Compositions – Inorganic luminescent compositions with organic...
Reexamination Certificate
2002-05-31
2004-01-13
Koslow, C. Melissa (Department: 1755)
Compositions
Inorganic luminescent compositions with organic...
C524S706000
Reexamination Certificate
active
06676852
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to thermoplastic compositions comprising one or more thermoplastic resins and a phosphorescent compound with an aluminate matrix. The compositions of the invention are particularly suitable for injection molding processes. The invention also relates to objects obtained by injection molding of the compositions according to the invention.
The addition of phosphorescent pigments to substantially transparent polymers generally provides the composition with good glow performance characteristics. The use of substantially transparent polymeric matrices such as polycarbonate allows the composition to be easily and efficiently excited by light. Moreover, the subsequent emissions of phosphorescent light from the composition are not filtered or scattered, except by the pigments themselves.
Phosphorescent compounds with an aluminate matrix are well known. U.S. Pat. No. 5,424,006 describes this type of phosphors and refers to the possibility to mix them into a plastic material.
U.S. Pat. No. 5,607,621 describes phosphorescent synthetic resin materials comprising about 5 to about 20% by weight of similar aluminate based phosphors and a synthetic resin. Many synthetic resins are mentioned by way of example.
U.S. Pat. No. 5,976,411 describes molded, extruded or formed phosphorescent plastic articles made out of a plastic composition comprising a thermoplastic or a thermosetting resin, about 1% to about 50% by weight of a phosphorescent pigment and about 0.001% to about 20% by weight of a laser energy absorbing additive. Polycarbonate has been mentioned as one of the many suitable resins.
U.S. Pat. No. B1-6,375,864 describes compositions and molded, extruded or formed phosphorescent plastic articles produced therefrom comprising phosphorescent phosphor pigments preferably in combination with polymer-soluble daylight fluorescent dyes.
JP-A-2000-034 414 describes semitransparent light-storing resins which contain in total 1-4% by weight of a light storing pigment. According to JP-A-2000-034 414 it was common to use pigments with a very wide range of particle sizes varying from several tens micrometers to hundreds of micrometers and an average particle size of about 10-20 micrometer. JP-A-2000-034 414 seeks to improve the balance of relative density of residual luminescence and the light transmission of the known compositions by using pigments with above described particle size. Upon incorporation of the pigments of JP-A-2000-034 414 in a polycarbonate resin, the favorable physical properties of the polycarbonate get lost. The aluminate particles are very hard and cause wear of the screws in injection molding machinery. The wear is so strong that graying of the composition processed with the screw may result.
U.S. patent application Ser. No. 09/922,624 filed on Aug. 6, 2001, describes transparent or translucent thermoplastic compositions comprising a thermoplastic polycarbonate resin and a phosphorescent pigment (phosphor). The phosphor is present in a quantity of 0.01 to 2.0% by weight. The phosphor should have a median particle size of less than 10 micrometer.
Unfortunately the addition of phosphorescent pigments (phosphors) causes degradation of the matrix because of the abrasive nature of the pigment particulates. This results in graying of the matrix due to polymer degradation during the compounding process. Further, the addition of very small quantities of phosphorescent pigment to a polycarbonate matrix causes a significant decrease in impact properties. There accordingly exists a need for polycarbonate components and parts that exhibit good glow performance characteristics, as well as low temperature ductility and impact strength.
It is a common belief that optimal phosphorescence can be obtained with transparent or translucent materials only.
SUMMARY OF THE INVENTION
It has now be found that it is possible to obtain thermoplastic compositions with a good phosphorescence even when the compositions are not transparent or highly translucent by incorporating in the thermoplastic composition a graft copolymer with a rubbery graft base upon which one or more monomers have been grafted. It has also become possible to obtain less graying of the composition of the invention when processed with the screws of injection molding machines.
The addition of graft copolymers to transparent polymers generally causes the blend to be translucent or opaque and it would therefore be anticipated that the addition of a graft copolymer to improve the impact properties of a polymer containing a phosphorescent pigment would therefore retard the afterglow characteristics of such a composition. It has been unexpectedly discovered however, that the addition of a graft copolymer to a thermoplastic resin containing phosphorescent pigments detailed below provides the composition with brighter and longer afterglow properties along with low temperature ductility. These compositions can be utilized in a large number of commercial applications especially in automobiles, decorative housing for computers and telecommunication equipment.
The invention deals with thermoplastic compositions comprising a thermoplastic resin or a blend of thermoplastic resins, a graft copolymer comprising a rubbery graft base upon which one or more monomers have been grafted and a phosphorescent pigment with an aluminate matrix expressed by M-Al, in which M is at least one metal element selected from calcium, strontium and barium and Al represents an aluminate group such as Al
2
O
4
.
The compositions of the invention preferably have a diffuse light transmission of less than 20% according to ASTM D1003 measured on parts with a thickness of 2.54 millimeter molded out of the thermoplastic composition.
The thermoplastic resin is preferably a polycarbonate resin or a blend of a polycarbonate resin and or more thermoplastic resins.
The rubbery graft base of the graft copolymer preferably has a glass transition temperature below room temperature or even more preferred below minus ten degrees Celsius. A preferred graft copolymer can be obtained by grafting one or more of the following monomers: acrylate, methacrylate, acrylonitril and a vinyl aromatic monomer on a rubbery graft base, comprising units derived from a diene.
It is possible to use aluminate phosphors that have been doped with Europium.
It is also possible to use aluminate phosphors that have been doped with Europium and at least one co-dopant like Dysprosium.
The compositions of the inventions preferably comprise per 100% by weight of the mentioned components taken together 50-98, more preferably 60-90% by weight of the thermoplastic resin or blend of thermoplastic resins, more than 1, more preferably 2-25% by weight of the graft copolymer and more than 0.01, more preferably 0.05-5% by weight of the phosphorescent pigment.
The invention also deals with concentrates suitable for making the compositions of the invention. It is possible that the concentrates are made by one company and the final composition by another company.
The concentrates of the invention comprise a thermoplastic resins and/or a graft copolymer comprising a rubbery graft base upon which one or more monomers have been grafted and a phosphorescent pigment (phosphor) with an aluminate matrix expressed by M-Al, in which M is at least one metal element selected from calcium, strontium and barium and Al represents an aluminate group such as Al
2
O
4
, in a quantity of at least 5% by weight, calculated with respect to the total quantity of the mentioned components.
Objects formed by injection molding of any of the compositions of the invention also form part of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The compositions of the invention comprise the following essential components:
(a) 50-99% by weight of a thermoplastic resin or a blend of thermoplastic resins; (b) 1-50% by weight of a graft copolymer comprising a rubbery graft base upon which one or more monomers have been grafted, the quantities of (a) and (b) being calculated with respect to the sum of component (a)
Brown Michael W.
Hurst Jeremy D.
Peak Steven Richard
Schottland Philippe
Timmerman Theodorus J. M.
General Electric Company
Koslow C. Melissa
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