WO2017070406A1

WO2017070406A1 - Method for producing solid particles

Info

Publication number: WO2017070406A1
Application number: PCT/US2016/058005
Authority: WO
Inventors: David Robert Evan Snoswell
Original assignee: Schlumberger Technology Corporation; Schlumberger Canada Limited; Services Petroliers Schlumberger; Schlumberger Technology B.V.
Priority date: 2015-10-22
Filing date: 2016-10-21
Publication date: 2017-04-27
Also published as: GB201518755D0; GB2543755A; GB2543755B

Abstract

A method of producing a plurality of solid particles or a solid surface of non-uniform depth of predetermined size and shape distribution by exposing a liquid to a first energy source of spatially varying intensity, forming the solid particles or the solid surface of non-uniform depth of pre-determined size and shape distribution. Additionally, the method may also comprise separating the solid particles from the liquid transferring the solid particles into a transparent medium; and exposing the solid particles to a second energy source.

Description

Method for Producing Solid Particles

CROSS-REFERENCE TO RELATED APPLICATION

The present document is based on and claims priority to GB Non-Provisional

Application Serial No. : 1518755.2 , filed October 22, 2015, which is incorporated herein by reference in its entirety.

BACKGROUND

Photocuring resins are widely used in the coatings industry as they do not require volatile organic solvents which can pose environmental and safety hazards. Curing of uniform layers is usually performed as a protective coating.

Photocuring resins are also widely used in 3D printing and additive manufacturing techniques. Printing is performed in a layer-by-layer process where often many hundreds of layers are required to achieve sub millimeter resolution of even small models. Much emphasis in the additive manufacturing industry is placed on printing larger and larger objects with almost no examples of mass production of small objects.

However, mass production of small obj ects are desirable in many industries. For example, granular catalyst support with precise packing geometry may be needed for industrial catalyst reactions.

Another example are loss circulation materials (LCM). In oil or gas well drilling, lost circulation occurs when drilling fluid, known commonly as "mud", flows into one or more geological formations instead of returning up the annulus. Lost circulation can be a serious problem during the drilling of an oil well or gas well. One way to address this problem is to add LCM to the drilling fluid in order to block the fractures.

The number of different LCM products currently available has been estimated at over 3000. The variety partly reflects the need to supply different sized particles but is also due to the large market and large number of small suppliers. The primary specification is particle size, but shape, density and elasticity (resilience) are also specifications. LCM is often supplied as dry particulates in sacks and is kept at the rig-site as an insurance against lost circulation events. Deliveries of LCM from regional warehouses is periodic, so rig site managers must estimate what products they may need and are prepared to store.

Many LCM products are very low cost and may be waste products of other processes. Nutshells, wood fibres, mica, graphite and limestone are all common examples of LCM materials.

SUMMARY

The present disclosure relates to a method of producing a plurality of solid particles or a solid surface of non-uniform depth of predetermined size and shape distribution by exposing a liquid to a first energy source of spatially varying intensity, forming the solid particles or the solid surface of non-uniform depth of pre-determined size and shape distribution. Additionally, the method may also comprise separating the solid particles from the liquid transferring the solid particles into a transparent medium; and exposing the solid particles to a second energy source.

A first aspect of the present disclosure relates to a method of producing solid particles, comprising: determining size and shape distribution of the solid particles to be produced; exposing a liquid to a first energy source of spatially varying intensity; and forming the solid particles of pre-determined size and shape distribution.

Liquid is solidified to a depth controlled by intensity of the energy source. Regions of higher intensity result in thicker solidified sections compared to regions of lower intensity. Depth of the resulting solid is therefore controlled spatially by spatial variation in intensity within a single exposure period.

This method allows for rapid production of small particles of predetermined size and shape distribution in large quantities using a single exposure of the energy source. Additionally, control of other properties of the solid particles such as density, elasticity, and resilience made be achieved by e.g. adjusting the composition of the liquid. The method may further comprise: separating the solid particles from the liquid. The solid particles may be separated from the remaining unsolidified liquid by filtration. After separation, the surfaces of the solid particles may still remain covered by a layer of liquid, which may be sticky.

The method may further comprise: transferring the solid particles into a transparent medium; and exposing the solid particles to a second energy source.

A second step exposure to a second energy source may be performed to solidify the surface layer, thus reducing the stickiness of the surfaces of the solid particles according to requirements. This also allows the core of the solid particles to be further hardened according to requirements.

The transparent medium may be a transparent liquid, or an Oxygen free gaseous environment. For free-radical polymerisations, Oxygen inhibits the solidification of the liquid, therefore an Oxygen free environment allows the surfaces of the particles to be solidified to reduce the stickiness of the surfaces in at least some embodiments.

An environment comprising Oxygen may be chosen if sticky surfaces are desirable. Therefore in some embodiments, the transparent medium may be an environment with a controlled oxygen concentration. The stickiness of the surfaces can be adjusted by controlling the amount of Oxygen in the environment.

The liquid may be a photocuring resin and the first energy source may be a collimated light source of spatially varying light intensity. The collimated light source of spatially varying light intensity may be provided by a light mask and a uniform intensity light source, or an electronically controlled image projection system, or two or more intersecting beams.

Alternatively, the liquid may be a heat triggered resin and the first energy source may be infrared source of spatially varying light intensity or an infrared laser scanned to create time- averaged spatially varying intensity. This method may be used to simultaneously produce a plurality of small solid particles by exposing the liquid to the first energy source once. The size of the solid particles depends on their intended application. In some embodiments, the maximum Feret diameter of each solid particle may be less than 100mm. Preferably the maximum Feret diameter of each solid particle may be less than 60mm.

For use as LCM, the maximum Feret diameter of each solid particle is preferably less than 20mm. More preferably, the maximum Feret diameter of each solid particle may be less than 10mm.

The method may further comprise: providing a surface on which the solid particles are formed. Preferably the surface may be an oxygen permeable surface. Oxygen can limit the solidification of a layer of liquid in a region close to the surface. Oxygen permeability of the surface can therefore limit adhesion between the desired obj ect and the supporting surface. In the absence of oxygen the solid particles may strongly adhere to the surface, making it difficult to remove the particles from the surface.

Each solid particle may be formed by exposing the liquid to the first energy source by a predetermined time and the predetermined time for each solid particle may be the same.

The method may further comprise: calculating the energy output of the first energy source of spatially varying intensity and the predetermined time needed for each solid particle based on the predetermined size and shape distribution of the solid particles to be produced. In addition, the energy output of the first energy source of spatially varying intensity and the predetermined time needed for each solid particle would also depend on the nature of liquid, the nature of the first energy source, temperature, pressure and other environmental factors.

The method may further comprise: moving the surface laterally in between the first energy source and the liquid. As the surface moves into the active region in between the first energy source and the liquid, the liquid is solidified into particles of predetermined sizes and shapes. As the surface moves away, it carries with it solid particles already formed and leaves the active region to be occupied by empty surface areas moving into the region. This allows even faster production of solid particles when an even larger quantity is needed. The movement may be periodic or continuous.

If it is continuous, some fibres may be produced on the solid particles and the shape of the solid particles may generally be deformed due to shear.

To avoid this, the movement may be periodic. A surface may be completely exposed before it is removed. A new surface is then placed in between the first energy source and the liquid to be exposed. Alternatively, the movement of the surface may be continuous, while the liquid is made to circulate in the same direction as the surface whereby reducing relative movement between the surface and the liquid, or eliminating relative movement if the liquid also circulates at the same speed as the surface.

To avoid deformation completely, the first energy source may be turned off after a surface is completely exposed, and turned on again after a new surface is in place.

A second aspect of the present disclosure relates to a method of producing a solid surface with non-uniform depth, comprising: determining size and depth distribution of the solid surface to be produced; exposing a liquid to a first energy source of spatially varying intensity; and forming the solid surface with the predetermined size and depth distribution. The method may further comprise: separating the solid surface with non-uniform depth from the liquid.

This is similar in principle to the first aspect, but a continuous surface with non-uniform depth is produced instead of a plurality of solid particles.

The continuous surface with non-uniform depth may be the desirable final product. Alternatively, a mould may be produced using the solid surface with non-uniform depth produced as a template. The mould may then be used to give shape to a hardening liquid which could be a molten material or a liquid solidified by chemical or actinic radiation.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig 1 shows single exposure manufacture of 3D particle shapes in example 2. Fig 2 shows depth control of curing in example 3.

Fig 3 shows block testing of pyramid LCM in example 4.

Fig 4 shows a selection of particle shapes produced in example 5.

Fig 5 shows exposure using two intersecting beams in example 6.

Fig 6 shows a sketch of an apparatus allowing continuous production of solid particles.

Fig 7 shows a picture of an apparatus allowing continuous production of solid particles.

Fig 8 shows a sketch of a machine comprising ten apparatus each allowing continuous production of solid particles.

DETAILED DESCRIPTION

The ensuing description provides preferred exemplary embodiment(s) only, and is not intended to limit the scope, applicability or configuration of the disclosure. Rather, the ensuing description of the preferred exemplary embodiment(s) will provide those skilled in the art with an enabling description for implementing a preferred exemplary embodiment of the disclosure, it being understood that various changes may be made in the function and arrangement of elements without departing from the scope of the disclosure.

Specific details are given in the following description to provide a thorough understanding of the embodiments. However, it will be understood by one of ordinary skill in the art that embodiments maybe practiced without these specific details. For example, well-known circuits, processes, algorithms, structures, and techniques may be shown without unnecessary detail in order to avoid obscuring the embodiments.

The present disclosure relates to a method for producing small polymer obj ects e.g. <10mm in large quantities, rapidly e.g. <5mins with low cost equipment such as patterned light source. The method produces solid polymer objects from a liquid photocuring resin cured using a light source with controlled spatial intensity. A range of precise shapes can be produced in a simple process that can be rapidly reconfigured. Spatial light intensity can be controlled using a collimated light source and light mask or dynamically by a projection system. In one example a greyscale light mask for generating tetrapods is shown to produce different size objects by changing only the light exposure time. Controlling light paths in the curing process allows wider range of particle shapes to be produced.

The current disclosure achieves a similar resolution to existing state of the art 3D printers using e.g. photocuring resins, but in a single exposure method at least 2 orders of magnitude faster. The technique is ideally suited to mass production of small shapes where rapid manufacture of bespoke particle shapes and sizes is an advantage. Changes to the particle size can be achieved with a single greyscale light mask by changing only the light intensity. Changes to particle shape can easily be achieved with an image projection system.

Experiment 1

The liquid may be any suitable photocuring resin and the first energy source may be a collimated light source of spatially varying light intensity. Suitable photoinitiators may be added to the resin mixture.

Suitable resin examples include:

• acrylate and methacrylate monomers (typically water-soluble):

Bis phenol A ethoxylate diacrylate

Ethylene glycol diacrylate (varying molecular weight)

Hexanediol diacrylate

Trimethyolpropane triacrylate

• Vinyl Ethers (both water and oil soluble variants):

Vectomers™: vinyloxybutyl benzoate and bis and tris variants.

Urethane di vinyl ethers.

Ethylene glycol divinyl ethers (varying molecular weight) • Vinyl functionalised polymers and oligomers such as polybutadienes or polyisoprenes, block copolymers such as styrene- butadiene, SEBS, SIS ... examples given by the Kraton polymers. They are primarily solvated in nonaqueous base fluids and would be especially useful for OBM.

Suitable photoinitiators include:

1) Free radical

Type I cleavable typically benzoin ethers, dialkoxy acetophenones , phosphine oxide derivatives, amino ketones. E.g. 2-dimethyl, 2-hydroxyacetophenone, bis(2,4,6-trimethyl benzoyl) phenyl phosphine oxide

Type II hydrogen abstraction or electron transfer (photoinitiator and synergist) typically aromatic ketones e.g. camphorquinone, anthraquinone, 1 -phenyl 1,2 propanedione, 2, combined with H donors such as alcohols, or electron donors such as amines.

2) Cationic Photoinitiation

Photoacid generators typically Diazonium or Onium salts eg diaryliodonium or triarylsulphonium PF6.

Density of the solid particles to be produced can be adjusted by adding additives to the resin formulation. For example, silica can be added to increase density, and porous powders can be added to decrease the density.

Additives can also be used to increase the brittleness, strength and abrasion resistance e.g. by adding silica or powdered plastic.

The method may comprise the following steps:

STEP 1 Liquid photocuring resin is exposed to collimated light at a surface with spatially varied light intensity. Spatial variation of light intensity can be achieved by a light mask and a uniform intensity light source OR an electronically controlled image projection system such as a data projector. Curing commences at the surface closest to the light source and propagates at a rate determined by the light intensity. The curing process has been shown to incorporate a delay and a predictable rate allowing for single exposure curing of a range of 3D shapes.

A grey scale mask can be a separate sheet from the surface on which the solid particles are to be produced. It should be placed in between the light source and the liquid.

Alternatively, a grey scale mask can be part of the surface, e.g. it can be printed on the surface. High quality inkj et printing (>600dpi) may be used to achieve this. There are also other methods like laser etching, chemical etching and even ebeam lithography.

Nevertheless projection of an image would be the preferred method as it would allow the particle shapes to be reconfigured more quickly. Using a mask has the advantage of lower cost in the light source and equipment.

By exposure to multiple light sources collimated in different directions, the range of 3D shapes is expanded. This may include curing resin between two illuminated surfaces to achieve more complex shapes as required.

Curing surfaces could also be modified to control geometry. For instance curing through a window of hemispherical indentations in an array to create particles with curved surfaces.

Shapes of equivalent precision and size produced by our commercial 3D printer (Connex 260) would typically be made of 100 layers taking several hours and would need support material removed in a lengthy caustic washing process. (~3 days). The current disclosure requires a single exposure that has been shown to be as short as 8seconds in lab experiments. No support material is required however solid particles must be removed from uncured resin in a filtration process (currently -10 mins). Curing rates are sensitive to the resin formulation and temperature. In addition to formulation and temperature control, consistent particle size manufacture may require size feedback and compensation of the average light exposure intensity and time.

STEP 2

Cured solid particles are removed from the uncured liquid resin by filtration. By curing on a surface which is oxygen permeable (most polymers), curing immediately adjacent to the illuminated surface is limited by trace oxygen and cured particles are not adhered, making separation from the surface unnecessary. Particles will suspend and flow with the liquid resin. If the particles are preferably produced on an oxygen impermeable surface they may be strongly adhered and hence may be damaged on removal by a scraping device.

STEP 3 (Optional)

Filtration will leave a layer of liquid resin around each solid particle. The particles could be directly dispersed into a drilling fluid, however it may be preferable to disperse them in a transparent liquid so that the uncured liquid resin layer can be further exposed to light and solidify. The degree to which the sticky liquid resin is cured to the less sticky solid state could control the stickiness of the particles themselves which may prove advantageous when sealing fractures.

Experiment 2

Resin formulations

Poly(ethylene glycol) Diacrylate 15.68

Fig 1 shows single exposure manufacture of 3D particle shapes. Experimental temperature is 22deg C (+-2 deg C).

A: Photocuring resin is exposed to collimated light through a greyscale mask.

Resin 55 contained in a polystyrene petri dish is exposed to light intensity 15000 LUX, light source CREE XM-L white light LED driven at 0.6 Amp

B; Pyramids are grown with height axis controlled by the light intensity.

Cured Tetrapods with 3mm edges are produced after 30s exposure time.

C Pyramids are filtered off and separated from the uncured resin that can be reused.

Experiment 3

Fig 2 shows depth control of curing. A:

Resin formulation 55 (see example 2 above) was cured at 22 Deg C, using Laser (540nm, <lmW). Pillar of 8mm long was produced after exposure of 16 seconds.

Absorption of blue-green light by the resin ensures the light intensity is greatest adjacent to the light source. A green laser pointed at the wall of a glass vial containing liquid photocuring resin causes a pillar of solid resin to "grow". Note the resin is strongly adhered to the glass surface which is not oxygen permeable.

The photocuring resin absorption spectrum in Fig 2A shows absorption of blue-green light by resin 55.

B: Resin formulation 30 was cured at 22 Deg C using white light source DELL 2400MP, light intensity 32000 LUX at sample. Exposure times are shown on the graph.

The depth of cure is controlled by both the light exposure time (30-120 secoonds) and the light intensity (30-100% arb).

C:

Resin 55 was cured at 22 Deg C using light intensity 15000 LUX, light source CREE XM-L white light LED 0.6Amp. Tetrapods with 3mm edges were produced after 30s exposure. Light mask for terapods with 5mm edges, linear gradient (30% edge to 100% centre) were used.

Using a greyscale mask resin is cured to different depths in a single exposure by controlling the spatial light intensity. Triangle based pyramids are generated with edges 1.6-1.9 mm in length.

Experiment 4

LCM particles produced in experiment 3C above have been used as primary bridging particles in laboratory block tests.

Fig 3 shows block testing results of pyramid LCM. The base fluid used was "Rheliant" oil based mud with 200g/L barite and 10 ppb G Seal+ added. The block was a 6" cube of sandstone with a 1" bore hole. The block was prefractured and the fracture opened to 1.5mm using brass shims. A: Stable fluid sealing is achieved up to 150psi only when pyramids are added. Without pyramids the fluid poured freely through the fracture. B: Images of the fracture and pyramids. Transparent pyramids can be seen near the fracture mouth mixed with black G Seal+ particles.

The block test proves that particles produced by this method can be effective in sealing large fractures. The disclosure provides a method to help achieve the optimal size and shape distribution on-demand without the need for a large inventory of LCM products.

Particle size and shape distribution is widely acknowledge to have an influence on LCM performance. An optimal blend of LCM is expected to be effective at lower particle loadings in the drilling fluid. Experiment 5

Fig 4 shows a selection of particle shapes is produced by using different masks.

Resin formulation 30 was exposed to white light source DELL 2400MP, light intensity 32000 LUX at sample at 22 Deg C for 90sec.

Particles on the 2-4mm scale are produced from a single exposure of photocuring resin using binary masks(A-I) and greyscale masks(J-N).

Experiment 6

Fig 5 shows double exposure or single simultaneous exposure by two intersected beams. A: Exposing the resin through a light mask angled away from normal incidence generates resin structures in the illumination direction. B: By changing the light angle, resin growth from a second exposure allows concave particle shapes to be made.

Using two or more intersecting beams allows a wider range of shapes to be produced.

Lost circulation events in particular would benefit from the rapid production of tailored particle sizes and size distributions. Loss circulation might happen during drilling, cementing or after fracturing.

Lost circulation events whilst drilling are not always predictable due to the variability of formations. Natural or drilling induced fractures can be responsible for the loss of drilling fluid at any time. Excessive fluid losses can prevent drilling and in some circumstances cause loss of well pressure control.

Current LCM products are often not available when required. The rig-site management must guess what might be required and will compromise on stocks based on cost, logistics and space. LCM stored at the rig site may never be used or worse still may be used in the wrong quantities adding to the variability of performance. The primary specification of LCM is size but quality control of this parameter is known to be a problem. Some LCM will break during transport and storage. In other cases material suppliers and grinding processes are responsible for variations in particle size outside of specification.

When losses of drilling fluid become unacceptable, rapid response is important to limit non productive time (NPT). LCM of the correct size distribution must be available at surface to add to the drilling fluid as quickly as possible. However LCM loading in the drilling fluid is often limited by the risk of blocking ("screen out") of the bottom hole assembly (BHA) so control of the size distribution is very important for the LCM to be effective. Nevertheless large stocks of LCM are not convenient or economic to store at the rig site, especially off shore, and so LCM stocks are rarely optimal.

In addition if wellbore fractures are large e.g.>lmm, the largest size fraction of LCM may also be limited by BHA screen out specifications. The largest size fractions of LCM need to be made of low density material to limit settling.

In this current disclosure the larger size fraction of the LCM blend (primary bridging particles) can be manufactured to the required size specification on-demand. Instead of needing to keep a range of LCM sizes on stock at the rig site, a single batch of liquid photocuring resin could be processed into particles of the desired size and shape as required. Furthermore being polymer based the photocured LCM is inherently low density (avoids settling issues) and can be tailored precisely, lowering the total LCM concentration required and reducing the risk of BHA blockage.

Commercial software for predicting the required LCM size distribution is already available, such as MI-SWACO's "OPTISTRESS" or Schlumberger's "Lost Circulation Advisor". If LCM manufacture was available at the rig site, the output size specification could be directly linked to the particle manufacturing system which could adjust the particle size produced dynamically through control of the spatial light intensity.

The technique provides the opportunity to tailor LCM size and shape dynamically in a manufacturing process that could be implemented at the rig site "on-demand". LCM size distribution is known to be critical and ideally should be tailored for every use. Current LCM distributions are often limited by LCM stocks. LCM shape is known to be important but currently there are few methods to control this. This method provides the opportunity to control LCM size, size distribution and shape on-demand at the rig site thereby optimizing the LCM performance (minimize loading), reducing rig LCM inventory/space/weight requirements, and simplifying the supply chain.

The method may further comprise: moving the surface laterally in between the first energy source and the liquid. This allows fast and continuous production of solid particles when an even larger quantity is needed e.g. at a rig site. The movement may be periodic or continuous.

A potential implementation of such an apparatus allowing continuous production is shown in Fig 6 and 7.

As shown in Fig 6 and 7, a cylindrical surface is provided which is rotatable around its axis. A first energy source is located inside the cylindrical surface. A container for a liquid is located underneath the cylindrical surface, and the cylindrical surface is positioned to be able to dip into and out of the liquid as it rotates. The first energy source is directed to the liquid so that the liquid may be exposed to the first energy source. A mask is located inside and next to the surface to create a spatially varying energy output.

As the surface dips into the liquid, the liquid is solidified into particles of predetermined sizes and shapes as dictated by the patterns on the mask. As the surface dips out of the liquid, it carries with it solid particles already formed and leaving space and allowing empty surface areas to dip into the liquid.

The solid particles formed on the surface are removed from the surface by a scraping device. The particles are collected at a platform and any excess liquid is filtered off and runs through the mesh of the platform into the liquid container to be re-used.

Multiple numbers of such apparatus can be used together to increase production speed even further. In the embodiment of Fig 8, ten such apparatus are used together. This current disclosure allows LCM to be manufactured at the rig with closely controlled size, size distribution and shape on-demand. Photocuring is a quick and solvent-free process that produces stable solid polymer particles with tunable physical properties (ie elasticity, stickiness). Curing is fast and does not require a physical mould or template. The process occurs at room temperature and the resin is relatively benign. Shape and size of the cured particles can be precisely controlled by simply changing the spatial pattern of light, which requires no major change in tooling or equipment. With a single liquid resin material source, a multitude of particles with various shapes and sizes can be custom made quickly.

The LCM manufacturing process described hereby could feasibly be performed downhole. Similar resins have been cured in weighted drilling fluids. If LCM are manufactured downstream of the BHA, limitations on loading and particle size can be lifted allowing a wider range of larger fracture sizes to be sealed. Response time to loss events is also reduced to an absolute minimum thereby limiting fluid losses and NPT even further.

If LCM is produced downhole, the same method can be used, and there are many possible implementations. For example a BHA or drill pipe may comprise a liquid storage, a first energy source and a transparent surface on which the solid particles are to be produced. The surface may be a ring shaped transparent structure around the external surface of the BHA or drill pipe, the liquid storage may be arranged to delivery liquid to the ring shaped structure, and the first energy source is preferably located inside the ring structure. Solid particles are produced on the ring structure before being scraped off and released to surrounding drilling fluid. In such cases, the solid particles may not be actively separated from the liquid, and some liquid might be released to the surrounding drilling fluid together with the solid particles.

Alternatively, a solid surface with non-uniform depth may be produced by exposing a liquid to a first energy source of spatially varying intensity. The principle is exactly the same and the only difference is that instead of producing a plurality of solid particles, particle arrays are produced for generating a solid surface with surface texture. In other words, the solid particles are j oint together to produce a continuous solid surface with non-uniform depth. This is achieved by adjusting spatial intensity of the first energy source so that the whole solid surface area is exposed to the first energy source to a greater or less degree.

Potential applications of this method include: 1. Producing a 3D map.

2. Making gaskets or moulds for gaskets - the technique could be ideal for rapid prototyping gaskets. Gasket design is extremely important in sealing downhole tools.

3. Solids control - Shaker screens that MI SWACO make have complex shapes and are frequently replaced. Being able to create templates for screens and/or adding texture to solids control equipment can enhance performance

4. Rapid prototyping of some parts. The disclosure is much quicker although limited in geometry.

5. 3D barcodes. There is interest in creating more secure barcodes that have "texture" as an added security feature.

The continuous solid surface with varying depth may be the final desirable product, or a mould can be made using the solid surface as a template.

If a mould is to be made, the solid surface template is preferably produced using an oxygen impermeable surface to cure on such as glass. The template may then be left attached to the oxygen impermeable surface such as glass. It can then be used to make a mould.

The mould itself is preferably made from a liquid that sets to a flexible solid so that it can be separated from the rigid particle template. This may be a silicone polymer which have nonstick properties and are easily released from the template. Alternatively the mould can be made of polyurethane.

The mould can then give shape to a molten material when it cools and hardens. The material poured into the mould could be a chemically set liquid (eg epoxy + catalyst) or a thermoset polymer (heat triggered curing) or a thermoplastic (liquid above melting point). Alternatively, the mould can be filled with another photocuring resin. Furthermore, moulds can also be filled with liquids highly loaded with solids. This can increase the brittleness, strength and abrasion resistance e.g. by adding silica or powdered plastic.

Claims

1. A method of producing a plurality of solid particles, comprising:

determining size and shape distribution of the solid particles to be produced;

exposing a liquid to a first energy source of spatially varying intensity; and

forming the solid particles of pre-determined size and shape distribution.

2. A method according to any one of claim 1, further comprising:

separating the solid particles from the liquid.

3. A method according to any one of claim 2, wherein the solid particles are separated from the liquid by filtration.

4. A method according to any one of claims 1 to 3, further comprising:

transferring the solid particles into a transparent medium; and

exposing the solid particles to a second energy source.

5. A method according to claim 4, wherein the transparent medium is a transparent liquid or an Oxygen free gaseous environment.

6. A method according to claim 4, wherein the transparent medium is an environment with a controlled oxygen concentration.

7. A method according to any one of claims 1 to 6, wherein the liquid is a photocuring resin and the first energy source is a collimated light source of spatially varying light intensity.

8. A method according to claim 7, wherein the collimated light source of spatially varying light intensity is provided by a light mask and a uniform intensity light source, or an electronically controlled image projection system, or two or more intersecting beams.

9. A method according to any one of claims 1 to 6, wherein the liquid is a heat triggered resin and the first energy source is infrared laser of spatially varying light intensity.

10. A method according to any one of claims 1 to 9, wherein the maximum Feret diameter of each solid particle is less than 100mm.

11. A method according to any one of claims 1 to 10, wherein the maximum Feret diameter of each solid particle is less than 20mm.

12. A method according to any one of claims 1 to 11, further comprising:

providing a surface on which the solid particles are formed.

13. A method according to claim 12, wherein the surface is an Oxygen permeable surface.

14. A method according to any one of claims 1 to 13, wherein each solid particle is formed by exposing the liquid to the first energy source by a pre-determined time.

15. A method according to claim 14, wherein the predetermined time for each solid particle is the same.

16. A method according to claim 14 or 15, further comprising

calculating the energy output of the first energy source of spatially varying intensity and the predetermined time needed for each solid particle based on the predetermined size and shape distribution of the solid particles to be produced.

17. A method according to any one of claims 11 to 16, further comprising

moving the surface laterally in between the first energy source and the liquid.

18. A method according to claim 17, the movement is periodic or continuous.

19. A method of producing a solid surface with non-uniform depth, comprising:

determining size and depth distribution of the solid surface to be produced;

exposing a liquid to a first energy source of spatially varying intensity; and

forming the solid surface with the predetermined size and depth distribution.

20. A method according to claim 19, further comprising separating the solid surface with non-uniform depth from the liquid.

21. A method according to claim 19 or 20, further comprising: calculating the energy output of the first energy source of spatially varying intensity and the predetermined time needed for every point on the solid surface based on the predetermined size and depth distribution of the solid surface to be produced.

22. A method for producing a mould using the solid surface with non-uniform depth produced according to claim 19 or 20 as a template.