WO2001051908A1

WO2001051908A1 - Method and apparatus for applying droplets to a test slide using an ink jet printer

Info

Publication number: WO2001051908A1
Application number: PCT/GB2001/000066
Authority: WO
Inventors: Michael John Fox
Original assignee: Willett International Ltd
Current assignee: Willett International Ltd
Priority date: 2000-01-14
Filing date: 2001-01-10
Publication date: 2001-07-19
Anticipated expiration: 2002-07-14
Also published as: AU2001225322A1; GB0000789D0

Abstract

The present invention provides a method for applying a marker material to a surface of a carrier so as to form deposits of a predetermined amount of one or more marker materials at one or more predetermined locations upon the surface of the carrier to which a sample of a product to be assessed can be applied so as to interact with the marker material in the deposit to provide a characteristic spectrum upon radiation of the predetermined location with IR, UV or other radiation, characterised in that the marker material is applied through the nozzle of a drop on demand or impulse jet ink jet printer which has been selected and/or whose operation and/or design has been modified so that the droplets of fluid striking the surface or the surface layer have a sufficiently low kinetic energy, preferably from 8 to 35 picojoules, that they do not cause an unacceptable level of disturbance of the layer and/or of scattering of the applied marker material upon the surface of the carrier, notably where the carrier is a planar glass slide having an absorbent layer comprising fumed silica in a gelatin binder to which the marker material is applied. The invention also provides apparatus for use in the method of the invention.

Description

METHOD AND APPARATUS FOR APPLYING DROPLETS TO A TEST SLIDE USING AN INK JET PRINTER

The present invention relates to a method and apparatus, notably to a method for applying a fluid to a test slide and apparatus for carrying out the method.

BACKGROUND TO THE INVENTION:

It has been proposed to verify the authenticity of a sample of a product, for example a fluid, by incorporating one or more marker materials therein or applying to an exposed surface thereof in the case of a solid product, which fluoresce when exposed to IR, UV or other radiation, see for example British Patent No 2,298,713 and US Patents Noose 5,292,855, 5,336,714, 5,614,008 and 5,665,151. Such processes operate to detect the presence or absence of the characteristic fluorescence when a sample of the product being assessed is exposed to specified radiation. However, such methods require the incorporation of the marker material into or onto the product or its packaging and this may be undesirable, for example when the product is a fragrance, beverage or foodstuff.

It has been proposed in for example US Patent No 5,753,511 to apply a marker chemical or other reagent to the surface of a slide or other carrier. The marker undergoes an interaction, which may be chemical, physical or some other change, with one or more of the components in the fluid to be assessed to give a material which gives a specific radiation or reflectance spectrum when the carrier is exposed to IR, UV or other radiation. The term marker is used herein to denote a material which is intended to undergo an interaction with a material to be assessed so as to give a resultant material which gives a characteristic spectrum when that material is exposed to IR, UV or other radiation. By applying a plurality of different marker materials to the carrier, a plurality of interactions can take place to provide a plurality of spectra whose combination provides a unique fingerprint to characterise the fluid being tested. In this way it is possible to determine whether an ink or other fluid is the authentic product of a given manufacturer. By suitable selection of the marker materials and/or by the use of a sufficiently large number of marker materials, the determination can be made sufficiently selective to be able to detect differences between batches of supposedly identical products from the same manufacturer or between products from different sites. By applying the marker material to the carrier and applying a sample of the fluid to be assessed to the carrier, problems of contamination of the fluid by the marker material are avoided.

By testing a sample of a product initially when it is produced, the manufacturer can provide a reference spectrum for that product. By applying a sample of the fluid under assessment to a carrier carrying the same marker materials, the characteristic spectrum of that sample can be determined. Comparison of that spectrum with the reference spectrum obtained initially, will enable the manufacturer or his customer readily to determine whether the sample corresponds to the authentic material .

Such a method of authentification is described in the specification of US Patent No 5,753,115 and the subject matter of that specification is incorporated herein by reference and is denoted hereinafter as the test method.

In order to carry out the test method, a suitable marker material is applied to a suitable carrier. The preferred carrier is a glass slide, since glass is usually substantially inert to any of the fluids to be assessed and will not generate extraneous spectra which could mask or distort the spectra from the marker material/sample interaction which it is desired to observe. It is also preferred to apply the marker material to a layer of an inert absorbent material applied to the surface of the carrier so that the amount of marker material carried by the carrier and its position on the carrier can be held to within specified tolerances. Preferably, the absorbent material is particulate silica, for example fumed silica, which is secured as a layer of predetermined thickness to the underlying glass slide by means of a film of gelatin or other inert binder/adhesive.

The marker material is applied to such a silica-coated slide to achieve the desired rate of application of the marker to a given area of the plan area of the slide. If desired, the surface of the slide can be sub-divided into a plurality of discrete areas, for example by a grid of upstanding walls or ridges on the surface of the slide. Each of the discrete areas carries a single selected marker material or mixture of marker materials. By applying different marker materials to different areas, a single slide carrying a plurality of marker materials could be produced so that a plurality of spectra could be generated by applying the fluid to be assessed to the surface of that slide. This would enhance the ability of the assessment to discriminate accurately between closely related samples. However, currently proposed methods for the application of the marker material to the surface of the slide are cumbersome and slow so that commercial scale production of the slides presents a problem. Furthermore, changes of the reservoirs containing the marker materials are required to permit application of different marker materials to a single slide, which is time consuming and may lead to misalignment of the application of the marker material to the carrier. An ink jet printer is a non-contact technique by which closely controlled droplets of a fluid can be accurately applied to a substrate. Prima facie, such a technique would seem suitable for applying the marker material to the slide or other carrier or to the absorbent layer on such a carrier. However, we have found that the use of a conventional continuous jet ink jet printer produces test slides which perform erratically. This would preclude the use of such printers to apply the marker materials to the slides or other carriers, especially where the carrier carries an absorbent layer.

We have found that the erratic performance is due to uneven application of the marker materials over the plan area of the slide and scattering of the re-radiated or reflected radiation. Where the marker fluid is applied directly to the surface of the carrier, this surface will usually be a non-absorbent surface and spattering and uneven film formation on the surface may occur. This will result in uneven application of the marker material and possible contamination of adjacent areas of the surface of the carrier to which different marker materials have been applied. Where the marker material is carried in an absorbent layer applied to the carrier, we have found that the layer is disturbed by the application of the droplets of the marker material .

We have further found that these problems are due to the fragility of the absorbent layer and the excessive kinetic energy in the droplets when they strike the surface of the carrier or the absorbent layer. Surprisingly, we have found that these problems can be reduced by using a drop on demand or impulse jet printer since we have found that the kinetic energy of the droplets produced from such printers is sufficiently low to cause minimal disturbance of the surface layer and/or spattering of the ink on the carrier surface. The kinetic energy of the droplets produced by an ink jet printer is not a factor which is considered when designing or selecting a printer for a given use .

SUMMARY OF THE INVENTION:

Accordingly, the present invention provides a method for applying a marker material as hereinbefore defined to a surface of a carrier so as to form deposits of a predetermined amount of one or more marker materials at one or more predetermined locations upon the surface of the carrier to which a sample of a product to be assessed can be applied so as to interact with the marker material in the deposit to provide a characteristic spectrum upon radiation of the predetermined location with IR, UV or other radiation, characterised in that a selected amount of the marker material is applied as a fluid to a selected area of the surface of the carrier or of a layer carried by the carrier using a drop on demand or impulse jet ink jet printer apparatus which has been selected and/or whose operation and/or design has been modified so that the droplets of fluid striking the surface or the surface layer do not cause an unacceptable level of disturbance of the layer and/or of scattering of the applied marker material upon the surface of the carrier.

Preferably the design and/or operation of the ink jet printer is such that the droplets striking the surface or surface layer or the carrier have a kinetic energy of less than about 40, preferably from 8 to 35, picojoules.

The kinetic energy of the droplets is notionally that of the droplet when it strikes the surface of the carrier or surface layer. However, it may be impractical to measure this and the kinetic energy for practical purposes will be that for the droplet as it is ejected from the nozzle orifice of the printer, since the kinetic energy lost during the flight of the droplet to the surface which it strikes is not significant. For convenience, the values for the kinetic energies quoted herein are those calculated for the droplets at the nozzle orifice of the printer .

The ability to use an ink jet printer to apply the marker material to the carrier enables the operator to apply many thousands of droplets of fluid containing the marker material per second accurately and rapidly. Since the positioning of the droplets onto the carrier can readily be controlled and varied, the invention enables a selected area of the surface or surface layer on the carrier to have the desired amount of marker material applied thereto rapidly, whereas other areas can have a different marker material applied thereto.

The term drop on demand ink jet printer is used herein to denote those non-contact printers in which ink or other fluid is applied under pressure, typically less than 1 bar, to a nozzle to eject droplets of ink from the nozzle orifice, the flow of ink to the nozzle being controlled by a valve mechanism. An impulse ink jet printer is a variation of a drop on demand printer in which ink is applied at a slight negative pressure to the nozzle orifice so that flow of ink through the nozzle orifice is restrained by the surface tension effects at the meniscus of the ink at the nozzle orifice; and means, usually a piezo-electric driver, are provided for causing a change of volume or a rise in pressure in a chamber upstream of the nozzle orifice so as to eject a droplet of ink upon actuation of the driver. Such printers are commercially available and may be used in their commercially available form without significant modification in the method of the invention. This is to be contrasted with the disturbance and spattering which occurs when a conventional continuous ink jet printer is used to apply the marker material. We have found that typically the kinetic energy of the droplets with a drop on demand or impulse jet printer is 20% or less, for example less than 12.5%, than that of the droplets formed using a conventional form of a continuous ink jet a printer. However, even allowing for this, it is surprising that satisfactory application of the marker material can be achieved using a drop on demand or impulse jet printer since such printers produce a number of droplets simultaneously from an array of nozzles. A continuous jet ink jet printer produces a series of individual droplets which are steered to the desired locations on the substrate so that droplets are applied sequentially to the substrate. It would have been expected that the disturbance effect of applying many droplets simultaneously would have been greater than the effect of applying individual droplets sequentially and hence that a drop on demand or impulse jet printer would have caused greater disturbance of the silica/gelatin layer or spattering than a continuous jet ink jet printer. Furthermore, drop on demand or impulse jet printers are simple and economic to produce and operate as compared to continuous jet ink jet printers or the apparatus described in US Patent No 5,753,115. However, if the droplets from a drop on demand or impulse printer do cause unacceptable disturbance of the absorbent layer or splattering of the marker material, the kinetic energy of the droplets can readily be reduced by reducing the nozzle orifice diameter and/or the open time of the valve controlling the flow of fluid through the nozzle or the change in volume of the ink chamber caused by the piezoelectric driver using known technology. . Another factor in the operation of the printer which can be modified to reduce the kinetic energy of the droplets formed is to reduce the pressure at which the fluid is fed to the nozzle of the printer. This will reduce the volume of fluid flowing per unit time through the nozzle orifice and hence the size of droplet formed. The pressure required to form droplets successfully at the nozzle outlet is however dependent upon the viscosity, and hence the temperature and composition, of the fluid being ejected through the nozzle. By suitable adjustment of each of these variables it is possible to produce droplets which have sufficiently low a kinetic energy to reduce the disruption of the absorbent layer or spattering of the marker material to an acceptable level whilst still retaining the advantages of high speed of fluid application and accuracy of placement of the droplets upon the surface of the carrier or the absorbent layer. The optimum nozzle orifice bore diameter, ink pressure, viscosity and other factors of the operation of the ink jet printer can be established by simple trial and error tests. For present use it is desirable to select, design or modify the printer and/or its operation so that the kinetic energy of the droplets is less than 40, typically 8 to 35, notably 10 to 25, for example about 20, picojoules .

The invention can be applied to the application of a wide range of fluids containing a wide range of marker materials to a wide range of absorbent layers or carriers, depending upon the fluids to be sampled and the nature of the carrier and absorbent layer. The optimum form of marker fluid can readily be determined from knowledge of the chemistry of the various components of the sample, the marker material and test slide using conventional chemical and physical techniques and ingredients . Suitable marker materials and their uses are described in for example US Patent No 5,753,115 and other marker materials include those described in US Patents Noose 5,292,855, 5,336,714, 5,614,008 and 5,665,151. Suitable fluid carrier media for the marker chemicals include water, lower alkanols, esters and ketones and mixtures thereof, notably those which are readily volatile and in which the alkyl moieties contain from 1 to 3 carbon atoms. The marker materials can be dissolved, emulsified or suspended in the carrier medium. If desired, the fluid compositions containing the marker materials can contain other ingredients to assist the jet- ability thereof and such other ingredients can be those conventionally used in ink jet formulations. For example, the composition can contain a film forming binder to aid formation of a deposit containing the marker material which is secured to the particles in the absorbent layer and thus reduce potential migration of the marker material within the absorbent layer or upon the surface of the slide or other carrier.

The carrier and the absorbent layer can be selected from a wide range, for example from amongst those described in US Patent No 5,753,115. The carrier can be a planar glass strip, slip or slide as described above. However, it is within the scope of the present invention to form the carrier as a plastic strip which carries one or more areas of marker material adjacent one end thereof. The plastic may comprise a laminate of materials, for example a colourless layer to discrete areas of which the marker material (s) is/are applied and an underlying white layer having apertures therein which are in register with the areas of the colourless layer to which the marker material (s) is/are applied. Such a construction provides a white background against which any colour or spectra developed in the marker material may be viewed and the rim of the aperture enables any edge effects in the spectra from the periphery of the area of the marker material to be screened out when the carrier is observed from its underside as opposed to from the side to which the marker material has been applied. If desired, the colourless layer may carry an apertured top layer to form recesses in the top face of the carrier to assist retention of the fluid composition containing the marker material in the desired location on the carrier whilst the composition gels, sets or cures. The ability to use a drop on demand or impulse jet printer to apply the marker material to the surface of the slide or other carrier or to the absorbent layer on the carrier enables high speed of formation of a test square or other discrete area on the carrier to be achieved. Since the ink jet printer achieves accurate placement of individual droplets of the marker material on the surface of the carrier or the absorbent or other surface layer, the printer can readily be operated, for example under micro- processor control, to form a plurality of individual discrete areas on the surface of the carrier or the surface layer. Furthermore, since the print head of a drop on demand or impulse jet printer can be formed as a compact unit, it is possible to form a single assembly for present use which comprises an array of two, four or more individual print heads, each fed with a different marker fluid. Such an assembly can form a plurality of discrete areas each carrying a different marker material simultaneously without the need to change reservoirs of marker material as with the application methods of the present proposals. Alternatively, a print head of a drop on demand or impulse jet printer typically comprises and array of individual nozzle fed with ink from a reservoir. If desired, the nozzles in such a print head can be fed with fluids from different reservoirs so that each nozzle or a combination of nozzles, can be used to apply one marker material to the surface of the carrier or absorbent layer. Other nozzles in the print head can be fed with a different marker material from another reservoir, further enhancing the flexibility of the operator in designing the shape and location of the areas of each marker material on the carrier or absorbent layer.

If desired, a series of arrays of print heads can be passed over a static carrier to apply a plurality of marker materials to the carrier. Alternatively, the carrier can be transported through a series of printer stations where arrays of print heads apply marker materials to different areas of the carrier successively. Such a transport mechanism could be a rotary table or an x/y movement and can be operated under microprocessor control to provide an automated operation for the application of marker materials to a slide.

The invention has been described above in terms of the application of a single marker material to a single selected area of the surface of the absorbent layer on a carrier. However, it will be appreciated that in some cases it may be possible to apply two or more marker materials to the same selected area. Furthermore, the surface to which the marker material is applied need not be absorbent, but may be structured in some other manner to define and retain the marker material within the confines of a selected area of the carrier surface, for example using the recessed top layer on the carrier as described above. Alternatively, the surface of the carrier may be subdivided physically by walls or the like into separate cells or areas, as is the case with an analytical cell, and the marker material applied in a binder which forms a film of the marker material upon the floor or base of the cells or areas. Such a form of construction may be desirable where the scanning of the test slide to which a sample of the fluid to be assessed is to be viewed in a conventional automated sample analysis machine.

The invention also provides an apparatus for applying a fluid containing a marker material for use in the test method, which apparatus comprises a mechanism for moving a carrier, upon which the marker material is to be applied, relative to an application mechanism by which a predetermined amount of the marker material is to be applied to a selected area of the carrier or a surface layer carried by the carrier, characterised in that the application mechanism comprises a drop on demand or impulse jet printer which has been selected and/or whose design and/or operation has been modified so that the kinetic energy of the droplets from the printer striking the carrier or surface is sufficiently low that no unacceptable spattering of the marker material or disturbance of the surface layer occurs.

Preferably, the kinetic energy of the droplets is less than 40 picojoules, eg. 8 to 40 picojoules.

It will be appreciated that the ink jet printer for present use may have been manufactured ab initio specifically for use in the method of the invention. In such a case the printer design and its operation will have been selected to ensure the desired low level of kinetic energy for the droplets. The term selected as used herein is therefore to be construed to include printers which have been designed and manufactured ab initio to meet the requirements of the present invention as well as printers existing which have been selected as suitable for present use because, co-incidentally, they produce droplets having sufficiently low a kinetic energy for present use.

The term acceptable is used herein in relation to the spattering of the marker material and disturbance of the surface layer carried by the carrier to denote that any such spattering or disturbance which may occur does not produce spectral information from inspection of the sample which cannot be used in the test method. The level of distortion which may be acceptable in any given case is readily determined by simple trial and error tests.

Claims

CLAIMS :

1. A method a method for applying a marker material as hereinbefore defined to a surface of a carrier so as to form deposits of a predetermined amount of one or more marker materials at one or more predetermined locations upon the surface of the carrier to which a sample of a product to be assessed can be applied so as to interact with the marker material in the deposit to provide a characteristic spectrum upon radiation of the predetermined location with IR, UV or other radiation, characterised in that a selected amount of the marker material is applied as a fluid to a selected area of the surface of the carrier or of a layer carried by the carrier using a drop on demand or impulse jet ink jet printer apparatus which has been selected and/or whose operation and/or design has been modified so that the droplets of fluid striking the surface or the surface layer do not cause an unacceptable level of disturbance of the layer and/or of scattering of the applied marker material upon the surface of the carrier.

2. A method as claimed in claim 1, characterised in that the kinetic energy of the droplets is less than 40 picojoules.

3. A method as claimed in claim 2, characterised in that the kinetic energy of the droplets is from 8 to 35 picojoules .

. A method as claimed in any one of the preceding claims, characterised in that the carrier is a planar glass strip or slide.

5. A method as claimed in any one of the preceding claims, characterised in that the carrier has an absorbent layer applied to a face thereof and the marker material is applied to that layer.

6. A method as claimed in claim 5, characterised in that the absorbent layer comprises silica particles in a gelatin binder.

7. A method as claimed in any one of the preceding claims, characterised in that the ink jet printer is an impulse jet printer.

8. A method as claimed in any one of the preceding claims, characterised in that a plurality of marker materials are applied to a single carrier.

9. A method as claimed in claim 1 for applying droplets of a marker material to the surface of a carrier using an ink jet printer substantially as hereinbefore described.

10. Apparatus for applying a fluid containing a marker material as hereinbefore defined to a surface of a carrier so as to form deposits of a predetermined amount of one or more marker materials at one or more predetermined locations upon the surface of the carrier to which a sample of a product to be assessed can be applied so as to interact with the marker material in the deposit to provide a characteristic spectrum upon radiation of the predetermined location with IR, UV or other radiation, which apparatus comprises a mechanism for moving the carrier, upon which the marker material is to be applied, relative to an application mechanism by which a predetermined amount of the marker material is to be applied to a selected area of the carrier or a surface layer carried by the carrier, characterised in that the application mechanism comprises a drop on demand or impulse jet ink jet printer which has been selected and/or whose design and/or operation has been modified so that the kinetic energy of the droplets from the printer striking the carrier or surface are reduced to a level at which any spattering of the droplets or disturbance of the surface layer are reduced to an acceptable level .

11. Apparatus as claimed in claim 11, characterised in that the kinetic energy of the droplets is less than 40 picojoules .