JPS58147333A - Blow molding method for thermosetting resin - Google Patents

Abstract

PURPOSE:To efficiently manufacture a blow-molded product, having an opening narrower than a hollow part, by an injection molding for a thermosetting resin, by the use of a core made of a metallic salt having a particular comparatively- low melting point. CONSTITUTION:A metallic salt, such as a mixture of 45wt% sodium nitrite, and 55wt% potassium nitrate (melting point; 142 deg.C), which prevents a cured resin from the production of a change in properties and the occurrence of pyrolysis and is molten at a comparatively-low temperature, is used. That is, a core made of said metallic salt is placed in a mold 2, and a molten thermosetting resin is pressed in a formed cavity 21 through a gate 4. After the resin is cured, it is removed from a mold 2, a thermosetting resin molded product 3 is heated at higher than a melting point of said metallic salt together with a core 1, and the molten core 1 is removed from the molded product 3 to obtain a blow-molded work serving a product.

Description

[Detailed description of the invention] The present invention relates to blow molding of thermosetting resins.

- First, thermosetting resins can be molded by compression molding, injection molding, transfer molding, etc., but when molding hollow products, only shapes that allow the core to be removed from the opening can be molded. Therefore, it was considered impossible to blow mold a thermosetting resin square with a narrow opening and a large hollow part. The present invention provides a method for obtaining a hollow product made of thermosetting resin, such as blow molding of thermoplastic resin, in which the opening is narrower than the hollow part. In the present invention, at the time when the thermosetting reaction of the thermosetting resin molded product is completed, the shape of the thermosetting resin molded product remains unchanged even when heated to tIA degree higher than the heating concentration during molding. Taking advantage of the fact that it can be maintained, the core material is heated to a temperature higher than the molding aI degree of the thermosetting resin, melting the core material into a liquid, and then taking out the core through a narrow opening.

That is, the thermoplastic resin blow molding method of the present invention includes the steps of placing a core made of metal salt in the cavity of a mold;
A process of pressurizing the thermosetting resin into the cavity in which the core is placed, a process of proceeding with the curing reaction of the thermosetting resin introduced into the cavity to obtain a thermosetting resin molded body, In the process of taking out the resin molding from the mold, the thermosetting resin molding together with the core is heated above the melting point of the metal salt in the core, the core is melted, and the molten metal salt flows out from the thermosetting resin molding. The method is characterized by a step of removing the material by removing it.

The metal salt used in the method of the present invention is of a type that dissolves the thermosetting resin at a relatively low concentration that does not cause deterioration or thermal decomposition. For example, sodium nitrite (NaNO-
Nitrites such as g) and nitrates such as potassium nitrate (KNO3) can be used. A mixed salt of 45% by weight of sodium nitrite and 55% by weight of potassium nitrate has a melting point of 142°C.
A core is formed from this relatively low melting point metal salt. The shape of the core can be arbitrary depending on the hollow part of the target thermosetting resin. The process of inserting a core into a mold is basically the same as inserting a core into a normal metal casting.

In order to securely insert and fix the core into the mold, the core can be supported in the cap of the mold by using the same resin as the intended thermosetting resin molded product. As the thermosetting resin, a thermosetting resin commonly used for injection molding or transfer molding can be used. However, since a core is used, it is not preferable to use molding pressure that is too high;
It is preferable to use a material that can be molded at a molding pressure of 0 to 100 ko/am2 culm. Other molding conditions such as mold temperature are the same as those for normal injection molding or transfer molding. The molding humidity of the mold is 20% higher than the melting point of the metal salt constituting the core.
It is preferable that it is below ℃. This is because when the temperature of the mold approaches the melting point of the molten salt that forms the core, there is a possibility that the core will melt or become deformed. The molded product is injection- or transfer-molded, and the curing reaction of the thermosetting resin progresses within the cavity of the mold. After the curing reaction is completed, the molded product is removed from the mold with the core inside. Next, this molded body is heated to a temperature higher than the melting point of the metal salt of the core. This heating can be accomplished by placing the molded article, including the core, in a suitable heating furnace. Then, the metal salt in the core is dissolved and the dissolved metal salt is allowed to flow out from the opening of the molded product. As a result, a hollow thermosetting resin molded article is obtained. In addition, when melting the core, it is not preferable to heat the thermosetting resin to a high concentration that causes deterioration or decomposition, and it is also not preferable to heat it for a long time. In order to speed up the melting of the core, it is preferable that the core itself be a hollow core. For molding the core itself, use a mold with a cavity equal to the shape of the core, place the molten metal salt into the cavity, move the core along the wall of the cavity, and press the mold. By cooling and solidifying the metal salt, the metal salt can be cooled along the cavity wall surface to form a hollow core. The thickness of the core should be determined in consideration of the pressure applied to the core during injection or transfer molding, and should have enough strength to withstand the molding pressure. To increase the strength of the core, reinforcing materials such as carbon fiber or metal fiber can be added to the metal salt.

This will be explained below using examples.

Sodium nitrite 45f! Using a mixed salt of 55% potassium nitrate and 55% potassium nitrate, this was heated and melted, placed in a two-part mold, and cooled while rotating the mold to form a hollow core 1. Next, this core 1 was placed in the cavity 21 of a two-part mold 2 divided into an upper mold and a lower mold. In addition, in order to form a certain gap between the inner wall of the cavity 21 of the mold 2 and the core 1, and to completely support the core 1 within the cavity 21, struts made of thermoplastic resin are installed in some places. The setting is Nakako 1
was fixed. Note that the mold 2 is maintained at 120°C.

Next, a thermosetting resin was injected into the cavity 21 from the gate 4 of the mold 2, and the cavity 21 around the core 1 was filled with the thermosetting resin.

The injection pressure was 50 kO/cl', and this pressure was maintained for 2 minutes to advance the curing reaction of the thermosetting resin in the mold 21 to obtain a thermosetting resin molded article 3. Subsequently, the mold 2 was opened and the thermosetting resin molded body 3 containing the core 1 was taken out from inside.

The thermosetting resin molded body 3 containing this core 1 was placed in an air drying oven heated to 150° C., and the core 1 was completely melted.

The melted core 1 was removed from the thermosetting resin molded body 3, and the desired thermosetting resin molded body was manufactured.

[Brief explanation of the drawing]

The figure is a sectional view showing the arrangement relationship between the core and the thermosetting resin placed in the mold. In the figure, 1 is the core, 2 is the mold,
3 is a thermosetting resin molded body, and 4 is a gate. Patent applicant: Toyota Motor Corporation Attorney: Hiroshi Okawa 2

Claims (4)

[Claims] (1) The process of placing a core made of metal salt in the cavity of the mold, the process of pushing thermosetting resin into the cavity where the core is placed, and holding the thermosetting resin pushed into the cavity. A process of advancing the curing reaction to obtain a thermosetting resin molded body, a process of taking out the thermosetting resin molded body together with the core from the mold, a process of heating the thermosetting resin molded body together with the core to a temperature higher than the melting point of the metal salt in the core. A method for blow molding a thermosetting resin, comprising the steps of heating to melt the core and removing molten metal salt from the thermosetting resin molded body. (2) The molding method according to claim 1, wherein the metal salt is a mixture of two types of metal salts. (3) The Ii degree of the mold is 2 of the melting point of the metal salt that makes up the core.
The molding method according to claim 1, wherein m degree C is 0°C or less. (4) The molding method according to claim 1, wherein the core is a hollow core having nine cavities inside.