High refractive index thin film with urethane primer and method of making the same

Abstract

An embodiment of the present invention provides a high refractive index film with a urethane base coat comprising: a substrate layer comprising a polyester polymer; and a primer layer formed by coating at least one surface of the substrate layer with a primer composition comprising an urethane composition consisting of: polyurethane resin A comprising a phosphorodiol and a sulfonic acid group; and polymer resin B comprising at least one selected from polyurethane resins and polyester copolymer resins that do not contain a phosphorodiol and a sulfonic acid group. This film exhibits high adhesion to a hard coating resin formed on the surface of the primer layer and, compared to conventional urethane base coats, has a higher refractive index, thus reducing rainbow effects caused by light interference and providing high visibility.

Description

Technical Field

[0001] This invention relates to a high refractive index film coated with a urethane base coat, and more specifically, to a high refractive index film coated with a urethane base coat and its preparation method as described below. The film exhibits high adhesion to the resin used for the hard coating formed on the film surface, and has a higher refractive index compared to existing urethane primers, thus exhibiting less rainbow effect caused by optical interference, resulting in excellent visibility and durability. Background Technology

[0002] Polyester films are generally widely used as optical films due to their excellent dimensional stability, thickness uniformity, and optical transparency. In particular, polyethylene terephthalate (PET), a semi-crystalline polymer synthesized by the condensation reaction of high-hardness aromatic terephthalic acid and alkyl diols such as ethylene glycol, exhibits higher durability compared to other polymers and demonstrates high transparency through film extrusion / stretching. Therefore, it has high application value as a substrate for optical films. For these reasons, PET films are not only widely used in industrial fields such as industrial materials but also as optical films for displays and other applications.

[0003] To facilitate the processing of this polyester film, it undergoes a corona treatment on its surface and / or back to form functional groups, or a process of coating it with a primer polymer that provides easy adhesion. In this case, the primers used to achieve the easy adhesion properties mainly include acrylic resins, urethane resins, polyester resins, and epoxy resins. Among them, urethane resins exhibit high adhesion (bonding strength) due to the hydrogen bonds formed by the urethane bonds.

[0004] In particular, polyester film is widely used as a substrate for hard-coated optical films. For optical applications, hard-coated optical films require low impurities, high light transmittance, and high visibility, while also possessing high durability and easy bondability to meet processability requirements. Given these requirements, various substrate films with urethane-based resins as primers coated on polyester films have been developed. However, due to the refractive index difference between polyester and air, rainbow effects are produced through interfacial reflection, resulting in visibility issues.

[0005] The visibility problem mentioned above can be minimized by introducing a primer layer with a medium refractive index between the polyester substrate and the air layer. However, existing urethane-based resins specifically designed for easy adhesion have the problem of difficulty in achieving a high refractive index. To solve this problem, a primer layer with a high refractive index is introduced by using urethane-based resins with an excessive amount of aromatic substances added to increase the refractive index. However, this has the disadvantage of poor adhesion.

[0006] Therefore, there is a need to develop a film that has excellent adhesion similar to existing urethane-based resins, while incorporating a primer layer with a high refractive index. Summary of the Invention

[0007] The problem to be solved The present invention is proposed to solve the problems mentioned above and meet existing needs. The technical problem to be solved by the present invention is to provide a high refractive index film with urethane base paint and a method for preparing the same, that is, it has high adhesion to the hard coating resin formed on the surface of the film, and at the same time has a higher refractive index than existing urethane-based resins, so as to minimize the rainbow phenomenon caused by light, thereby having high visibility and durability.

[0008] The above and other objects and advantages of the present invention will become more apparent from the preferred embodiments described below.

[0009] means for solving problems The objective can be achieved by a high-refractive-index film having a urethane base coat, the film comprising: a substrate layer comprising a polyester polymer; and a primer layer formed by coating at least one surface of the substrate layer with a primer composition comprising an urethane composition consisting of: polyurethane resin A comprising a phosphorodiol and a sulfonic acid group; and polymer resin B comprising at least one selected from polyurethane resins and polyester copolymer resins that do not contain a phosphorodiol and a sulfonic acid group.

[0010] Preferably, the polyurethane resin A containing phosphorodiol and sulfonic acid groups can be a compound containing the structure of the following chemical formula 1.

[0011] [Chemical Formula 1]

[0012] In Formula 1, R1, R2, and R4 are alkyl or phenyl groups, R3 is hexamethylene diisocyanate (HDI), methylene diphenyl diisocyanate (MDI), dicyclohexylmethane diisocyanate (HMDI), or isophorone diisocyanate (IPDI), x is an integer from 1 to 15, y is an integer from 3 to 10, and z is an integer from 2 to 5.

[0013] Preferably, the primer composition may contain 23 to 65 parts by weight of urethane composition relative to 100 parts by weight of the total amount of the primer composition.

[0014] Preferably, the weight ratio of polyurethane resin A containing phosphorodiol and sulfonic acid groups to polymer resin B can be from 6:4 to 9:1.

[0015] Preferably, the primer composition may further include at least one crosslinking agent selected from polyisocyanate compounds, oxazoline compounds, carbodiimide compounds, epoxy compounds, and melamine compounds. More preferably, the crosslinking agent may be a melamine compound.

[0016] Preferably, the primer composition may contain 50 to 300 parts by weight of a crosslinking agent relative to 100 parts by weight of the urethane composition.

[0017] Preferably, the primer composition may also contain inorganic particles.

[0018] Preferably, the primer composition may contain 0.1 to 20 parts by weight of inorganic particles relative to 100 parts by weight of the urethane composition.

[0019] Preferably, the inorganic particles may include: a first particle selected from at least one of zirconium oxide particles (ZrO2), titanium dioxide particles (TiO2), zinc oxide particles (ZnO), and barium titanate (BaTiO3); and a second particle selected from at least one of calcium carbonate particles, silicon dioxide particles, and polystyrene particles.

[0020] Preferably, the average particle size of the first particle can be greater than 0.02 μm and less than 0.3 μm, and the average particle size of the second particle can be greater than 0.3 μm and less than 2 μm.

[0021] Preferably, the weight ratio of the first particle to the second particle can be from 1:0.1 to 1:0.02.

[0022] Preferably, the primer composition may also contain a fluorinated surfactant.

[0023] Preferably, the primer composition may contain 2 to 10 parts by weight of a fluorinated surfactant relative to 100 parts by weight of the urethane composition.

[0024] Preferably, in a high refractive index film with an urethane base coat, the refractive index of the primer layer can be from 1.58 to 1.60.

[0025] Preferably, the thickness of the primer layer can be from 0.01 μm to 1 μm.

[0026] Preferably, when the high refractive index film with urethane base coat is subjected to a temperature of 60°C and a humidity of 90% for 200 hours on the surface of the primer layer, the adhesion can be more than 80% of the initial adhesion when the cross-cut adhesion test is performed.

[0027] Alternatively, the objective can be achieved by a method for preparing a high-refractive-index film with a urethane base coat. This method includes: a first step of preparing a primer composition; a second step of uniaxially stretching a polyester substrate along the mechanical direction (MD direction); a third step of coating the prepared primer composition onto the surface of the uniaxially stretched polyester substrate; a fourth step of biaxially stretching the polyester substrate coated with the primer composition along the transverse direction (TD direction) to prepare a film; and a fifth step of heat-treating the film.

[0028] Invention Effects The high refractive index thin film with urethane base paint and its preparation method according to the present invention have the following effects: a thin film is provided that has high adhesion to the resin for hard coating formed on the surface of the film, and has a higher refractive index compared with existing urethane base paints, thereby reducing rainbow phenomena caused by light interference and thus having high visibility.

[0029] In addition, the high refractive index film with urethane base coating of the present invention has the effect of providing a substrate film with excellent visibility and durability.

[0030] It should be noted that the effects of the present invention are not limited to those described above, and those skilled in the art can clearly understand other effects not described below based on the following description. Attached Figure Description

[0031] Figure 1 This is a structural diagram of a high refractive index thin film with urethane base paint according to an embodiment of the present invention.

[0032] Figure 2 This is a flowchart illustrating a method for preparing a high refractive index thin film with an urethane base coat according to an embodiment of the present invention.

[0033] (Explanation of reference numerals in the attached diagram) 110: Substrate layer 120: Primer layer Detailed Implementation Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, enabling those skilled in the art to readily implement the invention. The present invention can be implemented in various different forms and is not limited to the embodiments described herein.

[0034] To clearly illustrate the invention, parts unrelated to the description are omitted from the drawings. Throughout the specification, the same reference numerals are used in the drawings to refer to the same or similar constituent elements. Furthermore, in the drawings, the thickness of multiple layers and regions is enlarged to clearly show them. Additionally, in this specification, if a constituent element is described as being disposed "on" or "above" another constituent element, it means that the constituent element is directly disposed on the other constituent element, or that other constituent elements exist between the constituent elements. Conversely, if a constituent element is described as being directly disposed "on" or "above" another constituent element, it means that no other constituent elements are involved.

[0035] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as understood by those skilled in the art. In the event of conflict, the definitions used herein shall prevail. Furthermore, the same or equivalent methods and materials described herein may be used in the implementation or experimentation of the invention, and suitable methods and materials are described herein.

[0036] In this specification, "~ type resin", "~ type polymer" and / or "~ type copolymer" are broad concepts that include all "~ type resin", "~ type polymer", "~ type copolymer" and / or "~ type resin, polymer or copolymer derivatives". Additionally, in this specification, the term "polymer or copolymer crosslinked from these resins" means "polymer or copolymer crosslinked from the aforementioned resins".

[0037] In this specification, the term "compound" is used in a broad sense, including all "monoatomic molecules", "oligomers", and "polymeric compounds, including homopolymers and copolymers".

[0038] In this specification, unless otherwise expressly stated, the term "comprising" means that other constituent elements may be included, but are not excluded.

[0039] The term "these combinations" in this specification means a mixture or combination of one or more of the constituent elements described.

[0040] The term "and / or" in this specification means any and all combinations of more than one item described in connection with the description. The term "or" in this specification means "and / or". The use of "at least one" or "at least one" before a constituent element in this specification is to supplement the entire list of constituent elements, and not to supplement the individual constituent elements described.

[0041] Unless otherwise stated in this specification, all percentages, parts, and ratios are based on weight. Furthermore, when a quantity, concentration, or other value or parameter is given as any one of the categories of ranges, preferred ranges, or preferred upper and lower limits, it should be understood that, regardless of whether the range is disclosed individually, all ranges formed by any pair of any upper or preferred range limit and any lower or preferred range limit are specifically disclosed.

[0042] When a range of numerical values ​​is mentioned in this specification, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range. The scope of this invention is not intended to be limited to the specific values ​​mentioned when defining the range. In this specification, each constituent element includes both singular and plural concepts.

[0043] The constituent elements in this specification include the concepts of singular and plural.

[0044] Figure 1 This is a structural diagram of a high-refractive-index thin film with an urethane base coat according to an embodiment of the present invention. (Refer to...) Figure 1 An embodiment of the present invention provides a high refractive index film with an urethane base coat comprising: a substrate layer 110 comprising a polyester-based polymer; and a primer layer 120 formed by coating at least one surface of the substrate layer 110 with a primer composition.

[0045] 1. Substrate layer 110 The substrate layer 110 comprises a polyester-based polymer. In this invention, the substrate layer 110 is a high-functional polymer substrate with excellent dimensional stability, thickness uniformity and optical transparency. Its use is not particularly limited, but it preferably comprises polyester-based polymers such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN) and polycarbonate (PC).

[0046] As an example, more preferably, the substrate layer 110 comprises polyethylene terephthalate (PET). Compared with other polymers, PET has higher durability and can be made highly transparent through film extrusion / stretching, thus having high application value when used as an optical film.

[0047] As an example, the thickness of the substrate layer 110 is preferably 30 μm to 200 μm.

[0048] 2. Primer layer 120 The primer layer 120 can be formed by applying the primer composition to any one surface or both surfaces of the substrate layer 110.

[0049] The primer composition may comprise a polyurethane composition consisting of: polyurethane resin A, comprising phosphorodiol and sulfonic acid groups; and polymer resin B (base resin), comprising at least one selected from polyurethane resins and polyester copolymer resins that do not contain phosphorodiol and sulfonic acid groups (sulfonates).

[0050] As an example, the polyurethane resin A containing phosphorodiol and sulfonic acid groups in the urethane composition preferably contains the structure of the following chemical formula 1.

[0051] [Chemical Formula 1]

[0052] In chemical formula 1, R1, R2 and R4 are alkyl or phenyl, R3 is HDI, MDI, HMDI or IPDI, x is an integer from 1 to 15, y is an integer from 3 to 10, and z is an integer from 2 to 5.

[0053] On the other hand, in the above chemical formula 1, "HDI" is hexamethylenediisocyanate, "MDI" is methylene diphenyl diisocyanate, "HMDI" is dicyclohexylmethane diisocyanate, and "IPDI" is isophorone diisocyanate.

[0054] In addition, the polyurethane resin contained in the urethane composition that does not contain phosphorodiol and sulfonic acid groups may contain urethane, wherein the urethane is synthesized by selecting a polyol and a diisocyanate, wherein the polyol is selected from at least one of polycarbonate polyol, polyester polyol and polyether polyol, and the diisocyanate is selected from at least one of hexamethylene diisocyanate (HDI), methylene diphenyl diisocyanate (MDI), isophorone diisocyanate (IPDI) and 4,4'-methylene dicyclohexyl diisocyanate (H12MDI), but is not limited thereto, and can be prepared by various synthetic methods.

[0055] As an example, regarding the primer composition forming the primer layer 120, it is preferable to include 23 to 65 parts by weight of urethane composition relative to a total of 100 parts by weight. When the content of urethane composition is less than 23 parts by weight, there is a problem of insufficient resin adhesion; when it exceeds 65 parts by weight, there is a problem of insufficient substrate adhesion due to insufficient film hardness.

[0056] Furthermore, in the urethane composition, the weight ratio of polyurethane resin A to polymer resin B is preferably 6:4 to 9:1. When the weight ratio of polyurethane resin A to polymer resin B is less than 6:4 and the content of polyurethane resin A is insufficient, there is a problem of reduced refractive index of primer layer 120. When the weight ratio of polyurethane resin A to polymer resin B exceeds 9:1 and the content of polymer resin B is insufficient, there is a problem of reduced adhesion of primer layer 120.

[0057] More specifically, polyurethane resin A, comprising phosphorodiol and sulfonic acid groups, is preferably a water-dispersible polyurethane resin (aqueous dispersion of polyurethane resin). Typically, water-dispersible polyurethane resin can be prepared by reacting a polydiisocyanate with a monomer having a carboxyl functional group, such as dimethylolpropionic acid, to prepare a prepolymer with residual isocyanate groups. After dilution with acetone, an amine compound (such as isocyanate groups and triethylamine) is reacted to prepare the polyurethane resin. Water is then used to disperse the resin, and a chain extender is added to adjust the molecular weight to an appropriate level. Finally, the acetone is removed. However, in this invention, in order to improve the refractive index of the primer layer 120, when synthesizing polyurethane, a polyurethane resin A containing phosphorodiol and sulfonic acid groups can be used, that is, the polyurethane resin A containing phosphorodiol and sulfonic acid groups uses phosphorodiol as a polyol (diol) so that phosphorus (P) that can improve the refractive index can be included when synthesizing polyurethane, and it contains sulfonate groups (instead of carboxyl groups that are usually used for water dispersion of polyurethane) so that sulfur (S) that can improve the refractive index can be included.

[0058] However, the water-dispersible polyurethane resin of the present invention is not limited to the synthesis method described in the present invention, and can be prepared by a variety of synthesis methods, including those described later.

[0059] The water-dispersible polyurethane-based resin of the present invention can be synthesized by suspension polymerization, and can also be synthesized by the condensation reaction of diisocyanate and diol.

[0060] As an example, the polyisocyanate used to prepare the aqueous dispersion of polyurethane resin (aqueous dispersion of polyurethane resin) of the present invention is a compound represented by the general formula R(NCO)n (where R represents an organic compound containing any carbon, and n≥2). As an example, the polyisocyanate may representatively be isophorone diisocyanate (IPDI), methylene diphenyldiisocyanate (MDI), 4,4'-methylene dicyclohexyldiisocyanate (H12MDI), and hexamethylene diisocyanate (HDI), but is not limited to the above substances; any known substance may be used.

[0061] In particular, aromatic diisocyanates are preferred in terms of mechanical strength and refractive index. However, if an excessive amount of aromatic diisocyanate is used, the hardness of the coating will be excessively increased, which will reduce the adhesion between the substrate layer 110 and the primer layer 120 in terms of easy adhesion. Since excessive aromatic substances have disadvantages in terms of ultraviolet (UV) resistance, it will lead to defects in industrial fields where strong UV is used in subsequent processes.

[0062] On the other hand, regarding durability, scratch resistance, and lightfastness, aliphatic or alicyclic diisocyanates are preferred. Therefore, appropriately adjusting their ratio is the most common method for adjusting the refractive index of polyurethane resin. However, the primer layer 120 in this invention does not adjust the refractive index through aromatic content. Therefore, aliphatic or alicyclic diisocyanates are preferred, except for the minimum amount of aromatic diisocyanate required to ensure mechanical strength. Alternatively, the mechanical strength of the coating film can be improved by completely excluding aromatic diisocyanates and adding a small amount of polyfunctional alcohol monomers (such as trimethylpropanol).

[0063] Furthermore, the isocyanate content is preferably 10% relative to the water-dispersed polyurethane resin (solid content). 25% by weight.

[0064] In addition, the polyol compound used to prepare water-dispersible polyurethane resin (water-based dispersion of polyurethane resin) preferably has a hydroxyl value of 10 mg KOH / g to 350 mg KOH / g, and preferably uses high molecular weight polyols with a molecular weight of 2000 or more and low molecular weight polyols with a molecular weight of 300 or less.

[0065] In addition, to incorporate phosphorus (P) into the polyol compounds of the present invention, phosphorus-containing phosphonic dichloride molecules or dichlorophosphate compounds may be introduced into ethylene glycol. Examples include phenylphosphonic dichloride (PPDC) and allylphosphonic dichloride (APDC).

[0066] As an example, the polyol compound preferably accounts for 50% of the solid content of polyurethane resin. 85% by weight.

[0067] Among them, particularly representative examples of polyol compounds include ethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, polyethylene glycol, bisphenol A, hydroquinone, resorcinol di(2-hydroxyethyl) ether, and their epoxide alkane adducts.

[0068] Furthermore, in polyol compounds, hydrophilic groups are introduced into polyurethane resins by using polyols containing carboxylate groups and / or sulfonic acid groups (sulfonates). As a method for introducing carboxylate groups into polyurethane resins, the use of polyols containing carboxylate groups is preferred. Representative examples of polyols containing the aforementioned carboxylate groups include 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, 2,2-dimethylolbutyric acid, and 2,2-dimethylolvalerate.

[0069] In addition, any known method can be used as a method for introducing sulfonic acid groups into polyurethane resin, but it is preferable to combine the compound containing sulfonic acid groups with the aforementioned polyol compound and polycarboxylic acid to prepare a polyester polyol containing sulfonic acid groups and use it as a polyol compound.

[0070] As an example, representative compounds containing sulfonic acid groups include dicarboxylic acids such as 5-sulfoisophthalic acid and sulfoterephthalic acid, which contain metal ions such as Na, K, Li, and Ca, or polyols such as metal salts of polyols such as 2-sulfo-1,4-butanediol.

[0071] Furthermore, the content of carboxylate groups and / or sulfonate groups, which are hydrophilic groups, is related to the emulsion dispersion stability. It is preferable to adjust the content of these hydrophilic groups to 50% relative to the solid content of the urethane resin. The range of 1000 mmol / kg is more preferably adjusted to 70. The range is 250 mmol / kg. If the content of this hydrophilic group is within the above range, the content of the hydrophilic group is suitable, and stable polyurethane particles can be obtained.

[0072] As an example, the polymeric polyols used in this invention are preferably polyester polyols, or polycarbonate polyols, polyols containing phosphorus, and mixtures of polyols containing sulfonic acid groups.

[0073] The water-dispersible polyurethane synthesized according to the above description can use amine compounds as chain extenders to adjust the molecular weight. In this invention, the amine compounds used as chain extenders are polyamines with a molecular weight of 300 or less. Particularly representative examples of polyamines with a molecular weight of 300 or less include 1,2-ethylenediamine, 1,2-propanediamine or 1,3-propanediamine, 1,2-butanediamine or 1,3-butanediamine or 1,4-butanediamine, 1,5-pentanediamine, and 1,6-hexanediamine.

[0074] In the aqueous dispersion synthesis of polyurethane described above, after synthesis in an initial organic solvent, neutralization is performed using an amine compound such as triethylamine, followed by a water-based phase transition. Representative examples of organic solvents used to prepare aqueous dispersions of polyurethane resin include benzene, toluene, acetone, methyl ethyl ketone, diethyl ether, tetrahydrofuran, and chloroform, which can be used alone or as mixed solvents. After solvent removal, the amount of residual solvent in the aqueous dispersion can be less than 1% by weight. Furthermore, acetone and methyl ethyl ketone are particularly preferred as solvents with high solubility for polyurethane resin.

[0075] As an example, in the aqueous dispersion of polyurethane resin, the average particle size of polyurethane resin A containing phosphorodiol and sulfonic acid groups is preferably 0.02. 0.70 μm. When the average particle size of polyurethane resin A is less than 0.02 μm, it is too easy to adhere, which leads to the phenomenon of blocking when the prepared film is wound. When it exceeds 0.70 μm, the following problems exist: clogging of the coating liquid circulation filter during continuous coating process, or dispersion agglomeration based on van der Waals during resin storage.

[0076] As described above, the urethane composition included in the primer composition has the form of a mixture of polyurethane resin A and polymer resin B, wherein the polyurethane resin A (as a polyurethane resin containing phosphorus and sulfur) contains phosphorodiol and sulfonic acid groups, and the polymer resin B (as a base resin) contains at least one selected from polyurethane resins that do not contain phosphorodiol and sulfonic acid groups and polyester copolymer resins.

[0077] As an example, preferably, the primer composition further comprises at least one crosslinking agent (curing agent) selected from polyisocyanate compounds, oxazoline compounds, carbodiimide compounds, epoxy compounds, and melamine compounds. Among them, melamine compounds are most preferred.

[0078] On the other hand, while increasing the content of melamine compounds increases the adhesion of the primer layer 120, it also reduces UV resistance. Therefore, to address the reduced UV resistance in harsh UV environments, polyisocyanate compounds or oxazoline compounds are used together with a melamine crosslinking agent as a crosslinking agent. Thus, when the primer composition is used in harsh UV environments, a melamine compound may be included as a crosslinking agent, along with at least one compound selected from polyisocyanate compounds and oxazoline compounds.

[0079] Representative melamine crosslinking agents include hexamethoxymethylmelamine (HMMM) or tetramethoxymethylmelamine (TMMM), and polyisocyanate crosslinking agents include polyisocyanate compounds composed of trimers such as 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 4,4'-diisocyanate diphenylmethane (MDI), phenyl diisocyanate (XDI), and isophorone diisocyanate.

[0080] As an example, relative to 100 parts by weight of the urethane composition, the primer composition preferably contains 50 to 300 parts by weight of a crosslinking agent. When the content of the crosslinking agent is less than 50 parts by weight, there is a problem of insufficient adhesion; when it exceeds 300 parts by weight, the crosslinking density is too high, resulting in a decrease in the surface physical properties of the primer layer 120 and insufficient adhesion to the substrate. As described above, in the primer composition of the present invention, the weight ratio of the urethane composition to the crosslinking agent is preferably 1:0.5 to 1:3.

[0081] As an example, preferably, the primer composition forming the primer layer 120 further comprises inorganic particles. In this invention, inorganic particles with a refractive index higher than that of the substrate layer 110 are introduced into the primer composition forming the primer layer 120 to increase the refractive index of the primer layer 120.

[0082] As an example, the inorganic particles contained in the primer composition preferably include first particles for increasing the refractive index of the primer layer 120 and second particles for increasing the surface roughness of the primer layer 120.

[0083] The first particle preferably comprises at least one particle selected from zirconium oxide (ZrO2), titanium dioxide (TiO2), zinc oxide (ZnO), and barium titanate (BaTiO3), which have high refractive indices. By introducing the first particle, the refractive index can be maximized without compromising adhesion.

[0084] In addition, the second particle preferably comprises at least one particle selected from calcium carbonate particles, silica particles and polystyrene particles.

[0085] Generally, particles with an average particle size of less than 0.3 μm do not significantly increase the turbidity (haze) of the primer layer 120, but they are unlikely to increase the surface roughness of the primer layer 120. Particles with an average particle size greater than 0.3 μm can increase the surface roughness of the primer layer 120, but as their content increases, the turbidity of the primer layer 120 increases, and the turbidity of the primer layer 120 increases as a function of the square and fourth power of its content and diameter. Therefore, in this invention, in order to achieve low turbidity and high surface roughness of the primer layer 120, considering both the increase in turbidity (haze) and surface roughness of the primer layer 120, the first particle and the second particle preferably have different particle sizes.

[0086] As an example, preferably, the average particle size of the first particle is greater than 0.02 μm and less than 0.3 μm. When the average particle size of the first particle is less than 0.02 μm, particle agglomeration occurs due to the increase in surface energy, resulting in an increase in haze. When it exceeds 0.3 μm, the turbidity of the primer layer 120 increases.

[0087] Furthermore, preferably, the average particle size of the second particles is greater than 0.3 μm and less than 2 μm. When the average particle size of the second particles is less than 0.3 μm, there is a problem of reduced surface roughness of the primer layer 120; when it exceeds 2 μm, there is a problem of increased turbidity or reduced adhesion of the primer layer 120.

[0088] As an example, relative to 100 parts by weight of the urethane composition, the primer composition preferably contains 0.1 to 20 parts by weight of inorganic particles. When the content of inorganic particles is less than 0.1 parts by weight, there is a problem of reduced refractive index or reduced surface roughness of the primer layer 120; when it exceeds 20 parts by weight, there is a problem of increased turbidity or reduced adhesion of the primer layer 120.

[0089] Furthermore, the weight ratio of the first particle to the second particle is preferably between 1:0.1 and 1:0.02. When the weight ratio of the first particle to the second particle is less than 1:0.02, the content of the first particle is too high and the content of the second particle is insufficient, which leads to a decrease in the surface roughness of the primer layer 120. When the weight ratio of the first particle to the second particle exceeds 1:0.1, the content of the first particle is insufficient and the content of the second particle is excessive, which leads to a decrease in the refractive index and reduced adhesion of the primer layer 120.

[0090] As an example, preferably, the primer composition forming the primer layer 120 also contains a fluorinated surfactant. In this invention, when a primer composition comprising a polyurethane resin A containing phosphodiol and sulfonic acid groups, a polymer resin B, a crosslinking agent, and inorganic particles is applied to the surface of the substrate layer 110, a surfactant is preferably introduced into the primer composition for wetting. At this time, as a surfactant, even if a hydrocarbon-based surfactant, an ionic surfactant, or a silicone-based surfactant is used, as long as the target surface tension value is achieved, the same wetting effect can be achieved. However, when a fluorinated surfactant is used in the primer composition of this invention, it has been found to most effectively reduce surface tension, and this is applied in this invention.

[0091] Furthermore, regarding the molecular structure of fluorinated surfactants, it is possible to use hydrophobic portions containing 4 carbon atoms. The fluorinated alkyl group of 20% has a hydrophilic portion having a nonionic polar group or anionic, cationic, betaine, or other ionic polar group. For example, fluorinated surfactants preferably contain perfluoroalkyl carboxylates and perfluoroalkyl phosphates, and more preferably perfluoroalkyl carboxylates.

[0092] As an example, relative to 100 parts by weight of the urethane composition, the primer composition preferably contains 2 to 10 parts by weight of a fluorinated surfactant. When the fluorinated surfactant content is less than 2 parts by weight, the wettability of the substrate layer 110 is insufficient, and the primer composition is applied unevenly. When it exceeds 10 parts by weight, a large amount of foam is generated during application, resulting in appearance problems of the primer layer 120 such as amoeba marks and flow marks.

[0093] In addition, the method of adding surfactant to the primer composition is not particularly limited in this invention, but it can also be added in the initial step of the synthesis of polyurethane resin aqueous dispersion (polyurethane resin A containing phosphorodiol and sulfonic acid groups).

[0094] As described above, when the above-mentioned amount of fluorinated surfactant is added to the primer composition, the static surface tension of the primer composition is preferably about 40 mN / m, and the dynamic surface tension is preferably about 25 mN / m.

[0095] As an example, the thickness of the primer layer 120 is preferably 0.01 μm to 1 μm. When the thickness of the primer layer 120 is less than 0.01 μm, although the transparency is good, the adhesion decreases during post-processing. When it exceeds 1 μm, although the adhesion is excellent, the transparency and coatability decrease, so it is not preferred.

[0096] 3. High-refractive-index thin films with urethane base paint In one embodiment of the present invention, the refractive index of the primer layer 120 of the high refractive index film with urethane base paint is preferably 1.58 to 1.60. When the refractive index of the primer layer 120 is lower than 1.58, the film will produce a rainbow effect; when the refractive index exceeds 1.60, there is a problem of decreased transmittance.

[0097] For the surface of the primer layer of a high refractive index film with urethane base paint according to an embodiment of the present invention, after 200 hours at a temperature of 60°C and a humidity of 90%, the adhesion is preferably more than 80% of the initial adhesion when performing a cross-cut adhesion test. After 200 hours under the above temperature and humidity conditions, when the adhesion is lower than 80% of the initial adhesion during the cross-cut adhesion test, the adhesion of the primer layer 120 decreases over time, leading to a problem of reduced reliability of the high refractive index film with urethane base paint.

[0098] As an example, the surface roughness Ra of the high refractive index film with urethane base paint in one embodiment of the present invention is preferably 5 to 10 nm.

[0099] Figure 2This is a flowchart illustrating a method for preparing a high refractive index thin film with an urethane base coat according to an embodiment of the present invention.

[0100] Reference Figure 2 An embodiment of the present invention provides a method for preparing a high refractive index film with an urethane base coat, comprising: a first step (S201) of preparing a primer composition; a second step (S202) of uniaxially stretching a polyester substrate along the MD direction; a third step (S203) of coating the prepared primer composition onto the surface of the uniaxially stretched polyester substrate; a fourth step (S204) of biaxially stretching the polyester substrate coated with the primer composition along the TD direction to prepare a film; and a fifth step (S205) of heat-treating the film.

[0101] In the first step (S201) of preparing the primer composition, a urethane composition is formed, comprising: polyurethane resin A, containing phosphodiol and sulfonic acid groups; and polymer resin B, containing at least one selected from polyurethane resins and polyester copolymer resins that do not contain phosphodiol and sulfonic acid groups. A crosslinking agent, inorganic particles, and a surfactant are then mixed to form the primer composition. At this point, the specific composition of the primer composition is the same as described above. Figure 1 The content recorded in the document is the same, and repeated explanations have been omitted.

[0102] In addition, in the second step (S202) and the fourth step (S204), there are no special restrictions on the stretching ratio of MD stretching and TD stretching.

[0103] In addition, in the third step (S203) of coating the prepared primer composition onto the surface of the uniaxially stretched polyester substrate, the primer composition prepared in the first step (S201) is coated onto at least one surface of the substrate layer. At this time, the coating method can be a Mayer bar or a gravure roller, but the coating method is not limited to these.

[0104] Furthermore, preferably, the fourth step (S204) of biaxially stretching the polyester substrate coated with the primer composition along the TD direction to prepare a film is performed simultaneously with the fifth step (S205) of heat treating the film. That is, preferably, the polyester substrate coated with the primer composition is heat treated while being stretched along the TD direction.

[0105] Furthermore, the fifth step (S205) of heat treatment of the film is a process of drying, heat treatment, and heat setting. The drying temperature is preferably 120°C to 130°C, and the heat treatment temperature is preferably 200°C to 240°C. At this time, if the heat treatment temperature is lower than 200°C, there is a problem of increased overall shrinkage of the film. When it exceeds 240°C, there is a problem of decreased uniformity of the transverse physical properties of the film.

[0106] The high refractive index film with urethane base coat prepared according to the above preparation method of the present invention is an optical film or substrate film, which is formed by coating at least one surface of the substrate layer with a primer composition, has a reduced rainbow effect, and can be used in the field of optical hard coating or various industrial materials, etc.

[0107] The structure of the present invention and its effects will now be described in more detail through embodiments and comparative examples. However, these embodiments are only used to illustrate the purpose of the present invention more specifically, and the scope of the present invention is not limited to these embodiments.

[0108] Example [Example 1] As a urethane composition, a coating liquid with a solid content of 7.42% was prepared by adding 73.23g of water to a primer composition containing 1.5g of polyurethane resin A (Akuacure 5002, Unitech) containing phosphodiol and sulfonic acid groups and 1g of polyurethane resin B (HUX-487, Duksung) without phosphodiol and sulfonic acid groups. This mixture also included 3g of melamine crosslinking agent (SM-20, DIC), 0.02g of silica particles (average particle size 0.3μm), 0.30g of high-refractive-index titanium dioxide particles (average particle size 0.05μm), and 0.05g of fluorinated surfactant (GX-607, ADEKA). At this point, the weight ratio of polyurethane resin A to polyurethane resin B was 6:4.

[0109] The prepared coating liquid was applied to one surface of a polyethylene terephthalate film (Toray Advanced Materials Co., Ltd., 75 μm thick) that was uniaxially stretched along the MD direction using a #4 bar coater. Then, it was biaxially stretched along the TD direction, dried at 80°C for 1 minute, and heat-treated at a temperature above 200°C to prepare a film with a primer layer thickness of 85 nm.

[0110] [Example 2] Except that the content of polyurethane resin A was changed to 2g and the content of polyurethane resin B was changed to 0.5g, so that the weight ratio of the resins was changed to 8:2, the film was prepared in the same manner as in Example 1.

[0111] [Example 3] Except that the content of polyurethane resin A was changed to 2.225g and the content of polyurethane resin B was changed to 0.275g, so that the weight ratio of the resins was changed to 8.9:1.1, the film was prepared in the same manner as in Example 1.

[0112] [Example 4] The thin film was prepared in the same manner as in Example 1, except that the titanium dioxide particles were replaced with zirconium oxide particles.

[0113] [Example 5] Except for adding 51.4g of water to a primer composition containing 0.006g of silica particles, 0.094g of high-refractive-index titanium dioxide particles, and 0.02g of fluorinated surfactant to prepare a coating liquid with a solid content of 7.42%, the film was prepared in the same manner as in Example 1.

[0114] [Example 6] Except for the addition of 122g of water to a primer composition containing 3.6g of polyurethane resin A, 2.4g of polyurethane resin B, 0.04g of silica particles, 0.6g of high-refractive-index titanium dioxide particles, and 0.15g of fluorinated surfactant to prepare a coating liquid with a solid content of 7.43%, a film was prepared in the same manner as in Example 1.

[0115] [Comparative Example] [Comparative Example 1] The membrane was prepared in the same manner as in Example 1, except that polyurethane resin A was not used and only 2.5 g of polyurethane resin B was used.

[0116] [Comparative Example 2] Except that the contents of polyurethane resin A and polyurethane resin B were set to the same value of 1.25 g, so that the weight ratio of the resins was changed to 5:5, the film was prepared in the same manner as in Example 1.

[0117] [Comparative Example 3] Except that the content of polyurethane resin A was changed to 2.275g and the content of polyurethane resin B was changed to 0.225g, so that the weight ratio of the resins was changed to 9.1:0.9, the film was prepared in the same manner as in Example 1.

[0118] [Comparative Example 4] Except for adding 52.5g of water to a primer composition containing 0.54g of polyurethane resin A, 0.36g of polyurethane resin B, 0.01g of silica particles, 0.15g of high-refractive-index titanium dioxide particles, and 0.15g of fluorinated surfactant to prepare a coating liquid with a solid content of 7.42%, a film was prepared in the same manner as in Example 1.

[0119] [Comparative Example 5] Except that the content of polyurethane resin A was 4.32 g, the content of polyurethane resin B was 2.88 g, and 131.8 g of water was added to the primer composition to prepare a coating liquid with a solid content of 7.42%, a film was prepared in the same manner as in Example 1.

[0120] [Comparative Example 6] The thin film was prepared in the same manner as in Comparative Example 1, except that titanium dioxide particles were not used and only 0.32 g of silicon dioxide particles were used.

[0121] Using the films of Examples 1 to 6 and Comparative Examples 1 to 6 described above, the physical properties were measured through the following experimental examples, and the results are shown in Tables 1 and 2 below.

[0122] [Experimental Example] (1) Evaluation of refractive index For the films of the examples and comparative examples, after preparing test pieces with a width of 10 cm and a length of 20 cm, the back side was treated with reflective tape, and the thickness and refractive index of the primer layer were measured using an ellipsometer.

[0123] (2) Evaluation of adhesion properties (initial adhesion) using the cross-cut test One end of the film from the examples and comparative examples was fixed so that the surface of the primer layer faced the SUS board. Then, a hard coating resin was applied between the surface of the primer layer and the SUS board, and uniformly coated to a thickness of 10 μm using a hot roller laminator. The hard coating resin used was a mixture of 35 parts by weight of phenoxyethyl acrylate, 35 parts by weight of benzyl acrylate, and 30 parts by weight of hexamethylene diacrylate.

[0124] Next, after the resin is cured using a simple UV curing device, the SUS board is peeled off. A cross-cutting instrument with 11 blades spaced 1mm apart is used to make one cut each horizontally and vertically, forming a total of 100 evaluation areas. After applying the tape (Nichiban CT-405 tape), the tape is peeled off twice at an 80-degree angle. The peeling position is observed, and the number of remaining grids out of 100 is calculated after peeling.

[0125] (3) Reliability evaluation After exposing the films of the examples and comparative examples to 60°C and 90% humidity for 200 hours, the cross-cut adhesion was evaluated in the same manner as in Experimental Example 2, and the reliability was calculated. The reliability evaluation was then calculated as the ratio of the result of Experimental Example 2 (initial adhesion) to the result of Experimental Example 3.

[0126] (4) Visuality evaluation Observe the film with the naked eye at a 45° angle under a fluorescent lamp. After placing the film on the front surface of the display device, when confirming the film with the naked eye, if a rainbow phenomenon is observed in the film, mark it as "O"; if not, mark it as "X".

[0127] Table 1

[0128] Table 2

[0129] As shown in Table 1, the high-refractive-index films with urethane base coats in the embodiments all meet the requirements of the present invention. The high refractive index of the primer layer prevents the film from exhibiting a rainbow effect, and it also demonstrates excellent adhesion to the hard coating resin. Furthermore, it is evident that the reliability evaluation results of the high-refractive-index films with urethane base coats that meet the requirements of the present invention reach over 80%, and their adhesion does not decrease even under high temperature and high humidity environments, thus demonstrating high reliability.

[0130] Conversely, as shown in Table 2, Comparative Example 1 did not use polyurethane resin A containing phosphorodiol and sulfonic acid groups, resulting in a lower refractive index of the primer layer, which in turn caused the film to exhibit a rainbow effect.

[0131] In addition, in Comparative Example 2, the weight ratio of polyurethane resin A containing phosphorodiol and sulfonic acid groups to polymer resin B was less than 6:4. Due to the insufficient content of polyurethane resin A, the refractive index of the primer layer was low, resulting in the problem of rainbow phenomenon in the film.

[0132] Furthermore, as can be seen in Comparative Example 3, the weight ratio of polyurethane resin A containing phosphorodiol and sulfonic acid groups to polymer resin B exceeds 9:1, and the content of polymer resin B is insufficient, resulting in reduced adhesion and reliability.

[0133] Furthermore, as can be seen in Comparative Example 4, the insufficient content of the urethane composition resulted in reduced adhesion and reliability.

[0134] Furthermore, as can be seen in Comparative Example 5, an excessive amount of urethane composition resulted in insufficient film hardness, leading to inadequate adhesion to the substrate and a low reliability evaluation result for the adhesiveness.

[0135] In addition, Comparative Example 6 did not use particles with high refractive index (titanium dioxide particles), but only silicon dioxide particles, resulting in a low refractive index of the primer layer, which caused the film to produce a rainbow effect.

[0136] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto. However, this is not the only scope of the invention. Any modifications and improvements made by those skilled in the art using the basic concepts of the invention as defined in the claims are also within the scope of the invention.

Claims

1. A high-refractive-index thin film with an urethane base coat, characterized in that, include: The substrate layer comprises a polyester-based polymer; and A primer layer is formed by applying a primer composition to at least one surface of a substrate layer. The primer composition comprises an urethane composition consisting of the following components: Polyurethane resin (A), comprising phosphorodiol and sulfonic acid groups; and The polymer resin (B) comprises at least one selected from polyurethane resins and polyester copolymer resins that do not contain phosphorodiols and sulfonic acid groups.

2. The high refractive index film with urethane base paint according to claim 1, characterized in that, Polyurethane resin (A) containing phosphorodiol and sulfonic acid groups is a compound containing the structure of the following chemical formula 1: [Chemical Formula 1] In chemical formula 1, R1, R2 and R4 are alkyl or phenyl, R3 is hexamethylene diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate or isophorone diisocyanate, x is an integer from 1 to 15, y is an integer from 3 to 10, and z is an integer from 2 to 5.

3. The high refractive index film with urethane base paint according to claim 1, characterized in that, The primer composition comprises 23 to 65 parts by weight of urethane composition relative to 100 parts by weight of the total amount of the primer composition.

4. The high refractive index film with urethane base coating according to claim 1, characterized in that, The weight ratio of polyurethane resin (A) containing phosphorodiol and sulfonic acid groups to polymer resin (B) is 6:4 to 9:

1.

5. The high refractive index film with urethane base coating according to claim 1, characterized in that, The primer composition further comprises at least one crosslinking agent selected from polyisocyanate compounds, oxazoline compounds, carbodiimide compounds, epoxy compounds, and melamine compounds.

6. The high refractive index film with urethane base coating according to claim 5, characterized in that, The primer composition contains a melamine compound as a crosslinking agent.

7. The high refractive index film with urethane base paint according to claim 5, characterized in that, The primer composition contains 50 to 300 parts by weight of a crosslinking agent relative to 100 parts by weight of the urethane composition.

8. The high refractive index film with urethane base coating according to claim 1, characterized in that, The primer composition also contains inorganic particles.

9. The high refractive index film with urethane base paint according to claim 8, characterized in that, The primer composition comprises 0.1 to 20 parts by weight of inorganic particles relative to 100 parts by weight of the urethane composition.

10. The high refractive index film with urethane base coating according to claim 8, characterized in that, The inorganic particles comprise: a first particle selected from at least one of zirconium oxide particles, titanium dioxide particles, zinc oxide particles, and barium titanate; and a second particle selected from at least one of calcium carbonate particles, silicon dioxide particles, and polystyrene particles.

11. The high refractive index thin film with urethane base paint according to claim 10, characterized in that, The average particle size of the first particle is greater than 0.02 μm and less than 0.3 μm, and the average particle size of the second particle is greater than 0.3 μm and less than 2 μm.

12. The high refractive index film with urethane base coating according to claim 10, characterized in that, The weight ratio of the first particle to the second particle is 1:0.1 to 1:0.

02.

13. The high refractive index film with urethane base coating according to claim 1, characterized in that, The primer composition also contains a fluorinated surfactant.

14. The high refractive index film with urethane base coating according to claim 13, characterized in that, The primer composition contains 2 to 10 parts by weight of a fluorinated surfactant relative to 100 parts by weight of the urethane composition.

15. The high refractive index film with urethane base coating according to claim 1, characterized in that, The refractive index of the primer layer is 1.58 to 1.

60.

16. The high refractive index film with urethane base coating according to claim 1, characterized in that, The thickness of the primer layer is 0.01 μm to 1 μm.

17. The high refractive index film with urethane base coating according to claim 1, characterized in that, When the high refractive index film with urethane base coat is subjected to cross-cut adhesion evaluation after 200 hours at 60°C and 90% humidity, the adhesion is more than 80% of the initial adhesion.

18. A method for preparing a high refractive index thin film having the urethane base coat according to claim 1, characterized in that, include: The first step is to prepare the primer composition; The second step is to uniaxially stretch the polyester substrate along the mechanical direction. The third step is to coat the prepared primer composition onto the surface of a uniaxially stretched polyester substrate. The fourth step involves biaxially stretching the polyester substrate coated with the primer composition in the transverse direction to prepare a film; and The fifth step is to heat-treat the film.

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