MULTILAYER FORMING NOZZLE

Abstract: This invention provides a multilayer forming nozzle capable of accurately practicing the switching of a multilayer forming operation to a single layer forming operation or vice versa by opening and closing a flow passage, by means of a valve member actuated by resin pressure, into which a molten resin which is to form an intermediate layer of a multilayer molded product to be obtained by the injection molding is fed. This nozzle consists of a triple nozzle provided with concentrically formed first, second and third resin passages having a common injection port. The mouth portion of the third or central resin passage, which is positioned on the inner side of the mouth portion of the second resin passage, or the mouth portion of the second or intermediate resin passage, which is positioned on the inner side of the first resin passage, consists of the valve member adapted to be opened and closed as it is moved up and down by the resin pressure.

Description: FIELD OF THE ART This invention relates to a multi-layer molding nozzle used when a synthetic resin molded product whose sectional construction has a multilayer is injection molded. BACKGROUND A conventional multi-layer molding nozzle comprises a multiple nozzle in which a nozzle body having a mouth portion in a central portion at a tip thereof is interiorly provided with a plurality of resin paths in a concentric fashion, and different molten resins in the respective resin paths can be cavity-injected from said mouth of the nozzle. Formation of a synthetic resin molded product into a mulit-layer causes a quality of a thin-wall molded product as a beverage container to be further improved by the resin present as an intermediate layer. However, this poses a problem in that because of the provision of an intermediate layer, shock resistance of the product is lowered or the cost of the product increases, as compared with those of a single layer. In view of the foregoing, an attempt has been made so that a conventional double or three-layer nozzle is used to control injection pressure, time, injection timing or the like of the molten resin which forms an intermediate layer so as to injection-mold a product partly having an intermediate layer. However, it has been very difficult to mold an intermedite layer within a predetermined range in terms of resin pressure. Alternatively, there is a multiple nozzle in which a central path of a multiple resin path is made movable so that orifices of resin paths are selectively opened and closed to control molten resin, as disclosed in Japanese Patent Application Laid-Open n° 60-34819. However, in this case, a special valve device is required to control a flow of molten resin entering the central path passing through the orifice for injection, and in addition, the valve device is mechanically operated, and the nozzle has an extremely complicated construction. In the publication US-A-4 052 497 is disclosed a three-layer nozzle comprising a nozzle body with an injection opening, a first hollow core member in the interior of said body for determining therebetween a first resin path having a mouth portion, a second hollow core member in the interior of said first core member for determining therebetween a second resin path having a mouth portion positioned internally of said mouth portion of the first resin path, a third resin path formed in the interior of said second core member and having a mouth portion positioned internally of the mouth portion of the second resin path. Both the first and the second core members are mounted in a movable manner to control the circulation of the resin and the nozzle construction is not simple. DISCLOSURE OF THE INVENTION This invention has been achieved in order to solve the above-described problems with respect to the conventional multiple nozzle. An object of this invention is to provide a new multi-layer molding nozzle which is simple in construction, and in which a flowpassage of molten resin which is to form an intermedite layer is opened and closed by a valve member to be operated by resin pressure to always accurately switch a multiple layer to a single layer and vice versa. This invention having the aforesaid object overcomes the aforementioned problem encountered in the prior art by a three-layer nozzle as defined in claim 1. In the above-described structure, the molten resins of the respective resin paths applied with injection pressure are simultaneously injected from the mouth portion of the respective resin paths to cavities through the mouth portion of the nozzle. When the injection pressure of the second resin path is removed during the injection, the valve member is moved forward or backward by the resin pressure of the first or third resin path to close the second resin path to stop an outflow of the molten resin from the second resin path. Because of this, the molten resins of the first and third resin paths are merely injected to the cavity. When injection pressure is applied to the second resin path, the valve member is moved backward or forward due to a difference in pressure receiving area in the valve member to open the second resin path, and the molten resin is injected to the cavity together with the molten resin of the other resin paths. Accordingly, when the same kind of molten resin is used for the first and third resin paths and the different kind of molten resin is used for the second resin path, a molded product produced thereat is composed of a 2-kind 3-layer portion and a single layer portion. This invention will be further described in detail by way of examples shown in the drawings. BRIEF DESCRIPTION OF THE DRAWINGS The drawings show embodiments of a multi-layer molding nozzle according to this invention in which: FIG. 1 is a sectional view of a first embodiment; FIG. 2 is a sectional view of a second embodiment thereof; FIG. 3 is a sectional view in which a hot runner block is mounted; FIGS. 4 and 5 are respectively sectional views showing the molding steps; and FIGS. 6 to 8 are respectively sectional view of a preform having a bottom and a container. BEST MODE FOR CARRYING OUT THE INVENTION A nozzle body indicated at 1 with an injection opening 2 formed in the central portion in the end surface thereof is interiorly provided a first resin path 3, a second resin path 4 and a third resin path 5 in a concentric fashion. Each of the resin paths is formed with a first hollow core member 6 and a second hollow core member 7 having a spacer on the side thereof, which inserted from the opening at the rear end of the nozzle body 1 into the nozzle body in order. A three-layer nozzle shown in FIG. 1 has a construction in which a mouth portion 3a of the first resin path 3 connected to the injection opening 2 is internally provided with a mouth portion 4a of the second resin path 4,and a mouth portion 4a of the second resin path 4 is internally provided with a mouth portion 5a of the third resin path 5, the mouth portion 5a being formed from a valve member 8. The aforesaid valve member 8 comprises an annular body which is inserted so as to appear in the inner side of the end of the second core member 7. The inside diameter of the valve member 8 is substantially equal to the inside diameter of the mouth portion of the first resin path 3 and is smaller than the diameter of the third resin path 5, and the fore end 8a and the rear end 8b thereof are formed into a tapered surface on which resin pressure exerts. The ratio of a pressure receiving area between both the ends 8a and 8b is in the range of 0.5 < second resin path / third resin path < 4 in the projection plane, and as long as the aforementioned relevant formula is satisfied, even if the resin pressure of the third resin path 5 is being applied to the rear end 8b by the resin pressure of the second resin path 4 during the injection, the valve member 8 is moved into the end of the second core member 7 to maintain the second resin 4 open but when the injection pressure of the second resin path 4 is controlled to remarkably lower the resin pressure, the valve member 8 is immediately moved forward due to the resin pressure of the third resin path 5 exerting on the rear end 8b to close the second resin path 4. Accordingly, the valve member 8 is operated to open and close the second resin path 4 according to a difference between the resin pressures exerting on both the ends to control the injection of the molten resin from the second resin path 4. A three-layer nozzle shown in FIG. 2 has a construction in which opening and closing of the second resin path 4 may be accomplished by the resin pressure of the first resin path 3, and the valve member is inserted to as to appear in the end of the first core member 6. In this case, since the second resin path 4 is closed by the backward movement of the valve member 8, the end 7a of the second core member 7 is reduced in diameter, the end is extended frontwardly of the first resin path 3, the mouth portion 5a of the third resin path is made to front on the inner side of the mouth portion 3a, the second resin path 4 is opened at the side of the end portion, and the mouth portion 41 is constituted by the valve member 8 in the periphery of the end of the second core member 7 inserted into the end of the first core member 6. The inside diameter of the valve member 8 is larger than the outside diameter of the end portion of the second core member 7 to form a part of the second resin path 4 between it and the second core member 7, and when the rear end 8b comes into contact with a tapered shoulder 9 formed in the outer surface of the second core memebr 7, the second resin path 4 is closed. The ratio of a pressure receiving area between the fore end 8a and the rear end 8b of the valve member 8 formed into a tapered surface is in the range of 0.5 < second resin path / first resin path < 4 in the projection plane. Resins as material supplied to the respective resin paths are suitably selected depending on molded products, and in case of 3-kinds and 5-layers, different resins are supplied to the respective resin paths. In the case where a product having 2-kinds and 3-layers is injection molded, the resin material of the first resin path 3 is the same kind as that of the third resin path 5. The required number of the aforesaid three-layer nozzles are used while being mounted on a hot runner block 10. This embodiment shows the case where a 2-kind and 3-layer molded product is molded, in which the hot runner block 10 is interiorly provided with hot runners 13 and 41 connected to sprue bushes 11 and 12, respectively, arranged on the side thereof, and the hot runner 13, the hot runner 14 and a branch path 15 of the hot runner 14 are connected to the second resin path 4, the third resin path 5 and the first resin path 3, respectively, so that the same kind of resins can be injection from the first and third resin paths 3 and 5, and the different resins from the second resin path 4. Next, molding of a three-layer molded product having an intermediate layer by use of the three-layer nozzle shown in FIG. 1 will be described hereinafter. First, when injection pressure is applied to the first and third resin paths 3 and 5 to inject the same molten resins A and A, the valve member 8 together with the molten resins is moved forward simultaneously with the injection due to a pressure difference between the second resin path 4 and the third resin path 5 to close the second resin path 4 as shown in FIG. 4. Thereby, only the same molten resins A and A are injected to a cavity 16, and different molten resin B of the second resin path 4 will not be injected. Subsequently, at the time of completion of the injection of a predetermined quantity of molten resins A and A and when injection pressure is applied to the second resin path 4 while continuing the aforesaid injection, the valve member 8 is moved backward, as shown in FIG. 4, due to a difference in a pressure receiving area in the valve member 8, to open the second resin path 4 so that the molten resin B is cut in and between the molten resins A and A from the first and third resin paths 3 and 5 and flows out and is then injected into the cavity 16 together with the molten resins A and A from the injection opening 2. After the aforesaid injection has been completed, a product having three layers as a whole is molded, and when injection pressure of the second resin path 4 is disconnected, the valve member 6 is again moved forward by the resin pressure of the third resin path 5, as shown in FIG. 5, due to a difference in resin pressure at that time, to close the second resin path 4. Therefore, only the same molten resins A and A are again injected halfway, and a single layer is molded. The molten resin B injected from the second resin path 4 is to be positioned in the center between the molten resins A and A, and therefore, when the resin is filled and moved in the cavity, even if a skin layer caused by cooling should occur on the surfaces of the molten resins A and A in contact with the mold surface, the skin layer slowly influences thereon and the molten resin B is hard to form a skin layer halfway. A molded product 20 shown in FIG. 6 is a preform having a bottom comprising a three-layer of a mouth portion 21 alone obained by injecting and filling the molten resin B of the second resin path 4 and a single layer of a body 22 and a bottom 23 obtained by only the molten resin A, the chain line indicating a container 30 in which a preform having a bottom is orientation blow molded. A molded product 40 shown in FIG. 7 is a preform having a bottom comprising a three-layer obtained by injecting and filling the molten resin B of the second resin path 4 into a body 42 alone and a single layer of a mouth portion 41 and a bottom 43 merely filled with the molten resin A, the chain line indicating a container 50 in which a preform having a bottom is orientation blow molded. A molded product 60 shown in FIG. 8 is a preform having a bottom comprising a three-layer obtained by injecting and filling the molten resin B of the second resin path 4 into a bottom 63 alone and a single layer of a mouth portion 61 and a body 62 merely filled with the molten resin A, the chain line indicating a container 70 in which a preform having a bottom is orientation blow molded. The resin used as the molten resin A may comprise a resin such as a polyethylene terephthalate, and the molten resin B includes resins excellent in barrier properties such as methaxylene group contained polyamide, ethylene vinyl alcohol and high nitrile or resins having a heat resistance such as polycarbonate and U-polymer, which are used according to uses of containers molded thereby. For example, when a resin forming an intermediate laye 34 comprises a polycarbonate, formation of a mouth portion 31 of a container 30 into a multi-layer remarkably improves a heat resistance as compared with the case where it merely comprises a polyethylene terephthalate to prevent the mouth portion from being changed during heating and filling. Similarly, when a bottom 73 of a container 70 (FIG. 8) is formed into a multi-layer by an intermediate layer 78 of U-polyer, the heat resistance of the bottom 73 is improved, and even if heat treatment is conducted after filling a carbonated juice, a central portion thereof is not projected and deformed as in a bottom of a single layer. Furthermore, in a product in which only a body 52 is formed into a multi-layer by an intermediate layer formed of a methaxylene group contained polyamide, barrier properties are improved, peeling between between layers when a bottom is formed into a multi-layer can be prevented, and expensive resins used for the intermediate layer 54 can be saved. Next, one example of molding conditions in the case of the three-layer nozzle shown in FIG. 1 is given below. Sectional area of resin paths First resin path 34.56 mm² Second resin path 59.69 mm² Third resin path 21.23 mm² Diameter of injection opening 2.0 to 3.0 mm Pressure receiving area (projection area) of valve member Second resin path side (fore end) 25.13 mm² Third resin path side (rear end) 21.23 mm² Resin material First and third resin paths Polyethylene terephthalate Second resin path SM nylon Injection pressure First and third resin paths Primary pressure 140 kg/cm² Secondary pressure 58 kg/cm² Second resin path 100 kg/cm² INDUSTRIAL APPLICABILITY As mentioned above, according to this invention, a first, a second and a third resin paths are concentrically provided within a nozzle body, the second resin path being closed by a valve member which is actuated by resin pressure of the other resin paths to control a molten resin from the second resin path, whereby a position at which an intermediate layer is formed by the molten resin can be suitably set. Therefore, only the mouth portion, body or bottom of a molded product can be formed into a multilayer. Since the position of the intermediate layer can be set to a central portion, in injection molding of a multi-layer molded product, the effect is great, and it is industrially very effective and widely utilized.

Claims: A three-layer nozzle comprising a nozzle body (1) with an injection opening (2), a first hollow core member (6) in the interior of said body for determining therebetween a first resin path (3) having a mouth portion (3a), a second hollow core member (7) in the interior of said first core member (6) for determining therebetween a second resin path (4) having a mouth portion (4a) positioned internally of said mouth portion (3a) of the first resin path (3), wherein a third resin path (5) is formed in the interior of said second hollow core member (7) and has a mouth portion (5a) positioned internally of the mouth portion (3a) of the first resin path (4), characterized in that, said mouth portion (3a) of the first resin path {3) and said mouth portion (5a) of the third resin path (5) are always opened and connected to said injection opening (2) in order that molten resins may be simultaneously injected from said mouth portions of the first and third resin paths, and in that at the end of the second resin path (4) it is provided an ring-type valve member (8) which is separated from said core members and movable between a first position wherein it closes said second resin path (4) and a second position wherein it opens said second resin path (4), and the ratio between pressure receiving areas of the fore end and of the rear end of the valve member is in the range 0,5-4 in the projection plane. A three-layer nozzle according to claim 1 wherein said valve member (8) is inserted into the end of the second core member (7). A three-layer nozzle according to claim 1 wherein said valve member (8) is inserted into the end of the first core member (6). A multi-layer forming nozzle according to Claim 3, wherein an end portion (7a) of said second core member (7) is reduced in diameter and an end thereof is extended to the first resin path (3), a mouth portion (5a) of the third resin path (5) is made to front on an inner side of the mouth portion, the second resin path (4) being opened at the side of the end portion, said mouth portion being constituted by said valve member (8) in the periphery of the end portion of the first core member (6), and the rear end (8b) of the valve member comes into a tapered shoulder (9) formed on the outer side of the second core member to close the second resin path. A multi-layer forming nozzle according to Claim 2, wherein said valve member (8) has its inside diameter substantially equal to the inside diameter of the mouth portion (3a) of the first resin path (3) but smaller than the diameter of the third resin path (5), the fare end (8a) and rear end (8b) thereof being formed into a tapered surface, and the ratio between pressure receiving areas of the both ends is in the range of 0.5 < second resin path / third resin path < 4 in the projection plane. A multi-layer forming nozzle according to Claim 4, wherein said valve member (8) has its inside diameter formed to be larger than the outside diameter of the end portion (7a) of the second core member (7) to form a part of the second resin path between it and the second core member, and the ratio between pressure receiving areas of the fore end (8a) and the rear end (8b) of the valve member (8) formed into a tapered surface is in the range of 0.5 < second resin path / first resin path < 4 in the projection plane.

Inventors: FUKAI HIDEHIKO NISSEI ASB MACH, ORIMOTO HIROYUKI NISSEI ASB MA, SATOH KOUICHI NISSEI ASB MACHI, YOKOTA KATSUMASA NISSEI ASB MA, FUKAI, HIDEHIKO NISSEI ASB MACHINE CO., LTD., ORIMOTO, HIROYUKI NISSEI ASB MACHINE CO., LTD., SATOH, KOUICHI NISSEI ASB MACHINE CO., LTD., YOKOTA, KATSUMASA NISSEI ASB MACHINE CO., LTD.
Applicants: NISSEI ASB MACHINE CO LTD, NISSEI ASB MACHINE CO., LTD.
Application year: 1987
Main classification: B29C45
IPC codes: B29C45, A61F13