JPH0624172Y2 - Parison for injection blow of 4 or more cone-shaped bellows - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a parison for injection blow molding. More specifically, the present invention relates to a parison for injection blow molding of bellows products having a conical shape with four or more peaks.

(Prior Art) Injection blow molding is an injection process of injecting a molten resin into a mold to form a tubular parison with a bottom, and immediately enclosing the parison in a blow mold to expand it into a final shape. The process is carried out continuously (Plastic Processing Technology Handbook P287-288 Nikkan Kogyo Shimbun 1969
Published on December 5th). The material used in this injection blow molding is preferably a fluid material with low viscosity because it must be injection molded in a short time during the injection process, but on the other hand, before it solidifies in the blow process. Since it can be spread as it is in a molten state, it is a trade-off relationship that a higher viscosity is preferable. Therefore, the material is usually selected in accordance with the blow process, so that the material is difficult to flow in the injection process. For this reason, conventionally, it has been common knowledge that the parison is formed into a tube having a uniform thickness and a low flow resistance.

(Problems to be solved by the invention) However, when a conical hollow molded product or a conical tubular product having a complicated shape such as a bellows having a gradually increasing diameter is produced by using such a parison, it is difficult to blow in a blowing process. Products with locally different up ratios and greatly different wall thicknesses are produced. For this reason, conventionally, the injection blow molding method is not suitable for producing a conical hollow molded product having a uniform wall thickness, in particular, a product such as a conical bellows which has a complicated shape and spreads over the whole. ing.

Therefore, the inventor of the present invention considered eliminating the large difference in wall thickness when the parison was finished by pre-injecting the parison into a conical cylinder close to the product (final shape).

However, when the parison is injection-molded into a taper shape that spreads toward the end, the gas is contained in the resin as bubbles because the injection molding is performed at an open pressure. Further, since the resin flowing along the cavity mold and the resin flowing along the core mold have different flow velocities, the flow becomes complicated and the internal resistance tends to remain. For this reason, there has been a problem that many defective products such as sink marks, bubbles, and voids are generated in the parison.

An object of the present invention is to provide a parison suitable for manufacturing a bellows product having four or more cones by injection blow.

(Means for Solving the Problem) In order to achieve such an object, a parison for injection-blowing four or more conical bellows of the present invention has a thin conical surface portion and four or more thick wall portions. Is continuously formed, and the thick wall portion is formed at a position corresponding to the peak portion of the bellows, and the conical bellows shape and the thick wall portion are 0.1 ≦ (D−d) / 2L ... 1 .25ti ≦ Ti ≦ 5ti ... 2Ti ≦ Pi ≦ 20Ti.

(Operation) Therefore, at the time of injection molding, the thick portion becomes a flow resistance to increase the pressure, the flow of the molten resin is normalized, and the bubbles disappear. Further, after passing through the thick portion, the flow is disturbed again and bubbles start to be generated, but the bubbles disappear at the next thick portion.

(Embodiment) Hereinafter, the configuration of the present invention will be described in detail based on an embodiment shown in the drawings.

FIG. 1 shows an example of the parison of the present invention. The parison
A conical cylindrical body having a shape close to the product shape is formed of a thermoplastic resin, and a thick wall portion 3 and a portion 4 relatively thin with respect to the thick wall portion 3 are continuously formed on the conical surface portion 2. . That is, in the present embodiment, the parison 1 has a substantially uniform thickness as a whole except for the thick portion 3 serving as a reservoir, and the other portions except the thick portion 3 constitute the thin portion 4. is doing. The parison 1 is formed in the shape of a conical cylinder with a bottom that approximates the shape of the product, but 0.1 ≦ (D−d) / 2L ... D: diameter of the conical surface on the large end side, d: It is preferable to have at least the taper of the diameter of the small end side of the conical surface portion, L: the total length of the conical surface portion. At this time, it is sufficient if the taper condition of the formula is satisfied as a whole.

The thick portion 3 is provided by selecting a portion effective for preventing the adverse effect of the open pressure molding, that is, the generation of bubbles and the abnormal flow. For example, 2Ti ≦ Pi ≦ 20Ti ... Ti: the thickness of the i-th thick portion 3, Pi: the i-th pitch.

In the case of Pi <2Ti, the wall thickness becomes relatively large and air bubbles are generated therein, and in the case of Pi> 20Ti, the wall thickness becomes relatively thin so that it is the same as the conventional one, and sink marks and the like occur. Is.

It is preferable that the position of the thick portion 3 is appropriately selected within the above-mentioned conditions. For example, when a conical bellows (bellows) as shown in FIG. 3 is formed by using the parison 1 of the present invention, the thick wall portion 3 is located at a position corresponding to the mountain portion of the bellows in the range of the above conditions. Is preferably arranged.

Further, the wall thickness of the thick wall portion 3 is set to a thickness sufficient to eliminate the adverse effects caused by the open-pressure molding, that is, a thickness that causes a flow resistance change between the thin wall portion 4 and the thin wall portion 4. For example, 1.25 ti ≦ Ti ≦ 5 ti ... Ti: thickness of the i-th thin portion, Ti: thickness of the i-th thick portion, such that the thickness relationship is maintained.

In the case of Ti <1.25ti, the difference in wall thickness becomes too small to be the same as that of the conventional one, and sink marks are generated.
This is because when i <5ti, the difference in wall thickness becomes so large that air bubbles may be generated therein.

The shape of the thick portion 3 is preferably a curved surface or streamline as shown in the figure in order to prevent the flow of the molten resin from being disturbed, but the shape is not limited to this, and an appropriate shape is selected. It is possible. The point is that any shape and configuration can be used as long as it can form a pressure-increasing portion that throttles the flow of the molten material between the thick portion and the thin portion.

The above-described embodiment is one of the preferred embodiments, but the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention. For example, in the present embodiment, the thick portion 3 is formed on the outer peripheral surface of the conical surface portion 2, but the same effect can be obtained by forming it on the inner peripheral surface side. In addition, the thick portion 3 is formed by partially increasing the thickness of the conical surface portion 2.
However, it is also possible to form a relatively thick portion by partially forming a thin portion.

The parison configured as described above and the conical hollow molded product molded using the parison are molded as follows.

For example, the core mold 11 is installed in the cavity mold 10 that is a split mold, and then the cavity mold 10 is closed and the neck mold 12 is closed. Then, molten resin is injected around the core mold 11 from the small end side to mold the parison 1 [FIG. 2 (A)]. At this time. The cavity mold 10 is formed with recesses 13 having a predetermined depth and shape for forming the thick wall portion 3 at predetermined intervals. Then cavity mold 1
0 is opened and the parison 1 is taken out with the core mold 11 being supported [Fig. 2 (B)]. And blow mold 1
4 (FIG. 2 (C)), the blow mold 14 is closed, the air blow-in port 15 provided in the core mold 11 is opened, and air is blown into the mold [FIG. 2 (D)]. At this time, the thick-walled portion 3 retains heat more easily than the thin-walled portion 4 and is less likely to be cooled, so that the thick-walled portion 3 has higher fluidity than the thin-walled portion 4 and tends to expand, so that the blow-up ratio is increased. Therefore, the final product shape after blow molding has a smaller difference in wall thickness than the parison shape. After cooling, the neck mold 12 and the blow mold 14 are opened, and the molded product 16 is taken out [Fig. 2 (E)].

(Effect of Device) As is clear from the above explanation, the parison of the present invention is
In a parison for injection blow-molding four or more conical bellows with a bottom having a shape similar to that of a product, a thin portion and four or more thick portions are continuously formed on a conical surface portion,
And a conical cylindrical body having a gradient of 0.1 or more, and a thick portion 1.25 to 5 times thicker than the thin portion is formed on the conical surface portion thereof at a pitch 2 to 20 times thicker than the thin portion Since it is formed by, the flow resistance occurs due to the relative drawing between the thick part and the thin part during injection molding, and the flow of the raw material is normalized in the thick part and sink marks, bubbles, voids, etc. Disappears, and blow processing does not result in a defective product.

Therefore, when blow molding is performed using this parison, a bellows product having four or more peaks with almost uniform wall thickness without sink marks, bubbles, and voids can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of a parison of the present invention in a half section, FIG. 2 is a principle diagram of injection blow molding for explaining molding and blow molding of the parison of the present invention, and FIG. 3 is the same process. FIG. 3 is a front view of a semi-sectioned cross section showing an example of a conical tubular product manufactured by the method using a conical bellows. 1 ... Parison, 2 ... Conical surface part, 3 ... Thick part, 4 ... Thin part.

Claims (1)

[Scope of utility model registration request] 1. A parison for injection blow molding a conical bellows having four or more peaks with a bottom similar to a product shape, wherein a thin surface portion and four or more thick wall portions are continuously formed on a conical surface portion of the parison. And the thick portion is formed at a position corresponding to the peak portion of the bellows, and the conical bellows shape and the thick portion have the following condition 0.1 ≦ (D−d) / 2L. 1.25ti ≦ Ti ≦ 5ti ... 2Ti ≦ Pi ≦ 20Ti, where D: large end side diameter of conical surface portion, d: small end side diameter of conical surface portion, L: total length of conical surface portion, ti: Injection blow of 4 or more conical bellows characterized by satisfying the following: i: thickness of thin portion, Ti: thickness of i thick portion, Pi: i pitch Parison for.