Microfibrillated cellulose molded body and method for producing microfibrillated cellulose molded body

Abstract

This microfibrillated cellulose molded body is composed of microfibrillated cellulose and a melamine resin. The content ratio of the melamine resin is 20.0 mass% or more, and the water absorption rate when immersed in water at 20°C for 24 hours is 1.6% or less.

Description

Microfibrillated cellulose body and method for producing the same

[0001] The present disclosure relates to a microfibrillated cellulose body and a method for producing a microfibrillated cellulose body.

[0002] A high-strength material using cellulose microfibrils is disclosed in Japanese Patent No. 3641690 (Patent Document 1). Also, a method for producing a molded article of microfibrillated cellulose is disclosed in Japanese Patent Laid-Open No. 2009-96167 (Patent Document 2).

[0003] Japanese Patent No. 3641690 Japanese Patent Application Laid-Open No. 2009-96167

[0004] Microfibrillated cellulose molded articles have relatively high strength and are used in a variety of environments, but they are required to have high dimensional stability. Of course, when considering environmental resistance, it is desirable for materials to be adopted that contain as few substances as possible other than microfibrillated cellulose. The techniques disclosed in Patent Documents 1 and 2 described above have difficulty in addressing these problems.

[0005] Therefore, one of the objects is to provide a microfibrillated cellulose molded article that has good environmental resistance and can achieve high dimensional stability.

[0006] The microfibrillated cellulose molded article according to the present disclosure is composed of microfibrillated cellulose and a melamine resin, the melamine resin content is 20.0% by mass or more, and the water absorption rate when immersed in water at 20°C for 24 hours is 1.6% or less.

[0007] Such a microfibrillated cellulose molded article has good environmental resistance and can achieve high dimensional stability.

[0008] Fig. 1 is a schematic perspective view showing the configuration of a microfibrillated cellulose molded body according to one embodiment of the present disclosure. Fig. 2 is a schematic cross-sectional view of the microfibrillated cellulose molded body shown in Fig. 1. Fig. 3 is a flowchart showing typical production steps in a method for producing a microfibrillated cellulose molded body according to one embodiment of the present disclosure. Fig. 4 is a schematic cross-sectional view showing an example of a first preformed sheet. Fig. 5 is a schematic cross-sectional view of the first preformed sheet shown in Fig. 4. Fig. 6 is a schematic cross-sectional view showing the first preformed sheet being swollen with water. Fig. 7 is a schematic cross-sectional view showing the first preformed sheet immersed in a solution containing a melamine resin. Fig. 8 is a schematic cross-sectional view during heat pressing. Fig. 9 is a schematic cross-sectional view of four sheets of microfibrillated cellulose-containing composition stacked together and heat pressed.

[0009] [Description of Embodiments of the Present Disclosure] Hereinafter, embodiments of the present disclosure will be described. A microfibrillated cellulose molded article according to the present disclosure is composed of microfibrillated cellulose and a melamine resin. The melamine resin content is 20.0% by mass or more. The water absorption rate when immersed in water at 20°C for 24 hours is 1.6% or less.

[0010] The microfibrillated cellulose molded body (hereinafter sometimes simply referred to as "molded body") according to the present disclosure is composed of microfibrillated cellulose and melamine resin. Because the only material other than microfibrillated cellulose in such a microfibrillated cellulose molded body is melamine resin, it can have good environmental resistance. Furthermore, in such a microfibrillated cellulose molded body with a very high melamine resin content, the melamine resin is sufficiently embedded between the microfibrillated cellulose fibers, resulting in very few voids between the fibers through which moisture can penetrate. As a result, even when exposed to a humid environment, it hardly absorbs moisture. Therefore, high dimensional stability can be achieved.

[0011] Furthermore, the microfibrillated cellulose molded article according to the present disclosure is composed of microfibrillated cellulose, a melamine resin, and a dye. The melamine resin content is 20.0% by mass or more. The dye content is 0.3% or more. The water absorption rate when immersed in water at 20°C for 24 hours is 0.6% or less. Recently, there has been a demand for microfibrillated cellulose molded articles that can be colored in various colors. Melamine resin is colorless and transparent, making it easy to achieve color development with dyes. By employing a microfibrillated cellulose molded article having the above configuration, it is possible to obtain a microfibrillated cellulose molded article that has good environmental resistance, high dimensional stability, and is colored in a desired color.

[0012] In the microfibrillated cellulose article, the content of the melamine resin may be 31% by mass or less, which makes it possible to more reliably achieve good environmental resistance and high dimensional stability.

[0013] The microfibrillated cellulose article may have a water absorption rate of 0.6% or less, which allows the microfibrillated cellulose article to achieve even higher dimensional stability.

[0014] The microfibrillated cellulose molded article according to the present disclosure is in the form of a plate and is composed of microfibrillated cellulose and a melamine resin, the melamine resin content being 20.0% by mass or more, and the dimensional change in the thickness direction when immersed in water at 20°C for 24 hours is 0.6% or less.

[0015] Such a microfibrillated cellulose molded article can absorb moisture even in a high humidity environment, reducing the risk of swelling, resulting in insufficient strength, and warping, thereby providing a microfibrillated cellulose molded article with improved convenience.

[0016] The microfibrillated cellulose molded article according to the present disclosure is in the form of a plate and is composed of microfibrillated cellulose, a melamine resin, and a dye. The melamine resin content is 20.0% by mass or more. The dimensional change in the thickness direction when immersed in water at 20°C for 24 hours is 0.2% or less.

[0017] Such a microfibrillated cellulose molded article has good colorability and can absorb moisture even in a high humidity environment, reducing the risk of swelling, resulting in insufficient strength, and warping, thereby providing a microfibrillated cellulose molded article with improved usability.

[0018] The microfibrillated cellulose article may have a flexural modulus of 13.0 GPa or more. Such a microfibrillated cellulose article can be made less prone to deformation, improving its usability as a material.

[0019] The microfibrillated cellulose article may have a longitudinal dimensional change of 0.1% or less when immersed in water at 20° C. for 24 hours. Such a microfibrillated cellulose article can achieve high dimensional stability and can also be made more convenient as a material.

[0020] The method for producing a microfibrillated cellulose molded body according to the present disclosure is a method for producing a microfibrillated cellulose molded body composed of microfibrillated cellulose and melamine resin, and includes the steps of preparing a first preformed sheet composed of microfibrillated cellulose and 0% to 10% by mass of water; exposing the first preformed sheet to water for one hour or more to cause swelling, thereby obtaining a second preformed sheet; substituting the water contained in the second preformed sheet with a solution containing melamine resin, thereby obtaining a third preformed sheet; drying the obtained third preformed sheet; and hot-pressing the dried third preformed sheet at a temperature of 120°C to 200°C, applying a pressure of 1 MPa to 10 MPa in the thickness direction.

[0021] The method for producing a microfibrillated cellulose molded article according to the present disclosure includes the steps of preparing a first preformed sheet composed of microfibrillated cellulose and 0% to 10% by mass of water, exposing the first preformed sheet to water for at least one hour to swell the sheet, and obtaining a second preformed sheet. Because water has a high affinity for cellulose, it can penetrate sufficiently between the compressed microfibrillated cellulose fibers in the first preformed sheet, sufficiently swelling the first preformed sheet to obtain a second preformed sheet. The method then includes the step of substituting the water contained in the second preformed sheet with a solution containing a melamine resin to obtain a third preformed sheet. Since the second preformed sheet is sufficiently swollen by the water and the spacing between the microfibrillated cellulose fibers is widened, the solution containing the melamine resin can be sufficiently permeated between the microfibrillated cellulose fibers. That is, the water present between the microfibrillated cellulose fibers can be substituted with the solution containing the melamine resin, thereby disposing the solution containing the melamine resin between the microfibrillated cellulose fibers. The resulting product is then dried and heat-pressed at a temperature of 120°C to 200°C under a pressure of 1 MPa to 10 MPa in the thickness direction, thereby thermosetting the melamine resin between the microfibrillated cellulose fibers and obtaining a microfibrillated cellulose molded body. Because the melamine resin has sufficiently permeated the spaces between the fibers, the voids between the fibers that allow moisture to penetrate are extremely small. This minimizes moisture absorption even when exposed to a humid environment. Therefore, high dimensional stability can be achieved. Furthermore, because the heat-pressing can be performed at the temperature and pressure described above, high pressures, such as 100 MPa, are not required, resulting in good productivity.

[0022] In the method for producing a microfibrillated cellulose molded article, the hot-pressing step may include a step of hot-pressing a plurality of third preformed sheets one on top of the other. This makes it easier to obtain a microfibrillated cellulose molded article having a desired thickness, and also allows the melamine resin to penetrate more deeply into the microfibrillated cellulose molded article, thereby improving dimensional stability.

[0023] In the method for producing a microfibrillated cellulose article, the step of obtaining the second preformed sheet may include a step of immersing the first preformed sheet in water stored in a container for 1.5 hours to 24 hours, thereby enabling more efficient swelling with water.

[0024] In the method for producing a microfibrillated cellulose article, the third preformed sheet may contain 20.0% by mass or more and 31.0% by mass or less of melamine resin, thereby achieving high dimensional stability while maintaining high strength of the microfibrillated cellulose.

[0025] [Details of the embodiment of the present disclosure] Next, the configuration of a microfibrillated cellulose molded body according to an embodiment of the present disclosure will be described. Fig. 1 is a schematic perspective view showing the configuration of a microfibrillated cellulose molded body according to one embodiment of the present disclosure. Fig. 2 is a schematic cross-sectional view of the microfibrillated cellulose molded body shown in Fig. 1.

[0026] 1 and 2, a microfibrillated cellulose molded body 11 according to an embodiment of the present disclosure may be, for example, in the form of a plate. １ can be, for example, 0.1 mm or more and 2.0 mm or less. The thickness of the molded body 11 is the length from one surface 12a to the other surface 12b in the thickness direction (Z direction) of the microfibrillated cellulose molded body 11. The horizontal direction (width direction) of the molded body 11 is indicated by the X direction, and the vertical direction (depth direction) of the molded body 11 is indicated by the Y direction.

[0027] The microfibrillated cellulose molded body 11 is composed of microfibrillated cellulose and melamine resin. Since the only material other than the microfibrillated cellulose is the melamine resin, this microfibrillated cellulose molded body can have good environmental resistance.

[0028] The microfibrillated cellulose used in the microfibrillated cellulose article 11 according to the present disclosure is also called cellulose nanofiber, and is a microfibrillated cellulose fiber. Examples of raw materials for the microfibrillated cellulose include wood and cotton, which are derived from plants, and examples of raw materials for the microfibrillated cellulose that are derived from animals include chitin and chitosan.

[0029] The fiber diameter of the microfibrillated cellulose used is 10 nm or more and 1000 nm or less. This allows the microfibrillated cellulose to be more densely entangled in the molded body 11. Therefore, the strength of the obtained molded body 11 can be increased.

[0030] The melamine resin may be any known condensate obtained by condensing melamine or its derivatives with formaldehyde, and consisting of a monomer and a dimer or higher polymer. Examples of melamine derivatives include derivatives having an imino group, a methylol group, or an alkoxymethyl group such as a methoxymethyl group or a butoxymethyl group. Furthermore, a compound obtained by reacting a melamine derivative having a methylol group with an alcohol to partially or completely etherify it can also be used as a monomer.

[0031] The melamine resin content is 20.0% by mass or more of the total. Furthermore, the melamine resin content is preferably 31.0% by mass or less of the total. The microfibrillated cellulose content is preferably 69.0% by mass or more and 80.0% by mass or less of the total. By setting the microfibrillated cellulose content to 69.0% by mass or more and 80.0% by mass or less, sufficient strength of the molded body 11 can be ensured. Furthermore, by setting the melamine resin content to 20.0% by mass or more, the melamine resin can be sufficiently permeated between the fibers, reducing voids between the fibers and more reliably achieving high dimensional stability. Furthermore, by setting the melamine resin content to 31.0% by mass or less, high dimensional stability can be more reliably achieved while improving environmental resistance.

[0032] Here, the water absorption rate of the molded body 11 is 1.6% or less when immersed in water at 20°C for 24 hours. Such a molded body 11 can absorb water and reduce the risk of swelling, resulting in insufficient strength, or warping, even in a high humidity environment. Therefore, the molded body 11 can be made more convenient. The water absorption rate may be 0.6% or less. Such a molded body 11 can achieve even higher dimensional stability.

[0033] Furthermore, the dimensional change rate of the molded body 11 in the thickness direction when immersed in water at 20°C for 24 hours (hereinafter, sometimes referred to as "thickness change rate") is 0.6% or less. Such molded body 11 can absorb moisture and reduce the risk of swelling, resulting in insufficient strength, or warping, even in a high humidity environment. Therefore, the molded body 11 can be made more convenient. The thickness change rate may be 0.4% or less. Such molded body 11 can achieve even higher dimensional stability.

[0034] Furthermore, the dimensional change rate of the molded body 11 in the length direction when immersed in water at 20°C for 24 hours (hereinafter, sometimes referred to as "length change rate") is 0.1% or less. Such molded body 11 can absorb moisture and reduce the risk of swelling, resulting in insufficient strength, or warping, even in a high humidity environment. Therefore, the molded body 11 can be made more convenient. The length change rate may be 0.06% or less. Such molded body 11 can achieve even higher dimensional stability.

[0035] Furthermore, the content of the melamine resin in the molded body 11 is 20.0 mass % or more and 31.0 mass % or less, so that the molded body 11 can be made more reliably more convenient.

[0036] The molded body 11 has a flexural modulus of 13.0 GPa or more. Such molded body 11 can achieve high strength and further improve the convenience as a material. The flexural modulus may be 14.0 GPa or more.

[0037] The molded body 11 has a bending strength of 210 MPa or more. Such a molded body 11 can achieve high strength and further improve the convenience as a material. The bending strength may be 230 MPa or more.

[0038] The molded article may also be composed of microfibrillated cellulose, a melamine resin, and a dye. The melamine resin content may be 20.0% by mass or more. The dye content may be 0.3% or more. The water absorption rate when immersed in water at 20°C for 24 hours may be 0.6% or less. Recently, there has been a demand for microfibrillated cellulose molded articles that can be colored in various colors. Melamine resin has relatively high transparency, making it easy to achieve color development with dyes. By using a molded article having the above configuration, it is possible to obtain a molded article that is colored in a desired color while achieving good environmental resistance and high dimensional stability.

[0039] Next, a description will be given of a manufacturing method for manufacturing such a molded body 11. Fig. 3 is a flowchart showing typical manufacturing steps in a manufacturing method for a microfibrillated cellulose molded body according to one embodiment of the present disclosure.

[0040] Referring to Fig. 3, first, a first preformed sheet is prepared (step S11 in Fig. 3, hereinafter "step" will be omitted). The first preformed sheet is composed of microfibrillated cellulose and 0% by mass or more and 10% by mass or less of water.

[0041] Fig. 4 is a schematic cross-sectional view showing an example of a first preformed sheet. Fig. 5 is a schematic cross-sectional view of the first preformed sheet shown in Fig. 4. Referring to Figs. 4 and 5, the first preformed sheet 21a is in a sheet shape and has a thickness T ２ The thickness of the microfibrillated cellulose-containing composition is, for example, 0.1 mm or more and 0.5 mm or less. The first preformed sheet 21a can be obtained, for example, as follows. First, a dispersion liquid in which microfibrillated cellulose is dispersed in water is prepared, and this dispersion liquid is subjected to suction filtration to form a sheet, thereby obtaining a microfibrillated cellulose-containing composition having a moisture content of, for example, 65% by mass or more and 85% by mass or less. This microfibrillated cellulose-containing composition is compressed in the thickness direction to remove a certain amount of moisture, thereby obtaining a first preformed sheet 21a having a solid content of 90% by mass or more and 100% by mass or less. Multiple first preformed sheets are obtained in the same manner.

[0042] Next, the first preformed sheet 21a is exposed to water for at least one hour to swell, thereby obtaining a second preformed sheet (S12). Fig. 6 is a schematic cross-sectional view showing the state in which the first preformed sheet 21a is swollen by water.

[0043] Referring to FIG. 6 , in this step, a container 13 containing water 14 is first prepared. Then, a first preformed sheet 21a is immersed. Specifically, the first preformed sheet 21a is placed in the water 14 in the container 13 so that the entire surface of the first preformed sheet 21a is immersed in the water 14. In this manner, the first preformed sheet 21a is exposed to water. Thereafter, the first preformed sheet 21a is left for a predetermined time. Specifically, the first preformed sheet 21a is immersed in water 14 at a temperature of 20°C and left for 24 hours. As a result, the first preformed sheet 21a swells with the water 14. That is, the water 14 penetrates between the fibers of the microfibrillated cellulose that constitute the microfibrillated cellulose-containing composition. In this manner, a second preformed sheet is obtained. The second preformed sheet swells mainly in the thickness direction. The step of obtaining the second preformed sheet may include a step of immersing the first preformed sheet in water stored in a container for 72 hours or less. By doing so, swelling with water can be carried out more efficiently.

[0044] The thickness of the second preformed sheet may be 160% or more of the thickness of the first preformed sheet 21a, which makes it easier to impregnate the sheet with melamine resin and more reliably achieves high dimensional stability.

[0045] Next, the water contained in the second preformed sheet is replaced with a solution containing a melamine resin to obtain a third preformed sheet (S13). Fig. 7 is a schematic cross-sectional view showing the state after immersion in the solution containing a melamine resin.

[0046] 7, in this step, a container 15 is prepared that contains a solution 16 containing a melamine resin. Then, a second preformed sheet 23a is immersed in the solution 16. Specifically, the second preformed sheet 23a is placed in the solution 16 in the container 15 so that the entire surface of the second preformed sheet 23a is immersed in the solution 16.

[0047] Here, for example, an aqueous solution of melamine resin is used as the solution 16 containing melamine resin. That is, the solution 16 containing melamine resin contains water. In addition to water, water-soluble organic solvents such as methanol, ethanol, and isopropanol can be used. Furthermore, a mixture of water and a water-soluble organic solvent may also be used.

[0048] Next, the obtained third preformed sheet is dried (S14). The drying step is carried out, for example, by leaving it at room temperature (25° C.) for 24 hours.

[0049] Next, the dried third preformed sheet is heat-pressed at a temperature of 120° C. to 200° C. and a pressure of 1 MPa to 10 MPa in the thickness direction (S15). In this case, the heat-pressing step includes a step of heat-pressing a plurality of third preformed sheets one on top of the other. Fig. 8 is a schematic cross-sectional view of the heat-pressing step.

[0050] 8, the two prepared third preformed sheets 24a, 24b are placed one on top of the other between a pair of metal plates 17a, 17b heated to a temperature of 120° C. or more and 200° C. or less. １ A pressure of 1 MPa to 10 MPa is applied in the direction indicated by the arrow A. Specifically, for example, the temperature of the metal plates 17a and 17b is set to 150° C., and a pressure of 6.5 MPa is applied for 1.5 hours.

[0051] In this manner, a microfibrillated cellulose molded body 11 according to the present disclosure, as shown in FIG. 1 , is obtained. The microfibrillated cellulose molded body 11 produced by the above-described method for producing a microfibrillated cellulose molded body 11 is composed of microfibrillated cellulose and melamine resin. Because the only material other than microfibrillated cellulose in this microfibrillated cellulose molded body 11 is melamine resin, it can have good environmental resistance. The above-described method for producing a microfibrillated cellulose molded body also includes the steps of preparing a first preformed sheet 21a composed of microfibrillated cellulose and 0% to 10% by mass of water, exposing the first preformed sheet 21a to water for at least one hour to swell it, and obtaining a second preformed sheet 23a. Because water has a high affinity for cellulose, it can sufficiently penetrate between the fibers of the compressed microfibrillated cellulose in the first preformed sheet 21a, thereby sufficiently swelling the first preformed sheet 21a and obtaining the second preformed sheet 23a. Next, the method includes a step of substituting the water contained in the second preformed sheet with a solution containing a melamine resin to obtain a third preformed sheet. Here, the second preformed sheet is sufficiently swollen by the water, and the spacing between the microfibrillated cellulose fibers is widened, allowing the solution containing the melamine resin to thoroughly permeate the spaces between the microfibrillated cellulose fibers. That is, the water between the microfibrillated cellulose fibers is substituted with the solution containing the melamine resin, and the solution containing the melamine resin is disposed between the microfibrillated cellulose fibers. The resulting sheet is then dried and heat-pressed at a temperature of 120°C to 200°C and a pressure of 1 MPa to 10 MPa in the thickness direction to thermally cure the melamine resin between the microfibrillated cellulose fibers, thereby obtaining a microfibrillated cellulose molded body. In such a microfibrillated cellulose molded body, the melamine resin has sufficiently permeated the spaces between the fibers, minimizing the number of voids between the fibers that allow moisture to penetrate. This results in almost no moisture absorption, even when exposed to a humid environment. Therefore, high dimensional stability can be achieved.Furthermore, since the heat pressing can be carried out at the temperature and pressure described above, a high pressure such as 100 MPa is not required, and productivity is good.

[0052] As described above, such a method for producing a microfibrillated cellulose article has good productivity and can achieve high dimensional stability of the obtained microfibrillated cellulose article.

[0053] In this case, since the process includes a step of stacking and hot pressing multiple third preformed sheets 24a, 24b, it is easier to obtain a microfibrillated cellulose molded body 11 having the desired thickness, and the melamine resin can be more thoroughly permeated into the interior of the microfibrillated cellulose molded body 11, thereby improving dimensional stability.

[0054] Alternatively, the present invention may be produced as follows. The step of preparing a first preformed sheet includes a step of stacking and hot-pressing a plurality of sheets of a microfibrillated cellulose-containing composition made of microfibrillated cellulose to obtain a first preformed sheet. Fig. 9 is a schematic cross-sectional view of four sheets of a microfibrillated cellulose-containing composition stacked and hot-pressed.

[0055] Referring to FIG. 9, four sheets of microfibrillated cellulose-containing compositions 25a, 25b, 25c, and 25d are stacked and arranged between metal plates 18a and 18b. ２ Pressure is applied in the direction indicated by the arrow to obtain a first preformed sheet. The preformed sheet thus obtained is used to obtain a second preformed sheet in the same manner as above. After obtaining a third preformed sheet, heat pressing is performed to obtain a molded body 11.

[0056] In this case, it is possible to easily obtain a microfibrillated cellulose molded article having a desired thickness, thereby improving productivity.

[0057] In the above embodiment, the first preformed sheet is exposed to water and caused to swell by being immersed in water stored in a container, but this is not limited to this, and swelling with water can also be achieved by exposing the first preformed sheet to running water.

[0058] In the above embodiment, if the microfibrillated cellulose molding further contains a dye, a water-soluble dye may be added to a solution containing melamine resin and adjusted to a desired dye content, thereby producing a microfibrillated cellulose molding further containing a dye.

[0059] In the above embodiment, urea-melamine resin may be used instead of melamine resin.

[0060] In the above embodiment, a first preformed sheet is prepared, the first preformed sheet is exposed to water for at least one hour to swell the first preformed sheet to obtain a second preformed sheet, and the water contained in the second preformed sheet is then replaced with a solution containing a melamine resin to obtain a third preformed sheet. However, this is not limited to this, and the step of obtaining the second preformed sheet may be omitted. That is, after preparing the first preformed sheet, the sheet may be exposed to a solution containing a melamine resin rather than being exposed to water, and the solution containing the melamine resin may be allowed to permeate between the fibers of the microfibrillated cellulose to obtain a third preformed sheet. Sample 6, described below, was produced using this method.

[0061] Molded articles were molded according to the formulations and methods shown in Samples 1 to 10, and evaluation tests were conducted. The evaluation results are shown in Table 1. Samples 1 to 7 fall within the scope of the present invention. Samples 8 to 10 fall outside the scope of the present invention.

[0062] (Sample 1) Microfibrillated cellulose (BiNFi-S BMa10010 manufactured by Sugino Machine Co., Ltd.: fiber diameter 10 nm to 50 nm) dispersed in water at a concentration of 10% by mass was prepared. The resulting mixture was diluted with water to 1% by mass, and then filtered to remove water until the water content reached 85% by mass, yielding a sheet-like MFC-containing composition having a thickness of 2.0 mm.

[0063] Next, one sheet of this MFC-containing composition was applied to a substrate with a basis weight of 47 g / cm ２ The resulting sheet was sandwiched between two sheets of glass nonwoven fabric, sandwiched between two stainless steel metal plates, and heated and pressurized at 150°C for 2 hours to obtain a first preformed sheet. The pressure was increased stepwise from 0.5 MPa to a final pressure of 4 MPa. The resulting first preformed sheet had a thickness of 0.4 mm and a moisture content of 0% to 10% by mass.

[0064] The first preformed sheet was immersed in water at a temperature of 20° C. for 24 hours to obtain a second preformed sheet, which had a thickness of 0.7 mm.

[0065] Next, the second preformed sheet was immersed for 24 hours in a melamine resin solution (solid content 40% by mass) prepared by dissolving a water-soluble methylol melamine resin (Nikaredin S-260 manufactured by Nippon Carbide Industries Co., Ltd.) in warm water at 40°C, to obtain a third preformed sheet.

[0066] The resulting third preformed sheet was then dried for 24 hours at room temperature (25° C.) Two dried third preformed sheets were sandwiched between two stainless steel metal plates and subjected to heat and pressure molding at 150° C. and a pressure of 6.5 MPa for 1 hour to obtain a molded product composed of microfibrillated cellulose and melamine resin.

[0067] The obtained molded body was milky white, had a thickness of 1.0 mm, and a density of 1.41 g / cm ３ The content of melamine resin was 30.3% by mass. In addition, under an environment of a temperature of 20°C and a relative humidity of 65%, the flexural modulus was 14.2 GPa and the flexural strength was 247 MPa. When immersed in water at 20°C for 24 hours, the water absorption was 0.6% and the dimensional change in the thickness direction was 0.3%. When immersed in water at 20°C for 24 hours, the dimensional change in the length direction (hereinafter sometimes referred to as "length change") was 0.06%.

[0068] The water absorption rate was determined by the following method in accordance with "JIS A5905." A test piece (10 cm x 10 cm) of the molded product was cured in advance in an environment of a temperature of 20°C and a relative humidity of 65% for 72 hours or more, and then immersed in water at 20°C for 24 hours. The mass (W １ ) and the mass of the test piece after immersion (W ２ ) and the water absorption rate was calculated by the following formula (1).

[0069] Water absorption rate (%) = ((W ２ -W １ ) / W １ ) × 100 ... (1)

[0070] The thickness change rate was determined by the following method in accordance with "JIS A5905." A test piece (10 cm x 10 cm) of the molded product, which had been cured in advance for 72 hours or more in an environment of a temperature of 20°C and a relative humidity of 65%, was immersed in water at 20°C for 24 hours. The thickness of the test piece before immersion (T １ ) and the thickness of the test piece after immersion (T ２ ) and the thickness change rate was calculated by the following formula (2).

[0071] Thickness change rate (%) = ((T ２ -T １ ) / T １ ) x 100... (2)

[0072] The length change rate was determined by the following method in accordance with "JIS A5905." A test piece (10 cm x 10 cm) of the molded product, which had been cured in advance for 72 hours or more in an environment of a temperature of 20°C and a relative humidity of 65%, was immersed in water at 20°C for 24 hours. After that, the length of one side of the test piece before immersion (L １ ) and the length of one side of the test piece after immersion (L ２ ) and the length change rate was calculated by the following formula (3). １ ), length (L ２ ) The length of one side of the test piece was determined by the larger rate of change in the vertical or horizontal direction.

[0073] Length change rate (%) = ((L ２ -L １ ) / L １) × 100 ... (3)

[0074] The flexural modulus, flexural strength and density of this molded product were measured in accordance with JIS-K6911. The same applies to the measurements of the following samples.

[0075] (Sample 2) A molded body was obtained in the same manner as Sample 1, except that a third preformed sheet was obtained by immersing the sheet in an aqueous melamine resin solution (solid content: 40% by mass) for 1.5 hours. The obtained molded body was milky white, had a thickness of 0.95 mm, and a density of 1.39 g / cm. ３ The melamine resin content was 21.6% by mass. Furthermore, under an environment of a temperature of 20°C and a relative humidity of 65%, the flexural modulus was 15.4 GPa and the flexural strength was 225 MPa. Furthermore, when immersed in water at 20°C for 24 hours, the water absorption was 1.6%, and the length change rate and thickness change rate were 0.09% and 0.6%, respectively.

[0076] (Sample 3) A molded body was obtained in the same manner as Sample 1, except that a third preformed sheet was obtained by immersing the sample in an aqueous melamine resin solution (solid content: 40% by mass) for 3 hours. The obtained molded body was milky white, had a thickness of 1.0 mm, and a density of 1.41 g / cm ３ The melamine resin content was 25.7% by mass. Furthermore, under an environment of a temperature of 20°C and a relative humidity of 65%, the flexural modulus was 15.1 GPa and the flexural strength was 213 MPa. Furthermore, when immersed in water at 20°C for 24 hours, the water absorption was 1.1%, and the length change and thickness change were 0.07% and 0.4%, respectively.

[0077] (Sample 4) A molded body was obtained in the same manner as Sample 1, except that eight third preformed sheets were stacked and molded under heat and pressure. The obtained molded body was milky white, had a thickness of 4.0 mm, and a density of 1.41 g / cm ３The melamine resin content was 30.3% by mass. Furthermore, under an environment of a temperature of 20°C and a relative humidity of 65%, the flexural modulus was 14.2 GPa and the flexural strength was 247 MPa. Furthermore, when immersed in water at 20°C for 24 hours, the water absorption was 0.3%, and the length change rate and thickness change rate were 0.04% and 0.2%, respectively.

[0078] (Sample 5) A molded body was obtained in the same manner as Sample 1, except that 20 sheets of the third preformed sheet were stacked and molded under heat and pressure. The obtained molded body was milky white, had a thickness of 10.0 mm, and a density of 1.41 g / cm ３ The melamine resin content was 30.3% by mass. Furthermore, under an environment of a temperature of 20°C and a relative humidity of 65%, the flexural modulus was 14.2 GPa and the flexural strength was 247 MPa. Furthermore, when immersed in water at 20°C for 24 hours, the water absorption was 0.2%, and the length change rate and thickness change rate were 0.02% and 0.2%, respectively.

[0079] (Sample 6) A molded body was obtained in the same manner as Sample 1, except that the first preformed sheet was not immersed in water at a temperature of 20° C. The obtained molded body was milky white, had a thickness of 1.0 mm, and a density of 1.42 g / cm ３ The melamine resin content was 29.1% by mass. Furthermore, under an environment of a temperature of 20°C and a relative humidity of 65%, the flexural modulus was 13.7 GPa and the flexural strength was 218 MPa. Furthermore, when immersed in water at 20°C for 24 hours, the water absorption was 0.8%, and the length change rate and thickness change rate were 0.09% and 0.4%, respectively.

[0080] (Sample 7) A molded body was obtained in the same manner as Sample 1, except that 1 part by weight of a water-soluble black dye ("Direct Fast Black B 300%" manufactured by Okamoto Dye Co., Ltd.) was further added to the melamine resin solution. The obtained molded body was black, had a thickness of 1.0 mm, and a density of 1.39 g / cm ３The melamine resin content was 28.8% by mass. The dye content was 0.3% by mass. In addition, under an environment of a temperature of 20°C and a relative humidity of 65%, the flexural modulus was 13.4 GPa and the flexural strength was 230 MPa. When immersed in water at 20°C for 24 hours, the water absorption was 0.6%, and the length change and thickness change were 0.02% and 0.2%, respectively.

[0081] (Sample 8) Two sheets of a microfibrillated cellulose-containing composition, each having a moisture content of 85% by mass and a thickness of 2.5 mm, were laminated and molded under heat and pressure at a press temperature of 150°C, a press pressure of 4 MPa, and a press time of 2 hours to obtain a molded product. The obtained molded product was milky white, had a thickness of 1.0 mm, and a density of 1.33 g / cm. ３ In addition, under an environment of a temperature of 20°C and a relative humidity of 65%, the flexural modulus was 10.5 GPa and the flexural strength was 146 MPa. When immersed in water at 20°C for 24 hours, the water absorption rate was 55.8%, and the length change rate and thickness change rate were 0.94% and 62.0%, respectively.

[0082] (Sample 9) A molded body was obtained in the same manner as Sample 1, except that a phenolic resin was used instead of the melamine resin. The obtained molded body was brown in color, had a thickness of 1.0 mm, and a density of 1.40 g / cm ３ The phenol resin content was 26.5% by mass. Furthermore, under an environment of a temperature of 20°C and a relative humidity of 65%, the flexural modulus was 11.0 GPa and the flexural strength was 245 MPa. Furthermore, when immersed in water at 20°C for 24 hours, the water absorption was 1.9%, and the length change rate and thickness change rate were 0.19% and 1.4%, respectively.

[0083] (Sample 10) A molded body was obtained in the same manner as Sample 1, except that the resin impregnation time was 0.2 hours. The obtained molded body was milky white, had a thickness of 0.9 mm, and a density of 1.38 g / cm ３The melamine resin content was 11.7% by mass. Furthermore, under an environment of a temperature of 20°C and a relative humidity of 65%, the flexural modulus was 13.8 GPa and the flexural strength was 218 MPa. Furthermore, when immersed in water at 20°C for 24 hours, the water absorption was 2.0%, and the length change rate and thickness change rate were 0.12% and 2.0%, respectively.

[0084]

[0085] Referring to Table 1, Samples 1 to 7 all have a melamine resin content of 20.0% by mass or more and a water absorption rate of 1.6% or less. Specifically, the phenolic resin content is 31.0% by mass or less. Furthermore, when immersed in water at 20°C for 24 hours, the dimensional change rate in the thickness direction is 1.6% or less. Furthermore, when immersed in water at 20°C for 24 hours, the dimensional change rate in the length direction is 0.10% or less. Furthermore, the flexural modulus is 13.0 GPa or more. Furthermore, the flexural strength is 210 MPa or more. Furthermore, Samples 1 to 6 are milky white in color, and Sample 7 is black in color. Sample 7 fully expresses the color of the black dye.

[0086] In contrast, Sample 8 does not contain resin, and its water absorption rate is 55.8%, its thickness change rate is 62.0%, and its length change rate is 0.94%. It is believed that the absence of resin at the laminate interface of this molded body allows water to penetrate between the fibers that make up the molded body, resulting in swelling, resulting in increased water absorption rate, thickness change rate, and length change rate. Furthermore, its flexural modulus and flexural strength are also lower than those of Samples 1 to 7.

[0087] Sample 9, which uses phenolic resin instead of melamine resin, has a water absorption rate of 1.9%, a thickness change rate of 1.4%, and a length change rate of 0.19%. It is believed that the phenolic resin cannot sufficiently wet the laminated interface of the molded body, weakening the adhesive strength between the layers and increasing the water absorption rate, thickness change rate, and length change rate. The flexural modulus of Sample 9 is also lower than that of Samples 1 to 7.

[0088] For Sample 10, the resin impregnation time of the melamine resin was short, the resin content was 11.7% by mass, the water absorption rate was 2.0%, the thickness change rate was 2.0%, and the length change rate was 0.12%. For such a molded article, it is thought that the melamine resin was unable to sufficiently wet the laminated interface of the molded article, weakening the adhesive strength between the layers and resulting in large water absorption rates, thickness change rates, and length change rates.

[0089] It should be understood that the embodiments disclosed herein are illustrative in all respects and are not limiting in any respect. The scope of the present invention is defined not by the above description but by the claims, and it is intended to include all modifications within the meaning and scope of the claims.

[0090] 11 Microfibrillated cellulose molded body, 12a, 12b Surface, 13, 15 Container, 14 Water, 16 Solution, 17a, 17b, 18a, 18b Metal plate, 21a First preformed sheet, 23a Second preformed sheet, 24a, 24b Third preformed sheet, 25a, 25b, 25c, 25d Microfibrillated cellulose-containing composition.

Claims

1. A microfibrillated cellulose molding comprising microfibrillated cellulose and melamine resin, the melamine resin content being 20.0% by mass or more, and the water absorption rate when immersed in water at 20°C for 24 hours being 1.6% or less.

2. A microfibrillated cellulose molding comprising microfibrillated cellulose, melamine resin, and a dye, wherein the melamine resin content is 20.0% by mass or more, the dye content is 0.3% or more, and the water absorption rate when immersed in water at 20°C for 24 hours is 0.6% or less.

3. A microfibrillated cellulose molding according to claim 1 or 2, wherein the content of the melamine resin is 31.0 mass% or less.

4. A microfibrillated cellulose molded body according to claim 1 or 2, wherein the water absorption rate is 0.6% or less.

5. A microfibrillated cellulose molding which is in the form of a plate and is composed of microfibrillated cellulose and melamine resin, the content of the melamine resin being 20.0% by mass or more, and the dimensional change in the thickness direction when immersed in water at 20°C for 24 hours is 0.6% or less.

6. A microfibrillated cellulose molding which is in the form of a plate and is composed of microfibrillated cellulose, melamine resin, and a dye, the melamine resin content being 20.0% by mass or more, and the dimensional change in the thickness direction when immersed in water at 20°C for 24 hours is 0.2% or less.

7. A microfibrillated cellulose molding according to claim 5 or 6, having a flexural modulus of 13.0 GPa or more.

8. A microfibrillated cellulose molded article according to claim 5 or 6, which exhibits a dimensional change in the longitudinal direction of 0.1% or less when immersed in water at 20°C for 24 hours.

9. A method for producing a microfibrillated cellulose molded body composed of microfibrillated cellulose and melamine resin, comprising the steps of: preparing a first preformed sheet composed of microfibrillated cellulose and 0% to 10% by mass of water; exposing the first preformed sheet to water for one hour or more to cause it to swell, thereby obtaining a second preformed sheet; replacing the water contained in the second preformed sheet with a solution containing melamine resin, thereby obtaining a third preformed sheet; drying the obtained third preformed sheet; and hot pressing the dried third preformed sheet in the thickness direction at a temperature of 120°C to 200°C, applying a pressure of 1 MPa to 10 MPa.

10. The method for producing a microfibrillated cellulose molded article according to claim 9, wherein the heat pressing step includes a step of heat pressing a plurality of the third preformed sheets in a stack.

11. A method for producing a microfibrillated cellulose molded body as described in claim 9 or claim 10, wherein the step of obtaining the second preformed sheet includes a step of immersing the first preformed sheet in water stored in a container for a period of 1.5 hours or more and 24 hours or less.

12. A method for producing a microfibrillated cellulose molded body as described in claim 9 or claim 10, wherein the content of the melamine resin in the third preformed sheet is 20.0 mass% or more and 31.0 mass% or less.

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