Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – By mechanically introducing gas into material
Reexamination Certificate
1999-01-19
2002-08-13
Kuhns, Allan R. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
By mechanically introducing gas into material
C521S110000
Reexamination Certificate
active
06432335
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of flexible or supple materials made of expanded or foamed polymer which can be used in particular for the preparation of leaktight, insulation and/or damping components.
2. Description of the Background
In this field, synthetic materials in the form of foam or having a cellular structure, manufactured as a broad strip or as a strand, which is cut to the desired dimensions and which is applied to the corresponding surface via an adhesive layer, are known. A material widely used is PVC foam manufactured from a plastisol to which a foaming agent has been added. However, this is difficult to implement when the surface has a complex geometry. It can also take too long to carry out in the context of large scale mass production of parts.
For these applications, in particular in the automobile industry or in industries for the manufacture of various electrical devices, a technique has been developed for the production of a gasket foamed in situ or in place (formed in place foam gasket or foamed in place gasket—FIP) by deposition in place of a material with an appropriate viscosity which changes into a foam by crosslinking in the open air. The material can be applied into a groove, in a form or on a smooth surface in the case of thixotropic or three-dimensional systems.
A first alternative form of this technique uses, as the material to be deposited, a system with two components (two-component system) each of which are stored separately from one another and mixed in appropriate amounts just before application by devices for metering and mixing under reduced pressure. Two-component systems are known for forming silicone or polyurethane foams. This technique is disclosed in particular in EP-A-0,416,229.
A second alternative form of this technique eliminates the disadvantages related to metering and mixing at the time of use by using a so-called single component system: the material to be deposited is prepared in advance and is provided in a stable form which can be stored under an inert atmosphere until use.
A typical composition suited to this use is disclosed in EP-A-0,326,704. It comprises a first prepolymer component, which can self-crosslink with water, as an intimate mixture with a second noncrosslinked elastomer component, so as to constitute, after extrusion and crosslinking, a material of the interpenetrating polymer network type. Depending on the viscosity of the mixture and the treatment conditions, the extruded substance can form the foam spontaneously or the foaming can be obtained by virtue of a chemical or physical agent. An example of equipment suitable for extruding this substance in the presence of a foaming gas is disclosed in U.S. Pat. No. 4,405,063.
Although this technique relatively easily produces a foamed gasket having qualities which are sufficient for applications in sealing, insulation or others as mentioned above, it can be further improved in order to achieve improved performance.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a composition of substances having an improved ability to foam which makes it possible in particular to obtain products of relatively low relative density with mechanical properties at least as good as those of known products.
This object, as well as others which will become apparent subsequently, are achieved by using, as extrudable composition, a single-component product comprising a single macromolecular constituent containing a polyurethane prepolymer comprising isocyanate or trialkoxysilyl end groups which is self-crosslinkable with moisture.
Against all expectation, the Inventors found that it is possible to form a satisfactory foamed product without resorting to an interpenetrating network structure according to EP-A-0,326,704, in which structure the elastomer component serves to impart to the material the elasticity necessary for its mechanical strength, while the crosslinkable component contributes the thermosetting nature to the material. On the one hand, a composition comprising only a thermosetting polyurethane prepolymer lends itself perfectly to the technique of extrusion in the presence of pressurized gas: it does not present any problem of a rheological nature at the outlet of the extrusion nozzle, and the composition forms, fairly rapidly and without sagging, a foam which virtually instantaneously acquires dimensional characteristics very similar to the definitive characteristics. The flexible cellular material may therefore not include a noncrosslinked elastomer component, or the only organic polymer in the flexible cellular material may be one or more polyurethanes. Likewise, the polyurethane prepolymer may be the sole organic polymer in the extrudable composition, or the extrudable composition may not include a second elastomeric polymer.
On the other hand, under optimum manufacturing conditions, a composition comprising only a polyurethane prepolymer forms a foam with a lower relative density than a composition additionally comprising at least one other macromolecular constituent. The same volume of foamed material is thus obtained with a reduced amount of substance. A substantial saving in substance is achieved while retaining mechanical characteristics, in particular flexibility characteristics, which are sufficient for applications such as leaktight or insulation seals.
DETAILED DESCRIPTION OF THE INVENTION
The present invention produces cellular materials for which the density (after crosslinking) is less than 300 kg/m
3
, in particular on the order of 260 kg/m
3
or less, in particular on the order of 250 kg/m
3
or less, for example less than or equal to 200 kg/m
3
.
The cellular material obtained is flexible with, advantageously, a substantially elastic behaviour. The material can generally have a compression set at room temperature of less than 25%, advantageously on the order of 15% or less, in particular of less than or equal to approximately 10%, for example on the order of 5% or less. A low compression set indicates a good ability of the material to withstand compression. The values indicated above are compatible with a lasting leaktight capability in the usual applications.
Furthermore, the material as a crosslinked foam generally exhibits a smooth skin and a relatively fine to very fine cellular structure, which indicate the ability of the single-component product to prevent the bubbles of gas from bursting at the free surface of the extruded substance while preventing the coalescence of the bubbles of gas within the material. These characteristics make the material entirely suited to applications in leaktightness and/or insulation.
The cellular structure is advantageously such that the cells have a dimension of less than 0.3 mm, preferably of less than 0.2 mm. Structures comprising cells with a very small dimension, for example with a size of less than 0.1 mm, are particularly advantageous. “Fine” describes a structure in which the cells have dimensions of between approximately 0.1 and 0.3 mm, and “very fine” describes a structure in which the cells have dimensions of between approximately 0.03 and 0.2 mm.
In addition, the Inventors have demonstrated the fact that the foaming increases as the polymer system of the single-component product exhibits, at the supramolecular level, a reduced number of phases. Preferably, the polyurethane prepolymer forming the macromolecular constituent of the single-component product is essentially single-phase.
“Essentially single-phase” means a polymer system in which the macromolecular chains are essentially miscible. This is in particular the case when the polyurethane prepolymer is a homopolymer, the macromolecular chains being arranged in a single, perfectly homogeneous phase. This can also be the case when the prepolymer is a random copolymer. This can still be the case when the prepolymer is a block or grafted copolymer in which the various blocks (derived from at least two distinct monomers) are miscible with one another, optionally in a s
Ladang Michel
Mertens Marc
Petit Dominique
Kuhns Allan R.
Norton Performance Plastics
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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