Manufacturing method for molded products

Abstract

To provide a manufacturing method for obtaining a molding capable of achieving smoothness and 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 40 mPa s or more and 200 mPa s or less of setback viscosity (η50-η93) obtained by measuring by a rapid visco analyser (RVA) according to a measuring method of following (1) to (4). [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] This invention relates to a method for manufacturing a molded article. [Background technology]

[0002] The method of depositing fibrous materials and applying bonding forces between the deposited fibers to obtain a molded product has been practiced for a long time. For example, a dry method, which uses little to no water, is expected to be a promising method for manufacturing molded products containing cellulose fibers, such as paper, paper plates, and paper-like boards. Generally, a large amount of water is used when molding paper products, so development is underway to reduce the amount of water used.

[0003] For example, Patent Document 1 discloses a method for manufacturing cushioning material, etc., which involves defibrating waste paper to make a cotton-like material, adding mist-like water, adding a powdered or granular adhesive, and then molding and drying the material. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] JP-A-246465 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, in dry molding methods such as those described in Patent Document 1, clumps sometimes formed between the fibers and the binder (starch), resulting in unevenness on the surface of the molded product. This is thought to be because, when the starch wetting spreads widely, the binder powder entrains many fibers, forming clumps. On the other hand, when the starch wetting spread is small, the fibers are not bonded, resulting in a molded product with inferior strength. In other words, there was a need for a dry molding method that could achieve both smoothness and strength in the molded product. [Means for solving the problem]

[0006] One aspect of the method for manufacturing a molded article according to the present invention 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 setback viscosity (η) of the starch is determined by measuring it with a rapid viscometer (RVA) according to the following measurement methods (1) to (4). 50 -η 93 The pressure is between 40 mPa·s and 200 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 manufacturing method of the molded body according to this embodiment is a deposition step of depositing a mixture containing fibers and starch in the air, a humidifying step of imparting water to the mixture, a molding step of obtaining a molded body by heating and pressurizing the mixture to which water has been imparted, and includes the starch has a value represented by the following formula (I) obtained by measurement with a Rapid Visco Analyzer (RVA) according to the following measurement methods (1) to (4) and is 2000 or more and 10000 or less. 5000 - 30×T1 - 90×(T2 - T1)+2×η1 - 15×η2 ··· (I) (In formula (I), T1 represents the gelatinization start 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 a 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) above, the rotation speed of the paddle for RVA measurement is 960 rpm for 10 seconds after the start of viscosity measurement and 160 rpm after 10 seconds have elapsed.

[0010] 1. Manufacturing method of molded body 1.1. Molded body The molded body molded by the manufacturing method of this embodiment is not particularly limited as long as it is an object molded into a predetermined shape. The shape of the molded body is also not particularly limited and may be any shape such as a film shape, a sheet shape, a board shape, a block shape, etc. The use of the molded body is also not particularly limited. In the manufacturing method of this embodiment, in terms of having a deposition step, the shape of the molded body is more preferably a film shape or a sheet shape.

[0011] 1.2. Deposition process The deposition process involves depositing a mixture containing fibers and starch in the air.

[0012] 1.2.1. Fibers In the manufacturing method of this embodiment, a wide range of fibers can be used. Examples of fibers include natural fibers (animal fibers, plant fibers), chemical fibers (organic fibers, inorganic fibers, organic-inorganic composite fibers), and more specifically, fibers made from cellulose, silk, wool, cotton, hemp, kenaf, flax, ramie, jute, Manila hemp, sisal, coniferous trees, broadleaf trees, etc., as well as fibers made from rayon, lyocell, cupro, vinylon, acrylic, nylon, aramid, polyester, polyethylene, polypropylene, polyurethane, polyimide, carbon, glass, and metal. These may be used individually, in appropriate mixtures, or as regenerated fibers after purification. However, among these fibers, using naturally derived fibers is more effective. preferable.

[0013] Examples of raw materials for the fibers include recycled paper and recycled cloth, and it is sufficient that the fiber contains at least one of these fibers. The fibers may also be subjected to various surface treatments. Furthermore, the material of the fibers may be a pure substance or may contain multiple components such as impurities, starch particles, and other components.

[0014] The fibers used in this embodiment, when considered as a single independent fiber, have an average diameter (if the cross-section is not a circle, the longest length in the direction perpendicular to the longitudinal direction, or the diameter of a circle assuming an area equal to the area of ​​the cross-section (equivalent diameter of a circle)) that is, on average, 1 μm or more and 1000 μm or less, preferably 2 μm or more and 500 μm or less, and more preferably 3 μm or more and 200 μm or less.

[0015] The length of the fibers used in this embodiment is not particularly limited, but for a single independent fiber, the length along the longitudinal direction of the fiber is 1 μm to 5 mm, preferably 2 μm to 3 mm, and more preferably 3 μm to 2 mm. If the fiber length is short, it may be difficult to bind with the starch particles, resulting in insufficient sheet strength, but within the above range, a sheet with sufficient strength can be obtained.

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

[0017] 1.2.2. Starch Starch is a component of the molded product, contributing to the maintenance of its shape and maintaining and improving its properties such as strength. Starch can also function as a binder in the molded product, connecting the fibers together.

[0018] Starch is a polymer material in which multiple α-glucose molecules are polymerized by glycosidic bonds. Starch molecules may be linear or branched.

[0019] Starch can be derived from various plants. Examples of starch raw materials include grains such as corn, wheat, and rice; legumes such as broad beans, mung beans, and adzuki beans; tubers such as potatoes, sweet potatoes, and tapioca; wild plants such as dogtooth violets, 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 a more superior tensile strength for the resulting molded article. Furthermore, the reduced particle size increases the surface area per unit weight, making the starch more easily absorbed with water and reducing the amount of water consumed during dry molding. This is possible. Because the surface area per unit weight increases, the starch can absorb water more easily, and the amount of water consumed in dry molding can be reduced.

[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. Note that the starch content is NM The starch content can be measured by component analysis methods such as the R method, and pretreatment methods such as enzymatic decomposition can be used as needed. The starch content in the mixture can be adjusted by the amount mixed in the mixing process 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] If the amount of water added during the humidification process is less than 12% by mass, some of the starch in the mixture may not receive enough moisture, resulting in insufficient gelatinization of the starch and a decrease in tensile strength. If the amount of water added during the humidification process exceeds 50% by mass, the viscosity of the starch during retrogradation tends to decrease, and the number of unfibrillated clumps may increase. In addition, poor drying can easily lead to a decrease in tensile strength.

[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] If the heating temperature falls below 60°C, some of the starch in the mixture may not receive sufficient thermal energy, preventing them from fully developing their bonding strength and potentially resulting in insufficient tensile strength. If the heating temperature exceeds 200°C, the viscosity of the gelatinized starch decreases, causing it to spread over the fibers and tending to create larger clumps of undissolved starch. Furthermore, when fibers are pressurized at high temperatures, the cellulose crystal structure is damaged, weakening those areas and reducing their tensile strength.

[0042] 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.

[0043] If the pressurized pressure falls below 0.2 MPa, the starch may not be able to sufficiently wet and spread over the fibers, nor may it be able to adhere sufficiently to the fiber surface, which may reduce the tensile strength. If the pressurized pressure exceeds 10 MPa, the starch may spread excessively, promoting the formation of undissolved clumps, and a cutting effect may occur at the overlapping parts of the fibers, accelerating fiber damage, which may result in a decrease in tensile strength.

[0044] 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.

[0045] 1.6. Properties of Starch The starch used in the manufacturing method of the molded article of this embodiment has a setback viscosity (η) determined by measuring it with a rapid viscometer (RVA) according to the following measurement methods (1) to (4). 50 -η 93 The pressure is between 40 mPa·s and 200 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.

[0046] 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.

[0047] 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).

[0048] If stirring continues past the peak viscosity, the viscosity of the system decreases. The viscosity after this decrease 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.

[0049] 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.

[0050] In this embodiment, (1) a 25% by mass aqueous suspension of starch is introduced into the RVA as a measurement sample, 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 paddle for RVA measurement is set to 960 rpm for 10 seconds after the start of viscosity measurement, and 160 rpm after 10 seconds have elapsed.

[0051] And in this embodiment, the setback viscosity is the viscosity (η 50 ) when held at 50°C for 3 minutes in the step (3) above, and the viscosity (η 93 ) when held at 93°C for 7 minutes in the step (2) above, and the difference between them is defined as the setback viscosity (η 50 -η 93 )(mPa·s).

[0052] When the setback viscosity of starch (η 50 -η 93 ) is 40 mPa·s or more and 200 mPa / s or less, the contributions of the water absorption, gelatinization, and viscosity characteristics of starch are balanced in total, and a molded body with excellent surface flatness and mechanical strength can be obtained.

[0053] The finding that the above effects can be obtained when the setback viscosity (η 50 -η 93 ) is 40 mPa·s or more and 200 mPa / s or less was empirically obtained by the inventors through repeated experiments. Therefore, although the detailed mechanism by which such effects are obtained is not necessarily clear, it is considered that the behavior of starch in the molding process involving heating and pressurization is mainly involved.

[0054] The setback viscosity (η 50 -η 93 ) is 50 mPa·s or more and 150 mPa / s or less It is more preferable that the pressure be present, and even more preferable that it be between 60 mPa·s and 120 mPa / s. Using such starch makes it possible to obtain molded articles with even better surface smoothness and mechanical strength.

[0055] Setback viscosity of raw starch (η 50 -η 93 The setback viscosity (η) of the material is 40 mPa·s or higher, which moderately suppresses the spreading of starch particles immediately after the pressurized and heated molding process. This is thought to suppress the formation of fiber / starch aggregates that reduce surface smoothness, resulting in fewer clumps and better surface smoothness. 50 -η 93 If the pressure exceeds 200 mPa·s, the starch cannot spread sufficiently when heated and pressurized, resulting in insufficient adhesion area, which is thought to lead to insufficient paper 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 waxy corn starch was placed in a paddle dryer (manufactured by Nara Machine 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 eight levels of raw starch with different hydrolysis times (starch 1, starch 2, starch 3, starch 4, starch 5, starch 6, starch 7, starch 8). The viscosity of the starches (final viscosity of the amylogram) was measured and found to be 260 mPa·s (starch 1), 223 mPa·s (starch 2), 178 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). The final viscosity of the raw starch amylogram was 321 mPa·s (starch 0).

[0058] Setback viscosity (η) 50-η 93 The setback viscosity (η) of each starch was calculated by measuring the amylogram under the following conditions using an RVA4800 manufactured by NSP Corporation, and then measuring the trough viscosity and final viscosity. 50 -η 93 The setback viscosity of the starches was 175 mPa·s (starch 1), 148 mPa·s (starch 2), 114 mPa·s (starch 3), 96 mPa·s (starch 4), 61 mPa·s (starch 5), 47 mPa·s (starch 6), 42 mPa·s (starch 7), and 33 mPa·s (starch 8). The setback viscosity of the amylogram of the raw starch was 230 mPa·s (starch 0).

[0059] The measurement conditions for the amylogram are as follows: • 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.

[0060] As an example, the amylogram of starch 1 is shown in Figure 2.

[0061] 2.2. Production of starch containing inorganic oxide particles (1) Grinding of raw starch The starches prepared 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. For starch 4, three levels were prepared: average particle size of 5 μm, average particle size of 3 μm, and average particle size of 25 μm.

[0062] (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.

[0063] (3) Manufacturing of molded products The molded products of each example and comparative example were made into sheets. A modified PaperLabo A-8000 (dry sheet manufacturing machine) manufactured by Seiko Epson Corporation was modified to allow humidification of the sheets after forming and before pressurization. Cartridges filled with the types of starch listed in Table 1(1) and Table 1(2) were loaded into the machine. Used recycled copy paper (GR-70W: manufactured by FUJI XEROX) on which business documents had been printed 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 Recycled sheets were manufactured using the specified settings. The table shows the heating roller temperature, pressurized pressure, and humidified moisture content for each example.

[0064] (4) Method for evaluating the smoothness of the sheet surface The surface smoothness of each sheet was evaluated using the Beck smoothness test (values ​​obtained in accordance with JIS P8119:1998 "Paper and cardboard - Smoothness test method using a Beck smoothness tester"). Beck smoothness was measured using a Beck smoothness tester (HK model) manufactured by Kumagai Riki Kogyo Co., Ltd. Here, a higher Beck smoothness value indicates better smoothness. (For reference, uncoated paper has a Beck smoothness of 7 seconds to 14 seconds.)

[0065] The surface smoothness of each sheet was evaluated according to the following criteria, and the results are shown in the table. A: Beck smoothness is 12 seconds or more B: Beck smoothness is between 10 seconds and less than 12 seconds C: Beck smoothness is between 8 seconds and less than 10 seconds D: Beck smoothness between 6 seconds and less than 8 seconds E: Beck smoothness is less than 6 seconds

[0066] (5) Method for evaluating the tensile strength of the sheet 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

[0067] [Table 1]

[0068] 2.3. Evaluation Results Starch setback viscosity (η 50 -η 93 It was found that sheets from each example with a pressure of 40 mPa·s to 200 mPa / s yielded sheets with good smoothness and mechanical strength.

[0069] 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.

[0070] 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.

[0071] The following can be derived from the embodiments and modifications described above.

[0072] 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, The setback viscosity (η) of the starch is determined by measuring it with a rapid viscometer (RVA) according to the following measurement methods (1) to (4). 50 -η 93 The pressure is between 40 mPa·s and 200 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.

[0073] The setback viscosity derived from the amylogram measured according to the measurement methods (1) to (4) represents the degree of viscosity increase when the starch is gelatinized, cooled, and aged. According to this method for manufacturing molded articles, by controlling the setback viscosity within the range of 40 mPa·s to 200 mPa / s, a molded article with excellent strength and surface smoothness can be obtained. If the setback viscosity is too low, the starch will be excessively wetted and spread under pressure during the molding process, causing multiple fibers to become trapped and forming clumps, thus reducing the surface smoothness of the molded article. On the other hand, if the setback viscosity is too high, the starch will not be wetted and spread under pressure during the molding process, making it difficult for the fibers to bond together, thus reducing the strength of the molded article.

[0074] 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.

[0075] 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.

[0076] In the above method for manufacturing a molded article, The molding process may be carried out by a pair of heat rollers.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] In the above method for manufacturing a molded article, The starch particles may also contain inorganic oxide particles integrally.

[0085] 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, The setback viscosity (η) of the starch is determined by measuring it with a rapid viscometer (RVA) according to the following measurement methods (1) to (4). ５０ -η ９３ ) is between 40 mPa·s and 200 mPa·s, The starch is in powder form consisting of multiple starch particles, and the average particle size of the starch particles is 1.0 μm or more and 30.0 μm or less. The aforementioned starch particles integrally contain fumed silica, A method for producing a molded article, wherein the content of the fumed silica in the starch particles is 0.1 parts by mass or more and 5 parts by mass or less per 100 parts by mass of starch. [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 performed by a pair of heat rollers, and the method is a method for manufacturing a molded body.

4. In claim 1 or claim 2, 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 or claim 2, 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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