Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
1999-11-29
2001-07-17
Boykin, Terressa M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C528S198000
Reexamination Certificate
active
06262218
ABSTRACT:
CROSS REFERENCE TO RELATED PATENTS
None
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not applicable.
BACKGROUND OF THE INVENTION
This application relates to optical quality polycarbonates having reduced static charge, and to methods of preparing such materials.
Polycarbonates have become the material of choice for the manufacture of optical information storage media such as audio disks, digital video disks, laser disks, optical disk memories and magneto-optical disks to which information may be written and from which it may be read from a laser. For use in these applications, polycarbonates are preferably made by a melt process, such as that disclosed in U.S. Pat. No. 5,606,008, which is incorporated herein by reference. This type of process not only avoids the use of highly toxic phosgene, which is required for manufacture of polycarbonates using the older interfacial (IF) process, it also provides a product with superior optical properties. One of the challenges facing polycarbonates manufactured using a melt process, however, is the control of static charge, since such static charge can itself interfere with read/write functions and attract a film of dust which also reduces the performance of the optical information storage media prepared with the polycarbonate.
Reduction of static charge in polycarbonates has generally been achieved through the introduction of antistatic additives. For example, Japanese Patent No. 62207358 discloses the use of phosphoric acid esters as antistatic agents, while U.S. Pat. No. 5,668,202 discloses the use of sulfonic acid sulfonium salts. Additional additives which can function as antistatic agents are distearylhydroxylamine, triphenylphosphine oxide, pyridine-N-oxide and polyoxyethylene compounds as disclosed in commonly assigned U.S. patent application Ser. No. 08/989,552, filed Dec. 12, 1997, and Ser. No. 09/161,563, filed Sep. 28, 1998, which are incorporated herein by reference.
While such additives are effective to a substantial extent, they are not without some drawbacks. Like all additives which are not an integral part of the polymer structure, they are prone to leaching, and may also undergo side reactions or otherwise impair the properties of the polycarbonate product. Thus, there remains room for improvement in the manufacture of optical quality polycarbonates.
It is an object of the present invention to provide optical quality polycarbonates with reduced static charge.
It is a further object of the present invention to provide a method for making such polycarbonates.
SUMMARY OF THE INVENTION
We have discovered that increasing the endcap level to a level greater than about 90% for Optical Quality (OQ) Melt Polycarbonate significantly reduces the as-molded Static charge for injection molded parts for Optical Disc applications. The use of resins with higher endcap levels in combination with antistatic additives provides a highly robust formulation suitable for even the most demanding emerging formats, such as Digital Versatile Disc (DVD) and in all commercial Optical media molding machines. Thus, in accordance with the present invention, optical quality polycarbonates are prepared by a method comprising performing a base-catalyzed polymerization of a diaryl carbonate and a dihydric phenol under conditions effective to produce a polycarbonate product having an endcap level of 90% or greater.
DETAILED DESCRIPTION OF THE INVENTION
Polycarbonate resins are prepared in a melt process by the reaction of a diaryl carbonate and a dihydric phenol in the presence of a basic catalyst. Commonly, the diaryl carbonate is diphenyl carbonate and the dihydric alcohol is bisphenol A, and these reactants will be used for exemplary purposes throughout the present application. Many alternative materials have been proposed for use in preparing polycarbonates, however, and the utilization of such alternative materials is intended to be within the scope of the present invention.
When diphenyl carbonate reacts with bisphenol A, it produces a growing polymer having a reactive hydroxyl group which is available for the continued growth of the polymer chain. When an alternative reaction occurs which results in the incorporation of a moiety without this reactive hydroxyl group, the ability of the chain to continue the chain extension is terminated. Chains with terminal groups of this type are said to be endcapped. A variety of endcapping reagents have been disclosed in the art, including those described in U.S. Pat. Nos. 4,774,315, 5,028,690, 5,043,203, 5,644,017 and 5,668,202 which are incorporated herein by reference. In general such endcapping reagents are utilized when producing polycarbonates by interfacial processes, rather than melt processes because they can introduce complications to the recovery of various product and recycle streams. In melt processes, therefore, endcapping generally results from the reaction of the extending polymer with free phenol, which is released as a by-product of the polymerization reaction.
The endcapping level of a polycarbonate resin can be expressed a percentage value, by determining the number of chains which are terminated with a reactive hydroxyl group (uncapped) and then taking the remainder of the chain ends as being capped. Such a determination can be made using spectroscopic measurements. The level of endcapping (E/C%) is then given by the formula:
E/C
%=(capped chain ends/total chain ends)×100
Normal melt processing reaction conditions produce polycarbonate resin products with an endcap level in the range of 80-85%. However, endcap level is not variable which is generally controlled in the Melt process. Indeed, in contrast to interfacial processes where the amount of monofunctional endcapping reactant is used to control the average molecular weight of the finished product, in the melt process molecular weight is controlled by a number of process variables such as temperature, pressure and residence time, but typically not by controlling the endcap level (except in cases where the desired material is fully endcapped). Surprisingly, however, it has now been found that control of this variable permits the production of OQ Melt Polycarbonates with desirable properties, namely low positive static charge and low dust attraction. Since, high static charge impacts CD-manufacturing process negatively by causing yield losses due to disc sticking, dust attraction and non-dye wettability for CD-R applications, this represent a substantial improvement in the quality of the product.
Control of the endcap level can be achieved in two ways: (1) by control of the process parameters such that the amount of free diphenylcarbonate in the melt is increased at least during the latter portions of the reaction to increase the frequency of encapping; and (2) by adding a monofunction reagent which will compete with bisphenol A and free diphenylcarbonate to create endcapped polymers. In the first case, the level of endcapping can be increased by increasing the initial ratio of DPC to BPA, and/or by increasing the temperature and/or residence time in the reactor before the polymerization reaction is quenched. Preferred conditions have a DPC/BPA ratio of at least 1.05, and preferably 1.07 to 1.137, and a temperature in the last reactor of 286-309° C. Residence time can be varied by changing the feed rate of the reactor. The appropriate feed rate will of course vary depending on the size of the reactor. Catalyst concentration and level of vacuum have small effects on the endcap level.
As a model, we used a form of the second approach, in which phenyl chloroformate, which has a non-volatile leaving group, was used to compete with bisphenol A. Because the leaving group is non-volatile, it cannot be readily separated from the reaction (which normally occurs in a reactive distillation column) and would interfere with product performance, recovery of product and recycle streams if used in an actual production of polycarbonate.
Control of the endcap level does not preclude the use of other additives conventionally used in the prepara
Dardaris David M.
Hoeks Theodorus L.
Inoue Kazushige
Ishida Hiromi
Marugan Monica M.
Boykin Terressa M.
General Electric Company
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