JP2012000817A - Foam blow molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a blow molded plastic material with a high expansion ratio.SOLUTION: Plastic contains a pyrogenic foaming agent. After clamping molds, air in a cavity 4 between a parison 1 and molds 2, 3 is sucked for depressurization as a first step, and at the same time, air is sucked from a blow pin 7 that communicates with an atmosphere into the parison 1, and the parison 1 is expanded to be brought into tight contact with inner surfaces of the molds 2, 3. While continuing depressurization of the inside of the cavity 4, the air in the parison 1 is sucked from the blow pin 7 to depressurize the inside of the parison 1 as a second step. While maintaining depressurized states in the cavity 4 and parison 1, the parison 1 is cooled. The depressurized states are released and the molds are opened to take out a product.

Description

  The present invention relates to a foam blow molding method.

In foam blow molding, plastics mixed with a foaming agent are extruded from an extrusion die, the extruded parison is sandwiched between a pair of molds, and pressurized air is blown into the parison from a blow pin to perform blow molding.
Foaming agents include chemical foaming agents that have a chemical reaction during foaming and physical foaming agents that do not have a chemical reaction. Examples of the former include inorganic carbonates (such as sodium bicarbonate), citric acid, azodicarbonamide, Examples of the latter include aliphatic hydrocarbons, halogenated hydrocarbons, alcohols, ethers, carbon dioxide, nitrogen, water, carbonated water and the like.

The parison begins to foam when extruded from the die of the extruder. In foam blow molding, for example, as described in Patent Document 1, air is blown at a pressure lower than that of normal blow molding, but when the parison is in close contact with the inner surface of the mold, bubbles are generated by the air pressure. There is a problem that the foaming ratio is reduced by crushing (decreasing), and the wall thickness is reduced to 2/3 to 1/2 of the parison before blowing.
On the other hand, in order not to reduce the foaming ratio, instead of blowing in pressurized air, the inside of the cavity between the parison and the mold is sucked to keep the air pressure below atmospheric pressure, and suction inside the parison is started at the same time. For example, Patent Documents 2 to 4 propose air pressures equal to or lower than atmospheric pressure.

JP-A-6-285964 JP 60-11330 A JP 2000-280332 A JP 2001-18283 A

  Since the parison extruded from the die of the extruder is hot and the inner and outer surfaces of the parison are enveloped in high-temperature air, the foamed cells are growing in the parison immediately after extrusion. On the other hand, if the air in the cavity between the parison and the mold is sucked and decompressed after clamping, the hot air around the parison is discharged and adiabatic expansion is performed, so that the temperature of the air around the parison is increased. If the parison expands and closely contacts the inner surface of the mold, the parison surface rapidly cools and solidifies. For this reason, the temperature of the parison after clamping rapidly decreases, and as a result, the increase and growth of the foam cell cease, and the expansion ratio of the parison is sufficiently high despite maintaining the inside and outside of the parison at an air pressure lower than the atmospheric pressure. Does not rise.

  In the foam blow molding method in which the air pressure inside and outside the parison after mold clamping is maintained at atmospheric pressure or lower as described above, the present invention increases the foaming ratio of the parison and, as a result, produces a plastic blow molded article having a high foaming ratio. For the purpose.

The present invention relates to a plastic foam blow molding method, wherein the plastic contains an exothermic foaming agent, and after mold clamping, as a first step, air in the cavity between the parison and the mold is sucked and decompressed, and at the same time, Air is sucked into the parison from the blow pin communicating with the air, and the parison is inflated until it comes into close contact with the inner surface of the mold. And the inside of the parison is decompressed.
In the second stage, the depressurization level inside the parison may be equal to or higher than the depressurization level in the cavity (higher degree of vacuum).

According to the present invention, the plastic contains an exothermic foaming agent, and the inside of the parison is not pressurized to atmospheric pressure or higher once after clamping, and the inside of the parison is decompressed after closely contacting the inner surface of the mold. The foaming ratio can be increased as compared with blow molding without using an exothermic foaming agent.
In addition, by continuing foaming to a certain extent after mold clamping, it is possible to reduce the residue of unfoamed foaming agent. As a result, secondary foaming is less likely to occur, and even when burr or the like is recycled, the foaming ratio or The wall thickness is easy to stabilize.

It is sectional drawing explaining the foam blow molding method which concerns on this invention.

In the foam blow molding method according to the present invention, the plastic material contains an exothermic foaming agent. Examples of the exothermic foaming agent include azodicarbonamide, dinitrosopentamethylenetetramine, paratoluenesulfonylhydrazine, oxybisbenzenesulfonylhydrazine and the like. Other chemical foaming agents such as baking soda and physical foaming agents can be used in combination with the exothermic foaming agent. The exothermic foaming agent has an effect of increasing the temperature of the parison extruded from the extrusion die, preventing or mitigating the cooling of the parison even after clamping, or increasing the temperature.
If the amount of the exothermic foaming agent is excessive, large drawdown or lengthening of the foamed cell occurs when the parison foams, or the residual amount of unfoamed foaming agent increases. On the contrary, if the amount is too small, the heat generation amount is insufficient and the expansion ratio is not improved. From this viewpoint, an appropriate amount is added.

In the foam blow molding method according to the present invention, after mold clamping, as a first step, the air in the cavity between the parison and the mold is sucked and decompressed, and at the same time, air is sucked into the parison from the blow pin communicating with the atmosphere. Then, the parison is inflated until it is in close contact with the inner surface of the mold.
In addition, although the blow pin in the blow molding method of the present invention does not blow pressurized air into the parison, it is the same device as the blow pin in a general blow molding method, and is therefore also referred to as a blow pin.

  As shown in FIG. 1, after clamping, the air in the cavity 4 between the parison 1 and the molds 2 and 3 passes from the vent holes 5 formed in the molds 2 and 3 through the decompression pipe 6. Then, suction is performed by a vacuum pump (not shown), whereby the inside of the cavity 4 is decompressed. As the pressure in the cavity 4 is reduced, outside air is sucked into the parison 1 from the blow pin 7, whereby the parison 1 swells in the cavity 4 and finally comes into close contact with the inner surfaces of the molds 2 and 3. FIG. 1 shows a state before close contact. The decompression level in the cavity 4 is desirably a high vacuum state of 0.4 atm or less, for example. The decompression pipe 6 and the blow pin 7 can be switched to the atmosphere release side or the vacuum pump side by a switching valve (not shown).

  As the inside of the cavity 4 is depressurized, high-temperature air surrounding the outer surface of the parison 1 is discharged, and the temperature of the air outside the parison 1 decreases due to adiabatic expansion in the cavity 4. At the same time, the outside air is sucked into the parison 1 so that the air inside the parison 1 is mixed with the outside air and cooled. Such a decrease in the temperature of the air around the parison 1 is a cooling factor for the surface of the parison 1. Subsequently, when the parison 1 comes into close contact with the inner surface of the mold, the outer surface of the parison 1 is rapidly cooled.

  On the other hand, the parison 1 includes an exothermic foaming agent, and the exothermic foaming agent reacts after the parison 1 is extruded from an extrusion die (not shown) and generates heat, thereby increasing the temperature of the parison 1. For this reason, although it depends on the content of the exothermic foaming agent, the cooling of the parison 1 is prevented or alleviated even after clamping, or the temperature of the parison 1 rises. When the parison 1 is in close contact with the molds 2 and 3, the cooling action of the molds 2 and 3 is large, so the outer surface (skin) of the parison 1 is immediately cooled and solidified, and cooling penetrates into the wall thickness of the parison 1 from there. To go. However, due to the exothermic action of the exothermic foaming agent and the heat insulating action of the foamed cell, the temperature drop in the wall thickness and inner surface of the parison 1 is gradual compared to the case where no exothermic foaming agent is used, and the parison 1 foams. Continue for minutes. Furthermore, foaming stagnates and stops as the temperature decreases and / or due to consumption of the foaming agent.

  Subsequently, in the foam blow molding method according to the present invention, the blow pin 7 is moved to the atmosphere as the second stage in a state where the parison 1 is brought into close contact with the inner surfaces of the molds 2 and 3 while the pressure reduction in the cavity 4 is continued. The inside of the parison 1 is sucked from the blow pin 7 to reduce the pressure in the parison 1. This decompression expands and maintains the foamed cell that has been formed in the parison 1 until then, and foaming continues depending on the current temperature of the parison 1 and the residual amount of foaming agent. As a result, the expansion ratio is improved.

  Although the decompression level inside the parison 1 can be set as appropriate, it is desirable that the vacuum state be as high as possible, similar to the decompression level in the cavity 4, and if necessary, equal to or higher than the decompression level in the cavity 4 Degree of vacuum). Even if the decompression level inside the parison 1 is raised from the inside of the cavity 4, the outer skin of the parison 1 comes into close contact with the inner surfaces of the molds 2 and 3 and is cooled and solidified, and the foaming ratio is increased to increase the thickness of the parison 1. Since the rigidity of the parison 1 is increased, it is possible to prevent the parison 1 from being crushed as a whole.

  The reduced pressure state in the cavity 4 and the parison 1 continues until the parison 1 (product) is cooled and solidified, and the foamed cell can be maintained even if the reduced pressure state is released. Subsequently, the inside of the cavity 4 and the inside of the parison 1 are opened to the atmosphere, the mold is opened, and the product is taken out.

1 Parison 2, 3 Mold 4 Cavity 5 Vent hole 7 Blow pin

Claims (2)

In a plastic foam blow molding method, the plastic contains an exothermic foaming agent, and after mold clamping, as a first step, air in the cavity between the parison and the mold is sucked and decompressed, and at the same time, a blow pin communicating with the atmosphere The air is sucked from the inside of the parison and inflated until the parison comes into close contact with the inner surface of the mold, and then the air inside the parison is sucked from the blow pin as the second stage while continuing the decompression in the cavity. A foam blow molding method characterized by decompressing the inside. 2. The foam blow molding method according to claim 1, wherein in the second stage, the pressure reduction level in the parison is set to be equal to or higher than the pressure reduction level in the cavity.

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