JP6089915B2 - Water-based ink for inkjet - Google Patents

Description

  The present invention relates to a water-based white ink for ink jet having a low viscosity, a storage stability and an excellent pigment sedimentation property using titanium oxide as a pigment.

  The ink jet recording method is a recording method in which characters and images are obtained by ejecting ink droplets directly from a very fine nozzle onto a recording member and attaching them. According to this method, there is an advantage that not only the noise of the apparatus to be used is small and the operability is good, but also colorization is easy and plain paper can be used as a recording member. It is widely used as an output machine in offices and homes.

  On the other hand, in industrial applications, it is expected to be used as an output machine for digital printing due to improvements in inkjet technology, and even for non-absorbable substrates (plastic substrates such as PVC and PET) using solvent inks and UV inks. Printing machines capable of printing have actually been marketed. However, in recent years, the demand for water-based inks has increased from the standpoint of environmental friendliness.

  In industrial applications, printing on transparent substrates such as PET films and printing on colored substrates are also required. When only process color ink is printed on these substrates, an image having poor color developability and visibility may be obtained due to the color influence of the substrate. In order to solve this, a method using white ink is known. That is, by printing with white ink before printing with color ink and forming an image with color ink thereon, an image with excellent color development and visibility can be obtained. Therefore, the practical application of white water-based inkjet ink has been desired.

  Examples of white pigments include titanium oxide, hollow particles, and organic white pigments. Titanium oxide is often used in terms of cost and concealment. However, even when titanium oxide is used, a large amount of pigment must be contained in the ink in order to exhibit sufficient hiding properties. As the viscosity of the ink increases as the pigment increases, an attempt to provide sufficient concealment may deviate from the dischargeable viscosity of the inkjet head and may not be suitable as an inkjet ink. In addition, a decrease in ink stability due to high concentration is also a problem, and the degree of freedom of the solvent used in the ink is limited.

  Patent Document 1 proposes an aqueous dispersion of titanium oxide that improves the dispersibility of titanium oxide by performing surface treatment of titanium oxide with an inorganic phosphoric acid compound, and is excellent in stability. However, this method has insufficient stability, and when a highly hydrophobic solvent is used for printing on a plastic substrate, pigment aggregation occurs in a short period of time, which is unsuitable for practical use.

  Patent Document 2 proposes an aqueous dispersion of titanium oxide that promotes adsorption of the dispersion resin by performing a surface treatment of titanium oxide and has excellent dispersion stability. However, there is no description regarding the lowering of the viscosity of the dispersion, and it is considered that when this dispersion is used, it is impossible to produce a low-viscosity inkjet ink while exhibiting sufficient concealability.

JP 2002-348513 A JP 2011-225867 A

  An object of the present invention is to provide a water-based white ink for ink-jet which has titanium oxide as a pigment and has low viscosity, excellent storage stability and pigment precipitation.

That is, the present invention is an aqueous white ink for inkjet containing at least titanium oxide, a pigment dispersion resin, an organic solvent, and water,
The present invention relates to an aqueous white ink for ink jet, wherein at least a polyalkylene glycol group-introduced α-olefin-maleic acid resin is used as the pigment dispersion resin.

  The present invention also relates to the above-described aqueous white ink for ink jet, wherein an α-olefin having 8 or more carbon atoms is used as the α-olefin.

Or the present invention, the as a pigment dispersing resin, above, characterized in that use a lot containing pigment dispersing resin than the structure of the structure derived from maleic acid and / or maleic anhydride-derived α- olefin in a weight ratio in terms of The present invention relates to an aqueous white ink for inkjet.

  The present invention also relates to the above-described water-based white ink for ink jet, wherein the organic solvent contains 1,2-alkanediol having 4 to 8 carbon atoms.

  According to the present invention, it has become possible to provide an aqueous white ink for ink jet using titanium oxide as a pigment and having low viscosity, excellent storage stability, and excellent pigment sedimentation.

  Hereinafter, the present invention will be described with reference to preferred embodiments. In the following description, “parts” and “%” represent “parts by weight” and “% by weight”, respectively, unless otherwise specified.

  In the present invention, a resin obtained by copolymerizing an α-olefin with maleic acid and / or maleic anhydride is used as the pigment dispersion resin. By using this, the present inventors have found that the viscosity of the pigment dispersion becomes extremely low, and can be finished to a low viscosity when used as an inkjet ink, and the discharge stability can be improved. It was.

  Specific examples of α-olefins include 1-butene, isobutene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, diisobutylene, 1-nonene, 1-decene, 1-dodecene, 1 And α-olefins such as 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene, 1-docosene and 1-tetracocene. Among these, α-olefins having 8 or more carbon atoms are preferable. When the carbon number is 8 or more, the storage stability of the ink is improved. Further, if the carbon number becomes too large, the viscosity of the ink may increase and adversely affect ink ejection. Therefore, it is preferable to use one having 20 or less carbon atoms.

  In the present invention, a mixture of two or more α-olefins can be used. By mixing and using, it becomes easy to match | combine the solubility of a resin, a glass transition point, etc. to desired properties.

  The above α-olefin and maleic acid and / or maleic anhydride are polymerized by adding a radical initiator and a chain transfer agent to obtain an α-olefin-maleic anhydride resin. As the polymerization method, for example, a method in which maleic anhydride, a radical initiator and a chain transfer agent are added to a liquid α-olefin monomer and polymerized is preferable.

  As a ratio of the structure derived from α-olefin and the structure derived from maleic acid and / or maleic anhydride in the resin, it is preferable that the structure derived from α-olefin is large in terms of weight ratio. Increasing the structure derived from α-olefin can improve the viscosity stability of the ink.

  The obtained α-olefin- (maleic anhydride) resin can be treated with an acid and a base to open the maleic anhydride moiety to obtain an α-olefin-maleic acid resin. At this time, the alcohol skeleton can be introduced into the resin by allowing the alcohol to coexist and reacting with the carboxylic acid moiety.

  Any alcohol compound having a hydroxyl group can be introduced into the resin. For example, an alkyl group can be introduced by butanol, hexanol, octanol, or the like, an aromatic ring can be introduced by phenol, benzyl alcohol, or the like, or a polyalkylene glycol group can be introduced by glycol ether or the like.

  By introducing a polyalkylene glycol group, it is possible to suppress precipitation of the pigment, and it is preferable to introduce a polyalkylene glycol group by the above-described method. Examples of the alcohol used to introduce the polyalkylene glycol group include diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol mono Examples include butyl ether, tripropylene glycol monomethyl ether, polyethylene glycol, and polypropylene glycol.

  In the present invention, a polymerizable compound other than α-olefin and (anhydrous) maleic acid may be copolymerized with the pigment-dispersed resin. Examples of polymerizable compounds that can be copolymerized include styrene, (meth) acrylic acid esters, and vinyl ethers.

  The weight average molecular weight of the pigment-dispersed resin is preferably 3000 to 50000. When the molecular weight is 3000 or less, the dispersion stability may be lowered, and when the molecular weight is 50000 or more, ejection may be affected. More preferably, the molecular weight is 5000-30000, and still more preferably the molecular weight is 7000-20000.

  In the present invention, the acid value of the pigment dispersion resin is preferably 50 to 400 mgKOH / g. If the acid value is less than 50 mg KOH / g, the resin is difficult to dissolve in water, and the viscosity of the dispersion increases. Moreover, even when it is larger than 400 mgKOH / g, the interaction between the resins may be strengthened and the viscosity may be increased. The acid value of the pigment dispersion resin is preferably 100 to 350 mgKOH / g, and more preferably 150 to 300 mgKOH / g.

  The pigment-dispersed resin of the present invention preferably has a neutralized acid group in the resin with a base in order to increase the solubility in water. As the base, organic bases such as aqueous ammonia, dimethylaminoethanol, diethanolamine, and triethanolamine, and inorganic bases such as lithium hydroxide, sodium hydroxide, and potassium hydroxide can be used.

  The ratio of titanium oxide to pigment dispersion resin in the pigment dispersion of the present invention is preferably 2/1 to 100/1. When the ratio of the pigment dispersion resin is larger than 2/1, the viscosity of the pigment dispersion tends to increase. On the other hand, if it is less than 100/1, the dispersibility may be lowered and the stability may be lowered. The ratio of titanium oxide and pigment dispersion resin is more preferably 4/1 to 50/1, further preferably 5/1 to 25/1, and most preferably 10/1 to 20/1.

  In the present invention, titanium oxide is used as a white pigment. Titanium oxide pigments are white pigments that are widely used because they have high concealability and are inexpensive. As the titanium oxide used in the present invention, either an anatase type or a rutile type can be used, but it is preferable to use a rutile type in order to improve the concealability of printed matter. Moreover, although what was manufactured by any methods, such as a chlorine method and a sulfuric acid method, it is more preferable to use the titanium oxide manufactured by the chlorine method because whiteness is high.

  The dispersed particle diameter of the titanium oxide of the present invention is preferably 100 to 400 nm from the viewpoints of the sedimentation property of the pigment and the concealability of the printed matter. If the particle size is 100 nm or less, the titanium oxide does not easily settle, but the concealability is lowered and the practicality as a white ink is lowered. On the other hand, at 400 nm or more, the concealability is sufficient, but sedimentation is likely to occur, which may cause clogging of the flow path in the printer and non-ejection. The average particle diameter of titanium oxide is more preferably 150 to 350 nm, and further preferably 200 nm to 300 nm.

  In the present invention, the pigment concentration in the ink is preferably 5 to 25%. When the pigment concentration is less than 5%, sufficient concealment may not be obtained by one printing. On the other hand, if it is higher than 25%, the viscosity of the ink becomes high, making it difficult to eject from the inkjet head, and long-term printing stability may be reduced. The pigment concentration in the ink is more preferably 8% to 20%, and most preferably 10% to 15%.

  In the inkjet ink of the present invention, by using an organic solvent, the wettability of the ink with respect to the substrate can be improved, and a printed matter with good image quality can be obtained. As the organic solvent, an alkanediol solvent or an alkylene glycol alkyl ether solvent can be preferably used.

  Alkanediol solvents include 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1, Examples include 5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 2-methyl-2,4-pentanediol, and the like. Among these, the use of 1,2-alkanediols such as 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol, and 1,2-hexanediol improves the wettability of the substrate. This is preferable because print quality can be improved. Furthermore, it is preferable to use 1,2-alkanediol having 4 to 6 carbon atoms.

  Dialkylene glycol alkyl ether solvents include diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether Dipropylene glycol monopropyl ether, tripropylene glycol monomethyl ether, methoxybutanol, tetraethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol butyl methyl ether, triethylene glycol butyl methyl ether, tetraethylene Glycol butyl methyl ether, and the like. Among these, alkylene glycol monoalkyl ether is preferable, and propylene glycol monomethyl ether and methoxybutanol are more preferable.

  Other organic solvents can also be used for adjusting the moisture retention of the ink and the permeability to the substrate. Examples of other organic solvents include heterocyclic compounds such as 2-pyrrolidone, N-methylpyrrolidone, N-ethylpyrrolidone, N-methyloxazolidinone, N-ethyloxazolidinone, γ-butyrolactone, and ε-caprolactone.

  The organic solvent is preferably contained in the ink in an amount of 10 to 40%. When it is less than 10%, the wettability of the ink with respect to the base material becomes insufficient, and a problem such as repellency may occur depending on the base material. On the other hand, when the content is more than 40%, the viscosity becomes high, and it becomes difficult to discharge from the ink jet head, and the long-term printing stability may be lowered. More preferably 15 to 35% is included.

  In order to increase the resistance of the printed material, a binder resin can be further added in the present invention. Water-soluble resins and fine resin particles are generally known as binder resins for water-based inks. In general, resin fine particles have a higher molecular weight than water-soluble resins, and can achieve high resistance. In addition, the resin fine particles can lower the ink viscosity, and a larger amount of resin can be blended in the ink. Therefore, the resin fine particles are suitable for increasing the resistance of the ink-jet ink. Examples of the resin include acrylic, urethane, styrene butadiene, vinyl chloride, and polyolefin. In view of ink stability and printed material resistance, it is desirable to use acrylic resin fine particles.

  By increasing the glass transition temperature (Tg) of the binder resin, it is possible to improve resistance such as abrasion resistance and chemical resistance, preferably in the range of 50 to 120 ° C, more preferably in the range of 80 to 100 ° C. It is good to do. When the temperature is lower than 50 ° C., sufficient resistance cannot be obtained, and the ink coating film may be peeled off from the printed matter in practical use. In addition, when the temperature is higher than 120 ° C., the coating film becomes very hard, and cracking and cracking may occur on the printed surface when the printed material is bent.

  The content of the binder resin in the ink as described above is in the range of 2% or more and 30% or less of the total weight of the ink in solid content, more preferably in the range of 3% or more and 20% or less. Preferably, it is in the range of 6% or more and 15% or less.

  Further, a surfactant can be further added to improve the image quality of the printed matter. Examples of the surfactant include a silicon-based surfactant, a fluorine-based surfactant, and an acetylenic diol-based surfactant. Among these, it is preferable to use a silicon-based surfactant from the viewpoint of printing stability. The content of the surfactant is preferably in the range of 0.05% or more and 5% or less of the total weight of the ink. More preferably, it is in the range of 0.1% or more and 3% or less.

  In the present invention, not only a single color but also an ink set combining color inks such as cyan, magenta, yellow, and black can be used. When used as an ink set, finely adjust the composition between the inks, align the viscosity and surface tension, etc., and evenly spread and dry on the base material during printing, so that the print quality is uniform. Can be further improved.

  The substrate for printing the ink-jet ink of the present invention is not particularly limited, but paper substrates such as fine paper, coated paper, art paper, cast paper, synthetic paper, polycarbonate, hard vinyl chloride, soft vinyl chloride, polystyrene, polystyrene foam, Plastic substrates such as PMMA, polypropylene, polyethylene, and PET, metal substrates such as stainless steel, glass, and wood can be used. These substrates that are not white can be printed with white ink first and then with color ink to improve the color developability of the printed matter.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.

  The pigment-dispersed resin used in the present invention was produced by copolymerizing the polymerizable components shown in Table 1 by a known method, and then hydrolyzing the maleic anhydride portion to open the ring. Further, regarding the pigment dispersion resins 4, 5, and 8, the maleic acid-derived carboxylic acid contained in the obtained resin was esterified with alcohol. The weight average molecular weight was 9000 in all cases.

( Reference Example 1)
Use 50 parts of titanium oxide (average primary particle size 280 m) as pigment, 5 parts of pigment dispersion resin, and 45 parts of water with a disper, and then use a 0.6 L dyno mill filled with 1800 g of zirconia beads with a diameter of 0.5 mm. This dispersion was performed for 2 hours to obtain an aqueous pigment dispersion of the present invention. At this time, the ratio of the non-volatile component between the pigment and the dispersion resin is pigment / dispersion resin (non-volatile component) = 10/1.

  20 parts of the obtained aqueous pigment dispersion, 20 parts of fixing resin (styrene acrylic resin emulsion, Tg 80 ° C., Nv. 40%), 20 parts of propylene glycol as an organic solvent, 5 parts of diethylene glycol monobutyl ether, 40 parts of water Were sequentially added to the mixing container while stirring with a disper, and stirred until sufficiently uniform to produce a white ink for inkjet. The viscosity of this ink was 4.5 mPa · s.

(Measurement of viscosity of white ink for inkjet)
The viscosity of the obtained ink-jet white ink was measured using an E-type viscometer (TVE-20L, manufactured by Toki Sangyo Co., Ltd.) at 25 ° C. and a rotation speed of 50 rpm. When the measured viscosity was less than 5 mPa · s, it was judged as “good”, and when it was 5 mPa · s or more, it was judged as “poor”.

(Ink storage stability)
The pigment dispersion and ink-jet ink were stored in a thermostat at 70 ° C. and accelerated over time, and then the change in viscosity of the ink before and after aging was evaluated.
◎: Viscosity change rate after storage for four weeks is less than ± 10% ○: Viscosity change rate after storage for two weeks is less than ± 10% △: Viscosity change rate after storage for one week is less than ± 10% ×: Storage for one week Later viscosity change rate is more than ± 10

(Titanium oxide sedimentation)
By separating 20 ml of the prepared ink-jet white ink into a screw tube bottle (capacity: about 20 ml) whose side is transparent, and then visually observing the ink composition after standing at 25 ° C. for 1 day, the pigment The sedimentation property was evaluated. The evaluation criteria at this time are as follows.
◎: Pigment is not observed in the lower part of the container ○: Pigment is observed in the lower part of the container, but it is returned to the unsettled state by shaking the screw tube three times. X: A state in which the pigment settles in the lower part of the container is observed, and even if the screw tube bottle is shaken three times or more, it does not return to the unsettled state.

( Reference Examples 2, 3, 6, 7, 9, Examples 4, 5, 8, 10-12, Comparative Examples 1-3)
In the same manner as in Reference Example 1, ink was prepared by changing the pigment dispersion resin and the organic solvent as shown in Table 2, and evaluated.

  As a result of evaluation, in the examples, by using a resin obtained by copolymerization of α-olefin and maleic acid as a dispersion resin, the ink has a low viscosity, and can be made into an ink having good storage stability and pigment precipitation. done.

Claims (4)

At least an aqueous white ink for inkjet containing titanium oxide, a pigment dispersion resin, an organic solvent, and water,
An aqueous white ink for ink-jet recording, wherein at least a polyalkylene glycol group-introduced α-olefin-maleic acid resin is used as the pigment dispersion resin.   The aqueous white ink for inkjet according to claim 1, wherein an α-olefin having 8 or more carbon atoms is used as the α-olefin. 3. The pigment dispersion resin according to claim 1, wherein the pigment dispersion resin contains a structure derived from α-olefin in a weight ratio conversion more than the structure derived from maleic acid and / or maleic anhydride. Water-based white ink for inkjet. The aqueous white ink for inkjet according to any one of claims 1 to 3 , wherein the organic solvent contains 1,2-alkanediol having 4 to 8 carbon atoms.