JPS5932298B2 - Thermoplastic resin blow molding equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new and improved forming apparatus for improving the moldability of parts with complex shapes, particularly in the blow molding of synthetic resins.

Conventionally, plastic containers have been mainly molded by the so-called melt-blowing method in which resin is molded in a molten state, and in this case, molding can be easily performed even in relatively difficult places such as the mouth and screw parts of the container.

However, in recent years, in order to make more effective use of the inherent characteristics of the resin, the stretching orientation has been strengthened, and in order to improve properties such as drop strength and transparency, the once cooled parison is heated to the stretching temperature range and stretched in the longitudinal direction. The so-called biaxial stretch blowing method, in which blow molding is carried out, has been adopted for the molding of vinylidene chloride containers and polypropylene containers, and has achieved good results. However, in the case of stretch blowing, the resin is not melted, so it is difficult to mold and requires very high molding pressure. For example, in the case of melt blowing, molding air pressure of about 2 to 4 to 9/CTII is generally sufficient for forming, but in the case of polypropylene biaxial stretching blowing, even 7 to 10 to 9/crii can be used to form the threaded part of the container opening. The molding at the part where it enters is insufficient. However, using a blowing pressure higher than this is very problematic in terms of equipment.
For this reason, US Patent Nos. 3,632,264 and 36,491
No. 50, in which only the threaded portion is pressure-formed to obtain a molded product having a predetermined shape, has the disadvantage that the structure of the machine is extremely complicated. On the other hand, the present invention does not require mechanical pressure forming as in conventional methods, but can be formed uniformly even in places where threaded parts etc. are formed using the pressure of blow air as in the melt-blowing method. This is a device designed to produce molded products with excellent gloss. The present inventors believe that if only the surface of the part corresponding to the threaded part of the parison heated to the drawing temperature is heated to a temperature higher than the temperature of the parison body and close to the melting temperature of the resin, the threaded part can be melt-blown by the pressure during blow molding. I discovered that similar molding can be done.

If the surface of the parison before stretching, which corresponds to the threaded portion, is heated in a separate device, stretching unevenness will occur during longitudinal stretching. In addition, if the surface of the parison corresponding to the threaded portion is heated with hot air or radiant heating before being sandwiched between molds after longitudinal stretching, the parison may be stretched in the longitudinal direction and become thinner, or may be formed uniformly on the circumference. It is difficult to heat only the threaded part and may adversely affect other parts of the molded container. In the present invention, a mold for biaxial stretch blow molding of a thermoplastic resin parison is configured to be forcibly cooled by water or air, and has a small cross-sectional area and a threaded portion inserted into the side that contacts the parison. 5. A thin electrical resistor mold support having a shape such as 5), and a screw portion, etc. having a small cross-sectional area that is insulated and adhered to the inside of the mold support, and that enters the side that contacts the parison. The mold support is forcibly cooled with water or air, and a low voltage and high current is directly and intermittently applied to the thin electrical resistor mold. By energizing, the surface of the parison is heated by heating a thin-walled electrical resistor mold with a small cross-sectional area and a threaded part inserted into the side that contacts the parison for a short period of time, and when the energization is turned off, A thermoplastic resin biaxial stretch blow molding device characterized by being configured to be able to cool immediately, and a mold for biaxial stretch blow molding of a thermoplastic resin parison, forcibly cooled with water or air. 5. An electric resistor thin-walled mold support with a small cross-sectional area and a shape such as a threaded part inserted into the side that contacts the parison, and 5. It consists of a thin-walled electric resistor mold with a small cross-sectional area and a threaded part formed on the side that contacts the parison, and the mold support is forcibly molded with water or air. By cooling the electrical resistor thin-walled mold and intermittently applying low voltage and high current directly to the thin-walled electrical resistor mold, the shape of the thread, etc. that enters the side that contacts the parison is formed in a short time with a small cross-sectional area. A biaxial stretch blow molding apparatus for thermoplastic resin is used, which is characterized in that the surface of the parison is heated by heating a thin-walled electric resistor mold, and the parison surface is immediately cooled when the current is turned off. This makes it possible to mold even parts with complex shapes. At the same time, this significantly improves the surface gloss of these areas. The method of heating or cooling the mold surface in this way is to attach a thin mold (including a film mold) that serves as an electrical heating resistor to an electrically insulated mold support. By passing voltage and high current, only the local surface of the parison is heated to a specified temperature in a few seconds, and the resin is deformed to the mold wall. When the electricity is turned off, the heat of the resistor is transferred to the resin or the mold in a few seconds. It is absorbed by the support and cooled to a temperature at which the resin does not deform. In this case, only the surface portion of the local part of the parison that is in contact with the mold, which becomes the threaded portion, is heated. Stop heating for a short time, no longer than 10 seconds. As a result, the temperature inside the parison remains below the melting temperature, preferably at a temperature at which the resin is stretched and oriented. Embodiments of the invention will now be described in detail with reference to the accompanying drawings, but the invention and the drawings are merely illustrative of one preferred embodiment of the invention.

FIG. 3 is a partial sectional view of a mold showing an example of an embodiment of the present invention.

Thin-walled mold electrical resistors 4, 4'' each having a screw mold are attached on top of the two-split mold bodies 1, 1''.

FIG. 1 is a plan view of these 4, 41 viewed from above, and as shown in the figure, an insulating coating 3, 37 is provided on the mold support 2, 1, and a screw mold is mounted on it. Thin-walled mold electrical resistors 4 and 41 are attached, and lead wires 5 are attached to both ends of each.
, 6, 5'', 6'' are connected with bolts 7, 8, τ, 81. Of course, the bolts 7, 8, T, 87 are screw mold bodies 2, 27
It is electrically isolated from the In this condition, each lead wire 5
, 6, 5'', and 6', the mold inner wall 18, which has a relatively small cross-sectional area, generates heat.The idea in Figure 2 is the same as in Figure 1, but In this example, the mold supports 9 and 9' are made of an electrical insulator such as ceramic, and an electrical resistor 14 is placed thereon as shown in the enlarged views of FIGS. 2 and 5. , 14′, metal;
For example, nickel plating is applied, and terminals 10,
11, 101, 1' screws 12, 13, 127, 131
By stopping the terminals 10, 11, 10'', and 1'' with low voltage and high current, heat is generated.
This is a structure designed to reduce the cross-sectional area because if the cross-sectional area of the current-carrying part is large, a correspondingly larger current is required to generate the same heat generation temperature. To describe the effect of molding with a mold having such a structure, first, a vertically stretched tubular parison is sandwiched between split molds 1 and 17 and blow-molded, resulting in a mold as shown in the enlarged view of the threaded part in Figure 4. As shown, the resin comes into contact with the inner walls 15 and 16 of the screw and does not reach the depth 18 of the screw thread.

Therefore, in normal cases, it will solidify as it is. However, as in the present invention, when the thin-walled mold electrical resistors 4, 41 are heated when the resin comes into contact with the wall surface, the resin 17 melts at the contact portions 15, 16 with the thin-walled mold electrical resistors 4, 4'' and is blown away. Pressed by air pressure, the resin penetrates to the depths 18 of the screw thread.When the electricity is turned off, the heat of the thin-walled mold electrical resistors 4, 4'' is absorbed by the mold supports 2, 2' or the resin 17. Since the mold is cooled, the mold can be opened and the molded product can be easily removed. At this time, the screw mold support 2, 9, 9' and the split molds 1, 1' are heated, so they are constantly cooled forcibly with water or air. As mentioned above, the feature of the present invention is that the surface of the resin is partially heated to assist in molding of fine parts that are difficult to achieve with just blow air, such as in biaxial stretch blow molding. This is a device that deforms the resin into the desired shape and immediately cools and solidifies it.The purpose is achieved without applying mechanical pressure, so the structure is simple, and its use in mechanical pressure molding is easy. Although the scope is limited, the device according to the present invention can be adopted in a wide range of areas.

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[Brief explanation of the drawing]

Fig. 1 is a plan view of the screw mold part divided into two parts, Fig. 2 is a plan view of the screw mold part showing a structural example different from Fig. 1, and Fig. 3 is a cross section taken along the line A-A in Fig. 1. 4 is an enlarged view of the screw mold part of FIG. 1, and FIG. 5 is an enlarged view of the screw mold part of FIG. 2. 1, ``Harikin type, 2, 2! is a mold support, 3, 3' is an insulating coating, 4, 4'' is an electric resistor, 5, 5'', 6, 6
' is a lead wire, 9, 9' is a screw mold support, 10, 10
', 11, 1' are terminals, 14, 14' are electrical resistors, 1
5 and 16 are inner walls, 17 is resin, and 18 is the inside of the screw thread.

Claims (1)

[Scope of Claims] 1. A mold for biaxial stretching blow molding of a thermoplastic resin parison; (a) a side that is in contact with the parison and has a small cross-sectional area configured to be forcibly cooled by water or air; An electrical resistor thin-walled mold support in the shape of a threaded part, etc.
b) It consists of a thin-walled electrical resistor mold with a small cross-sectional area that is insulated and adhered to the inside of the mold support, and whose side that comes into contact with the parison has a shape such as a threaded part. The mold support is forcibly cooled with water or air and is brought into contact with the parison in a small cross-sectional area for a short period of time by directly and intermittent low-voltage high current passing through the electrical resistor thin-walled mold. The surface of the parison is heated by heating a thin-walled electric resistor mold with a threaded part inserted on the side to be heated.
1. A biaxial stretch blow molding apparatus for thermoplastic resin, characterized in that it is configured so that cooling can be performed immediately when the current is turned off. 2 A mold for biaxial stretch blow molding of a thermoplastic resin parison is constructed by (a) having a threaded portion that is configured to be forcibly cooled by water or air, has a small cross-sectional area, and enters the side that comes into contact with the parison; An electrical resistor thin-walled mold support with a shape of (
b) Consisting of a thin-walled electrical resistor mold with a small cross-sectional area attached to the inside of the mold support via an insulating film, and having a threaded part or the like inserted on the side that contacts the parison. The mold support is forcibly cooled with water or air, and a parison is formed in a short time and in a small cross-sectional area by directly and intermittently passing a low voltage and high current through the thin electrical resistor mold. The surface of the parison is heated by heating a thin-walled electrical resistor mold whose contact side is shaped like a threaded part, etc.
1. A biaxial stretch blow molding apparatus for thermoplastic resin, characterized in that it is configured so that cooling can be performed immediately when the current is turned off.