JPH106390A - Blow molding method and apparatus - Google Patents

Abstract

(57) [Problem] To provide a molding method and an apparatus for partially controlling the thickness of a synthetic resin hollow molded product without leaving appearance defects on the inner and outer surfaces of the molded product. SOLUTION: A cooled roll surface is brought into contact with at least one of inner and outer surface portions of a parison extruded from a die to partially cool a roll contact portion of the parison and then close a mold. A blow molding method for performing blow molding, and a blow molding apparatus, wherein a cooling roll is arranged between a die and a blow molding die so as to be able to contact at least one surface portion inside or outside of a parison extruded from the die. .

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 and a blow molding apparatus using a synthetic resin for preventing partial thickness deviation.

[0002]

2. Description of the Related Art As a problem of a blow molded product (hollow molded product) made of a synthetic resin, there is an unevenness in thickness distribution.
This is because, at the time of blow molding, the portion to be stretched is different between the portions of the molded product, so that there are portions that become thinner and portions that become thicker. In general, a thin portion of a product causes defects such as strength, durability, and appearance, and various methods for preventing the thinning have been considered. For example, a method in which the shape of a molded article is made into a shape close to a sphere so that the stretch ratio is constant, a method in which the overall thickness is increased to increase the minimum thickness of the product, and a shape of a parison (for example, a horizontal section) The method of changing the width of the slit of the die head to control the thickness of the parison in the vertical direction is performed.

[0003] However, these methods have a new problem that shape restrictions and an increase in product weight (compared to a uniform thickness molded product) cannot be avoided. In order to solve such a problem, Japanese Patent Application Laid-Open No. 51-14461 discloses a method in which, before blow molding, a parison portion corresponding to a local part where a thin wall is generated is cooled by blowing air from outside in advance.
A method and an apparatus have been proposed in which molding is performed while making it harder to stretch than other parts. However, in the case of JP-A-51-14461, when the air is blown to the outer surface of the soft parison, the surface of the parison is partially blown and dents and grooves are easily formed, and wrinkles are generated on the outer surface due to rapid cooling. There is a problem to do. These phenomena may be eliminated during the blowing process, but in most cases, traces are left on the outer surface of the molded product, resulting in impaired appearance.

In Japanese Patent Application Laid-Open No. 59-201825, a nozzle for spraying fluid is arranged on the inner surface of the parison, and air, carbon dioxide gas, water mist, etc. There has been proposed a method of reducing appearance defects generated on the outer surface of a product by spraying the above gas fluid. However, even in this method, of course, the inner surface of the parison is sprayed with the gas fluid,
The outer surface is also partly blown off and dents and grooves are likely to occur,
It easily remains on the outer surface of the product as it is. Further, the problem that wrinkles occur on the outer surface due to quenching cannot be solved. In particular, in the case of a thin product, the appearance often becomes poor, and this problem cannot be solved. In the case of blow molded products, there are also products that use molded products cut in half, such as pipe joints and cases where they are mounted on cars and used for skiing, etc. .

[0005]

SUMMARY OF THE INVENTION The present invention has been conceived in order to solve the problem of partially controlling the thickness of a molded product. It is an object of the present invention to provide a blow molding method and apparatus for partially controlling the thickness of a molded product without leaving a defective appearance.

[0006]

Means for Solving the Problems The inventors of the present invention have made intensive efforts to solve the above-mentioned problems, and as a result, when extruding from a die in blow molding, or after extruding, a predetermined amount on the circumference of the parison. The present invention was completed by finding that the problem can be solved by contacting the surface of the cooling roll with a part of the parison and partially cooling the parison surely. That is, claim 1 of the present invention relates to a method in which a cooled roll surface is brought into contact with at least one of an inner surface and an outer surface of a parison extruded from a die, and the parison is partially cooled before the mold is formed. A blow molding method characterized by closing and blow molding.

According to a second aspect of the present invention, there is provided a blow molding method in which cooling water is present on the surface of the cooled roll, and water is applied to a portion where the parison is in contact, thereby enhancing the cooling effect. According to a third aspect of the present invention, as the position where the parison is to be partially cooled, a part corresponding to a corner or a side of a molded product which is easily thinned in a mold is intensively selected. It is a molding method. According to a fourth aspect of the present invention, a cooling roll is provided between the die and the blow molding die, the cooling roll being capable of contacting at least one surface portion inside or outside the parison extruded from the die. Blow molding equipment.

Hereinafter, the present invention will be further described. In the blow molding method of the present invention, at the time of extruding the parison from the die, or after extruding, at least one of the inner and outer surface portions of the parison, in particular, the corners of the molded product which is easily thinned in the mold. The cooled roll surface is brought into contact with the portion corresponding to the edge and the side portion, and the parison is partially cooled. Thereafter, the mold is closed and blow-up is performed by blowing air. This ensures a temperature difference between the resin in the low-temperature portion in contact with the cooled roll surface and the resin in the other high-temperature portion, resulting in a difference in the elongation of the parison. In the portions corresponding to the parts and the sides, the thickness of the molded product can be controlled uniformly by avoiding the reduction in thickness.

In the present invention, unlike the method of blowing gas such as air or water mist, even if the surface of the cooling roller is in direct contact or even when the cooling water is further applied, the predetermined portion of the parison is surely formed with a uniform resistance. Can be cooled, so that non-uniform cooling such as deformation of the parison and mist due to spraying as described above does not occur. Also, almost no wrinkles or grooves are generated on the parison surface, and no defective appearance of the product occurs. The cooled roll may be installed on at least one of the inner side and outer side of the parison.However, it is better to provide both at the same position and contact them from both sides to prevent deformation when the parison is thin, or to use a multilayer parison. When the thickness is large, the cooling effect can be enhanced, which is preferable.

[0010] The cooling roll used in the present invention is preferably a free-roll type in which when it is brought into contact with a predetermined surface of the extruded parison, it freely rotates in accordance with the direction of extrusion of the parison. In addition, the shape of the cooling roll surface is made convex or concave according to the parison outer diameter or inner diameter so that the entire surface can easily contact the parison surface, and at the same time, if necessary, it is formed on the parison surface via a spring or adjustment wire. It is desirable to make them contact and separate.

When the cooling roll is installed outside the parison, the cooling roll may be installed by any supporting method between the die and the mold. On the other hand, when it is installed inside the parison, it is preferable to attach it to a hollow pipe protruding from the center end of the die, or to attach it to a support arm of a hollow pipe protruding vertically from the outside below the mold. Further, the cooling roll itself flows cooling water from the outside into the roll through a hollow pipe holding a central axis to cool the entire roll. In this case, by making the roll material porous so that the cooling water oozes from the roll outer peripheral surface,
Water is preferably applied to the portion where the parison has come into contact, which is preferable in that the cooling effect can be enhanced. As a material of such a roll, a sponge made of synthetic resin such as nylon, silicon, urethane or the like or a porous ceramic is preferable, but is not limited thereto. As the synthetic resin for parison applicable to the present invention, any thermoplastic resin such as general-purpose resin such as polypropylene, polyethylene, polystyrene and ABS resin and general-purpose engineering resin such as polycarbonate is applicable, and is not limited.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows the blow molding mold before closing the mold, and FIG. 2 shows the same blow molding mold after closing the mold.
BRIEF DESCRIPTION OF THE DRAWINGS It is the whole longitudinal cross-sectional schematic diagram which shows an example of the blow molding method of this invention. FIG. 3 is an enlarged perspective view showing an example of the cooling roll. 1 and 2, 1, 1 'and 1 "are cooling rolls, 2, 2' and 2" are roll arms, and 3,
3 "is a roll support arm, 4 is a die, 5 is a parison,
6, 6 'are blow molds, 7, 7' are blow mold mounting portions of the molding machine, and 8 is a blow pin. First, in FIG. 1, when the parison 5 is extruded from the die 4, the cooling rolls 1 provided outside the parison between the die and the blow mold are provided.
1 ′, 1 ″ is brought into contact with a part of the surface of the parison 5 to be cooled and extruded between the blow molds 6, 6 ′. Steps may be used, but for parts that need to increase the cooling effect,
It can also be arranged in a two-stage system like 1, 1 'on the left side.

The surface of the cooling roller 1 is brought into contact with a part of the outer surface on the circumference of the extruded parison (a part corresponding to a corner or a side of a molded product which is easily thinned in a mold). The parison 5 which was cooled while being freely rotated, or further cooled while applying cooling water exuding from the surface of the cooling roller, was cooled while descending between the blow molds 6, 6 '. The temperature difference between the resin corresponding to the corners and the sides and the other high-temperature portion is reliably generated, and the elongation of the resin is different. Then, as shown in FIG. 2, the left and right blow molds 6, 6 'are clamped, and air is blown from the blow pin 8 into the parison 5 to blow up, so that the cooled corners and sides are deformed. It is suppressed and not stretched, so that a molded article having a uniform thickness can be obtained without becoming thin.

FIG. 3 is an enlarged perspective view showing an example of the cooling roll used in FIGS. In FIG. 3, the center of the cooling roll has a concave shape so as to easily come into close contact with the outer shape of the parison. The arm 2 is a hollow stainless steel pipe for supplying cooling water from the outside, and a holding pipe 13 branched from the tip thereof is communicated with the central axis of the cooling roll 1 or penetrated by a nylon pipe. The roll 1 is freely rotatable. Inside the roll, a number of holes are provided in the central shaft or the holding pipe 13 so that cooling water from the outside can be supplied to the inside of the roll 1. The material of the roll is preferably a porous sponge or a porous ceramic so that the cooling water can seep to the surface portion, but is not limited thereto.

FIG. 4 shows another modification of the cooling roll.
(A) and (b). In particular, when the roll width is smaller than the diameter of the parison, when cooling from the inside of the flat roll and the parison in FIG. 4A or when applying cooling water, the center of the parison in FIG. A convex roll that is expanded so as to be in close contact with the inner diameter is suitable, but any of them may be used. The adjustment of the contact of the cooling rolls with the parison surface as described above is performed by pulling or loosening the adjusting wires 17, 17 'as shown in FIGS. The cooling water can be applied to all or a part of the cooling water.

FIG. 6 is a schematic vertical cross-sectional view of a whole of a blow mold when a two-stage roller is arranged at four positions in the circumferential direction and a blow mold is blow-molded in a modification of FIG. FIG. 7 is a view taken along the line AA ′ in FIG. Since the corners and sides of the box-shaped product are thinner at the corners and sides, two-stage rolls 1, 1 ", 9, 9" are provided at positions corresponding to the four sides in the vertical direction as shown in FIG. Apply water using. In this case, only the upper and lower parts 1, 1 'near the part corresponding to the product corner of the parison (the upper and lower corners of the box-shaped product)
1 ", 1"'is cooled using a two-stage roll. At the part corresponding to the vertical corner of the parison product (side end in the middle of the box-shaped product), as shown in FIG. The arm
By shrinking the 2 ', 2 "' so as not to contact the parison, it is also possible to use only the single roll of the upper 1,1". In this case, it is desirable that the same control is performed for the roll of 9, 9 ″ in the diagonal direction as well.

FIG. 9 is a modification of FIG. 6 in which the cooling rolls 1, 1 "and the like are arranged inside the parison.
Is a view taken along the line BB ′. Especially chill rolls 1,1 ", 1
This is an example in which the same effect as in FIGS. 6 and 7 can be obtained by disposing 0,10 "inside the parison as a two-stage roll.

FIG. 11 shows a modification of FIG. 9 described above, in which the support arm 3 can be moved up and down from the outside below the mold by rotating devices 21 and 21 'to apply cooling water to the parison. After that, it is lowered under the dies 6, 6 'to close the dies and blow up. In this case, since the cooling roll does not take up space, the mold can be raised, the entire parison can be shortened, and burrs are reduced, so that the yield is improved as compared with FIGS.

FIG. 12 shows an example in which cooling is performed simultaneously from inside and outside of the parison by combining FIGS. 6 and 9. This is effective when the parison is thick and the parison is difficult to cool. However, in this case, the parison may be cooled from the inside and the outside at the same time. However, in some cases, cooling from one side may be stopped, and the parison may be used simply as a pressure receiving roll surface for receiving contact pressure from the other side.

[0020]

The cooling rolls shown in FIG. 3 are arranged in a two-stage manner at four circumferential positions corresponding to the corners of the box-shaped product as shown in FIGS. The upper and lower two-stage rolls are brought into contact only near the part corresponding to the (corner), and the lower-stage roll is brought into contact with the one-stage roll by shrinking the arm of the lower roll at the part corresponding to the side wall of the parison in the product vertical direction. The method of changing the application amount of the cooling water in the vertical direction of the parison is as shown in FIG.
13 (b) and 13 (c) show the measurement results of the wall thickness at each part when a box-shaped product of mm is molded. At this time, the material of the cooling roll was nylon having a width of 50 mm and a typical diameter of 30 mm, and the roll surface was formed into a concave curved surface with a center recessed to 100R as shown in FIG. The molding material used was polypropylene. The horizontal axis of the graph in FIG.
13A shows the distance in the direction of the horizontal arrow A from the center of the left side to the corner of the box-shaped product in FIG. 13A, and shows the wall thickness distribution between the present invention and a conventional blow-molded product without using a cooling roll. Are shown in comparison. FIG. 13 (c) shows the state shown in FIG.
Shows the distance in the direction of the vertical arrow B from the center of the vertical wall to the upper corner of the box-shaped product, and compares the difference in wall thickness distribution between the present invention and a conventional blow-molded product without using a cooling roll. Shown.

In this example, it can be seen that the thickness distribution of the minimum thickness portion corresponding to the corner is thicker than the conventional method. This is because the parison is cooled at the corners and upper and lower corners by cooling with a cooling roll and application of water, and the parison is not stretched much at the time of blow-up, and the corners not cooled by the roll, parts other than the sides are Such a thickness distribution was obtained because the product was stretched into a product. Here, since the thickness distribution is also improved in the direction of the vertical arrow B in FIG.
The cooling effect is greater when the cooling roll is provided in two stages (multi-stage).

[0022]

According to the blow molding method and apparatus of the present invention described above, a large apparatus is not required.
The thickness of the synthetic resin hollow molded article can be partially controlled without leaving appearance defects on the inner and outer surfaces.

[Brief description of the drawings]

FIG. 1 is a schematic vertical cross-sectional view of an entire blow molding die before closing the die, showing an example of the present invention.

FIG. 2 is a schematic vertical sectional view of the entire blow molding die of FIG. 1 after the die is closed.

FIG. 3 is an enlarged perspective view showing an example of a cooling roll.

FIGS. 4A and 4B are enlarged perspective views showing other modified examples of the cooling roll.

FIGS. 5A and 5B are schematic longitudinal sectional views showing examples of adjusting contact of a cooling roll with a parison surface, respectively.

FIG. 6 is a schematic vertical cross-sectional view of the whole in which two-stage rollers are installed in a modification of FIG. 1;

FIG. 7 is a view taken in the direction of arrows A-A 'in FIG.

FIG. 8 is a schematic vertical cross-sectional view of a state in which the lower roll is contracted by a modification of FIG. 6;

FIG. 9 is a view showing a modification of FIG. 6 in which a cooling roll is arranged inside a parison.

FIG. 10 is a view on arrow B-B ′ of FIG. 9;

FIG. 11 is a view showing a modification of FIG. 9 in which the cooling roll 1 is arranged from the lower part of the blow mold.

FIG. 12 is a schematic longitudinal sectional view showing an example in which cooling is performed simultaneously from inside and outside of a parison.

FIG. 13 shows a comparison of the wall thickness distribution between the example and the conventional box-shaped molded product. (A) It is a perspective view which shows the thickness measurement position and direction of a box-shaped molded article. (B) is a graph showing the thickness distribution measurement results of the present invention and the conventional blow molding method of a molded product in the direction of the horizontal A arrow. (C) It is a graph which shows the thickness distribution measurement result of the present invention and the conventional blow molding method of the molded product of the vertical B arrow direction.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cooling roll 2 Arm 3 Support arm 4 Die 5 Parison 6 Mold 7 Molding machine mold attaching part 8 Blow pin 9 Cooling roll 10 Arm 11 Support arm 12 Parting position of molded product 13 Roll holding pipe 14 Tip arm 15 Former arm 16 Spring 17 Adjustment wire 18 Wire pulley 19 Cooling water supply pipe 20 Arm joint 22-27 Cooling roll 28-33 Arm 34-35 Support arm

Claims (4)

[Claims] 1. A cooled roll surface is brought into contact with at least one of an inner surface and an outer surface of a parison extruded from a die to partially cool the parison and then close the mold to blow molding. A blow molding method characterized by the above-mentioned. 2. The blow molding method according to claim 1, wherein cooling water is present on the cooled roll surface, and water is applied to the roll contact portion of the parison to enhance the cooling effect. 3. The blow molding method according to claim 1, wherein the portion for cooling the parison surface is a corresponding portion of a molded product which is easily thinned in a mold. 4. A blow molding apparatus, wherein a cooling roll is arranged between the die and the blow molding die so as to be able to contact at least one surface portion inside or outside the parison extruded from the die. .