JPS5950499B2 - injection blow molding equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a structure of a mold particularly suitable for hot runner injection blow molding of high density polyethylene.

Injection blow molding technology using a hot runner method is generally widely used, and its molded products are well known as containers for various beverages, household goods, and the like.

However, in the past, the molding materials were mainly limited to styrene resins. The reason for this is that in injection molding using the hot runner method, Parylin with a bottom is usually molded by injection from the center of the bottom, and the center of the bottom of the Parylin tends to become hotter than other parts. For Parilynn-based resins, even if Parilynn with a built-in injection core is transferred to a blow molding mold and blow-molded, there may be holes at the bottom of the Parylynn, abnormal blisters, or threads of resin when separated from the injection core. The reason is that there is almost no pulling phenomenon. On the other hand, however, stainless steel resins often pose hygiene problems in terms of leaching of additives and residual monomers, oil and fat resistance, etc., and depending on the filling contents, the use of high-density polyethylene is strongly desired. However, if high-density polyethylene is applied directly to the above-mentioned mold that previously used styrene-based resin, defects during blow molding such as the hole at the bottom of the parylene mentioned above will occur, making it impossible to produce a good product. . The inventors,
As a result of intensive research to overcome the above-mentioned drawbacks of injection blow molding using high-density polyethylene, we successfully solved the problem by using a new mold structure.

In other words, when molding a high-density polyethylene container with a flat center near the bottom by injection blow molding using a hot runner method, the blow molding bottom metal when the injection molding core is fixed in the blow molding cavity. The distance Tmm between the mold and the tip of the core for injection molding, the area S of the parallel surface portion where the distance is constant, and the wall thickness of the parallel surface portion of the injection molded bottomed parison (the center of the bottom of the parison) (This part is excluded because there is a protrusion of meat corresponding to the gate part)
Tmm and the volume of the gate part in injection molding Vmm. It has been found that the relational expression T - t = K - v / s holds true, and that good molding is possible when the coefficient K is 0.2 to 1.0.

Next, the present invention will be explained in detail using the drawings, which are one embodiment of the present invention.

Figure 1 shows the injection mold part, where 1 is a support rod for the core 2, 4 is a cavity, and the gap between 2 and 4 is filled with resin that is more plasticized than the injection port 7 through the gate part 6. It becomes parison 3. At this time, the resin present in the gate portion 6 (volume Vmm) remains in a protruding shape at the bottom of the parison 3. The area of the parallel surface portion 5 at the bottom of the parison corresponds to S. The planar part is the part indicated by the thick line. The parison bottom wall thickness is expressed as t as shown in the figure. next,
Cavity 4 is opened in two to form core 2 and parison 3.
Both are inserted into the blow molding mold 10 (FIG. 2), and the protruding part 8 corresponding to the gate part 6 is crushed and blow molded while expanding to the bottom surface of the container.

In this case, the core bottom surface 11 and the bottom of the blow mold 10. The distance between the surface portion 9 and the surface portion 9 is assumed to be T as shown in the figure. Figures 1 and 2
As is clear from the figure, T-t is the distance between the parallel surface portion 5 of the parison and the bottom surface portion 9 of the blow mold 10, and V/
S is (volume of gate part 6)/(parallel surface part 5 of parison)
area). T-t means the setting of the above-mentioned distance, and V/S means the degree of increase in wall thickness at the bottom of the product after the gate part 6 has expanded.
=K-V/S and found an appropriate range for K. If the distance T-t is too long, that is, if K exceeds l, it will tend to cause eccentricity of the center of the parison bottom during blow molding, poor thickness distribution at the bottom of the product, holes in the bottom of the product, etc. - If t is too short, that is, if K is less than 0.2, stringing may occur during mold release.

The conditions for using the apparatus of the present invention in injection blow molding are as follows:
It is similar to conventional injection molding and blow molding, so to speak, it is within the normal range, and the resin has a density of 0.945 g/Cm・or more,
It is a grade with good fluidity with a melt index of 1 g/10 mm or more, the resin temperature is 250 to 290°C, the injection cavity cooling water temperature is 30 to 80°C, and the injection core temperature is 1
40~170℃, injection pressure 110~135kg/C
m2, injection time is 1.5~3sec, cooling time is 0.3
~1sec, blow molding air pressure is 4 ~5.5kg/Cm
2, and although there may be slight differences in the melt viscosity and melt tension of the resins, the apparatus of the present invention is suitably used under such usage conditions. The present inventors performed injection blow molding using high-density polyethylene in different molds of T, t, v, and s, and took (T-t)Mm as the vertical axis and (v/s)Mm. Taking the horizontal axis, make a comprehensive judgment on whether the injection blow molding is good or bad (shape of the bottom of the product, eccentricity at the center of the bottom of the parison during blow molding, stringiness during mold release, wall thickness distribution at the bottom of the product, etc.) Figure 3 plots the results.

As shown in Figure 3, the value of K is approximately 0.24K41.
Must be at 0. In this example, high-density polyethylene resin S6Ol5 (manufactured by Showa Yuka Co., Ltd., density 0.960 g/Cm3, melt index 1.5 g/Cm3) was used.
10 mm), and the conditions during injection and blow molding were as follows. Resin temperature 285℃ Injection cavity cooling water temperature 70℃ Injection core temperature control oil temperature 160℃ Injection pressure 120g/Cm・Injection time 2.0sec Cooling time.

．． 6sec blow molding air pressure 4.5kg/Cm2

[Brief explanation of the drawing]

Figure 1 is a vertical cross-sectional view of the mold and parison showing the injection molded state, and Figure 2 shows the injection molded parison of Figure 1 and its core housed in the blow molding mold. FIG. 3 is a vertical cross-sectional view showing the T-t value on the vertical axis.
FIG. 3 is a diagram plotting formability with the value of v/s taken as the horizontal axis. 1... Core support punch, 2... Core, 3...
Parison, 4...Cavity, 5...Parallel bottom part of the parison, 6...Gate part, 7...
Injection port, 8...Protrusion, 9...Blow molding mold bottom part, 10...Blow molding mold, 11--core bottom surface.

Claims (1)

[Scope of Claims] 1. In an apparatus for molding a high-density polyethylene container having a flat center near the bottom by injection blow molding using a hot runner method, a bottom mold for blow molding and a tip end of a core for injection molding are used. The distance T (mm) is T-t=K・v/
s However, t: Thickness of the parison at the bottom of the injection molded parison excluding the protruding part corresponding to the gate part by injection molding (mm) K: 0.2 to 1.0 (coefficient) v: Gate in injection molding Volume of part (mm^3) s: Use a mold that has the relationship expressed by the area of the part where the bottom mold for blow molding and the bottom surface of the core for injection molding facing it are parallel to each other (mm^2). An injection blow molding device featuring: