A method for testing the storage stability of ink and its application

Abstract

This invention belongs to the field of ink technology and provides a method for testing the storage stability of ink and its application. First, based on Stokes' law, the centrifugation time is calculated using equivalent settling time and centrifugal force. Then, the ink to be tested is taken, centrifuged, and shaken. The solid content before and after centrifugation is recorded, the soft sediment ratio is calculated, and the time t required for the soft sediment ratio to reach 95±5% is recorded. This time is compared with the soft sediment recovery time T of a qualified product. If t≤T, the ink's storage stability is good and its quality is qualified; otherwise, the ink quality is unqualified. This invention tests the storage stability of ink by analyzing the speed of soft sediment recovery after centrifugation. It can be used to test the storage stability of ink, quickly screen ink formulations, shorten research and development time, and improve production efficiency.

Description

Technical Field

[0001] This invention relates to the field of ink technology, and more specifically, to a method for testing the storage stability of ink and its application. Background Technology

[0002] White inkjet ink (referred to as white ink) has excellent masking ability, which can conceal defects on the substrate and improve the contrast and vibrancy of color inkjet ink in surface printing or back printing modes. In surface printing mode, attaching a color image to a coating of white inkjet ink makes the color image stand out against a white background; in back printing mode, a color image is printed on a transparent substrate, and then white inkjet ink is attached to the color image, and the final image is observed through the transparent substrate. The higher the whiteness, the more vibrant the relative color contrast. To obtain high whiteness, high refractive index pigments are generally preferred for white ink pastes to achieve high masking efficiency. Currently, commonly used high refractive index white pigments mainly include zinc oxide, barium sulfate, calcium carbonate, and titanium dioxide. However, these inorganic pigment particles have a specific gravity (density) several times higher than traditional organic pigments (for example, titanium dioxide has a specific gravity of approximately 3.9-4.2 g / cm³). 3 Organic pigments have a specific gravity of approximately 0.9-1.2 g / cm³. 3 Because the specific gravity of inorganic pigment particles is 3-5 times that of the solvent, sedimentation of inorganic pigment particles in low-viscosity inks is unavoidable. In traditional coatings and printing inks, sedimentation can be delayed by increasing the viscosity of the ink (solvent). However, for low-viscosity (approximately 3-30 cps) inkjet ink systems, the high specific gravity of white pigments easily precipitates in the ink, forming hard clumps. This affects the redispersibility of the ink, leading to problems such as printhead clogging, misaligned printing, and ink interruption during inkjet printing. Therefore, the shelf life of white ink is generally only 6 months to avoid the formation of hard sediments due to prolonged storage, which would affect print quality. Thus, soft sedimentation is permissible in inkjet processes, but the formation of hard, clumped sediments must be avoided (soft sedimentation refers to sediments that can be easily redispersed by shaking, while hard sedimentation refers to clumps of sediments that cannot be redispersed by shaking). Since hard sedimentation is caused by the long-term deposition of white pigments, it often takes 3-6 months of standing storage to be detected. This has caused significant challenges to the development of white ink formulations and quality control in production. Newly developed ink products require a long period of settling before their quality can be confirmed, making rapid testing impossible and extending production timelines, which is not economically efficient. Therefore, developing a method for rapidly testing white ink and screening white ink formulations is of paramount importance.

[0003] The traditional method for judging ink quality is the high-temperature accelerated aging test, which mainly detects particle flocculation caused by high temperature. However, this method cannot effectively identify ink hard sedimentation caused by gravity.

[0004] Therefore, there is an urgent need to develop a method for testing the storage stability of ink, which can reduce product quality inspection time and can also be used to screen white ink formulations, improve the efficiency of white ink formulation development, screen out ink formulations that have a long standing storage time, are not prone to hard sedimentation and clumping, and have good redispersibility stability, thereby reducing problems such as inkjet printer nozzle clogging, skewed spraying, and ink interruption. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a method for testing the storage stability of ink and its application. This invention uses centrifugation to accelerate sedimentation and the soft sedimentation recovery time to quickly determine the storage stability of the ink, shortening product quality inspection time. Furthermore, the method provided by this invention can also be used to quickly screen ink formulations with excellent storage stability, improving R&D efficiency.

[0006] A first aspect of the present invention provides a method for testing the storage stability of ink.

[0007] Specifically, a method for testing the storage stability of ink includes the following steps:

[0008] (1) The ink to be tested includes the following components: dispersant, solvent, and pigment;

[0009] According to Stokes' law, first set an equivalent settling time t. eq When the centrifugal force is g2 and the ink solvent is the same, the equivalent settling time t is calculated according to formula (Ⅰ). eq The required centrifugation time t2; or when the ink solvents are different, including ink solvent 1 and ink solvent 2, the equivalent settling time t is calculated according to formula (II). eq The required centrifugation time t2; wherein, the equivalent settling time t eq The unit is minutes, the unit of centrifugation time t2 is minutes, μ1 is the viscosity of solvent 1 ink, μ2 is the viscosity of solvent 2 ink, and g1 is one gravitational acceleration (1G).

[0010] t2=t eq .g1 / g2 formula (I);

[0011] t2=t eq .g1 / g2.μ2 / μ1 formula (II);

[0012] (2) Take the ink to be tested, record the solid content of the ink before centrifugation, and then centrifuge it;

[0013] (3) Let it stand, shake it, record the solid content of the ink after shaking, and calculate the soft sedimentation ratio of each day according to the following formula (Ⅲ). Record the time required for the soft sedimentation ratio to reach 95±5%, i.e., the soft sedimentation recovery time t.

[0014] Soft sedimentation ratio = Solid content of ink after shaking / Solid content of ink before centrifugation (Formula III);

[0015] (4) Compare the soft sediment recovery time t of the ink to be tested with the soft sediment recovery time T of the qualified product. If t≤T, the ink quality is qualified; otherwise, the ink quality is unqualified.

[0016] This invention first utilizes Stokes' law, specifically the equivalent resting time t... eq Centrifugal force g2 is used to calculate centrifugation time t2. Then, the ink to be tested is taken and centrifuged. Centrifugation under high gravity accelerates pigment sedimentation. Under the action of high gravity centrifugation, pigment particles flocculate and are squeezed together to form precipitate. After shaking, the solid content of the ink before centrifugation is compared with the solid content of the ink after shaking, and the soft precipitate ratio is calculated. The time t required for the soft precipitate ratio to reach 95±5% is recorded. Finally, it is compared with the soft precipitate recovery time T of the qualified product. If t≤T, it indicates that soft precipitate has formed and the precipitate can recover particle independence in a short time (or within a time equivalent to that of the qualified product), indicating good storage stability and qualified quality of the ink. Otherwise, the ink quality is unqualified. Between different inks, the shorter the t, the better the storage stability of the ink. Using Stokes' Law to calculate the appropriate centrifugation time can ensure that sedimentation occurs. If the centrifugation time is too short, the particle settling distance is small, and the particles have not settled to the bottom, making it impossible to distinguish between good and bad ink. If the centrifugation time is too long, most particles will settle, making it impossible to distinguish between good and bad ink, and it is also time-consuming, failing to achieve the purpose of rapid detection.

[0017] Stokes' Law reveals that the settling velocity of particles is directly proportional to centrifugal force, directly proportional to the density difference between the particles and the solvent, and inversely proportional to the ink viscosity. This invention employs centrifugal sedimentation to accelerate pigment settling, simulating the settling process that occurs when ink is left to stand for an extended period. Under centrifugal force, pigment particles are compressed and agglomerate to form precipitate. At this point, ink formulations with excellent storage stability can restore particle independence after centrifugation stops due to interparticle repulsion or steric hindrance. The better the ink's storage stability, the faster and shorter the recovery time. However, for ink formulations with poor storage stability (binding properties), after centrifugal compression, the protective layer of dispersant adsorbed between particles is destroyed, preventing the particles from returning to their independent state. The clumps cannot be dispersed, resulting in a hard, irreversible precipitate. (This process can be visualized as the dispersant acting as a spring, with each pigment particle adsorbed onto the spring surface. Under normal circumstances, pigment particles cannot approach each other to form flocculation. The longer the centrifugal force acts, the longer the pigment particles are compressed, equivalent to a greater compression of the spring. The spring's elasticity comes from the polymer chains of the dispersant and the speed at which the solvent adsorbed by the dispersant is discharged. When the centrifugal force exceeds the spring's maximum compression limit, the spring can no longer be compressed. The polymeric dispersant, under stress and deformation, loses its steric hindrance and electrostatic repulsion protection, causing the pigment particles to come together tightly, forming a hard precipitate. When the centrifugal force disappears, the steric hindrance of the polymeric dispersant is restored, and the spring between the pigment particles rebounds, restoring relaxation, which corresponds to a soft precipitate.) Therefore, this invention utilizes appropriate centrifugal force to accelerate the sedimentation and agglomeration of pigments. If the ink can quickly restore the independence of the particles, it indicates that the ink has good storage stability and meets the requirements of qualified products.

[0018] Qualified product calibration soft sediment recovery time T: refers to the time required for qualified ink to achieve a soft sediment ratio of 95±5% after undergoing the same test.

[0019] Colloidal retention: According to the International Union of Pure and Applied Chemistry (IUPAC), dispersions with particles smaller than 1 micrometer are called colloids. Colloidal retention refers to the ability of a colloid to maintain a stable dispersion, or storage stability.

[0020] Soft sediment: refers to the sediment in ink that can be redispersed by shaking after centrifugation.

[0021] Hard sediment: refers to the clumps of sediment in ink after centrifugation that cannot be dispersed by shaking.

[0022] Centrifugal force: It is generally expressed as a multiple of gravitational acceleration (G). For example, centrifugal force = 10000G means that the centrifugal force is 10000 times the gravitational acceleration.

[0023] Equivalent standing time: i.e. the shelf life of the product.

[0024] Preferably, when the centrifugal force g2 is 10000G, and the equivalent settling time t is... eq If the time is 2 months and the centrifugation time t2 is 9 minutes, then the soft sediment recovery time T for qualified products is 2 days ± 10%.

[0025] When the equivalent set resting time t is set eq If the time is 4 months and the centrifugation time t2 is 18 min, then the soft sediment recovery time T for qualified products is 3 days ± 10%.

[0026] When the equivalent set resting time t is set eq If the time is 6 months and the centrifugation time t2 is 27 min, then the soft sedimentation recovery time T for qualified products is 4 days ± 10%.

[0027] When the equivalent set resting time t is set eq If the time is 9 months and the centrifugation time t2 is 40 min, then the soft sediment recovery time T for qualified products is 4 days ± 10%.

[0028] When the equivalent set resting time t is set eq If the time is 12 months and the centrifugation time t2 is 53 min, then the soft sedimentation recovery time T for qualified products is 4 days ± 10%.

[0029] According to Stokes' Law:

[0030] Where V is the Stokes particle settling velocity, d is the particle size, ρ is the particle density, and ρ o Let ρ be the solvent density, μ be the solvent viscosity, and g be gravity or centrifugal force. When the particles and solvent are fixed, d, ρ, ρo, and μ are all fixed. In this case, V is a function of g, denoted by V = f(g).

[0031] When the settling distance of Stokes particles is fixed, then:

[0032] Stokes particle settling distance = Stokes particle settling velocity (V) × settling time (t) = V1 × t eq =V2×t2=f(g1)×t eq = f(g2) × t2. Where V1 is the settling velocity of the Stokes particle under one gravitational constant, and t eq Let V2 be the equivalent settling time, V2 be the settling velocity of the Stokes particles under centrifugal force, t2 be the centrifugal time corresponding to the centrifugal force, g1 be the gravitational acceleration (1G), and g2 be the centrifugal force. Therefore, the equivalent settling time can be obtained from the above conversion.

[0033] Suppose we set an equivalent settling time and want to test whether the storage stability of a certain ink meets the requirements within that equivalent settling time. For example, if we set an equivalent settling time of one year and want to test whether the storage stability of a certain ink meets the requirements within one year, i.e., whether the shelf life can reach one year, then we calculate using an equivalent settling time of one year (356 days, or 525,600 min) and determine that the centrifugal force used is 10,000 G. The calculated centrifugation time t2 is 52.56 min. Similarly, if we set an equivalent settling time of six months (182.5 days, or 262,800 min) and the centrifugal force is 10,000 G, the calculated centrifugation time t2 is 26.28 min.

[0034] Assuming the solvent is different, then ρ and ρ' need to be considered. o μ, but since the specific gravity of the solvent changes little, the change in the specific gravity difference between the particles and the solvent can be ignored; only viscosity needs to be considered. The equivalent settling time t considering viscosity... eq It can be simplified to: Where μ1 = solvent viscosity of ink 1, and μ2 = solvent viscosity of ink 2.

[0035] Preferably, in step (3), the oscillation speed is 100-1000 rpm and the oscillation time is 0.5-5 min.

[0036] More preferably, the oscillation speed is 300-800 rpm, and the oscillation time is 0.75-4 min.

[0037] More preferably, the oscillation speed is 500-600 rpm, and the oscillation time is 1-3 min.

[0038] Preferably, the ink to be tested is inkjet ink.

[0039] Preferably, the viscosity of the ink to be tested is 3-30 cps at 25°C.

[0040] More preferably, the viscosity of the ink to be tested is 5-20 cps at 25°C.

[0041] More preferably, the viscosity of the ink to be tested is 5-8 cps at 25°C.

[0042] Preferably, the pigment is an inorganic pigment.

[0043] More preferably, the inorganic pigment includes at least one of the following: black pigment (such as manganese iron black PBr26, copper chromium black PBk28, titanium chromium black PBr29), white pigment (such as at least one of titanium dioxide PW6, zinc oxide, calcium carbonate, zinc sulfide, barium sulfate), blue pigment (such as at least one of cobalt blue PB28, cobalt chromium blue PB36, iron oxide blue), green pigment (such as cobalt green PG50 and / or iron oxide green), yellow pigment (at least one of titanium nickel yellow PY53, iron oxide yellow, zinc iron yellow manganese PY119), brown pigment (titanium chromium brown PBr24 and / or iron zinc chromium brown PBr33), and red pigment (at least one of iron oxide red PR101, iron oxide red PR130, cadmium red PR108, molybdenum chromium red).

[0044] Preferably, the specific gravity of the pigment is 2.5-7 g / cm³. 3 And / or the particle size of the pigment is 100-350 nm.

[0045] More preferably, the specific gravity of the pigment is 3.9-4.2 g / cm³. 3 And / or the particle size of the pigment is 150-300 nm.

[0046] More preferably, the particle size of the pigment is 200-280 nm.

[0047] Preferably, the pigment content in the ink is 3-20% by mass.

[0048] Since pigments are more prone to sedimentation in ink systems with high specific gravity and low viscosity, while high viscosity inks generally have less sedimentation and are not easily distinguishable, the method provided by this invention is more suitable for ink systems using high specific gravity pigments and low viscosity.

[0049] Preferably, the dispersant is a polymeric dispersant. Polymeric dispersants have multiple pigment anchoring sites, which can enhance the adsorption strength of the pigment surface. They also possess ionic electrostatic repulsion or steric hindrance, which can inhibit pigment particle flocculation. By selecting the appropriate polymeric dispersant, problems such as white ink sedimentation and particle coarsening clogging the printhead can be effectively delayed. To prevent the formation of hard precipitates in white ink, polymeric dispersants are preferred, as their polymeric segments can generate steric hindrance to obtain better adhesive retention. To achieve optimal steric hindrance performance, the solvent-loving polymeric segments in the dispersant must be able to fully extend in the solvent. Since the compatibility of the solvent-loving segments of the dispersant varies in different solvents, the steric hindrance effect of the dispersant also varies in different solvents. Therefore, the method of this invention can not only screen white ink formulations but also screen the compatibility between dispersants and solvents.

[0050] Preferably, the solvent includes water and / or an organic solvent.

[0051] Preferably, the organic solvent includes at least one of alcohols, ketones, esters, ethers, alcohol ethers, and polymer monomer solvents.

[0052] Preferably, the ink further includes additives, which include at least one of the following: humectant, wetting agent, leveling agent, penetrant, surface tension agent, initiator, stabilizer, and functional resin. Humectants can reduce the ink evaporation rate and prevent the ink from drying and clogging the nozzles. Wetting agents can wet the substrate, allowing the ink to effectively adhere to the substrate surface. Leveling agents can make the ink layer smooth and glossy. Penetrants can penetrate porous substrates, increasing adhesion and slowing down the drying rate. Surface tension agents can adjust the surface tension of the ink, making it suitable for inkjet printing. Initiators can undergo photo- or thermal polymerization reactions with monomers, thus curing the ink layer. Stabilizers can stabilize monomers and prevent abnormal polymerization of the ink.

[0053] Preferably, the method for preparing the ink includes the following steps:

[0054] The components are first mixed, dispersed, and filtered to obtain the ink.

[0055] Preferably, the dispersion is carried out using at least one of a mixer, homogenizer, sand mill, bead mill, two-roller or three-roller disperser, paint shaker, and high-pressure homogenizer.

[0056] A second aspect of the present invention provides an application of a method for testing the storage stability of ink.

[0057] The application of a method for testing the storage stability of ink in screening ink formulations.

[0058] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0059] This invention provides a method for testing the storage stability of ink. First, based on Stokes' law, the centrifugation time is calculated using equivalent settling time and centrifugal force. Then, the ink to be tested is taken, centrifuged, and shaken. The solid content before and after centrifugation is recorded, and the soft sediment ratio is calculated. The time t required for the soft sediment ratio to reach 95±5% is recorded and compared with the soft sediment recovery time T of a qualified product. If t≤T, the ink's storage stability is good and its quality is qualified; otherwise, the ink quality is unqualified. This invention tests the storage stability of ink by analyzing the speed at which the ink recovers its soft sediment after centrifugation. Among different inks, the shorter the t, the better the quality. The method provided by this invention can be used in product quality inspection to test the storage stability of ink. It can also be used to quickly screen ink formulations, shorten R&D time, improve production efficiency, and promote the research and development of high-quality inks with long storage time and fewer issues such as printhead clogging, misalignment, and ink interruption. Detailed Implementation

[0060] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0061] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0062] The data for the soft sediment recovery time T (centrifugal force 10000G) of qualified products (ink) are shown in the table below:

[0063] Table 1

[0064]

[0065] Example 1

[0066] Preparation of white ink sample: Add 1.5 kg of 1.0 mm diameter zirconia beads to a 1 L shaking flask, then add 9 g of random block dispersant solution SAI (prepared in Example 1 of Chinese Patent CN111205398A, effective part 50%), 216 g of isobornyl acrylate (organic solvent), 220 g of tetrahydrofuran acrylate, 10 g of diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide initiator, 0.1 g of BYK-361 leveling agent, 0.5 g of 4-methoxyphenol stabilizer, and 45 g of titanium dioxide white pigment to the shaking flask. Place the shaking flask in a paint shaker and mix and disperse for 6 h until the pigment particle size reaches 237 nm to obtain a white ink sample with a solid content of 9%. The viscosity of the ink is 6.2 cps at 25 °C.

[0067] A method for testing the storage stability of ink includes the following steps:

[0068] (1) The equivalent settling time is half a year (i.e., 262800 min), and the centrifugal force is 10000 G. According to Stokes' law, the corresponding centrifugation time t2 is calculated to be approximately 27 min using formula (Ⅰ);

[0069] t2=t eq .g1 / g2 formula (Ⅰ);

[0070] (2) After testing the solid content of the white ink to be tested before centrifugation, take 70g of this white ink into a 100mL centrifuge tube and centrifuge for 27min at a centrifugal force of 10000G.

[0071] (3) After standing for 4 days, shake the test tube at 500 rpm / min for 1 min, record the solid content of the white ink after shaking, and calculate the soft precipitation ratio according to the following formula (Ⅲ), and record the time t required for the soft precipitation ratio to reach 95±5%.

[0072] Soft sedimentation ratio = Solid content of ink after shaking / Solid content of ink before centrifugation (Formula III);

[0073] (4) The results showed that after centrifugation at 10000G for 27 min and standing for 4 days, the soft sedimentation rate of the white ink reached 98.6%, indicating that the time t required for the soft sedimentation rate of the ink to reach 95±5% was about 4 days. Compared with the soft sedimentation recovery time T of qualified products in Table 1, it was less than the soft sedimentation recovery time T of qualified products, indicating that the white ink was qualified and its shelf life could reach half a year.

[0074] Example 2

[0075] Preparation of white ink sample: Add 1.5 kg of 1.0 mm diameter zirconia beads to a 1 L shaking flask, then add 15 g of SA2 dispersant solution (prepared in Example 2 of Chinese Patent CN111116842A, effective content 40%), 339 g of deionized water, 50 g of glycerin humectant, 50 g of functional acrylic resin, 1 g of Air Chemical 420 wetting agent, and 45 g of titanium dioxide white pigment to the shaking flask. Place the shaking flask in a paint shaker and mix and disperse for 4 hours until the pigment particle size reaches 273 nm. A white ink sample with a solid content of 9% is obtained, and the ink viscosity at 25 °C is 5.8 cps.

[0076] A method for testing the storage stability of ink includes the following steps:

[0077] (1) The equivalent settling time is half a year (i.e., 262800 min), and the centrifugal force is 10000 G. According to Stokes' law, the corresponding centrifugation time t2 is calculated to be approximately 27 min using formula (Ⅰ);

[0078] t2=t eq .g1 / g2 formula (Ⅰ);

[0079] (2) After testing the solid content of the white ink to be tested before centrifugation, take 70g of this white ink into a 100mL centrifuge tube and centrifuge for 27min at a centrifugal force of 10000G.

[0080] (3) After standing for 4 days, shake the test tube at 500 rpm / min for 1 min, record the solid content of the white ink after shaking, and calculate the soft precipitation ratio according to the following formula (Ⅲ), and record the time t required for the soft precipitation ratio to reach 95±5%.

[0081] Soft sedimentation ratio = Solid content of ink after shaking / Solid content of ink before centrifugation (Formula III);

[0082] (4) The results showed that after centrifugation at 10000G for 27 min and standing for 4 days, the soft sedimentation rate of the white ink reached 96.7%, indicating that the time t required for the soft sedimentation rate of the ink to reach 95±5% was about 4 days. Compared with the soft sedimentation recovery time T of qualified products in Table 1, it was less than the soft sedimentation recovery time T of qualified products, indicating that the white ink was qualified and its shelf life could reach half a year.

[0083] Example 3

[0084] Preparation of white ink sample: Add 1.5 kg of 1.0 mm diameter zirconia beads to a 1 L shaking flask, then add 12 g of comb-shaped dispersant solution Comb1 (prepared in Example 1 of Chinese Patent CN113512201A, effective content 56.8%), 384 g of diethylene glycol diethyl ether solvent, 57 g of dipropylene glycol, 2 g of functional chloroacetic acid resin, and 45 g of titanium dioxide white pigment to the shaking flask. Place the shaking flask in a paint shaker and mix and disperse for 6 h until the pigment particle size reaches 223 nm, to obtain a white ink sample with a solid content of 9% and an ink viscosity of 5.2 cps at 25 °C.

[0085] A method for testing the storage stability of ink includes the following steps:

[0086] (1) The equivalent settling time is half a year (i.e., 262800 min), and the centrifugal force is 10000 G. According to Stokes' law, the corresponding centrifugation time t2 is calculated to be approximately 27 min using formula (Ⅰ);

[0087] t2=t eq .g1 / g2 formula (Ⅰ);

[0088] (2) After testing the solid content of the white ink to be tested before centrifugation, take 70g of this white ink into a 100mL centrifuge tube and centrifuge for 27min at a centrifugal force of 10000G.

[0089] (3) After standing for 4 days, shake the test tube at 500 rpm / min for 1 min, record the solid content of the white ink after shaking, and calculate the soft precipitation ratio according to the following formula (Ⅲ), and record the time t required for the soft precipitation ratio to reach 95±5%.

[0090] Soft sedimentation ratio = Solid content of ink after shaking / Solid content of ink before centrifugation (Formula III);

[0091] (4) The results showed that after the white ink was centrifuged at 10000G for 27 min and left to stand for 4 days, the soft sedimentation rate reached 97.2%, indicating that the time t required for the soft sedimentation rate of the ink to reach 95±5% was about 4 days. Compared with the soft sedimentation recovery time T of qualified products in Table 1, it was less than the soft sedimentation recovery time T of qualified products, indicating that the white ink was qualified and its shelf life could reach half a year.

[0092] Example 4

[0093] Three different white ink samples were prepared: 1.5 kg of 1.0 mm diameter zirconia beads were added to three 1 L shaking flasks respectively. Then, BYK-103 (40% effective content), BYK-111 (100% effective content), BYK-2205 (100% effective content), diethylene glycol diethyl ether solvent, dipropylene glycol, functional chloroacetic acid resin, and titanium dioxide white pigment were added to the shaking flasks respectively. The formulations are shown in Table 1. The shaking flasks were placed in a paint shaker and mixed and dispersed for 6 hours until the pigment particle size reached 150-350 nm. White ink samples with a solid content of 9% were obtained and numbered 1-3 respectively.

[0094] A method for testing the storage stability of ink includes the following steps:

[0095] (1) Set the equivalent settling time for white inks numbered 1-3 to 6 months, 4 months, and 2 months respectively, and the centrifugal force to 10000G for each. According to Stokes' law, calculate the corresponding required centrifugation time t2 using formula (Ⅰ);

[0096] t2=t eq .g1 / g2 formula (I);

[0097] (2) After testing the solid content of the white inks to be tested numbered 1-3 above before centrifugation, take 70g of each white ink and put it into a 100mL centrifuge tube. Centrifuge at 10000G for 27min, 18min and 9min respectively.

[0098] (3) Let it stand, shake it, record the solid content of the ink after shaking, and calculate the soft sedimentation ratio of each day according to the following formula (Ⅲ). Record the time required for the soft sedimentation ratio to reach 95±5%, i.e., the soft sedimentation recovery time t.

[0099] Soft sedimentation ratio = Solid content of ink after shaking / Solid content of ink before centrifugation (Formula III);

[0100] (4) The formulas and test results of the white inks numbered 1-3 above are shown in the table below.

[0101] Table 2

[0102]

[0103]

[0104] The results in the table above show that, under a centrifugal force of 10000G, the white ink No. 1 requires a settling time of more than 2 days to achieve a soft sedimentation rate of 95±5%, which translates to a shelf life of less than 2 months. The white ink No. 2 requires a settling time of more than 3 days to achieve a soft sedimentation rate of 95±5%, which translates to a shelf life of more than 2 months but less than 4 months. The white ink No. 3 requires a settling time of more than 4 days to achieve a soft sedimentation rate of 95±5%, which translates to a shelf life of more than 4 months but less than 6 months.

[0105] In summary, the method of this invention can quickly test the storage stability of white ink and determine its storage time, effectively shortening the quality inspection time and improving testing and production efficiency. For ink research and development, it can reduce development and testing time, screen formulation components (such as compatibility screening between dispersants and solvents), and specifically improve the problem of poor storage stability of the formulation.

Claims

1. A method for testing the storage stability of ink, characterized in that, Includes the following steps: (1) The ink to be tested includes the following components: dispersant, solvent, and pigment; According to Stokes' law, first set an equivalent settling time t. eq When the centrifugal force is g2 and the ink solvent is the same, the equivalent settling time t is calculated according to formula (Ⅰ). eq The required centrifugation time t2; or when the ink solvents are different, including ink solvent 1 and ink solvent 2, the equivalent settling time t is calculated according to formula (II). eq The required centrifugation time t2; wherein, the equivalent settling time t eq The unit is minutes, the unit of centrifugation time t2 is minutes, μ1 is the viscosity of solvent 1 ink, μ2 is the viscosity of solvent 2 ink, and g1 is one gravitational acceleration. t² = t eq g1 / g2 formula (I); t2=t eq . g1 / g2 . μ2 / μ1 formula (II); (2) Take the ink to be tested, record the solid content of the ink before centrifugation, and then centrifuge it; (3) Let it stand, shake it, record the solid content of the ink after shaking, and calculate the soft sedimentation ratio of each day according to the following formula (Ⅲ). Record the time required for the soft sedimentation ratio to reach 95±5%, i.e., the soft sedimentation recovery time t. Soft sedimentation ratio = Solid content of ink after shaking / Solid content of ink before centrifugation (Formula (III)). (4) Compare the soft sediment recovery time t of the ink to be tested with the soft sediment recovery time T of the qualified product. If t≤T, it means that the ink quality is qualified; otherwise, the ink quality is unqualified. The viscosity of the ink to be tested at 25°C is 3-30 cps; In step (3), the oscillation speed is 100-1000 rpm and the oscillation time is 0.5-5 min.

2. The method according to claim 1, characterized in that, When the centrifugal force g2 is 10000G, the equivalent settling time t is set. eq If the time is 2 months and the centrifugation time t2 is 9 minutes, then the soft sediment recovery time T for qualified products is 2 days ± 10%. When the equivalent set resting time t is set eq If the time interval is 4 months and the centrifugation time t2 is 18 minutes, then the soft sediment recovery time T for qualified products is 3 days ± 10%. When the equivalent set resting time t is set eq If the time interval is 6 months and the centrifugation time t2 is 27 minutes, then the soft sediment recovery time T for qualified products is 4 days ± 10%. When the equivalent set resting time t is set eq If the time interval is 9 months and the centrifugation time t2 is 40 min, then the soft sediment recovery time T for qualified products is 4 days ± 10%. When the equivalent set resting time t is set eq If the time is 12 months and the centrifugation time t2 is 53 min, then the soft sedimentation recovery time T for qualified products is 4 days ± 10%.

3. The method according to claim 1, characterized in that, The specific gravity of the pigment is 2.5-7 g / cm³. 3 And / or the particle size of the pigment is 100-350 nm.

4. The method according to claim 1, characterized in that, The ink to be tested contains 3-20% pigment by mass.

5. The method according to claim 3 or 4, characterized in that, The pigment is an inorganic pigment.

6. The method according to claim 1, characterized in that, The solvent includes water and / or organic solvents.

7. The method according to claim 1, characterized in that, The ink to be tested is inkjet ink.

8. The application of the method for testing ink storage stability according to any one of claims 1-7 in screening ink formulations.

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