U.S. patent application number 16/710605 was filed with the patent office on 2020-04-16 for additive manufacturing for an overhang.
The applicant listed for this patent is HEWLETT-PACKARD DEVELOPMENT COMPANY, L.P.. Invention is credited to Alejandro Manuel De Pena, Hou T. Ng.
Application Number | 20200114639 16/710605 |
Document ID | / |
Family ID | 55440210 |
Filed Date | 2020-04-16 |
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United States Patent
Application |
20200114639 |
Kind Code |
A1 |
Ng; Hou T. ; et al. |
April 16, 2020 |
ADDITIVE MANUFACTURING FOR AN OVERHANG
Abstract
In one example, a non-transitory processor readable medium with
instructions thereon that when executed cause an additive
manufacturing machine to inhibit build material from coalescing in
an area of a first layer of build material where a second slice of
an object will overhang a first slice of the object formed in the
first layer of build material.
Inventors: |
Ng; Hou T.; (Campbell,
CA) ; De Pena; Alejandro Manuel; (Sant Cugat del
Valles, ES) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HEWLETT-PACKARD DEVELOPMENT COMPANY, L.P. |
Spring |
TX |
US |
|
|
Family ID: |
55440210 |
Appl. No.: |
16/710605 |
Filed: |
December 11, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15306480 |
Oct 24, 2016 |
10543672 |
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PCT/US2014/053715 |
Sep 2, 2014 |
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16710605 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29C 64/165 20170801;
B33Y 10/00 20141201; B29C 64/393 20170801; B33Y 50/02 20141201;
B33Y 30/00 20141201 |
International
Class: |
B33Y 30/00 20060101
B33Y030/00; B29C 64/386 20060101 B29C064/386; B29C 64/165 20060101
B29C064/165; B33Y 50/02 20060101 B33Y050/02; B33Y 10/00 20060101
B33Y010/00 |
Claims
1-15. (canceled)
16. An additive manufacturing process, comprising: forming a first
layer of build material; dispensing a liquid, light absorbing
coalescing agent on to build material in the first layer in a
pattern of a first slice of an object; dispensing a liquid
coalescence modifier agent on to build material in the first layer
covering an overhang area where a second slice of the object will
overhang the first slice; exposing build material in the first
layer patterned with coalescing agent to light to generate heat to
melt patterned build material in the first layer; forming a second
layer of build material on the first layer of build material;
dispensing the liquid, light absorbing coalescing agent on to build
material in the second layer, including the overhang area, in a
pattern of the second slice; and exposing build material in the
second layer patterned with coalescing agent to light to generate
heat to melt patterned build material.
17. The process of claim 16, comprising, before exposing build
material in the second layer patterned with coalescing agent to
light to generate heat to melt patterned build material, dispensing
coalescence modifier agent on to build material in the second layer
along an edge of the overhang area.
18. A non-transitory processor readable medium having instructions
thereon that when executed cause an additive manufacturing machine
to: form a first layer of build material; dispense a liquid, light
absorbing coalescing agent on to build material in the first layer
in a pattern of a first slice of an object; dispense a liquid
coalescence modifier agent on to build material in the first layer
covering an overhang area where a second slice of the object will
overhang the first slice; expose build material in the first layer
patterned with coalescing agent to light to generate heat to melt
patterned build material in the first layer; form a second layer of
build material on the first layer of build material; dispense the
liquid, light absorbing coalescing agent on to build material in
the second layer, including the overhang area, in a pattern of the
second slice; and expose build material in the second layer
patterned with coalescing agent to light to generate heat to melt
patterned build material.
19. The processor readable medium of claim 16, having instructions
thereon to, before exposing build material in the second layer
patterned with coalescing agent to light to generate heat to melt
patterned build material, dispensing coalescence modifier agent on
to build material in the second layer along an edge of the overhang
area.
20. A computer program product that includes the processor readable
medium of claim 18.
21. An additive manufacturing machine controller that includes the
processor readable medium of claim 18.
22. An additive manufacturing machine, comprising: a first device
to layer powdered build material; a second device to dispense a
liquid, light absorbing coalescing agent on to build material; a
third device to dispense a liquid coalescence modifier agent on to
build material; a light source to apply light energy to build
material; and a controller to execute instructions to: cause the
first device to layer build material in a first layer; cause the
second device to dispense the coalescing agent on to build material
in the first layer in a first pattern of a first slice of an
object; cause the third device to dispense the coalescence modifier
agent on to build material in the first layer in an overhang area
where a second slice of the object will overhang the first slice;
cause the light source to apply light energy to build material in
the first layer patterned with coalescing agent to generate heat to
melt patterned build material in the first layer; cause the first
device to layer build material in a second layer on the first
layer; cause the second device to dispense the coalescing agent on
to build material in the second layer, including the overhang area,
in a pattern of the second slice; and cause the light source to
apply light energy to build material in the second layer patterned
with coalescing agent to generate heat to melt patterned build
material in the second layer.
23. The machine of claim 22, wherein the controller is to execute
instructions to cause the third device to, before causing the light
source to apply light energy to build material in the second layer,
dispense the coalescence modifier agent on to build material in the
second layer along an edge of the overhang area.
Description
BACKGROUND
[0001] Additive manufacturing machines produce 3D
(three-dimensional) objects by building up layers of material. Some
additive manufacturing machines are commonly referred to as "3D
printers" because they often use inkjet or other printing
technology to apply some of the manufacturing materials. 3D
printers and other additive manufacturing machines make it possible
to convert a CAD (computer aided design) model or other digital
representation of an object directly into the physical object.
DRAWINGS
[0002] FIGS. 1-10 present a sequence of sections illustrating one
example for additive manufacturing an object with an overhang.
[0003] FIGS. 11 and 12 are flow diagrams illustrating example
additive manufacturing processes.
[0004] FIG. 13 illustrating one example of a processor readable
medium with instructions to help form an overhang during the
additive manufacture of an object with an overhang.
[0005] FIG. 14 is a block diagram illustrating one example of an
additive manufacturing machine implementing a controller with a
processor readable medium with overhang instructions such as the
medium shown in FIG. 13.
[0006] FIG. 15 is a block diagram illustrating one example of an
additive manufacturing system implementing a CAD computer program
product with a processor readable medium with overhang instructions
such as the medium shown in FIG. 13.
[0007] The same part numbers designate the same or similar parts
throughout the figures.
DESCRIPTION
[0008] Additive manufacturing machines make a 3D object through the
solidification of one or more layers of a build material. Additive
manufacturing machines make objects based on data in a 3D model of
an object created, for example, with a CAD computer program
product. The model data is processed into slices each defining that
part of a layer or layers of build material to be solidified. The
examples of additive manufacturing described below use a technique
sometimes referred to as "light area processing" (LAP) in which a
light absorbing ink or other suitable coalescing agent is dispensed
on to a layer of build material in the desired pattern and then
exposed to light to solidify the patterned build material. LAP
coalescing agents absorb light to generate heat that sinters, melts
or otherwise solidifies (or initiates solidification of) the
patterned build material.
[0009] Coalescing agent may bleed into build material outside the
desired pattern, causing the unwanted solidification of build
material. Also, heat generated in the patterned build material can,
under some circumstances, propagate into and solidify surrounding,
unpatterned build material. The unwanted solidification of build
material can degrade the overall dimensional accuracy and
appearance of the manufactured object. Such degradation is often
manifested, for example, in poorly defined edges.
[0010] Modifier agents have been developed to block or neutralize
the effects of the coalescing agent. The unwanted solidification of
build material may be controlled by dispensing a coalescence
modifier agent on to unpatterned build material surrounding build
material patterned with a coalescing agent. For example, modifier
agents and additive manufacturing processes are described in
international patent application no. PCT/US14/36169 filed Apr. 30,
2014, and titled Three Dimensional Printing Method, to prevent or
reduce the degree of coalescence of targeted areas of build
material to help control the dimensional accuracy and surface
roughness along the edges in each layer of the manufactured
object.
[0011] It has been discovered that coalescence modifier agents may
also be used to control the unwanted fusing between layers of build
material, fusing that can lead to excessive surface roughness in
objects with overhangs. Accordingly, a new additive manufacturing
process has been developed to inhibit or prevent interlayer fusing
to obtain smooth, well defined overhangs. In one example, the new
process includes forming a first layer of build material,
solidifying build material in the first layer to form a first
slice, and dispensing a coalescence modifier agent on to build
material in the first layer covering an area where a second slice
will overhang the first slice. The modifier agent prevents, or at
least inhibits, build material in the second layer fusing with
build material in the first layer in the overhang area, so that the
bottom of the overhang in the second slice will be smoother and
more well defined. The modifier agent may be dispensed on to the
first layer of build material before solidification of the first
slice, for example to also provide edge control, or after
solidification of the first slice.
[0012] A processor readable medium with instructions for overhang
surface control using a coalescence modifier agent during additive
manufacturing may be implemented, for example, in a CAD computer
program product, in an object model processor, or in the controller
for the additive manufacturing machine.
[0013] As used in this document: a "coalescing agent" means a
substance that causes or helps cause a build material to coalesce
or solidify or to both coalesce and solidify; a "coalescence
modifier agent" means a substance that inhibits or prevents
solidification of a build material, for example by modifying the
effect of a coalescing agent; and a "slice" means one or more
slices of a multi-slice object or the object itself for a single
slice object.
[0014] The sequence of sections presented in FIGS. 1-10 illustrate
one example for manufacturing an object 10 (FIG. 10) with an
overhang 12 (FIG. 10). FIGS. 11 and 12 are flow diagrams
illustrating example additive manufacturing processes 100 and 120,
respectively, implemented in FIGS. 1-10. Referring to FIG. 1, in
this example a supply of powdered build material 14 is held on a
delivery piston 16 in a supply bed 18. A roller 20 or other
suitable layering device moves build material 14 from supply bed 18
to a receiving piston 22 in a manufacturing bed 24, as indicated by
arrow 26. Pistons 16 and 22 move up and down as build material 14
is moved from supply bed 18 to manufacturing bed 24. Any suitable
build material 14 may be used to make the desired solid object,
which may be hard or soft, rigid or flexible, elastic or inelastic.
Also, while a powdered build material 14 is depicted by particles
28 in this example, suitable non-powdered build materials could
also be used.
[0015] In FIG. 1, a first layer 30 of build material 14 is formed
in manufacturing bed 24 (block 102 in FIG. 11). In some
implementations, it may be desirable to pre-heat build material 14
in the first few layers to help keep each layer flat during
solidification. Individual layers of build material 14 may be
pre-heated in bed 24, as shown in FIG. 2, or build material 14 may
be pre-heated in supply bed 18. While the pre-heating temperature
will vary depending on the characteristics of build material 14,
the pre-heating temperature usually will be 5.degree. C. to
50.degree. C. below the melting point of the build material (e.g.,
150.degree. C. to 170.degree. C. for a PA 12 build material). Any
suitable heater 32 may be used.
[0016] In FIG. 3, a coalescing agent 34 is dispensed on to build
material 14 in layer 30 in a pattern corresponding to the object
slice (block 104 in FIG. 11), for example with an inkjet type
dispenser 36. This pattern for coalescing agent 34 is depicted by
an area 38 of dense stippling in the figures. In FIG. 4, a
coalescence modifier agent 40 is dispensed on to build material 14
in layer 30 covering an area 42 where a second object slice will
overhang the first slice (block 106 in FIG. 11), for example with
an inkjet type dispenser 44. Overhang area 42 covered by
coalescence modifier agent 40 is depicted by light stippling in the
figures. Coalescence modifier agent 40 may also be dispensed on to
other areas of build material layer 30 to help define other aspects
of the object slice, including interspersed with the pattern of the
coalescing agent to change the material characteristics of the
slice. Although two distinct inkjet type dispensers 36, 44 are
shown, agents 34 and 40 could be dispensed from the same dispensers
integrated into a single device, for example using different
printheads (or groups of printheads) in a single inkjet printhead
assembly.
[0017] In FIG. 5, the area of layer 30 patterned with coalescing
agent 34 is exposed to light to solidify build material and form
first object slice 46 (block 108 in FIG. 11). In FIG. 6, a second
layer 50 of build material 14 is formed in manufacturing bed 24
over first layer 30 (block 110 in FIG. 11). In FIG. 7, a coalescing
agent 34 is dispensed on to build material 14 in layer 50 in a
pattern in an area 52 corresponding to the second object slice
(block 112 in FIG. 11), including an area 54 overhanging first
slice 46. In FIG. 8, a coalescence modifier agent 40 is dispensed
on to build material 14 in layer 50 in area 56 to help prevent the
unwanted solidification of build material along the edge of the
overhang (block 114 in FIG. 11).
[0018] In FIG. 9, the area 52 of layer 50 patterned with coalescing
agent 34 is exposed to light to solidify build material to form
second object slice 58 overhanging first slice 46 (block 116 in
FIG. 11). Second slice 58 includes part 60 that hangs over first
slice 46. While distinct first and second slices 46 and 58 are
shown in FIG. 9, the two slices actually fuse together into a
single part upon solidification of the second slice. The now fused
slices 58, 46 may be removed from manufacturing bed 24 as a
finished object 10 shown in FIG. 10. While a simple two-slice
object 10 is shown, the same process steps may be used to form more
complex, multi-slice objects.
[0019] FIG. 12 illustrates an example of an additive manufacturing
process 120. Referring to FIG. 12, a first layer of build material
is formed (block 122) and build material in the first layer
solidified to form a first slice (block 124), for example as
described above with reference to FIGS. 1-3 and 5. A coalescence
modifier agent is dispensed on to build material in the first layer
covering an area where a second slice will overhang the first slice
(block 126), for example as described above with reference to FIG.
4. The coalescence modifier agent may be dispensed before, during
or after solidifying build material in the first layer at block
124. A second layer of build material is formed on the first layer
of build material (block 128) and build material in the second
layer is solidified to form a second slice overhanging the first
slice (block 130), for example as described above with reference to
FIGS. 6-9.
[0020] FIG. 13 is a block diagram illustrating a processor readable
medium 64 with instructions 66 to help form an overhang during the
manufacture of a 3D object. A processor readable medium 64 is any
non-transitory tangible medium that can embody, contain, store, or
maintain instructions for use by a processor. Processor readable
media include, for example, electronic, magnetic, optical,
electromagnetic, or semiconductor media. More specific examples of
suitable processor readable media include a hard drive, a random
access memory (RAM), a read-only memory (ROM), memory cards and
sticks and other portable storage devices.
[0021] Overhang instructions 66 include instructions to inhibit
build material from coalescing in an area of a first layer of build
material where a second slice of an object will overhang the first
slice, for example by dispense a coalescing modifier agent at block
126 in FIG. 12. Instructions 66 may include other additive
manufacturing instructions, for example instructions to form and
solidify shown at blocks 122, 124, 128 and 130 in FIG. 12.
Processor readable medium 64 with instructions 66 may be
implemented, for example, in a CAD computer program product, in an
object model processor, or in a controller for an additive
manufacturing machine. Control data to inhibit solidification can
be generated, for example, by processor readable instructions on
the source application, usually a CAD computer program product, in
an object model processor, or by processor readable instructions on
the additive manufacturing machine.
[0022] FIG. 14 is a block diagram illustrating one example of an
additive manufacturing machine 68 implementing a controller 70 with
overhang instructions 66. Referring to FIG. 14, machine 68 includes
controller 70, a manufacturing bed or other suitable support 24, a
roller or other suitable build material layering device 20, a
coalescing agent dispenser 36, a coalescence modifier agent
dispenser 44, a heater 32 and a light source 48. The in-process
object structure is supported on support 24 during manufacturing.
In some machines 68, support 24 may support the in-process
structure during uncaking. Also, in some machines 68, support 24 is
movable at the urging of controller 70 to compensate for the
changing thickness of the in-process structure, for example as
layers of build material are added during manufacturing.
[0023] Build material layering device 20 layers build material on
support 24 and on the in-process structures and may include, for
example, a device to dispense the build material and a blade or
roller to distribute the build material uniformly to the desired
thickness for each layer. Coalescing agent dispenser 36 dispenses
coalescing agent selectively at the direction of controller 70 on
to build material, for example as described above with reference to
FIGS. 1-11. Coalescence modifier agent dispenser 44 dispenses
modifier agent selectively at the direction of controller 70 on to
build material, for example as described above with reference to
FIGS. 1-11. While any suitable dispensers 36, 44 may be used,
inkjet printheads are often used in additive manufacturing machines
because of the precision with which they can dispense agents and
their flexibility to dispense different types and formulations of
agents. Manufacturing machine 68 may include a heater 32 if it is
desired to pre-heat the build material. Manufacturing machine 36
includes a light source 48 to apply light energy to solidify build
material treated with coalescing agent.
[0024] Controller 70 represents the processor (or multiple
processors), the associated memory (or multiple memories) and
instructions, and the electronic circuitry and components needed to
control the operative elements of machine 68. In particular,
controller 70 includes a memory 72 having a processor readable
medium 64 with overhang instructions 66 and a processor 74 to read
and execute instructions 66. For example, controller 70 would
receive control data and other instructions from a CAD program to
make an object that includes an overhang and execute local overhang
instructions 66 as part of the process of making the object.
[0025] Alternatively, overhang instructions 66 may be embodied in a
processor readable medium 64 separate from controller 70, for
example as part of a CAD computer program product shown in FIG. 15.
Referring to FIG. 15, an additive manufacturing system 76 includes
an additive manufacturing machine 68 operatively connected to a CAD
computer program product 78 with overhang instructions 66 residing
on a processor readable medium 64. Any suitable connection between
machine 68 and CAD program product 78 may be used to communicate
instructions and control data to machine 68 including, for example,
a wired link, a wireless link, and a portable connection such as a
flash drive or compact disk.
[0026] Light source 48 applies light energy to build material to
cause the solidification of portions of the build material
according to where coalescing agent has been delivered or has
penetrated. In some examples, light source 48 is an infra-red (IR)
or near infra-red light source, or a halogen light source. Light
source 48 may be a single light source or an array of multiple
light sources. In some examples, light source 48 is configured to
apply light energy in a substantially uniform manner simultaneously
to the whole surface of a layer of build material. In other
examples, light source 48 is configured to apply energy to only a
select areas of the whole surface of a layer of build material. In
these examples light source 48 may be moved or scanned across the
layer of build material such that a substantially equal amount of
energy is applied to the selected areas or across the whole surface
of a layer of build material.
[0027] The combination of build material, coalescing and
coalescence modifier agents, and light energy may be selected for
an object slice so that (1) build material with no coalescing agent
does not coalesce when the energy is applied, (2) build material
with only coalescing agent solidifies when energy is applied; or
(3) build material with both agents undergo a modified degree of
coalescence between no coalescence and solidification with or
without the application of energy.
[0028] Build material 14 may be a powder, a liquid, a paste, or a
gel. Examples of build material 14 include semi-crystalline
thermoplastic materials with a processing window of greater than
5.degree. C. (i.e., the temperature range between the melting point
and the re-crystallization temperature). Some specific examples of
the build material 14 include polyamides (e.g., PA or nylon 11, PA
or nylon 12, PA or nylon 6, PA or nylon 8, PA or nylon 9, PA or
nylon 66, PA or nylon 612, PA or nylon 812, PA or nylon 912, etc.).
Other specific examples of the build material 14 include
polyethylene, polyethylene terephthalate (PET), and amorphous
variation of these materials. Still other examples of suitable
build materials 16 include polystyrene, polyacetals, polypropylene,
polycarbonate, polyester, thermal polyurethanes, other engineering
plastics, and blends of any two or more of the polymers listed
herein. Core shell polymer particles of these materials may also be
used.
[0029] Build material 14 may have a melting point ranging from
about 50.degree. C. to about 400.degree. C. In some
implementations, it is desirable that the melting point of the
build material 14 be less than (lower than) the melting point of an
inorganic salt used in the modifying agent. As examples, polyamide
12 having a melting point of 180.degree. may be used, or thermal
polyurethanes having a melting point ranging from about 100.degree.
C. to about 165.degree. C. may be used. When a combination of
polymer particles is used in the build material 14, at least one of
the particles has a melting point below the melting point of the
inorganic salt. In an example, each of the plurality of polymer
particles used in the build material 14 has a melting point below
the melting point of the inorganic salt.
[0030] Build material 14 may be made up of similarly sized
particles or differently sized particles. In the example shown in
FIGS. 1-9, the build material 14 includes particles of three
different sizes. As one example of the different sizes for each of
the build material particles, the average of each size particle may
be greater than 50 .mu.m, between 10 .mu.m and 30 .mu.m, and less
than 10 .mu.m. In an example, the largest particles are present in
an amount ranging from 70 wt % to 95 wt %, the medium particles
present in an amount ranging from 0.5 wt % to 21 wt %, and the
smallest particles present in an amount ranging from greater than 0
wt % up to 21 wt %.
[0031] Build material 14 may include, in addition to polymer
particles, a charging agent and/or a flow aid. Charging agent(s)
may be added to suppress tribo-charging. Examples of suitable
charging agent(s) include aliphatic amines (which may be
ethoxylated), aliphatic amides, quaternary ammonium salts (e.g.,
behentrimonium chloride or cocamidopropyl betaine), esters of
phosphoric acid, polyethylene glycol esters, or polyols. Some
suitable commercially available charging agents include
HOSTASTAT.RTM. FA 38 (natural based ethoxylated alkylamine),
HOSTASTAT.RTM. FE2 (fatty acid ester), and HOSTASTAT.RTM. HS 1
(alkane sulfonate), each of which is available from Clariant Int.
Ltd.). In an example, the charging agent is added in an amount
ranging from greater than 0 wt % to less than 5 wt % based upon the
total wt % of the polymer particles. A flow aid improves the
flowability of build material 14 by reducing friction, lateral
drag, and tribo-charge buildup, and may be particularly desirable
when build material particles are less than 25 .mu.m in size.
Examples of suitable flow aids include tricalcium phosphate (E341),
powdered cellulose (E460(ii)), magnesium stearate (E470b), sodium
bicarbonate (E500), sodium ferrocyanide (E535), potassium
ferrocyanide (E536), calcium ferrocyanide (E538), bone phosphate
(E542), sodium silicate (E550), silicon dioxide (E551), calcium
silicate (E552), magnesium trisilicate (E553a), talcum powder
(E553b), sodium aluminosilicate (E554), potassium aluminium
silicate (E555), calcium aluminosilicate (E556), bentonite (E558),
aluminium silicate (E559), stearic acid (E570), or
polydimethylsiloxane (E900). In an example, the flow aid is added
in an amount ranging from greater than 0 wt % to less than 5 wt %
based upon the total wt % of the particles.
[0032] Suitable coalescing agents 34 include water-based
dispersions with an active, radiation absorbing binding agent. The
active agent may be, for example, an infrared light absorber, a
near infrared light absorber, or a visible light absorber. As one
example, the coalescing agent may be an ink-type formulation
including carbon black as the active material. An example of this
ink-type formulation is commercially known as CM997A available from
Hewlett-Packard Company. Examples of inks including visible light
enhancers as the active agent are dye based colored ink and pigment
based colored ink. Examples of pigment based inks include the
commercially available inks CM993A and CE042A, available from
Hewlett-Packard Company. The aqueous nature of some coalescing
agent enables the coalescing agent to penetrate the layer of build
material. For hydrophobic build materials the presence of a
co-solvent and/or a surfactant in the coalescing agent may assist
in obtaining the desired wetting. One or more coalescing agent may
be dispensed to form each slice.
[0033] Suitable coalescence modifier agents may separate individual
particles of the build material to prevent the particles from
joining together and solidifying as part of the slice. Examples of
this type of coalescence modifier agent include colloidal,
dye-based, and polymer-based inks, as well as solid particles that
have an average size less than the average size of particles of the
build material. The molecular mass of the coalescence modifier
agent and its surface tension should be such that it enables the
agent to penetrate sufficiently into the build material to achieve
the desired mechanical separation. In one example, a salt solution
may be used as a coalescence modifier agent. In other examples,
inks commercially known as CM996A and CN673A available from
Hewlett-Packard Company may be used as a coalescence modifier
agent.
[0034] Suitable coalescence modifier agents may act to modify the
effects of a coalescing agent by preventing build material from
reaching temperatures above its melting point during heating. A
fluid that exhibits a suitable cooling effect may be used as this
type of coalescence modifier agent. For example, when build
material is treated with a cooling fluid, energy applied to the
build material may be absorbed evaporating the fluid to help
prevent build material from reaching its melting point. Thus, for
example, a fluid with a high water content may be a suitable
coalescence modifier agent.
[0035] Other types of coalescence modifier agent may be used. An
example of a coalescence modifier agent that may increase the
degree of coalescence may include, for example, a plasticizer.
Another example of a coalescence modifier agent that may increase
the degree of coalescence may include a surface tension modifier to
increase the wettability of particles of build material.
[0036] In one example, the modifier agent includes an inorganic
salt, a surfactant, a co-solvent, a humectant, a biocide, and
water. In some examples, the modifier agent consists of these
components, and no other components. It has been found that this
particular combination of components effectively reduces or
prevents coalescence bleed, in part because of the presence of the
inorganic salt. An inorganic salt used in the modifier agent has a
relatively high heat capacity, but a relatively low heat
emissivity. These characteristics render the modifier agent capable
of absorbing the radiation (and its associated thermal energy)
applied thereto, and also capable of retaining a bulk of the
thermal energy therein. As such, very little, if any, of the
thermal energy is transferred from the modifier agent to the build
material.
[0037] In addition, the inorganic salt may also have a lower
thermal conductivity and/or a higher melting point than the thermal
conductivity and/or melting point of the build material and, in
some instances, of the active material in the coalescing agent.
Upon absorbing radiation and thermal energy, the inorganic salt
does not melt, and also does not transfer a sufficient amount of
heat to the surrounding build material. Therefore, the modifier
agent can effectively reduce curing of the build material when
build material is in contact with both the coalescing agent and the
modifier agent, and prevent curing when the build material is in
contact with the modifier agent alone.
[0038] An inorganic salt in the modifier agent may be water
soluble. Examples of suitable water soluble inorganic salts include
sodium iodide, sodium chloride, sodium bromide, sodium hydroxide,
sodium sulfate, sodium carbonate, sodium phosphate, potassium
iodide, potassium chloride, potassium bromide, potassium hydroxide,
potassium sulfate, potassium carbonate, potassium phosphate,
magnesium iodide, magnesium chloride, magnesium bromide, magnesium
phosphate, and combinations thereof. The inorganic salt may be
present in an amount ranging from about 5.0 wt % to about 50 wt %
with respect to a total weight of the modifier agent.
[0039] The modifier agent may also include the surfactant. The type
and amount of surfactant may be selected so that a contact angle
with the build material is less than 45.degree.. The components of
the modifier agent may be mixed together, and then the amount of
surfactant adjusted to achieve the desirable contact angle. It has
been found that a suitable amount of surfactant to achieve the
desired contact angle may range from 0.1 wt % to 10 wt % with
respect to the total weight of the modifier agent. Examples of
suitable surfactants include tetraethylene glycol, liponic ethylene
glycol 1 (LEG-1), a self-emulsifiable, nonionic wetting agent based
on acetylenic diol chemistry (e.g., SURFYNOL.RTM. SEF from Air
Products and Chemicals, Inc.), a nonionic fluorosurfactants (e.g.,
CAPSTONE.RTM. fluorosurfactants from DuPont, previously known as
ZONYL FSO), and combinations thereof.
[0040] As noted above, the modifier agent may include a co-solvent,
a humectant, and a biocide. In one example, a co-solvent is present
in an amount ranging from about 1.0 wt % to about 20 wt %, a
humectant in an amount ranging from 0.1 wt % to 15 wt %, and a
biocide in an amount ranging from 0.01 wt % to 5 wt %, each of
which is with respect to the total weight of the modifier agent.
Suitable co-solvents include 2-hydroxyethyl-2-pyrollidinone,
2-pyrollidinone, 1,6-hexanediol, and combinations thereof. Suitable
humectants include Di-(2-hydroxyethyl)-5,5-dimethylhydantoin (e.g.,
DANTOCOL.RTM. DHF from Lonza, Inc.), propylene glycol, hexylene
glycol, butylene glycol, glyceryl triacetate, vinyl alcohol,
neoagarobiose, glycerol, sorbitol, xylitol, maltitol, polydextrose,
quillaia, glycerin, 2-methyl-1,3-propanediol, and combinations
thereof. Suitable biocides include an aqueous solution of
1,2-benzisothiazolin-3-one (e.g., PROXEL.RTM. GXL from Arch
Chemicals, Inc.), quaternary ammonium compounds (e.g., BARDAC.RTM.
2250 and 2280, BARQUAT.RTM. 50-65B, and CARBOQUAT.RTM. 250-T, all
from Lonza Ltd. Corp.), and an aqueous solution of
methylisothiazolone (e.g., KORDEK.RTM. MLX from The Dow Chemical
Co.).
[0041] In one example, the balance of the modifier agent is water.
The amount of water may vary depending upon the amounts of
inorganic salt, surfactant, co-solvent, humectant, and biocide.
[0042] "A" and "an" used in the claims means one or more.
[0043] The examples shown in the figures and described above
illustrate but do not limit the invention, which is defined in the
following Claims.
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