Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Composite article making
Reexamination Certificate
2000-07-31
2001-03-13
Kuhns, Allan R. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
Composite article making
C264S046600, C264S046700, C264S276000, C264S510000
Reexamination Certificate
active
06200505
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an improved method for the manufacture of a pour-in-place (PIP) composite article. These composite articles comprise a porous exterior covering and a flexible polyurethane foam core. The improvement in the pour-in-place method according to the present invention comprises applying pressurized gas to the outside surface of the exterior covering at the point directly opposite the position that the reaction mixture will be injected into the mold either at some point prior to the reaction mixture is injected into the mold, or simultaneously at the point the reaction mixture is injected into the mold, and discontinuing the application of pressurized gas after the injection step is completed.
Most furniture and automotive vehicle seats, armrests and headrests have traditionally been produced from molded polyurethane foam cushions or parts. Subsequent to the foam molding process, the part is wrapped in pre-cut and pre-sewn fabric covers. This “pre-cut and sew” method has drawbacks in that it is very labor intensive and the seats produced by this method tend to deteriorate rapidly or pockets form after repeated use. It is also difficult to achieve a consistently perfect shape from seat to seat and to produce concave contours.
To overcome deficiencies of the “pre-cut and sew” method, the so called “pour-in-place” method was developed in the 1970's. The pour-in-place method involves pouring polyurethane foam reactants in a liquid form onto a pre-shaped cover and then allowing the foam to expand and cure to form an in-situ foamed molded part. Conventional pour-in-place (PIP) technology is known and described in, for example, U.S. Pat. Nos. 4,860,415, 4,959,184, 4,976,414, 5,124,368 and 5,360,831. In the 1970's, the pour-in-place method was applied for the production of office furniture and other simple-shaped articles such as tractor seating using impermeable PVC sheet covers. The pour-in-place method using fabric covers was introduced subsequently and is now referred to as the foam-in-fabric or foam-in-cover method.
In pour-in-place foaming technology, the exterior cover material can be a fabric backed by a thin layer of foam and a urethane film barrier (the so called “barrier” technique), or a fabric backed only by a thin layer of foam. Using the barrier technique, production of molded polyurethane foam filled articles by the PIP process is very efficient.
These “barrier” techniques may include textile composites with or without foam interliners laminated with a nonpermeable film backing. These are placed in a mold and shaped to fit the contours of the mold by applying vacuum. See 33
rd
Annual Polyurethane Technical/Marketing Conference, Sep. 30-Oct. 3, 1990, D. Murphy et al, Pp. 172-176 and F. W. Schneider et al, Pp. 32-39; as well as U.S. Pat. No. 4,738,809 and EP-A-1 901 828 and EP-A-1 181 604. The non-permeable film serves two purposes: (a) when vacuum is applied between the mold surface and the laminate, no air is sucked through the laminate and the laminate is pressed upon the mold surface and (b) the foam formulation which is poured in a liquid state on top of the laminate cannot penetrate or strike-through the non-permeable layer. This eliminates unacceptable stiffening and staining of the fabric. However, since the laminate is non-permeable to any fluid or gas, there is a definite drop in thermal comfort of the seats produced with this technique. This is a clear disadvantage for car seats because lack of “breathability” makes car seats particularly uncomfortable to use for an extended period of time.
When exterior covers are only foam backed (i.e., no urethane film is present), the liquid foaming reaction mixture frequently penetrates the foam layer and forms a hard spot on the fabric surface. Although this fabric type is much less expensive to use due to the absence of the urethane film barrier, this hard spot defect results in rejects during production, a loss in efficiency and costly manual recovery of the armature or support. The cover is not reusable and the cost of cover material and the manual sewing step is also lost.
Methods of increasing reaction speed and foam viscosity, well known in the industry, are ineffective at resolving this production problem. Improvement can be made by lowering machine output but this increases cycle time and lowers production rate. Thus, manufacturers are generally unwilling to do this.
One method of avoiding this problem, is to glue an extra piece of foam backed fabric cover material on to the interior of the presewn cover directly under where the liquid foaming urethane mixture is introduced into the cover under high pressure. This additional step, however, adds to the cost of the cover assembly.
Another solution has been to use a funnel designed to divert the reaction mixture being injected away from the bottom surface of the exterior cover where the penetration occurs. This also adds to the cost of production as these funnels are expensive to produce and more difficult to clean and reuse in production.
As discussed above, the lack of “breathability” is a clear disadvantage for car seats because this results in car seats that are particularly uncomfortable to use for an extended period of time. To overcome the “breathability” problem, a so-called “non-barrier” foam-in-fabric technique has recently been developed. According to the non-barrier technique, the fabric is laminated with a polyurethane slabstock foam layer of about 2 to 5 mm thickness but without the non-permeable fill. The slabstock foam layer can be of two types, having virtually zero or low air breathability. Low breathability slabstock foams usually have less than 1.0 cfm breathability as measured in accordance with ASTM Method D-3574 p. 9 Ref.: Air Flow Test.
When a slabstock foam layer is used which has virtually zero air breathability, it protects the fabric against liquid polyurethane foam reactants to almost the same extent that is achieved by using the non-permeable film. However, the low porosity of the foam layer produces little improvement to thermal comfort of a car seat compared to the one produced by the barrier technique.
On the other hand, when a slabstock foam backing is used which has some air breathability, it is obvious that polyurethane reactants can not be poured in liquid form since they will penetrate the foam layer creating a hard spot and staining the fabric.
In order to avoid penetration of the foam layer, two techniques are currently being used. One requires the use of foam formulations which have a very fast cream time (cream foams) as described in FR-A-2,470,566. Such cream foams, however, create a problem as foam flow is reduced and, for larger molds, filling problems occur. Thus, a cream foam technique is mainly applicable for production of small articles such as car head rests. Additionally, other problems are experienced such as fogging or chemical staining of the fabric by amine vapors due to the very high levels of amine catalysts required to produce the cream foam. The high catalyst level also leads to high foam compression set values, especially after humid ageing.
The other technique uses a pre-expansion chamber. In this technique, the liquid foam reactants, after mixing, are kept for a short time in a chamber where the reactions start. The reactive blend can, therefore, reach a creamy stage before being poured onto the fabric. A version of this device is described in U.S. Pat. No. 4,925,508. The disadvantage of this technique is that it is mechanically difficult to build a reusable preexpansion chamber due to the plugging of movable parts by the reactants.
That is the reason why, in U.S. Pat. No. 4,925,508, the pouring nozzle, acting as a pre-expansion chamber, is made out of plastic (polyethylene or polystyrene) and disposed of after each pour. The use of a pre-expansion chamber described in U.S. Pat. No. 4,925,508 will particularly be inconvenient and uneconomical for use of a typical molding line where several different parts would be produced.
It is known to use gases
Bayer Corporation
Brown N. Denise
Gil Joseph C.
Kuhns Allan R.
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