JP3478392B2 - Injection molding method for plastic products - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for injection-molding a plastic product, and more particularly to a method for reliably leaving a molded product on a target mold side when a mold is opened. The present invention relates to a plastic product injection molding method. 2. Description of the Related Art Generally, as shown in FIG. 1, a mold for injection molding is equipped with an ejector pin 4 (release device) on a movable mold 3. The ejector pin 4 fills the mold cavity with the molten resin from the sprue 2c and the gate 2d of the fixed mold 2 and, after the resin is solidified, pushes out the molded article 1 from the movable mold 3 when the mold is opened. To release the mold. Since a pin mark remains on the surface of a product manufactured using a mold equipped with the ejector pins 4, it is generally arranged on the non-visible side of the product. However, the ejector pin 4 may not be arranged at a desired portion depending on the use of the product or its shape. In such a case, similar to the present invention,
There has been proposed a method of using a gas and releasing a product with the pressure of the gas. For example, in the invention described in JP-A-64-87217, a mold having air permeability is used,
A method has been proposed in which a resin is filled in a mold cavity and then, when the mold is opened, a gas is injected through a mold, a molded product is extruded by this gas pressure, and the mold is released. Further, in the invention described in Japanese Patent Application Laid-Open No. HEI 8-118392, in the hollow molding of a deep-bottom molded product, the gas nozzle is advanced and retracted so that the high-pressure gas injected into the molded product and the cavity surface are removed. A method has been proposed in which the molded product is discharged to the boundary between the mold and the mold. [0005] Further, in the case of plastic products represented by the intake hold of automobile parts, the plastic invisible surface side is required from the viewpoint of mold structure problems and surface accuracy of the invisible surface side required for the product. In many cases, ejector pins cannot be installed. [0006] In the case of the above-described mold release method using gas, after filling the molten resin into the mold cavity, the resin is completely solidified and contracted, and then the gas is injected. In order to continuously inject a fluid such as a high-pressure gas, the gas is preferentially injected into a portion having the lowest internal cavity pressure. For this reason, in a product having a complicated shape, there is a problem that the mold is forcibly released by injecting a gas, and the released product has defects such as cracks, deformation, and whitening. On the other hand, in the method of forming an intake manifold or the like, as shown in FIG. 1A, the ejector pins 4 cannot be installed on the surface of the molded product 1 on which the ribs a are formed. 1B, as shown in FIG. 1B, it adheres to the side on which the rib a having a large release resistance, in which the ejector pin 4 is not incorporated, is formed, that is, to the fixed mold 2. Therefore, in order to reliably release the molded product 1 from the mold, a special mechanism using equipment such as a hydraulic unit and an air unit is required for the fixed mold 2, and the structure of the mold is complicated and high cost. There is a problem. In the in-mold welding method such as DSI molding, the release direction of each molded product to be welded is determined. The release direction of the molded product is important, but the shape of the molded product is complicated. Then, there arises a problem that each molded product is not released from the mold as desired. Also, Japanese Patent Application Laid-Open No.
Japanese Patent No. 9077 discloses a molding method in which a molded product is pressed against the cavity surface by gas pressure in a cavity to prevent sink marks. However, this method is intended to prevent sink marks and reduces mold release resistance. Is not the purpose. Furthermore, the method of injecting the molten resin and the mold cavity immediately after filling the molten resin into the mold is similar to the present invention,
The pressure of the gas to be injected differs from the present invention in that it is constant and continuous. An object of the present invention is to provide a method for injection-molding a plastic product which is capable of reliably leaving a molded product on a target mold side and free from problems such as cracking, deformation, whitening, etc. which occur during mold release. It is to provide an injection molding method. [0010] In order to achieve the above object, according to the first aspect of the present invention, in a method of injection molding a plastic product, when a mold is opened, a molded product is released. the gas inlet is formed in the cavity surface of the mold-side desired to be, by injecting resin filling completion later pressurized gas from the gas inlet to the skin layers of the cavity surface and the resin between the skin layer and the cavity face A mold release resistance reducing space is formed in a part of the mold, whereby the molded article is released from the mold in which the gas inlet is formed when the mold is opened, and the molded article is left on the intended mold side. Oite the injection molding method of plastic products, when injecting the pressurized gas, to generate tremors in the skin layer by intermittently injecting a pressurized gas, thereby forming the mold release resistance reduction space Features Is what you do. [00 11] According to the injection molding method in the present invention, after completion of the filling of the resin into the cavity via the gas inlet for injecting pressurized gas into the cavity surface and the skin layers.
At this time, when the pressure of the gas to be injected is varied, a release phenomenon occurs at a portion of the skin layer where the gas pressure acts higher than the resin pressure. At this time, since the gas pressure fluctuates, a slight movement (wave) phenomenon occurs in the skin layer, and the release is locally promoted. In the portion of the skin layer where the micromotion phenomenon occurs, the gas layer remains as it is even in the cooling step, and becomes an area where the release resistance is zero. As a result,
The mold release resistance is more reduced on the mold side where the gas is injected than on the mold side where no gas is injected, so that upon opening the mold, the molded product is left on the mold side that does not have a gas injection port. be able to. Injection timing of gas, or after the complete filling of the resin into the cavity, the timing, the type of the resin is determined by the shape of the molded article. [00 12] [Embodiment 1] FIG. 2 (A) (B) will be described in comparison with FIG. 1 the basic principle of the present invention has been described conventional methods for (A) (B). The difference is that the gas injection system 5 is formed in the fixed mold 2, and the gas injection port 5 a formed at the tip of the gas injection system 5 is connected to the molding portion 2 a of the molded product rib a in the fixed mold 2. This is the point formed on the base 2b. After clamping using this mold, sprue 2c, gate 2d
Fill the cavity with resin. This filling is complete
After that, the inert gas is continuously supplied to the gas injection path 5 → the gas injection port 5a → the inside of the cavity, or the gas pressure is varied between high and low, or the gas is injected intermittently. However, the gas injection pressure at this time must be a pressure that does not break through the skin layer. This is because when the injected gas breaks through the skin layer and a hollow is formed inside the molded product, the resin pressure inside the molded product increases, and as a result, the release resistance of each part of the molded product increases, and the mold release increases. This is because it is disadvantageous. For this purpose, the gas pressure may be initially low and controlled higher as the skin layer grows. Gas is made to be injected into the filling completion After the completion of the resin, the timing to stop is that when the gas layer formed between the skin layer and the cavity surface is no longer lost. [00 13] When injecting gas into this way the cavity, the gas enters the skin layers of the molded article cavity surface, it will form a gas layer (release space) 6 at the base of the rib a. As a result, when opening the mold,
In the portion of the gas layer 6, the mold release resistance is zero between the cavity surface and the formed product surface. By subtracting this, the mold release resistance as a whole is reduced to the other mold incorporating the mold release device. , And the molded product remains on the cavity surface on the side where the mold release device is incorporated. Therefore, the position of the gas inlet 5a,
The numbers and the like are calculated in the design stage of the mold so that the mold release resistance is surely smaller than the cavity surface of the mold incorporating the mold release device, and the mold is manufactured based on this. [00 14] injection pressure of gas, and it does not break per skin layer is a condition that holds the gas layer to the opening of the mold, in as long as this is satisfied, it is continuously injected Alternatively, the injection may be intermittent. The gas is required to be gradually increased so as to have a relationship with the filling pressure of the resin. However, if the gas layer can be held, a constant pressure may be used. It is necessary to provide the gas injection port 5a at a location where the mold release resistance is large, but it is not necessary to provide the gas layer on the cavity surface and the entire surface of the molded product. [00 15] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. First, the injection mold 2 shown in FIG.
0 and the gas injection device 7 manufactured in-house will be described. The configuration of the injection mold 20 includes a fixed mold 2, a movable mold 3,
Ejector pin 4, gas injection system 5, gas injection port 5
The injection port 5a in the cavity of the gas injection system path 5 is provided at the base 2b of the molded portion 2a of the rib a having high release resistance. 30 is a fixed mold 2 and a movable mold 3
It is a plastic molded article molded with a cavity formed when the mold is clamped. On the other hand, the in-house gas injection device 7 includes a high-pressure gas generator 8, a gas pressure regulator 9, a control unit 10, and an electromagnetic switching control valve 11 as main components. [00 16] The injection mold the gas injection device 7 20
, The gas can be injected into the cavity of the injection mold 20. In the present embodiment, a molding machine (manufactured by Nippon Steel Works Co., Ltd .; J2
20E2-P-2M). Impact-resistant polystyrene (Idemitsu Petrochemical Co., Ltd .; HT560) was used as the resin. At this time, the molded plastic article 30 has a length of 195 mm and a width of 150 mm as shown in FIGS.
mm, height 3.5 in the center of the visible surface side 15 with a thickness of 3.5 mm
Rib shape 12 of 0 mm and height 3 mm on the non-visible surface side
It has a rib shape 12 '. [00 17] The injection molding method according to this embodiment will be described with reference to FIG. In addition, since the injection timing of the gas is such that the thickness of the molded product is large, the filling of the molten resin into the cavity is completed, and the injection is performed after the skin layer is formed to some extent. By the configuration of the injection mold 20 and the gas injection device 7 shown in FIG.
0 sec, at a molten resin temperature of 230 ° C, 42 ° C with a temperature controller (Matsui Seisakusho; MC3-60L).
The molten resin was filled in the mold cavity (material S55C, nesting mold) set in the above, and injection molding was performed under a holding pressure of 55 MPa. After 5 seconds from the completion of filling the mold cavity with the molten resin, a nitrogen gas set at 7 MPa is applied for about 10 seconds in a cycle of 0.3 seconds between one side of the molded product and the corresponding cavity surface. The gas was intermittently injected from the injection port 5 a through the gas injection system 5. At this time, the gas injection time is 0.15 seconds, and the injection stop time is 0.15 seconds. As shown in FIG. 4A, a gas layer 6 was formed on the base 2b of the rib a by intermittent gas injection. [00 18] after gas injection, plastic moldings 30,
Since the release resistance of the fixed mold 2 is smaller than that of the movable mold 3 due to the effect of the gas layer 6 due to the gas injection, when the fixed mold 2 and the movable mold 3 are opened, FIG. As shown in B), the plastic molded product 30 was able to be taken out from the movable mold 3 by reliably releasing it from the fixed mold 4. [00 19] The injection-molded by an injection molding method described above 1
When the molded product was taken out of the injection molding die 20, it was confirmed which of the mold fixed side 2 and the movable mold 3 was released. Furthermore, the presence or absence of gas intrusion into the molded product and the presence or absence of defects such as cracks, deformation, and whitening that occurred when the mold was released from the movable side of the mold were confirmed. As a result, the molded product was released from the movable mold 3 with a high probability of 98%. In addition, a good molded product free of mold release failure was obtained on the product visible side 14. [00 20] In the Comparative Example 1 Example 1, except for not performing the injection of the gas was carried out exactly as molded as in Example 1. As a result, the plastic molded product 30 was released to the movable mold 3 with a probability of 10%. Further, as shown in FIG. 6, the releasability of the plastic molded product 30 was poor, so that deformation occurred when the molded product was released, and whitening 17 was observed. In [00 21] [Comparative Example 2] In Example 1, the 20-second injection time of the gas, except that no repeated injection and discharge of gas,
Molding was performed in exactly the same manner as in Example 1. As a result, the plastic molded product 30 was released to the mold movable side with a probability of 10%. Further, as shown in FIGS. 7A and 7B, gas intrusion 16 was observed from the corner of the rib portion 12 into the molded product. Further, whitening 17 due to forced release was confirmed on the product visible side 14. This is because the thickness of the molded product used in the experiment is as thick as 3.5 mm. Therefore, when the gas is continuously injected, the gas breaks through the skin layer and is injected at a stretch, and the inside of the plastic molded product 30 enters from the corner of the rib portion 12. Think to be injected into. For this reason, it is considered that no gas layer was formed between the skin layer and the cavity surface, and whitening occurred in the forcibly released molded article. [00 22] in the Example 2 Example 1, the time of the intermittent cycle performed at the time of injection of the gas 0.1 seconds, 0.5 seconds, except for using 1.0 seconds, Example Molding was performed in exactly the same manner as in No. 1. As a result, the plastic molded product 30 is transferred to the movable mold 3 by 9
The mold was released with a probability of 8%. In addition, plastic molded product 30
The mold was easily released from the mold, and a good molded product having no mold release failure was obtained on the visible side of the product. [00 23] In the Comparative Example 3 Example 1, the time of the intermittent cycle performed at the time of injection of the gas 0.05 seconds, except for using 2.0 seconds, in exactly the same manner as in Example 1 Molding was performed. as a result,
At 0.05 seconds, as in FIGS. 7A and 7B, gas infiltration was observed inside the molded article, and whitening 17 was observed on the visible side 14 of the molded article. This is presumably because the injection gas pressure did not change intermittently because one cycle was extremely short, and the injection gas pressure profile was close to that of Comparative Example 2. On the other hand, also at 2.0 seconds, gas intrusion 16 and whitening 17 were confirmed as in FIG. This is 1
The cycle time depends on the molded product thickness used in the experiment.
I think it was too long. In [00 24] Example 3 In Example 1, the timing of injection of the gas, complete filling of the molten resin, after 0.5 seconds,
The molding was carried out in exactly the same manner as in Example 1 except that the time was 1.0 second, 10 seconds, 15 seconds, and 20 seconds. as a result,
After 0.5 second and 1.0 second, the plastic molded product 30 was released to the movable mold 3 with a probability of 10%. 7A and 7B, gas intrusion 16 was observed in the plastic molded product 30, and whitening 17 due to forced mold release was confirmed on the product visible surface 14. After 5.0 seconds, as in Example 1, the plastic molded product 30 is
98% of the time remains on the mold movable side 3 and the product visible side 14
, A good molded product without mold release failure was obtained. After 15 seconds and 20 seconds, the molded product was released to the movable mold 3 with a probability of 10%. In this case, gas intrusion into the plastic molded product 30 was not confirmed, but the rib 12
Whitening was observed. It is considered that this whitening occurred because the gas was injected after the cooling and solidification of the molten resin was completely completed, so that the plastic molded product 30 was deformed by the gas pressure. In the molded article shapes used in the examples and comparative examples of the present invention, the optimal gas injection timing was 5.0 to 10 seconds after the completion of filling of the molten resin. [00 25] As described in the foregoing, according to the present invention,
After completing the filling of the resin into the mold cavity, until the opening is constant between or mold, the molded article sided pressurized gas between (a release device opposite side) and the cavity surface intermittently The space was formed by injection. As a result, the molded product can be reliably left on the target mold side when the mold is opened. In addition, it is possible to obtain a molded product free from mold release defects such as cracking, deformation, and whitening. Further, by using this release method, there is no need for a special device for forcibly leaving a molded product on the side of the mold where the release device is installed, so that the mold structure is simplified.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view of a conventional injection molding method. FIG. 2 is an explanatory view of a basic principle and operation of the present invention. FIG. 3 is a schematic view of a gas injection device for implementing the present invention. FIG. 4 is an explanatory view of a mold for injection molding. FIG. 4 is an explanatory view of an injection molding method according to Example 1. FIG. 5 is a plan view and a side view of a plastic molded product according to Examples 1, 2, and 3. FIG. 7 is a plan view and a cross-sectional view of a plastic molded product according to Comparative Example 2 of the present experiment. [Description of reference numerals] 1 Plastic molded product 2 Fixed side Mold 3 Movable mold 4 Ejector pin 5 Gas injection system 6 Gas layer 7 Gas injection device 8 High-pressure gas generator 9 Gas pressure regulating valve 10 Control unit 11 Electromagnetic switching control valve 12 Mold rib 14 Mold non-mold Visible surface side 15 Molded product visible surface side ( Gas injection side) 16 Gas intrusion 17 Whitening 18 Mold gate 20 Injection mold 30 Plastic molded a rib

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-66932 (JP, A) JP-A-10-156900 (JP, A) JP-A-11-58463 (JP, A) 162162 (JP, U) Shokai Sho 53-142559 (JP, U) Shoko 46-935 (JP, Y1) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 45/00-45 / 84

Claims (1)

(57) [Claims 1] When the mold is opened, a gas injection port is formed in the cavity surface on the mold side from which the molded product is to be released , and the resin is completely filled. completion later by injecting pressurized gas in the skin layers of the cavity surface and the resin from the gas inlet to form a mold release resistance reduction space portion between the skin layer and the cavity surface,
Thus, at the injection molding method of plastic products, characterized in that by releasing the molded product from the mold to form a gas inlet to the opening of the mold leaving a molded product in a mold side for the purpose <br/> A method of injection molding a plastic product in which the pressurized gas is injected intermittently to cause a fine movement phenomenon in the skin layer, thereby forming a space where the release resistance is reduced.