A base coat composition and a method for producing a decorative panel using electrostatic printing technology and applications thereof

Abstract

The application discloses a primer composition and a decorative panel preparation method adopting an electrostatic printing technology and application thereof. The primer composition comprises, by weight, 30-50 parts of a beta-hydroxy ester functional acrylate oligomer, 4-8 parts of an organic silane coupling agent, 0.5-1.8 parts of a titanium chelate catalyst containing a beta-diketone chelating ligand, 6-14 parts of a cyclic carbonate solvent with a boiling point of greater than or equal to 200 DEG C, 20-40 parts of a reactive diluent and 2-4 parts of a photoinitiator. The preparation method comprises primer preparation, substrate cleaning, coating, heat treatment, liquid electrostatic printing and ultraviolet light curing steps. The application realizes high adhesion and long-term durability of ink on a polycarbonate substrate through a double-interface chemical bridge molecule design without physical surface activation such as corona or plasma, and does not cause stress cracking of the substrate.

Description

Technical Field

[0001] This invention belongs to the field of decorative panel preparation technology, specifically relating to a base coating composition and a method for preparing decorative panels using electrostatic printing technology, as well as their applications. Background Technology

[0002] Polycarbonate (PC) is widely used in home appliance panels, automotive interiors, and architectural decoration due to its excellent optical transparency, high impact strength, and flame retardancy. With the increasing application of liquid electrostatic printing technology in the manufacture of high-resolution decorative panels, achieving long-term adhesion of UV-curable inks on polycarbonate substrates has become a key technical challenge.

[0003] Polycarbonate has a surface energy of approximately 42–45 mN / m and lacks active groups that can be chemically anchored by traditional primer resins; existing technologies cannot provide high-quality abrasion-resistant results when inkjet printing radiation-cured inks on untreated polycarbonate substrates.

[0004] To alleviate this problem, some have proposed physical surface activation of plastic substrates before printing, such as flame oxidation, corona treatment, or plasma treatment. However, these treatments are time-sensitive, and the surface can recover to near its pre-treatment level within hours to days, making them unsuitable for continuous industrial production.

[0005] While primer systems containing strong solvents such as dichloromethane or methyl ethyl ketone can improve short-term adhesion, their solubility parameters are very close to those of polycarbonate, leading to severe environmental stress cracking (i.e., silver streaks), and adhesion significantly degrades under harsh aging conditions. Although known organotitanates can catalyze transesterification reactions, traditional non-chelated titanates exhibit high catalytic activity at room temperature, resulting in insufficient storage stability of the primer composition. Organosilane coupling agents have limited adhesion-enhancing effects on polycarbonate because the polycarbonate surface lacks a large number of hydroxyl groups available for silane condensation. The controllable swelling ability of propylene carbonate on polycarbonate is well-known in the field of electroless plating pretreatment, but it is only used in conjunction with etchants to achieve physical roughening; its potential as a nanoscale swelling agent to promote interfacial covalent bonding reactions remains untapped.

[0006] The aforementioned existing technologies have the following systemic deficiencies: First, existing primer coating solutions generally involve a single interface bonding between the primer layer and the substrate (interface I) or between the primer layer and the ink layer (interface II), without simultaneously designing a bifunctional structure in the same primer molecule that can participate in the chemical bonding of the two interfaces; Second, conventional acrylic primer resins only contain acryloyl groups and do not contain β-hydroxy ester groups that can undergo transesterification reactions with polycarbonate carbonate bonds under mild conditions, thus failing to form covalent bonds with the substrate; Third, there is a lack of "temperature-responsive" catalysts that can remain inert at room temperature and selectively release catalytic activity at 60–80°C, as well as swelling auxiliary systems that do not cause stress cracking when used with such catalysts.

[0007] Therefore, there is an urgent need for a primer composition that can establish covalent chemical bonds at both interfaces of the primer layer under mild process conditions, so as to achieve the adhesion of the ink layer to the ASTM D3359 standard and maintain it for a long time under harsh aging conditions without causing stress cracking or surface degradation of the substrate. Summary of the Invention

[0008] To solve the above-mentioned technical problems, the present invention provides a primer composition, the raw materials comprising, by weight: 30-50 parts of β-hydroxy ester functional acrylate oligomer, wherein each molecule of the β-hydroxy ester functional acrylate oligomer contains at least one β-hydroxy ester group and at least one (meth)acryloyl group, wherein the hydroxyl group in the β-hydroxy ester group is located at the β position relative to the ester bond; 4-8 parts of organosilane coupling agent; 0.5-1.8 parts of titanium chelate catalyst, wherein the titanium chelate catalyst contains a β-diketone chelating ligand; 6-14 parts of cyclic carbonate solvent, wherein the boiling point of the cyclic carbonate solvent is ≥200℃; 20-40 parts of reactive diluent, wherein the reactive diluent is a polyfunctional (meth)acryloyl monomer containing at least two (meth)acryloyl groups; and 2-4 parts of photoinitiator.

[0009] As a preferred embodiment, the amount of the titanium chelate catalyst is 0.8 to 1.2 parts, and the amount of the cyclic carbonate solvent is 8 to 12 parts; the titanium chelate catalyst is diisopropoxybis(acetylacetone)titanium(IV); and the cyclic carbonate solvent is propylene carbonate.

[0010] As a preferred embodiment, the β-hydroxy ester functional acrylate oligomer is selected from one of the following: (i) glycerol dimethacrylate with a molecular weight of 226-230, wherein the two primary hydroxyl groups at positions 1 and 3 of the glycerol backbone are esterified with methacrylate to form two methacrylamide groups, and the secondary hydroxyl group at position 2 remains unreacted; or (ii) a ring-opening addition product of glycidyl methacrylate and acrylic acid with a number average molecular weight of 280-290, each molecule containing one methacrylamide group and one β-hydroxy ester group; the ring-opening addition product is prepared by mixing glycidyl methacrylate and acrylic acid in a 1:1 molar ratio, adding 0.5 wt% of triphenylphosphine as a catalyst, and reacting at 80°C for 6 hours.

[0011] As a preferred embodiment, the organosilane coupling agent is selected from at least one of 3-glycidoxypropyltrimethoxysilane and 3-aminopropyltriethoxysilane; the reactive diluent is selected from one or a mixture of 1,6-hexanediol diacrylate and tripropylene glycol diacrylate; the photoinitiator is selected from one or a mixture of 1-hydroxycyclohexylphenyl ketone and 2-hydroxy-2-methyl-1-phenyl-1-propanone; and the viscosity of the primer composition at 25°C is 10–80 mPa·s.

[0012] This invention also provides a method for preparing a decorative panel using electrostatic printing technology. Step (1) Preparation of the base coating composition: Mix each component of the base coating composition according to any one of claims 1 to 4 at 25°C and a stirring speed of 300 rpm for 30 minutes under light-protected conditions to obtain the base coating composition; Step (2) Substrate cleaning: Clean the surface of the engineering plastic substrate containing carbonate bonds and / or ester bonds by wiping with isopropanol or CO2 snow cleaning, and dry at room temperature for 5 minutes; The substrate surface is not subjected to corona treatment, plasma treatment or flame treatment; Step (3) Base coating: Apply the base coating composition obtained in step (1) to the cleaned substrate surface using a wire rod coater, roller coating, spraying or curtain coating method, and wet film Thickness is 1-8 μm; Step (4) Heat treatment: Under conditions without ultraviolet light irradiation, the coated substrate is placed in a hot air oven or infrared heating tunnel and heat-treated at 60-80℃ for 5-10 minutes, so that the β-hydroxy ester groups in the base coating composition undergo ester exchange reaction with the carbonate bonds on the substrate surface under the catalysis of titanium chelate catalyst to form interface I covalent bonding, and at the same time, the cyclic carbonate solvent achieves nanoscale swelling of the substrate surface layer; Step (5) Liquid electrostatic printing: Radiation-curable ink is applied to the surface of the heat-treated base coating by liquid electrostatic printing; Step (6) Ultraviolet curing: Irradiation is performed using an ultraviolet light source with a wavelength of 340-400 nm and an irradiation energy of 300-700 mJ / cm. 2 The curing time is 1 to 5 seconds, which allows the residual (meth)acryloyl groups in the base layer to undergo a free radical copolymerization reaction with the acrylate components in the ink layer to form interface II covalent bonds.

[0013] As a preferred embodiment, in step (4), the heat treatment temperature is 65-75℃, the heat treatment time is 6-9 minutes, and the relative humidity of the heat treatment environment is 30%-70%RH; the engineering plastic substrate in step (2) is a bisphenol A type polycarbonate sheet with a thickness of 1-3mm, and the use of acetone, dichloromethane or methyl ethyl ketone is strictly prohibited in the substrate cleaning process; the wet film thickness in step (3) is 2-5μm.

[0014] As a preferred embodiment, the ultraviolet light source in step (6) is a 365nm ultraviolet LED light source with an irradiation energy of 400–600 mJ / cm². 2The radiation-curable ink in step (5) comprises, by weight: 50 parts trimethylolpropane triacrylate, 18 parts polyurethane acrylate oligomer, 8 parts pigment, 2 parts charge control agent, 5 parts photoinitiator, and 3 parts polymeric dispersant. The viscosity of the radiation-curable ink at 25°C is 50 mPa·s. The DC voltage for liquid electrostatic printing is 1–4 kV, the printing resolution is 600–1200 dpi, and the substrate conveying speed is 10–30 m / min. Optionally, after step (6), step (7) is further included: spraying a 2–8 μm thick transparent UV-curable varnish onto the surface of the cured ink layer at a concentration of 300–700 mJ / cm². 2 Ultraviolet light curing is performed using irradiation energy.

[0015] The present invention also provides a decorative panel prepared by the above preparation method, wherein the decorative panel comprises, from the substrate outward, the following: an engineering plastic substrate layer containing carbonate bonds and / or ester bonds; a base layer, wherein the base layer and the substrate layer are covalently connected by mixed ester bonds formed by transesterification reaction catalyzed by titanium chelates, and the base layer and the ink pattern layer are covalently connected by CC bonds formed by free radical copolymerization of acrylates initiated by ultraviolet light; and a cured ink pattern layer.

[0016] As a preferred embodiment, the decorative panel shall have an initial adhesion grade of not less than 4B as determined by the cross-cut adhesion test according to ASTM D3359 standard; an adhesion grade of not less than 3B after immersion in boiling water at 100°C for 2 hours; an adhesion grade of not less than 3B after 100 cycles of thermal cycling from -40°C to 85°C; and no more than 3 streaks / cm under 1% bending strain. 2 The surface haze change ΔHaze ≤ 1.0%.

[0017] As a preferred embodiment, the decorative panel has an initial adhesion grade of 5B as determined by the cross-cut adhesion test according to ASTM D3359 standard. After being immersed in boiling water at 100°C for 2 hours, the adhesion grade is not lower than 4B. After 100 cycles of thermal cycling from -40°C to 85°C, the adhesion grade is not lower than 4B. After 500 hours of QUV-A ultraviolet aging, the adhesion grade is not lower than 4B. No silver streaks are generated under 1% bending strain, and the surface haze change ΔHaze is ≤0.3%.

[0018] Compared with the prior art, the present invention has the following beneficial technical effects:

[0019] (1) Significantly improved interfacial adhesion: The primer composition of the present invention uses the "dual-interface chemical bridge" molecular design of β-hydroxy ester functional acrylate oligomers to form interface I covalent bond between the primer layer and the substrate through a low-temperature ester exchange reaction catalyzed by titanium chelate, and interface II covalent bond between the primer layer and the ink layer through an acrylate copolymerization reaction initiated by ultraviolet light. There are no physical weak layers in either interface. The initial adhesion reaches ASTM D3359 standard 5B level. After soaking in boiling water at 100°C for 2 hours, it still maintains 5B level. After 100 cycles of cold and heat cycling from -40°C to 85°C, it maintains 4B to 5B level. After 500 hours of QUV-A ultraviolet aging, it maintains 4B level.

[0020] (2) Eliminating the risk of stress cracking: This invention uses propylene carbonate as a nanoscale synergistic swelling agent, whose solubility parameter (δ≈27.2MPa) 0.5 ) and polycarbonate (δ≈19.7MPa) 0.5 Approximately 7.5 MPa between ) 0.5 The moderate gap achieves controlled swelling rather than excessive swelling, does not cause silver streaks in the range of 6 to 12 parts, and no silver streaks are generated in the 1% bending strain superposition test, completely replacing solvents with high stress cracking risk such as dichloromethane and methyl ethyl ketone.

[0021] (3) Preservation of substrate optical properties: The change in haze on the substrate surface during the primer treatment is ΔHaze≤0.3%, which does not affect the optical transparency of the polycarbonate substrate and is suitable for decorative panel applications with strict requirements for optical properties.

[0022] (4) The process temperature is mild and no physical pretreatment is required: the heat treatment temperature of 60-80℃ is much lower than the glass transition temperature of polycarbonate, which does not affect the dimensional accuracy of the substrate; no physical surface activation steps such as corona, plasma or flame are required, which eliminates the constraints of surface energy recovery on production and reduces energy consumption and equipment purchase costs.

[0023] (5) Synergistic effect of multiple components: The functional components in the primer composition synergistically enhance the interfacial bonding efficiency in three aspects: catalytic driving, interfacial penetration and auxiliary anchoring. The adhesion of the complete formulation (5B grade) far exceeds the level when any single component is missing (0B to 3B grade). Each component plays a complementary and irreplaceable functional role in the same interfacial chemical process. Attached Figure Description

[0024] Figure 1 This is a schematic cross-sectional view of the layered structure of the decorative panel of the present invention;

[0025] Figure 2 This is a schematic diagram of the chemical bonding reaction mechanism at the two interfaces;

[0026] Figure 3This is a process flow diagram for the preparation of decorative panels;

[0027] Figure 4 Comparison of ATR-FTIR spectra for Example 1, Comparative Example 2, and Comparative Example 4;

[0028] Figure 5 The XPS spectra of the polycarbonate surface after washing with hexane in Example 1 are shown, where (a) is a broad scan spectrum and (b) is a high-resolution C1s spectrum.

[0029] Figure 6 This is a schematic diagram of the temperature response behavior of titanium chelate catalysts. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to specific embodiments. These embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified, specific conditions in the embodiments are performed under conventional conditions or conditions recommended by the raw material supplier. All raw materials used, unless otherwise stated, are commercially available conventional commodities.

[0031] The primer composition of this invention is a non-aqueous organic system. No aqueous phase is involved in the mixing, coating, and heat treatment processes of the components, and the pH value is not suitable for characterizing this system. However, the pretreatment of the aluminum alloy substrate in Example 9 involves an aqueous solution step, and the corresponding pH value of the aqueous solution is separately noted in this example.

[0032] raw material

[0033] The raw materials and their specifications used in the embodiments of this invention are as follows.

[0034] Glyceryl dimethacrylate (GDMA), CAS No. 1830-78-0, molecular weight approximately 228, purity ≥95%.

[0035] 3-Glycidoxypropyltrimethoxysilane (GPTMS), CAS No. 2530-83-8, purity ≥98%. 3-Aminopropyltriethoxysilane (APTES), CAS No. 919-30-2, purity ≥98%.

[0036] Diisopropoxybis(acetylacetone)titanium (IV), CAS No. 17927-72-9, with a titanium content of approximately 9.9 wt%, is available in products such as the TyzorAA series.

[0037] Propylene carbonate, CAS No. 108-32-7, purity ≥99.5%, boiling point 242℃, solubility parameter δ≈27.2MPa 0.5 .

[0038] 1,6-Hexanediol diacrylate (HDDA), CAS No. 13048-33-4, purity ≥97%.

[0039] Tripropylene glycol diacrylate (TPGDA), CAS No. 42978-66-5, purity ≥97%.

[0040] 1-Hydroxycyclohexylphenyl ketone (Irgacure184), CAS No. 947-19-3, purity ≥99%.

[0041] 2-Hydroxy-2-methyl-1-phenyl-1-propanone (Darocur1173), CAS No. 7473-98-5, purity ≥98%.

[0042] Hydroquinone monomethyl ether (MEHQ), CAS No. 150-76-5, purity ≥99%.

[0043] Glycidyl methacrylate (GMA), CAS No. 106-91-2, purity ≥97%.

[0044] Acrylic acid (AA), CAS No. 79-10-7, purity ≥99%.

[0045] Triphenylphosphine (TPP), CAS No. 603-35-0, purity ≥99%.

[0046] Trimethylolpropane triacrylate (TMPTA), CAS No. 15625-89-5, purity ≥99%.

[0047] The polyurethane acrylate oligomers are commercially available general-purpose aliphatic polyurethane acrylates.

[0048] Phthalocyanine Blue pigment (CIPigmentBlue 15:3).

[0049] Alkyl salicylate zinc is a commercially available liquid charge control agent for electrostatic printing.

[0050] The polymeric dispersant is a commercially available acrylate polymeric dispersant.

[0051] Isopropanol (IPA), CAS No. 67-63-0, analytical grade.

[0052] The polycarbonate sheet is Covestro Makrolon® 2407, 2mm thick, bisphenol A type. The aluminum alloy sheet is 5052-H32, 0.5mm thick.

[0053] Preparation Example 1: Preparation of glycidyl methacrylate-acrylic acid ring-opening addition product

[0054] To a 500 mL three-necked round-bottom flask equipped with a mechanical stirrer, reflux condenser, and thermometer, add 142.2 g (1.0 mol) glycidyl methacrylate (GMA) and 72.1 g (1.0 mol) acrylic acid (AA), with a molar ratio of GMA to AA of 1:1. Add 1.07 g of triphenylphosphine (TPP) as a catalyst, accounting for 0.5 wt% of the total reactant weight (214.3 g). Add 200 ppm of hydroquinone monomethyl ether (MEHQ) as a polymerization inhibitor to prevent thermal polymerization of (meth)acryloyl groups during heating. Under nitrogen protection, stir at 200 rpm and heat the reaction system to 80 °C (this system is non-aqueous, pH is not applicable). Maintain the reaction at 80 °C for 6 hours with stirring at 200 rpm. Monitor the conversion rate of GMA epoxy groups by epoxy value titration during the reaction. After 6 hours of reaction, the epoxy group conversion rate reaches over 95%. After the reaction, the mixture was allowed to cool naturally to 25°C, yielding a pale yellow, transparent, viscous liquid, which was the glycidyl methacrylate-acrylic acid ring-opening addition product. The product's number-average molecular weight, determined by gel permeation chromatography (GPC, calibrated with polystyrene standards), was approximately 284. Since GPC is calibrated using polystyrene as a standard, the apparent molecular weight of small molecular weight samples is usually higher than the absolute molecular weight. The theoretical molecular weight of the 1:1 addition product of GMA and AA is approximately 214. The higher apparent molecular weight determined by GPC is attributed to the systematic bias in polystyrene calibration regarding the hydrodynamic volume differences of small molecules. Each molecule of the product contains one methacrylamide group and one β-hydroxy ester group (the secondary hydroxyl group generated by the ring-opening addition reaction of the GMA epoxy group and the AA carboxyl group forms the β-hydroxy ester structure with the adjacent ester bond). The product was stored at 4°C in a light-protected, sealed environment for later use.

[0055] Preparation Example 2: Ink Formulation

[0056] The same radiation-curable liquid electrostatic printing ink was used in all examples and comparative examples. The ink was formulated according to the following parts by weight: 50g of trimethylolpropane triacrylate (TMPTA), 18g of polyurethane acrylate oligomer, 8g of phthalocyanine blue pigment (CIPigmentBlue 15:3), 2g of zinc alkyl salicylate (charge control agent), 5g of Darocur 1173 photoinitiator, and 3g of polymeric dispersant, totaling 86g of the six components. The above components were mixed at 25°C and a stirring speed of 500 rpm for 60 minutes under light-protected conditions, and then ground with a three-roll mill to a pigment particle size D. 50 ≤2μm. The resulting ink has a viscosity of 50 mPa·s at 25°C. This ink system is a non-aqueous organic system; pH is not applicable.

[0057] The process flow of the decorative panel preparation method of the present invention is as follows: Figure 3 As shown.

[0058] Example 1 (Standard Formulation)

[0059] This embodiment uses the following primer composition formulation (in grams): 40.0g glyceryl dimethacrylate (GDMA), 6.0g 3-glycidoxypropyltrimethoxysilane (GPTMS), 1.0g diisopropoxybis(acetylacetone)titanium (IV), 10.0g propylene carbonate, 30.0g 1,6-hexanediol diacrylate (HDDA), and 3.0g 1-hydroxycyclohexylphenyl ketone (Irgacure184), totaling 90.0g of the six components.

[0060] Step (1) Preparation of the primer composition: Under light-protected conditions (yellow light illumination room), add the above six components sequentially to a brown glass container, and stir at 300 rpm for 30 minutes at 25°C until the system is completely homogeneous and transparent. This primer composition is a non-aqueous organic system, and pH value is not applicable. After preparation, the viscosity at 25°C was measured using a rotational viscometer, and the measured value was 38 mPa·s, which meets the target range of 10–80 mPa·s.

[0061] Step (2) Substrate Cleaning: Take a Covestro Makrolon® 2407 polycarbonate sheet (2mm thick) and cut it into 100mm × 100mm samples. Wipe the substrate surface twice with a lint-free cloth soaked in isopropanol to remove surface oil and dust. Dry at room temperature (25°C) for 5 minutes. Do not subject the substrate surface to corona treatment, plasma treatment, or flame treatment. Acetone, dichloromethane, or methyl ethyl ketone must not be used to clean the polycarbonate surface.

[0062] Step (3) Primer coating: The primer composition obtained in step (1) is coated on the cleaned polycarbonate substrate surface using a #6 wire bar coater at room temperature (25°C) and the wet film thickness is about 3 μm.

[0063] Step (4) Heat Treatment: Immediately place the coated substrate into a preheated hot air oven at 70°C (preferably within the temperature range of 65–75°C) and maintain it for 8 minutes (preferably within the time range of 6–9 minutes) without ultraviolet light irradiation. A relative humidity of 30%–70% RH is recommended to ensure the supply of trace amounts of moisture required for the hydrolysis and condensation of GPTMS. In this step, the acetylacetone ligand of the titanium chelate catalyst partially dissociates at 70°C, releasing Lewis acid active titanium sites, such as… Figure 6As shown, the β-hydroxy ester groups of GDMA catalyze the transesterification reaction with the carbonate bonds on the polycarbonate surface to form interface I covalent bonds; propylene carbonate simultaneously achieves nanoscale swelling of approximately 2–10 nm depth on the polycarbonate surface layer, increasing the molecular-level contact area of ​​the transesterification reaction; GPTMS undergoes hydrolysis and condensation under the influence of ambient humidity to form a Si-O-Si crosslinked network that enhances the cohesive strength of the primer layer, and its epoxy groups undergo ring-opening addition reactions with the phenolic hydroxyl groups at the chain ends of the polycarbonate released by the transesterification reaction to provide auxiliary anchoring. Since there is no ultraviolet light irradiation and no thermal initiator in this step, the (meth)acryloyl groups in the primer composition do not polymerize, and the activity is completely retained until step (6). After the heat treatment is completed, the substrate is removed and allowed to cool naturally to room temperature.

[0064] Step (5) Liquid electrostatic printing: The cooled coated substrate is mounted on the liquid electrostatic printing device, and the radiation-curable ink prepared above is used for printing. Printing parameters: DC voltage 2.5kV (range 1~4kV), printing resolution 800dpi (range 600~1200dpi), substrate conveying speed 20m / min (range 10~30m / min).

[0065] Step (6) UV Curing: The printed substrate is irradiated and cured using a 365nm UV LED light source (wavelength range 340-400nm). Irradiation energy: 500mJ / cm² 2 (range 300~700mJ / cm) 2 The curing time is 2 seconds (range 1-5 seconds). In this step, Irgacure184 in the base coat and Darocur1173 in the ink layer simultaneously generate free radicals under ultraviolet irradiation, initiating a free radical copolymerization reaction between the residual methacryloyl groups (from GDMA and HDDA) on the base coat surface and the acrylate components (TMPTA and polyurethane acrylate oligomers) in the ink layer, forming a covalent CC crosslinked network across the base coat-ink layer interface, completing interface II covalent bonding. The mechanism of the above interface I transesterification reaction and interface II free radical copolymerization reaction is as follows: Figure 2 As shown.

[0066] Step (7) Surface protection treatment: Spray a transparent UV-curable varnish onto the surface of the cured ink layer, with a coating thickness of about 5 μm (range 2-8 μm), at a concentration of 500 mJ / cm². 2 Ultraviolet light curing is performed using irradiation energy.

[0067] like Figure 1As shown, the decorative panel of the present invention has a layered structure and a dual-interface chemical bonding mode. The resulting decorative panel comprises, from the substrate outwards: a polycarbonate substrate layer, a base layer, and a cured ink pattern layer. The base layer and the substrate layer are covalently connected by mixed ester bonds formed by transesterification, and the base layer and the ink pattern layer are covalently connected by CC covalent bonds formed by acrylate free radical copolymerization.

[0068] Example 2 (Low Catalyst Dosage)

[0069] Primer composition formulation (by weight): GDMA 40.0g, GPTMS 6.0g, diisopropoxybis(acetylacetone)titanium(IV) 0.5g, propylene carbonate 10.0g, HDDA 30.5g, Irgacure 184 3.0g, totaling 90.0g. Preparation conditions were the same as in Example 1 (25℃, 300rpm, 30 minutes, protected from light; pH not applicable for non-aqueous systems). The measured viscosity at 25℃ was 39 mPa·s. Substrate preparation, coating, heat treatment (70℃, 8 minutes, recommended relative humidity 30%–70%RH), liquid electrostatic printing (2.5kV, 800dpi, 20m / min), and UV curing (365nm, 500mJ / cm²). 2 The process (2 seconds) and optional protective layer treatment are the same as in Example 1. In this example, the catalyst dosage of 0.5 parts is at the lower limit of the range (0.5 to 1.8 parts), verifying the effect of low catalyst dosage on transesterification efficiency and adhesion.

[0070] Example 3 (High Catalyst Dosage)

[0071] The primer composition formulation (by weight) is as follows: GDMA 40.0 g, GPTMS 6.0 g, diisopropoxybis(acetylacetone)titanium(IV) 1.8 g, propylene carbonate 10.0 g, HDDA 29.2 g, and Irgacure 184 3.0 g, totaling 90.0 g. The preparation conditions were the same as in Example 1 (25°C, 300 rpm, 30 minutes, protected from light; pH value not applicable for non-aqueous systems). The measured viscosity at 25°C was 37 mPa·s. All other process steps were the same as in Example 1. In this example, the catalyst dosage of 1.8 parts is within the upper limit of the protected range (0.5–1.8 parts), verifying the effect of high catalyst dosage on the surface integrity and optical properties of polycarbonate.

[0072] Example 4 (Low propylene carbonate dosage)

[0073] The primer composition formulation (in grams) is as follows: GDMA 40.0g, GPTMS 6.0g, diisopropoxybis(acetylacetone)titanium(IV) 1.0g, propylene carbonate 6.0g, HDDA 34.0g, Irgacure 184 3.0g, totaling 90.0g. The preparation conditions are the same as in Example 1 (25°C, 300rpm, 30 minutes, protected from light; pH value is not applicable for non-aqueous systems). The measured viscosity at 25°C is 35 mPa·s. All other process steps are the same as in Example 1. In this example, the amount of propylene carbonate used is 6 parts, which is at the lower limit of the range (6–14 parts), verifying the interfacial contact area and adhesion level of the transesterification reaction under low swelling assisted conditions.

[0074] Example 5 (Dosage of propylene carbonate)

[0075] The primer composition formulation (by weight) is as follows: GDMA 40.0g, GPTMS 6.0g, diisopropoxybis(acetylacetone)titanium(IV) 1.0g, propylene carbonate 14.0g, HDDA 26.0g, Irgacure 184 3.0g, totaling 90.0g. The preparation conditions are the same as in Example 1 (25°C, 300rpm, 30 minutes, protected from light; pH value is not applicable for non-aqueous systems). The measured viscosity at 25°C is 42 mPa·s. All other process steps are the same as in Example 1. The amount of propylene carbonate used in this example, 14 parts, is at the upper limit of the range (6–14 parts), verifying adhesion and stress cracking safety under high swelling conditions.

[0076] Example 6 (APTES instead of GPTMS)

[0077] The primer composition formulation (by weight) is as follows: GDMA 40.0 g, 3-aminopropyltriethoxysilane (APTES) 6.0 g, diisopropoxybis(acetylacetone)titanium (IV) 1.0 g, propylene carbonate 10.0 g, HDDA 30.0 g, and Irgacure 184 3.0 g, totaling 90.0 g. The preparation conditions are the same as in Example 1 (25°C, 300 rpm, 30 minutes, protected from light; pH value is not applicable for non-aqueous systems). The measured viscosity at 25°C is 36 mPa·s. All other process steps are the same as in Example 1. This example uses APTES instead of GPTMS to verify the effect of different types of silane coupling agents on adhesion stability under humid and hot conditions. GPTMS forms covalent CO bonds through epoxy ring-opening addition, while APTES forms hydrogen bonds through amino groups. It should be noted that, since the primary amino group (-NH2) of APTES may undergo a certain degree of aza-Michael addition reaction with the C=C double bond of acrylate in HDDA at room temperature (R-NH2+CH2=CH-COOR'→R-NH-CH2-CH2-COOR'), APTES may exist in the actual system in part as an amino-acrylate adduct. However, since the amount of APTES is small (only 6.7 wt% of the total formulation), this side reaction does not affect the overall function and workability of the primer composition.

[0078] Example 7 (Optimal Formulation)

[0079] The primer composition formulation (in grams) is as follows: GDMA 42.0 g, GPTMS 6.0 g, diisopropoxybis(acetylacetone)titanium(IV) 1.0 g, propylene carbonate 10.0 g, HDDA 28.0 g, Irgacure 184 3.0 g, totaling 90.0 g of the six components. The preparation conditions are the same as in Example 1 (25°C, 300 rpm, 30 minutes, protected from light; pH value is not applicable for non-aqueous systems). The measured viscosity at 25°C is 40 mPa·s. All other process steps are the same as in Example 1. In this example, the catalyst dosage of 1.0 part is in the middle of the optimal range (0.8–1.2 parts), the propylene carbonate dosage of 10 parts is in the middle of the optimal range (8–12 parts), and the GDMA dosage is increased to 42 parts to further increase the interfacial concentration of β-hydroxy ester groups, which is the most preferred embodiment of the present invention.

[0080] Example 8 (GMA-AA addition product replacing GDMA)

[0081] Primer composition formulation (in grams): 40.0 g of glycidyl methacrylate-acrylic acid ring-opening addition product obtained in Preparation Example 1, 6.0 g of GPTMS, 1.0 g of diisopropoxybis(acetylacetone)titanium(IV), 10.0 g of propylene carbonate, 30.0 g of HDDA, and 3.0 g of Irgacure 184, totaling 90.0 g of the six components. Preparation conditions were the same as in Example 1 (25°C, 300 rpm, 30 minutes, protected from light; pH value not applicable for non-aqueous systems). The measured viscosity at 25°C was 45 mPa·s. All other process steps were the same as in Example 1. In this embodiment, the ring-opening addition product of GMA-AA (containing one methacrylyl group and one β-hydroxy ester group per molecule, with a number average molecular weight of about 284) was used instead of GDMA (containing two methacrylyl groups and one β-hydroxy ester group per molecule, with a molecular weight of about 228) to verify that the dual-interface bridging function of component (A) depends on the bifunctional structure of the molecule containing both β-hydroxy ester groups and acrylyl groups, rather than on a specific compound.

[0082] Example 9 (Aluminum Alloy Substrate)

[0083] The primer composition formulation and preparation conditions were exactly the same as in Example 1 (GDMA 40.0g, GPTMS 6.0g, diisopropoxybis(acetylacetone)titanium(IV) 1.0g, propylene carbonate 10.0g, HDDA 30.0g, Irgacure 184 3.0g, total of 90.0g for the six components, 25℃, 300rpm, 30 minutes, protected from light, pH value not applicable for non-aqueous systems), with a measured viscosity of 38mPa·s at 25℃. In this example, the substrate was changed to a 0.5mm thick aluminum alloy sheet (5052-H32), cut into 100mm×100mm samples.

[0084] Substrate pretreatment steps: First, alkaline washing is performed by immersing the aluminum alloy sample in a 5wt% NaOH aqueous solution (pH≈14) at 60℃ for 2 minutes with stirring at 100 rpm to remove the natural oxide film and grease from the surface. After removal, rinse three times with deionized water. Next, acid washing is performed by immersing the alkaline-washed sample in a 10wt% nitric acid aqueous solution (pH≈0.5) at room temperature (25℃) for 1 minute with stirring at 100 rpm to neutralize residual alkali and obtain a uniform activated alumina surface. After removal, rinse three times with deionized water and dry at room temperature for 5 minutes.

[0085] The process includes base coat application, heat treatment (70℃, 8 minutes, recommended ambient relative humidity 30%~70%RH), liquid electrostatic printing (2.5kV, 800dpi, 20m / min), and UV curing (365nm, 500mJ / cm). 2The steps (2 seconds) are the same as in Example 1. Since there are no carbonate bonds on the aluminum alloy surface, the ester exchange interface bonding mechanism is not applicable to this substrate. The adhesion mainly depends on the Si-O-Al covalent bonds formed between the GPTMS silane coupling agent and the aluminum alloy surface oxide layer, as well as the cohesive strength of the acrylate crosslinking network provided by GDMA and HDDA.

[0086] Example 10 (Verification of the lower limit of component A)

[0087] The primer composition formulation (in grams) is as follows: GDMA 30.0g, GPTMS 6.0g, diisopropoxybis(acetylacetone)titanium(IV) 1.0g, propylene carbonate 10.0g, HDDA 40.0g, and Irgacure 1843.0g, totaling 90.0g. The preparation conditions are the same as in Example 1 (25°C, 300rpm, 30 minutes, protected from light; pH value is not applicable for non-aqueous systems). The measured viscosity at 25°C is 32 mPa·s. All other process steps are the same as in Example 1. In this example, the GDMA dosage of 30 parts is at the lower limit, and the HDDA dosage of 40 parts is at the upper limit, verifying the adhesion performance at the lowest possible concentration of β-hydroxy ester groups at the interface. Due to the reduced GDMA dosage, the total amount of β-hydroxy ester groups participating in the interfacial I transesterification reaction decreases, and a decrease in adhesion compared to the standard formulation is expected.

[0088] Example 11 (Verification of the upper limit of component A)

[0089] The primer composition formulation (by weight) is as follows: GDMA 50.0 g, GPTMS 6.0 g, diisopropoxybis(acetylacetone)titanium(IV) 1.0 g, propylene carbonate 10.0 g, HDDA 20.0 g, and Irgacure 184 3.0 g, totaling 90.0 g. The preparation conditions are the same as in Example 1 (25°C, 300 rpm, 30 minutes, protected from light; pH value is not applicable for non-aqueous systems). The measured viscosity at 25°C is 48 mPa·s. All other process steps are the same as in Example 1. This example uses an upper limit of 50 parts GDMA and a lower limit of 20 parts HDDA to verify the adhesion performance and overall coating performance when the β-hydroxy ester group interfacial concentration is at its highest level. Increasing the GDMA content can improve the density of active sites in the interfacial I transesterification reaction, but decreasing the HDDA content may lead to a slight change in the crosslinking network density of the primer coating after UV curing.

[0090] Example 12 (TPGDA instead of HDDA)

[0091] The primer composition formulation (in grams) is as follows: GDMA 40.0g, GPTMS 6.0g, diisopropoxybis(acetylacetone)titanium(IV) 1.0g, propylene carbonate 10.0g, tripropylene glycol diacrylate (TPGDA) 30.0g, and Irgacure 184 3.0g, totaling 90.0g. The preparation conditions are the same as in Example 1 (25°C, 300rpm, 30 minutes, protected from light; pH value is not applicable for non-aqueous systems). The measured viscosity at 25°C is 42 mPa·s. All other process steps are the same as in Example 1. This example uses TPGDA instead of HDDA as the reactive diluent to verify the feasibility of this reactive diluent substitution option. Both TPGDA and HDDA are bifunctional acrylate monomers and are recognized as equivalent diluents in the field of UV-curable coatings. The difference lies in the fact that TPGDA contains a propylene glycol backbone with ether oxygen bonds, which gives the cured coating film higher flexibility.

[0092] Example 13 (Darocur1173 instead of Irgacure184)

[0093] The primer composition formulation (in grams) is as follows: GDMA 40.0 g, GPTMS 6.0 g, diisopropoxybis(acetylacetone)titanium(IV) 1.0 g, propylene carbonate 10.0 g, HDDA 30.0 g, and 2-hydroxy-2-methyl-1-phenyl-1-propanone (Darocur 1173) 3.0 g, totaling 90.0 g. The preparation conditions were the same as in Example 1 (25°C, 300 rpm, 30 minutes, protected from light; pH value not applicable for non-aqueous systems). The measured viscosity at 25°C was 37 mPa·s. All other process steps were the same as in Example 1. This example uses Darocur 1173 instead of Irgacure 184 as the photoinitiator to verify the feasibility of photoinitiator substitution. Irgacure184 and Darocur1173 both belong to the Norrish I type of α-hydroxy ketone photoinitiators. They both undergo α-cleavage under 340–400 nm ultraviolet irradiation to generate free radicals that initiate the polymerization of acrylates. Their absorption spectra and initiation efficiencies are similar.

[0094] Comparative Example 1 (without primer treatment)

[0095] This comparative example does not use any primer composition. Covestro Makrolon® 2407 polycarbonate sheets (2 mm thick, 100 mm × 100 mm) were wiped with isopropyl alcohol and dried at room temperature for 5 minutes. The substrate surface was not subjected to corona treatment, plasma treatment, or flame treatment. Radiation-curable ink was applied directly to the cleaned polycarbonate substrate surface using liquid electrostatic printing, with the same printing parameters as in Example 1 (2.5 kV, 800 dpi, 20 m / min). UV curing conditions were the same as in Example 1 (365 nm, 500 mJ / cm²). 2(2 seconds). This comparative example serves as a baseline reference to evaluate the adhesion level of ink to polycarbonate surfaces under no-primer conditions.

[0096] Comparative Example 2 (Titanium-free chelate catalyst)

[0097] Primer composition formulation (by weight): GDMA 40.0g, GPTMS 6.0g, titanium chelate catalyst (0g), propylene carbonate 10.0g, HDDA 31.0g (to make up for the missing catalyst 1.0g), Irgacure 1843.0g, totaling 90.0g of the six components. Preparation conditions were the same as in Example 1 (25℃, 300rpm, 30 minutes, protected from light; pH not applicable for non-aqueous systems). The measured viscosity at 25℃ was 37 mPa·s. Substrate preparation, coating (#6 wire rod, approximately 3μm), heat treatment (70℃, 8 minutes, no UV light, recommended relative humidity 30%–70%RH), liquid electrostatic printing (2.5kV, 800dpi, 20m / min), UV curing (365nm, 500mJ / cm²). 2 The time (2 seconds) was the same as in Example 1. This comparative example verifies that the titanium chelate catalyst is a necessary condition for establishing interface I covalent bonding in the transesterification reaction, that is, without a catalyst, the transesterification reaction between the β-hydroxy ester group and the polycarbonate carbonate bond cannot be effectively initiated under the conditions of 70°C × 8 minutes.

[0098] Comparative Example 3 (without propylene carbonate swelling agent)

[0099] Primer composition formulation (by weight): GDMA 40.0g, GPTMS 6.0g, diisopropoxybis(acetylacetone)titanium(IV) 1.0g, propylene carbonate-free (0g), HDDA 40.0g (to make up the missing propylene carbonate 10.0g), Irgacure 1843.0g, totaling 90.0g of the six components. Preparation conditions were the same as in Example 1 (25°C, 300rpm, 30 minutes, protected from light; pH value not applicable for non-aqueous systems). The measured viscosity at 25°C was 30mPa·s. Substrate preparation, coating (#6 wire rod, approximately 3μm), heat treatment (70°C, 8 minutes, no UV light, recommended ambient relative humidity 30%–70%RH), liquid electrostatic printing (2.5kV, 800dpi, 20m / min), UV curing (365nm, 500mJ / cm²). 2 The time (2 seconds) was the same as in Example 1. This comparative example verifies the necessary contribution of propylene carbonate nanoscale swelling to the interfacial covalent bond density. Without swelling assistance, the transesterification reaction only occurs at the physical contact surface between the base coating and the substrate, and the interfacial bond density is insufficient to achieve a high level of adhesion.

[0100] Comparative Example 4 (Titanium chelate catalyst exceeds the upper limit)

[0101] The primer composition formulation (in grams) is as follows: GDMA 40.0 g, GPTMS 6.0 g, diisopropoxybis(acetylacetone)titanium(IV) 3.0 g, propylene carbonate 10.0 g, HDDA 28.0 g (reduced by 2.0 g compared to Example 1 to compensate for the catalyst increment), and Irgacure 184 3.0 g, totaling 90.0 g of the six components. The preparation conditions were the same as in Example 1 (25°C, 300 rpm, 30 minutes, protected from light; pH value not applicable for non-aqueous systems). The measured viscosity at 25°C was 38 mPa·s. All other process steps were the same as in Example 1. The catalyst dosage in this comparative example, 3.0 parts, exceeds the upper limit (1.8 parts), verifying the excessive degradation effect of excess titanium catalyst on the polycarbonate surface. It is expected that the excessive Lewis acid-active titanium catalytic centers will accelerate the excessive breaking of carbonate bonds on the polycarbonate surface. The breaking rate will exceed the rate of new ester bond formation, leading to a decrease in the molecular weight and integrity of the polycarbonate surface layer. This will manifest as a significant increase in surface haze and a decrease in adhesion caused by insufficient cohesive strength within the degradation layer.

[0102] Comparative Example 5 (propylene carbonate exceeds the upper limit)

[0103] The primer composition formulation (in grams) is as follows: GDMA 40.0 g, GPTMS 6.0 g, diisopropoxybis(acetylacetone)titanium(IV) 1.0 g, propylene carbonate 22.0 g, HDDA 18.0 g (reduced by 12.0 g compared to Example 1 to compensate for the increased propylene carbonate content), and Irgacure 184 3.0 g, totaling 90.0 g. The preparation conditions were the same as in Example 1 (25°C, 300 rpm, 30 minutes, protected from light; pH value not applicable for non-aqueous systems). The measured viscosity at 25°C was 46 mPa·s. All other process steps were the same as in Example 1. The amount of propylene carbonate used in this comparative example, 22 parts, far exceeds the upper limit of the claim (14 parts), verifying the effect of excessive swelling on stress cracking of polycarbonate. It is expected that excessive propylene carbonate will cause the swelling depth and extent of the polycarbonate surface layer to exceed the safety window, generating an excessively large swelling stress gradient during heat treatment, causing streaks and impairing the mechanical integrity of the substrate.

[0104] Performance testing

[0105] The following performance tests were performed on the decorative panel samples prepared in Examples 1-13 and Comparative Examples 1-5.

[0106] Initial adhesion test: Performed according to ASTM D3359 standard method B (cross-cut test). Use a multi-blade cutter with 1mm spacing to cut 25 squares (5×5) on the surface of the ink layer. Apply 3M 610 test tape and pull it off with uniform force. The grade is determined according to the area of ​​peeling (5B = no peeling, 0B = peeling > 65%).

[0107] Adhesion test after boiling water immersion: Immerse the sample completely in boiling water at 100°C for 2 hours, remove it and dry it at room temperature for 30 minutes, and determine the adhesion grade according to ASTM D3359 Method B.

[0108] Adhesion test after thermal cycling: The sample is subjected to 100 cycles of -40℃ (hold for 30 minutes) → 85℃ (hold for 30 minutes) as one cycle. After removal, the sample is placed at room temperature for 2 hours, and the adhesion grade is determined according to ASTM D3359 Method B.

[0109] Adhesion test after UV aging: The sample was placed in a QUV-A accelerated UV aging tester (340nm fluorescent UV lamp, irradiance 0.89W / m). 2 / nm, blackboard temperature 60°C), continuous irradiation for 500 hours (Example 7 extended to 1000 hours), adhesion rating determined according to ASTM D3359 Method B.

[0110] Stress cracking test: Using the 1% bending strain superposition method, the sample coated with primer and heat-treated was bent to the radius of curvature corresponding to 1% surface strain and held for 24 hours. The number of silver streaks (streaks / cm) was observed and counted under a stereomicroscope (50×). 2 ) and length.

[0111] Surface haze change test: The surface haze of the polycarbonate substrate before and after the primer coating and heat treatment was measured using a haze meter (according to ASTM D1003 standard), and the haze change value ΔHaze (%) was calculated. This indicator is not applicable to the aluminum alloy substrate (Example 9), which is an opaque substrate.

[0112] ATR-FTIR characterization of interfacial chemical bonding: Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) was used, with diamond ATR crystal directly contacting the interface region of the heat-treated base coating / polycarbonate substrate. The scanning range was 4000–700 cm⁻¹. -1 4cm resolution -1 A total of 32 scans were performed. The focus was on analyzing the 1700–1800 cm area. -1 The carbonyl stretching vibration region and 3200–3600 cm⁻¹ are within the range. -1 The spectral peak changes in the hydroxyl stretching vibration region within the specified range were analyzed to confirm the occurrence of the transesterification reaction. Comparative analyses were performed on Example 1, Comparative Example 2, and Comparative Example 4.

[0113] XPS characterization of interfacial chemical bonding: X-ray photoelectron spectroscopy (XPS) was used with AlKα rays (1486.6 eV) as the excitation source to perform elemental analysis and high-resolution spectral analysis on the polycarbonate surface after thorough rinsing with n-hexane (immersion for 5 minutes × 3 times to remove physically adsorbed substrate components, retaining only chemically bonded components). The Ti2p, Si2p, and C1s signals were specifically detected. Example 1 was characterized.

[0114] The formulations of the primer compositions for each embodiment and comparative example are summarized in the table below.

[0115] Table 1. Formulations of primer compositions in Examples 1-7 (unit: g)

[0116] GDMA 40.0 40.0 40.0 40.0 40.0 40.0 42.0 GPTMS 6.0 6.0 6.0 6.0 6.0 - 6.0 APTES - - - - - 6.0 - Ti catalyst 1.0 0.5 1.8 1.0 1.0 1.0 1.0 propylene carbonate 10.0 10.0 10.0 6.0 14.0 10.0 10.0 HDDA 30.0 30.5 29.2 34.0 26.0 30.0 28.0 Irgacure184 3.0 3.0 3.0 3.0 3.0 3.0 3.0 total 90.0 90.0 90.0 90.0 90.0 90.0 90.0 Viscosity at 25℃ (mPa·s) 38 39 37 35 42 36 40

[0117] Note: "-" in the table indicates that the component is not included in the corresponding formula.

[0118] Table 2. Formulations of primer compositions for Examples 8-13 (unit: g)

[0119] GDMA - 40.0 30.0 50.0 40.0 40.0 GMA-AA Additive 40.0 - - - - - GPTMS 6.0 6.0 6.0 6.0 6.0 6.0 Ti catalyst 1.0 1.0 1.0 1.0 1.0 1.0 propylene carbonate 10.0 10.0 10.0 10.0 10.0 10.0 HDDA 30.0 30.0 40.0 20.0 - 30.0 TPGDA - - - - 30.0 - Irgacure184 3.0 3.0 3.0 3.0 3.0 - Darocur1173 - - - - - 3.0 total 90.0 90.0 90.0 90.0 90.0 90.0 Viscosity at 25℃ (mPa·s) 45 38 32 48 42 37

[0120] Note: "-" in the table indicates that the component is not included in the corresponding formulation. Example 9 uses an aluminum alloy sheet as the substrate.

[0121] Table 3. Formulations of primer compositions for Comparative Examples 1–5 (unit: g)

[0122] GDMA - 40.0 40.0 40.0 40.0 GPTMS - 6.0 6.0 6.0 6.0 Ti catalyst - 0 1.0 3.0 1.0 propylene carbonate - 10.0 0 10.0 22.0 HDDA - 31.0 40.0 28.0 18.0 Irgacure184 - 3.0 3.0 3.0 3.0 total No base coat 90.0 90.0 90.0 90.0 Viscosity at 25℃ (mPa·s) - 37 30 38 46

[0123] Note: Comparative Example 1 is direct printing without primer and does not involve primer formulation.

[0124] The performance test results of each embodiment and comparative example are summarized in the table below.

[0125] Table 4 Performance test results of Examples 1-7

[0126] Initial adhesion 5B 4B~5B 5B 4B 5B 5B 5B Adhesion after soaking in boiling water 5B 4B 4B~5B 3B~4B 4B~5B 4B 5B Adhesion after thermal cycling 4B~5B 4B 4B 3B~4B 4B 4B 5B Adhesion after 500 hours of UV aging 4B 3B~4B 4B 3B 4B 3B~4B 4B Adhesion after 1000 hours of UV aging - - - - - - 4B silver streaks (bars / cm 2 )]]> 0 0 0 0 ≤3 0 0 ΔHaze(%) ≤0.3 ≤0.3 0.8 ≤0.3 ≤0.5 ≤0.3 ≤0.3

[0127] Note: Only Example 7 underwent a 1000-hour UV aging extension test; the others are marked with "-".

[0128] Table 5 Performance test results of Examples 8-13

[0129] Initial adhesion 5B 4B~5B 4B 5B 5B 5B Adhesion after soaking in boiling water 4B~5B 4B 3B~4B 4B~5B 5B 5B Adhesion after thermal cycling 4B 3B~4B 3B 4B 4B~5B 4B~5B Adhesion after 500 hours of UV aging 4B 3B~4B 3B 3B~4B 4B 4B <![CDATA[Craze (number / cm 2 )]]> 0 0 0 0 0 0 ΔHaze(%) ≤0.3 N / A ≤0.3 ≤0.3 ≤0.3 ≤0.3

[0130] Note: Example 9 uses an opaque aluminum alloy substrate, so ΔHaze is not applicable and is marked "N / A".

[0131] Table 6 Performance test results for Comparative Examples 1-5

[0132] Initial adhesion 0B~1B 2B~3B 3B 3B~4B 4B~5B Adhesion after soaking in boiling water 0B 1B~2B 2B 2B~3B 3B Adhesion after thermal cycling 0B 1B~2B 2B~3B 2B~3B 3B Adhesion after 500 hours of UV aging 0B 1B~2B 2B 2B~3B 3B <![CDATA[Craze (number / cm 2 )]]> N / A 0 0 0 8～15 ΔHaze(%) 0 ≤0.3 ≤0.3 3.2 ≤0.5

[0133] Note: Comparative Example 1 has no base coating, so the silver streak test is not applicable. It is marked "N / A".

[0134] ATR-FTIR and XPS characterization results

[0135] ATR-FTIR comparative characterization of interfacial chemical bonding was performed on Examples 1, 2, and 4, while XPS characterization was performed on Example 1. The ATR-FTIR characterization results are as follows: Figure 4 As shown, curve a represents Example 1, curve b represents Comparative Example 2, and curve c represents Comparative Example 4.

[0136] ATR-FTIR characterization results showed that in Example 1, a 1768 cm⁻¹ was observed at the interface between the base coat and the polycarbonate substrate. -1 A new shoulder peak for the carbonyl stretching vibration of ester appears, relative to the carbonate bond in polycarbonate at 1775 cm⁻¹. -1 The characteristic peak at that location has a redshift of approximately 7 cm. -1 This new peak is attributed to the C=O stretching vibration in a new mixed ester bond formed during transesterification, where the chemical environment differs from the original carbonate bond. Simultaneously, at 3450 cm⁻¹... -1 The intensity of the hydroxyl stretching vibration peak at the coating site was significantly lower than before coating, consistent with the expectation that the secondary hydroxyl group of the β-hydroxy ester group in the GDMA molecule would be consumed in the transesterification reaction. As a control, Comparative Example 2 (without titanium chelate catalyst) did not show a peak intensity of 1768 cm⁻¹ under the same heat treatment conditions (70℃ × 8 min). -1 The new ester bond shoulder peak at 3450cm -1 The hydroxyl peak intensity showed no significant change, directly proving that the titanium chelate catalyst is a necessary condition for the transesterification reaction—relying solely on 70℃ thermal energy is insufficient to drive the transesterification reaction between β-hydroxy ester groups and polycarbonate carbonate bonds. Comparative Example 4 (3.0 parts of titanium chelate catalyst, exceeding the upper limit) showed an intensity at 1700–1750 cm⁻¹. -1 The appearance of new absorption peaks in the region, which are attributed to carbonate degradation products (including free carbonic acid and low molecular weight carbonate fragments), confirms that excessive catalyst leads to excessive cleavage and degradation of carbonate bonds on the polycarbonate surface.

[0137] The XPS characterization results of Example 1 are as follows: Figure 5 As shown, where Figure 5 (a) is the wide scan spectrum. Figure 5(b) is the C1s high-resolution spectrum. XPS characterization results show that after thorough rinsing with hexane (immersion for 5 minutes × 3 times) in Example 1, Ti2p signals (binding energy 458.3 eV, content approximately 0.4 at%) and Si2p signals (binding energy 102.1 eV, content approximately 1.2 at%) were still detectable on the polycarbonate surface. The physical adsorption layer could be completely removed by rinsing with organic solvents, while the remaining Ti and Si signals after hexane rinsing indicate that the primer components are anchored to the polycarbonate surface by chemical bonds rather than by physical adsorption. In the C1s high-resolution spectrum, a new fitted peak appears at 289.5 eV, which is about 0.6 eV lower than the original peak of C=O in polycarbonate at 290.1 ​​eV. This is attributed to the change in the chemical environment of the carbonyl carbon in the new ester bond generated by the transesterification reaction, further confirming the formation of interface I covalent bonds at the elemental chemical state level.

[0138] The following conclusions can be drawn from the data in Tables 4 to 6.

[0139] The initial adhesion of Examples 1 to 13 all reached level 4B or above, with the initial adhesion of Examples 1, 3, 5, 6, 7, 8, 11, 12, and 13 reaching level 5B. This proves that the dual-interface chemical bonding design of the primer composition of the present invention can achieve excellent interfacial adhesion under different formulation parameters, component substitutions, and dosage boundary conditions.

[0140] Comparing Example 1 (standard formulation, 5B) with Comparative Example 1 (no primer, 0B-1B), it can be seen that the primer composition improves the initial adhesion from 0B-1B to 5B, and the adhesion after boiling water immersion improves from 0B to 5B, representing a significant improvement in adhesion.

[0141] Comparing Example 1 with Comparative Example 2 (without catalyst, 2B-3B), it can be seen that the absence of titanium chelate catalyst leads to a decrease in adhesion from 5B to 2B-3B, proving that the catalyst is a necessary condition for the formation of interface I covalent bonds in the transesterification reaction.

[0142] ATR-FTIR characterization further confirmed this conclusion directly at the spectroscopic level—Example 1 at 1768 cm⁻¹ -1 A new ester bond shoulder peak appeared in Example 1, while it did not appear in Comparative Example 2. Comparing Example 1 with Comparative Example 3 (without propylene carbonate, 3B), it can be seen that the lack of propylene carbonate swelling assistance resulted in a decrease in adhesion from 5B to 3B, demonstrating the effect of nanoscale swelling on improving the interfacial contact area and covalent bond density of the transesterification reaction.

[0143] The adhesion of the complete formulation (Examples 1, 5B) far exceeded that of Comparative Examples 2 (2B–3B) and 3 (3B), demonstrating a significant over-addition and synergistic effect among the components. XPS characterization showed that Ti and Si signals were still detected after hexane rinsing, as well as a new C1s peak at 289.5 eV, directly confirming from the elemental chemical state level that the primer components are anchored to the polycarbonate surface through chemical bonds (rather than physical adsorption).

[0144] The comparison between Example 2 (0.5 parts catalyst, initial 4B-5B) and Example 3 (1.8 parts catalyst, initial 5B but ΔHaze=0.8%) shows that there is a narrow optimal window for catalyst dosage - if it is too low, the transesterification reaction efficiency is insufficient, resulting in a slight decrease in adhesion; if it is too high, the carbonate bonds on the polycarbonate surface are excessively broken, resulting in an increase in haze.

[0145] Comparative Example 4 (catalyst 3.0 parts exceeding the upper limit, initial 3B~4B, ΔHaze=3.2%) further confirmed this trend—after the catalyst dosage exceeded the upper limit by 1.8 parts, the adhesion decreased instead of increasing, and the surface haze increased significantly, with ATR-FTIR at 1700~1750 cm⁻¹. -1 The presence of characteristic absorption peaks from polycarbonate degradation products in the region confirms that excessive catalyst leads to chemical degradation of the polycarbonate surface layer, and the insufficient cohesive strength of the degradation layer becomes a weak point in adhesion. This result provides direct data support for setting the upper limit of catalyst at 1.8 parts.

[0146] Example 4 (6 parts propylene carbonate, initial 4B) and Example 5 (14 parts propylene carbonate, initial 5B but ≤3 streaks / cm) 2 The comparison of micro-stretch marks (micro-stretch marks) indicates that there is also a safe swelling window for the amount of propylene carbonate used. Comparative Example 5 (22 parts propylene carbonate, exceeding the upper limit, with 8-15 silver streaks / cm) 2 The fact that adhesion dropped to 3B after boiling water immersion further confirms this trend—when the amount of propylene carbonate far exceeds the upper limit of 14 parts, a large number of silver streaks appear on the polycarbonate surface, the mechanical integrity is damaged, and the adhesion decreases sharply after boiling water immersion. This result provides direct data support for the setting of the upper limit of 14 parts of propylene carbonate in claim 1.

[0147] The adhesion after thermal cycling (5B) and the adhesion after 1000 hours of UV aging (4B) of Example 7 (preferred formulation) are both better than those of Example 1, demonstrating the further improvement of the preferred formulation in long-term durability.

[0148] Example 6 (APTES instead of GPTMS, initial 5B but 4B after boiling water) compares with Example 1 (GPTMS, 5B after boiling water) to demonstrate that the covalent CO bonds formed by the ring-opening addition of the epoxy groups in GPTMS are more stable under humid and hot conditions than the hydrogen bonds formed by the amino groups in APTES. Example 8 (GMA-AA addition product instead of GDMA, initial 5B) demonstrates that the dual-interface bridging function of component (A) depends on the bifunctional structure containing both β-hydroxy ester groups and acryloyl groups in the molecule, and is not dependent on any specific compound. Example 9 (aluminum alloy substrate, initial 4B-5B lower than 5B on polycarbonate substrate) shows that there are no carbonate bonds on the aluminum alloy surface, the transesterification bonding mechanism is not applicable, and the adhesion mainly comes from the Si-O-Al covalent bonds formed by the silane coupling agent.

[0149] Examples 10 (30 parts GDMA, initial 4B) and 11 (50 parts GDMA, initial 5B) verified the effectiveness of component A at the upper and lower limits of the claims. At the lower limit of 30 parts GDMA, the reduced interfacial concentration of β-hydroxy ester groups led to insufficient transesterification bonding density, and the initial adhesion decreased to 4B, but was still significantly better than all comparative examples, demonstrating that 30 parts GDMA can still achieve meaningful bifacial chemical bonding. At the upper limit of 50 parts GDMA, the initial adhesion remained at 5B, and after boiling water immersion, it remained at 4B–5B, indicating that increasing the interfacial concentration of β-hydroxy ester groups can sufficiently improve the transesterification reaction efficiency, and that even with HDDA dosage reduced to the lower limit of 20 parts, sufficient UV-curable crosslinking network support can still be provided.

[0150] Examples 12 (TPGDA instead of HDDA, initial 5B, 5B after boiling water) and 13 (Darocur 1173 instead of Irgacure 184, initial 5B, 5B after boiling water) respectively verified the feasibility of the reactive diluent and photoinitiator substitution options. The ether-oxygen bonded propylene glycol backbone of TPGDA imparts cured coatings with adhesion and flexibility comparable to or even slightly superior to HDDA. The equivalence of Darocur 1173 and Irgacure 184 in UV curing initiation efficiency allows them to be used interchangeably without affecting the dual-interface bonding function of the primer composition.

[0151] The stress cracking results of all examples show that propylene carbonate does not cause or causes very few polycarbonate streaks within a safety window of 6–14 parts (0 streaks / cm in Examples 1, 2, 3, 4, 6, 7, 8, 9, 10, 11, 12, and 13). 2 Only in Example 5 (14 parts propylene carbonate, close to the upper limit) were very few micro-cracks (≤3 cracks / cm). 2 (Length <50μm), verifying the solubility parameter of propylene carbonate and polycarbonate is approximately 7.5MPa. 0.5The controlled swelling effect is achieved through a moderate difference in concentration. In contrast, Comparative Example 5 (22 parts propylene carbonate, exceeding the upper limit) exhibited numerous silver streaks (8–15 streaks / cm). 2 This clearly defines the upper limit boundary of the safety window.

[0152] Based on the analysis of all data in Tables 4 to 6, when the amount of titanium chelate catalyst is within the optimal range of 0.8–1.2 parts and the amount of propylene carbonate is within the optimal range of 8–12 parts (as in Examples 1 and 7), the resulting decorative panel can stably achieve comprehensive performance indicators of initial adhesion grade 5B, adhesion grade not lower than 4B after boiling water immersion, and adhesion grade not lower than 4B after thermal cycling. Formulations outside this optimal window but still within the range (as in Examples 2, 4, and 10), although showing a slight decrease in adhesion grade, are still significantly better than all comparative examples, indicating that the primer compositions within this range can achieve a meaningful dual-interface chemical bonding enhancement effect.

[0153] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A primer composition, characterized in that, Raw materials, by weight, include: 30 to 50 parts of β-hydroxy ester functional acrylate oligomer, wherein each molecule of the β-hydroxy ester functional acrylate oligomer contains at least one β-hydroxy ester group and at least one (meth)acryloyl group, wherein the hydroxyl group in the β-hydroxy ester group is located at the β position relative to the ester bond; 4–8 parts organosilane coupling agent; 0.5–1.8 parts of titanium chelate catalyst, wherein the titanium chelate catalyst contains β-diketone chelating ligands; 6 to 14 parts of cyclic carbonate solvent, wherein the boiling point of the cyclic carbonate solvent is ≥200°C; 20 to 40 parts of reactive diluent, wherein the reactive diluent is a polyfunctional (meth)acrylate monomer containing at least two (meth)acryloyl groups; 2 to 4 parts of photoinitiator.

2. The primer composition as claimed in claim 1, characterized in that, The amount of the titanium chelate catalyst is 0.8 to 1.2 parts, and the amount of the cyclic carbonate solvent is 8 to 12 parts; the titanium chelate catalyst is diisopropoxybis(acetylacetone)titanium(IV); and the cyclic carbonate solvent is propylene carbonate.

3. The primer composition as described in claim 1 or 2, characterized in that, The β-hydroxy ester functional acrylate oligomer is selected from one of the following: (i) Glyceryl dimethacrylate, with a molecular weight of 226–230, wherein the two primary hydroxyl groups at positions 1 and 3 of the glycerol backbone are esterified with methacrylate to form two methacryl groups, while the secondary hydroxyl group at position 2 remains unreacted; or (ii) A ring-opening addition product of glycidyl methacrylate and acrylic acid, having a number average molecular weight of 280-290, with each molecule containing one methacrylamide group and one β-hydroxy ester group; the ring-opening addition product is prepared by mixing glycidyl methacrylate and acrylic acid in a 1:1 molar ratio, adding 0.5 wt% of triphenylphosphine as a catalyst, and reacting at 80°C for 6 hours.

4. The primer composition according to any one of claims 1 to 3, characterized in that, The organosilane coupling agent is selected from at least one of 3-glycidoxypropyltrimethoxysilane and 3-aminopropyltriethoxysilane; the reactive diluent is selected from one or a mixture of 1,6-hexanediol diacrylate and tripropylene glycol diacrylate; the photoinitiator is selected from one or a mixture of 1-hydroxycyclohexylphenyl ketone and 2-hydroxy-2-methyl-1-phenyl-1-propanone; and the viscosity of the primer composition at 25°C is 10–80 mPa·s.

5. A method for preparing a decorative panel, characterized in that, Includes the following steps: Step (1) Preparation of the primer composition: Mix each component of the primer composition according to any one of claims 1 to 4 at 25°C and a stirring speed of 300 rpm for 30 minutes under light-protected conditions to obtain the primer composition; Step (2) Substrate cleaning: The surface of the engineering plastic substrate containing carbonate bonds and / or ester bonds is cleaned by wiping with isopropanol or CO2 snow cleaning, and dried at room temperature for 5 minutes; the substrate surface is not subjected to corona treatment, plasma treatment or flame treatment; Step (3) Primer coating: Apply the primer composition obtained in step (1) to the cleaned substrate surface using a wire bar coater, roller coating, spraying or curtain coating method, with a wet film thickness of 1 to 8 μm; Step (4) Heat treatment: Under conditions without ultraviolet light irradiation, the coated substrate is placed in a hot air oven or infrared heating tunnel and heat-treated at 60-80°C for 5-10 minutes, so that the β-hydroxy ester groups in the base coating composition undergo ester exchange reaction with the carbonate bonds on the substrate surface under the catalysis of titanium chelate catalyst to form interface I covalent bonding, and at the same time, the cyclic carbonate solvent achieves nanoscale swelling of the substrate surface layer; Step (5) Liquid electrostatic printing: Apply radiation-curable ink to the surface of the heat-treated base coating using liquid electrostatic printing; Step (6) Ultraviolet curing: Irradiation is performed using an ultraviolet light source with a wavelength of 340–400 nm and an irradiation energy of 300–700 mJ / cm². 2 The curing time is 1 to 5 seconds, which allows the residual (meth)acryloyl groups in the base layer to undergo a free radical copolymerization reaction with the acrylate components in the ink layer to form interface II covalent bonds.

6. The preparation method according to claim 5, characterized in that, In step (4), the heat treatment temperature is 65-75℃, the heat treatment time is 6-9 minutes, and the relative humidity of the heat treatment environment is 30%-70%RH; the engineering plastic substrate in step (2) is a bisphenol A type polycarbonate sheet with a thickness of 1-3mm, and the use of acetone, dichloromethane or methyl ethyl ketone is strictly prohibited in the substrate cleaning process; the wet film thickness in step (3) is 2-5μm.

7. The preparation method according to claim 5 or 6, characterized in that, The ultraviolet light source mentioned in step (6) is a 365nm ultraviolet LED light source with an irradiation energy of 400-600mJ / cm². 2 ; The radiation-curable ink in step (5) comprises, by weight: 50 parts trimethylolpropane triacrylate, 18 parts polyurethane acrylate oligomer, 8 parts pigment, 2 parts charge control agent, 5 parts photoinitiator, and 3 parts polymeric dispersant. The viscosity of the radiation-curable ink at 25°C is 50 mPa·s. The DC voltage for liquid electrostatic printing is 1–4 kV, the printing resolution is 600–1200 dpi, and the substrate conveying speed is 10–30 m / min. Optionally, after step (6), step (7) is further included: spraying a 2–8 μm thick transparent UV-curable varnish onto the surface of the cured ink layer at a concentration of 300–700 mJ / cm². 2 Ultraviolet light curing is performed using irradiation energy.

8. A decorative panel, characterized in that, The decorative panel is prepared by any one of claims 5 to 7, and comprises, from the substrate outwards: an engineering plastic substrate layer containing carbonate bonds and / or ester bonds; a base layer, wherein the base layer and the substrate layer are covalently connected by mixed ester bonds formed by transesterification reaction catalyzed by titanium chelates, and the base layer and the ink pattern layer are covalently connected by CC bonds formed by free radical copolymerization of acrylates initiated by ultraviolet light; and a cured ink pattern layer.

9. The decorative panel as described in claim 8, characterized in that, The decorative panel shall have an initial adhesion grade of no less than 4B as determined by the cross-cut adhesion test according to ASTM D3359 standard; an adhesion grade of no less than 3B after immersion in boiling water at 100°C for 2 hours; an adhesion grade of no less than 3B after 100 cycles of thermal cycling from -40°C to 85°C; and no more than 3 streaks / cm under 1% bending strain. 2 The surface haze change ΔHaze ≤ 1.0%.

10. The decorative panel as described in claim 9, characterized in that, The decorative panel has an initial adhesion grade of 5B as determined by the cross-cut adhesion test according to ASTM D3359 standard. After immersion in boiling water at 100°C for 2 hours, the adhesion grade is not lower than 4B. After 100 cycles of thermal cycling from -40°C to 85°C, the adhesion grade is not lower than 4B. After 500 hours of QUV-A ultraviolet aging, the adhesion grade is not lower than 4B. No silver streaks are generated under 1% bending strain, and the surface haze change ΔHaze is ≤0.3%.

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