Patent Application
20250115046
The present disclosure relates to an ink jet recording method.
In recent years, ink jet recording methods have been increasingly used in a field called sign and display, such as printing of posters and large-format advertisements. The recording area in this field is characteristically larger than the recording area of home ink jet recording apparatuses. Furthermore, since images need to attract attention, inks that can record images with high color developability are required.
In the sign and display field, non-absorptive record media formed of vinyl chloride (PVC), poly(ethylene terephthalate) (PET), or the like having a surface with almost no ink absorbency are often used. Thus, it is required to suppress blurring and nonuniformity of images on non-absorptive record media. Record media having a surface with almost no ink absorbency are hereinafter also referred to as “non-absorptive record media”. In an ink jet recording method for recording on a non-absorptive record medium, it is important to prevent an ink dot from being repelled on the record medium to suppress blurring. For this purpose, it is necessary to rapidly thicken and fix the ink applied to the record medium.
A recording method using a solvent-based ink composed mainly of an organic solvent or a curable ink containing a polymerizable monomer is known as a method for recording on a non-absorptive record medium. In recent years, however, from the perspective of environmental load and safety, there is an increasing need for a recording method for recording on a non-absorptive record medium using an aqueous ink.
A method for recording on a non-absorptive record medium using an aqueous ink may be a method of evaporating water in the ink on the surface of the non-absorptive record medium or a method of using a reaction liquid for aggregating a component of the ink. The former is advantageous from the perspective of running cost because it is not necessary to provide a unit for applying a reaction liquid, but is inferior in productivity because it is necessary to reduce the recording speed. Thus, a method of using a reaction liquid has been studied.
Furthermore, to improve productivity, it is necessary to shorten the time required for maintenance of a liquid ejection head and to enable continuous recording. The maintenance of a liquid ejection head is necessary to suppress a decrease in ejection properties due to thickening of a reaction liquid or an ink or solidification of a component, such as a pigment or a resin, in the reaction liquid or the ink in an ejection port not mainly used during continuous recording. Thus, there is a need for an ink jet recording method using a reaction liquid that maintains stable ejection without interruption of recording even in continuous recording for a long period.
A liquid ejection head has been proposed that has a mechanism to induce ink flow near an ejection port of the liquid ejection head to suppress stagnation of an ink component, such as a pigment or a resin, in an ink channel of the liquid ejection head (see Japanese Patent Laid-Open No. 2007-118611). Furthermore, to improve the cleaning recovery of an ejection port for ejecting a reaction liquid, an ink jet recording method using a liquid ejection head having a circulatory channel has been proposed (see Japanese Patent Laid-Open No. 2020-104487).
The present inventors have found that a liquid ejection head only having a circulatory channel can have some intermittent ejection stability in the liquid ejection head using a reaction liquid but causes image unevenness.
The present disclosure provides an ink jet recording method in which a reaction liquid or an ink has high ejection stability.
The present disclosure provides a liquid ejection apparatus ejecting an aqueous ink and an aqueous reaction liquid containing a reactant that reacts with the aqueous ink to record an image on a record medium. The liquid ejection apparatus includes an element substrate including: a plurality of individual channels having an ejection port configured to eject the liquid, a pressure chamber configured to supply the liquid to the ejection port, and an energy-generating element configured to generate energy to eject the liquid; an upstream channel configured to supply the liquid to the plurality of individual channels; and a downstream channel for outflow of the liquid from the plurality of individual channels. The ejection port has a protrusion protruding toward a center of the ejection port.
Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
The present disclosure is described in detail in the following embodiments. In the following description, an aqueous ink and a reaction liquid for ink jet may be referred to simply as an “ink” and a “reaction liquid”, respectively.
In an ink jet recording method according to the present disclosure, an aqueous ink and an aqueous reaction liquid described later is ejected from an ink jet liquid ejection head to record an image on a record medium. The method can include a reaction liquid ejection step of ejecting an aqueous reaction liquid containing a reactant that reacts with the aqueous ink from an ejection port onto a record medium and an ink application step of applying the aqueous ink so as to overlap at least part of a region to which the aqueous reaction liquid is applied. Furthermore, the reaction liquid ejection step can be provided before the ink application step, or the ink application step and the reaction liquid ejection step can be performed in parallel. In the present disclosure, it is not necessary to provide a step of curing an image by irradiation with an active energy ray or the like.
The record medium may be, but is not limited to, a transparent or colored record medium. The record medium may be a less absorbent medium (non-absorptive medium) with low liquid medium absorbency, such as a resin film. In the case of a so-called serial liquid ejection head and an ink jet recording method in which recording is performed while scanning a record medium, application of ink to a unit region of the record medium can be multipass recording performed by multiple times of relative scanning between the liquid ejection head and the record medium. In particular, when a white ink is used as described later, the application of the white ink and the application of a chromatic color ink or an aqueous reaction liquid to a unit region can be performed by different relative scans. In particular, the white ink and the chromatic color ink can be applied to the unit region by different relative scans. This increases the time intervals between inks coming into contact with each other and easily suppresses mixing of the inks. The unit region can be set as an arbitrary region, such as one pixel or one band.
Appropriate embodiments of a liquid ejection apparatus (ink jet recording apparatus) that can be used in an ink jet recording method according to the present disclosure are described in detail below with reference to the accompanying drawings. However, the following description does not limit the scope of the present disclosure. For example, the present embodiment employs a thermal system of generating a bubble by a heating element to eject liquid. The present disclosure can also be applied to a liquid ejection head utilizing a piezoelectric system of using a piezoelectric element as an energy-generating element to eject liquid or utilizing another liquid ejection system. A liquid ejection head according to the present disclosure that ejects liquid, such as ink, and a liquid ejection apparatus equipped with the liquid ejection head can be applied to a printer, a copying machine, a facsimile including a communication system, or a word processor including a printer unit. They can also be applied to an industrial recording apparatus combined with various processing apparatuses. For example, they can also be used in applications, such as biochip production, electronic circuit printing, and semiconductor substrate production.
The present embodiment is an ink jet recording apparatus (recording apparatus) in which liquid, such as ink, is circulated between a tank and a liquid ejection head, but another form is also possible. For example, instead of circulating the ink, two tanks may be provided on the upstream side and the downstream side of the liquid ejection head, and the ink may flow from one tank to the other tank to induce ink flow in the pressure chamber. Although the present embodiment is a so-called line (page wide) head with a length corresponding to the width of a record medium, the present disclosure can also be applied to a so-called serial liquid ejection head that performs recording while scanning a record medium. The serial liquid ejection head is, for example, but not limited to, a head with one element substrate for a black ink and one element substrate for a chromatic color ink. It also may be a short line head that has several element substrates arranged so that ejection ports overlap in the ejection port array direction and is shorter than the width of a record medium, and the record medium may be scanned with the short line head.
Examples of embodiments of the present disclosure are described below with reference to the drawings.
As described above, the ink application step can follow the reaction liquid ejection step, and the apparatus 1000 in
The record medium 2 is a cut paper in
The present embodiment describes an ink jet recording apparatus in which one liquid ejection head ejects one type of liquid, a liquid ejection head (first liquid ejection head) ejects the ink, and a liquid ejection head (second liquid ejection head) ejects the reaction liquid. However, one liquid ejection head may be configured to eject a plurality of types of liquids, and the present disclosure can be suitably used even in a configuration in which one liquid ejection head is configured to eject the aqueous ink and the aqueous reaction liquid.
During the ejection operation by the liquid ejection head 3, the control unit 500 drives a convey motor 503 to convey the record medium 2 in the X direction at a speed corresponding to the drive frequency. Consequently, an image corresponding to the image data received from the host apparatus 600 is recorded on the record medium 2. In the ROM 501, information on the use region of an ejection port used for ejection in the liquid ejection head 3 is stored in a rewritable manner for each liquid ejection head 3. A method of setting the use region is described in detail later.
The buffer tank 1003 as a sub tank connected to a main tank 1006 has an air communication port (not shown) for communication between the inside and outside of the tank and can discharge bubbles from liquid to the outside. The buffer tank 1003 is also connected to a replenishing pump 1005. When liquid is consumed in the liquid ejection head 3 by ejecting (discharging) the liquid from an ejection port of the liquid ejection head, such as ejecting the liquid for recording or suction recovery, the replenishing pump 1005 transfers the consumed liquid from the main tank 1006 to the buffer tank 1003.
The first circulation pump 1002 has a role of drawing liquid from a liquid connection portion 111 of the liquid ejection head 3 and causing the liquid to flow to the buffer tank 1003. When the liquid ejection head 3 is driven, a certain amount of liquid flows in a common collecting channel 212 by the first circulation pump 1002.
A negative pressure control unit 230 is provided in a path between a second circulation pump 1004 and a liquid ejection unit 300. The negative pressure control unit 230 has a function of operating so as to maintain the pressure on the downstream side (the liquid ejection unit 300 side) of the negative pressure control unit 230 at a preset constant pressure even when the flow rate of the circulation system fluctuates due to a difference in duty at which recording is performed.
As illustrated in
Thus, in the liquid ejection unit 300, there are a liquid flow through the common collecting channel 212 and a flow from the common supply channel 211 through each element substrate 10 to the common collecting channel 212. This can dissipate the heat generated in each element substrate 10 to the outside of the element substrate 10 by the flow from the common supply channel 211 to the common collecting channel 212. During recording with the liquid ejection head 3, such a configuration can generate a liquid flow even in an ejection port or a pressure chamber not involved in recording and can suppress the thickening of the liquid in these portions. Furthermore, thickened liquid or a foreign substance in the liquid can be discharged to the common collecting channel 212. Thus, the liquid ejection head 3 of the present embodiment can perform high-speed and high-quality recording.
The housing 80 is composed of a liquid ejection unit support portion 81 and an electric wiring board support portion 82, supports the liquid ejection unit 300 and the electric wiring board 90, and secures the rigidity of the liquid ejection head 3. The electric wiring board support portion 82 supports the electric wiring board 90 and is fastened with screws to the liquid ejection unit support portion 81. The liquid ejection unit support portion 81 has openings 83 and 84 into which a joint rubber 100 is inserted. The liquid supplied from the liquid supply unit 220 is guided to a second channel member 60 constituting the liquid ejection unit 300 via the joint rubber 100.
Next, the configuration of a channel member 210 in the liquid ejection unit 300 is described. As illustrated in
A plurality of support members 30 arranged in the Y direction are disposed on a surface of the first channel member 50 opposite the second channel member 60, and one element substrate 10 is disposed on each support member 30. The number of arrays of the ejection modules 200 can be adjusted to configure liquid ejection heads 3 of various sizes.
As illustrated in
As illustrated in
The element substrate 10 of the ejection module 200 is mounted on the communication port 51 of the first channel member 50 via the support member 30. Although only the communication port 51 corresponding to the common supply channel 211 is illustrated in
As described above, the common supply channel 211 is connected to the negative pressure control unit 230H with a relatively high pressure, and the common collecting channel 212 is connected to the negative pressure control unit 230L with a relatively low pressure. A supply path for supplying the liquid to a channel formed in the element substrate 10 through the common communication port 63 (see
The configuration of the element substrate 10 according to the embodiment is described below.
As illustrated in
As illustrated in
Next, the liquid flow in the element substrate 10 is described. Although four ejection port arrays are formed in a channel-forming member 12 of the element substrate 10 in
In other words, the liquid supplied from the liquid ejection apparatus main body to the liquid ejection head 3 flows in the following order and is supplied and collected. The liquid first flows from the liquid connection portion 111 of the liquid supply unit 220 into the liquid ejection head 3. The liquid is then supplied to the joint rubber 100, the common communication port 63 in the second channel member, the common channel 61 in the first channel member, and the communication port 51 in this order. The liquid is then supplied to the pressure chamber 23 via the communication port 31 in the support member 30, the openings 21 in the cover plate 20, and the liquid supply channel 18 and the supply port 17a in the substrate 11 in this order. The liquid supplied to the pressure chamber 23 and not ejected from the ejection port 13 flows through the collection port 17b and the liquid collecting channel 19 in the substrate 11, the openings 21 in the cover plate 20, and the communication port 31 in the support member 30 in this order. The liquid then flows through the communication port 51 and the common channel 62 in the first channel member, the common communication port 63 in the second channel member, and the joint rubber 100. The liquid then flows from the liquid connection portion 111 provided in the liquid supply unit to the outside of the liquid ejection head 3. In the form of the circulation path illustrated in
The liquid ejection head of the present embodiment further includes a temperature control mechanism in the element substrate 10.
<Liquid Flow near Pressure Chamber>
A plurality of supply ports 17a form a supply port array, and a plurality of collection ports 17b form a collection port array. An ejection port array of a plurality of ejection ports 13 arranged is formed between the supply port array and the collection port array. In the present embodiment, as described above, a pressure difference is provided between the liquid supply channel 18 and the liquid collecting channel 19. Due to this pressure difference, the liquid is introduced from the supply port 17a into the pressure chamber 23 through the inlet channel 24a, generating the circulatory flow C of the liquid flowing from the outlet channel 24b to the collection port 17b.
The heating resistance element 15 is provided on the bottom face of the pressure chamber 23 facing the ejection port 13. An ejection port portion (nozzle) 25 penetrates the channel-forming member 12 at a position facing the pressure chamber 23. An outer end portion of the ejection port portion 25, that is, an end portion opposite the heating resistance element 15, forms the ejection port 13 through which the liquid is ejected. The ejection port portion 25 or the ejection port 13 is provided at a position facing the heating resistance element 15. In the present specification, the ejection port 13 is an opening in an outer surface of the channel-forming member 12 facing the record medium 2, and the ejection port portion 25 is a portion that communicates between the ejection port 13 and the pressure chamber 23 and means a through-hole that penetrates the channel-forming member 12.
As illustrated in
In an ink jet printer used in the commercial and industrial sectors or the like, an ink with a high solid density is used in some cases from the perspective of image fastness, color developability, or the like. The term “solid density”, as used herein, refers to the density of the pigment, resin, wax, and the like in the ejection liquid. At this time, defective ejection caused by the concentration of ink due to the evaporation of water from the ink may be more significant. Thus, as in the present disclosure, since the liquid inside the pressure chamber can be circulated, even if water near the ejection port 13 evaporates, fresh liquid is supplied from the inlet channel 24a, and the effect of realizing stable ejection can be further achieved.
In the liquid ejection head of the present embodiment, the inlet channel 24a, the pressure chamber 23, the ejection port 13, the recording element 15, and the outlet channel 24b constitute an individual channel 24 as one ejection unit, and the liquid supply channel 18 (upstream channel) for supplying the liquid and the liquid collecting channel 19 (downstream channel) for liquid outflow are connected to a plurality of ejection units (individual channels). The upstream channel and the downstream channel separated from each other with the individual channel interposed therebetween can produce an effect of more easily preventing the ejection liquid from being concentrated.
It is effective to reduce the resistance against a droplet passing through the ejection port as a method of advancing the timing of the air communication and shortening the tail. Thus, the distance OH from the plane of the pressure chamber 23 having the recording element 15 to the ejection port 13 in the ejection direction is preferably 16 μm or less. Such a dimensional relationship can produce an effect of efficiently applying ejection energy from the recording element to an ejected droplet. This can also further increase the ejection speed of the ejected droplet at the time of the air communication and make the configuration stronger (more robust) against the disturbance of air flow or the like caused by the record medium. On the other hand, an excessively short OH results in excessively high flow resistance, and thus the OH is preferably 13 μm or more.
It is desirable that the inlet channel 24a and the outlet channel 24b have the same flow resistance. A bubble generated by the thermal energy spreads not only in the ejection direction but also in the directions of the inlet channel 24a and the outlet channel 24b (see
In the present disclosure, the ejection port has at least one protrusion protruding toward the center thereof. Thus, the contraction of the bubble narrows the trailing end portion in the ejection direction of the ejected droplet that has moved toward the central portion of the recording element 15, and narrows the tail. This can advance the timing of the air communication and shorten the tail length, thus suppressing the formation of a satellite due to the separation of a droplet from the main droplet. Even if a satellite separated from the main droplet is formed, due to the short tail length, the satellite is small and can be reduced in number.
Furthermore, the protrusions 27 with a thick tip (on the center F side) may result in two ejected droplets divided by the protrusions 27. Thus, the leading edge of each protrusion 27 desirably has a width 271 of 4.0 μm or less, for example, 2.0 μm in the present embodiment. When each protrusion has a rounded tip as in the present embodiment illustrated in
It is desirable that the two protrusions 27 extend in a direction approximately parallel to the conveying direction (X direction) of the record medium 2. Since the protrusions 27 have a very large influence on the ejection of a droplet, a slight variation in the shape of the two protrusions during production results in a droplet flying off in the direction of one of the protrusions and a landing position deviation. In general, a landing position deviation in the ejection port array direction (Y direction) is more easily visually recognized on the image than a landing position deviation in the record medium direction (X direction). Thus, making the direction of the protrusions approximately parallel to the conveying direction of the record medium 2 can suppress the deviation in the ejection port array direction and has an effect of maintaining good printing. Furthermore, it is desirable that the protrusions 27 extend in the flow direction of the liquid near the pressure chamber. In other words, it is desirable that the straight line L on which the protrusions are positioned forms an angle of 45 degrees or less with the channel axis connecting the liquid supply channel 18 and the liquid collecting channel 19 or connecting the inlet channel 24a and the outlet channel 24b.
Although the two protrusions 27 extend toward the center F of the ejection port in the present embodiment, even one protrusion 27 can maintain good droplet formation. In such a case, however, the landing may be largely deviated in a direction in which the protrusion 27 is not present, and the landing position may be less consistent. Thus, it is more desirable that the two protrusions 27 extend in the direction of the ejection port center F. The present disclosure can be suitably applied even to a liquid ejection head having an ejection port without the protrusions 27.
In other words, it can be said that the configuration of the ejection port 13 having the protrusions 27 as described above has a shape in which the ejection port is partially narrowed.
It is desirable that the ejection port 13 have an opening area of 100 μm2 or more. Alternatively, when the diameter of a circle with an area equal to the actual area of the ejection port 13 is defined as the effective diameter, the ejection port 13 desirably has an effective diameter of 11 μm or more. An excessively small opening area results in an increase in forward resistance during liquid ejection and a longer time required for passing. This may increase the tail length and the number of satellites. Furthermore, the opening area of the ejection port affects the ejection speed of a droplet from the ejection port described later. It should be noted that the ejection port having the protrusions 27 as in the present disclosure tends to have a smaller opening area and a lower ejection speed than an ejection port with the same diameter and without the protrusions.
In the liquid ejection head having the protrusions 27 in the ejection port 13 as in the present disclosure, the viscosity of the liquid near the ejection port increases due to water evaporation near the ejection port, making defective ejection more likely compared to a liquid ejection head without protrusions in the ejection port. This is due to the length of the periphery of an ejection port having protrusions longer than that of a circular nozzle and larger resistance of the liquid ejected from the ejection port 13. In the liquid ejection head of the present embodiment, since the liquid inside the pressure chamber can be circulated, even if water near the ejection port 13 evaporates, unevaporated fresh liquid is supplied from the inlet channel 24a. Thus, even when the ejection port 13 has the protrusions 27, stable ejection can be realized without excessively increasing the ejection speed.
<Conditions during Droplet Formation>
Furthermore, to achieve stable ejection quality and high recording quality, it is also desirable that the dot size of a landed droplet on the record medium 2 be relatively small and high definition. Thus, the liquid ejection head of the present embodiment has a relatively small ejection volume of 2.0 ng.
Droplet formation is also affected by the ejection speed of the droplet. At an excessively high ejection speed, the tip of the main droplet is ejected ahead of the tail, and the tail is likely to break and form a satellite. Thus, the ejection speed is desirably 12 m/s or less. On the other hand, at an excessively low droplet ejection speed, a component in the ejection liquid may burn and stick to the heating element. Thus, the ejection speed is desirably 7.0 m/s or more. In an ink jet printer used in the commercial and industrial sectors or the like that require better droplet formation, an ink with a high solid density is used in some cases from the perspective of image fastness, color developability, or the like. The term “solid density”, as used herein, refers to the density of the pigment, resin, wax, and the like in the ejection liquid. At this time, defective ejection caused by the concentration of ink due to the evaporation of water from the ink may be more significant. Although the ejection speed can be increased to suppress the concentration of ink, at an excessively high ejection speed, the tail is easily broken, and a satellite is likely to occur, as described above. In the liquid ejection head of the present embodiment, since the liquid inside the pressure chamber can be circulated, even if water near the ejection port 13 evaporates, unevaporated fresh liquid is supplied from the inlet channel 24a. Thus, even when the ejection liquid is an ink with a high solid density, stable ejection can be realized without excessively increasing the ejection speed. The ink with a high solid density is, for example, an ink with a nonvolatile solvent concentration adjusted to 10% by weight or more and 20% by weight or less, a pigment concentration adjusted to 3% by weight or more and 10% by weight or less, a solid density adjusted to 10% by weight or more and 30% by weight or less, and a viscosity adjusted to 0.003 Pa·s or more and 0.006 Pa·s or less.
Components and the like used in an aqueous reaction liquid of the present disclosure are described in detail below.
The reaction liquid comes into contact with an ink, reacts with the ink, and aggregates a component (a component with an anionic group, such as a resin or a self-dispersible pigment) in the ink, and contains a polyvalent metal salt, an organic acid, a cationic resin, or the like as a reactant. Any reactant can be added to the reaction liquid as long as desired characteristics, such as high storage stability of the reaction liquid, high intermittent ejection stability, and suppression of image unevenness, can be achieved.
In a reaction liquid containing a polyvalent metal salt, the polyvalent metal salt, which is a compound produced by bonding a divalent or higher-valent metal ion and an anion, is dissociated into a polyvalent metal ion in the reaction liquid and can aggregate a coloring material dispersed by the action of an anionic group contained in the ink.
The polyvalent metal ion is, for example, a divalent metal ion, such as Ca2+, Cu2+, Ni2+, Mg2+, Sr2+, Ba2+, or Zn2+, or a trivalent metal ion, such as Fe3+, Cr3+, Y3+ or Al3+. To contain a polyvalent metal ion in the reaction liquid, a polyvalent metal salt (which may be a hydrate) produced by bonding the polyvalent metal ion and an anion can be used. The anion is, for example, an inorganic anion, such as Cl−, Br−, I−, ClO−, ClO2−, ClO3−, ClO4−, NO2−, NO3−, SO42−, CO32−, HCO3−, PO43−, HPO42−, or H2PO4−; or an organic anion, such as HCOO−, (COO−)2, COOH(COO−), CH3COO−, C2H5COO−, CH3CH(OH)COO−, C2H4(COO−)2, C6H5COO−, C6H4(COO−)2, or CH3SO3−. The polyvalent metal salt content (% by mass) of the reaction liquid is preferably 1.0% by mass or more and 20.0% by mass or less, more preferably 1.0% by mass or more and 5.0% by mass or less, based on the total mass of the reaction liquid.
The polyvalent metal salt preferably has a water solubility (g/100 mL) of 25.0 g/100 mL or more at 25° C. A polyvalent metal salt with a water solubility of less than 25.0 g/100 mL tends to have an unstable dissolution state in the reaction liquid and tends to precipitate. A precipitated polyvalent metal salt may decrease the reactivity with the ink, and image unevenness therefore cannot be sufficiently suppressed in some cases. The solubility is preferably 50.0 g/100 mL or less.
A reaction liquid containing an organic acid has buffering capacity in an acid region (pH of less than 7.0, preferably pH in the range of 2.0 to 5.0), efficiently converts an anionic group of a component present in the ink into an acid form, and aggregates the component. The organic acid is, for example, a monocarboxylic acid, such as formic acid, acetic acid, propionic acid, butyric acid, benzoic acid, glycolic acid, lactic acid, salicylic acid, pyrrolecarboxylic acid, furancarboxylic acid, picolinic acid, nicotinic acid, thiophenecarboxylic acid, levulinic acid, or coumaric acid, or a salt thereof; a dicarboxylic acid, such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, itaconic acid, sebacic acid, phthalic acid, malic acid, or tartaric acid, or a salt or hydrogen salt thereof; a tricarboxylic acid, such as citric acid or trimellitic acid, or a salt or hydrogen salt thereof; or a tetracarboxylic acid, such as pyromellitic acid, or a salt or hydrogen salt thereof. When the organic acid is added, the organic acid content (% by mass) of the reaction liquid is preferably 1.0% by mass or more and 50.0% by mass or less based on the total mass of the reaction liquid.
The cationic resin is, for example, a resin with a primary to tertiary amine structure or a resin with a quaternary ammonium salt structure. Specific examples thereof include resins, such as vinylamine, allylamine, vinylimidazole, vinylpyridine, dimethylaminoethyl methacrylate, ethyleneimine, guanidine, diallyldimethylammonium chloride, or an alkylamine-epichlorohydrin condensate. To increase the solubility in the reaction liquid, a cationic resin and an acidic compound may be used in combination, or the cationic resin may be subjected to a quaternary treatment. When a cationic resin is added, the cationic resin content (% by mass) of the reaction liquid is preferably 0.1% by mass or more and 10.0% by mass or less based on the total mass of the reaction liquid.
The reaction liquid contains a nonionic surfactant with an HLB value of 14 or less. To further suppress image unevenness, the nonionic surfactant preferably has an HLB value of 12 or less. The “HLB value” of the nonionic surfactant in the present specification is a value determined by the Griffin method and is calculated based on the formula: HLB value=20×(formula weight of hydrophilic group of surfactant)/(molecular weight of surfactant). The HLB determined by the Griffin method is a physical property indicating the hydrophilicity or lipophilicity of the nonionic surfactant and ranges from 0 to 20. A lower HLB indicates higher lipophilicity, and a higher HLB indicates higher hydrophilicity. The nonionic surfactant preferably has an HLB value of 4 or more.
The nonionic surfactant may be a hydrocarbon, fluorinated, or silicone surfactant. The nonionic surfactant can be at least one selected from the group consisting of a hydrocarbon surfactant and a silicone surfactant. This is because such a surfactant has a high ability to wet and spread easily on a record medium due to the structure thereof and has action not easily impaired even when evaporation or the like changes the composition of the reaction liquid.
The hydrocarbon nonionic surfactant is, for example, a polyoxyethylene alkyl ether, an ethylene oxide adduct of acetylenic glycol, a poly(ethylene glycol)-poly(propylene glycol) block copolymer, or an ethylene oxide adduct of a polyhydric alcohol. The fluorinated nonionic surfactant is, for example, a perfluoroalkyl ethylene oxide adduct. The silicone nonionic surfactant is, for example, a polyether modified siloxane compound. In particular, both a hydrocarbon nonionic surfactant and a silicone nonionic surfactant can be used. When these are used in combination, the hydrocarbon nonionic surfactant content can be higher than the silicone nonionic surfactant content. The nonionic surfactant content (% by mass) of the reaction liquid is preferably 0.1% by mass or more and 4.0% by mass or less, more preferably 0.2% by mass or more and 2.0% by mass or less.
The ink may further contain various surfactants (other surfactants) other than the nonionic surfactant. The other surfactants may be an anionic surfactant, a cationic surfactant, and an amphoteric surfactant. The other surfactants may be a hydrocarbon surfactant, a fluorinated surfactant, a silicone surfactant, and the like, with an HLB value outside the above range. The surfactant (the nonionic surfactant and the other surfactants in total) content (% by mass) of the reaction liquid is preferably 0.1% by mass or more and 5.0% by mass or less, more preferably 0.2% by mass or more and 3.0% by mass or less, based on the total mass of the reaction liquid.
The reaction liquid contains an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. The water can be deionized water or ion-exchanged water. The water content (% by mass) of the reaction liquid is preferably 75.0% by mass or more based on the total mass of the reaction liquid. When the content is less than 75.0% by mass, the polyvalent metal salt may precipitate when a liquid component of the reaction liquid evaporates in continuous recording. Consequently, image unevenness may not be sufficiently suppressed. The water content (% by mass) of the reaction liquid is preferably 95.0% by mass or less based on the total mass of the reaction liquid.
The water solubility (g/100 mL) C of the polyvalent metal salt at 25° C., the polyvalent metal salt content (% by mass) c of the reactant liquid, and the water content (% by mass) W of the reactant liquid preferably satisfy the relationship W/(100×c/C)≥4.0. 100×c/C in the relational expression represents the amount of water (% by mass) required to dissolve the polyvalent metal salt. Thus, the relational expression means that the reaction liquid contains water in an amount of 4.0 times or more the amount of water required to dissolve the polyvalent metal salt. When the left side of the relational expression is less than 4.0 times, evaporation may make the dissolution of the polyvalent metal salt unstable, and the polyvalent metal salt may precipitate. Consequently, image unevenness may not be sufficiently suppressed.
The reaction liquid contains a first water-soluble organic solvent with an SP value of 14.8 or less and a second water-soluble organic solvent with an SP value of 14.8 or less and a vapor pressure of 1.0×10−3 kPa or more. In particular, a third water-soluble organic solvent with an SP value of 14.8 or less and a vapor pressure of 1.0×10−2 kPa or more can be contained. When the third water-soluble organic solvent is contained, during long-term image recording, the third water-soluble organic solvent evaporates easily among the liquid components in the reaction liquid and can therefore more effectively suppress the change in the composition of the liquid components. Consequently, image unevenness can be more effectively suppressed. The water-soluble organic solvent in the reaction liquid may be only one type. In other words, the first water-soluble organic solvent, the second water-soluble organic solvent, and the third water-soluble organic solvent may be the same. The first water-soluble organic solvent preferably has a vapor pressure of 1.0×10−1 kPa or less at 25° C. The first water-soluble organic solvent preferably has an SP value of 10.0 or more.
The water-soluble organic solvent satisfying these conditions may be propylene glycol (1,2-propanediol) (SP value: 13.5, vapor pressure: 1.8×10−2 kPa), ethylene glycol (1,2-ethanediol) (SP value: 14.8, vapor pressure: 1.2×10−2 kPa), 1,2-butanediol (SP value: 12.8, vapor pressure: 2.0×10−2 kPa), 1,2-hexanediol (SP value: 11.8, vapor pressure: 2.6×10−3 kPa), diethylene glycol monoethyl ether (SP value: 10.8, vapor pressure: 1.7×10−2 kPa), 2-methyl-1,3-propanediol (SP value: 14.8, vapor pressure: 3.0×10−3 kPa), or 2-pyrrolidone (SP value: 12.6, vapor pressure: 1.3×10−3 kPa). In particular, the first water-soluble organic solvent can contain a 1,2-alkanediol because image unevenness can be more efficiently suppressed. This is probably because it has a relatively small molecular weight, has a hydrophilic portion derived from the hydroxy group and a hydrophobic portion derived from the alkyl chain, and can function as a surfactant. The first water-soluble organic solvent can be a 1,2-alkanediol. In the present specification, the vapor pressure is a value at 25° C. and 1 atm.
The proportion (% by mass) of the second water-soluble organic solvent in the water-soluble organic solvent with an SP value of 14.8 or less in the reaction liquid is preferably 80.0% by mass or more. When the proportion is less than 80.0% by mass, evaporation is likely to change the orientation state of the surfactant, and image unevenness cannot be sufficiently suppressed in some cases. The proportion may be 100.0% by mass. The proportion (% by mass) of the third water-soluble organic solvent in the water-soluble organic solvent with an SP value of 14.8 or less in the reaction liquid is preferably 80.0% by mass or more. When the proportion is in the above range, a change in the orientation state of the surfactant due to evaporation can be further suppressed, and image unevenness can be efficiently suppressed. The proportion may be 100.0% by mass.
In the present specification, the SP value (δ) is a value calculated by the Fedors method based on the following formula. The unit of the SP value (δ) is ((cal/cm3)1/2), although the unit is omitted in the present specification.
(In the formula, ΔEvap denotes the molar heat of vaporization (cal/mol), and V denotes the molar volume (cc/mol) at 25° C.)
When the ink contains a plurality of water-soluble organic solvents, the SP value of the water-soluble organic solvents is calculated as an average SP value. The average SP value of the water-soluble organic solvents is calculated by multiplying the SP value of each water-soluble organic solvent by its proportion (% by mass) in the total amount of the water-soluble organic solvents in the ink and then summing the products.
A reaction liquid according to the present disclosure contains a resin. The resin may be an acrylic resin, a urethane resin, or a urea resin. In particular, an acrylic resin can be used. The resin content (% by mass) of the reaction liquid is preferably 1.00% by mass or more and 25.00% by mass or less, more preferably 3.00% by mass or more and 15.00% by mass or less, based on the total mass of the reaction liquid. In particular, 5.00% by mass or more and 15.00% by mass or less is particularly preferred.
The resin can be contained in a reaction liquid and an ink described later to improve various characteristics of an image to be recorded, such as scratch resistance and hiding power. The resin may be a block copolymer, a random copolymer, a graft copolymer, or a combination thereof. The resin may be a water-soluble resin that can be dissolved in an aqueous medium or resin particles to be dispersed in an aqueous medium. The resin particles do not need to contain a coloring material.
In the present specification, the phrase “resin is water-soluble” means that, when neutralized with an alkali in an amount equivalent to the acid value, the resin is present in an aqueous medium without a particle with a particle size measurable by a dynamic light scattering method. Whether or not the resin is water-soluble can be determined by the following method. First, a liquid (resin solid content: 10% by mass) containing a resin neutralized with an alkali (sodium hydroxide, potassium hydroxide, or the like) equivalent to the acid value is prepared. The prepared liquid is then diluted 10 times (on a volume basis) with pure water to prepare a sample solution. When the particle size of the resin in the sample solution is measured by the dynamic light scattering method, if a particle with a particle size is not observed, the resin can be determined to be water-soluble. The measurement conditions can be, for example, SetZero: 30 seconds, number of measurements: 3, and measurement time: 180 seconds. A particle size analyzer using a dynamic light scattering method (for example, trade name “UPA-EX150”, manufactured by Nikkiso Co., Ltd.) can be used as a particle size distribution analyzer. As a matter of course, the particle size distribution analyzer to be used, the measurement conditions, and the like are not limited to those described above.
The water-soluble resin preferably has an acid value of 80 mgKOH/g or more and 250 mgKOH/g or less, more preferably 100 mgKOH/g or more and 200 mgKOH/g or less. Resin particles, if present, preferably have an acid value of 0 mgKOH/g or more and 50 mgKOH/g or less. The resin preferably has a weight-average molecular weight of 1,000 or more and 30,000 or less, more preferably 5,000 or more and 15,000 or less. The weight-average molecular weight of the resin is a polystyrene equivalent molecular weight measured by gel permeation chromatography (GPC).
If necessary, the reaction liquid may contain various other components. The other components may be the other components that can be contained in an ink described later.
A reaction liquid that can be suitably used in a recording method according to the present disclosure is an aqueous reaction liquid applied to an ink jet system. Thus, from the perspective of reliability, the physical properties thereof can be appropriately controlled. More specifically, the reaction liquid preferably has a surface tension of 20 mN/m or more and 60 mN/m or less at 25° C. The reaction liquid preferably has a viscosity of 1.0 mPa·s or more and 10.0 mPa·s or less at 25° C. The reaction liquid preferably has a pH of 5.0 or more and 9.5 or less, more preferably 6.0 or more and 9.0 or less, at 25° C.
An ink that can be used for an ink jet recording method according to the present disclosure is described in detail below with reference to embodiments. In the present disclosure, with respect to a salt compound, although the salt is dissociated into ions in ink, for convenience, it is expressed as “the salt is contained”. An aqueous ink jet ink may be referred to simply as an “ink”. Unless otherwise specified, physical properties are values at normal temperature (25° C.). For recording of an image using a white ink, the white ink may be used as an underlayer treatment of a chromatic color ink. In such a case, an image may be recorded by applying a chromatic color ink (an ink of black, cyan, magenta, yellow, or the like) so as to overlap at least part of the region to which the white ink has been applied. It can also be used for back print of applying a white ink so as to overlap at least part of the region to which a chromatic color ink has been applied.
An ink according to the present disclosure is an aqueous ink jet ink containing a coloring material dispersed by the action of an anionic group. An ink according to the present disclosure is not necessarily a so-called “curable ink”. Thus, an ink according to the present disclosure does not necessarily contain a polymerizable monomer that can be polymerized by external energy, such as heat or light, or the like. Components constituting an ink according to the present disclosure, physical properties of the ink, a method for producing the ink, and the like are described in detail below.
The ink contains a coloring material dispersed by an anionic action. The coloring material can be a pigment or dye. The coloring material content (% by mass) of the ink is preferably 0.1% by mass or more and 15.0% by mass or less, more preferably 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink.
Specific examples of the pigment include inorganic pigments, such as carbon black and titanium oxide; and organic pigments, such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolone, diketopyrrolopyrrole, and dioxazine.
In a method of dispersing the pigment, a resin-dispersed pigment containing a resin as a dispersant, a self-dispersible pigment with a hydrophilic group bonded to the surface of a pigment particle, or the like can be used. Furthermore, a resin-bonded pigment with an organic group containing a resin chemically bonded to the surface of a pigment particle, a microcapsule pigment in which the surface of a pigment particle is coated with a resin or the like, or the like can be used. In particular, rather than the resin-bonded pigment or the microcapsule pigment, a resin-dispersed pigment in which a resin serving as a dispersant is physically adsorbed on the surface of a pigment particle can be used. Thus, the pigment can be dispersed by a resin with an anionic group (a resin dispersant).
A resin dispersant for dispersing the pigment in an aqueous medium is a resin dispersant capable of dispersing the pigment in the aqueous medium by the action of an anionic group. The resin dispersant can be a resin described later, particularly a water-soluble resin. The pigment content (% by mass) of the ink is preferably 0.3 times or more and 10.0 times or less the resin dispersant content in terms of mass ratio.
The self-dispersible pigment can be a pigment with an anionic group, such as a carboxylic acid group, a sulfonic acid group, or a phosphonic acid group, bonded to the surface of a pigment particle directly or via another atomic group (—R—). The anionic group may be an acid type or a salt type. The salt type may be in a partially dissociated state or in an entirely dissociated state. When the anionic group is a salt type, a cation serving as a counter ion may be an alkali metal cation, ammonium, or an organic ammonium. Specific examples of the other atomic group (—R—) include a linear or branched alkylene group with 1 to 12 carbon atoms; an arylene group, such as a phenylene group or a naphthylene group; a carbonyl group; an imino group; an amide group; a sulfonyl group; an ester group; and an ether group. A combination of these groups may also be used.
The dye is a dye with an anionic group. Specific examples of the dye include azo, triphenylmethane, (aza)phthalocyanine, xanthene, and anthrapyridone. The coloring material can be a pigment or a resin-dispersed pigment.
The present disclosure can be suitably used for an ink jet recording method using an ink containing titanium oxide as a coloring material. The ink can be a white ink because titanium oxide is a white pigment. As in the present disclosure, as described above, a non-absorptive record medium formed of vinyl chloride (PVC), poly(ethylene terephthalate) (PET), or the like is often used in an ink jet recording method using an aqueous reaction liquid containing a reactant that reacts with an aqueous ink. In such a case, regardless of the color of the record medium, image recording with high color development can be achieved by using a white ink containing titanium oxide. A coloring material in a white ink containing titanium oxide is described below.
The white ink contains titanium oxide as a coloring material (pigment). The titanium oxide may be titanium oxide particles subjected to surface treatment with a specific inorganic oxide. Thus, an ink may contain titanium oxide particles with a surface coated with a specific inorganic oxide. The titanium oxide particle content (% by mass) of the ink is preferably 0.10% by mass or more and 20.00% by mass or less based on the total mass of the ink. The titanium oxide particle content (% by mass) of the ink is more preferably 1.00% by mass or more and 20.00% by mass or less based on the total mass of the ink. The titanium oxide particle content (% by mass) of the ink is particularly preferably 1.00% by mass or more and 15.00% by mass or less based on the total mass of the ink.
Titanium oxide is a white pigment and has three crystal forms of a rutile type, an anatase type, and a brookite type. In particular, rutile titanium oxide can be used. Titanium oxide may be industrially produced by a sulfuric acid method or a chlorine method, and titanium oxide used in the present disclosure may be produced by any method.
Titanium oxide particles preferably have a volume-based cumulative 50% particle size (hereinafter also referred to as an average particle size) of 200 nm or more and 500 nm or less. In particular, titanium oxide particles more preferably have a volume-based cumulative 50% particle size of 200 nm or more and 400 nm or less. The volume-based cumulative 50% particle size (D50) of titanium oxide particles is the diameter of a particle at an integrated value of 50% based on the total volume of particles measured from the smallest particle size in a cumulative particle size curve. D50 of titanium oxide particles can be measured under the conditions of, for example, SetZero: 30 seconds, number of measurements: 3, measurement time: 180 seconds, shape: non-spherical, and refractive index: 2.60. A particle size analyzer using a dynamic light scattering method can be used as a particle size distribution analyzer. As a matter of course, the measurement conditions and the like are not limited to the above.
Titanium oxide may be subjected to surface treatment with alumina and silica. The surface treatment is expected to reduce photocatalytic activity and improve dispersibility. The term “alumina”, as used herein, is a general term for oxides of aluminum, such as aluminum oxide. The term “silica”, as used herein, is a general term for silicon dioxide or a substance composed of silicon dioxide. The majority of alumina and silica that coat titanium oxide is present in the form of silicon dioxide and aluminum oxide.
The titanium oxide content (% by mass) of titanium oxide particles is preferably 90.00% by mass or more based on the total mass of the titanium oxide particles. The titanium oxide content (% by mass) of titanium oxide particles is preferably 98.50% by mass or less based on the total mass of the titanium oxide particles. The alumina content (% by mass) of titanium oxide particles needs to be 0.50 times or more and 1.00 time or less the silica content (% by mass) in terms of mass ratio. A mass ratio of less than 0.50 times or more than 1.00 time results in an ink with low ejection stability. The silica content (% by mass) of titanium oxide particles is preferably 1.00% by mass or more and 4.00% by mass or less of the total mass of the titanium oxide particles. A silica content (% by mass) of less than 1.00% by mass may result in an insufficient affinity for a compound represented by the general formula (1) and an ink with insufficient ejection stability. A silica content (% by mass) of more than 4.00% by mass may result in a significant amount of compound represented by the general formula (1) adsorbed on titanium oxide particles even surface-treated with alumina and may result in an ink with insufficient ejection stability. The alumina content (% by mass) of titanium oxide particles is preferably 0.50% by mass or more and 4.00% by mass or less based on the total mass of the titanium oxide particles.
The alumina and silica contents of titanium oxide particles, that is, the amounts of alumina and silica coating may be measured, for example, by the quantitative analysis of aluminum and silicon elements using inductively coupled plasma (ICP) emission spectrometry. In such a case, it can be calculated by converting the obtained values of aluminum and silicon into their oxides, that is, alumina and silica, on the assumption that all the atoms covering the surface are oxides. The aluminum element content (% by mass) of titanium oxide particles determined by inductively coupled plasma emission spectrometry is 0.57 times or more and 1.13 times or less the silicon element content (% by mass) in terms of mass ratio. When this value is converted into oxides thereof, that is, alumina and silica, the alumina content (% by mass) of titanium oxide particles is 0.50 times or more and 1.00 time or less the silica content (% by mass) in terms of mass ratio.
The surface treatment method for titanium oxide may be wet processing, dry processing, or the like. For example, titanium oxide can be dispersed in a liquid medium and then reacted with a surface treating agent, such as sodium aluminate or sodium silicate, for surface treatment, and the ratio of the surface treating agent can be appropriately changed for adjustment to desired characteristics. In addition to alumina and silica, an inorganic oxide, such as zinc oxide or zirconia, or an organic substance, such as a polyol, can be used for the surface treatment without losing the advantages of the present disclosure.
A white ink may contain a pigment other than titanium oxide without losing the advantages of the present disclosure. In such a case, an ink of a color other than white ink may be used. The other pigment content (% by mass) of an ink is preferably 0.10% by mass or more and 5.00% by mass or less, more preferably 0.10% by mass or more and 1.00% by mass or less, based on the total mass of the ink.
An ink can contain a compound represented by the following general formula (1) as a dispersant for dispersing titanium oxide particles. The amount (% by mass) of compound represented by the general formula (1) in the ink is preferably 0.01% by mass or more and 1.00% by mass or less, 0.02% by mass or more and 0.50% by mass or less, based on the total mass of the ink.
(In the general formula (1), R1, R2, and R3 each independently denote a hydrogen atom or an alkyl group with 1 to 4 carbon atoms. R4s each independently denote an alkylene group with 2 to 4 carbon atoms. X denotes a single bond or an alkylene group with 1 to 6 carbon atoms. n ranges from 6 to 24. a ranges from 1 to 3, b ranges from 0 to 2, and a+b=3.)
In the general formula (1), R1, R2, and R3 each independently denote a hydrogen atom or an alkyl group with 1 to 4 carbon atoms. The alkyl group with 1 to 4 carbon atoms may be a methyl group, an ethyl group, a n-propyl group, an i-propyl group, or a n-butyl group. In particular, a methyl group can be used from the perspective of ease of hydrolysis. When R1, R2, and R3 each independently denote an alkyl group with more than 4 carbon atoms, it is difficult to form a silanol group by hydrolysis, and an affinity for titanium oxide particles cannot be obtained. Thus, titanium oxide particles cannot be stably dispersed, and the ink cannot have ejection stability. a that denotes the number of R1O ranges from 1 to 3, b that denotes the number of R2 ranges from 0 to 2, and a+b=3. In particular, a is preferably 3, and b is preferably 0, that is, all the three substituents on the silicon atom can be R1O.
In the general formula (1), R4s each independently denote an alkylene group with 2 to 4 carbon atoms. The alkylene group with 2 to 4 carbon atoms may be an ethylene group, a n-propylene group, an i-propylene group, or a n-butylene group. In particular, an ethylene group can be used. The number of OR4, that is, n (average value) that denotes the number of alkylene oxide groups ranges from 6 to 24. n of less than 6 results in an alkylene oxide chain with too short a length and consequently an insufficient repulsive force due to steric hindrance and an ink with low ejection stability. n of more than 24 results in an alkylene oxide chain with too long a length and consequently enhanced hydrophilicity and easy liberation in an aqueous medium. This results in an insufficient affinity for a surface hydroxy group of titanium oxide particles and aggregation of titanium oxide particles. Thus, titanium oxide particles cannot be stably dispersed, and the ink cannot have ejection stability.
In the general formula (1), X denotes a single bond or an alkylene group with 1 to 6 carbon atoms. When X denotes a single bond, it means that the silicon atom is directly bonded to OR4. The alkylene group with 1 to 6 carbon atoms may be a methylene group, an ethylene group, a n-propylene group, an i-propylene group, a n-butylene group, a n-pentylene group, a n-hexylene group, or the like. In particular, a n-propylene group can be used. When X denotes an alkylene group with more than 6 carbon atoms, a compound represented by the general formula (1) has excessively high hydrophobicity, titanium oxide particles cannot be stably dispersed, and the ink cannot have ejection stability.
A compound represented by the general formula (1), which is a dispersant for titanium oxide particles, can be a compound represented by the following general formula (2). Having three OR1s bonded to the silicon atom, a compound represented by the general formula (2) can be partially hydrolyzed in an aqueous medium and form three hydroxy groups bonded to the silicon atom, thus increasing a portion with an affinity for titanium oxide particles. A compound represented by the following general formula (2) has a repeating structure of an ethylene oxide group. Thus, the ethylene oxide chain can extend moderately in an aqueous medium, and a repulsive force due to steric hindrance can be obtained.
(In the general formula (2), R1 and R3 each independently denote a hydrogen atom or an alkyl group with 1 to 4 carbon atoms. m ranges from 8 to 24.)
The amount of compound represented by the general formula (1) (% by mass) in ink is preferably 0.002 times or more and 0.10 times or less the titanium oxide particle content (% by mass) in terms of mass ratio. A mass ratio of less than 0.002 times may result in a smaller effect of stably dispersing titanium oxide particles and an ink with insufficient ejection stability. A mass ratio of more than 0.10 times tends to result in too high a proportion of a compound represented by the general formula (1) and condensation (self-condensation) between molecules of a compound represented by the general formula (1). This may result in a compound represented by the general formula (1) consumed without acting as a dispersant, a weak action of stably dispersing titanium oxide particles, and an ink with insufficient ejection stability.
A compound represented by the general formula (1) is hydrogen-bonded to a surface hydroxy group of titanium oxide particles and is considered to partially form a covalent bond by a dehydration reaction. In the present disclosure, however, a compound represented by the general formula (1) can disperse titanium oxide particles without forming a covalent bond with the titanium oxide particles. Thus, the amount of a compound represented by the general formula (1) covalently bonded to titanium oxide particles is very small and is negligible. Thus, the titanium oxide particle content does not include a covalently bonded compound represented by the general formula (1). On the basis of study results by the present inventors, it has been found that too large an amount of a compound represented by the general formula (1) covalently bonded to titanium oxide particles results in an ink with lower ejection stability. The reason for this is considered as described below. In general, in a liquid medium with high permittivity, such as water, electrostatic attractive force is less likely to act, and titanium oxide particles move freely without significant environmental effects. When a compound represented by the general formula (1) is covalently bonded to titanium oxide particles, however, the hydrophilic portion (OR4 portion) of the structure of the general formula (1) forms a hydrogen bond with water molecules and may consequently affect the movement of the titanium oxide particles. Thus, in a situation where liquid is deformed by an instantaneous pressure as in ink jet ejection, the characteristics as described above appear as a difference in ejection characteristics. Thus, the amount (% by mass) of a compound represented by the general formula (1) covalently bonded to titanium oxide particles is preferably 0.001 times or less the titanium oxide particle content (% by mass) in terms of mass ratio. A mass ratio of more than 0.001 times may result in an ink with insufficient ejection stability. The mass ratio may be 0.0001 times or less. The amount of a compound represented by the general formula (1) covalently bonded to titanium oxide particles can be calculated by thermogravimetric analysis or the like.
The ink can contain a resin. The type and the range of the amount of a resin that can be used are the same as those of the resin contained in the reaction liquid described above and are not described here. The reaction liquid and the ink may contain different types of resins.
The ink is an aqueous ink containing water as an aqueous medium. The ink may contain water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. The water can be deionized water (ion-exchanged water). The water content (% by mass) of the ink is preferably 50.00% by mass or more and 95.00% by mass or less based on the total mass of the ink.
The water-soluble organic solvent is not particularly limited as long as the solvent is water-soluble (the solvent can dissolve in water at any ratio at 25° C.). More specifically, a monohydric or polyhydric alcohol, an alkylene glycol, a glycol ether, a nitrogen-containing polar compound, a sulfur-containing polar compound, or the like can be used. The water-soluble organic solvent content (% by mass) of the ink is preferably 3.00% by mass or more and 50.00% by mass or less, more preferably 10.00% by mass or more and 40.00% by mass or less, based on the total mass of the ink. A water-soluble organic solvent content (% by mass) of less than 3.00% by mass may result in solidification of the ink in an ink jet recording apparatus and insufficient sticking resistance. A water-soluble organic solvent content (% by mass) of more than 50.00% by mass may result in ink supply failure.
An ink may contain, in addition to the additive agents described above, other additive agents, such as a surfactant, a pH adjuster, an anticorrosive, a preservative, a fungicide, an antioxidant, a reducing inhibitor, an evaporation promoter, and/or a chelating agent, if necessary. In particular, the ink can contain a surfactant. The surfactant content (% by mass) of the ink is preferably 0.10% by mass or more and 5.00% by mass or less, more preferably 0.10% by mass or more and 2.00% by mass or less, based on the total mass of the ink. The surfactant may be an anionic surfactant, a cationic surfactant, or a nonionic surfactant. In particular, a nonionic surfactant that has a low affinity for titanium oxide particles and produces an effect even in a small amount can be used to adjust various physical properties of ink.
The ink is an ink applied to an ink jet system and can have physical properties appropriately adjusted for the ink jet system. The ink preferably has a surface tension of 10 mN/m or more and 60 mN/m or less, more preferably 20 mN/m or more and 40 mN/m or less, at 25° C. The surface tension of the ink can be adjusted by appropriately determining the type and amount of the surfactant in the ink. The viscosity at 25° C. is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The ink preferably has a pH of 7.0 or more and 9.0 or less at 25° C. When the ink has a pH in this range, a compound represented by the general formula (1) is hydrolyzed and forms a silanol group, thus effectively exhibiting a weak affinity for titanium oxide particles. The pH of the ink can be measured with a typical pH meter equipped with a glass electrode.
Although the present disclosure is described below in more detail in the exemplary embodiments, the present disclosure is not limited to these exemplary embodiments within the gist of the present disclosure. Unless otherwise specified, “part(s)” and “%” with respect to the amount of component are based on mass. A dispersion liquid of titanium oxide particles is referred to as a “pigment dispersion liquid”.
Commercially available rutile titanium oxide particles subjected to a surface treatment in advance were used. The volume-based cumulative 50% particle size (D50) of titanium oxide particles was measured with a particle size analyzer utilizing the dynamic light scattering method (trade name “Nanotrac WaveII-EX150”, manufactured by MicrotracBEL Corp.). Table 1 shows characteristics of titanium oxide particles.
A styrene-methyl methacrylate-methacrylic acid copolymer (resin 1) with an acid value of 150 mgKOH/g and a weight-average molecular weight of 10,000 was prepared. 20.0 parts of the resin 1 was neutralized with potassium hydroxide equimolar to the acid value thereof, and an appropriate amount of pure water was added to the resin 1 to prepare an aqueous solution of the resin 1 with a resin content (solid content) of 20.0%, 40.0 parts of the titanium oxide particles 1, 40.0 parts of the aqueous solution of the resin 1, and ion-exchanged water to make a total of 100.0 parts were mixed and pre-dispersed using a homogenizer. The product was then dispersed (main dispersion) at 25° C. for 12 hours with a paint shaker using 0.5 mm zirconia beads. The zirconia beads were filtered off, and an appropriate amount of ion-exchanged water was added as necessary to prepare a pigment dispersion liquid 1 with a titanium oxide particle content of 40.0% and a resin dispersant (resin 1) content of 8.0%.
25.0 parts of the pigment dispersion liquid 1 and the following components were mixed and stirred. Pressure filtration was then performed with a membrane filter (manufactured by Sartorius) with a pore size of 5.0 μm to prepare an ink 1.
Details of the mixed components are described below.
The viscosity (Pa·s) of the ink 1 and the density (g/cm3) of the liquid component were 8 Pa·s and 1.16 g/cm3, respectively.
The following components were mixed, sufficiently stirred, and subjected to pressure filtration through a cellulose acetate filter (manufactured by Advantec Toyo Kaisha, Ltd.) with a pore size of 3.0 μm to prepare a reaction liquid 1.
When magnesium sulfate was added, magnesium sulfate heptahydrate was used in an amount corresponding to the specified amount of magnesium sulfate.
A liquid ejection head illustrated in
A head 2 was prepared with the same configuration as that of the head 1 except that the shape of the ejection port 13 was a circular shape without the protrusions 27.
The ink 1 and the reaction liquid 1 were set in an ink jet recording apparatus equipped with the head 1 or the head 2, and the ink was ejected at a temperature of 25° C. and a relative humidity of 50%. As a result, it was confirmed that the ink jet recording apparatus with the head 1 fully has the advantages of the present disclosure.
The present disclosure can provide an ink jet recording method that has high ejection stability of a reaction liquid or an ink.
While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2023-173992 filed Oct. 6, 2023, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-173992 | Oct 2023 | JP | national |
