JPH05309725A - Manufacture of deformed hollow molded piece - Google Patents

Abstract

PURPOSE:To provide a manufacturing method for a deformed hollow molded piece having a uniform wall thickness by a method wherein the wall thickness is prevented from being biased in the hollow molded piece having a deformed sectional shape like a square shape. CONSTITUTION:When a hollow molded piece 10 is molded in a blow molding die 2 by blowing pressure fluid into a closed-end cylindrical parison 1 of thermoplactic resin of which temperature is controlled, blow molding is performed by expanding a diameter of the parison 1 by extruding a projected part 31 toward an inner wall of the parison 1 just before blowing the pressure fluid into the parison 1, or simultaneously when blowing in, or just after blowing in by using a parison diameter expander 3 having a projected part 31 which is inserted from an opening part of the parison 1 and made expandable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a modified hollow molded article.

[0002]

2. Description of the Related Art Conventionally, in blow molding, a parison whose temperature has been adjusted to a predetermined resin temperature is supplied into a blow molding die, and a pressurized fluid is blown in the die to expand the parison, so that the parison is expanded. It is pressed against a mold to produce a hollow molded body. In such a blow molding method, when a hollow parison having a bottomed cylindrical shape is used to manufacture a hollow molded body having a cylindrical shape or a shape close to a cylindrical shape, it is relatively easy to manufacture a hollow molded body having a uniform thickness. be able to.

However, in the case of manufacturing a rectangular hollow molding having a rectangular cross section, when a cylindrical bottomed parison is expanded in a mold, the parison first comes closest to the inner surface of the mold. Contact will occur from approximately the central portion of the sidewalls and bottom that are at a distance, then contact will occur with other portions, and finally the corners.

In this case, the parison is cooled from the central portion which first comes into contact with the mold, so that the elongation of the parison in that portion becomes small, resulting in a thick wall. On the other hand, the corners that are far from the center are cooled with a delay, so that the elongation is large and, as a result, the corners are thin. Therefore, in the case of a container in which the hollow molded body has a rectangular cross-sectional shape, there is a problem that only the central portions of the side wall portion and the bottom portion are thick and only the corner portions are thin.

If the wall thickness distribution does not matter,
It is sufficient to make the entire product thicker so that the minimum thickness of the corner can be secured, but in order to secure the minimum thickness of a certain thickness, making the entire product thicker increases the weight of the product. Not only that, but also wasteful materials are used, which is not preferable. Further, depending on the product or application, uniform wall thickness accuracy may be an important required quality.

[0006] Therefore, as a measure for making the wall thickness of the hollow molded body uniform, for example, there is considered a method in which the wall thickness of the parison is made uneven in advance and the portions corresponding to the corners are molded thicker than the other portions. .. However, this method requires a great deal of time and cost and is not practical because it adjusts the parison thickness deviation by trial and error.

Further, for example, the temperature-controlled core is partially brought into contact with the parison, and a low temperature portion is provided at a portion having a high draw ratio such as a corner portion of the molded product to reduce elongation and blow molding to thicken the wall. Method (Japanese Patent Laid-Open No. 60-73830), or by blowing a cooling gas to the corners of the molded article where the draw ratio becomes high to lower the temperature from the surroundings to lower the elongation and blow molding. Method of thickening the wall
No. 22529) is proposed.

However, each of the above methods is a method of partially cooling the parison and lowering the temperature to reduce the elongation to increase the thickness, and is effective for locally increasing the thickness. Even, it is difficult to cool the entire wall thickness to be uniform, and for example, when molding at a temperature close to the glass transition point, such as polycarbonate resin,
When the resin temperature is lowered to near the glass transition point, there is a problem that whitening occurs during stretching, resulting in deterioration of physical properties and poor appearance.

Further, since a crystalline resin such as polypropylene has a blow molding temperature close to its melting point and its ductility is sensitive to the temperature, if the temperature control becomes insufficient, a molded product having a uniform wall thickness will be obtained. Stable molding becomes difficult.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks, and an object thereof is to prevent uneven thickness of a hollow molded body having an irregular cross-sectional shape such as a prismatic shape. Another object of the present invention is to provide a method for producing a modified hollow molded article having a uniform wall thickness.

[0011]

The method for producing a modified hollow molded article according to the present invention comprises a bottomed cylindrical parison of a thermoplastic resin,
When molding a hollow molded product having a polygonal cross-sectional shape in a blow molding die by blowing a pressurized fluid, a parison expanding device having a projecting portion that can be expanded and contracted in the radial direction of the parison is used to open the parison. Before the blowing of the pressurized fluid into the parison, or at the same time as when the pressurized fluid is blown into the parison, the parison is expanded in the radial direction toward the corners of the blow molding die to expand the parison for blow molding. Therefore, the above object is achieved.

The present invention will be described in detail below. In the present invention, examples of the thermoplastic resin used for forming the parison include polyethylene, polypropylene, polybutene, polycarbonate, polystyrene, polyethylene ionomer, ethylene / vinyl acetate copolymer, ethylene / ethyl acrylate copolymer, and chloride. Blow molding of vinyl resin, chlorinated vinyl chloride resin, vinylidene fluoride resin, polytetrafluoroethylene, polyphenylene sulfide, polyamide, polysulfone, polyether sulfone, polyether ketone, acrylonitrile-butadiene-styrene copolymer, polyethylene terephthalate, etc. Any resin that can be used may be used, and these may be used alone, a mixture of two or more kinds may be used, or a laminated product composed of two or more kinds of resins may be used.

If necessary, these resins may be added with reinforcing fibers such as glass fibers, carbon fibers and polyimide fibers, fillers such as talc, calcium carbonate and mica, coloring agents such as carbon black and titanium oxide, and plasticizers. Agents, stabilizers, etc. may be included.

The parison used in the present invention is a hollow molded article molded by bottomed cylindrical injection molding.

The pressurized fluid used in the present invention includes:
A pressurized liquid such as water or oil can be used, but a pressurized gas such as air or nitrogen gas is preferable.

[0016] The pressure of the pressurized fluid, the following clamping force of the blow molding mold, resin properties and product form is used, it is suitably determined by the required quality, the range of 2~300kg / cm ² is preferred.

Prior to blow molding, the parison is preferably preheated within the range of the glass transition temperature to the melting point of the resin used for the parison.

The protrusion of the parison expanding device is extruded toward the corner in the radial direction of the blow molding parison, and the portion corresponding to the corner of the parison and the portion corresponding to the flat surface are formed in the cavity mold. It is preferable to expand the diameter so as to be substantially equidistant from the inner surface and perform blow molding.

[0019]

According to the present invention, since the portions corresponding to the corners of the parison and the flat surface are in contact with the inner surface of the cavity of the blow molding die at substantially the same time and are cooled, the corners and the flat surface of the molded product are The difference in wall thickness from the part is reduced. When the temperature of the protrusion is lower than the temperature of the parison, the parts corresponding to the corners are slightly thicker and contact the mold to cool, but the cooling rate after contacting the mold is slower than the flat part. Therefore, the fluid is easily plastically deformed by the pressurized fluid, the resin moves from the corner portion toward the flat surface portion, the thickening of the corner portion is prevented, and the wall thickness of the corner portion and the flat portion becomes uniform. When the temperature of the protrusion is higher than the temperature of the parison, the part corresponding to the flat part is slightly thick and contacts the mold to cool, but the cooling rate after contacting the mold is slower than the corners. Therefore, it is easily plastically deformed by the pressurized fluid, the resin moves from the flat portion toward the corners, and the thickening of the flat portion is prevented,
The thickness of the corners and the flat surface becomes uniform. Therefore, the obtained modified hollow molded article has a uniform wall thickness.

[0020]

EXAMPLES Examples of the present invention will be described below.

Blow molding die 2 used in the present invention
As shown in FIG. 1, the main part is composed of a pair of cavity mold 21, a pair of mouth mold 22 and a mouth core mold 23.

In FIG. 1, reference numeral 3 denotes a parison expanding device having a cylindrical cross section, and a projecting portion 31 which can be expanded and contracted is accommodated in the side part thereof. The protruding portion 31 is attached to one end of the drive portion 33 of the air cylinder 32.

The parison diameter-expanding device 3 is inserted into the parison 1 with the protruding portion 31 housed therein. Also,
The shape of the protrusion 31 is not particularly limited, but it is preferable that the surface of the protrusion 31 is smoothly processed so that the parison 1 is not damaged, and the contact portion with the parison 1 is rounded.

Further, inside the parison expanding device 3, in order to prevent the temperature from decreasing when the parison 1 comes into contact with the protruding portion 31 and to adjust the elongation of the parison 1,
An electric heater 34 for temperature adjustment may be incorporated.

If heat resistance is required, the material of the protruding portion 31 is preferably metal, ceramic, or the like, and if heat resistance is not so required, thermosetting resin or thermoplastic resin can be used. Is. Also, these materials may be used in combination.

Further, the contact surface between the protrusion 31 and the parison may be subjected to a treatment for preventing adhesion to the parison, for example, a fluororesin coating.

The air cylinder 32, to which the above-mentioned protruding portion 31 is attached, is connected to pipe lines 35 and 36 leading to a drive air pressure source (not shown), and pressurized gas is supplied to the air cylinder 32 through the pipe line 35. By supplying and extending the drive part 33, the protrusion part 31 is pushed out in the radial direction. Further, by supplying the pressurized gas to the air cylinder 32 through the conduit 36 and contracting the drive unit 33,
The protrusion 31 is stored in the original position of the parison diameter-expanding device 3.

The protruding portion 31 is not limited to being driven by the air cylinder 32 described above, and any known method such as an oil cylinder or an electric actuator can be adopted.

A method of manufacturing a hollow molded article having a rectangular cross section according to the present invention will be described with reference to FIGS. 1 and 2.

First, as shown in FIG. 1, the upper end of a cylindrical parison 1 having a bottom, which is adjusted to a temperature suitable for blow molding, is
The parison expanding device 3 is inserted into the parison 1 after being held by the mouth die 22 and the mouth core die 23 and fixed in the blow molding die 2.

Immediately before or simultaneously with the supply of the pressurized fluid into the parison 1 through the injection hole 24,
A portion that supplies pressurized gas to the air cylinder 32 of the parison diameter-expanding device 3 through the pipe line 35 so that the four protrusions 31 provided in the parison diameter-expanding device 3 form the corners of the inner wall of the parison 1. Push in four directions (in the direction of the arrow) toward.
As shown in FIG. 2, the extruded projections 31 expand the diameter of the molten parison 1 from the inner surface. Length to expand,
As for the time, the corner portion 11 and the flat surface portion 12 of the molded body are almost at the same time,
It is appropriately determined so as to come into contact with the inner surface of the cavity mold 21. When the corners 11 of the obtained molded product are thick, the length of diameter expansion is shortened, and when the corners 11 are thin, the length of diameter expansion is lengthened.

Simultaneously with or immediately after the extrusion of the protrusion 31, a pressurized fluid is blown into the inside of the parison 1 through the injection path 24 to expand the parison 1 along the inner surface of the cavity mold 21, and the parison 1 is expanded as shown in FIG. As shown in the cross sections of a) and FIG. 3 (b), the hollow molded body 10 having a square cross section is blow-molded.

The projecting portion 31 stores the parison 1 in the original position of the parison expanding device 3 immediately after expanding the diameter of the parison 1.

Next, after cooling in the blow molding die 2 until the hollow molded body 10 can be taken out, the mouth core mold 23 and the parison expanding device 3 are pulled out from the hollow molded body 10 and the cavity mold is removed. The mold 21 is opened and the hollow molded body 1
By taking out 0, a hollow molded body 10 having a square cross section and a uniform wall thickness can be obtained.

The number of protrusions and the extrusion length are determined according to the shape of the cross section of the hollow molded body and the size of the molded body. For example, when the cross section is a hexagon, six protrusions are used. The pressing device provided may be used.

It is also possible to mold a hollow molded article having a cross-section of an irregular shape such as a pentagon or a rectangle. In addition, by pressing the parison in a molten state from the inner surface to bring the corners into contact with the inner surface of the cavity earlier than the flat surface during cooling for cooling, it is possible to form the wall thickness of the corner thicker than the flat surface. it can.

Further, it is possible to adjust the wall thickness of the molded body by adjusting the pressure for pressing the parison from the inner surface and the clearance between the protrusion and the inner surface of the cavity mold.

(Example 1) Polycarbonate resin ("351-10" manufactured by Sumitomo Nogatak Co., Ltd.) was injection-molded,
A bottomed cylindrical parison 1 (wall thickness 6 mm, outer diameter 90 mm x length 155 mm) was molded. As shown in FIG. 1, the parison 1 was held in the mouth mold 22 and the core mold 23 of the mold 2 having a square cavity of 140 × 140 mm and transferred to the blow molding stage. The parison diameter-expanding device 3 was inserted through the opening. After adjusting the temperature of the parison 1 to 170 ° C., pressurized air is sent to the parison expanding device 3 so that the four protrusions 31 mounted on the parison expanding device 3 are radially moved for 0.3 seconds. 75 mm was extruded and 0.02 seconds passed after the expansion of the diameter of the molten parison 1 was completed, 9 kg / cm ² of pressurized air was blown into the parison 1 to perform blow molding, and the hollow molded body 10 (opening portion) was opened. Square with an outer diameter of 90 mm and a cross section of 140 x 140 mm)
Got

The parison expanding device 3 has an electric heater 34.
The internal diameter of the parison 1 was increased to 130 ° C. by energization to expand the diameter of the parison 1 in the radial direction, and the parison 1 was immediately stored in the original position after the expansion. After roughly cutting the center of one side surface of the obtained hollow molded body 10 in the lateral direction, the thickness of the cut cross section was measured, and the result is shown in FIG.

(Comparative Example 1) A cross section of 14 was obtained in the same manner as in Example 1 except that the extrusion of the protruding portion of the parison expanding device was stopped and the parison was not expanded in the radial direction.
After blow molding a 0 mm square hollow molded article, the wall thickness of the cross section of the molded article was measured, and the results are shown in FIG.

[0041]

According to the present invention, in a hollow molded article having a square irregular cross-sectional shape, it is possible to prevent uneven thickness of the corner portions and the flat portion and to adjust the thickness of the parison. A modified hollow molded article having a uniform wall thickness can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic view showing a parison expanding device inserted into a parison according to the present invention.

FIG. 2 is a schematic view showing a situation in which the diameter of the parison is expanded by pushing out the protrusion of the parison expanding device in the present invention.

FIG. 3A is a vertical cross-sectional view of a hollow molded body, and FIG.
FIG. 4 is a cross-sectional view of the hollow molded body taken along the line AA ′.

FIG. 4 is a graph showing the thickness distribution of the cross section AA ′ in FIG.

[Explanation of symbols]

 1 Parison 10 Hollow Molded Body 2 Mold 21 Cavity Mold 22 Mouth Mold 23 Core Mold 24 Injection Hole 3 Parison Expander 31 Projection 32 Air Cylinder 33 Drive

Claims (1)

[Claims] 1. When molding a hollow molded product having a polygonal cross-sectional shape in a blow molding die by blowing a pressurized fluid into a bottomed cylindrical parison of thermoplastic resin, the parison can expand and contract in the radial direction. Insert the parison expanding device with the projected part from the opening of the parison, and immediately before or at the same time as the pressurized fluid is blown into the parison, the parison is radially directed toward the corners of the blow mold. A method for producing an atypical hollow molded article, characterized in that the parison is expanded in diameter by extrusion and blow molded.