Moisture-resistant biodegradable sheet and food container using same

Abstract

A biodegradable sheet using fibers obtained from seaweed and a food container using same. An aspect includes a biodegradable sheet in the form of a web in which first fibers obtained from seaweed and second fibers obtained from wood and a plant are networked together, wherein a ratio L1 / L2 of an average length (L1) of the first fibers to an average length (L2) of the second fibers is 0.1-0.5, and the first fibers are uniformly inserted into the upper portion and pores of the web comprising the second fibers, the biodegradable sheet having a moisture content of 10 wt % or less with respect to dry weight and a bulk density of 5.0-7.0 g / cm3. Also, a moisture-resistant biodegradable sheet which, by comprising a moisture-resistant coating layer formed by coating or impregnating on one or both sides of the biodegradable sheet, has excellent water resistance and oil resistance.

Description

TECHNICAL FIELD

[0001] The present invention relates to a moisture-resistant biodegradable sheet and a food container using the same, and more particularly, to a biodegradable sheet using fibers obtained from seaweed and a food container using the same.BACKGROUND ART

[0002] Recently, disposable containers have been rapidly and increasingly used due to the spread of COVID-19. Plastic containers are used for most of the disposable containers, and there are concerns about environmental pollution due to difficulties in recycling and reusing the plastic containers.

[0003] Accordingly, there is increasing interest in materials capable of replacing plastic containers, and researches are increasing on materials that are environmentally friendly while also satisfying the mechanical strength of plastic containers. In this regard, the present applicant has applied for a method for manufacturing a mold using seaweed pulp in Korean Registered Patent Publication No. 10-2141932 (Jul. 31, 2020). It is confirmed that a mold manufactured according to the above disclosure can be manufactured into shapes such as food containers using seaweed pulp. However, the strength of the manufactured molded product is insufficient to replace currently used plastic containers.

[0004] (Patent Document 1) Korean Registered Patent Publication No. 10-2141932 (Jul. 31, 2020)DISCLOSURETechnical Problem

[0005] One object of the present invention is to provide a biodegradable sheet and a food container using the same to have flexibility while still providing mechanical strength capable of replacing conventional plastic containers.

[0006] In addition, an object of the present invention is to provide a biodegradable sheet and a food container using the same to have excellent biodegradability.

[0007] In addition, an object of the present invention is to provide a biodegradable sheet and a food container using the same to have excellent water resistance and oil resistance.Technical Solution

[0008] As a result of research to solve the problems in the related art, the applicant of the present invention has discovered providing a biodegradable sheet and a food container using the same, which are formed of an environmentally friendly material having flexibility, providing mechanical strength capable of replacing conventional plastic containers, having excellent biodegradability, and having excellent water resistance and oil resistance, and thus has completed the present invention.

[0009] One aspect of the present invention provides a moisture-resistant biodegradable sheet including: a biodegradable sheet in the form of a web in which first fibers obtained from seaweed and second fibers obtained from wood and plant are networked together, wherein a ratio L1 / L2 of an average length (L1) of the first fibers to an average length (L2) of the second fibers is 0.1-0.5, the first fibers are uniformly inserted into an upper portion and pores of the web composed of the second fibers, and the biodegradable sheet having a moisture content of 10 wt % or less with respect to dry weight and a bulk density of 0.4 to 1.2 g / cm3; and a moisture-resistant coating layer formed by coating or impregnating on one or both sides of the biodegradable sheet.

[0010] Another aspect of the present invention provides a molded body including the moisture-resistant biodegradable sheet according to the one aspect, and more specifically, provides a food container.Advantageous Effects

[0011] The biodegradable sheet according to one aspect of the present invention can be biodegraded within 60 days in an aerobic biodegradability test according to ISO 14855-1:2012.

[0012] In addition, the biodegradable sheet according to one aspect of the present invention has tensile strength of 5 KN / cm2 or more and elongation of 1.5% or more according to ISO 1924-2, tear strength of 4000 mN or more according to ISO 1974, and bursting strength of 350 kPa or more according to ISO 2758, so that the excellent mechanical properties can replace conventional plastic containers.

[0013] In addition, the biodegradable sheet according to one aspect of the present invention has a Cobb value of 30 g / m2 or less according to TAPPI T441, and a kit rating of 1 or higher according to TAPPI 559, thereby having excellent water-resistance and oil-resistance, so that the biodegradable sheet can be suitably used as a food container.DESCRIPTION OF DRAWINGS

[0014] FIG. 1 is a photograph showing a section of a biodegradable sheet according to Example 1 of the present invention.

[0015] FIG. 2 is a photograph showing a first surface of the biodegradable sheet according to Example 1 of the present invention.

[0016] FIG. 3 is a photograph showing a second surface of the biodegradable sheet according to Example 1 of the present invention.BEST MODEMode for Invention

[0017] Hereinafter, the present invention will be described in more detail. However, the following specific examples or embodiments are only the reference for describing the present invention in detail, and the present invention is not limited thereto and may be implemented in various forms.

[0018] In addition, unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by one of those having ordinary skill in the art. The term used in the description of the present invention is only for the purpose of effectively describing particular embodiments and is not intended to limit the present invention.

[0019] In addition, the singular forms used in the specification and the appended claims are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0020] In addition, when one component “includes” some elements, it does not exclude other elements, but may further include the other elements, unless particularly stated otherwise.

[0021] In addition, unless otherwise specifically defined in the present invention, when a layer or member is said to be located “on” other layer or member, this includes not only cases where a layer or member is in contact with the other layer or member, but also cases where another layer or member exists between the two layers or two members. In addition, the terms used in this specification, such as “about” and “substantially”, are used as being at or near the numerical value when manufacturing and material tolerances inherent in the meaning referred to are given, and may be used to prevent undue exploitation by unscrupulous infringers on the disclosed disclosure in which exact or absolute numerical values are stated in order to facilitate the understanding of the present invention.

[0022] One aspect of the present invention provides a moisture-resistant biodegradable sheet including: a biodegradable sheet in the form of a web in which first fibers obtained from seaweed and second fibers obtained from wood and plant are networked together, wherein a ratio L1 / L2 of an average length (L1) of the first fibers to an average length (L2) of the second fibers is 0.1-0.5, the first fibers are uniformly inserted into an upper portion and pores of the web composed of the second fibers, the biodegradable sheet has a moisture content of 10 wt % or less base on a dry weight and a bulk density is 0.4 to 1.2 g / cm3; and a moisture-resistant coating layer formed by coating or impregnating on one or both sides of the biodegradable sheet.

[0023] As one aspect, the biodegradable sheet may be biodegraded within 60 days in an aerobic biodegradability test according to ISO 14855-1:2012, and the present invention is not limited thereto.

[0024] As one aspect, the biodegradable sheet may have both surfaces with different surface roughness.

[0025] As one aspect, when the surface having a large surface roughness in the biodegradable sheet is referred to as a first surface, a density gradient may be configured to have a web density increasing from the first surface to the second surface. In other words, as shown in FIGS. 1 to 3, the first and second surfaces may have surface roughness different from each other, and the web density may be increased from the first surface to the second surface, that is, the web may be formed more densely.

[0026] As one aspect, the L1 may be 1 to 5 mm and the L2 may be 2 to 10 mm, and the present invention is not limited thereto.

[0027] As one aspect, the biodegradable sheet may have a basis weight of 400 to 800 g / m2, and the present invention is not limited thereto.

[0028] As one aspect, the biodegradable sheet may contain 50 wt % or less of the first fibers, and more specifically may contain 1 to 50 wt %, 10 to 50 wt %, or 10 to 30 wt %, but the present invention is not limited thereto.

[0029] As one aspect, the biodegradable sheet may be obtained by molding and then drying a pulp liquid formed by mixing the first fibers, the second fibers and water.

[0030] As one aspect, the mold may be formed by maintaining a moisture content of a sheet at 30 to 50 wt %, and maintaining a moisture content at 5 wt % or less after drying. It is preferable that the biodegradable sheet be manufactured within the above range to have flexibility and excellent mechanical strength, but the present invention is not limited thereto.

[0031] As one aspect, the residual moisture in the sheet after drying may form hydroxyl groups to induce hydrogen bonding, and accordingly, may provide a biodegradable sheet having more improved mechanical strength.

[0032] As one aspect, the water in the pulp liquid may have a content of 80 to 98 wt %, and a thickness of the biodegradable sheet may be controlled by adjusting the water content. Although not limited thereto, it may be preferred that the desired biodegradable sheet be provided with excellent mechanical strength in the above range.

[0033] As one aspect, the first fibers may be formed of seaweed pulp obtained by crushing dried seaweed and mixing and dissociating the crushed seaweed in water, and the second fibers may be formed of wood pulp obtained by dissociating wood and plants. As one aspect, the seaweed may be one selected from Gracilaria Lichenoides and Sargassum Horneri, or a mixture thereof. Although not limited thereto, a biodegradable sheet having more excellent mechanical properties may be provided when the above seaweed is used compared to when other seaweeds are used.

[0034] As one aspect, the biodegradable sheet may have tensile strength of 5 KN / cm2 or more and elongation of 1.5% or more according to ISO 1924-2, tear strength of 4000 mN or more according to ISO 1974, and bursting strength of 350 kPa or more according to ISO 2758.

[0035] As one aspect, the moisture-resistant coating layer may have a Cobb value of 30 g / m2 or less according to TAPPI T441, and a kit rating of 1 or higher according to TAPPI 559.

[0036] As one aspect, the moisture-resistant coating layer may be formed by applying or impregnating a chitosan solution containing 1 wt % or less of chitosan having a molecular weight of 50,000 to 400,000 Da.

[0037] As one aspect, the moisture-resistant coating layer may have a coating thickness of 1 mm or less.

[0038] Another aspect of the present invention provides a molded body including the biodegradable sheet according to the one aspect. More specifically, the molded body may be a food container, and for specific example, may be used as a container, such as a food tray, plate, or egg carton, for storing and transporting food.

[0039] Hereinafter, each component of the present invention will be described in more detail.

[0040] As one aspect, the biodegradable sheet may have a thickness of about 0.1 to 2 mm, 0.5 to 5 mm, or 1 to 1.5 mm, and the thickness may be adjust as needed. Thus, the present invention is not limited thereto. In addition, a basis weight may be 400 to 800 g / m2, or 400 to 600 g / m2, and the present invention is not limited thereto.

[0041] As one aspect, the biodegradable sheet may include 20 to 50 wt % of first fibers obtained from seaweed and 50 to 80 wt % of second fibers obtained from wood and plants, and more specifically, may include 30 to 50 wt % of the first fibers and 50 to 70 wt % of the second fibers. It is preferable that the biodegradable sheet exhibit excellent biodegradability and mechanical strength within the above range, but the present invention is not limited thereto.

[0042] As one aspect, the biodegradable sheet is in the form of a web in which first fibers obtained from seaweed and second fibers obtained from wood and a plant are networked together, and it refers to a sheet formed by uniformly inserting the first fibers into an upper portion and pores of the web composed of the second fibers. The web form refers to a network like a net, and may refer to a non-woven fabric formed by coupling single fibers.

[0043] A ratio L1 / L2 of an average length (L1) of the first fibers to an average length (L2) of the second fibers may preferably be 0.1 to 0.5, and specifically, may be between 0.2 and 0.5. It is preferable to manufacture the desired biodegradable sheet in the above range to have the mechanical strength while also being flexible, but the biodegradable sheet may also be manufactured beyond the range. In addition, the average length (L1) of the first fibers and the average length (L2) of the second fibers may be different from each other, and more preferably, the first fibers may be used to be shorter than the second fibers, thereby uniformly filling the first fibers into the upper portion and the pores of the web formed of the second fibers, so that a sheet having a higher bulk density may be provided, and accordingly, a biodegradable sheet capable of maintaining mechanical strength even when bent or transported may be provided. Specifically, the first fibers and the second fibers may be bound to each other in an entangled state.

[0044] More specifically, the average length (L1) of the first fibers may be 1 to 5 mm, and the average length (L2) of the second fibers may be 2 to 10 mm. More specifically the average length (L1) of the first fibers may be 1 to 4 mm, 1 to 3 mm, or 1 to 2 mm, and the average length (L2) of the second fibers may be 2 to 9 mm, 2 to 8 mm, 2 to 7 mm, 2 to 6 mm, 2 to 5 mm, 2 to 4 mm, or 2 to 3 mm, but the present invention is not limited thereto.

[0045] In addition, as shown in FIG. 1, the biodegradable sheet according to one aspect of the present invention may have two surfaces with surface roughness different from each other. The surface in which the first fibers are inserted more may have a lower surface roughness as shown in FIG. 3 and form a dense and smooth surface, and the surface in which relatively few first fibers are inserted may have a higher surface roughness as shown in FIG. 2. Accordingly, the different surface roughness of the both surfaces may be formed by immersing a mold having a shape to be formed into a pulp liquid, which is a mixture of the first fibers, the second fibers and water, taking the immersed mold out, and then drying moisture while the pulp liquid is put onto a surface of the mold in the same shape as the mold, and the present invention is not limited thereto. Specifically, it may be manufactured using a wet scheme, which is the same as the sheet forming scheme as a papermaking process. Accordingly, a plurality of second fibers arranged parallel to the surface of the mold may be formed in a laminated structure, the first fibers may be filled in empty spaces, and the first fibers, the second fibers or the first and second fibers may be bound while being entangled with each other.

[0046] In addition, as shown in FIG. 1, when the surface having the larger surface roughness is called the first surface, a density gradient may be configured to have a web density increasing from the first surface to the second surface. Alternatively, the density may be increased from the surface to a center, or the density may be increased from the center to the two surfaces, which may be adjusted depending on the manufacturing method, and the present invention is not limited thereto. However, as shown in FIG. 1, the web density is increased from the first surface to the second surface to have a denser web structure, so that the first surface relatively less dense and having the higher surface roughness may provide flexibility, and the second surface relatively more dense and having the lower surface roughness may provide mechanical strength. Accordingly, in a viewpoint of the perspective of providing the flexibility and the mechanical strength that can be used as a food container, it is preferable that the web densities of the first surface and the second surface are different from each other, and more specifically, that the density gradient has the web density increasing from the first surface to the second surface.

[0047] In addition, the biodegradable sheet may have a moisture content of 10 wt % or less, 5 wt % or less, or 3 wt % or less, specifically 0.1 to 10 wt %, 1 to 5 wt %, or 1 to 3 wt % based on dry weight. It is preferable to provide the biodegradable sheet in the above range to prevent gelation of fibers obtained from seaweed and have excellent mechanical properties, but the present invention does not exclude the scope beyond the range.

[0048] In addition, the biodegradable sheet may have a bulk density of 0.4 to 1.2 g / cm3, 0.4 to 1.0 g / cm3, or 0.4 to 0.6 g / cm3, and may be preferable to simultaneously provide flexibility and mechanical properties in the above range, but the present invention does not exclude the scope beyond the range.

[0049] As one aspect, the first fibers obtained from seaweed and the second fibers obtained from wood and plants may be manufactured by a method known in the art, and the manufacturing method is not limited thereto.

[0050] As one aspect, the first fibers obtained from the seaweed may be formed of seaweed pulp obtained by crushing dried seaweed and mixing and dissociating the crushed seaweed in water, and the second fibers may be formed of wood pulp obtained by dissociating wood and plants.

[0051] More specifically, the first fibers obtained from the seaweed may be manufactured as seaweed fibers after going through processes such as washing, drying, softening, pulping, and drying of the seaweed.

[0052] More specifically, the first fibers obtained from the seaweed may be obtained by process in which, for example, the seaweed is washed and dried, the seaweed is immersed in an extraction solvent capable of dissolving viscous ingredients, such as agar gel and alginate, for a predetermined period of time, the viscous ingredients are dissolved and removed through the extraction solvent, residual slurry is physically crushed, softened and pulpified to be dissociated and, as needed, bleached using a bleaching agent such as CI2O or H2O2, and only seaweed fibers are extracted.

[0053] Alternatively, the seaweed may be immersed in an acidic solution, washed with water and dehydrated, the dehydrated seaweed may be immersed in an extraction solvent such as water for a predetermined period of time to extract viscous ingredients such as agar gel and alginate, and then a residue may be bleached and collected, so that the seaweed fibers may be obtained.

[0054] The seaweed fibers are composed of fructose and cellulose as main ingredients and do not melt due to heat.

[0055] In one aspect, a method for manufacturing the biodegradable sheet of the present invention will be specifically described in detail as an example. First, after seaweed is dried to have a moisture content of 10 wt % or less, the seaweed is crushed into a size of 3 mm or less, more specifically 1 to 2 mm, and the crushed seaweed is mixed in a Na2SO3 aqueous solution and stirred to undergo a softening process. Then, the seaweed turns into a white, fibrous raw material. This raw material is washed with water and the pulp liquid, which is a mixture of pulp and purified water obtained from the softened seaweed, wood and plant is fed to a pulper. The raw material mixture is pumped into a dump chest and mixed using a stirrer. In the dump box, pH may be maintained at 5 or more, and a temperature may be maintained at 50 to 70° C. The mixed material is transferred to a pulp washing process, then mixed with water again and transferred to a molding machine having moving conveyor trays. The conveyor trays pass through internal channels of a drying oven, so that a final sheet may be dried to have a moisture content of 10 wt % or less, 5 wt % or less, or more preferably 1 to 3 wt %.

[0056] The seaweed pulp and the seaweed fibers manufactured in the above manner may be easily gelated. The gelation of seaweed pulp may signify that fibers of seaweed pulp absorb moisture and change into a gel form. When the seaweed pulp is gelated, viscosity and elasticity are rapidly increased to prevent condensation, thereby failing to be formed into a mold. In other words, the seaweed pulp cannot be formed into a mold in the same manner as the mold forming method using cotton pulp or wood pulp. Accordingly, in the process of drying after molding in the molding machine, it is preferable to include processes for adjusting the moisture content of the seaweed pulp and / or fiber. In other words, it is preferable to adjust the moisture content of the pulp liquid to 30 to 50 wt % to prevent the gelation. Next, during the molding process in the molding machine, a molded article may be manufactured by filling the mold with the pulp liquid and applying pressure. During the molding process, the moisture content of the pulp liquid may be adjusted once more to 30 to 50 wt % before molding the pulp liquid. Next, the molded article is transported to a drying device and dried. The drying device may include a conveyor belt that receives the molded article from the molding machine and a dryer (a blowing device and a heating device). The molded article may be dried in the drying process to become a finished product. The final sheet may be dried to have the moisture content of 10 wt % or less, 5 wt % or less, and more preferably 1 to 3 wt %, during the drying process, thereby allowing the remaining moisture after drying to form hydroxyl groups to induce hydrogen bonds, so that the mechanical strength of the sheet may be further improved.

[0057] The drying process may include drying at 150 to 250° C. for 30 to 60 minutes, but is not limited thereto.

[0058] In one aspect of the present invention, the seaweed may be one selected from Gelidium amansii, Eucheuma cottonli, Spinosum, Chondracanthus tenellus, laver, Digenea, Gloiopeltis tenax, Pterocladia Tenuis, Gelidium yoshidae, Hypnea asiatica, Ceramium kondoi, Ceramium boydenii, Campylaephora hypnaeoides, Grateloupia filicina, Green laver, chlorella, Cosmarium, Closterium, Codium fragile, Cheongtae, Undaria pinnatifida, Saccharina japonica, Sargassum fulvellum, Sargassum fusiforme, Ecklonia cava, Ecklonia Stolonifera, Eisenia bicyclis, Gracilaria lichenoides and Sargassumhorneri, or a mixture thereof, but the present invention is not limited thereto. More preferably, the seaweed may be one selected from Gracilaria Lichenoides and Sargassumhorneri or a mixture thereof. It is preferable to use these seaweeds, because a biodegradable sheet having excellent mechanical strength including tensile strength improved by more than 40% may be provided compared to using other types of seaweed such as Undaria pinnatifida and Saccharina japonica, but the present invention is not limited thereto. More preferably, Gracilaria Lichenoides and Sargassumhorneri may be mixed and used, and the mixing ratio is not limited, but may be mixed in a weight ratio of 0.1:99.9 to 99.9:0.1.

[0059] In one aspect of the present invention, the plant refers to a raw material capable of obtaining vegetable fibers other than wood and seaweed, and specifically, may be one, two or more selected from straw, corn stalks, reeds, bamboo, flax, cotton, hemp and sugarcane or a mixture thereof, but the present invention is not limited thereto.

[0060] The biodegradable sheet according to one aspect of the present invention may be biodegraded within 60 days in an aerobic biodegradability test according to ISO 14855-1:2012. In addition, the biodegradable sheet has tensile strength of 5 KN / cm2 or more and elongation of 1.5% or more according to ISO 1924-2, tear strength of 4000 mN or more according to ISO 1974, and bursting strength of 350 kPa or more according to ISO 2758. More specifically, the tensile strength may be 5 to 10 KN / cm2, the elongation may be 1.5 to 5%, the tear strength may be 4000 to 5000 mN, and the bursting strength may be between 350 and 700 kPa.

[0061] In addition, it is confirmed that it is suitable for use as a food container because no hazardous substances are detected in a hazardous substance test according to IEC62321.

[0062] As one aspect, the moisture-resistant biodegradable sheet of the present invention includes a moisture-resistant coating layer formed by coating or impregnating on one or both sides of the biodegradable sheet.

[0063] The moisture-resistant coating layer may be used without limitation when commonly used in the art, however, may be formed by applying or impregnating a chitosan solution in the present invention from a natural biodegradable and environmentally friendly perspective.

[0064] As one aspect, the chitosan solution may be formed by applying or impregnating a solution in which chitosan having a molecular weight of 50,000 to 400,000 Da, 50,000 to 195,000 Da, 200,000 to 400,000 Da, 200,000 to 300,000 Da or 305,000 to 400,000 Da is dispersed or dissolved. A scheme for the application is not limited, and the application includes applying using a roller, brush, spray or the like. The impregnation may be accomplished by immersing the biodegradable sheet in the chitosan solution. As one aspect, the chitosan solution may be obtained by dissolving chitosan powder in an acid solution such as acetic acid, and a content of chitosan in the chitosan solution may be 15 wt % or less, more specifically 0.01 to 15 wt %, or more specifically 0.05 to 10 wt % or 0.1 to 1 wt %. The content of chitosan is not limited thereto because it may be adjusted and used differently depending on the coating scheme. However, in the case of spray application, a concentration of 0.1 to 1 wt % may be used. It is confirmed that, when the chitosan solution prepared in the above manner is immersed or spray applied, the mechanical strength of the biodegradable sheet is increased overall, the degree of water absorption is decreased when the number of coating times is increased, and the surface becomes smooth due to repeated coating and drying processes. Specifically, it is confirmed that, when the moisture-resistant coating layer is formed by immersing or spray applying the chitosan solution, the tensile strength is increased compared to the uncoated sheet.

[0065] In other words, when tensile strength of the biodegradable sheet is T1 and tensile strength of a moisture-resistant biodegradable sheet formed with a moisture-resistant coating layer coated or impregnated on one or both sides of the biodegradable sheet is T2, a tensile strength change rate according to the following Equation 1 may be 20% or more, more specifically 20 to 30%.Tensile⁢ strength⁢ change⁢ rate⁢ (%)=(T⁢2-T⁢1) / T⁢1×100[Equation⁢ 1]

[0066] In addition, the tear strength and the bursting strength are also improved in addition to the tensile strength. For specific example, when the coating layer is formed using the chitosan solution, the tensile strength and the bursting strength may be improved by 20% or more, specifically 20 to 30%, compared to before the coating layer is formed.

[0067] In addition, it is confirmed that, when the biodegradable sheet formed having the moisture-resistant coating layer formed thereon is immersed in water at 80° C. for 10 minutes and then taken out to check, only some moisture is permeated to exhibit water-resistant properties. In addition, resulting from measurement of the content of chitosan leached into water after the biodegradable sheet having the moisture-resistant coating layer formed thereon is immersed in water at 80° C. for 10 minutes, it is confirmed that chitosan is prevented from being leached out and the coating layer is maintained. It is estimated that chitosan is prevented from being leached out because chitosan is strongly bound to the biodegradable sheet, and it is estimated that the moisture content of the biodegradable sheet after drying also affects the interaction between chitosan and the biodegradable sheet.

[0068] Accordingly, the biodegradable sheet and the moisture-resistant biodegradable sheets according to the present invention may be used appropriately for food containers, food packaging and the like.

[0069] Specifically, the moisture-resistant coating layer formed using the chitosan solution may have a Cobb value of 30 g / m2 or less, specifically 25 to 30 g / m2 according to TAPPI T441, so as to be resistant to moisture. This is evaluated by measuring an amount of water that has permeated the coating surface after having coming into contact with the water for a predetermined period of time. The amount of water is 80 to 120 ml, most preferably 100 ml, and the contact time is between 20 and 40 minutes, most preferably 30 minutes. The measurement is performed using hot water or cold water, depending on a final use. Preferably, resistance to hot water may have a higher priority to resistance to cold water. Since the measured value (Cobb value) is the amount of water absorbed by the sheet through the surface, the water resistance is better when the value is lower.

[0070] In addition, a kit rating of 1 or higher according to TAPPI 559. This is the result by using an eyedropper to drop a droplet of a mixture of castor oil, toluene and heptane onto the surface of the sheet and measuring a time taken for a stain. The surface may be oil-resistant when the stain is not generated in 15 seconds.

[0071] The moisture-resistant coating layer may have a thickness controlled by controlling the number of coating times, and the coating thickness may be 1 mm or more, 0.5 mm or more, or 0.1 mm or more. It may be preferable to adjust the thickness within the above range to provide water resistance and oil resistance without increasing production costs, but the present invention is not limited thereto.

[0072] In addition, a process of drying at 150 to 250° C. for 30 to 60 minutes after the application or immersion may be included. When the chitosan solution is coated and dried as described above, chitosan powder may be uniformly distributed on the surface and inside of the biodegradable sheet.

[0073] Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples. However, the following Examples and Comparative Examples are only examples for describing the present invention in more detail, and the present invention is not limited by the following Examples and Comparative Examples.

[0074] Hereinafter, physical properties will be evaluated as follows.1) Tensile Strength and Elongation

[0075] The tensile strength and the elongation of the biodegradable sheet is measured according to ISO 1924-2. The measurement condition is performed at 23.01° C., 50±2% RH.2) Tear Strength

[0076] The tear strength of the biodegradable sheet is measured according to ISO 1974. The measurement condition is performed at 23.0±1° C., 50±2% RH.3) Bursting Strength

[0077] The bursting strength of the biodegradable sheet is measured according to ISO 2758. The measurement condition is performed at 23.0±1° C., 50±2% RH.4) Bulk Density

[0078] The bulk density of the biodegradable sheet is measured according to KS M ISO 534, and calculated using the following equation.Bulk⁢ density=basis⁢ weight⁢ (g / m2) / thickness⁢ (mm)5) Moisture Content Based on Dry Weight

[0079] The moisture content based on dry weight of the biodegradable sheet is measured using a moisture content meter (METTLER TOLEDO, HC103 product).6) Aerobic Biodegradability Test

[0080] The aerobic biodegradability test is performed according to ISO 14855-1:2012.

[0081] When the sheet is biodegraded within 60 days, it is determined as a pass, and when the sheet is not biodegraded, it is determined as a fail.7) Water Resistance and Oil Resistance

[0082] The water resistance is measured by a Cobb value according to TAPPI T441, and the oil resistance is measured by a kit grade according to TAPPI 559.Preparing Example 1

[0083] A chitosan solution is prepared as follows.

[0084] A chitosan solution is prepared by dissolving 0.5 wt % of chitosan powder having a molecular weight of 100,000 Da in acetic acid.Example 11) Preparation of Biodegradable Sheet

[0085] A pulp solution is prepared by mixing and dissociating 3 wt % of first fibers having an average length of 2 mm obtained by using Gracilaria Lichenoides and Sargassumhorneri in a weight ratio of 1:1, 7 wt % of second fibers having an average length of 4 mm obtained from wood, and 90 wt % of water.

[0086] The prepared pulp liquid is supplied to a pulper, pumped into a dump chest, and mixed using a stirrer. In the dump box, pH is maintained at 6, and a temperature is maintained at 60° C. The mixture is transferred to a pulp washing process, mixed again with water and transferred to a molding machine equipped with moving conveyor trays. The moisture content of the pulp liquid injected into the mold is adjusted to maintain 50 wt %. The conveyor tray passes through an internal channel of a drying oven and dried at 200° C. until the moisture content of the sheet injected into the mold is 5 wt %. The dried sheet is separated from the mold.

[0087] Physical properties of the prepared biodegradable sheet are measured and are shown in Table 1 below.

[0088] In addition, FIG. 1 shows a section of the prepared biodegradable sheet, FIG. 2 shows a first surface, and FIG. 3 shows a second surface.2) Preparing Moisture-Resistant Biodegradable Sheet Having Moisture-Resistant Coating Layer Formed Thereon

[0089] The chitosan solution prepared in Example 1 is spray-coated on both sides of the prepared biodegradable sheet twice at a flow rate of 10 ml / min, and dried at 200° C. for 40 minutes, thereby forming a moisture-resistant coating layer.

[0090] Water resistance and oil resistance of the prepared moisture-resistant biodegradable sheet are evaluated and shown in Table 1.Example 2

[0091] A biodegradable sheet is prepared in the same manner as in Example 1 except that the contents of the first and second fibers are adjusted as shown in Table 1 below. Physical properties of the prepared biodegradable sheet are measured and are shown in Table 1 below.

[0092] The chitosan solution prepared in Example 1 is spray-coated on both sides of the prepared biodegradable sheet twice at a flow rate of 10 ml / min, and dried at 200° C. for 40 minutes, thereby forming a moisture-resistant coating layer.

[0093] Water resistance and oil resistance of the prepared moisture-resistant biodegradable sheet are evaluated and shown in Table 1.Example 3

[0094] A biodegradable sheet is prepared in the same manner as in Example 1 except that lengths of the first and second fibers are adjusted as shown in Table 1 below. In other words, a biodegradable sheet is prepared in the same manner as in Example 1 except that 4 wt % of the first fibers having an average length of 2 mm and 6 wt % of the second fibers having an average length of 10 mm are mixed and used.

[0095] Physical properties of the prepared biodegradable sheet are measured and are shown in Table 1 below.

[0096] The chitosan solution prepared in Example 1 is spray-coated on both sides of the prepared biodegradable sheet twice at a flow rate of 10 ml / min, and dried at 200° C. for 40 minutes, thereby forming a moisture-resistant coating layer.

[0097] Water resistance and oil resistance of the prepared moisture-resistant biodegradable sheet are evaluated and shown in Table 1.Comparative Example 1

[0098] A biodegradable sheet is prepared in the same manner as in Example 1 except that lengths of the first and second fibers are adjusted as shown in Table 1 below. In other words, a biodegradable sheet and a moisture-resistant biodegradable sheet are prepared in the same manner as in Example 1 except that 7 wt % of the first fibers having an average length of 1 mm and 3 wt % of the second fibers having an average length of 15 mm are mixed and used.

[0099] Physical properties of the prepared biodegradable sheet are measured and are shown in Table 1 below.Comparative Example 2

[0100] A biodegradable sheet is prepared in the same manner as in Example 1 except that lengths of the first and second fibers are adjusted as shown in Table 1 below. In other words, a biodegradable sheet and a moisture-resistant biodegradable sheet are prepared in the same manner as in Example 1 except that 1 wt % of the first fibers having an average length of 7 mm and 9 wt % of the second fibers having an average length of 10 mm are mixed and used.

[0101] Physical properties of the prepared biodegradable sheet are measured and are shown in Table 1 below.Comparative Example 3

[0102] A sheet is prepared in the same manner as in Example 1 except that the second fibers having an average length of 4 mm and obtained from wood without using seaweed fibers are solely used to prepare the sheet.

[0103] In addition, the prepared sheet is coated with the same chitosan solution as in Example 1 by using the same manner. As a result, it is confirmed that the Cobb value is 40 g / m2, and the water resistance slightly increased compared to before coated with the chitosan solution, but the water resistance is lower than in Example 1. Accordingly, it is estimated that water resistance is slightly exhibited through the effect of chitosan physically filling microscopic spaces present in the sheet, and Example 1 is estimated that seaweed fibers are included to cause the interaction between the seaweed fibers and chitosan, so that the water resistance is further improved.TABLE 1ExampleExampleExampleComparativeComparative123Example 1Example 2First fibers:Second3:75:54:67:31:9fibers(Weight ratio)L1(mm)22217L2(mm)44101510L1 / L20.50.50.20.070.6Bulk density(g / cm3)0.60.50.41.30.2Moisture content555112based on dryweight(wt %)AerobicPassPassPassFailFailbiodegradability testBasis weight(g / m2)6005004001300200Elongation (%)2.41.62.21.11.3TensileBefore7.356.537.204.83.5strengthcoating(KN / cm2)After8.9678.03198.7125.043.71coatingTearBefore49904480465038603950strengthcoating(mN)After61375465571940914147coatingBurstingBefore537560542345336strengthcoating(kPa)After687716430365369coatingWater resistance282828——Cobb value(g / m2)Oil111——resistance(Rating)

[0104] In Table 1, ‘Before coating’ refers to the properties of the biodegradable sheet before the moisture-resistant coating layer is formed, and ‘After coating’ refers to the properties of the moisture-resistant biodegradable sheet after the moisture-resistant coating layer is formed.

[0105] As shown in Table 1, it is confirmed that the biodegradable sheet according to the present invention has the excellent mechanical properties, and is biodegradable within 60 days in the aerobic biodegradability test. In addition, as shown in FIGS. 1 to 3, it is confirmed that the prepared biodegradable sheet has two surfaces with surface roughness different from each other and a density gradient. Specifically, it is confirmed that the web density is increased from the first surface having a low surface roughness to the second surface. Accordingly, it is confirmed that the sheet is prepared to have excellent mechanical strength as well as flexibility. In addition, it is confirmed that it has resistance to moisture since the average Cobb value is 25 g / m2 in the water resistance evaluation. In addition, it is confirmed that the kit rating is 1 or higher in the oil resistance evaluation, which signifies exhibition of oil resistance because the surface is not stained in 15 seconds when being exposed to a single droplet of pure castor oil.

[0106] In addition, it is confirmed that the tensile strength, the tear strength and the bursting strength are improved by 20% or more after the chitosan composition is coated, and it is confirmed that the surface is formed more smoothly.

[0107] In addition, when the moisture-resistant coating layer is coated with the chitosan composition, immersed in water at 80° C. for 10 minutes and taken out and then the water is analyzed, an amount of leached chitosan is very insignificant, which signifies that chitosan is firmly bound to the biodegradable sheet. This is estimated that the interaction between chitosan and seaweed fibers is very large due to electrostatic bonding.

[0108] It is confirmed that, when the average lengths between the first and second fibers are different significantly as in Comparative Example 1, bulk density is high, it exceeded 60 days in the aerobic biodegradability test, and mechanical properties are deteriorated.

[0109] It is confirmed that, even when the first fibers have low contents as in Comparative Example 2, it exceeded 60 days in the aerobic biodegradability test, and bulk density is low, and mechanical properties are deteriorated.

[0110] The present invention has been described with reference to limited examples and particular items, and it shall be understood that the above description has been merely provided for further understanding the invention, and the present invention is not limited to the above examples. It will be understood by those skilled in the art that various changes and modifications may be carried out from the above-mentioned description.

[0111] Therefore, the idea of the present invention will not be determined by the aforementioned embodiments only, and the following claims as well as all modifications or variations belonging to the equivalents of the claims will be within the scope of the invention.

Claims

1. A moisture-resistant biodegradable sheet comprising:a biodegradable sheet in a form of a web in which first fibers obtained from seaweed and second fibers obtained from wood and plant are networked together, whereina ratio L1 / L2 of an average length (L1) of the first fibers to an average length (L2) of the second fibers is 0.1 to 0.5,the first fibers are uniformly inserted into an upper portion and pores of the web composed of the second fibers, andthe biodegradable sheet has a moisture content of 10 wt % or less with respect to dry weight and a bulk density of 0.4 to 1.2 g / cm3; anda moisture-resistant coating layer formed by coating or impregnating on one or both sides of the biodegradable sheet.

2. The moisture-resistant biodegradable sheet of claim 1, wherein the biodegradable sheet is biodegraded within 60 days in aerobic biodegradability test according to ISO 14855-1:2012.

3. The moisture-resistant biodegradable sheet of claim 1, wherein the biodegradable sheet has both surfaces with surface roughness different from each other.

4. The moisture-resistant biodegradable sheet of claim 3, wherein the surface of the biodegradable sheet has a large surface roughness serving as a first surface, in which a density gradient is configured to have a web density increasing from the first surface to a second surface.

5. The moisture-resistant biodegradable sheet of claim 1, wherein L1 is 1 to 5 mm, and L2 is 2 to 10 mm.

6. The moisture-resistant biodegradable sheet of claim 1, wherein the biodegradable sheet has a basis weight of 400 to 800 g / m2.

7. The moisture-resistant biodegradable sheet of claim 1, wherein the biodegradable sheet includes 50 wt % or less of the first fibers.

8. The moisture-resistant biodegradable sheet of claim 1, wherein the biodegradable sheet is obtained by molding and then drying a pulp liquid formed by mixing the first fibers, the second fibers and water.

9. The moisture-resistant biodegradable sheet of claim 8, wherein the mold is formed by maintaining a moisture content of a sheet at 30 to 50 wt %, and maintaining a moisture content at 5 wt % or less after drying.

10. The moisture-resistant biodegradable sheet of claim 9, wherein a residual moisture in the sheet after drying forms hydroxyl groups to induce hydrogen bonding.

11. The moisture-resistant biodegradable sheet of claim 8, wherein the water in the pulp liquid has a content of 80 to 98 wt %.

12. The moisture-resistant biodegradable sheet of claim 1, wherein the first fibers are formed of seaweed pulp obtained by crushing dried seaweed and mixing, dissociating and stirring the crushed seaweed in water, and the second fibers are formed of wood pulp obtained by dissociating wood and plants.

13. The moisture-resistant biodegradable sheet of claim 1, wherein the seaweed includes one selected from Gracilaria Lichenoides and Sargassum Horneri, or a mixture thereof.

14. The moisture-resistant biodegradable sheet of claim 1, wherein the biodegradable sheet has tensile strength of 5 KN / cm2 or more and elongation of 1.5% or more according to ISO 1924-2, tear strength of 4000 mN or more according to ISO 1974, and bursting strength of 350 kPa or more according to ISO 2758.

15. The moisture-resistant biodegradable sheet of claim 1, wherein the moisture-resistant coating layer has a Cobb value of 30 g / m2 or less according to TAPPI T441, and a kit rating of 1 or higher according to TAPPI 559.

16. The moisture-resistant biodegradable sheet of claim 1, wherein the moisture-resistant coating layer is formed by applying or impregnating a chitosan solution containing chitosan having a molecular weight of 50,000 to 400,000 Da.

17. A molded body comprising a moisture-resistant biodegradable sheet selected from claim 1.

18. The molded body of claim 17, wherein the molded body includes a food container.

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