CA2118021A1 - Rapid prototype three-dimensional stereolithography - Google Patents

Abstract

Methods and apparatus are disclosed for the production of high precision large scale, micro and mini structures (24) using three-dimensional stereolithography. The objects (24) formed using these methods have minimal stress between layers and low curl distortion. The objects also have low warpage because no post-cure treatment is necessary. The methods include the use of elevated pressure, elevated temperature, or sequential polymerization of polymer precursor fluid (10), or a combination of these, in the three-dimensional stereolithographic process.

Description

' . W093/20993 ~ ~1 ~ 8 0 2 1 PCT/US93/03~ 1 ., .` ``` ; . 1 RAE'ID PROTO'TY~E
T~RE~-DIME~SIONAL, STE~EOhIT~OGR~P~Y

This in~ention is in the area of rapid prototype, high preci~ion three dimensional stereolitho~raphy BACKGROUND OF THE INVENTION f Three dimensional stereolithography is a v,_ry recently develc,ped proeotyping technology for the rapid production of models for form-fit-and-function testing. The process is a revolutlonary approach to:the preparation of a wide variety :IO of objects without tooling, with ehe assistance of ~omputer ; assisted design (CA~) and computer assisted manufacture ( CAM ) . :
~ As disciosed in U.S. Patent Nos. 4j575,330 and 4,929,402 to Hull, a CA~ file of the desire~ ob'ject is prepared and ~15 conver~ed mathematic~.~.ly into stacked:cro~-sections, or layers. The _irst l~y,-r of~the object is scanned with a polymerizat~.c~ inltiating.source,:tyFically~an ultra~iolet laser,:on th~. 3urface of a vat of ethylenically unsaturated mon er, or mixture ~of ~onomers. The;~irst~layer ,of the .~0 ;~ model,~;that is positione~ on an elevato~r platform in the vat, ` is:the~ lowered a pro~rammed amount with an actuator:~ :
mechanism, 90 that a~new~coating of polymerizable lif~Ui c~vers:~the~:solidified layer. ~A wiper blade perfects:the ~
~:~ '` coatl~g depth:, and~then the~laser draws a new:layer on top of `.25~ ` `the.prsceding~one.~ This~proc,~dure i5 repea~ted~until the~
deslred three dimens;iona1 structure:is~:comp1etsd. ~Webbings~ :
can be added to the~design a~ ~ecessary~to keep object~
~3t ~ ~ ns.:from~floati~ng away.~ The;prepared.ob~lect~(green ~ body)~; is:~a partial1y~cured structure. ~A~ter removal from `;~30~ .the~vat:,~:.the~green~body:~i's~;cured~ and sanded,`:oF otherwise: ; :smoothe~ as~ecessary.
Thè~'330~ patent~ see~FIG.~:~4 of :that~patent)~teache~, as an alternative::~em~odiment,~floating the ultraviolet curable ~ liquid~on:a~heavi:er, i ~ iscible, ultraviolet transpar2nt ~.35~ 1iquid::1ayer~in the~vat~ In this~:'e~ odimenti the W source W093/20993 ~ 2 1 PCT/~S93/03 radiates from below the vat through the ultraviole~
transparent material, and is focused at the interface of the two liquids. The object is pulled up out of the ultraviolet-curable liquid, rather than down and ~urther into the li~uid, as shown in FIG 3. of '330. This embodiment is useful to minimize the amount of curable material used, However, the incompletely polymerized greenbody may experience sagging and distortion .
U.S. Patent No. 5,011l635 to Murphy, et al., provides an apparatus for 3D-stereolithography that includes a fluid phase, a substantially impermeable, movable membrane posi.tioned on top of the fluid phase, a radiation-polymerizable liquid organic phase positioned on top of the membrane and a radiation source positioned above the organic phase. This system also allows a reduction in the volume of polymerizable ~at liquid needed in the apparatus. The presence of the membrane, however, adds complex material ~e~ection criteria, U.S. Patent No. 4,844,144 to Murphy discloses a method of investment casting using a model prepared by 3D-stereolithography, that includes using a polymer pre~ursor fluid in the prototyping that includes an ethylenically unsatura~ed liquid material that is mixed with an inert low thermoplastic material that weakens the pattern when heated in the investment casting process to prevent thermal expansion of the pattern from cxacking the mold. Weake~ing of parts may exacerbate distortion, leading to inexact finished objects.
The main problem associ~ted wi~h the use o~ 3D-,30 j stereolithography,for prototyping is the lack of precise' ¦ dimensional tolerance. One form of stress that causes distortion develops when material that is being converted ~, ~rom liquid to solid comes into contact with and bonds to pre~iously cured material. ~This stress can result in curl i'! 35 distortionl wherein i~dividual layers separate from the ', structure.

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~ WO93~20993 ~ 0 2 1 PCI/US93/03544 ~1 .

Another type of stress occurs when an incompletelypolymerized object is annealed (cured by additional heat or blanket radiation, or both simul~aneously), because the ~.
continuing reaction cause~ shrinkage of the precisely modeled part. Further, the high temperature needed for curing in the absence of radiation adversely affects the object. If the temperature of cure is too highl the object can soften, further losing its shape.
The extent of dimensional distortion is a function of the exact geometry and spatial design of the object, and the ability o the obje~t to withstand stressl and will vary at different locations on the object. Presentlyl 3D-stereolithography technique~ are limi~ed in exactness to the order of a few thousandths of an inch, e~en wi~h the use of sophisticated computer algorithms that predict and attempt to compensate for this shrinkage. Further, while post cure warpage may be decrea~ed ~y increasing the percentage of vat cure, curl distortion increases dramatically as the vat cure reaches completion, due to a buildup of internal stress accampanying successive layer deposition under ambient pressure.
An attempt to solv~ the problem of post cure distortion i5 disclosed in U.S. Pate~t No. 4,942,001 to Murphy, et al, that utiliæes a ~at soluticn that i~cludes from 20 to ~0 percent of a resinous polyacrylate or polymethacrylate di~solved in a combination of 10 to 45 weight percerit of a liquid polyacrylate or pol~methacrylate, which is preferably trifunctlonal, and lO to 45 weight perce~t of N-~inyl monomer. The solution, on curing, pro~ides a ligh~ly cross-~30 li~ked, sol~ent ~wellable, po~ymeric, ~hin walle~ elemenlt constituted by heat-sof~enable solid polymer. The addition of resinous polymers~with monomers may increase ~he viscosity of the polymerizable mixture, slowing down the fluid movement and aggravating curl distortion.
U.S. Patent No. 4,945,032 to Murphy, et al., discloses that post cure distortion can be reduced by stopping the ex~osure at any portion of the surface in the formation of :~ .

WO~3~2~g93 PCT/US93/03 ~ U2 1 4 the layer and then repeating the exposure at least once again in the production of each surface layer so that the strength and solvent resistance of the ~ormed object are increased.
The ultraviolet exposure of each surface layer is preferably carried out as a series of rapid repeated scans of a computer focused laser.
U.S. Patent 4,972,006 to Murphy, et al., discloses that the green body can be cured by immersing it in an aqueous solution bath that includes a water soluble ~ree radical catalyst that is absorbed by the green body. The bath is heated to complete the cure. Although additional c~re can be accomplished by the catalyst in the aqueous solution, this approach does not improve ~he residual warpage problem caused in the post cure step.
U.S. Patent Nos. 4,~99,143 and 5,059,359 to Hull, et al., disclose that curl and distortion can be reduced by, among other things, defining the object in a way to provide built-in supports for the object (webs), and by dividing the surface of the solid model into triangles (PHIGS) using CAD, for better surface resolution. This mechanistic-ba~ed approach, while use~ul, leads to unnecessary and unwanted webs and supports, which must be trimmed away.
U.S. Patent No. 5,015,424 to Smalley teaches that distortion can be reduced by isolating sections of an object 25 SQ that stress cannot be transmitted from one sec~ion to .
a~other. Layer sections prone to curling are isolated by de~igning 9mall holes or gaps at stress points in the CAD
design or the part. These gaps are called "smalleys."
Smalleys are also used ~o reduce birdsnesting (unsecured ,30 1 bound~ries in~tjhe object that mo~e up and down during manufacture, and give a rough surface finish to the object).
This mechanistic-based approach similarly in~roduces unnecessary complications.
U.S. Pa~ent Nos. 5,076,974 and 5,164,128 describes a new part building technique called "Wea~e", which improves :
dimensional tolerances. Typical x-y cross-hatching methods produce a rather fragile matrix of thin-walled chambers that ::

, ~ W0 ~3/20gg3 ~ 2 l PCT/US~3/03~

trap liquid or semi-cured resin inside in much the same way water is trapped in partially frozen ice cubes in a freezer tray.
Post cure warpage is reduced and surface finish improved as a greater portion of the liquid resin is cured in the vat.
Post-cure distortian decreases, in part, becau~e there is less post-cure shrinkage. However, curl distortion resulting from the separation of layer~ from the structure dramatically ~ reases as the extent of beam cross-hatching is increased and the degree of polymerization approaches 100~, due to the buildup of internal stress.
U.S. Patent Nos. 5,139,338 and 5,157,423, assigned to Cubital Ltd. disclose a~method to prepare three dimensional objects stereolithographlcally that employs a flood W curing process as a means to eliminate problems associated with post-curing. Like all rapid prototyping ]?rocesses, a solid or surface CAD modeI is first s..~ced into thin ~ross sections~ A slice is then transferxed from the computer to the mask generator, which operates like a pho~ocopier: a negative image of the cross ~ection i~ produced on a glass ma~ plate by charging portions of the surface and ~Ice~eloping~ the electrostatic image with toner powder.
Si~.~ulateou~ly, a thin layer of liquid photopolymer is spread ac~ s the surface of the workbench~ The mask plate with the negative image of the cross-~ectional slice is th~n po~itioned over the workbench. A shutter above b~th the mask and the worX~ench opens for two seco~ds, allowing strong W
liyht from a 2-kilowa~t lamp to solidify ~he exposed photopolymer layer all at once. Areas external to the model ~3l0 are left in liq~id form.
The exposed mask is then physically wiped down and electro~tatically~discharged, erasing ~he mask plate and preparing it for the next negative cross-section image. At ~ the same time, the uncured polymer is removed from the 3~5 ~ workbench by the combination of forced air and vacuum pressure a~d is collected for reuse. The workbench moves to -~ the next station, where hot wax is laid down to fill the :::

C~1`1`8021 W093/2~9~3 P~T/US93/03~ ' cavities left by the uncured polymer. At the next station, a cooling plate is applied to solidify the wax, which acts as a support structure to reduce distortion due to gravitational or shxinkage effects. Finally, the surface of the entire S polymer/wax layer is milled with a cutter to the desired thickness, which makes the workpiece surface ready to accept the next polymer layer. The steps are repeated until the part is completed. A~ter the model is constructed, the supporting wax is removed with microwave energy, hot air from a blower, and a rinse with solvent. Because each layer is fully cured, no post-curing is re~uired. Although this process can be used to make high precision parts, the parts still exhibit some distortion due ~o buildup of stress between layers during polymerization.
U.S. Patents Nos. 4,752,498 and 4,801,477 describe method for ~orming three dimensional objec~s stereolithographic~lly, in which a sufficiently rigid transparent plate or film is placed in contact with a liquid polymer precursor fluid to hold the fluid in a desired shape, and preferably exclude air from the reaction va~. The plate is not ~ealed on the ~at so that volume changes ln the vat are made up by the unrestricted suppl~ of fluid from around the irradiated area. It is further suggested that the r surface o~ the transparent plate be made of a material that leaves the irradiated polymer surface capable of further crosslinking so ~hat when a subsequent layer is formed it will adhere thereto. The patents teach that the plate should be made of or contain in its molecules oxy~en, copper or other inhibitors to aid in the release of the layer without 310 , di~torti~g the solidified photopolymer., The highest precision obtainable theoretically using the technique of three dimensional stereolithography is the -diffraction limit of light (submicron). While the above-described techniques have been used to reduce the distortion ~35 of objects made by 3D-stereolithography, fine precision has not~yet been attained. There remains a need to provide a method to produce ~orm-fit-and-function models by 3D-~`~ W093/20993 ~ O~ 1 PCT/US93/03 stereolithography that provides improved precision.
High precision is necessary in the production of micro and ministructures for us~ in microelectronics that have high aspect ratio and significant structural height. Micro and ministructures are typically prepared by optical litho~raphy, which has been perfected to attain a 0.5 ~m critical dimension (CD), that is necessary for the fabrication of 16 Mbit memory chips. This technology has been modified to make microsen~ors and microactuators by either bulk or micromachining on silicon wafers.
High aspect ratio microstructures have also been prepared using x-ray lithography with high quantum energy synchrotron radiation. The ~LIGA~ process (see Becker, et al., Mi~roelectro~ic ~gi~eering 4 (1986) 35-56, and U.S.
~tent No. 4,990,827) prc~uces microstructures with lateral -~sions in the micromec r range and structural heights of 3ral hundred micrometers. The LIG~ process is ematically illustrated in Figure 1. A polymeric material (resist) which changes its dissolution rate in a liquid solvent (developer) on high energy irradiation, is expo~ed through an x-ray mask to highly intense parallel x-rays. The radiation ~ource is an electron synchrotron or an electron storage ring that can generate the highly collimated photon flux in the ~pectral range required for precise deep-etch x-ray lithography in thick resist layers. As an example, a ;`~ pattern thickne3s between 10 and 1,000 ~m typically requires an optimal cxitical~ wavelength o~ synchrotron radiation of -; ~ from 0.1 and 1 nm.~ In the next step, the resist structure is used as a template in an electroforming process in which 30l metlallisi depositedionto the eléctrically conductive ~ubs~rate (galvanoformation). The polymeric resist is then removed to :
pro~ide a highly precise metal mold. The secondary plastic mold is prepared~by~introducing~a~polymeric mold material into the metal mold cavities through the holes of a gate - plate. ~The plate has a formlocking connection with the polymeric microstructure, and after hardening of the molding resin the plate serves as an electrode in a second W093/2~993 ~ PCT/US~3/03 . -8-electroforming process for generating secondary metallic microstructures. The LIGA process produces highly precise secondary structures, including those with an aspect ratio of up to lO0 and minimum lateral dimensions in the micrometer range.
The LIGA process has been used to produce microsensors, measuring devices for ~ibration and acceleration, microoptical devices and symmetry, fluidic devices, and electrical a~d optical microconnectors. Primary disadvantages associated with the LIG~ process are that i~
can only produce fully attached metal structures and tha~
the process requires the use of an electron syncrotron, that is not readily available.
Guckel et. al. (Proceedings of International Conferen~e lS on Solid-State Sensors and Actuators, l99l) reported a new process called sacrificial LIGA (SLlG~). The process is illustrated in Fig. 2. The addition of a sacrificial layer to the hIG~ process facilitates the fabrication of fully attached, partially attached or completely free metal 1 20 structures. Beca~se device thicknesses are typically larger I than lO ~m and smaller than 300 ~m, freestanding structures 1 do not distort geometrically if reasonable strain control of I the plated film i5 achieved. However, the process still ¦ requires the use of an electron syncrotron, that is not readily available. It would be useful to provide a process and apparatus for the production of high aspect ratio micro and ministructures for microelec~ronics that do not require the use of an electron syncrotron.
Therefore, it is an object of the present invention to ; 31 ~ pro~ide a method fo~ the preparation ofi objects by 3D-stereolithography that minimizes object distortion.
It is an additional object of the present invention to broaden the selection of polymer precursors to include slow-reacting systems and to i~clude particle-containing fluids that upon solidification form real parts that possess dual polymer a~d ceramic properties and/or magnetic, electrical, or optical attributes.

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`` W093/20993 ~ 0 2 ~ PCT/US93/~3~ `
_ 9 _ It is yet another object o~ the present invention to accomplish precision polymerization within a short time, so that real parts can be generated quickly.
It is still another object of the present invention to pro~ide a process and apparatus for the production of high aspect ratio micro and ministructures ~or microelectronics.

S~MARY OF T~E I~VENTION

Methods and apparatus are disclosed for the production of high precision large scale, micro and mini structures using three dimensional stereolithography. The objects formed using these rnethods have minimal stress between layers and low curl distortion. The obiects also have low warpage because no post-cure treatment is necessary.
In one embodiment, structures are prepared using ~hree-dimensional stereolithography under ele~ated pressure. Theuse of elevated pressure allows the use of eleva~ed temperatures and/or viscous polymeric precursors in the reaction Yat. The imposed pressure in the vat allows ~he formation of real objects (as opposed to prototypes) that include inert polymeric or nonpolymeric materials, including magnetic particles, dielectric particles, ceramic particles, liquid crystals, liguid crystal polymers, noncentrosymmetric moieties for nonlinear optics, conducti~e particles, and conducting pol~mers, in the solid~ The magnetic particles, ~25 li ~ id crystals, liquid crystal polymers, and noncentros ~ etrlc mo~ieties can be suitably aligned on the imposlti~on of a ma~netic or e~ectric field. ~
Xn another embodiment, an improvement in the proce~s of three dimensional stereolithograph~ ls provided wherein ~30 stress re}ated distortions~in the polymeric material are minimized by~causing the polymer precur~or fluid to polymerize in a differential fashion along a moving front, so that the material ahead of~the movlng polymer zone remains liquid, and the material that ~the front has passed is ::~ ` ` :
~: .

W093/2~9~3 ` P~T/US93/03~ ~

solidified. In a t~pical method, the moving front is a slit through which W light is transmitted In another method, the moving front is the radial opening of an iris diaphragm.
The still-liquid material ahead of the moving polymer zone can then flow freely, at a rate that equals the rate of shrinkage, and a distortion-free, reduced stress polymeric network is produced. Using this process, objects can he cast in a way to prevent cavitation, or voids caused by the shrinkage of material during polymerization. This method is referred to below as the "sequential polymerization"
modification of the three dimensional stereolithographic process.
The sequential polymerization modification of the three dimensional stereolithographic process can be performed at ambient pressure, or at elevated pressure or temperature, or at elevated temperature and pressure.
A biphasic vat solution can be used that includes an iner~ immiscible fluid below the polymer precur~ox fluid. In another embodiment, a multi-phasic system is used, wherein the upper space is a gaseous phase (or light ~luid that is W -transparent but immiscibIe with the polymer precursor fluid). The use of gas (inert or reactive) or an intervening fluid l~yer between the tra~sparent window and the reactive l-mix~ure prevents the sticking of the drawn layer to the window. The inert fluid also prevents the polymer precursor ~luid from adversely aEfecting the means for imposition of pre~sure.
Mini and microstructures for microelectronics can be prepared using the methods disclosed herein that exhibit the ~0 i precislion of structures prepared using`the LIGA or SLIGA
techni~ues. For ex~mple, as illustrated in Figure~ 3-5, polymer precursor fluid is sequentially irradiated by a -sequentially moving slit system (SMSS) or a computerized iris diaphra ~ (CID3 in a pattern created by a photomask under optional elevated pressure or temperature. After formation of the desired polymeric patterned layer, an actuator mechanism raise~ the layer (which is attache~ ~G an elevator :

~ `:" wo~3~20g93 ~ 2 1 PCT/U~93/03~ ~

platform) by a differential amount, allowing fresh polymer precursor ~luid to cover the layer. The fresh polymer precursor fluid is then polymerized on top of the prior formed layer in a desired patterned. This process is successively repeated until the desired three dimensional structure is built. After the high precision plastic mold is completed, it is removed from the vat and electroplated, typically with nickel. The plastic mold is then removed and free metaI structure;is cast.
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BRIEF DESCRIPTION OF T~E ~IG~R~S
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Figure 1 is a cross sectional illustration of an apparatus for high pressure three-dimensional ; stereolithography.
Figure 2 is a magnified view~of a local region of the ;~5 monomer/precursor pool during irradiat;ion, using three dimensional stereolithography.
Figure 3 is a ~cross sectional illustration of an ~ apparatus for high pressure three-dimension~l "~ ~st~reclithography that includes~a means for imposition of ~ . . ~ .
'20 ~electri~c or magnetic fields~to align magne;tic particle~
` di9persed in the polymeric precur~30:r~fluid.~
;'~ Figure 4 is a cross~sectional illustration of an appàratus for high;~pressure`three-dimensional ; 9tereolith:0graphy~that~incIudes a biphasic'vat fluidj and '`2~5 ~ ~wherein the lower~fluid is inert,~and the upper fluid is a ~ polymer~precursar;fluid.; ~
'~ ~ Figure 5 is a~cross sectional illustration of an apparatus for~h1gh~pressure threq-dimensional ~ ~ stereolithography~';that~'includes~a triphasic vat fluid, that 30~ includes~;~a~lower~fl~uld~that~is~inert,~a next layer of pol ~ er pre~cursor~flUi`d,~ and;~an upper~gaseous~ or light fluid phase that lS~ W -transpa`rent but immis~ible with the polymer precur~r~fluid.~
' Figure~6~is a~cross~sectional~illustration of an 35~ pparatus~for~high~pressure~three-dimen~ional I W093/20993 ~ PCT/US93/03 ? -12-stereolithography that includes a triphasic vat fluid, that includes a lower hydraulic fluid that is inert and W-transparent, a next layer of polymer precursor fluid, and an upper gaseous or light fluid phase that is immiscible with the polymer precursor fluid, and wherein the part is pulled up out of the polymer precursor fluid.
Figure 7 is a cross-sectional illustration of a method to prepare micro- and ministructures using LIGA technology.
Figure 8 is a cross-sectional illustration of a method to prepare micro- and ministructures using SLIG~ technology.
Figure 9a is a cross-sectional illustration of an ~ apparatus for the preparation of objects by three-dimensional !~ stereolithography wherein the polymer precursor fluid is i sequentia~ly polymerized (V1 is a first valve, V2 is a second valve, SV1 is a first solenoid valve, SV2 is a second solenoid val~e, and Q1 is a quick connect). Figure 9b includes a top ~iew of the apparatus illustrated in Figure 9a, with additional valve ports for the introduction and removal o~ desired materials, and a side ~iew of the apparatus that illustrates a wiper mechanism.
Figure 10 is a partial cross-~ectional illustration of an apparatus for the production of a three-dimensional object that include~ a sequentially moving slit system (SMSS)~
Figure 11 is a partial cross-sectional illustration of an apparatus for the production of a three-dimensionAl object that includes a computerized iris diaphragm ~CID).
Fiyure 12 is a magnified view of a local region of polymer precursor ~luid on irradiation by W light through a sequentially moving slit system.
Figure 13 is a schematic illustrat1on of an apparatus for efficient release of an object formed by three ~ dimensional stereolithography from the transparent plate to I which it becomes attached. The transparent plate is etched, and the etched depressions filled with a soft material that has a refractive index that matches the transparent plate. A
j` ~ tape is positioned o er the glass plate in such a ma~ner that ¦ the adhesive side of the tape is attached to the transparent I : ;
1 :

~ -i W093/20993 ;~ d2~ PCT/US~3/03~4 .~ -13-plate and the nonadhesive side of the tape inter~aces with the polymer precursor fluid and the object prepared from it.

Figure 14 is a cross-sectional schematic illustration of a method to prepare micro- and ministructures for microelectronics using the methods disclosed herein.
Figure 15 is a schematic illustration of examples of stnlctures that can be prepared using the method of three-dimensional stereolithography disclosed herein.
Figure 16 is a cross-sectional vlew of tapered honeycomb structure tha~ can be generated from a mold prepared accoxding to the methods described herein.

. . I
DETAIL~D DESCRIPTION OF T~E INVENTION

The term ministructure, as used herein, refers to a structurè that is typical~ly greater than approximately 10 microns in height and less than approximately 103 micro~s.
The term microstructure, as used herein, refers to a structure that is typically less than approximately 10 ; microns in height.~ ~
1'he term large scale structure refers to a structure that is greater than 1~03 micxons~
Methods and apparatus are disclosed for the production of high precision largé scale, micro and mini structures usi~g three dimensional~stereolithography. The methods include the use of elevated pressure, elevated temperature, or se ~ ential po1ymerizatlon~of polymer~pre~rsor f~luid,l or a combination of these, in the three dimensional stereol~ithograph~ process.; ~

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~ W~93/20993 ~ 2~ PCT/U~93/;~3~ f .
! ~ .
'j - 1 4 -I. Preparation o~ ObjPcts u~ing Three DimenQio~al 5ter~olithography u~der Ele~ated Pressure, Ele~ated Temperature, or Both Elevated Pres~ure and Elevated Temperature.
,, S A method and apparatus is disclosed for the preparation ! of objects with high precision using three-dimensional stereolithography under elevated pressure. The use of elevated pressure optionally allows the use of elevated temperatures and/or ViSCQUS polymeric precursors in the , 10 reaction vat. The use of high temperature in the reaction vat causes rapid polymerlzation to close-to-completion stages during greenbody formation, resulting in ~greatly minimized shrinkage and dimensional alterations accompanying annealing.
Since the high pressure process is inherently fast, it ~an force the reaction of partially polymerized starting materials, or other materials that do not polymerize as ea~ily as acrylates or methacrylates. Thus, the greenbody can be prepared from a greater variety of chemicals, with high polymerization rates, and with the ability to crosslink durin~ or after W exposure at selected spots.
The use of high pressure in the reaction process also allows the production of objects that include nonpolymerized materials, sùch as filler, additives, colloidal particles, magne.tic particles and inert polymers.
The process disclosed herein can be used to form complex thxee dimensional magnetic structures~such as permanent-¦ magnet structures for the production o~ transverse helical ¦ fields (IEEE Transactions on Magnetics, ~ol Mag 22(5), Se~tember 1986?~and~traveling wa~e tubes that have increased periodic magnetic fields (IEEE Transactions on Magnetics, Vol ` Mag 25(5), S~p~embe~r 1989).
Typical ethylenically unsaturated monomers that are used in the pxoduction of objects by three-dimensional stereolithography, such as acxylate and methacrylate esters, have a signi~icant vapor pre~sure at ambient or near ambient temperatùre. The closed reaction vat disclosed herein 1~; pre~ents e~aporation~. The use of elevated pressure in the 1;

;''.W093~20~93 ~ 2 1 P~T/US93/03~
, . : , . . ~ ! I ;

vat allows the polymerization reaction to be run at greatly elevated temperatures without inducing boiling or e~aporation of the monomer or precursor. Photopolymerization proceeds at an.increased rate at elevated temperatures. The high pre~sure minimizes the amount of shrinkage upon con~ersion of ~.-the monomer to polymer. ~ :
The method for improving the'~precision of parts made by 3D-stereolithography~described herein using~ increased ` hydrostatic pressure, and optional}y,~increased temperature, is not limited to any~one:type~of apparatus, but is instead a :~ general technique. As~discussed in the Background of the . `Invention, a number of~apparatuses have been developed for -rapid prototyping using the technique of three dimensional stereolithography. ;Equipment is sold by, among others, 3(D ..
Systems, Inc., Cubital America Inc., Quadrax Laser Technologies, Xnc.,~::hight;Sculpting,: Inc.,~and DTM
Co~rporation.~ The distortion of objects~made with any of these~ nown methods~and:~apparatuses for~three-~dimensional .
stereoli:thog~raphy`¢an~be ~improved by elevating.the '~2~0;~ hyd~ostà~tic:pressure~ Sy~tems~that:function:by raising the~
resin~}eYel instead:~of::~lowering:the~model can be adap:ted for use;with~this~process~.by~emp10ying a~pressurized gas phase, or;~by dra:ining:or~adding:inert;~f1u~ids and introducing the pol ~ rizi~ng~;fluid.
.~25'~ ; FIG: 1 is a cros~ sectionaI illustration:of one example of an~a aratus~for~hlgh~precision~three-dimens'ional .
stëreo1ithography~ Pol`~mer precursor:f1uid~10 is contained in the~reàction~vat~12.~ The~ reaction vat can~have any shape, : ;~
~ including:~:four~orthogonal sides~ as~in;a rectangular box, or, `~30~ alte~atively, cylindri'cal.~ ~A ~at~wi;th~a cylindrical cross-''sect:ion ~ y;~be~a~pre~e d~s~tr ctu ~ ,. pressuré~ ~:A means~.l4:~f:or el:evating the hydrostatic pressure~
'. ~.the~`: t~is~a t ~ ~t th ~ t~.~ No 1i 'ting ex ~ les~o~
means to elevate;~the':~pressure~ nc1ude,~:~but are not:limited :
~'~S.'~ to,;~à:`~ a~comp~rè'ssor~ such as:~that used~Qr HPLC or :
sùp r~ itica1~ 1ui:d~extrac'ion, a~ ~ d yllnd~ arrarge~ent~ On~s1de~of~Lhe reactlon vat 12 i-s.a b j _ : -W093/20993 ~1 1 8 ~ 1 PCT/US93/03~4 ~``

window 16 through which a polymeric initiating source 18 is transmitted. The initiating source 18, typically an ultra~iolet radiation laser, writes a pattern in the layer of precursor fluid close to the top sur~ace of the pool. The ' pattern is formed by the localized photo-polymerization of the pool in selec~ed regions indicated by the laser. Once a layer is finished, an actuator mechanism 20 lowers the imaged layer that sits on an elevator platform 22 by a differential amount, allowing fresh ~unexposed) precursor fluid 10 to cover the underlying written layer. The process is then repea~ed and a new pattern is thus overlaid.
Repeated usage of the laser in combination with platform ~lowering gradually builds up a complex 3-dime~sional structure 24 wherein the final part is constructed of successive layers of rigidized images. The unreacted fluid 10 drains off the part (greenbody).
Heating can be accomplished by standard means, including but not limited to a jacketed vat, immersed coils, IR heating lampsi, electrical cartridge heaters, wrapped heating tapes, microwave heaters, or by placing the vat in an oven.
Shrinkage of local polymerized region~ in the object is minimized using this technique, because as the polymerization occurs, more pol~me~ precursor fluid quickly enters the irradiated area, by ~irtue o~ the large hydrostatic pressure ~25 in the pool. The additional precursor fluid quickly polymerizes in the void space of the irradiated resulting from the shrinkage.~This is illustrated in FIG. 2, which is a magnified view of a~local-region of the precursor fluid pool 24 being irradiated by an ultraviolet laser beami26. The ~0i ~ shrinkage 28 is c~ompensated for by rapid influx of additional polymer precursor fluid 24 under high hydrostatic pressure.
The resulting greenbody 30 does not suffer much shrinkage during annealing becau~e it~is already nearly fully polymerized ~and in certain cases crosslinked).
~35~ ~ ~igh precision 3D-stereolithography minimizes curl distortion. Curl distortion is a complex phenomenon. It is primarily controlled~by the rate of stress relaxation at the I

~ :

W093/20993 ~ Q~ 2 1 PCT/US93/03 deposition temperature, and the total residual shrinkage after the newly-formed layer is anchored (attached) to the I underlying layer. The use of high temperature ensures rapid polymerization, so that the new layer i9 nearly completely S converted to polymer. Because of this, residual shrinkage is minimized. In addition, stress relaxation increases as temperature increases, and therefore can be reduced ¦ appropriately in the object by the careful choice of 3 temperature during manufacture.
The extent of curing that occurs in the closed vat can be easily assessed by extracting the uncured material in the object wlth a suitable solvent, and then comparing the weight -and size of the object before and after extraction. Methyl ethyl ketone is a common solvent used for this purpose.

Temperature ~
The temperature in the clo~ed and pressurized vat can range from ambient temperature or below to any ele~ated temperature that can be accommodated by the vat and that does not adversely affect the quality of the object, or induce undesired side reactions. Any means~known to those of ordinary skill in the art can be used to heat the reaction ;~ vat. The upper limit on the tempera~ure used is also ; influenced by a number of ~actors, including: (1) the material of construction of the~closed vat (as a nonlimiti~g ~ 25 example, an apparatus made from me~al, stainless steel, or ¦ alloy, with quartz or sapphire in ~hick glass as the window ~ can withs~and se~eral thousand paunds per square inch ¦ pressure and temperature); t2) volatility of the polymer i precursor fluidlt~for example,~by using;a monomer/polymer ~30 mixtu.re, the vapor pressure is lowered, and increased temperatures can be;~accompli3hed with less externally applied pressure)~;~ and~(3)~organic decomposition tempera~ures (oxidati~e~degrada~ion or~depolymerization), which are typicàlly relatively~high (400C or over, with exceptions).
~3~5; ~ Typi~cal temperatures for;the process described herein range from~30~;to` 300'C~and more typically, 100 to 300 C. It is W093/20~93 ; ~ g 02 118 PCT/US93/03 preferred to maintain a uniform temperature throughout the vat to prevent natural convection. The optimal working ', temperature for any given system can be determined easily, by carrying out the process at a range of temperatures.
S Superheated liquid can be used in this process. Care should be taken, howe~er, to avoid oxidation and heat-induced -polymerization.

~ .
~ny elevated pressure can be used in the closed vat that decreases the distortion or increases the general quality of the object under production. Pressures used in the vat can range from slightly above ambient pressure, for example, 50-- 100 psi , to 100,000 psi (pounds per square inch), and more typically, from 50 or 100 p~i up to 10,000 psi. The increased pressure decreases the risk of float-away pieces and the need for webbing support, through the ability to use viscous starting materials, and the exploitation of density contxol with bipha~ic and multiphasic systems.
The pre~sure and temperature relationship governed by monomer boiling or evaporation (which provides the minimum pressure requixed at a fixed operating temperature) is governed by the well-known Antoine Equation, or in the simpli.fied form, the Clasius-Clapeyron Equa~ion. The pressure and temperatuxe should be optimized for a given polymer precursor ~luid by testing a range of each. For example, if the monomer is not ~ery vola~ile, high pressure with slightly elevated temperature may be appropriate.
The transparent window must be attached to the container with an adhesive that will withstand the desired high temperature. AlternativeIy, 0-rings, or other materi~l that can withstand high pressure, can be used to attach the window.

Means ~or elevatinq pressure ; ~ ~ There are many known means for increasing the ~ hydrostatic pressure of a fluid in a vat. Any of these k~own mea~s can be used ln connection with ~his method. As an W093/20993 ~ o~ l PCT/US93/03 ~; .
., example, a simple pressure pump can be connected to the apparatus, as shown in ~FIG. 1. Other nonlimiting examples of means to elevate the pressure include, but are not limited to, a compressor, such as that used for HP~C or supercritical fluid extractio~, a hydraulic pump and a piston-cylinder arrangement, or a compressed gas source.

Polymerization initiatinq~source Any polymeric initiating source tha~ can travel through a window can be used wieh this~method. ~ preferred initiating source is an ultraviolet radiation laser, or W
light from a mercury làmp. The eypical wa~elength used is - between 300 and 400~nm. It is well known that W lasers can be transmit~ed through~ W~transparent windows prepared from quàrtz, sapphi~e, or fused silica. ~ Bk7 glass manufàcturèd by Schott is also suitable as a W transmitting window. Heat can also be used~às a~polymeric initiati~g 80UrCe, according to methods and conditions well known to those of skill in the ~; ~ art.

PolYmer Precurso~ Fluid ~`~ 20 ~ ;Fast curing monomers su~h as acrylate or methacrylate ` ;~ e8ter8 are optimal materials for~use as the polymer precursor .~
~ luid. Thé~acrylates or~methacrylates;can be monomeric,~
i ~ o~ligomeric or polymeric, or a mi~ture thereof. The higher the~percentage of~ac`rylate~component,~ the~faster~th~ cure in~
25~ general.~A~number~of~;polymer precursor fluids~are~known and~
co ~ ercially~availabl~e~for u~se~in~3D-stereolihography.~For ~; example, Ciba Geigy~Corporation~sells an acrylate based fluid ~ tha`~ ~s!iused~in~the apparatus~sold~by 3D Sygtems, Ihc.
"~ DeSoto`Chemicals~ I~c.~ also~sel~ls~an~acrylate;based ma~erial, 30~ useful~in the~apparatus sold~by~Quadrax Laser;Technologies,~
Inc..~ S~omos~2~10~0~photopolymer,;~ sold~by the du Pont/So Venture~ is~a~preGursor~fluld~that~contains~acrylates~as a minor~component.~ Another~sui~able~material is Potting~
;~ Compound~363~,~a~modl`fied~acrylate sold by~Locktite ; ~C~ ~ oration. ;W~curable~res~ins~are a~lso taught in U.S.

W093/20993 ~11 i3 ~ Z I PCT/US93/035~

Patent No~ 4,100,141, and 4,942,001. Other W -curable coatings, varnishes, and adhesives are well known to those skilled in the art.
Prior art 3D-stereolithographic systems have required the use of a low viscosity polymer precursor fluid ~such as ¦-that of free methacrylate or acrylate monomer) to allow fresh material to freely and quickly flow acro~s the surface of the newly formed polymeric layer. Resulting low molecular weight dead polymer is left in the ~inal part, causing long-term dimensional instability. The use of elevated pressures and temperatures allow the use of more ~iscous precuxsor fluids, I preferably, that include component or are reacted to form -materials with relati~e~y high molecular weights. One example is thermosetting precursor fluid. Thermosetting networks are typically highly crosslinked. Examples inc~ude W -curable epoxies, multifunctional acrylates, and polyunsaturated polymers. The u~e of thermosetting precursor ¦ fluid results in a green body with substantially decreased distortion, on the basis that the higher the existing degree ~0 of crosslinking at the moment of formation and deposition of the greenbody, the lower the residual distortion upon a~nealing.
Pol~mer~precursor fluids should cure fast enough under the conditions of use that a solid or sui~ably semisolid 2S layer is formed on initia~ion. The conditions of elevated pressure and, optionally, elevated temperature, used in the method described herein allow for the use of precursor fluids that previously could`not ha~e been used due to unacceptably slow polymerization times, including styrenics and allyl-'30 ~ terminated mo~omers.
Acrylate-terminated or othexwise unsaturated urethanes, carbona~es, and epoxies can aI~o be used in the rigid framework. An example of~an unsatura~ed carbona~e ls allyl - diglycol carbonate (CR-39). Unsa~urated epoxies that can be used include, but are not limited to, glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, and 1,2-epoxy-3-~ allyl propane.

:: :

W~93/20993 ~ PCT/US93~03~ ;

Other examples of monomers that can be used in the high pressure, hi.gh temperature 3D-stereolithographic vat are N-~inyl monomers, including N-vinyl pyrrolidine, bisphenol-A-bis-2-hydroxypropylmethacrylate, bisphenol-A-bis-2-hydroxypropylacrylate, bisphenol-A-ethoxy diacrylate, tri- or te~rafunctional acrylates or methacrylates, alkylene glycol ~, and polyalkylene glycol diacrylates and methacrylates, including e~hylene glycol dimethacrylate and ethyle~e glycol diacrylate, propoxylated neopentyl glycol diacr~late, vinyl or allyl acrylates or methacrylates, divinylbenzene, diallyldiglycol dicarbonate, diallyl maleate, diallyl ~ fumarate, diallyl itaconate, vinyl esters such as divinyl I -oxalate, divinyl malonate, diallyl succinate, triallyl isocyanurate, the dimethacrylates or diacrylates of bis-phenol A or ethoxylated bis-phenol A, methylene or polymethylene bisacrylamide or bismethacrylamide, including hexamethylene bisacrylamide or hexamethylene biYmethacrylamide, di(alkene) tertiary amines, trimethylol propane ~riacrylate, pentaerythritol tetraacrylate, divinyl ether, divinyl sulfone, diallyl phthalate, triallyl melamine, 2-isocyanatoethyl methacrylate, 2-i~ocyanatoethyl~crylate, 3-isocyanatopropylacrylate, 1-methyl-2-isocyanatoethyl methacrylate, and 1,1-dimethyl 2-isocyanaotoethyl acrylate.
~ Perfluorinated and semifluorinated deri~atives of the above-1 25 listed compounds are also suitable. The fluorinated monomers or polymers can be used, for example, in the preparation of ~ no~-sticking parts~.
¦~ Preformed polymers that have ethylenically unsaturated groups can also be used in the precursor pol~mer fluid, including acryIate-terminated novolacs, and polyurethanes, polymeric epoxies, and polycarbonates that have been deriva~ized ~o include acrylate, methacrylate, or other I un~aturated functional groups. These types of polymers are ¦ well known and commercially available. Examples of commercially available photocurable materials are the line of Sy~ocure products sold by Cray Valley Products (for example, Synocure 3101, a diacrylate derivative of bisphenol-A, and ~.

I ~ ~

0 2 ~ , . ' 093/~g93 PCT/~S93103~ i , Synocure 3134, an aliphatic urethane diacrylate), and the ; Epon products sold by Shell Corporation (for example, Epon ~ 1001 and Epon 828, which are both diacrylates of the !I~ diglycidyl ether of bisphenol-A). Vinyl-terminated liquid crystalline polymers can also be used.
j In an alternative embodiment/ inert polymers can be ! added to the starting mixture, to thicken the mixture, for ~i ease of handling, to reduce the total reaction time, or for other reasons. The inert polymeric material can be any ! 10 polymer, and can be used in any amount, that does not adversely affect the desired properties of the final material. Inert polymers in general are polymers that do not - react with other components in the reaction solution. In one embodiment, an inert polymer of the hard monomer or hard material is added to the polymerization solution. For 1 example, if methyl methacrylate is used as the hard monomer i in the macromolecular network, polymethylmethacrylate can be added to the polymerization solution.- Inert material can be present in the polymer precursor ~luid in any amount that produ~es a part with the desired properties. The inclu~iion 11~ o~ latex rubber~i endow the finished objects with exceptional impact resistance. The typical range o~ inert material is in the range of 1~ to 90~ by weight of the polymer precursor f~uid.
Nonpolymeric fillers can also be added to the polymer precursor fluid, including but not limited to carbonates, such as CaC03 and MgC03, clay, including attapulgite clay, ¦ borates, sulfates, phosphates, diatomaceous earth such as J celite and silica flour, alumina, colloidal silica, and zeollte solids Filler can be added up to the volume ~; fraction at which ~the mixture stops flowing no matter what pressure is app~ied. TypiCAlly~, there is a 64~ theoretical monodisperse sphere packin~ maximum.
Colloidal particles suspended by Brow~ian motion can be usedl~ including colloidal gold, titanium oxide, ~erric oxides (magnetic), co~alt, molybdenum oxide, vanadium oxide, nickel, alloys, transition metal-rare earth complexes, silicon ~` W033/20993 PCT/US93t~3~W

dioxidel silicon nitride, germanium oxide, silicon atom clusters, gallium arsenide, and other semiconducting particles.
Other inorganic particles, such as sulfides and chlorides can also be used. Organic par~icles can be crosslinked beads ~as small as colloids or as large as micron sized spheres). Since most organic materials are of compar~ble density, large organic particles can easily be dispersed throughout the fluid without ~ettling.

Inclusion~Aof Magnetic ~ rticles In an alternative embodiment, magnetic particles can be included in the polymer precursor solution. Nonlimiting examples include the magnetic particles mentioned above, including ferric oxide and transition metal/rare earth compounds in small particle form. Duxing laser irradiation, the N-S pole can be aligned, and th~ resin then hardened, in such a way that tiny magnetized regio~s are formed, for I example, tiny motors, actuators, and sensors. Complex keys ¦ and locks can be formed using this procedure. A lock reads the code by induced currents in coils. After one turn of the key, the embedded information is read.
It is possible to produce flne actuation by controlling an electric field through a coil that is attached to a rod prepared by 3D-stereo}ithography using magnetic particles in the polymer precursor fluid. A rod with complex information embedded in it by virtue of the placement of hardened tiny magnets in the resin is first prepared using the method described herein. The rod is then connected to a variable ,~ i voltage source. Each time the coil current changes, the rod mo~es in a controlled fashio~.
; Liquid crystal molecules (for example, ferroelectrics, choles~erics, nema~tics (nematogens), smetics, etc.) liquid crystal like molecules or aggregates can be aligned and trapped in resin for display or light piping applications.
~ No~linear optically active compounds such as noncèntrosymmetric molecules or block polymers, graft "I

W093t~0993 ~ 0 2 1 PCT/US93/03 ~,.~. .
, .
, -24- i ~ i :~ polymers, or copolymers can be frozen in a controlled way 3-, dimensionally, allowing very complex integrated optics to be prepared, with horizontal as well as vertical light~piping 3 ~ and light modulation capabilities.
'';!, 5 Figure 3 is an illustration of one apparatus for high pressure three-dimensional stereolithography that includes a means for imposition of electric or magnetic fields to align magnetic particles dispersed in the polymeric precursor fluid. Polymer precursor fluid 32 that contains magnetic particles or ferroelectric li~uid crystals is irradiated with an ultraviolet laser beam 34 between electrodes or magnets 36 and 38 to provide an object 40 that sits on platform 42.
-Hydrostatic pressure is imposed by means of pump 44, and elevated temperature is provided by heating means 46. The upper limit of the electric field is the breakdown strength of the fluid, typically in the range of 1 MV/cm. The upper limit of the magnetic field is the limit of ~he available r!~ electromagnet. Large electromagnets such as t~ose used in nuclear magnetic resonance can pro~ide a very ~trong magnetic ~ield. The field can be pulsed in a controlled fashion or reversed as desired. It can also be crossed or rotated. The resulting object can have regions that are magnetized and ; regions that are not maynetized.
The electric or magnetic field can be imposed in a 25 horizontal fashion as~well as in a ver~icle fashion. In additian, the particles in the object can be aligned differently, depending on when the field is turned on or off or rever ed. As clear from the deæcription herein, since high pressure three-dimensional stereolithography can 30 ;! accommodate the inclusion of filler, additives, or m~gnetic particles in ~he object, this techni~ue can be used to produce real parts, not just models or pro~otypes. In ; addition, it can produce parts that serve ac~ive functions, ~ such as motion control and~light guiding.

.3~
A¦
:'1,~ . `

Og3/20993 ~ 0 2 1 PCT/US93/03 , ~iphasic or Mul~iphasic Vat Fluid In another alternati~e embodiment, an immiscible fluid (inert fluid) can be used in the high pressure vat to conserve polymer precursor fluid and to function as hydraulic fluid for system pressurization. The inert material is typically at the bottom of the vat, as illustrated in Figures 4 and 5.
,~ The inert material should be immiscible with the W
} curable material, and have an intermediate density between the uncured and cured W -curable material. Upon curing, the cured fluid (now a polymer), becomes hea~ier (denser) than the inert material. Since the laser is typically focused ! - through a quartz or sapphire window on top of the closed and ~$, pressurized vessel, the inert material does not have to be UV
i 15 tran~pare~t. A membrane separating the two fluids, such as that disclosed in U.S. Patent No. 5,011,635, is not necessary , in this system. If the inert material is transparent, the W
irradia~ion can shine up from the bottom of the va~, as illustrated in Figure 6.
Silicones and fluoromers ~fluorocarbons or fluorocarbon liquids) are ideal candidates for the inert fluid. The density of these materials is greater than monomers or precursors of polymers, but lower than dead polymer (finished polymers). The buoyancy effect experienced by the part as it de3cends into the inert fluid keeps it from deforming (sagging) under gravity. Nonlimiting examples are perfluorinated alkanes and PF~. Fluorofluids are sold by E.
I. du Pont de NeMours and Company and Minnesota Mining and Manufacturing Company. 5ilicone fluids include 30~l polyd~methylsiloxane oligomers, and aromatic and allphatic siloxanes. Huls Corporation manufactures a complete line of silicone fluids.
The inert fluid can also be water, glycerol, glycol, alcohol or fluorinated derivatives of these liquids.
~ 35 The inert fluid serves at least three additional `~ important functions: it~scrubs ~he greenbody of excess ~ material (unpolymerized ma~erial clinging to the greenbody), J

~$
~ ' :

W093/20993 ~ ~t ~ PCT/US93/03 ~?, it transmits the high imposed pressure, and it physically separates the pump from the polymer precursor fluid. Since the va~ may be under elevated pressure due to a duct work ;~ attached to the vessel, the duct can be physically separated S from the polymer precursor material, preventing clogging. If i-W -curable fluid is in the pump duct~, even stray light may trigger enough undesirable polymerization to clog the opening.
FIG. ~ is a cross sectional illustration of one type of apparatus for high pressure three-dimensional stereolithography that includes a biphasic vat fluid.
Polymex precursor fluid 48 floats above the inert fluid 50 in -the pressurized reaction vat 52. A means 54 for elevating the hydrostatic pressure in the vat, typically a pump, is ~:~ 15 attached to the vat below the interface of the two fluids 56.
The polymer initiating:source~58 is transmitted through a window 60. The initiating'source 58, typically an ultraviolet radiation laser, writes a pattern in the layer of precursor fluid close to~the top:surface of the pool. Once a layer~is finished, an actuator mechanism 62 lowers the imaged polymerized layer (which now has a density that is higher than the inert fluid) into the inert fluid 50. Fresh , ~ (une~posed) precursor fluid 52 is then floated on top of the ,t ~ imaged layer at the interface of the two fluids. The process ~! ~ 25 is then repeated and a new pattern is thus overlaid.
;:: Repeated usage af the laser in combination with platform ;,' ; lowering gradually builds up a complex 3-dimensional s~ructure 64 on platform~ ~t6 wherein the final par~ is constructed of successi~e layers of rigidized images, and i~
31' 310! ~ submerged in the inert ~luid 50. ;The i'nert fluid SO scrubs `' the u~reacted fluld 48 drains~ off the part (greenbody).
In Figures 1-6, polymer precursor ~luid, inert fluid and ; gas or light fluid~are added~and removed as desired ~hrough `l ~ appropriately:placed ducts in the:apparatus, not illustrated.
!~ ```.,35 ~ ~Flgure 5 is~a,cross~ectional illustratian of an ~,: ~ apparatus for high pressure three-dimensional , ~ stereolithography~that includes a triphasic ~at fluidJ that i.
-:~ ,~

; " W093~20993 ~ o~ PCT/US93/035 !~ includes a lower ~luid that is inert, a next layer of polymer precursor fluid 70, and an upper gaseous or light fluid phase 72 that is W-transparent but immiscible with the polymer precursor fluid. A means 74 for elevating the hydrostatic pressure in the vat, txpically a pump, is attached to the vat below the polymer precursor fluid 70. The polymer initiating source 76 is transmitted through a window 78. The initiating source 76, typically an ultraviolet radiation laser, writes a . pattern in the layer of precursor ~luid close to the top surface of the pool. Once a layer is finished, an actuator , mechanism 80 lowers the imaged polymerized layer (which now has a density that is higher than the inert fluid) into the j _inert fluid 68. Fresh (unexposed) precursor fluid 70 is then floated on top of the imaged layer at the inter~ace of the two fluids. The process is then repeated and a new pattern is thus overlaid. Repeated usage of the laser in combination with platform lowering gradu~lly builds up a complex 3-dimensional structure 82 on ~latform 8~ wherein the final part is constructed of succ~ssive layers of rigidized images, a~d is ~ubmerged ln the inert fluid 68. The i~ert fluid 68 scrubs the unreacted fluid 7C drains off the part (greenbody).
Figure 6 is a cros~ sectional illustration of an apparatus ~or high pressuxe three-dimensional stereolithography that includes a tripha~ic vat fluid, that i~cludes a lower hydraulic fluid 88 that is inert and W-l transparent, a next layer of polymer precursor fluid 90, and 7 an upper gaseous or light fluid phase 92 that is immiscible ~!, with the polymer precursor fluid, and wherein ~he part is " ! ~0' i puIle~l Up out of the~polym~èr precursor fluid. A means 9~ for ~levating the hydrostatic pressure in the ~at, ~ypically a pump, is attached to the vat below the polymer precursor fluid 90. The polymer initiating source 96 is tra~smitted through a window~98. The initiating source 96, typically an ultravioIet radiation laser, writes a pattern i~ the layer o~
precursor fluid close to the bottom sur~ace of the pool on ~ platform 104. Once a layer is finished, an actuator ,.
i W093/~0993 ~ PCT/US93/03 mechanism 100 raises the imaged polymerized layer. Fresh ~, (unexposed) precursor fluid 90 is then floated on top of the imaged layer at the inter~ace of the two fluids. The process is then repeated and a new pat~ern is thus overlaid.
Repeated usage of the laser in combination with platform raising gradually builds up a complex 3-dimensional structure ~U2 on platform 104.

II. Praparatio~ of Objects u~ing Three Dimen ional Stereolithography that inclu~e~ the Seque~tial Polymerizatio~ of Polymer Precur~or Flu~d In an alternative embodiment, large scale, mini, and ~microstructures are prepared by three dimensional stereolithography in which the polymer precursor fluid is polymerized sequentially to reduce structure distortion caused by stress within and between layers. This method reduces curl distortion during the polymerization process.
The se~uential polymerization modification of the three dimensional stere~lithographic process can be carried out at ambient temperature and pressure, or at elevated pressure, elevated temperature, or elevated pressure and temperature.
The parameters and reaction con~itions described in Section I. apply to the method disclosed in Section II., including when perfQrmed under ambient conditions.
The sequen~ial polymerization technique is taught in general in U.S. Patent Nos. S,110,514 and 5,114,632 filed by David S. Soane. The sequential polymerization method minimizes stres~ and cavitation, or voids caused by the shrinkage of material durlng polymerization, tha would otherwise cause locked-in stress and decrease replication ~idelity. Stress in local polymerized re~ions of the object is mi~imized using this technique, because as the ;~ ~polymerization occurs sequentially within each layer, more polymer precursor fluid`quickly enters the irradiated area ~o repleni~h the instantaneous volume lost to polymerization ind~ced shrinkage. E~en though the ~low may be microscopic in quantity, the e~fect is profound, as intra and inter layer W093~20~93 ~ 8 ~ 2 1 PCT/US93/03~W

stress are minimi~ed or eliminated. The additional polymer ~ precursor fluid ~uickly polymerizes in the void space of the I irradiated region resulting from shrinkage. This is j i.llustrated in Figure 12, which provides a magnified ~iew of ¦ 5 a local region of the precursor fluid pool being irradiated Z by a W mercury lamp.
~ The se~uential polymerization process is easily adapted ¦ to either radiation or thermal curing. Radiation curing is preferred because it is more controllable, and in general re~uires a shorter cure time. Radiation curing can be ~ performed at moderately elevated temperatures to further il reduce polymerization time.
- A moving front of polymerization initiating source, typically W irradiation, can be accomplished by use of any appropriate means. In one embodiment, a sequentially moving ~ slit system (SMSS) is used, wherein a thiIl slit (typically ;~ between 1 ~m and 10 mm) of irradiation se~uentially passes over the polymer precursor fluid in such a manner that the material ahead of the moving polymer zone remains li~uid, and the material that the front has passed is solidified. In another method, the moving front is the radial opening of an '~ iris diaphragm. The still-liquid material ahead of the moving pol~mer zone flows freely, at a rate that equals the rate of shrinkage, and a distortion-free, reduced stress pol~meric network is produced.
Figure 9a is a schematic cross-sectional illustration of '¦ one apparatus for the preparation of objects by three-dimensional stereoIithography wherein the polymer precurssr fluid is sequentially polymerized (V1 is a first valve, V2 is '30l a second valve, SV1 is a first solenoid valve, SV2 is a second solenoid ~alve, and Q1 and Q2 are quick con~ects). This example is ~ot intended to limit the scope of the invention.
Other apparatus designs can be easily constructed using the ~3 35 methods disclosed herein, and all o~ these are considered to fall wlthin this invention ~;
i ;

2~ 2~ ' W~g3/20993 PCr/~S93/03 ~ As indicated in Figure 9a, data 110 is fed into a ¦ computer 120 to establish a C~D file for the desired object, which is converted mathematically into stacked cross-sections, or layers. The computer 120 in~erfaces with control box 130 that controls the operation of solenoid valve 160, solenoid valve 170, a~stepping motor 270, and an electronic shutter 220. Second solenoid valve 170 allows the release of pressure from the system as desired. Inert gas is fed through tube 155 (which has a quick connect joint 190, through valve 150 and solenoid valve 160, past quick connect 170 in~o reaction vat 205.
An elevator 260 controlled by stepping motor 270 is connected to platform 2I5. A thin layer of polymer precursor fluid 235 is introduced into the reaction vat 205 between platform 215 and W transparent window ~00 from tube 140 past valve 145. Valve 14S can be interfaced with computer ~20 through control box 130 as desired.
~: Power supply 250 feeds the W lamp ~30. The power of W
lamp typically ranges from hundreds to thousands of Wat~s.
W light from W lamp 230 is reflected o`ff mirror 240 through electronic shutter 220. The W light is then passed se~uentially through a photomask to the thin layer o~ polymer : precursor fluid. The means for moving the light sequentially 245 is located at any appropriate place between the point at which the W light is reflected off of the mirror, and the photomask 210. Two examples of means for sequential light : moveme~t, the sequentially moving slit system, and the iris diaphra~m, are illustrated in detail in Figures 10 and il.
. The photomask is located at a point between the means 30! for~3equential~1ight mo~ement 245, and~the polymer precursor;' fluid 235, and preferably, between the electronic shutter 220 .
and the transparent window 200. Any photomask ~ystem known :; to those skilled in the art can be used in this apparatus.
~: As~an~example, U.S. Patent Nos. 5~,157,423 and 5,139,338 : disclose a photomask system in which a CAD slice of an object is~transferred~from the::computer to a mask generator, which : operates 1ike a photocopier: a negative image of the cr~ss `` : W093/20993 ~ U~ ~ PCT/U~93/03 section is produced on a glass mask plate by charging portions of the sur~ace and ~developing~ the electrostatic image with toner powder. In another embodiment, negative slice images are transmitted directly to the polymer surface using a flat array of backlighted liquid crystals under individual control. Alternatively, the use of ~ sequentially moving slit system allows the "dot matrix' ~ype of programmable mask to be adopted. The photomask can be achieved by pixel reflectors actuated by piezoelectricity, as tiny de~lections are sufficient to darken/lighten the intended spots. As the sequential polymerization progresses, the slit-like mask is synchronously altered by si~ultaneously swi~ching on and off the in-line pixels.
In another embodiment, microbubble technology used in ink-jet printing is used to create the photomask.
Microelectrodes can be positioned in a liquid filled cylinder, and light pas~ed through the cylinder while the electrodes are heated. Upon transient heating, bubbles form at selected sites, and diffuse light tra~e~s through the cylindrical lens. The bubble spots correspond to dark, or unfocused pixels. The combination of dark and light spots forms the photomask image.
W light is passed through~the photomask 210 sequenti~lly to create the appropriate light pattern on the thin polymer precursor layer to provide a polymeric layer of desired shape. Once the layer is finished, the elevator 260 moves the imaged layer tha~ sits on elevator platform ~15 by a differential amount, allowi~g fresh (unexposed) precursor fluid to cover the underlying written layer. The process is 3!0l then~isuccessively repeated and new patterns o~erlaid, untilia complex 3-dimensional structure is pro~ided that is constructed o~ the successive layers of rigidized images.
This system, which integrates the concepts of sequential poly~merization with the~three dimensional stereolithographic process, provides an object with minimal stress and dimensional distortion.

W~93/20~93 -~ 2 ~ PCT/U~93/0 In this method, the polymer precursor fluid can be pro~ided as a very thin layer, alone or over an inert immiscible layer. The method has the advantage of limitlng layer thickness directly rather than relying solely upon W
~ 5 damping due to absorption to limit the depth of curing.
$ Ideally, an ultra thin laminae is provided. The ability to produce an ultra-thin laminae depends on the viscosity of the polymer precursor fluid and its tendency to spread out between the transparent window and the elevator plat~orm.
The use of elevated pressure and elevated temperature in the . process lowers the viscosity of the polymeric precursor fluid, facilitating this process.
Using this method, objects can be prepared that include layers that vary in physical properties. ~s an example, the first several polymeric layers can be constructed of a so~t, impact-resistant material, and successive layers formed from a hard thermoplastic material.
Figure 9b is a top view of the apparatus illustrated in Figure 9a, with additional valve ports for the introduction 2Q and removal of varying pol~mer precursor fluids, and a side ; view of the apparatus that illustrates a means for vacuum removal of the remaining pol~mer precursor fluid from the transparent plate. This apparatus embodiment can be used to ; prepare three dimensional objects from layers of differing pol~mer precu~sor fluids. As indicated, control box 130 signals the opening~of the desired valve (V1 and V3 through Vn) to provide a layer of first polymer precursox fluid between the tra~sparent plate and the platform. The IR
sensor sends a signal to the control box to close the valve 3!0! whenla~desired ~luid thic~ness~ has been acheived. The !
platform is then lowered to the fluid sur~ace, a~d the fluid cured in the desired~pattern. The platform is then moved an `~ appropriate~distance, and the vacuum wiper transverses the ` transparent plate to remove residual fluid. These steps are 35~ then repeated with a~second polymer precursor fluid, followed by other polymer precursor fluids, as re~uired.
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W~93/209~3 PCT/US93/035~

Figure 10 is a partial cross-sectional illustration of an apparatus for the production of a three-dimensional object that includes a sequentially moving slit system (SMSS). As indicated, ~he apparatus includes a movable and adjustable slit 280, a stepping motor 290 to control the speed of slit movement, an electric shutter 220, and a control box 130 that interfaces the stepping motor 290 and other programmable pieces, as described above in Figure 9, to a computer. The slit size can be varied a~cording to the type of polymer precursor fluid used. The mo~ing speed of the W light slit is dictated by the curing time of the polymer precursor fluid, typically between 2 and 30 seconds. In a typical run, _ the electronic shutter 220 opens, and the slit starts moving from one side of the photomask 210 to the other side. On completion of the sequential curing, the electronic shu~tter is closed. As described abo~e, once the layer is finished, the elevator 260 moves the imaged layer ~hat sits on elevator plat`form 215 by a differential amount, a~lowing fresh (unexpo~ed) precursor fluid to cover the underlying written layer.
Figure 11 is a partial cros~-sectional illustration of an apparatus for the production of a three-dimensional object in which sequentiaI polymeriza~ion is accomplished with a computerized iris diaphragm (CID~. The apparatus includes an iris diaphra~m 300, a computer controlled rotation stage 310, an electronic shut~er 22Q, and a control box 130 that i~ter~aces the rotation stage 310~, electronic shutter 220.
and other programmable pieces, as indicated in Figure 9, to a computer. The iris diaphragm is useful for the smooth cohtrol of a~Eadia~lly expanding or contracting beam of radiation, while keeping the energy per unit area constant.
~` The rotational stage is used to rotate the iris ~iaphragm, if ;` the iris diaphragm is not automated. The electronic shutter ~is opened first, and then the iris diaphrasm is opened at a .
35 ~ ~ desired rate. Af~er completion of cure, the electronic shutter is closed. The process is then repeated until the three dimensional object is constructed.
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W093/~0993 2 1 1 8 ~ 1 PCT/~S93/03~ t-Figure 13 is a schema~ic illustra~ion of an apparatus for efficient release of an object fonmed by three dimensional stereolithography from the transparent plate to which it may become attached. The tra~sparent plate is modified to have rises a~d depressions, and the depressions are filled with a so~t material that has a refractive index that matches that of the transparent plate, or alternatively, are filled with air. Figure 13 provides illustrations of two types of modi~ied transparent plate lp surfaces, a grid surface and a dotted surface. Other patterns can also be used to modify ~he surface as desired.
A tape that has an adhesive side and a nonadhesive side is positioned over the glass plate in such a manner that the adhesive side of the tape is attached to the mcdified surface of the transparent plate and the nonadhesive side of theltape interfaces with the polymer precursor fluid a~d the object prepared from the fluid. When the object has been completed, it can easily be separated from the nonadhesive tape surface, that is flexible due to the cushioned effect of the soft ~illing or air in the modified transparent plate.
An example of a suitable transparent tape for quick release of the object from the transparent plate is T flon-FEP, manufactured by E.I. DuPont NeMours and Company.
One side of the Teflon-~EP film has a pressure sensitive ~25 adhesive, so that it is easy to apply to the plate. The ~ elastic deformation of the soft material triggers ~acuum ; releaiie. CHR Inc. sells Teflon-FEP under the catalog name "C", and also sells other suitable transparent polyester tapes, i~cluding M52, M60, M69, and M56.

i 30 III. Prepara~io~ o ~icro and ~i~istructure~ for ~ 1croe1ectronic Applications Using the three dimensional stereolithographic methods disclosed herein,~high precision micro and ministructures can be prepared that are suitable for microelec~ronic 35~ applications. Examples of specl~1c structures that can be :
I ` W0~3/2~99~ 0 2 1 PCT~ US93/03~

made using these techniques include magnetic micromotors, toroidal transfonmers, metal flexure actuators, pressure transducers, microturbines, and intermeshing microcoils.
Mini and microstructures for micxoelectronics can be prepared using the methods disclosed herein that exhibit the precision of structures prepared using the LIGA or SLIGA
techni~ues. As illustrated in Figure 14, after a high precision plastic mold is completed, it is removed from the vat and electroplated, typically with nickel. The plastic mold is then removed and free metal structure i5 cast.
This technique can provide structures of highly complex shapes. The process is more flexible than the LIGA and SLIGA
techni~les because photomask generation through the use of CAD programs is easy and fully automated. Figure 9 is an lS illustration of complex structures that can be prepared using this ~echnique, incl~lding half domes, cones and pyramids. As the number of layers used to build the structure increases, the ~moothne~s of the surface increases. Fig 16 is an illustration of a tapered honeycomb shape that can be built using this process. The tapered honeycomb is useful in the area of bio-separation.
The mold building process disclosed herein represents a significant improvement over the LIGA and SLIGA techniques, in that 1) there is no need for x-ray irra~iation; 2) no alignment is re~uired (in SLIGA, the x-ray mask m~st be geometrically aligned to the patterned sacrificial layer and the pxocessed substrate~; 3) mold building time is reduced dramatica}ly; 4~ the mold design is simplified due to automatic photomask generation hy CAD; 6) there is no ' !30 struCtural height limit; 7) the mold can have complex sidewall profiles and can be made of several materials in successive layers.
This invention~has been described with reference to its preferred embodiments. Variations and modifications of the ~ 3~5 invention described hexein wiil be obvious to those skilled ¦~ in the art from the foregoing detailed description of ~he ~ invention. It is intended that all of these variations and .~

W093/20993 PCT~U~93/03~ -C~ 3 0 2 1 , , -modifications be included within the scope of the appended claims.

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Claims

We claim:
1. In the method for producing a three-dimensional object stereolithographically from a polymer precursor fluid capable of solidification on exposure to a polymerization initiating source, the improvement which comprises closing the vat to the outside environment, and imposing an elevated pressure and temperature in the vat.
2. The improvement of claim 1, wherein the imposed pressure ranges from slightly above ambient pressure to 100,000 psi.
3. The improvement of claim 1, wherein the imposed pressure ranges between 5,000 and 8,000 psi.
4. The improvement of claim 1, wherein the imposed temperature in the vat ranges from 30 degrees C to 300 degrees C.
5. The improvement of claim 1, wherein the polymer initiating source is ultraviolet radiation.
6. The improvement of claim 1, wherein the polymer precursor fluid has a viscosity of greater than methacrylate or acrylate monomers.
7. The improvement of claim 1, wherein the viscous polymer precursor fluid comprises a thermosetting fluid.
8. The improvement of claim 1, wherein the polymer precursor fluid includes an inert polymer.
9. The improvement of claim 1, wherein the polymer precursor fluid includes inert polymer.
11. The improvement of claim 1, wherein the polymer precursor fluid includes a nonpolymeric inert material.
12. The improvement of claim 11, wherein the nonpolymeric inert material is selected from the group consisting of CaCO3 and MgCO3, clay, borates, sulfates, phosphates, diatomaceous earth such as celite and silica flour, alumina, colloidal silica, and zeolite solids.
13. The improvement of claim 1, wherein the polymeric precursor fluid includes colloidal particles.
14. The improvement of claim 13, wherein the colloidal particles are selected from the group consisting of colloidal gold, titanium oxide, ferric oxides (magnetic), cobalt, molybdenum oxide, vanadium oxide, nickel, alloys, transition metal-rare earth complexes, silicon dioxide, silicon nitride, germanium oxide, silicon atom clusters, gallium arsenide, and other semiconducting particles.
15. The improvement of claim 1, wherein the polymer precursor fluid includes organic crosslinked beads.
16. The improvement of claim 1, wherein the polymer precursor fluid includes magnetic particles.
17. The improvement of claim 16, wherein the during formation of the 3-dimensional object, magnetic particles are aligned such that tiny magnetized regions are formed.
18. The improvement of claim 17, wherein magnetic particles are aligned to form tiny motors, actuators, or sensors.
19. The improvement of claim 1, wherein the polymeric precursor fluid includes a liquid crystal or liquid crystal aggregate.
20. An apparatus for the production of objects by high pressure three-dimensional stereolithography that includes:
a polymer precursor fluid that is capable of being transformed into a solid, polymeric object on exposure to a polymerization initiating source;
a reaction vat in which the polymer precursor fluid is contained, through which the polymerization initiating source is transmitted;
a polymerization initiating source that is transmitted through the vat;
a platform on which the object rests;
an actuator means to move the object as necessary; and a means for moving the polymer initiating source sequentially across the polymer precursor fluid.
21. The apparatus of claim 20, wherein the reaction vat is closed to the outside environment.
22. The apparatus of claim 21, further comprising a means to impose pressure in the vat.
23. The apparatus of claim 20, further comprising a means to elevate the temperature in the vat.
24. The apparatus of claim 20, wherein the means for moving the polymerization initiating source sequentially across the polymer precursor fluid is an iris diaphragm.
25. The apparatus of claim 20, wherein the means for moving the polymerization initiating source sequentially across the polymer precursor fluid is a sequentially moving slit system.
26. The apparatus of claim 20, further comprising a photomask that images the polymerization initiating source such that the polymer precursor fluid is polymerized in a desired pattern.
28. The apparatus of claim 26, wherein the photomask image is generated by piezoelectricity.
29. The apparatus of claim 26, wherein the photomask image is generated by microbubbles.