KR102408611B1 - Reinforced transparent composite and preparation method thereof - Google Patents

Abstract

The present invention relates to a reinforced transparent composite material comprising a hydrophobic nanofiber sheet and a method for manufacturing the same.

Description

Reinforced transparent composite material and manufacturing method thereof

The present invention relates to a reinforced transparent composite material comprising a hydrophobic nanofiber sheet and a method for manufacturing the same.

Glass is transparent, strong, and has a low coefficient of thermal expansion, so it is used in real life and throughout industry, but it has a fatal disadvantage of being easily broken. As optical materials to replace glass, there are various optical plastics such as PC (polycarbonate), PMMA (polymethyl methacrylate), and PET (polyethylene terephthalate), but they are not as strong as glass, deform easily, and have poor thermal stability. There is a limit to replacing glass.

To compensate for the shortcomings of optical plastics, a glass fiber reinforced transparent composite material reinforced with a transparent glass fiber reinforced material was developed. It has been in the spotlight as a replacement material for glass due to its strength and low coefficient of thermal expansion compared to glass, but it is difficult to accurately match the refractive indices of glass fiber and transparent resin in the visible light region, and the turbidity characteristics are poor due to poor surface flatness. If the turbidity is not good, the transmitted light is visible, so there is a limit to its use as an optical material.

Recently, research using nano-diameter cellulose fibers rather than glass fibers as a reinforcement for transparent composite materials is being conducted. Nanofibers are as strong and transparent as glass, and because the fiber diameter (<100 nm) is much smaller than the wavelength of visible light (400-800 nm), light does not recognize the fiber well, so the excellent optical properties (transmittance) of the composite material and turbidity). In addition, since cellulose has a low coefficient of thermal expansion, a composite material based thereon can also reduce the coefficient of thermal expansion by cellulose similarly to glass, which can be significantly improved compared to plastics in terms of thermal stability.

Until now, composite materials using nanofibers have been made as thin as 100 μm or less to produce transparent films, or thicker than several mm to produce plates with increased strength. However, in the former case, it has been pointed out that the strength is low because it is too thin to ensure transparency, and in the latter case, it is optically opaque.

There are two methods for manufacturing the conventional nanofiber-reinforced composite material as described above. The first is a method of manufacturing nanofibers by dispersing them in a transparent resin and then heat or photocuring, and the second is a method of manufacturing the nanofibers in a sheet form like a nonwoven fabric, impregnating them with a transparent resin, and then heat or photocuring them. .

The first method has a disadvantage in that a large amount of fibers cannot be input because the nanofibers have a very small fiber diameter of 100 nm or less, a large surface area to volume ratio, and the nanofibers are irregularly arranged in the transparent resin. Therefore, it is possible to obtain a transparent composite material, but the strength of the nanofiber is not high because the reinforcing effect is not large.

In the second method, a nanofiber sheet is formed through a process of filtering the nanofiber aqueous dispersion solution, and there is a high possibility that the nanofibers are combined with each other in the process of removing water and drying, thereby increasing the size of the fibers. Closed pores may form between the fibers. Therefore, in the impregnation process of penetrating the transparent resin into the sheet, it is difficult for the transparent resin to enter, and as the fiber size becomes 100 nm or more, there is a problem in that the optical properties are deteriorated.

Accordingly, there is a continuing demand for a transparent composite material with excellent high strength and high transparency that can replace glass in the technical fields such as electronic device display, automobile glass, and window glass, and with significantly improved optical properties.

It is an object of the present invention to provide a reinforced transparent composite material comprising a hydrophobic nanofiber sheet.

Another object of the present invention is to provide a method for manufacturing the reinforced transparent composite material comprising a hydrophobic nanofiber sheet.

In order to achieve the above object, the reinforced transparent composite material according to an embodiment of the present invention includes a hydrophobic nanofiber sheet.

The hydrophobic nanofiber may have a surface tension of 40 to 70 mN/m based on a 1 wt% aqueous solution.

The hydrophobic nanofiber may be derived from a plant.

The plants are green (lovegrass), bamboo (bamboo), silver maple tree (silver maple tree), tulip tree (tulip tree), Chinese maple (trident maple), rice (rice), lotus (lotus) and pyracantha (pyracantha) It may be one or more selected from the group consisting of.

The plant may be bamboo.

The hydrophobic nanofiber may have a diameter of 5 to 100 nm.

The hydrophobic nanofiber sheet may have a thickness of 20 to 1,000 μm.

The reinforced transparent composite material may include two or more hydrophobic nanofiber sheets.

The reinforced transparent composite material may have a thickness of 0.2 to 1.5 mm.

A method for manufacturing a reinforced transparent composite material according to another embodiment of the present invention comprises the steps of: (i) preparing a hydrophobic nanofiber sheet; (ii) impregnating the hydrophobic nanofiber sheet in a transparent resin; and (iii) forming the impregnated hydrophobic nanofiber sheet.

Step (ii) may involve heating.

The transparent resin may have a viscosity of 100 to 10,000 cps.

Step (iii) may be performed by thermal curing.

Step (iii) may involve pressurization.

The step (iii) may further include a drying step before molding.

The step (ii) may further include laminating by impregnating two or more hydrophobic nanofiber sheets.

In the method, the hydrophobic nanofiber may have a surface tension of 40 to 70 mN/m based on a 1 wt% aqueous solution.

In the method, the hydrophobic nanofiber may be derived from a plant.

In the above method, the plant is green leaf (lovegrass), bamboo (bamboo), silver maple tree (silver maple tree), tulip tree (tulip tree), Chinese maple (trident maple), rice (rice), lotus (lotus) and blood It may be one or more selected from the group consisting of Lakansas (pyracantha).

In the method, the plant may be bamboo.

In the method, the hydrophobic nanofiber may have a diameter of 5 to 100 nm.

In the method, the hydrophobic nanofiber sheet may have a thickness of 20 to 1,000 μm.

Hereinafter, the present invention will be described in more detail.

In one embodiment, the transparent reinforced composite material of the present invention comprises a hydrophobic nanofiber sheet. The present invention relates to a reinforced transparent composite material, and more particularly, to a reinforced transparent composite material manufactured by fabricating a sheet with hydrophobic nanofibers and then impregnating them in a transparent resin.

The present invention uses plant-derived fiber raw materials to obtain nanofibers for reinforcing material, and in particular, when plants with hydrophobic properties are used, it reduces the aggregation of nanofibers by hydrogen bonding, which causes closed pores during the nanofiber sheet formation process, and reduces It is based on the fact that it is possible to secure pores through which transparent resin can penetrate.

Because nanofibers have a small secondary moment of cross-section, they are easily deformed, and since they have very strong cohesive force, compatibility with resins is generally not good. Therefore, the process of suppressing the aggregation of nanofibers is essential, and it is necessary to find a way to sufficiently and uniformly penetrate the transparent resin into the fine pores between the fibers. In addition, in the method of manufacturing a transparent composite material, if the method of forming a nanofiber sheet and impregnating it in the transparent resin without dispersing the nanofiber itself in the transparent resin is used, a larger amount of fibers This method is preferred because the reinforcing effect can be greatly seen. However, when using plant-derived nanofibers as a material, when the cellulose aqueous dispersion solution is filtered to form a nanofiber sheet, water is removed and present in cellulose molecules during drying As the hydroxyl groups (-OH) form strong hydrogen bonds, bonding between nanofibers occurs frequently. Due to this, the size of the fibers increases and closed pores are formed between the fibers. As a result, in the impregnation process of penetrating the transparent resin into the sheet, it is difficult for the transparent resin to penetrate, and when the combined fiber size is 100 nm or more, there is a problem in that the optical properties are deteriorated.

In the molecular structure, cellulose has a hydroxyl group on the side along the polymer chain and a hydrocarbon group on the top and bottom, showing a surface anisotropy having hydrophilicity on the side and hydrophobicity on the top and bottom ( FIG. 1 ). Plant-derived nanofibers are formed in a crystal structure in which cellulose molecules are arranged, and the size of hydrophobicity or hydrophilicity varies according to the arrangement structure. Here, hydrophobicity and hydrophilicity are relative concepts, and when hydrophobicity increases, hydrophilicity decreases. In the case of nanofibers in which cellulose molecules are arranged in a rhombus shape, relatively more hydrophilic aspects are exposed on the surface to have hydrophilicity. In the case of arrangement, the hydrophobic upper and lower surfaces are exposed a lot on the surface of the nanofiber, indicating hydrophobicity (FIG. 1). These hydrophilic / hydrophobic properties can be relatively compared by measuring the surface tension of the plant-derived aqueous nanofiber solution.

In general, plant-derived cellulose fibers have been widely used in the papermaking field, so hardwoods or softwoods, which are inexpensive to manufacture, have been used, and nanofibers have been mainly produced using hardwoods or softwoods as raw materials. However, as can be seen in Table 1 below, according to the measurement results of the surface tension of the 1 wt% aqueous solution of nanofibers, the surface tension of bamboo nanofibers was evaluated to be lower than that of conifers and hardwoods.

bamboo nanofiber
aqueous solution Hardwood Nanofibers
aqueous solution Softwood Nanofiber Aqueous Solution surface tension*
(mN/m) 59.11 72.33 81.08

From the surface tension measurement results, it can be seen that bamboo has a relatively low affinity for water and hydrophobicity compared to conifers or broad-leaved trees. When nanofiber sheets prepared using bamboo, broadleaf and softwood nanofibers are observed through an electron microscope, differences in surface shape can be seen. , it can be seen that, in particular, in the case of bamboo nanofibers, the inter-fiber bonding is small and the pores between the fibers are maintained (Fig. 2).

Therefore, as in the present invention, when a nanofiber sheet is prepared using a plant-derived natural cellulose nanofiber exhibiting hydrophobicity, the cellulose molecule has a relatively high fraction arranged in a block form, so the hydrophilic side exposing hydroxyl groups is hidden. Since the upper and lower hydrophobic surfaces are exposed on the surface of the nanofiber, hydrogen bonding is prevented and aggregation between the nanofibers is prevented, and as a result, the nanofiber sheet can maintain open pores (FIG. 2). That is, the reinforced transparent composite material including the hydrophobic nanofiber sheet of the present invention includes nanofibers in the form of a sheet to ensure its strength, and in particular, includes hydrophobic nanofibers, and conventional plant-derived cellulose nanofiber sheets such as conventional conifers and broadleaf trees. It solves the problem of closed pores of the material, and the penetration of the transparent resin through the sufficiently secured open pores is very easy, so it is possible to significantly improve the optical properties of the material. The nanofiber-reinforced transparent composite material comprising the hydrophobic nanofiber sheet according to the present invention can exhibit a transmittance of 90% or more and turbidity of less than 1% even when manufactured to a thickness of 1 mm or more, and has stronger impact resistance and tensile strength than glass has improved mechanical strength.

As described above, the reinforced transparent composite material of the present invention can be implemented through a method of forming a nanofiber sheet and impregnating it in a transparent resin. The transparent resin usable in the present invention may be used without limitation as long as it is a resin commonly used in transparent composite materials, for example, acrylic resin, methacrylic resin, epoxy resin, urethane resin, olefin resin, phenol resin, melamine resin, novolak resin , Urea resin, guanamine resin, alkyd resin, unsaturated polyester resin, vinyl ester resin, diallyl phthalate resin, silicone resin, furan resin, ketone resin, xylene resin, thermosetting polyimide, styrylpyridine resin, tria A sine-based resin etc. are mentioned. Among these, epoxy resins, silicone resins, acrylic resins, and methacryl resins with particularly high transparency may be preferable. These transparent resins may be used individually by 1 type, and may mix and use 2 or more types.

In a specific embodiment, the transparent resin may be a thermoplastic resin or a thermosetting resin.

The content of the reinforcing material in the transparent composite material of the present invention, that is, the content of the hydrophobic nanofiber sheet may be 5 to 60% by weight, preferably 10 to 40% by weight, more preferably 10 to 30% by weight. By setting the content of the reinforcing material to 5% by weight or more, effects such as improvement of mechanical strength, reduction of thermal expansion coefficient, and improvement of elastic modulus at high temperature can be obtained, and by setting it to about 60% by weight or less, transmittance of the transparent composite material It is possible to obtain effects such as suppression of reduction, suppression of increase in turbidity, and reduction of moisture absorption.

In a specific embodiment, the transparent composite material of the present invention may contain one or more additives at a level that does not impair the transparency of the material and the effects of the present invention. Specific examples of the additive include compatibilizers such as maleic anhydride and modified polypropylene; Surfactants; polysaccharides such as starch and alginic acid; natural proteins such as gelatin glue and casein; inorganic compounds such as tannins, zeolites, ceramics, and metal powders; coloring agent; plasticizer; Spices; pigment; fluidity modifiers; leveling agent; conductive agent; antistatic agent; UV absorbers; UV dispersants; and deodorants, but is not limited thereto. When using such an additive, you may use individually by 1 type, and may mix and use 2 or more types.

The refractive index of the transparent resin contained in the transparent composite material of the present invention may be in the range of 1.53 to 1.59, and in this range, it is possible to obtain a transparent composite material particularly close to the rate of refraction of plant fibers. Since the refractive index of the hydrophobic nanofiber of the present invention may be in the range of 1.54 to 1.58, by matching the refractive index of the hydrophobic nanofiber and the transparent resin, an improvement effect of increasing transmittance and reducing turbidity can be obtained.

In a specific embodiment, in the nanofiber sheet included in the reinforced transparent composite material of the present invention, the surface tension of the hydrophobic nanofibers constituting the sheet may be 40 to 70 mN/m based on 1 wt% aqueous solution. Preferably, the surface tension of the hydrophobic nanofibers may be 45 to 65 mN/m, more preferably 50 to 60 mN/m. By setting the surface tension of the hydrophobic nanofibers to 40 mN/m or more, while maintaining open pores in the nanofiber sheet, hydrogen bonds are formed at the overlapping portions where the nanofibers meet to create a network-like structure, improving mechanical strength and modulus of elasticity This is because, by setting it to 70 mN/m or less, the permeability of the hydrophobic transparent resin into the nanofiber sheet is improved, thereby improving the transmittance of the transparent composite material and improving the turbidity.

In a specific embodiment, as a raw material for the nanofiber used in the reinforced transparent composite material according to the present invention, bamboo is preferable, and the surface tension of the bamboo-derived nanofiber based on a 1 wt% aqueous solution is 40 to 70 mN/m, Preferably, it may be 45 to 65 mN/m.

In a specific embodiment, the hydrophobic nanofiber may be derived from a plant. The plants are green (lovegrass), bamboo (bamboo), silver maple tree (silver maple tree), tulip tree (tulip tree), Chinese maple (trident maple), rice (rice), lotus (lotus) and pyracantha (pyracantha) It may be one or more selected from the group consisting of. As described above, the reinforced transparent composite material of the present invention includes a sheet containing hydrophobic nanofibers, and therefore any leaf of a plant exhibiting the desired hydrophobicity may be used. The hydrophobicity desired in the reinforced transparent composite material of the present invention is that the surface tension of the nanofiber aqueous solution can be measured as 40 to 70 mN/m based on the 1 wt% aqueous solution as described above. Particularly preferably, the plant may be bamboo.

In a specific embodiment, the nanofibers constituting the hydrophobic nanofiber sheet may have a diameter of 5 to 100 nm. Preferably, the nanofiber may have a diameter of 10 to 60 nm, more preferably 20 to 40 nm. If the diameter of the nanofiber is 5 nm or more, it is possible to suppress too many pores in the nanofiber sheet, thereby increasing the nanofiber content when manufacturing a transparent composite material, so that effects such as improvement of mechanical strength and improvement of elastic modulus can be obtained. , if it is less than 100 nm, visible light does not recognize the nanofibers well, so that excellent optical properties (transmittance and turbidity) of the transparent composite material can be obtained. That is, basically, when a fiber having a diameter larger than the wavelength of the visible light region is combined with a transparent resin as a reinforcing material, visible light scattering occurs and as a result, the transparency of the resin is damaged. Therefore, the diameter of the nanofiber occurs By setting the range of 5 to 100 nm, the nanofiber can be usefully function as a material for reinforcing the transparent resin.

In a specific embodiment, the hydrophobic nanofiber sheet included in the reinforced transparent composite material of the present invention may have a thickness of 20 to 1,000 μm. Preferably, the hydrophobic nanofiber sheet may have a thickness of 30 to 500 μm, more preferably 50 to 200 μm. By setting the thickness of the nanofiber sheet to 20 μm or more, the sheet thickness is thin and it is prevented from being damaged or deformed by a thermal process when manufacturing a composite material. By setting it to 1,000 μm or less, the sheet has a uniform density in the thickness direction and is a transparent resin This is because it is easy to penetrate into the inside of the sheet, thereby improving the transmittance of the composite material and improving the turbidity.

In a specific embodiment, the transparent reinforced composite material of the present invention may include two or more hydrophobic nanofiber sheets. By stacking two or more hydrophobic nanofiber sheets to form a reinforced transparent composite material, its thickness and strength can be adjusted to be suitable as a target part.

In a specific embodiment, the reinforced transparent composite material of the present invention may have a thickness of 0.2 mm to 1.5 mm. Preferably, the thickness of the reinforced transparent composite material may be 0.4 mm to 1.0 mm, more preferably 0.5 mm to 0.7 mm. By setting the thickness of the reinforced transparent composite material to 0.2 mm or more, it is possible to prevent breakage because the thickness is thin, and to replace the glass used in thin electronic devices by setting it to 1.5 mm or less.

A method for manufacturing a reinforced transparent composite material according to another embodiment of the present invention comprises the steps of: (i) preparing a hydrophobic nanofiber sheet; (ii) impregnating the hydrophobic nanofiber sheet in a transparent resin; and (iii) forming the impregnated hydrophobic nanofiber sheet.

The (i) step of preparing the hydrophobic nanofiber sheet begins with a process of dissolving the agglomeration of cellulose fibers in dry plant fibers and dissolving them to make a part of the plant fibers into nanofibers. At this time, it is preferable to break the fibers with an average fiber diameter of about 5 to 200 μm to obtain adequate freeness. As a method of fibrillating plant fibers, a known method can be employed, for example, by mechanically pulverizing a water suspension or slurry of the raw material containing the cellulose fibers with a refiner high-pressure homogenizer, grinder, bead mill, etc. to fibrillate. method can be used. Alternatively, nanofibers can be obtained by mechanically dissolving raw material leaf powder in a dry state. The water content of the raw material at the time of fibrillation may be 3 wt% or more, preferably 4 wt% or more, and more preferably 5 wt% or more. The fibrillation becomes insufficient because the bond develops and the mechanical fibrillation effect can be reduced.

In order to form a sheet from the nanofiber aqueous solution, the forming method is not particularly limited, but a method of vacuum filtering or pressure filtering on a suction filtration filter for the nanofiber aqueous solution slurry obtained through the dissolution process, for example, can be used. After filtering, it may be molded into a sheet through additional processes such as drying and heating and compression, and the drying process may be performed at 100 to 150°C. This is because a temperature of 100°C or higher is required for the evaporation of water, and at a temperature of 150°C or higher, the nanofiber may be damaged by heat.

Then, the nanofiber sheet is impregnated with a transparent resin (step (ii)), the transparent resin used at this time is the same as described above for the reinforced transparent composite material of the present invention. Step (ii) may involve heating.

The viscosity of the transparent resin may be 100 to 10,000 cps, preferably 200 to 7,000 cps, more preferably 250 to 5,000 cps. In particular, in order to penetrate well between the pores between the nanofibers, it is preferable that the viscosity is 10,000 cps or less, and when heat is applied at 60 to 90° C. during impregnation, the viscosity of the transparent resin is reduced, so that penetration between the pores can be enhanced. When the viscosity is 100 cps or less, the transparent resin does not stay in the nanofiber sheet during heating and comes out easily, so that the composite material becomes opaque, so it is preferably 100 cps or more. Through the impregnation process, the nanofiber sheet becomes transparent. It is important to sufficiently penetrate the transparent resin between the nanofibers, so this impregnation step can be carried out in part or all while changing the pressure. In the case of reduced pressure or pressurization, it becomes easy to replace the air present between the nanofibers with the transparent resin, and it is possible to prevent the remaining of air bubbles.

Thereafter, the impregnated nanofiber sheet is subjected to a molding step (step (iii)), which is a process of curing the nanofiber sheet impregnated in the transparent resin. This curing process may be made by a polymerization reaction, a crosslinking reaction, a chain extension reaction, or the like. In addition, it may be made by removing the solvent in the transparent resin. The solvent removal may include evaporative removal under reduced pressure as well as evaporative removal under normal pressure.

In this case, step (iii) may be performed by, for example, curing by heating/cooling, photo-curing, etc., which is performed by conventional curing for molding a transparent composite material, but is not limited thereto. In particular, the forming step may be performed by thermosetting and may be accompanied by pressing. For example, the sheet may be press thermoformed with a hot press. At this time, when two or more hydrophobic nanofiber sheets are impregnated and laminated in step (ii), a transparent composite material whose thickness can be adjusted to be suitable as a target part in this step (iii) can be obtained. The pressure applied during thermoforming is preferably 100 to 600 MPa, because if the pressure is too low, voids in the sheet or gaps between the laminated sheets are widened, making it difficult to obtain uniform properties. Heat treatment conditions are preferably at 100 to 170 ° C. for 2 hours or more, because when the transparent resin is cured at 100 ° C. or more and the heat treatment temperature is too high, damage to the nanofibers and the transparent resin may occur and discoloration may occur. In addition, by fixing the nanofiber entanglement by the thermal pressure treatment, the effect of reducing the coefficient of thermal expansion of the transparent composite material or improving the Young's modulus can be expected.

In a specific embodiment, step (iii) may further include a drying step before molding.

In a specific embodiment, the hydrophobic nanofiber used in the method may have a surface tension of 40 to 70 mN/m based on a 1 wt% aqueous solution. Preferably, the surface tension of the hydrophobic nanofibers may be 45 to 65 mN/m, more preferably 50 to 60 mN/m. By setting the surface tension of the hydrophobic nanofibers to 40 mN/m or more, while maintaining open pores in the nanofiber sheet, hydrogen bonds are formed at the overlapping portions where the nanofibers meet to create a network-like structure, improving mechanical strength and modulus of elasticity This is because, by setting it to 70 mN/m or less, the permeability of the hydrophobic transparent resin into the nanofiber sheet is improved, thereby improving the transmittance of the transparent composite material and improving the turbidity.

In certain embodiments, the hydrophobic nanofibers used in the method may be derived from plants.

In a specific embodiment, the plant used in the method is lovegrass, bamboo, silver maple tree, tulip tree, trident maple, rice, It may be at least one selected from the group consisting of lotus and pyracantha. As described above, the reinforced transparent composite material of the present invention includes a sheet containing hydrophobic nanofibers, and therefore, in the method, any leaf of a plant exhibiting the desired hydrophobicity may be used. The hydrophobicity desired in the reinforced transparent composite material of the present invention prepared by the above method is that the surface tension of the nanofiber aqueous solution can be measured as 40 to 70 mN/m based on the 1 wt% aqueous solution as described above.

In a specific embodiment, the plant used in the method may be bamboo.

In a specific embodiment, the hydrophobic nanofiber used in the method may have a diameter of 5 to 100 nm. Preferably, the nanofiber may have a diameter of 10 to 60 nm, more preferably 20 to 40 nm. When the diameter of the nanofiber is 5 nm or more, it is possible to increase the nanofiber content when manufacturing the transparent composite material by suppressing too many pores in the nanofiber sheet. This is because, when it is less than 100 nm, visible light does not recognize the nanofibers well, so that excellent optical properties (transmittance and turbidity) of the transparent composite material can be obtained. That is, basically, when a fiber having a diameter larger than the wavelength of the visible light region is combined with a transparent resin as a reinforcing material, visible light scattering occurs and as a result, the transparency of the resin is damaged. Therefore, the diameter of the nanofiber occurs By setting the range of 5 to 100 nm, the nanofiber can be usefully function as a material for reinforcing the transparent resin.

In a specific embodiment, the hydrophobic nanofiber sheet used in the method may have a thickness of 20 to 1,000 μm. Preferably, the hydrophobic nanofiber sheet may have a thickness of 30 to 500 μm, more preferably 50 to 200 μm. By setting the thickness of the nanofiber sheet to 20 μm or more, when the transparent composite material manufacturing method of the present invention is implemented, the sheet thickness is thin to prevent damage or deformation by a thermal process, and by setting it to 1,000 μm or less, the sheet thickness direction This is because it has a uniform density and it is easy for the transparent resin to penetrate to the inside of the sheet, so that it is possible to obtain the effect of improving the transmittance and turbidity of the transparent composite material obtained by the above method.

The present invention relates to a transparent composite material manufactured by manufacturing a hydrophobic nanofiber sheet and then impregnated with a transparent resin and molded to provide a reinforced transparent composite material, and a method for manufacturing the same. According to the present invention, the nanofiber composite material is transparent and resistant to breakage compared to glass, so the front cover of a mobile device display, the front cover of a flexible device, a window glass of a transportation device such as a car, train, ship, airplane, etc., camera, camcorder image reproduction Glasses for equipment, printing equipment, internal parts such as photocopying equipment, building materials, organic EL displays, transparent substrates for organic EL lighting and solar cells, transparent parts for touch panels and headlights, etc. It is possible to use instead of

According to the present invention, it is possible to solve the conventional problem that it is difficult to simultaneously retain strong and transparent optical properties in manufacturing a nanofiber-reinforced composite material, so that the strength and optical properties of the nanofiber-reinforced composite material can be significantly improved at the same time have. The reinforced transparent composite material according to the present invention exhibits a transmittance of 90% or more and turbidity < 1% at a thickness of 1 mm. In addition, since plant-derived fibers are used as reinforcing materials, compared to composite materials using glass fibers as reinforcing materials, transparency is maintained and specific gravity is low according to temperature changes.

1 is a conceptual diagram illustrating the hydrophilic/hydrophobic properties of plant leaves according to the molecular structure of cellulose and the cellulose molecular arrangement structure.
Figure 2 is an electron micrograph of the surface shape of the nanofiber sheet according to the plant fiber raw material.
3 is a manufacturing process diagram of the reinforced transparent composite material of the present invention according to an embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in several different forms and is not limited to the embodiments described herein.

Example One

1. Preparation of nanofiber sheets

Bamboo pulp fibers were repeatedly ground 60 times or more with a grinder (Super Masscolloider, Masuko Sangyo Co., Ltd) to prepare bamboo nanofibers, and the concentration was adjusted to 1% by weight by diluting with water. The diluted solution was treated with a homogenizer (T18 basic ULTRA-TURRAX,IKA) at 10,000 rpm for 3 minutes, and 30% output with an ultrasonic homogenizer (VC505 Vibra cell, SONICS) for 30 minutes to obtain a uniformly dispersed aqueous solution of nanofibers. got it By spin-coating an aqueous nanofiber solution on a silicon substrate (3,000 rpm, 30 seconds), it was confirmed that the nanofiber diameter was 100 nm or less with a scanning electron microscope (SEM) and an atomic force microscope (AFM). could In addition, as a result of measuring the aqueous nanofiber solution with a surface tension meter (DSA100, KRUSS), a surface tension of 59.11 mN/N was confirmed. A PVDF (Polyvinylidene fluoride) filter and a reduced pressure filter system (ADVENTEC) were used to prepare the nanofiber sheet, and after filtering 80 ml of an aqueous solution, it was dried at 100° C. for 1 hour to obtain a sheet with a thickness of about 100 μm.

2. Manufacture of transparent resin

Bisphenol A epoxy (Bisphenol A diglycidyl ether, KDS8128, Kukdo Chemical), anhydrous curing agent (Methylhexahydrophthalicanhydride, KFH271, Kukdo Chemical), and low-viscosity diluent (3-ethyl-3-hydroxymethyl-oxetane, OXT-101, Toagosei) in a weight ratio of 100 each After mixing at 110:15, 2-?ethyl-?4-?methylimidazole (sigma aldrich) was added as an initiator in an amount of 0.15% by weight of the transparent resin to prepare a transparent resin. The transparent resin was maintained at 90°C for 2 hours and then heated at 150°C for 2 hours to be cured.

3. Manufacture of transparent composite material

In order to allow the transparent resin to penetrate into the pores between the nanofibers, the nanofibers were immersed in a transparent resin solution and placed in a vacuum oven (OV11, Jiotech), and the pressure was reduced to 0.1 MPa at 70° C. and maintained for 2 hours. Seven nanofiber sheets impregnated with resin were laminated and inserted into a mold capable of manufacturing a plate with a thickness of 1 mm, and then a pressure of 30 MPa was applied with a hot press and heated at 150° C. for 3 hours to prepare a reinforced transparent composite material. . The content of nanofibers in the prepared composite material was 10.88 wt%.

comparative example One

The hardwood pulp was treated in the same manner as in Example 1 to prepare a composite material, and 7 nanofiber sheets were used in the same manner, but the permeability of the transparent resin was lowered, and a large number of pores were present in the composite material, so the nanofiber content could be calculated. there was no

comparative example 2

The softwood pulp was treated in the same manner as in Example 1 to prepare a composite material, and 7 nanofiber sheets were used in the same manner, but the permeability of the transparent resin was lowered, and a large number of pores were present in the composite material, so the nanofiber content could be calculated. there was no

Physical property evaluation

For the composite materials prepared in Examples and Comparative Examples, transmittance and turbidity at a wavelength of 360 to 740 nm were measured using a Spectrophotometer CM-5 of KONICA MINOLTA, and 3 points based on ASTM D790 measurement using UTA500 of Yeonjin Corporation The bending strength was measured. The results are shown in Table 2 below.

bamboo nanofiber hardwood
nanofiber softwood
nanofiber resin penetrability O X X Transmittance (%) 91.2 79.4 57.0 Turbidity (%) 0.6 27.1 60.2 Flexural strength (MPa) 261 112 43

Although preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims are also provided. is within the scope of the

Claims (22)

To include a hydrophobic nanofiber sheet,
The hydrophobic nanofiber sheet is of plant origin, and the plant is bamboo,
The hydrophobic nanofiber sheet has a surface tension of 40 to 70 mN/m based on a 1 wt% aqueous solution,
Maintaining open pores and forming a network structure by forming hydrogen bonds between the hydrophobic nanofibers,
Reinforced transparent composite material. delete delete delete delete The reinforced transparent composite material of claim 1, wherein the hydrophobic nanofibers have a diameter of 5 to 100 nm. The reinforced transparent composite material of claim 1, wherein the hydrophobic nanofiber sheet has a thickness of 20 to 1,000 μm. According to claim 1, Reinforced transparent composite material comprising two or more hydrophobic nanofiber sheets. The reinforced transparent composite material of claim 8, wherein the thickness is 0.2 to 1.5 mm. (i) preparing a hydrophobic nanofiber sheet;
(ii) impregnating the hydrophobic nanofiber sheet in a transparent resin; and
(iii) as comprising the step of forming the impregnated hydrophobic nanofiber sheet,
The hydrophobic nanofiber sheet is of plant origin, and the plant is bamboo,
The hydrophobic nanofiber sheet has a surface tension of 40 to 70 mN/m based on a 1 wt% aqueous solution,
Maintaining open pores and forming a network structure by forming hydrogen bonds between the hydrophobic nanofibers,
A method for manufacturing a reinforced transparent composite material. delete ◈Claim 12 was abandoned when paying the registration fee.◈ The method of claim 10, wherein the transparent resin has a viscosity of 100 to 10,000 cps. ◈Claim 13 was abandoned when paying the registration fee.◈ 11. The method according to claim 10, wherein step (iii) is performed by thermal curing. ◈Claim 14 was abandoned at the time of payment of the registration fee.◈ 11. The method of claim 10, wherein step (iii) involves pressurization. ◈Claim 15 was abandoned when paying the registration fee.◈ 11. The method of claim 10, wherein step (iii) further comprises a drying step prior to molding. ◈Claim 16 was abandoned when paying the registration fee.◈ The method of claim 10, wherein step (ii) further comprises impregnating and laminating two or more hydrophobic nanofiber sheets. delete delete delete delete ◈Claim 21 has been abandoned at the time of payment of the registration fee.◈ The method of claim 10 , wherein the hydrophobic nanofibers are 5 to 100 nm in diameter. ◈Claim 22 was abandoned when paying the registration fee.◈ The method of claim 10 , wherein the hydrophobic nanofiber sheet is 20 to 1,000 μm thick.

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