PRINTING PRIMER COMPOSITION FOR CONDITIONING SUBSTRATES - Patent application

Abstract

The present disclosure relates to a primer composition for improving the ink receptivity of a polymer surface. More specifically, the primer composition comprises a first polymer binder component A having a first polar contribution pc1 of less than 20%; a second component B comprising inorganic particles B' and / or a second polymer binder component B", where the polymer binder component B" has a second polar contribution pc2 of equal to or greater than 20%; the amount of A, B', and / or B", if present, is such that B' / (A+B"+B') is less than 15%, based on the dry weight of the composition; the first polar contribution pc1 and the second polar contribution pc2 are determined by using the Owens-Wendt-Rabel-Kaelble method using 6 gsm dry layers of components A and B, respectively.

Description

Detailed Description of the Invention

[0001]

[0001] The present invention relates to the technical field of digital printing on paper or polymeric film substrates with water-based inks. It should be noted that the paper or polymeric film substrate may be part of a cardboard, a label, a laminate, etc. More particularly, the present invention relates to the use of a printing primer composition to improve the ink receptivity of the substrate to improve print quality.

[0002]

[0002] Substrates such as paper or polymer films are already used in the printing industry. However, many of the paper substrates are endowed with certain properties, such as water resistance or repellency, ink retention, smoothness, gloss, etc. Unfortunately, this often makes it more difficult for water-based inks to spread sufficiently and thereby achieve good print quality in industrial single-pass printing. Similarly, when printing flat untreated polymer films with water-based inks, poor ink wetting is often observed.

[0003]

[0003] Ink wetting is commonly referred to as "dot gain" in inkjet printing. Insufficient dot gain results in white voids between the dots (or streaks in single pass printing), resulting in reduced color strength, also known as optical density.

[0004]

[0004] With regard to paper substrates, the most problematic for achieving good print quality with water-based inkjet inks is coated paper substrates, because the ink droplet absorption by coated paper substrates is very limited. Normally, the ink absorption by the paper is one of the main factors that causes the ink to spread. Apparently, flat polymer films may not even have any absorption at all.

[0005]

[0005] The lack of ink absorption in coated papers and polymeric films can also lead to other image defects: in fact, the wet ink layer is susceptible to the formation of "mottle" or "intercolor bleed" if the ink does not dry quickly enough.

[0006]

[0006] One way to deal with the complexities of coated substrates is to adapt the ink based on the type of coating. However, an inkjet ink formulation may work well on one substrate but not on another. Thus, to achieve the same image quality on multiple substrate types, the ink composition may need to be adjusted significantly. However, changing inks on industrial digital presses is very time-consuming, dramatically reducing the advantages of digital over analog printing. Moreover, fine-tuning the ink formulation is far from trivial in terms of maintaining optimal jetting behavior (surface tension, viscosity, particle size) and good storage stability.

[0007]

[0007] Another method used in industrial printing is the use of primers to enhance the imaging properties of the ink on these various types of substrates, such as color strength (optical density), adhesion, image sharpness, etc.

[0008]

[0008] A first known primer type (US8562126B1) contains a "flocculant" or "aggregating agent" such as a polyvalent metal salt, an acidic compound or a cationic polymer in combination with a polymeric binder such as an acrylate or polyurethane. However, such "flocculant primers" have the drawback that when the ink comes into contact with the flocculant, the liquid viscosity increases rapidly, which makes the ink spreading very easy when the ink viscosity is still low, thus reducing the dot gain of the deposited ink droplets. This is even more true when this type of primer is used on coated paper or film substrates that have limited or no porosity and where only surface tension effects act as the driving force for the ink spreading.

[0009] Another drawback of such "flocculant primers" is related to what we call "misting" during primer laydown, i.e. fine mist particles can form during primer laydown. This problem can occur in analog flood coating stations, but is even more relevant when the primer itself is applied by inkjet printing. Indeed, if the primer is not applied beforehand or in a separate priming unit, but inline, said mist particles can reach the nozzle plate of other inkjet printing stations and cause irreversible nozzle clogging due to the destruction of anionically stabilized ink components such as pigments or binders due to the presence of flocculants such as polyvalent metal salts, cationic polymers or organic acids.

[0010] A final drawback of having a flocculant in the primer is that anionic binders cannot be used, as the binder's dispersion stability or solubility is compromised. Thus, primers containing such flocculants can only be combined with cationic or nonionic polymeric binders. Most commercially available binders are anionically stabilized / solubilized, so the choice of suitable primers is very limited.

[0011]

[0009] A second known primer type (EP 2332734 B1) is a porous ink-receptive coating composition containing monodisperse, spherical cationic colloidal silica particles having an average particle size of 30 nm to 60 nm.

[0012] The drawback of this technology is the complex laydown method and expense of such primer coatings. To have a functional amount of voids to absorb the ink liquid, the coating layer must have a minimum dry coat weight of 4 gsm, which usually means a wet coating film of 10-20 gsm, which requires very high drying efficiency to dry completely. As a result, it is nearly impossible to do this in-line in a high speed single pass printing process. Moreover, another drawback of porous ink receptive coatings is that it is very difficult to find a balance between binder content and pigment concentration to achieve high capillarity, yet still show sufficient adhesion to the substrate and avoid dusting effects.

[0013] Finally, coating with a porous structure usually reduces the gloss of the paper, so to obtain a glossy appearance a thin second overlayer of colloidal inorganic particles bound with resin must be applied, further increasing the complexity and expense.

[0014] [overview]

[0010] It is therefore an object of the present invention to provide a technique for improving the ink receptivity of such coated substrates in order to achieve adequate print quality with sufficient dot gain without intercolor bleeding and to avoid one or more of the above-mentioned disadvantages.

[0015]

[0011] Thus, a first aspect of the present invention provides a primer composition for forming a primer layer PL on a substrate to be printed with an ink I, in particular a pigmented inkjet ink for digital printing. This composition comprises the components as claimed: a first polymeric binder component A having a first polar contribution pc1 of less than 20%; a second component B comprising optional inorganic particles B' and a second polymeric binder component B", wherein said polymeric binder component B" has a second polar contribution pc2 equal to or greater than 20%; the amounts of A, B' and / or B", if present, are such that B' / (A+B"+B') is less than 15%, based on the dry weight of the composition.

[0016] The first polar contribution pc1 and the second polar contribution pc2 are determined using the Owens-Wendt-Rabel-Kaelble method with 6 gsm dry layers of components A and B, respectively. This very thick polymer layer of 6 gsm is used to eliminate any residual influence of the material underneath the polymer film. The polar contribution is the contribution of the polar component to the total surface energy.

[0017]

[0013] Surprisingly, it has been found that when printing low-absorption media, such as coated paper and polymeric films, with water-based digital printing inks, some image quality improvements can be achieved by applying a layer comprising the primer composition described above, even at relatively low thicknesses, such as less than 10 gsm wet weight thickness, and even less than 3 gsm wet weight in preferred cases. Several tests have shown promising results for primer layers comprising the primer composition according to the invention on various types of substrates.

[0018] The results show increased color density, increased dot gain (hence improved optical density), and reduced banding and intercolor bleeding or mottle, with no loss of gloss due to the porous structure.

[0019] Moreover, it has been found that such desired primer qualities are achieved without the need for flocculants or the like, thereby avoiding the risk of irreversible nozzle clogging. Moreover, the primer composition of the present invention is compatible with both anionic binders and cationic or non-ionic polymeric binders, thereby broadening the selection of commercially available binders. An advantage of the primer composition of the present invention is that a primer layer with a dry coat weight of less than 4 gsm (i.e., a wet coating film of less than 10 gsm) can be applied to a substrate. Thus, drying times can be improved and / or the need for high drying efficiency can be reduced compared to conventional primer technology.

[0020] In fact, improved image quality can be achieved even at relatively low thicknesses: the thickness of the pretreatment liquid layer is preferably between 0.5 gsm and 10 gsm, more preferably between 0.5 and 9 gsm, even more preferably between 0.5 and 8 gsm, and the amount of solids is preferably between 1 gsm and 5 gsm.

[0021] It has been found that when using primer compositions and working within these thickness ranges, the primer composition can be applied in-line at high speeds without the need for high-capacity drying stations that require a lot of operating energy. The amount of solids remaining on the substrate after drying of the pretreatment liquid layer is then 3 gsm or less. With primer thicknesses of less than 8 gsm wet weight, it is possible to apply the primer in-line in single-pass high-speed printing processes of more than 30 m / min, even more than 90 m / min. In fact, with such small wet weight thicknesses with limited amounts of water, the primer layer can be dried before the substrate arrives at the first color printing station. If the primer is not dry, there may be a risk of intercolor bleeding. It is therefore preferred that the primer is substantially dry before the first color ink is printed.

[0022]

[0014] In fact, it has been found that by having a first polymer binder component A having a polar contribution of less than 20%, in combination with either or both of inorganic particles B' and a second polymer binder having a polar contribution of more than 20%, more preferably more than 22%, more preferably more than 24%. It has been found that by having components B' and / or B", it is possible to improve dot gain and achieve the desired optical density while maintaining sufficient spreading of the aqueous inkjet droplets.

[0023]

[0015] It is preferred that the dry weight ratio A / (B' and / or B") is between 0.05 and 20, more preferably between 0.15 and 6. In this way, when said substrate is pretreated with a primer layer comprising the primer composition described herein, a suitable balance between ink receptivity, wetting and dot gain is set, such that the ink can be applied to several different types of substrates without image defects and without the need to tweak and / or modify the inkjet ink.

[0024]

[0016] It is further preferred that the combined solids content of component A, optional inorganic particles B', and component B" is at least 12%, more preferably at least 14%, and even more preferably at least 15%, based on the wet weight of the primer composition. By increasing the solids content of the primer composition, the composition dries faster. The drying rate also depends on the layer thickness. Thinner layers dry quickly and can technically utilize lower solids contents. However, thin layers with low solids content will not provide a useful primer coating because there will be little primer present on the substrate.

[0025]

[0017] It is further preferred that both components A and B are anionic or nonionic. By having such binders, one is not limited to cationic or nonionic polymeric binders. Thus, one can work with most of the commercially available binders that are anionically stabilized / solubilized without compromising dispersion stability or solubility.

[0026]

[0018] As mentioned above, it is preferred that the composition is essentially free of flocculating agents. More preferably, such flocculating agents are present in an amount of less than 0.05 wt. % based on the total weight of the primer composition. Said flocculating agents include, but are not limited to, polyvalent metal salts, calcium chloride, cationic polyelectrolytes, polydiallyldimethylammonium chloride, and / or (inorganic) organic acids, acetic acid. In this way, it is possible to avoid the inability to use anionic binders due to possible compromise of the binder's dispersion stability or solubility.

[0027] A flocculant is a compound or agent added to aggregate particles to form larger particle aggregates; such agents are often used in prior art primer compositions to achieve certain benefits. However, it has now surprisingly been found that such benefits and adequate image quality can still be achieved with the primer compositions described herein without the need for flocculants. As a result, the risk of "misting" and irreversible nozzle clogging can be avoided. Examples of flocculants that cause nozzle clogging are polyvalent metal salts, such as calcium chloride, cationic polyelectrolytes, such as polydiallyldimethylammonium chloride, and / or (inorganic) organic acids, such as acetic acid. When present, the flocculant should be kept below 0.5 wt%, preferably below 0.2 wt%, more preferably below 0.05 wt%, and most preferably below 0.02 wt%, based on the total weight of the primer composition.

[0028]

[0019] Component A preferably has a MFFT value of less than 80°C, preferably less than 40°C, more preferably less than 35°C, where MFFT represents the minimum film-forming temperature. The inclusion of component A with a low MFFT value in the composition ensures that the printed primer layer formed from the primer composition will be cleanly filmed when applied in-line in a printing process where the substrate is sufficiently covered with a uniform layer of the primer layer. As mentioned above, the advantage of the primer composition is that it can be applied in-line in a single-pass high-speed printing process of more than 30 m / min, even more than 90 m / min.

[0029]

[0020] Preferably, the average particle size of the inorganic particles is more than 0.3 μm, preferably more than 1 μm, preferably between 1 μm and 20 μm, as measured according to ISO13320:2020. In particular, when the primer composition has a polymeric binder component A and an inorganic particle component B', but does not have a polymeric binder component B" with a non-polar contribution of more than 20%, it is preferred that the average particle size of the inorganic particle component is more than 0.3 μm, preferably more than 1 μm. By having sufficiently large particles, the risk of losing the function of the inorganic particles is reduced. That is, if the inorganic particles have a small size, they may penetrate deeply into the primer composition and / or into the pores of the substrate, thereby causing the particle's function at the surface of the primer layer to be reduced. Therefore, it is preferred that the average particle size is sufficiently large to realize the advantage that the inorganic particles in the primer composition impart the desired functions at the surface of the primer layer, including slight matt properties and anti-abrasion properties. In preferred embodiments, the average particle size of the inorganic particles B' is less than 0.3 μm, preferably more than 1 μm, in the dried primer layer. 50% of the thickness of the dried primer layer. Furthermore, small nano-sized particles such as silica are difficult to obtain and usually more expensive. In more preferred embodiments, the average particle size of the inorganic particles B' is greater than the thickness of the dried primer layer, for example, the average particle size of the inorganic particles B' is 100-200% of the thickness of the dried primer layer. This improves the functionality of the particles at the surface of the dried primer layer, further improving the ink receptivity of the primer layer. In the most preferred embodiments, the thickness of the average particle size is 110-130% of the thickness of the dried primer layer. Surprisingly, a ratio of the average particle size to the thickness of the primer layer of 110-130% achieves an optimal balance between the effect of the organic particles on the ink and the effect of other components in the dried primer layer on the ink, thereby improving the overall ink receptivity of the dried primer layer.

[0030] It is further preferred that component B″ has a surface free energy of 9 mN / m or more of polar portion as determined by the Owens-Wendt-Rabel-Kaelble (OWRK) method on a 6 gsm dry polymer layer measured on a Dataphysics OCA25 instrument. Having component B″ with such a relatively high polar portion of 9 mN / m or more in the composition ensures proper wetting of water-based inks such that dot gain can be improved and proper optical density can be achieved.

[0031]

[0022] A second aspect of the present invention provides a primer kit for conditioning the surface of a substrate with a printing primer (P3), comprising a first primer P1 having a first polymer component A1 and a second component B1.

[0032] The first polymer component has a polar contribution pc2 less than 20%. The second component B1 comprises inorganic particles B1' and / or a second polymer binder component B1", in particular the second component B1 comprises optional inorganic particles B1' and a second polymer binder component B1". Said polymer binder component B1" has a second polar contribution pc2 equal to or greater than 20%.

[0033] The primer kit further includes a second primer P2 having a third polymer component A2 and / or a fourth component B2. The third polymer component A2 has a polar contribution of less than 20%. The fourth component B2 is selected from one or more of: inorganic particles B2', a fourth polymer binder component B2" having a polar contribution of equal to or greater than 20%.

[0034]

[0023] The composition of A1+B1 in the first primer P1 is different from the composition of A2+B2 in the second primer P2. Thus, the weight % ratio of (A1 and A2) / (B1 and B2) in the printing primer P3 may be adjusted by mixing a first amount of the first primer and a second amount of the second primer, and the surface of the substrate is adjusted as desired by applying the printing primer P3 thus obtained to the substrate.

[0035] The polar contribution is determined using the Owens-Wendt-Rabel-Kaelble method with a 6 gsm dry layer of the mentioned polymer binder component. In particular, the polar contribution to surface tension is the ratio of the polar portion of the surface energy to the total surface free energy. The surface energy value is determined using three reference liquids and measuring the contact angle of a drop of each on the substrate. The substrate can be covered with a 6 gsm dry layer of the primer component according to the invention. Furthermore, the total surface energy, polar component, and dispersive component are obtained using the Owens-Wendt-Rabel-Kaelble calculation method.

[0036] This aspect is based on the insight that different types of coated substrates with different wetting properties and / or types of inks may require different primer approaches. By having a primer kit with said first primer P1 and second primer P2, the third printing primer P3 can be adapted accordingly to obtain the right image quality. Such a primer kit is beneficial as it is easy to adapt and work with different types of (coated) substrates with different wetting properties. Having a primer kit at one's disposal allows easy adaptation to such substrates and thereby achieving good image quality.

[0037] Components with low polarity contribution, i.e., less than 20%, are also described herein as "low or moderate wetting."

[0038] It should be understood that when referring to the A1+B1 composition (or the A2+B2 composition), reference is made to the type of components and / or the weight percent amounts of the components in the first primer P1 (or the second primer P2). For example, component B1 in the first primer may be of a different type than component B2 in the second primer, and / or component B1 in the first primer may be the same as component B2 in the second primer, but may be present in a different weight percent amount relative to the total weight of the first primer compared to the weight percent amount of B2 relative to the total weight of the second primer. The first polymer component A1 and the third polymer component A2 may be different or the same. The second polymer component B1 and the fourth polymer component B2 may be different or the same. The first polymer component A1 is different from the third polymer component A2, or the second polymer component B1 is different from the fourth polymer component B2.

[0039]

[0024] By virtue of the A1+B1 composition of the first primer P1 being different from the A2+B2 composition of the second primer P2, the ratio applied between the component A having a polar contribution of less than 20% and the other component B, either inorganic particles and / or polymeric components, in the printing primer P3 can be easily varied to provide optimal images on a wide range of coated paper liners as well as polymeric film substrates such as labels and flexpacks during high speed single pass printing.

[0040] For example, when working with highly hydrophobic substrates where the inkjet droplets exhibit a high contact angle, a printing primer P3 having a higher amount of component B″ is required, whereas when the inkjet droplets exhibit a low contact angle, the substrate requires a primer having a lower amount of component B″.

[0041]

[0026] Thus, a third aspect of the invention is provided, which provides a method for obtaining a printing primer P3 for adjusting the ink receptivity of a substrate by applying said printing primer P3 to said substrate, said method comprising the steps of: Providing a first primer P1 comprising: a first polymer component A1 having a polar contribution of less than 20%; and / or a second component B1 comprising inorganic particles B1' and / or a second polymer binder component B1", said second component B1" having a second polar contribution pc2 equal to or greater than 20%. Providing a second primer P2 comprising: a third polymer component A2 having a polar contribution pc3 of less than 20%; and / or a fourth component B2 comprising inorganic particles B2′ and / or a fourth polymer binder component B2″; said polymer binder component B2″ having a second polar contribution pc4 of equal to or greater than 20%. Includes; However, at least one of the primers P1, P2 comprises a polymer component having a polar contribution of less than 20%, and the other of the primers P1, P2 comprises a component selected from one or more of inorganic particles and polymer components having a polar contribution of equal to or greater than 20%. In one embodiment, the proviso in the above method is such that at least one of the primers P1, P2 comprises a polymer component having a polar contribution of less than 20%, and at least one of the primers P1, P2 comprises a polymer component having a polar contribution of equal to or greater than 20%, in particular in that one of the primers P1, P2 comprises a component having a polar contribution of equal to or greater than 20%, and in that the further component is selected from one or more of inorganic particles and polymer components having a polar contribution of equal to or greater than 20%. The amount of A and B in at least one of the primers P1, P2 is usually different from the amount of A and B in the other of the primers P1, P2. In this way, the presence of both components A, also called "low polarity contribution component" or "low or medium wettability component", and B is ensured in the printing primer. Preferably, a proviso in the above method is that at least one of the primers P1, P2 comprises a polymer component A with a polarity contribution of less than 20%, and the other of the primers P1, P2 comprises component B", which is a polymer component with a polarity contribution of equal to or more than 20%, and optionally inorganic particles. In this way, color density, dot gain can be improved, and banding and intercolor bleeding or mottling problems are reduced. Furthermore, there is no loss of gloss due to the porous structure that is unavoidable for many known primer types. The method further comprises mixing a first amount p1 of the first primer P1 and a second amount p2 of the second primer P2 to form a printing primer P3, and applying the printing primer P3 to the surface of the substrate.The method further comprises a step of testing the ink receptivity by printing a test image, e.g., a test pattern (including geometric features for evaluating line width, dot size, intercolor bleeding, etc.), and, if necessary, adjusting the first amount p1 and / or the second amount p2 based on the features of the printed test image to set the weight % ratio of (A1 and A2) / (B1 and B2) in the printing primer P3. By following the above procedure, a printing primer with improved ink receptivity and image quality is obtained when the printing primer P3 is printed. By repeating this procedure for different substrates, a primer solution that is effective for a wide range of substrates can be easily produced using a minimum amount of different starting materials.

[0042]

[0027] A further aspect of the invention provides a method for printing with ink on a substrate such as paper coated with a polymeric film, the method comprising the steps of: providing a substrate; forming a primer layer PL on the substrate by applying a primer composition as described herein or by applying a printing primer P3 as described herein; and applying ink to the substantially dry primer layer. Those skilled in the art will appreciate that "substantially dry" refers to the state of the primer layer being dry enough to accept ink without image defects.

[0043]

[0028] The primer layer can be produced by applying the primer composition or the printing primer P3 as appropriate in an analogue printing process or in a digital printing process, such as a digital flexographic printing process.

[0044] In certain embodiments, the primer composition or primer P3 is applied using a piezo inkjet nozzle, thus achieving the ink characteristics of the inkjet nozzle without having nozzle clogging problems.

[0045]

[0030] Preferably, the primer composition or printing primer P3 is applied at a functional amount of less than 16 gsm wet weight thickness, more preferably less than 12 gsm, even more preferably less than 10 gsm wet weight thickness, most preferably less than 8 gsm wet weight thickness. By having the primer composition or printing primer P3 described herein, adequate primer capacity is achieved even at relatively low wet weight thicknesses, which has the advantage of reducing the need for high drying capacity. In this way, the operating costs of the printing process can be reduced. Preferably, the substrate is fed at a single pass speed of more than 20 m / min.

[0046]

[0031] Even more preferably, the primer composition or printing primer P3 is applied such that its wet weight thickness is between 0.5 gsm and 8 gsm. It has been found that the primer composition or printing primer P3 described herein allows such low thicknesses without reversing primer capabilities such as ink receptivity. The term "ink receptivity" is herein understood as the ability and willingness to accept ink such that an ink image can be formed without image defects. It has been found that when the wet weight thickness is between 0.5 gsm and 8 gsm, the substrate can be fed at relatively high printing speeds, i.e. single in-line pass speeds of more than 30 m / min, even more than 45 m / min, preferably more than 90 m / min. In this way, the primer composition or printing primer P3 can be applied in-line to said substrate at high speeds without reducing the ink receptivity. In this way, advantageously, a larger amount of substrate can be printed per unit time. A particular embodiment relates to a set of primer kits as described herein for obtaining a printing primer P3 for adjusting the ink receptivity of a substrate by applying said printing primer P3 to said substrate, further comprising one or more inkjet inks.

[0047] [Detailed Description]

[0032] The term "flocculant" and the like, as used herein, means any material capable of causing colloidal particles, such as pigment particles or lattices, to settle or cluster together.

[0048]

[0033] Ink Inks to be applied to the primer layer are known. The ink is preferably a water-based or aqueous ink. The aqueous ink can be roughly classified into pigment dispersion ink and dye ink. In recent years, there has been an increasing demand for pigment dispersion inks that exhibit excellent color development, as well as solvent resistance, gas resistance, and (ultraviolet) light resistance. On the other hand, in the case of pigment aqueous dispersion inks, satisfactory pigment dispersibility cannot be achieved in many cases because the pigment is insoluble in water. Therefore, in order to maintain good pigment dispersibility in aqueous inks, pigment dispersing resins are used to improve the dispersion stability of the pigment in water. These pigments are also believed to perform well against migration into food. The use of colorants in inks as described above is the most essential form of water-based inks. Aqueous inks used in inkjet printing methods also often contain a water-soluble solvent with a high boiling point and good solubility in water to prevent the ink, usually aqueous inks, from drying out at the nozzle. This type of solvent is considered a water retention agent in aqueous inks. In addition, the aqueous inks used in inkjet printing processes also typically contain one or more surfactants to allow for minimal wetting and spreading of the water-based ink in the printhead, on the substrate, etc. Finally, the aqueous ink composition may also contain various types of additives, such as defoamers, thickeners, binders, and preservatives, as required. The addition of these types of additives to the aqueous ink composition makes the composition more suitable for use as an inkjet ink.

[0049] Ink-jet inks are preferably optimized to maintain optimal jetting behavior (surface tension, viscosity, particle size) and good storage stability.

[0050]

[0034] Base material Substrates based on paper or polymeric films are known and can be appropriately selected depending on the main end use (retail, food, beverage, household appliances, etc.). An example of the structure of such a substrate is bleached or unbleached chemical pulp coated with one or more coatings. A preferred substrate is also described as "(kraft) liner". Preferably, the substrate comprises polymeric film and / or paper, such as used in liners, labels, laminates, food packaging, and / or flexible packaging, for example, solid board, graphic arts paper, corrugated board, and preferably the substrate comprises coated paper. Coated paper substrates are generally known to be less receptive to aqueous inkjet inks due to low surface porosity as a result of calendaring and / or application, paper sizing, and one or more hydrophobic coating layers. The resulting low porosity and hydrophobicity means that there are fewer paths accessible to the ink vehicle, which can result in slower drying of the ink and therefore image defects such as intercolor bleeding. Furthermore, the hydrophobicity of the paper coating reduces the wetting and spreading of the water-based inks when printed, which can then lead to ink droplets pooling on the media surface. When printing water-based inks directly onto coated substrates, the combined effect of less spreading and slower drying of the dots creates more image defects.

[0051] The same problem occurs when printing with water-based inks on polymeric film substrates such as flexible packaging or self-adhesive labels, as these materials are naturally hydrophobic and completely non-porous. Typical polymeric film materials include PE, PP, PET, and biodegradable materials including PLA, cellulose (cellophane), or other plant-derived materials. However, the films are not limited to these types. Preferably, the substrate is a polymeric film or coated paper substrate, and preferably said substrate is selected from liners used in one or more of the following: corrugated board, labels, laminates, food packaging, flexible packaging, solid board, graphic arts paper.

[0052] Polymer Binders A and B" The primer composition further comprises a first polymer binder component A having a first polar contribution pc1 of less than 20% and, in some embodiments, a second polymer binder B″ component having a second polar contribution pc2 of equal to or greater than 20%. The polar contribution is the polar component divided by the sum of the dispersive and polar components. The factor is present in the surface free energy of the solid (e.g., the dried primer film) since the surface free energy includes the dispersive and polar components. A first polymer binder component A having a first polar contribution pc1 of less than 20% can be selected by the skilled person using the Owens-Wendt-Rabel-Kaelble method for determining the polar contribution. This method can be carried out by the following means: Apply a 6 gsm dry layer of component A or B" respectively; A 1 μL drop of ethylene glycol is applied to the dried layer and the contact angle A1 is measured after an equilibration time of 10 s; A 1 μL drop of diiodomethane is applied to the dried layer and the contact angle A2 is measured after an equilibration time of 10 s; Apply a 1 μL drop of thiodiglycol to the dried layer and measure the contact angle A3 after an equilibration time of 10 s; Calculate the polar surface free energy, the dispersive surface free energy, and the total surface free energy, where the total surface free energy is the sum of the polar surface free energy and the dispersive surface free energy, the calculations being performed using the Owens-Wendt-Rabel-Kaelble method using A1, A2, and A3 as input values; The first polar contribution pc1 and the second polar contribution pc2 are the ratios, expressed as percentages, of the polar surface free energies to the total surface free energy values ​​determined for components A and B″, respectively.

[0053] The method used herein to determine the polar contribution pc1 involves applying a 1 μl droplet of ethylene glycol, diiodomethane, thiodiglycol (which are liquids with known total, polar, and dispersion surface tensions) to a 6 gsm dried layer of the first component A (or a 6 gsm dried layer of the second component B″ if the polar contribution pc2 of the second component B″ is to be determined) formed on a substrate, where the contact angle of the droplet is measured after a 10 second equilibration period. The three contact angles measured for each of the reference solvents ethylene glycol, diiodomethane, and thiodiglycol on the dried layer are used as inputs for the Owens-Wendt-Rabel-Kaelble calculation method (OWRK method). The OWRK method determines the total surface free energy, the polar surface energy, and the dispersion surface energy, where the total surface free energy is the sum of the polar surface free energy and the dispersion free energy. Thus, the polar contribution pc1 (or the second polar contribution pc2) is the ratio of the polar surface free energy to the total free energy value, expressed as a percentage. The carrier is mostly water, and the binder may also contain small amounts of organic solvents and additives.

[0054] Such calculations are often pre-programmed into commercially available contact angle goniometers, such as the Dataphysics OCA25. It should be noted that other reference solvents can be used in place of ethylene glycol, diiodomethane, and thiodiglycol, provided that the total, polar, and dispersive surface tensions of the reference solvents are known. The method is described, for example, in Owens et al., J. Appl. Polym. Sci. 13. (1969), 1741; Kaelble, J., Adhesion 2 (1970) 66. The terms "surface energy" and "surface free energy" are used interchangeably.

[0055] The polymer chemistry of the binder is not particularly limited and can be, for example, (meth)acrylate, vinyl, or polyurethane based. Mixing multiple chemistries in the primer can also be an option. Vinyl acetates are particularly preferred because these binders are low cost and often non-ionically stabilized, making them compatible with most other ionic primer components, such as coalescents, surfactants, and other binder chemistries.

[0056] The polymeric binder components A and / or B″ can be based on (meth)acrylate, acrylic, vinyl, or polyurethane polymers or copolymers, preferably vinyl acetate polymers, provided they have the following respective polar contributions:

[0057] The polymeric binder component A can be based, for example, on acrylic polymers, vinyl acetate polymers, copolymers of vinyl acetate and ethylene, polyester polymers, acrylic-styrene copolymers, polyurethanes. More specifically, the binder can be based on alkali-soluble acrylic polymers, copolymers of vinyl acetate and ethylene, anionic acrylic dispersions, nonionic polyester urethane polymers, anionic acrylic-styrene copolymer emulsions, aqueous dispersions of polyester polymers stabilized with sulfonic acid groups, anionic polyurethane dispersions with polyester backbones, anionic stabilized acrylic-styrene copolymer dispersions, cationic polyurethane dispersions, vinyl acetate ethylene copolymers stabilized with nonionic surfactants, anionic emulsion polymers based on styrene and acrylates, nonionic homopolymer emulsions based on vinyl acetate.

[0058] The polymeric binder component B″ can be based on, for example, acrylic copolymers, such as alkali soluble acrylic polymers, vinyl acetate, such as homopolymeric vinyl acetate emulsions.

[0059] The polymer can be made water compatible by cationic or anionic functional groups and / or non-ionic hydrophilic groups. Since priming polymers are usually anionic, it is preferable to use non-ionic or anionic stabilized priming polymers to improve compatibility with aqueous inkjet inks. Thus, the risk of cross-contamination of primers throughout the inkjet printer can be reduced. In some methods, applying the primer in-line in the printing process can lead to the formation of ink particle agglomerates in the printhead and even clogging of the inkjet nozzles.

[0060]

[0036] Inorganic particles B' Besides the aforementioned polymer binder B″, inorganic particles B′ can also be used, including, but not limited to, kaolin clay, kaolin clay, diatomaceous earth, calcium carbonate, calcined clay, silica gel, fumed silica, colloidal silica, talc, fumed alumina, colloidal alumina, titanium dioxide, zinc oxide, zinc sulfide, and barium sulfate. In particular, the inorganic particles B′ can be silica particles. The particle size can be varied from the nanometer range up to several microns in order to adjust the gloss level of the primer layer. In preferred embodiments, the inorganic particles have an average particle size of more than 0.3 μm, preferably more than 1 μm, preferably between 1 μm and 20 μm, as measured according to ISO13320:2020. As explained above, an average particle size of more than 0.3 μm has the advantage that the inorganic particles do not penetrate deep into the pores of the substrate, such as the pores of paper. The average By making the particle size sufficiently large, the functionality of the inorganic particles at the surface of the primer layer formed is improved. In particular, the primer layer is formed with a primer composition that does not include the polymer binder component B'. By improving the functionality of the particles at the surface, some mattness and abrasion resistance can be imparted. Furthermore, nano-sized particles such as nano-sized silica are more difficult to manufacture and are usually more expensive. Preferably, the inorganic particles B' are present in an amount of less than 10 wet weight %, more preferably less than 9 wet weight %, and even more preferably less than 8 wet weight %, based on the total composition of the primer composition. The wet weight percentage, also written as wet weight %, is indicated as the wet weight of each component relative to the total wet weight of the primer formulation. The advantage of a low amount of inorganic particles is a reduced risk of dust formation, reduced loss of gloss. Furthermore, a high amount of inorganic particles can cause the particles to settle irreversibly.

[0061] Additives Other possible primer components include biocides, antifoam agents, slip additives (e.g., wax particles), corrosion inhibitors, coalescing agent solvents to lower the film-forming temperature of the binder emulsion, etc.

[0062] In particular, for primer application by spray technology or digital primers applied by inkjet, it is preferred that the primer does not contain a flocculant. These two methods are very sensitive to the formation of fine mist particles that can cause pigment agglomeration that cross-contaminates the color printing stations and leads to nozzle clogging. Furthermore, it was found that the salts of polyvalent metals used in the "flocculants" of the prior art can react with carbon dioxide CO2 in the air to form salt precipitates. Such salt precipitates lead to clogging of the primer application unit. Nevertheless, misting can also occur in flexo or gravure roller application, which is one of the most commonly used methods. It is therefore preferred that the printing primer does not contain any agent, such as a flocculant, that is used to remove suspended solids from the liquid by inducing agglomeration. Such agents can cause the solids to start agglomerating to form flakes that can then settle and cause nozzle clogging.

[0063]

[0038] Printing method The printing process uses a primer application step followed by an inkjet printing step. Primer application is preferably done in-line in an analog manner using rollers, flexographic plates, offset plates, curtain coating, etc., but can also be done by spraying, or digitally using inkjet printheads, either piezo or inkjet, and possibly piston-based inkjet, commercially available from Valvejet. When using an analog roller system, a two-roller system with a doctor roller and application roller can be used, or a three-roll system can be used in which the anilox roll is contacted with a metering roller to ensure a constant amount of primer in the anilox roll, which is then transferred to the application roller for final transfer to the substrate. The final laydown on the substrate can be adjusted by adjusting the nip pressure, the speed of the rollers, the anilox pattern, the hardness of the rollers, etc. The detailed design of the three-roll system to ensure a very controlled laydown is a closed chamber design. It is very important to choose a design that allows a very uniform application of the primer layer, especially when a thin layer is required. This can be achieved more easily, for example, with an anilox pattern with high screening and honeycomb cell structure. The inkjet step can be performed using any type of printhead: thermal, piezo, continuous inkjet. It is unlikely that a Valvejet-like printhead is used to generate the image. Between these (at least two) steps (primer application step followed by inkjet printing step) one or more drying steps can be incorporated. The primer step, i.e. the step of creating the primer layer, and the inkjet printing step can be immediately followed by another inkjet printing step, but new primer and inkjet printing steps can also be used. The primer application step is followed by an inkjet printing step with an optional drying step in between.The drying means can be of any kind related to the inkjet ink or primer technology used. It can be thermally based (hot air, infrared, near infrared, or a combination thereof) or actinic radiation based, and the drying strength or capacity does not have to be the same for the primer composition and the inkjet ink. Also, the printed product can be dried using an additional final drying step of any kind and strength. A corona or plasma treatment device can be optionally included before the priming station or after each primer drying unit. Optionally, the substrate is preheated before the primer application step in an in-line or offline method. Drying of the ink can be done by an intercolor drying unit, a final drying step after the color printing is completed, or a combination of both. The method and strength of drying the primer and ink can result in different image quality or can be purposefully adopted to adjust the amount of ink spreading, mottle, and bleeding for one or more inks. This is especially true when using intercolor drying methods.

[0064] [Example] The present invention will now be described with reference to the following examples, which are not intended to limit the scope of the invention.

[0065] 1. Testing of individual substrates and primer components. Individual primer components were tested by measuring the contact angle and determining the surface free energy.

[0066] Contact angle is the angle at which a liquid-vapor interface, such as an ink droplet-air interface, meets a solid surface, such as a dried primer layer. Contact angle can quantify wettability. Surface free energy can be thought of as the surface tension of a solid resulting from interactions at the vapor-solid interface and can be used to predict the spreading behavior of a liquid when placed on said solid surface.

[0067] Both parameters were measured and determined on the polymer components using a Dataphysics OCA25 instrument.

[0068] The effect of substrate type on contact angle and surface energy was tested by applying a water-based ink (WIC2503) to the substrate, as shown in Tests 1-3.

[0069] Subsequently, the effect of having a primer layer formed as a 6 gsm dry layer on the substrate surface was tested, as shown in tests 4-6. More specifically, a coating film with a thickness of about 6 gsm of the individual primer components was applied to the substrate: Metsaboard Pro WKL, a double coated white top kraft liner. A thick layer of 6 gsm was applied to eliminate any effect of the surface energy of the paper itself. The following components used within the coating film on the substrate refer to their parameters MFFT, particle size, and solids content according to the data sheets provided by the respective suppliers: [Table 1] TIFF2025504354000002.tif198149 TIFF2025504354000003.tif58149

[0070] The contact angles of 1 μL droplets of ethylene glycol, diiodomethane, and thiodiglycol droplets were then determined, and the dispersion, polarity, and total surface energy values ​​were determined from the measured contact angles using the Owens-Wendt-Rabel-Kaelble (OWRK) calculation method (e.g., as described in Owens et al., J. Appl. Polym. Sci. 13 (1969), 1741; Kaelble, J., Adhesion 2 (1970) 66). The measurements were repeated on the paper itself, without any coating. The DIN EN ISO 3251 standard used is the standard stated in the supplier's data sheet and may be the 2019 standard. [Table 2] TIFF2025504354000005.tif119149

[0071] The contact angle values ​​in Table 2 above show that the ink spread is greatest on Rieger OC-D (lowest contact angle), smallest on MM X Liner HD and smallest on Metsaboard Pro WKL (highest contact angle). The ink spread on these substrates was determined by measuring the contact angle of a 1 μL drop after an equilibration time of 10 seconds. It was found that the presence of the individual primer components formed as a dried primer film on the substrate can increase the wetting on said substrate. Indeed, as derived from further examples herein, by having a combination of both components A and B, the surface of a liner that is normally difficult to print on can be set as desired, more specifically the surface can be set to be more receptive to the ink, thus improving the ink receptivity. It is noted that the test ink WI-C2503 has already been optimized to achieve a very high level of spreading on coated paper substrates.

[0072] As can be seen from Tests 4-6, it was found that it was not possible to determine whether a component would cause sufficient ink spreading based on contact angle alone. Therefore, it was necessary to determine the surface energy component. Furthermore, it was not possible to derive from the chemical properties of the primer component whether it constituted an A or B component. For example, NeoCryl-BT-20 and Makrovil V108 are both B” components, but have different chemical properties, an acrylic copolymer and a vinyl acetate polymer, respectively. However, for example, Vinamul 3231 also constitutes a vinyl acetate polymer, but is an A component. Therefore, it is not possible to determine from the chemical properties alone whether a component constitutes an A or B” component.

[0073] Therefore, to be able to determine whether a component is an A or a B″ component, the polar contribution to the surface free energy needs to be determined.

[0074] Data regarding particle size of each primer component was not always available, and the inventors do not believe that characterization of this parameter is essential to the invention.

[0075] Primer Components Component B” with a polar contribution of more than 20%. NeoCryl BT-20 is an anionic acrylic emulsion from DSM (Waalwijk, The Netherlands) that is classified as a polymer with a high surface free energy (9.46 mN / m) of the polar component in the dry polymer layer, which greatly increases wetting. Table 2 shows that NeoCryl BT-20 has a high polar contribution to the surface energy (26%), making it very suitable for water-based inks to spread easily on the substrate. This compatibility between water-based inks and substrates is confirmed by contact angle measurements using the test ink WI-C2503.

[0076] Makrovil V108 is a homopolymer emulsion from Indulor (Ankum, Germany) that is classified as a polymer that has a high surface free energy (9.73 mN / m) of the polar component in the dry polymer layer, which greatly increases wetting. Table 2 shows that Makrovil V108 has a high polar contribution to the surface energy (22%), making it very suitable for water-based inks to spread easily on the substrate.

[0077] Component A having a polar contribution of less than 20%. NeoCryl D-2204 is an anionic acrylic dispersion from DSM and is classified as a medium wetting polymer. For the test ink WI-C2503, the polar contribution of NeoCryl D-2204 (17%) is significantly lower than that of Neocryl BT-20, but it is still sufficient to spread a 1 μL ink droplet. It can therefore be considered a medium wetting polymer.

[0078] Exopur 4109 is an anionic acrylic emulsion with acrylic copolymers from EOC (Oudenaarde, Belgium) and is classified as a low polarity polymer. However, the properties of Exopur 4109 appear to be very similar to those of the reference substrate, so that the difference in the contact angle of the test ink droplet between the substrate and the polymer film on the substrate is minimal in this case. Therefore, Exopur 4109 is classified as a low polarity polymer.

[0079] Vinamul 3231 is a poorly ionic vinyl acetate and ethylene copolymer emulsion manufactured by Celanese (Irving, TX, USA). Although the polar contribution of 18% is significant, experiments have determined that Vinamul 3231 is classified as a low polarity polymer and still requires combination with other primer components to achieve sufficient wetting of the ink.

[0080] Baybond PU404 is a non-ionic polyester urethane polymer obtained from Covestro Coating Resins (Waalwijk, The Netherlands). It has a very low polar contribution of 2.21%, which is ideal for preventing excessive spreading of the ink on the substrate.

[0081] Neocryl XK-205 is an anionic acrylic styrene copolymer emulsion obtained from Covestro Coating Resins (Waalwijk, The Netherlands).

[0082] Eastek 1200 is an aqueous dispersion of polyester polymer obtained from Eastman (Kingsport, Tenn., USA).

[0083] Daotan 7001 is an anionic polyurethane dispersion with a polyester backbone manufactured by Allnex (Frankfurt am Main, Germany). Based on its high polar surface energy (8.48 mN / m) and moderate polar contribution value (18%), this polymer was tested as a replacement for B″, but ultimately showed poor wetting of the ink on the substrate. Furthermore, this polymer did not positively affect other image quality properties such as ink intercolor bleed. Therefore, based on the measurements of Daotan 7001, it was determined that the lower limit of the polar contribution of the surface energy should be greater than 18%.

[0084] Neocryl A1120 is a modified acrylic styrene copolymer dispersion from Covestro Coating Resins (Waalwijk, The Netherlands).

[0085] Esacote P1 C1 is a cationic polyurethane dispersion from Lamberti (Gallate, Italy).

[0086] Vinamul 3171 is a non-ionic vinyl acetate ethylene copolymer manufactured by Celanese (Irving, TX, USA). This polymer has been found to give good image quality results when printed with digital inks on substrates primed with this polymer, but only in combination with other polymers that provide better wetting due to its moderate polar surface energy value (6.55 mN / m) and polar contribution (16%).

[0087] Induprint SE375 is an anionic emulsion polymer based on styrene and acrylates manufactured by Indulor (Ankum, Germany).

[0088] Makrovil V205 is a vinyl acetate-based non-ionic homopolymer emulsion manufactured by Indulor (Ankum, Germany).

[0089] Any polymer binder component (component A) having a polar contribution of less than 20% has been found to be inadequate by itself to adequately promote wetting of the ink on the substrate, and therefore requires combination with a primer component (B") having a polar contribution of 20% or more.

[0090] 2. Evaluation of the examples. Ink spread evaluation Next, the characteristics of having a primer layer are evaluated, especially the evaluation of image quality and the evaluation of bleeding. Evaluation of image quality, especially the spreading of the ink to avoid poor dot gain and the resulting white streaks, was performed. A 600 dpi Kyocera KJ4B was used to print 100% 3pxl cyan lines on two types of substrates at a speed of 1 m / s: substrate type 1: substrate with a primer layer as described herein; substrate type 2: substrate without a primer layer (blanco) or substrate with a poorly designed primer layer. After applying the primer to the paper substrate, it was allowed to dry for at least 5 minutes at ambient room temperature conditions before printing. Immediately after printing the cyan line, infrared drying was used to ensure that the ink layer was dried and most of the liquid in the ink layer was removed. The infrared drying station was installed after all color printing units and was equipped with 4 x 1330 W lamps (1.3 μm wavelength) each emitting 52 W / cm.

[0091] The width of the 3pxl cyan line on the dried prints was measured using a PIAS™-II Personal Image Analysis System (Quality Engineering Associates). The following abbreviations were used for the evaluation: A > 150μm: Ink spread is excellent and there are no streaks B 125μm~150nm: Ink spreading is improved and streaks are at an acceptable level. C <125μm: Ink spreading is unacceptable, streaking is at a high level

[0092] Bleeding evaluation First, 18 pL of single layer yellow 100% was printed on the substrate at 1 m / s speed using a 600 dpi Kyocera KJ4B, followed by 100% 3 pxl 18 pL cyan line printed on top of the yellow single layer patch. Since both color printing units were used, an infrared drying unit was run after each of the two color printing units during printing to ensure (partially) removing the liquid of the ink layer. This means that infrared drying was performed after printing the yellow single layer and a second infrared drying was performed after printing the cyan pattern. For the dried prints, the width of the 3 pxl cyan line was measured with a PIAS™-II Personal Image Analysis System (Quality Engineering Associates). The following abbreviations were used for the evaluation: A <125μm: Very good, no to very little visible bleeding B 125~150μm: acceptable C >150μm: Unacceptable

[0093] 3. Primer formulation examples. Test ink Water-based inks C (WI-C2503) and Y (WI-Y2502) were prepared by mixing the components listed in Table 3 below for 30 minutes. The amounts in Table 3 are in weight percent based on the total weight of the water-based ink. The amount of water is added to total 100% by weight. The ink was then filtered through a 1 μm filter. The viscosity of the ink was approximately 6 mPa.s, which is within the specifications of the Kyocera KJ4BYH 600 dpi and Fuji Samba G3L 1200 dpi heads. [Table 3]

[0094] Base material During the experiment, various types of substrates were tested, some of which are shown in Table 4 below. [Table 4]

[0095] Primer formulation for application to substrate Additionally, various formulations of primer were prepared with the individual primer components present in different amounts. [Table 5] TIFF2025504354000009.tif107149

[0096] The above primer formulations can be used to improve the surface of the liner, and more particularly to improve the ink compatibility properties, such as a desired level of ink spreading and dot gain.

[0097] Primer kit for preparing the above formulation When formulating the example primers shown in Table 5, one starts with a primer kit consisting of two (or more) primers, such as PK1 with a first primer 1-P1 and a second primer 1-P2. Such primers can be provided, for example, in a bottle with the following types / amounts of components: [Table 6] TIFF2025504354000011.tif128149

[0098] It can be seen that in Kit A, primer P1 includes a combination of A and B', i.e., 33.75% by wet weight of Neocryl D-2204 and inorganic particles Z89. It can be seen that in Kit B, Kit D, and Kit E, primer P1 includes a combination of A and B'', e.g., 30% by wet weight of NeoCryl D-2204 and 30% by wet weight of NeoCryl BT-20 in Kit B. It can be seen that in Kit C, primer P1 includes a combination of A and B', i.e., 30% by wet weight of Exopur 4109 and 3% by wet weight of inorganic particles Z89. Therefore, it can be seen that there is always one type of primer in a primer kit having a combination of A and B, and by having the combination, the primer layer formed by the primer of the primer kit can achieve proper ink receptivity.

[0099] Making a printing primer starting from a primer kit In fact, by selecting the right primers of the primer kit in the appropriate amount to apply the primer layer to the substrate to form a printing primer, a well-designed primer layer can be formed on the substrate to adjust the surface properties of the substrate. In this way, the ink receptivity and print quality can be improved. More specifically, the desired ink spread and intercolor bleeding (preferably no bleeding) can be achieved. In fact, by having various types of primers at one's disposal in the primer kit, when various types of substrates are used, the ink receptivity of said substrate can be adapted and set as desired by mixing the primers of the primer kit and applying the mixture to the substrate as a printing primer in order to adjust the ink receptivity of the substrate and achieve the proper print quality. For example, the following mixing ratios of the primer kit examples in Table 6 were used to form the formulations shown in Examples 1 to 5 in Table 5. [Table 7]

[0100] Various types of coated substrates with different ink wettability and / or type may require different primer approaches. By having a primer kit including the first primer P1 and the second primer P2, the amount of P1 and P2 can be adjusted to make the third printing primer P3, and sufficient image quality can be obtained for all three liners in Table 4. For example, when having a primer kit A with the first primer 1-P1 and the second primer 1-P2, the printing primer can be made and the primer layer can be formed using a large amount of primer 1-P1 and a smaller amount of 1-P2 (e.g., made with primer example 1) for substrates that do not need to have high ink wettability, since bottle 1-P2 has a solution containing a large amount of silica. When the substrate has low wettability, it may be beneficial for image quality to use a larger amount of bottle 1-P2 relative to the amount of bottle 1-P1 (e.g., made with primer example 2). The mixing ratio of 2-P1; 2-P2 and 3-P1 and 3-P2 should be selected according to how much component B is needed based on the surface characteristics of the substrate when preparing a formulation for forming a primer layer on the substrate. By selecting the appropriate mixing ratio, it is possible to prepare the same primer using different kits. Primer examples 4 and 4' are the same, but are prepared by mixing 3-P1 and 3-P2 or 2-P1 and 2-P2, respectively, in the appropriate mixing ratio.

[0101] 4. Ink results in printing primer [Table 8]

[0102] From Comparative Examples 1-6 it can be seen that printed samples that do not contain a primer according to the present invention, for example, no primer or a primer with only Part A or Part B, have unacceptable scores for wetting or intercolor bleed, or both.

[0103] From examples 7-10 it can be seen that in primer kit 1 using components A and B', different mixing ratios of P1 and P2 (primer 1 and primer 2) can be used to adjust the substrate wetting without reaching unacceptable levels of intercolor bleeding: for the most wettable substrates (e.g. Rieger, example 10), primer 1 is already sufficient to obtain acceptable results, whereas for the less wettable substrates (e.g. Metsaboard, example 7), primer 2 with more component B' is more suitable and recommended to obtain the same results.

[0104] From examples 11 to 19, it can be seen that in these examples different components A+B' and / or B" are used. In examples 12 and 13, the same effect as in examples 7 to 10 is observed, that is, by changing the mixing ratio of P1 and P2 in primer kit 2 (primers 3 and 4) and thus the ratio of A and B", the wetting of the board can be adjusted.

[0105] While with primer 3 acceptable wetting and intercolor bleed can already be obtained on the most wettable substrate (Rieger OCD), further improved image quality can be achieved by using primer 4. Also, for substrates such as MM XL HD and Metsaboard Pro, the best possible print quality is achieved with primer 5, so it may be beneficial to additionally use the combination A+B'+B" (see examples 11, 14, 15). Note that primers 4 and 5 can be made with primer kit 3.

[0106] From the above table, it can be seen that the use of a primer formulation having both components A and B provides improved printing results over the printing results of substrates that are not primed. In practice, it is preferred to adjust the mixing ratio based on the printed test image.

[0107] Based on the above description, a person skilled in the art will understand that the aspects of the present invention can be implemented in various ways and based on various principles. In this regard, the present invention is not limited to the above implementations and / or examples, since the above implementations and / or examples are merely illustrative and serve only to enhance the understanding of the aspects of the present invention. Therefore, the aspects are limited to the implementations described herein, but are defined in the claims.

Claims

1. 1. A primer composition for forming a primer layer on a substrate to be printed with an ink, said composition comprising: a first polymer binder component A having a first polar contribution pcl of less than 20%; A second component B comprising a second polymer binder component B″ and optionally inorganic particles B′; wherein the polymer binder component B″ has a second polar contribution pc2 equal to or greater than 20%. Includes: the amounts of component A, component B", and optionally B', if present, are such that B' / (A+B"+B') is less than 15%, based on the dry weight of the composition; and the first polar contribution pcl and second polar contribution pc2 are determined by the following method: Apply a 6 gsm dry layer of component A or B″, respectively; Applying a 1 μL drop of ethylene glycol to the dried layer and measuring the contact angle A1 after an equilibration time of 10 seconds; Applying a 1 μL drop of diiodomethane to the dried layer and measuring the contact angle A2 after an equilibration time of 10 seconds; Applying a 1 μL drop of thiodiglycol to the dried layer and measuring the contact angle A3 after an equilibration time of 10 seconds; calculating the polar surface free energy, the dispersive surface free energy, and the total surface free energy, wherein the total surface free energy is the sum of the polar surface free energy and the dispersive surface free energy, and wherein the calculations are performed using the Owens-Wendt-Rabel-Kaelble method using A1, A2, and A3 as input values; wherein the first polar contribution pc1 and the second polar contribution pc2 are the ratios, expressed as percentages, of the polar surface free energy to the total surface free energy values ​​determined for components A and B″, respectively.

2. The primer composition of claim 1 , wherein the second polar contribution pc2 of the second component B is greater than 22%, more preferably greater than 24%.

3. 2. The primer composition of claim 1, wherein the dry weight ratio of A / (B' and / or B") is between 0.05 and 20, more preferably between 0.15 and 6.

4. 2. The primer composition of claim 1, wherein the combined solids content of Component A, inorganic particles B', and / or Component B" is at least 12%, more preferably at least 14%, and even more preferably at least 15%, based on the wet weight of the primer composition.

5. The primer composition of claim 1 , wherein components A and B are anionic or nonionic.

6. The primer composition of claim 1 , wherein the composition is essentially free of a flocculating agent.

7. 2. The primer composition of claim 1, wherein component A has an MFFT value of less than 80°C, preferably less than 40°C, and more preferably less than 35°C.

8. 2. The primer composition of claim 1, wherein the inorganic particles have an average particle size of more than 0.3 μm, preferably between 1 μm and 20 μm, as measured according to ISO 13320:2020.

9. 2. The primer composition according to claim 1, wherein the polar portion of the surface free energy of component B is 9 mN / m or more.

10. The primer composition of claim 1 , wherein the second polymeric binder component B″ is present as a water-based emulsion.

11. A primer kit for conditioning the surface of a substrate with a printing primer (P3), the primer kit comprising: A first primer P1 comprising: a first polymer component A1 having a polar contribution of less than 20%; and a second component B1 comprising inorganic particles B1′ and / or a second polymer binder component B1″, said polymer binder component B1″ having a second polar contribution pc2 equal to or greater than 20%; A second primer P2 comprising: a third polymer component A2 having a polar contribution of less than 20%; and / or a fourth component B2 selected from one or more of inorganic particles B2′ and a fourth polymer binder component B2″ having a polar contribution equal to or greater than 20%; Including, the A1+B1 composition in the first primer P1 is different from the A2+B2 composition in the second primer P2, preferably at least one of B1″ and B2″ is present; As a result, a first amount of a first primer and a second amount of a second primer may be mixed to adjust the weight % ratio of (A1 and A2) / (B1 and B2) in the printing primer P3, and the printing primer P3 thus obtained is applied to the substrate to prepare the surface of the substrate as desired; The polar contribution is determined by the following method: Apply a 6 gsm dry layer of component A or B″, respectively; Applying a 1 μL drop of ethylene glycol to the dried layer and measuring the contact angle A1 after an equilibration time of 10 seconds; Applying a 1 μL drop of diiodomethane to the dried layer and measuring the contact angle A2 after an equilibration time of 10 seconds; Applying a 1 μL drop of thiodiglycol to the dried layer and measuring the contact angle A3 after an equilibration time of 10 seconds; calculating the polar surface free energy, the dispersive surface free energy, and the total surface free energy, wherein the total surface free energy is the sum of the polar surface free energy and the dispersive surface free energy, and wherein the calculations are performed using the Owens-Wendt-Rabel-Kaelble method using A1, A2, and A3 as input values; The polar contribution is the ratio, expressed as a percentage, of the polar surface free energy to the total surface free energy value determined for each of components A and B″.

12. The primer kit of claim 11 , wherein the first polymer component A1 and the third polymer component A2 can be different or the same.

13. The primer kit of claim 11 , wherein the second polymer component B1 and the fourth polymer component B2 can be different or the same.

14. 12. The primer kit of claim 11, wherein the first polymer component A1 is different from the third polymer component A2, or the second polymer component B1 is different from the fourth polymer component B2.

15. 12. A substrate having a primer layer formed thereon, said primer layer comprising the primer composition of claim 1 or comprising printing primer P3 as defined in claim 11; and said primer layer having a dry primer layer thickness of less than 3 gsm, more preferably less than 1.5 gsm.

16. 1. A method for obtaining a printing primer P3 for adjusting the ink receptivity of a substrate by applying said printing primer P3 to said substrate, comprising the steps of: providing a first primer P1 comprising: a first polymer component A1 having a polar contribution pc1 of less than 20%; and / or a second component B1 comprising inorganic particles B1′ and / or a second polymer binder component B1″; the polymer binder component B1″ having a second polar contribution pc2 equal to or greater than 20%; providing a second primer P2 comprising: a third polymer component A2 having a polar contribution pc3 of less than 20%; and / or a fourth component B2 comprising inorganic particles B2′ and / or a fourth polymer binder component B2″; wherein the polymer binder component B2″ has a second polarity contribution pc4 equal to or greater than 20%; However, at least one of the primers P1 and P2 contains a polymer component having a polar contribution rate of less than 20%, and the other of the primers P1 and P2 contains a component selected from one or more of inorganic particles and a polymer component having a polar contribution rate of more than 20%; mixing a first amount p1 of the first primer P1 and a second amount p2 of the second primer P2 to form the printing primer P3; applying the printing primer P3 to the surface of the substrate; testing the ink receptivity by printing a test image and, if necessary, adjusting the first amount p1 and / or the second amount p2 based on the characteristics of the printed test image to set the weight % ratio of (A1 and A2) / (B1 and B2) in the printing primer P3; Including, The polar contribution is determined by the following method: Apply a 6 gsm dry layer of component A or B″, respectively; Applying a 1 μL drop of ethylene glycol to the dried layer and measuring the contact angle A1 after an equilibration time of 10 seconds; Applying a 1 μL drop of diiodomethane to the dried layer and measuring the contact angle A2 after an equilibration time of 10 seconds; Applying a 1 μL drop of thiodiglycol to the dried layer and measuring the contact angle A3 after an equilibration time of 10 seconds; calculating the polar surface free energy, the dispersive surface free energy, and the total surface free energy, wherein the total surface free energy is the sum of the polar surface free energy and the dispersive surface free energy, and wherein the calculations are performed using the Owens-Wendt-Rabel-Kaelble method using A1, A2, and A3 as input values; and wherein the polar contribution is the ratio, expressed as a percentage, of the polar surface free energy to the total surface free energy value determined for each of components A and B″.

17. A printing primer P3 obtainable by the method according to claim 16.

18. 1. A method of printing with ink onto a substrate, comprising: providing the substrate; forming a primer layer PL on the substrate by applying the primer composition according to claim 1 or by applying the printing primer P3 according to claim 17; applying the ink to the substantially dried primer layer. A method comprising:

19. 19. The method according to claim 18, wherein the primer composition or the printing primer P3 is applied by an analog printing process, such as a spray coating process, and / or a digital printing process, such as inkjet printing.

20. 19. The method of claim 18, wherein the primer composition or the printing primer P3 is applied by means of a piezo inkjet nozzle.

21. 20. The method of claim 18, wherein the substrate is a polymeric film or coated paper substrate, preferably selected from liners used in one or more of corrugated board, labels, laminates, food packaging, flexible packaging, solid board, graphic arts paper.

22. 19. The method according to claim 18, wherein the primer composition or printing primer P3 is applied at a functional amount of less than 16 gsm wet weight thickness, more preferably less than 12 gsm, even more preferably less than 10 gsm wet weight thickness, and most preferably less than 8 gsm.

23. 19. The method of claim 18, wherein the substrate is fed at a single pass speed of more than 20 m / min, preferably more than 30 m / min, most preferably more than 90 m / min.

24. 19. The method of claim 18, wherein the primer composition or printing primer P3 is applied to a wet weight thickness of between 0.5 gsm and 8 gsm.

25. 12. A set of primer kits according to claim 11 for obtaining a printing primer P3 for adjusting the ink receptivity of a substrate by applying said printing primer P3 to said substrate, said set further comprising one or more inkjet inks.