JP5782859B2 - Blow molding method for soft resin by cold parison method - Google Patents

Description

  The present invention relates to a soft resin blow molding method by a cold parison method in which a parison made of a soft resin is molded into a hollow molded body having a predetermined shape.

For example, blow molding by a cold parison method is mentioned as a method for forming a hollow molded body such as a beverage bottle or an air conditioning duct. In the blow molding, a parison formed in a hollow shape with a resin is softened by reheating in a heating tank, and then plugs are inserted into both ends of the parison, set in a mold, and clamped. By sending pressurized air into the inside of the parison through one plug and inflating the parison in accordance with the cavity shape of the mold, thereby forming a hollow molded body of a predetermined shape from the parison. Yes (see Patent Documents 1 and 2, for example)
The resin used as the material of the parison includes a hard resin and a soft resin, and in the ordinary cold parison method blow molding, the hard resin and the soft resin are handled in the same manner.
The soft resin is a resin having an elastic modulus smaller than 68.6 MPa as measured by a tensile test or a bending test according to ASTM D747 , 638, 882, and the hard resin is ASTM D747 , 638. , A resin having an elastic modulus of 68.6 MPa or more as measured by tensile or bending test according to 882.

JP-A-10-193444 JP 2002-67127 A

When re-heating the parison in a heating tank in the blow molding by the cold parison method, in order to maintain the shape of the parison, the holding rod as a shape maintaining means is heated while being inserted into the parison. Yes. As the material of the holding rod, a metal such as iron or stainless steel is generally used as a hard material having heat resistance at a reheating temperature. As described above, a parison and a soft resin made of a hard resin are used. When the parison made of the same was handled in the same manner, various problems occurred in the parison made of the soft resin.
That is, since the soft resin has a low softening point, it is difficult to take out the softened parison from the heating tank because the softened parison is fused to the surface of the holding rod or is easily deformed. Is likely to be. Furthermore, since the softened parison is so soft that it is easily deformed, it is very difficult to insert plugs at both ends thereof.
The problems relating to the soft resin as described above can be solved by lowering the heating temperature in the heating tank to alleviate the softening of the parison, but if the heating temperature of the parison is lowered, the material of the parison Since the tensile elastic modulus of the soft resin is high, the shrinkage at the time of blow molding increases, resulting in a new problem that the dimensional stability of the obtained molded product is deteriorated.

This invention makes it a subject to solve the said conventional problem, and with respect to the said subject, in this invention, the state which softened the parison which consists of soft resin by reheating to the temperature which can be blow-molded in a heating tank. After installing the plugs at both ends and inserting the mold into the blow mold and clamping the mold, the compressed air is sent to the inside of the parison through the plug to form a parison made of a soft resin. Is a blow molding method for a soft resin by a cold parison method for forming a hollow molded body of a predetermined shape, and when the parison is reheated and softened, at least a surface portion is present inside the parison. A holding rod made of a fluororesin is inserted, and a jig made of a hard material having heat resistance at a temperature at which the blow molding can be performed is attached to both ends of the parison, After the parison is reheated and softened, the plug is attached with the jig attached to both ends of the parison. A molding method is provided.
In general, the soft resin is defined as a resin having an elastic modulus smaller than 68.6 MPa measured by a tensile test or a bending test according to ASTM D747 , 638, and 882.
The jig is formed in a collar shape having a cylindrical main body portion inserted into the parison and a folded portion extending so as to be folded outward from the outer peripheral edge of one end of the main body portion. And the folded portion is provided with a plurality of cut portions along the axial direction of the main body portion, and an end portion of the parison is formed in a holding portion formed between the main body portion and the folded portion. It is desirable to be configured so as to be pinched.

[Action]
In the present invention, the holding rod used as a holding means for holding the shape of the parison when the parison is reheated to a temperature at which blow molding can be performed, and at least the surface portion thereof is made of a fluororesin. Since the softened parison can be prevented from being fused to the surface of the holding rod, the parison is fused to the holding rod at the time of taking out from the heating tank, so that it is not difficult to take out. .
Jigs are attached to both ends of the parison during reheating. Since this jig is formed of a hard material having heat resistance at a temperature at which the parison can be blow-molded, deformation and softening at the temperature during reheating are prevented. Moreover, since the said parison after reheating is made into the state which attached the said jig | tool at the both ends, this parison at the time of taking out from the said heating tank because this jig hold | maintains the shape of this parison. The deformation of the plug can be suppressed, and the plug can be inserted very easily.
The jig is formed in a collar shape by a cylindrical main body part and a folded part extending so as to be folded outward from one outer peripheral edge of the main body part. The main body part and the folded part The end of the parison is inserted into a sandwiching portion formed between the two and the end of the parison is sandwiched by the sandwiching portion, so that the jig can be easily and firmly attached to the end of the parison. be able to. In addition, since the folded portion is provided with a plurality of cut portions along the axial direction of the main body portion, the folded portion is easily bent and radially opened so that the cut portions are widened. The end of the parison can be easily inserted into the holding portion of the jig.

〔effect〕
In the present invention, the soft resin hollow molded body can be blow-molded accurately and easily by the cold parison method.

Explanatory drawing of the state which inserted the holding rod in the parison. Explanatory drawing of the state which attaches a jig | tool to the end of a parison. The sectional side view which shows the state which attached the jig | tool to the end of a parison. The perspective view of a plug. The sectional side view of the state where the plug was attached.

An embodiment embodying the blow molding method for a soft resin by the cold parison method of the present invention will be described.
In the blow molding method for soft resin by the cold parison method, the parison which is an intermediate molded body is formed in a hollow shape by a molding method such as extrusion molding or injection molding, and then the parison is blown in a heating tank in the softening process. After reheating at a moldable temperature and softening, in the expansion molding process, the softened parison is set in a mold, pressurized air is pressed into the inside of the parison, and the internal shape of the mold ( A hollow molded body is obtained by expanding the parison in accordance with the cavity shape.
The parison is made of a soft resin and is mainly formed in a cylindrical shape such as a cylindrical shape. The soft resin is a resin whose elastic modulus measured by a tensile or bending test according to ASTM D747, 638, 882 is smaller than 68.6 MPa , and is soft polyvinyl chloride, polypropylene, polyethylene, styrene elastomer, olefin Examples include elastomers.

As shown in FIG. 1, in the softening step, the parison 1 is prevented from being deformed by softening at the time of reheating by inserting a holding rod 2 therein.
The holding rod 2 includes a rod-shaped core material 3 and a surface portion 4 that covers the entire peripheral surface of the core material 3. The core material 3 is formed of a metal such as iron or stainless steel in order to prevent deformation and softening at the reheating temperature. The surface portion 4 prevents melting, cracking, deformation, and the like at the temperature at the time of reheating, and also prevents the parison 1 made of a soft resin from being fused to the holding rod 2 in a softened state. , Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), perfluoroalkoxy fluororesin (PFA), ethylene tetrafluoride-hexafluoropropylene copolymer (FEP), ethylene It is made of a fluororesin such as a fluorinated ethylene copolymer (ETFE).
As the method for forming the surface portion 4, the surface of the core material 3 is coated or coated with the liquid fluororesin, and the surface of the core material 3 is covered with a cylindrical cover material made of the fluororesin. There are various methods.

As shown in FIGS. 2 and 3, jigs 5 are attached to both ends of the parison 1 in the softening step.
The jig 5 has a cylindrical main body portion 6 and a folded portion extending so as to be folded outward from the peripheral edge of one end side (the outer end side which is the back side in FIG. 2) of the main body portion 6. 7 is formed in a collar shape. The folded portion 7 is formed with a concave groove 8 on the outer surface in the middle thereof, so that the portion of the concave groove 8 is thin. Further, the folded portion 7 is provided with a plurality of cut portions 9 extending along the axial direction of the main body portion 6 from the concave groove 8 to the tip (inner end on the front side in FIG. 2). It has been. And in this jig | tool 5, the clamping part 10 is formed by providing a clearance gap between this main-body part 6 and this folding | returning part 7. FIG.
Since the jig 5 is heated when the parison 1 is reheated in the heating tank, a hard material having heat resistance at the reheating temperature (the temperature at which the parison 1 can be blow-molded). Is formed by. Examples of such a hard material having heat resistance include the metal exemplified in the core material 3 of the holding rod 2, thermosetting resins such as phenol resin, melamine resin, urea resin, diallyl phthalate resin, or fiber reinforced resin. Examples thereof include (FRP) and carbon fiber reinforced resin (CFRP).

In the softening step, the jig 5 is attached to both ends of the parison 1 in advance during reheating, and the parison 1 is attached to the holding portion 10 of the jig 5 by attaching the parison 1 to the parison 1. It is extremely easy and can be done in a short time just by inserting the end.
When the end portion of the parison 1 is inserted into the holding portion 10, the folded portion 7 is provided with a plurality of cut portions 9 and is thin at the portion of the concave groove 8 provided on the outer surface thereof. Therefore, it is easy to bend outward from the groove 8 as a starting point, and it is easy to open radially so that each cut portion 9 is widened. Therefore, it is easy to insert the end portion of the parison 1 into the holding portion 10 and the jig 5 is formed of a hard material as described above. The end portion of the parison 1 is preferably held by trying to restore the original shape from the radially expanded state by the insertion.
Further, a claw 7A is projected on the inner surface at the tip of the folded portion 7, and the claw 7A bites into the end portion of the parison 1 sandwiched by the sandwiching portion 10 and engages with the parison. Hold the end of 1 firmly.

In the softening step, the parison 1 is held by the holding rod 2 by inserting the holding rod 2 in the state where the jig 5 is attached to both ends, and is not shown in the drawing. It is inserted into the tank and reheated and softened to such an extent that it can be blow molded. In the insertion of the holding rod 2, the main body portion 6 of the jig 5 has a cylindrical shape, and the outer end side thereof is opened. Insert inside Parison 1.
Then, after the softening step, the parison 1 is taken out from the heating tank, extracted from the holding rod 2, and then the jig 5 is attached to both ends thereof to the expansion molding step. Migrated.

In the expansion molding step, a plug 11 is inserted into the parison 1 from the outside of the jig 5 attached to one end.
As shown in FIGS. 4 and 5, the plug 11 includes a cylindrical insertion portion 12 having a pressure air introduction hole 13 formed therein, a flange portion 14 having a larger diameter than the insertion portion 12, and The pressure air discharge path 15 communicates with the pressure air introduction hole 13 of the insertion portion 12 and the pressure air introduction path 16 orthogonal to the pressure air discharge path 15.
The plug 11 is inserted so that the insertion portion 12 is inserted into the main body portion 6 of the jig 5. Therefore, the main body portion 6 of the jig 5 is formed so that the inner diameter thereof is substantially equal to the outer diameter of the insertion portion 12 in order to suppress leakage of pressurized air. Further, a packing 17 is mounted on the outer peripheral surface of the insertion portion 12, and the seal 17 seals between the main body portion 6 and the insertion portion 12, so that leakage of pressurized air is effectively prevented. It is suppressed.
A blind plug (not shown) is inserted into the other end portion of the parison 1 so as to close the opening of the body portion 6 of the jig 5 and is preferably inflated by pressurized air.
The parison 1 is placed in a state where a plug 11 is inserted into the jig 5 at one end and a blind plug is inserted into the jig 5 at the other end. Thereafter, the mold is clamped, and pressurized air is press-fitted into the inside of the parison 1 from the pressurized air introduction path 16 of the plug 11 so that the parison 1 conforms to the cavity shape of the mold. By expanding, cooling, mold opening, etc., a hollow molded body by cold parison blow molding is obtained.

  In the present invention, in the blow molding by the cold parison method, since the fluororesin is present at least on the surface as the holding rod for holding the soft resin parison when it is reheated, the heated and softened parison is formed on the holding rod. Since the plug for blow molding is easily attached to the parison which is not fused and softened by heating, it can be used industrially.

DESCRIPTION OF SYMBOLS 1 Parison 2 Holding rod 5 Jig 6 Main-body part 7 Folding part 10 Clamping part 11 Plug

Claims (2)

Reheat the parison made of a soft resin whose elastic modulus is less than 68.6 MPa measured by ASTM D 747, 638, 882, or bending test to a temperature at which blow molding is possible in a heating tank. After inserting the plugs at both ends thereof and inserting the mold into the blow molding mold and clamping the mold, by sending pressurized air into the interior of the parison through the plug, A blow molding method for a soft resin by a cold parison method for molding a parison made of a soft resin into a hollow molded body of a predetermined shape,
When the parison is reheated to be in a softened state, a holding rod having at least a surface portion made of a fluororesin is inserted into the parison, and the blow molding can be performed at both ends of the parison. Attach a jig made of a hard material with heat resistance at temperature,
After the parison is reheated and softened, the plug is mounted with the jig attached to both ends of the parison. Molding method. The jig is formed in a collar shape having a cylindrical main body portion inserted into the parison and a folded portion extending so as to be folded outward from the outer peripheral edge of one end of the main body portion. And
The folded portion is provided with a plurality of cut portions along the axial direction of the main body portion,
The blow molding method for soft resin by the cold parison method according to claim 1, wherein an end portion of the parison is sandwiched by a sandwiching portion formed between the main body portion and the folded portion.

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