METHOD FOR MANUFACTURING RIM COMPOSITES

Abstract: A polyurethane RIM method has two mixheads. Reactants are brought to each mixhead and are supplied as separate streams to two spaced cavities in a mold having a pre-formed porous mat separating the two cavities. One stream contains an isocyanate, polyol, chain extender and crosslinker selected to have a very low viscosity and which reacts to produce a high modulus armature or load bearing member. The other stream contains a polyol and isocyanate with additives that have relatively high viscosity to produce a semi-rigid polyurethane foam. At each mixhead the proportions of ingredients are controlled to give a desired isocyanate index to control the flex modulus and other properties of the loading bearing member and foam molded components of the product. The low viscosity material penetrates the porous mat to reinforce it and the porosity of the mat prevents the high viscosity material from entering the armature cavity so as to reduce the load capacity of the finished product.

Description: This invention relates to a multi-injection process for molding polyurethane products by reaction injection molding (hereinafter 'RIM'). More particularly, this invention is a polyurethane molding System wherein first reaction ingredients are brought to a first RIM mixhead and mixed independently in the first mixhead in such proportions as may be desired to make a molded armature of high modulus physical properties for supporting a load. The molding system includes a separate source of reaction ingredients for supplying a second mixhead with isocyanate and polyol catalyzed materials to produce the semi-rigid foam material which is molded on the armature. The present invention is a polyurethane RIM process with a mold having an open cavity member and a movable lid. The mold cavity is capable of rapid and repeated opening for de-molding the product and closing to receive the next shot. The reactants include the customary long chain polyol, a chain extender, a crosslinker, the isocyanate and usually additives such as a mold release agent and, in the case of the foam material, suitable foaming agents. The reactants are supplied to each mixhead from a common source of isocyanate. Foamed articles with outer skins and load-supporting armatures have become widely used. For example, such articles are used for instrument panels in automobiles. Such RIM composites provide load support for instrument clusters supported on the armature while the foam layer and skin provide a high quality product appearance. Heretofore the manufacture of RIM composite articles required a plurality of steps, that is, the outer shell was formed with a cavity disposed therein to receive a pre-formed vinyl skin which was inserted in the cavity of the mold, along with a pre-formed armature; then an inner core was foamed within the cavity. Examples of such articles and the prior method of manufacture are shown in US-A-4,420,447, and US-A-4,228,115. Such methods require a series of separate manufacturing processes, thereby increasing the cost and reducing the efficiency of the overall manufacturing operation. Injection molding of polyester liquid against opposite sides of a filler glass mat is shown in US-A-2,903,388. Injection of plastic material between two glass mats to form insulation panels is shown in US-A-3,309,450. Laminated sheet for plastic vehicle body panels is shown in US-A-4,034,137. US-A-4,474,635 shows a cushioned panel in which molten material is forced into interstices of a surface fabric. US-A-3,918,863 discloses a method of manufacturing a composite RIM article which comprises the steps of providing a RIM mould with a female body having a cavity, therein; locating a divider in the cavity to divide it into lower and upper air-filled spaces; premixing two RIM mixtures and simultaneously injecting the RIM mixtures as separate streams into the lower and upper air-filled spaces respectively, in amounts to fill such spaces; and allowing the RIM materials to react and set within the mould to form a composite rim article in a one-step process. The present invention provides a method as disclosed in US-A-3,918,863, characterised in that one of said RIM mixtures is a low viscosity RIM mixture and the other of said RIM mixtures is a high viscosity RIM mixture, said divider has a preselected porosity, said high viscosity RIM mixture is injected at a rate that prevents high viscosity material from passing into the pores of the divider and said low viscosity RIM mixture is injected at a rate that permits the low viscosity material to penetrate the pores of the divider but without significant amounts of the low viscosity material mixing with the high viscosity material, the high viscosity material forms a foam region in one of said spaces and the low viscosity material forms a high strength region in the other of said spaces and a high strength inferface boundary between said regions. A pre-formed outer skin is loaded into the open cavity member. A pre-formed glass mat of preselected porosity is supported in the mold after the skin is loaded. The mat has sufficient stiffness to be self-supporting. The mat is located in the mold so that when the lid is closed it forms two separate mold cavities, one of which is supplied with a low viscosity mixture which reacts to form a high modulus armature and the other of which is supplied with a higher viscosity mixture that reacts to form a lower modulus semi-rigid foam material which backs the preformed skin and is molded to the armature. The low viscosity mixture and the porosity of the glass mat are selected so that the low viscosity material will penetrate into the porous mat while the porous mat prevents flow of the higher viscosity foam material into the upper cavity of the mold. Further embodiments of the invention are defined in the features of the dependent claims. Other objects and attendant advantages of the instant invention will be readily appreciated as the same become better understood by reference to the following detailed description, by way of example only, of a preferred embodiment in conjunction with the accompanying drawings wherein: Figure 1 is a diagrammatic view of a RIM mixing system used to practice the method of the instant invention. Figures 2-3 are diagrammatic views of the mold assembly for practicing the invention; and Figure 4 is a fragmentary, enlarged sectional view of a composite RIM product formed by the invention. With reference to the drawing, illustrated is a three-stream polyurethane RIM process for practicing the teachings of this invention. An isocyanate stream composed of an MDI prepolymer is prepared and stored at 10, a polyol stream A is prepared and stored at 12 and the polyol B stream is prepared and stored at 14. Each of these streams is conducted by manifolds 16, 18 and 20 to feed lines and hence to mixheads 22, 24, respectively, under control of supply control valves 26, 28 and supply control valves 30, 32. Mixheads 22, 24 have bypass control valves 34, 36 and 38, 40, respectively, to recirculate material during cure periods. For mixhead station 24, the polyol B stream is introduced from line 20 by line 42 through control valve 32, and sufficient isocyanate from manifold 16 is added via line 44 and control valve 30 to give an isocyanate index of 80 to 105. Similarly, polyol A is supplied to mixhead 22 via line 46 and control valve 26. Isocyanate is added by line 48 and control valve 28 to give an isocyanate index of 100 to 120. The reaction injection molding mixture from outlet 50 of mixhead 22 is directed through inlet sprue 52 to a mold assembly 54 and the mixture from outlet 55 of mixhead 24 is directed through inlet sprue 56 to mold assembly 54. Usually, with this type of RIM process, injection or mold filling is completed in less than 5 seconds, and the product is de-molded in less than a minute thereafter. For example, the time from the initial mixing of the two ingredients in the mixheads to complete filling of the mold in each cycle may be less than 1.2 seconds. Cure times are quite rapid, and products may be de-molded from the molds in less than two minutes from the time of completion of injection into the molds. As shown in Figures 2 and 3, the mold assembly 54 has a mold cavity 58 defined by a female body member 60 and a cover member 62. The mold assembly is understood to include any standard clamping means (not shown) for holding and sealing the cover member 62 to the body member 60. Within the mold cavity 58 and temporarily secured to the cover member 62 is a porous glass fiber divider 64. The divider 64 separates the mold cavity 58 into two sections, an upper or load-bearing armature defining space 66 and a lower or foam backing space 68. Glass fiber mat 64 has a preselected porosity that permits "low viscosity" material from mixhead outlet 50 to penetrate into the glass fiber mat as the upper open space 66 is filled with the reacting mix of polyol A and isocyanate but at a rate which will prevent any significant overflow into the foam space 68. The glass fiber mat has sufficient strength to support the weight of material inflow into upper open space 66. The porosity of the mat 64 is selected to prevent the "high viscosity" reacting material from mixhead outlet 55 from passing upwardly through the divider 64 into the space which is being filled with high strength armature material. Consequently, the divider 64 is impregnated mainly with high strength material to define a high strength interface boundary at the armature and foam cover. The divider means 64 can be made of a variety of porous materials such as woven glass mat or porous board which will define and maintain the desired shape of the final armature section. Preferably, the divider 64 has enough rigidity to accurately maintain the load armature shape and the depth of the foam layer during mold fill and cure. The mold cover member 62 includes pour hole or passage 70 which communicates through sprue 56 with the space 68 and a pour hole or passage 72 which is in communication with the space 66 through sprue 52. When the mold cover member 62 is clamped in place with the divider 64 held within the mold cavity to define the armature space 66 and foam spaces 68, the mold assembly 56 is ready to receive the two separate flow streams. In one application of the inventive process, an outer vinyl skin layer 74 is loaded into the female body member 60. The preformed glass divider 64, stiff enough to support its own mass, is then added to the cavity, but spaced a finite distance above the skin material by a spacer 76. Optional at this point, additional non-formed glass fiber may be added on top of the preformed divider. The lid of the mold is then closed to allow a net air-filled space defined by space 68 between the vinyl skin layer and divider 64 and an air-filled space between the divider 64 and the mold cover member 62. By then using two separate mixheads, the "to be" armature component, polymer A, is introduced into the upper air space and the polymer B, is added to the lower air space. The function of the glass preform is to effect a barrier to migration of higher viscosity polyurethane from the lower space but allow migration of the low viscosity polymer A into the glass mat preform below it. Polymer B is a material known in the art to form a polyurethane foam backing layer made by high pressure impingement mixing of isocyanate and polyol catalyzed materials. Polymer A is a polymer, such as polyurethane/polyester/polyamide/polyolefin made by the liquid RIM process, but of a very low viscosity to permeate the divider. Polymer A forms a high modulus weight supporting armature 78 for the resultant RIM composite product. The injection operation is timed so that as the materials fill the two sections of the mold cavity the divider 64 will not be distorted but will maintain its original shape to produce a desired armature shape. The duration and relative timing of the two shots of reacting polymeric material depend on the reactivity of each material used. The semi-rigid foamable material expands at a rate which causes no significant distortion or change in the position of the divider 64 and its viscosity is high enough to prevent significant intrusion into the armature region. The viscosity of the higher modulus material enables it to penetrate the divider 64 so that the divider becomes an integral part of the armature. The inflow is at a rate that prevents the high viscosity material from passing into the pores of the divider and which permits the low viscosity material to penetrate the pores of the divider without significant amounts of the low viscosity material mixing with the high viscosity material. The resultant article includes the armature 78, a polyol A impregnated divider 64 and a semi-rigid foam layer 82, all shown in Figure 4. The materials having been injected are allowed to cure as is the normal practice. The RIM composite article is then removed from the mold cavity and the divider with its impregnation of polymer A material remains an integral part thereof. It is to be understood that the divider 64 may be selected for its contributory physical properties; that is, the thickness, composition, or design may be varied to allow it to contribute to the load support capabilities of the composite article. The method is not restricted to two-layer articles because it is obvious that additional divider means and pour holes may be provided so that three or four layers of high modulus material and foam material may be produced. By the method and provisions thereof set forth in the preceding description, a method for manufacturing a composite RIM article and in particular a load support armature and foam backed skin covered interior automobile part is disclosed. While a novel method and mold assembly for manufacturing a specific form of RIM article have been illustrated and described in the foregoing specification and accompanying drawings, it should be understood that the invention is not limited to the exact method and assembly shown but that various alternatives in the construction and form are possible.

Claims: A method of manufacturing a composite RIM article which comprises the steps of providing a RIM mould with a female body (60) having a cavity (66,68), therein; locating a divider (64) in the cavity to divide it into lower and upper air-filled spaces (68,66); pre-mixing two RIM mixtures and simultaneously injecting the RIM mixtures as separate streams into the lower and upper air-filled spaces respectively, in amounts to fill such spaces; and allowing the RIM materials to react and set within the mould to form a composite RIM article in a one-step process; characterised in that one of said RIM mixtures is a low viscosity RIM mixture and the other of said RIM mixture is a high viscosity RIM mixture, said divider (64) has a preselected porosity, said high viscosity RIM mixture is injected at a rate that prevents high viscosity material from passing into the pores of the divider and said low viscosity RIM mixture is injected at a rate that permits the low viscosity material to penetrate the pores of the divider but without significant amounts of the low viscosity material mixing with the high viscosity material, the high viscosity material forms a foam region (82) in one of said spaces and the low viscosity material forms a high strength region (78) in the other of said spaces and a high strength interface boundary (64) between said regions. A method as claimed in claim 1, wherein said female body (60) is pre-loaded with a preformed vinyl skin (74). A method as claimed in claim 1 or claim 2 wherein said divider (64) is composed of glass fibre material. A method as claimed in any preceding claim wherein said low viscosity RIM material is selected to have an isocyanate index in the range of 100 to 120 to produce a load carrying member in the composite RIM article. A method as claimed in any preceding claim wherein said high viscosity RIM material is selected to have an isocyanate index of 80 to 105 to produce a semi-rigid foam layer in the composite RIM article. A method as claimed in any preceding claim wherein the low viscosity RIM mixture is selected from polyurea, polyester and polyamide. A method as claimed in any preceding claim of making an instrument panel, wherein said high-strength region (78) is formed as a load-bearing armature portion of the instrument panel.

Inventors: PRESTON, FRANK J.
Applicants: EX-CELL-O CORPORATION
Application year: 1987
Main classification: B29C67
IPC codes: B29C45, B29K105, B29C44, B29C67, B29C70, B29K75, B29C39