Method for Manufacturing Silicone Ink with Improved Dispersion Stability and Printing Quality

Abstract

The present invention relates to a method for manufacturing silicone ink with improved dispersion stability and print quality. The method for manufacturing silicone ink according to the present invention comprises the steps of: mixing a pigment and a functional additive with a silicone base resin (S100); feeding the mixture into a three-roll mill controlled by a specific rotational speed ratio and roll gap to disperse it (S200); and stirring and degassing the dispersed mixture in a vacuum stirrer under specific stirring speed and high vacuum conditions (S300).

Description

Technology Field

[0001] The present invention relates to a method for manufacturing silicone ink, and more specifically, to a method for manufacturing silicone ink with improved long-term storage stability and print quality by uniformly dispersing a pigment in a high-viscosity silicone base resin and completely removing incorporated air bubbles. Background Technology

[0003] Silicone ink is widely used to print logos or patterns on surfaces such as textiles, clothing, leather, and various films due to its advantages, such as excellent heat resistance, weather resistance, flexibility, and harmlessness to the human body.

[0004] Generally, silicone ink is manufactured by mixing color-imparting pigments into a high-viscosity silicone-based resin. However, silicone-based resins have very high viscosity, which presents a problem in that it is difficult to uniformly disperse pigment particles.

[0005] Conventional methods using only a simple stirrer make it difficult to effectively break up pigment aggregates, resulting in uneven dispersion and large particle sizes. This lowers the color expression of the ink and causes the screen mesh to clog or the printed surface to become rough during printing. Furthermore, in inks with incomplete dispersion suffer from reduced storage stability, as pigments may settle again or layers may separate during long-term storage.

[0006] Meanwhile, a large amount of air is incorporated into the ink during the mixing process of high-viscosity raw materials. These residual bubbles, particularly microbubbles, cause surface defects such as pinholes after printing and curing, becoming a major cause of increased product defect rates.

[0007] Meanwhile, Korean Registered Patent No. 10-2481852 (published on December 28, 2022) discloses a manufacturing apparatus and method for precisely printing silicone brush pattern labels. The prior art focuses on the configuration of an apparatus that uniformly controls the tension of a screen printing plate, finely adjusts the printing position, and repeats printing and drying processes. However, this prior art focuses only on improving the mechanical precision of the printing apparatus to obtain high-quality printed materials, and fails to provide a concrete solution for securing the physical properties of the silicone ink itself, which fundamentally determines printing quality. Even when using a precision printing apparatus, if pigments are unevenly dispersed within the ink or microbubbles remain, problems such as color non-uniformity, surface roughness, and pinhole formation cannot be avoided.

[0008] Therefore, in order to maximize the quality of the final product, such as by improving pigment dispersibility, achieving vivid colors and excellent opacity, and completely eliminating microbubbles, there is an urgent need to develop a new technology capable of producing high-quality silicone ink that is fundamentally superior in pigment dispersibility and stability and is free of defects, starting from the stage before it is introduced into the printing process. The problem to be solved

[0010] The present invention aims to solve the problems of conventional technology by providing a silicone ink with excellent color expression and storage stability by maximizing the dispersibility of pigments and preventing re-aggregation.

[0011] In addition, the present invention aims to provide a method for manufacturing silicone ink that can effectively remove even microbubbles incorporated within the ink to form a high-quality printed film free from surface defects such as pinholes during printing. means of solving the problem

[0013] According to an embodiment of the present invention, a method for manufacturing a silicone ink comprising a silicone base resin, a pigment, and a functional additive comprises the steps of: mixing the pigment and the functional additive with the silicone base resin to prepare a mixture (S100); feeding the mixture into a three-roll mill to disperse it (S200); and feeding the dispersed mixture into a vacuum stirrer to stir and degas (S300).

[0014] Additionally, the above step (S200) utilizes a three-roll mill comprising a first rotating roll into which raw material is fed, a second rotating roll receiving raw material from the first rotating roll, and a third rotating roll receiving raw material from the second rotating roll, wherein the rotational speed ratio of the first rotating roll, the second rotating roll, and the third rotating roll is 1:2.5:8, and the gap between the second rotating roll and the third rotating roll may be 5 to 20 μm.

[0015] In addition, the above step (S300) preferably controls the rotational speed of the blade of the vacuum stirrer to 30 to 60 rpm and the orbital speed to 15 to 40 rpm, and maintains the vacuum level inside the stirring tank of the vacuum stirrer at -700 mmHg or lower.

[0016] In addition, the functional additive is characterized by comprising, with respect to 100 parts by weight of the silicone base resin, 1 to 5 parts by weight of a dispersion stabilizer selected from the group consisting of polyether-modified polysiloxane, polyester-modified polysiloxane, and alkyl-modified polysiloxane; and 0.5 to 3 parts by weight of a silane coupling agent having an organic functional group including an epoxy group, an amino group, or a vinyl group. Effects of the invention

[0018] According to the present invention, pigment coagulants can be finely and uniformly dispersed to the nanometer level through optimized three-roll mill process conditions, thereby improving the color expression, clarity, and hiding power of silicone ink.

[0019] In addition, the present invention can secure excellent storage stability by stabilizing the surface of dispersed pigment particles using a dispersion stabilizer having a specific chemical structure, thereby preventing precipitation or layer separation of the pigment even during long-term storage.

[0020] In addition, the present invention can remove even micro-sized bubbles incorporated into the ink through an optimized vacuum stirring and degassing process, thereby forming a smooth, uniform, high-quality printed film without surface defects such as pinholes after printing and curing. Brief explanation of the drawing

[0022] FIG. 1 is a flowchart of a method for manufacturing silicone ink according to one embodiment of the present invention. FIG. 2 is a schematic diagram of a three-roll mill used in a dispersion step according to one embodiment of the present invention. FIG. 3 is a schematic diagram of a vacuum stirrer used in the stirring and degassing step according to one embodiment of the present invention. FIG. 4 is a drawing for explaining the configuration of a stirring blade according to one embodiment of the present invention. FIG. 5 is a drawing illustrating a compression sealer for sealing and packaging silicone ink manufactured according to one embodiment of the present invention. Specific details for implementing the invention

[0023] The present invention is capable of various modifications and may take various forms, and embodiments (aspects or examples) are to be described in detail. However, this is not intended to limit the present invention to the specific disclosed forms, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0024] The terms used in this specification are used merely to describe specific embodiments (aspects or examples) and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, terms such as “comprising” or “consisting of” are intended to indicate the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0025] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application.

[0026] The terms "~1~," "~2~," etc., described in this specification are used merely to distinguish different components and are not bound by the order of manufacture; furthermore, the names may not match those in the detailed description of the invention and the claims.

[0027] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings.

[0028] FIG. 1 is a flowchart of a method for manufacturing silicone ink according to an embodiment of the present invention. As shown in FIG. 1, the method for manufacturing silicone ink according to the present invention is largely composed of a raw material mixing step (S100), a dispersion step (S200), and a stirring and degassing step (S300).

[0029] First, a preliminary mixture is prepared by adding pigments and functional additives to a silicone base resin. The silicone base resin may be an addition-curing or condensation-curing silicone oligomer or polymer, and preferably, it may be an addition-curing silicone resin with polydimethylsiloxane (PDMS) having vinyl groups at both ends of the molecule or at the side chains as the main component. At this time, considering the viscosity and physical properties of the ink, it is preferable to have a viscosity in the range of 10,000 to 1,000,000 cps (25°C).

[0030] Pigments are raw materials used to impart color to the ink, and commonly used inorganic or organic pigments, such as titanium dioxide (TiO2), carbon black, iron oxide, and organic phthalocyanine pigments, may be used. Functional additives may include dispersion stabilizers, silane coupling agents, etc.

[0031] In the raw material mixing step (S100), it is preferable to use a general stirrer such as a butterfly mixer or a disperser to mix each raw material at a low speed for 10 to 30 minutes so that it is uniformly mixed without lumps.

[0032] Next, the mixture prepared in the raw material mixing step (S100) is fed into a three-roll mill and dispersed. The dispersion step (S200) serves to finely crush pigment aggregates and uniformly disperse them within the silicone base resin.

[0033] FIG. 2 is a schematic diagram of a three-roll mill used in a dispersion step according to one embodiment of the present invention.

[0034] As shown in FIG. 2, the three-roll mill (10) may include a first rotating roll (11), a second rotating roll (12), a third rotating roll (13), and a scraper (14) that rotate in mesh with each other.

[0035] Generally, the first rotating roll (11) and the third rotating roll (13) rotate in the same direction, and the second rotating roll (12) located between them rotates in the opposite direction. As a result, contact points are formed between the first rotating roll (11) and the second rotating roll (12), and between the second rotating roll (12) and the third rotating roll (13), where raw materials are compressed and a strong shear force is generated.

[0036] The raw material is fed between the first rotating roll (11) and the second rotating roll (12), and is primarily dispersed by a strong transmission force generated by the difference in rotation direction and speed between the two rolls. The raw material that is primarily dispersed adheres to the surface of the second rotating roll (12), which has higher viscosity, and moves, and is secondarily dispersed by a higher shear force as it passes between the second rotating roll (12) and the third rotating roll (13). Finally, the finely dispersed raw material is collected by a scraper (14) on the surface of the third rotating roll (13).

[0037] In the present invention, the rotational speed ratio of each rotating roll is limited to achieve optimal dispersion efficiency. Preferably, the rotational speed ratio of the first, second, and third rotating rolls (11, 12, 13) is 1:2.5:8. This speed ratio is a critical condition for applying the most effective shear force to the mixture passing between the rolls. If the speed ratio is smaller than the optimal speed ratio (e.g., 1:2:4), the shear force is insufficient, so pigment aggregates cannot be effectively crushed and the degree of dispersion decreases. Conversely, if the speed ratio is excessively large (e.g., 1:3:10), excessive frictional heat is generated, which may cause localized deterioration of the high-viscosity silicone resin or an early curing reaction, thereby impairing the physical properties of the ink. Therefore, the optimal speed ratio (1:2.5:8) can simultaneously ensure maximum dispersion efficiency and the stability of the raw material.

[0038] Additionally, a gap can be set between the second rotating roll (12) and the third rotating roll (13). In this case, the gap is preferably 5 to 20 μm. This gap is an important factor in determining the size of the final dispersed particles. If the gap is too narrow, less than 5 μm, the high-viscosity mixture cannot pass through smoothly, causing an overload on the rolls, and the silicone polymer chains may be destroyed due to excessive shear stress, which may result in a decrease in the viscosity of the ink. On the other hand, if the gap exceeds 20 μm, the shear force is not sufficiently transmitted, so fine pigment aggregates cannot be crushed, making it difficult to obtain the desired level of dispersion, and the opacity and color clarity of the ink may decrease. Therefore, a gap of 5 to 20 μm is the optimal condition range for achieving the target particle size distribution while ensuring process stability.

[0039] Next, the mixture that has undergone the dispersion step (S200) is fed into a vacuum stirrer (20) and stirred.

[0040] and degassing. The stirring and degassing step (S300) serves to remove air that may have been reintroduced during the three-roll mill process and to stabilize the dispersed pigment particles so that they do not re-aggregate.

[0041] FIG. 3 is a schematic diagram of a vacuum stirrer used in the stirring and degassing step according to one embodiment of the present invention, and FIG. 4 is a diagram for explaining the configuration of a stirring blade according to one embodiment of the present invention.

[0042] As illustrated in FIGS. 3 and 4, the vacuum stirrer (20) may include a pressure indicator (21), an internal observation unit (22), a vacuum supply unit (23), a stirring blade (24), and a stirrer (25).

[0043] The stirring blade (24) comprises a pair of blades consisting of a blade coupling part (241), a vertical blade part (242), and a horizontal blade part (243), and it is preferable to use a planetary vacuum mixer in which the pair of blades each rotate while simultaneously orbiting around a central axis. This planetary stirring can uniformly mix the entire contents without any blind spots inside the stirring tank.

[0044] In the present invention, stirring conditions and vacuum levels can be controlled to achieve optimal degassing and stabilization effects. Preferably, the rotational speed of the stirring blade (24) is controlled to 30 to 60 rpm, and the orbital speed to 15 to 40 rpm. If the speed is slower than the range, the fluidity of the mixture is not sufficiently secured, making it difficult for microbubbles trapped inside to rise to the surface and burst. Additionally, the dispersed particles may gradually re-aggregate. Conversely, if the speed is faster than the range, the phenomenon of air being drawn back into the mixture by stirring occurs, which lowers the degassing efficiency and may generate unnecessary heat in the raw material due to excessive shearing.

[0045] In addition, it is desirable to maintain the vacuum level inside the stirring tank (25) at -700 mmHg or lower. If the vacuum level is higher than -700 mmHg, it is not possible to effectively expand and remove microbubbles of several tens of micrometers in size that are trapped inside the high-viscosity silicone matrix. Since these residual microbubbles are the main cause of pinhole defects in the final printed material, it is essential to maintain a high vacuum state of -700 mmHg or lower.

[0046] The functional additive used in the present invention is composed of a special composition to improve dispersion stability and adhesion. Preferably, the functional additive may comprise 1 to 5 parts by weight of a dispersion stabilizer and 0.5 to 3 parts by weight of a silane coupling agent per 100 parts by weight of a silicone base resin.

[0047] A dispersion stabilizer adsorbs to the surface of pigment particles and provides a steric hindrance effect, thereby preventing the dispersed particles from clumping together again and imparting long-term storage stability to the ink. In the present invention, it is preferable to use one or more selected from the group consisting of polyether-modified polysiloxane, polyester-modified polysiloxane, and alkyl-modified polysiloxane. The polysiloxane portion has excellent compatibility with the silicone-based resin, and the polyether, polyester, or alkyl portion has high affinity with the pigment surface, allowing for the formation of an effective stabilization layer. If the content of the dispersion stabilizer is less than 1 part by weight, the pigment particles cannot be sufficiently coated, resulting in a negligible effect on improving storage stability. On the other hand, if it exceeds 5 parts by weight, an excessive amount of additive may interfere with the curing reaction or seep into the surface of the cured film, causing stickiness or adverse effects such as reduced adhesion.

[0048] Silane coupling agents simultaneously possess hydrolyzable groups capable of reacting with silicone resin and organic functional groups capable of reacting with attachments within their molecules, thereby serving to strengthen the interfacial bonding force between the ink and the attachments. In the present invention, it is preferable to use a silane coupling agent having organic functional groups including epoxy groups, amino groups, or vinyl groups. If the content of the silane coupling agent is less than 0.5 parts by weight, the effect of improving adhesion to the attachments is insufficient, which may result in reduced washability or abrasion resistance. On the other hand, if it exceeds 3 parts by weight, the excess coupling agent may cause a self-condensation reaction within the ink, destabilizing physical properties or making the cured film too hard, thereby impairing flexibility.

[0049] Meanwhile, the method for manufacturing silicone ink according to the present invention may further include a step (S400) of sealing and packaging the high-quality silicone ink produced through a stirring and degassing step (S300).

[0050] FIG. 5 is a drawing illustrating a compression sealer for sealing and packaging silicone ink manufactured according to one embodiment of the present invention. As shown in FIG. 5, the compression sealer (30) may include a support member (31) that firmly fixes the equipment to the bottom surface, a press part (32) that lowers a pressing plate (33) by hydraulic pressure, and a pressing plate (33) that directly presses a drum cover.

[0051] Specifically, the press unit (32) may include a central press (321) that provides strong central pressure and a pair of sub-presses (322) that evenly distribute pressure. The operator places a drum cover on top of a drum (34) containing finished silicone ink, and then positions the drum under the pressing plate (33). Afterward, the press unit (32) is operated to press the drum cover strongly and evenly with the pressing plate (33), thereby perfectly sealing the drum (34) and the drum cover.

[0052] At this time, the pressing plate (33) can be replaced with various sizes to fit the specifications of the drum (34) to be packaged, and through this compression sealing step (S400), the silicone ink, which is in the best condition with microbubbles completely removed, is prevented from being contaminated by the external environment, thereby maintaining its initial quality until the end user uses it.

[0053] Preferred embodiments and comparative examples are presented below to aid in understanding the present invention; however, the following embodiments are for the purpose of explaining the present invention only, and the scope of the present invention is not limited thereby.

[0055] [Example 1] Optimal conditions according to the present invention

[0056] For every 100 parts by weight of silicone base resin (viscosity 50,000 cps), 15 parts by weight of pigment (carbon black), 3 parts by weight of dispersion stabilizer (polyether-modified polysiloxane), and 1.5 parts by weight of silane coupling agent (containing vinyl groups) were pre-mixed in a butterfly mixer for 20 minutes.

[0057] Afterwards, the mixture was fed into a three-roll mill (10) and dispersed, with the rotational speed ratio set to 1:2.5:8 and the gap between the second and third rotating rolls (12, 13) set to 10 μm, and passed through three times.

[0058] The dispersed mixture was fed into a planetary vacuum stirrer (20), and the final silicone ink was prepared by stirring and degassing for 30 minutes under conditions of a rotational speed of 45 rpm, an orbital speed of 30 rpm, and a vacuum of -750 mmHg.

[0059] [Comparative Example 1]

[0060] A silicone ink was prepared by keeping all conditions the same as in Example 1, except that the three-roll mill rotation speed ratio was changed to 1:2:4.

[0061] [Comparative Example 2]

[0062] A silicone ink was prepared by keeping all conditions the same as in Example 1, except that the gap between the second and third rotating rolls (12, 13) was changed to 30 μm.

[0063] [Comparative Example 3]

[0064] Silicone ink was prepared by keeping all conditions the same as in Example 1, except that the vacuum level of the vacuum stirrer (20) was changed to -600 mmHg.

[0065] [Comparative Example 4]

[0066] A silicone ink was prepared by keeping all conditions the same as in Example 1, except that the content of the dispersion stabilizer was changed to 0.5 parts by weight.

[0067] [Comparative Example 5]

[0068] A silicone ink was prepared by high-speed stirring for 2 hours using only a general disperse stirrer and without using a three-roll mill, using raw materials with the same composition as in Example 1.

[0069] [Experimental Example] Evaluation of Physical Properties of Manufactured Silicone Ink

[0070] The physical properties of each silicone ink prepared in Example 1 and Comparative Examples 1 to 5 were evaluated in the following manner, and the results are shown in Table 1 below.

[0071] 1) Dispersibility

[0072] The manufactured silicone ink was placed on a grind gauge to measure the particle size. Smaller particle sizes indicate better dispersibility.

[0073] 2) Surface appearance

[0074] The manufactured silicone ink was applied to a PET film to a thickness of 100 µm and cured at 130°C for 3 minutes, after which the occurrence of pinholes on the surface of the film was observed using a 50x magnification microscope. O means 'no pinholes at all', △ means 'many pinholes found', and X means 'pinholes occurring across the entire surface'.

[0075] 3) Storage stability

[0076] After storing the manufactured silicone ink in a 50°C oven for 4 weeks, the presence of pigment sedimentation at the bottom of the container and the phenomenon of layer separation of the ink were observed visually. O means 'no change at all', △ means 'layer separation or soft sedimentation occurred', and X means 'hard sedimentation occurred'.

[0077] division Dispersibility (particle size, μm) Surface appearance (presence of pinholes) Storage stability Example 1 5 or less O O Comparative Example 1 15 O △ Comparative Example 2 25 △ △ Comparative Example 3 10 X O Comparative Example 4 10 O X Comparative Example 5 40 or more X X

[0079] As shown in Table 1, Example 1, prepared under the conditions according to the present invention, showed excellent results in all items such as dispersibility, surface appearance, and storage stability.

[0080] On the other hand, Comparative Examples 1 and 2, in which the speed ratio and gap of the three-roll mill were outside the scope of the present invention, showed significantly reduced dispersibility, which led to a decrease in long-term storage stability. Comparative Example 3, in which the vacuum level was -600 mmHg, had incomplete removal of microbubbles, resulting in surface pinhole problems.

[0081] In addition, Comparative Example 4, which had insufficient dispersion stabilizer content, had good initial physical properties, but stability decreased as the pigment aggregated again during long-term storage. Furthermore, Comparative Example 5, which used a conventional method, showed significantly lower quality in all categories. Therefore, it can be seen that the optimal conditions and composition according to the present invention are conditions for manufacturing high-quality silicone ink.

[0083] The present invention, as described above with reference to the attached drawings, is susceptible to various modifications and alterations by a person skilled in the art, and such modifications and alterations not limited by the claims should be interpreted as being included within the scope of the rights of the present invention. Explanation of the symbols

[0085] 10 : Three-roll mill 11: 1st rotary roll 12: Second rotating roll 13: Third rotating roll 14 : Scraper 20 : Vacuum stirrer 21: Pressure indicator 22 : Internal observation section 23 : Vacuum supply unit 24: Stirring blade 241: Blade joint 242 : Vertical wing section 243: Horizontal wing section 25 : Stirring tank 30 : Press sealer 31 : Support member 32 : Press section 321 : Central Press 322 : Subpress 33 : Pressing plate 34 : Drums

Claims

Claim 1 A method for manufacturing a silicone ink comprising a silicone base resin, a pigment, and a functional additive, comprising the steps of: mixing the pigment and the functional additive with the silicone base resin to prepare a mixture (S100); and feeding the mixture into a three-roll mill to disperse it (S200). and the dispersed mixture is fed into a vacuum stirrer to be stirred and degassed (S300); wherein the step (S200) utilizes a three-roll mill comprising a first rotating roll into which raw materials are fed, a second rotating roll receiving raw materials from the first rotating roll, and a third rotating roll receiving raw materials from the second rotating roll, wherein the rotational speed ratio of the first rotating roll, the second rotating roll, and the third rotating roll is 1:2.5:8, and the gap between the second rotating roll and the third rotating roll is 5 to 20 μm, wherein the step (S300) controls the rotational speed of the blades of the vacuum stirrer to 30 to 60 rpm and the orbital speed to 15 to 40 rpm, and maintains the vacuum level inside the stirring tank of the vacuum stirrer at -700 mmHg or less, and wherein the functional additive comprises, with respect to 100 parts by weight of the silicone base resin, a polyether-modified polysiloxane, a polyester-modified polysiloxane, and an alkyl-modified A method for manufacturing silicone ink characterized by comprising: 1 to 5 parts by weight of a dispersion stabilizer selected from the group consisting of polysiloxanes; and 0.5 to 3 parts by weight of a silane coupling agent having an organic functional group including an epoxy group, an amino group, or a vinyl group. Claim 2 delete Claim 3 delete Claim 4 delete

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