JP2020168807A - Inkjet recording method - Google Patents

Abstract

To provide an inkjet recording method capable of preparing a workpiece without impairing designability by recording an easily foldable folding line without requiring additional processing in preparing a workpiece by folding a recording medium such as paper composed mainly of cellulose.SOLUTION: There is provided an inkjet recording method which comprises a step of recording a folding line in order to form a workpiece by imparting an aqueous decoloring ink containing a pH indicator which develops color in an alkaline ink and erases color due to a decrease in pH after imparted to a recording medium.SELECTED DRAWING: Figure 1

Description

The present invention relates to an inkjet recording method.

Conventionally, in order to produce a paper work such as a paper craft work or a package, it has been common to record a desired pattern on a paper material, cut it out, or then bend it without cutting it out. If the part to be bent is a simple straight line, it is relatively easy to make a workpiece. However, if the part to be bent is intricate or curved, it is difficult to fold it accurately without any work, and a certain level of skill was required to create the work as imagined. There is also a method of making a streak in the bent portion using a spatula or making a perforation with a perforation cutter to make it easier to fold, but there is a problem that it takes time and effort. Further, when the fold line is a curved line, it is difficult to apply a ruler to make streaks and perforations, and it is difficult to produce a workpiece including a curved surface.

There are known methods of mechanically making streaks and perforations and recording fold lines with ink in order to make it easier to fold with fold lines. However, little is known about how to make curved fold lines easier to fold. As a related prior art, a method has been proposed in which a large amount of permeable colored ink is applied to a predetermined place to reduce the rigidity of the paper and facilitate the production of an envelope by bending (Patent Document 1).

Decolorizing ink is used for lot management of products by taking advantage of its erasing property. For example, a method of recording manufacturing information that disappears with time by a decolorizing ink for an inkjet containing a pH indicator on a paper pack has been proposed (Patent Document 2).

Japanese Unexamined Patent Publication No. 2012-40850 Japanese Unexamined Patent Publication No. 63-286481

However, in the case of the method proposed in Patent Document 1, there is a problem that the design of the work is impaired because the folds of the finally produced paper work are colored. If clear ink that does not contain a coloring material is used in order to avoid impairing the design of the workpiece, it is possible to reduce the rigidity of the paper, but the visibility of the fold line is reduced, so that the workpiece is deteriorated. It becomes difficult to manufacture.

In order to ensure the visibility and design of the fold line, there is also a method of recording the fold line with a light color ink having a reduced content of the coloring material. However, since it is necessary to inject a large amount of ink into thick paper, even if light-colored ink is used, the fold lines are deeply colored, and the design of the workpiece is likely to be impaired.

Therefore, an object of the present invention is to record easy-to-fold fold lines that do not require additional machining when folding a recording medium such as paper mainly composed of cellulose to prepare a workpiece, without impairing the design of the workpiece. It is an object of the present invention to provide an inkjet recording method capable of producing the above.

That is, according to the present invention, it is an inkjet recording method used when a recording medium mainly composed of cellulose is bent to produce a workpiece, and the color is developed in alkaline ink and is applied to the recording medium. An inkjet recording comprising a step of applying a water-based decoloring ink containing a pH indicator, which is decolorized by a decrease in pH, to the recording medium and recording a fold line for forming the workpiece. A method is provided.

According to the present invention, when a recording medium such as paper mainly composed of cellulose is folded to produce a workpiece, a foldable line that does not require additional machining is recorded to produce the workpiece without impairing the design. A possible inkjet recording method can be provided.

It is a schematic diagram which shows the application pattern of ink to a recording medium. It is a schematic diagram which shows the application pattern of ink to a recording medium. It is a schematic diagram which shows the application pattern of ink to a recording medium. It is a figure which shows typically an example of the inkjet recording apparatus used in the inkjet recording method of this invention, (a) is the perspective view of the main part of the inkjet recording apparatus, (b) is the perspective view of the head cartridge.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is dissociated into ions and exists in the ink, but for convenience, it is expressed as "containing a salt". Further, the water-based ink for an inkjet may be simply referred to as "ink". Unless otherwise specified, the physical property values are values at normal temperature (25 ° C.) and normal pressure (1 atm). The "unit" of a resin means a repeating unit derived from one monomer. Moreover, when described as "(meth) acrylic acid" and "(meth) acrylate", it means "acrylic acid, methacrylic acid", "acrylate, methacrylate", respectively.

When the paper gets wet with water, the hydrogen bonds of cellulose, which is the main component of the paper, are broken by the water, so that the rigidity of the wet portion decreases. Water is a familiar substance that efficiently cleaves hydrogen bonds in cellulose, and organic solvents cannot cleave hydrogen bonds as efficiently as water. In the inkjet recording method of the present invention, a water-based decolorizing ink is applied to a recording medium mainly composed of cellulose to record fold lines for forming a workpiece. By recording the fold line with the water-based decoloring ink, the rigidity of the recording medium at the portion where the fold line is recorded can be reduced, and the fold line can be easily bent. In the past, when folding origami paper, the corners of the paper were butted against each other, and the characteristic parts of the paper were used to get an idea of where to fold. On the other hand, if a water-based decolorizing ink is used, a fold line can be recorded at a desired location, so that the degree of freedom in manufacturing the workpiece can be increased.

<Inkjet recording method>
The inkjet recording method of the present invention is a method used when a recording medium mainly composed of cellulose is bent to prepare a workpiece, and a water-based decolorizing ink containing a pH indicator is applied to the recording medium for machining. It has a step of recording a fold line for shaping an object. The pH indicator contained in the decolorizing ink is a component that develops a color in an alkaline ink and is decolorized by a decrease in pH after being applied to a recording medium.

(Inkjet recording device)
FIG. 4 is a diagram schematically showing an example of an inkjet recording device used in the inkjet recording method of the present invention, (a) is a perspective view of a main part of the inkjet recording device, and (b) is a perspective view of a head cartridge. Is. The inkjet recording device is provided with a transport means (not shown) for transporting the recording medium 32 and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 includes recording heads 38 and 40, and is configured so that the ink cartridge 42 is set. While the head cartridge 36 is conveyed along the carriage shaft 34 in the main scanning direction, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. Then, the recording medium 32 is conveyed in the sub-scanning direction by the conveying means (not shown), so that the image is recorded on the recording medium 32.

(recoding media)
The recording medium is a material for recording mainly composed of cellulose, and specifically, paper or the like can be used. So-called resins and metals that are not mainly cellulose are not used as recording media. This is because even if a water-based decolorizing ink is applied to a resin-made or metal-made recording medium, the rigidity is not substantially lowered and the recording medium cannot be easily broken. As the paper mainly composed of cellulose, paper obtained by using pulp fiber as a raw material can be used, but paper produced by cutting wood into thin pieces cannot be used. Wood is made up of fibrils, which are bundles of cellulose, further bundled together, and has strong hydrogen bonding and intermolecular forces that are incomparable to paper. Therefore, even if water-based decoloring ink is applied to paper produced by cutting wood into thin pieces, it cannot be easily broken.

From the above points, suitable examples of recording media are non-coated paper such as high-quality paper, medium-quality paper, and Kent paper; coated paper such as art paper, coated paper, and cast paper; and information paper such as finely coated paper. ; Wrapping paper such as kraft paper and imitation paper; Board paper such as cardboard; and the like.

(Decoloring ink)
The decolorizing ink is a water-based ink containing a pH indicator. The pH indicator is a component such as a dye that develops a color in an alkaline ink and is decolorized by a decrease in pH after being applied to a recording medium. Therefore, the fold line recorded with the alkaline decoloring ink is colored, and it is possible to easily grasp which part is to be folded. In addition, the portion where the fold line is recorded with the water-based decoloring ink containing water is easily bent because the rigidity is lowered due to the influence of water. Furthermore, if the recording medium bent at a predetermined location is left as it is, the pH indicator will be discolored due to the influence of acid gas components (carbon dioxide, etc.) in the air, and the pH indicator will be decolorized, and the design of the workpiece will be improved. The fold line can be eliminated to the extent that the fold line is not impaired.

The term "decoloring" as used herein means that the color of the pH indicator under alkaline conditions not only changes to colorless as the pH decreases, but also changes to a light color within a range that does not impair the design of the workpiece. Means to do. For example, thymol blue turns blue in alkaline inks, but turns pale yellow due to acid gas components in the air. Such pH indicators can also be used in the present invention. In addition, cresolphthalein turns blue in alkaline ink, but changes to colorless due to the acid gas component in the air. In the present invention, any pH indicator can be used. Of these, it is preferable to use a pH indicator that is colorless under neutral or acidic conditions.

The content (mass%) of the pH indicator in the decolorizing ink is preferably 0.01% by mass or more and 3.00% by mass or less, and 0.25% by mass or more and 2.00% by mass, based on the total mass of the ink. It is more preferably mass% or less.

Specific examples of the pH indicator include cresolphthalein, phenolphthalein, thymolphthalein, thymol blue, bromothymol blue, phenol red, alizarine yellow R and the like. Of these, cresolphthalein, phenolphthalein, and thymolphthalein are preferable.

The decolorizing ink can be used for purposes other than recording fold lines. For example, to clearly indicate where to attach a sticker; to make it easier to distinguish whether the crease is a "mountain fold" or a "valley fold"; to instruct work such as "cutting"; signs and characters An image serving as a mark such as may be recorded with decoloring ink.

If the decolorizing ink applied to the recording medium dries quickly, the hydrogen bonds of the cut cellulose are also quickly recombined, making it difficult to maintain the foldability for a certain period of time. Therefore, it is preferable that the decolorizing ink further contains a moisturizing agent. By using the decolorizing ink containing the moisturizing agent, the drying speed of the decolorizing ink applied to the recording medium can be slowed down, and the time required for manufacturing the workpiece can be more sufficiently secured. Examples of the moisturizing agent include glycerin, polyethylene glycol, triethylene glycol, and trimethanolpropane. Of these, glycerin is preferable because it has an effect of effectively weakening the hydrogen bond of cellulose.

The content (mass%) of the moisturizing agent in the decolorizing ink is preferably 1.00% by mass or more and 30.00% by mass or less, and 5.00% by mass or more and 15.00% by mass, based on the total mass of the ink. It is more preferably mass% or less.

The decolorizing ink can further contain an aqueous medium other than water and other components such as resin. Since some pH indicators have low water solubility, a solubilizing agent such as ethanol may be contained.

The amount of decolorizing ink applied to the recording medium is preferably adjusted as appropriate depending on the type of recording medium (paper), the basis weight, and the like. For example, a small amount of decolorizing ink is applied to a recording medium such as thin paper that can be easily folded with a small amount of water. On the other hand, for recording media such as paperboard that require a certain amount of water to be easily folded, the amount of decolorizing ink applied is increased.

The shape of the fold line may be a straight line or a curved line. That is, the shape of the fold line can be selected according to the shape of the target workpiece. For example, when producing a three-dimensional workpiece including a curved surface, it is preferable that at least a part of the fold line is a curved line.

In order to make the recording medium foldable efficiently, it is preferable to continuously apply decolorizing ink to the recording medium to record the fold line which is a continuous line. Further, for example, different types of lines such as continuous lines, dotted lines, and broken lines may be appropriately combined and the thickness of the lines may be changed so that the "mountain fold line" and the "valley fold line" can be distinguished. Furthermore, the "mountain fold line" is recorded with a decolorizing ink that turns red under alkaline conditions, and the "valley fold line" is recorded with a decolorizing ink that turns blue under alkaline conditions. The decolorizing ink may be used properly depending on the type of.

(Colored ink)
The inkjet recording method of the present invention preferably further includes a step of applying a water-based coloring ink containing a coloring material to a recording medium to record an image. That is, it is possible to record the fold line, which is a crease when the work is manufactured, with the decolorizing ink, and to record the image such as a pattern, a pattern, and a character with the coloring ink. For example, when trying to make a work that imitates an animal, images such as animal patterns and facial parts are recorded with colored ink. In addition, when trying to make a workpiece such as a box, an image or the like according to the purpose is recorded with colored ink.

When the image recorded with the coloring ink straddles the fold line recorded with the decoloring ink, both the coloring ink and the decoloring ink are applied to the portion where the fold line is recorded. In such a case, if the surface tension of the decolorizing ink is lower than the surface tension of the coloring ink, the coloring ink easily flows into the decoloring ink. As a result, in the image recorded with the colored ink, the hue (optical density) of the portion near the fold line tends to be low, and the design of the workpiece may be slightly deteriorated. Therefore, the surface tension of the decolorizing ink is preferably higher than the surface tension of the coloring ink. By using a decolorizing ink whose surface tension is higher than the surface tension of the colored ink, the image recorded with the colored ink can be maintained in high quality, and a workpiece having better design can be produced.

For example, even if an image is recorded on the entire recording medium with colored ink, if the amount of ink applied to the image is small, the foldability of the fold line recorded with the decolorizing ink is not easily impaired. On the other hand, if the amount of ink applied to the image recorded on the entire recording medium by the coloring ink is large, the rigidity of the entire recording medium tends to decrease, so only the fold lines recorded by the decolorizing ink are selectively folded. Things can be a little difficult. However, even when the amount of ink applied to the image recorded with the coloring ink is large, if the fold line does not overlap with the fold line recorded with the decolorizing ink and is arranged at a sufficiently distant position, the fold line The selective easiness of breaking is not easily impaired. That is, when the colored ink is applied to the recording medium to record an image, it is preferable to set the position of the image and the amount of ink applied so that the foldability (processability) of the fold line is ensured.

The coloring ink is a water-based ink containing a coloring material. Hereinafter, the components constituting the colored ink and the like will be described. The components constituting the decolorizing ink will also be described. Hereinafter, the term "ink" simply means both "colored ink" and "decoloring ink".

[Color material]
Pigments and dyes can be used as the coloring material to be contained in the coloring ink. The content (mass%) of the coloring material in the coloring ink is preferably 0.50% by mass or more and 15.00% by mass or less, and 1.00% by mass or more and 10.00% by mass, based on the total mass of the ink. It is more preferably% or less.

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.

As a pigment dispersion method, a resin-dispersed pigment using a resin as a dispersant, a self-dispersing pigment in which a hydrophilic group is bonded to the particle surface of the pigment, or the like can be used. Further, a resin-bonded pigment in which an organic group containing a resin is chemically bonded to the surface of the pigment particles, a microcapsule pigment in which the surface of the pigment particles is coated with a resin or the like can be used. Of these, it is preferable to use a resin-dispersed pigment in which a resin as a dispersant is physically adsorbed on the particle surface of the pigment, instead of a resin-bound pigment or a microcapsule pigment.

As the resin dispersant for dispersing the pigment in the aqueous medium, it is preferable to use a resin dispersant capable of dispersing the pigment in the aqueous medium by the action of an anionic group. As the resin dispersant, a resin as described later, particularly a water-soluble resin, can be preferably used. The content (mass%) of the pigment in the coloring ink is preferably 0.3 times or more and 10.0 times or less in terms of the mass ratio with respect to the content of the resin dispersant.

As the self-dispersing pigment, an anionic group such as a carboxylic acid group, a sulfonic acid group, or a phosphonic acid group is used, which is bonded directly to the particle surface of the pigment or via another atomic group (-R-). be able to. The anionic group may be of either an acid type or a salt type, and when it is a salt type, it may be in a state in which a part thereof is dissociated or a state in which the whole is dissociated. When the anionic group is a salt type, examples of the cation that becomes a counter ion include alkali metal cations, ammonium, and organic ammonium. Specific examples of the other atomic group (-R-) include a linear or branched alkylene group having 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. Group; ester group; ether group and the like can be mentioned. Further, it may be a group in which these groups are combined.

As the dye, it is preferable to use a dye having an anionic group. Specific examples of the dye include dyes such as azo, triphenylmethane, (aza) phthalocyanine, xanthene, and anthrapyridone. The coloring material contained in the coloring ink is preferably a pigment, and more preferably a resin-dispersed pigment.

[resin]
The ink can contain a resin. The content (mass%) of the resin in the ink is preferably 0.10% by mass or more and 20.00% by mass or less, and 0.50% by mass or more and 15.00% by mass or less, based on the total mass of the ink. Is more preferable.

The resin can be added to the ink in order to (i) stabilize the dispersed state of the pigment, that is, as a resin dispersant or an auxiliary thereof. In addition, (ii) can be added to the ink in order to improve various characteristics of the recorded image. Examples of the form of the resin include block copolymers, random copolymers, graft copolymers, and combinations thereof. Further, the resin may be a water-soluble resin that can be dissolved in an aqueous medium, or may be resin particles dispersed in the aqueous medium. The resin particles do not need to contain a coloring material.

In the present specification, "the resin is water-soluble" means that when the resin is neutralized with an acid value and an equivalent amount of alkali, it is aqueous in a state where particles whose particle size can be measured by a dynamic light scattering method are not formed. It means that it exists in the medium. Whether or not the resin is water-soluble can be determined according to the method shown below. First, a liquid (resin solid content: 10% by mass) containing a resin neutralized with an alkali (sodium hydroxide, potassium hydroxide, etc.) equivalent to the acid value is prepared. Next, the prepared liquid is diluted 10 times (volume basis) with pure water to prepare a sample solution. Then, when the particle size of the resin in the sample solution is measured by the dynamic light scattering method, if the particles having the particle size are not measured, it can be determined that the resin is water-soluble. The measurement conditions at this time can be, for example, as follows.
[Measurement condition]
SetZero: 30 seconds Number of measurements: 3 Measurement time: 180 seconds

As the particle size distribution measuring device, a particle size analyzer (for example, trade name “UPA-EX150”, manufactured by Nikkiso Co., Ltd.) by a dynamic light scattering method can be used. Of course, the particle size distribution measuring device and the measuring conditions to be used are not limited to the above.

The acid value of the water-soluble resin is preferably 100 mgKOH / g or more and 250 mgKOH / g or less. The acid value of the resin constituting the resin particles is preferably 5 mgKOH / g or more and 100 mgKOH / g or less. The weight average molecular weight of the water-soluble resin is preferably 3,000 or more and 15,000 or less. The weight average molecular weight of the resin constituting the resin particles is preferably 1,000 or more and 2,000,000 or less. The volume average particle diameter of the resin particles measured by the dynamic light scattering method is preferably 50 nm or more and 500 nm or less.

Examples of the resin include acrylic resins, urethane resins, and olefin resins. Of these, acrylic resins and urethane resins are preferable.

As the acrylic resin, those having a hydrophilic unit and a hydrophobic unit as constituent units are preferable. Of these, a resin having a hydrophilic unit derived from (meth) acrylic acid and a hydrophobic unit derived from at least one of a monomer having an aromatic ring and a (meth) acrylic acid ester-based monomer is preferable. In particular, a resin having a hydrophilic unit derived from (meth) acrylic acid and a hydrophobic unit derived from at least one monomer of styrene and α-methylstyrene is preferable. Since these resins are likely to interact with pigments, they can be suitably used as resin dispersants for dispersing pigments.

The hydrophilic unit is a unit having a hydrophilic group such as an anionic group. The hydrophilic unit can be formed, for example, by polymerizing a hydrophilic monomer having a hydrophilic group. Specific examples of the hydrophilic monomer having a hydrophilic group include an acidic monomer having a carboxylic acid group such as (meth) acrylic acid, itaconic acid, maleic acid, and fumaric acid, and anions such as anhydrides and salts of these acidic monomers. Examples thereof include sex monomers. Examples of the cation constituting the salt of the acidic monomer include ions such as lithium, sodium, potassium, ammonium and organic ammonium. The hydrophobic unit is a unit that does not have a hydrophilic group such as an anionic group. The hydrophobic unit can be formed, for example, by polymerizing a hydrophobic monomer having no hydrophilic group such as an anionic group. Specific examples of the hydrophobic monomer include monomers having an aromatic ring such as styrene, α-methylstyrene, and benzyl (meth) acrylate; methyl (meth) acrylate, butyl (meth) acrylate, and (meth) acrylic acid 2. -A (meth) acrylic acid ester-based monomer such as ethylhexyl can be mentioned.

The urethane resin can be obtained, for example, by reacting a polyisocyanate with a polyol. Further, the chain extender may be further reacted. Examples of the olefin resin include polyethylene and polypropylene.

[Aqueous medium]
The ink (colored ink and decolorizing ink) is a water-based ink containing at least water as a water-based medium. The ink may contain water or an aqueous medium which is a mixed solvent of water and a water-soluble organic solvent. As the water, it is preferable to use deionized water or ion-exchanged water. The water content (mass%) in 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 content (mass%) of the water-soluble organic solvent in the ink is preferably 3.00% by mass or more and 50.00% by mass or less based on the total mass of the ink. As the water-soluble organic solvent, any solvent that can be used for inkjet inks such as alcohols, (poly) alkylene glycols, glycol ethers, nitrogen-containing compounds, and sulfur-containing compounds can be used.

[Surfactant]
It is preferable that the ink contains a surfactant. Examples of the surfactant include anionic, cationic, amphoteric and other ionic surfactants; nonionic surfactants. Of these, nonionic surfactants are preferable. The content (mass%) of the surfactant in the ink is preferably 0.05% by mass or more and 1.00% by mass or less based on the total mass of the ink.

[Other additives]
The ink may further contain a water-soluble organic compound that is solid at 25 ° C., such as urea and its derivatives, trimethylolpropane, and trimethylolethane. In addition to the above components, various additions such as defoaming agents, pH adjusting agents, viscosity adjusting agents, rust inhibitors, preservatives, fungicides, antioxidants, and reducing agents are added to the ink as needed. The agent may be contained.

[Physical properties of ink]
Both the coloring ink and the decoloring ink are water-based inks applied to the inkjet method. Therefore, from the viewpoint of reliability, it is preferable to appropriately control those physical property values. Specifically, the surface tension of the ink at 25 ° C. is preferably 20 mN / m or more and 60 mN / m or less. The viscosity of the ink at 25 ° C. is preferably 1.0 mPa · s or more and 10.0 mPa · s or less.

The pH of the colored ink at 25 ° C. is preferably 6.0 or more and 12.0 or less. The pH of the decolorizing ink at 25 ° C. is preferably 10.0 or more, and preferably 14.0 or less. The pH of the decolorizing ink is preferably adjusted as appropriate according to the type of pH indicator. The higher the pH of the decolorizing ink, the longer the time from when it is applied to the recording medium until it is decolorized. Therefore, it is preferable to appropriately adjust the pH of the decolorizing ink according to the purpose. For example, in the case of immediately producing a workpiece, it is preferable to set the pH of the decolorizing ink to a low value (about 10.0 to 13.0) so that the time required for decoloring is shortened. On the other hand, when it takes time to complete the workpiece, such as when folding is complicated, the pH of the decolorizing ink is increased (about 13.0 to 14.0) so that the time required for decoloring becomes longer. ) Is preferable.

(Recording method)
In the inkjet recording method of the present invention, the above-mentioned ink is ejected from an inkjet recording head and applied to a recording medium. Examples of the method of ejecting ink include a method of applying mechanical energy to the ink and a method of applying thermal energy to the ink. Of these, it is particularly preferable to adopt a method of applying thermal energy to the ink to eject the ink. Other than using the above-mentioned ink, the steps of the inkjet recording method may be known.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples as long as the gist thereof is not exceeded. Unless otherwise specified, the amounts of components described as "parts" and "%" are based on mass.

<Manufacturing of resin>
(Resin 1)
After putting 200 parts of methyl ethyl ketone in a flask equipped with a stirrer, a nitrogen introduction tube, a reflux cooling device, and a thermometer, the temperature was raised to 80 ° C. while stirring in a nitrogen atmosphere. A mixture of 50 parts of styrene, 30 parts of n-butyl acrylate, and 20 parts of acrylic acid, 1.9 parts of a polymerization initiator (trade name "V-59", manufactured by Wako Pure Chemical Industries, Ltd.) and 20 parts of methyl ethyl ketone. And were added dropwise while maintaining 80 ° C. over 2 hours. After the dropping, the mixture was further stirred at 80 ° C. for 4 hours to obtain a resin methyl ketone solution. After adding 0.9 times equivalent potassium hydroxide to the acid value of the resin and an appropriate amount of ion-exchanged water, methyl ethyl ketone was removed under reduced pressure to obtain a liquid containing the water-soluble resin 1. The content of the water-soluble resin (solid content) in the liquid containing the resin 1 was 25.0%.

(Resin 2)
0.9 parts of styrene, 14.4 parts of ethyl methacrylate, 2.7 parts of methyl methacrylate, 2.0 parts of n-hexadecane, and 2.0 parts of 2,2'-azobis- (2-methylbutyronitrile). Was mixed and stirred for 30 minutes to obtain a mixed solution. The obtained mixed solution was added dropwise to 76.0 parts of an aqueous solution of a 5% surfactant (trade name “Nikkol BC15”, manufactured by Nikko Chemicals), and the mixture was stirred for 30 minutes. Using an ultrasonic irradiator (trade name "S-150D Digital Sonifier", manufactured by Branson), after dispersing for 3 hours under the conditions of 400 W and 20 kHz, a polymerization reaction was carried out at 80 ° C. for 4 hours in a nitrogen atmosphere to carry out a resin. A dispersion of particles was obtained. Ion-exchanged water was added to the obtained dispersion and then concentrated using an evaporator to obtain a liquid containing the resin 2 having a particle amount. The content of the resin particles (solid content) in the liquid containing the resin 2 was 35.0%.

<Preparation of dye (pH indicator)>
The types of dyes (pH indicators) shown in Table 1 were prepared.

<Preparation of decolorizing ink>
Each component (unit: part) shown in Tables 2-1 and 2-2 is mixed, sufficiently stirred, and then pressure-filtered with a microfilter (manufactured by FUJIFILM) having a pore size of 3.0 μm to decolorize ink 1. ~ 20 were prepared. The surface tensions of inks 1 to 20 were measured using an automatic surface tension meter (trade name "DY-300", manufactured by Kyowa Interface Science Co., Ltd.). As a result, the surface tensions of the decolorizing inks other than the decolorizing inks 7, 10 and 16 to 19 were all higher than the surface tensions of all the coloring inks described later. In addition, the pH of the decolorizing ink measured using a pH meter (trade name "F-21", manufactured by HORIBA, Ltd.) exceeds 11.0, and all except ink 17 are compatible with coloring materials. , The color on the high pH side in Table 1 was exhibited. In Tables 2-1 and 2-2, "acetylenol E100" is a trade name of a nonionic surfactant (acetylene glycol ethylene oxide adduct) manufactured by Kawaken Fine Chemicals. The inks 1 to 16 were inks that were decolorized when the pH was lowered after being applied to the recording medium, but the inks 18 to 20 were inks that were not decolorized even when the pH was lowered.

<Preparation of colored ink set>
Commercially available inks (manufactured by Canon) were combined as shown in Table 3 to prepare a colored ink set. The inks in Table 3 are all water-based inks containing a coloring material.

<Preparation of recording medium>
The A4 size recording medium shown in Table 4 was prepared. The basis weight of the recording medium 1 is close to the basis weight of general origami.

<Evaluation>
An inkjet recording device (trade name "PIXUS Pro10", manufactured by Canon) that ejects ink from a recording head by the action of heat energy was prepared. The resolution of this inkjet recording device is 600 dpi × 600 dpi, and the recording duty of an image recorded under the condition that two drops of 4.5 ng ink are applied to a unit area of 1/600 inch × 1/600 inch is 100%. Is defined as. Each ink was filled in an ink cartridge and mounted on the recording head of an inkjet recording device. After continuous ejection for 1 minute at an ejection frequency of 10 kHz, predetermined fold lines and images were recorded on the recording medium under the conditions shown in Tables 5-1 and 5-2, and each evaluation shown below was performed. The recording medium was used after being acclimatized overnight or more in an environment having a temperature of 15 ° C. and a relative humidity of 10%. In the evaluation criteria of each item shown below, "A" and "B" were set as preferable levels, and "C" was set as an unacceptable level. The evaluation results are shown in Table 6.

The patterns of applying ink to the recording medium are shown in FIGS. The fold line pattern recorded with the decolorizing ink is a pattern assuming that a box surrounded on all sides is manufactured as a work piece. When the decolorizing ink pattern “a” was selected, the decolorizing ink was applied to the portion indicated by the short straight broken line in FIG. 1, and the fold line was recorded. The broken line represented by the imparting pattern “c” in FIG. 2 is four curves connecting adjacent corners among the four corners of the recording medium. In addition to the amount of decolorizing ink applied, the continuity of application (continuous or broken line), line thickness (dots), and the like were appropriately selected. As shown in FIG. 3, the image recorded with the coloring ink is a rainbow-colored star-shaped solid image. The imparting pattern “d” in FIG. 3 is an image recorded with colored ink that does not overlap with the fold line recorded with the decolorizing ink. The imparting pattern “e” in FIG. 3 is an image recorded with colored ink that overlaps with the fold line recorded with the decolorizing ink. Further, the imparting pattern “f” in FIG. 3 is a solid image recorded by applying colored inks of all colors to the entire recording medium. For example, when the recording duty of the image of the imparting pattern "f" and the image of the imparting pattern "d" are both 50%, the recording duty of the image of the imparting pattern "d" is substantially 100%.

(Easy to fold)
The force required to fold the recorded fold line using the pad of the finger was confirmed, and the fold line after folding was visually observed, and "ease of folding" was evaluated according to the evaluation criteria shown below. The time from the start of folding to the end of folding was less than 1 minute.
A: Compared to folding a fold line drawn with a pencil with a writing pressure that does not cause streaks on the paper, it broke easily with a weak force. Moreover, when the bent portion formed by folding was viewed from the side, it was thin and sharp.
B: Compared with the case of folding a fold line drawn with a pencil with a writing pressure that does not cause streaks on the paper, it broke easily with a weak force. Further, when the bent portion formed by folding was viewed from the side, it had a slight thickness and was dull.
C: The same force was required as compared with the case where the fold line drawn with a pencil was folded with a writing pressure that did not cause streaks on the paper. In addition, when the folded part formed by folding is viewed from the side, it has the same thickness and sharpness as the case where the folded line drawn with a pencil is folded with a writing pressure that does not cause streaks on the paper. I couldn't see the fold line.

(Creativity)
The work made by folding the recorded fold line was stored in a room not exposed to sunlight for 3 days. The colored lines of the fold lines of the work after storage were visually observed, and the design of the work was evaluated according to the evaluation criteria shown below.
A: The fold line was discolored, and the design of the work was high.
B: The fold line was discolored to some extent, and the design of the workpiece was high to some extent.
C: The fold line was not discolored, and the design of the workpiece was low.

Claims (6)

This is an inkjet recording method used when a recording medium mainly composed of cellulose is bent to produce a workpiece.
To form the workpiece by applying a water-based decolorizing ink containing a pH indicator, which develops color in an alkaline ink and is applied to the recording medium and then decolorizes by a decrease in pH, to the recording medium. An inkjet recording method comprising a step of recording a fold line. The inkjet recording method according to claim 1, wherein the workpiece is a three-dimensional workpiece including a curved surface. The inkjet recording method according to claim 1 or 2, wherein at least a part of the fold line is a curved line. The inkjet recording method according to any one of claims 1 to 3, further comprising a step of applying a water-based coloring ink containing a coloring material to the recording medium to record an image. The inkjet recording method according to claim 4, wherein the surface tension of the decolorizing ink is higher than the surface tension of the coloring ink. The inkjet recording method according to any one of claims 1 to 5, wherein the decolorizing ink further contains glycerin.

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