Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-01-15
2001-06-05
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
Reexamination Certificate
active
06242511
ABSTRACT:
TECHNICAL FIELD
This invention relates to an oligomeric silane treated metal hydroxide product for use as a component in an elastomeric or polymeric composition. More particularly, the invention relates to a silane treated, ground alumina trihydrate product that provides improved mechanical properties and high levels of flame retardancy and smoke suppression in an end use application. The invention also relates to a method of preparing an oligomeric silane treated metal hydroxide product.
BACKGROUND OF THE INVENTION
Alumina trihydrate (also referred to as aluminum hydroxide, ATH, alumina, hydrated alumina, and aluminum trihydroxide) is a white crystalline powder used as a flame retardant and smoke suppressant in a number of applications including polymeric wire and cable compositions. When heated, ATH absorbs heat and releases water. This lowers the surface temperature of the polymeric composition to which the ATH is added which provides a barrier to combustion and dilutes the gases of combustion.
ATH occurs naturally as the mineral gibbsite or hydragyllite, or it is obtained directly from bauxite by the Bayer process which involves the treatment of bauxite with alkali under pressure. A common type of ATH utilized in elastomeric or polymeric compositions is an ultrafine precipitated grade ATH (PATH). PATH has been known to undesirably raise the level of the viscosity of the composition to which it is added. In order to minimize the increase in the viscosity of the composition, it is known to treat the PATH with a silane. Some commonly used silanes used in the treatment of ATH are described in U.S. Pat. Nos. 4,526,922 and 4,550,056. While the silane treatment of PATH promotes lower compound viscosity, the PATH particles still yield relatively high viscosities when added to elastomeric or polymeric formulations.
Ground ATH (GATH) has certain advantages over precipitated materials. For example, GATH filled polymeric composites typically yield lower compound viscosities and improved processing. Further, the surface area of the particles of precipitated ATH products are typically lower than the surface area of the particles of ground ATH products of the same average particle size. Higher surface area provides better flame retardancy and smoke suppression in polymeric formulations. However, this higher surface area of the ground ATH particles, particularly in vinyl silane coupled, peroxide or radiation cured compounds, has a negative impact on elongation at break. The low elongation has prevented GATH grades from replacing PATH grades in many applications such as wire and cable insulation and jacketing compounds.
SUMMARY OF THE INVENTION
The present invention is designed to overcome the deficiencies of the prior art discussed above. It is an object of the invention to provide an oligomeric silane treated metal hydroxide product that provides increased flame retardancy and smoke suppression in elastomeric and polymeric compositions.
It is a further object of the invention to provide such a metal hydroxide product which, when added to a polymeric composition, does not have a significant impact on the physical properties of the same.
It is another object of the invention to provide a method of treating a metal hydroxide product with an oligomeric silane that promotes improved manufacturing quality and consistency.
In accordance with the illustrative embodiments and demonstrating features of the present invention, there is provided an oligomeric silane treated metal hydroxide product for use in an elastomeric or polymeric formulation. The product comprises a plurality of metal hydroxide particles such as ground alumina trihydrate particles and an oligomeric silane which includes alkenyl and alkyl groups. The metal hydroxide particles are surface treated by the oligomeric silane. The alkenyl content of the oligomeric silane utilized to treat the ground alumina trihydrate is preferably less than about 12% by wt.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In accordance with the preceding summary, the present invention is directed toward an oligomeric silane treated metal hydroxide product having improved physical characteristics. The invention is also related to a method of making such a product.
The mechanism for attaching a silane to a mineral surface, e.g. alumina trihydrate, is well understood. When the mineral is treated with a silane it is imperative that the silane comes into contact with substantially every mineral particle. Moisture, present on the surface of the mineral and in the air causes the silane to hydrolyze. The resulting silanol is then free to react, first by hydrogen bonding and then via a condensation reaction, with a hydroxyl group on the mineral surface. Certain processing problems are known to exist. Specifically, since monomeric silanes have low molecular weights, a certain amount of the silane is vaporized during to the treatment process and never makes it to the mineral surface. This is particularly the case in surface treatment processes where the freshly treated product is air conveyed to packaging stations or storage silos (i.e., continuous processes). The lost silane ends up in a dust collector or is blown off into the atmosphere.
Two known monomeric silanes are vinyltriethoxysilane and vinyltrimethoxysilane. Ground ATH products treated with such monomeric silanes do not yield sufficient physical properties in end use applications. Another commercially available vinyl silane is vinyl-tris(2-methoxyethoxy) silane. However, this silane has been identified as a teratogen and its use has, therefore, been limited. A fourth known silane is believed to be a blend of an oligomeric methyl silane and a monomeric vinyl silane. Such a blend was developed by Union Carbide and is sold under the trade name RC-1 by Witco. While RC-1 offers some improvement over monomeric silanes, a drawback associated with RC-1 is that during treatment of the ground ATH more of the volatile monomeric vinyl silane component is lost than the oligomeric methyl silane. This is attributed to the fact that the reaction rate between the silane blend and the ATH is relatively slow. FTIR analysis has shown that the ratio of monomeric vinyl silane to oligomeric methyl silane changes depending on the type of process used to treat the ATH. The loss of vinyl content has a negative impact on end use performance. Further, silane loss results in increased manufacturing costs. Each of the above referenced silanes are described in U.S. Pat. Nos. 4,526,922 and 4,550,056. GATH products treated with these silanes do not provide compound elongation properties high enough to meet many industry specifications. As a result end users are not able to take advantage of GATH's lower compound viscosity and improved flame retardant and smoke suppressant properties.
A comparison of the performance of each of these silanes on a 1.5 micron GATH product sold under the mark Micral® 1500 by J. M. Huber Corporation is set forth in Table I.
TABLE I
Cross-Linked EVA 55% Loading of 1.5 micron Micral ® 1500 GATH
100%
Tensile
Final Mix
Modulus
Strength
Elongation
Torque (m-g)
psi
psi
%
Vinyltrimethoxysilane
8,800
2598
2822
128
Vinyltriethoxysilane
8,700
2477
2823
159
Vinyl-tris(20-
9,200
1996
2114
245
methoxyethoxysilane)
RC-1
9,000
2171
2547
179
Table II shows the effect of these silanes on a 1 micron PATH product sold under the mark Micral® 9400.
TABLE II
Cross-Linked EVA 55% Loading of 1 micron Micral ® 9400 PATH
100%
Tensile
Final Mix
Modulus
Strength
Elongation
Torque (m-g)
psi
psi
%
Vinyltrimethoxysilane
9,400
1985
2762
183
Vinyltriethoxysilane
10,700
1760
2486
191
Vinyl-tris(20-
10,600
1674
2127
258
methoxyethoxysilane)
RC-1
10,600
1684
2472
141
It is well known that the high surface area of GATH provides more surface for interfacial bonding with the resin than lower surface area PATH. During a peroxide or radiation (free radical) cure the vinyl groups attached to the ATH form covalent bonds coupling the resin to the ATH. More coupling occurs in the case of GATH so more of the resin becomes im
Hendrix Allen Clay
Schultz Robert Eugene
J. M. Huber Corporation
Michl Paul R.
Nieves Carlos
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