JPS5825576B2 - Manufacturing method of rotomolded products - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing rotomolded products such as tanks.

Conventionally, rotomolding is a method that is extremely difficult to mold unless the resin flows well, so polyethylene rotomolded products are made using polyethylene with good melting properties, and the rotomolding temperature is set to a high temperature of 170 to 270°C. It was manufactured by

This method is possible when using uncrosslinked polyethylene, but in that case, heat resistance, environmental stress cracking resistance, solvent resistance, etc. are insufficient, so it is not possible to use uncrosslinked polyethylene. could not be used.

In order to improve the above properties, polyethylene is usually cross-linked, but when polyethylene containing a general-purpose cross-linking agent such as dicumyl peroxide is molded at the above-mentioned high temperatures, the cross-linking agent is It has the disadvantage that it partially decomposes and causes early crosslinking, causing scorch and impairing processability.

In addition, the degree of crosslinking is easily affected by subtle differences in molding conditions (and is not consistent), often resulting in poor appearance such as rough skin and voids, and problems with properties.

Another drawback was that mold corrosion was likely to occur.

The inventors of the present invention have taken into consideration the above-mentioned drawbacks and have found that if hydrolytically crosslinkable silicone-grafted polyethylene is used as the polyethylene, the above-mentioned drawbacks will not occur even at high molding temperatures, and it can be crosslinked, making it extremely useful. Ta.

That is, the present invention is characterized in that, in producing a rotationally molded article made of polyethylene, hydrolytically crosslinkable silicone-grafted polyethylene is rotomolded at 170 to 270°C and crosslinked to a gel fraction of 10 to 60%. The present invention relates to a method of manufacturing a rotationally molded product.

Hydrolytically crosslinkable silicone-grafted polyethylene used in the present invention is produced by adding unsaturated polyethylene such as vinyltrimethoxysilane (VTMO8) or vinyltriethoxysilane to polyethylene in the presence of an organic peroxide such as dicumyl peroxide (DCP). A silicone-grafted polyolefin, which is grafted by reacting silane, and a catalyst masterbatch, which is prepared by adding a silanol condensation catalyst such as dibutyltin dilauret (DBTDL) or tin-octoate to polyethylene, are kneaded at a certain ratio. obtained or DCP
, VTMO8, and DBTDL are kneaded with polyethylene in one step, and crosslinking progresses by supplying moisture.

Conversely, in the absence of moisture, crosslinking will not proceed, and it can be handled in the same manner as uncrosslinked polyethylene, and rotational molding can be applied.

After molding, crosslinking occurs even at room temperature with a small amount of moisture in the air, so compared to conventional methods of crosslinking by decomposing organic peroxides, no special crosslinking is required, and therefore no crosslinking equipment is required.

Of course, warm water or the like may be used to speed up crosslinking.

In the present invention, the polyethylene includes low density polyethylene, high density polyethylene, etc., but high density polyethylene (density 0.930 to 0.970) is particularly preferred from the viewpoint of heat resistance.

In the present invention, it is appropriate for the hydrolytically crosslinkable silicone-grafted polyethylene to have a gel fraction of 10 to 60% after complete crosslinking; if the gel fraction is smaller than this, the heat resistance and environmental stress cracking resistance will be significantly reduced. However, if it is thicker than this, it will cause rough skin and voids.

Since the gel fraction is correlated with the grafting rate, for example, polyethylene 1
00 parts by weight to VTMO31.4 to 2.8 parts by weight,
DCPo, the grafting rate is adjusted by selecting 02 to 0.10 parts by weight, or silicone-grafted polyethylene with a grafting rate such that the gel fraction is 60% or more;
It is also possible to make the gel fraction 60% or less by blending non-grafted polyethylene.

The hydro-crosslinkable silicone-grafted polyethylene used in the present invention contains antioxidants commonly used in polyethylene, such as Antique Crystal (trade name, manufactured by Kawaguchi Chemical Co., Ltd.) and Irganox 1010 (trade name, manufactured by Nippon Ciba Geigy Co., Ltd.). can also be added.

Also, for the purpose of improving weather resistance, MARK1413, MAR
A benzophenone stabilizer such as K LA-72-A (trade name, manufactured by Adeka Argus) may also be added.

Next, an example will be described.

Example The silicone-grafted polyethylene shown in Table 1 and the catalyst masterbatch were kneaded at a ratio of 19:1, and the mixture was heated at 200°C.
Rotational molding was performed to produce a rotary molded product.

The gel fraction and environmental stress cracking resistance of this product were as shown in Table 2.

For comparison, Table 3 shows the properties of a product crosslinked with a conventional organic peroxide.

As is clear from the above results, the present invention has a stable degree of crosslinking and excellent environmental cracking resistance, has a good surface condition, and has improved processability, and can be used to manufacture gasoline tanks, solvent tanks, etc. It is extremely effective.

Claims (1)

[Claims] 1. In producing a rotomolded product made of polyethylene, 1.
Rotational molding at 70-270℃, gel fraction 10-60%
A method for producing a rotationally molded product, characterized by crosslinking it so that it becomes . 2. The method for manufacturing a rotomolded product according to claim 1, wherein the polyethylene is high-density polyethylene.