JP5015412B2 - Oil-based ink for inkjet printer - Google Patents

Description

  The present invention relates to a pigment-type oil-based ink for a piezo-type ink jet printer (hereinafter sometimes simply referred to as “ink”). More specifically, the printer nozzle has no ink clogging, excellent ink ejection properties and ejection recovery properties, and The present invention relates to an ink excellent in fixing property and drying property of an ink to a recording material.

  Conventional inkjet recording methods include a continuous method in which continuously ejected ink is selectively landed on an adherend and a drop-on-demand method in which ink is selectively ejected. Demand-type printers are the mainstream. For drop-on-demand printers, there is a bubble system that ejects ink using bubbles generated by abruptly heating ink, and a piezo system that ejects ink using ceramic (piezo) that deforms when a voltage is applied. There is.

  The above-mentioned piezo type using conventional oil-based ink is a system that uses a piezo element as a pump to convert electrical energy into mechanical energy and ejects ink. Therefore, basically, various ink materials are used. It can be discharged. However, in this method, in order to eject ink depending on the presence or absence of signals, the solvent in the ink evaporates on the nozzle end surface where the ink ejection is interrupted, so that the ink is deposited due to the precipitation of solid components in the ink. Since ink ejection is hindered by clogging or ink viscosity increase in the nozzle accompanying ink concentration, minor maintenance is required. In particular, the ink used to create printed materials for outdoor use uses a non-absorbing substrate that is a plastic film, such as a polyvinyl chloride sheet, as the printing substrate, so a relatively volatile solvent is used as the ink solvent. For this reason, the ink dries quickly and clogging of the ink occurs remarkably.

  In addition, when the amount of air dissolved in the ink exceeds a certain amount, the cavitation caused by the high-frequency vibration of the piezo element causes the micro bubbles generated in the printer nozzle to absorb the pressure and drive responsiveness decreases. Or In addition, abnormal discharge may be caused by the generation of bubbles in the nozzle accompanying the change in the outside air temperature.

From the above, an inkjet pigment ink (Patent Document 1) using a high boiling point solvent instead of the conventional oil-based ink has been proposed. However, in the ink disclosed in Patent Document 1, as a non-aqueous organic solvent, a glycol ether ester alone or a mixture of two or more thereof is used for the purpose of preventing thickening of ink during storage and pigment aggregation. Therefore, the solubility of the solid component such as resin in the ink in the solvent has been improved, but when used in the piezo ink jet printer as described above, sufficient ink ejection properties cannot be obtained, In addition, when printing is temporarily interrupted and printing is continued again, the ink ejection recoverability deteriorates, and a printed matter with stable quality cannot be obtained.
JP 2003-96370 A

  Accordingly, an object of the present invention is to provide pigment-type piezo-type ink jet printer oil-based inks with no ink clogging at the printer nozzle during printing, excellent ink ejection and ejection recovery, and fixability to recording materials. And providing an ink having excellent drying properties.

（上記一般式（１）中のＸ₁はアルキル基を、Ｘ₂は水素原子またはアルキル基を、ｎは１〜４の整数を表わす。） The above object is achieved by the present invention described below. That is, the present invention contains a fixing resin, a pigment, and a solvent, and the solvent contains a compound represented by the following general formula (1) (hereinafter referred to as “Compound A”) and a cyclic ester. The amount of is 1 to 60 parts by mass per 100 parts by mass of the following compound A.

(X ₁ in the general formula (1) represents an alkyl group, X ₂ represents a hydrogen atom or an alkyl group, and n represents an integer of 1 to 4.)

  As a result of intensive studies to solve the above-mentioned problems, the present inventor compared the pigment-type oil-based ink using a conventional solvent, particularly when used in a piezo-type ink jet printer. In addition, there is no clogging of the ink due to precipitation of solids in the ink on the end face of the printer nozzle, and even when printing is interrupted once and printing is resumed, ink discharge recovery is excellent, and ink concentration It has been found that the ink discharge property is not lowered due to the increase in the viscosity of the ink in the nozzle, and the ink has excellent fixability and drying property to the recording material.

  According to the present invention, by replacing the solvent in the pigment-type oil-based ink with a specific mixture solvent, particularly when printing with a piezo-type ink jet printer, precipitation of solids in the ink on the nozzle end face, There is provided an ink in which the ink viscosity does not increase due to the ink concentration in the nozzle, and the ink is ejected and recovered from the printer nozzle, and the fixing property and drying property of the ink to the recording material are excellent.

  Next, the present invention will be described in more detail with reference to the best mode for carrying out the invention. The solvent that mainly characterizes the present invention is a mixture of Compound A and a cyclic ester, and the cyclic ester is in a ratio of 1 to 60 parts by mass per 100 parts by mass of Compound A. Ink using each of the compound A and the cyclic ester alone as a solvent does not have sufficient effects of ejecting ink from a printer nozzle, fixing to a recording material, and drying during printing. In the present invention, when these compounds A and cyclic esters are mixed and used as an ink solvent in an appropriate ratio, when printing with a piezo ink jet printer using the ink, solids in the ink are formed on the nozzle end face. This suppresses ink precipitation due to ink deposition and ink concentration in the nozzles, and prevents ink from clogging the nozzles and improves ink ejection and ejection recovery.

  When the amount of the cyclic steal is too large, the pigment dispersibility and storage stability of the obtained ink are lowered, and the ink repelling phenomenon occurs depending on the type of recording material. On the other hand, if the amount of cyclic ester is too small, the nozzle end face of the piezo ink jet printer induces precipitation of solids in the ink and an increase in ink viscosity due to ink concentration in the nozzle. Clogging prevention properties and ink discharge and discharge recovery properties are significantly reduced.

  Examples of the compound A include, for example, ethylene glycol monomethyl ether acetate, monoethyl ether acetate, and monobutyl ether acetate, propylene glycol monomethyl ether acetate, diethylene glycol n-propyl ether acetate, and n-butyl ether acetate, triethylene glycol. Ethyl glycol monobutyl ether acetate such as ethyl ether acetate and n-butyl ether acetate are particularly preferable.

  In addition, the above cyclic ester, particularly in a piezo ink jet printer, does not give a satisfactory result with Compound A alone. The viscosity of ink due to precipitation of solids in the ink at the nozzle end face or ink concentration in the nozzle. It is used for the purpose of suppressing the rise and further improving the ink ejection and ejection recovery properties.

（上記一般式（２）中のＸ₃およびＸ₄は、水素原子または炭素数１〜７のアルキル基またはアルケニル基を、ｍは１〜３の整数を表わす。） The above cyclic ester is a cyclic ester compound such as β-lactones, γ-lactones, δ-lactones, ε-lactones, etc., which are liquid at room temperature containing an ester functional group in the ring, preferably the following general formula ( And cyclic ester compounds represented by 2).

(X ₃ and X ₄ in the general formula (2) represent a hydrogen atom or an alkyl group or alkenyl group having 1 to 7 carbon atoms, and m represents an integer of 1 to 3).

  Examples of the cyclic ester represented by the general formula (2) include γ-lactone and δ-valerolactone such as γ-butyrolactone, γ-valerolactone, γ-caprolactone, γ-caprolactone, and γ-laurolactone. Ε-lactone such as δ-lactone and ε-caprolactone. Of the lactones, γ-butyrolactone and / or γ-valerolactone is particularly preferable.

  The total amount of the compound A and the cyclic ester is preferably an amount occupying 80 to 98% by mass in the total ink. When the total amount exceeds the upper limit, the printability of the resulting ink is reduced. On the other hand, when the total amount is less than the lower limit, an increase in the viscosity of the ink is induced, and the discharge property of the ink from the nozzle is reduced. .

  Moreover, the thing whose boiling point of the said compound A and cyclic ester is 130-250 degreeC is used preferably. When the boiling point is too high, the drying property of the ink is lowered, and blocking or the like is induced in the printed matter. On the other hand, when the boiling point is too low, the printability is deteriorated, for example, the resulting ink is dried too quickly and the printer nozzles are clogged.

  The fixing resin used in the present invention is a water-insoluble resin that fixes a pigment as a colorant to a printing substrate, and is a known natural or synthetic resin that is compatible with the compound A and the cyclic ester. Any of those that do not interfere with the object of the present invention can be used. As the fixing resin, acrylic resin; vinyl resin such as vinyl chloride / vinyl acetate copolymer resin, polyvinyl acetate resin, butyral resin; polyester resin; polyamide resin; fiber resin; epoxy resin A rosin derivative such as a rosin-modified phenolic resin, a petroleum resin, preferably an acrylic resin and / or a vinyl chloride / vinyl acetate copolymer resin.

  Examples of the acrylic resin include a polymer made of (meth) acrylate ([(meth) acrylate] means both acrylate and methacrylate) and a copolymer thereof. Examples of the (meth) acrylate include alkyl (meth) acrylates such as ethyl, propyl, or butyl (meth) acrylate; hydroxymethyl, hydroxyethyl, bisoxypropyl, hydroxybutyl, hydroxypentyl (meth) acrylate, and the like. Examples thereof include hydroxyalkyl (meth) acrylate. Specific examples of the polymer and copolymer include, for example, methyl methacrylate polymer, methyl methacrylate / butyl methacrylate copolymer, methyl methacrylate / butyl acrylate / hydroxyethyl methacrylate / methacrylic acid copolymer, styrene / Copolymers of (meth) acrylate copolymers and other comonomers such as acrylic acid, methacrylic acid, styrene, acrylamide, vinyltoluene, glycidyl methacrylate, and hydroxyethyl acrylate. And mixtures thereof. As an example of the above acrylic resin, it can be obtained from Rohm and Haas Co. under the trade name [Paraloid B-66] and used in the present invention.

  Examples of the vinyl chloride / vinyl acetate copolymer resin include vinyl chloride / vinyl acetate copolymer, vinyl chloride / vinyl acetate / maleic acid copolymer, vinyl chloride / vinyl acetate / vinyl alcohol copolymer. And mixtures thereof. As an example of the above vinyl chloride / vinyl acetate copolymer resin, it can be obtained from Nippon Union Carbide under the trade name [VYHH] and used in the present invention.

  The acrylic resin and the vinyl chloride / vinyl acetate copolymer resin can be used alone or in combination with each other. When the above resins are used in combination, the mixing ratio is preferably acrylic resin / (vinyl chloride / vinyl acetate copolymer resin) = 1-9 / 1 (mass ratio). These fixing resins are preferably used in a proportion of 1 to 10% by mass in the total amount of ink.

  Examples of the pigment used in the ink of the present invention include phthalocyanine series such as phthalocyanine blue and phthalocyanine green, pyranthrone series such as carbon black, pyranthrone orange, and pyranthrone red, permanent red 2B, pigment scarlet, and lithol red. Soluble azo pigments such as benzidine yellow, hansa yellow, toluidine red and other insoluble azo pigments, quinophthalone such as quinophthalone yellow, thioindigo, benzimidazolone, anthraquinone, dioxazine, diketopyrrolopyrrole, isoindolinone And organic pigments such as titanium oxide, quinacridone, and inorganic pigments such as titanium oxide, ultramarine blue, bitumen, dial, zinc white, calcium carbonate, and barium sulfate. These pigments are preferably used at a ratio of 0.5 to 8% by mass in the total amount of ink.

  Further, in the ink of the present invention, additives such as a polymer dispersant, a surfactant, a plasticizer, an antistatic agent, a viscosity modifier, an antifoaming agent, an antioxidant, and an ultraviolet absorber are added as necessary. It can be added and used within a range not impeding the achievement of the object of the invention. As the polymer dispersant, for example, the main chain is made of polyester, polyacryl, polyurethane, polyamine, polycabrolactone, etc., and the side chain is an amino group, carboxyl group, sulfone group, A dispersant having a polar group such as a hydroxyl group, preferably a polyester polymer dispersant is used.

  The ink of the present invention is prepared by uniformly kneading and dispersing each of the above components by a known method. The preparation method is, for example, as an example, adding the dispersant and pigment in the solvent and uniformly kneading and dispersing with 0.3 mm zirconia beads for 3 hours to prepare a pigment dispersion, The fixing resin and solvent are added thereto to prepare an ink. Preferably, the ink viscosity is 8 to 15 mPa · s at 25 ° C. and the flash point is 60 ° C. or higher. The ink viscosity is a value measured with a falling ball viscometer (AMVn) manufactured by Nippon Sebel Hegner. If the ink viscosity is too high, ink clogging tends to occur at the printer nozzles, and the head must be heated to reduce the viscosity, which tends to evaporate the solvent in the ink and further clog the ink. Will increase. On the other hand, when the ink viscosity is too low, printability is lowered. Printing on a known recording material such as a plastic film such as a polyvinyl chloride film using the above ink can be performed using a normal piezo ink jet printer.

  Next, the present invention will be described more specifically with reference to examples and comparative examples. In the text, “part” or “%” is based on mass unless otherwise specified. In addition, this invention is not limited to the following example.

(Examples 1-4)
Using the following fixing resin a, pigment b, and solvent c, each of them is blended as shown in Table 1, and uniformly kneaded and dispersed so that the ink viscosity is 8 to 15 mPa · s at 25 ° C. Inks R1 to R4 were prepared. The fixing resin a, pigment b, and solvent c in Table 1 are as follows.
Fixing resin a:
a1 = acrylic resin (Rohm and Haas, Paraloid B-66)
a2 = Vinyl resin (made by Nippon Union Carbide, VYHH)
Pigment b:
Phthalocyanine blue / solvent c:
c1 = ethylene glycol monobutyl ether acetate c2 = γ-butyrolactone c3 = γ-valerolactone

なお、表中の数値は部数である。

The numbers in the table are the number of copies.

(Comparative Examples 1-3)
[Comparative Example 1]
A comparative ink S1 was prepared in the same manner as in Example 2 except that γ-valerolactone in Example 2 was not used and 59.5 parts of ethylene glycol monobutyl ether acetate was replaced with 89.5 parts of propylene glycol monomethyl ether acetate. did.

[Comparative Example 2]
A comparative ink S2 was prepared in the same manner as in Example 2 except that γ-valerolactone in Example 2 was replaced with cyclohexanone.

[Comparative Example 3]
A comparative ink S3 was prepared in the same manner as in Example 3 except that γ-butyrolactone in Example 3 was replaced with cyclohexanone.

  Using each of the inks obtained above, a 200 μm polyvinyl chloride film (WIDEFLEX-made by Kambo Plus, Inc.) was used as a printing substrate in a piezo-type SPECTRA NOVA discharge head tester equipped with 256 head nozzles. PL4) was printed, and the following measurement methods were used to evaluate ink ejection properties, ink fixing properties, and drying properties during printing. Table 2 shows the evaluation results.

(Ink ejection properties)
After printing for a few seconds, stop printing, leave the head, start printing again, and nozzles with poor ink ejection that cause ink to bend and eject from the head nozzle immediately after printing, or bend or become impossible to eject The evaluation was performed based on the standing time of the head until 5 or more were expressed.
Evaluation point A: The head is left for 5 minutes or more until 5 or more nozzles with poor ink ejection appear.
B: The head is left for 2 minutes or more and less than 5 minutes until 5 or more nozzles with poor ink ejection appear.
C: The head is left for less than 2 minutes until 5 or more nozzles with poor ink ejection appear.

(Ink fixability)
Solid printing and character printing were performed. Immediately after printing, the printed surface was rubbed with a finger, and the ink smudged state and the ink peeled state of the printed surface were evaluated with the naked eye.
Evaluation point A: Ink stains and peeling phenomenon are not observed on the printed surface.
B: Stain and peeling phenomenon of ink are observed on the printing surface.

(Ink drying)
After printing, the dry time of touching the printed surface was measured, and the drying property was evaluated according to the following criteria.
A: The touch drying time is less than 3 minutes.
B: The touch drying time is 3 minutes or more.

  Due to the ink ejection properties of the above evaluation results, even if printing is repeated, practically ink ejection defects from the nozzles are unlikely to occur, and even if the printer head is left undisturbed, the ejection recovery properties are good. The adhesion of the ink to the recording material is excellent due to the fixing property, and the ink drying property proves that even if continuous printing is performed, stable printing is performed without blocking the printed matter. Yes.

  According to the ink of the present invention, there is no clogging of the ink in the printer head nozzle even after continuous printing, and the ink discharge recoverability and ink are good even when the head is left between printing. The fixing property and the ink drying property are excellent, and the ink can be effectively used as an ink for a piezoelectric ink jet printer.

Claims (7)

An oil-based ink for printing on a polyvinyl chloride film,
A fixing resin, a pigment, a polymer dispersant, and a solvent , wherein the solvent contains ethylene glycol monobutyl ether acetate and a cyclic ester, and the cyclic ester is γ-butyrolactone and / or γ-valerolactone. The amount of the cyclic ester is 1 to 60 parts by mass per 100 parts by mass of the ethylene glycol monobutyl ether acetate, and the fixing resin is an acrylic resin and / or a vinyl chloride / vinyl acetate copolymer resin. Oil-based ink for piezo inkjet printers.   The ink according to claim 1, wherein the total amount of the ethylene glycol monobutyl ether acetate and the cyclic ester occupies 80 to 98% by mass in the total ink.   The fixing resin is a mixture of acrylic resin and vinyl chloride / vinyl acetate copolymer resin, and acrylic resin / (vinyl chloride / vinyl acetate copolymer resin) = 1-9 / 1 (mass ratio). The ink according to claim 1, wherein   The ink according to claim 1, wherein the viscosity is 8 to 15 mPa · s at 25 ° C.   The ink according to claim 1, having a flash point of 60 ° C or higher.   The acrylic resin is selected from the group consisting of methyl methacrylate polymer, methyl methacrylate / butyl methacrylate copolymer, methyl methacrylate / butyl acrylate / hydroxyethyl methacrylate / methacrylic acid copolymer, and styrene / (meth) acrylate copolymer. The ink according to claim 1, wherein the ink is a polymer. The ink according to claim 1 , wherein the polymer dispersant is a polyester polymer dispersant.