Hot-pressing strippable coating composition with Fresnel lens effect and preparation method of hot-pressing strippable coating composition

Abstract

The invention provides a hot-pressing strippable coating composition with a Fresnel lens effect. The hot-pressing strippable coating composition comprises the following components in parts by weight: 20-50 parts of polyurethane resin with active groups; 2-6 parts of solid acrylic resin; 1-3 parts of cellulose ester resin; 1-5 parts of a latent curing agent; 0-0.3 part of an auxiliary agent; 40 to 60 parts of a solvent; wherein the glass transition temperature (Tg) of the polyurethane resin with the active groups is 25 to 50 DEG C. The method has the beneficial effects that the system provided by the invention is high in practicability, simple and easy to operate. And the introduced low-Tg (25-50 DEG C) polyurethane resin with active groups can easily reach a softening point during hot pressing, has excellent flowability, can well fill a fine grating of a Fresnel lens, and has a full replication effect. The polyurethane resin is matched with a latent curing agent and is stable at normal temperature; and when the hot-pressing temperature threshold value is reached, a cross-linking reaction is initiated. The mechanism improves the temperature-resistant effect of the system, and solves the problems that low-Tg resin is easy to stick and reverse light in the later period.

Description

Technical Field

[0001] This invention belongs to the field of packaging and printing materials technology, specifically relating to a coating for transfer processing, and more particularly to a heat-pressable Fresnel lens effect peelable coating composition and its preparation method. Background Technology

[0002] In the packaging and printing industry, transfer printing is often used to give packaging products unique visual effects and anti-counterfeiting features. This process typically involves coating a transfer coating onto a plastic base film, followed by drying, embossing to create a laser effect (such as a Fresnel lens effect), vacuum evaporation, coating with transfer adhesive, and finally transferring the coating onto the packaging cardboard, after which the base film is peeled off. Finished products produced using this process do not contain non-biodegradable aluminum foil or plastic film, meeting green and environmentally friendly requirements.

[0003] The Fresnel lens effect (commonly known as "cat's eye") offers excellent 3D effects and deep raster textures. Currently, there are two main methods for creating this effect: 1. UV curing process: UV coatings are in a liquid state before curing, which can fill the grating well and produce good replication results. However, its disadvantage is that the plastic base film usually cannot be peeled off, making the final packaging material difficult to degrade and not environmentally friendly.

[0004] 2. Traditional hot pressing process: The coating becomes solid after drying. To meet the temperature resistance requirements of subsequent processing, the glass transition temperature (Tg) of the coating is usually designed to be high. However, this results in poor fluidity of the coating during hot pressing, making it difficult to fill deep gratings and leading to unsatisfactory replication effects. If the coating is designed to be a low Tg system, although stereoscopic replication can be achieved during hot pressing, the coating is too soft and prone to problems such as "scratching" and "reflection" in later stages, affecting the preservation of the Fresnel lens effect.

[0005] Therefore, developing a coating composition that can achieve both environmentally friendly peeling and hot-press filling properties as well as post-heat-setting properties is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to resolve the contradiction between the molding replication effect and temperature resistance and adhesion resistance in existing hot-pressed Fresnel lens effect coatings, and to provide a hot-pressable Fresnel lens effect peelable coating composition and its preparation method.

[0007] To achieve the above objectives, the present invention provides a heat-pressable Fresnel lens effect peelable coating composition, comprising the following components in parts by weight: 20-50 parts of polyurethane resin with active groups; 2-6 parts of solid acrylic resin; 1-3 parts of cellulose ester resin; 1-5 parts of latent curing agent; 0-0.3 parts of additives; and 40-60 parts of solvent; wherein the glass transition temperature (Tg) of the polyurethane resin with active groups is 25-50°C; preferably, the preparation method of the polyurethane resin with active groups is as follows: adding a macromolecular polyol and an isocyanate in a molar ratio of 0.5-0.8 into a reaction vessel, heating to 70-80°C under stirring, reacting for 1.5-2.5 hours, adding acetone or butanone of equal weight to the reaction system, cooling to 30-40°C, adding a measured amount of diamine chain extender, and reacting for 1-1.5 hours to obtain the final product. More preferably, the macromolecular polyol is one or more of PPG (polypropylene glycol) and PEG (polyethylene glycol), with a molecular weight of 2000-3000. More preferably, the isocyanate is one or more of IPDI (isophorone diisocyanate), TDI (toluene diisocyanate), HMDI (dicyclohexylmethane diisocyanate), and HDI (hexamethylene diisocyanate). More preferably, the diamine chain extender is one or more of isophorone diamine and m-phenylenediamine.

[0008] Preferably, the solid acrylic resin is a polymer formed by polymerizing one or more monomers selected from methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, butyl acrylate, and ethyl acrylate. The glass transition temperature of the solid acrylic resin is 70~100℃, and the molecular weight is 50,000~120,000.

[0009] Preferably, the cellulose ester resin is one or more of cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate with a molecular weight of 30,000 to 90,000.

[0010] Preferably, the latent curing agent is a blocked isocyanate curing agent, such as one or more of BL-3851, Trixene® BI7982, and DXB-3375.

[0011] Preferably, the solvent is one or more selected from ethyl acetate, n-propyl acetate, n-butyl acetate, n-propanol, isopropanol, acetone, butanone, propylene glycol methyl ether, and propylene glycol ethyl ether.

[0012] Preferably, the additive is one or more of a leveling agent, a defoamer, and an anti-scratch agent; the leveling agent is selected from one or more of Glide410, Glide435, Glide450, BYK-306, BYK-333, BYK-323, DC11, DC57, and DC56; the defoamer is selected from one or more of BYK-052, BYK-051, BYK-066N, Airex900, Airex910, Airex920, DC62, and DC65; and the anti-scratch agent is selected from one or more of DC51, DC29, and DC27.

[0013] The present invention also provides a method for preparing the above-mentioned heat-pressable Fresnel lens effect peelable coating composition, comprising the following steps: Step 1, adding solvent into a reaction vessel, heating to 45~50℃, and maintaining a stirring speed of 60~80 rpm; Step 2, adding solid acrylic resin, polyurethane resin with active groups, and cellulose ester resin into the reaction vessel, and stirring continuously for 2~3 hours; Step 3, adding additives and latent curing agent into the reaction vessel, stirring for 0.5~1 hours, stopping stirring, cooling the product, filtering, and then packaging to obtain the final product.

[0014] The beneficial effects of this invention are as follows: 1. The system provided by this invention is highly practical, simple and easy to operate, and the usage process is completely consistent with existing products, without the need to modify existing equipment and processes.

[0015] 2. The introduced low Tg (25-50℃) polyurethane resin with active groups easily reaches its softening point during hot pressing, exhibiting excellent fluidity and effectively filling the fine gratings of Fresnel lenses, resulting in full replication effects.

[0016] 3. This polyurethane resin, when combined with a latent curing agent, is stable at room temperature; however, it initiates a cross-linking reaction upon reaching the hot-pressing temperature threshold. This "softening and molding first, then cross-linking and curing" mechanism improves the system's temperature resistance and solves the problems of easy staining and gloss reversal associated with low-Tg resins in the later stages. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to specific embodiments.

[0018] Example 1: A heat-pressable Fresnel lens-effect peelable coating composition and its preparation method, comprising: Step 1: Place 10 kg of ethyl acetate (Shanghai Xiangjiang Chemical Co., Ltd.), 10 kg of butanone (Shanghai Xiangjiang Chemical Co., Ltd.), 5 kg of n-propyl acetate (Shanghai Xiangjiang Chemical Co., Ltd.), and 5 kg of propylene glycol methyl ether (Shanghai Mingdu Chemical Co., Ltd.) as solvents into a reaction vessel according to weight. Heat the reaction vessel to 50°C and turn on the stirring device, maintaining the stirring speed at 70 rpm until the mixture is homogeneous. Step 2: Add 3 kg of solid acrylic resin (Mitsubishi methyl methacrylate and butyl methacrylate copolymer, Tg 95℃, molecular weight 75000), 1 kg of cellulose acetate butyrate resin (Eastman CAB), and 20 kg of low Tg polyurethane resin with active groups to the reactor by weight, and continue stirring for 2 hours. Step 3: Add 0.01 kg of leveling agent BYK-333 (BYK Chemicals) and 0.2 kg of latent curing agent (BL-3851 from Shanghai Bolino New Materials Co., Ltd.) to the reactor, stir for 1 hour until homogeneous, then stop stirring. Cool the product to 20°C, filter, and then package to obtain a peelable coating composition product with a heat-pressable Fresnel lens effect.

[0019] The preparation method of the low Tg polyurethane resin with active groups in step two is as follows: 2 kg of 2000 molecular weight polyether polyol PPG (Bluestar Dongda Chemical Co., Ltd.) and 0.444 kg of isocyanate IPDI (Covestro) are added to a reaction vessel, and then heated to 75°C with stirring, controlling the temperature fluctuation within 1°C. The reaction is carried out for 2 hours, 2.44 kg of acetone (Shanghai Xiangjiang Chemical Co., Ltd.) is added, the temperature is lowered to 40°C, isophorone diamine (BASF) is added, and the reaction is carried out for 1 hour. No NCO groups are detected, thus obtaining the low Tg (Tg around 45°C) polyurethane resin with active groups.

[0020] Example 2: A heat-pressable Fresnel lens-effect peelable coating composition and its preparation method, further comprising: Step 1: Place 20 kg of ethyl acetate (Shanghai Xiangjiang Chemical Co., Ltd.), 5 kg of butanone (Shanghai Xiangjiang Chemical Co., Ltd.), 5 kg of n-propyl acetate (Shanghai Xiangjiang Chemical Co., Ltd.), and 10 kg of propylene glycol methyl ether (Shanghai Mingdu Chemical Co., Ltd.) as solvents into a reaction vessel according to weight. Heat the reaction vessel to 50°C and turn on the stirring device, maintaining the stirring speed at 80 rpm until the mixture is homogeneous. Step 2: Add 2 kg of solid acrylic resin (Mitsubishi methyl methacrylate and butyl methacrylate copolymer, Tg 100℃, molecular weight 80000), 1.5 kg of cellulose acetate propionate resin (Eastman CAP), and 40 kg of low Tg polyurethane resin with active groups to the reactor by weight, and continue stirring for 2.5 h. Step 3: Add 0.02 kg of leveling agent Glide450 (Dega additive) and 0.5 kg of latent curing agent (Lanxess Bassington Trixene® BI7982) to the reactor, stir for 1 hour until homogeneous, then stop stirring. Cool the product to 20°C, filter, and then package to obtain a heat-pressable Fresnel lens effect peelable coating composition product.

[0021] The preparation method of the low Tg polyurethane resin with active groups in step two is as follows: 3 kg of 3000 molecular weight polyether polyol PPG (Lanxing Dongda Chemical Co., Ltd.) and 0.35 kg of isocyanate TDI (Yantai Wanhua) are added to a reaction vessel, and then heated to 70°C with stirring, controlling the temperature fluctuation within 1°C. The reaction is carried out for 2 hours, 3.35 kg of acetone (Shanghai Xiangjiang Chemical Co., Ltd.) is added, the temperature is lowered to 30°C, and m-phenylenediamine (Jinan Juyang Chemical Technology Co., Ltd.) is added. The reaction is carried out for 1 hour, and no NCO groups are detected, thus obtaining the low Tg (Tg around 30°C) polyurethane resin with active groups.

[0022] Example 3: A heat-pressable Fresnel lens-effect peelable coating composition and its preparation method, further comprising: Step 1: Place 15 kg of ethyl acetate (Shanghai Xiangjiang Chemical Co., Ltd.), 15 kg of butanone (Shanghai Xiangjiang Chemical Co., Ltd.), 5 kg of n-propyl acetate (Shanghai Xiangjiang Chemical Co., Ltd.), and 5 kg of propylene glycol methyl ether as solvents into a reaction vessel. Heat the reaction vessel to 45°C and turn on the stirring device, maintaining the stirring speed at 75 rpm until the mixture is homogeneous. Step 2: Add 6 kg of solid acrylic resin (Mitsubishi methyl methacrylate and ethyl methacrylate copolymer, Tg 95℃, molecular weight 70000), 3 kg of cellulose acetate butyrate resin (Eastman CAB), and 50 kg of low Tg polyurethane resin with active groups to the reactor by weight, and continue stirring for 3 hours. Step 3: Add 0.03 kg of leveling agent BYK-333 (BYK Chemicals) and 0.5 kg of latent curing agent (BL-3851 from Shanghai Bolino New Materials Co., Ltd.) to the reactor, stir for 1 hour until uniform, then stop stirring. Cool the product to 20°C, filter, and then package to obtain a peelable coating composition product with a heat-pressable Fresnel lens effect.

[0023] The preparation method of the low Tg polyurethane resin with active groups in step two is as follows: 4 kg of 2000 molecular weight polyether polyol PPG (Bluestar Dongda Chemical Co., Ltd.) and 0.667 kg of isocyanate IPDI (Covestro) are added to a reaction vessel, and then heated to 80°C with stirring, controlling the temperature fluctuation within 1°C. The reaction is carried out for 2 hours, and then 4.667 kg of acetone (Shanghai Xiangjiang Chemical Co., Ltd.) is added. The temperature is lowered to 40°C, and then isophorone diamine (BASF) is added. The reaction is carried out for 1 hour, and no NCO groups are detected. Thus, the low Tg (Tg around 25°C) polyurethane resin with active groups is obtained.

[0024] Performance tests were conducted on Examples 1-3, and the results are shown in Table 1 below.

[0025] Sample Preparation: The coatings prepared in the examples and the comparative samples were coated onto the surface of a PET film, baked at 110℃ for 10-15 seconds, with a dry coating weight of 1.2-1.4g. The coating was then molded at 180-185℃, followed by vacuum metallization. The coating was then transferred to cardboard using adhesive, and the transferred cardboard was subjected to relevant performance tests. Temperature resistance was tested using a heat sealer at 2 kg pressure for 2 seconds, observing the color change. Embossing resistance was tested by pressing the coating surface at room temperature under 25 kg pressure for one week, observing the changes. Peel resistance was tested by coating the PET film surface, baking at 110℃ for 10-15 seconds, with a dry coating weight of 1.2-1.4g, and then applying 3MScotch 600 tape to the coating surface. A pull test was performed; complete peeling was considered excellent, minor residue (1-3%) was considered average, and residue exceeding 10% was considered poor.

[0026] Table 1 Performance testing Example 1 Example 2 Example 3 Coating transparency transparent transparent transparent Temperature resistance 120℃ 130℃ 135℃ Molding effect full full full Pressure-resistant flowers No significant changes No significant changes No significant changes Peeling performance excellent excellent excellent As shown in Table 1, the coating compositions provided by the present invention, while ensuring a full molding effect, all exhibit excellent temperature resistance (above 120℃) and embossing resistance, as well as excellent peeling performance.

[0027] The above is a detailed description of the embodiments, which is intended to enable those skilled in the art to correctly understand and use the present invention. Any improvements or modifications to technical solutions obtained by those skilled in the art based on the present invention and on the existing technology, without innovative effort but only through analysis, analogy, or limited enumeration, should be within the scope of protection defined by the claims.

Claims

1. A heat pressable, Fresnel lens effect, peelable coating composition characterized in that, The composition comprises the following components by weight: polyurethane resin with active groups 20-50 parts, the glass transition temperature of the polyurethane resin is 25-50℃; solid acrylic resin 2-6 parts; cellulose ester resin 1-3 parts; latent curing agent 1-5 parts; auxiliary 0-0.3 parts; Solvent 40-60 parts; the preparation method of the polyurethane resin with active groups is as follows: macromolecular polyol and isocyanate are added into the reaction kettle according to the molar ratio of 0.5-0.8, heated to 70-80℃ under stirring, and reacted for 1.5-2.5 hours; the same weight of acetone or butanone as the reaction system is added, and the temperature is lowered to 30-40℃; diamine chain extender is added, and reacted for 1-1.5 hours.

2. A heat pressable, Fresnel lens effect, strippable coating composition according to claim 1, characterized in that, The macromolecular polyol is one or more of polypropylene glycol and polyethylene glycol, and the molecular weight of the macromolecular polyol is 2000-3000.

3. The heat pressable, Fresnel lens effect, strippable coating composition according to claim 1, characterized in that, The isocyanate is one or more of isophorone diisocyanate, toluene diisocyanate, dicyclohexylmethane diisocyanate, and hexamethylene diisocyanate.

4. The heat pressable, Fresnel lens effect, strippable coating composition according to claim 1, characterized in that, The diamine chain extender is one or more of isophorone diamine and m-xylylenediamine.

5. The heat pressable, Fresnel lens effect, strippable coating composition according to claim 1, wherein, The solid acrylic resin is a polymer polymerized from one or more monomers of methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, butyl acrylate, and ethyl acrylate; the glass transition temperature of the solid acrylic resin is 70-100℃, and the molecular weight is 50-120 thousand.

6. A heat pressable, Fresnel lens effect, strippable coating composition according to claim 1, characterized in that, The cellulose ester resin is one or more of cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate, and the molecular weight of the cellulose ester resin is 30-90 thousand.

7. A heat pressable, Fresnel lens effect, strippable coating composition according to claim 1, characterized in that, The latent curing agent is a blocked isocyanate curing agent selected from one or more of 3,5-dimethylpyrazole blocked isocyanate, caprolactam blocked isocyanate, and oxime blocked isocyanate.

8. The heat pressable, Fresnel lens effect, strippable coating composition according to claim 1, wherein, The solvent is one or more of ethyl acetate, n-propyl acetate, n-butyl acetate, n-propanol, isopropyl alcohol, acetone, butanone, propylene glycol methyl ether, and propylene glycol ethyl ether; the auxiliary is one or more of leveling agent, defoaming agent, and anti-scratch agent; wherein the leveling agent is selected from polyether modified polydimethylsiloxane or polyacrylate leveling agent; the defoaming agent is selected from silicone defoaming agent or polymer type non-silicon defoaming agent; and the anti-scratch agent is selected from ultra-high molecular weight polydimethylsiloxane dispersion or silicone anti-scratch agent.

9. A process for the preparation of a heat pressable, Fresnel lens effect, strippable coating composition according to any one of claims 1 to 8, characterized in that, The method comprises the following steps: Step one, pour the solvent into the reaction kettle, heat to 45-50℃, and maintain stirring; Step two, add the solid acrylic resin, polyurethane resin with active groups, and cellulose ester resin into the reaction kettle, and continue stirring for 2-3 hours; Step three, add the auxiliary and latent curing agent into the reaction kettle, stir for 0.5-1 hour, then stop stirring, cool the product, and filter, and the product is obtained.