JPH10244582A - Rib-forming blow molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a rib normal to the surface of a parison under the condition that the surface is prevented from sinking by a method wherein a rib-forming blade is projected within the range not coming into contact with its opposite side parison so as to blow high pressure air in a mold in order to fill the interior of the mold and, at the same time, the rib-forming blade is retreated. SOLUTION: When a parson P is pinched between both molds 8 and 8, a rib-forming blade 20 is projected within the range that the parison P at the tip part of the rib-forming blade does not come into contact with the rear surface of its opposite side parison. At this time, the rib-forming blade 20 is normal to the molding surface of the mold. After the molds are closed, high pressure sir is blown in the parison P so as to fill the interior of the molds and, at the same time, gradually retreat the rib-forming blade 20 in the mold 8. As a result, two sheets of rib portions bent in a U-shape projected in the hollow part of the parison P are fused into an integral body by means of the pressing force of the high pressure air applied to both the sides of the rib portions so as to be formed normal to the surface of the parison P. In addition, since the tip part of the rib does not abut against the rear surface of the opposite side parison P, no sink mark develops in the opposite side parison.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rib forming blow molding method in which a reinforcing rib is formed inside a hollow portion of a parison, and more particularly, to a rib forming for preventing the occurrence of sink marks due to the rib forming on the outer surface of the parison. The present invention relates to a blow molding method.

[0002]

2. Description of the Related Art In blow molding for producing a hollow resin product from a parison injected or extruded into a cylindrical shape from a die head, a parison is injected or extruded from a die head, and a pre-blow is applied to a parison formed into a bag by a parison pinch. Line, inflate it slightly, put it in an open mold, close the mold, evacuate the gas in the cavity formed by the mold and the parison, and then vacuum pump the device through a small air vent hole to the mold surface Then, high-pressure air is blown into the parison to form the parison into a predetermined shape based on the cavity, and the parison is cooled with a mold to complete the molding. In this way, the molded resin product is opened and taken out. FIG. 3 shows a conventional blow molding machine. FIG. 3 shows a so-called side-feed type blow molding machine 1 that supplies molten resin from one side of the die head 2, and the resin in a high-temperature molten state pressed by the injection device 4 is supplied to the resin supply port 2 a. Through the annular passage provided between the die head 2 and the mandrel 3 and discharged from the annular space passage 7 at the lowermost end to form a parison P. A passage 2b and a valve 5 (or plug) provided outside the passage 2b are disposed at a position 180 ° away from the resin supply port 2a of the die head 2. The core 3a is connected to a paricon rod 6a penetrating the mandrel 3, and is slightly advanced and retracted in the vertical direction by the operation of the paricon cylinder 6, and a gap (gap) in the annular space passage 7 is used to control the thickness of the parison P. ) Can be adjusted. Conventionally, a method of forming a reinforcing rib in a hollow portion by using such a blow molding machine to improve product rigidity of a molded product has been performed. In this method, as shown in FIG. 4, a rib-forming blade which is movable forward and backward is provided so as to protrude from the mold surface, and the parison is moved forward and backward while projecting in the parison direction while scissoring the parison with a mold. The portion is brought into contact with and fused to the back surface on the opposite side of the parison to form a rib crossing the parison hollow portion as shown in FIG.

[0003]

However, in such a conventional rib forming blow molding method, the reinforcing strength of the hollow molded product is improved by forming the rib, but at the same time, the rib tip comes into contact with the opposite side of the parison. For example, as shown in FIG. 5, sinking occurs on the outer surface of the parison on the opposite side, resulting in a problem that the appearance is significantly impaired and the product value is reduced. That is, the advance / retreat timing of the rib-forming blade at the time of blow molding is delicate, and there is a problem that wrinkles are formed on the surface of the molded product, a stable product cannot be obtained continuously, and reproducibility is poor. In order to overcome this problem, as shown in FIG. 6, a rib forming method in which the tip of the rib does not abut against the back surface of the opposite parison has been considered as a countermeasure for preventing surface sink, although the effect of enhancing the reinforcing rigidity is somewhat inferior. However, in this method, since the rib does not abut on the opposite side parison, as shown in FIG. 7, the rib falls down to one side while being soft during molding, and the reinforcing effect due to the rib formation is further reduced. There was a problem.

[0004]

In order to solve the above-mentioned problems, in order to produce a molded article having no ribs on its surface and having ribs formed in a hollow portion at right angles to the parison surface, According to the present invention, a rib for forming a hollow product in which a parison discharged from an annular resin passage between a die head and a core attached to a lower end of a mandrel is sandwiched between a pair of left and right molds and a rib is formed inside. In a forming blow molding method, when the mold is closed and the parison is sandwiched between both molds, the mold is closed at least until the mold is completely closed as long as the parison at the tip of the rib forming blade does not abut against the back surface of the opposite parison. The rib forming blade is projected at right angles from the mold forming surface, and after closing the mold, high-pressure air is blown into the parison to fill the inside of the parison, and the protruding rib forming blade is inserted into the mold. And to form a rib on the hollow molded article is gradually retracted.

In the second invention, the rib forming blade is heated to the softening point or melting point of the molding resin before the mold is closed, and the rib forming blade is heated before the mold closing is started or simultaneously with the mold closing operation. The rib-forming blade is projected from the mold-forming surface at a right angle, and the rib-forming blade is gradually retracted into the mold while cooling the mold while blowing the high-pressure air into the parison. The two rib portions bent in a U-shape were fused and integrated into the parison inside the parison by projecting the blade to form ribs.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, when the mold is closed and the parison is sandwiched between the two dies, the parison at the tip of the rib forming blade does not contact the back surface of the opposite parison.
At least until the mold closing is completed, the rib forming blade is projected at a right angle from the mold molding surface, and after closing the mold, high-pressure air is blown into the parison to fill the inside of the parison, and the rib formation is projected. The blade is gradually retracted into the mold to form a rib inside the hollow molded product, so that two U-shaped bent rib portions protruding into the parison hollow portion receive high pressure air received from both sides. It fuses and integrates with the pressing force, and is formed perpendicular to the parison surface without falling. In addition, since the rib tip does not abut on the back surface of the opposite parison, sink does not occur on the surface of the opposite parison.

In the second invention, the rib-forming blade is heated to the softening point or the melting point of the molding resin before the mold is closed, and the rib-forming blade is heated before the mold closing or simultaneously with the mold closing operation. The rib-forming blade is projected from the mold-forming surface at right angles, and the high-pressure air is blown into the parison, and while cooling the mold, the rib-forming blade is gradually retracted into the mold. Two ribs bent into a U shape inside the parison by fusion are fused and integrated to form a rib. As the mold cools, the rib also solidifies quickly and the rib can fall down The strength is further reduced, and a strong rib perpendicular to the surface is formed.

[0008]

Embodiments of the present invention will be described below in detail with reference to the drawings. 1 and 2 relate to an embodiment of the present invention. FIG. 1 is an overall vertical sectional view of a blow molding machine, and FIG. 2 is an explanatory view showing an operation procedure of a blow molding method. In FIG. 1, a pair of left and right dies 8 and 8 are disposed below and below a die head 2 of a blow molding machine 1 so as to be able to freely contact with and separate from each other. A pinch device (not shown) for binding is arranged.

On the other hand, a portion of the mold 8 facing the cavity surface is provided with a medium passage 8a through which a cooling medium for cooling the cavity surface of the mold 8 passes, and is connected to a medium supply device (not shown). In addition, a flat rib-forming blade (also referred to as a blade) 20 is provided, which is horizontally movable in a space provided through the mold 8 from the outer surface of the mold 8 perpendicularly to the mold cavity surface. The air cylinder 22 is connected to a piston rod 22a of the air cylinder 22 so that the air cylinder 22 can move forward and backward.

A heater 24 for heating the rib-forming blade 20 is disposed on the outer periphery of the rib-forming blade 20 so as to be integrated with the rib-forming blade 20, so that the heater 24 can be heated to a desired temperature. Have been. Alternatively, a heater may be embedded inside the rib forming blade 20. In the mold 8, a plurality of vent holes (not shown) for penetrating into the mold cavity and discharging air in the mold cavity are arranged at appropriate intervals. Further, in order to positively suck the air discharged from these vent holes, a collecting duct is provided so as to cover the outside of the mold 8, and an exhaust pipe provided with a solenoid valve and a suction fan is provided. Alternatively, the mold 8 may be made of a metal provided with countless fine vents, that is, a porous metal, instead of the vent holes.

[0011] The blow pressure of the blow after the mold is closed completely eliminates air between the mold cavity and the surface of the parison P that comes into contact with the mold cavity, and air remains between the two to generate air bubbles on the surface of the molded product. Pressure is set to at least 1 kgf / cm ² in order to prevent transfer failures caused by the formation of

When the parison P is an ABS resin, the parison P is set to about 220 ° C.
Close the mold as ℃. The heating temperature of the rib forming blade 20 is set to 130 ° C. which is equal to or higher than the softening point temperature of the resin (the ABS resin Vicat softening point is 75 to 125 ° C.). Various oils, water, pressurized water (steam) and the like are used as a medium for controlling the mold temperature.

The operation of the rib forming blow molding method of the present invention in the blow molding machine 1 configured as described above will be described with reference to FIG. First, the parison P is discharged from the lower end of the die head 2 by the injection device 4 or the like while holding both the dies 8, 8 in the mold open state. Thereafter, after the parison P is hung down and stopped, the upper and lower ends of the parison P are bound by a pinch device.

Next, before the mold closing operation, the heater 24 is energized to heat the forming blade 20 to a predetermined temperature. If the molding resin is an amorphous resin, the predetermined temperature is set to a softening temperature or a glass transition point. If the molding resin is a crystalline resin, the predetermined temperature is heated to a melting point or higher, and the air cylinder 24 is driven in advance. The rib forming blade 20 in the retracted state is advanced in the mold 8 or advanced together with the mold closing operation to close the molds 8 and 8 (state a in FIG. 2). That is, when the mold is closed and the parison is sandwiched between the two molds 8, 8, at least until the mold is completely closed, as long as the parison P at the tip of the rib forming blade 20 does not contact the back surface of the opposite parison P. The rib forming blade 20 is projected perpendicularly from the mold forming surface.

A blow pin (not shown) is inserted into the parison P, and high-pressure air is blown to bring the parison P into close contact with the mold cavity surface to enhance transferability. The blade 20 is gradually retracted during the blowing of the high-pressure air (the state b in FIG. 2 →
c), the space between the two bent parisons P after the blade 20 retreats is pinched by the pressing force of the high-pressure air, and this space is crushed and is in contact with the heated blade 20 2 Since the inner surfaces of the parisons are heated and are in a molten state, the two parisons are fused and integrated to form ribs that strengthen strong reinforcing rigidity.

Thereafter, a cooling medium is passed through the medium passage 8a of the mold 8, and the mold cavity surface of the mold 8 is rapidly cooled, so that the parison P is cooled and solidified, and the formed rib R is also solidified. Thus, a strong rib R perpendicular to the parison surface is formed. Further, since the rib tip does not abut on the opposite parison P, the surface of the opposite parison does not have sink marks as in the conventional method, and a blow-molded article with a beautiful appearance is completed.

If the blade 20 is formed of a heat insulating material such as a heat-resistant resin or ceramic, or the blade surface is covered with the heat insulating material (for example, Teflon or polyimide film), Because the latent heat of Parison P delays the transfer to blade 20,
The blade heating temperature of the heater 24 can be lowered, which is economical. Preferably, the blade surface has a surface on which the parison P is slippery, such as, for example, Teflon, and when coated with a material having low wettability with resin, the retreating operation of the blade 20 proceeds smoothly, and the rib R This is convenient because it is less likely to fall.

[0018]

As described above, in the present invention,
Since there is no sink mark on the surface and strong ribs protruding into the hollow portion at right angles to the parison surface can be formed, an excellent rib-formed blow molded product having high reinforcing rigidity can be obtained.

[Brief description of the drawings]

FIG. 1 is an overall vertical sectional view of a blow molding machine according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an operation procedure of a blow molding method according to an embodiment of the present invention.

FIG. 3 is an overall vertical sectional view of a conventional blow molding machine.

FIG. 4 is a schematic perspective view of a rib forming blade.

FIG. 5 is a perspective view of a conventional rib-formed blow molded product.

FIG. 6 is a perspective view of another conventional rib-formed blow molded product.

FIG. 7 is a perspective view of a conventional rib-formed blow molded product.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 blow molding machine 2 die head 2 a resin supply port 3 mandrel 3 a core 4 injection device 5 valve 6 paricon cylinder 6 a paricon rod 7 annular space passage 8 mold 8 a medium passage 20 rib forming blade 22 air cylinder 22 a piston rod 24 heater H sink P parison R rib

Claims (2)

[Claims] 1. A hollow product having ribs formed therein by sandwiching a parison discharged from an annular resin passage between a die head and a core attached to a lower end of a mandrel by a pair of left and right molds. A rib forming blow molding method, in which, when the mold is closed and the parison is sandwiched between both molds, at least until the mold is completely closed as long as the parison at the tip of the rib forming blade does not abut against the back surface of the opposite parison. The rib forming blade is projected perpendicularly from the mold forming surface, and after closing the mold, high-pressure air is blown into the parison to fill the inside of the parison, and the protruding rib forming blade is inserted into the mold. A rib forming blow molding method in which a rib is gradually retracted to form a rib inside a hollow molded product. 2. A rib-forming blade is heated to the softening point or melting point of the molding resin before the mold is closed, and the rib-forming blade is moved from the mold molding surface before the mold-closing starts or simultaneously with the mold-closing operation. The rib-forming blade is projected at a right angle, and the high-pressure air is blown into the parison, and the rib-forming blade is gradually retracted into the mold while cooling the mold.
2. The rib forming blow molding method according to claim 1, wherein the rib is formed by fusing and integrating two rib portions bent in a U-shape inside the parison by projecting the rib forming blade.