Pulp molded products

Abstract

To provide a pulp mold molded article that is resistant to buckling even when loaded, for example, when containers are filled with contents and stacked when used as containers.SOLUTION: A pulp mold molded article of the present invention has a thickness of 1.5 mm or less and an ISO ring crush compressive strength in the range of 6 to 25 kN / m.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to pulp molded articles. [Background technology]

[0002] In recent years, environmental problems related to the increase in waste have become frequent. In light of this, paper containers are increasingly being used instead of plastic and metal containers for storing toiletries, beverages, and food. For example, liquid paper containers such as milk cartons are made of cardboard coated with polyethylene resin on both sides and have a gable roof shape at the top, known as gable-top paper containers. Such paper containers contribute to resource and energy conservation, and also contribute to environmental protection by being easy to recycle or incinerate when disposed of. For this reason, paper containers are becoming widespread in various fields.

[0003] However, the paper containers described above are formed by folding and laminating cardboard, resulting in a complex manufacturing process and high production costs. Furthermore, the limited flexibility in shape of these paper containers prevents them from fully leveraging the product's appeal based on its form.

[0004] One method for increasing the freedom of shape in paper containers is pulp molding, which involves manufacturing molded products from a slurry containing pulp and water. In pulp molding, the pulp in the slurry is generally deposited on a mold to form a pulp layer, this pulp layer is dewatered, and then dried in a furnace. The molded products obtained by this technology, i.e., pulp molded products, have excellent physical properties such as heat resistance, cold resistance, and moisture absorption and release, which are characteristic of paper-based packaging materials, and are increasingly being used as paper tray containers for food and as cushioning materials for fixing fruits, etc. (Patent Document 1). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2008-285188 [Overview of the project] [Problems that the invention aims to solve]

[0006] The present invention aims to provide a pulp molded product that is less prone to buckling even when a load is applied, such as when the container is filled with contents and stacked. [Means for solving the problem]

[0007] According to one aspect of the present invention, a pulp molded article having a thickness of 1.5 mm or less and an ISO ring crush compressive strength in the range of 6 to 25 kN / m is provided.

[0008] According to another aspect of the present invention, the density is 0.5 to 1.15 g / cm³. 3 A pulp molded product relating to the above-mentioned side within the range is provided.

[0009] According to yet another aspect of the present invention, a pulp molded article relating to any of the above aspects is provided, wherein the average fiber length of the pulp is in the range of 0.7 to 3.0 mm.

[0010] According to yet another aspect of the present invention, the density is 0.5 to 1.15 g / cm³. 3 A pulp molded product relating to any of the above-mentioned sides is provided, which is within the range and has an average fiber length of pulp within the range of 0.7 to 3.0 mm.

[0011] In yet another aspect of the present invention, a pulp molded article relating to any of the above aspects, including non-wood pulp, is provided.

[0012] According to yet another aspect of the present invention, a pulp molded article is provided which has an opening and tapers toward the direction away from the opening, relating to any of the above-mentioned sides.

[0013] According to still another aspect of the present invention, there is provided a pulp mold molded article related to any of the above-mentioned side surfaces which is a container.

[0014] According to still another aspect of the present invention, there is provided a method for manufacturing a pulp mold molded article, including: preparing a slurry containing pulp and water; depositing the pulp on a forming mold having a three-dimensional shape to form a pulp layer; dehydrating the pulp layer to obtain an intermediate molded article; and sandwiching the undried intermediate molded article between a male mold and a female mold, and heating it at a temperature within the range of 120 to 250 °C while applying pressure within the range of 0.5 to 10 MPa.

Advantages of the Invention

[0015] According to the present invention, it is possible to provide a pulp mold molded article that is unlikely to buckle even when a load is applied, such as when the container is filled with contents and stacked.

Brief Description of the Drawings

[0016] [Figure 1] A perspective view showing a pulp mold molded article according to an embodiment of the present invention. [Figure 2] A diagram schematically showing an example of a manufacturing apparatus that can be used for manufacturing the pulp mold molded article of FIG. 1. [Figure 3] A diagram showing a pulp layer forming step in pulp mold molding using the apparatus of FIG. 2. [Figure 4] A cross-sectional view schematically showing an example of a pulp layer formed on a forming mold. [Figure 5] A diagram showing a dehydration step in pulp mold molding using the apparatus of FIG. 2. [Figure 6] A diagram showing a conveying step of a pulp layer in pulp mold molding using the apparatus of FIG. 2. [Figure 7] A diagram showing a hot press forming step in pulp mold molding using the apparatus of FIG. 2. [Figure 8] A cross-sectional view schematically showing an example of a pulp mold molded article obtained by a hot press step. [Figure 9] This figure shows the transport process for pulp molded products in pulp molding using the apparatus shown in Figure 2. [Figure 10] Figure 9 shows the state after the transport process has been completed. [Modes for carrying out the invention]

[0017] Embodiments of the present invention will be described below with reference to the drawings. The embodiments described below are more specific to any of the above aspects. The matters described below can be incorporated into each of the above aspects, individually or in combination.

[0018] Furthermore, the embodiments shown below illustrate configurations for realizing the technical concept of the present invention, and the technical concept of the present invention is not limited by the material, shape, and structure of the components described below. Various modifications can be made to the technical concept of the present invention within the technical scope defined by the claims described in the claims.

[0019] Elements with similar or identical functions are given the same reference numerals in the drawings referenced below, and redundant explanations are omitted. Furthermore, the drawings are schematic, and the relationships between dimensions in one direction and those in another, and the relationships between the dimensions of one component and those of another, may differ from reality.

[0020] <1> Pulp molded products Figure 1 is a perspective view showing a pulp molded product according to one embodiment of the present invention. The pulp molded product MP2 shown in Figure 1 has an opening and tapers away from the opening. This pulp molded product MP2 is a container. This pulp molded product MP2 includes a bottom and side walls and is open at the top.

[0021] The bottom has a disc shape. The orthogonal projection of the bottom onto a plane perpendicular to the depth direction of the container may have a shape other than a circle, such as a polygon such as a square.

[0022] The side walls have a cylindrical shape extending upward from the edge of the bottom. The side walls widen in diameter from the bottom towards the opening. The inner and outer surfaces of the side walls may be perpendicular to the top surface of the bottom. However, pulp molded products MP2 with side walls that widen in diameter from the bottom towards the opening are advantageous in achieving high release properties and are easy to stack. In addition, with such a shape, the volume of a laminate formed by stacking multiple pulp molded products MP2 can be reduced.

[0023] Pulp molded articles MP2 can have various shapes, such as cup, bowl, tray, and box shapes. Pulp molded articles MP2 do not have to be containers, as long as they are three-dimensional molded articles, i.e., not two-dimensional like a sheet.

[0024] The pulp molded product MP2 has a thickness of 1.5 mm or less. Preferably, the thickness of the pulp molded product MP2 is 1.2 mm or less, more preferably 1 mm or less. There is no particular lower limit for the thickness, but for example, it is 0.6 mm or more. The thickness of the pulp molded product MP2 is the thickness of the wall portion of the pulp molded product MP2, in this case, the thickness of the bottom portion and the side wall portion. If the wall thickness differs between the bottom portion and the side wall portion, the thickness of the pulp molded product MP2 is the thickness of the thinner of the bottom portion and the side wall portion.

[0025] Here, the thickness of the pulp molded product MP2 is obtained by the following method: Five test pieces are cut from any position on the pulp molded product MP2. Then, the thickness of each test piece is measured. For thickness measurement, for example, a thickness gauge manufactured by Mitutoyo Corporation is used. The thickness of the pulp molded product MP2 is taken as the average value of the measurement results obtained from the five test pieces.

[0026] The pulp molded article MP2 has an ISO ring crush compressive strength in the range of 6 to 25 kN / m. Preferably, the ISO ring crush compressive strength of the pulp molded article MP2 is in the range of 8 to 24 kN / m, more preferably in the range of 9 to 24 kN / m.

[0027] Here, the ISO ring crush compressive strength of the pulp molded product MP2 is the value obtained by the method specified in JIS P8126:2015 "Compressive strength test method - Ring crush method". The compressive strength is determined by placing a long, slender test piece bent into a cylindrical (ring) shape between parallel upper and lower compression plates, applying a compressive load to cause buckling, obtaining the maximum load, and dividing the obtained maximum load by the length of the test piece. In this test method, the long, slender test piece is prepared by cutting a strip-shaped test piece with a width of 15 mm and a length of 145 mm from the pulp molded product MP2. Therefore, if the ISO ring crush compressive strength of the pulp molded product MP2 is high, buckling is less likely to occur even when a load is applied. However, if the ISO ring crush compressive strength of the pulp molded product MP2 is too high, it becomes more susceptible to breakage when subjected to impact loads such as drops.

[0028] Despite its thinness, the pulp molded product MP2 is resistant to buckling even under load. For example, when using pulp molded product MP2 as a container, buckling is unlikely even when the product is filled with contents and stacked. In addition, pulp molded product MP2 is resistant to breakage even under impact load. Furthermore, because of its thinness, pulp molded product MP2 is lightweight and does not take up much space when stacked. Therefore, pulp molded product MP2 is convenient for storage and use. Also, making the walls of pulp molded product MP2 thin is advantageous in that it allows for quick drying during manufacturing.

[0029] Pulp molded products MP2 have a density of 0.5 to 1.15 g / cm³.3 It is preferable that it be within the range of 0.6 to 1.15 g / cm³. 3 It is more preferable for the density to be within this range. Higher density means improved density of the pulp mold, which provides resistance when external forces are applied, and is thought to contribute to improved strength, such as ISO ring crush compressive strength. However, if the density is too high, the hardness increases, making it more susceptible to breakage when subjected to impact loads such as drops.

[0030] Here, the density mentioned above is obtained by the following method: A square or rectangular test piece is cut from the non-curved portion of the pulp molded product MP2, and its dimensions, mass, and thickness are measured. The density is then calculated from the obtained values.

[0031] Pulp molded products MP2 have a basis weight of 550 to 980 g / m². 2 Preferably, it should be within the range of 580 to 950 g / m². 2 It is more preferable that the basis weight is within the specified range. A higher basis weight means improved density of the pulp mold, which provides resistance when external forces are applied, and is thought to contribute to improved strength, such as ISO ring crush compressive strength. However, if the basis weight is too high, the hardness increases, making it more susceptible to breakage when subjected to impact loads such as drops.

[0032] Here, the basis weight mentioned above is obtained by the following method: Similar to obtaining the density value, a square or rectangular test piece is cut from the non-curved portion of the pulp molded product MP2, and its dimensions and mass are measured. The basis weight is then calculated from the obtained values.

[0033] In the pulp molded product MP2, the average fiber length of the pulp is preferably in the range of 0.7 to 3.0 mm, and more preferably in the range of 1 to 2 mm.

[0034] If the average fiber length of the pulp is long, the strength of the pulp molded product MP2, such as the ISO ring crush compressive strength, decreases. If the average fiber length of the pulp is short, it becomes easier to increase the density of the pulp molded product MP2, and the strength, such as the ISO ring crush compressive strength, increases. However, if the average fiber length of the pulp is short, distortion is more likely to occur in the pulp molded product MP2 during drying, which can easily cause irregularities on the surface of the pulp molded product MP2. Furthermore, if the average fiber length of the pulp is made excessively short, it becomes difficult to complete the drying process in a short time during manufacturing, or cracks and reduced release properties due to insufficient drying are more likely to occur.

[0035] Here, the average fiber length of the pulp is obtained by the following method. First, a 5g test piece is taken from the pulp molded product MP2. Next, this test piece is finely shredded and immersed in 500mL of water overnight. Then, it is stirred with a stirrer to separate the pulp from each other. In this way, a dispersion containing pulp is obtained. Next, 10g is taken from this dispersion and diluted with water. This dilution is performed so that the total mass is 200g. Using the sample obtained in this way, the fiber length is measured according to JIS P8226-2:2011 "Pulp - Method for determining fiber length by optical automated analysis - Part 2: Non-polarized method". The average fiber length of the pulp is the length-weighted average fiber length L L It refers to.

[0036] The pulp suspension obtained by dispersing the pulp contained in the pulp molded product MP2 in water preferably has a Canadian standard filtration efficiency (CSF) of 700 mL or less, and more preferably 680 mL or less. If the Canadian standard filtration efficiency is high, the strength of the pulp molded product MP2, such as the ISO ring crush compressive strength, tends to decrease.

[0037] The above Canadian standard water content is preferably 500 mL or more, and more preferably 550 mL or more. If the Canadian standard water content is low, the strength of the pulp molded product MP2, such as the ISO ring crush compressive strength, will be high, but the pulp molded product MP2 is more prone to distortion during drying, which can easily result in unevenness on the surface of the pulp molded product MP2. In addition, if the Canadian standard water content is low, the drying time during manufacturing tends to be longer.

[0038] Here, the Canadian standard filtration rate mentioned above is obtained by the following method. First, a test specimen is taken from the pulp molded product MP2, and a dispersion containing pulp is obtained by the same method as described above. Next, this dispersion is diluted with water to obtain an aqueous suspension of pulp with a solid content concentration of 0.3% by mass. Then, 1 L of this suspension is used to perform the measurement specified in JIS P8121-2:2012 "Pulp - Test method for filtration rate - Part 2: Canadian standard filtration rate method". For this measurement, for example, a Canadian Free Tester manufactured by Kumagai Riki Kogyo Co., Ltd. is used. The measured value is corrected by referring to a correction table with the temperature of the suspension, which has been measured in advance. In this way, the Canadian standard filtration rate is obtained.

[0039] The pulp molded product MP2 preferably has a compressive strength of 0.65 kN or more, and more preferably 0.7 kN or more. There is no particular upper limit for the compressive strength, but one example is 2.2 kN. In other words, if the pulp molded product MP2 has a high compressive strength, it is less likely to undergo compressive deformation even when a load is applied. For example, when the pulp molded product MP2 is used as a container, even when it is filled with contents and stacked, compressive deformation is less likely to occur.

[0040] Here, compressive strength is the maximum compressive load at which the molded product maintains its shape when the load applied in the vertical direction is increased, as specified in JIS Z0212:1998 "Packaged goods and containers - Compression test method". In this test, a box-shaped pulp molded product is used as the molded product, with a square base having sides of 150 mm and four walls with a height of 40 mm.

[0041] Pulp molded product MP2 may further contain paper strength enhancers such as polyacrylamide. The use of paper strength enhancers can increase the strength of pulp molded product MP2.

[0042] Pulp molded products MP2 manufactured using paper strength enhancers have a higher nitrogen content compared to pulp molded products MP2 manufactured without paper strength enhancers. The nitrogen content of pulp molded products MP2 manufactured using paper strength enhancers is, in one example, 300 μg / g or more, and in other examples, 500 μg / g or more. While there is no upper limit to the nitrogen content of pulp molded products MP2, in one example, it is 1000 μg / g or less.

[0043] The nitrogen content of the pulp molded product MP2 is obtained by the following method. First, two test pieces are taken from any position on the pulp molded product MP2. The mass of each test piece is 10 mg. Next, each test piece is measured by the chemiluminescence method specified in JIS K2609:1998 "Crude oil and petroleum products - Nitrogen analysis test method". For this measurement, for example, the TN-2100H manufactured by Nitto Seiko Airanatech Co., Ltd. can be used. The nitrogen content is the average value of the measurement results obtained from the two test pieces. Note that the pulp molded product MP2 described above can maintain high strength even without paper strength enhancers.

[0044] <2> Manufacturing equipment for pulp molded products Next, we will describe the manufacturing equipment available for producing pulp molded products MP2. Figure 2 is a schematic diagram showing an example of a manufacturing apparatus that can be used to produce the pulp molded product shown in Figure 1.

[0045] The manufacturing apparatus 1 shown in Figure 2 includes a support 10, a first station 20, a second station 30, and a third station 40.

[0046] The support 10 includes a frame and rails installed on its upper part.

[0047] The first station includes a container 210, a lifting device 220, a cover body 230, a mold 240, a moving device 250, a lifting device 260, and an upper mold 270.

[0048] The container 210 is installed within the frame of the support 10. The container 210 is open at the top. The container 210 contains a slurry S containing pulp and water.

[0049] The lifting device 220 is mounted above the container 210 and attached to the frame of the support 10. The lifting device 220 includes, for example, a hydraulic cylinder. The lifting device 220 supports the cover body 230. The lifting device 220 can raise and lower the cover body 230 to the position of the opening of the container 210.

[0050] The cover body 230 is a hollow body with an opening at the top. A pump (not shown) is connected to the cover body 230.

[0051] The mold 240 is fixed to the opening of the cover body 230. Specifically, the mold 240 is fixed to the opening of the cover body 230 such that one side of the mold 240 and the adjacent space are enclosed by the mold 240 and the cover body 230.

[0052] The mold 240 is a liquid-permeable mold. The mold 240 has a three-dimensional shape. That is, the mold 240 has one or more protrusions and / or one or more recesses on the surface where the pulp is deposited. Specifically, the outer surface of the mold 240, i.e., the back surface of the surface adjacent to the above-mentioned space, has a shape corresponding to the pulp molded product. Here, the mold 240 is a male mold with a protruding top surface.

[0053] The mold 240 includes, for example, a mold body having numerous through holes and an outer surface shaped to correspond to a pulp molded product, and a mesh body provided on the outer surface of the mold body so as to follow the outer surface. The mold body is made of a hard material such as metal.

[0054] The mobile device 250 is movable between the first station 20 and the second station 30 along rails on the support 10. The mobile device 250 includes, for example, a motor as a power source. A lifting device 260 is attached to the mobile device 250, which can be transported between the first station 20 and the second station 30.

[0055] The lifting device 260 is attached to the moving device 250 as described above. The lifting device 260 includes, for example, a hydraulic cylinder. The lifting device 260 supports the upper mold 270. The lifting device 260 can raise and lower the upper mold 270.

[0056] The upper mold 270 is a holder that holds the pulp layer, described later, between itself and the paper mold 240 using vacuum suction. The upper mold 270 is made of a hard material such as metal. The lower surface of the upper mold 270 has a shape corresponding to the outer surface of the paper mold 240. Here, the upper mold 270 is a female mold with a concave lower surface. For example, the upper mold 270 has numerous through holes, one end of which opens at the lower surface and the other end of which is connected to a pump.

[0057] The second station 30 is located near the first station 20. The second station 30 includes a base 310, a lower die 320, a moving device 330, a pressing device 340, and an upper die 350.

[0058] The base 310 is installed inside the frame of the support 10. The lower mold 320 is installed on the base 310.

[0059] The lower mold 320 is a mold that is permeable to gas and / or liquid. The lower mold 320 is made of a hard material such as metal. The upper surface of the lower mold 320 has a shape that corresponds to the outer surface of the mold 240. Here, the lower mold 320 is a male mold with a protruding upper surface. The lower mold 320 has, for example, numerous through holes and a smooth surface that has a shape corresponding to the outer surface of the mold 240.

[0060] The mobile device 330 is movable along rails on the support 10 between the second station 30 and a fourth station (not shown). The mobile device 330 includes, for example, a motor as a power source. When the mobile device 330 is located at the second station 30, its movement in the vertical, horizontal, and longitudinal directions can be restricted by a locking mechanism. A press device 340 is also attached to the mobile device 330, which can be transported between the second station 30 and the fourth station.

[0061] The press device 340 is attached to the moving device 330 as described above. The press device 340 includes, for example, a hydraulic cylinder. The press device 340 supports the upper die 350. The press device 340 can raise and lower the upper die 350.

[0062] The upper mold 350 is a mold that is impermeable to gases and liquids. The upper mold 350 is made of a hard material such as metal. The lower surface of the upper mold 350 has a shape corresponding to the outer surface of the mold 240. Here, the upper mold 350 is a female mold with a concave lower surface. The upper mold 350 has a smooth surface that has a shape corresponding to the outer surface of the mold 240.

[0063] The second station 30 further includes a heater and a pump (neither of which are shown). The heater heats at least one of the lower mold 320 and the upper mold 350. The pump is connected to the lower space of the lower mold 320.

[0064] The third station 40 is located near the second station 30. The third station 40 includes a platform 410, a moving device 420, a lifting device 430, and a holder 440.

[0065] The base 410 is installed inside the frame of the support 10. A pulp molded product is placed on the base 410.

[0066] The mobile device 420 is movable between the second station 30 and the third station 40 along rails on the support 10. The mobile device 420 includes, for example, a motor as a power source. A lifting device 430 is attached to the mobile device 420, which can be transported between the second station 30 and the third station 40.

[0067] The lifting device 430 is attached to the moving device 420 as described above. The lifting device 430 includes, for example, a hydraulic cylinder. The lifting device 430 supports the holder 440. The lifting device 430 can raise and lower the holder 440.

[0068] The holder 440 is a holder that holds the pulp molded product, described later, by vacuum suction. The lower surface of the holder 440 has a shape corresponding to the outer surface of the mold 240. Here, the holder 440 has a concave shape on its lower surface. The holder 440 has, for example, a number of through holes, one end of which opens on the lower surface and the other end of which is connected to a pump.

[0069] <3> Method for manufacturing pulp molded products In a manufacturing method according to one embodiment of the present invention, for example, a pulp molded product MP2 is manufactured using the manufacturing apparatus 1 described above. This will be explained with reference to Figures 1 to 10.

[0070] Figure 3 shows the pulp layer formation process in pulp molding using the apparatus shown in Figure 2. Figure 4 is a schematic cross-sectional view showing an example of a pulp layer formed on a mold. Figure 5 shows the dewatering process in pulp molding using the apparatus shown in Figure 2. Figure 6 shows the pulp layer transport process in pulp molding using the apparatus shown in Figure 2. Figure 7 shows the hot press forming process in pulp molding using the apparatus shown in Figure 2. Figure 8 is a schematic cross-sectional view showing an example of a pulp molded product obtained by the hot press process. Figure 9 shows the transport process of the pulp molded product in pulp molding using the apparatus shown in Figure 2. Figure 10 shows the state after the transport process in Figure 9 has been completed.

[0071] In this method, first, prepare slurry S. As described above, slurry S contains pulp and water. Slurry S is a suspension in which pulp is dispersed in water and has high viscosity. The pulp contained in slurry S has almost the same characteristics as the pulp contained in pulp molded product MP2, as described above.

[0072] There are no particular restrictions on the type of pulp used in Slurry S. As pulp, for example, wood pulp such as bleached kraft pulp (NBKP) or unbleached kraft pulp (NUKP) of softwood and bleached kraft pulp (LBKP) or unbleached kraft pulp (LUKP) of hardwood, which are commonly used as raw material pulp in papermaking, or non-wood pulp such as straw, cotton, kenaf, bamboo, and sugarcane can be used individually or in any proportion of two or more types.

[0073] The pulp preferably contains non-wood pulp, and more preferably contains non-wood pulp as the main component (i.e., in an amount greater than 50% by mass of the pulp). Non-wood pulp is superior in that it can be used to produce pulp molded products MP2 with strength comparable to that of wood pulp, and also in that it can reduce the environmental impact.

[0074] Pulp varies in fiber length and other characteristics depending on its raw materials and manufacturing methods. For example, pulp made from sugarcane generally has a shorter average fiber length than pulp made from bamboo. Furthermore, the average fiber length of pulp can be adjusted by any method, such as mechanical processing like beating or crushing. Therefore, pulp with certain characteristics can be obtained, for example, by selecting an appropriate type from among several types of pulp, or by appropriately combining two or more types of pulp.

[0075] In this method, the hot pressing process is carried out on an undried pulp layer. That is, the hot pressing process is carried out on a pulp layer with a high moisture content. Therefore, if the average fiber length of the pulp is too short, unevenness in the rate of moisture evaporation is likely to occur during the hot pressing process, and uneven shrinkage during drying can occur, potentially leading to wrinkles, cracks, or a decrease in strength.

[0076] If the average fiber length of the pulp is long, the likelihood of uneven drying within the pulp layer during the hot pressing process is reduced. Therefore, it is possible to prevent the production of pulp molded products with defects in appearance or reduced strength.

[0077] The pulp content of slurry S is preferably in the range of 0.01 to 3.0% by mass, and more preferably in the range of 0.01 to 0.5% by mass. If the pulp content is too low, it is difficult to achieve high productivity. If the pulp content is too high, there is a possibility that the thickness of the pulp layer will vary greatly.

[0078] The slurry S may further contain additives. These additives may include organic low-molecular-weight materials, organic high-molecular-weight materials, inorganic materials, or combinations thereof. Examples include agents that impart water resistance or oil resistance; however, the appropriate agent should be selected according to the required performance of the pulp molded container. The proportion of additives to the total of pulp and additives is preferably 10% by mass or less, and more preferably 5% by mass or less. That is, the proportion of pulp to the total solid content of slurry S is preferably 90% by mass or more, and more preferably 95% by mass or more.

[0079] Next, slurry S is supplied into the container 210. Then, as shown in Figure 3, the cover body 230 is lowered by the lifting device 220 so that the upper surface of the mold 240 is positioned well below the liquid level of slurry S. This immerses the mold 240, which is installed on top of the cover body 230, in the slurry. In this state, the pump is driven to reduce the pressure in the space enclosed by the cover body 230 and the mold 240. This creates a flow of slurry S across the mold 240, causing pulp to accumulate on the mold 240. In this way, a pulp layer MP1 is formed on the mold 240 as shown in Figure 4.

[0080] Next, with the pump still running, the cover body 230 is raised by the lifting device 220 as shown in Figure 5, so that the lower part of the mold 240 is positioned well above the liquid surface of the slurry S. This dewaters the pulp layer MP1 under reduced pressure. Next, the lifting device 260 is driven to lower the upper mold 270 until its lower surface contacts the pulp layer MP1. Note that the pulp layer MP1 is not shown in Figure 5. This dewatering process is carried out without heating either the upper mold 270 or the mold 240.

[0081] The depressurization time in the dewatering process is preferably within the range of 1 to 60 seconds, and more preferably within the range of 1 to 10 seconds.

[0082] The moisture content of the pulp layer MP1 immediately after dewatering is preferably in the range of 40 to 90% by mass, and more preferably in the range of 50 to 70% by mass. If the moisture content is too low, the in-plane movement of fibers within the pulp layer may be insufficient during the hot pressing process. If the moisture content is too high, the in-plane movement of fibers within the pulp layer may be excessive during the hot pressing process, or the shape retention of the pulp layer MP1 may be insufficient during the period between the end of the dewatering process and the start of the hot pressing process.

[0083] After stopping the depressurization and pressurization of the above-mentioned space, the pump is driven to adsorb and hold the pulp layer MP1 on the upper mold 270. Note that the suction by the pump and the upper mold 270 does not cause further dewatering of the pulp layer MP1.

[0084] Next, with the pulp layer MP1 adsorbed and held on the upper die 270, the lifting device 260 is driven to raise the upper die 270, as shown in Figure 2. This peels the pulp layer MP1 from the mold 240.

[0085] Next, the moving devices 250 and 330 are driven to move the press device 340 and upper die 350 from the second station 30 to the fourth station, as shown in Figure 6, and the lifting device 260 and upper die 270 from the first station 20 to the second station 30. Subsequently, the lifting device 260 is driven to lower the upper die 270 until the pulp layer MP1 contacts the lower die 320. After that, the suction by the pump and the upper die 270 is stopped to release the pulp layer MP1 from the upper die 270. Then, the lifting device 260 is driven to raise the upper die 270. In this way, the pulp layer MP1 is transferred from the first station 20 to the second station 30 and placed on the lower die 320.

[0086] Next, the moving devices 250 and 330 are driven to move the lifting device 260 and the upper die 270 from the second station 30 to the first station 20, as shown in Figure 2, and the pressing device 340 and the upper die 350 from the fourth station to the second station 30. Subsequently, the pressing device 340 is driven to lower the upper die 350, as shown in Figure 7. Then, the pulp layer MP1 sandwiched between the upper die 350 and the lower die 320 is pressurized. At the same time, the heater is driven to heat the pulp layer MP1. Furthermore, the pump is driven to suck and remove water and / or water vapor from the space sandwiched between the upper die 350 and the lower die 320. This smooths the surface shape of the pulp layer MP1 and densifies and dries the pulp layer MP1. In this way, the pulp molded product MP2 shown in Figure 8 is obtained.

[0087] Furthermore, the moisture content of the pulp layer MP1 immediately before starting this hot pressing process is approximately equal to the moisture content of the pulp layer MP1 immediately after the dewatering process is completed.

[0088] In this hot pressing process, the pressing pressure is preferably in the range of 0.5 to 10 MPa, and more preferably in the range of 1 to 9.5 MPa. If the pressing pressure is too low, it may not be possible to obtain a pulp molded product MP2 with high strength. If the pressing pressure is too high, variations in the thickness of the pulp molded product MP2 are likely to occur.

[0089] In this hot pressing process, the heating temperature of the pulp layer MP1, i.e., the temperature of the upper mold 350 or lower mold 320 heated by the heater, is preferably in the range of 120 to 250°C, and more preferably in the range of 150 to 200°C. If the heating temperature is too low, it will take a long time to dry the pulp layer MP1. If the heating temperature is too high, the shrinkage of the pulp layer MP1 due to drying will be greater, which may result in greater distortion in the pulp molded product MP2.

[0090] As described above, heating with the heater may be applied to only one of the upper mold 350 and the lower mold 320, or to both. When heating with the heater is applied to only one of the upper mold 350 and the lower mold 320, their temperatures become approximately equal due to heat conduction from one to the other. Therefore, in either case, the drying of the pulp layer MP1 proceeds almost simultaneously across its entire thickness. Consequently, no distortion occurs in the pulp molded product MP2 due to differences in drying speed.

[0091] The pressing time in the hot pressing process depends on the heating temperature, the shape of the molded product, etc., but is preferably in the range of 10 to 300 seconds, and more preferably in the range of 20 to 200 seconds.

[0092] When the above hot pressing process is completed, the press device 340 is driven to raise the upper die 350, causing the pulp molded product MP2 to detach from the upper die 350.

[0093] Next, the moving devices 330 and 420 are driven to move the press device 340 and upper die 350 from the second station 30 to the fourth station, as shown in Figure 9, and the lifting device 430 and holder 440 are moved from the third station 40 to the second station 30. Subsequently, the lifting device 430 is driven to lower the holder 440 until it contacts the pulp molded product MP2. Air is blown from inside the lower die to release the pulp molded product MP2 from the lower die, and then the pump is driven to hold the pulp molded product MP2 in place by suction on the holder 440.

[0094] Next, with the pulp molded product MP2 held by the holder 440, the lifting device 430 is driven to raise the holder 440. Subsequently, the moving devices 330 and 420 are driven to move the lifting device 430 and the holder 440 from the second station 30 to the third station 40, as shown in Figure 10, and the press device 340 and the upper die 350 from the fourth station to the second station 30. Subsequently, the suction by the pump and the holder 440 is stopped, releasing the pulp molded product MP2 from the holder 440. In this way, the pulp molded product MP2 is transferred from the second station 30 to the third station 40, and the pulp molded product MP2 is placed on the base 410. The pulp molded product MP2 is manufactured in the manner described above.

[0095] Subsequently, if necessary, the pulp molded product MP2 is subjected to post-processing, such as printing with patterns or blanks, coating, or a combination thereof. The coating layer formed by post-processing may be, for example, a layer containing agents that impart water resistance or oil resistance, a layer filled with materials that impart heat insulation, a layer foamed with a foaming agent, or a combination thereof. By performing post-processing, for example, the aesthetic appeal of the pulp molded product MP2 can be further enhanced, or new functions can be added to the pulp molded product MP2.

[0096] The pulp molded product MP2 obtained by the above method has excellent surface properties, and is particularly superior in that it has few irregularities on its surface. The reason for this is explained below.

[0097] When drying is performed using an oven instead of a hot pressing process, the pulp layer develops significant surface irregularities due to shrinkage. Furthermore, the pulp layer is not sufficiently densified using this method, resulting in pulp molded products with high porosity. Consequently, it is not possible to manufacture pulp molded products with superior surface properties in this case.

[0098] Furthermore, if drying is performed using an oven after the dewatering process, and the dried product is humidified as needed before being subjected to a heat press treatment, the height differences of the surface irregularities created during drying can be reduced by the subsequent humidification and heat press treatment. Also, the porosity can be reduced by the humidification and heat press treatment. However, the height differences of the surface irregularities created during oven drying are very large, so they cannot be sufficiently reduced by the subsequent humidification and heat press treatment. Moreover, even if humidification and heat press treatment are performed after drying, it is difficult to sufficiently reduce the porosity.

[0099] In the method described with reference to Figures 2 to 10, the pulp layer MP1 is dried during the hot pressing process. That is, in the above method, the hot pressing process is carried out after the dewatering process without going through the drying process. Furthermore, the pulp used has an average fiber length within the range described above.

[0100] Since no drying process is performed before the hot pressing process, large unevenness in height does not occur on the surface of the pulp layer MP1. During the hot pressing process, the upper die 350 and lower die 320 prevent deformation of the pulp layer MP1 due to drying. Furthermore, since the hot pressing process is performed on the pulp layer MP1 with a high moisture content and an average fiber length within the above-mentioned range, moderate in-plane fiber movement can occur within the pulp layer MP1. As a result, the pulp layer MP1 can be densified while suppressing variations in thickness.

[0101] Therefore, according to the method described with reference to Figures 2 to 10 (hereinafter also referred to as the first method), a pulp molded product MP2 with excellent surface properties can be manufactured. Specifically, a pulp molded product MP2 with few surface irregularities can be obtained. Such a pulp molded product MP2 has excellent aesthetic appeal and facilitates the formation of printed or coated layers.

[0102] General pulp molded articles can be manufactured by methods other than the first method. However, the aforementioned pulp molded article MP2, which has excellent surface properties, is difficult to manufacture by methods other than the first method. This will be explained below with an example of another method (hereinafter referred to as the second method).

[0103] In the second method, first, a female mold is prepared as a mold. This mold includes a mold body with numerous through holes and an upper surface recessed to a shape corresponding to the pulp molded product, and a mesh body provided on the inner surface of the mold body so as to follow the inner surface.

[0104] Next, the mold is positioned so that its opening faces upward. Then, a slurry containing pulp and water is supplied into the cavity of the mold to fill it with slurry. Furthermore, the supply of slurry into the mold is continued to deposit pulp on the mesh. The supply of slurry into the mold is carried out in such a way that the slurry inside the mold is pressurized.

[0105] After a sufficient amount of pulp has accumulated on the mesh, the supply of slurry into the mold is stopped. Subsequently, any water remaining in the mold is discharged. For example, air is injected into the mold to discharge any remaining water.

[0106] Next, the pulp layer is pressed between the papermaking mold and the upper mold (which is the male mold) to dewater the pulp layer. This dewatering process is carried out without heating either the upper mold or the papermaking mold. The moisture content of the pulp layer immediately after dewatering is the same as the moisture content of the pulp layer MP1 immediately after dewatering in the first method.

[0107] Next, the pulp layer is adsorbed and held by the upper mold, and the upper mold is raised in this state. This separates the pulp layer from the mold.

[0108] Next, the upper mold, which is holding the pulp layer by adsorption, is moved to the position of the lower mold, which is the female mold. Then, the upper mold is lowered until the pulp layer comes into contact with the lower mold. After that, the suction is stopped and the pulp layer is released from the upper mold. In this way, the pulp layer is placed on the lower mold.

[0109] Next, a pulp layer is placed between an upper die and a lower die for hot pressing, and the pulp layer between them is pressurized. At the same time, a heater is driven to heat the pulp layer. Furthermore, a pump is driven to suck and remove water and / or steam from the space between the upper and lower dies. In the second method, a pulp molded product is obtained in the manner described above.

[0110] In the second method, a circulating slurry flow can be generated within the mold from the start of slurry supply to the mold until the mold is completely filled with slurry. This circulating flow can prevent pulp sedimentation. However, in the second method, since the mold must be filled with slurry, the mold cannot be designed to allow water to be quickly discharged. Therefore, after the mold is completely filled with slurry, even if the slurry pressure is increased, a circulating slurry flow sufficient to prevent pulp sedimentation will not be generated, and pulp sedimentation will occur in the slurry within the mold.

[0111] As a result, the amount of pulp that accumulates on the side walls of the mold is greater at the bottom compared to the top. When slurry is supplied until a sufficient amount of pulp accumulates on the upper side walls of the mold, an excess amount of pulp will accumulate at the bottom of the mold. Excessive pulp accumulation leads to greater variation in the amount of pulp accumulated. For example, there may be a large difference in the amount of pulp accumulated near through holes in the mold body and at positions further away from them.

[0112] Thus, the second method results in significant variation in the amount of pulp deposited. During the hot pressing process, fibers can move in the in-plane direction within the pulp layer, but the movement of each fiber is limited to a narrow range. In other words, the variation in the amount of pulp deposited is not eliminated by the movement of fibers during the hot pressing process. Therefore, the second method cannot produce pulp molded products with a smooth surface.

[0113] In contrast, in the first method, a mold 240 is placed on top of the cover body 230, and the composite is immersed in the slurry S. The depth of the slurry S is much greater than the height of the mold 240. Therefore, even if pulp sedimentation occurs in the slurry S, the pulp concentration does not differ significantly between the upper and lower positions of the mold 240. Consequently, according to the first method, pulp can be deposited almost uniformly on the mold 240, and a pulp molded product MP2 with few irregularities on the surface can be manufactured.

[0114] Furthermore, in the first method, if the pulp layer MP1 is sandwiched between one of the upper or lower molds 350 and an elastic body and then pressed, instead of being pressed by the upper mold 350 and the lower mold 320, deformation of the elastic body occurs. Therefore, insufficient pressure is applied to the pulp layer MP1, and it is not possible to obtain a pulp molded product with excellent surface properties.

[0115] Furthermore, it goes without saying that in the second method, even if one of the upper or lower molds used in the hot pressing process is changed to an elastic material, it is not possible to obtain a pulp molded product with superior surface properties.

[0116] Note that FIGS. 2 to 10 are provided to facilitate the understanding of the method for manufacturing a pulp molded product according to an embodiment of the present invention. The above-described method can also be implemented using a manufacturing apparatus having other structures. For example, in the manufacturing apparatus 1, the upper mold 270 and the upper mold 350 are female molds, and the forming mold 240 and the lower mold 320 are male molds. The upper mold 270 and the upper mold 350 may be male molds, and the forming mold 240 and the lower mold 320 may be female molds. Thus, various modifications are possible for the above-described manufacturing apparatus 1 and manufacturing method.

Example

[0117] Specific examples of the present invention are described below. The present invention is not limited to these specific examples.

[0118] <1>Manufacture of Pulp Molded Product (Example 1) Using a pulper, a slurry composed of pulp and water was prepared. As the pulp, bamboo pulp having an average fiber length of 1.6 mm was used. The pulp content of the slurry was 0.3% by mass.

[0119] Using this slurry, a pulp molded product was manufactured by the method (i.e., the first method) described while referring to FIGS. 2 to 10. Here, the dehydration step was performed such that the water content of the pulp layer immediately after dehydration was 60% by mass. The hot press step was performed with a heating temperature of 180°C, a press pressure of 1.2 MPa, and a press time of 80 seconds. In the dehydration step and the hot press step, the clearance between the upper mold and the lower mold was set to 1.1 mm so that a pulp molded product having a wall thickness of 1.1 mm could be obtained. As described above, a container was manufactured as a pulp molded product. The obtained pulp molded product had a wall thickness of 1.1 mm, a density of 0.71 g / cm 3 , and a basis weight of 780 g / m 2 .

[0120] (Example 2) A pulp molded product was manufactured using the same method as in Example 1, except that the pulp deposition amount was adjusted, the clearance between the upper and lower molds was set to 0.9 mm, and the pressing time was set to 82 seconds. The resulting pulp molded product had a wall thickness of 0.9 mm and a density of 0.94 g / cm³. 3 , basis weight 850g / m² 2 That was the case.

[0121] (Example 3) In Example 3, a mixture of 70% by mass of bamboo pulp (average fiber length: 1.6 mm) and 30% by mass of sugarcane pulp (average fiber length: 0.9 mm) was used as the pulp, with an average fiber length of 1.4 mm. Aside from using the above pulp and adjusting the pulp deposition amount to set the clearance between the upper and lower molds to 1.0 mm, the pulp molded product was manufactured using the same method as in Example 1. The resulting pulp molded product had a wall thickness of 1.0 mm and a density of 0.63 g / cm³. 3 , basis weight 600g / m² 2 That was the case.

[0122] (Example 4) A pulp molded product was manufactured using the same method as in Example 3, except that the amount of pulp deposited was adjusted and the clearance between the upper and lower molds was set to 0.7 mm. The resulting pulp molded product had a wall thickness of 0.7 mm and a density of 0.93 g / cm³. 3 The basis weight is 653 g / m². 2 That was the case.

[0123] (Example 5) A pulp molded product was manufactured using the same method as in Example 3, except that the amount of pulp deposited was adjusted, the clearance between the upper and lower molds was set to 1.1 mm, and the pressing time was set to 100 seconds. The resulting pulp molded product had a wall thickness of 1.1 mm and a density of 0.78 g / cm³. 3 The basis weight is 860 g / m². 2 That was the case.

[0124] (Example 6) A pulp molded product was manufactured using the same method as in Example 3, except that the pulp deposition amount was adjusted, the clearance between the upper and lower molds was set to 1.05 mm, and the pressing time was set to 110 seconds. The resulting pulp molded product had a wall thickness of 1.05 mm and a density of 0.89 g / cm³. 3 , basis weight 930g / m² 2 That was the case.

[0125] (Example 7) A pulp molded product was manufactured using the same method as in Example 3, except that the pulp deposition amount was adjusted, the clearance between the upper and lower molds was set to 0.9 mm, the press pressure was 5.7 MPa, and the press time was 110 seconds. The resulting pulp molded product had a wall thickness of 0.9 mm and a density of 1.02 g / cm³. 3 The basis weight is 910 g / m². 2 That was the case.

[0126] (Example 8) A pulp molded product was manufactured using the same method as in Example 3, except that the pulp deposition amount was adjusted, the clearance between the upper and lower molds was set to 0.8 mm, the press pressure was 9.6 MPa, and the press time was 110 seconds. The resulting pulp molded product had a wall thickness of 0.8 mm and a density of 1.10 g / cm³. 3 The basis weight is 935 g / m². 2 That was the case.

[0127] (Example 9) In Example 9, a mixture of 50% by mass of bamboo pulp (average fiber length: 1.6 mm) and 50% by mass of sugarcane pulp (average fiber length: 0.9 mm) was used as the pulp, with an average fiber length of 1.3 mm. Aside from using the above pulp, adjusting the pulp deposition amount, setting the clearance between the upper and lower molds to 0.9 mm, and the pressing time to 130 seconds, the pulp molded product was manufactured using the same method as in Example 1. The resulting pulp molded product had a wall thickness of 0.9 mm and a density of 1.10 g / cm³. 3 , basis weight 930g / m² 2 That was the case.

[0128] (Example 10) In Example 10, a mixture of 20% by mass of bamboo pulp (average fiber length: 1.6 mm) and 80% by mass of sugarcane pulp (average fiber length: 0.9 mm) was used as the pulp, with an average fiber length of 1.1 mm. Aside from using the above pulp, adjusting the pulp deposition amount, setting the clearance between the upper and lower molds to 0.8 mm, and the pressing time to 150 seconds, the pulp molded product was manufactured using the same method as in Example 1. The resulting pulp molded product had a wall thickness of 0.8 mm and a density of 1.15 g / cm³. 3 , basis weight 930g / m² 2 That was the case.

[0129] (Example 11) In Example 11, softwood pulp with an average fiber length of 2.5 mm was used as the pulp. Apart from the use of the above pulp, the adjustment of the pulp deposition amount, the clearance between the upper and lower molds being 0.9 mm, and the pressing time being 82 seconds, the pulp molded product was manufactured using the same method as in Example 1. The resulting pulp molded product had a wall thickness of 0.9 mm and a density of 0.94 g / cm³. 3 The basis weight is 860 g / m². 2 That was the case.

[0130] (Comparative Example 1) In Comparative Example 1, a mixture of 70% by mass of bamboo pulp (average fiber length: 1.6 mm) and 30% by mass of sugarcane pulp (average fiber length: 0.9 mm) was used as the pulp, with an average fiber length of 1.4 mm. A pulp molded product was manufactured using the same method as in Example 1, except for the use of the above pulp, adjustment of the pulp deposition amount to set the clearance between the upper and lower molds to 1.5 mm, the press pressure to 0 MPa, and the press time to 600 seconds. The resulting pulp molded product had a wall thickness of 1.5 mm and a density of 0.46 g / cm³. 3 , basis weight 690g / m² 2 That was the case.

[0131] (Comparative Example 2) In Comparative Example 1, a mixture of 70% by mass of bamboo pulp (average fiber length: 1.6 mm) and 30% by mass of sugarcane pulp (average fiber length: 0.9 mm) was used as the pulp, with an average fiber length of 1.4 mm. A pulp molded product was manufactured using the same method as in Example 1, except for the use of the above pulp, adjustment of the pulp deposition amount, setting the clearance between the upper and lower molds to 1.0 mm, the press pressure to 5.7 MPa, and the press time to 150 seconds. The resulting pulp molded product had a wall thickness of 1.0 mm and a density of 1.79 g / cm³. 3 The basis weight is 1700g / m². 2 That was the case.

[0132] <2> evaluation For each of the pulp molded articles produced in Examples 1 to 11 and Comparative Examples 1 to 2, various measurements were performed using the methods described above. The "ISO ring crush compressive strength" was measured according to the method specified in JIS P8126:2015 "Compressive strength test method - Ring crush method" as described above. In this measurement, test specimens were prepared by cutting out strip-shaped test specimens with a width of 15 mm and a length of 145 mm from the pulp molded article. The "compressive strength" was measured according to the method specified in JIS Z0212:1998 "Packaged goods and containers - Compression test method" as described above. For "Damage / cracking upon dropping," a box-shaped molded article with a width of 150 mm, a depth of 150 mm, and a height of 50 mm was used as a sample, and it was evaluated by visually observing whether damage or cracking occurred in the sample when it was dropped to the ground from a height of 120 centimeters.

[0133] The results are shown in Tables 1 and 2 below.

[0134] [Table 1]

[0135] [Table 2]

[0136] In Examples 1 to 11, it was possible to manufacture pulp molded articles with a thickness of 1.5 mm or less and an ISO ring crush compressive strength in the range of 6 to 25 kN / m. The pulp molded articles of Examples 1 to 11 also had high compressive strength in the box shape and excellent resistance to drop impact. The pulp molded articles of Examples 1 to 11 had excellent strength despite their small thickness.

[0137] On the other hand, in Comparative Example 1, a pulp molded product was manufactured with a thickness of 1.5 mm or less, but with an ISO ring crush compressive strength less than 6 kN / m. The pulp molded product of Comparative Example 1 also had low compressive strength in the box shape. In Comparative Example 2, a pulp molded product was manufactured with a thickness of 1.5 mm or less, but with an ISO ring crush compressive strength greater than 25 kN / m. As is clear from the density and basis weight values, the pulp molded product of Comparative Example 2 was much harder and was damaged or cracked when subjected to impact from a drop. [Explanation of symbols]

[0138] 1...Manufacturing equipment, 10...Support, 20...First station, 30...Second station, 40...Third station, 210...Container, 220...Lifting device, 230...Cover body, 240...Mold making, 250...Moving device, 260...Lifting device, 270...Upper mold, 310...Base, 320...Lower mold, 330...Moving device, 340...Pressing device, 350...Upper mold, 410...Base, 420...Moving device, 430...Lifting device, 440...Holder, MP1...Pulp layer, MP2...Pulp molded product, S...Slurry.

Claims

1. A pulp molded product having a thickness of 1.5 mm or less and an ISO ring crush compressive strength in the range of 6 to 25 kN / m.

2. Density of 0.5 to 1.15 g / cm³ ３ A pulp molded article according to claim 1, which is within the range of [specified range].

3. The pulp molded article according to claim 1, wherein the average fiber length of the pulp is in the range of 0.7 to 3.0 mm.

4. Density of 0.5 to 1.15 g / cm³ ３ The pulp molded article according to claim 1, wherein the average fiber length of the pulp is within the range of 0.7 to 3.0 mm.

5. A pulp molded article according to claim 1, comprising non-wood pulp.

6. A pulp molded article according to claim 1, having an opening and tapering away from the opening.

7. A pulp molded article according to claim 1, which is a container.

Images