GB2066725A

GB2066725A - Method and apparatus for heating a parison neck in stretching blow moulding

Info

Publication number: GB2066725A
Application number: GB8038010A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-11-30
Filing date: 1980-11-27
Publication date: 1981-07-15
Also published as: DE3044928C2; JPS6255488B2; FR2470670A1; JPS5678944A; DE3044928A1; GB2066725B; FR2470670B1

Abstract

A method of heating a parison neck in stretching blow moulding, wherein an injection moulded synthetic resin parison (11) is adjusted in temperature while a neck (11a) of the parison is held in a neck mould (12), after which the parison is stretched and expanded to form a container such as a bottle, the method comprising, at the time of adjusting the temperature of the parison, heating a lower end of the neck mould and applying sufficient heat to prevent formation of an annular constriction in the moulded product after blowing in the border zone between the parison neck covered by the neck mould and the body of the parison. In one embodiment the lower end of the neck mould is heated by a metal heating member (14) held in place by screws against an insulating layer (13). In another embodiment, the insulating layer is dispensed with. In both embodiments the neck mould is brought, during the temperature adjustment, into contact with a heated ring located above the temperature adjustment device, the ring causing the member (14) to be heated. <IMAGE>

Description

SPECIFICATION Method and apparatus for heating a parison neck in stretching blow moulding This invention relates to a method and apparatus for heating a parison neck which, when an injection moulded synthetic resin parison is moulded into a container such as a bottle by stretching blow moulding after adjustment of temperature, can prevent formation of an annular constriction in a border zone between the neck and body of the parison.

According to the invention, there is provided a method of heating a parison neck in stretching blow moulding, wherein a body of an injection moulded synthetic resin parison is adjusted in temperature by secondary heating while a neck of the parison is held in a neck mould, after which the parison is stretched and blown to form a container such as a bottle, the method comprising heating a lower end of the neck mould during secondary heating of the parison body and supplying sufficient heat to prevent formation of an annular constriction in the blown product in the border zone between the parison neck covered by the neck mould and the parison body.

The invention also provides apparatus for moulding an injection moulded synthetic resin parison by stretching blow moulding, comprising a neck mould for holding a neck of the parison, a secondary heating device for adjusting the temperature of a body of the parison while the neck is held by the neck mould, and means for heating the lower end of the neck mould during secondary heating of the parison body and supplying sufficient heat to prevent formation of an annular constriction in the blown product in the border zone between the parison neck covered by 4 the neck mould and the parison body.

The invention further provides any novel feature or combination of features herein disclosed.

In order that the invention may be readily understood, an embodiment thereof will now be described, by way of example, with reference to the accompanying drawings, in which: FIGURE 1(1) is a longitudinal sectional view of a parison neck and a neck mould for explaining the phenomenon which occurs when the parison is subjected to stretching blow moulding; FIGURE 1 (II) is a longitudinal sectional view of an upper portion of a moulded bottle; FIGURE 2 is a longitudinal sectional view of part of a parison and a neck mould used in performing this invention; FIGURE 3 is a longitudinal sectional view of a parison and a neck mould showing another embodiment of a lower end portion of the neck mould; and FIGURE 4 is a partial view in longitudinal section showing the lower end portion of the neck mould and a heating means with which the lower end portion of the neck mould is placed in contact.

When bottles and hollow moulded necked products are manufactured by stretching blow moulding, there is a disadvantage in that an annular constriction is produced in a border zone between a neck and a body of the product depending on the shape and wall thickness of the neck of the moulded product. This annular constriction is produced due to a temperature difference between a neck portion of the parison which is held in a neck mould and a body portion of the parison which is subjected to secondary heating by means of a temperature adjusting device, and because a portion of the parison in contact with the end of the neck mould is not sufficiently stretched.

More specifically, referring to Figure 1, in this kind of moulding method, an upper or neck portion 1 a of parison 1 is clamped in a neck mould 2 which opens and closes to left and right. The parison 1 is then transferred together with the neck mould 2 to a temperature adjusting device (not shown in Figure 1), and the lower or body portion 1 b of the parison is inserted into the temperature adjusting device for secondary heating. Thereafter, in the blow moulding mould, the body portion is stretched and blow moulded to form a hollow moulded product 3 such as a bottle.

In this case, an annular constriction A shown in Figure 1 (II) is always produced in the moulded product close to the lower opening of the neck mould 2, but nowhere else. The present inventor has measured the temperature distribution of the body 1 b after the secondary heating of the body portion of the parison and has found that the temperature of a portion of the parison from the lower surface of the neck mould up to approximately 1.5 mm from the lower surface of the neck mould 2 decreases greatly to a temperature which is not suitable for stretching blow moulding. It is considered that such decrease in temperature is due to the presence of the neck mould 2.Thus heat escapes into the neck mould from a portion of the parison close to the neck mould 2 due to the temperature difference, so that a region of radius B (approximately 1.5 mm) as shown including a portion below the neck mould 2 lowers in temperature.

For the above-mentioned reasons, an attempt has been made to apply heat insulation to the circumference of the lower opening of the neck mould to prevent the lowering of temperature in the said portion of the parison before stretching blow moulding takes place and, as a consequence, an annular constriction A was not produced but instead a sore-like portion was produced in the portion of the parison in contact with the heat insulating material due to poor cooling.

The present invention aims to provide a method of heating the circumference of a lower opening of the neck mould 2 so as to produce neither the above-mentioned annular constriction A nor a sore-like portion due to overheating.

In a method embodying the invention, a lower end of a neck mould is heated to a predetermined temperature by contact thereof with a heating body to prevent escape of heat from a neck of a parison in contact with the circumference of a lower opening of the mould and to avoid formation of an annular constriction in a moulded product during stretching blow moulding due to the lowering of temperature as encountered in the prior art. Since partial heating is applied to the neck mould, the product is easily cooled after stretching blow moulding and heat is rarely accumulated, thereby producing no sore-like portion in the surface of a parison neck due to overheating.

In a preferred method of heating a parison neck embodying the invention, a heating body is included in the device for adjusting the temperature of the parison to effect heating of the parison neck during the temperature adjustment of the parison, and which affords advantages that the method can be applied even to conventional stretching blow moulding because of a simple construction in which the heating body is merely mounted on the temperature adjusting device.

Referring to Figures 2 to 4, reference numeral 1 1 designates a parison and 12 designates a neck mould. A parison neck 11 a forming an upper part of a hollow moulded product is held in close contact with the neck mould 12 in a similar manner to that of the above-mentioned prior art, the parison body 11 b projecting from the lower surface of the neck mould.

The circumference of a lower opening of the neck mould 12 is formed by a metallic heating member 14 which is fitted to the neck mould with the interposition of a thin layer of a heat insulating material 13 (for example, heat insulating paper) by means of screws 15. The heating member 14 has the desired height and the neck 1 la a of the parison 11 is shaped by an inner surface of the heating member 14 and the inner surface of the neck mould.

It should be noted that the heat insulating material 13 may be omitted under suitable circumstances. The reason is that this heat insulating material 13 is provided to prevent ths whole neck mould from being heated by repetitive heating, and the heat insulating material 13 is not particularly provided to act on and heat the parison neck 11 a.

Also, the neck mould 12 is always partly heated, and if such heating should be extended over the whole neck mould, such partly applied heat is absorbed by the neck mould and a member holding the neck mould when such heat is moved away from the heating body so that there is significant preheating.

The heating member 14 is formed of a metal having better heat transfer than the metal from which the neck mould 12 is made, and fitting may be accomplished directly in the way shown in Figure 3.

Thus, prior to transfer of the neck mould 12 to a blow moulding mould, the prearranged heating body and heating member 14 are brought into contact and the circumference of a lower opening of the neck mould 12 is maintained at a suitable temperature by the heating member 14 to prevent a portion of the parison close to the lower surface of the neck mould 12 from being lowered in temperature.

Most preferably, application of heat to the heating member 14 by the aforementioned heating body is effected by a temperature adjusting device in which the body 11 b of the parison 11 is subjected to secondary heating to a temperature suitable for the process of stretching blow moulding.

Figure 4 shows a second heating device for adjusting parison temperature in which annular heating elements 16 and heat insulating materials 17 are alternately stacked to form a parison receiving cavity 18, and an iron frame 19 mounted on the uppermost one of said heating elements 16 is fastened to a support post 20. A heating body 21 is vertically movably mounted on the temperature adjusting device with a spring 23 being interposed on a bolt 22 threadedly engaging the iron frame 1 9. The upper surface of the heating body 21 is formed so as to be fitted onto the lower portion of the neck mould 12 in contact with the heating member 14. The boundary zone between the neck and body of the parison is heated to a suitable temperature by means of a heater 24 which is mounted on the outer periphery of the body 21 and can be adjusted in temperature. Accordingly, when the lower surface of the neck mould 12 moved down together with the parison 11 is in contact with the heating body 21 , the body 1 b of the parison 1 1 is subjected to secondary heating and at the same time, the heating member 14 is supplied with heat by contact with the heating body 21 and partially heats the parison neck 11 a in contact with the inner surface thereof to prevent the portion of the parison at the circumference of the lower opening of the neck mould 12 from being lowered in temperature.

Claims

1. A method of heating a parison neck in stretching blow moulding, wherein a body of an injection moulded synthetic resin parison is adjusted in temperature by secondary heating while a neck of the parison is held in a neck mould, after which the parison is stretched and blown to form a container such as a bottle, the method comprising heating a lower end of the neck mould during secondary heating of the parison body and supplying sufficient heat to prevent formation of an annular constriction in the blown product in the border zone between the parison neck covered by the neck mould and the parison body.

2. A method according to claim 1, wherein a heating member made of a metal having better heat transfer than that of metal forming the neck mould is provided at the lower end of the neck mould, and a heating body is brought into contact with the heating member during secondary heating of the parison body to apply heat to the border zone between the parison neck and the parison body.

3. A method according to claim 1 or 2, wherein a heating body provided with a heater is arranged above a secondary heating means for effecting temperature adjustment of the parison and upon insertion of the parison into the said heating means, the lower end of the neck mould and the heating body are brought into contact with each other.

4. A method of heating a parison neck according to claim 1, wherein a neck mould closing portion and a heating body are placed in contact with each other in a state where the heating body is supported by means of a buffer material.

5. Apparatus for moulding an injection moulded synthetic resin parison by stretching blow moulding, comprising a neck mould for holding a neck of the parison, a secondary heating device for adjusting the temperature of a body of the parison while the neck is held by the neck mould, and means for heating the lower end of the neck mould during secondary heating of the parison body and supplying sufficient heat to prevent formation of an annular constriction in the blown product in the border zone between the parison neck covered by the neck mould and the parison body.

6. Apparatus according to claim 5, wherein a heating member made of a metal having better heat transfer than that of metal forming the neck mould is provided at the lower end of the neck mould and a heating body is provided for contacting the heating member during the secondary heating of the parison body.

7. Apparatus according to claim 5 or 6 wherein a heating body provided with a heater is arranged above the secondary heating device so that, upon insertion of the parison body into the secondary heating device, the heating body comes into contact with the lower end of the neck mould.

8. A method of heating a parison neck substantially as hereinbefore described with reference to the accompanying drawings.

9. Apparatus for moulding an injection moulded synthetic resin parison substantially as hereinbefore described with reference to, and as illustrated in the accompanying drawings.

10. Any novel feature or combination of features herein disclosed.