Synthetic paper, filter base paper, and filter

Abstract

To provide a synthetic pulp, filter base paper, and a filter using the same, that can reduce a dropout amount of diatomite even if used for an extended period.SOLUTION: Synthetic paper includes a polyolefin-based synthetic pulp (A) and diatomite (B), wherein the Canadian standard freeness of the polyolefin-based synthetic pulp (A) is 100 ml-750 ml.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to synthetic paper, filter base paper, and filters. [Background technology]

[0002] Filtration filters (hereinafter simply referred to as "filters") are widely used in applications requiring filtration separation, such as solid-liquid separation. In particular, filters that can remove fine particles are widely used in beverages, foods, pharmaceuticals, and other applications.

[0003] For example, Patent Document 1 describes a filter base paper containing pulp, diatomaceous earth, and a cationic resin, and the filter base paper has a basis weight of 1000 to 2000 g / m 2 The filter base paper is disclosed, in which the freeness of the pulp is 200 to 600 ml, the content of the diatomaceous earth is 40 to 80 mass% relative to the total mass of the filter base paper, and the content of the cationic resin is 2 to 6 mass parts relative to 100 mass parts of the pulp. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-159150 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in Patent Document 1, the diatomaceous earth sometimes falls off after long-term use.

[0006] The present invention has been made in view of the above points, and aims to provide synthetic pulp, filter base paper, and a filter using the same that can reduce the amount of diatomaceous earth that falls off even after long-term use. [Means for solving the problem]

[0007] In order to solve the above problems, one aspect of the present invention relates to synthetic paper according to [1] to [7].

[0008] [1] Polyolefin-based synthetic pulp (A), Diatomaceous earth (B), The polyolefin synthetic pulp (A) has a Canadian standard freeness of 100 ml to 750 ml. Synthetic paper.

[0009] [2] The ratio of the mass of the polyolefin synthetic pulp (A) to the total mass of the synthetic paper is 20% by mass to 60% by mass, The content ratio of the diatomaceous earth (B) relative to the total mass of the synthetic paper is 20% by mass to 70% by mass. [1] The synthetic paper according to [1].

[0010] [3] The polyolefin synthetic pulp (A) includes a polyolefin synthetic pulp having a Canadian standard freeness of 200 ml to 650 ml, The ratio of the content mass of the polyolefin synthetic pulp having a Canadian standard freeness of 200 ml to 650 ml to the total mass of the polyolefin synthetic pulp (A) is 30 mass% or more. [1] or [2].

[0011] [4] Contains short-cut fibers (C), The melting point of the short cut fiber (C) is 70°C to 190°C, The average fiber length of the short-cut fibers (C) is 3.0 mm to 20.0 mm, The ratio of the mass of the short-cut fibers (C) to the total mass of the synthetic paper is 3% by mass to 30% by mass. The synthetic paper according to any one of [1] to [3].

[0012] [5] Contains natural pulp (D), The natural pulp (D) has a Canadian standard freeness of 100 ml to 800 ml; the ratio of the content of the natural pulp (D) to the total mass of the synthetic paper is 5% by mass to 30% by mass; The ratio of the content of the natural pulp (D) to the total mass of the polyolefin synthetic pulp (A) is 5.3 mass% to 60 mass%. The synthetic paper according to any one of [1] to [4].

[0013] [6] The polyolefin-based synthetic pulp (A) contains an olefin-based polymer, The olefin polymer is an ethylene polymer. The synthetic paper according to any one of [1] to [5].

[0014] [7] The polyolefin synthetic pulp (A) contains at least two types of polyolefin synthetic pulp having different melting points; The synthetic paper according to any one of [1] to [6].

[0015] In order to solve the above problems, one aspect of the present invention relates to a filter base paper according to [8].

[0016] [8] [1] to [7], containing the synthetic paper according to any one of the above. Filter base paper.

[0017] To solve the above problem, one aspect of the present invention relates to the filter of [9].

[0018] [9] [8] The filter base paper is included. filter. [Effects of the Invention]

[0019] According to the present invention, there are provided synthetic pulp, filter base paper, and a filter using the same, which can reduce the amount of diatomaceous earth that falls off when used for a long period of time. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a micrograph of the synthetic paper of Example 1. [Figure 2] 1 is a micrograph of the synthetic paper of Comparative Example 1. [Figure 3] 1 is a micrograph of the synthetic paper of Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0021] The following description of the components may be based on representative embodiments of the present disclosure, but the present disclosure is not limited to such embodiments.

[0022] In the present disclosure, combinations of preferred aspects are more preferred aspects.

[0023] In the present disclosure, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0024] In the numerical ranges described in stages in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples.

[0025] In the present disclosure, when a plurality of substances corresponding to each component are present in the composition, the amount of each component in the composition means the total amount of the plurality of substances present in the composition, unless otherwise specified.

[0026] In the present disclosure, "contains mainly" means that the target substance is contained in the largest amount relative to the whole. For example, it means that the content of the target substance is 50% by mass or more as a percentage of the whole.

[0027] In this disclosure, "mass%" and "wt%" are synonymous, and "parts by mass" and "parts by weight" are synonymous. In this disclosure, "%" indicating the amount of a component is based on mass unless otherwise specified.

[0028] 1. Synthetic paper The synthetic paper according to this embodiment contains polyolefin synthetic pulp (A) and diatomaceous earth (B), and the polyolefin synthetic pulp (A) contains polyolefin synthetic pulp having a Canadian standard freeness of 100 ml to 750 ml.

[0029] The synthetic paper according to this embodiment is a mixture of synthetic pulp fibers and sheath-core fibers, with the fibers and voids between the fibers randomly mixed together. The synthetic pulp fibers are branched, with the tips of the fibers thin and branched into many strands that are entangled with the sheath-core fibers.

[0030] The synthetic paper according to this embodiment contains a polyolefin-based synthetic pulp (A) and diatomaceous earth (B). By using the polyolefin-based synthetic pulp (A), diatomaceous earth can easily fit into the gaps formed between the branches of the polyolefin-based synthetic pulp. Furthermore, the surface of the synthetic pulp, which is a thermoplastic resin, melts and adheres to the diatomaceous earth during drying and heat treatment, making it easier to reduce the amount of diatomaceous earth that falls off, even over long periods of use. On the other hand, natural pulp does not typically melt (it undergoes thermal decomposition before reaching its melting temperature when heated), so the aforementioned adhesive effect with diatomaceous earth does not occur, making it difficult to reduce the amount of diatomaceous earth that falls off.

[0031] Furthermore, Canadian standard freeness is a physical property closely related to the state of each fiber in synthetic pulp. The less branching or entanglement of each fiber in synthetic pulp, the higher the Canadian standard freeness. By using polyolefin-based synthetic pulp (A) with a Canadian standard freeness of 100 ml or more, it is possible to easily increase the filtration rate and balance the filtration performance and filtration rate. Furthermore, by using polyolefin-based synthetic pulp (A) with a Canadian standard freeness of 750 ml or less, it is possible to improve the retention of diatomaceous earth and easily reduce the rate of diatomaceous earth shedding.

[0032] The basis weight of the synthetic paper according to this embodiment is 10.0 g / m 2 ~2000.0g / m2 It is preferable that the density is 30.0 g / m 2 ~500.0g / m 2 It is more preferable that the basis weight is 10.0 g / m 2 By setting the basis weight at 2000.0 g / m or more, it is possible to easily increase the tensile strength of the synthetic paper. 2 The weight of synthetic paper can be reduced by the following: The basis weight of synthetic paper is a value determined by measuring the weight of a certain area (for example, 25 cm square) of synthetic paper and dividing by the area.

[0033] The thickness of the synthetic paper according to this embodiment is preferably 0.10 mm to 5.00 mm, more preferably 0.15 mm to 3.00 mm, and even more preferably 0.15 mm to 2.00 mm. By making the thickness 0.10 mm or more, the tensile strength of the synthetic paper can be increased. By making the thickness 5.00 mm or less, the weight of the synthetic paper can be reduced. The thickness of the synthetic paper is a value measured in accordance with JIS P 8118:2014.

[0034] The density (basis weight / thickness) of the synthetic paper according to this embodiment is 100 kg / m 3 ~1000kg / m 3 is preferred, and 110 kg / m 3 ~500kg / m 3 The density of the synthetic paper is a value determined by dividing the basis weight of the synthetic paper measured above by the thickness of the synthetic paper.

[0035] 1-1. Polyolefin-based synthetic pulp (A) The polyolefin synthetic pulp (A) may be a synthetic pulp mainly containing an olefin polymer, or may be a composition partially containing components other than the olefin polymer, provided that the content of the olefin polymer by mass relative to the total mass of the polyolefin synthetic pulp (A) is preferably 80 mass% or more.

[0036] The olefin polymer constituting the polyolefin synthetic pulp (A) may be a homopolymer of one type of olefin or a copolymer of two or more types of olefins, where the carbon number of the olefin constituting the olefin polymer is preferably 2 to 10.

[0037] Examples of olefin polymers contained in the polyolefin synthetic pulp (A) include polyethylene (ethylene homopolymer), polypropylene (propylene homopolymer), ethylene-propylene copolymer, ethylene-butene-1 copolymer, and ethylene-4-methylpentene-1 copolymer. In this specification, the term "olefin polymer" also includes ethylene-vinyl acetate copolymer, ethylene-(meth)acrylic acid copolymer, ethylene-(meth)acrylic acid ester copolymer, and the like, which are polymerized with an olefin and a monomer other than an olefin. In this case, the proportion of non-olefin structural units is preferably 50 mol% or less, more preferably 40 mol% or less, of the total structural units. In this specification, the term "olefin polymer" also includes graft-modified polyolefins grafted with unsaturated carboxylic acid monomers.

[0038] Among these, from the viewpoint of easily suppressing the diatomaceous earth from falling off, the olefin polymer is preferably an ethylene polymer, and particularly preferably an ethylene homopolymer, an ethylene-α-olefin copolymer (the α-olefin preferably has 2 to 10 carbon atoms), or a polymer obtained by graft-modifying any of these with an unsaturated carboxylic acid monomer. Note that the ethylene polymer refers to a polymer containing 50% by mass or more of structural units derived from ethylene.

[0039] When the olefin polymer is an ethylene homopolymer, the melt flow rate (hereinafter also referred to as "MFR") measured in accordance with ASTM D1238 at 190°C under a load of 2.16 kg is preferably 0.1 g / 10 min to 100 g / 10 min, more preferably 0.1 g / 10 min to 60 g / 10 min. When an ethylene homopolymer having an MFR within the above range is used, it becomes more likely to be entangled with the diatomaceous earth (B) described below, and in the resulting synthetic paper and in the filter base paper and filters using the same, the diatomaceous earth can be prevented from falling off and the strength can be further increased.

[0040] The Canadian standard freeness (hereinafter also referred to simply as "freeness") of the polyolefin synthetic pulp (A) is 100 ml to 750 ml, preferably 230 ml to 750 ml, and more preferably 230 ml to 550 ml. The freeness is a value measured in accordance with JIS P 8121:2012. When the freeness is 750 ml or less, the diatomaceous earth can be prevented from falling off. Furthermore, when the freeness is 550 ml or less, the diatomaceous earth collection rate of the synthetic paper can be easily increased, and the diatomaceous earth falling off rate can be easily reduced. Furthermore, the freeness of polyolefin synthetic pulp (A) refers to the freeness of the polyolefin synthetic pulp when the synthetic paper contains only one type of polyolefin synthetic pulp, and refers to the freeness of the mixture obtained by measuring the mixture of polyolefin synthetic pulps in accordance with JIS P 8121:2012 when the synthetic paper contains two or more types of polyolefin synthetic pulp.

[0041] The polyolefin synthetic pulp (A) preferably contains a polyolefin synthetic pulp having a Canadian standard freeness of 200 ml to 650 ml. By containing such a polyolefin synthetic pulp, it becomes easier to suppress the diatomaceous earth from falling off.

[0042] The ratio of the mass of the polyolefin synthetic pulp having a freeness of 200 ml to 650 ml to the total mass of the polyolefin synthetic pulp (A) is preferably 30 mass% or more, more preferably 50 mass% or more, and even more preferably 70 mass% or more. There is no particular upper limit, but it may be 100 mass% or less. The freeness of the polyolefin synthetic pulp (A) can be adjusted by treating it with a disk refiner or the like when producing the polyolefin synthetic pulp (A).

[0043] The length of each fiber in the polyolefin synthetic pulp (A) is appropriately selected depending on the desired texture, etc., and is preferably 0.05 to 50 mm, more preferably 0.05 to 10 mm. The average fiber length is preferably 0.1 mm or more and less than 3.0 mm, more preferably 0.5 to 2.5 mm. The fiber length and average fiber length can be adjusted, for example, by processing with a disk refiner.

[0044] Here, the average fiber length of the polyolefin synthetic pulp (A) can be determined by the following procedure. The fibers constituting the polyolefin synthetic pulp (A) are classified into length classes in 0.05 mm increments. Then, the actual fiber length of the fibers contained in each class (length) and the number of fibers contained in each class are measured. The measurement can be performed on 12,000 to 13,000 fibers. Then, from the measurement results, the number average fiber length Ln (mm) of each class is calculated using the following formula: Ln=ΣL / N L: Actual fiber length of the fiber contained in one grade (mm) N: Number of fibers in one grade

[0045] Then, the average fiber length (mm) of the fibers constituting the polyolefin synthetic pulp (A) is calculated using the following formula. Average fiber length = Σ(Nn × Ln 2 ) / Σ(Nn×Ln) Nn: Number of fibers in each grade

[0046] On the other hand, the fiber length can be determined by dispersing polyolefin synthetic pulp (A) in water to a concentration of 0.02% by mass and measuring the length of each fiber using an automatic fiber measuring instrument (product name: FiberLab-3.5) manufactured by Metso Automation Co., Ltd. In this measuring instrument, a xenon lamp light is irradiated onto the fibers as they flow through the capillary, and a CCD (charge-coupled device) sensor collects video signals, which are then analyzed.

[0047] The melting point of the polyolefin synthetic pulp (A) is preferably 70°C to 130°C, more preferably 80°C to 120°C, and even more preferably 90°C to 110°C. Generally, the melting point of the polyolefin synthetic pulp (A) depends on the melting point of the olefin polymer that constitutes it. The melting point of the polyolefin synthetic pulp (A) is preferably higher than the melting point of the short-cut fiber (C). If the melting point of the polyolefin synthetic pulp (A) is 130°C or lower, the polyolefin synthetic pulp (A) is more likely to fuse to the diatomaceous earth (B) or the like during the production of a nonwoven fabric. As a result, the shape retention and other properties of the resulting nonwoven fabric are more likely to be improved. On the other hand, if the melting point of the polyolefin synthetic pulp (A) is 70°C or higher, the heat resistance of the resulting nonwoven fabric is improved. The melting point of the polyolefin synthetic pulp (A) is measured using a differential scanning calorimeter.

[0048] It is preferable that the polyolefin synthetic pulp (A) contains at least two types of polyolefin synthetic pulp with different melting points. In this embodiment, the pulp with the lowest melting point can be melted in stages, and it is easy to control the fiber state to easily achieve both good liquid permeability and high diatomaceous earth capture rate, which tends to increase the diatomaceous earth capture rate.

[0049] The polyolefin synthetic pulp (A) may contain components other than polyolefins, provided that the object of the present invention is not impaired. Specifically, it may contain antibacterial agents, heat stabilizers, weather stabilizers, various stabilizers, antioxidants, dispersants, antistatic agents, slip agents, antiblocking agents, antifogging agents, lubricants, dyes, natural oils, synthetic oils, waxes, fillers, etc.

[0050] The method for preparing the polyolefin synthetic pulp (A) is not particularly limited. For example, the method described in detail in Encyclopedia of Chemical Technology, 3rd ed., Vol. 19, pp. 420-425, etc. may be used. The polyolefin synthetic pulp (A) is preferably prepared by flash spinning a solution or emulsion containing an olefin polymer and additives. The emulsion flash method using polyvinyl alcohol (hereinafter also referred to as "PVA") as a hydrophilizing agent is particularly preferred. The amount of PVA used is preferably 0.01 to 10% by mass relative to the total mass of the polyolefin synthetic pulp (A). If necessary, the fibrous material after melt flashing or emulsion flashing may be beaten.

[0051] On the other hand, commercially available products may be used as the polyolefin synthetic pulp (A). Examples of commercially available polyolefin synthetic pulp (A) include SWP (trade name) manufactured by Mitsui Chemicals, Inc.

[0052] The content by mass of polyolefin synthetic pulp (A) relative to the total mass of the synthetic paper is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less. On the other hand, it is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more. When the amount of polyolefin synthetic pulp (A) is 20% by mass or more, the diatomaceous earth (B) can be uniformly dispersed within the synthetic paper, making it easier to retain the diatomaceous earth (B). On the other hand, when the amount of polyolefin synthetic pulp (A) is 60% by mass or less, the amount of diatomaceous earth (B) becomes relatively sufficient, and filter performance is likely to be improved.

[0053] 1-2. Diatomaceous earth (B) Diatomaceous earth plays a role in improving the filtering performance of the filter base paper or filter. Either freshwater or seawater diatomaceous earth can be used, and acid-washed diatomaceous earth is preferred.

[0054] The diatomaceous earth is not particularly limited, and may be uncalcined or calcined. Calcined or flux-calcined diatomaceous earth can be used. The particle size distribution of the diatomaceous earth is not particularly limited, but classified diatomaceous earth is preferred. The particle size of the diatomaceous earth used ranges from about 0.01 μm to about 1 mm, preferably 0.1 μm to 100 μm, more preferably 0.5 μm to 50 μm, and particularly preferably 1 μm to 30 μm.

[0055] As mentioned above, it is also preferable to use multiple types of diatomaceous earth with different particle sizes in combination in the composite material. Specific examples of diatomaceous earth include commercially available products that can be used as is or after appropriate treatment, such as the various grades of Tokoro Ichiban No. 1, Tokoro Ichiban C, Tokoro Ichiban No. 4, Tokoro Ichiban R, Tokoro Ichiban White, and Tokoro Ichiban White No. 2, which are flux-calcined products manufactured by Tsuchida Foods Co., Ltd., as well as calcined products such as Tokoro Ichiban No. 2, Tokoro Ichiban Red, Tokoro Ichiban No. 3, and Tokoro Ichiban No. 6 (trade names).

[0056] Commercially available diatomaceous earth can be processed, for example, by sieving or classification, to size the particles into fractions with a narrower particle size distribution. Generally, the size of diatomaceous earth used in filter aid particles can range from about 0.01 μm to about 5 mm, preferably from about 10 μm to about 500 μm in some embodiments, from about 40 μm to about 200 μm in other embodiments, and from about 0.1 μm to about 50 μm in other embodiments. In still other embodiments, it can range from about 0.01 μm to about 50 μm. For coarse filtration, diatomaceous earth with a relatively large median diameter is used, and for fine filtration, diatomaceous earth with a smaller median diameter is used.

[0057] The content of diatomaceous earth in the synthetic paper is preferably 20 to 70 mass% relative to the total mass of the synthetic paper, and more preferably 45 to 70 mass%. If the content of diatomaceous earth is 40 mass% or more, filtration performance is improved. On the other hand, if the content of diatomaceous earth is 80 mass% or less, an increase in pressure loss can be suppressed. In addition, since the content of components other than diatomaceous earth (particularly pulp) can be sufficiently ensured, it becomes easier to obtain a filter base paper that can sufficiently withstand the pressure when passing filtrate through it. The content of diatomaceous earth in the filter base paper can be measured in accordance with JIS P 8251:2003.

[0058] If other inorganic substances are present in the filter base paper, the diatomaceous earth and other inorganic substances can be qualitatively and quantitatively identified by observing them using SEM images and performing elemental analysis of the incineration residue using an energy dispersive X-ray spectrometer (EDS).

[0059] 1-3. Short-cut fiber (C) The synthetic paper of this embodiment may further contain short-cut fibers (C). The short-cut fibers (C) are fibers used to bind the polyolefin synthetic pulp (A) and diatomaceous earth (B) together. The short-cut fibers (C) preferably have a melting point of 70°C to 190°C and an average fiber length of 3.0 mm to 20.0 mm. That is, the short-cut fibers (B) and the polyolefin synthetic pulp (A) can be distinguished by their appearance and average fiber length under a microscope. Regarding the appearance of the fibers under a microscope, the short-cut fibers (B) have a straight, unbranched shape, while the polyolefin synthetic pulp (A) has branched fibers. On the other hand, the short-cut fibers (C) and the natural pulp (D) described below can be distinguished by the difference in the materials contained therein. That is, the natural pulp (D) refers to fibers containing cellulose and / or hemicellulose, with the total mass of cellulose and hemicellulose being 50% by mass or more.

[0060] The melting point of the short cut fibers (C) is more preferably 100° C. to 185° C. When the melting point is within this range, it becomes possible to bind the polyolefin synthetic pulp (A), diatomaceous earth (B), etc. without excessively increasing the temperature.

[0061] The average fiber length of the short cut fibers (C) is more preferably 3.0 to 10.0 mm. When the average fiber length of the short cut fibers (C) is within this range, they tend to bind other components more easily and bond each component more evenly. The average fiber length of the short cut fibers (C) is measured by the same method as that for the polyolefin synthetic pulp (A) described above.

[0062] The cross-sectional shape of the short cut fibers (C) may be circular, elliptical, polygonal, star-shaped, gear-shaped, etc. The maximum diameter is preferably 0.1 to 200 mm, more preferably 10 to 200 mm. When the maximum diameter of the short cut fibers (C) is 0.1 mm or more, the strength of the short cut fibers (C) is increased and the components are easily bonded together. On the other hand, when the maximum diameter is 200 mm or less, the fibers are easily entangled when mixed with other components.

[0063] When the short-cut fibers (C) are composite fibers containing two or more resins, the melting point of the short-cut fibers (C) refers to the melting point of the surface of the short-cut fibers (C). For example, in the case of core-sheath composite fibers, if the melting point of the sheath is within the above range, it is included in the short-cut fibers (C) specified in this specification. The melting points of the core and sheath of the short-cut fibers (B) are values ​​measured by a differential scanning calorimeter. Specifically, using a PerkinElmer DSC Pyris1 or SII NanoTechnology DSC7020 differential scanning calorimeter (DSC), a sample (approximately 5 mg) was heated under a nitrogen atmosphere (20 mL / min) to a temperature set for each thermoplastic resin (230 °C for propylene-based polymers), held at that temperature for 3 min, then cooled to 30 °C at 10 °C / min, held at 30 °C for 1 min, and then heated to the target temperature at 10 °C / min. The melting point (Tm) was calculated from the peak apex of the crystalline melting peak during the heating process. If multiple crystalline melting peaks were observed, the higher peak was used as the melting point (Tm).

[0064] The short cut fibers (C) may be bonded to the polyolefin synthetic pulp (A) or diatomaceous earth (B) by heat fusion or by chemical reaction.

[0065] When polyolefin synthetic pulp (A), diatomaceous earth (B), or the like is bonded by heat fusion or the like, the polyolefin synthetic pulp (A), diatomaceous earth (B), or the like is mixed with short-cut fiber (C) during nonwoven fabric production, and the mixture is heated above the temperature at which the short-cut fiber (C) melts but below the temperature at which the polyolefin synthetic pulp (A) melts, melting and bonding the short-cut fiber (C). Examples of such heat-fusible short-cut fiber (C) include polyethylene fibers, low-melting-point polyester fibers, acrylic fibers, composite fibers (sheath-core or side-by-side) using low-melting-point resins such as polyethylene / polypropylene composite fibers, polyethylene / polyethylene terephthalate composite fibers, low-melting-point polyethylene, and low-melting-point SWP. Among these, composite fibers (sheath-core or side-by-side) using low-melting-point resins such as polyethylene / polypropylene composite fibers, polyethylene / polyethylene terephthalate composite fibers, and the like are particularly well known.

[0066] On the other hand, chemical bonding is carried out by a method such as spray coating using an emulsion of fibrous polyvinyl acetate or low-melting polyolefin.

[0067] The content of short-cut fiber (C) in the synthetic paper is preferably 3% by mass to 50% by mass, more preferably 3% by mass to 30% by mass, from the viewpoint of suppressing the shedding of diatomaceous earth, and further preferably 3% by mass to 15% by mass, most preferably 3% by mass to 8% by mass, from the viewpoint of improving the diatomaceous earth collection rate of the synthetic paper.

[0068] 1-4.Natural pulp (D) The natural pulp (D) used in the present invention is not particularly limited as long as it can be used for papermaking. When synthetic paper contains natural pulp (D), the tensile strength and water absorption of the synthetic paper are increased.

[0069] Natural pulp (D) is pulp containing natural fibers, and includes wood pulp and non-wood pulp. Wood pulp is pulp obtained from wood such as coniferous and broad-leaved trees. Specifically, these trees are pulped by chemical pulping methods such as the kraft method, soda method, and sulfite method, semi-chemical pulping methods such as the neutral sulfite method and the acid sulfite method, or other known pulping methods. Among these, coniferous kraft pulp (NBKP) is preferred from the viewpoints of moisture absorption, ease of availability, supply amount, etc.

[0070] On the other hand, non-wood pulp is pulp obtained from raw materials other than wood. Examples of raw materials other than wood include plant fibers. Plant fibers include bast fibers such as Manila hemp, flax, hemp, jute, paper mulberry, mitsumata, and gampi; cotton fibers such as cotton and cotton linters; straw; bamboo; esparto; bagasse; and the like. These plant fibers are obtained by pulping using known pulping methods such as chemical pulping, semi-chemical pulping, chemi-ground pulping, and mechanical pulping. Non-wood pulp may contain multiple types of plant fibers. Among these, non-wood pulp containing Manila hemp is preferred in terms of its oil and fat absorption, ease of availability, supply volume, and the like.

[0071] The natural pulp (D) may contain one type of wood pulp or non-wood pulp, or may contain multiple types of wood pulp and / or non-wood pulp.

[0072] From the viewpoint of easily suppressing the dropping of diatomaceous earth, the freeness of the natural pulp (D) is preferably 100 ml to 800 ml or less, and more preferably 350 ml to 780 ml or less. The freeness is a value measured in accordance with JIS P 8121:2012. Furthermore, the freeness of the natural pulp (D) refers to the freeness of the natural pulp when the synthetic paper contains only one type of natural pulp, and refers to the freeness of the mixture obtained by measuring the mixture of natural pulps in accordance with JIS P 8121:2012 when the synthetic paper contains two or more types of natural pulp.

[0073] The average fiber length of the natural pulp (D) is preferably 1 mm to 80 mm, more preferably 2 mm to 50 mm, from the viewpoint of suppressing the shedding of diatomaceous earth. The average fiber length of the natural pulp (D) is measured in the same manner as the average fiber length of the polyolefin-based synthetic pulp (A). By setting the average fiber length within the above range, the paper texture of the nonwoven fabric can be improved.

[0074] The content by mass of natural pulp (D) relative to the total mass of the synthetic paper is preferably 5% by mass to 30% by mass, more preferably 6% by mass to 25% by mass, and even more preferably 10% by mass to 25% by mass, from the viewpoint of easily increasing the tensile strength.

[0075] Furthermore, from the viewpoint of increasing the tensile strength while improving the diatomaceous earth capture rate, the ratio of the mass of the natural pulp (D) to the total mass of the polyolefin synthetic pulp (A) is preferably 60.0 mass% or less, more preferably 50.0 mass% or less, and even more preferably 40.0 mass% or less. There is no particular lower limit, but, for example, it is preferably 0 mass% or more, and more preferably 5.3 mass% or more.

[0076] 1-5. Physical properties of synthetic paper The diatomaceous earth collection rate of the synthetic paper is preferably 20.0% to 100.0%, and more preferably 25.0% to 100.0%. The diatomaceous earth collection rate is an index showing the degree to which the diatomaceous earth charged as a raw material is retained in the filter, with a higher value indicating better performance. A diatomaceous earth collection rate of 20.0% or higher indicates that the diatomaceous earth used in the charge is sufficiently retained in the filter. The diatomaceous earth collection rate is calculated using the following formula. (Diatomaceous earth capture rate (%)) = (diatomaceous earth basis weight (g / m 2 )) / (Diatomaceous earth charge amount (g / m 2 ))×100 In addition, the basis weight of diatomaceous earth (g / m 2 ) is the basis weight (g / m2) of the synthetic paper measured by the above method. 2 ) from the basis weight (g / m 2) is subtracted from the value.

[0077] The diatomaceous earth shedding rate of synthetic paper is preferably 0.0% to 1.8%, and more preferably 0.0% to 1.5%. The diatomaceous earth shedding rate is an index that indicates the amount of diatomaceous earth that falls off after long-term use. If the diatomaceous earth shedding rate is 1.8% or less, the diatomaceous earth is less likely to fall off even after long-term use. The diatomaceous earth shedding rate is calculated using the following formula. (Diatomaceous earth shedding rate (%)) = (amount of diatomaceous earth removed (g / m 2 )) / (Diatomaceous earth basis weight (g / m 2 ))×100 The amount of diatomaceous earth that fell off was measured as follows: First, synthetic paper was cut into a 70 mm diameter circle and placed in a filtration test nutsche. 1 L of tap water was suction filtered using a water pump, and the synthetic paper was completely dried after filtration. 2 converted to the weight of the diatomaceous earth after filtration (g / m 2 Next, calculate the diatomaceous earth basis weight (g / m) calculated by the above method. 2 ) and the diatomaceous earth weight after filtration (g / m 2 ) and the value is the amount of diatomaceous earth that has fallen off (g / m 2 )

[0078] The lower limit of the tensile strength of the synthetic paper is preferably 1.0 N / 15 mm or more, and more preferably 2.0 N / 15 mm or more. The upper limit of the tensile strength is not particularly limited, but may be, for example, 50 N / 15 mm or less. A tensile strength of 2.0 N / 15 mm or more increases the strength, making it easier to use as a filter.

[0079] The tensile strength of synthetic paper is a value measured in accordance with JIS P 8113: 2006. Specifically, a test piece 15 mm wide x 200 mm long is taken from synthetic paper produced by the method described in the Examples below, and measurements are taken at three points using a tensile tester (Shimadzu Corporation Autograph EZ-test EZ-S) with a chuck distance of 100 mm and a head speed of 10 mm / min, and the tensile strength (N / 15 mm) is calculated by averaging the values.

[0080] 2. Synthetic paper manufacturing method The method for producing the synthetic paper of the present invention is not particularly limited, and any known method can be used. Examples include a dry method called an airlaid method and a wet method called a papermaking method. In order to impart texture to the synthetic paper, the wet method is preferred.

[0081] For example, a laboratory papermaking method may be a method for preparing hand-made paper in accordance with JIS P 8222: 2015. Alternatively, a dynamic papermaking method may be used as a laboratory papermaking method.

[0082] From the viewpoint of environmental considerations, a papermaking method using a completely closed system in which water during the papermaking process is not intentionally discharged is preferred. In the laboratory, this can be verified by reusing papermaking white water multiple times or by using pseudo-white water that theoretically reproduces white water in a closed state. When making paper in the laboratory, it is preferable to use pseudo-white water.

[0083] The drying temperature of the synthetic paper is preferably a temperature equal to or higher than the initial melting point of the short-cut fibers (C) used, more preferably a temperature equal to or higher than the initial melting point of the short-cut fibers (C) and lower than the melting point of the polyolefin synthetic pulp (A), specifically, 70°C to 135°C.

[0084] In order to achieve the desired smoothness of the synthetic paper of the present invention, a heat treatment may be further carried out. The heat treatment may be carried out using a drum dryer, an air-through dryer, or the like. Alternatively, a heat-treating calendering machine may be used to carry out calendering while the heat treatment is being carried out. The temperature at which the heat treatment is carried out is preferably 95°C to 165°C. Typically, the heat treatment is carried out at a temperature 10°C to 55°C higher than the drying temperature.

[0085] There are no particular limitations on the actual equipment used to produce the synthetic paper of the present invention, and examples include a combination of a paper machine such as a Fourdrinier paper machine, a cylinder paper machine, a cylinder / short-wire combination paper machine, or an inclined wire paper machine with a dryer such as a Yankee dryer, an air-through dryer, or a drum dryer, but any method may be used.

[0086] 3. Uses of synthetic paper The synthetic paper of the present invention may be used as filter paper. The filter paper may be used as a filter as is, or multiple sheets of filter paper may be combined to form a filter. When multiple sheets of filter paper of the present invention are combined, the filter paper sheets may be of the same type or different types. A filter may also be constructed by combining the filter paper of the present invention with other filter paper or a component other than filter paper.

[0087] Filters equipped with filter base paper are suitable for applications involving the removal of fine particles, and can be used to remove fine particles in the manufacturing process of various products, such as beverages such as alcoholic beverages and soft drinks, foods, pharmaceuticals, etc. Specific examples include filters for filtering out foreign matter from raw water sources for drinking water, and filters for removing yeast from draft beer. [Example]

[0088] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The materials, amounts used, proportions, and processing procedures shown in the following examples can be changed as appropriate without departing from the spirit of the present invention.

[0089] [1] Measurement and evaluation methods Various physical properties were measured and evaluated by the following methods.

[0090] [1.1] Thickness (mm) The thickness of the synthetic paper was measured in accordance with JIS P 8118:2014.

[0091] [1.2] Basis weight of synthetic paper (g / m 2 ) The mass of a test piece (produced in the Examples and Comparative Examples) measuring 25 cm in width and 25 cm in length was measured using a square paper machine. 2 The weight of the synthetic paper is converted to the basis weight (g / m 2 ) was calculated.

[0092] [1.3] Freeness of each pulp (ml) The freeness of each of the polyolefin synthetic pulp (A) and natural pulp (D) was determined as follows. 24 g of bone-dry pulp was weighed out and 2000 ml of water was added to adjust the consistency to approximately 1.2%. The pulp was then disintegrated in a disintegrator specified in JIS P 8220-1:2012 at 30,000 rpm (10 minutes). The fully disintegrated fibers were diluted with water to a consistency of approximately 0.3% by mass, and the water temperature was adjusted to 20.0 ± 0.5°C. 1000 ml of the disintegrated pulp slurry was measured, and the amount of wastewater discharged from the side pipe was measured using a Canadian Standard Freeness Tester.

[0093] [1.4] Average fiber length (mm) The average fiber length of polyolefin synthetic pulp (A) and short-cut fiber (B) was determined as follows. Polyolefin synthetic pulp (A) or short-cut fiber (B) was dispersed in water to a concentration of 0.02% by mass, and the length of each fiber constituting the synthetic pulp was measured using an automatic fiber measuring instrument (product name: Valmet FS5) manufactured by Valmet Automation, Finland. Each fiber was classified into length classes in 0.05 mm increments. The actual fiber length of the fibers contained in each class (length) and the number of fibers contained in each class were then measured. Measurements were performed on 12,000 to 13,000 fibers. The number-average fiber length Ln (mm) of each class was then calculated from the measurement results using the following formula: Ln=ΣL / N L: Actual fiber length of the fiber contained in one grade (mm) N: Number of fibers in one grade Then, the average fiber length (mm) of each fiber was calculated using the following formula. Average fiber length = Σ(Nn × Ln 2 ) / Σ(Nn×Ln) Nn: Number of fibers in each grade

[0094] [1.5] Melting point of polyolefin synthetic pulp (A) (°C) The melting point of the polyolefin synthetic pulp (A) was determined as follows. 10 mg of each fiber was used as a sample. The sample was (i) heated to 250°C at 100°C / min and held at 250°C for 5 minutes, then (ii) cooled to 30°C at 10°C / min, and (iii) heated again to 340°C at 10°C / min. The highest endothermic peak temperature observed in the differential scanning calorimetry curve (DSC curve) during the second heating process (iii) was taken as the melting point of the polyolefin synthetic pulp (A). The endothermic peak observed in the differential scanning calorimetry curve (DSC curve) during the second heating process (iii) may be a single peak. In this case, the temperature of the single endothermic peak observed was taken as the melting point.

[0095] [1.6] Melting point of short cut fiber (B) (℃) The melting points of the core and sheath of the short-cut fiber (B) were determined as follows: Using a differential scanning calorimeter (DSC), a sample (approximately 5 mg) was heated to 230°C under a nitrogen atmosphere (20 mL / min), held at that temperature for 3 minutes, then cooled to 30°C at 10°C / min, held at 30°C for 1 minute, and heated to the temperature at 10°C / min. The melting point (Tm) was calculated from the peak apex of the crystalline melting peak during the heating process. If multiple crystalline melting peaks were observed, the peak on the higher temperature side was used as the melting point (Tm).

[0096] [1.7] Diatomaceous earth basis weight (g / m 2 ) The diatomaceous earth basis weight was calculated by subtracting the basis weight of the total amount of materials other than diatomaceous earth, such as polyolefin synthetic pulp, natural pulp, and short-cut fiber, from the basis weight of the synthetic paper obtained above.

[0097] [1.8] Diatomaceous earth capture rate (%) The algal earth collection rate was calculated using the following formula based on the amount of diatomaceous earth charged and the diatomaceous earth basis weight calculated above. (Diatomaceous earth capture rate (%)) = (diatomaceous earth basis weight (g / m 2 )) / (Diatomaceous earth charge amount (g / m 2 ))×100

[0098] [1.9] Diatomaceous earth after filtration The synthetic paper was cut into a 70 mm diameter circle and placed on a filtration test nutsche. 1 L of tap water was suction filtered using a water pump, and the synthetic paper was completely dried after filtration. 2 converted to the weight of the diatomaceous earth after filtration (g / m 2 ) was calculated.

[0099] [1.10] Diatomaceous earth shedding Diatomaceous earth basis weight (g / m) calculated using the above method 2 ) and the diatomaceous earth weight after filtration (g / m 2 ) and the value is the amount of diatomaceous earth that has fallen off (g / m 2 ) was decided.

[0100] [1.11] Diatomaceous earth shedding rate The diatomaceous earth dropout rate was calculated using the following formula based on the amount of diatomaceous earth that had fallen off and the basis weight of diatomaceous earth calculated above. (Diatomaceous earth shedding rate (%)) = (amount of diatomaceous earth removed (g / m 2 )) / (Diatomaceous earth basis weight (g / m 2 ))×100

[0101] [1.12] Tensile strength Measurements were made in accordance with JIS P 8113: 2006. Test pieces measuring 15 mm wide x 200 mm long were taken from the synthetic paper, and measurements were taken at three points using a tensile testing machine (Shimadzu Autograph model under review) with a chuck distance of 100 mm and a head speed of 10 mm / min, and the average value was calculated to determine the tensile strength (N / 50 mm).

[0102] [2] Preparation example [2.1] Preparation of polyolefin-based synthetic pulp (A) Polyolefin synthetic pulps (A-1) to (A-5) used were SWP manufactured by Mitsui Chemicals, Inc. The brands of polyolefin synthetic pulps (A-1) to (A-5) and their physical properties are shown in Table 1 below.

[0103] [Table 1]

[0104] [2.2] Preparation of diatomaceous earth (B) Diatomaceous earth (B-1): Radiolite F, manufactured by Showa Chemical Industry Co., Ltd.

[0105] [2.3] Preparation of short-cut fibers (C) The short cut fibers (C-1) to (C-2) were prepared. The brands and physical properties of the short cut fibers (C-1) to (C-2) are shown in Table 2 below.

[0106] [Table 2]

[0107] [2.4] Preparation of natural pulp (D) Natural pulps (D-1) to (D-2) were prepared as follows. The natural pulps (D-1) to (D-2) were prepared as follows, and their outlines and physical properties are shown in Table 3.

[0108] D-1: North American NBKP was disintegrated using a standard disintegrator to obtain a 1% concentration slurry. D-2: North American NBKP was beaten using a Niagara Beater (manufactured by Kumagai Riki Kogyo Co., Ltd.) to obtain a slurry with a concentration of 1%.

[0109] [Table 3]

[0110] [3] Example Example 1 2.5 g (bone dry weight) of polyolefin synthetic pulp (A-1) was placed in a 2 L household mixer and filled with water to open the fibers, producing a slurry solution of polyolefin synthetic pulp (A-1). A 1% slurry solution of diatomaceous earth (B-1) was also prepared. 250 ml (2.5 g) of the diatomaceous earth (B-1) slurry solution and the entire amount of the polyolefin synthetic pulp (A-1) slurry solution were added and mixed uniformly with a spoon. This was then placed in a square papermaking machine measuring 25 cm long x 25 cm wide x 30 cm high, and sheets were produced.

[0111] Next, the sheet was peeled off from the wire mesh of the paper machine and sandwiched between filter paper to squeeze out the water. After that, it was dried and heat-treated in a rotary dryer set at 125°C to obtain synthetic paper. The total weight of the polyolefin synthetic pulp (materials other than diatomaceous earth) was 40.0 g / m 2 It was.

[0112] Example 2 2.25 g (bone dry weight) of polyolefin synthetic pulp (A-1) was placed in a 2 L household mixer and filled with water to open the fibers, creating a slurry solution of polyolefin synthetic pulp (A-1). A pulp slurry equivalent to 0.25 g (bone dry weight) of disintegrated natural pulp (D-1) was prepared, and a 1% slurry solution of diatomaceous earth (B-1) was also prepared.

[0113] The entire amount of the slurry solution of polyolefin synthetic pulp (A-1) and the slurry solution of natural pulp (D-1) were added and mixed uniformly with a spoon. Finally, 250 ml of the slurry solution of diatomaceous earth (B-1) (2.5 g of diatomaceous earth) was added and mixed again with a spoon to uniformly mix. This was placed in a square papermaking machine measuring 25 cm in length, 25 cm in width, and 30 cm in height, and paper was made into a sheet. The total weight of the polyolefin synthetic pulp and natural pulp (materials other than diatomaceous earth) charged was 40.0 g / m 2 It was.

[0114] Example 3 2.375 g (bone dry weight) of polyolefin synthetic pulp (A-1) was placed in a 2 L household mixer and filled with water to open the fibers, creating a slurry solution of polyolefin synthetic pulp (A-1). Next, 0.125 g (bone dry weight) of short-cut fiber (C-1) was placed in a 2 L household mixer and filled with water to open the fibers, creating a slurry solution of short-cut fiber (C-1). Also, a disintegrated slurry of natural pulp (D-1) was prepared, and a slurry equivalent to 0.25 g (bone dry weight) was collected. A 1% slurry solution of diatomaceous earth (B-1) was prepared.

[0115] The entire amount of the slurry solution of polyolefin synthetic pulp (A-1) and the slurry solution of short-cut fiber (C-1) were added and mixed uniformly with a spoon. Finally, 250 ml of the slurry solution of diatomaceous earth (B-1) (2.5 g of diatomaceous earth) was added and mixed again with a spoon to uniformly mix. This was placed in a square papermaking machine measuring 25 cm in length, 25 cm in width, and 30 cm in height, and paper was made into a sheet. The total weight of the polyolefin synthetic pulp, natural pulp, and short-cut fiber (materials other than diatomaceous earth) charged was 40.0 g / m 2 It was.

[0116] (Examples 4 to 12, Comparative Examples 1 to 3) Synthetic papers of Examples 4 to 12 and Comparative Examples 1 to 3 were produced in the same manner as in Example 3, except that the types and addition ratios of polyolefin synthetic pulp, natural pulp, and short-cut fiber were changed as shown in Tables 4 and 5.

[0117] The evaluation results of the synthetic papers are shown in Tables 4 and 5. In Comparative Example 3, papermaking was not possible and evaluation was not possible.

[0118] [Table 4]

[0119] [Table 5]

[0120] As shown in Tables 4 and 5, it was found that synthetic paper containing polyolefin-based synthetic pulp (A) and diatomaceous earth (B), where the polyolefin-based synthetic pulp (A) has a Canadian standard freeness of 100 ml to 750 ml, has good diatomaceous earth shedding rate and diatomaceous earth collection rate. [Industrial Applicability]

[0121] The synthetic paper according to the present invention has an excellent diatomaceous earth shedding rate, and even after long-term use, the amount of diatomaceous earth shedding can be reduced. Therefore, the synthetic paper can be used as filter base paper or filters, and is useful as a filter medium.

Claims

1. A polyolefin-based synthetic pulp (A); Diatomaceous earth (B), The polyolefin synthetic pulp (A) has a Canadian standard freeness of 100 ml to 750 ml. Synthetic paper.

2. The ratio of the mass of the polyolefin synthetic pulp (A) to the total mass of the synthetic paper is 20% by mass to 60% by mass, The content ratio of the diatomaceous earth (B) relative to the total mass of the synthetic paper is 20% by mass to 70% by mass. The synthetic paper according to claim 1 .

3. The polyolefin synthetic pulp (A) includes a polyolefin synthetic pulp having a Canadian standard freeness of 200 ml to 650 ml, The ratio of the content mass of the polyolefin synthetic pulp having a Canadian standard freeness of 200 ml to 650 ml to the total mass of the polyolefin synthetic pulp (A) is 30 mass% or more; The synthetic paper according to claim 1 .

4. Contains short cut fibers (C), The melting point of the short cut fiber (C) is 70°C to 190°C, The average fiber length of the short cut fibers (C) is 3.0 mm to 20.0 mm, The ratio of the content mass of the short-cut fibers (C) to the total mass of the synthetic paper is 3% by mass to 30% by mass. The synthetic paper according to claim 1 .

5. Contains natural pulp (D), The natural pulp (D) has a Canadian standard freeness of 100 ml to 800 ml, the ratio of the content of the natural pulp (D) to the total mass of the synthetic paper is 5% by mass to 30% by mass; The ratio of the content of the natural pulp (D) to the total mass of the polyolefin synthetic pulp (A) is 5.3% by mass to 60.0% by mass. The synthetic paper according to claim 1 .

6. The polyolefin synthetic pulp (A) contains an olefin polymer, The olefin polymer is an ethylene polymer. The synthetic paper according to claim 1 .

7. The polyolefin synthetic pulp (A) contains at least two types of polyolefin synthetic pulp having different melting points. The synthetic paper according to claim 1 .

8. The synthetic paper according to any one of claims 1 to 7, Filter base paper.

9. The filter base paper according to claim 8, filter.

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