Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Composite article making
Reexamination Certificate
1999-06-10
2002-03-19
Kuhns, Allan R. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
Composite article making
C264S046400
Reexamination Certificate
active
06358445
ABSTRACT:
The present invention relates to the preparation of multilayered polyurethane foam articles by the pouring of different foam formulations into a mold.
Multilayered or multihardness polyurethane foams are defined as layers of flexible foams of different hardness (load bearing) and/or density which have a common flat boundary. These foams are usually used to make seat cushions or squabs which have high SAG factors (that is, the ratio of hardness at high deflection to hardness at low deflection) and superior comfort, especially regarding H-point retention (seat occupant's vertical position).
Various methods are known for the preparation of multilayered polyurethane foams. However the known methods suffer many disadvantages such as, for example, low productivity, thus high production costs; long foam formulations pouring times; commingling of the foam formulations resulting in a deformation of foam layers' boundaries, thus inferior seating comfort for seat occupants.
One method for the preparation of multilayered polyurethane foam seating is described in U.S. Pat. No. 4,190,697. This patent describes a process which involves pouring into a mold the first foam formulation which is a hard foam formulation, allowing it to rise for up to 45 seconds, and then pouring the second foam formulation which is a soft foam formulation on top of the first foam formulation. The second foam formulation (soft foam) goes through the first foam formulation (hard foam) and spreads as a liquid underneath the first foam formulation which has already risen to at least 10 to 80 percent of its potential. This process is based on the principle that the rising foam has lower specific density than the fresh liquid foam formulation. This process is not practical for large industrial productions since it requires a long pouring time and, consequently is not widely used.
Another method for the preparation of multilayered polyurethane foam seating is described in European Patent No. 0'251'659. This patent describes a process which involves pouring sequentially two or more foam formulations, designed to produce two or more foams of differing hardness, onto a given point in the bottom of a seat mold and thereafter allowing the foam formulations to rise and cure. The seat mold is inclined to the horizontal plane and pouring point is located at, or near, the top of the inclined bottom surface of the mold. It is a feature of this process that the formulations are poured sequentially without any waiting time between, therefore in general little or no foaming of any of the formulations takes place on a time scale on which pouring occurs. Although, according to the patent, it would be expected that under such conditions, the formulations would mix, this does not, however, occur and, after curing, a foam seat comprising a discrete layer of the various foams is produced. The discrete foam layers are found to be bonded to one another. In this process various foam formulations, which may, for example, be hard and soft foam formulations, originate from the same outlet on the mixing head producing the formulations. The natural flow of each foam formulation down the inclined surface of the bottom of the mold is relied on to fill the mold evenly. This leads to a problem when such a process is applied to large molds, for example, those used for the manufacture of rear seats for automobiles. In such cases, it is not only difficult to obtain uniform coverage of the bottom surface of the mold, but it is necessary that the formulations have relatively long cream times to ensure that coverage is completed while the formulation(s) are still in an essentially liquid state. Another disadvantage of this process is that the time lag between pouring of two different foam formulations must be kept very short to avoid intermingling of the foam formulations in the lower part of the mold which would result in the deformation of the layers' boundaries.
Another method for the preparation of multilayered polyurethane foam seating is described in European Patent No. 0'279'324. This process involves pouring a foam formulation designed to produce a soft foam onto a given point in the bottom of a seat mold and allowing it to cream up, and then pouring a second foam formulation designed to produce a harder foam next to the first foam formulation at the time when the first foam formulation has reached a suitable density and viscosity so that the first foam formulations is lifted up and enveloped by the second foam formulation. The fact that the first foam formulation must be partially expanded before the second foam formulation is poured into the mold gives the same disadvantages as the process described in U.S. Pat. No. 4,190,697, that is, it is not practical for large industrial productions since it requires long pouring times.
Still another method for the preparation of multilayered polyurethane foam seating is described in European Patent No. 0'393'827. This patent describes a process which involves pouring two different foam formulations strip-wise into the inclined mold from two different outlets which are arranged in a line. The two outlets pour simultaneously different foam formulations while they move across and above the mold. The two outlets are attached to a single robot arm and the distance between them is less than the width of the mold. Although the speed of the robot arm is not indicated in this patent, it is obvious that the time interval between pouring the two different foam formulations is quite short. It has been found that with short time intervals between pouring of the two different foam formulations when the outputs of the foam formulations are increased, or when there is a need to pour the foam formulations very close to the upper side-wall of the mold, problems of turbulence may occur due to the velocity of the two liquids when they hit the bottom surface of the mold. The effect is that the second foam formulation which is poured onto the first foam formulation tends to push the first foam formulation downwards with intermingling of the two foams in the lower part of the mold. The resulting layered-foam article has inferior comfort properties. Moreover, due to the fact that the two pouring outlets are attached to a single robot arm and the foam formulations are poured simultaneously into the mold, the respective waiting and pouring times cannot be adjusted for different mold designs.
It is evident that there is still a need for a process for preparing multilayered foam articles which process is versatile with respect to different mold designs, giving good foam vibration properties and still allowing for fast pouring of liquid foam formulations into a mold to be viable for use on fast moving industrial foam production lines.
It has now been discovered that the problems found in the aforementioned patents can be overcome by certain modifications to the procedure by which the foam formulations are poured into the mold.
In particular, it has surprisingly been discovered that pouring the second liquid foam formulation designed to produce a hard foam onto the bottom mold surface inclined to the horizontal plane at a place which has not been wetted by the first poured liquid foam formulation designed to produce a soft foam, contrary to the teachings of European Patent No. 0'251'659, produces a laminar flowing of the second liquid foam formulation on top of the first foam formulation.
It has also been surprisingly discovered that the strip-wise pouring of liquid foam formulations according to the present invention allows not only for a longer time interval between pouring of the two foam formulations than with the fixed (one place) pouring, but also produces the flow of the second liquid foam formulation on top of the first liquid foam formulation. Thus the two-step pouring regiment can be accommodated on a dual-hardness foaming equipment with only one mixing head. In addition, the two-step strip-wise pouring allows pouring of liquid foam formulations on mold surfaces which are
Bocquel Patrice
Brown Michael J.
Casati Francois M.
Kuhns Allan R.
The Dow Chemical Company
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