JP2009262324A - Injection molding nozzle for rubber product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To develop an injection molding nozzle with simple structure for rubber products, which prevents temperature rise of a nozzle block and reduces product defect caused by occurrence of scorch. <P>SOLUTION: The injection molding nozzle for the rubber products is formed by forming an inner cylinder section 23 by making the inner diameter of the inner face of a nozzle body 21 of a metallic nozzle 2 to be mounted on the tip of an injection cylinder of a rubber injection molding machine larger than an injection port diameter while leaving an injection port 22, and forming the nozzle inner face for passing injection raw material rubber in the formed inner cylinder section 23 with a heat-resistant organic material, for instance, a plastic cylindrical heat insulation material 24. Here, the plastic cylindrical heat insulation material 24 is formed by pressing a rod-like molded body having an outer diameter slightly larger than the inner diameter of the inner cylinder section 23 into the inner face inner cylinder section 23 of the nozzle 2 body up to the vicinity of the nozzle injection port 22 from a nozzle mounting base part 25 to the injection cylinder, and cutting the nozzle inner wall 26. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a nozzle for injection molding of rubber products in an injection molding apparatus mainly used for vulcanization molding of rubber products.

  When trying to obtain products with sufficient precision and fusion strength by injection molding of general industrial precision rubber products including rubber products for automobiles, injection and injection with good fluidity into the product cavity, and It is necessary to prevent scorch (early vulcanization) from occurring during the flow of the raw rubber as much as possible. However, if the material injection temperature is relatively high in order to inject with good fluidity, scorch is likely to occur before the rubber material reaches the product cavity gate. Also, if the fluidity is low, the flow rate in the cavity is slow, scorching occurs before fusing, and a fusing line (weld mark) tends to occur on the product surface.

  Therefore, in order to obtain a fusion strength, it is necessary to perform injection molding at a relatively high pressure (high speed). However, when trying to injection mold at a high pressure, it is necessary to relatively reduce the viscosity at a high temperature. When injected into the product cavity with the injection temperature kept high, the material flow resistance is increased by scorch in the cavity of the molding material, resulting in fusion joint / strength failure and filling failure (short shot). Cheap. That is, a lot of defective molded products are generated.

  As a technique for solving this problem, Patent Document 1 discloses that an injection pot is a plunger fitting portion in which a tip portion continuous with an injection nozzle has a shape corresponding to the tip shape of the plunger, and the plunger of the injection nozzle and the injection pot. The thing which formed the heat insulation coating layer in each inner surface of a fitting part is seen. This heat insulation coating layer is usually formed of a ceramic spray coating layer. For example, it is assumed that the surface is polished with a total thickness of 80 μm (undercoat and topcoat) with 50/50 alumina / titania. As a result, heat dissipation from the injection pot wall surface of the molten rubber in the injection pot is blocked, so that the temperature or viscosity in the pot of the molten rubber can be easily achieved. Yes.

  Further, as a means for preventing temperature propagation from the mold, it has long been proposed to use ceramic or stainless steel having poor thermal conductivity for the sprue bush, although it is not an injection nozzle (for example, Patent Document 2). .

  Further, recently, as seen in Patent Document 3, a cold runner device is provided in an injection mold for mainly vulcanizing a molded product such as a rubber product. The nozzle structure of this cold runner device An injection mold having a cold runner device is fastened via a heat insulating material layer to an upper and lower molds that can be opened and closed to form a molding cavity, and an injection nozzle. And a cold runner block that forms a cold runner for feeding the rubber material injected from the cavity to the cavity, and a nozzle block constituting a nozzle for injecting the rubber material from the cold runner into the cavity on the lower surface of the cold runner block Is attached. Both the upper and lower molds are provided with a flow passage for passing a heating medium for heating the mold, while the cold runner block has a flow passage for passing a cooling medium through the upper and lower runner plates constituting the block. In addition to being provided, a flow path through which the cooling medium passes is also provided in the nozzle block attached to the lower surface thereof. In addition, in order to cut off the heat from the mold, the nozzle block has a required space around the recess of the upper mold, and only the nozzle tip is used as a part of the inlet to the cavity in the upper mold. What was made to contact is proposed.

JP 2005-279949 A ([0020] [0038]) Japanese Patent Publication No.42-1194 (second page, left column) JP 2004-243745 A ([0004] [0005])

  As seen in these above-mentioned patent documents, in order to prevent the temperature rise of the nozzle block and reduce the product failure due to the occurrence of scorch, as a means to block the heat conduction from the mold, (a) the injection nozzle and the injection Form a thermal spray coating layer on each inner surface of the pot plunger fitting part, (b) Use ceramic or stainless steel with poor thermal conductivity for the nozzle block, or (c) Nozzle block Means are provided to provide a flow passage for passing a cooling medium around the nozzle.

  However, the thermal insulation coating material is an inorganic ceramic, lacking in molding processability and thermal spraying processability, and although it has poor thermal conductivity, stainless steel is not a good thermal insulation efficiency as long as it is a metal. Forming the medium flow path in the nozzle block leads to an increase in manufacturing cost.

  The present invention aims to further improve the temperature rise prevention means of the nozzle block found in these prior arts, and seeks a heat insulating material for a heat resistant organic material that has never been considered so far. As a result of various investigations as to whether or not the material can be solved, if it is a heat resistant plastic or the like, it is easy to process, and it is possible to achieve the purpose of preventing the temperature rise of the nozzle block and reducing product defects due to the occurrence of scorch. It has been established as a technology.

  That is, the configuration of the present invention is a metal nozzle that is attached to the tip of an injection cylinder of a rubber injection molding machine, and the inner surface of the nozzle body of the metal nozzle is made larger than the injection port diameter while leaving the injection port. This is a nozzle for injection molding of a rubber product in which the inner surface of the nozzle through which the injection raw rubber passes is formed with a heat-resistant organic material cylindrical heat insulator.

  Here, the heat-resistant organic material cylindrical heat insulator is a rod-shaped molded body of a heat-resistant organic material having an outer diameter slightly larger than the inner diameter of the inner surface of the nozzle body from the nozzle mounting base to the vicinity of the nozzle injection port. After press-fitting, a heat-resistant organic material cylindrical heat insulator is formed by cutting the inner wall of the nozzle. Alternatively, when the heat-resistant organic material cylindrical insulator is a plastic material, the plastic cylindrical insulator itself is made into a cylindrical molded body that has been finished up to the nozzle inner wall by injection molding or the like, and then press-fitted into the pocket of the nozzle body. It can also be made into a heat insulator.

  Moreover, this plastic cylindrical heat insulating body may form a cylindrical molded body directly on the inner surface of the nozzle body by plastic injection molding. In this case, the nozzle main body is mounted in the mold, and the plastic melt constituting the plastic cylindrical heat insulating body can be integrated by injection molding as a cavity having the shape of the plastic cylindrical heat insulating body.

  The plastic material of the plastic cylindrical heat insulator used for the cylindrical molded body is a heat-resistant plastic having a heat insulating effect that maintains the temperature at which the injection raw rubber passing through the nozzle does not reach a temperature higher than its scorch temperature. Usually, the continuous use temperature is 100 ° C. or higher, preferably 120 ° C. or higher, and more preferably 150 ° C. or higher. More preferably, the plastic may be 170 ° C. or higher and can withstand higher temperatures. Specific plastic materials that can be used include polyethylene terephthalate (PEТ) 100 to 150 ° C., polyamide (PA, nylon) 120 to 150 ° C., polyetherimide (PEI) 170 ° C., polyphenylene sulfide (PPS) 220 ° C., poly Examples include ether ether ketone (PEEK) 250 ° C., polytetrafluoroethylene (PТFE) 260 ° C., polyimide (PI) 304 ° C., polybenzimidazole (PBI) 310 ° C., and the like.

  In addition to these thermoplastic resins (plastics), phenolic resins, melamine resins, epoxy resins, unsaturated polyester resins, diallyl phthalate resins, thermosetting resins such as thermosetting polyimide, and wood materials are also heat-resistant organic material cylindrical insulators Can be used as In the case of a wood material, a hard oak tree or a chestnut tree is preferable, and a material impregnated with a heat resistant resin is useful.

  Since the nozzle for injection molding of the rubber product of the present invention is configured as described above, the heat insulating property of the rubber flow path in the nozzle is good, and the raw rubber passing therethrough is not easily affected by the heat from the mold, so that the tip of the nozzle There is no scorch and effective in preventing defects in vulcanized rubber. In addition, because of the good releasability between the raw rubber fabric and the heat-resistant organic material cylindrical heat insulator, especially plastics such as PEEK and PТFE, the rubber flows smoothly and does not stagnate, which is not possible with conventional nozzles. Fast injection molding of raw rubber has become possible.

  Further, the nozzle structure is simple because it does not provide a gas or liquid refrigerant passage, and it is not necessary to install a supply device for these refrigerants, which is useful for reducing manufacturing facilities.

  Hereinafter, the nozzle for injection molding of the rubber product of the present invention will be specifically described with reference to the drawings. FIG. 1 is a side view showing a schematic structure of a vertical rubber injection molding machine equipped with a nozzle of the present invention. FIG. 2 is a longitudinal sectional view showing a structure example of the nozzle of the present invention.

  As is apparent from FIG. 1, a normal vertical rubber injection molding machine has a nozzle 2 attached below the injection cylinder 1, and an upper heat insulating board 5 and an upper heating board between the fixed board 3 and the operation board 4. 6, a mold 10 is provided through a lower heat insulating board 7 and a lower heat board 8.

  The mold 10 includes an upper mold 11 and a lower mold 12. The upper mold 11 is heated by the upper heating plate 6, and the lower mold 12 is heated by the lower heating plate 8. The upper part of the upper heating plate 6 in the mold 10 is provided with a sprue gate 13 in contact with the tip of the nozzle 2, and a heat-resistant sprue bushing 14 is fitted, from which the sprue 15 of the upper mold 11 in the mold 10 and the runner 16. The branched gate 17 leads to each cavity 18 provided at the boundary between the upper and lower molds.

  The rubber product injection molding nozzle 2 of the present invention is a nozzle that is attached to the tip of an injection cylinder 1 of a rubber injection molding machine. As shown in the cross-sectional view of FIG. The nozzle 23 is formed by forming the pocket portion 23 with the inner diameter larger than the injection port diameter and forming the inner surface of the nozzle through which the injection raw rubber passes through the formed pocket portion 23 with a plastic cylindrical heat insulator 24.

  Here, the heat-resistant organic material cylindrical heat insulating body is a plastic cylindrical heat insulating body 24, and this cylindrical heat insulating body is a nozzle body 21 inner surface pocket 23 from the nozzle mounting base 25 to the vicinity of the nozzle injection port 22 to the injection cylinder. In addition, after press-fitting a rod-shaped molded body having an outer diameter slightly larger than the inner diameter of the pocket 23, the nozzle inner wall 26 is formed by cutting. Alternatively, a cylindrical molded body that has been finished up to the nozzle inner wall 26 by injection molding or the like can be press-fitted into the plastic cylindrical heat insulating body 24.

  Further, the plastic cylindrical heat insulator 24 forms a cylindrical molded body directly by plastic injection molding on the inner surface 23 of the nozzle body 21 from the nozzle mounting base 25 to the injection cylinder 1 to the vicinity of the nozzle injection port 22. May be. In this case, the nozzle main body is mounted in the mold, and the plastic melt constituting the plastic cylindrical heat insulator 24 is integrally formed by injection molding as a cavity having the shape of the plastic cylindrical heat insulator.

  The plastic material of the plastic cylindrical heat insulator 24 used for the cylindrical molded body is a heat-resistant plastic having a heat insulating effect that maintains a temperature at which the injection raw rubber passing through the nozzle 1 does not reach a temperature higher than its scorch temperature. PEEK and PPS having a continuous heat resistant temperature of 250 ° C. or higher were good. Hereinafter, the configuration of the injection molding nozzle for rubber products of the present invention will be described more specifically with reference to examples.

Examples 1-6
As heat-resistant organic material cylindrical heat insulators, heat-resistant plastics PE, nylon, PVDF, PPS, PEEK and PI shown in Table 1 were used. The nozzle structure is as shown in FIG. 2 and has a size of 85 mm × 45φ and a nozzle hole diameter of 5φ. The inner surface of the nozzle body from the nozzle mounting base to the injection cylinder and the vicinity of the nozzle injection hole is punched to 20φ, and a plastic rod-shaped molded body having an outer diameter slightly larger than the inner diameter is press-fitted, and then the inner wall of the nozzle is cut As a result, the heat-resistant cylindrical heat insulator shown in FIG. 2 was formed.

  Using these plastic cylindrical heat insulators, the vertical rubber injection molding machine shown in Fig. 1 was used to convert a conventional natural rubber vulcanized composition to a muffler hanger (major axis 80mm, minor axis 55mm, thickness 20mm) at a mold temperature of 170 ° C. Was molded. Each of the occurrence of rubber burn during molding, the wear resistance of the nozzle, the defect rate, and the workability, and the overall added value obtained from this were evaluated in four stages. The results are shown in Table 1.

As is apparent from the results in Table 1, the nozzles into which the heat-resistant organic material cylindrical heat insulator of the present invention has been inserted are common sense so far, that is, it is considered that an injection molding material such as plastic is used for the injection molding nozzle. This is a breakthrough of what is not possible. That is, when these resins such as plastics are actually used by the method of the present invention, they are excellent in heat insulation and wear resistance, and particularly in rubber injection molding, sufficient durability and good workability are obtained. As a result, the defective rate of the product was remarkably reduced and a high degree of added value was shown.

Examples 7-10
In this example, a thermosetting resin or wood material was used instead of the plastic material, and the nozzle having the structure shown in FIG. Although these have some problems in processability than heat-resistant plastics, the object of the present invention can be sufficiently achieved.

  The injection molding conditions for the phenol resin nozzle in Example 7 were performed at a mold temperature of 170 to 190 ° C, a cylinder temperature of 90 to 100 ° C, and an injection pressure of 70 MPa. The results are summarized in Table 2.

Comparative Examples 1 and 2
As Comparative Examples 1 and 2, the performance evaluation of each nozzle based on performance data of a conventional metal nozzle and a thermal spray coating layer of alumina / titania ceramic powder formed in a thickness of about 100 μm inside the nozzle is shown in the latter part of Table 2. Summarized in Plastics and other materials have a low thermal conductivity of 1/70 compared to metals, and are less affected by external temperature. In addition, although plastic is inferior in strength to metal, there is no problem in mechanical properties because metal is used at the tip of the mold to compensate for the defects of the resin. Since Comparative Example 2 has an alumina / titania coating layer compared to a metal nozzle and its thermal conductivity is around 0.5, which is higher than that of plastic and is a thin layer, it cannot be expected to make a significant improvement except for wear resistance. It is.

  Table 3 shows the result of 100-shot injection molding experiments using the metal nozzle inserted with the PEEK heat-resistant plastic cylindrical body of Example 5 and the metal nozzle of Comparative Example 1 to mix the vulcanized rubber of the products indicated as defective items. The rate of pinholes due to air rate and air contamination was investigated. As is apparent from the results, the defect occurrence rate was reduced by 86% compared to the prior art. In other words, by using the nozzle of the present invention, the material and work man-hours were greatly improved compared to the metal nozzle.

  Table 4 shows a comparison between Table 3 and natural rubber vulcanized composition that is easy to burn, and is obtained by comparing the molding cycle time reduction effect and material loss. This means that the PEEK nozzle time is 90 when the molding cycle time of the nozzle is 100, and this time shortening effect is reduced by 10%. In addition, the material loss reduction is the same, and 5g which is easy to vulcanize (easily burn) is not discarded every shot. Therefore, the material loss is zero and the productivity improvement rate reaches 100%. As a result, it is expected that a productivity improvement rate of 10% can be expected for the former and 100% for the latter. In other words, a material with a high vulcanization speed in a rubber fabric will be defective if the burnt rubber in the nozzle is not removed every time after taking out the product. Table 4 shows that the rubber removal man-hours are almost eliminated, the molding cycle is shortened, and the productivity is improved. Furthermore, as described above, the conventional metal nozzle generates burnt rubber at each shot, but if the nozzle of the present invention is used, the countermeasure against burnt rubber can be almost complete, leading to a significant reduction in material costs. It turned out.

1 is a side view showing a schematic structure of a vertical rubber injection molding machine equipped with a nozzle of the present invention. It is a longitudinal cross-sectional view which shows the structural example of the nozzle of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Injection cylinder 2 Nozzle 3 Fixed board 4 Operation panel 5 Upper heat insulation board 6 Upper heat board 7 Lower heat insulation board 8 Lower heat board
10 Mold
11 Upper mold
12 Lower mold
21 Nozzle body
22 Injection port
23 Nozzle inside the nozzle body
24 Plastic tubular insulation
25 Nozzle mounting base
26 Nozzle inner wall

Claims (6)

A metal nozzle that is attached to the tip of an injection cylinder of a rubber injection molding machine. The inner surface of the nozzle body of the metal nozzle is made larger than the diameter of the injection port while leaving the injection port. A nozzle for injection molding of rubber products, in which the inner surface of the nozzle through which raw rubber passes is formed of a heat-resistant organic material cylindrical insulator. A rod-shaped molded body of a heat-resistant organic material having an outer diameter slightly larger than the inner diameter is press-fitted into the inner surface of the nozzle body from the nozzle mounting base to the vicinity of the nozzle injection port, and then the inner wall of the nozzle is heat-resistant by cutting. 2. A nozzle for injection molding of a rubber product according to claim 1, wherein the organic material cylindrical heat insulator is formed. The heat-resistant organic material cylindrical heat insulating body is made of a plastic material, and is formed by press-fitting a pre-formed cylindrical molded body into the inner surface of the nozzle body from the nozzle mounting base to the vicinity of the nozzle injection port. Nozzle for injection molding of rubber products. The heat-resistant organic material cylindrical heat insulating body is made of a plastic material, and a cylindrical molded body is formed by plastic injection molding on the inner surface of the nozzle body from the nozzle mounting base to the injection cylinder and the vicinity of the nozzle injection port. Nozzle for injection molding of rubber products. The plastic material of the heat-resistant organic material cylindrical heat insulator is a heat-resistant plastic that maintains a temperature that does not reach a temperature higher than the scorch temperature of the injection raw rubber, and the continuous use temperature is 100 ° C or higher. Nozzle for molding. 6. The nozzle for rubber product injection molding according to claim 1, wherein the heat-resistant organic material cylindrical heat insulator uses a thermosetting resin or a wood material instead of the plastic material.

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