WO2018222108A1

WO2018222108A1 - A process for fabricating a flame retarded thermoplastic product through additive manufacturing and a use of a thermoplastic composition in additive manufacturing

Info

Publication number: WO2018222108A1
Application number: PCT/SE2018/050527
Authority: WO
Inventors: Vanessa MAURIN; Pia WENNERBERG; Magnus KOKKO; Emelie RYDÉN; Martin Olofsson; Stefan Lundmark; Peter Johansson; Linda ZELLNER
Original assignee: Perstorp Ab
Priority date: 2017-05-30
Filing date: 2018-05-24
Publication date: 2018-12-06

Abstract

Method for fabricating flame retarded thermoplastic products through additive manufacturing, comprising the steps; a) Computing a first, bulk, rendition of a digital three dimensional model and an optional second rendition being an outer surface, b) Printing the first rendition with a composition comprising, 20 – 60 % by weight of polycaprolactone (PCL) having a molecular weight of at least 50.000, 20 – 50 % by weight of polylactide (PLA) having a average molecular weight of at least 100.000, 20 – 40 % by weight of aluminium trihydrate having an average particle size in the range 0.2 μm and 20 μm, c) The optional second rendition may be printed onto the first rendition with the same thermoplastic composition as defined in b) but being printed with a high resolution. The invention also refers to use of a thermoplastic composition for additive manufacturing of fire retarded products.

Description

A PROCESS FOR FABRICATING A FLAME RETARDED THERMOPLASTIC PRODUCT THROUGH ADDITIVE MANUFACTURING AND A USE OF A THERMOPLASTIC COMPOSITION IN ADDITIVE MANUFACTURING.

The present invention refers to a process for fabricating a flame retarded thermoplastic product through additive manufacturing. The present invention also relates to thermoplastic compositions intended for use in additive manufacturing and methods for manufacturing.

FIELD OF THE INVENTION

Additive manufacturing has been known in the industry for several decades and has primarily been used as a method for creating visual three dimensional prototypes in the development process. This was made possible through computer assisted three dimensional design which could be used for guiding the manufacturing process. Early in the development of this technology, UV-curing monomers were used and cured, layer upon layer, by means of a UV laser, until the prototype was fully formed. The problems with this early technology was that the prototypes were rather brittle and that the time for fabricating them was very long. The brittleness problem has improved significantly over the years, but is still a problem. The long times needed for fabricating remains. The time consumption can to some extent be solved by increasing the thickness of each layer, i.e. decreasing the resolution. The physical appearance of such a product will however leave something to be desired.

The great advantage with additive manufacturing is that the production cost will be the same, regardless if you manufacture one product or thousands of them. This will provide a great flexibility in production since the basic only difference between two different products is digital information. The material and production machine is the same. In practice, the competing technologies are methods such as injection moulding. For this technology one will need a mould and a moulding machine. The disadvantage with injection moulding is that the investment in a mould is rather high and that it takes months to manufacture a mould. One will accordingly have to produce a significant amount of identical products using injection moulding technology to reach a reasonable price per part.

In additive manufacturing the problem is the opposite. The cost for designing, i.e. creating the digital three dimensional rendition, will be the same regardless of whether additive manufacturing or injection moulding is used. In additive manufacturing you can start fabricating immediately as you will not have to wait for the mould to be made. You will accordingly have the first product available months before the injection moulding alternative. Secondly you will not have to invest in the rather expensive mould. The disadvantage is however that, while cycle times, -the time for fabricating one product, is calculated in minutes, or in some cases even parts of minutes for injection moulding technology, the corresponding cycle time for additive manufacturing is calculated in hours and even days. There will accordingly be a breakeven point, -a point in numbers of identical products fabricated where it is economically viable to choose injection moulding over additive manufacturing.

Still, the cost per part is on the high end side for products created through additive manufacturing. One main reason is the long cycle time. A problem is that customers have become used to the cost and durability of injection moulded mass produced parts and additive manufacturing will have problems to compete with this. The negative feature with injection moulding is the lack of flexibility, -to customise for individual desires.

Fused Filament Fabrication (FFF) also known as Fused Deposition Moulding (FDM™) is perhaps the fastest technology today when it comes to printing speeds. However, the surface properties are in most cases not acceptable for consumer goods. The mechanical properties are still not at a level making products durable enough for more functional parts. Here the most commonly used materials are polylactic acid (PLA) and acrylonitrile- butadiene-styrene co-polymer (ABS) supplied in filaments. To increase the output, -that is shortening cycle times, in additive manufacturing with maintained, acceptable or even improved resolution, -the resolution being the perhaps most important part of the physical appearance of the product, has been a problem, i.e.

achieving the desired mechanical properties of products without affecting or even improving the physical or aesthetic appearance as well as output.

Another problem is the connected to fire resistance. So far, products manufactured through additive manufacturing have more or less only been used for prototyping where needs for safety is not so pronounced. However, with increased output and improved mechanical properties, products achieved through additive manufacturing can, -and will be used in the same way as products produced through methods that are more traditional. With the possibility of more practical use comes also need for fire resistance and food contact safety.

SUMMARY OF THE INVENTION

The present invention relates to a method for fabricating a product through additive manufacturing. The invention also relates to thermoplastic compositions with properties designed to meet requirements regarding;

-processability before and during additive manufacturing, such as melt flow viscosity at specific temperature and at temperature ranges, thermal conductivity and crystallization characteristics,

-mechanical properties in manufactured products, such as impact resistance, elongation at break, softening temperature, tensile strength, crystallinity, density, fire resistance, food contact safety, thermal and electric conductivity and,

-aesthetic surface properties in manufactured products, both visual as well as tactile. Accordingly the method for fabricating a flame retarded thermoplastic product through additive manufacturing comprises the steps of;

a) computing at least a first rendition of a digital three dimensional model, the first rendition being the bulk of a structure and an optional second rendition being an outer surface, b) printing the first rendition with a composition comprising, 20 - 60 % by weight of polycaprolactone (PCL) having an weight average molecular weight of at least 50.000, 20 - 50 % by weight of polylactide (PLA) having a weight average molecular weight of at least 100.000, 20 - 40 % by weight of aluminium trihydrate having an average particle size in the range 0.2 μιη and 20 μηι,

c) printing the optional second rendition onto the first rendition with a composition comprising, 20 - 60 % by weight of polycaprolactone (PCL) having an weight average molecular weight of at least 50.000, 20 - 50 % by weight of polylactide (PLA )having a weight average molecular weight of at least 100.000, 20 - 40 % by weight of aluminium trihydrate having an average particle size in the range 0.2 μιη and 20 μιη the second rendition being printed with a high resolution.

The composition used for printing the first rendition may advantageously further comprise 0.5 - 50 % by weight of a performance additive selected from the group consisting of, octadecanoic acid, ethylene bis stearamide, polytetrafluoroethylene, calcium carbonate, mica, talcum, cellulose, dolomite, starch, graphite, graphene, graphene oxide, graphyne, graphdiyne, cellulose, carbon fibre, glass fibre, aramid fibre and combinations thereof.

The composition used for printing the optional second rendition may advantageously further comprise 0.5 - 50 % by weight of a performance additive selected from the group consisting of, octadecanoic acid, ethylene bis stearamide, polytetrafluoroethylene, calcium carbonate, mica, talcum, cellulose, dolomite, starch, graphite, graphene, graphene oxide, graphyne, graphdiyne and combinations thereof. The cellulose is preferably in the form of nano- cellulose.

The expression rendition is to be understood as the processing of the three dimensional digital creation into layers the printer can handle. These layers can accordingly be of low resolution meaning thick layers, hard on the eye but quick to print, or of high resolution which is aesthetically pleasing but time consuming to print. Low resolution layers will also build in more heat into the printed product which puts some very specific demands on the

thermoplastic composition to be used in order to avoid gravity induced shrinkage, also known as Z-axis shrinkage. The thermoplastic composition can be supplied to the printer as filaments or as granulate. The second rendition printing can advantageously be guided by a sensor. The result of the first rendition printing and/or the second rendition printing is accordingly continuously or discontinuously scanned via laser scanner or another optical device. These measurements of the partly printed object are then compared with the digital version of the design and the printing is adjusted to compensate for deviations from the digital version. Such a method of guiding the printing process can of course be completely automated through algorithms in the guiding programming of the printer. It will of course also be possible to utilize such guiding also for the printing of the first rendition.

As is discussed in the present application, gravity induced, or so called Z-axis shrinkage is a common problem in FFF technology. This Z-axis shrinkage is of course affected by the mechanical properties of the thermoplastic composition but will of course be affected also by the design of the object to be printed. Especially top-heavy designs will suffer more from Z- axis shrinkage than bottom heavy designs.

According to one embodiment of the invention the first rendition is being printed with a thermoplastic composition by means of a CAM (Computer Aided Manufacturing) guided heated nozzle moveable in at least 3-axis, said nozzle being used for printing the

thermoplastic composition.

According to one special embodiment of the invention the CAM guided CNC (Computer Numerical Control) machine have a CAM guided cooling nozzle. This cooling nozzle is used for rapidly cooling and setting the newly printed thermoplastic composition. An effluent selected from the group consisting of; liquid carbon dioxide, liquid water, cooled air and a combination thereof, is supplied to the cooling nozzle. Advantageously, the position of the cooling nozzle and the amount of effluent ejected from the cooling nozzle is guided through means of algorithms calculated to create an even temperature profile in newly printed thermoplastic composition and to counteract hot-spots in the products caused by parts of the product with low surface to mass ratio. The cooling nozzle can possibly be arranged adjacent to the CAM guided heated nozzle. The cooling nozzle is then suitably guided in at least 4-axis as in relation to the printed product.

One should note that the above described forced cooling method, including the effluent selected, needs to be adapted to the thermoplastic composition used. Some thermoplastic compositions such as lactic acid or caprolactone based polyester thermoplastics (PLA and PCL respectively) will not obtain their full mechanical strength if cooled too rapidly, while other thermoplastic compositions such as a polyolefin thermoplastic can accept more rapid cooling. It will however still be possible to utilize a balanced cooling even in more sensitive thermoplastic composition selections to counteract hot-spots in parts of the printed product with heavier goods thickness.

According to one special embodiment of the invention the CAM guided heated nozzle has an adjustable orifice. The adjustable orifice can then be adjusted between a large orifice with high output of molten thermoplastic and a small orifice with low output of molten thermoplastic composition.

High and low output, respectively is to be understood as that a high output large nozzle allows at least twice the amount per weight of thermoplastic composition to be printed in set time unit, as that of a small orifice with low output.

The size of the orifice of the CAM guided heated nozzle is hereby suitably guided by algorithms in a CNC machine and that the CAM guided heated nozzle is operating in at least a 4-axis mode during portions of the printing.

The printing may accordingly be running with fluent resolution i.e. alternating between coarse and fine resolution as the CAM / CNC preparation renders the printout. The CNC operated printer can thus make a first run with a large orifice creating a first portion of the print with say 3mm resolution in a 3-axis mode. The expression "first run" is to be understood as one or a few vertical layers of the print. This may then be followed by a second run creating a skin with a fine orifice with say 0.1mm resolution in a 5-axis mode. Another run with a large orifice may follow on that and the process of printing alternately with large and fine resolution can continue until the product is printed. It is of course possible to use multiple resolutions to achieve the quickest and most visually pleasing results.

As described above, the CAM guided CNC machine may advantageously have a CAM guided cooling nozzle used for rapidly cooling and setting the newly printed thermoplastic composition. This will allow an increase in the printing speed which otherwise could be hampered by the fact that more heat will be stored in thicker goods. An effluent is as above, selected from the group consisting of; liquid carbon dioxide, liquid water and cooled air which is supplied to the cooling nozzle. The position of the cooling nozzle and the amount of effluent ejected from the cooling nozzle can be guided through means of algorithms calculated to create an even temperature profile in newly printed composition and to counteract hot-spots in the products caused by parts of the product with low surface to mass ratio. The cooling nozzle is arranged adjacent to the CAM guided heated nozzle and the cooling nozzle is guided in at least 4-axis as in relation to the printed product. One possibility is to arrange the cooling nozzle in a swivelling position on the heated printing nozzle in a 1 - 3 axis mode in relation to the heated printing nozzle.

According to one embodiment of the invention, the temperature of the orifice is guided by means of algorithms controlled by output ratio and orifice size. Due to lower counter pressure in larger orifices it will be possible to utilize lower temperature when using large orifice allowing a composition to have higher viscosity and hence being less prone to shrink in z- axis. This temperature control may be achieved in two ways. A first manner of controlling the temperature is by adjusting the energy to the heater. This will however create some delay, also known as lag, which will create problems when switching between small and large orifice at short intervals. A second manner is by actively cooling or heating the outer tip of the orifice which will create a much shorter adjustment time. The latter will, of course, be possible to combine with control of the heating chamber.

According to one special embodiment of the invention the thermoplastic composition used for the printing comprises at least one polyester selected from the group consisting of polylactic acid (PLA) and polycaprolactone (PCL) and at least one performance additive selected from the group consisting of CaC03 and talcum. The thermoplastic composition is preferably a compound of 50 - 95 parts per weight of PLA with a weight average molecular weight in the range of 50.000 M_w - 150.000 M_w and 5 - 50 parts per weight of PCL with a weight average molecular weight in the range of 10.000 M_w - 120.000 M_w.

The performance additive is preferably present to an amount of 5 - 40 parts by weight of the total composition of thermoplastic composition (performance additive included). The performance additive is suitably present as a blend, whereby at least 5% by weight of the blend is CaCCb and at least 5% by weight of the blend is talcum.

In a preferred embodiment of the invention CaCC and talcum is present in ratio 60-80 % by weight of CaCCb and 20-40% by weight of talcum and said performance additive blend is present to a level of 25 -35% by weight of the thermoplastic composition. According to a special embodiment of the above composition, said composition further comprises 0.1 - 3% by weight of a carbon compound selected from the group consisting of; graphite, graphene, graphene oxide, graphyne, graphdiyne and combinations thereof. According to an alternative of the embodiment thermoplastic composition further comprises a nucleating agent allowing annealing treatment of a printed product. Such an annealing process is known in polylactic acid esters, and the mechanical properties such as improved impact resistance and improved e-modulus. The annealing process will also increase the softening temperature of the thermoplastic composition. It has surprisingly been found that the annealing temperature can be lowered by at least 10°C by manufacturing a compound between PLA and PCL as described above. This will radically reduce the risk of warping and other deformations of the printed product during this annealing process. The performance additive described above will further reduce this risk.

Above reducing the risk for warping, also the reduction in power consumption and shortening of the annealing time is a desired property. The annealing will as understood by the above increase the useful temperature range of a product that has undergone this procedure as the softening temperature is increased considerably. This could of course be achieved by selecting a thermoplastic composition with higher softening temperature from the beginning. This would however make the printing process more energy consuming and more difficult to control. It would also be practically impossible to print minute details when working at higher temperatures. The above described thermoplastic compositions is particularly useful in the herein described process using both large and small orifices due to its amorphous property. It is accordingly also very useful in the small orifice fine printing used today with great advantage. The above described thermoplastic composition has been shown to provide excellent surface properties, dimension stability as well mechanical properties during experimentation within the present invention.

The above described thermoplastic compositions has also shown to be remarkably insensitive to printer settings hereby providing a large process window. That implies that, for example, temperature settings and printer nozzle distance from the object is not critical. This is particularly important for less advanced printers and printers operated only on occasional basis as well as by less experienced operators.

According to one embodiment of the invention a first CAM guided heated nozzle has a large orifice with high output of molten thermoplastic composition and at least one second CAM guided fine resolution nozzle having a small orifice with low output of molten thermoplastic composition.

The first CAM guided heated nozzle with large output is guided by algorithms in a CNC machine in at least a 3 -axis mode and that the at least one second CAM guided fine resolution nozzle or nozzles is/are guided by algorithms in the CNC machine and operated in at least a 4-axis mode.

The printing may be run as first printing a coarse resolution and then print a fine resolution onto the first print. An alternative is to alternate between coarse and fine resolution print. Yet another, and preferred alternative is to simultaneously print coarse and fine resolution prints. In this preferred alternative the fine resolution print is printed with a predetermined delay or lag. Accordingly the CNC operated printer can make a first run with a large nozzle creating a first portion of the print with say 3mm resolution in a 3-axis mode. The expression "first run" is to be understood as one or a few vertical layers of the print. The fine resolution nozzle may then commence creating a skin with a fine nozzle with say 0.1mm resolution in a 5-axis mode. It is of course possible to use multiple fine resolution nozzles to achieve the quickest and most visually pleasing results. The fine resolution nozzle may also have an adjustable orifice so that larger recesses in the coarse print may be filled quickly and to gradually decrease the orifice size and hence increase the resolution the closer to the final outer surface of the finished product you get. Also in this embodiment the CAM guided CNC machine advantageously have a CAM guided cooling nozzle used for rapidly cooling and setting the newly printed thermoplastic composition. This will allow an increase in the printing speed which otherwise could be hampered by the fact that heat will be stored in thicker goods. An effluent selected from the group consisting of; liquid carbon dioxide, liquid water and cooled air is supplied to the cooling nozzle. The position of the cooling nozzle and the amount of effluent ejected from the cooling nozzle can be guided through means of algorithms calculated to create an even temperature profile in newly printed thermoplastic composition and to counteract hot-spots in the products caused by parts of the product with low surface to mass ratio. The cooling nozzle is arranged adjacent to the CAM guided heated nozzle and the cooling nozzle is guided in at least 4-axis as in relation to the printed product. One possibility is to arrange the cooling nozzle in a swivelling position on the heated printing nozzle in a 1 - 3 axis mode.

According to a special embodiment of the invention a method for fabricating a product through additive manufacturing the method comprising the steps of;

a) computing a first and a second rendition of a digital three dimensional model, the first rendition being a carrying structure and the mould rendition being an outer surface, b) printing the first rendition with a low resolution,

c) shaping the outer surface by means of at least one moveable moulding tool.

The first rendition is accordingly printed with a thermoplastic composition by means of a CAM guided heated nozzle moveable in at least 3-axis. The nozzle is used for printing the thermoplastic composition wherein the at least one moveable moulding tool is guided by CAM in a CNC machine. Said at least one moulding tool is shaping the outer surface while still hot and malleable and at the same time cooling said surface so that it sets into the desired shape.

Advantageously, an effluent selected from the group consisting of; liquid carbon dioxide, liquid water, cooled air is supplied to the at least one moulding tool. The at least one moulding tool is suitably arranged adjacent to the CAM guided heated nozzle. The at least one moulding tool is guided in at least 4-axis as in relation to the printed product.

In principle the moulding tool can be seen as a partial temporary mould following the CAM guided heated nozzle. This moulding tool may advantageously be shaped as a matrix printer head with several stacked moveable sub moulds having the desired resolution, say 0.1 mm in vertical axis. The profile of this matrix moulding tool is then guided and positioned in at least a 5 -axis mode by means of the CAM guided CNC machine. Water, CO2 or cool air act as coolant and lubricant between mould and thermoplastic to minimize risk for smearing. The effluent of CO2 or cooled air would then act as a lubricating air cushion between the moulding tool and the still malleable thermoplastic composition. PTFE coating of the moulding tool have also shown to be advantageous.

The CAM guided CNC machine may advantageously also have a CAM guided cooling nozzle used for cooling and setting the newly printed thermoplastic composition in portions not reached by the moulding tool. This will allow an increase in the printing speed which otherwise could be hampered by the fact that heat will be stored in thicker goods. An effluent selected from the group consisting of; liquid carbon dioxide, liquid water, cooled air is supplied to the cooling nozzle. The position of the cooling nozzle and the amount of effluent ejected from the cooling nozzle can be guided through means of algorithms calculated to create an even temperature profile in newly printed thermoplastic composition and to counteract hot-spots in the products caused by parts of the product with low surface to mass ratio. The cooling nozzle is arranged adjacent to the CAM guided heated nozzle and the cooling nozzle is guided in at least 4-axis as in relation to the printed product. One possibility is to arrange the cooling nozzle in a swivelling position on the heated printing nozzle in a 1 - 3 axis mode. The process may be seen as a kind of partial low pressure blow moulding if the cooling nozzle air pressure is applied from the inside towards the moveable mould. This would however be possible to utilize only on larger hollow objects.

It is important to note that some thermoplastic composition thereof are not well suited for very rapid or intense cooling as it affects the crystallisation process. The natural mechanical properties, such as impact resistance, may simply be hampered if these compositions are cooled too quickly or to a too low temperature. As examples of such compositions we can mention polylactic acid polymers (PLA), polycaprolactone (PCL) as well as compounds and co-polymers thereof. Even though some compositions will lose some of their natural mechanical properties if submitted to rapid cooling, it will still be possible to submit them to some degree of cooling, just enough to increase the viscosity in order to decrease the vertical, gravity induced shrinkage, also known as z-axis shrinkage, without affecting the mechanical properties too much. So called hot-spots, i.e. parts of the product with thicker goods, low surface to volume ratio, may also be counteracted by CAM guided cooling in order to achieve a more uniform temperature profile of the product during manufacturing. The invention also refers to a use of a thermoplastic composition for production of flame retarded products through additive manufacturing wherein the composition comprises;

20 - 60 parts by weight of polycaprolactone having an weight average molecular weight of at least 50.000,

20 - 50 parts by weight of polylactide having a weight average molecular weight of at least 100.000,

20 - 40 parts by weight of aluminium trihydrate having an average particle size in the range 0.2 μηι and 20 μιη and,

optionally 0.5 - 50 parts by weight of a performance additive selected from the group consisting of, octadecanoic acid, ethylene bis stearamide, polytetrafluoroethylene, calcium carbonate, mica, talcum, cellulose, dolomite, starch, graphite, graphene, graphene oxide, graphyne, graphdiyne, cellulose, carbon fibre, glass fibre, aramid fibre and combinations thereof.

The above thermoplastic composition is suitably in the form of filament, pellets, granulate or powder.

According to one embodiment of the invention the first rendition is being printed with a thermoplastic composition by means of a CAM guided heated nozzle moveable in at least 3- axis. The nozzle is used for printing the thermoplastic composition. The thermoplastic composition is a random or block co-polymer with 0.1 - 30 mol%, preferably 0.2 - 5 mol%, more preferably 0.3 - 3 mol% grafted sites for radical polymerisation. The thermoplastic composition is printed with a high output nozzle. The second rendition, comprising a radiation curing monomer or oligomer is then printed by means of at least one inkjet nozzle, onto the printed thermoplastic composition. The radiation curing monomer or oligomer is cured with itself and with the grafted sites of the thermoplastic composition by means of irradiation. It will not be necessary to add photo initiators to the thermoplastic polymer. It is of course possible to add a photo initiator also to the thermoplastic composition. It will, however be sufficient to add photo initiator in the inkjet composition.

The thermoplastic composition is selected from the group consisting of (co)oligo or (co)poly caprolactones, lactides, (meth)acrylics, (meth)allylics, benzimidazoles, carbonates, ether sulphones, ether ketones, ether imides, alkylenes, alkylene phthalates (such as PET, PBT and S-PET), butadienes (such as ABS), alkylene oxides, alkylene sulphides (alkylene being ethylene, propylene or butylene etc.), styrenes (PVC), vinyl or vinylidene halides (chlorides, fluorides), having at least one group or site reactive to >C=C<, -C≡C-, epoxy and oxetane.

Said second rendition preferably comprises an oligo or polymer having at least one site or function selected from >C=C<, -C≡C-, epoxy and oxetane. The >C=C<, -C≡C-, epoxy and oxetane is suitably selected among oligo or poly (meth)acrylics, (meth)allylics, vinylics, epoxies and oxetanes. Said first and/or said second rendition suitably comprises such as for instance Capa™ (co)oligo/polymers, oligo/polycarbonates having at least one >C=C<, -C≡C-, epoxy and oxetane. As examples of compositions providing reactive sites when co- polymerized with the thermoplastic can be mentioned, cinnamic acid, 4-hydroxycinnamic acid, 3,4-dihydroxycinnamic acid, caffeic acid, 3,4-diacetoxycinnamic acid, a dimer of methyl vinvl glycolate and a dimer of methyl vinyl glycolate and lactic acid.

It is common practice to utilize photo initiators in above described technology. It will however, as mentioned earlier, be somewhat impractical to add a photo-initiator to the thermoplastic composition with radical polymerization sites described above. The primary reason is that such a composition would have a reduced shelf life since curing may be initiated by light pollution or even warm storage. Instead, the most practical way is to add the photo-initiator together with the second rendition photopolymer which then would initiate the reaction when irradiated. A small amount of curing between the radical polymerisation within the thermoplastic composition will happen. This is of course a positive effect as it will make the printed structure more rigid. The most pronounced effect, which is also the primary effect of the invention, is a bond through reaction between the inner thermoplastic part of the product and the outer photopolymer part of the product. It is known that some of the best aesthetic results, -due to the very high resolution possible, is achieved with photopolymer technology in additive manufacturing through 3D inkjet printing. In this case the photo- initiator is added to the photopolymer to be printed onto the thermoplastic structure achieved in the first rendition print.

The photo initiator is then a free radical, cation or anion photo initiator. The photo initiator is hence selected among a sulphonium antimonate, a sulphonium fluoroantimonate, a sulphonium fluorophosphate, a sulphonium nitrate, a sulphonium triflate, an iodonium fluorophophate such as bis(4-tert-butylphenyl)iodonium hexafluorophosphate, a

hydroxy(cyclo)alkylaryl ketone, a metallocene, a ketoprofen, a benzoin ether, a benzil ketal, an acetophenone, a benzophenone, an amino(cyclo)alkylphenone, an acylphosphine oxide, a benzoephenone, a thixantone, an anthraquinone, ethyl 4-dimethylaminobenzoate and/or a camphorquinone.

PLA based thermoplastic compositions are very popular today and are very well suited for additive manufacturing as herein disclosed. This composition group is however rather hydrolytically instable which means that products made of this composition will decompose in humid or wet environment. This will of course limit the practical use of products fabricated from PLA based compositions. The herein disclosed process of printing a first crude but swift print utilizing PLA based compositions herein disclosed, followed by a second fine and delicate print utilizing radiation curing photopolymers by means of at least one inkjet nozzle will offer a solution to this problem. The outer layer of photopolymer will, besides providing the desired, aesthetically pleasing resolution, also protect the PLA core of the printed product from deterioration. Advantageously, as herein disclosed, the PLA based composition is modified by producing the composition as a PLA based co-polymer with 0.1 - 5% by weight randomly arranged grafted sites suited for radical polymerisation hereby allowing a chemical bond between the PLA-based core and the surface layer.

In another aspect of the invention it is known that thermoplastic compositions are subject to static charging. It will accordingly be possible to provide the crudely printed thermoplastic core with an outer layer of a photopolymer modified by any known means to conduct electricity to a small degree. In the electronic industry the conductivity needed is classified as dissipative.

In a further aspect of the invention the outer layer of the photopolymer may, in addition to provide the aesthetically pleasing shape, also be provided with colouration by adding pigment or dye to the photopolymer. It will of course be possible to print said outer layer with multiple colours just like when printing a photograph, in the case of the present of the invention, on a three dimensional surface. In order to give an illustrative example, a person is scanned in 3 dimensions with a laser scanner. At the same time digital photos are taken and rendered as a surface on the 3D digital model of the person. A miniature model of the person may then be printed in accordance with the invention whereupon the final layer is printed with multicolour inkjet onto the surface of the miniature model, catching every colour nuance of the persons clothing, skin and hair etc. The possibility to utilize a photopolymer ink will make sure that the colouration will become an integrate part of the printed model.

In yet a further aspect of the invention the outer layer of photopolymer may provide a desired tactile property. Such a property is known as haptic coating. Suitable basic haptic compositions is known through WO 2016/089271. According to one embodiment of the invention the thermoplastic composition used for additive manufacturing is caprolactone polymer (PCL) with a weight average molecular weight in the range 10.000 M_w - 120.000 M_w. The polymer comprises 0.5 - 50 % of a performance additive selected from the group consisting of, calcium carbonate, mica, talcum, dolomite, starch, cellulose fiber, graphite, graphene, graphene oxide, graphyne, graphdiyne and combinations thereof. The thermoplastic composition is preferably a composition comprising PCL with a weight average molecular weight in the range 40.000 M_w - 100.000 Mw and a performance additive comprising calcium carbonate and talcum, said performance additive being present in the range 15 - 45% by weight of the thermoplastic composition and that said performance additive is comprised of at least 55% by weigh of calcium carbonate and at least 10% by weight of talcum.

According to one embodiment of the invention the thermoplastic composition is a random or block co-polymer between caprolactone and lactic acid with a weight average molecular weight in the range 50.000 M_w to 150.000 M_w. Caprolactone is then suitably present in the range 10 - 60% by weight of the total weight of the co-polymer. The co-polymer

advantageously comprises 0.5 - 50 % by weight of a performance additive selected from the group consisting of, calcium carbonate, mica, talcum, dolomite, starch, graphite, graphene, graphene oxide, graphyne, graphdiyne, cellulose fibre, carbon fibre, glass fibre, aramid fibre and combinations thereof.

It has during initial experimentation been found that a caprolactone/lactide block copolymer of A-B-A type with a core of caprolactone with a molecular weight of approximately 15.000 Mw having two lactide tails of each around 18.000 M_w has shown to have some very interesting properties. The composition has a very low viscosity measured as a MFI (melt flow index) of 67 (at 2.16kg load) at 190°C, a medium viscosity measured as a MFI of 39 (at 2.16kg load) at 180°C and becomes practically solid, MFI of 0 (at 2.16kg load) at 160°C. This property allows for an increased printing speed and at the same time a lower amount of gravity induced shrinkage. The above mentioned co-polymer is more suited for advanced printers and experienced operators due to its narrow melt curve. The advantage is as mentioned above shorter cycle times which is very much desired in professional and continuous production, for which the composition is very well suited.

According to one embodiment of the invention a thermoplastic composition suitable for additive manufacturing would comprise PCL with a molecular weight of 35.000 - 85.000 to an amount of 55 - 90 % by weight, CaCC to an amount of 10 - 45 % by weight and talcum to an amount of 0 - 15% by weight. According to a variation of the above embodiment a carbon compound selected from the group consisting of; graphite, graphene, graphene oxide, graphyne, graphdiyne and combinations thereof, is added to an amount of 0.1 - 3% by weight to the composition.

In another embodiment of the invention the thermoplastic composition comprises PCL with a molecular weight of 35.000 M_w - 100.000 M_w to an amount of 55 - 90 % by weight, CaCCb to an amount of 10 - 45 % by weight, talcum to an amount of 0 - 15% by weight and cellulose fibres to an amount of 5 - 30 % by weight. These cellulose fibres are preferably nano-fibrillated cellulose fibres. According to a variation of the above embodiment a carbon compound selected from the group consisting of; graphite, graphene, graphene oxide, graphyne, graphdiyne and combinations thereof, is added to an amount of 0.1 - 3% by weight to the composition.

The thermoplastic composition used for the first rendition b) preferably has a higher melt viscosity than that of a thermoplastic composition used in the second rendition c). This can be achieved by selecting the thermoplastic composition used in the first rendition b) with a higher molecular weight at >70.000 M_w than the thermoplastic composition of the second rendition at <50.000 M_w. It is also possible to utilise compositions with higher amount of performance additives whereby the thermoplastic composition used in the first rendition b) comprises a performance additive selected from the group consisting of; calcium carbonate, mica, talcum, dolomite, starch, graphite, graphene, graphene oxide, graphyne, graphdiyne, cellulose, glass fibre, aramid fibre, carbon fibre and a combination thereof.

The performance additives serve the purpose of both improving the mechanical properties, aesthetic properties included, of the product, but also make the newly printed layer more stable and less inclined to shrink in the horizontal direction due to gravity and pressure from layers above, also known as Z-axis shrinkage. Fibre reinforcements are therefore of particular interest, but also particulate performance additives like for example mica will serve a purpose. Also thermoplastic compositions with higher molecular weight will be beneficial to counteract such shrinkage. High amounts of such performance additives as herein described will not cause any problems when using nozzles with a large orifice and high output rate. Performance additives may advantageously also be used in the thermoplastic compositions used in the second rendition, however at lower levels. In the second rendition printing it is advantageous to avoid reinforcing fibre altogether or to use micro- or even nano-fibre in order to secure a good flow through the rather narrow orifice nozzle utilized here. It may also prove wise to use compositions with lower molecular weight to secure a good flow.

As discussed above, forced and guided cooling is an advantageous method for quickly setting the printed composition in the desired shape, this is more important for the composition printed with a printing nozzle having a large, high output, orifice. EMBODIMENT EXAMPLES

Example 1

A set of compositions aimed for additive manufacturing was designed. The compositions comprised the polylactic acid ester PLA 4043D and the polycaprolactone ester Capa™ 6500. The two polyesters were compounded in different ratios in an extruder.

Two sets of samples were then printed, one set of so-called dog-bone with 0.8 mm goods thickness for tensile stress testing and/or elongation at break testing and one set of blocks with 4.0 mm goods thickness for impact stress testing. The samples were printed with a 0.4 mm printing nozzle with a horizontal print separation of 0.4 mm of three circumscribing outer walls in each vertical layer. The outer walls consisting of the three parallel printed lines had the horizontal width of 1.2 mm. The empty space within the border of the outer walls of each layer was then infilled with 100% density in 45° towards the outer wall. Next Z-axis infill layer was printed 90° towards the previous infill layer. Each Z-axis layer had a vertical height (Z-axis) of 0.06 mm.

The following results were achieved.

Table 1.

The experiments show that the impact resistance is greatly improved by compounding even very small amounts of Capa™ 6500 into PLA 4034D, while elongation at break is acceptable at all levels. However, in some applications the need for higher elongation at break is needed. In these cases it is noteworthy that a PLA/Capa™ compound comprising 20 - 40% as in examples lc-le, of Capa™ 6500 shows good improvement. In example If, example lc was repeated by replacing Capa™ 6500 with Capa™ 6800. The impact resistance was radically improved, however not as much as in example lc. On the other hand the tensile strength showed great improvement, both in relation to examples la and lc.

Example 2.

A set of compositions aimed at additive manufacturing was designed. The compositions comprised the polycaprolactone ester Capa™ 6500 and CaCCb. The components were compounded in different ratios in a compounder.

Two sets of samples were then printed, one set of so-called dog-bone with 0.8 mm goods thickness for tensile stress testing and/or elongation at break testing and one set of blocks with 4.0 mm goods thickness for impact stress testing and for measuring softening temperature. The samples were printed with a 0.4 mm printing nozzle with a horizontal print separation of 0.4 mm of three circumscribing outer walls in each vertical layer. The outer walls consisting of the three parallel printed lines had the horizontal width of 1.2 mm. The empty space within the border of the outer walls of each layer was then infilled with 100% density in 45° towards the outer wall. Next Z-axis infill layer was printed 90° towards the previous infill layer. Each Z-axis layer had a vertical height (Z-axis) of 0.06 mm.

The following results were achieved.

Table 2

It was found that the impact resistance was radically improved by adding around 20% by weight of CaC03 to the polycaprolactone. During trials with additive manufacturing it was found that the composition according to example 2c had surprisingly low z-axis shrinkage and provided excellent surface properties as well as desired mechanical properties.

Example 3

A set of compositions aimed at additive manufacturing was designed. The compositions comprised the polycaprolactone ester Capa™ 6500, Capa™ 6800, CaCCb and talcum respectively. The components were compounded in different ratios.

Two sets of samples were then printed, one set of so-called dog-bone with 0.8mm goods thickness for tensile stress testing and/or elongation at break testing and one set of blocks with 4.0 mm goods thickness for impact stress testing and for measuring softening temperature. The samples were printed with a 0.4 mm printing nozzle with a horizontal print separation of 0.4 mm of three circumscribing outer walls in each vertical layer. The outer walls consisting of the three parallel printed lines had the horizontal width of 1.2 mm. The empty space within the border of the outer walls of each layer was then infilled with 100% density in 45° towards the outer wall. Next Z-axis infill layer was printed 90° towards the previous infill layer. Each Z-axis layer had a vertical height (Z-axis) of 0.06 mm. The following results were achieved.

Table 3.

It was surprisingly found that elongation at break as well as tensile strength were radically improved by changing the performance additive composition from 30% by weight of CaCC to 21% by weight of CaCC and 9 % by weight of talcum. During trials with additive manufacturing it was found that the composition according to example 3b had surprisingly low z-axis shrinkage and provided excellent surface properties as well as mechanical properties. It was further found that the composition was possible to process at a large temperature span which will make it possible to use at lower temperatures in large orifice nozzles and at higher temperatures in small orifice nozzles. It was also noted that example 3c obtained a greatly improved impact resistance.

Example 4

A set of compositions aimed at additive manufacturing was designed. The compositions comprised the polylactic acid ester PLA 4043D, the polycaprolactone ester Capa™ 6500, CaCCb and talcum. The components were compounded in different ratios in a compounder. Two sets of samples were then printed, one set of so-called dog-bone with 0.8 mm goods thickness for tensile stress testing and/or elongation at break testing and one set of blocks with 4.0 mm goods thickness for impact stress testing and for measuring softening temperature. The samples were printed with a 0.4 mm printing nozzle with a horizontal print separation of 0.4 mm of three circumscribing outer walls in each vertical layer. The outer walls consisting of the three parallel printed lines had the horizontal width of 1.2 mm. The empty space within the border of the outer walls of each layer was then infilled with 100% density in 45° towards the outer wall. Next Z-axis infill layer was printed 90° towards the previous infill layer. Each Z-axis layer had a vertical height (Z-axis) of 0.06 mm.

The following results were achieved.

Table 4.

The experiments show that in spite of increasing the amount of CaC03 and talcum from 10% of the composition to 20% between example 4a and 4b of the composition the vicat softening temperature is virtually unaffected, so is elongation at break, while tensile strength is radically improved in examples 4c, 4d. During trials with additive manufacturing it was found that the composition according to example 4b had surprisingly low z-axis shrinkage and provided excellent surface properties as well as mechanical properties. It was further found that the composition was possible to process at a large temperature span which will make it possible to use at lower temperatures in large orifice nozzles and at higher temperatures in small orifice nozzles.

The above described thermoplastic compositions has also shown to be remarkably insensitive to printer settings hereby providing a large process window. That implies that, for example, exact temperature settings and printer nozzle distance from the object is not critical. This is particularly important for less advanced printers and printers operated only on occasional basis as well as by less experienced operators.

Example 5.

A set of samples comprising polycaprolactone (PCL), polylactide (PLA) and performance additive where compounded in formulations as specified in table 5.1. All figures presented as % are by weight. A worst case was selected by printing thin sheets with 0.5 mm thickness. Test samples with the dimension 40 x 100 mm where arranged on a wire and then subjected to open flame from a gas burner for fifteen seconds in accordance with DIN 4102. The results of the experiments are presented in table 5.2

Table 5.1

PLA = polylactide

PCL = polycaprolactone

ATH = aluminium trihydrate Table 5.2; results

Samples of the different compositions were also tested for mechanical properties such as tensile stress and elongation. The tested compositions were found to have acceptable and useful mechanical properties for several application areas as shown in table 5.3.

Table 5.3; results

ccor ng to nvent on Figure 1 shows a part of a cross-section of an object printed with large orifice nozzle and fine orifice nozzle respectively.

Accordingly, figure 1 schematically shows a coarse print 1 achieved with a first CAM guided heated nozzle with a large orifice and with high output of molten thermoplastic and a fine print from a second CAM guided fine resolution nozzle having a small orifice with low output of molten thermoplastic composition.

The first CAM guided heated nozzle with large output is guided by algorithms in a CNC machine in a 3 -axis mode. The second CAM guided fine resolution nozzle is guided by algorithms in the CNC machine and operated in at least a 4-axis mode.

The printing may be run as first printing a coarse resolution and then print a fine resolution onto the first print. An alternative is to alternate between coarse and fine resolution print. Yet another, and preferred alternative is to simultaneously print coarse and fine resolution print. In this preferred alternative the fine resolution print is printed with a predetermined delay or lag. Accordingly the CNC operated printer can make a first run with a large nozzle creating a first portion of the print with say 3mm resolution in a 3-axis mode. The expression "first run" is to be understood as one or a few vertical layers of the print. The fine resolution nozzle may then commence creating a skin with a fine nozzle with say 0.1mm resolution in a 5-axis mode. It is of course possible to use multiple fine resolution nozzles to achieve the quickest and most visually pleasing results. The fine resolution nozzle may also have an adjustable orifice so that larger recesses in the coarse print may be filled quickly and to gradually decrease the orifice size and hence increase the resolution the closer to the final outer surface of the finished product you get.

It has shown advantageous to have a higher viscosity in the first, coarse print 1 in order to avoid or minimize gravity induced shrinkage. The higher viscosity can be achieved by utilising a lower temperature during printing. PCL / PLA blends have shown to provide properties suitable for this. It is also possible to provide the thermoplastic compositions with performance additives such as minerals and fibres. A third alternative is to utilize a caprolactone/lactide co-polymer having a very narrow melting curve. Such a

caprolactone/lacide co-polymer would solidify completely when the temperature has decreased by as little as 10 - 30°C.

Claims

1. A method for fabricating a flame retarded thermoplastic product through additive manufacturing, the method comprising the steps of;

a) computing at least a first rendition of a digital three dimensional model, the first rendition being the bulk of a structure and an optional second rendition being an outer surface,

b) printing the first rendition with a composition comprising, 20 - 60 % by weight of polycaprolactone (PCL) having an weight average molecular weight of at least 50.000, 20 - 50 % by weight of polylactide (PL A) having a weight average molecular weight of at least 100.000, 20 - 40 % by weight of aluminium trihydrate having an average particle size in the range 0.2 μιη and 20 μηι,

c) printing the optional second rendition onto the first rendition with a composition comprising, 20 - 60 % by weight of polycaprolactone (PCL) having an weight average molecular weight of at least 50.000, 20 - 50 % by weight of polylactide (PLA) having a weight average molecular weight of at least 100.000, 20 - 40 % by weight of aluminium trihydrate having an average particle size in the range 0.2 μιη and 20 μιη the second rendition being printed with a high resolution.

2. A method according to claim 1, wherein the composition used for printing the first rendition further comprises 0.5 - 50 % by weight of a performance additive selected from the group consisting of, octadecanoic acid, ethylene bis stearamide,

polytetrafluoroethylene, calcium carbonate, mica, talcum, cellulose, dolomite, starch, graphite, graphene, graphene oxide, graphyne, graphdiyne, cellulose, carbon fibre, glass fibre, aramid fibre and combinations thereof.

3. A method according to claim 1, wherein the composition used for printing the optional second rendition further comprises 0.5 - 50 % by weight of a performance additive selected from the group consisting of, octadecanoic acid, ethylene bis stearamide, polytetrafluoroethylene, calcium carbonate, mica, talcum, cellulose, dolomite, starch, graphite, graphene, graphene oxide, graphyne, graphdiyne and combinations thereof.

4. A method according to claim 1, wherein the first rendition is being printed with a thermoplastic composition by means of a CAM guided heated nozzle moveable in at least 3-axis, said nozzle being used for printing the thermoplastic composition.

5. A method according to claim 4, wherein a CAM guided CNC machine have a CAM guided cooling nozzle, said cooling nozzle being used for rapidly cooling and setting the newly printed thermoplastic composition, that an effluent selected from the group consisting of; liquid carbon dioxide, liquid water, cooled air and a combination thereof, is supplied to the cooling nozzle and that the amount of effluent ejected from the cooling nozzle is guided through means of algorithms calculated to create an even temperature profile in newly printed composition and to counteract hot-spots in the products caused by parts of the product with low surface to mass ratio.

6. A method according to claim 1, wherein the CAM guided heated nozzle has an

adjustable orifice, that the adjustable orifice can be adjusted between a large orifice with high output of molten thermoplastic and a small orifice with low output of molten composition, that the size of the orifice of CAM guided heated nozzle is guided by algorithms in a CNC machine and that the CAM guided heated nozzle is operating in at least a 4-axis mode during portions of the printing and that the temperature of the orifice is guided by means of algorithms controlled by output ratio and orifice size.

7. A method according to claim 1, wherein the performance additive is present to an amount of 5 - 40 parts by weight of the total composition, thermoplastic composition + performance additive.

8. A method according to claim 7, wherein the performance additive is present in a

blend, whereby at least 5% by weight the blend is CaCCb and at least 5% by weight of the blend is talcum.

9. A method according to claim 1, wherein the CAM guided heated nozzle has a large orifice with high output of molten thermoplastic and at least one CAM guided fine resolution nozzle having a small orifice with low output of molten thermoplastic low output of molten thermoplastic composition.

10. A method according to claim 9, wherein the CAM guided heated nozzle with large output is guided by algorithms in a CNC machine in at least a 3 -axis mode and that the at least one CAM guided fine resolution nozzles is guided by algorithms in the CNC machine and operated in at least a 4-axis mode.

11. A method according to claim 1, wherein the first rendition is being printed with a thermoplastic composition by means of a CAM guided heated nozzle moveable in at least 3-axis, said nozzle being used for printing the thermoplastic composition and wherein at least one moveable moulding tool is guided by CAM in a CNC machine, that said at least one moulding tool is shaping the outer surface while still hot and at the same time cooling said surface so that it sets into the desired shape.

12. A method according to claim 11, wherein an effluent selected from the group consisting of; liquid carbon dioxide, liquid water, cooled air is supplied to the at least one moulding tool, that the at least one moulding tool is arranged adjacent to the CAM guided heated nozzle, and that the at least one moulding tool is guided in at least 4- axis as in relation to the printed product.

13. Use of a thermoplastic composition for production of flame retarded products through additive manufacturing wherein the composition comprises;

20 - 60 parts by weight of polycaprolactone (PCL) having an weight average molecular weight of at least 50.000,

20 - 50 parts by weight of polylactide (PLA) having a weight average molecular weight of at least 100.000,

20 - 40 parts by weight of aluminium trihydrate having an average particle size in the range 0.2 μιη and 20 μιη and,

optionally 0.5 - 50 parts by weight of a performance additive selected from the group consisting of, octadecanoic acid, ethylene bis stearamide,