UV-LED curing type heat-sensitive protective varnish and coating method thereof

Abstract

This invention relates to the field of thermosensitive protective varnish technology, and discloses a UV-LED curable thermosensitive protective varnish and its coating method, comprising 40-70% photocurable resin, 15-45% reactive diluent, 2-6% UV-LED matched photoinitiator system, 0.1-3% additives, and 0.1-3% inert viscosity reducer. The photocurable resin is composed of the following materials: 30-60% flexible modified epoxy acrylate, 20-40% hyperbranched acrylic resin, and 20-40% silicone modified resin. This invention overcomes the contradiction that high hardness in traditional varnishes inevitably leads to high shrinkage. By introducing hyperbranched acrylic resin to reduce the viscosity of the system and strictly limiting the amount of trifunctional monomers (such as TMPTA) to below 10%, combined with the balancing effect of difunctional TPGDA, the curing shrinkage rate is controlled within 3-5%. Combined with the volume expansion characteristics of the cationic hybrid system, the internal stress of the coating is greatly reduced, so that the protective film maintains excellent adhesion when the thermosensitive substrate is repeatedly bent, without cracking or peeling.

Description

Technical Field

[0001] This invention belongs to the field of thermosensitive protective varnish technology, specifically a UV-LED curable thermosensitive protective varnish and its coating method. Background Technology

[0002] With the rapid development of digital printing, logistics labeling and medical imaging industries, the application of thermal substrates (such as thermal printing paper, PVC film, PET / PETG label surface layer, etc.) is becoming increasingly widespread. In order to protect the thermal coating from wear, oxidation and chemical corrosion, it is usually necessary to coat its surface with a protective varnish.

[0003] Currently, the industry generally adopts the following technical solutions: traditional solvent-based or water-based varnishes: although they are low in cost, they contain a large amount of volatile organic compounds (VOCs), which do not meet environmental protection requirements. Moreover, the drying process is energy-intensive and can easily cause the heat-sensitive substrate to deform, curl, or the color layer to develop color prematurely. Therefore, we propose a UV-LED curable heat-sensitive protective varnish and its coating method. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention provides a UV-LED curable thermosensitive protective varnish and its coating method, which effectively solves the above problems.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a UV-LED curable thermosensitive protective varnish, comprising 40-70% UV-curable resin, 15-45% reactive diluent, 2-6% UV-LED matched photoinitiator system, 0.1-3% additives, and 0.1-3% inert viscosity modifier;

[0006] The photocurable resin is composed of the following materials: 30-60% flexible modified epoxy acrylate, 20-40% hyperbranched acrylic resin, 20-40% silicone modified resin, and the remainder is aliphatic polyurethane acrylate, wherein the aliphatic polyurethane acrylate (FPUA) can be selected from: CN9006, CN9013 (Sartomer), Ebecryl8402, the hyperbranched acrylic resin can be pentaerythritol core hyperbranched polyester acrylate, and the silicone modified resin can be polydimethylsiloxane grafted PUA.

[0007] The active diluent is composed of the following materials: 40-60% monofunctional, 30-50% difunctional, 5-10% trifunctional, and 5-10% special materials. Monofunctional materials (softening, viscosity reducing, and shrinkage reducing) can be IBOA (isobornyl acrylate), 2-EHA (2-ethylhexyl acrylate), or LauryylAcrylate (LA); difunctional materials can be TPGDA (tripropylene glycol diacrylate), HDDA (1,6-hexanediol diacrylate), or NPGDA (neopentyl glycol diacrylate); trifunctional materials can be TMPTA (trimethylolpropane triacrylate) or EOTMPTA (ethoxylated TMPTA); and special materials can be 2-HEA-P (2-hydroxyethyl methacrylate phosphate) or β-CEA (β-carboxyethyl acrylate).

[0008] The UV-LED matching photoinitiator system comprises 30-50% acylphosphine oxides, 10-20% second-generation phosphine oxides, 10-20% α-aminoketones, 30-50% co-initiators or hydrogen donors, and 5-10% visible light initiators. Acylphosphine oxides (the main component) can be TPO or 819 (Bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide); second-generation phosphine oxides can be TPO-L (Ethyl(2,4,6-trimethylbenzoyl)phenylphosphinate).

[0009] The α-aminoketones may be 907 (2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one) + co-initiator;

[0010] The co-initiator / hydrogen donor may be an acrylated active amine (such as GenocureLTM) or ITX (isopropylthioxanthraquinone).

[0011] The visible light initiator can be camphor quinone (CQ) + amine.

[0012] The additives consist of 60-90% leveling agent and 25-40% defoamer.

[0013] Leveling agents such as BYK-307 / 333 and TegoGlide410 can be used.

[0014] Defoamers such as BYK-052 and TegoFoamex810 can be used. Their function is to disrupt the foam stability of polydimethylsiloxane / polyethersiloxane copolymers and prevent the generation of microbubbles during stirring and coating.

[0015] TegoWet270 / 280 can be used as a substrate wetting agent;

[0016] The polymerization inhibitor (stable during storage and transportation) can be MEHQ (p-methoxyphenol);

[0017] Nano-wear-resistant fillers: Fumed silica (Aerosil200 / R972) and nano-alumina can be used;

[0018] Anti-aging stabilizers can be: Tinuvin 123 (HALS) and Irganox 1010 (antioxidant).

[0019] Preferably, it further includes 1-3% surface enhancer, wherein the surface enhancer comprises 40-60% fluorescent whitening agent and 40-60% infrared absorber;

[0020] The fluorescent whitening agent (FWA) can be Tinopal CBS-X or Uvitex OB;

[0021] The infrared absorber is made of ITO slurry or copper phthalocyanine.

[0022] Preferably, it also includes 1-3% functional microspheres, wherein the polyurethane microspheres comprise 30-60% and the hollow glass microspheres comprise 40-70%;

[0023] The polyurethane microspheres can be SokenChemPSRseries, JSRMicrosphere;

[0024] The hollow glass microspheres can be made of 3M Glass Bubbles.

[0025] Preferably, it also includes a barrier material, which may be one or more of the following raw materials in combination as needed: PVDC emulsion, EVOH, graphene / nanoclay dispersion;

[0026] PVDC emulsions (polyvinylidene chloride) can be made from DowSaran or SolvayIxan.

[0027] EVOH (ethylene-vinyl alcohol copolymer) can be produced using KurarayEval;

[0028] The graphene / nanoclay dispersion can be prepared using Nanocor I.44P.

[0029] Preferably, it also includes a secondary curing agent, wherein the secondary curing agent is classified as 1-3% of the total amount, and the material of the secondary curing agent is one or more combinations of moisture-curing isocyanate, aziridine crosslinking agent, and carbodiimide crosslinking agent;

[0030] The moisture-curing isocyanate can be Desmodur N series or Tolonate HDT;

[0031] The aziridine crosslinking agent can be CX-100 (NeoRezR-9320);

[0032] The carbodiimide crosslinking agent can be Carbodilite V-02 or a hydrolysis stabilizer.

[0033] Preferably, it also includes additives, including antislip / texturing agents, rheology modifiers, and special substrate wetting agents;

[0034] The anti-slip / texturing agent can be SYLOIDRAD2100 (silica) or Sandorin Micro;

[0035] The rheology modifier (thixotropic agent) may be BYK-410 (polyurethane) or DeuRheo229.

[0036] A method for applying a UV-LED curable thermosensitive protective varnish:

[0037] The coating method specifically includes the following steps:

[0038] S1: Production Preparation

[0039] The raw materials are processed to obtain a protective varnish;

[0040] S2: Substrate Pretreatment (Surface Treatment)

[0041] Corona / Plasma Treatment: For low surface energy substrates such as PET / PVC, online corona treatment is required before coating. The dyn value needs to reach 38-42 dyn / cm to ensure varnish wetting.

[0042] Dust removal: Static electricity and dust on the substrate surface are removed by sticky rollers and high-pressure ion air bars;

[0043] Preheating (caution): If the substrate has a high moisture content, far-infrared low-temperature preheating (<50℃) can be used to remove surface moisture, but it needs to be cooled to below 30℃ before coating.

[0044] Process parameters:

[0045] Dyne pen test: 38-42 dyn / cm;

[0046] Surface resistance: <10^11Ω, preventing static electricity from attracting dust;

[0047] S3: Precision Coating (Coating Method)

[0048] Micro-grooved roller coating:

[0049] - Anilox roller: Select a ceramic anilox roller with 60-120 lines / cm;

[0050] - Rubber roller: Hardness 70-80 Shore A, to prevent damage to heat-sensitive substrate;

[0051] - Coating gap: The gap between the anilox roller and the substrate is controlled at 0.5-1.0mm;

[0052] Slit coating (high-end): The die temperature is controlled at 30-35℃ to prevent viscosity changes from causing streaks;

[0053] Process parameters:

[0054] Wet film thickness: Monitored online using a wet film thickness gauge.

[0055] Viscosity: Controlled at 25℃ between 200-800 cps (depending on the coating method);

[0056] S4: Leveling and Infrared Shielding

[0057] Dust-free constant temperature leveling: stay in the sealed cavity for 3-8 seconds, and use hot air (<45℃) or far-infrared (shielding medium wave IR) to assist leveling;

[0058] Key point: Quartz glass heat insulation panels need to be installed in the leveling section to prevent the heat from the subsequent UV lamps from flowing back into the substrate;

[0059] Process parameters:

[0060] Surface condition: No orange peel texture, no ripples;

[0061] Temperature: Substrate surface temperature < 40℃;

[0062] S5: UV-LED Curing (The CoreStep)

[0063] Light source configuration: 395nm light source is used as the main light source (taking into account both penetration and surface curing);

[0064] Energy control: Monitor using a radiometer, with a recommended energy density of 600-1200 mJ / cm² and peak irradiance of 2-4 W / cm².

[0065] Segmented curing: The first lamp is pre-cured at low energy (30%) to prevent pinholes caused by surface tension gradient; the second lamp is fully cured at high energy (100%).

[0066] Cooling system: The LED lamp head must be water-cooled or powerfully air-cooled to ensure that the junction temperature of the LED beads is <65℃ to prevent wavelength drift.

[0067] Process parameters:

[0068] Curing degree: Double bond conversion rate was measured by acetone wiping method or FT-IR (>90%).

[0069] Adhesion: Grade 0 in cross-cut adhesion test;

[0070] S6: Post-processing

[0071] Slow cooling: The temperature of the newly cured film is relatively high, and it needs to be cooled to room temperature by cooling rollers (15-20℃ circulating water);

[0072] Tension control: The winding tension needs to be gradually reduced to prevent the heat-sensitive substrate from "bursting" or deforming due to internal stress shrinkage;

[0073] Aging: After winding, place at 25°C for 24-48 hours to allow intermolecular forces (hydrogen bonds) to fully recombine and achieve optimal performance;

[0074] Process parameters:

[0075] Winding hardness: Moderate hardness;

[0076] No collapsed residual solvent: ND (not detected).

[0077] Compared with the prior art, the beneficial effects of the present invention are:

[0078] 1. This invention overcomes the contradiction that high hardness in traditional varnishes inevitably leads to high shrinkage. By introducing hyperbranched acrylic resin to reduce the viscosity of the system and strictly limiting the amount of trifunctional monomers (such as TMPTA) to below 10%, combined with the balancing effect of difunctional TPGDA, the curing shrinkage rate is controlled within 3-5%. Combined with the volume expansion characteristics of the cationic hybrid system, the internal stress of the coating is greatly reduced, so that the protective film maintains excellent adhesion when the heat-sensitive substrate is repeatedly bent, without cracking or peeling.

[0079] 2. This invention employs a UV-LED light source with a peak wavelength of 365–405nm, combined with a photothermal separation mechanism, to ensure that the irradiated surface temperature is strictly controlled below 40℃. Furthermore, the low-shrinkage combination of aliphatic polyurethane acrylate and monofunctional IBOA completely eliminates the problems of curling, deformation of the heat-sensitive substrate, and miscoloration of the heat-sensitive layer caused by heat accumulation or volume shrinkage.

[0080] 3. For substrates such as thermal paper that are highly sensitive to color, this invention uses a second-generation phosphine oxide initiator to replace or partially replace traditional TPO, and combines it with water-white acyl phosphine oxide to eliminate the slight yellowing after the varnish is cured from the source.

[0081] 4. For different coating methods such as gravure coating, kiss coating, and slot extrusion, specific formula viscosity adjustment windows and precise proportions of leveling agents are provided. In particular, the "pre-dissolved initiator" and "vacuum degassing" processes solve the problems of roller blockage and pinholes in high solids systems in gravure coating, achieving millisecond-level instant curing and adapting to high-speed production lines with speeds >100m / min. Attached Figure Description

[0082] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0083] In the attached diagram:

[0084] Figure 1 This is a flowchart of the coating process of the present invention. Detailed Implementation

[0085] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0086] Example 1: A UV-LED curable thermosensitive protective varnish:

[0087] It includes 40-70% UV-curable resin, 15-45% reactive diluent, 2-6% UV-LED matched photoinitiator system, 0.1-3% additives, and 0.1-3% inert viscosity modifier;

[0088] The UV-curable resin is composed of the following materials: 30-60% flexible modified epoxy acrylate, 20-40% hyperbranched acrylic resin, 20-40% silicone modified resin, and the remainder is aliphatic polyurethane acrylate. The UV-curable resin forms the "skeleton" of the varnish, determining its flexibility, adhesion, shrinkage, and resistance. Among these, the aliphatic polyurethane acrylate (FPUA) can be selected from: CN9006, CN9013 (Sartomer), and Ebecryl8402. Its aliphatic structure provides excellent resistance to yellowing; the urethane bonds in the molecular chain provide hydrogen bonding, resulting in high abrasion resistance and strong adhesion; the polyether / polyester soft segments provide flexibility, ensuring low-shrinkage adhesion to heat-sensitive plastics such as PVC / PET. For epoxy acrylates, long-chain fatty acid-modified EA can be selected to provide higher hardness and chemical resistance (alcohol resistance, acid and alkali resistance). However, due to its rigid benzene ring structure, the proportion must be strictly controlled, otherwise it will increase brittleness and cause the paint film to crack when the heat-sensitive substrate is bent. Hyperbranched acrylic resins can use pentaerythritol core hyperbranched polyester acrylates, which are low viscosity magic. Their spherical molecular structure can significantly reduce the viscosity of the system and reduce the amount of monomers used. At the same time, the high functionality brings fast curing and high gloss without sacrificing flexibility. Organosilicon-modified resins can use polydimethylsiloxane grafted PUA, which has a smooth feel. The introduction of Si-O-Si bonds greatly improves the smoothness (reduces the coefficient of friction), weather resistance and water repellency, making it particularly suitable for label surface oils that require tactile protection.

[0089] The active diluent is composed of the following materials: 40-60% monofunctional, 30-50% bifunctional, 5-10% trifunctional, and 5-10% special materials. Monofunctional diluents (for softening, reducing viscosity, and reducing shrinkage) can use IBOA (isoborneol acrylate), 2-EHA (2-ethylhexyl acrylate), or LaurylAcrylate (LA). Their function is to create flexible chains. IBOA has a unique rigid cage-like structure, providing good hardness and low shrinkage while reducing viscosity. 2-EHA provides excellent flexibility. Note: 2-EHA has strong skin penetration, so the dosage needs to be controlled. Bifunctional diluents (for main balance) can use TPGDA (tripropylene glycol diacrylate), HDDA (1,6-hexanediol diacrylate), or NPGDA (neopentyl glycol diacrylate). Their function is to fill the backbone. HDDA has a fast reaction, high cross-linking density, and good durability, but it is slightly more irritating to the skin. TPGDA has lower volatility and is gentler, making it the current mainstream choice. Trifunctional diluents (for accelerating hardening)... However, for shrinkage, TMPTA (trimethylolpropane triacrylate) and EOTMPTA (ethoxylated TMPTA) can be used. Their function is to improve hardness. TMPTA can significantly improve wear resistance and curing speed, but the higher the functionality, the greater the volume shrinkage (up to 10% or more). It must be used sparingly in heat-sensitive formulations (≤10%). EOTMPTA, due to the introduction of ethoxy chains, reduces irritation and has better flexibility. Special materials (adhesion enhancer / shrinkage reducer) can be 2-HEA-P (2-hydroxyethyl methacrylate phosphate) and β-CEA (β-carboxyethyl acrylate). Their function is to act as adhesion anchors. Phosphate groups have extremely strong chemical bonding to metallized layers (hot stamping layers) or difficult-to-adhere PET barrier layers. Carboxyl groups can improve adhesion to polar surfaces. The principle of heat-sensitive formulation is: monofunctional (IBOA) + low-irritation bifunctional (TPGDA) as the main components, and strictly control the proportion of trifunctional. It is better to appropriately increase the concentration of photoinitiator or extend the light exposure time than to allow high-shrinkage monomers to tear the heat-sensitive film.

[0090] The UV-LED matching photoinitiator system uses 30-50% acylphosphine oxides, 10-20% second-generation phosphine oxides, 10-20% α-aminoketones, 30-50% co-initiator or hydrogen donor, and 5-10% visible light initiator. Acylphosphine oxides (the main type) can be TPO or 819 (Bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide). Note: It has strong absorption at 365-405nm. Its function is to be the king of deep curing. After pyrolysis, it produces two free radicals with extremely high efficiency. However, TPO may have migration risks in thick films or at high temperatures and may have a slight yellowing effect. 819 has higher activity and is suitable for dark or thick coatings. Second-generation phosphine oxides can be TPO-L (Ethyl(2,4,6-trimethylbenzoyl)phenylphosphinate). It also needs to be matched with LEDs. Its function is to have low migration. It is lighter in color, has a lower odor, and a lower migration rate than TPO, making it very suitable for food contact grade or high-transparency protective varnishes.

[0091] α-Aminoketones can be used with 907 (2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one) + co-initiator. Note: It needs to be combined with an amine for synergy. Function: It is useful in colored systems / thick films, but it is often used as an auxiliary agent in varnishes.

[0092] The co-initiator / hydrogen donor can be an acrylated active amine (such as GenocureLTM) or ITX (isopropylthioxanthraquinone). Its function is to solve the problem of oxygen inhibition of polymerization. Oxygen in the air will quench free radicals and cause the surface to become sticky. The active amine can quickly donate hydrogen to form more active amino free radicals, ensuring that the surface layer is completely cured.

[0093] The visible light initiator can be camphorquinone (CQ) + amine. Note: 470nm. Function: Only use in small amounts when dual curing (UV + heat / humidity) or deep shadow curing is required.

[0094] The additives consist of 60-90% leveling agent and 25-40% defoamer;

[0095] Leveling agents such as BYK-307 / 333 and TegoGlide410 can be used. Their function is to modify polyether polysiloxanes, reduce surface tension, eliminate orange peel and pinholes, and provide a balance between long-wave leveling and short-wave leveling.

[0096] Defoamers such as BYK-052 and TegoFoamex810 can be used. Their function is to disrupt the foam stability of polydimethylsiloxane / polyethersiloxane copolymers and prevent the generation of microbubbles during stirring and coating.

[0097] The substrate wetting agent can be TegoWet270 / 280. Its function is as a fluorinated modified surfactant, which greatly reduces the surface tension and ensures that the varnish is fully spread on low surface energy substrates (such as silicone release layers and certain plastics) to prevent pinholes.

[0098] The polymerization inhibitor (for storage and transportation stability) can be MEHQ (p-methoxyphenol), with an action of 50–200 ppm. It captures accidentally generated free radicals, preventing thermal polymerization (dark reaction) during transportation and storage.

[0099] Nano-abrasion-resistant fillers: Fumed silica (Aerosil200 / R972) and nano-alumina can be used. Function: 0.3–1.5%. R972 is hydrophobic, easy to disperse, and provides anti-slip and scratch resistance, but excessive amount will affect the ultimate transparency and gloss.

[0100] Anti-aging stabilizers can be: Tinuvin 123 (HALS), Irganox 1010 (antioxidant). Note: Add in trace amounts. Although UV-LEDs do not age with ultraviolet light, hindered amine light stabilizers are still needed to protect resin segments in high temperature and high humidity environments.

[0101] Inert viscosity modifier: Strictly speaking, 100% solid UV varnish without solvent, but for some high-viscosity FPUA systems and some coating processes (gravure / micro-gravure roller), a small amount of low-volatility inert diluent (propylene glycol methyl ether acetate / butyl acetate) may be added to adjust the viscosity.

[0102] It also includes 1-3% surface enhancer, which includes 40-60% fluorescent whitening agent and 40-60% infrared absorber;

[0103] Fluorescent whitening agents (FWA) such as Tinopal CBS-X and Uvitex OB can be used. Their function is to neutralize yellowing. Since initiators such as TPO may cause slight yellowing, adding a trace amount of FWA absorbs ultraviolet light and emits blue light, which optically cancels out the yellowing and makes the coating "look more transparent".

[0104] The infrared absorber uses ITO paste, copper phthalocyanine, and its function is to provide heat insulation. For special heat-sensitive documents, adding this material can absorb light of specific wavelengths to prevent copying or counterfeiting, while also blocking infrared rays to prevent the heat-sensitive layer from developing colors incorrectly.

[0105] It also includes 1-3% functional microspheres, 30-60% polyurethane microspheres, and 40-70% hollow glass microspheres;

[0106] Polyurethane microspheres (Deburring beads) can be made from SokenChemPSR series or JSRMicrosphere. Their function is to provide an elastic feel and matte finish. Unlike the dryness of silica, PU microspheres provide a rubber-like elastic touch and can be physically rolled to achieve a matte effect without relying on chemical matting agents.

[0107] Insulating glass microspheres can be made of 3M Glass Bubbles. Their function is to reduce weight and provide thermal insulation. The extremely light hollow spheres reduce the density of the varnish, while the hollow structure provides a certain degree of thermal insulation and protects the heat-sensitive layer.

[0108] It also includes barrier materials, which are coated on or under the varnish to block the migration of specific substances (such as oxygen, water vapor, plasticizers). These materials can be one or more of the following raw materials in combination as needed: PVDC emulsion, EVOH, graphene / nanoclay dispersion.

[0109] PVDC emulsion (polyvinylidene chloride) can be made from DowSaran or SolvayIxan. Its function is high barrier. It is applied under the varnish to specifically prevent plasticizers in the PVC film from migrating into the varnish layer, thus preventing the varnish from becoming brittle, yellowing, or peeling off.

[0110] EVOH (ethylene-vinyl alcohol copolymer) can be KurarayEval, which serves to block oxygen and moisture, and is used in high-value thermal labels to prevent oxygen from penetrating the varnish and causing oxidation and discoloration of the underlying ink or aging of the substrate.

[0111] The graphene / nanoclay dispersion can use Nanocor I.44P. Its function is to act as a nano barrier. Even a very small amount of it can create a "maze effect" in the varnish layer, which greatly extends the permeation path of oxygen and water vapor.

[0112] It also includes a secondary curing agent, which is classified as 1-3% of the total amount. The material of the secondary curing agent is one or more of the following: moisture-curing isocyanate, aziridine crosslinking agent, and carbodiimide crosslinking agent.

[0113] Moisture-curing isocyanates such as Desmodur N series and Tolonate HDT can be used. Their function is dual curing (UV + moisture). A small amount of blocked or polyisocyanate is introduced into the varnish formulation. After UV curing, the residual NCO groups react with moisture in the air to form urea bonds, which greatly improves water resistance and adhesion.

[0114] Aziridine crosslinking agent CX-100 (NeoRezR-9320) can be used. Its function is to crosslink at room temperature. As an additive (<2%), it can be mixed into varnish and react with the carboxyl groups (-COOH) in the resin to instantly improve the ethanol wiping resistance and anti-blocking properties of the paint film. It is especially suitable for the protective layer of thermal printing paper.

[0115] Carbodiimide crosslinking agents such as Carbodilite V-02 and hydrolytic stabilizers can be used. Their function is to specifically target polyester / polyurethane resins, react with the ester bonds in the resin, prevent hydrolytic chain breakage in humid and hot environments, and extend the life of the protective film.

[0116] It also includes additives, including antislip / texturing agents, rheology modifiers (thixotropic agents), and special substrate wetting agents;

[0117] Anti-slip / texturing agents such as SYLOIDRAD2100 (silica) and Sandorin Micro can be used. Their function is to provide a matte / anti-slip finish, offering a delicate frosted feel and anti-slip effect while maintaining transparency, and preventing labels from sticking together when stacked.

[0118] Rheology modifiers (thixotropic agents) such as BYK-410 (polyurethane) and DeuRheo229 can be used. Their function is to prevent sagging. For vertical coating or thick coating processes, they provide pseudoplastic fluid properties to prevent varnish from sagging before curing. Special substrate wetting agents such as BYK-349 (silicone) and Surfynol104E (acetylene glycol) can be used. Their function is to provide dynamic wetting. When coating at high speeds (>100m / min), they prevent pinholes caused by uneven surface energy of the substrate and provide extremely fast wetting speed.

[0119] Please see Figure 1 A method for applying a UV-LED curable thermosensitive protective varnish includes the following steps:

[0120] S1: ...

[0121] Example 1: The chicken biscuits have a pure taste, soft and chewy texture, and are full of fresh and fragrant flavors. They are sweet and salty with an unforgettable aftertaste. After sending them to a friend for invention, and following up with the friend, it was found that the chicken biscuits processed in this way received a 96% positive feedback rate after eating them.

[0122] Example 2:

[0123] Please see Figure 1 A method for applying a UV-LED curable thermosensitive protective varnish includes the following steps:

[0124] S1: Production Preparation

[0125] The raw materials are processed to obtain a protective varnish;

[0126] S2: Substrate Pretreatment (Surface Treatment)

[0127] Corona / Plasma Treatment: For low surface energy substrates such as PET / PVC, online corona treatment is required before coating. The dyn value needs to reach 38-42 dyn / cm to ensure varnish wetting.

[0128] Dust removal: Static electricity and dust on the substrate surface are removed by sticky rollers and high-pressure ion air bars;

[0129] Preheating (caution): If the substrate has a high moisture content, far-infrared low-temperature preheating (<50℃) can be used to remove surface moisture, but it needs to be cooled to below 30℃ before coating.

[0130] Process parameters:

[0131] Dyne pen test: 38-42 dyn / cm;

[0132] Surface resistance: <10^11Ω, preventing static electricity from attracting dust;

[0133] S3: Precision Coating (Coating Method)

[0134] Micro-grooved roller coating:

[0135] - Anilox roller: Select a ceramic anilox roller with 60-120 lines / cm;

[0136] - Rubber roller: Hardness 70-80 Shore A, to prevent damage to heat-sensitive substrate;

[0137] - Coating gap: The gap between the anilox roller and the substrate is controlled at 0.5-1.0mm;

[0138] Slit coating (high-end): The die temperature is controlled at 30-35℃ to prevent viscosity changes from causing streaks;

[0139] Process parameters:

[0140] Wet film thickness: Monitored online using a wet film thickness gauge.

[0141] Viscosity: Controlled at 25℃ between 200-800 cps (depending on the coating method);

[0142] S4: Leveling and Infrared Shielding

[0143] Dust-free constant temperature leveling: stay in the sealed cavity for 3-8 seconds, and use hot air (<45℃) or far-infrared (shielding medium wave IR) to assist leveling;

[0144] Key point: Quartz glass heat insulation panels need to be installed in the leveling section to prevent the heat from the subsequent UV lamps from flowing back into the substrate;

[0145] Process parameters:

[0146] Surface condition: No orange peel texture, no ripples;

[0147] Temperature: Substrate surface temperature < 40℃;

[0148] S5: UV-LED Curing (The CoreStep)

[0149] Light source configuration: 395nm light source is used as the main light source (taking into account both penetration and surface curing);

[0150] Energy control: Monitor using a radiometer, with a recommended energy density of 600-1200 mJ / cm² and peak irradiance of 2-4 W / cm².

[0151] Segmented curing: The first lamp is pre-cured at low energy (30%) to prevent pinholes caused by surface tension gradient; the second lamp is fully cured at high energy (100%).

[0152] Cooling system: The LED lamp head must be water-cooled or powerfully air-cooled to ensure that the junction temperature of the LED beads is <65℃ to prevent wavelength drift.

[0153] Process parameters:

[0154] Curing degree: Double bond conversion rate was measured by acetone wiping method or FT-IR (>90%).

[0155] Adhesion: Grade 0 in cross-cut adhesion test;

[0156] S6: Post-processing

[0157] Slow cooling: The temperature of the newly cured film is relatively high, and it needs to be cooled to room temperature by cooling rollers (15-20℃ circulating water);

[0158] Tension control: The winding tension needs to be gradually reduced to prevent the heat-sensitive substrate from "bursting" or deforming due to internal stress shrinkage;

[0159] Aging: After winding, place at 25°C for 24-48 hours to allow intermolecular forces (hydrogen bonds) to fully recombine and achieve optimal performance;

[0160] Process parameters:

[0161] Winding hardness: Moderate hardness;

[0162] No collapsed residual solvent: ND (not detected).

[0163] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A UV-LED curable thermosensitive protective varnish, characterized in that: It includes 40-70% UV-curable resin, 15-45% reactive diluent, 2-6% UV-LED matched photoinitiator system, 0.1-3% additives, and 0.1-3% inert viscosity modifier; The photocurable resin is composed of the following materials: 30-60% flexible modified epoxy acrylate, 20-40% hyperbranched acrylic resin, 20-40% silicone modified resin, and the remainder is aliphatic polyurethane acrylate, wherein the aliphatic polyurethane acrylate (FPUA) can be selected from: CN9006, CN9013 (Sartomer), Ebecryl8402, the hyperbranched acrylic resin can be pentaerythritol core hyperbranched polyester acrylate, and the silicone modified resin can be polydimethylsiloxane grafted PUA. The active diluent is composed of the following materials: 40-60% monofunctional, 30-50% difunctional, 5-10% trifunctional, and 5-10% special materials. Monofunctional materials (softening, viscosity reducing, and shrinkage reducing) can be IBOA (isobornyl acrylate), 2-EHA (2-ethylhexyl acrylate), or LauryylAcrylate (LA); difunctional materials can be TPGDA (tripropylene glycol diacrylate), HDDA (1,6-hexanediol diacrylate), or NPGDA (neopentyl glycol diacrylate); trifunctional materials can be TMPTA (trimethylolpropane triacrylate) or EOTMPTA (ethoxylated TMPTA); and special materials can be 2-HEA-P (2-hydroxyethyl methacrylate phosphate) or β-CEA (β-carboxyethyl acrylate). The UV-LED matching photoinitiator system comprises 30-50% acylphosphine oxides, 10-20% second-generation phosphine oxides, 10-20% α-aminoketones, 30-50% co-initiators or hydrogen donors, and 5-10% visible light initiators. Acylphosphine oxides (the main component) can be TPO or 819 (Bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide); second-generation phosphine oxides can be TPO-L (Ethyl(2,4,6-trimethylbenzoyl)phenylphosphinate). The α-aminoketones may be 907 (2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one) + co-initiator; The co-initiator / hydrogen donor may be an acrylated active amine (such as GenocureLTM) or ITX (isopropylthioxanthrone). The visible light initiator can be camphor quinone (CQ) + amine; The additives consist of 60-90% leveling agent and 25-40% defoamer. Leveling agents such as BYK-307 / 333 and TegoGlide410 can be used. Defoamers such as BYK-052 and TegoFoamex810 can be used. Their function is to disrupt the foam stability of polydimethylsiloxane / polyethersiloxane copolymers and prevent the generation of microbubbles during stirring and coating. TegoWet270 / 280 can be used as a substrate wetting agent; The polymerization inhibitor (stable during storage and transportation) can be MEHQ (p-methoxyphenol); Nano-wear-resistant fillers: Fumed silica (Aerosil200 / R972) and nano-alumina can be used; Anti-aging stabilizers can be: Tinuvin 123 (HALS) and Irganox 1010 (antioxidant).

2. The UV-LED curable thermosensitive protective varnish according to claim 1, characterized in that: It also includes 1-3% surface enhancer, wherein the surface enhancer comprises 40-60% fluorescent whitening agent and 40-60% infrared absorber; The fluorescent whitening agent (FWA) can be Tinopal CBS-X or Uvitex OB; The infrared absorber is made of ITO slurry or copper phthalocyanine.

3. The UV-LED curable thermosensitive protective varnish according to claim 1, characterized in that: It also includes 1-3% functional microspheres, of which 30-60% are polyurethane microspheres and 40-70% are hollow glass microspheres; The polyurethane microspheres can be SokenChemPSRseries, JSRMicrosphere; The hollow glass microspheres can be made of 3M Glass Bubbles.

4. The UV-LED curable thermosensitive protective varnish according to claim 1, characterized in that: It also includes barrier materials, which may be one or more of the following raw materials in combination as needed: PVDC emulsion, EVOH, graphene / nanoclay dispersion; PVDC emulsions (polyvinylidene chloride) can be made from DowSaran or SolvayIxan. EVOH (ethylene-vinyl alcohol copolymer) can be produced using KurarayEval; The graphene / nanoclay dispersion can be prepared using Nanocor I.44P.

5. The UV-LED curable thermosensitive protective varnish according to claim 1, characterized in that: It also includes a secondary curing agent, which is classified as 1-3% of the total amount, and the material of the secondary curing agent is one or more of moisture-curing isocyanates, aziridine crosslinking agents, and carbodiimide crosslinking agents; The moisture-curing isocyanate can be Desmodur N series or Tolonate HDT; The aziridine crosslinking agent can be CX-100 (NeoRezR-9320); The carbodiimide crosslinking agent can be Carbodilite V-02 or a hydrolysis stabilizer.

6. The UV-LED curable thermosensitive protective varnish according to claim 1, characterized in that: It also includes additives, including antislip / texturing agents, rheology modifiers, and special substrate wetting agents; The anti-slip / texturing agent can be SYLOIDRAD2100 (silica) or Sandorin Micro; The rheology modifier (thixotropic agent) may be BYK-410 (polyurethane) or DeuRheo229.

7. A method for applying a UV-LED curable thermosensitive protective varnish according to any one of claims 1-6, characterized in that: The coating method specifically includes the following steps: S1: Production Preparation The raw materials are processed to obtain a protective varnish; S2: Substrate Pretreatment Corona / plasma treatment: For low surface energy substrates such as PET / PVC, online corona treatment is required before coating. The dyn value needs to reach 38-42 dyn / cm to ensure varnish wetting. Dust removal: Static electricity and dust on the substrate surface are removed by sticky rollers and high-pressure ion air bars; Preheating (caution): If the substrate has a high moisture content, far-infrared low-temperature preheating can be used to remove surface moisture, but it needs to be cooled to below 30°C before coating. Process parameters: Dyne pen test: 38-42 dyn / cm; Surface resistance: <10-11Ω, to prevent static electricity from attracting dust; S3: Precision Coating Micro-grooved roller coating: - Anilox roller: Select a ceramic anilox roller with 60-120 lines / cm; - Rubber roller: Hardness 70-80 Shore A, to prevent damage to heat-sensitive substrate; - Coating gap: The gap between the anilox roller and the substrate is controlled at 0.5-1.0mm; Slot coating: The die temperature should be controlled at 30-35℃ to prevent viscosity changes from causing streaks; Process parameters: Wet film thickness: Monitored online using a wet film thickness gauge; Viscosity: Controlled at 25℃ between 200-800 cps; S4: Leveling and Infrared Shielding Dust-free constant temperature leveling: stay in the sealed cavity for 3-8 seconds, and use hot air or far-infrared assisted leveling; Key point: Quartz glass heat insulation panels need to be installed in the leveling section to prevent the heat from the subsequent UV lamps from flowing back into the substrate; Process parameters: Surface condition: No orange peel texture, no ripples; Temperature: Substrate surface temperature < 40℃; S5: UV-LED curing Light source configuration: 395nm as the primary light source; Energy control: Use a radiometer for monitoring, and the recommended energy density is 600-1200 mJ / cm², with a peak irradiance of 2-4 W / cm². Segmented curing: The first lamp is pre-cured at low energy (30%) to prevent pinholes caused by surface tension gradient; the second lamp is fully cured at high energy (100%). Cooling system: The LED lamp head must be water-cooled or powerfully air-cooled to ensure that the junction temperature of the LED beads is <65℃ to prevent wavelength drift; Process parameters: Curing degree: Double bond conversion rate was measured by acetone wiping method or FT-IR (>90%). Adhesion: Grade 0 in cross-cut adhesion test; S6: Post-processing and winding Slow cooling: The temperature of the newly cured film is relatively high, and it needs to be cooled to room temperature by cooling rollers; Tension control: The winding tension needs to be gradually reduced to prevent the heat-sensitive substrate from "bursting" or deforming due to internal stress shrinkage; Curing: After winding, place at 25°C for 24-48 hours to allow intermolecular forces (hydrogen bonds) to fully recombine and achieve optimal performance; Process parameters: Winding hardness: Moderate hardness; No collapsed residual solvent: ND.

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