Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-09-01
2002-05-28
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S131000, C525S457000, C525S453000, C525S122000, C525S227000, C525S121000, C525S903000, C522S121000, C522S142000, C522S182000
Reexamination Certificate
active
06395844
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to interpenetrating polymer networks and semi-interpenetrating polymer networks comprising a fluorescent dye or non-fluorescent having enhanced durability.
BACKGROUND OF THE INVENTION
Articles containing colorants are known to lose their color when exposed to solar radiation for extended times. In particular, fluorescent colorants degrade more quickly than conventional colorants, often turning colorless on exposure to daily solar radiation in a matter of days or months. Even though they are less durable, fluorescent dyes are commonly used for increased visibility of an article due to the visual contrast between a dyed article and its surroundings. Increased visibility is particularly important, for instance, in the traffic sign industry. Fluorescent colored signs have been shown to increase motorist and pedestrian safety, but their use remains limited due to their poor color stability and the need to frequently replace them in order to maintain effective performance.
Attempts to maintain color of fluorescent articles have included adding ultraviolet (UV) overlay screens which effectively filter radiation below 380 nm. Such protective overlays add cost and complexity to otherwise low-maintenance articles. Hindered amine light stabilizers (HALS) have been added to polycarbonate matrixes to enhance the durability of fluorescent dyes contained therein.
Interpenetrating polymer networks (IPNs), systems comprising two independent crosslinked polymer networks, have been described. See, for example,
Encyclopedia of Polymer Science and Engineering
Vol. 8; John Wiley & Sons, New York (1987) p. 279 and L. H. Sperling,
Introduction to Physical Polymer Science,
John Wiley & Sons (1986) pp. 46-47. In particular, IPNs comprising acrylate and urethane networks have been prepared by either sequential or simultaneous (but independent) polymerization of free-radically polymerizable ethylenically-unsaturated acrylate-type monomers and urethane precursors (i.e., polyisocyanate and polyhydroxy coreactants). See, for example, U.S. Pat. Nos. 4,128,600, 4,342,793, 4,921,759, 4,950,696, 4,985,340, 5,147,900, 5,256,170, 5,326,621, 5,360,462, and 5,376,428.
Single phase polymers comprising pigments or dyes have been disclosed. See, for example, U.S. Pat. Nos. 3,253,146, 5,605,761, and 5,672,643.
SUMMARY OF THE INVENTION
Briefly, the present invention provides an interpenetrating polymer network (IPN) or semi-interpenetrating polymer network (semi-IPN) comprising
a) a first phase being a continuous phase and comprising a flexible polymer, and
b) a second phase being a fluorescently durable dispersed or continuous phase and comprising a fluorescent dye and a polymer, wherein the polymer enhances durability of the fluorescent dye.
Preferably the polymer of the first phase has a Tg of at most 40° C., preferably at most 30° C. to impart flexibility of the IPN or semi-IPN under use conditions.
In another aspect, the present invention provides a multilayer construction comprising a substrate having on at least one surface thereof a substantially transparent fluorescent layer, the multilayer construction being a pavement marking tape.
In yet another aspect, this invention relates to an IPN or semi-IPN in which a conventional dye replaces the fluorescent dye described above.
In still a further aspect, this invention provides a method of enhancing the color durability of a fluorescent or non-fluorescent dye in an IPN or semi-IPN comprising the step of:
providing an IPN or semi-IPN comprising:
a first phase being a continuous phase and comprising a flexible polymer, and
a second phase being a durable colored dispersed or continuous phase comprising a dye therein, wherein the polymer enhances durability of the dye.
In the present invention, the mechanical properties of the IPN or semi-IPN are controlled by the first phase polymer, and the local environment of the dye is controlled by the second phase. This provides the advantage of optimizing the mechanical properties, such as flexibility, conformability, abrasion-resistance, and toughness, and the dye environment independently of one another.
A dye can be covalently bound to the polymer in the second phase, or it can be soluble in the polymer of the second phase. Preferably, it is covalently bound to the polymer of the second phase.
In this application:
“acrylate” means acrylic and methacrylic acid and esters thereof;
“conventional colorant” means colorants which do not exhibit fluorescent properties to the unaided eye;
“dye” means a colorant that can be dissolved in the matrix in which it resides;
“flexible” means capable of bending around a mandrel of 3 mm diameter without cracking at 23° C.;
“fluorescent dye” means a compound that exhibits fluorescent properties to the unaided eye;
“fluorescently durable” means enhanced retention of fluorescence relative to a single phase system upon exposure to weathering;
“group” or “compound” or “ligand” or “monomer” or “polymer” means a chemical species that allows for substitution or which may be substituted by conventional substitutents which do not interfere with the desired product; e.g., substitutents can be alkyl, alkoxy, aryl, phenyl, halo (F, Cl, Br, I), cyano, nitro, etc.;
“hindered amine light stabilizer” means sterically hindered amines of the class of compounds preferably represented by 2,2,6,6-tetraalkyl piperidines;
“interpenetrating polymer network” means a network of two or more polymers (two phases) that is formed by independent polymerization of two or more monomers in the presence of each other so that the resulting independent crosslinked polymer networks are physically intertwined but are essentially free of chemical bonds between them; there is produced an entangled combination of two crosslinked polymers that are not bonded to each other;
“organometallic compound” means a chemical substance in which at least one carbon atom of an organic group is bonded to a metal atom (
Basic Inorganic Chemistry,
F. A. Cotton, G. Wilkinson, Wiley, N.Y., 1976, p. 497); and “metal” means any transition metal from Periodic Groups 4-10;
“semi-interpenetrating polymer network” means a polymer network of two or more polymers that is formed by independent polymerization of two or more monomers so that the polymers (two phases) are independent but are physically intertwined and are essentially free of chemical bonds between them and wherein at least one polymer is crosslinked, i.e., thermoset, and at least one is uncrosslinked, i.e., thermoplastic; there is produced an entangled combination of two polymers, one of which is crosslinked, that are not bonded to each other; and
“weathering” means exposing an article to either natural or artificial environments which include heat, moisture, and radiation.
There is a continuing need for articles that exhibit enhanced fluorescence and color durability. In particular, fluorescent articles that retain their color and/or fluorescent properties out of doors without requiring, e.g., protective overlays, are needed.
A desire for flexible fluorescent products has led to work in polyvinylchloride, olefin copolymers and polyurethanes. Unfortunately, when these resins are employed as hosts for fluorescent dyes, poor color retention results. Factors contributing to the reduction in color include lack of dye solubility in the host matrix, dye migration, and minimal protection offered by the resin against photodegradation.
Dispersal of a second phase, preferably an acrylate phase, more preferably an aromatic acrylate phase, into these thermoplastic resins reduces the above mentioned drawbacks. Preferably, it provides for the covalent attachment of the fluorescent dye, thus preventing physical loss of the dye and provides a protective environment for the dye against photodegradation.
IPNs or semi-IPNs can include polymers that can comprise as a first phase any of crosslinked and/or thermoplastic polyurethanes, polyolefins, copolymers of olefins preferably with acrylates, block copolymers, polyvinyl chloride, natural and synthetic rubbers, as wel
Barrera Denise A.
Harelstad Roberta E.
Joseph William D.
Pavelka Lee A.
Dahl Phillip Y.
Rajguru U. K
Seidleck James J.
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