Low-viscosity flux composition usable for printing using digital inkjet head

Abstract

To provide a low-viscosity flux composition usable for printing using digital inkjet head.SOLUTION: A low-viscosity flux composition usable for printing using digital inkjet head includes: a common solvent, which accounts for 63 wt% to 98.5 wt% of a total weight of the flux composition, and includes propylene carbonate and at least one hydroxyl-containing organic solvent, wherein a weight ratio of the propylene carbonate to the hydroxyl-containing organic solvent ranges from 0.02 to 0.83; and an organic acid, which accounts for 1.5 wt% to 20 wt% of the total weight of the flux composition, and includes at least one hydroxyl-containing organic acid.EFFECT: The low-viscosity flux composition according to the present invention has appropriate viscosity itself, and can be directly applied to commercially available inkjet heads for printing, without the need for complicated temperature rising mechanism to reduce the viscosity; also, the printed pattern can remain clear without bleeding, eliminating the need for lowering the temperature after printing to restore the viscosity and reduce the flowability.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a flux composition, and more particularly to a low viscosity flux composition that can be used for printing with a digital inkjet head. [Background technology]

[0002] In general soldering, the flux acts by chemically removing metal oxides from the surfaces of the two objects to be soldered, wetting and spreading the flux over the surfaces, allowing the solder to adhere and fix to the interface (e.g., the metal interface) between the two objects during the subsequent soldering process, resulting in a strong joint.

[0003] Digital printing technology can print (apply) ink by spraying ink onto the surface of a substrate, and this technology not only saves time and materials, but also avoids the expense and time costs of pre-making and future screen plate storage management compared to traditional screen printing. It also saves materials compared to spin coating. Therefore, we are developing a technology to print flux using digital printing technology.

[0004] However, when digitally printing with high-viscosity flux, the flux's viscosity must be reduced before it is stored in a reservoir tank for supply to the head. A heating mechanism must be installed between the head and the piping connecting the head and the reservoir tank to raise the temperature and further reduce the flux's viscosity, making it easier to spray onto the substrate surface. A rapid-cooling mechanism must also be installed on the base on which the substrate is placed to cool the flux and prevent it from leaking or moving. This technical challenge is described, for example, in Patent Document TW I392423B.

[0005] Therefore, in view of the above problems, the present invention was born. Summary of the Invention [Problem to be solved by the invention]

[0006] In order to solve the above problems, the present invention aims to provide a low-viscosity flux composition that can be used for printing with a digital inkjet head, which has an appropriate viscosity itself, does not require a complicated heating mechanism to lower the viscosity, and can be used for printing with a commercially available general head.In addition, it is not necessary to lower the temperature after printing to restore the viscosity and reduce fluidity, and therefore the clarity of the printed pattern can be maintained and bleeding can be prevented. [Means for solving the problem]

[0007] The low viscosity flux composition according to the present invention is characterized by utilizing a ratio adjustment between the organic solvent and the hydroxy resin to obtain a flux composition having an appropriate viscosity range.

[0008] Therefore, in order to achieve the above object, the present invention provides a low-viscosity flux composition that can be used for printing with a digital inkjet head, comprising: a co-solvent that accounts for 63 wt% to 98.5 wt% of the total weight of the flux composition and contains propylene carbonate and at least one hydroxyl-containing organic solvent, wherein the weight ratio of the propylene carbonate to the hydroxyl-containing organic solvent is 0.02 to 0.83; and an organic acid that accounts for 1.5 wt% to 20 wt% of the total weight of the flux composition and contains at least one hydroxyl-containing organic acid.

[0009] According to one embodiment, the flux composition further comprises at least one hydroxyamine comprising 10 wt % or less of the total weight of the flux composition, the hydroxyamine comprising at least one of ethanolamine, N,N-dimethylethanolamine, N,N-dimethylaminoethoxyethanol, cyclohexyliminobisethanol, isopropanolamine, diisopropanolamine, and triisopropanolamine.

[0010] According to one embodiment, the flux composition further comprises at least one hydroxyl group-containing resin, accounting for 20 wt% or less of the total amount of the flux composition, wherein the hydroxyl group-containing resin comprises at least one of hydrogenated or non-hydrogenated rosin resin, polyvinyl alcohol, polyvinyl butyral, and polyketone resin.

[0011] According to one embodiment, the hydroxy-containing organic acid comprises at least one of glycolic acid, salicylic acid, citric acid, tartaric acid, and malic acid.

[0012] According to one embodiment, the organic acid may or may not further include at least one organic acid that does not contain a hydroxy group, and the organic acid that does not contain a hydroxy group may include at least one of benzoic acid, levulinic acid, lauric acid, malonic acid, succinic acid, glutaric acid, adipic acid, diglycolic acid, maleic acid, fumaric acid, and dimer acid.

[0013] According to one embodiment, the viscosity of the flux composition is 3 mPa·s or more and 30 mPa·s or less.

[0014] According to one embodiment, the surface tension of the flux composition is 25 dyne / cm or more and 40 dyne / cm or less.

[0015] According to one embodiment, the pH value of the flux composition is less than 10 and greater than 2.

[0016] According to one embodiment, the conductivity of the flux composition is less than or equal to 1 mS / cm.

[0017] According to one embodiment, the flux composition forms a thin, viscous film having a thickness of 0.2 μm or more and 20 μm or less when the solvent evaporates.

[0018] According to one embodiment, the hydroxyl group-containing organic solvent includes at least one of an alcohol-based solvent and an alcohol ether-based solvent.

[0019] According to one embodiment, the hydroxyl group-containing organic solvent includes at least one of n-butanol, diacetone alcohol, 1,2-butanediol, 1,5-pentanediol, 1,2-hexanediol, ethylene glycol monobutyl ether, propylene glycol methyl ether, diethylene glycol monoethyl ether, and dipropylene glycol methyl ether. [Effects of the Invention]

[0020] As described above, the low-viscosity flux composition according to the present invention can have an appropriate viscosity range by controlling the ratio between the co-solvent (and optional hydroxyl-containing organic acid and hydroxylamine) and the hydroxyl-containing resin, which eliminates the need for a process of increasing the temperature of the flux composition to reduce the flux viscosity before jetting, and then decreasing the temperature to restore the viscosity and reduce the fluidity.

[0021] The low-viscosity flux composition according to the present invention uses propylene carbonate as a cosolvent with a hydroxyl-containing organic solvent, which allows the flux composition to maintain a clear printed pattern, prevent bleeding, and sufficiently wet and spread the solder during soldering. Therefore, the flux composition of the present invention can be directly applied to flatbed printers equipped with commercial heads, and is compatible with the viscosity specifications of various commercially available heads. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention will be described in detail below, and the advantages, features, and embodiments of the present invention will become clear. However, it should be noted that the present invention is not limited to the following embodiments and can be implemented in various forms.

[0023] Furthermore, unless otherwise specified, numerical values ​​referred to in this specification can be considered as approximate values ​​rather than absolute values, that is, have an error or range expressed, for example, as "about," "approximately," or "roughly." Those skilled in the art will generally understand that the numerical values ​​referred to may include manufacturing tolerances, measurement errors, etc. The tolerance or error range may be within plus or minus 20%, within plus or minus 10%, or within plus or minus 5%.

[0024] Unless inconsistent, the technical features, components, contents, etc. of any embodiment described in this specification may be applied to other embodiments of the present invention.

[0025] The present invention provides a low-viscosity flux composition that can be used for printing with a digital inkjet head. Since the composition itself has an appropriate viscosity, there is no need to add a heating or cooling device to change the viscosity. The composition can be directly applied to various commercially available heads, and the printed flux can maintain its clarity and prevent bleeding.

[0026] The flux composition of the present invention comprises a co-solvent comprising propylene carbonate and at least one hydroxyl-containing organic solvent, the co-solvent accounting for 63 wt% to 98.5 wt%, preferably 63 wt% to 95 wt%, more preferably 63 wt% to 89 wt% of the total weight of the flux composition, wherein the weight ratio of the propylene carbonate to the hydroxyl-containing organic solvent is 0.02 to 0.9, preferably 0.08 to 0.85, more preferably 0.13 to 0.83; and an organic acid comprising at least one hydroxyl-containing organic acid, the co-solvent accounting for 1.5 wt% to 20 wt%, preferably 2 wt% to 15 wt%, more preferably 2.5 wt% to 12 wt% of the total weight of the flux composition.

[0027] In the current CoWoS manufacturing process, the space between the wafer and the micro PCB is limited, and excess flux in areas other than pinpoints can cause short circuits after reflow, significantly impacting yield. Therefore, the addition of propylene carbonate keeps the printing pattern low in fluidity, maintaining the clarity of the printed flux print and preventing bleeding.

[0028] In the present invention, one type of hydroxy group-containing organic solvent may be used, or a plurality of hydroxy group-containing organic solvents may be used in combination.

[0029] The addition of a hydroxyl group-containing organic solvent reduces the viscosity of the flux composition and also helps the flux composition adhere to the surface of the object to be soldered (e.g., a substrate) after printing, thereby allowing the solder to be sufficiently wetted and spread during the subsequent soldering process, and further aiding in the dissolution of the organic acid (especially the hydroxyl group-containing organic acid) and the hydroxyl resin described below.

[0030] The hydroxy group-containing organic solvent may include at least one of an alcohol solvent (particularly a monoalcohol solvent and a dialcohol solvent) and an alcohol ether solvent.

[0031] The hydroxy group-containing organic solvent may include at least one of n-butanol, diacetone alcohol, 1,2-butanediol, 1,5-pentanediol, 1,2-hexanediol, ethylene glycol monobutyl ether, propylene glycol methyl ether, diethylene glycol monoethyl ether, and dipropylene glycol methyl ether.

[0032] In the present invention, one type of organic acid may be used, or a plurality of organic acids may be used in combination.

[0033] By adding an organic acid, the organic acid acts as a low-viscosity flux component to provide the function of flux and at the same time, the viscosity of the flux composition can be appropriately adjusted. Furthermore, the organic acid can remove metal oxides on the surface of the object to be soldered or the solder, thereby reducing the electrical resistance of the surfaces to be joined.

[0034] In the flux composition of the present invention, the organic acid specifically refers to an organic carboxylic acid. The organic acid must include at least one hydroxyl-containing organic acid, and may include at least one of glycolic acid, salicylic acid, citric acid, tartaric acid, and malic acid. However, when multiple organic acids are used simultaneously, an organic acid that does not contain a hydroxyl group may also be included.

[0035] The reason why the organic acid must contain at least one hydroxyl group-containing organic acid is that hydroxyl group-containing organic acids have high solubility in hydroxyl group-containing organic solvents, which makes them more likely to adhere to the metal surface of the object to be soldered and allows metal oxides on the surface to be removed.

[0036] Because of the above-mentioned constitution, the viscosity of the flux composition of the present invention can be adjusted within an appropriate range of 3 mPa·s or more and 30 mPa·s or less, preferably 4 mPa·s or more and 20 mPa·s or less, and more preferably 5 mPa·s or more and 15 mPa·s or less. A flux composition within this low viscosity range is very suitable for commercial heads, because such a flux can be directly stored and used without the need for an additional heating and cooling mechanism.

[0037] Furthermore, because of the above-mentioned constitution, the surface tension of the flux composition of the present invention can be adjusted within an appropriate range of 25 dyne / cm or more and 40 dyne / cm or less, preferably 27.5 dyne / cm or more and 37.5 dyne / cm or less, and more preferably 30 dyne / cm or more and 35 dyne / cm or less. A flux composition within this surface tension range can wet and spread well on the bonded surfaces, while maintaining the clarity of the printed pattern and preventing bleeding.

[0038] Furthermore, due to the above-mentioned constitution, the pH value of the flux composition of the present invention may be 10 or less and 2 or more, preferably 8 or less and 2.5 or more, and more preferably 7 or less and 3 or more.

[0039] Furthermore, due to the above-mentioned constitution, the conductivity of the flux composition of the present invention may be 1 mS / cm or less, preferably 0.95 mS / cm or less, and more preferably 0.91 mS / cm or less.

[0040] Furthermore, due to the above-mentioned constitution, the flux composition of the present invention forms a low-viscosity film having a thickness of 0.2 μm or more and 20 μm or less, preferably 0.5 μm or more and 18 μm or less, and more preferably 0.8 μm or more and 15 μm or less, after the solvent has completely evaporated by printing.

[0041] This microviscosity film is the residue of a flux composition that does not contain a cosolvent, i.e., a hydroxyl-containing organic acid, or a mixture of a hydroxyl-containing organic acid and a non-hydroxyl-containing organic acid, or a mixture of a hydroxyl-containing organic acid, a non-hydroxyl-containing organic acid, and a hydroxylamine, or a mixture of a hydroxyl-containing organic acid, a non-hydroxyl-containing organic acid, a hydroxylamine, and a hydroxyl-containing resin. The microviscosity films of different thicknesses and compositions all exhibit good solderability and conductivity after solder balls are attached to a microcircuit board and resoldered to the device.

[0042] According to one embodiment of the present invention, the organic acid may further include at least one organic acid that does not contain a hydroxy group, such as at least one of benzoic acid, levulinic acid, lauric acid, malonic acid, succinic acid, glutaric acid, adipic acid, diglycolic acid, maleic acid, fumaric acid, and dimer acid.

[0043] According to one embodiment of the present invention, the flux composition may further comprise at least one hydroxyamine, accounting for 10 wt% or less, preferably 1 wt%-7.5 wt%, more preferably 2 wt%-5 wt% of the total weight of the flux composition.

[0044] The hydroxyamine may include at least one of ethanolamine, N,N-dimethylethanolamine, N,N-dimethylaminoethoxyethanol, cyclohexyliminobisethanol, isopropanolamine, diisopropanolamine, and triisopropanolamine.

[0045] According to one embodiment of the present invention, the flux composition may further comprise at least one hydroxy group-containing resin, which accounts for 20 wt% or less, preferably 12 wt% or less of the total weight of the flux composition.

[0046] The hydroxyl group-containing resin particularly refers to a polymer resin, and may include at least one of hydrogenated or non-hydrogenated rosin resin, polyvinyl alcohol, polyvinyl butyral, and polyketone resin.

[0047] Most of the components used in the flux composition of the present invention have a hydroxyl group, because the presence of the hydroxyl functional group enhances the mixing effect between the various composition components, thereby increasing the stability of the low viscosity flux composition, and also maintains the wetting and spreading properties of the hydroxyl group-containing components after mixing the various hydroxyl group-containing composition components with propylene carbonate, while propylene carbonate has the properties of maintaining the clarity of the printed pattern and preventing bleeding.

[0048] Furthermore, like organic acids (both hydroxyl-containing and hydroxyl-free), hydroxyamines are also low-viscosity flux components, and therefore, while providing the same flux function, the viscosity of the flux composition can be appropriately adjusted to suit the printing specifications of various commercial heads, thereby further improving the effectiveness of the flux composition of the present invention.

[0049] Like organic acids (whether hydroxyl-containing or hydroxyl-free), hydroxyamine can remove metal oxides from the surface of the object to be soldered or the solder, thereby reducing the electrical resistance of the surfaces to be joined, thereby further improving the effect of the flux composition of the present invention.

[0050] Furthermore, the hydroxyl group-containing resin is a high-viscosity component, and by using it in combination with other low-viscosity components, the viscosity of the flux composition can be adjusted within an appropriate range.

[0051] In the present invention, the viscosity of the flux composition is reduced to increase its fluidity. Since the flux composition is mainly used in digital printing, a low-viscosity flux can be precisely printed on the joint surfaces between the objects to be soldered, effectively preventing excess flux from contaminating surrounding electronic components, reducing flux waste and the time required to clean large areas of non-soldered areas.

[0052] When the low-viscosity flux composition of the present invention is applied to digital printing technology, it is necessary to print the flux composition precisely only on the soldered portion, and it is also necessary to maintain the integrity of the pattern formed by the printed ink on the substrate and avoid excessive bleeding (spreading) afterward. Therefore, in the present invention, propylene carbonate is added to maintain low fluidity of the printed pattern, thereby maintaining a clear and precise state.

[0053] The hydroxyl group-containing organic solvent not only serves to reduce the viscosity of the flux, but also helps dissolve the organic acid.

[0054] In addition, because the hydroxyl group-containing organic solvent easily guides and adheres the flux to the metal surface of the object to be soldered, when used in combination with propylene carbonate, it has the property of maintaining the clarity and precision of the printed pattern. By adjusting the ratio of these two components, it is possible to maintain the integrity of the printed pattern without contaminating surrounding components. Furthermore, by adhering the flux to the surface of the object to be soldered, it is possible to smoothly wet and spread the molten solder and fix it between the objects to be soldered during the future soldering process, making it practical.

[0055] In particular, because the flux composition of the present invention has the above-described structure, the viscosity of the flux inkjet ink can be adjusted to a low viscosity range of 3 mPa·s to 30 mPa·s. This viscosity range is applicable to commercially available inkjet heads, and the ink can be directly stored and used.

[0056] In terms of application, the low-viscosity flux composition of the present invention that can be used for digital inkjet head printing has a suitable viscosity range, so it can be directly filled into an ink cartridge or ink bag, and then directly applied to a flatbed printer equipped with a commercial inkjet head. This eliminates the need for a process of heating the flux composition to reduce its viscosity for printing, and then lowering the temperature to restore the viscosity and reduce fluidity.

[0057] Specifically, different heads all have their appropriate ink (i.e., the low-viscosity flux composition of the present invention) viscosity. For example, the appropriate ink viscosity for Epson DX5 / DX7 / I3200E / I3200U series heads is 3 to 7 mPa·s, the appropriate ink viscosity for Kyocera KJ4A series heads is 6 to 7.5 mPa·s, the appropriate ink viscosity for Kyocera KJ4C series heads is 10 to 18 mPa·s, the appropriate ink viscosity for Xaar 1001 heads is 7 to 50 mPa·s, the appropriate ink viscosity for Ricoh Gen 4 heads is 10 to 12 mPa·s, the appropriate ink viscosity for Trident 256Jet heads is 20 to 30 mPa·s, the appropriate ink viscosity for Konica Minolta KM 512 / 512i / 1024 / 1024i series heads is 6 to 12 mPa·s, and the appropriate ink viscosity for Fujifilm (R) The suitable ink viscosity for the Dimatix StarFire SG1024 head is 8 to 20 mPa·s.

[0058] Therefore, by adjusting the proportions of each component of the flux composition within the appropriate ranges set forth in this invention, the viscosity of the flux composition can be directly adjusted to meet the viscosity specifications of commercially available heads.

[0059] For example, controlling the content of various co-solvents and hydroxyl-containing resins is the most effective way to obtain flux compositions that correspond to the different viscosities of various commercially available heads. For example, by increasing the amount of co-solvent, decreasing the amount of hydroxyl-containing resin, or even eliminating the hydroxyl-containing resin, a flux composition with a lower viscosity can be effectively obtained. Conversely, by increasing the amount of hydroxyl-containing resin or decreasing the amount of co-solvent, a flux composition with a higher viscosity can be effectively obtained.

[0060] By adjusting the waveform on the electronic board that controls the printing by the head, the flux composition and head voltage can be perfectly matched to achieve precise printing applications.

[0061] Furthermore, even for heads of different model numbers from the same manufacturer's brand, or even for heads of various model numbers from different manufacturer's brands, simply by matching the head design and driver board, the size of the ejected droplets can be appropriately controlled to achieve precise printing applications.

[0062] Example Flux composition production and testing The low-viscosity flux compositions of the examples of the present invention and the comparative examples were manufactured by mixing the raw materials in the weight ratios shown in Tables 1 and 2 below and stirring until a clear liquid was obtained. After filtering the mixed flux composition liquid, basic physical properties such as viscosity, surface tension, pH value, and conductivity were measured, and the printing reliability of the flux composition using a commercially available flatbed printer, the completeness of the printed pattern, and the degree of bleeding were evaluated. The film thickness after solvent evaporation was also recorded, and the results are recorded in Tables 1 and 2.

[0063] The viscosity values ​​in Tables 1 and 2 were measured using a Brookfield rotational viscometer (model DV-E) at a constant temperature of 25°C. The surface tension values ​​in Tables 1 and 2 were measured using a surface tensiometer (model CBVP-A3) manufactured by Kyowa Interface Science Co., Ltd. of Japan at a constant temperature of 25°C.

[0064] The pH and conductivity values ​​in Tables 1 and 2 were measured using individual diluted solutions of each flux composition, and the dilution ratios were measured after mixing 1 part by weight of the flux composition with 39 parts by weight of deionized water and stirring at room temperature for 1 hour. Here, the pH values ​​were measured using a pH meter (model PH 200) from Clean Instruments, and the conductivity values ​​were measured using a conductivity meter (model Cond 3310) from WTW.

[0065] The printing tests of the flux compositions, including evaluation of print reliability, print pattern integrity, and the degree of bleeding, were conducted using a Roland VS-300 and a Mimaki UJF-3042 flatbed printer, specifically for flux compositions with viscosities of approximately 4 to 7 mPa·s and approximately 8 to 20 mPa·s, respectively. The ink jet volume may be controlled, and either a single print or multiple prints may be performed.

[0066] The film thicknesses (μm) in Tables 1 and 2 were determined by printing each flux composition onto a circuit board using a Roland VS-300 and a Mimaki UJF-3042 flatbed printer, heating the printed material together with the circuit board, removing the organic solvent, and then measuring the thickness of each microviscosity film using a non-contact film thickness meter (Keyence CLPT010).

[0067] Printing reliability evaluation standard for flux compositions ⊚: The flux composition is printed by the printer: no ink droplets scatter, and there are no missing nozzles in the nozzle check pattern.

[0068] ◯: The flux composition is printed by the printer: ink droplets are slightly scattered or the number of missing nozzles in the nozzle check test pattern is 2 or less.

[0069] ×: The flux composition was printed by the printer: printing was not possible, or large ink droplets were scattered, or the nozzle check test pattern had three or more missing nozzles.

[0070] Printer standby evaluation standard for flux composition (printing reliability evaluation × person omitted) ⊚: After the flux composition was left overnight in the printer, the inside of the printer was not cleaned, and the nozzle check pattern showed no missing nozzles.

[0071] ○: After the flux composition was left overnight in the printer, the inside of the printer was not cleaned and there were missing nozzles in the nozzle check pattern, but after the inside of the printer was cleaned within two times, there were no missing nozzles in the nozzle check pattern.

[0072] ×: After the flux composition was left overnight in the printer, the inside of the printer was not cleaned, and there were missing nozzles in the nozzle check pattern. Even after cleaning the inside of the printer two or more times, it was not possible to remove the missing nozzles from the nozzle check pattern.

[0073] Evaluation standards for printed materials after printing After printing, the solvent is dried, the pattern is observed under an optical microscope, and the film thickness of each print is recorded.

[0074] ◎: The pattern is clear and there is no bleeding. ○: The pattern is clear or there is slight bleeding. ×: The pattern is not clear or there is significant bleeding.

[0075] [Table 1]

[0076] [Table 2]

[0077] Note: The viscosity, surface tension, pH, and conductivity of the flux compositions in Tables 1 and 2 were all measured at a constant temperature of 25°C. A modified Roland VS-300 flatbed printer was used for Examples 1 to 5 and 8 to 10 in Table 1 and Comparative Examples C1 to C3 in Table 2, while a Mimaki UJF-3042 flatbed printer was used for Examples 6 to 7, 11 and 12 in Table 1, and Comparative Example C4 in Table 2. Print reliability evaluation, standby evaluation, and print evaluation were performed, and the print thickness was the average thickness after printing the flux composition one or more times and then volatilizing the co-solvent.

[0078] The flux compositions of Examples 1 to 12 in Table 1 were printed on a microcircuit board using a flatbed printer, Roland VS-300 or Mimaki UJF-3042. After solder balls were attached and the components were resoldered, good solderability and conductivity were obtained in all cases.

[0079] In Comparative Examples C1 and C2 in Table 2, propylene carbonate was not added, so the printed patterns were significantly blurred and not clear. In contrast, in Examples 1 to 12, propylene carbonate was added, so the printed patterns were clear or sharp.

[0080] The results of Examples 2 and 4 show that when the weight ratio of propylene carbonate to all hydroxyl group-containing organic solvents is 0.02 to 0.83, good (○) to excellent (◎) print reliability evaluations, standby evaluations, and printed matter evaluations can be obtained. When the weight ratio of propylene carbonate to all hydroxyl group-containing organic solvents is increased to 0.13, as in Example 5, excellent (◎) print reliability evaluations, standby evaluations, and printed matter evaluations can be obtained.

[0081] From the results of Example 6 and Example 1, it was found that when the total amount of co-solvents was 63 wt% to 98.5 wt% of the flux composition, the print reliability evaluation, standby evaluation, and print evaluation were all good (○) to excellent (◎). From the results of Example 9, it was found that when the total amount of co-solvents was 89 wt% of the flux composition, the print reliability evaluation, standby evaluation, and print evaluation were all excellent (◎).

[0082] From the results of Examples 1 and 8, it was found that when the weight of all organic acids accounted for 1.5 wt% to 20 wt% of the total flux composition, the print reliability evaluation, standby evaluation, and print evaluation were all good (○) to excellent (◎).

[0083] From the results of Comparative Examples C3 to C4, it was found that when the content of organic acid exceeded 20% by weight of the total flux composition, the conductivity was too high and the pH value was too low, and the actual machine data showed defects such as being unsuitable for standby and even unsuitable for digital printing.

[0084] From the results of Examples 1-2 and 10, it was found that when no hydroxyamine was added or the amount of hydroxyamine added was less than 10 wt% of the total flux composition, a flux composition with good print reliability and good evaluation of the printed matter could be obtained, and when the amount of hydroxyamine added was 2 wt% to 5 wt% of the total flux composition, a flux composition with excellent print reliability and good evaluation of the printed matter could be obtained.

[0085] From the comparison results of Examples 1 to 5 with Examples 6 and 12, it was found that the addition of a hydroxyl group-containing resin effectively increases the viscosity of the flux composition, making it suitable for use with heads that require relatively high viscosity ink, and that the viscosity of the flux composition can be adjusted to be higher as the amount of hydroxyl group-containing resin added increases.

Claims

1. A low viscosity flux composition that can be used for printing with a digital inkjet head, comprising: a co-solvent comprising propylene carbonate and at least one hydroxyl group-containing organic solvent, the co-solvent accounting for 63 wt % to 98.5 wt % of the total amount of the flux composition, wherein the weight ratio of the propylene carbonate to the hydroxyl group-containing organic solvent is 0.02 to 0.83; an organic acid comprising at least one hydroxyl group-containing organic acid, the organic acid comprising 1.5 wt % to 20 wt % of the total amount of the flux composition.

2. 10. The flux composition of claim 1, further comprising at least one hydroxyamine comprising up to 10 wt% of the total amount of the flux composition.

3. 3. The flux composition of claim 2, wherein the hydroxyamine comprises at least one of ethanolamine, N,N-dimethylethanolamine, N,N-dimethylaminoethoxyethanol, cyclohexyliminobisethanol, isopropanolamine, diisopropanolamine, and triisopropanolamine.

4. 10. The flux composition of claim 1, further comprising at least one hydroxy group-containing resin comprising up to 20 wt% of the total amount of the flux composition.

5. 5. The flux composition of claim 4, wherein the hydroxy group-containing resin comprises at least one of hydrogenated or non-hydrogenated rosin resin, polyvinyl alcohol, polyvinyl butyral, and polyketone resin.

6. 2. The flux composition of claim 1, wherein the hydroxy-containing organic acid comprises at least one of glycolic acid, salicylic acid, citric acid, tartaric acid, and malic acid.

7. 2. The flux composition of claim 1, wherein the organic acid further comprises at least one organic acid that does not contain a hydroxy group, the organic acid that does not contain a hydroxy group comprising at least one of benzoic acid, levulinic acid, lauric acid, malonic acid, succinic acid, glutaric acid, adipic acid, diglycolic acid, maleic acid, fumaric acid, and dimer acid.

8. 2. The flux composition according to claim 1, wherein the viscosity of the flux composition is 3 mPa·s or more and 30 mPa·s or less.

9. 2. The flux composition according to claim 1, wherein the flux composition has a surface tension of 25 dyne / cm or more and 40 dyne / cm or less.

10. 2. The flux composition of claim 1, wherein the pH value of the flux composition is 10 or less and 2 or more.

11. 10. The flux composition of claim 1, wherein the conductivity of the flux composition is 1 mS / cm or less.

12. 2. The flux composition according to claim 1, wherein the flux composition forms a thin film having a thickness of 0.2 μm or more and 20 μm or less when the solvent evaporates.

13. 2. The flux composition according to claim 1, wherein the hydroxy group-containing organic solvent includes at least one of an alcohol-based solvent and an alcohol ether-based solvent.

14. 2. The flux composition of claim 1, wherein the hydroxy group-containing organic solvent comprises at least one of n-butanol, diacetone alcohol, 1,2-butanediol, 1,5-pentanediol, 1,2-hexanediol, ethylene glycol monobutyl ether, propylene glycol methyl ether, diethylene glycol monoethyl ether, and dipropylene glycol methyl ether.

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