Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-10-21
2002-11-12
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S416000, C524S417000, C379S386000, C379S387020, C186S002000, C186S002000, C186S002000, 28, 28, 28
Reexamination Certificate
active
06479574
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention involves improving the fire resisting properties of resinous composite materials. Composite materials, most commonly fiber glass reinforced plastics, often in the form of laminates, offer a number of advantages in replacing conventional building materials such as wood, concrete, or metal. However, a disadvantage heretofore for composites has been their relatively poor ability to resist the spread of fire. This shortcoming is addressed herein.
It has been known to use intumescent coatings to provide prolonged structural integrity to walls, beams and other elements of buildings or vessels when subjected to the stress of fire. This approach is exemplified by U.S. Pat. No. 4,529,467 (Ward et al.). Intumescent compositions contain ingredients that react upon heating to generate gases and form a residue with low combustibility. The generated gases expand the residue into a foam layer with thermal insulating properties. Typically, the residue is a carbon char formed by the dehydration of a polyhydric substance such as a polyalcohol. The gas generating components of the coating are selected so that their products of decomposition do not readily support combustion, e.g., water, carbon dioxide, or ammonia. While these intumescent coatings are suitable for application onto metal surfaces in industrial settings such as refineries, ships, and drilling platforms, their textured appearance does not lend themselves to some uses. In particular, it is not considered esthetically acceptable to apply such coatings onto composite panels that otherwise present a smooth, hard, finished surface. These panels may find use, for example in transit vehicle components and in interior building modules, where appearance and a durable finish are important considerations. Compatibility of such coatings with the polymeric surfaces of the composite materials is also a concern.
Separately from the intumescent coating approach, considerable effort has been made to improve the fire resistance of polymeric materials themselves, some of them intended for use in composites. Various combinations of additives have been proposed for blending with the polymeric resin systems used for molding or laminating composites. Inorganic fillers are included in some compositions to reduce their combustion potential, but inclusion in composite resins in significantly effective amounts can compromise the strength and/or appearance of the composite. Many of the proposals involve adding a halogenated compound to the resin, but this has the drawback of generating corrosive gases and smoke upon combustion. Other additives such as arsenic or antimony compounds also have toxicity concerns.
Other approaches involve adding easily decomposable substances to the polymers that generate incombustible gases upon heating such as ammonium phosphates or hydrated alumina. Commonly used are the ammonium polyphosphates having the general formula:
(NH
4
)
n+2
P
n
O
3n+1
in which n is an integer equal to or higher than 2, preferably higher than 20 to provide low water solubility. An example of such a polyphosphate is “Phos-Chek P\30” (manufactured and sold by Solutia, Inc.) having the composition (NH
4
PO
3
)
n
, in which n is higher than 50. Other phosphate examples include those derived from amines, such as dimethylammonium and diethylammonium phosphate, ethylenediamine phosphate, and melamine ortho- or pyrophosphate.
It has also been suggested to add compounds to plastic that produce the intumescent effect; that is, upon thermal decomposition, provide gaseous products and carbonaceous residues. For this reason, the following have been disclosed as additives: polyalcohols, such as glycerol, trimethylol-ethane, trimethylol-propane, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,6-hexane-triol; carbohydrates in general (starch, cellulose, sugars); and nitrogen containing compounds, such as melamine, cyanuric acid, urea, thiourea, dicyandiamide, benzoguanamine and derivatives and condensation products thereof. In particular, it is known to yield a flame-retarding effect by combinations of a hydroxyalkyl-derivative of isocyanuric acid such as tris-(2-hydroxyethyl)-isocyanurate, together with a phosphorus-based product, such as ammonium polyphosphate, and another nitrogen-containing product, such as melamine, cyanuric acid, melamine salts, e.g., melamine cyanurate. The amounts of these additives that can be incorporated into the resins are also limited by the need to maintain the physical properties and appearance of the composites.
It would be desirable to improve the degree of fire retardance in composites by means of additives to the resins that are used to make the composites, without significantly compromising the physical properties or appearance of the composites.
SUMMARY OF THE INVENTION
The present invention provides a fire retardant additive combination that can be incorporated into conventional curable resin systems used to make composites, whereby the composites are provided with intumescent properties that provide significant reductions in the flame spread index while using relatively small amounts of the additive. The invention also encompasses uncured resin compositions incorporating such an additive combination, as well as the resulting composites.
The fire retardant additive of the present invention comprises the combination of a polyhydroxy compound, a polyphosphate, a nitrogen-containing compound, and a monomer having polyvinylic unsaturation such as a polyacrylate monomer. Although the first three constituents of this combination have been used in flame retardant compositions in the past, it has been found surprisingly that a significant lowering of the flame spread index can be obtained when such a combination further includes the monomer having polyvinylic unsaturation. The effectiveness of this additive combination permits use of relatively small amounts of flame retardant additive in resin systems commonly used for making composites, such that physical characteristics of the composites are not significantly affected.
Preferred embodiments of the compositions of the present invention have demonstrated flame spread index (as defined in ASTM E 162) below 15, and even below 10 in the most preferred embodiments. In these embodiments the resin content can advantageously be maintained above 30 weight percent, preferably above 40 weight percent, of the total weight of the resin system plus fire retardant additives.
The composition of the present invention does not require the use of halogens and is compatible with the curing mechanisms of thermosetting resin systems commonly used in composites. Viscosities of the compositions are suitable for the intended application without the need for detrimental levels of pigment loading.
DETAILED DESCRIPTION OF THE INVENTION
The curable resins to which are added a novel combination of fire retardant compounds in the present invention comprise conventional curable resin systems. The conventional curable resin systems are well known to those in the art of composite materials and are available from many commercial sources. By “curable” is meant that the composition has an initial state (either liquid or powder) in which it can be conveniently applied to a surface, and a final state in which it has been transformed into a more solid, coalesced state by chemical reaction, heat, or both. Typically the chemical reactions involve a main polymeric resin having reactive groups and a crosslinking monomer or oligomer. Catalysts may be employed to enable the crosslinking reaction to be carried out at lower temperatures. Other resin systems may be self-crosslinking, in which case a separate crosslinking monomer may not be necessary. As used herein, “curable” is intended to also include those resin systems that are thermoplastically affixed onto a composite structure, in which case, “curing” would entail heating the resin to at least its deformation temperature, but without involving any essential chemical reactions. For these thermoplastic syste
Greigger Paul P.
Liptak Stephen C.
Ward Thomas A.
Lee Rip A.
Miles Jacques B.
Millman Dennis G.
PPG Industries Ohio Inc.
Wu David W.
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