Synthetic paper, reflection sheet, surface light source device, and liquid crystal display device

Abstract

To provide synthetic paper having a balance of whiteness and tensile strength, and a reflection sheet, a surface light source device, and a liquid crystal display device using the same.SOLUTION: Synthetic paper including a polyolefin-based synthetic pulp (A), wherein the Canadian standard freeness of the polyolefin-based synthetic pulp (A) is 100 ml to 700 ml, and the ratio of the Oken-type air permeability of the synthetic paper to the basis weight of the synthetic paper ([Oken-type air permeability / basis weight]) is 0.24 s m2 / g or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to synthetic paper, a reflective sheet, a surface light source device, and a liquid crystal display device. [Background technology]

[0002] In recent years, reflective sheets have been widely used as a key component of liquid crystal display devices for mobile phones, personal computers, televisions, etc. In particular, it is important that liquid crystal display devices used in mobile phones be thin, energy-efficient, and lightweight, and there is also a demand for improved display quality of liquid crystal display devices, which requires supplying a large amount of light to the liquid crystal portion. To meet these requirements, it is necessary to increase the amount of light supplied from the light source, and reflective sheets that have high reflection efficiency (whiteness) and can provide high brightness are required.

[0003] There are two types of backlight units for LCD displays: one in which the light source is placed directly below the LCD section, and one in which the light source is placed next to a transparent light guide plate. In the former type, the reflective sheet is placed below the LCD section to reflect the light from the lamp, while in the latter type, it is placed next to the light guide plate to cover the lamp, and below the light guide plate to reflect the light from the light guide plate. When an LCD display device is used for an extended period of time, the heat from the light from the lamp and the moisture absorption and desorption of the components can cause the surrounding components of the reflective sheet to warp, which can easily place stress on the reflective sheet. Therefore, a reflective sheet with high strength is required to prevent warping.

[0004] For example, Patent Document 1 describes a light reflecting sheet that includes a sheet containing fibers with a number average diameter of 1 to 1000 nm and has a reflectance of 95% or more for light at a wavelength of 560 nm. It is said that the invention described in Patent Document 1 has made it possible to obtain a thin light reflecting sheet with high reflectance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-233344 Summary of the Invention [Problem to be solved by the invention]

[0006] A balance between whiteness and tensile strength is sometimes required for a reflective sheet, and the reflective sheet disclosed in Patent Document 1 has room for improvement in the balance between whiteness and tensile strength.

[0007] The present invention has been made in view of the above circumstances, and aims to provide a synthetic paper and a reflective sheet that have a good balance between whiteness and tensile strength, as well as a surface light source device and a liquid crystal display device that use the synthetic paper. [Means for solving the problem]

[0008] In order to solve the above problems, one aspect of the present invention relates to synthetic paper according to [1] to [5].

[0009] [1] Synthetic paper containing polyolefin-based synthetic pulp (A), The polyolefin synthetic pulp (A) has a Canadian standard freeness of 100 ml to 700 ml; The ratio of the Oken air permeability of the synthetic paper to the basis weight of the synthetic paper ([Oken air permeability / basis weight]) is 0.24 s m 2 / g or more, Synthetic paper.

[0010] [2] The ratio is 0.40 s m 2 / g or more, [1] The synthetic paper according to [1].

[0011] [3] The ratio is 0.60 s m 2 / g or more, [1] or [2].

[0012] [4] The synthetic paper has an Oken air permeability of 30.0 s or more; The synthetic paper has a basis weight of 50.0 g / m 2 That's all. The synthetic paper according to any one of [1] to [3].

[0013] [5] The Canadian standard freeness of the polyolefin synthetic pulp (A) is 200 ml to 500 ml. The synthetic paper according to any one of [1] to [4].

[0014] In order to solve the above problems, one aspect of the present invention relates to a reflecting sheet [6].

[0015] [6] The synthetic paper according to any one of [1] to [5] is included. Reflective sheet.

[0016] In order to solve the above problems, one aspect of the present invention relates to a surface light source device according to [7].

[0017] [7] [6] Including the reflective sheet described in Surface light source device.

[0018] In order to solve the above problems, one aspect of the present invention relates to a liquid crystal display device according to [8].

[0019] [8] The surface light source device according to [7] is used as a backlight light source means. Liquid crystal display device. [Effects of the Invention]

[0020] The present invention provides a synthetic paper and a reflective sheet that have a good balance between whiteness and tensile strength. The present invention also provides a surface light source device and a liquid crystal display device that use the synthetic paper. 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 the polyolefin synthetic pulp (A) has a Canadian standard freeness of 100 ml to 700 ml, and the ratio of the Oken air permeability of the synthetic paper to the basis weight of the synthetic paper ([Oken air permeability / basis weight]) is 0.24 s m 2 / g or more.

[0029] The synthetic paper according to this embodiment is a mixture of synthetic pulp fibers and sheath-core fibers, with these fibers and voids between the fibers randomly mixed together. Synthetic pulp fibers are branched, with the tips of the fibers branching into many thin strands and entangled with the sheath-core fibers. Generally, when light is irradiated onto a reflective sheet, the light is reflected and refracted on the surface of the fibers, dispersing in multiple directions. The light is repeatedly reflected and refracted in multiple directions on the fiber surface, and travels straight through voids. The more times light hits the fibers, the more reflections and refractions can occur, which tends to increase whiteness.

[0030] Canadian Standard Freeness is a physical property closely related to the state of each fiber in synthetic pulp. The more branches or entanglements of fibril fibers in synthetic pulp, the lower the Canadian Standard Freeness. As a result, incident light is repeatedly reflected and refracted at the branched and entangled parts, which tends to increase the whiteness of synthetic paper made using this material. Similarly, the entanglement of fibril fibers also tends to increase the tensile strength of synthetic paper made using this material.

[0031] In addition, the ratio of the Oken air permeability of synthetic paper to its basis weight ([Oken air permeability / basis weight]) is a physical property closely related to the state of each fiber in the synthetic pulp. Oken air permeability refers to the time it takes for a certain amount of air to pass through synthetic paper, and in synthetic paper where this ratio is within the above range, fibril fibers with a specific fiber diameter are appropriately branched, and the fibril fibers are entangled or cross each other. This allows incident light to be repeatedly reflected and refracted, which tends to increase the whiteness of the synthetic paper. Similarly, the entanglement of fibril fibers also tends to increase the tensile strength of the synthetic paper.

[0032] The ratio of the Oken air permeability of synthetic paper to the basis weight of the synthetic paper ([Oken air permeability / basis weight]) is 0.24 s m 2 / g or more, it is possible to easily increase both the whiteness and the tensile strength. 2 / g or more, and 0.60 s m 2 / g or more is more preferable. The upper limit is not particularly limited, but for example, 1.00 s m 2 / g or less. The Oken air permeability is a value measured in accordance with JIS P8117:2009, and the basis weight is a value measured by measuring the weight of a certain area of ​​synthetic paper (for example, 25 cm square) and dividing by the area. Furthermore, the ratio of the Oken air permeability of the synthetic paper to the basis weight of the synthetic paper ([Oken air permeability / basis weight]) is calculated by dividing the Oken air permeability of the synthetic paper by the basis weight.

[0033] From the viewpoint of achieving an excellent balance between whiteness and tensile strength, the lower limit of the Oken air permeability of the synthetic paper is preferably 10.0 s or more, more preferably 10.5 s or more, and even more preferably 30.0 s or more. The upper limit of the Oken air permeability is not particularly limited, but may be, for example, 100 s or less.

[0034] The lower limit of the basis weight of the synthetic paper according to this embodiment is 10.0 g / m 2 It is preferable that the content is 30.0 g / m or more. 2 More preferably, it is 39.5 g / m or more. 2 More preferably, it is 50.0 g / m or more. 2 The upper limit of the basis weight is most preferably 300.0 g / m or more. 2 Preferably, it is 200.0 g / m or less. 2 More preferably, it is 100.0 g / m or less. 2 It is more preferable that the basis weight is 10.0 g / m or less. 2 By setting the above, the amount of light that passes through the reflective sheet when the reflective sheet is irradiated with light is reduced, and the reflectance is improved.

[0035] The thickness of the synthetic paper according to this embodiment is usually 300 μm to 700 μm. If it is too thick, flexibility will be lost, making it difficult to take out the product in roll form and making it difficult to handle. If it is too thin, light will pass through the reflective sheet without being reflected or refracted, which is undesirable.

[0036] The synthetic paper according to this embodiment may contain other fibers, resins, or additives, as long as the object of the present invention is not impaired. For example, the synthetic paper may contain an antioxidant or an antistatic agent to suppress deterioration due to light or to suppress static electricity in the sheet. Various additives, such as lubricants, paper strength agents, and pigments, may also be added to improve the strength and abrasion resistance of the paper, improve the feel, and impart design features. Whitening agents, such as inorganic oxides, and reflective materials may also be added to improve reflectivity.

[0037] 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 is preferably 80% by mass or more from the viewpoint of a balance between high reflectivity, light weight, and low breathability.

[0038] 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.

[0039] 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 amount of structural units other than the olefin is preferably 50 mol% or less, more preferably 40 mol% or less, based on the total structural units. In this specification, the term "olefin polymer" also includes graft-modified products in which a polyolefin is graft-modified with an unsaturated carboxylic acid monomer.

[0040] Among these, for example, when used as a reflective sheet, from the viewpoint of enhancing reflectivity, the olefin polymer is preferably an ethylene polymer containing mainly ethylene, 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 these with an unsaturated carboxylic acid monomer. The resin constituting the polyolefin synthetic pulp (A) may be bio-derived.

[0041] When the olefin polymer is an ethylene homopolymer, the melt flow rate (hereinafter also referred to as "MFR") measured at 190°C under a load of 2.16 kg in accordance with ASTM D 1238 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 in the above range is used, it becomes easy to entangle with the short-cut fiber (B) described later, and an excellent balance between whiteness and tensile strength is achieved.

[0042] The polyolefin synthetic pulp (A) has a Canadian standard freeness (hereinafter simply referred to as "freeness") of 100 ml to 700 ml. The freeness is a value measured in accordance with JIS P 8121-2:2012. The freeness of the polyolefin synthetic pulp (A) is preferably 200 ml to 500 ml. Furthermore, by including polyolefin synthetic pulp (A) having a freeness of 200 ml to 500 ml, an excellent balance between whiteness and tensile strength is achieved. The freeness of the polyolefin synthetic pulp (A) can be adjusted by treating the polyolefin synthetic pulp (A) with a disc refiner or the like during production.

[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 mm to 50 mm, more preferably 0.05 mm to 10 mm. The average fiber length is preferably 0.1 mm or more and less than 3.0 mm, and more preferably 0.5 mm or more and less than 1.5 mm from the viewpoint of a balance between high reflectivity, light weight, and low breathability. The fiber length and average fiber length can be adjusted, for example, by processing using 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 160°C, more preferably 70°C to 130°C. The polyolefin synthetic pulp (A) may be two types of pulp with different melting points, one of which preferably has a melting point of 70°C to 130°C. By using polyolefin synthetic pulp (A) with a melting point of 130°C or lower, some components are more likely to fuse together during drying and heat treatment, which increases the tensile strength. 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 (B). The melting point of the polyolefin synthetic pulp (A) is measured using a differential scanning calorimeter.

[0048] 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.

[0049] 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% by mass 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.

[0050] 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.

[0051] 1-2. Short-cut fiber (B) The synthetic paper according to this embodiment may further contain short-cut fibers (B), which are fibers for binding the polyolefin synthetic pulp (A) described above.

[0052] The short-cut fibers (B) preferably have a melting point of 70°C to 190°C and an average fiber length of 1.5 mm to 9.0 mm. The short-cut fibers (B) and the polyolefin-based synthetic pulp (A) can be distinguished by the appearance of the fibers under a microscope and their Canadian standard freeness. That is, the short-cut fibers (B) have a straight shape without branches and a Canadian standard freeness of more than 700 ml.

[0053] The melting point of the short cut fiber (B) is more preferably 80° C. to 120° C. When the melting point is within this range, it becomes possible to bind the polyolefin synthetic pulp (A) without excessively increasing the temperature, thereby obtaining synthetic paper that balances high reflectivity, light weight, and low breathability.

[0054] The average fiber length of the short-cut fibers (B) is more preferably 2.0 mm to 8.0 mm. When the average fiber length of the short-cut fibers (B) is within this range, they can easily bind other components and easily bond each component evenly. This makes it possible to obtain synthetic paper that balances high reflectivity, light weight, and low breathability. The average fiber length of the short-cut fibers (B) can be measured by the same method as that for the polyolefin synthetic pulp (A) described above.

[0055] The cross-sectional shape of the short cut fibers (B) 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 (B) is 0.1 mm or more, the strength of the short cut fibers (B) 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.

[0056] When the short-cut fibers (B) are composite fibers (sheath-core fibers) containing two or more resins, the melting point of the short-cut fibers (B) refers to the melting point of the sheath portion, which is the surface portion of the short-cut fibers (B). For example, in the case of a sheath-core fiber, if the melting point of the sheath portion is within the above range, it is included in the short-cut fibers (B) specified in this specification. The melting points of the core and sheath portions of the short-cut fibers (B) are values ​​measured using 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).

[0057] The short cut fibers (B) may be bonded to the polyolefin synthetic pulp (A) by heat fusion or the like, or may be bonded by chemical reaction.

[0058] When polyolefin synthetic pulp (A) is bonded by heat fusion or the like, the polyolefin synthetic pulp (A) and short-cut fibers (B) are mixed during synthetic paper production, and the mixture is heated above the melting point of the short-cut fibers (B) but below the melting point of the polyolefin synthetic pulp (A), melting the short-cut fibers (B) and bonding them together. Examples of such heat-fusible short-cut fibers (B) include polyethylene fibers, low-melting polyester fibers, acrylic fibers, low-melting polyethylene fibers, and low-melting SWP fibers. However, composite fibers (core-sheath or side-by-side) using a low-melting resin (vinyl acetate resin) in the sheath, such as vinyl acetate resin (preferably EVA) / polypropylene composite fibers, are preferred. The resin constituting the short-cut fibers (B) may be bio-derived.

[0059] 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.

[0060] 1-3. Brightness and tensile strength of synthetic paper The whiteness of the synthetic paper is preferably 80% to 100%, and more preferably 85% to 100%. Increasing the whiteness tends to increase the reflection efficiency, and for example, when used in a liquid crystal display, the brightness tends to increase.

[0061] The whiteness of the synthetic paper was measured in accordance with JIS P 8148:2018 using a 150 mm (MD) x 150 mm (CD) test piece taken using a spectrophotometer PF-10 manufactured by Nippon Denshoku Industries Co., Ltd.

[0062] The lower limit of the tensile strength of the synthetic paper is preferably 2.0 N / 15 mm or more, and more preferably 3.0 N / 15 mm or more. The upper limit of the tensile strength is not particularly limited, but may be, for example, 20.0 N / 15 mm or less. When the tensile strength is 2.0 N / 15 mm or more, the strength is increased, and when used in, for example, a liquid crystal display, the reflective sheet is less likely to bend even after long-term use.

[0063] 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.

[0064] Additionally, the product of whiteness and tensile strength (%·N / 15mm) shown in the following formula was used as an index of the balance between whiteness and tensile strength of synthetic paper. The product of whiteness and tensile strength is preferably 300%·N / 15mm or more, and more preferably 350%·N / 15mm or more. There is no particular upper limit to the product of whiteness and tensile strength, but it may be, for example, 1000%·N / 15mm or less. When the product of whiteness and tensile strength is 350%·N / 15mm or more, it can be said that the balance between whiteness and tensile strength is achieved, and when used in, for example, an LCD display, the brightness tends to increase and the paper is less likely to warp even after long-term use.

[0065] 2. Synthetic paper manufacturing method The method for producing the synthetic paper according to this embodiment is not particularly limited, and any known method can be used. Examples include a dry method known as the airlaid method and a wet method known as the papermaking method. Note that the wet method is preferred in order to impart texture to the synthetic paper.

[0066] 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.

[0067] 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.

[0068] When short-cut fibers (B) are used, 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 (B) used. Furthermore, a temperature equal to or higher than the initial melting point of the short-cut fibers (B) and lower than the melting point of the polyolefin synthetic pulp (A) is preferred. Specifically, a temperature of 70°C to 135°C is preferred.

[0069] To achieve the desired smoothness of the synthetic paper according to this embodiment, the synthetic paper may be further subjected to a heat treatment. The heat treatment can be carried out using a drum dryer, an air-through dryer, or the like. Alternatively, a calendering machine capable of heat treatment 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.

[0070] There are no particular limitations on the actual equipment used to produce the synthetic paper according to this embodiment, 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.

[0071] 3. Uses of synthetic paper The synthetic paper according to this embodiment is used for nonwoven fabrics, reflective sheets, and the like.

[0072] The nonwoven fabric according to this embodiment can be used alone or laminated with other members or other nonwoven fabrics for a variety of applications. Specific examples of applications of the nonwoven fabric include sanitary goods, wrapping paper, printed paper (synthetic paper), clothing, and wiping cloths. As described above, the nonwoven fabric of the present invention can be folded into any shape and can maintain the shape in a folded state. Furthermore, it can easily return to its original shape. In addition, the shape-retaining member (C) does not protrude during use, making it extremely safe. Therefore, it is very useful as sanitary goods, wrapping paper, printed paper, and the like.

[0073] The synthetic paper according to this embodiment is used as a reflective sheet, for example, a reflective sheet for a surface light source device, a back reflective sheet for an illuminated signboard, a back reflective sheet for a solar cell, etc.

[0074] The surface light source device according to the present embodiment includes the reflective sheet. Examples of the surface light source device include, but are not limited to, backlight sources for liquid crystal displays and display devices. In particular, the surface light source device according to the present embodiment is suitable for use as a thin backlight unit for a thin panel that uses an LED or a cold cathode fluorescent lamp as a light source, such as in a mobile phone or a PDA.

[0075] In addition, the liquid crystal display device according to this embodiment can use a surface light source device using the reflective sheet as a backlight source means. [Example]

[0076] 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, ratios, and processing procedures shown in the following examples can be changed as appropriate without departing from the spirit of the present invention.

[0077] [1] Measurement and evaluation methods Various physical properties were measured and evaluated by the following methods.

[0078] [1.1] Oken style air permeability (s) Test pieces of 150 mm (MD) x 150 mm (CD) were taken from synthetic paper produced by the method described in the Examples below, and the air permeability was measured using an Oken air permeability tester in accordance with JIS P 8117: 2009. The average value of n = 5 was used as the measured value.

[0079] [1.2]Basic weight (g / m 2 ) The weight of synthetic paper (25 cm x 25 cm) produced by the method described in the Examples below was measured and the basis weight was calculated.

[0080] [1.3] Freeness [ml] 24 g of bone-dry polyolefin synthetic pulp (A) was weighed out and 2000 ml of water was added to a concentration of 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 completely disintegrated fibers were diluted with water to a concentration 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.

[0081] [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

[0082] [1.5] Melting point of polyolefin synthetic pulp (A) [℃] 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 250°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.

[0083] [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).

[0084] [1.7] Whiteness (%) Test pieces of 150 mm (MD) x 150 mm (CD) were taken from synthetic paper produced by the method described in the Examples below, and the whiteness was measured using a spectrophotometer PF-10 manufactured by Nippon Denshoku Industries Co., Ltd. in accordance with JIS P 8148:2018.

[0085] [1.8] Tensile strength (N / 15mm) The tensile strength of synthetic paper produced by the method described in the Examples below was measured in accordance with JIS P 8113: 2006. Specifically, a test piece 15 mm wide x 200 mm long was taken from the synthetic paper produced by the method described in the Examples below, and measurements were 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) was calculated by averaging the values.

[0086] [2] Preparation example [2.1] Preparation of polyolefin-based synthetic pulp (A) The polyolefin synthetic pulps (A-1) to (A-2) used were SWP manufactured by Mitsui Chemicals, Inc. The brands of the polyolefin synthetic pulps (A-1) to (A-2) and their physical properties are shown in Table 1 below.

[0087] [Table 1]

[0088] [2.2] Preparation of short-cut fibers (B) (B-1) to (B-2) were prepared as the short cut fibers (B). The brands and physical properties of the short cut fibers (B-1) to (B-2) are shown in Table 2 below.

[0089] [Table 2]

[0090] [3] Example [3.1] Example 1 2.25 g (bone-dry weight) of SWP (registered trademark) E620 (manufactured by Mitsui Chemicals, Inc.), a synthetic pulp made from high-density polyethylene, and 0.25 g (bone-dry weight) of SWP (registered trademark) UL410 (manufactured by Mitsui Chemicals, Inc.) were placed in a 2-liter household mixer, filled with water, and the fibers were opened. This was then placed in a rectangular papermaking machine measuring 25 cm long x 25 cm wide x 30 cm high and made into a paper sheet.

[0091] Next, the synthetic paper was peeled off from the wire mesh of the paper machine, sandwiched between filter paper to squeeze out the water, and then dried and heat-treated in a rotary dryer set at 120°C until the basis weight reached 40.6 g / m 2 Synthetic paper of

[0092] [3.2] Example 2 2.25 g (bone dry weight) of olefin-based synthetic pulp (A-1) was placed in a 2 L household mixer and filled with water to open the fibers, thereby preparing a slurry solution of olefin-based synthetic pulp (A-1).

[0093] 0.25 g (bone dry weight) of the short cut fiber (B-1) was placed in a 2 L household mixer and filled with water to open the fiber, thereby preparing a slurry solution of the short cut fiber (B-1).

[0094] The slurry solution of the olefin synthetic pulp (A-1) and the slurry solution of the short-cut fiber (B-1) were all added and mixed uniformly with a spoon, and then the mixture was put into a square paper machine measuring 25 cm in length, 25 cm in width, and 30 cm in height, and paper was made.

[0095] Next, the synthetic paper was peeled off from the wire mesh of the paper machine, sandwiched between filter paper to squeeze out the water, and then dried and heat-treated in a rotary dryer set at 120°C until the basis weight reached 40.2 g / m 2 As a result, synthetic paper of

[0096] [3.3] Example 3 2.50 g (bone dry weight) of SWP (registered trademark) E620 (manufactured by Mitsui Chemicals, Inc.), a synthetic pulp made from high-density polyethylene, was placed in a 2-L household mixer, filled with water, and the fibers were opened. This was then placed in a square papermaking machine measuring 25 cm length x 25 cm width x 30 cm height and made into a paper sheet.

[0097] Next, the synthetic paper was peeled off from the wire mesh of the paper machine, sandwiched between filter paper to squeeze out the water, and then dried and heat-treated in a rotary dryer set at 120°C until the basis weight reached 39.6 g / m 2 As a result, synthetic paper of

[0098] [3.4] Example 4 The same method as in Example 3 was used except for changing the basis weight, and the basis weight was 70.1 g / m 2 As a result, synthetic paper of

[0099] [3.5] Comparative Example 1 A spunbonded ... 2 As a result, synthetic paper of

[0100] [3.6] Comparative Example 2 The same method as in Example 3 was used except for changing the basis weight, and the basis weight was 19.8 g / m 2 As a result, synthetic paper of

[0101] The evaluation results of the synthetic paper are shown in Table 3.

[0102] [Table 3]

[0103] As shown in Table 3, the synthetic paper contains polyolefin synthetic pulp (A), the Canadian standard freeness of the polyolefin synthetic pulp (A) is 100 ml to 700 ml, and the ratio of the Oken air permeability of the synthetic paper to the basis weight of the synthetic paper ([Oken air permeability / basis weight]) is 0.24 s m 2 It was found that synthetic paper with a tensile strength of 1 / g or more had good values ​​for both brightness and tensile strength. [Industrial Applicability]

[0104] The synthetic paper according to the present invention exhibits excellent performance in both whiteness and tensile strength, and is therefore useful as a reflective member in reflective sheets, surface light source devices, and liquid crystal display devices.

Claims

1. A synthetic paper containing polyolefin-based synthetic pulp (A), The polyolefin synthetic pulp (A) has a Canadian standard freeness of 100 ml to 700 ml, The ratio of the Oken air permeability of the synthetic paper to the basis weight of the synthetic paper ([Oken air permeability / basis weight]) is 0.24 s m ２ / g or more, Synthetic paper.

2. The ratio is 0.40 s m ２ / g or more, The synthetic paper according to claim 1 .

3. The ratio is 0.60 s m ２ / g or more, The synthetic paper according to claim 1 .

4. The synthetic paper has an Oken air permeability of 30.0 s or more, The synthetic paper has a basis weight of 50.0 g / m ２ That's all. The synthetic paper according to claim 1 .

5. The polyolefin synthetic pulp (A) has a Canadian standard freeness of 200 ml to 500 ml. The synthetic paper according to claim 1 .

6. The synthetic paper according to any one of claims 1 to 5, Reflective sheet.

7. The reflective sheet according to claim 6, Surface light source device.

8. The surface light source device according to claim 7 is used as a backlight source means. Liquid crystal display device.

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