Method for manufacturing printed corrugated board

Abstract

This invention relates to a method for manufacturing printed corrugated cardboard, the method comprising the steps of: a) providing a paper backing board (23) having an ink receiving layer; and b) using a paper backing board having an external nozzle surface area NS less than 500 μm. 2 The piezoelectric current-carrying printhead (25) of the nozzle prints an image on the ink receiving layer using one or more colored water-based inkjet inks; wherein the one or more colored water-based inkjet inks contain an amount of water in the form of A wt% as defined below: wherein the wt% is based on the total weight of the water-based inkjet ink; wherein sqrt(NS) represents the square root of the surface area NS of the outer nozzle; and wherein A wt% ≥ 40 wt%.

Description

[0001] This application is a divisional application of the following application: application date September 10, 2020, application number 202080067191.7, invention title "Method for manufacturing printed corrugated cardboard". Technical Field

[0002] This invention relates to a method for manufacturing printed corrugated cardboard. Background Technology

[0003] Corrugated cardboard is a preferred packaging material because it is inexpensive and lightweight. Lightweight packaging materials reduce transportation costs and facilitate handling during delivery to customers. A further benefit is that corrugated cardboard boxes are stackable, making them easy to store and transport.

[0004] Corrugated cardboard is a packaging material formed by gluing one or more grooved cardboard sheets (called corrugated media) to one or more flat liner sheets (called face sheets). There are four common types: (1) single-sided: one grooved sheet is glued to one face sheet (two sheets in total); (2) single-wall: one grooved sheet sandwiched between two face sheets (three sheets in total), also known as double-sided or single-layer; (3) double-wall: one single-sided sheet is glued to one single-wall, such that two grooved sheets are alternately sandwiched between three flat sheets (five sheets in total), also known as double-pad or double-layer; and (4) triple-wall: two single-sided sheets are glued to one single-wall, such that three grooved sheets are alternately sandwiched between four flat sheets (seven sheets in total), also known as triple-layer.

[0005] Traditionally, images are printed on corrugated cardboard using flexographic and offset printing techniques. As e-commerce plays an increasingly important role, direct contact between sellers and customers is decreasing. Companies are exploring ways to maintain and enhance customer experience and engagement. Packaging is becoming a way to achieve this through customized or even personalized messaging. However, printing such messaging using flexographic or offset printing is extremely expensive. A preferred alternative is inkjet printing, which offers no press setup time (no platens and plate changes) and allows for short delivery cycles.

[0006] Because packaging has a significant impact on consumer purchasing decisions, there is a need to improve image quality. For example, EP3360934A (FUJIFILM) discloses an inkjet ink kit for corrugated cardboard that contains five colors of ink with different hues, whereas to date, a four-color ink kit consisting of yellow (Y), magenta (M), cyan (C), and black (K) ink has been commonly used.

[0007] Beyond image quality, high productivity is also essential in industrial environments. Reliability is paramount, especially when using single-pass inkjet printing systems. Single-pass inkjet machines operate at very high speeds, some even reaching 150 m / min. For example, ink clogging one or more nozzles can lead to line artifacts in the printed image, material waste, and interruptions in the printing process. This represents not only financial losses but also a loss of productivity.

[0008] There is still a need for improved methods to manufacture printed corrugated cardboard using inkjet printing methods with high reliability and improved image quality in an economical manner. Summary of the Invention

[0009] To overcome the above problems, a preferred embodiment of the present invention has been achieved by the method of manufacturing printed corrugated cardboard as defined in claim 1.

[0010] Surprisingly, it was found that for some piezoelectric printheads, there is a relationship between the outer nozzle surface area of ​​the nozzle in the printhead and the water content in the water-based inkjet ink, which enables reliable inkjet printing.

[0011] The object of this invention is to provide a nozzle with an external nozzle surface area NS less than 500 μm. 2 An improved method for manufacturing printed corrugated cardboard using specific water-based inkjet inks in a piezoelectric current-carrying printhead with a nozzle.

[0012] Another object of the present invention is to provide an external nozzle with a surface area NS of less than 500 μm. 2 The combination of a piezoelectric printhead with a nozzle and specific colored water-based inks from a water-based inkjet ink kit is used to produce corrugated cardboard with high image quality and reliability.

[0013] These and other purposes will become apparent from the detailed description below. Attached Figure Description

[0014] Figure 1 The structure of corrugated cardboard formed by gluing grooved cardboard (1) to paper linerboard (2) and paper linerboard (3) with glue (4) is explained.

[0015] Figure 2 .A The diagram shows a cross-section of an end-jet printhead, wherein the printhead wall (10) surrounds an ink channel (14) through which inkjet ink is supplied via an ink inlet (12), and the ink can only exit the printhead as jetted ink droplets (17) via ink jetting (11) through nozzles (16) in the nozzle plate (15) of the printhead. The piezoelectric elements of the printhead used to form the jetted droplets (17) are not shown in the schematic diagram.

[0016] Figure 2 .BThe diagram shows a cross-section of a flow-through printhead, wherein the printhead wall (10) surrounds an ink channel (14) through which inkjet ink is supplied via an ink inlet (12), and exits the ink channel (14) continuously via an ink outlet (13), and exits the ink channel (14) only when necessary via ink jet (11) through a nozzle (16) in the nozzle plate (15) of the printhead as ejected ink droplets (17). The piezoelectric elements of the printhead used to form the ejected droplets (17) are not shown in the schematic diagram.

[0017] Figure 3 .A This shows a cross-section of the area surrounding the nozzle (16) in the nozzle plate (15) attached to the printhead wall (10), wherein the nozzle (16) has an outer nozzle diameter (19) through which ink ejection (11) occurs and a larger inner nozzle diameter (18).

[0018] Figure 3 .B Showing a top view taken from inside the printhead and showing the area around the nozzle (16) in the nozzle plate (15) attached to the printhead wall (10), wherein the outer nozzle diameter (19) of the nozzle (16) is smaller than the inner nozzle diameter (18).

[0019] Figure 4 An embodiment of a method for manufacturing printed corrugated cardboard is shown, wherein a single-wall corrugated cardboard (20) having grooved cardboard (21) between two paper backings (22, 23) is first printed with an ink acceptor layer by a flexographic printing roller (24), an image is then printed by an inkjet printhead (25), and finally printed with a protective varnish layer by a second flexographic printing roller (26).

[0020] Figure 5 A preferred embodiment of a method for manufacturing printed corrugated cardboard is shown, comprising an inkjet printing step A and a lamination step B. In step A, a backing board (23) is first printed with an ink acceptor layer using a flexographic printing roller (24), followed by an image being printed using an inkjet printhead (25), and finally printed with a protective varnish layer using a second flexographic printing roller (26). In step B, the inkjet-printed paper backing board (27) obtained in step A is laminated onto a single-faced corrugated cardboard (28) using adhesive via two lamination rollers (29).

[0021] Figure 6 The graph shows the results obtained by determining the short latency of two inks, A and B, after 0.5 s. Detailed Implementation

[0022] definition

[0023] The term "water solubility" refers to the property of being soluble in water at a certain concentration or higher. Preferably, it refers to the property of dissolving 5g or more (more preferably 10g or more) in 100g of water at 25°C.

[0024] The term "alkyl" refers to all possible variants of an alkyl group for each number of carbon atoms, namely, methyl; ethyl; for three carbon atoms: n-propyl and isopropyl; for four carbon atoms: n-butyl, isobutyl and tert-butyl; for five carbon atoms: n-pentyl, 1,1-dimethyl-propyl, 2,2-dimethylpropyl and 2-methyl-butyl, etc.

[0025] Unless otherwise stated, substituted or unsubstituted alkyl groups are preferably C1-C6-alkyl groups.

[0026] Unless otherwise stated, the substituted or unsubstituted alkenyl group is preferably a C2-C6-alkenyl group.

[0027] Unless otherwise stated, the substituted or unsubstituted alkynyl group is preferably C2-C6-alkynyl.

[0028] Unless otherwise stated, the substituted or unsubstituted aralkyl group is preferably a phenyl or naphthyl group comprising one, two, three or more C1-C6-alkyl groups.

[0029] Unless otherwise stated, substituted or unsubstituted alkylaryl groups are preferably C1-C6 alkyl groups including phenyl or naphthyl groups.

[0030] Unless otherwise stated, the substituted or unsubstituted aryl group is preferably phenyl or naphthyl.

[0031] Unless otherwise stated, the substituted or unsubstituted heteroaryl group is preferably a five- or six-membered ring substituted with one, two or three oxygen atoms, nitrogen atoms, sulfur atoms, selenium atoms or combinations thereof.

[0032] In the context of substituted alkyl groups, the term "substituted" means that the alkyl group can be replaced by atoms other than those normally present in such groups (i.e., carbon and hydrogen). For example, substituted alkyl groups can include halogen atoms or thiol groups. Unsubstituted alkyl groups contain only carbon and hydrogen atoms.

[0033] Unless otherwise stated, substituted alkyl, substituted alkenyl, substituted alkynyl, substituted aralkyl, substituted alkylaryl, substituted aryl and substituted heteroaryl are preferably substituted with one or more of the following substituents: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl and tert-butyl, ester, amide, ether, thioether, ketone, aldehyde, sulfoxide, sulfone, sulfonate, sulfonamide, -Cl, -Br, -I, -OH, -SH, -CN and -NO2.

[0034] Manufacturing method

[0035] A preferred embodiment of the present invention is a method for manufacturing printed corrugated cardboard, the method comprising the steps of: a) providing a paper backing board (23) having an ink receiving layer; and b) using a paper backing board having an external nozzle surface area NS less than 500 μm. 2 A piezoelectric current-carrying printhead (25) inkjet prints an image onto an ink receiving layer using one or more colored water-based inkjet inks, wherein the nozzle; and wherein the one or more colored water-based inkjet inks contain water in an amount of A% by weight as defined by formula (I):

[0036] 100wt%-sqrt(NS)×3.8wt% / μm≤Awt%≤100wt%-sqrt(NS)×2.2wt% / μm Formula (I)

[0037] The weight percentage is based on the total weight of the water-based inkjet ink; sqrt(NS) represents the square root of the surface area NS of the outer nozzle; and A weight percentage is ≥ 40% by weight. A weight percentage of 40% by weight is required to avoid haze formation and to achieve an acceptable drying rate. Preferably, A weight percentage is ≥ 44% by weight, more preferably A weight percentage is ≥ 45% by weight.

[0038] The manufacturing method preferably includes step c) of laminating an inkjet-printed paper backing onto the grooved corrugated cardboard of the corrugated board. Figure 5 This visualization method is beneficial for image quality. (In the process of...) Figure 4 In alternative methods of direct printing on corrugated cardboard, flexographic printing rollers (24, 26) can produce a so-called squeegee effect by applying pressure to the corrugated cardboard. This is not achieved when flexographic printing rollers (24, 26) apply an ink-receiving layer and a protective varnish layer to an inkjet-printed paper backing board, which is then glued to one side. In contrast to flexographic printing rollers, which can print layers in an image-like manner, the smaller pressure applied by the laminating rollers is uniformly applied and does not produce a squeegee effect.

[0039] In a preferred embodiment of the manufacturing method, inkjet printing is performed according to a single-pass printing method. This results in a much higher productivity.

[0040] The manufacturing method preferably also includes the step of applying a protective varnish layer to the inkjet-printed image. Such a protective varnish layer typically also increases the gloss of the inkjet-printed image, which is beneficial to image quality.

[0041] In a particularly preferred embodiment of the manufacturing method, an ink-receiving layer and / or a protective varnish layer are applied by flexographic printing. This is beneficial for productivity. The ink-receiving layer and protective varnish layer can also be applied by coating (e.g., using a blade coater). However, coating methods generally produce more waste because it takes some time to achieve a stable coating state of good quality. Flexographic printing has the advantage that flexographic printing rollers can be easily incorporated into inkjet printing systems and operated at the same printing speed.

[0042] In a particularly preferred embodiment, the method for manufacturing printed cardboard according to the invention is used to manufacture corrugated cardboard boxes, wherein the inkjet-printed image is located inside the corrugated cardboard box. Such boxes may be printed only internally, or alternatively, the exterior of the box may be printed with, for example, the brand of an e-commerce company selling goods for the manufacturer.

[0043] By printing inside the box or only inside, customers can choose to skip printing custom or personalized messages to enhance the customer experience and engagement on the outside of the packaging. The result of printing inside the box is a huge, unparalleled experience by cleverly placing branding and messages in a way that surprises and delights the customer. Furthermore, it reduces theft and provides privacy. Because the inside printing is featureless, people are less likely to steal packaging whose contents are not readily apparent. Additionally, many delivered packages end up with wear and tear on the outside. When the customer opens the box, the undamaged interior will be the focus.

[0044] In a preferred embodiment of the invention, the above-described method for manufacturing printed cardboard is used to manufacture corrugated cardboard boxes, wherein the inkjet-printed image is located inside the corrugated cardboard box.

[0045] When inkjet printing images, one or more colored water-based inkjet inks are preferably not water-based UV-curable inkjet inks. This means that one or more colored water-based inkjet inks do not contain photoinitiators or polymerizable compounds that may migrate into the contents of corrugated cardboard boxes (e.g., food) and thus pose a health risk, especially when the inkjet-printed image is located inside the corrugated cardboard box.

[0046] Corrugated cardboard

[0047] Cardboard can have various structures, such as honeycomb cardboard. However, for easy folding into packaging boxes, cardboard using a grooved medium is used. Such cardboard is called corrugated cardboard. The grooved pattern provides strength to the cardboard. This is important for delivery capability, as companies risk their reputation if goods do not arrive at the customer's hands intact.

[0048] The preferred corrugated cardboard in this invention is single-walled or double-walled, with single-walled corrugated cardboard being more preferred because it is strong enough and creases easily. Single-walled corrugated cardboard is generally not strong enough to hold commercial products, while three-layer corrugated board is generally more difficult to fold into packaging boxes.

[0049] The paperboard (e.g., kraft paper) used for corrugated cardboard is typically brown. In a preferred embodiment of the above manufacturing method, in Figure 4 and Figure 5 The paper backing board 23 is white. Enhanced image quality is achieved by having a white background. Colors printed on a white paper backing board (23) have a much higher vibration than those printed on a brown kraft paper backing board. The white background also contributes to the customer experience, as customers perceive it as a more luxurious product. Alternatively, the white background can be applied as a layer by coating or printing prior to inkjet printing. However, a white paper backing board is preferred because it enhances the reliability of the printing method by eliminating potential problems that may occur during the coating or printing of a white layer.

[0050] Suitable paperboards with a white background include white-topped kraft paperboard and white-coated kraft paperboard.

[0051] In a preferred embodiment of the manufacturing of printed corrugated cardboard, such as by... Figure 5 As noted, single-faced corrugated board is used in roll form rather than sheet form. Using single-faced board supplied by roll helps increase productivity and reliability because gluing inkjet-printed paper backing to the single-faced board can be done faster and with fewer errors than using individual single-faced sheets.

[0052] As in Figure 4 The corrugated cardboard used is preferably in the form of corrugated rolls. Alternatively, corrugated cardboard can be used in a fan-fold form. A fan-fold is a continuous sheet of corrugated cardboard that is scored and folded like a fan.

[0053] Roll-form corrugated cardboard typically possesses resilient properties due to its special soft lining that allows for roll delivery. For customers with many different product sizes and using a wide variety of packaging specifications, corrugated rolls are a productive solution.

[0054] Fan-folding offers a cost-effective solution by reducing inventory, as fewer specifications require stock. For manual packing methods, the board can be easily scored along its length, making it easy to fold into the desired size. Specialized fan-folding cutters are also available, allowing for the production of customized, measured packages on a customer-specified basis.

[0055] Combination of inkjet ink and printhead

[0056] A preferred embodiment of the present invention is a combination for manufacturing printed corrugated cardboard, the combination comprising:

[0057] a) The external nozzle surface area NS is less than 500μm 2 The nozzle of the piezoelectric current-carrying printhead; and

[0058] b) Water-based inkjet inks from a water-based inkjet ink kit, wherein the water-based inkjet ink kit comprises:

[0059] - Cyan water-based inkjet ink containing β-copper phthalocyanine pigment;

[0060] - Magenta or red water-based inkjet ink containing pigments selected from CI Pigment Red 57 / 1, CI Pigment Red 122, CI Pigment Violet 19 and their mixtures.

[0061] - Yellow water-based inkjet ink containing pigments selected from CI Pigment Yellow 74, CI Pigment Yellow 138, CI Pigment Yellow 151, and their mixtures; and

[0062] - Black water-based inkjet ink containing carbon black pigment;

[0063] The water-based inkjet ink contains water in an amount of A% by weight as defined by formula (I):

[0064] 100wt%-sqrt(NS)×3.8wt%μm≤Awt%≤100wt%-sqrt(NS)×2.2wt% / μm Formula (I)

[0065] The weight percentage is based on the total weight of the water-based inkjet ink;

[0066] Where sqrt(NS) represents the square root of the surface area NS of the external nozzle; and where A wt% ≥ 40 wt%.

[0067] The above combination of piezoelectric current-carrying printhead and water-based inkjet ink is included in an inkjet printing apparatus (preferably a single-pass inkjet printing apparatus).

[0068] Suitable inkjet inks and piezoelectric printheads are described in more detail below.

[0069] piezoelectric printing head

[0070] Two aspects of piezoelectric printheads are found to be essential for improving the reliability of inkjet printing: 1) the current flow type of the piezoelectric printhead, and 2) the external nozzle surface area being less than 500 μm. 2 .

[0071] Piezoelectric inkjet printing is based on the movement of a piezoelectric ceramic transducer when a voltage is applied. The applied voltage changes the shape of the piezoelectric ceramic transducer in the printhead, creating a void, which is then filled with ink. When the voltage is removed again, the ceramic expands back to its initial shape, ejecting ink droplets from the printhead.

[0072] The difference between piezoelectric current-carrying printheads and other piezoelectric printheads is due to Figure 2 Display. In the end-jet printhead, compared with... Figure 2 Similar to the printhead shown in A, and often referred to as a single-ended printhead, ink flows into the ink channel (14) through the ink inlet (12) of the printhead and exits only through the nozzle (16). In a flow-through printhead, as in Figure 2 Similar to the printhead shown in .B, and often referred to as a recirculating printhead, ink flows continuously through the ink channel (14) via the ink inlet (12) and exits the nozzle (16) only when needed, otherwise the ink exits the ink channel via the ink outlet (13) of the printhead.

[0073] Commercial examples of end-jet printheads are, for example, the piezoelectric printheads Gen5 and Gen5S from RICOH and the KJ4B from KYOCERA. Suitable piezoelectric printheads for obtaining the present invention are the printheads Samba G3L and G5L from FUJI DIMATIX and the 5601 printhead from XAAR.

[0074] The nozzles in a nozzle plate typically have an outer nozzle orifice smaller than the inner nozzle orifice. The inner nozzle orifice faces the ink channel, while the outer nozzle orifice faces the external environment of the printhead. The nozzle orifice is typically circular, elliptical, square, or rectangular, but can also have other more complex shapes.

[0075] The nozzle surface area NS is calculated based on the dimensions of the outer nozzle using a well-known mathematical formula for surface area. For example, in the case of a circular nozzle, the nozzle surface area NS is calculated using the formula NS = πxr. 2 Calculate, where the radius r is Figure 3 The diameter of the outer nozzle (19) is half of the diameter of the outer nozzle.

[0076] The above-mentioned water-based inkjet ink kit is used with an external nozzle surface area NS less than 500μm. 2 The nozzle is a piezoelectric current-carrying printhead assembly. The external nozzle surface area (NS) is preferably between 100-300 μm. 2 Between 150-250 μm, more preferably between 150-250 μm 2 Between these ranges, the printhead may produce images of excellent image quality.

[0077] The natural droplet size is the droplet volume of a single droplet under normal printing conditions, which implies a standard waveform and reference voltage. In this invention, the natural droplet size of the piezoelectric current-carrying printhead is preferably between 2.0 and 5.5 pL, more preferably between 2.2 and 5.0 pL. Within these small natural droplet size ranges, line artifacts caused by faulty nozzles may be slightly masked, thus leading to greater productivity.

[0078] Water-based inkjet ink kit

[0079] Inkjet inks contain pigments as colorants. Colored pigments have a higher water fastness than dyes. This is important because inkjet-printed images may be exposed to rain during transport and delivery.

[0080] Water-based inkjet inks for coloring are preferably formed into inkjet ink kits. Preferred ink kits are CMYK inkjet ink kits. Such ink kits provide a high color gamut that is beneficial to image quality. CMYK inkjet ink kits can also be extended with additional inks (e.g., red, green, blue, and / or orange) to further expand the color gamut of the image. Inkjet ink kits can also be extended by combining full-density inkjet inks with light-density inkjet inks. Combinations of dark and light inks and / or black and gray inks improve image quality by reducing graininess.

[0081] In a particularly preferred embodiment, the coloring aqueous inkjet ink kit includes:

[0082] a) Cyan water-based inkjet ink containing β-copper phthalocyanine pigment;

[0083] b) Magenta or red water-based inkjet ink containing pigments selected from CI Pigment Red 57 / 1, CI Pigment Red 122, CI Pigment Violet 19 and their mixtures.

[0084] c) A yellow water-based inkjet ink containing pigments selected from CI Pigment Yellow 74, CI Pigment Yellow 138, CI Pigment Yellow 151, and their mixtures; and

[0085] d) Black water-based inkjet ink containing carbon black pigment.

[0086] Water-based inkjet inks are preferably characterized by a surface tension between 18.0 and 28.0 mN / m at 25°C. Water-based inkjet inks with a surface tension less than 18.0 mN / m at 25°C typically require a large amount of surfactant, which may cause foaming problems. A surface tension greater than 28.0 mN / m at 25°C may cause fouling on the nozzle plate of the printhead and / or wetting of the ink circuitry within the printhead.

[0087] Inkjet ink at 1,000s -1The viscosity at 32°C under a certain shear rate is preferably in the range of 1.0 mPa·s to 15.0 mPa·s, more preferably 2.0 mPa·s to 10.0 mPa·s. Most preferably, one or more water-based inkjet inks for use in the manufacturing method of the present invention have a viscosity of 1,000 s. -1 The viscosity at 32°C under certain shear rates is between 3.0 and 8.0 mPa·s, more preferably between 3.5 and 6.0 mPa·s. Such viscosity has been found to provide increased reliability for inkjet printing methods.

[0088] Colored pigments

[0089] Colorants in one or more water-based inkjet inks include colored pigments.

[0090] One or more colored water-based inkjet inks preferably contain a dispersant for dispersing pigments, more preferably a polymeric dispersant. They may contain a dispersing synergist to improve dispersion quality and ink stability.

[0091] Colored pigments may be selected from those disclosed in HERBST, Willy et al., Industrial Organic Pigments, Production, Properties, Applications. 3rd ed. Wiley-VCH, 2004. ISBN 3527305769.

[0092] Color pigments can be selected based on the color of the image to be formed. Preferably, inkjet ink kits contain inks with yellow, red or magenta, blue or cyan, and black pigments respectively.

[0093] Preferred examples of yellow pigments include CI Pigment Yellow (hereinafter referred to as "PY") 1, PY3, PY12, PY13, PY14, PY17, PY34, PY35, PY37, PY55, PY74, PY81, PY83, PY93, PY94, PY95, PY97, PY108, PY109, PY110, PY137, PY138, PY139, PY151, PY153, PY154, PY155, PY157, PY166, PY167, PY168, PY180, PY185 and PY193.

[0094] Preferred examples of red or magenta pigments include CI Pigment Red (hereinafter referred to as "PR") 3, PR5, PR19, PR22, PR31, PR38, PR43, PR48:1, PR48:2, PR48:3, PR48:4, PR48:5, PR49:1, PR53:1, PR57:1, PR57:2, PR58:4, PR63:1, PR81, PR81:1, PR81:2, PR81:3, PR81:4, PR88, PR104, PR108, PR112, P R122, PR123, PR144, PR146, PR149, PR166, PR168, PR169, PR170, PR177, PR178, PR179, PR184, PR185, PR208, PR216, PR226 and PR257, and CI Pigment Violet (hereinafter referred to as "PV")3, PV19, PV23, PV29, PV30, PV37, PV50 and PV88, and CI Pigment Orange (hereinafter referred to as "PO")13, PO16, PO20 and PO36.

[0095] Preferred examples of blue or cyan pigments include CI Pigment Blue (hereinafter referred to as "PB") 1, PB15, PB15:1, PB15:2, PB15:3, PB15:4, PB15:6, PB16, PB17-1, PB22, PB27, PB28, PB29, PB36 and PB60.

[0096] Preferred examples of green pigments include CI Pigment Green (hereinafter referred to as "PG") 7, PG26, PG36 and PG50.

[0097] Preferred examples of black pigments include CI Pigment Black (hereinafter referred to as "PBk") 7, PBk26, and PBk28. For black inks, suitable pigment materials include carbon black, such as Regal from Cabot Co. TM 400R, Mogul TM L, Elftex TM 320, or Carbon Black FW18 or Special Black from DEGUSSA Co. TM 250, SpecialBlack TM 350, Special Black TM 550, Printex TM 25. Printex TM 35. Printex TM 55. Printex TM90. Printex TM 150T, MA8, obtained from MITSUBISHI CHEMICAL Co.

[0098] Mixed crystals can also be used. Mixed crystals are also called solid solutions. For example, under certain conditions, different quinacridones are mixed together to form a solid solution, which is very different from both the physical mixture of the compounds and the compounds themselves. In a solid solution, the molecules of the components enter the same crystal lattice, usually but not always into the lattice of one of the components. The X-ray diffraction pattern of the resulting crystalline solid is characteristic of the solid and can be clearly distinguished from the pattern of a physical mixture of the same components in the same proportion. In such a physical mixture, the X-ray pattern of each component can be distinguished, and the disappearance of many of these lines is one of the criteria for the formation of a solid solution. A commercially available example is Cinquasia from Ciba Specialty Chemicals. TM Magenta RT-355-D.

[0099] Mixtures of pigments can also be used. For example, black inkjet inks that include carbon black pigments may further include at least one pigment selected from blue, cyan, magenta, and red pigments. The discovery of such more neutral black inkjet inks allows for easier and better color management.

[0100] The pigment particles in colored inkjet inks should be small enough to allow the ink to flow freely through the inkjet printing apparatus, especially at the jet nozzles. It is also desirable to use sufficiently small particles to maximize color intensity and slow down sedimentation.

[0101] To achieve high printing reliability, the number-average particle size of the pigments in the colored inkjet ink is preferably between 50 nm and 250 nm. More preferably, the number-average pigment particle size is between 100 nm and 200 nm.

[0102] The number-average particle size is best determined using a 4mW HeNe laser at 633nm wavelength via photon correlation spectroscopy on diluted samples of colored inkjet ink. A suitable particle size analyzer is the Malvern, available from Goffin-Meyvis. TM nano-S.

[0103] Color pigments are preferably used in water-based inkjet inks for coloring at an amount of 0.1-10% by weight. A concentration of 1.5-6.0% by weight is preferred, and more preferably 2.0-5.0% by weight, based on the total weight of the colored inkjet ink. A pigment concentration of at least 2% by weight is preferred to reduce the amount of inkjet ink required to produce the desired inkjet image, resulting in increased productivity because less water and solvent must be removed through drying. When printing light colors, pigment concentrations above 5% by weight result in graininess, which is detrimental to image quality.

[0104] polymer dispersants

[0105] Water-based inkjet inks preferably contain polymeric dispersants for dispersing pigments. One or more water-based inkjet inks may also contain dispersing synergists to further improve dispersion quality and ink stability.

[0106] Suitable polymer dispersants are copolymers of two monomers, but they can contain three, four, five, or even more monomers. The properties of a polymer dispersant depend on both the properties of the monomers and their distribution in the polymer. Copolymer dispersants preferably have the following polymer composition:

[0107] Statistical polymerization of monomers (e.g., monomers A and B polymerize into ABBAABAB);

[0108] Alternating polymerization of monomers (e.g., monomers A and B polymerize into ABABABAB);

[0109] Monomers that undergo gradient (gradual) polymerization (e.g., monomers A and B polymerize into AAABAABBABBBB);

[0110] Block copolymers (e.g., monomers A and B polymerized into AAAAABBBBBB) have block lengths (2, 3, 4, 5 or even more) that are important for the dispersing ability of polymer dispersants.

[0111] Graft copolymers (graft copolymers consist of a polymer backbone and polymer side chains attached to the backbone); and

[0112] These polymers are in mixed forms, such as block gradient copolymers.

[0113] A suitable commercial dispersant is DISPERBYK, which is available from BYK CHEMIE. TM Dispersant, JONCRYL, available from JOHNSONPOLYMERS TM Dispersant and SOLSPERSE available from ZENECA TMDispersants. Details of non-polymer and some polymeric dispersants are published by MC CUTCHEON. Functional Materials, North American Edition. Glen Rock, NJ: Manufacturing Confectioner Publishing Co., 1990, pp. 110-129.

[0114] The polymer dispersant preferably has a number average molecular weight Mn between 500 and 30,000, and more preferably between 1,500 and 10,000.

[0115] The polymer dispersant preferably has a weight-average molecular weight (Mw) of less than 100,000, more preferably less than 50,000, and most preferably less than 30,000.

[0116] In a particularly preferred embodiment, the polymeric dispersant for the water-based inkjet ink used for coloring is a copolymer containing 3-11 mol% of aliphatic long-chain (meth)acrylates, wherein the aliphatic long chains contain at least 10 carbon atoms.

[0117] The preferred aliphatic long-chain (meth)acrylate contains 10-18 carbon atoms. The preferred aliphatic long-chain (meth)acrylate is decyl (meth)acrylate. The polymer dispersant can be prepared by simple controlled polymerization of a mixture of monomers and / or oligomers comprising 3-11 mol% of aliphatic long-chain (meth)acrylate, wherein the aliphatic long chain contains at least 10 carbon atoms.

[0118] Commercially available polymer dispersants containing copolymers of aliphatic long-chain (meth)acrylates between 3 and 11 mol% are Edaplan. TM 482 is a polymer dispersant derived from MUNZING.

[0119] For dispersing CI Pigment Yellow 150 and its mixed crystals, an acrylic block copolymer dispersant is preferred because very good ink stability has been observed with such dispersants. A commercial example is from BASF's Dispex. TM Ultra PX 4575.

[0120] Aqueous dispersion media

[0121] Water-based inkjet inks contain solid components (e.g., color pigments) and liquid components. The liquid component forms a dispersion medium, and in this invention, the liquid component contains at least water and preferably one or more water-soluble organic solvents. Regarding the water-soluble solvent, known solvents can be used without particular limitation.

[0122] When the inkjet printhead or some of its nozzles are in non-printing mode (printing idle time), evaporation of liquid components may occur. When the printhead or idle nozzles are activated after an extended non-printing time, some nozzles may become clogged (= faulty nozzles). This phenomenon is called latency. Latency caused by evaporation can be addressed by using one or more organic solvents with a boiling point higher than water. However, large amounts of such organic solvents also reduce productivity because they take longer to dry inkjet-printed samples.

[0123] Another reason for the latency period is the suboptimal dispersion of colored pigments. Colored pigments are typically dispersed using polymeric dispersants, which have a hydrophobic anchor portion attached to the hydrophobic surface of the pigment particles and a hydrophilic portion dissolved in an aqueous dispersion medium, to achieve steric stability of the colored pigment. Adding large amounts of organic solvents tends to dissolve the hydrophobic portion from the pigment surface and reduces the solubility of the hydrophilic portion of the dispersant, leading to pigment precipitation.

[0124] Typically, latency is evaluated over a long period of hours or days. However, there are also so-called short latency periods, which occur during printing and are evaluated over a short period of seconds or even fractions of a second. After a printing idle time, such as half a second, the nozzle tends to eject the first ink droplet at a much lower drip rate than when in a steady state of continuous ink droplet printing. This is due to... Figure 4 The results show that after a 0.5-second printing idle time, ink A has a better short latency than ink B. The curves for inks A and B were determined by continuously measuring the droplet velocity of the nth droplet ejected from the inkjet printhead, where n is 1, 2, 3, 4, and 10.

[0125] In this invention, it was found that for nozzles with an external nozzle surface area NS less than 500 μm 2 A piezoelectric current-driven printhead can enhance the printing reliability of water-based inkjet inks by controlling the water content within a certain range. Such water-based inkjet inks contain water in an amount defined as A% by weight, as shown in formula (I):

[0126] 100wt%-sqrt(NS)×3.8wt% / μm≤Awt%≤100wt%-sqrt(NS)×2.2wt% / μm Formula (I)

[0127] The percentage by weight is based on the total weight of the water-based inkjet ink;

[0128] Where sqrt(NS) represents the square root of the external nozzle surface area NS; and where A is ≥ 40% by weight.

[0129] Suitable organic solvents include triacetin, N-methyl-2-pyrrolidone, 2-pyrrolidone, glycerol, urea, thiourea, ethylidene urea, alkylurea, alkylthiourea, dialkylurea and dialkylthiourea, and glycols (including ethylene glycol, propylene glycol, glycerol, butanediol, pentanediol and hexanediol). Preferred organic solvents are glycerol and 1,2-hexanediol, as the latter two have been found to be most effective in improving latency.

[0130] Organic solvents are not only included in aqueous dispersion media to improve latency. Some organic solvents (even those with a boiling point lower than water) can be added to promote the dissolution of certain solid components (e.g., surfactants, dispersants, and biocides). However, based on the total weight of organic solvents present in the water-based inkjet ink, it is preferable that more than 60% by weight, most preferably 90-100% by weight, have an organic solvent with a boiling point higher than water, and more preferably a boiling point higher than 150°C at standard atmospheric pressure (1013.25 mbar).

[0131] To adjust the viscosity of water-based inkjet inks, it is preferable to use polyalkylene glycol dialkyl ethers represented by formula (A) in the water-based dispersion medium:

[0132]

[0133] In this context, R1 and R2 are each independently selected from alkyl groups having 1-4 carbon atoms; Y represents ethylene or propylene; and n is an integer selected from 5-20. The alkyl groups R1 and R2 in the polyalkylene glycol dialkyl ether according to formula (A) preferably represent methyl and / or ethyl. Most preferably, both alkyl groups R1 and R2 are methyl.

[0134] In a preferred embodiment, the polyalkylene glycol dialkyl ether according to formula (A) is a polyethylene glycol dialkyl ether, preferably a polyethylene glycol dimethyl ether, because they are very easy to mix with water to provide an aqueous pigment dispersion.

[0135] Instead of pure compounds, mixtures of polyalkylene glycol dialkyl ethers can also be used. Suitable mixtures of polyalkylene glycol dialkyl ethers include mixtures of polyethylene glycol dimethyl ethers with an average molecular weight of at least 200, such as Polyglycol DME 200 obtained from CLARIANT. TM Polyglycol DME 250 TM and Polyglycol DME 500 TM The polyalkylene glycol dialkyl ethers used in water-based inkjet inks preferably have an average molecular weight between 200 and 800.

[0136] Other preferred organic solvents with good water solubility include ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol, 1,3-propanediol, 1,2-butanediol, 2,3-butanediol, 1,3-butanediol, 1,2,3-trihydroxypropane (glycerol), 1,4-butanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-pentanediol, 2,4-pentanediol, 2-methyl-2,4-pentanediol, 1,5-pentanediol, 1,6-hexanediol, 2-ethyl-1,3-hexanediol, and 1,2-hexanediol. And 2,5-hexanediol, dipropylene glycol monomethyl ether, dipropylene glycol n-propyl ether, tripropylene glycol methyl ether, tripropylene glycol n-propyl ether, propylene glycol phenyl ether, propylene glycol n-butyl ether, propylene glycol tert-butyl ether, diethylene glycol methyl ether, ethylene glycol n-propyl ether, triethylene glycol methyl ether, triethylene glycol ethyl ether, diethylene glycol n-hexane ether and ethylene glycol phenyl ether, 2-pyrrolidone, N-methylpyrrolidone, N-ethylpyrrolidone, 2,5,7,10-tetraoxaundecane (TOU), 1,3-dioxolane, 1-(2-butoxy-1-methylethoxy)-2-propanol (solvenol) DPnB or 1 (or 2)-(2-butoxymethylethoxy)propanol (Dowanol DPnB), butyl diethylene glycol, N,N-dimethyl lactamide, 3-methoxy-N,N-dimethylpropionamide, 3-methoxy-3-methyl-1-butanol (MMB) and α-methyl-γ-butyrolactone (MBL).

[0137] surfactants

[0138] Water-based inkjet inks preferably contain at least one surfactant. One or more surfactants may be anionic, cationic, nonionic, or amphoteric surfactants, and are typically added in a total amount of less than 1% by weight, and particularly, in a total amount of less than 0.3% by weight, based on the total weight of the inkjet ink. All total amounts are expressed in dry solids.

[0139] Suitable surfactants for water-based inkjet inks include fatty acid salts, ester salts of higher alcohols, alkylbenzene sulfonates, sulfosuccinate salts, and phosphate salts of higher alcohols (e.g., sodium dodecylbenzene sulfonate and sodium dioctyl sulfosuccinate), ethylene oxide adducts of higher alcohols, ethylene oxide adducts of alkylphenols, ethylene oxide adducts of polyol fatty acid esters, and acetylene glycol and its ethylene oxide adducts (e.g., polyoxyethylene nonylphenyl ether and SURFYNOL™ 104, 104H, 440, 465 and TG, available from AIR PRODUCTS & CHEMICALS INC.).

[0140] The preferred surfactant is selected from fluorine-based surfactants, such as fluorinated hydrocarbons.

[0141] Suitable examples of anionic fluorinated surfactants include Capstone. TM FS-63, Capstone TM FS-61 (manufactured by DU PONT), Ftergent TM 100. Ftergent TM 110 and Ftergent TM 150 (manufactured by Neos Co. Ltd.); and Chemguard TM S-760P (manufactured by Chemguard, Inc.).

[0142] The preferred fluorinated surfactant is Capstone, derived from DU PONT. TM FS3100.

[0143] In a preferred embodiment of the water-based inkjet ink, the surfactant is a fluorinated surfactant, more preferably an alkoxylated fluorinated surfactant, and most preferably an alkoxylated fluorinated surfactant containing a sulfonic acid group or its salt.

[0144] Especially preferred are alkoxylated fluorinated surfactants according to formula (FI):

[0145]

[0146] Formula (FI),

[0147] in

[0148] Z1, Z2, and Z3 are independently structures R(O(CR1R2)). c -(CR3R4) d ) e - A branched or unbranched alkyl group, wherein at least one of Z1, Z2 and Z3 represents the structure R(O(CR1R2)). c -(CR3R4) d ) e - group;

[0149] The exponents c and d are independent of each other and range from 0 to 10, provided that c and d are not both 0 at the same time;

[0150] e is 0-5;

[0151] R is a branched or unbranched fluorinated alkyl group;

[0152] R1 to R4 are independently hydrogen, branched alkyl, or unbranched alkyl;

[0153] Y1 is an anionic polar group and Y2 is a hydrogen atom, or vice versa; and

[0154] X is a cation, preferably selected from Na. + Li + K + and NH4 + cations.

[0155] In a preferred embodiment, R1 to R3 represent hydrogen and R4 represents methyl, and more preferably the anionic polar group is a sulfonic acid group or a salt thereof.

[0156] Particularly preferred examples of alkoxylated fluorinated surfactants according to formula (FI) are shown in Table 1.

[0157] Table 1

[0158]

[0159] biocides

[0160] Suitable biocides for use in the aqueous inkjet inks of the present invention include sodium dehydroacetate, 2-phenoxyethanol, sodium benzoate, sodium pyridine thio-1-oxide, ethyl p-hydroxybenzoate, and 1,2-benzisothiazolin-3-one and their salts.

[0161] The preferred biocide is Proxel, which is available from ARCH UK BIOCIDES. TM GXL, Proxel TM K and Proxel TM Ultra 5 and Bronidox available from COGNIS TM .

[0162] The particularly preferred biocides are biocides based on 1,2-benzisothiazolin-3-one.

[0163] The biocides are preferably added in an amount of 0.001-3.0% by weight, more preferably 0.01-1.0% by weight, each based on the total weight of the water-based inkjet ink.

[0164] pH adjuster

[0165] From the perspective of dispersion stability, inks with a pH of 7.5 or higher at 25°C are preferred.

[0166] Water-based inkjet inks may contain at least one pH adjuster. Suitable pH adjusters include NaOH, KOH, NET3, NH3, HCl, HNO3, H2SO4, and (poly)alkanolamines (e.g., triethanolamine and 2-amino-2-methyl-1-propanol).

[0167] Preferred pH adjusters are triethanolamine, NaOH, and H2SO4.

[0168] It is preferable to adjust the pH to a value between 7.5 and 10.0, more preferably between 8.0 and 9.0; the latter pH range has been observed to result in improved ink stability and optimal compatibility with piezoelectric inkjet printheads.

[0169] Other components

[0170] In addition to the components mentioned above, inks may include other components as needed.

[0171] Examples of other components include known additives such as colorfastness inhibitors, emulsion stabilizers, penetration enhancers, UV absorbers, preservatives, antifungal agents, viscosity modifiers, rust inhibitors, and chelating agents.

[0172] Preferred UV absorbers include benzophenone compounds, benzotriazole compounds, salicylate compounds, and hydroxyphenyltriazine compounds.

[0173] Manufacturing of inkjet ink

[0174] Colored water-based inkjet inks can be prepared by precipitating or grinding colored pigments in a dispersion medium in the presence of a polymer dispersant, or simply by mixing self-dispersible colored pigments into the ink.

[0175] Mixing equipment may include pressure kneaders, open kneaders, planetary mixers, dissolvers, and Dalton Universal mixers. Suitable grinding and dispersing equipment includes ball mills, bead mills, colloid mills, high-speed dispersers, two-roll mills, bead mills, coating conditioners, and three-roll mills. Dispersions can also be prepared using ultrasonic energy.

[0176] If inkjet ink contains more than one pigment, the colored ink can be prepared using a separate dispersion for each pigment, or alternatively, several pigments can be mixed and co-milled when preparing the dispersion.

[0177] The dispersion process can be carried out in continuous, intermittent, or semi-intermittent modes.

[0178] The preferred amounts and ratios of the components in the abrasive can vary depending on the specific pigment. The contents of the abrasive mixture include the abrasive and the abrasive media. The abrasive contains pigment, dispersant, and liquid carrier (preferably water). For water-based inkjet inks, the pigment is typically present in the abrasive at 10-30% by weight, excluding the abrasive media. The weight ratio of pigment to dispersant is preferably 20:1 to 1:2.

[0179] The grinding time can vary widely and depends on the pigment, the selected machinery and residence conditions, the initial and desired final particle size, etc. In this invention, pigment dispersions with an average particle size of less than 100 nm can be prepared.

[0180] After grinding, conventional separation techniques (e.g., filtration, sieving, etc.) are used to separate the grinding media from the ground particulate product (in dry or liquid dispersion form). Typically, sieves are incorporated into the mill, such as for a bead mill. Filtration is preferred for separating the ground pigment concentrate from the grinding media.

[0181] Typically, it is desirable to prepare concentrated, abrasive-based colored inks, which are then diluted to a suitable concentration for inkjet printing systems. This technique allows for the preparation of larger quantities of colored ink from the equipment. If the abrasive is prepared in a solvent, it is diluted to the appropriate concentration with water and optionally other solvents. If prepared in water, it is diluted with additional water or a water-miscible solvent to prepare the abrasive at the desired concentration. By dilution, the ink is adjusted to the viscosity, color, hue, saturation density, and print coverage desired for a specific application. Viscosity can also be adjusted by using low molecular weight polyethylene glycol (e.g., number average molecular weight between 200 and 800). An example is PEG 200 from CLARIANT.

[0182] Ink receiving layer

[0183] In the manufacturing method according to the invention, the paper backing board (23) is provided with an ink receiving layer.

[0184] In a preferred embodiment, the ink acceptor layer is applied precisely prior to inkjet printing. The application of the liquid used to form the ink acceptor layer (ink acceptor liquid) can be performed by any known method (e.g., coating method, flexographic printing method, or inkjet method). Coating can be performed according to known coating methods, using a bar coater, extrusion die coater, air knife coater, doctor blade coater, bar coater, doctor blade coater, extrusion coater, reverse roller coater, or bar coater. However, it is preferred that the ink acceptor liquid be applied by flexographic printing.

[0185] The ink acceptor liquid preferably has a composition such that, when it comes into contact with ink on the paper backing, the components of the ink aggregate on the paper backing, thereby inhibiting the ink from penetrating into the paper backing, which is beneficial to image quality.

[0186] In a preferred embodiment, the ink acceptor liquid comprises compounds that induce the aggregation of ink components, such as acidic compounds and polyvalent cationic compounds.

[0187] Suitable acidic compounds are those that can lower the pH of the ink.

[0188] Regarding acidic compounds, either organic or inorganic acidic compounds may be used, and two or more compounds selected from organic and inorganic acidic compounds may be used in combination.

[0189] Organic acidic compounds can be organic compounds having acidic groups. Examples of acidic groups include phosphate groups, phosphonic acid groups, phosphonoglycerate groups, sulfate groups, sulfonic acid groups, sulfinic acid groups, and carboxyl groups. From the viewpoint of ink aggregation rate, the acidic group is preferably a phosphate group or a carboxyl group, and more preferably a carboxyl group.

[0190] Preferred examples of organic compounds (organic carboxylic acids) having a carboxyl group include polyacrylic acid, acetic acid, glycolic acid, malonic acid, malic acid (preferably DL-malic acid), maleic acid, ascorbic acid, succinic acid, glutaric acid, fumaric acid, citric acid, tartaric acid, phthalic acid, 4-methylphthalic acid, lactic acid, pyrrolidone carboxylic acid, pyranone carboxylic acid, pyrrolic carboxylic acid, furan carboxylic acid, pyridine carboxylic acid, coumaric acid, thiophene carboxylic acid, nicotinic acid, derivatives of these compounds, and their salts (e.g., polyvalent metal salts). These compounds can be used alone or in combination of two or more.

[0191] Regarding organic carboxylic acids, from the viewpoint of ink aggregation rate, divalent or higher-valent carboxylic acids, also known as polyvalent carboxylic acids, are preferred. More preferably, the ink acceptor layer includes at least one selected from malonic acid, malic acid, maleic acid, succinic acid, glutaric acid, fumaric acid, tartaric acid, 4-methylphthalic acid, and citric acid; and even more preferably, it includes at least one selected from malonic acid, malic acid, tartaric acid, and citric acid. The organic acidic compound preferably has a low pKa value.

[0192] Suitable inorganic acid compounds include phosphoric acid, nitric acid, nitrous acid, sulfuric acid, and hydrochloric acid; however, inorganic acid compounds are not particularly limited to these. From the viewpoint of ink aggregation rate, phosphoric acid is the most preferred inorganic acid compound.

[0193] In a more preferred embodiment, the ink accepting layer comprises a polyvalent metal salt.

[0194] Preferred examples of polyvalent metal salts include salts of any alkaline earth metal belonging to Group II of the periodic table (e.g., magnesium and calcium) and salts of cations belonging to Group XIII of the periodic table (e.g., aluminum). As metal salts, carboxylates (formates, acetates, benzoates, etc.), nitrates, chlorides, and thiocyanates are preferred. In particular, calcium or magnesium salts of carboxylic acids (e.g., formates, acetates, and benzoates), calcium or magnesium salts of nitric acids, calcium chloride, magnesium chloride, and calcium or magnesium salts of thiocyanate are preferred.

[0195] The content of acidic compounds and / or polyvalent metal salts is preferably 30-80% by weight, more preferably 40-60% by weight, based on the total dry weight of the ink acceptor layer.

[0196] For reliable processing, the ink receiving layer preferably contains a binder. The binder is preferably a polyvinyl alcohol-based polymer or copolymer.

[0197] Preferred polymers for the ink receiving layer are polyvinyl alcohol (PVA), vinyl alcohol copolymers, or modified polyvinyl alcohol. Modified polyvinyl alcohol can be cationic polyvinyl alcohol, such as cationic polyvinyl alcohol grades from Kuraray, or POVAL from Nippon Goshei. TM C506, POVAL TM C118.

[0198] Other suitable adhesives for ink receiving layers include polymeric adhesives selected from the following: hydroxyethyl cellulose; hydroxypropyl cellulose; hydroxyethyl methyl cellulose; hydroxypropyl methyl cellulose; hydroxybutyl methyl cellulose; methyl cellulose; sodium carboxymethyl cellulose; sodium carboxymethyl hydroxyethyl cellulose; water-soluble ethyl hydroxyethyl cellulose; cellulose sulfate polyvinyl acetal; polyvinylpyrrolidone; polyacrylamide; acrylamide / acrylic acid copolymer; polystyrene, styrene copolymer; acrylic or methacrylic acid polymers; styrene / acrylic acid copolymers; ethylene-vinyl acetate copolymers; vinyl- Methyl ether / maleic acid copolymers; poly(2-acryloylamino-2-methylpropanesulfonic acid); poly(diethylenetriamine-co-adipic acid); polyvinylpyridine; polyvinylimide; modified polyethyleneimine epichlorohydrin; ethoxylated polyethyleneimine; polymers containing ether bonds, such as polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), and polyvinyl ether (PVE); polyurethane; melamine resins; gelatin; carrageenan; dextran; gum arabic; casein; pectin; albumin; chitosan; chitosan; starch; collagen derivatives; linoleum and agar.

[0199] In a particularly preferred embodiment of the manufacturing method, the ink receiving layer contains a polymer or copolymer based on polyvinyl alcohol and a polyvalent inorganic salt (preferably CaCl2, Mg(NO3)2, or Ca(NO3)2). Excellent image quality results have been found for this combination.

[0200] The ink acceptor layer preferably contains a compound for crosslinking the polymer in the ink acceptor layer. The crosslinking agent is preferably included in an amount between 5-10% by weight, based on the total weight of the polymer in the ink acceptor layer. A preferred crosslinking agent is boric acid, especially in combination with polyvinyl alcohol.

[0201] In the manufacturing method according to the present invention, the dry weight of the ink receiving layer is preferably less than 0.8 g / m³. 2 More preferably, it is 0.1-0.6 g / m 2 Between. This is not only cost-effective, but also does not provide a significant embossed effect on corrugated cardboard that would cause an undesirable tactile experience.

[0202] From the viewpoint of ink aggregation rate, the viscosity of the ink acceptor liquid is preferably in the range of 1 mPa·s to 20 mPa·s, and more preferably in the range of 1 mPa·s to 10 mPa·s.

[0203] At 25°C, the surface tension of the ink acceptor liquid is preferably from 20 mN / m to 50 mN / m, and even more preferably from 30 mN / m to 45 mN / m. This is advantageous when the surface tension is within the above range because it suppresses the occurrence of coating unevenness.

[0204] Protective clear coat

[0205] Inkjet-printed images can be protected by laminating a transparent foil. However, it is preferable to apply a protective varnish layer to the inkjet-printed image. This offers advantages in productivity. For example, the protective varnish layer only needs to be applied to the areas where the inkjet-printed image is present.

[0206] The protective varnish layer is preferably applied after inkjet printing. The application of the protective varnish layer can be performed by any known method (e.g., coating method, flexographic printing method, or inkjet method). Coating can be performed according to known coating methods, using a bar coater, extrusion die coater, air knife coater, doctor blade coater, bar coater, doctor blade coater, extrusion coater, reverse roller coater, or bar coater. However, the protective varnish is preferably applied via flexographic printing because it has been found to be the most economical method.

[0207] The preferred polymer for the protective varnish layer is a polyurethane-based polymer, preferably as a polymer dispersion, such as a self-dispersing polyurethane latex.

[0208] Suitable protective varnish layers are well known to those skilled in the art, as so-called overprint varnishes have been frequently used in flexographic printing of corrugated cardboard.

[0209] The protective varnish layer can be made with a UV-curable overprint varnish, but a water-based overprint varnish is preferred.

[0210] Suitable examples include Digiguard from MICHELMAN. TM 520IJ, obtained from SIEGWERK's TP-Unilac TM High-gloss OPV and Unilac TM Postprint Glossy OPV.

[0211] The dry weight of the protective varnish layer is preferably 0.5-4.0 g / m³. 2 More preferably, it is between 1.0-3.0 g / m 2 The presence of a protective varnish layer within this range is usually sufficient to maintain image quality by preventing scratches.

[0212] inkjet printer

[0213] Piezoelectric printheads are incorporated into inkjet printers. Water-based inkjet ink is ejected from these printheads, which in a controlled manner propel small droplets through nozzles onto a substrate that moves relative to the printhead. In multi-pass inkjet printing methods, the inkjet printhead scans back and forth across the moving ink-receiving surface in the lateral direction. Sometimes the inkjet printhead does not print on its return journey. However, bidirectional printing is preferred for productivity. However, for optimal productivity, printing via a single-pass printing method is preferred. This can be achieved by using page-width inkjet printheads or multiple staggered inkjet printheads that cover the entire width of the ink-receiving surface. In single-pass printing methods, the inkjet printhead typically remains stationary while the substrate surface is transported beneath the inkjet printhead. The use of multiple staggered inkjet printheads is preferred because it is more cost-effective than page-width inkjet printheads when a printhead contains one or more faulty nozzles and must be replaced.

[0214] In a preferred embodiment of the present invention, the inkjet printer is a single-pass inkjet printing device, comprising an external nozzle with a surface area NS of less than 500 μm. 2 The combination of the above-mentioned piezoelectric printing head with the nozzle and the above-mentioned water-based inkjet ink.

[0215] Inkjet printing apparatus may include a dryer for removing at least a portion of the aqueous dispersion medium. Suitable dryers include devices that circulate hot air, ovens, infrared dryers, and devices that use air suction.

[0216] Preferred drying apparatuses use carbon infrared radiation (CIR) or include NIR sources that emit near-infrared radiation. NIR radiation can rapidly penetrate deep into the inkjet ink layer and remove water and solvents from the entire layer thickness, while conventional infrared and hot air energy are mainly absorbed at the surface and slowly conducted into the ink layer, which typically results in slower removal of water and solvents.

[0217] The maximum emission value of an effective infrared radiation source is between 0.8 and 1.5 μm. Such infrared radiation sources are sometimes called NIR radiation sources or NIR dryers. The preferred NIR radiation source is in the form of an NIR LED, which, due to its compact size, can be easily mounted near the inkjet printhead.

[0218] Example

[0219] Material

[0220] Unless otherwise stated, all materials used in the following examples are readily available from standard sources (e.g., Aldrich Chemical Co. (Belgium) and Acros (Belgium)). When used, the water is demineralized water.

[0221] PB15:3 is used for Sunfast TM The abbreviation for Blue 15:3 (CI pigment blue 15:3 pigment) is derived from SUNCHEMICAL.

[0222] PR122 is an abbreviation for INK JET MAGENTA E 02 (CI Pigment Red 122 Pigment), derived from CLARIANT.

[0223] PY151 is an abbreviation for Ink Yet Yellow H4G LV 3853 (CI Pigment Yellow 151 Pigment), derived from CLARIANT.

[0224] PBL7 is used for Printex TM The abbreviation for 60 (carbon black pigment) comes from EVONIK.

[0225] Edaplan is used for Edaplan TM 482 is an abbreviation for polymer dispersant, derived from MUNZING.

[0226] Joncryl is used for Joncryl TM 8078 is an abbreviation for polymer dispersant, derived from JOHNSON POLYMER B.V.

[0227] Tegowet is used for Tegowet TM270 is an abbreviation for polyether siloxane surfactant, derived from EVONIK.

[0228] PEG 200 is polyethylene glycol with an average molecular weight of 200, derived from CLARIANT.

[0229] TEA is triethanolamine.

[0230] Proxel is an abbreviation for a 5% aqueous solution of 1,2-benzisothiazolin-3-one. TM K was obtained from YDS CHEMICALS NV.

[0231] PVA is a polyvinyl alcohol solution, which can be obtained from UNILIN as PVA56-98-sol.

[0232] Measurement methods

[0233] 1. Average particle size

[0234] Dilute the ink sample with demineralized water to a pigment concentration of 0.002% by weight. Use Nicomp. TM The 380Particle Sizing System determines the number-average particle size of pigment particles based on the principle of dynamic light scattering. It uses a laser with an emission wavelength of 633nm and measures the size at a 90-degree scattering angle.

[0235] 2. Viscosity

[0236] Using a Brookfield DV-II+ viscometer at 1,000 s -1 The viscosity of the inkjet ink was measured at 32°C under a certain shear rate.

[0237] 3. External nozzle surface area

[0238] The dimensions of the nozzle orifices on the nozzle plate of the printhead were determined using a Nikon SMZ1500 stereo microscope at 11.25x magnification. The average of the determined dimensions for ten nozzles was taken. The determined nozzle dimensions are the necessary dimensions for calculating the external nozzle surface area. For example, the nozzle diameter was determined for a circular nozzle, while both the length and width were measured for a rectangular nozzle.

[0239] 4. Short-term incubation period

[0240] Using JetXpert TMThe "Latency Option" determines a short latency period, which allows measurement of the droplet velocity and volume of a specific target ink droplet within a series of ink droplets ejected from the printhead. The droplet velocity of the second ink droplet is determined during print idle times of 0.5 s and 1.0 s. The printhead is set with appropriate voltage and ink temperature to achieve a steady-state droplet velocity of 6 m / s. A droplet velocity loss of less than 20% for the second ink droplet is considered a good short latency period.

[0241] 5. Fog formation

[0242] Fog formation was visually evaluated in printing experiments where all nozzles ejected ink droplets in an 8kHz, 1dpd printing mode. Fog was generated by trailing ink droplets, which had too low a droplet velocity to form satellites in the printed image, but instead formed an "ink droplet cloud" around the nozzle plate of the printhead.

[0243] 6. Average drying rate

[0244] A glass container with a diameter of 5 cm was filled with 100 g of water-based inkjet ink, weighed, and placed in a ventilated oven at 60 °C. After a first drying period of 1800 s, the glass container was weighed again, and the weight loss Δ wt% was recorded (1). The same glass container was placed back in the oven for another 9000 s, and then weighed again, and the weight loss Δ wt% was recorded (2).

[0245] The average drying rate (ADS) is calculated according to formula (2) and expressed as a percentage loss per second (wt%).

[0246]

[0247] To achieve an acceptable drying rate in a single-pass inkjet printing unit without an excessively large dryer, the ADS should be greater than 0.0025 wt% loss / second.

[0248] Example 1

[0249] This embodiment illustrates a method for external nozzles with a surface area NS less than 500μm. 2 The reliability of water-based inkjet inks in piezoelectric current-driven printheads. This invention describes a cyan ink composition containing β-copper phthalocyanine pigment and water content within the range defined by formula (I).

[0250] Preparation of concentrated pigment dispersions

[0251] Using Disperlux TM A mixer was used to prepare a concentrated aqueous pigment dispersion by mixing the compositions according to Table 2 for 30 minutes.

[0252] Table 2

[0253] Component weight %: CP-1 PB15:3 15.00 Edaplan 15.00 water 70.00

[0254] Then use Dynomill TM KDL and 0.4mm yttrium-stabilized zirconium beads YTZ TM The concentrated pigment dispersion was ground using grinding media (available from TOSOH Corp.). The grinding mill was filled halfway with grinding beads and ground for 3 hours at a flow rate of 200 mL / min and a rotation speed of 15 m / s. After grinding, the dispersion was separated from the beads. The resulting concentrated pigment dispersion CP-1 was used as the base for preparing the corresponding water-based cyan inkjet ink. The average particle size (APD) was 138 nm.

[0255] Preparation of Cyan Inkjet Ink

[0256] Using concentrated pigment dispersion CP-1, four cyan water-based inkjet inks Ink-1 to Ink-4 were prepared according to Table 3, with different amounts of water and organic solvent PEG200.

[0257] Table 3

[0258] Component weight %: Ink-1 Ink-2 Ink-3 Ink-4 PB15:3 2.20 2.20 2.20 2.20 Edaplan 2.20 2.20 2.20 2.20 Proxel 0.20 0.20 0.20 0.20 1,2-Hexanediol 3.00 3.00 3.00 3.00 glycerin 20.00 20.00 20.00 10.00 PEG200 14.00 33.00 24.00 14.00 water 58.10 39.10 48.10 68.10 TEA 0.30 0.30 0.30 0.30

[0259] Evaluation and Results

[0260] After determining the external nozzle surface area NS using a microscope, the following combinations of printheads and inkjet inks listed in Table 4 were evaluated. End-jet piezoelectric printheads are identified by END, while through-flow piezoelectric printheads are identified by TF.

[0261] Table 4

[0262]

[0263] The short-term latency and haze formation of the printhead and water-based inkjet ink combination in Table 4 were evaluated. The average drying rates of the water-based inkjet inks Ink-1 to Ink-4 were determined and are shown in Table 5.

[0264] Table 5

[0265]

[0266] As can be seen from Table 5, only the combinations INV-1 to INV-3 according to the present invention can achieve a good short latency period, exhibiting no haze formation and a good average drying rate.

[0267] It should be clear that unless the functional relationship between equation (I) and water content is known, it is difficult to design an inkjet printing apparatus with a combination of printheads and inks that provides good printing reliability in an economical manner. For example, the COMP-3, INV-1, and INV-3 combinations all use the same ink, Ink-3, containing 48.1% by weight water. The external nozzle surface area of ​​the end-jet printhead of COMP-3 is between that of the external nozzle surface areas of the flowheads of INV-1 and INV-3, but it fails during the short latency period due to the droplet velocity of the second droplet being less than 1 m / s during the 0.5 s and 1.0 s printing idle times. The droplet velocities of INV-1 and INV-3 are both 5.7 m / s during the 0.5 s printing idle time, while their droplet velocities during the 1.0 s printing idle time are 5.5 m / s and 5.1 m / s, respectively. If the water content is increased too much, the jetting becomes unstable, as illustrated by the COMP-5 combination relative to INV-1 and the COMP-6 combination relative to INV-3. Replacing too much water in the inks of the INV-3 blend with organic solvents resulted in haze formation and unacceptable drying speeds, as demonstrated by the COMP-7 blend, although a short latency could be maintained (droplet velocity of 5.6 m / s at a 0.5 s print idle time and 5.0 m / s at a 1.0 s print idle time). For completeness, at 32°C and at 1,000 s... -1 At the shear rate, the viscosities of the inkjet inks Ink-1 and Ink-3 used in combinations INV-1 to INV-3 were determined to be 3.5 mPa·s and 5.5 mPa·s, respectively.

[0268] Example 2

[0269] This embodiment illustrates a water-based inkjet ink kit suitable for reliably printing color images with high image quality on corrugated cardboard.

[0270] Preparation of concentrated pigment dispersions CPK, CPC, CPM and CPY

[0271] Concentrated pigment dispersions CPC, CPM, CPY, and CPK were prepared in the same manner as described in Example 1 for concentrated pigment dispersion CP-1, except that the compositions according to Table 6 were used.

[0272] Table 6

[0273] Component weight %: CPC CPM CPY CPK PB15:3 15.0 --- --- --- PR122 --- 15.0 --- --- PY151 --- --- 15.0 --- PB7 --- --- --- 15.0 Edaplan482 7.5 15.0 12.5 --- Joncryl8078 --- --- --- 10.0 water 77.5 70.0 62.5 70.0

[0274] Preparation of water-based inkjet ink kits

[0275] Subsequently, the concentrated pigment dispersions CPC, CPM, CPY, and CPK were diluted with the other ink components according to Table 7, and the concentrated pigment dispersions were used in the same manner to prepare the corresponding inkjet inks C, M, Y, and K. % by weight is based on the total weight of the ink.

[0276] Table 7

[0277]

[0278]

[0279] Preparation of ink acceptor layer

[0280] Prepare a coating composition COAT-1 having the composition according to Table 8.

[0281] Table 8

[0282] Component weight %: COAT-1 PVA 52.98 <![CDATA[CaCl2]]> 4.64 boric acid 6.00 water 36.38

[0283] Evaluation and Results

[0284] Equipped with Samba technology from FUJIFILM DIMATIX Inc. TM G3L inkjet printhead (NS=240μm) 2 JetXpert TM The ejection performance of all inkjet inks was tested on a droplet observer. Stable ejection with 100% ink coverage was observed for 5 minutes at 20 kHz, 40 kHz, and 60 kHz for all inkjet ink sets.

[0285] The coating composition COAT-1 was applied to a white Fusion coating derived from SAPPI at a wet layer thickness of 4 μm. TM The coating was applied to the top liner. It was then dried in an oven at 60°C to obtain a dry weight thickness of 0.36 g / m². 2 Ink receiving layer. Using Samba TM The G3L inkjet printhead uses the CMYK inkjet inks listed in Table 7 to print images on the ink receiving layer.

[0286] List of reference numerals

[0287] Table 9 lists the reference numerals used for the accompanying drawings.

[0288] Table 9

[0289] 1 Groove cardboard 2 Paper backing board 3 Paper backing board 4 glue 10 Printing head wall 11 Inkjet 12 Ink Inlet 13 ink export 14 Ink Channel 15 Nozzle plate 16 nozzle 17 Sprayed ink droplets 18 Inner nozzle diameter 19 outer nozzle diameter 20 Single-wall corrugated cardboard 21 Groove cardboard 22 Paper backing board 23 Paper backing board 24 Flexographic printing rollers for ink receiving layer 25 Inkjet printhead 26 Flexographic printing rollers for protective varnish layers 27 Inkjet printed paper backing 28 Single-faced corrugated cardboard 29 Laminating rollers

Claims

1. A method for manufacturing printed corrugated cardboard, the method comprising the following steps: a) Provide a paper backing board (23) with an ink-receiving layer; and b) Use nozzles with an external nozzle surface area NS less than 500μm 2 The piezoelectric printing head (25) of the nozzle inkjet prints an image on the ink receiving layer using one or more colored water-based inkjet inks; The one or more colored water-based inkjet inks contain water in an amount of A% by weight as defined by formula (I): 100wt%-sqrt(NS)x3.8wt% / μm≤Awt%≤100wt%-sqrt(NS)x2.2wt% / μm Formula (I) The weight percentage is based on the total weight of the water-based inkjet ink; Where sqrt(NS) represents the square root of the surface area NS of the external nozzle; and Where A by weight ≥ 40% by weight, and The application of the ink acceptor liquid used to form the ink acceptor layer is performed by inkjet printing.

2. The manufacturing method as claimed in claim 1, comprising step c) laminating an inkjet-printed paper backing board (27) onto a grooved corrugated cardboard.

3. The manufacturing method of claim 1, wherein the inkjet printing is performed according to a single-pass printing method.

4. The manufacturing method of claim 1, wherein the ink acceptor liquid comprises an acidic compound or a polyvalent cationic compound.

5. The manufacturing method of claim 1, comprising the step of applying a protective varnish layer onto the inkjet-printed image.

6. The manufacturing method of claim 5, wherein the protective varnish layer is applied by inkjet printing.

7. The manufacturing method of claim 1, wherein the surface area NS of the external nozzle is less than 300 μm. 2 .

8. The manufacturing method of claim 1, wherein the one or more water-based inkjet inks are used in 1,000 s. -1 The viscosity at 32°C under certain shear rates is between 3.0 and 8.0 mPa·s.

9. The manufacturing method of claim 1, wherein the dry weight of the ink receiving layer is less than 0.8 g / m³. 2 .

10. The manufacturing method of claim 1, wherein the paper liner (23) is provided in the form of a roll.

11. The manufacturing method of claim 1, wherein the coloring aqueous inkjet ink comprises: a) Cyan water-based inkjet ink containing β-copper phthalocyanine pigment; b) Magenta or red water-based inkjet ink containing pigments selected from CI Pigment Red 57 / 1, CI Pigment Red 122, CI Pigment Violet 19 and their mixtures. c) A yellow water-based inkjet ink containing pigments selected from CI Pigment Yellow 74, CI Pigment Yellow 138, CI Pigment Yellow 151, and their mixtures; and d) Black water-based inkjet ink containing carbon black pigment.

12. The manufacturing method of claim 1, wherein the paper backing board (23) is white.

13. The manufacturing method of claim 1, wherein the printed corrugated cardboard is single-wall corrugated cardboard.

14. An inkjet printing apparatus for manufacturing printed corrugated cardboard, said apparatus comprising: a) The external nozzle surface area NS is less than 500μm 2 The nozzle of the piezoelectric current-carrying printing head; and b) Water-based inkjet inks from a water-based inkjet ink kit, wherein the water-based inkjet inks contain water in an amount of A% by weight as defined by formula (I): 100wt%-sqrt(NS)x3.8wt% / μm≤Awt%≤100wt%-sqrt(NS)x2.2wt% / μm Formula (I) The weight percentage is based on the total weight of the water-based inkjet ink; Where sqrt(NS) represents the square root of the surface area NS of the external nozzle; and Where A is ≥ 40% by weight.

15. The inkjet printing apparatus as claimed in claim 14, wherein it is a single-pass inkjet printing apparatus.

16. The inkjet printing apparatus of claim 15, wherein the single-pass inkjet printing apparatus uses a plurality of staggered inkjet printheads.

17. The inkjet printing apparatus of claim 15, wherein A by weight ≥ 44% by weight.

18. The inkjet printing apparatus of claim 15, wherein the surface area NS of the external nozzle is less than 300 μm. 2 .

19. The inkjet printing apparatus of claim 14, wherein the water-based inkjet ink is applied in 1,000 seconds. -1 The viscosity at 32°C under certain shear rates is between 3.0 and 8.0 mPa·s.

20. The inkjet printing apparatus of claim 15, comprising an NIR dryer.

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