JPS5831101B2 - Manufacturing method for foamed polyolefin molded articles - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for producing a foamed polyolefin molded article.

BACKGROUND ART Conventionally, a method of producing a foamed polyolefin molded article using a chemical blowing agent such as azodicarbonamide (ADCA) has been known.

Generally, in such a method, a masterbatch method is adopted because a small amount of chemical blowing agent is used.

A masterbatch containing a chemical blowing agent is produced by mixing a sticky substance such as polybutene with a chemical blowing agent to form a paste, and kneading this into polyolefin using, for example, an open roll. This method requires a long time for kneading, making it unsuitable for mass production. In addition, there is a risk that dust and other impurities may be mixed in during the kneading process, and there is also a risk that a portion of the biochemical blowing agent will decompose. There was also a quality problem.

It is also possible to mix the granular polyolefin and a chemical blowing agent, feed the mixture directly to the extruder, and knead it in the extruder. There was a drawback that the chemical foaming agent was separated and unevenly distributed in the hopper, making it impossible to obtain a homogeneous foamed molded product.

The present inventors carried out research in order to eliminate such conventional drawbacks, and found that by mixing a chemical blowing agent with fine particle silica,
By sprinkling a chemical blowing agent around the periphery of the granular silica and then stirring it at high speed together with the granular polyolefin in a high-speed stirrer, the silica particles and the chemical blowing agent firmly adhere to the periphery of the granular polyolefin, forming a dense coating layer. was discovered to form.

The layer of fine silica particles and chemical blowing agent formed in this way does not peel off even in the air transport pipe, and when it is fed to an extruder and extruded at a temperature above the decomposition temperature of the blowing agent, it becomes homogeneous. A foamed polyolefin shaped body is formed.

The drawing shows a mixture of particulate silica and a chemical blowing agent (weight ratio 4).
0:60) and polyethylene pellets l- (small cylindrical bodies) adhered or coated with this mixture. (X200), Figure 2 shows the mixture 1 adhered to the surface of polyethylene pellets 20 by normal stirring [magnification, X200], Figure 3 shows the polyethylene pellets and the mixture mixed in a Henschel mixer. Mixture 2 was deposited in a dense layer on the surface of polyethylene pellets by stirring at a high speed of 26 Orpm (magnification, x200), and Figure 4 shows a cross section of this (magnification, x700). are shown respectively.

The thickness of the 10 layers of the mixture in FIG. 4 is approximately 10 μm.

Note that the mixture 1 of silica and chemical blowing agent is in a state of agglomeration in the form of nodules as shown in Figure 5 (enlarged photograph of Figure 1) before high-speed stirring (magnification, After stirring at high speed together with the pellets, the pellets are deformed into scales as shown in FIG. 6 (enlarged photograph of FIG. 3) (magnification: 3000).

It is not always clear why a mixture of particulate silica and a chemical blowing agent forms such a dense layer;
The electrostatic potential when polyethylene pellets alone are stirred at high speed is 4000V, the electrostatic potential when polyethylene pellets and a chemical blowing agent alone are stirred at high speed is 2700V, and the electrostatic potential when a mixture of polyethylene pellets and particulate silica-chemical blowing agent is stirred. The following can be considered from the fact that the electrostatic potential is 200 V and the micrographs shown in FIGS. 5 and 6.

That is, at the initial stage of high-speed stirring, the mixture of fine silica and chemical blowing agent is attracted to the surface of the polyethylene pellets by the attraction force due to static electricity, and then the chemical blowing agent acts as a binder due to collisions between the polyethylene pellets. Transform the nodule-like mixture into scales,
It is presumed that adjacent scale-like mixtures eventually join together to form a single, dense layer.

As the granular polyolefin used in the present invention, pellets of high density, medium density or low density polyethylene, silyl modified polyethylene or polypropylene are suitable.

The fine particle silica used in the present invention has an average particle size of 1 to 10 μm.
2 m is suitable, and as chemically bound water
Those containing ~20% water by weight are suitable.

This bound water is heated and dissociated in the extruder, promoting the foaming of the polyolefin, and also acts on cyanuric acid, which is produced as a by-product due to the decomposition of the chemical blowing agent, to decompose it and decompose it around the die hole of the extrusion die. Acts to prevent residue from adhering.

In addition to ADCA, chemical blowing agents include P-t-
Luene sulfonyl semicarbazide, trihydrazino(reazine) and other known chemical blowing agents can be used.

The mixing ratio of particulate silica and chemical blowing agent is 3 to 5:5.
(weight ratio) is suitable.

In addition, the mixing ratio of granular polyolefin and chemical blowing agent is
Approximately 100:0.05 to 100:1.0 (weight ratio) is suitable.

In the present invention, the above-mentioned components are charged into a high-speed stirrer equipped with stirring blades and stirred at a rotation speed of 100 rpm or more.

The stirring time is appropriately adjusted depending on the rotation speed from about 10 minutes at 100 m/p to about 30 seconds at 100 or/pom.

The granular polyolefin coated with the mixture of fine-particle silica and a chemical blowing agent obtained in this way is densified and firmly adhered to the granular polyolefin, so that it can be easily transported by air. The foamed polyolefin molded product does not peel off, and a homogeneous foamed polyolefin molded product can be formed by supplying it to an extruder together with a color masterbatch if necessary and extruding it under heating.

Next, examples will be described.

Examples High-density polyethylene pellets (melt index 0.40, density: 0.950) (Mitsui Petrochemicals, trade name Hi-Zex 5305 EF) ioo parts by weight (B) ADCA (60% by weight) and fine particle silica ( 40% by weight) (water content of fine particle silica: 10% by weight)
, surface area 200 m/? ) 0.35 parts by weight of the above components A and B were put into a 10,001 capacity Henschel mixer and stirred for 2 minutes at a stirring speed of 260 r, p, m.

As shown in the photographs in Figures 3 and 4, component B is adhered to the surface of the polyethylene pellet in a dense layer, and this layer shows almost no change even after air transportation. Ta.

Next, this pellet was supplied to the head of an extruder, and was extruded and coated onto a copper wire having an outer diameter of 0.5 mm (0.502 to 0.504 mm) under the following extrusion conditions to produce a communication cable core.

The outer diameter variation during manufacturing 40000m core is 0.73
5~0.742mvt, and the underwater capacitance is 297~
305PF7m, and no inferiority was observed compared to the core manufactured by the conventional masterbatch method.

[Brief explanation of drawings]

Figure 1 is a microscopic photograph of a mixture of fine silica particles sprinkled with a chemical blowing agent, and Figure 2 is a microscopic photograph showing a mixture of fine silica particles and a chemical blowing agent adhered to the surface of polyethylene pellets by normal stirring. , FIG. 3 is a micrograph showing the surface condition of the fine particle silica-chemical blowing agent mixture layer on the surface of the polyethylene pellet obtained according to the present invention;
FIG. 4 is a cross-sectional micrograph of the same, FIG. 5 is an enlarged photograph of FIG. 1, and FIG. 6 is an enlarged photograph of FIG. 3. 1...Mixture of particulate silica and chemical blowing agent, 2
...Polyethylene pellets.

Claims (1)

[Claims] 1. A chemical blowing agent is attached to the surface of particulate silica, and this is stirred at high speed with a high-speed stirrer together with particulate polyolefin to form a dense coating layer consisting of particulate silica and the chemical blowing agent on the surface of particulate polyolefin. A method for producing a foamed polyolefin molded article, which comprises: supplying the granular polyolefin coated with fine silica particles and a chemical blowing agent to an extruder and extruding it under heating. 2. The method for producing a foamed polyolefin molded article according to claim 1, wherein the fine particle silica contains 2 to 20% by weight of bound water. 3. The method for producing a foamed polyolefin molded article according to claim 1 or 2, wherein the granular polyolefin is a small cylindrical polyethylene body. 4 The ratio of particulate silica to chemical blowing agent is 3 near to 5
:5 (weight ratio). 5 The ratio of granular polyolefin to chemical blowing agent is 10
The method for producing a foamed polyolefin molded article according to any one of claims 1 to 4, wherein the ratio is 0:0.05 to 100:1.0 (weight ratio).