JP2011073423A - Molding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a molding method, which utilizes a sheet improving moldability as well as molding efficiency. <P>SOLUTION: The molding method includes a step for positioning a sheet of a thermoplastic resin material in a melt state between a pair of molds of a dividing type, a step for forming a first sealed space between the cavity of one mold 32B and one surface of the sheet opposed to the cavity, a step for a first shaping by suctioning the sheet from one mold cavity side through the first sealed space, a step for moving the other mold toward one mold until an annular part of the sheet corresponding to the tip of an annular projection hits the cavity of the other mold 32A to clamp a pair of molds of a dividing type, and a step for a second shaping by pressurizing the sheet from the cavity side of the other mold through a second sealed space formed between the other mold cavity and the other surface of the sheet opposed to the cavity by the mold-clamping step. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a molding method, and more particularly to a molding method using a single sheet that improves moldability and improves molding efficiency.

Conventionally, a technique of molding using a single resin sheet by a vacuum suction method has been used.
Patent Document 1 discloses that a support system component for an electroacoustic transducer is vacuum-formed using a single thermoplastic resin sheet, and more specifically, a heated sheet is placed on a vacuum-molding die. Then, it is attached to a vacuum forming die by vacuum drawing to form a thin sheet.
Patent Document 2 discloses a point in which a skin material is attached to the surface of a base material and vacuum-formed, and more specifically, a base material is placed on a lower mold, and the skin is placed between the upper mold and the lower mold. After carrying in the material, both molds are closed, the skin material is attached to the base material, and then vacuum suction is performed from the lower mold side to perform molding.
Patent Document 3 discloses the point of vacuum forming various parts of automobiles, home appliances, daily necessities, etc. using a thermoplastic resin film, and more specifically, covers a vacuum shaping mold with a heated thermoplastic resin film, The thermoplastic resin film is sandwiched between the press box and the vacuum shaping mold so that a sealing surface is formed between the thermoplastic resin film and the outer periphery of the vacuum shaping mold, and vacuum suction is performed by the vacuum shaping mold.

According to the molding techniques disclosed in these patent documents, it is possible to perform vacuum molding using a film or a sheet, but the following technical problems exist.
First, in Patent Document 2 using an upper mold and a lower mold, and in Patent Document 3 using a vacuum shaping mold and a press box, the mold is clamped before vacuum forming. The moldability around the periphery of the film or sheet sandwiched between the two dies is deteriorated.
More specifically, when vacuum forming is performed with the mold clamped, since the peripheral portion of the film or sheet sandwiched between the two molds is fixed, the film or sheet is stretched, and accordingly, the film or sheet near the peripheral portion is The sheet is dragged toward the cavity, and it is difficult to obtain a desired formability.
In particular, according to vacuum suction, the film or sheet cannot be pressed against the cavity due to high pressure, so it is difficult to shape a fine texture pattern or the like on the sheet surface, resulting in restrictions on formability. .

Second, since all of Patent Document 1 to Patent Document 3 are trimmed separately from the burr after vacuum forming, the overall forming efficiency is lowered.
More specifically, according to Patent Document 1 and Patent Document 3, the molded product taken out from the mold after vacuum forming and cooled is trimmed by a post-process, while according to Patent Document 2, once after vacuum forming, After opening the mold and mounting the cutting blade, trimming is performed again using the clamping force.
JP 2003-78998 A JP 2004-209839 A JP2001-138389

  In view of the above technical problems, an object of the present invention is to provide a molding method using a single sheet that improves moldability and improves molding efficiency.

In order to achieve the above object, the molding method of the present invention comprises:
A molding method using one sheet,
Positioning a sheet of molten thermoplastic resin material between a pair of split molds in a form that protrudes from an annular protrusion provided at the periphery of the cavity of one mold of the pair of split molds When,
Forming a first sealed space between a cavity of one mold and one surface of the sheet facing the cavity;
Suctioning the sheet from the cavity side of one mold through the first sealed space to press the sheet against the cavity and performing a first shaping;
The pair of split molds are clamped by moving the other mold and one mold close to each other until the annular portion of the sheet corresponding to the tip of the annular projection hits the cavity of the other mold. And the stage of
In the mold clamping step, the sheet is pressed from the cavity side of the other mold through a second sealed space formed between the cavity of the other mold and the other surface of the sheet facing the cavity. Thus, the sheet is pressed against the cavity of one mold to perform the second shaping.

  According to the molding method having the above configuration, since the sheet is sucked and first shaped before clamping the pair of split molds, the periphery of the sheet is sandwiched between the pair of split molds. It is possible to improve the formability of the peripheral edge of the sheet in that the suction is not performed in the pressed state, and after the molds of the pair of divided molds are clamped, the first shaping is performed to some extent to form the cavity. Since the sheet is second-shaped by pressurizing the sheet that is familiar with the surface, it is possible to form a finer wrinkle pattern on the sheet surface, coupled with the fact that it can be molded at a higher pressure than suction. Is possible. At that time, by clamping the pair of molds, the annular protrusion provided on the periphery of the cavity of one mold presses the sheet toward the cavity of the other mold. Since the annular portion of the sheet corresponding to is at least thinned, it is possible to use this thinned portion without using a separate cutting device and jig, and to use the thinned portion for the burr portion outside the annular portion and the product portion inside the annular portion. Can be separated from each other, and an improvement in molding efficiency can be achieved.

The mold clamping step includes a step of thinning an annular portion of the sheet corresponding to the tip of the annular projection by the tip of the annular projection,
Preferably, the method further includes a step of cutting the thin portion of the sheet after the second shaping step.
Further, the mold clamping step may include a step of pressing and cutting off the annular portion of the sheet corresponding to the tip of the annular projection by the tip of the annular projection.
Furthermore, the annular protrusion is provided so as to be movable forward and backward in the mold clamping direction with respect to the one mold provided with the annular protrusion.
It is preferable to adjust the thickness of the thin portion of the sheet by adjusting the amount of advance and retreat of the annular protrusion in the mold clamping direction.
In addition, the annular protrusion is provided so as to be movable back and forth in the mold clamping direction with respect to the one mold provided with the annular protrusion.
It is preferable to adjust the separation of the sheet by adjusting the amount of advance and retreat of the annular protrusion in the mold clamping direction.

Furthermore, the step of forming the first sealed space includes a step of moving one mold toward the other mold until the tip of the annular protrusion of one mold hits one surface of the sheet. Good.
Furthermore, in the step of forming the first sealed space, an annular outer frame that is externally fitted to the peripheral edge of one mold so as to advance and retreat in the mold clamping direction is applied to one surface of the sheet toward the other mold. It is good to have the step to move to.
In addition, the second shaping step may suck the sheet through the first sealed space while pressurizing the sheet through the second sealed space.

Embodiments according to the present invention will be described below in detail with reference to the drawings.
In the present embodiment, a single sheet-like molded product is targeted as the resin molded product.
First, the shaping | molding apparatus for enforcing the shaping | molding method of this invention is demonstrated below.
As shown in FIG. 1, a molding device 10 for a resin molded product has an extrusion device 12 and a mold clamping device 14 disposed below the extrusion device 12, and is a molten sheet extruded from the extrusion device 12. The parison P is fed to the mold clamping device 14, and the mold-like clamping device 14 forms the molten sheet parison P.

  The extruding device 12 is a conventionally known type, and a detailed description thereof is omitted. However, a cylinder 18 provided with a hopper 16, a screw (not shown) provided in the cylinder 18, and a screw are connected to the screw 18. The hydraulic motor 20, an accumulator 24 that communicates with the inside of the cylinder 18, and a plunger 26 provided in the accumulator 24, and resin pellets that are introduced from the hopper 16 are screwed by the hydraulic motor 20 in the cylinder 18. The molten resin is melted and kneaded by the rotation of the resin, and the molten resin is transferred to the accumulator 24 chamber and stored in a certain amount. The plunger 26 is driven to feed the molten resin toward the T die 28, and the continuous sheet is passed through the extrusion slit 34. A sheet-like parison P is extruded and a pair of robots arranged at intervals. While being clamped by the error 30 is fed downward is suspended between the split mold blocks 32. Thereby, as will be described in detail later, the sheet-like parison P is disposed between the split molds 32 in a state where the sheet-like parison P has a uniform thickness in the vertical direction (extrusion direction).

The extrusion capability of the extrusion device 12 is appropriately selected from the viewpoint of the size of the resin molded product to be molded, the draw-down of the sheet parison P, or the prevention of neck-in occurrence. More specifically, from a practical point of view, the extrusion amount of one shot in intermittent extrusion is preferably 1 to 10 kg, and the extrusion rate of the resin from the extrusion slit 34 is several hundred kg / hour or more, more preferably 700 kg / hour or more. Further, from the viewpoint of preventing the draw-down or neck-in of the sheet-like parison P, the extrusion process of the sheet-like parison P is preferably as short as possible and generally depends on the type of resin, MFR value, and melt tension value. The extrusion process should be completed within 40 seconds, more preferably within 10 to 20 seconds. For this reason, the unit area and the amount of extrusion per unit time from the extrusion slit 34 of the thermoplastic resin are 50 kg / hour cm ² or more, more preferably 150 kg / hour cm ² or more.

  By feeding the sheet-like parison P sandwiched between the pair of rollers 30 by the rotation of the pair of rollers 30 downward, the sheet-like parison P can be stretched and thinned, and the extruded sheet-like parison P is extruded. By adjusting the relationship between the speed and the delivery speed of the sheet-like parison P by the pair of rollers 30, it is possible to prevent the occurrence of drawdown or neck-in, so the type of resin, particularly the MFR value and melt tension. It is possible to reduce the restriction on the value or the extrusion amount per unit time.

  As shown in FIG. 1, the extrusion slit 34 provided in the T die 28 is disposed vertically downward, and the continuous sheet-like parison P extruded from the extrusion slit 34 is suspended from the extrusion slit 34 as it is. , So that it is sent vertically downward. The extrusion slit 34 can change the thickness of the continuous sheet-like parison P by making the interval variable.

The pair of rollers 30 will be described. In the pair of rollers 30, the rotation axes of the pair of rollers 30 are arranged substantially horizontally in parallel with each other, one is the rotation drive roller 30A, and the other is driven to rotate. The roller 30B. More specifically, as shown in FIG. 1, the pair of rollers 30 are arranged so as to be line-symmetric with respect to the sheet-like parison P extruded in a form that hangs downward from the extrusion slit 34.
The diameter of each roller and the axial length of the roller may be appropriately set according to the extrusion speed of the sheet-like parison P to be molded, the length and width of the sheet in the extrusion direction, and the type of resin. As will be described, from the viewpoint of smoothly feeding the sheet-like parison P downward by rotation of the roller with the sheet-like parison P sandwiched between the pair of rollers 30, the diameter of the rotation drive roller 30A is the rotation-driven roller. It is preferably slightly larger than the diameter of 30B. The diameter of the roller is preferably in the range of 50 to 300 mm. If the curvature of the roller is too large or too small in contact with the sheet-like parison P, the sheet-like parison P may be wound around the roller. Become.

  On the other hand, the mold clamping device 14 is also a conventionally known type like the extrusion device 12, and detailed description thereof will be omitted, but the two divided molds 32A and 32B and the molds 32A and 32B are melted. A mold driving device that moves between an open position and a closed position in a direction substantially orthogonal to the supply direction of the sheet-like parison P.

As shown in FIG. 1, the two divided molds 32 </ b> A and 32 </ b> B are arranged with the cavities 116 facing each other, and the cavities 116 are arranged so as to face substantially vertically. The surface of each cavity 116 is provided with a concavo-convex portion according to the outer shape and surface shape of a molded product molded based on the melted sheet-like parison P.
In each of the two divided molds 32A and 32B, a pinch-off part 118 is formed around the cavity 116. The pinch-off part 118 is formed in an annular shape around the cavity 116, and the opposing molds 32A and 32B are formed. Protrusively toward. As a result, when the two divided molds 32A and 32B are clamped, the tip portions of the pinch-off portions 118 come into contact with each other so that the parting line PL is formed at the periphery of the melted sheet-like parison P. I have to.
As will be described later, the pinch-off portion 118 can be thinned by sandwiching the annular portion of the sheet-like parison P corresponding to the tip of the pinch-off portion 118 by clamping the opposing molds 32A and 32B. As long as it is provided, it may be provided only on one of the mold 32A and the mold 32B.

  The molds 33A and B are slidably fitted to the outer peripheral portions of the two divided molds 32A and B in a sealed state, and the molds 33A and B are respectively fitted by a mold moving device (not shown). It can be moved relative to the molds 32A and 32B. More specifically, the mold 33A can be brought into contact with one side surface of the sheet-like parison P disposed between the molds 32A and 32B by projecting toward the mold 32B with respect to the mold 32A. In addition, the mold frame 33B protrudes toward the mold 32A with respect to the mold 32B, thereby being able to contact the other side surface of the sheet-like parison P disposed between the molds 32A and 32B.

  The mold driving device is the same as the conventional one, and the description thereof is omitted. However, the two divided molds 32A and 32B are respectively driven by the mold driving device and are divided into two in the open position. A melted continuous sheet-like parison P can be disposed between the molds 32A and 32B, and the pinch-off portions 118 of the two divided molds 32A and 32B are brought into contact with each other in the closed position, and an annular pinch-off portion When 118 is in contact with each other, a sealed space is formed in the two divided molds 32A and 32B. In addition, about movement of each metal mold | die 32A, B from an open position to a closed position, a closed position is made into the position of the centerline of the continuous sheet-like parison P of a molten state, and each metal mold | die 32A, B is carried out by a metal mold drive device. It is driven to move toward that position.

  As shown in FIG. 4, a vacuum suction chamber 120 is provided inside one of the divided molds 32, and the vacuum suction chamber 120 communicates with the cavity 116 through the suction hole 122. By sucking through 122, the sheet-like parison P is adsorbed toward the cavity 116 and shaped into a shape along the outer surface of the cavity 116.

  The sheet-like parison P is made of a sheet formed from polypropylene, engineering plastics, olefin resin, or the like. More specifically, the sheet-like parison P is preferably made of a resin material having a high melt tension from the viewpoint of preventing the occurrence of thickness variations due to drawdown, neck-in, etc., while being transferred to a mold. It is preferable to use a resin material with high fluidity in order to improve the property and followability.

A molding method using the molding apparatus 10 for a resin molded product having the above configuration will be described below with reference to the drawings.
First, a predetermined amount of the melted and kneaded thermoplastic resin is stored in the accumulator 24, and the stored thermoplastic resin is intermittently discharged at a predetermined extrusion amount per unit time from the extrusion slits 34 provided in the T die 28. By extruding, the thermoplastic resin swells and is extruded at a predetermined extrusion speed with a predetermined thickness so as to hang downward into a molten sheet.

  Next, the pair of rollers 30 is moved to the open position, and the gap between the pair of rollers 30 disposed below the extrusion slit 34 is widened from the thickness of the sheet-like parison P, so that the molten sheet is pushed downward. The lowermost part of the parison P is smoothly supplied between the pair of rollers 30. In addition, the timing which makes the space | interval of the rollers 30 wider than the thickness of the sheet-like parison P may be performed after the end of the secondary molding for each one shot, not after the start of extrusion.

  Next, the pair of rollers 30 are moved closer to each other and moved to the closed position, the sheet-like parison P is sandwiched by narrowing the interval between the pair of rollers 30, and the sheet-like parison P is sent downward by the rotation of the rollers.

Next, as shown in FIG. 2, the sheet-like parison P having a uniform thickness in the extrusion direction is disposed between the divided molds 32 disposed below the pair of rollers 30.
Next, as shown in FIG. 3, the mold 33B is moved toward the sheet-shaped parison P with respect to the mold 32B until it contacts the surface of the sheet-shaped parison P facing the mold 32B.
Next, as shown in FIG. 4, vacuum suction is performed through a first sealed space 200 configured by the cavity 116 of the mold 32 </ b> B, the inner peripheral surface of the mold 33 </ b> B, and the surface of the sheet-like parison P facing the mold 32 </ b> B. By sucking from the chamber 120 through the suction hole 122, the sheet parison P is pressed against the cavity 116, and the sheet parison P is shaped into a shape along the uneven surface of the cavity 116. As a result, the sheet-like parison P can be blended to some extent along the concavo-convex surface of the cavity 116 as a preliminary shaping for the final shaping after the mold clamping of the mold 32, which will be described later. Since the mold is not sucked in the clamped state, it is possible to prevent the moldability deterioration around the pinch-off portion.
Next, as shown in FIG. 5, the split mold 32 is clamped, and as shown in FIG. 6, the sheet-like parison P is sandwiched between the pinch-off part 118A of the mold 32A and the pinch-off part 118B of the mold 32B. Then, the thin portion 202 is formed, and the annular portion of the sheet-like parison P corresponding to the pinch-off portion 118 is pushed through to separate the burr portion outside the annular portion and the product portion inside the annular portion.
In this case, the pinch-off part 118 is provided so as to be movable forward and backward in the mold clamping direction with respect to the mold 32 provided with the pinch-off part 118, and the amount of separation of the seat is adjusted by adjusting the amount of advance and retreat in the mold clamping direction of the pinch off part 118. You may adjust. In particular, when a molded product is repeatedly molded, the advance / retreat amount of the pinch-off portion 118 in the mold clamping direction may be adjusted while observing how the burrs are separated from the molded product.
Next, as shown in FIG. 5, the sheet-shaped parison P is pressurized from the mold 32A side through the second sealed space 204 formed by the mold 32A and the surface of the sheet-shaped parison P facing the mold 32A. At the same time, the sheet resin is sucked from the mold 32 </ b> B through the first sealed space 200.
Thereby, it is possible to shape a fine texture pattern or the like on the surface of the sheet resin facing the mold 32B.

Next, as shown in FIG. 7, the split mold 32 is opened, the molded resin molded product is taken out, and the molding is completed.
By repeating the above steps each time the molten resin is intermittently extruded in the primary molding, a sheet-like resin molded product can be molded one after another.
As described above, the thermoplastic resin is intermittently extruded as a melted sheet-like parison P by primary molding (extrusion molding), and the sheet-like parison P extruded by secondary molding (blow molding or vacuum molding) is molded into a mold. It is possible to mold using

  In this case, since the sheet is first shaped by suction before clamping the pair of split molds, the sheet is not sucked in a state where the periphery of the sheet is sandwiched between the pair of split molds. In this case, it is possible to improve the formability of the peripheral edge of the sheet, and after clamping the pair of split molds, the sheet is molded to some extent by the first shaping and is applied to the surface of the cavity. In addition, since the sheet is secondly shaped by pressurization, it is possible to form a fine grained pattern or the like on the sheet surface in combination with being capable of being molded at a higher pressure than suction. At that time, by clamping the pair of molds, the annular protrusion provided on the periphery of the cavity of one mold presses the sheet toward the cavity of the other mold. Since the annular portion of the sheet corresponding to is at least thinned, it is possible to use this thinned portion without using a separate cutting device and jig, and to use the thinned portion for the burr portion outside the annular portion and the product portion inside the annular portion. Can be separated from each other, and an improvement in molding efficiency can be achieved.

Although the embodiments of the present invention have been described in detail above, various modifications and alterations can be made by those skilled in the art without departing from the scope of the present invention. For example, in the present embodiment, the sheet-like parison P is pushed and cut off by the tip of the annular protrusion through the mold clamping, but the present invention is not limited thereto, and the annular protrusion through the mold clamping is not limited thereto. The sheet-shaped parison P is thinned by the tip of the sheet, and after the molding of the sheet-shaped parison P by pressurization, the sheet-shaped parison P is formed using a thin-walled portion formed in an annular shape after the mold is opened. Without using the burr, the burr may be efficiently separated manually. In this case, the pinch-off portion, which is an annular projection, is provided so as to be movable forward and backward in the mold clamping direction with respect to the mold provided with the pinch-off portion, and the thin portion of the sheet is adjusted by adjusting the amount of movement of the pinch off portion in the mold clamping direction. The thickness may be adjusted.
Further, in the present embodiment, the sheet-shaped parison has been described as being formed, but the present invention is not limited thereto, and a sheet obtained by extrusion molding or the like in advance is cut into an appropriate size and then heated with a heater or the like. A sheet of a thermoplastic resin material in a molten state that is heated to a molten state may be used.
Further, in the present embodiment, when the sheet-like parison P is sucked, the annular outer frame of one mold is moved toward the other mold until it contacts one surface of the sheet. Instead, one mold itself may be moved toward the other mold until the tip of the annular projection of one mold contacts one surface of the sheet.
Furthermore, in the present embodiment, the case where the sheet is sucked while being pressed after the mold is clamped has been described, but the present invention is not limited thereto, and the sheet may be simply pressed.

  It is a schematic side view of the shaping | molding apparatus which concerns on embodiment of this invention.   In the shaping | molding apparatus which concerns on embodiment of this invention, it is a figure similar to FIG. 1 which shows the state by which the sheet-like parison P was arrange | positioned between division molds.   In the molding apparatus which concerns on embodiment of this invention, it is a figure similar to FIG. 1 which shows the state which moves the outer frame of a division mold toward the sheet-like parison P. FIG.   In the shaping | molding apparatus which concerns on embodiment of this invention, it is a figure similar to FIG. 1 which shows the state which attracts | sucks the sheet-like parison P. FIG.   In the molding apparatus which concerns on embodiment of this invention, it is a figure similar to FIG. 1 which shows the state which clamped the division mold.   In the molding apparatus which concerns on embodiment of this invention, it is a fragmentary figure around the pinch-off part which shows the state which thins the sheet-like parison P by mold clamping of a division mold.   In the molding apparatus which concerns on embodiment of this invention, it is a figure similar to FIG. 1 which shows the state which open | released the split mold.

P sheet-like parison PL parting line 10 molding device 12 extrusion device 14 mold clamping device 16 hopper 18 cylinder 22 hydraulic motor 24 accumulator 26 plunger 28 T die 30 roller 32 split mold 34 extrusion slit 116 cavity 200 first sealed space 202 Thin part 204 Second sealed space

Claims (8)

A molding method using one sheet,
Positioning a sheet of molten thermoplastic resin material between a pair of split molds in a form that protrudes from an annular protrusion provided at the periphery of the cavity of one mold of the pair of split molds When,
Forming a first sealed space between a cavity of one mold and one surface of the sheet facing the cavity;
Suctioning the sheet from the cavity side of one mold through the first sealed space to press the sheet against the cavity and performing a first shaping;
The pair of split molds are clamped by moving the other mold and one mold close to each other until the annular portion of the sheet corresponding to the tip of the annular projection hits the cavity of the other mold. And the stage of
In the mold clamping step, the sheet is pressed from the cavity side of the other mold through a second sealed space formed between the cavity of the other mold and the other surface of the sheet facing the cavity. By pressing the sheet against the cavity of one mold and performing the second shaping,
A molding method characterized by comprising: The mold clamping step includes the step of thinning the annular portion of the sheet corresponding to the tip of the annular projection by the tip of the annular projection,
The molding method according to claim 1, further comprising a step of cutting a thin portion of the sheet after the second shaping step.         2. The molding method according to claim 1, wherein the clamping step includes a step of pressing and cutting off an annular portion of the sheet corresponding to the tip of the annular projection by the tip of the annular projection. The annular protrusion is provided so as to be movable forward and backward in a clamping direction with respect to one mold provided with the annular protrusion.
The molding method according to claim 2, wherein the thickness of the thin portion of the sheet is adjusted by adjusting an advancement / retraction amount of the annular protrusion in the mold clamping direction. The annular protrusion is provided so as to be movable forward and backward in a clamping direction with respect to one mold provided with the annular protrusion.
The molding method according to claim 3, wherein the separation / adjustment of the sheet is adjusted by adjusting an advance / retreat amount of the annular protrusion in a mold clamping direction.         The step of forming the first sealed space includes a step of moving one mold toward the other mold until a tip of an annular protrusion of one mold hits one surface of the sheet. The forming method according to 1.         In the step of forming the first sealed space, an annular outer frame that is externally fitted to the periphery of one mold so as to be movable forward and backward in the mold clamping direction is moved toward the other mold until it contacts one surface of the sheet. The molding method according to claim 1, comprising steps.         The molding method according to claim 1, wherein in the second shaping step, the sheet is sucked through the first sealed space while the sheet is pressurized through the second sealed space.

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