WO2018189516A1

WO2018189516A1 - Force sensitive resistor uv ink

Info

Publication number: WO2018189516A1
Application number: PCT/GB2018/050940
Authority: WO
Inventors: John Cunningham; Charles Jonathan Kennett
Original assignee: Rainbow Technology Systems Ltd
Current assignee: Rainbow Technology Systems Ltd
Priority date: 2017-04-10
Filing date: 2018-04-09
Publication date: 2018-10-18
Anticipated expiration: 2019-10-10
Also published as: GB201705751D0

Abstract

The present invention relates to radiation curable coatings for use in a printing and/or moulding process. More particularly, the present invention relates to pressure sensitive force sensing resistor formed from radiation curable coatings in the form of 100% or substantially 100% solids radiation curable coatings for use in a printing and/or moulding process wherein a substrate is printed with a wet radiation curable photopolymer to form images such as electrical circuits or other features used in the manufacture of sensors and touch sensors such as for example lines, squares, spirals, circles, or other geometric and non-geometric shapes. These are then coated directly on to a sensor with a radiation curable FSR ink to create a pressure sensitive electrode which can be used to control hand held or other devices.

Description

FORCE SENSITIVE RESISTOR UV INK

FIELD OF THE INVENTION

The present invention relates to radiation curable coatings for use in a printing and/or moulding process. More particularly, the present invention relates to pressure sensitive force sensing resistor formed from radiation curable coatings in the form of 100% or substantially 100% solids radiation curable coatings for use in a printing and/or moulding process wherein a substrate is printed with a wet radiation curable photopoiymer to form images such as electrical circuits or other features used in the manufacture of sensors and touch sensors such as for example lines, squares, spirals, circles, or other geometric and non-geometric shapes. These are then coated directly on to a sensor with a radiation curable Force Sensitive Resistor (FSR) ink to create a pressure sensitive electrode which can be used to control hand held or other devices BACKGROUND OF THE INVENTION

In the prior art current water based and solvent based FSR ink technology cannot be printed directly on to a sensor circuit without the circuit remaining permanently on. The present invention addresses this problem and seeks to print radiation curable FSR ink directly onto a sensor arrangement printed on a plastic substrate e.g. polyester and then cured.

The present invention therefore addresses the problem of providing an improved method of forming pressure sensitive force sensing resistor formed from radiation curable coatings.

It is therefore an object of at least one aspect of the present invention to at least obviate or mitigate problems found in the prior art.

It is a further object of at least one aspect of the present invention to provide an improved method of forming pressure sensitive force sensing resistors.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a curable photopoiymer comprising:

a curable resin present in an amount of 10% to 80% by weight

a mix of conductive particles between 0.2% and 30% by weight

at least one filler between 1 % to 15% by weight;

at least one photoinifiator between 1 % and 12% by weight;

at least one additive between 0.1 % and 2,5% by weight;

wherein the curable photopoiymer is capable of being cured with energy of less than about 1 ,000 mJ and where there is no pre-drying prior to curing or imaging in a photoimaging process.

The present invention provides an improved method of forming a radiation curable photopolymer which is capable of functioning as a pressure sensitive force sensing resistor when coated directly onto the electrode arrangement such as in Figure 1 and Figure 2.

Herein a Force Sensitive Resistor (FSR) is a material whose resistance changes when a force or pressure is applied.

The force-sensing resistors of the present invention may consist of a conductive polymer, which changes resistance in a predictable manner following application of feree to its surface.

The conductive polymer may comprise both electrically conducting and non-conducting particles suspended in a matrix.

The particles may be sub-micron such as in the nanometre range in size, and may be formulated to reduce the temperature dependence, improve mechanical properties and increase surface durability.

Applying a force to a surface of the sensor may cause particles to touch conducting electrodes, changing the resistance of the force sensing resistor.

The UV radiation curable ink used to form the curable photopolymer also inherently shows a wide variation of electrical resistance upon mechanical deformation allowing the use of 2D and 3D force sensors and sensor matrices on both rigid and flexible substrates to be used for example in embedded sensor applications or touch interactive surfaces or even printed strain gauges and other sensing equipment. The UV curable photopolymer of the present invention may therefore be described as a Force Sensitive Resistor ink.

The radiation curable FSR ink may be printed directly onto a sensor arrangement. The FSR ink may be printed separately on a plastic substrate e.g. polyester and then brought into contact with radiation energy.

The UV curable FSR ink may have high resistance in the steady state. The resistance may drop with pressure touch sufficiently to allow activation of a control circuit.

The UV curable FSR ink may be essentially 100% solids and may cure with any UV combination of light sources (from 200 nm - 420 nm wavelength).

The FSR ink may therefore be printed directly onto a plastic surface such as polyester and then brought into contact with UV radiation. The printed FSR ink may have high resistance in the steady state and the resistance may drop with pressure touch sufficiently to allow activation of a control circuit.

The FSR ink may show resistance drops in-line with insulation resistance.

The FSR ink may show resistance drops proportionally with activation resistance The FSR ink may show that the resistance changes proportionally with force and that that force change is suitable to aliow fine voltage control such as in a hand held device or console such as in a car or touch screen.

The said FSR ink can be integrated in 3 different states:

a. Adhere FSR ink sensor circuit onto a sheet of Thermoplastic Elastomer (TPE) b. 2D TPE can over mould as FSR ink sensor circuit

c. 3D TPE can over mould as FSR sensor circuit

The FSR ink may be suitable for printing with a range of processes including but not restricted to: screen; flexographic; lithographic; gravure; ink jet; letterpress; intaglio; rotogravure and rotary screen.

The conductive particles may be in a variety of forms including any one of or a mixture of any of the following: graphite; graphene; graphene oxide; modified graphene; metal oxides; carbon black; carbon nanotubules both single walled and multi-walled; PEDOT:PSS and PEDOT-TMA.

The conductive particles may have a sub-micron size.

Typically, the conductive particles may have a size of about 0.1 - 500 nm; 0.1 - 200 nm; 0.1 - 100 nm or 0.1 - 50 nm.

The photoinitiator may be capable of initiating crosslinking in the curable photopolymer. The photoinitiator may initiate the crosslinking of the material and may selected from any one of or combination of the following: 1-hydroxy-cyclohexyl-phenylketone; 2-hydroxy- 2-methyl-1-phenyl-1-propanone; 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1- propanone;alpha-dimethoxy-alpha-phenylacetophenone; 2-benzyl-2-(dimethylamino)-1-[4(4- morpholinyl)-1-butanone); 2- methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone; diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide; phosphine oxide; phenyl bis(2,4,6- trimethyl benzoyl); phosphine oxide iodonium and (4-methylphenyl)[4-(2- methylpropyl)phenyl]- hexafluorophosphate.

The photoinitiators may initiate the crosslinking of the material and may be selected from any one of or combination of the following: 2,4,6- triorganobenzoyldiarylphosphine oxides: 2,4,8-trimethylbenzoyldiphenylphosphine oxide; 2,4,6- triethylbenzoyldinaphthylphosphineoxide; 2,4,6-triorganobenzoyl diorganophosphonai.es, such as, 2,4,6-trimethylbenzoyl diethylphosphonate and 2,4,6- triethylbenzoyl diphenyiphosphonate; 2,4,6-triorganobenzoyidiaryiphosphine sulfides, such as 2,4,6- trimethyibenzoyldiphenylphosphine sulfide commerciaily available under the lrgacure or Darocur trademarks from BASF; mixed arylsuifonium hexafiuoroantimonate salts; mixed arylsuifonium hexofluorophosphate salts, commerciaily available under the Cyracure trademark from Dow Chemical; benzophenone; 4-phenyl benzophenone; 4-methyi benzophenone; 2-isopropyl thioxanthone; 2-chlorothioxanthone; 2,4-diethylthioxanthone: commercially available under the Omnirad trademark from IGM resins. The curable photopolymer may be included in the curable photopolymer to initiate the crosslinking of the material and are selected from any one of or combination of the following: 2- dimethylamino-ethylbenzoate;ethyl-4-(dimethyIamino)benzoate; 2-ethyI-4- (dimethylamino)benzoate; isoarnyi 4-(N,N-dimethylamino)benzoate commercially available from under the Omnirad trademark from IGM resins.

The photoinitiators may be present in the range of about 0.1 % to about 15% or about 0.1 % to about 1.5% weight on weight of the composition for cationic coatings and preferably in the range of about 8.0% to about 10.0% weight on weight of the composition for free radical coatings,

The at least one additive may comprise a wetting agent and may be capable of providing any one of or combination of the following: humidity resistance; surface wetting and levelling properties which enables the curable photopolymer to be evenly spread onto a surface where imaging is to occur.

The additive may also comprise an adhesive agent.

The adhesive agent may be capable of providing adhesion for the bonding of the curable photopolymer to various substrates including metals, glass and plasties.

The additive may be present in an amount from 0.1 % and 2.5% by weight; 0.1 % and 2% by weight; 0.1 % and 1 % by weight; 0.1 % and 0.5% by weight.

The curable photopolymer may be all solids or substantially ail solids and is therefore solvent free or substantially solvent free with no volatile organic content.

The curable photopolymer may comprise less than about 1 % solvent less than about 3% solvent, less than about 10% solvent or less than about 15% solvent curable photopolymer.

The curable photopolymer may be cured with energy of about 0 - 20 mJ, about 0 - 50 mJ, about 50 - 500 mJ or about 1 00 - 1 , 000 mJ.

The curable photopolymer may be curedwith avery low energy radiation inthe range of about 0.5 - 20 m J or about 1 .5 m J - 2.0 m J.

The curable photopolymer may be cured with energy of wavelength from about 200 nm to about 500 nm, about 365 nm to about 415 nm or about 395nm to about 405nm.

The curable photopolymer may have good adhesion to copper, polyester, FR4, glass and polyimide substrates.

The curable photopolymer may also comprise any one of or combination of the following: UV or visible light or IR photoinitiator(s); UV curable resin(s); acrylate and/or methacrylate monomer(s); UV stabilizers; rheology modifier(s); adhesive promoter(s) and/or self-levelling agent(s).

The curable photopolymer may also comprise aromatic ketones {e.g. Methyibenzoyl formate and 1 -Hydroxycyclohexyl phenyl ketone). The curable resin may be present in an amount of 5% to 80% by weight or 10% to 30% by weight of the curable photopoiymer.

The curable resins may be selected from any one of or combination of the following: aliphatic linear polyether urethane acrylate; aliphatic polyester urethane acrylate; and polyester acrylated monomer blends with fast cure characteristics.

The curable resins may be UV curable resins selected from any one of or combination of the following: pentaerythritol tri/tetra-acrylate (PETA); trimethylolpropane triacrylate (TMPTA): trimethylolpropane ethoxy triacrylate (TMPEOTA); hexamethylene diacrylate (HDDA); Dipropyleneglycol diacrylate (DPGDA); tripropyleneglycol diacrylate (TPGDA); Isobornyl acrylate (I BOA) and Hexylethyi acrylate (HEA).

The curable resins may be selected from any one of or combination of the following: isobornyl acrylate; cyclohexyl acrylate; tert-butyi acrylate; 2-ethyihexyl acrylate; dicyclopentenyl acrylate; tetrahydrofurfuryl acrylate; cyclic trimethylopropane formal acrylate and vinyl caprolactam.

The curable resins may be selected from acrylate monomers which are monofunctionai and multifunctionai acrylates e.g. methacrylate monomers which are monofunctionai and multifunctional meth acrylates.

The curable photopoiymer may also comprise any one of or combination of the following to improve adhesion to metal or glass surfaces: Acrylic acid; CE.A; Epoxy Silane and Trifuncfional acid esters.

The curable photopoiymer may also comprise any one of or combination of the following wetting agents in the range of about 0.1 % to about 5% w/w:

a. a blend of acrylate copolymers;

b. polyether modified polydimethylsiioxane:

c. polyether modified dimethyisiloxane;

d. polyether modified polydimethylsiioxane;

e. polyether modified dimethyisiloxane;

f. polymeric dispersant;

g. polymeric dispersant; and

h. polyether amino acid polyamine derivative;

The curable photopoiymer may also comprise any one of or combination of the following:

a. surfactants;

b. antioxidants;

c. thixotropes;

d. diiatants;

e. reinforcement materials;

f. silane functional perfluoroether;

g. phosphate functional perfluoroether; h. silanes;

i. titanates;

j. wax;

k. air release agents;

i. flow additives;

m. adhesion promoters;

n. rheology modifiers;

o. surfactants; and

p. spacer beads

The curable photopolymer may further comprise the following:

resins in the amount of 10% to 60% by weight e.g. acrylate and/or methacrylate monomers;

photoinitiators 2% to 12% by weight;

levelling agents 0.3% to 1 % by weight; stabilizers 0.1 % to

0.5% by weight;

adhesion promoters 5% to 10% by weight;

rheology modifiers 0.1 % to 5.0% by weight; and

wetting agents 0.01 % to 0.5% by weight.

The curable photopolymer may comprise:

about 1 w/w% to 60 w/w% of an acidic acrylate monomer;

about 1 w/w% to 50 w/w% of a urethane acrylate monomer;

about 25 w/w% to 90 w/w% of di-, tri- and hexa-acrylate monomer consisting essentially of a mixture of about 20 w/w% to 90 w/w% of hexanediol diacrylate; and about 10 w/w% to 80 w/w% of a mono-functional branched or carbocyciic acrylate; and about 1 w/w% to 15 w/w% of a photoinitiator or blend of photoinitiators.

According to a second aspect of the present invention there is provided a cured photopolymer as described in the first aspect in a control circuit, hand held device or console such as in a car or touch screen.

A user may press and apply pressure to the cured photopolymer to change the resistance of the force sensing resistor and thereby change the operation of the device.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the following Figures:

Figure 1 relates to a radiation curable photopolymer which is capable of functioning as a pressure sensitive force sensing resistor when coated directly onto the electrode arrangement according to an embodiment of the present invention; Figure 2 relates to a radiation curable photopolymer which is capable of functioning as a pressure sensitive force sensing resistor when coated directly onto the electrode arrangement according to a further embodiment of the present invention;

Figures 3 relates to inks which were coated using a lab screen printer with mesh using the template of Figure 1 according to an embodiment of the present invention;

Figure 4 relates to inks which were coated using a lab screen printer with mesh using the template of Figure 2 according to a further embodiment of the present invention; and

Figure 5 relates to FSR Sensor arrangements where pressure was brought to bear on the FSR using an Instron 3342 increasing step by step the pressure from ON to 100N.

BRIEF DESCRIPTION

There is herein described a UV curable photopolymer which is capable of functioning as a pressure sensitive force sensing resistor in the form of a sensor.

The force-sensing resistor consists of a conductive polymer, which changes resistance in a predictable manner following application of force to its surface. The conductive polymer comprises both electrically conducting and non-conducting particles suspended in a matrix.

The particles are sub-micron such as in the nanometre range in size, and may be formulated to reduce the temperature dependence, improve mechanical properties and increase surface durability.

Applying a force to a surface of the sensor causes particles to touch conducting electrodes, changing the resistance of the force sensing resistor.

The UV curable ink used to form the curable photopolymer also inherently shows a wide variation of electrical resistance upon mechanical deformation allowing the use of 2D and 3D force sensors and sensor matrices on both rigid and flexible substrates to be used for example in embedded sensor applications or touch interactive surfaces or even printed strain gauges and other sensing equipment. The UV curable photopolymer of the present invention may therefore be described as a Force Sensitive Resistor ink.

The FSR ink is printed separately on a plastic substrate e.g. polyester and then brought into contact with UV radiation.

The UV curable FSR ink is printed directly onto a sensor arrangement.

The UV curable FSR ink has high resistance in the steady state. The resistance drops with pressure touch sufficiently to allow activation of a control circuit.

The UV curable FSR ink is essentially 100% solids and cures with any UV combination of light sources (from 200 nm - 420 nm wavelength).

The FSR ink is therefore be printed directly onto a plastic surface such as polyester and then brought into contact with UV radiation.

The FSR ink shows resistance drops in-line with insulation resistance.

The FSR ink shows resistance drops proportionally with activation resistance The FSR ink shows that the resistance changes proportionally with force and that that force change is suitable to allow fine voltage control such as in a hand held device or console such as in a car or touch screen.

The said FSR ink can be integrated in 3 different states:

a. Adhere FSR ink circuit onto a sheet of Thermoplastic Elastomer (TPE) b. 2D TPE can over mould as FSR ink circuit

c. 3D TPE can over mould as FSR circuit

The FSR ink may is suitable for printing with a range of processes including: screen; flexographic; lithographic: gravure; ink jet: letterpress; intaglio; rotogravure and rotary screen.

The conductive particles may be in a variety of forms including any one of or a mixture of any of the following: graphite; metal oxides; carbon black; carbon nanotubules both single walled and multi-walled; PEDOT:PSS and PEDOT-TMA.

Figure 1 relates to an interdigitated sensor electrode 10. The interdigitated sensor electrode 10 comprises an enclosed area 14 within which there is the FSR print area 12. The radiation curable photopolymer is therefore capable of functioning as a pressure sensitive force sensing resistor when coated directly onto the electrode arrangement.

Figure 2 relates to a spiral sensor electrode 20. The spiral sensor electrode 20 comprises an enclosed area 124 within which there is the FSR print area 22 in a spiral form. The radiation curable photopolymer is therefore capable of functioning as a pressure sensitive force sensing resistor when coated directly onto the electrode arrangement.

Whist specific embodiments of the present invention have been described above, it will be appreciated that departures from the described embodiments may still follow within the scope of the present invention. For example, any suitable type of UV curing may be used along with any suitable mix of conductive and non-conductive particles.

Inks A1 , A2 and A3 were coated using a lab screen printer with 24 mesh using the templates as laid out in Fig 3 and Fig 4. The ink was cured using a Natgraph Air Force Combination drier model 90-22201 R with 2 UV lamps at full power, belt speed @ 6m/min.

Resistance measurements were taken using a Kewtech KT117 Multimeter (Auto).

CONCLUSIONS

The sample prepared using the carbon nano tubes (CNT) was significantly more conductive than the samples prepared using graphene. As we are seeking to have a very low resting conductivity in the ΜΏ range the CNT sample would not be suitable.

It is surprising to find that there is very little overall difference in performance between the 7mm and 10mm sensor arrangements as we thought that the relatively larger surface area of the smaller electrodes would allow more current to pass. It seems reasonable to conclude then that the FSR ink itself is responsible for the initial resistance reading rather than the sensor filament interdigitated track size as the readings are within a reasonable tolerance for both 7mm and 10mm sensors.

Interdigitated spiral sensors were more sensitive than interdigitated lines dropping to a lower k'Ω figure when pressed.

Examination of varying Pressure on the FSR

FSR Sensor arrangements were set up as in Figures 1 and 2. Pressure was then brought to bear on the FSR using an Instron 3342 increasing step by step the pressure from ON to 100N.

Claims

1. A radiation curable photopoiymer comprising:

A radiation curable resin(s) present in an amount of 10% to 80% by weight;

a mix of conductive particie(s) between 0.2% and 30% by weight:

a spacer material(s) in an amount between 1% and 15% by weight

at least one photoinitiator between 1 % and 12% by weight;

at least one additive between 0.1% and 2.5% by weight;

2. A radiation curable photopoiymer according to any preceding claim, wherein the curable photopoiymer is printed directly onto a sensor arrangement.

3. A radiation curable photopoiymer according to claim 1 , wherein the curable ink is printed directly onto an electrode located on a plastic surface such as polyester and then brought into contact with UV radiation.

4. A radiation curable photopoiymer according to claim 1 , wherein the cured photopoiymer forms a cured photopoiymer which is capable of functioning as a pressure sensitive force sensing resistor when applied to a sensor arrangement.

5. A radiation curable photopoiymer according to any of claims 1 or 2, wherein the cured photopoiymer forms force-sensing resistors which change resistance in a predictable manner following application of force to its surface when in direct contact with electrodes.

6. A radiation curable photopoiymer according to any preceding claim, wherein conductive particles are in the form of a conductive polymer which comprises both electrically conducting and non-conducting particles suspended in a matrix of radiation curable photopolymers.

7. A radiation curable photopoiymer according to any preceding claim, wherein the UV curable photopoiymer is printed directly on top an electrode array such as a copper or silver on a polyester sheet and then brought into contact with UV radiation,

8. A radiation curable photopoiymer according to any preceding claim, wherein the radiation curable photopoiymer has high resistance in the steady state when printed directly onto a sensor electrode and drops with pressure touch sufficiently to allow activation of a control circuit.

9. A radiation curable photopoiymer according to any preceding claim, wherein the radiation curable ink is essentially 100% solids and cures with any radiation combination of energy sources (from 100 nm - 1 120 nm wavelength).

10. A radiation curable photopoiymer according to any preceding claim, wherein the cured photopolymers when printed directly onto a sensor electrode show resistance drops proportionally with activation resistance and the resistance changes proportionally with force and that that force change is suitable to allow fine voltage control such as in a hand held device or console such as in a car or touch screen.

1 1. A radiation curable photopoiymer according to any preceding claim, wherein the curable photopoiymer can be integrated in 3 different states after printing directly onto a sensor electrode:

c. 3D TPE can over mould as FSR circuit.

12. A radiation curable photopoiymer according to any preceding claim, wherein the curable photopoiymer is suitable for printing with a range of processes including but not restricted to: screen; flexographic; lithographic; gravure; ink jet; letterpress; intaglio; rotogravure and rotary screen.

13. A radiation curable photopoiymer according to any preceding claim, wherein conductive particles in the curable photopoiymer includes any one of or a mixture of any of the following: graphite; graphene; graphene oxides; modified graphene; metal oxides; carbon black; carbon nanotubules both single walled and multi-walled; PEDOT:PSS and PEDOT-TMA.

14. A radiation curable photopoiymer according to any preceding claim, wherein the photoinitiator is capable of initiating crosslinking in the curable photopoiymer.

15. A curable photopoiymer according to any preceding claim, wherein the photoinitiator initiates the crosslinking of the material and is selected from any one of or combination of the following: 1 -hydroxy-cyclohexyl-phenylketone; 2-hydroxy-2-methyl-1 -phenyl-1- propanone; 2-hydroxy-1 -[4-(2-hydroxyethoxy)phenyl]-2-methyl-1 -propanone;alpha- dimethoxy-alpha-phenylacetophenone; 2-benzyl-2-(dimethylamino)-1-[4(4-morpholinyl)-1- butanone); 2- methyl-1-[4-(methylthio)phe^

trimethylbenzoyl)-phosphine oxide; phosphine oxide; phenyl bis(2,4,6-trimethyl benzoyl); phosphine oxide iodonium and (4-methylphenyl)[4-(2-methylpropyl)phenyl]- hexafluorophosphate.

18. A curable photopolymer according to any preceding claim, wherein the photoinitiator initiates the crosslinking of the material and is selected from any one of or combination of the following: 2,4,6- triorganobenzoyidiarylphosphine oxides; 2,4,6- trimethyibenzoyldiphenylphosphine oxide; 2,4,6-triethyibenzoyldinaphthylphosphineoxide; 2,4,6-triorganobenzoyl diorganophosphonates, such as, 2,4,6-trimethylbenzoyl diethylphosphonate and 2,4,6- triethylbenzoyi diphenylphosphonate; 2,4,6- triorganobenzoyldiarylphosphine sulfides, such as 2,4,6-trimethylbenzoyldiphenylphosphine sulfide commercially available under the Irgacure or Darocur trademarks from Ciba Speciaity Chemicals; mixed arylsulfonium hexafluoroantimonate salts; mixed arylsuifonium hexofluorophosphate salts, commercially available under the Cyracure trademark from Dow Chemical; benzophenone; 4-phenyl benzophenone; 4-methyl benzophenone; 2-isopropyi thioxanthone; 2-chlorothioxanthone; 2,4-diethylthioxanthone; commercially available under the Omnirad trademark from lGM resins.

17. A radiation curable photopolymer according to any preceding claim, wherein the curable photopolymer is included in the curable photopolymer to initiate the crosslinking of the material and are selected from any one of or combination of the following: 2- dimethylamino- ethyi benzoate; ethyi-4-{dimethyiamino) benzoate; 2-ethyi-4-(dimethylamino) benzoate; isoamyl 4-(N, N-dimethylamino) benzoate commercially available from under the Omnirad trademark from IGM resins.

18. A radiation curable photopolymer according to any preceding claim, wherein the photoinitiators are present in the range of about 0.1 % to about 15% or about 0.1 % to about 1.5% weight on weight of the composition for cationic coatings and preferably in the range of about 8.0% to about 10.0% weight on weight of the composition for free radical coatings,

19. A radiation curable photopolymer according to any preceding claim, wherein at least one additive comprises a wetting agent and is capable of providing any one of or combination of the following: humidity resistance; surface wetting and levelling properties which enables the curable photopolymer to be evenly spread onto a surface where imaging is to occur.

20. A radiation curable photopolymer according to any preceding claim, wherein the at least one additive also comprises an adhesive agent.

21. A radiation curable photopoiymer according to ciaim 20, wherein the adhesive agent is capable of providing adhesion for the bonding of the curable photopoiymer to various substrates including metals, glass and plastics.

22. A radiation curable photopoiymer according to any of claims 20 to 21 , wherein the additive is present in an amount from 0.1 % and 2.5% by weight: 0.1 % and 2% by weight; 0.1 % and 1% by weight; 0.1 % and 0.5% by weight

23. A radiation curable photopoiymer according to any preceding ciaim, wherein the curable photopoiymer is ail solids or substantially all solids and is therefore solvent free or substantially solvent free with no volatile organic content.

24. A radiation curable photopoiymer according to any preceding claim, wherein the curable photopoiymer comprises less than about 1 % solvent, less than about 3% solvent, less than about 10% solvent or less than about 15% solvent curable photopoiymer.

25. A radiation curable photopoiymer according to any preceding ciaim, wherein the curable photopoiymer is cured with energy of about 0 - 20 mJ, about 0 - 50 mJ. about 50 - 500 mJ or about 100 - 1 ,000 mJ.

26. A radiation curable photopoiymer according to any preceding claim, wherein the curable photopoiymer is cured with a very low energy radiation in the range of about 0.5 - 20 m J or about 1 .5 mJ ~ 2.0 mJ.

27. A radiation curable photopoiymer according to any preceding claim, wherein the curable photopoiymer is cured with energy of wavelength from about 100 nm to about 500 nm, about 365 nm to about 415 nm or about 395nm to about 405nm or about 400nm to about 1200nm.

28. A radiation curable photopoiymer according to any preceding claim, wherein the curable photopoiymer has good adhesion to copper, polyester, FR4, glass and polyimide substrates.

29. A radiation curable photopoiymer according to any preceding ciaim, wherein the curable photopoiymer also comprises any one of or combination of the following: UV or visible light photoinitiator(s); UV curable resin(s); acrylate and/or methacrylate monomer(s); UV stabilizers; rheology modifier(s); fillers for spacing; adhesive promoter(s) and/or self-levelling agent(s).

30. A radiation curable photopoiymer according to any preceding claim, wherein the curable photopoiymer may also comprise aromatic ketones (e.g. Methylbenzoyl formate and 1- Hydroxycyclohexyi phenyl ketone).

31. A radiation curable photopoiymer according to any preceding claim, wherein the curable photopoiymer(s) is/are present in an amount of 5% to 80% by weight or 10% to 30% by weight of or 20% to 80%the curable photopoiymer.

32. A radiation curable photopoiymer according to any preceding claim, wherein resins in the curable photopoiymer are selected from any one of or combination of the following: aliphatic linear polyether urethane acrylate; aliphatic polyester urethane acrylate; and polyester acrylated monomer blends with fast cure characteristics.

33. A radiation curable photopoiymer according to any preceding claim, wherein the curable resins are radiation curable resins selected from any one of or combination of the following: pentaerythritol tri/tetra-acryiate (PETA); trimethyiolpropane triacrylate (TMPTA); trimethylolpropane ethoxy triacrylate (TMPEOTA); hexamethylene diacryiate (HDDA); Dipropyleneglycol diacryiate (DPGDA); tripropyieneglycol diacryiate (TPGDA); Isobornyl acrylate (IBOA) and Hexyiethyl acrylate (HEA).

34. A radiation curable photopoiymer according to any preceding claim, wherein the curable resins are selected from any one of or combination of the following: isobornyl acrylate; cyclohexyl acrylate; tert-butyl acrylate; 2-ethylhexyl acrylate; dicyciopentenyl acrylate; tetrahydrofurfuryl acrylate: cyclic trimethylopropane formal acrylate and vinyl caprolactam.

35. A radiation curable photopoiymer according to any preceding claim, wherein the curable resins are selected from acrylate monomers which are monofunctional and multifunctional acrylates e.g. methacrylate monomers which are monofunctional and multifunctional methacrylates.

36. A radiation curable photopoiymer according to any preceding claim, wherein the curable photopoiymer may also comprise any one of or combination of the following to improve adhesion to metal or glass surfaces: Acrylic acid; CEA; Epoxy Siiane and Trifunctional acid esters.

37. A radiation curable photopoiymer according to any preceding claim, wherein the curable photopoiymer may also comprise any one of or combination of the following wetting agents in the range of about 0.1 % to about 5% w/w:

a. a blend of acryiate copolymers;

b. poiyether modified polydimethylsiloxane;

c. poiyether modified dimethylsiioxane;

d. poiyether modified poiydimethyisiloxane;

e. poiyether modified dimethylsiioxane:

f. polymeric dispersant;

g. polymeric dispersant; and

h. poiyether amino acid polyamine derivative.

38. A radiation curable photopolymer according to any preceding claim, wherein the curable photopolymer also comprises any one of or combination of the following:

a. surfactants;

b. antioxidants;

c. thixotropes;

d. diiatants;

e. reinforcement materials;

f. silane functional perfluoroether;

g. phosphate functional perfluoroether;

h. silanes;

i. fitanates;

j. wax;

k. fillers

l. air release agents;

m. flow additives;

n. adhesion promoters;

o. rheology modifiers;

p. surfactants; and

q. spacer beads.

39. A radiation curable photopolymer according to any preceding claim, wherein the curable photopolymer further comprises the following:

resins in the amount of 10% to 60% by weight e.g. acryiate and/or methacrylate monomers;

photoinitiators 2% to 12% by weight;

levelling agents 0.3% to 1 % by weight; stabilizers 0.1%

to 0.5% by weight; filler spacing material 1% - 15% by weight

adhesion promoters 5% to 10% byeight;

rheoiogy modifiers 0.1% to 5.0% by weight; and

wetting agents 0.01 % to 0.5% by weight.

40. A radiation curable photopolymer according to any preceding claim, wherein the curable photopolymer comprises:

about 1 w/w% to 60 w/w% of an acidic acrylate monomer:

about 1 w/w% to 50 w/w% of a urethane acrylate monomer;

1 w/w% to 15% of a spacer filler material;

about 25 w/w% to 90 w/w% of dh tri- and hexa-acrylate monomer

consisting essentially of a mixture of about 20 w/w% to 90 w/w% of a mix of monomers hexanediol diacryiate, GPTA, CTFA, DPHA, IBOA; and about 10 w/w% to 80 w/w% of a mono-functional branched or carbocyclic acrylate; and about 1 w/w% to 15 w/w% of a photoinitiator or blend of photoinitiators.

41. A radiation cured photopolymer FSR sensor arrangement according to any preceding claim moulded in the form of a hand held device or console such as in a car or touch screen.