U.S. patent application number 14/712116 was filed with the patent office on 2015-12-10 for method and apparatus for manufacture of 3d objects.
The applicant listed for this patent is Massivit 3D Printing Technologies LTD. Invention is credited to Victoria GORDON, Nataly LISITSIN, Yoav MILLER, Moshe UZAN, Igor YAKUBOV.
Application Number | 20150352782 14/712116 |
Document ID | / |
Family ID | 52338977 |
Filed Date | 2015-12-10 |
United States Patent
Application |
20150352782 |
Kind Code |
A1 |
LISITSIN; Nataly ; et
al. |
December 10, 2015 |
METHOD AND APPARATUS FOR MANUFACTURE OF 3D OBJECTS
Abstract
The current three-dimensional object manufacturing technique
relies on the deposition of a pseudoplastic material in gel
aggregate state. The gel flows through a deposition nozzle because
the applied agitation and pressure shears the bonds and induces a
breakdown in the material elasticity. The elasticity recovers
immediately after leaving the nozzle, and the gel solidifies to
maintain its shape and strength.
Inventors: |
LISITSIN; Nataly; (Holon,
IL) ; MILLER; Yoav; (Rehovot, IL) ; YAKUBOV;
Igor; (Herzlia, IL) ; UZAN; Moshe; (Bet
Shemesh, IL) ; GORDON; Victoria; (Jerusalem,
IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Massivit 3D Printing Technologies LTD |
Lod |
|
IL |
|
|
Family ID: |
52338977 |
Appl. No.: |
14/712116 |
Filed: |
May 14, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62009241 |
Jun 8, 2014 |
|
|
|
Current U.S.
Class: |
264/401 ;
425/113; 522/64 |
Current CPC
Class: |
B29C 64/118 20170801;
B29C 64/135 20170801; B33Y 10/00 20141201; B29C 64/106 20170801;
C08K 3/36 20130101; B29C 64/129 20170801; B29C 48/92 20190201; B29C
48/0013 20190201; B33Y 30/00 20141201; B29L 2009/00 20130101; B33Y
70/00 20141201; C09D 133/14 20130101 |
International
Class: |
B29C 67/00 20060101
B29C067/00; B29C 47/00 20060101 B29C047/00; B29C 47/92 20060101
B29C047/92; C08K 3/36 20060101 C08K003/36 |
Claims
1. A method of forming a three-dimensional object comprising: a)
providing a highly viscous pseudoplastic material having a first
viscosity and agitating the material to shear the pseudoplastic
material thereby decreasing viscosity to a second viscosity and to
cause the pseudoplastic material to flow through a delivery system
to an extrusion unit; b) employing an extrusion unit to extrude a
first portion of the pseudoplastic material in image-wise manner,
the first portion having a cross section with a diameter; c)
illuminating the first extruded portion to harden the pseudoplastic
material; d) extruding a second portion of the pseudoplastic
material adjacent to the first portion and contacting the first
portion at least one contact point, wherein a cross section of the
second portion is shifted in an axis perpendicular to gravitational
force compared to the cross section of the first portion; e)
obtaining a common contact section between surfaces of the first
and second extruded portions by forming an envelope into which a
segment of the first portion protrudes by sliding, due to the
gravitational force, of the second portion along the circumference
of the surface of the first portion hardened in step c), wherein
the surface of the second portion wets the surface of the first
portion at the common contact section; f) illuminating the extruded
second portion to harden the pseudoplastic material and to form a
bond between the first and second portions of pseudoplastic
material at the common contact section; g) adjusting the relative
position between extrusion unit and extruded second portion such
that the second portion obtains the location of the extruded first
portion of step b); and repeating steps d) to g) until the
three-dimensional object has been formed.
2. The method of forming a three-dimensional object according to
claim 1, wherein the pseudoplastic material immediately upon
leaving the extrusion unit recovers at least 50% of the first
viscosity.
3. The method of forming a three-dimensional object according to
claim 2, wherein the pseudoplastic material immediately upon
leaving the extrusion unit recovers 50 to 90% of the first
viscosity.
4. The method of forming a three-dimensional object according to
claim 1, wherein the first portion or strip of pseudoplastic
material supports the second and additional portions or strips of
the pseudoplastic material.
5. The method of forming a three-dimensional object according to
claim 1, wherein the cross section of the second portion or strip
is shifted by at least 1/20 of the diameter of the extruded portion
or strip of pseudoplastic material compared to the cross section of
the first portion.
6. The method of forming a three-dimensional object according to
claim 1, wherein the three-dimensional object comprises a structure
having a cantilever ratio of at least 1:4.
7. The method of forming a three-dimensional object according to
claim 1, wherein the pseudoplastic material comprises a composition
comprising at least one curable oligomer, at least one reactive
diluent, at least one rheology modifier, and at least one curing
agent, and optionally at least one performance additive or
filler.
8. The method of forming a three-dimensional object according to
claim 1, wherein the pseudoplastic material extruded from the
extrusion unit is continuously illuminated, wherein optionally
illuminating is carried out by ultra violet radiation with a
wavelength in the range of 360 to 485 nm.
9. The method of forming a three-dimensional object according to
claim 1, wherein the pseudoplastic material extruded from the
extrusion unit is continuously illuminated, wherein optionally
illuminating is carried out by ultra violet radiation with a
wavelength in the range of 380 to 420 nm.
10-16. (canceled)
17. The method of forming a three-dimensional object according to
claim 1, wherein the pseudoplastic material comprises: 30-70
weight-% of at least one curable oligomer; 30-70 weight-% of at
least one reactive diluent; 0.2-7 weight-% of at least one curing
agent; 1-10 weight-% of at least one rheology modifier; and 0-30
weight-% of at least one performance additive/filler.
18. The method of forming a three-dimensional object according to
claim 7, wherein the curable oligomer is at least one curable
oligomer of a group of oligomers having at least one ethylenically
unsaturated group comprised of urethane, epoxy, ester and/or ether
units; and/or wherein the reactive diluent is one of a group of low
molecular weight compounds having at least one functional group
reactive with the oligomer in the presence of a curing agent,
wherein the reactive diluent optionally is selected from acrylate
esters consisting of monoacrylates, diacrylates, triacrylates,
mono-, di-, or tri-methacrylates; and/or wherein the curing agent
is a photo initiator of an alpha cleavage type absorbing light
between about 230 and 420 nm, wherein the curing agent optionally
is 1-hydroxy-cyclohexyl-phenylketone,
2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone-1,
bis(2,4,6-trimethylbenzoyl)phenylphosphinoxid, or
diphenyl(2,4,6-trimethylbenzoyl)-phosphinoxide; and/or wherein the
rheology modifier is fumed silica.
19. The method of forming a three-dimensional object according to
claim 1, wherein a first viscosity of the material before extrusion
is in a range of about 120,000.00 mPas to about 500,000.00 mPas at
atmospheric pressure; and/or wherein a second viscosity of the
material when a force is applied is in a range of about 250 to
about 700 mPas.
20. The method of forming a three-dimensional object according to
claim 1, wherein the pseudoplastic material comprises a performance
additive selected from a group of additives consisting of pigments,
fillers such as glass beads, glass fibers, surfactants, wetting and
dispersing additives, impact modifiers, and/or flame
retardants.
21. The method of forming a three-dimensional object according to
claim 1, wherein the three-dimensional object is free of any
conventional support structures.
22. The method of forming a three-dimensional object according to
claim 8, wherein illuminating is carried out by ultra violet
radiation with a wavelength in the range of 360 to 485 nm.
23. The method of forming a three-dimensional object according to
claim 9, wherein illuminating is carried out by ultra violet
radiation with a wavelength in the range of 380 to 420 nm.
Description
[0001] The present application claims priority to U.S. Provisional
Patent Application No. 62/009,241 filed on 8 Jun. 2014, the
complete disclosure of which is incorporated herein by
reference.
FIELD OF THE TECHNOLOGY
[0002] The present invention relates to a method of additive
manufacturing and an apparatus useful therefor, particularly with
additive manufacturing devices.
BACKGROUND
[0003] Three dimensional objects manufacturing process includes
deposition of a resin layer, imaging of the layer and curing or
hardening of the imaged segments of the layer. The layers are
deposited (added) on top of each other and hence the process is
called additive manufacturing process by means of which a computer
generated 3D model is converted into a physical object. The process
involves generation of a plurality of material layers of different
or identical shape. The layers are laid down or deposited on top
(or bottom) of each of the preceding layer until the amount of
layers results in a desired three dimensional physical object.
[0004] The material from which the layers of the three-dimensional
physical object are generated could come in liquid, paste, powder,
gel and other forms. Conversion of such materials into a solid form
is typically performed by suitable actinic radiation or heat.
[0005] The deposited material layers are thin twenty to forty
micron layers. Printing or manufacture of a three-dimensional
object is a relatively long process. For example, manufacture of a
100.times.100.times.100 mm.sup.3 cube would require deposition of
4000 of layers. Such thin layers are mechanically not strong and
when a cantilever or a hollow three-dimensional object has to be
printed or manufactured there is a need to introduce different
structural support elements that would maintain the desired
strength of the printed three-dimensional object.
[0006] Manufacturing of 3D objects spans over a large range of
applications. This includes prototype manufacture, small runs of
different products manufacture, decorations, sculptures,
architectural models, and other physical objects.
[0007] Recently, manufacture of relatively large size physical
objects and models has become popular. Large size statues, animal
figures and decorations are manufactured and used in different
carnivals, playgrounds, and supermarkets. Where the manufacturing
technology allows, some of these physical objects are manufactured
as a single piece at 1:1 scale and some are coming in parts
assembled into the physical object at the installation site.
[0008] The time required to build a three-dimensional object
depends on various parameters, including the speed of adding a
layer to the three-dimensional object and other parameters such as
for example, curing time of resin using ultra-violet (UV)
radiation, the speed of adding solid or liquid material to the
layer which depends on the material itself, layer thickness, the
intensity of the curing agent and the desired resolution of the
three-dimensional object details.
[0009] Manufacture of large objects requires a large amount of
manual labor and consumes large amount of relatively expensive
materials. In order to save on material costs large objects are
printed as shells or hollow structures. The shells could warp, or
otherwise deform even in course of their manufacture and multiple
support structures integral with the shells or constructed at the
installation sites are required to prevent warping or collapse.
Since the objects manufactured as shells have their inner space
hollow or empty the support structures are mounted or manufactured
to be located inside the three-dimensional object.
[0010] It is the purpose of this disclosure to provide apparatus,
methods and materials that support faster manufacturing of
three-dimensional objects in spite of the limitation of different
technology elements of the process.
DEFINITIONS
[0011] Shear thinning or pseudoplasticity as used in the current
disclosure, means an effect where a substance, for example a fluid
or gel or paste, becomes more fluid upon application of force, in
particular a mechanical force such as shear or pressure. The
applied force can be agitating, stirring, pumping, shaking or
another mechanical force. Many gels are pseudoplastic materials,
exhibiting a stable form at rest but become fluid when agitated or
pressure is applied to them. Some pseudoplastic fluids return to a
gel state almost instantly, when the agitation is discontinued.
[0012] The term "gel" when used in the present application refers
to a composition comprising a crosslinked system and a fluid or gas
dispersed therein, which composition exhibits no or substantially
no flow when in the steady-state. The gel becomes fluid when a
force is applied, for example when the gel is pumped, stirred, or
shaken, and resolidifies when resting, i.e. when no force is
applied. This phenomen includes also thixotropy. Although by weight
the major part of a gel is liquid, such as up to more than 99%,
gels behave like solids due to the three-dimensional network.
[0013] The term "cantilever" as used in the present disclosure
means a structure resting on a single support vs. a bridge having
two supports. Typically, cantilever support is located at one of
the ends of the cantilever.
[0014] The term "cantilever ratio" as used in the present
disclosure means a ratio of the extruded pseudoplastic material
cross section to the length of unsupported material.
[0015] The terms "strip" and "portion" are both used for a part of
pseudoplastic material that has been extruded. Both terms are used
exchangeably.
[0016] The term "image" refers to a layer of a product produced in
one cycle of extrusion, i.e. a layer that is printed in one step by
movement of the extrusion unit.
[0017] The term "curable monomer" refers to a compound having at
least one reactive group that can react with other reactive groups,
for example with other monomers, with oligomers or reactive
diluents, or can be oligomerized or polymerized, in particular when
radiated with suitable radiation. Examples for monomers are acryl
based monomers, epoxides and monomers forming polyesters,
polyethers and urethanes.
[0018] The term "ethylenically unsaturated monomer" refers to
monomers that have unsaturated groups that can form radicals when
radiated with suitable radiation. The monomers have at least one
unsaturated group, such as an .alpha.,.beta.-ethylenically
unsaturated group or a conjugated unsaturated system, such as a
Michael system.
[0019] The term "actinic radiation" refers to electromagnetic
radiation that can produce photochemical reactions.
[0020] The term "photocuring" refers to a reaction of monomers
and/or oligomers to actinic radiation, such as ultraviolet
radiation, whereby reactive species are produced that promote
cross-linking and curing of monomers or oligomers, particularly
cross-linking and curing of unsaturated groups. The term
"photocurable" refers to material that can be cross-linked or cured
by light.
[0021] The term "harden" when used in the present description
refers to a reaction that crosslinks or otherwise reacts oligomers
and/or reactive diluent, in particular it refers to the reaction
between oligomers and reactive diluent resulting in a crosslinked
material.
[0022] The term "oligomer" refers to polymerized monomers having 3
to 100, such as 5 to 50, or 5 to 20 monomer units.
[0023] "Curable oligomers" that are used in the present invention
are oligomers having functional groups that can be cured or
cross-linked by activation such as by radiation.
[0024] The term "reactive diluent" refers to a compound that
provides at least one, such as 1, 2, 3, or more functional groups
that can react with a curable monomer or oligomer. A reactive
diluent can comprise reactive groups like hydroxy groups,
ethylenically unsaturated groups, epoxy groups, amino groups, or a
combination thereof. For example, a reactive diluent can comprise
one or more hydroxy groups and one or more amino groups,
ethylenically unsaturated groups etc. Examples of reactive diluents
include monofunctional and polyfunctional compounds, such as
monomers containing a vinyl, acryl, acrylate, acrylamide, hydroxyl
group among others. A reactive diluent typically is a mono-, di- or
trifunctional monomer or oligomer having a low molecular weight.
Typical examples are acrylate and methacrylate esters including
mono-, di-, and tri-(meth)acrylates and -acrylates.
[0025] A cross-linking component should provide at least two
curable terminal groups. The "cross-linking component" can comprise
one or more reactive diluents and further di-, tri-, or
multifunctional compounds, if necessary.
[0026] A "photoinitator" is a chemical compound that decomposes
into free radicals when exposed to light. Suitable photoinitiators
are among the group of aromatic .alpha.-keto carboxylic acid and
their esters, .alpha.-aminoalkyl phenone derivatives, phosphine
oxide derivatives, benzophenones and their derivatives and other
photocuring compounds that are well-known in the art.
[0027] The term "rheology modifier" as used in the present
invention refers to components that control viscosity and/or can
have a thickening action, or are suspending or gelling agents,
preventing sedimentation. Rheology modifiers that are useful for
the present invention comprise organic and anorganic rheology
modifiers and associative as well as non-associative modifiers.
Organic rheology modifiers comprise products based on natural
materials, like cellulose, cellulose derivatives, alginates, or
polysaccharides and their derivatives, like xanthan, or synthetic
polymeric materials like polyacrylates, polyurethanes or
polyamides. Anorganic rheology modifiers comprise clays, like
bentonite clays, attapulgite clays, organoclays, kaolin, and
treated or untreated synthetic silicas, like fumed silicas.
Inorganic rheology modifiers tend to have high yield values and are
characterized as thixotropes.
[0028] The term "non-associative rheology modifier" comprises
modifiers that act via entanglements of soluble, high molecular
weight polymer chains ("hydrodynamic thickening"). The
effectiveness of a non-associative thickener is mainly controlled
by the molecular weight of the polymer.
[0029] The term "associative rheology modifiers" refers to
substances that thicken by non-specific interactions of hydrophobic
end-groups of a thickener molecule both with themselves and with
components of the coating. They form a so called "physical
network".
[0030] "Viscosity" refers to dynamic viscosity. It is measured
using a rheometer, in particular a shear rheometer such as one with
a rotational cylinder or with cone and plate, at room temperature,
i.e. at 25.degree. C.
[0031] The term "extrusion unit" refers to any unit that is capable
of extruding a pseudoplastic material. An extrusion unit includes
at least one screw and at least one discharge port such as an
extrusion head, extrusion nozzle, extrusion die or any other type
of extrusion outlet. The terms extrusion nozzle, extrusion die and
extrusion head can be used interchangeably.
SUMMARY
[0032] The current three-dimensional object manufacturing technique
relies on the deposition of a pseudoplastic material in gel
aggregate state. A gel is provided that flows through a deposition
nozzle because of the applied agitation and the gel's elasticity
recovers immediately after leaving the nozzle, and the gel
solidifies to maintain or regain its shape and strength. Without
being bound by theory it is assumed that shear stress generated by
agitation breaks the three-dimensional network bonds within the
liquid. After leaving the nozzle the material is no longer under
stress and the network recovers immediately after leaving the
nozzle, resulting in the gel resolidifying.
[0033] Described is a process for producing a three-dimensional
object using a pseudoplastic material, an apparatus configured to
use the pseudoplastic material and a method of three-dimensional
object manufacture using the pseudoplastic material and the current
apparatus. The process allows to produce objects that have
structures that are difficult to build without supporting
structures such as cantilever-like objects.
LIST OF FIGURES AND THEIR DESCRIPTION
[0034] FIG. 1 is a schematic illustration of an example of an
apparatus for manufacture of a three-dimensional object;
[0035] FIGS. 2A and 2B are examples of a three-dimensional object
manufactured using the present apparatus;
[0036] FIG. 3A-3C are illustrations explaining printing or
manufacture of a 3D object with the present pseudoplastic
material/gel;
[0037] FIG. 4 is an example of a hollow rectangular prism with 90
degrees angles; and
[0038] FIG. 5 is a graph that demonstrates the variations of
viscosity vs shear rate.
DESCRIPTION
[0039] The present invention is concerned with methods for the
manufacture of three-dimensional structures by printing, i.e. by
so-called 3D-printing, a material and an apparatus useful
therefore, and the use of a pseudoplastic material for 3D
printing.
[0040] It has been found that using pseudoplastic material, i.e. a
composition with decreasing viscosity when shear force is applied,
allows to produce sophisticated and complex three-dimensional
structures by 3D printing, in particular hollow structures and
structures that are cantilever-like, without the need for
supporting elements during manufacture.
[0041] The pseudoplastic material used according to the present
invention shows shear-thinning in a range such that the starting
composition having high viscosity when it is transferred to and
through an extrusion unit has a viscosity low enough for the
transfer and for creating a portion of a 3D structure, such as a
strip, or a layer or an image, but has an increased viscosity
within short term when it arrives at its predetermined position.
Viscosity of the starting composition is also called "first
viscosity" and viscosity after application of a force, such as at
the outlet of the extrusion unit, is also called "second
viscosity". In one embodiment a gel is used which viscosity
decreases to about 700-250 mPas at a pressure higher than
atmospheric pressure. A composition that is useful for this purpose
is as defined below.
[0042] One three-dimensional object manufacturing technique relies
on the deposition of material in gel aggregate state. The gel flows
through a deposition nozzle because the applied agitation and
pressure shears the inter-particle bonds and induces a breakdown in
the elasticity of the material. The material recovers immediately
after leaving the nozzle, and the pseudoplastic material or gel
almost immediately solidifies to maintain its shape.
[0043] A method of forming a three-dimensional object is provided
which comprises the following steps:
[0044] a) providing a highly viscous pseudoplastic material having
a first viscosity and agitating the material to shear the
pseudoplastic material and cause it to flow through a delivery
system to an extrusion unit;
[0045] b) employing an extrusion unit to extrude a strip of the
pseudoplastic material in image-wise manner;
[0046] c) extruding a second strip of the pseudoplastic material,
the second strip adjacent to the first strip and contacting the
first strip at at least one contact point;
[0047] d) continuously illuminating the first and the second strip
to harden the pseudoplastic material; and
[0048] e) continue to extrude the pseudoplastic material in an
image-wise manner and continuously illuminate extruded material to
form a three-dimensional object.
[0049] Furthermore a method of forming a three-dimensional object
is provided comprising:
[0050] a) providing a highly viscous pseudoplastic material having
a first viscosity and agitating the material to shear the
pseudoplastic material thereby decreasing viscosity to a second
viscosity and to cause it to flow through a delivery system to an
extrusion unit;
[0051] b) employing an extrusion unit (116) to extrude a first
portion of the pseudoplastic material (204-1) in image-wise manner,
the first portion having a cross section with a diameter;
[0052] c) illuminating the first extruded portion to harden the
pseudoplastic material;
[0053] d) extruding a second portion (204-2) of the pseudoplastic
material adjacent to the first portion and contacting the first
portion at at least one contact point, wherein a cross section of
the second portion is shifted (304) in an axis perpendicular to the
gravitational force compared to the cross section of the first
portion;
[0054] e) obtaining a common contact section between the surfaces
of the first and second extruded portions by forming an envelope
into which a segment of the first portion protrudes by sliding
(308), due to the gravitational force, of the second portion along
the circumference of the surface of the first portion hardened in
step c), wherein the surface of the second portion wets the surface
of the first portion at the common contact section;
[0055] f) illuminating the extruded second portion to harden the
pseudoplastic material and to form a bond between the first and
second portions of pseudoplastic material at the common contact
section;
[0056] g) adjusting the relative position between extrusion unit
and extruded second portion such that the second portion obtains
the location of the extruded first portion of step b); and
[0057] h) repeating steps d) to g) until the three-dimensional
object has been formed.
[0058] The present application also discloses a method of additive
manufacture of a three-dimensional object which comprises the
following steps:
[0059] a) providing a tank with a high viscosity pseudoplastic
material and acting to reduce the material viscosity in the tank to
shear thin the material;
[0060] b) applying to the pseudoplastic material pressure exceeding
atmospheric pressure to cause the pseudoplastic material to flow
through a delivery system to an extrusion nozzle;
[0061] c) extruding in an image-wise manner a first portion of the
pseudoplastic material; extruding in an image-wise manner at least
a second portion of the pseudoplastic material; and
[0062] d) wherein the second portion of pseudoplastic material has
at least one common contact section with the first portion of the
pseudoplastic material; and
[0063] e) wherein the pseudoplastic material immediately upon
extrusion from the nozzle changes the viscosity to a viscosity
substantially higher than the viscosity at the pressure exceeding
atmospheric pressure.
[0064] A three-dimensional object can be obtained with any of the
above mentioned methods and the objects obtained are also part of
the present invention.
[0065] An apparatus that is useful for manufacture of a
three-dimensional object comprises a tank for storing a
pseudoplastic material at atmospheric pressure; a pump configured
to apply agitation to the pseudoplastic material to shear thin the
pseudoplastic material and reduce the pseudoplastic material
viscosity such as to cause the material to flow; an extrusion unit
comprising an extrusion nozzle, an extrusion head, or an extrusion
die, configured to extrude in image-wise manner the pseudoplastic
material at a pressure exceeding atmospheric pressure; and an X-Y-Z
movement system configured to move at least the extrusion nozzle in
a three coordinate system.
[0066] A system of the present invention is described in detail by
reference to FIG. 1 which is a schematic illustration of an example
of a system suitable for manufacture of three-dimensional objects
or structures. A system of the present invention comprises at least
a container such as a tank to receive the pseudoplastic material, a
pump to apply a force to the pseudoplastic material, an extrusion
unit comprising a nozzle to extrude the pseudoplastic material, and
a movement system comprising a control unit, such as a
computer.
[0067] System 100 includes a container for pseudoplastic material,
such as a storage or material supply tank 102 adapted to store a
pseudoplastic high viscosity material 104, a pump 108 configured to
apply a force to the gel, for example by agitating and shear
thinning the pseudoplastic high viscosity material or gel 104, to
reduce material 104 viscosity to cause the material to flow. Pumps
for such purpose are well-known in the art and any pump that can
apply shear to the gel to be extruded is useful. Pump 108 could be
such as Graco S20 supply system commercially available from Graco
Minneapolis, Minn. U.S.A., or a barrel follower dispensing pump
Series 90 commercially available from Scheugenpflug AG, 93333
Neustadt a.d. Donau Germany. Pump 108 in addition to agitation also
develops a pressure higher than atmospheric pressure such that the
pseudoplastic material 104 flows through a delivery tubing or
system 112 to an extrusion (unit) nozzle 116. The higher than
atmospheric pressure developed by the pump is communicated to the
dispenser and could be such as 0.1 bar to 30.0 bar and typically
from 1.0 bar to 20.0 bar and sometimes 2.0 bar to 10.0 bar.
[0068] System 100 includes an X-Y-Z movement system 124 configured
to move the extrusion nozzle 116 in a three coordinate system.
Alternatively, a table 120 could be made to move in a three
coordinate system. In another example, the movement in three
directions (X-Y-Z) could be divided between the extrusion nozzle
116 and table 120. System 100 also includes a control unit, such as
computer 128 configured to control operation of movement system
124, pump 108 pseudoplastic material steering operation and value
or magnitude of the pressure higher than atmospheric pressure. The
control unit, computer 128 is further adapted to receive the
three-dimensional object 132 data and generate from the received
data the X-Y-Z movement commands and distance such that the
pseudoplastic material 104 is extruded through extrusion unit 114
and nozzle 116 in an image wise manner. The X-Y-Z movement could be
performed in a vector mode or raster mode, depending on the object
to be printed. Computer 128 could also be configured to optimize
the decision on the printing mode.
[0069] System 100 further includes a source of radiation for curing
the pseudoplastic material. Any illuminator providing radiation
that is useful for curing can be used. In FIG. 1 it is a UV LED
based source of radiation 136. An example for a source of radiation
136 is a FireJet FJ200 commercially available from Phoseon
Technology, Inc., Hillsboro Oreg. 97124 USA. A suitable source of
radiation 136 provides UV radiation with total UV power of up to
900 W and with a wavelength that normally is in the range of
230-420 nm, but can also be in the range of 360-485 nm, for example
a wavelength in the range of 380-420 nm. Alternatively, a UV lamp
such as for example, mercury vapor lamp model Shot 500 commercially
available from CureUV, Inc., Delray Beach, Fla. 33445 USA can be
used, or any other UV lamp that is available. In one embodiment the
source of UV radiation 136 operates in a continuous manner and the
UV radiation is selected to harden the pseudoplastic material 104.
Computer 128 could also be configured to control operation of
source of UV radiation 136 and synchronize it with the printing
mode.
[0070] Manufacture or formation of a three-dimensional object 132
takes place by extrusion. Initially, a highly viscous pseudoplastic
material 104, such as the one that will be described below under
test name BGA 0, is provided in tank 102. The pseudoplastic
material has a first viscosity or starting viscosity before the
material is conveyed to the extruder unit. By application of shear
the viscosity is reduced so that the material has a second
viscosity which is in a range such that the material easily flows.
After extrusion the material rests and regains at least a
percentage of the first viscosity.
[0071] A suitable first or starting viscosity for the pseudoplastic
material 104 could be in the range of about 120,000 to 500,000
mPas, such as 100,000 to 40,000 mPas at a low shear rate. The
viscosity after application of shear can decrease as low as 250
mPas. As is shown in FIG. 1, Pump 108 is operative to agitate and
deliver material 104 through the delivery system 112 to the
extrusion unit 114 and to nozzle 116 and apply to it a varying
pressure exceeding the atmospheric pressure. The tested
pseudoplastic material formulation has shown different degrees of
shear thinning properties and viscosity under different pressure.
The pressure applied would typically be in range of 1.0 bar to 5.0
bar. Application of agitation and pressure to material 104 reduces
the viscosity of material 104 by a shear thinning process to about
250-700 mPas and typically to about 450 to 550 mPas. The pressure
higher than atmospheric pressure applied to the pseudoplastic
material with reduced viscosity is sufficient to shear the
pseudoplastic material 104 and cause it to flow through a delivery
system 112 to extrusion unit 114 to be extruded through nozzle
116.
[0072] In some examples the agitation intensity and application of
higher than atmospheric pressure could vary. Extrusion unit 114 or
nozzle 116 extrudes a strip or a portion of the pseudoplastic
material 104 in image-wise manner. The system can comprise one
extrusion unit or more than one unit and one unit can comprise one
nozzle or more. There could be one or more extrusion units 114 or
nozzles 116 and their diameter could be set to extrude a strip or a
portion of the pseudoplastic material 104 with a diameter of 0.5 to
2.0 mm. The diameter of a nozzle can have different forms as is
known in the art. Other than round nozzle 116 cross sections are
possible and generally a set of exchangeable nozzles with different
cross sections could be used with apparatus 100.
[0073] The control unit, such as computer 128, is adapted to
receive the three-dimensional object 132 data and generate from the
received data the X-Y-Z movement commands and length of strips of
pseudoplastic material 204-1, 204-2 (FIG. 2B) and so on, such that
the pseudoplastic material 104 extruded through extrusion (unit)
nozzle 116 in an image wise manner resembles a slice of object 132.
In a similar manner a second strip or a portion of the
pseudoplastic material 104 is extruded.
[0074] FIGS. 3A-3C are illustrations explaining printing or
manufacture of a 3D object with a pseudoplastic material or gel of
the present invention. As shown in FIG. 3 B, when producing
horizontally oriented segments of a three-dimensional object, each
next or adjacent strip or portion of pseudoplastic material 204-4
or 204-5 is extruded or printed. Strip or drop 204-5 could slightly
shift or slide in a direction indicated by arrow 312 at about the
boundary 304 of the previously extruded strip, for example 204-4 or
204-3. The shift or slide 308 could be in a range of 1/5 to 1/35,
such as 1/10 or 1/30 of the extruded strip diameter and the shift
or slide value could vary in the process of the three-dimensional
object manufacture. Drop or strip 204-5 slides as shown by arrow
312 from its unstable position to a more stable position dictated
by the solidification rate of the pseudoplastic material that could
be attributed to the material viscosity increase and gravitational
forces. The cross-section of the second strip or drop 204-5 is
shifted (304) in an axis perpendicular to the gravitational force
compared to the cross-section of the first strip or drop 204-4.
[0075] Without being bound by theory it is assumed that in the
course of a sliding movement of drop or strip 204-5 along the
circumference of the adjacent strip, drop or strip 204-5 wets the
surface of the adjacent strip 204-4 and the still at least
partially liquid drop 204-5 is forming an envelope into which a
segment of the previously printed drop or strip 204-4 protrudes.
Furthermore, it is assumed that the large contact surface between
earlier printed drop/strip and the later extruded drop or strip
contributes to extraordinary strength of the bond between the
strips/drops. In addition to this, viscosity of the extruded
drop/strip is rapidly increasing limiting to some extent the slide
of the drop and further contributing to the bond strength. Curing
radiation sources 136 are operative in course of printing and by
the time drop/strip 204-5 reaches its stable position drop/strip
204-5 solidifies or hardens. In some examples, a shift of a
drop/strip can be intentionally introduced.
[0076] The bond between the later and earlier extruded strips of
pseudoplastic material 104 becomes strong enough to support in a
suspended state the later extruded and additional strips of the
present pseudoplastic material until the later extruded strip of
pseudoplastic material has dropped into a horizontal position
alongside the earlier extruded strip of pseudoplastic material.
[0077] This bond is sufficiently strong to support printing of
hollow and/or cantilever-like structures or three-dimensional
objects with a cantilever ratio of at least 1:5 and up to 1:200 and
even more without any conventional support structures. Objects of
FIGS. 2A and 2B have been printed by strips with diameter of 1.3
mm. Objects of FIGS. 2A and 2B had a cantilever ratio from 1:5 up
to more than 1:200. No support structures have been required.
[0078] FIG. 3C illustrates manufacture or printing of a vertical
segment of a 3D object. In the example of FIG. 3C drops 204 are
positioned on top of each other and before the pseudoplastic
material solidifies the later printed drop or strip 204-5 wets the
surface of the adjacent strip 204-4 and the still, at least
partially liquid drop 204-5, is forming an envelope into which a
segment of the previously printed drop or strip 204-4 protrudes.
Without being bound by theory it is assumed that concurrently to
the increase in the viscosity of the extruded drop/strip and the
solidification of the pseudoplastic material there is an increase
in surface tension of the later extruded drop/strip that further
contributes to the bond strength.
[0079] The method and system of the present invention are useful
for manufacturing hollow articles in a size not available until now
without support structures. With the new system it is possible to
prepare hollow figures of big size that are stable. FIG. 4 is an
example of a hollow rectangular prism with 90 degrees angles. The
dimensions of prism 404 cross section are 150.times.150 mm.sup.2.
The extruded strips 408 has a square cross section with dimensions
of 1.8.times.1.8 mm.sup.2. No internal support structures are
required.
[0080] The source of radiation that is used according to the
present invention can be operated in a continuous mode or a
discontinuous mode. The skilled person can choose the mode that is
best suited for a specific object and material, respectively. In a
continuous mode the source of radiation 136 irradiates the strips
of the three-dimensional object 132 being manufactured to harden
the extruded material 104. Concurrently, extrusion unit 114 can
continue to extrude the pseudoplastic material in an image-wise
manner and source of radiation 136 could operate to continuously
illuminate or irradiate extruded pseudoplastic material 104 to form
a three-dimensional object. In a discontinuous mode the source of
radiation is adapted to irradiate the extruded material when it is
necessary.
[0081] The pseudoplastic material has a first viscosity at
atmospheric pressure and a second viscosity at a pressure exceeding
atmospheric pressure. The second viscosity is lower than the first
viscosity and as the material 104 is leaving the extrusion unit
(nozzle) it immediately upon leaving the extrusion nozzle recovers
a significant fraction of the first viscosity, such as at least
30%, suitably at least 40%, in particular at least 50% of the first
viscosity. The recovered viscosity in a preferred embodiment is
between 60 to 90% or even more of the first viscosity.
[0082] The formulation of the pseudoplastic or gel material will
now be described. The pseudoplastic material or gel used for the
present invention comprises at least one curable oligomer, at least
one reactive diluent, at least one curing agent, at least one
rheology modifier, and optionally at least one performance
improving additive and/or further additives.
[0083] The curable oligomers used in the present curable
composition can be oligomers having at least one ethylenically
unsaturated group and can be comprised for example of urethane,
epoxy, ester and/or ether units. Oligomers such as acrylated and
methacrylated oligomers such as acrylated epoxies, polyesters,
polyethers and urethanes are useful. Examples of oligomers useful
in the present invention are acryl based or methacryl based
oligomers, olefine based oligomers, vinyl based oligomers, styrene
oligomers, vinyl alcohol oligomers, vinyl pyrrolidone oligomers,
diene based oligomers, such as butadiene or pentadiene oligomers,
addition polymerization type oligomers, such as oligoester acrylate
based oligomers, for example oligoester (meth)acrylate or
oligoester acrylate, polyisocyanate oligomers, polyether urethane
acrylate or polyether urethane methacrylate oligomers, epoxy
oligomers among others. Those oligomers are known in the art and
are commercially available.
[0084] Aliphatic polyether urethane acrylate or methacrylate
compounds that are useful as oligomers for the present invention
can be prepared by reacting an aliphatic diisocyanate with one or
more polyether or polyester diols. Useful as oligomers or reactive
diluents are polyols having at least two hydroxy groups per
molecule such as polyether diols. Another group are polyester diols
which can be obtained from dibasic acids and dibasic alcohols, i.e.
glycols. Dibasic acids are well-known and commercially available,
examples are succinic, glutaric, adipic, pimelic and subaric acid
or phthalic acids and derivatives of these acids. Examples for
suitable glycols are ethylene glycol, propylene glycol,
trimethylene glycol, tetramethylene glycol, isobutylene glycol and
mixtures thereof.
[0085] The reactive diluents used for the pseudoplastic composition
of the present invention are mono- or multifunctional compounds,
such as monomers or oligomers carrying one, two, three or more
functional groups that can react in a curing reaction. A useful
reactive diluent is for example a low molecular compound having at
least one functional group reactive with the oligomer in the
presence of a curing agent. Typical examples are low molecular
weight acrylate esters including mono-, di-, and tri-methacrylates,
monoacrylates, diacrylates and triacrylates, or mixtures
thereof.
[0086] The rheology modifier acts as thickening agent, it can be an
organic or inorganic rheology modifier, both of which are
well-known in the art. The most common types of modified and
unmodified inorganic rheology modifiers that are useful for the
present invention, are attapulgite clays, bentonite clays,
organoclays, and treated and untreated synthetic silicas, such as
fumed silica. Most inorganic thickeners and rheology modifiers are
supplied as powders. If they are properly dispersed into a coating,
they usually function as suspending or gelling agents and, thus,
help to avoid sedimentation. Inorganic rheology modifiers tend to
have high yield values and are characterized as thixotropes.
[0087] Organic rheology modifiers that are useful for the present
invention can be subdivided into products based on natural raw
materials, like cellulose or xanthan, and products based on
synthetic organic chemistry, like polyacrylates, polyurethanes or
polyamides. Other rheology modifiers and thickeners such as
polyamides, organoclays etc., can also be used.
[0088] The curing agent used for the present invention suitably is
at least one photoinitiator. It can be another initiator that is
known for this type of reactions, i.e. a compound that generates
radicals under predetermined conditions. A useful curing agent can
be selected depending for example on the UV source or other
reaction condition. It has been found that photoinitiators, such as
.alpha.-hydroxyketone, .alpha.-aminoketone, phenylglyoxylate,
benzyldimethyl-ketal, etc., are suitable. In one embodiment for a
specific formulation phosphine oxide is used.
[0089] Examples for photoinitiators suitable for the present
invention are 1-hydroxy-cyclohexyl-phenylketone, available as
Irgacure 184 (CAS 94719-3),
2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1,
available as Irgacure 369 (CAS 119313-12-1) from BASF Ludwigshafen,
Germany, bis(2,4,6-trimethylbenzoyl)-phenylphosphinoxide, available
as Irgacure 819 (CAS 162881-26-7),
diphenyl-(2,4,6-trimethylbenzoyl)phosphinoxide, available as TPO
(CAS 75980-60-8), available from BASF Ludwigshafen, Germany.
[0090] In one example, the pseudoplastic material or gel 104
comprises of:
[0091] Curable oligomer: 30-70%
[0092] Reactive diluent: 30-70%
[0093] Curing agent: 0.2-7%
[0094] Rheology modifier: 1-10%
[0095] Performance improving additive/filler 0-30%.
[0096] The oligomer typically is one of the family of curable
oligomers as described above, for example one having at least one
ethylenically unsaturated bond such as acrylated and methacrylated
oligomers and in particular acrylated epoxies, polyesters,
polyethers and urethanes. The oligomer typically is present be in a
proportion of 30-70% by weight.
[0097] The reactive diluent can be a substance as described above
and typically can be a mono, di and tri functional monomer and the
proportion would be about 30-70% by weight. The reactive diluents
or monomers would typically be low molecular weight acrylate esters
including methacrylates, monoacrylates, diacrylates and
triacrylates.
[0098] The rheology modifier can be one or more of the substances
described above and suitable for use in the current material
composition is a filler that provides for a suitable viscosity of
the material to be extruded and enhances the shear-thinning
properties, such as fumed silica or clay.
[0099] The curing agent can be a compound as described above, in
particular a photo initiator, and a useful initiator is an alpha
cleavage type unimolecular decomposition process photo initiator
that absorbs light between 230 and 420 nm, to yield free
radical(s). Examples of such alpha cleavage photo initiators could
be Irgacure 184 (CAS 947 19-3), Irgacure 369 (CAS 119313-12-1),
Irgacure 819 (CAS 162881-26-7) and TPO (CAS 75980-60-8) available
from BASF Ludwigshafen Germany.
[0100] Examples for further useful additives are performance
improving additives and/or fillers. Fillers are well-known in the
art and can be used in amounts that are commonly used. Suitable
performance improving additives and fillers are for example
pigments, glass beads, glass fibers, surfactants, wetting and
dispersing additives, impact modifiers, and/or flame
retardants.
EXAMPLE
[0101] In the following example some commercially available
materials have been used: BR 144 and BR 441-B are polyether and
polyester urethane acrylates available from Dymax Corporation,
Torrington Conn. 06790 U.S.A. and a number of other suppliers. CN
981 is urethane acrylate from Sartomer Americas, Exton Pa. 19341
U.S.A. Ebecryl 3300 is epoxy acrylate from Allnex S.A. Anderlecht,
B-1070 Belgium. 03-849 is polyester acrylate from Rahn AGCH-8050
Zurich Switzerland.
[0102] TPO is phosphine oxide photo initiator from BASF.
[0103] SR 506D, SR 238, SR 833S, SR 351 are mono, di and tri
functional reactive diluents available from Sartomer.
[0104] Aerosil 200 is fumed silica such as Evonic-Aerosil 200
commercially available from Evonic Corporation Persippany, N.J.
07054 USA.
[0105] The table below provides four tested formulations of the
pseudoplastic material or gel 104. All percentages refer to weight
parts of component or compound per weight of the total
composition.
TABLE-US-00001 Formula- Formula- Formula- Formula- Ingredient tion
#1 tion #2 tion #3 tion #4 Polyether and 36% 16 35 polyester
urethane acrylates Urethane acrylate 20 Polyether and 16 polyester
urethane acrylates Epoxy acrylate 20 Polyester acrylate 12
phosphine oxide 0.5 1 2 3 photo initiator Mono, di and 56% 55 10
tri functional reactive diluents Mono, di and 20 tri functional
reactive diluents Mono, di and 45 12.5 tri functional reactive
diluents Mono, di and 10 tri functional reactive diluents Fumed
silica 7.5 8 7 7.5 Urethane acrylate 36% 36% 37.5% 35 Epoxy
acrylate 20 Polyester acrylate 12 Photoinitiator 0.5% 3% 2% Mono.
di and 56% 33% 37.5% 45.5 tri functional reactive diluent Filler
(Flame 15 retardant) Fumed Silica 7.5% 8% 6 7 Surfactant 2
Mechanical 0.5 strength additive
[0106] The formulation was prepared by dissolving the curing agent,
which could be a photoinitiator, in the reactive diluent and then
adding the solution to the oligomer. Performance additives, such as
surfactants, fillers, and pigments, could be added at the mixing
stage and rheology modifiers could be added close to the end of the
mixing stage. Different mixing orders have been tested, but no
significant changes in the pseudoplastic material properties have
been noted.
[0107] The mix was prepared by using a planetary mixer and under
reduced pressure or vacuum to accomplish simultaneous formulation
degassing.
[0108] The prepared formulation of the pseudoplastic material had a
viscosity of about 200,000.00 mPas to 400,000 mPas at atmospheric
pressure. The viscosity was measured at room temperature
(25.degree. C.) by using a rotational rheometer model AR2000,
commercially available from TA Instruments New Castle, Del. 19720
U.S.A.
[0109] The pseudoplastic material formulation has shown different
degrees of shear thinning properties under different degrees of
agitation and pressure. FIG. 5 is a graph that demonstrates the
variations of viscosity and different shear rates.
[0110] It is to be understood that the foregoing illustrative
embodiments have been provided merely for the purpose of
explanation and are in no way to be construed as limiting of the
invention. Words used herein are words of description and
illustration, rather than words of limitation. In addition, the
advantages and objectives described herein may not be realized by
each and every embodiment practicing the present invention.
Further, although the invention has been described herein with
reference to particular structure, steps and/or embodiments, the
invention is not intended to be limited to the particulars
disclosed herein. Rather, the invention extends to all functionally
equivalent structures, methods and uses, such as are within the
scope of the appended claims. Those skilled in the art, having the
benefit of the teachings of this specification, may affect numerous
modifications thereto and changes may be made without departing
from the scope and spirit of the invention.
* * * * *