CN110819169B - Ink for ink jet - Google Patents

Abstract

The invention provides an ink for ink jet, which has excellent ejection stability in an ink jet printer, and has excellent adhesion to the surface of a printed object, cleaning resistance after printing and solvent resistance. In particular, with respect to ejection stability, stable ejection performance is exhibited even when an ink jet printer having a small nozzle diameter is used, and with respect to solvent resistance, not only good solvent resistance with respect to alcohol but also good solvent resistance with respect to other solvents such as acetone is exhibited. The inkjet ink of the present invention contains a ketone solvent as a main component of a solvent, and further contains: a colorant, a poly (p-vinylphenol) resin, and a blocked isocyanate.

Description

Ink for ink jet

Technical Field

The present invention relates to an ink jet ink used in an ink jet printer.

Background

In general, as a recording method on plastic, glass, metal, or the like, an ink jet printer capable of easily printing variable information in a non-contact manner is widely used. As an ink jet ink used in the ink jet printer, an ink obtained by dissolving an oil-based dye, vinyl chloride resin, vinyl acetate resin, acrylic resin, butyral resin, or the like in a solvent such as methyl ethyl ketone or alcohol is known.

However, although the ink using the above resin is designed to sufficiently impart stability and resolubility when ejected by an ink jet printer, the stability in the printer is very good, but the ink is likely to be eluted even when the ink is sufficiently dried because the printed material formed on the surface of the printed material has a problem of solvent resistance.

Therefore, in order to obtain solvent resistance, there is a method of using a component that does not dissolve after drying as a component of the ink.

For example, a so-called UV (ultraviolet) curable ink or EB (electron beam irradiation) curable ink in which a monomer is crosslinked by irradiation of ultraviolet light or an electron beam is known.

However, the UV-curable ink requires a complicated and expensive structure as a printing environment because a UV irradiation device is relatively expensive and generation of ozone is accompanied by UV irradiation. On the other hand, the EB curing ink is more expensive in the EB apparatus, and needs to be prepared in a vacuum system or a nitrogen atmosphere, and there is a disadvantage that introduction is not easy.

In addition, as another method for imparting solvent resistance, there is also performed: a step of using a curing agent to react the resin with a catalyst or heat to impart solvent resistance and the like.

However, the above-mentioned method using a curing agent has a problem that gelation of the ink is likely to occur due to a temperature change or the like in the inkjet printer even if the curing property after printing is good, and it is not easy to obtain a stable ink.

Under the above circumstances, the present applicant has proposed an ink for inkjet printers which contains a ketone solvent and a colorant, and which further contains a blocked isocyanate (see patent document 1).

The ink described in patent document 1 is excellent in adhesion to a printed body, and is blocked with isocyanate, so that the ink is excellent in ejection stability and resolubility. In addition, the solvent resistance is also excellent due to thermal curing.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2013-18939

Disclosure of Invention

The present invention is intended to achieve the object of the invention of patent document 1 at a higher level.

Specifically, for example, in the examples of patent document 1, the solvent resistance was evaluated with respect to ethanol resistance, but there is room for improvement when attempting to verify the acetone resistance.

Further, regarding the evaluation of the ejection stability, there is still room for improvement if an attempt is made to reduce the nozzle diameter for verification. If the ink is excellent in ejection stability even when the nozzle diameter is reduced, the print area can be reduced, and high resolution can be achieved.

In view of the above, an object of the present invention is to provide an ink for inkjet which has excellent ejection stability in an inkjet printer and excellent adhesion to the surface of a printed object, and excellent cleaning resistance and solvent resistance after printing.

In order to solve the above problems, the present invention includes the following configurations.

That is, the ink jet ink according to the present invention contains a ketone solvent as a main component of a solvent, and further contains: a colorant, a poly (p-vinylphenol) resin, and a blocked isocyanate.

Effects of the invention

The ink jet ink of the present invention has excellent ejection stability in an ink jet printer, and also has excellent adhesion to the surface of a printed object, excellent cleaning resistance after printing, and excellent solvent resistance.

In particular, the ink jet recording head is excellent in ejection stability and solvent resistance, and in the ejection stability, stable ejection performance is exhibited even when an ink jet printer having a small nozzle diameter is used.

Drawings

Fig. 1 is a photograph of a two-dimensional code in the ejection stability test (40 μm) of example 1.

Fig. 2 is a photograph of the two-dimensional code in the ejection stability test (40 μm) of comparative example 1.

Detailed Description

The ink jet ink according to the present invention will be described in detail below, but the scope of the present invention is not limited to the description, and other than the following examples, the present invention can be modified as appropriate within a scope not impairing the gist of the present invention.

[ ink for inkjet ]

The inkjet ink (hereinafter, may be simply referred to as "ink") of the present invention includes: ketone solvent, colorant, poly-p-vinylphenol resin and blocked isocyanate.

< coloring agent >

The colorant used in the present invention includes pigments and dyes, and both of them may be used in combination.

In the case of using a pigment, any of an inorganic pigment and an organic pigment may be used.

Examples of the inorganic pigment include: titanium oxide, calcium carbonate, iron oxide, cobalt blue, and the like.

Examples of the organic pigment include: quinacridone series, phthalocyanine series, benzimidazolone series, isoindolinone series, quinophthalone series, condensed azo series, isoindoline series, pyrrolopyrroledione series, and the like.

The above-mentioned pigments are excellent in light resistance, and therefore, are particularly preferable in applications requiring light resistance. In addition, titanium oxide is preferably used in view of stability with respect to a resin and a blocked isocyanate described later, because the pigment obtained by treating the surface of the pigment with an aluminum-based, zinc-based, or silica-based surface treatment agent is excellent in dispersibility, anti-settling property, thickening property with time, anti-coagulation property, and the like.

Specific examples of the organic pigment include: insoluble azo pigments such as toluidine red, toluidine maroon, hansa yellow, benzidine yellow, pyrazolone red, and the like; soluble azo pigments such as lithol red, solar date red, scarlet pigment, permanent red 2B and the like; alizarin, indanthrene, thioindigo maroon and other derivatives derived from vat dyes; phthalocyanine systems such as phthalocyanine blue and phthalocyanine green; quinacridone series such as quinacridone red and quinacridone magenta; perylene series such as perylene red, perylene scarlet and the like; isoindolinone-based compounds such as isoindolinone yellow and isoindolinone orange; pyranthrone-based materials such as pyranthrone red and pyranthrone orange; thioindigo series; condensing azo system; benzimidazolone-based pigments include, for example: flavanthrone yellow, acylamide yellow, quinophthalone yellow, nickel azo yellow, copper methyleneamine yellow, Vaseline brilliant orange, anthrone orange, dianthraquinone red, dioxazine violet, pyrrolopyrroledione, and the like.

If the above pigments are represented by a color index (c.i.) number, there can be exemplified: c.i. pigment yellow 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 109, 110, 117, 125, 128, 129, 137, 138, 139, 147, 148, 151, 153, 154, 181, 166, 168, 185; c.i. pigment orange 16, 36, 43, 51, 55, 59, 61; c.i. pigment red 9, 48, 49, 52, 53, 57, 97, 122, 123, 149, 168, 177, 180, 192, 202, 206, 215, 216, 217, 220, 223, 224, 226, 227, 228, 238, 240; c.i. pigment violet 19, 23, 29, 30, 37, 40, 50; c.i. pigment blue 15, 15: 1. 15: 3. 15: 4. 15: 6. 22, 60, 64; c.i. pigment green 7, 36; and c.i. pigment brown 23, 25, 26, etc.

When a pigment is used, it is preferably dispersed so that the average particle diameter (median diameter (D50) in cumulative distribution) measured by a particle size distribution meter is in the range of 10 to 300nm and the maximum particle diameter is 1 μm or less. The average particle diameter of these pigments is preferably 0.3 μm or less.

If the average particle diameter is larger than 0.3. mu.m, the dispersion stability of the ink is deteriorated and the amount of generated sediment is increased. In particular, if the maximum particle diameter is 1 μm or more, the sedimentation of the pigment becomes remarkable, and there is a possibility that the printing stability is deteriorated. On the other hand, when the average particle diameter is 10nm or less, there is no particular problem, but since the particle diameter is too small, light resistance may be easily deteriorated.

As described above, the pigment used in the present invention is preferably fine pigment particles, but in order to produce an ink for inkjet, it is preferable to further add a dispersant and to stir at high speed by a disperser to produce a stable dispersion liquid.

The pigment is preferably contained in an amount of 0.5 to 20 wt% based on the total weight of the inkjet ink, in order to obtain sufficient density of an image and sufficient light resistance after recording.

In the present invention, as described above, a dye may be used.

The dye is not particularly limited as long as it can be dissolved in a ketone solvent. However, from the viewpoint of solvent resistance, if the solvent to be contacted after curing of the printed matter is alcohol, it is preferably a dye insoluble in alcohol.

Specifically, for example, as represented by the color index number, there can be mentioned: solvent yellow 2, 14, 16, 19, 21, 34, 48, 56, 79, 88, 89, 93, 95, 98, 133, 137, 147; solvent orange 5, 6, 45, 60, 63; solvent red1, 3, 7, 8, 9, 18, 23, 24, 27, 49, 83, 100, 111, 122, 125, 130, 132, 135, 195, 202, 212; solvent blue 2, 3, 4, 5, 7, 18, 25, 26, 35, 36, 37, 38, 43, 44, 45, 47, 48, 51, 58, 59: 1. 63, 64, 67, 68, 69, 70, 78, 79, 83, 94, 97, 98, 99, 100, 101, 102, 104, 105, 111, 112, 122, 124, 128, 129, 132, 136, 137, 138, 139, 143; solvent green 5, 7, 14, 15, 20, 35, 66, 122, 125, 131; solvent black 1, 3, 6, 22, 27, 28, 29; solvent violet 13; and solvent brown 1, 53, etc., and these dyes may be used alone or in combination of 2 or more.

In addition, basic oily dyes may also be used.

Examples of such a basic oily dye include: C.I.basic Violet3, C.I.basic Red1, C.I.basic Red 8, C.I.basic Black2, etc.

< blocked isocyanate >

The inks of the present invention contain blocked isocyanates.

The blocked isocyanate is a compound having a blocked isocyanate group, and can be obtained by reacting an isocyanate compound with a blocking compound (blocking agent).

The blocked isocyanate is inactive at normal temperature, but when heated, the protecting group is dissociated to regenerate the isocyanate group. Therefore, if not heated, it may be pre-compounded with the compound having an active hydrogen group.

The compound having an isocyanate group may contain 1 or 2 or more isocyanate groups in 1 molecule, and examples thereof include: aliphatic, aromatic or alicyclic monoisocyanate, diisocyanate or triisocyanate compound.

Examples of the blocking agent for protecting an isocyanate group include: alcohol compounds, phenol compounds, lactam compounds, oxime compounds, alkyl acetoacetate compounds, alkyl malonate compounds, phthalimide compounds, imidazole compounds, and the like.

The blocked isocyanate used in the present invention is sufficiently dissolved in a ketone solvent, which is a main solvent component of the ink, in the ink state to be in a stable state. The blocked isocyanate functions to strengthen the coating film of the printed ink together with a resin component described later, or to strengthen the coating film of the printed ink by reacting with a part of the resin component, or to strengthen the coating film of the printed ink by reacting with a part of the object to be printed, when any heat is applied thereto in the drying step after printing and the heating step after printing.

However, since the blocked isocyanate can react at a temperature exceeding a certain temperature, problems such as thickening and gelation due to natural reaction with time can be prevented.

As the above-mentioned blocked isocyanate, known are: blocked isocyanates such as dimethylpyrazole, diethyl malonate, methyl ethyl ketoxime, caprolactam, etc. are introduced as blocking agents into the molecular structure of the isocyanate.

The temperature of the blocking dissociation of these blocking agents can be adjusted depending on the kind thereof, but it is preferable that the dissociation is performed at 100 ℃ or higher from the viewpoint of the temperature in the inkjet printer, the storage temperature suitability, the actual post-treatment step, or the like, and the dissociation is performed at 250 ℃ or lower from the viewpoint of energy efficiency.

In order to impart adaptability under the above conditions, as the blocking agent, for example, dimethylpyrazole, diethyl malonate, methyl ethyl ketoxime, or caprolactam is preferably used, and among these, dimethylpyrazole is particularly preferably selected as the main component. Diethyl malonate tends to crystallize after curing, and may not be satisfactory in view of the properties of the coating film. Further, methyl ethyl ketoxime is dissociated at a relatively high temperature, and therefore, a very large amount of energy for curing is required. Further, caprolactam type caprolactam has a problem that a deposit (viscous substance) is easily formed in a facility for solidification treatment.

Further, blocked isocyanates of a system in which one or two or more of diethyl malonate, methyl ethyl ketoxime, and caprolactam are mixed with dimethylpyrazole are preferable in order to favorably adjust the appropriate curability and curing characteristics of dimethylpyrazole.

It is preferable to adjust the heat treatment environment after long-term circulation and printing in the printer. In addition, when the base material of the object to be printed is coated with a thermosetting material in advance, it is necessary to set the conditions within the range not departing from the curing conditions. Since a wide allowable value can be set by using dimethylpyrazole as the main component, adjustment for meeting the above-described demand can be easily performed.

The solvent resistance and coating hardness described later are improved as the amount of the blocked isocyanate added to the ink increases, but if the amount is too large, not only is the stability of the ink easily lowered (for example, viscosity is increased, coagulation and gelation), but also the strength of the coating is lowered due to the presence of the remaining blocked isocyanate which has not reacted with the resin, and the thermosetting property is rather lowered. If the amount is too small, the thermosetting property is lowered, and the coating film strength, which can be judged from solvent resistance and the like, is not improved.

From the above viewpoint, the blocked isocyanate is preferably used in an amount of 0.1 to 10% by weight, more preferably 3 to 9% by weight, based on the total weight of the ink.

< resin >

The ink of the present invention contains a poly (p-vinylphenol) resin as a resin component.

The poly (p-vinylphenol) resin is a polymer having p-vinylphenol as a monomer unit. The copolymer may have a monomer unit other than p-vinylphenol as long as the effect of the present invention is not impaired.

The poly (p-vinylphenol) resin has high solubility in ketone solvents, and therefore, exhibits excellent ejection stability and re-solubility, and also exhibits high solvent resistance when cured thermally in combination with a blocked isocyanate.

The molecular weight of the poly (p-vinylphenol) resin is not particularly limited, and for example, the weight average molecular weight is preferably in the range of 1000 to 30000, more preferably 1500 to 15000. If the weight average molecular weight is too large, the ink may gel and the storage stability may be impaired, or the ejection from the printer may proceed abnormally; if the weight average molecular weight is too small, sufficient coating film strength may not be obtained.

< solvent >

As the solvent used in the present invention, a ketone solvent is used as a main component of the solvent.

Examples of the ketone solvent include: acetone, methyl ethyl ketone, dipropyl ketone, methyl isobutyl ketone, methyl isopropyl ketone, cyclopentanone, and the like. Among them, methyl ethyl ketone is preferably used in the ink for a continuous ink jet printer in view of the solubility of the resin, the dispersibility of the pigment, the conductivity, and the drying property of the ink.

In the above, the "main component of the solvent" means: in addition to the case where the solvent is composed of only a ketone solvent, other solvents may be contained within a range not to impair the effects of the present invention. Generally, the term "solvent" refers to a ketone solvent used in a proportion of 50 wt% or more of the total amount of the solvent. The ketone solvent is more preferably used in an amount of 60 wt% or more, still more preferably 70 wt% or more, still more preferably 80 wt% or more, particularly preferably 90 wt% or more, and most preferably only the ketone solvent is used as the solvent.

Examples of the solvent other than the ketone solvent include: ethyl acetate, n-propyl acetate, butyl acetate, toluene, xylene, isopropyl alcohol, butanol, dioxane, 2- (methoxymethoxy) ethanol, 2-butoxyethanol, 2- (isopentyloxy) ethanol, 2- (hexyloxy) ethanol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, liquid polyethylene glycol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, low molecular weight polypropylene glycol, and the like.

The amount of the ketone solvent used is not particularly limited, but is preferably 60% by weight or more based on the total weight of the ink, from the viewpoints of solubility of the resin, dispersibility of the pigment, conductivity, and drying property of the ink. In particular, methyl ethyl ketone is preferably used in a proportion of 55% by weight or more based on the total weight of the ink.

< other ingredients >

The ink of the present invention can be preferably used in an ink jet printer, particularly a charged dot continuous discharge type, that is, a continuous ink jet printer. In this case, a conductive agent is used to adjust the amount of deflection of ink droplets ejected from the printer due to an electric field.

As the conductive agent, for example, there can be used: ammonium thiocyanate, potassium thiocyanate, sodium thiocyanate, lithium nitrate, tetrabutylammonium hexafluorophosphate, tetrabutylammonium bromide, tetraphenylammonium borate, and the like. Among them, if the stability of the ink is evaluated from the viewpoint of compatibility with the blocked isocyanate, an organic conductive agent such as tetrabutylammonium hexafluorophosphate or tetraphenylammonium borate exhibits stable characteristics over a long period of time, and thus is preferable.

The conductive agent is preferably used in an amount of 0.5 to 2.5 wt% based on the total weight of the ink. If the content of the conductive agent is less than 0.5 wt%, sufficient conductivity may not be obtained, and the deviation in the printer may not be stably maintained. On the other hand, if the content of the conductive agent is more than 2.5 wt%, compatibility with each material may not be maintained, and stability with time may be lowered, resulting in an unstable printing state in the printer. Conductive agents other than those described above may cause poor dispersion or aggregation of the pigment, and therefore, attention is required for addition.

In the ink of the present invention, a dispersant may be used to improve the dispersibility of the pigment.

Examples of the dispersant for the pigment include: hydroxyl-containing carboxylic acid esters, salts of long-chain polyaminoamides with high-molecular-weight acid esters, salts of high-molecular-weight polycarboxylic acids, salts of long-chain polyaminoamides with polar acid esters, high-molecular-weight unsaturated acid esters, high-molecular copolymers, modified polyurethanes, modified polyacrylates, polyether ester type anionic activators, naphthalenesulfonic acid-formaldehyde condensate salts, special aromatic sulfonic acid-formaldehyde condensate salts, polyoxyethylene alkylphosphate esters, polyoxyethylene nonylphenyl ether, octadecylamine acetate, and the like.

Specifically, the following can be exemplified: Anti-Terra-U, Anti-Terra-203/204, Disperbyk-101, 107, 110, 130, 161, 162, 163, 164, 165, 166, 170, 400, Bykumen, ByK-P104, P105, P104S, 240S, Lactimon, Efka CHEMICALS Efka 44, 46, 47, 48, 49, 54, 63, 64, 65, 66, 71, 701, 764, 766, Efka polymer 100, 150, 400, 401, 402, 403, 450, 451, 452, 453, 745, Cogrong chemical company Floen TG-710, Flowson SH-290, SP-1000, Polyflow No.50E, No.300, Aesper fine technology company Ajis PB, Psjsper 821, Parlon 860, Sp-5000, Sp-873, Sp-2153, Sp-2150, Sol-1000, Sp-WO 9824, Sp-S-S.S.S.S.S.S.S.S.S.S.S.S.S.S.K.K.K.S.S.K.S., 13240. 13940, 17000, 22000, 24000, 28000, 32000, 38500, Nikkol T106 manufactured by Sun chemical Co., Ltd., MYS-IEX, Hexagline 4 a-U, and the like.

Further, as the adjusting agent for the dot formation, a silicon-based surfactant or a fluorine-based surfactant can be used. When an inorganic pigment having a large specific gravity such as titanium oxide or iron oxide is used, an anti-caking agent based on an unsaturated carboxylic acid can be used to prevent caking due to sedimentation.

< combination of ingredients >

The mixing ratio of the respective components is not particularly limited, and for example, it is preferable that the mixing ratio of the colorant is 2 to 15% by weight, the mixing ratio of the poly (p-vinylphenol) resin is 1 to 20% by weight, the mixing ratio of the blocked isocyanate is 0.1 to 10% by weight, the mixing ratio of the conductive agent is 0.3 to 2.5% by weight, and the balance is a solvent containing a ketone solvent, based on the total weight of the ink.

Further, when an optimum range of the mutual ratio of the poly-p-vinylphenol resin and the blocked isocyanate is exemplified, for example, on a weight basis, the poly-p-vinylphenol resin: the blocked isocyanate is preferably 1: 1-3: 1, more preferably 1.5: 1-2.5: 1. if the amount of the poly (p-vinylphenol) resin is too large (if the amount of the blocked isocyanate is too small), there is a possibility that the strength of the coating film may be decreased due to the presence of the remaining poly (p-vinylphenol) resin which is not reacted with the blocked isocyanate; if the amount of the poly (p-vinylphenol) resin is too small (if the amount of the blocked isocyanate is too large), the strength of the coating film may be reduced due to the presence of the remaining blocked isocyanate which has not reacted with the poly (p-vinylphenol) resin.

[ use of ink ]

Examples of the object to be printed, which is the object to be printed with the ink of the present invention, include: metals, glass, plastics, and coatings applied to the surfaces of these materials. The heat-resistant temperature of the printed material is preferably 100 ℃ or higher because of thermal curing.

The printed matter is subjected to a treatment of forming a print (print) of various codes such as characters, bar codes, and two-dimensional codes by spraying the ink with an ink jet printer, and then subjected to a heating step of 100 ℃ or higher for 10 to 60 minutes. The preferable heating temperature is 130 to 250 ℃, and more preferably 150 to 210 ℃. The preferable heating time is about 15 to 30 minutes. The heating conditions are preferably used in view of solvent resistance, adhesion, and resistance to washing with an aqueous surfactant solution, and thus the accuracy of the reading rate in a reader for reading a barcode, a two-dimensional code, or the like can be sufficiently exhibited.

The viscosity of the ink of the present invention is preferably adjusted to a range of, for example, 3.2 to 5.5 mPas (20 ℃) in order to expand a suitable printable region in an ink jet printer. If the viscosity of the ink is less than 3.2 mPas, the formation of ink dots on the surface of the object to be printed is poor, and the density of the formed print (print density) becomes low. On the other hand, if the viscosity of the ink exceeds 5.5mPa · s, problems such as ejection failure of ink droplets and drying failure after printing tend to occur.

Examples

Hereinafter, the ink according to the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

[ example 1 ]

15 parts by weight of a poly (p-vinylphenol) resin (weight average molecular weight Mw 11000) and 3 parts by weight of Solsperse 38500 (dispersant: manufactured by Rabowet) were dissolved in 58.5 parts by weight of methyl ethyl ketone and 5 parts by weight of cyclopentanone to prepare a solution, and titanium oxide (treated with Al. Si, rutile type TiO) was added to the solution₂Average particle diameter 0.24 μm)10 parts by weight, and the resulting mixture was fed to a horizontal sand mill to disperse titanium oxide.

To the dispersion, 7 parts by weight of blocked isocyanate containing dimethylpyrazole as a blocking agent was added and mixed, and 1.5 parts by weight of tetrabutylammonium hexafluorophosphate was further added and mixed by high-speed stirring.

Then, the mixed dispersion was filtered through a filter having a mesh size of 1.0 μm to obtain an ink for an ink jet printer.

In the trial production of the ink, all the components constituting the ink may be placed in one container and uniformly dispersed, but from the viewpoint of obtaining a stable ink, it is preferable to prepare the ink by dispersing the pigment in a concentrated system using only a part of the pigment, the dispersant, the resin, and the solvent, adding the blocked isocyanate and the conductive agent after the dispersion, mixing them, and dissolving them.

[ examples 2 to 10, comparative examples 1 and 2 ]

Inks of examples 2 to 10 and comparative examples 1 and 2 were prepared in the same manner as in example 1 except that the raw materials were changed as shown in table 1 below. Table 1 also shows the recipe of example 1.

In table 1, the numerical values given in the prescription column all represent weight% relative to the total weight of the ink.

TABLE 1

[ evaluation of physical Properties of ink ]

The physical properties of the ink were evaluated and are also shown in Table 1 above.

Details of the evaluation items are as follows.

< viscosity >

The measurement was carried out at 20 ℃ using an EH type viscometer.

< conductivity >

The measurement was carried out at 20 ℃ using a conductivity meter. In the continuous ink jet printer, the conductivity is preferably 0.5mS/cm or more from the viewpoint of accurate dot deflection control.

< dispersibility >

When the pigment resin liquid was dispersed by a horizontal sand mill, the state of the pigment resin liquid was evaluated as to whether it was lumps or coarse particles remaining little and having fluidity. The case where the dispersion state including the average particle diameter was very good was evaluated as "very excellent", and the case where the surface state of the blade coating film and the fluidity at the time of dispersion were good was evaluated as "o".

< average particle diameter >

The particle diameter (nm) of D50 was measured with a laser-detectable particle size distribution meter (UPA-150, manufactured by Nikkiso K.K.).

< ejection stability >

The inks given in the respective examples were printed on the resin-coated surface of the glass substrate with a 50 μm nozzle and a 40 μm nozzle by a continuous ink jet printer (CCS 3000P manufactured by jis technikagai corporation), and the state of the printed matter was visually evaluated. In addition, with respect to the ejection characteristics, the ejection states of the nozzles in the continuous printing were also evaluated simultaneously based on the state of the obtained print.

The case where a dot was broken in the middle of printing or each printed dot was not printed at a predetermined position even though continuous printing was performed was evaluated as "x". Further, the two-dimensional bar code printed by the reader was read to confirm the accuracy of reading, and the case of abnormal reading was evaluated as "x". The case where each print dot was continuously printed accurately to a predetermined position and the read of the printed two-dimensional barcode was normal by the reader was evaluated as "o".

Fig. 1 and 2 show photographs of the two-dimensional code printed by the 40 μm nozzle in example 1 and comparative example 1, respectively.

< storage stability >

The ink was sealed in a sealed container, stored at 45 ℃ and the change in the appearance and viscosity of the ink was confirmed after 2 months. The case where the appearance and viscosity were not changed to a predetermined level or more (thickening of 8% or more) was evaluated as "o", and the case where the appearance and viscosity were changed to a predetermined level or more was evaluated as "x".

< thermosetting >

As conditions for thermally curing the printed body after printing, curability at 170 ℃ for 30 minutes and curability at 200 ℃ for 15 minutes were confirmed. The thermosetting property was confirmed by applying alcohol to the cured surface cured by heat and confirming the thermosetting property depending on whether or not the heat-cured printed material was dissolved. The case where no dissolution was observed was evaluated as "O", and the case where a portion of the dissolution was observed as "X".

< alcohol resistance >

The surface of the printed material after the thermal curing of the printed body was wiped with a cotton swab soaked with alcohol, and the dissolution and peeling of the printed dots on the surface of the printed material were confirmed. The case of wiping 50 times or more without peeling was evaluated as "excellent", the case of wiping 20 to 50 times without peeling was evaluated as "o", and the case of peeling was evaluated as "x".

< acetone resistance >

The surface of the printed material after the thermal curing of the printed body was wiped with a cotton swab soaked with acetone, and the dissolution and peeling of the printed dots on the surface of the printed material were confirmed. The case of wiping 20 to 30 times without peeling was evaluated as "excellent", the case of wiping 10 to 20 times without peeling was evaluated as "o", and the case of peeling was evaluated as "x".

< cleaning Property >

A printed material on which a two-dimensional barcode or a two-dimensional code was printed was immersed in a 0.25% nonionic active agent aqueous solution, and a cleaning test was performed by ultrasonic irradiation for 15 minutes to evaluate whether or not the printed two-dimensional barcode or the two-dimensional code could be read by a reader. The case where there was no read abnormality was evaluated as "o", and the case where there was a read abnormality was evaluated as "x".

< adhesion >

A transparent tape was attached to the surface of the object on which the two-dimensional code was printed, and whether or not the printed dots (printed body) constituting the two-dimensional code peeled off when the transparent tape was peeled off was evaluated. The case where the printed dot was not peeled off was evaluated as "O", and the case where there was peeling was evaluated as "X".

[ result investigation ]

From the results of the above examples 1 to 10 shown in table 1 and fig. 1, it is understood that the ink of the present invention has excellent physical properties in all the evaluation items of dispersibility, ejection stability, storage stability, thermosetting property, solvent resistance, cleanability, and adhesion.

From the results shown in Table 1 and FIG. 2, it can be said that the ink of comparative example 1 is an ink showing basically excellent physical properties, but the ejection stability when a 40 μm nozzle is used is insufficient, and the acetone resistance is inferior to the inks of examples 1 to 10. In comparative example 1, the ink using a butyral resin and a rosin-modified maleic acid resin as the resins and not containing a poly (p-vinylphenol) resin did not satisfy the conditions of the present invention, and thus it was found that: the use of a poly (p-vinylphenol) resin as the resin improves ejection stability (40 μm) and solvent resistance.

The ink of comparative example 2 was insufficient in ejection stability (40 μm) and storage stability, and was inferior in acetone resistance to the inks of examples 1 to 10. Comparative example 2 does not use a ketone solvent as a main component of the solvent, and does not satisfy the conditions of the present invention. From these results, it is found that a ketone solvent is required as a main component of the solvent in order to obtain the effects of the present invention.

In addition, the white inks (examples 1 to 8) were subjected to a reading test of two-dimensional barcodes immersed in ethanol, and as a result, the speed of reading and confirmation was high. Similarly, the white inks (examples 1 to 8) were subjected to a reading test using a two-dimensional bar code immersed in acetone, and the speed of reading and confirming was still high. From these results, it was also confirmed that the ink of the present invention has high solvent resistance.

Claims (6)

1. An ink for ink jet printing, wherein,

the ink for inkjet includes: a solvent, a colorant, a poly (p-vinylphenol) resin, a blocked isocyanate, and a conductive agent, wherein the solvent contains a ketone solvent in a proportion of 50 wt% or more of the total amount of the solvent,

the colorant is contained in an amount of 2 to 15 wt%, the poly-p-vinylphenol resin is contained in an amount of 1 to 20 wt%, the blocked isocyanate is contained in an amount of 0.1 to 10 wt%, the conductive agent is contained in an amount of 0.3 to 2.5 wt%, and the balance is a solvent containing a ketone solvent, based on the total weight of the ink.

2. The ink for inkjet according to claim 1, wherein,

in the blocked isocyanate, the blocking agent to be introduced comprises: one or more selected from the group consisting of dimethylpyrazole, diethyl malonate, methyl ethyl ketoxime, and caprolactam.

3. The ink for inkjet according to claim 2, wherein,

the blocking agent to be introduced into the blocked isocyanate contains dimethylpyrazole as a main component, and further contains: one or more selected from the group consisting of diethyl malonate, methyl ethyl ketoxime and caprolactam.

4. The ink for inkjet according to any one of claims 1 to 3, wherein,

the weight average molecular weight of the poly-p-vinylphenol resin is within the range of 1000-30000.

5. The ink for inkjet according to any one of claims 1 to 3, wherein,

the conductive agent is at least 1 of tetrabutylammonium hexafluorophosphate and tetraphenyl ammonium borate.

6. The ink for inkjet according to claim 4, wherein,

the conductive agent is at least 1 of tetrabutylammonium hexafluorophosphate and tetraphenyl ammonium borate.

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