SE430234B - METHOD OF APPLICATION AND REACTIVE EXPRESSION APPARATUS - Google Patents

Description

Examples of the resin compositions used in reaction injection molding include various polymerizable materials, for example, polyurethane, polyester, epoxy, phenol aldehyde and urea aldehyde resins, which can be obtained by commercially known manufacturing methods. . For example, polyurethane resins are usually made by polymerizing polyols and polyisocyanates in combination with various catalyzing, foaming, emollient, constituents. For typical examples of various compositions that can be used in the process, reference is made to US-Ä-4,055,548 and 4,112,014. There are a huge number of useful resin compositions that can be used, the choice depending on the final desired chemical and physical properties of the product.

The term resin composition is used herein in a generic sense to denote polymerizable plastic blends of either the foam type or non-foam type. The term is not used here to denote only one component, ie polyol which sometimes occurs in factory hose.

It has previously been proposed to incorporate various particulate materials into reactive liquid plastic blends made by reaction injection molding to modify the physical properties of the articles formed from such plastic blends. The said particulate additives comprise glass fiber, in order to increase the strength of the shaped product and also to better match the coefficient of expansion of the shaped product with that of a base part (for example metal) to which it may be connected. Special examples of the latter can be found in car parts made of cellular plastic and other plastic. Reaction injection molding of plastic is often a very satisfactory manufacturing method, due to the fact that such a system allows the use of viscous fast-curing mixtures, whereby as a result increased production rates and better physical properties are obtained.

However, the addition of particulate matter to such mixtures causes problems. A common method of making fiber-reinforced plastic products is described, for example, in US-A-4,073,840.

According to this patent, a suspension of glass fiber and one or more of the resin components is formed. The suspension is stirred to keep the fibers suspended and the suspension is then pumped to a mixing head, where it is mixed with the additional resin components comprising blowing agents and / or curing agents required to make the moldable resin mixture. The temperature and viscosity of the components have a great effect on the curing time and the final physical properties of the product. For this purpose, the components are continuously returned in the unmixed state between their respective storage containers and the mixing head in order to continuously pass through heat exchangers and thereby maintain optimal temperature conditions. In this way, the development between the forming phases of low-temperature coatings of the many components in the passages up to and in the vicinity of the mixing head becomes as small as possible.

The incorporation of fiber or other particulate material into a resin component as proposed in the above-mentioned patent involves the incorporation of the particles directly into the main supply of one of the components. Consequently, the system has the disadvantage that if it is desired to change the resin mixture formulation, all traces of the preceding particle-bearing component must be removed from the storage tank, supply and return lines, and so on. Another and even more troublesome inconvenience with the known system arises due to the abrasive action of the fiber-bearing component during the high operating pressures which occur during reaction injection molding when the component passes through the internal channels of the mixing head. At the normal operating pressure of the components up to 18 MPa used in reaction injection molding, this abrasion becomes difficult, especially when the amount of fiber involved is increased to the levels often desired. The mixing head common in this context has a control piston, which is very carefully machined to extremely fine tolerances to give a closed, tight, sliding fit in a similarly carefully machined cylinder, which delimits the mixing chamber. The piston also includes axial recirculation grooves to enable the components to be returned in a separate unmixed state during the non-forming periods. The piston and its grooves are therefore particularly sensitive to abrasion of particulate matter in the liquid constituents to be mixed and expensive maintenance and repair work can be expected. Current technology has nevertheless endured these problems to meet the demand for shaped resin products with the improved properties obtained by admixture of particulate matter. According to the invention, there is provided a method and apparatus which allows the incorporation of particulate matter, such as reinforcing and coloring materials, into reactive resin compositions made by reaction injection molding but without the disadvantages set forth above. mentioned. Briefly, the invention comprises mixing a particulate material into a separate or auxiliary part of one or more of the reactive liquid components to prepare a suspension therewith. This suspension is pumped separately at low pressure which is only a fraction of the normal operating pressure during reaction injection molding to a mixing head orifice and a hydrocarbon feed groove separate from those used for the primary non-particulate resin components. It is surprisingly found that although the pressure of the suspended resin auxiliary component is very low compared to that of the main components, injection of the low pressure liquid and mixing it with the primary components can occur in the mixing chamber and nevertheless do so in an efficient manner. Due to the lower operating pressure in the particulate suspension, a significant reduction in the abrasive effect of the particulate material is achieved in the system's passage channels and a significant reduction in maintenance and longer * life of the mixing head.

Additional objects and advantages of the invention include simplifying the conversion from one type of particulate material to another, without altering or affecting the storage systems of the primary components. Other objects and advantages of the invention will become apparent or become apparent from the following detailed description of the system described below with reference to the accompanying drawings.

Fig. 1 is a flow chart of a reaction injection molding system also incorporating the present invention for introducing particulate matter into a foam mixture prior to molding, and Fig. 2 is a side view of the head of the system of Fig. 1. Referring to Fig. 1yi of the accompanying drawing, schematically shows a two-component reaction injection molding system for the production of, for example, polyurethane foam. In the system shown, a mixing head 10 is fed with two primary components, component A and component B, one of which consists of the isocyanate and the other contains the polyol and also the catalyst, the blowing agent and so on. The component circulation systems are identical and consequently only the one for component A is shown for simplicity.

A storage tank 12 contains the primary component A which is pumped with a low pressure pump 14 through a heat exchanger 16, where heat is supplied or removed from the liquid to maintain desired operating conditions. Component A is further passed through a filter 18, from which it is then passed through a reducing valve 20 to supply the line 22 to a spray nozzle (not shown) in the mixing head 10.

During the non-mixing phase, the control piston (not shown) in the mixing head is located in its fully extended position in the mixing chamber, thus filling the chamber and blocking access of the two components to the chamber. Each component is thus pumped at low pressure, so that the component flows along its respective axial grooves in the piston and is transported through the return line back to the storage tank. Line 26 is the return line for component A. This low pressure flow enables components with the correct temperature to be available directly at the mixing chamber of the mixing head 10, whenever a mixing and forming cycle is started in the mixing head. When such a cycle is initiated, the piston of the mixing head is moved to its retracted position, in which the piston no longer blocks the syringe openings into the mixing head. At the same time, a high-pressure pump 28 is activated so that component A is exposed to the usual operating pressures for reaction injection molding. The reducing valve 20 prevents counterflow to the low pressure side. At the same time, a high-pressure pump is started in the system for component B. These pumps dispense the respective components and force them through the openings of the mixing head and generate high-speed currents in the open mixing chamber of the head. In the condition described, streams of components A and B penetrate at high speed into the mixing chamber of the head and provide the desired intimate mixture of and the reaction between the components to form the resin mixture. The time of the mixing / forming phase is determined by suitable apparatus to provide the desired volume of foamable mixture in the mixing chamber, at the end of which the high pressure pumps are switched off. At the same time, the piston of the mixing head is moved back to its extended position, cleans the chamber of mixture and further blocks access for the components. The resin mixture is ejected through the effluent nozzle 30 into a suitable injection mold (not shown) where it is formed and polymerized into a resin product of the desired appearance. So much of the system is standard.

As explained above, attempts have previously been made to blend fibers or particulate matter into one or both of the primary components to achieve improved properties of the finished resin product. Although severe erosion and abrasion of the carefully machined piston, recirculation grooves and mixing head of the mixing head, as well as the pumps and lines of the many component systems, have caused serious problems, no other solution has been found.

The present invention is based on the discovery that the erosion problems of the previous systems can be remedied in a relatively simple manner, with the least possible change in existing equipment. Referring again to Fig. 1, the device according to the invention comprises the normal systems for each of the primary components A and B, but in addition a separate auxiliary component system is included. This auxiliary system consists of a storage tank 32, in which a part of one of the primary components, preferably the high-output component, is mixed with the particulate materials, for example glass fiber, to be introduced.

A stirrer 34 was used in the tank to maintain a homogeneous suspension. This is then pumped with the low pressure pump 36 through a standard heat exchanger and filter 38 resp. 40 (similar to those of components A and B) to the supply lines 42. The lines 42 lead to channels forming spray nozzles in the mixing head 10 separated from the spray nozzles of components A and B.

.These channels are exposed when the piston of the mixing head is retracted at the same time as the spray nozzles for the primary components are exposed. Thus, the particle-containing suspension is injected directly into the mixing chamber in the presence of the penetrating high velocity streams of the primary components. Contrary to what might be expected of those skilled in the art of injection molding, only a very low pressure had to be applied to the particle-bearing suspension to cause it to penetrate the mixing chamber. In practice, it was found that a pressure of the order of as low as 0.28 MPa and up to -1.38 MPa is sufficient for a polyol fiber glass suspension with viscosities of 20,000 - 50,000 cP, while an operating pressure of about 18 MPa is maintained for each of the primary components A and B. Although the pressure of the primary components is extremely large than that of the suspension, it appears that the pressure drop which occurs at the entry of the primary components into the chamber is fast enough to allow introduction of the particle-bearing suspension at the low pressure level. which is even more surprising is that introduction of the suspension at the low pressure nevertheless produces an intimate mixture of the particles in the whole formed resin mixture when it is ejected by the piston in the mixing head into an injection mold.

The particle-carrying auxiliary system includes a return line 44 which leads from the mixing head to the tank 32, so that the suspension is constantly returned during the non-mixing, non-forming periods, in the same way as the primary components. As shown in Fig. 1, both the supply and return lines 42, 44 are preferably branched, to provide for insertion of the suspension at two diametrically opposite locations in the mixing chamber of the mixing head. The arrangement is further shown in Fig. 2 of the accompanying drawing.

In practice, for example, up to 25% by weight of glass fiber calculated on the total blend weight has been successfully blended into a urethane blend of the type described in the patent referred to above. The fiber consisted of randomly chopped lengths up to 6 mm. To simplify handling, it is preferred to suspend the fiber in a separate part of the polyol component.

Such a component may be of the same or different composition as that of the primary polyol component. Similarly, other particulate inclusions such as finely ground color pigments, mineral oxides and the like may be incorporated into up to 50% by weight of the mixture.

Claims (8)

10 15 _20 25 Bö 35 79Q8841-5 Patent claims A reaction injection molding process in which particulate material having two or more primary liquid resin components which can react to produce a moldable plastic mixture is mixed to form a plastic particle, characterized in that provides a reaction head injection type mixing head (10) having a mixing chamber with channels opening into said chamber during axial mutual cutting, providing separate stores (12) of said primary reactive liquid components and supplying them separately at high altitudes. pressure (28,22,22 ') to openings in said head (10), to provide another separate supply (32) for liquid component, to mix said particulate material in said second separate supply of liquid component to to obtain a particle-containing suspension 7, to supply said particulate suspension under low pressure (36, 42) to another channel in said mixing head , wherein said suspension is mixed into the reactive mixture of said primary reactive components formed in said mixing chamber and expelling (30) said mixture from said mixing chamber in a mold to produce said plastic particle. 2. A method according to claim 1, characterized in that said particle-containing liquid component is introduced into the mixing chamber from diametrically opposite sides thereof. 3. A method according to claim 1, characterized in that said second separate supply of liquid component has the same composition as one of said primary components. A process according to claim 1, characterized in that said primary components comprise a polyisocyanate with conventional catalysts and blowing agents involved therein, that said second component contains a polyol and that said separate supply of liquid component in which said particulate material is suspended , comprises the same or another polyol. 10 15 25 30 35 7903841-5 9 5. A method according to claim 1, characterized in that said particulate material is selected from glass, carbon, graphite or other mineral or metal fibers or granules, mineral or metal oxides, color pigments and the like. Reaction injection molding apparatus for mixing particulate material with two or more primary liquid resin components, which can react to form a moldable plastic mixture to form a plastic article, characterized in that it comprises a mixing head (10). of the injection molding type having a mixing chamber with openings opening into said chamber arranged in axial section, separate storage devices (12) for respective stores of said primary liquid components, conduit (22,22 ') and pump means (28) each connecting said storage means and mixing head and supplying said primary components separately at high pressure to different openings in said head for insertion thereof as shocks currents in said mixing chamber, another separate storage device (32) for a liquid component with said particulate material therein and forming a suspension therewith; and other means comprising conduits (42, 44) and a low pressure pump (36) connecting said second storage device (32) and second of said openings in said mixing head (10) for introducing said suspension into said mixing chamber for mixing with said primary components. Apparatus according to claim 6, characterized in that said conduit device which supplies said primary components to said mixing head is connected to openings located opposite each other in said mixing head. 8. Apparatus according to claim 6 or 7, characterized in that said second conduit means for said suspension to said mixing head are connected to each other located by said separate openings in said head.