JP2000108199A - Method and apparatus for blow molding hollow molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for blow molding without generating residual water in a molding capable of cooling in a short time in the case of blow molding. SOLUTION: In the case of blow molding a resin hollow molding 16, a mold 11 is cooled to cool an outer surface of the molding. Then a mist of 200 μm or less is sprayed plural times from an air blowing nozzle 12 of blowing air toward a center of a hollow cavity 111 by regulating a blowing amount according to a blowing time, thereby cooling an inner surface of the molding 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for blow-molding a hollow molded article made of a resin such as high-density polyethylene, low-density polyethylene, polypropylene, ABS, polyvinyl chloride, and the like, and a blow molding apparatus used for the method.

[0002]

2. Description of the Related Art Conventionally, blow molding, which is known as a method for manufacturing bottles and containers, includes a parison molding process, a mold closing process, a blow process, a cooling / solidifying process, an exhaust process, a mold opening process, It is a multi-stage complicated forming method consisting of each step of the take-out step. In order to perform optimum forming, research is being conducted by theoretical analysis and simulation of each step, in addition to empirical rules.

[0003] In the production of blow molded articles, it is generally important to shorten the molding time to increase the efficiency of the molding cycle and improve the productivity. In the process, evacuation and unloading process, it is necessary to perform sufficient cooling especially to prevent the shrinkage deformation of the molded product when removing the molded product from the mold by shortening the cooling and solidifying process. As a method of forcibly cooling a molded article blown in a mold, a cooling medium is supplied from a parison to the inside of the molded article to forcibly cool the molded article.

[0004]

However, the technique for forced cooling of a molded product obtained by blow molding a parison has the following problems.

When the molding cycle is shortened by forced internal cooling, the amount of water required for internal cooling can be obtained by calculating the heat capacity consumed for internal cooling from the sensible heat and latent heat of vaporization of water. Even if the required amount of water is sprayed by a single mist spraying, the amount of water that exceeds the saturated amount of evaporation becomes water droplets even if the required amount of water is sprayed with a single mist spray. And stay as residual water.

When mist spraying is repeated a plurality of times,
Since the temperature of the blow-molded product decreases each time, if the amount of mist sprayed each time is the same, the amount of saturated evaporation decreases as the number of times increases, the amount of mist that cannot be evaporated increases, and the water drops And remains in the hollow part.

The present invention has been made intensively to solve the problems of the prior art described above,
An object of the present invention is to provide a blow molding method and a blow molding apparatus used for a blow molded article blow-molded with a mold, in which cooling is performed in a short time and there is no residual water after molding.

[0008]

The feature of the blow molding method according to claims 1 to 3 of the present invention which solves the above-mentioned problem is that a parison which is extruded into a tube from a die head and hung down is blown into a hollow cavity of a mold. In blow molding to mold a resin hollow molded product, cool it and take it out of the mold,
In order to cool the molded product blown in the blowing step in the molding die, the outer surface of the molded product is cooled by cooling the die, and while maintaining the inside of the molded product at a predetermined pressure, 200 μm or less is formed in the molded product hollow. After cooling the inner surface of the molded product by discharging air in the molded product as necessary while maintaining the inside of the molded product at the pressure and spraying the cooling mist, stopping the spray of the mist, Next, the process of supplying cooling air and discharging / circulating cooling air in the molded product by performing the blowing of the cooling air and the exhausting of the molded product air in parallel through the position of the blow air blowing port is repeated twice or more. Alternatively, the inner surface of the molded article is cooled.

In the method of the invention described above, the temperature of the parison when the blow air is blown for the blow molding is set at, for example, 18 degrees, at which the resin to be molded easily deforms.
Since the temperature is about 0 ° C., the parison is easily deformed to the shape of the inner surface of the mold by this air blowing, and exhibits a shape following the inner surface of the mold. And in the present invention,
The inside of the parison reaches a predetermined pressure by blowing blow air,
The parison cools the outer surface to a shape following the predetermined shape and sprays a cooling mist into the molded product to cool the inner surface.In this case, the mist spraying and the supply / discharge / circulation of the cooling air are repeated a plurality of times. It is essential to perform the mist spraying each time so as to be equal to or less than the saturated evaporation amount at the volume of the molded product and the temperature at the time of spraying, and to perform air circulation according to the spraying amount. By spraying the mist in this manner, the entire shell wall of the molded article is cooled to about 60 ° C., and no residual water is generated in the molded article. On the other hand, the required amount of water for cooling promotion is sprayed by one mist spraying, or residual water is generated in the molded product if the mist spraying amount in each time is the same even if divided into multiple times I do.

[0010] The pressure increased by blowing the cooling air is:
In the same manner as described above, the air is exhausted to the outside through the pressure holding means such as the relief valve of the exhaust system, and therefore, the supply and exhaust of the differential pressure is performed.

According to the present invention, the steam and warmed air retained in the molded article are exhausted, and the cooling air is blown, so that the cooling proceeds smoothly. Therefore, the hollow molded product can be quickly cooled from the inner and outer surfaces while the parison is deformed according to the shape of the cavity of the mold by the cooling of the mold and the latent heat of vaporization due to mist evaporation, and residual water is removed. Does not occur.

According to a fourth aspect of the present invention, in each of the above aspects, the size of the cooling mist to be sprayed is 10 μm or less, thereby further reducing the possibility that water droplet marks remain on the inner surface of the hollow molded article. Is done.

[0013] The invention of the blow molding apparatus according to claim 5 of the present application is as follows.
What is claimed is: 1. A blow molding apparatus for blow molding a resin hollow molded article, comprising a hollow cavity having a shape of the hollow molded article, and a parison supplied from a blow die head being confined in the cavity. A mold cooling means for cooling the mold, and a blow air blowing nozzle provided to face the inside of the mold to blow blow air for molding into the parison confined in the mold. The nozzle can serve both as a mist spray port for spraying a cooling mist of 200 μm or less into the molded article hollow and a cooling air blowing port into the blow-molded molded article. It has an exhaust port for exhausting to the outside, and the exhaust port is connected to pressure holding means for maintaining the air pressure in the molded product at a predetermined pressure.

The cooling means for molding is usually provided as a jacket-type cooling structure for circulating a cooling medium inside the wall, and water is generally used as a cooling medium.

In the above construction, the blow air blowing nozzle can serve as a blow air blowing port, a cooling mist spraying port and a cooling air blowing port, and has an exhaust port for exhausting air in the molded product to the outside. However, this is an unavoidable configuration when it is not possible to provide an air supply / discharge port to the outside in addition to the blow-in port for the blow-molded hollow molded product. The structure for providing the cooling mist spray port, the cooling air blow port and the exhaust port in the air blow nozzle for the blow molding is not particularly limited, but in the present invention, the inside of the blow air blow nozzle is The air supply path is divided into an air exhaust path, and the air supply path is also used for blowing the blow air and the cooling air, and the tip openings thereof are used as the blow air and the cooling air blowing port and the exhaust port, respectively. can do. The mist spray port can be exemplified by a configuration in which a mist spray nozzle is provided inside a blow air blowing nozzle. Further, the mist spray nozzle can be provided so as to be relatively movable in the axial direction with respect to the blow air blowing nozzle. In this way, it is possible to insert the spray port of the mist spray into the mold so as to preferably give the mist spray. Can be.

Further, in the above configuration, a blow-air blowing nozzle having a mist spray port for spraying a cooling mist and a cooling air blowing port into a blow-molded molded product; In the case of a molded article having a large number of ribs, the exhaust port for exhausting the air to the outside can be separately provided in consideration of the mist circulation passage.

The resin-made hollow molded products blow-molded in this embodiment include various shapes such as a vertical cylindrical shape (cylindrical, elliptical, and long cylindrical) with upper and lower ends closed, a rectangular parallelepiped shape, and a cubic shape. Although not particularly limited, typical examples include a plastic drum, a pallet, a water supply tank, and a kerosene can.

The progress of the process operations of blowing blow air, spraying mist, supplying and discharging cooling air, and exhausting the internal pressure of a molded product can be performed by sequence program control using computer technology or the like.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 This embodiment shows a typical embodiment of the method according to claims 1 to 4 and the apparatus according to claims 5 to 7.

The blow molding apparatus 10 of the present embodiment shown in FIGS. 1 and 2 is for molding a cylindrical container body and a hollow container having a mouth on its upper surface in an inverted state by using a mold 11. FIG. 1 is a longitudinal sectional view showing a closed state of a mold 11 composed of a pair of mold pieces for containing a parison (not shown) supplied from a blow die head (not shown). In the mold 11, a cooling-medium flow path is formed within the thickness of the mold to form a cooling device, but this is omitted because the drawing is complicated.

Reference numeral 12 denotes an air supply / discharge type nozzle (hereinafter, referred to as an "air blowing nozzle"), and an air supply path for blowing blow air and cooling air to a parison confined in the mold 11, and a molding. A mist nozzle 15 for spraying mist is provided inside the air supply passage, while having an air exhaust passage for exhausting air in the product.

The mist nozzle 15 is provided with a plurality of small holes as mist spray holes on the conical tip-end closed wall surface, and sprays mist from the mist spray holes. In addition, these mist spray holes are arranged so that the spray direction of the mist is directed to the center of the figure of the hollow cavity 111 of the mold 11 in combination with the conical shape of the closed wall surface at the tip of the mist nozzle 15. This mist nozzle 15 is 200 μm or less, preferably 10 μm
It is to generate the following mist.

The blow pressure and blow time of blow molding using the apparatus of the present embodiment vary depending on the volume of the hollow molded product and the diameter of the air blowing nozzle 12, and are as follows, for example.

When the size of the mist is 10 μm, in order not to wet the inner surface of the hollow molded article,
Blow time is in the range of 5 to 30 seconds, mist spraying, cooling air supply / discharge / circulation time is in the range of 20 to 90 seconds, and exhaust time is 5 to
It is preferable to set the range to 20 seconds.

Next, the procedure and operation of blow molding by the molding apparatus of this embodiment will be described.

First, the parison is extruded from the blow die head into the opened mold 11.

Next, the mold 11 is closed, the air blowing nozzle 12 is moved upward from below to the air blowing position, and air is blown from the air supply passage of the air blowing nozzle 12 into the parison housed in the hollow cavity. Blow molding. When the inside of the parison reaches a predetermined pressure, the shape follows the inner surface of the cavity of the mold (hereinafter, the parison in this state is referred to as “molded product 16”), blowing of blow air is stopped, and the mist nozzle 15 200 μm or less, preferably 10 μm from the tip of
A mist of μm or less is sprayed so that the mist is in direct contact with the inner surface of the parison. The mist spray amount at this time is
The amount is set to be equal to or less than the saturated evaporation amount with respect to the temperature of the parison in the molded product inner volume. By this mist spraying, the inner surface of the parison is rapidly cooled by a latent heat effect when the mist in contact with the inner surface of the parison evaporates and evaporates. Further, when the mist to be sprayed is particularly 10 μm or less, the mist evaporates at the moment of contact with the inner surface of the hollow molded product, so that an uneven surface is generated on the inner surface of the hollow molded product due to the collision with the hollow molded product. Never.

After the mist spraying is performed for a predetermined time, the spraying is stopped, and then the supply and discharge / circulation of the cooling air is performed while maintaining the internal pressure by the blowing pressure of the air, and the air is circulated inside the hollow molded article. The inner surface of the hollow molded article is further uniformly cooled by circulating air. The mist spray and cooling air supply / discharge
The circulation step is repeated a plurality of times. Thereafter, the pressurized air in the molded product is exhausted to atmospheric pressure, the mold 11 is opened, and the molded product 16 is taken out.

At the time of mist spraying and air supply / discharge / circulation, the exhaust path is connected to a relief valve (not shown) to maintain the inside of the molded product at a predetermined pressure (generally, the pressure at the final stage of blow air blowing). To be maintained.

In parallel with the cooling of the inner surface of the hollow molded article,
The outer surface of the molded product is cooled by the coolant flowing through the coolant passage hole (not shown) of the mold 11.

With the above, the blow molding of this embodiment is completed. Supply (blowing) of air accompanying this series of blow molding,
FIG. 4 shows the procedure of supplying (spraying) and exhausting the mist.

The mist nozzle 15 can be provided in a fixed relation to the air blowing nozzle 12, but can also be provided so as to be relatively movable in parallel. The mist nozzle 15 can also be made to protrude from the opening at the tip of the nozzle 12 to a position indicated by mist spraying.

[0033]

EXAMPLES The apparatus of Embodiment 1 was blow-molded under the following conditions in the following Example 1 and Comparative Examples 1 to 3 to form a resin hollow molded article.

Target material: high-density polyethylene HDPE 8700 <manufactured by Tosoh Corporation> (melt index HLMI = 8.5 g /
10 minutes, density d = 0.949 g / cm ³ ) Blow molded product: cylindrical drum with an inner volume of 100 liter (diameter 40c)
m, height 80 cm, average thickness 5 mm) Blow molding method: Lower blow molding method (based on air blow molding): Extrusion cylinder temperature 190 ° C Mold cooling temperature 23 ° C Injection time 10 seconds Blow pressure 4. 5 kg / cm ² (Method of measuring temperature of blow-molded product) At 90 seconds after the start of mold opening, the temperature of the inner surface of the blow-molded product is measured by thermography (manufacturer: Nippon Avionics Co., Ltd., model TVS).
-2100MKIIST) at five points shown in FIG. 3, and the results of each example are shown in Table 1 below.

Example 1 After 15 seconds from the start of air blowing for blow molding, the air blowing was stopped, and a mist of water (size: 10 μm) was used as a cooling medium on the inner surface of the hollow molded product.
Spraying, mist spraying stop, supply / discharge / circulation of cooling air 11 seconds,
A second 20 g spray, cooling air supply / discharge / circulation 8 seconds, a third 15 g spray, cooling air supply / discharge / circulation 7 seconds, a fourth 5 g spray, cooling air supply / discharge / circulation 5 seconds, and an exhaust time 5 The molding was performed for a total of 70 seconds.

Comparative Example 1 No mist spraying was performed, air was used as a cooling medium on the inner surface of the hollow molded article, and after blowing of blow air was stopped, a cooling time of 70 seconds (total of blowing time 65 seconds and exhaust time 5 seconds) was used. )
Molded.

COMPARATIVE EXAMPLE 2 Mist spraying was not performed, air was used as a cooling medium on the inner surface of the hollow molded article, and after blowing of blow air was stopped, cooling time was 100 seconds (total of blow time 93 seconds and exhaust time 7 seconds). ).

COMPARATIVE EXAMPLE 3 After stopping the blowing of the blow air, the cooling medium on the inner surface of the hollow molded article was changed to water mist (size: 10 μm), mist spraying and air circulation were repeated four times, and the cooling time was 70 seconds ( Blow time 13 seconds, mist spray time 7 seconds, circulation time 6
(Total of seconds and evacuation time of 5 seconds).

The mist spray amount was 60 g each time.

[0040]

[Table 1]

As can be seen from this table, the temperature distribution at a cooling time of 70 seconds by mist spraying shows almost the same temperature distribution as that at a cooling time of 100 seconds by ordinary air molding. Has been shortened.

The generation of residual water is reduced by changing the mist spray amount according to the time of spraying.

[0043]

According to the blow molding method and the blow molding apparatus of the present invention, the outer surface is cooled by cooling the mold and the inner surface is sprayed while the parison is deformed according to the shape of the cavity of the mold. The mist of 200 μm or less comes into contact with the inner surface of the hollow molded product in a high temperature state and is evaporated, so that the mist is rapidly cooled by the action of latent heat of vaporization during the evaporation,
Thus, the hollow molded article can be uniformly and rapidly cooled from the inner and outer surfaces. Therefore, the efficiency of the cooling process can be increased, the molding cycle time can be shortened, and high productivity can be obtained.

[Brief description of the drawings]

FIG. 1 is a vertical sectional front view showing an outline of a configuration of a blow molding apparatus according to a first embodiment of the present invention, particularly showing a positional relationship between a mold and an air blowing nozzle.

FIG. 2 is a vertical sectional side view showing a state in which a mold is opened after exhaustion in a blow molding operation.

FIG. 3 is a diagram showing a temperature measurement point on the inner surface of a blow molded product.

FIG. 4 is a diagram showing an example of an operation procedure relationship between supply and discharge of air and spraying of mist during molding.

[Explanation of symbols]

 10: Blow molding apparatus 11: Mold 111: Hollow cavity 12: Air blowing nozzle 15: Mist nozzle 16: Molded product

Claims (7)

[Claims] In a blow molding, a parison extruded into a tube shape from a die head and hung down is blown in a hollow cavity of a mold to form a resin hollow molded article, and cooled and taken out of the mold. In order to cool the molded product blown in the molding die, the outer surface of the molded product is cooled by cooling the die, and the inside of the molded product is maintained at a predetermined pressure, and the molded product is blown from the position of the blow air blowing port. After spraying a cooling mist of 200 μm or less into the hollow of the molded article, and cooling the inner surface of the molded article by exhausting air in the molded article as necessary while maintaining the inside of the molded article at the above pressure, The process of stopping spraying of mist and then injecting cooling air and exhausting air in the molded product in parallel through the position of the blow air inlet to supply / discharge / circulate cooling air in the molded product is repeated twice or more. There, a blow molding method of a resin hollow molded article, characterized in that cooling by changing the mist spray amount in each time. 2. The blow molding of a resin hollow molded article according to claim 1, wherein the mist spray amount is not more than a saturated vapor amount according to the internal volume of the molded article and the resin temperature at the time of the mist spray. Law. 3. The resin hollow molded article according to claim 1, wherein the supply amount of the cooling air (A) is adjusted so that A ≧ 300B with respect to the mist spray amount (B). Blow molding method. 4. A blow molding method for a resin hollow molded article according to claim 1, wherein the size of the cooling mist to be sprayed is 10 μm or less. 5. A blow molding apparatus for blow-molding a hollow molded article made of resin, comprising a hollow cavity having a molding shape of said hollow molded article, wherein said parison supplied from a blow die head is provided in said cavity. Mold, a mold cooling means for cooling the mold, and a blow air blower provided to face the mold to blow blow air for molding into the parison trapped in the mold. Nozzle, the nozzle having a hollow shape.
A mist spray port for spraying a cooling mist of 0 μm or less can be used as both a mist spray port and a cooling air blow-in port for blow-molded molded products, and has an exhaust port for exhausting air in the molded products to the outside. A blow molding apparatus characterized in that the exhaust port is connected to pressure holding means for maintaining the air pressure in the molded product at a predetermined pressure. 6. The blow-air blowing nozzle provided to face the inside of the mold for blowing blow air for molding into the parison confined in the mold according to claim 5, Combines the mist spray port for spraying the following cooling mist and the cooling air blowing port into the blow-molded molded product, and exhausts the air from the blowing port and the air in the molded product to the outside A blow molding apparatus characterized in that exhaust ports are separately provided. 7. The blow molding apparatus according to claim 5, wherein the mist spray port sprays a mist of 10 μm or less, and the amount of the mist sprayed can be changed each time. .