Polyvinyl alcohol-polyvinyl butyral film having core-shell structure with controlled surface properties and manufacturing method therefor

Abstract

The present invention relates to a polyvinyl alcohol-polyvinyl butyral film having a core-shell structure, with controlled surface properties, and a manufacturing method therefor. More specifically, the present invention relates to: a polyvinyl alcohol-polyvinyl butyral film having a core-shell structure, with controlled surface properties; and a manufacturing method therefor, wherein the degree of saponification of a polyvinyl alcohol precursor and polyvinyl alcohol in the film is easily controlled through continuous processes of heterogeneous saponification and heterogeneous acetalization, and the proportion of a polyvinyl butyral precursor is easily controlled by the heterogeneous acetalization reaction of a polyvinyl butyral precursor film having the controlled degree of saponification. By precisely controlling surface properties of the film, such as hydrophilicity or hydrophobicity, roughness, and optical properties, enhanced performance is provided in specific application fields.

Description

Polyvinyl alcohol-polyvinyl butyral film with core-shell structure having controlled surface properties and method for manufacturing the same

[0001] The present invention relates to a polyvinyl alcohol-polyvinyl butyral film with a core-shell structure having controlled surface properties and a method for manufacturing the same. By finely controlling surface properties such as hydrophilicity or hydrophobicity, roughness, and optical properties of the film surface, the invention relates to a polyvinyl alcohol-polyvinyl butyral film with a core-shell structure having controlled surface properties having improved performance in specific application fields (automotive industry, construction, electronic devices, solar panel bonding layers, etc.) and a method for manufacturing the same.

[0002] This project (result) is the result of the 3rd stage LINC 3.0 project, which was funded by the Ministry of Education and the National Research Foundation of Korea.

[0003] Polyvinyl butyral film is an essential synthetic resin for ensuring the safety of automotive and architectural glass, playing a crucial role in preventing accidents by preventing glass fragments from scattering upon breakage. Specifically, polyvinyl butyral film is bonded to glass through a lamination process and is used in the manufacture of safety glass.

[0004] A technique is known to suppress the occurrence of porosity by roughening the surface of a polyvinyl butyral film to effectively remove the air layer formed between the glass and the film during the lamination process. This is because if the film surface is smooth, air vent channels close prematurely, making it easy for air to get trapped between the bonding surfaces, whereas forming air vent channels allows for the effective removal of residual air. Therefore, in order to achieve effective anti-shatter performance that prevents glass fragments from scattering, adhesion must be achieved between the glass and the polyvinyl butyral film without any gaps.

[0005] Meanwhile, in order to increase the production efficiency of polyvinyl butyral industrially, an excess amount of reactants is often added, but excessive amounts of strong acid oxidize butylaldehyde to produce by-products. In addition, butylaldehyde remaining in the film causes yellowing of the bonded film and affects its mechanical properties. Furthermore, surfactants are added to stably disperse the highly cohesive polyvinyl butyral, but if the amount of residual surfactant in the bonded film is excessive, yellowing occurs due to high temperatures during the lamination process.

[0006] To prevent this, the inventors developed a polyvinyl alcohol film with increased surface roughness through a heterogeneous saponification reaction in which the conversion reaction is carried out while maintaining the film form, as seen in prior patent 10-1577911, rather than a general homogeneous saponification. The aforementioned prior patent discloses a polyvinyl alcohol film with an improved specific surface area without using a surfactant.

[0007] Furthermore, the inventors confirmed that the specific surface area of ​​the film is further improved when a heterogeneous acetalization process is additionally and continuously introduced to the film manufactured from the aforementioned prior patent. In this way, the inventors have completed the present invention by developing a polyvinyl alcohol-polyvinyl butyral film in which adhesion is improved solely through the process of converting polyvinyl alcohol to polyvinyl butyral without special post-processing, while simultaneously improving transparency and preventing yellowing.

[0008]

[0009] The present invention aims to solve the aforementioned problems by providing a polyvinyl butyral / polyvinyl alcohol film in which the ratio of polyvinyl butyral precursor within the film is easily controlled and surface characteristics are controlled through a continuous process of heterogeneous saponification and heterogeneous acetalization.

[0010] In addition, the present invention aims to provide a polyvinyl alcohol-polyvinyl butyral film with improved adhesion, transparency, and yellowing properties by improving the specific surface area of ​​the film surface solely through the process of converting polyvinyl alcohol to polyvinyl butyral without special post-processing.

[0011] A preferred embodiment of the present invention for achieving the above objective comprises a method for manufacturing a polyvinyl alcohol-polyvinyl butyral film with a core-shell structure having controlled surface properties, characterized by comprising the steps of: (a) preparing a polyvinyl alcohol (PVA) precursor solution; (b) casting the polyvinyl alcohol precursor solution to produce a polyvinyl alcohol precursor film; (c) immersing the polyvinyl alcohol precursor film in a saponification solution; and (d) immersing the polyvinyl alcohol film saponified by the above step in an acetalization solution to produce a partially acetalized polyvinyl butyral (PVB) precursor film.

[0012] In one embodiment of the present invention, in step (a), the polyvinyl alcohol (PVA) precursor may be one or more polymers selected from the group consisting of polyvinyl acetate (PVAc), polyvinyl pivalate (PVPi), polyvinyl butyral (PVB), polyvinyl trifluoroacetate, polyvinyl trichloroacetate, and polyvinyl propionate; copolymers thereof; or a mixture thereof.

[0013] In one embodiment of the present invention, in step (c), the saponification solution may include a swelling agent, a salting-out agent, or a catalyst.

[0014] In one embodiment of the present invention, in step (c), the immersion may be performed at 40 to 60°C for 30 to 120 hours.

[0015] In one embodiment of the present invention, the saponified polyvinyl alcohol film may have a degree of saponification of 60 to 99.99% by a heterogeneous saponification reaction from the polyvinyl alcohol precursor film.

[0016] In one embodiment of the present invention, in step (c), the saponified polyvinyl alcohol film may have a roughness formed on its surface with fine curvature of 10 nm to 3 μm.

[0017] In one embodiment of the present invention, in step (d), the acetalization solution may comprise a swelling agent, a salting-out agent, a catalyst, and butyraldehyde.

[0018] In one embodiment of the present invention, in step (d), the immersion may be performed for 5 to 300 hours at a temperature range of 10°C to 100°C.

[0019] In one embodiment of the present invention, in step (d), the partially acetalized polyvinyl butyral (PVB) precursor film may have a roughness formed on its surface with fine curvature of 5 nm to 1 μm.

[0020] In one embodiment of the present invention, in step (d), the partially acetalized polyvinyl butyral (PVB) precursor film may have a surface acetalization conversion rate of 10% to 99.9% by heterogeneous acetalization reaction.

[0021]

[0022] And another preferred embodiment of the present invention provides a polyvinyl alcohol-polyvinyl butyral film with a core-shell structure having controlled surface properties as another means of solving the problem.

[0023] In one embodiment of the present invention, the core may have a surface saponification degree of 60 to 99.99% by heterogeneous saponification reaction from a precursor of polyvinyl alcohol (PVA).

[0024] In one embodiment of the present invention, the polyvinyl alcohol (PVA) precursor may be one or more polymers selected from the group consisting of polyvinyl acetate (PVAc), polyvinyl pivalate (PVPi), polyvinyl butyral (PVB), polyvinyl trifluoroacetate, polyvinyl trichloroacetate, and polyvinyl propionate; copolymers thereof; or a mixture thereof.

[0025] In one embodiment of the present invention, the repeating unit of the polyvinyl butyral may be 1:0.5 to 2 with respect to the polyvinyl alcohol.

[0026] In one embodiment of the present invention, the shell may have a surface acetalization conversion rate of 10% to 99.9% by heterogeneous acetalization reaction from the polyvinyl alcohol.

[0027] In one embodiment of the present invention, the contact angle (°) of the polyvinyl alcohol-polyvinyl butyral film may be 30 to 77°.

[0028]

[0029] The present invention provides a method for manufacturing a polyvinyl butyral / polyvinyl alcohol film, wherein a polyvinyl alcohol precursor film is manufactured and a heterogeneous saponification reaction and a heterogeneous acetalization reaction are sequentially performed to control the degree of saponification within the film, and the reaction proceeds from the surface of the polyvinyl alcohol film with the controlled degree of saponification to control the ratio of the polyvinyl butyral precursor within the film.

[0030] Furthermore, the present invention has the effect of providing a polyvinyl alcohol-polyvinyl butyral film with improved adhesion, transparency, and anti-yellowing properties by enhancing the specific surface area of ​​the film surface solely through the process of converting polyvinyl alcohol to polyvinyl butyral without special post-processing. It is expected that this film can be utilized in various application fields beyond the automotive industry, such as construction, protection of electronic devices like displays, and as a bonding layer for solar panels due to its excellent durability and transparency.

[0031]

[0032] FIG. 1 is a flowchart illustrating a method for manufacturing a polyvinyl alcohol-polyvinyl butyral film according to a preferred embodiment of the present invention.

[0033] Figure 2 is a scanning electron microscope image showing the heterogeneous acetalization reaction of Example 6 of the present invention before and after.

[0034] FIG. 3 is a graph showing the conversion rate and contact angle for the films of Comparative Examples 1 to 3 and Examples 1 to 6 according to the present invention.

[0035]

[0036] The present invention will be described in detail below according to preferred embodiments with reference to the attached drawings, but specific descriptions of configurations and operations that are readily known to those skilled in the art will be omitted. Furthermore, it should be noted that the present invention is not necessarily limited by the following embodiments and that various modifications can be made to the invention within the scope of the technical concept of the invention.

[0037] The terms used in this specification have been selected to be as widely used as possible, taking into account their functions in the present invention; however, in specific cases, terms have been arbitrarily selected by the applicant, and in such cases, their meanings will be described in detail in the description of the invention. Accordingly, the terms used in this invention should be defined not merely by their names, but based on their meanings and the overall content of the invention.

[0038]

[0039] Hereinafter, a polyvinyl alcohol-polyvinyl butyral film with a core-shell structure having controlled surface characteristics and a method for manufacturing the same, according to a preferred embodiment of the present invention, will be described in detail.

[0040]

[0041] A method for manufacturing a core-shell structured polyvinyl alcohol-polyvinyl butyral film with controlled surface characteristics according to the present invention (hereinafter also referred to as a 'polyvinyl alcohol-polyvinyl butyral film') may include, as shown in FIG. 1, (a) a step of preparing a polyvinyl alcohol (PVA) precursor solution; (b) a step of preparing a polyvinyl alcohol precursor film by casting the polyvinyl alcohol precursor solution; (c) a step of immersing the polyvinyl alcohol precursor film in a saponification solution; and (d) a step of preparing a partially acetalized polyvinyl butyral (PVB) precursor film by immersing the polyvinyl alcohol film saponified by step (c) in an acetalization solution.

[0042]

[0043] First, the present invention may include the step of (a) preparing a polyvinyl alcohol (PVA) precursor solution. This step involves dissolving a polyvinyl alcohol precursor in an organic solvent to prepare a polyvinyl alcohol (PVA) precursor solution.

[0044] The above polyvinyl alcohol (PVA) precursor may be one or more polymers selected from the group consisting of polyvinyl acetate (PVAc), polyvinyl pivalate (PVPi), polyvinyl butyral (PVB), polyvinyl trifluoroacetate, polyvinyl trichloroacetate, and polyvinyl propionate; copolymers thereof; or mixtures thereof.

[0045] The molecular weight (M) of the above polyvinyl alcohol (PVA) precursor n The molecular weight can be 50,000 to 500,000 g / mol. As the molecular weight increases, the density of the polymer network within the final manufactured film increases, which can result in higher mechanical strength, and as the molecular weight decreases, a thin and transparent film can be manufactured, so the molecular weight can be selected according to the characteristics of the final product to be made. However, if the molecular weight exceeds the above range, the viscosity of the film increases, and there is a risk that voids may form because the film does not spread evenly on the glass surface during the lamination process.

[0046] The above organic solvent may be one or more selected from the group consisting of methanol, ethanol, acetone, ethyl acetate, dichloromethane, benzene, toluene, hexane, and carbon tetrachloride.

[0047] The concentration of the above polyvinyl alcohol (PVA) precursor solution may be 60 to 120 g / L, and more preferably 80 to 100 g / L.

[0048] The above dissolution may be performed by stirring at 20 to 50°C for 1 to 5 hours.

[0049]

[0050] Next, the present invention may include the step of (b) manufacturing a polyvinyl alcohol precursor film by casting the polyvinyl alcohol precursor solution.

[0051] This step involves degassing the polyvinyl alcohol precursor solution using a vacuum oven, then casting the solution onto a Teflon dish and drying it to produce a polyvinyl alcohol precursor film.

[0052] The above drying can be performed for 10 to 14 hours.

[0053]

[0054] Next, the present invention may include (c) a step of immersing the polyvinyl alcohol precursor film in a saponification solution.

[0055] This step involves immersing the polyvinyl alcohol precursor film in a saponification solution to perform a heterogeneous reaction, characterized by the gradual impregnation of the saponification solution from the surface to the core of the film, unlike a homogeneous reaction. In other words, rather than saponifying the polyvinyl alcohol precursor while it is dissolved in a solvent, the polyvinyl acetate film may be manufactured and then saponified while maintaining its film form.

[0056] Through this, the surface of the polyvinyl alcohol precursor film may undergo a partial saponification reaction, thereby converting a portion of the surface of the polyvinyl alcohol precursor film into a film containing polyvinyl alcohol or a polyvinyl alcohol copolymer. That is, the immersed polyvinyl alcohol precursor film may comprise the polyvinyl alcohol precursor within the film; and the polyvinyl alcohol or polyvinyl alcohol copolymer partially converted by the saponification reaction.

[0057] At this time, the immersed polyvinyl alcohol precursor film may have a degree of saponification from a heterogeneous saponification reaction from the polyvinyl alcohol precursor film prior to immersion of 60 to 99.99%. That is, the technical feature of the present invention is to provide a film in which the degree of saponification from a polyvinyl alcohol precursor film to polyvinyl alcohol or a polyvinyl alcohol copolymer is controlled to the above range.

[0058] The number average degree of polymerization of the above-described immersed polyvinyl alcohol precursor film may be 500 to 10,000.

[0059] The alternating group content of the above-described immersed polyvinyl alcohol precursor film may be 51% to 65%.

[0060] Through the above immersion step, a polyalcohol vinyl precursor film with wrinkles formed on the film surface can be manufactured. More specifically, the immersed polyvinyl alcohol precursor film, i.e., the saponified polyvinyl alcohol film, may have a roughness formed on its surface with fine undulations of 10 nm to 3 μm.

[0061]

[0062] Meanwhile, the saponification solution may contain a swelling agent, a salting-out agent, or a catalyst.

[0063] The above swelling agent may be one or more selected from the group consisting of water, methanol, ethanol, propanol, ethylene glycol, propylene glycol, tetrahydrofuran, dimethyl sulfoxide, benzene, and acetone. More preferably, methanol may be used as it is easy to obtain, inexpensive, has a low boiling point, and is easy to handle.

[0064] The above salting-out agent may be one or more selected from the group consisting of sodium sulfate, sodium sulfite, calcium sulfate, ammonium sulfate, magnesium sulfate, sodium chloride, potassium chloride, calcium chloride, magnesium chloride, sodium phosphate, potassium phosphate, sodium acetate, ammonium chloride, lithium sulfate, and potassium carbonate.

[0065] The above catalyst may be an acidic or basic catalyst.

[0066] The above acidic catalyst may use sulfuric acid, hydrochloric acid, nitric acid, acetic acid, oxalic acid, methanesulfonic acid, para-toluenesulfonic acid, or a mixture thereof. Among these, the acetic acid, oxalic acid, and para-toluenesulfonic acid are characterized by being able to be utilized by forming a eutectic solvent with choline chloride, dodecyltrimethylammonium chloride, and benzyltrimethylammonium chloride.

[0067] The above basic catalyst may be sodium chloride, sodium hydroxide, potassium hydroxide, or a mixture thereof, but is not limited thereto.

[0068]

[0069] For example, when the polyvinyl alcohol precursor film contains polyvinyl acetate (PVAc), if it is immersed in the saponification solution, the ester bonds of the polyvinyl acetate are broken down, the acetyl groups are removed, and hydroxyl groups (-OH) are generated, thereby producing a film containing polyvinyl alcohol that has been partially converted from the surface of the film.

[0070]

[0071] The above immersion may be performed at 40 to 60°C for 30 to 120 hours, and more preferably at 40 to 60°C for 48 to 96 hours. At this time, the polyvinyl alcohol precursor film may be completely immersed in the saponification solution. Specifically, the film surface area is 1 cm² 2 The volume of the above saponification solution may be at least 10 mL or more.

[0072]

[0073] The polyvinyl alcohol precursor film prepared above may further include a step of immersing it in distilled water, undergoing a washing process, and then drying it at room temperature. Through this process, impurities of the saponification solution remaining in the prepared polyvinyl alcohol film can be removed, and severe shrinkage of the film can be prevented while maintaining its shape.

[0074]

[0075] Next, the present invention may include the step of (d) immersing the polyvinyl alcohol film saponified by step (c) in an acetalization solution to produce a partially acetalized polyvinyl butyral (PVB) precursor film.

[0076] This step is a step of inducing a surface acetalization reaction by immersing the polyvinyl alcohol or polyvinyl alcohol copolymer film, which has been partially converted from the saponification reaction, in the acetalization solution again by immersing it in the acetalization solution following the saponification reaction of the film.

[0077] Through this, the surface of a polyvinyl butyral (PVB) precursor film immersed in an acetalization solution can be partially converted into a film containing polyvinyl butyral (PVB) or a polyvinyl butyral copolymer through a partial acetalization reaction. That is, the partially acetalized polyvinyl butyral (PVB) precursor film may comprise, within the film, the polyvinyl alcohol precursor; a polyvinyl alcohol or polyvinyl alcohol copolymer partially converted by a saponification reaction; and a polyvinyl butyral or polyvinyl butyral copolymer partially converted by an acetalization reaction.

[0078]

[0079] At this time, the saponified polyvinyl alcohol film may be immersed in an acetalization solution containing a swelling agent, a salting-out agent, a catalyst, and butyraldehyde to produce a polyvinyl butyral film.

[0080] The above swelling agent may be one or more selected from the group consisting of water, methanol, ethanol, propanol, ethylene glycol, propylene glycol, tetrahydrofuran, dimethyl sulfoxide, benzene, and acetone.

[0081] The above salting-out agent may be one or more selected from the group consisting of sodium sulfate, sodium sulfite, calcium sulfate, ammonium sulfate, magnesium sulfate, sodium chloride, potassium chloride, calcium chloride, magnesium chloride, sodium phosphate, potassium phosphate, sodium acetate, ammonium chloride, lithium sulfate, and potassium carbonate.

[0082] The above catalyst may be an acidic or basic catalyst.

[0083] The above acidic catalyst may use sulfuric acid, hydrochloric acid, nitric acid, acetic acid, oxalic acid, methanesulfonic acid, para-toluenesulfonic acid, or a mixture thereof. Among these, the acetic acid, oxalic acid, and para-toluenesulfonic acid are characterized by being able to be utilized by forming a eutectic solvent with choline chloride, dodecyltrimethylammonium chloride, and benzyltrimethylammonium chloride.

[0084] The above basic catalyst may be one or more selected from the group consisting of sodium methoxide, sodium ethanolate, potassium tert-butoxide, titanium isopropoxide, lithium ethoxide, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and sodium hydroxide, but is not limited thereto.

[0085]

[0086] The above saponified polyvinyl alcohol film may be immersed in an acetalization solution for 5 to 300 hours at a temperature range of 10°C to 100°C to produce a partially acetalized polyvinyl butyral (PVB) precursor film. More preferably, it may be immersed in an acetalization solution for 24 to 120 hours at a temperature of 40°C to 70°C.

[0087] Likewise, the saponified polyvinyl alcohol film may be completely immersed in the acetalization solution. Specifically, the film surface area is 1 cm² 2 The volume of the above-mentioned acetalization solution may be at least 10 mL or more for immersion.

[0088]

[0089] By immersing the saponified polyvinyl alcohol film in the acetalization solution, a gradual conversion reaction occurs from the surface to the core of the film, and the surface of the final obtained film may have micro-ridges. This enhancement of surface characteristics is formed as partial dissolution and aggregation occur on the surface converted to polyvinyl butyral, and the surface roughness may be 5 nm to 1 μm.

[0090] In addition, the immersed partially acetalized polyvinyl butyral (PVB) precursor film may have a surface acetalization conversion rate of 10% to 99.9% by a heterogeneous acetalization reaction.

[0091]

[0092] Through this, the present invention can produce a core-shell structured polyvinyl alcohol-polyvinyl butyral film in which the degree of saponification of the polyvinyl alcohol precursor and polyvinyl alcohol is controlled through a continuous process of heterogeneous saponification and heterogeneous acetalization from a polyvinyl alcohol precursor, and the surface characteristics are controlled by a heterogeneous acetalization reaction of a polyvinyl butyral precursor having the controlled degree of saponification.

[0093]

[0094] The present invention can provide a polyvinyl alcohol-polyvinyl butyral film with controlled surface properties having a core-shell structure comprising polyvinyl alcohol (PVA) and polyvinyl butyral (PVB) (hereinafter also referred to as a 'polyvinyl alcohol-polyvinyl butyral film').

[0095]

[0096] The polyvinyl alcohol-polyvinyl butyral film according to the present invention may have a core-shell structure comprising polyvinyl alcohol (PVA) in the core and polyvinyl butyral (PVB) in the shell.

[0097] The above core may have a surface saponification degree of 60 to 99.99% by heterogeneous saponification reaction from a precursor of polyvinyl alcohol (PVA).

[0098] At this time, the polyvinyl alcohol (PVA) precursor may be one or more polymers selected from the group consisting of polyvinyl acetate (PVAc), polyvinyl pivalate (PVPi), polyvinyl butyral (PVB), polyvinyl trifluoroacetate, polyvinyl trichloroacetate, and polyvinyl propionate; copolymers thereof; or mixtures thereof.

[0099] The above shell may have a surface acetalization conversion rate of 10% to 99.9% by heterogeneous acetalization reaction from the above polyvinyl alcohol.

[0100] The repeating unit of the above polyvinyl butyral may be 1:0.5 to 2 with respect to the above polyvinyl alcohol.

[0101] The contact angle (°) of the above polyvinyl alcohol-polyvinyl butyral film may be 30 to 77°.

[0102]

[0103] As such, since the reaction proceeds on a structurally stable film and therefore surfactants are not used, the present invention can minimize the yellowing phenomenon, which is a disadvantage of reduced transmittance in the final film product. Furthermore, the present invention can provide a core-shell structured polyvinyl alcohol-polyvinyl butyral film with controlled surface characteristics, having a micro-wrinkled surface, by minimizing butylaldehyde residue after a heterogeneous acetalization reaction using an acetalization reaction solution and forming micro-ridges on the film surface.

[0104]

[0105] The above film can primarily be used as a bonding film for safety glass. For example, when the film is used as a bonding film between two sheets of automotive tempered glass, it provides safety by preventing the glass from shattering in the event of an external impact. In addition to automotive tempered glass, it can be used as a protective film for automotive exterior parts (side mirrors, chrome trim, headlights, etc.). Furthermore, beyond the automotive industry, it can be utilized in various application fields such as architecture, protection of electronic devices like displays, and as a bonding layer for solar panels due to its excellent durability and transparency.

[0106]

[0107] Hereinafter, the present invention will be described in detail with reference to examples to aid in understanding. However, the following examples are merely illustrative of the content of the present invention and the scope of the present invention is not limited to the following examples.

[0108]

[0109]

[0110] 1. Preparation of polyvinyl alcohol precursor film

[0111] <Preparation Example 1>

[0112] Polyvinyl acetate having a molecular weight of 300,000 to 320,000 was added to methanol at a concentration of 88.5 g / L and stirred at 40°C for 3 hours to prepare a polyvinyl alcohol precursor solution. The solution was placed in a vacuum oven and degassed for 30 minutes, then cast onto a Teflon dish and dried for 12 hours to produce a polyvinyl acetate film. Separately, an aqueous sodium hydroxide (NaOH) solution dissolved at a concentration of 100 g / L was mixed with methanol (MeOH) in a volume ratio of 10:1 and gently stirred at a stirring speed of 100 rpm to prepare a saponification solution. The prepared saponification solution was applied to the obtained polyvinyl acetate film, wherein the film surface area was 1 cm² 2 The above saponification solution was immersed until its volume was 20 mL. This was immersed at 50°C for 48 hours to produce a polyvinyl alcohol film with a controlled degree of saponification.

[0113]

[0114] <Preparation Example 2>

[0115] The procedure was carried out in the same manner as in Preparation Example 1 above, but the film was immersed at 50°C for 72 hours.

[0116]

[0117] <Preparation Example 3>

[0118] The procedure was carried out in the same manner as in Preparation Example 1 above, but the film was immersed at 50°C for 96 hours.

[0119]

[0120] 2. Preparation of partially acetalized polyvinyl butyral precursor film

[0121] <Comparative Example 1>

[0122] An acetalization solution was prepared by sequentially adding 10 parts by weight of 99.8% purity methanol, 10 parts by weight of 99% purity sodium sulfate, 10 parts by weight of 37% purity hydrochloric acid, and 10 parts by weight of 98% purity butylaldehyde to 100 parts by weight of distilled water and stirring.

[0123] The temperature of the above acetalization solution was raised to 50°C, and when the temperature was maintained constant, the film of Preparation Example 1 was immersed in the above acetal solution for 24 hours.

[0124] At this time, under stirring, the surface area of ​​the film is 1 cm² 2 The sample was immersed in 20 mL of the above-mentioned acetalization solution. Through this, the preparation of a partially acetalized polyvinyl butyral precursor film was completed.

[0125]

[0126] <Comparative Example 2>

[0127] The procedure was carried out in the same manner as Comparative Example 1 above, but the film of Preparation Example 1 above was immersed in the acetal solution for 72 hours.

[0128]

[0129] <Comparative Example 3>

[0130] The procedure was carried out in the same manner as Comparative Example 1 above, but the film of Preparation Example 1 above was immersed in the acetal solution for 120 hours.

[0131]

[0132] <Example 1>

[0133] The procedure was carried out in the same manner as Comparative Example 1 above, but the film of Preparation Example 2 above was immersed in the acetal solution for 24 hours.

[0134]

[0135] <Example 2>

[0136] The procedure was carried out in the same manner as in Example 1 above, but the film of Preparation Example 2 was immersed in the acetal solution for 72 hours.

[0137]

[0138] <Example 3>

[0139] The procedure was carried out in the same manner as in Example 1 above, but the film of Preparation Example 2 was immersed in the acetal solution for 120 hours.

[0140]

[0141] <Example 4>

[0142] The procedure was carried out in the same manner as Comparative Example 1 above, but the film of Preparation Example 3 above was immersed in the acetal solution for 24 hours.

[0143]

[0144] <Example 5>

[0145] The procedure was carried out in the same manner as in Example 4 above, but the film of Preparation Example 3 was immersed in the acetal solution for 72 hours.

[0146]

[0147] <Example 6>

[0148] The procedure was carried out in the same manner as in Example 4 above, but the film of Preparation Example 3 was immersed in the acetal solution for 72 hours.

[0149]

[0150] The experimental conditions of Comparative Examples 1 to 3 and Examples 1 to 6 above are summarized and shown in [Table 1] below.

[0151]

[0152] Classification Heterogeneous Acetalization Reactor Reaction Temperature (°C) Reaction Time (hr) Distilled Water (mL) MeOH (g) Na2SO4 (g) HCl (g) Butyralaldehyde (g) Comparative Example 1 100 10 10 10 10 50 24 Comparative Example 2 100 10 10 10 10 50 72 Comparative Example 3 100 10 10 10 10 50 120 Example 1 100 10 10 10 50 24 Example 2 100 10 10 10 10 50 72 Example 3 100 10 10 10 10 50 120 Example 4 100 10 10 10 10 50 24 Example 5 100 10 10 10 10 50 72 Example 6 100 10 10 10 50 120

[0153]

[0154] 2. Characteristic Analysis

[0155] <Experimental Example 1>

[0156] As a result calculated through 1H-NMR analysis to analyze the degree of saponification of Preparation Examples 1 to 3 above, as shown in Table 2 below, it can be seen that the degree of saponification of Preparation Example 1 is 39.39%, whereas the degree of saponification of Preparation Examples 2 and 3 is approximately 91.6% or higher.

[0157] This means that the longer the polyvinyl alcohol precursor film is immersed in the saponification solution, the greater the degree of saponification—that is, the more the ester groups (-OCOCH3) of polyvinyl acetate are converted into hydroxyl groups (-OH). Meanwhile, as the number of hydroxyl groups increases, the interactions (hydrogen bonding) between polymers within the film increase, resulting in a uniform structure and increased transparency of the film. On the other hand, if the number of hydroxyl groups (-OH) increases excessively, it exhibits excessive hydrophilicity and high water absorption, causing light scattering within the film and potentially lowering its transparency.

[0158] Accordingly, the present invention has the effect of producing a film with the highest transparency through a balance of ester groups and hydroxyl groups by maintaining an appropriate degree of saponification from the following results for the films of Preparation Examples 1 to 3.

[0159]

[0160] Classification Degree of Saponification (%) Preparation Example 139.39 Preparation Example 291.63 Preparation Example 397.57

[0161]

[0162] <Experimental Example 2>

[0163] To analyze the contact angles (°) of Comparative Examples 1 to 3 and Examples 1 to 6 above, a contact angle measuring instrument (AM7013MZT, Dino-Lite Korea, Korea) was used. 5 μL of distilled water was used for the measurement, and the average contact angle was analyzed by measuring each sample 5 times. As shown in Table 3 below, it can be seen that the contact angle of Comparative Example 1 was the lowest at 20.71°, and the contact angle of Example 6 was the highest at 76.54°. Furthermore, from the results of Comparative Examples 1 to 3 or Examples 1 to 3, it can be seen that as the conversion rate for the heterogeneous acetalization reaction increases, the hydrophobic groups on the surface become relatively dominant, resulting in an effect of increasing the contact angle.

[0164]

[0165] Classification Conversion Rate (%) Contact Angle (°) Comparative Example 1 10.7 ± 2.4 20.71 Comparative Example 2 16.7 ± 1.5 27.44 Example 3 26.2 ± 2.1 36.16 Example 1 18.6 ± 2.6 30.33 Example 2 30.3 ± 3.7 41.21 Example 3 53.2 ± 2.0 69.19 Example 4 21.6 ± 3.1 34.11 Example 5 39.4 ± 1.9 49.15 Example 6 58.2 ± 1.8 76.54

[0166]

[0167] First, as in Comparative Example 1, as the contact angle decreases, not only does the hydrophilicity of the film surface increase, but the interaction of polymers within the film also increases, forming a uniform structure and thus increasing transparency. However, due to the increase in hydrophilicity, moisture adsorption on the film surface is easy, and there is a concern that this may accelerate oxidation and cause yellowing by promoting chemical reactions on surfaces activated by UV or heat.

[0168] On the other hand, as in Example 6, the hydrophobicity of the film surface increases as the contact angle increases. Such a hydrophobic surface has fine roughness, and as a result, light is scattered in various directions, causing more light reflection and potentially reducing transmittance. For reference, Figure 2 is a scanning electron microscope image taken before and after the heterogeneous acetalization reaction of Example 6 of the present invention. As is generally known, compared to Figure 2(a), Figure 2(b) shows that the surface is formed roughly due to micro-ridges on the film surface created through the acetalization reaction. That is, while the adhesion of the film is greatly improved, there is a concern that transparency may be further reduced due to scattering.

[0169] As such, if the contact angle is too small or too large, there is a possibility of yellowing or reduced transparency; therefore, it is important to delicately control surface characteristics to ensure an appropriate contact angle. Accordingly, the present invention has the effect of providing a film with improved performance in specific applications by delicately controlling surface characteristics such as hydrophilicity or hydrophobicity, roughness, and optical properties of the film surface.

[0170]

[0171] Although a polyvinyl alcohol-polyvinyl butyral film with a core-shell structure having controlled surface characteristics and a method for manufacturing the same have been described according to a preferred embodiment of the present invention as described above, this is merely an example, and those skilled in the art will understand that various changes and modifications are possible within the scope of the technical spirit of the present invention.

Claims

1. (a) A step of preparing a polyvinyl alcohol (PVA) precursor solution; (b) a step of preparing a polyvinyl alcohol precursor film by casting the above polyvinyl alcohol precursor solution; (c) a step of immersing the above polyvinyl alcohol precursor film in a saponification solution; (d) A method for manufacturing a polyvinyl alcohol-polyvinyl butyral film with a core-shell structure and controlled surface properties, characterized by including the step of immersing the polyvinyl alcohol film saponified by step (c) above in an acetalization solution to produce a partially acetalized polyvinyl butyral (PVB) precursor film.

2. In Paragraph 1, In step (a) above, The above polyvinyl alcohol (PVA) precursor is, A method for manufacturing a polyvinyl alcohol-polyvinyl butyral film with a core-shell structure having controlled surface properties, characterized by comprising: one or more polymers selected from the group consisting of polyvinyl acetate (PVAc), polyvinyl pivalate (PVPi), polyvinyl butyral (PVB), polyvinyl trifluoroacetate, polyvinyl trichloroacetate, and polyvinyl propionate; copolymers thereof; or a mixture thereof.

3. In Paragraph 1, In step (c) above, The above saponification solution is, A method for manufacturing a core-shell structured polyvinyl alcohol-polyvinyl butyral film with controlled surface properties, characterized by including a swelling agent, a salting-out agent, or a catalyst.

4. In Paragraph 1, In step (c) above, The above immersion is, A method for manufacturing a core-shell structured polyvinyl alcohol-polyvinyl butyral film with controlled surface properties, characterized by performing the process at 40 to 60°C for 30 to 120 hours.

5. In Paragraph 1, In step (d) above, The above saponified polyvinyl alcohol film is, A method for manufacturing a core-shell structured polyvinyl alcohol-polyvinyl butyral film with controlled surface properties, characterized by a degree of saponification of 60 to 99.99% by a heterogeneous saponification reaction from the above-mentioned polyvinyl alcohol precursor film.

6. In Paragraph 1, In step (d) above, The above saponified polyvinyl alcohol film is, A method for manufacturing a core-shell structured polyvinyl alcohol-polyvinyl butyral film with controlled surface properties, characterized by having fine undulations of 10 nm to 3 μm and roughness formed on the surface.

7. In Paragraph 1, In step (d) above, The above acetalization solution is, A method for manufacturing a core-shell structured polyvinyl alcohol-polyvinyl butyral film with controlled surface properties, characterized by comprising a swelling agent, a salting-out agent, a catalyst, and butyraldehyde.

8. In Paragraph 1, In step (d) above, The above immersion is, A method for manufacturing a core-shell structured polyvinyl alcohol-polyvinyl butyral film with controlled surface properties, characterized by performing the process for 5 to 300 hours in a temperature range of 10℃ to 100℃.

9. In Paragraph 1, In step (d) above, The above partially acetalized polyvinyl butyral (PVB) precursor film is, A method for manufacturing a core-shell structured polyvinyl alcohol-polyvinyl butyral film with controlled surface properties, characterized by having fine undulations of 5 nm to 1 μm and roughness formed on the surface.

10. In Paragraph 1, In step (d) above, The above partially acetalized polyvinyl butyral (PVB) precursor film is, A polyvinyl alcohol-polyvinyl butyral film with a core-shell structure having controlled surface properties, characterized by a surface acetalization conversion rate of 10% to 99.9% via a heterogeneous acetalization reaction.

11. A core-shell structured polyvinyl alcohol-polyvinyl butyral film with controlled surface properties, characterized by having a core-shell structure comprising polyvinyl alcohol (PVA) and polyvinyl butyral (PB).

12. In Paragraph 11, The above core is, A polyvinyl alcohol-polyvinyl butyral film with a core-shell structure having controlled surface properties, characterized by a surface degree of saponification of 60 to 99.99% by a heterogeneous saponification reaction from the above-mentioned polyvinyl alcohol (PVA) precursor.

13. In Paragraph 12, The precursor of the above polyvinyl alcohol (PVA) is, A polyvinyl alcohol-polyvinyl butyral film having a core-shell structure with controlled surface properties, characterized by comprising: one or more polymers selected from the group consisting of polyvinyl acetate (PVAc), polyvinyl pivalate (PVPi), polyvinyl butyral (PVB), polyvinyl trifluoroacetate, polyvinyl trichloroacetate, and polyvinyl propionate; copolymers thereof; or a mixture thereof.

14. In Paragraph 11, The repeating unit of the above polyvinyl butyral is, A method for manufacturing a core-shell structured polyvinyl alcohol-polyvinyl butyral film with controlled surface properties, characterized by a ratio of 1:0.5 to 2 with respect to the polyvinyl alcohol.

15. In Paragraph 11, The above shell is, A polyvinyl alcohol-polyvinyl butyral film with a core-shell structure having controlled surface properties, characterized in that the surface acetalization conversion rate by a heterogeneous acetalization reaction from the above polyvinyl alcohol is 10% to 99.9%.

16. In Paragraph 11, A polyvinyl alcohol-polyvinyl butyral film with a core-shell structure having controlled surface properties, characterized in that the contact angle (°) of the polyvinyl alcohol-polyvinyl butyral film is 30 to 77°.

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