FR3113860A1 - Ink drying process and associated system - Google Patents

Abstract

"Ink drying method and associated system" The invention relates to an ink drying method comprising a step of irradiating ink to be dried with at least one monochromatic electromagnetic radiation, emitted by an emission means , said method comprising modulating, over time and/or in space, a surface power density of the at least one monochromatic electromagnetic radiation. 2

Description

Ink drying process and related system

The present invention relates to the field of drying material on a substrate aimed at making the substrate functional or immobilizing the ink on the substrate.

The present invention relates, in particular, to the field of drying ink or material previously deposited on a substrate.

State of the prior art

Processes for drying inks by thermal drying using resistance heaters or infrared radiation are known in the state of the art. Although these processes make it possible to dry all types of inks, they are energy-intensive, slow, lead to significant heating of the entire production chain and do not make it possible to treat temperature-sensitive substrates.

In the state of the art, drying by UV annealing is known. These processes are limited to the use of inks containing agents capable of crosslinking. This type of process is described by document US2016/0083596. In addition, these processes are based on the emission of UV radiation which causes the deterioration of the inks.

In the state of the art, drying by photonic annealing is known. This type of process is described by the document US6889608. This process is suitable for most inks but requires the use of broad-spectrum lamps, typically between 350 and 700 nm, and high power. The high power lamps used consume a large amount of energy, are likely to deteriorate the inks to be dried and are complex to use. In addition, these processes deteriorate the substrates sensitive to temperature and/or having too much absorption in the emission range of the lamps such as polymeric substrates.

Near-infrared (NIR) radiation drying processes are also known in the state of the art. The lamps used emit broad-spectrum radiation typically between 250 and 3400 nm, with a minimum range necessarily between 600 and 1200 nm. Document EP3124261 illustrates this type of process. This process is suitable for most inks but also causes deterioration of fragile substrates and is also likely to deteriorate the inks used.

An object of the invention is in particular to propose a process:

- compatible with any type of ink, and/or
- compatible with any type of substrate, and/or

- which does not damage the inks to be dried or the substrate, and/or
- whose drying rate is compatible with industrial requirements, and/or
- which consumes as little energy as possible.

Presentation of the invention

To this end, an ink drying method is proposed comprising a step of irradiating the ink to be dried with at least one monochromatic electromagnetic radiation, emitted by an emission means.

Preferably, the method comprises:
- a modulation, over time and/or in space, of a power surface density of at least one monochromatic electromagnetic radiation, and/or
- an injection of a gas stream, by a gas injection means and/or a gas extraction, by a gas extraction means.

According to the invention, it is understood by monochromatic radiation whose half-height bandwidth, relative to a monochromatic reference value, is less than 10 nm.

The emitting means may include a light emitting diode (LED). Preferably, the transmission means comprises at least three LEDs.

The method according to the invention does not include a step of irradiating the ink to be dried with electromagnetic radiation having a bandwidth at mid-height greater than 10 nm.

Preferably, the irradiation of ink to be dried is carried out in an irradiation zone. The irradiation zone can be a volume of space or a surface.

Preferably, the power surface density of the at least one monochromatic electromagnetic radiation is modulated according to one, several or each of the inks to be dried. Preferably, the method comprises controlling the modulation of the power surface density of the at least one monochromatic electromagnetic radiation as a function of one, several or each of the inks to be dried.
Preferably, the power surface density of the at least one monochromatic electromagnetic radiation is modulated according to the nature of the ink, the type of ink or the chemical composition of the ink. Preferably again, the power surface density of the at least one monochromatic electromagnetic radiation is modulated according to the pigment(s) that the ink contains.

The at least one monochromatic electromagnetic radiation can be emitted by at least one LED.

Preferably, each monochromatic electromagnetic radiation among the at least one monochromatic electromagnetic radiation is emitted by a distinct LED.

The method can be implemented from ink comprising or not comprising an additional additive added specifically for drying, such as, for example, an organic or inorganic compound sensitive to at least one monochromatic electromagnetic radiation from the photoinitiator. Preferably, the process is implemented using ink that does not include any additional additive added specifically for drying

The method may or may not include an additive addition step. Preferably, the method does not include a step for adding an additive such as, for example, a photoinitiator.

Preferably, each ink to be dried is irradiated with two or more monochromatic electromagnetic radiations of different wavelengths.

Preferably, the method does not include irradiating radiation having a half-height emission spectral width greater than 50 nm, more preferably 25 nm, more preferably 10 nm.

Preferably, the method is intended for use on substrates sensitive to temperature and/or irradiation, such as, by way of example, substrates based on thermosensitive polymers, for example cellulose for paper and cardboard or polysulfones, polyimides, polyethylenes, polyamides, polypropylene, polyethylene, polyvinyl chloride, polybutadiene or polymethyl methacrylate, poly(ethylene terephthalate) and their derivatives.

According to the invention, it can be understood by ink:
- traditional inks for graphic printing or desktop publishing (so-called CMYK inks for cyan, magenta, yellow (yellow) and black (key) or UV curing inks),
- inks or pastes or a mixture of inks and/or pastes, called functional:
● conductive, by way of non-limiting example, containing metallic nanoparticles or microparticles or a mixture of the latter or metallic-organic decomposition inks (known as MOD types for Metal Organic Decomposition),
● semiconductors, by way of non-limiting example, containing semiconductor nanoparticles (such as zinc oxide (ZnO), azo particles (AZO), tin oxide (SnO)) ,
● conductive or semi-conductive polymers, by way of non-limiting example, PEDOT:PSS ((poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)), polyaniline, polypyrrole),
- pastes, by way of non-limiting example, aqueous CMYK pastes for screen printing or desktop publishing and crosslinking pastes,
- any composition, having a very low viscosity, of the order of 1 centipoise cP, to very high, of the order of 100,000 cP, and which may comprise organic and/or inorganic matter.

The step of modulating the power surface density of the at least one monochromatic electromagnetic radiation may comprise a variation:

- of an intensity of at least one monochromatic electromagnetic radiation, and/or
- A period during which the ink to be dried is exposed to at least one monochromatic electromagnetic radiation.

Ink to be dried may be irradiated by a single monochromatic electromagnetic radiation among the at least one monochromatic electromagnetic radiation.

The method may comprise a sequence, preferably temporal, of irradiation in which the ink to be dried is irradiated, concomitantly or successively, by at least two monochromatic electromagnetic radiation, among the at least one monochromatic electromagnetic radiation, from distinct wavelengths.

Preferably, the at least two monochromatic electromagnetic radiation of distinct wavelengths are emitted by two distinct LED means.

Preferably, the method comprises controlling the irradiation step according to a sequence in which at least two monochromatic electromagnetic radiation, among the at least one monochromatic electromagnetic radiation, of distinct wavelengths irradiate, concomitantly or successively , ink to dry.

The irradiation sequence can be a function, preferably determined according to the nature, the type of ink, the chemical composition or the pigment(s) that the ink contains

The method may comprise concomitantly or successively irradiating the same area of space or distinct areas of space with two or more monochromatic electromagnetic radiation, from among the at least one monochromatic electromagnetic radiation, of lengths d distinct waves.

Preferably, the space zone or zones are parts of the irradiation zone.

Preferably, the two or more electromagnetic radiations are emitted by two separate LEDs.

The injection of the gas flow can be implemented:
- upstream of a zone for irradiating the ink to be dried, called the irradiation zone, with respect to a direction for conveying the ink to be dried, and along the direction for conveying the ink to be dried, Or
- Downstream of the irradiation zone, relative to the direction of conveying the ink to be dried, and in a direction opposite to the direction of conveying the ink to be dried.

Preferably, the injection of the gas flow upstream of the irradiation zone and in the direction of conveying the ink to be dried is implemented prior to or concomitantly with the irradiation step.

Preferably, the injection of the gas flow upstream of the irradiation zone in a direction opposite to the conveying direction of the ink to be dried is implemented subsequently or concomitantly with the irradiation step.

It can be understood by injection, a projection of the flow of gas. Preferably, the flux is injected in the direction or parallel to the ink to be dried.

Preferably, the gas flow comes into contact with ink to be dried. Preferably, the gas flow is injected close to, for example at a distance of between 1 cm and 50 cm, the ink to be dried.

Gas extraction can be implemented:
- downstream of the irradiation zone, with respect to the direction of conveying the ink to be dried, the gas flow being injected upstream of the irradiation zone with respect to the direction of conveying the ink to to dry, or
- upstream of the irradiation zone, relative to the direction of conveying the ink to be dried, the gas flow being injected downstream of the irradiation zone, relative to the direction of conveying the ink to dry.

It can be understood by extraction, aspiration or gas pumping.

Preferably, the extraction of the gas is carried out near, for example at a distance of between 1 cm and 50 cm, from the ink to be dried.

The extracted gas may be identical or different, in whole or in part, from the gas constituting the gas stream injected.

The method may comprise the step of providing a drying channel, downstream or upstream of the irradiation zone with respect to the conveying direction of the ink to be dried, in which the ink to be dried is intended to pass. to dry and in which the atmosphere is regulated.

It can be understood by regulation of the atmosphere, a regulation of the temperature, of a water vapor content, of a nature of the gas or gases constituting the atmosphere, of a pressure, of a regulation of a flow of gas constituting the injected gas flow, a regulation of a gas pumping flow.

According to the process:
- the injection of the gas flow is carried out downstream, or respectively upstream, of the drying channel, with respect to the conveying direction of the ink to be dried, and in the direction opposite to, or respectively in the same direction that, the conveying direction of the ink to be dried, and/or
- the gas extraction is carried out:
● upstream of the irradiation zone, relative to the direction of conveyance of the ink to be dried, the gas flow being injected downstream of the drying channel, relative to the direction of conveyance of the ink to be dried , or respectively
● downstream of the drying channel, with respect to the direction of conveyance of the ink to be dried, the gas flow being injected upstream of the irradiation zone with respect to the direction of conveyance of the ink to be dried.

The gas flow injected may include:

- a gas whose water vapor content is lower than a water vapor content of a gas surrounding the ink(s) to be dried, and/or
- a gas whose temperature is above 30°C.

It can be understood by surrounding gas, one or more gases close to the ink or inks to be dried, that is to say in direct contact or at a distance of less than 1 meter from the ink or inks to be dried. to dry. Preferably, the surrounding gas or gases are located in the irradiation zone and/or in the channel and/or in the ambient air.

The method may comprise irradiation of at least two distinct zones of space, each of the at least two zones of space being irradiated by the at least one monochromatic electromagnetic radiation or by two distinct electromagnetic radiations of the same length of wave among the at least one monochromatic electromagnetic radiation.

Preferably, the two electromagnetic radiations are emitted by two separate LEDs.

The method may include emitting two or more monochromatic electromagnetic radiation, of the at least one monochromatic electromagnetic radiation, at distinct positions in space.

The two or more monochromatic electromagnetic rays emitted at distinct positions in space can be:
- the at least two monochromatic electromagnetic rays of predetermined wavelengths intended to irradiate the given ink(s) to be dried, and/or
- the at least two monochromatic electromagnetic radiation of distinct wavelengths.

Preferably, the two or more monochromatic electromagnetic radiations of the same wavelength are emitted by two distinct LEDs arranged in distinct positions in space.

Preferably, at least one monochromatic electromagnetic radiation, among the two or more monochromatic electromagnetic radiations, has a wavelength greater than 600, preferably greater than 650 nm, more preferably greater than 700 nm.

The at least one monochromatic electromagnetic radiation, preferably each of the at least one monochromatic electromagnetic radiation, may have a wavelength less than 1400 nm.

Each of the at least one monochromatic electromagnetic radiation may have a wavelength greater than 250 nm, preferably greater than 300 nm, more preferably greater than 350 nm. Each of the at least one monochromatic electromagnetic radiation may have a wavelength greater than 400 nm.

According to the invention, there is also proposed an ink drying system comprising:
- an emission means arranged to emit, preferably in an ink irradiation zone to be dried, at least one monochromatic electromagnetic radiation,
- A control unit arranged to control the emission of the at least one monochromatic electromagnetic radiation by the emission means.

Preferably:
- the emission means comprises at least three LEDs arranged, preferably spatially arranged, to each emit monochromatic electromagnetic radiation and to form:
● at least one network of contiguous LEDs comprising:
▪ at least one succession or series of LEDs, among the at least three LEDs of the system, extending along a first direction; at least two LEDs among the succession of LEDs extending along the first direction emit monochromatic electromagnetic radiation of distinct wavelength, and/or
▪ at least one succession of LEDs extending along a direction different from the first direction, called the second direction; at least two LEDs among the succession of LEDs extending along the second direction emit monochromatic electromagnetic radiation of distinct wavelength, and/or
▪ at least two sub-arrays, preferably contiguous, of contiguous LEDs each comprising at least three LEDs and extending along the first and second directions; at least two LEDs among the at least three LEDs of each of the at least two sub-arrays emit monochromatic electromagnetic radiation of distinct wavelength, and/or
● at least three networks of contiguous LEDs each being arranged relative to a collimator so that the monochromatic electromagnetic radiation emitted by the LEDs of each of the at least three networks are emitted in the direction of the collimator and form, at the output of the collimator, a beam of single irradiation comprising the monochromatic electromagnetic radiation from the LEDs of each of the at least three networks.

It can be understood by "the second direction extends along, or according to, a direction different from the first direction", the fact that the first direction and the second direction form a non-zero angle, preferably an angle of 45°, more preferably an angle of 90°, between them.

Preferably, the control unit is arranged for:
● modulating a power surface density of at least one of the monochromatic electromagnetic radiation emitted by at least one LED of the system, among at least three LEDs of the emission means being arranged, preferably spatially arranged, to each emit monochromatic electromagnetic radiation , and or
● applying an irradiation sequence in which the ink to be dried is irradiated, concomitantly and/or successively, by at least one LED among the at least three LEDs of the system each emitting monochromatic electromagnetic radiation of wavelengths distinct.

Preferably, the at least three LEDs of the system constitute the means of transmission.

Preferably, the control unit is arranged to control each of the emissions from each of the at least three LEDs of the system.

The control unit may be a processing unit.

It can be understood by network, a matrix. The network can be 2D, preferably extending along a surface, or 3D.

It can be understood as contiguous, adjacent or adjoining.

Preferably, the first direction extends along a path, a trajectory, a direction or a direction of conveying the ink in the system.

It can be understood by "at least two LEDs among the succession of LEDs extending along the first direction, or respectively the second direction, emitting monochromatic electromagnetic radiation of distinct wavelength", the fact that at least one LED among the succession of LEDs extending along the first direction, or respectively the second direction, emits monochromatic radiation of wavelength different from the wavelength of the monochromatic radiation emitted by at least one other LED among the succession of LEDs extending along the first direction, or respectively the second direction.

Preferably, the at least two sub-arrays of contiguous LEDs form the at least one array of contiguous LEDs. Thus, at least one LED from one of the sub-networks can be contiguous with at least one LED from another of the sub-networks.

Preferably, the LEDs of one network are not contiguous with any LEDs of any other network.

Preferably, the drying system includes the collimator.

Preferably, one or more of the at least three LEDs is arranged to emit monochromatic electromagnetic radiation with a wavelength greater than 700 nm.

Preferably, the LEDs have a surface power density of between 0.5 W/cm² and 20 W/cm².

The drying system may comprise means for injecting a flow of gas arranged to inject said flow of gas:
- upstream of a zone for irradiating the ink to be dried, called the irradiation zone, with respect to a direction for conveying the ink to be dried, and along the direction for conveying the ink to be dried, Or
- Downstream of the irradiation zone, relative to the direction of conveying the ink to be dried, and in a direction opposite to the direction of conveying the ink to be dried.

The drying system may comprise a gas extraction means arranged to extract gas:
- downstream of the irradiation zone, with respect to the direction of conveying the ink to be dried, the gas flow being injected upstream of the irradiation zone with respect to the direction of conveying the ink to to dry, or
- upstream of the irradiation zone, relative to the direction of conveying the ink to be dried, the gas flow being injected downstream of the irradiation zone, relative to the direction of conveying the ink to dry.

The drying system may comprise a drying channel disposed, preferably, downstream or upstream of the irradiation zone with respect to the conveying direction of the ink to be dried, in which the ink to be dried is intended to pass. to dry.

The drying channel may comprise means for regulating the atmosphere of the drying channel. The means for regulating the atmosphere of the drying channel can be arranged outside or inside the drying channel.

The drying channel can be arranged downstream or upstream of the irradiation zone with respect to the conveying direction of the ink to be dried.

It can be heard by channel, a conduit. The channel may include walls.

The channel may include an opening, called the upstream opening, through which the ink to be dried is intended to enter the channel and an opening, called the downstream opening, through which the ink to be dried is intended to exit the conduit.

The channel can be an enclosure comprising the upstream opening and the downstream opening.

The gas flow injection means, or the gas flow injection means and the gas extraction means, may be arranged to regulate the atmosphere within the drying channel.

The means for injecting the gas stream or the means for injecting the gas stream and the means for extracting gas can be the means for regulating, arranged outside the drying channel, the atmosphere of the channel of drying.

Use of the drying system according to the invention to implement the drying process according to the invention.

Preferably, the drying system according to the invention is arranged to implement the drying method according to the invention.

Preferably, the drying system according to the invention is arranged to implement the drying process according to the invention.

Preferably, the drying process according to the invention is implemented by the drying system according to the invention.

Description of figures

Other advantages and particularities of the invention will appear on reading the detailed description of implementations and non-limiting embodiments, and of the following appended drawings:

FIGURE 1 illustrates the modulation of the power surface density of the at least one monochromatic electromagnetic radiation by varying the pulse duration of the at least one monochromatic radiation during which ink to be dried is exposed to the at least one monochromatic electromagnetic radiation,

. FIGURE 2 illustrates the control of the modulation of the power surface density of monochromatic electromagnetic radiation emitted, in several spectral domains, by the LEDs individually and/or by group of LEDs,

FIGURE 3 is a graph depicting an irradiation spectrum comprising a set of monochromatic wavelengths used for drying aqueous CMYK organic chilli inks,

FIGURES 4a, 4b, 4c and 4d illustrate schematic representations of networks and sub-networks of contiguous LEDs spatially arranged in the form of matrices,

FIGURE 5 is a schematic representation of arrays of LEDs and a collimator arranged to generate a single irradiation beam comprising the monochromatic electromagnetic radiation from the LEDs of each of the at least three arrays,

FIGURE 6 is a schematic representation of the drying system comprising an emission means, a gas injection means and a gas extraction means,

FIGURE 7 is a schematic representation of the drying system of FIGURE 6 further comprising a drying channel,

FIGURE 8 illustrates the relative humidity and temperature control of an ambient gas intended to be injected into the drying system.

The embodiments described below being in no way limiting, variants of the invention may in particular be considered comprising only a selection of characteristics described, isolated from the other characteristics described (even if this selection is isolated within a sentence including these other features), if this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the state of the prior art. This selection includes at least one feature, preferably functional without structural details, or with only part of the structural details if only this part is sufficient to confer a technical advantage or to differentiate the invention from the state of the prior art .

The various results presented below were produced on a KELENN Technology brand R2R (Roll to Roll) printer with an inkjet print engine equipped with an inkjet module with a resolution of 1200 dpi or 600 dpi. The printed patterns corresponded to flat areas of the different CMYK colors.

Siegwerk commercial aqueous CMYK ink with organic pigments, Sun Chemical commercial aqueous CMYK ink with inorganic pigments and Kao Collins commercial aqueous CMYK ink with organic dyes (dye) were used.

The prints were made on two types of substrate: Polyethylene terephthalate (PET) and paper.

Print speeds range from 5 meters per minute (m/min) to 200 m/min. According to the embodiment, the various drying devices, called dryers, tested are integrated after the KEOS print engine and before the first wrapper roll before the substrate (PET or paper) is rewound on the winder. The distance between the print engine and the first wrap roller is 120 cm.

Drying was assessed and verified as follows:
- after printing and drying, the quality of the drying is visualized by passing a finger over the printed part; if ink is transferred to the substrate out of the printed pattern with presence on the finger, the ink is deemed not to have dried,
- if ink is transferred to the first wrap roller and to the following rollers (rewinder rollers), then the ink is considered not dry.

As a preamble, the drying process described in the patent documents EP3124261 and US6889608 were implemented and the drying verified.

In accordance with the process described by document EP3124261, a dryer comprising water-cooled LEDs, of the Phoseon brand, emitting at 395 nm and having a surface power density of 20 W/cm² was placed after the print engine. The LEDs were used at 50% and 100% of their power. All tests showed that illuminated inks, regardless of color and exposure time, did not dry out.

In accordance with the process described by document US6889608, a dryer comprising three LASER diodes of the "ThorLabs" brand cooled by a water system and emitting at 405 nm with a surface power density of 31.8 W/cm², at 450 nm with a pfd of 50.93 W/cm² and at 520 nm with a pfd of 50.92 W/cm². The three diodes were used at 50% and 100% of their power. All tests showed that illuminated inks, regardless of color and exposure time, did not dry out.

It is only by adding in the dryer, in addition to the LEDs, an infrared lamp of the "Adphos" brand with a power density of approximately 11 W/cm² emitting a range of wavelengths between 780 and 3000 nm that drying of the illuminated inks was observed. The use of this type of lamp is known in the state of the art and described in the document EP3124261. However, the use of a dryer comprising such an infrared lamp has systematically degraded the substrate by deforming it, burning it and/or piercing it.

Also, in order to overcome the shortcomings and drawbacks of existing methods, and with reference to FIGURES 1 to 5, there is presented an ink drying method comprising a step of irradiating ink to be dried with at least one monochromatic electromagnetic radiation emitted by an emission means 2 of an ink drying system 1. According to the embodiment, the emission means 2 can be one or a set of LEDs 3. The method comprises a modulation, during the time and/or in space, of a power surface density of the at least one monochromatic electromagnetic radiation. The at least one monochromatic electromagnetic radiation has a wavelength less than 1400 nm. With reference to FIGURE 3, the ink drying system 1 is presented which comprises an emission means comprising at least three LEDs 3 arranged to each emit monochromatic electromagnetic radiation. The ink drying system 1 also comprises a control unit (not shown) arranged to modulate a power surface density of at least one of the monochromatic electromagnetic radiation emitted by at least one of the LEDs 3 of the system 1.

The drying system comprises a belt conveyor 4 on which the substrate is intended to rest. The substrate is thus mobile in the drying system 1.

The LEDs 3 used are power LEDs or laser diodes cooled by a water system and emitting between 245 nm and 1400 nm with a surface power density of between 0.5 and 50 W/cm². The minimum power areal density is 0.5 W/cm².

With reference to FIGURE 1, there is illustrated the modulation of the surface power density by variation of a time during which the ink to be dried is exposed to at least one monochromatic electromagnetic radiation. It is, in practice, the variation of the duration of a pulse of at least one monochromatic radiation. The use of pulses 32 of high instantaneous intensity but over short times makes it possible to reduce the average intensity emitted, and therefore the surface power density 31, and therefore to limit the heating of the substrate (and therefore its degradation) while maintaining good ink drying quality. For example, the surface power density 31 can be 10 W/cm² for a pulse duration 32 of 100 milliseconds. This corresponds to a surface energy density of 20 J/cm².

For example, it is possible to modulate the surface power density 31 by varying the number of pulses 32, the duration of the pulses and/or the (rest) time 33 between two pulses. The time 33 between two pulses is, for example, 100 milliseconds.

FIGURE 2 illustrates the spatial modulation (in several spatial zones along the path of the ink (or the path of the substrate on which the ink is intended to be deposited) and temporal (concomitant or successive irradiation):
- the surface density of a monochromatic beam emitted by an LED 3 or of monochromatic beams emitted by a set of LEDs 3, and
- the irradiation of the zones of space by the monochromatic beams emitted by the at least three LEDs 3. The zones of space are zones, for example contiguous and successive, distributed along the direction 5 of conveying of the ink.
In particular, the method comprises the concomitant and successive irradiation:
- of the same zone of space with several monochromatic radiations of distinct lengths, and
- several areas of space with several monochromatic rays of distinct lengths.
Preferably, the at least three LEDs 3 are arranged so that at least one LED 3 emits in the UV, at least one LED 3 emits in the visible and at least one LED 3 emits in the infrared or the near infrared. .

With reference to FIGURES 2 to 4, the method comprises irradiation of at least two distinct zones of space, each of the at least two zones of space being irradiated by two distinct electromagnetic radiations of the same wavelength.

The method also comprises irradiating the same area of space with at least two monochromatic electromagnetic radiation of distinct wavelengths. Depending on the composition and the number of pigments contained in the ink to be dried and the pattern deposited on the substrate, the irradiation, by the at least two monochromatic rays of distinct wavelengths, of the same zone of space is carried out concurrently or successively.

FIGURE 3 illustrates an example of an irradiation spectrum of ink to be dried. Such an irradiation spectrum is particularly suitable for aqueous inks CMYK with organic pepper. The set or group of monochromatic rays used, as illustrated in Figure 3, is suitable for the majority of inks. This group includes the following monochromatic wavelengths:
● for the UV zone, LEDs emitting at 300 nm, 365 nm, 385 nm or 395 nm,
● for the visible zone of the LEDs emitting at:
◦ the violet/blue range 405 nm, 455 nm,
◦ the 528 nm green range,
◦ the red range 620 nm, 656 nm, 730 nm,
● for the NIR zone of LEDs emitting at 850 nm, 940 nm, 1050 nm, 1150-1200 nm.

Depending on the type of ink or materials to be dried, different combinations can be used.

For aqueous CMYK inks with organic, inorganic or dye pigments, the combinations by way of non-limiting example which can be used are:
● for Cyan: UV (385 nm), visible red (620 nm) and NIR (850 nm),
● for Yellow: UV (385 nm), visible blue (453 nm) and NIR (850 nm),
● for Magenta: UV (385 nm), visible green (528 nm) and NIR (850 nm),
● for Black: UV (385 nm) and NIR (850 nm).

For metallic screen printing pastes or inks based on metallic nanoparticles which can be, by way of non-limiting example, based on copper silver or their alloys, the combinations by way of non-limiting example which can be used are:
● 840nm,
●940nm,
● 840 and 940 nm.

The ratios between the intensities can be modulated according to the type of ink to be dried. Monochromatic radiation can be emitted simultaneously and/or sequentially in space and time. They are preferably emitted sequentially in space (see FIGURE 4).

With reference to FIGURES 3 and 4, an irradiation sequence is illustrated in which ink to be dried is irradiated by at least two monochromatic electromagnetic radiation of distinct wavelengths.

FIGURE 4 illustrates examples of networks 6 of contiguous LEDs 3 spatially arranged in the form of matrices 6. The transmission means 2 comprises a single network 6 or several networks 6, for example a succession of networks 6 along the direction 5 conveying the ink to dry.

With reference to FIGURE 4, the ink to be dried is irradiated, depending on the composition and the number of pigments contained in the ink to be dried and according to the pattern deposited, concomitantly or successively by at least two monochromatic electromagnetic rays.

Depending on the composition and the number of pigments contained in the ink to be dried and according to the pattern deposited, the modulation of the surface power density comprises one or more successive pulses of at least one monochromatic electromagnetic radiation. Referring to FIGURE 4d, the power flux density modulation comprises one or more successive pulses of monochromatic electromagnetic radiation of the same wavelength. With reference to FIGURES 4a, 4b and 4c, the modulation of the surface power density comprises one or more successive pulses of monochromatic electromagnetic radiation of different wavelengths.

The at least three LEDs 3 of the ink drying system 1 are arranged to form at least one network 6 of contiguous LEDs 3. The network 7 of LEDs 3 comprises at least a succession of LEDs 3 extending along a first direction 5. At least two LEDs 3 among the succession of LEDs 3 extending along the first direction 5 emit monochromatic electromagnetic radiation of length d distinct wave.

The at least three LEDs 3 of the ink drying system 1 are arranged to form at least a succession of LEDs 3 extending along a direction different from the first direction 5, called the second direction.

At least two LEDs 3 among the succession of LEDs 3 extending along the second direction emit monochromatic electromagnetic radiation of distinct wavelength.

Referring to FIGURE 4d, the at least three LEDs 3 of the ink drying system 1 are arranged to form at least two contiguous sub-arrays 7 of contiguous LEDs each comprising at least three LEDs 3 and extending along the first 5 and second directions. At least two LEDs 3 among the at least three LEDs 3 of each of the at least two sub-arrays 7 emit monochromatic electromagnetic radiation of distinct wavelength. According to the embodiment, each of the LEDs 3 of the at least two sub-arrays 7 emit monochromatic radiation of distinct wavelength.

In particular, FIGURE 4 illustrates four examples of spatial arrangement of LEDs 3 to achieve efficient drying. The at least three LEDs 3 are arranged to form a succession of LEDs extending along a direction forming an angle of 45° with respect to the first direction 5 and a succession of LEDs extending along a direction forming an angle of 90° with respect to the first direction.

The LEDs 3 are spatially arranged in a sequence (chain or succession) so that two successive contiguous LEDs 3, in the direction 5 of conveying the ink to be dried, emit monochromatic radiation of distinct wavelengths. In FIGURES 4a and 4b, the drying device comprises rows of LEDs 3 extending in the direction perpendicular to the ink conveying direction 5 which emit monochromatic radiation of identical wavelength, for example simultaneously. With reference to FIGURES 4c and 4d, the LEDs 3 are spatially arranged in a sequence so that two successive contiguous LEDs 3, in the direction perpendicular to the ink conveying direction 5, emit monochromatic radiation of wavelength distinct, for example simultaneously.

With reference to FIGURES 4a, 4b and 4c, the LEDs are arranged in sub-arrays 7 (in the form of columns) extending along the ink conveying direction 5 and are distributed according to a given sequence. For example, the LEDs of a sub-array 7 (that is to say a succession of LEDs, in the form of lines, extending along the ink conveying direction 5) emit their monochromatic radiation successively after the others so as to irradiate the ink to be dried in a particular sequence.

Referring to FIGURE 4d, the LEDs are arranged in 7-square subarrays. The LEDs of the same sub-network 7 emit simultaneously. The sub-networks 7 of the same line (extending in the direction perpendicular to the ink conveying direction 5) emit their monochromatic radiations simultaneously. The sub-arrays 7 of the same column (extending along the ink conveying direction 5) emit their monochromatic radiation successively one after the other so as to irradiate the ink to be dried in a particular sequence.

Referring to FIGURE 5, each of the at least three networks 6 of contiguous LEDs 3, three networks 6 according to the embodiment, is arranged relative to a collimator 8, a cross prism 8 according to the invention, so that the monochromatic electromagnetic radiation emitted by the LEDs 3 of each of the three arrays 6 are emitted in the direction of the collimator 8. The monochromatic radiation emitted by the LEDs 3 of the three arrays 6 of LEDs form, at the output of the collimator 8, an irradiation beam single 9 comprising the monochromatic rays of the LEDs 3 of each of the at least three networks 6.

Referring to FIGURE 6, the drying process comprises an injection of the gas flow 10, by the gas injection means 11 arranged to inject the gas flow 10, downstream of the irradiation zone 12, relative to the direction 5 of conveying the ink to be dried, and in a direction opposite to the direction 5 of conveying the ink to be dried.

The method also comprises gas extraction, by gas pumping system 13, typically a primary vacuum pump 13, upstream of the irradiation zone 12, with respect to the direction 5 of conveying the ink to be dried.

The gas flow injected is between 30 m3/h and 600 m3/h. The extraction rate is defined in relation to the injection rate, it is preferably identical to the injection rate.

This configuration improves drying and drying speed. This configuration also avoids the accumulation of solvent vapors in the drying system. This configuration also makes it possible to avoid the condensation of solvent vapors in the drying system, and in particular on the LEDs 3 and on the substrate.

With reference to FIGURE 7, the system comprising a drying channel 14 arranged downstream of the irradiation zone 12 with respect to the direction 5 of conveying the ink to be dried, in which the ink to be dried is intended to pass. to dry. According to the embodiment, the drying system 1 comprises a cover 15 disposed relative to the conveying means 4 (belt conveyor 4) so as to form the drying channel 14.

The injection of the gas flow 10 is carried out downstream of the drying channel 14, relative to the direction 5 of conveying the ink to be dried, and in the direction opposite to the direction 5 of conveying the ink to be dried. . In a complementary or alternative manner, the gas extraction 13 is carried out upstream of the irradiation zone 12, with respect to the direction 5 of conveying the ink to be dried, the flow of gas 10 being injected downstream of the channel drying 14, relative to the direction 5 of conveying the ink to be dried.

The drying channel 14 improves drying and drying speed. The association of the channel 14 with the gas injection means 11 and/or with the gas extraction means 14 makes it possible to improve the drying and the drying speed even more significantly.

Referring to FIGURE 8, there is presented a system 16, called regulator 16, for regulating the physico-chemical properties of the gas intended to be injected 10 into the drying system 1. The regulator 16 comprises an element for regulating the humidity 17, such as a dehydrator, for example absorption, and a gas heating element 18. The regulator 16 also includes temperature 19 and humidity 20 sensors.

The regulator 16 comprises a control unit (not shown) arranged to regulate the temperature and the water vapor content of the surrounding gas, from the data measured by the sensors 19, 20, so that the gas injected 10 into the drying system 1 has:
- a regulated water vapor content lower than a water vapor content of a gas surrounding 22 the ink(s) to be dried, and
- additionally or alternatively, a regulated temperature above 30°C.

According to the embodiment, the surrounding gas 22 is ambient gas 22 under atmospheric conditions. The temperature of the injected gas 10 is 70°C. The relative humidity of the injected gas 10 is less than 10%. Preferably, the relative humidity of the injected gas 10 is equal to 0%. Preferably, the water vapor concentration of the injected gas 10 is less than 5 g/m ³ , preferably of the order of 2 g/m ³ .

The regulation of the moisture content in the injected gas 10 makes it possible to improve the drying and the speed of drying.

Of course, the invention is not limited to the examples which have just been described and many adjustments can be made to these examples without departing from the scope of the invention.

Thus, in combinable variants of the embodiments previously described:
- in a complementary or alternative manner, the modulation of the power surface density of the at least one monochromatic electromagnetic radiation comprises:
● a variation in the intensity of the at least one monochromatic electromagnetic radiation emitted, and/or
● an intensity gradient of at least one monochromatic electromagnetic radiation, and/or
- the method comprises the irradiation of at least two distinct zones of space, each of the at least two zones of space being irradiated by the at least one monochromatic electromagnetic radiation, and/or
- in a complementary way, space zones can also be distributed along the direction perpendicular to the ink conveying direction 5 and/or along the direction forming an angle of 45° with respect to the direction 5 conveying, and/or
- the injection of a gas flow 10 is carried out by a gas injection means 11 arranged to inject the gas flow 10 upstream of the irradiation zone 12 of the ink to be dried with respect to the direction 5 for conveying the ink to be dried, and in the direction 5 for conveying the ink to be dried., and/or
- the gas extraction 13 is carried out by a gas extraction means 14 arranged to extract gas 13 downstream of the irradiation zone 12, with respect to the direction 5 of conveying the ink to be dried, the flow of gas 10 being injected upstream of the irradiation zone 12 with respect to the direction 5 of conveying the ink to be dried, and/or
- the injection of the gas flow 10 is carried out upstream of the drying channel 14, with respect to the direction 5 of conveying the ink to be dried, and in the same direction as the direction 5 of conveying the ink to to dry and/or the extraction of gas 13 is carried out downstream of the drying channel 14, with respect to the direction 5 of conveying the ink to be dried, the flow of gas 10 being injected upstream of the irradiation zone 12 with respect to the direction 5 of conveying the ink to be dried, and/or
- the drying system 1 comprises a drying channel 14 arranged upstream of the irradiation zone 12 with respect to the direction 5 of conveying the ink to be dried, and/or
- the drying channel 14 comprises means for regulating the atmosphere inside the drying channel 14, and/or
- the regulator 16 constitutes the means for regulating the atmosphere arranged inside the drying channel 14, and/or
- The drying channel 14 is arranged upstream of the irradiation zone 12 with respect to the direction 5 of conveying the ink to be dried.

In addition, the different features, forms, variants and embodiments of the invention may be associated with each other in various combinations insofar as they are not incompatible or exclusive of each other.

Claims (17)

Process for drying ink comprising a step of irradiating ink to be dried with at least one monochromatic electromagnetic radiation, emitted by an emission means, said process comprising modulation, over time and/or in space , with a power surface density of at least one monochromatic electromagnetic radiation. Method according to claim 1, in which the modulation of the power surface density of the at least one monochromatic electromagnetic radiation comprises a variation:
- of an intensity of at least one monochromatic electromagnetic radiation, and/or
- A period during which the ink to be dried is exposed to at least one monochromatic electromagnetic radiation. A method according to claim 1 or 2, wherein modulating the power flux-density comprises:
- an intensity gradient of at least one monochromatic electromagnetic radiation, and/or
- One or more successive pulses of at least one monochromatic electromagnetic radiation. Method according to any one of the preceding claims, comprising an irradiation sequence in which the ink to be dried is irradiated, concomitantly and/or successively, by at least two monochromatic electromagnetic rays of distinct wavelengths. Method according to any one of the preceding claims, comprising concomitantly or successively irradiating the same area of space with at least two monochromatic electromagnetic radiation of distinct wavelengths. A method according to any preceding claim, comprising injection of a gas stream, by gas injection means:
- upstream of a zone for irradiating the ink to be dried, called the irradiation zone, with respect to a direction for conveying the ink to be dried, and along the direction for conveying the ink to be dried, Or
- Downstream of the irradiation zone, relative to the direction of conveying the ink to be dried, and in a direction opposite to the direction of conveying the ink to be dried. Process according to the preceding claim, comprising an extraction of gas, by means of gas extraction:
- downstream of the irradiation zone, with respect to the direction of conveying the ink to be dried, the gas flow being injected upstream of the irradiation zone with respect to the direction of conveying the ink to to dry, or
- upstream of the irradiation zone, relative to the direction of conveying the ink to be dried, the gas flow being injected downstream of the irradiation zone, relative to the direction of conveying the ink to dry. A method according to any preceding claim, comprising the step of providing a drying channel, downstream or upstream of the irradiation zone with respect to the conveying direction of the ink to be dried, in which is intended to convey the ink to be dried and in which the atmosphere is regulated. Process according to the preceding claim, in which:
- the injection of the gas flow is carried out downstream, or respectively upstream, of the drying channel, with respect to the conveying direction of the ink to be dried, and in the direction opposite to, or respectively in the same direction that, the conveying direction of the ink to be dried, and/or
- the gas extraction is carried out:
● upstream of the irradiation zone, relative to the direction of conveyance of the ink to be dried, the gas flow being injected downstream of the drying channel, relative to the direction of conveyance of the ink to be dried , or respectively
● downstream of the drying channel, with respect to the direction of conveyance of the ink to be dried, the gas flow being injected upstream of the irradiation zone with respect to the direction of conveyance of the ink to be dried. A method according to any of claims 6 to 9, wherein the injected gas stream comprises:
- a gas whose water vapor content is lower than a water vapor content of a gas surrounding the ink(s) to be dried, and/or
- a gas whose temperature is above 30°C. Method according to any one of the preceding claims, comprising irradiating at least two distinct zones of space, each of the at least two zones of space being irradiated by the at least one monochromatic electromagnetic radiation or by two distinct electromagnetic fields of the same wavelength. A method according to any preceding claim, wherein the at least one monochromatic electromagnetic radiation has a wavelength below 1400 nm. Ink drying system including:
- at least three light-emitting diodes (LEDs) arranged to each emit monochromatic electromagnetic radiation,
- A control unit arranged to modulate a power surface density of at least one of the monochromatic electromagnetic radiation emitted by at least one of the LEDs of the system. An ink drying system according to claim 13, wherein the at least three LEDs are arranged to form:
- at least one network of contiguous LEDs comprising:
● at least one succession of LEDs extending along a first direction; at least two LEDs among the succession of LEDs extending along the first direction emit monochromatic electromagnetic radiation of distinct wavelength, and/or
● at least one succession of LEDs extending along a direction different from the first direction, called the second direction; at least two LEDs among the succession of LEDs extending along the second direction emit monochromatic electromagnetic radiation of distinct wavelength, and/or
● at least two sub-arrays of contiguous LEDs each comprising at least three LEDs and extending along the first and second directions; at least two LEDs among the at least three LEDs of each of the at least two sub-arrays emit monochromatic electromagnetic radiation of distinct wavelength, and/or
- at least three networks of contiguous LEDs each being arranged relative to a collimator so that the monochromatic electromagnetic radiation emitted by the LEDs of each of the at least three networks are emitted in the direction of the collimator and form, at the output of the collimator, a beam of single irradiation comprising the monochromatic electromagnetic radiation from the LEDs of each of the at least three networks. An ink drying system according to claim 13 or 14, comprising gas flow injection means arranged to inject said gas flow:
- upstream of a zone for irradiating the ink to be dried, called the irradiation zone, with respect to a direction for conveying the ink to be dried, and along the direction for conveying the ink to be dried, Or
- Downstream of the irradiation zone, relative to the direction of conveying the ink to be dried, and in a direction opposite to the direction of conveying the ink to be dried. An ink drying system according to any of claims 13 to 15, comprising gas extraction means arranged to extract gas:
- downstream of the irradiation zone, with respect to the direction of conveying the ink to be dried, the gas flow being injected upstream of the irradiation zone with respect to the direction of conveying the ink to to dry, or
- upstream of the irradiation zone, relative to the direction of conveying the ink to be dried, the gas flow being injected downstream of the irradiation zone, relative to the direction of conveying the ink to dry. An ink drying system according to any one of claims 13 to 16, comprising a drying channel arranged downstream or upstream of the irradiation zone with respect to the conveying direction of the ink to be dried, in which is intended to transit the ink to dry.