Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Reexamination Certificate
2002-01-10
2004-06-15
Gorr, Rachel (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
C428S425100, C156S331700, C524S013000, C524S014000
Reexamination Certificate
active
06750310
ABSTRACT:
This invention relates to polyisocyanate compositions and, in particular, to polyisocyanate compositions containing certain organometallic compositions based on Group IVB metals and which utility in accelerating the binding of the lignocellulosic material used in the manufacture of waferboard (known extensively as oriented strand board), medium density fiberboard and particle board (also known as chipboard).
The use of organic polyisocyanates as binders for lignocellulosic material in the manufacture of sheets or moulded bodies such as waferboard, chipboard, fiberboard and plywood is well known. In a typical process the organic polyisocyanate, optionally in the form of a solution, dispersion or aqueous emulsion, is applied to the lignocellulosic material which is then subjected to heat and pressure.
It has now been surprisingly found that specific Titanium compositions enhance the cure rate of binders such as starch, isocyanates when used for binding lignocellulosic materials especially oriented strand board
Furthermore it has been surprisingly found that certain polyisocyanate compositions containing certain compounds of Group IVB metals and acetoacetate esters are very stable on prolonged storage and provide significant acceleration to the binding of lignocellulosic material used in the core layers of waferboard (known extensively as oriented strand board), medium density fiberboard and particleboard while maintaining excellent physical properties.
According to the invention, a polyisocyanate composition comprising a titanium composition in which the molar ratio of Ti to acetoacetate ester is in the range 1:2.0 to 1:8 and said acetoacetate ester is an ester of an alcohol containing 1 to 4 carbon atoms.
The titanium composition used in the polyisocyanate composition of the invention is described herein as a “complex”. It is believed that some of the acetoacetate ester will be chemically bound to the metal (Ti) but some can be described as “free” ester. The exact proportions which are bound and free will depend partly upon the exact molar ratios present in the complex but it has been shown that the “free” ester does influence the properties, particularly the stability on storage, of the polyisocyanate composition as a binder for lignocellulosic materials. The use of the word “complex” does not imply that said complex is necessarily separately prepared before addition to a polyisocyanate to form the compositions of the invention. The complex can be formed by preparing the inventive composition using several alternative methods as described hereinafter.
The molar ratio of titanium to acetoacetate ester in the complex is in the range 1:2.0 to 1:8. Preferably, in the range of 1:2.0 to 1:6 and more preferably in the range 1:2.5 to 1:5. In agreement with conventional theories about the co-ordination chemistry of titanium, it is believed that two molecules of acetoacetate ester will be chemically bound to a titanium atom and the remainder will be “free”.
The preferred acetoacetate ester for preparing the complex is ethyl acetoacetate. The complex can be prepared from more than one acetoacetate ester but preferably only one acetoacetate ester is present in the complex.
Typically, the complex of titanium is prepared from a titanium alkoxide having the general formula M(OR)
4
in which M is Ti and R is a substituted or unsubstituted, cyclic or linear, alkyl, alkenyl group. Preferably, R contains up to 6 carbon atoms and, more preferably, up to 4 carbon atoms. Generally, all four OR groups will be identical but alkoxides derived from a mixture of alcohols can be used and mixtures of alkoxides can be employed when more than one metal is present in the complex. Suitable alkoxides include tetramethoxytitaniun, tetra-ethoxytitanium, tetra-isopropoxytitanium, tetra-n-propoxytitanium, tetrabutoxytitanium, tetrakis(2-ethylhexoxy)titanium, tetrakis(2-etoxyethoxy)-titanium.
Alternatively, the complex can be prepared from condensed alkoxides of titanium. These compounds can be represented by the general formula RO[M(OR)
2
O]
x
R, wherein M and R have the same meaning as discussed above and x is an integer. Generally, these condensed alkoxides consist of a mixture containing compounds of the above formula with x having a range of values. Preferably, x has an average value in the range 2 to 16 and, more preferably, in the range 2 to 8. A condensed alkoxide is usually prepared by the controlled addition of water to an alkoxide, followed by removal of alcohol which is displaced. Suitable condensed alkoxides include the compounds known as polybutyl titanate and polyisopropyl titanate. Complexes of condensed alkoxides can also be prepared by forming a complex of an acetoacetate ester with an alkoxide, adding water to the complex and removing any by-product alcohol.
Other titanium compounds, such as titanium tetrachloride or alkoxides which have been substituted with, for example, glycol or phosphorus substiuents can be used as raw materials for the formation of the complex used in the invention.
The complex can be readily prepared by mixing, for example, an alkoxide or condensed alkoxide with an appropriate amount of acetoacetate ester. Alcohol from the alkoxide will be displaced by the acetoacetate ester and, preferably, the displaced alcohol is removed by, for example, distillation. In a preferred method, 2 moles of acetoacetate ester per atom of Ti are added to an alkoxide or condensed alkoxide and the displaced alcohol is removed by distillation. Any additional acetoacetate ester required is then added to the stripped product. This method is advantageous because it provides a consistent product of known stoichiometry. It is possible to add all the acetoacetate ester in one charge and subsequently remove all the displaced alcohol but some of the “free” acetoacetate ester is usually accidentally removed during this process, leading to inconsistent products and contamination of the displaced alcohol.
Alternatively, a product containing, for example, 2 moles of acetoacetate ester per Ti can be prepared according to the method outlined above and this can be mixed with a polyisocyanate. Any additional acetoacetate ester required to produce the polyisocyanate composition of the invention can be added to the polyisocyanate before or after the titanium-compound has been added. Other methods of preparing the composition of the invention will be apparent to a person skilled in this art.
The amount of titanium complex present in the polyisocyanate composition of the invention is usually in the range 0.01 to 5% by weight, based on the polyisocyanate and, preferably, the amount is in the range 0.03 to 1%. More preferably, the amount of complex present is in the range 0.05 to 0.5% by weight with respect to polyisocyanate.
Polyisocyanates for use in the composition of the present invention may be any organic polyisocyanate compound or mixture of organic polyisocyanate compounds, provided said compounds have at least 2 isocyanate groups. Organic polyisocyanates include diisocyanates, particularly aromatic diisocyanates, and isocyanates of higher functionality.
Examples of organic polyisocyanates which may be used in the composition of the present invention include aliphatic isocyanates such as hexamethylene diisocyanate; and aromatic isocyanates such as m- and p-phenylene diisocyanate, tolylene-2,4- and tolylene-2,6-diisocyanate, diphenyl-methane-4,4′-diisocyanate, chlorophenylene-2,4-diisocyanate, naphthylene-1,5-diisocyanate, diphenylene-4,4′-diisocyanate, 4,4′-diisocyanate-3,3′-dimethyl-diphenyl, 3-methyldiphenylmethane-4,4′-diisocyanate and diphenyl ether diisocyanate; and cycloaliphatic diisocyanates such as cyclohexane-2,4- and -2,3-diisocyanate, 1-methylcyclohexyl-2,4- and -2,6-diisocyanate and mixtures thereof and bis-(isocyanatocyclohexyl)methane and triisocyanates such as 2,4,6-triisocyanatotoluene and 2,4,4-triisocyanatodiphenylether.
Modified polyisocyanates containing isocyanurate, carbodiimide or uretonimine groups may be employed as well. Further blocked polyis
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