CA2045216A1

CA2045216A1 - Method and apparatus for fabricating three dimensional objects from photoformed precursor sheets

Info

Publication number: CA2045216A1
Application number: CA002045216A
Authority: CA
Inventors: Eustathios Vassiliou; John A. Lawton
Original assignee: Individual
Current assignee: EIDP Inc
Priority date: 1990-06-26
Filing date: 1991-06-21
Publication date: 1991-12-27
Also published as: CN1031114C; US5094935A; DE69113342T2; AU7928291A; EP0467097A1; DE69113342D1; KR0128666B1; EP0467097B1; JPH0780245B2; CN1057723A; KR920000463A; JPH05237941A

Abstract

ABSTRACT

An imaging method and apparatus produces an integral three-dimensional object from a multiplicity of cross sectional portions of the object. The cross sectional portions correspond to photohardened portions of contiguous photoformed precursor sheets of a photohardenable liquid composition.

Description

20~5~

METHOD AND APP~RATUS FOR FABRICATING THREE DIMENSIONAL
OBJECT5 FROM PHOTOFO~MED PRECURSOR SHEETS

BAC~GROUND OF THE IEYE~

1. Field of the invention:
.

This invention pertains to a method and apparatus for fabricating an integral three-di~ension~l ob~ect from a multiplicity of cross 6ectional portions of the ob~ect.
The cross sectional portions correspond to photohardened portions of contiguous photoformed precursor sheet~ o~ a photohardenable liquid composition.

2~ Des~ription of Related Art:

Many systems ~or production of three-dimensional modeling by photohardening have been propo~ed. European Patent Appl~ca~ion No. 250,121 fil~d by 8citex Corporation Ltd., on ~une 5, 1987~ disGlos~s a three-dimensional modeling apparatus u~ing a ~olidi~able liquid, and provides a good ummary o~ documents pertinent to this art. U.S. Patent No. 4,575t330, issued to C. W. Hull on March 1~, 1986, describes a system for ~enerating three-dimen~onal objects by creating a cross-sectional patt~rn of the ob~ect t~ be formed at a ~elected surace of a ~luid medium capable of altering its physical state in re~ponse to appropriate ~ynargistic stimulation by impinging radiation, particle bombardment or chemical reaction.
Successive adjacent laminae, representing ~orresponding successive adjacent cross-sectlon~ of the object, are automatically formed and integrated together to provide a step-wise laminar buildup o~ th2 desired object, whereby a three-dimensional ob~ect is formed and drawn from a substantially planar surface of the fluid m~dium during the forming process. V.S. Patent 4,752,498, issued to E. V. Fudim on June 21, 1988, describes an improved me~hod o~ forming th:ree-di~ensional obj~cts, which ccmprises irradiating a~ uncured photopolymer by transmitting ~n ef~ective ~mount oP photapolymer solidifying radiation through a~ radiation transmitting material which is in contact ~with the uncured liquid photopolymer. The transmittinq mat~rial is a material which leaves the irradiated surface ~apable o~ further crosslinking ~o that when ~ubsequent layer i~ formed it will adhere thereto. Using th~s method, ~ultilayer objects can be made. U.S. Patent ~,~01,477, issued also to Fudim on Jan. 31, 1989, ~ention is made of a light guide, which may be mad~ of material containlng copper, oxygen, or other ingredients that m~y inhibit photopolymer cro~s linking.

A publication entitled s'Automatic ~e~hod for fabricaking a three-dimensional plastic model with photohardening polymer" by Hideo Kodama, RevO Sci~ Instrum. 52(11), 1770-17~3, Nov. lg81, describes a method for automatic ~abrication of a three-dimensional plastic nodel. The solid model i~ fa~ricated by expo~ing liquid photohardening polymer to ultraviolet rays, and stacking the CrO55 ectional solidified layers.
publication enti~led "Solid Object G~nera~ion" by ~lan J
Herbert, Journal o~ Applied Photographic Engineering, 8(4), 185 1~8, Aug. 1982, describes an appara~us which ;~

2(1~ 6 can produce a replica of a solid or three-dimensional object much as a photocopier i~ capable of performing the same task ~or a two-dimensional object. The apparatus is capable oP generating, in photopol~mer, simple three-dimensional object~s from informatioJl f tored in computer memory. ~ good revi~w of the different methods ~s also give~ ~y a most recent publication entitled "A review o~ 3D Solid Object Generation" by A.
J. Herbert, Jour~al of Imaging Technology 15: 186-lgO
(1989).

Most of these approaches relate to the formation of solid ~ectors of three-dimensional ob~ects in steps by sequential irradiation of area~ or volumes sought to be solidified. Various masking techniques are descr~bed as well as the use o~ direct laser writ~ng, ire., exposlng a photohardenable composition with a laser beam according to a desired pattern and building a three-dimensional model, layer by lay~r~ In a~dition to various exposure te~hniques, several ~ethods of creating ~hin liquid layers are described ~hich allow both coating a platform ini~ially and coating ~uccessive - layers previously exposed and solidified.

The aforemen~ioned ~ethods of f oating, however, are not capable of ensuring flat uni~orm lay~r thickne~s or of producing such layers quickly, or they do not eff~ctively prevent damage or dist~rtlon to previo~sly formed layers during ~he successive ~oa~ing proce~s and they involve coating only liquid ~formulations of preferably low viscosity. Furthermore, they omi~ to recogni2e very important parameter~ involved in the coating process such as the ~ffects of having bo~h solid and liquid regions present during the formation of the thin liquid layersf the effects of $1uid flow and rheological characteristic of ~he li~lid, the tendency for thin photohardened layers to sasily become distorted by fluid flow during coating, and the effects of weak forces such as hydrogen bonds and substantially ~kronger ~orce~ such as mechanical bonds and vacuum or pressure differential forces on those thin layers and on the part being formed.

The Hull patent, for examplle, describe~ a dipping process where a plat~orm is dip~ped below the distance of one layer in a vat, then brought up to wlthin one layer thickness o~ the ~ur~ac~ o~ the photohardenable liquid. Hull further ~uggests that low viscos~ty liquids are preferab1e but, for other pr~ctical reasons, the photohardenable liquids are generally high v1scosity liquids. Motion of the platform and parts, which have cantilevered or beam regions (unsupported in the Z
direction by previous layer ~ections) within the liquid, creates deflections in the layers, contributing to a lack of tolerance in the fini hed part. In addition, this method is rather slow.
:
U.S. Patent No. 2,775,758, issued to 0. J. ~unz on December 25, 1956, and the Scitex application describe ~5 methods by which the photohardenable liquid is introduced into a vat by means o~ a pump or similsr apparatus such that the new liguid lev~l ~ur~ace ~orms in one layer thickness over the previously ~xposed layers. Such methods have the aforementioned disadvantag~s 3f the ~ull l~ethod ~xc:ept that the deflection of the layers during coating is rQduced.

The patent issued to Fudim describes the use of a transmitting ~aterial to fix the surface of a photopolymer liquid to a desired shape, assumably flat, 2~L~
through which photopolymer~ of de~ir~ ~hickn~s~ are solidified. The transmitting material i~ usually rigid and either coated or inherently non-adherent to the solidified photopoly~er. The ~ethods describ~d by Fudim do not address the probl~ms inherent in ~parating ~uch a transmitting material fro~ a photopolymer formed in intimate contact with the surface of the transmitting material. Whereas the effects of chemical bonding may be reduced ~ignificantly by suitable coatings or inherently ~uitable films, the mechanical bonds ~lon~
with hydrogen bonds, vacuum Porces, and the like are still present and in some cas~s substantial enough to cause damage or disto~tion to the photopolymer during removal from the transmitting mat~rial ~urface.
Fabrication of three-dimensional object~ iro~ sheets o~
laminated solid photocurable compositions have been disclosed in the Scitex application, in the Japanese Patent Appli~ation SH0 63-45540 dated February 27, 1988, which was laid open to the public under No ~EI 1-218831 on September 1, 1989, as well as in the International Publication W0 89/11~0 Al, with a Public~tion Date o~
November 30, 1989. There are ~wo serious disadvantages, among others, in using laminated solid films for fabricating three dimensional cbjects. First, the pho~ocuring and adhesion of the layers to ~ach other are difficult since the mQbility Or th~ photoac~ive groups is considerably reduced in a solid structure as compared to the mobility af gimilar groups in a less rigid structure, such as ~or example a ~el or a liquid structure. Second, removal of the rem~ining parts of the laminated ~hee s after photocuring is also dif~icult, due ~o the structural strength a~ well as ~he solvent resistance of these parts, properties nec~ssarily imparted to the sheets in order to w~th tand the conditions of the processes described thereln.

An ~pparatus and method for forming an integral three dimensional ob~ect ~rom laminations is disclosed in U.S.
S Patent 4,752,352, issued to Feygin on June 21, 1988. The apparatus includes a supply station, a work ~tation ~or forming a material into a plurality of lam$nations, ~n assembling station ~or stackin~ the lamlnation~ in sequence, and bonding the laminations to complete the three-dimensional object.

Also, Fudlm in U.S. Patent 4,752,498 diplo~s ~ ~ethod ~o produce complex object~ by treating photopolymers with radiation through a transpar~nt material which lS would pre~erably exclude air, and building separately a number of three dimensional portions or slices, that have two eurfaces which are capable o~ further cross-linking, and attaching the slices together. The slices can be then joined by radiation, preferably in the absence of oxygen and other inhibitors.

SUMMARY oF T~E_INVEN~ON

The present invention provides a ~ethod and apparatus for fabricating an integral threeNdimensional object from a multiplicity of cross ~ectional portions o~ the object. The cross sectional portions correspond to photoh~rdened portion o~ cvntiguou~ photoformed precur or sheets of a photohardenable liquid composition.

More particularly, the instant invention pert~ins to an improved me~hod for ~abrieating an ~n~egral three~
dimensional ~bject by imagewise exposing succe5sive ~ ~5 ~ 6 photohardenable ~heets to actinic rad.iation, said ~ethod including contair~ing a photohardenable liquid composition within a vessel. The improvement in said method comprises:

~a) exposing to ~ctin~c radiation a ~irst ~rea of ~he c~mposition to pho~o~orm a precursor ~;heet;

(b) trans~erring the precursor ;E;heet to a ~econd area of the composition;

(c) exposing lmagewlse the preourcor 6heet to produce photohArdened and non photohard~ned area~:
(d) exposing again to actinic radiation the first area o~ the composition to photoform ~ new precursor sheet;

(e) transferring the new precursor sheet to the second area of the composition on ~op of the previously imagewise exposed precur~or sheet;

(f~ exposing imagewise the new precur~or sheet to also produce photohardened and non photohard~ned areas; and (g) repeating ~eps (d~ through (g) until th2 three dimensional object has been completed~
In more detail, the presant invention i~ direct2d to a method for fabricating an integral thre~-di~ensional object from a multiplicity of cross sectional portions of the ob;ect, the cross ~c~ional por~ions corresponding to photohardened portions of son~iguous ~o~
photoformed precursor s~eets o~ a photohardenable liquid composition, comprising ~he stepls of:

(a) entirely exposing to actinic radiation a ~irst area of the composition adequately to photofo~m a first precursor sheet having high enough integrity to be handled and transferred without being destroyed, but still maintaining the integrity low enough, so that the precursor sheet remains ~ubjec~
to destruction in a disintegrative environment;

(b~ transferring the ~heet to a ~econd area~

(c) imagewi~e expos~ng to acti~c radiation the transferred precursor ~heet in a pattern corresponding to a respectlve cross 6ectional portion of the object, adequately to pho.ohard~n the cros~ s~ctional portion, the ~heet b~ing thus segregated to a photohardened portion and to ~ non-photohardened portion:

(d) ~ntirely exposing to actinic radiation the first area o~ the compo ition adequately to photo~orm a new precursor ~heet having high enough integrity to be handled and tran~erred without being destroyed, but still ~aintaining the integrity low ~nough, 50 that the new precursor sheet remains subject to destruction in a disintegrative environ~ent;
(e) transferring and depositing th~ new ~h~et on the shee~ previously su~jected to ~eps (a) through ~c~;

~f) imagewise ~xposing to actinic radia~ion the ~O~r.i~ L~
n~wly deposited precur~or ~h~ek ln a patt~rn corresponding to another respective cross sectional portion o~ the object, ~dequately to photoharden and connect the photohardened portion to any immediately underlying photohardened portion, the new sheet being also segregat~d to a photohaxdened portion and t~ a ~on-photohardened portion; and (g) repeating steps ~d) through ~) until ail lo cross-sectional p~rtions corre~ponding to the three-dimen~ional object h,ave been completed and connected to each oth~r.

The present invention also pertains to an apparatus for 1~ fabricating an integral three-dimensional ob;ect from a multiplicity o~ cross sectional portion~ oP the ob;ect, the cross sectional portions c:orresponding to photohardened portions of contiguous photoformed precursor sheets of a photohard~nable liquid compositionr comprising:

a fir~ exposure ~lemen~ ~or entirely ~xposing t~
actin1c radiation a first area of the com2osition to photoform a precursor sheet;
means for transferring the precursor sheet from the ~irst area to ~he second area; and a second exposure element for imagewi~e exposing to actinic radiatic~n the precursor sheet in a ~econd area in a pa~tern corr~sponding to the cross sectional portion of the object.

2~52 ~_IEE DESCRIpTION OF THE DRAWINGS

The reader's understanding o~ practical implementat~on of preferred embodiments of the invention will be enhanced by reference to the following detailed description t~ken in conjunction with perusal of the drawing fiyures, wherein:

Figure 1 is a diagrammatic view ~how~ng the pre~erred embodiment of this invention.

Figure 2 ie an elevation view showin~ an alternate preferred embodiment o~ the prese~nt ~nvention.

DETAILED ~ESCRIPTION OF THE PREFERRED EMBODIMEN~S

The pre~ent invention is directed to ~ethod and apparatus for fabricating an integral three-dimensional objec~ from a multiplicity of cross sectional portions of the object. The cross 6ectional portions correspond to photohardened portions o~ contiguous photofonmed precursor sheets of a photohardenable liquid composition. Initially, a precursor sheet 1~ photoform~d by entirely exposing ~o ac:tinic radiation a ~ir~t area of the composition adequately to produce the precursor sheet with high enough integrity to be handled and transferred to a ~econd area without being destroyed, ~ut ~ill with low enough integr~ty, 80 tha~ the precursor sheet remains subject to d~stru~tion in a disintegrative environment. After the ~heet has been transferred to the second area, 1t is imagewise ~xposed to actinic radiation in a pattern corresponding tv the cross sectional portion o~ the object, adequately to photoharden the cross sectional portion. Another sheet lV

is thsn photoformed using the ~ame technigue, and it i~
transferred and deposited on the previously treated precursor shee~. The newly deposited preoursor ~heet is again imagewi~e exposed to actinic radiation in a pattern corre~pondin~ to another respective cross sectional portion o~ the object, adequately ~o be photohardened and be connecte~ to th~ photohardened portion of any immediately underlyin~ photohardened portionO The ~ame procedure is rep~ated until all cross-sectional porti~ns correspond~ng to the three-dimensional object have been .completad and connect~ to each other. The non-photohardened portionæ may then be easily removed by ei~her ~echanical ~eans or by u~e o~
solvents. The precursor sheets may b~ in the for~ of individual pieces being stacked and imayewise exposed one on top of the other, or th~y may be a ~ontinuous sheet, preferably being rolled and imagewisa exposed to actinic radiation during the process of rolling.

Some of the main advantages of the method and apparatus of this invention using precursor sheet as compared ~o the teachings of the related art disclosing use oP
uncured solid shee~s to make three dimensional ob~ects, are:
The precursor sheets (as compared to solid uncured ~heets) are produced in the ~ame apparatus by the ~ame simple ~echnique of photoimaglng, whish is used for photohardening the respective cross sectional portions o~ the three dim~nsional ob~ect.
Thus, separate handling ~nd stocking of ~heets is eliminated.

Since the precur~or ~heats (as compared ~o ~olid uncured sheets) are immediat21y used and minimally handled, they do not have to possess ~trony structural properties, and thu~ they ~nay havQ a very low Tg, which facllitates ~a~ter rate of photohardening and better bonds betw~en photohardened layers.

The method itself of pholto~orming the precursc)r ~heets inherently provides them with at lea~t one of the two sur~aces less photocured than the m~in body o~ the ~heet, 2S ~t will be e~pl~ined hereinbelow, which provides excellent adhesion o~
one ~heet to the other ~t the later photohardened area~, while it still redu~ onsiderably shrinkage and promotes flatness and ~ccuracy~
Since the precursor æheets do not have to po~se~s strong structural properties, th~ir non photohardened portions may be remov~d considerably more easily than the necessarlly structurally stronger uncured parts of the ~heets di~clo~ed in the related art, in order to produce the ~inal three-dimensional object.

Figure 1 i~ a dia~rammatic view showing the preferred embodiment of this invention. There is provided an imaging station 70 includi~g a radiat~on ~ource lO, a modulator 14, ~ computer 34, a fir~t exposure element 16'~ and a ~econd expo~ure element 1~. There is al~o provided a work station ~0. Th~ radiation means 10 is preferably a la~er, producing a rad:latlon beam 12. E~eing desirable to produce ~olid objects at h~gh speed, t~e apparatus of the instant inYentic~n pre~erably utilize relatively high power radii ation ~ans ~Lo, ~uc:h a~ a high power laser, whish may have ~ajor bands in the visible, infrared, or ultraviolet r~yionEi. ~igh pow~r is ~o~
cons.id0red to be a power greater than 20mW, and preferably over 100 mW as mea~ur~d from the intensity of radiation beam 12. The selection o~ a certain type of laser should be coordinated with the selection o~ the photohardenable composition ln a way that the sensitivity of the photohardenable composition agrees reasonably well with the wavelength of the laser's emission. Other types of radiation means may also be utilized such ~s electron beam~;, x-rays, and the l$ke, as long as their energy type ~8 ~atched with the sensitivity of the photohardenable composition, and the appropriate cond.itions ~or the.Lr handling ~re ob~erved according to established ways, well known in th~ art.
Although ~eans may be.provided to modify the shape o~
the beam cross--section to any desirable ~hape, the ordinary shape is circular, and the profile of the intensity of the beam is gaussian with a maximu~ at the center of the circular shape.

The radiation beam 12 passes through the modulator ~, which is preferably an acousto-optical modulator. The modulated radiation beam 12' passes in turn through the second exposure element 16, which compri~es two mirrors 20 and 22, each mirror having an axis ~not shown), allowing reflection of thP beam towards the work station 80 ln the X and Y directions, the X and Y
directions being perpendicular to each other. The mirrors 20 and 22 may rotatably move aroun~ their corresponding axes by ~eans of motors 24 and 26, respectively for controllably de~lecting the beam in a vector s~anning mode, in the X and Y d~rections ~oward~
predetermined positions o~ the work station ~0.

As th~ beam is guided by the seoond exposur~ element 16, it assumes an acceleration from zero level to a maximum acoeleration and a velocity ~rom zero level to a ~axlmum constant velocity. The ve].ocity and the intensity of the beam remain proportional to each other, so that the exposure remains substantially consta~t. The beam 12"
exposes imagewise presele~ted portion~ of a precursor sheet as descxibed below. For the purpo~es of this invention in general, the radiation beam 12l' may be not only a ~ocused beam from a laser, but al60 other light source or light, modified in a number o~ dif~erent way#.
For example, it may be transmitt~d through any type o~
variable optical density phot:oma~k ~uch a~ a liquid crystal di6play, ~ er halide film, electro-deposlted mask etc., or reflected off of any variable optical density device, such as a reflective llguid crystal cell. In that respect, exposura elements 16 and 16' may also comprise or constitute such devices, or they may even be in the form of beams of ~ctinic radiation.
, The function of the ~irst exposure element 16' is to provide aot~nic radiation to a ~irst area 51 of the composi~ion in order to produce a precursor ~heet 48, as it will be explained in more det~il later. Th~ ~econd exposure element 16 can be u~ed by itself to per~orm all ~unctions. However, by using only the ~econd exposure element 16 which is preferably a scanner, the speed of forming the three dimensional. object may be reduced considerably. It is, therefore, advantageous in most occasions ~o use a combina~ion of expo~ure elaments 16, and 16l, especially because th~ ~irst expssure element 16' may provide repeatable and\or con~inuous ~lood exposure. The pre~erred type of ~canning i5 vec~or scanning. However, for the purposes of this invention any other type o~ ~anning may b~ used, 8uch as ~xample raster, helical, and the like. Also any other type of exposing imagewise may be us~d, ~u~h as a variable . 14 ~t3 optical density photomask, and the like.

The work ~tation 80 compris~s a vessel 44 for contain~ng the photohardenabl~ compositlon 40 which presents a ~ree S surf~ce 53. The vessel 44 has preferably a ~hallow segment 44', over which the precursor sheet 48 may be made in a first area 51. A platfor~ 41 h~ving ~n upper surface 41' is disposed within the vessel 44. The position of the platform 41 is controlled by plac~ment means 42. The placement ~eans 42 may be completely immersed in the composition ~O a~ ~hown ln Figure 1 ~or simplicity purpose~, or ~ore prePerably it may be positioned at an ~rea external to the ve~sel 44 and operated through a hent ~upporting arm passing around the top of the vessel in order to ~e connected to and support the platform 41. There are ~lso provided means (not ~hown in the ~igure ~or ~impli~ity purpose~) for transferring the photofor~ed pre~ursor ~heet ~8 ~rom the first area 51 to th~ second area 51'. ~ny conventional device which ~ay gently grab the sheet 43 at the ~rea 51 and gently pull it to the area 51' $~ ~uitable for this purpose. It is desirable to ~a~ntain the contact area o~
the grabbing device with the sheet large enough to avoid tearing o~ the ~heet.
A number of communication lines 50, 52, 54, 58 and 60, are al~o provided ~or the computer 34 to control the modulator 14, the radiation ource lO, the second exposure element 16, the ~ir~t exposure element ~6', and the pla~ement means 4~, respec~ivel~. The ~ans ~or transf~rring the preGursor ~he~t from the ~irst ~o th~
second area are also controlled by the computer 34.
Controlling different components ~nd functions by a computer with data stored in the computer is a conventional and well known art.

~S~6 In operation o~ the preferred embodiment of this invention, the first exposure element 16' ~ntirely exposes to actinic radiation the ~irst area 51 o the S composition adequately to produce a first precursor sheet 48 in a way that the ~heet ha~ high enough integrity to be handled and transferred to the second area 51' without being destroyed, but ~till maintain~ng the integrity o~ the ~heet low enough, ~o that the precursor ~heet rema$ns sub~ect to de~truction in a disintegrative environment. ~h.is condition i important 50 that at a later ~tage, part o~ the ~heet 48 may be removed easily, while initially it may 6till be gently handled without damage during the tra~s~er process to the second area 5~'. Optimizat~on o~ the desired structural properties of the prscursor ~heet 48 ~5 a very simple matter of coordinating ~he characteristics o~ the composition 40 with the exposure.

The fir t precursor s~eet 48 i~ ~hen trans~erred to the ~econd area 51', where it i~ deposited on the upper sur~ace 41t o~ the platform 41. The upper surface 41~ of the platform 41, and also the ~econd area 51' are pre~erably at this point in the vicinity of the ~ree ~urface 53 of the composition 40. The t~rm "vicinity of the free surface'l denote~ the region contained within the thickness of one ~heet a~ove and one ~heet below the free surface 53, with preference to th~ region above the free sur~ace. After the ~h~et ~8 has been deposit~d on the upper sur~ace 41' of the plat~orm 41, it is exposed imagewise to actini~ radiation by the be~m 12" in a p~ttern corresponding to a r~spe~tlve cross ~ect~onal portion of the three dim~nsional ob~ct. The exposure is adequate to photoharden the cross sectional portion, 3S thus segregating the sheet to a photohardened portion 11 and to a non-photohardened portion 11'. The exposure is preferably also high enough to ensure adherence of the photo~ardened portion ~f the first precursor heet to the upper sur~ace 41' o~ th~ plat~orm 41.
Another precursor sheet is photoformed ~n the ~ame manner and deposited on the first precursor sheet, where it is again lmagewise exposed to act~nic radlation by the beam 12" in a patt~rn corresponding to ~noth~r resp~ctive cross sectional portion o~ the object. The exposure i8 ade~uate ~o photoharden and con~ect the photoharden~d portion to ~ny immediately underlying photohaxdened poxtions o~ the previous lay~r. Th~ n~w ~heet is thus al~o ~egregated to a photohard~ned portion and to a non-photohardened portion. In most ~a~es it i~
deslrable that at the same time when a precursor sheet is imagewise photohardened ~n the ~econd position 51l a new precursor ~heet is being ~ormed at the ~irst position 51' for the operation to b~ aster.
The same procedure i~ repeated until all cross-seetional portions corresponding to the three-dimensional object have been completed and connected to each other.

The thr~e dimensional object, beinq a photohardened mass surroun~ed by ~asily removabla non-photohardened por~ions of the precursor ~hests, may be withdrawn ~rom the platform and treated further. The non-photohardened portions may be then rsmoved either by mechanical means, such as brushing, ~ha~ing, mil~ ~anding, blowing of gas, such ~s ~ir or nitrogen for example, or liqu~d~ ~uch as water for example, and the like, or by dissolving them parti~lly or totally in solvents whi~h do not substantially affect the photohardened portions. The selection o~ the solvent or solvent~ depends on the nature of the photohardenable composition, the degree o~
exposure for the photo~ormat:Lon o~ the precursor ~;h~et, ~nd the degree o~ photohardening during the imag~wi6e exposure 6tep. Combination of mechanical means and solvent means is very effective in this respect.

Figure 2 illustrates th2 work ~t~tion 180 o~ a different embodiment of this invention. ~he imaging 6tation is substantially the ~ame as the $~aging statiGn 70 shown ~n Figure 1~ Here allso, there i~ provid~d a vessel lq4 ~or co~taining a photohardenable co~position 140. The wsrk station lB0 comprise~ al~o a roller 141, which is turnable by any conventional ~eans, such a~ a motor, through a 6haPt 149, which ln turn i~ ~ounted at one end o~ a base 145. ~he other end of the base 145 is secured on a supporting bent arm 143, which may be raised or lowered by placement ~eans 142.

The operation of this embodiment is simllar to the operation of the ~mbodiment of Figure 1, except as indicated hereinaPter. A first exposure ~ nt 116', exposes to actinic radiation a first area 151 e~tirely and continuously photo~orm a precursor ~heet, which is continuously pulled and wound around the roller 141.
The roller 141 is positioned by the place~ent means such that part of ~he continuous precursor heet 148 is always present at a second position 151', pref~rably in the vicinity (as ~rlier dPfined) of the free ~urface 153 of the photohardenable compo~ on 140. A~ the ~heet is being rolled on roller 141, it i~ ~lso ~ub~cted to imagewise exposure of act~nlc radiation provided by a la~er ~eam ~12" throu~h a ~econ~ exposur~ e~emen~ 116, in order to be photohardened in a pattern corr~sponding ~o the cross sectional ~onfiguration of the three dimensional object. After photohard¢n~ng o~ the thr~e 5~
dimensional object, the non photohardened portions are removed hy any of the techniques discussed above.

~egardless of whether the precursor sheet ls photoformed S continuously or in segments, one or both types of exposures may be through a 601id transparent element in contact with the photohardenable composition. In guch occasions it is pre~erable that photohardening inhibitlon conditions prevail ~t the interiace of the transparent elemen ~nd the photohardenable composition, in order to avoid adherence o~ the precursor ~heet to the transparent element.

Since ~he exposure to actinic radiat~on decreases with depth due to absorption, ~ca~tering, and other radiation losses, the surface opposite to the one ~rom which the exposure is provided will necessarily be less cured than ~he main body of the precursor sheet during the sheet'~
formation. The decreased cure will be also gradual rather than abrupt, which promotes bett2r blending of one sheet with the nsxt one at a later ~stage of the process, and r~duces localized stresse~, which in turn improves adhesion. If the surface of the ~heet ~rom wh~ch the exposure i~ provided i~ in an environment 2S which tends ~o inhi~it curing or photohardening, then the sheet will have both ~urfaces at a 1~5E~ cured ~ta~us than the main body of the ~heet. ~his i~ even more e~fective in the respect discu~sed above. In the caees where oxygen is an i~h~bitor of the photohardening process, for example from the atmosphere, the precursor sheet photoformed as illustrated in Figures 1 and 2, will have bo~h ~urfaces less cured than the main ~ody of precursor ~heet. ~ost ~ree radical pol~merizat~on~ are inhibited more or less by oxy~en. In the embodiments shown in Figures 1 and 2, the precursor sheet is ~sx~
photoformed in an environment where the surPace of th~
sheet ~rom which the exposure is madl~ ~s 6ub~ect to inhibition from the oxygen in the air, pro~ided the photohardenable composition may be inhibited by oxygen.
The photohardenable compositlons which may be used in the practice o~ ~he pre~;ent invention are any compositions whirh undexyo ~oliclification under exposure to actinic radiation. Such compo~itions comprise usually but not necessarily a photosensitive material and a photoinitiator. The word 'lphotQ~ used her~ to denote not only light, ~ut also any other type o~
actinic radiation which may transform a d~ormable composition, preferably a liquid, to a solld by ~xpo ure to s,uch radiation. Cationic or anionic polymerization, as well as condensation and free radical poly~erization and combinations thereof ar~ examples of such behavior.
Cationic polymerization is pre~erable, and ~ree radical polymerization even more preferable.
One or more monomers may be used in the composition.
Monomers may be mono-, difunctional, tri~unctional or multifunctional acrylates, methacrylates, vinyl, allyl, and the like. They may compriæe other functional and/or pho~osensi~ive groups , such as epoxy, vinyl, isocyanate, urethane, and like, either by themselv~s if they are capable o~ render~ng the ~onomer photoformable, or in ~ddi~ion to acrylates or methacrylat~s. Examples of ~uitable ethyl~nlcally unsaturated monom~rs which can be used ~lone or in combination with o~her monomers include but ~re no~
limited to t-butyl acrylate and methacrylate, 1,5-pen~anediol ~iacrylate and dimethac~ylate, N,N-diethylamînoethyl acrylate and me~a~ryl~t~, ethylene glycol diacrylate and dimethacrylate, 1,4-butanediol . 20 ;~O~LS~6 diacrylate and dimethacrylate, diethylene glycol diacrylate and dimethacrylate, hexa:methylene glycol diacrylate and dimethacrylate, 1,3~propanediol diacrylate and dimethacrylate, decamethylene glycol diacrylate and dimethacrylate, 1,4-cycl~hexanediol diacrylate and dimethacrylate, 2,2-dimethylolpropane diacrylate and dimethacrylate, glycerol diacrylate and dimethacrylate, tripropylene glycol diacrylate ~nd dimethacrylate, qlycerol triacrylate and trimethacrylate, trimethylolpropane tr~acrylate and trimethacrylate, pentaery~hritol triacrylate and trimethacrylate, polyoxyethylated tr~methylolpropana triacrylate and trimethacrylate and similar compounds as disclosed in U.5. Pat. No. 3,380,831, 2,2-di(p-hydroxyphenyl)-propane diacrylate, pentaerythritol tetraacrylate and ~etramethacrylate, 2,2-di-(p-hydroxyphenyl)-propane dimethacrylate, triethy~ene glycol diacrylate, polyoxy~thyl-2,2-di(p-hydroxyphenyl)propane dimethacrylate, di-(3-methacryloxy-2~hydroxypropyl) ether of bisphenol-A, dl-(2-methacryloxyethyl) ether of bisphenol-A, di-(3-acryloxy-2-hydroxypropyl) ether o~
bisphenol-A, di (2-acryloxyethyl) ether of bisphenol~A, di-(3-m~thacryloxy-2-hydroxypropyl) ether of 1,4-butanediol, tr~ethylene glycol di~ethacrylate, polyoxypropyltrimethylol propane triacrylate, butylene glycol diacrylate and dimethacrylate, 1,2,4-butanetri~l triacrylate and trime~hacryla~e, 2 9 2,~-~rimethyl-1,3-p~ntanediol diacrylate and d~methacrylate, 1-ph~nyl ethylene-1,2-dimethacrylate, diallyl ~umarate, ~tyrene, 1,4-benzenediol dimethacrylate, 1,4-diisopropenyl benzene, and 1,3,5-trii~opropenyl 3S benzene. Also use~ul are ethylenically unsat~lrated ~O~
compounds havin~ a molecular weight of at lea~t 300, e.g., alkylene or a polyalkylene glycol diacrylate prepared from an alkylens glycol o:E 2 to 15 car}: ons or a poly~lkyl~ne ether glycol of 1 to 10 ether linkages, and those disclosed in U . S . Palt . No . 2, 927, 022, e . g ., those having a plurality of addition polymerizable ethylenic linkages partic:ularly when present a~ ~erminal linkages. Also included l~re all methacrylates, tetrahydro furfuryl methacrylat~, c:ycloh~xyl methacrylate, diallylfumarate, n-berlzylacrylate, carbowax 550 acrylate, methyl cellosolve acrylat~, dicyclopentenyl acrylat~ ode~yl acrylatQ, 2 (2-ethoxyethoxy) ethylacrylate, poybutadiene diacrylate, tris (2-hydroxyethyl) iso cyanurate triacrylate, epoxy diacrylate tetrabromo bisphenol A diacrylate. Monomers with vinyl group like vinyl pyrol, N-v~nyl pyrrolidons and vinyl ethers are usable. Also, oligomers with ~ono or multifunctional groups such as the ones with carbon s~roup for alkali removability, and the ones with both acrylate and isocyanate end yroups are useful.
Particularly preferred monomer~ are polyoxyethylated trimethylolpropane triacryla~e, ethylated pentaerythritol triacrylake, dipenta~rythritol monohydroxypentaacrylate and 1,10 decanediol dimethylacrylate. Others ~re caprolactone a~rylates and methacryla~es, propoxylated neopentyl glycol diacrylates and methacrylates.
.

Di-(3-acryloxy-2-hydxoxypr~pyl~ ether of ~isphenol A and Di-(3-methacryloxy-2-hydroxypropyl) ether o~ bisphenol A
oligomers, generally referred to as unsatural:ed bisphenol A oligomers are o~ particular interest becau~e they provide higher photospeed: also urethane diacrylates and metha~rylates with aliphatic or arom~tic . ~2 backbones, re~erred to ~s unsaturated urethane oligomers are of particular interest, because they provide both higher photospeed and higher flexibility.

Monomers which expand on polymerization can be used in part wîth ~h~ standard monomer~s to achieve compositions giving no ~hrinkage or warpage upon ~xposure. These mono~ers are based on polycyclic riny opening mechanisms. Spiro orthocarbonatesl ~piroorthoesters and bicyclic ortho esters are ~nown to belong ~o ~his class. Typical monomer~ are norboren~ ~piro orthocarbonate, and bismethylene ~piro orthocarbonate.
Monomers which undergo cationic polymerization are also useful in this invention. ~epresentative classes of monomers are cyclic ethers cyclic formals and acetals, lactones, vinyl monomers, ~ulfur c:ontaining mono~ners, organosilicone monomers, mono~unctional epoxies, difunctional epoxies~ epoxy prepolymer~ and higher oligomers and epoxy end-capped sllicone resins. They can be found in the open literature. On~ ~uch re~erence is "Photoinitiated cationlc polymerizationl' by James V.
Crivello in "W Curing: S~ nce and q'eshnology" edited by S. P. Pappas, published by Technology Marketing Corporation, 1978. Other ring opening monomers can be found in "Ring Opening Polymerization" Edited by X.J.
Ivin and T. Saegusa, E:Lse~vier Applied Science Publishers, London ~nd New York, 19~4.

Examples o~ photoinitia~oxs which ar~ u~e~ul in tlle present invention alorle or ~n ~ombinat~s:n ~re de~cribed in V.S. Pat. No. 2,760,863 and in::lude vicinal ketaldonyl alcuhols ~uch as benzoirl, pivaloin, acyloin ethers, e.g., benzoin ~ethyl and ethyl ethers, benzil dimethyl ketal: a-hydrocarbon-substituted aromatic acyloins, including a methylbenzoin a~allylbenzoin and a-phenylbenzoin, other~ are 1 hydxoxycyclobenyl phenol one, diethoxyphenol acetophenone, 2-~ethyl~ 4-(methyl thio)phenylJ, 2~orpholino-pr~pane-1, benzophenone, michler'~ ketone, ~ubstituted triphenyl imidazolyl dimers wi~h c:hain tran~er agent camphoquinone etc. Photoreduclbl~ dyes ~nd reducing agent~ disclosed ~n U.S. Pat. Nos. 2,850,445, 2,875,047, 3,097,096, 3~074,97~, 3,097,097 and 3,145,104, as well as dyes o~ the phena2ine, oxaæine, ~nd quinone classes, Miehlerl'~ ketone, benzopheno~e, acryloxy benzophenone, 2,4,5-triphenylimidazolyl dimers with hydrogen donors including leuco dyes and mixtures thereo~ a~ described in U.S. Pat. No~. 3,427,161, lS 3,~79,1R5 and 3,549,367 oan be used as initi~tors. Al o useful with photoinitiators and photoinhibitors are sensitizers disclosed in U.S. Pat No. 4,162,162. The photoini~iator or photoinitiator sy~tem ~ present in 0.05 to 10% by weight based on the to~al weiqht of the photoformable co~position. Other ~uitable photoinitiation sy~tems which are ~her~ally ln~tive but whic~h generate free radicals upon expo~ure to actinic liyht ~t or below 185 oC include th~
substituted or unsubstituted polynuclear quinones which are compounds having two intracyclic carbon atoms in a conjugated ~arbo~yclic ring ~ystem, e.g~, 9,10-anthraquinone, 2~ethylanthraquinone, 2-ethyl~nthraquinon~, 2 -ter~-butylarl~hraquinone, octame~hylan~hraquinone, 1, ~-naph~hoquinone, 9, lo-3o phenanthr~quinone, benz (a) anthracen~-7, 12 -d~ one, 2, 3-naphthacene-5,12-dione, 2-methyl~ naphthoquinone, 1,4-dimethyl-anthraquinone, ~,3-dimethylanthraquinone, ph~nylanthraquinone, 2,3-diphenylanthraquino~e, retenequinone, 7,8,9~10-tetrahydronaphthacene-5,12-~ ~5 dione, and 1,2,3,4~t~trahydrobenz(a)anthracene-7,12-dione~ Also, alpha amino aromatic ketones, halogenated c~mpounds like Trichlorom~thyl substi uted cyclohexadienones and t r i a z i n e s o r c h lori~ated acetophenone deri~atives, thioxanthones in prasences or kertiary ami~es, and tita~ocenes.

Typical c~sses o~ initiator~ ~or ~ationic polymerization are aryldiazonium salts, diaryliodonium ~alts comprising nonnucl~ophi:lic counterions 6uch as SbF6-, BF4-, PF~ , ~104-, CF3S03~s A~F6-~
triacylsulfonium Gal~s, triarylselenium ~alts or Iron arene complex. Examples of these lnclude but are not limited to 2,5-diethoxy ~4-(p-tolylmercapto) benzene diaæonium PP6-, 4- dimethylamine -naphthalen~ diaæonium PF6-, diphenyliodonium hexafluoroarsenate, di-t-butyldiphenyliodonium hexaflurophosphate FX-512 sulfonium salt (by 3M Company), trlethylsulfonium iodide, CG24-61 (by Ciba Geigy).
One good re~eren~e book is Photoinitlation o~ Ca~lonic Polymerization mentionQd earlier.

Sensitizer~ u~eful with these photoinit~tors for radical polymerization inclu~P but arP not li~ited to m2thylene blue and ~hose disclosed in U.S. Patents 3~554/753; 3,S63,750: 3,563,751; 3,~7,467: 3,~52,275;
~,162,162; 4,268,~67: 4,351,8~3: ~,454,21~; 4,535,052;
and 4,565,7~9. A preferred yroup of ~ensitizers include the bis (p~di~lkylaminobenzylidine) ketones disclosed in Baum et al., U.S. Pat~nt 3,652,275 ~nd the arylyidene aryl ketones disclosed in ~ueber, U.S.
Patenk 4,162,~62, as well as in UOS. Patent 4,268,667 and 4,351,393. Useful ~nsi~izer~ are also listed in Dueber, U.S. Patent 4,162,162 column 6, line 1 to line 21~S2~
65. Parkicularly preferred sensit~ Y,ers is~clude the following- D~C, i.e., cyclopentanone; 2,5-bis-[4-(diethylami~o)-2-methylph~nyl]methylenel-; DE~W, l.e., c y c 1 o p e n t a n o n e , 2 , 5 - b i 8 t 4 ~
( diethylamino) ph~snyl ] methylene ] -: dimethoxy~JDI, i . e ., lH -inden-1-one, 2, 3-dihydro-5, 6-di~Qethoxy-2 ~ ( 2, 3, 6, 7-tetrahydro-lH, 5H benzo[ i, ~ J quinoliz~n-9 yl)methylene]-, and JAW, ~.e., ~yclopentanone, 2,5-bis[(2,3,6,7 te~xahydro-lH,5~-b-enzo[i,~]quinolizin~
yl)methylene]-. Also useful are cyclopent~none 2,5-bis~2-(1,3-dihydro~1,3,3-l:r~methyl-2H-lndol-2-ylidene)ethylidene~, C~S 27713-~5-5; and cyclopentanone, 2,5 bis-t2-ethyln~phtho~L,2-d~tb~azol-2(1H~-ylidene)ethylid~ne], CAS ~7714-25-6.
Sen~itizers for cationic polymerizativn include but are not limited to perylene, acridine orange, acridine yellow, phosphene R, benzoflavin ~ Setoflavin T.

Hydrogen donor compounds useful as chain transf~r ~gents in the photopolymer compositio~s include: 2~
mercaptobenzoxazole, 2-mercapto-ben20thlazole, 4-methyl-4H-1,2,~,triazole-3-thiol, and the like; as well as various types oP compounds, e.g., (a) eth~rs, ~b) esters, ~c) alcohols, (d) compounds Gontaining allylic or benzylic hydrogen cumene, (e) ~cet~ls, (f) aldehydes, and ~g) amides as disclosed in column ~2, lines 18 to 58 of MacLachlan, U.~. Pat~nt 39390,996 Other ~omponents may also be pre~ent in th~
photoformable compositions, e.g., dyes, pigmen~s, extenders, organic or inorganic illers, organlc or inorganic rein~orcement ~ibers, poly~rization inhibitors, thermal stabilizexs~ viscosity ~odi~i~rs, interlayer and g nerally interfacial adhesion . 26 s~
promoters, ~uch as organosilane coupling ayents, coating aids, etc., so long as the photoformable compositions retain their essentia:L properties.

Although the Applicants have herein disclosed specific preferred embodiments of the instant invention, the general scope of this invention is limited only by the appended claims and their equivalents.

Claims

What is claimed is:

1. In a method for fabricating an integral three-dimensional object by imagewise exposing successive photohardenable sheets to actinic radiation, said method including containing a photohardenable liquid composition within a vessel, the improvement in said method comprising:

(a) exposing to actinic radiation a first area of the composition to photoform a precursor sheet;

(b) transferring the precursor sheet to a second area of the composition;

(c) exposing imagewise the precursor sheet to produce photohardened and non-photohardened areas;

(d) exposing again to actinic radiation the first area of the composition to photoform a new precursor sheet;

(e) transferring the new precursor sheet to the second area of the composition on top of the previously imagewise exposed precursor sheet;

27a (f) exposing imagewise the new precursor sheet to also produce photohardened and non-photohardened areas: and (g) repeating steps (d) through (g) until the three dimensional object has been completed.

2. A method for fabricating an integral three-dimensional object from a multiplicity of cross sectional portions of the object, the cross sectional portions corresponding to photohardened portions of contiguous photoformed precursor sheets of a photohardenable liquid composition, comprising the steps of:

(a) entirely exposing to actinic radiation a first area of the composition adequately to photoform a first precursor sheet having high enough integrity to be handled and transferred without being destroyed, but still maintaining the integrity low enough, so that the precursor sheet remains subject to destruction in a disintegrative environment;

(b) transferring the sheet to a second area:

(c) imagewise exposing to actinic radiation the transferred precursor sheet in a pattern corresponding to a respective cross sectional portion of the object, adequately to photoharden the cross sectional portion, the sheet being thus segregated to a photohardened portion and to a non-photohardened portion;

(d) entirely exposing to actinic radiation the first area of the composition adequately to photoform a new precursor sheet having high enough integrity to be handled and transferred without being destroyed, but still maintaining the integrity low enough, so that the new precursor sheet remains subject to destruction in a disintegrative environment;

(e) transferring and depositing the new sheet on the sheet previously subjected to steps (a) through (c);

(f) imagewise exposing to actinic radiation the newly deposited precursor sheet in a pattern corresponding to another respective cross sectional portion of the object, adequately to photoharden and connect the photohardened portion to any immediately underlying photohardened portion, the new sheet being also segregated to a photohardened portion and to a non-photohardened portion; and (g) repeating steps (d) through (f) until all cross-sectional portions corresponding to the three-dimensional object have been completed and connected to each other.

3. A method as defined in claim 1 or 2, further comprising the step of removing the non-photohardened portions.

4. A method as defined in claim 3, wherein the exposing steps (a) and (d) are performed by flood exposing.

5. A method as defined in claim 3, wherein the imagewise exposing steps (c) and (f) are performed by a laser beam.

6.A method as defined in claim 3, wherein the imagewise exposing steps (c) and (f) are performed through a variable optical density photomask.

7. A method as defined in claim 3, wherein the entirely exposing steps (a) and (d) are performed by a laser beam.

8. A method as defined in claim 3, wherein the precursor sheet is formed in a continuous manner in the first area, and it is wound in the form of a roll in the second area.

9. A method as defined in claim 3, wherein the photohardenable composition presents a free surface, and the first area is part of the free surface.

10. A method as defined in claim 9, wherein the second area is in the vicinity of the free surface.

11. A method as defined in claim 10, wherein the first precursor sheet is deposited on a platform.

12. A method as defined in claim 11, further comprising the step of lowering the platform by the thickness of a cross-sectional portion after step (c) and before step (e).

13. An apparatus for fabricating an integral three-dimensional object from a multiplicity of cross sectional portions of the object, the cross sectional portions corresponding to photohardened portions of contiguous photoformed precursor sheets of a photohardenable liquid composition, comprising:

a first exposure element for entirely exposing to actinic radiation a first area of the composition to photoform a precursor sheet;

means for transferring the precursor sheet from the first area to the second area;and a second exposure element for imagewise exposing to actinic radiation the precursor sheet in a second area in a pattern corresponding to the cross sectional portion of the object.

14. An apparatus as defined in claim 13, wherein the precursor sheets are in a discrete form.

15. An apparatus as defined in claim 13, wherein the precursor sheets are in a continuous form.

16. An apparatus as defined in claim 13, wherein the first and the second exposure elements constitute a single element.

17. An apparatus as defined in clalm 15, further comprising means in the second position for rolling the continuous precursor sheets.