GB2173914A

GB2173914A - ir-Dye pattern

Info

Publication number: GB2173914A
Application number: GB08604991A
Authority: GB
Inventors: Paul Francis Gordon
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1985-03-25
Filing date: 1986-02-28
Publication date: 1986-10-22
Also published as: GB8604991D0; GB8507690D0

Abstract

A process for the formation of a substantially two-dimensional pattern of an ir dye comprising the formation of a layer of a uv and ir transparent material containing an ir dye or ir-dye composition which is unstable to ultra-violet (uv) irradiation, hereinafter referred to as a "uv-unstable ir dye" and selectively irradiating a pre- determined area of the layer with uv radiation, preferably until the ir-dye in the area is rendered non-absorptive to ir irradiation, whereby a predetermined pattern of the ir dye may be formed in the layer.

Description

SPECIFICATION Infra-red pattern This specification describes an invention relating to patterns formed by compounds which absorb infra-red radiation, hereinafter referred to as "ir dyes", to a process for forming the patterns and to the use of such patterns in security systems.

A number of security systems currently available, such as computer controlled locks, are based on the recognition of a pattern of light beams passing through a coded card with the facility for frequent alteration of the pattern and the coded card. A serious security problem with the system based upon visible radiation is that the code in the card is visible to the eye and can easily be copied and a counterfeit card readily produced. There is, therefore, a need for nonvisible system in which the pattern and coded card can be easily and frequently changed in order to maintain security.

According to the present invention there is provided a process for the formation of a substan tially two-dimensional pattern of an ir dye comprising the formation of a layer of a uv and ir transparent material containing an ir dye which is unstable to ultra-violet (uv) irradiation, hereinafter referred to as a "uv-unstable ir dye" and selectively irradiating a predetermined area of the layer with uv radiation, preferably until the ir-dye in the area is rendered non-absorptive to ir irradiation, whereby a pre-determined pattern of the ir dye may be formed in the layer.

The uv-unstable ir dye may be an ir dye which is itself unstable to uv radiation and can be photolytically "bleached" to a non-ir absorbing species or it may be a composition of a uvstable ir dye with a compound or composition which, under uv irradiation, produces species which will chemically "bleach" the ir dye to a non-ir absorbing compound.

Examples of suitable uv-unstable ir dyes are dithiolenes, especially metal dithiolenes of the general formula:

wherein R & R2 are each independently optionally substituted alkyl or aryl groups; and M is a metal from Group Ib, llb, Vllb, or Vlllb of the Periodic Table, pyrylium and thiopyrylium salts, cyanines and cyanine derivatives, triphenylmethane and triphenylmethane derivatives and squarylium compounds.

The material forming the layer in which the ir dye is contained is conveniently a polymeric or resinous binder which protects the ir dye and either forms a substrate for the ir dye or binds it to a suitable substrate, such as a card.

The layer of the ir dye may be formed by deposition of a fluid composition of the ir dye and binder, preferably in a solvent, onto the surface of a substrate by an impact or non-impact process. The layer may be formed in a discontinuous pattern which is subsequently altered by uv-bleaching or it may be continuous, the pattern being formed solely by means of uv-bleaching.

For added protection and security, the layer may be encased within a substrate, such as a plastics material, which is transparent to ir radiation.

The formation of the pattern may be effected by exposing the layer to a bank of uv radiation sources each capable of producing a separate beam of uv radiation and operable individually in accordance with a pre-determinable electrical signal. This allows the sources to be activated in any one of a number of patterns and to produce the same pattern in the layer by bleaching the ir dye. Bleaching of the ir-dye need not be complete provided sufficient ir dye is destroyed to give a detectable difference in transmissivity between the area of the layer which has been subjected to uv radiation and that which has not.

It is generally preferred to use uv irradiation in the region 185-400 nm for the bleaching operation.

According to another feature of the present invention there is provided a substantially twodimensional layer of a uv and ir transparent material containing a pre-determined pattern of a uvunstable ir dye whereby ir radiation directed at the layer is selectively absorbed in the area of the layer containing the ir dye.

The layer is conveniently formed by depositing a composition of the ir dye with a binder on the surface of a card, and the pattern formed by exposing the layer to a patterned uv source for sufficient time to at least partially decompose the ir dye. The layer may then be further protected from visual inspection and damage by covering with an ir-transparent card so that it is sandwiched between two cards. If both cards are ir-transparent the patterned layer of ir-dye may be examined from either side.

Specific examples of suitable uv-unstable ir dyes are set out in the following table which gives, for each dye, the extent of bleaching of a solution of the dye in chloroform after 5 minutes exposure to uv radiation in the region 250-350 nm from a HANOVIA, 125 watt, unfiltered, mercury-vapour uv-lamp.

Table 1 Compound Z of Original Absorbance after 5 minutes irradiation

Table 1 (cont'd)

Compound % of Original Absorbance after 5 minutes irradiation NH2 O CN # # ##### 5.0% # # KN O # R wherein R is -#-N(CH3)2 Pb Pb # # S#-CH-CH - CH -#N + 0% # # Pb Pb wherein Ph is # CH3 CH3 CH3 CH3 # # ## ## # ######- (CH = CH)3-####### 0% K+ N # # CH3 CH3 (CH3)2N N(CH3)2 # # ##### # + Cl- 10.8% N(CH3)2 R +O#- R < 1.0% R wherein R is - CH - CH -#- H(CH3)2

Claims

1. A process for the formation of a substantially two-dimensional pattern of a compound which absorbs infra-red radiation, "an ir dye", comprising the formation of a layer of a uv and ir transparent material containing an ir dye which is unstable to ultra-violet (uv) irradiation, "a uvunstable ir dye", and selectively irradiating a predetermined area of the layer with uv radiation, preferably until the uv-unstable ir dye in the area is rendered non-absorptive to infra-red radiation, whereby a pre-determined pattern of the ir dye may be formed in the layer.

2. A substantially two-dimensional layer of uv and ir transparent material containing a uvunstable ir dye in a pre-determined pattern whereby ir radiation directed at the layer is selectively absorbed in the area of the layer containing the ir dye.

3. A security card comprising a layer according to Claim 2 or Claim 3.

3. A layer according to Claim 2 wherein the uv-unstable ir dye is any of those exemplified in the specification.