Patent Description:
One of the most used 3D printing technologies or additive manufacturing technologies is the fused deposition modeling (FDM), also known as fused filament fabrication process (FFF). For the production of three-dimensional objects, usually filaments of thermoplastic materials, provided on a spool, are deposited layer-by-layer through a heated nozzle on a base. Therefore, the thermoplastic material is heated to a temperature past its melting and/or glass transition temperature. The thermoplastic material and the temperature gradient are selected to enable its solidification essentially immediately upon contacting the base or a preceding layer of thermoplastic material extruded.

In order to form each layer, drive motors are provided to move the base and/or the extrusion nozzle (dispending head) relative to each other in a predetermined pattern along the x-, y- and z-axis. Fused deposition modeling (FDM) was first described in <CIT>.

Industrially, thermoplastic materials in general are of particular importance on account of their very good mechanical properties. In particular, they possess high strength, stiffness, and toughness, good chemical resistance, and a high abrasion resistance and tracking resistance. Nevertheless, for some applications, for example in the automotive industry, it is necessary to further improve the chemical resistance, stiffness and dimensional stability of the thermoplastic materials. Therefore, they are usually strengthened by fibrous fillers.

However, the production of three-dimensional objects comprising fibrous fillers by fused filament fabrication is only possible if the content of the fibrous fillers in the filament does not exceed <NUM> % by weight. Otherwise, the filaments cannot be rolled on a spool and have difficulties being fed into 3D printer nozzles due to their surface roughness and lack of lubricative properties.

<CIT> discloses a filament comprising a core material coated with a layer of shell material, wherein the core material comprises an inorganic powder and a binder and the shell material comprises a thermoplastic polymer. The filament can be used for the production of three-dimensional metallic or ceramic objects.

However, the application of filaments comprising a core material (CM) comprising a fibrous filler and a first thermoplastic polymer, coated with a shell material comprising a second thermoplastic polymer, is not disclosed.

<CIT> discloses 3D printer inputs including filaments comprising separated layers or sections. These inputs, particularly including filaments, may be prepared by co-extrusion, microlayer co-extrusion or multicomponent/fractal coextrusion.

However, filaments comprising a core material coated with a layer of shell material, wherein the core material (CM) comprises a fibrous filler and a first thermoplastic polymer and the shell material comprises a second thermoplastic polymer, are not described.

A core/shell filament for 3D printing is also disclosed in <CIT>.

Therefore, the object underlying the present invention is to provide new filaments for an application in an extrusion-based additive manufacturing system that can overcome the aforementioned disadvantages.

This object is achieved by a filament comprising a core material (CM) coated with a layer of shell material (SM), according to claim <NUM>.

One advantage of the inventive filaments is their higher mechanical stability compared to filaments prepared from the same core material (CM) but without the shell material (SM). In particular, the inventive filaments can be rolled on a spool, while filaments without shell material (SM) (monofilaments) are usually too brittle and therefore are not suited to be spooled.

Since the mechanical properties and therefore the processability of the inventive filaments in a conventional machine for a fused filament fabrication process (FFF) are mainly determined by the shell material (SM), there is more freedom of variation in regard to the composition of the core material (CM) compared to filaments without a shell material (SM).

For example, the inventive shell material (SM)-core material (CM) configuration allows for the use of significantly higher loads of fibrous filler (FF) in the core material (CM) that could result in a more brittle core. Actually, loads of fibrous filler (FF) up to <NUM> % by weight, based on the total weight of the core material (CM), can be applied. Without a layer of shell material (SM) according to the invention it was not possible to consistently feed highly brittle material in the conventional machines used in the fused filament fabrication process (FFF).

In other words, the flexural radius at break of the inventive filaments is smaller than the flexural radius at break of the monofilaments. The flexural radius at break is the radius at which the (mono)filaments break. The smaller the flexural radius at break of the (mono)filaments, the more they can be bent around and the better they can be rolled on a spool.

Furthermore, it is also possible that the inventive filaments exhibit a tacky or extremely tacky core material (CM), which would without the presence of the shell material (SM) block the feeder mechanism. Consequently, by the inventive process, filaments for the application in a fused filament fabrication process (FFF) can be realized, which obtain a core material (CM) of ultra-low viscosity or of extreme tackiness.

In addition, in the fused filament fabrication process (FFF), the shell material (SM) of the inventive filaments functions as an adhesive between the layers of the three-dimensional body. Therefore, the inventive three-dimensional bodies exhibit an increased mechanical strength along the z-axis and hence a higher dimensional stability.

Moreover, the inventive three-dimensional bodies are already the finished component. Further treatment steps are not required. Thus, by using the inventive filaments, it is possible to prepare three-dimensional bodies with high loads of fibrous fillers in a very fast and simple way.

For the purpose of the present invention, the term "fibrous filler (FF)" means a filler which is significantly longer than it is wide and has the shape of a fiber. Preferably, the length-to-diameter ratio of the fibrous filler (FF) in the filament is from <NUM>:<NUM> to <NUM>:<NUM>, more preferably from <NUM>:<NUM> to <NUM>:<NUM>, most preferably from <NUM>:<NUM> to <NUM>:<NUM>.

In a preferred embodiment, the fibrous filler (FF) in the filament has a length of <NUM> to <NUM>, more preferably of <NUM> to <NUM> and most preferably of <NUM> to <NUM>. Further, in the filament, the fibrous filler (FF) has preferably a diameter of <NUM> to <NUM>, more preferably of <NUM> to <NUM> and most preferably of <NUM> to <NUM>.

The invention is specified in more detail as follows.

The filament comprises a core material (CM) coated with a layer of shell material (SM).

The filament may exhibit any length and/or diameter as deemed appropriate by the person skilled in the art.

Preferably, the diameter of the filament is <NUM> to <NUM>, more preferably <NUM> to <NUM>, most preferably <NUM> to <NUM>.

The layer of shell material (SM) may have any thickness as deemed appropriate by the person skilled in the art.

Preferably, the thickness of the layer of shell material (SM) is <NUM> to <NUM>, more preferably <NUM> to <NUM>.

The core material (CM) may have any diameter as deemed appropriate by the person skilled in the art.

Preferably, the diameter of the core material (CM) is <NUM> to <NUM>, more preferably <NUM> to <NUM>, most preferably <NUM> to <NUM>.

The core material (CM) comprises the components a) to c).

As component a), the core material (CM) comprises the at least one fibrous filler (FF).

The terms "component a)" and "fibrous filler (FF)" for the purpose of the present invention are synonymous and are used interchangeably throughout the present invention. "Fibrous filler (FF)" means precisely one fibrous filler (FF) as well as a mixture of two or more fibrous fillers (FF).

The core material (CM) comprises <NUM> to <NUM> % by weight of the at least one fibrous filler (FF), more preferably <NUM> to <NUM> % by weight, and most preferably <NUM> to <NUM> % by weight, based on the total weight of the core material (CM).

As component a), the fibrous filler is selected from glass fibers composed of E, A, C glass and carbon fibers.

The glass fibers can be used as rovings (continuous-filament fibers) or in the commercially available forms of chopped glass fibers (staple).

Preferably, the at least one fibrous filler (FF) is carbon fibers.

In one embodiment of the present invention, in case the fibrous fillers (FF) are carbon fibers, the carbon fibers do not comprise any metals and/or metal alloys and/or ceramic materials. Preferably, the carbon fibers do not comprise any metals, metal alloys and ceramic materials within this embodiment.

To improve the compatibility between the at least one thermoplastic polymer (TP1) or the at least one thermoplastic polymer (TP2) and the at least one fibrous filler (FF), the surface of the fibrous filler can be treated with a silane compound.

Suitable silanes are those according to the general formula (I).

(X-(CH<NUM>)g)k-Si-(O-Ch H<NUM>+<NUM>)<NUM>-k     (I).

Preferably, the silane compound is selected from the group consisting of aminopropyltrimethoxysilane, aminobutyltrimethoxysilane, aminopropyltriethoxysilane, aminobutyltriethoxysilane and also the corresponding silane compounds which contain a glycidyl group as substituent X.

Preferably, the fibrous filler (FF) comprises the silane compound in an amount of from <NUM> to <NUM> % by weight, preferably of from <NUM> to <NUM> % by weight and especially of from <NUM> to <NUM> % by weight, based on the total weight of the fibrous filler (FF).

Suitable carbon fibers are commercially available under the trade name Tenax®, suitable glass fibers under the trade name Chopvantage®.

It is also possible to purchase thermoplastic polymers already reinforced by fibrous fillers (FF). For example, polyamides, reinforced by glass or carbon fibers, are available from BASF SE under the tradename Ultramid.

As component b), the core material (CM) comprises the at least one thermoplastic polymer (TP1).

The terms "component b)" and "thermoplastic polymer (TP1)" for the purpose of the present invention are synonymous and are used interchangeably throughout the present invention. "Thermoplastic polymer (TP1)" means precisely one thermoplastic polymer (TP1) as well as a mixture of two or more thermoplastic polymers (TP1).

The at least one thermoplastic polymer (TP1) may comprise thermoplastic homopolymers, thermoplastic copolymers, as well as blends of thermoplastic polymers.

The core material (CM) comprises <NUM> to <NUM> % by weight of the at least one thermoplastic polymer (TP1), more preferably <NUM> to <NUM> % by weight and most preferably <NUM> to <NUM> % by weight, based on the total weight of the core material (CM).

The at least one thermoplastic polymer (TP1) of the core material (CM) is a polyamide selected from:.

These polyamides and their preparation are known. A person skilled in the art can find details regarding their preparation in "<NPL>, "<NPL>, and also <NPL>(keyword "Polyamide" and the following).

The polyamides (PA) generally have a viscosity number in the range of <NUM> to <NUM>/g, preferably in the range of <NUM> to <NUM>/g, and especially preferably in the range from <NUM> to <NUM>/g. The viscosity number is determined in a solution of <NUM>% by weight of the polyamides (PA) in <NUM> of <NUM>% strength by weight sulfuric acid at <NUM> in accordance with ISO <NUM>.

The weight-average molecular weight (Mw) of the polyamides (PA) is customarily in the range from <NUM> to <NUM><NUM><NUM>/mol, preferably in the range from <NUM> to <NUM><NUM>/mol, and especially preferably in the range from <NUM><NUM> to <NUM><NUM>/mol. The weight-average molecular weight (Mw) is determined according to ASTM D4001.

The melting temperature TM of the polyamides (PA) is customarily in the range from <NUM> to <NUM>, preferably in the range from <NUM> to <NUM>, and especially preferably in the range from <NUM> to <NUM>, determined by differential scanning calorimetry (DSC) or by dynamic mechanical thermoanalysis (DMTA) for semicrystalline polyamides. For amorphous polyamides, TM is defined as the temperature at which the at least one polyamide (A) (having a minimum solution viscosity of <NUM>/g to ISO <NUM> in sulfuric acid) has at least a zero shear viscosity of <NUM> Pa s and hence is processable in the melt (measured on a DHR-<NUM> rotational rheometer from TA Instruments, plate/plate geometry, plate diameter <NUM> and sample height <NUM>. Deformation <NUM>%, preheat time <NUM>, and material dried under reduced pressure at <NUM> for <NUM> days beforehand).

The polyamides (PA) usually have a glass transition temperature (Tg). The glass transition temperature (Tg) of the polyamides (PA) are usually in the range from <NUM> to <NUM> and preferably in the range from <NUM> to <NUM>.

The glass transition temperature (Tg) is determined via differential scanning calorimetry (DSC). The measurement of the glass transition temperature (Tg) is carried out under nitrogen atmosphere in heat/cool/heat cycles of <NUM>/min, <NUM>/min and <NUM>/min, respectively. For the measurement, approximately <NUM> to <NUM> of the substance were sealed in an aluminum crucible. In the first heating run, the samples are heated to <NUM>, then rapidly cooled to <NUM> and then in the second heating run, heated to <NUM>. The respective Tg value is determined from the second heating run. This procedure to determine the glass transition temperature (Tg) is known to the person skilled in the art.

As component c), the core material (CM) optionally comprises at least one additive (A).

The terms "component c)" and "additive (A)" for the purpose of the present invention are synonymous and are used interchangeably throughout the present invention. "Additive (A)" means precisely one additive (A) as well as a mixture of two or more additives (A).

The core material (CM) comprises <NUM> to <NUM> % by weight, more preferably <NUM> to <NUM> % by weight, and most preferably <NUM> to <NUM> % by weight, based on the total weight of the core material (CM) of the at least one additive (A).

As component c), any known additives (A) can be used. Preferably, the additive (A) is selected from the group consisting of dispersants, stabilizers, pigments and tackifiers.

Dispersants are known per se and are commercially available.

Examples for suitable dispersants are oligomeric polyethylene oxides having a low molecular weight of from <NUM> to <NUM>/mol, stearic acid, stearamides, hydroxystearic acids, fatty alcohols, fatty alcohol, fatty acid esters, sulfonates and block copolymers of ethylene oxide and propylene oxide and also, particularly preferably, polyisobutylene. Further, the additive (A) may be selected from stabilizers, like UV-stabilizers and/or antioxidants.

The additive (A) may be selected from pigments, such as organic dyes and/or inorganic pigments.

The additive (A) may be selected from tackifiers, like polymers with a glass transition temperature below room temperature, which is preferably below <NUM>° C and/or terpenederivatives.

The additive (A) may also be selected from the tackifiers as disclosed in <CIT>. An example for a commercially available tackifier is Acronal® A107.

Based on <CIT> and applying the definitions of the components of the tackifiers in <CIT>, as tackifiers preferably dispersions are applied comprising at least one in water soluble dispersed polymerisate with a weighted average molecular weight of less than <NUM> and a glas transition temperature higher or equal to -<NUM> to lower or equal <NUM>, preferably higher or equal -<NUM> or equal <NUM>, preferable of a monomer mixture comprising.

wherein the amounts of the monomers are based on the sum of all monomers.

Furthermore, tackifiers may be applied as disclosed in <CIT> and as specified in the following <NUM> paragraphs.

According to <CIT>, the tackifier may be rosin or a derivative of rosin having a ring and ball softening temperature from about <NUM>° to <NUM>° C. , preferably from about <NUM>° to <NUM>° C.

Suitable tackifiers include rosin, hydrogenated rosin esters, glycerol of rosin such as triglycerol rosin esters, C<NUM>-<NUM> alkylene esters of rosin such as triethylene glycol esters of rosin and tripropylene glycol esters of rosin; rosin salts, disproportionated rosin salts, pentaerythritol and the polyterpene resins including alpha and beta pinene. Suitable resins are sold under the tradenames Staybelite Ester <NUM>, Staybelite Ester <NUM>, Pentalyn Hand Hercolyn D.

The tackifier resin may be a C<NUM> or C<NUM> synthetic tackifier resin having a ring and ball softening point from about <NUM>° to <NUM>° C. , preferably from about <NUM>° to <NUM>° C. Suitable resins are sold under the tradenames Piccovar, Hercotac, Picconal and Piccolyte. These tackifiers are polymerized from C<NUM> monomers, preferably aromatic and C<NUM> monomers, preferably aliphatic.

The shell material (SM) comprises the components d) to f).

As component d), the shell material (SM) comprises the at least one thermoplastic polymer (TP2).

The terms "component d)" and "thermoplastic polymer (TP2)" for the purpose of the present invention are synonymous and are used interchangeably throughout the present invention. "Thermoplatic polymer (TP2)" means precisely one thermoplastic polymer (TP2) as well as a mixture of two or more thermoplastic polymers (TP2).

The at least one thermoplastic polymer (TP2) may comprise thermoplastic homopolymers, thermoplastic copolymers, as well as blends of thermoplastic polymers.

The shell material (SM) comprises <NUM> to <NUM> % by weight, more preferably <NUM> to <NUM> % by weight, and most preferably <NUM> to <NUM> % by weight, based on the total weight of the shell material (SM), of the at least one thermoplastic polymer (TP2).

The thermoplastic polymer (TP2) in the shell material (SM) is the same as the at least one thermoplastic polymer (TP1) of the core material (CM).

The shell material (SM) can comprise as component e) the at least one fibrous filler (FF).

The shell material (SM) comprises <NUM> to <NUM> % by weight of the at least one fibrous filler (FF), more preferably <NUM> to <NUM> % by weight, and most preferably <NUM> to <NUM> % by weight, based on the total weight of the shell material (SM).

The at least one fibrous filler of the shell material (SM) is identical to the fibrous filler (FF) defined for the core material (CM).

In a preferred embodiment, the shell material (SM) comprises <NUM> % by weight, based on the total weight of the shell material (SM), of the at least one fibrous filler (FF) and therefore there is preferably no component e) present in the shell material (SM).

As component f), the shell material (SM) can comprise the at least one additive (A).

The shell material (SM) comprises <NUM> to <NUM> % by weight of the at least one additive (A), more preferably <NUM> to <NUM> % by weight, and most preferably <NUM> to <NUM> % by weight, based on the total weight of the shell material (SM).

The at least one additive of the shell material (SM) is identical to the additive (A) defined for the core material (CM).

In one embodiment of the invention the core material (CM) comprises the components a), b) and c).

In a further embodiment of the invention the core material (CM) comprises the components a), b) and c).

A further subject of the invention is a process for the preparation of the filament as described above, wherein a core material (CM) is coated with a layer of a shell material (SM) by co-extrusion of the core material (CM) with the shell material (SM).

The co-extrusion technique as such is known to the person skilled in the art.

Based on the applied materials for the core and the shell material, the person skilled in the art may choose the respective appropriate co-extrusion temperatures and process parameters.

Another subject of the invention is a process for preparation of a three-dimensional object by a fused filament fabrication process, comprising at least the steps a), b), c),.

The fused filament fabrication process for the production of three-dimensional objects is well known in the state of the art and detailed explained in the above cited documents. The fused filament fabrication process is also denominated as 3D-printing process.

According to step a), the filament according to the present invention, is provided on a spool to a nozzle.

According to step b), the filament is heated to a temperature (TM). The temperature (TM) is above the melting point of the at least one thermoplastic polymer (TP1). Methods for the determination of the melting point of the at least one thermoplastic polymer (TP1) are known to the skilled person. For example, the melting point of the at least one thermoplastic polymer (TP1) can be estimated by differential scanning calorimetry (DSC).

In a preferred embodiment according to the present invention, in process step b) the filament is heated to a temperature (TM) that is at least <NUM>, preferably at least <NUM> and particularly preferably at least <NUM> above the melting point of the at least one thermoplastic polymer (TP1).

In another preferred embodiment the filament is heated to a temperature (TM) in the range of from <NUM> to <NUM>, preferably of from <NUM> to <NUM>.

According to step c), the filament is deposited into a build plate using the layer-based additive technique. The temperature of the build plate is usually in the range of from <NUM> to <NUM>, preferably of from <NUM> to <NUM> and particularly preferably of from <NUM> to <NUM>.

In other words, in step a) to c) of the inventive process, the filament generally is initially present in a solid state and thereafter melted and printed to form a three-dimensional object comprising the filament.

A further subject of the invention is also the three-dimensional object prepared by the processes as specified above.

The following examples further illustrate the invention.

The filaments in the examples E1 and E2 (according to the invention) were prepared by co-extrusion of the core material (CM) and the shell material (SM) applying the following materials, equipment and processing parameters.

Core material (CM) for examples E1 and E2 (according to the invention):.

Shell material (SM) for examples E1 and E2 (according to the invention):.

All polymers were dried before processing at <NUM> using an air dryer and conveyer speed of <NUM>/min.

The monofilaments in the examples C3 and C4 (comparative examples) were prepared by extrusion applying the following materials, equipment and processing parameters.

The monofilaments were prepared from the same core material (CM) as the examples according to the invention but without the shell material (SM).

The flexural radius at break of the filaments in the examples E1 and E2 (according to the invention) and of the monofilaments in the examples C3 and C4 (comparative examples) was measured (Table <NUM>).

The flexural radius at break of the (mono)filaments is the radius at which the (mono)filaments break. The smaller the flexural radius at break of the (mono)filaments, the more they can be bent around and consequently, the better they can be rolled on a spool.

Claim 1:
A filament comprising a core material (CM) coated with a layer of shell material (SM), wherein
the core material (CM) comprises the components a) to c)
a) <NUM> to <NUM> % by weight, based on the total weight of the core material (CM), of at least one fibrous filler (FF),
b) <NUM> to <NUM> % by weight, based on the total weight of the core material (CM), of at least one thermoplastic polymer (TP1), and
c) <NUM> to <NUM> % by weight, based on the total weight of the core material (CM), of at least one additive (A),
and the shell material (SM) comprises the components d) to f)
d) <NUM> to <NUM> % by weight, based on the total weight of the shell material (SM), of at least one thermoplastic polymer (TP2),
e) <NUM> to <NUM> % by weight, based on the total weight of the shell material (SM), of at least one fibrous filler (FF), and
f) <NUM> to <NUM> % by weight, based on the total weight of the shell material (SM), of at least one additive (A), wherein the at least one thermoplastic polymer (TP2) of the shell material (SM) is the same as the at least one thermoplastic polymer (TP1) of the core material (CM), and wherein the at least one thermoplastic polymer (TP1) is a polyamide (PA) selected from the group consisting of polyamide <NUM>, polyamide <NUM>, polyamide <NUM>, polyamide <NUM>, polyamide <NUM>/<NUM>, polyamide <NUM>/<NUM>, polyamide 6T, polyamide 9T, polyamide 6I, polyamide <NUM>/6T and polyamide 6I/6T, and wherein the at least one fibrous filler (FF) is selected from glass fibers composed of E, A, or C glass and carbon fibers.