WO2023123482A1

WO2023123482A1 - Two-part silicone composition for additive manufacturing

Info

Publication number: WO2023123482A1
Application number: PCT/CN2021/143981
Authority: WO
Inventors: Liya JIA; Yuanzhi YUE; Genli WU
Original assignee: Elkem Silicones Shanghai Co., Ltd.
Priority date: 2021-12-31
Filing date: 2021-12-31
Publication date: 2023-07-06

Abstract

The present invention refers to a method for additive manufacturing a silicone elastomer and the silicone elastomer obtained therefrom. The present invention further refers to a two-part silicone composition W used in additive manufacturing such silicone elastomer. Wherein the first part of the silicone composition is charged into a liquid bath and the second part is charged into a dispensing head of a 3D printer. Proper selection of rheology behaviour for the first part in liquid bath has a contribution to the well-formed printed article.

Description

Two-part Silicone Composition for Additive Manufacturing

Technical Field

The present invention refers to the field of additive manufacturing a silicone elastomer. In particular, the present invention refers to a method for additive manufacturing a silicone elastomer and the silicone elastomer obtained therefrom. The present invention further refers to a two-part silicone composition W used in additive manufacturing such silicone elastomer.

Background Art

In recent years, a new kind of manufacturing method, additive manufacturing (AM) , also refers to 3D printing technique is emerging and has attracted extensive attention in industry. Compared with traditional removal type processes such as molding or machining, additive manufacturing (AM) can obtain desired 3D objects by adding materials through layer by layer process. Such technology makes it possible to achieve intended articles in any shape, especially for those with more complex geometry. Besides, the low cost and short production cycle in combination with less waste are also important advantages for manufacturers.

Currently, more and more polymeric materials have been attempted to be used for 3D printing process including FDM, SLA, DLP and the like. Silicone materials may impart the final articles favorable properties such as low elastic modulus, high extensibility, toughness, in addition with excellent thermal and oxidative stability as well as chemical inertness. However, silicone materials are different from rigid materials. It is difficult to form some silicone elastomer articles using conventional 3D printing techniques due to the properties for silicone materials used. Thus, additive manufacturing technique suitable for rigid materials are highly advanced in comparison to the techniques available for silicone materials.

There are challenges for 3D printing silicone materials. Direct-ink-writing process has been used to print silicone composition via extrusion technology. Even if the silicone compositions can retain its shape during additive manufacturing via layer by layer process, it is difficult to keep their shape as the height of printed layer increases. Meanwhile, due to gravity and movement of nozzle, the slight displacement might take place in certain printed layer, which would inevitably lead to deformed printed objects. What’s more, the problem would be even worse when the intended object having more complex structure such as hollow or overhanging portions.

In prior art, for 3D printing objects with overhanging portions, support systems are normally required to prevent the printed materials from falling under gravity. For example, US5503785, EP1773560A2, WO2010045147A3 all employ support materials or structures to keep the printed materials in place.

CN106313505 discloses a two-components silicone 3D printer and a printing method thereof. The two-components of silicone materials are charged into two pressure barrels, respectively, and are mixed before extruding through the printing nozzle. However, this method utilizes the conventional printing platform which would still need a support material or structure if objects with overhanging structures are to be printed.

CN106433142 refers to a silicone 3D printer and a printing method thereof. The silicone 3D printer comprises a movement module, a printing module and a software controlling system. Although a support material or structure may be eliminated, this reference is silent about the effect of the rheology properties for silicone material on the printing process and curing process.

US20210363340A1 mentions an organic microgel system as support material for 3D printing of silicone materials and 3D printing method using the same. Specifically, the organic microgel system comprises a plurality of microgel particles formed by blending a di-block copolymer and a tri-block copolymer in an organic solvent. The organic microgel system may allow 3D printing of silicone objects in high precision. However, a support material is still required in this reference.

As shown from above, none of the prior art pays attention to the effect of the rheology behavior of silicone material in liquid bath on the printing process and curing process. There is still a need to provide an improved silicone material suitable for additive manufacturing which enables stable and fully cured printed layers and thus the well-formed printed objects as the printing process proceeds without supporting materials. Also, there is still a need to provide a method for additive manufacturing the silicone elastomer article from such special silicone materials.

Contents of the Invention

Accordingly, an objective of the present invention is to provide a method for additive manufacturing a silicone elastomer article from a two-part silicone composition W.

Another objective of the present invention is to provide a silicone elastomer article obtained from such method.

A further objective of the present invention is to provide a use of the silicone elastomer article obtained from such method.

A still further objective of the present invention is to provide a two-part silicone composition W used in the method in accordance with the present invention.

A yet still further objective of the present invention is to provide a use of the two-part silicone composition W for additive manufacturing a silicone elastomer article.

These objectives, among others, are achieved by the present invention which relates first to a method for additive manufacture a silicone elastomer article from a two-part silicone composition W, comprising:

i) charging the first part of the silicone composition W into a liquid bath of a 3D printer;

ii) charging the second part of the silicone composition W into a dispensing head of the 3D printer;

iii) dispensing the second part of the silicone composition W into the first part of the silicone composition W in the liquid bath to form a first printed layer;

iv) optionally repeating step iii) for additional layers needed;

v) allowing the printed layers in the liquid bath to partially or totally crosslink, optionally by heating, to obtain a silicone elastomer article;

vi) removing the resulting silicone elastomer article from the liquid bath, wherein the two-part silicone composition W comprises:

(a) at least one organopolysilicone;

(b) at least one crosslinking agent; and

(c) at least one catalyst;

wherein the first part of the silicone composition W comprises components (a) and (c) and the second part comprises component (b) , or otherwise the first part of the silicone composition W comprises components (a) and (b) and the second part comprises component (c) ,

the first part of the silicone composition W has a dynamic viscosity in the range of 500 mPa·s to 1,000,000 mPa·s, preferably in the range of 5,000 mPa·s to 500,000 mPa·s, more preferably in the range of 10,000 mPa·s to 300,000 and even more preferably from 15,000 mPa·s to 200,000 mPa·s,

the ratio of the dynamic viscosity at 2rpm to the dynamic viscosity at 20rpm for the first part of the silicone composition W (Viscosity-2 /Viscosity-20) is in the range of 1 to 6, preferably in the range of 1 to 5.5, more preferably in the range of 1 to 4, and even more preferably in the range of 1 to 3.

The present invention further refers to a silicone elastomer article obtained from the present method.

The present invention still further refers to a two-part silicone composition W used in the present method as indicated above.

The present invention further refers to the use of the two-part silicone composition W in accordance with the present invention for additive manufacturing a silicone elastomer article.

It has surprisingly found by the present inventor that the rheology behavior for the first part of the silicone composition W in liquid bath plays a very key role in the status of the printed layers as well as the curing state thereof and thus the quality of the final printed objects. Such rheology behavior comprises the viscosity characterized by the dynamic viscosity at 2rpm (Viscosity-2) and the thixotropy characterized by the ratio of the dynamic viscosity at 2rpm to the dynamic viscosity at 20rpm (Viscosity-2 /Viscosity-20) . Proper selection of the viscosity (Viscosity-2) and thixotropy (Viscosity-2 /Viscosity-20) for the first part in liquid bath are required for stable and fully cured printed layers and thus well-formed printed objects when the printing procedure is in progress.

Too high viscosity and thixotropy would lead to relatively slow mixing of the first and second part in liquid bath, resulting in the printed layer uncured inside. Meanwhile, it might be difficult for the printing nozzle to move correctly as intended path. Otherwise, too low viscosity and thixotropy allows the fast diffusion of the second part prior to reacting with the first part in place which might cause the wider printed layers and thus the failure of the printing process.

The proper selection of the viscosity (Viscosity-2) and thixotropy (viscosity-2 /viscosity-20) for the first part in liquid bath enables the printed layer to be self-supported without support materials.

By the terminology of “unstable printed layers” , as used in the present invention, it means the width of the printed layers varies outside acceptable range. On contrary, the term of “stable printed layers” refers to the width of the printed layers varies within acceptable range during the 3D printing process.

By term of “viscosity ratio” , or in other words “viscosity-2/viscosity-20” or “ratio of viscosity” , it refers to the ratio of the dynamic viscosity at 2rpm to the dynamic viscosity at 20rpm for the first part of the silicone composition W in liquid bath.

Method for additive manufacturing

3D printing is generally associated with a host of related technologies used to fabricate physical objects from computer generated, e.g. computer-aided design (CAD) , data sources.

The present invention generally incorporates ASTM Designation F2792-12a, “Standard Terminology for Additive Manufacturing Technologies” .

“3D printer” is defined as “a machine used for 3D printing” and “3D printing” is defined as the fabrication of objects through the deposition of a material using nozzle (s) of printing head, or another printer technology.

“Additive manufacturing (AM) ” is defined as “a process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing methodologies. Synonyms associated with and encompassed by 3D printing include additive fabrication, additive processes, additive techniques, additive layer manufacturing, layer manufacturing, and freeform fabrication. Additive manufacturing (AM) may also be referred to as rapid prototyping (RP) . As used herein, “3D printing" is generally interchangeable with "additive manufacturing” and vice versa.

As used herein, “3D or three-dimensional article, object or part” means an article, object or part obtained by additive manufacturing or 3D printing as disclosed above.

In general, all 3D printing processes have a common starting point, which is a computer-generated data source or program which may describe an object. The computer-generated data source or program can be based on an actual or virtual object. For example, an actual object can be scanned using a 3D scanner and scan data can be used to make the computer-generated data source or program. Alternatively, the computer-generated data source or program may be designed from scratch.

The computer-generated data source or program is typically converted into a standard tessellation language (STL) file format; however other file formats can also or additionally be used. The file is generally read into 3D printing software, which takes the file and optionally user input to separate it into hundreds, thousands, or even millions of “slices. ” The 3D printing software typically outputs machine instructions, which may be in the form of G-code, which is read by the 3D printer to build each slice of the precursor of the silicone elastomer article. The machine instructions are transferred to the 3D printer, which then builds the objects, layer by layer, based on this slice information in the form of machine instructions. Thicknesses of these slices may vary.

“Material jetting” is defined as ”an additive manufacturing process in which droplets of build material are selectively deposited” . The material is applied with the aid of a printing head in the form of individual droplets, discontinuously, at the desired location of the work plane (Jetting) . 3D apparatus and a process for the step-by-step production of 3D structures with a printing head arrangement comprising at least one, preferably 2 to 200 nozzles of printing head, allowing the site-selective application suitable for a plurality of materials. The application of the materials by means of inkjet printing imposes specific requirements on the viscosity of the materials.

In a 3D jetting printer one or a plurality of reservoirs are subject to pressure and being connected via a metering line to a metering nozzle. Upstream or downstream of the reservoir there may be devices which make it possible for multicomponent silicone compositions to be homogeneously mixed and/or to evacuate dissolved gases. One or a plurality of jetting apparatuses operating independently of one another may be present, to construct the precursor of the silicone elastomer article from different silicone compositions, or, in the case of more complex structures, to permit composite parts made from silicone elastomers and other plastics.

The individual metering nozzles can be positioned accurately in x-, y-, and z-directions to permit precisely targeted deposition of the silicone composition drops and on the substrate or, in the subsequent course of formation of shaped parts, on the precursor of the silicone elastomer article, which has already been placed.

The average diameter of the nozzle defines the thickness of the layer. Typically, the diameter of the nozzle is comprised from 50 to 3,000μm, preferably from 100 to 2000μm and most preferably from 100 to 1000 μm.

The materials to be dispensed through the nozzles may be supplied from cartridge-like systems. The cartridges may include a nozzle or nozzles with an associated fluid reservoir or fluids reservoirs. It is also possible to use a coaxial two cartridges system with a static mixer and only one nozzle.

Pressure will be adapted to the fluid to be dispensed, the associated nozzle average diameter and the printing speed. Cartridge pressure could vary from 1 to 28 bars, preferably from 2 to 25 bars and most preferably from 4 to 8 bars. When nozzle diameters lower than 100μm are used, cartridge pressure shall be higher than 20 bars to get good material extrusion. An adapted equipment using aluminium cartridges shall be used to withstand such a pressure.

The nozzle and/or build platform moves in the X-Y (horizontal plane) to complete the cross section of the object, before moving in the Z axis (vertical) plane once one layer is complete. The nozzle has a high XYZ movement precision around 10μm. After each layer is printed in the X, Y working-plane, the nozzle is displaced in the Z direction far away enough to apply the next layer in the X, Y working-plane. In this way, the objects can be built one layer at a time from the bottom upwards.

As disclosed before, the distance between the nozzle and the previous layer is an important parameter to assure good shape. Preferably, it should be comprised from 70 to 130 %, preferably from 80 to 120 %of the average diameter of the nozzle.

Advantageously, printing speed is comprised between 1 and 100 mm/s, preferably between 3 and 50 mm/s to obtain the optimal balance between good accuracy and manufacture speed.

In the present invention, the method for additive manufacturing a silicone elastomer article from a two-part silicone composition W in accordance with the present invention uses an extrusion 3D printer. An extrusion 3D printer is a printer where the material is extruded through a nozzle, syringe or orifice during the additive manufacturing process. The 3D printer can have one or more nozzle, syringe or orifice. Material extrusion generally works by extruding material through a nozzle, syringe or orifice to print one cross-section of an object, which may be repeated for each subsequent layer. The extruded material bonds to the layer underneath thereof during printing process.

In the present invention, the 3D printer utilizes a nozzle of a dispenser head for dispensing the second part of the silicone composition W into the first part of the silicone composition W in liquid bath. Meanwhile, the 3D printer utilizes a liquid bath to contain the first part of the silicone composition W. Optionally, either the liquid bath or the nozzle (s) of the dispensing head (s) may be heated, before, during, or otherwise after the dispensing step, simultaneously or respectively. More than one nozzle of a dispensing head or more than one dispensing head may be utilized with each containing different components of the second part of the silicone composition W, respectively. Alternatively, or in addition, one nozzle of a dispensing head may be utilized to dispense all the components of the second part of the silicone composition W.

By “dispensing” as used herein, it might comprise extruding, injecting, jetting, spraying, depositing, printing or any other suitable process for bringing the first and second part of the silicone composition W to contacting with each other.

In a preferred embodiment, the method for additive manufacture a silicone elastomer article from a two-part silicone composition W in accordance with the present invention, comprising:

iii) dispensing the second part of the silicone composition W into the first part of the silicone composition W in liquid bath to form a first printed layer;

iv) optionally repeating step iii) for additional layers needed;

v) allowing the printed layers in liquid bath to partially or totally crosslink, optionally by heating, to obtain a silicone elastomer article; and

vi) removing the resulting silicone elastomer article from the liquid bath.

The two-part silicone composition W as well as the first and second part thereof would be discussed in detail below.

In a preferred embodiment of the present method, it further comprises a step vii) of washing the silicone elastomer article obtained in step vi) .

In a preferred embodiment of the present method, the 3D printer is an extrusion 3D printer.

In a preferred embodiment of the present method, in step iii) the second part of the silicone composition W is extruded through at least one nozzle of at least one dispensing head, preferably at a speed of 1 to 100 mm/s, more preferably at speed of 3 to 50 mm/s.

In a preferred embodiment of the present method, each component in the second part of the silicone composition W is extruded through a nozzle of the same dispensing head.

In a preferred embodiment of the present method, each component in the second part of the silicone composition W is extruded through nozzle (s) of different dispensing heads, respectively.

In a preferred embodiment of the present method, the liquid bath and the nozzle (s) of the dispensing head (s) may be heated before, during or after step iii) , respectively or simultaneously.

In a preferred embodiment of the present method, when the second part of the silicone composition W is dispensed into the first part in liquid bath, the time period for the formation of gel might below 5mins, preferably below 1 mins, more preferably below 15s.

In a preferred embodiment of the present method, the diameter of the nozzle is in the range comprised from 50 to 5,000μm, preferably from 100 to 800 μm and most preferably from 100 to 500μm.

In a preferred embodiment of the present method, the 3D printer comprising at least one cartridge comprising the second part of the silicone composition W to be dispensed through nozzle (s) , the diameter of the nozzle being comprised from 50 to 5,000μm, preferably from 100 to 800μm and most preferably from 100 to 500μm, and the cartridge pressure being preferably comprised from 1 to 28 bars.

In a preferred embodiment of the present invention, the two-part silicone composition W may be a room temperature vulcanizing (RTV) liquid silicone rubber typically suitable for mould making and casting. Thus, the crosslinking step v) is performed at room temperature for a period from 10 min to 24 hours.

Alternatively, the two-part silicone composition W is cured in the presence of heating. In the condition where the crosslinking step v) is performed at ambient temperature, the printed article obtained in step (vi) or (vii) might need to be subjected to a post-curing process by heating at a temperature in the range of 50℃ to 200℃, preferably in the range of 60℃ to 100℃, preferably for a period from 10 min to 24 hours. In the condition where the crosslinking step v) is performed when the liquid bath or nozzle (s) of the dispensing head (s) is heated at a temperature in the range of 50℃ to 200℃, preferably in the range of 60℃ to 100℃, the post-curing process might be eliminated.

For medical applications, a sterilization of the final elastomer article can be obtained for example: by heating either in a dry atmosphere or in an autoclave with vapor, for example by heating the object at a temperature greater than 100℃ under gamma ray, sterilization with ethylene oxide, sterilization with an electron beam.

The obtained silicone elastomer article can be any article with simple or complex geometry. It can be for example anatomic models (functional or non-functional) such as heart, lung, kidney, prostate..., models for surgeons and educative world or orthotics or prostheses or even implants of different classes such as long term implants: hearing aids, stents, larynx implants, etc.

The obtained silicone elastomer article can also be an actuator for robotics, a gasket, a mechanical piece for automotive/aeronautics, a piece for electronic devices, a package for the encapsulation of components, a vibrational isolator, an impact isolator or a noise isolator.

Two-part silicone composition W

In an embodiment of the present invention, the two-part silicone composition W comprise:

(a) at least one organopolysilicone;

(b) at least one crosslinking agent; and

(c) at least one catalyst;

In a preferred embodiment of the present invention, the first or second part of the silicone composition W further comprises at least one non-reactive diluent.

In a preferred embodiment of the present invention, the first or second part of the silicone composition W further comprises at least one thixotropic agent.

In a preferred embodiment of the present invention, the thixotropic agent is used in an amount from greater than 0wt%to 20wt%, preferably from 0.01 wt%to 10wt%, more preferably from 0.1wt%to 5wt%, based on the total weight of the first part of the silicone composition W when present in the first part.

In a preferred embodiment of the present invention, the first or second part of the silicone composition W further comprises at least one filler.

In a preferred embodiment, the two-part silicone composition W in accordance with the present invention comprises:

(a) at least one organopolysiloxane A;

(b) at least one organohydrogenopolysiloxane B;

(c) at least one catalyst C;

(d) at least one non-reactive diluent D;

(e) at least thixotropic agent E;

(f) at least one filler F,

wherein the first part of the silicone composition W comprises components (a) , (b) , optional (e) to (f) , and the second part of the silicone composition W comprises components (c) and optional (d) to (f) , or otherwise

wherein the first part of the silicone composition W comprises components (a) , (c) , optional (e) to (f) , and the second part of the silicone composition W comprises components (b) and optional (d) to (f) .

In yet a preferred embodiment, the two-part silicone composition W in accordance with the present invention comprises:

(a) from 55%to 85%by weight, preferably from 60%to 85%by weight, more preferably from 70%to 80%by weight of at least one organopolysiloxane A in relative to the total weight of the first part of the silicone composition W;

(b) from 0.1%to 20%by weight, preferably from 1%to 5wt%by weight, more preferably from 3%to 5%by weight of at least one organohydrogenopolysiloxane B in relative to the total weight of the first part of the silicone composition W;

(c) from 0.002%to 5%by weight, preferably from 0.005%to 0.1%by weight, more preferably from 0.01%to 0.02%by weight of at least one catalyst C in relative to the total weight of the second part of the silicone composition W;

(d) from 0 to 99%by weight, preferably from 50%to 99%by weight, more preferably from 85%to 99%by weight of at least one non-reactive diluent D in relative to the total weight of the second part of the silicone composition W;

(e) from 0 to 20%by weight, preferably from 0.01%to 10%by weight, more preferably from 0.1%to 5%by weight of at least thixotropic agent E in relative to the total weight of the first part of the silicone composition W;

(f) from 5 to 40 %by weight, preferably from 5 to 30wt%, more preferably from 5%to 20%by weight of at least one filler F in relative to the total weight of the first part of the silicone composition W,

wherein the first part of the silicone composition W comprises components (a) , (b) , optional (e) and optional (f) , and the second part of the silicone composition W comprises components (c) and optional (d) .

Alternatively, in the embodiment where the first part of the silicone composition W comprises components (a) , (c) , optional (e) and optional (f) , and the second part of the silicone composition W comprises components (b) and optional (d) to (f) , it is well known for the skilled person to select the appropriate amount of each component in the silicone composition W.

In addition, when the second part of the silicone composition W is dispensed into the first part in liquid bath, the time period for the formation of gel is important for 3D printing. Typically, the time period is below 5mins, preferably below 1 mins, more preferably below 15s.

The two-part silicone composition W may be crosslinked via polyaddition reaction or polycondensation reaction, suitable for 3D printing, which is well known for the person skilled in the art.

In one embodiment, the silicone composition W is a silicone composition crosslinkable through polyaddition reaction. In this embodiment, the composition W comprises:

(a) at least one organopolysiloxane A comprising, per molecule at least two C ₂-C ₆ alkenyl radicals bonded to silicon atoms,

(b) at least one organohydrogenopolysiloxane B comprising, per molecule, at least two hydrogen atoms bonded to an identical or different silicon atom,

(c) at least one catalyst C consisting of at least one metal or compound, from the platinum group,

(d) optional non-reactive diluent D, preferably non-reactive silicone oil;

(e) optional a thixotropic agent E; and

(f) optionally a filler F.

Organopolysiloxane A

According to a particularly advantageous mode, the organopolysiloxane A comprising, per molecule, at least two C ₂-C ₆ alkenyl radicals bonded to silicon atoms, comprises:

(i) at least two siloxyl units (A. 1) , which may be identical or different, having the following formula:

in which:

- a= 1 or 2, b= 0, 1 or 2 and a+b= 1, 2 or 3;

- the symbols W, which may be identical or different, represent a linear or branched C ₂-C ₆ alkenyl group,

- and the symbols Z, which may be identical or different, represent a monovalent hydrocarbon-based group containing from 1 to 30 carbon atoms, preferably chosen from the group formed by alkyl groups containing from 1 to 8 carbon atoms and aryl groups containing between 6 and 12 carbon atoms, and even more preferentially chosen from the group formed by methyl, ethyl, propyl, 3, 3, 3-trifluoropropyl, xylyl, tolyl and phenyl radicals,

(ii) and optionally at least one siloxyl unit having the following formula:

in which:

- a= 0, 1, 2 or 3,

- the symbols Z ¹, which may be identical or different, represent a monovalent hydrocarbon-based group containing from 1 to 30 carbon atoms, preferably chosen from the group formed by alkyl groups containing from 1 to 8 carbon atoms inclusive and aryl groups containing between 6 and 12 carbon atoms, and even more preferentially chosen from the group formed by methyl, ethyl, propyl, 3, 3, 3-trifluoropropyl, xylyl, tolyl and phenyl radicals.

Advantageously, Z and Z ¹ are chosen from the group formed by methyl and phenyl radicals, and W is chosen from the following list: vinyl, propenyl, 3-butenyl, 5-hexenyl, 9-decenyl, 10-undecenyl, 5, 9-decadienyl and 6-11-dodecadienyl, and preferably, W is a vinyl. In a preferably embodiment, in formula (A. 1) a=1 and a+b=2 or 3 and in formula (A. 2) c=2 or 3.

These organopolysiloxane A may have a linear, branched or cyclic structure. Their degree of polymerization is preferably between 2 and 5000.

When they are linear polymers, they are essentially formed from siloxyl units D chosen from the group formed by the siloxyl units W ₂SiO _2/2, WZSiO _2/2 and Z ¹ ₂SiO _2/2, and from siloxyl units M chosen from the group formed by the siloxyl units W ₃SiO _1/2, WZ ₂SiO _1/2, W ₂ZSiO _1/2 and Z ¹ ₃SiO _1/2. The symbols W, Z and Z ¹ are as described above. As examples of end units M mentions may be made of trimethylsiloxy, dimethylphenylsiloxy, dimethylvinylsiloxy or dimethylhexenylsiloxy groups. As examples of units D, mention may be made of dimethylsiloxy, methylphenylsiloxy, methylvinylsiloxy, methylbutenylsiloxy, methylhexenylsiloxy, methyldecenylsiloxy or methyldecadienylsiloxy groups. Said organopolysiloxane A may be oils with a dynamic viscosity from about 10 to 1000000 mPa. s at 25℃, generally from about 1000 to 120000 mPa. s at 25℃.

When organopolysiloxane A are cyclic organopolysiloxane, they are formed from siloxyl units D having the following formulae: W ₂SiO _2/2, Z ₂SiO _2/2 or WZSiO _2/2, which may be of the dialkylsiloxy, alkylarylsiloxy, alkylvinylsiloxy or alkylsiloxy type. Examples of such siloxyl units have already been mentioned above. Said cyclic organopolysiloxane A have a viscosity from about 1 to 5000 mPa. s at 25℃. Preferably, the organopolysiloxane A has a weight content of Si-vinyl units of between 0.001 and 30%, preferably between 0.01 and 10%.

Advantageously, the organopolysiloxane A is used in an amount from 55%to 85%by weight, preferably from 60%to 85%by weight, more preferably from 70%to 80%by weight in relative to the total weight of the first part of the two-part silicone composition W.

Organohydrogenpolysiloxane B

According to a preferred embodiment, the organohydrogenopolysiloxane B is an organopolysiloxane containing at least two hydrogen atoms per molecule, bonded to an identical or different silicon atom, and preferably containing at least three hydrogen atoms per molecule directly bonded to an identical or different silicon atom.

Advantageously, the organohydrogenopolysiloxane B is an organopolysiloxane comprising:

(i) at least two siloxyl units and preferably at least three siloxyl units having the following formula:

in which:

- d= 1 or 2, e = 0, 1 or 2 and d+e= 1, 2 or 3,

- the symbols Z ³, which may be identical or different, represent a monovalent hydrocarbon-based group containing from 1 to 30 carbon atoms, preferably chosen from the group formed by alkyl groups containing from 1 to 8 carbon atoms and aryl groups containing between 6 and 12 carbon atoms, and even more preferentially chosen from the group formed by methyl, ethyl, propyl, 3, 3, 3-trifluoropropyl, xylyl, tolyl and phenyl radicals, and

(ii) optionally at least one siloxyl unit having the following formula:

in which:

- c= 0, 1, 2 or 3,

- the symbols Z ², which may be identical or different, represent a monovalent hydrocarbon-based group containing from 1 to 30 carbon atoms, preferably chosen from the group formed by alkyl groups containing from 1 to 8 carbon atoms and aryl groups containing between 6 and 12 carbon atoms, and even more preferentially chosen from the group formed by methyl, ethyl, propyl, 3, 3, 3-trifluoropropyl, xylyl, tolyl and phenyl radicals.

The organohydrogenopolysiloxane B may be formed solely from siloxyl units of formula (B. 1) or may also comprise units of formula (B. 2) . It may have a linear, branched or cyclic structure. The degree of polymerization is preferably greater than or equal to 2. More generally, it is less than 5000. Examples of siloxyl units of formula (B. 1) are especially the following units: H (CH ₃) ₂SiO _1/2, HCH ₃SiO _2/2 and H (C ₆H ₅) SiO _2/2.

When they are linear polymers, they are essentially formed from:

- siloxyl units D chosen from the units having the following formulae Z ² ₂SiO _2/2 or Z ³HSiO _2/2, and

- siloxyl units M chosen from the units having the following formulae Z ² ₃SiO _1/2 or Z ³ ₂HSiO _1/2,

the symbols Z ² and Z ³ are as described above.

These linear organopolysiloxane may be oils with a dynamic viscosity from about 1 to 100000 mPa. s at 23℃, generally from about 10 to 5000 mPa. s at 23℃, or high viscous oils with a viscosity of about 1000000 mPa. s or more at 23℃.

When they are cyclic organopolysiloxane, they are formed from siloxyl units D having the following formulae Z ² ₂SiO _2/2 and Z ³HSiO _2/2, which may be of the dialkylsiloxy or alkylarylsiloxy type or units Z ³HSiO _2/2 solely. They then have a viscosity from about 1 to 5000 mPa. s.

Examples of linear organohydrogenopolysiloxane B are selected from: dimethylpolysiloxanes bearing hydrogenodimethylsilyl end groups, dimethylhydrogenomethylpolysiloxanes bearing trimethylsilyl end groups, dimethylhydrogenomethylpolysiloxanes bearing hydrogenodimethylsilyl end groups, hydrogenomethylpolysiloxanes bearing trimethylsilyl end groups, and cyclic hydrogenomethylpolysiloxanes.

The oligomers and polymers corresponding to the general formula (B. 3) are especially preferred as organohydrogenopolysiloxane compound B:

in which:

- x and y are an integer ranging between 0 and 200,

- the symbols R ¹, which may be identical or different, represent, independently of each other:

· a linear or branched alkyl radical containing 1 to 8 carbon atoms, optionally substituted with at least one halogen, preferably fluorine, the alkyl radicals preferably being methyl, ethyl, propyl, octyl and 3, 3, 3-trifluoropropyl,

· a cycloalkyl radical containing between 5 and 8 cyclic carbon atoms,

· an aryl radical containing between 6 and 12 carbon atoms, or

· an aralkyl radical bearing an alkyl part containing between 5 and 14 carbon atoms and an aryl part containing between 6 and 12 carbon atoms.

The following compounds are particularly suitable for the invention as organohydrogenopolysiloxane B:

with a, b, c, d and e defined below:

- in the polymer of formula S1:

- 0 ≤ a ≤ 150, preferably 0 ≤ a ≤ 100, and more particularly 0 ≤ a ≤ 20, and

- 1 ≤ b ≤ 90, preferably 10 ≤ b ≤ 80 and more particularly 30 ≤ b ≤ 70,

- in the polymer of formula S2: 0 ≤ c ≤ 15

- in the polymer of formula S3: 5 ≤ d ≤ 200, preferably 20 ≤ d ≤ 100, and

2 ≤ e ≤ 90, preferably 10 ≤ e ≤ 70.

In particular, an organohydrogenopolysiloxane B that is suitable for use in the invention is the compound of formula S1, in which a = 0. Preferably, the organohydrogenopolysiloxane B has a weight content of SiH units of between 0, 2 and 91%, preferably between 0, 2 and 50%.

In an embodiment, the organohydrogenopolysiloxane B is a branched polymer. Said branched organohydrogenopolysiloxane compound B comprises:

a) at least two different siloxyl units selected from siloxyl unit M of formula R ₃SiO _1/2, siloxyl unit D of formula R ₂SiO _2/2, siloxyl unit T of formula RSiO _3/2 and siloxyl unit Q of formula SiO _4/2, in which R denotes monovalent hydrocarbon group with 1 to 20 carbon atoms or an hydrogen atom, and

b) provided that at least one of these siloxyl units is siloxyl unit T or Q and at least one of siloxyl units M, D or T contains a Si-H group.

Thus, according to one preferable embodiment, the branched organohydrogenopolysiloxane B can be selected from the following groups:

- organopolysiloxane resin of formula M’Q, which is essentially formed from:

(a) monovalent siloxyl unit M’ of formula R ₂HSiO _1/2; and

(b) tetravalent siloxyl unit Q of formula SiO _4/2; and

- organopolysiloxane resin of formula MD’Q, which is basically constituted of the following units:

(a) divalent siloxyl unit D’ of formula RHSiO _2/2;

(b) monovalent siloxyl unit M of formula R ₃SiO _1/2; and

(c) tetravalent siloxyl unit Q of formula SiO _4/2;

wherein R represents monovalent hydrocarbyl having 1 to 20 carbon atoms, preferably represents monovalent aliphatic or aromatic hydrocarbyl having 1 to 12, more preferably 1 to 8 carbon atoms.

As a further embodiment, a mixture of at least a linear organohydrogenopolysiloxane B and at least a branched organohydrogenopolysiloxane B can be used. In this case, the linear and branched organohydrogenopolysiloxane B can be mixed in any proportion in a wide range, and the mixing proportion may be adjusted depending on the desired product properties such as hardness and the ratio of Si-H to alkenyl group.

In the context of the invention, the proportions of the organopolysiloxane A and of the organohydrogenopolysiloxane B are such that the mole ratio of the hydrogen atoms bonded to silicon (Si-H) in the organohydrogenopolysiloxane B to the alkenyl radicals bonded to silicon (Si-CH=CH ₂) in the organopolysiloxane A is between 0.2 and 20, preferably between 0.5 and 15, more preferentially between 0.5 and 10 and even more preferentially between 0.5 and 5.

Advantageously, the organohydrogenopolysiloxane B is used in an amount from 0.1%to 20%by weight, preferably from 1%to 5%by weight, more preferably from 3%to 5%by weight, based on the total weight of the first part of the silicone composition W when present in the first part. In the embodiment where the organohydrogenopolysiloxane B is present in the second part of the silicone compositioni W, the amount of organohydrogenopolysiloxane B used could be selected by the skilled person through common knowledge.

Catalyst C

Catalyst C consisting of at least one metal, or compound, from the platinum group are well known. The metals of the platinum group are those known under the name platinoids, this term combining, besides platinum, ruthenium, rhodium, palladium, osmium and iridium. Platinum and rhodium compounds are preferably used. Complexes of platinum and of an organic product described in patents US3159601A, US3159602A, US3220972A and European patents EP0057459A, EP0188978A and EP0190530A, and complexes of platinum and of vinylorganosiloxane described in patents US3419593A, US3715334A, US3377432A and US3814730A may be used in particular. Specific examples are: platinum metal powder, chloroplatinic acid, a complex of chloroplatinic acid with β-diketone, a complex a chloroplatinic acid with olefin, a complex of a chloroplatinic acid with 1, 3-divinyltetramethyldisiloxane, a complex of silicone resin powder that contains aforementioned catalysts, a rhodium compound, such as those expressed by formulae: RhCl (Ph ₃P) ₃, RhCl ₃ [S (C ₄H ₉) ₂] ₃, etc.; tetrakis (triphenyl) palladium, a mixture of palladium black and triphenylphosphine, etc.

Advantageously, the catalyst C is used in an amount from 0.002%to 5%by weight, preferably from 0.005%to 0.1%, more preferably from 0.01%to 0.02%by weight, based on the total weight of the second part of the silicone composition W when present in the second part. In the embodiment where the catalyst C is present in the first part of the silicone compositioni W, the amount of catalyst C used could be selected by the skilled person through common knowledge.

Non-reactive diluent D

Preferably, the non-reactive diluent D might be non-reactive silicone oil having dynamic viscosity from 20 mPa·s to 10,000 mPa·s, preferably from 30 mPa·s to 5,000 mPa·s, more preferably from 50 mPa·s to 2,000 mPa·s at 23℃, which usually refers to a polysiloxane compound that maintains a liquid state at room temperature with Si-O-Si as the main chain. Such silicone oil may have a general formula (I) represented by:

In the above general formula (I) ,

- Me denotes methyl radical,

- R, R' and X, each of which may be identical or different, represent, independently of each other:

· a cycloalkyl radical containing between 5 and 8 cyclic carbon atoms,

· an aryl radical containing between 6 and 12 carbon atoms, or

· an aralkyl radical bearing an alkyl part containing between 5 and 14 carbon atoms and an aryl part containing between 6 and 12 carbon atoms, preferably, all of R, R' and X excludes hydroxyl group and/or hydrogen;

- each of n and m may be an integer from 100 to 4000, preferably from 500 to 3000.

Depending on the difference between R and R', silicone oil is classified into two categories: linear silicone oil and modified silicone oil. Linear silicone oils include non-functional silicone oils and silicon functional silicone oils. Among them, non-functional silicone oil refers to a silicone oil in which the substituents on the silicon atom are all inactive hydrocarbon groups, for example dimethyl silicone oil, diethyl silicone oil or methyl phenyl silicone oil etc. Silicon functional silicone oil refers to the silicone oil with functional groups bonded directly to some of the silicon atoms, for example, vinyl silicone oil etc.

In addition, modified silicone oil can be regarded as a liquid polymer wherein some of the hydrocarbon groups bonded to silicon atoms in the non-functional silicone oil molecule are replaced by carbon functional groups or polymer chains, or wherein silicon heterochains are embedded in the molecule. Such modified silicone oil may usually be carbon-functional silicone oil, copolymer silicone oil and main chain modified silicone oil. Among them, carbon-functional silicone oil refers to a silicone oil wherein substituents on some of the silicon atoms are carbon-functional groups, for example epoxyalkyl silicone oil, methacryloxyalkyl silicone oil, mercaptoalkyl silicone oil, chloroalkyl silicone oil, cyanoalkyl silicone oil, etc. While the copolymer silicone oil refers to silicone oil containing polymer chains on the silicon atom, for example polyether silicone oil, long-chain alkyl silicone oil, long-chain alkoxy silicone oil, fluoroalkyl silicone oil, etc. In addition, the main chain modified silicone oil refers to a liquid organic polymer wherein the main chain of the molecule contains a certain degree of silicon hybrid chain besides Si-O-Si bonds, for example silazane silicone oil, silicon alkylene silicone oil, silicon arylene silicone oil etc.

Advantageously, the silicone oil as used herein may be methyl silicone oil or polydimethylsiloxane.

Preferably, the non-reactive diluent is used in an amount from 0 to 99%by weight, preferably from 50%to 99%by weight, more preferably from 85%to 99%by weight in relative to the total weight of the second part of the silicone composition W when present in the second part. In the embodiment where the non-reactive diluent is present in the first part of the silicone compositioni W, the amount thereof used could be selected by the skilled person through common knowledge.

Thixotropic agent E

Optionally, the two-part silicone composition W can further comprise a thixotropic agent E.

In a preferred embodiment, the thixotropic agent E contains polar groups. Preferably the thixotropic agent E can be selected from the group consisting of : an organic or organosilicon compound having at least one epoxy group, an organic or organopolysiloxane compound having at least one (poly) ether group, an organic compound having at least (poly) ester group, an organopolysiloxane having at least one aryl group and any combination thereof.

In another preferred embodiment, the thixoropic agent E can be an organopolysiloxane-polyoxyalkylene copolymer. Organopolysiloxane-polyoxyalkylene copolymer, also known as polydiorganosiloxane-polyether copolymers or polyalkylene oxide modified polymethylsiloxane, are organopolysiloxanes containing siloxyl units which carry alkylene oxide chain sequences. Preferably, organopolysiloxane-polyoxyalkylene copolymer are organopolysiloxanes containing siloxyl units which carry ethylene oxide chain sequences and/or propylene oxide chain sequences.

In a preferred embodiment the organopolysiloxane-polyoxyalkylene copolymer is an organopolysiloxane containing siloxyl comprising units of the formula (F-1) :

[R ¹ _aZ _bSiO _(4-a-b) /2] _n (F-1)

in which

each R ¹ is independently selected from hydrocarbon-based group containing from 1 to 30 carbon atoms, preferably chosen from the group formed by alkyl groups containing from 1 to 8 carbon atoms and aryl groups containing between 6 and 12 carbon atoms; each Z is a group -R ²- (OC _pH _2p) _q (OC _rH _2r) _S-OR ³,

where

n is an integer greater than 2;

a and b are independently 0, 1, 2 or 3; and a+b=0, 1, 2 or 3,

R ² is a divalent hydrocarbon group having from 2 to 20 carbon atoms or a direct bond;

R ³ is an hydrogen atom or a group as defined for R ¹;

p and r are independently an integer from 1 to 6;

q and s are independently 0 or an integer such that 1<q + s< 400;

and wherein each molecule of the organopolysiloxane-polyoxyalkylene copolymer contains at least one group Z.

In a preferred embodiment, in the formula (F-1) above:

n is an integer greater than 2; and a+b=0, 1, 2 or 3,

a and b are independently 0, 1, 2 or 3;

R ¹ is an alkyl group containing from 1 to 8 carbon atoms inclusive, and most preferably R ¹ is a methyl group,

R ² is a divalent hydrocarbon group having from 2 to 6 carbon atoms or a direct bond;

p=2 and r=3,

q is comprised between 1 and 40, most preferably between 5 and 30,

s is comprised between 1 and 40, most preferably between 5 and 30,

and R ³ is an hydrogen atom or an alkyl group containing from 1 to 8 carbon atoms inclusive, and most preferably R ³ is an hydrogen atom.

In a most preferred embodiment, the organopolysiloxane-polyoxyalkylene copolymer is an organopolysiloxane containing a total number of siloxyl units (F-1) comprised between 1 and 200, preferably between 50 and 150 and a total number of Z groups comprised between 2 and 25, preferably between 3 and 15.

An example of organopolysiloxane-polyoxyalkylene copolymer that can be used in the method of the invention corresponds to the formula (F-2)

R ^a ₃SiO [R ^a ₂SiO] _t [R ^aSi (R ^b- (OCH ₂CH ₂) _x (OC ₃H ₆) _y-OR ^c) O] _rSiR ^a ₃ (F-2)

where

each R ^a is independently selected from alkyl groups containing from 1 to 8 carbon atoms and preferably R ^a is a methyl group,

each R ^b is a divalent hydrocarbon group having from 2 to 6 carbon atoms or a direct bond, and preferably R ^b is a propyl group,

x and y are independently integers comprised from 1 to 40, preferably from 5 and 30, and most preferably from 10 to 30,

t is comprised from 1 to 200, preferably from 25 to 150,

r is comprised from 2 to 25, preferably from 3 to 15, and

R ^c is H or alkyl group preferentially H or CH ₃ group.

Advantageously, in an embodiment the organopolysiloxane-polyoxyalkylene copolymer is:

Me ₃SiO [Me ₂SiO] ₇₅ [MeSi ( (CH ₂) ₃- (OCH ₂CH ₂) ₂₂ (OCH ₂CH (CH ₃) ) ₂₂-OH) O] ₇SiMe ₃.

In a still preferred embodiment, the thixotropic agent E is selected from methyl vinyl phenyl polysiloxane, epoxy-containing polysiloxane and dimethylsiloxane- (propylene oxide-ethylene oxide) block copolmer.

Advantageously, the thixotropic agent E is used in an amount from 0 to 20%by weight, preferably from 0.01%to 10%by weight, more preferably from 0.1%to 5%by weight, based on the total weight of the first part of the silicone composition W when present in the first part. In the embodiment where the thixotropic agent E is present in the second part of the silicone compositioni W, the amount of thixotropic agent E used could be selected by the skilled person through common knowledge.

Filler F

To allow a sufficiently high mechanical strength the addition-crosslinking silicone compositions can comprise filler, such as for example silica fine particles, as reinforcing fillers F. Precipitated and fumed silicas and mixtures thereof can be used. The specific surface area of these actively reinforcing fillers ought to be at least 50 m ²/g and preferably in the range from 100 to 400 m ²/g as determined by the BET method. Actively reinforcing fillers of this kind are very well-known materials within the field of the silicone rubbers. The stated silica fillers may have hydrophilic character or may have been hydrophobized by known processes.

In a preferred embodiment, the silica reinforcing filler is fumed silica with a specific surface area of at least 50 m ²/g and preferably in the range from 100 to 400 m ²/g as determined by the BET method. Fumed silica may be used as is, in an untreated form, but is preferably subjected to hydrophobic surface treatment. In those cases, where a fumed silica that has undergone hydrophobic surface treatment is used, either a fumed silica that has been subjected to preliminary hydrophobic surface treatment may be used, or a surface treatment agent may be added during mixing of the fumed silica with the organopolysiloxane A, so that the fumed silica is treated in-situ.

The surface treatment agent may be selected from any of the conventionally used agents, such as alkylalkoxysilanes, alkylchlorosilanes, alkylsilazanes, silane coupling agents, titanate-based treatment agents, and fatty acid esters, and may use either a single treatment agent, or a combination of two or more treatment agents, which may be used either simultaneously or at different timings.

The silicone compositions according to the invention may also comprise other fillers like a standard semi-reinforcing or packing filler, hydroxyl functional silicone resins, pigments, or adhesion promoters.

Non siliceous minerals that may be included as semi-reinforcing or packing mineral fillers can be chosen from the group constituted of: carbon black, titanium dioxide, aluminium oxide, hydrated alumina, calcium carbonate, ground quartz, diatomaceous earth, zinc oxide, mica, talc, iron oxide, barium sulfate and slaked lime.

Advantageously, the filler F is used in an amount from 5 to 40%by weight, preferably from 5 to 30%by weight, more preferably from 5%to 20%by weight, based on the total weight of the first part of the silicone composition W when present in the first part. In the embodiment where the filler F is present in the second part of the silicone compositioni W, the amount of filler F used could be selected by the skilled person through common knowledge.

If the quantity is less than 5 %by weight, then adequate elastomer strength may not be obtainable, whereas if the quantity exceeds 40%by weight, the actual blending process may become difficult.

In another embodiment, the silicone composition W is a silicone composition crosslinkable through polycondensation reaction which are well known by the skilled person. In this embodiment, the composition W comprises:

(a) at least one organopolysiloxane A’ comprising at least two groups chosen in the group consisting of OH groups and hydrolysable groups;

(b) optionally at least one crosslinking agent B’;

(c) at least one polycondensation catalyst C’;

(d) optional at least one non-reactive diluent D as discussed before;

(e) optional at least one thixotropic agent E as disclosed before;

(f) optional at least one filler F as discussed before.

Wherein the first part of the silicone composition W comprises component (a) , (c) and optional (d) to (f) , and the second part comprises component (b) and optional (d) to (f) , or otherwise the first part of the silicone composition W comprises component (a) , (b) and optional (d) to (f) , and the second part comprises component (c) and optional (d) to (f) .

Preferably, the organopolysiloxane A’ comprises at least two groups chosen in the group consisting of: hydroxy, alcoxy, alcoxy-alkylene-oxy, amino, amido, acylamino, aminoxy, iminoxy, cetiminoxy, acyloxy and enoxy groups.

Advantageously, polyorganosiloxane A’ comprises:

(i) at least two siloxyl units of formula (V) :

in which:

R ¹, identical or different, represent monovalents hydrocarbon radicals comprising from 1 to 30 carbon atoms;

Y, identical or different, represent each an hydrolysable and condensable group or a hydroxy group, and are preferably chosen in the group consisting of hydroxy, alkoxy, alcoxy-alkylene-oxy, amino, amido, acylamino, aminoxy, iminoxy, cetiminoxy, acyloxy, iminoxy, cetiminoxy and enoxy group,

g is 0, 1 or 2, h is 1, 2 or 3, the sum g + h is 1, 2 or 3, and

(ii) optionally one or more siloxyl unit (s) of formula (VI) :

in which:

R ², identical or different, represent monovalents hydrocarbon radicals comprising from 1 to 30 carbon atoms optionally substituted by one or more halogen atoms or by amino, ether, ester, epoxy, mercapto or cyano groups, and

i is 0, 1, 2 or 3.

As example of hydrolysable and condensable group Y of alkoxy type it is possible to cite groups having from 1 to 8 carbon atoms such as methoxy, ethoxy, n-propoxy, iso-propoxy, n-butoxy, iso-butoxy, sec-butoxy, tert-butoxy, 2-methoxyethoxy, hexyloxy or octyloxy.

As example of hydrolysable and condensable group Y of alcoxy-alkylene-oxy type, it is possible to cite methoxy-ethylene-oxy. As example of hydrolysable and condensable group Y of amino type, it is possible to cite methylamino, dimethylamino, ethylamino, diethylamino, n-butylamino, sec-butylamino or cyclohexylamino. As example of hydrolysable and condensable group Y of amido type, it is possible to cite N-methyl-acetamido. As example of hydrolysable and condensable group Y of acylamino type, it is possible to cite benzoyl-amino. As example of hydrolysable and condensable group Y of aminoxy type, it is possible to cite dimethylaminoxy, diethylaminoxy, dioctylaminoxy ou diphenylaminoxy. As example of hydrolysable and condensable group Y of iminoxy and in particulier cetiminoxy type, it is possible to cite groups derived from the following oximes: acetophenone-oxime, acetone-oxime, benzophenone-oxime, methyl-ethyl-cetoxime, di-isopropylcetoxime or methylisobutyl-cetoxime. As example of hydrolysable and condensable group Y of acyloxy type, it is possible to cite acetoxy. As example of hydrolysable and condensable group Y of enoxy type, it is possible to cite 2-propenoxy.

The viscosity of the organopolysiloxane A’ is generally comprised between 50 mPa. s and 1000000 mPa. s at 23℃.

Preferably, organopolysiloxane A’ is of formula (VII) :

Y _jR ³ _3-j Si ─ O ─ (SiR ³ ₂ ─ O) _p ─ SiR ³ _3-jY _j (VII)

In which:

Y, identical or different, represent each a hydrolysable and condensable group or a hydroxy group, and preferably are chosen in the group consisting of hydroxy, alkoxy, alkoxy-alkylene-oxy, amino, amido, acylamino, aminoxy, iminoxy, cetiminoxy, acyloxy and enoxy,

R ³, identical or different, represent monovalent hydrocarbon radical comprising from 1 to 30 carbon atoms and optionally substituted by one or more halogen atoms or amino, ether, ester, epoxy, mercapto or cyano groups,

j is 1, 2 or 3, preferably is 2 or 3, and when Y is a hydroxyl group then j = 1,

p is an integer equal or greater than 1, preferably p is an integer comprised between 1 and 2000.

In formula (V) , (VI) and (VII) , R ¹, R ² and R ³ are preferably:

alkyl radicals comprising from 1 to 20 carbon atoms, optionally substituted by one or more aryl or cycloalkyl groups, by one or more halogen atoms or by amino, ether, ester, epoxy, mercapto, cyano or (poly) glycol groups. For exemple methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, ethyl-2 hexyle, octyle, decyl, trifluoro-3, 3, 3 propyl, trifluoro-4, 4, 4 butyl, pentafluoro-4, 4, 4, 3, 3 butyl;

cycloalkyl and halogenocycloalkyl groups comprising from 5 to 13 carbon atoms such as cyclopentyl, cyclohexyl, methylcyclohexyl, propylcyclohexyl, difluoro-2, 3 cyclobutyl, difluoro-3, 4 methyl-5 cycloheptyl;

aryl and halogenoaryl mononuclear comprising from 6 to 13 carbon atoms such as: phenyle, tolyle, xylyle, chlorophenyle, dichlorophenyle, trichlorophenyle; or

alcenyl radicals comprising from 2 to 8 carbon atoms such as: vinyl, allyl and butene-2 yl.

In the particular embodiment when A’ is of formula (VII) with Y of hydroxyl type, thus d is preferably 1. In this case, it is preferably to use poly (dimethylsiloxane) having terminal silanols groups (also called 《alpha-omega 》position) .

Organopolysiloxane A’ can also be chosen in the group consisting of organopolysiloxane resins carrying at least one hydroxy or alkoxy group, groups which are either condensable or hydrolysable, which comprise at least two different siloxyl units chosen among groups of formula M, D, T and Q with:

M = (R ⁰) ₃SiO _1/2,

D = (R ⁰) ₂SiO _2/2,

T = R ⁰SiO _3/2,

Q = SiO _4/2;

formula in which R ⁰ represents a monovalent hydrocarbon group comprising from 1 to 40 carbon atoms, and preferably from 1 to 20 carbon atoms, or a group –OR” ^’ with R” ^’ = H or an alkyl radical comprising from 1 to 40 carbon atoms, and preferably from 1 to 20 carbon atoms; with the condition that the resins comprise at least one motif T or Q unit.

Said resin has preferably a weight content of hydroxy or alcoxy substituants comprised between 0.1 and 10%by weight with respect to the weight of the resin, and preferably a weight content of hydroxy or alkoxyl substituants comprised between 0.2 and 5%by weight with respect to the weight of the resin.

The organopolysiloxane resins have generally about 0.001 to 1.5 OH groups and/or alkoxyl per silicium atom. These organopolysiloxane resins are generally prepared by co-hydrolysis and co-condensation of chlorosilanes such as the ones of formula (R ¹⁹) ₃SiCl, (R ¹⁹) ₂Si (Cl) ₂, R ¹⁹Si (Cl) ₃ or Si (Cl) ₄, radicals R ¹⁹ are identical or different and are in the group consisting of linear or branched alkyl in C ₁ to C ₆, phenyl and trifluoro-3, 3, 3 propyl. For example, R ¹⁹ is methyl, ethyl, isopropyle, tertiobutyl and n-hexyl. Examples of resins are silicic resins of T (OH) , DT ^(OH) , DQ ^(OH) , DT ^(OH) , MQ ^(OH) , MDT ^(OH) , MDQ ^(OH) type or a mixture.

In a preferred embodiment, the two-part silicone composition W crosslinkable through polycondensation reaction can further comprise such crosslinking agent B’. It is preferably an organosilicium compound carrying per molecule more than 2 hydrolysable and condensable groups linked to the silicium atoms. Such agents are well known from the skilled person and are commercially available.

The crosslinking agent B’ is preferably a silicium compound wherein each molecule comprises at least 3 hydrolysable and condensable Y groups, said agent B’ having formula (VIII) :

R ⁴ _(4-k) SiY _k (VIII)

In which:

R ⁴ radicals, identical or different, represent monovalent hydrocarbon radicals in C ₁ to C ₃₀, Y, identical or different, are chosen in the group consisting of alkoxy, alkoxy-alkylene-oxy, amino, amido, acylamino, aminoxy, iminoxy, cetiminoxy, acyloxy or enoxy groups, and preferably Y is an alcoxy, acyloxy, enoxy, cetiminoxy or oxime group,

k = 2, 3 or 4, preferably k = 3 or 4.

Examples of Y groups are the same as the ones cited for A’ above when Y is a hydrolysable and condensable group.

Other examples of crosslinking agent B’, are alkoxysilanes and partial hydrolysis products of silane of formula (IX) :

R ⁵ _l Si (OR ⁶) _(4-l) (IX)

in which :

R ⁶, identical or different, represent alkyl radical comprising from 1 to 8 carbon atoms such as methyl, ethyl, propyl, butyl, pentyl, ethyl-2 hexyl, octyl and decyl, oxyalkylenes groups in C ₃-C ₆,

R ⁵, identical or different, represent a saturated or unsaturated, linear or branched aliphatic hydrocarbon group, carbocycle group, saturated or unsaturated and/or aromatic, monocycle or polycycle, and

l is 0, 1 or 2.

Among crosslinking agent B’, alcoxysilanes, cetiminoxysilanes, alkyl silicates and alkyl polysilicates, in which the organic radicals are alkyl radical shaving from 1 to 4 carbon atoms are prefered. Preferably, the following crosslinking agent H, are used alone or in mixture selected from:

ethyl polysilicate and n-propyl polysilicate;

alkoxysilanes such as dialkoxysilanes, for example dialkyldialkoxysilanes, trialkoxysilanes, for example alkyltrialkoxysilanes, and tetraalkoxysilanes, preferably propyltrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, propyltriethoxysilane, tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, 1, 2-bis (trimethoxysilyl) ethane, 1, 2-bis (triethoxysilyl) ethane, tetra-isopropoxysilane, phenyltriethoxysilane, phenyltrimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane and those of following formula: CH ₂=CHSi (OCH ₂CH ₂OCH ₃) ₃ , Si (OC ₂H ₄OCH ₃) ₄ and CH ₃Si (OC ₂H ₄OCH ₃) ₃, acyloxysilanes such as the following acetoxysilanes: tetraacetoxysilane, methyl-triacetoxysilane, ethyltriacetoxysilane, vinyltriacetoxysilane, propyltriacétoxysilane, butyltriacetoxysilane, phenyltriacetoxysilane, octyltriacetoxysilane, dimethyldiacetoxysilane, phenylmethyldiacetoxysilane, vinylmethyldiacetoxysilane, diphenyldiacetoxysilane and tetraacetoxysilane, silanes comprising alkoxy and acetoxy groups such as: methyldiacetoxymethoxysilane, methylacetoxydimethoxysilane, vinyldiacetoxymethoxysilane, vinylacetoxydimethoxysilane, methyldiacetoxyethoxysilane and methylacetoxydiethoxysilane, methyltris (methylethyl-cetoximo) silane, 3-cyanopropyltrimethoxysilane, 3-cyanopropyl-triethoxysilane, 3- (glycidyloxy) propyltriethoxysilane, vinyltris (methylethylcetoximo) silane, tetra-kis (methylethylcetoximo) silane.

Generally from 0.1 to 60 parts by weight of crosslinking agent B’ are used for 100 parts by weight of polyorganosiloxane A’. Preferably, 0.5 to 15 parts by weight of crosslinking agent H are used for 100 parts by weight of polyorganosiloxane A’.

The polycondensation catalyst can be a tin, zinc, iron, zirconium, bismuth or titanium derivative or organic compounds as amine or guanidines as disclosed for example in EP2268743 and EP2222688. Use may be made, as tin-derived condensation catalyst, of tin monocarboxylates and dicarboxylates, such as tin 2-ethylhexanoate, dibutyltin dilaurate or dibutyltin diacetate (see the work by Noll, “Chemistry and Technology of Silicone” , page 337, Academic Press, 1968, 2nd edition, or the patents EP147323 or EP235049) . Other possible metal derivatives include chelates, for example dibutyltin acetoacetonate, sulfonates, alcoholates, etc.

The two-part silicone composition W crosslinkable through polycondensation reaction may further comprise a thixotropic agent E. Detailed information can be found hereinbefore for the silicone composition W cured through polyaddition reaction. For example, the thixotropic agent E contains polar groups. Preferably the thixotropic agent E can be selected from the group consisting of : an organic or organosilicon compound having at least one epoxy group, an organic or organopolysiloxane compound having at least one (poly) ether group, an organic compound having at least (poly) ester group, an organopolysiloxane having at least one aryl group and any combination thereof.

The two-part silicone composition W (either by polycondensation or polyaddition) can further comprise functional additives usual in silicone composition. The following functional families of additives can be cited:

- adhesion promoter;

- silicon resins;

- crosslinking inhibitor;

- coloring agent and

- additives for thermal resistance, oil resistance and fire resistance, for example metallic oxides.

Adhesion promoter are largely used in silicone composition. Advantageously, in the process according to the invention it is possible to use one or adhesion promoter chosen in the group consisting of:

- alkoxylated organosilanes comprising, per molecule, at least one C ₂-C ₆ alkenyl group,

- organosilicate compounds comprising at least an epoxy radical

- chelates of metal M and/or metallic alkoxydes of formula:

M (OJ) _n, in which

M is chosen in the group consisting of: Ti, Zr, Ge, Li, Mn, Fe, Al and Mg or their mixtures n = valence of M and J = linear or branched alkyl in C ₁-C ₈,

Preferably M is chosen in the group consisting of: Ti, Zr, Ge, Li or Mn, and more preferably M is Titane. It is possible to associate for example an alkoxy radical of butoxy type.

Silicon resins are branched organopolysiloxane well known and commercially available. They present, in their structure, at least two different units chosen among those of formula R ₃SiO _1/2 (M unit) , R ₂SiO _2/2 (D unit) , RSiO _3/2 (T unit) and SiO _4/2 (Q unit) , at least one of these units being a T or Q unit. Radical R are identical or different and chosen in the group consisting in alkyl linear or branched in C1 -C6, hydroxyl, phenyl, trifluoro-3, 3, 3 propyl. Alkyl radicals are for example methyl, ethyl, isopropyl, tertiobutyl and n-hexyl. As examples of branched oligomers or organopolysiloxane polymers, there can be cited MQ resins, MDQ resins, TD resins and MDT resins, the hydroxyl functions can be carried by M, D and/or T units. As examples of resins that are particularly well suited, there can be cited hydroxylated MDQ resin having from 0.2 to 10%by weight of hydroxyl group.

Crosslinking inhibitors are commonly used in addition crosslinking silicone compositions to slow the curing of the composition at ambient temperature. The crosslinking inhibitor may be chosen from the following compounds:

- acetylenic alcohols.

- organopolysiloxane substituted with at least one alkenyl that may optionally be in cyclic form, tetramethylvinylcyclotetrasiloxane being particularly preferred,

- pyridine,

- organic phosphines and phosphites,

- unsaturated amides, and

- alkyl or alkenyl maleates.

These acetylenic alcohols (see FR-B-1 528 464 and FR-A-2 372 874) , which are among the preferred hydrosilylation-reaction thermal blockers, have the formula:

(R') (R") (OH) C -C ≡ CH

in which: R' is a linear or branched alkyl radical, or a phenyl radical; and -R" is H or a linear or branched alkyl radical, or a phenyl radical; the radicals R' and R" and the carbon atom α to the triple bond possibly forming a ring.

The total number of carbon atoms contained in R' and R" being at least 5 and preferably from 9 to 20. For the said acetylenic alcohols, examples that may be mentioned include:

- 1-ethynyl-1-cyclohexanol;

- 3-methyl-1-dodecyn-3-ol;

- 3, 7, 11-trimethyl-1-dodecyn-3-ol;

- 1, 1-diphenyl-2-propyn-1-ol;

- 3-ethyl-6-ethyl-1-nonyn-3-ol;

- 2-methyl-3-butyn-2-ol;

- 3-methyl-1-pentadecyn-3-ol; and

- diallyl maleate or diallyl maleate derivatives.

In a preferred embodiment, the crosslinking inhibitor is 1-ethynyl-1-cyclohexanol.

To obtain a longer working time or “pot life” , the quantity of the inhibitor is adjusted to reach the desired “pot life” . The concentration of the catalyst inhibitor in the present silicone composition is sufficient to slow curing of the composition at ambient temperature. This concentration will vary widely depending on the particular inhibitor used, the nature and concentration of the hydrosilylation catalyst, and the nature of the organohydrogenopolysiloxane. Inhibitor concentrations as low as one mole of inhibitor per mole of platinum group metal will in some instances yield a satisfactory storage stability and cure rate. In other instances, inhibitor concentrations of up to 500 or more moles of inhibitor per mole of platinum group metal may be required. The optimum concentration for an inhibitor in a given silicone composition can be readily determined by routine experimentation.

Advantageously, the amount of the crosslinking inhibitor in the addition-crosslinking silicone compositions is in the range from 0.01%to 0.5%weight, preferably from 0.03%to 0.3%weight with respect to the total weight of the silicone composition.

The use of the inhibitor is effective to avoid the premature curing of the silicone composition on the tip of the nozzle and subsequent disfiguration of the printed layer.

The silicone composition W is a two-part composition comprising these components in two parts. The first part of the silicone composition W is to be charged into the liquid bath, and the second part of the silicone composition W is to be charged into the dispensing head of a printer.

Each part of the two-part silicone composition W is typically prepared by combining the principal components and any optional ingredients in the stated proportions at ambient temperature. The order of addition of the various components is not critical if the composition is to be used immediately. Combining can be accomplished by any of the techniques understood in the art such as, blending or stirring, either in a batch or continuous process in a particular device. The particular device is determined by the viscosity of the components and the viscosity of the final composition.

In certain embodiments, when the second part of the silicone composition W comprises more than one component, each component may be mixed in a dispense head, e.g. a dual dispense head, prior to and/or during printing. Alternatively, each component may be combined immediately prior to printing.

Description of the Figure

Figure 1 is a diagram illustrating the method for additive manufacturing a silicone elastomer article from the two-part silicone composition W in accordance with the present invention.

Mode of Carrying Out the Invention

The scope and interest of the invention will be better understood based on the following examples which are intended to illustrate certain embodiments of the present invention and are non-limitative.

Examples

The raw materials used for preparing the two-part silicone composition W in examples are listed in Table 1 below. The composition of the second part of the silicone composition is listed in Table 2 below. The composition of the first and second part of the silicone composition W as well as the test results for the printing and curing process are summarized in Table 3 below.

Table 1. The description or structure of raw materials used

Table 2. Composition of catalyst composition (second part) in dispensing head of the printer

Rheological test: two kinds of rheological behavior were evaluated as indicated below. Brookfield DV2TXX was used to determine the rheological behavior for all samples of present examples and comparative examples.

Viscosity property:

According to ASTM D445, the viscosity of the sample mixture was tested at 23℃, the detail of testing conditions can be seen in the Table 3, in which, for example, the expression (7#, 2rpm) denotes that the viscosity is measured at 2 rpm by using spindle 7.

Thixotropic property:

Normally the thixotropic property of the non-Newton fluid could be evaluated by a dynamic viscosity ratio measured at lower rotation speed and higher rotation speed that differ by a factor of 10. Herein, the thixotropy of the first part of the two-part silicone composition W was characterized by the ratio of the dynamic viscosity at 2rpm (designated as Viscosity-2) to the dynamic viscosity at 20rpm (designated as Viscosity-20) (Viscosity-2/Visocisty-20) .

Table 3. The composition of the first part (in liquid bath) and the second part (in dispensing head of the printer) as well as the test result for printing and curing process

^a how fast the diffusion of the second part in liquid bath would be occurred;

^b curing speed is represented by the speed of gel formation. “proper” represents the gel is formed within 10s. “slower” represents the gel is formed greater than 10s.

^c stable represents the width of printed layers varies within acceptable range while unstable represents the width of printed layers varies outside the acceptable range.

^d the status for the curing of the printed layer;

^e the tendency for the printed article to sink in the liquid bath

f non-acceptable for Comparative Example 1 is due to that the width of the printed layers varies outside acceptable range, while the non-acceptable for Comparative Example 2 is due to the uncured inside.

^Note: all the viscosity in Table 3 refer to the viscosity for the first part of the silicone composition W.

Preparation of first and second part of the two-part silicone composition W

In Example 1, the first part to be charged in liquid bath was prepared by combining all the raw materials in accordance with the weight ratio as indicated in Table 3. Specifically, 81.35 parts of a vinyl terminated polydimethylsiloxane A-1 was mixed with 2.2 parts of a hydrogen-containing polysiloxane B-1, then 1.52 parts of a hydrogen-containing polysiloxane B-2, 1.43 parts of a hydrogen-containing polysiloxane B-3 and 13.5 parts of treated silica F-1 were added and stirred to obtain the first part of the silicone composition. Then 0.02 parts of Pt catalyst C1 and 99.98 parts of diluent silicone oil D-1 was mixed and stirred to obtain the second part of the silicone composition.

3D printing process

The 3D printing process was carried out by using a 3D printer mounted with a liquid bath and dispensing heads via extrusion process, which can be seen in Figure 1. The liquid bath was used to contain the first part of the silicone composition W and the dispensing heads with nozzles were used to dispense the second part of the silicone composition W.

Printing process comprises the following steps:

i) charging the first part of the silicone composition W into a liquid bath of the 3D printer;

ii) charging the second part of the silicone composition W into the dispensing head of the 3D printer;

iii) adjusting the level of the liquid bath and setting printing parameters;

iv) dispensing the second part of the silicone composition W into the first part of the silicone composition W in liquid bath to form a first printed layer;

v) optionally repeating step iii) for additional layers needed;

vi) allowing the printed layers in liquid bath to partially or totally crosslink, to obtain a silicone elastomer article;

vii) removing the resulting silicone elastomer article from the liquid bath; and

viii) washing the silicone elastomer article obtained in step vii) , preferably with water and solvent;

ix) post-curing the silicone elastomer article obtained in step viii) by heating to a temperature of 80℃ for 1h.

The diameter of the nozzle of the dispensing head used was 0.8mm. The distance between the nozzle and the substrate was about 0.4 mm. No heating was used. The second part of the silicone composition (catalyst composition) W was extruded thought the nozzle of the dispensing head for the printer at a speed of 20mm/s.

Examples 2-4 and Comparative Examples 1-2 were carried out similarly to Example 1, except for the composition for the first and second part of the silicone composition W.

According to the present examples, superior printing process and curing process could be realized for the present silicone composition crosslinkable through polyaddition reaction. As shown from Examples 1 to 4 in Table 3, the first part of the silicone composition with required ranges of viscosity (Viscosity-2) and thixotropy (viscosity-2/viscosity-20) in liquid bath enables stable and fully-cured printed layers and thus the well-formed printed objects as the printing process proceeds without supporting materials.

However, higher viscosity and thixotropy for the first part in the liquid bath are not suitable for 3D printing. As can be seen from Comparative Example 2, higher viscosity and thixotropy would lead to relatively slow diffusion of the second part in the first part in liquid bath, resulting in the printed layer not cured inside. Meanwhile, another problem arising from this situation was that it is difficult for the printing nozzle to move correctly as intended path. The displacement of printed layer in X axis occurred due to the shear force from nozzle.

In addition, lower viscosity and thixotropy are also not useful for 3D printing. Diffusion of the printed layer in liquid bath would probably take place in that condition. According to Comparative Example 1, stable printed layer could no longer be obtained due to very fast diffusion of the catalyst composition in the first part of silicone composition in liquid bath, which leads to the failure of printing process.

In the present invention, the inventor has surprisingly found the proper rheology property of the silicone materials suitable for the additive manufacturing a silicone elastomer article via layer by layer process. Proper selection of the viscosity (Viscosity-2) in conjunction with the ratio of the viscosity (Viscosity-2 /Viscosity-20) for the first part of the silicone composition in liquid bath has made a contribution to the successful 3D printing process and thus the well-formed printed objects.

Furthermore, the scope of the general inventive concepts is not intended to be limited to the particular embodiments described herein. From the disclosure given, those skilled in the art will not only understand the general inventive concepts and their attendant advantages but will also find apparent various changes and modifications to the methods and products disclosed. It is sought, therefore, to cover all such changes and modifications as fall within the spirit and scope of the general inventive concepts, as described and suggested herein, and any equivalents thereof.

Claims

Method for additive manufacture a silicone elastomer article from a two-part silicone composition W, comprising:

i) charging the first part of the silicone composition W into a liquid bath of a 3D printer;

ii) charging the second part of the silicone composition W into a dispensing head of the 3D printer;

iii) dispensing the second part of the silicone composition W into the first part of the silicone composition W in the liquid bath to form a first printed layer;

iv) optionally repeating step iii) for additional layers needed;

v) allowing the printed layers in the liquid bath to partially or totally crosslink, optionally by heating, to obtain a silicone elastomer article;

vi) removing the resulting silicone elastomer article from the liquid bath, wherein the two-part silicone composition W comprises:

(a) at least one organopolysilicone;

(b) at least one crosslinking agent; and

(c) at least one catalyst;

wherein the first part of the silicone composition W comprises components (a) and (c) and the second part comprises component (b) , or otherwise the first part of the silicone composition W comprises components (a) and (b) and the second part comprises component (c) ,

the first part of the silicone composition W has a dynamic viscosity in the range of 500 mPa·s to 1,000,000 mPa·s, preferably in the range of 5,000 mPa·s to 500,000 mPa·s, more preferably in the range of 10,000 mPa·s to 300,000 and even more preferably from 15,000 mPa·s to 200,000 mPa·s,

the ratio of the dynamic viscosity at 2rpm to the dynamic viscosity at 20rpm for the first part of the silicone composition W (Viscosity-2 /Viscosity-20) is in the range of 1 to 6, preferably in the range of 1 to 5.5, more preferably in the range of 1 to 4, and even more preferably in the range of 1 to 3.
The method according to claim 1, further comprises a step vii) of washing the silicone elastomer article obtained in step vi) .
The method according to any one of preceding claims, wherein the 3D printer is an extrusion 3D printer.
The method according to any one of preceding claims, wherein in step iii) the second part of the silicone composition W is extruded through at least one nozzle of at least one dispensing head, preferably at a speed of 1 to 100 mm/s, more preferably at speed of 3 to 50 mm/s.
The method according to claim 4, wherein each component in the second part of the silicone composition W is extruded through a nozzle of the same dispensing head.
The method according to claim 4, wherein each component in the second part of the silicone composition W is extruded through nozzle (s) of different dispensing heads, respectively.
The method according to any one of preceding claims, wherein the liquid bath and the nozzle (s) of the dispensing head (s) may be heated, before, during or after step iii) , respectively or simultaneously.
The method according to any one of preceding claims, when the second part of the silicone composition W is dispensed into the first part in liquid bath, the time period for formation of gel is below 5mins, preferably below 1 mins, more preferably below 15s.
Silicone elastomer article obtainable by the method according to any one of preceding claims.
Use of the silicone elastomer article according to claim 9 for a medical material such as medical implant, an actuator for robotics, a gasket, a mechanical piece for automotive/aeronautics, a piece for electronic devices, a package for the encapsulation of components, a vibrational isolator, an impact isolator or a noise isolator.
Two-part silicone composition W used in the method according to any one of claims 1-8, comprising:

(a) at least one organopolysilicone;

(b) at least one crosslinking agent; and

(c) at least one catalyst;

wherein the first part of the silicone composition W comprises components (a) and (c) and the second part comprises component (b) , or otherwise the first part of the silicone composition W comprises components (a) and (b) and the second part comprises component (c) ,

the first part of the silicone composition W has a dynamic viscosity in the range of 500 mPa·s to 1,000,000 mPa·s, preferably in the range of 5,000 mPa·s to 500,000 mPa·s, more preferably in the range of 10,000 mPa·s to 300,000 and even more preferably from 15,000 mPa·s to 200,000 mPa·s,

the ratio of the dynamic viscosity at 2rpm to the dynamic viscosity at 20rpm for the first part of the silicone composition W (Viscosity-2 /Viscosity-20) is in the range of 1 to 6, preferably in the range of 1 to 5.5, more preferably in the range of 1 to 4, and even more preferably in the range of 1 to 3.
The two-part silicone composition W according to claim 11, wherein the first or second part of the silicone composition W further comprises at least one non-reactive diluent.
The two-part silicone composition W according to any one of preceding claims, wherein the first or second part of the silicone composition W further comprises at least one thixotropic agent.
The two-part silicone composition W according to claim 13, wherein the thixotropic agent is used in an amount from greater than 0wt%to 10wt%, preferably from 0.2 wt%to 5wt%, more preferably from 0.5wt%to 2wt%, based on the total weight of the first part of the silicone composition W when present in the first part.
The two-part silicone composition W according to any one of preceding claims, wherein the first or second part of the silicone composition W further comprises at least one filler.
The two-part silicone composition W according to any one of preceding claims, wherein the two-part silicone composition W is crosslinkable through polyaddition reaction or polycondensation reaction.
The two-part silicone composition W used in the method according to any one of claims 1-8, comprising:

(a) at least one organopolysiloxane A;

(b) at least one organohydrogenopolysiloxane B;

(c) at least one catalyst C;

(d) at least one non-reactive diluent D;

(e) at least thixotropic agent E;

(f) at least one filler F,

wherein the first part of the silicone composition W comprises components (a) , (b) , optional (e) to (f) , and the second part of the silicone composition W comprises components (c) and optional (d) to (f) .
The two-part silicone composition W used in the method according to any one of claims 1-8, comprising:

(a) at least one organopolysiloxane A;

(b) at least one organohydrogenopolysiloxane B;

(c) at least one catalyst C;

(d) at least one non-reactive diluent D;

(e) at least thixotropic agent E;

(f) at least one filler F,

wherein the first part of the silicone composition W comprises components (a) , (c) , optional (e) to (f) , and the second part of the silicone composition W comprises components (b) and optional (d) to (f) .
The two-part silicone composition W according to claim 17, comprising:

(a) from 55%to 85%by weight, preferably from 60%to 85%by weight, more preferably from 70%to 80%by weight of at least one organopolysiloxane A in relative to the total weight of the first part of the silicone composition W;

(b) from 0.1%to 20%by weight, preferably from 1%to 5wt%by weight, more preferably from 3%to 5%by weight of at least one organohydrogenopolysiloxane B in relative to the total weight of the first part of the silicone composition W;

(c) from 0.002%to 5%by weight, preferably from 0.005%to 0.1%by weight, more preferably from 0.01%to 0.02%by weight of at least one catalyst C in relative to the total weight of the second part of the silicone composition W;

(d) from 0 to 99%by weight, preferably from 50%to 99%by weight, more preferably from 85%to 99%by weight of at least one non-reactive diluent D in relative to the total weight of the second part of the silicone composition W;

(e) from 0 to 20%by weight, preferably from 0.01%to 10%by weight, more preferably from 0.1%to 5%by weight of at least thixotropic agent E in relative to the total weight of the first part of the silicone composition W;

(f) from 5 to 40 %by weight, preferably from 5 to 30wt%, more preferably from 5%to 20%by weight of at least one filler F in relative to the total weight of the first part of the silicone composition W,

wherein the first part of the silicone composition W comprises components (a) , (b) , optional (e) and optional (f) , and the second part of the silicone composition W comprises components (c) and optional (d) .
Use of the two-part silicone composition W according to any one of claims 11 to 19 for additive manufacturing a silicone elastomer article.