, and this powder is put into a cylindrical container-shaped mold and rotated under the conditions of a mold temperature of 270 ° C. and a molding time (heating 8 minutes, smoothing 2 minutes, cooling 5 minutes). Molding was performed to obtain a molded body having a wall thickness of 3 mm.

Test pieces were taken from the molded cylindrical container and tested for impact strength, rigidity and stress crack resistance (ESCR), and the results are shown in Table 1. The test was performed by the following method. (1) Izod impact test: Based on JIS K-7110, it was performed at -20 ° C under notched conditions. The unit is kg · cm / cm ² . (2) Olsen Rigidity Test: Conducted in accordance with ASTM D-747. The unit is shown in kg / cm ² . (3) Stress cracking property test: ASTM D-169
Compliant with 8 and 100% Antarox (C0-630)
It was carried out at 50 ° C. using the solution. The numerical value shows 50% breaking time (hr).

[0015]

[Table 1] * NB indicates that the test piece did not break in the impact test.

Claims (1)

[Claims] 1. A density of 0.920 to 0.955 (g / c)
m ³ ), melting index (MFR) 1 to 20 (g / 10 mi)
n) and a random copolymer of ethylene and α-olefin having a molecular weight distribution (Mw / Mn) of 2 to 3 and having a particle size of 30 mesh or less.