JP2007137008A - Manufacturing process of resin molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing process of a resin molding which prevents sink marks from occurring and the molding cycle time from getting longer to some extent, when resin molding partially having thick portions is manufactured. <P>SOLUTION: The manufacturing process relates to a resin molding 8 partially having a thick portion 85. It comprises a mold heating step in which the temperature of the mold 1 having a cavity 15 corresponding to the shape of the resin molding 8 is kept lower than the injection temperature of the resin filled into the cavity 15 and the mold is heated at least to ≥50°C, a pressurizing step in which the designed surface 81 of the filled resin is pressed against the cavity surface 151 by introducing pressured gas into the cavity 15 from the back side of the filled resin, immediately after the resin is injected into and filled the cavity 15, a mold cooling step in which the temperature of the mold 1 is cooled to a temperature allowing the mold to be opened while maintaining the pressurized state by the pressured gas and a depressurizing step in which the pressurized state by the pressured gas is released, after the mold cooling step is completed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a manufacturing method capable of preventing the occurrence of sink marks when a resin molded product having a partially thick part is manufactured by injection molding.

When a resin molded product that partially has a thick portion such as ribs, bosses, and uneven thickness portions protruding from the back surface opposite to the design surface is manufactured by injection molding, the design surface where the thick portion is present In some cases, so-called sink marks may occur due to shrinkage accompanying cooling during production.
Therefore, conventionally, in order to prevent deterioration in the appearance quality of the design surface due to the occurrence of the above-described sink marks, the thick wall portion is set at a position separated from the back side surface of the design surface, and an expensive and complicated incorporating a movable type or the like. Measures such as molding using a mold have been implemented.

  On the other hand, as a method for preventing sink marks in the case of having a thick portion partly, a pressurized gas is injected between the back side surface of the filling resin injected and filled into the mold cavity and the cavity surface of the mold, and the filling resin A molding method has been proposed in which the design surface is pressed against the cavity surface of a mold (Patent Document 1). In this method, an effect of preventing sink marks can be obtained to some extent by taking a long time for pressing against the mold, but a sufficient effect may not always be obtained.

  In addition, a heat insulating material is arranged on the cavity surface on the design surface side, and when the filled resin is pressed in the direction of the cavity surface on the design surface side by the pressurized gas, the fluidity of the resin on the design surface side is maintained, and mold reproducibility is maintained. A method for improving it has also been proposed (Patent Document 2). However, according to this method, there is a problem that due to the presence of the heat insulating material, it takes a long time to cool the mold to a temperature at which the product can be taken out, and the molding cycle becomes long.

JP 50-75247 A Japanese Patent No. 3226369

  The present invention has been made in view of such conventional problems, and is capable of preventing the occurrence of sink marks and producing a long molding cycle when a resin molded product having a partially thick portion is produced. It is an object of the present invention to provide a method for producing a resin molded product that can suppress the occurrence of the problem to some extent.

The present invention, in a method for producing a resin molded product partially having a thick portion protruding from the back surface opposite to the design surface,
Mold heating treatment for heating so that the temperature of the mold having a cavity corresponding to the shape of the resin molded product is lower than the injection temperature of the resin filling the cavity and rises to a heating temperature of at least 50 ° C. When,
Immediately after injecting and filling the resin into the cavity, by introducing a pressurized gas into the cavity from the back side of the filled resin, a pressure treatment for pressing the design surface of the filled resin against the cavity surface;
A mold cooling process for reducing the temperature of the mold to a mold opening possible temperature while maintaining the pressurized state by the pressurized gas;
A method for producing a resin molded product is characterized in that after completion of the mold cooling process, a decompression process for releasing the pressurized state by the pressurized gas is performed.

  In the present invention, the mold heat treatment is performed before the resin is injected and filled into the mold. In this mold heat treatment, the mold temperature is raised to a heating temperature of at least 50 ° C. or higher and lower than the resin injection temperature. Then, the resin is filled in the cavity of this high-temperature mold, and the above heat treatment is performed. Thereby, compared with the case where the said pressurization process is performed without performing the said heat processing which raises metal mold | die temperature, a sink mark prevention effect can be improved significantly.

  That is, the mold temperature is raised to the heating temperature in advance by the mold heat treatment. As a result, the fluidity of the resin injected and filled in the cavity is suppressed from being lowered by rapid cooling due to contact with the mold. And by the said pressurization process, filling resin is pressurized immediately after filling, and the design surface is pressed against a cavity surface. Therefore, by starting the pressurizing process, the design surface is in a very excellent state where the cavity surface is transferred. The pressurizing process starts immediately after the resin filling, but immediately after this, it is sufficient if the timing is as early as possible after the filling is completed within the range of the normal equipment capacity.

  Next, the occurrence of sink marks is accompanied by contraction during cooling and solidification, but in the present invention, the temperature of the mold is lowered to the temperature at which the mold can be opened while maintaining the pressurized state by the pressurized gas. A mold cooling process is performed. That is, the pressurized state by the pressurized gas is maintained during cooling. Thereby, even if shrinkage occurs during cooling and solidification, the filling resin is always pressed to the design surface side by the pressurized gas, so that the occurrence of sink marks can be prevented.

  Further, in the present invention, since the mold itself is actively heated as described above and then injection filling is performed, it is not necessary to incorporate a heat insulating material as in the prior art. Therefore, the mold cooling process can be performed faster as much as there is no such thing as a cooling material that hinders cooling. Further, the mold cooling treatment may be natural cooling, but in order to further shorten the cycle time, it is preferable to actively cool as described later. In particular, in the present invention, the state of the desired design surface is created immediately after the pressure treatment, and cooling is performed while maintaining the state with the pressurized gas. Therefore, even if the cooling time is as early as possible, the quality is affected. There is no.

  As described above, according to the method of the present invention, when a resin molded product having a partially thick part is produced, the occurrence of sink marks can be prevented, and the molding cycle can be suppressed to some extent. The manufacturing method of the resin molded product which can be performed can be provided.

In the mold heat treatment of the present invention, as described above, the mold temperature is raised to a heating temperature that is at least 50 ° C. or higher and lower than the resin injection temperature. The specific preferable heating temperature depends on the type of resin to be injected and filled, the shape of the molded product, the shape of the thick portion, etc., but is at least 50 ° C. or higher. When the temperature is lower than 50 ° C., the effect of performing the mold heat treatment may not be sufficiently obtained. The heating temperature is lower than the resin injection temperature. Thereby, the subsequent mold cooling process can be performed more efficiently.
Generally, the injection temperature of the resin is in the range of 150 ° C to 300 ° C. And the preferable range of the said heating temperature is 50-120 degreeC, and it is the most preferable to obtain | require experimentally and determine the temperature which can suppress sink | sink generation | occurrence | production every time the shape etc. of a molded article differ in this range. .

  Moreover, it is preferable that the said mold cooling process actively cools the said mold so that it may become a cooling rate more than natural cooling (Claim 2). As described above, in the manufacturing method of the present invention, there is almost no quality restriction in increasing the cooling rate in the mold cooling process. Therefore, by actively increasing the cooling rate, the processing cycle can be accelerated, and the efficiency can be improved.

Moreover, it is preferable to perform the said mold heating process and the said mold cooling process by introduce | transducing a high-temperature or low-temperature heat medium into the heat-medium circulation path previously provided in the said metal mold | die (Claim 3). Thereby, positive heating and positive cooling can be performed with a relatively simple device. In addition, as a high-temperature heat medium for heating, for example, warm water, steam, or the like can be used. Moreover, water etc. can be used as a low-temperature heat medium for cooling.
The mold heat treatment can take another method such as a method including a heater, and the mold cooling treatment can take another method such as a method including a refrigerator. Is also possible.

  Moreover, it is preferable that the pressure of the said pressurized gas introduce | transduced into the said cavity in the said pressurization process is 1-30 Mpa. If the pressure of the pressurized gas is less than 1 MPa, the effect of pressing the design surface of the filled resin against the cavity surface may not be sufficiently obtained. On the other hand, when the pressure of the pressurized gas exceeds 30 MPa, there is a possibility that the sealing performance of the mold sliding portion (extruded pin or the like) is deteriorated and the pressurized gas leaks when it is repeatedly molded. is there.

  As the pressurized gas, various gases can be applied as long as they do not react with the filling resin. For example, nitrogen and air are preferable because they are easily available.

  Moreover, it is preferable to perform the said pressurization process by introduce | transducing the said pressurized gas with respect to the surface between the thick part which protruded from the back surface of the said filling resin, and a thick part (Claim 5). In this case, since the presence of the thick portion serves as a weir that suppresses leakage of the introduced pressurized gas, the pressurization can be performed very efficiently.

Example 1
A method for producing a resin molded product according to an embodiment of the present invention will be described with reference to FIGS.
As shown in FIGS. 8 and 9, this example is a method for manufacturing a resin molded product 8 partially having a thick portion 85 protruding on the back surface 82 opposite to the design surface 81. The resin molded product 8 is specifically an automobile grill radiator, and its design surface 81 is required to have a high-quality appearance without sink marks. Conventionally, a rib as the thick portion 85 is used. It has been performed at a position separated from the back surface 82 which is the surface opposite to the design surface 81. As shown in FIG. 9, the resin molded product 8 of this example is provided with a rib as the thick portion 85 directly on the back side of the design surface 81. The thickness T1 of the general portion 88 (the portion without the thick portion) of the resin molded product 8 is 2.7 mm, the protruding height (the amount of the thick portion) L of the thick portion 85 is 20 mm, and the thickness of the thick portion 85. T2 is 2.0 mm. In the figure, this is added to clarify the positional relationship between a mold 1 and a gas introduction path 155, which will be described later, at the time of manufacture.
In manufacturing the resin molded product 8, a mold heating process, a pressurizing process, a mold cooling process, and a depressurizing process are sequentially performed using the mold 1 having the configuration shown in FIG. 1.
This will be described in detail below.

  As shown in FIG. 1, the mold 1 used in this example is configured so that a cavity 15 corresponding to the shape of a resin molded product is formed by a fixed mold 11 and a movable mold 12. A cavity surface 151 corresponding to the design surface is provided on the fixed mold 11 side, and a cavity surface 152 corresponding to the back surface is provided on the movable mold 12 side.

The cavity surface 152 of the movable mold 12 is provided with a gas introduction path 155 for introducing a pressurized gas in a pressurizing process described later. The gas introduction path 155 is connected to an external high-pressure gas supply device 4 and is configured to appropriately introduce nitrogen as a high-pressure gas. Further, as shown in FIGS. 2 and 3, the gas introduction path 155 of the present example has a pin 156 disposed inside the hole, and a clearance between the inner surface of the gas introduction path 155 and the outer surface of the pin 156 is provided. The pressurized gas is configured to be introduced therethrough. Thereby, it is possible to introduce the pressurized gas while preventing the back flow of the resin.
Moreover, the said gas introduction path 155 is arrange | positioned so that it may introduce | transduce into the surface between the thick part 85 and the thick part 85, as shown in FIGS.

Heat medium circulation paths 21 and 22 are provided inside the fixed mold 11 and the movable mold 12. These heat medium circulation paths 21 and 22 are supplied to the supply pipe 31 and the recovery pipe 32 of the heat medium supply device 3 that supplies hot water as a high-temperature heat medium and cold water as a low-temperature heat medium. Connected in parallel.
As shown in the figure, the heat medium supply device 3 includes a hot water supply device 35, a cold water supply device 36, and a hot water / cold water switching valve 37 that is connected to both and switches the supply target.

  Next, when the resin molded product 8 is manufactured, first, as shown in FIG. 2, a mold heat treatment is performed in a mold-clamped state. In this example, the temperature of the mold 1 is raised to a heating temperature of 60 ° C. This heating was performed by circulating 120 ° C. hot water through the heat medium circulation paths 21 and 22 of the mold 1 using the heat medium supply device 3 (FIG. 1). This heating temperature is lower than the injection temperature 240 ° C. of the resin (material ABS) of this example.

  Next, as shown in FIGS. 4 and 5, immediately after the resin 80 is injected and filled into the cavity 15 from the injection nozzle 19, the pressurized gas 7 having a pressure of 10 MPa is applied from the back side of the filled resin 80 as shown in FIG. 4. By introducing into the cavity 15, pressure treatment is performed to press the design surface of the filling resin 80 against the cavity surface 151 that is the inner surface of the cavity 15. At this time, in this example, since the pressurized gas 7 is introduced between the thick portion 85 and the thick portion 85, the thick portions 85 themselves on both sides exhibit a role like a weir, and the pressurized gas 7 Can be suppressed, and pressurization can be performed efficiently.

  Next, a mold cooling process is performed in which the temperature of the mold 1 is lowered to a mold opening temperature (50 ° C.) while maintaining the pressurized state with the pressurized gas 7. This cooling was performed by circulating 10 ° C. cold water through the heat medium circulation paths 21 and 22 of the mold 1 using the heat medium supply device 3.

Then, when the mold temperature reaches 50 ° C., a decompression process is performed to release the pressurized state by the pressurized gas 7 and decompress the cavity 15. Thereafter, as shown in FIG. 6, the fixed mold 11 of the mold 1 was moved to open the mold, and the resin molded product 8 was taken out.
As shown in FIG. 7, the obtained resin molded product 8 did not have any sink marks on the design surface 81 corresponding to the position of the thick portion 85, and the appearance quality was very excellent.

(Example 2)
In this example, in order to further quantitatively evaluate the effects of the present invention, a plurality of resin molded products having different dimensions and shapes were actually manufactured and evaluated under different conditions.
As shown in Table 1, the sample (resin molded product) produced in this example has a constant thickness (T1) of the general portion (the portion having no thick portion on the back side of the design surface) of 2.7 mm, A rib with a height (L) of 20 mm was adopted as the part, and the thickness (T2) of the rib was changed from 1.5 mm to 3.0 mm at a pitch of 0.5 mm. And 4 types of manufacturing conditions (other conditions are the same as Example 1) which changed the heating temperature in a metal mold | die heat processing in the range of 50 to 80 degreeC with a 10 degreeC pitch were applied to said 4 types of samples. The resin material was ABS.

The evaluation was performed by measuring the depth of occurrence of sink marks (μm) on the design surface at the position where the thick part (rib) is present in the obtained resin molded product. The measurement results are shown in Table 1 and FIG.
In the figure, the horizontal axis represents the rib thickness (mm), the vertical axis represents the amount of sink (μm), and the plotted data is connected by a line for each heating temperature in the mold heat treatment.

  As can be seen from Table 1 and FIG. 10, when the thickness of the general part is 2.7 mm as in this example, a heating temperature of 50 ° C. or higher should be used when the rib thickness is 1.5 mm. For example, the amount of sink marks is 2.0 μm or less, and it can be seen that a very good appearance quality can be obtained. Similarly, a heating temperature of 60 ° C. or higher is employed when the rib thickness is 2.0 mm, 70 ° C. or higher when the rib thickness is 2.5 mm, and 80 ° C. or higher when the rib thickness is 3.0 mm. Thus, it can be seen that the amount of sink marks is 2.0 μm or less, and a very excellent appearance quality can be obtained.

(Example 3)
Also in this example, in order to further quantitatively evaluate the effects of the present invention, a plurality of resin molded products having different dimensions and shapes were actually manufactured and evaluated under different conditions.
As shown in Table 2, the sample (resin molded product) prepared in this example has a constant thickness of 2.7 mm (T1) in the general part (the part having no thick part on the back side of the design surface). A boss having a height (L) of 20 mm was adopted as the part, and the thickness (T2) of the boss was changed to four types in a range from 1.9 mm to 4.8 mm. And 4 types of manufacturing conditions (other conditions are the same as Example 1) which changed the heating temperature in a metal mold | die heat processing in the range of 50 to 80 degreeC with a 10 degreeC pitch were applied to said 4 types of samples. The resin material was ABS.

The evaluation was performed by measuring the depth of occurrence of sink marks (μm) on the design surface at the position where the thick-walled portion (boss) of the obtained resin molded product was present. The measurement results are shown in Table 2 and FIG.
In the figure, the horizontal axis indicates the thickness (mm) of the boss, the vertical axis indicates the amount of sink (μm), and the plotted data is connected by a line for each heating temperature in the mold heat treatment.

  As can be seen from Table 2 and FIG. 11, when the thickness of the general part is 2.7 mm as in this example, the heating is 70 ° C. or more when the thickness of the boss is 1.9 mm to 2.6 mm. It can be seen that if the temperature is adopted, the amount of sink marks is 2.0 μm or less, and a very excellent appearance quality can be obtained. Similarly, when the rib wall thickness is 3.0 mm, the use of a heating temperature of 80 [deg.] C. or higher can reduce the sink amount to 2.0 [mu] m or less, and a very excellent appearance quality can be obtained. .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram illustrating an overall configuration of a mold according to a first embodiment. Explanatory drawing which shows the state in which the metal mold | die heat processing is performed in the state which clamped the metal mold | die in Example 1. FIG. FIG. 3 is an explanatory diagram showing details of a pressurized gas introduction path of a mold in the first embodiment. Explanatory drawing which shows the state which implemented the pressurization process immediately after injecting and filling resin in the metal mold | die in Example 1. FIG. Explanatory drawing which shows the state in which filling resin is pressed by the pressurization process in Example 1. FIG. Explanatory drawing which shows the state which opened the metal mold | die in Example 1. FIG. FIG. 3 is a partially cutaway cross-sectional view showing a resin molded product that has been molded in Example 1. Explanatory drawing which looked at the resin molded product in Example 1 from the design surface. Sectional drawing of the thick part vicinity of the resin molded product in Example 1 (AA arrow directional cross-sectional view of FIG. 8). Explanatory drawing which shows the relationship between the mold temperature in the metal mold | die heat processing in Example 2, and rib thickness and the amount of sink marks. Explanatory drawing which shows the relationship between the mold temperature in metal mold | die heat processing, the boss | hub thickness, and the amount of sink marks in Example 3. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Mold 15 Cavity 151,152 Cavity surface 21,22 Heat medium circulation path 3 Heat medium supply apparatus 4 High pressure gas supply apparatus 7 Pressurized gas 8 Resin molding 81 Design surface 85 Thick part

Claims (5)

In the manufacturing method of the resin molded product partially having a thick part protruding from the back surface opposite to the design surface,
Mold heating treatment for heating so that the temperature of the mold having a cavity corresponding to the shape of the resin molded product is lower than the injection temperature of the resin filling the cavity and rises to a heating temperature of at least 50 ° C. When,
Immediately after injecting and filling the resin into the cavity, by introducing a pressurized gas into the cavity from the back side of the filled resin, a pressure treatment for pressing the design surface of the filled resin against the cavity surface;
A mold cooling process for reducing the temperature of the mold to a mold opening possible temperature while maintaining the pressurized state by the pressurized gas;
A method for producing a resin molded product, comprising: performing a decompression process for releasing a pressurized state by the pressurized gas after the completion of the mold cooling process.   2. The method for producing a resin molded product according to claim 1, wherein the mold cooling treatment actively cools the mold so as to have a cooling rate higher than that of natural cooling.   3. The resin according to claim 1, wherein the mold heating treatment and the mold cooling treatment are performed by introducing a high-temperature or low-temperature heat medium into a heat medium circulation path provided in advance in the mold. Manufacturing method of molded products.   The method for producing a resin molded article according to any one of claims 1 to 3, wherein the pressure of the pressurized gas introduced into the cavity in the pressure treatment is 1 to 30 MPa.   5. The pressure treatment according to claim 1, wherein the pressurizing process is performed by introducing the pressurized gas into a surface between the thick portion protruding from the back surface of the filling resin and the thick portion. A method for producing a resin molded product.

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