JPH0729320B2 - Reaction injection molding method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for molding a norbornene-type polymer molded article by a reaction injection molding (hereinafter referred to as RIM) method, and more particularly to molding without defective curing or generation of voids. The present invention relates to a reaction injection molding method for obtaining a product.

2. Description of the Related Art When a polymer (molded product) is produced from a norbornene-type monomer such as dicyclopentadiene by the RIM method, it is necessary to eliminate oxygen and water that hinder the ring-opening polymerization reaction as much as possible. Therefore, the reaction liquid is prepared and mixed in the presence of an inert gas such as dried nitrogen gas.
However, since the polymerization reaction in the mold is extremely rapid, polymerization and molding are performed without purging the mold with nitrogen. By the way, generally, in order to avoid the state where the reaction liquid or resin is not completely filled due to the residual air pressure in the mold, air is exhausted by a mold structure having an air vent groove such as an air vent groove. .

In the RIM method, the reaction liquid mixture is injected into the mold from the top or side of the mold from the reaction liquid mixing head or via a piston device (FIGS. 3 to 6).
See figure). However, in this way, when the reaction solution mixture is injected from the upper part or the side part of the mold, the reaction solution mixture sprinkles the air in the mold to cause partial curing failure, and there are many voids (air bubbles). It becomes a molded product (see FIGS. 7 to 10). Therefore, in molding by the RIM method using a norbornene-type monomer as a molding material, a method has been proposed in which the mold is tilted at about 45 ° during injection / filling of the reaction liquid mixture in order to reduce air intake ( Japanese Patent Laid-Open No. 59-51111, refer to Example 3), but even with this method, air entrainment cannot be avoided and the operation is complicated.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention is directed to RI using a norbornene-type monomer as a molding material.
It is an object of the M method to provide a molding method in which air is not entrained in a mold.

Means for Solving the Problems As a result of intensive studies, the present inventors have found that in the RIM method using a norbornene-type monomer as a molding material, the reaction liquid mixture is injected from the lower part of the mold to obtain a mold. The present inventors have found that the inside of the mold can be completely filled with the reaction solution mixture by pushing the air inside to the upper part and successively exhausting it from the air escape port to the outside, and arrived at the present invention.

That is, the gist of the present invention is a method for molding a molded article from a norbornene-type monomer by a reaction injection molding method, wherein the reaction liquid mixture is injected into the mold from a lower part of the mold. It is in.

The components of the present invention will be described below.

(Norbornene Type Monomer and Reaction Liquid) The norbornene type monomer used in the present invention is a monomer containing a norbornene group, and is a substituted or unsubstituted norbornene, dicyclopentadiene, dihydrodicyclopentadiene, trimer of cyclopentadiene, or tetrane. Such as cyclododecene and mixtures thereof,
Specific examples include dicyclopentadiene and methyltetracyclododecene.

As the reaction catalyst, a known compound such as a tungsten compound such as tungsten hexachloride, an organic ammonium molybdate such as tri (tridecylammonium) molybdate, or an organic ammonium tungstate can be used.

Further, as the activator (co-catalyst), an alkylaluminum halide such as diethylaluminum chloride can be preferably used, and particularly when alcohols such as n-propyl alcohol are used together as an activity controlling agent, the pot life of the reaction mixture is increased. It is preferable because it can be extended.

The reaction solution usually consists of the following two solutions.

(Liquid A) A solution containing a norbornene-type monomer and a catalyst.

(Solution B) A solution containing a norbornene-type monomer and an activator (and an activity regulator).

The norbornene-type monomer may be contained in only one of the A and B liquids.

In the RIM process, both liquids A and B are mixed by a mixing head, then injected into a mold, and polymerized and cured in the mold under high temperature.

(Mold) As shown in FIGS. 1 and 2, the mold used in the present invention is provided with a reaction solution mixture injection port in the lower portion. Further, it is preferable that the air escape port (air vent) is provided in a portion where the reaction liquid mixture is difficult to fill or a portion where the reaction liquid mixture is filled last.

Action In the injection molding method, the molten resin that has entered the mold expels air and fills it. The air in the mold easily escapes from the dividing surface of the mold, the ejector pin hole, the clearance of the nest, etc. However, when defective exhaust becomes a problem, the air vent groove is provided as described above. However, the reaction liquid mixture using the norbornene-type monomer not only hinders the ring-opening polymerization reaction due to oxygen, but also has an extremely low viscosity as compared with the molten resin, and thus tends to be entrained with air. Therefore, when the reaction liquid mixture is injected from the upper part of the mold, it is presumed that the air retained in the lower part of the mold is instantaneously introduced. However, according to the method of the present invention, when the reaction solution mixture is injected from the lower part of the mold, the air in the mold is pushed up to the upper part, and then it is exhausted from the clearance of the mold and the air vent, and the air is successively sprinkled. It can be considered that the entire mold is filled with the reaction solution mixture without any treatment.

Example Dicyclopentadiene monomer was put in two containers, and in one of them, 0.0033 molar concentration of diethylaluminum chloride and n-propyl alcohol were added to 1 mole of the monomer.
Each was added so that the concentration would be 0.00495 molar (A
liquid). On the other hand, tri (tridecylammonium) molybdate was added to the monomer (1 mol) at a concentration of 0.0004 mol (solution B). 1 to 1 of these two reaction solutions
Mix with a mixing head to a volume ratio of
Mold with 200cc space volume heated to room (Fig. 1)
It was injected into the inside through an injection port provided in the lower part, and the reaction was performed for 3 minutes.

When the mold was opened after the reaction was completed, a good molded product having a smooth inner surface and no voids was obtained.

For comparison, when the same reaction mixture was injected from the upper part of the mold (Fig. 3), the reaction solution was entrained with air, resulting in a molded product with voids and poor surface conditions due to partial curing. (See FIG. 7). When the reaction mixture was injected from the side of the mold (Fig. 5), the same defective product was obtained (see Fig. 9).

In addition, the part indicated by 5 of the molded product in FIGS. 7 to 10 shows the state of the part in which the surface condition of the molded product is deteriorated due to the fact that the reaction liquid mixture entrains air and partially causes curing failure. It corresponds to the case of using the molds of FIGS. 3 to 6, respectively.

Effects of the Invention In molding by the RIM method using a norbornene-type monomer, since the reaction liquid mixture is injected from the lower part of the mold, the air in the mold is easily exhausted and the reaction liquid sprinkles the air. Therefore, it is possible to obtain a good molded product having a beautiful appearance and no void.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 and FIG. 2 are schematic sectional views of a mold applicable to the method of the present invention. 3 to 6 are schematic sectional views of a conventional mold. FIGS. 7 to 10 are views showing molded products obtained by using the molds of FIGS. 3 to 6 and their surface states. 1 ... Mold, 2 ... Air vent, 3 ... Injection port, 4 ...
Molded product, 5 ... The part where curing failure occurred.

Claims (2)

[Claims] 1. A method for molding a molded article from a norbornene-type monomer by a reaction injection molding method, which comprises injecting a reaction liquid mixture into the mold from a lower part of the mold. 2. The reaction injection molding method according to claim 1, wherein a mold provided with an air vent in a portion where the reaction liquid mixture is difficult to fill or a portion where the reaction liquid mixture is filled last is used.