JPH03216A - Multi-layered rotationally molded body - Google Patents

Abstract

PURPOSE:To obtain a rotationally molded body, the thickness of each layer of which is uniform and which has excellent layer constitution, by a method wherein the melt tension of resins excluding the resin used in the innermost layer are controlled in multi-layered rotational molding. CONSTITUTION:Materials used in all the layers excluding the material used in the innermost layer are selected from resins, the melt tensions at 230 deg.C of which are larger than 0.5g. The innermost layer is formed at the final stage in multi-layered molding and can be made of polyolefin, ethylene-vinyl acetate copolymer, ABS resin or the like. Resin powder for outer layer 2 is charged in a rotationally molding metal mold and thermally melted in a furnace, the temperature of which is held at 240 deg.C, under the condition that the mold is under rotation. At the time when the melting of the powder completes, heating is discontinued so as to charge stock resin powder for inner layer 1 by opening the opening of the mold. After that, the resins are again melted and shaped in the furnace held at 240 deg.C under the condition that the mold is under rotation. After the finish of melting, the mold is taken out of the furnace and cooled down so as to obtain a two-layered rotationally molded product.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a multilayer rotomolded body obtained by a new molding method, and more specifically, to an excellent multilayer rotomolded body with a uniform interlayer thickness structure. It is related to.

[Conventional technology] Conventionally, the single-turn molding method has lower mold manufacturing costs than other molding methods, so it is suitable for obtaining large molded products in high-mix, low-volume production. It is preferred for manufacturing large tanks made of stainless steel.

The resins used in this rotational molding method include high-density, medium-density, or low-density polyethylene, EVA, ABS,
They were polyamide, polycarbonate, etc.

In rotomolding, if different types of resins are combined to produce a multilayer rotomolded product, it is expected that by taking advantage of the characteristics of each resin, it will be possible to obtain superior properties not found in current single-layer rotomolded products. .

Attempts were made to do so, but due to the following technical difficulties,
At present, it has hardly been commercialized.

[Problem to be solved by the invention] That is, the biggest technical difficulty is that the principle of shaping in the rotational molding method depends only on the natural flowability of the entire molten resin in the mold under gravity. Therefore, it is difficult to obtain a uniform thickness structure of each layer as in other multilayer molding methods, such as coextrusion molding.

The inventors of the present invention have conducted various studies regarding the reason. 2. After the molding of the layers other than the innermost layer is completed, and while the molding of each layer is continued until the subsequent stage reaches the innermost layer, It has been found that the viscosity of the layer decreases due to the increase in temperature of the layer during additional heating, and that excessive fluidity is the main cause of disturbance in the thickness of the layer.

[Means for Solving the Problem] As a result of intensive studies on this point, the inventors have discovered that by regulating the melt tension of the resin used for layers other than the innermost layer in rotational molding, the thickness structure of each layer can be made uniform. The present invention was completed by discovering that a multilayer rotomolded body of excellent quality could be obtained.

That is, in the present invention, all layers except the innermost layer are heated to 230°C.
This is a multilayer rotomolded body characterized by being made of a resin having a melt tension of more than 0.5 g.

Here, melt tension is an index for determining the degree of moldability difficulty due to elongation flow during melt molding processing of a thermoplastic resin, and is measured by the following method.

Using a heating furnace specified in 1 failure tension (JIS K7210fMFR test method), the melt tension is the tension shown when the melted discharged resin is withdrawn from an orifice of specified dimensions at a constant speed under the following conditions.

Measurement conditions Melting temperature = 230℃ Load applied to molten resin: 2.16kg (cylinder diameter 0
．． 955cn+) Orifice dimensions: Diameter 0.2095cIT+Length 0
．． 8 cm Take-up speed: 3.9 m7 minutes Equipment name: Melt tension tester (newly manufactured by Toyo Seiki Seisakusho) Materials for layers below the innermost layer In the present invention, the material used for all layers except the innermost layer is 230
melt tension at °C greater than 0.5 g, preferably 1 g
It is necessary to choose a resin that is larger.

The melt tension at 230°C used for the layer in the present invention is 0.
．． To obtain a material that satisfies the condition that the weight is greater than 5g, 2. For example, in the case of polyethylene, M of high-pressure polyethylene manufactured under a pressure of 1500kg/cm or more
F R (190°C, 2.16 kg) is lower than 10 g 710 minutes, and among medium and low pressure polyethylene produced at a pressure of 300 kg/cm" or less, the MFR is 1.

It is possible to easily select from among those lower than g710 minutes. The material is not limited to polyethylene, but may be any material that satisfies the above conditions, and may include powdered blends of various resins,
Alternatively, it may be mixed as a powder.

The innermost layer of the above-mentioned multilayer rotomolded body is molded at the last stage of multilayer molding.The raw materials for the innermost layer used in the present invention include polyolefin and ethylene-vinyl acetate copolymer. (E
VA), ABS resin, as well as engineering plastics such as polyamide polycarbonate and polyvinylene fluoride, any resin used for known rotational molding can be selected depending on the purpose, and there are no particular limitations. If we take polyethylene as an example,
MFR (190℃, 2.16kg) is 1-20g/10
It is preferable to use up to 10 minutes, especially in the range of 2 to 10 g/10 minutes. If the MFR is larger than 20, the resin sag on the inner surface tends to be thick and the MFR
When FR is less than 1, the smoothness of the inner surface tends to be insufficient. Note that, of course, materials for layers other than the above-mentioned innermost layer may be used as the material for the innermost layer.

The multilayer rotomolded article referred to in the present invention can be produced using known rotomolding equipment, regardless of whether it is a direct heating method or an indirect heating method.

The resin powder used for rotational molding has a particle size of 20 to 5
A material having a mesh size of 0 mesh or less, preferably 30 to 40 meshes is used, and usually a mechanically pulverized resin pellet is used, but the resin powder obtained in the polymerization process may be used as it is.

First, raw resin powder for the first layer (outermost layer) and an appropriate amount of mold release agent powder as needed are put into a rotary molding mold.
Is it similar to the known rotational molding method? The resin is heated and melted from the outside of the mold to a temperature above the melting point of the resin by heating the mold directly with a burner or indirectly in a furnace while simultaneously rotating or swinging the mold around two axes that are perpendicular to each other. The material is flowed and blown, and shaped into a mold shape.

When shaping is almost completed, heating of the mold is stopped. Alternatively, the mold is taken out of the heating furnace, the injection port of the mold is opened, the resin raw material powder for the second layer is introduced, and the second layer resin is melted and shaped while being rotated and heated again.

In principle, any number of layers after the third layer can be formed using the same procedure if necessary depending on the design of the layer structure of the product.

In this case, it is preferable that the interruption of heating for inputting raw materials for the second and subsequent layers be as short as possible from the viewpoint of uniformity of layer thickness, preferably within 3 minutes, and more preferably within 1 minute.

Examples of products made by multilayer rotational molding include tanks with improved heat resistance or chemical resistance. In this case, it is conceivable to use an inexpensive polyolefin as a structural material for the outer layer, and to use a resin with excellent heat resistance or chemical resistance for the innermost layer that comes into contact with the contents. Furthermore, if necessary, an adhesive layer may be provided in the middle, and if the appearance of the product is important, the outermost layer may be painted or textured.

[Example] In the following Examples and Comparative Examples, the MFR of the raw resin is a value measured at 190°C and a load of 2.16 kg, and the melt tension is measured at a temperature of 230°C using a melt tension tester type II owned by Toyo Seiki. , extrusion speed 0.716ctm3/
The measurement was carried out under conditions of 3-9 m and 7 minutes of take-up speed.

Example 1 As shown in Table 1, Mitsubishi Yuka High Density Polyethylene [DPEI B Z 50A] was used as the resin for the outer layer, and polyvinylidene fluoride (PVDFJ Kynar 710 manufactured by Penwald Co., Ltd.) was used as the resin for the inner layer. The powder was pulverized using a type 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 rotary molding mold with a capacity of 2
The mold was heated and melted in a furnace maintained at 40° C. while rotating the mold. When the melting was completed, the heating was temporarily interrupted, the mold opening was opened, and the raw material resin powder for the inner layer was introduced, and then the mold was rotated again in the furnace at 240° C. to melt and shape the resin.

After the melting was completed, the product was taken out of the furnace and cooled to give a rotomolded product having a two-layer structure as shown in FIG. 1. The layer structure was such that the outer layer 2 had a thickness of 4 mm and the inner layer 1 had a thickness of 1 mm, and as shown in FIG. 2, the thickness was uniform and good.

Example 2 The resin for the outer layer in Example 1 was changed from high-density polyethylene to the same high-density polyethylene and Mitsubishi Yuka's linear low-density polyethylene + LLDPE) Z90H at a weight ratio of 60:
Molding was carried out in the same manner as in Example 1 except that the mixture was changed to No. 40. The cross section of the molded product was good as shown in FIG.

Example 3 Example 2 except that the blending ratio of high-density polyethylene and low-density polyethylene was changed to 30:70.

It was molded in the same manner as in Example 2. The cross section of the molded product was good as shown in FIG.

Comparative Example 1 Molding was carried out 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 290F (manufactured by Mitsubishi Yuka Corporation). The cross section of the molded product is shown in Figure 3. As shown in the figure, there was a variation in the thickness of the outer layer, indicating that the product was defective.

Comparative Example 2 Molding was carried out 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 890K manufactured by Mitsubishi Yuka. As shown in FIG. 4, the cross section of the molded product was found to be defective, with significant thickness variations in the outer layer.

Measured values of VFR and melt tension of the raw resins of each of the above Examples and Comparative Examples are shown in Table 1.

[Effects of the Invention] According to the present invention, when carrying out multilayer rotational molding, by regulating the melt tension of resins other than the innermost layer, it is possible to obtain a rotationally molded body with uniform thickness of each layer and excellent layer structure. I can do it.

[Brief explanation of the drawing]

FIG. 1 shows a vertical cross-sectional view of two-layer rotomolded bottles molded in Examples and Comparative Examples. 2 to 4 are enlarged views of section A in FIG. 1. l: Inner layer 2: Outer layer

Claims (1)

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