Color paste composition for silk-screen printing and preparation method thereof

Abstract

The invention discloses a color paste composition for silk-screen printing and a preparation method thereof. The color paste is composed of base ink, white ink, flaky pearl powder, hole protection particles, an orientation induction auxiliary agent and a solvent, the flaky pearl powder has bimodal sheet diameter distribution, and the hole protection particles are silane modified spherical silicon dioxide or hollow glass beads. The color paste prepared from the composition has the advantages of excellent screening property, stable orientation and small color difference fluctuation, and can realize the consistency of metal texture and hue in continuous printing of decorative paper.

Description

Technical Field

[0001] This invention relates to the technical field of printing and coating materials, and in particular to a color paste composition for screen printing and its preparation method. Background Technology

[0002] Screen printing technology is widely used in the decorative paper industry, mainly due to its unique advantages of thick ink layers and strong texture. However, in mass production, a core technical problem that has long plagued the industry has not been effectively solved: the difficulty in consistently reproducing the consistency of metallic luster and hue. The mechanism of this problem can be further deduced and analyzed from the following aspects:

[0003] First, in screen printing, the process of ink passing through the mesh is a complex flow within a confined channel. During this process, the ink undergoes complex coupling effects of shearing, compression, and backflow within the mesh. This multi-physics coupling effect leads to non-uniform transport of pigment and matrix in time and space. Specifically, the distribution of pigment particles is uneven at different locations and time points, thus affecting the hue and gloss of the final printed product.

[0004] Secondly, the evolution of the wet film after its formation is also a crucial factor. After formation, the wet film undergoes a process from spreading to curing, during which the simultaneous evolution of viscosity and volatility has a significant impact on the final optical performance. Any slight deviation at this stage will be nonlinearly amplified in the final optical response.

[0005] Furthermore, numerous factors influence these two stages, including mesh size, squeegee conditions, and wet film thickness. Even minor changes in any of these stages can lead to significant differences in optical response. Specifically, the contribution ratio between specular reflection and bulk scattering is highly sensitive to local film thickness and micro-orientation; any minute changes in thickness or orientation directly affect light reflection and scattering. In addition, a mismatch between the early flow and later locking rhythms can create subtle orientation differences and thickness fluctuations within the same printing plate. These minute differences are visually magnified, resulting in perceptible color differences and gloss fluctuations.

[0006] The cumulative effect of these complex factors causes color differences and gloss fluctuations to repeatedly occur in different batches, on different equipment, and even in long-term continuous printing of the same batch, making them difficult to completely eliminate through conventional empirical parameter adjustment methods. This problem seriously affects the quality and consistency of decorative paper products, becoming a bottleneck restricting the industry's development.

[0007] Therefore, there is an urgent need in this field to establish an operable stable window and constraint mechanism across the entire chain of "wire flow field—film thickness evolution—optical response." By precisely controlling the parameters of each stage, the aforementioned nonlinear amplification effect can be suppressed, thereby effectively solving the problem of inconsistent appearance and improving the overall quality and market competitiveness of decorative paper products. This is not only an optimization and improvement of existing technologies, but also a key step in promoting the industry to a higher level. Summary of the Invention

[0008] The purpose of this invention is to overcome the above-mentioned problems existing in the prior art and to provide a color paste composition for screen printing and its preparation method.

[0009] To achieve the above objectives, a first aspect of the present invention provides a color paste composition for screen printing, comprising base ink, white ink, flake pearlescent powder, pore-protecting particles, orientation-inducing agent, and solvent; wherein:

[0010] a) The lamellar pearlescent powder has a bimodal diameter distribution, wherein the median volume diameter D of the first peak is... 50 The effective mesh opening size is 0.15 to 0.3 times that of the second peak, and the volume median diameter D is... 50 The effective mesh opening size is 0.5 to 0.8 times that of the mesh, and the mass ratio of the first peak to the second peak is 7 to 17:3;

[0011] b) The protective particles are spherical silica or hollow glass microspheres, D 50 The particle size is 0.2 to 0.45 times the opening size of the printing screen and accounts for 0.3 to 1.2 wt% of the total mass of the pigment.

[0012] When screen printing ink is pressed through the mesh, the squeegee creates a complex flow within the mesh, primarily characterized by steady flow but also incorporating some compression. If the flake ink has only a single particle size, and this particle size is close to the actual opening of the mesh, two size-related deviations occur: larger particles are more likely to get stuck at the edge of the opening, while smaller particles are more likely to pass through the opening and enter the wet film below. The combination of these two deviations results in a predominance of smaller particles falling into the wet film, which visually appears grayish and reduces the metallic sheen.

[0013] This invention employs pearlescent powder with a bimodal flake size distribution. The small-diameter particles occupy the channels with the highest original velocity at narrow orifice openings, reducing the tendency for small particles to be preferentially carried away. Furthermore, the small particles fill in the micropores in the early stages of the wet film, limiting the secondary movement and lateral classification of large particles on the film surface. Simultaneously, with the small particles elevating and limiting their position, the accumulation and adhesion of large particles at the orifice openings during screen passing are significantly reduced. Therefore, without significantly increasing apparent viscosity, selective carry-out during screen passing is minimized.

[0014] The protective particles form multiple points of contact with the mesh and flake pigment at the narrow opening, which is equivalent to creating small, rolling fulcrums. This reduces the direct contact area and contact time between the large particles and the mesh, thereby reducing friction and adhesion and preventing the formation of pocket-like blockages at the opening.

[0015] Secondly, the pore-protecting particles disperse the high-speed slurry flow that was originally concentrated in the center of the pore into multiple streams, reducing local shear peaks and negative pressure adsorption, reducing the amount carried out and backflow during the scraper's return stroke, and at the same time, the tiny gaps between the particles and the plates can also prevent the plates from biting together and bridging at the pore opening.

[0016] In addition, when the scraper is pushed, the protective particles move in a way that combines rolling and sliding, which is equivalent to providing a reversible rolling layer in a local area, reducing the overall frictional work between the scraper, the screen and the pigment, and avoiding re-adhesion caused by local heating and instantaneous increase in viscosity.

[0017] As a further improvement of the present invention, the orientation induction agent comprises a combination of a fluorinated block copolymer and a comb-shaped polyether-polyester leveling agent, wherein the amount of the fluorinated block copolymer added is 0.1 to 0.4 wt%, and the amount of the comb-shaped polyether-polyester leveling agent added is 0.2 to 0.6 wt%.

[0018] As a further improvement of the present invention, the fluorinated block copolymer is a PFPE-acrylate block copolymer with a fluorine mass fraction of 15-25 wt% and a number-average molecular weight of 8 × 10⁻⁶. 3 ~2.0×10 4 The comb-shaped polyether-polyester leveling agent is a polyester-acrylate comb copolymer with a number-average molecular weight of 1.0 × 10⁻⁶. 4 ~3.0×10 4 Acid value ≤10 mg KOH / g.

[0019] Fluorinated block copolymers (PFPE-acrylate block copolymers, fluorine content 15%-25% by mass) have extremely low surface energy, enabling them to self-assemble into orientation-induced films at the interface between flake pearlescent powder and the matrix. This film reduces the local interfacial tension gradient during printing shearing, allowing the flake pearlescent powder to lay flat and reducing secondary disturbances during the squeegee return process. Its number-average molecular weight is 8 × 10⁻⁶. ³ Up to 2.0×10 4 It can balance liquidity and targeted stability.

[0020] Comb-shaped polyether-polyester leveling agent (molecular weight 1.0×10⁻⁶) 4 Up to 3.0×10 4(Acid value not exceeding 10 mg KOH / g), the flexible polyether chain provides dynamic leveling and viscoelastic buffering, while the rigid polyester backbone participates in film densification during the drying stage, forming a continuous flow-curing conversion path. The preferred addition amount (0.2% - 0.6% mass fraction) allows the system to have good flowability during the initial solvent evaporation period and lock the sheet orientation during the subsequent rapid curing.

[0021] The combination of these two agents stabilizes the orientation of flake pigments during film formation, suppresses orientation drift and color instability, and reduces haze and color difference. Compared to single leveling agent systems, this invention maintains metallic luster and hue consistency within a wet film thickness range of 12-25 μm, exhibiting excellent process tolerance.

[0022] This invention is the first to combine fluorinated block copolymers with comb-shaped polyether-polyester leveling agents as orientation-inducing aids, constructing a self-regulating orientation balance mechanism. The fluorinated block copolymers reduce interfacial energy and induce orientation, while the comb-shaped polyether-polyester leveling agents provide flow windows and mechanical support. The two work synergistically under the solvent evaporation rhythm to achieve controllable spreading and rapid locking of pigment plate orientation.

[0023] As a further improvement of the present invention, the solvent is a binary system of a high-boiling-point component at 180-250°C and a low-boiling-point component at 80-150°C, wherein the mass ratio of the high-boiling-point component to the low-boiling-point component is 5-6:1.

[0024] Specifically, low-boiling-point components (such as isopropanol and ethyl acetate) evaporate rapidly at the initial stage of printing, reducing the surface viscosity of the system and promoting the uniform spreading of base ink, white ink, and flake pearlescent powder through the screen, thus improving ink layer spreadability and line clarity, and reducing bubbles and pinholes. High-boiling-point components (such as diethylene glycol butyl ether and propylene glycol methyl ether acetate) evaporate slowly during the drying stage, maintaining a moderate amount of solvent residue, prolonging the wet film flow time, and allowing the flake pearlescent powder to spread evenly. In the later stage, the high-boiling-point solvent escapes, the film viscosity increases, and orientation locking occurs, preventing the flake pigments from tilting or flipping.

[0025] When the mass ratio of high to low boiling points is 5 to 6:1, the system can balance early spreading and late curing, avoid problems of drying too fast or too slow, achieve continuous connection between rheological adjustment of printing paste and orientation curing, and ensure that the film layer obtains stable metallic luster and uniform hue.

[0026] As a further improvement of the present invention, the volume fraction of the flake pearlescent powder and the volume fraction of the white ink satisfy the following ratio range: within a wet film thickness range of 12–25 μm, the equivalent contrast ratio R is between 0.8 and 1.4, wherein... ,

[0027] n represents the volume fraction of the flake-shaped pearlescent powder. p For its refractive index, n mThe refractive index of the matrix is... κ represents the volume fraction of white ink. s With σ s These are the absorption and scattering coefficients of white ink, respectively.

[0028] By introducing a control parameter range for the volume fraction ratio between white ink and flake pearlescent powder, and using the equivalent contrast ratio R as a characterization index, this invention successfully achieves quantitative control over the optical behavior of the system. Specifically, the R value can accurately reflect the relative balance between the refractive effect of the flake pearlescent powder and the scattering effect of the white ink. By limiting the R value to a specific range of 0.8 to 1.4, the dynamic balance between reflected and transmitted light intensity can be effectively maintained within a wet film thickness range of 12 to 25 μm, thereby ensuring that the metallic luster and the brightness of the base color remain highly consistent under different construction thicknesses, significantly reducing the visual color difference problem caused by local thickness deviations.

[0029] Within this parameter range, the directional reflection of the flake pearlescent powder and the multidirectional scattering of the white ink particles form a good complementary relationship: when the R value is low, the scattering effect of the white ink dominates, resulting in a weakened metallic feel and a grayish hue; conversely, when the R value is high, the specular reflection effect of the flake pearlescent powder dominates, easily leading to excessive highlights and reduced hiding power. By controlling the R value within a balanced range of 0.8 to 1.4, a dynamic constraint on the optical contributions of both is achieved, thereby constructing a reflection and scattering system with self-balancing capabilities.

[0030] Furthermore, the combined effect of this ratio range and the bimodal particle size structure is also crucial. Small-diameter particles effectively fill the mesh gaps, significantly improving the continuity of the screen printing process, while large-diameter particles provide the dominant specular reflection effect. Together, they form a stable layered structure within the orientation-inducing system, allowing for precise control of the reflected light distribution angle and further reducing the amplifying effect of film thickness fluctuations on color difference and metallic finish. Therefore, even within the conventional process deviation range of screen printing, a consistent hue and uniform metallic finish can still be achieved, greatly enhancing the overall aesthetics and consistency of the product.

[0031] As a further improvement of the present invention, the pigment system is used at 20-30°C and a shear rate of 200-1500 s. -1 The apparent viscosity η within the range satisfies the shear response relationship:

[0032] η = η0 / [1 + (γ / γ0)] m ],

[0033] Where η0 is the zero-shear viscosity, γ is the shear rate, γ0 is the critical shear rate, and m is 1.0 to 1.5;

[0034] As a further improvement of the present invention, the critical shear rate γ0 is 400–800 s. -1 The viscosity change rate Δη / η0 of the system within this rate range is 35%–55%.

[0035] When the relationship between η and γ satisfies this form and the critical shear rate γ0 is controlled between 400 and 800 s⁻¹ -1 Within the specified range, the pigment can maintain sufficient structural viscosity in the low-shear stage to prevent edge bleeding during actual printing, achieve sufficient thinning in the medium-shear stage to promote the flattening of flake pigments, and quickly restore its structure after the high-shear stops, thereby obtaining excellent screen transfer properties, orientation stability and film uniformity.

[0036] As a further improvement of the present invention, the surface of the protective particles is modified with methylsilane or fluoropropylsilane.

[0037] As a further improvement of the present invention, the titanium dioxide in the white ink is rutile.

[0038] A second aspect of the present invention provides a method for preparing the screen printing pigment composition as described above, comprising the following steps:

[0039] S1: Prepare flake-shaped pearlescent powder with bimodal particle size distribution according to the effective opening size of the selected screen.

[0040] S2: Select spherical silica or hollow glass microspheres as pore-protecting particles, modify them with methylsilane or fluoropropylsilane, and then dry them for later use.

[0041] S3: Dissolve fluorinated block copolymer and comb-shaped polyether-polyester leveling agent in a binary system composed of high-boiling-point and low-boiling-point solvents to form an orientation-inducing agent premix;

[0042] S4: At 20–30°C, the flake pearlescent powder and pore-protecting particles are sequentially added to the orientation-inducing agent premix solution, using a segmented shearing method: the first stage has a low shear rate of 200–400 s. -1 Maintain for 3–5 minutes for wetting, then increase to 1000–1500 seconds in the second stage. -1 Maintain dispersion for 2–5 minutes, then reduce to 300–500 seconds in the third stage. -1 Maintain for 2 minutes to level and defoam, and obtain a uniform slurry;

[0043] S5: Add base ink and white ink in three progressive steps to the obtained slurry, with the rheological viscosity change rate not exceeding 5% as the control condition;

[0044] S6: Vacuum degassing is performed on the mixed color paste under an absolute pressure not exceeding 0.02 MPa. After filtration through a 200 μm wet sieve, the paste is allowed to stand for 12–24 hours to mature, thus obtaining the finished color paste.

[0045] The present invention, by adopting the above technical solution, has the following beneficial effects:

[0046] 1. By constructing a bimodal particle size distribution in the flake pearlescent powder, the small-diameter flakes create a occupancy effect at the orifice, limiting the accumulation and deviation of large particles, while the large particles provide the main contribution to specular reflection. The synergistic effect of both effectively suppresses the "selective carry-out" phenomenon, making the pigment distribution more uniform during screen printing and reducing color differences and flicker fluctuations between batches and in long-distance printing.

[0047] 2. Silane-modified spherical silica or hollow glass microspheres form multi-point rolling support at the mesh openings, reducing direct friction and adsorption between the doctor blade and the mesh wires and pigments, and lowering local shear peaks and negative pressure adsorption effects. This not only significantly improves the continuity and durability of printing but also maintains high-resolution lines and a uniform ink layer.

[0048] 3. The synergistic effect of fluorinated block copolymers and comb-shaped polyether-polyester leveling agents: the former induces pigment spreading by reducing interfacial energy, while the latter provides flow windows and curing support. Under the solvent evaporation rhythm, the two work together to complete the continuous process of "orientation formation - flow adjustment - lock-in curing", which stabilizes the orientation of flake pigments and significantly reduces color shifting, haze, and metallic fluctuations.

[0049] 4. By setting the mass ratio of high-boiling-point solvents to low-boiling-point solvents at 5-6:1, the system can spread rapidly in the early stage and solidify steadily in the later stage; and the relationship between apparent viscosity and shear rate is limited to η=η0 / [1+(γ / γ0)]. m The critical shear rate γ0 is between 400 and 800 s⁻¹. -1 The range enables dynamic matching of rheology and directional stability during the printing stage, fundamentally suppressing color difference instability caused by thickness fluctuations and improving process adaptability and repeatability. Attached Figure Description

[0050] Figure 1 The graph shows the apparent viscosity-shear rate of the pigment paste in Example 1. Detailed Implementation

[0051] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0052] Unless otherwise defined, all scientific and technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art.

[0053] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0054] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0055] The present invention will now be described in detail with reference to specific embodiments, which are intended to understand rather than limit the invention.

[0056] Example 1

[0057] This embodiment provides a method for preparing a color paste composition for screen printing suitable for 325 mesh screens (effective opening size of about 45 μm).

[0058] I. Raw Material Description

[0059] The total mass of the color paste in this embodiment is 1000g, and its components and sources are as follows:

[0060] (1) 500g of base ink (50wt% of total mass), using water-based acrylic emulsion (45% solid content, pH 8.0), provided by Nippon Paint Industrial Coatings Co., Ltd.

[0061] (2) 150g of white ink (accounting for 15wt% of the total mass) was made from rutile TiO2 slurry (70% solid content) provided by Shanghai Zhongtai Pigment Co., Ltd.

[0062] (3) 100g of flake pearlescent powder (accounting for 10wt% of the total mass), which is mica-based TiO2 pearlescent powder (model WT-45, refractive index 1.80, original D 50 (24 μm). D was obtained by wet fractionation. 50 For 9μm fine sheets and D 50 The coarse film with a diameter of 30 μm was compounded at a mass ratio of 13:3 to form a bimodal film diameter distribution.

[0063] (4) 8g of pore-protecting particles (0.8wt% of total mass), which are spherical silica microspheres (model HM-Si16, D) 50 (16μm), specific surface area 50m² 2 / g, density 2.0g / cm³ 3 Its surface is modified with methyltrimethoxysilane (MTMS).

[0064] (5) Orientation-inducing agent 6.5g (0.65wt% of total mass), comprising:

[0065] ① Fluorinated block copolymer (using Synesqo Fluorolink® AD 1700) 2.5g (0.25wt%);

[0066] ② Comb-shaped polyether-polyester leveling agent (BASF EFKA® FL 3750) 4.0g (0.40wt%).

[0067] (6) Solvent 235.5g (accounting for 23.55wt% of the total mass) is a binary system: 55g of dipropylene glycol n-butyl ether and 10g of isopropanol, with a mass ratio of 5.5:1.

[0068] II. Preparation Method

[0069] S1: Preparation of flake-shaped pearlescent powder with bimodal particle size distribution

[0070] Weigh 100g of raw pearlescent powder and add it to 1L of deionized water. Use a wet centrifuge (3000rpm, 15min) to separate the fine flakes (D). 50 =9μm) and coarse film (D 50 =30μm), then mix them at a mass ratio of 13:3 and stir with a planetary stirrer at 400rpm for 10min to obtain a pearlescent powder with a bimodal flake size distribution.

[0071] S2: Silane modification of pore-protecting particles

[0072] Weigh 50g of silica microspheres and disperse them in 500mL of an ethanol / water mixture (9:1 volume ratio) and stir magnetically at 400rpm. Add 0.5g of methyltrimethoxysilane (MTMS) (1.0wt% of SiO2 mass) and adjust the pH to 4.5. Hydrolyze at 40℃ for 20min, then raise the temperature to 60℃ and react for 45min. After filtration and washing, dry at 110℃ for 2h to obtain methylsilane-modified pore-protecting particles.

[0073] S3: Preparation of orientation-inducing agent premix

[0074] Add 55g of DPB and 10g of IPA to a 250mL beaker and stir at 300rpm. Then add 1.25g of PFPE-acrylate block copolymer and 2.0g of comb-shaped polyether-polyester leveling agent in sequence, and stir at 25℃ for 30min to obtain a clear and transparent orientation induction aid premix.

[0075] S4: Dispersion and compounding pulping

[0076] Add the premixed liquid obtained from S4 to a planetary dispersion vessel (5L), and then add 100g of coated pearlite obtained from S2 and 8g of modified SiO2 pore-protecting particles obtained from S3 at 25℃.

[0077] Segmented cutting method is used:

[0078] Phase 1: Rotation speed 800 rpm (corresponding to a shear rate of 200 s) -1 Maintain for 4 minutes;

[0079] Second stage: Rotation speed 4000 rpm (corresponding to a shear rate of 1200 s) -1 Maintain for 3.5 minutes;

[0080] Third stage: Rotation speed 1000 rpm (corresponding to a shear rate of 400 s) -1 (), maintain for 2 minutes.

[0081] A uniform slurry is obtained.

[0082] S5: Addition of base ink and white ink

[0083] Add 500g of base ink and 150g of white ink in three progressive steps, with a 5-minute interval between each addition. After each addition, measure the viscosity change rate of the system, Δη / η0 ≤ 5%.

[0084] S6: Degassing, Filtration and Curing

[0085] The slurry obtained from S5 was placed in a vacuum tank and degassed for 15 minutes under an absolute pressure of 0.02 MPa. After being filtered through a 200 μm wet sieve, it was allowed to stand and mature at 25°C for 18 hours to obtain the finished color paste composition for screen printing.

[0086] III. Color Paste Performance Testing

[0087] 1. Using a rotational rheometer at 25℃, the shear rate was measured from 200 to 1500 s⁻¹. -1 The apparent viscosity η within the range, the test results are as follows Figure 1 As shown, the following was obtained through fitting:

[0088] Zero-shear viscosity η0 = 12.3 Pa·s;

[0089] Critical shear rate γ0 = 620 s -1 ;

[0090] The exponent m = 1.25;

[0091] The calculated viscosity change rate of the system at γ0 is Δη / η0 = 44%.

[0092] 2. The surface tension was measured to be 31 mN / m using an automatic tensiometer, and the pH was measured to be 8.1 using a pH meter.

[0093] 3. Seal the sample in a 100 mL brown bottle and store it in a constant temperature environment of 25 ± 1 ℃. After standing for 30 days, visually inspect for stratification or precipitation. Take samples from the top and bottom layers and test their viscosity and color difference. If ΔE* < 1.0, the system is considered stable.

[0094] The test results showed ΔE* = 0.45, indicating that the system is stable in the long term.

[0095] 4. Calculate the optical ratio using the Kubelka–Munk method. = 0.081, = 0.066, n p / n m = 1.22, κ s σ s = 0.74, substitute

[0096] , n represents the volume fraction of the flake-shaped pearlescent powder. p For its refractive index, n m The refractive index of the matrix is... κ represents the volume fraction of white ink. s With σ s These are the absorption and scattering coefficients of white ink, respectively.

[0097] We get R = 1.10.

[0098] Example 2

[0099] The preparation method in this embodiment is the same as that in Example 1, except that the mesh specifications and the proportions of each component are adjusted.

[0100] The differences are as follows:

[0101] (1) A 380-mesh screen was used, with an effective opening size of approximately 35 μm; the flake pearlescent powder was graded to obtain D 50 = 7 μm, D 50 = 21 μm, the two are mixed in a mass ratio of 11:3.

[0102] (2) The protective pore particles were changed to D. 50 = 10.5 μm spherical silica microspheres, at an amount of 0.6 wt%, modified with methyltrimethoxysilane.

[0103] (3) The mass ratios of base ink, white ink, pearlescent powder, and solvent were adjusted to 52 wt%, 12 wt%, 12 wt%, and 22.7 wt%, respectively, with the remainder being orientation-inducing auxiliaries.

[0104] (4) The solvent system is dipropylene glycol n-butyl ether and isopropanol, with a mass ratio of 6:1.

[0105] Example 3

[0106] This embodiment adjusts the ratio of flake pearlescent powder to white ink based on Embodiment 1 to enhance the hiding power.

[0107] The differences are as follows:

[0108] (1) Base ink 54 wt%, white ink 18 wt%, flake pearlescent powder 6 wt%, pore-protecting particles 0.5 wt%.

[0109] (2) Pore-protecting particles D 50 = 12 μm, modified with MTMS.

[0110] (3) The solvent mass ratio is 5:1 (DPnB:IPA).

[0111] (4) Flake pearlescent powder is graded to obtain D 50 = 10 μm, D 50 = 32 μm, mass ratio 13∶3.

[0112] Example 4

[0113] This embodiment increases the content of flake pearlescent powder based on Example 1 to obtain a high metallic luster.

[0114] The differences are as follows:

[0115] (1) 15 wt% flake pearl powder, 10 wt% white ink, 42 ​​wt% base ink, 1.0 wt% pore-protecting particles, 0.85 wt% orientation induction agent, and 31.15 wt% solvent.

[0116] (2) Bimodal particle size distribution D 50 = 9 μm, D 50 = 30 μm, mass ratio 13∶3.

[0117] (3) PFPE addition amount 0.35 wt%, comb leveling agent 0.50 wt%.

[0118] Example 5

[0119] This embodiment changes the type of protective particles, using hollow glass microspheres to improve anti-settling and continuous printing performance.

[0120] The differences are as follows:

[0121] (1) The protective particles are hollow glass microspheres (density 0.5 g / cm³). 3 D 50= 14 μm), modified with fluoropropyltriethoxysilane.

[0122] (2) The dosage is 0.8 wt%, and the remaining components are the same as in Example 1.

[0123] (3) The mesh size remains 325.

[0124] Comparative Example 1

[0125] This comparative example is the same as Example 1, with the only difference being:

[0126] After grading, flake pearlescent powder is obtained as D 50 = 18 μm (approximately 0.40 times the mesh opening size), D 50 = 30μm, the mass ratio remains 13∶3.

[0127] Comparative Example 2

[0128] This comparative example is the same as Example 1, except that the amount of protective particles is reduced from 0.8 wt% to 0.15 wt%.

[0129] All other conditions, shearing parameters, and maturation conditions are completely identical.

[0130] Comparative Example 3

[0131] This comparative example is based on Example 1, but without PFPE and comb-shaped leveling agent, and without adding any orientation-inducing aids.

[0132] The remaining formula ratios and operating conditions remain unchanged.

[0133] Comparative Example 4

[0134] Same as in Example 1, but the mass ratio of high-boiling-point to low-boiling-point solvents is changed to 3:1.

[0135] The remaining proportions remain unchanged.

[0136] Comparative Example 5

[0137] Based on Example 1, the ratio of flake pearlescent powder to white ink was adjusted to: 15 wt% pearlescent powder, 10 wt% white ink, and a wet film thickness of 25 μm.

[0138] Comparative Example 6

[0139] This comparative example adds 0.3 wt% polyurethane thickener to Example 1 to enhance the pseudoplasticity of the system.

[0140] Performance testing

[0141] The printing process used 325-mesh stainless steel wire (23 μm wire diameter, 45 μm effective opening), with a 65° squeegee angle, a printing speed of 100 mm / s, and a wet film thickness of 18 μm. The printing substrate was sized white decorative paper (80 g / m² basis weight). 2 ). Continuous printing 1500 times: no screen blockage or broken lines observed.

[0142] According to standard testing:

[0143] 1. Gloss testing was conducted according to GB / T9754-2007 "Paints and Varnishes - Determination of 20°, 60° and 85° Specular Gloss of Paint Films Without Metallic Pigments". A gloss meter with an incident angle of 60° was used, and the average value was taken from three points on the surface of the printed sample film under the conditions of 25°C and relative humidity (50±5)%.

[0144] 2. Color difference testing was conducted according to GB / T11186.3-1989 "Methods for measuring the color of coatings - Part 3: Calculation of color difference". An integrating sphere spectrophotometer (light source D65, observation angle 10°) was used. The sample film prepared on the day of preparation was used as the standard sample, and the sample film after 1500 consecutive printings was used as the test sample. The color difference ΔE* (CIEL*a*b*) was calculated.

[0145] 3. Adhesion test was conducted according to GB / T9286-2021 "Cross-cut test for paints and varnishes". One hundred 1mm×1mm squares were cut on the sample film surface using a six-blade cross-cut tester. After applying standard tape, it was peeled off evenly at a 90° angle. The paint film peeling was observed. An adhesion grade of 0 indicates that the paint film is firmly bonded to the paper base.

[0146] 4. Abrasion resistance testing was conducted according to GB / T1768-2006 "Determination of Abrasion Resistance of Paints and Varnishes - Rotating Rubber Grinding Wheel Method". A Taber rotating abrasion tester was used, with a CS-10 grinding wheel, a 500g load applied, and the mass loss and brightness change ΔL* were measured after 500 rotations.

[0147] 5. The surface drying time test was conducted in accordance with GB / T1728-2020 "Determination of Drying Time of Paint Film and Putty Film". The sample film was placed at 25℃ and relative humidity (50±5)%. The state of the paint film was checked every 1 minute using the light touch method. When the surface was no longer sticky to the touch and left without any marks, it was considered to be surface dry.

[0148] 6. The anti-tack test shall be conducted in accordance with GB / T1762-1980 "Determination of Tackiness of Coating Film". Two film samples shall be bonded together and left to stand for 24 hours at 25℃ and relative humidity (50±5)%. After that, they shall be peeled off and the presence of adhesion or surface contamination shall be checked.

[0149] The test results are as follows:

[0150] Table 1

[0151]

[0152] Table 2

[0153]

[0154] Experimental results show that when the bimodal particle size distribution of the flake pearlescent powder is properly matched, the pigment flakes can form a parallel orientation in the shear field, resulting in smooth flow through the screen and a uniform gloss and no accumulation in the printed film. If the particle size ratio is unbalanced, screen clogging, streaks, and local color differences are likely to occur. The particle size and dosage of the protective particles have a significant impact on the stability of the printing process. A reasonable protective structure can form a reversible support channel at the moment of printing, maintaining the open state of the screen and inhibiting the early aggregation of solids. However, insufficient or excessive addition will lead to flux fluctuations and film defects.

[0155] The synergistic effect of fluorinated block copolymers and comb-shaped polyether-polyester leveling agents is the key to the orientation locking and leveling stability of the system. The former forms a low-energy barrier at the pigment interface, promoting the alignment of flake pigments along the flow direction, while the latter balances stress through molecular chain reflux at the end of drying. The absence of either component will result in decreased gloss and scattered reflection direction.

[0156] The ratio of high- and low-boiling-point components in the solvent system controls the difference in evaporation rate and film formation rhythm. High-boiling-point solvents provide sufficient flow period to complete pigment orientation, while low-boiling-point solvents ensure a balanced surface tension gradient. Deviations in the ratio can easily lead to drying defects such as pinholes and edge shrinkage.

[0157] Rheological results show that the nonlinear response between the system viscosity and shear rate is in the range of 200–1500 s⁻¹. -1 The stability within the specified range indicates that the pigment paste exhibits good fluidity under high shear and can quickly recover its structure upon resting, ensuring consistent film thickness and controllable color difference after multiple printings. Through 1500 consecutive screen printing cycles and standard performance tests, the gloss of the example samples remained between 84 and 91 GU, the color difference was less than 1.0, the adhesion was grade 0, the abrasion resistance ΔL* was less than 0.6, and the surface drying time did not exceed 13 minutes. All samples showed no re-adhesion or screen clogging. The comparative samples showed significant performance degradation when any key parameter deviated, including uneven gloss, increased color difference, unstable flow, and continuous printing failures. The overall results demonstrate that this system, through the synergistic control of multiple parameters including structural scale, interfacial energy, and rheological behavior, achieves a balance between high metallic sheen, high opacity, and long-term stability in screen printing, significantly improving the problems of screen clogging, color difference accumulation, and uneven reflection in traditional metallic pearlescent pigment pastes during fine-screen printing.

[0158] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A color paste composition for screen printing, characterized in that, It consists of 40–60 wt% base ink, 10–20 wt% white ink, 5–15 wt% flake pearlescent powder, 0.3–1.2 wt% pore-protecting particles, and the balance solvent; wherein: a) The lamellar pearlescent powder has a bimodal diameter distribution, wherein the median volume diameter D of the first peak is... 50 The effective mesh opening size is 0.15 to 0.3 times that of the second peak, and the volume median diameter D is... 50 The effective mesh opening size is 0.5 to 0.8 times that of the mesh, and the mass ratio of the first peak to the second peak is 7 to 17:3; b) The protective particles are spherical silica or hollow glass microspheres, D 50 The particle size is 0.2 to 0.45 times the opening size of the printing screen and accounts for 0.3 to 1.2 wt% of the total mass of the pigment.

2. The screen printing paste composition according to claim 1, characterized in that, The color paste composition further includes an orientation induction aid, which comprises a combination of a fluorinated block copolymer and a comb-shaped polyether-polyester leveling agent, wherein the amount of the fluorinated block copolymer added is 0.1 to 0.4 wt%, and the amount of the comb-shaped polyether-polyester leveling agent added is 0.2 to 0.6 wt%.

3. The screen printing paste composition according to claim 2, characterized in that, The fluorinated block copolymer is a PFPE-acrylate block copolymer with a fluorine mass fraction of 15–25 wt% and a number-average molecular weight of 8 × 10⁻⁶. 3 ~2.0×10 4 The comb-shaped polyether-polyester leveling agent is a polyester-acrylate comb copolymer with a number-average molecular weight of 1.0 × 10⁻⁶. 4 ~3.0×10 4 Acid value ≤10 mg KOH / g.

4. The screen printing pigment composition according to claim 1, characterized in that, The solvent is a binary system consisting of a high-boiling-point component at 180–250°C and a low-boiling-point component at 80–150°C, with a mass ratio of high-boiling-point to low-boiling-point component of 5–6:

1.

5. The screen printing paste composition according to claim 1, characterized in that, The volume fraction of the flake pearlescent powder and the volume fraction of the white ink satisfy the following ratio range: within a wet film thickness range of 12–25 μm, the equivalent contrast ratio R is between 0.8 and 1.4, wherein... , n represents the volume fraction of the flake-shaped pearlescent powder. p For its refractive index, n m The refractive index of the matrix is... κ represents the volume fraction of white ink. s With σ s These are the absorption and scattering coefficients of white ink, respectively.

6. The screen printing pigment composition according to claim 1, characterized in that, The pigment system is subjected to a temperature of 20–30°C and a shear rate of 200–1500 s. -1 The apparent viscosity η within the range satisfies the shear response relationship: η=η0 / [1+(γ / γ0) m ], Where η0 is the zero-shear viscosity, γ is the shear rate, γ0 is the critical shear rate, and m is 1.0 to 1.

5.

7. The screen printing paste composition according to claim 6, characterized in that, The critical shear rate γ0 is 400–800 s. -1 The viscosity change rate Δη / η0 of the system within this rate range is 35%–55%.

8. The screen printing paste composition according to claim 1, characterized in that, The surface of the protective particles is modified with methylsilane or fluoropropylsilane.

9. The screen printing paste composition according to claim 1, characterized in that, The titanium dioxide in the white ink is rutile.

10. A method for preparing a screen printing pigment composition according to any one of claims 1 to 9, characterized in that, Includes the following steps: S1: Prepare flake-shaped pearlescent powder with bimodal particle size distribution according to the effective opening size of the selected screen. S2: Select spherical silica or hollow glass microspheres as pore-protecting particles, modify them with methylsilane or fluoropropylsilane, and then dry them for later use. S3: Dissolve fluorinated block copolymer and comb-shaped polyether-polyester leveling agent in a binary system composed of high-boiling-point and low-boiling-point solvents to form an orientation-inducing agent premix; S4: At 20–30°C, the flake pearlescent powder and pore-protecting particles are sequentially added to the orientation-inducing agent premix solution, using a segmented shearing method: the first stage has a low shear rate of 200–400 s. -1 Maintain for 3–5 minutes for wetting, then increase to 1000–1500 seconds in the second stage. -1 Maintain dispersion for 2–5 minutes, then reduce to 300–500 seconds in the third stage. -1 Maintain for 2 minutes to level and defoam, and obtain a uniform slurry; S5: Add base ink and white ink in three progressive steps to the obtained slurry, with the rheological viscosity change rate not exceeding 5% as the control condition; S6: Vacuum degassing is performed on the mixed color paste under an absolute pressure not exceeding 0.02 MPa. After filtration through a 200 μm wet sieve, the paste is allowed to stand for 12–24 hours to mature, thus obtaining the finished color paste.

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