Composition suitable for 3D printing

Abstract

The present invention relates to a composition suitable for 3D printing, comprising: - a polyester derived from an aliphatic polyol having from 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having from 3 to 15 carbon atoms, said polyester having a degree of polymerization of at most 0.6, which is the ratio of the reacted fraction of functional groups to the maximum of those which can react; - a solid filler; - a diluent. The present invention also relates to a process for the preparation of a shaped object comprising the steps of: - providing a composition as described herein, - extruding said composition through a printer nozzle to form layers of the composition having a desired shape, causing the layers to accumulate on one another to form a shaped object, - subjecting said shaped object to a curing step to form a cured shaped object, wherein said curing step occurs during and / or after said extruding step. The shaped object is also claimed.

Description

[0001] The present invention relates to a composition suitable for 3D printing. The present invention also relates to the use of the composition in 3D printing, and to the shaped object thus obtained.

[0002] 3D printing is an attractive method to obtain custom-made objects. It is widely used in many fields of application.

[0003] The current state of the art for 3D printed objects has the problem that, while it allows to print thermoplastic polymers, the processing of thermoset polymers is rather difficult.

[0004] There is a need in the art for a composition that can be processed by 3D printing to form a shaped object based on a thermoset polymer, showing good thermal stability. Such a composition based on bio-based, fossil-free components is particularly attractive. The composition should allow to provide a 3D shape with good stability and an attractive visual appearance. The composition is recyclable and / or biodegradable, which would be particularly attractive.

[0005] The present invention provides such a composition.

[0006] The present invention provides a composition suitable for 3D printing, comprising:

[0007] - a polyester derived from an aliphatic polyol having 2-15 carbon atoms and an aliphatic polycarboxylic acid having 3-15 carbon atoms, the polyester having a degree of polymerization of at most 0.6, which is the ratio of the reacted fraction of functional groups to the maximum of those functional groups that can react,

[0008] - a solid filler,

[0009] - a diluent.

[0010] The composition according to the present invention can be processed using a 3D printer to form a shaped object, which can be subjected to a curing step during or after printing. The polyester used in the present invention is a thermoset material, which leads to a shaped object with good thermal stability. By appropriate selection of the filler and the origin of the polyester, a bio-based, fossil-free, renewable, recyclable and / or biodegradable composition can be obtained. Further advantages of the composition and specific embodiments thereof, as well as further embodiments of the present invention will become apparent from the further description.

[0011] The present invention also provides a method of preparing a shaped object, comprising the steps of:

[0012] - providing a composition as described herein

[0013] - extruding the composition through a printer nozzle to form layers of the composition in the desired shape, the layers being built on top of each other to form the shaped object,

[0014] - To subject the molded object to a curing step to form a cured molded object, wherein the curing step occurs during and / or after the extrusion step.

[0015] The present invention also provides a 3D printed object comprising a polyester and filler, the polyester being derived from an aliphatic polyol having 2-15 carbon atoms and an aliphatic polycarboxylic acid having 3-15 carbon atoms, the polyester having a degree of polymerization of at least 0.5, particularly at least 0.6, which is the ratio of the reactive functional group portion to the maximum value of those reactive functional groups.

[0016] The invention will now be described in more detail.

[0017] Polyesters

[0018] The starting composition according to the invention comprises a polyester derived from an aliphatic polyol having 2-15 carbon atoms and an aliphatic polycarboxylic acid having 3-15 carbon atoms, the polymer having a degree of polymerization of 0.1-0.6, which is the ratio of the maximum value of the reacted functional group portion to those that are reactive.

[0019] The aliphatic polyols used in this invention contain at least two hydroxyl groups, particularly at least three. Typically, the number of hydroxyl groups will be 10 or fewer, more particularly 8 or fewer, or even 6 or fewer, particularly 2 or 3. The polyols have 2-15 carbon atoms. More specifically, the polyols have 3-10 carbon atoms. The polyols preferably do not contain heteroatoms. More specifically, the polyols are aliphatic polyalkanols containing only C, H, and O atoms. The polyols preferably do not contain non-carbon groups other than hydroxyl groups. In a preferred embodiment of the invention, the polyol contains a relatively large number of hydroxyl groups compared to its number of carbon atoms. For example, the ratio between the number of hydroxyl groups and the number of carbon atoms ranges from 1:4 (i.e., one hydroxyl group for every four carbon atoms, or eight carbon atoms per diol) to 1:1 (i.e., one hydroxyl group for every carbon atom). In particular, the ratio between the number of hydroxyl groups and the number of carbon atoms ranges from 1:3 to 1:1, more specifically, from 1:2 to 1:1. A particularly preferred group of polyols is the group in which the ratio is in the range of 1:1.5 to 1:1.

[0020] Compounds with a hydroxyl group to carbon atom ratio of 1:1 are considered particularly preferred.

[0021] Examples of suitable polyols include triols selected from glycerol, sorbitol, xylitol, and mannitol, and diols selected from 1,2-propanediol, 1,3-propanediol, and 1,2-ethylenediol. Compounds selected from glycerol, sorbitol, xylitol, and mannitol are preferred, with glycerol being particularly preferred.

[0022] The preference for glycerol is based on the following: First, glycerol has a melting point of 20°C, making it easy to process, especially compared to xylitol, sorbitol, and mannitol, whose melting points are all much higher than 90°C. Furthermore, glycerol has been found to provide a high-quality polymer, thus combining the use of readily available raw materials, favorable processing conditions, and a high-quality product. Mixtures of different types of alcohols can also be used.

[0023] However, the preferred polyol contains at least 50 mol%, preferably at least 70 mol%, more particularly at least 90 mol%, or even at least 95 mol% of glycerol, xylitol, sorbitol, or mannitol, especially glycerol. In one embodiment, the polyol is essentially composed of glycerol.

[0024] Glycerol is a byproduct of biodiesel production via transesterification of glycerol esters with monools, and its use is one specific embodiment of this invention. Suitable monools include C1-C10 monools, particularly C1-C5 monools, and more particularly C1-C3 monools, specifically methanol. Glycerol esters are mono- and diesters and esters of glycerol and fatty acids, which typically have 10-18 carbon atoms, and suitable processes for producing biodiesel containing the relevant glycerol are known in the art.

[0025] The aliphatic polycarboxylic acids used in this invention contain at least two carboxylic acid groups, particularly at least three. Typically, the number of carboxylic acid groups will be 10 or fewer, more particularly 8 or fewer, or even 6 or fewer. The polycarboxylic acids have 3-15 carbon atoms. More particularly, the polycarboxylic acids have 3-10 carbon atoms. The polycarboxylic acids preferably do not contain N or S heteroatoms. More particularly, the polycarboxylic acids are aliphatic polycarboxylic acids containing only C, H, and O atoms.

[0026] In one embodiment, a dicarboxylic acid is used. The dicarboxylic acid (if used) can be any dicarboxylic acid having two carboxylic acid groups and typically up to 15 carbon atoms. Examples of suitable dicarboxylic acids include itaconic acid, malic acid, succinic acid, glutaric acid, adipic acid, and sebacic acid. Itaconic acid and succinic acid are preferred.

[0027] In one embodiment, a tricarboxylic acid is used. The tricarboxylic acid (if used) can be any tricarboxylic acid having three carboxylic acid groups and typically up to 15 carbon atoms. Examples include citric acid, isocitric acid, aconitic acid (cis and trans), and 3-carboxy-cis,cis-mucoconic acid. Citric acid is considered preferred for cost and availability reasons.

[0028] Where applicable, polycarboxylic acids may be provided in whole or in part as anhydrides (e.g., citric anhydride).

[0029] Studies have found that the use of tricarboxylic acids can impart attractive properties to polyesters. Therefore, in one embodiment, the polybasic acid comprises at least 10 wt.% of a tricarboxylic acid, whether or not it is combined with dicarboxylic acids, other tricarboxylic acids, or mixtures thereof. In one embodiment, the polybasic acid comprises at least 30 wt.% of a tricarboxylic acid, preferably at least 50 wt.% based on the total amount of the polybasic acid. In one embodiment, the amount of tricarboxylic acid is at least 70 wt.%, more particularly at least 90 wt.%, or even at least 95 wt.%. In one embodiment, the polybasic acid is substantially composed of tricarboxylic acids, wherein this statement substantially means that the presence of other acids does not affect the properties of the material.

[0030] In another embodiment of the invention, the acid comprises at least 10 wt.% of a dicarboxylic acid, preferably at least 30 wt.%, more preferably at least 50 wt.%, based on the total amount of the acid. In one embodiment, the amount of the dicarboxylic acid is at least 70 wt.%.

[0031] In one embodiment, the acid comprises a combination of at least 10 wt.% tricarboxylic acid and at least 2 wt.% dicarboxylic acid; more particularly, it comprises at least 10 wt.% tricarboxylic acid and at least 5 wt.% dicarboxylic acid; or at least 10 wt.% tricarboxylic acid and at least 10 wt.% dicarboxylic acid. In this embodiment, the weight ratio between the two types of acid can vary over a wide range, depending on the properties of the desired material. In one embodiment, the dicarboxylic acid comprises 2 to 90 wt.% of the total amount of dicarboxylic and tricarboxylic acids, particularly 5 to 90 wt.%, and more particularly 10 to 90 wt.%, depending on the properties of the desired material. Note that the preferred range of tricarboxylic acids indicated above also applies to this embodiment. It has been found that the use of tricarboxylic acids, particularly citric acid, results in the formation of high-quality composite materials, especially in combination with the use of triols (e.g., glycerol).

[0032] Not wanting to be bound by theory, we believe that the use of triacids, especially in combination with triols, can form high-quality composite materials for several reasons. First, the use of triacids, particularly in combination with triols, forms highly cross-linked polymers, resulting in increased strength.

[0033] The molar ratio between polyols and polyacids depends on the ratio of the number of reactive groups in the alcohol and acid used. Typically, the ratio of OH groups to acid groups is 5:1 to 1:5. More specifically, this ratio can be 2:1 to 1:2, even more specifically 1.5:1 to 1:1.5, and more preferably 1.1:1 to 1:1.1. The theoretical molar ratio is 1:1.

[0034] Optionally, suitable catalysts can be used to prepare polyesters. Suitable catalysts for the manufacture of polyesters are known in the art. Preferred catalysts are those that do not contain heavy metals. Useful catalysts are strong acids, such as, but not limited to, hydrochloric acid, hydroiodic acid and hydrobromic acid, sulfuric acid (H₂SO₄), nitric acid (HNO₃), chloric acid (HClO₃), boric acid, perchloric acid (HClO₄), trifluoroacetic acid, p-toluenesulfonic acid and trifluoromethanesulfonic acid. Catalysts such as zinc acetate and manganese acetate can also be used, although they may be less preferred.

[0035] In one embodiment, compounds are added to increase the interaction between the polymer and the hydrophobic material, or to increase the water resistance of the final product. Suitable compounds include, for example, C5 to C22 saturated or unsaturated fatty acids or salts thereof, C5 to C22 saturated or unsaturated fatty alcohols, and dimer and trimer fatty acids or alcohols. For example, glyceryl monostearate, triethyl citrate, and valeric acid can be used in this invention.

[0036] Compounds that increase hydrophobicity are typically applied in amounts of 0.1–5 wt.%, more specifically in amounts of 0.3–3 wt.%, calculated in terms of the amount of polymer.

[0037] Prior to 3D printing, the degree of polymerization of the polyester present in the composition is at most 0.6. If the degree of polymerization is higher than 0.6, the processability of the polyester may decrease, and in some embodiments, an unacceptably large amount of water may be required to maintain a sufficiently low viscosity of the composition for 3D printing. Excessive evaporation of water may reduce attractiveness as it can cause the composition to shrink. The degree of polymerization of the composition prior to 3D printing is preferably at most 0.5.

[0038] Prior to 3D printing, the degree of polymerization of the polyester is preferably at least 0.1, particularly at least 0.2, more particularly at least 0.25, and even more particularly at least 0.3. A higher degree of polymerization before printing ensures that less curing is required after printing. This results in a more efficient process. Furthermore, a higher degree of polymerization helps to limit excessive interaction between the polymer and the filler.

[0039] The polymer is formed by the combination of alcohol and acid to form a liquid phase. Depending on the nature of the compound, this can be done, for example, by heating the mixture of components to a temperature in which the acid dissolves in the alcohol, particularly glycerol. Depending on the nature of the compound, this may be, for example, at temperatures in the range of 20-250°C, such as 40-200°C, such as 60-200°C, or 90-200°C. In one embodiment, the mixture can be heated and mixed for 5 minutes to 2 hours, more specifically for a period of 10 minutes to 45 minutes, at temperatures of 100-200°C, particularly 100-150°C, and more particularly in the range of 100-140°C.

[0040] The composition prior to 3D printing typically contains at least 5 wt.% polyester. If less than 5 wt.% polyester is present, the formed object will not have the polyester content required to achieve the desired properties. The composition preferably contains at least 10 wt.% polyester, particularly at least 20 wt.%. The composition typically contains up to 85 wt.% polyester. If more than 85 wt.% polyester is present, there is insufficient space to accommodate the other components of the composition. The composition preferably contains up to 75 wt.% polyester, particularly up to 60 wt.% polyester, and in some embodiments, up to 50 wt.% polyester.

[0041] Fillers

[0042] This composition includes solid fillers. The presence of fillers is required to give the composition formability during printing and to prevent or limit foam formation. Solid fillers can also impart specific properties to the final product, such as a desired appearance and feel, or a particular texture. The presence of fillers can also increase the strength of the product. The density of the final product can be affected by selecting the density of the filler.

[0043] The composition prior to 3D printing typically contains at least 10 wt.% filler. If less than 10 wt.% filler is present, it is difficult to form a shaped object. The composition preferably contains at least 20 wt.% filler. The composition typically contains up to 85 wt.% filler. If more than 85 wt.% filler is present, there is insufficient space to accommodate the other components of the composition. The composition preferably contains up to 80 wt.% filler, particularly up to 70 wt.% filler, and in some embodiments, up to 60 wt.% filler, or even up to 50 wt.% filler.

[0044] The filler used in the compositions according to the invention can be any solid material in a form that allows it to be processed by the nozzle of a contemplated 3D printer. It will be apparent to those skilled in the art that the paste composition to be printed must be compatible with the nozzle of the 3D printer, and vice versa. Such compatibility is within the scope of those skilled in the art.

[0045] Typically, the filler is a granular material, but the use of yarn-type fibers can also be combined with 3D printing processes equipped for processing yarn-type fibers. Such printer nozzles are known in the art.

[0046] When using granular fillers, they typically have a maximum particle size ranging from 50 mm to 10 mm, determined along their longest axis, depending on the material type. In the context of this specification, the term "granular" does not impose any requirements on the shape of the material. Granular materials can be fibrous or non-fibrous. If the particles are non-fibrous, the filler typically has a maximum particle size ranging from 10 mm to 10 mm, determined along its longest axis, depending on the material type. A combination of larger and smaller particles is preferred.

[0047] In one embodiment, the average particle size (determined along its longest axis) used is at most 5 mm, particularly at most 2 mm. As a minimum, an average particle size of 0.001 mm may be mentioned.

[0048] In one embodiment, relatively small particles are used. In this case, the average particle size is preferably at most 0.5 mm. In some embodiments, the average particle size is at most 0.1 mm, or even at most 0.05 mm.

[0049] In another embodiment, larger particles are used. In this case, the average particle size is, for example, in the range of 0.5-5 mm, particularly 0.5-2 mm.

[0050] For objects with relatively smooth surface finishes, the filler portion preferably has a maximum particle size (Dv90) of up to 1 mm, particularly up to 0.5 mm. For objects with relatively rough surface finishes, the filler preferably contains a portion of particles, for example, 5 to 50 vol.% particles with a particle size of at least 1 mm.

[0051] In one embodiment, the filler comprises natural materials, such as materials derived from plants or animals.

[0052] Examples of plant-based materials include cellulose-based materials such as fresh or used paper, fresh or used cardboard, wood, or any other form of plant material, or combinations thereof. In one embodiment, a cellulose-based material derived from so-called virgin pulp obtained directly from a wood pulping process is used. This pulp can be derived from any plant material, but primarily from wood. Wood pulp comes from softwood trees such as spruce, pine, fir, larch, and hemlock, as well as hardwoods such as eucalyptus, poplar, aspen, and birch. In one embodiment, the cellulose-based material includes cellulose materials derived from recycled paper, such as cellulose pulp derived from recycled books, paper, newspapers and periodicals, egg cartons, and other recycled paper or cardboard products. A particular source is the use of waste paper fibers, which are too short for papermaking. Combinations of cellulose sources may also be used. Other examples of plant-derived materials include cotton, flax, hemp, grass, reeds, bamboo, coffee grounds, seed husks, and materials derived from rice, burlap, kenaf, ramie, sisal, etc. Generally, plant materials that have been crushed to the appropriate particle size and dried to the appropriate moisture content if necessary can be used.

[0053] Examples of animal-derived materials include feathers, down, hair and their derivatives, such as wool, but also bone meal.

[0054] It has been found that using cellulose-based materials, such as sawdust, wood pulp, and dust and pulp derived from other cellulose-based materials (such as hemp), can produce particularly attractive results.

[0055] Other examples of suitable fillers include ceramic materials, including oxides such as alumina, beryllium oxide, cerium dioxide, zirconium oxide, silicon dioxide, titanium dioxide, and mixtures and combinations thereof; and non-oxides such as carbides, borides, nitrides, silicides, and mixtures and combinations thereof, such as silicon carbide. For the purposes of this specification, glass is considered a ceramic material. For example, glass can be used in the form of short fibers, solid or hollow glass beads, and frosted glass particles. Suitable fillers also include materials such as mica fillers, calcium carbonate, and minerals such as layered silicates. Clay, sand, etc., may also be used.

[0056] Suitable fillers also include polymer fillers, such as polyethylene, polypropylene, polystyrene particles or short fibers, polyesters such as polyethylene terephthalate, polyvinyl chloride, polyamides (e.g., nylon 6, nylon 6.6, etc.), polyacrylamide, and aramid polymers such as aramid. Suitable fillers also include carbon fibers and carbon particulate materials. The pulverized and cured polyester resin used in this invention can also be used as a filler. Pulverized and cured polyester resins containing fillers can also be used. This allows the articles used to be recycled into new articles according to this invention.

[0057] Composite materials can also be used as fillers, for example, polymer particles with fillers.

[0058] Other suitable fillers include materials such as starch, which are soluble in polyester compositions at low concentrations. If this type of material is used, it should be used in an amount sufficient to ensure that the material is also present in solid form.

[0059] Combinations of different types and materials of fillers can also be used.

[0060] Diluents

[0061] The 3D printing-suitable compositions according to the invention contain a diluent. It has been found necessary to use a diluent to ensure that the composition has sufficient viscosity at all stages of its production process when supplied to the 3D printer. A diluent is particularly needed to ensure a workable viscosity during mixing, especially when a large amount of filler will be incorporated into the polyester.

[0062] A suitable diluent needs to meet several requirements: it is a low-viscosity liquid; it is non-reactive or minimally reactive with polyols and carboxylic acids; and it should be a good solvent for them. After 3D printing, it should easily evaporate from the composition. This last point is necessary to ensure that the printed product has sufficient stability to maintain its shape, even before the curing step.

[0063] While other liquids are possible, the use of water is considered preferred for technical, economic, and environmental reasons. Therefore, diluents typically contain at least 50 wt.% water, particularly at least 70 wt.%, more especially at least 90 wt.%, and even more especially at least 95 wt.%.

[0064] Compositions suitable for 3D printing typically contain at least 5 wt.% diluent. The aforementioned effects cannot be achieved with insufficient diluent. The amount of diluent is preferably at least 10 wt.%, particularly at least 15 wt.%, and even more particularly at least 20 wt.%. On the other hand, the amount of diluent should not be too high. It is typically at most 70 wt.%. At higher percentages, unless very high printing temperatures are used, the stability of the resulting object may be insufficient. It is preferable to use at most 60 wt.% diluent, particularly at most 50 wt.%.

[0065] Other components

[0066] The composition may include other components, such as stabilizers.

[0067] In one embodiment, the stabilizer is used to improve the composition’s properties and processability before printing by increasing the interaction between the diluent, filler, and polyester, thereby helping to provide a processable material without causing the diluent to separate from the other components.

[0068] In another embodiment, stabilizers are added to improve the properties and processability of the composition during and after printing but before curing. In this case, stabilizers are added to ensure that the printed composition has an appropriately high viscosity under printing conditions and that the printed object has sufficient rigidity after printing but before curing. Typically, these stabilizers increase the pseudoplasticity of the composition by binding water, polyester, and fillers, which allows for the addition of "overhangs," the extent to which a cantilever can extend to the bottom of the object. Suitable stabilizers include polymers such as starch, carboxymethyl cellulose, polyethylene glycol, hydroxyl or carboxypropyl cellulose, hydroxyl or carboxyethyl cellulose; and proteins. Suitable stabilizers also include inorganic salts such as calcium oxide, calcium hydroxide, and calcium carbonate. Inorganic salts are found attractive if a rapid curing of the composition is required. On the other hand, they can sometimes lead to increased brittleness in the final product, depending on its further composition.

[0069] The amount of stabilizer added will depend on the desired effect and the other components in the composition. Typically, stabilizers are added in amounts of 0.1–30 wt.%, calculated based on the weight of the starting composition before printing. Using too little stabilizer will not produce any effect. Using too much stabilizer may result in an unacceptably high viscosity of the composition, preventing the attainment of any further beneficial effects. Amounts of 0.1–25 wt.%, particularly 0.5–20 wt.%, and more particularly 1–15 wt.%, are generally preferred.

[0070] The composition may contain other components. Examples of other components that may be attractively added, as described above, include pigments, dyes, and pulverized recycled materials according to the invention. The addition of cured particles comprising polyesters derived from aliphatic polyols having 2-15 carbon atoms and aliphatic polycarboxylic acids having 3-15 carbon atoms, whether or not they contain fillers, may also be considered.

[0071] In one embodiment, a composition suitable for 3D printing is provided, comprising 20-50 wt.% of a polyester derived from glycerol and citric acid, with a degree of polymerization of 0.1-0.6, particularly 0.2-0.6. This can be combined with fillers, preferably in a total amount of 10-80 wt.%. For example, the filler can be selected from cellulose-containing materials, such as wood pulp, sawdust, or paper fibers. For example, the filler can be selected from glass spheres, particularly hollow glass spheres, to obtain low-density materials or cotton fibers. Combinations of various types of fillers can also be used. The use of cured polyester particles (optionally containing fillers) derived from aliphatic polyols having 2-15 carbon atoms and aliphatic polycarboxylic acids having 3-15 carbon atoms is also attractive. The composition preferably contains stabilizers, particularly starch, in an amount of, for example, 0.5-25 wt.%, particularly 1-20 wt.%; or calcium hydroxide, in an amount of, for example, 0.5-20 wt.%, or 1-15 wt.%, as these stabilizers have been found to provide good results.

[0072] Manufacture and use of the composition

[0073] The composition can be obtained by mixing various components. Generally, it is preferred to first prepare the polymer, optionally in the presence of water, by starting with a solution of the monomer, and then adding other components. Other components can be added in one or more steps at the same or different temperatures.

[0074] The present invention also relates to a method for preparing a shaped object, comprising the following steps:

[0075] - Provides a composition comprising the polyester, filler, and diluent as described above.

[0076] - The composition is extruded through the printer nozzle to form layers of the composition in the desired shape, and the layers are stacked on top of each other to form a shaped object.

[0077] - and during and / or after the extrusion step, subjecting the molded object to a curing step to form a cured molded object.

[0078] This method is also referred to as 3D printing in this paper.

[0079] The extrusion step includes the step of extruding the composition through a printer nozzle. The viscosity of the composition is adapted to the desired printer nozzle by means of a person skilled in the art, for example, by adjusting the temperature of the composition, or by selecting an appropriate amount of diluent, or in the presence of a stabilizer.

[0080] The lowest temperature is the melting point of the diluent because the diluent must be in the liquid phase in the composition.

[0081] Extrusion at high temperatures produces compositions with suitable viscosity. The extrusion step is preferably carried out at a high temperature, for example, at least 25°C, particularly at least 40°C, determined according to the composition prior to extrusion. The temperature is preferably below the boiling point of the diluent, as treatment above the boiling point of the diluent may lead to uncontrolled gas formation.

[0082] The temperature can be increased to the desired value by providing an airflow, especially hot air, or by using microwaves or infrared radiation, or other suitable heating means that are obvious to those skilled in the art.

[0083] Depending on the temperature during the extrusion step, polymer curing can occur during or after extrusion. However, it is generally preferred to perform a separate (additional) curing step.

[0084] If necessary, a drying step can be performed on the molded object before the curing step. The drying step is typically carried out at room temperature, such as 15°C or 20°C to 100°C, to remove the diluent from the molded object. Drying is preferably performed at relatively low temperatures, such as below 80°C or below 50°C, due to low energy consumption. Drying can be carried out, for example, from 0.1 hours to 3 days, or from 0.25 hours to 3 days, depending on the size and shape of the object, the amount of water present therein, and the amount of water in the molded object. Selecting suitable drying conditions is within the scope of those skilled in the art. The use of a vacuum can be considered to help increase water evaporation.

[0085] The curing step aims to further polymerize the polyester. A key aspect of the curing step is that the polyester is at the reaction temperature, for example, a product temperature of 80-250°C, particularly 100-200°C. Curing can be carried out using heating techniques known in the art, for example, in ovens with temperatures ranging from 80°C to up to 450°C. Different types of ovens can be used, including but not limited to belt ovens, convection ovens, microwave ovens, infrared ovens, hot air ovens, conventional ovens, and combinations thereof. Curing can be completed in one step or in multiple steps. Curing times range from 5 seconds to up to 24 hours, depending on the size and shape of the object, as well as the type and temperature of the oven used. Selecting suitable curing conditions is within the scope of those skilled in the art. Since longer curing times may be less attractive, curing times are preferably from 5 seconds to 12 hours, particularly from 5 seconds to 8 hours, more specifically from 5 seconds to 4 hours, or from 5 seconds to 2 hours. Especially for larger objects, it is preferable to apply a temperature gradient during curing, wherein the temperature at the beginning of the curing step is lower than the temperature at the end of the curing step. Applying a temperature gradient allows for control over the rate of moisture removal from the object, which helps prevent the formation of surface inhomogeneities. For larger objects, the aforementioned preliminary drying step is considered preferred.

[0086] After curing, the degree of polymerization, as determined by gravimetric analysis, is typically at least 0.5, particularly at least 0.6, more particularly at least 0.7, still more particularly at least 0.8, and in some embodiments at least 0.9. The theoretical maximum degree of polymerization is 1.0.

[0087] After curing, the moisture content of the cured molded object is typically less than 10 wt.%, particularly less than 5 wt.%, and even more particularly less than 2 wt.%.

[0088] The present invention also relates to a 3D printed object comprising a polyester, filler, and typically less than 10 wt.% water, wherein the polyester is derived from an aliphatic polyol containing 2-15 carbon atoms and an aliphatic polycarboxylic acid containing 3-15 carbon atoms, the polymer having a degree of polymerization which is the ratio of the maximum number of reacted functional groups to the maximum number of reactive functional groups, the degree of polymerization being at least 0.5, particularly at least 0.6.

[0089] The aforementioned preferred composition, water content, and degree of polymerization of the latter two types of cured objects also apply to this embodiment.

[0090] The cured object can be post-processed as known in the art, such as sanding, coating or polishing, painting or other surface treatments.

[0091] This invention is applicable to providing objects for many applications, including decorative objects, furniture, etc. A specific use is in the production of large prototypes. The use of 3D printing enables customized production at a lower cost than processing substrates and is less sensitive to deformation than thermoplastic materials used in 3D printing.

[0092] As will be apparent to those skilled in the art, preferred embodiments of various aspects of the invention can be combined unless they are mutually exclusive.

[0093] The present invention is illustrated by the following examples, but the present invention is not limited thereto.

[0094] Example 1: Preparation of a polyester polymer solution

[0095] 1.0 kg of glycerol (>99% purity) and 2.0 kg of citric acid (>99% purity) were placed in a stirred and heated reactor. 9 g of boric acid (0.5 mM, >99% purity) was also added. The mixture was heated to 135°C over approximately 15 minutes and maintained at that temperature for 15 minutes. It was then diluted with tap water to a water content of 60% and further cooled. The degree of polymerization of the resulting polymer was 0.4.

[0096] Example 2: Manufacture of shaped objects with wood flour and starch

[0097] A composition suitable for 3D printing was prepared as follows. 10 kg of the polyester polymer as described in Example 1 was heated to 90°C and combined with 0.75 kg of starch and 0.75 kg of sawdust, then stirred. The mixture was cooled to below 50°C, and an additional 1.5 kg of starch and 1.5 kg of sawdust were added, followed by mixing.

[0098] The resulting composition consisted of 28 wt.% polyester, 15 wt.% starch, 15 wt.% sawdust, and 42 wt.% water. The degree of polymerization of the polyester was maintained at 0.4.

[0099] This composition is used for printing shaped objects in a 3D printer. The composition is supplied to the nozzle of the 3D printer at a temperature of 50-60°C and extruded through an 8mm nozzle at a rate of 20mm / sec with a layer thickness of 3mm. After exiting the nozzle, the material is jetted with hot air (above 200°C). The hot air jetting aims to stimulate the binding properties of the starch.

[0100] Subsequently, the object is dried and cured in a hot air circulating oven at 200°C for 2 hours.

[0101] The cured object has a water content of less than 5 wt.%. The degree of polymerization of the object is greater than 0.8.

[0102] Figure 1 The image shows an object during printing. It can be seen that the present invention allows for the manufacture of objects of complex shapes in a controlled and reproducible manner, and that the objects are stable enough that the present invention can print objects with "protruding ends," i.e., where the sides of the object extend beyond the sides of the base.

[0103] Example 3: Manufacture of shaped objects with wood flour, starch and hollow glass beads

[0104] 15 g of starch was mixed with 300 g of the resin from Example 1 (containing 40 wt.% polymer and 60 wt.% water). The mixture was heated to 80°C and stirred until the starch dissolved. It was then cooled to below 50°C, and another 30 g of starch was added. 40 g of sawdust and 45 wt.% hollow glass beads were added, and then mixed. The resulting composition consisted of 28 wt.% polyester, 10 wt.% starch, 10 wt.% sawdust, 10 wt.% hollow glass beads, and 42 wt.% water.

[0105] The degree of polymerization of the polyester is 0.4.

[0106] As described in Example 2, the mixture was 3D printed, dried, and cured. The cured object had a moisture content of less than 5 wt.%. The degree of polymerization of the object was greater than 0.8.

[0107] Solidified objects such as Figure 2As shown, this invention allows for the fabrication of objects with complex shapes and sufficient stability, enabling the printing of objects with "protruding ends," where the sides of the object extend beyond the sides of the base. Using hollow glass beads allows for the formation of objects with low density, yet still possessing a natural look and feel, similar to that obtained from using wood chips.

[0108] Example 4: Manufacture of shaped objects with wood flour and calcium hydroxide

[0109] Mix 30 g of calcium hydroxide and 70 g of sawdust. While ensuring the temperature does not exceed 50°C, add the mixture in portions to 300 g of the resin from Example 1 (containing 40 wt.% polymer and 60 wt.% water). The resulting composition contains 30 wt.% resin, 7.5 wt.% calcium hydroxide, 17.5 wt.% sawdust, and 45 wt.% water. The degree of polymerization of the polyester is 0.4.

[0110] As described in Example 2, the mixture was 3D printed, dried, and cured. The cured object had a moisture content of less than 5 wt.%. The degree of polymerization of the object was greater than 0.8.

[0111] Solidified objects such as Figure 3 As shown in the figure, this composition allows for the printing of complex 3D shapes with high precision.

[0112] Example 5: Manufacture of shaped objects with starch and cotton fibers

[0113] 15 g of starch was mixed with 300 g of the resin from Example 1 (containing 40 wt.% polymer and 60 wt.% water). The mixture was heated to 80°C and stirred until the starch dissolved. It was then cooled to below 50°C, and another 30 g of starch was added. 75 g of cotton fiber and 10 g of aerosil (fumed silica) were added as a thickener, and then mixed. The resulting composition consisted of 28 wt.% polyester, 10 wt.% starch, 17 wt.% cotton fiber, 2 wt.% aerosol, and 42 wt.% water.

[0114] The degree of polymerization of the polyester is 0.4.

[0115] As described in Example 2, the mixture was 3D printed, dried, and cured. The cured object had a moisture content of less than 5 wt.%. The degree of polymerization of the object was greater than 0.8.

[0116] Solidified objects such as Figure 4 As shown in the figure, this composition containing longer fibers results in a rough surface on the object, demonstrating that the present invention can print complex 3D shapes.

[0117] Example 6: Manufacture of shaped objects with CMC and waste paper fibers

[0118] 300 g of the resin from Example 1 was heated to 80°C. 75 g of waste paper fiber and 9 g of carboxymethyl cellulose stabilizer were added, and then mixed. The resulting composition consisted of 31 wt.% polyester, 2 wt.% CMC, 20 wt.% waste paper fiber, and 47 wt.% water. The degree of polymerization of the polyester was 0.4.

[0119] As described in Example 2, the mixture was 3D printed, dried, and cured. The cured object had a moisture content of less than 5 wt.%. The degree of polymerization of the object was greater than 0.8.

[0120] Solidified objects such as Figure 5 As shown in the figure, this invention can transform waste paper fibers into products with attractive 3D shapes. Waste paper fibers are a waste stream in the paper recycling industry. They contain fibers that are too short to be recycled for new paper. In addition to fibers, this fraction also contains 10-30 wt.% calcium carbonate.

[0121] Example 7: Manufacture of large objects based on hemp particles

[0122] In a 25-liter planetary mixer, 5 kg of water was heated to 100°C. 0.75 kg of starch was mixed with 1 kg of hemp granules, and the mixture was added to the water. The hemp granules were a mixture of hemp fragments and fibrous material containing materials of varying particle sizes, with the largest particles being approximately 5 mm. Then, 5 kg of the resin prepared according to Example 1 was added. The mixture was stirred and allowed to cool to room temperature. 0.35 kg of hemp granules was mixed with 1 kg of calcium hydroxide. Half of this mixture was added to the resin composition, and the mixture was stirred for 1 hour. The other half of the hemp and calcium hydroxide mixture was then added, and the mixture was stirred again. The resulting composition consisted of 31 wt.% polyester, 10 wt.% hemp granules, 8 wt.% CaOH, 6 wt.% starch, and the balance being water. The degree of polymerization of the polyester was 0.4.

[0123] This composition is used to print shaped objects using a 3D printer. The composition is fed to the nozzle of the 3D printer at a temperature of 70°C and extruded through an 11mm nozzle at a rate of 20mm / sec with a layer thickness of 5mm. After exiting the nozzle, the material is jetted with hot air (above 200°C). The hot air jetting aims to stimulate water evaporation, resulting in increased stability of the object.

[0124] Subsequently, the shaped object is dried and cured in a hot air circulating oven at 160°C for 2 hours.

[0125] The solidified object has a water content of less than 5 wt.%. The degree of polymerization of the object is greater than 0.8.

[0126] Images of 3D printed objects, such as Figure 6 As shown. Images of the cured object are as follows. Figure 7 As shown (the pen in the image is used to indicate scale or size), the object is stable and self-supporting. The object has the following dimensions: height 35cm, width 43cm, and thickness 13cm.

Claims

1. A method for preparing a shaped object, comprising the following steps: - Provides a composition comprising: - A polyester, derived from aliphatic polyols having 2-15 carbon atoms and aliphatic polycarboxylic acids having 3-15 carbon atoms, said polyester having a degree of polymerization of up to 0.6, said degree of polymerization being the ratio of the reactive functional group portion to the maximum value of those reactive functional groups. - Solid filler, -Diluent; - The composition is extruded through a printer nozzle to form layers of the composition in the desired shape, with each layer stacked on top of the other to form a shaped object. - To subject the shaped object to a curing step to form a cured shaped object, wherein the curing step occurs during and / or after the extrusion step.

2. The method of claim 1, wherein a separate curing step is performed after the extrusion step.

3. The method according to claim 1, wherein curing is carried out at a temperature of 80-250°C.

4. The method according to claim 3, wherein curing is carried out at a temperature of 100-200°C.

5. The method of claim 1, wherein the cured molded object has a degree of polymerization and / or water content determined by gravimetric analysis, the degree of polymerization being at least 0.5; and the water content being less than 10 wt.%.

6. The method of claim 1, wherein the degree of polymerization of the polyester is at least 0.1 prior to 3D printing.

7. The method according to claim 1, wherein the composition contains 0.1-30 wt% of a stabilizer.

8. The method of claim 7, wherein the stabilizer is selected from polymers and inorganic salts.

9. The method of claim 1, wherein the polycarboxylic acid comprises at least 10 wt.% of tricarboxylic acids, calculated based on the total amount of the polycarboxylic acid.

10. The method of claim 9, wherein the polycarboxylic acid comprises at least 50 wt% of a tricarboxylic acid.

11. The method according to claim 9, wherein the tricarboxylic acid is citric acid.

12. The method of claim 1, wherein the polyol comprises at least 50 mol% glycerol.

13. The method of claim 1, wherein the composition contains 20-50 wt.% polyester.

14. The method of claim 1, wherein the composition comprises 10-85 wt.% filler in total.

15. The method of claim 1, wherein the filler is selected from one or more of the following: cellulose-containing materials; glass spheres; optionally, cured polyester particles containing filler; the cured polyester being derived from aliphatic polyols having 2-15 carbon atoms and aliphatic polycarboxylic acids having 3-15 carbon atoms.

16. The method of claim 1, wherein the composition contains 20-70 wt.% of a diluent.

17. The method of claim 16, wherein the diluent is water.

18. A 3D printed object obtained by the method of any one of claims 1-17, comprising a polyester and a filler, said polyester being derived from an aliphatic polyol having 2-15 carbon atoms and an aliphatic polycarboxylic acid having 3-15 carbon atoms, said polyester having a degree of polymerization of at least 0.5, said degree of polymerization being the ratio of the reactive functional group portion to the maximum value of those reactive functional groups, and said 3D printed object having a water content of less than 10 wt.%.

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