Low warping and deformation anti-scratch coating, low warping and deformation anti-scratch film and preparation method thereof

Abstract

The present invention relates to a low-warping anti-scratch coating, a low-warping anti-scratch film and a preparation method thereof, and belongs to the technical field of photocurable anti-scratch coatings. The low-warping anti-scratch coating of the present invention comprises the following components by mass percentage: 30-50% acrylate prepolymer, 1-15% acrylate active monomer, 10-30% multifunctional hyperbranched active diluent, 20-30% cationic photocurable monomer, 1-3% free radical photoinitiator, 1-3% cationic photoinitiator; wherein the multifunctional hyperbranched active diluent is formed by introducing acrylate functional groups through a polymer esterification reaction of polyhydroxy hyperbranched polyethylene and methacrylic acid; the cationic photocurable monomer is an epoxy compound. The low-warping anti-scratch coating of the present invention is coated on the surface of a BOPP film and photocured to form a low-warping anti-scratch film, which can solve the warping deformation problem of the existing BOPP anti-scratch film and improve the scratch resistance of the film surface.

Description

Technical Field

[0001] The invention relates to the technical field of photocurable scratch-resistant coatings, and in particular to a low-warping and deformation scratch-resistant coating, a low-warping and deformation scratch-resistant film and a preparation method thereof. Background Art

[0002] Biaxially oriented polypropylene (BOPP) film is currently the most widely used plastic film packaging material, but due to the poor scratch resistance of polypropylene, the surface of BOPP film is easily scratched and left with marks, affecting the appearance and use. The scratch-resistant modification of the surface of BOPP film is generally carried out by coating the surface of BOPP film with a scratch-resistant coating through a coating device, forming a layer of scratch-resistant and wear-resistant polymer coating on the surface of BOPP film, thereby giving the surface of BOPP film high gloss, high hardness and excellent scratch resistance, and improving the added value of the film material.

[0003] Anti-scratch coatings are shifting towards solvent-free coatings, with light-curing anti-scratch coatings being the most representative. Light-curing anti-scratch coatings have a solid content of nearly 100%, contain almost no volatile solvents and diluents, do not cause environmental pollution, and are green and environmentally friendly. After curing, a coating with high cross-linking density, excellent anti-scratch performance and solvent resistance can be obtained.

[0004] At present, photocurable scratch-resistant coatings are generally acrylate / methacrylate compounds, and their photocuring process is usually a free radical polymerization reaction, but the polymerization reaction is prone to produce large curing shrinkage. From the perspective of chemical reaction mechanism, the photocuring process of photocurable scratch-resistant coatings is a transformation process from small molecules to long-chain or three-dimensional network macromolecules, and its molecular structure has undergone great changes. Before the photocurable scratch-resistant coating is photocured, the force between acrylate / methacrylate monomers or prepolymers (C=C bond length is generally 0.133 nm) is van der Waals force, and the distance between molecules is van der Waals distance (0.3-0.5 nm); when the polymerization reaction occurs and the coating is cured, the original intermolecular distance becomes a covalent bond distance (CC bond length averages 0.154 nm), and the covalent bond distance is much smaller than the van der Waals force distance. The large change in the intermolecular distance leads to volume shrinkage during the curing process, which in turn leads to product warping and deformation.

[0005] In addition to free radical photocurable scratch-resistant coatings, cationic photocurable scratch-resistant coatings initiate cationic polymerization under ultraviolet light, and the prepolymers and active monomers used are mainly epoxy compounds, vinyl ethers, lactones, acetals, cyclic ethers, etc. The advantages of cationic photocurable scratch-resistant coatings are wear resistance, high hardness, good mechanical properties, and small volume shrinkage. The disadvantages are that the curing is affected by moisture, the curing speed is slow, the raw material types are few, and the price is high. Among them, the slow curing speed is the biggest disadvantage, making it unsuitable for high-speed roll-to-roll coating production of thin films.

[0006] With the implementation of environmental protection policies such as plastic reduction and lightweighting in the BOPP film industry, BOPP film is developing in a thinner direction. The thickness of the commonly used BOPP film is already below 12μm. The BOPP anti-scratch film produced by this method has an increasingly large warping deformation, is not easy to flatten when compounded with other materials, and is prone to wrinkles and other defects during composite use, causing great inconvenience and loss during use. Summary of the invention

[0007] Based on this, the purpose of the present invention is to provide a low warping and deformation anti-scratch coating, a low warping and deformation anti-scratch film and a preparation method thereof. The low warping and deformation anti-scratch coating of the present invention is coated on the surface of a BOPP film and photocured to form a low warping and deformation anti-scratch film (also called a BOPP anti-scratch film), which can solve the warping and deformation problem of the existing BOPP anti-scratch film and improve the scratch resistance of the film surface, especially meet the composite use requirements of thinner BOPP anti-scratch films, and is suitable for high-speed roll-to-roll coating production of thin films.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] The present invention first provides a low warpage and anti-scratch coating, which comprises the following components by mass percentage: 30-50% of acrylate prepolymer, 1-15% of acrylate active monomer, 10-30% of multifunctional hyperbranched active diluent, 20-30% of cationic photocuring monomer, 1-3% of free radical photoinitiator, and 1-3% of cationic photoinitiator; wherein the multifunctional hyperbranched active diluent is formed by introducing acrylate functional groups through a polymer esterification reaction of polyhydroxy hyperbranched polyethylene and methacrylic acid; the multifunctional hyperbranched active diluent has a number average molecular weight of 5000-20000 g / mol, a branching degree of (85-110) / 1000C, and a functionality of 5-7; and the cationic photocuring monomer is an epoxy compound.

[0010] The present invention provides the low warping and anti-scratch coating, which belongs to a hybrid photocuring system and utilizes the synergistic mechanism of two curing methods. After ultraviolet light curing, a coating with an interpenetrating network structure (IPN) is obtained, which improves the anti-scratch performance of the coating and inhibits the volume shrinkage and warping deformation of the coating during curing.

[0011] The low warpage and deformation scratch-resistant coating of the present invention is a hybrid photocurable scratch-resistant coating, which adopts the free radical photoinitiator and the cationic photoinitiator, provides two curing modes through the two photoinitiators, and utilizes the synergistic mechanism thereof, thereby overcoming the problems of slow curing speed and production difficulty of cationic polymerization, maintaining the respective advantages of free radical polymerization and cationic polymerization, and having fast curing speed, small volume shrinkage rate, and high mechanical strength. Among them, the free radical photoinitiator, under the irradiation of ultraviolet light, first generates a free radical active center to initiate free radical polymerization, and at the same time, the free radical fragments generated by the photolysis of the free radical photoinitiator can reduce the cationic photoinitiator, electron transfer occurs, indirect photolysis is achieved, a cationic active center is generated, and a cationic polymerization reaction is initiated. In addition to the electron transfer effect, the free radical photoinitiator can also directly photosensitize the cationic photoinitiator to a certain extent, thereby making full use of the long-wave ultraviolet light and improving the curing speed of cationic polymerization.

[0012] The acrylate prepolymer has excellent flexibility and wear resistance, and can improve the mechanical properties of the coating formed by the low warpage anti-scratch coating. However, the viscosity of the acrylate prepolymer is large (generally above 2000 mPa•s), and the adhesion to the BOPP film is low. The present invention reduces the viscosity of the coating system by adding the acrylate reactive monomer and the multifunctional hyperbranched reactive diluent to the low warpage anti-scratch coating, and the acrylate prepolymer can polymerize with the acrylate reactive monomer and the multifunctional hyperbranched reactive diluent to form a cross-linking system, so that the coating formed by polymerization has good scratch resistance and high adhesion to the BOPP film, thereby improving the problems of poor production applicability and low adhesion of the coating caused by the high viscosity of the acrylate prepolymer.

[0013] Generally, the viscosity of the photocurable scratch-resistant coating increases rapidly with the increase of the prepolymer content, and the mechanical properties are improved, but the high-viscosity coating is not suitable for thin film coating processing; the present invention adds the acrylate reactive monomer and the multifunctional hyperbranched reactive diluent to the low warpage scratch-resistant coating to reduce the viscosity of the coating. The acrylate reactive monomer is a free radical reactive diluent (the viscosity is usually less than 50 mPa•s), which can significantly reduce the viscosity of the coating, and participates in the cross-linking reaction during the curing process, and does not produce volatile organic compounds (VOCs). The acrylate reactive monomer is added in an amount of 1-15wt% in the low warpage scratch-resistant coating. Since the acrylate reactive monomer has a small molecular weight and is a small molecule reactive diluent, if the amount of the acrylate reactive monomer added is too large, the curing cross-linking density of the coating formed by the low warpage scratch-resistant coating will be too large, the volume shrinkage of the coating will increase, and the coating will become brittle and the adhesion will decrease. The product warpage is difficult to control.

[0014] The multifunctional hyperbranched reactive diluent is a functionalized hyperbranched polyethylene, which is formed by introducing acrylate functional groups through a high molecular esterification reaction between polyhydroxy hyperbranched polyethylene and methacrylic acid. The multifunctional hyperbranched reactive diluent, as a polyethylene-based copolymer, can effectively wet the surface of the BOPP film, and the multifunctional hyperbranched reactive diluent is in a non-crystalline state. After being attached to the surface of the BOPP film, it can diffuse into the inside of the BOPP film, entangle with the molecular chain segments on the surface of the BOPP film, and enhance the intermolecular force. The mutual entanglement between the molecular chain segments enhances the adhesion between the coating formed by the low warpage deformation anti-scratch coating and the BOPP film. The acrylate functional groups at the molecular chain ends of the multifunctional hyperbranched reactive diluent participate in the free radical photocuring reaction, and are cross-linked to the coating through chemical bonds, which can effectively overcome the problems of excessive crosslinking density, large volume shrinkage, brittle coating and insufficient adhesion after free radical photocuring, and form an interpenetrating network structure (IPN) with cationic polymerization to obtain a coating with extremely low warpage deformation and high scratch resistance. The content of the multifunctional hyperbranched reactive diluent in the low warpage anti-scratch coating is 10-30wt%. If the content of the multifunctional hyperbranched reactive diluent is too low, it cannot reduce the viscosity of the coating and prevent the coating from becoming brittle, and cannot effectively improve the problem of low adhesion of the coating on the surface of the BOPP film; if the content of the multifunctional hyperbranched reactive diluent is too low, the cost increases, and at the same time the hardness of the coating decreases, affecting the scratch resistance of the coating.

[0015] The multifunctional hyperbranched reactive diluent described in the present invention is neither a multifunctional small molecule reactive diluent nor a linear high molecular prepolymer. The linear polyethylene molecular chain structure has high regularity and is very easy to crystallize, but as the degree of branching increases, the regularity of the polyethylene molecular chain structure is destroyed, so that the crystallinity of the polyethylene decreases, and the polyethylene molecular chain segments begin to be easy to thermally move. The present invention utilizes the above characteristics to limit the branching degree of the multifunctional hyperbranched reactive diluent to (85-110) / 1000C. The branching degree of the multifunctional hyperbranched reactive diluent forms a spherical topological structure at (85-110) / 1000C, is completely non-crystalline at room temperature, has good flow permeability, and has strong adhesion to BOPP film. The spherical topological structure of the multifunctional hyperbranched active diluent is dense in structure, small in fluid mechanics radius, no intrachain entanglement, small intermolecular friction compared with the linear macromolecules of random coils, thus realizing active dilution in the coating system and reducing viscosity; it is not easy to be entangled with the IPN system during the photocuring process, thus playing the role of active dilution and lubrication; the multifunctional hyperbranched active diluent is evenly distributed in the coating, the photocuring cross-linking reaction is complete, and the problem of residual unreacted free radicals is improved. The present invention limits the number average molecular weight of the multifunctional hyperbranched reactive diluent to between 5000 and 20000 g / mol. When the molecular weight of the multifunctional hyperbranched reactive diluent is too low, the topological structure of the polyethylene molecular segment in its structure tends to be linear, and it is easy to entangle with itself and the acrylate prepolymer in the coating system, and it does not play the role of a diluent; when the molecular weight of the multifunctional hyperbranched reactive diluent is too high, the multifunctional hyperbranched reactive diluent is difficult to dissolve in the coating system, and phase separation and stratification are easy to occur. The functionality of the multifunctional hyperbranched reactive diluent is 5-7, which can ensure that the crosslinking density is moderate. If the functionality is too large, it is easy to cause the coating crosslinking density to be too large, the volume shrinkage is large, and the coating becomes brittle and the adhesion is insufficient.

[0016] When the cationic photocurable monomer, i.e., the epoxy compound, undergoes cationic ring-opening polymerization initiated by light, two CO covalent bonds on the alicyclic ring are broken and intermolecular covalent bonds are generated simultaneously, and the intermolecular distance does not change significantly. Therefore, the epoxy compound has a very small volume shrinkage during the polymerization reaction, and effectively controls the volume shrinkage of free radical polymerization in the coating of the IPN system, thereby inhibiting the warping deformation of the product. The cationic photocurable monomer, i.e., the epoxy compound, is added in an amount of 20-30wt% in the low warpage anti-scratch coating, which can ensure that the low warpage anti-scratch coating has a low viscosity and good production applicability, while satisfying the small volume shrinkage of the coating during curing, thereby overcoming the problem of product warpage deformation. If the cationic photocurable monomer is added in an excessive amount in the low warpage anti-scratch coating, due to the high viscosity of the cationic photocurable monomer (generally above 200 mPa•s), it is easy to cause the viscosity of the low warpage anti-scratch coating to be too high, and the high viscosity coating is not suitable for the coating process of BOPP film.

[0017] Furthermore, the acrylate prepolymer is an aliphatic polyurethane acrylate, and the functionality of the aliphatic polyurethane acrylate is 2-4. The present invention uses an aliphatic polyurethane acrylate with a functionality of 2-4, so that the coating formed by the low warpage deformation anti-scratch coating has good scratch resistance and good flexibility. If the functionality of the aliphatic polyurethane acrylate is too high, although the coating formed by the polymerization has a large cross-linking density, a large hardness, and good scratch resistance, the excessive cross-linking density will lead to the problem of brittle coating and reduced flexibility. Preferably, the molecular weight of the aliphatic polyurethane acrylate is 1000 g / mol.

[0018] Furthermore, the acrylate reactive monomer is a difunctional or trifunctional acrylate compound. Preferably, the acrylate reactive monomer is one or more of EGDA (ethylene glycol diacrylate, viscosity: 8 mPa•s), NPGDA (neopentyl glycol diacrylate, viscosity: 10 mPa•s), TPGDA (tripropylene glycol diacrylate, viscosity: 13 mPa•s), and ETPTA (ethoxylated trihydroxymethylpropane triacrylate, viscosity: 25 mPa•s).

[0019] Furthermore, the multifunctional hyperbranched active diluent is prepared by the following steps: catalyzing the copolymerization reaction of ethylene and acrylate monomers with silane-protected hydroxyl groups under the action of a late transition metal palladium-diimine catalyst, and the product is precipitated with ethanol to obtain a colorless transparent oily substance; then the colorless transparent oily substance is treated with a tetra-n-butylammonium fluoride solution to remove the protection of the hydroxyl group to obtain a polyhydroxy hyperbranched polyethylene containing multiple hydroxyl groups, and the polyhydroxy hyperbranched polyethylene and methacrylic acid are introduced into the acrylate functional group through a polymer esterification reaction to form the multifunctional hyperbranched active diluent. The multifunctional (functionality 5-7) hyperbranched active diluent obtained by the present invention using the late transition metal palladium-diimine catalytic polymerization has a spherical topological structure, is completely non-crystalline at room temperature, has good flow permeability, and has strong adhesion to BOPP film.

[0020] Furthermore, the cationic photocurable monomer is one or both of EEC (3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylate) and BEA (bis(3,4-epoxycyclohexylmethyl)adipate).

[0021] Further, the free radical photoinitiator is one or more of benzoin, benzoin ether, acetophenone, and acetophenone ketal compounds. Preferably, the free radical photoinitiator is one or more of photoinitiator 184, photoinitiator 1173, photoinitiator TPO, and photoinitiator 907. These free radical photoinitiators can effectively generate free radicals during the photocuring process to promote the rapid curing of the coating.

[0022] Further, the cationic photoinitiator is one or more of diaryliodonium salts, triarylsulfonium salts, and alkylsulfonium salt compounds. Preferably, the cationic photoinitiator is one or more of photoinitiator PAG208, photoinitiator PAG202, photoinitiator UVI6976, and photoinitiator UVI6974. These cationic photoinitiators can effectively generate cations under the irradiation of ultraviolet light, thereby initiating and accelerating cationic polymerization reactions.

[0023] The present invention also provides a low warping and scratch-resistant film (also called BOPP scratch-resistant film), comprising a coating and a BOPP film layer; the coating is formed by coating any of the above-mentioned low warping and scratch-resistant coatings on the surface of the BOPP film layer; the BOPP film layer is a BOPP film.

[0024] The low warping and deformation scratch-resistant film of the present invention solves the problems of warping and deformation of the existing BOPP scratch-resistant film and insufficient adhesion of the scratch-resistant coating on the surface of the BOPP film. The low warping and deformation scratch-resistant film of the present invention improves the scratch resistance and wear resistance of the coating, has high adhesion between the coating and the BOPP film, is not prone to warping and deformation, and meets the high-end composite requirements of BOPP scratch-resistant films.

[0025] Furthermore, the dry weight of the coating is 1-3 g / m 2 The thickness of the BOPP film layer is 8-12 μm. The dry weight of the coating on the thinner (8-12 μm) BOPP film surface is 1-3 g / m 2 The coating produces a low warping and scratch-resistant film (BOPP scratch-resistant film), which is not prone to warping and deformation and is easy to flatten when compounded with other materials, improving defects such as wrinkles during composite use. It especially meets the composite use needs of thinner BOPP scratch-resistant films and is suitable for high-speed roll-to-roll coating production of thin films.

[0026] The present invention also provides a method for preparing any of the above-mentioned low warping and deformation scratch-resistant films, comprising the following steps:

[0027] S1: mixing the components according to mass percentage to prepare any of the above-mentioned low warpage and anti-scratch coatings;

[0028] S2: The low warpage and anti-scratch coating is coated on the surface of the BOPP film using a coating machine, and irradiated with ultraviolet light for 40-60 seconds to obtain the low warpage and anti-scratch film.

[0029] Compared with existing technology:

[0030] The low warpage anti-scratch coating of the present invention has good fluidity, viscosity ≤ 300 mPa·s (30°C), and meets the requirements of mature industrial coating processes such as traditional roller coating, spray coating, and scraper coating; it has a low curing volume shrinkage rate, and the volume shrinkage rate after curing is ≤4%. The present invention solves the production applicability of the light-cured anti-scratch coating and the warpage problem of the BOPP anti-scratch film. The low warpage anti-scratch coating of the present invention is simple and easy to use, and has strong practicality and commercial prospects; in addition, the low warpage anti-scratch coating of the present invention has a 100% solid content, no volatile organic compound (VOC) emissions, no odor generation, and is green and environmentally friendly. DETAILED DESCRIPTION

[0031] In order to facilitate the understanding of the present invention, the present invention will be described more fully below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

[0032] The invention provides a low-warping and anti-scratch coating, which comprises the following components by mass percentage: 30-50% of acrylate prepolymer, 1-15% of acrylate active monomer, 10-30% of multifunctional hyperbranched active diluent, 20-30% of cationic photocuring monomer, 1-3% of free radical photoinitiator, and 1-3% of cationic photoinitiator; the multifunctional hyperbranched active diluent is formed by introducing acrylate functional groups into multihydroxy hyperbranched polyethylene and methacrylic acid through a macromolecular esterification reaction; the multifunctional hyperbranched active diluent has a number average molecular weight of 5000-20000, a branching degree of (85-110) / 1000C, and a functionality of 5-7; and the cationic photocuring monomer is an epoxy compound.

[0033] The preparation method of the multifunctional hyperbranched active diluent comprises the following steps: catalyzing the copolymerization reaction of ethylene and acrylate monomers with silane-protected hydroxyl groups under the action of a late transition metal palladium-diimine catalyst, and obtaining a colorless transparent oily substance after the product is precipitated by ethanol; then treating the colorless transparent oily substance with a tetra-n-butylammonium fluoride solution to remove the protection of the hydroxyl group, thereby obtaining a multi-hydroxy hyperbranched polyethylene containing multiple hydroxyl groups; and introducing an acrylate functional group into the multi-hydroxy hyperbranched polyethylene and methacrylic acid through a high molecular esterification reaction, thereby forming the multifunctional hyperbranched active diluent.

[0034] Among them, taking a multifunctional hyperbranched active diluent with a number average molecular weight of 20,000, a branching degree of 100 / 1000C, and a functionality of 7 as an example, the specific operation process is as follows: a low-pressure glass reactor is connected to a circulating vacuum pump, and high-temperature drying is performed under infrared light for more than 3 hours, and then cold pumping is performed for 1 hour to keep the glass reactor absolutely dry. 100 mmol of late transition metal palladium-diimine catalyst is dissolved in anhydrous dichloromethane. Under nitrogen protection, the dichloromethane solution containing the catalyst and 0.02 mol of trimethylsilane-protected hydroxyethyl acrylate (HEA-TMS) monomer solution are added to a dry and sealed glass reactor, and ethylene is introduced to control the set pressure to 0.1-5 atm, and the temperature is set to 0-5°C. After reacting in a constant temperature water bath for 24 hours, a small amount of ethanol is added to terminate the reaction to obtain a mixture of copolymers containing ethylene and HEA-TMS. After dissolving the above mixture with an appropriate amount of dichloromethane, pour it into cold anhydrous ethanol for precipitation, and let it stand until the precipitation is complete to remove the catalyst and comonomer to obtain a colorless transparent oil. The above colorless transparent oil is dissolved in 100 ml of tetrahydrofuran, and the dissolution time is 2-3 hours. After adding tetrahydrofuran solution of tetra-n-butylammonium fluoride for 1 hour, concentrated hydrochloric acid is added. After 0.5 hours, the reaction is stopped, the product is separated, and an excess of methanol is added to precipitate the polymer, which is washed with methanol several times and dried in a vacuum oven to obtain a multi-hydroxy hyperbranched polyethylene; then the prepared multi-hydroxy hyperbranched polyethylene is reacted with methacrylic acid through a high molecular weight esterification reaction to introduce acrylate functional groups to obtain a multi-functional hyperbranched active diluent with a number average molecular weight of 20,000 g / mol, a branching degree of 100 / 1000C, and a functionality of 7. The preparation of multifunctional hyperbranched reactive diluents with other number average molecular weights, branching degrees, and functionalities can be controlled by regulating the polymerization time, ethylene pressure, and polymerization temperature, which can be routinely adjusted by those skilled in the art according to the above preparation method and will not be described in detail here.

[0035] Example 1

[0036] The present embodiment provides a low warpage and scratch-resistant coating, which includes the following components by mass percentage: 50% acrylate prepolymer (aliphatic polyurethane acrylate, molecular weight 1000 g / mol), 10% acrylate reactive monomer (EGDA), 10% multifunctional hyperbranched reactive diluent (number average molecular weight Mn: 20000 g / mol, branching degree: 100 / 1000C, functionality: 7), 27.5% cationic photocurable monomer (EEC), 1% free radical photoinitiator (photoinitiator 184), and 1.5% cationic photoinitiator (photoinitiator UVI6974).

[0037] This embodiment also provides a low warping and scratch-resistant film, comprising a coating and a BOPP film layer, wherein the coating is formed by coating the above-mentioned low warping and scratch-resistant coating on the surface of the BOPP film layer; and the BOPP film layer is a BOPP film.

[0038] This embodiment also provides a method for preparing a low-warping and anti-scratch film, comprising the following steps:

[0039] S1: According to the mass percentage components of the low warpage and anti-scratch coating of this embodiment, the raw materials of each component are added into a constant temperature sealed high-speed stirring tank and stirred to obtain the low warpage and anti-scratch coating; wherein the stirring speed is 1500 rpm, the temperature is controlled at 30° C., and the stirring time is 4 hours;

[0040] S2: The low warpage anti-scratch coating is coated on the surface of a 12 μm thick BOPP film by using a coating machine and a micro-concave roller coating method; the film is cured by ultraviolet light irradiation for 40 seconds to form a BOPP anti-scratch film, namely, the low warpage anti-scratch film.

[0041] In the low warpage anti-scratch film of this embodiment, the dry weight of the coating is 1 g / m 2 .

[0042] Example 2

[0043] The present embodiment provides a low warpage and anti-scratch coating, which includes the following components by mass percentage: 41% acrylate prepolymer (aliphatic polyurethane acrylate, molecular weight 1000 g / mol), 5% acrylate reactive monomer (ETPTA), 30% multifunctional hyperbranched reactive diluent (number average molecular weight Mn: 5500 g / mol, branching degree: 86 / 1000C, functionality: 5), 20% cationic photocurable monomer (BEA), 2.5% free radical photoinitiator (photoinitiator TPO), and 1.5% cationic photoinitiator (UVI6976).

[0044] This embodiment also provides a low warping and scratch-resistant film, comprising a coating and a BOPP film layer, wherein the coating is formed by coating the above-mentioned low warping and scratch-resistant coating on the surface of the BOPP film layer; and the BOPP film layer is a BOPP film.

[0045] This embodiment also provides a method for preparing a low-warping and anti-scratch film, comprising the following steps:

[0046] S1: According to the mass percentage components of the low warpage and anti-scratch coating of this embodiment, the raw materials of each component are added into a constant temperature sealed high-speed stirring tank and stirred to obtain the low warpage and anti-scratch coating; wherein the stirring speed is 1500 rpm, the temperature is controlled at 30° C., and the stirring time is 3 hours;

[0047] S2: The low warpage anti-scratch coating is coated on the surface of a 10 μm thick BOPP film by using a coating machine and a micro-concave roller coating method; the film is cured by ultraviolet light irradiation for 60 seconds to form a BOPP anti-scratch film, namely the low warpage anti-scratch film.

[0048] In the low warpage anti-scratch film of this embodiment, the dry weight of the coating is 3 g / m 2 .

[0049] Example 3

[0050] The present embodiment provides a low warpage and anti-scratch coating, which includes the following components by mass percentage: 30% acrylate prepolymer (aliphatic polyurethane acrylate, molecular weight 1000 g / mol), 15% acrylate reactive monomer (ETPTA), 20% multifunctional hyperbranched reactive diluent (number average molecular weight Mn: 10000 g / mol, branching degree: 95 / 1000C, functionality: 6), 30% cationic photocurable monomer (BEA), 2.5% free radical photoinitiator (photoinitiator 1173), and 2.5% cationic photoinitiator (photoinitiator PAG202).

[0051] This embodiment also provides a low warping and scratch-resistant film, comprising a coating and a BOPP film layer, wherein the coating is formed by coating the above-mentioned low warping and scratch-resistant coating on the surface of the BOPP film layer; and the BOPP film layer is a BOPP film.

[0052] This embodiment also provides a method for preparing a low-warping and anti-scratch film, comprising the following steps:

[0053] S1: According to the mass percentage components of the low warpage and anti-scratch coating of this embodiment, the raw materials of each component are added into a constant temperature sealed high-speed stirring tank and stirred to obtain the low warpage and anti-scratch coating; wherein the stirring speed is 1500 rpm, the temperature is controlled at 30° C., and the stirring time is 3 hours;

[0054] S2: The low warpage anti-scratch coating is coated on the surface of a 10 μm thick BOPP film by using a coating machine and a micro-concave roller coating method; the film is cured by ultraviolet light irradiation for 50 seconds to form a BOPP anti-scratch film, namely the low warpage anti-scratch film.

[0055] In the low warpage anti-scratch film of this embodiment, the dry weight of the coating is 2 g / m 2 .

[0056] Comparative Example 1

[0057] The present comparative example provides a photocurable coating, which comprises the following components by mass percentage: 50% acrylate prepolymer (aliphatic polyurethane acrylate, molecular weight of 1000 g / mol), 38% acrylate reactive monomer (EGDA), 10% multifunctional hyperbranched reactive diluent (number average molecular weight Mn: 20000 g / mol, degree of branching: 100 / 1000C, functionality: 7), and 2% free radical photoinitiator (photoinitiator 184).

[0058] This comparative example also provides a photocurable coating film, comprising a coating layer and a BOPP film layer, wherein the coating layer is formed by coating the above-mentioned photocurable coating on the surface of the BOPP film layer; and the BOPP film layer is a BOPP film.

[0059] This comparative example also provides a method for preparing a photocurable coating film, comprising the following steps:

[0060] S1: According to the mass percentage components of the photocurable coating of this comparative example, the raw materials of each component are added into a constant temperature sealed high-speed stirring tank and stirred to obtain the photocurable coating; wherein the stirring speed is 1500 rpm, the temperature is controlled at 30° C., and the stirring time is 4 hours;

[0061] S2: The photocurable coating is coated on the surface of a 12 μm thick BOPP film by using a coating machine and a micro-concave roller coating method; the film is cured by ultraviolet irradiation for 40 seconds to form a BOPP coating film, namely, the photocurable coating film.

[0062] In the low warpage anti-scratch film of this comparative example, the dry weight of the coating is 1 g / m 2 .

[0063] Comparative Example 2

[0064] The present comparative example provides a photocurable coating, which comprises the following components by mass percentage: 50% acrylate prepolymer (aliphatic polyurethane acrylate, molecular weight 1000 g / mol), 20% acrylate active monomer (EGDA), 27.5% cationic photocurable monomer (EEC), 1% free radical photoinitiator (photoinitiator 184), and 1.5% cationic photoinitiator (photoinitiator UVI6974).

[0065] This comparative example also provides a photocurable coating film, comprising a coating layer and a BOPP film layer, wherein the coating layer is formed by coating the above-mentioned photocurable coating on the surface of the BOPP film layer; and the BOPP film layer is a BOPP film.

[0066] This comparative example also provides a method for preparing a photocurable coating film, comprising the following steps:

[0067] S1: According to the mass percentage components of the photocurable coating of this comparative example, the raw materials of each component are added into a constant temperature sealed high-speed stirring tank and stirred to obtain the photocurable coating; wherein the stirring speed is 1500 rpm, the temperature is controlled at 30° C., and the stirring time is 4 hours;

[0068] S2: The photocurable coating is coated on the surface of a 10 μm thick BOPP film by using a coating machine and a micro-concave roller coating method; the film is cured by ultraviolet irradiation for 40 seconds to form a BOPP coating film, namely, the photocurable coating film.

[0069] In the low warpage anti-scratch film of this comparative example, the dry weight of the coating is 1 g / m 2 .

[0070] Performance Testing

[0071] The following performance tests were performed on the coatings and anti-scratch films (coating films) of Examples 1-3 and Comparative Examples 1-2, respectively. Please refer to Tables 1 and 2 for the results.

[0072] Pencil hardness: According to the standard of JIS K5400-1990 "Determination of adhesion performance of powder coating film", the pencil hardness of the scratch-resistant and wear-resistant layer is tested.

[0073] Adhesion of coating: According to the standard of GB1720-1979 "Determination of paint film adhesion", the adhesion of the scratch-resistant and wear-resistant layer is tested, where 100 / 100 means no film peeling, and 90 / 100 means 10% peeling.

[0074] Scratch / abrasion resistance test: The abrasion resistance of the scratch-resistant coating was tested according to HG / T 4303-2012 "Test method for abrasion resistance of surface hardened polyester film", using 0000# steel wool, 1000gf / cm 2 The wear resistance of the film can be judged by testing the limit of the number of times the diaphragm surface can be worn without scratches.

[0075] Volume shrinkage test: Test in accordance with the relevant provisions of international standard ISO 3521.

[0076] Table 1 Coating test of Examples 1-3 and Comparative Examples 1-2

[0077]

[0078] Table 2 Test results of anti-scratch film (coating) samples of Examples 1-3 and Comparative Examples 1-2

[0079]

[0080] It is well known to those skilled in the art that the existing commonly used low warping and anti-scratch coatings usually have a volume shrinkage rate greater than 5%. The BOPP anti-scratch film prepared by coating it on the surface of a BOPP film with a thickness of less than 12 μm has a large warping and deformation problem.

[0081] It can be seen from the test data in Table 1 and Table 2 that the low warpage anti-scratch coatings of Examples 1-3 of the present invention have lower viscosity and volume shrinkage, and the produced low warpage anti-scratch film (BOPP anti-scratch film) effectively overcomes the warpage problem. At the same time, the adhesion of the coating to the BOPP film is qualified, and the anti-scratch / wear resistance is also improved.

[0082] In the photocurable coating of Comparative Example 1, no cationic photocurable monomer and cationic photoinitiator are added. It is a pure free radical photocurable scratch-resistant coating. The produced BOPP coating film has severe warping and deformation. At the same time, due to the lack of interpenetrating network structure (IPN) generated by simultaneous polymerization of cationic species, the scratch resistance of the BOPP coating film is reduced.

[0083] In the photocurable coating of Comparative Example 2, no multifunctional hyperbranched reactive diluent is added. The coating formed by the photocurable coating of Comparative Example 2 lacks components that promote adhesion to the BOPP film. The coating partially falls off when tested with a tape, and the adhesion to the BOPP film is unqualified. At the same time, since the photocurable coating of Comparative Example 2 uses a large amount of small molecule reactive diluent (i.e., acrylate reactive monomer) in order to maintain the low viscosity state of the coating, the volume shrinkage after curing is difficult to be suppressed by the IPN system, and the product has serious warping and deformation.

[0084] Compared with the prior art, the low warpage anti-scratch coating of the present invention uses a general coating process, is coated on the surface of the BOPP film once, and forms a low warpage anti-scratch film after light curing, which can solve the problems of warpage and deformation of the existing BOPP anti-scratch film and insufficient adhesion of the coating on the surface of the BOPP film, improve the scratch resistance / wear resistance of the coating, and meet the high-end composite requirements of BOPP anti-scratch film. The low warpage anti-scratch coating has good fluidity, viscosity ≤ 300 mPa•s, and a low curing volume shrinkage rate, with a volume shrinkage rate of ≤4% after curing. It can be applied to BOPP films with a thickness of less than 12μm and used to prepare low warpage BOPP anti-scratch films.

[0085] The above-mentioned embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and the present invention is also intended to include these modifications and modifications.

Claims

1. A low warping and anti-scratch coating, characterized in that: The invention comprises the following components by mass percentage: 30-50% acrylate prepolymer, 1-15% acrylate active monomer, 10-30% multifunctional hyperbranched active diluent, 20-30% cationic photocuring monomer, 1-3% free radical photoinitiator, and 1-3% cationic photoinitiator; wherein the multifunctional hyperbranched active diluent is formed by introducing acrylate functional groups into multihydroxy hyperbranched polyethylene and methacrylic acid through a high molecular esterification reaction; the multifunctional hyperbranched active diluent has a number average molecular weight of 5000-20000 g / mol, a branching degree of (85-110) / 1000C, and a functionality of 5-7; and the cationic photocuring monomer is an epoxy compound.

2. The low warpage anti-scratch coating according to claim 1, characterized in that: The acrylate prepolymer is aliphatic polyurethane acrylate, the functionality of the aliphatic polyurethane acrylate is 2-4, and the molecular weight of the aliphatic polyurethane acrylate is 1000 g / mol.

3. The low warpage anti-scratch coating according to claim 1, characterized in that: The acrylate reactive monomer is one or more of ethylene glycol diacrylate, neopentyl glycol diacrylate, tripropylene glycol diacrylate, and ethoxylated trihydroxymethylpropane triacrylate.

4. The low warpage anti-scratch coating according to claim 1, characterized in that: The multifunctional hyperbranched active diluent is prepared by the following steps: catalyzing the copolymerization reaction of ethylene and acrylate monomers with silane-protected hydroxyl groups under the action of a late transition metal palladium-diimine catalyst, and obtaining a colorless transparent oily substance after the product is precipitated by ethanol; then treating the colorless transparent oily substance with a tetra-n-butylammonium fluoride solution to remove the protection of the hydroxyl group, thereby obtaining a polyhydroxy hyperbranched polyethylene containing multiple hydroxyl groups; and introducing an acrylate functional group into the polyhydroxy hyperbranched polyethylene and methacrylic acid through a high molecular esterification reaction, thereby forming the multifunctional hyperbranched active diluent.

5. The low warpage anti-scratch coating according to claim 1, characterized in that: The cationic photocurable monomer is one or two of 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylate and di(3,4-epoxycyclohexylmethyl)adipate.

6. The low warpage anti-scratch coating according to claim 1, characterized in that: The free radical photoinitiator is one or more of benzoin, benzoin ether, acetophenone, and acetophenone ketal compounds.

7. The low warpage anti-scratch coating according to claim 1, characterized in that: The cationic photoinitiator is one or more of diaryl iodonium salts, triaryl sulfonium salts, and alkyl sulfonium salt compounds.

8. A low warping and anti-scratch film, characterized in that: It comprises a coating and a BOPP film layer; the coating is formed by coating the low warpage and scratch-resistant coating according to any one of claims 1 to 7 on the surface of the BOPP film layer; the BOPP film layer is a BOPP film.

9. The low warping and anti-scratch film according to claim 8, characterized in that: The dry weight of the coating is 1-3 g / m 2 ; The thickness of the BOPP film layer is 8-12μm.

10. A method for preparing a low warping and scratch-resistant film according to claim 8 or 9, characterized in that: The following steps are involved: S1: According to the low warpage anti-scratch coating formula of any one of claims 1 to 7, the components are mixed to prepare the low warpage anti-scratch coating; S2: The low warpage and anti-scratch coating is coated on the surface of the BOPP film using a coating machine, and irradiated with ultraviolet light for 40-60 seconds to obtain the low warpage and anti-scratch film.

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