Colour changing composition and colouring polymeric articles made therefrom

Abstract

A process is provided for producing a polymeric layer having a desired image thereon or a three dimensional article comprising a number of such layers in which a layer of a liquid photocurable composition which comprises photo colourable particles is cured by light and selected areas thereof are irradiated with light of a different dose, thereby forming the desired image which composition comprises particles dispersed in it which are micro-capsules containing a photosensitive colour changing composition within a barrier layer which is substantially impermeable to the components of the colour changing composition or are solid particles comprising an immobilised photosensitive colour changing composition. The process permits the use of the same initiating mechanism to cure the resin and to change the colour of the particles.

1  A process for producing a polymeric layer having a desired image thereon or a three dimensional article comprising a number of such layers in which a layer of a liquid photocurable composition which comprises photo colourable particles is cured by light and selected areas thereof are irradiated with light of a different dose, thereby forming the desired image which composition comprises particles dispersed in it which are micro-capsules containing a photosensitive colour changing composition within a barrier layer which is substantially impermeable to the components of the colour changing composition or are solid particles comprising an immobilised photosensitive colour changing composition.  
     
     
         2  A process as in  claim 1  in which the composition is both cured and coloured by cationic initiators.  
     
     
         3  A process as claimed in  claim 1  or  2  in which the colour changing composition comprises a photo initiator and a colour former, and in which the initiator is sensitive to the light used for curing and in which the particles comprise a light absorbing substance which absorbs at least part of the light whereby initiation of the full colour change requires a greater dose of light in intensity or duration than is needed for curing.  
     
     
         4  A process as claimed in  claim 3  in which the light absorbing substance is present in the barrier of the micro-capsule.  
     
     
         5  A process as claimed in any preceding claim in which a cationic initiator is used as a photo initiator and the particles comprise an alkali capable of neutralising cations initially produced in the initiating process.  
     
     
         6  A process as claimed in any preceding claim which comprises forming a stereo lithographic image.  
     
     
         7  Particles for carrying out a process as claimed in any of  claims 1  to  6  which are micro-capsules containing a photosensitive colour changing composition Within a barrier layer which is substantially impermeable to the components of the colour changing composition and which is sufficiently robust to resist rupture when the particles are mixed with an epoxy or vinyl ether or acrylic resin and subjected to photo initiation in the said process or which are solid particles comprising an immobilised photosensitive colour changing composition.  
     
     
         8  Particles as claimed in  claim 7  in which the photo sensitive colour changing composition is in a liquid phase which is surrounded by a containing wall.  
     
     
         9  Particles as claim d in claims  7  or  8  which are of 1 to 50 microns average diameter.  
     
     
         10  Particles as claimed in claims  7 ,  8  or  9  in which the total wall thickness comprises 15 to 50% of the diameter of the particle.  
     
     
         11  A particle as claimed in any of  claims 7  to  10  which comprises a cationic initiator and an alkaline substance in a quantity sufficient to neutralise some but not all of the cations producible by the initiators whereby the particles are maintained in an unchanged state of colour until subjected to an initiating dose of light.  
     
     
         12  A particle as claimed in any of claims  7 ,  8 ,  9  or  10  which comprises an aminoplast wall.  
     
     
         13  A process of producing particles as claimed in any of  claims 7  to  12  which comprises spray drying a dispersion of the particles in an aqueous medium.  
     
     
         14  A process of producing a particle as claimed in any of  claims 7  to  12  which comprises contacting the particle with ammonia to decolourise and/or provide a reserve alkalinity in the particle.  
     
     
         15  A micro-capsule as claimed in any preceding claim in which the barrier wall is sufficiently robust to remain intact in the finished product after colour formation.  
     
     
         16  A particle as claimed in any of  claims 7  to  15  which comprises a colour stabiliser.  
     
     
         17  A process or particle as claimed in any preceding claim which comprises an ultra violet absorber.  
     
     
         18  A particle as claimed in  claim 17  in which the ultra violet absorber is a component of the wall of a micro-capsule.  
     
     
         19  A composition for carrying out a process as claimed in any of  claims 1  to  6  which comprises a photocurable resin and particles as claimed in any one of  claims 7  to  18  dispersed in said resin.  
     
     
         20  A Composition for carrying out the process as claimed in any of  claims 1  to  6  or which comprises particles as claimed in any of  claims 7  to  18  in which different particles have different colour former systems thereby providing a multi-colour image in a final product, in which each colour is developed at a different energy to those used for other colours.  
     
     
         21  A composition as claimed in  claim 19  in which a photo initiator which does not generate acid when irradiated is included, the said photo initiator being sensitive to high ultra violet wavelength light and facilitating a post cure of the resin without unwanted colour formation.  
     
     
         22  A product produced by a process as claimed in any of  claims 1  to  6  containing particles as claimed in any of  claims 7  to  18  or produced using a composition as claimed in claims  19  or  20  which comprises a surrounding visually transparent layer which absorbs the light capable of generating further colour change.