Porous powder-containing paper, method for manufacturing the same, and processed products

Abstract

The present invention provides porous powder-containing paper that can suppress ink bleed-through even without a coating layer on its surface, a method for manufacturing the same, and processed products thereof. [Solution] The porous powder-containing paper comprises one or more paper substrate layers having a plurality of fibrous materials and a plurality of calcium-containing porous powders mixed with the plurality of fibrous materials and provided at least between the plurality of fibrous materials.

Description

[Technical Field]

[0001] This invention relates to porous powder-containing paper, a method for producing the same, and processed products thereof. [Background technology]

[0002] Traditionally, paper has been required to have high printability, and consequently, efforts have been made to improve the printability of paper.

[0003] For example, Patent Document 1 describes coated paper for suppressing ink bleed-through. In the coated paper of Patent Document 1, a coating agent containing an ethylene-vinyl alcohol copolymer, in which the ethylene unit content is 1 mol% or more and less than 20 mol%, and the ethylene unit block character is 0.90 to 0.99, is applied to the surface of the paper.

[0004] Patent Document 1 describes how coating the surface of coated paper to form a coating layer, thereby suppressing ink bleed-through. However, although the coated paper has a coating layer on its surface, the suppression of ink bleed-through was insufficient. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6865334 [Overview of the project] [Problems that the invention aims to solve]

[0006] The object of the present invention is to provide porous powder-containing paper that can suppress ink bleed-through even without a coating layer on its surface, a method for manufacturing the same, and processed products thereof. [Means for solving the problem]

[0007] [1] A porous powder-containing paper comprising one or more paper substrate layers having a plurality of fibrous materials and a plurality of calcium-containing porous powders mixed with the plurality of fibrous materials and provided at least between the plurality of fibrous materials. [2] The porous powder-containing paper according to [1] above, wherein the plurality of calcium-containing porous powders are porous powders of biological origin. [3] The porous powder-containing paper according to [1] or [2] above, wherein the plurality of calcium-containing porous powders are porous eggshell powder. [4] The porous powder-containing paper according to any one of [1] to [3] above, wherein the plurality of calcium-containing porous powders contain at least one element selected from the group consisting of Na, P, S, and K. [5] The porous powder-containing paper according to any one of [1] to [4] above, wherein the content of the plurality of calcium-containing porous powders contained in the porous powder-containing paper is 5% or more and 10% or less. [6] The porous powder-containing paper according to any one of [1] to [5], wherein the porous powder-containing paper comprises a plurality of paper substrate layers, and the content of the plurality of calcium-containing porous powders in the thickness direction of the porous powder-containing paper increases from the paper substrate layer located on the surface of the porous powder-containing paper toward the paper substrate layer located in the middle of the porous powder-containing paper. [7] The basis weight of the porous powder-containing paper is 50 g / m². 2 More than 1000g / m 2 The porous powder-containing paper described in any one of the above [1] to [6] is as follows: [8] A processed product made using porous powder-containing paper as described in any one of [1] to [7] above. [9] A method for producing porous powder-containing paper, comprising a forming step of forming one or more paper substrate layers in which multiple calcium-containing porous powders are mixed with multiple fibrous materials and provided at least between the multiple fibrous materials.

[10] The method for producing porous powder-containing paper according to [9] above, wherein the plurality of calcium-containing porous powders used in the forming step are eggshell powders produced by an egg-breaking step, a washing step, an eggshell membrane separation step and a fine grinding step, wherein the egg-breaking step separates the egg into contents and eggshell, the washing step washes the eggshells obtained in the egg-breaking step with a washing solution, the eggshell membrane separation step separates the eggshell membrane from the washed eggshells obtained in the washing step, and the fine grinding step grinds the eggshells obtained in the eggshell membrane separation step into powder, and the time from the start of the egg-breaking step to the completion of the eggshell membrane separation step is within one day. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide porous powder-containing paper that can suppress ink bleed-through even without a coating layer on its surface, a method for manufacturing the same, and processed products thereof. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a cross-sectional view and a partially enlarged cross-sectional view showing an example of porous powder-containing paper according to the embodiment. [Figure 2] Figure 2 is a cross-sectional view showing another example of the porous powder-containing paper of the embodiment, and a graph showing an example of the distribution of multiple calcium-containing porous powders within the cross-section. [Figure 3] Figure 3 is an SEM image of the calcium-containing porous powder extracted from the porous powder-containing paper produced in Example 1. [Figure 4] Figure 4 is a magnified SEM image of region A in Figure 3. [Modes for carrying out the invention]

[0010] The embodiments will be described in detail below.

[0011] Conventionally, the surface of paper is processed, for example, by providing a coating layer to improve the resistance to ink strike-through and printing performance. As a result of extensive and intensive studies, the present inventors have focused on the internal structure of paper, and found that ink strike-through of porous powder-containing paper can be suppressed even without providing a coating layer on the surface of the porous powder-containing paper, leading to the completion of the present invention based on such findings.

[0012] The porous powder-containing paper of the embodiment includes one or more paper substrate layers each having a plurality of fibrous substances, and a plurality of calcium-containing porous powders mixed with the plurality of fibrous substances and disposed at least between the plurality of fibrous substances.

[0013] The method for producing a porous powder-containing paper of the embodiment includes a forming step of forming one or more paper substrate layers in which a plurality of calcium-containing porous powders are mixed with a plurality of fibrous substances and disposed at least between the plurality of fibrous substances.

[0014] First, the porous powder-containing paper of the embodiment will be described. FIG. 1 is a cross-sectional view and a partially enlarged cross-sectional view showing an example of the porous powder-containing paper of the embodiment.

[0015] As shown in FIG. 1, the porous powder-containing paper 1 of the embodiment includes one or more paper substrate layers 10. The porous powder-containing paper 1 and the paper substrate layer 10 are each in the form of a sheet. FIG. 1 shows the porous powder-containing paper 1 provided with one paper substrate layer 10.

[0016] The paper substrate layer 10 constituting the porous powder-containing paper 1 has a plurality of fibrous substances 11 and a plurality of calcium-containing porous powders 12. The plurality of fibrous substances 11 are present in countless numbers while being intertwined with each other over the thickness direction of the porous powder-containing paper 1 and the in-plane direction of the porous powder-containing paper 1. The plurality of calcium-containing porous powders 12 are mixed with the plurality of fibrous substances 11 and disposed at least between the plurality of fibrous substances 11.

[0017] Preferably, the multiple calcium-containing porous powders 12 are not present on one surface 1a of the porous powder-containing paper 1, but are present in portions of the porous powder-containing paper 1 at a predetermined depth or greater in the thickness direction. More preferably, in the thickness direction of the porous powder-containing paper 1, the calcium-containing porous powders 12 are not present from the surface 1a to a depth of 20 μm, but are present in portions at a depth of 20 μm or greater.

[0018] Similarly, it is preferable that the calcium-containing porous powder 12 is not present on the other surface 1b of the porous powder-containing paper 1, but is present in a portion of the porous powder-containing paper 1 at a depth greater than a predetermined depth in the thickness direction. More preferably, in the thickness direction of the porous powder-containing paper 1, the calcium-containing porous powder 12 is not present in the portion from the surface 1b to a depth of 20 μm, but is present in the portion at a depth of 20 μm or more.

[0019] Surfaces 1a and 1b of the porous powder-containing paper 1 are the main surfaces of the sheet-like porous powder-containing paper 1.

[0020] The multiple fibrous materials 11 constituting the paper base material layer 10 are fibrous materials and are not made of chemical fibers. The multiple fibrous materials 11 are not particularly limited as long as they are not chemical fibers, and examples include natural fibers. Examples of natural fibers include plant fibers such as cotton and animal fibers such as wool. The multiple fibrous materials 11 may consist of one type of fiber used alone, or multiple types of fibers may be mixed and used.

[0021] The multiple calcium-containing porous powders 12 constituting the paper substrate layer 10 are porous powders and contain at least calcium. The multiple calcium-containing porous powders 12 may also contain various elements in addition to calcium. The multiple calcium-containing porous powders 12 may be used individually or as a mixture of multiple types of powders.

[0022] As shown in the enlarged view of Figure 1, the multiple calcium-containing porous powders 12 mixed with the multiple fibrous materials 11 are scattered in countless numbers, at least between the multiple fibrous materials 11. These spaces between the multiple fibrous materials 11 include the spaces between the outer peripheries of adjacent fibrous materials 11, the spaces between the ends of adjacent fibrous materials 11, and the spaces between the outer periphery of adjacent fibrous materials 11 and the ends of fibrous materials 11.

[0023] When ink is sprayed onto the surface 1a or surface 1b of the porous powder-containing paper 1, the ink is first absorbed from the surface 1a or surface 1b, which is the ink-sprayed surface. The absorbed ink penetrates between the multiple fibrous materials 11 and reaches the multiple calcium-containing porous powders 12 provided between the multiple fibrous materials 11. Because the multiple calcium-containing porous powders 12 are porous, the ink is absorbed into the interior of the multiple calcium-containing porous powders 12 and becomes fixed there. The ink also becomes fixed between the multiple fibrous materials 11.

[0024] In this way, the multiple calcium-containing porous powders 12 present inside the porous powder-containing paper 1 can hold ink within themselves. The multiple calcium-containing porous powders 12 are present in both the thickness direction and the in-plane direction of the porous powder-containing paper 1. Therefore, since ink bleeding in the thickness direction of the porous powder-containing paper 1 can be suppressed, ink see-through to the non-ink-sprayed surface, which is the back surface of the ink-sprayed surface of the porous powder-containing paper 1, can be suppressed even without a coating layer on the surface of the porous powder-containing paper 1. Furthermore, since ink bleeding in the in-plane direction of the porous powder-containing paper 1 can be suppressed, the clarity of the printed surface of the porous powder-containing paper 1 can be improved. For these reasons, the porous powder-containing paper 1 is suitable for printing paper.

[0025] Furthermore, as will be described later, even if the multiple calcium-containing porous powders 12 are much larger than the non-porous calcium carbonate particles used in the coating layer of general paper, preferably, the amount of calcium-containing porous powders 12 present in portions shallower than a predetermined depth in the thickness direction of the porous powder-containing paper 1 is small, and more preferably, the multiple calcium-containing porous powders 12 are not present in portions shallower than a predetermined depth in the thickness direction of the porous powder-containing paper 1, thereby suppressing paper peeling of the porous powder-containing paper 1 starting from the calcium-containing porous powders 12.

[0026] On the other hand, conventional techniques for improving paper printing, as mentioned above, involve applying a coating layer containing various substances such as calcium carbonate to the surface of the paper. This coating layer then holds the ink on its surface or within the coating layer, suppressing the ink from penetrating the paper.

[0027] Furthermore, since the multiple calcium-containing porous powders 12 are porous, they can retain moisture within themselves. For example, when the amount of moisture in the space where the porous powder-containing paper 1 is installed is high, the moisture is adsorbed into the multiple calcium-containing porous powders 12, and when the amount of moisture in the space is low, the moisture adsorbed into the multiple calcium-containing porous powders 12 is released into the space. Therefore, the porous powder-containing paper 1 can regulate the humidity of the space. For these reasons, the porous powder-containing paper 1 is suitable for wallpaper and food paper containers.

[0028] Furthermore, the content of the multiple calcium-containing porous powders 12 in the porous powder-containing paper 1 is preferably 5% or more, more preferably 6%. When the above content of calcium-containing porous powders 12 is 5% or more, it is possible to further improve the suppression of ink bleed-through, the clarity of the printed surface, and humidity control in the porous powder-containing paper.

[0029] Furthermore, the content of the multiple calcium-containing porous powders 12 in the porous powder-containing paper 1 is preferably 10% or less, more preferably 8% or less. When the content of calcium-containing porous powders 12 is 10% or less, the shedding of calcium-containing porous powders 12 from the paper substrate layer 10 can be suppressed, making it possible to easily manufacture a high-quality paper substrate layer 10.

[0030] Furthermore, the size of the multiple calcium-containing porous powders 12 is preferably 5 μm or larger, more preferably 10 μm or larger, and even more preferably 20 μm or larger. When the size of the multiple calcium-containing porous powders 12 is 5 μm or larger, aggregation of the multiple calcium-containing porous powders 12 is suppressed, and the multiple calcium-containing porous powders 12 can be uniformly distributed within the paper substrate layer 10. As a result, ink bleed-through, print clarity, and humidity control in porous powder-containing paper can be further improved.

[0031] Furthermore, the size of the multiple calcium-containing porous powders 12 is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less. When the size of the multiple calcium-containing porous powders 12 is 200 μm or less, the multiple calcium-containing porous powders 12 can be efficiently arranged between the multiple fibrous materials 11. Therefore, it is possible to further improve the suppression of ink bleed-through, the clarity of the printed surface, and humidity control in porous powder-containing paper.

[0032] The size of the multiple calcium-containing porous powders 12 is the maximum external dimension. The size of the multiple calcium-containing porous powders 12 can be measured by observing the calcium-containing porous powders 12 with a scanning electron microscope (SEM). The size of the calcium-containing porous powders 12 is significantly larger than the non-porous calcium carbonate particles commonly used in paper coating layers.

[0033] Furthermore, the average length and average width of the multiple fibrous materials 11 can be appropriately selected according to the application and required performance of the porous powder-containing paper 1.

[0034] Furthermore, it is preferable that the multiple calcium-containing porous powders 12 are porous powders of biological origin. Among these, it is preferable that the multiple calcium-containing porous powders 12 are porous eggshell powders.

[0035] By subjecting animal and plant residues to a predetermined treatment, porous powder derived from animal and plant residues, i.e., porous powder of bio-derived materials, can be obtained. This porous powder of bio-derived materials can be effectively utilized as calcium-containing porous powder 12. In this way, by recycling animal and plant residues and converting them into resources, industrial waste can be reduced. Furthermore, by replacing a portion of the fibrous material 11, or so-called pulp, with the recyclable calcium-containing porous powder 12, the amount of fibrous material 11 can be reduced, thereby reducing the manufacturing cost of porous powder-containing paper 1.

[0036] In particular, animal eggshells, especially chicken eggshells, are processed in large quantities as industrial waste. Therefore, by using porous eggshell powder, especially porous chicken eggshell powder, in the form of calcium-containing porous powder 12 in porous powder-containing paper 1, instead of treating it as industrial waste, eggshells can be recycled and the environmental burden can be reduced.

[0037] On the other hand, if the multiple calcium-containing porous powders 12 are porous powders derived from mineral materials, then achieving recycling and reducing environmental impact is not as easy as when the multiple calcium-containing porous powders 12 are derived from bio-based materials, because mineral-derived materials are minerals, which are natural resources.

[0038] Furthermore, the multiple calcium-containing porous powders 12 preferably contain at least one element selected from the group consisting of Na, P, S, and K, and more preferably contain at least one element selected from the group consisting of Na, P, S, and K in total of 0.05% by mass or more, more preferably 0.10% by mass or more, even more preferably 0.15% by mass or more, and even more preferably 0.20% by mass or more. In addition, the multiple calcium-containing porous powders 12 preferably contain 0.03% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.07% by mass or more for each of the elements Na, P, S, and K. Furthermore, the multiple calcium-containing porous powders 12 preferably contain more than 0.15% by mass, more preferably 0.20% by mass or more, even more preferably 0.25% by mass or more, and even more preferably 0.30% by mass or more of Mg. When the multiple calcium-containing porous powders 12 contain the above elements in the above proportions, the calcium-containing porous powders 12 can be easily manufactured.

[0039] Figure 2 is a cross-sectional view showing another example of the porous powder-containing paper of the embodiment, and a graph showing an example of the distribution of multiple calcium-containing porous powders within the cross-section.

[0040] As shown in Figure 2, the porous powder-containing paper 1 may have multiple paper base layers 10. When the porous powder-containing paper 1 has multiple paper base layers 10, the porous powder-containing paper 1 is a laminate formed by stacking the multiple paper base layers 10 on each other in the thickness direction of the porous powder-containing paper 1. Figure 2 shows a cross-sectional view of the porous powder-containing paper 1 having three paper base layers 10. Preferably, the porous powder-containing paper 1 has five to ten paper base layers 10.

[0041] When the porous powder-containing paper 1 comprises multiple paper base layers 10, as shown in Figure 2, it is preferable that the content of the multiple calcium-containing porous powders 12 in the thickness direction of the porous powder-containing paper 1 increases from the paper base layers 10a and 10c located on the surface of the porous powder-containing paper 1 towards the paper base layer 10b located in the middle of the porous powder-containing paper 1.

[0042] The porous powder-containing paper 1 having such a configuration can further suppress the shedding of calcium-containing porous powder 12 from the surface of the porous powder-containing paper 1. Furthermore, the paper substrate layer positioned in the middle and near the middle of the porous powder-containing paper 1 in the thickness direction can further suppress ink bleed-through of the porous powder-containing paper 1.

[0043] Furthermore, the surface 1a and surface 1b of the porous powder-containing paper 1 may be provided with a porous powder-free paper substrate layer (not shown) that does not contain calcium-containing porous powder 12. The porous powder-free paper substrate layer is, for example, a paper substrate layer 10 from which multiple calcium-containing porous powders 12 have been removed. When the porous powder-free paper substrate layer is provided on the outermost surface of the porous powder-containing paper 1, the shedding of calcium-containing porous powder 12 from the surface of the porous powder-containing paper 1 can be further suppressed.

[0044] Furthermore, a porous powder-free paper substrate layer (not shown) may be provided between multiple paper substrate layers, for example, between paper substrate layer 10a and paper substrate layer 10b, or between paper substrate layer 10b and paper substrate layer 10c in Figure 2.

[0045] Furthermore, the surface 1a and surface 1b of the porous powder-containing paper 1 may be provided with a coating layer (not shown) that is commonly used on paper. When a coating layer is provided on the surface of the porous powder-containing paper 1, the surface smoothness and surface strength of the porous powder-containing paper 1 can be improved.

[0046] Furthermore, to the extent that ink bleed-through of the porous powder-containing paper 1 is suppressed, the porous powder-containing paper 1 may contain various functional substances such as fixatives in addition to the multiple fibrous materials 11 and the multiple calcium-containing porous powders 12. The amount of each functional substance contained in the porous powder-containing paper 1 can be appropriately selected according to the application and required performance of the porous powder-containing paper 1. In addition, the porous powder-containing paper 1 and the paper base layer 10 do not contain chemical fibers.

[0047] For porous powder-containing paper 1, the lower limit for basis weight is 50 g / m². 2Preferably, it should be 100g / m² or more. 2 It is more preferable that it be greater than or equal to 1000 g / m², with an upper limit of 1000 g / m². 2 Preferably, the basis weight of the porous powder-containing paper 1 is 50 g / m². 2 As described above, porous powder-containing paper 1 is suitable for use in cardboard where suppression of ink bleed-through is required, even without a surface coating layer. Furthermore, porous powder-containing paper 1 has a basis weight of 1000 g / m². 2 The following conditions make it easy to print and process porous powder-containing paper 1.

[0048] Furthermore, processed products made using the porous powder-containing paper 1 described above can suppress ink bleed-through even without a coating layer, similar to the porous powder-containing paper 1. Moreover, they can regulate the humidity inside the processed product and the humidity around it. Examples of such processed products include panels and boxes.

[0049] Next, the method for producing porous powder-containing paper according to the embodiment will be described.

[0050] The method for manufacturing porous powder-containing paper according to the embodiment includes a forming step of forming one or more paper substrate layers. In the paper substrate layers, multiple calcium-containing porous powders are mixed with multiple fibrous materials and are provided between at least multiple fibrous materials. This forming step is carried out in any of the steps, part of any of the steps, any of the multiple steps, or any of the multiple steps of the method for manufacturing porous powder-containing paper according to the embodiment.

[0051] A method for producing porous powder-containing paper includes, for example, a pulping step, a beating step, a calcium-containing porous powder generation step, a mixing step, a papermaking step, a dewatering step, and a drying step.

[0052] If the multiple fibrous materials 11 are composed of plant fibers, the pulping process involves boiling the wood in a digester to separate the lignin and obtain the multiple fibrous materials. Alternatively, the obtained multiple fibrous materials may be subjected to treatments such as washing, foreign matter removal, and bleaching to whiten them.

[0053] In the beating process, which follows the pulping process, multiple fibrous materials are mixed with water and beaten in a beating machine. This process fluffs up the fibers, making them more likely to intertwine.

[0054] Furthermore, if the calcium-containing porous powder is porous eggshell powder, the production process includes an egg-breaking step, a washing step, an eggshell membrane separation step, and a fine grinding step.

[0055] In the egg-breaking step of the calcium-containing porous powder production process, eggs, such as chicken eggs, are separated into their contents (egg yolk) and eggshell using an egg-breaking machine. This yields the eggshell. The contents (egg yolk and egg white) are used in various food products.

[0056] In the washing process, which is carried out after the egg-breaking process, the eggshells obtained in the egg-breaking process are washed with a washing solution such as water. Alternatively, the washed eggshells may be coarsely crushed to a size of a few millimeters. The eggshell membrane remains attached to the eggshells in this state.

[0057] In the eggshell membrane separation process, which is carried out after the washing process, the eggshell membrane is separated from the washed eggshells obtained in the washing process, making the eggshells porous. For example, methods such as removing the eggshell membrane by stirring in a liquid tank, removing the eggshell membrane by immersing the eggshells in a weakly acidic aqueous solution such as hydrochloric acid, sulfuric acid, or acetic acid, or separating the eggshell and eggshell membrane by utilizing the difference in specific gravity between the eggshell and the eggshell membrane can be employed individually or in combination. In this way, porous eggshells from which the eggshell membrane has been separated are obtained.

[0058] In the process of producing calcium-containing porous powder, if the time from the start of the egg-breaking process to the completion of the eggshell membrane separation process—that is, the total time for the egg-breaking, washing, and eggshell membrane separation processes—is within one day, then the porous structure of the eggshells obtained in the eggshell membrane separation process can be efficiently and effectively achieved. On the other hand, normally, due to factors such as the lack of nearby facilities for each process, the high cost of equipment, and the complexity of each process, it takes more than one day from the start of the egg-breaking process to the completion of the eggshell membrane separation process. As a result, it becomes difficult to separate the eggshell membrane from the eggshell, and the amount of eggshell membrane remaining on the eggshell as foreign matter increases, making it impossible or difficult to achieve porous eggshell powder.

[0059] In the fine grinding process, which follows the eggshell membrane separation process, the porous eggshells obtained in the eggshell membrane separation process are ground into powder using a mill or similar device. In this way, eggshell powder as a calcium-containing porous powder is obtained. Calcium carbonate is the main component of the various calcium-containing porous powders obtained in the fine grinding process.

[0060] Furthermore, the multiple calcium-containing porous powders obtained in the fine grinding process may be calcined. The calcination temperature is preferably 850°C or higher, more preferably 900°C or higher. In the calcium-containing porous powder after calcination, calcium oxide is the main component. When using the calcium-containing porous powder after calcination in the mixing process described later, in order to avoid the strong heat generation caused by the dissolution of calcium oxide in the calcium-containing porous powder in water, water is added to the calcium-containing porous powder after calcination. In the calcium-containing porous powder after water is added, calcium hydroxide becomes the main component. When calcium-containing porous powder with calcium hydroxide as the main component is used in the mixing process described later, the papermaking raw material becomes a strongly alkaline aqueous solution, and a sterilizing effect is obtained.

[0061] Alternatively, commercially available calcium-containing porous powder may be prepared without performing the above-described process for producing calcium-containing porous powder.

[0062] Next, in the mixing step, the multiple fibrous materials obtained in the beating step and the multiple calcium-containing porous powders are mixed to obtain a slurry-like papermaking raw material. For example, calcium-containing porous powders are added to a stirring device that stores the slurry-like fibrous material obtained through the beating step, and mixing and stirring are performed to produce a papermaking raw material containing water, fibrous materials, and calcium-containing porous powders. The content of the multiple fibrous materials and the content of the multiple calcium-containing porous powders in the papermaking raw material are appropriately selected according to the desired design of the porous powder-containing paper to be manufactured.

[0063] Furthermore, it is preferable that the papermaking raw material contains a fixative. When a fixative is included in the papermaking raw material, multiple calcium-containing porous powders are more likely to adhere between multiple fibrous materials. The fixative is preferably a water-soluble inorganic salt or a polymer electrolyte.

[0064] Furthermore, the papermaking raw materials may contain viscosity modifiers such as starch. Adjusting the viscosity of the papermaking raw materials with viscosity modifiers improves the moldability of the sheet sample, such as adjusting the thickness of the sheet sample, in the papermaking process described later.

[0065] In the papermaking process, which follows the mixing process, a sheet-like papermaking material (hereinafter also referred to as a sheet sample) is formed by attaching the papermaking material to a planar mesh using a cylinder-type papermaking method. In the cylinder-type papermaking process, a portion of a drum-shaped mesh is immersed in the slurry-like papermaking material stored in a storage tank, and the mesh is rotated to obtain a single-layer sheet sample by placing the papermaking material scooped from the mesh onto felt.

[0066] If the porous powder-containing paper to be manufactured has multiple paper substrate layers, multiple drum-shaped mesh bodies are provided, and the papermaking raw materials picked up by each mesh body are laminated onto felt to obtain a laminate that is a multi-layer sheet sample. At this time, the multiple mesh bodies may be rotated while immersed in the papermaking raw materials in one storage tank, or each of the multiple mesh bodies may be rotated while immersed in the papermaking raw materials in each of the multiple storage tanks.

[0067] Furthermore, if the porous powder-containing paper to be manufactured comprises multiple paper substrate layers, and the content of multiple calcium-containing porous powders in some or all of the paper substrate layers differs, a multi-layer sheet sample with different calcium-containing porous powder content in some or all of the layers is obtained by stacking the papermaking raw materials, each scooped up by a mesh from multiple storage tanks containing different calcium-containing porous powder content, onto felt.

[0068] In the dewatering process, which is carried out after the papermaking process, the sheet sample is dewatered by sandwiching it between a pair of press rollers.

[0069] In the drying process performed after the dewatering process, the dewatered sheet sample is dried by bringing it into contact with a heated roller, thereby obtaining a paper substrate layer. In this way, porous powder-containing paper can be manufactured.

[0070] Furthermore, if the porous powder-containing paper includes a porous powder-free paper substrate layer, the porous powder-free paper substrate layer is prepared in the same manner as the method for producing the porous powder-containing paper described above, except that the calcium-containing porous powder production process is not carried out and the calcium-containing porous powder is not added.

[0071] According to the embodiments described above, in contrast to conventional technologies that process the surface of paper by providing a coating layer to improve ink bleed-through resistance, the present invention focuses on the internal structure of the paper. By mixing multiple fibrous materials and multiple calcium-containing porous powders, and arranging multiple calcium-containing porous powders between at least multiple fibrous materials, the porous powder-containing paper can suppress ink bleed-through even without a coating layer on its surface.

[0072] Although embodiments have been described above, the present invention is not limited to the embodiments described above, and includes all aspects included in the concepts and claims of this disclosure, and can be modified in various ways within the scope of this disclosure. [Examples]

[0073] Next, examples and comparative examples will be described, but the present invention is not limited to these examples.

[0074] (Example 1) The above-described pulping process, beating process, calcium-containing porous powder generation process, mixing process, papermaking process, dewatering process, and drying process are carried out, resulting in a product with a calcium-containing porous powder content of 7% and a basis weight of 350 g / m². 2 A porous powder-containing paper with nine paper base layers was manufactured. Plant fibers were used as the fibrous material. Porous eggshell powder from chicken eggs was used as the calcium-containing porous powder.

[0075] Elemental analysis was performed on calcium-containing porous powder extracted from the manufactured porous powder-containing paper using a fluorescence X-ray analyzer (ZSX Primus, Rigaku), with the tube set to Rh, the target element to be measured to 9F-92U, the irradiation area to 30mmΦ, and the FP method quantification program set to SQX calculation. The results are shown in Table 1 (mass%). As shown in Table 1, the calcium-containing porous powder contained the elements in the amounts shown in Table 1. In particular, the calcium-containing porous powder contained 0.09 mass% Na, 0.32 mass% Mg, 0.09 mass% P, 0.10 mass% S, and 0.06 mass% K.

[0076] Furthermore, the calcium-containing porous powder extracted from the manufactured porous powder-containing paper was observed using a scanning electron microscope (SEM) (JSM-7800F field emission scanning electron microscope, manufactured by JEOL) with an acceleration voltage of 2.0 kV, and the resulting SEM image is shown in Figure 3. An enlarged SEM image of region A in Figure 3 is shown in Figure 4. As shown in Figures 3-4, the calcium-containing porous powder had an amorphous shape of less than 100 μm, and numerous circular pores of several hundred nanometers were present on the surface of the calcium-containing porous powder. Thus, it was confirmed that the calcium-containing porous powder is a porous material with numerous pores.

[0077] Further, with the acceleration voltage set to 15.0 kV, a cross-section of the produced porous powder-containing paper was observed by SEM. It was found that the plurality of calcium-containing porous powders were mixed with the plurality of fibrous substances, and were present at least between the plurality of fibrous substances. Furthermore, in the thickness direction of the porous powder-containing paper, the calcium-containing porous powder was not present in the region from the surface of the porous powder-containing paper to a depth of 30 μm, but was present in the region at a depth of 30 μm or more. As described above, the calcium-containing porous powder was not present in the surface portion of the porous powder-containing paper, but was present in a large amount on the inner side of the porous powder-containing paper.

[0078] Further, ink was sprayed onto the surface of the produced porous powder-containing paper, and 5 minutes later, the back surface of the ink-sprayed side of the porous powder-containing paper was visually observed. As a result, no ink bleeding was confirmed. As described above, the porous powder-containing paper was able to suppress ink strike-through even without having a coating layer on the surface.

[0079] (Comparative Example 1) A general-purpose cardboard containing no calcium carbonate particles (basis weight 350 g / m 2 , 9 layers) was prepared. Then, the ink strike-through resistance of the general-purpose cardboard was measured under the same conditions as in Example 1, and as a result, ink bleeding was confirmed. As described above, the general-purpose cardboard of Comparative Example 1 was inferior in ink strike-through resistance to the porous powder-containing paper of Example 1.

[0080]

Table 1

Description of Symbols

[0081] 1 Porous powder-containing paper 1a One surface of the porous powder-containing paper 1b The other surface of the porous powder-containing paper 10, 10a, 10b, 10c Paper base material layer 11 Fibrous substance 12 Calcium-containing porous powder

Claims

1. Multiple fibrous materials, A plurality of calcium-containing porous powders are mixed with the plurality of fibrous materials and provided at least between the plurality of fibrous materials, A porous powder-containing paper comprising one or more paper substrate layers having the following properties.

2. The porous powder-containing paper according to claim 1, wherein the plurality of calcium-containing porous powders are porous powders of biological origin.

3. The porous powder-containing paper according to claim 1, wherein the plurality of calcium-containing porous powders are porous eggshell powders.

4. The porous powder-containing paper according to claim 1, wherein the plurality of calcium-containing porous powders contain at least one element selected from the group consisting of Na, P, S, and K.

5. The porous powder-containing paper according to claim 1, wherein the content of the plurality of calcium-containing porous powders contained in the porous powder-containing paper is 5% or more and 10% or less.

6. The porous powder-containing paper comprises a plurality of paper substrate layers, The porous powder-containing paper according to claim 1, wherein the content of the plurality of calcium-containing porous powders in the thickness direction of the porous powder-containing paper increases from the paper substrate layer located on the surface of the porous powder-containing paper toward the paper substrate layer located in the middle of the porous powder-containing paper.

7. The basis weight of the aforementioned porous powder-containing paper is 50 g / m². ２ More than 1000g / m ２ The porous powder-containing paper according to claim 1, which is as follows:

8. A processed article made using porous powder-containing paper according to any one of claims 1 to 7.

9. A method for producing porous powder-containing paper, comprising a forming step of forming one or more paper substrate layers in which multiple calcium-containing porous powders are mixed with multiple fibrous materials and provided between at least the multiple fibrous materials.

10. The plurality of calcium-containing porous powders used in the formation process are eggshell powders produced by an egg-breaking process, a washing process, an eggshell membrane separation process, and a fine grinding process. In the aforementioned egg-breaking process, the egg is separated into its contents and eggshell. In the washing step, the eggshells obtained in the egg-breaking step are washed with a washing solution. In the eggshell membrane separation step, the eggshell membrane is separated from the washed eggshells obtained in the washing step. In the aforementioned fine grinding step, the eggshell obtained in the eggshell membrane separation step is ground into powder. The method for producing porous powder-containing paper according to claim 9, wherein the time from the start of the egg-breaking step to the completion of the eggshell membrane separation step is within one day.

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