Flame-retardant paper for radio wave absorber components and its manufacturing method

Abstract

[Problem] The present invention addresses the problem of providing, in particular, flame-resistant paper that is for a radio wave absorber member, and that, in addition to having high flame-resistance suitable for a radio wave absorber member, is unlikely to tear during the production process, and has favorable productivity.　The flame-resistant paper for a radio wave absorber member according to the present invention contains pulp, aluminum hydroxide, guanidine phosphate, a binder, and a conductive substance. The contained amount of the pulp is 5-20 mass%, the contained amount of the aluminum hydroxide is 40-70 mass%, the contained amount of the guanidine phosphate is 10-20 mass%, the contained amount of the binder is 5-10 mass%, and the contained amount of the conductive substance is 0.1-12 mass%.

Description

[Technical field]

[0001] The present invention relates to a flame-retardant paper for use as a radio wave absorber member and a method for producing the same. [Background technology]

[0002] In order to reduce radio disturbances such as radio interference, radio wave absorbers are used in anechoic chambers, which are facilities for evaluating radio noise generated by various electronic devices and communication devices and evaluating whether malfunctions due to radio waves occur. In recent years, they have also been used in wireless communication systems such as ETC, wireless LAN, and automatic driving systems.

[0003] These radio wave absorbers absorb radio waves by converting radio wave energy into thermal energy, so there is a possibility that the radio wave absorbers may burn when irradiated with high-energy radio waves. In particular, radio wave absorbers used in anechoic chambers are required to have flame retardancy in order to ensure safety against fires and other hazards.

[0004] As a flame-retardant paper for radio wave absorber components that has flame retardancy, is resistant to discoloration over a long period of time, and does not lose its flame retardancy, a flame-retardant paper for radio wave absorber components that contains a flame retardant made of aluminum hydroxide powder and polyborate, and pulp, has been proposed (see Patent Document 1).

[0005] Furthermore, a flame-retardant paper containing pulp, aluminum hydroxide, a guanidine-based flame retardant, and a urethane resin has been proposed as a flame-retardant paper that is flame-retardant, resistant to breakage, and has good productivity (see Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2017 / 002863 [Patent Document 2] JP 2020-23759 A Summary of the Invention [Problem to be solved by the invention]

[0007] According to the findings of the present inventor, the flame-retardant paper for radio wave absorber components proposed in the above Patent Document 1 (hereinafter, sometimes simply referred to as "flame-retardant paper") has a relatively low toughness. Therefore, the flame-retardant paper tends to break during drying, which is performed after impregnation or coating of a chemical solution containing a chemical, and during secondary processing, such as making slits in the flame-retardant paper or printing on the flame-retardant paper. Furthermore, breakage of the flame-retardant paper during the above drying or secondary processing poses a processing problem in that the productivity of the flame-retardant paper decreases.

[0008] Patent Document 2 discloses a flame-retardant paper containing urethane resin in addition to aluminum hydroxide and a guanidine flame retardant. Although this flame-retardant paper contains urethane resin, the content of the urethane resin is small, so the toughness is insufficient. In addition, this flame-retardant paper has a problem that it is prone to breakage when tension is applied during the production process because the tensile strength is insufficient.

[0009] Therefore, an object of the present invention is to provide a flame-retardant paper for radio wave absorber components that is particularly suitable for use as a radio wave absorber component, and in addition to having excellent flame retardancy, has high tensile strength and is difficult to break, and is less likely to break during the above-mentioned drying and secondary processing such as slitting and printing, thereby providing good productivity. [Means for solving the problem]

[0010] In order to achieve the above objective, the present invention provides: (1) A flame-retardant paper for a radio wave absorber member, comprising pulp, aluminum hydroxide, guanidine phosphate, a binder, and a conductive substance, the pulp content being 5 to 20 mass %, and the hydroxide aluminumthe content of the guanidine phosphate is 10 to 20 mass %, the content of the binder is 5 to 10 mass %, and the content of the conductive material is 0.1 to 12 mass %; and (2) A method for producing the flame-retardant paper for radio wave absorbing members, comprising the steps of: preparing a slurry containing pulp, aluminum hydroxide, a binder and a conductive material; A step of wet-processing the slurry to obtain a flame-retardant paper substrate for a radio wave absorbing member; and impregnating the flame-retardant paper base material for radio wave absorbing members with an aqueous solution containing guanidine phosphate, in this order. Effect of the Invention

[0011] According to the present invention, it is possible to obtain flame-retardant paper for radio wave absorber components which is suitable for radio wave absorber components and has excellent flame retardancy, as well as high tensile strength and resistance to breakage, and which is less likely to break during drying or secondary processing such as slitting or printing, making it easy to produce. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] An example of an embodiment of the present invention will now be described.

[0013] The flame-retardant paper for radio wave absorber members of the present invention contains pulp, aluminum hydroxide, guanidine phosphate, a binder, and a conductive substance, and the pulp content is 5 to 20 mass %. aluminum The content of guanidine phosphate is 10 to 20 mass %, the content of binder is 5 to 10 mass %, and the content of conductive material is 0.1 to 12 mass %.

[0014] The flame-retardant paper for radio wave absorber components of the present invention, which has the above-mentioned configuration, is suitable for use as a radio wave absorber component and has excellent flame retardancy. In addition, it causes less contamination during the chemical application process, such as impregnation or coating, and is less likely to break during drying or secondary processing such as slitting or printing, resulting in excellent productivity.

[0015] The reason is presumed as follows. First, as will be described in detail below, the flame-retardant paper for radio wave absorber members needs to contain a specific amount of pulp or more in order to be formed into paper. Pulp is a relatively flammable material. Therefore, in order to ensure sufficient flame retardancy of the flame-retardant paper for radio wave absorber members, the content of a flame retardant such as aluminum hydroxide or guanidine phosphate needs to be a specific amount or more. On the other hand, if the content of the flame retardant in the flame-retardant paper for radio wave absorber members increases, the tensile strength and toughness of the flame-retardant paper for radio wave absorber members decrease. Drying is usually performed in the papermaking process and the chemical application process in which impregnation, coating, etc. are performed, and the above-mentioned decrease in tensile strength and toughness increases the frequency of breakage of the flame-retardant paper for radio wave absorber members during drying performed in these processes and during secondary processing such as slitting and printing. Such an increase in the frequency of breakage of the flame-retardant paper for radio wave absorber members due to a decrease in tensile strength and toughness means that the formability of the flame-retardant paper for radio wave absorber members deteriorates. Conversely, if the tensile strength and toughness are excellent, and the frequency of breakage of the flame-retardant paper for telephone absorber components is reduced, this means that the moldability is improved.

[0016] On the other hand, the flame-retardant paper for radio wave absorber members in the present invention contains a binder, and further contains pulp, aluminum hydroxide, guanidine phosphate, and a binder in specific contents, respectively. This results in higher tensile strength and toughness of the flame-retardant paper for radio wave absorber members. As a result, the flame-retardant paper for radio wave absorber members has high levels of strength, toughness, and flame retardancy as paper, respectively, and therefore it is presumed that the occurrence of breakage of the flame-retardant paper for radio wave absorber members during drying in the papermaking process or the chemical application process, during secondary processing, etc., is suppressed, and it is possible to obtain a flame-retardant paper for radio wave absorber members that is excellent in productivity and flame retardancy. Note that, due to the above circumstances, the strength, toughness, and flame retardancy as paper of the flame-retardant paper for radio wave absorber members are essentially in a trade-off relationship.

[0017] Pulps used in the flame-retardant paper for radio wave absorber members of the present invention include pulps made of vegetable fibers such as softwood pulp, hardwood pulp, thermomechanical pulp, groundwood pulp, linter pulp, and hemp pulp, pulps made of regenerated fibers such as rayon, and synthetic fiber pulps made of vinylon, polyester, etc., from which one or more types of pulp can be appropriately selected for use. Softwood pulp is preferred because it is easy to obtain strength.

[0018] The flame-retardant paper for radio wave absorber members of the present invention contains 5 to 20% by mass of pulp based on the entire flame-retardant paper for radio wave absorber members. If the pulp content is less than 5% by mass, the entanglement strength of the pulp is weak in the papermaking process, making it difficult to form a sheet. On the other hand, if the pulp content is more than 20% by mass, there is a tendency that sufficient flame retardancy as a flame-retardant paper for radio wave absorber members cannot be obtained.

[0019] In this way, a sheet of flame-retardant paper for radio wave absorber members with excellent flame retardancy can be obtained by setting the pulp content in the range of 5 to 20% by mass, with a range of 10 to 18% by mass being particularly preferable.

[0020] The flame-retardant paper for radio wave absorber members of the present invention contains 40 to 70 mass % of aluminum hydroxide. Since the aluminum hydroxide is preferably supported in a state where it is sufficiently dispersed throughout the flame-retardant paper for radio wave absorber members, the aluminum hydroxide is preferably in the form of powder.

[0021] Here, aluminum hydroxide dehydrates and decomposes at high temperatures, and the endothermic effect of this process provides a flame-retardant effect. This flame-retardant effect does not decrease over time even after long-term storage, making it possible to maintain the flame-retardant effect imparted to the flame-retardant paper for radio wave absorber components for a long period of time.

[0022] In addition, by adding an appropriate amount of papermaking chemicals such as a retention aid made of a cationic or anionic polymer compound or a paper strength agent during papermaking of the flame-retardant paper for use as a radio wave absorber member, the aluminum hydroxide is adsorbed onto the pulp, thereby contributing to improving the flame retardancy of the flame-retardant paper for use as a radio wave absorber member.

[0023] In addition, since aluminum hydroxide is a white powder, the color of the flame-retardant paper for radio wave absorber members containing aluminum hydroxide at a specific content or more is white. Therefore, when the flame-retardant paper for radio wave absorber members of the present invention is used in a radio wave absorber for an anechoic chamber, the lighting effect in the room can be improved. Furthermore, since aluminum hydroxide does not discolor and the flame-retardant paper for radio wave absorber members can maintain its white color, it is important in the present invention that the flame-retardant paper for radio wave absorber members contains aluminum hydroxide.

[0024] If the content of aluminum hydroxide is less than 40 mass %, the flame-retardant paper for radio wave absorber members may not have sufficient flame retardancy.

[0025] On the other hand, if the aluminum hydroxide content exceeds 70 mass %, the flame-retardant paper for radio wave absorber components will have high flame retardancy, but the flame-retardant paper for radio wave absorber components may break during drying in the chemical application process such as impregnation or coating, or during secondary processing such as slitting or printing, resulting in poor handleability and processability.

[0026] In this way, by setting the content of aluminum hydroxide in the range of 40 to 70 mass%, it is possible to obtain a flame-retardant paper for radio wave absorber members having excellent flame retardancy and whiteness retention. In particular, it is preferable to set the content in the range of 45 to 65 mass%. Aluminum hydroxide can be purchased from Wako Pure Chemical Industries, Ltd., Sigma-Aldrich Japan Co., Ltd., etc.

[0027] The flame-retardant paper for radio wave absorber members of the present invention contains 10 to 20 mass % of guanidine phosphate relative to the entire flame-retardant paper for radio wave absorber members. In general, if the required amount of flame retardant is large, the toughness of the flame-retardant paper for radio wave absorber members decreases, and the flame-retardant paper for radio wave absorber members is likely to break during drying or slitting in the chemical application process such as impregnation or coating, or during secondary processing such as printing. In addition, the tendency of guanidine phosphate to reduce the tensile strength of the flame-retardant paper for radio wave absorber members is smaller than that of aluminum hydroxide. Therefore, in order to achieve both excellent flame retardancy and suppression of breakage of the flame-retardant paper for radio wave absorber members, it is important that the flame-retardant paper for radio wave absorber members of the present invention contains guanidine phosphate in addition to aluminum hydroxide. In addition, it is necessary to use guanidine phosphate because a small content can achieve high flame retardancy of the flame-retardant paper for radio wave absorber members, there is no decrease in flame retardancy over time due to hydrolysis, and there is little discoloration due to changes over time.

[0028] If the content of guanidine phosphate in the entire flame-retardant paper for radio wave absorber members is less than 10 mass %, the flame retardancy of the member formed by bonding the flame-retardant paper for radio wave absorber members to polystyrene foam tends to be insufficient.

[0029] On the other hand, if the content of guanidine phosphate in the entire flame-retardant paper for radio wave absorber members is more than 20% by mass, the flame-retardant paper for radio wave absorber members may break during drying in the chemical application process by impregnation or coating, or during secondary processing such as slitting or printing, resulting in poor handling and processability. In addition, when used as flame-retardant paper for radio wave absorber members, discoloration over time becomes significantly noticeable. From the above viewpoint, the content of guanidine phosphate is more preferably 15% by mass or less.

[0030] The flame-retardant paper for radio wave absorber members of the present invention contains 5 to 10% by mass of a binder based on the entire flame-retardant paper for radio wave absorber members. The binder preferably contains 8 to 10% by mass. By containing the binder in the flame-retardant paper for radio wave absorber members, the tensile strength and toughness can be improved, and furthermore, the falling off of aluminum hydroxide from the flame-retardant paper for radio wave absorber members can be suppressed, so that high productivity can be realized by suppressing breakage of the flame-retardant paper for radio wave absorber members during drying in the papermaking process and chemical application process and during secondary processing such as slitting and printing, and high flame retardancy of the flame-retardant paper for radio wave absorber members can be realized.

[0031] If the binder content in the entire flame-retardant paper for radio wave absorber components is less than 5 mass%, the flame-retardant paper for radio wave absorber components may break during drying in the papermaking process or chemical application process, or during secondary processing such as slitting or printing, resulting in poor handleability and processability.

[0032] On the other hand, if the content of the binder in the entire flame-retardant paper for radio wave absorber members is more than 10 mass %, the flame retardancy may decrease due to the influence of the binder.

[0033] Here, the binder used in the present invention is not particularly limited, and examples thereof include organic binders such as polyvinyl alcohol resin, vinyl acetate resin, acrylic resin, urea resin, epoxy resin, styrene-acrylic copolymer resin, polyester resin, and polyolefin resin, and inorganic binders such as alumina sol and silica sol. One of these binders listed above can be used as the binder, or a mixture of two or more of these binders can be used as the binder. Among them, the binder is preferably at least one selected from the group consisting of polyvinyl alcohol resin, acrylic resin, and styrene-acrylic copolymer resin, because of its high hydrophilicity and excellent papermaking properties.

[0034] The form of the binder used as a raw material includes liquid binders such as emulsions and solutions, and fibrous or powdery solid binders. Among them, it is preferable that at least a part of the binder contains a fibrous binder, from the viewpoint of not hindering contact between conductive materials and exhibiting excellent radio wave absorption performance. As the fibrous binder, a single-component fibrous binder, 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, and a bimetal type composite fiber in which a high melting point polymer and a low melting point polymer are arranged in parallel with each other, and other composite fibrous binders can be used. In addition, it is more preferable to use a fibrous binder in combination with a liquid binder or a powdery solid binder, because in addition to the adhesion between the fibers by the fibrous binder, the liquid binder or the powdery solid binder adheres to the vicinity of the intersections between the fibers, thereby further increasing the adhesive strength.

[0035] Here, hydroxide aluminum The mass ratio of aluminum hydroxide to binder (aluminum hydroxide content / binder content) is 83 / 17 to 91 / 9, and aluminum It is also preferable that the ratio of the total content of 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 above mass ratio is rounded off to one decimal place. The flame-retardant paper for radio wave absorber components having the above characteristics can achieve both excellent papermaking properties and excellent flame retardancy, and further has excellent handleability. Here, excellent handleability specifically means that the occurrence of breakage in the flame-retardant paper for radio wave absorber components is suppressed in the process of applying an agent to the flame-retardant paper for radio wave absorber components, the process of slitting, and the process of printing.

[0036] The flame-retardant paper for radio wave absorber members of the present invention may contain inorganic fibers such as glass fibers, rock wool, and basalt fibers. These inorganic fibers can improve the flame retardancy of the flame-retardant paper for radio wave absorber members, and since they are highly rigid fibers, the flame-retardant paper for radio wave absorber members can exhibit high rigidity, thereby improving the handleability of the flame-retardant paper for radio wave absorber members. The content of the inorganic fibers is preferably in the range of 1 to 30% by mass, assuming that the entire flame-retardant paper for radio wave absorber members of the present invention is 100% by mass. More preferably, it is 15% by mass or less. By setting the content in this range, a flame-retardant paper for radio wave absorber members having high rigidity can be stably produced.

[0037] The flame-retardant paper for radio wave absorber members of the present invention contains 0.1 to 12% by mass of a conductive material based on the entirety of the flame-retardant paper for radio wave absorber members. Furthermore, the content is preferably 4% by mass or less, more preferably 3% by mass or less. The conductive material in the present invention is a material that converts radio wave energy into a minute current and then into thermal energy to attenuate radio waves, i.e., absorb radio waves. Examples of the conductive material include conductive particles and conductive fibers. Here, examples of the conductive particles include metal particles, carbon black particles, carbon nanotube particles, carbon microcoil particles, and graphite particles. Examples of the conductive fibers include carbon fibers and metal fibers, and examples of the metal fibers include stainless steel fibers, copper fibers, silver fibers, gold fibers, nickel fibers, aluminum fibers, and iron fibers. In addition, non-conductive particles and fibers that have been given conductivity by plating, vapor deposition, or spraying metal can also be cited as conductive materials.

[0038] Among these conductive materials, it is preferable to use conductive fibers, and among conductive fibers, it is more preferable to use conductive short fibers from the viewpoint of uniform dispersion. Since conductive short fibers have a large aspect ratio, the fibers are easily in contact with each other, and compared with powder, even a small amount can effectively obtain radio wave absorption performance. Among conductive short fibers, carbon fibers are particularly preferably used because the fibers are rigid and easily oriented in the substrate, and there is almost no change in performance over long-term use. Regarding conductive short fibers, the length of the conductive short fibers is preferably 0.1 mm or more, more preferably 1.0 mm or more, from the viewpoint of ease of contact between the fibers and dispersibility of the slurry in the papermaking manufacturing process described later. On the other hand, it is preferably 15.0 mm or less, more preferably 10.0 mm or less.

[0039] Furthermore, when the flame-retardant paper for radio wave absorber members is used in radio wave anechoic chambers, it is preferable that the conductive fiber content is 0.5 to 2 mass % and the relative dielectric constant of the flame-retardant paper for radio wave absorber members is 10 to 250. When the conductive fiber content is 0.5 mass % or more, better radio wave absorbing performance can be obtained. On the other hand, when the conductive fiber content is 2 mass % or less, reflection of radio waves is suppressed, and thus the radio wave absorbing performance is better.

[0040] Furthermore, when the flame-retardant paper for radio wave absorber members is used in a noise suppression sheet that absorbs electromagnetic noise generated from small electronic devices, etc., it is preferable that the conductive fiber content is 5 to 12 mass % and the transmission attenuation rate of the flame-retardant paper for radio wave absorber members is 20 dB or more. By having the conductive fiber content of 5 to 12 mass %, a more excellent noise suppression effect can be obtained. In particular, the conductive fiber content is 5 to 10 mass %.

[0041] The basis weight of the flame-retardant paper for radio wave absorber members of the present invention is 50 to 200 g / m 2It is preferable that the weight is in the range of 80 g / m. By containing 0.1 to 12% by mass of conductive material and having a basis weight in the above range, good radio wave absorbing properties can be obtained. Furthermore, by having the basis weight in this range, the tensile strength and toughness of the flame-retardant paper for radio wave absorber components can be improved, and breakage of the flame-retardant paper can be suppressed during secondary processing such as drying in the papermaking process and chemical application process, and slitting and printing. The basis weight is 80 g / m 2 More than 150 g / m 2 The following is more preferred:

[0042] Next, the method for producing the flame-retardant paper for use in a radio wave absorber member according to the present invention will be described.

[0043] The method for producing the flame-retardant paper for use in a radio wave absorber member of the present invention can include, in this order, a step of obtaining a flame-retardant paper base material for use in a radio wave absorber member by wet-laid papermaking of pulp, aluminum hydroxide, a binder, and a conductive substance so that the pulp content in the flame-retardant paper for use in a radio wave absorber member is 5 to 20% by mass, the aluminum hydroxide content is 40 to 70% by mass, the binder content is 5 to 10% by mass, and the conductive substance content is 0.1 to 12% by mass, and a step of applying guanidine phosphate to the flame-retardant paper base material for use in a radio wave absorber member so that the guanidine phosphate content in the flame-retardant paper for use in a radio wave absorber member is 10 to 20% by mass. That is, the manufacturing method of the flame-retardant paper for radio wave absorber components of the present invention comprises, in this order, a step of preparing a slurry containing pulp, aluminum hydroxide, a binder and a conductive substance, a step of wet-laid papermaking the slurry to obtain a flame-retardant paper base material for radio wave absorber components, and a step of impregnating the flame-retardant paper base material for radio wave absorber components with an aqueous solution containing guanidine phosphate.

[0044] Here, when the amount of binder contained in the flame-retardant paper base material for radio wave absorbing members is increased, the tensile strength of the flame-retardant paper tends to improve, but generally, when the amount of binder is increased, the flame retardancy of the flame-retardant paper decreases, so there is a trade-off between the improvement of the tensile strength and the flame retardancy in the flame-retardant paper. However, in the process of wet-processing the slurry to obtain the flame-retardant paper base material for radio wave absorber members, the slurry contains a binder, so that it is possible to improve the paper strength of the flame-retardant paper even with a small amount of binder. Furthermore, since the binder is also contained in the flame-retardant paper base material for radio wave absorber members, breakage of the flame-retardant paper for radio wave absorber members can be suppressed in all processes other than the process of obtaining the base material such as wet-processing, such as the process of adding guanidine phosphate and the secondary processing process such as printing.

[0045] As a method for adding conductive fibers to a flame-retardant paper for a radio wave absorber member, as described above, there are a method in which a slurry used for wet papermaking is made to contain conductive fibers and is incorporated into a flame-retardant paper base material for a radio wave absorber member, a method in which conductive fibers are mixed into a binder material and applied to a flame-retardant paper base material for a radio wave absorber member using a device such as a size press coater, a roll coater, a blade coater, a bar coater, or an air knife coater, a method in which a flame-retardant paper base material for a radio wave absorber member is impregnated with an aqueous solution in which conductive fibers are dispersed, etc. Among these, the method in which a slurry used for wet papermaking is made to contain conductive fibers and is incorporated into a flame-retardant paper for a radio wave absorber member is preferred because the conductive fibers contained in the flame-retardant paper for a radio wave absorber member can be uniformly dispersed in the flame-retardant paper for a radio wave absorber member.

[0046] As an example of a method for producing the flame-retardant paper for radio wave absorber members of the present invention, a method using papermaking from known paper materials can be used, such as a wet papermaking method in which the constituent materials of the flame-retardant paper for radio wave absorber members of the present invention, such as fibers (pulp), aluminum hydroxide, a binder, and a conductive substance, are mixed with water to form a slurry, which is then papered using a papermaking machine.

[0047] As the papermaking machine, any of the following types of papermaking machines can be used: cylinder, short wire, fourdrinier, perchformer, rotoformer, hydroformer, etc. As the dryer, any of the following types of dryers can be used: Yankee type, multi-cylinder type, through-type, etc.

[0048] Furthermore, the method of incorporating guanidine phosphate into the flame-retardant paper for use as a radio wave absorber member is not particularly limited. For example, impregnation by dip / mangle, impregnation application, coating application, etc. can be exemplified. For impregnation application or coating application, a coating device such as a size press coater, roll coater, blade coater, bar coater, or air knife coater can be used, and these devices can be used on-machine or off-machine. Among them, impregnation by dip / mangle is preferred because it is easy to uniformly impregnate the entire flame-retardant paper for use as a radio wave absorber member.

[0049] One of the major features of the method for producing flame-retardant paper for radio wave absorber members of the present invention is that after obtaining a flame-retardant paper substrate for radio wave absorbing members containing a binder, the flame-retardant paper substrate for radio wave absorbing members is impregnated with an aqueous solution containing guanidine phosphate to impart guanidine phosphate to the flame-retardant paper substrate for radio wave absorbing members. As described above, by imparting guanidine phosphate to the flame-retardant paper substrate for radio wave absorbing members after obtaining a flame-retardant paper substrate for radio wave absorbing members containing a binder, breakage during drying of the paper can be further suppressed, and in the step of imparting guanidine phosphate, adhesion of the binder to the roll in addition to the guanidine phosphate can be suppressed. It is also possible to impart a binder such as a polyurethane resin together with the guanidine phosphate. However, this method is preferable because, as described later, when the flame-retardant paper substrate for radio wave absorbing members impregnated with a solution containing guanidine phosphate and a binder is pressed and dehydrated by passing it between a pair of rolls or between flat plates, it is easy to adhere to the surface of the roll, etc. Furthermore, if the binder adheres to the roll, the binder will dry and adhere to the roll, contaminating the roll and tending to reduce the productivity of the flame-retardant paper for radio wave absorber components; therefore, it is advisable to take this into consideration when adopting this method.

[0050] Here, the temperature of the aqueous solution containing guanidine phosphate is preferably 40°C to 70°C. More preferably, it is 45°C to 65°C. If the temperature is lower than 40°C, guanidine phosphate may precipitate, making stable processing difficult. On the other hand, if the temperature is higher than 70°C, the binder in the flame-retardant paper substrate for radio wave absorber members may be eluted or softened when immersed in the aqueous solution, making it easier to break, and further, water may evaporate, making it difficult to maintain the concentration of the aqueous solution of guanidine phosphate at a constant level.

[0051] In addition, after the step of impregnating the flame-retardant paper substrate for use in an electric wave absorbing member with an aqueous solution containing guanidine phosphate, it is preferable to have, in this order, a step of pressing the flame-retardant paper substrate for use in an electric wave absorbing member and a step of drying the flame-retardant paper substrate for use in an electric wave absorbing member at a temperature of 80 to 170° C. It is more preferable that the drying temperature be 100 to 160° C. in terms of good efficiency in drying water.

[0052] The process of pressing the flame-retardant paper substrate for radio wave absorbing members will be described below. After impregnating the flame-retardant paper for radio wave absorbing members with an aqueous solution of guanidine phosphate, it is preferable to pressurize and dehydrate it by passing it between a pair of rolls or between flat plates. Among them, it is preferable to pressurize and dehydrate it by passing it between a pair of rolls, since it has better processability compared to flat plates. By pressing and dehydrating, the amount of guanidine phosphate impregnation can be kept constant, and further, the dehydration reduces the amount of water contained in the flame-retardant paper substrate for radio wave absorbing members, thereby increasing the drying efficiency. The pressure to be applied is preferably 20 kgf / cm (196 N / cm) to 300 kgf / cm (2.94 kN / cm), and more preferably 30 kgf / cm (294 N / cm) to 150 kgf / cm (1.47 N / cm). If it is lower than 20 kgf / cm (196 N / cm), there is a possibility that dehydration cannot be performed sufficiently. If it is higher than 300 kgf / cm (2.94 kN / cm), wrinkles are likely to occur. The material of the rolls can be any material, such as a metal roll, a rubber roll, or a paper roll, but from the viewpoint of applying pressure uniformly and being less susceptible to the effects of unevenness of the flame-retardant paper for the radio wave absorber component, it is preferable that at least one of the rolls is a rubber roll.

[0053] The process of drying the flame-retardant paper base material for radio wave absorbers at a temperature of 80 to 170°C will be described below. The dryer may be any of steam cylinder type dryers such as Yankee drum type and multi-cylinder type dryers, infrared type dryers, and hot air type dryers. In the steam cylinder type, the flame-retardant paper for radio wave absorbers in a wet state comes into direct contact with a high-temperature cylinder, and migration such as aggregation of guanidine phosphate is likely to occur at the contacted portion. Furthermore, the obtained flame-retardant paper for radio wave absorbers tends to have reduced toughness and is prone to breakage and wrinkles. On the other hand, infrared type dryers and air-through type dryers are preferred because the obtained flame-retardant paper for radio wave absorbers has a small difference between the front and back sides, and is less likely to have reduced toughness and to breakage. Here, the infrared type dryer may be any of electric infrared dryers and gas type infrared dryers, and refers to a dryer that dries the flame-retardant paper for radio wave absorbers by irradiating infrared rays. An air-through type dryer is a dryer that dries using air heated directly or by heat exchange using fire, an electric heater, steam, etc.

[0054] The drying temperature is preferably 80 to 170° C. When the drying temperature is 80° C. or higher, the flame-retardant paper substrate for the radio wave absorbing member can be sufficiently dried. On the other hand, when the drying temperature is 170° C. or lower, breakage of the flame-retardant paper substrate for the radio wave absorbing member due to excessive drying can be suppressed, and further, yellowing of the pulp can be suppressed, and as a result, yellowing of the flame-retardant paper for the radio wave absorbing member can be suppressed. EXAMPLES

[0055] The flame-retardant paper of the present invention will now be described in more detail with reference to the following examples. The performance values ​​shown in the examples were measured by the following methods.

[0056] [Measurement method] (1) Confirmation of ingredients contained in flame-retardant paper The components contained in the flame retardant paper are confirmed as follows: Using an ultra-high resolution field emission scanning electron microscope (SEM, Hitachi High-Technologies SU-8010), a total of five areas are photographed, including four areas around points shifted 2.5 cm vertically and horizontally 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 around a point in the center of the test piece, and the presence of specific elements is confirmed with an energy dispersive X-ray analyzer (EDX), and the components contained in the flame retardant paper and their amounts are confirmed based on the results of measuring the test piece using an infrared spectrophotometer (FT-IR, Shimadzu IR PRESTIGE-21).

[0057] (2) Basis weight of flame-retardant paper Five pieces of flame-retardant paper were cut into squares with sides of 300 mm, the mass was measured, and 2 The weight is calculated by converting it into the mass per unit and taking the average.

[0058] (3) Flame retardancy of flame retardant paper The evaluation is based on the 20 mm vertical flame test (UL94 V-0) in the UL94 safety standard ("Flammability test for plastic materials in equipment and appliance parts"). Here, UL is a safety standard for electronic devices established and approved by Underwriters Laboratories Inc. in the United States, and UL94 is also a flame retardant standard. The evaluation was performed using five rectangular samples measuring 13 mm wide and 125 mm long. ◎: None of the five samples continued to burn for more than 10 seconds, and the total burning time for the five samples after 10 exposures to flame did not exceed 50 seconds, and none of the samples burned up to the position of the fixing clamp, and none of the samples continued to glow red for more than 30 seconds after the second exposure to flame. ×: At least one of the five samples continued to burn for 10 seconds or more, or the total burning time for the five samples after 10 flame applications was 50 seconds or more, or at least one sample burned all the way to the fixing clamp, or at least one sample continued to glow red for 30 seconds or more after the second flame application.

[0059] (4) Flame retardancy of a component made by bonding flame retardant paper for radio wave absorber components and polystyrene foam (flame retardancy of the laminate) A component in which the flame-retardant paper and the polystyrene foam with a thickness of 10 mm were bonded together was created by bonding the flame-retardant paper and the polystyrene foam with double-sided tape (recycled paper double-sided tape NWBB-15, manufactured by Nichiban Co., Ltd.) The size of the sample was 50 mm wide and 150 mm long, and five samples were prepared with lines drawn along the length at positions 25 mm and 125 mm from one end.

[0060] The burning rate of the above-mentioned components is evaluated in accordance with the foamed material horizontal burning test (UL94 HBF) in the UL94 safety standard ("Flammability test of plastic materials for equipment and appliance parts"). ◎: For all five levels, the burning time over a 100 mm distance (from the 25 mm line to the 125 mm line) is measured, the burning speed is calculated, and no sample must burn at a burning speed exceeding 40 mm / min. Alternatively, the sample must be extinguished before the flames or sparks reach the 125 mm line. Furthermore, the average burning speed of the burned samples must be less than 35 mm / min. ○: For all five levels, the burning time over 100 mm (from the 25 mm line to the 125 mm line) is measured, the burning speed is calculated, and no sample must burn at a burning speed exceeding 40 mm / min. Alternatively, the sample must be extinguished before the flames or sparks reach the 125 mm line. Furthermore, the average burning speed of the burned samples must be between 35 mm / min and 40 mm / min. · ×: At least one of the five does not meet the above ◎ and / or ○ criteria.

[0061] (5) Tensile strength In accordance with JIS P 8113:2006, using a tensile tester "Autograph, Model: AGS-J" (Shimadzu Corporation), three strips of 15 mm x 150 mm with the long side in the MD direction (the direction in which the paper flows during papermaking) and three strips of 15 mm x 150 mm with the long side in the TD direction (approximately perpendicular to the MD direction) were cut to prepare test pieces. These were tensioned at a constant speed with a chuck distance of 100 mm and a chuck movement speed of 100 mm / min, and the strength at which the test pieces broke was measured, and the overall average was calculated. From the viewpoint of stable productivity and ease of handling, the following was determined. ·〇:30N / 15mm or more △: 12N / 15mm or more and less than 30N / 15mm ×: Less than 12N / 15mm

[0062] (6) Dielectric constant A polystyrene foam spacer (thickness 14 mm) of the same size and shape as the aluminum plate with a foaming ratio of 70 times was placed on the top surface of an aluminum plate measuring 30 cm in length, 30 cm in width, and 5 mm in thickness. A radio wave absorber sheet material of the same size as the aluminum plate was further placed on top of this spacer. The transmitting and receiving antennas were set directly above the center point of the polystyrene foam spacer (on the surface opposite to the surface of the polystyrene foam spacer facing the aluminum plate and at the intersection of two diagonals of the polystyrene foam spacer) and 1.4 m away from the center point so that the incident angle of the radio waves was 7°. Radio waves in the frequency range of 2 to 4 GHz were incident on the sample, and the input impedance was measured using a vector network analyzer (model: N5230, manufactured by Agilent Technologies). Thereafter, the radio wave absorber sheet material was removed, and the input impedance was measured in the same manner as above with the radio wave absorber sheet material removed, and the complex dielectric constant of the radio wave absorber sheet material was calculated from the difference in input impedance between with and without the radio wave absorber sheet material, and the real part εr' of the complex dielectric constant at a frequency of 3 GHz was read. Different radio wave absorber sheet materials were used for the measurement, N=3, and the real part εr' of the complex dielectric constant was measured for each radio wave absorber sheet material in the direction parallel to any one side and in the direction perpendicular to that side, and the average value of the six measured values ​​obtained was taken as the real part εr' of the complex dielectric constant.

[0063] (7) Transmission attenuation rate The evaluation was performed in accordance with Section 4.3 "Transmission attenuation power ratio: Rtp" in the IEC standard 62333-2 "Noise suppression sheet for digital devices and equipment". This evaluation method was performed using a microstrip line (MSL) jig, and the noise suppression sheet was placed on this MSL to measure the conduction noise suppression degree Rtp (dB). Using a vector network analyzer (model: N5230, manufactured by Agilent Technologies), measurements were performed in the frequency range of 4 to 6 GHz, and the frequency of 5 GHz was read, with 20 dB or more being ◯, 3 dB or more but less than 20 dB being △, and less than 3 dB being ×. The size of the noise suppression sheet sample was 10 cm x 5 cm.

[0064] (8) Papermaking productivity In the case of wet papermaking using the continuous papermaking method, stable continuous productivity was confirmed by the following evaluations. A: Paper production was stable. B: During papermaking, the paper occasionally broke, or guanidine phosphate adhered to the coating equipment, impregnation equipment, and drying rolls, making it impossible to produce stable paper. B-: Paper occasionally broke during papermaking, or guanidine phosphate adhered to the coating equipment, impregnation equipment, or drying rolls. The frequency of breaks and / or the extent of guanidine phosphate adhesion were higher than in B, making it impossible to produce stable paper. C: The tensile strength was weak, and the paper frequently broke during papermaking, guanidine phosphate treatment, and winding.

[0065] [Example 1] The flame-retardant paper for radio wave absorber components was mixed with 18% by mass of softwood pulp with a fiber length of 5 mm, 48% by mass of aluminum hydroxide (manufactured by Wako Pure Chemical Industries, Ltd.), 10% by mass of glass fiber (fiber diameter 7 μm, fiber length 6 mm), 8% by mass of polyvinyl alcohol fiber ('Vinylon' manufactured by Kuraray Co., Ltd., fiber diameter 11 μm, fiber length 3 mm) and 2% by mass of styrene-acrylic copolymer resin (water-based emulsion, manufactured by Toagosei Co., Ltd.) as solids (10% by mass of binder), and 1% by mass of carbon fiber ('Torayca' manufactured by Toray Industries, Inc., fiber diameter 7 μm, fiber length 6 mm) as conductive material, and wet-sheeted using a continuous papermaking method to create a flame-retardant paper base for radio wave absorber components.

[0066] This flame-retardant paper base material for radio wave absorber components was impregnated with an aqueous solution of guanidine phosphate (liquid temperature 55°C) using a size press coater so that the amount of guanidine phosphate ('Non-Nen' (registered trademark) 985, manufactured by Marubishi Yuka Kogyo Co., Ltd.) was 13% by mass relative to the entire flame-retardant paper, and the impregnated paper was dried in a gas-type infrared dryer (drying temperature 150°C) to a basis weight of 115 g / m 2 The papermaking productivity was rated as A.

[0067] The obtained flame-retardant paper for use as a radio wave absorber component was evaluated. The results are shown in Table 1. The burning rate of the flame-retardant paper for use as a radio wave absorber component was slow, and it passed UL94 V-0 (evaluated as ◎). The burning rate of the component laminated with polystyrene foam was also slow, and it passed UL94 HBF (evaluated as ◎). In addition, the tensile strength was sufficient. The relative dielectric constant was 130, making it suitable for use as a radio wave absorber, but the transmission attenuation rate was low and the noise suppression effect was △.

[0068] [Example 2] A paper having a basis weight of 115 g / m2 was prepared in the same manner as in Example 1, except that the pulp content was 15 mass%, the aluminum hydroxide content was 45 mass%, the glass fiber content was 15 mass%, the binder content was 7 mass% of polyvinyl alcohol fiber and 2 mass% of styrene-acrylic copolymer resin (9 mass% of binder), and the guanidine phosphate content was 15 mass%. 2The papermaking productivity was rated as A.

[0069] The obtained flame-retardant paper for use as a radio wave absorber component was evaluated. The results are shown in Table 1. The burning rate of the flame-retardant paper for use as a radio wave absorber component was slow, and it passed UL94 V-0 (evaluated as ◎). The burning rate of the component laminated with polystyrene foam was also slow, and it passed UL94 HBF (evaluated as ◎). In addition, the tensile strength was sufficient. The relative dielectric constant was 130, making it suitable for use as a radio wave absorber, but the transmission attenuation rate was low and the noise suppression effect was △.

[0070] [Example 3] A paper having a basis weight of 115 g / m2 was prepared in the same manner as in Example 1, except that the pulp content was 10 mass%, aluminum hydroxide content was 65 mass%, glass fiber content was 5 mass%, polyvinyl alcohol fiber content was 7 mass%, styrene-acrylic copolymer resin content was 2 mass% (binder content was 9 mass%) as a binder, and guanidine phosphate content was 10 mass%. 2 The papermaking productivity was rated as A.

[0071] The obtained flame-retardant paper for use as a radio wave absorber component was evaluated. The results are shown in Table 1. The burning rate of the flame-retardant paper for use as a radio wave absorber component was slow, and it passed UL94 V-0 (evaluated as ◎). The burning rate of the component laminated with polystyrene foam was also slow, and it passed UL94 HBF (evaluated as ◎). In addition, the tensile strength was sufficient. The relative dielectric constant was 130, making it suitable for use as a radio wave absorber, but the transmission attenuation rate was low and the noise suppression effect was △.

[0072] [Example 4] The same procedure as in Example 1 was repeated except that the pulp content was 15 mass%, the aluminum hydroxide content was 55 mass%, the glass fiber content was 8 mass%, the binder content was 5 mass% of polyvinyl alcohol fiber and 1 mass% of styrene-acrylic copolymer resin (6 mass% of binder), and the guanidine phosphate content was 15 mass%, and the basis weight of Example 4 was 115 g / m. 2 The papermaking productivity was rated as A.

[0073] The obtained flame-retardant paper for use as a radio wave absorber component was evaluated. The results are shown in Table 1. The burning rate of the flame-retardant paper for use as a radio wave absorber component was slow, and it passed UL94 V-0 (evaluated as ◎). The burning rate of the component laminated with polystyrene foam was also slow, and it passed UL94 HBF (evaluated as ◎). In addition, the tensile strength was sufficient. The relative dielectric constant was 130, making it suitable for use as a radio wave absorber, but the transmission attenuation rate was low and the noise suppression effect was △.

[0074] [Example 5] A paper having a basis weight of 85 g / m2 in Example 5 was prepared in the same manner as in Example 1, except that the pulp content was 12 mass%, aluminum hydroxide content was 52 mass%, glass fiber content was 8 mass%, polyvinyl alcohol fiber content was 8 mass%, styrene-acrylic copolymer resin content was 1 mass% (binder content was 9 mass%) as a binder, and guanidine phosphate content was 18 mass%. 2 The papermaking productivity was rated as A.

[0075] The obtained flame-retardant paper for use as a radio wave absorber component was evaluated. The results are shown in Table 1. The burning rate of the flame-retardant paper for use as a radio wave absorber component was slow, and it passed UL94 V-0 (evaluated as ◎). The burning rate of the component laminated with polystyrene foam was also slow, and it passed UL94 HBF (evaluated as ◯). In addition, the tensile strength was sufficient. The relative dielectric constant was 130, making it suitable for use as a radio wave absorber, but the transmission attenuation rate was low, and the noise suppression effect was △.

[0076] [Example 6] Basis weight 74g / m 2 Except for the above, the flame-retardant paper for radio wave absorber members was obtained in the same manner as in Example 5. The papermaking productivity was rated as B because the paper was somewhat prone to tearing.

[0077] The obtained flame-retardant paper for use as a radio wave absorber component was evaluated. The results are shown in Table 1. The burning rate of the flame-retardant paper was slow, and it passed UL94 V-0 (evaluated as ◎). The burning rate of the component laminated with polystyrene foam was also slow, and it passed UL94 HBF (evaluated as ◯). In addition, the tensile strength was somewhat weak. The relative dielectric constant was 130, making it suitable as a radio wave absorber, but the transmission attenuation rate was low, and the noise suppression effect was not sufficient, earning a rating of △.

[0078] [Example 7] The same procedure as in Example 1 was repeated except that the pulp content was 13 mass%, the aluminum hydroxide content was 57 mass%, the glass fiber content was 9 mass%, the binder content was 8 mass% of polyvinyl alcohol fiber and 1 mass% of styrene-acrylic copolymer resin (9 mass% of binder), and the guanidine phosphate content was 11 mass%. 2 The papermaking productivity was good.

[0079] The obtained flame-retardant paper for use as a radio wave absorber component was evaluated. The results are shown in Table 1. The burning rate of the flame-retardant paper for use as a radio wave absorber component was slow, and it passed UL94 V-0 (evaluated as ◎). The burning rate of the component laminated with polystyrene foam was also slow, and it passed UL94 HBF (evaluated as ◎). In addition, the tensile strength was sufficient. The relative dielectric constant was 130, making it suitable for use as a radio wave absorber, but the transmission attenuation rate was low and the noise suppression effect was △.

[0080] [Example 8] Basis weight 225g / m 2 A flame-retardant paper for a radio wave absorber member of Example 8 was obtained in the same manner as in Example 7, except for the above. The papermaking productivity was rated as B, since guanidine phosphate was precipitated on the size press roll and drying defects were likely to occur.

[0081] The configurations and evaluation results of the flame-retardant papers for wave absorber members of Examples 1 to 8 are shown in Table 1. The relative dielectric constant was 130, which was suitable as a wave absorber, but the transmission attenuation rate was low and the noise suppression effect was fair.

[0082] [Table 1]

[0083] [Example 9] A flame-retardant paper for radio wave absorber members of Example 9 was obtained in the same manner as in Example 1, except that the size press coater was changed to a dip / mangle. The papermaking productivity was rated as A.

[0084] The obtained flame-retardant paper for use as a radio wave absorber component was evaluated. The results are shown in Table 2. The burning rate of the flame-retardant paper for use as a radio wave absorber component was slow, and it passed UL94 V-0 (evaluated as ◎). The burning rate of the component laminated with polystyrene foam was also slow, and it passed UL94 HBF (evaluated as ◎). In addition, the tensile strength was sufficient. The relative dielectric constant was 130, making it suitable for use as a radio wave absorber, but the transmission attenuation rate was low and the noise suppression effect was rated as △.

[0085] [Example 10] Flame-retardant paper for radio wave absorber members of Example 10 was obtained in the same manner as in Example 9, except that the liquid temperature of the guanidine phosphate aqueous solution was 15° C., and the gas-type infrared dryer was a multi-cylinder type (6 cylinders) steam cylinder type dryer (drying temperature 120° C.). Papermaking productivity was rated as B, as guanidine phosphate was precipitated on the mangle and paper breaks occurred occasionally during the steam cylinder type dryer process (however, the rating was higher than that of Example 14 described below).

[0086] The obtained flame-retardant paper for use as a radio wave absorber component was evaluated. The results are shown in Table 2. The burning rate of the flame-retardant paper for use as a radio wave absorber component was slow, and it passed UL94 V-0 (evaluated as ◎). The burning rate of the component laminated with polystyrene foam was also slow, and it passed UL94 HBF (evaluated as ◎). The tensile strength was somewhat weak. The relative dielectric constant was 130, making it suitable as a radio wave absorber, but the transmission attenuation rate was low and the noise suppression effect was rated as △.

[0087] [Example 11] The same procedure as in Example 9 was repeated except that the glass fiber content was 10.5 mass% and the carbon fiber content was 0.5 mass%, to obtain a sheet having a basis weight of 115 g / m in Example 11. 2 The papermaking productivity was rated as A.

[0088] The obtained flame-retardant paper for use as a radio wave absorber component was evaluated. The results are shown in Table 2. The burning rate of the flame-retardant paper for use as a radio wave absorber component was slow, and it passed UL94 V-0 (evaluated as ◎). The burning rate of the component laminated with polystyrene foam was also slow, and it passed UL94 HBF (evaluated as ◯). In addition, the tensile strength was sufficient. The relative dielectric constant was 130, making it suitable as a radio wave absorber, but the transmission attenuation rate was low, and the noise suppression effect was △.

[0089] [Example 12] Pulp 17% by mass, hydroxide aluminum The same procedure as in Example 9 was repeated except that the amount of 46 mass% of the polyester fiber, 5 mass% of the carbon fiber, and 12 mass% of the guanidine phosphate were used to produce a polyester fiber having a basis weight of 115 g / m2 in Example 12. 2 The papermaking productivity was rated as A.

[0090] The obtained flame-retardant paper for use as a radio wave absorber component was evaluated. The results are shown in Table 2. The burning rate of the flame-retardant paper for use as a radio wave absorber component was slow, and it passed UL94 V-0 (evaluated as ◎). The burning rate of the component laminated with polystyrene foam was also slow, and it passed UL94 HBF (evaluated as ◯). In addition, the tensile strength was sufficient. The relative dielectric constant was 300, which is too high for a radio wave absorber, but the transmission attenuation rate was high and the noise suppression effect was rated ◯.

[0091] [Example 13] Pulp 16% by mass, hydroxide aluminum The same procedure as in Example 9 was repeated except that the content of the binder was 9% by mass (8% by mass of polyvinyl alcohol fiber and 1% by mass of styrene-acrylic copolymer resin), 10% by mass of carbon fiber, and 12% by mass of guanidine phosphate, and the basis weight of Example 13 was 115 g / m. 2The papermaking productivity was rated as A.

[0092] The obtained flame-retardant paper for use as a radio wave absorber component was evaluated. The results are shown in Table 2. The burning rate of the flame-retardant paper for use as a radio wave absorber component was slow, and it passed UL94 V-0 (evaluated as ◎). The burning rate of the component laminated with polystyrene foam was also slow, and it passed UL94 HBF (evaluated as ◯). In addition, the tensile strength was sufficient. The relative dielectric constant was 300, which is too high for a radio wave absorber, but the transmission attenuation rate was high and the noise suppression effect was rated ◯.

[0093] [Example 14] Pulp 15% by mass, hydroxide aluminum A flame-retardant paper substrate for a radio wave absorber member was prepared in the same manner as in Example 1, except that the content of the flame-retardant paper was 55 mass%, the content of the glass fiber was 8 mass%, and the content of the binder was 0 mass%. In the same manner as in Example 1, guanidine phosphate and a urethane resin as a binder (product name Superflex 150 (product name), manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) were added to this flame-retardant paper substrate for a radio wave absorber member in amounts of 15 mass% and 6 mass% (binder was 6 mass%) relative to the entire flame-retardant paper, respectively, to produce a flame-retardant paper substrate with a basis weight of 115 g / m in Example 14. 2 The paper broke occasionally during the papermaking process, and guanidine phosphate and urethane resin adhered to the roll of the size press coater, so that the papermaking productivity was rated as B-.

[0094] The obtained flame-retardant paper for radio wave absorber components was evaluated. The results are shown in Table 2. The burning rate of the flame-retardant paper for radio wave absorber components was slow, and it passed UL94 V-0 (evaluated as ◎). The burning rate of the component laminated with polystyrene foam was also slow, and it passed UL94 HBF (evaluated as ◯). On the other hand, the tensile strength was somewhat weak. The relative dielectric constant was 300, which is too high for a radio wave absorber, but the transmission attenuation rate was high and the noise suppression effect was rated ◯.

[0095] Table 2 shows the configurations and evaluation results of the flame-retardant papers for radio wave absorber members of Examples 9 to 1413.

[0096] [Table 2]

[0097] [Comparative Example 1] A paper having a basis weight of 115 g / m2 in Comparative Example 1 was prepared in the same manner as in Example 1, except that the pulp content was 3 mass%, aluminum hydroxide content was 73 mass%, glass fiber content was 9 mass%, polyvinyl alcohol fiber content was 4 mass%, styrene-acrylic copolymer resin content was 1 mass% (binder content was 5 mass%), and guanidine phosphate content was 10 mass%. 2 The paper was weak and frequently broke, making it unsuitable for production, and was given a C rating for papermaking productivity.

[0098] The obtained flame-retardant paper for radio wave absorber components was evaluated. The results are shown in Table 3. The burning rate of the flame-retardant paper for radio wave absorber components was slow, and it passed UL94 V-0 (evaluated as ◎). The burning rate of the component laminated with polystyrene foam was also slow, and it passed UL94 HBF (evaluated as ◯). In addition, the tensile strength was weak. The relative dielectric constant was 130, making it suitable as a radio wave absorber, but the transmission attenuation rate was low and the noise suppression effect was △.

[0099] [Comparative Example 2] The same procedure as in Example 1 was repeated except that the pulp content was 25% by mass, the aluminum hydroxide content was 37% by mass, the glass fiber content was 17% by mass, the binder content was 7% by mass of polyvinyl alcohol fiber and 1% by mass of styrene-acrylic copolymer resin (binder content was 8% by mass), and the guanidine phosphate content was 13% by mass. The basis weight of Comparative Example 2 was 115 g / m. 2 The papermaking productivity was rated as A.

[0100] The obtained flame-retardant paper for use as a radio wave absorber component was evaluated. The results are shown in Table 3. The burning rate of the flame-retardant paper for use as a radio wave absorber component was fast, and it failed UL94 V-0 (evaluated as ×). The burning rate of the component laminated with polystyrene foam was also fast, and it failed UL94 HBF (evaluated as ×). The tensile strength was sufficient. The relative dielectric constant was 130, making it suitable as a radio wave absorber, but the transmission attenuation rate was low and the noise suppression effect was rated as fair.

[0101] [Comparative Example 3] The same procedure as in Example 1 was repeated except that the pulp content was 20 mass%, the aluminum hydroxide content was 52 mass%, the glass fiber content was 13 mass%, the binder content was 8 mass% of polyvinyl alcohol fiber and 2 mass% of styrene-acrylic copolymer resin (10 mass% of binder), and the guanidine phosphate content was 5 mass%, and the basis weight of Comparative Example 3 was 115 g / m. 2 The papermaking productivity was rated as A.

[0102] The obtained flame-retardant paper for radio wave absorber components was evaluated. The results are shown in Table 3. The burning rate of the flame-retardant paper for radio wave absorber components was slow, and it passed UL94 V-0 (evaluated as ◎). On the other hand, the burning rate of the component laminated with polystyrene foam was fast, and it failed UL94 HBF (evaluated as ×). The tensile strength was sufficient. The relative dielectric constant was 130, making it suitable as a radio wave absorber, but the transmission attenuation rate was low and the noise suppression effect was △.

[0103] [Comparative Example 4] The same procedure as in Example 1 was repeated except that the pulp content was 16% by mass, the aluminum hydroxide content was 41% by mass, the glass fiber content was 9% by mass, the binder content was 8% by mass of polyvinyl alcohol fiber and 1% by mass of styrene-acrylic copolymer resin (9% by mass of binder), and the guanidine phosphate content was 25% by mass. The basis weight of Comparative Example 4 was 133 g / m. 2 The papermaking productivity was rated C because guanidine phosphate precipitated on the size press coater and a stable content could not be maintained.

[0104] The obtained flame-retardant paper for radio wave absorber components was evaluated. The results are shown in Table 3. The burning rate of the flame-retardant paper for radio wave absorber components was slow, and it passed UL94 V-0 (evaluated as ◎). The burning rate of the component laminated with polystyrene foam was also slow, and it passed UL94 HBF (evaluated as ◎). The tensile strength was sufficient. The relative dielectric constant was 130, making it suitable as a radio wave absorber, but the transmission attenuation rate was low and the noise suppression effect was △.

[0105] [Comparative Example 5] Comparative Example 5 was produced in the same manner as in Example 1, except that the pulp content was 20% by mass, the aluminum hydroxide content was 50% by mass, the glass fiber content was 14% by mass, and only polyvinyl alcohol fiber was used as the binder at 3% by mass (the binder content was 3% by mass). 2 The paper was weak and frequently broke, making it unsuitable for production, and was given a C rating for papermaking productivity.

[0106] The obtained flame-retardant paper for radio wave absorber components was evaluated. The results are shown in Table 3. The burning rate of the flame-retardant paper for radio wave absorber components was slow, and it passed UL94 V-0 (evaluated as ◎). The burning rate of the component laminated with polystyrene foam was also slow, and it passed UL94 HBF (evaluated as ◎). The tensile strength was weak. The relative dielectric constant was 130, which was suitable as a radio wave absorber, but the transmission attenuation rate was low and the noise suppression effect was △.

[0107] [Comparative Example 6] The same procedure as in Example 1 was repeated except that the pulp content was 15 mass%, the aluminum hydroxide content was 48 mass%, the glass fiber content was 9 mass%, and the binder content was 13 mass% of polyvinyl alcohol fiber and 2 mass% of styrene-acrylic copolymer resin (the binder content was 15 mass%). 2 The papermaking productivity was rated as A.

[0108] The obtained flame-retardant paper for use as a radio wave absorber component was evaluated. The results are shown in Table 3. The burning rate of the flame-retardant paper for use as a radio wave absorber component was fast, and it failed UL94 V-0 (evaluated as x). The burning rate of the component laminated with polystyrene foam was also fast, and it also failed UL94 HBF (evaluated as x). The tensile strength was strong. The relative dielectric constant was 130, making it suitable as a radio wave absorber, but the transmission attenuation rate was low and the noise suppression effect was rated as fair.

[0109] [Comparative Example 7] The same procedure as in Example 1 was repeated except that the pulp content was 19% by mass and the carbon fiber content was 0% by mass. Comparative Example 7 had a basis weight of 115 g / m 2 The papermaking productivity was rated as A.

[0110] The obtained flame-retardant paper for use as a radio wave absorber component was evaluated. The results are shown in Table 3. The burning rate of the flame-retardant paper for use as a radio wave absorber component was slow, and it passed UL94 V-0 (evaluated as ◎). The burning rate of the component laminated with polystyrene foam was also slow, and it passed UL94 HBF (evaluated as ◎). The tensile strength was sufficient. The relative dielectric constant was 4, which was low, and it was unsuitable as a radio wave absorber. In addition, the transmission attenuation rate was low, and no noise suppression effect was obtained, so it was rated as ×.

[0111] [Comparative Example 8] The same procedure as in Example 14 was repeated except that the pulp content was 17% by mass, the aluminum hydroxide content was 54% by mass, the glass fiber content was 13% by mass, the binder made of urethane resin was 2% by mass (the binder content was 2% by mass), and the guanidine phosphate content was 13% by mass. The basis weight of Comparative Example 8 was 115 g / m. 2 The paper broke during the papermaking process when it was wound up after being impregnated with guanidine phosphate, and the papermaking productivity was rated C.

[0112] The obtained flame-retardant paper for radio wave absorber components was evaluated. The results are shown in Table 3. The burning rate of the flame-retardant paper for radio wave absorber components was slow, and it passed UL94 V-0 (evaluated as ◎). The burning rate of the component laminated with polystyrene foam was also slow, and it passed UL94 HBF (evaluated as ◎). The tensile strength was weak. The relative dielectric constant was 130, making it suitable as a radio wave absorber, but the transmission attenuation rate was low and the noise suppression effect was △.

[0113] [Table 3]

[0114] In Examples 1 to 14, flame-retardant paper for radio wave absorber components was obtained that had excellent flame retardancy, and the flame retardancy, tensile strength, and papermaking productivity of the component formed by bonding the flame-retardant paper for radio wave absorber components with polystyrene foam was excellent.

[0115] On the other hand, Comparative Example 1 had a weak tensile strength and could not be stably manufactured. Comparative Examples 2 and 3 had excellent tensile strength, but the flame retardancy of the flame-retardant paper for radio wave absorber members and the laminated product was poor. Comparative Example 4 had excellent flame retardancy, but the tensile strength was somewhat weak, and stable manufacturing was not possible. Comparative Example 5 had excellent flame retardancy for the flame-retardant paper for radio wave absorber members and the laminated product, but the tensile strength was weak, and stable manufacturing was difficult. Comparative Example 6 had high tensile strength and excellent stable productivity, but the flame retardancy of the flame-retardant paper for radio wave absorber members and the laminated product was poor. Comparative Example 7 had excellent productivity and flame retardancy, but the relative dielectric constant and transmission attenuation rate were small, and the radio wave absorption was poor. Comparative Example 8 had excellent radio wave absorption performance and flame retardancy, but the tensile strength was weak, and stable manufacturing was not possible.

Claims

1. A flame-retardant paper for a radio wave absorber member, comprising pulp, aluminum hydroxide, guanidine phosphate, a binder, and a conductive material, The content of the pulp is 5 to 20% by mass, The content of the aluminum hydroxide is 40 to 70 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 in the flame-retardant paper for radio wave absorber members is 0.1 to 12 mass %.

2. 2. The flame-retardant paper for a radio wave absorber member according to claim 1, wherein a mass ratio of the aluminum hydroxide to the binder (aluminum hydroxide content / binder content) is 83 / 17 to 91 / 9, and a ratio of a total content of the aluminum hydroxide and the guanidine phosphate to a total content of the pulp and the binder (aluminum hydroxide content+guanidine phosphate content) / (pulp content+binder content) is 67 / 33 to 80 / 20.

3. The flame-retardant paper for radio wave absorber members according to claim 1 , wherein the conductive material is a conductive fiber.

4. The content of the conductive fibers is 0.5 to 2 mass %, The flame-retardant paper for radio wave absorber members according to claim 3, which has a relative dielectric constant of 10 to 250.

5. The content of the conductive fibers is 5 to 12 mass %, 4. The flame-retardant paper for radio wave absorber members according to claim 3, which has a transmission attenuation rate of 20 dB or more.

6. Basis weight: 80 to 200 g / m ２ The flame-retardant paper for radio wave absorber members according to any one of claims 1 to 5,

7. 7. The flame-retardant paper for radio wave absorber members according to claim 1, wherein the binder is at least one selected from the group consisting of polyvinyl alcohol resins, acrylic resins, and styrene-acrylic copolymer resins.

8. A method for producing the flame-retardant paper for radio wave absorbing members according to any one of claims 1 to 7, preparing a slurry containing pulp, aluminum hydroxide, a binder and a conductive material; A step of wet-processing the slurry to obtain a flame-retardant paper substrate for a radio wave absorbing member; and impregnating the flame-retardant paper base material for radio wave absorbing members with an aqueous solution containing guanidine phosphate, in this order.

9. After the step of impregnating the flame-retardant paper substrate for radio wave absorbing members with the aqueous solution containing guanidine phosphate, A step of pressing the flame-retardant paper substrate for radio wave absorbing members; and drying the flame-retardant paper substrate for a radio wave absorbing member at a temperature of 80 to 170° C., in this order.

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