JPH0379181B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing hollow molded products, such as concave double-walled hollow molded products used as containers such as cases, trays, containers, and housing members for electrical appliances, automobile parts, office machines, tools, and others. . This kind of concave hollow double-wall molded product is generally hollow-formed by blow molding or vacuum molding, and the material used for this has good moldability.
Moreover, polyethylene is commonly used because it is inexpensive. However, the above-mentioned polyethylene has poor reproducibility of the mold cavity surface during molding, and it is not possible to clearly mold minute uneven surfaces such as embossed patterns, grained patterns, and fine engravings. surface appearance characteristics are poor;
In addition, there was a problem that the gloss and smoothness were poor, and flow lines of parison were likely to appear in the molded product. Conventional methods for solving the surface appearance characteristics of polyethylene molded products include (1) increasing the melting temperature of polyethylene, (2) increasing the temperature of the mold cavity surface, etc. With the method (2), the parison will cause drawdown, resulting in uneven wall thickness of the molded product and even difficulty in molding, and with the method (2), the molding cycle will be longer, making it impractical. In addition, there is a problem in that a heating device is required, which increases costs, and even with this method, the reproducibility of the mold is not satisfactory. It was difficult to mold the surface of the hollow molded product. Although the above conventional examples have been described using polyethylene as the molding material, substantially the same results will be obtained even if other polyolefin resins other than polyethylene are used, such as polypropylene. Further, in the case of a concave hollow double-wall molded product made of polyolefin resin, there was a problem in that a line-like bending line appeared at the bending part, impairing the surface appearance. The present invention has been developed in view of the above, and has made it possible to improve the surface appearance without significantly impairing the good blow moldability and low cost characteristic of polyolefin resins. It is an object of the present invention to provide a method for manufacturing a concave hollow double-walled molded product. Embodiments of the present invention will be described below with reference to the drawings. Fig. 1 shows a container with a hollow double-wall structure, in which the inner wall and other main layer 2 of the container 1 are made of polyethylene, and the outer skin layer 3 is made of ionomer resin. There is. The ionomer resin is a resin formed by crosslinking the linear chains of a base copolymer consisting of α-olefin units and unsaturated carboxylic acid units with metal ions that ionically bond to side chains of carboxylic acid groups.
In addition, α-olefin is an olefin consisting of unsaturated hydrocarbons with the general formula Cn- _H2n and has 5 to 20 carbon atoms, and unsaturated carboxylic acids are acrylic acid, methacrylic acid, etc. , maleic acid, etc., and metal ions include zinc, sodium, magnesium, etc. Examples of ionomer resins that have been commercialized include EI Dupont's "Surlyn," Mitsui Polychemical Co., Ltd.'s "Himilan," and Asahi Dow Co., Ltd.'s "Copolene."
The ionomer resin used in the present invention may contain other resins or additives as long as the properties of the ionomer are not impaired. Although the above ionomer resins are more expensive than polyolefin resins containing polyethylene, they have extremely good mold reproducibility and can be used to create extremely fine patterns on the mold, such as embossed patterns with an uneven surface of 0.5 mm or less in depth. It has the property of faithfully reproducing grain patterns, fine engravings, etc. Furthermore, the above-mentioned ionomer resin has better wear resistance than EVA resin or polyethylene. For this reason, the container 1 has its outer wall 3 made of ionomer resin.
An embossed pattern, a grained pattern, or a finely carved pattern can be applied to the surface, and the surface appearance can be made extremely good. In addition, by composing the skin layer with ionomer resin as described above, in addition to the surface with fine irregularities such as the embossed pattern mentioned above, it also has excellent mold reproducibility even on a flat surface. A glossy and smooth surface can be obtained without parison flow lines appearing on the surface of the product. Next, the method for manufacturing the container 1 is shown in Figures 3 to 5.
This will be explained with reference to the figures. First, polyethylene and ionomer are melt-kneaded using separate extruders. Then, both are supplied to one coextrusion die and extruded from an extrusion head 5 as a parison 4. At this time, only the outer wall surface of the molded article of the parison 4 is made of ionomer 5, for example, as shown in FIG. Such a parison 4 is positioned between the molds 7 and 8, the molds 7 and 8 are closed, and compressed air is then supplied into the parison 4 using the blowing needle 9 to perform expansion molding within the molds 7 and 8. do. After that, the molds 7 and 8 are cooled to cool the molded product,
The molds 7 and 8 are opened, the molded product is taken out, excess burrs are removed, and the molded product is obtained. In addition, in the present invention, in addition to the two layers consisting of ionomer resin/polyolefin resin, it is also possible to have two or more layers, such as four layers of ionomer resin/non-polyolefin resin/polyolefin resin/non-polyolefin resin. Examples and comparative examples of the present invention are shown below. This example and comparative example are 40mmφ, L/D=
Extruded with 18 extruder, total wall thickness 3mm, outer diameter
A container as shown in FIG. 1 was molded by blow molding using a 230 mm parison at a blowing pressure of 6 kg/cm ³ . The dimensions of this molded container are
It is 440mm long, 330mm wide, 45mm high, 15mm thick, 2mm thick on average, and weighs 1750g. The thickness of the skin layer of the parison and the depth of the embossing on the inner surface of the cavity were changed for each example and comparative example, and the moldability of the embossing formed on the surface of the skin layer and the surface appearance of the molded product were evaluated. Each was evaluated in three stages: ◯, △, and ×. Regarding the embossing formability, ◯ is good, △ is partially poor, and × is that almost no embossing is formed. Regarding the surface appearance of the molded product, ◯ indicates that the surface is good, △ indicates that streak-like roughness appears in some areas, and × indicates that almost the entire surface is rough. In Examples 1 to 10, the main layer was made of high-density polyethylene, and the outer skin layer of this main layer was made of ionomer. Comparative Example 1 is a single layer of high density polyethylene. Comparative Examples 2 and 3 used high-density polyethylene for the inner main layer and low-density polyethylene for the outer skin layer. Comparative Examples 4 and 5 used high-density polyethylene for the inner main layer and ethylene and vinyl acetate copolymer for the outer skin layer. The physical properties of the high-density polyethylene in each row above are MI 0.2g/10min, density 0.955g/cm ³ , hardness 68
(Short D), softening temperature 126 (Vikat ℃), and the ionomer is an ethylene-methacrylic copolymer crosslinked with zinc ions, and its physical properties are MI 0.7g/10min, density 0.95g/ cm ³ , hardness 65 (Shore D), and softening temperature 64 (Vikat ℃). Furthermore, the physical properties of the low density polyethylene used in Comparative Examples 2 and 3 are MI18g/10min, density 0.92
g/ ^cm3 . Cotylene used in Comparative Examples 4 and 5
The physical properties of the vinyl acetate copolymer are MI3g/10min density 0.94g/cm ³ . Regarding each of the above physical properties, MI (melt index) is based on ASTM-D-1238, and density is based on ASTM-D.
-1505, hardness is ASTM-D-1706, softening temperature is
Based on ASTM-D-1525.

【table】

[Table] In each of the above embodiments of the present invention, an example was shown in which the main layer was made of polyethylene, but
This is not limited to polyethylene; high
Polyolefin resins other than medium and low density polyethylene, such as ethylene such as polypropylene;
In addition to propylene homopolymers, ethylene and propylene, ethylene and 1-butene, ethylene and 1-
A copolymer of olefins such as hexene may also be used. The concave hollow double-walled molded product according to the present invention is as detailed above, and is molded with polyolefin resin as the main layer and ionomer resin as the skin layer, so it has good blow moldability, which is a characteristic of polyolefin resin. And, without sacrificing low cost, it also has extremely good surface appearance, for example,
It is possible to faithfully reproduce embossed patterns and fine engravings on the outer surface with an uneven surface of 0.5 mm or less in depth. Furthermore, the wear resistance of the ionomer resin constituting the skin layer is superior to other resins such as EVA resin and polyethylene, so a blow molded product with excellent wear resistance can be obtained. In addition, the above-mentioned concave hollow double-walled molded product is coextruded from an extruder using a polyolefin resin as the main layer and an ionomer resin as the skin layer as a multilayer parison, and this parison is blow-molded along the mold cavity. Therefore, the thickness of the expensive ionomer resin that forms the skin layer can be made extremely thin, and
By laminating the ionomer resin partially in the circumferential direction of the parison, only a partial skin layer of the molded article, for example, only the outer wall, can be laminated with the ionomer resin, thereby suppressing cost increase. In addition, when obtaining a container as shown in Figure 1, at the mold mating surfaces during molding, a parison part is made of two layers of ionomer resin/polyolefin resin, and a parison part is made of a single layer of polyolefin resin. By pinching off the boundary part, the boundary between the surface on which the skin layer is formed and the surface on which no skin layer is formed becomes clear, increasing the commercial value. In addition, in the case of a conventional concave container, for example, a line-like crease line clearly appeared on the surface of the bent part of the outer periphery of the bottom surface as shown in FIG. Even if a line occurs, that part is completely covered with the skin layer formed along the cavity surface, so the crease line does not appear visually and the appearance is not impaired.

[Brief explanation of drawings]

The drawings show embodiments of the present invention; FIG. 1 is a partially cutaway perspective view of a container, FIG. 2 is an enlarged sectional view of the container shown in FIG. 1, and FIGS. FIG. 5 is an enlarged sectional view taken along the - line in FIG. 3, which is an explanatory view of the method.

Claims (1)

[Claims] 1. A polyolefin resin as a main layer and an ionomer resin as a skin layer are coextruded from an extruder as a multilayer parison, and this parison is placed along a mold cavity having a minute uneven surface, with a polyolefin resin as the main layer, and an ionomer resin as the main layer. A method for manufacturing a concave hollow double wall molded article, characterized in that a concave hollow double wall body having a skin layer made of resin is hollow-molded.