Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2001-08-20
2003-03-11
McKane, Joseph K. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
active
06531613
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to new thioxanthone compounds having utility as fluorescent dyes. The dyes are useful in films and coating for various articles including, for example, traffic signs.
BACKGROUND OF THE INVENTION
Benzothioxanthene compounds are known for imparting color to certain plastic materials such as polymethylmethacrylate, polycarbonate, polystyrene, and polyester. The compounds are described, for example, in FR 2,124,384, DE-A 2,613,493, DE-A 2,815,031, IT 1,061,813 and in
Dyes and Pigments
Vol. 3 (1982), pp. 59-69. Their preparation is described in DE-B 2,134,517 and DE-B 2,134,518.
In particular, 14H-anthra[2,1,9-mna]thioxanthene-14-one compounds are described by Carlini et al. in
Dyes and Pigments
Vol. 3 (1982), pp. 59-69. One known photostable fluorescent colorant described by Carlini is 6-methoxy-14H-anthra[2,1,9-mna]thioxanthene-14-one. However, this colorant has the disadvantage of being poorly soluble in many of the polymers used to make coating and films for traffic sheeting. There is a need to find colorants of similar color and photostability with improved solubility.
SUMMARY OF THE INVENTION
The present invention provides new 14H-anthra[2,1,9-mna]thioxanthene-14-one compounds that are fluorescent colorants with improved solubility characteristics, good photodurability, and which can be made commercially at reasonable costs.
Accordingly, the present invention includes compounds of the formula
wherein R
1
is a branched alkyl group having from 3 to 22 carbon atoms; R
2
, R
3
and R
4
are each, independently, hydrogen or alkyl having from 1 to 4 carbon atoms.
The compounds of formula I are useful as fluorescent dyes in various articles and in particular retroreflective sheeting for traffic signs.
DETAILED DESCRIPTION OF THE INVENTION
Definitions
As referred to herein, the term “colorant” shall mean pigments and/or dyes or other substances used to impart hue and chroma and value to an article.
As referred to herein, the term “conventional colorant” or “ordinary colorant” are used interchangeably and shall mean colorants which do not exhibit fluorescent properties.
As referred to herein, the term “dye” shall mean substances which impart color to a substrate by selective absorption of light. Dyes are soluble and/or go through an application process which, at least temporarily, destroys any crystal structure of the color substances. Dyes are retained in the substrate by absorption, solution, and mechanical retention, or by ionic or covalent chemical bonds.
As referred to herein, the term “fluorescent dye” shall mean a dye which absorbs light at a first wavelength and emits light at a second wavelength which is longer than the first wavelength.
As used herein, the term “fluorescent pigment” refers to a particle which includes one or more fluorescent dyes in a polymer matrix of a polycarbonate, a polyester or a mixture thereof. The particle may be of any size and shape depending on the desired use.
As used herein, the term “equivalent diameter” shall mean the size that passes a rectangular opening in a screen of that dimension.
The luminance factor (CIE tristimulus value Y) is a standard measure of the amount of light (electromagnetic radiant power that is visually detectable by the normal human observer) radiating from a surface weighted by the eye's efficiency to convert the light to luminous sensation. It is defined as the ratio of the total luminance of a specimen to that of a perfect diffuse reflector illuminated and viewed under the same conditions. For a fluorescent material, the luminance factor is the sum of two quantities, the reflected luminance factor (Y
R
) and the fluorescence luminance factor (Y
F
). The fluorescence luminance factor (Y
F
) is the ratio of the fluorescence luminance (luminance due to emitted light) of the specimen to the luminance reflected by a perfect diffuser similarly illuminated and viewed. Under any specified conditions of illumination and viewing Y=Y
R
+Y
F
. It is the existence of fluorescence luminance (Y
F
>0) which differentiates fluorescent color specimens from their non-fluorescent counterparts and other non-fluorescent high luminance colored materials. The fluorescence luminance factor (Y
F
) measured under specified illumination and viewing conditions is a measure of a material's efficiency to convert absorbed electromagnetic radiant power into luminous sensation. The daytime chromaticity (x,y), total luminance factor (Y
T
), and fluorescence luminance factor (Y
F
) calculated for the CIE D65 and the CIE 1931 observer can be determined with a Labsphere BFC-450 Bispectral Colorimeter commercially available from Labsphere, North Sutton, N.H.
The present invention provides novel benzothioxanthone compounds, particularly 6-branched chain alkoxy-14H-anthra[2,1,9-mna]thioxanthene-14-one. The compounds are of formula I
wherein R
1
is a branched alkyl group having from 3 to 22 carbon atoms; R
2
, R
3
and R
4
are each, independently, hydrogen or alkyl having from 1 to 4 carbon atoms. The term “branched alkyl group” refers to a linear hydrocarbon chain which has at least one subordinate hydrocarbon chain on one or more of the carbon atoms of the primary chain. The above compounds of the present invention are photostable fluorescent dyes having a fluorescence luminance, Y
F
, greater than 3, preferably greater than about 8 and more preferably greater than about 12. The compounds have improved solubility characteristics and are soluble in a variety of solvents and polymer matrices. The compounds are used to provide articles, films, coatings and the like.
The compounds of formula I are predominantly red in color when used alone in the absence of other colorants. Preferred compounds of formula I include those where R
2
, R
3
and R
4
are hydrogen; more preferred are those wherein R
1
is a branched C
5
- to C
12
-alkyl group with C
8
- and C
9
-alkyl groups being most preferred. Particularly valuable dyes of the present invention are 6-[(2-ethylhexyl)oxy]-14H-anthra[2,1,9-mna]thioxanthene-14-one and 6-(1-isobutyl-3-methylbutoxy)-14H-anthra[2,1,9-mna]thioxanthene-14-one.
The compounds of formula I may be prepared by known methods. By way of illustration, the following schematic diagram shows a method of making 14H-anthra[2,1,9-mna]thioxanthene-14-one compounds wherein R
1
is a branched alkyl group.
Generally, a 2-hydroxybenzanthrone may be alkylated with an alkyl halide in the presence of sodium or potassium carbonate in a polar-aprotic solvent to provide the desired 2-alkoxy compound. Bromination of the alkoxy compound with n-bromo succinimide (NBS) provides the neighboring 3-bromo substituent which is then reacted with ortho-amino thiophenol at reflux in a polar-aprotic solvent such as, for example, dimethylformamide (DMF). The product is then ring-closed by treatment with hydrochloric acid, followed by reaction with sodium nitrite and then addition of a copper sulfate catalyst.
The above-described synthesis of the compounds of the present invention employs 2-oxybenzanthrones as starting materials. These starting materials can be made as described in U.S. Pat. No. 4,036,859, which patent is incorporated herein by reference.
The compounds of the present invention as fluorescent dyes may be used in a variety of ways in producing a variety of articles, laminates, pigments, articles containing pigment particles with a binder, and coating compositions for various non-retroreflective and retroreflective films, sheeting and articles. A particular use of these dyes is in traffic signage.
Compounds of the present invention may thus be admixed by blending or extruding with a polymer matrix to form various articles. The polymer matrix serves as the host for the dye and other optional adjuvants, as desired. The solubility of the compounds in the polymer matrix provides the advantage of compatibility with the polymer matrix, in addition to photostablility and effective color. The amount of comp
3M Innovative Properties Company
Fischer Carolyn A.
McKane Joseph K.
Small Andrea D.
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