Compositions – Inorganic luminescent compositions with organic...
Reexamination Certificate
2002-05-31
2004-02-17
Koslow, C. Melissa (Department: 1755)
Compositions
Inorganic luminescent compositions with organic...
C524S786000
Reexamination Certificate
active
06692659
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to thermoplastic compositions comprising a thermoplastic resin 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.
The thermoplastic compositions can comprise a blend of thermoplastic resins. The compositions of the invention are particularly suitable for injection molding processes and film/sheet extrusion. The invention also relates to concentrates suitable for making the compositions of the invention and to objects obtained by injection molding or extrusion of the compositions according to the invention.
Phosphorescent compounds with an aluminate matrix are well known. U.S. Pat. No. 5,424,006 describes this type of phosphorescent pigments 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 phosphorescent pigments 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.
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-12-034 414 describes semitransparent light-storing resins which contain in total 1-4% by weight of a light storing phosphorescent pigment. Strontium aluminates are used in the examples of this Japanese patent application. According to JP-A-12-034 414 it was common to use phosphorescent 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 micrometers. JP-A-12-034 414 seeks to improve the balance of relative density of residual luminescence and the light transmission of the known compositions by using phosphorescent pigments with a particular particle size.
The aluminate particles suitable for use in the compositions of the invention are very hard and might cause wear of the screws in injection molding and extrusion machinery. In general, the aluminate particles can cause enough wear to remove the carbon build-up on the screws thus leading to graying of the composition processed with the screws.
It is desirable to find phosphorescent pigments that cause less graying and that can be used in smaller quantities to get the same optical effect as obtained with larger quantities of previously used pigments.
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. It is stated that graying of the composition can be minimized by selecting this particle size.
SUMMARY OF THE INVENTION
It has now be found that by incorporating phosphorescent pigments which have been coated with a silicone oil in thermoplastic resins it is possible to get less graying of the composition of the invention when processed with the screws of injection molding machines.
The invention deals with thermoplastic compositions comprising a thermoplastic resin 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 is an aluminate group, wherein the phosphorescent pigment has been coated with a silicone oil.
The thermoplastic compositions of the invention are preferably transparent or translucent to get an optimal optical effect.
It is possible to use aluminate phosphorescent pigments that have been doped with Europium.
It is also possible to use aluminate phosphorescent pigments that have been doped with Europium and at least one co-dopant like Dysprosium.
Objects formed by injection molding or extrusion of thermoplastic composition of any of the compositions of the invention also form part of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The processing of long afterglow phosphorescent pigments in polycarbonate is usually a very complex task. Since the hardness of these pigments is generally very high, extruder screws are “scrubbed” during compounding or even during the injection-molding process. This results in graying of the resin and/or the final part. A solution to this problem is to feed the pigment downstream during the extrusion. Unfortunately, although this decreases the graying issue, it does not eliminate the problem. An alternate solution is to use extremely fine pigments (maximum particle size below about 10 microns). This technique has proven useful for the further reduction of the graying issues. Downstream feeding of the pigments is the preferred method of addition of phosphorescent pigments (in powder form or dispersed in a masterbatch). Downstream feeding is not even required when extremely fine pigments are used and even a single screw extruder can compound the complete resin formulation. However, it is well known to those skilled in the art that the large phosphorescent pigment particles exhibit by far the brightest and most durable glow before being compounded in the thermoplastic resin. But it is also a well-established fact that these large particles are creating the most visible graying issues even when fed downstream during the extrusion process.
It has now been found that the graying can be minimized by using the compositions of the invention.
A. One or more thermoplastic resins and
B. 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, wherein the phosphorescent has been coated with a silicone oil.
The use of the coated pigments of the invention gives additional benefits: the moisture sensitivity of the pigments is reduced and the polymer matrix will less easily react with the pigments which sometimes can affect the properties of the thermoplastic resins.
The invention also claims thermoplastic compositions wherein the phosphorescent pigment has been coated with two different subsequently applied silicone oils. The phosphorescent pigment can have a first coating comprising a hydrogen-alkyl siloxane oil and a second coating comprising a poly dialkyl siloxane oil. The order of the coating may also be reversed. These coating steps are performed prior to compounding.
The coating is usually present in a quantity of about 0.05 to 20, more preferably 0.1 to 10 or most preferred of about 0.5 to 5% by weight with respect to the phosphorescent pigment.
The thermoplastic composition of the invention can comprise colorants that have been added to provide daylight color.
The thermoplastic compositions of the invention may comprise per 100 parts by weight of thermoplastic resin or resins 0.1 to 40, preferably 0.1 to 30, and even more preferably 0.1 to 10 parts by weight of the phosphorescent pigment.
The invention also deals with concentrates suitable for the manufacture of the thermoplastic composition of the invention. The concentrates may comprise per 100 parts by weight thermoplastic resin or resins 5-50 parts by weight of the phosphorescent pigment.
The resin compositions of the invention could appear transparent, translucent or opaque. As known by those skilled in the art, appearance depends on the exact nature and used quantities of the components of the compositions of this invention.
The thermoplastic compositions of the invention are preferably used
Brown Michael W.
Rosendale David
Schottland Philippe
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