JP2001315194A - Blow molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a blow molding method capable of preventing the reduction of the wall thickness of a blow molded article by adding simple equipment. SOLUTION: In the blow molding method wherein a parison is held in split molds and pre-blow air is blown in the parison and, thereafter, the split molds are closed to hold the parison and high pressure air is blown in the parison to shape the parison into a predetermined shape, the parison is pushed in the molds by a push-in means during the period from the start of the closing of the molds to the completion thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blow molding method for a thermoplastic resin, and more particularly to a blow molding method for preventing local thinning of a blow molded product.

[0002]

2. Description of the Related Art Conventionally, in order to prevent local thinning of a blow-molded product (that is, to make the thickness distribution uniform), it has been practiced to increase the pre-blow of the parison. It is well known that this method makes it possible to uniform the thickness distribution of the parison even in the concave portion of the mold and to form the product without relatively thinning the thickness of the product. However, even in the method using the pre-blow, the blow molded product has a problem that a difference in wall thickness occurs between a portion where the parison first comes into contact with the mold and a portion where the parison comes into contact with the die later. This is the process of closing the mold,
This is because the parison is crushed, the part of the parison not yet in contact with the mold expands, and the parison itself becomes thin.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a blow molding method which can overcome the conventional disadvantages and can prevent the thickness of a blow molded product from being reduced by adding simple equipment.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, closed the mold while pushing the extra portion of the parison that protruded out of the mold, thereby forming a parison along the shape of the mold. It has been found that by forming a preform, it is possible to prevent the thickness of a blow molded product from being reduced, and the present invention has been completed.

That is, in the first invention of the present invention, the parison is held in a split mold, pre-blowing air is blown into the parison, the split mold is closed to sandwich the parison, In the blow molding method in which high-pressure air is blown into the parison to form the parison into a predetermined shape, the parison is pushed into the mold by a pushing means between the start of mold closing and the closing of the mold. Blow molding method.

According to a second aspect of the present invention, in addition to the blow molding method of the first aspect, the pre-blowing air blown into the parison is controlled and exhausted from the start of closing the mold to the closing of the mold. This is a blow molding method.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The blow molding method of the present invention will be specifically described below. In the blow molding method of the first invention of the present invention, the parison is held in a split mold, and after blowing pre-blown air into the parison, the split mold is closed, the parison is sandwiched, and then the parison is sandwiched. In the blow molding method in which high-pressure air is blown into the parison to shape the parison into a predetermined shape, the parison is pushed into the mold by a pushing means between the start of mold closing and the closing of the mold. Blow molding that reduces the blow-up ratio and prevents thinning of blow-molded products by closing the mold while pressing the excess parison outside the mold into the mold and forming a parison preform that conforms to the mold shape Is the law.

FIG. 1 is an explanatory view of an example of a blow molding method according to the first invention of the present invention, wherein a parison of a thermoplastic resin injected from a die core is vertically divided and opposed to each other. FIG. 3 is a cross-sectional plan view of a pair of blow molding dies that are arranged and freely attached and detached. In FIG. 1 (a), a parison 1 of a thermoplastic resin injected between the blow molding dies 2 and 2 'is installed, and after pre-blowing, the molds 2 and 2' are closed. , Pushing means 3, 3 '
To start pushing the parison 1 into the mold in the direction of the arrow (, '). In FIG. 1 (b), the parison 1 is pressed by the pressing means 3, 3 'while the molds 2, 2' are moved inward (, ') in the horizontal direction to close the molds. 'After pushing it in, return the pushing means (,
') To start. In FIG. 1 (c), the pushing means 3,
3 'is completely returned to the original position, and the molds 2, 2' are closed in the (, ') direction. In FIG. 1 (d),
After closing the molds 2 and 2 ′, high-pressure air is blown into the parison to blow-mold a hollow body having a shape that resembles the internal shape of the molds 2 and 2 ′ (5 is a burr portion). is there.).

In the method according to the invention, the pushing means 3, 3 '
Is a plate or bar having a length corresponding to the product shape. Further, it is preferable that the pushing means be made of a material that does not weld to the parison when it comes into contact with the parison. By using a material that does not fuse with the parison, the pressed preform of the parison becomes closer to the mold shape, thereby reducing the blow-up ratio and preventing the blow molded product from being thinned. As a material of the pushing means, for example, when polyethylene is used as the thermoplastic resin of parison, a plate made of Teflon (registered trademark) is preferable.

The pushing of the parison using the pushing means is as follows.
It must be performed between the start of closing the mold and the closing of the mold. As the timing of pushing the pushing means, in the distance between the molds from the start of closing the mold to the closing of the mold, a method of pressing the mold at an arbitrary distance and performing the return by the distance between the molds,
There is a method based on a mold closing time in which the mold is pushed and returned at an arbitrary time in a period from the start of mold closing to the mold closing. As a method based on the distance between the dies, it is preferable to start the pressing of the pressing means at a distance of 50 to 150 mm and return the pressing means at a distance of 20 to 100 mm. Further, as a method based on the mold closing time, a method is preferable in which the pushing is started by the pushing means 5 to 15 seconds before the completion of the mold closing, and the pushing means is returned 2 to 10 seconds before the completion of the mold closing.

The distance at which the parison is pushed by the pushing means is preferably pushed inside the mold pinch portion in the mold, more preferably 0 to 50 m from the mold pinch portion inner wall.
It is preferable to push it to a distance of m. By doing so, the burr portion can be reduced, and thinning can be prevented.

[0012] The blow molding method according to the second invention of the present invention comprises the following steps:
In the blow molding method of the present invention, when the parison is pushed into the mold by the pushing means between the start of closing the mold and the closing of the mold, the pre-blow air is controlled and exhausted. In this way, the parison internal pressure and the pressing force of the pressing means are balanced, the mold is closed while pushing the extra thickness of the parison out of the mold into the mold, and a parison preform along the mold shape is formed. It is possible to arbitrarily adjust the amount of the resin to be pushed into the mold, so that the blow-up ratio is reduced and the blow-molded product is prevented from being thinned.

FIG. 2 is an explanatory view of an example of the blow molding method according to the second invention of the present invention, in which a parison of a thermoplastic resin injected from a die core is vertically divided and opposed to each other. FIG. 3 is a cross-sectional plan view of a pair of blow molding dies that are arranged and freely attached and detached. In FIG. 2 (a), after the parison 1 of the thermoplastic resin injected between the blow molds 2 and 2 'is set, the lower part of the parison is expanded by an expander, and the parison is pinched by a pre-pinch plate. Is closed and the pre-blow is started (arrow C). In FIG. 2 (b), after the completion of the pre-blow, the control exhaust (arrow C ') is started and the two dies 2, 2' are started.
Is moved inward (, ') in the horizontal direction to start closing the mold, and the pushing of the parison 1 is started by the pushing means 3, 3'. In FIG. 2C, the control exhaust (internal pressure control) is completed, the tension of the parison is reduced by reducing the inner pressure of the parison, the pushing means 3, 3 'is returned to the original position, and the dies 2, 2' are formed. The mold is further closed in the (, ') direction. In FIG. 2D, the closing of the molds 2 and 2 'is completed, high-pressure air is blown into the parison, and a hollow body having a shape that resembles the internal shape of the molds 2 and 2' is blow-molded ( However, 5 is a burr part.).

Here, the controlled exhaust means that the pre-blown air blown into the parison is exhausted by controlling the pressure in the parison and the shape of the parison while corresponding to the mold closing speed.

In the method of the present invention, the control exhaust is performed at an arbitrary timing between the time after pinching by the pre-pinch plate, the time when mold closing starts and the time when mold closing starts after the parison where the parison becomes a closed system is expanded by an expander. Do with. Specifically, the expander is formed in a cylindrical shape, an air exhaust path is provided to the outside of the parison, an opening / closing valve is provided at the end of the exhaust path, and the air in the parison is exhausted by opening and closing the valve.

The opening and closing timing of the valve must be adjusted between the start of closing the mold and the closing of the mold. The control exhaust is performed at a distance between the molds from the start of closing the mold to the closing of the mold. There is a method based on a mold closing time performed by time.
As a method based on the distance between the molds, the distance between the molds is 50-1.
A method of opening the valve at 50 mm and closing the valve at a distance between the molds of 0 to 100 mm is preferred. In addition, as a method based on the mold closing time, it is preferable to open the valve 1 to 5 seconds after the pinch and close the valve 3 to 15 seconds after the pinch.

By controlling and exhausting the pre-blow air, it is possible to balance the internal pressure of the parison and the pressing pressure of the pressing means and adjust the excess thickness to be pressed into the mold, thereby preventing the blow molded product from being thinned. Can be.

The blow-molded article obtained by the blow-molding method of the present invention, even if it has a complicated shape, can prevent the thinning of the portion corresponding to the concave portion and the projecting portion of the mold, and can provide a uniform thickness. The thickness can be maintained, and a product with improved strength can be obtained.
The effect is particularly remarkable in gasoline tanks and the like.

The thermoplastic resin used for the body of the blow-molded article of the present invention includes polyethylene, polypropylene, polybutene-1, polystyrene, polyvinyl chloride, polyamide, polyacrylonitrile, polycarbonate, and ethylene-vinyl acetate copolymer. , Polyphenylene oxide, polyacetal, polyarylene sulfide, ethylene-propylene rubber, ethylene-butene rubber, ethylene-octene rubber, ethylene-propylene-
Blow-moldable thermoplastic resins such as diene rubber, styrene-ethylene-butene-styrene rubber, and styrene-ethylene-propylene-styrene rubber can be used.
Mixing more than one kind of thermoplastic resin, silica, mica,
Fillers such as talc and calcium carbonate, or plasticizers,
Those containing a stabilizer, a colorant, an antistatic agent, a flame retardant, a foaming agent and the like as required can also be used.

[0020]

The present invention will be described more specifically below with reference to examples and comparative examples. Example 1 A high-density polyethylene (HB214R manufactured by Nippon Polychem) was used using a large blow molding machine (NB30 manufactured by Japan Steel Works).
W) was used to blow-mold a flat hollow body of 600 × 500 × 80 (mm) (FIG. 3). Parison 210
After injection at ~ 220 ° C and pre-blowing, the parison is closed, and the parison is pushed into the pinch portion of the mold by means of a Teflon plate-like material 7 seconds before the mold closing is completed, and the mold closing is completed. The pressing means was returned two seconds before, the mold was closed, and then high-pressure air was blown to obtain a blow-molded product.
The thickness of the general surface (10 in FIG. 3) and the thickness of the corner portion (11 in FIG. 3) of the obtained blow molded product were measured. Table 1 shows the results.

Example 2 A blow-molded product was obtained in the same manner as in Example 1 except that the control exhaust of the pre-blow air was started 3 seconds after pinching and stopped after 7 seconds. The thickness of the general surface (10 in FIG. 3) and the thickness of the corner portion (11 in FIG. 3) of the obtained blow molded product were measured. Table 1 shows the results.

Comparative Example 1 A blow-molded product was obtained in the same manner as in Example 1, except that the parison was not pushed by the pushing means. General surface of the obtained blow molded product (10 in FIG. 3)
And the thickness of the corners (11 in FIG. 3) were measured.
Table 1 shows the results.

[0023]

[Table 1]

As is apparent from Table 1, according to the blow molding method of the present invention, the thickness on the general surface was reduced, and the thickness of the corners was increased, so that the product thickness was made uniform.

[0025]

According to the blow molding method of the present invention, it is possible to prevent a local thinning of a blow molded product by adding simple equipment, and the effect is remarkable especially in a gasoline tank and the like. Yes, it is an industrially useful technology.

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating an example of a blow molding method according to a first invention of the present invention.

FIG. 2 is a diagram schematically illustrating an example of a blow molding method according to a second invention of the present invention.

FIG. 3 is a perspective view of a blow molded body according to an example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 parison 2, 2 ′ mold 3, 3 ′ pressing means 4, 4 ′ mold pinch portion 5 burr 10 general surface of blow molded product 11 corner portion of blow molded product

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Koichiro Hayashi 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Katsuyuki 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F Term (reference) 4F208 AG07 LA01 LB01 LG23 LG38 LH18 LN01

Claims (3)

[Claims] 1. A parison is held in a split mold, pre-blown air is blown into the parison, the split mold is closed to sandwich the parison, and then high-pressure air is blown into the parison. A blow molding method for shaping a parison into a predetermined shape by pressing a parison into a mold by a pushing means from the start of mold closing to the closing of the mold. 2. The blow molding method according to claim 1, further comprising the step of performing controlled exhaust of pre-blown air blown into the parison from the start of closing the mold to the closing of the mold. Molding method. 3. The blow molding method according to claim 1, wherein the pressing means does not fuse with the parison when the pressing means comes into contact with the parison.