Polymerization process

Abstract

The invention relates to a device (1) for polymerizing a material (M) containing a polymerizable resin, deposited on a substrate (S), the device (1) comprising at least one UV source (2) capable of polymerizing the material (M), wherein said at least one UV source (2) is pulsed. Abbreviated figure: Figure 1

Description

Title of the invention: Polymerization process technical field

[0001] The invention relates to a polymerization process. Previous technique

[0002] It is known to harden a material containing a polymerizable resin by supplying it with energy. This energy is conventionally supplied in the form of heat or light. In the case of light, the use of ultraviolet or UV light is particularly advantageous.

[0003] The polymerization of a material containing a polymerizable resin is used in many fields.

[0004] One example is the application of surface coatings / deposits using paint, lacquer, or varnish, where the constituents, such as pigments, are mixed with a polymerizable resin. This allows for deposition in the fluid phase onto a substrate and subsequent hardening by in-situ polymerization. This opens up applications in building construction, decoration, automotive bodywork, aviation, marine, and aerospace.

[0005] Another example is the complete fabrication of an object using composite materials, where a resin matrix is ​​hardened around a possible fiber reinforcement, for example, of glass or carbon. Other constituents, such as wood, can be added to the resin. 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.

[0006] The fields of nail care or dentistry can also be cited for the production of prostheses. Summary of the invention

[0007] In general, the invention is applicable wherever a polymerizable resin is cured by means of a UV source.

[0008] The invention offers a significant improvement to the conventional UV lighting technique.

[0009] To this end, the invention relates to a device for polymerizing a material containing a polymerizable resin, the material deposited on a substrate, 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.

[0010] Specific features or embodiments, usable alone or in combination, are: - the pulse of the UV source has a luminous power between 1 and 50 W / cm2, preferably between 1 and 25 W / cm2, preferably equal to 12 W / cm2,

[0011] - the UV source has an emission wavelength centered on a length reaction wave of the photo-initiators of polymerization of the polymerizable resin of the material, - the pulse frequency of said at least one UV source is between 1 and 1000 Hz, - said at least one UV source includes at least one LED, - said at least one UV source comprises an array of LEDs, linear or surface-mounted, - 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, - 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, - 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, - 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, - said at least one UV source is moved so as to remain permanently at a substantially constant distance from the substrate, - said at least one UV source is oriented so that its luminous axis remains permanently substantially perpendicular to the surface of the substrate, - the pulse of said at least one UV source is adjusted, in luminous power and / or in frequency according to a position of the UV source relative to the surface of the substrate.

[0012] According to another aspect, a process for polymerizing a material containing a polymerizable resin by means of a UV source, employing such a device. Brief description of the drawings

[0013] 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:

[0014] [Fig-1] shows, in schematic axial sectional view, a device of polymerization according to the invention,

[0015] [Fig.2] shows, in perspective view, a polymerization device according to the invention,

[0016] [Fig.3] shows, the distribution of the light power emitted by a polymerization device according to the invention, [Fig.4] shows an embodiment of a UV source using an LED matrix. Description of the implementation methods

[0017] The invention relates to a device 1 for polymerizing a material M containing a polymerizable resin, the material deposited on a substrate S. In a known manner, the device 1 comprises a UV source 2 suitable for polymerizing the material M. According to the prior art, the UV illumination is continuous. This is typically achieved using a discharge lamp.

[0018] On the contrary, according to a particularly ingenious feature of the invention, the UV source 2 is pulsed. By pulsed, we mean that the supply voltage of the UV source 2 is modulated in the form of regularly emitted discrete pulses, producing UV radiation comprising similar discrete pulses.

[0019] It is possible to vary both the light power of the light pulses produced and their frequency, depending on the amount of energy that one wishes to emit to carry out the polymerization.

[0020] Replacing a continuous UV 2 source with a pulsed UV 2 source has many advantages.

[0021] 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, said surface reflects, in steady state, a significant portion of the UV radiation. Conversely, when a pulse of UV radiation is applied, the surface does not have time to react, and the UV radiation penetrates said surface, and this penetration occurs to a greater depth. This advantageously allows for deeper polymerization.

[0022] 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.

[0023] This increased penetration allows for faster polymerization. This is advantageous, in particular because it prevents any potential dripping of the polymerizable resin from the material M.

[0024] The use of a pulsed UV 2 source consumes significantly less energy than a conventional UV source. This is true in two ways. Firstly, the improved efficiency / penetration reduces the energy required, while maintaining constant polymerization. Secondly, 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.

[0025] According to another feature, the UV source 2 emits light pulses with a power between 1 and 50 W / cm², and preferably between 1 and 25 W / cm². Good results on paints and varnishes, in particular, have been obtained with a power of around 12 W / cm². The power can be chosen inversely proportional to the pulse frequency. Thus, if the pulse frequency is chosen to be high, the power is chosen to be low, and vice versa, depending on the reactivity of the resin to be polymerized.

[0026] 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 the material M and the polymerizable resin it contains.

[0027] According to another feature, the pulse frequency of said at least one UV source 2 is between 1 and 1000 Hz. The frequency is chosen in practice by tests based on the response time of the UV source and / or based on the reactivity of the resin to be polymerized.

[0028] In one example, the invention can be used for the polymerization of a varnish or paint layer 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 is, for example, a piece of street furniture, a boat hull, etc. The penetration depth of the UV ray, and therefore of the polymerization, depends on the transparency of the fibers, in addition to the properties of the UV source.

[0029] Figure 3 illustrates an example of the distribution D of light energy distributed over the surface of the material M to be polymerized. This distribution D is essentially 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.

[0030] According to another feature, the UV source 2 comprises at least one light-emitting diode or LED. Such a UV LED is capable of producing UV radiation that is entirely satisfactory for polymerization.

[0031] The advantages of LEDs are numerous. One or more LEDs make it possible to create a UV 2 source that is much smaller in size and consumes significantly less current than the discharge lamps conventionally used for the polymerization applications envisaged.

[0032] The use of one or more LEDs is therefore synergistic with the pulse characteristic. It allows for a further reduction in electrical energy consumption.

[0033] An LED can advantageously be chosen to emit at a target wavelength: the wavelength of the polymerization initiators. This is advantageous compared to a broad-spectrum UV source. Indeed, UV radiation with wavelengths outside the target wavelength tends to react with the resin and produce ozone, which is detrimental. Moreover, the energy transmitted at wavelengths outside the target wavelength is energy lost to the expected reaction.

[0034] One consequence of the reduced energy consumption is that the UV 2 source heats up less. Advantageously, this allows for a simpler cooling method for the source. Such a cooling method is smaller, easier to integrate or mount, and consumes less energy.

[0035] It is possible to implement the UV 2 source with one or more LEDs. According to another feature, the UV 2 source comprises an array of LEDs.

[0036] This matrix can be linear. In this case, the LEDs are arranged in 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 advantageously allows for the creation of 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, makes it possible to scan a material M to be cured in strips of said width in a single pass.

[0037] The matrix can be surface-based, as illustrated in [Fig. 4]. In this case, the LEDs are arranged in a two-dimensional array, advantageously rectangular. This provides the same advantages as the previous vector array, but with increased UV radiation power.

[0038] In the case of a matrix, linear or surface, all the LEDs are preferentially synchronized, so as to emit their pulses simultaneously.

[0039] Matrix arrangements, linear or surface, advantageously allow polymerization to be carried out on surfaces with complex geometries, including with significant curvatures, adapting the shape of the matrix to the profile of the part to be polymerized as needed.

[0040] According to another feature, 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, each voltage peak creating a light peak. The non-zero DC base voltage can be relatively low, even insufficient to illuminate the UV source 2. It advantageously ensures that the UV source 2 is never unpowered. This is particularly important when the UV source 2 includes LEDs. Indeed, a power interruption after each pulse risks damaging the UV source 2, especially in the case of an LED. Therefore, the presence of a non-zero DC base voltage ensures that the UV source 2, and particularly an LED, is never switched off, but is constantly supplied with at least one of said 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.

[0041] According to one embodiment, the device 1 comprises a movable carriage 3. This carriage 3 can be moved relative to the surface of the material M comprising the resin to be polymerized. In one example, the carriage is mounted to slide ([Fig. 1] and on [Fig. 2]) along a direction Y on a gantry which 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.

[0042] The UV source 2 is advantageously fixed on the carriage 3. This allows the UV radiation to be directed towards the material M.

[0043] Such a mobile trolley on a gantry, itself mobile, can be used to polymerize in the mass the composite material M, material formed in a mold for example.

[0044] According to another embodiment, the carriage also carries a deposition means 4, suitable for depositing the material M comprising a resin, on the surface of a substrate S.

[0045] The substrate S may be a part receiving a deposit of material M such as paint or varnish. The substrate S may also be a mold or a part to be overmolded in the case of manufacturing from a composite material. The substrate S may also be a layer of previously polymerized material M.

[0046] 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.

[0047] In this embodiment, advantageously, the UV source 2 is fixed to the carriage 3 and positioned at the rear of the deposition means 4 ([Fig. 1] and [Fig. 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.

[0048] According to another feature, the carriage 3 is carried by any structure. This structure can be, for example, a Cartesian gantry comprising three prismatic axes X, Y, Z substantially orthogonal to each other and a fourth axis rotating about the third Z axis. Alternatively, the carriage 3 can be carried by a robotic arm, comprising between 2 and 4 rotating axes.

[0049] 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 having locally large radii of curvature.

[0050] According to another feature, the UV source 2 is oriented so that its light axis remains permanently 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 for adjusting the orientation of the UV source 2 relative to the carriage 3. This actuator can advantageously be servo-controlled to this orientation.

[0051] According to yet 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 a thickness of material M to be polymerized at the position of the carriage 3. This allows for local adjustment of the polymerization depth and the thickness of material M. This can be achieved, for example, by an actuator for adjusting the light intensity and / or the pulse frequency of the UV source as a function of the position of the UV source 2 relative to the surface of the material M.

[0052] 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.

[0053] 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 signs

[0054] 1: device, 2: UV source, 3: trolley, 4: deposition medium, D: distribution, M: material, S: substrate, X, Y, Z: axis of movement.

Claims

Demands

1. Device (1) for polymerizing a material (M) containing a polymerizable resin, material deposited on a substrate (S), 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 (2) is pulsed.

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

3. Device according to any one of the preceding claims, wherein the UV source has a UV emission wavelength centered on a reaction wavelength of the polymerization photoinitiators of the polymerizable resin of material M.

4. Device (1) according to any one of claims 1 to 3, wherein the pulse frequency of said at least one UV source (2) is between 1 and 1000 Hz.

5. Device (1) according to any one of claims 1 to 4, wherein said at least one UV source (2) comprises at least one LED.

6. Device (1) according to any one of claims 1 to 5, wherein said at least one UV source (2) comprises an array of LEDs, linear or surface.

7. Device (1) according to any one of claims 5 or 6, 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 7 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 8 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 8 or 9, wherein: - the trolley (3) is carried by a Cartesian gantry comprising three prismatic axes (X, Y, Z) substantially orthogonal to each other and a fourth axis rotating about 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 8 to 10, 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 8 to 11, 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 8 to 12, wherein the pulse of said at least one UV source (2) is adjusted, in luminous power and / or in pulse 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.

Images