Preparation method of optical thin film, optical thin film and display screen

Abstract

The invention discloses a preparation method of an optical thin film, the optical thin film and a display screen, and relates to the technical field of optical thin films, the preparation method of the optical thin film comprises the following steps: S10, mixing and grinding a white pigment and carboxyl-containing oil soluble resin to obtain a first mixture; s20, mixing the first mixture, an amino-containing compound and water, carrying out a neutralization reaction, and stirring to obtain an emulsion, namely a second mixture; and S30, mixing the second mixture with auxiliary materials to prepare the optical thin film. According to the method disclosed by the invention, the white pigment in a solid form is converted into an emulsion droplet form, so that the water dilutability of the white pigment is improved, the number of small black spots on the optical film is finally reduced, and the covering power of the optical film is improved.

Description

Technical Field

[0001] The invention relates to the technical field of optical films, and in particular to a method for preparing an optical film, an optical film and a display screen. Background Art

[0002] White optical film refers to a type of film material with a white appearance and specific optical properties. This type of film has high reflectivity and can scatter or block light, and is suitable for use in automotive glass, display backlights, lighting equipment, solar panels, and projection systems.

[0003] However, the quality of the white optical film prepared by the existing process is unstable, usually has many small black spots, and its optical performance and overall quality are poor. Summary of the invention

[0004] The main purpose of the present invention is to provide a method for preparing an optical film, an optical film and a display screen, aiming to solve the problem that the white optical film in the prior art has many small black spot defects.

[0005] To achieve the above object, the present invention provides a method for preparing an optical film, comprising the following steps:

[0006] S10, mixing and grinding a white pigment and an oil-soluble resin containing a carboxyl group to obtain a first mixture;

[0007] S20, mixing the first mixture, the amino-containing compound and water, performing a neutralization reaction, and stirring to obtain an emulsion, which is a second mixture;

[0008] S30, mixing the second mixture with auxiliary materials to prepare an optical film.

[0009] In one embodiment, in step S10:

[0010] The oil-soluble resin containing carboxyl groups includes one or more of oil-soluble acrylic resin containing carboxyl groups, oil-soluble polyester resin containing carboxyl groups and oil-soluble polyurethane resin containing carboxyl groups, wherein the oil-soluble acrylic resin containing carboxyl groups includes solid oily acrylic resin containing carboxyl groups or liquid oily acrylic resin containing carboxyl groups; and / or,

[0011] The molecular weight of the oil-soluble resin containing carboxyl groups is 50,000 to 100,000 Da; and / or,

[0012] The acid value of the oil-soluble resin containing a carboxyl group is A, A>20; and / or,

[0013] The particle size of the first mixture is B, and B≤5 μm.

[0014] In one embodiment, step S10 includes:

[0015] The white pigment, the oil-soluble resin containing a carboxyl group and the aqueous dispersant are mixed and ground to obtain a first mixture.

[0016] In one embodiment, in step S10:

[0017] The mass ratio of the white pigment, the oil-soluble resin containing a carboxyl group, and the aqueous dispersant is (40-60): (30-50): (0.2-2); and / or,

[0018] The white pigment comprises one or more of titanium dioxide and zinc oxide; and / or,

[0019] The aqueous dispersant includes one or more of anionic dispersants, polyvinyl alcohol dispersants, polyvinyl alcohol and acryl alcohol block copolymer dispersants, and hyperbranched polyether dispersants.

[0020] In one embodiment, step S20 includes:

[0021] The first mixture and the amino group-containing compound are mixed to carry out a neutralization reaction. After the neutralization reaction is completed, water is added and mixed, and stirred to obtain an emulsion, which is the second mixture.

[0022] In one embodiment, step S20 includes:

[0023] The first mixture, the amino-containing compound and water are mixed, the pH of the system is adjusted to 8.0-8.5, a neutralization reaction is carried out, and the mixture is stirred to obtain an emulsion, which is the second mixture.

[0024] In one embodiment, in step S20:

[0025] The mass ratio of the first mixture, the amino group-containing compound, and the water is (70-115): (1-5): (30-50); and / or,

[0026] The amino group-containing compound includes one or more of 2-amino-2-methyl-1-propanol and N,N-dimethylethanolamine.

[0027] In one embodiment, in step S30:

[0028] The auxiliary materials include a cosolvent and a curing agent, the cosolvent includes one or more of water, isopropanol, propylene glycol methyl ether, ethylene glycol methyl ether, ethylene glycol butyl ether, diethylene glycol butyl ether, propylene glycol ethyl ether and dipropylene glycol methyl ether, the curing agent includes water-based polyisocyanate, and / or,

[0029] The method for preparing the optical film includes spray coating, spin coating, flow coating, roller coating, dip coating, blade coating, micro-concave transfer or slit coating.

[0030] The present invention also provides an optical film, which is prepared by the above-mentioned method for preparing the optical film.

[0031] The present invention also provides a display screen, comprising an optical film prepared by the above-mentioned method for preparing the optical film.

[0032] In the technical scheme of the present invention, the oil-soluble resin containing carboxyl groups wraps and dissolves the white pigment during the mixing and grinding process. Since the white pigment is oil-soluble, it can be soluble in the oil-soluble resin; the amino group in the amino-containing compound undergoes an acid-base neutralization reaction with the carboxyl group in the oil-soluble resin containing carboxyl groups in the first mixture, so that the carboxyl group on the oil-soluble resin is partially ionized and partially hydrophilic, thereby improving the hydrophilicity of the oil-soluble resin. At this time, under stirring conditions, the oil-soluble resin, as an amphiphilic molecule, emulsifies water, the oil-soluble white pigment and part of the oil-soluble resin to obtain an emulsion. The stability of the emulsion droplets is good, which prevents the added auxiliary materials from breaking up the emulsion droplets and exposing the white pigment therein, thereby improving the water dilution of the white pigment, reducing the number of small black spots on the prepared optical film, and improving the hiding power of the optical film. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0034] Figure 1 This is a diagram showing the effect of the emulsion obtained by stirring in Example 1 provided by the present invention being coated on a PET film;

[0035] Figure 2 This is a diagram showing the effect of the emulsion obtained by stirring in Comparative Example 5 provided by the present invention being coated on a PET film.

[0036] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0037] To make the purpose, technical scheme and advantages of the embodiment of the present invention clearer, the technical scheme in the embodiment of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiment, it is carried out according to the normal conditions or the conditions recommended by the manufacturer. If the reagents or instruments used do not specify the manufacturer, they are all conventional products that can be purchased commercially. In addition, the meaning of "and / or" appearing in the full text includes three parallel schemes, taking "A and / or B" as an example, including scheme A, or scheme B, or schemes that A and B meet at the same time. In addition, the technical schemes between the various embodiments can be combined with each other, but must be based on the ability of ordinary technicians in the field to achieve. When the combination of technical solutions is contradictory or cannot be achieved, it should be considered that the combination of such technical solutions does not exist, and is not within the scope of protection required by the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work belong to the scope of protection of the present invention.

[0038] White optical film refers to a type of film material with a white appearance and specific optical properties. This type of film has high reflectivity and can scatter or block light, and is suitable for use in automotive glass, display backlights, lighting equipment, solar panels, and projection systems.

[0039] However, the quality of the white optical film prepared by the existing process is unstable, usually has many small black spots, and its optical performance and overall quality are poor.

[0040] The existing process mainly involves adding a large amount of aqueous dispersant to grind white pigments. Since white pigments themselves are insoluble in water and the surface tension of water is also high, it is difficult to wet and disperse white pigments. In the existing process, a large amount of aqueous dispersant is added to grind white pigments to obtain aqueous white slurry, but the disadvantages of this method are: (a) the white pigment needs to be ground to the nanometer level to improve water dilution, the formula cost is high, the production efficiency is low, and the equipment requirements are high; (b) the optical film finally prepared by the obtained aqueous white slurry has low whiteness and poor hiding power.

[0041] In view of this, the present invention provides a method for preparing an optical film, comprising the following steps:

[0042] S10, mixing and grinding a white pigment and an oil-soluble resin containing a carboxyl group to obtain a first mixture;

[0043] S20, mixing the first mixture, the amino group-containing compound and water, performing a neutralization reaction, and stirring to obtain an emulsion, which is a second mixture;

[0044] S30, mixing the second mixture with auxiliary materials to prepare an optical film.

[0045] In the technical scheme of the present invention, the oil-soluble resin containing carboxyl groups wraps and dissolves the white pigment during the mixing and grinding process. Since the white pigment is oil-soluble, it can be miscible with the oil-soluble resin; the amino groups in the amino-containing compound undergo an acid-base neutralization reaction with the carboxyl groups in the oil-soluble resin containing carboxyl groups in the first mixture, so that the carboxyl groups on the oil-soluble resin are partially ionized and partially hydrophilic, thereby improving the hydrophilicity of the oil-soluble resin. At this time, under stirring conditions, the oil-soluble resin, as an amphiphilic molecule, emulsifies water, the oil-soluble white pigment and part of the oil-soluble resin to obtain an emulsion. The stability of the emulsion droplets is good, which prevents the added auxiliary materials from breaking up the emulsion droplets and exposing the white pigment therein, thereby improving the water dilution of the white pigment, reducing the number of small black spots on the prepared optical film, and improving the hiding power of the optical film.

[0046] The oil-soluble resin refers to a resin that can be dissolved and dispersed in an organic solvent and has a good affinity for oily substances.

[0047] The improvement of this scheme is that the white pigment and the oil-soluble resin containing carboxyl groups are mixed and ground, and then a compound containing amino groups is added for neutralization reaction to make one side of the resin hydrophilic, and water is added and stirred to obtain an aqueous solution of the emulsion, thereby improving the stability of the white pigment in the system. Therefore, when preparing the optical film, the emulsion is not easily dispersed and demulsified by external solvents, causing the white pigment to aggregate, thereby causing the optical film to produce more black spots.

[0048] In some embodiments of the present invention, in step S10: the oil-soluble resin containing carboxyl groups includes one or more of oil-soluble acrylic resin containing carboxyl groups, oil-soluble polyester resin containing carboxyl groups, and oil-soluble polyurethane resin containing carboxyl groups, wherein the oil-soluble acrylic resin containing carboxyl groups includes solid oily acrylic resin containing carboxyl groups or liquid oily acrylic resin containing carboxyl groups; the oil-soluble polyester resin containing carboxyl groups and the oil-soluble polyurethane resin containing carboxyl groups can also be in a liquid or solid state. Compared with other oil-soluble resins, the above-mentioned oil-soluble resin containing carboxyl groups has better lipophilicity and can better dissolve and stably coat white pigments. Among them, the oil-soluble acrylic resin containing carboxyl groups can be obtained by polymerizing at least acrylic monomers; the oil-soluble polyester resin containing carboxyl groups can be obtained by polymerizing at least polyester monomers; the oil-soluble polyurethane resin containing carboxyl groups can be obtained by polymerizing at least polyurethane monomers.

[0049] In some embodiments of the present invention, in step S10: the molecular weight of the oil-soluble resin containing carboxyl groups is 50000-100000Da. The molecular weight of the oil-soluble resin containing carboxyl groups can be 100000Da, 100000Da or 100000Da. The molecular weight within the above range can ensure that the molecular weight of the oil-soluble resin containing carboxyl groups is large, the encapsulation of white pigments is good, and the solubility of white pigments is good, which can improve the dispersibility of white pigments in the oil-soluble resin containing carboxyl groups. If the molecular weight is too large, the wettability and fluidity of the prepared coating product will be deteriorated, affecting the construction operation; if the molecular weight is too small, the chemical resistance, weather resistance, scratch resistance and other performance of the prepared coating product will be reduced.

[0050] In some embodiments of the present invention, in step S10: the acid value of the oil-soluble resin containing carboxyl groups is A, A>20. The acid value of the oil-soluble resin containing carboxyl groups can be 21, 41 or 61, or even higher. The acid value reflects the carboxyl content in the oil-soluble resin. In the present invention, the acid value refers to the number of milligrams of potassium hydroxide required to neutralize 1g of the oil-soluble resin, in units of mg KOH / g. The acid value within the above range can ensure that the oil-soluble resin containing carboxyl groups has more carboxyl groups, increase the neutralization reaction rate of its carboxyl groups with amino groups in amino compounds, increase the ionization ratio and hydrophilicity of its carboxyl groups, and help to improve the hydrophilicity of the above resin, so that the above resin has better amphiphilicity, which can promote the formation of subsequent emulsions.

[0051] In some embodiments of the present invention, in step S10: the particle size of the first mixture is B, B≤5μm. The particle size of the first mixture can be 5μm, 1μm or 0.1μm, or even smaller. The particle size of the first mixture within the above range can ensure that the particle size of the white pigment wrapped by the oil-soluble resin containing carboxyl groups is smaller, that is, the smaller the resin particles containing white pigments, the better the dispersibility of the white pigments, and the lower the probability of agglomeration of the white pigments; on the other hand, the resin particles containing white pigments have a small particle size, which makes it easier to react with amino compounds for neutralization, thereby increasing the ionization ratio and hydrophilicity of the carboxyl groups in the resin, so that the white pigment and water in the subsequent process form an emulsion faster under the action of the resin, thereby reducing the particle size of the emulsion droplets, facilitating the stability of the emulsion droplets, and not being easily dispersed and demulsified by external reagents.

[0052] In some embodiments of the present invention, step S10 includes: mixing and grinding a white pigment, an oil-soluble resin containing a carboxyl group, and an aqueous dispersant to obtain a first mixture. The aqueous dispersant is an amphiphilic molecule that can wet the white pigment and assist in grinding the white pigment, thereby improving grinding efficiency and reducing process time. That is, the aqueous dispersant has stronger polarity and wetting and dispersibility, which can accelerate the dispersion of large white pigment particles into small particles, thereby making the small particles of white pigment easier to be wrapped by the oil-soluble resin containing a carboxyl group.

[0053] In some embodiments of the present invention, in step S10: the mass ratio of the white pigment, the oil-soluble resin containing carboxyl groups, and the aqueous dispersant is (40-60): (30-50): (0.2-2). The mass ratio of the white pigment, the oil-soluble resin containing carboxyl groups, and the aqueous dispersant can be 40:50:2, 50:40:1, or 60:30:0.2. The mass ratio within the above range can promote the encapsulation or dispersion of the white pigment by the oil-soluble resin containing carboxyl groups. The mass ratio is too high: if the content of the oil-soluble resin containing carboxyl groups is too low, the encapsulation of the white pigment by the oil-soluble resin will be insufficient, affecting the subsequent neutralization and emulsification, resulting in demulsification, coarsening, etc.; if the content of the aqueous dispersant is too high, the dilution of the white pigment will be easily deteriorated, and coarsening will occur easily. And the storage stability of the coating will be deteriorated. Its mass ratio is too low: if the content of oil-soluble resin containing carboxyl is too high, the overall viscosity of the emulsion will be too high, the fluidity will be poor, and the construction will be affected; if the content of water-based dispersant is too high, the cost will be greatly increased, and the water resistance of the coating will be reduced, affecting the long-term use of the product.

[0054] In some embodiments of the present invention, in step S10: the white pigment includes one or more of titanium dioxide and zinc oxide. Compared with other white pigments, titanium dioxide and zinc oxide have better hiding power. The white pigment is preferably rutile titanium dioxide.

[0055] In some embodiments of the present invention, in step S10: the aqueous dispersant includes one or more of anionic dispersants, polyvinyl alcohol dispersants, polyvinyl alcohol and acryl alcohol block copolymer dispersants, and hyperbranched polyether dispersants. Among them, the anionic dispersant includes anionic acrylic dispersants, anionic polyester dispersants, or anionic polyurethane dispersants; the polyvinyl alcohol dispersants include PEO-600, PEO-800, or PEO-1000; the molecular weight of the polyvinyl alcohol and acryl alcohol block copolymer dispersant can be 800Da, 1000Da, or 1500Da; the hyperbranched polyether dispersant includes hyperbranched acrylic polyether dispersants, hyperbranched polyester polyether dispersants, and hyperbranched polyurethane polyether dispersants. The above aqueous dispersants can be purchased, such as from Jiangsu Haian Petrochemical Company. Compared with other aqueous dispersants, the above aqueous dispersants can better wet white pigments and have excellent compatibility with the carboxyl-containing oil-soluble resin used.

[0056] In some embodiments of the present invention, step S20 includes: mixing the first mixture and the compound containing an amino group, performing a neutralization reaction, and after the neutralization reaction is completed, adding water and mixing, and stirring to obtain an emulsion, which is the second mixture.

[0057] In the technical scheme of the present invention, the first mixture and the compound containing amino are first subjected to neutralization reaction, so that the carboxyl group of the oil-soluble resin containing carboxyl in the first mixture can be subjected to a more sufficient neutralization reaction with the amino group in the compound containing amino. In the neutralization reaction, a proton is transferred from the carboxyl group to the amino group, and the amino group is converted into a positively charged ammonium salt, while the carboxyl group is converted into a negatively charged carboxylate ion, thereby more fully realizing the partial ionization of the carboxyl group, making some resins become amphiphilic molecules, which are in close contact with the white pigment. After the neutralization reaction is completed, water is added to mix (providing an aqueous phase), the white pigment and the oily resin with unionized carboxyl groups are used as the oil phase, and stirred, and the resin with ionized carboxyl groups reduces the surface tension of the aqueous phase on the one hand, and is in close contact with the white pigment on the one hand, and even soluble, so that the oil phase and the aqueous phase are rapidly emulsified to form an emulsion, which is the second mixture.

[0058] In some embodiments of the present invention, step S20 includes: mixing the first mixture, the amino-containing compound and water, adjusting the pH of the system to 8.0-8.5, performing a neutralization reaction, and stirring to obtain an emulsion, which is the second mixture.

[0059] In the technical solution of the present invention, the pH of the system is adjusted to 8.0, 8.3 or 8.5. The pH value within the above range can ensure that the amino-containing compounds are relatively stable in the system and not easily volatile. On the other hand, under alkaline conditions, the OH in the solution - The higher the concentration, the more carboxyl groups lose H +, forming -COO - , increase the ionization ratio of carboxyl groups in oil-soluble resins. Too high pH value will bring bad odor and easily cause the coating obtained during emulsion coating to turn yellow, thus affecting the performance of the final optical film.

[0060] In some embodiments of the present invention, in step S20: the mass ratio of the first mixture, the amino-containing compound, and the water is (70-115): (1-5): (30-50). The mass ratio of the first mixture, the amino-containing compound, and the water can be 70:5:50, 90:3:40, or 115:1:30. The mass ratio within the above range can ensure that the neutralization reaction between the first mixture and the amino-containing compound is more sufficient, the carboxyl group of the oil-soluble resin in the first mixture is more fully ionized, the hydrophilicity is better, and it is more conducive to emulsification with water to form an emulsion.

[0061] In some embodiments of the present invention, in step S20: the amino group-containing compound includes one or more of 2-amino-2-methyl-1-propanol and N,N-dimethylethanolamine. That is, the amino group-containing compound may include 2-amino-2-methyl-1-propanol, or may include 2-amino-2-methyl-1-propanol and N,N-dimethylethanolamine. The amino group-containing compound has high neutralization efficiency, better compatibility, lower volatility, is easy to store, and can improve the storage stability of the emulsion product.

[0062] In some embodiments of the present invention, in step S30: the auxiliary materials include a cosolvent and a curing agent, the cosolvent includes one or more of water, isopropanol, propylene glycol methyl ether, ethylene glycol methyl ether, ethylene glycol butyl ether, diethylene glycol butyl ether, propylene glycol ethyl ether and dipropylene glycol methyl ether, and the curing agent includes an aqueous polyisocyanate. A cosolvent refers to a solvent that assists the dissolution and dispersion of the emulsion, and is used to adjust the viscosity of the emulsion and the volatilization rate of the coating obtained by emulsion coating. A curing agent refers to a component that cross-links with an oil-soluble resin, and is used to improve the density and chemical resistance of the coating obtained by emulsion coating. The above-mentioned cosolvent and curing agent can be selected to prepare a coating with good appearance and physical properties. The cosolvent can be any one of water, isopropanol, propylene glycol methyl ether, ethylene glycol methyl ether, ethylene glycol butyl ether, diethylene glycol butyl ether, propylene glycol ethyl ether or dipropylene glycol methyl ether, or two or more of water, isopropanol, propylene glycol methyl ether, ethylene glycol methyl ether, ethylene glycol butyl ether, diethylene glycol butyl ether, propylene glycol ethyl ether and dipropylene glycol methyl ether, all within the protection scope of the present invention. The curing agent includes water-based polyisocyanate, specifically including water-based HDI type polyisocyanate, water-based IPDI type polyisocyanate or water-based MDI type polyisocyanate.

[0063] In some embodiments of the present invention, in step S30: the method for preparing the optical film includes spray coating, spin coating, flow coating, roller coating, dip coating, blade coating, micro-concave transfer method or slit coating method. The spray coating method is to atomize the liquid material and spray it onto the surface of the substrate through a spray gun, which is suitable for large-area coating; the spin coating method is to drop a small amount of liquid material on the surface of the rotating substrate, and evenly distribute the material and form a thin film through centrifugal force; the shower coating method is to immerse the substrate vertically in the liquid material, and then pull it out at a constant speed, and the liquid material forms a thin film under the action of gravity; the roller coating method is to coat the liquid material on the moving substrate through one or more coating rollers; the dip coating method is to completely immerse the substrate in the coating liquid for a period of time and then take it out; the scraping method is to scrape the excess liquid material from the surface of the substrate through a fixed or moving blade, leaving a uniform film; the micro-concave transfer method is to transfer a precise amount of liquid material to the surface of the substrate through a roller with fine grooves; the slit coating method is to evenly coat the liquid material on the substrate through a coating head with a slit. Using the above method for preparing optical films, optical films can be obtained relatively quickly.

[0064] The present invention also provides an optical film, which is prepared by the above optical film preparation method. Therefore, it has all the beneficial effects of the above optical film preparation method, which will not be described in detail here. The thickness of the optical film coating is preferably 5 to 10 μm.

[0065] The present invention also provides a display screen, comprising an optical film prepared by the above-mentioned method for preparing an optical film, so that the display screen has all the beneficial effects of the above-mentioned method for preparing an optical film, which will not be described in detail here.

[0066] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments and drawings. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention.

[0067] Example 1

[0068] A method for preparing an optical film comprises the following steps:

[0069] S10, 40 g of rutile titanium dioxide (i.e., titanium dioxide) and 30 g of an oil-soluble resin containing a carboxyl group (acrylic resin having an acid value of 21 and a molecular weight of 70,000 Da) were uniformly dispersed by a high-speed disperser, and then repeatedly ground by a horizontal sand mill to a final particle size of 5 μm, thereby obtaining a first mixture;

[0070] S20, under stirring condition (rotation speed of 1000r / min), mixing the first mixture, 1g of 2-amino-2-methyl-1-propanol and 30g of water, performing neutralization reaction for 20min, and continuing stirring for 40min to obtain an emulsion, which is a second mixture;

[0071] S30. After diluting the second mixture with deionized water, the mass ratio of the second mixture to deionized water is 1:1, 6 g of propylene glycol methyl ether and 4.5 g of HDI type water-based diisocyanate curing agent are added and stirred, and then coated on a 38 μm PET film with a 30 μ wire rod, and dried in an oven at 50° C. for 2 minutes to obtain an optical film.

[0072] Example 2

[0073] A method for preparing an optical film comprises the following steps:

[0074] S10, 50 g of rutile titanium dioxide (i.e., titanium dioxide) and 40 g of an oil-soluble resin containing a carboxyl group (acrylic resin having an acid value of 21 and a molecular weight of 70,000 Da) are uniformly dispersed by a high-speed disperser, and then repeatedly ground by a horizontal sand mill to a final particle size of 1 μm, thereby obtaining a first mixture;

[0075] S20, under stirring condition (rotation speed of 1000 r / min), mixing the first mixture, 3 g of N,N-dimethylethanolamine and 40 g of water, performing a neutralization reaction, and continuing to stir to obtain an emulsion, which is a second mixture;

[0076] S30, diluting the second mixture with deionized water, the mass ratio of the second mixture to deionized water being 1:2, adding 6 g of propylene glycol methyl ether and 4.5 g of HDI type water-based diisocyanate curing agent, stirring and mixing, and then coating the mixture on a 38 μm PET film using a 30 μm wire rod, and drying in an oven at 50° C. for 2 minutes to obtain an optical film.

[0077] Example 3

[0078] A method for preparing an optical film comprises the following steps:

[0079] S10, 60g of rutile titanium dioxide (i.e., titanium dioxide) and 50g of an oil-soluble resin containing a carboxyl group (acrylic resin having an acid value of 88 and a molecular weight of 100,000 Da) were uniformly dispersed by a high-speed disperser, and then repeatedly ground by a horizontal sand mill to a final particle size of 700nm, thereby obtaining a first mixture;

[0080] S20, under stirring condition (rotation speed of 1000r / min), mixing the first mixture, 5g of 2-amino-2-methyl-1-propanol and 30g of water, performing a neutralization reaction, and continuing to stir to obtain an emulsion, which is a second mixture;

[0081] S30, diluting the second mixture with deionized water, the mass ratio of the second mixture to deionized water being 1:3, adding 6 g of propylene glycol methyl ether and 4.5 g of HDI type water-based diisocyanate curing agent, stirring and mixing, and then coating the mixture on a 38 μm PET film using a 30 μm wire rod, and drying in an oven at 50° C. for 2 minutes to obtain an optical film.

[0082] Example 4

[0083] Compared with Example 3, Example 4 is different in that:

[0084] The particle size of the first mixture was 5 μm.

[0085] Example 5

[0086] Compared with Example 1, Example 5 is different in that:

[0087] In step S10, 2 g of polyvinyl alcohol dispersant PEO-600 was also added.

[0088] Example 6

[0089] Compared with Example 1, Example 6 is different in that:

[0090] In step S20, the first mixture and 1 g of 2-amino-2-methyl-1-propanol are first mixed for neutralization reaction. After 20 minutes, the neutralization reaction is completed, and then 30 g of water is added and mixed. The mixture is stirred at a speed of 1000 r / min to obtain an emulsion, which is the second mixture.

[0091] Example 7

[0092] Compared with Example 1, Example 7 is different in that:

[0093] In step S20, the first mixture, 1 g of 2-amino-2-methyl-1-propanol and 30 g of water are mixed, the pH is adjusted to 8.0, a neutralization reaction is carried out, and stirring is continued to obtain an emulsion, which is the second mixture.

[0094] Comparative Example 1

[0095] Compared with Example 5, Comparative Example 1 is different in that:

[0096] No oil-soluble resin containing carboxyl groups is added.

[0097] Comparative Example 2

[0098] Compared with Example 3, Comparative Example 2 is different in that:

[0099] No oil-soluble resin containing carboxyl groups is added.

[0100] Comparative Example 3

[0101] Compared with Example 1, Comparative Example 3 is different in that:

[0102] 40 g of rutile titanium dioxide was directly ground to a particle size of 5 μm, and mixed with 30 g of an oil-soluble resin containing a carboxyl group and 30 g of water to obtain a mixture. The mixture was used to replace the second mixture in step S30 to perform step S30 in Example 1.

[0103] Comparative Example 4

[0104] 40 g of rutile titanium dioxide and 20 g of polyvinyl alcohol dispersant PEO-600 were mixed and ground to μm to obtain a mixture, and the mixture was used to replace the second mixture in step S30 to perform step S30 in embodiment 1.

[0105] Comparative Example 5

[0106] Compared with Example 1, Comparative Example 5 is different in that:

[0107] 40 g of rutile titanium dioxide and 30 g of aqueous acrylic emulsion resin (Bayhydrol A2846, Covestro, Germany) were directly mixed and ground to a particle size of 5 μm. The ground product was used to replace the second mixture in step S30 to perform step S30 in Example 1.

[0108] Comparative Example 6

[0109] Compared with Example 1, Comparative Example 6 is different in that:

[0110] In step S20, 2-amino-2-methyl-1-propanol is not added.

[0111] Performance Testing

[0112] The optical films prepared in Examples 1 to 7 and Comparative Examples 1 to 6 were prepared in such a way that the mass ratios of the second mixture and deionized water in step S30 were 1:1, 1:2 and 1:3, respectively. The number of black spots, hiding power and whiteness of the obtained optical films were tested. The number of black spots was tested by laying the optical film flat on a light-emitting plate and performing a light transmission inspection. The number of black spots was measured by the number of black spots per square meter (pcs / m 2 ); the hiding property test method is: paint a black dot on white paper, lay the optical film flat on the black dot, if one film can almost cover the black dot, the hiding property is excellent; if two films are needed, the hiding property is good; if three films are needed, the hiding property is poor; whiteness is measured using a whiteness meter. The results are shown in Table 1.

[0113] Table 1 Characterization of the optical films in Examples 1 to 7 and Comparative Examples 1 to 6

[0114]

[0115]

[0116] As shown in Table 1, since no neutralizer was added to Comparative Example 3, the oil-soluble resin could not be made hydrophilic, and a uniform coating and film could not be prepared subsequently. Comparative Example 5 directly used water-based acrylic emulsion resin for grinding, but during the stirring process, strong shear force would cause the emulsion resin to demulsify (such as Figure 2 As shown in the figure, when coated on the film surface, many particles appeared on the optical film, and the coating was uneven in white (i.e., it was impossible to prepare a uniform coating), which seriously damaged the stability and uniformity of the product. Comparative Example 6 still belongs to an oily system and is not hydrophilic because no neutralizer was added, so it was impossible to add water to dilute and prepare a uniform coating.

[0117] Examples 1-7 illustrate that the dispersion and coating effect of titanium dioxide mixed with carboxyl-containing oil-soluble resin is good, and strong shear force during stirring will not cause the emulsion to break (such as Figure 1 As shown, when coated on the surface of the film, no particles are precipitated, and the coating is white and uniform, and the coating prepared finally has good performance. Among them, the particle size of the first mixture in Example 4 is micrometer level, while that in Example 3 is nanometer level. Since the larger the particle size of titanium dioxide, the better the hiding power; the smaller the particle size of titanium dioxide, the worse the hiding power; and whiteness is directly related to hiding power, the better the hiding power, the higher the whiteness; but in terms of the number of black spots, the number of black spots in Example 3 is less than that in Example 4.

[0118] Comparative Examples 1-6 show that if titanium dioxide is not first mixed and ground with an oil-soluble resin containing a carboxyl group, the dispersion of titanium dioxide is poor and coarsening is likely to occur. The final coating prepared has poor performance. Moreover, the more water is added, the more obvious the titanium dioxide agglomeration and coarsening will be, and the more black spots will be present.

[0119] In summary, through the method of the present invention, the white pigment is converted from a solid form into an emulsion droplet form, which improves the water dilution of the white pigment, ultimately reducing the number of small black spots on the final optical film and improving the hiding power of the optical film.

[0120] The above are only preferred embodiments of the present invention, and do not limit the patent scope of the present invention. For those skilled in the art, the present invention may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the patent protection scope of the present invention.

Claims

1. A method for preparing an optical film, characterized in that: The following steps are involved: S10, mixing and grinding a white pigment and an oil-soluble resin containing a carboxyl group to obtain a first mixture; S20, mixing the first mixture, the amino-containing compound and water, performing a neutralization reaction, and stirring to obtain an emulsion, which is a second mixture; S30, mixing the second mixture with auxiliary materials to prepare an optical film.

2. The method for preparing an optical film according to claim 1, wherein: In step S10: The oil-soluble resin containing carboxyl groups includes one or more of oil-soluble acrylic resin containing carboxyl groups, oil-soluble polyester resin containing carboxyl groups and oil-soluble polyurethane resin containing carboxyl groups, wherein the oil-soluble acrylic resin containing carboxyl groups includes solid oily acrylic resin containing carboxyl groups or liquid oily acrylic resin containing carboxyl groups; and / or, The molecular weight of the oil-soluble resin containing carboxyl groups is 50,000 to 100,000 Da; and / or, The acid value of the oil-soluble resin containing a carboxyl group is A, A>20; and / or, The particle size of the first mixture is B, and B≤5 μm.

3. The method for preparing an optical film according to claim 1, wherein: Step S10 includes: The white pigment, the oil-soluble resin containing a carboxyl group and the aqueous dispersant are mixed and ground to obtain a first mixture.

4. The method for preparing an optical film according to claim 3, wherein: In step S10: The mass ratio of the white pigment, the oil-soluble resin containing a carboxyl group, and the aqueous dispersant is (40-60): (30-50): (0.2-2); and / or, The white pigment comprises one or more of titanium dioxide and zinc oxide; and / or, The aqueous dispersant includes one or more of anionic dispersants, polyvinyl alcohol dispersants, polyvinyl alcohol and acryl alcohol block copolymer dispersants, and hyperbranched polyether dispersants.

5. The method for preparing an optical film according to claim 1, wherein: Step S20 includes: The first mixture and the amino group-containing compound are mixed to carry out a neutralization reaction. After the neutralization reaction is completed, water is added and mixed, and stirred to obtain an emulsion, which is the second mixture.

6. The method for preparing an optical film according to claim 1, wherein: Step S20 includes: The first mixture, the amino-containing compound and water are mixed, the pH of the system is adjusted to 8.0-8.5, a neutralization reaction is carried out, and the mixture is stirred to obtain an emulsion, which is the second mixture.

7. The method for preparing an optical film according to claim 1, wherein: In step S20: The mass ratio of the first mixture, the amino group-containing compound, and the water is (70-115): (1-5): (30-50); and / or, The amino group-containing compound includes one or more of 2-amino-2-methyl-1-propanol and N,N-dimethylethanolamine.

8. The method for preparing an optical film according to claim 1, wherein: In step S30: The auxiliary materials include a cosolvent and a curing agent, the cosolvent includes one or more of water, isopropanol, propylene glycol methyl ether, ethylene glycol methyl ether, ethylene glycol butyl ether, diethylene glycol butyl ether, propylene glycol ethyl ether and dipropylene glycol methyl ether, the curing agent includes water-based polyisocyanate, and / or, The method for preparing the optical film includes spray coating, spin coating, flow coating, roller coating, dip coating, blade coating, micro-concave transfer or slit coating.

9. An optical film, characterized in that: The optical film is prepared by the method for preparing the optical film according to any one of claims 1 to 8.

10. A display screen, characterized in that: The invention comprises an optical film prepared by the method for preparing an optical film according to any one of claims 1 to 8.

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