Polymerisation device and method

Abstract

The invention relates to a device (1) for polymerising a material (M) containing a polymerisable resin, the device (1) comprising at least one UV source (2) capable of polymerising the material (M), wherein the at least one UV source is pulsed and wherein the frequency of pulsation of the at least one UV source (2) is higher than 500 Hz. The material may be deposited on a substrate or in a mould.

Description

[0001] Description

[0002] Title of the invention: Polymerization device and method

[0003] technical field

[0004] The invention relates to a polymerization device and method.

[0005] Previous technique

[0006] It is known that a material containing a polymerizable resin can be hardened by supplying it with energy. This energy is typically supplied in the form of heat or light. In the case of light, the use of ultraviolet (UV) light is particularly advantageous.

[0007] The polymerization of a material containing a polymerizable resin is used in many fields.

[0008] One example is the application of surface coatings using paint, lacquer, or varnish, where components such as pigments are mixed with a polymerizable resin. This allows for deposition in a fluid phase onto a substrate and subsequent hardening through in-situ polymerization. This opens up applications in building construction, decoration, automotive bodywork, aviation, marine, and aerospace.

[0009] We can also mention the complete production of objects using composite materials, where a resin matrix is ​​hardened around a possible fiber reinforcement, for example, of glass or carbon. The resin can be combined with other components, such as wood. This is applied to the manufacture of boat hulls. It can also be applied to the manufacture of street furniture, interior furnishings, and outdoor children's play equipment.

[0010] We can also mention the fields of nail care or dentistry, for the production of prostheses.

[0011] Summary of the invention

[0012] In general, the invention is applicable wherever a polymerizable resin is cured using a UV source. The invention offers a significant improvement over conventional UV illumination techniques.

[0013] To this end, the invention relates to a device for polymerizing a material containing a polymerizable resin, the device comprising at least one UV source capable of polymerizing the material. The invention is characterized in that said at least one UV source is pulsed and its pulse frequency is greater than 500 Hz. The material can be deposited onto a substrate or into a mold.

[0014] Specific characteristics or embodiments, usable alone or in combination, are:

[0015] - the pulse frequency of said at least one UV source is between 500 Hz and 1500 Hz, preferably between 750 and 1250 Hz,

[0016] - the duration of the light pulses is less than 0.75 times, and preferably less than 0.5 times, a pulse period,

[0017] - The pulse of the UV source has a luminous power output between 1 and 50 W / cm² 2 preferably between 1 and 25 W / cm² 2 , preferably equal to 12 W / cm² 2 ,

[0018] - the polymerizable resin comprises polymerization photoinitiators having a reaction wavelength and the UV source has a UV emission wavelength centered on said reaction wavelength of the photoinitiators,

[0019] - said at least one UV source comprises at least one LED or an array of LEDs, linear or surface-mounted,

[0020] - the pulse control voltage of said at least one UV source comprises a non-zero DC base voltage to which is added a positive pulsed voltage, comprising voltage peaks according to the pulse frequency, a voltage peak creating a light peak,

[0021] - the device comprises a trolley that is movable relative to the surface of the substrate, carrying a deposition means suitable for depositing the material onto the surface of the substrate, and said at least one UV source is fixed to the trolley,

[0022] - the device further comprises a deposition means capable of depositing the material onto the surface of the substrate; the deposition means is fixed to the trolley, and said at least one UV source is disposed substantially behind the deposition means, relative to the trajectory of the trolley,

[0023] - the trolley is carried by a Cartesian gantry comprising three prismatic axes substantially orthogonal to each other and a fourth axis rotating around the third axis, or the trolley is carried by a robotic arm, comprising between 2 and 4 rotating axes,

[0024] - said at least one UV source is moved so as to remain permanently at a substantially constant distance from the substrate,

[0025] - said at least one UV source is oriented so that its luminous axis remains permanently substantially perpendicular to the surface of the substrate,

[0026] - the pulse of said at least one UV source is adjusted, in luminous power and / or frequency, according to a position of the UV source relative to the surface of the substrate.

[0027] According to another aspect, a process for polymerizing a material containing a polymerizable resin using a UV source, employing such a device.

[0028] Brief description of the drawings

[0029] The invention will be better understood upon reading the following description, given solely by way of example, and with reference to the figures in the appendix in which

[0030] [Fig. 1] shows, in schematic axial sectional view, a polymerization device according to the invention,

[0031] [Fig. 2] shows, in perspective view, a polymerization device according to the invention,

[0032] [Fig. 3] shows the distribution of the light power emitted by a polymerization device according to the invention,

[0033] [Fig. 4] shows an embodiment of a UV source using an LED matrix.

[0034] Description of the implementation methods

[0035] The invention relates to a device 1 for polymerizing a material M containing a polymerizable resin; the material can be deposited onto a substrate S or into a mold (not shown). In a known manner, the device 1 comprises a UV source 2 suitable for polymerizing the material M. According to the prior art, UV illumination is continuous. This is typically achieved using a discharge lamp. In contrast, according to an ingenious feature of the invention, the UV source 2 is pulsed. Pulsed means that the supply voltage of the UV source 2 is modulated into regularly emitted discrete pulses, producing UV radiation comprising similar discrete pulses.

[0036] It is possible to vary both the light power of the light pulses produced and their frequency and duration, depending on the amount of energy that one wishes to emit to achieve polymerization.

[0037] Replacing a continuous UV 2 source with a pulsed UV 2 source offers many advantages.

[0038] Due to a principle of action and reaction, UV radiation penetrates material M to a greater depth. Indeed, when, according to the prior art, continuous UV radiation is applied perpendicularly to the surface of material M, the surface reflects a significant portion of the UV radiation in steady state. Conversely, when a pulse of UV radiation is applied, the surface does not have time to react, and the UV radiation penetrates the surface, reaching a greater depth. This advantageously allows for deeper polymerization.

[0039] A pulse allows penetration, even in the presence of an oxidized surface layer. Such an oxidized surface layer is particularly reflective to continuous UV radiation.

[0040] This increased penetration allows for faster polymerization. This is advantageous, in particular because it prevents any potential dripping of the polymerizable resin from material M.

[0041] Using a pulsed UV 2 source consumes significantly less energy than a conventional UV source. This is true for two reasons. First, the improved efficiency and penetration reduce the energy required, while maintaining a constant polymerization rate. Second, drawing power from the UV 2 source limits current consumption to the duration of the pulses, which is considerably lower than the consumption during continuous operation.

[0042] According to an advantageous characteristic, the pulse frequency of at least one UV source is greater than 500 Hz. As mentioned above, applying pulsed light facilitates the penetration of the light beam into the resin. However, due to the principle of action and reaction, the resin at the core of the layer to be polymerized tends to repel the penetrating light beam, and the penetrating light beam thus tends to spread within the resin layer in a plane substantially perpendicular to the beam's penetration axis.

[0043] On the one hand, this phenomenon limits the penetration depth of the light beam. Since only the illuminated thickness of the resin polymerizes, if the beam doesn't penetrate deeply enough, the resin layer is polymerized on the surface, to a certain thickness, but not in depth. With a pulse frequency above 500 Hz, the material is illuminated with a very short-duration peak; it doesn't have time to react, and the light beam, paradoxically, penetrates deeper.

[0044] On the other hand, this action / reaction phenomenon limits the resolution of the illuminated (and therefore polymerized) portion of resin; indeed, this phenomenon causes a spreading of the beam, the illuminated area in the resin has, in a plane perpendicular to the axis of penetration of the beam, a larger cross-section than the cross-section of the light beam penetrating the resin.

[0045] A pulse frequency above 500 Hz allows for at least one pulse every 2 ms, resulting in very short pulses. The pulse frequency is selected through experimentation based on the material and its thickness. Experiments have shown that such short pulses provide significant beam penetration and sufficiently fine resolution for most intended applications.

[0046] According to one embodiment, the pulse frequency of said at least one UV source 2 is between 500 and 1500 Hz, preferably between 750 and 1250 Hz, and even more preferably between 900 and 1100 Hz. Tests have shown that a frequency within this pulse frequency range gives good results for the polymerization of thin layers, such as surface coatings like varnish or paint. The beam penetrates sufficiently to reach the coated substrate, allowing polymerization of the coating layer throughout its entire thickness and up to the coating / substrate interface, thus ensuring good adhesion of the polymerized layer to the substrate.

[0047] In a concrete example of a varnish layer of the order of 30 to 60 micrometers on a vehicle body part, a pulse frequency around 1000 Hz gave good results.

[0048] In one embodiment, the duration of the light pulses is less than 0.75 times, and preferably less than 0.5 times, the pulse period. The pulse period is, by definition, the inverse of the pulse frequency. The unlit time between two pulses allows the resin to return to its initial resting state before receiving a new light pulse, thus further limiting the action / reaction phenomenon mentioned above. The pulse duration is determined through testing based on the material and its thickness.

[0049] The tests performed yielded good results for a pulse duration less than 0.75 times the pulse period. In a concrete example of a thin layer of varnish on a body panel, the best results were obtained for a pulse duration less than 0.5 times the pulse period.

[0050] On the contrary, the usual solution to go deeper is to increase the power of the light signal.

[0051] Also, pulsation, in particular pulsation at a frequency above 500 Hz, allows penetration to be deeper while consuming less energy; this results in less heating of the light source; this also results in less heating of the resin layer, thus preventing degradation of the resin material; Finally, the substrate is also less heated; it thus becomes possible to use the device according to the invention to polymerize coating layers on substrates with low heat resistance.

[0052] According to another characteristic, the UV 2 source emits light pulses with a power between 1 and 50 W / cm² 2 , and preferably between 1 and 25 W / cm² 2 Good results were obtained on paints and varnishes in particular, with a power of around 12 W / cm². 2The power can be chosen inversely proportional to the pulse frequency. Thus, if the pulse frequency is chosen high, the power is chosen low, and vice versa, depending on the reactivity of the resin to be polymerized.

[0053] For maximum absorption of UV radiation by the polymerizable resin of material M, the wavelength of UV emission is preferentially centered on the reaction wavelength of the photo-initiators of polymerization of the polymerizable resin of material M. Also, this wavelength depends on material M and the polymerizable resin it contains.

[0054] In one example, the invention can be used for polymerizing a layer of varnish or paint a few micrometers thick on a substrate such as an automotive body part. In another example, the invention can be used for the complete polymerization of a part a few centimeters thick made of a material comprising fibers bonded by a polymerizing resin. Such a part might be, for example, a piece of street furniture, a boat hull, etc. The penetration depth of the UV ray, and therefore the polymerization depth, depends on the transparency of the fibers, in addition to the properties of the UV source.

[0055] Figure 3 illustrates an example of the light energy distribution D on the surface of the material M to be polymerized. This distribution D is approximately Gaussian. In practice, this distribution can be adjusted by modifying the parameters of the UV source as well as the parameters for moving the UV source near the surface to be treated.

[0056] Another characteristic of the UV source 2 is that it includes at least one light-emitting diode, or LED. Such a UV LED is capable of producing UV radiation that is perfectly adequate for polymerization.

[0057] The advantages of LEDs are numerous. One or more LEDs allow for the creation of a UV 2 source that is significantly smaller and consumes considerably less current than the discharge lamps traditionally used for the intended polymerization applications. The use of one or more LEDs is therefore synergistic with the pulsed characteristic, further reducing electrical energy consumption.

[0058] A polymerizable resin is advantageously enhanced by the addition of polymerization photoinitiators. These compounds help initiate or accelerate the polymerization reaction. Each polymerization photoinitiator exhibits increased sensitivity (defined by a light absorption coefficient) at a given wavelength, more precisely a nearly Gaussian wavelength range centered on a wavelength known as the reaction wavelength.

[0059] An LED can advantageously be chosen to emit at a given wavelength. Furthermore, according to another feature of the invention, the wavelength of said at least one UV source 2 is advantageously chosen to be centered on the reaction wavelength of the polymerization initiators. This is an advantage compared to a broad-spectrum UV source. Indeed, UV radiation with wavelengths outside the reaction wavelength tends to react with the resin and produce ozone, which is detrimental. This ozone destroys the photoinitiators necessary for the polymerization of the resin. Moreover, the energy transmitted at wavelengths outside the reaction wavelength is energy lost to the expected reaction.

[0060] One consequence of reduced energy consumption is that the UV 2 source heats up less. Advantageously, this allows for a simpler cooling system for the source. Such a cooling system is smaller, easier to integrate or mount, and consumes less energy.

[0061] It is possible to create the UV 2 source with one or more LEDs. Alternatively, the UV 2 source may consist of an LED array.

[0062] This matrix can be linear. In this case, the LEDs are arranged as a vector. This vector can be straight. It can also be a curved line. The curvature of this line, which can be multidimensional, can advantageously follow the profile of the part to be cured. This makes it advantageous to create a UV 2 source capable of curing over a width equal to the length of said line. Thus, such a linear UV 2 source, moved perpendicularly to its direction of extension, allows a material M to be cured to be scanned in strips of said width in a single pass.

[0063] The array can be surface-based, as illustrated in Figure 4. In this case, the LEDs are arranged in a two-dimensional, advantageously rectangular, array. This offers the same advantages as the previous array, but with increased UV radiation power.

[0064] In the case of a matrix, linear or surface, all the LEDs are preferentially synchronized, so as to emit their pulses simultaneously.

[0065] Matrix arrangements, linear or surface, advantageously allow polymerization to be carried out on surfaces with complex geometries, including with significant curvatures, by adapting the shape of the matrix to the profile of the part to be polymerized if necessary.

[0066] According to another characteristic, the pulse control voltage of at least one UV source comprises a non-zero DC base voltage to which is added a positive pulsed voltage, comprising voltage peaks according to the pulse frequency, each voltage peak creating a light peak. The non-zero DC base voltage can be relatively low, even insufficient to illuminate the UV source. It advantageously ensures that the UV source is never unpowered. This is particularly important when the UV source includes LEDs. Indeed, a power interruption after each pulse risks damaging the UV source, especially in the case of an LED. Therefore, the presence of a non-zero DC base voltage ensures that the UV source, and particularly an LED, is never switched off, but is constantly powered by at least one of these base voltages.The pulse periodically increases the voltage by adding a voltage pulse. Preferably, the base voltage is equal to or slightly greater than the threshold voltage of an LED. In one example, the base voltage is between 1 and 1.25 times the threshold voltage of an LED.

[0067] In one embodiment, the device 1 includes a movable carriage 3. This carriage 3 can be moved relative to the surface of the material M containing the resin to be polymerized. In one example, the carriage is mounted to slide (Figure 1 and Figure 2) along a direction Y on a gantry that is itself movable in translation along a direction X perpendicular to Y, the gantry being positioned as close as possible to the surface of the material M and such that the plane (X, Y) is as nearly parallel as possible to the surface of the material M.

[0068] The UV source 2 is advantageously fixed on the trolley 3. This allows the UV radiation to be directed towards the material M.

[0069] Such a mobile trolley on a mobile gantry can be used to polymerize in bulk the composite material M, a material formed in a mold for example.

[0070] According to another embodiment, the trolley also carries a depositing means 4, suitable for depositing the material M comprising a resin, onto the surface of a substrate S.

[0071] The substrate S can be a part receiving a deposit of material M such as paint or varnish. The substrate S can also be a mold or a part to be overmolded in the case of composite manufacturing. The substrate S can also be a layer of previously polymerized material M.

[0072] Depending on the intended application, the deposition means 4 is, for example, a print head capable of projecting a jet of drops of ink or varnish, a paint head capable of projecting a continuous jet of paint, or a means of filling a mold with material M.

[0073] In this embodiment, advantageously, the UV source 2 is fixed to the carriage 3 and positioned at the rear of the deposition means 4 (Figure 1 and Figure 2). "Rear" is understood here relative to the trajectory of the carriage 3, such that the UV source 2 follows the deposition means 4. This allows the UV radiation to be directed towards the material M immediately after its deposition onto the substrate S, thus limiting the risk of material M running off.

[0074] According to another characteristic, the carriage 3 is carried by any structure. This structure can be, for example, a Cartesian gantry comprising three prismatic axes X, Y, Z that are substantially orthogonal to each other and a fourth axis rotating around the third Z axis. Alternatively, the carriage 3 can be carried by a robotic arm, comprising between 2 and 4 rotating axes.

[0075] According to another feature, the UV source 2 is moved so as to remain permanently at a substantially constant distance b from the substrate S. This can be achieved by the carriage 3 itself, driven in such a way as to maintain substantially constant the distance b with the surface of the material M or with the distance to the substrate S. This can alternatively or complementaryly be achieved by an actuator allowing adjustment of a distance b between the carriage 3 and the UV source 2. This actuator can advantageously be servo-controlled to said distance b. This makes it possible to work on parts or supports of various shapes, surfaces, and dimensions, including parts or supports with locally significant radii of curvature.

[0076] According to another feature, the UV source 2 is oriented so that its light axis remains constantly substantially perpendicular to the surface of the substrate S. This ensures optimal polymerization. As before, this can be achieved by the carriage 3 itself, driven in such a way as to maintain substantially constant the orientation a relative to the surface of the material M or the substrate S. This can alternatively or complementaryly be achieved by an actuator that allows adjustment of the orientation of the UV source 2 relative to the carriage 3. This actuator can advantageously be servo-controlled to this orientation.

[0077] According to another feature, the UV source 2 and, where applicable, the deposition means 4 are controlled according to the position of the carriage 3 relative to the surface of the material M and according to the thickness of the material M to be cured at the position of the carriage 3. The power, pulse frequency, and pulse duration of the UV LED source can be adjusted very rapidly during operation. This allows for local adjustment of the curing depth and the thickness of the cured material M. This can be achieved, for example, by an actuator that adjusts the light power and / or the frequency and / or the pulse duration of the UV source according to the position of the UV source 2 relative to the surface of the material M.

[0078] The invention further relates to a method of polymerizing a material M containing a polymerizable resin by means of a UV source 2. This method advantageously employs a device 1 according to any one of the embodiments previously described.

[0079] The invention has been illustrated and described in detail in the drawings and the preceding description. This description is to be considered illustrative and given by way of example and not as limiting the invention to this single description. Numerous embodiments are possible. List of reference symbols

[0080] 1: device,

[0081] 2: UV source, 3: trolley,

[0082] 4: means of deposit,

[0083] D: distribution,

[0084] M: material,

[0085] 5: substrate, X, Y, Z: axis of movement.

Claims

Demands

1. Device (1) for polymerizing a material (M) containing a polymerizable resin, the device (1) comprising at least one UV source (2) capable of polymerizing the material (M), characterized in that said at least one UV source is pulsed and a pulse frequency of said at least one UV source (2) is greater than 500 Hz.

2. Device (1) according to claim 1, wherein the pulse frequency of said at least one UV source (2) is between 500 and 1500 Hz and preferably between 750 and 1250 Hz.

3. Device according to any one of claims 1 to 3, wherein a duration of light pulses is less than 0.75 times, and preferably less than 0.5 times a pulse period.

4. A device according to any one of claims 1 or 2, wherein the pulse of said at least one UV source (2) has a luminous power between 1 and 50 W / cm² 2 preferably between 1 and 25 W / cm² 2 , and preferably equal to 12 W / cm² 2 .

5. Device according to any one of claims 1 to 3, wherein the polymerizable resin comprises polymerization photoinitiators having a reaction wavelength and wherein the UV source has a UV emission wavelength centered on said reaction wavelength of the photoinitiators.

6. Device (1) according to any one of claims 1 to 4, wherein said at least one UV source (2) comprises at least one LED or LED array, linear or surface.

7. Device (1) according to any one of claims 1 to 5, wherein the pulse control voltage of said at least one UV source (2) comprises a non-zero DC base voltage to which is added a positive pulsed voltage, comprising voltage peaks according to the pulse frequency, a voltage peak creating a light peak.

8. Device (1) according to any one of claims 1 to 6 comprising a trolley (3) movable relative to the surface of the substrate (S), wherein said at least one UV source (2) is fixed on the trolley (3).

9. Device (1) according to claim 7 further comprising a deposition means (4) capable of depositing the material (M) on the surface of the substrate (S), wherein the deposition means (4) is fixed on the carriage (3), and said at least one UV source (2) is disposed substantially behind the deposition means (4), relative to the trajectory of the carriage (3).

10. Device (1) according to any one of claims 7 or 8, wherein: - the carriage (3) is carried by a Cartesian gantry comprising three prismatic axes (X, Y, Z) substantially orthogonal to each other and a fourth axis rotating around the third axis (Z), or - the trolley (3) is carried by a robotic arm, comprising between 2 and 4 rotating axes.

11. Device (1) according to any one of claims 7 to 9, wherein said at least one UV source (2) is moved so as to remain permanently at a substantially constant distance (b) from the substrate (S).

12. Device (1) according to any one of claims 7 to 10, wherein said at least one UV source (2) is oriented so that its light axis remains permanently substantially perpendicular to the surface of the substrate (S).

13. Device (1) according to any one of claims 7 to 11, wherein the pulsation of said at least one UV source (2) is adjusted, in luminous power and / or in pulsation frequency, as a function of a position of the UV source (2) relative to the surface of the substrate (S).

14. A method for polymerizing a material (M) containing a polymerizable resin by means of a UV source (2), characterized in that it employs a device (1) according to any one of the preceding claims.

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