Manufacturing method for molded products

Abstract

To provide a manufacturing method for obtaining a molding having a better mechanical strength using starch and fibers.SOLUTION: A molding manufacturing method includes an accumulation step to accumulate a mixture containing fibers and starch in the air, a humidification step to add water to the mixture, and a molding step to obtain a molding by heating and pressurizing the mixture added with water. The starch has 2000 or more and 10000 or less of a value obtained by measuring by a rapid visco analyser (RVA) according to a measuring method of following (1) to (4) and expressed by a following formula (I): 5000-30×T1-90×(T2-T1)+2×η1-15×η2...(I) (In the formula (I), T1 is gelatinization starting temperature (°C); T2 is gelatinization peak temperature (°C); η1 is gelatinization peak viscosity (mPa s); and η2 is trough viscosity (mPa s)). [Measuring method] (1) 25 mass% aqueous suspension of the starch is introduced to the RVA as a measurement sample, and temperature of the measurement sample is raised to 50°C and held for one minute. (2)The temperature of the measurement sample is raised from 50°C to 93°C in 4 minutes and held at 93°C for 7 minutes. (3) The temperature of the measurement sample is decreased from 93°C to 50°C in 4 minutes and held for 3 minutes at 50°C. (4) In (2) and (3) above, revolution speed of a paddle for measurement of the RVA is set to 960 rpm for 10 seconds after starting viscosity measurement, and 160 rpm after 10 seconds have elapsed.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing a molded body.

Background Art

[0002] It has long been practiced to deposit fibrous substances and allow binding force to act between the deposited fibers to obtain a molded body. For example, as a method for producing molded bodies containing cellulose fibers such as paper, paper plates and paper boards, a method called dry process that uses no or almost no water is expected. Generally, a large amount of water is used when forming paper products, and therefore development is being carried out from the perspective of reducing the amount of water used, among other aspects.

[0003] For example, Patent Document 1 discloses a method for producing cushioning materials and the like, in which waste paper is defibrated into a cotton-like material, mist-like moisture is added thereto, powdery or granular paste material is added, and molding and drying are performed.

Prior Art Literature

Patent Literature

[0004]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0005] However, in dry molding as in Patent Document 1, even if a powdery binding material (starch) is simply mixed with fibers, the resulting molded body may be inferior in strength. Therefore, it is demanded to obtain a molded body with better mechanical strength using starch and fibers.

Means for Solving the Problem

[0006] One aspect of the method for producing a molded body according to the present invention is: a deposition step of depositing a mixture containing fibers and starch in air; a humidification step of applying water to the mixture; A molding process to obtain a molded body by heating and pressurizing the mixture to which water has been added, Includes, The starch is measured using a rapid viscoanalytic analyzer (RVA) according to the following measurement methods (1) to (4), and the value represented by the following formula (I) is between 2000 and 10000. 5000-30×T1-90×(T2-T1)+2×η1-15×η2...(I) (In equation (I), T1 represents the gelatinization onset temperature (°C), T2 represents the gelatinization peak temperature (°C), η1 represents the gelatinization peak viscosity (mPa·s), and η2 represents the trough viscosity (mPa·s).) [Measurement method] (1) A 25% by mass aqueous suspension of the starch is introduced into the RVA as the measurement sample, and the temperature of the measurement sample is raised to 50°C and held for 1 minute. (2) The temperature of the sample to be measured is raised from 50°C to 93°C over 4 minutes, and then held at 93°C for 7 minutes. (3) The temperature of the sample to be measured is lowered from 93°C to 50°C over 4 minutes, and then held at 50°C for 3 minutes. (4) In (2) and (3) above, the rotation speed of the RVA measuring paddle shall be 960 rpm for the first 10 seconds after the start of viscosity measurement, and 160 rpm thereafter. [Brief explanation of the drawing]

[0007] [Figure 1] Outline of an amylogram obtained using a rapid viscoanalytic analyzer. [Figure 2] An example of an amylogram related to a manufacturing example. [Modes for carrying out the invention]

[0008] Embodiments of the present invention are described below. The embodiments described below illustrate examples of the present invention. The present invention is not limited in any way to the embodiments described below and includes various modifications that are implemented without changing the gist of the present invention. Not all of the configurations described below are necessarily essential to the present invention.

[0009] The method for manufacturing a molded article according to this embodiment is: A deposition process in which a mixture containing fibers and starch is deposited in the air, A humidification step of adding water to the mixture, A molding process to obtain a molded body by heating and pressurizing the mixture to which water has been added, Includes, The starch is measured using a rapid viscoanalytic analyzer (RVA) according to the following measurement methods (1) to (4), and the value represented by the following formula (I) is between 2000 and 10000. 5000-30×T1-90×(T2-T1)+2×η1-15×η2...(I) (In equation (I), T1 represents the gelatinization onset temperature (°C), T2 represents the gelatinization peak temperature (°C), η1 represents the gelatinization peak viscosity (mPa·s), and η2 represents the trough viscosity (mPa·s).) [Measurement method] (1) A 25% by mass aqueous suspension of the starch is introduced into the RVA as the measurement sample, and the temperature of the measurement sample is raised to 50°C and held for 1 minute. (2) The temperature of the sample to be measured is raised from 50°C to 93°C over 4 minutes, and then held at 93°C for 7 minutes. (3) The temperature of the sample to be measured is lowered from 93°C to 50°C over 4 minutes, and then held at 50°C for 3 minutes. (4) In (2) and (3) above, the rotation speed of the RVA measuring paddle shall be 960 rpm for the first 10 seconds after the start of viscosity measurement, and 160 rpm thereafter.

[0010] 1. Method for manufacturing molded articles 1.1. Molded body The molded product molded by the manufacturing method of the present embodiment is not particularly limited as long as it is an object molded into a predetermined shape. The shape of the molded product is also not particularly limited, and may be any shape such as, for example, a film shape, a sheet shape, a board shape, a block shape, or the like. There are also no particular limitations on the use of the molded product. Since the manufacturing method of the present embodiment includes a deposition step, the molded product is more preferably formed into a film shape or a sheet shape.

[0011] 1.2. Deposition Step In the deposition step, a mixture containing fibers and starch is deposited in air.

[0012] 1.2.1. Fibers A wide range of fibers can be used in the manufacturing method of the present embodiment. Examples of the fibers include natural fibers (animal fibers, plant fibers) and chemical fibers (organic fibers, inorganic fibers, organic-inorganic composite fibers); more specifically, fibers made of cellulose, silk, wool, cotton, cannabis, kenaf, flax, ramie, jute, Manila hemp, sisal hemp, conifers, broadleaf trees and the like, and fibers made of rayon, lyocell, cupra, vinylon, acrylic, nylon, aramid, polyester, polyethylene, polypropylene, polyurethane, polyimide, carbon, glass, and metal. These fibers may be used alone, may be used in appropriate mixture, or may be used as regenerated fibers subjected to purification or the like. However, among these fibers, it is more preferable to use naturally-derived fibers.

[0013] Examples of raw materials for the fibers include waste paper, used cloth, and the like, and the fibers only need to contain at least one of these fibers. Further, the fibers may be subjected to various surface treatments. Furthermore, the material of the fibers may be a pure substance, or may contain a plurality of components such as impurities, starch particles and other components.

[0014] When the fibers used in the present embodiment are in the form of individual single fibers, the average diameter thereof (for a fiber with a non-circular cross-section, this refers to the maximum length in the direction perpendicular to the longitudinal direction, or the diameter of a circle (equivalent circle diameter) assumed to have an area equal to the area of the cross-section) is on average 1 µm or more and 1000 µm or less, preferably 2 µm or more and 500 µm or less, more preferably 3 µm or more and 200 µm or less.

[0015] The length of the fibers used in the present embodiment is not particularly limited. For an individual single fiber, the length along the longitudinal direction of the fiber is 1 µm or more and 5 mm or less, preferably 2 µm or more and 3 mm or less, more preferably 3 µm or more and 2 mm or less. If the fiber length is too short, it is difficult for the fibers to bind to starch particles, which may result in insufficient sheet strength; however, a sheet with sufficient strength can be obtained when the fiber length falls within the above range.

[0016] The thickness and length of fibers can be measured by various optical microscopes, scanning electron microscopes (SEM), transmission electron microscopes, fiber testers, and the like.

[0017] 1.2.2 Starch Starch is one component of the produced molded article. It contributes to maintaining the shape of the molded article, and is a component that maintains and improves properties such as the strength of the molded article. In the molded article, starch can function as a binder that binds fibers to each other.

[0018] Starch is a polymer material in which a plurality of α-glucose molecules are polymerized via glycosidic bonds. Starch molecules may be linear or may contain branches.

[0019] Starch derived from various plants can be used. Examples of raw materials for starch include cereals such as corn, wheat and rice, beans such as broad bean, mung bean and adzuki bean, tubers such as potato, sweet potato and tapioca, wild herbs such as dogtooth violet, bracken and kudzu, and palms such as sago palm.

[0020] Modified starch and altered starch may also be used as starch. Examples of modified starch include acetylated adipic acid crosslinked starch, acetylated starch, acetylated starch, oxidized starch, sodium octenyl succinate starch, hydroxypropyl starch, hydroxypropylated phosphate crosslinked starch, phosphorylated starch, phosphate esterified phosphate crosslinked starch, urea phosphorylated esterified starch, sodium starch glycolate, and high amylose corn starch. Examples of altered starch include pregelatinized starch, dextrin, lauryl polyglucose, cationized starch, thermoplastic starch, and carbamate starch.

[0021] It is preferable that the starch be mixed with the fibers in powder form, consisting of multiple starch particles. Supplying the starch in powder form allows for more efficient mixing with the fibers. The average particle size of the starch particles in the starch powder is preferably 0.5 μm to 100.0 μm, more preferably 1.0 μm to 50.0 μm, and even more preferably 1.0 μm to 30.0 μm. Having the starch particles within this range makes them easier to disperse, resulting in superior tensile strength for the resulting molded article. Furthermore, the improved dispersibility leads to superior tensile strength for the resulting molded article. Additionally, reducing the particle size increases the surface area per unit weight, making it easier for the starch to absorb water and reducing the amount of water consumed during dry molding.

[0022] The particle size of starch particles can be adjusted, for example, by grinding, and grinders such as hammer mills, pin mills, cutter mills, pulperizers, turbo mills, disc mills, screen mills, and jet mills can be used.

[0023] Furthermore, the starch particles may also contain inorganic oxide particles. In other words, the starch particles may be a composite material containing starch and inorganic oxide particles.

[0024] Various types of inorganic oxide particles can be used, but it is preferable to use those that are arranged on the surface of the starch particles (or coated). Examples of such inorganic oxide particles include fine particles made of inorganic material, and by arranging these on the surface of the starch particles, an excellent effect of suppressing the aggregation of starch particles can be obtained.

[0025] Specific examples of materials used for inorganic oxide particles include silica, titanium oxide, aluminum oxide, zinc oxide, cerium oxide, magnesium oxide, zirconium oxide, strontium titanate, barium titanate, and calcium carbonate.

[0026] The average particle diameter (number-average particle diameter) of the inorganic oxide particles is not particularly limited, but is preferably 0.001 μm to 1 μm, and more preferably 0.006 μm to 0.6 μm. If the particle diameter of the primary inorganic oxide particles is within the above range, a good coating can be applied to the surface of the starch particles, and a sufficient anti-aggregation effect of the starch particles can be provided. However, if the starch particles and inorganic oxide particles are not combined but are separate, inorganic oxide particles are not always present between certain starch particles, so the anti-aggregation effect between starch particles is considered to be smaller compared to when they are combined.

[0027] In starch particles that integrate starch particles and inorganic oxide particles, the inorganic oxide particle content is preferably 0.1 parts by mass or more and 5 parts by mass or less per 100 parts by mass of starch. With such a content, the above effects can be obtained.

[0028] Various methods can be considered for forming starch particles integrated with inorganic oxide particles by arranging (coating) inorganic oxide particles on the surface of starch particles. One method involves simply mixing the starch particles and inorganic oxide particles and allowing them to adhere to the surface by electrostatic force or van der Waals force. However, in this embodiment, there remains a concern that the inorganic oxide particles may detach from the surface of the starch particles. Therefore, a method of uniformly mixing the starch particles and inorganic oxide particles by introducing them into a high-speed rotating mixer is more preferable. Known devices can be used for this purpose, and this can be done using FM mixers, Henschel mixers, super mixers, etc. By this method, inorganic oxide particles can be integrally arranged on the surface of the starch particles. It should be noted that the inorganic oxide particles do not necessarily have to cover the entire surface of the starch particles. Also, the coverage rate may exceed 100%, and an appropriate coverage rate can be selected depending on the situation.

[0029] By having inorganic oxide particles integrally with the starch particles, the surface of the starch particles can be kept in a dry state, suppressing the loss of charge due to moisture. As a result, the starch particles do not aggregate within the mixture and are uniformly dispersed, leading to superior strength in the resulting molded product.

[0030] The starch content in the total amount of the mixture is preferably 2.0% by mass or more and 70.0% by mass or less, more preferably 3.0% by mass or more and 65.0% by mass or less, and even more preferably 3.5% by mass or more and 30.0% by mass or less. The starch content can be measured by component analysis such as NMR, and can be measured using pretreatment methods such as enzymatic decomposition as needed. The starch content in the mixture can be adjusted by the amount mixed in the mixing step described later.

[0031] 1.2.3. Deposition of mixtures The mixture is obtained by mixing at least the aforementioned fibers and starch. Mixing is preferably carried out in air. "Mixing in air" means mixing by the action of airflow. For example, a method of introducing fibers and starch into an airflow and allowing them to diffuse to each other in the airflow (dry method) is preferred. The fibers and starch may be mixed simultaneously or sequentially. The order of mixing is not particularly limited.

[0032] Mixing can be carried out using known devices such as FM mixers, Henschel mixers, and super mixers. The device may be one that uses high-speed rotating blades for agitation, or one that utilizes the rotation of a container, such as a V-type mixer. Furthermore, it may be a batch-type or continuous-type device.

[0033] 1.3. Humidification process In the humidification process, water is added to the mixture. Tap water, purified water, recycled water, ion-exchanged water, ultrafiltered water, reverse osmosis water, and distilled water can be used. Of these, using pure or ultrapure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, or distilled water, and especially sterilizing this water by ultraviolet irradiation or hydrogen peroxide addition, is preferable because it can suppress the growth of mold and bacteria for a long period.

[0034] The method for adding water to the mixture in the humidification process is not particularly limited, but can be done by spraying, showering, steam humidification, immersion in water, etc.

[0035] The amount of water added in the humidification process is preferably 10% to 50% by mass of the total mass of the mixture, more preferably 12% to 40% by mass, and preferably 12% to 40% by mass.

[0036] According to this method for manufacturing molded articles, by reducing the amount of water added, excessive wetting and spreading of starch particles can be suppressed, and the occurrence of fiber clumps in the molded article can be further suppressed.

[0037] 1.4. Molding process In the molding process, a molded body is obtained by heating and pressurizing the deposited and water-added mixture. The method of heating and pressurizing is not particularly limited and can be performed, for example, by a pair of heat rollers capable of heating and pressurizing, a hot press, etc. Also, pressurizing and heating may be performed simultaneously or sequentially. The humidified mixture may be molded into, for example, a web shape. Furthermore, the heating section may have the function of molding the mixture into a predetermined shape.

[0038] By selecting a pair of heat rollers capable of both heating and pressurizing, it becomes unnecessary to provide separate pressure rollers for pressurizing the mixture and heat rollers for heating the mixture. Heating and pressurizing the mixture can be performed simultaneously using only the pair of heat rollers. This allows for a more compact overall system, for example, in manufacturing.

[0039] When the mixture is heated and pressurized, the fibers and starch bind together. "Binding of fibers and starch" means a state in which the fibers and additives are difficult to separate, or a state in which starch is placed between the fibers, making it difficult for the fibers to separate via the starch. Furthermore, binding is a concept that includes adhesion and includes a state in which two or more objects come into contact and become difficult to separate. In addition, when fibers bind together via starch, the fibers may be parallel or intersecting, or multiple fibers may be bound to a single fiber.

[0040] The heating temperature of the mixture in the molding process is preferably 50°C to 210°C, more preferably 60°C to 200°C, even more preferably 70°C to 180°C, and especially preferably 90°C to 110°C. By setting the temperature in the molding process within this range, even in situations where the viscosity of the starch does not increase easily with relatively low heating temperatures, a molded article with excellent strength and surface smoothness can be obtained due to the properties of the starch. Furthermore, by lowering the heating temperature, damage to the fibers due to heating can be reduced.

[0041] The pressure applied during the molding process is preferably between 0.1 MPa and 15.0 MPa, more preferably between 0.2 MPa and 10.0 MPa, and even more preferably between 0.3 MPa and 8.0 MPa. By setting the pressure within this range, relatively low pressure is applied, which suppresses fiber damage and results in a molded article with superior strength.

[0042] 1.5. Other processes The method for manufacturing the molded article of this embodiment may include steps other than those described above. Examples of such steps include preparation steps such as a step of defibrating the raw material to obtain fibers, a step of classifying the fibers and starch, and processing steps such as cutting and machining the heated and pressurized molded article.

[0043] 1.6. Properties of Starch The starch used in the method for manufacturing the molded article of this embodiment has a value expressed by the following formula (I), which is determined by measuring it with a rapid viscoanalytic analyzer (RVA) according to the following measurement methods (1) to (4), and is between 2000 and 10000. 5000-30×T1-90×(T2-T1)+2×η1-15×η2...(I) (In equation (I), T1 represents the gelatinization onset temperature (°C), T2 represents the gelatinization peak temperature (°C), η1 represents the gelatinization peak viscosity (mPa·s), and η2 represents the trough viscosity (mPa·s).) [Measurement method] (1) A 25% by mass aqueous suspension of the starch is introduced into the RVA as the measurement sample, and the temperature of the measurement sample is raised to 50°C and held for 1 minute. (2) The temperature of the sample to be measured is raised from 50°C to 93°C over 4 minutes, and then held at 93°C for 7 minutes. (3) The temperature of the sample to be measured is lowered from 93°C to 50°C over 4 minutes, and then held at 50°C for 3 minutes. (4) In (2) and (3) above, the rotation speed of the RVA measuring paddle shall be 960 rpm for the first 10 seconds after the start of viscosity measurement, and 160 rpm thereafter.

[0044] 1.6.1. Rapid Viscometer A rapid viscometer (RVA) is a device capable of measuring the viscosity properties of starch, grains, flour, etc. It is a rotational viscometer that allows for temperature control and setting of rotation conditions. RVAs are available from companies such as Newport Scientific, PerkinElmer, and NSP Co., Ltd. Rapid viscometers can measure small sample sizes (e.g., about 3g), and the measurement time is, for example, about 20 minutes. In addition, the rotation speed of the rotating paddle (stirrer) and the temperature gradient can be freely set, and the gelatinization characteristics of the sample can be recorded as a viscosity curve.

[0045] 1.6.2. Viscosity curves of rapid viscometers Figure 1 shows a typical example of a viscosity curve (amylogram) of a starch and water mixture measured using a rapid viscoanalytic converter. The viscosity, temperature, etc., will be explained while referring to Figure 1. At the start of measurement, the stirring bar is rotated to raise the system temperature. As the temperature rises, the viscosity gradually increases, and starch gelatinization begins. This temperature is defined as the gelatinization onset temperature (T1). After gelatinization, the heating is stopped for a certain period of time, and stirring is continued while measuring the viscosity. A peak appears on the viscosity curve; the viscosity at this peak is defined as the gelatinization peak viscosity (η1), and the temperature at this peak is defined as the gelatinization peak temperature (T2).

[0046] If stirring continues past the peak viscosity, the viscosity of the system decreases. This decreased viscosity is defined as the trough viscosity (η²). Next, the temperature of the system is lowered to a predetermined temperature. The viscosity at the predetermined temperature is defined as the final viscosity. The difference between the final viscosity and the trough viscosity is defined as the setback viscosity.

[0047] An amylogram contains information such as the behavior of starch crystals, gelatinization behavior, interaction with water molecules, swelling behavior of starch particles, the properties and origin of starch, the water retention capacity of starch, the higher-order structure of starch, and starch retrogradation.

[0048] In this embodiment, (1) a 25% by mass aqueous suspension of starch is introduced into the RVA as the measurement sample, and the temperature of the measurement sample is raised to 50°C and held for 1 minute. (2) The temperature of the measurement sample is raised from 50°C to 93°C over 4 minutes and held at 93°C for 7 minutes. (3) The temperature of the measurement sample is lowered from 93°C to 50°C over 4 minutes and held at 50°C for 3 minutes. (4) In (2) and (3), the rotation speed of the measurement paddle of the RVA is set to 960 rpm for the first 10 seconds after the start of viscosity measurement, and to 160 rpm thereafter.

[0049] 1.7. Value represented by equation (I) In the manufacturing method of this embodiment, starch is used in which the value of the following formula (I) is between 2000 and 10000. 5000-30×T1-90×(T2-T1)+2×η1-15×η2...(I) (In equation (I), T1 represents the gelatinization onset temperature (°C), T2 represents the gelatinization peak temperature (°C), η1 represents the gelatinization peak viscosity (mPa·s), and η2 represents the trough viscosity (mPa·s).) This allows the water absorption, gelatinization, and viscosity properties of starch to be combined in a well-balanced manner, resulting in a molded product with superior mechanical strength.

[0050] The finding that the above effect is obtained when the value (5000) and coefficients (-30, -90, +2, -15) appearing in equation (I), and when the value of equation (I) is between 2000 and 10000, was obtained empirically by the inventors through repeated experiments. Therefore, the detailed mechanism by which such an effect is obtained is not entirely clear, but it is thought that the behavior of starch during the molding process involving heating and pressurization is mainly involved.

[0051] The second term of equation (I), (-30 × T1), indicates that a lower gelatinization onset temperature is advantageous for improving paper strength. It is thought that a lower gelatinization onset temperature leads to higher gelatinization efficiency of the starch binder, resulting in improved paper strength. Furthermore, the third term of equation (I), (-90 × (T2 - T1)), indicates that a smaller temperature difference from the start of gelatinization to the peak, i.e., a larger temperature gradient, results in higher paper strength. This temperature gradient reflects the water absorption rate of the starch, and a larger temperature gradient indicates a higher water absorption rate. It is thought that a higher water absorption rate leads to improved paper strength.

[0052] The fourth term (+2 × η1) in equation (I) indicates that a higher gelatinization peak viscosity leads to improved paper strength. The gelatinization peak viscosity reflects the water absorption capacity of the raw starch during gelatinization. It is thought that as the starch absorbs more water, the gelatinization reaction due to heating progresses, increasing the binding force of the starch, and consequently improving paper strength. Furthermore, the fifth term (-15 × η2) in equation (I) indicates that starch with a low trough viscosity is advantageous for improving paper strength. It is thought that a lower trough viscosity allows the binder to wet and spread more widely on the fiber surface during pressurized heating, resulting in a larger bonding area and consequently higher paper strength.

[0053] Gelatinization characteristics vary depending on the amylose / amylopectin ratio, molecular structure, molecular weight, degree of branching, and degree of acid treatment reaction of each raw starch species.

[0054] Paper strength is the result of a balance between water absorption, gelatinization, and viscosity properties, and the overall properties must be defined. If the calculated values ​​in the relational formula are too low, the water absorption, gelatinization, and viscosity properties will be insufficient, and for the reasons mentioned above, it will be impossible to ensure sufficient paper strength. If the calculated values ​​in the relational formula are too high, the water absorption and gelatinization viscosity will be too high. If the water absorption is too high, drying will be poor, and if the gelatinization viscosity is too high, the bonding area will be insufficient, both of which will reduce the paper strength.

[0055] The value obtained by formula (I) is more preferably between 2100 and 9300, and even more preferably between 2500 and 8000. Using such starch makes it possible to obtain molded articles with even greater mechanical strength.

[0056] 2. Experimental Examples The present invention will be further explained by the following experimental examples, but the present invention is not limited in any way by these examples.

[0057] 2.1. Production of raw starch 4.5 kg of potato starch was placed in a paddle dryer (manufactured by Nara Machinery Works Co., Ltd., 10 L capacity), and 200 g of 5N hydrochloric acid aqueous solution was sprayed onto it while stirring. After stirring and mixing to homogenize, it was heated to 70°C and pre-dried to a moisture content of 7.5%. Next, the heating temperature was increased to 120°C and the reaction time was adjusted to obtain seven levels of raw starch (starch 2, starch 3, starch 4, starch 5, starch 6, starch 7, starch 8) with different hydrolysis times. The viscosity of the starch (final viscosity of the amylogram) was measured and found to be 149 mPa·s (starch 2), 143 mPa·s (starch 3), 140 mPa·s (starch 4), 112 mPa·s (starch 5), 86 mPa·s (starch 6), 74 mPa·s (starch 7), and 58 mPa·s (starch 8). Furthermore, the final viscosity of the raw starch amylogram was 151 mPa·s (starch 1).

[0058] By replacing the potato starch with waxy cornstarch and performing the same treatment, starch 9 (starch viscosity 260 mPa·s), starch 10 (same 223 mPa·s), starch 11 (same 178 mPa·s), starch 12 (same 137 mPa·s), and starch 13 (same 91 mPa·s) were replaced with tapioca starch to obtain starch 14 (same 124 mPa·s), starch 15 (same 96 mPa·s), starch 16 (same 64 mPa·s), starch 17 (same 51 mPa·s), and starch 18 (same 45 mPa·s).

[0059] 2.2. Measurement of starch gelatinization properties Amylograms were measured using an RVA4800 manufactured by NSP Corporation under the following conditions. The table shows the gelatinization onset temperature (°C), gelatinization peak temperature (°C), gelatinization peak viscosity (mPa·s), trough viscosity (mPa·s), final viscosity (mPa·s), and setback viscosity (mPa·s) read from the amylograms of starch 1 to starch 18, respectively. The table also shows the calculated values ​​of formula (I) for starch 1 to starch 15. The results for starch 1 to 18 are described in the columns for Production Examples 1 to 18, respectively.

[0060] • Sample concentration: 25% by mass aqueous suspension • Paddle rotation speed: 960 rpm for the first 10 seconds after viscosity measurement begins, and 160 rpm thereafter. • Temperature profile settings Hold at 50°C for 1 minute. Heats up to 93℃ in 4 minutes. Maintain 93°C for 7 minutes. Cools down to 50℃ in 4 minutes Maintain 50°C for 3 minutes.

[0061] As an example, the amylogram of starch 6 is shown in Figure 2.

[0062] 2.3. Production of starch containing inorganic oxide particles (1) Grinding of raw starch The starches prepared as described above were used as raw materials and ground using a fluidized bed counter-jet mill (Counter Jet Mill AFG-R: manufactured by Hosokawa Micron Corporation). Starch particles (in powder form) with an average particle size of 5 μm were obtained at a compressed air pressure of 6 bar.

[0063] (2) Integration of inorganic oxide particles Starch particles and fumed silica (HM-30S, manufactured by Tokuyama Corporation) were introduced into a Henschel mixer (FM mixer, manufactured by Nippon Coke Industries Co., Ltd.) and mixed at a frequency of 60 Hz for 10 minutes. The mixing ratio was 100:2 by mass, consisting of starch particles to fumed silica. Subsequently, the mixture was sieved with a mesh size of 30 μm to obtain starch containing inorganic oxide particles.

[0064] (3) Manufacturing of molded products The molded products for each manufacturing example were made into sheets. A modified Seiko Epson PaperLabo A-8000 (dry sheet manufacturing machine) was used, modified to allow humidification of the sheets after forming and before pressurization. Cartridges filled with the starch for each example were loaded into this modified machine. Manufacturing examples 1 to 18 used the aforementioned starches 1 to 18, respectively. Used recycled copy paper (GR-70W: manufactured by FUJI XEROX) with business documents printed on it using an inkjet printer was loaded into the sheet feeder, with a starch concentration of 6% by mass and a basis weight of 80 g / m². 2 The settings allowed for the production of recycled sheets.

[0065] (4) Method for evaluating sheet tensile strength A 100mm x 20mm strip was cut from a recycled sheet immediately after manufacturing, and the breaking strength was measured along the longitudinal direction of the strip. A Shimadzu Autograph AGS-iN measuring instrument was used to measure the breaking strength at a tensile speed of 20mm / sec, and the specific tensile strength was calculated from this. Based on the calculated specific tensile strength, the breaking strength was evaluated according to the following criteria, and the results are shown in the table. A:40Nm / g or more B: 30 Nm / g or more and less than 40 Nm / g C: 20 Nm / g or more and less than 30 Nm / g D: 10 Nm / g or more and less than 20 Nm / g E: Less than 10 Nm / g

[0066] [Table 1]

[0067] 2.4. Evaluation Results It was found that the sheets of manufacturing examples 2-8 and 14-15, whose value represented by formula (I) is between 2000 and 10000, exhibit good mechanical strength.

[0068] The embodiments described above are merely examples and are not limited to them. For example, each embodiment and each variation can be combined as appropriate.

[0069] The present invention includes configurations substantially identical to those described in the embodiments, for example, configurations with the same function, method, and results, or configurations with the same purpose and effect. Furthermore, the present invention includes configurations in which non-essential parts of the configurations described in the embodiments are replaced. Furthermore, the present invention includes configurations that produce the same effects or achieve the same purpose as those described in the embodiments. Finally, the present invention includes configurations that add known technology to the configurations described in the embodiments.

[0070] The following can be derived from the embodiments and modifications described above.

[0071] The method for manufacturing a molded product is: A deposition process in which a mixture containing fibers and starch is deposited in the air, A humidification step of adding water to the mixture, A molding process to obtain a molded body by heating and pressurizing the mixture to which water has been added, Includes, A method for manufacturing a molded article, wherein the starch is measured using a rapid viscoanalytic analyzer (RVA) according to the following measurement methods (1) to (4), and the value represented by the following formula (I) is between 2000 and 10000. 5000-30×T1-90×(T2-T1)+2×η1-15×η2...(I) (In equation (I), T1 represents the gelatinization onset temperature (°C), T2 represents the gelatinization peak temperature (°C), η1 represents the gelatinization peak viscosity (mPa·s), and η2 represents the trough viscosity (mPa·s).) [Measurement method] (1) A 25% by mass aqueous suspension of the starch is introduced into the RVA as the measurement sample, and the temperature of the measurement sample is raised to 50°C and held for 1 minute. (2) The temperature of the sample to be measured is raised from 50°C to 93°C over 4 minutes, and then held at 93°C for 7 minutes. (3) The temperature of the sample to be measured is lowered from 93°C to 50°C over 4 minutes, and then held at 50°C for 3 minutes. (4) In (2) and (3) above, the rotation speed of the RVA measuring paddle shall be 960 rpm for the first 10 seconds after the start of viscosity measurement, and 160 rpm thereafter.

[0072] According to this method for manufacturing molded articles, the value obtained by formula (I) is controlled to be between 2000 and 10000, and a dry-molded article with excellent strength can be obtained. In other words, the strength of the molded article obtained by this manufacturing method is due to a balanced combination of the contributions of the water absorption, gelatinization, and viscosity properties of starch. In formula (I), the smaller the value of T1, the earlier the timing of starch gelatinization and the exertion of binding force, resulting in superior molded article strength. Also, in formula (I), the value of (T2-T1) is thought to reflect the rate at which starch absorbs water, and the smaller this value, the more rapidly the starch absorbs water, making it easier to gelatinize with a small amount of water even in dry molding, resulting in superior molded article strength. Furthermore, in formula (I), the larger the value of η1, the more viscous the starch becomes when gelatinized, resulting in a molded article with superior strength. Furthermore, in formula (I), the smaller the value of η2, the easier it is for the starch to wet and spread during pressurization and heating, resulting in a molded article with superior strength.

[0073] In the above method for manufacturing a molded article, The heating temperature of the mixture in the molding process may be 60°C or higher and 200°C or lower.

[0074] According to this method for manufacturing molded articles, even in situations where the viscosity of starch does not easily increase with relatively low heating temperatures, a molded article with excellent strength and surface smoothness can be obtained due to the properties of the starch. Furthermore, by lowering the heating temperature, damage to the fibers due to heating can be reduced.

[0075] In the above method for manufacturing a molded article, The molding process may be carried out by a pair of heat rollers.

[0076] According to this method of manufacturing molded products, there is no need to separately provide a pressure roller for pressurizing the mixture and a heat roller for heating the mixture; heating and pressurizing the mixture can be performed simultaneously with only a pair of heat rollers. Therefore, the overall equipment used in manufacturing can be made smaller.

[0077] In the above method for manufacturing a molded article, The pressure applied in the molding process may be between 0.2 MPa and 10.0 MPa.

[0078] According to this method for manufacturing molded articles, by applying pressure at a relatively low pressure, fiber damage can be suppressed, resulting in a molded article with superior strength.

[0079] In the above method for manufacturing a molded article, The amount of water added in the humidification step may be 12% by mass or more and 40% by mass or less of the total mass of the mixture.

[0080] According to this method for manufacturing molded articles, by reducing the amount of water added, excessive wetting and spreading of starch particles can be suppressed, further reducing the occurrence of fiber clumps in the molded article. In addition, the energy required for molding can be reduced.

[0081] In the above method for manufacturing a molded article, The starch is in powder form consisting of multiple starch particles, and the average particle size of the starch particles may be 1.0 μm or more and 30.0 μm or less.

[0082] According to this method for manufacturing molded articles, the average particle size of the starch particles falls within a specified range, making them easier to disperse, resulting in a molded article with excellent tensile strength. Furthermore, reducing the particle size increases the surface area per unit weight, making it easier for the starch to absorb water and thus reducing the amount of water consumed during dry molding.

[0083] In the above method for manufacturing a molded article, The starch particles may also contain inorganic oxide particles integrally.

[0084] According to this method for manufacturing molded articles, the starch particles, by integrally containing inorganic oxide particles, can maintain a dry surface state, thereby suppressing the loss of charge due to moisture. As a result, the starch particles do not aggregate within the mixture but are uniformly dispersed, leading to superior strength in the resulting molded article.

Claims

1. A deposition process in which a mixture containing fibers and starch is deposited in the air, A humidification step of adding water to the mixture, A molding process to obtain a molded body by heating and pressurizing the mixture to which water has been added, Includes, A method for manufacturing a molded article, wherein the starch is measured using a rapid viscoanalytic analyzer (RVA) according to the following measurement methods (1) to (4), and the value represented by the following formula (I) is between 2,000 and 10,000. 5000-30×T1-90×(T2-T1)+2×η1-15×η2...(I) (In equation (I), T1 represents the gelatinization onset temperature (°C), T2 represents the gelatinization peak temperature (°C), η1 represents the gelatinization peak viscosity (mPa·s), and η2 represents the trough viscosity (mPa·s).) [Measurement method] (1) A 25% by mass aqueous suspension of the starch is introduced into the RVA as the measurement sample, and the temperature of the measurement sample is raised to 50°C and held for 1 minute. (2) The temperature of the sample to be measured is raised from 50°C to 93°C over 4 minutes, and then held at 93°C for 7 minutes. (3) The temperature of the sample to be measured is lowered from 93°C to 50°C over 4 minutes, and then held at 50°C for 3 minutes. (4) In (2) and (3) above, the rotation speed of the RVA measuring paddle shall be 960 rpm for the first 10 seconds after the start of viscosity measurement, and 160 rpm thereafter.

2. In claim 1, A method for manufacturing a molded article, wherein the heating temperature of the mixture in the molding step is 60°C or higher and 200°C or lower.

3. In claim 1 or claim 2, The molding process is carried out by a pair of heat rollers, and the method is a method for manufacturing a molded body.

4. In claim 1, A method for manufacturing a molded article, wherein the pressure applied in the molding process is 0.2 MPa or more and 10.0 MPa or less.

5. In claim 1, A method for manufacturing a molded article, wherein the amount of water added in the humidification step is 12% by mass or more and 40% by mass or less relative to the total mass of the mixture.

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