JP2012096424A - Manufacturing method for thermoplastic resin molded article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for a thermoplastic resin molded article wherein lowering of strength at its weld part is small under lower molding pressure upon molding.SOLUTION: The manufacturing method for a thermoplastic resin molded article comprises using a molding die having the first die for molding a cavity and the second die on either of which plural number of gates having opening-closing mechanisms are provided, and the method comprises a supply step of supplying molten thermoplastic resin into the cavity by opening the plural number of gates, a clamping step of clamping the molding die while the molten thermoplastic resin is supplied and a closing step of closing each of the gates comprising closing the plural number of the gates at different timing and closing the last closing gate after completion of the clamping step in the supplying step.

Description

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

  A molded body made of a thermoplastic resin is manufactured by a molding method such as injection molding or compression molding. For example, Patent Document 1 discloses an injection molding method in which the length from the first branch point of the runner to each gate is set to a predetermined range, and the resin filling and filling in the pressure holding process is performed from the gate closest to the branch point. It is disclosed.

JP-A-10-21635

However, the method described in Patent Document 1 cannot improve the weld strength unless it is a mold having a specific runner shape, and the mold having an existing general runner shape cannot improve the weld strength. It was difficult.
The present invention provides a thermoplastic resin capable of obtaining a molded body with a small decrease in strength of the weld portion and capable of lowering the molding pressure during molding even for a mold having a general runner shape. It aims at providing the manufacturing method of a molded object.

The present invention has a first mold and a second mold for forming a cavity, and a molding die in which a plurality of gates having an opening / closing mechanism are provided in the first mold or the second mold. A method of manufacturing a thermoplastic resin molded body using a supply step of opening the molding die, opening a plurality of gates and supplying a molten thermoplastic resin into the cavity, and the melting A mold clamping step of clamping the molding die while supplying a thermoplastic resin, and closing the plurality of gates opened in the supply step at different timings, and finally closing the gate A method for producing a thermoplastic resin molded body having a gate closing step performed after completion of the mold clamping step.
In the present invention, “strength” means bending strength, flexural modulus, impact strength, and the like.

  ADVANTAGE OF THE INVENTION According to this invention, the thermoplastic resin which can obtain the molded object with few strength reductions of a weld part using the metal mold | die which has a general runner shape, and can make low the molding pressure at the time of shaping | molding. The manufacturing method of a molded object can be provided.

It is the figure which showed an example of the metal mold | die preferably used with the manufacturing method of the thermoplastic resin molding which concerns on this invention. It is the figure which showed the time-axis of each process of the manufacturing method of the thermoplastic resin molding which concerns on this invention. It is the figure which showed the mode of the supply process in this embodiment. It is the figure which showed the cross section of the weld part of a molded object. FIG. 3 is a diagram illustrating a time axis of each process of Example 1. 6 is a diagram showing a time axis of each process of Comparative Example 1. FIG.

Hereafter, the manufacturing method of the thermoplastic resin molding of this invention is demonstrated for every process using figures. In the present embodiment, the same components are denoted by the same reference numerals, and the description thereof is omitted.
First, a molding die that is preferably used in the present invention will be described.

[Mold for molding]
FIG. 1 is a view showing a cross section of a molding die used in the present invention. In the molding die 1, a first die (male die) 10 and a second die (female die) 20 are arranged to face each other. The second mold 20 reciprocates by an opening / closing mechanism (not shown) that is operated by hydraulic pressure or an electric motor. The first mold 10 and the second mold 20 are in a “closed state” where the first mold 10 and the second mold 20 are in contact with the reciprocating motion of the second mold 20, and the first mold 10. The first mold 10 and the second mold 20 form a cavity 30 having a desired shape between the first mold 10 and the second mold 20.

The first mold 10 is provided with a plurality of gates for supplying a molten thermoplastic resin (hereinafter referred to as a molten resin). The number of gates varies depending on the shape and size of the cavity, but it is necessary to be at least two or more. In the present embodiment, a molding die having two gates is used.
In FIG. 1, one end of each of the two gates 11 a and 11 b is connected to a molten resin supply path 12. The molten resin supply path 12 is connected to an injection nozzle of an injection device. The molten resin plasticized by the injection device is supplied into the cavity 30 through the molten resin supply path 12. Each gate 11a, 11b is provided with an opening / closing mechanism such as a valve pin, and the timing of supplying the molten resin can be freely controlled.
In this example, since the cavity uses a horizontal mold as shown in the drawing, the mold can be opened and closed in the vertical direction. However, even if the cavity is a mold that can be opened and closed in the horizontal direction in the vertical direction. Well, these differences are not the essence of the present invention.

[Method for producing thermoplastic resin molded article]
FIG. 2 is a diagram showing a time axis of each step of the method for producing a thermoplastic resin molded body according to the present embodiment. In this embodiment, the molding die shown in FIG. 1 is used.
As shown in FIG. 2, since the supply process is continuously performed after at least one gate is opened until a predetermined number of gates are closed, the start time of the supply process is set to zero ( Time), and the end time was t5 (time). The mold clamping process is a process of performing mold clamping while supplying molten resin into the cavity. Clamping is started after a lapse of a predetermined time from the start of the supply process (time t2 (time)), and is completed after the lapse of a predetermined time (time t4 (time)).
In the gate closing process, the plurality of gates opened in the supplying process are closed at different timings. The last gate may be closed at time t5 (time), and the remaining gates may be closed at any timing after the start of the supply process. Therefore, gates other than the last gate are appropriately closed at any time between time t1 and t5 (time), for example, time t3 (time). Thus, the mold clamping process and the gate closing process are performed independently after a predetermined time has elapsed from the start of the supply process.

<Supply process>
FIG. 3 is a view showing a supply process in which the molding die 1 shown in FIG. 1 is opened, the gates 11 a and 11 b are opened, and the molten resin 13 is supplied into the cavity 30. The timing of opening the gates 11a and 11b may be the same or different, but a predetermined number (two or more) of gates necessary for supply are opened by the completion of the mold clamping process (t4 in FIG. 2). There is a need. Although a plurality of gates need to be opened, there may be a gate that is not opened depending on the shape of the cavity. By opening a plurality of gates before completion of the mold clamping process, it becomes possible to lower the molding pressure as compared with the case where the molten resin is supplied with the mold closed, as in a normal injection molding method. .
Further, the supply of the molten resin 13 is continuously performed even after completion of a mold clamping process described later. After completion of the mold clamping process, it is not necessary to supply the resin from all the gates, and it is sufficient that the molten resin 13 continues to be supplied from at least one gate 11a or 11b. By continuing the supply of the molten resin 13 even after the mold clamping process is completed, in the weld portion formed by the molten resin 13 supplied from the gates 11a and 11b, the resin on the side where the resin pressure is strong is wedged to the resin on the weak side. The strength of the weld portion can be increased.
The mold cavity clearance (L1) at the start of the supply of the molten resin 13 is not particularly limited as long as it is larger than the clearance at the completion of mold clamping.

In this step, after the first mold and / or the second mold are moved to a predetermined position and the cavity volume is reduced, a predetermined number of the plurality of gates is opened, and molten resin is supplied into the cavity. The first mold and / or the second mold may be moved to a predetermined position, and the molten resin may be supplied while increasing the cavity volume.
When the cavity volume is reduced, it is sufficient that molten resin is supplied from at least one gate, but the remaining gates are sequentially opened, and a plurality of gates need to be opened by the end of the mold clamping process. is there.

When the molten resin is supplied while opening the molding die, first, the supply of the molten resin is started after the distance between the first mold and the second mold is closed to a predetermined distance (L2). Although there is no restriction | limiting in particular in the space | interval (L2) of a 1st type | mold and a 2nd type | mold, It is preferable to set it as 1 mm or more and 10 mm or less. By setting the interval to 1 mm or more and 10 mm or less, the supply pressure of the molten thermoplastic resin can be lowered and the appearance of the molded body can be improved.
Next, the first mold and the second mold are opened until a predetermined distance (L3) is reached. Although there is no restriction | limiting in particular in the space | interval (L3) at this time, When not using a skin material, it is preferable from a viewpoint of the external appearance of a molded object to set it as molded object thickness +20 mm or less. In the case of using a skin material, there is no particular limitation because there is no influence on the appearance even if the distance (L3) is large. However, if it is made larger than necessary, it takes time to open the mold. preferable.

Examples of a method for adjusting the positions of the first mold and the second mold include a method of adjusting by mechanical control using a mold clamping device of an injection molding machine. When the cavity clearance between the first mold and the second mold is enlarged, the mold clamping force of the mold clamping device is set low enough to be slightly opened by the molten resin supply pressure, and the molten resin supply pressure is set. The method of enlarging may be taken.
The enlargement speed when the cavity clearance is enlarged by mechanical control is preferably 0.5 mm / second or more and 20 mm / second or less. When the enlargement speed is less than 0.5 mm / second, the time required for enlargement becomes long, so that the molding cycle becomes long. In the case of exceeding 20 mm / second, the molten resin cannot follow the mold enlargement speed, and the force of pressing the molten resin surface on the mold cavity surface becomes weak, and the appearance of uneven gloss etc. on the surface of the molded body Prone to defects. Further, the speed at which the cavity clearance is enlarged may be reduced or increased in the middle.

<Clamping process>
The mold clamping step in the present invention is a step of clamping a molding die at an arbitrary timing after the start of the supplying step. As shown in FIG. 2, the mold clamping is performed independently of the gate closing process described later. Clamping is performed by moving at least one of the first mold and the second mold. The mold clamping timing is not particularly limited as long as it is after the supply process is started and before the supply process is completed. In FIG. 2, after the gate closing process, it starts at time t2, but it may be performed before or simultaneously with the start of the gate closing process.
The clamping speed when clamping the molding die is not particularly limited, but is preferably 1 mm / second or more and 300 mm / second or less, more preferably 3 mm / second or more and 100 mm / second or less. The mold clamping speed may be changed by increasing or decreasing the speed. As the mold clamping speed in the present invention, a value calculated from the position of the mold and the mold clamping time in the mold clamping process is used. The mold clamping speed can be controlled by the flow rate of oil when a hydraulic molding machine is used, and by the number of revolutions of the motor when an electric molding machine is used.

<Gate closing process>
The gate closing step in the present invention is a step of closing a plurality of gates opened in the supplying step at different timings and closing the gate that is finally closed after completion of the mold clamping step. Since the resin is not supplied from the gate after this process is completed, the supply process is completed simultaneously with the completion of this process.
In the weld portion where the flows of the molten resin merge, the weld strength differs depending on whether the merge is performed at the same resin pressure or a different pressure. As shown in FIG. 4, the weld portion formed by the molten resin joined at different pressures is formed in a state where the resin 4 on the side having a higher resin pressure is deeply embedded in the resin 5 on the side having a lower resin pressure. Compared with a weld part formed of a molten resin joined at the same pressure, the weld strength is high. For this reason, by closing the gate at different timings and closing the gate at the end after the mold clamping process is completed, it is possible to make a difference in the resin pressure for forming the weld portion, and to improve the strength of the weld portion. it can.

  As shown in FIG. 2, the gate closing process is performed independently of the mold clamping process. The timing of starting this process, that is, the timing of closing at least one gate is not particularly limited, but is preferably before the completion of the mold clamping process. By starting the gate closing process before the mold clamping process is completed, the difference in resin pressure when forming the weld portion becomes larger, and the resin on the side with the higher resin pressure may be caused to sink more into the resin on the lower side. This makes it possible to further improve the weld strength.

  When the molding die has three or more gates, it is preferable that the timing of closing adjacent gates is different. By shifting the timing of closing adjacent gates, a difference in resin pressure is likely to occur, and the weld strength can be further improved. Moreover, it is preferable that the timing of closing the gate to be closed later among the adjacent gates is after completion of the mold clamping process.

  It is preferable to use a method for closing the gates by attaching a timer to each gate and individually closing at a timing when the time from the start of the supply process becomes a predetermined time.

After completion of the gate closing step, the molten resin supplied into the cavity is cooled, and the thermoplastic resin molded body is taken out from the molding die.
The molded products obtained in this way are widely used as automotive interior parts and exterior parts, parts in engine rooms, parts in trunk rooms, motorcycle parts, furniture and electrical parts, housing-related parts, etc. be able to.

〔Thermoplastic resin〕
As the thermoplastic resin used in the method for producing a thermoplastic resin molded body according to the present invention, a resin usually used in compression molding, injection molding, extrusion molding or the like can be used.
Examples of such resins include thermoplastic resins such as polypropylene, polyethylene, acrylonitrile-styrene-butadiene block copolymer, polystyrene, nylon, polyvinyl chloride, polycarbonate, acrylic resin, styrene-butadiene block copolymer, and EPM. And thermoplastic elastomers such as EPDM. These may be used singly or as a mixture of two or more. A polymer alloy may be used as the mixture.

  The thermoplastic resin may contain reinforcing fibers in order to enhance the effect of improving the weld strength. Examples of the reinforcing fiber include glass fiber, alumina fiber, carbon fiber, organic fiber, and a mixture thereof. Of these, glass fiber or organic fiber is preferably used. Examples of the organic fiber include polyethylene fiber, polypropylene fiber, aramid fiber, polyester fiber, vinylon fiber, cotton, hemp, silk, bamboo and the like.

  In addition, as necessary, thermoplastic resins are antioxidants, heat stabilizers, neutralizers, UV absorbers and other stabilizers; silica and other anti-blocking agents; bubble inhibitors; flame retardants; flame retardant aids; Agents; antistatic agents; lubricants; colorants such as dyes and pigments; plasticizers; nucleating agents and crystallization accelerators may be contained. Further, it may contain inorganic compounds such as glass flakes, mica, glass powder, glass beads, talc, clay, alumina, carbon black, wall snite, and the like, powdery and whisker-like inorganic compounds.

The thermoplastic resin may contain a foaming agent such as a chemical foaming agent and a physical foaming agent. Chemical foaming agents include inorganic foaming agents such as sodium bicarbonate, ammonium bicarbonate and ammonium carbonate, nitroso compounds such as N, N′-dinitrosopentamethylenetetramine, azodicarbonamide and azo such as azobisisobutyronitrile. Examples thereof include sulfonyl hydrazides such as compounds, benzenesulfonyl hydrazide, toluenesulfonyl hydrazide, diphenylsulfone-3,3′-disulfonyl hydrazide, and p-toluenesulfonyl semicarbazide. Moreover, you may add a salicylic acid, urea, and the foaming adjuvant containing these as needed. Examples of physical foaming agents include carbon dioxide and nitrogen. These are preferably in a supercritical state.
The type of foaming agent is selected in consideration of the melting temperature of the thermoplastic resin to be used, the target foaming ratio, and the like. The addition amount is adjusted in consideration of the strength, density and the like of the target molded article, but is generally 0.1 to 5 parts by mass with respect to 100 parts by mass of the resin.

  A skin material may be bonded to a part of the surface of the thermoplastic resin molded body obtained by the method according to the present invention. Examples of the skin material used in the present invention include woven fabrics and knitted fabrics such as moquettes and tricots, nonwoven fabrics such as needle punch carpets, metal foils, sheets and films of thermoplastic resins and thermoplastic elastomers, and the like. When the skin material is bonded and integrated to a part of the surface of the molded body, the skin material may be previously molded at a predetermined position between the molds.

Examples of the fibers constituting the nonwoven fabric include natural fibers such as cotton, wool, silk, and hemp, and synthetic fibers such as polyamide, polyester, and nylon. The nonwoven fabric may be composed of a single type of fiber or may be composed of two or more types of fibers. Moreover, you may be comprised with the mixture of a natural fiber and a synthetic fiber. Nonwoven fabrics are classified into needle punch, thermal bond, spunbond, meltblown, and spunlace types, and any nonwoven fabric produced by any method can be applied to the present invention.
Examples of the thermoplastic resin and thermoplastic elastomer sheets and films include thermoplastic resins such as polypropylene and polyethylene, and polyolefin thermoplastic elastomer sheets and films, and thermoplastic resins used as base resins and Those having good fusibility are preferably used.

These skin materials may be multilayer skin materials having a foam layer or a backing layer.
Examples of the foam layer include polyolefin foams such as polypropylene and polyethylene, polyvinyl chloride foams, soft or semi-rigid polyurethane foams, and the like.
Moreover, as a backing layer, a nonwoven fabric, a synthetic resin sheet, a film, etc. are mentioned, for example.

  In addition, these multilayer skin materials are those having good thermal fusion with a thermoplastic resin from the viewpoint of adhesion to a base material portion made of a thermoplastic resin, or a molten thermoplastic resin on the back surface of the skin material. Those that can be bonded to the base resin by impregnating with are preferably used.

  EXAMPLES Hereinafter, although this invention is demonstrated in more detail based on an Example, this invention is not limited to these Examples.

[Evaluation methods]
(1) Flexural modulus The flexural modulus of the molded bodies produced in Examples and Comparative Examples was measured under the following conditions in accordance with ASTM D790.
Measurement temperature: 23 ° C
Sample thickness: 4.0 mm
Span: 50mm
Bending speed: 2mm / min

(2) Bending strength The bending strength of the molded bodies produced in the examples and comparative examples was measured under the following conditions in accordance with ASTM D790.
Measurement temperature: 23 ° C
Sample thickness: 4.0 mm
Span: 50mm
Bending speed: 2mm / min

(3) Impact strength The impact strength of the molded bodies produced in Examples and Comparative Examples was measured according to ASTM D256 under the following conditions.
Measurement temperature: 23 ° C
Sample thickness: 4.0 mm (no V notch)

[Example 1]
The product name SLIM1016 (manufactured by Sato Iron Works, mold clamping force 980 kN, injection capacity 1600 cc) is used as the molding device, and the product name Smithtran PG 4060B (manufactured by Sumitomo Chemical Co., Ltd., long fiber reinforced polypropylene, containing 40% glass fiber) is used as the thermoplastic resin. Using a mold of 270 × 340 mm and a thickness of 4.0 mm and a two-point gate (gate A, gate B), a molded body having a weld formed in the center is molded, and the weld portion of the obtained molded body is molded. The strength was measured.

<Molding conditions>
The molded body was manufactured by using the above injection molding and setting the resin temperature to 220 ° C. and the mold temperature to 30 ° C.
As shown in FIG. 5, the timing of opening the gate in the supplying step was two points at the same time, and the cavity clearance when starting the supply of the molten resin into the cavity was the molded body thickness + 8 mm.
The mold clamping process was started 0.5 seconds after the supply process was started. The mold clamping speed at this time was 10 mm / sec. In addition, the supply amount of the molten resin supplied into the cavity after the completion of mold clamping (1.3 seconds after the start of the supply process) was 20% of the total supply amount.
The timing of closing the gate in the gate closing process was 1.2 seconds after the start of the supply process for Gate A (during the mold clamping process), and after completion of the mold clamping process for Gate B.
After the gate closing step, the molded body was taken out from the cavity after cooling for 60 seconds.

[Comparative Example 1]
As shown in FIG. 6, the molding conditions were started 0.9 seconds after the start of the clamping process, and the amount of molten resin supplied into the cavity after completion of clamping was set to 0% of the total supply amount. The molded body was manufactured in the same manner as in Example 1 except that the timing of closing the gate B in the gate closing process was after all the molten resin was supplied into the cavity (during the mold clamping process).

DESCRIPTION OF SYMBOLS 1 Molding die 10 1st type | mold 11a-11f Gate 12 Molten resin supply path 13 Molten resin 20 2nd type | mold 30 Cavity 4 Resin with a high resin pressure 5 Resin with a low resin pressure

Claims (5)

Thermoplastic using a molding die having a first die and a second die forming a cavity, and a plurality of gates having an opening / closing mechanism are provided in the first die or the second die. A method for producing a resin molded body, comprising:
A supply step of opening the molding die, opening a plurality of gates, and supplying a molten thermoplastic resin into the cavity;
A clamping step of clamping the molding die while supplying the molten thermoplastic resin;
A method for producing a thermoplastic resin molded body comprising: a gate closing step in which the plurality of gates opened in the supplying step are closed at different timings, and the gate to be closed last is closed after completion of the mold clamping step.   The method for producing a thermoplastic resin molded body according to claim 1, wherein the timing for starting the gate closing step is before completion of the mold clamping step. In the supplying step, the first mold and / or the second mold of the molding die in an open state are moved to a predetermined position, and after reducing the cavity volume, at least one gate is opened. Start supplying the molten thermoplastic resin into the cavity,
The heat according to claim 1 or 2, which is a step of supplying the molten thermoplastic resin while moving the first mold and / or the second mold to a predetermined position and increasing the cavity volume. A method for producing a plastic resin molding.   The method for producing a thermoplastic resin molded article according to any one of claims 1 to 3, wherein the thermoplastic resin contains reinforcing fibers.   The method for producing a thermoplastic resin molded article according to claim 4, wherein the reinforcing fibers are glass fibers and / or organic fibers.

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