This invention relates to photocurable compositions, to a process for tne r polymerisation by means of actinic radiation, to a process for tne production cf tr.ree-dimensicnal articles rrom tne compositions ana to articles so prepared. 5 It is Known that complicated tnree-dimensicnal art c_eε can ce prcαuced from liquid, photocurable compositions by means of sterεol tnograpny. One sucn process is described m Hull's US Patent 4,575,330. Articles are built up in layers, each new curable layer of resin being firmly attached to the preceding pre-cured layer by preliminary C curing Dy means of UV/VTS light. The overall construction cf tne three- dimensional article is normally controlled by computer. Photocurable compositions (e.g. liquid resins and resin mixtures) and tneir use as coating agents, adhesives and photoresists are Known. However, the majority of such compositions are not suitable for the production cf 5 solidified three-dimensional articles by stereolithography because some are too viscous, wnilst others are insufficiently light-sensitive, cure slowly or suffer from excessive shrinking or curling when they are cured.

Ideally photocurable compositions for stereolithography cure reasonably quickly and have a small volume shrinkage in the transition from 0 the liquid to solid state. The so-called "curl factor" is often quoted as a measure of shrinkage induced deformation and a curl factor cf 30% is considered by many as being the maximum acceptable, depending cπ what the article is, and curl factors of below 20% are preferred.

Canadian Patent application 2028541 suggests pnctocurable 5 compositions for stereolithography. Whilst these compositions do worκ tney tend to have a high curl distortion and high viscosity.

According tc the present invention there is provided a liquid composition comprising: a) 2 to 2C parts of a monomeric pcly( eth) crylate naving a 3 functionality of at least 3 and a MW of at least 650; o 20 to 60 parts of a urethane(meth)acrylate having a functionality cf 2 to 4 and a mi cf 400 to 10,000; c) 20 to ΞC parts of- a monomeric or c_ιgomenc di 'meth) acry_ate caseα on ιoιspπεπr_ A or o sphenol F; and 5 x) 3.1 to 13 parts of a pnotoiπ tiator,- wherein all parts are oy weight and tne total number of parts of ai - c) - c) -I- d) add up to 100.

Tne liquid composition of tne invention preferacly comprises or consists essentially cf 5 to 13 parts, more prεreraciy S to _6 parts of ^" component a) , 23 to 53 parts, more preferacly 25 to 45 parts or component π) , 23 to 73 parts, more preferably 20 to 60 parts, especially 35 to 55

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parts, more especially 40 to 50 parts cf component c) ; and 1 to 9 parts, more preferably 2 to 8 parts, especially 3 to 7 parts of component d) ,- wherein ail parts are by weight and the total number of parts of a) + b) - c) - d) add up to 100.

In a particularly preferred embodiment the liquid composition cf the invention comprises or consists essentially of S to 16 parts of component a) ,- 25 to 45 parts of component b) ,- 40 to 50 parts cf component c) ,- and 3 to 7 parts of component d) ,- wherein all parts are by weight and the total number of parts of a) + b) + c) + d) add up to 100.

Component a) preferably has a MW (i.e. molecular weight) greater than SOC, more preferably in the range 880-1200, especially m the range 900- 1100.

Examples cf suitable compounds which may be used as component (a) are tri-, tetra- and penta- (meth)acrylates (including mixtures thereof) , especially those of the formulae I, II, and III:

R ¹ CH, (CH ₂ -R (I)

R- CH (CH, ^■ R ^' >, (in)

jr.er' hydrogen atom, methyl, hydroxyl or a grout ;ne rormu a

O CH, ^■ C (CH, m.

CH, OH (IV)

wherein P.- is a group cf the formula V:

O R ⁴

O (CH CH, -O) _n —C ^■ C -CH ,

(V)

R ^J wherein n is from 3 to 8, preferably 4 to 8, and F. and R are each independently hydrogen or methyl.

Compounds of the formulae I to III which are particularly preferred are those of the formula I in which R ^: is methyl or a group of the formula IV, R ^: is a group of the formula V wherein n is 4 or 5, and R ^"' and R" are as hereinbefore defined.

As examples of compounds which can be used as component a) there may be mentioned highly propoxylated and ethoxylated 1, 1, 1-trimethylolpropane triacrylate or trimethacrylate and mixtures thereof. Compounds of this type are known and some are commercially available, for example SARTOMER products cf Cray Valley Co. Limited, Newport, Wales and Sartomer Company supply such compounds under the product names SR-9021 and SR-9035.

One may use known urethane acrylates as component b) in compositions according to the invention and these can be prepared in a known manner, for example by reacting a hydroxyl-terminated polyurethane with acrylic acid or methacrylic acid to give the corresponding urethane(meth)acrylate, or by reacting an isocyanate-terminated prepoiymer with hydroxyalkyi acrylates or methacrylates to give the urethane(meth) acrylate. Appropriate processes are discicsεd in, for example, published European patent applications 114,982 and 123,903. The molecular weight of such acrylates is generally within the range from 400 to 13,000 preferably between 500 and 7, 003.

Urethane (meth)acrylates are also available commercially under the trade marks NeoRad from Zeneca Resins, EBECRYL from UCE, Uvi hane from

Morton Thiokci and SR 9504, SR 9600, SR 9610, SR 9620, SR 9630, SR 9640 and SR 9653 from the Sartomer Company.

It is preferable to use urethane acrylates of MW 500-7000 derived

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from aliphatic starting materials.

Di (meth) acrylates cased on bisphenol A and bispnenol F wh cπ can be used in or as component c) include cispnencl A diacrylates and dimetnacryiates and bisphenol F diacrylates and oimethacrylateε and tne diacrylates cr dimethacrylates cf alkoxyiated, preferacly ethoxylated or propoxylated, bisphenol A or F. The acrylates ootamacle by reaction cf cispnencl A or bisphenol F diglycidyl ether with (meth) acrylic acid are also suitable, especially mixtures consisting of ethoxylated bispnenol A diacryiate and ethoxylated bisphenol A dimethacrylate. Monomeric or oligomeric di (meth)acrylates of this type are also known and some are availacie commercially, for example from the Sartomer Company under the product name SR-348 for ethoxylated bisphenol A dimethacrylate and under tne product name SR-349 for ethoxylated bisphenol A diacryiate. It is preferacle to use the di (meth)acrylates of bispnenol A or F and cf etncxylated bisphenol A or of ethoxylated bisphenol F and mixtures thereof as the component c) .

Preferably component c) has a MW of 300-1000.

Any type of photoimtiator which forms free radicals when irradiated suitably can be employed as the component d) in the mixtures according to the invention. Suitable classes of known photoimtiators include benzoins; benzoin ethers, for example benzoin methyl ether, ethyl ether and isopropyl ether, benzoin phenyl ether and benzoin acetate; acetophenones, e.g. acetophenone, 2, 2-dιmethoxyacetophenone and 1, 1-dιchloroacetophenone; benzil; benzil ketals, e.g. benzil dimethyl ketal and benzil diethyl ketal; anthraqumones, e.g. 2-methylanthraqumone, 2-ethylanthraqumone, 2-tert- outyianthraqumone, 1-chloroanthraqumone and 2-amylanthraqumone; triphenylphosphme ; benzoylphosphine oxides, e.g. 2,4,6- trimethylbenzoyldiphenylphospme oxide (Luziπn TPO) ,- benzophenones, e.g. oenzophenone and 4, 4-bιs- (N,N-dιmethylamιno) -benzophenone; thioxanthones and xanthones ; acridme derivatives; phenazme derivatives; qumoxalme derivatives and 1-pnenyι-i,2-propanedιone-2-0-benzoyl oxime; 1-ammophenyi tetones and 1-hydroxyphenyl ketones, e.g. 1-hydroxycyclohexyl phenyl Ketone, phenyl 1-nydroxyιεopropyl ketone and 4-ιsopropylpπenyl-l- πydroxyisopropyl ketone; all cf which are known compounds. Photoimtiators whicn are particularly suitaoie for use ,-nen tne accιπ_o radiation is from a Hg-Cd laser are acetophenones, e g 2,2- dιalκcxybenzophenones, and α-nydroxyphenyl κetones, g. 1- nyoroxycyclohexyl pnenyl Ketone and 2-nydroxyιsoρropyl pnenyl κetone ⁽ =2- r.yaroxy-2 , 2-dιmethylacetopnenone) . A class of photoimtiators d) particularly εαιtac_e for argon ion

_^ asers are benzil ketals, for example benzil dimethyl κeta_, and especially ar. α-nydroxyphenyl Ketone, oenzii dimethyl et _^ or 2,4,6- trimetnyioenzoyidiphenyipnospnine oxide. _β AD

Another class of suitable photciπitiatorε d) are the ionic dye- counter ion compounds which are capable of absorbing actinic radiation and producing free radicals which initiate polymerisation cf the components. The mixtures according to the invention containing ionic dye-counter icn compounds can be cured in a fairly variable manner m this way w th visible light having a wavelength cf 400-700nm. Ionic dye-counter ion compounds and their mode cf action are known, for example from EP-A- 0,222,587 and US Patents 4,751,102, 4,772,530 and 4,772,541. Examples cf suitable ionic dye-counter ion compounds which may be mentioned are the anicnic dye-iodoπium ion complexes, the anionic dye-pyryiium ion complexes and especially, the cationic dye-borate anion compounds of the formula VI:

R< R ₇

\ /

B (VI)

/ \

R« R*

wherein X' is a cationic dye and R ₅ , R,, R-, and R _q are each independently alkyl, aryl, alkaryl, allyl, aralkyl, alkenyl or alkinyl group, an alicyclic group or a saturated or unsaturated heterocyciic group.

The photoinitiators are added in effective amounts, i.e. in amounts of about 0.1 to about 10 parts by weight, relative to the total amount of the components a) to d) . If the mixtures according to the invention are used for stereolithographic processes in which laser radiation is used, it is preferred that the absorption capacity of the compositions is so adjusted by means of the type and concentration of the photoinitiator that the depth of curing at normal laser speed is approximately 0.1 to 2.5mm.. Compositions according to the invention can contain a plurality of photoinitiators which have a different radiation sensitivity at different wavelengths. This achieves, for example, better utilisation of a UV/VIS light source which radiates emission lines cf different wavelengths. It is advantageous in this case if the various photoinitiators are so chosen and employed in such a -concentration that a uniform optical absorption is produced in the case cf the emission lines used.

As will be understood from the foregoing description and from the Examples, the specified amounts cf components a) to d) refer to the total number of parts by weight cf each of the defined component types. For example a mixture of 18 parts of an ethoxylated bisphenol A diacryiate and

13 parts of ethoxylated bisphenol A dimethacrylate constitute 35 parts n total and as such satisfy the definition for component C) .

To the compositions cf the invention there may be added small amounts

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(0 to 4 percent by weight, preferacly C percent) cf the diacryiate and dimethacrylate esters cf aliphatic or cycioaliphatic dioiε. Examples of such diols are 1,3-butylene glycol, 1, 4-butanediol, neopentyl glycol, 1,5- hexaπedicl, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol 400, polyethylene glycol 600, tricropylene glycol, ethoxylated or propoxylated neopentyl glycol, 1,4- dihydroxymethyicyclohexane, 2 , 2-bis- (4-hydroxycyclohexyl) -propane cr bis- (4-hydroxycyclohexyl) -methane. However, it is preferred that the composition is free from di (meth)acrylate esters of aliphatic and cycioaliphatic diols.

If desired one may add customary additives to the compositions, for example stabilisers, e.g. UV stabilisers, polymerisation inhibitors, mould release agents, wetting agents, flow control agents, infra-red absorbers, sensitiserε, anti-sedimentation agents, surface-active agents, dyes, pigments and fillers.

Compositions according to the invention can be prepared in a known manner, for example by premixing individual components and subsequently mixing these premixes or by mixing all the components by means of customary devices, such as stirred vessels, in the absence of light and, if appropriate, at a slightly elevated temperature.

Liquid compositions according to the invention can be polymerised by irradiation with actinic light, for example, by means of electron or X-ray beams or UV or VIS light, e.g. by means of radiation within the wavelength range from 280 to 650nm. Laser radiation from HeCd, argon ions, or nitrogen ions and also metal vapour and NdYAG lasers of multiplied frequency are particularly suitable. It is known to those skilled in the art that a suitable photoinitiator must be selected and, if appropriate, sensitised for each light source selected.

The invention also relates to a process for polymerising liquid compositions according to the invention by irradiating them with actinic light.

Liquid compositions according to the invention preferably have a viscosity of 300 to 3000 mPa.s at 30 ^" C, more preferably 400 to 1300 mPa .ε and especially 500 to 1200 mPa.s. Compositions according to the invention have surprisingly low viscosity and this enables fast processing times in stereolithography. The low viscosity is achieved without adversely affecting physical cr mechanical properties of articles produced.

The invention also relates to a process for the production of a three-dimensional solidified article from the liquid compositions according to the invention, preferacly by stereolithography. Preferably this entails (a) the surface of a layer of the liquid composition according to the invention being irradiated either as the -whole surface or m a oredetermined pattern, by means of a UV/VI3 (i.e. ultraviolet cr visible)

iignt source, such that a layer is solidified m a desired layer thickness in tne irradiated areas; (b) then a new layer cf a composition according to tne invention is termed on the solidified layer, and this is also irradiated eitr.er as tne whole surface or m a predetermined pattern,- ana (c) cy repeating steps (a) and (b) a three-dimensional article composed cf severa_ solidified layers adhered to one another is octamed.

The numcer of times steps (a) and (b) are repeated depends on the thicKness of the resultant solidified layers and the size of the article. Thus steps (a) and (o) could be repeated 10 times if eacn solidified layer was 1mm deep and tne article 1cm high and 500 times f each solidified layer was 0.5mm deep and the article 25cm hign. Preferacly the solidified layers each independently have a depth of 0.1 to 1mm, more preferably 0.2 to 3.6mm, especially 0.25 to 0.4mm. The solidified layers do not need to all oe of the same depth. Repetition of steps (a) and (b) from 10 to 10,00c, preferacly 20 to 2000 times, forms one aspect cf the invention. The process for forming a three-dimensional article preferably uses a stereolithography apparatus, for example the SLA 250 or 500 supplied by 3D-Systems cr the Stereos 300, 400 and 600 supplied by EOS.

There is no particular limit on what the three dimensional article can ce, for example one may use the process to form ornamental and industrial articles and models of plant and animal parts. Industrial articles include mechanical parts, especially those used m automobiles, and models and prototypes thereof. Animal parts include bones, organs, tissues and comcinations thereof. Examples of bones include joints (e.g. call and socket joints such as the hip and shoulder, hinge joints such as the Knee and elbow) the skull, aw, spine, ribs, collarbone, shoulder blade, numerus, radius, ulna, teeth, finger and hand bones, breast bone, femur, ticia and fibula. Examples of organs include tne liver, heart, lungs, Sidneys, bladder, brain, eyes, intestines, pancreas and reproductive organs. Examples of tissue include muscle and cartilage.

As desired the tnree dimensional article can be a model wnicn is the same size, smaller or larger than the original article The lev; curl distortion and nign rate cf cure mean tnat sucn articles can ce prepared quιcκ_y and accurately. It is preferab-e to use a laser oea as the radiation source in tπis process .

Compositions according to tne invention may also ce used as coating agents; clear and hard coatings can be obtained on wood, paper, meta , ceramics or otner surf ces. The coating thιcκneεε can ce varied cetweer. i.iαe for example from 1 micrometer to Imm. Pelief imageε ror printed circuits cr printing plates can be produced direct from compositions according to the invention oy irradiating tne mixtures for example oy means or a computer-controlled laser cea cf suitable wavelengtn

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cr using a photomask and a corresponding light source.

The curl factcr is determined on test specimens produced by stereolithographic processes, the deformation of a self-supporting part of the test specimen being determined by shrinkage. The curl factcr is the ratio cf the height of a deformed, fixed segment cf the test specimen to the height of the non-deformed segment.

The invention is further illustrated by the following examples in which all parts and percentages are by weight unless stated ether-wise.

Viscosities were measured at 30 ^C C on a Brookfield viscometer RVTV-II using spindle 27 at 100 rpm.

The Tensile moduli, strength at break and elongation at break were measured using tensile testing bars prepared to ISO 527 and tested on an INSTRON 1122 fitted with a 1 N load cell.

Surface tension was measured using a torsion balance.

Linear shrinkage (L.S.) on cure was calculated by measuring the densities of the resins before and after curing. Linear shrinkage (%) was calculated by the equation:

Processing parameters Ec and Dp mean respectively critial cure energy (mJcm ^" -) and penetration depth (mils) and were measured using a 3D systems SLA250 stereolithography apparatus.

The rate cf cure was measured using the Real Time Infra-Red technique described b\ Davies in Radiation Curing Polymers speciaJ publication No 89, Royal Society of Chemistry, ISBN 0-85186-3 ^{^} 7-9.

The following abbreviations are used m the Examples :- SR-348: Ethoxylated bisphenol A dimethacrylate of MW 452, supplied by

Sartomer. SR-349: Ethoxylated bisphenol A diacryiate of MW 424 supplied by Sartomer. SR-9035: CH CH-C- [CH _; 0(CHCHO),COCH=CH ] wherein n= 5 of MW 955 supplied by Sartomer. NR-272C: A urethane acrylate of formula

(H-C=CHC _: CH _; CH_ (0C0C. _: H, ).OCONH-C.H_ -) -CH - wherein n= 2 of Ml-;

950 supplied by Zeneca Resins US. DAR1173: U.V. Photoinitiator of formula Ph-CO-C (CH ) OH. _βAD O IGINAL J>

IRG: Irgacure 651, a U.V. Photoinitiator from Ciba Geigy.

ΞB-27C: Aliphatic urethane acrylate of MW approximately 1500 supplied by UCB Chemicals . DC190: a εilicone type surfactant supplied by Dow Corning Ltd. Examples 1 to 6

Liquid compositions according to the invention were prepared by stirring together at room temperature the number cf parts by weight of components indicated in Table 1 below. After stirring for a few hours the homogenous mixtures were transferred into separate bottles for storage. Table 1

For comparison commercially available liquid compositions were obtained from Ciba-Geigy (XB5143) and DuPont (SOMOS 3110) . Testing

The viscosity, tensile modulus, strength at break, elongation and surface tension of the exemplified compositions and the two commercially available resins XB5143 and SOMOΞ 3110 were measured as described above. The results are shown in Table 2 below:-

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Table

* Comparative

The linear shrinkage on cure, shore hardness, Ec, Dp, rate of cure and curl factor were measured as described above. The results are shown in Table 3 below:-

Tfr lg 3

Comparative

Examples 7 to 19 rurther liquid compositions may be prepared having the formulations given in Table 4 below: Tafcl-g 4