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
1997-12-11
2001-03-27
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...
C524S115000, C524S323000, C385S141000, C428S375000
Reexamination Certificate
active
06207747
ABSTRACT:
This invention relates to processes, continuous processes and related compositions for producing a more photo-thermally stable flexible light pipe (“FLP”) based on polymerized units of one or more acrylic esters, and the improved FLP product which the process produces.
An effective process for preparation of acrylic-based flexible light pipe is disclosed in two patents to Bigley et al., U.S. Pat. Nos. 5,406,641 and 5,485,541. In a preferred aspect of this process, a crosslinkable core mixture is present which comprises an uncrosslinked copolymer formed mainly from acrylic esters and monomers with functionally reactive alkoxysilane groups, along with a reactive additive to cure the uncrosslinked core polymer by crosslinking it, the reactive additive preferably being water and a silane condensation reaction catalyst, such as an organotin dicarboxylate. The core mixture is preferably polymerized by a bulk (non-solvent) process, more preferably by a continuous bulk process, the uncrosslinked copolymer preferably being devolatilized prior to co-extrusion with a cladding, preferably of a fluoropolymer, into a core/clad composite which is then separately cured to the final flexible light pipe.
The process based on a monomer such as ethyl acrylate taught by Bigley et al. yields a flexible light pipe or optical conduit which has high white light transmission, and acceptable flexibility and hardness for a variety of uses where light is to be conveyed from a remote source to a target and where the conduit needs to be flexible to follow a tortuous path, yet hard enough to retain its critical geometry.
The existing process further produces a FLP of adequate thermal (exposure to heat in the absence of visible light being conducted through the light pipe) and photo-thermal (Joint exposure to heat and to visible light conducted through the light pipe, which may contain light of wavelengths known as the “near ultraviolet”) stability even after exposures to long hours of light and ambient heat. The prior art polymer has adequate stability for exposure to higher temperatures, including those up to about 90° C., for shorter use times.
However, there is a potential large market for light pipe which is thermally and photo-thermally stable at higher temperatures and longer exposure times, such as in automotive uses where the light is conducted near the engine compartment, and temperatures of 120° C. or higher may be reached. Other potential uses where high temperatures may be encountered may be when the light source is not adequately shielded from the connection with the FLP, or where the light source is of extremely high intensity. Photo-thermal stability becomes important when the light is conveyed through the FLP for long periods of time, accompanied by exposure to temperatures well above room temperature. Bigley et al. teach in general the use of stabilizers as part of the core component, but do not specifically teach or suggest an acceptable answer to this important stabilization problem.
We have discovered an improved process by which to prepare a crosslinkable acrylic core for a FLP which, after curing to crosslink, exhibits surprisingly improved stability to thermal and photo-thermal aging while detaining its other desirable properties of good initial clarity, absence of initial color, good flexibility, and adequate hardness to prevent physical distortion. An improved product, especially toward thermal aging in the absence of light being bassed through the core, can be prepared by carefully controlling the temperature of the process, preferably shortening somewhat the residence time in the reactor, and controlling the nature of the initiator, so as to decrease the number of terminal vinyl groups in the polymer. This invention is specifically addressed in a provisional United States application by several of the present inventors filed Oct. 8, 1996, as Ser. No. 60/27,942. However, the photo-thermal stability conferred by the process changes is not sufficient to enable the FLP to be used under certain demanding end-use conditions. By specific choice of a combination of antioxidants and thermal stabilizers, preferably in combination with the process improvements, the target of acceptable photo-thermal stabilization has been accomplished.
More specifically, we have discovered a crosslinkable core mixture for a subsequently-cure cured composite which mixture contains a thermoplastic core polymer, the thermoplastic core polymer having a weight average molecular weight from about 2,000 to about 250,000 daltons and preferably a vinyl end-group content of below 0.5 per 1000 monomer units, the core mixture comprising
(a) a thermoplastic core polymer comprising
i) from 80 to 99.9 weight percent of polymerized units of a C
1
-C
18
alkyl acrylate or mixtures thereof with up to 50 weight percent of the components of (a)(i) of polymerized units of a C
1
-C
18
alkyl methacrylate;
ii) from 0.1 to 18.2 weight percent of polymerized units of a functionally reactive monomer, and
iii) from 0 to about 10 weight percent of polymerized units of a refractive index increasing monomer selected from styrene, benzyl acrylate, benzyl methacrylate, phenylethyl acrylate or phenylethyl methacrylate;
iv) 0.002 to 0.3, preferably 0.01 to 0.3, weight percent of residual molecules of or of decomposition products of an initiator of polymerization, including end groups on the thermoplastic core polymer, the initiator preferably having a half-life at 60° C. of 20 to 400 minutes, more preferably 100-250 minutes;
v) 0.2 to 2.0, preferably 0.6 to 1.5, weight percent of residual molecules of or of decomposition products of a chain transfer agent, including end groups on the thermoplastic core polymer;
(b) from 0.1 to 10 weight percent, based on the crosslinkable core mixture weight, of a reactive additive; and
(c) from 0.01 to 1.0 weight percent, based on the crosslinkable core mixture weight, of a stabilizer/antioxidant combination comprising 20-80 weight percent, based on the combination, of an organic phosphite which is hydrolytically stable and 80-20 weight percent, based on the combination, of a hindered phenol, the phenol preferably separately exhibiting an absorbance of less than 1 in a 5% ethyl acetate solution in a 10 cm. cell at a wavelength of 400 Å.
The word “hindered” appears in many forms in the definition of the invention, but it is maintained because terms such as “hindered phenol” are well-known to the skilled artisan involved with polymer stabilization. The following defines terms used in the specification and claims:
(a) hindered phenol: a phenol having at the ortho position relative to the hydroxyl group of the phenol at least one alkyl group, preferably at least one tertiary(t)-alkyl group, more preferably having two alkyl groups, and most preferably having two t-alkyl groups, such as two t-butyl groups, and further when there is only one substitution at the ortho position, there is further at least one alkyl group, preferably a t-alkyl group, at the meta position;
(b) hydrolytically stable organic phosphite: an organic phosphite having at least one, preferably two, and most preferably three, aryl groups, preferably phenyl, attached through carbon-oxygen-phosphorus bonding, wherein the aryl group has at the ortho position relative to the phenolic group at least one alkyl group, preferably at least one tertiary (t)-alkyl group, more preferably having two alkyl groups, and most preferably having two t-alkyl groups, such as two t-butyl groups. Such materials are known to be hydrolytically stable in contrast, e.g., to trisalkyl phosphites.
An especially preferred stabilizer/antioxidant combination is from 500 to 3000 parts per million (ppm), i.e., 0.05 to 0.3 weight percent, of octadecyl 3,5-di-t-butyl-4-hydroxyhydrocinnamate and 500 to 1500 ppm of tris(2,4-di-t-butylphenyl) phosphite.
It is preferred that the crosslinkable core mixtures exhibit the percentage of polymerized units of a C
1
-C
18
alkyl acrylate as 80 to 99.5 weight percent ethyl acrylate, further preferred that the chain transfer agent is an
Hallden-Abberton Michael Paul
Ilenda Casmir Stanislaus
Johnson Phelps Brian
Bruzga Charles E.
Egwim Kelechi C.
Fiberstors Incorporated
Wu David W.
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