JP2009233910A - Manufacturing method of molded body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a molded body with preferable appearance by suppressing occurrence of defects like ring marks, gloss unevenness or transfer unevenness of the molded body. <P>SOLUTION: The manufacturing method of the molded body includes: a first mold fastening process of fastening a pair of molds having a cavity face forming a cavity, until the cavity clearance in the mold fastening direction becomes a given position; a supply process of supplying thermoplastic resin into the cavity while opening the molds; and a second mold fastening process fastening the mold before completion of supply of the thermoplastic resin. The supply process includes at least a first supply process having a mold opening speed of the molds of a given speed of V<SB>1</SB>and a second supply process of opening the molds at a speed V<SB>2</SB>lower than that of the first supply process. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a molded body made of a thermoplastic resin.

  A molded body made of a thermoplastic resin is widely used in the fields of automobile interior parts and exterior parts, home appliances, housing-related products and the like because of economy, light weight, and good formability.

It is known that such a thermoplastic resin molded body can be manufactured by a molding method such as injection molding or compression molding. For example, there is a method for manufacturing a molded product by performing mold clamping after opening a mold until a cavity clearance reaches a predetermined value while supplying a molten thermoplastic resin between male and female molds in a closed state. It is known (see Patent Document 1).
JP-A-4-138233

According to the above method, a molded product having a good appearance can be obtained at a low pressure. However, depending on molding conditions, the generation of ring marks formed on the obtained molded product can be suppressed, and uneven gloss and uneven transfer can be generated. There is a need to improve the suppression of this.
In view of the above problems, an object of the present invention is to provide a method for producing a molded article having a good appearance by suppressing the occurrence of defects such as ring marks, gloss unevenness and transfer unevenness of the molded article.

  The present inventors have found that the object of the present invention can be achieved by adopting the following configuration, and have completed the present invention. Specifically, the following are provided.

That is, the present invention provides a first mold clamping step of clamping a pair of molds having a cavity surface forming a cavity until a cavity clearance in a mold clamping direction reaches a predetermined position, and the cavity while opening the mold. A method for producing a molded body, comprising: a supplying step of supplying a thermoplastic resin to the second mold clamping step, and a second clamping step of clamping the mold until the supply of the thermoplastic resin is completed. Comprises at least a first supply step in which the mold opening speed of the mold is set to a predetermined speed, and a second supply step of opening the mold at a speed slower than the first supply process. A method for producing a molded article is provided.
In this specification, “clamping” means that a pair of molds are relatively brought close to each other until a cavity having a predetermined dimension is formed by the cavity surface of each mold, or the dimension of the formed cavity is This means holding the mold so that it does not change. “Opening the mold” means that the pair of molds are relatively separated from each other.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to suppress generation | occurrence | production of defects, such as a ring mark of a molded object, gloss unevenness, and transfer unevenness, and to provide a molded object with a favorable external appearance.

  The manufacturing method of the molded object which concerns on this invention has a 1st mold clamping process, a supply process, and a 2nd mold clamping process. Hereinafter, it demonstrates in detail using figures. In addition, the same code | symbol shows the same member and the description is abbreviate | omitted.

〔Mold〕
First, the metal mold | die used in the manufacturing method of the molded object which concerns on this invention is demonstrated. The shape of the mold is not particularly limited as long as it is a mold used for normal injection molding or press molding.

  FIG. 1 is a view showing a mold preferably used in the present invention. The mold 10 is composed of a male and female pair of a female mold 20 and a male mold 30, and a cavity 40 is formed inside the female mold 20 and the male mold 30 in a closed state.

  The male mold 30 is provided with a plurality of temperature control passages 310 for heating or cooling the cavity surface 31 on the surface opposite to the cavity surface 31 forming the cavity 40. A heat exchange medium supply device (not shown) is connected. The cavity surface 31 is provided with at least one resin supply gate 320 for supplying the molten thermoplastic resin into the cavity 40. The resin supply gate 320 communicates with a resin supply passage 32 formed in the male mold 30. The resin supply passage 32 is connected to an injection nozzle of an injection apparatus 50 that can melt and inject a predetermined amount of thermoplastic resin, thereby supplying the molten thermoplastic resin into the cavity 40. it can.

  Similarly, in the female mold 20, a plurality of temperature control passages 220 for heating or cooling the cavity surface 21 are formed on the surface opposite to the cavity surface 21 forming the cavity 40. Is connected to a heat exchange medium supply device (not shown).

  In the pair of molds 10 including the female mold 20 and the male mold 30 described above, the male mold 30 is fixed to a stationary platen of a press device (not shown), the female die 20 is fixed to a movable platen, and is movable by a driving device. The mold can be clamped by moving the board in the direction of the fixed board. The female mold 20 may be fixed to the stationary platen, and the male mold 30 may be fixed to the movable platen, or both the female mold 20 and the male die 30 can be moved by changing the fixed platen to the movable platen. It may be.

[First mold clamping process]
Subsequently, the manufacturing method of the molded object which concerns on this invention is demonstrated. The first mold clamping process is a process of clamping the mold until the cavity clearance in the mold clamping direction is a predetermined position. Here, the predetermined position in the present invention, as shown in C ₇ of C ₁ or 4 in FIG. 3, or equal to the mold cavity clearance first supplying step to be described later (C ₂ or C _8), There is no particular limitation as long as the clearance is smaller than that.
In FIG. 1, a male die 30 is fixed to a fixed platen of a press device (not shown), the other is fixed to a movable platen, and the movable platen moves toward the fixed platen by a driving device to perform mold clamping. Examples of the drive device include a hydraulic drive device and an electric drive device, and an electric drive device is preferably used. When a hydraulic drive device is used, responsiveness deteriorates due to the effect of oil compression, and the mold clamping speed as set may not be achieved, or the speed may decrease immediately before mold clamping. When the electric drive device is used, the responsiveness is improved, the mold clamping speed can be accurately controlled, and the speed can be easily increased.

[Supply process]
Next, a molten thermoplastic resin is supplied to the cavity while opening the clamped mold. As a method for supplying the thermoplastic resin, a commonly used supply method may be used. For example, as shown in FIG. 2, a molten thermoplastic resin from a resin supply gate 320 is inserted into a cavity 40 formed by a pair of male and female molds 10 via a resin supply passage 32 formed in the male mold 30. The method of supplying 51 is mentioned.

In the present invention, the supply process includes at least a first supply process in which the mold opening speed of the mold is a predetermined speed, and a second supply process in which the mold is opened at a speed slower than the first supply process. Have. By making the mold opening speeds different from each other in this way, it becomes possible to reduce the change in the flow speed when the molten thermoplastic resin flows on the mold cavity surface. The difference in transfer state can be reduced. As a result, it is possible to suppress the occurrence of defects such as ring marks, gloss unevenness, and transfer unevenness of the molded body, and provide a molded body with a good appearance.
The mold opening speed (V ₂ ) of the second supply process is not particularly limited as long as it is slower than the mold opening speed (V ₁ ) of the first supply process, but the ratio of V ₁ and V ₂ (V ₁ / V ₂ ) is more preferably 1.5 to 10, and further preferably 2 to 6. By setting the ratio of V ₁ and V ₂ (V ₁ / V ₂ ) within the above range, it is possible to make the change in the flow rate of the thermoplastic resin within an appropriate range when the mold opening is stopped. . As a result, ring marks, gloss unevenness, and transfer unevenness can be prevented from occurring in the molded body.
“Mold opening speeds V ₁ and V ₂ ” in the present invention are values obtained by continuously monitoring the position of the movable platen of the press device and calculating the amount of change per unit time from the amount of movement and the time required for movement. Used.

V ₁ is preferably ₁ mm / sec or more and 10 mm / sec or less, and more preferably 2 mm / sec or more and 8 mm / sec or less. On the other hand, V ₂ is preferably 0.5 mm / sec or more and 5 mm / sec or less, and more preferably 0.5 mm / sec or more and 3 mm / sec or less.
By setting V ₁ to 1 mm / sec or more, the time required for mold opening becomes too long, and the resin supply is completed before the mold is opened to the required position (C _{3 in} FIG. ₃ or C _{9 in} FIG. 4). Can be prevented. Further, by setting V ₁ to 10 mm / sec or less, it is possible to prevent the occurrence of ring marks, gloss unevenness, and transfer unevenness by increasing the change in flow rate when mold opening stops. Become.
Further, by setting V ₂ to 0.5 mm / sec or more, the time required for mold opening becomes too long, and the resin is supplied until the mold is opened to a necessary position (C _{4 in} FIG. 3 or C _{10 in} FIG. 4). Can be prevented from ending. Further, by setting V ₂ to 5 mm / sec or less, it is possible to prevent the occurrence of ring marks, gloss unevenness, and transfer unevenness by increasing the change in flow rate when mold opening is stopped. Become.

The mold cavity clearance (C ₂ ) when starting to supply the molten thermoplastic resin (first supply step) is preferably 0.5 mm or more and 6 mm or less, and more preferably 1 mm or more and 5 mm or less. By setting the cavity clearance to 0.5 mm or more, the pressure during injection can be kept low. Moreover, it becomes possible to keep the external appearance of a molded object favorable by setting it as 6 mm or less.
The time between the first mold clamping process and the supply process is not particularly limited, but is preferably as short as possible in terms of the molding cycle.

The timing for switching from the first supply process to the second supply process is not particularly limited, but a position where the cavity clearance (C ₃ ) is about 60% to 95% of the maximum value (C ₄ ) of the mold cavity clearance. (See FIG. 3).
Moreover, you may provide the 3rd supply process, the 4th supply process, etc. which made mold opening speed still slower after a 2nd supply process.

Note that the molten thermoplastic resin is supplied at a slower rate, and the flow rate when flowing on the mold cavity surface becomes slower and the difference from the flow rate at the time of clamping becomes larger. In some cases, the difference in the transfer state increases, resulting in transfer unevenness. For this reason, the supply rate of the molten thermoplastic resin is preferably 600 cc / sec or more, and more preferably 800 cc / sec or more. Moreover, you may change the supply speed | rate of a molten thermoplastic resin in the middle.
The “feed rate” of the molten thermoplastic resin in the present invention refers to the injection capacity per unit time calculated from the resin capacity injected from the injection apparatus and the injection time.

[Second mold clamping process]
After reaching the maximum value (C ₄ ) of the mold cavity clearance, the mold opening is stopped and the supply of the thermoplastic resin is continued (see FIG. 3). Thereafter, the mold clamping is started before the supply of the molten thermoplastic resin is completed, and the mold clamping is completed (C ₆ ) after the supply of the molten thermoplastic resin is completed (C ₅ ).
By starting the mold clamping before the supply of the thermoplastic resin is completed, shaping can be performed without stopping the flow of the molten thermoplastic resin, and the generation of ring marks can be prevented. Further, by completing the mold clamping after the supply of the molten thermoplastic resin is completed, the resin can be supplied at a low pressure. The timing for starting the mold clamping is not particularly limited as long as the supply of the molten thermoplastic resin is completed.
The clamping speed (V ₃ ) when clamping the male and female dies is not particularly limited, but the maximum value is preferably more than 30 mm / sec and not more than 300 mm / sec. By exceeding 30 mm / sec, the force required for mold clamping can be reduced. Moreover, it becomes possible to reduce the impact which concerns on a metal mold | die at the time of mold clamping by setting it as 300 mm / sec or less.

Note that the mold clamping speed may be changed midway as long as the maximum value exceeds 30 mm / sec and is 300 mm / sec or less. For example, as shown in FIG. 4, the molten thermoplastic resin to the start of the supply, after reaching a predetermined mold cavity clearance (see C ₁₀ in FIG. 4), clamping before the molten thermoplastic resin to complete feed The mold clamping may be started at a speed (see V _{6 in} FIG. 4), and thereafter (see C _{11 in} FIG. 4), and then the mold clamping speed may be increased (see V _{7 in} FIG. 4). Also at this time, in order to make the difference in the flow velocity flowing on the mold cavity surface as small as possible and to perform molding at a low pressure, the mold clamping speed (see V _{6 in} FIG. 4) is higher than the mold clamping speed (see FIG. it is preferable to increase the V reference _7). 3 and 4, mold clamping speeds V _{1 to} V ₇ indicate the inclinations of straight lines connecting the respective cavity clearances.

[Cooling process]
In this invention, you may have a cooling process which cools the thermoplastic resin supplied after the said 2nd mold clamping process.
As a specific cooling method for each of the cavity surfaces 21, 31, for example, water is provided in the temperature adjustment passage 220 provided in the female mold 20 shown in FIG. 1 and the temperature adjustment passage 310 formed in the male mold 30. A method of cooling the cavity surfaces 21 and 31 by circulating a cooling medium such as
In addition, as cooling time, it is preferable that it is the temperature which does not deform | transform, when a molded object is taken out. Specifically, it is preferably 1 second to 60 seconds, and more preferably 1 second to 40 seconds. By setting the cooling time within the above range, it is possible to prevent a decrease in productivity.

After the above steps, the movable platen of the apparatus is moved, the cavity is opened, and the molded body obtained from the inside is taken out.
The molded body according to the present invention can be obtained by the above steps.
In the figure, 1 and 2 show an example of clamping in the vertical direction, but the clamping direction may be the vertical direction or the horizontal direction.

  Here, examples of the thermoplastic resin that can be used in the production method according to the present invention include thermoplastic resins that are usually used in compression molding, injection molding, extrusion molding, and the like. Examples of such resins include general polypropylene, polyethylene, acrylonitrile-styrene-butadiene block copolymers, polyamides such as polystyrene and nylon, polyvinyl chloride, polycarbonate, acrylic resins, styrene-butadiene block copolymers, and the like. And thermoplastic elastomers, thermoplastic elastomers such as ethylene / propylene rubber (EPM, EPDM), mixtures thereof, and polymer alloys using these.

  Moreover, these thermoplastic resins may contain fillers, such as an inorganic and organic filler normally used as needed. Moreover, you may contain various additives, such as various pigments normally used, a lubricant, an antistatic agent, and a stabilizer.

  The molded body obtained by the method according to the present invention is suitably used for interior parts and exterior parts such as automobile door trims and instrument panels, interior and exterior parts of household electrical appliances, and housing-related parts such as bathroom panels and floors. It is possible.

It is the figure which showed the cross section of the metal mold | die preferably used with the manufacturing method of the molded object which concerns on this invention. It is the figure which showed the supply process in the manufacturing method of the molded object which concerns on this invention. It is the figure which showed the relationship between a mold cavity clearance and supply time in a supply process. It is the figure which showed the relationship between a mold cavity clearance and supply time in a supply process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Mold 20 Female mold 21, 31 Cavity surface 30 Male mold 32 Resin supply passage 220, 310 Temperature control passage 320 Resin supply gate 40 Cavity 50 Injection device 51 Thermoplastic resin

Claims (6)

A first mold clamping step of clamping a pair of molds having a cavity surface forming a cavity until a cavity clearance in a mold clamping direction reaches a predetermined position;
Supplying a thermoplastic resin to the cavity while opening the mold; and
A method for producing a molded body having a second mold clamping step for clamping the mold before the supply of the thermoplastic resin is completed,
The supply process includes at least a first supply process in which a mold opening speed of the mold is set to a predetermined speed, and a second supply process in which the mold is opened at a speed slower than the first supply process. The manufacturing method of the molded object characterized by the above-mentioned. The ratio (V ₁ / V ₂ ) between the mold opening speed (V ₁ ) of the first supply process and the mold opening speed (V ₂ ) of the second supply process is 1.5 to 10. The manufacturing method of the molded object of description.   The method for producing a molded body according to claim 1 or 2, wherein a mold opening speed in the first supply step is 1 mm / sec or more and 10 mm / sec or less.   The mold opening speed of said 2nd supply process is 0.5 mm / sec or more and 5 mm / sec or less, The manufacturing method of the molded object in any one of Claim 1 to 3.   The method for producing a molded body according to any one of claims 1 to 4, wherein a mold clamping speed in the second mold clamping step is more than 30 mm / sec and not more than 300 mm / sec.   The method for producing a molded body according to any one of claims 1 to 5, wherein a supply rate of the thermoplastic resin is 600 cc / sec or more.

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