A mirror-finish metallic screen printing ink for IMD injection molding and its preparation method

Abstract

This invention relates to the field of screen printing ink technology, specifically to an IMD injection molded mirror metallic screen printing ink and its preparation method. The ink is a two-component system: Component A contains a resin liquid composed of polyvinyl butyral, nitrocellulose, modified polyester resin, and polyarylate resin, flake aluminum silver powder, and additives; Component B is a phthalic diisocyanate polymer. Ethylene glycol monobutyl ether is the main solvent, ketones / esters / aromatic hydrocarbons are prohibited, and it has no corrosive effect on polycarbonate. The mass ratio of aluminum silver powder to resin solids is controlled at 0.6:1-1.2:1. The process involves preparing the resin liquid and dispersing the aluminum silver powder and additives, followed by degassing and filtration to obtain component A; before use, component B is pre-diluted with ethylene glycol monobutyl ether, added dropwise at a low shear rate of A:B = 100:8-12, and cured. The resulting ink exhibits high mirror gloss and clarity, high-temperature adhesion resistance, and MEK wiping resistance. Under IMD injection molding conditions, it demonstrates excellent consistency in appearance and structure, making it suitable for bright silver mirror-like decoration.

Description

Technical Field

[0001] This invention relates to the field of screen printing ink technology, specifically to an IMD injection molded mirror metallic screen printing ink and its preparation method. Background Technology

[0002] In-Mold Decoration (IMD) technology is an advanced process that involves placing a pre-printed decorative film (usually polycarbonate (PC) film) into an injection mold, and then injecting molten resin to integrally form the decorative layer with the plastic substrate. This technology not only enables high-precision decoration of complex three-dimensional shapes but also offers advantages such as wear resistance, weather resistance, and the elimination of the need for subsequent assembly. Therefore, it is widely used in consumer electronics, automotive interiors, home appliances, and medical equipment, becoming an important solution for high-end exterior decoration.

[0003] In the IMD (In-Mold Design) process, screen printing inks are used to form the pattern layer, directly determining the decorative performance and molding reliability of the final product. Especially during the injection molding stage, the processing temperature of engineering plastics such as molten polycarbonate (PC) reaches as high as 300-330℃, accompanied by high pressure and high flow rate injection, which often generates strong thermal-mechanical impact on the ink layer. If the ink lacks sufficient thermal stability and adhesion, it is very easy to cause failure problems such as ink splattering, cracking, oil spreading, or metallic pigment migration and delamination, which seriously affect the consistency and yield of IMD parts.

[0004] To achieve a metallic finish, aluminum powder is typically added to screen printing inks. However, in existing technologies, the silver powder tends to form a disordered arrangement in the resin system, resulting in chaotic reflection directions and only producing a matte metallic look, making it difficult to achieve a mirror-like reflection effect. Furthermore, a common method to improve the heat resistance of the ink layer is to introduce a highly cross-linked film-forming resin, but an excessively rigid structure can restrict pigment rearrangement, further impairing brightness and adhesion, and even causing problems such as brittleness and silver powder floating during the injection molding stage.

[0005] To achieve solubility and drying performance in existing systems, ketones, esters, or aromatic hydrocarbon solvents are often introduced. However, these solvents pose a significant risk of corrosion to PC substrates, potentially leading to stress cracking, decreased interfacial adhesion, and other failure risks. Therefore, maintaining the solubility, flowability, and printability of the ink system without using ketones, esters, or aromatic hydrocarbons is a major challenge in practical development.

[0006] In summary, existing IMD screen printing inks cannot simultaneously achieve the desired mirror-like reflective effect, high-temperature injection molding impact resistance, and compatibility with PC. There is an urgent need to develop a high-performance screen printing ink system that can maintain a mirror-like metallic texture under high-temperature injection molding conditions, possess structural stability, and pose no risk of corrosion to PC substrates. Summary of the Invention

[0007] This invention aims to overcome the technical defects of existing IMD mirror metallic screen printing inks, such as ink smudging, dull color, insufficient metallic feel, and decreased adhesion, which are prone to occur under high temperature injection molding conditions. It provides a screen printing ink with mirror reflection effect, excellent high temperature resistance and good compatibility with polycarbonate substrates, as well as its preparation method.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A mirror-finish metallic screen printing ink for IMD injection molding, comprising component A ink base, characterized in that the ink base comprises the following components:

[0010] The resin solution is composed of polyvinyl butyral and at least one other film-forming resin.

[0011] The solvent is ethylene glycol monobutyl ether as the main solvent, and the proportion of ethylene glycol monobutyl ether in the total mass of the solvent is not less than 70%; wherein, the solvent contained in the resin liquid is included in the total mass of the solvent; the solvent does not include ketones, esters or aromatic hydrocarbon solvents that have a significant corrosive effect on polycarbonate;

[0012] Flake-shaped aluminum silver powder with a median particle size of 5-10 micrometers (D50);

[0013] Additives, including one or more of fumed silica, dimethyl silicone oil and leveling agents.

[0014] Furthermore, the screen printing ink also includes a B component curing agent, which is mixed with the A component ink feed before use. The B component curing agent is an orthophthalic diisocyanate polymer (XDI), and the mass ratio of the added component is A component: B component = 100:(8-12).

[0015] Further, the resin liquid has the following mass percentage composition: 5.0%-8.0% polyvinyl butyral, 0.5%-2.0% nitrocellulose, 1.0%-3.0% modified polyester resin, and 2.0%-5.0% polyarylate resin, with the sum of the mass percentages of the above resins being 8%-15%, and the balance being ethylene glycol monobutyl ether.

[0016] Furthermore, the mass percentages of the ink base component A are as follows: resin liquid 85.0%-92.0%, flake aluminum silver powder 8.0%-12.0%, fumed silica 0.3%-0.6%, dimethyl silicone oil 0.1%-0.3%, and leveling agent 0.1%-0.3%, with the total mass percentage of the above components being 100%.

[0017] Furthermore, the mass percentage of the polyvinyl butyral ester in the resin solids is not less than 50%, and the mass ratio of the flake aluminum powder to the resin solids is 0.6:1-1.2:1.

[0018] Furthermore, the resin liquid can maintain its structural integrity at an injection molding temperature of 300℃-330℃, and there are no ink spillage, cracking, or oil spreading phenomena. The rotational viscosity of the resin liquid at 25℃ is 2000-4000 centipoise, and the rotational viscosity of the final ink at 25℃ is 3000-5000 centipoise.

[0019] Furthermore, the phthalic diisocyanate polymer is the only curing agent used; or, when used in conjunction with other curing agents, the mass proportion of the phthalic diisocyanate polymer is not less than 50% based on the active components of all curing agents.

[0020] This invention also proposes a method for preparing mirror metallic screen printing ink for IMD injection molding, characterized by comprising the following steps:

[0021] S1. Preparation of resin solution: Add ethylene glycol monobutyl ether to a stirring container, control the speed at 500-800 rpm, add polyvinyl butyral ester, nitrocellulose, modified polyester resin and polyarylate resin in sequence, stir continuously for 120 minutes, and then filter using a filter bag with a filtration accuracy of not less than 420 mesh / inch to obtain resin solution.

[0022] S2. Preparation of ink base material: Add flake aluminum silver powder, fumed silica, dimethyl silicone oil and leveling agent to the resin liquid, stir for 60 minutes to obtain a uniformly dispersed ink base material;

[0023] S3. Filtration and Packaging: After the ink base material is allowed to stand and degas, it is filtered through a filter bag with a mesh size of not less than 350 mesh / inch and packaged as component A ink base material without curing agent.

[0024] This invention also proposes a method for using mirror metallic screen printing ink in IMD injection molding, comprising the following steps:

[0025] U1. Before use, add the phthalic diisocyanate polymer as component B to the ink base of component A. The mass ratio of A to B is 100:(8-12).

[0026] U2. Stir at a low shear rate of no more than 150 rpm at 25℃ and let stand for 60-90 minutes to mature.

[0027] U3. After the filtration accuracy is not less than 350 mesh / inch, screen printing is performed, followed by polycarbonate IMD injection molding.

[0028] Furthermore, the phthalic diisocyanate polymer is pre-diluted with ethylene glycol monobutyl ether at a mass ratio of 1:1 to 1:3 before being added to form a mother liquor, which is then slowly added to the ink base by dripping.

[0029] The present invention has the following beneficial effects:

[0030] (1) Achieving a high-brightness mirror-like metallic appearance: By controlling the particle size of the flake aluminum silver powder and the solid content of the resin, the silver powder is arranged in an orderly and oriented manner after the ink film is dried, which significantly improves the consistency of light reflection and the mirror strength, and obtains a mirror-like bright silver effect, overcoming the problem of heavy particle texture and dull reflection of traditional silver ink.

[0031] (2) Excellent heat resistance and impact resistance under injection molding conditions: The main resin is polyvinyl butyral, which is supplemented with polyarylate and XDI crosslinking curing agent to form a high thermal stability network structure. It can withstand the high temperature and high pressure injection impact of polycarbonate melt at 300-330℃ during the IMD injection molding process. The ink layer does not experience ink flushing, cracking or oil spreading, and the molding stability is significantly improved.

[0032] (3) Highly compatible with PC sheets and strong adhesion: The solvent system is mainly composed of ethylene glycol monobutyl ether (≥70%), completely avoiding the use of ketone, ester or aromatic hydrocarbon solvents that pose a risk of stress cracking to PC, effectively protecting the PC film substrate and improving the adhesion stability of the ink layer.

[0033] (4) Excellent pigment dispersibility and film fineness: Flake-shaped aluminum silver powder with a D50 median particle size of 5-10 micrometers is selected.

[0034] In conjunction with additives such as fumed silica, dimethyl silicone oil, and leveling agents, it effectively promotes the stable dispersion and directional arrangement of pigments in the system, significantly reduces the graininess, and makes the film layer uniform and delicate with a high degree of consistency in decorative effect.

[0035] (5) Optimize screen printing suitability and process adaptability: control the viscosity of resin liquid and final ink at 2000-4000 centipoise and 3000-5000 centipoise (25℃) respectively. This viscosity range matches the requirements of screen printing process well, and has excellent leveling, squeegeeing and interlayer bonding, meeting the dual needs of industrial printing for efficiency and quality.

[0036] (6) Controllable process and stable quality: XDI is added by pre-dilution and dripping, combined with low-speed stirring and maturation, which effectively avoids uneven local cross-linking, residual bubbles or printing deviations, improves batch consistency, and facilitates factory-level production control and storage management. Attached Figure Description

[0037] Figure 1 This is a schematic diagram showing the composition and relationship between the A and B components of the ink of this invention;

[0038] Figure 2 This is a schematic diagram of the ink preparation and application process of the present invention;

[0039] Figure 3 A schematic diagram comparing the effects of ethylene glycol monobutyl ether and ketone solvents on the interface of PC substrates;

[0040] Figure 4 This is a schematic diagram of the mirror-like metallic appearance after ink printing in Example 1;

[0041] Figure 5 This is a comparison chart of different samples in terms of key performance indicators. Detailed Implementation

[0042] To facilitate understanding and implementation of the present invention by those skilled in the art, the present invention will be further described below in conjunction with the accompanying drawings and embodiments. The following embodiments are used to illustrate the present invention and do not constitute a limitation on the scope defined by the claims. Any equivalent substitutions or modifications made without departing from the spirit of the present invention should be considered to fall within the protection scope of the present invention.

[0043] Example 1

[0044] This embodiment provides a mirror-metallic screen printing ink for IMD injection molding, the specific composition of which is as follows:

[0045] The screen printing ink is a two-component system, comprising a pre-prepared A-component ink base and a B-component crosslinking curing agent added before use.

[0046] Component A of the ink base contains resin liquid, metallic pigments, and additives.

[0047] The resin solution is composed of polyvinyl butyral, nitrocellulose, modified polyester resin, and polyarylate resin. The mass percentages of polyvinyl butyral are 6.5%, nitrocellulose 1.0%, modified polyester resin 1.5%, and polyarylate resin 4.0%. Ethylene glycol monobutyl ether is the sole solvent used, comprising 87.0% of the total mass. The solids content of this resin solution system is 13%, and its rotational viscosity at 25°C is approximately 3100 centipoise. Ethylene glycol monobutyl ether constitutes 100% of the total solvent mass, and the system contains no ketones, esters, or aromatic hydrocarbon solvents.

[0048] The metallic pigment selected is flake-shaped aluminum silver powder with a D50 median particle size of 5-10 micrometers, and its addition amount is [amount missing]% of the total mass of component A.

[0049] 10.0%. Calculated based on resin solids, the mass ratio of aluminum silver powder to resin solids is approximately 0.77:1, which is beneficial for forming a mirror effect.

[0050] The additives include fumed silica, dimethyl silicone oil, and leveling agents, added at amounts of 0.5%, 0.2%, and 0.2%, respectively. These additives work together to improve the dispersibility, surface uniformity, and structural stability of the ink.

[0051] Based on component A, its composition is as follows: 89.1% resin liquid, 10.0% flake aluminum silver powder, 0.5% fumed silica, 0.2% dimethyl silicone oil, and 0.2% leveling agent, totaling 100%.

[0052] The crosslinking curing agent for component B is phthalic diisocyanate polymer (XDI), which is added to component A at a mass ratio of A:B=100:10 before printing. No other crosslinking agents are used in this embodiment; XDI is the only curing agent.

[0053] The preparation method of component A ink base includes the following steps:

[0054] S1. Preparation of Resin Solution: Ethylene glycol monobutyl ether was added to a stainless steel stirred tank equipped with a condenser. Stirring was started and the speed was controlled at 600 rpm. After a stable vortex formed on the liquid surface, polyvinyl butyral, nitrocellulose, modified polyester resin, and polyarylate resin were added sequentially. Stirring was continued for 120 minutes to ensure the resin was fully dissolved, forming a transparent and homogeneous resin solution. The resin solution was filtered using a filter bag with a filtration precision of 420 mesh / inch. The resulting liquid exhibited good flowability and film-forming properties.

[0055] S2. Preparation of Ink Base Material: Measure the above resin solution and add flake aluminum silver powder, fumed silica, dimethyl silicone oil, and leveling agent sequentially. Maintain a stirring speed of 700 rpm and continue stirring for 60 minutes until the ink is evenly dispersed, has a fine texture without particles, and the viscosity tends to stabilize. The resulting ink base material has a rotational viscosity of approximately 3900 centipoise at 25°C, which meets the viscosity range required for screen printing.

[0056] S3. Filtration and Packaging: After the ink base material is allowed to stand and degas, it is filtered through a filter bag with a mesh size of not less than 350 mesh / inch, and then packaged and sealed to obtain component A ink base material.

[0057] The usage of screen printing ink is as follows:

[0058] Addition of U1 and B component curing agents: Pre-dilute the phthalic diisocyanate polymer (XDI) and ethylene glycol monobutyl ether at a mass ratio of 1:2 to prepare a crosslinking agent stock solution. Before use, slowly add it dropwise to the ink base of component A at a ratio of component A: component B = 100:10.

[0059] U2. Mixing and Curing: At 25℃, stir with low shear at a speed not exceeding 150 rpm to fully disperse the crosslinking agent. After stirring evenly, let it stand for 60-90 minutes to complete degassing and crosslinking pre-reaction. Final ink viscosity

[0060] It is approximately 4200 centipoise at 25°C.

[0061] U3. Filtration and Printing: After the cured ink is filtered through a filter bag with a filtration precision of no less than 350 mesh / inch, it can be used for screen printing. Use a 250-300 mesh screen to print on the surface of PC sheet, and after drying, perform IMD injection molding.

[0062] After screen printing on PC sheets, the ink forms a uniform and dense mirror-like ink layer with a good metallic luster. After injection molding at 310℃, the ink layer did not exhibit defects such as ink bleeding or cracking, demonstrating excellent adhesion and a stable and consistent overall appearance.

[0063] Example 2

[0064] This embodiment provides a mirror-metallic screen printing ink for IMD injection molding, the composition of which is as follows:

[0065] The screen printing ink is a two-component system, comprising a pre-prepared A-component ink base and a B-component crosslinking curing agent added before use.

[0066] Component A of the ink base contains resin liquid, metallic pigments, and additives.

[0067] The resin solution is composed of polyvinyl butyral, nitrocellulose, modified polyester resin, and polyarylate resin. Polyvinyl butyral accounts for 5.0% by mass, nitrocellulose 0.5%, modified polyester resin 1.0%, and polyarylate resin 2.0%. These four resins together account for 8.5% of the total mass of the resin solution. Ethylene glycol monobutyl ether, as the sole solvent, accounts for 91.5% by mass. This resin solution contains no ketones, esters, or aromatic hydrocarbon solvents, and its rotational viscosity at 25°C is approximately 2000 centipoise.

[0068] The metallic pigment selected is flake-shaped aluminum silver powder with a D50 median particle size of 5-10 micrometers, and its addition amount is [amount missing]% of the total mass of component A.

[0069] 8.0%. Calculated based on resin solids, the mass ratio of aluminum silver powder to resin solids is 0.94:1, which is beneficial for specular reflection alignment.

[0070] The additives include fumed silica, dimethyl silicone oil, and leveling agent, added at amounts of 0.3%, 0.1%, and 0.1%, respectively. These three components work synergistically to improve the ink's dispersion stability, coating uniformity, and screen printing suitability.

[0071] Based on component A, its composition is as follows: 91.5% resin liquid, 8.0% flake aluminum silver powder, 0.3% fumed silica, 0.1% dimethyl silicone oil, and 0.1% leveling agent, with the sum of the mass percentages of each component being 100%.

[0072] The crosslinking curing agent for component B is phthalic diisocyanate polymer (XDI), which is added to component A at a mass ratio of A:B = 100:8 before use. No other crosslinking agents were used in this embodiment; XDI was the only curing agent used in component B.

[0073] The preparation method of component A ink base includes the following steps:

[0074] S1. Preparation of Resin Solution: Ethylene glycol monobutyl ether was added to a stainless steel stirred tank equipped with a condenser, and the stirring speed was controlled at 600 rpm. Polyvinyl butyral, nitrocellulose, modified polyester resin, and polyarylate resin were added sequentially, and the mixture was stirred continuously for 120 minutes until the resin was fully dissolved, forming a transparent and homogeneous resin solution. The solution was filtered using a 420 mesh / inch filter bag to obtain a clear and impurity-free resin solution.

[0075] S2. Preparation of Ink Base Material: Measure the above resin solution and add flake aluminum silver powder, fumed silica, dimethyl silicone oil, and leveling agent sequentially. Maintain a stirring speed of 700 rpm and continue stirring for 60 minutes until the system is homogeneous, has a fine texture, and is free of visible particles. The resulting ink base material has a rotational viscosity of approximately 3000 centipoise at 25°C.

[0076] S3. Filtration and Packaging: After the ink base material is allowed to stand and degas, it is filtered using a 350 mesh / inch filter bag to remove potential gel or large particle impurities, and then packaged and sealed to obtain component A ink base material.

[0077] The usage of screen printing ink is as follows:

[0078] Addition of Curing Agents for Components U1 and B: Pre-dilute phthalic diisocyanate polymer (XDI) and ethylene glycol monobutyl ether at a mass ratio of 1:3 to prepare a crosslinking agent stock solution. Before use, slowly add the stock solution dropwise to the ink base of Component A at a ratio of Component A:Component B = 100:8.

[0079] U2. Mixing and Curing: At 25°C, perform low-shear stirring at a speed not exceeding 150 rpm to ensure thorough and uniform dispersion of the crosslinking agent. After stirring, allow to stand for 60 minutes to complete the degassing and crosslinking pre-reaction process. The final ink rotational viscosity at 25°C is approximately 3200 centipoise.

[0080] U3. Filtration and Printing: After the ink has matured, it is filtered through a filter bag with a filtration precision of at least 350 mesh / inch before it can be used for screen printing. Using a 250-300 mesh screen, the ink is printed onto the surface of the PC sheet. After drying, the IMD injection molding process is performed at an injection temperature of 310℃.

[0081] After printing, the ink forms a dense and uniform mirror-like metallic layer with a bright, smooth surface and a strong metallic texture. After high-temperature injection molding, the ink layer exhibits excellent adhesion, with no ink bleeding, loss of gloss, cracking, or oil spreading, meeting the high reliability requirements of IMD mirror-like silver decoration.

[0082] Example 3

[0083] This embodiment provides a mirror-metallic screen printing ink for IMD injection molding, the composition of which is as follows:

[0084] The screen printing ink is a two-component system, comprising a pre-prepared A-component ink base and a B-component crosslinking curing agent added before use.

[0085] Component A of the ink base contains resin liquid, metallic pigments, and additives.

[0086] The resin solution is composed of polyvinyl butyral, nitrocellulose, modified polyester resin, and polyarylate resin. Polyvinyl butyral accounts for 8.0% by mass, nitrocellulose 2.0%, modified polyester resin 3.0%, and polyarylate resin 2.0%. These four resins together account for 15.0% of the total mass of the resin solution. Ethylene glycol monobutyl ether, as the sole solvent, accounts for 85.0% by mass. This resin solution does not contain any ketones, esters, or aromatic hydrocarbon solvents, and its rotational viscosity at 25°C is approximately 4000 centipoise.

[0087] The metallic pigment selected is flake-shaped aluminum silver powder with a D50 median particle size of 5-10 micrometers, and its addition amount is [amount missing]% of the total mass of component A.

[0088] 12.0%. Calculated based on resin solids, the mass ratio of aluminum silver powder to resin solids is 0.80:1, which helps to improve the orderliness of reflection and enhance the metallic texture of the mirror.

[0089] The additives include fumed silica, dimethyl silicone oil, and leveling agent, added at amounts of 0.6%, 0.3%, and 0.3%, respectively. The three work synergistically to significantly improve the ink's dispersion stability, leveling, and surface uniformity.

[0090] Based on component A, its composition is as follows: 86.8% resin liquid, 12.0% flake aluminum silver powder, 0.6% fumed silica, 0.3% dimethyl silicone oil, and 0.3% leveling agent, with the sum of the mass percentages of each component being 100%.

[0091] The crosslinking curing agent for component B is phthalic diisocyanate polymer (XDI), which is added to component A at a mass ratio of A:B=100:12 before use. No other type of curing agent was used in this embodiment.

[0092] The preparation method of component A ink base includes the following steps:

[0093] S1. Preparation of Resin Solution: Ethylene glycol monobutyl ether was added to a stainless steel stirred tank equipped with a condenser, and the stirring speed was controlled at 600 rpm. Polyvinyl butyral, nitrocellulose, modified polyester resin, and polyarylate resin were added sequentially, and the mixture was stirred continuously for 120 minutes until the resin was fully dissolved. The solution was filtered through a 420 mesh / inch filter bag to obtain a uniform and transparent resin solution.

[0094] S2. Preparation of ink base: Measure the above resin solution and add flake aluminum silver powder, fumed silica, dimethyl silicone oil, and leveling agent sequentially. Maintain a stirring speed of 700 rpm and continue stirring for 60 minutes to obtain a uniformly dispersed ink base. The rotational viscosity of this base at 25°C is approximately 4950 centipoise.

[0095] S3. Filtration and Packaging: After the ink base material is allowed to stand and degas, it is filtered using a 350 mesh / inch filter bag, and then packaged and sealed to obtain component A ink base material.

[0096] The usage of screen printing ink is as follows:

[0097] Addition of Curing Agents for Components U1 and B: Pre-dilute the phthalic diisocyanate polymer (XDI) and ethylene glycol monobutyl ether at a mass ratio of 1:1 to prepare a crosslinking agent stock solution. Before use, slowly add this stock solution dropwise to the ink base of Component A at a ratio of Component A:Component B = 100:12.

[0098] U2. Mixing and Curing: At 25°C, perform low-shear stirring at a speed not exceeding 150 rpm. After thorough mixing, allow to stand for 90 minutes to complete the degassing and crosslinking pre-reaction process. The final ink rotational viscosity at 25°C is approximately 5000 centipoise.

[0099] U3. Filtration and Printing: After the ink has matured, it is filtered through a filter bag with a filtration precision of not less than 350 mesh / inch before being used for screen printing. The ink is printed onto the surface of the PC sheet using a 250-300 mesh screen. After drying, it is subjected to IMD injection molding at a temperature of 310℃.

[0100] When printed on PC sheets, this ink forms a smooth, bright, mirror-like metallic layer with uniform reflection and a texture close to that of mirror silver. During IMD injection molding, the ink layer structure remains stable, without ink bleeding, cracking, loss of gloss, or oil spreading, demonstrating excellent adhesion and decorative consistency.

[0101] Comparative Example 1

[0102] This comparative example provides a screen printing ink whose ink base composition is consistent with that of Example 1. Both inks contain polyvinyl butyral, nitrocellulose, modified polyester resin, and polyarylate resin as film-forming resins, ethylene glycol monobutyl ether as a solvent, flake aluminum silver powder as a metallic pigment, and auxiliary components. The ink was not cross-linked with phthalic acid diisocyanate polymer before use, nor was it pre-diluted or cured.

[0103] Comparative Example 2

[0104] This comparative example provides a screen printing ink with the following specific formulation: 5.0% polyvinyl butyral, 0.5% nitrocellulose, 1.0% modified polyester resin, and 1.5% polyarylate resin. The sum of the mass percentages of the film-forming resins is 8.0%, and the remainder is ethylene glycol monobutyl ether, accounting for 92.0%.

[0105] Comparative Example 3

[0106] This comparative example provides a screen printing ink with the same formulation as Example 1, except that the mass ratio of ethylene glycol monobutyl ether in the solvent system is 60.0%, and the remaining 40.0% is replaced with methyl ethyl ketone solvent.

[0107] Comparative Example 4

[0108] This comparative example provides a screen printing ink with the same formulation as Example 1, except that the mass ratio of ethylene glycol monobutyl ether in the solvent system is 65.0%, and the remaining 35.0% is replaced with dipropylene glycol monobutyl ether.

[0109] Comparative Example 5

[0110] This comparative example provides a screen printing ink in which the mass percentage of the film-forming resin is 30.0% polyvinyl butyral, with the remainder being modified polyester resin, nitrocellulose, and polyarylate resin. The ethylene glycol monobutyl ether, flake aluminum powder, and additives in the formulation are the same as in Example 1.

[0111] Comparative Example 6

[0112] This comparative example provides a screen printing ink in which the mass percentages of each film-forming resin in the resin solution are as follows: 7.5% polyvinyl butyral, 1.0% nitrocellulose, 1.5% modified polyester resin, 0% polyarylate resin, and the remainder is ethylene glycol monobutyl ether, accounting for 90.0%.

[0113] Comparative Example 7

[0114] This comparative example provides a method for preparing mirror metallic screen printing ink. The screen printing ink formulation is the same as in Example 1, but the following key process differences exist:

[0115] 1) The phthalic diisocyanate polymer and ethylene glycol monobutyl ether were not pre-diluted in the correct proportion before being added directly to the ink;

[0116] 2) Increase the stirring speed to 1000 rpm during the stirring process;

[0117] 3) The ink body standing and defoaming time is shortened to 10 minutes;

[0118] 4) Only filter bags with a filtration accuracy of 200 mesh / inch are used for filtration.

[0119] To verify the effects of the formulation structure and preparation process of the screen printing ink of this invention on film-forming properties, high-temperature injection molding stability, and mirror decoration effect, the following experimental scheme was formulated:

[0120] Samples were prepared according to Examples 1-3 and Comparative Examples 1-7, for a total of 10 groups. Each group of samples required at least: ≥3 printed sheets for appearance and routine performance testing; and ≥2 IMD injection molded parts for post-injection evaluation and control. Except for the variable under investigation, all other formulations and process conditions were consistent with Example 1 (including the use of the same batch of substrate, the same screen printing plate, and consistent drying and injection molding parameters).

[0121] (1) Experimental materials and equipment

[0122] Substrate: PC sheet;

[0123] Screening and filtration: 280-300 mesh / inch screen; resin liquid filtration uses 420 mesh / inch filter bags; finished ink filtration uses filter bags with a mesh size of not less than 350 mesh / inch.

[0124] Main equipment: NDJ-8S rotational viscometer (with thermostat), 60° gloss meter, DOI tester, cross-cut tester and tape, pencil hardness tester, MEK double-scratch tester, microscope, constant temperature and humidity chamber, injection molding machine and matching IMD mold.

[0125] (2) Sample preparation and pretreatment

[0126] Preparation of ink base material for component A: The ink base material for each group of samples was prepared according to the steps S1-S3 described in the examples and comparative examples.

[0127] Component B should be mixed before use (only for sample groups involving Component B):

[0128] For samples containing phthalic acid diisocyanate polymer as component B curing agent, component B is added to component A at a predetermined mass ratio and at 25°C before screen printing:

[0129] The phthalic diisocyanate polymer (XDI) should be pre-diluted with ethylene glycol monobutyl ether at a mass ratio of 1:1 to 1:3; it should be slowly added to the ink component A by dropwise addition, mixed with low shear stirring, and allowed to mature and stand for 60-90 minutes before use; the final ink must be filtered through a filter bag of not less than 350 mesh / inch before printing.

[0130] Screen printing: Environmental conditions are 23±2℃ and relative humidity is 50±5%; uniform screen and squeegee parameters; target dry film thickness is controlled at 10±2μm.

[0131] Drying and maturation: The medium-low temperature drying process was set according to the example, and then the product was allowed to stand and mature at room temperature after completion.

[0132] IMD molding: The qualified sheet material after screen printing is loaded into the IMD mold and injection molded.

[0133] (3) Test items and methods

[0134] Rheological properties: Resin viscosity: Measured at 25℃, with appropriate rotor and speed selected to ensure the instrument torque is within the range of 10%-90%, and the viscosity value is recorded; Final ink viscosity: Measured at 25℃, and the viscosity value is recorded.

[0135] Appearance and mirror performance: 60° gloss: 5 points were randomly selected for measurement, the average value was taken, and the minimum and average values ​​were recorded at the same time; DOI: 5 points were randomly selected for measurement, the average value was taken, and the haze was recorded at the same time; Microscopic observation: Defects such as particles, flow marks, haze, pinholes, shrinkage spots, and mirror cracks were inspected under 10x magnification.

[0136] Film formation and interface properties: Adhesion: Using the cross-cut adhesion test with a blade spacing of 1mm, the tape is pulled up at a 180° angle, and the grade is recorded (grade 0 is the best); Pencil hardness: Under a load of 500g, tests are conducted from 6B to 9H, and the grade that leads to film failure is recorded; Solvent resistance: Using the MEK double rub test, the test is conducted at the specified load and speed, and the number of back-and-forth rubs before failure is recorded, or the set threshold is reached (e.g., ≥100 times is considered qualified).

[0137] IMD molding adaptability: Observe and record whether phenomena such as ink splashing, oil spreading, warping, cracking, bottom biting, loss of gloss, and delamination occur during and after injection molding.

[0138] (4) IMD injection molding conditions

[0139] Melt temperature: 310℃ for PC material; Mold temperature: 80±5℃; Injection method: medium injection speed; Initial injection pressure: 40%-60% of the equipment's rated pressure; Holding time: 8-12s, holding pressure: 40%-60% of the peak injection pressure; Cooling time: 8-12s before normal demolding.

[0140] All samples in all groups were subjected to the same injection molding settings. When fine adjustments were needed to ensure stable mold filling, the adjustment range should not exceed ±10%. The test results are shown in Tables 1 and 2.

[0141] Table 1 Comparison of viscosity and optical properties of different ink samples

[0142]

[0143] Note: DOI is the resolution index; all viscosities are rotational viscosities; sampling was random, with an ambient temperature of 23±2℃ and relative humidity of 50±5%.

[0144] Table 2. Adhesion and molding adaptability analysis results of different ink samples

[0145]

[0146] Note: "0 is the best" for the cross-cut test; "MEK double rub" is the round-trip count; "IMD appearance" is a description of the main defects after molding.

[0147] Based on the experimental observations and the analysis of the data in the table, the comprehensive comparison of each sample in terms of key indicators is as follows:

[0148] The inks prepared in Examples 1 to 3 all exhibited excellent overall performance, with final viscosities falling within the target window of 3000 to 5000 centipoise. They maintained high levels of 60° gloss and DOI value, achieved a cross-cut adhesion rating of 0, and demonstrated a MEK double-rub cycle count of at least 118. After IMD injection molding, the inks showed a complete and defect-free appearance. Examples 2 and 3 represent the lower and upper limits of this performance range, respectively, and still meet all technical specifications. Furthermore, the two-component system, consisting of ethylene glycol monobutyl ether as the main solvent (comprising at least 70% of the total solvent mass) and component B curing agent added before use, is a fundamental prerequisite for achieving a stable mirror-like metallic effect and consistent injection molding.

[0149] In contrast, each comparative example exhibited varying degrees of performance defects due to certain technical features exceeding the specified limits. For instance, although Comparative Example 1, which did not contain a crosslinking curing agent, had acceptable viscosity, its MEK double-rub count was significantly reduced, its adhesion dropped to level 2, and it showed oil dispersion and cracking after IMD injection molding. This indicates that the crosslinking network plays a crucial role in the heat resistance, solvent resistance, and interfacial stability of the ink.

[0150] In Comparative Example 2, the mass ratio of aluminum silver powder to resin solids was increased to 1.25:1, which exceeds the 0.6 to 1.2 range of this invention, resulting in a significant decrease in gloss and DOI value, as well as the appearance of graininess and shrinkage spots; this indicates that excessive flake metallic pigments will exceed the coating and orientation capabilities of the film-forming resin.

[0151] Comparative Example 3, which used ketone solvents, performed the worst, with the lowest gloss and DOI values ​​among all groups. It also exhibited significant undercut and cracking after IMD injection molding. The root cause lies in the significant erosive effect of ketone solvents on polycarbonate, which disrupts the wetting uniformity and surface smoothness of the resin-substrate interface. This directly interferes with the orderly "flattening" arrangement of the flake aluminum powder during film formation, thus significantly weakening the specular reflection effect. Therefore, the solvent system must be limited to ethylene glycol monobutyl ether as the main solvent and must not contain ketones, esters, or aromatic hydrocarbons.

[0152] Comparative Example 4 reduced the proportion of ethylene glycol monobutyl ether in the solvent to below 70%. The optical performance indicators were close to the critical value, and fogging and flow marks appeared after IMD injection molding. This indicates that insufficient proportion of main solvent will cause abnormal drying gradient and uneven pigment orientation, which verifies the rationality of the proportion of ethylene glycol monobutyl ether.

[0153] Comparative Example 5 reduced the proportion of polyvinyl butyral in the resin solids to below 50%, resulting in decreased adhesion and solvent resistance. After IMD injection molding, warping and microcracks appeared, indicating that the main film-forming resin plays an irreplaceable role in forming a continuous phase and a heat-resistant skeleton.

[0154] Comparative Example 6 is a formulation without polyarylate resin. The conventional indicators at room temperature are still at a moderate level, but after IMD injection molding, failure characteristics such as delamination and melted edges appear, indicating that polyarylate resin has a significant effect on improving the structural stability and pattern integrity of the ink layer under high temperature and high pressure injection molding conditions of 300-330℃.

[0155] Comparative Example 7 was prepared under non-standard process conditions, and the DOI value and IMD appearance of the finished product were significantly deteriorated, with the appearance of gel particles, pinholes and mirror cracks. This indicates that the feeding method, mixing and shearing conditions, degassing and filtration processes are the key steps to achieve uniform crosslinking and dense film.

[0156] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. An IMD injection molded mirror metallic color printing ink, comprising an A component ink base and a B component curing agent, characterized in that: the curing agent is mixed with the ink base before use, the curing agent is xylene diisocyanate polymer (XDI), the xylene diisocyanate polymer is pre-diluted with ethylene glycol monobutyl ether at a mass ratio of 1:1-1:3 before being added, and the mother liquor is slowly added to the ink base in a dropwise manner, low shear stirring is carried out at a speed of not more than 150 rpm at 25°C, and standing and curing for 60-90 minutes; the ink base comprises the following components: a resin solution, the mass percentage composition of the resin solution is: polyvinyl butyral ester 5.0%-8.0%, nitrocellulose 0.5%-2.0%, modified polyester resin 1.0%-3.0%, polyarylate resin 2.0%-5.0%, the sum of the mass percentages of the above resins is 8%-15%, and the balance is ethylene glycol monobutyl ether, and the mass percentage of the polyvinyl butyral ester in the resin solid content is not less than 50%; a solvent, ethylene glycol monobutyl ether is used as the main solvent, and the proportion of ethylene glycol monobutyl ether in the total mass of the solvent is not less than 70%; wherein the solvent contained in the resin solution is included in the total mass of the solvent; the solvent does not include ketone, ester or aromatic hydrocarbon solvents which have obvious corrosion effect on polycarbonate; flaky aluminum silver powder, the D50 median particle size of the flaky aluminum silver powder is 5-10 microns, and the mass ratio of the flaky aluminum silver powder to the resin solid content is 0.6:1-1.2:1; and an additive, including one or more of fumed silica, dimethyl silicone oil and leveling agent; the resin solution is obtained by adding ethylene glycol monobutyl ether into a stirring container to control the stirring speed at 500-800 rpm, and sequentially adding polyvinyl butyral ester, nitrocellulose, modified polyester resin and polyarylate resin, and then filtering with a filter bag with a filtering precision of not less than 420 mesh / inch after continuous stirring for 120 minutes; the ink base is obtained by adding the flaky aluminum silver powder, fumed silica, dimethyl silicone oil and leveling agent into the resin solution, stirring for 60 minutes, standing and defoaming, and filtering with a filter bag with a filtering precision of not less than 350 mesh / inch. The mass ratio of the ink base to the curing agent is 100:(8-12). The mass percentages of the ink base are: resin solution 85.0%-92.0%, flaky aluminum silver powder 8.0%-12.0%, fumed silica 0.3%-0.6%, dimethyl silicone oil 0.1%-0.3%, and leveling agent 0.1%-0.3%, and the sum of the mass percentages of the above components is 100%. The resin solution can still maintain structural integrity at an injection molding temperature of 300°C-330°C, and there is no ink bleeding, cracking or oil scattering phenomenon, the rotational viscosity of the resin solution at 25°C is 2000-4000 centipoise, and the rotational viscosity of the final ink at 25°C is 3000-5000 centipoise. ​ ​ ​ ​ ​ 2. The screen printing ink according to claim 1, characterized in that, ​ 3. The screen printing ink according to claim 1, characterized in that, ​ 4. The screen printing ink according to any one of claims 1 to 3, characterized in that, ​ 5. The screen printing ink according to claim 2, wherein The o-tolidine diisocyanate polymer is the only curing agent used; or, when used together with other curing agents, the mass proportion of o-tolidine diisocyanate polymer is not less than 50% based on the active components of all curing agents.

6. A method of preparing the screen printing ink according to any one of claims 1 to 5, characterized in that, The method comprises the following steps: S1, preparing a resin liquid: ethylene glycol monobutyl ether is added to a stirring container, the stirring speed is controlled at 500-800 rpm, polyvinyl butyral ester, nitrocellulose, modified polyester resin and polyarylate resin are sequentially added, after continuous stirring for 120 minutes, filtration is performed using a filter bag with a filtration precision of not less than 420 mesh / inch to obtain the resin liquid; S2, preparing an ink base: flaky aluminum silver powder, fumed silica, dimethyl silicone oil and a leveling agent are added to the resin liquid, stirring is performed for 60 minutes to obtain a uniformly dispersed ink base; S3, filtering and packaging: after the ink base is left to deaerate, it is filtered using a filter bag with a precision of not less than 350 mesh / inch, and is packaged as an A-component ink base without a curing agent.

7. A method of using the screen printing ink according to any one of claims 1 to 5, characterized in that, The method comprises the following steps: U1, before use, o-tolidine diisocyanate polymer is added to the A-component ink base as a B-component, the mass ratio of A:B is 100:(8-12); U2, low-shear stirring is performed at a speed of not higher than 150 rpm at 25°C, and the mixture is left to mature for 60-90 minutes; U3, after filtration with a precision of not less than 350 mesh / inch, screen printing is performed, and polycarbonate IMD injection molding is implemented.

8. The method of use of claim 7, wherein, The o-tolidine diisocyanate polymer is pre-diluted with ethylene glycol monobutyl ether at a mass ratio of 1:1-1:3 before being added, and is slowly added to the ink base in the form of a mother liquor by dropwise addition.

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