Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Composite article making
Reexamination Certificate
2001-10-09
2003-10-21
Lovering, Richard D. (Department: 1712)
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
Composite article making
C264S046900, C264S478000, C428S313500, C521S056000, C521S904000
Reexamination Certificate
active
06635203
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a composite polymeric material having high resistance to impact energy.
Specifically, the present invention relates to a composite polymeric material, to the corresponding preparation process and to manufactured articles having high impact energy absorption.
Currently, manufactured articles for automotive parts capable of absorbing impact energy, such as structures for vehicle interiors and exteriors, motorcycle crash helmets and others, are made of a single material having a polymeric base, such as expanded polystyrene, expanded polypropylene, or polyurethane foams.
These manufactured articles are generally produced with a molding technology which entails injecting an expandable polymer into a mold having a preset shape and then expanding the polymer in the presence of catalysts and/or expansion agents. At the end of the expansion, the polymer hardens and acquires the preset shape of the mold.
In particular, in the production of polyurethane manufactured articles, polyisocyanates and polyesters or glycols are injected into the mold and are made to polymerize in the presence of catalysts and expansion agents. During polymerization, the polyurethane foam forms and, by expanding, takes the shape of the mold.
However, manufactured articles resistant to impact energy made of a single polymeric material produced according to conventional technology are not free from having drawbacks in use, mainly due to the fact that they are made of a single polymeric material which does not provide an adequate resistance response to the impact, and to the shock wave. In particular, the only variable that is available to the designer is the density of the material.
For example, impact-resistant manufactured articles made of a single polymer according to the prior art, particularly expanded polystyrene helmets for motorcycles, have the drawback that they lose their impact-resistance characteristics after a single impact that causes a permanent deformation of the structure.
In the case of fenders for cars or of motorcycle helmets, permanent deformation after an impact accordingly compromises their safety characteristics, forcing the user to replace the manufactured article.
SUMMARY OF THE INVENTION
One of the aims of the present invention is to eliminate or substantially lessen the drawbacks of the prior art.
Another object of the present invention is to provide a composite polymeric material which has high-level impact energy resistance characteristics and has a long life.
A further object of the present invention is to provide a composite polymeric material which is simple to produce and does not entail high production costs.
Yet another object is to provide a manufactured article made of composite polymeric material which combines low weight with high mechanical strength characteristics.
Another object of the invention is to provide a method for producing manufactured articles made of an impact-resistant composite material whose execution entails modest operating and energy-related costs.
With the foregoing and other objects in view, there is provided, in accordance with a first aspect of the present invention, a composite material comprising a pre-expanded polymer, preferably in granular form, selected from the group consisting of polystyrene, polypropylene, a copolymer of polystyrene with a melting point above 90° C. and mixtures thereof, dispersed in a resin selected from the group consisting of melaminic resin, phenolic resin, polyurethane resin and mixtures thereof, the polyurethane resin being the preferred one among them. The expression “polystyrene copolymer” denotes a product of polymerization of polystyrene with another polymer or an alloy of polystyrene with another polymer.
DESCRIPTION OF PREFERRED EMBODIMENTS
Among polystyrene copolymers having a melting point above 90° C., preference is given to those with a melting point above 100° C.; among these, particular preference is given to the copolymer of polyphenylene oxide (PPO) and polystyrene (PS). By way of example, mention is made of the copolymer of polyphenylene oxide and polystyrene marketed under the trade-name NORYL EF (in granules or expandable beads) by the General Electric Co., USA, and of the product of the Huntsman Chemical Co., Chesapeake, Va., USA, marketed under the trade-name GECET (polymeric alloy of PS-PPO).
The pre-expanded polymer used in the present invention has advantageously been subjected beforehand to an expansion process and has a granular, spherical or bead-like shape.
The composite polymeric material according to the present invention preferably consists of a uniform dispersion of pre-expanded granules or beads in a matrix of a polyurethane, melaminic or phenolic resin.
Preferably, the polyurethane used in the present invention is obtained by condensation of an isocyanate or polyisocyanate with a compound possessing active hydrogen, both selected so as to have the following characteristics:
low reactivity; a delayed polymerization time of at least about 30 seconds allows the two components still in a fluid state to easily reach the lowest part of a mold wherein pre-expanded granules or beads are packed and then initiate the polymerization phase, so that when the polymerisation phase is completed, all (or almost all) the voids among the beads are filled with polyurethane (about 50% of the total volume of the mold);
optimal cohesion properties and adherence to the expanded beads;
optimal mechanical resistance;
low initial viscosity of the mixture of the two components, allowing an easy penetration in the voids created among the expanded beads;
high expansion capacity allowing the complete filling of the free spaces so as to obtain a homogeneous structure of the composite material;
high heat resistance;
high self-extinction.
Examples of such components are the isocyanate marketed by Dow Chemical Co., USA under the name VORACOR CD 526 and the polyol marketed by Dow Chemical Co., USA, under the name VORACOR CD 443.
The composite material having a polymeric base, according to the present invention, has high impact energy absorption because, following an impact, the impact energy is transmitted along the resinous structure, which has acquired a cellular structure whose cells internally contain the expanded polymeric granules, which undergo elastic deformation and considerably contribute to damping propagation of the shock wave and to ensuring the preservation of impact energy-absorbing properties even with subsequent impacts.
In view of these characteristics, the composite material according to the invention is particularly suitable to provide lightweight manufactured articles having high mechanical strength and resistance to impact energy and to repeated impacts.
Said manufactured articles comprise, in variable amounts, the composite material according to the invention, alone or associated with other impact-resistant materials.
Comparative tests have shown that the manufactured articles according to the invention have higher energy absorption than polystyrene and, for an equal density with respect to polyurethane, are more resistant to impact energy and to repeated impacts.
The manufactured articles according to the present invention can be entirely made of the above-described composite material or are constituted by multilayer structures in which, for example, one or more layers are made of the composite material and the remaining layers are made of other materials (polymeric and nonpolymeric).
According to another aspect of the present invention, said manufactured article is a liner for helmets, for example of the type for motorcycles, cars, work or sport. Helmet liners manufactured with the composite polymeric material according to the invention are highly resistant to impact energy and in particular maintain their impact-resistance characteristics substantially unchanged even after one or more impacts.
In particular, it has been observed that the permanent deformation of the surface structure of the manufactured article according to the invention
Guido Moniano
Josif Albert
O'Byrne Daniel
LandOfFree
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