JPH02301411A - Reaction injection molding method - Google Patents

Abstract

PURPOSE:To inject into a mold immediately after starting operation and eliminate material loss and operation loss by substituting air in a mixing chamber for manufacturing a urethane liquid raw material with carbon dioxide gas preliminarily. CONSTITUTION:Polyisocyanate, an active liquid raw material, to generate reaction to make into urethane and an active hydrogen containing component are fed into a mixing chamber (mixing head G) at the desired ratio, and said liquid raw materials are agitated forcibly to manufacture a urethane liquid raw material. The urethane liquid raw material thus manufactured is injected into a mold M and reaction cured. In that case, air in the mixing chamber for obtaining the urethane liquid raw material is substituted with carbon dioxide gas. As dissolving properties of carbon dioxide gas to the urethane raw material are remarkably higher than that of air, the foams of carbon dioxide gas mixed therein is not likely to appear as the foams in the mixed liquid raw material. The substitution of the air in a mixing head G with carbon dioxide gas is carried out by reducing the pressure in the mixing head C and blowing the carbon dioxide gas via an exhaust nozzle opening or a gas compressive feeding opening provided separately.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an improvement in a method for reaction injection molding of polyurethane, in which a desired molded article is obtained by pouring an active liquid raw material into a mold and reacting and curing it.

(Prior art) In recent years, it has become common practice to mix two or more active liquid raw materials that exhibit a liquid state with room temperature or slight heating, and to cast the resulting mixed liquid into a closed mold with a partitioned product cavity. Reaction injection molding method (discharge) to obtain a molded product by reacting and curing in a cough mold (
Reaction InjectionMolding
, hereinafter referred to as the RIM method) has been put into practical use and is widely used, particularly for automobile parts, housings for office equipment, and electrical insulation materials.

The materials used in the RIM method, that is, the high molecular weight materials that are made into molded products by reaction-curing liquid raw materials, are as follows:
In particular, polyurethane is mainly used because its physical properties can be characterized over a wide range and its physical properties are well balanced. FIG. 1 shows an example of the process for obtaining this polyurethane molded body.

Two material tanks A and B are installed, and these tanks A and B
In this step, active liquid raw materials that can be mixed to produce polyurethane in predetermined amounts, namely polyisocyanate A and polyol B, are separately charged, and the inside of each tank is vacuumed to completely remove air bubbles in the raw materials. 6 Next, pipes C and D
Then, predetermined amounts of polyisocyanate A1 and polyol B are measured using metering pumps E and F, respectively, and introduced into a mixing head G, where both are forcibly mixed and stirred.Next, this mixture is passed through a discharge nozzle H into a mold M. A molded polyurethane having a high molecular weight is obtained by injecting it into the cavity N and curing it by reaction.

(Problem to be Solved by the Invention) In the above-mentioned RTM method for obtaining such conventional polyurethane molded articles, a problem often arises is that after the liquid raw materials polyisocyanate and polyol are forcedly mixed and stirred in the mixing head, the mixing time is 5 to 10 minutes. The disadvantage is that injection of the mixed liquid from the discharge nozzle into the mold must be avoided and must be discarded. The reason for this is that the air in the mixing head is drawn into the liquid raw materials immediately after mixing, resulting in a large amount of air bubbles being mixed into the mixed liquid, and it takes 5 to 10 minutes for these air bubbles to disappear. It is from. The inclusion of air bubbles in the mixed liquid causes voids to appear in the molded product, resulting in a significant deterioration of the properties.

The above-mentioned waste of the mixed liquid for as long as 5 to 10 minutes is a significant loss of liquid raw material depending on the discharge speed into the mold, and also results in a large loss of working time. Particularly in the production of a wide variety of products in small quantities, this raw material loss and operational loss pose a major problem in terms of product costs.

(Means for Solving the Problems) The inventors hereby proposed that in the reaction injection molding method for obtaining the above-mentioned polyurethane molded article, the inventors started forced mixing and stirring of the liquid raw material polyisocyanate and the active hydrogen-containing compound. As a result of intensive research into methods for dispensing a mixed liquid immediately without air bubbles, we found that, before mixing and stirring the liquid raw materials,
They discovered that the above problem could be solved by replacing the air in the mixing head with carbon dioxide gas, and completed this invention.

That is, the present invention provides a means for supplying polyisocyanate and an active hydrogen-containing compound, which are active liquid raw materials that cause a urethanization reaction, to a mixing chamber in a desired ratio, and a method for forcibly stirring these liquid raw materials in the mixing chamber to form urethane. In a reaction injection molding method comprising a means for obtaining a liquid raw material and a means for injecting the obtained liquid urethane raw material into a mold and curing it by reaction, the air in a mixing chamber for obtaining the liquid urethane raw material is replaced with carbon dioxide gas. This is a reaction injection molding method for polyurethane characterized by the following.

The active hydrogen-containing compound used in the present invention includes polyether polyols with a molecular weight of 800 to 12,000, or polyester polyols with a molecular weight of 62
Diols, triols, polyfunctional polyols or diamines, and polyfunctional polyamines are used.

In addition, examples of polyisocyanates include tolylene diisocyanate, diphenylmethane diisocyanate, xylene diisocyanate, isophoroledi isocyanate, polymethylene poly(phenylisocyanate) and chemically modified products of these polyisocyanates, as well as these isocyanate compounds and polyols. reactant of,
Or a mixture of these polyisocyanates is used.

Furthermore, tertiary amines and organic tin compounds are used as catalysts.

Color paste, carbon black, internal mold release agent.

Antioxidants, flame retardants, other auxiliaries, fillers such as calcium carbonate, and reinforcing agents such as carbon fiber, glass fibers, aramid fibers, etc. can also be blended as necessary.

Next, as shown in the figure, the reaction injection molding machine used in the present invention stores two or more active liquid raw materials separately, and is equipped with a degassing device to remove air bubbles from the liquid raw materials. A tank, a metering pump, preferably a gear pump, that individually measures a predetermined amount of the liquid raw material from the tank and supplies it to a mixing chamber, and a mixing chamber for forcibly mixing and stirring the liquid raw materials metered and supplied by the metering pump. A device equipped with a so-called mixing head and piping connecting these is used.

In the present invention, the air in the mixing head is replaced with carbon dioxide gas before mixing and stirring the liquid raw materials. The reason for this is that the solubility of carbon dioxide gas in liquid raw materials (urethane raw materials) is significantly higher than that in air.
This is because the bubbles of carbon dioxide mixed in are difficult to appear as bubbles in the mixed liquid raw material.

A specific method for replacing the air in the mixing head with carbon dioxide gas is to reduce the pressure inside the mixing head and inject carbon dioxide gas through the discharge nozzle hole or a separately provided gas injection hole at a pressure of several kg/d. This is done by blowing.

(Function) In the present invention, polyisocyanate and an active hydrogen-containing compound, which are active liquid raw materials that cause a urethanization reaction, are supplied to a mixing chamber in a desired ratio, and these liquid raw materials are forcibly stirred to produce urethane. A liquid raw material is injected into a mold and cured by reaction.

By replacing the air in the mixing chamber where the urethane liquid raw material is obtained with carbon dioxide gas, the carbon dioxide gas exhibits an effect that unlike air, it is difficult to appear as bubbles.

(Example) The present invention will be specifically explained below with reference to Examples.

(manufactured by Mitsui Toatsu ■)) Free NCO group content 8.8χ Liquid B: Low molecular weight ditol (Hypreni zQc-6062 parts by weight (manufactured by Mitsui Toatsu ■)) Amici equivalent 313 Free NCO group content 8.8χ dibutyltin Silaurylate (DBTDL)
0.01f (1 part A, using the two-component gear pump metering type reaction injection molding machine described above,
Weigh both liquids B at a ratio of 100g:62.01g, and then use the equipped dynamic mixer to weigh them per minute.
It was discharged at a total IJ of 300 g/sin.

When we visually observed the state of air bubbles in the mixed and stirred liquid raw materials according to the comparative example (the air inside the mixing head remained) and the example (the air inside the mixing head was replaced with carbon dioxide gas), we found the following results. Indicated.

Comparative example: There are many air bubbles in the mixed and stirred liquid raw materials,
Cloudy liquid continued to be discharged for about 10 minutes.

Example: There were no bubbles in the mixed and stirred liquid raw materials, and a transparent mixture was obtained immediately after discharge.

According to this result, by converting the air in the mixing head to carbon dioxide gas before mixing the liquid raw materials,
It can be seen that injection into the mold becomes possible immediately from the start of the mixing.

(Effects of the Invention) The method of the present invention involves supplying polyisocyanate and an active hydrogen-containing compound, which are active liquid raw materials that cause a urethanization reaction, to a mixing chamber in a desired ratio, and forcibly stirring these liquid raw materials to produce urethane. When pouring the liquid raw material into a mold and causing it to react and harden, the air in the mixing chamber for obtaining the urethane liquid raw material is replaced with carbon dioxide gas in advance.9 According to the method of the present invention, carbon dioxide gas is different from air. It has the effect of preventing the urethane liquid raw material from appearing as bubbles, and can be injected into the mold immediately after the start of operation, which has the effect of eliminating the material loss and operational loss described above.

[Brief explanation of the drawing]

The drawing is a schematic explanatory diagram of a reactive injection molding machine for urethane molded bodies. A, B...tank, A,,B,...active liquid raw material,
E. F...metering pump, G...mixing head, M.
・Molding mold.

Claims (1)

[Claims] Means for supplying polyisocyanate and an active hydrogen-containing compound, which are active liquid raw materials that cause a urethanization reaction, to a mixing chamber in a desired ratio, and a means for forcibly stirring these liquid raw materials in the mixing chamber. In a reaction injection molding method comprising a means for obtaining a urethane liquid raw material and a means for injecting the obtained urethane liquid raw material into a mold and reaction-curing, the air in a mixing chamber for obtaining the urethane liquid raw material is replaced with carbon dioxide gas in advance. A method for reaction injection molding of polyurethane, which is characterized by: