Flame-retardant paper for radio wave absorber member and method for producing the same

Abstract

The present invention provides a flame-retardant paper for a radio wave absorber component and a method for manufacturing the same. The flame-retardant paper is particularly suitable for components of a radio wave absorber and, in addition to having high flame retardancy, is less likely to break during the manufacturing process, resulting in excellent productivity. The present invention provides a flame-retardant paper for a radio wave absorber component, comprising pulp, aluminum hydroxide, guanidine phosphate, a binder, and a conductive substance. The flame-retardant paper comprises 5% to 20% by mass of pulp, 40% to 70% by mass of aluminum hydroxide, 10% to 20% by mass of guanidine phosphate, 5% to 10% by mass of the binder, and 0.1% to 12% by mass of the conductive substance.

Description

Technical Field

[0001] The present invention relates to flame-retardant paper for radio wave absorber components and a method for manufacturing the same. Background Art

[0002] Radio wave absorbers are used in anechoic chambers, which are designed to reduce radio wave interference and other radio wave obstructions, allowing evaluation of radio wave noise generated by various electronic and communication devices, as well as evaluation of malfunctions caused by radio waves. Furthermore, in recent years, they have also been used in wireless communication systems such as electronic toll collection (ETC), wireless local area networks (LANs), and autonomous driving systems.

[0003] These radio wave absorbers absorb radio waves by converting their energy into heat. Therefore, exposure to high-energy radio waves can cause them to burn. In particular, radio wave absorbers used in anechoic chambers are required to be flame-retardant to ensure safety against fire hazards.

[0004] As flame-retardant paper for radio wave absorber members that is flame-retardant, does not easily discolor over a long period of time, and does not degrade in flame retardancy, a flame-retardant paper for radio wave absorber members containing a flame retardant including aluminum hydroxide powder and polyborate and pulp has been proposed (see Patent Document 1).

[0005] Furthermore, as a flame-retardant paper having excellent flame retardancy, being less prone to breakage, and having good productivity, a flame-retardant paper comprising pulp, aluminum hydroxide, a guanidine-based flame retardant, and a urethane resin has been proposed (see Patent Document 2).

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: International Publication No. 2017 / 002863

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 2020-23759 Summary of the Invention

[0010] Problems to be solved by the invention

[0011] According to the inventors, the flame-retardant paper for radio wave absorber components proposed in Patent Document 1 (hereinafter sometimes referred to as "flame-retardant paper") has relatively low toughness. Consequently, the paper tends to break during drying after impregnation or coating with a chemical solution containing a chemical, or during secondary processing such as forming slits or printing on the paper. Furthermore, this breakage during drying or secondary processing poses a processing problem, resulting in reduced productivity.

[0012] Patent Document 2 discloses flame-retardant paper containing a urethane resin in addition to aluminum hydroxide and a guanidine-based flame retardant. While this flame-retardant paper contains a urethane resin, the low content of the resin results in insufficient toughness. Furthermore, this flame-retardant paper suffers from insufficient tensile strength, making it prone to breakage when tension is applied during the production process.

[0013] Therefore, the object of the present invention is to provide a flame-retardant paper for radio wave absorber components that is particularly suitable for components of radio wave absorbers and, in addition to having excellent flame retardancy, has high tensile strength and is not prone to breakage. Furthermore, the flame-retardant paper for radio wave absorber components is not prone to breakage during drying or secondary processing such as slitting or printing, thereby improving productivity.

[0014] Technical means to solve the problem

[0015] In order to achieve the above-mentioned object, the present invention is

[0016] (1) A flame-retardant paper for a radio wave absorber member, comprising pulp, aluminum hydroxide, guanidine phosphate, a binder, and a conductive substance, wherein the pulp content in the flame-retardant paper for a radio wave absorber member is 5% to 20% by mass, the aluminum hydroxide content is 40% to 70% by mass, the guanidine phosphate content is 10% to 20% by mass, the binder content is 5% to 10% by mass, and the conductive substance content is 0.1% to 12% by mass; and

[0017] (2) A method for producing flame-retardant paper for a radio wave absorber member, the method comprising:

[0018] A process for preparing a slurry comprising pulp, aluminum hydroxide, a binder, and a conductive material;

[0019] a step of wet-making the slurry to obtain a flame-retardant paper substrate for a radio wave absorber member; and

[0020] A step of impregnating the flame-retardant paper substrate for the radio wave absorber member with an aqueous solution containing guanidine phosphate.

[0021] Effects of the Invention

[0022] According to the present invention, flame-retardant paper for radio wave absorber components can be obtained. The flame-retardant paper is suitable for components of radio wave absorbers and, in addition to having excellent flame retardancy, has high tensile strength and is not easy to break. The flame-retardant paper is not easy to break during drying or secondary processing such as slits or printing, and has good productivity. DETAILED DESCRIPTION

[0023] Hereinafter, examples of embodiments of the present invention will be described.

[0024] The flame-retardant paper for radio wave absorber components of the present invention is a flame-retardant paper for radio wave absorber components containing pulp, aluminum hydroxide, guanidine phosphate, an adhesive, and a conductive substance, wherein the pulp content is 5% to 20% by mass, the aluminum hydroxide content is 40% to 70% by mass, the guanidine phosphate content is 10% to 20% by mass, the adhesive content is 5% to 10% by mass, and the conductive substance content is 0.1% to 12% by mass.

[0025] Moreover, the flame-retardant paper for radio wave absorber components of the present invention adopting the above-mentioned structure is suitable for components of radio wave absorbers. In addition to having excellent flame retardancy, it produces less dirt during the process of applying the agent by impregnation or coating, and is less likely to break during drying and secondary processing such as slit or printing, and also has excellent productivity.

[0026] The reasons for this are speculated as follows. First, as described in detail below, in order to form the flame-retardant paper for radio wave absorber components into paper, the flame-retardant paper for radio wave absorber components needs to contain a specific amount or more of pulp. Moreover, pulp is a relatively flammable raw material. Therefore, in order to make the flame-retardant paper for radio wave absorber components sufficiently flame-retardant, it is necessary to set the content of flame retardants such as aluminum hydroxide or guanidine phosphate to be above a specific amount. On the other hand, if the content of flame retardants in the flame-retardant paper for radio wave absorber components increases, the tensile strength or toughness of the flame-retardant paper for radio wave absorber components decreases. Drying is usually performed in the papermaking process or in the process of applying a drug such as impregnation or coating, but the reduction in tensile strength or toughness will increase the frequency of fracture of the flame-retardant paper for radio wave absorber components during drying performed in these processes or during secondary processing such as slit or printing. This increase in the frequency of fracture of the flame-retardant paper for radio wave absorber components caused by the reduction in tensile strength or toughness means that the formability of the flame-retardant paper for radio wave absorber components is deteriorated. On the contrary, if the frequency of occurrence of breakage of the flame-retardant paper for a radio wave absorber member is suppressed due to excellent tensile strength or toughness, it means that the formability is improved.

[0027] On the other hand, the flame-retardant paper for radio wave absorber components of the present invention contains a binder, and further contains pulp, aluminum hydroxide, guanidine phosphate, and a binder in specific amounts. As a result, the tensile strength and toughness of the flame-retardant paper for radio wave absorber components become higher. As a result, the flame-retardant paper for radio wave absorber components has high levels of strength, toughness, and flame retardancy as paper. Therefore, it is speculated that the occurrence of breakage of the flame-retardant paper for radio wave absorber components during drying or secondary processing in the papermaking process or the drug application process can be suppressed, and flame-retardant paper for radio wave absorber components with excellent productivity and flame retardancy can be obtained. Furthermore, the strength or toughness of the flame-retardant paper for radio wave absorber components as paper and the flame retardancy are originally in a trade-off relationship depending on the above situation.

[0028] Examples of pulp used in the flame-retardant paper for the radio wave absorber member of the present invention include pulp containing plant fibers such as coniferous tree pulp, broadleaf tree pulp, thermogrind pulp, ground wood pulp, cotton linter pulp, and hemp pulp, pulp containing recycled fibers such as rayon, and synthetic fiber pulp containing vinylon or polyester. One or more types of pulp can be appropriately selected from these. Coniferous tree pulp is preferred because it can easily provide strength.

[0029] The flame-retardant paper for radio wave absorber components of the present invention contains 5% to 20% by mass of pulp relative to the total mass of the flame-retardant paper for radio wave absorber components. If the pulp content is less than 5% by mass, the pulp's wrapping force during the papermaking process is weakened, making it difficult to form a sheet. On the other hand, if the pulp content exceeds 20% by mass, the flame-retardant paper for radio wave absorber components tends to fail to achieve sufficient flame retardancy.

[0030] By setting the pulp content in the range of 5% to 20% by mass, a flame-retardant paper sheet for a radio wave absorber member having excellent flame retardancy can be obtained, preferably in the range of 10% to 18% by mass.

[0031] The flame-retardant paper for a radio wave absorber member of the present invention contains 40% to 70% by mass of aluminum hydroxide. The aluminum hydroxide is preferably supported on the entire flame-retardant paper for a radio wave absorber member in a well-dispersed state, and therefore the aluminum hydroxide is preferably in the form of a powder.

[0032] Here, aluminum hydroxide undergoes dehydration and decomposition at high temperatures, achieving a flame-retardant effect due to the heat absorption. This flame-retardant effect does not degrade over time even with long-term storage, allowing the flame-retardant effect imparted to the flame-retardant paper for radio wave absorber members to be maintained over a long period of time.

[0033] In addition, when making flame-retardant paper for radio wave absorber components, it is appropriate to add papermaking agents such as yield improvers or paper strength enhancers containing cationic polymer compounds or anionic polymer compounds, thereby allowing aluminum hydroxide to be adsorbed on the pulp, which further helps to improve the flame retardancy of flame-retardant paper for radio wave absorber components.

[0034] Aluminum hydroxide is a white powder, so flame-retardant paper for radio wave absorber components containing aluminum hydroxide at a specific content or above becomes white. Therefore, when used as a radio wave absorber in an anechoic chamber, the flame-retardant paper for radio wave absorber components of the present invention can improve the lighting effect within the chamber. Furthermore, aluminum hydroxide maintains the white color of the flame-retardant paper for radio wave absorber components without discoloration. Therefore, in the present invention, the inclusion of aluminum hydroxide in the flame-retardant paper for radio wave absorber components is crucial.

[0035] When the content of aluminum hydroxide is less than 40% by mass, the flame-retardant paper for a radio wave absorber member may not have sufficient flame retardancy.

[0036] On the other hand, when the aluminum hydroxide content exceeds 70% by mass, the flame-retardant paper for the radio wave absorber component can obtain high flame retardancy, but the flame-retardant paper for the radio wave absorber component may break during drying in the agent application process implemented by impregnation or coating, and during secondary processing such as slit or printing, and there is a possibility that the operability or process passability may deteriorate.

[0037] Thus, by setting the aluminum hydroxide content in the range of 40% to 70% by mass, a flame-retardant paper for a radio wave absorber member having excellent flame retardancy and white color retention can be obtained. A range of 45% to 65% by mass is preferred. Aluminum hydroxide can be purchased from Wako Pure Chemical Industries, Ltd. and Sigma-Aldrich Japan Co., Ltd., among others.

[0038] The flame-retardant paper for radio wave absorber components of the present invention contains 10% to 20% by mass of guanidine phosphate relative to the total mass of the flame-retardant paper for radio wave absorber components. Generally speaking, if the required amount of flame retardant is large, the toughness of the flame-retardant paper for radio wave absorber components decreases. Therefore, during drying in the agent imparting process implemented by impregnation or coating, or during secondary processing such as slits and printing, the flame-retardant paper for radio wave absorber components tends to break easily. In addition, guanidine phosphate is less likely to reduce the tensile strength of the flame-retardant paper for radio wave absorber components than aluminum hydroxide. Therefore, in order to give both the excellent flame retardancy of the flame-retardant paper for radio wave absorber components and the suppression of the breakage of the flame-retardant paper for radio wave absorber components, it is important that the flame-retardant paper for radio wave absorber components of the present invention contains guanidine phosphate in addition to aluminum hydroxide. Guanidine phosphate is also required because it can achieve high flame retardancy in flame-retardant paper for radio wave absorber members at a low content, does not deteriorate in flame retardancy over time due to hydrolysis, and exhibits minimal discoloration over time.

[0039] When the content of guanidine phosphate relative to the entire flame-retardant paper for a radio wave absorber member is less than 10% by mass, the flame retardancy of the member obtained by laminating the flame-retardant paper for a radio wave absorber member to foamed polystyrene tends to be insufficient.

[0040] On the other hand, if the guanidine phosphate content exceeds 20% by mass relative to the overall flame-retardant paper for radio wave absorber components, the flame-retardant paper may break during drying during the agent application process, such as impregnation or coating, and during secondary processing, such as slitting or printing, potentially deteriorating its operability and process performance. Furthermore, when used as flame-retardant paper for radio wave absorber components, discoloration due to changes over time becomes noticeable. From this perspective, the guanidine phosphate content is more preferably 15% by mass or less.

[0041] The flame-retardant paper for radio wave absorber components of the present invention contains 5% to 10% by mass of a binder relative to the entire flame-retardant paper for radio wave absorber components. Preferably, it contains 8% to 10% by mass of a binder. By containing the binder in the flame-retardant paper for radio wave absorber components, the tensile strength and toughness can be improved, and the aluminum hydroxide can be suppressed from falling off the flame-retardant paper for radio wave absorber components. Therefore, by suppressing the breakage of the flame-retardant paper for radio wave absorber components during drying in the papermaking process or the drug application process and during secondary processing such as slit or printing, high productivity can be achieved, and high flame retardancy of the flame-retardant paper for radio wave absorber components can be achieved.

[0042] When the content of the binder relative to the total mass of the flame-retardant paper for radio wave absorber components is less than 5% by mass, the flame-retardant paper for radio wave absorber components may break during drying in the papermaking process or the agent application process, or during secondary processing such as slitting or printing, which may deteriorate the operability or process passability.

[0043] On the other hand, when the content of the binder relative to the entire flame-retardant paper for a radio wave absorber member is more than 10% by mass, the flame retardancy may be reduced due to the influence of the binder.

[0044] The binder used in the present invention is not particularly limited. Examples include organic binders such as polyvinyl alcohol resins, vinyl acetate resins, acrylic resins, urea resins, epoxy resins, styrene-acrylic acid copolymer resins, polyester resins, and polyolefin resins, and inorganic binders such as alumina sol and silica sol. The binder may be used singly or as a mixture of two or more of these binders. In particular, the binder is preferably at least one selected from the group consisting of polyvinyl alcohol resins, acrylic resins, and styrene-acrylic acid copolymer resins, in view of their high hydrophilicity and excellent papermaking properties.

[0045] As the adhesive used as the raw material, there are liquid adhesives such as emulsions or solutions, and fibrous or powdered solid adhesives. Among them, from the perspective of not being easily hindered from contacting the conductive materials with each other and exerting excellent radio wave absorption performance, it is preferred to include a fibrous adhesive in at least a portion. As the fibrous adhesive, a single-component fibrous adhesive, or a core-sheath type composite fiber with a high melting point polymer as the core component and a low melting point polymer as the sheath component, or a composite fibrous adhesive such as a bimetallic composite fiber in which a high melting point polymer and a low melting point polymer are arranged with each other can be used. Moreover, if a fibrous adhesive is used in combination with a liquid adhesive or a powdered solid adhesive, then in addition to the adhesion between the fibers performed by the fibrous adhesive, the liquid adhesive or the powdered solid adhesive will also adhere to the intersection of the fibers, thereby further improving the bonding strength, which is more preferred in terms of the above aspect.

[0046] Here, it is preferred that the mass ratio of aluminum hydroxide to the binder (aluminum hydroxide content / binder content) is 83 / 17 to 91 / 9, and the ratio of the total content of aluminum hydroxide and guanidine phosphate to the total content of pulp and binder (aluminum hydroxide content + guanidine phosphate content) / (pulp content + binder content) is 67 / 33 to 80 / 20. The mass ratio is set to the value after rounding off to the first decimal place. The flame-retardant paper for radio wave absorber components having the above characteristics can take into account both excellent papermaking properties and excellent flame retardancy, and thus the operability is also excellent. Here, the excellent operability specifically refers to the suppression of the flame-retardant paper for radio wave absorber components from breaking in the process of imparting the agent to the flame-retardant paper for radio wave absorber components, the process of imparting the slit, and the process of printing processing.

[0047] The flame-retardant paper for radio wave absorber components of the present invention may also contain inorganic fibers such as glass fiber, rock wool, and basalt fiber. These are inorganic fibers, so the flame retardancy of the flame-retardant paper for radio wave absorber components can be improved, and they are fibers with high rigidity, so a high level of rigidity can be exhibited in the flame-retardant paper for radio wave absorber components, thereby improving the operability of the flame-retardant paper for radio wave absorber components. As the content of the inorganic fibers, when the entire paper of the flame-retardant paper for radio wave absorber components of the present invention is set to 100% by mass, it is preferably in the range of 1% to 30% by mass. It is further more preferably 15% by mass or less. By setting it to the above range, flame-retardant paper for radio wave absorber components with a high level of rigidity can be stably manufactured.

[0048] The flame-retardant paper for radio wave absorber components of the present invention contains 0.1% to 12% by mass of a conductive substance relative to the total mass of the flame-retardant paper for radio wave absorber components. Furthermore, the content is preferably 4% or less by mass, and more preferably 3% or less by mass. The so-called conductive substance in the present invention is a material that attenuates radio waves, i.e., absorbs radio waves, by converting radio wave energy into tiny currents and then into heat energy. Examples of conductive substances include conductive particles or conductive fibers. Here, examples of conductive particles include metal particles, carbon black particles, carbon nanotube particles, carbon microcoil particles, and graphite particles. Examples of conductive fibers include carbon fibers and metal fibers, and examples of metal fibers include stainless steel fibers, copper fibers, silver fibers, gold fibers, nickel fibers, aluminum fibers, and iron fibers. Furthermore, examples of conductive substances include those obtained by applying metal plating to non-conductive particles and fibers and then performing vapor deposition or spraying to impart conductivity.

[0049] Among these conductive materials, it is also preferred to use conductive fibers. Among the conductive fibers, it is more preferred to use conductive short fibers from the perspective of uniform dispersion. The aspect ratio of conductive short fibers is large, so the fibers are easy to contact each other, and even a small amount can effectively obtain radio wave absorption performance compared to powders. In addition, among the conductive short fibers, carbon fibers are particularly preferably used because they are rigid, easy to orient in the substrate, and have almost no performance changes during long-term use. With regard to the conductive short fibers, the length of the conductive short fibers is preferably 0.1 mm or more, and more preferably 1.0 mm or more, in terms of the ease of contact between the fibers and the dispersibility of the slurry in the papermaking manufacturing process described later. On the other hand, it is preferably 15.0 mm or less, and more preferably 10.0 mm or less.

[0050] When the flame-retardant paper for radio wave absorber components is used in an anechoic chamber, the conductive fiber content is preferably 0.5% to 2% by mass, and the relative dielectric constant of the flame-retardant paper for radio wave absorber components is preferably 10 to 250. A conductive fiber content of 0.5% or greater achieves even better radio wave absorption performance. On the other hand, a conductive fiber content of 2% or less suppresses radio wave reflection, resulting in even better radio wave absorption performance.

[0051] Furthermore, when the flame-retardant paper for radio wave absorber components is used as a noise suppression sheet for absorbing electromagnetic noise generated by small electronic devices, etc., the conductive fiber content is preferably 5% to 12% by mass, and the transmission attenuation rate of the flame-retardant paper for radio wave absorber components is preferably 20 dB or higher. A conductive fiber content of 5% to 12% by mass achieves a more excellent noise suppression effect. The conductive fiber content is preferably 5% to 10% by mass.

[0052] The weight per square meter of the flame-retardant paper for the radio wave absorber member of the present invention is preferably 50 g / m 2 ~200g / m 2 By containing 0.1% to 12% by mass of conductive material and being within the weight per square meter range, good radio wave absorption characteristics can be obtained. Furthermore, by having the weight per square meter within the range, the tensile strength and toughness of the flame-retardant paper for the radio wave absorber component are improved, and the breakage of the flame-retardant paper can be suppressed during drying in the papermaking process or the drug imparting process and during secondary processing such as slit or printing processing. The weight per square meter is more preferably 80g / m 2 On the other hand, it is more preferably 150g / m 2 the following.

[0053] Next, a method for producing the flame-retardant paper for a radio wave absorber member according to the present invention will be described.

[0054] The method for manufacturing flame-retardant paper for radio wave absorber components of the present invention can be listed as a manufacturing method having the following steps in sequence: a step of wet-papering pulp, aluminum hydroxide, adhesive and conductive material in a manner such that the content of pulp relative to the flame-retardant paper for radio wave absorber components is 5% to 20% by mass, the content of aluminum hydroxide is 40% to 70% by mass, the content of adhesive is 5% to 10% by mass, and the content of conductive material is 0.1% to 12% by mass, thereby obtaining a flame-retardant paper substrate for radio wave absorber components; and a step of imparting guanidine phosphate to the flame-retardant paper substrate for radio wave absorber components in a manner such that the content of guanidine phosphate relative to the flame-retardant paper for radio wave absorber components is 10% to 20% by mass. That is, the method for manufacturing flame-retardant paper for radio wave absorber components of the present invention sequentially comprises: a step of preparing a slurry containing pulp, aluminum hydroxide, a binder, and a conductive substance; a step of wet-papering the slurry to obtain a flame-retardant paper substrate for radio wave absorber components; and a step of impregnating the flame-retardant paper substrate for radio wave absorber components in an aqueous solution containing guanidine phosphate.

[0055] Here, increasing the amount of binder contained in the flame-retardant paper substrate for the radio wave absorber component tends to increase the tensile strength of the flame-retardant paper. However, generally speaking, increasing the amount of binder reduces the flame retardancy of the flame-retardant paper, so there is a trade-off between increasing the tensile strength and the flame retardancy of the flame-retardant paper. However, in the process of wet-papering the slurry to obtain the flame-retardant paper substrate for the radio wave absorber component, the slurry contains a binder, which can improve the paper strength of the flame-retardant paper even if the amount of binder is small. Furthermore, since the flame-retardant paper substrate for the radio wave absorber component also contains a binder, it is possible to suppress the breakage of the flame-retardant paper for the radio wave absorber component in all processes other than the process of obtaining the substrate, such as the process of applying guanidine phosphate and the secondary processing process such as printing.

[0056] Furthermore, as methods for adding conductive fibers to flame-retardant paper for radio wave absorber components, as described above, there are the following methods: preparing a slurry for wet papermaking containing conductive fibers and then blending the slurry into a flame-retardant paper base material for radio wave absorber components; mixing conductive fibers with an adhesive material and applying the resultant mixture onto the flame-retardant paper base material using a size press coater, roll coater, knife coater, rod coater, or air knife coater; and impregnating the flame-retardant paper base material with an aqueous solution containing dispersed conductive fibers. Of these, the method of preparing a slurry for wet papermaking containing conductive fibers and blending the slurry into the flame-retardant paper base material for radio wave absorber components is preferred because it allows for uniform dispersion of the conductive fibers contained in the flame-retardant paper for radio wave absorber components.

[0057] Furthermore, as a method for producing the flame-retardant paper for the radio wave absorber member of the present invention, a papermaking method using existing paper materials can be used, for example, a wet papermaking method in which a slurry is prepared by mixing fibers (pulp), aluminum hydroxide, a binder, and a conductive material, which are the structural materials of the flame-retardant paper for the radio wave absorber member of the present invention, with water, and then rolling up the paper using a papermaking machine.

[0058] As a papermaking machine, any papermaking machine such as a cylinder wire, short wire, fourdrinier wire, birch former, vacuum cylinder wire, or hydroformer can be used. In addition, as a dryer, any dryer such as a Yankee type, a multi-drum type, or a through-type can be used.

[0059] Furthermore, the method for incorporating guanidine phosphate into the flame-retardant paper for radio wave absorber components is not particularly limited. Examples include impregnation using a dip / roller, impregnation coating, and coating. Coating devices such as a sizing coater, roll coater, blade coater, rod coater, and air knife coater can be used for impregnation or coating, and these devices can be used on-machine or off-machine. Impregnation using a dip / roller is preferred because it allows for a uniform impregnation of the entire flame-retardant paper for radio wave absorber components.

[0060] Furthermore, a major feature of the method for manufacturing flame-retardant paper for radio wave absorber components of the present invention is that, after obtaining a flame-retardant paper substrate for radio wave absorber components containing an adhesive, the flame-retardant paper substrate for radio wave absorber components is impregnated with an aqueous solution containing guanidine phosphate to impart guanidine phosphate to the flame-retardant paper substrate for radio wave absorber components. As described above, imparting guanidine phosphate to the flame-retardant paper substrate for radio wave absorber components after obtaining the flame-retardant paper substrate for radio wave absorber components containing an adhesive can further suppress breakage during papermaking drying, and during the guanidine phosphate imparting step, it is possible to suppress adhesion of adhesives other than guanidine phosphate to rollers. Alternatively, an adhesive such as a polyurethane resin can be imparted along with the guanidine phosphate. However, as described later, in the method, when the flame-retardant paper substrate for radio wave absorber components impregnated with a solution containing guanidine phosphate and an adhesive is passed between a pair of rollers or flat plates for pressurization and dehydration, it easily adheres to the surface of rollers, etc., making this method preferably employed. Furthermore, if the adhesive adheres to the roller, the adhesive adhered to the roller dries and fixes to the roller, thereby contaminating the roller and tending to reduce the productivity of the flame-retardant paper for radio wave absorber components. Therefore, when adopting this method, it is ideal to pay attention to the above aspects.

[0061] The temperature of the aqueous solution containing guanidine phosphate is preferably 40°C to 70°C, more preferably 45°C to 65°C. If the temperature is below 40°C, guanidine phosphate may precipitate, making stable processing difficult. On the other hand, if the temperature is above 70°C, the binder and other components present in the flame-retardant paper substrate for the radio wave absorber member may dissolve and soften during immersion in the aqueous solution, potentially causing breakage. Furthermore, water evaporation may make it difficult to maintain a constant concentration of the guanidine phosphate aqueous solution.

[0062] Furthermore, after the step of impregnating the flame-retardant paper substrate for the radio wave absorber member with an aqueous solution containing guanidine phosphate, it is preferred to sequentially include the steps of pressurizing the flame-retardant paper substrate for the radio wave absorber member and drying the flame-retardant paper substrate for the radio wave absorber member at a temperature of 80°C to 170°C. Furthermore, in terms of achieving good drying efficiency of moisture, the drying temperature is more preferably 100°C to 160°C.

[0063] The following describes the process of pressurizing the flame-retardant paper substrate for the radio wave absorber component. Preferably, after the flame-retardant paper for the radio wave absorber component is impregnated with an aqueous solution of guanidine phosphate, it is pressurized and dehydrated between a pair of rollers or a flat plate. In particular, pressurization and dehydration between a pair of rollers are preferred in terms of good process flowability compared to a flat plate. By pressurizing and dehydrating, the amount of guanidine phosphate impregnation can be maintained at a certain amount, and further, by dehydration, the amount of moisture contained in the flame-retardant paper substrate for the radio wave absorber component is reduced, thereby improving the drying efficiency. The pressurization pressure is preferably 20kgf / cm (196N / cm) to 300kgf / cm (2.94kN / cm), and more preferably 30kgf / cm (294N / cm) to 150kgf / cm (1.47N / cm). If it is less than 20kgf / cm (196N / cm), sufficient dehydration may not be achieved. If the force exceeds 300 kgf / cm (2.94 kN / cm), wrinkles are likely to form. The roller material is not particularly limited to metal rollers, rubber rollers, or paper rolls, but from the perspective of applying pressure evenly without being affected by the unevenness of the flame-retardant paper for the radio wave absorber member, at least one of the rollers is preferably a rubber roller.

[0064] The following describes the process of drying the flame-retardant paper substrate for the radio wave absorber component at a temperature of 80°C to 170°C. The dryer may be any of a steam cylinder type such as a Yankee drum type or a multi-cylinder cylinder type, an infrared type, or a hot air type. Regarding the steam cylinder type, since the moist flame-retardant paper for the radio wave absorber component is in direct contact with the high-temperature cylinder, migration such as aggregation of guanidine phosphate is likely to occur at the contact portion. As a result, the toughness of the flame-retardant paper for the radio wave absorber component obtained is reduced, and it tends to break easily and wrinkle easily. On the other hand, an infrared type dryer or a hot air (air through) type dryer is preferred because the flame-retardant paper for the radio wave absorber component obtained has little difference between the inside and outside, and the toughness is not easily reduced and it is not easy to break. Here, the infrared type dryer may be any of an electric infrared dryer and a gas infrared dryer, and refers to a dryer that dries the flame-retardant paper for the radio wave absorber component by irradiating infrared rays on the flame-retardant paper for the radio wave absorber component. The term "hot air dryer" refers to a dryer that dries directly using heat, an electric heater, steam, or the like, or dries using air heated by heat exchange.

[0065] The drying temperature is ideally between 80°C and 170°C. A drying temperature of 80°C or higher allows for sufficient drying of the flame-retardant paper substrate for the radio wave absorber member. On the other hand, a drying temperature of 170°C or lower prevents breakage of the flame-retardant paper substrate for the radio wave absorber member caused by overdrying, thereby suppressing yellowing of the pulp and the like. Consequently, yellowing of the flame-retardant paper for the radio wave absorber member can be suppressed.

[0066] Example

[0067] Next, the flame-retardant paper of the present invention will be described in more detail with reference to examples. The performance values ​​shown in the examples are obtained by measuring using the following methods.

[0068] [Measurement method]

[0069] (1) Confirmation of ingredients contained in flame retardant paper

[0070] The components contained in the flame-retardant paper were confirmed as follows. Specifically, an ultra-high-resolution field-emission scanning electron microscope (SEM, SU-8010, manufactured by Hitachi High-technologies) was used to image five areas, including four areas surrounding points offset 2.5 cm in both the vertical and horizontal directions from the four corners of a 10 cm x 10 cm flame-retardant paper test piece toward the center of the test piece, and one area surrounding a point in the center of the test piece. An energy dispersive X-ray spectrometer (EDX) was used to confirm the presence of specific elements. The results of measuring the test piece using an infrared spectrophotometer (FT-IR, IR PRESTIGE-21 manufactured by Shimadzu Corporation) were then used to confirm the components contained in the flame-retardant paper and their content.

[0071] (2) Weight per square meter of flame retardant paper

[0072] Cut five sheets of flame retardant paper into squares with a side of 300 mm and measure the mass, and convert it into per 1 m 2 The mass of each square meter is calculated by taking the average value.

[0073] (3) Flame retardancy of flame retardant paper

[0074] Evaluation was conducted based on the 20mm vertical flame test (UL94 V-0) in the UL94 safety standard ("Fire Resistance Tests for Plastic Materials for Parts of Devices and Appliances"). UL is a safety standard for electronic devices established and approved by Underwriters Laboratories Inc. in the United States, and UL94 also defines flame retardancy. Evaluation was performed using five 13mm wide and 125mm long strips.

[0075] ◎: For all five samples, no sample continued to burn for more than 10 seconds. No sample burned for less than 50 seconds in the total burning time for the 10 flame contacts with the five samples and burned to the position of the fixing clamp. No sample continued to be red hot for more than 30 seconds after the second flame contact.

[0076] ×: For one or more of the five samples, burning continued for more than 10 seconds, or the total burning time for the five samples after 10 flame contacts was 50 seconds or more, or one or more of the samples burned to the position of the fixing clamp, or one or more of the samples remained red hot for more than 30 seconds after the second flame contact.

[0077] (4) Flame retardancy of a member formed by laminating flame-retardant paper for a radio wave absorber member to foamed polystyrene (flame retardancy of the laminated product)

[0078] Flame-retardant paper and 10 mm thick expanded polystyrene were bonded together using double-sided tape (NWBB-15 recycled paper double-sided tape, manufactured by Nichiban Co., Ltd.) to create a joint between the flame-retardant paper and expanded polystyrene. The sample dimensions were 50 mm wide and 150 mm long. Five samples were prepared, with lines drawn along the length at 25 mm and 125 mm from one end.

[0079] The burning speed of the member was evaluated in accordance with the horizontal flammability test for foamed materials (UL94 HBF) in the UL94 safety standard (“Burning Test for Plastic Materials for Parts of Devices and Appliances”).

[0080] ◎: For all five samples, the burning time was measured over a 100mm interval (25mm to 125mm) and the burning rate was calculated. No sample burned at a rate exceeding 40mm / min. Alternatively, no sample extinguished before the flame reached the 125mm line. Furthermore, the average burning rate of the burned samples must be less than 35mm / min.

[0081] ○: For all five samples, the burning time was measured over a 100mm interval (25mm to 125mm) and the burning rate was calculated. No sample burned at a rate exceeding 40mm / min. Alternatively, the sample must have extinguished before the flame or ignition reached the 125mm line. Furthermore, the average burning rate of the samples after burning must be between 35mm / min and 40mm / min.

[0082] ×: At least one of the five does not satisfy the criteria of ◎ and / or ○.

[0083] (5) Tensile strength

[0084] In accordance with Japanese Industrial Standards (JIS) P 8113:2006, a tensile testing machine "Autograph, Model: AGS-J" (manufactured by Shimadzu Corporation) was used to cut three 15 mm x 150 mm strips with the long side in the MD direction (the direction of paper flow during papermaking) and three 15 mm x 150 mm strips with the long side in the TD direction (a direction approximately perpendicular to the MD direction) to prepare test pieces. With the inter-grip distance set at 100 mm and the grip travel speed set at 100 mm / min, tension was applied at a constant speed. The strength of the test pieces at break was measured, and the overall average was calculated. From the perspective of stable productivity and operability, the following procedure was used.

[0085] ○: 30N / 15mm or more

[0086] △: 12N / 15mm or more and less than 30N / 15mm

[0087] ×: less than 12N / 15mm

[0088] (6) Relative dielectric constant

[0089] The upper surface of an aluminum plate measuring 30 cm in length, 30 cm in width, and 5 mm in thickness is overburdened with a foamed polystyrene spacer (14 mm thick) having a foaming ratio of 70 times and the same size and shape as the aluminum plate. A sheet for a radio wave absorber having the same size as the aluminum plate is further overburdened on the spacer. Transmitting and receiving antennas are set at a position 1.4 m directly above the center point of the foamed polystyrene spacer (on the surface opposite to the aluminum plate side of the foamed polystyrene spacer and at the intersection of two diagonal lines of the foamed polystyrene spacer) with an incident angle of 7° for the radio wave. Radio waves in the frequency range of 2 GHz to 4 GHz are incident on the sample, and the input impedance is measured using a vector network analyzer (model: N5230, manufactured by Agilent Technologies). The radio wave absorber sheet was then removed, and the input impedance without the radio wave absorber sheet was measured in the same manner as described above. The complex relative permittivity of the radio wave absorber sheet was calculated based on the difference in input impedance between the presence and absence of the radio wave absorber sheet, and the real part εr' of the complex relative permittivity at a frequency of 3 GHz was read. The measurement was performed using different radio wave absorber sheets, with N = 3. For each radio wave absorber sheet, the real part εr' of the complex relative permittivity was measured in a direction parallel to and perpendicular to any one side. The average of the six measured values ​​was used as the relative permittivity of the real part εr' of the complex relative permittivity.

[0090] (7) Transmission attenuation rate

[0091] The evaluation was conducted in accordance with Item 4.3 "Transmission attenuation power ratio: real-time transport protocol (Rtp)" in the International Electrotechnical Commission (IEC) standard 62333-2 "Noise suppression sheet for digital devices and equipment". The evaluation method was implemented using a microstrip line (MSL) fixture, placing a noise suppression sheet on the MSL, and measuring the conducted noise suppression Rtp (dB). A vector network analyzer (model: N5230, manufactured by Agilent Technologies) was used to measure the frequency range of 4 GHz to 6 GHz, reading the frequency of 5 GHz. 20 dB or more was set to ○, 3 dB or more and less than 20 dB was set to △, and less than 3 dB was set to ×. The size of the noise suppression sheet sample was 10 cm × 5 cm.

[0092] (8) Papermaking productivity

[0093] When wet papermaking was performed by a continuous papermaking method, stable continuous productivity was confirmed by the following evaluation.

[0094] A: Papermaking production can be carried out stably.

[0095] B: Paper breaks may occur during papermaking, or guanidine phosphate may adhere to the coating equipment, impregnation equipment, or drying rollers, making stable papermaking impossible.

[0096] B-: Paper breaks may occur during papermaking, or guanidine phosphate may adhere to the coating equipment, impregnation equipment, or drying rollers. The frequency of breakage and / or the degree of guanidine phosphate adhesion are higher than those in B, making stable papermaking impossible.

[0097] C: The tensile strength is weak, and the paper frequently breaks during papermaking, guanidine phosphate application, or winding.

[0098] [Example 1]

[0099] A flame-retardant paper for a radio wave absorber member was prepared by mixing 18% by mass of softwood pulp (5 mm fiber length), 48% by mass of aluminum hydroxide (manufactured by Wako Pure Chemical Industries, Ltd.), and 10% by mass of glass fiber (7 μm fiber diameter, 6 mm fiber length). The mixture was also mixed with 8% by mass of polyvinyl alcohol fiber (11 μm fiber diameter, 3 mm fiber length, "Vinylon" manufactured by Kuraray Co., Ltd.) as a binder, 2% by mass of a styrene-acrylic acid copolymer resin (aqueous emulsion, manufactured by Toagosei Co., Ltd.) (binder: 10% by mass), and 1% by mass of carbon fiber (7 μm fiber diameter, 6 mm fiber length, "Torayca" manufactured by Toray Industries, Ltd.) as a conductive material. The mixture was wet-formed using a continuous papermaking method to produce a flame-retardant paper substrate for a radio wave absorber member.

[0100] The flame-retardant paper substrate for the radio wave absorber member was impregnated with an aqueous solution of guanidine phosphate (liquid temperature 55°C) using a size coater so that the content of guanidine phosphate (manufactured by Maruryoshi Oil Chemical Industry Co., Ltd., "Nonnen" (registered trademark) 985) relative to the entire flame-retardant paper was 13% by mass. The mixture was then dried using a gas-type infrared dryer (drying temperature 150°C) to obtain a weight per square meter of 115 g / m 2 Flame-retardant paper for radio wave absorber members. Papermaking productivity was rated A.

[0101] The flame-retardant paper for radio wave absorber components obtained was evaluated. The results are shown in Table 1. The flame-retardant paper for radio wave absorber components exhibited a slow burning rate, passing UL94 V-0 (evaluated as ◎). Furthermore, components laminated with expanded polystyrene also exhibited a slow burning rate, passing UL94 HBF (evaluated as ◎). Furthermore, the paper exhibited sufficient tensile strength. While the relative dielectric constant was 130, making it suitable for use as a radio wave absorber, the transmission attenuation performance was low, and the noise suppression effect was rated as △.

[0102] [Example 2]

[0103] The weight per square meter of Example 2 was 115 g / m2, obtained in the same manner as in Example 1 except that the composition was 15% by mass of pulp, 45% by mass of aluminum hydroxide, 15% by mass of glass fiber, 7% by mass of polyvinyl alcohol fiber as a binder, 2% by mass of styrene-acrylic acid copolymer resin (9% by mass of binder), and 15% by mass of guanidine phosphate. 2 Flame-retardant paper for radio wave absorber members. Papermaking productivity was rated A.

[0104] The flame-retardant paper for radio wave absorber components obtained was evaluated. The results are shown in Table 1. The flame-retardant paper for radio wave absorber components exhibited a slow burning rate, passing UL94 V-0 (evaluated as ◎). Furthermore, components laminated with expanded polystyrene also exhibited a slow burning rate, passing UL94 HBF (evaluated as ◎). Furthermore, the paper exhibited sufficient tensile strength. While the relative dielectric constant was 130, making it suitable for use as a radio wave absorber, the transmission attenuation performance was low, and the noise suppression effect was rated as △.

[0105] [Example 3]

[0106] The weight per square meter of Example 3 was 115 g / m2, obtained in the same manner as in Example 1 except that the composition was 10% by mass of pulp, 65% by mass of aluminum hydroxide, 5% by mass of glass fiber, 7% by mass of polyvinyl alcohol fiber as a binder, 2% by mass of styrene-acrylic acid copolymer resin (9% by mass of binder), and 10% by mass of guanidine phosphate. 2 Flame-retardant paper for radio wave absorber members. Papermaking productivity was rated A.

[0107] The flame-retardant paper for radio wave absorber components obtained was evaluated. The results are shown in Table 1. The flame-retardant paper for radio wave absorber components exhibited a slow burning rate, passing UL94 V-0 (evaluated as ◎). Furthermore, components laminated with expanded polystyrene also exhibited a slow burning rate, passing UL94 HBF (evaluated as ◎). Furthermore, the paper exhibited sufficient tensile strength. While the relative dielectric constant was 130, making it suitable for use as a radio wave absorber, the transmission attenuation performance was low, and the noise suppression effect was rated as △.

[0108] [Example 4]

[0109] The weight per square meter of Example 4 was 115 g / m2, obtained in the same manner as in Example 1 except that the composition was 15% by mass of pulp, 55% by mass of aluminum hydroxide, 8% by mass of glass fiber, 5% by mass of polyvinyl alcohol fiber as a binder, 1% by mass of styrene-acrylic acid copolymer resin (binder was 6% by mass), and 15% by mass of guanidine phosphate. 2 Flame-retardant paper for radio wave absorber members. Papermaking productivity was rated A.

[0110] The flame-retardant paper for radio wave absorber components obtained was evaluated. The results are shown in Table 1. The flame-retardant paper for radio wave absorber components exhibited a slow burning rate, passing UL94 V-0 (evaluated as ◎). Furthermore, components laminated with expanded polystyrene also exhibited a slow burning rate, passing UL94 HBF (evaluated as ◎). Furthermore, the paper exhibited sufficient tensile strength. While the relative dielectric constant was 130, making it suitable for use as a radio wave absorber, the transmission attenuation performance was low, and the noise suppression effect was rated as △.

[0111] [Example 5]

[0112] The weight per square meter of Example 5 was 85 g / m2, obtained in the same manner as in Example 1 except that the composition was 12% by mass of pulp, 52% by mass of aluminum hydroxide, 8% by mass of glass fiber, 8% by mass of polyvinyl alcohol fiber as a binder, 1% by mass of styrene-acrylic acid copolymer resin (9% by mass of binder), and 18% by mass of guanidine phosphate. 2 Flame-retardant paper for radio wave absorber members. Papermaking productivity was rated A.

[0113] The flame-retardant paper for radio wave absorber components obtained was evaluated. The results are shown in Table 1. The flame-retardant paper for radio wave absorber components exhibited a slow burning rate, passing UL94 V-0 (evaluated as ◎). Furthermore, components laminated with expanded polystyrene also exhibited a slow burning rate, passing UL94 HBF (evaluated as ○). Furthermore, the paper exhibited sufficient tensile strength. While the relative dielectric constant was 130, making it suitable for radio wave absorbers, its transmission attenuation performance was low, and its noise suppression effect was rated as △.

[0114] [Example 6]

[0115] Set the weight per square meter to 74g / m 2 , flame-retardant paper for a radio wave absorber member of Example 6 was obtained in the same manner as in Example 5 except for the above. Regarding papermaking productivity, it was evaluated as B because it was slightly easy to cut.

[0116] The resulting radio wave absorber component was evaluated using flame-retardant paper. The results are shown in Table 1. The flame-retardant paper exhibited a slow burning rate, passing UL94 V-0 (evaluated as ◎). Furthermore, the component laminated with expanded polystyrene also exhibited a slow burning rate, passing UL94 HBF (evaluated as ○). Furthermore, the tensile strength was slightly weak. The relative dielectric constant was 130, making it suitable for use as a radio wave absorber. However, the transmission attenuation performance was low, and the noise suppression effect was sufficient, with a rating of △.

[0117] [Example 7]

[0118] The weight per square meter of Example 7 was 185 g / m2, obtained in the same manner as in Example 1 except that the composition was 13% by mass of pulp, 57% by mass of aluminum hydroxide, 9% by mass of glass fiber, 8% by mass of polyvinyl alcohol fiber as a binder, 1% by mass of styrene-acrylic acid copolymer resin (9% by mass of binder), and 11% by mass of guanidine phosphate. 2 Flame-retardant paper for radio wave absorber components. Excellent papermaking productivity.

[0119] The flame-retardant paper for radio wave absorber components obtained was evaluated. The results are shown in Table 1. The flame-retardant paper for radio wave absorber components exhibited a slow burning rate, passing UL94 V-0 (evaluated as ◎). Furthermore, components laminated with expanded polystyrene also exhibited a slow burning rate, passing UL94 HBF (evaluated as ◎). Furthermore, the paper exhibited sufficient tensile strength. While the relative dielectric constant was 130, making it suitable for use as a radio wave absorber, the transmission attenuation performance was low, and the noise suppression effect was rated as △.

[0120] [Example 8]

[0121] Set the weight per square meter to 225g / m 2 The flame-retardant paper for a radio wave absorber member of Example 8 was obtained in the same manner as in Example 7. Regarding papermaking productivity, guanidine phosphate was precipitated on the coating roller and drying failure was likely to occur, so it was rated B.

[0122] The structures and evaluation results of the flame-retardant papers for radio wave absorber members of Examples 1 to 8 are shown in Table 1. The relative dielectric constant was 130, which was suitable as a radio wave absorber, but the transmission attenuation performance was low and the noise suppression effect was Δ.

[0123] [Table 1]

[0124]

[0125] [Example 9]

[0126] The flame-retardant paper for a radio wave absorber member of Example 9 was obtained in the same manner as in Example 1 except that the size coater was changed to a dip / nip roll. The papermaking productivity was evaluated as A.

[0127] The flame-retardant paper for radio wave absorber components obtained was evaluated. The results are shown in Table 2. The flame-retardant paper for radio wave absorber components exhibited a slow burning rate, passing UL94 V-0 (evaluated as ◎). Furthermore, components laminated with expanded polystyrene also exhibited a slow burning rate, passing UL94 HBF (evaluated as ◎). Furthermore, the paper exhibited sufficient tensile strength. While the relative dielectric constant was 130, making it suitable for use as a radio wave absorber, its transmission attenuation performance was low, and its noise suppression effect was rated as △.

[0128] [Example 10]

[0129] The flame-retardant paper for a radio wave absorber member of Example 10 was obtained in the same manner as in Example 9, except that the temperature of the guanidine phosphate aqueous solution was set to 15°C and the gas infrared dryer was a multi-cylinder (six-cylinder) steam cylinder dryer (drying temperature 120°C). Regarding papermaking productivity, guanidine phosphate precipitated on the rolls and paper breakage occurred occasionally during the steam cylinder dryer process, resulting in a papermaking productivity evaluation of B (which was higher than that of Example 14 described below).

[0130] The resulting flame-retardant paper for radio wave absorber components was evaluated. The results are shown in Table 2. The flame-retardant paper for radio wave absorber components exhibited a slow burning rate, passing UL94 V-0 (evaluated as ◎). Furthermore, components laminated with expanded polystyrene also exhibited a slow burning rate, passing UL94 HBF (evaluated as ◎). The tensile strength was slightly weak. The relative dielectric constant was 130, making it suitable for radio wave absorbers. However, the transmission attenuation performance was low, and the noise suppression effect was rated as △.

[0131] [Example 11]

[0132] The weight per square meter of Example 11 was 115 g / m2, obtained in the same manner as in Example 9 except that the glass fiber was 10.5 mass % and the carbon fiber was 0.5 mass %. 2 Flame-retardant paper for radio wave absorber members. Papermaking productivity was rated A.

[0133] The flame-retardant paper for radio wave absorber components obtained was evaluated. The results are shown in Table 2. The flame-retardant paper for radio wave absorber components exhibited a slow burning rate, passing UL94 V-0 (evaluated as ◎). Furthermore, components laminated with expanded polystyrene also exhibited a slow burning rate, passing UL94 HBF (evaluated as ○). Furthermore, the paper exhibited sufficient tensile strength. While the relative dielectric constant was 130, making it suitable for radio wave absorbers, its transmission attenuation performance was low, and its noise suppression effect was rated as △.

[0134] [Example 12]

[0135] The weight per square meter of Example 12 was 115 g / m2, obtained in the same manner as Example 9 except that the pulp was 17% by mass, aluminum hydroxide was 46% by mass, carbon fiber was 5% by mass, and guanidine phosphate was 12% by mass. 2 Flame-retardant paper for radio wave absorber members. Papermaking productivity was rated A.

[0136] The flame-retardant paper for the radio wave absorber component obtained was evaluated. The results are shown in Table 2. The flame-retardant paper for the radio wave absorber component exhibited a slow burning rate, passing UL94 V-0 (evaluated as ◎). Furthermore, the component formed by laminating with expanded polystyrene also exhibited a slow burning rate, passing UL94 HBF (evaluated as ○). Furthermore, the tensile strength was sufficient. While the relative dielectric constant was 300, which is too high for a radio wave absorber, the transmission attenuation performance was high, and the noise suppression effect was rated as ○.

[0137] [Example 13]

[0138] The weight per square meter of Example 13 was 115 g / m2, obtained in the same manner as in Example 9 except that the composition was 16% by mass of pulp, 44% by mass of aluminum hydroxide, 9% by mass of glass fiber, 9% by mass of binder (8% by mass of polyvinyl alcohol fiber and 1% by mass of styrene-acrylic acid copolymer resin), 10% by mass of carbon fiber, and 12% by mass of guanidine phosphate. 2 Flame-retardant paper for radio wave absorber members. Papermaking productivity was rated A.

[0139] The flame-retardant paper for the radio wave absorber component obtained was evaluated. The results are shown in Table 2. The flame-retardant paper for the radio wave absorber component exhibited a slow burning rate, passing UL94 V-0 (evaluated as ◎). Furthermore, the component formed by laminating with expanded polystyrene also exhibited a slow burning rate, passing UL94 HBF (evaluated as ○). Furthermore, the tensile strength was sufficient. While the relative dielectric constant was 300, which is too high for a radio wave absorber, the transmission attenuation performance was high, and the noise suppression effect was rated as ○.

[0140] [Example 14]

[0141] A flame-retardant paper substrate for a radio wave absorber member was prepared in the same manner as in Example 1, except that the composition was 15% by mass of pulp, 55% by mass of aluminum hydroxide, 8% by mass of glass fiber, and 0% by mass of binder. As in Example 1, guanidine phosphate and a urethane resin (product name: Super flex 150 (trade name), manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a binder were incorporated into the flame-retardant paper substrate for a radio wave absorber member in amounts of 15% by mass and 6% by mass (binder: 6% by mass) relative to the total flame-retardant paper, respectively. This yielded a weight per square meter of 115 g / m² in Example 14. 2 Flame-retardant paper for radio wave absorber components. Paper breakage occurred during papermaking, and guanidine phosphate and urethane resin adhered to the size coater rollers, resulting in a B- rating for papermaking productivity.

[0142] The resulting flame-retardant paper for radio wave absorber components was evaluated. The results are shown in Table 2. The flame-retardant paper for radio wave absorber components exhibited a slow burning rate, passing UL94 V-0 (evaluated as ◎). Furthermore, components laminated with expanded polystyrene also exhibited a slow burning rate, passing UL94 HBF (evaluated as ○). On the other hand, the tensile strength was somewhat weak. While the relative dielectric constant was 300, too high for a radio wave absorber, the transmission attenuation performance was high, and the noise suppression effect was rated as ○.

[0143] Table 2 shows the structures and evaluation results of the flame-retardant papers for radio wave absorber members of Examples 9 to 14.

[0144] [Table 2]

[0145]

[0146] [Comparative Example 1]

[0147] The weight per square meter of Comparative Example 1 was 115 g / m², obtained in the same manner as in Example 1 except that the composition was 3% by mass of pulp, 73% by mass of aluminum hydroxide, 9% by mass of glass fiber, 4% by mass of polyvinyl alcohol fiber as a binder, 1% by mass of styrene-acrylic acid copolymer resin (5% by mass of binder), and 10% by mass of guanidine phosphate. 2 Flame-retardant paper for radio wave absorber components. The paper was weak and frequently cut, making it unsuitable for production. The papermaking productivity rating was C.

[0148] The resulting flame-retardant paper for radio wave absorber components was evaluated. The results are shown in Table 3. The flame-retardant paper for radio wave absorber components exhibited a slow burning rate, passing UL94 V-0 (evaluated as ◎). Furthermore, components laminated with expanded polystyrene also exhibited a slow burning rate, passing UL94 HBF (evaluated as ○). Furthermore, the paper exhibited weak tensile strength. While its relative dielectric constant was 130, making it suitable for use as a radio wave absorber, its transmission attenuation performance was low, and its noise suppression effect was rated as △.

[0149] [Comparative Example 2]

[0150] The weight per square meter of Comparative Example 2 was 115 g / m², obtained in the same manner as in Example 1 except that the composition was 25% by mass of pulp, 37% by mass of aluminum hydroxide, 17% by mass of glass fiber, 7% by mass of polyvinyl alcohol fiber as a binder, 1% by mass of styrene-acrylic acid copolymer resin (8% by mass of binder), and 13% by mass of guanidine phosphate. 2 Flame-retardant paper for radio wave absorber members. Papermaking productivity was rated A.

[0151] The flame-retardant paper for radio wave absorber components obtained was evaluated. The results are shown in Table 3. The flame-retardant paper for radio wave absorber components had a high burning rate and failed to pass UL94 V-0 (evaluated as ×). The component formed by laminating with expanded polystyrene also had a high burning rate and failed to pass UL94 HBF (evaluated as ×). The tensile strength was sufficient. The relative dielectric constant was 130, which was suitable for use as a radio wave absorber, but the transmission attenuation performance was low and the noise suppression effect was △.

[0152] [Comparative Example 3]

[0153] The weight per square meter of Comparative Example 3 was 115 g / m², except that the composition was 20% by mass of pulp, 52% by mass of aluminum hydroxide, 13% by mass of glass fiber, 8% by mass of polyvinyl alcohol fiber as a binder, 2% by mass of styrene-acrylic acid copolymer resin (binder: 10% by mass), and 5% by mass of guanidine phosphate. 2 Flame-retardant paper for radio wave absorber members. Papermaking productivity was rated A.

[0154] The flame-retardant paper obtained for radio wave absorber components was evaluated. The results are shown in Table 3. The flame-retardant paper for radio wave absorber components had a slow burning rate and passed UL94 V-0 (evaluated as ◎). On the other hand, the component formed by laminating with expanded polystyrene had a fast burning rate and passed UL94 HBF (evaluated as ×). The tensile strength was sufficient. The relative dielectric constant was 130, making it suitable for radio wave absorbers, but the transmission attenuation performance was low and the noise suppression effect was △.

[0155] [Comparative Example 4]

[0156] The weight per square meter of Comparative Example 4 was 133 g / m², obtained in the same manner as in Example 1 except that the composition was 16% by mass of pulp, 41% by mass of aluminum hydroxide, 9% by mass of glass fiber, 8% by mass of polyvinyl alcohol fiber as a binder, 1% by mass of styrene-acrylic acid copolymer resin (9% by mass of binder), and 25% by mass of guanidine phosphate. 2 Flame-retardant paper for radio wave absorber members. Regarding papermaking productivity, guanidine phosphate precipitated on the size coater, failing to maintain a stable content, resulting in an evaluation of C.

[0157] The resulting flame-retardant paper for radio wave absorber components was evaluated. The results are shown in Table 3. The flame-retardant paper for radio wave absorber components exhibited a slow burning rate, passing UL94 V-0 (evaluated as ◎). Furthermore, components laminated with expanded polystyrene also exhibited a slow burning rate, passing UL94 HBF (evaluated as ◎). The paper exhibited sufficient tensile strength. While its relative dielectric constant was 130, it was suitable for use as a radio wave absorber. However, its transmission attenuation performance was low, and its noise suppression effect was rated as △.

[0158] [Comparative Example 5]

[0159] The weight per square meter of Comparative Example 5 was 115 g / m2, obtained in the same manner as in Example 1 except that the composition was 20% by mass of pulp, 50% by mass of aluminum hydroxide, 14% by mass of glass fiber, and 3% by mass of polyvinyl alcohol fiber alone as a binder (the binder was 3% by mass). 2 Flame-retardant paper for radio wave absorber components. The paper was weak and frequently cut, making it unsuitable for production. The papermaking productivity rating was C.

[0160] The resulting flame-retardant paper for radio wave absorber components was evaluated. The results are shown in Table 3. The flame-retardant paper for radio wave absorber components exhibited a slow burning rate, passing UL94 V-0 (evaluated as ◎). Furthermore, components laminated with expanded polystyrene also exhibited a slow burning rate, passing UL94 HBF (evaluated as ◎). The tensile strength was weak. The relative dielectric constant was 130, making it suitable for use as a radio wave absorber. However, the transmission attenuation performance was low, and the noise suppression effect was rated as △.

[0161] [Comparative Example 6]

[0162] The weight per square meter of Comparative Example 6 was 115 g / m², obtained in the same manner as in Example 1 except that the composition was 15% by mass of pulp, 48% by mass of aluminum hydroxide, 9% by mass of glass fiber, 13% by mass of polyvinyl alcohol fiber as a binder, and 2% by mass of styrene-acrylic acid copolymer resin (binder was 15% by mass). 2 Flame-retardant paper for radio wave absorber members. Papermaking productivity was rated A.

[0163] The flame-retardant paper for radio wave absorber components obtained was evaluated. The results are shown in Table 3. The flame-retardant paper for radio wave absorber components had a high burning rate and failed to pass UL94 V-0 (evaluated as ×). Furthermore, the component formed by laminating with expanded polystyrene also had a high burning rate and failed to pass UL94 HBF (evaluated as ×). The tensile strength was strong. The relative dielectric constant was 130, making it suitable for use as a radio wave absorber. However, the transmission attenuation performance was low and the noise suppression effect was △.

[0164] [Comparative Example 7]

[0165] The weight per square meter of Comparative Example 7 was 115 g / m2, obtained in the same manner as in Example 1 except that the pulp was 19% by mass and the carbon fiber was 0% by mass. 2 Flame-retardant paper for radio wave absorber members. Papermaking productivity was rated A.

[0166] The flame-retardant paper for the radio wave absorber component obtained was evaluated. The results are shown in Table 3. The flame-retardant paper for the radio wave absorber component had a slow burning rate and passed UL94 V-0 (evaluated as ◎). The component formed by laminating with expanded polystyrene also had a slow burning rate and passed UL94 HBF (evaluated as ◎). The tensile strength was sufficient. However, the relative dielectric constant was 4, which was low and unsuitable for use as a radio wave absorber. In addition, the transmission attenuation performance was low, and the noise suppression effect could not be achieved, so it was judged as ×.

[0167] [Comparative Example 8]

[0168] The weight per square meter of Comparative Example 8 was 115 g / m², obtained in the same manner as in Example 14 except that the composition was 17% by mass of pulp, 54% by mass of aluminum hydroxide, 13% by mass of glass fiber, 2% by mass of a binder containing a urethane resin (binder was 2% by mass), and 13% by mass of guanidine phosphate. 2 Flame-retardant paper for radio wave absorber members. During papermaking, the paper broke while being wound up after being impregnated with guanidine phosphate, resulting in a C rating for papermaking productivity.

[0169] The resulting flame-retardant paper for radio wave absorber components was evaluated. The results are shown in Table 3. The flame-retardant paper for radio wave absorber components exhibited a slow burning rate, passing UL94 V-0 (rated as ◎). A component laminated with expanded polystyrene also exhibited a slow burning rate, passing UL94 HBF (rated as ◎). The tensile strength was weak. The relative dielectric constant was 130, making it suitable for use as a radio wave absorber. However, the transmission attenuation performance was low, and the noise suppression effect was rated as △.

[0170] [Table 3]

[0171]

[0172] In Examples 1 to 14, flame-retardant paper for radio wave absorber members having excellent flame retardancy, flame retardancy, tensile strength, and papermaking productivity of the flame-retardant paper for radio wave absorber members and the laminated member of the flame-retardant paper for radio wave absorber members and foamed polystyrene were obtained.

[0173] On the other hand, the tensile strength of Comparative Example 1 is also weak, making stable production impossible. In addition, although the tensile strength is excellent in Comparative Examples 2 and 3, the flame retardancy of the flame-retardant paper and laminated products for the radio wave absorber components is poor. Although the flame retardancy is excellent in Comparative Example 4, the tensile strength is slightly weak, and stable production cannot be carried out. Although the flame retardancy of the flame-retardant paper and laminated products for the radio wave absorber components in Comparative Example 5 is excellent, the tensile strength is weak, making stable production difficult. Although the tensile strength is strong and the stable productivity is excellent in Comparative Example 6, the flame retardancy of the flame-retardant paper and laminated products for the radio wave absorber components is poor. Although the productivity and flame retardancy of Comparative Example 7 are excellent, the relative dielectric constant and transmission attenuation rate are small, and the radio wave absorption performance is poor. Although the radio wave absorption performance and flame retardancy of Comparative Example 8 are excellent, the tensile strength is weak, and stable production cannot be carried out.

Claims

1. A flame-retardant paper for a radio wave absorber member, comprising pulp, aluminum hydroxide, guanidine phosphate, a binder, and a conductive substance, wherein: The content of the pulp is 5% to 20% by mass. The content of the aluminum hydroxide is 40% to 70% by mass. The content of the guanidine phosphate is 10% to 20% by mass. The content of the binder is 5% to 10% by mass. The content of the conductive material is 0.1% to 12% by mass. The mass ratio of the aluminum hydroxide to the binder, i.e., (aluminum hydroxide content / binder content), is 83 / 17 to 91 / 9, and the ratio of the total content of the aluminum hydroxide and the guanidine phosphate to the total content of the pulp and the binder, i.e., (aluminum hydroxide content + guanidine phosphate content) / (pulp content + binder content), is 67 / 33 to 80 / 20. The weight per square meter of the flame-retardant paper for the radio wave absorber member is 80 g / m 2 ~200g / m 2 , The binder is at least one selected from the group consisting of polyvinyl alcohol resin, acrylic resin, and styrene-acrylic acid copolymer resin. 2 . The flame-retardant paper for a radio wave absorber member according to claim 1 , wherein the conductive substance is conductive fiber.

3. The flame-retardant paper for a radio wave absorber member according to claim 2, wherein the content of the conductive fiber is 0.5% to 2% by mass, The relative dielectric constant is 10~250.

4. The flame-retardant paper for a radio wave absorber member according to claim 2, wherein the content of the conductive fiber is 5% to 12% by mass, The transmission attenuation rate is above 20dB.

5. A method for producing flame-retardant paper for a radio wave absorber member, the method comprising: A process for preparing a slurry comprising pulp, aluminum hydroxide, a binder, and a conductive material; a step of wet-making the slurry to obtain a flame-retardant paper substrate for a radio wave absorber member; and A step of impregnating the flame-retardant paper substrate for the radio wave absorber member with an aqueous solution containing guanidine phosphate.

6. The method for producing flame-retardant paper for a radio wave absorber member according to claim 5, comprising, after the step of impregnating the flame-retardant paper substrate for a radio wave absorber member with the aqueous solution containing guanidine phosphate, sequentially: a step of pressurizing the flame-retardant paper substrate for the radio wave absorber member; and A step of drying the flame-retardant paper substrate of the radio wave absorber member at a temperature of 80°C to 170°C.

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