A method for printing a fluid material using a continuous jet printing technique and curable composition for use in said method

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DESCRIPTION

Method for printing a fluid material using a continuous jet printing technique and curable composition for use in said method.

The present invention relates to a curable composition, a method for printing a flowable material using a continuous jet printing technique, and a cured article comprising said curable composition.

Radiation curing technology has been used in the graphic arts industry for more than 20 years. A key factor in the adoption of this technology for environmental and safety reasons is the reduction of volatile organic compounds, a result of the elimination of solvents. UV technology has been limited to specific ink jet printing methods, methods that require either high printing temperatures or very low viscosity at room temperature. These methods can be used to form articles, such as an RP product, RM product, or LMT product. The UV inks used in them employ a carrier solvent. These solvents are used to control the viscosity of the ink and to promote adhesion to a substrate. Furthermore, it has been observed that curable compositions should usually contain as little solvent as possible in order to obtain the favorable physical and chemical properties of the cured composition. Furthermore, the curable compositions should preferably contain no salt or a minimal amount thereof, as salt is considered to be detrimental to the favorable physical and chemical properties of the cured composition.

Inkjet printers can be divided into "Drop-on-demand" (DOD) and Continous Inkjet (CIJ) systems. In DOD systems, each drop is generated on demand as soon as the nozzle is placed on top of the substrate. On the other hand, in CIJ systems a flow of ink droplets is generated at high and constant pressure. The ink droplets are charged and can be selectively deflected to obtain a desired droplet distribution across the substrate. Subsequently, the diverted droplets can be recycled. To be charged, the ink must be electrically conductive.

As noted above, when used in a "drop on demand" (DOD) or continuous ink jet (CIJ) ink jet printer, a composition (UV curable) must have a sufficiently low viscosity. For most ink compositions, the applied viscosity is approximately 100 mPas at room temperature, although more typically the application viscosity at print temperature is less than 70 mPas in the case of CIJ technology and less than 20 mPas in the case of DOD technology. It will be understood that the viscosity of a composition can be influenced by the ink jet recording temperature.

The more conventional film-forming compositions for other applications, such as coatings, however, have a significantly higher viscosity, which makes them unsuitable for ink jet printing processes.

Oxygen inhibition is another factor that affects the performance of UV-curable materials. Fast cure speeds are required to ensure good print quality and production efficiency. As a result, highly functional materials are necessary. However, these materials should not show high film shrinkage, which would adversely affect ink and ink adhesion. Therefore, these materials are preferably applied at or near cure temperature. In this sense, DOD technology is less favorable, since this technology needs to use unfavorably high printing temperatures. Alternatively, DOD technology needs to use very low viscosity formulations at room temperature leading to very dense networks, resulting in brittle materials and therefore unsuitable for 3D modeling.

In conventional UV inks an epoxy, urethane or modified polyester acrylate is typically used as the backbone of the ink composition. However, the specific chemistry of epoxy is affected by high molecular weights and viscosities, high film shrinkage, and limited pigmentation ability. Therefore, epoxy-based compositions are not suitable for ink jet applications, since for these applications they have to contain large amounts of solvents. Also, for typical cationic ring-opening polymerization (epoxides and oxetanes), the shrinkage can be very low, much lower than for acrylates and therefore can be very interesting for 3D, RP and MR. The disadvantages of these systems are, however, that the polymerization in the latter cases is relatively slow and is inhibited by proton acceptors (such as water).

The use of conventional polyester urethanes and acrylates have better overall physical properties, but their viscosities are still very high, which makes them not particularly suitable for ink jet applications.

In addition, it is observed that the conventional reactive monomers and oligomers that are usually used in UV systems are not soluble in water, while the traditional photoinitiators have little compatibility with water, since they do not disperse well in water due, for example, to its polar nature.

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In an article by J. Klang and J. Balcerski of Sartomer, PA, USA (2004), UV curable compositions are described, which contain a monomer, an oligomer, photoinitiators, pigments and additives. These compositions are preferably solvent-free to reduce or minimize the amount of volatile organic compounds that are released upon curing of the article obtained. Furthermore, these compositions have a low viscosity to allow their application in ink jet systems. Solvent-free compositions can be used in particular cases for DOD systems, although still relatively high application temperatures are required to lower the viscosity of the composition.

It is noted, however, that these solvent-free compositions cannot be used in continuous ink jet printing, since these compositions are not sufficiently conductive or non-conductive at all.

A further disadvantage is that these compositions, when used in drop-on-demand ink jet systems, must be heated to about 80 ° C in order to give these compositions the necessary viscosity. However, a high temperature is generally detrimental to these compositions, due not only to stability, but also at these temperatures the homogeneity of these compositions deteriorates.

Furthermore, processing of compositions at higher temperatures causes the compositions to thermally compress when deposited, which is unfavorable and therefore undesirable. Furthermore, a lot of energy is consumed in order to heat the composition, which is a further disadvantage.

US Patent No. 4,990,360 discloses electrically conductive compositions containing organosiloxane / oxyalkylene copolymers with acrylate functionalities and a solubilized lithium salt. However, the use of these compositions is limited to gel formation after curing. Therefore, it is not possible to form solid articles with these compositions. Furthermore, the compositions mentioned in this document are solvent-based, which is undesirable, for example, from an environmental point of view. Another disadvantage is that these compositions have only a limited range of viscosities. Furthermore, the materials described in this patent are polymeric and would have viscosities that would be too high for solvent-free ink jet printing.

The object of the present invention is to provide a curable composition for use in a continuous ink jet printing method, which has a higher conductivity and a relatively high viscosity, the composition of which comprises only a limited amount of solvent and, preferably minimal or no solvent at all.

Surprisingly, it has been found that the above objective can be achieved by using a flowable material comprising a liquid component with a high dielectric constant, a lipophilic salt and a liquid component with a particular viscosity.

Accordingly, a first aspect of the present invention is to provide a method for printing a fluid material using a continuous jet printing technique, in which fluid material is passed under pressure from a reservoir through a channel to at least one channel outlet opening, after which the flowable material is passed through the outlet opening, where the pressure is at least a part of the channel upstream of the outlet opening is in the range of 15-600 bar [ξ15 · 10⁵ to 600 10⁵ Pa], the flowable material of which comprises a curable composition comprising

In all curable compositions to be used according to the present invention, the weight% given refers to the weight percent of the respective compounds or components based on the total weight of the curable composition.

Preferably, according to the present invention, the fluid material as it flows out through the outlet opening has a viscosity that is in the range of 150 to 400 mPas.

In the curable composition to be used according to the present invention, crosslinked and / or polymeric structures are formed upon curing. Liquid component B, responsible for the formation of cross-linked and / or polymeric-like structures, can comprise various classes of polymer-forming compounds, such as radiation-curable monomers / oligomers, heat-curable monomers / oligomers or even more broadly and simpler, monomers / oligomers that ultimately form cross-linked or polymeric-like structures, that is, that cure themselves.

If radiation is used to cure the curable composition, ultraviolet radiation can be conveniently used, but the use of other forms of radiation is also envisaged.

The curable composition to be used according to the present invention comprises a component A having a particular dielectric constant, which further allows the droplets to be used to obtain the charge required in continuous ink jet printing. The use of component A is very advantageous, since it allows a better distribution of the drops on the substrate. However, conventionally applied solvent-free curable compositions have very low electrical conductivity, rendering them unsuitable for use in continuous ink jet printing.

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Liquid component A is present in an amount of 1-15% by weight, preferably in an amount of 110% by weight, based on the total composition. Component A is preferably used in an amount less than 10% by weight, because larger amounts can be detrimental to specific mechanical properties and should therefore be avoided, unless gel-type systems are desired. According to the present invention, component A is most preferably present in an amount in the range of 3% by weight - 10% by weight, based on the total composition. If the amount of the liquid component A is too low, the drops may be insufficiently charged, while if the amount is too high the physical properties of the article to be shaped will be unsatisfactory.

It is believed, without wishing to be bound by any particular theory, that component A, among other factors, acts as a means of improving electrical conductivity. Furthermore, the high dielectric constant compound is believed to contribute to the solubility of the lipophilic salt.

In a preferred embodiment of the present invention, liquid component A has a dielectric constant in the range 15-89.7 (determined at 0 ° C). More preferably, the dielectric constant of the liquid component A is in the range of 30-89.7, even more preferred in the range of 50-89.7. It should be noted, however, that liquid components A having dielectric constants exceeding 89.7 could also be used. In general, dielectric constant values ​​can be found in manuals, such as the CRC Manual of Chemistry and Physics.

If the dielectric constant of component A is too low, the effect of improving electrical conductivity is either too low or it is necessary to use too high an amount of component A to obtain this effect. At the higher end, there appears to be no limitation on the dielectric constant value.

Liquid component A with a high dielectric constant is selected from the group consisting of acetamide, acetone, acetonitrile, amyl alcohol, antimony trichloride, 1-butanol, citraconic anhydride, cyanoacetic acid, deuterium oxide, DMSO, ethanol, ethylene cyanide, acid formic, formamide, furfural, glycerin, glycerol, glycol, hydrazine, hydrocyanic acid, hydrogencyanide, HFI, hydrogen peroxide, hydrofluoric acid, hadrocin, iodine, lactonitrile, lead nitrate, maleic anhydride, malonic anhydride, malonitrile, MEK, methanol, methyl pyrrolidones, methylthiocyanate, nitrobenzaldoxime, N, N-dimethylformamide (DMF), nitromethane, nitrosodimethylamine, p-nitro-aniline, plastic grains, 1-propanol, sulfuric acid , thallium chloride, titanium dioxide, titanium oxide, trimethylsulfanilic acid, and water, and mixtures thereof. Preferably, liquid component A is selected from the group comprising acetone, acetonitrile, 1-butanol, DMSO, ethanol, formamide, formic acid, methanol, MEK, N, N-dimethylformamide (DMF), methylpyrrolidone, 1-propanol, and water, and mixtures thereof.

Water is a compound that is preferably used, more preferably deionized water is used. If water is used in the curable composition, it will contribute to conductivity. It should be noted that water is added due to its high dielectric constant and its impact on the conductivity of the composition.

In this way, the present invention allows the use of a relatively small percentage of the liquid component A. In combination with a lipophilic salt, it is now possible to obtain the level of conductivity that is required for the deviation of the drops in a system by jets of continuous ink.

It should be noted that the liquid component A is preferably removed before or during curing, since it is potentially detrimental to the physical and chemical properties of the article to be formed.

On the other hand, if a conductive material is required, a technology that introduces conductivity after curing can also be used. For example, strong lasers can sinter (melt) metal particles into conductive bands. These particles can be premixed with the curable liquid composition.

The composition according to the present invention further comprises a lipophilic salt.

The lipophilic salt is present in an amount in the range of 1 to 15% by weight, based on the total composition. The amount of salt depends on the desired application. Preferably, an amount in the range of 1 to 12% by weight is used, more preferably in the range of 1 to 10% by weight, and even more preferably in the range of 5 to 10% by weight, for the development of prototypes. 3D. If the amount of lipophilic salt is too high, the mechanical properties of the final product, such as hardness and impact resistance, may deteriorate.

The lipophilic salt is selected from the group consisting of lithium salts, tetraalkyl ammonium salts, alkyl sulfonates, derivatives of alkyl sulfonates, alkyl sulfates, derivatives of alkyl sulfates, alkyl benzyl sulfonates, derivatives of alkyl benzyl sulfonates, alkyl benzyl sulfates, derivatives of alkyl benzyl sulfates, salts of tetrabenzyl ammonium, derivatives of salts of tetrabenzyl ammonium, salts of trialkyl monobenzyl ammonium, derivatives of salts of trialkyl monobenzyl ammonium, dibenzyl dialkyl ammonium salts, derivatives of dialkyl dibenzyl ammonium salts, monoalkyl tribenzyl ammonium salts, derivatives of monoalkyl tribenzyl ammonium salts, salts of cholic acid, derivatives of salts of cholic acid, derivatives of salts of cholic acid, derivatives of salts of cholic acid derivatives, digitonins, digitonin derivatives, docusates, docusate derivatives, sarcosine, sarcosine derivatives, benzalkonium salts, benzalkonium salts derivatives, tonzonium salts, Derivatives of tonzonium salts, fatty acid salts and derivatives of fatty acid salts. Preferred lipophilic salts are the lithium salts and tetraalkyl ammonium salts and the most preferred are the lithium salts.

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Preferably, the lithium salts are selected from the group comprising LiClO₄, LiCF₃SW₃ (LiTf), Lil, LiPF₆, LiBr and LiBF₄, even more preferably the salt is selected from LiClO₄ and LiTf.

The curable composition to be used according to the present invention suitably has a conductivity (20 ° C) of 50-5000 pS / cm, preferably 100-1000 pS / cm and more preferably 200-500 pS / cm.

Of course, the conductivity of the curable composition can be varied by adding more or less salt and / or water. Alternatively, particular monomers / oligomers can be selected, since the conductivity also depends on the viscosity of the curable composition.

Conductivity is measured with a 4-point Jandel probe, equipped with an Ecolab galvanostat, which provides a 4-point measurement.

The curable composition to be used in the present method may further include one or more general purpose coating additives. Conveniently, the amount used is at most 10% by weight, preferably in the range of 1-5% by weight. The present composition may contain practically no additive or no other additive at all, if the amount of salt itself is high enough to achieve the necessary conductivity.

Coating additives can be selected from the group of pigments, dyes, colorants, flow promoters, antioxidants, filters, fillers, stabilizers, metal particles, compatibilizers, metal deactivators, metal oxides, blowing agents, waxes, processing aids, agents. humectants, and adhesion promoters.

Any compound known from the group of pigments, dyes, colorants, flow promoters, antioxidants, filters, fillers, stabilizers, metal particles, compatibilizers, deactivating metals, metal oxides, blowing agents, waxes, processing aids, agents. humectants, and adhesion promoters, which can generally be added to a curable composition in an amount sufficient to obtain the desired effect or to fulfill the desired function for this compound.

Typical examples of fillers are silica, TiO₂, CaCO₃, Mg (OH)₂, Mg₂Or, carbon black, etc.

In addition, blowing agents may be present in the curable compositions to be used in the present method. The presence of these blowing agents allows the formation of a polymer foam, when the composition is extruded. Examples of such blowing agents are volatile hydrocarbons, hydro fluorocarbons, and the chlorofluorocarbons.

It may be beneficial or desirable to add compounds such as colorants and adhesion promoters (for example, if one wants to improve layer-by-layer adhesion in a 3D jet printed RP or RM article).

The curable composition to be used in the present method comprises a liquid component B. The viscosity of the liquid component B used in ink jet printing temperature should be sufficiently low, that is, in the range of 50 to 2000 mPas. Viscosity is measured using a Physica UDS200 Rotation Rheometer, either using a cone-plate geometry (cone diameter: 5 cm, cone angle = 1 °) or a bowl-spindle geometry. Alternatively, the viscosity was measured using an Anton-Paar AMVn Microviscometer, based on the drop ball method. In the context of the present invention, the ink jet recording temperature resembles the conventional ink jet temperature, which is normally in the range of 20 ° C to 80 ° C.

The liquid component B has a viscosity at the ink jet recording temperature in the range of 50-2000 mPas. Preferably, the viscosity at the ink jet recording temperature is in the range of 50 to 1000 mPas, more preferably in the range of 50 to 500 mPas, even more preferably in the range of 50 to 200 mPas.

The liquid composition B that is used has a "low shear viscosity" (22 ° C) in the range of 50-1500 mPas, preferably 50-1000 mPas, more preferably 50-500 mPas and most preferably 50- 100 mPas. Low shear viscosity is measured by a Physica UDS200 Rotation Rheometer, either using a cone-plate geometry (cone diameter: 5 cm, cone angle = 1 °) or a bowl-spindle geometry. Alternatively, the viscosity was measured using an Anton-Paar AMVn Microviscometer, based on the drop ball method.

If a liquid exhibits Newtonian behavior, the low shear viscosity is the same as the viscosity, since the viscosity is not dependent on the shear rate.

Conveniently, the liquid component B is present in an amount in the range of 30 to 90% by weight, preferably 70 to 90% by weight, based on the total composition.

Since most of the curable composition generally comprises liquid component B, the curable composition conveniently has a viscosity at ink jet recording temperature in the range of 50-2000 mPas. Preferably, the viscosity at the ink jet recording temperature is in the range

ES 2 334 824 T3 from 50 to 1000 mPas, more preferably in the range of 50 to 500 mPas, even more preferably in the range of 50 to 200 mPas.

The curable composition to be used according to the present invention has a "low shear viscosity" (22 ° C) in the range of 50-1500 mPas, preferably 50-1000 mPas, more preferably 50-500 mPas and so on. more preferably 50-100 mPas.

Liquid component B may conveniently include one or more types of curable monomers that provide low viscosity, increase cure speed, and improve adhesion. The curable monomer or mixture of curable monomers is believed to act as a reactive diluent, as a polymer forming and / or crosslinking agent, as well as a performance property enhancer. Typically, the curable monomers will have a molecular weight that is less than that of the curable oligomers. The functionality of the curable monomers can vary. Conveniently, mono, di and trifunctional monomers are used, but monomers with higher functionalities can also be applied.

Conveniently, the curable monomer, or a mixture comprising the curable monomers, is present in an amount ranging from 0 to 100% by weight; preferably 30 to 90% by weight, more preferably 70 to 90% by weight, based on the total amount of liquid component B.

A wide variety of curable monomers can be used in accordance with the present invention, thereby allowing formulators to achieve the proper performance properties for the desired application, these performance properties include, for example, density and amount of crosslinking. I polymer formation on curing, resulting in more or less hardness, etc.

Conveniently, the viscosities of the individual curable monomers can range from 4-250000 mPas at the ink jet recording temperature, preferably they range from 50-100000 mPas, more preferably they range from 100-10000 mPas. In cases where a monomer with a very high viscosity is used, for example 200000 mPas, the viscosity of the liquid component B is lowered by adding at least one monomer with a low viscosity, in order to form a mixture having a suitable viscosity at the printing temperature.

The curable monomer is selected from the group consisting of methacrylates, acrylates, epoxies, oxetanes, epoxy / acid combinations (eg those that cure with IR radiation), epoxy / amine combinations (eg those that cure with IR radiation) , vinyl derivatives, maleimides and allyl derivatives. The preferred curable monomers are acrylates and / or methacrylates.

Preferably, the curable methacrylate and / or acrylate monomer is selected from the group comprising BisGMA, HEMA, TEGDMA, SR344 (Cray Valley), ethylene glycol-based acrylates, in which the ethylene glycol-based chains have different lengths, DPGDA, TPGDA, TIEGDA, PONPGDA, TCDDMDA, oligo (ether) acrylates, poly (ether) acrylates, urethane acrylates, epoxy acrylates, amino acrylates, and poly (ether) acrylates with any degree of functionality. The active component in SR344 is a functionalized oligo (ethylene glycol) diacrylate.

The curable oligomer of liquid component B is generally used in smaller amounts than the monomers to provide the desired film-forming properties and sufficient pigment dispersion. In contrast, some oligomers, such as polyester acrylates, already have a low viscosity. In the latter case, only a little or no monomer is necessary for the reduction of the viscosity. It is further noted that the film-forming properties depend on the interaction between the ink and the substrate, including wetting properties. It is further noted that the oligomers have film-forming properties similar to the monomers. The same holds for pigment dispersions. For example, the use of specific oligomers can lower the network density to obtain harder (less brittle) materials. The use of specific oligomers can further reduce polymerization shrinkage. The reduction in polymerization shrinkage is believed to be a natural consequence of a more open network structure (fewer crosslinks per unit volume).

Conveniently, the curable oligomer is present in an amount in the range of 0 to 100% by weight, preferably 30 to 90% by weight, more preferably 70 to 90% by weight, based on the total amount of liquid component B .

Conveniently, the curable oligomers used have a molecular weight (Mw) in the range of 400-30000. This is believed to determine the predominant physical properties of the finished article, such as density and hardness. As mentioned above, oligomers, compared to monomers, reduce the crosslink density of the network, which generally leads to a reduction in hardness and an increase in strength. A wide variety of curable oligomers can be used in accordance with the present invention, thus allowing formulators to obtain the performance properties for the desired application. These properties include the density and amount of crosslinking after curing. The curable oligomers are selected from acrylated urethanes, epoxies, epoxides, epoxy acrylates, oxetanes, phenolics, carbonates, ethers, polyester and / or acrylics, with any degree of functionality. Liquid component B may include one or more types of curable oligomers.

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Liquid component B may comprise one or more types of so-called dual cure monomers and oligomers. These dual cure monomers and oligomers, for example, combine acrylate and epoxide or oxetane functionalities in one molecule.

It should be understood that the curable monomer (s) and / or the curable oligomer (s), which form a polymer, must be present in an amount to achieve sufficient crosslinking and / or polymer formation upon curing. The amount of crosslinking and / or polymer formation can vary from application to application. The curable monomer and / or the curable oligomer can be exchanged relatively easily, for example, with respect to crosslinking ability, viscosity and amounts.

The curable composition to be used in the present method has the advantages that it can be used at a relatively low temperature, such as room temperature, and that it has better conductivity. Another advantage is that the curable compositions according to the present invention are very environmentally friendly, since the amount of solvent used can be very low or practically zero. Furthermore, such a composition can be cured more easily.

Another advantage of the curable composition to be used is that it comprises a broad spectrum of available curable monomers and oligomers, which can be used, for example, in ink jet printers at a lower temperature, such as room temperature.

Furthermore, the curable composition to be used can be cured, either while depositing and / or after depositing such a composition, or both.

The curable composition to be used in the present method can be deposited dropwise, preferably by ink jet printing technology, forming a 2D and / or 3D article. Such an article may comprise more than one curable composition, thereby allowing the incorporation of various desirable chemical and physical properties into the article. Therefore, it is possible that part of such an article according to the present invention can be conductive, non-conductive and semiconductive.

When it is desired that an open network be formed in the article, preferably a large amount of oligomer (s) is used, whereas when a more closed network is required, a greater amount of monomer (s) is preferably used. In the latter case, the monomer (s) may have high functionality.

A system is also envisioned in which separate fractions form the curable composition that is used in the present method during the ink jet printing process. The fractions can be present in different containers, which fractions can be deposited or printed, for example, by means of a multi-nozzle device (for example, an epoxy-amine composition). Preferably, however, the composition is homogeneous before curing. Therefore, the composition is preferably mixed before printing.

The curable composition to be used in the present method may further include a compatibilizer. By the term "compatibilizer" is meant a compound that compatibilizes a component of the curable composition with another component, such as the lipophilic salt present in the composition and the monomer and / or oligomer of component B.

It should be noted that in some cases the components will be compatible by their nature and / or one of the components may also act as a compatibilizer, for example SR 344.

Conveniently, such a compatibilizer is present in an amount of 0.2-10% by weight, preferably in an amount of 1-5% by weight, based on the total composition.

A compatibilizer may also be necessary in order to accommodate component A, for example water. The choice of a compatibilizer will depend on the other components present, components that may inherently by their nature have a compatibilizing effect with component A or, conversely, an incompatibilizing effect. It is further observed that when water is added, in some cases, a compatibilizer, such as HEMA, may be necessary, while in other cases with the presence of reasonable amounts (more than 20%) of (other) water-soluble compounds , such as acrylates, such as oligo or polyethylene oxide based ether acrylates, such as, for example, SR344, no compatibilizer will be necessary. The person skilled in the art will know how to select this compatibilizer, when necessary and in what quantity.

In another embodiment, the curable composition to be used in the present method may further comprise an activator, preferably in an amount in the range of 0 to 10% by weight, based on the total composition. Depending on the type of monomers or oligomers used, it may be necessary for an activator to be present to cure the system, which activator can be a photoinitiator.

For UV and electron beam (“E-beam”) curing, an activator (or initiator) must be present. This activator is preferably present in an amount in the range of 0.01 to 5%, based on the total composition.

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Also, in cases where acrylate mixtures are cured with thermal energy, a thermal initiator must be present.

No initiator is required for γ-ray curing of acrylate mixtures. Also, no initiator is necessary to cure epoxy / acid or epoxy / amine systems.

Suitable initiators for, for example, acrylic systems include benzophenone, dimethyl benzyl acetal, and 2-hydroxy (2) methyl-1-phenyl-1-propanone, as well as commercial photoinitiators supplied by Ciba Geigy, such as Irgacure® 184 , 819, 500, 784 and 2959.

Suitable initiators for cationic systems (epoxides and oxetanes) include salts of SbF₆^-, PF6^- and BF4 ^- of arylsulfonium and arilyodonium cations. Commercially available examples sold by Dow are Cyracure® UVI 6974 and UVI 6990.

The present invention further relates to a method for preparing a 2D or 3D article, in which the article is prepared by deposition of drops of the flowable material on a substrate and in which the drops are allowed to cure when deposited on the substrate. .

Another aspect of the present invention relates to the curable composition to be used in the method according to the present invention. Therefore, the present invention further provides any of the curable compositions as defined above.

Conveniently, the 2D article prepared in this way is an article with a small dimension, such as a line, whereas by 3D article is meant any article that is designed with a specific length, thickness and height. The 2D and 3D articles can be articles that comprise one or more distinguishable parts, which parts are themselves also 2D or 3D articles, such as individual conductive strips.

Preferably, the article comprises an RP product, an RM product, an LMT product, a coating, an ionic polymeric medium, a tag, a battery, or a code.

Items such as surface prints, electronic circuits, photographs, batteries, barcodes, coding of bottles, cans, boxes, etc. are also envisaged.

The present invention further relates to an article comprising the curable composition as defined above. Preferably this article is cured.

Another class of attractive articles that can be made by the method according to the present invention are biocompatible bone implants. These implants can advantageously be manufactured at room temperature rather than at elevated temperatures, which is crucial for bio-applications, since proteins are destroyed at elevated temperatures.

The present invention also relates to the use of an article according to the present invention.

Typically, the article according to the present invention is placed on a substrate. Therefore, the present invention provides an article that is placed on a substrate. The article may have a part that has been selected from the group of conductive subparts, non-conductive parts, and semiconductor subparts.

In such an article, the conductivity of a specific part can be adjusted as desired and sub-parts with various conductivities can be formed as desired. Some parts can be, for example, conductive, while other parts can be non-conductive, insulating or semi-conductive. Conveniently, the resistivity of a conductive part is less than 10^-5 Ω / m, while for a non-conductive part it is conveniently greater than 1 Ω / m and for a semiconductor part it is conveniently in the range of 10 ⁵ - 1 Ω / m. Therefore, the person skilled in the art can form relatively complicated (micro) structures, such as conductive wires connecting electrical components, supports, such as for mobile phones, heat-dissipating structures, etc.

Preferably, in the method according to the present invention an apparatus is used that comprises a tank for storing the fluid material, a channel connected to the tank, which is provided with at least one outlet opening from which, during use, flows a jet of liquid material that breaks up into drops and a pressure regulation mechanism to vary the pressure of the fluid material upstream of the outlet opening in order to obtain the jet that breaks up into drops, the apparatus being also equipped pressure generating means for passing the fluid material at a predetermined pressure through the channel in the direction of the outlet opening, whereby the pressure generating means is positioned to apply the predetermined pressure to the fluid material in the channel hydraulically and / or pneumatically.

Hydraulically, it is understood to mean: by means of a liquid; and it is understood that pneumatically means: with a gas. By the ability to apply the defined pressure to the fluid material in the channel using a gas or a liquid, a fluid material can be passed through the channel in the direction of the outlet opening in a stable manner at a very high pressure, much higher than 8 bars.

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The uniformity of the drops in the disintegration of the jet into drops, also at high working pressures, depends only on the pressure regulating mechanism instead of depending on both the variation in the working pressure and the variation resulting from the regulation mechanism of the Pressure.

This apparatus enables new applications such as rapid prototyping development.

Preferably, in an apparatus of this type the pressure generation means comprise a gas source coupled to the tank and / or channel through a gas connection. With the gas source, the viscous fluid in the channel can be adjusted to both a high and at the same time constant pressure of, for example 200 bar [ξ200-10⁵ Pa]. It is important that the pressure is as constant as possible, since in case of irregular pressure fluctuations, the viscous fluid cannot be passed through the channel and through the outlet opening in a sufficiently gradual manner. These irregular pressure fluctuations mean that the quality of the printed result is poor.

By virtue of the elevated pressure, it is possible to print the fluid materials described above when they are being processed. An embodiment of said apparatus is characterized in that the gas source comprises a gas bottle.

In a preferred embodiment, the apparatus is further provided with a plunger pump connected to the gas bottle through a gas connection with a stopcock, to pressurize the gas bottle and the gas bottle is connected through a stopcock with the tank and the channel. The gas bottle works here as an intermediate storage. The gas bottle serves to generate the mentioned pressure in the channel, while the flow rate of the gas stream flowing from the gas bottle can be relatively low. This means, among other things, that the gas bottle can be made of a relatively small design. After the pressure in the gas bottle has dropped during use, the gas bottle can be adjusted back to a desired pressure with the help of the plunger pump. To do this, the stopcock in the connection between the piston pump and the gas bottle is opened, while the connection between the gas bottle and the channel / tank can be closed. Since the gas bottle can be relatively small, it is possible to carry out a practical compact embodiment of the apparatus.

In a preferred embodiment, the apparatus is characterized in that the gas source comprises a second gas bottle coupled to the tank and / or the channel through a gas connection with a stopcock. The second gas bottle can be coupled to the plunger pump or to a second plunger pump. According to this embodiment, one of the gas bottles can be used to adjust the channel to a necessary pressure and keep the channel there, while the other gas bottle, adjusted to a desired pressure, prepares to take over this task. . In this way, the apparatus can operate without interruption. Optionally, the stopcocks can be controlled by an automatic control system.

In particular, the predetermined pressure is a pressure between 15 and 600 bar.

In a particularly attractive embodiment the apparatus is characterized in that the pressure regulating mechanism comprises a movable control needle, which control needle can be moved in a longitudinal direction towards / from the outlet opening, so that one end of the needle Control valve can be placed at a predetermined distance, for example in the distance range of 15-500 pm, from the outlet opening, to vary the pressure adjacent the outlet opening. In operation, the control needle vibrates with the desired droplet frequency to vary the pressure adjacent to the outlet opening. The control needle is, for example, in the channel, the longitudinal direction being directed preferably substantially perpendicular to the plane of the outlet opening. Because the distances in the distance range are relatively small, a relatively large pressure regulation range is carried out. In this way, at a relatively high pressure in the channel, a sufficiently large pressure regulation range (about 10% of the pressure in the channel) can also be achieved. Control of the control needle in the distance interval is preferably carried out with a relatively precise pressure regulating mechanism, in view of the relatively small distances. The exact distance range in which the control needle is operatively regulated depends on the viscosity of the liquid material.

In the printing of flowable materials, which have a particularly high viscosity, the work is carried out at a relatively high average pressure in the channel and, therefore, a relatively large regulating range is required. To achieve this, the distance from the end to the outlet opening must be relatively small to achieve the aforementioned relatively large pressure regulation range. In known systems operating with pressures up to 5 bar [ξ5-10⁵ Pa], this distance is, for example, in the order of 1.5 mm. Therefore, for the pressure regulating mechanism according to the present invention, this distance is preferably considerably smaller.

The pressure regulating mechanism may comprise piezoelectric element to drive the movable control needle. With the piezoelectric element, precise control can be achieved. Preferably, the piezoelectric element is insulated with a thermal shield (insulating ring) of optionally heated fluid, to guarantee a precise operation of the pressure regulating mechanism (see also the description of the drawings). Since the end of the control needle has a relatively small surface, for example 10mm², it is possible, with a relatively small driving force, for example 100 N on the control needle, to effect a relatively large pressure variation, for example 30 bar [ξ30-10⁵ Pa] and thus carry out a pressure interval

ES 2 334 824 T3 regulated large enough. Therefore, the pressure regulating mechanism is particularly suitable for use in such an apparatus.

An advanced embodiment of the apparatus that can be conveniently used in the method according to the present invention is characterized in that the diameter of the outlet opening is in the range of 20-100 jum. Preferably, the longitudinal direction of the control needle is directed transversely to the outlet opening.

According to a preferred embodiment, said apparatus is equipped with an adjustable heating element for heating (temperature range 15-700 ° C) of the viscous fluid in the channel. By regulating the temperature of the fluid, the liquid can acquire a particular viscosity for the purpose of processing (printing). This makes it possible to print viscous fluids like different types of plastics and also metals (like solder).

The apparatus which can be conveniently used in the method according to the present invention will now be further described with reference to the drawing, in which:

Figure 1 is a schematic view of an apparatus according to the present invention;

Figure 2 is a schematic cross section of a recording head of an apparatus according to Figure 1;

Figure 3 is a schematic expanded representation of the print head according to Figure 2.

Figure 1 schematically shows an apparatus (2) for printing a fluid material (4) on a material (6) in the form of a sheet or plate by means of a continuous jet printing technique. The apparatus comprises a reservoir (8) for storing the fluid material (4) and a channel (10) connected to the reservoir (8). The channel (10) connects the reservoir (8) with the print head (12). The channel in the printing head (12) is provided with at least one outlet opening (14) through which the fluid material (4) comes out under pressure in the form of a jet that breaks up into drops, at effects that these drops, after being selectively deflected or directed, are printed on the material (6). A transverse dimension of the outlet opening (14) may be in the range of 30-100 jum.

In this example, the channel (10) comprises a downstream part of the outlet opening (14) which is provided with a stopcock (15). By opening the stopcock (15), the print head (12) can be cleaned with wash material / wash ink that is present in the channel.

The apparatus (2) is a continuous jet type printer, by means of which a continuous flow of drops is formed to be printed, in contrast to a drop-on-demand type printer in which drops are produced through the opening of output only if the print head has been activated for this purpose. In order to form a jet that breaks up into drops, the apparatus (2) is provided with a pressure regulation mechanism for varying the pressure of the fluid material (4) upstream of the outlet opening.

In this example, the apparatus (2) is provided with a steering system (16.1), (16.2) that allows the drops to be deflected in two directions to determine the printing location of the drops on the material (6). To this end, the steering system (16.1), (16.2) is provided, for example, with a charged electrode by means of which the drops can be provided with an electrical charge. Furthermore, the steering system (16.1), (16.2) may be provided, for example, with a capacitor by means of which the electrically charged drops can be deflected on their way. Furthermore, the apparatus (2) may be provided with a collection channel (18) through which certain drops can be captured, so that these drops are not imprinted on the material (6).

The apparatus (2) is provided with pressure generating means for passing the flowable material (4) at a predetermined pressure through the channel in the direction of the outlet opening (14). The pressure generating means are arranged to apply the predetermined pressure to the fluid material (4) hydraulically and / or pneumatically. In this example, the pressure generating means comprise a gas source which, in this example, comprises two gas cylinders (20.1), (20.2) which are filled, for example, with nitrogen. The gas bottles (20.1), (20.2) are connected through a (gas) connection (22) with the tank (8). Optionally, in the (gas) connection between the gas bottles and the reservoir (8), a pressure regulating valve is included (not shown) to keep the pressure constant. In operation, the pressure in the gas bottles will be higher than the desired pressure which is regulated by means of a pressure regulating valve. When the pressure in one of the bottles drops below the desired pressure, a switch can be made to the other bottle. In a practical variant, the connection (22) ends at the top of the reservoir (8), so that a gas pressure can be applied to a surface of the viscous fluid in the reservoir (8). The channel (10) for the transport of the viscous fluid material (4) can be connected to the tank (8) in the lower part thereof.

In the connection (22), stopcocks (24.1), (24.2) are included, by means of which it can be determined which gas bottle or bottles are in open communication with the tank (8). The stopcocks can also be designed as a pressure regulating valve or with the same. In this case, there is in no case an open communication. A gas bottle that is in open communication with the tank (8) can provide pressure to the tank (8). Under this pressure, the viscous fluid (4) housed in the reservoir is forced through the channel (10) to the outlet opening (14) in the print head (12). Next, the viscous fluid material (4) is forced through the outlet opening (14) into the material (6).

ES 2 334 824 T3

The apparatus (2), according to figure 1 is also provided with a plunger pump (26) which, through a connection (28) that includes the stopcocks (30.1), (30.2), is in communication with the gas bottles (20.1), (20.2). With the piston pump (26), the gas bottles (if the respective stopcocks -30- are opened) can be adjusted to a desired pressure. This pressure can be, for example, in the range of 20-300 bar [ξ20 · 10⁵ to 300 10⁵ Pa]. While the apparatus (print head -12-) is in operation, the gas bottles (20.1), (20.2) may alternatively be in communication with the reservoir (8). This means, for example, that in a first phase the gas bottle (20.1), through a connection (22) with an open stopcock (24.1), is in open communication with the tank (8). The stopcock (24.2) and the stopcock (30.1) are closed. The stopcock (30.2) can then be temporarily opened, so that the piston pump (26) can adjust the gas bottle (20.2) to the required pressure through the connection (28), without causing alterations in the pressure. Irregular pressure, for example in channel (10). As soon as the pressure in the gas bottle (20.1) becomes too low for a good operation of the apparatus (2), this gas bottle can be closed outside the channel (10) by closing the stopcock (24.1). The gas bottle (20.2) can take over the function of the gas bottle (20.1), for which the stopcock (24.2) is opened. In this way, the gas bottles can be used so that the apparatus (2) can operate continuously. In the example of figure 1, the apparatus is provided with an automatic control system (32) to operate the stopcocks (24.1), (24.2), (30.1), (30.2), the gas bottles (20.1) , (20.2) and the plunger pump (26). Thus, automatic and satisfactory cooperation of the different parties is obtained. The gas cylinders serve, in operation, to provide the channel with a certain pressure, while the flow rate of gas flowing from the gas cylinders can be relatively low. For that among other reasons it is possible, without any objection, that the gas bottles (20.1), (20.2) are relatively small (or, in the case where the appliance is designed with only one gas bottle, the gas bottle gas can be relatively small), so that the apparatus (2) can be made relatively compact in design.

Preferably, the apparatus (2) is provided with a heating element (34) to adjust the viscous fluid to a desired temperature. By adjusting the temperature of the viscous fluid, the viscosity of the fluid can (to some extent) be regulated (further). The heating element can be included in the print head (12) or near the channel (10).

Figure 2 shows a cross section of a recording head (12) that can be used in the apparatus (2), according to the present invention. The print head (12) comprises a pressure regulating mechanism for varying the pressure of the viscous fluid exiting through the outlet opening (14) in a regular, predetermined manner. In this example, the pressure regulating mechanism comprises a piezoelectric element (36.1) and a movable control needle (36.2). The piezoelectric element (36.1) is a regulating element by means of which the control needle (36.2) can be controlled, allowing the control needle (36.2) to move in the longitudinal direction of the control needle (36.2) towards / from the outlet opening (14), to vary the pressure adjacent to the outlet opening (14). The control needle (36.2) is movable, so that one end (37) of the control needle (36.2) is movable relative to the outlet opening (14) in the nozzle plate (38) by an adjustable distance which is in a distance range of 15-500 pm (reference can be made to figure 3). For particular applications where a viscous fluid is printed with a particularly high viscosity, for example 300 mPas, a distance range of 15-30 pm can be used.

Because the end (37) has a relatively small surface area, for example, 1-5 mm², it is possible, by means of relatively small driving forces generated by the element (36.1), through the end (37) of the control needle (36.2), to effect relatively large pressure variations adjacent to the outlet opening (14). The driving force is then, for example, 250 N. By creating pressure variations in a regular manner by the motive force, a uniform distribution of viscous fluid droplets exiting through the outlet opening is obtained. As an indication of the magnitude of the pressure regulation range, it may serve as an example that at an average pressure in the order of magnitude of 200 bar [ξ200 · 10⁵ Pa] in channel (10), the desired pressure regulation range is in the order of magnitude of approximately 40 bar [ξ40 · 10⁵ Pa].

The outlet opening (14) is included in a relatively thin nozzle plate (38) (reference can be made to Figure 3). The nozzle plate (38) can be a plate made from a metal sheet, 0.3 mm thick. In this example, the outlet opening (14) in the plate (38) has a diameter of 50 pm.

The printing head (12) is also provided with a support plate (42) that is compatible with the nozzle plate (38), so that the latter does not contract at the high pressure in the channel (10) (see Figures 2 , 3). The support plate is provided with an opening (44) which is located opposite the outlet opening (14). The diameter of the opening (44) can be an order of magnitude greater than the diameter of the outlet opening (14). The support plate (42) can be connected with screws (46) to a first annular part (48) (figure 2). In this first cylindrical part (48) the channel (10) is located, at least in part. Furthermore, the cylindrical part (48) is provided with a central cavity through which the control needle (36.2) can be passed.

The first cylindrical part (48) can be connected by screws (50) to a second cylindrical part (52) and a third cylindrical part (56). The second cylindrical part (52) is provided with flexible sealing O-rings (54) (figure 2) which are clamped, among other things, against the control needle (36.2). Preferably, the sealing O-rings (54) can follow the movements of the control needle (36.2) by mechanical deformation without the contact surfaces of the sealing O-rings (54) with the control needle (36.2) moving relative to the control needle (36.2). With the sealing O-rings (54), a leak-free seal is obtained, so that, at a minimum, almost none of the viscous flowable material can leak out of the channel (10).

ES 2 334 824 T3

Located between the second cylindrical part (52) and the third -cylindrical- part (56) is a toroidal shielding or thermal insulation gasket (58). This insulating O-ring 58 can be designed as a zirconium oxide plate. The low heat conduction of zirconium oxide generates a very favorable thermal shielding of the piezoelectric element from the optionally heated viscous fluid. This thermal shielding of the piezoelectric element is specifically relevant at relatively high temperatures of the viscous fluid. When the viscous fluid (4) to be printed has been heated by the heating element (34) to give the fluid a certain viscosity, the insulating O-ring (58) can prevent the disturbance of the operation of the pressure regulating mechanism due to the fact that the operation of the piezoelectric element (36.1) is being adversely affected. The heating element can be located in the first cylindrical part (48). The piezoelectric element (36.1) can optionally be provided with an active cooling, such as a water cooling.

The third cylindrical part (56) can be connected to a frame-shaped body (60) in which among other things the piezoelectric element (36.1) can be accommodated (see figure 2). The piezoelectric element is then located between a cover plate (64) fitted to the frame-shaped body (60) with a screw (62) and the control needle (36.2). The control needle (36.2) is passed through the central openings, respectively, of the first cylindrical part (48), the second cylindrical part 52, the insulating O-ring (58) and the third cylindrical part (56).

It will be apparent from the aforementioned that the predetermined pressure which is applied hydraulically and / or pneumatically to the flowable material (4) in the channel, with a viscosity of 150 mPas on exit and at the printing temperature, can be between 15 and 600 bar. It is also possible, however, that the predetermined pressure is between 100 and 600 bar. In that case, when an average size nozzle is used, a flowable material with a viscosity of 150 mPas on exit and at the printing temperature can be continuously printed with an apparatus according to the present invention. It is further possible that the predetermined pressure is between 200 and 600 bar. In that case, when using an average size nozzle, a flowable material with a viscosity of 300-400 mPas when exiting and at the printing temperature can be continuously printed with such an apparatus. Also, the preset pressure may be between 300 and 600 bar. This allows, using an average size nozzle, the continuous printing of a material with a viscosity of 500-600 mPas on exit and at printing temperature. In addition, the predetermined pressure can be between 400 and 600 bar for continuous printing, using an average size nozzle, for example, of a material with a viscosity of 700-800 mPas at exit and at the printing temperature.

The curable compositions according to the present invention are described below by the following non-limiting examples.

Examples

Example 1

The following curable composition (PRUV-7) was prepared:

TEGDMA (73.6 g), HEMA (31.8 g) and BisGMA (71.8 g) were mixed until a homogeneous mixture was obtained. BisGMA was heated using a hot air gun, as it was too viscous to handle at room temperature. The viscosity of the acrylate mixture was low enough for efficient stirring at room temperature. A solution of lithium perchlorate (5.2 g) in water (17.6 g) was added dropwise to the vigorously mechanically stirred TEGDMA / BisGMA mixture. A clear and homogeneous formulation was obtained. Finally, the Irgacure 819 photoinitiator (2 g) was added with stirring. The formulation was left stirring in the dark until the photoinitiator was completely dissolved. The curable product obtained had the following composition:

<td>TEGDMA</td><td>36.4 * by weight</td>

<td>BisGMA</td><td>35.5% by weight</td>

<td>2-hydroxyethyl methacrylate (HEMA)</td><td>15.7% by weight</td>

<td>Water</td><td>8.7% by weight</td>

<td>LiClOj</td><td>2.6% by weight</td>

<td>Irgacure 819</td><td>1.0% by weight</td>

The composition obtained had the following conductivity and low shear viscosity values:

• Conductivity: σ (23 ° C) = 252 pS / cm.

σ (31 ° C) = 370 pS / cm.

• Low shear viscosity: η (22 ° C) = 65 mPas

ES 2 334 824 T3

Example 2

The following composition (PRUV-8) was prepared:

Cray Valley SR344 (148 g) and BisGMA (27 g) were mixed until a homogeneous mixture was obtained. BisGMA was heated using a hot air gun, as it was too viscous to handle at room temperature. The viscosity of the acrylate mixture was low enough for efficient stirring at room temperature. A solution of lithium perchlorate (5.6 g) in water (19.4 g) was added dropwise to the vigorously stirred SR344 / BisGMA mixture. A clear and homogeneous formulation was obtained. Finally, the Irgacure 819 photoinitiator (2 g) was added with stirring. The formulation was left stirring in the dark until the photoinitiator was completely dissolved.

The curable product obtained had the following composition:

<td>SR344</td><td>73.3 * by weight</td>

<td>BisGMA</td><td>13.4 * by weight</td>

<td>Water</td><td>9.6% by weight</td>

<td>LiClO,</td><td>2.8 * by weight</td>

<td>Irgacure 819</td><td>1.0 * by weight</td>

The composition obtained had the following conductivity and shear viscosity values:

• Conductivity: σ (23 ° C) = 230 pS / cm.

σ (31 ° C) = 380 juS / cm.

• Low shear viscosity: η (22 ° C) = 100 mPas

Example 3

The following composition (PRUV-11) was prepared:

TEGDMA (108.2 g), BisGMA (63.2 g) and SR344 (6.8 g) were mixed until a homogeneous mixture was obtained. The BisGMA was heated using a hot air gun, as it was too viscous to handle at room temperature. The viscosity of the acrylate mixture was low enough for efficient stirring at room temperature. A solution of lithium trifluoromethanesulfonate (= lithium triflate) (9.8 g) in water (12 g) was added dropwise to the mechanically vigorously stirred TEGDMA / BisGMA / SR344 mixture. A clear and homogeneous formulation was obtained. Finally, the Irgacure 819 photoinitiator (2 g) was added with stirring. The formulation was left stirring in the dark until the photoinitiator was completely dissolved.

The curable product obtained had the following composition:

<td>TEGDMA</td><td>53.6% by weight</td>

<td>BisGMA</td><td>31.3 * by weight</td>

<td>SR344</td><td>3.4 * by weight</td>

<td>Water</td><td>5.9% by weight</td>

<td>LiCFjSO;</td><td>4.9% by weight</td>

<td>Irgacure 819</td><td>1.0% by weight</td>

The composition obtained had the following conductivity and low shear viscosity values:

• Conductivity: σ (21 ° C) = 135 pS / cm.

σ (34 ° C) = 258 juS / cm.

• Low shear viscosity: η (22 ° C) = 70 mPas

ES 2 334 824 T3

Example 4

The following composition (PRUV-15) was prepared:

TEGDMA (5.6 g), HEMA (85.2 g) and BisGMA (85.2 g) were mixed until a homogeneous mixture was obtained. BisGMA was heated by a hot air gun as it was too viscous to handle at room temperature. The viscosity of the acrylate mixture was low enough for efficient stirring at room temperature. A solution of lithium trifluoromethanesulfonate (8.8 g) in water (15.2 g) was added dropwise to the vigorously mechanically stirred TEGDMA / BisGMA mixture. A clear and homogeneous formulation was obtained. Finally, the Irgacure 819 photoinitiator (2 g) was added with stirring. The formulation was left stirring in the dark until the photoinitiator was completely dissolved.

The curable product obtained had the following composition:

<td>TEGDMA</td><td>2.8% by weight</td>

<td>BisGMA</td><td>42.6% by weight</td>

<td>HEMA</td><td>42.6% by weight</td>

<td>Water</td><td>7.5% by weight</td>

<td>LiCF, SO;</td><td>4.4% by weight</td>

<td>Irgacure 819</td><td>1.0% by weight</td>

The composition obtained had the following conductivity and low shear viscosity values:

• Conductivity: σ (22 ° C) = 269 pS / cm.

• Low shear viscosity:

The low shear viscosity of the obtained product was measured as a function of temperature at Anton Paar (Austria) using a falling ball viscometer. The values ​​measured at different temperatures were as follows:

η (20 ° C) = 119 mPas;

η (30 ° C) = 61 mPas;

η (40 ° C) = 35 mPas;

η (50 ° C) = 22 mPas.

Example 5

The following composition was prepared:

TEGDMA (5.6 g), HEMA (85.2 g) and BisGMA (85.2 g) were mixed until a homogeneous mixture was obtained. BisGMA was routinely heated by a hot air gun as it was too viscous to handle at room temperature. The viscosity of the acrylate mixture was low enough for efficient stirring at room temperature. A solution of lithium trifluoromethanesulfonate (8.8 g) in water (15.2 g) was added dropwise to the vigorously mechanically stirred TEGDMA / BisGMA mixture. A clear and homogeneous formulation was obtained. Irgacure 819 photoinitiator (2 g) was added with stirring. The formulation was left stirring in the dark until the photoinitiator was completely dissolved. Finally, 0.2 g of UV3510 humectant from BYK (0.1% by weight of the total of the components mentioned above) was added with gentle stirring. The solution was allowed to stir until a homogeneous mixture was obtained.

The curable product obtained had the following composition:

<td>TEGDMA</td><td>2.8% by weight</td>

<td>BisGMA</td><td>42.1% by weight</td>

<td>HEMA</td><td>42.1% by weight</td>

<td>Water</td><td>7.5% by weight</td>

<td>LiCFjSO;</td><td>4.4% by weight</td>

<td>Irgacure 819</td><td>1.0%. in weigh</td>

<td>BYK UV3510</td><td>0.1% by weight</td>