JP2739654B2 - Multi-layer rotary molding - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a molded article obtained by a novel molding method called a multilayer rotational molded article, and more particularly, to an excellent multilayer rotational molded article having a uniform interlayer thickness structure. It is about.

[Prior art] Conventionally, the rotational molding method is suitable for obtaining large-sized molded products of small-scale production of many kinds because the mold manufacturing cost is lower than other molding methods. It is used to manufacture large tanks made of steel.

The resin used in this rotational molding method was high density, medium density or low density polyethylene, EVA, ABS, polyamide, polycarbonate and the like.

In this rotational molding, if a multi-layer rotational molded article is manufactured by combining different kinds of resins, it is expected that the characteristics of each resin will be utilized and excellent characteristics not present in the present single-layer rotational molded product will be obtained. Attempts have been made, but at present it has hardly been commercialized due to the following technical difficulties.

[Problems to be Solved by the Invention] That is, of the technical difficulties, the biggest one is that the principle of shaping in the rotational molding method depends only on the natural fluidity of the molten resin in the mold under gravity. Therefore, it is difficult to obtain a uniform thickness configuration of each layer as in other multilayer molding methods, for example, a coextrusion molding method.

The present inventors have conducted various studies on the reason, and as a result, the layers other than the innermost layer, after the molding of the layer itself is completed, while the molding of each layer is continued until the subsequent stage reaches the innermost layer, In addition, it was further heated, during which the viscosity of the layer was reduced by the increase in temperature, and it was found that excessive fluidity was the largest cause of disturbing the thickness of the layer.

[Means for Solving the Problems] As a result of intensive studies on this point, the inventors have found that by regulating the melt tension of the resin used for the layers other than the innermost layer in rotational molding, the thickness configuration of each layer is uniform. The present invention has been accomplished by finding that a multilayer rotational molded article of excellent quality can be obtained.

That is, in the present invention, all layers except the innermost layer
Is a resin having a melt tension of more than 0.5 g.

Here, the melt tension is a judgment index of the moldability difficulty due to the elongational flow during melt molding of the thermoplastic resin,
It is measured by the following method.

Melt tension Using a heating furnace specified in JIS K7210 (MFR test method), the tension indicated when the molten resin discharged from the orifice of the specified dimensions is taken out at a constant speed under the following conditions is defined as the melt tension.

Measurement conditions Melting temperature: 230 ° C Load applied to the molten resin: 2.16 kg (cylinder diameter 0.955 cm) Orifice dimensions: diameter 0.2095 cm length 0.8 cm Take-off speed: 3.9 m / min Equipment name: Melt tension tester (Toyo Seiki Seisakusho) Materials of layers other than the innermost layer In the present invention, the material used for all the layers other than the innermost layer is 230
It is necessary to choose from resins whose melt tension at 0 ° C. is greater than 0.5 g, preferably greater than 1 g.

The melt tension at 230 ° C. used for the layer in the present invention is 0.5
To obtain a material satisfying the conditions that it is larger than g, such MFR (190 ° C. Among the high-pressure polyethylene manufactured under 1500 kg / cm ² or more pressure if polyethylene, 2.16K
g) is lower than 10 g / 10 minutes, and the above-mentioned MFR is 10 g among medium- and low-pressure polyethylene produced at a pressure of 300 kg / cm ² or less.
It is easy to choose from those lower than / 10 minutes. In addition, the material is not limited to polyethylene, as long as it satisfies the above conditions,
Powdered materials obtained by blending various resins, or powdered materials may be used.

Material of innermost layer The innermost layer of the above-mentioned multilayer rotomolded article is formed at the last stage of the multilayer forming, and the raw material of the innermost layer used in the present invention includes polyolefin, ethylene-vinyl acetate copolymer (EVA), ABS In addition to resins, polyamide, polycarbonate, including engineering plastics such as polyvinylidene fluoride, any resin used for known rotary molding can be selected according to the purpose, and is not particularly limited. However, taking polyethylene as an example,
Preferably, the MFR (190 ° C., 2.16 kg) is up to 1 to 20 g / 10 minutes, and particularly preferably in the range of 2 to 10 g / 10 minutes. MFR is 20
If it is larger, the sagging of the resin on the inner surface tends to increase, and if MFR is smaller than 1, the smoothness of the inner surface tends to be insufficient. Of course, a material of a layer other than the above innermost layer may be used as a material of the innermost layer.

Rotational Molding The multilayer rotationally molded article referred to in the present invention can be produced using a known rotational molding equipment regardless of a direct heating method or an indirect heating method.

The resin powder used for rotational molding has a particle size of 20 to 50.
Mesh or less, preferably 30 to 40 mesh, is used. Usually, resin pellets obtained by mechanical pulverization are used, but resin powder obtained in the polymerization step may be used as it is.

First, the raw material resin powder for the first layer (outermost layer) and, if necessary, an applied amount of the release agent powder are charged into the mold for rotation molding, and the mold is set at a right angle in the same manner as in the known rotation molding method. While simultaneously rotating or swinging around the two axes forming the direction,
The resin is heated and melted from the outside of the mold to a temperature higher than the melting point of the resin by heating directly with a burner or indirectly in a furnace to give fluidity and shape the mold.

When the shaping is almost completed, the heating of the mold is stopped. Alternatively, the mold is taken out of the heating furnace, the inlet of the mold is opened, the resin raw material powder of the second layer is charged, and the second layer resin is melt-shaped while rotating and heating again.

If necessary according to the design of the layer structure of the product, the third and subsequent layers can be formed in the same procedure in principle for any number of layers.

In this case, it is preferable to interrupt the heating for charging the raw material after the second layer as short as possible from the viewpoint of uniformity of the thickness of the layer, preferably within 3 minutes, more preferably within 1 minute.

Multi-layer rotational molded article Examples of products produced by multilayer rotational molding include tanks having improved heat resistance or chemical resistance. In this case, it is conceivable that an inexpensive polyolefin is used as a structural material for the outer layer, and a resin having excellent heat resistance or chemical resistance is used for the innermost layer that contacts the contents. If necessary, an adhesive layer may be provided in the middle, and if the appearance of the product is valued, the outermost layer may be painted or textured.

[Examples] In the following Examples and Comparative Examples, the MFR of the raw material resin was 1
Measured at 90 ° C under a load of 2.16 kg.The melt tension was measured using a Toyo Seiki Seisakusho's melt tension tester type II.
The measurement was performed at 230 ° C., an extrusion speed of 0.716 cm ³ / min, and a take-up speed of 3.9 m / min.

Example 1 As shown in Table 1, high-density polyethylene (HDPE) BZ50A manufactured by Mitsubishi Yuka Co., Ltd. was used as the resin for the outer layer, and polyvinylidene fluoride (PVDF) Kiner 710 manufactured by Penwort was used as the resin for the inner layer. Each was pulverized by a mechanical pulverizer to obtain a powder that passed through a 30-mesh wire mesh but did not pass through a 40-mesh wire mesh. First, the resin powder for the outer layer was put into a 5-volume rotary molding die, and heated and melted in a furnace maintained at 240 ° C. while rotating the die. When the melting was completed, the heating was temporarily stopped, the opening of the mold was opened, and the raw material resin powder for the inner layer was charged. Then, the mold was again rotated in a furnace at 240 ° C. to melt and shape the resin.

By taking out from the furnace after the completion of melting and cooling,
A rotary molded product having a two-layer structure as shown in FIG. 1 was taken out. The outer layer 2 has a thickness of 4 mm and the inner layer 1 has a thickness of 1 mm.
As shown in the figure, the thickness was uniform and good.

Example 2 Except for changing the resin for the outer layer in Example 1 from a high-density polyethylene to a 60:40 weight ratio of the same high-density polyethylene and Mitsubishi Yuka Linear Low Density Polyethylene (LLDPE) Z90H The molding was performed in the same manner as in Example 1. The cross section of the molded product was good as shown in FIG.

Example 3 Molding was carried out in the same manner as in Example 2 except that the mixing ratio of high-density polyethylene and low-density polyethylene in Example 2 was changed to 30:70. The cross section of the molded product was good as shown in FIG.

Comparative Example 1 A molding was performed in the same manner as in Example 1 except that the resin for the outer layer in Example 1 was changed from high-density polyethylene to linear low-density polyethylene Z90H manufactured by Mitsubishi Yuka Corporation. As shown in FIG. 3, the cross section of the molded product was defective because the thickness of the outer layer varied.

Comparative Example 2 Molding was performed in the same manner as in Example 1 except that the resin for the outer layer in Example 1 was changed from high-density polyethylene to linear low-density polyethylene R90K manufactured by Mitsubishi Yuka Corporation. As shown in FIG. 4, the cross section of the molded product was defective because the outer layer had a remarkable thickness variation.

Table 1 shows the measured values of the MFR and the melt tension of the raw material resins of the above Examples and Comparative Examples.

[Effects of the Invention] According to the present invention, when performing multi-layer rotational molding, by controlling the melt tension of the resin other than the innermost layer, it is possible to obtain a rotational molded body having a uniform thickness of each layer and an excellent layer configuration. Can be.

[Brief description of the drawings]

FIG. 1 is a vertical cross-sectional view of a two-layer rotomolded bottle formed in Examples and Comparative Examples. 2 to 4 are enlarged views of a portion A in FIG. 1: Inner layer, 2: Outer layer

Claims (1)

(57) [Claims] 1. A multilayer rotomolded article wherein all layers except the innermost layer are made of a resin having a melt tension at 230 ° C. of more than 0.5 g.