JPH0564667B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an ink composition for inkjet recording, and more particularly, to an ink composition for inkjet recording.
The present invention relates to an ultraviolet curable inkjet recording ink composition useful for marking on non-absorbing material surfaces such as metals. (Prior technology) The inkjet recording method involves introducing ink into a metal or glass nozzle with an inner diameter of approximately 20 to 300 microns, pressurizing and vibrating it, and ejecting uniformly charged fine ink particles from the tip of the nozzle. death,
Ink particles are electrostatically deflected by a deflection electrode in front of the nozzle, and characters, etc. are printed according to a predetermined dot matrix method. In printing using this method, the ink must be stably atomized and must have the ability to receive electrical signals and form a desired record on the printed matter.
To have such functionality, these inks must have a viscosity of 1 to 15 cps, a surface tension of 20 to 60 dyne/cm,
It is desirable to have general physical properties such as specific resistance of 2000 Ω·cm or less and specific gravity of 0.8 to 1.2. An inkjet recording ink that hardens by exposure to ultraviolet light is disclosed in U.S. Patent No.
As disclosed in the specification of No. 4228438, an ink using an epoxy-modified acrylic resin and a urethane-modified acrylic resin as a binder, and a pigment in the form of particles of 5 microns or less as a coloring component;
Alternatively, an ink using a cationically polymerizable epoxy resin as a binder is known, as disclosed in Japanese Patent Application Laid-Open No. 58-32674. (Problems to be Solved by the Invention) Although the ink described in the above document uses a pigment as a coloring component, it does not disclose anything about the most important problem of fineness and stability of the pigment. In the inkjet recording system, clogging of nozzles due to pigment particles is a problem that must be avoided, and practical inks cannot be provided unless the pigment is made finer and the agglomeration of the pigment particles is prevented. Moreover, these documents do not disclose any effective means for imparting electrical conductivity to the ink. As a result of extensive research into fine stabilization of pigments, which are the coloring components of conventionally known ultraviolet curable inkjet recording ink compositions, the present inventors discovered that by allowing specific materials to exist in these ink compositions, ink compositions can be stabilized. The present invention was completed based on the finding that the pigment in the composition is finely stabilized for a long period of time and that the physical properties of the ink film formed are significantly improved. (Means for Solving the Problems) That is, the present invention provides an ultraviolet curable inkjet recording ink containing an ultraviolet curable resin, a thermoplastic resin, a pigment, a conductivity imparting agent, a photoreaction initiator, and a solvent as essential components. In the composition, the thermoplastic resin is contained in an amount of 20 to 200% by weight based on the pigment, the particle size of the pigment is 3 microns or less, and the ultraviolet curable resin is contained in an amount of 10 to 50% by weight in the ink composition. The ink composition for ultraviolet curable inkjet recording further contains 5 to 100% by weight of at least trifunctional or higher-functional polyacrylate. The above-mentioned ultraviolet curable inkjet recording ink composition of the present invention uses a pigment that remains finely and stably for a long period of time as a coloring component, thereby achieving extremely clear and concealing properties regardless of the color of the recording medium. For example, plastics such as epoxy resin, polybutylene terephthalate, polyacetal, polycarbonate, etc. can provide an excellent printing surface.
After printing, the printing surface of a molded article made of metal such as aluminum or iron is irradiated with ultraviolet rays to give a print with extremely excellent solvent resistance, adhesion, scratch resistance, etc. Preferred constituent components of the inkjet recording ink composition of the present invention will be explained in more detail below. (Ultraviolet curable resin) The ultraviolet curable resin used in the present invention is already a known material, and a typical example of a preferable ultraviolet curable resin has an unsaturated double bond capable of radical polymerization in its molecular structure. Relatively low molecular weight polyester resins, acrylic resins, epoxy resins, urethane resins, alkyd resins, oligomers or prepolymers such as acrylates and methacrylates such as polyhydric alcohols, and styrene, methylstyrene, divinylbenzene, acrylic acid (or methacrylic acid) It contains an addition polymerizable compound such as acrylic acid ester as a film-forming component. In the present invention, these ultraviolet curable resins are used in an amount of about 10 to 50% by weight of the ink composition, and about 5 to 100% by weight of the ultraviolet curable resin is trifunctional or higher functional polyacrylate such as triacrylate or trimethacrylate. It is desirable to use polyacrylate, etc. If the content of such polyacrylate is less than 5% by weight, an ink film with sufficient surface hardness and solvent resistance cannot be formed. (Thermoplastic resin) Pigments are used as coloring components in the present invention, but due to the problem of clogging of filters and nozzles, it is necessary for the pigments to be stably dispersed for a long period of time and not to cause aggregation. The viscosity of the inkjet recording ink composition is
Stable formation of ink particles cannot be achieved unless it is 20 cps or less. However, such low viscosity tends to cause problems such as pigment aggregation and sedimentation, so conventional UV-curable paints, UV-curable screen inks, UV-curable offset inks, etc. are simply diluted with a solvent. It is difficult to use the composition as an ink composition for inkjet recording only by lowering the viscosity. Pigments are generally agglomerated into primary particles by mechanical grinding or dispersion, and the particles are then transferred into a liquid vehicle, where each particle must be stably dispersed. In order to determine whether pigment particles dispersed in this way can maintain their stable state for a long period of time, it is necessary to fully understand the final form of the dispersion and consider the composition of pigments, binders, solvents, additives, etc. It won't happen. Also,
In order to finely pulverize pigments, applying a strong mechanical impact force using ultraviolet curable resins with high radical reactivity as a dispersion medium will cause these ultraviolet curable resins to gel, so it is important to select a dispersing machine and dispersion properly. This is not preferable due to problems such as subsequent stability. In view of the above, the present inventors have conducted extensive research and found that thermoplastic resin is used as a pigment dispersion medium, and after dispersing the pigment in the thermoplastic resin, these dispersions are mixed with ultraviolet curable resin, etc. The present invention was completed based on the finding that an ultraviolet curable inkjet recording ink composition in which pigment particles are stable for a long time can be obtained by blending the pigment particles with other necessary components. Thermoplastic resin is 20% to 200% by weight relative to the pigment.
% by weight, and preferably an organic solvent containing ketone and/or alcohol as the main solvent is added to dissolve the resin. This is then processed using a dispersing machine such as a ball mill so that the particle size of the pigment is 3 microns or less and 70% by weight of the pigment is dispersed.
Disperse to 1.0 micron or less. The desired inkjet recording ink composition of the present invention can be obtained by blending necessary components such as a predetermined amount of an ultraviolet curable resin, a photoreaction initiator, a conductivity imparting agent, and a solvent. These thermoplastic resins must be compatible with ultraviolet curable resins, and examples of resins used therefor include styrene-maleic acid copolymers and derivatives thereof, vinyl acetate-vinyl chloride copolymers, polyvinyl butyral, Copolymers of nitrocellulose, cellulose esters, acceleric acid, methacrylic acid, and alkyl esters thereof, and the like are preferably used. The thermoplastic resin is preferably one that is effective not only in stabilizing the dispersion of the pigment but also in improving the properties of the ultraviolet curable resin coating film after curing. For example, by adding 20% by weight of polyvinyl butyral to the UV-curable resin, the adhesion to polybutylene terephthalate increases, making it easier to select objects to adhere to than when preparing an ink composition using only the UV-curable resin. Sexuality expands. However, if the value of the ultraviolet curable resin/thermoplastic resin in the coating film component is less than 1, it is not preferable because the performance merits of using the ultraviolet curable resin are reduced, such as a decrease in the solvent resistance of the coating. (Photoreaction initiator) The photoreaction initiator used in the present invention is a compound that generates free radicals due to the energy of ultraviolet rays, is compatible with the above resin component, and is compatible with the solvent constituting the ink composition. It is necessary to be soluble. Examples of the photoreaction initiator include carbonyl compounds such as benzoin, benzophenone or esters thereof, and sulfur compounds such as diphenyl disulfide. The photoreaction initiator is selected in combination with the ultraviolet curable resin used and the pigment, which is a coloring component, and the amount added is preferably 1 to 15% by weight based on the ultraviolet curable resin (pigment).The coloring component is: Both inorganic pigments and organic pigments can be used. Sufficient coloring power and high clarity can be obtained when the pigment accounts for ~15% by weight of the ink composition. It is preferably 5 to 10% by weight for inorganic pigments and 3 to 8% by weight for organic pigments. Since the pigment concentration has a significant effect on the viscosity of the ink composition, it is desirable to use a pigment with high coloring power and hiding power and to keep the pigment concentration low. Particularly in the case of white, titanium oxide is preferable. Furthermore, from the viewpoint of sedimentation properties, it is preferable to use pigments with low specific gravity and small primary particle diameter, and organic pigments are superior to inorganic pigments in this respect. The pigment concentration in the coating film affects solvent resistance, scratch resistance, and adhesion, and if the pigment concentration exceeds 30% by weight of the binder, these properties will deteriorate, so it is desirable to keep it below this range. Preferably used pigments include, for example, titanium oxide, carbon black, phthalocyanine blue, phthalocyanine green, brilliant carmine 6B, Lake Red C, Watching Red, and Disazo Yellow. (Conductivity imparting agent) The conductivity imparting agent is added to impart conductivity to the ink composition, and any salt soluble in the solvent constituting the ink can be used. Examples of such salts include alkali metal and alkaline earth metal halides, nitrates, thiocyanates, and the like. However, when considering the dispersion stability of the pigment, potassium thiocyanate, sodium thiocyanate, or lithium nitrate is preferable. The amount added is preferably in the range of about 0.2% to 4% by weight of the ink composition. (Solvent) As the solvent in the present invention, any solvent may be used as long as it dissolves all the components of the ink composition except the pigment well and quickly evaporates after printing. The solvent used for this purpose preferably has a ketone and/or alcohol as the main solvent, and for example, acetone, methyl ethyl ketone, methyl isobutyl ketone, methanol, ethanol, isopropanol, etc. are preferably used alone or in combination. These solvents are also used to adjust the physical properties such as viscosity of the ink composition, and they
A proportion of ~80% by weight is preferred. Although the ink composition of the present invention is composed of the above-mentioned components, other known additives such as various activators and anti-settling agents can be used as appropriate. The present invention will be explained in more detail below using Examples and Comparative Examples. In addition, parts and percentages in the text are based on weight unless otherwise specified. Example 1 Titanium oxide (manufactured by Ishihara Sangyo, rutile type, average particle size
0.4 μm) 20 parts Vinyl chloride-vinyl acetate copolymer (manufactured by Sekisui Kagaku) 10 parts Methyl ethyl ketone 40 parts The above components were dispersed using a sand mill to obtain a mill base of titanium oxide. To this, 150 parts of bisphenol A type epoxy resin modified acrylate (bifunctional type), 15 parts of dipentaerythritol hexaacrylate, 10 parts of benzyl dimethyl ketal,
A solution of 1.5 parts of 2-chlorothioxanthone and 4 parts of sodium thiocyanate dissolved in 200 parts of methyl ethyl ketone was added, and coarse particles were removed by pressure filtration with a 3 micron filter. An ultraviolet curable inkjet recording ink composition of the present invention having a tension of 23 dyne/cm and a specific gravity of 1.0 was obtained. When the fine dispersion stability of the pigment in this ink composition was measured using a light transmission particle size distribution analyzer, the results shown in Table 1 below were obtained. Further, using this ink composition, printing was carried out on a polybutylene terephthalate resin plate by an inkjet method. After the printed area was cured by ultraviolet irradiation, an adhesion test and a solvent resistance test were conducted on the printed area, and good results were obtained as shown in Table 2 below. Example 2 Titanium oxide (manufactured by Ishihara Sangyo, rutile type, average particle size
0.4 μm) 30 parts Nitrocellulose (manufactured by Daicel) 30 parts Methyl ethyl ketone 20 parts Ethanol 20 parts The above components were dispersed using a sand mill to obtain a mill base of titanium oxide. To this, 110 parts of trifunctional oligoester acrylate, 2-hydroxy-2-
5 parts of methyl-1-phenylpropan-1-one and 4 parts of lithium nitrate were added to 100 parts of methyl ethyl ketone.
part and dissolved in 100 parts of alcohol,
Coarse particles were removed by pressure filtration with a 3 micron filter to obtain an ultraviolet curable inkjet recording ink composition of the present invention having a viscosity of 7.5 cps, a specific resistance of 960 Ω·cm, a surface tension of 29 dyne/cm, and a specific gravity of 1.0. . When the fine dispersion stability of the pigment in this ink composition was measured using a light transmission particle size analyzer, the results shown in Table 1 below were obtained. Further, using this ink composition, printing was performed on a polybutylene terephthalate resin plate by an inkjet method. After the printed area was cured by ultraviolet irradiation, an adhesion test and a solvent resistance test were conducted on the printed area, and good results were obtained as shown in Table 2 below. Example 3 Carbon black (manufactured by Mitsubishi Kasei, average particle size
0.03μm) 10 Styrene-maleic acid copolymer (ARCO
(manufactured by Chem.) 6 parts Methyl ethyl ketone 40 parts The above components were dispersed using a sand mill to obtain a carbon black mill base. To this, 150 parts of urethane resin modified acrylate (bifunctional type),
dipentaerythritol hexaacrylate 15
parts, benzyl dimethyl ketal 10 parts, 2-chlorothioxanthone 3 parts and sodium thiocyanate 4 parts
1 part dissolved in 200 parts of methyl ethyl ketone was added, and coarse particles were removed by pressure filtration with a 3 micron filter.
An ultraviolet curable inkjet recording ink composition of the present invention having a surface tension of 32 dyne/cm and a specific gravity of 0.9 was obtained. When the fine dispersion stability of the pigment in this ink composition was measured using a light transmission particle size analyzer, the results shown in Table 1 below were obtained. Further, using this ink composition, printing was performed on a polybutylene terephthalate resin plate by an inkjet method. After the printed area was cured by ultraviolet irradiation, an adhesion test and a solvent resistance test were conducted on the printed area, and good results were obtained as shown in Table 2 below. Example 4 Copper phthalocyanine blue (manufactured by Dainichiseika Kagaku Kogyo, average particle size 0.1 μm) 20 parts Polyvinyl butyral (manufactured by Sekisui Chemical) 10 parts Methyl ethyl ketone 40 parts The above components were dispersed in a sand mill to obtain a blue millbase. In this, 100 parts of novolac-type epoxy resin-modified acrylate (polyfunctional), 50 parts of trimethylolpropane triacrylate, 6 parts of benzophenone, 6 parts of 1-hydroxy-cyclohexyl phenyl ketone, and 4 parts of potassium thiocyanate were dissolved in 200 parts of methyl ethyl ketone. was added and filtered under pressure with a 3 micron filter to remove coarse particles, resulting in a viscosity of 9 cps and a specific resistance of 850 Ω.
An ultraviolet curable inkjet recording ink composition of the present invention having a surface tension of 30 dyne/cm and a specific gravity of 1.0 was obtained. When the fine dispersion stability of the pigment in this ink composition was measured using a light transmission particle size analyzer, the results shown in Table 1 below were obtained. Further, using this ink composition, printing was performed on a polybutylene terephthalate resin plate by an inkjet method. After the printed area was cured by ultraviolet irradiation, an adhesion test and a solvent resistance test were conducted on the printed area, and good results were obtained as shown in Table 2 below. Reference example 1 Titanium oxide (manufactured by Ishihara Sangyo, rutile type, average particle size
0.4μm) 20 parts Novolac type epoxy resin modified acrylate 40 parts Methyl ethyl ketone 40 parts I tried to disperse the above ingredients with a sand mill, but
During the process, significant thickening of the millbase occurred, and the dispersion treatment was stopped. Reference example 2 Titanium oxide (manufactured by Ishihara Sangyo, rutile type, average particle size
0.4 μm) 20 parts Bisphenol A type epoxy resin modified acrylate 20 parts Methyl ethyl ketone 40 parts The above components were dispersed in a sand mill to obtain a titanium oxide millbase. To this, 140 parts of bisphenol A type epoxy resin-modified acrylate, 10 parts of benzyl dimethyl ketal, 1.5 parts of 2-chlorothioxanthone and 4 parts of sodium thiocyanate were dissolved in 150 parts of methyl ethyl ketone, and
Coarse particles were removed by pressure filtration with a 3 micron filter to obtain a comparative ink composition having a roughness of 8 cps, a specific resistance of 900 Ω·cm, a surface tension of 28 dyne/cm, and a specific gravity of 1.0. The ink composition of this comparative example was also tested in the same manner as the ink composition of the present invention, and the results are shown in Tables 1 and 2 below. From the data in Tables 1 and 2, it is clear that the pigments in the ink composition of the present invention stably maintain their fine state for a significantly longer period of time than in the ink composition of the comparative example. It is clear that the adhesion to the printed surface is also extremely excellent.

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Claims (1)

[Scope of Claims] 1. In an ink composition for ultraviolet curable inkjet recording which contains an ultraviolet curable resin, a thermoplastic resin, a pigment, a conductivity imparting agent, a photoreaction initiator, and a solvent as essential components, the thermoplastic resin is a pigment. against 20
-200% by weight of the ink composition, and the particle size of the pigment is 3 microns or less, and the ultraviolet curable resin is contained in the ink composition in an amount of 10 to 50% by weight, and at least 5 to 50% of the trifunctional or higher-functional polyacrylate is contained in the ink composition.
An ultraviolet curable inkjet recording ink composition characterized by containing 100% by weight. 2. The ink composition according to claim 1, wherein the pigment accounts for 2 to 15% by weight of the ink composition. 3. The ink composition according to claim 1, wherein the conductivity imparting agent is at least one selected from the group consisting of sodium thiocyanate, potassium thiocyanate, and lithium nitrate. 4. The ink composition according to claim 1, wherein the conductivity imparting agent accounts for 0.2 to 4% by weight of the ink composition. 5 The photoreaction initiator is 1 to 15 of the ultraviolet curable resin.
% by weight of the ink composition according to claim 1. 6. The ink composition of claim 1, wherein the solvent accounts for about 30-80% by weight of the ink composition. 7. The ink composition according to claim 1, wherein the solvent is a solvent containing alcohol and/or ketone as an essential component.