JP3717008B2 - Spruce molding method and mold - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sprueless molding method for injection-molding a bottomed molded product having no sprue at the bottom and a mold that can be used in the molding method.
[0002]
[Problems to be solved by the invention]
A sprue protrudes at the center of the bottom of a bottomed product formed by ordinary injection molding. This sprue is removed by post-processing, but some materials are difficult to cut. In particular, with a material resin such as polyester, polycarbonate, and polyamide, it is not easy to cut the solidified sprue, and it cannot be easily excised like a soft material resin such as polyethylene or polypropylene.
[0003]
Therefore, configure the mold so that the gate can be cut, or crush or cut the soft sprue immediately after molding to the extent that it does not interfere with the molded product, to eliminate the sprue obstacle in the molded product. Has been done.
[0004]
The injection molding of a spruleless molded product can be carried out by employing an extended nozzle type mold, a well type mold, a pinpoint gate, or the like. However, in the extended nozzle type, the nozzle tip is repeatedly touched for each molding to prevent heat conduction to the mold because the heated nozzle tip surface is brought into contact with the cooled mold cavity gate for injection filling. It is necessary to prevent the resin from solidifying by rapidly cooling the nozzle tip.
[0005]
Even with this prevention by repeated nozzle touches, the resin in the gate is solidified by cooling when used in a long molding cycle, so its use is limited to injection molding of molded products with a short molding cycle, and the temperature near the gate tends to decrease. For this reason, in molding a resin that requires high temperature, a bush is provided to prevent the nozzle from directly contacting the cavity gate. For this reason, a metal mold | die becomes complicated and it is limited to the metal mold | die which has a structure which can repeat a nozzle touch.
[0006]
In the well type mold, a cavity gate is provided in the bush that forms the resin reservoir, and the nozzle tip surface is touched to this bush for injection filling, so the molten resin in the bush prevents a temperature drop near the gate. However, since the molten resin in the bush is not heated, the temperature in the vicinity of the gate decreases with time. For this reason, it is suitable for molding of resin that is insensitive to temperature, such as polyethylene and polypropylene, but in the case of resin that requires high-temperature molding such as polycarbonate, a heater is attached to the bush and heated. It is necessary to insert a nozzle tip to prevent cooling near the gate.
[0007]
Pinpoint gates used for polyethylene molding have a very small cross-sectional area so that the gate is cut when released, so there is no sprue. Is solidified, and the gate cross-sectional area is in a very limited state, so there is a problem in molding of resins other than polyethylene.
[0008]
Thus, in the conventional sprueless molding and mold, there is a problem in the solidification of the resin by cooling in the vicinity of the gate, and since the solution is performed by adopting a bush and heating means, it is difficult to adopt depending on the mold structure, Both are unsuitable for long molding cycles.
[0009]
The present invention was conceived in order to solve the above-described problems of conventional sprueless molding and molds, and its purpose is to eliminate the need for a bush or heating means and eliminate the need for repeated nozzle touches for each molding. Another object of the present invention is to provide a new molding method and mold capable of injection-molding a sprule-less molded product having a flat bottom without being limited by the length of molding cycle, molding temperature, and material resin.
[0010]
[Means for Solving the Problems]
According to the molding method of the present invention for the above purpose, the tip of the nozzle member inside the needle valve is fitted into the opening at the center of the bottom of the injection cavity, and the nozzle center is formed by forming the center of the bottom with a flat nozzle tip. Combined with the cavity gate, the required clearance is provided between the nozzle tip surface and the cavity bottom surface in the opening, and the injection cavity is filled with molten resin from the nozzle tip in contact with the bottom mold plate that is constantly cooled. And forming the bottom center part of the bottomed molded product with the nozzle tip surface extended to the cavity bottom surface due to thermal expansion of the nozzle tip due to the molten resin being filled, and the nozzle port is then formed by the valve tip surface of the needle valve. Closes the nozzle tip surface flush with the nozzle, and forms a bottomed molded product with no sprue protrusion at the center of the bottom, while stopping injection of molten resin The shrinkage due to temperature drop of the Hare nozzle tip is that, to re-form the clearance.
[0011]
In addition, the mold of the present invention that enables the above-described sprueless molding method is an injection mold of a bottomed molded product in which the center of the bottom surface of the injection cavity is formed in an opening having a required inner diameter, and an outer mold that fits the opening. A nozzle for injection that has a nozzle tip with a flat nozzle tip surface with a diameter, and a needle valve with a truncated cone shape that closes the nozzle port of the nozzle tip surface with a flat valve tip surface. The tip of the nozzle member is fitted into a bottom mold plate having a cooling path, the nozzle tip is fitted into the opening in the bottom of the cavity, and the nozzle tip in the opening is fitted to the bottom of the cavity as required. The nozzle port is also used as a cavity gate with clearance provided, and the injection key has the nozzle tip surface extended to the bottom of the cavity due to thermal expansion of the nozzle tip. While complement the molding surface of the central portion of the bottom surface of the Activity flat, the constitution to reform the clearance by the contraction due to temperature drop of the nozzle tip caused by the injection filling stop of the molten resin, is that.
[0013]
According to the present invention, the spout-less molded product is injected by preventing the cooling of the nozzle port also serving as a gate by the clearance of the nozzle tip surface, extending due to thermal expansion of the nozzle tip during injection filling, and closing the nozzle port by the needle valve. Since it can be molded, there is no need for bushing or heating means for cooling near the gate, which is required for conventional sprue molding and molds, and there is no need for nozzle touch by mechanical operation for each molding. The injection molding of products is easier than before, and even in a long molding cycle, there is no temperature drop near the nozzle gate that has become a cavity gate, so there is no restriction on molding temperature or material resin, and the material resin is polyester, polycarbonate Injection molding of sprue-less molded products with a uniform bottom shape even for resins such as APEL It is possible.
[0014]
With regard to the mold structure, the nozzle tip of the hot runner nozzle member need only be inserted into the opening formed at the center of the cavity bottom portion with a required clearance, and the nozzle port is flush with the needle valve. The main structure of the mold is not required to make the nozzle mouth small to make it sprueless or to make the nozzle mouth special structure so that it can be cut at the time of mold release. Therefore, the mold structure is not particularly complicated in comparison with the conventional structure.
[0015]
In addition, since there is no sprue on the bottom of the injection-molded molded product, it can be said that it is extremely suitable for injection molding of stretch blow-molded preforms. As a result, the molding cycle can be improved and the loss can be reduced. In particular, in the hot parison system, the injection-molded sprless preform can be immediately molded into a hollow molded product such as a container, which further increases the productivity.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows one embodiment of a mold that can be used for carrying out the molding method of the present invention. 1 is a cavity mold of an injection mold, 2 is a neck mold, 3 is a core mold, and 4 is a nozzle member for injection. Reference numeral 5 denotes a blow mold.
[0017]
The cavity mold 1 is composed of a cylindrical main body 11 having a cavity forming hole at the center, and a bottom mold plate 12 in contact with the bottom surface of the main body 11. A recess serving as the bottom of the cavity is formed at the site where the portion overlaps. A cooling path 13 is provided in the body around the hole and in the bottom mold plate around the recess.
[0018]
The core mold 3 has a cooling passage 14 therein, and passes through the neck mold 2 that is in contact with the upper end of the main body 11 when the mold is closed, and is inserted from the opening of the hole to the recess. A cavity 15 is formed between the mold 1 and the bottomed preform 6.
[0019]
The center of the bottom surface of the injection cavity 15 due to the recess of the bottom mold plate 12 is formed in an opening 16 having a required inner diameter, as shown in FIG. An insertion hole 17 is provided at the tip of the nozzle member 4 which is reduced in diameter and formed in multiple stages.
[0020]
The nozzle member 4 has a shape generally referred to as a flat nozzle in which the tip is partially projected from the end surface of the member and the nozzle tip surface is formed flat, and the nozzle tip 41 fits the opening 16. The outer diameter is formed.
[0021]
Further, the nozzle member 4 includes a needle valve 43 having a truncated cone shape in which the end surface of the valve tip 42 is formed flat inside so as to be movable back and forth in the axial direction, and the valve tip surface has a normal size of the nozzle tip surface. In order to be able to close the nozzle port to the design top surface with the nozzle tip surface, the resin path in the nozzle member is sequentially reduced in diameter from the tip part to the nozzle port to form an inclined surface with the same angle as the valve tip part. It is.
[0022]
Such a nozzle member 4 is screwed and attached to a nozzle holder 45 projecting from an upper portion of a hot runner block 44 located on the lower side of the injection mold, and from the injection device by communication between the hot runner and the resin path. The molten resin is injected and filled into the injection cavity 15.
[0023]
The needle valve 43 penetrates the hot runner block 44 and is connected to a piston of a hydraulic cylinder attached to the lower side of the block, and is moved forward and backward by the piston to open and close the nozzle port. Consists of configuration.
[0024]
The nozzle member 4 projecting above the hot runner block 44 is fitted with the insertion hole 17 at the tip end of which the outer periphery is knurled by the installation of the cavity mold 1 and fits below the injection mold. With this fit, the nozzle tip 41 is fitted into the opening 16 at the center of the bottom of the injection cavity 15 so that the nozzle tip surface faces the cavity bottom surface. When the number of injection cavities is large, the nozzle member 4 is attached to the hot runner block 44 for each number of injection cavities and disposed below the injection mold.
[0025]
The insertion of the nozzle tip 41 into the opening 16 is performed by providing a clearance 18 that allows for the expansion of the nozzle tip due to the thermal expansion because the nozzle tip thermally expands due to the temperature of the molten resin being injected and filled. . The set dimension of this clearance 18 varies depending on the melting temperature of the resin used as the molding material. However, when the molding material is APEL and the dimensions of the preform 6 are 4.5 mm in height and 1.5 mm in outer diameter, The thickness of the cavity bottom may be 2.0 mm, the inner diameter of the opening 16 may be 8.0 mm, and the clearance 18 may be about 1.7 mm.
[0026]
In this state where the clearance 18 is provided and the nozzle tip surface faces the cavity bottom surface, the nozzle port also serves as a cavity gate. Therefore, when the injection of the molten resin is started by retreating the needle valve 43, the nozzle tip 41 expands to a position substantially coincident with the bottom surface of the cavity by thermal expansion while injecting and filling molten resin into the injection cavity 15 from the nozzle port formed as a cavity gate. By this extension, the nozzle front end surface complements the center of the bottom surface of the cavity 15, which was the opening 16, to form a molding surface, and the bottom surface of the preform 6 is molded flat.
[0027]
When the needle valve 43 is moved forward simultaneously with the completion of injection filling, the valve tip 42 moves to a position where the valve tip surface is flush with the nozzle tip surface, closes the nozzle port, and sprues are generated by the nozzle port. To prevent. As a result, the preform 6 having a flat bottom portion 32 which is thinner than the body portion 31 and has no sprung projection at the bottom center is formed.
[0028]
Further, when the nozzle opening is closed and the injection filling of the molten resin is stopped, the tip of the nozzle in the insertion hole 17 is in contact with the constantly cooled bottom mold plate 12, so that the contact area is reduced by the knurl. However, the bottom mold plate 12 lowers the temperature of the nozzle tip so that thermal expansion can be accommodated. As the temperature decreases, the nozzle tip contracts and returns to the original position, and the clearance 18 is formed again.
[0029]
The overlap between the nozzle tip 41 and the opening 16 at the nozzle tip restored to the original shape is slightly (about 0.3 mm) as shown in FIG. 3 due to the formation of the clearance 18, and the inner wall of the nozzle tip is not inside the nozzle member. Since the valve tip 42 of the needle valve 43, which is constantly heated by the molten resin, is in contact with the nozzle resin 41, the temperature of the nozzle tip 41 is unlikely to decrease, and the next injection filling can be performed without hindrance.
[0030]
As described above, the center of the bottom surface is formed flat by the nozzle tip surface of the nozzle member 4, and the center of the bottom surface is closed by the valve tip surface of the needle valve 43 so as to be flush with the nozzle tip surface. As shown in FIG. 6, the preform 6 formed into a spruce can be stretch blow molded into the thin container 7 shown in FIG. 6 by the blow mold 5 as it is.
The stretch blow molding of the preform 6 can employ either a hot parison method or a cold parison method.
[0031]
FIG. 2 shows a blow mold 5 comprising a pair of split molds 51 movably mounted on a pedestal 53 and a bottom mold 52 provided so as to be movable up and down between the pedestal 53 and the bottom of the mold. The state in which the reform 6 is stretch blow molded into the container 7 is shown.
[0032]
The injection-molded preform 6 is formed by holding the neck portion with the neck mold 2 at the center of the pair of split molds 51 in the mold open state and closing the split mold 51. Set in the center of the blow cavity 54. Further, a blow core 55 through which the extending rod 56 is inserted is fitted into the neck mold 2 from above, whereby the core tip portion 57 is airtightly accommodated in the opening of the preform 6 and the tip end portion of the extending rod 56 is the central portion of the cavity. It is located on the inner bottom surface of the preform 6 set in.
[0033]
The axial stretching of the preform 6 by the stretching rod 56 and the expansion and stretching in the radial direction by the blow air from the blow core 55 are performed almost at the same time. Becomes the container 7 whose bottom surface 72 is pushed up by the bottom mold 52. The molding of the bottom surface 72 by the bottom mold 52 is performed uniformly because there is no protrusion due to the sprue at the center of the bottom surface of the preform 6, and an annular ground contact surface is beautifully formed around the bottom surface even with a slight push-up amount.
[0034]
Although the mold surface facing the blow cavity 54 of the illustrated bottom mold 52 is flat, the mold surface may be a convex surface. In this case, the bottom surface of the container 7 except for the inside of the annular ground surface is a concave curved surface. It is formed.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of an injection mold in a state where a bottomed preform is molded by the sprueless molding method of the present invention.
FIG. 2 is a longitudinal sectional view of a blow mold showing a state in which a preform formed by the same spurless molding method is stretch blow molded into a container.
FIG. 3 is a longitudinal sectional view of a main part showing a nozzle tip position of an injection mold before preform molding.
FIG. 4 is a longitudinal sectional view of a main part showing a nozzle tip position of an injection mold during preform molding.
FIG. 5 is a longitudinal sectional front view of a preform molded by the sprueless molding method of the present invention.
FIG. 6 is a longitudinal front view of a container formed by stretching and blowing the above preform.
[Explanation of symbols]
1 Cavity mold 2 Neck mold 3 Core mold 4 Nozzle member 5 Blow mold 6 Preform 7 Container 11 Cavity mold body 12 Bottom mold plate 15 Injection cavity 16 Opening 17 Insertion hole 18 Clearance 41 Nozzle tip 42 Valve tip 43 Needle valve 51 Split Mold 52 Bottom Mold 54 Blow Cavity 55 Blow Core 71 Container Body 72 Container Bottom

Claims (2)

  The tip of the nozzle member inside the needle valve is inserted into the opening at the center of the bottom of the injection cavity, the center of the bottom is formed by a flat nozzle tip, and the nozzle port is also used as the cavity gate. The required clearance is provided between the tip surface and the bottom surface of the cavity, and the injection resin is injected and filled into the injection cavity from the nozzle tip that is in contact with the constantly cooled bottom mold plate, and the nozzle made of the molten resin being filled The bottom center of the bottomed molded product is formed with the nozzle tip extending to the bottom of the cavity due to the thermal expansion of the tip, and then the nozzle port is closed flush with the nozzle tip by the valve tip of the needle valve. While forming a bottomed molded product that does not have a sprue at the center of the bottom surface, it is possible to reduce Supururesu molding, which comprises re-forming the clearance by.   The bottom of the injection cavity has an injection mold with a bottomed molded product that has an opening with a required inner diameter, and a nozzle tip with a nozzle tip that is flat with an outer diameter that fits the opening. The tip of the nozzle surface of the tip surface is closed by a flat valve tip surface, and the tip shape is composed of an injection nozzle member having a truncated cone shaped needle valve, and the tip portion of the nozzle member has a cooling passage. The nozzle tip is fitted into the plate and the nozzle tip is inserted into the opening on the bottom surface of the cavity, and the nozzle tip is used as a cavity gate with the nozzle tip surface in the opening facing the bottom surface of the cavity. The nozzle tip extended to the bottom of the cavity due to the thermal expansion of the tip complements the molding surface at the center of the bottom of the injection cavity flatly, while Supururesu mold, characterized in that the constitution to reform the clearance by the contraction due to temperature drop of the nozzle tip caused by the injection filling stopping.

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