JP3873044B2 - Inkjet recording ink manufacturing method and inkjet recording apparatus - Google Patents

Description

  The present invention relates to an ink jet recording ink manufacturing method and an ink jet recording apparatus.

  As a technique for printing a high-definition image with an inkjet printer, it is known to use a solvent-based ink or a solvent-based liquid toner containing a pigment and an organic solvent, as in a printing machine using a plate. However, with this technique, when a certain number of copies are printed, a non-negligible amount of organic solvent volatilizes. For this reason, there is a problem of atmospheric contamination due to the volatilized organic solvent, and it is necessary to provide an exhaust facility and a solvent recovery mechanism.

  As an effective solution to such a problem, photosensitive ink and a printer system using the same have begun to attract attention. The photosensitive ink contains a radical polymerizable monomer, a photopolymerization initiator, and a pigment as essential components, and an image can be obtained by quickly photocuring the photosensitive ink discharged onto the printing surface.

  According to this technique, since the ink layer can be made non-fluidized by light irradiation, a printed matter having a relatively high quality can be obtained. However, the ink used here contains a large amount of carcinogenic components such as a radical generator, and the volatile acrylic acid derivative used as the radical polymerizable monomer has large skin irritation and odor. That is, the above-described photosensitive ink requires attention in handling. Further, radical polymerization is significantly inhibited by the presence of oxygen in the air, and the pigment contained in the ink absorbs exposure light. For this reason, the exposure amount tends to be insufficient in the deep part of the ink layer. Therefore, the above-described photosensitive ink has low sensitivity to light, and in order to obtain a high-quality printed matter with this technique, a very large exposure system is required.

  As a solution to these problems, cationic curable inks that are cured by irradiation with active energy rays have been proposed (see, for example, Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4). In this case, for example, a cation curable ink is ejected from an ink jet print head to form an ink layer corresponding to an image on a recording medium. The ink layer is cured by irradiating active energy rays such as ultraviolet rays or electron beams.

  In the ink jet recording apparatus, the influence of the viscosity stability of the ink composition on the print quality is great. When the ink viscosity changes, the ink ejection volume changes, so strict management and quality are required.

  For example, in the case of an ink jet recording apparatus that discharges 40 pl, the discharge volume decreases by about 1 pl when the viscosity increases by about 10% at the rate of increase in viscosity. Therefore, when an image is formed, the dot area is reduced, and print quality is affected.

  In addition, there is a problem that the flying shape of the ink is disturbed, the print reproducibility is reduced, and in the worst case, the ink jetting easily occurs and a fatal state such as ink clogging is likely to occur.

The photocation curable ink for ink jet recording has high chemical activity as compared with other types of inks and the like, and therefore, there is a problem such as change with time when applied in an ink jet recording apparatus. In order to perform stable printing with good reproducibility in an ink jet recording apparatus, it is necessary to prevent an increase in viscosity of the ink used for ink jet recording.
Japanese Patent Laid-Open No. 9-183928 JP 2001-220526 A JP 2002-188025 A JP 2002-317139 A

  An object of the present invention is to provide an ink for ink jet recording having high storage stability with reduced change in viscosity.

  Another object of the present invention is to provide an ink jet recording apparatus that is excellent in reproducibility and capable of stable printing.

A method for producing an ink for ink jet recording according to one aspect of the present invention is a method for producing an ink for ink jet recording having a viscosity at 25 ° C. of 50 mPa · s or less, wherein at least one epoxy polymerized in the presence of an acid compound, a photoacid generator which generates the dissolved and acid by light irradiation in the solvent, and the color components dissolved or dispersed in the solvent, a step of mixing a basic compound to obtain an ink composition The step of filtering the ink composition, and heating aging by heating the filtered ink composition at a temperature not lower than the temperature used in ink jet recording and not higher than 65 ° C. stabilizes the increase in the viscosity of the ink. characterized in that it comprises a step of reduction.

  An ink jet recording apparatus according to one embodiment of the present invention uses an ink for ink jet recording manufactured by the above-described method.

  According to one embodiment of the present invention, an ink for inkjet recording with high storage stability and reduced viscosity change is provided. According to another aspect of the present invention, there is provided an ink jet recording apparatus that is excellent in reproducibility and capable of stable printing.

  Embodiments of the present invention will be described below.

  The present inventors include at least one solvent that polymerizes in the presence of an acid, a photoacid generator that dissolves in the solvent and generates an acid upon irradiation with light, and a color component that is dissolved or dispersed in the solvent. And the viscosity increase of the ink for ink jet recording containing the viscosity stabilizer, the following knowledge was obtained. The ink jet recording ink having the basic composition as described above has a large increase in viscosity by mixing raw material components and preparing the ink, followed by heating at a constant temperature for a predetermined time. Moreover, after the viscosity increases to some extent, the rate of increase in viscosity decreases. The present invention has been made based on these findings.

  The ink for inkjet recording manufactured by the method according to the embodiment of the present invention is a photocationic curable type. Since the ink is used for ink jet recording, this ink has fluidity at room temperature, and the viscosity at 25 ° C. is preferably 50 mPa · s or less, and more preferably 30 mPa · s or less. (Viscosity at 45 ° C. is 20 mPa · s or less) In order to constitute such an ink, an epoxy compound having an alicyclic skeleton and / or an aliphatic skeleton having a viscosity of 30 mPa · s or less at 25 ° C. is used as a solvent. It is desirable to contain 50 parts by weight or more.

  Therefore, as a solvent (acid polymerizable compound) that polymerizes in the presence of an acid, for example, it has a viscosity of 50 mPa · s or less at 50 ° C. and normal pressure, and has an alicyclic skeleton and / or an aliphatic skeleton, Epoxy compounds that can be polymerized in the presence of an acid are used. Although depending on the operating environment in which the ink is ejected, the ink viscosity is required to be at least 50 mPa · s or less in an environment of 50 ° C. that is assumed as the maximum use environment. This is because if the viscosity exceeds 50 mPa · s, ink ejection becomes unstable or cannot be ejected. Similarly, in a normal room temperature environment, it is preferable that the viscosity is at least 50 mPa · s or less.

  As such a solvent, specifically, at least one selected from the group consisting of an oxirane group-containing compound, an oxetane ring-containing compound, and a vinyl ether compound that polymerizes in the presence of an acid can be used.

  As the color component, any of a pigment and a dye may be used, and any of organic and inorganic may be used.

  Examples of the photoacid generator include onium salts, diazonium salts, quinonediazide compounds, organic halides, aromatic sulfonate compounds, bisulfone compounds, sulfonyl compounds, sulfonate compounds, sulfonium compounds, sulfamide compounds, iodonium compounds, sulfonyldiazomethane compounds, And mixtures thereof can be used.

  The basic compound acts as a viscosity stabilizer, and any inorganic base and organic base that can be dissolved in the above-described acid-polymerized solvent can be used. In particular, an organic base is preferably used because of its solubility. Examples of the organic base include ammonia and ammonium compounds, substituted or unsubstituted alkylamines, substituted or unsubstituted aromatic amines, and organic amines having a heterocyclic skeleton such as pyridine, pyrimidine, and imidazole. Instead of the basic compound or in combination with the basic compound, a compound for adjusting the basicity can also be blended as a viscosity stabilizer.

  In the production of ink for inkjet recording, for example, 60 to 90 parts by weight of the epoxy compound is added to 3 to 10 parts by weight of the color component, and 1 to 10 parts by weight of the photoacid generator is added to the epoxy compound. To do. Further, a basic compound is added in an amount of about 1 mol% to 30 mol% with respect to the photoacid generator, and mixed uniformly to obtain an ink composition, which is filtered using a PTFE filter or the like. . By subjecting the filtered ink composition to heat aging, an ink for inkjet recording is produced by the method according to the embodiment of the present invention.

  Heat aging is performed by heating the ink composition at a temperature equal to or higher than the temperature used. Specifically, heat aging can be performed by storing the ink composition in a thermostat set to a predetermined temperature. The temperature of heat aging is not particularly limited as long as it is equal to or higher than the temperature at which the ink is used, but if it is excessively high, the ink characteristics may be impaired.

  The mechanism of increase in the viscosity of the ink is considered to be due to the influence of a photoacid generator that decomposes with time or an incomplete photoacid generator that easily decomposes. That is, when the acid polymerizable compound is partially polymerized, the viscosity of the ink for ink jet recording increases. In the embodiment of the present invention, among these causes, it is possible to suppress the increase in the viscosity of the ink for ink jet recording as much as possible by suppressing the increase in the viscosity due to the influence of the incomplete photoacid generator that is easily decomposed. .

  Hereinafter, the present invention will be described in more detail with reference to specific examples.

  First, in order to investigate the influence of the temperature on the increase in the viscosity of the ink, three types of ink were prepared and an experiment was performed.

As a solvent for polymerization in the presence of an acid, an epoxy compound shown in the following chemical formula 1 was prepared.

These were mixed at the ratio shown in Table 1 below to obtain epoxy compositions (acid polymerizable compositions) a to c.

  The carbon black pigment as the color component was kneaded with an acrylic resin in an amount corresponding to 5% by weight. This kneaded material and 200 ppm of nonionic surfactant (manufactured by Sumitomo 3M) were added to each of the epoxy compositions a to c described above. Thereafter, these mixtures were dispersed by a paint shaker for a whole day and night to obtain black compositions a (B) to c (B).

Black compositions a (B) to c (B), a photoacid generator, and a basic compound were mixed and stirred at the ratio shown in Table 2 below. The obtained mixture was filtered through a 5 μm PTFE filter to obtain ink compositions (liquid inks) 1 to 3. Ink compositions (liquid inks) 1 and 2 are referred to as H024 and H025, respectively.

Here, PAG3 used as a photoacid generator is a solution obtained by dissolving an equal mixture of compounds PAG1 and PAG2 represented by the following chemical formula in propylene carbonate at a concentration of 50%. This is commercially available as UVACURE1591 (manufactured by Daicel UCB).

As the basic compound, a compound BA represented by the following chemical formula was used.

  Each ink composition was stored in a thermostat set to a predetermined temperature, and the storage stability was examined by measuring the viscosity after a predetermined time. Ink compositions H024 (ink composition 1) and H025 (ink composition 2) were stored at three temperatures of 25 ° C., 45 ° C., and 65 ° C. Ink composition 3 was stored at four temperatures of 25 ° C., 45 ° C., 55 ° C., and 65 ° C.

  The viscosity of the ink was measured using an E-type viscometer manufactured by Toki Sangyo Co., Ltd. at a measurement temperature of 25 ° C. and a shear rate of 250 rpm.

  The measurement results of the viscosity changes of the ink compositions 1, 2, and 3 are shown in the graphs of FIGS.

  Usually, the increase in the viscosity after storage at 25 ° C. for 6 months is required to be within ± 10% of the initial viscosity as a specification of the ink for ink jet recording. Although it is not originally stored at a temperature of 25 ° C. or higher, it is generally performed to evaluate storage acceleration on a trial basis. Since the increase rate of the viscosity of the ink is caused by the phenomenon that the polymerization reaction of the solvent starts due to the influence of the acid generated by the decomposition, the increase rate of the viscosity and the polymerization (reaction) rate are closely related. It is said that the chemical (polymerization) reaction rate is generally about twice as fast as the temperature rises by 10 ° C. By conducting an accelerated test by high-temperature storage, the viscosity during storage at 25 ° C for 6 months can be easily reduced in a short time. I can know.

  From the results shown in FIGS. 1 to 3, it can be seen that the viscosity of the ink increases in two stages. In the first stage, the viscosity increases rapidly, and in the second stage, the increase in viscosity is suppressed and the rate of increase in viscosity decreases. That is, in the first stage, the viscosity increases rapidly due to the influence of an incomplete photoacid generator that is easily decomposed. It is considered that the increase in the viscosity due to the influence of normal thermal decomposition is started after the impurity photoacid generator that is easily decomposed is consumed. The present invention is implemented by utilizing this phenomenon.

  In other words, by increasing the viscosity by a predetermined increase by heating the ink for a certain time, it is possible to suppress the subsequent increase in viscosity. If the viscosity increase in the first stage is cut, an ink composition that can suppress the increase in viscosity can be prepared as a result.

  If an ink composition that has achieved the first-stage viscosity increase is prepared in advance, the remaining viscosity increase is only the second-stage viscosity increase. Compared with the ink composition in which the first-stage and second-stage viscosity increases occur collectively, the increase in viscosity can be suppressed. By preparing the raw material components in anticipation of the viscosity after heat aging, the increase in viscosity after storage can be significantly suppressed.

  Further, the curability of the ink compositions 1 to 3 described above was measured as follows.

  First, ink was dropped on a film having an inert surface such as a PET film with a disposable syringe, and then stretched to a thickness of about 4 μm with a bar coater to form a coating film. Next, ultraviolet rays were irradiated by passing under a fusion UV irradiator (HP-6) at a speed of 25 m / min. Then, it heated at 100 degreeC for 1 minute with the hotplate etc., and produced the ink cured film. The resulting ink cured film was measured for curability by the scratch hardness method (pencil method) (JIS K 5600-5-4).

  As a result, it was confirmed from the result of the curing test that the ink compositions 1 to 3 described above were cured at a pencil hardness of F or higher even after being stored under any conditions. That is, when heat aging is performed, there is no influence on the curability of the ink after thickening.

  Next, seven types of samples were prepared by changing the heating aging time, and the influence of the difference in viscosity increase due to heating aging on the subsequent viscosity increase was examined.

  In preparing the sample, first, the epoxy compounds (Ep1 and Ep3) described above were mixed as shown in Table 1 to obtain an epoxy composition (acid-polymerizable composition) d. At this time, in order to substantially equalize the initial viscosity after heat aging, the blending ratio of the two epoxy compounds was slightly changed for each sample.

  Next, carbon black pigment corresponding to 5% by weight previously kneaded with an acrylic resin and 200 ppm nonionic surfactant (manufactured by Sumitomo 3M) were added to the epoxy composition. Thereafter, these mixtures were dispersed by a paint shaker for a whole day and night to obtain a black composition d (B) (not shown). The composition d (B), the photoacid generator PAG3, and the viscosity stabilizer BA were mixed at a ratio shown in Table 2 and stirred, and then filtered through a 5 μm PTFE filter to obtain an ink composition 4. It was.

  In this ink composition 4, the initial viscosity was adjusted by finely adjusting the blending ratio of the epoxy compounds Ep1 and Ep3 for each sample in order to make the experimental starting viscosity substantially constant (approximately 8 mPa · s).

  The obtained ink composition was subjected to aging at 65 ° C. while changing the heating time as shown in Table 3 below, and six types of samples were prepared. A sample not subjected to heat aging is used as a reference sample, and the rate of increase in viscosity after heat aging is summarized in Table 3 below together with the heating time. The viscosity increase rate after aging represents the viscosity increase rate before and after heat aging, and represents the viscosity increase rate after aging = 100 × (viscosity after aging−viscosity before aging) / (viscosity before aging).

The ink viscosity was measured at 45 ° C. by the method described above. The increase in viscosity is seen as the rate of increase with respect to the initial viscosity and does not depend on the measurement temperature (the increase in viscosity at 25 ° C is the same as the increase in viscosity at 45 ° C) It is known that the difference in measured temperature is not a problem here.

  As shown in Table 3, the viscosity increase rate increases as the heat aging time increases. Therefore, the heat aging time may be set as appropriate according to the desired viscosity increase rate.

The above seven types of samples were stored in a constant temperature bath at 65 ° C., and the viscosity was examined by the method described above. The result is shown in the graph of FIG. Further, Table 4 below summarizes the curing characteristics after aging, the initial viscosity and the viscosity after 11 days, and the viscosity increase rate after 11 days.

  The curing characteristics after heat aging serve as an index of the curing characteristics of the heat-aged ink sample. The case where the pencil hardness of the cured ink film cured on the film was F or more (hardness judged to be cured) was designated as “◯”.

  The initial viscosity represents the viscosity immediately before the storage test performed for the purpose of investigating the increase in the viscosity of the ink, that is, after the heat aging. As described above, the composition ratio of each sample is adjusted so that the initial viscosity is about 8 mPa · s (@ 45 ° C.).

  The viscosity after 11 days represents the viscosity after 11 days from the start of storing these seven types of samples all at once in an environment of 65 ° C. The chemical (polymerization) reaction rate is generally said to increase about twice as much as the temperature increases by 10 ° C. Here, the experiment was conducted by estimating the equivalent of storage at 25 ° C. for 6 months (180 days) as approximately 11 days at 65 ° C.

  The viscosity increase rate represents the rate of increase in viscosity before and after a storage test conducted for the purpose of investigating the increase in ink viscosity. Here, the rate of increase in viscosity after storage in an environment of 65 ° C. is represented. Viscosity increase rate = 100 × (viscosity after 11 days of storage−viscosity before storage) / (viscosity before storage). In other words, it means that the lower the viscosity increase rate after storage at high temperature, the lower the viscosity increase rate at room temperature storage.

  In the reference sample not subjected to heat aging, the rate of increase in viscosity is 75.6%, which is the highest. When the ink having this composition is stored as it is, the viscosity increase rate is expected to increase by about 18% to 30%.

  Incidentally, the test specification is within + 15% with respect to the initial viscosity when stored at 25 ° C. for 6 months. This is because the initial viscosity target is adjusted to −5% lower than the specified viscosity (considering measurement error and viscosity variation), and within + 15% of the viscosity is considered the viscosity specification.

  The reference sample corresponds to a conventional ink, and in such an ink, the thickening was suppressed by improving the composition material. However, there is a limit to the improvement of the composition material, and the viscosity increase rate of the conventional ink is as large as 18% to 30%, so that it was difficult to satisfy the specifications.

  From the results shown in Table 4, it can be seen that the longer the heating aging time, the lower the viscosity increase rate. That is, by performing heat aging, it has become possible to produce an ink in which the increase in the viscosity of the ink is stabilized (the increase in the ink viscosity is suppressed).

  In the case of an ink composition having basically the same composition as Samples 1 to 6, it has been confirmed that an increase in viscosity after storage can be suppressed by performing heat aging in a 65 ° C. environment for at least 8 hours. Therefore, it is preferable to perform heat aging so that a viscosity increase rate of at least 5% is achieved.

  On the other hand, if the rate of increase in viscosity after heat aging exceeds 80%, the photoacid generator is excessively decomposed by heat to deteriorate the curing characteristics, and the absolute viscosity after aging becomes too high. For this reason, it is desirable to keep the rate of increase in viscosity after heat aging to less than 80% at the maximum.

  As shown in Table 4, the viscosity increase rate of the reference sample is 75.6%, whereas the viscosity increase rates of the samples 1 to 6 are all lower than this. The effect can be obtained by performing heat aging so that the viscosity increases at an increase rate of about 5% to about 63% compared to the initial value.

  In the ink jet recording apparatus according to the embodiment of the present invention, ink for ink jet recording manufactured by performing heat aging as described above is used. An ink jet recording apparatus according to an embodiment of the present invention will be described with reference to FIGS.

  FIG. 5 shows an ink jet recording apparatus, and FIG. 6 shows a control block diagram of this recording apparatus. In recording, the recording medium 101 set in advance in the recording medium supply unit 103 is conveyed by the recording medium conveyance unit 102. The recording medium conveyance unit 102 includes a driving roller 107, a driven roller 108, and a conveyance belt 109 supported by these rollers.

  The recording medium 101 is conveyed while the conveyance speed is controlled by the recording medium conveyance control unit 204 as shown in FIG. 6 in synchronization with the timing at which ink is ejected from the inkjet recording head 105. The ink ejected to the recording medium 101 is cured by the ultraviolet rays irradiated from the bulb 110 of the UV irradiation unit 106 and fixed to the recording medium 101.

  A control block diagram of the ink jet recording apparatus shown in FIG. 6 will be described as follows. The print data input to the recording apparatus control unit 201 is transferred to the print data control circuit 202 and driven and controlled by the head drive circuit 203, and ink is ejected from the ink jet recording head 105. At the same time, the recording medium 101 is conveyed while being controlled by the conveyance control unit 204, and printing is performed on the recording medium 101 at a predetermined timing. After printing, ultraviolet rays are irradiated at a predetermined timing from the ultraviolet irradiation unit 106 and heated at the same time, and the ink layer is cured to be fixed on the recording medium 101. Ultraviolet rays are irradiated from the bulb 110, reflected by the reflecting plate 111, and collected on the surface of the recording medium 101.

  Ink is printed on the recording medium 101 by such a series of flows. In particular, when the print data is gradation data and high image quality is required, it is necessary to strictly control the ink discharge amount. In addition, strict control of the amount of ink penetrating into the recording medium is required. Since these factors are highly dependent on the ink viscosity, it is necessary to maintain the stability of the ink viscosity.

  Since the ink produced by the method according to the embodiment of the present invention is subjected to the heat aging treatment, the subsequent thickening is reduced, so that stable printing can be reproduced when applied to an ink jet recording apparatus. It can be done with good quality.

The graph showing the viscosity change of an ink composition. The graph showing the viscosity change of an ink composition. The graph showing the viscosity change of an ink composition. The graph showing the viscosity change of an ink composition. 1 is a schematic view of an ink jet recording apparatus according to an embodiment of the present invention. FIG. 6 is a control block diagram of the ink jet recording apparatus shown in FIG. 5.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Recording medium, 102 ... Recording medium conveyance part, 103 ... Recording medium supply part, 105 ... Inkjet recording head, 106 ... Ultraviolet irradiation part, 107 ... Driving roller, 108 ... Drive roller, 109 ... Conveyance belt, 110 ... Valve, DESCRIPTION OF SYMBOLS 111 ... Ultraviolet irradiation board, 201 ... Recording device control part, 202 ... Print data control part, 203 ... Head drive circuit, 204 ... Recording medium conveyance control part, 205 ... UV irradiation part control part.

Claims (3)

A method for producing an inkjet recording ink having a viscosity at 25 ° C. of 50 mPa · s or less,
At least one epoxy compound that is polymerized in the presence of an acid; a photoacid generator that dissolves in the solvent and generates an acid upon irradiation with light; a color component dissolved or dispersed in the solvent; and a basic compound To obtain an ink composition by mixing
Filtering the ink composition;
The method comprises the step of stabilizing the increase in viscosity of the ink by performing heat aging by heating the ink composition after filtration at a temperature not lower than the temperature used in ink jet recording and not higher than 65 ° C. Method. 2. The method for producing an ink for inkjet recording according to claim 1, wherein the heat aging is performed such that the viscosity of the ink composition after the filtration is increased at a rate of 5% to 80%.   An ink jet recording apparatus using the ink for ink jet recording produced by the method according to claim 1.

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