JPH0651324B2 - Hot runner mold for injection molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a hot runner type mold among injection molds used for injection molding of plastic, that is, a melt injected and injected from an injection molding machine. Regarding the molding die equipped with a hot runner that guides the resin to the cavity of the molding die while maintaining the molten state, in detail, it is contaminated by the stabilizer contained in the resin and the adhered matter is attached. The present invention relates to a molding die provided with a hot runner and a molding method using the same.

[Prior Art] When plastic molding is performed by injection molding, a hot runner type in which hot chips are arranged can be used as a mold for injection molding, in addition to a cold runner type. The latter is advantageous for efficient molding. An example of this hot runner type molding die will be described with reference to FIG. 2. The die 1 has a fixed side cavity core 2 and a moving side core 3 each having an appropriate shape. The cavity 4 of the mold is formed by joining the cores. In the fixed side cavity core 2,
The fixed core 6 having the gate 5 is adjacent to the core 5, and the molten resin is injected into the cavity 4 from the gate 5.
The flow path for guiding the molten resin to the gate 5 is a sprue 8 extending from an injection hole 7 that receives a nozzle of an injection molding machine.
And a runner 9 for guiding the molten resin from the sprue 8 to the gate 5, and a hot tip 10 arranged in the runner 9 and functioning as a heater for keeping the molten state of the resin. As the material of hot tip and hot runner,
Generally, S55C steel is used, and SUS steel is used for some purposes. Further, in order to help the injected resin to cool in the mold cavity 4, necessary cooling grooves and accompanying seal members are arranged, but they are shown in the drawing for simplification. Not not.

The operation of the hot runner type injection molding die having such a hot chip is well known, and when the molten resin is injected into the injection hole 7 from the nozzle of the injection molding machine (not shown), the resin becomes a cartridge. After passing through the runner 9 heated by the heater 20, it is heated by the hot tip 10 and filled in the cavity 4 from the gate 5. Depending on the shape of the hot runner, the hot tip 10 and the band heater 21 may be used together. The resin with which the cavity is filled is taken out as a molded product by being cooled and solidified, and then the moving core 3 is moved and the mold 1 is opened.

[Problems to be Solved by the Invention] However, it is usual that various stabilizers and other additives are added to the resin introduced into the mold from the injection molding machine for various purposes. . In a hot runner type injection molding die, since such resin stays in a molten state, the contact surface between the molten resin and the flow path of the resin in which the components of the stabilizer or decomposition products of the resin itself have melted It was found that the contaminants tended to be formed easily because they tended to adhere to the surface of the hot chip and the vicinity of the heating element. If molding is continued in such a case, the deposited contaminants will be injected into the cavity together with the resin, and will adhere to or be mixed with the molded product, which will have a great adverse effect on the appearance and the like. Therefore, an object of the present invention is to provide a hot runner type injection molding die that prevents adhesion and contamination of a flow path by a stabilizer or the like in a molten resin and does not cause stains on a molded product.

[Means for Solving the Problems] That is, the present invention provides a hot runner mold having a runner in which a heat source such as a hot chip is arranged between the downstream end of the sprue and the gate of the cavity. Hot runner mold for injection molding, characterized in that the material of the surface of the hot chip in contact with the molten resin in the runner part and the surface of the runner part where the heat source exists are composed of chromium, nickel or chromium-nickel alloy Which solves the above problems.

Thermoplastic resins used in injection molding, for example, polybutylene terephthalate resin, polyethylene terephthalate resin, aromatic polyester resin such as polyacrylate resin, polyacetal resin, polyamide resin, polystyrene resin, polycarbonate resin, polyethylene resin,
Resins mainly composed of polypropylene resin, ABS resin, EVA resin, vinyl chloride resin, fluorine resin, etc. include phenol-based, phenone-based, triazine-based, sulfur-based, phosphorus-based, amine-based, amide-based, amidine-based, metal Various stabilizers such as soaps are usually blended. In addition, additives such as lubricants, nucleating agents, release agents, antistatic agents and other surfactants, plasticizers, pigments, dyes, flame retardants, various organic polymer substances, inorganic fillers, etc. are compounded according to the purpose. Has been done. The inventors of the present invention have made the flow path surface of any material in order to prevent adhesion contamination due to decomposition products generated by heating of these stabilizers, additives, resins themselves, etc. and their polycondensates. We have conducted intensive research into whether or not it should be constructed by. As a result, among the contact surfaces between the flow path from the sprue of the mold to the gate and the molten resin, the formation of contaminated deposits may occur especially on the contact surface of the heating body such as the hot tip or the like arranged in the runner part or its vicinity. It was discovered that it was remarkable that it was extremely effective to form the contact surface of this portion with chromium, nickel or a chromium-nickel alloy. It is preferable that these metal materials substantially consist of chrome or nickel alone or an alloy of chrome and nickel, and that these metal components are 99% or more. In order to form such a resin contact surface, it is achieved by means such as surface processing of the runner portion surface of the metal material that has been conventionally used, particularly the contact surface at least near the heating body of the runner portion. Examples of the surface processing method include electroplating, electroless plating, and padding. In particular, the electroless plating method of nickel is preferable because it is possible to perform uniform surface processing with no pinholes and fine details of a complicated shape, and the metal structure becomes smoother than that of the electroplating method. In some cases, further heat treatment or the like can be performed to increase the surface hardness. The surface is processed by using chromium, nickel alone, or a chromium-nickel alloy for the whole or a part of the runner portion where the heating element is arranged from the sprue end to the gate. In particular, it is preferable to surface-treat the hot runner portion and the hot tip portion heated by the heater and the portion in contact with the molten resin. But,
Appropriate design changes, such as surface treatment of only the places where the adhered contamination is likely to occur in the runner portion, are of course within the scope of the present invention. In particular, the mold of the present invention is suitable for molding polyacetal resin and polyester resin.

[Examples] Hereinafter, the present invention will be described with reference to Examples, but the present invention is not limited to these Examples.

Examples 1 and 2 and Comparative Examples 1 and 2 As shown in FIG. 1, a molten resin flow path of a hot runner type injection molding die 11, that is, from a sprue 12, a runner 13 to a gate 14, and The surface of the hot chip 15 in contact with the molten resin was surface-treated with the metals shown in Table 1 to form the coating layer 16. Using this mold 11, 0.5 wt% of polyamide resin as stabilizer and 0.5 wt of 2,2′-methylenebis (4-methyl-6-t-butylphenol) were used.
% Of polyacetal resin was used to continuously mold the molded article for 300 hours.

The presence / absence of deposits on the channel surface (especially the hot chip surface) due to this is visually evaluated, and 2
The number of 00 pieces was evaluated by the number of formed articles in which foreign matter was found adhering to the surface of the formed article. The results are shown in Table-1. Further, the same evaluation was performed for a mold that was not surface-treated, and the results are also shown in Table 1 as a comparative example. The contact surface of the hot runner with the molten resin when the surface treatment is not performed is made of S55C steel.

The molding conditions used in these tests are as follows.

Resin temperature in the mold 210 ° C. Molding cycle 20 seconds Examples 3 and 4 and Comparative Examples 3 and 4 30 wt% of glass fiber was added as an additive to the entire composition by using a mold surface-treated as in FIG. A molded product (10 cm × 10 cm × 0.5 cm) was continuously molded for 300 hours using a polybutylene terephthalate resin containing 7 wt% of a halogen-containing organic compound, 7 wt% of antimony trioxide and 5 wt% of asbestos as a flame retardant, and evaluated in the same manner. Table 2 shows the metals used for the surface treatment and the test results.

The molding conditions used in these tests are as follows.

Resin temperature in the mold 260 ℃ Molding cycle 40 seconds [Effects of the Invention] As is clear from the above results, the hot runner type injection molding die of the present invention is derived from the stabilizer and the like in the molten resin, and is particularly caused by the remarkable adhesion of contaminants in the hot runner portion. It eliminates the conventional problems, which allows the injection molding operation to proceed very efficiently.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an embodiment of a hot runner type injection molding die of the present invention having a hot runner portion surface-treated, and FIG. 2 is a schematic view of a conventional hot runner type injection molding die. FIG. 1 ... Mold, 2 ... Fixed side cavity core 3 ... Moving side core, 4 ... Cavity, 5 ... Gate 6 ... Fixed side core, 7 ... Injection hole, 8 ... Sprue 9 ... Runner , 10 …… hot tip, 11 …… mold 12 …… sprue, 13 …… runner, 14 …… gate 15 …… hot tip, 16 …… coating layer 20 …… cartridge heater, 21 …… band heater

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Claims (3)

[Claims] 1. An injection molding die having a hot runner having a hot tip for introducing a molten resin injected from an injection molding machine into a cavity of the injection molding die.
A hot runner type injection molding die, wherein a contact surface between a molten resin flow path and a molten resin in a hot runner portion having at least a heat source is made of chromium, nickel or a chromium-nickel alloy. 2. A hot runner type injection molding according to claim 1, wherein chromium, nickel or a chromium-nickel alloy is processed on the contact surface with the molten resin by electroplating, electroless plating or padding. Mold for. 3. A hot runner type injection molding die according to claim 1 or 2, wherein nickel is surface-processed on the contact surface with the molten resin by electroless nickel plating.