JPS6058009B2 - Multilayer container manufacturing method and molding mold - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for molding a multi-layered plastic container made of two or more types of thermoplastic resins, and a molding die used therein. The present invention relates to a method for manufacturing a multilayered plastic container by injecting two or more thermoplastic resins into a cavity from the same gate (or spool), and a mold used for the same.

Methods of manufacturing multilayer articles by sequentially injecting two or more resins into the same mold cavity are well known in the art.

These have been mainly used to manufacture large, thick molded products using foamed resin mixed with a foaming agent or gas as the inner core material and non-foamed resin as the outer skin material. However, this mold is designed so that the wall thickness of the finished molded product is relatively uniform everywhere, and this mold can be used to create molded products using two or more types of non-foaming resin. When a thin-walled plastic container is molded, the skin material 2 near the gate becomes extremely thin as shown in FIG. 1, which causes stress to easily occur and reduces drop strength. For example, as an example of molding using a conventional molding die, a modified polypropylene resin is used as the outer skin material, nylon 6 resin is used as the inner core material 3, and as shown in Fig. 2, at the center gate,
First, heat-melted modified polypropylene resin (skin material) 2 is placed in an injection mold with a uniform wall thickness for a molded product in an amount insufficient to fill the mold cavity (20 to 4
Salvation percentage) injection, the modified polypropylene resin 2
Before the center of the mold has solidified, heated and melted nylon 6 resin (inner core material) 3 is injected into the modified polypropylene resin 2 in the mold cavity, filling the mold cavity with the resin and cooling. There is a manufacturing method in which the modified polyolefin resin layer 2 near the gate is easily cracked by a light impact and easily peeled off from the gate portion. In addition, the adhesive strength between the modified polyolefin resin 2 and the nylon 6 resin 3 on the opposite side of the gate is 20 when peeled off in a T-shape.
In some cases, the strength is as low as g/15wt or less, and the strength is almost that of an unbonded adhesive. The inventor is
The object of the present invention is to provide a method for manufacturing a multilayer plastic container that eliminates the above-mentioned drawbacks, and a mold for use in the same. That is, the manufacturing method of the present invention is a method for manufacturing a multilayer container by sequentially injecting two or more types of thermoplastic resins into the same mold cavity. The total cross-sectional area S of the cross section at is a certain distance R
2, and near the gate Rl, r2,
and Rl such that the molded product thickness Tl, t2, t3 at each point R3, which is farther from the gate than R2, satisfies the following formula 1.
, r2, and r3, (b) first inject the outer skin material into the mold cavity in an amount greater than the volume from the gate to R2 and less than the volume of the mold cavity, and then inject one or more of the following: This is a method for manufacturing a multilayer container characterized by sequentially injecting the above-mentioned inner core materials.

In addition, it is preferable that it is 0.9 t3 or less, and more preferably about 0.4-0.8 t3. FIG. 3 is a sectional view showing this mold and its surroundings, and FIG. 4 is an enlarged sectional view near the gate. FIG. 5 is a partial cross-sectional view of a container obtained according to the invention, which corresponds to the position of the mold in FIG. Further, FIG. 6 is an explanatory diagram for explaining the cross-sectional area of the container at the same position, and since this cross-sectional area coincides with the cross-sectional area S inside the cavity, the same symbol S is attached.
FIG. 7 is a sectional view showing equipment around a mold for manufacturing containers. Further, FIGS. 8 and 9 show the relationship between the distance r from the gate of the mold shown in FIG. 3 and the total cross-sectional area at that distance, and the relationship between the distance r from the gate and the thickness of the molded product. Hereinafter, the present invention will be explained using this drawing. First, a thermoplastic resin (for example, polypropylene graft-modified with maleic anhydride) 2 that will become the outer skin material and a thermoplastic resin (for example,
Nylon 6) 3 is heated and melted, and each is weighed and filled into independent injection cylinders 5. Then, from the center gate 4 of the mold cavity of the present invention, the outer skin material is first applied in an amount that is at least more than the volume of the mold cavity from the gate 4 to a point corresponding to point R2, and less than or equal to the volume of the mold cavity. Fill by injection. At this time, if possible, before the outer skin material 2 is completely removed from the injection cylinder 4 and after the outer skin material 2 has filled the mold cavity from the gate to the point corresponding to point R2, the inner core material 2 The inner core material 3 is injected into the outer skin material 2 in the mold cavity by making the injection pressure higher than the injection pressure of the outer skin material 2, and the injection of the inner core material 3 is completed, At the same time as the resin in the mold cavity decreases, the outer skin material 2 is injected and filled into the mold cavity once again to completely fill the mold cavity with resin, and the resin is cooled and solidified. As shown in FIG. 3, when injection molding is performed using the mold cavity of the present invention,
As shown in FIG. 5, a uniform multilayer molded product can be obtained near the gate of the molded product, and there is little stress. As shown in FIG. 6, the cross-sectional area S in the present invention is defined by the molded product thickness t.
is multiplied by the distance r from the gate and twice the circumference, that is, expressed by the following equation 2.

(7) The difference between r and S is shown in FIG. 8, and S is relatively large at point r1 near the gate.
It becomes minimum at a certain distance R2, and a point R3 farther than this
It's a big deal. Further, as shown in FIG. 9, the molded product thickness t becomes minimum at a distance R2, and is larger at a point r1 closer to the gate and at a point R3 farther from the gate.

Tl, t2, and t3 satisfy Equation 1 below. The resin used in the present invention may be any thermoplastic resin, but examples include modified polyolefins (polyolefins graft-modified with monomers such as unsaturated polycarboxylic acids and their acid anhydrides), polyamide resins, Possible combinations include a modified polyolefin, a saponified ethylene-vinyl acetate copolymer modified polyolefin, and polyvinylidene chloride, a modified polyolefin and polyester, an inorganic-filled modified polyolefin, a polyolefin, and a polyamide resin.

The container manufactured according to the present invention has uniform wall thickness in each layer, so
Compared to conventional molds that use the same resin in the same amount, a container with lower moisture permeability and higher gas barrier properties can be created, with less stress, improved impact strength and drop strength, and improved adhesion between resin layers. Strength is also improved.

[Brief explanation of the drawing]

Figures 1 and 2 are explanatory diagrams explaining the conventional method, Figure 3 is a sectional view of the mold of the present invention, Figure 4 is a partially enlarged view of Figure 3, and Figure 5 is a portion of the molded product. Cross-sectional view, Fig. 6 is an explanatory drawing, Fig. 7
The figure is a partial sectional view of the device, and FIGS. 8 and 9 are graphs showing the relationship between the distance r from the gate, the cross-sectional area S, and the molded product thickness t. 1... Container, 2... Shell material, 3...
... Inner core material, 4 ... Gate, 5 ... Injection cylinder, 6 ... Mold cavity.

Claims (1)

[Claims] 1. A method for manufacturing a multilayer container by sequentially injecting two or more thermoplastic resins into the same mold cavity, comprising: (a) equidistant r from the gate of the mold cavity; The total cross-sectional area S of the cross section becomes minimum at a certain distance r_2, and the thickness of the molded product t_1 at each point near the gate r_1, r_2, and point r_3 farther from the gate than r_2.
, t_2, t_3 satisfy the following formula (1), r_1,
Using a mold in which r_2 and r_3 exist, 0.9t_1>
t_2, t_3>t_2... (1) (b) First, the outer skin material is injected into this mold cavity in an amount greater than the volume from the gate to r_2 and less than the volume of the mold cavity, and then one kind of A method for manufacturing a multilayer container, characterized by sequentially injecting inner core materials of 1 or more core materials. 2 In a mold for injection molding, the total cross-sectional area S of a cross section located at an equal distance r from the gate of the mold cavity is a certain distance r
It becomes minimum at _2, and near the gate r_1, r
The molded product thicknesses t_1, t_2, and t_3 at each of _2 and point r_3 farther from the gate than r_2 are expressed by the following formula (1).
A mold for forming a multilayer container, characterized by the existence of r_1, r_2, and r_3 that satisfy the following. 0.9t_1>t_2, t_3>t_2...(
1)