Patent Publication Number: US-2010119785-A1

Title: Film formation and evaluation

Description:
This invention relates to the formation of films on the surfaces of substrates and to the evaluation of characteristics of such films. 
     Coatings are widely used in both industrial and domestic environments to enhance the functionality and add-on value of bulk materials and articles and to enhance the appearance of structures. Other applications include non-continuous coatings such as inks. Organic coatings are particularly widely used in many industrial protective/decorative applications, such as automobile top clear coatings, automotive and decorative paints and lacquers, pigmented and unpigmented coatings, eg primer-, under- and top-coat paint systems, etc, and in inks. Other types of organic coatings include, for example, protective and anticorrosive coatings, adhesive and release coatings, environmental barrier coatings, electric conductive/optic transparent coatings and scratch resistant hard coatings. Although such coatings may consist solely of organic components, other coatings may contain inorganic elements such as metal oxide pigments, conductive metal particles, inorganic particle fillers, clays such as vermiculite and similar well known inorganic particles. 
     There are also many forms of inorganic coatings which may contain organic binders or alternatively may be formed from aqueous dispersions. Other forms of inorganic coatings may be formed by the direct application of the coating materials to substrates using techniques such as sputtering and chemical or physical vapour deposition. 
     In food and other applications, it may also be useful to form foodstuffs or other materials into films for testing or comparative purposes. Such foodstuffs and other materials that may be tested or compared are, for example, dough, starch films, sauces, mustards and the like and, in personnel care applications, toothpastes, shaving gels and the like. 
     The ability to test new combinations of ingredients for coating materials or new processing conditions, especially rapidly and in large numbers of samples, to discover next generation materials or new, cost-effective manufacturing methods is high on the agenda of many manufacturers to enable them to obtain commercial advantages over competitors. Also of significant importance is the ability to test existing formulations for performance drift, especially when substituting alternative ingredients or alternatively-sourced ingredients. 
     Such aspirations also apply more generally to other materials such as structural materials, particularly when at least some of the properties of interest of such materials may be determined from film samples of such materials. 
     Additionally, the generation of materials having multiple layers either for testing or for manufacture is of interest. Examples of such multilayer materials include the use of multiple layers of different adhesives for example to generate adhesion between substrates having different surface energies and, hence, different adhesion properties; primer, under and top coat paint systems; and multilayer semiconductor devices wherein the overall properties of such devices are highly dependent on not only the intrinsic properties of the constituent materials in each of the layers but also the particular layer stacking sequence, the interface and surface structures used in making such devices. 
     There have been attempts to generate and test samples of materials in high numbers, for example as disclosed in U.S. Pat. No. 6,482,264 B1, US 2003/0224105 A1, US 2004/0071888 A1 and DE 10136448 A1. These publications disclose a variety of methods of depositing and spreading samples on substrates to form films, including in some, spreading the liquid samples using non-contact methods, for example spinning or oscillating the substrate or using an air knife to spread the liquid samples or spraying the liquid samples onto the substrate. The deposition of adhesives to backing tapes in making self-adhesive tapes and sheets is also known and is described in GB 916406. 
     Such methods suffer from the disadvantage that, owing to the small amounts of liquid deposited on the substrates, the uniformity of the films formed may vary significantly and, consequently, the measured parameters may not be accurately determined. Whilst this may not be significant for some materials or for screening materials, for example on a pass/fail basis, it may, however, in other applications be more critical. For example, in determining colour specifications for paints, lacquers, inks etc, the thickness and uniformity of the film may significantly affect the colour determination process. Additionally, the amount of shear the sample is subjected to during spreading may affect the dispersion of pigment particles and, therefore, the uniformity of the resultant colour of the film sample. 
     Other techniques for forming films for testing, especially for forming films capable of being subjected to electrical resistivity measurements or for use in mechanical testing such as dynamic mechanical thermal analysis (DMTA), are known. Such techniques consist of forming a channel of a specified width and depth on a substrate, for example, a glass microscope slide or a substrate from which the film is easily released, by applying adhesive tapes of known thickness parallel to each other at a selected separation on the substrate, depositing a liquid sample in the channel and drawing a doctor blade across the upper surfaces of the tapes to remove excess liquid from the channel formed on the substrate. However, these techniques are time consuming, especially if multiple samples of the same or similar compositions are required or samples having multiple layers of materials are to be made. 
     It is an object of the present invention to reduce or obviate at least one of the aforementioned disadvantages. 
     According to a first aspect of the present invention, a method of forming a film on a surface of a substrate comprises providing a reservoir containing a liquid sample to be formed into a film at a sample location position on the substrate surface, said reservoir having an outlet comprising a die having a planar face which is contactable with said substrate to define therewith a channel for receiving at least a portion of said liquid sample from said reservoir, contacting said die with said substrate at one end of said sample location position, causing said liquid sample to extrude through said die and into said channel whilst substantially simultaneously moving said die and said substrate in contact with and relative to one another whereby said die moves towards a remote end of said sample location position to deposit a film of said liquid sample at said sample location position. 
     Although within the overall scope of the present invention, the reservoir may be any suitable shape provided that pressure may be applied to a liquid sample in it; in a preferred embodiment the reservoir is of a general cylindrical shape in which a piston is movable. In a particularly preferred embodiment, the reservoir is a commercially-available cartridge, such as plastic syringes available from EFD. Typically, the cartridge or syringe may have a volume in the range 5 ml to 100 ml, more preferably 5 ml to 50 ml and typically has a volume of 10 ml. 
     Preferably, the syringe is sealed at its outlet with a cap which is removable to permit fitting of said die thereto. Preferably, said die has an annular projection on the side opposite said planar face which is a push fit on to the outlet portion of the syringe in place of the cap. The annular projection defines part of a passage through said die through which a liquid sample may be extruded from the reservoir. 
     In the method of the invention, said liquid sample may flow through the die under capillary action of said liquid sample in contact with said substrate at said sample location position. Alternatively, or possibly in combination with capillary action, said liquid sample may flow through the die by having pressure applied to it. 
     Preferably, the method includes applying pressure to said liquid sample in the reservoir to cause said liquid sample to flow sufficiently to fill a prime volume in said die. 
     In a preferred embodiment of the present invention, said method comprises forming said channel by providing in the planar face of said die a rebate into which said passage opens. 
     In one embodiment, said rebate may extend longitudinally completely across the planar face of said die to opposed ends of said die to form openings thereat. 
     In an alternative embodiment, said rebate preferably extends only partially longitudinally across the planar face of said die at least from said passage to one end of said die to form an opening thereat. In this instance, said method comprises moving said die and said substrate relative to one another such that the end of the die in which said opening is located trails the direction of relative movement of said die. Preferably, said rebate extends a short distance past said passage towards the opposed end of said die whereby a dead space is formed. 
     In yet another alternative embodiment, said method comprises forming said channel by providing in said substrate at said sample location a groove whereby, when said die is contacted with said substrate at said one end of said sample location position, said channel is formed. Preferably, said groove is of predetermined length. 
     In yet a further alternative embodiment, said method comprises forming said channel by providing a rebate as previously described in the planar face of said die and a groove as previously described in said substrate at said sample location whereby, when said die is contacted with said substrate at said one end of said sample location position, said rebate and said groove together form said channel. 
     In the afore-described embodiments, preferably the rebate and/or the groove are of predetermined cross-section. 
     In preferred embodiments of the invention, the planar face of said die is flat. However, it is envisaged that it is within the scope of the invention to form films that are curved along their lengths, in which instance the substrate and the planar face of said die may be arcuate and complementary to one another in the direction of relative movement thereof. 
     Once the film has been deposited by said relative movement of the die and the substrate, the application of pressure to said liquid sample in the reservoir is ceased and the die is removed from the substrate. 
     As will be appreciated, when the method of the present invention utilises a die having a rebate, the method relies on the dynamic viscosity of the liquid sample deposited to maintain the film shape or cross-section. Consequently, when utilising such a die, the liquid will require a dynamic viscosity such that it maintains the film shape or cross-section. Typically, films have been formed using liquid samples having a dynamic viscosity in the range of about 0.05 Pa·s up to about 100 Pa·s. 
     However, the surface energy of the substrate surrounding the sample location position may be adjusted to permit the formation of films using liquid samples having a dynamic viscosity lower than about 0.05 Pa·s. 
     Additionally, when the method of the present invention utilises a substrate in which a groove is formed, it may also possible to form films from liquid samples having a lower dynamic viscosity, for example liquid samples having a dynamic viscosity of below about 0.05 Pa·s. 
     If arcuate films are to be formed, then clearly the dynamic viscosity of the liquid sample would have to be relatively high to enable it to retain its shape after deposition. 
     The force used to contact the die with the substrate is typically in the range from about 10N to about 100N, more typically about 15N to about 35N. 
     The force used to extrude the liquid sample from the reservoir will depend upon the dynamic viscosity of the liquid sample, a higher viscosity requiring a higher force. Typically, however, the force applied is in the range from about 0N to about 200N, depending on whether capillary action alone is relied upon or whether a positive force is applied. More preferably, the force applied is in the range from about 0.1 N to about 200N. 
     For many applications, it is preferred that the method of the invention comprises treating the film of liquid sample so formed to solidify it. This may involve no more than permitting solvent and/or carrier fluid to evaporate at ambient temperature. It may, however, include subjecting the liquid film to lyophilisation and/or heating and/or a reduced pressure environment to aid removal of the solvent and/or carrier fluid. Depending upon the chemical system under consideration in the film, the liquid sample may be cured and/or polymerised either at ambient temperature and/or pressure or below or above ambient temperature and/or pressure and/or using incident radiation, for example such as UV radiation, or by any other technique as is well understood in the art. 
     The method of the invention includes forming a film which comprises a composite film having at least two film layers, said composite film being formed by depositing a first film layer on the substrate by any of the embodiments herein before described and then depositing a second film layer onto the first film layer and, if desired, subsequent film layers in sequence on the second film layer and subsequent film layers. Depending on the embodiment used to deposit the first film layer on the substrate, ie whether the channel is defined by a groove and die without a rebate or a die having a rebate whether or not extending longitudinally of the planar face of the die or a combination thereof, a second film layer may be deposited on the first film layer using a die having a rebate which may or may not extend completely longitudinally of the planar face of the die. Subsequent film layers may be deposited on top of the uppermost film layer using a die having a rebate which extends completely longitudinally of the planar face of the die. At least one die having a rebate which extends completely longitudinally of the planar face of the die may be used to form at least one uppermost film layer, the depth of the rebate being greater than the thickness of the deposited film layer(s) protruding above the surface of the substrate. 
     To enable the first and subsequent film layers to withstand the deposition of a second and subsequent film layers thereon, the film layer receiving the further film layer has to be sufficiently stable to retain its shape during the deposition process. Such stability may at least in part be imparted by the die supporting the film layer during the deposition process. Alternatively, or additionally, the film layer receiving the further deposition of liquid sample may have a dynamic viscosity sufficiently high to retain its shape during the deposition of a further film layer or may be solidified as described above. The dynamic viscosity of the film layer receiving the further deposition of liquid sample may be inherently high or may be increased to a sufficient level by using the techniques described above to solidify the film. 
     The method of the invention includes forming a plurality of films on the substrate surface by depositing films at respective sample location positions on said surface that are in space relationship from one another. Conveniently, the number of samples dispensed on said surface is not more than 100, but typically may be 2 or more, for example 4, 8, 16, 32 or 64. 
     Preferably, the films formed on the substrate surface are discrete from one another. 
     Typically, the or each film formed has a width in the range of about 1 mm to about 150 mm, a length in the range about 5 mm to about 50 mm and a depth in the range 20 μm to 1000 μm, more typically 25 μm to 800 μm. It will be appreciated, however, that film size may be application dependent and may by higher or lower that the ranges quoted. 
     Although an array of films may on the surface of a single substrate, in alternative embodiments, single or multiple films may be formed on the surfaces of an array of substrates. For example, the substrate may be a microscope glass slide and have deposited thereon a single film. Alternatively, the substrate may have significant area and have deposited thereon more than one film. The material of the substrate may be any convenient material and typically may be glass, metal, plastics. The material of the substrate may have release qualities, for example a substrate of PTFE, whereby films capable of being free standing may be removed from the substrate for subsequent testing. 
     Once the film is formed, at least one characteristic of the film is determined. Without being limited to the following examples, the characteristic may be physical, eg colour, transparency, scratch resistance, wear; chemical, eg environmental stability/resistance; mechanical, eg strength, modulus; or electrical, eg resistance; conductivity. 
     In a particularly preferred embodiment of the invention, a method of forming a plurality of films at respective sample location positions on a surface of a substrate comprises:
     (a) providing a plurality of liquid samples in respective syringes, which syringes being closed at their outlet ends by respective caps;   (b) either in parallel or preferably sequentially removing the cap from each syringe and fitting a die to the outlet end of the syringe, each said die being contactable with said substrate to define therewith a respective channel for receiving at least a portion of a liquid sample;   (c) either in parallel or preferably sequentially contacting said respective die with said substrate at one end of a respective said sample location position;   (d) either in parallel or preferably sequentially causing the liquid sample in each respective syringe to extrude through said respective die and into said respective channel whilst simultaneously moving said die and said substrate in contact with and relative to one another whereby said die moves towards a remote end of said sample location position to deposit a film of said liquid sample at said sample location position.   

     The features of the invention described previously apply mutatis mutandis to this particularly preferred embodiment of the invention as the context permits. 
     Preferably, the methods of the invention include the step of removing the die from the syringe and re-capping the syringe. 
     The invention also includes apparatus by which the methods of the invention may be performed. 
     More particularly, according to a second aspect of the invention, apparatus for forming a film on a surface of a substrate comprises a substrate support means and a dispensing system for dispensing at least one liquid sample at a sample locatio position on a surface of a substrate supported by said substrate support means during operation of said apparatus, said dispensing system comprising gripper means for holding a reservoir which, in use, contains a liquid sample, said reservoir having an outlet comprising a die having a planar face which is contactable with said substrate to define therewith a channel for receiving at least a portion of said liquid sample from said reservoir, said dispensing system being operable to contact said die with said substrate at one end of said sample location position whilst substantially simultaneously being operable to move said die and said substrate in contact with and relative to one another whereby said die moves towards a remote end of said sample location position to deposit a film of said liquid sample at said sample location position. 
     Apparatus features described previously in connection with the methods of the invention apply mutatis mutandis to apparatus according to the invention as the context permits. 
     Preferably, said dispensing system comprises means to apply pressure to a liquid sample in said reservoir. 
     Preferably, the dispensing system comprises a piston rod engageable with a piston in said reservoir whereby said piston is movable to effect positive displacement or drawback of said liquid sample in said reservoir. Preferably, said piston rod is movable relative to said gripper means by motive means preferably comprising a lead screw driven by, for example, a stepper motor, which is connected to said piston rod. Preferably, the motor is an MDrive stepper motor, available from IMS, USA, which provides a linear resolution of 1 μm. 
     Preferably, said piston rod is engageable with said piston by second gripper means. The second gripper means preferably comprises at least one, more preferably two, grippers movable between an inactive position and an active position in which the or each gripper engages said piston. Preferably, the or each gripper comprises spring steel and has radially-outwardly facing barbs that engage with said piston. 
     Preferably, said piston rod is hollow and has a diametral slot extending from its lower end over a part of its length, the or each gripper being mounted adjacent said lower end and being movable radially outwardly to said active position by radially-outward movement of opposed halves of said lower end of the piston rod against its natural resilience and being returned to said inactive position by radially-inward movement of the opposed halves of the piston rod under the natural resilience thereof. Radial movement of opposed halves of said piston rod is preferably achieved by axial displacement of a central member having an enlarged end and being mounted in said piston rod for movement relative thereto, for example using a pneumatic actuator. 
     The apparatus of the invention includes automated handling equipment for indexing said substrate support and said dispensing system relative to one another whereby, in use, at least two films may be deposited on a substrate surface at sample location positions on said surface that are in space relationship from one another. 
     The method and the apparatus of the invention also include such features as may be described below in connection with the accompanying drawings. 
     The invention also includes a die as herein described. The die may be made of any convenient material. For example, the die may be made of plastic material or metal. In either instance, depending upon the nature of the liquid samples and the materials of the dies, the dies may be either disposed of or, preferably, cleaned using solvents or other cleaning methods for subsequent re-use. 
     Preferably, the passage through the die terminates in a slot extending generally transversely of the die. Preferably, the slot extends substantially across the whole width of said channel definable between said die and a corresponding substrate with which said die is to be used. 
     As discussed earlier, coatings may be made of a wide variety of materials and, within the context of the present invention, films may be made from both organic and inorganic materials provided the materials are in liquid form, or in solution or dispersed in a liquid carrier. Typical applications include adhesives, polymers, resins, paints, inks, metal solutions, starches, dispersions, including nanoparticle dispersions, multi-layer semiconductor materials etc. In many such applications, the materials may be either conductive or non-conductive. 
     The present invention also includes at least one array of films, more preferably a library of films comprising at least two arrays of films each on a substrate, wherein each film is uniformly located with reference to a sample location position in the array. 
    
    
     
       The invention will now be illustrated by reference to the accompanying drawings and following examples. In the drawings: 
         FIG. 1  is a schematic plan view of apparatus in accordance with the invention; 
         FIG. 2  is a schematic side view in partial section of a dispensing system of the apparatus shown in  FIG. 1 ; 
         FIGS. 3A to 3C  are respectively a cross-section on line A-A in  FIG. 3C , a cross-section on line B-B in  FIG. 3A  and an elevation on arrow C in  FIG. 3A  of a die used in the method and apparatus of the invention. 
         FIG. 4  is a schematic vertical section through the lower end of the piston rod  86  shown in  FIG. 2 ; 
         FIG. 5  is a schematic side elevation, partly in section, of the syringe cap and die removal station  32  of  FIG. 1 ; 
         FIGS. 6A to 6C  are respectively a cross-section on line A-A in  FIG. 6C , a cross-section on line B-B in  FIG. 6A  and an elevation on arrow C in  FIG. 6A  of another embodiment of a die used in the method and apparatus of the invention; and 
         FIGS. 7 and 8  are microscope images of sectioned composite films as described in Examples 3 and 4 below. 
     
    
    
     Apparatus  10  according to the invention is shown in  FIG. 1 . The apparatus  10  has a frame  12  on which is mounted an automated XYZ handling system  14 . Also located on the base plate  16  of the frame  12  are:
         a rack  18  containing syringes  20 , for example 10 ml syringes available from EFD;   two racks  22  into each of which may be securely mounted for example thirty two glass slides (not shown) on each of which a liquid film may be deposited in use of the apparatus  10 , each rack having an upper plate (as shown) having elongate slots  24  corresponding to but slightly larger than a sample location position on the respective glass slide;   a rack  26  for containing dies  30  (described in more detail below);   a rack  28  for containing new syringe caps  36 ;   a syringe cap and die removal station  32 ;   a reception container (not shown), which may contain solvent or other liquid, which is located beneath an aperture in the base plate  16  for receiving removed syringe caps  36  and dies  30 ;   a reception container (not shown) which is located beneath an aperture in the base plate  16  for receiving syringes  20  that have been used; and   a dispensing system  34  (see  FIG. 2 ) mounted on the handling system  14  for vertical movement (Z axis) relative to the frame  12 .       

     Although glass slides have been exemplified as the substrates for receiving films of liquid samples, it will be appreciated from the earlier description, that other materials and other sizes of substrate may be readily used with the apparatus  10  of the invention. 
     The dies  30 , according to the invention, (see  FIGS. 3A to 3C ) may be made of plastic or metal, for example brass, and each have an elongate body  40  which, in this embodiment, has rounded ends  42 ,  44  and, on the upper surface thereof, a centrally-located annular projection  46  coaxial with a cylindrical hole  48  in the body  40 . The upper end of the annular projection  46  is countersunk at  47  to aid location of the outlet ends of syringes  20 . 
     The cylindrical hole  48  terminates within the body  40  of the die  30  and is intersected at its inner end by a slot  50  extending transversely of the body  40 . 
     The lower planar surface  52  of the body  40  of the die  30  has machined or moulded therein a rebate  54  which is open at and extends from one end  42  longitudinally of the body  40  towards the opposite end  44  for an amount greater than half the length of the body  40  whereby it terminates at a position past the slot  50  to provide a liquid dead space  56 . The provision of such a dead space  56  is preferred as it is thought to act as a small liquid reservoir to accommodate minor pressure fluctuations and possibly to aid surface wetting. The rebate  54  will be dimensioned to produce a film of required dimensions as previously described. 
     The syringe cap and die removal station  32  has a first, upper wedge  60  having a U-shaped aperture  62  for receiving a lower end of a syringe  20  (shown with a cap  36 ) carried by the dispensing system  34 , the portions of the wedge  60  forming the limbs of the aperture  62  being sufficiently close together to engage the cap  36  or die  30  to be removed. The first wedge  60  is tapered towards the open end of the aperture  62  and has a horizontally-oriented upper surface and an inclined lower surface and is mounted on a bearing (not shown) for reciprocal vertical movement as indicated by the arrow. The station  32  also has a second wedge  64 , having a U-shaped aperture  66 , substantially the same as the first wedge  60  but having an orientation which is inverted as compared to the orientation of the first wedge  60 . The second wedge  64  is mounted on a pneumatic actuator (not shown) for reciprocal horizontal movement as indicated by the arrow relative to the XY position of the first wedge  60 . Movement of the second wedge  64  towards the first wedge  60  causes the lower, horizontal surface of the second wedge  64  to engage the cap  36  (or die  30 ) and to move the first wedge  60 , together with the dispensing system  34 , vertically to separate the syringe  20  from the cap  36  (or die  30 ). 
     The dispensing system  34  is mounted on a Z axis support member  70  of the handling system  14  through a linear bearing  72 . The dispensing system  34  is retained relative to the support member  70  by a compression spring  74  mounted on the support member  70  by a bracket  76 . 
     The dispensing system  34  has a frame  78 , which is U-shaped in section, mounted on the linear bearing  72 . Pneumatically-operated gripper members  80  for holding a syringe  20  are mounted on the lower limb of the frame  78 . An electric stepper motor  82  is mounted on the upper limb of the frame  78 . The motor  82  is used to drive a lead screw  84  which is supported in threaded apertures in the limbs of the frame  78 . 
     Mounted for vertical movement on the lead screw  84  is a hollow piston rod  86  mounted within the lower end of which is a spreader member  88  which is movable axially of the piston rod  86 . Also mounted on the lower end of the piston rod  86  are two radially opposed spring steel grippers  90  having at their lower ends slight barbs  92 . Axial movement upwards of the member  88  causes the lower ends of the grippers  90  to move radially outwardly and engage a piston head member (not shown) in the syringe  20  whilst reversal of that movement allows the grippers  90  to return radially inwardly owing to their inherent resilience and disengage from such a piston member. 
     The handling system  14  and other actuators forming part of the apparatus  10  are controlled using a computer (not shown) which is programmable with the required sequence of operation of the apparatus  10 . 
     In operation, the dispensing system  34  is moved by the handling system  14  to rack  18  and picks up a first syringe  20 . As the volumes of materials in the syringes  20  are not known, before the grippers  80  grip a syringe  20 , the piston rod  86  is lowered using the motor  82  and the lead screw  84  into the syringe  20  until upward movement, owing to contact with the piston head member in the syringe  20 , of the dispensing system  34  is sensed. Following sensing of such movement, movement of the piston rod  86  is stopped and the piston rod  86  is moved down by a user-determined amount to prime the die with liquid from the syringe  20 . The grippers  80  are then closed to grip the syringe  20 . 
     The dispensing system  34  is then moved to the syringe cap and die removal station  32  whereat the syringe  20  is located relative to the first wedge  60 . The second wedge  64  is then moved horizontally to engage the cap  36  and the first wedge  60  to cause vertically movement of the first wedge  60  to remove the cap  36  from the syringe  20  and let it drop into the reception container. The dispensing system  34  is then moved to rack  26  to a position over a first die  30  and lowered to engage the outlet end of the syringe  20  in the annular projection  46  of the die  30 . To ensure the syringe  20  and die  30  are correctly engaged, after initial contact the grippers  80  release the syringe  20  and then re-grip it whilst the dispensing system applies downward force to it. 
     The dispensing system  34  is then moved to a first dispensing position on the first rack  22  and is lowered to contact the planar face  52  of the die  30  with the glass slide located at that dispensing position. The die  30  is located at on end of a sample location position on the glass slide, the die  30  being orientated such that the end  44  thereof is facing the direction in which the die  30  will be moved. The die  30  contacts the glass slide with a pressure that is a combination of the weight of the dispensing system  34  and pressure applied by the spring  74 . The amount of contact pressure generated is a function of the weight of the dispensing system  34 , the spring constant of the spring  74  and the amount of compression applied to the spring  74 . Typically, it may be in the region of around 10N to 35N. 
     The piston rod  86  is lowered to dispense liquid from the syringe  20  whilst at the same time the dispensing system  34 , and hence the die  30  still in contact with the glass slide, is moved towards the remote end of the sample location position. Under this combined action, liquid flows into the channel defined by the planar surface  52  and the rebate  54  of the die  30  together with the glass slide and is deposited on the glass slide as the die  30  moves along it. 
     As the die  30  nears the end of the sample location position, movement of the piston rod  86  relative to the syringe  20  is stopped and, as it reaches the end of the sample location position, the dispensing system  34  is moved upwardly to lift the die  30  from contact with the glass slide whilst at the same time the piston rod  86  is retracted slightly relative to the syringe  20 . 
     If the liquid sample in syringe  20  is to be used to form more than one film, the dispensing system  34  is moved to a second, and, if necessary, subsequent, glass slide on the rack  22  and the dispensation procedure is repeated. In a typical experimental set up, up to four films may be formed from each syringe  20 . 
     Once the film or films have been formed, the dispensing system  34  is then moved to the syringe cap and die removal station  32  whereat the die  30  is removed from the syringe  20  similarly to the removal of the cap  36  therefrom as previously described. 
     The dispensing system  34  is then moved to rack  28  and positioned over a first cap position and is lowered to engage the end of the syringe  20  with a new cap  36 . The dispensing system  34  is then moved to the location of the reception container for used syringes  20  and the syringe  20  is released to fall into the container. The used syringes  20  may be either disposed of or, if they contain liquid formulations that are still of interest, collected for re-use. If the latter, the reception container may be environmentally controlled, for example by being cooled. 
     The sequence is repeated for other syringes  20 . 
     Once a rack  22  has had films formed on all of its glass slides, the computer may be paused to permit removal of that rack  22  from the frame  12 , and optionally, replenishment of the syringe rack  18  and the die and cap racks  26  and  28 , and insertion of a freshly loaded rack  22  into the frame  12 . The glass slides may then be treated as previously described to form solid films. 
     In an alternative embodiment, dies  30 A, according to the invention, (see  FIGS. 6A to 6C ) each have an elongate body  40 A which, in this embodiment, has rounded ends  42 A,  44 A and, on the upper surface thereof, a centrally-located annular projection  46 A coaxial with a cylindrical hole  48 A in the body  40 A. The upper end of the annular projection  46 A is countersunk at  47 A to aid location of the outlet ends of syringes  20 . 
     The cylindrical hole  48 A terminates within the body  40 A of the die  30 A and is intersected at its inner end by a slot  50 A extending transversely of the body  40 A. 
     The lower planar surface  52 A of the body  40 A of the die  30 A has machined or moulded therein a rebate  54 A which is open at and extends along the full length of the die  30 A from one end  42 A longitudinally of the body  40 A to the opposite end  44 A. The rebate  54  will be dimensioned to produce a film of required dimensions as previously described. 
     The invention will now be described further with reference to the following Examples. 
     EXAMPLE 1 
     10 ml syringes  20  were prepared with paint samples, having a viscosity of about 5 Pa·s, and adhesive samples (Ablebond 8200C, a silver-filled epoxy resin adhesive available from Ablestik), having a dynamic viscosity of about 10 Pa·s. The syringes were used to generate films on glass microscope slides in accordance with the invention using dies  30  as described with reference to  FIGS. 3A to 3C . The rebates in the dies  30  were 17 mm long, 10 mm wide and had depths of 75 μm and 450 μm, respectively. The slot  50  of the die  30  that opens into the rebate is 10 mm from the front end of the die  30  and is 1 mm wide. The paint films were allowed to dry at ambient temperature. The adhesive films were cured in a box oven at about 175° C. 
     The films were then measured using a micrometer at three positions (Positions  1 ,  2  and  3  in the Tables) located on the longitudinal axes of the films, Position  2  being approximately half way along the lengths of the films and Positions  1  and  3  being either side of Position  2 . 
     The paint sample films made using a die having a depth of 75 μm were numbered 1 to 8 and the paint sample films made using a die having a depth of 450 μm were numbered 9 to 16 and the results of the measurements made are given in Table 1. The % age relative standard deviations (% RSD) of each set of measurements along the length of the film are given and the % RSD of each set of measurements at each measurement point. Similarly, the adhesive sample films were numbered 17 to 24 and 25 to 32, respectively, the results being given in Table 2. 
     EXAMPLE 2 
     Comparative 
     The liquid samples used in Example 1 were used to generate two sets of films on glass microscope slides on which channels were formed using a tape of approximately 130 μm, the first set of slides having only a single layer of tape along each side thereof and the second set of slides having three layers of tape along each side thereof. The liquid samples deposited on the slides were leveled using a doctor blade. The films were allowed to dry or were cured as described in Example 1 and the thicknesses of the films were measured as described in Example 1. 
     The paint sample films made using a single tape thickness, ie in a channel having a nominal depth of approximately 130 μm, were numbered 1C to 8C and the paint sample films made using a triple tape thickness, ie in a channel having a nominal depth of approximately 390 μm, were numbered 9C to 16C, the results being given in Table 3. Similarly, the adhesive sample films were numbered 17C to 24C and 25C to 32C, respectively, the results being given in Table 4. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Sample 
                 Position 1 
                 Position 2 
                 Position 3 
                 % RSD 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 26 
                 28 
                 29 
                 5.52 
               
               
                 2 
                 33 
                 32 
                 33 
                 1.77 
               
               
                 3 
                 29 
                 31 
                 31 
                 3.81 
               
               
                 4 
                 34 
                 32 
                 27 
                 11.63 
               
               
                 5 
                 30 
                 32 
                 33 
                 4.82 
               
               
                 6 
                 32 
                 34 
                 34 
                 3.46 
               
               
                 7 
                 30 
                 28 
                 25 
                 9.10 
               
               
                 8 
                 31 
                 33 
                 31 
                 3.65 
               
               
                 % RSD 
                 8.19 
                 7.11 
                 10.44 
               
               
                 9 
                 114 
                 129 
                 120 
                 6.24 
               
               
                 10 
                 109 
                 119 
                 118 
                 4.78 
               
               
                 11 
                 113 
                 122 
                 112 
                 4.76 
               
               
                 12 
                 123 
                 131 
                 127 
                 3.15 
               
               
                 13 
                 119 
                 124 
                 123 
                 2.17 
               
               
                 14 
                 127 
                 132 
                 126 
                 2.50 
               
               
                 15 
                 128 
                 133 
                 131 
                 1.93 
               
               
                 16 
                 126 
                 129 
                 130 
                 1.62 
               
               
                 % RSD 
                 6.12 
                 4.01 
                 5.34 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Sample 
                 Position 1 
                 Position 2 
                 Position 3 
                 % RSD 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 17 
                 45 
                 46 
                 50 
                 5.63 
               
               
                 18 
                 51 
                 44 
                 44 
                 8.72 
               
               
                 19 
                 49 
                 49 
                 49 
                 0.00 
               
               
                 20 
                 48 
                 42 
                 41 
                 8.67 
               
               
                 21 
                 46 
                 46 
                 40 
                 7.87 
               
               
                 22 
                 48 
                 48 
                 48 
                 0.00 
               
               
                 23 
                 45 
                 45 
                 44 
                 1.29 
               
               
                 24 
                 48 
                 43 
                 43 
                 6.46 
               
               
                 % RSD 
                 4.36 
                 5.26 
                 8.29 
               
               
                 25 
                 189 
                 176 
                 187 
                 3.80 
               
               
                 26 
                 187 
                 178 
                 182 
                 2.47 
               
               
                 27 
                 185 
                 176 
                 177 
                 2.75 
               
               
                 28 
                 182 
                 176 
                 184 
                 2.30 
               
               
                 29 
                 184 
                 179 
                 182 
                 1.39 
               
               
                 30 
                 176 
                 177 
                 169 
                 2.51 
               
               
                 31 
                 186 
                 176 
                 186 
                 3.16 
               
               
                 32 
                 176 
                 177 
                 173 
                 1.19 
               
               
                 % RSD 
                 2.65 
                 0.64 
                 3.56 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Sample 
                 Position 1 
                 Position 2 
                 Position 3 
                 % RSD 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                  1C 
                 56 
                 57 
                 65 
                 8.31 
               
               
                  2C 
                 47 
                 43 
                 40 
                 8.10 
               
               
                  3C 
                 39 
                 42 
                 40 
                 3.79 
               
               
                  4C 
                 48 
                 55 
                 55 
                 7.67 
               
               
                  5C 
                 59 
                 57 
                 54 
                 4.44 
               
               
                  6C 
                 50 
                 50 
                 59 
                 9.80 
               
               
                  7C 
                 61 
                 55 
                 57 
                 5.30 
               
               
                  8C 
                 82 
                 69 
                 81 
                 9.35 
               
               
                 % RSD 
                 26.42 
                 17.79 
                 26.09 
               
               
                  9C 
                 134 
                 136 
                 140 
                 2.24 
               
               
                 10C 
                 130 
                 129 
                 127 
                 1.19 
               
               
                 11C 
                 126 
                 129 
                 114 
                 6.45 
               
               
                 12C 
                 141 
                 140 
                 134 
                 2.74 
               
               
                 13C 
                 138 
                 142 
                 136 
                 2.20 
               
               
                 14C 
                 137 
                 123 
                 140 
                 6.81 
               
               
                 15C 
                 129 
                 125 
                 114 
                 6.33 
               
               
                 16C 
                 137 
                 134 
                 133 
                 1.55 
               
               
                 % RSD 
                 3.89 
                 5.22 
                 8.18 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                 Sample 
                 Position 1 
                 Position 2 
                 Position 3 
                 % RSD 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 17C 
                 62 
                 61 
                 57 
                 4.41 
               
               
                 18C 
                 67 
                 69 
                 69 
                 1.69 
               
               
                 19C 
                 65 
                 69 
                 70 
                 3.89 
               
               
                 20C 
                 67 
                 67 
                 70 
                 2.55 
               
               
                 21C 
                 60 
                 58 
                 61 
                 2.56 
               
               
                 22C 
                 56 
                 61 
                 60 
                 4.48 
               
               
                 23C 
                 56 
                 59 
                 61 
                 4.29 
               
               
                 24C 
                 59 
                 60 
                 63 
                 3.43 
               
               
                 % RSD 
                 7.32 
                 7.25 
                 7.96 
               
               
                 25C 
                 166 
                 166 
                 171 
                 1.72 
               
               
                 26C 
                 168 
                 167 
                 174 
                 2.23 
               
               
                 27C 
                 169 
                 173 
                 167 
                 1.80 
               
               
                 28C 
                 175 
                 167 
                 173 
                 2.43 
               
               
                 29C 
                 182 
                 175 
                 184 
                 2.62 
               
               
                 30C 
                 172 
                 171 
                 174 
                 0.89 
               
               
                 31C 
                 163 
                 164 
                 168 
                 1.60 
               
               
                 32C 
                 179 
                 178 
                 181 
                 0.85 
               
               
                 % RSD 
                 3.81 
                 2.89 
                 3.39 
               
               
                   
               
            
           
         
       
     
     As can be seen from a comparison of the % RSD figures for each film and the % RSD figures for each measurement point on the films, films formed in accordance with the invention are at least comparable with films formed using the known technique. Additionally, the repeatability of film formation (% RSD figures of measurement points), especially for thinner films and for lower viscosity materials, is enhanced in films made in accordance with the method of the invention as compared to the films made using the known technique. 
     EXAMPLE 3 
     An adhesive multilayer composite film  100  on a glass slide  102  was prepared using the method of the invention. A first film layer  104  of a first conductive adhesive was deposited onto the glass slide  102  using a die  30 A as described with reference to  FIGS. 6A to 6C , the die  30 A having a rebate 20 mm long (measured at the apices of the rounded ends  42 A,  44 A thereof), 10 mm wide and a depth of 220 μm. The first film layer  104  was then oven cured. 
     A second film layer  106  of a second, different conductive adhesive, was deposited on top of the first film layer  104  using a second die  30 A as described with reference to  FIGS. 6A to 6C , the die  30 A having a rebate 20 mm long (measured at the apices of the rounded ends  42 A,  44 A thereof), 10 mm wide and a depth of 500 μm. The second film layer  106  was then oven cured. 
     To enable the composite film  100  to be examined, the composite film  100  on the glass slide  102  was encapsulated in epoxy resin  108  which was then cured and the encapsulated composite film  100  and glass slide  102  was sectioned and polished. A microscope image of the cross-section of the multilayer composite film  100  is shown in  FIG. 7 . The interface between the two film layers  104 ,  106  of the adhesives may be clearly seen in the image. The thickness of the first film layer  104  was about 145 μm and of the second film layer  106  about 85 μm. Overall, the thickness of the multilayer composite film  100  was about 230 μm. The profile of the composite film  100  was studied using a laser profilometer, the three dimensional image from which showed the thickness of the composite film  100  was very uniform along its length and width and was consistent with the thickness obtained from microscope image. 
     EXAMPLE 4 
     To demonstrate a paint multilayer composite film  110 , a first film layer  114  of a water-based emulsion paint, was deposited onto a glass slide  112  using a die  30 A as described with reference to  FIGS. 6A to 6C , the die  30 A having a rebate 20 mm long (measured at the apices of the rounded ends  42 A,  44 A thereof), 10 mm wide and a depth of 220 μm. The first film layer  114  was then allowed to dry in ambient conditions. 
     A second film layer  116  of a water-based paint, but being of a different colour, was deposited on top of the first film layer  114  using a second die  30 A as described with reference to  FIGS. 6A to 6C , the die  30 A having a rebate 20 mm long (measured at the apices of the rounded ends  42 A,  44 A thereof), 10 mm wide and a depth of 500 μm. The second film layer  116  was then allowed to dry in ambient conditions. 
     To enable the composite film  110  to be examined, the composite film  110  on the glass slide  112  was encapsulated in epoxy resin  118  which was then cured and the encapsulated composite film  110  and glass slide  112  was sectioned and polished. A microscope image of the cross-section of the multilayer composite film  110  is shown in  FIG. 8 . The interface between the two film layers  114 , 116  of the paints may be clearly seen in the image. The thickness of the first film layer  114  was about 47 μm and of the second film layer  116  about 74 μm. Overall, the thickness of the multilayer composite film  110  was about 121 μm. The profile of the composite film  110  was studied using a laser profilometer, the three dimensional image from which showed the thickness of the composite film  110  was very uniform along its length and width and was consistent with the thickness obtained from microscope image. 
     As will be appreciated, the use of paints of different colours in this example was merely for convenience to demonstrate the formation of a multilayer composite film and that other paint systems, for example using pigmented and unpigmented coatings such as primer-, under- and top-coat paints, may be studied using the methods and apparatus of the invention.