JPH04356569A - Hot-melt ink operation - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-melt ink composition containing a substance that is solid at room temperature and a dye, which is ejected from an inkjet recording device at a temperature higher than room temperature, and a method for producing the same.

0002

[Prior Art] The inkjet recording method is a simple process because it is direct recording, it is noiseless because it is not an impact method, it is capable of high-speed recording, and it has high resolution because it ejects minute ink droplets. It has excellent features such as being able to record images, and its future potential is attracting attention. However, although it differs slightly depending on the method, in conventional inkjet recording, the ink is a liquid and is recorded by soaking into the paper, so depending on the type of transfer target, the ink may smear and the periphery of the recorded dots becomes unclear. The disadvantage is that the print quality deteriorates and high-quality recorded images cannot be obtained. For this reason, as an ink composition that provides good print quality regardless of paper quality, U.S. Pat.
90369, 4484948, JP-A-55-54368
, JP-A No. 58-108271 discloses that a hot-melt ink composition is made of a wax that is solid at room temperature, a higher fatty acid, etc. as a base material, and a dye is added, and the solid ink is heated and melted at a high temperature. A method has been proposed in which recording dots are formed by causing the recording dots to fly and cooling and solidifying on recording paper.

0003

However, due to the manufacturing process, dyes contain metals such as iron, nickel, zinc, manganese, and phosphorus as impurities. Furthermore, since the dyes used in hot-melt ink compositions are required to have heat resistance, metal complex dyes such as copper, cobalt, and chromium are often used, and metals released from these metal complex dyes may also be used. Contains it as an impurity. For example, C.I., which is a chromium complex type dye. I. Solvent Yellow 79 contains a large amount of chromium as an impurity.

[0004] If ink is prepared containing these impurities, the following problems arise. When hot-melt ink compositions are used for inkjet recording,
In order to achieve proper and stable ejection performance, the ink must exhibit a constant viscosity at an ejection temperature of 50 mPa·s or less, but for this purpose, the ejection temperature must be at least 20°C below the melting point of the hot-melt ink composition. There must be more than that. This is because, when the temperature is lower than 20° C., the rate of change in viscosity with respect to temperature changes is large, so fluctuations in discharge temperature due to changes in environmental temperature affect variations in viscosity and make discharge characteristics unstable. In addition, in general, substances that are solid at room temperature have higher viscosity the closer to their melting point, making it impossible to eject them from an inkjet head. Therefore, the hot-melt ink composition is exposed to a high temperature of 20° C. or more above its melting point during printing in the inkjet head. The substance that is solid at room temperature and used in the hot-melt ink composition is disclosed in the above-mentioned U.S. Pat.
390369, 4484948, JP-A-55-5436
8. As shown in JP-A-58-108271, waxes, higher fatty acids, etc. are generally used. However, these waxes and higher fatty acids are subject to thermal deterioration such as cleavage of molecular chains, bonds between cleaved molecules, and other changes to foreign substances due to reactions caused by heat. The impurity metals mentioned above act as catalysts and further accelerate this thermal deterioration, accelerating the occurrence of precipitation and the like due to deterioration.

[0005] The deposits generated in this manner cause clogging of the ejection nozzles of the inkjet head. On top of that,
This also leads to deterioration of the reliability of the ink composition itself, such as deterioration of ejection characteristics and print quality due to deterioration of the quality of the ink composition. Further, when a third component such as a resin is added to the ink composition, the metal impurities not only promote oxidative deterioration of the resin but also become a factor that corrodes the material of the inkjet head.

[0006]The present invention is intended to solve these problems, and its purpose is to prevent clogging of ejection nozzles in hot-melt ink compositions and ensure long-term reliability of inkjet heads. Moreover, it also extends the life of the ink composition itself. Another object of the present invention is to provide a manufacturing method that prevents clogging of ejection nozzles, ensures long-term reliability of an inkjet head, and extends the life of the ink composition itself.

[0007]

[Means for Solving the Problems] The hot-melt ink composition of the present invention is a hot-melt ink composition containing a substance that is solid at room temperature and a dye, which is ejected from an inkjet recording device at a temperature higher than room temperature. In the product, the metal content in the hot melt ink composition is 300 pp.
m or less, and the substance that is solid at room temperature is wax or a higher fatty acid and a derivative thereof, and the metal is copper, cobalt, chromium, iron, nickel, zinc, manganese, phosphorus. Among the metals, the content of copper, cobalt, or chromium is 200 ppm or less.

[0008] Furthermore, the method for producing a hot melt ink composition of the present invention includes a hot melt ink composition containing a substance that is solid at room temperature and a dye, which is ejected from an inkjet recording device at a temperature higher than room temperature. In the manufacturing method, the content of metal in the hot-melt ink composition is adjusted to 300 ppm or less, and the substance that is solid at room temperature is a wax or a higher fatty acid and a derivative thereof. The metal is selected from copper, cobalt, chromium, iron, nickel, zinc, manganese, and phosphorus, and the content of copper, cobalt, or chromium among the metals is 200%.
It is characterized in that it is prepared so that it is less than ppm.

[0009]

[Example] The present invention will be explained in detail by giving specific examples below.

The basic components of the hot-melt ink composition used in the present invention are a substance that is solid at room temperature and a dye that dissolves therein. The main vehicle is a substance that is solid at room temperature,
Wax, higher fatty acids and their derivatives are mainly used. Specifically, natural waxes such as carnauba wax, candelilla wax, beeswax, and wood wax, paraffin wax, microcrystalline wax, polyethylene wax, ester wax, montan wax, Fischer-Tropsch wax, etc., and higher fatty acids. Stearic acid, behenic acid, etc. are used. In addition to these, higher fatty acid derivatives such as stearamide, behenic acid amide, oleic acid amide, stearone, and lauron can also be used. Resin is usually added to these substances that are solid at room temperature for the purpose of imparting strength. Examples of the resin include ethylene copolymers such as ethylene-ethyl acrylate copolymer, ethylene-vinyl acetate copolymer, and ethylene-α-olefin copolymer, acrylic resin, polyethylene resin, and alicyclic hydrogenated aromatic resin. Examples include resins, rosin/rosin derivatives, terpenes/terpene derivatives, styrene resins, and the like. The aforementioned dyes that are soluble in solid substances at room temperature are mainly oil-soluble dyes, disperse dyes, and basic dyes, but direct dyes, reactive dyes, acid dyes, etc. may also be used as long as they are soluble. However, in the present invention, metal complex type oil-soluble dyes are preferred from the viewpoint of solubility and heat resistance. For example, C. I. Solvent Black 45, C. I. Solvent red 8, 91, 127,
C. I. Solvent Yellow 79, C. I. Solvent Brown 28 grade. Furthermore, in order to improve heat resistance and light resistance, antioxidants, ultraviolet absorbers, and the like are appropriately added as necessary.

[0011] The content of the substance which is solid at room temperature and serves as the main vehicle in the ink composition is 50 to 95%, preferably 70% by weight, based on the total weight of the ink composition.
It is in the range of ~90%. The amount of resin added is in the range of 5 to 50%, preferably 8 to 20%. Also,
The dye is added in an amount of 1 to 15%, preferably 2 to 10%, based on the total weight of the ink composition. Small amounts of additives such as antioxidants and ultraviolet absorbers may be added within a range of 1% or less, if necessary.

The hot-melt ink composition of the present invention is prepared from such components. During preparation, physical properties,
The goal is to have a good balance in ejection stability, storage stability, light resistance, weather resistance, etc.

The present invention will be explained in more detail with reference to the following examples.

In the following Examples and Comparative Examples, all percentages in the table indicate weight percentages.

(Example 1) Carnauba wax
50
% paraffin wax
13
% microcrystalline wax
13%
Behenic acid
20
% Dye (C.I. Solvent Black 45
) 4% Each of the above components was melt-mixed to obtain a hot-melt ink composition. This is highly purified tetrahydrofuran (abbreviated as THF: purity >
99.5%). The residue was filtered through a membrane filter made of polytetrafluoroethylene (PTFE) with a pore size of 5 μm, and then purified by ion exchange separation. Then, this purified solution was passed through a spray dryer to volatilize THF as a solvent. In this way, a purified hot-melt ink composition was obtained. The metal content in this ink composition is determined by atomic absorption spectrophotometry.
As a result of measurement by inductively coupled plasma (ICP) emission spectroscopy, the metal content was 250 ppm. Of these, chromium was 150 ppm. All other metals were below 15 ppm.

This ink was evaluated as follows.

(Evaluation 1) Long-term storage stability: Even after the ink was sealed in a glass container and left in a constant temperature bath at 150° C. for 3 months, no precipitation of insoluble matter was observed. Also,
There was no change in the physical properties or color tone of the ink, and the print quality was as clear as before.

(Evaluation 2) Ejection stability: Using the above ink, a hot melt inkjet recording device
Continuous printing was performed for 00 hours, and stable printing was possible from beginning to end. (Evaluation 3) Ejection response: Ink immediately after manufacture and 150°C
The ink was left in the environment for one month and was printed at a high frequency of 4 kHz to check its responsiveness.In both cases, the nozzles were not clogged and stable responsiveness was shown.

(Evaluation 4) Corrosion of head materials: Each material constituting the inkjet head was immersed in the above ink and left in an environment of 150°C for 3 months, and the surface condition of each material was observed. , there was no change.

(Examples 2 to 4) Hot-melt ink compositions having the compositions shown in Table 1 below, which were purified by the same method as in Example 1, were prepared, and each was evaluated in the same manner as in Example 1. I did it. These are all Example 1
showed excellent results as well.

Table 1 also shows the metal content of each ink composition.

[0022]

[Table 1]

In the above examples, the hot melt type ink composition of the present invention was prepared by the purification method shown in Example 1, but the solvent for dissolving the ink components or the ink composition itself was different from that of the ink components. There is no particular limitation as long as the solubility and purity are high, and general tetrahydrofuran (THF), methyl ethyl ketone (MEK), ethyl alcohol, acetone, toluene, etc. can be used. These may be mixed and used if necessary.

In the present invention, the metal content in the hot-melt ink composition may be adjusted to 300 ppm or less, but is not limited thereto. Another example of the manufacturing method of the present invention is shown. For example, a substance that is solid at room temperature and serves as a vehicle is heated, stirred, and mixed in an aqueous acid solution such as hydrochloric acid or nitric acid, and the metal contained therein is eluted into the acid solution. Thereafter, the acid aqueous solution in which the metal has been eluted and the substance that is solid at room temperature are filtered and separated. By repeating this process, the amount of metal contained is reduced. Furthermore, in the case of an oil-soluble dye, the metal content is reduced by the same process as above. After being purified in this manner, the hot melt ink composition of the present invention can be obtained by melt-mixing each.

In the above example, the ink component or the ink composition itself is dissolved in a solvent and then purified. It goes without saying that there is no problem in obtaining the ink composition.

(Comparative Example) Unrefined ink compositions were prepared for each of the compositions of Examples. Table 1 also shows the metal content of each ink composition.

For these ink compositions, Example 1
As a result of conducting the same evaluation as shown in , in both cases, precipitation of insoluble matter occurred after one month in terms of long-term storage, and clogging often occurred during discharge. Moreover, the head material corroded within one month in both cases.

[0028]

As described above, according to the present invention, in a hot-melt ink composition composed of a substance that is solid at room temperature and a dye, by adjusting the metal content to a certain amount or less, insoluble matter can be reduced. This has the effect of suppressing precipitation, preventing clogging of ejection nozzles, and extending the life of the ink composition itself. Furthermore, corrosion of the inkjet head material due to metal is also prevented, ensuring long-term reliability of the inkjet head.

Claims (4)

[Claims] 1. A hot melt ink composition containing a substance that is solid at room temperature and a dye, which is ejected from an inkjet recording device at a temperature higher than room temperature, wherein the hot melt ink composition contains a metal. The amount is 300pp
A hot-melt ink composition characterized in that the ink composition is not more than m. 2. The hot-melt ink composition according to claim 1, wherein the substance that is solid at room temperature is a wax or a higher fatty acid or a derivative thereof. 3. The metal is copper, cobalt, chromium,
2. The hot-melt ink composition according to claim 1, wherein the hot-melt ink composition is selected from iron, nickel, zinc, manganese, and phosphorus. 4. The hot-melt ink composition according to claim 1, wherein the content of copper, cobalt, or chromium among the metals is 200 ppm or less.