JP5598251B2 - Molding method of resin molded products - Google Patents

Description

  The present invention relates to a method for molding a resin molded product such as an automotive part, particularly a molded product using a crystalline polymer resin, and belongs to the field of resin molded product molding technology.

  Conventionally, so-called general-purpose plastics such as polypropylene, polyethylene, polystyrene, and polyvinyl chloride are widely used in various fields as a material for resin molded products because they are inexpensive and have excellent moldability. However, since it is inferior in mechanical strength, heat resistance, etc., it is disadvantageous in that it is not suitable as a material for industrial products such as automobile parts and machine parts, although these characteristics are required.

  Therefore, as materials for industrial products for such applications, so-called engineering plastics such as polyethylene terephthalate, polycarbonate, or polyamide, which are expensive but have excellent mechanical strength and heat resistance, are used.

  In order to deal with such a situation, Patent Document 1 discloses that engineering plastics can be used while using a general-purpose plastic material such as polypropylene by greatly improving the crystallization rate at the time of molding a crystalline polymer resin melt. An invention that realizes mechanical strength and heat resistance corresponding to the above is disclosed.

  The present invention is characterized in that a melt of a crystalline polymer resin is stretched at a strain rate equal to or higher than a critical elongation strain rate in a state below the melting point and above the crystallization temperature, in other words, in a supercooled state. According to this, a large number of polymer chains having a large number of nuclei serving as crystallization starting points are formed in an oriented state, and crystals grow from these nuclei to form a dense and highly oriented film in a short time. Crystals are supposed to be formed, and it is expected that a molded article having excellent mechanical strength and heat resistance will be obtained.

  Here, the critical elongation strain rate is a rate at which the crystal size becomes discontinuously small when the supercooled melt is stretched and the strain rate in the stretching direction is increased. By stretching at a speed higher than the speed, the crystallization rate is greatly improved as compared with the case of crystallization by the conventional method.

  And in the said patent document 1, as a method for implement | achieving the elongation strain rate beyond a critical velocity, the sample of a disk-shaped polymer resin melt is pinched | interposed between the upper and lower plates, and this is maintained in a supercooled state. , A method of crushing by moving one plate toward the other plate at a constant speed, a method of discharging the polymer resin melt at a high speed while rapidly cooling from the discharge port of the die, a polymer resin by a pair of drawing rollers A method of drawing a melt from a die while rapidly cooling it is disclosed.

International Publication WO2008 / 108251

  However, in the method of sandwiching the polymer resin melt sample between the upper and lower plates described in Patent Document 1, it is necessary to prepare the sample in advance and the periphery has an irregular shape. Other processes such as molding are required.

  In addition, the method of discharging the polymer resin melt from the die can only obtain a long product having a constant cross-sectional shape, and the method of drawing the polymer resin melt with a pair of rollers is also in the form of a film. In order to obtain a product by laminating them, the resin must be melted again, and the strength improved by crystallization is reduced.

  Note that the normal injection molding method using a mold has a higher degree of freedom in the product shape than the above methods, but only a shear strain occurs during injection, and even if it is injected into the mold at a high speed, it is critically stretched. The strain rate cannot be obtained.

  Therefore, the present invention uses a crystalline polymer resin and uses the above-described method for improving the crystallization rate, and has a high degree of freedom in product shape and a process in which a final shape product is relatively easy. It is an object of the present invention to provide a method for molding a resin molded product to be obtained.

  In order to solve the above problems, the present invention is configured as follows.

  First, the invention according to claim 1 of the present application is a method for molding a resin molded product, in which a crystalline polymer resin is melted in a molding die in which a movable die is set away from a fixed die from a clamping position. A first injection step of injecting the liquid in a short shot state, and in a state where the temperature of the melt is lower than the melting point and higher than the crystallization temperature, The movable mold is clamped at a high speed to bring the melt into an oriented state and maintain the state for crystallization, and within the mold or other mold, the crystallization process A second injection step of injecting a melt of an additional resin around the molded intermediate molded product and molding the peripheral part of the intermediate molded product into a final shape.

  Here, the crystalline polymer resin includes not only general-purpose plastics such as polypropylene, polyethylene, and polyvinyl chloride, but also crystalline engineering plastics such as polyamide.

  The invention according to claim 2 is characterized in that, in the invention according to claim 1, the first injection step, the crystallization step, and the second injection step are performed in the same mold.

  The invention described in claim 3 is characterized in that, in the invention described in claim 1 or 2, the crystalline polymer resin and the additional resin are the same resin. Here, the homogeneous resin means a resin having the same main skeleton.

  Furthermore, the invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the crystalline polymer resin is a general-purpose plastic.

  The invention according to claim 5 is the invention according to claim 4, wherein the general-purpose plastic is polypropylene.

  With the above configuration, according to the invention of each claim of the present application, the following effects can be obtained.

  First, according to the invention described in claim 1, as the first injection step, a melt of the crystalline polymer resin is injected into the molding die in a state where the movable die is separated from the fixed die from the clamping position, Thereafter, the melt is brought into a supercooled state, and in the crystallization step, the movable mold is clamped at high speed until the cavity shape becomes the final shape of the molded product.

  At this time, the melt is sandwiched between the movable mold and the fixed mold and flows so as to spread around the mold, but the mold clamping is performed so that the elongation strain rate at that time is equal to or higher than the critical elongation strain rate. Therefore, as described above, a large number of polymer chains having a large number of nuclei as crystallization base points are formed in an oriented state, and crystals grow from these nuclei, so that the orientation can be achieved in a short time. A dense crystal body is formed. As a result, a high-strength portion having a high crystallization ratio and excellent mechanical strength and heat resistance can be obtained as an intermediate molded product.

  In that case, the injection amount of the melt of the crystalline polymer resin is an amount corresponding to a short shot state, that is, an amount smaller than an amount necessary for forming a final shape molded product. Even when the mold is clamped to the final shape, an unfilled portion of the resin melt remains in the cavity. In this way, the flow of the melt is prevented by not completely filling the cavity. The speed, that is, the elongation strain rate of the melt can be increased, and the critical elongation strain rate can be reliably achieved.

  Then, in the second injection step, with the intermediate molded product formed in the crystallization step being in the molding die, a melt of additional resin is injected into the molding die, and the melt around the intermediate molded product is injected. A part corresponding to the unfilled part of the liquid is additionally molded, and if the mold is opened after the melt is solidified, a molded product having a final shape can be obtained.

  In that case, since the additional molding part is not actively crystallized, the mechanical strength and heat resistance are inferior to those of the intermediate molded part, but the flow rate of the melt is relatively low. Therefore, it is molded faithfully to the molding surface of the mold and molded with high dimensional accuracy. As a result, a molded product having both mechanical strength, heat resistance and dimensional accuracy required for each part can be manufactured in a simple process with a high degree of freedom in shape compared to the method described in Patent Document 1. Will be.

  According to the invention of claim 2, since the first injection step and the crystallization step and the second injection step are performed in the same mold, these steps can be performed continuously, Equipment and work can be simplified, and the manufacturing cost of the molded product can be reduced.

  According to the invention of claim 3, since the crystalline polymer resin injected in the first injection step and the additional resin injected in the second injection step are the same resin, the intermediate molded portion And good compatibility at the boundary between the additional molded portion and a molded product in which both portions are firmly integrated. Moreover, since it is not necessary to separate both parts at the time of recycling, a molded product excellent in recyclability can be obtained.

  Furthermore, according to the invention described in claim 4, since a general-purpose plastic such as polypropylene, polyethylene, or polyvinyl chloride is used as the crystalline polymer resin, a molded product can be manufactured at low cost. .

Further, according to the invention described in claim 5, since polypropylene that is widely used as the general-purpose plastic is adopted, it is further advantageous in terms of price and availability.

It is a front view of the door module carrier of the motor vehicle shown as an example of the molded article shape | molded by the method of this invention. It is a perspective view of an instrument panel core member similarly. It is a block diagram of the shaping | molding apparatus used by 1st Embodiment of this invention method. It is explanatory drawing which shows the process of the same embodiment. It is sectional drawing of the molded article shape | molded by the method of the embodiment. It is a block diagram of the shaping | molding apparatus used by 2nd Embodiment of this invention method. It is explanatory drawing which shows the process of the same embodiment.

  Hereinafter, embodiments of the present invention will be described.

  First, an example of a resin molded product formed by the method of the present invention will be described. A molded product 1 shown in FIG. 1 is a door module carrier installed in a door of an automobile, and a door body is formed in a peripheral portion 1a. In order to ensure sealing performance in close contact with the inner panel or the outer panel, there is a portion that requires high dimensional accuracy, and a non-peripheral portion 1b on the inside thereof has an attachment portion for attaching the carrier 1 to the door body, Since various devices such as a power window motor and attachment parts for members are provided, high mechanical strength is required.

  The molded product 2 shown in FIG. 2 is an automotive instrument panel core member, and a part such as a defroster blowing part is exposed to the outside in the peripheral part 2a. In addition, since various devices and members such as meters and airbags are attached to the inner non-peripheral portion 2b, high mechanical strength is required.

  FIG. 3 shows the configuration of the molding apparatus used in the first embodiment of the present invention. The molding apparatus 10 includes a molding die 11 composed of a lower fixed mold 12 and an upper movable mold 13, and a movable mold. A mold clamping device 14 formed of, for example, a high-speed hydraulic cylinder that lifts and lowers the mold 13 to perform mold clamping and mold opening, and a first resin that injects a resin melt into a cavity 15 formed with the fixed mold 12 and the movable mold 13. An injection device 16 and a second injection device 17 are included.

  Each of the first and second injection devices 16 and 17 heats and melts the cylinders 16a and 17a, the hoppers 16b and 17b for supplying the resin material into the cylinders 16a and 17a, and the supplied resin material, Screws 16d and 17d for pumping the melt of the resin material toward discharge passages 16c and 17c provided at the ends of the cylinders 16a and 17a.

  The fixed die 12 is connected to the discharge passage 16c of the first injection device 16, and the first injection passage 18 communicates with the central portion of the molding surface 12a constituting the cavity 15 on the upper surface of the fixed die 12. A second injection passage 19 connected to the discharge passage 17c of the second injection device 17 and leading to the peripheral portion of the molding surface 12a is provided.

  Next, the molding method of the resin molded product according to the present embodiment using the molding apparatus 10 will be described. As shown in FIG. 4A, first, the movable mold 13 is moved from the mold clamping position by the mold clamping apparatus 14. The cavity 15 ′ having a volume larger than the volume of the final shape of the molded product is formed by lowering to a position separated from the fixed mold 12 by a predetermined distance X.

  In parallel with this, the hoppers 16b and 17b of the first and second injection devices 16 and 17 are provided with a solid crystalline polymer resin material A and a normal (crystalline or non-crystalline) polymer resin. The material B is charged and the screws 16d and 17d are operated to heat and melt the resin materials A and B to the melting point or higher. The melts A ′ and B ′ are discharged into the discharge passages 16c and 17c and the first The second injection passages 18 and 19 can be injected into the cavity 15 '.

  Next, as a first injection step, as shown in FIG. 4B, the first injection device 16 injects a melt A ′ of crystalline polymer resin material into the cavity 15 ′. At this time, the injection amount of the melt A ′ is set to an amount corresponding to the short shot state.

  At this time, the first injection passage 18 for injecting the melt A ′ into the cavity 15 ′ communicates with the central portion of the molding surface 12 a on the upper surface of the fixed mold 12, and the temperature of the melt A ′ decreases. As a result, the viscosity increases, and therefore, as shown in FIG. 4B, the fluid rises at the center of the molding surface 12a without flowing to the entire area of the cavity 15 ′.

  Next, as a crystallization step, when the temperature of the melt A ′ of the crystalline polymer resin injected into the cavity 15 is cooled to a temperature lower than the melting point and higher than the crystallization temperature, that is, When the melt A ′ is supercooled, the mold clamping device 14 is operated at a high speed to rapidly lower the movable mold 13 to the mold clamping position, as shown in FIG.

  As a result, the melt A ′ is abruptly sandwiched between the molding surfaces 12a and 13a of both molds 12 and 13, and the melt A ′ spreads around the cavity 15 ″ having the same shape as the final shape of the molded product. In this case, the lowering speed of the movable mold 13 is set so that the elongation strain rate due to the flow of the melt A ′ is equal to or higher than the critical speed. Accordingly, the melt A ′ extends at a critical elongation strain rate or higher.

  In this case, since the injection amount of the melt A ′ is an amount corresponding to the short shot state, when the mold is clamped until the cavity shape reaches the final shape, Although the unfilled portion a of the melt A ′ remains, in this way, by not completely filling the cavity 15 ″, the stretch strain rate of the melt A ′ is surely made higher than the critical stretch strain rate. It becomes possible.

  As described above, the melt A ′ of the supercooled crystalline polymer resin is stretched at a speed equal to or higher than the critical elongation strain rate, whereby the crystallization of the melt A ′ is promoted and the cavity 15 ″ A high-strength intermediate molded product C with high crystallinity is formed in the portion excluding the peripheral portion.

  Next, as a second injection step, as shown in FIG. 4D, a normal polymer resin material melt B ′ is injected into the cavity 15 ″ by the second injection device 17. At this time, Since the second injection passage 19 for injecting the melt B ′ into the cavity 15 ″ communicates with the peripheral portion of the molding surface 12a on the upper surface of the fixed mold 12, the melt B ′ is in the peripheral portion of the cavity 15 ″. It is injected into the unfilled portion a of the melt A ′ and supplied around the intermediate molded product C.

  As a result, the entire cavity 15 ″ having the same shape as the final shape of the molded product is filled. After the melts A ′ and B ′ are cured, the movable mold 13 is raised and the mold is opened, as shown in FIG. In addition, a molded product D having a predetermined shape is obtained.

  In that case, since the peripheral part D1 made of the normal polymer resin material B has a relatively slow flow rate of the melt B ′, the molded product D is formed by the molding surfaces 12a and 13a constituting the cavity 15 ″. In addition, a high dimensional accuracy and a good surface appearance can be obtained, and the non-peripheral portion D2 corresponding to the intermediate molded product C made of the crystalline polymer resin material A on the inside thereof has a crystallinity as described above. Therefore, high mechanical strength and heat resistance can be obtained, and a molded product suitable for the door module carrier 1 and the instrument panel core member 2 shown in FIGS.

  In the above embodiment, all of the first injection process, the crystallization process, and the second injection process are performed using the single molding apparatus 10, and therefore these processes can be performed continuously. Equipment and work will be simplified.

  In addition, since the resin materials A and B are separately injected by the first and second injection devices 16 and 17, select appropriate ones according to the respective requirements of the non-peripheral part D2 and the peripheral part D1. However, if a homogeneous resin material having the same main skeleton is used, good compatibility is obtained at the boundary surface D3 between the peripheral portion D1 and the non-peripheral portion D2 of the molded product D, and both portions D1, D2 are obtained. Can be obtained.

  Next, a second embodiment of the present invention will be described. In the following description, the same reference numerals are used for the same components as those in the first embodiment.

  FIG. 6 shows a configuration of a molding apparatus 20 used in this embodiment. This molding apparatus 20 is similar to the molding apparatus 10 according to the first embodiment, and includes a lower fixed mold 22 and an upper movable body. The mold 21 includes a mold 21 and a mold clamping device 24 including a high-speed hydraulic cylinder that lifts and lowers the movable mold 23 to perform mold clamping and mold opening. The molding apparatus 20 includes the fixed mold 22. And a single injection device 26 for injecting the resin melt into the cavity 25 formed by the movable mold 23.

  The injection device 26 includes a cylinder 26a, a hopper 26b that supplies a resin material into the cylinder 26a, and heats and melts the supplied resin material, and discharges a melt of the resin material provided at the tip of the cylinder 26a. And a screw 26d that pumps toward the passage 26c.

  The fixed mold 22 is provided with an injection passage 27 having an upstream end connected to the discharge passage 26c of the injection device 26 and branched into a first branch passage 27a and a second branch passage 27b. The downstream end of the first branch passage 27a opens at the center of the molding surface 22a constituting the cavity 25 on the upper surface of the fixed mold 22, and the second branch passage 27b opens at the periphery of the molding surface 22a. .

  The first and second on-off valves 28a and 28b for opening and closing the passages 27a and 27b are respectively provided immediately before the openings to the molding surface 22a of the first and second branch passages 27a and 27b. Is provided.

  Next, the molding method of the resin molded product according to the present embodiment using the molding apparatus 20 will be described. First, as shown in FIG. 7A, the movable mold 23 is moved from the mold clamping position by the mold clamping device 24. The cavity is lowered to a position separated from the fixed mold 22 by a predetermined distance to form a cavity 25 ′ having a volume larger than the final shape volume of the molded product.

  In parallel with this, the solid crystalline polymer resin material A is put into the hopper 26b of the injection device 26, and the screw 26d is operated to heat and melt the resin material A to the melting point or higher. The melt A ′ is supplied up to the position immediately before the first and second on-off valves 28a and 28b in the first and second branch passages 27a and 27b of the discharge passage 26c and the injection passage 27, and these on-off valves 28a and 28b. Is opened, the melt A ′ can be injected into the cavity 25 ′ from the branch passage where the valve is opened.

  Next, as the first injection step, as shown in FIG. 5B, the first on-off valve 28a is opened to open the first branch passage 27a of the injection passage 27 and the injection device 26 is operated. Then, the melt A ′ of the crystalline polymer resin material is injected into the cavity 25 ′ by an amount corresponding to the short shot state, and then the first on-off valve 28a is closed.

  At this time, since the first branch passage 27a communicates with the central portion of the molding surface 22a on the upper surface of the fixed mold 22, the melt A ′ is spread throughout the cavity 25 ′ as in the first embodiment. It does not flow and rises to the center of the molding surface 22a.

  Next, as a crystallization step, when the temperature of the melt A ′ injected into the cavity 25 ′ is cooled to a temperature lower than the melting point and higher than the crystallization temperature, FIG. As shown, the mold clamping device 24 is operated at a high speed to rapidly lower the movable mold 23 to the mold clamping position.

  As a result, the melt A ′ is abruptly sandwiched between the molding surfaces 22a and 23a of both molds 22 and 23, and spreads in the peripheral part of the cavity 25 ″ having the same shape as the final shape of the molded product. However, the lowering speed of the movable mold 23 is set so that the elongation strain rate due to the flow of the melt A ′ is higher than the critical speed. Liquid A ′ extends at a critical elongation strain rate or higher.

  In this case, since the injection amount of the melt A ′ is set to an amount corresponding to the short shot state, an unfilled portion a of the resin melt remains in the peripheral portion in the cavity 25 ″. By not completely filling the cavity 25 ″, the tensile strain rate of the melt A ′ can be surely made higher than the critical tensile strain rate.

  As described above, the melt A ′ of the supercooled crystalline polymer resin is stretched at a speed equal to or higher than the critical elongation strain rate, whereby the crystallization of the melt A ′ is promoted and the cavity 25 ″ Inside, a high-strength intermediate molded product C having a high degree of crystallinity is formed.

  Next, as the second injection step, as shown in FIG. 4D, the second on-off valve 28b is opened to shut off the first branch passage 27a of the injection passage 27 and open the second branch passage 27b. In this state, the injection device 26 is operated, and the melt A ′ of the crystalline polymer resin material is injected again into the cavity 25 ″. At this time, the opened second branch passage 28b is formed in the fixed die 22. The melt A ′ is injected into the unfilled portion a of the melt A ′ in the peripheral portion of the cavity 25 ″ and supplied to the periphery of the intermediate molded product C because it communicates with the peripheral portion of the upper molding surface 22a. Will be.

  As a result, the entire cavity 25 ″ having the same shape as the final shape of the molded product is filled, and after the melt A ′ is solidified, the movable mold 23 is raised and the mold is opened to open the first embodiment shown in FIG. Like the molded product D, the peripheral part has high dimensional accuracy and a good surface appearance, and the non-peripheral part corresponding to the intermediate molded product C inside has high crystallinity and high mechanical strength. A molded article having

  In this case, in this embodiment, since the single injection device 26 is used, the peripheral portion and the non-peripheral portion of the molded product are always formed of the same resin material. Good compatibility at the interface with the part is obtained, and a molded product in which both parts are firmly bonded and integrated is obtained.

  In this embodiment as well, since each process is performed continuously using a single molding apparatus 20, facilities and work are simplified. In the first and second embodiments, intermediate molding is performed. The first injection process and the crystallization process until the product C is formed and the second injection process may be performed using different molding apparatuses.

  Next, examples implemented by the method according to the first embodiment will be described.

  In this example, a product made by Nippon Steel Works, a mold having a clamping force of 220 tons and equipped with two injection devices is used as a crystalline polymer resin material. (Trade name: Novatec) was used.

  Then, the melting temperature of the resin material in the injection device is set to 180 ° C., the mold temperature is set to 150 ° C., and first, the movable mold is opened to the position where the opening amount (dimension X in FIG. 4A) is 25 mm. The cavity was lowered to form a cavity having a volume larger than that of the final shape of the molded product between both molds.

Next, as a first injection step, the crystalline polymer resin material melt is injected at a relatively slow rate of 134 cm ^{3 with} a first injection device, and then the temperature of the melt decreases to 160 ° C. It waited for about 10 seconds until it did. This temperature was lower than the melting point of the resin and higher than the crystallization temperature, whereby the melt became supercooled.

  Next, as a crystallization process, the movable mold of the mold is clamped at the maximum speed (1000 mm / sec), leaving an unfilled portion of the melt at the periphery of the cavity to form an intermediate molded product with a plate thickness of 3 mm. did.

  Thereafter, as a second injection step, a melt of the same resin as the crystalline polymer resin is injected into an unfilled portion around the cavity at a temperature of 200 ° C. and an injection speed of 200 mm / second by a second injection device. did. Then, after cooling the mold to 80 ° C., the mold was opened and the molded product was taken out.

  As a result, crystallization is promoted, and a molded product in which a non-peripheral portion having high mechanical strength and heat resistance and a peripheral portion having the same dimensional accuracy as that of normal injection molding around the periphery is obtained. It was.

  As described above, according to the method for molding a resin molded product according to the present invention, a high strength portion with high crystallization rate and high mechanical strength and durability and a portion with high dimensional accuracy around it are integrated. Therefore, there is a possibility that it is suitably used in the technical field of manufacturing, for example, automobile parts, in which mechanical strength and dimensional accuracy are required for each part.

1, 2, D Molded product 1a, 2a, D1 Peripheral part 1b, 2b, D2 Non-peripheral part 10, 20 Molding device 11, 21 Molding tool 14, 24 Clamping device 16, 17, 26 Injection device

Claims (5)

A first injection step of injecting a melt of a crystalline polymer resin in a short shot state into a molding die set in a state where the movable die is separated from the fixed die from the clamping position;
The movable mold is clamped at a high speed so that the melt expands at a strain rate equal to or higher than the critical elongation strain rate when the temperature of the melt is equal to or lower than the melting point and the crystallization temperature. A crystallization step of crystallizing while maintaining an orientation state and maintaining the state;
In the molding die or another molding die, a second resin melt is injected around the intermediate molded product molded in the crystallization step to mold the peripheral portion of the intermediate molded product into a final shape. A molding method of a resin molded product comprising an injection step.   The method for molding a resin molded product according to claim 1, wherein the first injection step, the crystallization step, and the second injection step are performed in the same mold.   The method for molding a resin molded product according to claim 1, wherein the crystalline polymer resin and the additional resin are the same resin.   The method for molding a resin molded product according to any one of claims 1 to 3, wherein the crystalline polymer resin is a general-purpose plastic.   The method for molding a resin molded product according to claim 4, wherein the general-purpose plastic is polypropylene.

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