Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing
Reexamination Certificate
1999-12-08
2001-09-11
Nazario-Gonzalez, Porfirio (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heavy metal containing
C252S182110, C252S182280, C252S182330
Reexamination Certificate
active
06288255
ABSTRACT:
This invention relates to organometallic compositions based on Group IVB metals and which are useful in polyisocyanate compositions especially compositions for binding lignocellulosic material.
The use of organic polyisocyanates as binders for lignocellulosic material in the manufacture of sheets or moulded bodies such as waferboard, chipboard, fibreboard 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.
One suitable polyisocyanate composition is disclosed in PCT Application WO 97/17388. This composition comprises a Group IVB metal compound, preferably a titanium chelate, optionally in combination with a compatibilising compound and/or conventional release agents. Although these compositions perform well as binders for lignocellulosic material and provide good release performance, it is desirable to develop a more economical composition which provides improved stability on storage before use, together with good curing properties and excellent bonding strength when applied to the lignocellulosic material.
It has now been surprisingly found that certain compounds of Group IVB metals and acetoacetate esters can be used to cure polyisocyanate compositions and these compositions are very stable on prolonged storage and economical when used for binding lignocellulosic material.
According to the invention, an organometallic composition comprises a complex of at least one metal selected from the group consisting of titanium, zirconium and hafnium and an acetoacetate ester in which the molar ratio of Ti or Hf to acetoacetate ester is in the range 1:2.5 to 1:10 or the molar ratio of Zr to acetoacetate ester is in the range 1:4.5 to 1:10 and said acetoacetate ester is an ester of an alcohol containing 1 to 6 carbon atoms.
The titanium, zirconium or hafnium 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, Zr or Hf) 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 and which metal, or metals, are used, but it has been shown that the “free” ester does influence the properties, particularly the stability on storage of polyisocyanate compositions containing the complexes.
The molar ratio of titanium or hafnium to acetoacetate ester in the complex is in the range 1:2.5 to 1:10. When the metal is titanium, the molar ratio is preferably in the range 1:2.5 to 1:8 and more preferably in the range 1:3 to 1:6. Particularly preferred compounds have a molar ration in the range 1:4 to 1:6. 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”. When the metal is hafnium, the molar ratio is preferably 1:4.5 to 1:10 and more preferably 1:4.5 to 1:8, hafnium to acetoacetate ester. When the metal is zirconium, the molar ratio is from 1:4.5 to 1:10 and preferably from 1:4.5 to 1:8, zirconium to acetoacetate ester. For hafnium or zirconium, again in accordance with conventional theory, it is believed that, for complexes which contain 4 or more moles of acetoacetate ester, 4 molecules of acetoacetate ester are chemically bound to each atom of zirconium or hafnium and the remainder are “free”.
Preferably, the complex is a complex of at least one of titanium and zirconium.
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 complexes of titanium, zirconium or hafnium are prepared from titanium, zirconium or hafnium alkoxides having the general formula M(OR)
4
in which M is Ti, Zr or Hf and R is a substituted or unsubstituted, cyclic or linear, alkyl, alkenyl, aryl or alkyl-aryl group or mixtures thereof. Preferably, R contains up to 8 carbon atoms and, more preferably, up to 6 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 tetramethoxytitanium, tetra-ethoxytitanium, tetra-isopropoxytitanium, tetra-n-propoxytitanium, tetrabutoxytitanium, tetrakis(2-ethylhexoxy)titanium, tetrakis(2-ethoxyethoxy)titanium, tetracyclohexyloxytitanium, tetraphenoxy-titanium, tetrapropoxyzirconium, tetrabutoxyzirconium, tetra-n-propoxyhafnium and tetra-n-butoxyhafnium.
Alternatively, the complex can be prepared from condensed alkoxides of titanium, zirconium or hafnium. 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, polybutyl zirconate 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, zirconium or hafnium compounds, such as titanium, zirconium or hafnium tetrachloride or alkoxides which have been substituted with, for example, glycol or phosphorus substituents 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 or 4 moles of acetoacetate ester per atom of Zr or Hf 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, when an organometallic composition according to the invention is used in a polyisocyanate composition, a product containing, for example, 2 moles of acetoacetate ester per Ti atom or 4 moles of acetoacetate ester per Zr or Hf atom 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 organometallic composition of the invention can be added to the polyisocyanate before or after the titanium, zirconium or hafnium compound has been added. This effectively results in the preparation of an organometallic composition according to this invention in situ in the polyisocyanate composition. Other methods of preparing the composition of the invention will be apparent to a person skilled in this art.
The organometallic complexes of the invention are particularly useful as curing agents in polyisocyanate compositions and compositions suitable for use with the organometallic compositions of the present invention may be any organic polyisocyanate compound or mixture
Imperial Chemical Industries plc
Nazario-Gonzalez Porfirio
Pillsbury & Winthrop LLP
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