JPS6233926B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in the reaction injection molding (RIM) technique of reactive liquid resin mixtures in the production of foamed or non-foamed plastic products, and more particularly relates to improvements in reaction injection molding (RIM) technology for reactive liquid resin mixtures in the production of foamed or non-foamed plastic products, and more particularly, to provide greater strength, better insulation properties. or incorporating into such plastic products various granules, fibrous granules, etc. which serve as reinforcement of the final product to meet lower expansivity requirements or perform other functions such as coloring, flame retardant functions, etc. Regarding things.

In a typical RIM system for manufacturing plastic products, two or more liquid polymer precursors in a reactive mixture are stored separately in large tanks;
The precursors are pumped separately to a mixing head where they are injected at high pressure from an orifice in the head to form an impinging flow within the mixing chamber of the head.
The introduction of the ingredients into the mixing chamber is controlled by a plunger, which has two positions: an extended position where the plunger blocks the mixing chamber and prevents the inflow of ingredients from the injection port or orifice; and a retracted position that allows the flow of components from each orifice. This introduction is in the form of high velocity streams, as described above, which impinge within the mixing chamber to provide intimate mixing and polymerization reactions. next,
The mixing components in the chamber are ejected into the appropriate mold from the ejection port of the mixing head when the plunger returns to its original position. Such return simultaneously prevents further flow of the components into the mixing chamber and returns the individual components through their respective recirculation conduits to their respective storage tanks. A typical RIM mixhead is disclosed in U.S. Pat. No. 4,082,512, to which reference is made for further details of the known device.

Examples of resin compositions used in RIM production include:
A variety of polymeric materials are mentioned which can be obtained by commercially known manufacturing methods, such as polyurethane, polyester, epoxy, phenol-aldehyde and urea-aldehyde resins. For example, polyurethane resins are commercially produced by polymerizing polyols and polyisocyanates in combination with various catalyst, blowing agent, plasticizer components, and the like. For typical examples of various compositions useful in this method, see U.S. Pat.
Please refer to the specification. There is a large number of useful resin compositions that can be used, the selection of which depends on the ultimately desired chemical and physical properties of the foamed product.

In this text, resin composition is used in a generic sense to mean polymerizable plastic mixtures, whether foamed or non-foamed. This term is not used herein to designate only the -component (i.e., polyol), as is sometimes used by manufacturers.

In the past, it has been proposed to incorporate various particulate materials into reactive liquid plastic mixtures produced by RIM technology to modify the physical properties of articles formed from such plastic mixtures. Particulate additives mentioned include glass fibers for the purpose of increasing the strength of the molded article and making the coefficient of expansion of the molded article better match that of the base (e.g. metal) component with which it can be combined. It will be done.
A particular example of this is found in foamed and non-foamed plastic automotive parts. Reaction injection molding of plastics is a particularly satisfactory manufacturing method due to the fact that such systems allow the use of viscous, fast-curing mixtures, resulting in increased production rates and better physical properties. This is often the case. However, incorporating particulate matter into such mixtures is problematic. A typical method for manufacturing fiber reinforced plastic products is disclosed, for example, in US Pat. No. 4,073,840. According to this patent, a slurry is formed from glass fibers and one or more resin components. The slurry is stirred to suspend the fibers and then
The slurry is pumped to a mixing head where it is mixed with reinforcing resin components including blowing agents and/or curing agents necessary to produce a moldable resin mixture. The temperature and viscosity of the ingredients have a large effect on curing time and final physical properties of the product. For this purpose, the components are continuously recirculated in an unmixed state between their respective reservoirs and the mixing head.
In this case, it is continuously passed through a heat exchanger, thereby maintaining an optimum temperature condition. In this way,
Unusual temperature increases of several components during passage through and adjacent to the mixing head between forming "shots" are minimized.

The incorporation of fibers or other particulate materials into the resin component, as proposed in the aforementioned patents,
This includes directly blending the granules into one main feed. This system therefore has the disadvantage that if it is desired to change the resin mix composition, the previous particulate-carrying components must be removed to trace amounts from the storage tank, supply and return lines, etc. Another even more troubling disadvantage of conventional systems is the high RIM associated with the fiber-supported components as they pass through the internal passages of the mixing head.
This occurs due to the abrasive effects under operating pressure. At common component operating pressures of up to 2600 psi used in RIM manufacturing, this wear becomes excessive, especially as fiber loading rates are increased to often desirable levels.
Ordinary RIM mixing heads are very carefully machined to close tolerances and use a control plunger that overlaps an equally carefully machined cylinder that defines the mixing chamber to provide a leak-tight sliding fit. do. In addition, the plunger is
Includes an axial recirculation groove to allow return of components (another unmixed state) during the non-molding cycle of operation.
The plunger and its groove are therefore particularly sensitive to the abrasive effects of particulate matter in the liquid components to be mixed and are subject to expensive maintenance and repair. Still, the prior art has struggled with these problems in order to meet the need for molded resin products with the improved properties provided by such particulate formulations.

According to the present invention, particulate materials for reinforcement and coloring are used.
A method and apparatus are provided that allow reactive resin compositions produced by the RIM method to be formulated without encountering the drawbacks mentioned above. Briefly stated, the present invention involves incorporating particulate material into a separate or reinforcing portion of one or more reactive liquid components to form a slurry. This slurry is pumped separately into a mix head orifice and plunger recirculation groove that are separate from those used for the main (granule-free) resin component at low pressures that are only a small fraction of normal RIM operating pressures. be sent. Surprisingly, although the pressure of the auxiliary slurry resin component is very low compared to the pressure of the main component, injection of the low pressure fluid and mixing with the main component can and does occur effectively in the mixing chamber. was discovered. Due to the lower pressure operating conditions available with the granulate slurry, the abrasive effect of the granules on the passage through the system is substantially reduced, resulting in a significant reduction in mix head maintenance and an extended operating life of the mix head. be done.

Another object and advantage of the present invention is that one type of particulate material can be easily changed to another type of particulate material without changing or affecting the primary component storage system. include.
Other objects and advantages of the invention will become apparent from the following description with reference to the accompanying drawings.

Referring to FIG. 1, a two-component RIM system for the production of polyurethane foams, for example, is schematically shown. In the illustrated system, RIM mixing head 10 contains two major components, component A and component B.
are supplied, one component of which consists of an isocyanate and the other component contains a polyol;
Furthermore, it contains a catalyst, a blowing agent, etc. The component circulation system is the same, therefore, for simplicity, component A
Only those for are shown.

Storage tank 12 contains a feed of main component A, which is passed through heat exchanger 16 to low pressure pump 1
4 and in a heat exchanger, the liquid is added to or removed from heat to maintain the desired operating conditions. Component A is further passed through strainer 18 and from there through check valve 20 and via feed conduit 22 to an injection port (not shown) of mixhead 10.

In the non-mixing operating condition, the control plunger of the mixing head is in a fully extended position within the mixing chamber, which is occluded and prevented from entering the co-component chamber. Each component is therefore pumped at low pressure to flow along each axial groove of the plunger and is supplied by a return conduit to a storage tank. Conduit 26 is the return conduit for component A. This low pressure flow ensures that the components at the appropriate temperature are directly available in the mixing chamber of mix head 10 whenever the mix head mix and mold cycle is initiated. When such a cycle is initiated, the mix head plunger is moved to a retracted position in which the mix head injection orifice opening is no longer obstructed. At the same time, the high pressure pump 28 is activated, so that component A is
Receives RIM operating pressure. A check valve or safety valve is
Prevents backflow to the low pressure side. At the same time, the high pressure pump of component B system is activated. These pumps meter and force each component out of the mixing head orifice, creating a high velocity flow in the open mixing chamber of the head. In this condition, the streams of components A and B collide under high velocity within the mixing chamber of the head, resulting in the desired intimate mixing and reaction of the components to provide a resin mixture. The mixing/forming "shot" is timed with suitable equipment to provide the desired volume of foamable mixture within the mixing chamber, and at the end of the shot the high pressure pump is stopped. At the same time, the mixing head plunger is returned to the extended position and the plunger purges the mixture from the chamber and prevents further ingress of the ingredients. The resin mixture is discharged from the discharge nozzle 30 into a suitable mold (not shown), where it is molded and polymerized into a resin product of the desired shape. Most of the systems are standard.

As mentioned above, conventional attempts have been made to incorporate fibers or particulate materials into one or both of the major components to obtain improved properties in the final resin product. Severe corrosion and wear of the carefully machined plungers, recirculation grooves and mixing chambers of the mixing head and pumps and conduits of several component systems have posed significant problems, but no other solutions have emerged.

The present invention is based on the discovery that the corrosion problems of conventional systems can be overcome in a relatively simple manner with minimal changes to existing equipment. Referring to FIG. 1, a device incorporating the present invention includes a conventional system for each of the major components A and B, but also includes a separate subcomponent system. This auxiliary system consists of a storage tank 32 in which a portion of one of the main components, preferably the high output component, is mixed with the particulate material to be introduced, such as glass fibers. An agitator 34 is used to maintain a uniform slurry within the tank.
This mixture is then passed through a standard heat exchanger and strainer 38, 40 (component A
and B) respectively into the supply conduit 42. Conduit 42 leads to a port that constitutes an injection orifice for components A and B and another mixing head 10. These ports are uncovered at the same time as the main component injection ports are uncovered when the mix head plunger is retracted. Therefore, the particulate-containing slurry is directly injected into the mixing chamber in the presence of high velocity impinging streams of the major components. Contrary to what would be expected by those experienced in RIM technology, very low pressure is required to force the particulate-containing slurry into the mixing chamber. In fact, the viscosity is 20,000~
Lower pressures of 40 to 200 psi are sufficient for 50,000 polyol-glass fiber slurries, while
Approximately 2600 psi is found to be maintained for major components A and B. Even if the pressure of the major component is excessively greater than the pressure of the slurry, the pressure drop that occurs as the major component enters the chamber is likely to be rapid enough to cause the particulate-containing slurry to be introduced at the lower pressure level mentioned above. It is. What is even more surprising is that the low pressure introduction of the slurry nevertheless causes the particulates to be intimately mixed throughout the resulting resin mixture up to the point where they are ejected into the mold by the mixing head plunger.

The auxiliary particulate containing system includes a return conduit 44 leading from the mixing head to tank 32, so that
The slurry, like the main components, is constantly recycled during the no-mix, no-molding operation. As shown in FIG. 1, both supply conduit 42 and return conduit 44 preferably branch to introduce slurry at two diametrically opposed points into the mixing chamber of the mixing head. This arrangement is further explained in FIG.

In fact, for example, up to 25
Up to % by weight of glass fibers have been successfully incorporated into urethane mixtures of the type described in said patent. The fibers consisted of randomly cut lengths up to 1/4 inch in length. For ease of handling, the fibers are preferably slurried with another portion of the polyol component. Such components can be of the same or different composition as the main polyol component. Similarly, other particulate formulations such as finely divided color pigments, mineral oxides, etc. can be incorporated up to 50% by weight of the mixture.

[Brief explanation of the drawing]

1 is a schematic flow sheet of a RIM system incorporating the present invention for introducing particulate material into a foamed plastic mixture prior to molding; FIG.
Figure 3 is a schematic end view of the RIM head of the system shown; 10...RIM mixing head, 12...storage tank, 14...pump, 16...heat exchanger, 18...
... Strainer, 20 ... Check valve, 22 ... Supply conduit, 26 ... Conduit, 28 ... Pump, 30 ...
... Nozzle, 32 ... Storage tank, 34 ... Stirrer, 36 ... Pump, 38 ... Heat exchanger, 40 ...
...Strainer, 42, 44... Conduit.

Claims (1)

Claims: 1. Reaction injection molding (RIM) for incorporating particulate material into two or more primary liquid resin components that may form a plastic mixture that can be reacted and formed into plastic articles. ) a RIM-type mixing head having a mixing chamber, the mixing chamber being provided with orifices communicating with the chamber in an axially transverse arrangement; a source of each of the principal liquid components; separate storage devices for; conduits interconnecting each of said storage devices and a mixing head and for supplying said principal components separately at high pressure to different orifices of said head and introduced as impinging streams into said mixing chamber; and a pumping device; another storage device for a liquid component having said granular material and forming a slurry with said material; said other storage device and said slurry being introduced into said mixing chamber to introduce said main component into said mixing chamber. An apparatus as described above, characterized in that it comprises further devices including a conduit interconnecting the orifice with another orifice of the mixing head and a low pressure pump for mixing with the orifice. 2. Apparatus according to claim 1, wherein the conduit arrangement for supplying the principal components to the mixing head is connected to oppositely disposed orifices of the head. 3. Apparatus according to claim 1 or 2, wherein said further conduit arrangement for supplying said slurry to said mixing head is connected to a different orifice of said oppositely arranged orifices of said head.