Optical brightening agent

Details Optical brightening agent Optical brightening agent

1999-07-06

2001-02-13

Kelly, C. H. (Department: 1721)

Compositions

Organic luminescent material containing compositions

Optical brightening compositions

C252S589000

Reexamination Certificate

active

06187224

ABSTRACT:

DESCRIPTION
According to Römpps Chemie Lexikon (Römpp Hermann [original author]; Falbe, Jürgen [editor]; Chemie Lexikon, Georg Thieme Verlag, Stuttgart 1991) optical brighteners are chemical compounds which remove graying and yellowing from textiles, paper, plastics etc.; like dyes, they are drawn out of the liquor onto the fiber or are incorporated into the material in question, and bring about brightening and at the same time simulate a bleaching action by converting (invisible) ultraviolet radiation into (visible) light of longer wavelength. The ultraviolet light absorbed from the sunlight is reradiated as weak bluish fluorescence, i.e. in the complementary color of yellowing. These organic luminescent pigments (fluorescent dyes) thus act like optical transformers.
Optical brighteners known from the prior art comprise, for example, derivatives of 4,4′-diamino-2,2′-stilbenedisulfonic acid (flavonic acid), 4,4′-distyrylbiphenylene, methylumbelliferone, coumarin, dihydroquinolinone, 1,3-diarylpyrazoline, naphthalimide, benzoxazole, benzisoxazole and benzimidazole systems linked via CH═CH bonds, or pyrene derivatives substituted by heterocycles.
Although the known optical brighteners achieve very good results, there is a continuing need for novel improved systems since the requirements, for example as regards brightness, fastness toward sunlight, washing, ironing, additives simultaneously used, environmental compatibility and cost efficiency, are also continually increasing.
Surprisingly, it has now been found that organic spiro compounds which comprise a conjugated system are particularly suitable for use as optical brighteners.
Spiro compounds have at least one tetravalent spiro atom which links two ring systems together. This is explained in the Handbook of Chemistry and Physics, 62nd ed. (1981-2), p. C-23 to 25.
The invention thus provides an optical brightener comprising one or more spiro compounds of the formula (I),
where K
1
and K
2
, independently of one another, are conjugated systems, and &psgr; is C, Si, Ge, Sn, Pb, preferably C or Si, particularly preferably C.
Compared with conventional optical brighteners, the compounds used according to the invention have exceptional temperature stability. This is evident, for example, from the fact that the emission maximum of the compounds after heating decreases only slightly, and in some cases not at all, and that in the case of many of these compounds, even an increase in the emission maximum after heating is observed. This makes it possible to brighten those polymeric materials in which the brightener can only be incorporated into the polymeric material in the melt process (in particular industrial polymeric materials, e.g. aramid fibers). The high temperatures required for this purpose lead, in the case of the brighteners customary hitherto, to their thermal decomposition. In the production of conventional fibers, the wet spinning process can here be replaced by the melt process, which is solvent-free and therefore to be preferred for ecological reasons.
Compared with brighteners known hitherto, as well as thermal stability, improved photostability, preferably in the case of carbocyclic aromatic systems, is also achieved.
Because of the relatively high thermal and photochemical stability compared with prior art brighteners, brightening is also possible in fields of application which have hitherto been excluded. For example, these compounds can, in principle, also be used for brightening geotextiles and, because the brightener molecules have a low tendency to migrate, packaging materials.
The fluorescence quantum yield of the spiro compounds in solution and in the solid matrix can be greater than 95%. As a result, lower brightener concentrations are required for the same or, in most cases, improved brightening effect, which is advantageous both for cost reasons and for ecological reasons. Aggregation phenomena, often a problem with conventional brighteners, do not arise in the case of spiro compounds because of their structure. As a result, a favorable and, for some areas of application, necessary molecularly disperse distribution is achieved. The low tendency toward aggregation can be further utilized to achieve very high brightener concentrations, up to the pure, preferably amorphous, compound, for example in the form of a film, but nevertheless to obtain a high fluorescence quantum yield, i.e. concentration quenching does not take place.
Furthermore, these compounds are notable for high temperature stability with regard to color stability and fluorescence quantum yield. This means that the emission maximum in the range from 380 to 750 nm, measured at room temperature, decreases by no greater than 25%, relative to the initial state, after the material, applied in a thickness of no greater than 1 &mgr;m to a quartz substrate, has been heated to 250° C. in an inert atmosphere at a pressure no greater than 1 mbar for 30 min.
The reduction in the emission maximum is preferably no greater than 20%, particularly preferably 15%, relative to the initial state before thermal treatment.
The invention thus further provides an optical brightener
a) which has a fluorescence quantum yield of ≧40%, preferably ≧50%, particularly preferably ≧60% in the, preferably amorphous, solid, and
b) the emission maximum in the range from 380 to 750 nm, measured at room temperature, decreases by no greater than 25%, relative to the initial state, after the material, applied in a thickness of no greater than 1 &mgr;m to a quartz substrate, has been heated to 250° C. in an inert atmosphere at a pressure no greater than 1 mbar for 30 min.
Using the Spiro compounds, it is also possible to adjust the color shade by varying the substituents on the spirobifluorene parent substance.
For some applications, for example as effective, thin UV filters, it is also advantageous if the spiro compounds used according to the invention can be prepared amorphously. For filter applications it is advantageous if the compounds have very high extinction coefficients in the UV region, preferably between 250 and 380 nm, and can be prepared in very high brightener concentrations, up to the pure film (100%), as amorphous, thin films (for example by spin coating or sublimation).
The term amorphous is used to describe the state of solids whose molecular building blocks are arranged not in crystal lattices, but irregularly. Unlike a crystal where there is short-range order (i.e. constant distances to the nearest neighboring atoms) and long-range order (regular repetition of a base lattice) between the atoms, the amorphous state has only short-range order. The amorphous material has no physically distinguishable direction; it is isotropic. All amorphous substances strive, to varying degrees, to achieve the more energetically favorable crystalline state. In the diffraction of X-rays, electron rays and neutron rays, amorphous solids do not give sharp interference rings, as in a crystal, but only diffuse interference rings at low diffraction angles (halos).
The amorphous state is thus clearly distinguishable from the crystalline, liquid or liquid-crystalline state.
Compared with many known systems, the spiro compounds according to the invention are also readily soluble, particularly in polar solvents, in particular dichloromethane and chloroform (>30 g/l), meaning that spin coating and film formation inter alia are possible.
Processability from aqueous systems is achieved by substitution of the spiro compounds for strongly polar groups, such as carboxylic acid, carboxylate, sulfonic acid, sulfonate and quatemary ammonium groups.
The emission properties of the compounds used according to the invention can be adjusted over the entire region of the visible spectrum through the choice of suitable substituents. Furthermore, the covalently bonded arrangement of the two parts of the spiro compound permits a molecular structure such that in both halves of the molecule certain properties can be established independently of one another,

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