Fluorescent cyanoacrylate adhesive

Details Fluorescent cyanoacrylate adhesive Fluorescent cyanoacrylate adhesive

1999-04-23

2001-03-20

Sanders, Kriellion (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C252S182150, C428S412000, C428S500000, C428S522000, C522S079000

Reexamination Certificate

active

06204309

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a cyanoacrylate adhesive containing a pyrylium salt as a fluorescent dye and to its use.
2. Discussion of Related Art
Adhesives of this type are already known. Thus, EP 0 105 062 B1 describes a cyanoacrylate adhesive containing at least one dye from the group consisting of C.I. Solvent Green 5, C.I. Acid Red 50 and C.I. Acid Red 52 in a quantity of 5 to 1000 ppm, based on the monomers. The disadvantage of these dyes lies in their bright, clearly visible color, particularly where the parts to be joined are transparent. In addition, the dyes are poorly soluble in the monomers. Accordingly, it is not possible to prepare a master batch of cyanoacrylates and the dye, i.e. a stock mixture of cyanoacrylates with a high concentration of dye which the user himself is then able to dilute to the extent required by the particular situation.
Against the background of this prior art, the problem addressed by the present invention was to provide a cyanoacrylate adhesive containing a fluorescent dye, the dye showing very little, if any, inherent coloration in visible light and lending itself to use in relatively large quantities without any adverse effect on the storage stability and adhesive properties of the adhesive.
SUMMARY OF THE INVENTION
The solution provided by the invention is defined in the claims and consists in a highly specific choice of the pyrylium salt. The cyanoacrylate adhesives according to the invention are characterized by an effective concentration of at least one pyrylium salt corresponding to the following general formula:
in which R
1
to R
5
represent hydrogen, alkyl and aryl groups or a fused aromatic radical at two vicinal positions. The substituents may in turn bear alkyl, aryl, alkoxy, aryloxy groups, halogen or pseudohalogen atoms. The total number of carbon atoms in the substituents should be from 1 to 18 and, more particularly, from 6 to 10. The substituents may be the same or different. The counterion A
−
may be selected from non-nucleophilic anions such as, for example, hexafluorophosphate, hexafluoroantimonate, tetrafluoroborate, perchlorate and tetrachloroferrate. Dyes used in accordance with the invention include 2,4,6-triphenyl pyrylium tetrafluoroborate, 2,4,6-triphenyl pyrylium trifluoromethane sulfonate, 2,4-ditert-butyl-6-(2-methoxyphenyl)-pyrylium tetrafluoroborate, 1,4-phenylene-4,4″-bis-(2,6-diphenyl-4-pyrylium tetrafluoroborate), 2,4-diphenyl-6-(4-methoxyphenyl)pyrylium perchlorate; 2,4-diphenyl-6-(p-tolyl)-pyrylium tetrachloroferrate.
DETAILED DESCRIPTION OF THE INVENTION
The dyes are present in the adhesive in concentrations of 5 to 50,000 ppm and, more particularly, 20 to 10,000 ppm.
The adhesive is preferably free from solvents or solubilizers for the dyes and the monomers. Solvents are preferably used where a concentration of more than 0.3% by weight of dye is to be dissolved.
The following example illustrates the high solubility of the dyes used in accordance with the invention:
2,4,6-triphenyl pyrylium tetrafluoroborate
can be introduced into ethyl cyanoacrylate at room temperature in a quantity of up to about 2.5%. By contrast, other dyes, such as for example Acid Red 50 and Acid Red 52, only dissolve in concentrations of up to a few hundred ppm at room temperature.
This high concentration enables the master batch process to be applied. If, for example, the stock solution has a concentration of 2.5% by weight, the user can easily dilute it to the required concentration without encountering dosage or homogeneity problems. The stock solution preferably has a concentration of 0.1 to 5% by weight of pyrylium salt (the upper limit being determined by the solubility factor).
Another unexpected advantage of the dyes used in accordance with the invention is their fastness to light. In the liquid state, a cyanoacrylate adhesive colored with the pyrylium salts mentioned above shows no reduction in fluorescence intensity, even after several minutes' exposure to UV light (254 and 365 nm).
In addition, the relatively low inherent coloration of the dyes used in accordance with the invention in visible light enables them to be universally used because bonds established with the correspondingly colored adhesives do not show any visible inherent coloration in the adhesive joint, even where the joined parts are transparent. They fluoresce on exposure to short-wave light. The fluorescence signal reflected by the adhesive present on the substrate enables the application of the adhesive to be controlled with the assistance of a luminescence probe.
In the context of the invention, “&agr;-cyanoacrylates” are understood to be both typical monocyanoacrylates and also biscyanoacrylates.
“Typical monocyanoacrylates” encompass compounds corresponding to the following general formula:
H
2
C═C(CN)—CO—O—R  (II)
in which R is an alkyl, alkenyl, cycloalkyl, aryl, alkoxyalkyl, aralkyl or haloalkyl group containing 1 to 24 carbon atoms and, more particularly, 1 to 12 carbon atoms, more especially a methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, pentyl, hexyl, allyl, methallyl, crotyl, propargyl, cyclohexyl, benzyl, phenyl, cresyl, 2-chloroethyl, 3-chloropropyl, 2-chlorobutyl, trifluoroethyl, 2-methoxyethyl, 3-methoxybutyl, 2-methoxyisopropyl and 2-ethoxyethyl group. The cyanoacrylates mentioned above are known to the expert on adhesives, cf. Ullmann's Encyclopaedia of Industrial Chemistry, Vol. A1, page 240, Verlag Chemie Weinheim (1985) and U.S. Pat. No. 3,254,111 and U.S. Pat. No. 3,654,340. Preferred monomers are the allyl, methoxyethyl, ethoxyethyl, methyl, ethyl, propyl, isopropyl or butyl esters of 2-cyanoacrylic acid.
“Bis(cyanoacrylates)” are understood to be compounds corresponding to the following general formula:
[H
2
C═C(CN)—CO—O]
2
R
6
  (III)
in which R
6
is a branched or unbranched difunctional alkane radical containing 2 to 18 and, more particularly, 6 to 12 carbon atoms which may additionally contain hetero atoms, such as halogens and oxygen, or aliphatic or aromatic rings. However, R
6
is preferably a pure hydrocarbon.
It is important that the bis(cyanoacrylates) should be particularly pure. This requirement is satisfied, for example, by the following methods of production and purification. Essentially, monocyanoacrylates are transesterified with diols and the reaction mixtures are then worked up by fractional crystallization. Accordingly, a suitable method for the production of biscyanoacrylates comprises transesterifying 2-cyanoacrylic acid or alkyl esters thereof corresponding to the following general formula:
H
2
C═C(CN)—CO—O—R
7
  (IV)
in which R
7
is a branched or unbranched radical containing 1 to 6 carbon atoms, with diols corresponding to the following general formula:
[HO]
2
R
1
  (V)
in which R
1
is a branched or unbranched difunctional alkane radical containing 2 to 18 carbon atoms which may additionally contain hetero atoms, such as halogens and oxygen, or aliphatic or aromatic rings, to form bis(cyanoacrylates) corresponding to general formula III and then purifying the reaction mixture by fractional crystallization. Further particulars can be found in WO 95/33708.
Besides these two key components, the cyanoacrylate adhesive also contains typical stabilizers, for example hydroquinone, sulfur dioxide, boron trifluoride and methane sulfonic acid, in the usual quantities.
In addition, the adhesive according to the invention may contain other additives, for example plasticizers, activators or accelerators, thickeners and/or elasticizers, coupling agents and other dyes.
The adhesives according to the invention are prepared in the usual way by mixing the components.
The adhesives according to the invention may be used for bonding typical substrates, more particularly substrates of the same material or of different materials, for example metal, elastomers and plastics, and above all for bonding transparent substrates of polystyrene, polymethyl methacryla

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